Pressure-activated adhesive

Abstract

A pressure-activated adhesive article comprises a substrate and a pressure-activated adhesive layer disposed on the substrate. The pressure-activated adhesive layer is a crosslinked adhesive composition having a crosslinked siloxane polymer and at least one siloxane tackifier. The pressure-activated adhesive has a Tg of at least 50°C as measured by DMA (dynamic mechanical analysis), is non-adhesive at room temperature, but adheres to the substrate when pressure is applied to the adhesive layer.

Description

[Technical Field]

[0001] This specification discloses pressure-activated adhesives, pressure-activated adhesive compositions, and adhesive structures prepared from pressure-activated adhesive articles. A pressure-activated adhesive article comprises a first substrate having a first main surface and a second main surface, and a pressure-activated adhesive layer disposed on at least a portion of the second main surface of the first substrate. The pressure-activated adhesive layer comprises a crosslinked adhesive composition. The crosslinked adhesive composition comprises at least one crosslinked siloxane polymer and at least one siloxane tackifier. The adhesive composition is a pressure-activated adhesive having a Tg of at least 50°C as measured by DMA (Dynamic Mechanical Analysis), being non-adhesive at room temperature, but adhering to the substrate when pressure is applied to the adhesive layer.

[0002] Methods for forming adhesive structures are also disclosed. In some embodiments, a method for forming an adhesive structure includes providing a surface to be bonded, providing an adhesive article having an exposed adhesive surface, wherein the exposed adhesive surface comprises a pressure-activated adhesive, bringing the exposed adhesive surface of the adhesive article into contact with the surface to be bonded, and applying pressure to bond the adhesive article to the surface to be bonded. Pressure-activated adhesives are described above. [Modes for carrying out the invention]

[0003] Adhesives have been used for a variety of marking, retention, protection, sealing, masking, and sealing purposes. Adhesive tapes generally consist of a backing material or substrate and an adhesive. Pressure-sensitive adhesives, one type of adhesive, are particularly useful in many applications.

[0004] It is well known to those skilled in the art that pressure-sensitive adhesives, at room temperature, possess certain properties including: (1) strong and permanent tackiness, (2) adhesion under pressure less than finger pressure, (3) sufficient ability to be retained on a substrate, and (4) sufficient cohesive force to be easily removed from the substrate. Materials found to function well as pressure-sensitive adhesives are polymers designed and formulated to exhibit the viscoelastic properties necessary to provide a desirable balance of tackiness, peel strength, and shear strength. The polymers most commonly used in the preparation of pressure-sensitive adhesives are natural rubber, synthetic rubber (e.g., styrene / butadiene copolymers (SBR) and styrene / isoprene / styrene (SIS) block copolymers), various (meth)acrylate (e.g., acrylate and methacrylate) copolymers, and silicones. Each of these classes of materials has its advantages and disadvantages.

[0005] A wide range of adhesive articles typically involve placing the adhesive article on a surface and then removing it to provide surface protection and seal the surface for a limited time. Examples include protective films and sealing tapes. Among the uses for sealing articles, one that is becoming increasingly common is cover tape for medical diagnostic devices (microplates or microcards). Many medical diagnostic microplates have a contoured surface area with an array of microchannels and microcavities, and adhesive articles must conform to the surface of a specific shape when mechanically applied, thus presenting certain challenges in these uses. Mechanical application of adhesive articles and achieving a complete seal on the device surface can be difficult. There are several reasons for this difficulty. In some cases, the adhesive may briefly come into contact with other surfaces before adhering to the substrate surface. In this case, the adhesive article may bond prematurely to undesirable surfaces and therefore fail to seal the diagnostic device. Furthermore, if the adhesive article is displaced when it comes into contact with the surface, accurately removing the adhesive article from the surface and re-adhering it to the surface can be difficult and time-consuming. This process is called "repositionability."

