# Patent

## Title
Pressure sensitive adhesive comprising blend of synthetic rubber and functionalized synthetic rubber bonded to an acrylic polymer

## Abstract

A pressure sensitive adhesive composition is described comprising unfunctionalized (e.g. polyisobutylene) synthetic rubber and an acrylic polymer having functionalized polyisobutylene polymer bonded to the acrylic polymer. In some embodiments, the functionalized polyisobutylene polymer has a first functional group hydrogen bonded with a second functional group present in the acrylic polymer backbone. In other embodiments, the functionalized polyisobutylene polymer is covalently bonded to the acrylic polymer backbone. Also described are adhesive articles, such as a tape, methods of adhesively bonding, and methods of making a pressure sensitive adhesive.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a national stage filing under 35 U.S.C. 371 of PCT/US2010/056646, filed Nov. 15, 2010, which claims priority to Provisional Application No. 61/262,611, filed Nov. 19, 2009, the disclosure of which is incorporated by reference in its/their entirety herein.


BACKGROUND
Pressure sensitive adhesives (PSAs) are an important class of materials. In recent years, there has been a significant increase in the use of plastics, vulcanized rubbers, and thermoplastic vulcanizates (“TPV”) in the automotive, appliance and electronics markets. Generally, these materials combine the desirable characteristics of vulcanized rubber with the processing ease of thermoplastics. However, bonding to these and other low surface energy substrates currently requires priming the substrate surface prior to bonding with a pressure sensitive adhesive (“PSA”). The priming process can be expensive and labor intensive, and may present environmental concerns.
Accordingly, industry would find advantage in new pressure sensitive adhesives that can exhibit good adhesion to a variety of substrates, such as low surface energy substrates.
SUMMARY
In one embodiment, a pressure sensitive adhesive composition is described comprising unfunctionalized (e.g. polyisobutylene) synthetic rubber and an acrylic polymer having functionalized polyisobutylene polymer bonded to the acrylic polymer. In some embodiments, the functionalized polyisobutylene polymer has a first functional group hydrogen bonded with a second functional group present in the acrylic polymer backbone. In other embodiments, the functionalized polyisobutylene polymer is covalently bonded to the acrylic polymer backbone.
In another embodiment, a pressure sensitive adhesive coated article is described, such as a tape. The article comprises a substrate and the pressure sensitive adhesive describe herein coated on at least one surface of the substrate.
In another embodiment, a method of bonding is described comprising providing a substrate, applying the pressure sensitive adhesive described herein on a surface of the substrate, and contacting the pressure sensitive adhesive with another substrate.
In another embodiment, a method of making a pressure sensitive adhesive is described. The method comprises blending an unfunctionalized synthetic rubber and an acrylic polymer having functionalized polyisobutylene polymer bonded to the acrylic polymer.
In each of these embodiments, the functionalized polyisobutylene is typically a relatively low molecular weight liquid polymer, having a number average molecular weight of less than 10,000 g/mole. The unfunctionalized (e.g. PIB) synthetic rubber is typically a relatively high molecular weight polymer, having a weight average molecular weight ranging from about 75,000 g/mole to 4,000,000 g/mole.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a microscopic (10×) image of a blend of unfunctionalized polyisobutylene totaling 50 wt-% and 50 wt-% acrylic polymer.
FIG. 2 is a microscopic (10×) image of a blend of functionalized and unfunctionalized polyisobutylene totaling 50 wt-% and 50 wt-% acrylic polymer.
FIG. 3 is a microscopic (20×) image of a blend of functionalized and unfunctionalized polyisobutylene totaling 75 wt-% and 25 wt-% acrylic polymer.
FIG. 4 is a microscopic (20×) image of a blend of functionalized and unfunctionalized polyisobutylene totaling 50 wt-% and 50 wt-% acrylic polymer.
FIG. 5 is a microscopic (20×) image of a blend of functionalized and unfunctionalized polyisobutylene totaling 25 wt-% and 75 wt-% acrylic polymer.
FIG. 6 depicts the reaction product of functionalized PIB and an acrylic polymer.
FIG. 7 depicts the reaction product of functionalized PIB and an acrylic polymer when the pressure sensitive adhesive (e.g. precursor) further comprises a chemical crosslinker.



