Patent Application
20100236707
The invention relates to a method of bonding a first substrate to a second substrate by means of a radiation-curable adhesive composition comprising a photolatent base.
Finding the right balance between formulation stability and reactivity at low temperature under ambient atmosphere is a major concern for most of the adhesive systems.
2K adhesives generally based on NCO/OH, NCO/SH and epoxy/amines require the addition of a catalyst to cure in a short period of time at low temperature, which shortens the pot life of the formulation.
1K adhesives, generally based on epoxies or moisture-cured isocyanates also require the presence of a catalyst in order to speed up the curing at low temperature which here again shows the major drawback of negatively affecting the formulation stability. Other 1K adhesive formulations such as cyanoacrylates or silane-modified polymer also react with ambient humidity at room temperature, giving formulations of poor stability.
Anaerobic adhesives, usually containing small amounts of peroxide and accelerators, remain liquid as long as they are in contact with atmospheric oxygen, but cure generally within a few hours once placed in an inert atmosphere or in contact with a metallic surface. For storage, it is necessary to fill half of the flask with air to avoid any premature gelling.
UV-curable adhesive systems react at room temperature after light activation and remain stable in the dark. Cure is however either partly inhibited by dissolved and diffusing oxygen in the case of acrylates or sensitive to moisture in the case of epoxies. The choice of UV-curable groups is also limited to epoxies or double bonds so far.
Hotmelts or plastisol have to be processed at high temperature (between 120° C. and 240° C.) prior to use, which limits the application range to substrates which are resistant to heat.
The European Patent EP898202B1 (Ciba) describes base catalyzed curable compositions comprising alpha-aminoketone compounds as latent base and its use in adhesives based on epoxide resins (see paragraph 0002). A suitable resin is for example a polyacrylate with 3-5% carboxylic function and an epoxy phenol novolac (see Ex. 1).
The International application WO01/92362 (AKZO) relates to a photoactivatable coating composition comprising at least one polyisocyanate and at least one compound comprising isocyanate reactive groups. The isocyanate reactive groups comprise at least one thiol group and the photoinitiator is a photolatent base. The coating compositions show particular utility as clear coats, base coats, pigmented top coats, primers, and fillers. WO01/92362 appears to provide no suggestion for use of any such copolymer as or in an adhesive.
The International application WO06008251 (Ciba) describes a process for the application of a photolatent base wherein an adhesive comprising said catalyst is subjected to irradiation before being further processed. However, the adhesive properties are not sufficient.
It has now been found that exposure after the lamination results in faster curing. Furthermore, the diamine catalyst usually present in OH/NCO or SH/NCO systems can be replaced by the latent base.
Thus, the present invention relates to a method of bonding a first substrate to a second substrate, comprising the steps of
a) applying an UV-curable adhesive resin composition comprising a photolatent base to at least one transparent surface of at least one of said first and second substrates,
b) bringing said first and second substrates together with said adhesive composition there between,
c) exposing said adhesive composition to actinic radiation to effect curing.
A further subject of the invention is a method of bonding a first substrate to a second substrate, comprising the steps of
a) applying an UV-curable adhesive resin composition comprising a photolatent base to one surface,
b) exposing said adhesive composition to actinic radiation to effect curing
c) bringing said first and second substrates together with said adhesive composition there between.
In one embodiment of the invention at least one substrate has to be transparent and is preferably selected from glass, fiberglass, ceramic material, paper and plastics such as polyester, polyethylene, polycarbonate, polyethylene, polypropylene, polystyrene, polyvinylchloride, rubbers and the like.
The other substrate (or both substrates in another embodiment of the invention) is for example non-transparent and may be in addition metal, ceramic, wood, rubber, non-transparent plastic, e.g. colored plastic, as described above, and the like.
UV-curable adhesives are preferably OH/NCO or SH/NCO systems. These adhesives are produced by the condensation reaction of an organic polyisocyanate with an active hydrogen-containing compound.
