Radiation stable pressure sensitive adhesive

Abstract

A radiation stable adhesive article includes a substrate and an adhesive composition layer. The adhesive composition is an acrylate-methacrylate copolymer prepared from a reaction mixture comprising at least one alkyl acrylate having an alkyl group having at least 4 carbon atoms and at least one alkyl methacrylate having an alkyl group having 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 Newton / 25 mm, and after being subjected to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof, the peel adhesion to protein leather is at least 0.5 Newton / 25 mm. The peel adhesion is at least 80% of the peel adhesion of the same composition that is not subjected to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof.

Description

SUMMARY

[0001] Disclosed herein are radiation-stable adhesive compositions and adhesive articles. In some embodiments, the adhesive composition comprises an acrylate-methacrylate copolymer 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 alkyl group comprising at least 4 carbon atoms. The adhesive composition is a pressure sensitive adhesive and is radiation stable, where radiation stable means that the peel adhesion to protein leather is at least 0.5 Newtons per 25 millimeters and after being subjected to 30 KGy - 60 KGy of electron beam radiation, 30 KGy - 60 KGy of gamma radiation, 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 subjected to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof.

[0002] Also disclosed are adhesive articles comprising a first substrate having 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, wherein the first pressure sensitive adhesive layer is a layer of the adhesive composition described above. DETAILED DESCRIPTION

[0003] The use of adhesive products in the medical industry is long-standing and increasing. However, while adhesives and adhesive articles have shown themselves to be very useful for medical applications, there are also problems with the use of adhesives and adhesive articles. In particular, desirable adhesive properties are often contradictory. For example, it is desirable for an adhesive to have high adhesion to an array of surfaces, including human skin, and it is also desirable for the adhesive to be removable without damaging the skin. In addition, medical articles are being worn for longer periods of time, require to remain adhered, and also need to be removable without damaging the skin or leaving residue.

[0004] Skin damage associated with medical adhesives (MARSI) has a significant negative impact on patient safety. Skin damage associated with medical adhesive use is a common but under-recognized complication that occurs in all care settings and in all age groups. In addition, treating skin damage is costly in terms of service provision, time, and additional treatment and supplies.

[0005] Skin damage occurs when the surface layers of the skin are removed with a medical adhesive product, which not only affects the integrity of the skin, but can also cause pain and the risk of infection, increase wound size, and delay healing, all of which reduce the patient's quality of life.

[0006] However, the pathophysiology of MARSI is only partially understood. Skin damage occurs when the attachment of the skin to the adhesive is stronger than the attachment of skin cell to skin cell. Cohesive failure occurs within the skin cell layer when the adhesive strength exceeds the strength of the skin cell to skin cell interaction.

[0007] Typical medical adhesive articles include an adhesive layer and a substrate layer, which can be, for example, a tape backing. Other medical adhesive articles have other substrate layers and can include multiple layers, devices, and the like. The inherent characteristics of all components of the adhesive article must then be considered to address these factors that can lead to MARSI. The properties of the adhesive to be considered include tack and corresponding adhesive strength over time, the properties of the tape / backing / dressing to be considered include breathability, stretch, conformability, flexibility, and strength.

[0008] A class of adhesive materials that has been used extensively as pressure sensitive adhesives is (meth)acrylate-based pressure sensitive adhesives. These materials have a number of desirable characteristics, such as often being inherently tacky and thus not requiring the use of added tackifiers, they are typically formed by free radical polymerization to high conversion, meaning that little or no un-polymerized monomer is left in the formed pressure sensitive adhesive, and a wide variety of monomers can be used to form (meth)acrylate-based copolymers to tailor the desired properties of the pressure sensitive adhesive.

[0009] The use of adhesives and adhesive articles is growing, with uses beyond the traditional use of applying to a wound area. A wide variety of medical articles, such as tapes and drape, are not applied to the wound area itself, but rather serve an ancillary therapeutic role, such as holding an absorbent material or medical device in place on the skin. Examples of medical devices held in place with tape include tubing, catheters, ostomy appliances, sensors, and the like.

