EP4713408A1

EP4713408A1 - Radiation-stable pressure sensitive adhesives

Info

Publication number: EP4713408A1
Application number: EP24734264.5A
Authority: EP
Inventors: Yasuhiro Kinoshita; Lili QIE; Bret W. Ludwig; Ryoko Kunibu; Jun Fujita; Audrey A. Sherman; Ying Zhang
Original assignee: Solventum Intellectual Properties Co
Current assignee: Solventum Intellectual Properties Co
Priority date: 2023-05-17
Filing date: 2024-05-15
Publication date: 2026-03-25
Also published as: WO2024238668A1; CN121013897A

Abstract

Radiation-stable adhesive articles include a substrate and a layer of an adhesive composition. The adhesive composition is an acrylate-methacrylate co-polymer prepared from a reaction mixture including at least one alkyl acrylate having an alkyl group with at least 4 carbon atoms, and at least one alkyl methacrylate having an alkyl group with at least 4 carbon atoms. The adhesive composition is a pressure sensitive adhesive and is radiation-stable, meaning that the Peel Adhesion to PROTEIN LEATHER is at least 0.5 Newtons/25 millimeters and after exposure to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof, the Peel Adhesion is at least 80% of the Peel Adhesion of the same composition that has not been exposed to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof.

Description

RADIATION-STABLE PRESSURE SENSITIVE ADHESIVES

Summary

Disclosed herein are adhesive compositions and adhesive articles that are radiation-stable. In some embodiments, the adhesive composition comprises an acrylate-methacrylate co-polymer prepared from a reaction mixture comprising at least one alkyl acrylate having an alkyl group comprising at least 4 carbon atoms, and at least one alkyl methacrylate having an alk l group comprising at least 4 carbon atoms. The adhesive composition is a pressure sensitive adhesive and is radiation-stable, where being radiation-stable means that the Peel Adhesion to PROTEIN LEATHER is at least 0.5 Newtons/25 millimeters and after exposure to electron beam radiation of 30-60 KGy, gamma radiation of 30-60 KGy. X-ray radiation of at least 25 KGy, or a combination thereof, the Peel Adhesion to PROTEIN LEATHER is at least 80% of the Peel Adhesion to PROTEIN LEATHER of the same composition that has not been exposed to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof.

Also disclosed are adhesive articles comprising a first substrate with a first major surface and a second major surface, and a first pressure sensitive adhesive layer disposed on the second major surface of the first substrate, where the first pressure sensitive adhesive layer is a layer of the adhesive composition described above.

Detailed Description

The use of adhesive products in the medical industry has long been prevalent and is increasing. However, while adhesives and adhesive articles have shown themselves to be very useful for medical applications, there are also issues in the use of adhesives and adhesive articles. In particular, the desired properties for adhesives are often contradictory. For example, it is desirable that the adhesives have high adhesion to an array of surfaces, including human skin, and yet the adhesive also is desirably removable without damaging the skin. Additionally, medical articles are being worn for longer periods of time, needing to remain adhered and yet need to be removable without damaging the skin or leaving residue.

Medical adhesive-related skin injury (MARSI) has a significant negative impact on patient safety. Skin injury related to medical adhesive usage is a prevalent but under-recognized complication that occurs across all care settings and among all age groups. In addition, treating skin damage is costly in terms of service provision, time, and additional treatments and supplies.

Skin Injury occurs when the superficial layers of the skin are removed along with the medical adhesive product, which not only affects skin integrity but can cause pain and the risk of infection, increase wound size, and delay healing, all of which reduce patients’ quality of life. While the pathophysiology of MARSI is only partially understood. Skin injury results when the skin to adhesive attachment is stronger than skin cell to skin cell attachment. When adhesive strength exceeds the strength of skin cell to skin cell interactions, cohesive failure occurs within the skin cell layer.

Typical medical adhesive articles include an adhesive layer and a substrate layer, where the substrate layer may for example be a tape backing. Other medical adhesive articles have other substrate layers and may include multiples layers, devices, and the like. The intrinsic characteristics of all components of an adhesive article must then be taken into account to address these factors that may lead to MARSI. Properties of the adhesive to be considered include cohesiveness over time and the corresponding adhesion strength, properties of the tape/backing/dressing to be considered include breathability , stretch, conformability', flexibility, and strength.

