Patent Application
20220056312
The present invention relates to adhesive tapes comprising a polyurethane-based carrier, to a process for producing the adhesive tapes, and to the use thereof for bonding of components in electronic devices.
DE 102012223670 A1 describes a pressure-sensitive adhesive film strip composed of at least two, especially three, layers that can be redetached without residue or destruction by stretching essentially in the plane of the bond, having a carrier on which there is a first, outer adhesive layer on at least one side, wherein the adhesive layer consists of an adhesive based on vinylaromatic block copolymers and tackifying resins, wherein at least 75% (based on the total resin content) of the resin selected is one having a DACP (diacetone alcohol cloud point) of greater than −20° C., preferably greater than 0° C., and the carrier has at least one layer consisting of a polyurethane having an elongation at break of at least 100% and a resilience of more than 50%.
DE 102015206076 A1 describes a pressure-sensitive adhesive strip that can be redetached without residue or destruction by stretching essentially in the plane of the bond, composed of one or more adhesive layers that all consist of a pressure-sensitive adhesive foamed with microballoons, and optionally of one or more carrier interlayers, characterized in that the pressure-sensitive adhesive strip consists exclusively of the adhesive layers mentioned and any intermediate carrier layers present, and one outer upper and one outer lower face of the pressure-sensitive adhesive strip are formed by said adhesive layer(s).
EP 3075772 A1 describes a pressure-sensitive adhesive strip that can be redetached without residue or destruction by stretching essentially in the plane of the bond, comprising an adhesive layer, wherein the adhesive layer consists of a pressure-sensitive adhesive based on vinylaromatic block copolymers and tackifying resins, wherein at least 75% by weight (based on the total resin content) of the resin selected is one having a DACP (diacetone alcohol cloud point) of greater than −20° C., preferably greater than 0° C., and a softening temperature (Ring & Ball) of not less than 70° C., preferably not less than
100° C., and wherein the pressure-sensitive adhesive has been foamed.
DE 102016224646 A1 describes a pressure-sensitive adhesive strip comprising at least one layer SK1, preferably exactly one layer SK1, of a self-adhesive composition based on a vinylaromatic block copolymer composition foamed with microballoons, where the mean diameter of the voids formed by the microballoons in the self-adhesive composition layer SK1 is 45 to 110 μm.
KR 101680827 B1 describes a process for producing a shock-resistant foam structure, comprising the steps of:
producing a foam composition in which pre-expanded particles and a binder composition are mixed, applying the foam composition to a substrate, performing a preliminary heat treatment on the foam composition applied in order to form a pre-foam, and converting the pre-foam by heat treatment to a heat-resistant foam structure composed of shock-resistant particles, wherein the pre-expanded particles are expanded.
U.S. 2017121573 A1 describes an adhesive formulation comprising 50% to 99% adhesive component, 0% to 3% crosslinker, 0% to 3% antioxidant, and 0.1% to 10% expandable microspheres distributed within the formulation.
EP 3623400 A1 describes a polyurethane foam obtainable by mechanical foaming of a starting mixture of a polyurethane dispersion, where the polyurethane is composed of at least one polyisocyanate component and at least one polyol component, and at least one surfactant, characterized in that the polyol component or at least one of the polyol components includes at least one comonomer having flame-retardant action and containing two hydroxyl groups.
WO 2015135134 A1 describes an adhesive tape detachable by stretching, comprising a carrier having a first surface and a second surface, wherein the carrier has been produced from crosslinked thermoplastic polyurethane, and pressure-sensitive adhesive disposed on at least one of the first and second surfaces, wherein the pressure-sensitive adhesive has been formed from an acrylic copolymer comprising a polyurethane having a terminal functional group, wherein the adhesive tape has a thickness in the range between 0.05 and 0.10 mm and extensibility in longitudinal direction of between 850% and 2200%, wherein the adhesive tape can be firmly bonded to a substrate and then can be removed therefrom after it has been stretched at an angle of 90° or more away from the surface of the substrate, without fracturing of the carrier prior to the removal of the adhesive tape from the substrate, and without leaving significant residues of the pressure-sensitive adhesive on the substrate.
WO 2020035761 A1 describes a surface film comprising a base layer, wherein the base layer comprises a thermoplastic polyurethane film comprising a reaction product of a reaction mixture comprising a diisocyanate, a polyester polyol having a melting temperature of at least about 30° C., and a diol chain extender.
Proceeding from the prior art, it is thus a particular object of the present invention to provide an adhesive tape which is conveniently redetachable by stretching, has high tear resistance and has high shock resistance.
The object is firstly achieved by an adhesive tape according to Claim 1. Claim 1 relates to an adhesive tape of thickness 40 to 300 μm that can be redetached without residue or destruction by stretching essentially in the plane of the bond, comprising
at least one, typically exactly one, carrier of thickness 10 to 150 μm comprising at least one layer based on preferably uncrosslinked thermoplastic polyurethane and having a Shore A hardness of not more than 87, preferably not more than 85 and especially less than 70, where the carrier has a ratio of force at 400% elongation F400% to breaking force Fbreak of not more than 45%, preferably not more than 40%,
on which a pressure-sensitive adhesive layer is disposed on at least one side, preferably both sides,
wherein the adhesive tape has a ratio of stripping force Fstrip to breaking force Fbreak of less than
60%, preferably less than 50%. The adhesive tape may therefore be a single-sided adhesive tape or a double-sided adhesive tape, and is preferably double-sided.
Typically, in the carrier, the at least one layer based on preferably uncrosslinked thermoplastic polyurethane has been produced by means of extrusion. In addition, the carrier preferably has a force at 400% elongation F400% of not more than 15 N/mm2.
In the adhesive tape according to Claim 1, the desired ratio of F400% to Fbreak of the carrier can be achieved, for example, in that (i) preferably (a total of) less than 0.3% by weight, more preferably less than 0.1% by weight, of processing auxiliaries such as waxes, lubricants and/or antiblocking agents (for example SiO2 particles) is used in the carrier, based in each case on the total mass of the carrier, where the carrier is especially preferably free of processing auxiliaries, and in that (ii) there are preferably no crystalline superstructures in the carrier. The aforementioned proportions by weight of processing auxiliary each mean the total amount of processing auxiliary in the carrier, based on the total mass of the carrier. In a further preferred embodiment, less than 0.1% by weight of waxes, less than 0.1% by weight of lubricant and/or less than 0.1% by weight of antiblocking agent is present in the carrier, based in each case on the total mass of the carrier. According to the present application, ageing stabilizers are not considered to be processing auxiliaries. A low stripping force with simultaneously high tear resistance and good shock properties of the adhesive tape can be achieved in particular by a Shore A hardness of the at least one layer based on preferably uncrosslinked thermoplastic polyurethane of not more than 87, a ratio of F400% to Fbreak of the carrier of not more than 45%, and a suitable selection of the carrier thickness (10 to 150 μm) and of the adhesive.
The invention likewise relates to a process for producing an adhesive tape according to Claim 1, in which a carrier as defined in Claim 1
so as to result in an adhesive tape.
The object underlying the present invention can alternatively also be achieved by an adhesive tape according to Claim 4. Claim 4 relates to an adhesive tape of thickness 40 to 300 μm that can be redetached without residue or destruction by stretching essentially in the plane of the bond, comprising at least one, typically exactly one, carrier of thickness 10 to 150 μm comprising at least one layer based on preferably uncrosslinked polyurethane that has been produced from a preferably anionically stabilized dispersion and has a modulus at 100% elongation of not more than 1.8 MPa, preferably not more than 1.5 MPa, where the carrier has a ratio of force at 400% elongation F400% to breaking force Fbreak of not more than 30%, preferably not more than 20%,
on which a pressure-sensitive adhesive layer is disposed on at least one side, preferably both sides,
wherein the adhesive tape has a ratio of stripping force Fstrip to breaking force Fbreak of less than
60%, preferably less than 50%. The adhesive tape may therefore be a single-sided adhesive tape or a double-sided adhesive tape, and is preferably double-sided. The polyurethane is additionally typically thermoplastic.
The carrier preferably has a force at 400% elongation F400% of not more than 15 N/mm2.
In a further preferred embodiment of the adhesive tape according to Claim 4, less than 0.1% by weight of waxes, less than 0.1% by weight of lubricant and/or less than 0.1% by weight of antiblocking agent is present in the carrier, based in each case on the total mass of the carrier. A low stripping force with simultaneously high tear resistance and good shock properties of the adhesive tape can be achieved in particular by a modulus at 100% elongation of the at least one layer based on preferably uncrosslinked polyurethane of not more than 1.8 MPa, a ratio of F400% to Fbreak of the carrier of not more than 30%, and a suitable selection of the carrier thickness (10 to 150 μm) and of the adhesive. Carrier layers based on preferably uncrosslinked polyurethane that have been produced from a dispersion lead to particularly low stripping forces.
The invention likewise relates to a process for producing an adhesive tape according to Claim 4, in which a dispersion based on preferably uncrosslinked polyurethane
so as to result in an adhesive tape.
Preferred embodiments of the adhesive tapes according to Claim 1 and Claim 4 and of the processes for production thereof can be found in the dependent claims. The preferred embodiments of the adhesive tapes are additionally also preferred embodiments of the processes for production thereof.
The invention also relates to the use of an adhesive tape according to the invention for bonding of components in electronic devices.
Typical finished forms of the adhesive tapes according to the invention are adhesive tape rolls—the adhesive tapes, especially in elongate sheet form, can be produced in the form of rolls, i.e. rolled up in the form of Archimedean spirals—and adhesive strips as obtained, for example, in the form of diecuts.
Preferably, all layers are essentially in the shape of a cuboid. Further preferably, all layers are bonded to one another over the full area.
The general expression “adhesive tape”, or else synonymously “adhesive strips”, in the context of this invention, encompasses all sheetlike structures such as films or film sections extending in two dimensions, tapes having extended length and limited width, tape sections and the like, and lastly also diecuts or labels.
The adhesive tapes thus have a longitudinal extent (x direction) and a lateral extent (y direction). The adhesive tapes also have a thickness (z direction) that runs perpendicular to the two extents, the lateral extent and longitudinal extent being several times greater than the thickness. The thickness is very substantially the same, preferably exactly the same, over the entire areal extent of the adhesive tapes determined by their length and width.
The adhesive tapes according to the invention are especially in elongate sheet form. An elongate sheet is understood to mean an object, the length of which (extent in the x direction) is several times greater than its width (extent in the y direction), and the width over the entire length remains roughly and preferably exactly the same.
In double-sided adhesive tapes, the two pressure-sensitive adhesive layers are preferably identical in terms of their composition. Alternatively, they may also differ with regard to their composition. The two pressure-sensitive adhesive layers preferably also have the same thickness in double-sided adhesive tapes. Alternatively, they may also differ with regard to their thickness.
Advantageously, the outer, exposed faces of the pressure-sensitive adhesive layers of the adhesive tapes according to the invention can be provided with anti-adhesive materials, such as a release paper or a release film, also called liner. A liner may also be a material having anti-adhesive coating on at least one side, preferably on both sides, for example double-sidedly siliconized material. A liner, or in more general terms a temporary carrier, is not part of an adhesive tape, but merely an auxiliary for production and/or storage thereof and/or for further processing by die-cutting. Furthermore, a liner, as opposed to a permanent carrier, is not firmly bonded to an adhesive layer, but rather functions as a temporary carrier, i.e. as a carrier that can be pulled away from the adhesive layer. “Permanent carriers” are also referred to synonymously simply as “carriers” in the present application.
Since the adhesive tapes according to the invention comprise pressure-sensitive adhesives, the adhesive tapes according to the invention are also referred to as pressure-sensitive adhesive tapes.