[0006] Many techniques have been developed to manufacture adhesive articles with features that make them easy to apply. Typically, these techniques involve modifying the adhesive surface by imparting a microstructured surface to the adhesive surface or by placing non-adhesive elements in the adhesive to prevent the adhesive surface from prematurely contacting and adhering to the surface. In this way, the adhesive article can be positioned in proper alignment with the surface to which it is to be bonded, and then the adhesive is pressed, typically, onto the substrate surface to form an adhesive bond. An example of such a technique is described in PCT Publication No. 03 / 05019, which describes a “tack on demand” adhesive in which spacers (such as beads) are placed at intervals on the adhesive surface. The spacers provide a barrier between the substrate surface and the adhesive layer to provide repositionability, and when pressure is applied, the adhesive surface contacts the substrate surface and an adhesive bond is formed.

[0007] While this technology is effective in some applications, it also has drawbacks. Because these elements are non-adhesive, the areas where they are located on the adhesive surface are non-adhesive spots, which, when attached to the substrate surface, can form areas of poor adhesion and poor sealing. Poor adhesion can cause the adhesive article to lift from the substrate surface, or lead to leakage, wrinkling, and / or other non-uniformity in the bonded adhesive article. Furthermore, positioning non-adhesive elements on the adhesive surface can be a very complex process. Moreover, adhesive articles are often supplied either on a release liner or in the form of a roll, where the adhesive surface contacts the back surface of the adhesive article during roll formation. Having protrusions or other spacers located on the surface of the adhesive layer generally requires a special liner with recesses to accommodate the spacers on the adhesive surface. Therefore, it is desirable to develop new and different adhesive articles that are repositionable.

[0008] Another desirable feature of adhesives is their ability to selectively adhere to surfaces, meaning that only a portion of the adhesive layer can be bonded without bonding the entire layer, or without bonding one portion more strongly than the other. Recently, a journal article by Deneke et al. in Adv. Mater. 2023, 35, 2207337 describes what they call "Pressure-Tunable Adhesives" (PTAs). These adhesives are in contrast to pressure-sensitive adhesives because PSAs bond at very low pressure, and the level of adhesion does not increase with additional pressure, whereas PTAs show increased adhesion with increasing pressure. A highly tunable, expandable, and multifunctional PTA is presented, based on the self-assembly of rigid microscale irregularities on an elastomer substrate via thin-film dewetting. In this way, the PTA physically alters the adhesive layer, and the irregularities change the physical properties of the adhesive surface.

[0009] Another complex characteristic of adhesive articles, particularly in medical applications, is that many of the surfaces to which the adhesive articles are to be attached are inert, non-reactive, and therefore made from low-surface-energy materials. However, since it is desirable for medical adhesive articles to adhere to a wide range of surfaces, the adhesive articles must be able to adhere to a wide range of surfaces.

[0010] This disclosure describes a repositionable adhesive article, which is made “pressure-activatable” by modifying the chemical properties of the adhesive, rather than by modifying the surface structure of the adhesive so that the adhesive does not come into contact with the substrate surface when the adhesive article is applied to the substrate surface. The adhesive described herein has very little or no initial wet-out on the substrate surface to enable repositionability, but when pressure is applied, the adhesive forms an adhesive bond on the substrate surface.

[0011] As used herein, the term “adhesive” refers to a polymer composition useful for bonding two adherends together. Examples of adhesives include pressure-sensitive adhesives, heat-activated adhesives, and pressure-activated adhesives.

[0012] It is well known to those skilled in the art that pressure-sensitive adhesive compositions have the following properties: (1) strong and permanent tackiness, (2) adhesion under pressure less than finger pressure, (3) sufficient ability to be retained on the substrate, and (4) sufficient cohesive force to be cleanly removed from the substrate. Materials found to function well as pressure-sensitive adhesives are polymers designed and formulated to exhibit the viscoelastic properties necessary to provide a desirable balance of tackiness, peel adhesion, and shear retention. Achieving the right balance of properties is not an easy process.

[0013] Thermally activated adhesives are non-tacky at room temperature but become tacky at high temperatures, allowing them to bond to the substrate. These adhesives are typically used at temperatures higher than room temperature. g (Glass transition temperature) or melting point (T m ) has. The temperature is T g or T mAs the temperature increases, the storage modulus of elasticity usually decreases, and the adhesive becomes tacky.