DETAILED DESCRIPTION
As used in the art, the term “pressure-sensitive adhesive” refers to adhesive compositions that have (1) aggressive and persistent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength to be cleanly removable from the adherend.
The pressure sensitive adhesive composition described herein comprises at least one polyisobutylene having a first functional group, also referred to herein as the “functionalized polyisobutylene”. The functional group of the functionalized polyisobutylene is typically a (e.g. terminal) group that can hydrogen bond or covalently bond to (e.g. pendant carboxylic acid groups of) of backbone of an acrylic polymer or a functional group appended to the (e.g. backbone) of the acrylic polymer.
In some embodiments, the functionalized polyisobutylene is a functionalized homopolymer of isobutylene. In other embodiments, the functionalized polyisobutylene is a copolymer comprising isobutylene repeat units and a small amount of units derived from another monomer such as, for example, styrene, isoprene, butene, or butadiene. These copolymers are typically prepared from a monomer mixture that includes at least 70 weight percent, at least 75 weight percent, at least 80 weight percent, at least 85 weight percent, at least 90 weight percent, or at least 95 weight percent isobutylene based on the weight of monomers in the monomer mixture. Typically, at least 70 weight percent, at least 75 weight percent, at least 80 weight percent, at least 85 weight percent, or at least 90 weight percent of the polyisobutylene copolymer is formed from isobutylene repeat units. Exemplary copolymers include isobutylene copolymerized with isoprene.
The functionalized polyisobutylene is typically a liquid polymer having a relatively low to intermediate number average (Mn) molecular weight. The Mn is typically at least 500 g/mole, 750 g/mole, or about 1,000 g/mole. In some embodiments, the Mn of the functionalized polyisobutylene is no greater than 25,000 g/mole, or 10,000 g/mole, or 5,000 g/mole.
The functionalized polyisobutylene typically has a glass transition temperature of no greater than about −30° C. or less, no greater than about −50° C., or no greater than about −70° C., as determined by differential scanning calorimetry (DSC).
The functional group of the functionalized PIB can be any functional group that forms a hydrogen bond or covalent bond with (e.g. pendant carboxylic acid groups of) the backbone of an acrylic polymer or a functional group appended to the (e.g. backbone) of the acrylic polymer.
In some embodiments, the first functional group and second functional group form a hydrogen bond. In this embodiment, the predominant bond between the functional group of the polyisobutylene and the acrylic polymer is a hydrogen bond. Hence, in this embodiment, such functional groups do not form a covalent bond. A hydrogen bond is an attractive force, or bridge, occurring in polar compounds in which a hydrogen atom of one molecule or functional group is attracted to unshared electrons of another. The hydrogen atom is the positive end of one polar molecule or functional group (otherwise known as a hydrogen bond donor) and forms a linkage with the electronegative end of another molecule or functional group (otherwise known as a hydrogen bond acceptor). Functional groups that have non-polar covalent bonds do not form hydrogen bonds.
Common hydrogen-bond donors include carboxylic acids, phosphonic acids, phosphoric acid esters, sulfonic acids, sulfuric acids, alcohols, and phenols.
Common hydrogen-bond acceptors include nitrogen containing groups such as amines, amides, imines, imides, nitriles and ureas as well as aromatic nitrogen-based functional groups such as pyridines, imidazoles, etc. Other hydrogen-bond acceptors include carboxylate groups (carboxylic acid, carboxylic ester), phosphonates, sulfoxides, sulfones, and carbamates.
In one embodiment, the acrylic polymer has carboxylic acid functionality and the functionalized PIB has a functional (e.g. terminal) group that hydrogen bonds with the carboxylic acid group of the acrylic polymer. In this embodiment, the functional group of the functionalized PIB is not acrylate, methacrylate, or any other functional group that covalently bonds with a (meth)acrylate group via free radical polymerization. This approach can be preferred since it can utilize commercially available functionalized PIB having a terminal nitrogen-containing group such as an amine or imide.
Various functionalized PIB materials are commercially available. For example, polyisobutyleneamine having a number average molecular weight (Mn) of about 1,000 grams/mole and a molar mass distribution Mw/Mn=1.6) is commercially available from BASF Corporation (Florham Park, N.J.) under the trade designation “Kerocom® PIBA03”. Further, polyisobutene succinimide is available from BASF under the trade designation “Kerocom® PIBSI”. An anhydride-terminated polyisobutylene (Mn) of about 1,000 grams/mole) is available from BASF under the trade designation “Glissopal SA”.
The commercially available functionalized PIB materials are suitable for the formation of hydrogen bonds wherein the carboxylic acid group is the proton donor (i.e. H-bond donor) and the nitrogen-containing group (i.e. amine or imide) is the proton acceptor (i.e. H-bond acceptor).
However, it is appreciated that the functional groups can be reversed. For example, the functionalized PIB may have a (e.g. terminal) carboxylic acid group, provided that the carboxylic acid groups of the acrylic polymer are pre-reacted to convert these groups to a functional group that will then in turn form a hydrogen bond with the carboxylic acid groups of the PIB.
For example, polyisobutyleneamine (e.g. Kerocom® PIBA03) could be reacted with an anhydride (such as succinic anhydride or glutaric anhydride) to provide a carboxylic acid-functionalized PIB material. A carboxylic acid-functionalized PIB could also be prepared by reaction of anhydride-terminated polyisobutylene (e.g. Glissopal SA) with an alcohol (such as 1-octanol) to provide a PIB chain terminated with an ester and a carboxylic acid.
Amine-functionalized acrylic polymers can be prepared by copolymerization of at least one amino comonomer with alkyl (meth)acrylate monomers. Suitable amino comonomers are olefinically unsaturated, polymerizable compounds that contain at least one primary or secondary amino group, e.g. amino methacrylates such as tert-butylaminoethyl methacrylate or meta-isopropenyl-α,α-dimethylbenzylamine. Amino groups can also be obtained by the reaction of acid polymers with aziridines such as ethylene imine as well as other techniques known for adding amine functionality to polymers.
Various amino comomomers are known including for example N,N-dimethylaminopropyl methacrylamide (DMAPMAm); N,N-diethylaminopropyl methacrylamide (DEAPMAm); N,N-dimethylaminoethyl acrylate (DMAEA); N,N-diethylaminoethyl acrylate (DEAEA); N,N-dimethylaminopropyl acrylate (DMAPA); N,N-diethylaminopropyl acrylate (DEAPA); N,N-dimethylaminoethyl methacrylate (DMAEMA); N,N-diethylaminoethyl methacrylate (DEAEMA); N,N-dimethylaminoethyl acrylamide (DMAEAm); N,N-dimethylaminoethyl methacrylamide (DMAEMAm); N,N-diethylaminoethyl acrylamide (DEAEAm); N,N-diethylaminoethyl methacrylamide (DEAEMAm); N,N-dimethylaminoethyl vinyl ether (DMAEVE); N,N-diethylaminoethyl vinyl ether (DEAEVE); and mixtures thereof. Other useful basic monomers include vinylpyridine, vinylimidazole, tertiary amino-functionalized styrene (e.g., 4-(N,N-dimethylamino)-styrene (DMAS), 4-(N,N-dimethylamino)-styrene (DEAS)), and mixtures thereof.