As described, the pressure-sensitive adhesive tapes according to the invention can be redetached without residue or destruction by stretching essentially in the plane of the bond. What is meant in accordance with the invention by “detachment without residue” of the adhesive tapes is that they do not leave any adhesive residues on the bonded surfaces of the components on detachment. Moreover, what is meant in accordance with the invention by “detachment without destruction” of the adhesive tapes is that they do not damage, for example destroy, the bonded surfaces of the components on detachment.
In order that adhesive tapes can be redetached without residue or destruction by stretching in the bonding plane, they must have specific adhesive properties. For instance, there must be a distinct fall in the tack of the adhesive tapes on stretching. The lower the bonding performance in the stretched state, the less significant the damage to the substrate on detachment or the less significant the risk that residues will remain on the bonding substrate. This property is particularly clearly apparent in the case of pressure-sensitive adhesives based on vinylaromatic block copolymers in which tack falls to below 10% in the region of the yield point.
In order that adhesive tapes can be redetached easily and without residue by stretching, they must also have particular mechanical properties as well as the above-described adhesive properties. Particularly advantageously, the ratio of tear strength and stripping force is greater than two, preferably greater than three. Stripping force is that force that has to be expended in order to redetach an adhesive tape from an adhesive bond by stretching in the plane of the bond. This stripping force is composed of the force which is needed as described above for the detachment of the adhesive tape from the bonding substrates and the force that has to be expended for deformation of the adhesive tape. The force required to deform the adhesive tape depends on the thickness of the adhesive tape. The force required for detachment, by contrast, is independent of the thickness of the adhesive tape within the range of thickness of the adhesive tape under consideration.
In the adhesive tapes according to Claims 1 and 4, the polyurethane of the carrier is preferably uncrosslinked in each case. In the context of the present application, uncrosslinked polyurethane means a polyurethane that has not been covalently crosslinked, i.e. not chemically crosslinked. In an uncrosslinked polyurethane, in the context of the present application, however, there may independently be other types of crosslinking, for example coordinate crosslinks, hydrogen bonds, interloops and/or physical crosslinks via crystals, if the polyurethane is semicrystalline. In an alternative embodiment, in the adhesive tape according to Claim 1 or 4, the polyurethane of the carrier is crosslinked, i.e. covalently crosslinked.
a) Carrier Based on Thermoplastic Polyurethane, Typically Produced by Means of Extrusion:
The at least one carrier of the adhesive tape according to Claim 1 contains at least one, preferably exactly one, layer based on preferably uncrosslinked thermoplastic polyurethane that has typically been produced by means of extrusion. Such a layer based on thermoplastic polyurethane typically means a layer having a proportion of thermoplastic polyurethane of at least 50% by weight. The proportion of thermoplastic polyurethane in the layer is preferably at least 90% by weight; the layer especially consists essentially of thermoplastic polyurethane.
The preferably uncrosslinked thermoplastic polyurethane for the at least one carrier layer is preferably polyester-based (but may alternatively also be polyether-based, for example based on poly-THF as polyol). The thermoplastic polyurethane based on polyester or polyether is typically thermoplastic polyurethane based on aliphatic polyester or aliphatic polyether. The glass transition temperature (Tg) of the soft molecular chain of the thermoplastic polyurethane is preferably between −20° C. and 40° C., and the glass transition temperature of the hard molecular chain of the thermoplastic polyurethane is preferably between 60 and 110° C. The thermoplastic polyurethane typically has a tear strength of more than 20 MPa, preferably more than 35 MPa, and the Shore A hardness is preferably between 55 and 85, such as, in particular, between 55 and 70. In an alternatively preferred embodiment, the Shore hardness is between 70 and 85.
The thermoplastic polyurethane is preferably a reaction product of a reaction mixture comprising at least one diisocyanate, at least one polyester polyol (or polyether polyol) and optionally at least one chain extender, where the polyester polyol (or polyether polyol) typically has a melting temperature of at least 30° C., for example at least 100° C. or at least 200° C. The choice of a suitable melting temperature may contribute to an increase in the level of crystallinity of the layer. The level of crystallinity can be determined by differential scanning calorimetry (DSC), and is expressed as the fraction of crystallinity in the thermoplastic polyurethane film.
The proportion of diisocyanate in the reaction mixture is preferably 0.5% to
47% by weight, more preferably 1% to 40% by weight and especially 10% to 25% by weight. The amount of the diisocyanate in the reaction mixture may also be expressed as the isocyanate index. An isocyanate index may generally be understood such that it relates to the ratio of the equivalent amount of functional isocyanate groups used to the equivalent amount of functional hydroxyl groups. The isocyanate index of the reaction mixture is preferably within a range from 0.99 to 1.20, such as 1.00 to 1.10.
The diisocyanate is preferably a diisocyanate having the structure from formula I
O═C═N—R—N═C═O (Formula I)
in which R is selected from substituted and unsubstituted (C1-C40)-alkylene, (C2-C40)-alkenylene, (C4-C20)-arylene, (C4-C20)-arylene-(C1-C40)-alkylene-(C4-C20)-arylene, (C4-C20)-cycloalkylene and (C4-C20)-aralkylene. In further examples, the diisocyanate is selected from dicyclohexylmethane 4,4′-diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, phenylene 1,4-diisocyanate, phenylene 1,3-diisocyanate, m-xylylene diisocyanate, tolylene 2,4-diisocyanate, toluene 2,4-diisocyanate, tolylene 2,6-diisocyanate, poly(hexamethylene diisocyanate), cyclohexylene 1,4-diisocyanate, 4-chloro-6-methylphenylene 1,3-diisocyanate, hexamethylene diisocyanate, diphenylmethane 4,4′-diisocyanate, 1,4-diisocyanatobutane, 1,8-diisocyanatooctane, toluene 2,6-diisocyanate, toluene 2,5-diisocyanate, toluene 2,4-diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, methylenebis(o-chlorophenyl diisocyanate), methylene diphenylene 4,4′-diisocyanate, (4,4′-diisocyanato-3,3′,5,5′-tetraethyl)diphenylmethane, 4,4′-diisocyanato-3,3′-dimethoxybiphenyl (o-dianisidine diisocyanate), 5-chlorotoluene 2,4-diisocyanate, 1-chloromethyl-2,4-diisocyanatobenzene, tetramethyl-m-xylylene diisocyanate, 1,6-diisocyanatohexane, 1,12-diisocyanatododecane, 2-methyl-1,5-diisocyanatopentane, methylene dicyclohexylene 4,4′-diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate, 2,2,4-trimethylhexyl diisocyanate or a mixture thereof.
The diisocyanate used is more preferably diphenylmethane 4,4′-diisocyanate (MDI), hexane diisocyanate (HDI), isophorone diisocyanate (IPDI) or hexamethylene diisocyanate (HMDI), for example MDI. The polyisocyanate, such as typically diisocyanate, may thus, in a preferred embodiment, be an aromatic polyisocyanate (diisocyanate).
The proportion of polyester polyol (or polyether polyol) in the reaction mixture is preferably in the range from 43% by weight to 70% by weight, more preferably 50% by weight to 60% by weight.
The polyester polyol may contain any suitable number of hydroxyl groups. For example, the polyester polyol may contain four hydroxyl groups or three hydroxyl groups. The polyester polyol may even contain two hydroxyl groups, such that the polyester polyol is a polyester diol. In general, the polyester polyol may be a product of a condensation reaction, such as a polycondensation reaction. However, the polyester polyol is typically not produced via a ring-opening polymerization reaction product.
In examples in which polyester polyol is prepared by a condensation reaction, the reaction between one or more carboxylic acids and one or more polyols may take place. One example of a suitable carboxylic acid comprises a carboxylic acid of formula II having the structure:
In the formula II, R1 is typically selected from substituted and unsubstituted (C1-C40)-alkylene, (C2-C40)-alkylene, (C2-C40)-alkenylene, (C4-C20)-arylene, (C4-C20)-cycloalkylene and (C4-C20)-aralkylene. Examples of suitable carboxylic acids include glycolic acid (2-hydroxyethanoic acid), lactic acid (2-hydroxypropanoic acid), succinic acid (butanedioic acid), 3-hydroxybutanoic acid, 3-hydroxypentanoic acid, terephthalic acid (benzene-1,4-dicarboxylic acid), naphthalenedicarboxylic acid, 4-hydroxybenzoic acid, 6-hydroxynaphthalene-2-carboxylic acid, oxalic acid, malonic acid (propanedioic acid), adipic acid (hexanedioic acid), pimelic acid (heptanedioic acid), ethoic acid, suberic acid (octanedioic acid), azelaic acid (nonanedioic acid), sebacic acid (decanedioic acid), glutaric acid (pentanedioic acid), dodecanedioic acid, brassylic acid, thapsic acid, maleic acid, fumaric acid, glutaconic acid, 2-decenoic acid, muconic acid, glutinic acid, citraconic acid, mesaconic acid, itaconic acid, malic acid (2-hydroxybutanedioic acid), aspartic acid (2-aminobutanedioic acid), glutamic acid (2-aminopentanedioic acid), tartaric acid (2,3-dihydroxybutanedioic acid), diaminopimelic acid, saccharic acid, mesoxalic acid, oxaloacetic acid, acetonecarboxylic acid (3-oxopentanedioic acid), arabinaric acid, phthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid or a mixture thereof. Adipic acid is particularly preferred.
One example of a suitable polyol comprises a polyol of formula III having the structure:
In the formula III, R2 is selected from substituted and unsubstituted (C1-C40-alkylene, (C2-C40)-alkenylene, (C4-C20-arylene, (C1-C40-acylene, (C4-C20-cycloalkylene, (C4-C20-aralkylene and (C1-C40-alkoxylene, and R3 and R4 are independently selected from —H, —OH, substituted and unsubstituted (C1-C40-alkyl, (C2-C40-alkenyl, (C4-C20-aryl, (C1-C20-acyl, (C4-C20-cycloalkyl, (C4-C20)aralkyl and (C1-C40-alkoxy. The polyol used is more preferably ethylene glycol, butanediol, hexanediol, neopentyl glycol or a mixture thereof.
If a chain extender is used, it is preferably present in the reaction mixture in an amount of 1% to 13% by weight, especially 2% to 10% by weight.
The diol chain extender typically has a weight-average molecular weight of less than about 250 daltons. For example, a weight-average molecular weight of the diol chain extender may be within a range from 30 daltons to 250 daltons, preferably 50 daltons to 150 daltons. The diol chain extender may contain any suitable number of carbons. For example, the diol chain extender may have a number-average number of 2 carbons to 20 carbons, preferably 3 carbons to 10 carbons. Such diol chain extenders may contribute to strengthening the TPU-based layer (“PU” and “TPU” in the present application mean “polyurethane” and “thermoplastic polyurethane” respectively). This may be because the relatively short chains can be stiffer than a longer-chain diol. The short-chain diols may be stiffer, for example, because the short-chain diol is more restricted in terms of rotation about the individual bonds along the chain. Examples of suitable diol chain extenders include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, propane-1,3-diol, butane-1,3-diol, butane-1,4-diol, neopentyl glycol, hexane-1,6-diol, cyclohexane-1,4-dimethanol or a mixture thereof. The diol chain extender used is more preferably butanediol.
Particularly preferred polyester polyols are accordingly polyalkylene adipates.
The TPU-based carrier layer is preferably free of additives such as antiblocking agents and waxes. In addition, the polyurethane preferably does not have a crystalline superstructure (a crystalline superstructure is manifested in a DSC peak >210° C.).
In a preferred embodiment, the TPU-based carrier layer is foamed. The foaming is preferably effected with microballoons. Alternatively, it is also possible to use chemical and/or physical blowing agents. The details relating to foaming that follow with regard to the carrier based on preferably uncrosslinked polyurethane produced from a dispersion are analogously applicable to the TPU-based carrier.