[0014] Pressure-activated adhesives (PAAs) are adhesives that differ from pressure-sensitive or heat-activated adhesives in that they are non-adhesive, non-tacky, or have very low tackiness at room temperature. PAAs have a Young's modulus of 1.0 MPa or higher, measured by DMA (dynamic mechanical analysis) at room temperature, exceeding Dahlquist's tackiness criterion of 0.3 MPa, are not self-wettable, and may have a Tg (transition time) above 50°C, measured by DMA. PAAs are not heat-activated, but the adhesive layer adheres to the substrate when pressure is applied. In other words, the adhesive layer does not adhere to the substrate surface until substantial pressure is applied to the adhesive layer, at which point it forms an adhesive bond to the substrate. The definition of a pressure-sensitive adhesive states that it adheres with finger pressure, or in other words, very light pressure. Pressure-activated adhesives, on the other hand, require greater pressure than finger pressure.

[0015] The adhesive properties used herein include "self-wettability" and "repositionable," where the term self-wettability refers to the ability of an adhesive layer to spontaneously wet the substrate surface it contacts. Self-wettability is often a property of pressure-sensitive adhesives, but not of the pressure-activated adhesives of this disclosure. Repositionability refers to the ability of an adhesive layer to be positioned on a surface, easily removed from the surface, and reattached to the surface. Repositionability is often not a property of pressure-sensitive adhesives, particularly self-wettable ones, but is a property of the pressure-activated adhesives of this disclosure.

[0016] The term "(meth)acrylate" refers to an ester of an alcohol of monomeric acrylic acid or methacrylic acid. Acrylates and methacrylate monomers or oligomers are collectively referred to as "(meth)acrylate" in this specification. A material referred to as "(meth)acrylate functional" is a material containing one or more (meth)acrylate groups.

[0017] As used herein, the term "siloxane-based" refers to a polymer or a polymer unit containing siloxane units. The terms silicone or siloxane are used interchangeably and refer to units having dialkyl or diaryl siloxane (-SiR2O-) repeating units.

[0018] The terms "room temperature" and "ambient temperature" are used interchangeably to mean a temperature in the range of 21°C to 25°C.

[0019] The terms "Tg" and "glass transition temperature" are used interchangeably. When measured, the Tg value is determined by dynamic mechanical analysis (DMA) at a frequency of 1 Hz, unless otherwise indicated. Typically, the Tg value of a copolymer is not measured, but as understood by those skilled in the art, it is calculated using the well-known Fox equation using the homopolymer Tg values provided by the monomer suppliers.

[0020] As used herein, the term "adjacent" when referring to two layers means that the two layers are in proximity to each other without an intervening open space therebetween. They may be in direct contact with each other (e.g., laminated together), or there may be intervening layers.

[0021] The terms "polymer" and "macromolecule" are used herein in accordance with their general usage in chemistry. Polymers and macromolecules are composed of many repeating subunits. As used herein, the term "macromolecule" is used to describe a group bonded to a monomer having a plurality of repeating units. The term "polymer" is used to describe the resulting material formed from a polymerization reaction.

[0022] The term "alkyl" refers to a monovalent group that is a radical of an alkane, which is a saturated hydrocarbon. Alkyl can be linear, branched, cyclic, or a combination thereof, and typically has from 1 to 20 carbon atoms. In some embodiments, the alkyl group contains from 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.

[0023] The term "aryl" refers to a monovalent group that is aromatic and carbocyclic. Aryl can have from 1 to 5 rings attached or fused to the aromatic ring. The other ring structures can be aromatic, non-aromatic, or a combination thereof. Examples of aryl groups include, but are not limited to, phenyl, biphenyl, terphenyl, anthryl, naphthyl, acenaphthyl, anthraquinonyl, phenanthryl, anthracenyl, pyrenyl, perylenyl, and fluorenyl.

[0024] The terms "free-radical polymerizable" and "ethylenically unsaturated" are used interchangeably and refer to a reactive group containing a carbon-carbon double bond that can polymerize via a free-radical polymerization mechanism.

[0025] Unless otherwise indicated, the terms "optically transparent" and "visible light transmissive" are used interchangeably and refer to an article, film, or adhesive that has a high light transmittance over at least a portion of the visible light spectrum (from about 400 to about 700 nm). Typically, an optically transparent article has at least 80% visible light transmittance and less than 5% haze.

