Patent Application
20250084244
This disclosure relates to an impact resistant adhesive comprising a (meth)acrylate-based matrix with a plurality of polymeric microspheres dispersed therein.
In electronic devices, particularly mobile electronic devices (e.g., handheld or wearable electronic devices), pressure sensitive adhesives (PSAs) are typically used to bond the cover glass (or lens) to the underlying display module, bond the touch sensor to the cover glass and the display, or bond the lower components of the display to the housing. The pressure-sensitive adhesives used in mobile electronic devices are usually optically clear adhesives (OCAs). For these applications (commonly referred to as electronics bonding, or e-bonding), PSAs and OCAs should have an adhesive strength that is sufficiently strong to properly maintain good adhesion to those components, not only when the mobile electronic devices are operating under normal conditions, but also when they are deformed by external forces (e.g., bending, folding, flexing), subjected to traumatic forces (e.g., dropping of the mobile electronic device onto a hard surface), or subjected to extreme environmental conditions (e.g. high temperatures and/or high humidity conditions). Regarding deformation, the components of the electronic devices may be deformed when a user sits in a chair while the electronic device is in their pocket or presses down on the electronic device with their hips. Under such conditions, the pressure sensitive adhesives should have strength of adhesion sufficient to maintain the adhesion to, for example, the cover glass (sometimes referred to as anti-lifting properties). Regarding traumatic forces, the pressure sensitive adhesives should have sufficient drop/impact resistance such that the pressure sensitive adhesive maintains adhesion of the components even when large instantaneous impacts are applied to the mobile electronic device when dropped.
Given the electronics industry's trend towards device simplification (i.e., combining layers and/or layer functions) and reducing bonding area and overall device thickness, (and moreover demanding enhanced flexibility), there exists a growing need for adhesive tapes that have good impact resistance, compliance, and recovery. Adhesives having this balance of dichotomous properties are needed.
In one aspect, a composition is disclosed. The composition comprises: (i) a plurality of polymeric microspheres, wherein the polymeric microspheres are derived from 20 to 100 wt % of a (meth)acrylate monomer having a glass transition temperature (Tg) above room temperature; and (ii) a polymerizable matrix comprising: (a) a (meth)acrylate macromer, wherein the (meth)acrylate macromer comprises a poly(ethylene oxide) group, a poly(propylene oxide) group, a poly(ethylene oxide-co-propylene oxide), a poly(tetrahydrofuran) group, or combinations thereof, (b) one or more of a C1 to C20 (meth)acrylate ester monomer; and (c) a cross-linking agent.
In another aspect, a composition is disclosed. The composition comprises: (i) a plurality of polymeric microspheres, wherein the polymeric microspheres are derived from 20 to 100 wt % of a (meth)acrylate monomer having a Tg above room temperature; and (ii) a matrix derived from (a) a (meth)acrylate macromer, wherein the (meth)acrylate macromer comprises a poly(ethylene oxide) group, a poly(propylene oxide) group, a poly(ethylene oxide-co-propylene oxide), a poly(tetrahydrofuran) group, or combinations thereof, (b) one or more of a C1 to C20 (meth)acrylate ester monomer; and (c) a cross-linking agent.
In another aspect, an adhesive article is described. The adhesive article comprising a composite adhesive composition derived from one of the compositions described above, wherein the composite adhesive composition is disposed on a substrate.
In yet another embodiment, a method of making an adhesive article is described. The method comprising:
In still another embodiment, a method of making an adhesive article is described. The method comprising:
The above summary is not intended to describe each embodiment. The details of one or more embodiments of the invention are also set forth in the description below. Other features, objects, and advantages will be apparent from the description and from the claims.
Embodiments of the present disclosure are illustrated by way of example, in the accompanying drawings, which are for illustrative purposes only and not drawn to scale.
As used herein, the term
Herein, the term “glass transition temperature”, which can be written interchangeably as “Tg”, of a monomer refers to the glass transition temperature of the homopolymer formed from the monomer, which can be a macromer. The glass transition temperature for a polymeric material is typically measured by Dynamic Mechanical Analysis (DMA) as the maximum in tan delta (δ).
As used herein, the term “macromer” refers to a monomer having a polymeric group. A macromer is a subset of the term “monomer”.
The term “monomeric unit” refers to the reaction product of a polymerizable component (i.e., a monomer (including a macromer)) within the (meth)acrylate copolymer. As an example, the monomeric unit of acrylic acid
where the asterisks (*) indicate the attachment site to another group such as another monomeric unit or terminal group in the (meth)acrylate copolymer.
The term “(meth)acrylate macromer” refers to a monomer having a single (meth)acryloyloxy group (i.e., a group of formula CH2═CR—(CO)—O— where R is hydrogen or methyl) plus a poly(ethylene oxide) group, poly(propylene oxide) group, poly(ethylene oxide-co-propylene oxide) group, or poly(tetrahydrofuran) group.
The term “poly(ethylene oxide) group” refers to a group that contains at least 3 ethylene oxide (—(C2H4O)—) groups and the term “poly(propylene oxide) group” refers to a group that contains at least 3 propylene oxide (—(C3H6O)—) groups.
The term “poly(ethylene oxide-co-propylene oxide) group” contains at least 3 groups that include at least one ethylene oxide group and at least one propylene oxide group. The poly(ethylene oxide-co-propylene oxide) group is a copolymeric group.
The term “poly(tetrahydrofuran) (meth)acrylate macromer” refers to a monomer having a single (meth)acryloyloxy group (i.e., a group of formula CH2═CR—(CO)—O— where R is hydrogen or methyl) plus a poly(tetrahydrofuran) group that contains at least three —(C4H8O)— groups. The term “poly(tetrahydrofuran)” can be used interchangeably with the terms “poly(tetramethylene oxide)” and “poly(tetramethylene glycol)”.
Also herein, recitation of ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 10 includes 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10).
Also herein, recitation of “at least” followed by a number include the recited number and all numbers greater (for example, “at least one” includes at least 2, at least 4, at least 6, at least 8, at least 10, at least 25, at least 50, at least 100, etc.).
The adhesives of the present disclosure are a composite comprising a plurality of polymeric microspheres dispersed in a (meth)acrylate-based matrix.
The polymeric microspheres of the present disclosure are derived from a first (meth)acrylate monomer, wherein a homopolymer of the first (meth)acrylate monomer has a glass transition temperature (Tg) above room temperature (e.g., 23° C.), 50, 80, 100, or even 150° C. In one embodiment, the first (meth)acrylate monomer has a Tg no greater than 200, or even 250° C. Such first (meth)acrylate monomers include alkyl(meth)acrylates comprising at least 1, 2, 4, 6, 8, 10, 12, or even 14 carbon atoms; and at most 16, 18, 20, 25, or even 30 carbon atoms. Examples of such first (meth)acrylate monomers include: methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl (meth)acrylate, cyclohexyl methacrylate, isobornyl (meth)acrylate, stearyl (meth)acrylate, phenyl (meth)acrylate, benzyl methacrylate, 2-phenoxyethyl methacrylate, and 3,3,5 trimethylcyclohexyl (meth)acrylate. In one embodiment, the polymeric microspheres are derived from at least 20, 25, 30, 40, 50, 55, 60, 65, 70, or even 75 wt % of the first (meth)acrylate monomer, which includes all first (meth)acrylate monomers that meet the requisite Tg. In one embodiment, the polymeric microspheres are derived from at most 70, 75, 80, 85, 90, 95, 99, 99.5, or even 100 wt % of the first (meth)acrylate monomer, which includes all first (meth)acrylate monomers which meet the requisite Tg. The amount of the first (meth)acrylate used to make the plurality of polymeric microspheres can be adjusted based on the application. In one embodiment, additional comonomers may be used in addition to the first (meth)acrylate monomer. In one embodiment, the additional comonomers are those monomers that have a Tg lower than room temperature. These comonomers, when polymerized with the first (meth)acrylate monomers, result in a copolymer having a Tg of room temperature or above. Exemplary additional comonomers include: 2-ethyl hexyl (meth)acrylate and n-butyl acrylate.
