Tackifier composition

Abstract

A tackifier polymer additive comprising the emulsion polymerization reaction product of (a) at least one aromatic monomer, (b) at least one acrylate or methacrylate monomer, and (c) at least one chain transfer agent, and a tackified acrylic adhesive composition comprising (I) at least one acrylic adhesive polymer and (II) the tackifier polymer additive described above.

Description

[Technical field]

[0001] The present invention relates to a tackifier polymer additive, more particularly, the present invention relates to a tackifier polymer additive for adhesives. [Background technology]

[0002] Pressure sensitive adhesives are characterized by both the adhesive's adhesion to the substrate (peel, tack) and the adhesive's internal cohesion (shear resistance). However, adhesion and cohesion are two properties that are usually inversely related. Certain applications require improvement of both adhesion and cohesion, but these two properties are difficult to obtain by traditional polymer design or additive methods.

[0003] One common method to increase the adhesive strength of pressure sensitive adhesives is to add polymeric additives called tackifiers to the adhesive. Tackifiers function to increase the self-adhesive strength (tack) of the adhesive. Several classes of polymers, such as rosin and rosin derivatives, terpene resins, and hydrocarbon resins, are known to be used as tackifiers. Nevertheless, these known tackifiers suffer from several problems, including, for example, poor compatibility with acrylic adhesive polymers, undesirable color, and a significant decrease in cohesive strength of adhesives formulated with such tackifiers. Also, currently, the above known tackifiers are not readily available.

[0004] An alternative approach to providing tackifiers for adhesives is to prepare tackifier polymers from vinyl aromatic or (meth)acrylic monomers. For example, US Patent No. 4,912,169 discloses that polymer additives are prepared from C1 to C 20The present invention describes adhesive polymers tackified with the claimed polymeric additives, which are polymerized from alkyl and cycloalkyl (meth)acrylates, olefinic acids, and other ethylenically unsaturated monomers. Here, the polymeric additives have a number average molecular weight (Mn) of less than (<) 35,000 and a softening point of greater than (>) 40 degrees Celsius (°C). These manufactured tackifier polymers address issues related to undesirable color and availability of various resins. However, adhesives formulated using the manufactured tackifier polymers still suffer from a significant loss of cohesive strength. Additionally, some of the raw materials useful for making the polymeric additives, such as isobutyl methacrylate (IBMA) and isobornyl methacrylate (IBOMA), are difficult to obtain.

[0005] For example, several prior art references, including U.S. Pat. Nos. 4,912,169, 5,028,484, 5,236,991, 6,989,413, 7,262,242, 7,723,466, 7,332,540, 9,605,188, and 9,657,204, as well as U.S. Patent Application Publication Nos. US2002 / 0055587, CN1429259, WO2016 / 160250, and EP2847290, disclose the use of tackifier materials in various polymer compounds. However, the above references do not disclose a tackifier material that combines the following qualities: (1) compatibility with adhesive polymers. (2) A glass transition temperature (Tg) high enough so as not to substantially reduce shear (e.g., >0° C.). (3) Enhance the adhesive's adhesion (peel or tack) upon formulation. In some known adhesive compositions, the adhesion of the adhesive decreases to undesirably low levels, resulting in adhesion lower than that of the adhesive without the tackifier material. Summary of the Invention [Problem to be solved by the invention]

[0006] Thus, there remains a need in the adhesives industry for tackifier materials that (1) can be produced using readily available raw materials, (2) can be prepared using standard emulsion polymerization equipment instead of specialized equipment, (3) have good compatibility with acrylic adhesive polymers, (4) can improve the peel and tack adhesion properties of the adhesive, and (5) do not substantially reduce the shear resistance properties of the adhesive.

[0007] In one general embodiment, the present invention relates to a tackifier polymer additive comprising the emulsion polymerization reaction product of: (a) at least one styrene, methyl methacrylate, alpha-methylstyrene, or other aromatic monomer having a homopolymer Tg greater than 80°C; (b) at least one acrylate or methacrylate monomer; and (c) at least one chain transfer agent (CTA). The tackifier polymer additive exhibits several beneficial properties, such as a Tg of the tackifier polymer additive >0°C, an Mn of the tackifier polymer additive of 1,200 Daltons (Da) to 20,000 Da, and a polymer miscibility score of >0. The monomer selection, Tg, Mn, and polymer miscibility score significantly differentiate the tackifier polymer additive of the present invention from known additives.

[0008] Furthermore, the tackifier polymer additives made according to the criteria of the present invention described herein unexpectedly improve the adhesive properties of the adhesive composition without substantially decreasing the shear resistance properties of the adhesive composition, and the tackifier polymer additives of the present invention have good compatibility with acrylic adhesive polymers. Furthermore, the raw materials used to prepare the tackifier polymer additives of the present invention are readily available materials.

[0009] In another general embodiment, the present invention relates to a tackified acrylic adhesive composition comprising (I) at least one acrylic adhesive polymer and (II) at least one of the tackifier polymer additives described above. Advantageously, the adhesive strength of the tackified adhesive composition of the present invention can be increased without substantially decreasing the cohesive strength (shear resistance) of the tackified adhesive composition of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] "Adhesion" herein refers to the peel adhesion test or loop tack test of pressure sensitive adhesives as measured by PSTC 101 or PSTC 16.