[0026] Unless otherwise specified, “optically clear” refers to an adhesive or article having high light transmittance over at least a portion of the visible light spectrum (approximately 400 to 700 nm) and exhibiting low haze, typically less than approximately 5%, or even less than approximately 2%. In some embodiments, an optically clear article exhibits haze of less than 1% at a thickness of 50 micrometers, or even less than 0.5% at a thickness of 50 micrometers. Typically, an optically clear article has a higher visible light transmittance, such as at least 85%, often 88%, 90%, or even 91% or more.

[0027] As used herein when referring to PAA coating compositions, the term “solvent-free” means that the PAA coating composition is essentially solvent-free. Essentially solvent-free means that no solvent is added to the composition, the coating composition is essentially 100% solid, and the coating composition is formulated, coated, and cured without any preparation for removing the solvent.

[0028] This specification discloses pressure-activated adhesive (PAA) articles. A pressure-activated adhesive article comprises a first substrate having a first main surface and a second main surface, and an adhesive layer disposed on at least a portion of the second main surface of the first substrate. The adhesive layer comprises a crosslinked adhesive composition, which comprises at least one crosslinked siloxane polymer and at least one siloxane tackifier. The adhesive composition is a pressure-activated adhesive that is non-adhesive at room temperature and has a Tg of at least 50°C as measured by DMA (dynamic mechanical analysis). In some embodiments, the adhesive composition has a Young's modulus of at least 1.0 MPa at room temperature as measured by DMA, and is not inherently self-wetting, but when pressure is applied to the adhesive layer, the adhesive layer adheres to the substrate surface.

[0029] A pressure-activated adhesive article comprises a first substrate. Examples of preferred first substrates are release liners or tape backings. Release liners are well-known in the field of adhesives and are films that allow for the easy removal of adhesive compositions or coatings. Exemplary release liners are those made from paper (e.g., kraft paper) or polymer materials (e.g., polyolefins such as polyethylene or polypropylene, ethylene vinyl acetate, polyurethane, polyesters such as polyethylene terephthalate, and combinations thereof). At least some release liners are coated with a layer of release agent, such as a fluorosilicone-containing material or a fluorocarbon-containing material.

[0030] Suitable tape backing materials include polymer films, foils, cloths, nonwovens, foams, paper, meshes, or combinations thereof. In some embodiments, the backing material includes an optically clear polymer film without background fluorescence. In some embodiments, the optically clear polymer film backing material has punch resistance. Examples of such backing materials, methods for producing such films, and methods for testing their optical properties are described, for example, in U.S. Patents 3,645,835 and 4,595,001. Typically, such backing materials are polyolefin films.

[0031] In many embodiments, the backing material conforms to the contour surface. Therefore, when the backing material is applied to a contour surface, it conforms to the surface even if the surface moves. Examples of such backing materials can be found in U.S. Patents No. 5,088,483 and 5,160,315, and include elastomer polyurethane, polyester, or polyether block amide films. These films possess a desirable combination of properties, including resilience, high water vapor permeability, and transparency.

[0032] In some embodiments, the tape backing material is optically transparent and includes, but is not limited to, polyester, polycarbonate, PS (polystyrene), CBC (cyclic block copolymer), polyolefin (BOPP (biaxially oriented polypropylene), COP (cyclic olefin polymer), COC (cyclic olefin copolymer), polypentene, glass film (e.g., ultrathin glass film commercially available from Nippon Electric Glass), or combinations thereof.

[0033] In some embodiments, the pressure-activated adhesive article includes a second substrate. In many embodiments, the second substrate is a release liner. The second substrate has a first main surface and a second main surface, the first main surface of the second substrate includes a release coating and is placed on the adhesive layer. If the first substrate is also a release liner, the pressure-activated tape article is a transfer tape.

[0034] The pressure-activated adhesive articles of this disclosure also include an adhesive layer disposed on at least a portion of a second main surface of a first substrate. The adhesive layer comprises a crosslinked adhesive composition, which comprises at least one crosslinked siloxane polymer and at least one siloxane tackifying resin. It should be understood that the at least one siloxane polymer may refer to a single type of siloxane polymer or a mixture of siloxane polymers.