Among the classes of adhesive materials that have found widespread use as pressure sensitive adhesives are (meth)acrylate-based pressure sensitive adhesives. These materials have many desirable features such as frequently being inherently tacky and thus not requiring the use of added tackifying agents, they are typically formed by free radical polymerization to a high conversion, meaning that little or no un-polymerized monomer is left in the formed pressure sensitive adhesive, and a wide range of monomers can be used to form (meth)acrylate-based copolymers to tailor the desired properties of the pressure sensitive adhesive.

Among the growing use of adhesives and adhesive articles are uses that go beyond the traditional uses of application to wound areas. A wide range of medical articles, such as tapes and drapes, are not applied to the wound area itself but rather play a supporting role to treatment such as holding absorbent materials or medical devices in place on the skin. Examples of medical devices that are held in place with tapes include tubing, catheters, ostomy appliances, sensors, and the like.

However, while adhesives and adhesive articles have shown themselves to be very useful for medical applications, there are also issues in tire use of adhesives and adhesive articles. One developing issue is that many medical adhesive articles are sterilized using radiation such as gamma radiation, electron beam (E-beam) radiation, or X-ray radiation. Each of these sterilization techniques has advantages and disadvantages and each is summarized below.

Gamma radiation is comprised of photons generated bv the decay' of a radioactive rmcieus (cobalt-60 for instance), arid therefore die dose rate is governed by the decay. Photons have no mass and may penetrate deeper into marter, bat no changes cart be made to affect its energy spectrum. As a result, medram- to high-densit • products are ideal for gamma processing.

The exposure of adhesive articles, especially (meth)acrylate-based adhesive articles, to such radiation can have adverse side effects. E-beain, gamma, and X-ray radiation is known to cause the formation of free radicals in such polymeric matrices, and these free radicals form crosslinks within the polymeric matrix. In many instances, this crosslinking adversely affects the adhesive properties of the adhesive articles.

One technique used to offset the crosslinking of adhesive articles when exposed to sterilizing E-beam, gamma, or X-ray radiation is to include additives, such as materials used as tackifying resins, in the polymeric matrix to prevent the crosslinking from occurring. Examples of such materials include rosin hydrides, hydrogenated rosin esters, hydrogenated terpene resins, aliphatic petroleum resins and the like. However, these additives can be problematic in adhesive layers that are attached to mammalian skin since they can cause irritation of the skin and other problems.

Disclosed herein is a methodology for retaining the adhesive properties of adhesive layers upon exposure to sterilizing E-beam, gamma, or X-ray radiation by building an adhesive matrix that is designed to compensate for the crosslinking associated with exposure to radiation.

It has been discovered that the use of a mixhire of acrylate-functional monomers and methacrylate -functional monomers produces a matrix that upon exposure to sterilizing E-beam, gamma, or X-ray radiation not only forms crosslinks but also has chain scission. In this way, the formation of chemical bonds through crosslinking is balanced by the breaking of chemical bonds within the matrix. The result of this balance is that upon exposure to sterilizing E-beam, gamma, or X-ray radiation, rather than forming a highly crosslinked adhesive matrix and thus a matrix with decreased adhesive properties or a non-adhesive matrix, the matrix retains its adhesive properties.

Disclosed herein are adhesive compositions comprising an acrylate-methacrylate copolymer prepared from a reaction mixture comprising at least one alky l acrylate and at least one alkyl methacrylate. The adhesive composition is a pressure sensitive adhesive and is radiationstable. By being radiation-stable it is meant that the Peel Adhesion to PROTEIN LEATHER is at least 0.5 Newtons/25 millimeters and after exposure to electron beam radiation of 30-60 KGy, gamma radiation of 30-60 KGy. at least 25 KGy of X-ray radiation, or a combination thereof, the Peel Adhesion to PROTEIN LEATHER is at least 80% of the Peel Adhesion to PROTEIN LEATHER of the same composition that has not been exposed to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof. Also disclosed are adhesive articles that contain these adhesive compositions.

The term “adhesive” as used herein refers to polymeric compositions useful to adhere together two adherends. Examples of adhesives are pressure sensitive adhesives.

Pressure sensitive adhesive compositions are well known to those of ordinary skill in the art to possess properties including the following: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength to be cleanly removable from the adherend. Materials that have been found to function well as pressure sensitive adhesives are polymers designed and formulated to exhibit the requisite viscoelastic properties resulting in a desired balance of tack, peel adhesion, and shear holding power. Obtaining the proper balance of properties is not a simple process.

The term “(meth)acrylate” refers to monomeric acrylic or methacrylic esters of alcohols. Acrylate and methacrylate monomers or oligomers are referred to collectively herein as "(meth)acrylates”. Materials referred to as "(meth)acrylate functional” are materials that contain one or more (meth)acrylate groups.