The isocyanate compound may be any aromatic, aliphatic, cycloaliphatic, acryl aliphatic, or heterocyclic isocyanate or polyisocyanate, and the prepolymers or mixtures thereof. The term “polyisocyanates” includes diisocyanates, triisocyanates, tetraisocyanates, etc., and mixtures thereof. Suitable isocyanate compounds are for example commercially available from Bayer under the name Desmodur® or from Rhodia under the trade name Tolonate®.
The active hydrogen containing compound has functional groups which are for example selected from the group consisting of —COOH, —OH, —NH2, —NH—, —CONH2, —SH, and —CONH—. Preferably the active hydrogen containing compound is OH or SH resulting in OH/NCO and SH/NCO resins.
For example the active hydrogen and/or isocyanate component can be blocked to increase the formulation shelf life. The blocking agent is released under the action of heat and/or of the active catalyst. Examples of suitable blocked components are known to the person skilled in the art.
OH/NCO systems are known as polyurethane adhesives. Polyurethane adhesives are for example one-component polyurethane adhesives (1K PU adhesives) or two-component polyurethane adhesives (1K PU adhesives).
Polyester polyols and polyether polyols preferably used as active hydrogen containing compound in OH/NCO resins are for example commercially available materials.
Suitable polyesterpolyols are commercially available, for example under the trade name Desmophen® and Baycoll®.
Optionally a multifunctional aliphatic amine chain extender is present in the adhesive composition. Examples of additional chain extenders in the binder are given in “Formulierung von Kleb- and Dichtstoffen, B. Müller, W. Rath, Vincentz Network, Hannover, 2004, p. 121”, e.g. diols or triols of relatively low molecular weight such as 1,2-ethandiol, 1,4-butandiol, 1,6-hexandiol, 2-ethyl-1,3-hexandiol and 1,4-cyclohexandimethanol. Such compounds further include ethylene diamine, 1,4-butanediamine, isophorene diamine, triethylenetetraamine, and triethylene oxide diamine.
Furthermore desiccants may be present such as for example Baylith L.
Suitable thiol group containing compounds are those as described in WO01/92362. As disclosed therein the most preferred thiol-functional compounds are pentaerythritol tetrakis(3-mercaptopropionate) and 3-mercaptopropionate.
Any photolatent bases possessing suitable basicity are applicable in the context of the present invention.
Thus, the photolatent base is for example a compound of the formula (I) as disclosed in EP970085 (Ciba) or WO03/033500 (Ciba) (the disclosure of these documents hereby is incorporated by reference)
in which
R1 is phenyl, biphenylyl, naphthyl, anthryl or anthraquinonyl all of which are unsubstituted or substituted by one or more of the substituents C1-C4-alkyl, C2-C4-alkenyl, CN, OR10, SR10, COOR12, halogen or a substituent of structure (II)
or
R1 is a substituent of formula (IIIa) or (IIIb)
in which
R13 is phenyl, biphenylyl, naphthyl, anthryl or anthraquinonyl all of which are unsubstituted or substituted by one or more of the substituents C1-C4-alkyl, C2-C4-alkenyl, CN, OR10, SR10, COR11, COOR12, or halogen;
R14 is hydrogen
R15. is hydrogen or C1-C4-alkyl;
R2 and R3 independently of each other are hydrogen or C1-C6-alkyl;
R4 and R6 together form a C2-C6-alkylene bridge that is unsubstituted or substituted by one or more C1-C4-alkyl; or
R5 and R7, together form a C2-C6-alkylene bridge that is unsubstituted or substituted by one or more C1-C4-alkyl;
R10, R11 and R12 independently of each other are hydrogen or C1-C6-alkyl.
Especially preference is given to a compound of the formula (I)
in which
R1 is phenyl, biphenylyl or naphthyl all of which are unsubstituted or substituted by one or more of the substituents C1-C4-alkyl, CN, OR10, SR10, COOR12, or a substituent of structure (II)
or
R1 is a substituent of formula (III)
in which
R13 is phenyl, biphenylyl or naphthyl all of which are unsubstituted or substituted by one or more of the substituents C1-C4-alkyl, CN, OR10, SR10, or COOR12;
R14 and R15 are hydrogen;
R2 and R3 independently of each other are hydrogen or C1-C6-alkyl;
R4 and R6 together form a C3-alkylene bridge that is unsubstituted or substituted by one or more C1-C4-alkyl; or
R5 and R7, together form a C3-C5-alkylene bridge that is unsubstituted or substituted by one or more C1-C4-alkyl;
R10 and R12 independently of each other are hydrogen or C1-C6-alkyl.