[0035] A wide range of siloxane polymers are preferred. In this disclosure, four types of siloxane polymers are particularly preferred. These types are silanol-functionalized siloxane polymers end-capped with siloxane tackifiers, silanol-functionalized siloxane polymers end-capped with siloxane tackifiers and containing at least one functional group, non-functionalized siloxane polymers, and siloxane block copolymers. Each of these types will be discussed in detail below. Mixtures and blends of these types of siloxane polymers can also be used if desired.

[0036] In some embodiments, the siloxane polymer includes a silanol-functionalized siloxane polymer end-capped with a siloxane tackifier. An example of an end-capped polymer is described in PCT Publication No. 2020 / 099999. The silanol groups present on the silanol-functionalized siloxane polymer condense with the hydroxyl groups on the siloxane tackifier to form the end-capped polymer.

[0037] Generally, silanol-functionalized siloxane polymers are fluids represented by the following formula 1:

[0038] [ka] (In the formula, R1, R2, R3, and R4 are independently selected from the group consisting of alkyl groups or aryl groups, each R5 is an alkyl group, each X is a hydroxyl group, n and m are integers, and at least one of m or n is not zero). In some embodiments, R1 and R2 are alkyl groups and n is 0, i.e., the material is poly(dialkylsiloxane). In some embodiments, the alkyl group is a methyl group, i.e., poly(dimethylsiloxane), "PDMS". In some embodiments, R1 is an alkyl group and R2 is an aryl group and n is 0, i.e., the material is poly(alkylarylsiloxane). In some embodiments, R1 is a methyl group and R2 is a phenyl group, i.e., the material is poly(methylphenylsiloxane). In some embodiments, R1 and R2 are alkyl groups and R3 and R4 are aryl groups, i.e., the material is poly(dialkyldiarylsiloxane). In some commercially available embodiments, R1, R2, R3, R4, and R5 are all methyl groups, and the material is polydimethylsiloxane or PDMS material. In other embodiments, at least some of R1, R2, R3, and R4 are aryl groups.

[0039] The kinematic viscosity at 25 °C of the silanol-terminated linear organopolysiloxane is generally about 50 mm 2 / s or more, 500 mm 2 / s or more, about 1000 mm 2 / s or more, or about 2000 mm 2 / s or more, and about 10,000,000 mm 2 / s or less, about 1,000,000 mm 2 / s or less, or about 500,000 mm 2 / s or less.

[0040] The silanol equivalent of the silanol-terminated linear organopolysiloxane can also be about 300,000 g / mol or less, about 200,000 g / mol or less, about 100,000 g / mol or less, about 50,000 g / mol or less, about 40,000 g / mol or less, or about 500 g / mol or more, or about 1000 g / mol or more.

[0041] The silanol-functional siloxane polymer is end-capped with a siloxane tackifier resin. The siloxane tackifier resin has been called a "silicate" tackifier resin in the past, but the terminology has been replaced by the term "siloxane tackifier resin". In the present disclosure, the terms "silicate" and "siloxane" are used interchangeably when referring to the tackifier resin.

[0042] Suitable siloxane tackifier resins include the following structural units M (i.e., monovalent R’3SiO 1 / 2 units), D (i.e., divalent R’2SiO 2 / 2 units), T (i.e., trivalent R’SiO 3 / 2 units), and Q (i.e., tetravalent SiO 4 / 2Examples include resins composed of siloxanes (units), and combinations thereof. Typical exemplary siloxane resins include MQ siloxane tackifiers, MQD siloxane tackifiers, and MQT siloxane tackifiers. These siloxane tackifiers typically have a number-average molecular weight in the range of 100 to 50,000 gm / mol, for example, 500 to 15,000 gm / mol, and generally the R' group is a methyl group.

[0043] MQ siloxane tackifying resins are copolymer resins in which each M unit is bonded to a Q unit, and each Q unit is bonded to at least one other Q unit. Some Q units are bonded only to other Q units. However, some Q units are bonded to hydroxyl radicals and HOSiO 3 / 2 The unit is, "T" OH This results in a unit of "", which in turn accounts for a portion of the silicon-bonded hydroxyl content of the siloxane tackifying resin.

[0044] Depending on the molecular weight of the MQ resin, the level of silicon-bonded hydroxyl groups (i.e., silanols) on the MQ resin may be 10% by weight, 5% by weight, 1.0% by weight, or 0.5% by weight, based on the weight of the silicate tackifying resin.