The terms "room temperature" and "ambient temperature" are used interchangeably to mean temperatures in the range of 20°C to 25°C.

The terms “Tg” and “glass transition temperahire” are used interchangeably. If measured, Tg values are determined by⁷ DMA (Dynamic Mechanical Analysis) at 1 Hz. unless otherwise indicated. Oftentimes, Tg values for copolymers are not measured but are calculated using the well-known Fox Equation, using the monomer homopolymer Tg values provided by the monomer supplier, as is understood by one of skill in the art.

The term “adjacent” as used herein when referring to two layers means that the tw o layers are in proximity with one another with no intervening open space betw een them. They may be in direct contact with one another (e.g. laminated together) or there may be intervening layers. The terms “polymer” and “macromolecule” are used herein consistent with their common usage in chemistry. Polymers and macromolecules are composed of many repeated subunits. As used herein, the term “macromolecule” is used to describe a group attached to a monomer that has multiple repeating units. The term “polymer” is used to describe the resultant material formed from a polymerization reaction.

The term “alkyl” refers to a monovalent group that is a radical of an alkane, which is a saturated hydrocarbon. The alky l can be linear, branched, cyclic, or combinations thereof and typically has 1 to 20 carbon atoms. In some embodiments, the alkyl group contains 1 to 18, 1 to 12. 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl. isobutyl, tert-butyl, n-pentyl. n-hexyl, cyclohexyl, n-heptyl, n-octyl, and ethylhexyl.

The term “ary l” refers to a monovalent group that is aromatic and carbocyclic. The ary l can have one to five rings that are connected to or fused to the aromatic ring. The other ring structures can be aromatic, non-aromatic, or combinations thereof. Examples of aryl groups include, but are not limited to, phenyl, biphenyl, terphenyl, anthryl, naphthyl, acenaphthyl, anthraquinonyl, phenanthryl, anthracenyl, pyrenyl, perylenyl, and fluorenyl.

The term “alkylene” refers to a divalent group that is a radical of an alkane. The alkylene can be straight-chained, branched, cyclic, or combinations thereof. The alkylene often has 1 to 20 carbon atoms. In some embodiments, the alkylene contains 1 to 18, 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. The radical centers of tire alkylene can be on the same carbon atom (i.e., an alkylidene) or on different carbon atoms.

The term “arylene” refers to a divalent group that is carbocyclic and aromatic. The group has one to five rings that are connected, fused, or combinations thereof. The other rings can be aromatic, non-aromatic, or combinations thereof. In some embodiments, the arylene group has up to 5 rings, up to 4 rings, up to 3 rings, up to 2 rings, or one aromatic ring. For example, the arylene group can be phenylene.

The term “heteroalkylene” refers to a divalent group that includes at least two alkylene groups connected by a thio, oxy, or -NR- where R is alkyl. The heteroalkylene can be linear, branched, cyclic, substituted with alkyl groups, or combinations thereof. Some heteroalkylenes are poloxyyalkylenes where the heteroatom is oxygen such as for example, -CH₂CH₂(OCH₂CH₂)_nOCH₂CH₂-.

The terms “free radically polymerizable” and “ethylenically unsaturated” are used interchangeably and refer to a reactive group which contains a carbon-carbon double bond which is able to be polymerized via a free radical polymerization mechanism. The term “radiation-stable” and “radiation stability” as used herein referring to adhesives means that the adhesive retains at least one adhesive property upon exposure to E-beam radiation, gamma radiation, X-ray radiation or a combination thereof. In many embodiments, the retained adhesive property described is Peel Adhesion to PROTEIN LEATHER, and retention of this property refers to the maintaining of at least 80% of the Peel Adhesion to PROTEIN LEATHER after exposure to radiation when compared to the same composition that has not been exposed to radiation. Other measurement techniques can also be used to determine radiation stability.

Disclosed herein are adhesive compositions. Many of these adhesive compositions are suitable for use in medical applications, especially medical articles. The adhesive compositions comprise an acrylate-methacrylate co-polymer prepared from a reaction mixture comprising at least one alkyl acrylate and at least one alkyl methacrylate. The adhesive composition is a pressure sensitive adhesive and is radiation-stable. By being radiation-stable it is meant that the Peel Adhesion to PROTEIN LEATHER is at least 0.5 Newtons/25 millimeters and after exposure to electron beam radiation of 30-60 KGy, gamma radiation of 30-60 KGy, at least 25 KGy of X- ray radiation, or a combination thereof, the Peel Adhesion to PROTEIN LEATHER is at least 80% of die Peel Adhesion to PROTEIN LEATHER of the same composition that has not been exposed to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof.