Preferred are compounds like
wherein Ar phenyl, biphenylyl or naphthyl all of which are unsubstituted or substituted by one or more of the substituents C1-C4-alkyl, CN, OH, O—C1-C6alkyl, SH, S—C1-C6alkyl, COOH, COO—C1-C6alkyl.
An especially preferred example is 5-benzyl-1,5-diazabicyclo[4.3.0]nonane
Concerning the compounds of formula I wherein R1 is a substituent of formula III, examples are
Furthermore the photolatent base to be used in the present method is a compound of the formula IV as disclosed in EP898202 (Ciba), (the disclosure of said document hereby is incorporated by reference).
in which
Ar1 is an aromatic radical of formula V or VIII
V has the meaning of U or is a direct bond;
R1 and R2 are each independently of each other
R11 is C1-C4-alkyl;
R12 is unbranched or branched C2-C16-alkylene which can be interrupted by one or more —O— or —S—;
R13 is hydrogen or C1-C4-alkyl;
R14, R15 and R16 are each independently of one another hydrogen or C1-C4-alkyl, or
R14 and R15 together are C3-C4-alkylene;
R17 is hydrogen, C1-C12-alkyl, C3-C6-alkenyl, C2-C6-alkyl which is substituted by —CN, —OH or —COO(C1-C4-alkyl);
R18 is hydrogen, C1-C12-alkyl, C3-C6-alkenyl, C2-C12-alkyl which is substituted by —OH, —CN, —COO(C1-C4-alkyl);
R19 and R20 are each independently of the other C1-C6-alkyl, C2-C4-hydroxyalkyl, C2-C10-alkoxyalkyl, C3-C5-alkenyl, phenyl-C1-C3-alkyl, phenyl which is unsubstituted or substituted by C1-C4-alkyl or C1-C4-alkoxy, or R19 and R20 are C2-C3-alkanoyl or benzoyl, or R19 and R20 are —O(CO—C1-C8)o—OH;
o is 1-15;
or R19 and R20 together are C4-C6-alkylene which can be interrupted by —O—, —N(R22)— or —S—, or R19 and R20 together are C4-C6-alkylene which can be substituted by hydroxyl, C1-C4-alkoxy or —COO(C1-C4-alkyl);
R22 is C1-C4-alkyl, phenyl-C1-C3-alkyl, —CH2CH2—COO(C1-C4-alkyl), —CH2CH2CN, —CH2CH2—COO(CH2CH2O)q—H or
and
q is 1-8.
Preferred are compounds of the formula (IV)
in which
R1 and R2 are each independently of each other
or R1 and R2 together are unbranched or branched C4-C6-alkylene;
Ar2 is phenyl which is unsubstituted or substituted by OH, C1-C6-alkyl, or is substituted by C1-C4-alkyl, which is substituted by OH, C1-C4-alkoxy, —COO(C1-C4-alkyl), or the radical phenyl is substituted by C1-C4-alkoxy, —(OCH2CH2)nOH, or —(OCH2CH2)nOCH3;
n is 1-3;
R3 is C1-C4-alkyl, C2-C4-alkyl which is substituted by —OH, —C1-C4-alkoxy, —CN, or —COO(C1-C4-alkyl), or R3 is C3-alkenyl, or phenyl-C1-alkyl-;
R4 is C1-C4-alkyl, C2-C4-alkyl which is substituted by —OH, —C1-C4-alkoxy, —CN, or —COO(C1-C4-alkyl), or R3 is C3-alkenyl, or phenyl-C1-alkyl-, or R3 and R4 together are C4-C5-alkylene which can be interrupted by —O—;
R7 and R8 are hydrogen;
R5, R6, and R9 are each independently of one another are hydrogen, halogen, C1-C4-alkyl, phenyl, benzyl, or a group —OR17, —SR18, —N(R19)(R20);
R13 is hydrogen or methyl;
R14, R15 and R16 are each independently of one another hydrogen or methyl;
R17 is hydrogen, C1-C6-alkyl, C3-C6-alkenyl;
R18 is hydrogen, C1-C4-alkyl, C3-C6-alkenyl;
R19 and R20 are each independently of the other C1-C6-alkyl, C2-C4-hydroxyalkyl, C2-C10-alkoxyalkyl, C3-C5-alkenyl, phenyl-C1-C3-alkyl, or R19 and R20 are —O(CO—C1-C8)o—OH or R19 and R20 together are C4-C5-alkylene which can be interrupted by —O—, —N(R22)— or —S—;
o is 1-10;
R22 is C1-C4-alkyl, phenyl-C1-C3-alkyl, —CH2CH2—COO(C1-C4-alkyl), —CH2CH2—COO(CH2CH2O)q—H or
and
q is 1-6.