[0010] However, while adhesives and adhesive articles have shown themselves to be very useful for medical applications, there are also problems with the use of adhesives and adhesive articles. One developing problem is that many medical adhesive articles use radiation, such as gamma radiation, electron beam (E-beam) radiation, or X-ray radiation, for sterilization. Each of these sterilization techniques has advantages and disadvantages, and are summarized as follows.

[0011] Gamma radiation consists of photons produced by the decay of a radioactive nucleus (e.g., cobalt-60), so the dose rate is determined by the decay. Photons have no mass and can penetrate deeper into a material, but cannot be altered to affect their energy spectrum. Therefore, products of medium to high density are ideal for gamma processing.

[0012] Electron beam radiation refers to high-energy electrons generated by a machine. Since electrons have mass, penetration is limited by energy. This makes the use of electron beam technology very useful for low to medium density products and more favorable to box processing relative to the entire pallet. Moreover, given the nature of the technology, electron beams are well suited for sensitive products since the dose can be delivered significantly faster than gamma or x-rays - we are talking seconds or minutes instead of hours. Then, since the lifetime to occur a reaction is reduced by several orders of magnitude, the deleterious effects are also reduced.

[0013] Industrial x-rays are generated via the use of an electron beam accelerator coupled with a metal target. When electrons hit the metal target, x-rays are generated. X-rays are also composed of photons (but with different energies than gamma), so x-rays can also be well suited for medium to high density products. The dose rate is also higher than gamma since they are also machine powered, but limited or slower compared to electron beams. For example, to deliver a standard sterilization dose of 25 kGy, it would take about 2.5 hours or more of treatment time using gamma radiation, as opposed to 45 minutes to an hour using x-rays, and seconds to minutes using electron beam technology.

[0014] Exposing adhesive articles, especially (meth)acrylate-based adhesive articles, to such radiation can have adverse side effects. Electron beam, gamma, and X-ray radiation are known to induce the formation of free radicals in such polymer matrices, and these free radicals form crosslinked moieties within the polymer matrix. In many cases, this crosslinking adversely affects the adhesive properties of the adhesive article.

[0015] One technique for countering the crosslinking of adhesive articles when subjected to sterilizing electron beam, gamma, or X-ray radiation is to include additives in the polymer matrix, such as materials used as tackifying resins, to prevent crosslinking from occurring. Examples of such materials include rosin hydride, hydrogenated rosin ester, hydrogenated terpene resin, aliphatic petroleum resin, and the like. However, these additives can be problematic in adhesive layers that are attached to mammalian skin, as they can cause skin irritation and other issues.

[0016] Disclosed herein is a method of preserving the adhesive properties of an adhesive layer when subjected to sterilizing electron beam, gamma, or X-ray radiation by constructing an adhesive matrix designed to compensate for the crosslinking associated with being subjected to radiation.

[0017] It has been discovered that using a mixture of acrylate and methacrylate functional monomers produces a matrix that, upon exposure to sterilizing electron beams, gamma rays, or X-rays, not only forms cross-linked portions but also exhibits chain scission. In this way, the formation of chemical bonds through cross-linking is balanced by the disruption of chemical bonds within the matrix. As a result of this balance, upon exposure to sterilizing electron beams, gamma rays, or X-rays, instead of forming a highly cross-linked adhesive matrix and thus a matrix with reduced adhesive properties or a non-adhesive matrix, the matrix retains its adhesive properties.

[0018] This document discloses adhesive compositions comprising an acrylate-methacrylate copolymer prepared from a reaction mixture comprising at least one alkyl acrylate and at least one alkyl methacrylate. The adhesive compositions are pressure-sensitive adhesives and are radiation-stable. Radiation stability means that the peel adhesion to protein leather is at least 0.5 N / 25 mm, and that after exposure to 30 KGy-60 KGy of electron beam radiation, 30 KGy-60 KGy of gamma radiation, 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 of the same composition to protein leather without exposure to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof. Adhesive articles containing these adhesive compositions are also disclosed.

[0019] As used herein, the term "adhesive" refers to a polymer composition that can be used to attach two adhesives together. An example of an adhesive is a pressure-sensitive adhesive.