[0045] Suitable siloxane tackifying resins are commercially available from suppliers such as Dow Corning (e.g., DC2-7066), Momentive Performance Materials (e.g., SR545 and SR1000), and Wacker Chemie AG (e.g., BELSIL TMS-803).

[0046] Furthermore, linear organopolysiloxanes with end caps in silicate resins can be produced by a condensation reaction between a silanol-terminated linear organopolysiloxane and a silicate resin. The condensation reaction can generally be carried out using a catalyst. Examples of catalysts include metal hydroxides containing lithium hydroxide, sodium hydroxide, potassium hydroxide, and calcium hydroxide; carbonates containing sodium carbonate and potassium carbonate; bicarbonates containing sodium bicarbonate; metal alkoxides containing sodium methoxide or potassium butoxide; organometallic compounds containing butyllithium; complexes of potassium hydroxide and siloxane; and nitrogen compounds containing ammonia gas, aqueous ammonia solutions, 1,5-diazabicyclo[4.3.0]-5-nonene, 1,8-diazabicyclo[.4.0]-7-undecene (DBU), pyridine, N,N-dimethyl-4-aminopyridine, guanidine, 2,4,6-tris(dimethylaminomethyl)phenol, methylamine, trimethylamine, and triethylamine. Since the catalyst can be easily removed using vacuum stripping, it is advantageous to use ammonia gas or aqueous ammonia solution as the catalyst.

[0047] The condensation reaction may be carried out in the presence or absence of a solvent. Examples of suitable solvents include aromatic hydrocarbons including toluene and xylene; linear or branched aliphatic hydrocarbons including hexane, heptane, octane, isooctane, decane, cyclohexane, methylcyclohexane, and isoparaffin; hydrocarbon solvents including industrial gasoline, petroleum benzine, and solvent naphtha; acetone, methyl ethyl ketone, 2-pentanone, 3-pentanone, 2-hexanone, 2-heptanone, 4-heptanone, methyl isobutyl ketone, diisobutyl ketone, acetonylacetone, and cetone. Examples include ketones such as chlorohexanone; esters including ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, and isobutyl acetate; ethers including diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, 1,2-dimethoxyethane, and 1,4-dioxane; substituted acetate solvents including 2-methoxyethyl acetate, 2-ethoxyethyl acetate, propylene glycol monomethyl ether acetate, and 2-butoxyethyl acetate; and mixtures thereof. In some embodiments, the solvent is an aromatic hydrocarbon, a linear or branched aliphatic hydrocarbon, or a mixed solvent of a linear or branched aliphatic hydrocarbon and an ether, ester, or substituted acetate. When the condensation reaction is carried out in the absence of a solvent, it is typically carried out in a twin-screw extruder.

[0048] The temperature of the condensation reaction can generally be about 20°C or higher, about 30°C or higher, or about 40°C or higher, and about 150°C or lower, about 110°C or lower, or about 80°C or lower. The condensation reaction can be carried out at the reflux temperature of any selected solvent.

[0049] The condensation reaction can be carried out until approximately 50%, 70%, or 90% or more of the silanol groups in the silanol-terminated linear organopolysiloxane have reacted. In some embodiments, substantially all of the silanol groups in the silanol-terminated linear organopolysiloxane are consumed by a condensation reaction with a silicate resin using an excess molar equivalent of silicate.

[0050] The duration of the condensation reaction is not particularly limited, but it can generally be about 0.5 hours or more, or about 1 hour or more, and about 48 hours or less, or about 24 hours or less.

[0051] After the condensation reaction, a neutralizing agent may be added as needed to neutralize the base catalyst. Examples of neutralizing agents include acidic gases containing hydrogen chloride and carbon dioxide; organic acids containing octic acid and citric acid; and mineral acids containing hydrochloric acid, sulfuric acid, and phosphoric acid. In addition to, or instead of, neutralization, the base catalyst can be removed by vacuum defloration or washing with water.

[0052] In addition to catalyst neutralization and vacuum deflation, additional end-capping groups for residual silanol groups remaining after the condensation reaction may be used as needed or desired. The most typical examples are silylating agents, such as chlorotrimethylsilane, 1,1,1,3,3,3-hexamethyldisilazane, and N,N'-bis(trimethylsilyl)urea. Silylamines such as 1,1,1,3,3,3-hexamethyldisilazane do not form salts as by-products, so the amines formed in subsequent processes can be removed by vacuum deflation or heat drying processes.