The polymeric microspheres may be made using techniques known in the art. In one embodiment, the polymeric microspheres can be made via suspension polymerization of a reaction mixture comprising the first (meth)acrylate monomer, optional comonomers, and a stabilizer.
In some embodiments, a suspension of monomers is formed, and polymerization is carried out using thermal initiation. The suspension may be a water-in-oil or an oil-in-water suspension. In some such embodiments, the suspension is an oil-in-water suspension, wherein the monomers are stabilized in a bulk water phase by employing one or more stabilizers. Stabilizers useful in embodiments of the present disclosure can include, for example, inorganic stabilizers, surfactants, polymer additives, and combinations thereof.
In some embodiments, the stabilizer may be an inorganic stabilizer such as those used in Pickering emulsion polymerizations (e.g., colloidal silica).
In some embodiments, the stabilizer may be a polymer additive. Polymer additives useful in embodiments of the present disclosure may include, for example, polyacrylamide, polyvinyl alcohol, partially acetylated polyvinyl alcohol, hydroxyethyl cellulose, N-vinyl pyrrolidone, carboxymethyl cellulose, gum arabic, and mixtures thereof. In some embodiments, the polymer additive includes those sold under the trade designation “SUPERFLOC” (e.g., “SUPERFLOC N-300”) by Kemira Oyj, Helsinki, Finland.
In some embodiments, the stabilizer may be a surfactant. In some embodiments, the surfactant may be anionic, cationic, zwitterionic, or nonionic in nature and the structure thereof not otherwise particularly limited. In some embodiments, the surfactant is also a monomer and becomes incorporated within the polymer microsphere molecules. In other embodiments, the surfactant is present in the polymerization reaction vessel, but is not incorporated into the polymer microsphere as a result of the polymerization reaction.
Non-limiting examples of anionic surfactants useful in embodiments of the present disclosure include sulfonates, sulfolipids, phospholipids, stearates, laurates and sulfates. Sulfates useful in embodiments of the present disclosure include sulfates sold under the trade designation “STEPANOL” by the Stepan Company, Northfield IL, and “HITENOL” by the Montello, Inc., Tulsa, OK, and mixtures thereof.
Non-limiting examples of nonionic surfactants useful in embodiments of the present disclosure include block copolymers of ethylene oxide and propylene oxide, such as those sold under the trade designations “PLURONIC”, “KOLLIPHOR”, or “TETRONIC”, by the BASF Corporation of Charlotte, NC; ethoxylates formed by the reaction of ethylene oxide with a fatty alcohol, nonylphenol, dodecyl alcohol, and the like, including those sold under the trade designation “TRITON”, by the Dow Chemical Company of Midland, MI; oleyl alcohol; sorbitan esters; alkylpolyglycosides such as decyl glucoside; sorbitan tristearate; and combinations of one or more thereof.
Non-limiting examples of cationic surfactants useful in embodiments of the present disclosure include cocoalkylmethyl[polyoxyethylene (15)]ammonium chloride, benzalkonium chloride, cetrimonium bromide, demethyldioctadecylammonium chloride, lauryl methyl gluceth-10 hydroxypropyl diammonium chloride, tetramethylammonium hydroxide, monoalkyltrimethylammonium chlorides, monoalkyldimethylbenzylammonium chlorides, dialkylethylmethylammonium ethosulfates, trialkylmethylammonium chlorides, polyoxyethylenemonoalkylmethylammonium chlorides, and diquaternaryammonium chlorides; the ammonium functional surfactants sold by Akzo Nobel N.V. of Amsterdam, the Netherlands, under the trade designations “ETHOQUAD”, “ARQUAD”, and “DUOQUAD”; and mixtures thereof.
In some embodiments, where a stabilizer is employed in an oil-in-water suspension polymerization reaction, it is employed in an amount of at least 0.01, 0.05, 0.1, 0.5, or even 1.0 wt %, based on the total weight of solids in the aqueous polymerizable reaction mixture. In some embodiments where a stabilizer is employed in an oil-in-water suspension polymerization reaction, it is employed in an amount of up to 4.0 or even 5.0 wt %, based on the total weight of solids in the aqueous polymerizable pre-adhesive reaction mixture.
In some embodiments, a cross-linking agent may be used in the microsphere reaction mixture to modify the properties of the resultant microspheres. Nonlimiting examples of suitable cross-linking agents include multifunctional (meth)acrylate(s), e.g., butanediol diacrylate or hexanediol diacrylate, hexanediol diacrylate or other multifunctional cross-linkers such as divinylbenzene and mixtures thereof. In some embodiments, at least 0.005, 0.01, 0.02, 0.05, or even 0.08 wt % of the cross-linker is used based on the total weight of monomers used in the polymerization of the polymeric microspheres. In some embodiments, at most 0.1, 0.2, 0.5, 1, 2, or even 5 wt % of the cross-linker is used based on the total weight of monomers used in the polymerization of the polymeric microspheres.
In some embodiments, an initiator is used that will generate cross-linking in situ by abstracting hydrogens from the polymer in the microspheres allowing cross-linking. Such initiators can include: some peroxide initiators such as benzoyl peroxide and/or azo initiators. Typically, these cross-linking initiators are used in concentrations similar to the cross-linking agent described above (e.g., 0.005 to 5 wt %).
The polymerization of the aqueous polymerizable reaction mixture may be carried out using conventional suspension polymerization techniques familiar to those of ordinary skill in the relevant arts.
In some embodiments where thermal decomposition is employed to initiate polymerization, suspension polymerization of the monomers employed to make the polymer microspheres of the present disclosure may be carried out by blending the stabilizer(s) with water to provide an aqueous phase and blending the monomer composition and a thermal initiator to provide an oil phase. The aqueous phase and the oil phase may then be combined and stirred vigorously enough to form a suspension. The suspension may generally be formed, for example, by stirring the combined aqueous and oil phases with a 3-blade or 4-blade stirrer at a speed of 500 to 1500 (e.g., 1000) revolutions per minute (“rpm”). In some instances, high shear mixing may be used to generate smaller particle sizes such as those less than 10 μm. Exemplary speeds include those at 5000, 10,000, 20,000 or even 50,000 rpm. In some embodiments, a static shear mixer may be used. The suspension may then be heated to a temperature wherein decomposition of the initiator occurs at a rate suitable to sustain a suitable rate of polymerization (e.g., 60° C.).
Non-limiting examples of suitable thermal initiators include organic peroxides or azo compounds conventionally employed by those skilled in the art of thermal initiation of polymerization, such a dicumyl peroxide, benzoyl peroxide, or 2,2′-azo-bis(isobutyronitrile) (“AIBN”) and thermal initiators sold under the trade designation “VAZO” by Chemours Canada Company, ON, Canada. In some embodiments an oil-soluble initiator (e.g., 2-2′-azobis(2,4-dimethylvaleronitrile)) is preferred. The amount of initiator is typically in a range of 0.05 to 2 wt % or in a range of 0.05 to 1 wt %, or in a range of 0.05 to 0.5 wt % based on the total weight of monomers used to prepare the polymeric microspheres.
In some embodiments, water is present in the polymerizable reaction mixture, for example, in an amount of at least 35, 40, 45, or even at least 50 wt %. In some embodiments, water is present in the polymerizable reaction mixture, for example, in an amount of up to 90, 80, 70, or even 60 wt %.
In some such embodiments, the temperature of the suspension is adjusted prior to and during the polymerization is 30° C. to 100° C., or 40° C. to 80° C., or 40° C. to 70° C., or to 45° C. to 65° C. In some embodiments, the peak temperature during the exotherm may reach as high as 75, 90, or even 110° C.