[0020] Pressure-sensitive adhesive compositions are well known to those skilled in the art and possess properties including: (1) strong and durable tack; (2) adhesion not exceeding finger pressure; (3) sufficient ability to hold onto the adhesive; and (4) sufficient bond strength for clean removal from the adhesive. Materials that have been found to function well as pressure-sensitive adhesives are polymers designed and formulated to exhibit the necessary viscoelastic properties, achieving a desired balance between tack, peel adhesion, and shear retention. Achieving this proper balance of properties is not a simple process.

[0021] The term "(meth)acrylate" refers to the monomeric acrylate or methacrylate of an alcohol. Acrylates and methacrylate monomers or oligomers are collectively referred to herein as "(meth)acrylate". Materials described as "(meth)acrylate functional" are materials containing one or more (meth)acrylate groups.

[0022] The terms “room temperature” and “ambient temperature” are used interchangeably to refer to temperatures in the range of 20°C to 25°C.

[0023] The terms "Tg" and "glass transition temperature" are used interchangeably. In the case of the measurement, unless otherwise specified, the Tg value is determined by DMA (Dynamic Mechanical Analysis) at 1 Hz. Typically, the Tg value of the copolymer is not measured, but rather calculated using the well-known Fox formula with the Tg values ​​of the monomer homopolymer provided by the monomer supplier, as understood by those skilled in the art.

[0024] As used herein, when referring to two floors, the term "adjacent" means that the two floors are close to each other and there is no intervening open space between them. They may be in direct contact with each other (e.g., stacked together), or there may be an intervening floor.

[0025] The terms “polymer” and “macromolecule” as used herein are consistent with their common usage in chemistry. Polymers and macromolecules consist of many repeating subunits. As used herein, the term “macromolecule” is used to describe a group attached to a monomer having multiple repeating units. The term “polymer” is used to describe the material obtained by a polymerization reaction.

[0026] The term "alkyl" refers to a monovalent group that is a free radical of an alkane, which is a saturated hydrocarbon. Alkyl groups can be linear, branched, cyclic, or combinations thereof, and typically have 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.

[0027] The term "aryl" refers to a monovalent group that is both an aromatic group and a carbocyclic ring. An aryl group may have one to five rings attached to or fused to an aromatic ring. Other ring structures may be aromatic, non-aromatic, or combinations thereof. Examples of aryl groups include, but are not limited to: phenyl, biphenyl, terphenyl, anthryl, naphthyl, acenaphthenic, anthraquinone, phenanthryl, anthracenyl, pyrene, peryl, and fluorenyl.

[0028] The term "alkylene" refers to a divalent group that is a free radical of an alkane. Alkylenes can be straight-chain, branched, cyclic, or a combination thereof. Alkylenes typically have 1 to 20 carbon atoms. In some embodiments, alkylenes contain 1 to 18, 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. The radical center of an alkylene can be on the same carbon atom (i.e., an alkylidene group) or on different carbon atoms.

[0029] The term "arylene" refers to a divalent group that is both a carbocyclic and aromatic ring. This group has one to five linked, fused, or combined rings. Other rings can be aromatic, non-aromatic, or combinations thereof. In some embodiments, the arylene group has up to five rings, up to four rings, up to three rings, up to two rings, or one aromatic ring. For example, the arylene group can be phenylene.

[0030] The term "heteroalkylene" refers to a divalent group comprising at least two alkylene groups linked by a thio, oxygen, or -NR- (where R is an alkyl group). Heteroalkylene groups can be linear, branched, cyclic, substituted with alkyl groups, or combinations thereof. Some heteroalkylene groups are polyoxyalkylenes, where the heteroatom is oxygen, such as, for example,

[0031] -CH2CH2(OCH2CH2) n OCH2CH2-.

[0032] The terms “free radical polymerizable” and “olefinic unsaturation” are used interchangeably and refer to reactive groups containing carbon-carbon double bonds capable of polymerization via a free radical polymerization mechanism.

[0033] As used herein, the terms "radiation-stable" and "radiation-resistant" in relation to adhesives mean that the adhesive retains at least one adhesive property when subjected to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof. In many embodiments, the retained adhesive property is peel adhesion to protein leather, and the retention rate of this property means that, when subjected to radiation, the peel adhesion to protein leather is maintained at at least 80% compared to the same composition without radiation. Other measurement techniques can also be used to determine radiation stability.