In the context of the present invention all defined alkyl, alkylene and oxaalkylene, uninterrupted or interrupted, are meant to be linear (unbranched) or branched, even if not expressly stated in the definition as such.
Examples of specific compounds are:
The adhesive composition of the invention optionally also contains other compounds such as antioxidants (especially Hals-compounds), filler resins, thickeners, fluidity adjusting agents, plasticizers, defoaming agents and the like, known in the art for such compositions.
The photolatent base is for example used in an amount between 0.01 to 10 wt. % on solid curable material, preferably 0.05 to 5 wt. %, more preferably 0.05 to 3 wt. %.
The polyisocyanate may be mixed with the compound having a OH/SH function by any suitable technique known in the art.
The pre-polymerized adhesives containing isocyanate and the reactive groups (protected or not) are for example processed at high temperature and coated onto the substrate following the hotmelt process, afterwards full cure is achieved by an additional curing step involving the reactive groups, which is realized by photoactivation of the photolatent catalyst (i.e. the photolatent base compound).
Hotmelt adhesives are interesting as pressure sensitive adhesives (PSA) and suitable to replace the use of solvent based compositions, which from an environmental point of view are disadvantageous. The hotmelt extrusion process necessitates high application temperatures in order to achieve the high flow viscosity. The compositions of the present invention comprising reactive groups are suitable as crosslinkers in the preparation of a hotmelt coating, where the crosslinkers enter into a chemical reaction with the functional comonomers of the (meth)acrylate PSA. After the coating operation, the PSAs are first crosslinked thermally, or, implementing the dual crosslinking mechanism, the PSA is subsequently crosslinked with UV light. UV crosslinking irradiation for example is effected by means of shortwave ultraviolet radiction in a wavelength range from 200 to 400 nm, depending on the UV photoinitiator. Such systems and processes are for example described in US 2006/0052472.
Suitable radiation is present, for example, in sunlight or light from artificial light sources. Consequently, a large number of very different types of light source are employed. Both point sources and arrays (“lamp carpets”) are suitable. Examples are carbon arc lamps, xenon arc lamps, medium-, high- and low-pressure mercury lamps, possibly doped with metal halide (metal-halogen lamps), microwave-excited metal vapour lamps, excimer lamps, superactinic fluorescent tubes, fluorescent lamps, argon incandescent lamps, electronic flashlamps, photographic floodlamps, light emitting diodes (LED, OLED), electron beams and X-rays, produced by means of synchrotrons or laser plasma. Fluorescent lamps are preferred which produce UV A light. A suitable lamp is, for example the actinic blue lamp Philips TL20W/05 which emits light between 300 nm and 400 nm.
The thickness of the formed adhesive film is preferably from 5 to 200 μm.
Employing photolatent bases to trigger the cure of adhesives using light would allow a fast cure at low temperature while keeping the adhesive formulation stable in the dark. Cure is not inhibited by oxygen or moisture.
The examples which follow illustrate the invention in more detail, without restriciting the scope said examples only. Parts and percentages are, as in the remainder of the description and in the claims, by weight, unless stated otherwise. Where alkyl radicals having more than three carbon atoms are referred to in the examples without any mention of specific isomers, the n-isomers are meant in each case.
