WO2019113780A1

WO2019113780A1 - Ultra-removable and solvent resistant pressure-sensitive adhesives

Info

Publication number: WO2019113780A1
Application number: PCT/CN2017/115627
Authority: WO
Inventors: Biao SHEN; Yurun Yang; Yihua Wang
Original assignee: Avery Dennison Corporation
Priority date: 2017-12-12
Filing date: 2017-12-12
Publication date: 2019-06-20
Also published as: CN110003818B; CN110003818A; TW201930519A; TWI813606B

Abstract

Provided herein is a pressure sensitive adhesive (PSA) composition having high levels of removability, peel strength and solvent resistance. This PSA composition comprises a unique mixture of a polyacrylate base polymer, an epoxy crosslinker, and an optional isocyanate crosslinker. The PSA contains less than 6 wt. %of tackifier. The polyacrylate base polymer has an acid value ranging from 2 to 90 mg KOH/g and has a Tg above -41 ℃. The PSA is solvent-based and can be prepared in any of a number of solvents, including toluene and ethyl acetate.

Description

ULTRA-REMOVABLE AND SOLVENT RESISTANT PRESSURE-SENSITIVE ADHESIVES

FIELD OF THE INVENTION

The present invention relates generally to pressure-sensitive adhesives (PSAs) , in particular, to improved pressure-sensitive adhesives that have well balanced mechanical performance, removability, and solvent resistance. This application also relates to labels containing the improved pressure-sensitive adhesive as well as to methods of producing the same.

BACKGROUND OF THE INVENTION

Pressure-sensitive adhesives (PSAs) are compositions known to provide adhesiveness or tack to various substrates when applied at room temperature. This adhesiveness can provide for instantaneous adhesion to the substrate when subjected to pressure. PSAs are generally easy to handle in solid form and have a long shelf-life, so they are widely used for the manufacture of, for example, self-adhesive labels.

PSAs can generally be divided into two categories: permanent PSAs and removable PSAs. Typically, permanent PSAs are designed to adhere to a substrate without edge lifting These PSAs cannot be removed without damaging either the label or the substrate. Removable PSAs can stick to a substrate without edge lifting and can be removed without damage to either the label or the substrate. Removable PSAs are especially useful when it is desirable to remove and/or reposition the PSAs after being adhered to items. Examples include labelled packages and/or containers that may be subjected to cleaning or recycling to reuse or recover of the actual package/container material after removal of the contents. Such treatments often require the label to be completely separated from the package or container to which it is fastened, without leaving adhesive residues on the surface of the article, so as to simplify the cleaning or recycling process. Having a PSA that can be recyclable and compostable also improves the environmental friendliness of the PSA and facilitates its easy disposal.

On the other hand, in some applications, it is desirable that a PSA have high peel strength so that the label can be stably affixed to the article for desired period of time. A PSA with high peel strength requires a relatively high amount of force to peel the PSA from the substrate or article to which it is affixed. For example, for wet tissue packages, it is desirable to have the covers laminated with an adhesive that has high removability, so that when the packages are being opened and closed repeatedly, adhesive residue is not left on a surface when the package is opened (the label is separated from the substrate) . In some scenarios, the PSAs are applied to substrate surface that is wet or the substrate is often exposed to organic cleaning solvents or detergents. The contact with these solvents, e.g., water and alcohol, can lead to cloudiness and weakening of the bond between the PSA and substrate. These applications require the PSAs to possess good solvent resistance and can withstand the deteriorating effect of these solvents.

Currently available PSAs are unable to meet these needs. Thus, the need remains for PSAs that provide balanced performance characteristics, which include a combination of good peel adhesion, high removability and excellent solvent resistance.

SUMMARY OF THE INVENTION

In some embodiments, the present disclosure provides an adhesive composition comprising: a polyacrylate base polymer having an acid value ranging from 2 to 90 mg KOH/g and having a Tg above -41 ℃, a first crosslinker comprising an epoxy resin, wherein the first crosslinker is present in an amount that is greater than 0.15 wt. %based on the total dry weight of the adhesive composition, wherein the adhesive composition comprises less than 6 wt. %tackifier.

In some embodiments, the adhesive composition comprising: a polyacrylate base polymer having an acid value ranging from 2 to 90 mg KOH/g and having a Tg above -41 ℃, a first crosslinker comprising an epoxy resin, wherein the first crosslinker is present in an amount that is greater than 0.15 wt. %based on the total dry weight of the adhesive composition, wherein the adhesive composition comprises less than 6 wt. %tackifier. In some embodiments, the adhesive composition has a haze value of less than 15 %after the adhesive composition is immersed in a solvent for at least 3 days when tested according to a ASTM D1003 test. In some embodiments, The adhesive composition of Embodiment 2, wherein the solvent is water or ethanol.

In some embodiments, when the adhesive composition is removed from a surface of a substrate that has been in contact with the adhesive, the adhesive leaves residues on less than 3%of the surface area.

In some embodiments, the polyacrylate base polymer of the adhesive composition has an acid value ranging from 4 to 76 mg KOH/mg. In some embodiments, the polyacrylate base polymer has an acid value ranging from 36 to 76 mg KOH/g, wherein the epoxy resin is present in an amount of 0.2 wt. %-0.5 wt. %, and wherein the tackifier is present in an amount of less than 1 wt. %, wherein the haze value of the adhesive is less than 10%after the adhesive composition is immersed in a solvent for at least 3 days when tested according to a ASTM D1003 test.

In some embodiments, the polyacrylate base polymer of the adhesive composition has an acid value ranging from 60 to 76 mg KOH/g and the epoxy resin is present in an amount of 0.2 wt. %-0.5 wt. %. In these embodiments, the tackifier that is present in the adhesive composition in an amount of less than 0.5 wt. %, and the haze value of the adhesive is less than 8%after the adhesive composition is immersed in a solvent for at least 3 days when tested according to a ASTM D1003 test. In these embodiments, when the adhesive composition is removed from a surface of a substrate that has been in contact with the adhesive, the adhesive leaves residues on less than 3%of the surface area.

In some embodiments, the polyacrylate base polymer has an acid value ranging from 60 to 76 mg KOH/g. In these embodiments, the epoxy resin contains one or more tertiary amine groups and is present in an amount of 0.2 wt. %-0.5 wt. %. In these embodiments, the tackifier is present in an amount of less than 0.5 wt. %, and the haze value of the adhesive is less than 8%when the adhesive composition is immersed in a solvent for at least 3 days, tested according to a ASTM D1003 test. In these embodiments, when the adhesive is removed from a surface of a substrate that has been in contact with the adhesive, the adhesive leaves residues on less than 3%of the surface area.

In some embodiments, the polyacrylate base polymer has a glass transition temperature (Tg) ranging from -40℃ to -5℃. In some embodiments, the polyacrylate base polymer is not a block copolymer. In some embodiments, the polyacrylate base polymer contains alkyl groups that contains between 2 to 14 carbon atoms. In some embodiments, the average molecular weight of the polyacrylate base polymer ranges from 50000 to 1500000 g/mol. In some embodiments, the molecular weight distribution index of the polyacrylate polymer ranges from 2 to 8. In some embodiments, the polyacrylate base polymer does not comprise unsaturated groups. In some embodiments, the polyacrylate base polymer comprises hydroxyl groups and has a hydroxyl value ranging from 0 to 100 mg KOH/g.

In some embodiments, the adhesive composition comprises 0.10 to 1.0 wt. %of the first crosslinker. In some embodiments, the first crosslinker is an epoxy resin and has an epoxide equivalent weight ranging from 60 to 300 g/eq. In some embodiments, the epoxy resin comprises one or more tertiary amine groups in the chemical structure. In some embodiments, the epoxy resin of the first crosslinker comprising comprises a one or more tertiary amine group has the chemical structure of selected from the group consisting of

and mixtures thereof.

In some embodiments, the adhesive composition further comprises a second crosslinker comprising an isocyanate resin. In some embodiments, the adhesive composition comprises 0.05 to 0.8 wt. %of the second crosslinker. In some embodiments, wherein the isocyanate resin has an NCO content ranging from 10 to 30 wt. %. In some embodiments, The adhesive composition of any of Embodiments 20 –22, wherein the weight ratio of the first crosslinker to the second crosslinker ranges from 0.6 to 20.

In some embodiments, the weight ratio of the polyacrylate base polymer to the first crosslinker ranges from 100: 0.9 to 100: 0.01 (100: 0.6 to 100: 0.03 is preferred) and the adhesive composition has a peel strength from 2 to 10 N/inch on stainless steel according to the FINAT-1 method. In some embodiments, the adhesive composition has a gel content that ranges from 40 to 95 wt. %. In some embodiments, the adhesive composition has a pot life above greater than 4 hours. In some embodiments, the adhesive composition has a curing time ranging from 0.3 to 5 minutes, when cured at 120℃. In some embodiments, the adhesive is substantially free of natural rubber.

In some embodiments, this disclosure provides a label comprising an adhesive layer comprising an adhesive composition provided herein. In some embodiments, the label comprises a facestock layer in contact with the adhesive layer.