[0011] "Cohesion" or "shear resistance" herein refers to the shear resistance test of a pressure sensitive adhesive as measured by PSTC 107.

[0012] With respect to a tackifier polymer additive, "polymer miscibility score" herein means a calculated measure of the miscibility of the tackifier polymer additive with an acrylic adhesive polymer based on the monomer composition of the tackifier polymer additive, the Mn of the tackifier polymer additive, and optionally, the monomer composition of the acrylic adhesive polymer.

[0013] In a broad embodiment, the present invention comprises a tackifier polymer additive that is an emulsion polymerization reaction product of: (a) at least one monomer, such as styrene, methyl methacrylate, alpha-methylstyrene, or other aromatic monomer having a homopolymer Tg >80°C; (b) at least one acrylate or methacrylate monomer; (c) at least one chain transfer agent; such that the glass transition temperature (Tg) of the tackifier polymer additive is >0°C, the Mn of the tackifier polymer additive is from 1200 Da to 20,000 Da, and the polymer miscibility score of the tackifier polymer additive is >0.

[0014] Component (a) of the tackifier polymer additive of the present invention includes, for example, at least one monomer having a homopolymer Tg greater than 80° C. The homopolymer Tg of a monomer can be measured by using the midpoint temperature using differential scanning calorimetry (DSC), for example, as described in ASTM 3418 / 82.

[0015] In some embodiments, the monomer having a homopolymer Tg > 80°C can be an aromatic monomer known in the art that can be polymerized with at least one acrylate or methacrylate monomer to produce a tackifier resin. The term "aromatic monomer" means a monomer that contains at least one group of unsaturated cyclic hydrocarbons containing one or more rings. Examples of aromatic monomers useful in the present invention include, but are not limited to, olefin-substituted aromatics such as styrene, alpha-methylstyrene, vinyltoluene, indene, methylindene, divinylbenzene, dicyclopentadiene, methyl-dicyclopentadiene, and mixtures thereof. In one preferred embodiment, the aromatic monomer can be styrene. In another embodiment, the monomer having a homopolymer Tg > 80°C can be methyl methacrylate. In yet another embodiment, two or more monomers having a homopolymer Tg > 80°C can be used in combination.

[0016] Generally, the homopolymer Tg of the monomers may be >80°C in one embodiment, from 80°C to 110°C in another embodiment, and from 95°C to 160°C in yet another embodiment.

[0017] The amount of FR agent used to make the FR epoxy resin composition can be, for example, 80% to 30% by weight in one embodiment, 75% to 25% by weight in another embodiment, and 75% to 20% by weight in yet another embodiment. Above or below the above amount ranges, the tackifier polymer additive will not meet the compatibility and Tg requirements of the present invention.

[0018] Component (b) of the tackifier polymer additive of the present invention comprises, for example, at least one acrylate or methacrylate monomer known in the art capable of polymerizing with a monomer with a homopolymer Tg >80°C.

[0019] In one embodiment, the acrylate monomer has the following general formula (I): R1-CH=CR2-COOR3 Formula (I) wherein R1 is selected from the group consisting of hydrogen, an aliphatic group, and an aromatic group; R2 is selected from the group consisting of hydrogen, an aliphatic group, and an aromatic group; and R3 is selected from the group consisting of hydrogen, an aliphatic group, and an aromatic group.

[0020] The term "aliphatic" is defined as a straight or branched chain arrangement of constituent carbon atoms, including, but not limited to, alkanes, alkenes, alkadienes, and alkynes. Aliphatic groups can contain functional groups such as, but not limited to, hydroxyl, cycloaliphatic, acid, epoxide, amide, acrylonitrile, and acrylate. In one preferred embodiment, the aliphatic group can have from 1 carbon atom to 20 carbon atoms, and in another embodiment, from 1 carbon atom to 12 carbon atoms.

[0021] The term "aromatic group" refers to at least one group of unsaturated cyclic hydrocarbons containing one or more rings. The aromatic group may be selected from the group consisting of both unsubstituted and substituted aromatic groups having components with up to 6 carbon atoms. In one preferred embodiment, the aromatic group may have 6 carbon atoms to 20 carbon atoms. The aromatic group may include, but is not limited to, functional groups such as hydroxyl, cycloaliphatic, acid, epoxide, amide, acrylonitrile, and acrylate. In some embodiments, the above functional groups may result in an acrylate monomer having more than one reactive site for polymerization or other reactions. In one preferred embodiment, both R1 and R2 of the acrylate monomer of formula (I) are hydrogen. When the acrylate monomer is a methacrylic compound, R2 is a CH3 group.

[0022] In other embodiments, for acid functional monomers, R3 in formula (I) can be hydrogen, forming monomers such as acrylic acid and methacrylic acid. Acid functional monomers can also include difunctional components such as, for example, maleic acid, and fumaric acid. And in yet other embodiments, acid functional monomers can include the anhydride forms of the above components.

[0023] In yet another embodiment, the functional group can be found in the R3 group of formula (I). Suitable examples useful in the present invention include hydroxyethyl acrylate, glycidyl methacrylate, and 1,3-butanediol dimethyl acrylate.