The acrylate-methacrylate co-polymer is prepared from a reaction mixture comprising at least one alkyl acrylate of Fonnula 1 :

CH₂=CR¹-(CO)-OR²

Formula 1 where R¹ is hydrogen; -(CO)- is a carbonyl group C=O, and R² is an alkyl group comprising at least 4 carbon atoms, and at least one alkyl methacrylate of Formula 2:

CH₂=CR³-(CO)-OR⁴

Formula 2 where R³ is a methyl group, -(CO)- is a carbonyl group C=O, and R⁴is an alkyl group comprising at least 4 carbon atoms.

A wide range of acrylates are suitable as the at least one alkyl acrylate of Formula 1. Typically, the alkyl acrylates have alkyl groups with at least 4 carbon atoms. Mixtures of alkyl acrylates are also suitable. Examples of suitable alkyl acrylates include butyl acrylate, isobutyl acrylate, pentyl acrylate, 2-ctliylliye.xyl acrylate, iso-octyl acrylate, n-octyl acrylate, isononyl acrylate, n-nonyl acrylate, isoamyl acrylate, n-decyl (meth)acrylate. isodecyl acrylate, dodecyl acrylate, isobomyl acry late, cyclohexyl acrylate, isostearyl acrylate, 2-methylbutyl acrylate, and combinations thereof. In some embodiments, the at least one alkyl acrylate of Formula 1 comprises at least one alkyl acrylate of Formula 1 where R² is an alkyl group with at least 8 carbon atoms. The composition may additionally include other alkyl acrylates.

In some embodiments, the at least one alkyl acrylate of Formula 1 comprises at least one alkyl acrylate of Formula 1 where R² is an alkyl group with at least 12 carbon atoms. The composition may additionally include other alkyl acrylates.

A wide range of methacry lates are suitable as the at least one alkyl methacrylate of Formula 2. In some embodiments, the at least one methacrylate monomer comprises n-butyl methacrylate, iso-butyl methacrylate, tert -butyl methacrylate, lauryl methacrylate. 2-ethylhexyl methacrylate, n-stearyl methacrylate, iso-stearyl methacrylate, isodecyl methacrylate, or a combination thereof.

In some embodiments, it may be desirable to choose methacrylate monomers that have a relatively low Tg. Relatively low Tg in this context means monomers selected to give the formed copolymer a Tg of less than 0°C. In some embodiments, the copolymer Tg may be less than - 10°C, or even less than -15°C. Having methacry late monomers with a relatively low Tg helps the adhesive composition to adhere quickly and strongly to substrates such as mammalian skin. hi some embodiments, the at least one alkyl methacrylate monomer comprises a mixture of methacrylate monomers, the mixture comprising up to 30% by weight of tert-butyl methacrylate and at least one additional methacrylate monomer of Formula 2.

As mentioned above, the application of radiation to the adhesive composition causes the formation of chemical bonds through crosslinking, but this crosslinking is balanced by the breaking of chemical bonds within the matrix. This balance is achieved through a reaction mixture that contains both acrylate and methacrylate monomers. The reaction mixture can comprise a wide range of compositional mixtures. In some embodiments, the reaction mixture comprises at least 10 mol% of methacrylate monomers. In other embodiments, the reaction mixture comprises at least 20 mol% of methacrylate monomers. In still other embodiments, the reaction mixture comprises at least 40 mol% of methacrylate monomers.

The adhesive composition can optionally contain one or more additional components. In some embodiments, the reaction mixture further comprises at least one co-polymerizable monomer. In some embodiments, the co-polymerizable monomer may⁷ be a crosslinking monomer. Particularly suitable are photocrosslinkers. Photocrosslinkers have a free radically polymerizable group to co-polymerize with the monomers described above, and also contain a photosensitive group. Upon exposure to the right wavelength of light, typically high intensity ultra-violet (UV) radiation, the photosensitive group forms free radicals which can form crosslinks in the polymer. Suitable photocrosslinkers in the mono-ethylenically unsaturated aromatic ketone comonomers that are free of ortho-aromatic hydroxyl groups such as those described in US Patent No. 4,737,559 (Kellen et al.). Specific examples include para-acryloxybenzophenone (ABP), para-acryly oxy ethoxy benzophenone. para-N-(methylacryloxyethyl)- carbamoylethoxybenzophenone, para-acryloxyacetophenone, ortho-acrylamidoacetophenone, acrylated anthraquinones, and the like. Particularly suitable are ABP para-acryloxybenzophenone and AeBP Acryloxy Ethyl Benzophenone.