In some embodiments, this disclosure provides a method of producing an adhesive formulation, comprising: dissolving in a solvent at a temperature of less than 50℃ a) a polyacrylate base polymer, and b) a first crosslinker comprising an epoxy resin that is greater than 0.15 wt. %based on the total dry weight of the adhesive composition, wherein the adhesive formulation contains less than 6 wt. %of tackifier. In some embodiments, the first crosslinker comprises one or more catalytic units. In some embodiments, the one or more catalytic units are one or more tertiary amines. In some embodiments, the first crosslinker ranges from 0.15 wt%to 0.9 wt. %based on the dry weight of the adhesive composition. In some embodiments, the epoxy resin of the first crosslinker has an epoxide equivalent weight ranging from 60 to 300 g/eq. In some embodiments, the solvent is selected from the group consisting of toluene, ethyl acetate, Isopropanol, xylene, n-hexane, n-heptane, methyl cyclohexane, butyl acetate, acetone, butanone, and 2-Acetoxy-1-methoxypropane. In some embodiments, the method further comprises: coating a facestock with the adhesive formulation, and drying the adhesive formulation. In some embodiments, wherein the method further comprise applying a label comprising the adhesive to a substrate.

In some embodiments, this disclosure provides an adhesive system comprising: a first component comprising i) a polyacrylate base polymer having acid groups and having an acid value ranging from 2 to 90 mg KOH/g, ii) a solvent; and a second component comprising a first crosslinker comprising an epoxy resin in a solvent; and wherein the first component is separate from the second component.

In some embodiments, this disclosure provides a labeled container comprising an adhesive composition disclosed herein.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates generally to pressure sensitive adhesives (PSAs) that provide advantageous performance characteristics, specifically well balanced peel strength, removability, and solvent resistance. These characteristics together can be particularly important when the PSAs are utilized for applications requiring the adhesive to hold a label firmly in place, without leaving adhesive residue when the label is removed, and also requiring the adhesive to have resistance to various solvents.

As noted herein, a variety of conventional PSAs are known in the art. Many of these adhesives, however, have been developed for applications where either high removability or high peel strength is preferred. Generally, PSAs known in the art do not demonstrate both high removability and high peel strength. In fact, components used to contribute to improved adhesion (and therefore to increased peel strength) often have detrimental effects on removability and solvent resistance. Similarly, known PSAs that are removable without forming or leaving significant amounts of residue on a substrate are generally demonstrate poor adhesion.

For example, US Publication No. 2016/0280967A1 describes a water-based emulsion PSA, in which the polymers are emulsified in water in the presence of a surfactant. And the surfactant is generally required for stabilizing the emulsion. The surfactant negatively affects the crosslinking of the desired polymer and therefore decreases the removability and solvent resistance of the PSA. In addition, US Publication No. 2016/0280967A1 does not disclose the acid and hydroxyl value of the acrylate polymer or the epoxide equivalent range and content of its epoxy resin. Chinese Patent Application No. 103827238A discloses a PSA containing acrylate base polymer and epoxy resin. This PSA does not contain tackifier (s) . The acrylate base polymer is formed from a first monomer that is a primary alcohol R1-OH, (meth) acrylic acid alkyl ester and a second monomer that is an ethylenically unsaturated group. The polymer does not contain any acid monomers and thus does not have sufficient acid value, which would adversely affect removability due to the inefficient crosslinking between epoxy resin and acrylate base polymer.

The inventors have discovered that particular combinations of a polyacrylate base polymer, a crosslinker comprising epoxy resin, optionally utilized in specific amounts, surprisingly provide for high performance PSAs that demonstrate both high peel strength, high levels of removability, and superior solvent resistance. Importantly, the inventors have found that tackifiers have an adverse effect on the solvent resistance of the resultant PSA. In view of this finding, the PSA of the invention contains little, if any, tackifier, e.g., less than 6 wt. %, less than 5 wt. %, preferably 0 wt. %tackifier. For example, when a polyacrylate base polymer having acid groups, e.g., carboxyl groups, and an acid value ranging from 2 to 90 mg KOH/g, is utilized with a crosslinker comprising an epoxy resin (and little or no tackifier) , the resultant PSA surprisingly and advantageously demonstrates high peel strength and removability as well as excellent solvent resistance. Importantly, it has been found that the PSA may be produced by dissolving the components in particular solvents (see discussion below) . In some cases, the solvent-based PSA can be used to produce a label or other commercial product that has good removability while still having high peel strength and solvent resistance.

Some specific components of the invention are described in detail below. Unless expressly noted otherwise, all percentages are weight percentages based on the total dry weight of the PSA.

Polyacryate Base Polymer

The polymer of the solvent-based PSA comprises a polyacrylate base polymer. Various acrylate polymers are known in the art and these polymers generally contain monomers based on the acrylic acid structure, e.g., monomers that consist of a vinyl group and a carboxylic acid terminus, or derivatives thereof. In some cases, the polymer may comprise a single type of acrylate monomer, while in other cases, the polymer may comprise a combination of different types of acrylate monomers. In some embodiments, the acrylate monomers used in the polyacrylate base polymer include butyl acrylate.

In some embodiments, the polyacrylate base polymer contains acid groups and/or hydroxyl groups. In some embodiments, the monomers that form the polyacrylate base polymer include acrylic acid monomers and/or acrylate ester monomers. In some embodiments, the monomers that form the polyacrylate base polymer further include monomer that contain a hydroxyl group ( “hydroxyl group donor” ) and the amount of which present in the polymer directly correlated with the hydroxyl value of the polyacrylate base polymer. Non-exemplary hydroxyl group donors include hydroxyethylacrylate (HEA) , hydroxyl propyl alginate (HPA) and hydroxybenzoic acid (HBA) . The amount of the hydroxyl group donor may be in the range of 0.3 wt. %to 3 wt. %based on the total weight of the monomers that form the polyacrylate base polymer, e.g., 0.4-2 wt. %, or 0.5-1wt. %. In terms of upper limits, the amount of the hydroxyl group donor may be less than 3 wt%, less than 2 wt. %, or less than 1 wt. %. In terms of lower limits, the amount of the hydroxyl group donor may be present in an amount that is greater than 0.3 wt. %, greater than 0.4 wt. %or greater than 0.5 wt. %.

Importantly, the amount of acrylic acid monomers incorporated into the polyacrylate may be directly correlated with the amount of acid groups, e.g. carboxylic acids, in the polyacrylate base polymer; and the amount of acrylic ester monomers incorporated into the polyacrylate base polymer may be directly correlated to the amount of hydroxyl groups in the polyacrylate base polymer. The inventors have found that maintaining specific ratios of the monomers to acid or hydroxyl groups leads to the production of PSAs having the aforementioned combination of desired performance characteristics, e.g., high peel strength and high removability. In some embodiments, the PSA does not comprise any acrylic ester monomer. In some embodiments, the ratio between the acrylic ester monomers and acrylic acid monomers may range from 5.6: 1 to 499: 1, e.g., from 10: 1 to 400: 1, from 20: 1 to 300: 1, from 30: 1 to 200: 1, from 50: 1 to 100: 1, or from 70: 1 to 90: 1, e.g., about 82: 1. In terms of upper limits, the ratio between the acrylic ester monomers and acrylic acid monomers is less than 499: 1, less than 200: 1, less than 150: 1, less than 100: 1, or less than 90: 1. In terms of lower limits, the ratio between the acrylic ester monomers and acrylic acid monomers is greater than 5.6: 1, 8: 1, 10: 1 or 20: 1, e.g., 9: 1. Without being bound by theory, it is believed that base polymers having few or no acid groups (the acid value being 0) , cannot be crosslinked by the (epoxy) crosslinker.

In some cases, the amount of the acid groups in the polyacrylate base polymer is expressed by an acid value. The acid value of the polyacrylate base polymer is the mass of potassium hydroxide (KOH) , in milligrams, that is required to neutralize one gram of the polyacrylate base polymer. In some embodiments, the acid value of the polyacrylate base polymer ranges from 2 mg KOH/g to 90 mg KOH/g, e.g., from 4 mg KOH/g to 75 mg KOH/g, from 5 mg KOH/g to 35 mg KOH/g, 4 mg KOH to 36 mg KOH, or from 8 mg KOH/g to 75 mg KOH/g. In terms of upper limits, the acid value of the polyacrylate base polymer is less than 90 mg KOH/g, less than 80 mg KOH/g, less than 75 mg KOH/g, less than 50 mg KOH/g, or less than 40 mg KOH/g. In terms of lower limits, the acid value of the polyacrylate base polymer is greater than 2 mg KOH/g, greater than 4 mg KOH/g, greater than 10 mg KOH/g, greater than 20 mg KOH/g, or greater than 25 mg KOH/g. The inventors have discovered surprisingly that when the polyacrylate base polymer has acid values within the above-referenced ranges and when the amount of epoxy resin is also present within proper ranges (as further described below) , crosslinking of the polymer can occur more efficiently, which can result in superior properties of good removability and solvent resistance.

In some embodiments, the amount of the hydroxyl groups present in the polyacrylate base polymer is expressed by a hydroxyl value. The hydroxyl value of the polyacrylate base polymer is the mass of potassium hydroxide (KOH) , in milligrams, required to neutralize the acetic acid taken up on the acylation of one gram of the polyacrylate base polymer. In some embodiments, the hydroxyl value of the polyacrylate base polymer ranges from 0 mg KOH/g to 100 mg KOH/g, e.g., from 0 to 90 mg KOH/g, from 1 to 50 mg KOH/g, from 5 to 50 mg KOH/g, from 10 to 50 mg KOH/g, form 20 to 80 mg KOH/g, e.g., from 30 to 55 mg KOH/g. Notably, some embodiments of the PSA include a polyacrylate base polymer with no free hydroxyl groups. Those embodiments thus include a polyacrylate base polymer with a hydroxyl value equal to 0 mg KOH/g. In terms of upper limits, the hydroxyl value of the polyacrylate base polymer is less than 100 mg KOH/g, less than 80 mg KOH/g, less than 50 mg KOH/g, less than 20 mg KOH/g, less than 10 mg KOH/g, less than 5 mg KOH/g. In terms of lower limits, the acid value of the polyacrylate base polymer is greater than 0 mg KOH/g, greater than 1 mg KOH/g, greater than 5 mg KOH/g, greater than 10 mg KOH/g, greater than 20 mg KOH/g, or greater than 25 mg KOH/g.