Other functionalized polyisobutylene can be prepared by various methods as known in the art. For example, hydroxy-functionalized PIBs could also be synthesized by reacting anhydride-terminated polyisobutylene (e.g. Glissopal SA) with amino alcohols or diols, or by reacting poly-isobutyleneamine (e.g. Kerocom PIBA03) with 2-chloroethanol or epoxides. Pyridine-functionalized PIB-based materials can be synthesized by reacting an amino or hydroxy-bearing pyridine compound with a polyisobutylene (e.g. succinic) anhydride (e.g. Glissopal® SA). Alternatively, poly-isobutyleneamine (e.g. Kerocom® PIBA03) can be reacted with 3-(chloromethyl)pyridine to provide a pyridyl-substituted PIB derivative. Carbamate-functionalized PIB could be obtained by reacting poly-isobutyleneamine (e.g. Kerocom® PIBA03) with isocyanate electrophiles.
Alternatively, the first functional group of the functionalized PIB and second functional group of the acrylic polymer form a covalent bond. In this embodiment, the first functional group of the functionalized PIB can be any functional group that forms a covalent bond with the backbone of an acrylic polymer. Alternatively, the first functional group of the functionalized PIB is a polymerizable (meth)acrylate functionality that can be copolymerized with typical alkyl (meth)acrylate monomers.
Many common functional groups can be used to form covalent bonds between the PIB material and acrylic polymer. For example, amine- or alcohol-functionalized PIB materials could be reacted with (meth)acrylate polymers that comprise activated ester-type functional groups. Such activated esters include anhydrides, N-hydroxysuccinimide esters, pentafluorophenyl esters, and acid chlorides. For example, an acrylate polymer containing N-hydroxysuccinimide ester functional groups can be prepared by using acrylic acid N-hydroxysuccinimide ester as an acrylate monomer. Alternatively, carboxylic acid residues in the (meth)acrylate polymer could be converted to activated esters by common methods known to those skilled in the art. Another route to making covalently bonded PIB-acrylate materials would be to react amine- or alcohol-functionalized PIB materials with (meth)acrylate polymers that contained azlactone rings. (Meth)acrylate polymers that bear azlactone rings can be prepared by using 2-vinyl-4,4-dimethyl-5-oxazolone as a comonomer. A suitable amine-functionalized PIB material is Kerocom® PIBA03.
Yet another strategy to make covalently bonded PIB-(meth)acrylate materials is to react amine- or hydroxy-functionalized PIB-materials with an isocyanate-functionalized (meth)acrylate polymer. Such (meth)acrylate polymers can be prepared by using 2-isocyanatoethyl methacrylate as a comonomer.
It is also possible to reverse the first and second reacting functional groups. For example, amine- or hydroxy-functionalized (meth)acrylate polymers can be reacted with a PIB polymer that is functionalized with an activated ester. Amine-functionalized (meth)acrylate polymers can be prepared by using an amine-functionalized (meth)acrylate monomer (see above) as a comonomer. Alcohol-functionalized (meth)acrylate polymers can be prepared, for example, by using 2-hydroxyethyl acrylate or 2-hydroxyethyl methacrylate as a comonomer in the preparation of the (meth)acrylate polymer. A suitable reaction partner for amine- or alcohol-functionalized (meth)acrylate polymers would be an anhydride-functionalized PIB material such as Glissopal® SA.
Methacrylate- and acrylate-functionalized PIB can be synthesized as known in the art. See for example WO2008/066914,U.S. Pat. No. 5,171,760, and “Sytheses and Characterization of Polyisobutylene Macromonomer with Methacrylate, Acrylate, Glycidyl Ether, or Vinyl Ether End-Functionality”, (Macromolecules 2009, 42, 3958-3964). Further, U.S. Pat. No. 5,665,823 and U.S. Pat. No. 6,0554,549 describe PIB-based materials having a silanol end group that can be used to make acrylate-functionalized PIB polymers that have a siloxane linkage between the PIB chain and the acrylate functionality.
The presence and concentration of functional groups within a functionalized PIB material can be determined by Proton Nuclear Magnetic Resonance. Typically, the functionalized PIB material comprises at least 3 mol-% of functional groups. The concentration of functional groups is generally no greater than 10 mol-%.
The amount of functionalized PIB material in the pressure sensitive adhesive composition can vary depending on the desired end use of the adhesive composition. Typically, however, the concentration of functionalized PIB material is at least 2 wt-%, or 5 wt-%, or 10 wt-% in order to improve adhesion with low surface energy substrates such as those prepared from polyolefins. The concentration of functionalized PIB material is typically no greater than 40 wt-%. Particularly when the pressure sensitive adhesive composition is also intended for use with higher surface energy substrates, the concentration of functionalized PIB material is typically 5 wt-% to 30 wt-%, when utilizing a functionalized PIB material having a relatively low molecular weight (e.g. Mn less than 10,000 g/mole).
With reference to FIGS. 1-2, the functionalized PIB material is surmised to compatibilize the relatively high molecular weight PIB material with the acrylic polymer material. The weight ratio of functionalized PIB material to unfunctionalized (e.g. PIB) synthetic rubber material can range from about 1:1 to about 1:3.
The pressure sensitive adhesive composition described herein further comprises at least one acrylic polymer. The acrylic polymer generally comprises the reaction product of at least one alkyl (meth)acrylate and at least one comonomer, most commonly a carboxylic acid, that provides functional groups along the backbone of the acrylic polymer. In some embodiments, the acrylic copolymer of the adhesive composition comprises at least about 70 wt-%, in some embodiments, at least about 80 wt-%, at least about 90 wt-%, at least about 95 wt-%, or even about 98 wt-% of at least one alkyl (meth)acrylate.
In some embodiments, the alkyl (meth)acrylate contains 4 to 20 carbon atoms, e.g., 4 to 8 carbon atoms. Exemplary alkyl (meth)acrylates include isooctyl acrylate (IOA), 2-octyl acrylate (2-OA), 2-ethylhexyl acrylate (2-EHA), butyl acrylate (BA), isobornyl acrylate (IBA), and combinations thereof. In some embodiments, the acrylic copolymer utilized in the PSA comprises at least two of such alkyl (meth)acrylates, such as isooctyl acrylate and isobornyl acrylate.
In some embodiments, acrylic adhesive composition comprises no greater than 10 parts of comonomer, such as carboxylic acid. Since, in some embodiments, the comonomer provides the functional groups that compliment the functionality of the PIB, the concentration of comonomer is typically at least 0.5, 1, 2, 3, 4, or 5 wt-%. Exemplary comonomers include carboxylic acids such as acrylic acid or methacrylic acid. In some embodiments, a comonomer (e.g. (meth)acrylate acid) concentration of 5 wt-% to 10 wt-% or 15 wt-% provides increased cohesive strength, as evident by the shear values.
The amount of acrylic polymer in the pressure sensitive adhesive composition can vary depending on the desired end use of the adhesive composition. Typically, however, the concentration of acrylic polymer is at least 20 wt-% or 25-wt-%. The concentration of acrylic polymer may range up to 75 wt-% or 80 wt-%. Particularly when the pressure sensitive adhesive composition is also intended for use with both low and higher surface energy substrates, the concentration of acrylic polymer typically ranges from 30 wt-% to 70 wt-%, 35 wt-% to 65 wt-%, or 40 wt-% to 60 wt-%. With reference to FIGS. 3-5, as the weight ratio of acrylic polymer to total PIB polymer (i.e. the total amount of both functionalized and unfunctionalized PIB approaches 1:1, the blend can have a bicontinuous phase morphology (i.e. a semi-interpenetrating network).