Agitation of the suspension at elevated temperature is carried out for a suitable amount of time to decompose substantially all of the thermal initiator and react substantially all of the monomers added to the suspension to form a polymerized suspension. In some embodiments, elevated temperature is maintained for a period of 1 hour to 48 hours, 2 hours to 24 hours, or 4 hours to 18 hours, or 8 hours to 16 hours.
During polymerization, it may be necessary in some embodiments to add additional thermal initiator to complete the reaction of substantially all of the monomer content added to the reaction vessel to prepare the microspheres. It will be appreciated that completion of the polymerization is achieved by careful adjustment of conditions, and standard analytical techniques, such as gas chromatographic analysis of residual monomer content, will inform the skilled artisan regarding the completion of polymerization of the polymeric microspheres.
In other embodiments, the polymerization of the microspheres may occur in an aqueous mixture that may also include an organic solvent. Examples of suitable organic solvents and solvent mixtures include, in various embodiments, one or more of ethanol, methanol, toluene, methyl ethyl ketone, ethyl acetate, isopropyl alcohol, tetrahydrofuran, 1-methyl-2-pyrrolidinone, 2-butanone, acetonitrile, dimethylformamide, dimethyl sulfoxide, dimethylacetamide, dichloromethane, t-butanol, methyl isobutyl ketone, methyl t-butyl ether, and ethylene glycol. If used, between 30 to 70 wt % organic solvent is used in the microsphere reaction mixture.
Following polymerization, the thus obtained polymeric microspheres can be collected using conventional means such as filtering, optionally washed, and dried.
The particles of the present disclosure are typically spherical-shaped particles. In preferred embodiments, polymeric microspheres of the present disclosure have an average particle diameter of at least 1, 5, 10, 20, 30, 40, or even 50 micrometers (μm). In some embodiments, the polymeric microspheres of have an average particle size at most 60, 80, 90, 100, 120, 150, 180, or even 200 μm. The particle size may be measured by conventional means using, for example, a Horiba LA 910 particle size analyzer (Horiba, Ltd, Kyoto, Japan).
Depending on the selection of the monomers used to synthesis the polymeric microspheres, the polymeric microspheres may or may not be tacky (i.e., sticky). Preferably, the polymeric microspheres are non-tacky and behave as a powder, whereas the tacky polymeric microspheres tend to stick together more. Generally, the more high Tg monomer present, the less tacky the polymeric microsphere. Because a majority of the monomers used to synthesize the polymeric microspheres have a higher Tg, the polymeric microspheres of the present disclosure are comprised of an amorphous polymer. In one embodiment, the polymeric microspheres disclosed herein have a Tg of at least 20, 25, or even 30° C. In one embodiment, the polymeric microspheres disclosed herein have a Tg of at most 30, 50, 70, 100, 125, or even 150° C.
In the present disclosure, the plurality of microspheres are dispersed in a (meth)acrylate-based matrix to form a composite adhesive.
The matrix of the adhesive of the present disclosure is (meth)acrylate-based, derived from a (meth)acrylate macromer and a second (meth)acrylate monomer.
The (meth)acrylate macromer included in the polymerizable components used to form the (meth)acrylate-based matrix has a (meth)acryloyloxy group plus (i) a poly(ethylene oxide) group, (ii) poly(propylene oxide) group, (iii) poly(ethylene oxide-co-propylene oxide) group, which can also be referred to as a poly(ethylene glycol), poly(propylene glycol), or poly(ethylene glycol-co-propylene glycol) groups respectively, (iv) a poly(tetrahydrofuran) group, or (v) combinations thereof. If the macromer contains a poly(ethylene oxide) group, it can be referred to as a poly(ethylene oxide) (meth)acrylate. If the macromer contains a poly(propylene oxide) group, it can be referred to as a poly(propylene oxide) (meth)acrylate. If the macromer contains a poly(ethylene oxide-co-propylene oxide) group, it can be referred to as a poly(ethylene oxide-co-propylene oxide) (meth)acrylate, which is a copolymer. If the macromer contains a poly(tetrahydrofuran) group, it can be referred to as a poly(tetrahydrofuran) (meth)acrylate.
The (meth)acrylate macromer typically has a number average molecular weight in a range of 350 to 10,000 Daltons. For example, the (meth)acrylate macromer has a number average molecular weight no greater than 10,000, 8000, 6000, 4000, 2000, 1000, 800, 650, or even 500 Daltons. The number average can be determined by gel permeation chromatography using techniques known in the art.
The (meth)acrylate macromer often has a Tg (as measured using a homopolymer of the macromer) that is no greater than −10° C. For example, the glass transition temperature can be no greater than −10, −20, −30, or even −40° C. In one embodiment, the Tg is less than −70 or even −80° C. Such a low macromer Tg imparts compliance and flexibility to the (meth)acrylate copolymer and to the adhesive composition.
Examples of such commercially available (meth)acrylate macromers include poly(ethylene glycol) methyl ether acrylate, such as that having a reported number average molecular weight (Mn) of 480 Daltons (available from Sigma-Aldrich) and poly(propylene glycol) acrylate, such as that having a reported number average molecular weight of 475 Daltons (available from Sigma-Aldrich). Other suitable macromers are available under the trade designation BISOMER from Geo Specialty Chemicals, Ambler, PA, such as BISOMER PPA6 (poly(propylene glycol) acrylate reported to have a number average molecular weight of 420 Daltons), BISOMER PEM63P HD (a mixture of poly(ethylene glycol) methacrylate and poly(propylene glycol) reported to have a number average molecular weight of 524 Daltons), BISOMER PPM5 LI (poly(propylene glycol) methacrylate reported to have a number average molecular weight of 376 Daltons), BISOMER PEM6 LD (poly(ethylene glycol) methacrylate reported to have a number average molecular weight of 350 Daltons), BISOMER MPEG350MA (methoxy poly(ethylene glycol) methacrylate) reported to have a number average molecular weight of 430 Daltons), and BISOMER MPEG550MA (methoxy poly(ethylene glycol) methacrylate reported to have a number average molecular weight of 628 Daltons). Other suitable macromers are available under the trade designation MIRAMER from Miwon Specialty Chemical Company, Gyeonggi-do, Korea, such as MIRAMER M193 MPEG600MA (methoxy poly(ethylene glycol) methacrylate reported to have a number average molecular weight of 668 Daltons, MIRAMER M164 (nonyl phenol poly(ethylene glycol) acrylate reported to have a number average molecular weight of 450 Daltons), MIRAMER M1602 (nonyl phenol poly(ethylene glycol) acrylate reported to have a number average molecular weight of 390 Daltons), and MIRAMER M166 (nonyl phenol poly(ethylene glycol) acrylate reported to have a number average molecular weight of 626 Daltons. Still other suitable macromers are available from Sans Esters Corporation, New York, NY such as MPEG-A400 (methoxy poly(ethylene glycol) acrylate reported to have a number average molecular weight of 400 Daltons), and MPEG-A550 (methoxy poly(ethylene glycol) acrylate reported to have a number average molecular weight of 550 Daltons. Various combinations of such macromers may be used if desired.
The macromer having the poly(tetrahydrofuran) group can be prepared, for example, by polymerizing tetrahydrofuran using cationic polymerization. More specifically, the polymerization reaction can occur at room temperature (e.g., 20 to 25° C.) using trifluoromethanesulfonate as the initiator to form an intermediate (A) where n is equal to the number of —CH2CH2CH2CH2O— groups. Intermediate (A) is then reacted with hydroxybutyl acrylate in the presence of N,N-diisoproylethylamine to form the poly(tetrahydrofuran) (meth)acrylate macromer. The weight average molecular weight of the poly(tetrahydrofuran) (meth)acrylate macromer is typically in a range of 350 to 10,000 Daltons, which can be determined using known methods such as gel permeation chromatography with polystyrene standards. If the molecular weight is higher, it may not be miscible with the other components in the polymerizable composition and/or it may crystallize before, during, or after polymerization of the matrix. In many embodiments, the poly(tetrahydrofuran) (meth)acrylate macromer has a weight average molecular weight of at least 500, 600, 800, 1,000, 2,000 or even 3,000 Daltons and up to 10,000, 8,000, 6,000, 5,000, or even 3,000 Daltons.