[0024] Examples of suitable acrylate or methacrylate monomers useful in the present invention include esters of monoethylenically unsaturated carboxylic acids having from 3 carbon atoms to 24 carbon atoms, particularly esters of acrylic and methacrylic acid, including methyl acrylate ("MA"), ethyl acrylate ("EA"), butyl acrylate ("BA"), butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, isoamyl acrylate, isoamyl methacrylate, 2-ethylhexyl methacrylate, isooctyl acrylate, isooctyl methacrylate, n-propyl acrylate, isopropyl acrylate, methyl methacrylate ("MMA"), decyl acrylate, decyl methacrylate, dodecyl acrylate, dodecyl methacrylate, and mixtures thereof.

[0025] Also suitable for use in the present invention are α,β-monoethylenically unsaturated mono- or dicarboxylic acids of 3 carbon atoms to 6 carbon atoms, such as acrylic acid ("AA"), methacrylic acid, itaconic acid, fumaric acid, maleic acid, and mixtures thereof, as well as anhydrides of monoolefinically unsaturated dicarboxylic acids, such as maleic anhydride, itaconic anhydride, and mixtures thereof.

[0026] Other tackifier polymer additives useful in the present invention may include other monomers including hydroxyalkyl acrylates and methacrylates, such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, and mixtures thereof.

[0027] In some preferred embodiments, the acrylate or methacrylate monomers may include n-butyl acrylate, t-butyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, n-butyl methacrylate, i-butyl methacrylate, s-butyl methacrylate, t-butyl methacrylate, and mixtures thereof. In yet other embodiments, two or more acrylate or methacrylate monomers may be used in combination.

[0028] The amount of acrylate or methacrylate monomer used to make the tackifier polymer additive can be, for example, 90% to 20% by weight in one embodiment, 80% to 25% by weight in another embodiment, and 70% to 25% by weight in yet another embodiment. Above or below the above amount ranges, it will be difficult to achieve the Tg and compatibility properties of the tackifier polymer additive of the present invention.

[0029] The acrylate or methacrylate monomers of component (b) exhibit some advantageous properties themselves before being used to make the tackifier polymer additive. For example, monomers with acid functionality as described above may improve the stability of the polymer in the final application. Monomers with more than one reactive site may allow branching or crosslinking reactions.

[0030] Component (c) of the tackifier polymer additive of the present invention, for example, comprises at least one CTA. Examples of chain transfer agents that can be used in the present invention include long chain alkyl mercaptans such as t-dodecyl mercaptan and n-dodecyl mercaptan (n-DDM), 3-mercaptopropionic acid and its esters such as methyl 3-mercaptopropionate (MMP) and butyl 3-mercaptopropionate, carbon tetrachloride, tetrachloroethylene and trichloro-bromoethane, and mixtures thereof.

[0031] In some embodiments, the chain transfer agent can be a dithioester or trithioester that is known to act as a chain transfer agent in free radical polymerization.Examples of chain transfer agents that can be used in the present invention include 2-(dodecylthiocarbono-thioylthio)-2-methylpropionic acid, poly(ethylene glycol) methyl ether (4-cyano-4-pentanoate dodecyl trithiocarbonate), 2-cyano-2-propyl dodecyl trithiocarbonate, 2-cyano-2-propyl dodecyl trithiocarbonate, 4-cyano-4-(phenylcarbonothioylthio) pentanoic acid, 2-phenyl-2-propyl benzodithioate, 2-cyano-2-propyl benzodithioate, and mixtures thereof.

[0032] The amount of chain transfer agent used to make the tackifier polymer additive can be an amount selected to achieve a target Mn of the tackifier polymer additive, for example, from 1,200 Da to 20,000 Da, according to, for example, the following relationship:

number

[0033] The amount of chain transfer agent used to make the tackifier polymer additive can depend on the particular CTA used to make the additive, and the amount of other ingredients in the additive. However, as an exemplary embodiment, and not limited thereby, if the CTA used in the present invention is, for example, n-DDM, the amount of chain transfer agent can be 1 wt% to 17 wt%, or if the CTA used in the present invention is, for example, MMP, the amount of chain transfer agent can be 0.6 wt% to 10 wt%.

[0034] The CTA, component (c), exhibits some advantageous properties by itself before it is used to make a tackifier polymer additive. For example, the properties of the CTA can include solubility in water so that it can be transported through the water phase to the growing polymer particles in emulsion polymerization, or to act primarily on polymerization in the water phase. Other chain transfer agents may have lower water solubility and higher solubility in organic solvents so that they act primarily on polymerization of monomer-swollen polymer particles. Still other chain transfer agents may support reverse transfer reactions to enable reversible addition-fragmentation chain transfer (RAFT) polymerization.

[0035] In other embodiments, the tackifier polymer additive of the present invention can include, for example, at least one or more additional optional ingredients, compounds or agents. In one embodiment, the additional ingredient (d) useful in the present invention can include, for example, water.

[0036] The amount of water used to make the tackifier polymer additive may be, for example, 25% to 80% by weight in one embodiment, 30% to 75% by weight in another embodiment, and 30% to 60% by weight in yet another embodiment. In another embodiment, one or more optional surfactants may be added to the tackifier polymer additive. Examples of surfactants suitable for use in accordance with the present invention may include, but are not limited to, cationic surfactants, anionic surfactants, zwitterionic surfactants, nonionic surfactants, and combinations thereof. Examples of cationic surfactants useful in the present invention may include, but are not limited to, quaternary amines, lauryl pyridinium chloride, cetyl dimethylamine acetate, alkyl dimethyl benzyl ammonium chloride (wherein the alkyl group has 8 carbon atoms to 18 carbon atoms), and mixtures thereof. Examples of anionic surfactants useful in the present invention may include, but are not limited to, sulfonates, carboxylates, phosphates, and mixtures thereof. Examples of nonionic surfactants useful in the present invention may include, but are not limited to, block copolymers containing ethylene oxide and silicone surfactants, such as ethoxylated linear or branched fatty alcohols, ethoxylated fatty acids, sorbitan derivatives, lanolin derivatives, alkoxylated polysiloxanes, and mixtures thereof.