The carrier layer based on thermoplastic polyurethane has suitable mechanical properties for use in an adhesive tape detachable by stretching. The carrier layer preferably has an elongation at break in longitudinal direction of at least 600%, more preferably at least 800%.
The carrier layer may be opaque, optically clear or transparent.
The main process used for film production is conventionally the blown film process for multiple layers. A PE layer (i.e. a polyethylene layer) and the actual TPU layer are produced here as a coextruded film in the blown film process (in other words, the PE layer functions as support carrier that imparts the necessary mechanical stability to the extrudate). The PE support carrier is thus removed in the application prior to the production of the adhesive tape, i.e. constitutes a temporary carrier. For production of a corresponding blown film, however, numerous additives such as what are called antiblocking agents (e.g. silicate particles) and lubricant waxes are needed to prevent blocking of the PU film when the bubble collapses in the blown film process. The problem here is that TPUs are still tacky about 1 h after melting. Both factors (crystalline superstructure and additives, in particular silicate particles) lead to an adverse effect on mechanical properties. Both the silicate particles in the film (=defects) and the crystalline superstructure (=hard inflexible domains) lead to lower extensibility and, in particular, to a higher tendency to breaks in use, i.e. on stretching. The waxes additionally lead to problems with reduction of adhesive force (through migration of the waxes to the PSA surface, i.e. surface of the pressure-sensitive adhesive), and to difficulties in the anchoring of the PSA on the film. An additional advantageous factor for high extensibility and a low tendency to breaks is a high molecular weight of the PU polymer (increase in the toughness of the film).
b) Polyurethane-Based Carrier Produced from Dispersion:
The at least one carrier of the adhesive tape according to Claim 4 contains at least one, preferably exactly one, layer based on preferably uncrosslinked polyurethane that has been produced from a dispersion. Such a layer based on polyurethane typically means a layer having a proportion of polyurethane of at least 50% by weight. The proportion of polyurethane in the layer is preferably at least 90% by weight. The polyurethane is typically thermoplastic.
The polyurethane is especially composed of at least one polyisocyanate component and at least one polyol component, i.e. the reaction product of at least the components mentioned.
Polyurethane dispersions used in the context of the present invention may especially include the following dispersions, optionally in combination:
The polyurethane dispersions are those having a high solids content (about 30% to 70% by weight, preferably 50% to 60% by weight). All products mentioned above under a) to d) are typically free of organic cosolvents.
The polyurethane here is more preferably aliphatic polyester polyurethane or aliphatic polyether polyurethane, i.e. the polyurethane in this case is based on aliphatic polyester or aliphatic polyether.
The polyurethane dispersions of the present invention are aqueous. They are preferably free of organic solvents, but may optionally contain organic solvents.
The at least one polyisocyanate component is preferably a diisocyanate. Aromatic diisocyanates may be used, such as toluene diisocyanate (TDI) (particularly preferred), p-phenylene diisocyanate (PPDI), diphenylmethane 4,4′-diisocyanate (MDI), bisphenyl p,p′-diisocyanate (BPDI), or especially aliphatic diisocyanates, such as isophorone diisocyanate (IPDI), hexamethylene 1,6-diisocyanate (HDI) or 4,4′-diisocyanatodicyclohexylmethane (H12MDI). Likewise useful are diisocyanates having substituents in the form of halo, nitro, cyano, alkyl, alkoxy, haloalkyl, hydroxyl, carboxyl, amido, amino or combinations thereof.
Overall, it is possible to use all aliphatic, cycloaliphatic, araliphatic and preferably aromatic polyfunctional isocyanates that are known per se.
Specific examples include the following: alkylene diisocyanates having 4 to 12 carbon atoms in the alkylene radical, such as dodecane 1,12-diisocyanate, 2-ethyltetramethylene 1,4-diisocyanate, 2-methylpentamethylene 1,5-diisocyanate, tetramethylene 1,4-diisocyanate, and preferably hexamethylene 1,6-diisocyanate; cycloaliphatic diisocyanates such as cyclohexane 1,3-diisocyanate and cyclohexane 1,4-diisocyanate and any mixtures of these isomers, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate), 2,4- and 2,6-hexahydrotolylene diisocyanate and any mixtures of these isomers, dicyclohexylmethane 4,4′-, 2,4′- and 2,2′-diisocyanate and any mixtures of these isomers, and preferably aromatic di- and polyisocyanates, for example tolylene 2,4- and 2,6-diisocyanate and the corresponding isomer mixtures, diphenylmethane 4,4′-, 2,4′- and 2,2′-diisocyanate and the corresponding isomer mixtures, mixtures of diphenylmethane 4,4′- and 2,4′-diisocyanates, polyphenyl polymethylene polyisocyanates, mixtures of diphenylmethane 4,4′-, 2,4′- and 2,2′-diisocyanates and polyphenyl polymethylene polyisocyanates (crude MDI) and mixtures of crude MDI and tolylene diisocyanates. The organic di- and polyisocyanates may be used individually or in the form of mixtures thereof.
The polyisocyanate component preferably has a number-average molecular weight of 60 to 50000 g/mol, especially of 400 to 10000 g/mol, preferably of 400 to 6000 g/mol.
Also frequently used are what are called modified polyfunctional isocyanates, i.e. products that are obtained by chemical reaction of organic di- and/or polyisocyanates. Examples include di- and/or polyisocyanates containing ester, urea, biuret, allophanate, carbodiimide, isocyanurate, uretdione and/or urethane groups. Specific examples include: organic, preferably aromatic, polyisocyanates containing urethane groups and having NCO contents of 33.6% to 15% by weight, preferably of 31% to 21% by weight, based on the total weight. Examples are low molecular weight diols, triols, dialkylene glycols, trialkylene glycols or polyoxyalkylene glycols having number-average molecular weights up to 6000 g/mol, especially up to 1500 g/mol, modified crude MDI or tolylene 2,4- or 2,6-diisocyanate. Examples of suitable di- or polyoxyalkylene glycols are diethylene glycols, triols and/or tetraols, dipropylene glycols, triols and/or tetraols, polyoxyethylene glycols, triols and/or tetraols, polyoxypropylene glycols, triols and/or tetraols, and polyoxypropylene-polyoxyethylene glycols, triols and/or tetraols. Also suitable are prepolymers containing NCO groups and having NCO contents of 25% to 3.5% by weight, preferably of 21% to 14% by weight, based on the total weight, prepared from polyester polyols and/or preferably polyether polyols, and diphenylmethane 4,4′-diisocyanate, mixtures of diphenylmethane 2,4′- and 4,4′-diisocyanate, tolylene 2,4- and/or 2,6-diisocyanate or crude MDI. Other useful starting materials have been found to be liquid polyisocyanates containing carbodiimide groups and/or isocyanurate rings and having NCO contents of 33.6% to 15% by weight, preferably 31% to 21% by weight, based on the total weight, for example based on diphenylmethane 4,4′-, 2,4′- and/or 2,2′-diisocyanate and/or tolylene 2,4- and/or 2,6-diisocyanate.
The modified polyisocyanates may be mixed with one another or with unmodified organic polyisocyanates, for example diphenylmethane 2,4′-, 4,4′-diisocyanate, crude MDI, tolylene 2,4- and/or 2,6-diisocyanate.
Particularly useful isocyanates have been found to be diphenylmethane diisocyanate isomer mixtures or crude MDI, and especially crude MDI having a diphenylmethane diisocyanate isomer content of 30% to 55% by weight, and polyisocyanate mixtures based on diphenylmethane diisocyanate that contain urethane groups and have an NCO content of 15% to 33% by weight.
Preferred proportions by weight of the polyisocyanate component are from 10% to 40% by weight, especially 13% to 35% by weight and more preferably 15% to 30% by weight.
According to the invention, polyol component means not just polymers having at least two hydroxyl groups but generally compounds having at least two hydrogen atoms that are active toward isocyanates.
The polyol component is preferably a diol, a polyether diol, a polyester diol, a polycarbonate diol, a polycaprolactone polyol or a polyacrylate polyol, particular preference being given to polyether diol, polyester diol and polycarbonate diol, especially glycol, propanediol, butanediol, pentanediol, hexanediol, cyclohexanediol, cyclohexyldimethanol, octanediol, neopentyl glycol, diethylene glycol, triethylene glycol, trimethylpentanediol, benzenedimethanol, benzenediol, methylbenzenediol, bisphenol A, poly(butanediol-co-adipate) glycol, poly(hexanediol-co-adipate) glycol, poly(ethanediol-co-adipate) glycol, polytetramethylene glycol, polypropylene glycol, polyethylene glycol, or a mixture thereof.
The main function of the polyol component is to react with the polyisocyanate component to give the polyurethane polymer. In addition, however, the polyol component also serves as a physical conditioner, since the elasticity of the polyurethane depends on the molecular weight of the polyol component. In general, the higher the molecular weight of the polyol component, the softer the resulting polyurethane.
The polyol component preferably has a number-average molecular weight of 60 to 50000 g/mol, especially of 400 to 10000 g/mol, preferably of 400 to 6000 g/mol.
For adjustment of the properties of the polyurethane carrier to be produced, it may be advantageous for the starting mixture to additionally comprise at least one further dispersion, typically selected from the group consisting of polyurethane dispersions, polyurethane dispersions wherein the polyol component includes a comonomer having flame-retardant action, synthetic rubber dispersions, natural rubber dispersions and polyacrylate dispersions. In this way, it is possible to improve the stability of the polyurethane carrier and its elongation at break inter alia.
Polyacrylate dispersions comprise water-insoluble polyacrylate, which is typically dispersed in water by means of an emulsifier. They contain, for example, about 30% to 60% by weight of polyacrylate and about 3% by weight of emulsifier. According to the invention, the polyacrylate is a water-insoluble polyacrylate or polymethacrylate, a mixture thereof or a copolymer with other monomers. The emulsifier may be an ionic, nonionic or steric emulsifier. This is normally not fixedly incorporated into the polymer chains. Acrylate dispersions may comprise further additives, such as film formers or cosolvents, defoamers, flame retardants and/or wetting agents.
Acrylate dispersions are typically obtained by the emulsion polymerization of suitable monomers. For this purpose, these are finely distributed in water by means of an emulsifier. A water-soluble free-radical initiator is added to the emulsion of the monomers in water. Since the free radicals formed therefrom dissolve preferentially in water, the concentration thereof in the monomer droplets is low, and so the polymerization can proceed very uniformly therein. After the polymerization has ended, the dispersion can be used directly, but it is often admixed with additives such as defoamers, film formers and/or wetting agents in order to further improve the properties.
It is optionally possible to catalyse the reaction of the OH groups of the polyol component with the isocyanate groups. Useful catalysts include, in particular:
organic metal compounds, preferably organic tin compounds, such as tin(II) salts of organic carboxylic acids, for example tin(II) acetate, tin(II) octoate, tin(II) ethylhexanoate, tin(II) laurate and dialkyltin(IV) salts of organic carboxylic acids, for example dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate, dioctyltin diacetate and tertiary amines such as triethylamine, tributylamine, dimethylcyclohexylamine, dimethylbenzylamine, N-methylimidazole, N-methyl-, N-ethyl-, N-cyclohexylmorpholine, N,N,N′,N′-tetramethylethylenediamine, N,N,N′,N′-tetramethylbutylenediamine, N,N,N′,N′-tetramethylhexylene-1,6-diamine, pentamethyldiethylenetriamine, tetramethyldiaminoethyl ether, bis(dimethylaminopropyl)urea, dimethylpiperazine, 1,2-dimethylimidazole, 1-azabicyclo-[3.3.0]-octane, 1,4-diazabicyclo-[2.2.2]-octane, and also alkanolamine compounds such as triethanolamine, trisisopropanolamine, N-methyl- and N-ethyldiethanolamine and dimethylethanolamine.