In some embodiments, the alkyl (meth)acrylate monomer(s) and functionalizing comonomer(s) are prepolymerized into an acrylic polymer and then combined with the functionalized PIB.
In other embodiments, the alkyl (meth)acrylate monomer(s) and functionalizing comonomer(s) are combined with the functionalized PIB and then the monomers are polymerized. The alkyl (meth)acrylate monomers and functionalized PIB can be polymerized by use of a thermal initiator or photoinitiator. The thermal initiator is often a peroxide, hydroperoxide, or azo compound. Alternatively, the alkyl(meth)acrylate monomers can be polymerized using ultraviolet radiation by use of an alpha-cleavage type photoinitiator including but not limited to benzoin or benzoin alkyl ethers. Either method of preparation results in a composition comprising a blend of functionalized PIB and acrylic polymer wherein the functionalized PIB is hydrogen- or covalently bonded to the functional groups along the backbone of the acrylic polymer.
For embodiments wherein the alkyl (meth)acrylate monomer(s) and functionalizing comonomer(s) are prepolymerized into an acrylic polymer and then combined with the functionalized PIB, the reaction product of the functionalized PIB and the acrylic polymer can be represented as shown in FIG. 6, wherein Z represents a hydrogen-bond or covalent bond between complimentary functional groups.
In some embodiments, the adhesive may comprise solely the functionalized PIB hydrogen- or covalently bonded to the acrylic polymer and the unfunctionalized (e.g. PIB) synthetic rubber, in the absence of crosslinker or any other optional components.
In other embodiments, the adhesives of the present disclosure may be crosslinked to improve their mechanical properties. In many embodiments, chemical crosslinking is preferred to improve the cohesive strength (as indicated by the static shear) of the pressure sensitive adhesive. For example, the adhesive may comprise a chemical crosslinker that is suitable for crosslinking the (e.g. carboxylic acid) functional groups of the acrylic polymer with each other or functional groups of the acrylic polymer with functional groups of the functionalized PIB. Suitable crosslinkers are known in the art such as aziridine or bisaziridine crosslinkers. One suitable bisaziridine crosslinker is prepared as described in U.S. Provisional Application No. 61/158,485, filed Mar. 9, 2009 (Peiwang Zhu et al. AZIRIDINE CROSSLINKING AGENTS FOR ACRYLIC ADHESIVES).
When the pressure sensitive adhesive (e.g. precursor) further comprises a chemical crosslinker, the reaction product of the functionalized PIB and the acrylic polymer can be represented as shown in FIG. 7.
When present, the concentration of chemical crosslinker in the pressure sensitive adhesive composition is typically at least 0.025 wt-% and no greater than 2 wt-%.
The adhesive further comprises at least one unfunctionalized (e.g. PIB) synthetic rubber material. The unfunctionalized (e.g. PIB) synthetic rubber material typically has substantially higher molecular weight than the functionalized (e.g. PIB) synthetic rubber material. In some embodiments, the weight average molecular weight (Mw) of the unfunctionalized (e.g. PIB) synthetic rubber material is at least 75,000 grams per mole, at least 100,000 grams per mole, at least 250,000 grams per mole, at least 500,000 grams per mole, or even at least 1,000,000 grams per mole. The weight average molecular weight is typically no greater than 4,000,000 g/mole.
The unfunctionalized (e.g. PIB) synthetic rubber material can be a homopolymer, copolymer, or a mixture thereof. Copolymers can be random or block copolymers. Block copolymers can include the polyisobutylene sections in the main backbone, in a side chain, or in both the main backbone and a side chain of the polymeric material. The polyisobutylene material is typically prepared by polymerizing isobutylene alone or by polymerizing isobutylene plus additional ethylenically unsaturated monomers in the presence of a Lewis Acid-catalyst such as aluminum chloride, boron trichloride (with titanium tetrachloride as a cocatalyst), or boron trifluoride.
Unfunctionalized polyisobutylene materials are commercially available from several manufacturers. Homopolymers are commercially available, for example, under the trade designation OPPANOL (e.g., OPPANOL B10, B15, B30, B50, B100, B150, and B200) from BASF Corp. (Florham Park, N.J.). These polymers often have a weight average molecular weight (Mw) in the range of about 40,000 to 4,000,000 grams per mole. Still other exemplary homopolymers are commercially available from United Chemical Products (UCP) of St. Petersburg, Russia in a wide range of molecular weights. For example, homopolymers commercially available from UCP under the trade designation SDG have a viscosity average molecular weight (Mv) in the range of about 35,000 to 65,000 grams per mole. Homopolymers commercially available from UCP under the trade designation EFROLEN have a viscosity average molecular weight (Mv) in the range of about 480,000 to about 4,000,000 grams per mole. Homopolymers commercially available from UCP under the trade designation JHY have a viscosity average molecular weight in the range of about 3000 to about 55,000 grams per mole. These homopolymers typically do not have reactive double bonds. It is appreciated that the unfunctionalized (e.g. PIB) synthetic rubber may have a very small concentration of reactive double bonds or other functional groups that are residual to the polymerization thereof. The concentration of such reactive double bonds or other functional groups is typically less than 5, 4, 3, or 2 mol %. Such olefinic unsaturations are generally non-polar and thus not suitable functional groups for the formation of hydrogen bonds. Such olefinic unsaturations are also typically not suitable functional groups for formation of covalent bonds via free-radical polymerization.
The concentration of unfunctionalized (e.g. PIB) synthetic rubber material in the pressure sensitive adhesive composition is typically at least 5 wt-%, 10 wt-%, or 15 wt-% and no greater than 40 wt-% or 50 wt-%. In some embodiments, the concentration range of the unfunctionalized (e.g. PIB) synthetic rubber is based on the unfunctionalized (e.g. PIB) synthetic rubber having a molecular weight of about 500,000 g/mole.
In some embodiments, the adhesive comprises the functionalized (e.g. PIB) synthetic rubber hydrogen or covalently bonded to the acrylic polymer, crosslinker, and both a high molecular weight unfunctionalized (e.g. PIB) synthetic rubber and low molecular weight unfunctionalized (e.g. PIB) synthetic rubber. The low molecular weight (e.g. PIB) synthetic rubber materials are liquids at room temperature and can function as a plasticizer with a variety of elastomeric materials. Generally, such polyisobutylene materials have a number average molecular weight of no greater than 10,000 g/mole, e.g., no greater than 5,000 g/mole, or even no greater than 2,000 g/mole. The number average molecular weight is typically at least about 500 g/mole or 1000 g/mole. The ratio of the weight average molecular weight to the number average molecular weight is typically in the range of about 1.6 to 2.0.