In preferred embodiments, the polyacrylate base polymer is not a block copolymer. A block copolymer is a copolymer formed with two or more monomers that cluster together and form blocks of repeating units. For example, a polymer made up of X and Y monomers joined together like: Y-Y-Y-Y-Y-X-X-X-X-X-Y-Y-Y-Y-Y-X-X-X-X-X-is a block copolymer where -Y-Y-Y-Y-Y-and -X-X-X-X-X-groups are the blocks. Although the polyacrylate base polymer of the invention may comprise more than one types monomers, these monomers are distributed evenly in the polymer chain and do not form blocks of repeating units.

In some embodiments, the polyacrylate base polymer may comprise acrylate monomers that also include alkyl chains. These alkyl chains may vary widely, e.g., linear, branched, cyclical, aliphatic, aromatic, saturated, or unsaturated. The number of carbon atoms in the alkyl chain (s) of the acrylate monomer may vary, ranging from 1 to 20 carbon atoms, e.g., from 2 to 15, from 2 to 13, from 4 to 10, from 4 to 8 carbons. In preferred embodiments, these alkyl chains comprise no more than 20 carbon atoms, e.g., no more than 15 carbon atoms, no more than 12 carbon atoms, no more than 8 carbon atoms, no more than 6 carbon atoms, no more than 5 carbon atoms, or no more than 4 carbon atoms. In preferred embodiments these alkyl chains comprise greater than 1 carbon atom, e.g., greater than 1, greater than 3, greater than 4, or greater than 5 carbon atoms.

The polyacrylate base polymer may contain unsaturated carbon groups, but preferably, the acrylate polymer does not contain any unsaturated carbon groups. In some cases, the acrylate monomer of the polymer may contain an aromatic ring; but preferably, the acrylate monomer of the polymer does not contain an aromatic ring. Monomers have aromatic rings often cannot form high degree of polymerization, and thus may have decreased cohesion and adhesion properties as compared to monomers that do not.

The polyacrylate base polymer, in some embodiments, has a glass transition temperature (Tg) within appropriate ranges and/or limits. The glass transition temperature defines the region where the polymer transitions from a hard, glassy material to a soft, rubbery material. It has surprisingly been found that when a polyacrylate base polymer having a Tg ranging from -40℃ to -15℃ (including the endpoints) , e.g., from -40 ℃ to -15 ℃, from -35℃ to -15℃, from -35℃ to -20℃, from -31 ℃ to -25 ℃, or, about -26.8 ℃, a superior combination of performance features may be achieved, e.g., optimal peel adhesion and removability

The average molecular weight of the polyacrylate base polymer may vary widely. In some cases, the average molecular weight may range from 50,000 to 1,500,000 g/mol, e.g., from 70,000-1, 200,000 g/mole, from 100,000-600,000 g/mole, from 200,000-800,000 g/mole, from 300,000-600,000 g/mole or about 450,000. In terms of upper limits, the polyacrylate base polymer can have an average molecular weight of less than 1,500,000 g/mole, e.g., less than 800,000 g/mole, less than 600,000 g/mole. In terms of lower limits, the polyacrylate base polymer can have an average molecular weight of greater than 50,000 g/mole, e.g., greater than 100,000 g/mole, or less than 300,000 g/mole. In some embodiments, the polyacrylate base polymer contains from 2 to 40 wt. %, e.g., from 6 to 30 wt. %, from 10 to 20 wt. %of polymers having a molecular weight of 10,000 g/mole or less based on the total dry weight of the polyacrylate base polymer.

The polyacrylate base polymer may have a molecular weight distribution index ranging from 2 to 8, e.g., from 2 to 5, from 1 to 4, from 2 to 3, from 3 to 4, or from 3 to 4. Molecular weight distribution index refers to the broadness of a molecular weight distribution of a polymer, the larger the index, the broader the molecular weight distribution.

Suitable commercially available polyacrylate base polymers include Y-1510, Y-1310, Y-1500W, Y-1210, Y-2100 from YASUSA Chemical, BPS5375 from Toyo ink, Etrac7017B, Etarc77307, Etarac7709, Etarac7055 from Eternal, PS8249 and PS8245 from Sumei, Ulrta-Reclo 236A, Ulrta-Reclo 247A from Henkel, NC-310 from Soken.

Crosslinker

The PSA of the present invention comprises one or more crosslinkers. This crosslinker functionally links one polymer chain to another. In preferred embodiments, one crosslinker, e.g., a first crosslinker, comprises an epoxy resin, which may react with the acid groups in the polyacrylate base polymer. The epoxy resin opens the ring and generate one hydroxyl group. The PSA may comprise from 0.16 wt. %to 1.0 wt. %of the first crosslinker, e.g., from 0.16 wt. %to 1.0 wt. %, from 0.18 wt. %to 0.9 wt. %, from 0.25 wt. %to 1 wt. %, from 0.20 wt. %to 0.75 wt. %, from 0.3 wt. %to 0.70 wt. %, and from 0.35 wt. %to 0.5 wt. %, e.g., about 0.25 wt. %based on the total dry weight of the PSA. In terms of upper limits, the PSA comprises epoxy in an amount of less than 1 wt. %, less than 0.9 wt. %, and less than 0.7 wt. %, based on the total dry weight of the PSA. In terms of lower limits, the PSA comprises epoxy in an amount of greater than 0.15 wt. %, e.g., greater than 0.20 wt. %, greater than 0.25 wt. %based on the total dry weight of the PSA.

In preferred embodiments, the epoxy resin may comprise one, two, three, or more tertiary amines. Advantageously, epoxy resins having such properties, when used at appropriate amounts as described above, have been found to be able to react with the polyacrylate base polymer, especially the ones having acid value as disclosed above, with higher rates and at relatively moderate temperatures. As a result, the time required for the crosslinking, i.e., the curing time, is beneficially dramatically shortened. Stated another way, the use of the epoxy crosslinkers having the specific properties, e.g., having one or more tertiary amines, surprisingly has been found to advantageously increase crosslinking efficiency, e.g., shortened curing time and/or lower temperatures required for curing. Unlike conventional PSAs that usually take 30 minutes to 1 hour to cure at a temperature range of 120 –130 ℃, the PSA of the present invention can be cured within a few minutes at similar temperatures, and in some cases at even relatively moderate, lower temperatures, e.g., at 30 ℃ -100 ℃, or 50 ℃ -90 ℃, 45 ℃ -80 ℃, or 50 ℃ -70 ℃. In terms of upper limits, the curing temperature for the PSAs can be less than 100 ℃, less than 90 ℃, less than 80 ℃, or less than 70 ℃. In terms of lower limits, the curing temperature for the PSAs can be greater than 30 ℃, greater than 40 ℃, or greater than 45 ℃.

Curing time disclosed herein refers to the amount of time necessary for a polymer composition to toughen or harden by the crosslinking of polymer chains. In general, if a higher cure temperature is utilized, a shorter curing time can be expected.

Epoxy resins suitable for use in the invention may include but are not limited to the following:

(I) Glycidyl ether of m-xylenediamine

(II) Glycidyl ether of m-cyclohexyldiamine

(III) N, N-Bis (2, 3-epoxypropyl) isopropylamine

(IV) N, N-Bis (2, 3-epoxypropyl) cyclohexylamine

Suitable commercially available epoxy resin crosslinkers include, but are not limited to, ERISYS GA-240 from CVC (having the structure I) , BXX5983 from Toyoink (having structure II) , and Y-202 from YASUSA Chemical (having the structure III) .

It is believed that high epoxy equivalent weight of the epoxy resin used is associated with increased reaction rates and/or degree of crosslinking of the base polyacrylate polymer. Epoxide equivalent weight (EEW) is a parameter that defines the weight of the resin in grams that contains one gram -equivalent of epoxy. In preferred embodiments, the epoxy resin of the PSA has a EEW ranging from 60 to 300 g/eq, e.g., from 60 to 100 g/eq, from 60 to 150 g/eq, from 60 to 250 g/eq, from 75 to 125 g/eq, from 75 to 200 g/eq, from 90 to 120 g/eq, and from 100 to 200 g/eq, or about 100 g/eq. In terms of upper limits, the epoxy resin of the PSA has a EEW that is less than 300 g/eq, less than 250 g/eq, or less than 200 g/eq. In terms of lower limits, the epoxy resin of the PSA has a EEW that is greater than 60 g/eq, greater than 75 g/eq, or greater than 80 g/eq.

In some embodiments, the weight ratio of the polyacrylate base polymer to the first crosslinker in the PSA ranges from 111 to 10,000, e.g., from 166 to 3,333, from 1,000 to 5,000, or from 2,000 to 3,000. In terms of upper limits, the weight ratio of the polyacrylate base polymer to the first crosslinker is less than 10,000, less than 5,000, or less than 4,000. In terms of lower limits, the weight ratio of the polyacrylate base polymer to the first crosslinker is greater than 100, e.g., greater than 200, greater than 1,000, greater than 2,000, or greater than 3,000.

In some embodiments, the PSA may also include a second crosslinker, which may comprise an isocyanate resin. The isocyanate resin may react with the hydroxyl group of the polyacrylate base polymer, as shown in the reaction scheme below.