Useful catalysts further include: tris(dialkylamino)-s-hexahydrotriazines, especially tris(N,N-dimethylamino)-s-hexahydrotriazine, tetraalkylammonium salts, for example N,N,N-trimethyl-N-(2-hydroxypropyl) formate, N,N,N-trimethyl-N-(2-hydroxypropyl) 2-ethylhexanoate, tetraalkylammonium hydroxides such as tetramethylammonium hydroxide, alkali metal hydroxides such as sodium hydroxide, alkali metal alkoxides such as sodium methoxide and potassium isopropoxide, and alkali metal or alkaline earth metal salts of fatty acids having 1 to 20 carbon atoms and optionally pendant OH groups.
Preference is given to using tertiary amines, tin compounds, alkali metal and alkaline earth metal carboxylates, quaternary ammonium salts, s-hexahydrotriazines and tris(dialkylaminomethyl)phenols.
Preferably 0.001% to 5% by weight, especially 0.002% to 2% by weight, of catalyst or catalyst combination is used, based on the total weight of the starting mixture.
The polyurethane may optionally include an active hydrogen-containing component that can form a hydrophilic group, preferably from 1% to 15% by weight, especially from 3% to 10% by weight and more preferably from 4% to 7% by weight. What is meant here by “active hydrogen” is that the hydrogen atom of the component is unstable in that it can readily enter into a chemical reaction, for example a substitution reaction, with other compounds, so as to form a hydrophilic group. The effect of this component is that the polyurethane can be efficiently dispersed in water. Useful hydrophilic groups especially include: —COO—, —SO3−, —NR3+, or —(CH2CH2O)n—. The component containing an active hydrogen may be, for example: dimethylolpropionic acid (DMPA), dimethylolbutyric acid (DMBA), poly(ethylene oxide) glycol, bis(hydroxylethyl)amines, or sodium 3-bis(hydroxyethyl)aminopropanesulfonate.
The component containing an active hydrogen is optional, as described above. For the purpose of dispersion, the polyurethane dispersion alternatively or additionally frequently contains at least one surfactant.
Particularly suitable surfactants that also act as foam stabilizer especially include Stokal® STA (ammonium stearate) and Stokal® SR (succinamate) from Bozzetto Group.
However, further surfactants are also useful, which may especially be selected from the group consisting of ether sulfates, fatty alcohol sulfates, sarcosinates, organic amine oxides, sulfonates, betaines, amides of organic acids, sulfosuccinates, sulfonic acids, alkanolamides, ethoxylated fatty alcohols, sorbates and combinations thereof.
As a further optional component, the starting mixture may comprise a thickener. It is possible here to use Borchi® Gel 0625 for example. Further suitable thickeners are polyetherurethane solutions, for example Ortegol PV301 from Evonik Industries. A thickener especially ensures stability on drying.
The starting mixture may comprise further additives such as stabilizers or light stabilizers. Solvents may also be added as further additives, in which case the proportion of the solvent may be up to 50% by weight, based on the total amount of the finished starting mixture. Suitable solvents for preparation of polyurethane materials are solvents such as low-boiling hydrocarbons having boiling points below 100° C., preferably below 50° C., but also other solvents, for example paraffins, halogenated hydrocarbons, halogenated paraffins, ethers, ketones, alkyl carboxylates, alkyl carbonates or additional liquid flame retardants such as alkyl phosphates, for example triethyl phosphate or tributyl phosphate, halogenated alkyl phosphates, for example tris(2-chloropropyl) phosphate or tris(1,3-dichloropropyl) phosphate, aryl phosphates, for example diphenyl cresyl phosphate, phosphonates, for example diethyl ethanephosphonate. Likewise usable are mixtures of the solvents mentioned.
Further optional additives are cell regulators of the type known per se, such as paraffins or fatty alcohols or dimethylpolysiloxanes, flame retardants, pigments or dyes, stabilizers against ageing and weathering influences, plasticizers, fungistatic and bacteriostatic substances, fillers such as barium sulfate, bentonite, kaolin, glass powder, glass beads, glass fibres, calcium carbonate, kieselguhr, quartz sand, fluoropolymers, thermoplastics, microbeads, expandable graphite, carbon black or suspended chalk or combinations thereof.
In a preferred embodiment, it is likewise possible to add expandable microballoons that are expanded when the carrier composition is dried. Alternatively, it is possible to add pre-expanded microballoons. The remarks that follow with regard to the microballoons as used in preferred pressure-sensitive adhesive layers according to the invention are applicable here analogously. In this way, it is possible to produce polyurethane-based carriers foamed by microballoons, i.e. polyurethane foams.
The present invention also encompasses a process for producing a carrier based on polyurethane that has been produced from a dispersion, in which the foaming has been achieved by means of frothing. The process typically comprises the following steps:
a) initially charging a polyurethane dispersion as described above and at least one surfactant, and optionally further components, such as further dispersions in particular, to form a starting mixture,
b) mechanically foaming the starting mixture to form a moist polyurethane foam composition, optionally with addition of further components, such as fillers and/or further additives in particular,
c) applying the moist polyurethane foam composition to a surface (typically of a temporary carrier, such as that of a liner in particular, or of a pressure-sensitive adhesive layer),
d) drying the moist polyurethane foam composition to obtain the polyurethane foam.
The polyurethane dispersion can be produced here in the manner described hereinafter:
The at least one polyol component and optionally the active hydrogen-containing component and solvent (e.g. acetone or N-methylpyrrolidone) are introduced into a vessel under a nitrogen atmosphere and stirred—for example with a paddle stirrer. Once the components have been mixed well, the at least one polyisocyanate component is added, and the vessel is heated to about 40 to 90° C. for four to six hours and then cooled down. Once the vessel has cooled down to 30° C. to 50° C., a basic solution, for example triethylamine, is added while stirring and the mixture is neutralized for fifteen to twenty minutes. The mixture is then added to water; it is optionally possible to add a chain extender at this point. The polyurethane dispersion according to the invention is obtained.
For formation of the polyurethane foam, the starting mixture, i.e. the polyurethane dispersion produced as above or in some other way, together with the at least one surfactant, and optionally a solvent and/or the further optional constituents, is mechanically beaten and foamed. It is optionally possible to add a thickener after the beating.
Alternatively, what is produced at first is not a polyurethane dispersion. Instead, a prepolymer dispersion is used, and the prepolymer polymerizes in the course of mechanical beating/foaming to give the polyurethane.
Additionally or alternatively, it is possible to add a physical blowing agent. For example, the starting mixture can be foamed in the presence of a gas such as air, nitrogen or a noble gas, for example helium, neon or argon. Blowing agents may be used individually or as a mixture of various blowing agents. Blowing agents may be selected from a large number of materials including the following: hydrocarbons, ethers and esters, and the like. Typical physical blowing agents have a boiling point in the range from −50° C. to +100° C., and preferably from −50° C. to +50° C. Preferred physical blowing agents include hydrocarbons such as n-pentane, isopentane and cyclopentane, methylene chloride, or any combinations of the aforementioned compounds. Such blowing agents may preferably be used in amounts of 5% by weight to 50% by weight of the reaction mixture, especially of 10% by weight to 30% by weight of the reaction mixture.
Additionally or alternatively, it is likewise possible to add a chemical blowing agent. Chemical blowing agents are substances that eliminate gas only during the processing operation on account of a chemical reaction—usually initiated by supply of heat—and hence enable the creation of a foam structure in the polymer. The cause of the elimination of gas may either be the thermal breakdown of the blowing agent or a chemical reaction of various substances present in the blowing agent. The gas formed is usually N2, CO2 or CO.
Foamed carriers based on polyurethane preferably have a density of 250 kg/m3 to 500 kg/m3, more preferably 350 kg/m3 to 450 kg/m3.
A film may optionally be applied above the foam layer. If it is under tension, the film can limit the thickness of the foam layer. The film may alternatively function merely as a cover.
In a further preferred embodiment, the foam can be applied to the temporary carrier, such as liner in particular, or the pressure-sensitive adhesive layer by means of a blade or a knife, which achieves a homogeneous thickness of the foam layer before it is introduced or run into the drying oven. Alternatively, it is also possible to provide rollers in order to adjust the thickness of the foam layer.
Application of the foam layer to the carrier and optional coverage with a film are followed by drying, preferably in a drying oven. Preferred temperatures for drying are from 50° C. to 180° C., preferably from 50° C. to 120° C., especially from 70° C. to 115° C., most preferably from 100° C. to 115° C. The temperature is preferably at least 50° C., especially at least 60° C., preferably at least 70° C., especially at least 80° C., even more preferably at least 90° C., especially at least 100° C., especially at least 110° C., very preferably at least 120° C., especially at least 130° C. In addition, the temperature is preferably at most 180° C., especially at most 170° C., more preferably at most 160° C., especially at most 150° C.
The drying in step d) of the above-specified process sequence is preferably effected in at least two stages, with increasing drying temperature from one step to the next. Unlike when high starting temperatures (e.g. 120° C.) are used in the course of drying, a staged increase in the drying temperature enables homogeneous drying, which leads to a homogeneous distribution of the cell sizes. There is at first relatively homogeneous predrying of the entire foam at lower temperature, and removal of the residual moisture at higher temperature in the further step.
However, it may also be desirable to achieve a cell size that varies over the cross section. In this case, a high drying temperature should be employed from the start. This ensures that the foam dries rapidly at the surface, but remains moist for a long time in the interior, which results in the different cell size distribution over the cross section.
The drying in step d) is more preferably effected in two stages, where the drying temperature in the 1st step is from 50° C. to 100° C., preferably 70° C. to 90° C., especially 80° C., and the drying temperature in the 2nd step is from 105° C. to 180° C., preferably 110° C. to 150° C., especially 120° C.
The PU-based carrier layer made from dispersion is preferably free of additives such as antiblocking agents and waxes. Likewise preferably, the polyurethane does not have a crystalline superstructure.
The PU-based carrier layer made from dispersion or the adhesive tape comprising this layer will additionally typically have been subjected to a heat treatment at at least 150° C. in order to optimize tensile strength.
Pressure-Sensitive Adhesives According to the Invention:
In the adhesive tapes according to the invention, a pressure-sensitive adhesive layer is disposed on at least one side of the at least one carrier.
What is understood in accordance with the invention by a “pressure-sensitive adhesive”, as is generally customary, is a substance which is permanently tacky and adhesive—especially at room temperature. It is characteristic feature of a pressure-sensitive adhesive that it can be applied to a substrate by pressure and adheres there, with no specific definition of the pressure to be expended and the time for which this pressure is applied. In some cases, depending on the exact type of pressure-sensitive adhesive, temperature and air humidity, and the substrate, the application of a brief
minimal pressure not exceeding a light touch for a brief moment is sufficient to achieve the adhesion effect; in other cases, even a prolonged period of application of a high pressure may be necessary.
Pressure-sensitive adhesives have particular characteristic viscoelastic properties that lead to permanent tack and adhesiveness. It is a characteristic feature of these that, when they are mechanically deformed, the result is both viscous flow processes and the development of elastic resilience forces. Both processes are in a particular ratio to one another in terms of their respective proportions, depending both on the exact composition, structure and level of crosslinking of the pressure-sensitive adhesive and on the speed and duration of the deformation, and on the temperature.
The viscous flow component is necessary for achievement of adhesion. Only the viscous components caused by macromolecules having relatively high mobility enable good wetting and good adaptation to the substrate to be bonded. A high proportion of viscous flow leads to high pressure-sensitive adhesiveness (also referred to as tack or surface tack) and hence often also to a high bonding force. Highly crosslinked systems, or polymers that are crystalline or solidify in vitreous form, generally have at least only low pressure-sensitive adhesion, if any, for lack of free-flowing components.