The radiation stability' of the adhesive compositions of this disclosure can be determined in a variety' of ways. As mentioned above, the stability of the peel adhesion to PROTEIN LEATHER is one indicator that the adhesive compositions have radiation stability. In some embodiments, radiation stability' can be measured by DMA (Dynamic Mechanical Analysis). Some embodiments of the adhesive composition have a stable tan delta value at a temperature of 160°C greater than the Tg of the adhesive composition. By stable, it is meant that the tan delta value after exposure to 30-60 KGy of electron beam radiation, 30-60 KGy of gamma radiation, at least 25 KGy of X-ray radiation or a combination thereof, is at least 80% of the tan delta value of the same composition that has not been exposed to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof. Tan delta is the ratio of the storage modulus (G”) to the loss modulus (G‘) as measured by DMA and Tg is likewise measured by DMA, at 1 Hz. A wide range of embodiments have this tan delta property, especially the embodiments that comprise at least 40 mol% of methacrylate monomers.

The adhesive composition may additionally comprise non-reactive additives to modify the properties of the adhesive composition as long as the additives do not adversely affect the adhesive properties or the radiation stability properties of the adhesive compositions. In some embodiments, the adhesive composition further comprises at least one additive selected from a plasticizer or a liquid resin. Examples of suitable plasticizers include IOP (Isooctyl palmitate) from Nikko, RHEODOL MO-60 (Glycerol monool eate) from Kao Chemical, and KEYDOL (Liquid Paraffin) from Sonneborn. Examples of suitable liquid resins include ESTERGUM HT (hydrogenated rosin ester) from Arakawa Chemical. ESTERGUM AT (rosin ester) from Arakawa Chemical, YS RESIN CP (hydrogenated rosin ester) from Yasuhara Chemical, and DIMERONE (mixture of terpene polymer and petroleum hydrocarbon) from Yasuhara Chemical. Polyols may also be suitable, especially the polyester polyols available under the tradename PRIPLAST from Croda.

Also disclosed herein are adhesive articles. In some embodiments, the adhesive article comprises a first substrate with a first major surface and a second major surface, and a first pressure sensitive adhesive layer disposed on the second major surface of the first substrate. The first pressure sensitive adhesive layer comprises an adhesive composition prepared from a reaction mixture as described above. In some embodiments, the reaction mixture comprises at least one alkyl acrylate of Formula 1 :

CH₂=CR¹-(CO)-OR²

Formula 1 where R¹ is hydrogen, -(CO)- is a carbonyl group C=O. and R² is an alkyl group comprising at least 4 carbon atoms; and at least one alkyl methacrylate of Formula 2:

CH_:=CR³-(CO)-OR⁴

Formula 2 where R³ is a methyl group. -(CO)- is a carbonyl group C=O, and R⁴ is an alkyl group comprising at least 4 carbon atoms. As described above, the adhesive composition is a pressure sensitive adhesive and is radiation-stable, wherein being radiation-stable means that the Peel Adhesion to PROTEIN LEATHER is at least 0.5 Newtons/25 millimeters and after exposure to electron beam radiation of 30-60 KGy, gamma radiation of 30-60 KGy, at least 25 KGy of X-ray radiation, or a combination thereof, the Peel Adhesion to PROTEIN LEATHER is at least 80% of the Peel Adhesion to PROTEIN LEATHER of the same composition that has not been exposed to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof.

A wide variety of substrates are suitable. In some embodiments. The substrate comprises a release liner or a tape backing. Release liners are well known in the adhesive arts and are films from which adhesive compositions or coatings can be readily removed. Exemplary release liners include those prepared from paper (e.g., Kraft paper) or polymeric material (e.g., polyolefins such as polyethylene or polypropylene, ethylene vinyl acetate, polyurethanes, polyesters such as polyethylene terephthalate, and the like, and combinations thereol). At least some release liners are coated with a layer of a release agent such as a fluorosilicone-containing material or a fluorocarbon-containing material.

In some embodiments, the release liner may be a microstructured release liner. Microstructured release liners are well-known in the adhesive arts. Typically, microstructured release liners are prepared by embossing a release liner with an embossable surface to a structured tool to impart a structured surface to the release liner. The microstructured release liner imparts a microstructured surface to the adhesive layer to which it is disposed.