Reaction Scheme (I) :

In some embodiments, the PSA comprises from 0.05 wt. %to 0.8 wt. %of the second crosslinker based on the total dry weight of the PSA, e.g., from 0.005 wt. %to 0.4 wt. %, from 0.01 wt. %to 0.4 wt. %, from 0.03 wt. %to 0.3 wt. %, from 0.05 wt. %to 0.2 wt. %, and from 0.08 wt. %to 0.15 wt. %. In terms of upper limits, the PSA comprises the second crosslinker in an amount of less than 0.4 wt. %, less than 0.3 wt. %, less than 0.2 wt. %, or less than 0.15 wt. %. In terms of lower limits, the PSA comprises the second crosslinker in an amount of greater than 0.005 wt. %, greater than 0.01 wt. %, greater than 0.03 wt. %, or greater than 0.05 wt. %.

It is believed that the NCO content of any isocyanate resin, which refers to the weight percent of the N=C=O functional group relative to the total resin, affects the rates and efficiency of the crosslinking reaction. In preferred embodiments, the second crosslinker is an isocyanate resin that has an NCO content ranging from 10 to 30 wt. %based on the total dry weight of the isocyanate resin, e.g., from 10 to 15 wt. %, from 10 to 20 wt. %, from 12 to 15 wt. %, from 15 to 25 wt. %, or from 15 to 30 wt. %. Isocyanate resins having NCO content higher this range typically have low molecular weight and high volatility, and thus may be harmful to the environment or user. In terms of upper limits, the second crosslinker of the PSA has an NCO content that is less than 30 wt. %, less than 25 wt. %, or less than 20 wt. %. In terms of lower limits, the second crosslinker of the PSA has an NCO content that greater than 10 wt. %, greater than 12 wt. %, greater than 15 wt. %based on the total dry weight of the isocyanate resin.

Suitable, commercially available isocyanate resin crosslinkers include, but are not limited to, Desmodur L75, Desmodur N100, and Desmodur N3390 from Covestro.

In some embodiments the PSA comprises both a first and a second crosslinkers. On one hand, it has been discovered that epoxy resin crosslinks polyacrylate base polymer and generates a higher crosslinking density than isocyanate resin does. Thus, PSAs having too high an amount of epoxy resin may have an excessively high crosslinking density, which may lead to poor anchorage when applied to substrate by a transfer coating. On the other hand, it has been discovered that increasing the amount of isocyanate resin can increase pot life but may decrease removability. Thus PSAs having too high an amount of isocyanate resin may exhibit poor removability. Accordingly, the inventors have found that specific ratios of epoxy resin to isocyanate resin advantageously provide unexpected combinations of performance features. For example, as disclosed above, the weight ratio of the epoxy crosslinker to the isocyanate crosslinker may range from 0.6 to 20, e.g., from 0.7 to 15, from 1 to 10, from 1 to 8, from 1 to 4, e.g., about 1.25, 1.33 or about 3.5. In term of upper limits, the weight ratio of the first crosslinker to the second crosslinker is less than 20, less than 15, less than 10, less than 8, less than 4. In terms of lower limits, the weight ratio of the first crosslinker to the second crosslinker is greater than 0.5, greater than 0.7, or greater than 1. Maintaining the proper ratio between the first and second crosslinker has been found to be important for controlling the curing reaction speed such that it the PSA can be efficiently cured and also has desired pot life and workability, as shown below. The proper ratio between the first and second crosslinkers is also beneficial for improving the peel strength of the PSA.

Tackifier

Tackifiers are compounds that are used to increase the tack, the stickiness of the surface of the adhesive. Commonly used tackifiers include rosin resins, polyterpene resins, hydrocarbon resin (e.g., C ₉ tackifier) , phenolic resins, or combinations thereof. Importantly, the PSA of the invention comprises less than 5 wt. %, less than 2.5 wt. %, less than 1 wt. %, less than 0.5 wt. %, less than 0.1 wt. %, e.g., less than 0.05 wt. %tacikifer. Preferably the PSA of the invention does not contain any tackifier. The inventors have discovered surprisingly that tackifiers may negatively affect the solvent resistance of the PSA, see Example 2, and thus it is beneficial to exclude tackifiers from the PSA.

Labels

In some cases, the solvent-based PSA can be used to produce a label or other commercial product that has good removability while still having high peel strength. Accordingly, the disclosure also provides a label that comprises the PSA disclosed above. The labels may comprise a facestock layer and an adhesive layer comprising the PSA. In some cases, the label further comprises one or more primer layers and/or a liner, as further described below.

In some embodiments, the label comprises a PSA layer that may comprise a thickness ranging from 10 to 40 microns, e.g., from 15 to 35 microns, from 18 to 30 microns, from 20 to 40 microns, or other ranges in the foregoing amounts. In terms of lower limits, the facestock layer may have a thickness of at least 10 micron, e.g., at least 15 microns, at least 18 microns. In terms of upper limits, the polyolefin films may have a thickness less than 40 microns, e.g., less than 35 microns, or less than 30 microns.

Facestock Layer

The label may have one or more facestock layers. In one embodiment, from the perspective of looking downward to the substrate, the facestock layer is on the top surface of the label, exposed to the environment and is configured to receive printable information, such as barcode or alphanumeric characters.

The facestock layer can include, for example, glassine, kraft, and polyesters, such as polyethylene terephthalate (PET) , polyamides (PA) , polyethylene naphthalate (PEN) , cotton, tissue, paper, fiberglass, synthetic textiles, and polyolefins, such as polypropylene (PP) , ethylene-propylene copolymers, polyethylene (PE) , and combinations thereof. Other polymeric film materials include urethane based polymers such as polyether urethane and polyester urethane; amide based polymers including polyether polyamide copolymers; acrylic based polymers including a polyacrylate, and ethylene/vinyl acetate copolymer; polyester based polymers including a polyether polyester; a vinyl chloride; a vinylidene chloride; a polystyrene; a polyacrylonitrile; a polycarbonate; a polyimide; ABS; polyacrylate; polycarbonate (PC) ; polyamide; polyimide (PI) ; polyamidoimide; polyacetal; polyphenylene oxide (PPO) ; polysulfone, polyethersulfone (PES) ; polyphenylene sulfide; polyether ether ketone (PEEK) ; polyetherimide (PEl) ; metallized polyethylene terephthalate (PET) ; polyvinyl fluoride (PVF) ; polyethylene ether (PEE) ; fluorinated ethylene propylene (FEP) ; polyurethane (PUR) ; liquid crystal polymers (LCPs, class of aromatic polyester) ; polyvinylidene fluoride (PVDF) ; aramid fibers; DIALAMY, (polymer alloys) ; polyethylene naphthalate (PEN) ; ethylene/tetrafluoroethylene; (E/TFE) ; polyphenyl sulfone (PPSU) ; and polymers or polymer alloys containing one or more of these materials.

The thickness or coating weight of the facestock layer may vary depending on the stiffness of the label desired for particular applications. The facestock layer according to certain embodiments of the present invention may comprise a thickness ranging from 100 to 1,000 microns, e.g., from 200 to 800 microns, from 150 to 500 microns, from 300-600 microns, or from 450 to 900 microns, or other ranges in the foregoing amounts. In terms of lower limits, the facestock layer may have a thickness of at least 100 micron, e.g., at least 150 microns, at least 200 microns, or at least 300 micros. In terms of upper limits, the polyolefin films may have a thickness less than 1000 microns, e.g., less than 800 microns, less than 500 microns, less than 400 microns, or less than 300 microns. In some embodiments, the facestock layer is 125 microns.

The facestock layer may optionally be configured to be receptive to printing. For example, the facestock layer may contain one or more printable layers containing an ink-receptive composition that is utilized to form the printable information. A variety of such compositions are known in the art, and these compositions generally include a binder and a pigment, such as silica or talc, dispersed in the binder. Optionally, the printable layer comprises a crosslinker CX-100 (DSM’s polyfunctional aziridine liquid crosslinker) . A number of such ink-receptive compositions are described in US Patent No. 6,153,288, the disclosure of which is hereby incorporated by reference. Printable information can be deposited on the facestock layer using various printing techniques, such as screen printing, dot-matrix, ink jet, laser printing, laser marking, thermal transfer, and so on. In some cases, the facestock layer is receptive to thermal transfer printing.

The inks used for printing on the facestock layer may vary widely and may include commercially available water-based, solvent-based or radiation-curable inks. Examples of these inks include Sun Sheen (a product of Sun Chemical identified as an alcohol dilutable polyamide ink) ,

MP (a product of Sun Chemical identified as a solvent-based ink formulated for surface printing acrylic coated substrates, PVDC coated substrates and polyolefin films) , X-Cel (a product of Water Ink Technologies identified as a water-based film ink for printing film substrates) , Uvilith AR-109 Rubine Red (a product of Daw Ink identified as a UV ink) and CLA91598F (a product of Sun Chemical identified as a multibond black solvent-based ink) .

The facestock layer may contain one or more topcoats, which enhances printing performance, durability and/or solvent resistance. In one embodiment, the topcoat layer is configured as having its top surface in contact with the bottom surface of the printable layer in the facestock layer. In one embodiment, the topcoat layer of the label typically comprises a resin. Non-limiting examples of the resins that are suitable for use as topcoat include polyester-amino resin and a phenoxy resin, polyester-isocyanate, polyurethane, and polyacrylate.

In some cases, the facestock layer may be a facestock that utilizes activatable inks, e.g., stimulus-activatable inks, such as (for example) laser-activated, pressure-activated, or temperature-activated inks.

The topcoat layer, in accordance with certain embodiments of the present invention, may be applied onto the facestock portion of the facestock layer by any known techniques in the art, such as spray, roll, brush, or other techniques. The printable layer can be formed by depositing, by gravure printing or the like, on the topcoat layer, with the bottom surface in contact with the top surface of the topcoat layer.