[0037] The amount of any optional surfactant when used to make the tackifier polymer additive can be, for example, from 0 wt % to 5 wt % in one embodiment, from 0.01 wt % to 3 wt % in another embodiment, and from 0.1 wt % to 2 wt % in yet another embodiment.

[0038] In other embodiments, the tackifier polymer additive of the present invention can include, for example, at least one or more initiators. Examples of initiators useful in the present invention can include thermal initiators, redox initiators, or mixtures thereof. Examples of thermal initiators useful in the present invention can include, but are not limited to, sodium persulfate, ammonium persulfate, and mixtures thereof. When the initiator useful in the present invention is a redox initiator, the reducing agent can be, for example, ascorbic acid, sulfoxylate, or erythorbic acid, while the oxidizing agent used can be, for example, a peroxide or a persulfate. In general, the amount of initiator used can be greater than 1 weight percent in one embodiment, based on the total weight of the monomers in the monomer mixture.

[0039] In general, the process for making a tackifier polymer additive comprises the copolymerization of (a) at least one monomer having a homopolymer Tg greater than 80° C., and (b) at least one acrylate or methacrylate monomer in the presence of (c) at least one chain transfer agent; and any desired optional compounds, additives or agents.

[0040] In a preferred embodiment, the tackifier polymer additive can be prepared by an emulsion polymerization method. The parameters of the emulsion polymerization can be adjusted by those skilled in the art of emulsion polymerization. For example, one or more monomers and a chain transfer agent may be emulsified in the aqueous phase prior to emulsion polymerization. The polymerization can be initiated from new particles formed from the polymerization of the monomers or in the presence of a previously prepared seed polymer. The initiator can be added at the beginning of the polymerization or according to a feed schedule. In another preferred embodiment, the tackifier polymer additive can be prepared by a semi-batch emulsion polymerization method in which a mixture of monomers is gradually fed into a polymerization reactor.

[0041] The tackifier polymer additives of the present invention have several beneficial properties and performance attributes including, for example, high Tg, high Mn, and high polymer miscibility scores.

[0042] For example, the Tg of the tackifier polymer additive can be >0°C in one embodiment; 0°C to 50°C in another embodiment; 10°C to 50°C in yet another embodiment; and 15°C to 40°C in yet another embodiment. The Tg of the tackifier polymer additive can be measured by the midpoint temperature using a differential scanning calorimetry (DSC) curve, for example, as described in ASTM 3418 / 82. If the Tg of the tackifier polymer additive is less than 0°C, the shear of the adhesive formulated from the tackifier polymer additive and the acrylic adhesive can be less than 70 hours (hr).

[0043] For example, the Mn of the tackifier polymer additive may be from 1,200 Da to 20,000 Da in one embodiment, from 1500 Da to 15,000 Da in another embodiment, from 1,800 Da to 10,000 Da in yet another embodiment, and from 2,500 Da to 10,000 Da in yet another embodiment. As the molecular weight of the tackifier polymer additive increases, the compatibility and adhesive strength of the tackifier polymer additive may decrease. As the molecular weight of the tackifier polymer additive decreases, the Tg of the additive may decrease, tending to result in a lower cohesive strength of the final adhesive film. The Mn of the tackifier polymer additive may be measured by gel permeation chromatography (GPC), such as size exclusion chromatography.

[0044] Most emulsion polymer additives consisting of styrene and methyl methacrylate do not act as tackifiers (do not increase adhesion). However, in the present invention, a superior tackifier can be obtained by selecting the additive based on the polymer miscibility score. More specifically, the polymer miscibility score of the tackifier polymer additive of the present invention can be calculated using the following formula (I):

number

[0045] For purposes of calculating the polymer compatibility score of a tackifier polymer additive, the following formula (II) is used: p Calculate.

number

[0046] The HSP of a polymer can be calculated, for example, by referring to Hansen, CM; Hansen Solubility Parameters: A User's Handbook, 2 ndFor tackifier polymer additives or acrylic adhesive polymers, the HSP can be calculated by a linear combination of the HSPs of each component monomer weighted by weight fraction using the HSP data contained in the Journal of Polymeric Materials, Vol. 13, No. 1, 2007, CRC Press, Boca Raton. The polymer HSP of a polymer prepared from 82.4 wt. % EHA, 16.6 wt. % MMA, and 1 wt. % AA, derived from the HSPs of the following monomers, is δ D = 15.0, δ P = 5.0, and δ Η =3.8(J / cm 3 ) 1 / 2 It is. [Table 1]

[0047] If the HSP of a monomer is not available, the HSP can be estimated by the group contribution method from the relevant monomer and group contribution terms. Hansen, CM; Hansen Solubility Parameters: A User's Handbook, 2 nd According to the group contribution method described in Ed.: 2007, CRC Press, Boca Raton, the HSP terms can be estimated as the sum of contributions from different groups within a monomer using the following equation (III):

number

[0048] As an example, δ of SVS H、 can be calculated using the following formula (IV):

number

[0049] It will be readily apparent to those skilled in the art how to calculate the HSP of other monomers using the above group contribution method. ndThe HSP can also be calculated from experimental data for the monomer of interest using the methods described in, for example, Phys. Phys. 1999, 1999, Ed.: 2007, CRC Press, Boca Raton.