The second (meth)acrylate monomer in the polymerizable matrix is a C1 to C20 (meth)acrylate ester monomer. Useful C1 to C20 (meth)acrylate ester monomers include at least one monomer selected from the group consisting of a monofunctional (meth)acrylate ester of a linear, branched, and/or cyclic non-tertiary alkyl alcohol, the alkyl group of which comprises at least 1, 2, 3, 4, 5, 6, 7, 8 or even 10 carbon atoms; and at most 14, 16, 18 or even 20 carbon atoms. In one embodiment, the (meth)acrylate ester monomer comprises 1 to 20 carbon atoms. Exemplary second (meth)acrylate monomers include, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, butyl acrylate, 2-methylbutyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl acrylate, n-pentyl (meth)acrylate, iso-pentyl (meth)acrylate, n-hexyl (meth)acrylate, iso-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, phenyl (meth)acrylate, n-octyl (meth)acrylate, iso-octyl (meth)acrylate, 2-octyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, lauryl (meth)acrylate, 2-propylheptyl (meth)acrylate, stearyl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, octadecyl acrylate, nonyl acrylate, dodecyl acrylate, isophoryl (meth)acrylate, dodecyl (meth)acrylate, and any combinations or mixtures thereof.
In one embodiment, the second (meth)acrylate monomer used for the matrix is copolymerized with polar copolymerizable monomers. The polar copolymerizable monomers can be acid or non-acid functional polar monomers such as acrylic acid, hydroxyethyl acrylate, N-methyl acrylamide, or any monomer having a sidechain containing at least one of the following: alcohol, carboxylic acid, amine, amide, imide, thiol, ester, phosphate, and combinations thereof. Exemplary polar monomers include: acrylic acid, methacrylic acid, itaconic acid, fumaric acid, crotonic acid, citraconic acid, and maleic acid, hydroxyalkyl acrylates, acrylamides and substituted acrylamides (such as N,N-dialkylaminoalkyl (meth)acrylates), acrylamines and substituted acrylamines, lactams and substituted lactams, β-carboxyethylacrylate, N-vinyl-2-pyrrolidone, N-vinyl caprolactam, acrylonitrile, and any combinations or mixtures thereof.
When copolymerized with strongly polar monomers, the second (meth)acrylate monomer generally comprises at least about 75 wt % of the polymerizable monomer composition for the matrix. When copolymerized with moderately polar monomers, the (meth)acrylate ester monomer generally comprises at least about 50 wt % of the polymerizable monomer composition for the matrix. Strongly polar monomers include monoolefinic mono- and dicarboxylic acids, hydroxy alkyl acrylate, cyanoalkyl acrylates, acrylamides or substituted acrylamides, or from moderately polar monomers such as N-vinyl pyrrolidone, acrylonitrile, vinyl chloride or diallyl phthalate. The strongly polar monomer preferably comprises up to about 25 wt %, more preferably up to about 15 wt %, of the polymerizable monomer composition for the matrix. The moderately polar monomer preferably comprises up to about 30 wt %, more preferably from about 5 wt % to about 30 wt % of the polymerizable monomer composition for the matrix.
Additional monomers may be added to the polymerizable matrix composition to alter the performance of the matrix in the adhesive, such as a non-polar monomer. The non-polar monomer may be a non-polar ethylenically unsaturated monomer selected from monomers comprising a hydrocarbon sidechain. Examples of suitable non-polar comonomers include 3,3,5-trimethylcyclohexyl acrylate, cyclohexyl acrylate, n-octyl acrylamide, t-butyl acrylate, methyl methacrylate, ethyl methacrylate, and combinations thereof.
A cross-linking agent is used to create a three-dimensional polymer network and to achieve high internal strength of the (meth)acrylate-based matrix within the adhesive. Useful cross-linking agents include photosensitive cross-linking agents, which are activated by ultraviolet (UV) light. Useful cross-linking agents include: multifunctional (meth)acrylates, triazines, and combinations thereof. Exemplary cross-linking agents include substituted triazines such as 2,4,-bis(trichloromethyl)-6-(4-methoxy phenyl)-s-triazine, 2,4-bis(trichloromethyl)-6-(3,4-dimethoxyphenyl)-s-triazine, and the chromophore-substituted halo-s-triazines disclosed in U.S. Pat. Nos. 4,329,384 and 4,330,590 (Vesley). Other useful cross-linking agents include multifunctional alkyl acrylate monomers such as trimetholpropane triacrylate, pentaerythritol tetra-acrylate, 1,2 ethylene glycol diacrylate, 1,4 butanediol diacrylate, 1,6 hexanediol diacrylate, and 1,12 dodecanol diacrylate. Various other cross-linking agents with different molecular weights between (meth)acrylate functionality may also be useful.
In the present disclosure, the (meth)acrylic ester (such as a C1 to C20 (meth)acrylate ester) monomer, the (meth)acrylate macromer, and any optional comonomer are polymerized to form the (meth)acrylate-based matrix.
In one embodiment, the polymer of the matrix comprises at least 10, 20, 30, 40, 50, 60, 70, or even 75% by weight; at most 80, 85, 90, 95, 97, or even 99.5% by weight of a C1 to C20 (meth)acrylate ester monomer relative to the other monomers. A higher amount of the C1 to C20 (meth)acrylate ester monomer relative to the other comonomers affords adequate adhesion at low temperatures (e.g., below room temperature) and/or higher debonding rates (e.g., >12 in/min).
Optionally, the polymer of the matrix comprises at least 0.5, 1.0, 2.5, 5, 8, or even 10% by weight; at most 15, 18, 20, 25, 30, 35, 40, 45, or even 50% by weight of a polar monomer relative to the other monomers present in the (meth)acrylate-based matrix.
In one embodiment, the (meth)acrylate-based matrix contains at least 5, 10, 15, 20, 25, 30, or even 35 weight percent, and up to 60, 55, 50, 45, or even 40 weight percent of the (meth)acrylate macromer. The amount of (meth)acrylate macromer used is based on the total weight of polymerizable components (e.g., monomers) in the matrix.
In one embodiment, a cross-linking agent may be added at a level of at least 0.01, 0.1, 0.5, 1.0, 1.5, or even 2 part solid; at most 3, 4, 5, 6, 8, or even 10 part solid per 100 parts solid versus the weight of all of the polymerizable components used in the preparation of the (meth)acrylate-based matrix. In another embodiment, an initiator is used that will generate cross-linking in situ by abstracting hydrogens from the polymer in the matrix allowing cross-linking of the (meth)acrylate-based matrix. Typically, a cross-linking initiator is used in concentrations of at least 0.01, 0.1, 0.5, 1.0, 1.5, or even 2 part solid; at most 3, 4, 5, 6, 8, or even 10 part solid per 100 parts solid versus the weight of all of the monomers used in the preparation of the (meth)acrylate-based matrix.
In one embodiment, the polymer in the (meth)acrylate-based matrix has a weight average molecular weight of at least 100,000; 200,000; 300,000; 400,000; 500,000; 750,000; or even 1,000,000 grams per mole; at most 20,000,000; 25,000,000; or even 30,000,000 grams per mole. The molecular weight of the polymer can be determined by gel permeation chromatography as is known in the art. The polymer typically has a molecular weight dispersity that can be calculated as the weight average molecular weight versus the number average molecular weight of the polymer. The inherent viscosity is related to the molecular weight of the polymer, but also includes other factors, such as concentration of the polymer. In the present disclosure, the inherent viscosity of the polymer may be at least 0.4, 0.45, 0.5, 0.6, 0.7, or even 0.8; at most 0.7, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8 or even 2,3 as measured in ethyl acetate at a concentration of 0.15 grams/deciliter (g/dL).