Examples of suitable tape backings include a polymeric film, a foil, a fabric, a non-woven, a foam, a paper, a mesh, or a combination thereof. In many embodiments, the backing is conformable to contour surfaces. As such, when the backing is applied to a contour surface, it conforms to the surface even when the surface is moved. Examples of such backings can be found in US Patent Nos. 5,088,483 and 5.160,315, and include elastomeric polyurethane, polyester, or polyether block amide films. These films have a combination of desirable properties including resiliency, high moisture vapor permeability, and transparency.

In some embodiments, the tape backing is optically transparent and comprises polyester, polycarbonate, PS (polystyrene), CBC (cyclic block copolymers), polyolefin, including but not limited to BOPP (biaxially oriented polypropylene, COP (cyclic olefin polymer), COC (cyclic olefin copolymer), polypentene, or a combination thereof.

In some embodiments, the adhesive article further comprises a second pressure sensitive adhesive layer disposed on the first major surface of the first substrate, where die second pressure sensitive adhesive layer is the same as the first pressure sensitive adhesive layer or different from the first pressure sensitive adhesive layer. Such articles are double-sided tapes.

The reaction mixtures suitable for forming the pressure sensitive adhesive layers, the pressure sensitive adhesive compositions, and the components of the reaction mixtures are described in detail above.

The pressure sensitive adhesive layers can have a wide range of thicknesses. Generally, the pressure sensitive adhesive layers have a thickness of from 10 micrometers to 1 millimeter.

Examples

These examples are merely for illustrative purposes only and are not meant to be limiting on the scope of the appended claims. All parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight, unless noted otherwise. The following abbreviations are used: cm = centimeters; mm = millimeters: in = inch; RPM = revolutions per minute; kg = kilograms; kGy = kiloGrays; keV = kiloelectron Volts: Hz = Hertz: sec = seconds; min = minutes; hrs = hours. The terms “weight %”, “% by weight”, and “wt%” are used interchangeably.

Table of Abbreviations Test Methods

Rheology Testing

Tangent delta retention

A PSA sample with 8mm diameter and 1mm thickness was prepared, and rheology data before and after E-Beam or Gamma treatment was measured using a Rheometer MCR302 (Anton Parr) or ARES-G2 (TA Instrument). A temperature ramp (-50° C. to 180° C) test method was used with oscillatory shear (frequency=l Hz), and tan delta at a temperature of 160°C greater than the Tg (peak temperature of tan delta curve).

Calculation formula:

Tan delta retention = Tan delta at a temperature of 160°C greater than the Tg after treatment / Tan delta at a temperature of 160°C greater than the Tg before treatment xl00%

Adhesive Testing

Adhesion retention

25mm x 75mm size tape sample was laminated on 30mm x 100mm size Protein Leather by using a 2kg roller. The applied tape was removed with T-peel at 90 inch/min (230 cm/min) test speed by using SP-2100 (IMASS). The average peel force was measured before and after E-Beam or Gamma treatment. The calculation formula of adhesion retention is as follows:

Calculation formula:

Adhesion retention = Adhesion after treatment / Adhesion before treatment xl00%

Electron beam treatment

Samples were treated with E-Beam having an acceleration voltage of 200keV and a 60kGy dose.

Gamma ray treatment

Samples were treated with Gamma radiation having with a 30 or 60kGy dose.

Study 1 Examples

Examples 1-3

Radiation stable adhesive layers were prepared according to the composition descriptions given below and tested according to the procedures given above and the data are presented in the tables below. Polymer formation

Adhesive compositions were prepared by preparing the Reaction Mixtures shown in Table 1 below and labeled as Compositions 1-3. The reaction components and 119 parts by weight of water were put in a bottle and homogenized at 15,000 rpm for 15 min. The dispersion and 0.2 part of initiator- 1 were put in a glass jar. After nitrogen purging for 10 min, polymerization was carried out at 65°C for 20 hrs, and a copolymer emulsion with 45% solids was prepared.

Thickener was added to the copolymer emulsion and the pH was adjusted to 7 to 8 with NH₃ aq to obtain a viscous emulsion.

The viscous emulsion was coated on the TSC surface of Liner- 1. After drying in an oven (60°C for 7 min and 120°C for 2 min), the formed PSA layer with a thickness of 3 mil (76 micrometers) was covered by Liner -2.

Table 1

Adhesive Tape Formation

Adhesive tape samples were prepared by removing Liner-2 and laminating Backing-1 by using a heat laminator after corona treatment on the adhesive surface.