Primer layers

Optionally, the label disclosed herein comprises one or more primer layers and the one or more primer layers may be situated between the facestock layer and the adhesive layer.

Optional Components

In some cases, the PSAs, facestock layer, topcoat layer, or primer layer may optionally include one or more fillers, antioxidants, UV-absorbers, photo-stabilizers, and/or fillers. These additives may be incorporated into the adhesive in conventional quantities using conventional equipment and techniques. For example, representative fillers can include tale, calcium carbonate, organo-clay, glass fibers, marble dust, cement dust, feldspar, silica or glass, fumed silica, silicates, alumina, various phosphorus compounds, ammonium bromide, titanium dioxide, antimony trioxide, antimony trioxide, zinc oxide, zinc borate, barium sulfate, silicones, aluminum silicate, calcium silicate, glass microspheres, chalk, mica, clays, wollastonite, ammonium octamolybdate, intumescent compounds and mixtures of two or more of these materials. The fillers may also carry or contain various surface coatings or treatments, such as silanes, fatty acids, and the like. Still other fillers can include flame-retardant agents, such as the halogenated organic compounds. In certain embodiments, the topcoat layer may include one or more thermoplastic elastomers that are compatible with the other constituents of the layer, such as etherified melamine, hydroxylated polyester, polyester-melamine, and other suitable elastomers.

Liner

In some embodiments, the label further includes a liner deposited on the opposite side of the surface of the reactive adhesive layer that contacts the facestock layer. A releasable liner can be positioned adjacent to the reactive adhesive layer such that the reactive adhesive layer is disposed, or sandwiched, directly or indirectly between the bottom surface of facestock layer and the releasable liner. The releasable liner may function as a protective cover such that the release liner remains in place until the label is ready for attachment to an object. If a liner or release liner is included in the label, a wide array of materials and configurations can be used for the liner. In many embodiments, the liner is a paper or paper-based material. In many other embodiments, the liner is a polymeric film of one or more polymeric materials. Typically, at least one face of the liner is coated with a release material such as a silicone or silicone-based material. As will be appreciated, the release coated face of the liner is placed in contact with the otherwise exposed face of the adhesive layer. Prior to application of the label to a surface of interest, the liner is removed to thereby expose the adhesive face of the label. The liner can be in the form of a single sheet. Alternatively, the liner can be in the form of multiple sections or panels.

The liner used in the label may have a thickness ranging from 20 to 150 micron, e.g., from 30 to 120 micron, from 60 to 100 micron, or from 50 to 90 micron. In terms of upper limits, the thickness of the label is less than 150 micron, e.g., less than 130 micron, or less than 100 micron. In terms of lower limits, the thickness of the label is greater than 20 micron, e.g., greater than 30 micron, or greater than 40 micron.

Various additives can also be added to one or more of the facestock layer, the primer layer, the adhesive layer, or liner layers to obtain a certain desired characteristic. These additives can include, for example, one or more waxes, surfactants, talc, powdered silicates, filler agents, defoamers, colorants, antioxidants, UV stabilizers, luminescents, crosslinkers, buffer agents, anti-blocking agents, wetting agents, matting agents, antistatic agents, acid scavengers, flame retardants, processing aids, extrusion aids, and others.

Peel strength

The PSA of the present invention demonstrates high peel strength. Peel strength is the average force required to remove an adhesive laminated under specified conditions on a substrate, from the substrate at constant speed and at a specified angle. Peel strength evaluations can be performed by testing 180° stainless steel peel for 20 minutes and for 24 hours according to the FINAT Test Method 1 (2017) ( “FINAT-1” ) . When applied on stainless steel, the PSA may demonstrate a peel strength from 2 N/inch to 10 N/inch according to the FINAT-1 method, e.g., from 2 N/inch to 7 N/inch, from 3 N/inch to 9 N/inch, from 5 N/inch to 10 N/inch, and from 7 N/inch to 10 N/inch. In terms of upper limits, the PSA demonstrated a peel strength of less than 10 N/inch, e.g., less than 9 N/inch, or less than 8 N/inch on stainless steel. In terms of lower limits, the PSA demonstrated peel strength of greater than 2 N/inch, greater than 3 N/inch, greater than 5 N/inch on stainless steel.

Removability

As discussed above, the PSA of the present invention demonstrates a high degree of removability. This high degree of removability is believed to be attributed, at least in part, to the presence of the crosslinkers as disclosed above. The inclusion of crosslinkers increases the cohesion properties of the PSA such that the adhesive can be removed from surface of the substrate without leaving residues. The removability properties of the PSA can be typically determined as follows:

· adhere the PSA to the surface of a substrate (e.g., stainless steel) for a period of time, e.g., at least three, at least five, at least ten days to age the PSA at a high temperature and an environment having humidity above 80%. Typically, the temperature ranges from 40 ℃ to 90 ℃; then

· peel the PSA from the surface; then

· visually inspect the surface for any adhesive residue remaining --less residue remaining on the substrate surface indicates a higher removability; then

· assign a numerical value based on the amount of remaining adhesive.

The numerical value may be based on a scale of 1 to 5, with 5 being leaving no residue on the substrate after the label is peeled (e.g., leaving residue on less than 3%of the surface area that has been in contact with the PSA) , 3 leaving a little residue (e.g., leaving residue on less than 20%of the surface area that has been in contact with the PSA) , and 1 leaving a significant amount (e.g., more than 40%) of residue on the substrate. In general, the removability of 4 or 5 is considered acceptable for most applications.

Curing Time

The PSA of the present invention surprisingly and unexpectedly demonstrates high crosslinking efficiency. It is believed that this high crosslinking efficiency is a result of the appropriate amounts and the properties of the one or more crosslinkers used in the PSA. For example, epoxy crosslinker having one or more tertiary amines can significantly improve the curing efficiency. This is often reflected in that, as compared to conventional PSAs, the PSA disclosed herein has a relatively shorter curing time (see above) . In preferred embodiments, when cured at 120 ℃, the curing time of the PSA may range from 0.5 to 5 minutes, e.g., from 0.5 minute to 1 minute, from 1 minute to 2 minutes, from 1 minute to 3 minutes, from 2 minutes to 4 minutes, or from 4 minutes to 5 minutes. In terms of upper ranges, the curing time is less than 7 minutes, less than 6 minutes, less than 5 minutes, or less than 3 minutes. In terms of lower ranges, the curing time is greater than 0.5 minute, greater than 1 minute, greater than 2 minutes, or greater than 3 minutes.

Gel Content

The PSA of the invention also has high gel content as a result of sufficient crosslinking of the polyacrylate base polymer by the crosslinker. Gel content is typically determined by dissolving the adhesive in a suitable solvent for at least one day and separating the solution containing the soluble fraction of the adhesive from the insoluble fraction of the adhesive. The insoluble fraction, i.e., the gel, is dried and weighed against the total dry weight of the adhesive. Gel content in general is positively correlated with the degree of crosslinking, the cohesion strength of the PSA, and the removability of the PSA. In some embodiments, the gel content of the PSA ranges from 40 to 95 wt. %based on the total dry weight of the PSA, e.g., from 45 to 95 wt. %, from 50-90 wt. %, or from 60 to 85 wt. %.

Solvent resistance

The PSA of the present invention demonstrates excellent solvent resistance. This feature is desirable for applications in which the PSAs are in contact with solvents, e.g., water, ethanol, and oil. Solvent resistance may be measured by immersing the PSA in the solvent for an extended period of time, for example at least 60 min, at least 5 hours, or at least 3 days. The appearance and/or properties of PSA before and after the solvent treatment are then assessed and compared. Because solvent typically causes the PSA to appear opaque, accordingly, in one embodiment, the solvent resistance can be measured by optical methods to measure the opacity of the PSA. With good water resistant adhesive, very small increase in opacity is seen with little or no visual differences before and after immersion in water. One of the commonly used methods to assess opacity is a haze test; haze reflects the amount of light scattering when light passes the PSA and it can be used to quantify surface or internal specimen defects that may appear as opaque. The PSA before solvent treatment is generally transparent and therefore the haze value is close to 0. A low haze value of the PSA after treatment denotes low opacity, representing that the PSA is more resistant to the solvent. The haze values of the PSAs can be determined in accordance with ASTM D 1003.

The present PSAs comprising the unique combination and proportions of, among others, the PSA demonstrates a haze value of 0%-15%, e.g., 1%-10%, 2%-8%, 3%-7%, or 4%- 6%. In terms of upper limits, the haze value is less than 15%, less than 12%, less than 10%. In terms of lower limits, the haze value is greater than 0%, greater than 1%, or greater than 2%. The inventors have found that by using polyacrylate base polymer having acid values of 2-90 mg KOH/g and having a Tg above -41 ℃, using epoxy resin at an amount of greater than 0.15 wt. %, and using little or no tackifier can increase the solvent resistance of the PSA. Without being bound by theory, it is believed that good haze values may be attributed, at least in part, to the excellent crosslinking efficiency that is achieved when utilizing the claimed components. Additional contributing factors include high gel content, and the very low amounts of low molecular weight components, such as tackifiers.