The molecular weight of the polymer in the (meth)acrylate-based matrix may be controlled using techniques known in the art. For example, during polymerization, a chain transfer agent may be added to the monomers to control the molecular weight. Useful chain transfer agents include, for example, those selected from the group consisting of carbon tetrabromide, alcohols, mercaptans, and mixtures thereof. Exemplary chain transfer agents are isooctylthioglycolate and carbon tetrabromide. At least 0.01, 0.05, 0.1, 0.15, 0.2, 0.3, or even 0.4 parts by weight of a chain transfer agent may be used; at most 0.1, 0.2, 0.3, 0.4, 0.5, or even 0.6 parts by weight of a chain transfer agent may be used based upon 100 parts versus the weight of all of the monomers used in preparation of the (meth)acrylate-based matrix.
The (meth)acrylate-based matrix used in the adhesive of the present disclosure may be polymerized by techniques known in the art, including, for example, the conventional techniques of solventless polymerization. The polymerization of the monomers “substantially solvent free”, that less than 5%, 2%, 1% or even 0.5% by weight of solvent is used based on the weight of the monomers, and more preferably no additional solvent is added during the polymerization. The term “solvent” refers both to water and to conventional organic solvents used in the industry which are volatilized in the process.
Described below is more detail on the preparation of the composite adhesive according to the present disclosure.
The mixture of plurality of polymeric microspheres along with the polymerizable matrix including the (meth)acrylate macromer and the second (meth)acrylate monomer along with optional comonomers can be polymerized by various techniques, with photoinitiated bulk polymerization being preferred. An initiator is preferably added to aid in polymerization of the monomers or pre-polymerized syrup. The type of initiator used depends on the polymerization process. In a preferred embodiment, photoinitiators are used to initiate the polymerization. Photoinitiators that are useful for polymerizing the acrylate monomers include benzoin ethers such as benzoin methyl ether or benzoin isopropyl ether, substituted benzoin ethers such as 2-methyl-2-hydroxypropiophenone, aromatic sulfonyl chlorides such as 2-naphthalenesulfonyl chloride, and photoactive oxides such as 1-phenyl-1,2-propanedione-2-(o-ethoxycarbonyl)oxime. An example of a commercially available photoinitiator is “IRGACURE 651” available from Ciba, having a formula of 2,2-dimethoxy-1,2-diphenylethane-1-one. Generally, the photoinitiator is present in an amount of about 0.005 to 1 weight percent based on the weight of the monomers. In another embodiment, a thermal initiator may be used, such as for example, AIBN (azobisisobutyronitrile) and/or peroxides. The polymerization may be carried out in the presence of at least one free-radical initiator. Useful free-radical UV initiators include, for example, benzophenones.
In a preferred practice of the disclosure, the polymeric microspheres are blended with the acrylate monomers or an acrylic syrup (which becomes part of the (meth)acrylate-based matrix). As used herein a syrup refers to a mixture that has been thickened to a coatable viscosity, i.e., preferably between about 300 and 10,000 centipoise or higher depending upon the coating method used, and include mixtures in which the monomers are partially polymerized to form the syrup, and monomeric mixtures which have been thickened with fillers such as silicas and the like.
The composite compositions of the present disclosure (i.e., comprising the polymeric microspheres and the acrylate monomers or acrylic syrup used to from the (meth)acrylate-based matrix) may be irradiated with activating ultraviolet (UV) radiation having a UV A maximum in the range of 280 to 425 nanometers to polymerize the monomer component(s). UV light sources can be of various types. Low light intensity sources, such as blacklights, generally provide intensities ranging from 0.1 or 0.5 mW/cm2 (millwatts per square centimeter) to 10 mW/cm2 (as measured in accordance with procedures approved by the United States National Institute of Standards and Technology as, for example, with a UVIMAP UM 365 L-S radiometer manufactured by Electronic Instrumentation & Technology, Inc., in Sterling, VA). High light intensity sources generally provide intensities greater than 10, 15, or 20 mW/cm2 ranging up to 450 mW/cm2 or greater. In some embodiments, high intensity light sources provide intensities up to 500, 600, 700, 800, 900 or 1000 mW/cm2. UV light to polymerize the monomer component(s) can be provided by various light sources such as light emitting diodes (LEDs), blacklights, medium pressure mercury lamps, etc. or a combination thereof. The composite composition can also be polymerized with higher intensity light sources as available from Fusion UV Systems Inc., Gaithersburg, MD. The UV exposure time for polymerization and curing can vary depending on the intensity of the light source(s) used. For example, complete curing with a low intensity light course can be accomplished with an exposure time ranging from about 30 to 300 seconds; whereas complete curing with a high intensity light source can be accomplished with shorter exposure time ranging from about 5 to 20 seconds. Partial curing with a high intensity light source can typically be accomplished with exposure times ranging from about 2 seconds to about 5 or 10 seconds.
Preferably, the syrups of the present disclosure are formed by partial polymerization of the monomers by free radical initiators, which are known in the art and can be activated by thermal energy or radiation such as ultraviolet light. In some instances, it may be preferred to add additional monomer to the syrup, as well as further photoinitiator and other additives. An effective amount of at least one free radical initiator is added to the (meth)acrylate monomers or syrup comprising the polymeric microspheres. The mixture is then coated onto a substrate such as a transparent polyester film, which may optionally be coated with a release coating, and exposed to UV radiation in a nitrogen rich atmosphere to form an adhesive. Alternatively, oxygen can be excluded by overlaying the coated adhesive with a second release coated polyester film and exposed to UV radiation. Subsequent exposure of the adhesive to a second source of energy can be used to cross-link or further cure the adhesive. Such sources of energy include heat, electron beam, gamma radiation, and high intensity ultraviolet lamps, such as mercury are lamps.
The adhesives of the present disclosure can also be prepared by bulk polymerization methods in which the macromer and monomers for the (meth)acrylate-based matrix, the polymeric microspheres, the cross-linking agent, the free radical initiator, and optional additional components described below is coated onto a flat substrate such as a polymeric film and exposed to an energy source, such as a UV radiation source, in a low oxygen atmosphere, i.e., less than 1000 parts per million (ppm), and preferably less than 500 ppm, until the polymerization is substantially complete, i.e., residual monomers are less than 10%, and preferably less than 5%.
Alternatively, a sufficiently oxygen free atmosphere can be provided by enclosing the polymerizable composite composition with, for example, a polymeric film. In one embodiment, the film can be overlaid on top of the coated adhesive composition before polymerization. In another embodiment, the adhesive composition is placed in receptacles, which can be optionally sealed, and then exposed to energy, such as heat or ultraviolet radiation to cross-link the adhesive. The adhesive can then either be dispensed from the receptacles for use, or the receptacles can be fed to a hot melt coater and coated onto a substrate to make tapes or other types of adhesive coated substrates (e.g., labels). In the latter case, the receptacle material should be hot melt coatable with the adhesive in the receptacle, and the receptacle material does not deleteriously affect the desired end properties of the adhesive.
The adhesive composition may comprise additional components to impact the performance and/or properties of the composition. Such additives include plasticizers, tackifiers, antistatic agents, colorants, antioxidants, pigments, dyes, fungicides, bactericides, organic and/or inorganic filler particles, and the like. Use of such additives is well known to those of ordinary skill in the art. In one embodiment, the additives are present at amounts such that the solids in the curable adhesive composition (or the cured adhesive) comprise at least 65 wt % of the (meth)acrylate-based matrix. Therefore, the total amount of additives should be less than 35, 30, 25, 20, 10, 5, or even 1 wt % of the solids. Certain additives may be of lower weight percent, e.g., a pigment may be added at less than 0.05% or even less than 0.005% by weight solids. In some embodiments, such as the instance of inorganic fillers, large amounts of the inorganic fillers may be used (for example greater than 60, 70, 80 or even 95 wt % solids).