The elastic resilience force components are needed for achievement of cohesion. They are caused, for example, by very long-chain and entangled macromolecules that are crosslinked physically or chemically, and enable transmission of the forces that attack an adhesive bond. They have the effect that an adhesive bond can withstand a sustained stress acting thereon, for example in the form of a sustained shear stress, to a sufficient degree over a prolonged period of time.
For more exact description and quantification of the degree of elastic and viscous components and of the relative ratio of the components, it is possible to use the parameters of storage modulus (G′) and loss modulus (G″) that can be determined by means of dynamic-mechanical analysis (DMA). G′ is a measure of the elastic component, G″ a measure of the viscous component of a substance. Both parameters are dependent on deformation frequency and temperature.
The parameters can be ascertained with the aid of a rheometer. The material to be examined is subjected here to a sinusoidally oscillating shear stress, for example in a plate-plate arrangement. In the case of shear stress-controlled devices, deformation is measured as a function of time and of the time delay of this deformation with respect to the onset of shear stress. This time delay is referred to as the phase angle δ.
The storage modulus G′ is defined as follows: G′=(τ/γ)·cos(δ) (τ=shear stress, γ=deformation, δ=phase angle=phase shift between shear stress vector and deformation vector). The definition of the loss modulus G″ is: G″=(τ/γ)·sin(δ) (τ=shear stress, γ=deformation, δ=phase angle=phase shift between shear stress vector and deformation vector).
A substance is generally considered to be pressure-sensitively adhesive and is defined as being pressure-sensitively adhesive for the purposes of the invention when, at room temperature, here by definition at 23° C., G′ is at least partly within the range from 103 to 107 Pa within the deformation frequency range from 100 to 101 rad/sec, and when G″ is likewise at least partly within this range. What is meant by “partly” is that at least a section of the G′ curve is within the window defined by the deformation frequency range from 100 to 101 rad/sec inclusive (abscissa) and the range of G′ values from 103 to 107 Pa inclusive (ordinate). This is correspondingly true of G″.
The pressure-sensitive adhesive layers of the adhesive tapes according to the invention may be based on polymers of different chemical structure. For example, they may be based on acrylate (co)polymer, silicone (co)polymer, nitrile rubber, i.e. acrylonitrile-butadiene rubber, or chemically or physically crosslinked synthetic rubber.
In a preferred embodiment, they are based on acrylate (co)polymer.
More preferably, the pressure-sensitive adhesive layers of the adhesive tapes according to the invention consist of a pressure-sensitive adhesive based on vinylaromatic block copolymer, such as styrene block copolymer in particular. What this typically means is that the elastomer component of the pressure-sensitive adhesive consists to an extent of at least 50% by weight of vinylaromatic block copolymer. The elastomer component preferably consists to an extent of at least 90% by weight of vinylaromatic block copolymer and especially essentially of vinylaromatic block copolymer. In a further preferred embodiment, the pressure-sensitive adhesive, aside from vinylaromatic block copolymer, does not contain any further elastomers in amounts that significantly affect the essential properties of the vinylaromatic block copolymer.
The vinylaromatic block copolymer used is preferably at least one synthetic rubber in the form of a block copolymer having an A-B, A-B-A, (A-B)n, (A-B)nX or (A-B-A)nX structure, in which
More particularly, all synthetic rubbers of the pressure-sensitive adhesive according to the invention are block copolymers having a structure as detailed above. The pressure-sensitive adhesive according to the invention may thus also comprise mixtures of various block copolymers having a structure as above.
Suitable block copolymers (vinylaromatic block copolymers) thus comprise one or more rubber-like blocks B (soft blocks) and one or more glass-like blocks A (hard blocks). More preferably, at least one synthetic rubber of the pressure-sensitive adhesive according to the invention is a block copolymer having an A-B, A-B-A, (A-B)3X or (A-B)4X structure, where the above meanings are applicable to A, B and X, and where at least one block copolymer contains at least two hard blocks. Most preferably, all synthetic rubbers in the pressure-sensitive adhesive according to the invention are block copolymers having an A-B, A-B-A, (A-B)3X or (A-B)4X structure, where the above meanings are applicable to A, B and X. More particularly, the synthetic rubber in the pressure-sensitive adhesive according to the invention is a mixture of block copolymers having an A-B, A-B-A, (A-B)3X or (A-B)4X structure, preferably comprising at least diblock copolymers A-B and/or triblock copolymers A-B-A.
Also advantageous is a mixture of diblock and triblock copolymers and (A-B)n or (A-B)nX block copolymers with n not less than 3.
The pressure-sensitive adhesives employed are preferably those based on block copolymers comprising polymer blocks predominantly formed from vinylaromatics (A blocks), preferably styrene, and those predominantly formed by polymerization of 1,3-dienes (B blocks), for example butadiene and isoprene or a copolymer of these. The products here may also be partly or fully hydrogenated in the diene block. Block copolymers of vinylaromatics and isobutylene are likewise utilizable in accordance with the invention.
The block copolymers of the pressure-sensitive adhesives preferably have polystyrene end blocks.
The block copolymers that result from the A and B blocks may contain identical or different B blocks. The block copolymers may have linear A-B-A structures. It is likewise possible to use block copolymers in radial form and star-shaped and linear multiblock copolymers. Further components present may be A-B diblock copolymers. The aforementioned polymers may be used alone or in a mixture with one another, although A-B diblock copolymers are not usable alone.
Rather than the preferred polystyrene blocks, vinylaromatics used may also be polymer blocks based on other aromatic-containing homo- and copolymers (preferably C8 to C12 aromatics) having glass transition temperatures of greater than 75° C., for example a-methylstyrene-containing aromatic blocks. In addition, it is also possible for identical or different A blocks to be present.
Vinylaromatics for formation of the A block preferably include styrene, α-methylstyrene and/or other styrene derivatives. The A block may thus be in the form of a homo- or copolymer. More preferably, the A block is a polystyrene.
Preferred conjugated dienes as monomers for the soft block B are especially selected from the group consisting of butadiene, isoprene, ethylbutadiene, phenylbutadiene, piperylene, pentadiene, hexadiene, ethylhexadiene and dimethylbutadiene, and any desired mixtures of these monomers. The B block may also be in the form of a homopolymer or copolymer. More preferably, the conjugated dienes as monomers for the soft block B are selected from butadiene and isoprene. For example, the soft block B is a polyisoprene, a polybutadiene or a partly or fully hydrogenated derivative of one of these two polymers, such as polybutylene-butadiene in particular, or a polymer formed from a mixture of butadiene and isoprene. Most preferably, the B block is a polybutadiene.
A blocks in the context of this invention are also referred to as “hard blocks”. B blocks, correspondingly, are also called “soft blocks” or “elastomer blocks”. This reflects the inventive selection of the blocks in accordance with their glass transition temperatures (for A blocks at least 25° C., more particularly at least 50° C., and for B blocks at most 25° C., more particularly at most −25° C.).
In a preferred configuration, the total proportion of the vinylaromatic block copolymers, especially styrene block copolymers, based on the overall pressure-sensitive adhesive, is 15% to 40% by weight, more preferably 20% to 35% by weight. Too low a proportion of vinylaromatic block copolymers has the result that the cohesion of the pressure-sensitive adhesive is relatively low, and so the tear strength required for stripping is too low. Too high a proportion of vinylaromatic block copolymers in turn results in barely any pressure-sensitive adhesion in the pressure-sensitive adhesive.
Pressure-sensitive adhesives according to the invention are especially based on vinylaromatic block copolymers such as styrene block copolymers. The pressure-sensitive adhesion is achieved by addition of tackifying resins that are miscible with the elastomer phase. The pressure-sensitive adhesives include, as well as the at least one vinylaromatic block copolymer, at least one tackifying resin in order to increase the adhesion in the desired manner. The tackifying resin should be compatible with the elastomer block of the block copolymers.
A “tackifying resin”, according to the general understanding of those skilled in the art, is understood to mean an oligomeric or polymeric resin that increases adhesion (tack, intrinsic tackiness) of the pressure-sensitive adhesive compared to the pressure-sensitive adhesive that does not contain any tackifying resin but is otherwise identical.
In a preferred embodiment, the adhesive layer consists of a pressure-sensitive adhesive formed on the basis of vinylaromatic block copolymers and tackifying resins, with selection preferably to an extent of at least 30% by weight, and preferably to an extent of at least 50% by weight (based in each case on the total tackifying resin content), of a tackifying resin having a DACP (diacetone alcohol cloud point) of greater than −20° C., preferably greater than 0° C., and a softening temperature (Ring & Ball) of not less than 70° C., preferably not less than 100° C.
More preferably, the tackifying resins comprise at least 30% by weight, such as, in particular, at least 50% by weight (based in each case on the total tackifying resin content), of hydrocarbon resins or terpene resins or a mixture of the same.
It has been found that tackifying resins advantageously usable for the pressure-sensitive adhesive(s) are especially nonpolar hydrocarbon resins, for example hydrogenated and non-hydrogenated polymers of dicyclopentadiene, non-hydrogenated, partly, selectively or fully hydrogenated hydrocarbon resins based on C5, C5/C9 or C9 monomer streams, and polyterpene resins based on α-pinene and/or β-pinene and/or δ-limonene. The aforementioned tackifying resins may be used either alone or in a mixture. It is possible to use either room temperature solid resins or liquid resins. Tackifying resins, in hydrogenated or non-hydrogenated form, which also contain oxygen, can optionally and preferably be used in the adhesive up to a maximum proportion of 70% by weight, based on the total mass of the resins.
The proportion of the resins that are liquid at room temperature, in a preferred variant, is up to 15% by weight, preferably up to 10% by weight, based on the overall pressure-sensitive adhesive.
The pressure-sensitive adhesive according to the invention preferably contains 20% to 60% by weight, based on the total weight of the pressure-sensitive adhesive, of at least one tackifying resin. More preferably, tackifying resins are present to an extent of 30% to 50% by weight, based on the total weight of the pressure-sensitive adhesive.
Further additives which may typically be utilized are:
The nature and amount of the blend components can be selected as required.
It is also in accordance with the invention when the adhesive does not include some of and preferably any of the respective admixtures mentioned.
In one embodiment of the present invention, the pressure-sensitive adhesive also comprises further additives; nonlimiting examples include crystalline or amorphous oxides, hydroxides, carbonates, nitrides, halides, carbides or mixed oxide/hydroxide/halide compounds of aluminium, of silicon, of zirconium, of titanium, of tin, of zinc, of iron or of the alkali metals/alkaline earth metals. These are essentially aluminas, for example aluminium oxides, boehmite, bayerite, gibbsite, diaspore and the like. Sheet silicates are very particularly suitable, for example bentonite, montmorillonite, hydrotalcite, hectorite, kaolinite, boehmite, mica, vermiculite or mixtures thereof. But it is also possible to use carbon blacks or further polymorphs of carbon, for instance carbon nanotubes.
The adhesives may also be coloured with dyes or pigments. The adhesives may be white, black or coloured.
Plasticizers incorporated by metered addition may, for example, be (meth)acrylate oligomers, phthalates, cyclohexanedicarboxylic esters, water-soluble plasticizers, plasticizing resins, phosphates or polyphosphates.
The addition of silicas, advantageously of precipitated silica surface-modified with dimethyldichlorosilane, can be utilized in order to adjust the thermal shear strength of the pressure-sensitive adhesive.
In a preferred embodiment, the at least one pressure-sensitive adhesive layer has been foamed, especially by means of microballoons.
In a preferred embodiment of the invention, the adhesive consists solely of vinylaromatic block copolymers, tackifying resins, microballoons and optionally the abovementioned additives.