Exemplary low molecular weight polyisobutylene homopolymers are commercially available under the trade designation GLISSOPAL (e.g., GLISSOPAL 1000, 1300, and 2300) from BASF Corp. (Florham Park, N.J.). These polyisobutylene materials usually have terminal double bonds and are considered to be reactive polyisobutylene materials.
When present, the concentration of unfunctionalized low molecular weight polyisobutylene (e.g. PIB) material in the pressure sensitive adhesive composition is typically at least 5 wt-%, 10 wt-%, or 20 wt-% and no greater than 30 wt-%.
In some embodiments, the adhesive may comprise the functionalized (e.g. PIB) synthetic rubber hydrogen bonded to the acrylic polymer, crosslinker, unfunctionalized high molecular weight (e.g. PIB) synthetic rubber materials, in the absence of any tackifier(s) or plasticizer(s). In other embodiments, the adhesive comprises at least one tackifier(s), plasticizer(s), or mixtures thereof.
The tackifier can have any suitable softening temperature or softening point. The softening temperature is often less than 200° C., less than 180° C., less than 160° C., less than 150° C., less than 125° C., or less than 120° C. In applications that tend to generate heat, however, the tackifier is often selected to have a softening point of at least 75° C. Such a softening point helps minimize separation of the tackifier from the rest of the adhesive composition when the adhesive composition is subjected to heat such as from an electronic device or component. The softening temperature is often selected to be at least 80° C., at least 85° C., at least 90° C., or at least 95° C. In applications that do not generate heat, however, the tackifier can have a softening point less than 75° C.
Exemplary tackifiers include hydrocarbon resins and hydrogenated hydrocarbon resins, e.g., hydrogenated cycloaliphatic resins, hydrogenated aromatic resins, or combinations thereof. Suitable tackifiers are commercially available and include, e.g., those available under the trade designation ARKON (e.g., ARKON P or ARKON M) from Arakawa Chemical Industries Co., Ltd. (Osaka, Japan); those available under the trade designation ESCOREZ (e.g., ESCOREZ 1315, 1310LC, 1304, 5300, 5320, 5340, 5380, 5400, 5415, 5600, 5615, 5637, and 5690) from Exxon Mobil Corporation, Houston, Tex.; and those available under the trade designation REGALREZ (e.g., REGALREZ 1085, 1094, 1126, 1139, 3102, and 6108) from Eastman Chemical, Kingsport, Tenn.
The concentration of tackifier can vary depending on the intended adhesive composition. In some embodiments, the amount of tackifier is at least 10 wt-% or 20 wt-%. The maximum amount of tackifier is typically no greater than 40 wt-%, 50 wt-%, or 60 wt-%.
Other optional additives can include, for example, initiators, ultraviolet absorbents (e.g., benzotriazole, oxazolic acid amide, benzophenone, or derivatives thereof), ultraviolet stabilizers (e.g., hindered amines or derivatives thereof, imidazole or derivatives thereof, phosphorous-based stabilizers, and sulfur ester-based stabilizers), antioxidants (e.g., hindered phenol compounds, phosphoric esters, or derivatives thereof). Exemplary antioxidants include those available from Ciba Specialty Chemicals Incorporated, Tarrytown, N.Y.
The adhesives of the present disclosure may be combined with a substrate to form any number of typical adhesive articles, e.g., single- and double-coated tapes, and laminating adhesives. Generally, laminating adhesives may comprise either a free film of adhesive or an adhesive film embedded with a support, e.g., a woven or non-woven scrim. Such products can be formed by applying (e.g., coating, casting, or extruding) the adhesive onto a release liner, and drying and/or curing the adhesive.
The adhesives of the present disclosure may also be applied to one or both sides of a substrate to form a single- or double-coated tape. Any know substrate, including single and multi-layer substrates comprising one or more of paper, polymeric film, and metal (e.g., metal foil) may be used. In some embodiments, one or more layers of the substrate may be foam. In some embodiments, one or both adhesive layers may be bonded directly to the substrate. In some embodiments, one or both adhesive layers may be indirectly bonded to the substrate. For example, in some embodiments, one or more intermediate layers (e.g., primer layers) may be interposed between the substrate and the adhesive layer.
The adhesive is useful for bonding to a variety of metal and polymeric materials. Metals typically have a surface energy of at least about 500 dynes/cm. For example stainless steel is reported to have a surface energy of about 700-1100 dynes/cm. Inorganic oxides generally have a surface energy less than that of metals. For example, glass is reported to have a surface energy of about 250-500 dynes/cm. The adhesive is particularly useful for bonding to various polymeric materials. Polymeric materials such as plastics generally have a surface energy of less than 100 dynes/cm, 75 dynes/cm, or 50 dynes/cm. For example, polyester is reported to have surface energy of 43 dynes/cm; polycarbonate 42 dynes/cm; polyvinyl chloride 39 dynes/cm; and acrylic 38 dynes/cm. Even lower surface energy materials have a surface energy of less than 37 dynes/cm. These include for example polyvinyl acetate, polystyrene, acetal, ethylene vinyl acetate, and polyethylene reported to have a surface energy of 31 dynes/cm.
The pressure sensitive adhesive can exhibit various peel and shear properties, depending on the intended end use.
In some embodiments the 90 degree peel to glass, stainless steel, high density polyethylene (HDPE), polypropylene (PP), or EPDM is at least 5 oz/inch (5 N/dm) for a temporary removable or low temperature PSA. For masking tapes, the 90 degree peel to glass, stainless steel, HDPE, PP, or EPDM is typically 15-20 oz/inch (16-22 N/dm). In other embodiments the 90 degree peel to glass, stainless steel, HDPE, or PP is at least 50, 60, 70, 80 or 90 oz/inch (55, 66, 77, 88 or 99 N/dm). In at least some embodiments, the shear at room temperature (23° C.) is at least 300 minutes, 500 minutes, or 800 minutes. In some favored embodiments, the adhesive exhibits good adhesion to both high and low surface energy substrates. In such embodiments, the 90 degree peel to glass or stainless steel is at least 50, 60, 70, 80 or 90 oz/inch (55, 66, 77, 88 or 99 N/dm) in combination with the 90 degree peel to PP being at least 30, 40, 50, or 60 oz/inch. Further, the 90 degree peel to EPDM is typically at least 30, 40, or 50 oz/inch; whereas the 90 degree peel to HDPP is at least 30, 40, or 50 oz/inch. In some favored embodiment, the shear at room temperature (23° C.) or 70° C. is at least 2,000 minutes; 4,000 minutes; 8,000 minutes; or 10,000 minutes.
The following, non-limiting, examples further describe exemplary adhesives and adhesive articles of the present disclosure, as well as exemplary methods for making such adhesives and adhesive articles. All percents are by weight unless otherwise indicated.
Test Methods:
90° Angle Peel Adhesion Strength Test.
Evaluation of peel adhesion strength at an angle of 90° was performed as described in the ASTM International standard, D3330, Method F, with a 1.3 cm×20 cm (1⁄2 in.×8 in.) test specimen using an IMASS SP-200 slip/peel tester (available from IMASS, Inc., Accord, Mass.) at a peel rate of 305 mm/minute (12 inches/minute). The samples were adhered to the test panels by rolling down the tapes with a 2.0 kg (4.5 lb.) rubber roller using 4 passes. The test panels included:












Material
Description
Source







EPDM
Ethylene/propylene-diene class M rubber;
Zatkoff Seals &



having a durometer hardness of 60,
Packings,



measuring 5.1 × 12.7 × 0.15 cm
Warren, MI



(2 × 5 × 0.059 in.); available as EPDM,



Part No. RZW07-015


PP
Polypropylene (0.91 g/cc) (Quadrant EPP



Proteus Natural Homopolymer



Polypropylene);


Stainless
SS, 304, 18 gauge stainless steel, bright
ChemInstruments,


Steel
annealed finish.
Incorported,




Fairfield, OH


HDPE
2′′ × 5′′, 0.2′′ thick, 0.96 g/cc high density
obtained from



polyethylene (Quadrant EPP HDPE)
Aeromat Plastics




Inc., Burnsville,




MN


Glass
6′′ × 6′′, 1⁄4′′ float glass









The test panels were cleaned with a 1:1 isopropyl alcohol/water mixture and thoroughly dried prior to use. The peel tests were performed after a 15 min dwell time in a controlled environment room on the test panel, unless otherwise stated. The average peel adhesion force required to remove the tape from the panel was measured in ounces and is expressed in Oz/inch, based on 2 test samples.
Static Shear Strength at 23° C./50% Relative Humidity:
Evaluation of static shear strength was performed as described in the ASTM International standard, D3654, Procedure A, with a 1.3 cm×2.5 cm (1⁄2 in.×1 in.) test specimen and a 1000 g load. The test panels were stainless steel (“SS”). Time to failure in minutes was recorded. If no failure was observed after 10,000 minutes, the test was stopped and a value of >10,000 minutes was recorded.
Static Shear Strength at 70° C.:
Evaluation of static shear strength was performed as described in the ASTM International standard, D3654, Procedure A, with a 1.3 cm×2.5 cm (1⁄2 in.×1 in.) test specimen and a 500 g load. The test panels were stainless steel (“SS”). Time to failure in minutes was recorded. If no failure was observed after 10,000 minutes, the test was stopped and a value of >10,000 minutes was recorded.
Materials













Material
Abbreviation
Function
Manufacturer







Polyisobutylene
B100
Unfunctionalized
BASF


(High MW 1000K

Synthetic


g/mol)

Rubber


Polyisobutylene
B268
Unfunctionalized
Exxon


(Medium MW 500K

Synthetic


g/mol)

Rubber


Polyisobutylene
G1000
Unfunctionalized
BASF


(Low MW 1000

Synthetic


g/mol)

Rubber


Kerocom ® PIBA03
PIBA03
Functionalized
BASF


(~1000 g/mol of

Synthetic


amine-terminated

Rubber


PIB)


Acrylic copolymer
IOA/AA


of isooctyl acrylate


and acrylic acid


Isobornyl acrylate
IBA


Foral 85
F85
Tackifier
Eastman


Eastotac 1310
E1310
Tackifier
Eastman








Crosslinker
The bisaziridine crosslinker utilized in the



examples was prepared according to 3M patent



application No. 61/158,485, filed Mar. 9, 2009)









General Procedures. All reactions were performed in round-bottomed flasks or glass jars/vials using commercial reagents as received.
Adhesive compositions further comprising unfunctionalized PIB were prepared according to the following procedure: Kerocom® PIBA03 was added to a glass vial. Next, the isooctyl acrylate/acrylic acid copolymer solution (e.g. 94:6 isooctyl acrylate:acrylic acid or 90:10 isooctyl acrylate:acrylic acid in a 35% wt % ethyl acetate solution) was added, followed by adding unfunctionalized PIB (in a 15 wt-% toluene solution) with tackfier (e.g. E1310). Additional toluene was added to make the total solids concentration equal 35 wt %. The concentration of each component in the various formulations is illustrated in the tables. The components were mixed well by shaking until the solution turned translucent and the components were uniformly dispersed. Immediately before coating, bisaziridine crosslinker (a 15 wt % solution in toluene) was added and the formulation was again shaken and mixed well. A hand spread was pulled onto a silicone release liner (Silphan S36 M74A) using a 9 mill gap. The film was dried in an oven at 70° C. for 30 minutes. Next, the adhesive film was allowed to cool to room temperature. The adhesive film was 0.0019′′ thick. During the cohesion and adhesion strength testing, 2 mil (0.0020′′) thick anodized aluminum was laminated on the PSA tape as adhesive backing.
