Exemplary tackifier include: C5-resins, terpene phenol resins, (poly)terpenes and rosin esters, hydrogenated hydrocarbons, and non-hydrogenated hydrocarbon resins. When used, the tackifiers may be added at a level of at least 5, 8, 10, or even 12 parts; and at most 15, 20, 25, or even 30 parts per 100 parts versus the weight of all of the (meth)acrylate-based matrix.
In one embodiment, the composite adhesive disclosed herein is not a foam, meaning that the (meth)acrylate-based matrix comprises less than 5% by volume of voids, where the voids may be obtained by cells formed by gas, or due to the incorporation of hollow fillers, such as hollow polymeric particles, hollow glass microspheres, or hollow ceramic microspheres.
The composite adhesives disclosed herein may advantageously be used to prepare a wide range of adhesive tapes and articles. Many of these tapes and articles contain backings or release liners used to support the layer of adhesive. As used herein a backing is a permanent support intended for final use of the adhesive article. A liner, on the other hand, is a temporary support that is not intended for final use of the adhesive article and is used during the manufacture or storage to support and/or protect the adhesive article. A liner is removed from the adhesive article prior to final use. To facilitate easy removal from the adhesive layer, the liner is typically coated with a release coating comprising a release agent, Such release agents are known in the art and are described, for example in “Handbook of Pressure Sensitive Adhesive Technology,” D. Satas, editor, Van Nostrand Reinhold, New York, N.Y., 1989, pp. 585-600. In one embodiment, the release agent migrate to the surface (on the liner or release coating) to provide the appropriate release properties. Examples of release agents include carbanates, silicones and fluorocarbons. Illustrative examples of surface applied (i.e., topical) release agents include polyvinyl carbamates such as disclosed in U.S. Pat. No. 2,532,011 (Dahlquist et al.), reactive silicones, fluorochemical polymers, epoxysilicones such as are disclosed in U.S. Pat. No. 4,313,988 (Bany et al.) and U.S. Pat. No. 4,482,687 (Kessel et al.), polyorganosiloxane-polyurea block copolymers such as are disclosed in EP Pat. No. 0250248 B1 (Leir et al.), etc.
In one embodiment, the adhesive article is a double-sided tape, featuring adhesive on opposite sides of a backing layer. The adhesives (i.e., a first adhesive layer and a second adhesive layer) on the two sides may be the same or different. The backing layer may be a film, a non-woven web, paper, or a foam as further described below. The double-sided tape may comprise one or two release liners protecting the adhesive surface not in contact with the backing layer. In one embodiment, the adhesive layer is disposed between two release liners, which may be the same or different. In another embodiment, the adhesive layer is disposed on a backing and the opposing side of the backing comprises a release agent. The adhesive article is wound upon itself such that the exposed surface of the adhesive layer (opposite the backing) contacts the release-coated backing forming, for example, a roll of tape. In yet another embodiment, the adhesive is disposed between a backing and release liner. In some embodiments, the adhesive tapes and articles do not contain a backing and therefore are free standing adhesive layers. Transfer adhesive tapes are an example of such an adhesive article. Transfer adhesives tapes, also called transfer tapes, have an adhesive layer delivered on one or more release liners. The adhesive layer has no backing within it so once delivered to the target substrate and the liner is removed, there is only adhesive. Some transfer tapes are multi-layer transfer tapes with at least two adhesive layers that may be the same or different. Transfer tapes are widely used in the printing and paper making industries for making flying splices, as well as being used for a variety of bonding, mounting, and matting applications both by industry and by consumers.
In one embodiment, the composite adhesive compositions may be easily coated upon a carrier film to produce adhesive coated sheet materials cured via ultraviolet radiation. Coating techniques known in the art may be used such as spray coating, flood coating, knife coating, Meyer bar coating, gravure coating, and double roll coating. The coating thickness will vary depending upon various factors such as, for example, the particular application or the coating formulation. Coating thicknesses of at least 10, 20, 25, 30, 40, 50, 60, 75, or even 100 μm are contemplated.
The carrier film may be a flexible or inflexible backing material, or a release liner. Exemplary materials useful as the carrier film for the adhesive articles of the disclosure include, but are not limited to, polyolefins such as polyethylene, polypropylene (including isotactic polypropylene and high impact polypropylene), polystyrene, polyester, including poly(ethylene terephthalate), polyvinyl chloride, poly(butylene terephthalate), poly(caprolactam), polyvinyl alcohol, polyurethane, poly(vinylidene fluoride), cellulose and cellulose derivatives, such as cellulose acetate and cellophane, and wovens and nonwovens. Commercially available carrier film include kraft paper (available from Monadnock Paper, Inc.); spun-bond poly(ethylene) and poly(propylene), such as those available under the trade designations “TYVEK” and “TYPAR” (available from The Chemours Co.); and porous films obtained from poly(ethylene) and poly(propylene), such as those available under the trade designations “TESLIN” (available from PPG Industries, Inc.), and “CELLGUARD” (available from Hoechst-Celanese). The carrier film delivers the composite adhesive of the present disclosure to the desired substrate. The carrier film may comprise on the surface opposite the composite adhesive, a pigment, indicia, text, design, etc., which is then fixedly attached to the surface of the substrate or the carrier film may be free of such pigments and/or markings.
The thickness of the composite adhesive layer is typically at least 10, 15, 20, or even 25 microns (1 mil) and at most 50, 60, 70, 80, 90, 100, or even 400 microns (10 mil) thickness. In some embodiments, the thickness of the composite adhesive layer is no thicker than 100, 150, or even or even 200 microns and at most 300, 500, 1000, 1500, or even 2000 microns (80 mils). The adhesive can be coated in single or multiple layers. The thickness of the adhesive layer should be at least as thick, preferably thicker than the average particle diameter of the polymeric microspheres contained therein.
In one embodiment, the composite adhesive of the present disclosure comprises at least 0.5, 1, 2, 4, 5, or even 10 grams of the plurality of polymeric microspheres per 100 grams of the (meth)acrylate-based matrix. In one embodiment, the composite adhesive composition comprises at most 10, 15, 20, 25, 30, or even 35 grams of the plurality of polymeric microspheres per 100 grams of the (meth)acrylate-based matrix.
Typically, the polymeric microspheres are homogeneously dispersed throughout the (meth)acrylate-based matrix in layer of the adhesive as shown in
In one embodiment, the composite adhesive compositions of the present disclosure are a pressure sensitive adhesive. Pressure sensitive adhesive compositions are well known to those of ordinary skill in the art to possess properties including the following: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength. Materials that have been found to function well as pressure sensitive adhesives are polymers designed and formulated to exhibit the requisite viscoelastic properties resulting in a desired balance of tack, peel adhesion, and shear holding power.
In one embodiment, the pressure sensitive adhesive composition has a viscoelastic window as defined by E.P. Chang, J. Adhesion, vol. 34, pp. 189-200 (1991) such that the dynamic mechanical properties of the pressure sensitive adhesive composition as measured by well-known techniques fall within the following ranges measured at 25° C.:
The (meth)acrylate-based matrix, which is the other component of the adhesive composition, plays a role of bonding between two adherends and may be tacky at ordinary temperature, or may not be initially tacky and adhesion builds over time.
In one embodiment, the composite adhesive compositions of the present disclosure are heat-activated film adhesive, wherein a film, upon heating becomes tacky (i.e., Dahlquist criterion for tack has a shear storage modulus of less than 0.3 MPa at an angular frequency of 1 Hz.