Further preferably, the adhesive consists of the following composition:
Further preferably, the adhesive consists of the following composition:
In a preferred embodiment, the pressure-sensitive adhesive according to the invention has been foamed. The foaming is typically effected by the introduction and subsequent expansion of microballoons.
“Microballoons” are understood to mean hollow microbeads that are elastic and hence expandable in their ground state, having a thermoplastic polymer shell. These beads have been filled with low-boiling liquids or liquefied gas. Shell material employed is especially polyacrylonitrile, PVDC, PVC or polyacrylate. Suitable low-boiling liquids are especially hydrocarbons from the lower alkanes, for example isobutane or isopentane, that are enclosed in the polymer shell under pressure as liquefied gas.
Action on the microballoons, especially by the action of heat, results in softening of the outer polymer shell. At the same time, the liquid blowing gas present within the shell is converted to its gaseous state. This causes irreversible extension and three-dimensional expansion of the microballoons. The expansion has ended when the internal and external pressure are balanced. Since the polymeric shell is conserved, what is achieved is thus a closed-cell foam.
A multitude of microballoon types are commercially available, which differ essentially in terms of their size (diameter 6 to 45 μm in the unexpanded state) and the starting temperatures that they require for expansion (75 to 220° C.). One example of commercially available microballoons is the Expancel® DU products (DU=dry unexpanded) from Nouryon.
Unexpanded microballoon products are also available in the form of an aqueous dispersion having a solids/microballoon content of about 40% to 45% by weight, and additionally also in the form of polymer-bound microballoons (masterbatches), for example in ethylene-vinyl acetate with a microballoon concentration of about 65% by weight. Both the microballoon dispersions and the masterbatches, like the DU products, are suitable for production of a foamed pressure-sensitive adhesive according to the invention.
A foamed pressure-sensitive adhesive according to the invention can also be produced with what are called pre-expanded microballoons. In the case of this group, the expansion already takes place prior to mixing into the polymer matrix. Pre-expanded microballoons are commercially available, for example, under the Dualite® name or with the product designation Expancel xxx DE (dry expanded) from Nouryon.
According to the invention, the average diameter of the voids formed by the microballoons in the foamed pressure-sensitive adhesive layers is preferably 10 to 200 μm, more preferably from 15 to 200 μm. Since it is the diameters of the voids formed by the microballoons in the foamed pressure-sensitive adhesive layers that are being measured here, the diameters are those diameters of the voids formed by the expanded microballoons. The average diameter here is the arithmetic average of the diameters of the voids formed by the microballoons in the respective pressure-sensitive adhesive layer. The average diameter of the voids formed by the microballoons in a pressure-sensitive adhesive layer is determined using 5 different cryofracture edges of the adhesive tape in a scanning electron microscope (SEM) with 500-fold magnification. The diameters of the microballoons visible in the micrographs are determined by graphical means in such a way that the maximum extent thereof in any (two-dimensional) direction is inferred from the scanning electron micrographs for each individual microballoon in the pressure-sensitive adhesive layer to be examined and regarded as the diameter thereof.
If foaming is effected by means of microballoons, the microballoons can then be supplied to the formulation as a batch, paste or unblended or blended powder. In addition, they may be suspended in solvents.
In a preferred embodiment of the invention, the proportion of microballoons in the adhesive is between greater than 0% by weight and 10% by weight, especially between 0.25% by weight and 5% by weight, very particularly between 0.5% and 1.5% by weight, based in each case on the overall composition of the adhesive. The figure is based on unexpanded microballoons.
A polymer composition according to the invention, comprising expandable hollow microbeads, may additionally also contain non-expandable hollow microbeads. What is crucial is merely that virtually all gas-containing caverns are closed by a permanently impervious membrane, no matter whether this membrane consists of an elastic and thermoplastically extensible polymer mixture or, for instance, of elastic and—within the spectrum of the temperatures possible in plastics processing—non-thermoplastic glass.
Also suitable for the pressure-sensitive adhesive according to the invention—selected independently of other additives—are solid polymer beads, hollow glass beads, solid glass beads, hollow ceramic beads, solid ceramic beads and/or solid carbon beads (“carbon microballoons”).
The absolute density of a foamed pressure-sensitive adhesive according to the invention is preferably 220 to 990 kg/m3, more preferably 300 to 970 kg/m3, even more preferably 450 to 900 kg/m3, especially 500 to 850 kg/m3. The relative density describes the ratio of the density of the foamed pressure-sensitive adhesive according to the invention to the density of the unfoamed pressure-sensitive adhesive according to the invention having an identical formulation. The relative density of a pressure-sensitive adhesive according to the invention is preferably 0.20 to 0.99, more preferably 0.30 to 0.97, especially 0.45 to 0.90, for example 0.50 to 0.85.
In one embodiment of the invention, one or both surfaces of the pressure-sensitive adhesive layers have been physically and/or chemically pretreated. Such a pretreatment can be effected, for example, by plasma pretreatment and/or primer treatment. If both surfaces of the pressure-sensitive adhesive layers have been pretreated, the pretreatment of each surface may have been different or, more particularly, both surfaces may have been given the same pretreatment.
The plasma treatment—especially low-pressure plasma treatment—is a known process for surface pretreatment of adhesives. The plasma leads to activation of the surface in the sense of a higher reactivity. This results in chemical changes to the surface, as a result of which, for example, the characteristics of the adhesive with respect to polar and nonpolar surfaces can be influenced. This pretreatment essentially comprises surface phenomena.
Primers refer generally to coatings or basecoats which especially have an adhesion-promoting and/or passivating and/or corrosion-inhibiting effect. In the context of the present invention, it is the adhesion-promoting effect that is especially important. Adhesion-promoting primers, often also called adhesion promoters, are in many cases known in the form of commercial products or from the technical literature.
The pressure-sensitive adhesive layers according to the invention typically have a thickness of 10 to 200 μm, preferably of 15 to 100 μm and especially of 25 to 60 μm.
Process for Producing TPU Carriers by Means of Extrusion:
The following are not shown:
a) Extrusion and Coating of Compact TPU:
All constituents of the formulation based on TPU to be produced are first dried in a pellet dryer (T=90° C., 3 h) and then supplied to a continuous mixing or conveying unit with mixing section 1 via metering orifices 13 and metering or conveying systems. The temperature is controlled in accordance with the optimal conditions required for the production of a homogeneous mixture G.
The outlet 12 from the continuous conveying unit with mixing section or mixing unit, or the further components for conveying of the extrudate to the preliminary forming via a nozzle or distributor channel or directly to the coating unit 4, may have different configurations. In order to coat a flat film, a slot die is suitable for preliminary forming of the extrudate or of a melt film. The latter is deposited directly onto a rotating, generally chilled roll (called a chill roll), in which case the layer thickness can be regulated additionally via the takeoff speed. Alternatively, it is coated directly onto a preliminary material, for example (temporary) carrier or functional layer, such as a pressure-sensitive adhesive layer in particular.
In a particularly advantageous process according to the invention, the previously homogenized mixture, extrudate, is formed by means of a slot die to give a melt film and coated directly onto a first adhesive layer disposed on a temporary carrier, such as a (siliconized) liner in particular. This prefabricated functional layer is supplied beforehand via the chill roll via an unwinding station.
This composite composed of temporary carrier (liner), adhesive layer and PU layer, before being wound to give a bale, is laminated with a second prefabricated adhesive layer on a temporary carrier (such as a release liner in particular). The end product now consists of three layers (adhesive-PU carrier-adhesive), sandwiched between two temporary carriers (such as liners in particular). A temporary carrier (such as a liner in particular) may be removed before winding to a bale.
This procedure has many advantages: a multilayer product can be produced particularly efficiently; bond strength/anchoring between adhesive (or any kind of functional/carrier layer) and TPU layer is improved; the often problematic intermediate step of transfer coating (TPU to release carrier) is avoided in a simple manner. For instance, even particularly soft TPU types are amenable to production, and there is no need for processing auxiliaries, such as waxes and/or lubricants, co-extruded support carriers or additional auxiliary liners as typically required in the production of TPU carriers.
b) Extrusion and Coating of Foamed TPU:
All constituents of the formulation based on TPU (after drying) to be produced, including the unexpanded microballoons, are supplied to a continuous mixing or conveying unit with mixing section 1 via metering orifices 13 and metering or conveying systems. The temperature is controlled in accordance with the optimal conditions required for the production of a homogeneous mixture G and the foaming of the microballoons. Up to the outlet 12, there is a continuous opposing pressure in order to avoid premature expansion of the microballoons.
The outlet 12 from the continuous conveying unit with mixing section or mixing unit, or the further components for conveying of the extrudate to the preliminary forming via a nozzle or distributor channel or directly to the coating unit 4, may have different configurations. In order to coat a flat film, a slot die is suitable for preliminary forming of the extrudate or of a melt film. In order to prevent the expanding microballoons from penetrating the coated surface and hence producing a rough surface, which in turn causes poor anchoring to the functional layer, an opposing pressure during the coating operation is required. This may be, for example, an impression roll or opposing roll against the coating roll, or the coating is performed directly in a calender. Here too, it may be coated directly onto a preliminary material, for example a (temporary) carrier or a functional layer, such as a pressure-sensitive adhesive layer in particular.
This composite composed of temporary carrier (liner), adhesive layer and PU layer, before being wound to give a bale, is laminated with a second prefabricated adhesive layer on a temporary carrier (such as a release liner in particular), or any other kind of functional layer on the opposite side.
The end product now consists of three layers (adhesive-foamed PU carrier-adhesive), sandwiched between two temporary carriers (such as liners). A temporary carrier (liner) may be removed before winding to a bale. Direct coating onto additional functional layers has many advantages: a multilayer product can be produced particularly efficiently; bond strength/anchoring between adhesive or any kind of functional/carrier layer and TPU layer is improved; the often problematic intermediate step of transfer coating (TPU to release carrier) is avoided in a simple manner. For instance, even particularly soft TPU types are amenable to production, and there is no need for processing auxiliaries, such as waxes and/or lubricants, co-extruded support carriers or additional auxiliary liners as typically required in the production of TPU carriers.
Closed-cell TPU foams containing microballoons are not commercially available, and so this process according to the invention and the resulting carrier layers form the basis for innovative products.
Further options for production of open-cell TPU foams are available: the addition of chemical blowing agents or the controlled injection of gas, i.e. a physical blowing agent.
The chemical blowing agent is added directly with the starting materials to the continuous conveying unit with a mixing section, or via one of the additional metering orifices. Processing and coating are effected as described above.
Gas is injected via an additional metering orifice into the extruder, into the melt mixture. The gas is supplied in a controlled manner, such that the gas content in the mixture and the resulting density can be adjusted. The processing and coating are effected as described above.
Process for producing PU carriers from dispersion:
a) Production and Coating of PU Dispersions:
The production of a homogeneous, bubble-free dispersion mixture requires stirring equipment suitable for dispersions. Thickeners and/or other additives are usually predispersed with water and then supplied to the PU dispersion in portions while constantly stirring cautiously.
In the course of the stirring process, vortices or excessively rapid speeds should be avoided in order to prevent unwanted stirring-in of air. It is advisable to make up the blend a few hours prior to the coating in order to promote escape of small air bubbles that have been stirred in.
The coating can be effected by means of different application systems, for example squeegee, nozzle or distributor channels etc. The coated PU dispersion is dried via supply of heat in a drying tunnel with different heating zones. The coating of the PU dispersion can be effected either onto a (temporary) carrier or directly onto a functional layer, such as a pressure-sensitive adhesive layer in particular. After the drying and before the winding, a second functional layer may be laminated onto the opposite side, such that it is possible to produce a multilayer product in one step. The multilayer composite thus produced is wound up to give a bale. A liner or other auxiliary carrier may be removed beforehand.