Pot life

The PSA of the invention has improved pot life. Pot life refers to the amount of time it takes for the viscosity of an initially mixed composition to double. Pot life is a good indication how fast the PSA cures and also the workability of the PSA. Typically, timing begins from the time the product is mixed, and is measured at working temperature, e.g., room temperature. For commercial production of a PSA, it is important that the pot life be long enough to permit handling of the composition in a manufacturing line but not so long as to slow the manufacturing process. The PSA disclosed herein comprises crosslinkers, e.g., epoxy, at appropriate amounts so that optimal pot life can be obtained. The PSA of the present invention generally has a pot life ranging from 4 hours to 32 hours, e.g., from 4 hours to 8 hours, from 4 hours to 16 hours, from 8 hours to 10 hours, from 8 hours to 16 hours, and from 16 hours to 32 hours. In terms of lower limits, the PSA has a pot life that is greater than 4 hours, e.g., greater than 8 hours, greater than 10 hours, or greater than 15 hours. In terms of upper limits, the PSA has a pot life that is less than 32 hours, e.g., less than 25 hours, less than 20 hours, or greater than 16 hours

Adhesive formulation

This disclosure also provides an adhesive formulation which comprises a solvent, a polyacrylate base polymer, a first crosslinker comprising epoxy, and optionally a second crosslinker comprising isocyanate resin, as disclosed above. Suitable solvents include but are not limited to, toluene and ethyl acetate.

Production of the PSA

The present invention also relates to methods of producing a PSA. The methods include providing a solvent, a first crosslinker comprising an epoxy resin, optionally a second crosslinker, and polyacrylate base polymer having an acid value ranging from 2 to 90 mg KOH/g; and mixing the solvent, the first crosslinker, and the polymer to form an adhesive formulation. Any of the aforementioned embodiments of the polyacrylate base polymer, the first cross-linker, and/or the second crosslinker can be used to produce an adhesive formulation. An exemplary PSA formulation is shown in Table 1. This process is commonly referred to as compounding. The compounding can occur under a temperature less than 50 ℃, e.g., between 20 ℃ and 40 ℃, or between 20 ℃ and 30 ℃, or under any temperature below the triggering temperature for curing.

A variety of solvents can be used to dissolve the components of the PSA. Suitable solvents include those that demonstrate proper evaporation rate and in which the various components show good solubility. In preferred embodiments, the solvent is a petroleum-based solvent. Suitable solvents include but are not limited to, aromatic solvents, aliphatic solvents, ester solvents, xylene, ethyl benzene, isopropyl alcohol, and combinations thereof. Examples of aromatic solvents include aromatic rings with alkyl substitution (e.g. toluene) . Examples of ester solvents include esters of 3 or more carbon atoms (e.g. methyl acetate, or ethyl acetate) . In some embodiments, two or more solvents can be used to dissolve various components above to produce the adhesive formulation.

The amount of solvent (s) used for producing the adhesive formulation may vary depending on the desired viscosity that is suitable for coating on the substrate or other layers. Typically, the solvent is present in the adhesive formulation in an amount ranging from 5 to 50 wt. %, e.g., e.g., from 8 to 45 wt. %, from 10 to 40 wt. %, from 15 to 25 wt. %, e.g., about 17 wt. %. In terms of lower limits, the solvent is present in an amount of greater than 5 wt. %, e.g., greater than 8 wt. %, greater than 10 wt. %, or greater than 12 wt. %, greater than 15 wt. %, or about 17 wt. %, based on the total weight of the adhesive formulation. In terms of upper limits, the solvent is present in an amount of less than 50 wt. %, e.g., less than 40 wt. %, less than 30 wt. %, or less than 20 wt. %, based on the total weight of the adhesive formulation.

Typically, when in storage, the solution containing the polyacrylate base polymer is kept separate from the crosslinkers to prevent undesired crosslinking. The crosslinkers can be added to the solution containing the polyacrylate base polymer immediately prior to the producing of the adhesive and/or the labels. Thus, in some embodiments, the disclosure provides an adhesive system comprising: a polyacrylate base polymer having acid groups and having an acid value ranging from 2 to 90 mg KOH/g, a first crosslinker comprising an epoxy resin; wherein the crosslinker is separate from the polyacrylate base polymer.

The adhesive formulation, as prepared above, has good coatability with a typical viscosity of 100-5,000 cps, e.g., 200-4,000 cps, 300-3,000 cps, 400-2,000 cps, 300-600 cps, or about 500 cps. In terms of lower limits, the viscosity is greater than 100, e.g., greater than 200 cps, greater than 300 cps, or greater than 400 cps. In terms of upper limits, the viscosity is less than 5,000, less than 4,000 cps, less than 2,000 cps, less than 1,000 cps. Methods for measuring viscosity are well known, for example using the Brookfield Viscometer method, testing the flow resistance of the fluid by low and medium rate rotation.

In some embodiments, the adhesive formulation as produced above can then be coated onto a facestock using a solvent coater by knife over roll, slot die, or comma coating. The formulation may be coated to form an adhesive layer having a coat weight of at least 5 grams per square meter (gsm) , e.g., at least 10 gsm or at least 15 gsm. In terms of upper limits, the formulation may be coated to form an adhesive layer having a coat weight of 60 gsm or less, e.g., 50 gsm or less, or 40 gsm or less. In terms of ranges, the formulation may be coated to form an adhesive layer having a coat weight from 5 to 60 gsm, e.g., from 10 to 50 gsm or from 15 to 40 gsm, depending on the end use of the adhesive layer. The facestock/liner coated with the formulation above then can be dried as further described below and processed into labels. In some cases, it is used as a transfer adhesive without being associated with a facestock.

The coating process is typically performed in an oven having multiple temperature zones, e.g., at least 2 zones, at least 3 zones, at least four zones, at least five zones, or at least six zones. The temperature zones may range from 30 to 200 ℃, e.g., from 40 to 150 ℃ or from 60 to 130 ℃. The temperature may increase from the first to last zone, though multiple zones may be at the same temperature.

Once coated, the adhesive may be dried in an oven, for a predetermined drying time. The drying oven can have a temperature of greater than 100 ℃. The rate of solvent evaporation increases with temperature. The drying time can be at least 2 minutes, at least 4 minutes, at least 6 minutes, at least 8 minutes, at least 10 minutes, at least 15 minutes, at least 20 minutes, at least 25 minutes, at least 30 minutes, at least 40 minutes, at least 50 minutes, or at least 1 hour.

In some embodiments, the adhesive can is laminated onto a liner. Suitable liners are described above.

Labeling articles

The present invention also relates to methods of applying a label comprising the PSA to an article and labeled articles. The methods include providing an article defining an outer surface, and a label in accordance with an embodiment. The methods further include affixing the label to the outer surface of the article, thereby applying the label to the article. In some embodiments, the article is a container, a book, or a package that has a cover that the reclosure and repositioning of which is frequently required. The adhesive can be affixed to the cover.

The labels can be affixed to the articles in a batch, continuous, or semi-continuous fashion. Prior to application, one or more liners can be removed from the labels to thereby expose the adhesive face of the labels. The adhesive face and label is then contacted with the container (s) or article (s) and the labels applied thereto. Adhering may also include one or more operations of pressing or otherwise applying a pressing force against the label to promote contact and/or adhesion with the container; activating and/or curing of the adhesive such as by heating and/or exposure to UV light; and/or drying operations.

Adhesive system

Also provided is an adhesive system comprising: a first component comprising a polyacrylate base polymer having acid groups and having an acid value ranging from 2 to 90 mg KOH/g, and a solvent. The first component can be prepared by dissolving the polyacrylate base polymer in the solvent. The system further comprises a second component comprising a first crosslinker comprising an epoxy resin in a solvent. Typically, the first component and the second component are stored separately and only mixed to produce the PSA disclosed above shortly before applying to substrate, e.g., less than 16 hours, less than 8 hours, or less than 4 hours before the application. This prevents premature crosslinking of the polyacrylate polymer and increases workability. The solvent used in the first component may be the same as or different from the solvent used in the second component.

In some embodiments, the second component may further comprise a second crosslinker comprising isocyanate, as described above.

The materials in the first and/or second components of the adhesive system may be present in the amounts such that the PSAs produced have the properties described in this disclosure.

Embodiments

Exemplary embodiments of the invention are as follows:

Embodiment 1: An adhesive composition comprising: a polyacrylate base polymer having an acid value ranging from 2 to 90 mg KOH/g and having a Tg above -41 ℃, a first crosslinker comprising an epoxy resin, wherein the first crosslinker is present in an amount that is greater than 0.15 wt. %based on the total dry weight of the adhesive composition, wherein the adhesive composition comprises less than 6 wt. %tackifier.

Embodiment 2: The adhesive composition of Embodiment 1, wherein the adhesive composition has a haze value of less than 15 %after the adhesive composition is immersed in a solvent for at least 3 days when tested according to a ASTM D1003 test.

Embodiment 3: The adhesive composition of Embodiment 2, wherein the solvent is water or ethanol.

Embodiment 4: The adhesive composition of Embodiment 1, wherein when the adhesive composition is removed from a surface of a substrate that has been in contact with the adhesive, the adhesive leaves residues on less than 3%of the surface area.

Embodiment 5: The adhesive composition of Embodiment 1, wherein the polyacrylate base polymer has an acid value ranging from 4 to 76 mg KOH/mg.

Embodiment 6: The adhesive composition of Embodiment 1, wherein the polyacrylate base polymer has an acid value ranging from 36 to 76 mg KOH/g, wherein the epoxy resin is present in an amount of 0.2 wt. %-0.5 wt. %, and wherein the tackifier is present in an amount of less than 1 wt. %, wherein the haze value of the adhesive is less than 10%after the adhesive composition is immersed in a solvent for at least 3 days when tested according to a ASTM D1003 test.