[0034] This document discloses adhesive compositions. Many of these adhesive compositions are suitable for use in medical applications, particularly medical articles. The adhesive compositions comprise acrylate-methacrylate copolymers prepared from a reaction mixture comprising at least one alkyl acrylate and at least one alkyl methacrylate. The adhesive compositions are pressure-sensitive adhesives and are radiation-stable. Radiation stability means that the peel adhesion to protein leather is at least 0.5 N / 25 mm, and that after exposure to 30 KGy-60 KGy of electron beam radiation, 30 KGy-60 KGy of gamma radiation, 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 of the same composition to protein leather without exposure to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof.

[0035] The acrylate-methacrylate copolymer is prepared from a reaction mixture comprising: at least one alkyl acrylate of formula 1.

[0036] CH2=CR 1 -(CO)-OR 2

[0037] Formula 1

[0038] Where R 1 It is hydrogen; -(CO)- is a carbonyl group C=O, and R 2 It is an alkyl group containing at least 4 carbon atoms; and at least one alkyl methacrylate of formula 2:

[0039] CH2=CR 3 -(CO)-OR 4

[0040] Formula 2

[0041] Where R 3 The group is a methyl group, -(CO)- is a carbonyl group (C=O), and R 4 It is an alkyl group containing at least 4 carbon atoms.

[0042] Various acrylates are suitable as at least one alkyl acrylate of Formula 1. Typically, alkyl acrylates have an alkyl group containing at least four carbon atoms. Mixtures of alkyl acrylates are also suitable. Examples of suitable alkyl acrylates include butyl acrylate, isobutyl acrylate, amyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, n-octyl acrylate, isononyl acrylate, n-nonyl acrylate, isoamyl acrylate, n-decyl (meth)acrylate, isodecyl acrylate, dodecyl acrylate, isobornyl acrylate, cyclohexyl acrylate, isostearyl acrylate, 2-methylbutyl acrylate, and combinations thereof.

[0043] In some embodiments, the at least one alkyl acrylate of formula 1 comprises at least one alkyl acrylate of formula 1, wherein R 2 It is an alkyl group having at least 8 carbon atoms. The composition may additionally include other alkyl acrylates.

[0044] In some embodiments, the at least one alkyl acrylate of formula 1 comprises at least one alkyl acrylate of formula 1, wherein R 2 It is an alkyl group having at least 12 carbon atoms. The composition may additionally include other alkyl acrylates.

[0045] Various methacrylates are suitable as at least one alkyl methacrylate of Formula 2. In some embodiments, the at least one methacrylate monomer includes n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, isostearyl methacrylate, isodecanyl methacrylate, or combinations thereof.

[0046] In some embodiments, it may be desirable to select methacrylate monomers with a relatively low Tg. In this context, a relatively low Tg means that the selected monomer imparts a Tg of less than 0°C to the formed copolymer. In some embodiments, the copolymer Tg may be less than -10°C, or even less than -15°C. Methacrylate monomers with a relatively low Tg facilitate rapid and firm adhesion of the adhesive composition to a substrate such as mammalian skin.

[0047] In some embodiments, the at least one alkyl methacrylate monomer comprises a mixture of methacrylate monomers, the mixture containing up to 30% by weight of tert-butyl methacrylate and at least one additional methacrylate monomer of formula 2.

[0048] As described above, applying radiation to the adhesive composition induces the formation of chemical bonds through crosslinking, but this crosslinking is balanced by the disruption of chemical bonds within the matrix. This balance is achieved through a reaction mixture containing both acrylate and methacrylate monomers. The reaction mixture can contain a wide range of compositions. In some embodiments, the reaction mixture contains at least 10 mol% of methacrylate monomers. In other embodiments, the reaction mixture contains at least 20 mol% of methacrylate monomers. In still other embodiments, the reaction mixture contains at least 40 mol% of methacrylate monomers.