This procedure has many advantages: a multilayer product can be produced particularly efficiently; bond strength/anchoring between adhesive or any kind of functional/carrier layer and PU layer is improved; the often problematic intermediate step of transfer coating (PU to release carrier) is avoided in a simple manner.
The PU-based carrier layer made from dispersion or the adhesive tape comprising this layer is additionally typically subjected to a heat treatment at at least 150° C. in order to optimize tensile strength.
b) Production and Coating of Foamable PU Dispersions:
The production of a homogeneous, bubble-free dispersion mixture foamable with microballoons requires stirring equipment suitable for dispersions. Thickeners and/or other additives, including the unexpanded microballoons, are usually predispersed with water and then supplied to the PU dispersion in portions while constantly stirring cautiously. In the course of the stirring process, vortices or excessively rapid speeds should be avoided in order to prevent unwanted stirring-in of air. It is advisable to make up the blend a few hours prior to the coating in order to promote escape of small air bubbles that have been stirred in.
The coating can be effected by means of different application systems, for example squeegee, nozzle or distributor channels etc. The coated PU dispersion is dried via supply of heat below the foaming temperature in a drying tunnel with different heating zones. The coating of the PU dispersion can be effected either onto a (temporary) carrier or directly onto a functional layer, such as a pressure-sensitive adhesive layer in particular. After the drying and before the winding, a second functional layer may be laminated onto the opposite side, such that it is possible to produce a multilayer product in one step.
The multilayer composite thus produced is wound up to give a bale. A liner or other auxiliary carrier may be removed beforehand. This procedure has many advantages: a multilayer product can be produced particularly efficiently; bond strength/anchoring between adhesive or any kind of functional/carrier layer and PU layer is improved; the often problematic intermediate step of transfer coating (PU to release carrier) is avoided in a simple manner.
In a further operating step, the overall composite or a single layer of the foamable PU carrier is sandwiched with temporary carrier, such as auxiliary liner in particular, and partly or fully foamed by further supply of heat through a heating tunnel or heatable contact rolls, i.e. the microballoons are expanded. The sandwiching of the foamable PU carrier with carrier, auxiliary liner or functional layer prevents penetration of the surface by the expanding microballoons, such that a good bond strength is achieved between the individual layers. The foaming with microballoons produces a closed-cell PU foam. Typically, the PU-based carrier layer made from dispersion or the adhesive tape comprising this layer is subjected to a heat treatment at at least 150° C. in order to optimize tensile strength.
By stirring in a controlled amount of air, called “frothing”, it is additionally possible to produce an open-cell PU foam. Here, by means of stirring equipment suitable for the purpose and special stirring conditions, the beating-in of air is induced in a controlled manner. The continuation of the production process is effected analogously to the process described above.
The invention is elucidated in detail hereinafter by a few illustrative adhesive tapes. With reference to the examples described hereinafter, particularly advantageous executions of the invention will be elucidated in detail, without any intention to unnecessarily restrict the invention thereby.
Table 1 shows the (raw) materials used in the (comparative) examples. Tables 2 and 3 show the formulations of the carriers and pressure-sensitive adhesive layers produced in the (comparative) examples.
Table 4 shows the structure of the adhesive tapes of the (comparative) examples that are formed by combination of the aforementioned carriers from Table 2 and pressure-sensitive adhesives from Table 3. The adhesive tapes are each double-sided, meaning that a pressure-sensitive adhesive layer is disposed on each side of the carrier.
The production of the individual adhesive tapes was performed as follows:
Production of the Adhesive Tapes with TPU Core Layers TPU 2-TPU 4 (Examples 6 to 13):
All pellets of thermoplastic polyurethane, i.e. TPU pellets, are predried prior to processing in a pellet dryer (Somos) at 80° C. for at least 3 hours. The pellets are supplied to the single-screw extruder (Collin, 25D), called SSE hereinafter, via the intake zone via a simple reservoir vessel/funnel. The SSE temperature is controlled in accordance with the optimal processing temperature for the respective TPU pellets. After the pellets have been melted, the extrudate is transferred via a hose into a feed block and then into the slot die. Table 5 shows the control of the SSE temperature, including the slot die.
The preformed melt film is then deposited onto a steel roll. Since the TPU variants having lower Shore A hardness have somewhat greater pressure-sensitive adhesion and are thus more difficult to remove again from the steel roll, it has been found to be useful to coat directly onto a PET carrier having release function, i.e. temporary carrier or liner, which is supplied via an unwinder and by wrapping halfway around the takeoff roll, and then wound up. The TPU carriers (TPU core layers) produced are free of processing auxiliaries and do not have a crystalline superstructure.
After the desired layer thickness has been established, at the unwinder, the bale with the PET carrier having release function is exchanged for the prefabricated functional layer, i.e. the pressure-sensitive adhesive layer A or B. In this way, coating is effected directly onto the functional layer. By means of a further unwinder, the second prefabricated functional layer (pressure-sensitive adhesive layer A or B), having the same thickness as the first pressure-sensitive adhesive layer, is laminated by means of the guide roll or contact pressure roll onto the open TPU layer at the top. The microballoons are still in unexpanded form in the pressure-sensitive adhesive layers A, i.e. the pressure-sensitive adhesive layers A are yet to be foamed. The pressure-sensitive adhesive layers B do not contain any microballoons. The pressure-sensitive adhesive layers A (containing unexpanded microballoons) and B mentioned are produced as follows in the (comparative) examples:
First of all, a 40% by weight adhesive solution of the elastomer component, resin component, optionally plasticizing resin component and additive is prepared in benzine/toluene/acetone. The solution is then admixed with the microballoons if appropriate, i.e. according to the pressure-sensitive adhesive layer to be produced, with use of the microballoons as a suspension in benzine. The mixture obtained is then coated with a coating bar onto a PET liner provided with a silicone release agent in the desired layer thickness, then the solvent is evaporated off at 100° C. for 15 min and so the composition layer is dried. If present, the microballoons are still in unexpanded form therein, i.e. the corresponding pressure-sensitive adhesive layer is yet to be foamed.
The three-layer product is then wound up. The overall composite composed of carrier and pressure-sensitive adhesive layers is subjected to a further thermal treatment step for better anchoring and, if the pressure-sensitive adhesive layers contain unexpanded microballoons, for foaming of the pressure-sensitive adhesive layers. For this purpose, the material wound up, with a temperature profile having three zones at 120° C./135° C./170° C., at a belt speed of 6 m/min, is run through a tunnel system and then wound up again. This results in the double-sided adhesive tapes having the TPU core layers TPU 2-TPU 4.
Production of the Adhesive Tapes with TPU Core Layer TPU 1 (Comparative Examples 1 and 3 to 5):
The purchased processing auxiliary-containing TPU core layers TPU 1 (in various thicknesses) are laminated on either side with the pressure-sensitive adhesive layers A and C. Prior to the lamination of the TPU core layers TPU 1 with the pressure-sensitive adhesive layers, the PE support carrier is pulled off the TPU core layer in each case. The pressure-sensitive adhesive layers on either side of the carrier have the same thickness. The microballoons are still in unexpanded form in the pressure-sensitive adhesive layers A and C, i.e. the pressure-sensitive adhesive layers A and C are yet to be foamed. The pressure-sensitive adhesive layers C are produced analogously to the manner described above for the pressure-sensitive adhesive layers A and B.
The overall composite composed of carrier and pressure-sensitive adhesive layers, for better anchoring and foaming of the pressure-sensitive adhesive layers, is subjected in each case to a further thermal treatment step. For this purpose, the material wound up, with a temperature profile having three zones at 120° C./135° C./170° C., at a belt speed of 6 m/min, is run through a tunnel system and then wound up again. The result in each case is a foamed double-sided adhesive tape having a TPU core layer TPU 1.
Production of the Adhesive Tape with SBC Core Layer (Comparative Example 2):
The SBC core layer is produced analogously to the production of the pressure-sensitive adhesive layers as described above. The SBC core layer is laminated on either side with a pressure-sensitive adhesive layer A of the same thickness. The microballoons are still in unexpanded form in the pressure-sensitive adhesive layers A, i.e. the pressure-sensitive adhesive layers A are yet to be foamed.
The overall composite composed of carrier and pressure-sensitive adhesive layers, for better anchoring and foaming of the pressure-sensitive adhesive layers, is subjected to a further thermal treatment step. For this purpose, the material wound up, with a temperature profile having three zones at 120° C./135° C./170° C., at a belt speed of 6 m/min, is run through a tunnel system and then wound up again. The result is a foamed double-sided adhesive tape having an SBC core layer.
Production of the Adhesive Tapes with PUD Core Layers PUD 1 to PUD 4 (Examples 14 to 26):
If a thickener is used, the polyurethane dispersion (PU dispersion, PUD) is blended with the thickener by means of a conventional vertical stirrer apparatus with a Visco Jet stirrer. In this case, the polyurethane dispersion is initially charged in a sufficiently large vessel and stirred cautiously. Formation of vortices or any stirring-in of air should be avoided throughout the blending process.
If used, the Ortegol PV301 thickener (solids content 25% by weight) or the BorchiGel 0625 thickener (solids content 33% by weight) is prediluted with water in a ratio of 1:2 and then fed into the initially charged polyurethane dispersion in portions with constant stirring. In order to obtain a homogeneous mixture, a stirring time of at least 30 minutes is observed. The thickened polyurethane dispersion thus made up is ideally produced one day prior to coating. Small air bubbles that have been stirred in can thus still escape. Then the blended polyurethane dispersions (or polyurethane dispersions without added thickener) can be coated by means of a coating system, i.e. application system, with a drying tunnel. Table 7 shows relevant parameters for the coating system and drying tunnel. The PUD core layers produced are free of processing auxiliaries (apart from surfactant) and do not have a crystalline superstructure.
Table 7 shows relevant parameters for the coating system and drying tunnel.
By means of 2 unwinders, either a PET carrier with release function or a prefabricated functional layer, i.e. pressure-sensitive adhesive layer, on a PET carrier with release function is provided. It has been found to be useful to establish the desired layer thickness on PET carrier and then to switch to the prefabricated functional layer (pressure-sensitive adhesive layer A, B, D or E) and coat it directly. Before winding, a controllable contact pressure roll is then used to laminate the second functional layer (pressure-sensitive adhesive layer A, B, D or E), having the same thickness as the first pressure-sensitive adhesive layer, therewith. The microballoons are still in unexpanded form in the pressure-sensitive adhesive layers A and D, i.e. the pressure-sensitive adhesive layers A and D are yet to be foamed. The pressure-sensitive adhesive layers B and E do not contain any microballoons. The pressure-sensitive adhesive layers D and E are produced analogously to the manner described above for the pressure-sensitive adhesive layers A and B.
The three-layer product thus produced is then wound up. The overall composite composed of PU carrier and pressure-sensitive adhesive layers is subjected to a further thermal treatment step for optimization of the tensile strength of the carrier, for better anchoring and, if the pressure-sensitive adhesive layers contain unexpanded microballoons, for foaming of the pressure-sensitive adhesive layers. For this purpose, the material wound up, with a temperature profile having three zones at 120° C./135° C./170° C., at a belt speed of 6 m/min, is run through the same tunnel system and then wound up again. This results in the double-sided adhesive tapes having the PUD core layers PUD 1 to PUD 4.
Results:
Table 8 shows the mechanical properties of the adhesive tapes produced and of the carriers present therein.
In the case of the adhesive tape with SBC carrier, i.e. with carrier based on styrene block copolymer, as shown by Comparative Example 2, there is still a need for improvement with regard to the breaking force of the adhesive tape, especially in order to further improve the ratio of stripping force to breaking force and tear resistance.