The present disclosure has identified that a composite comprising a plurality of particles dispersed within a (meth)acrylate-based matrix results in an adhesive composition having good impact resistance in resisting tensile impact forces and resistance to shear deformation. Typically, the addition of the plurality of particles increases the shear storage modulus (G′) of the resulting composition. It is inferred that the increased shear storage modulus is related to the adhesives' shear resistance to deformation. In other words, the addition of the plurality of polymeric microspheres, makes the composite adhesive more “stiff”. Typically, the addition of the (meth)acrylate macromer in the composition of the present disclosure is thought to decrease the shear storage modulus and Tg of the resulting composition, enabling the resulting composite adhesive to have improved resistance to tensile debonding as demonstrated by improved performance in the Guided Free Fall Testing. As shown in the example section, when a “softer” (meth)acrylate resin (i.e., a resin with a shear storage modulus below 80, or even 60 kPa) is used, the addition of the plurality of polymeric microspheres increases the shear storage modulus, however, the Guided Free Fall testing suffers. Thus, addition of the (meth)acrylate macromer helps to balance the resistance to tensile debonding enabling these softer resins to resist both tensile impact forces and resistance to shear deformation.
In one embodiment, the composite adhesives disclosed herein have a shear storage modulus (G′) at 25° C. and 1 Hz of at least 50, 100, 150, 200, 300, or even 400 kPa (kiloPascals).
Generally, due to the composite nature of the adhesive of the present disclosure, two peak tan deltas are observed when tested. In one embodiment, the lowest temperature peak tan delta of the composite adhesives is at least −40, −30, −20, −10, −5, 0, or even 5° C. In one embodiment, the lowest temperature peak tan delta of the composite adhesives is no more than 60, 50, 40, 30, 20, or even 10° C.
In one embodiment, the composite adhesives disclosed herein, when assembled as tested as disclosed in the Guided Free Fall Testing are dropped at 40 cm (centimeters) 10 times, the sample did not fail. In one embodiment, the composite adhesives disclosed herein, when assembled as tested as disclosed in the Guided Free Fall Testing are dropped at 70 cm height 10 times, the sample did not fail. In one embodiment, the composite adhesives disclosed herein, when assembled as tested as disclosed in the Guided Free Fall Testing are dropped at 120 cm height 10 times, the sample did not fail. In one embodiment, the composite adhesives disclosed herein, when assembled as tested as disclosed in the Guided Free Fall Testing are dropped at 200 cm height 10 times, the sample did not fail.
In one embodiment, the composite adhesives according to the present disclosure not only have good adhesion to substrates having a high surface energy, but also demonstrate good adhesion to low surface energy substrates. In one embodiment, the adhesive of the present disclosure has a peel value greater than 0.4, 0.5, 0.6, or even 0.8 N/mm when tested according to ASTM D 3330/D3330M on a stainless steel substrate with an adhesive thickness of 8 mils (200 micrometers) when laminated and peeled at room temperature. The peel strength may be adjusted based on the required application, with some applications requiring a higher peel strength (for example from at least 0.5, 0.6, 0.7, or even 0.8 N/mm and at most 2.5, 2.2, 2.1, or even 2.0 N/mm).
In one embodiment, the composite adhesives disclosed herein are optically clear. In one embodiment, the difference between the refractive index of the plurality of polymeric microspheres and the refractive index of the (meth)acrylate-based matrix is less than 0.2, 0.1, or even 0.05. The refractive index can be determined by using techniques known in the art. For example, the Becke Line Method wherein certified refractive test liquids are used along with a microscope to determine the refractive index of a material or the refractive index may be determined by using a refractometer and measuring the bend of a wavelength of 589 nm (sodium D line) at 25° C. in air.
The composite adhesive compositions described herein are suitable for use in the areas of electronics, appliances, automotive, and general industrial products. In some embodiments, the adhesive can be utilized in (e.g., illuminated) displays that can be incorporated into household appliances, automobiles (e.g., adhering to panels), computers (e.g., tablets), and various hand-held devices (e.g., phones).
In some embodiments, the composite adhesive compositions described herein are suitable for bonding internal components or external components of illuminated display devices such as liquid crystal displays (“LCDs”) and light emitting diode (“LEDs”) displays such as cell phones (including Smart phones), wearable (e.g. wrist) devices, car navigation systems, global positioning systems, depth finders, computer monitors, notebook and tablet computer displays or bonding items (e.g., handles, display holders) to the exterior of electronic devices.
Advantages and embodiments of this disclosure are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention. In these examples, all percentages, proportions and ratios are by weight unless otherwise indicated.
All materials are commercially available, for example from Sigma-Aldrich Chemical Company; or known to those skilled in the art unless otherwise stated or apparent.
These abbreviations are used in the following examples: ° C.=degree Celsius, cP=CentiPoise, g=gram, lb=pound, kg=kilograms, mL=milliliter, mol=mole, min=minutes, cm=centimeter, Hz=Hertz, J=Joule, kDa=kiloDalton, 1=liter, mm=millimeter, mW=milliWatt, N=Newton, nm=nanometer, Pa=Pascal, rpm=revolutions per minute, ppm=parts per million, and wt=weight.
Microsphere particle-size measurements were performed using a Horiba LA 910 particle size analyzer (Horiba, Ltd, Kyoto, Japan). The particle sizes are reported in micrometers the standard deviation.
The glass transition temperature was measured on a TA Instruments Q1000 Differential Scanning Calorimeter (New Castle, DE). The glass transition temperature was measured as the midpoint on the second heating ramp from 0-150° C. at a rate of 10° C./min.
Nuclear Magnetic Resonance Spectroscopy was performed on a Bruker 500 MHz instrument, Billerica, MA. 1H-NMR was in CDCl3 (residual solvent referenced to 7.26 ppm).
The molecular weight (both number average, M., and weight average, Mw) and polydispersity were determined using size exclusion chromatography with polystyrene standards. The chromatography system included an instrument available under the trade designation “ACQUITY” (Waters Corporation, Milford, MA) and the following columns in order (going downstream): Styragel guard column (20 μm, 4.6 mm×30 mm) and a first Styragel HR 5E column (mixed bed, 5 μm, 7.8 mm×300 mm, 2K-4M) and a second Styragel HR 5E column (all columns are available from Waters Corporation). Analysis was done using a THF mobile phase at flow rate of 1 mL/min.
For all peel adhesion testing, the RF02N release liner was removed from the transfer tape sample, and the exposed adhesive side of the transfer tape was contacted to the plasma treated side of a 6 inch (15 cm) wide plasma treated polyester film (3M, 2-mil (50-μm) biaxially oriented PET film whose surface had undergone plasma treatment conditions described in U.S. Pat. No. 10,134,566 (David et al.)). Then, a 6 inch (15 cm) rubberized hand roller (Polymag Tek, NY) was rolled by hand over the construction ensuring no air bubbles were trapped between the adhesive and the primed polyester film. Peel adhesion was measured at an angle of 180 degrees. Peel adhesion testing was performed on annealed 18 gauge, 304 stainless steel (SS) test panel from Chem. Instruments, Fairfield, OH). The RF12N release liner was removed from the tapes on PET backings and the exposed adhesive side was laminated directly to the 2-inch×6-inch (5.08 cm×15.24 cm) stainless steel test panel using a weighted rubberized (4.5 lb, 2.04 kg) hand roller with 4 repetitions of 3 second roll downs. The transfer tape, stainless steel test panel, and the transfer tape applied to the stainless steel (SS) test panel were conditioned in a controlled temperature and humidity (CTH) room (set at 23° C., 50% RH (relative humidity)) prior to peel testing. SS test panels were cleaned with methyl ethyl ketone (MEK) before and after testing. Peel testing was done using an SP-2100 iMass (iMass Inc., Accord, MA USA) at a rate of 12 inches/min (0.3 m/min). Each sample was peeled at least three times from the same substrate and averages of all three measurements are reported. The peel adhesion force and the failure mode were recorded. Adhesive failure refers to the failure occurring between the adhesive and the SS test panel. Cohesive failure occurs when adhesive remains on both the SS test panel and the polyester film. A #2 bond failure refers to the failure occurring between the adhesive and the polyester film.