[0049] The adhesive composition may optionally contain one or more additional components. In some embodiments, the reaction mixture further contains at least one copolymerizable monomer. In some embodiments, the copolymerizable monomer may be a crosslinking monomer. A photocrosslinking agent is particularly suitable. The photocrosslinking agent has a free radical polymerizable group to copolymerize with the aforementioned monomer and also contains a photosensitive group. When exposed to light of a suitable wavelength (typically high-intensity ultraviolet (UV) radiation), the photosensitive group forms free radicals that can form crosslinked portions in the polymer.

[0050] Suitable photocrosslinkers in monoolefinically unsaturated aromatic ketone comonomers are free of ortho-aromatic hydroxyl groups, such as those described in U.S. Patent No. 4,737,559 (Kellen et al.). Specific examples include p-acryloyloxybenzophenone (ABP), p-acryloyloxyethoxybenzophenone, p-N-(methacryloyloxyethyl)-carbamoylethoxybenzophenone, p-acryloyloxyacetophenone, ortho-acrylamidoacetophenone, acrylated anthraquinone, etc. Particularly suitable are ABP p-acryloyloxybenzophenone and AeBP acryloyloxyethyl benzophenone.

[0051] The radiation stability of the adhesive compositions disclosed herein can be determined in various ways. As mentioned above, the stability of peel adhesion to protein leather is an indicator of the radiation stability of the adhesive composition. In some embodiments, radiation stability can be measured by DMA (Dynamic Mechanical Analysis). Some embodiments of the adhesive compositions have a stable tanδ (loss tangent) value at a temperature greater than 160°C. Stability means that the tanδ value after exposure to 30-60 kGy electron beam radiation, 30-60 kGy gamma radiation, at least 25 kGy X-ray radiation, or a combination thereof is at least 80% of the tanδ value of the same composition without exposure to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof. Tanδ is the ratio of storage modulus (G'') to loss modulus (G') measured by DMA, and Tg is also measured by DMA at 1 Hz. Many embodiments have this tanδ characteristic, especially those containing at least 40 mol% methacrylate monomers.

[0052] The adhesive composition may be supplemented with non-reactive additives to modify the properties of the adhesive composition, provided that the additives do not adversely affect the adhesive properties or radiation stability of the adhesive composition. In some embodiments, the adhesive composition further comprises at least one additive selected from plasticizers or liquid resins. Examples of suitable plasticizers include IOP (isooctyl palmitate) from Nikko, RHEODOL MO-60 (glyceryl monooleate) 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 (a mixture of terpene polymers and petroleum hydrocarbons) from Yasuhara Chemical. Polyols can also be suitable, especially polyester polyols from Croda, which are traded under the name PRIPLAST.

[0053] This document also discloses adhesive articles. In some embodiments, the adhesive article includes a first substrate having a first main surface and a second main surface, and a first pressure-sensitive adhesive layer disposed on the second main surface of the first substrate. The first pressure-sensitive adhesive layer comprises an adhesive composition prepared from the reaction mixture as described above. In some embodiments, the reaction mixture comprises: at least one alkyl acrylate of formula 1:

[0054] CH2=CR 1 -(CO)-OR 2

[0055] Formula 1

[0056] Where R 1 It is hydrogen, -(CO)- is a carbonyl group C=O, and R 2 It is an alkyl group containing at least 4 carbon atoms; and at least one alkyl methacrylate of formula 2:

[0057] CH2=CR 3 -(CO)-OR 4

[0058] Formula 2

[0059] Where R 3 The group is a methyl group, -(CO)- is a carbonyl group (C=O), and R 4The alkyl group comprises at least four carbon atoms. As described above, the adhesive composition is a pressure-sensitive adhesive and is radiation-stable, wherein radiation stability means that the peel adhesion to protein leather is at least 0.5 Newtons / 25 mm, and that after exposure to electron beam radiation of 30 KGy-60 KGy, gamma radiation of 30 KGy-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 of the same composition to protein leather without exposure to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof.

[0060] Various substrates are suitable. In some embodiments, the substrate includes a release liner or tape backing. Release liners are well known in the adhesives industry and are films from which adhesive compositions or coatings can be easily removed. Exemplary release liners include those made of paper (e.g., kraft paper) or polymeric materials (e.g., polyolefins such as polyethylene or polypropylene, ethylene vinyl acetate, polyurethane, polyesters such as polyethylene terephthalate, etc., and combinations thereof). At least some release liners are coated with a layer of release agent (such as a fluorosilicone-based material or a fluorocarbon-based material).