In order to further improve the tear resistance of an adhesive tape, proceeding from Comparative Example 3, the thickness of the carrier layer used is increased (or is constant in Comparative Example 1, where only the pressure-sensitive adhesive layer has a different composition there). The adhesive tapes of the comparative examples mentioned all comprise the carrier (core) TPU1 (TPU in the application stands for thermoplastic polymer) having a Shore A hardness of 86, but in different layer thicknesses. If only the core thickness is increased with the same product thickness of 150 μm, the ratio of stripping force to breaking force is advantageously improved and the tear resistance is increased, but at the same time there is a very significant rise in the stripping force, and so damage is caused to the materials to be separated and hence there is a deterioration in the shock properties (DuPont z). There is thus a need for improvement with regard to the balance in the product performance.
In order to achieve improved tear resistance of the adhesive tape in the adhesive tapes having a TPU core and simultaneously to reduce the stripping force of the adhesive tape, what is required is surprisingly a TPU core having a Shore A hardness of not more than 87. PU films are not commercially available without addition of processing auxiliaries, for example lubricants, waxes and/or antiblocking agents. Therefore, a process according to the invention for production of PU layers having a Shore A hardness of not more than 87 has been developed, these serving as carrier for a multilayer product which is conveniently redetachable, i.e. strippable, by stretching, and giving another distinct improvement in tear resistance. Compared to the comparative examples, with falling Shore A hardness, there is a drop in the ratio of stripping force to breaking force, a distinct improvement in tear resistance and a drop in stripping force to such an extent as to assure destruction-free detachment or separation of the components. In all examples, the adhesive tapes did not have any tears in the tearing test.
The inventive use of core layers (carriers) based on PU dispersions, i.e. PUD carriers, has been found to be particularly advantageous since there is a distinct reduction here in the ratio of stripping force to breaking force compared to the comparative examples, which in turn leads to very good tear resistance. The stripping forces are simultaneously at a very low level, and so there is no question of destruction of the components to be separated. In all examples, the adhesive tapes did not have any tears in the tearing test.
Unless stated otherwise, all measurements are conducted at 23° C. and 50% relative air humidity. The mechanical and adhesive data were ascertained as follows:
In the tearing test, a first test plate of polyethylene and a second test plate of steel are used. The first test plate of polyethylene has been wrapped with a Tesa® 67215 double-sided adhesive tape, to which a “battery film” has then been applied. The Tesa® 67215 adhesive tape has a total thickness of 150 μm and contains a polyurethane carrier of thickness 30 μm, on each side of which is disposed a 60 μm-thick foamed pressure-sensitive adhesive layer based on vinylaromatic block copolymer. The “battery film” is an aluminium-laminated polymer film of thickness 88 μm from DNP—the film is typically used for production of lithium polymer batteries.
Specimens of width 8 mm and length 60 mm are diecut or lasered out of the adhesive tape to be examined. The specimens are stuck over a length of 50 mm onto the above-described battery film-wrapped first test plate of polyethylene, so as to leave a tab of length 10 mm. The tab is covered on either side with 36 μm of PET. The second test plate of steel, after cleaning with acetone and preconditioning for 1 to not more than 10 min at 23° C. and 50% relative air humidity, is stuck onto the reverse side of the bonded strip (i.e. specimen) such that the two test plates lie flush, i.e. congruent, with one another. A 4 kg roller is run 10 times over the composite on the reverse side of the steel plate (back and forth five times). After an attachment time of at least 4 h at 23° C. and 50% relative air humidity, the strips are stripped out of the adhesive join using the tab by means of a tensile tester (from Zwick) at a constant speed of 800 mm/minute at an angle of 90° via the edge of the battery film-wrapped first test plate of polyethylene. The test specimen is fixed here with an angle-adjustable adapter, and the tab is clamped perpendicularly in the middle of the clamping jaws.
Measurement is made at an angle of 90°, during which the force continuously required for stripping out the sample is recorded by the tensile tester—called the stripping force Fstrip. The measurement is ended as soon as the sample has been stripped out completely between the two test plates or the sample has torn during the measurement. At least 6 measurements per specimen are conducted. The test conditions are 23° C. and 50% rel. air humidity.
Reporting of Results:
Tearing at 90°—the test is considered to be passed if less than 20% of the specimens tear during the stripping operation.
Fstrip 90° [N/cm]—force required to strip the specimen out of the adhesive join at angle 90° (stripping force)
Strips of width 15 mm and having a length of about 150 mm are cut out of the sample to be examined (adhesive tape, i.e. Carrier preferably provided with adhesive on either side, or plain carrier only) in longitudinal direction by means of a strip cutter or razor blade. The sample that had been preconditioned under the test conditions for 24 h is clamped at right angles in the middle of the clamping jaws with a clamped length of 10 mm and stretched at a speed of 800 mm/min until it tears. The break is supposed to occur in about the middle of the strip. If the break is close to the jaws (closer than 1 cm), the value should be rejected and a further strip should be tested instead. 5 measurements are conducted per sample variant. The test conditions are 23° C. and 50% rel. air humidity. The measurements are in accordance with EN ISO 527.
Reporting of Results:
Fx % [N/cm], [N/mm2]—force at x % elongation
Fbreak [N/cm], [N/mm2]—force at sample tear/break (i.e. tear strength)
EB [%]—elongation at break, i.e. percentage elongation at sample tear/break
A square sample in the shape of a frame is cut out of the adhesive tape to be examined (external dimensions 33 mm×33 mm; border width 2.0 mm; internal dimensions (window cut-out) 29 mm×29 mm). This sample is stuck to a polycarbonate (PC) frame (external dimensions 45 mm×45 mm; border width 10 mm; internal dimensions (window cut-out) 25 mm×25 mm; thickness 3 mm). A PC window of 35 mm×35 mm is stuck to the other side of the double-sided adhesive tape. The bonding of PC frame, adhesive tape frame and PC window is effected such that the geometric centres and the diagonals are each superimposed on one another (corner-to-corner). The bonding area is 248 mm2. The bond is subjected to a pressure of 248 N for 5 s and stored under conditions of 23° C./50% relative humidity for 24 hours.
Immediately after the storage, the adhesive composite composed of PC frame, adhesive tape and PC window is braced by the protruding edges of the PC frame in a sample holder such that the composite is aligned horizontally. The PC frame rests flat on the protruding edges of the sample holders, such that the PC window is free-floating (held by the adhesive tape specimen) below the PC frame. The sample holder is then inserted centrally into the intended receptacle of the “DuPont Impact Tester”. The impact head of weight 150 g is used in such a way that the circular impact geometry with a diameter of 24 mm impacts centrally and flush on the face of the PC window freely accessible from above.
A weight having a mass of 150 g guided on two guide rods is allowed to drop vertically from a height of 5 cm onto the composite composed of sample holder, sample and impact head thus arranged (test conditions: 23° C., 50% relative humidity). The height from which the weight is dropped is increased in 5 cm steps until the impact energy introduced destroys the sample as a result of the penetration stress and the PC window parts from the PC frame.
In order to be able to compare experiments with different samples, the energy is calculated as follows:
Energy E[J]=Height [m]*mass weight [kg]*9.81 kg/m*s2
Five samples per product are tested, and the mean energy is reported as index for penetration resistance.
The Shore A hardness of a sample is ascertained to ASTM D2240.
The modulus at 100% elongation, or elongation at break, of a sample is ascertained to DIN 53504.
The thickness of an adhesive layer can be determined by determining the thickness of a section, defined in terms of its length and width, of such an adhesive layer applied to a liner, minus the (known or separately determinable) thickness of a section of the same dimensions of the liner used. The thickness of the adhesive layer can be determined by means of commercial thickness measuring instruments (caliper test instruments) with accuracies of less than a 1 μm deviation. If variations in thickness are found, the average of measurements at at least three representative sites is reported, i.e. more particularly not measured at creases, folds, specks and the like.
Like the thickness for an adhesive layer as above, it is also possible to ascertain the thickness of an adhesive tape (adhesive strip) or of a carrier in an analogous manner by means of commercial thickness measuring instruments (caliper test instruments) with accuracies of less than a 1 μm deviation. If variations in thickness are found, the average of measurements at at least three representative sites is reported, i.e. more particularly not measured at creases, folds, specks and the like.
The density of the unfoamed and foamed adhesive layers is ascertained by forming the quotient of mass applied and thickness of the adhesive layer applied to a liner.
The mass applied can be determined by determining the mass of a section, defined in terms of its length and width, of such an adhesive layer applied to a liner, minus the (known or separately determinable) mass of a section of the same dimensions of the liner used.
The thickness of an adhesive layer can be determined by determining the thickness of a section, defined in terms of its length and width, of such an adhesive layer applied to a liner, minus the (known or separately determinable) thickness of a section of the same dimensions of the liner used. The thickness of the adhesive layer can be determined by means of commercial thickness measuring instruments (caliper test instruments) with accuracies of less than a 1 μm deviation. If variations in thickness are found, the average of measurements at at least three representative sites is reported, i.e. more particularly not measured at creases, folds, specks and the like.
The density of a carrier can be determined analogously.
Glass transition points—referred to synonymously as glass transition temperatures—are reported as the result of measurements by means of differential scanning calorimetry (DSC) according to DIN 53765, especially sections 7.1 and 8.1, but with uniform heating and cooling rates of 10 K/min in all heating and cooling steps (cf. DIN 53765; section 7.1; note 1). The sample weight is 20 mg.
The values reported for number-average molecular weight Mn and weight-average molecular weight Mw in this document relate to determination by gel permeation chromatography (GPC). The determination is carried out using a clear-filtered 100 μl sample (sample concentration 4 g/l). The eluent used is tetrahydrofuran with 0.1% by volume of trifluoroacetic acid. The measurement is made at 25° C. The precolumn used is a column of the PSS-SDV type, 5 μm,
103 Å, ID 8.0 mm*50 mm (values here and hereinafter in the following sequence: type, particle size, porosity, internal diameter*length; 1 Å=10−10 m). For separation, a combination of the columns of the PSS-SDV type, 5 μm, 103 Å and 105 Å and 106 Å each with
8.0 mm*300 mm is used (columns from Polymer Standards Service; detection by means of Shodex RI71 differential refractometer). The flow rate is 1.0 ml per minute. In the case of polar molecules, for example the starting materials for the polyurethane, calibration is effected against PMMA standards (polymethylmethacrylate calibration), and otherwise against PS standards (polystyrene calibration).
The tackifying resin softening temperature is carried out in accordance with the relevant methodology, which is known as Ring & Ball and is standardized according to ASTM E28.
5.0 g of test substance (the tackifying resin sample to be examined) are weighed into a dry test tube, and 5.0 g of xylene (isomer mixture, CAS [1330-20-7], 98.5%, Sigma-Aldrich #320579 or comparable) are added. The test substance is dissolved at 130° C. and then cooled down to
80° C. Any xylene that escapes is made up for with fresh xylene, such that 5.0 g of xylene is present again. Subsequently, 5.0 g of diacetone alcohol (4-hydroxy-4-methyl-2-pentanone, CAS [123-42-2], 99%, Aldrich #H41544 or comparable) are added. The test tube is shaken until the test substance has dissolved completely. For this purpose, the solution is heated up to
100° C. The test tube containing the resin solution is then introduced into a Novomatics Chemotronic Cool cloud point measuring instrument and heated therein to 110° C. It is cooled down at a cooling rate of 1.0 K/min. The cloud point is detected optically. For this purpose, that temperature at which the turbidity of the solution is 70% is registered. The result is reported in ° C. The lower the DACP value, the higher the polarity of the test substance.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2020 210 503.0 | Aug 2020 | DE | national |
| 10 2020 210 505.7 | Aug 2020 | DE | national |