Stainless
PP 90°
EPDM 90°








Steel 90°
Peel
Peel





IOA/AA
Cross-

Peel oz/in
oz/in
oz/in


Example
B268
PIBA03
94:6
linker
E1310
(N/dm)
(N/dm)
(N/dm)























Control A
0.00
0.00
99.80
0.20
0.00
63 (69)
15 (16)
16 (18)


Control B
49.95
0.00
49.95
0.10
0.00
49 (54)
17 (19)
16 (18)


Ex. 1
29.97
19.98
49.95
0.10
0.00
36 (39)
27 (30)
20 (22)


Ex. 2
27.25
18.17
45.41
0.09
9.08
49 (54)
42 (46)
26 (28)









With reference to FIGS. 1-2, the morphology of the compositions of Control B and Example 1 were examined via microscopy (10×). With reference to FIG. 2, the adhesive of Example 1, comprising the functionalized PIB (e.g. PIBA03) bonded to the acrylic polymer, exhibits a more uniformly dispersed phase domain than FIG. 1, the adhesive of Control B lacking the functionalized PIB. Without intending to be bound by theory, the dispersion uniformity of the phase domain is surmised to closely relate to the adhesion properties. For example, Control B exhibits lower peel adhesion to low surface energy substrates such as PP and EPDM. Such results are comparable to Control A, a pure Acrylic-PSA. However, Examples 1 and 2, exhibit more homogeneous phases and smaller phase domains. Hence, it can be concluded that the presence of the functionalized PIB compatiblizes the two immiscible phases of unfunctionalized high molecular weight (e.g. PIB) synthetic rubber and the acrylic polymer. The resulting adhesive compositions exhibit improved peel adhesion to low energy surface substrate.




















Acrylic

Stainless
PP 90°






Copolymer

Steel 90°
Peel
Shear





IOA/AA
Cross-
Peel oz/in
oz/in
@ R.T.


Example
B100
PIBA03
(90:10)
linker
(N/dm)
(N/dm)
(min)a






















Control C
60
40
0
0
25 (27)
24 (26)
192


Ex. 3
44.98
29.99
24.99
0.05
35 (38)
23 (25)
4891


Ex. 4
29.97
19.98
49.95
0.10
40 (44)
23 (25)
>10000


Ex. 5
14.98
9.99
74.89
0.15
53 (58)
17 (19)
6721









With reference to FIGS. 3-5, the morphology of the compositions of Examples 3-5 was also examined via microscopy (20×). FIG. 3, the blend with 75 wt-% PIB (45 wt-% unfunctionalized and 30 wt-% functionalized) exhibited a continuous PIB domain as evident by the lighter areas in FIG. 3 and also dark coalescences of acrylic copolymer domains. In FIG. 4, the blend with 50 wt-% PIB the morphology changed to bicontinuous phases, (i.e. a semi-interpenetrating network). As evident in FIG. 5, in the blend having 25 wt-% PIB, the PIB domains became droplets embedded in a continuous acrylic copolymer phase.




























Stainless
PP 90°










Steel 90°
Peel
Shear






IOA/AA
Cross-

Peel oz/in
oz/in
@ R.T.


Example
B100
B268
PIBA03
90:10
linker
E1310
(N/dm)
(N/dm)
(min)a





Ex. 6
24.98
0.00
24.98
49.95
0.10
0.00
68 (74)
31 (34)
>10000


Ex. 7
0.00
29.97
19.98
49.95
0.10
0.00
63 (69)
32 (35)
5095


Ex. 8
27.25
0.00
18.17
45.41
0.09
9.08
143 (157)
48 (53)
>10000


Ex. 9
23.06
0.00
15.37
38.43
0.08
23.06
90 (99)
62 (68)
>10000


Ex. 10
27.25
0.00
18.17
45.41
0.09
9.08b
70 (77)
52 (57)
>10000





















IOA/AA





Example
B268
PIBA03
G1000
(94:6)
Crosslinker
E1310
F85





Ex. 11
33.33
11.11
22.22
0.00
0.00
33.33
0.00


Ex. 12
21.41
7.14
14.28
35.69
0.07
21.41
0.00


Ex. 13
18.74
6.25
12.49
31.23
0.06
18.74
12.49


Ex. 14
15.37
5.38
9.99
46.11
0.09
23.06
0.00


Ex. 15
13.32
4.66
8.66
39.97
0.08
19.98
13.32

















Stainless
PP 90°
HDPE 90°
EPDM 90°





Steel 90°
Peel
Peel
Peel
Shear
Shear



Peel oz/in
oz/in
oz/in
oz/in
@ R.T.
@


Example
(N/dm)
(N/dm)
(N/dm)
(N/dm)
(min)a
70° C. (min)a





Ex. 11
47 (51)
53 (58)
36 (39)
33 (36)
13
0


Ex. 12
54 (59)
39 (43)
44 (48)
22 (24)
>10000
634


Ex. 13
47 (51)
55 (60)
27 (30)
19 (21)
>10000
1784


Ex. 14
70 (77)
54 (59)
42 (46)
37 (40)
>10000
>10000


Ex. 15
40 (44)
49 (54)
50 (55)
33 (36)
>10000
>10000





aShear data were obtained using 0.5′′ × 1.0′′ strips on stainless steel with a 1000 g load, at room temperature around 30° C.


band 10 wt-% F85






PIB-Acrylate Macromonomer.
A 4 ounce amber bottle was equipped with a plastic cap with an approximately 1⁄8′′ hole. Glissopal® SA (60.0 g) and a magnetic stir bar were added. Next, 2-hydroxyethyl acrylate (6.00 mL, 6.07 g, 52.2 mmol) and 4-(dimethylamino)pyridine (0.0520 g, 0.426 mmol) were added. The reaction was capped with the plastic cap and a piece of Teflon® tubing was threaded through the hole and pushed into the bottom of the reaction mixture. Air was passed through the tubing and bubbled through the reaction mixture throughout the course of the reaction. The reaction was placed in an oil bath and heated to 100° C. with stirring. After 3 days, the reaction was removed from the oil bath and allowed to cool to room temperature. The acrylate product was obtained as a pale yellow, very viscous liquid.