Embodiment 7: The adhesive composition of Embodiment 1, wherein the polyacrylate base polymer has an acid value ranging from 60 to 76 mg KOH/g, wherein the epoxy resin is present in an amount of 0.2 wt. %-0.5 wt. %, and wherein the tackifier is present in an amount of less than 0.5 wt. %, wherein the haze value of the adhesive is less than 8%after the adhesive composition is immersed in a solvent for at least 3 days when tested according to a ASTM D1003 test, and wherein when the adhesive composition is removed from a surface of a substrate that has been in contact with the adhesive, the adhesive leaves residues on less than 3%of the surface area.

Embodiment 8: The adhesive composition of Embodiment 1, wherein the polyacrylate base polymer has an acid value ranging from 60 to 76 mg KOH/g, wherein the epoxy resin is present in an amount of 0.2 wt. %-0.5 wt. %, wherein the epoxy resin contains one or more tertiary amine groups, wherein the tackifier is present in an amount of less than 0.5 wt. %, wherein the haze value of the adhesive is less than 8%after the adhesive composition is immersed in a solvent for at least 3 days when tested according to a ASTM D1003 test, and wherein when the adhesive is removed from a surface of a substrate that has been in contact with the adhesive, the adhesive leaves residues on less than 3%of the surface area.

Embodiment 9: The adhesive composition of any of the preceding Embodiments, wherein the polyacrylate base polymer has a glass transition temperature (Tg) ranging from -40℃ to -5℃.

Embodiment 10: The adhesive composition of any of the preceding Embodiments, wherein the polyacrylate base polymer is not a block copolymer.

Embodiment 11: The adhesive composition of any of the preceding Embodiments, wherein the polyacrylate base polymer contains alkyl groups that contains between 2 to 14 carbon atoms.

Embodiment 12: The adhesive composition of any of the preceding Embodiments, wherein the average molecular weight of the polyacrylate base polymer ranges from 50000 to 1500000 g/mol.

Embodiment 13: The adhesive composition of any of the preceding Embodiments, wherein the molecular weight distribution index of the polyacrylate polymer ranges from 2 to 8.

Embodiment 14: The adhesive composition of any of the preceding Embodiments, wherein the polyacrylate base polymer does not comprise unsaturated groups.

Embodiment 15: The adhesive composition of any of the preceding Embodiments, wherein the polyacrylate base polymer comprises hydroxyl groups and has a hydroxyl value ranging from 0 to 100 mg KOH/g.

Embodiment 16: The adhesive composition of any of the preceding Embodiments, wherein the adhesive composition comprises 0.10 to 1.0 wt. %of the first crosslinker.

Embodiment 17: The adhesive composition of any of the preceding Embodiments, wherein the epoxy resin of the first crosslinker has an epoxide equivalent weight ranging from 60 to 300 g/eq.

Embodiment 18: The adhesive composition of any of the preceding Embodiments, wherein the epoxy resin of the first crosslinker comprises one or more tertiary amine groups in the chemical structure.

Embodiment 19: The adhesive composition of any of the preceding Embodiments, wherein the epoxy resin of the first crosslinker comprising comprises a one or more tertiary amine group has the chemical structure of selected from the group consisting of

and mixtures thereof.

Embodiment 20: The adhesive composition of any of the preceding Embodiments, wherein the adhesive composition further comprises a second crosslinker comprising an isocyanate resin.

Embodiment 21: The adhesive composition of Embodiment 20, wherein the adhesive composition comprises 0.05 to 0.8 wt. %of the second crosslinker.

Embodiment 22: The adhesive composition of Embodiment 20 or 21, wherein the isocyanate resin has an NCO content ranging from 10 to 30 wt. %.

Embodiment 23: The adhesive composition of any of Embodiments 20 –22, wherein the weight ratio of the first crosslinker to the second crosslinker ranges from 0.6 to 20.

Embodiment 24: The adhesive composition of any of the preceding Embodiments, wherein the weight ratio of the polyacrylate base polymer to the first crosslinker ranges from 100: 0.9 to 100: 0.01 (100: 0.6 to 100: 0.03 is preferred) .

Embodiment 25: The adhesive composition of any of the preceding Embodiments, wherein the adhesive composition has a peel strength from 2 to 10 N/inch on stainless steel according to the FINAT-1 method.

Embodiment 26: The adhesive composition of any of the preceding Embodiments, wherein the adhesive composition has a gel content that ranges from 40 to 95 wt. %.

Embodiment 27: The adhesive composition of any of the preceding Embodiments, wherein the adhesive composition has a pot life above greater than 4 hours.

Embodiment 28: The adhesive composition of any of the preceding Embodiments, wherein the adhesive composition has a curing time ranging from 0.3 to 5 minutes, when cured at 120℃.

Embodiment 29: The adhesive composition of any of the preceding Embodiments, wherein the adhesive is substantially free of natural rubber.

Embodiment 30: A label comprising an adhesive layer comprising the adhesive composition of any of the Embodiments 1 –29.

Embodiment 31: The label of Embodiment 30, further comprising a facestock layer in contact with the adhesive layer.

Embodiment 32: A method of producing an adhesive formulation, comprising: dissolving in a solvent at a temperature of less than 50℃ a) a polyacrylate base polymer, and b) a first crosslinker comprising an epoxy resin that is greater than 0.15 wt. %based on the total dry weight of the adhesive composition, wherein the adhesive formulation contains less than 6 wt. %of tackifier.

Embodiment 33: The method of Embodiment 32, wherein the first crosslinker comprises one or more catalytic units.

Embodiment 34: The method of any of Embodiments 32 to 33, wherein the one or more catalytic units are one or more tertiary amines.

Embodiment 35: The method of Embodiment 32, wherein the first crosslinker ranges from 0.15 wt%to 0.9 wt. %based on the dry weight of the adhesive composition.

Embodiment 36: The method of Embodiment 32 or 35, wherein the epoxy resin of the first crosslinker has an epoxide equivalent weight ranging from 60 to 300 g/eq.

Embodiment 37: The method of any of Embodiments 32 –36, wherein the solvent is selected from the group consisting of toluene, ethyl acetate, Isopropanol, xylene, n-hexane, n-heptane, methyl cyclohexane, butyl acetate, acetone, butanone, and 2-Acetoxy-1-methoxypropane.

Embodiment 38: The method of any of Embodiments 32 –37, further comprising: coating a facestock with the adhesive formulation, and drying the adhesive formulation.

Embodiment 39: The method of any of Embodiments 32 –38, wherein the method further comprise applying a label comprising the adhesive to a substrate.

Embodiment 40: An adhesive system comprising: a first component comprising i) a polyacrylate base polymer having acid groups and having an acid value ranging from 2 to 90 mg KOH/g, ii) a solvent; and a second component comprising a first crosslinker comprising an epoxy resin in a solvent; and wherein the first component is separate from the second component.

Embodiment 41: A labeled container comprising an adhesive composition of any of the Embodiments 1-29.

EXAMPLES

The following examples are offered to illustrate, but not to limit the claimed invention.

Example I: The Effect of Tackifier on Solvent Resistance

An exemplary PSA composition (Ex. 1) is shown in Table 1 below. The PSA composition comprised a polyacrylate base polymer Y-1130 from YASUSA Chemical, epoxy resin GA-240 from CVC (first crosslinker) , isocyanate resin L75 from Covestro (second crosslinker) having a NCO content of 13.3 wt. %based on the total dry weight of the isocyanate resin. The polymer had a Tg of -20 ℃ by rotation rheology analysis. The PSAs were tested for removability, solvent resistance, and peel strength using methods as described above. The results are shown in Table 1.

*Rated on a scale from 1 to 5, where 1 is the worst and 5 is the best. As shown in Table 1, the PSA having polyacrylate base polymer having an acid value of 60 mg KOH/g and hydroxyl value of 10 mg KOH/g, an epoxy crosslinker of 0.35 wt. %, and isocyanate crosslinker of 0.15 wt. %had excellent removability, solvent resistance, as well as good mechanical performance.

Example II: The Effect of Tackifier on Solvent Resistance

Four adhesive compositions were prepared as above. The adhesive compositions comprised Y-1130 from YASUSA Chemical as the polyacrylate base polymer, Y-202 from YASUSA Chemical as an epoxy resin (the first crosslinker) . In some examples, the PSA further comprised L75 as an isocyanate resin (the second crosslinker) . The polyacrylate base polymer had an acid value of 36 mg KOH/g, a hydroxyl value of 3 mg KOH/g, and a Tg of -27℃. Amounts of crosslinkers and tackifiers were varied as shown in Table 2, and polyacrylate base polymer makes up the rest of the PSA.

*Rated on a scale from 1 to 5, where 1 is the worst and 5 is the best.

As shown above, Ex. 2, which comprised 0.4 wt. %epoxy resin but no isocyanate resin, had a low haze value (i.e., high solvent resistance) when exposed to either ethanol or water. In contrast, Comparative Ex. A, which comprised no epoxy resin but 0.5 wt. %isocyanate resin, had a high haze value of 20 (indicating a low solvent resistance) when exposed to ethanol and a low removability of 3. These results show that the use of epoxy resin surprisingly provides for superior results (as compared to isocyanate) in terms of removability and solvent resistance.

In addition, Exs. 3 and 4, had haze values of 5 and 6, respectively, when exposed to ethanol and water. In contrast, Comparative Ex. B comprised 20 wt. %Tackifier and showed significantly higher haze values when exposed to ethanol or water –23 and 20, respectively. These results indicate that the presence of tackifier surprisingly impairs the solvent resistance of the PSA. Adding 5 wt. %tackifier to the PSA (Ex. 4) , although slightly deceased the removability of the PSA and the gel content, the PSA retained good solvent resistance and is still suitable for many applications..