[0053] In addition to the first type of siloxane polymer described above, a second type of end-cap polymer containing additional functional groups can be formed. These polymers can be represented by the following formula 1A:

[0054] [ka] (In the formula, R1, R2, R3, and R4 are independently selected from the group consisting of alkyl groups, aryl groups, or functional groups; each R5 is an alkyl group; each X is a hydroxyl group; n and m are integers; and at least one of m or n is not zero.) Preferred functional groups include alkene groups, vinyl ether groups, (meth)acrylate groups, and thiol groups. Functional polysiloxanes described by formula 1A include polysiloxanes in which at least one of R1, R2, R3, and R4 is a functional group, and the polysiloxanes may be described as vinyl-functional or allyl-functional polysiloxanes (alkene group); vinyl ether-functional polysiloxanes (vinyl ether group); (meth)acrylate-functional polysiloxanes ((meth)acrylate group); mercapto-functional polysiloxanes (thiol group); or combinations thereof.

[0055] Functionalized siloxane polymers are crosslinked not only by the methods described below, namely peroxide curing and curing by ionizing radiation, but also by free radical polymerization (using vinyl ether and (meth)acrylate functionalized polymers) and thiol-ene reactions (when the siloxane polymer contains both alkene and thiol groups). A single siloxane polymer can contain both functional groups of a reactive pair, such as alkene and thiol groups, but it is more common to use a blend of alkene-functionalized siloxanes and thiol-functionalized siloxanes. Typically, these curing reactions require a catalyst or initiator and may require the input of heat or UV radiation. These curing reactions are further described below.

[0056] In other embodiments, the siloxane polymer includes a non-functional siloxane polymer (third type) or a siloxane block copolymer (fourth type).

[0057] An example of a non-functional fluid siloxane polymer is described by the following formula 1B:

[0058] [ka] (In the formula, R1, R2, R3, and R4 are independently selected from the group consisting of alkyl groups, aryl groups, and functional groups; each R5 is an alkyl group; each X is a non-functional group; n and m are integers; and at least one of m or n is not zero.)

[0059] In the above formula 1, X=OH. In this context, X=OH is considered a non-functionalized siloxane polymer because the hydroxyl group does not have the reactivity to form a crosslinked siloxane. Recently, silicone adhesives made from such non-functionalized siloxane polymers are described in U.S. Patent Application Publication 2011 / 0206924 (Liu et al.). These materials are described by formula 1B where X=R5 and by formula 1B where X=OH. Materials where X=OH are considered "non-functionalized materials" in this reference because the hydroxyl group is not used as a "functional group" for the curing reaction, i.e., the polymerization reaction does not involve a reaction with the hydroxyl group. These "non-functionalized materials" have been found to crosslink when exposed to an electron beam or gamma ray to form a cured siloxane network.

[0060] A wide variety of non-functionalized siloxane polymers can be used to form the adhesive layer of this article. One preferred class is the hydroxyl-functionalized material described above as a precursor for end-cap siloxane polymers. Other materials include the non-functionalized material of formula 1B where X=R5. Many examples of such materials are commercially available.

[0061] The advantage of using non-functionalized polysiloxane materials is that they can be crosslinked without the need for initiators or catalysts, as the non-functionalized materials themselves can be used.

[0062] Other suitable siloxane polymers in a different class include, for example, urea-based siloxane copolymers, oxamide-based siloxane copolymers, amide-based siloxane copolymers, urethane-based siloxane copolymers, and siloxane block copolymers comprising mixtures thereof.

[0063] Useful siloxane polyurea block copolymers are disclosed, for example, in U.S. Patents 5,512,650, 5,214,119, 5,461,134, and 7,153,924, as well as PCT Publications 96 / 35458, 98 / 17726, 96 / 34028, 96 / 34030, and 97 / 40103.

[0064] Another useful class of siloxane polymers are oxamide-based polymers, such as polydiorganosiloxane polyoxamide block copolymers. An example of a polydiorganosiloxane polyoxamide block copolymer is presented, for example, in U.S. Patent Publication 2007-0148475.