[0061] In some implementations, the release liner can be a microstructured release liner. Microstructured release liners are well known in the adhesives industry. Typically, microstructured release liners are prepared by embossing a release liner with an embossed surface onto a structuring tool to impart a structured surface to the release liner. Microstructured release liners impart a microstructured surface to the adhesive layer on which they are disposed.

[0062] Examples of suitable tape backings include polymer films, foils, fabrics, nonwoven materials, foams, paper, mesh, or combinations thereof. In many embodiments, the backing is conformable to a contoured surface. Therefore, when the backing is applied to a contoured surface, it conforms to that surface even when the surface is moved. Examples of such backings can be found in U.S. Patents 5,088,483 and 5,160,315, and include elastomeric polyurethane, polyester, or polyether block amide films. These films have a combination of desired properties, including resilience, high moisture permeability, and transparency.

[0063] In some embodiments, the tape backing is optically transparent and includes polyester, polycarbonate, PS (polystyrene), CBC (cyclic block copolymer), polyolefin (including but not limited to BOPP (biaxially oriented polypropylene), COP (cyclic olefin polymer), COC (cyclic olefin copolymer), polypentene) or combinations thereof.

[0064] In some embodiments, the adhesive article further includes a second pressure-sensitive adhesive layer disposed on a first main surface of the first substrate, wherein the second pressure-sensitive adhesive layer is the same as or different from the first pressure-sensitive adhesive layer. Such articles are double-sided tapes.

[0065] The reaction mixture, pressure-sensitive adhesive composition, and components of the reaction mixture suitable for forming a pressure-sensitive adhesive layer are described in detail above.

[0066] Pressure-sensitive adhesive layers can have a wide range of thicknesses. Generally, pressure-sensitive adhesive layers have a thickness of 10 micrometers to 1 millimeter.

[0067] Examples

[0068] These embodiments are for illustrative purposes only and are not intended to limit the scope of the appended claims. Unless otherwise specified, all parts, percentages, ratios, etc., in the embodiments and the remainder of the specification are by weight. The following abbreviations are used: cm = centimeter; mm = millimeter; in = inch; RPM = revolutions per minute; kg = kilogram; kGy = kilogra; keV = kiloelectron volt; Hz = hertz; sec = second; min = minute; hrs = hour. The terms "weight % (weight %, % by weight and wt%)" are used interchangeably.

[0069]

[0070] Test Methods

[0071] Rheological Property Testing

[0072] Tangent Delta Retention

[0073] PSA samples with an 8 mm diameter and a 1 mm thickness were prepared, and rheological properties were measured before and after electron beam or γ-ray treatment using a rheometer MCR302 (Anton Parr) or ARES-G2 (TA Instrument). Temperature ramp (-50 °C to 180 °C) testing was used, along with oscillating shear (frequency = 1 Hz) and tanδ at 160 °C (the peak temperature of the tanδ curve) above Tg.

[0074] Calculation Formula :

[0075] Tanδ retention rate = (Tanδ after treatment at 160°C above Tg) / (Tanδ before treatment at 160°C above Tg) × 100%

[0076] Adhesive Testing

[0077] Adhesion Retention

[0078] A 25mm × 75mm adhesive tape sample was laminated onto a 30mm × 100mm protein leather sample using a 2kg roller. The applied adhesive tape was removed by T-peeling using an SP-2100 (IMASS) at a test speed of 90 inches / minute (230cm / min). The average peel force was measured before and after electron beam or gamma treatment. The adhesion retention rate was calculated using the following formula:

[0079] Calculation Formula :

[0080] Adhesion retention rate = (Adhesion after treatment / Adhesion before treatment) × 100%

[0081] Electron Beam Treatment

[0082] The sample was treated with an electron beam with an accelerating voltage of 200 keV and a dose of 60 kGy.

[0083] Gamma Ray Treatment

[0084] The samples were treated with gamma radiation doses of 30 kGy or 60 kGy.