[0050] For example, the polymer miscibility score of the tackifier polymer additive as calculated using formula (I) above can be greater than 0 in one embodiment, from 0 to 3 in another embodiment, from 0 to 1 in yet another embodiment, and from 0.05 to 0.9 in yet another embodiment. If the polymer miscibility score of the tackifier polymer additive is less than 0, then the adhesion of an adhesive formulated from the tackifier polymer additive to an acrylic adhesive is likely to be equal to or less than the adhesion of an acrylic adhesive that is not formulated with the tackifier polymer additive.

[0051] In another broad embodiment, the present invention comprises a tackified adhesive composition that is a mixture of (I) at least one adhesive polymer and (II) at least one of the tackifier polymer additives described above. The tackified adhesive composition of the present invention can be distinguished from tackified compositions disclosed in the prior art by increasing adhesion without substantially decreasing the cohesive strength (shear resistance) of the tackified adhesive composition of the present invention, as compared to tackified compositions disclosed in the prior art that do not include the tackifier polymer additive of the present invention.

[0052] The adhesive polymers of component (I) include, for example, rubbers such as isoprene and acrylonitrile-butadiene-styrene, and polymers or copolymers prepared from styrene, butadiene, ethylene, vinyl acetate, acrylic acid and its esters, and methacrylic acid and its esters. In a preferred embodiment, the adhesive polymer is a pressure-sensitive adhesive polymer that is a polymer or copolymer of styrene, butadiene, ethylene, vinyl acetate, acrylic acid and its esters, and methacrylic acid and its esters.

[0053] The amount of acrylic adhesive polymer, component (I), used to make the tackified acrylic adhesive composition can be, for example, 45% to 99% by weight in one embodiment, 60% to 95% by weight in another embodiment, and 50% to 90% by weight in yet another embodiment.

[0054] Component (II), the tackifier polymer additive, of the present invention comprises one or more of the tackifier polymer additives described above.

[0055] The amount of tackifier polymer additive, component (II), mixed with the acrylic adhesive polymer, component (I), to make a tackified acrylic adhesive composition can be, for example, from 1 wt % to 55 wt % in one embodiment, from 5 wt % to 40 wt % in another embodiment, and from 10 wt % to 50 wt % in yet another embodiment.

[0056] To make the tackified acrylic adhesive composition of the present invention, optional compounds, agents and additives can be added to the composition as component (IV). Such optional components (IV) can include, for example, plasticizers, crosslinkers, polyvalent metal ion salts, defoamers, thickeners, rheology modifiers, stabilizers, pigments, wetting agents, and mixtures thereof. Furthermore, in addition to the tackifier polymer additive, other classes of tackifiers can also be added.

[0057] In general, the process for making a tackified acrylic adhesive composition involves mixing (I) at least one acrylic adhesive polymer with (II) at least one tackifier polymer additive as described above, to which optional ingredients can be added as needed.

[0058] The tackified acrylic adhesive compositions of the present invention have several beneficial properties and performance including, for example, increased adhesion, no substantial loss of cohesive strength (shear resistance), and enhanced low surface energy adhesion, for example, adhesion to materials with non-polar surfaces such as polyethylene, including HDPE (high density polyethylene), polypropylene and other polyolefin films. In some embodiments, the low surface energy surface has a surface energy of 35 milliNewtons per meter (mN / m) or less.

[0059] The tackified acrylic adhesive composition increases the adhesive properties (peel) such that the peel of the tackified composition is greater than or at least 90 percent (%) greater than the peel of the untackified adhesive polymer. For example, the adhesive properties (peel) of the tackified acrylic adhesive composition relative to the peel of the untackified adhesive polymer can be 90% to 1,000% in one embodiment, 100% to 500% in another embodiment, and 120% to 500% in yet another embodiment. In yet another embodiment, it can be 150% to 400%. The adhesive properties of the tackified acrylic adhesive composition can be measured by Instron according to the PSTC 101 standard peel adhesion measurement.

[0060] For example, the cohesive (shear resistance) properties of the tackified acrylic adhesive composition may be greater than 70 hours in one embodiment, from 71 hours to greater than 500 hours in another embodiment, from 78 hours to greater than 200 hours in yet another embodiment, and from 100 hours to greater than 200 hours in yet another embodiment. The cohesive (shear resistance) properties of the tackified acrylic adhesive composition may be measured by PSTC107.

[0061] The tackified acrylic adhesive composition of the present invention can be used in a variety of applications, such as any pressure sensitive label adhesive including, for example, paper labels, pressure sensitive tapes, overlaminate films, etc. In a preferred embodiment, the tackified acrylic adhesive composition can be used, for example, in pressure sensitive paper label applications. EXAMPLES

[0062] The following examples are presented to further illustrate the invention, but should not be construed as limiting the scope of the claims. All parts and percentages are by weight unless otherwise indicated.