Example III: Effect of Acid Value and Hydroxyl Value on Haze and Removability

Seven (7) adhesive compositions were prepared comprising a polyacrylate base polymer. The amounts of epoxy and/or isocyanate crosslinkers were varied as shown in Table 3. The adhesive compositions contained no tackifiers. The acid value, hydroxyl value of the base polymer are shown in Table 3. The removability and haze value (solvent resistance) were also tested.

*Rated on a scale from 1 to 5, where 1 is the worst and 5 is the best

The results show that in the absence of tackifiers, Exs. 5 –9 showed good solvent resistance as indicated by a haze value of less than 5%, further demonstrating that tackifiers negatively impact the solvent resistance of the PSA.

Also, Comparative Ex. C, which had no acid groups (the acid value being 0) , showed a low gel content of 9%and a low removability of 1. It is speculated that this is due to the fact that the epoxy cannot crosslink polyacrylate base polymer in the absence of the acid groups.

Exs. 5-8 all had an acid value of 76 mgKOH/g and demonstrated excellent removability and high gel content as compared to comparative Ex. C, which indicates that the presence of the acid groups in the polyacrylate base polymer is beneficial. Further, Ex. 5, which had 0.3 wt. %of epoxy resin but no isocyanate resin, had comparable haze value (solvent resistance) but lower removability as compared to Ex. 6, which has an additional crosslinker isocyanate resin at an amount of 0.2 wt. %, indicating when the epoxy resin is at relative low amount, e.g., 0.3 wt. %, the additional isocyanate resin may enhance the removability and increase gel content. Exs. 7 and 8 showed good removability despite the fact that both had a hydroxyl value of 0, indicating that the presence of hydroxyl groups in the polyacrylate polymer, although preferred, is not required to maintain the removability of the PSA.

While the invention has been described in detail, modifications within the spirit and scope of the invention will be readily apparent to those of skill in the art. In view of the foregoing discussion, relevant knowledge in the art and references discussed above in connection with the Background and Detailed Description are all incorporated herein by reference. In addition, it should be understood that aspects of the invention and portions of various embodiments and various features recited above and/or in the appended claims may be combined or interchanged either in whole or in part. In the foregoing descriptions of the various embodiments, those embodiments which refer to another embodiment may be appropriate combined with other embodiments as will be appreciated by one of skill in the art. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention.

Claims

An adhesive composition comprising:

a polyacrylate base polymer having an acid value ranging from 2 to 90 mg KOH/g and having a Tg above -41 ℃,

a first crosslinker comprising an epoxy resin, wherein the first crosslinker is present in an amount that is greater than 0.15 wt.%based on the total dry weight of the adhesive composition,

wherein the adhesive composition comprises less than 6 wt.%tackifier.
The adhesive composition of claim 1, wherein the adhesive composition has a haze value of less than 15 %after the adhesive composition is immersed in a solvent for at least 3 days when tested according to a ASTM D1003 test.
The adhesive composition of claim 2, wherein the solvent is water or ethanol.
The adhesive composition of claim 1, wherein when the adhesive composition is removed from a surface of a substrate that has been in contact with the adhesive, the adhesive leaves residues on less than 3%of the surface area.
The adhesive composition of claim 1, wherein the polyacrylate base polymer has an acid value ranging from 4 to 76 mg KOH/mg.
The adhesive composition of claim 1, wherein the polyacrylate base polymer has an acid value ranging from 36 to 76 mg KOH/g,

wherein the epoxy resin is present in an amount of 0.2 wt.%-0.5 wt.%, and wherein the tackifier is present in an amount of less than 1 wt.%,

wherein the haze value of the adhesive is less than 10%after the adhesive composition is immersed in a solvent for at least 3 days when tested according to a ASTM D1003 test.
The adhesive composition of claim 1, wherein the polyacrylate base polymer has an acid value ranging from 60 to 76 mg KOH/g,

wherein the epoxy resin is present in an amount of 0.2 wt.%-0.5 wt.%, and wherein the tackifier is present in an amount of less than 0.5 wt.%,

wherein the haze value of the adhesive is less than 8%after the adhesive composition is immersed in a solvent for at least 3 days when tested according to a ASTM D1003 test, and

wherein when the adhesive composition is removed from a surface of a substrate that has been in contact with the adhesive, the adhesive leaves residues on less than 3%of the surface area.
The adhesive composition of claim 1,

wherein the polyacrylate base polymer has an acid value ranging from 60 to 76 mg KOH/g,

wherein the epoxy resin is present in an amount of 0.2 wt.%-0.5 wt.%,

wherein the epoxy resin contains one or more tertiary amine groups,

wherein the tackifier is present in an amount of less than 0.5 wt.%,

wherein the haze value of the adhesive is less than 8%after the adhesive composition is immersed in a solvent for at least 3 days when tested according to a ASTM D1003 test, and

wherein when the adhesive is removed from a surface of a substrate that has been in contact with the adhesive, the adhesive leaves residues on less than 3%of the surface area.
The adhesive composition of any of the preceding claims, wherein the polyacrylate base polymer has a glass transition temperature (Tg) ranging from -40℃ to -5℃.
The adhesive composition of any of the preceding claims, wherein the polyacrylate base polymer is not a block copolymer.
The adhesive composition of any of the preceding claims, wherein the polyacrylate base polymer contains alkyl groups that contains between 2 to 14 carbon atoms.
The adhesive composition of any of the preceding claims, wherein the average molecular weight of the polyacrylate base polymer ranges from 50000 to 1500000 g/mol.
The adhesive composition of any of the preceding claims, wherein the molecular weight distribution index of the polyacrylate polymer ranges from 2 to 8.
The adhesive composition of any of the preceding claims, wherein the polyacrylate base polymer does not comprise unsaturated groups.
The adhesive composition of any of the preceding claims, wherein the polyacrylate base polymer comprises hydroxyl groups and has a hydroxyl value ranging from 0 to 100 mg KOH/g.
The adhesive composition of any of the preceding claims, wherein the adhesive composition comprises 0.10 to 1.0 wt.%of the first crosslinker.
The adhesive composition of any of the preceding claims, wherein the epoxy resin of the first crosslinker has an epoxide equivalent weight ranging from 60 to 300 g/eq.
The adhesive composition of any of the preceding claims, wherein the epoxy resin of the first crosslinker comprises one or more tertiary amine groups in the chemical structure.
The adhesive composition of any of the preceding claims, wherein the epoxy resin of the first crosslinker comprising comprises a one or more tertiary amine group has the chemical structure of selected from the group consisting of

and mixtures thereof.
The adhesive composition of any of the preceding claims, wherein the adhesive composition further comprises a second crosslinker comprising an isocyanate resin.
The adhesive composition of claim 20, wherein the adhesive composition comprises 0.05 to 0.8 wt.%of the second crosslinker.
The adhesive composition of claim 20 or 21, wherein the isocyanate resin has an NCO content ranging from 10 to 30 wt.%.
The adhesive composition of any of claims 20–22, wherein the weight ratio of the first crosslinker to the second crosslinker ranges from 0.6 to 20.
The adhesive composition of any of the preceding claims, wherein the weight ratio of the polyacrylate base polymer to the first crosslinker ranges from 100: 0.9 to 100: 0.01 (100: 0.6 to 100: 0.03 is preferred) .
The adhesive composition of any of the preceding claims, wherein the adhesive composition has a peel strength from 2 to 10 N/inch on stainless steel according to the FINAT-1 method.
The adhesive composition of any of the preceding claims, wherein the adhesive composition has a gel content that ranges from 40 to 95 wt.%.
The adhesive composition of any of the preceding claims, wherein the adhesive composition has a pot life above greater than 4 hours.
The adhesive composition of any of the preceding claims, wherein the adhesive composition has a curing time ranging from 0.3 to 5 minutes, when cured at 120℃.
The adhesive composition of any of the preceding claims, wherein the adhesive is substantially free of natural rubber.
A label comprising an adhesive layer comprising the adhesive composition of any of the claims 1–29.
The label of claim 30, further comprising a facestock layer in contact with the adhesive layer.
A method of producing an adhesive formulation, comprising:

dissolving in a solvent at a temperature of less than 50℃

a) a polyacrylate base polymer, and

b) a first crosslinker comprising an epoxy resin that is greater than 0.15 wt.%based on the total dry weight of the adhesive composition,

wherein the adhesive formulation contains less than 6 wt.%of tackifier.
The method of claim 32, wherein the first crosslinker comprises one or more catalytic units.
The method of any of claims 32 to 33, wherein the one or more catalytic units are one or more tertiary amines.
The method of claim 32, wherein the first crosslinker ranges from 0.15 wt%to 0.9 wt.%based on the dry weight of the adhesive composition.
The method of claim 32 or 35, wherein the epoxy resin of the first crosslinker has an epoxide equivalent weight ranging from 60 to 300 g/eq.
The method of any of claims 32–36, wherein the solvent is selected from the group consisting of toluene, ethyl acetate, Isopropanol, xylene, n-hexane, n-heptane, methyl cyclohexane, butyl acetate, acetone, butanone, and 2-Acetoxy-1-methoxypropane.
The method of any of claims 32–37, further comprising:

coating a facestock with the adhesive formulation, and

drying the adhesive formulation.
The method of any of claims 32–38, wherein the method further comprise applying a label comprising the adhesive to a substrate.
An adhesive system comprising:

a first component comprising i) a polyacrylate base polymer having acid groups and having an acid value ranging from 2 to 90 mg KOH/g, ii) a solvent; and

a second component comprising a first crosslinker comprising an epoxy resin in a solvent; and

wherein the first component is separate from the second component.
A labeled container comprising an adhesive composition of any of the claims 1-29.