The adhesive samples were tested using the rheology test method described above and the tape samples were tested using the adhesion test methods described above. The adhesive samples and tape samples were exposed to E-beam radiation according to the treatment procedure described above and tested according to the methods described above. The data are present in Tables 2 and 3. Example numbers correspond to Composition numbers in Table 1.

Table 2 Table 3

Study 2 Examples

Examples 4-26

Radiation stable adhesive layers were prepared according to the composition descriptions given below and tested according to the procedures given above and the data are presented in the tables below.

Polymer formation

Adhesive compositions were prepared by preparing the Reaction Mixtures shown in Tables 4-7 below and labeled as Compositions 4-26. The reaction components were put in a bottle. Solvent was 100 parts by weight toluene for Compositions 4-17 and 100 parts by weight EtOAC for the remaining compositions. -After nitrogen purging of the solution for 2 min, polymerization was carried out at 70°C for 20 hours, and a viscous polymer solution was prepared. Depending on the formulation, additives were mixed, and viscous coating solutions were obtained.

The viscous coating solutions were coated on the TSC surface of Liner-1 . After drying in an oven (60°C for 2 min and 120°C for 2 min), the formed polymer layer with a thickness of 80 micrometers was prepared. The polymer layer was exposed to 200mJ/cm2 UV-C and the polymer layer was then covered by Liner-2.

Table 4

Table 5

Table 6

5 Table 7

Adhesive Tape Formation

The adhesive samples were tested using the rheology test method described above and the tape samples were tested using the adhesion test methods described above. The adhesive samples and tape samples were exposed to E-beam or gamma radiation according to the treatment procedure described above and tested according to the methods described above. The data are presented in Tables 8-12. Example numbers correspond to Composition numbers in Tables 4-7.

Table 8 Table 9

Table 10 Table 11

Table 12

Claims

What is claimed is:

1. An adhesive composition comprising: an aery late -methacrylate co-polymer prepared from a reaction mixture comprising: at least one alkyl acrylate of Formula 1.

CH₂=CR¹-(CO)-OR²

Formula 1 wherein R¹ is hydrogen;

-(CO)- is a carbonyl group C=O; and

R² is an alkyl group comprising at least 4 carbon atoms; and at least one alkyl methacrylate of Formula 2

CH_:=CR³-(CO)-OR⁴

Formula 2 wherein R³ is a methyl group;

-(CO)- is a carbonyl group C=O; and

R⁴ is an alkyd group comprising at least 4 carbon atoms, wherein the adhesive composition is a pressure sensitive adhesive and is radiation-stable, wherein being radiation-stable means that the Peel Adhesion to PROTEIN LEATHER is at least 0.5 Newtons/25 millimeters and after exposure to electron beam radiation of 30-60 KGy, gamma radiation of 30-60 KGy, at least 25 KGy of X-ray radiation, or a combination thereof, the Peel Adhesion to PROTEIN LEATHER is at least 80% of the Peel Adhesion to PROTEIN LEATHER of the same composition that has not been exposed to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof.

2. The adhesive composition of claim 1, wherein the at least one alky l acrylate comprises butyl acrylate, isobutyl acrylate, pentyd acrylate, 2-ethylhyexy 1 acry late, iso-octyl acrylate, n-octyl acrylate, isononyl acrylate, n-nonyl acrylate, isoamyl acrylate, n-decyl (meth)acrydate, isodecyl acrylate, dodecyl acrylate, isobomyl acrylate, cyclohexyl acrylate, isostearyl acrylate, 2- methylbuty 1 acrylate, isodecyl acrylate, and combinations thereof.

3. The adhesive composition of claim 1. wherein the at least one alkyl acry late comprises at least one alkyl acrylate monomer of Formula 1, wherein R² is an alkyl group with at least 8 carbon atoms.

4. The adhesive composition of claim 1. wherein the reaction mixture comprises at least 10 mol% of the at least one methacrylate monomer.

5. The adhesive composition of claim 1. wherein the reaction mixture comprises at least 20 mol% of the at least one methacrylate monomer.

6. The adhesive composition of claim 1, wherein the reaction mixture further comprises at least one co-polymerizable monomer.

7. The adhesive composition of claim 1, wherein being radiation-stable further comprises meaning that the tan delta value which is the ratio of the storage modulus (G”) to the loss modulus (G’) as measured by DMA (Dynamic Mechanical Analysis) at a temperature of 160°C greater than the Tg of the adhesive composition where Tg is measured by DMA, at 1 Hz after exposure to 30-60 KGy of electron beam radiation, 30-60 KGy of gamma radiation, at least 25 KGy of X-ray radiation, or a combination thereof, is at least 80% of the tan delta value of the same composition that has not been exposed to electron beam radiation, gamma radiation, X-ray radiation or a combination thereof.