[0063] Various raw materials or components used in the inventive examples (Inv. Ex.) and comparative examples (Comp. Ex.) are described as follows: Triton XN-45S is a surfactant available from The Dow Chemical Company.

[0064] Various terms and names used in the examples are explained as follows: "Sty" stands for styrene. "MAA" stands for methacrylic acid. "nDDM" stands for n-dodecyl mercaptan. "BMA" stands for n-butyl methacrylate. "MMA" stands for methyl methacrylate.

[0065] Examples 1-4 and Comparative Examples A-C: General Procedure for Tackifier Polymer Additives to Prepare Emulsions A charge consisting of 0.6 g of sodium carbonate, 720 grams (g) of deionized water, 7.2 g of an aqueous solution of sodium dodecylbenzenesulfonate, and 13.2 g of methyl beta cyclodextrin was prepared using a flask equipped with a mechanical stirrer. It was warmed to 87°C. An emulsion was prepared consisting of 11.2 g of Triton XN-45S, 13.4 g of an aqueous solution of sodium dodecylbenzenesulfonate (22% strength), 3.3 g of methacrylic acid, 250 g of water, 491.8 g of styrene, and 107.9 g of butyl methacrylate. A portion of the emulsion (43.9 g) was transferred to the flask. Then, 20.1 g of an aqueous solution of ammonium persulfate at a concentration of 33% in water was poured into the flask. After the initiation of polymerization and the initial exotherm, 67 g of n-dodecyl mercaptan was added to the emulsion. The emulsion was gradually dispensed into the flask over a period of 3.0 hours. At the start, for the first 10 minutes (min), the rate of emulsion addition to the flask was 2.65 grams per minute (g / min). The rate of emulsion addition to the flask was then increased to 5.3 g / min for the remainder of the feed time (3 hours). From the beginning of the emulsion feed, 111.2 g of a 6% strength ammonium peroxodisulfate solution in water was added at a constant rate over a period of 3.0 hours, keeping the reaction medium at 85-87°C.

[0066] After the feeds are complete, at approximately 75° C., a solution of 3.38 g of sodium formaldehyde sulfoxylate and 31.5 g of water and simultaneously 37.9 g of a 16.9% strength solution of tert-butyl hydroperoxide are dispensed into the flask over 30 minutes.

[0067] The emulsion compositions set forth in Table III were prepared using the general procedure described above.

[0068] Molecular weight measurement For the measurements of Mn and weight average molecular weight (Mw), the tackifier polymer additives shown in Table III were prepared in tetrahydrofuran (THF) (Fisher high performance liquid chromatography (HPLC) grade) at a concentration of approximately 2 milligrams per gram (mg / g). The samples were allowed to equilibrate overnight at ambient temperature (approximately 25 °C) on a mechanical shaker. Before subjecting the sample solutions to the SEC (size exclusion chromatography) method, the sample solutions were filtered using a 0.45 micron (μm) polytetrafluoroethylene (PTFE) filter.

[0069] Setting up SEC separation SEC separations were performed on a liquid chromatograph consisting of an Agilent 1100 model isocratic pump, vacuum degasser, variable injection size autosampler, and an Agilent 1100 HPLC G1362A refractive index detector. Data were processed using Agilent ChemStation, version B.04.03, with the Agilent GPC-Addon, version B.01.01.

[0070] SEC separation was performed at 1 milliliter / minute (mL / min) in THF (Fisher HPLC grade) using a SEC column set consisting of two PLgel MIXED-D columns (available from Agilent) in neat THF with narrow cutoff polystyrene standards from 580 Daltons to 371,000 Daltons fitted to a first-order fitting calibration curve. One hundred microliters (μL) of sample was subjected to SEC separation.

[0071] SEC separation conditions Column: PLgel MIXED-D column (300 × 7.5 millimeters (mm) inner diameter (ID)) and guard (50 mm × 7.5 mm ID), particle size 5 μm Eluent: THF (HPLC grade, Fisher) Flow rate: 1.0mL / min, Sample solvent: THF Sample concentration: Approximately 2 mg / g (0.2%) Sample solution injection volume: 100μL Calibration: Narrow-cut polystyrene standards with peak molecular weights ranging from 580 Daltons to 371,000 Daltons at a concentration of approximately 0.5 milligrams per milliliter (mg / mL) in THF were used to construct a 10-point calibration curve (first order fitting) and used to estimate the relative molecular weights of the analyzed samples. Detection: Refractive Index (RI)

[0072] The Tg of the polymeric tackifier additives listed in Table III was measured using a TA Instruments Differential Scanning Calorimeter (DSC) according to the following method steps. 1. Ramp to 150°C at 20°C / min. Isothermal for 2.5 min. 3. Equilibrate at -90°C. 4.Modulates + / - 1.00°C every 40 seconds. Isothermal for 5.5 min. 6. Ramp 3.00°C / min to 150°C. [Table 3]

[0073] The Comp.Ex. additives listed in Table III have a Tg below 0°C or a miscibility (compatibility) score below 0.