[0085] Study 1 Examples

[0086] Examples 1-3

[0087] A radiation-stable adhesive layer was prepared according to the composition description given below, and tested according to the procedure given above. The data are presented in the table below.

[0088] Polymer Formation

[0089] Adhesive compositions were prepared by preparing the reaction mixtures shown in Table 1 below, and labeled as Compositions 1 to 3. The reaction components and 119 parts by weight of water were placed in a bottle and homogenized at 15,000 rpm for 15 minutes. The dispersion and 0.2 parts of initiator-1 were placed in a wide-mouth glass bottle. After purging with nitrogen for 10 minutes, polymerization was carried out at 65°C for 20 hours, and a copolymer emulsion with a solids content of 45% was prepared.

[0090] A thickener was added to the copolymer emulsion, and the pH was adjusted to 7 to 8 with NH3 aq to obtain a viscous emulsion.

[0091] The viscous emulsion was coated onto the TSC surface of pad-1. After drying in an oven (7 minutes at 60°C and 2 minutes at 120°C), the resulting PSA layer with a thickness of 3 mils (76 micrometers) was covered with pad-2.

[0092]

[0093] Adhesive Tape Formation

[0094] Adhesive tape samples were prepared by laminating backing-1 using a thermal laminator after removing backing-2 and corona treating the adhesive surface.

[0095] The adhesive samples were tested using the rheological property testing method described above, and the adhesive tape samples were tested using the adhesion testing method described above. The adhesive and adhesive tape samples were subjected to electron beam irradiation according to the above-described procedure and tested according to the above method. The data are presented in Tables 2 and 3. The example numbers correspond to the composition numbers in Table 1.

[0096]

[0097]

[0098] Study 2 Examples

[0099] Examples 4-26

[0100] A radiation-stable adhesive layer was prepared according to the composition description given below, and tested according to the procedure given above. The data are presented in the table below.

[0101] Polymer Formation

[0102] Adhesive compositions were prepared by preparing the reaction mixtures shown in Tables 4 to 7 below, and labeled as compositions 4 to 26. The reactants were placed in bottles. For compositions 4 to 17, the solvent was 100 parts by weight of toluene; for the remaining compositions, the solvent was 100 parts by weight of EtOAC. After purging the solution with nitrogen for 2 minutes, polymerization was carried out at 70°C for 20 hours, resulting in a viscous polymer solution. Additives were mixed according to the formulation to obtain a viscous coating solution.

[0103] The viscous coating solution was applied to the TSC surface of pad-1. After drying in an oven (2 minutes at 60°C and 2 minutes at 120°C), a polymer layer with a thickness of 80 micrometers was prepared. The polymer layer was subjected to 200 mJ / cm² UV-C, and then pad-2 was used to cover the polymer layer.

[0104]

[0105]

[0106]

[0107]

[0108] Adhesive Tape Formation

[0109] Adhesive tape samples were prepared by laminating backing-1 using a thermal laminator after removing backing-2 and corona treating the adhesive surface.

[0110] The adhesive samples were tested using the rheological property testing method described above, and the adhesive tape samples were tested using the adhesion testing method described above. The adhesive and adhesive tape samples were subjected to electron beam or gamma radiation according to the above processing procedure and tested according to the above method. The data are presented in Tables 8 to 12. The example numbers correspond to the composition numbers in Tables 4 to 7.

[0111]

[0112]

[0113]

[0114]

[0115]

Claims

1. An adhesive composition comprising: An acrylate-methacrylate copolymer prepared from a reaction mixture, wherein the reaction mixture comprises: At least one alkyl acrylate of formula 1, CH2=CR 1 -(CO)-OR 2 Formula 1 Where R 1 It is hydrogen; -(CO)- is a carbonyl group C=O; and R 2 An alkyl group containing at least four carbon atoms; and At least one alkyl methacrylate of formula 2 CH2=CR 3 -(CO)-OR 4 Formula 2 Where R 3 It is a methyl group; -(CO)- is a carbonyl group C=O; and R 4 An alkyl group containing at least four carbon atoms. The adhesive composition is a pressure-sensitive adhesive and is radiation-stable, wherein radiation stability means that the peel adhesion to protein leather is at least 0.5 N / 25 mm, and that after exposure to electron beam radiation of 30 KGy-60 KGy, gamma radiation of 30 KGy-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 without exposure to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof.