Samples were tested for ‘guided free fall’ using a tensile drop configuration. The adhesive composition was used to bond an aluminum frame to a polycarbonate panel (51 mm width×102 mm length×3 mm thickness, available from Chem Instruments, Fairfield, OH, USA). In the tensile drop, the adhesive was pulled in a tensile mode by the polycarbonate panel from the aluminum frame while being dropped. The test is described in U.S. Pat. Publ. No. 2015/0030839 (Satrijo et al.). The aluminum-adhesive-polycarbonate construction was assembled as follows: first, the adhesive transfer tape was cut into two 51 mm long×2 mm wide strips. The RF02N release liner was removed from each strip and the exposed adhesive side was bonded to the aluminum frame parallel to, and 14 mm away from; the outer shorter side edge of the Al frame. Then the RF12N liner was removed from the strips and a polycarbonate panel was laminated to the now exposed adhesive. The adhesive bonded aluminum frame-adhesive-PC panel assembly was allowed to dwell for 48 hours at 23° C. and 50% RH. The bonded article was then evaluated for drop resistance in a tensile mode using a drop tester (DT-202TBW, available from Shinyei Corporation of America, New York, New York, USA) and a horizontal orientation of the bonded article with the PC substrate facing downward. The bonded article was dropped at 40 cm onto a 1.2 cm thick steel plate. If the sample did not fail (i.e., the polycarbonate panel did not detach from at least a portion of the aluminum frame) at 40 cm after 10 successive drops, the sample was then dropped at 70 cm (10 drops), and then 120 cm (10 drops), and then 200 cm (10 drops) if no failure at the lower height. A numerical value other than 10 in the results table indicates at which number of fall the sample failed.
Both the RF02N and RF12N liners where removed from the transfer tape samples and the adhesive composite was tested on an TA Instruments discovery hybrid rheometer (DHR-3, New Castle, DE). The sample was heated from room temperature up to 40° C. at a rate of 3° C./min then cooled to −50° C. at a rate of 3° C./min, warming up to 20° C. and then heating the sample from 20° C. to 140° C. at a rate of 3° C./min. The data was collected during the second heating cycle using an oscillatory frequencies of 1 Hz with strain values in the linear viscoelastic regime (typically <5%). The glass transition temperature (at 1 Hz) was determined as the peak of the tan(δ) curve from the rheology plot of G′ and G″ (y axis −1) vs. temperature (° C.), (x axis) and tan(δ) (y axis-2). The peak (i.e., highest value) in tan(δ) was selected from y axis-2, and the corresponding temperature on the x axis was selected as the glass transition temperature. Tan(δ) is an abbreviation for the tangent of the phase angle between the stress and strain oscillation waves in the shear rheology oscillation. Samples that passed the rheology requirements had a shear storage modulus (G′) of >100 kPa at 25° C.
To a 1-neck, 1-1 flask dried in an oven, equipped with a stir bar was added 500 g (6.93 mol) THF straight from an unopened bottle of THF. The flask was immediately capped with a septum and 4.7 mL (7.0 g, 0.042 mols) methyl trifuoromethanesulfonate was injected, and the reaction stirred for 7 minutes. At this time the reaction was quenched by sequential addition of 7.7 ml (5.7 g, 0.044 mols) and 6.3 mL of HBA (6.55 g, 0.045 mols). The reaction was allowed to stir at room temperature overnight. The residual THF was removed by rotary evaporation and the polymer dissolved in 700 mL of MTBE. This solution was washed with deionized water (5×200 mL). The organic layer was dried over MgSO4, filtered, and the solvent removed by rotary evaporation. Residual solvent was removed by bubbling air through the polymer. The number average molecular weight of the dried sample was determined by 1H-NMR and found to be Mn=3.9 kDa.
A 1000 mL resin flask (4 inch (10 cm) diameter) was charged with STEPANOL AMV (4.2 g), HITENOL BC-1025 (4.2 g), and water (422 g) to provide an aqueous phase. In a separate flask, an oil phase was prepared by mixing C12 acrylate blend (105.5 g), IBOA (316.5 g), HDDA (2.1 g of a 10 weight % solution of HDDA in n-butyl acrylate), and VAZO 52 (0.42 g). After complete mixing with a polytetrafluoroethylene-coated magnetic stir bar, the oil phase was added to the aqueous phase. An overhead stirrer equipped with a glass trailing edge (3 blade) stir rod was used to mix the phases at a rate of 1000 rpm. During the agitation, the multi-phase mixture was degassed by sparging with nitrogen for 30 minutes. After degassing, the mixture was heated to 60° C. The peak temperature during the exotherm typically reached as high as 85° C. The mixture was allowed to cool to 60° C. and was then maintained at that temperature for 8 hours. The mixture was cooled to room temperature. The solid microspheres were filtered in a Buchner funnel onto filter paper, washed with water and dried under vacuum.
Microspheres M2, M4, M5, M6, and M7 were prepared following the same procedure as described above for M1 except the reagents and amounts listed in Table 2 were used in the oil phase.
Representative Microsphere Preparation 2: Synthesis of 1 Micrometer Diameter Microspheres (M3)
A 500 mL beaker was charged with STEPANOL AMV (2 g), HITENOL BC-1025 (2 g), and water (200 g) to provide an aqueous phase. In a separate beaker, an oil phase was prepared by mixing IBOA (200 g), HDDA (1 g of a 10 wt % solution in n-butyl acrylate), and VAZO 52 (0.20 g). After complete mixing with a polytetrafluoroethylene-coated magnetic stir bar, the oil phase and aqueous phase were combined. The phases were mixed at approximately 20,000 rpm using a homogenizer (PR0250, PRO Scientific, Oxford, CT) for 2 minutes. After mixing, the heterogenous suspension was transferred to a 1000 mL resin flask (4 inch (10 cm) diameter). An overhead stirrer equipped with a glass 4-pitched blade stir rod was used to agitate the mixture at 350 rpm. During the agitation, the multi-phase mixture was degassed by sparging with nitrogen for 15 minutes. After degassing, the mixture was heated to 60° C. The peak temperature during the exotherm typically reached as high as 80° C. The mixture was allowed to cool to 60° C. and was then maintained at that temperature for 8 hours. The mixture was cooled to room temperature. The solid microspheres were filtered in a Buchner funnel onto filter paper, washed with water, and dried under vacuum.
Shown in Table 2 are the weight (wt) % of the monomers that went into making the microspheres. The microspheres were then tested for particle size and Tg using the Particle Size Analysis and the Differential Scanning Calorimetry Test Methods described above. As used in the Example Section, phr refers to parts per 100 parts resin, meaning the amount of the component used (e.g., g) versus 100 parts (e.g., g) of the polymerizable/polymerized monomers.
Syrups SRP-1 to SRP-3 were synthesized by adding the monomers (as specified in Table 4) together at the appropriate wt % loadings, adding IRG 651 (0.02 phr with respect to total monomers at 100 phr) and exposing the mixture to 0.3 mW/cm2 UV-LED irradiation (365 nm) until the mixture had a higher viscosity (about 1,000 cP). Shown in Table 5 is the molecular weight in megaDaltons (MDa) and the polydispersity of the resulting syrups as determined by the SEC Test Method described above.
Curable compositions were made using the components as listed in Table 6. The designated syrup was used at 100 parts and the rest of the components were added at the amounts listed.
Then each curable composition was coated between two release liners (RF12N and RF02N). The samples then were cured under 405 nm UV-LED lights with a total dosage of 3.1 J/cm2 as measured with a radiometer equipped with a high power sensing head (available under the trade designation “POWER PUCK II” from EIT Incorporated, Sterling, VA), resulting in transfer tapes, which had an adhesive layer thickness of 8 mils (200 μm).
The transfer tapes were then tested following the Peel Adhesion, Guided Free Fall, and Rheology and Glass Transition Temperature Test Methods described above. The results are summarized in tables 7-10 below.
Foreseeable modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention. This invention should not be restricted to the embodiments that are set forth in this application for illustrative purposes.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2023/051850 | 2/28/2023 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63319942 | Mar 2022 | US |