[0074] Examples 5-8 and Comparative Examples D-F: Pressure-Sensitive Adhesive Polymers Pressure sensitive adhesive polymers were prepared by blending the polymeric tackifier additives described in Table III with a butyl acrylate-based pressure sensitive adhesive polymer (BA-PSA) at a solids loading of 25 parts additive per 100 parts adhesive solids. [Table 4]

[0075] Examples 9-12 and Comparative Examples GI: Films made with adhesive Pressure-sensitive adhesive polymers from Inv. Ex. 5-8 and Comp. Ex. DF were used to prepare adhesive films by applying wet adhesive to silicone-coated release paper and then drying the adhesive at 80°C for 5 minutes. The dried adhesive was then transferred to a 2 mil PET film for adhesion testing.

[0076] Test results Blends of the above additives with butyl acrylate adhesive polymers were tested for pressure sensitive adhesive (PSA) properties (according to PSTC 101 (peel adhesion test), PSTC-16 (loop tack test) and PSTC 107 (shear test) methods) against stainless steel and high density polyethylene (HDPE) substrates. The results of the PSA tests are shown in Table V. Comp. Ex. G was not tested due to poor compatibility (i.e., poor film clarity). Comp. Ex. I also had poor film clarity and gave poor results with EHA-based adhesives. [Table 5]

[0077] The inventive examples provide enhanced adhesion such that the peel results for the inventive examples exceed those of the adhesive without the additive without a drop in shear resistance below 72 hours. For Comp. Ex. H, the shear resistance is reduced to 70 hours.

[0078] Examples 13-16 and Comparative Examples JL: Pressure-Sensitive Adhesive Polymers The polymeric tackifier additives described in Table III were blended with 2-ethylhexyl acrylate-based pressure-sensitive adhesive polymers at a solids loading of 25 parts additive per 100 parts adhesive solids to prepare the pressure-sensitive adhesive polymers described in Table VI. [Table 6]

[0079] Examples 17 to 20 and Comparative Examples MO: Films prepared using adhesive Pressure sensitive adhesive polymers from Inv. Ex. 13-16 and Comp. Ex. JL were used to create adhesive films by applying wet adhesive to silicone coated release paper and drying the adhesive at 80°C for 5 minutes. The dried adhesive was then transferred to 2 mil PET film for adhesion testing.

[0080] The film clarity of the resulting blends was evaluated qualitatively as an indication of the compatibility of the additive with the acrylic adhesive polymer. Film clarity was determined by visual inspection of the films. Comparative examples of films using comparative additives with miscibility scores less than 0 had "poor" film clarity, while inventive examples of films using inventive additives with miscibility scores greater than 0 had "good" film clarity. "Very good" film clarity as judged by visual inspection.

[0081] The blends were then tested for PSA properties against stainless steel and HDPE substrates. The results of the PSA tests are shown in Table VII. Comp. Ex. J was not tested due to its poor compatibility (i.e., poor film clarity). [Table 7]

[0082] Inv.Ex. enhances the adhesion so that in most cases the peel results of Inv.Ex. are greater than those of the adhesive without additive and in all cases are higher than 90% of the adhesive without additive without decreasing the shear resistance below 72 hours. On the contrary, the 20 minute peel results of Comp.Ex.N are less than 90% of the results of the adhesive without additive.

[0083] Other embodiments The tackifying polymer additive of the present invention comprises the emulsion polymerization reaction product of: (a) at least one monomer having a homopolymer glass transition temperature of >80° C. in one embodiment, and 0° C. to 60° C. in another embodiment, as a monomer selected from the group consisting of aromatic monomers, methyl methacrylate, and mixtures thereof; (b) at least one acrylate or methacrylate monomer; and (c) at least one chain transfer agent, wherein the tackifying polymer additive has a polymer miscibility score (which is a general calculation of the score that is not specific to a given adhesive blend) of >0 in one embodiment, and >0 to 3 in another embodiment.

[0084] In one embodiment, the monomer having a homopolymer glass transition temperature of greater than 80° C. of the tackifying polymer additive may be selected from the group consisting of styrene, methyl methacrylate, alpha-methyl styrene, and mixtures thereof.

[0085] In another embodiment, the at least one chain transfer agent of the tackifier polymer additive can be selected from the group consisting of t-dodecyl mercaptan, n-dodecyl mercaptan, 3-mercaptopropionic acid, methyl 3-mercaptopropionate, butyl 3-mercaptopropionate, isopropanol, isobutanol; lauryl alcohol, t-octyl alcohol, carbon tetrachloride; tetrachloroethylene, trichloro-bromoethane, and mixtures thereof.