General Procedure for the Preparation of Acrylate Copolymers Using the PIB Macromonomer.
PIB macromonomer (1.00 g) was added to a 4 ounce amber bottle with Teflon®-wrapped threads. Hexane (8.50 mL, 5.60 g) was added and the mixture was sonicated for 40 minutes to dissolve the macromonomer. Next, isooctyl acrylate (2.00 g), acrylic acid (0.150 g) and Vazo® 67 (0.010 g) were added and the mixture was mixed until homogeneous. The reaction was sparged with nitrogen for 7 minutes and then quickly sealed with a Teflon®-lined plastic cap. The reaction was further sealed with Teflon® tape and electrical tape. The reaction was placed in a water bath/shaker at 65° C. and gently agitated. After 24 hours, the reaction was removed from the water bath and was allowed to cool to room temperature. The reaction mixture was then added to methanol (100 mL) with stirring to precipitate the polymer product. The hazy methanol solution was decanted and the viscous pale yellow material was washed with methanol (3×5 mL). The precipitated product was transferred to a 20 mL glass vial with hexane and was then dried in vacuo to provide the polymer product (2.31 g, 73.1%) as a clear, pale yellow rubbery solid.




The acrylate-PIB copolymer was then utilized to prepare adhesive compositions in the same manner as previously described.

























48% PIB-
Peeling
Peeling








48% IOA-
on SS
on PP
Shear





IOA/AA
Cross-
2% AA
in/oz
in/oz
@ RT



B100
PIBA03
90/10
linker
Copolymer
(N/dm)
(N/dm)
(min)





Ex. 16
27.25
18.17
45.41
0.09
9.08
18 (20)
46 (51)
92


Ex. 17
40.89
27.26
22.72
0.05
9.09
38 (42)
23 (25)
662


Ex. 18
13.62
9.08
68.09
0.14
9.08
43 (47)
26 (29)
27










32% PIB-
Peeling
Peeling







63% IOA-
on SS
on PP
Shear





IOA/AA
Cross-
5% AA
in/oz
in/oz
@ RT



B100
PIBA03
90/10
linker
Copolymer
(N/dm)
(N/dm)
(min)





Ex. 19
27.25
18.17
45.41
0.09
9.08
73 (80)
40 (44)
6681


Ex. 20
13.62
9.08
68.09
0.14
9.08
70 (77)
48 (53)
1208










63% PIB-
Peeling
Peeling







32% IOA-
on SS
on PP
Shear





IOA/AA
Cross-
5% AA
in/oz
in/oz
@ RT



B268
PIBA03
94/6
linker
Copolymer
(N/dm)
(N/dm)
(min)





Ex. 21
32.70
21.80
36.34
0.07
9.08
44 (48)
39 (43)
2193


Ex. 22
27.25
18.17
45.41
0.09
9.08
37 (41)
33 (36)
2396


Ex. 23
21.79
14.53
54.49
0.11
9.08
46 (51)
26 (29)
3304










47.5% PIB-
Peeling
Peeling







47.5% IOA-
on SS
on PP
Shear





IOA/AA
Cross-
5% AA
in/oz
in/oz
@ RT



B268
PIBA03
94/6
linker
Copolymer
(N/dm)
(N/dm)
(min)





Ex. 24
32.70
21.80
36.34
0.07
9.08
30 (33)
22 (24)
3912


Ex. 25
27.25
18.17
45.41
0.09
9.08
30 (33)
18 (20)
3191


Ex. 26
21.79
14.53
54.49
0.11
9.08
42 (46)
39 (43)
3341

## Claims

1. A pressure sensitive adhesive composition comprising:
unfunctionalized synthetic rubber; and
an acrylic polymer wherein the acrylic polymer is a copolymer of at least one alkyl(meth)acrylate and at least one carboxylic acid, the copolymer having functionalized polyisobutylene polymer bonded to pendent carboxylic acid groups of the acrylic polymer.

2. The pressure sensitive adhesive of claim 1 wherein the functionalized polyisobutylene polymer has a first functional group hydrogen bonded with a second functional group present in the acrylic polymer backbone.

3. The pressure sensitive adhesive composition of claim 2 wherein the first or second functional group is a hydrogen bond acceptor and the other functional group is a hydrogen bond donor.

4. The pressure sensitive adhesive of claim 1 wherein the functionalized polyisobutylene polymer is covalently bonded to the acrylic polymer backbone.

5. The pressure sensitive adhesive composition of claim 4 wherein the functionalized polyisobutylene polymer covalently bonded to the acrylic polymer backbone is prepared from polymerizing (meth)acrylate-functionalized PIB and alkyl (meth)acrylate monomers.

6. The pressure sensitive adhesive composition of claim 1 wherein the unfunctionalized synthetic rubber comprises polyisobutylene.

7. The pressure sensitive adhesive composition of claim 1 wherein the functionalized polyisobutylene has a number average molecular weight of less than 10,000 g/mole.

8. The pressure sensitive adhesive composition of claim 1 wherein the unfunctionalized synthetic rubber has a weight average molecular weight ranging from about 75,000 g/mole to 4,000,000 g/mole.

9. The pressure sensitive adhesive composition of claim 1 wherein the alkyl (meth)acrylate is a C4 to C20 alkyl (meth)acrylate.

10. The pressure sensitive adhesive composition of claim 1 wherein the alkyl (meth)acrylate is a C4 to C8 alkyl (meth)acrylate.

11. The pressure sensitive adhesive composition of claim 2 wherein the adhesive composition further comprises a chemical crosslinker that covalently crosslinks the functional groups.

12. The pressure sensitive adhesive composition of claim 11 wherein the crosslinker is selected from an aziridine crosslinker.

13. The pressure sensitive adhesive composition of claim 1 wherein the composition comprises an unfunctionalized polyisobutylene having a number average molecular weight of less than 10,000 g/mole.

14. The pressure sensitive adhesive composition of claim 1 further comprising a tackifying resin, a plasticizer, or a mixture thereof.

15. The pressure sensitive adhesive composition of claim 1 wherein the functionalized polyisobutylene polymer and unfuntionalized synthetic rubber material are present in a weight ration from about 1:1 to about 1:3.

16. A method of making a pressure sensitive adhesive comprising blending:
an unfuntionalized synthetic rubber; and
an acrylic polymer wherein the acrylic polymer is a copolymer of at least one alkyl(meth)acrylate and at least one carboxylic acid, the copolymer having functionalized polyisobutylene polymer bonded to pendent carboxylic acid groups of the acrylic polymer.