The following photolatent base compounds are used in the examples:
PLB-1 is dissolved in the thiol component and isocyanate is added shortly before application. A 120 μm thick film is applied onto a glass plate (plate A). A second glass plate (plate B), not coated with the adhesive, is pressed on plate A. After laminating plate A and plate B, the system is irradiated for 5 minutes under a fluorescent lamp (Philips TL20W/05). After irradiation, it is no more possible to separate both glass plates. As a comparison, the same experiment is repeated with a system stored for 5 minutes in the dark instead of being irradiated. Both glass plates can be easily detached, the formulation being still liquid.
Component A (OH component)
A formulation having the following composition is prepared:
A 10 μm thick film of the above mentioned formulation is laminated between two BaF2 crystals and further exposed to UV light (medium pressure mercury lamp AETEK International, one pass at a belt speed of 5 m/min with 2 lamps at 80 W/cm). The reaction is monitored by IR spectroscopy by following the decrease of the isocyanate peak at 2271 cm−1 at room temperature after UV-exposure. The lower the NCO content, the better are the adhesive properties of the film.
As a comparison, the same experiment is performed for a non-laminated film and for a non-exposed film. Results are given in the table below, and clearly show that the curing of the adhesive is faster for the exposed and laminated film.
Component A (OH component):
A formulation having the following composition is prepared:
PLB-1 is dissolved in the component A and the isocyanate is added shortly before application.
A 100 μm thick film is applied onto a glass plate (plate A). The film is dried for 10 minutes at 40° C. A second glass plate (plate B), not coated with the adhesive, is pressed on plate A. After laminating plate A and plate B, the system is exposed to UV light (medium pressure mercury lamp from 1ST, one pass at a belt speed of 5 m/min with 2 lamps at 80 W/cm). 30 minutes after irradiation, it is no more possible to separate both glass plates. As a comparison, the same experiment is repeated with a system stored for 30 minutes in the dark instead of being irradiated. Both glass plates can be easily detached, the formulation being still liquid.
A composition with the following ingredients is prepared:
The photolatent base is dissolved in the thiol-component and the isocyanate is added shortly before application.
Samples with PLB-2, PLB-3, PLB-4 and PLB-5 are prepared.
A 100 μm thick film is applied onto a glass plate (plate A). The film is dried for 10 minutes at 40° C. A second glass plate (plate B), not coated with the adhesive, is pressed on plate A. After laminating plate A and plate B, the samples are exposed for 5 minutes to a fluorescent lamp (Philips TL40W/05).
After irradiation, with all samples it is no more possible to separate both glass plates. As a comparison, the same experiment is repeated with a system stored for 5 minutes in the dark instead of being irradiated. Both glass plates can be easily detached, the formulation being still liquid.
A composition with the following ingredients is prepared:
PLB-1 is dissolved in the thiol component and the isocyanate is added shortly before application.
A 100 μm thick film is applied onto an opaque substrate (plate A). The film is dried for 10 minutes at 40° C. The system is exposed for 1 minute to a fluorescent lamp (Philips TL40W/05). Immediately after exposure, a second opaque substrate (plate B), not coated with the adhesive, is pressed on plate A. After 10 seconds, it is no more possible to separate both plates.
Component A (OH component):
A formulation having the following composition is prepared:
PLB-6 and the sensitizer are dissolved in the component A and the isocyanate is added shortly before application.
A 100 μm thick film is applied onto a glass plate (plate A). The film is dried for 10 minutes at 40° C. A second glass plate (plate B), not coated with the adhesive, is pressed on plate A. After laminating plate A and plate B, the system is exposed to UV light (medium pressure mercury lamp from 1ST, one pass at a belt speed of 5 m/min with 2 lamps at 80 W/cm). 100 minutes after irradiation, it is no more possible to separate both glass plates.
| Number | Date | Country | Kind |
|---|---|---|---|
| 06117329.0 | Jul 2006 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2007/056917 | 7/9/2007 | WO | 00 | 1/8/2009 |