2. The adhesive composition according to claim 1, wherein the at least one alkyl acrylate comprises butyl acrylate, isobutyl acrylate, amyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, n-octyl acrylate, isononyl acrylate, n-nonyl acrylate, isoamyl acrylate, (meth)acrylate n-decyl acrylate, isodecyl acrylate, dodecyl acrylate, isobornyl acrylate, cyclohexyl acrylate, isostearyl acrylate, 2-methylbutyl acrylate, isodecyl acrylate, and combinations thereof.

3. The adhesive composition according to claim 1, wherein the at least one alkyl acrylate comprises at least one alkyl acrylate monomer of formula 1, wherein R 2 It is an alkyl group having at least 8 carbon atoms.

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

5. The adhesive composition according to 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 copolymerizable monomer.

7. The adhesive composition of claim 1, wherein radiation stabilization further means that, after exposure to 30 KGy-60 KGy of electron beam radiation, 30 KGy-60 KGy of gamma radiation, at least 25 KGy of X-ray radiation, or a combination thereof, the tanδ value as the ratio of storage modulus (G'') to loss modulus (G') measured by DMA (dynamic mechanical analysis) at a temperature of 160°C greater than the Tg of the adhesive composition is at least 80% of the tanδ value of the same composition not exposed to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof, wherein Tg is measured by DMA at 1 Hz.

8. The 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 according to claim 1, wherein the at least one methacrylate monomer comprises n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, isostearyl 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=CR 3 -(CO)-OR 4 Formula 2 Where R 3 It is a methyl group; -(CO)- is a carbonyl group C=O; and R 4 It is an alkyl group containing 8 to 12 carbon atoms.

11. The adhesive composition of claim 1, wherein the adhesive composition further comprises at least one additive selected from plasticizers or liquid resins.

12. An adhesive article, said adhesive article comprising: A first substrate, the first substrate having a first main surface and a second main surface; and A first pressure-sensitive adhesive layer disposed on the second main surface of the first substrate, the first pressure-sensitive adhesive layer comprising an adhesive composition prepared from a reaction mixture, the reaction mixture comprising: At least one alkyl acrylate of formula 1, CH2=CR 1 -(CO)-OR 2 Formula 1 Where R 1 It is hydrogen; -(CO)- is a carbonyl group C=O; and R 2 An alkyl group containing at least four carbon atoms; and At least one alkyl methacrylate of formula 2 CH2=CR 3 -(CO)-OR 4 Formula 2 Where R 3 It is a methyl group; -(CO)- is a carbonyl group C=O; and R 4 An alkyl group containing at least four carbon atoms. The adhesive composition is a pressure-sensitive adhesive and is radiation-stable, wherein radiation stability means that the peel adhesion to protein leather is at least 0.5 N / 25 mm, and that after exposure to electron beam radiation of 30 KGy-60 KGy, gamma radiation of 30 KGy-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 without exposure 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 main surface of the first substrate, wherein the second pressure-sensitive adhesive layer is the same as 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 copolymerizable monomer.

17. The adhesive article of claim 12, wherein radiation stability further means that after exposure to 30 KGy-60 KGy of electron beam radiation, 30 KGy-60 KGy of gamma radiation, at least 25 KGy of X-ray radiation, or a combination thereof, the tanδ value as the ratio of storage modulus (G'') to loss modulus (G') measured by DMA (dynamic mechanical analysis) at a temperature of 160°C greater than the Tg of the adhesive composition is at least 80% of the tanδ value of the same composition not exposed to electron beam radiation, gamma radiation, X-ray radiation, or a combination thereof, wherein Tg is measured by DMA at 1 Hz.

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, isobutyl methacrylate, tert-butyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, isostearyl 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 tert-butyl methacrylate and at least one additional methacrylate monomer of formula 2: CH2=CR 3 -(CO)-OR 4 Formula 2 Where R 3 It is a methyl group; -(CO)- is a carbonyl group C=O; and R 4 It is an alkyl group containing 8 to 12 carbon atoms.

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