8. Tire adhesive composition of claim 7, wherein the reaction mixture comprises at least 40 mol% of the at least one methacrylate monomer.

9. The adhesive composition of claim 1, wherein the at least one methacrylate monomer comprises n-butyl methacrylate, iso-butyl methacrylate, tert-butyl methacrylate, lauryl methacrylate. 2-ethylhexyl methacrylate, n-stearyl methacrylate, iso-stearyl methacrylate, or a combination thereof.

10. The adhesive composition of claim 8, wherein the at least one methacrylate monomer comprises a mixture of methacrylate monomers, wherein the mixture comprises up to 30% by weight of tert-butyl methacrylate and at least one additional methacrylate monomer of Formula 2:

CH₂=CR³-(CO)-OR⁴

Formula 2 wherein R³ is a methyl group;

-(CO)- is a carbonyl group C=O; and

R⁴is an alkyl group comprising 8-12 carbon atoms.

11. The adhesive composition of claim 1, further comprising at least one additive selected from a plasticizer or a liquid resin.

12. An adhesive article comprising: a first substrate with a first major surface and a second major surface; and a first pressure sensitive adhesive layer disposed on the second major surface of the first substrate, the first pressure sensitive adhesive layer comprising an adhesive composition prepared from a reaction mixture comprising: at least one alkyl acrylate of Formula 1,

CH_;=CR^I-(CO)-OR^:

Formula 1 wherein R¹ is hydrogen;

-(CO)- is a carbonyl group C=O; and

R² is an alky l group comprising at least 4 carbon atoms; and at least one alkyd methacrylate of Formula 2

CH₂=CR³-(CO)-OR⁴

Formula 2 wherein R³ is a methyl group;

-(CO)- is a carbonyl group C=O; and

R⁴ is an alky 1 group comprising at least 4 carbon atoms, wherein the adhesive composition is a pressure sensitive adhesive and is radiation-stable, wherein being radiation-stable means that the Peel Adhesion to PROTEIN LEATHER is at least 0.5 Newtons/25 millimeters and after exposure to electron beam radiation of 30-60 KGy, gamma radiation of 30-60 KGy, at least 25 KGy of X-ray radiation, or a combination thereof, the Peel Adhesion to PROTEIN LEATHER is at least 80% of the Peel Adhesion to PROTEIN LEATHER of the same composition that has not been exposed to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof.

13. The adhesive article of claim 12, wherein the substrate comprises a release liner or a tape backing.

14. The adhesive article of claim 12. further comprising a second pressure sensitive adhesive layer disposed on the first major surface of the first substrate, wherein the second pressure sensitive adhesive layer is the same as the first pressure sensitive adhesive layer or different from the first pressure sensitive adhesive layer.

15. The adhesive article of claim 12, wherein the reaction mixture comprises at least 10 mol% of the at least one methacrylate monomer.

16. The adhesive article of claim 12, wherein the reaction mixture further comprises at least one co-polymerizable monomer.

17. The adhesive article of claim 12. wherein being radiation-stable further comprises meaning that the tan delta value which is the ratio of the storage modulus (G”) to the loss modulus (G’) as measured by DMA (Dynamic Mechanical Analysis) at a temperature of 160°C greater than the Tg of the adhesive composition where Tg is measured by DMA, at 1 Hz after exposure to 30-60 KGy of electron beam radiation, 30-60 KGy of gamma radiation, at least 25 KGy of X-ray radiation, or a combination thereof, is at least 80% of the tan delta value of the same composition that has not been exposed to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof.

18. The adhesive article of claim 12, wherein the reaction mixture comprises at least 40 mol% of the at least one methacrylate monomer.

19. The adhesive article of claim 17, wherein the at least one methacrylate monomer comprises n- butyl methacrylate, iso-butyl methacrylate, tert-butyl methacrylate, lauryl methacrylate. 2- ethylhexyl methacrylate, n-stearyl methacrylate, iso-stearyl methacrylate, or a combination thereof.

20. The adhesive article of claim 19, wherein the at least one methacrylate monomer comprises a mixture of methacrylate monomers, wherein the mixture comprises up to 30% by weight of tertbutyl methacrylate and at least one additional methacrylate monomer of Formula 2:

CH₂=CR³-(CO)-OR⁴

Formula 2 wherein R³ is a methyl group;

-(CO)- is a carbonyl group C=O; and

R⁴is an alkyl group comprising 8-12 carbon atoms.