[0086] In yet another embodiment, the tackifier polymer additive of the present invention may have a glass transition temperature of the tackifier polymer additive >0° C. In one embodiment, the number average molecular weight is from 1200 Da to 20,000 Da, and in another embodiment, from 1500 Da to 10,000 Da. The tackifier polymer additive has a polymer miscibility score >0. The present invention may include the following aspects. [1] 1. A tackifier polymer additive comprising: (a) at least one monomer having a homopolymer glass transition temperature greater than 80°C; (b) a compound represented by the following general formula (I): R1-CH=CR2-COOR3 formula (I) wherein R1 is selected from the group consisting of hydrogen, aliphatic groups, and aromatic groups; R2 is selected from the group consisting of hydrogen, aliphatic groups, and aromatic groups; and R3 is selected from the group consisting of hydrogen, aliphatic groups, and aromatic groups; and (c) a tackifier polymer additive comprising an emulsion polymerization reaction product of at least one chain transfer agent, the polymer having a polymer miscibility score greater than 0. [2] The tackifier polymer additive has a glass transition temperature greater than 0° C., a number average molecular weight of the tackifier polymer additive is from 1200 Daltons to 20,000 Daltons, and a polymer miscibility score of the tackifier polymer additive is greater than 0. [3] 2. The tackifier polymer additive of claim 1, wherein the monomer having a homopolymer glass transition temperature greater than 80° C. is selected from the group consisting of aromatic monomers, methyl methacrylate, and mixtures thereof. [4] The tackifier polymer additive of [1], wherein the at least one monomer of component (b) is an acrylate monomer or a methacrylate monomer. [5] [4] The tackifier polymer additive of [4], wherein component (b) is selected from the group consisting of n-butyl acrylate, t-butyl acrylate, i-butyl acrylate, s-butyl acrylate, methyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, n-butyl methacrylate, i-butyl methacrylate, s-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, and mixtures thereof. [6] 2. The tackifier polymer additive of claim 1, wherein the at least one chain transfer agent is selected from the group consisting of alkyl mercaptans, esters of mercaptans, alcohols, and mixtures thereof. [7] 1. A process for making a tackifier polymer additive, comprising: (a) at least one aromatic monomer having a homopolymer glass transition temperature greater than 80°C; (b) at least one acrylate or methacrylate monomer; (c) mixing at least one chain transfer agent, wherein the tackifier polymer additive has a polymer miscibility score greater than 0. [8] [7] The process according to [7], wherein the mixing is carried out by emulsion polymerization. [9] (I) at least one acrylic adhesive polymer; (II) at least one tackifier polymer additive according to [1]; (III) optionally, water.

[10] 9. A tackified acrylic adhesive composition according to claim 9, wherein the peel adhesion strength of the tackified acrylic adhesive composition is 90 percent to 1,000 percent compared to an untackified adhesive without a substantial loss in cohesive strength (shear resistance), and the cohesive strength (shear resistance) of the tackified acrylic adhesive composition is greater than 71 hours.

[11] 1. A process for making a tackified acrylic adhesive composition comprising: (I) at least one acrylic adhesive polymer; (II) at least one tackifier polymer additive according to [1].

[12] An article comprising the tackified acrylic adhesive composition according to [9].

Claims

1. 1. A tackifier polymer additive comprising: (a) at least one monomer having a homopolymer glass transition temperature greater than 80° C., as measured in accordance with ASTM 3418 / 82, the at least one monomer being styrene; (b) two or more acrylate monomers, which are n-butyl methacrylate, methacrylic acid, and optionally methyl methacrylate; and (c) at least one chain transfer agent, said at least one chain transfer agent being selected from the group consisting of t-dodecyl mercaptan, n-dodecyl mercaptan (n-DDM), 3-mercaptopropionic acid and its esters, methyl 3-mercaptopropionate (MMP), butyl 3-mercaptopropionate, carbon tetrachloride, tetrachloroethylene, trichloro-bromoethane, and mixtures thereof; and having a polymer miscibility score greater than 0, said miscibility score being determined by the following formula (I): [0010] where δ Ｄ２ = 15.2, δ Ｐ２ = 5.4, and δ Ｈ２ = 4.2, The tackifier polymer additive has a glass transition temperature greater than 0° C. and a number average molecular weight of 1200 to 20,000 daltons. Tackifier polymer additives.

2. 1. A process for making a tackifier polymer additive, comprising: (a) at least one aromatic monomer having a homopolymer glass transition temperature greater than 80° C., as measured in accordance with ASTM 3418 / 82, the at least one aromatic monomer being styrene; (b) two or more acrylate monomers, which are n-butyl methacrylate, methacrylic acid, and optionally methyl methacrylate; and (c) at least one chain transfer agent, said at least one chain transfer agent being selected from the group consisting of t-dodecyl mercaptan, n-dodecyl mercaptan (n-DDM), 3-mercaptopropionic acid and its esters, methyl 3-mercaptopropionate (MMP), butyl 3-mercaptopropionate, carbon tetrachloride, tetrachloroethylene, trichloro-bromoethane, and mixtures thereof; wherein the tackifier polymer additive has a polymer miscibility score greater than 0, the miscibility score being determined by the following formula (I): [0025] where δ Ｄ２ = 15.2, δ Ｐ２ = 5.4, and δ Ｈ２ = 4.2, The process wherein the tackifier polymer additive has a glass transition temperature greater than 0° C. and a number average molecular weight of the tackifier polymer additive is from 1200 Daltons to 20,000 Daltons.

3. The process of claim 2 , wherein said mixing is performed by emulsion polymerization.

4. (I) at least one acrylic adhesive polymer; (II) at least one tackifier polymer additive according to claim 1; (III) optionally, water.

5. 5. The tackified acrylic adhesive composition of claim 4, wherein the peel adhesion of the tackified acrylic adhesive composition is from 90 percent to 1,000 percent compared to an untackified adhesive without loss of cohesive strength (shear resistance), and the cohesive strength (shear resistance) of the tackified acrylic adhesive composition is greater than 71 hours as measured by PSTC 107 Shear Resistance Test.

6. 1. A process for making a tackified acrylic adhesive composition comprising: (I) at least one acrylic adhesive polymer; (II) at least one tackifier polymer additive according to claim 1.

7. An article comprising the tackified acrylic adhesive composition of claim 4.

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