[0065] Another useful class of siloxane block copolymers is amide siloxane polymers. Such polymers are similar to urea polymers, but instead of urea bonds (-N(D)-C(O)-N(D)-), they have amide bonds (-N(D)-C(O)-), where C(O) represents a carbonyl group and D is hydrogen or an alkyl group.

[0066] Another useful class of siloxane polymers is urethane-based siloxane polymers, such as siloxane polyurea-urethane block copolymers. Siloxane polyurea-urethane block copolymers contain reaction products of polydiorganosiloxanediamine (also known as siloxanediamine), diisocyanate, and organic polyol. Such materials are structurally very similar to urea copolymers, except that the polymer contains urethane bonds (-N(D)-C(O)-O-) and urea bonds. Examples of such polymers are presented, for example, in U.S. Patent No. 5,214,119.

[0067] The siloxanes described above are crosslinked by thermosetting, radiation curing, or a combination thereof to form a polymer siloxane matrix. The crosslinking method used depends on the properties of the siloxane polymer, i.e., whether it is a functional or non-functional polymer.

[0068] Functionalized siloxane polymers can be cured via their functional groups, and also by the peroxide curing and ionizing radiation curing mechanisms described below. Depending on the functional groups present on the siloxane polymer, it may be crosslinked by free radical polymerization or thiol-ene reactions.

[0069] Any siloxane polymer containing ethylenically unsaturated groups can be cured by free radical polymerization. Typically, UV curing is used, meaning that a UV-sensitive free radical initiator is present in the curable composition and free radical polymerizable groups are present on the reactants. UV irradiation is used to activate the free radical initiator, which forms free radicals that initiate the curing reaction. Free radical polymerization can be carried out under a variety of conditions using various different types of free radical initiators. Photoinitiators have been found to be particularly preferred, as described in U.S. Patent No. 5,514,730 (Mazurek).

[0070] Another curing mechanism is the thiol-ene reaction. In this reaction, an ethylenically unsaturated group ("ene") reacts with a thiol group (-SH), resulting in the addition of -S and H groups across the ene group to form a thioether bond. The thiol-ene reaction is typically a free radical-initiated reaction and is therefore a Michael addition reaction catalyzed by either a photoinitiator such as those mentioned above, or by either a base or a nucleophile.

[0071] An example of thermocuring that can be used with both functionalized and unfunctionalized siloxanes is peroxide curing. In peroxide curing, a peroxide initiator is added to the uncrosslinked siloxane composition. Upon heating, the peroxide decomposes to form radicals, which react with the siloxane to form polymer radicals. The polymer radicals bond to form crosslinks. A wide variety of peroxides, such as diacyl peroxides and peroxyesters, have been found to be suitable. When the siloxane contains vinyl groups, the crosslinking reaction is generally much easier, and these materials can be crosslinked using a class of peroxides called "vinyl-specific peroxides." Examples of vinyl-specific peroxides include dialkyl peroxides, alkylaralkyl peroxides, and dialkyl peroxides. Thus, peroxide curing can be achieved using either unfunctionalized siloxane materials or vinyl-functionalized siloxane materials.

[0072] A particularly preferred curing mechanism for forming the crosslinked siloxane matrix of this disclosure is radiation curing using ionizing radiation. Various ionizing radiation sources are preferred, in particular E-beams (electron beams) and gamma-ray emission as described in U.S. Patent Application Publication No. 2011 / 0206924. The advantage of E-beams and gamma-ray emission is that non-functional siloxane materials can thus be cured without the need for initiators or catalysts. Furthermore, the desired level of crosslinking can be controlled by controlling the level of E-beam or gamma-ray emission used. Moreover, unlike thermal crosslinking chemistry, E-beam crosslinking enables hot-melt processing of high-viscosity, solvent-free siloxane formulations without concerns about premature crosslinking in siloxane formulation and thickening processes.

[0073] While peroxide curing can be used to form a crosslinked polymer siloxane layer, in many embodiments, particularly when PAA is hot-melt compounded in a twin-screw extruder in the absence of a solvent, electron beam, gamma-ray emission, or a combination thereof is used to form the crosslinked polymer siloxane layer.

[0074] Various procedures for E-beam and gamma-ray curing are well known. Curing depends on the specific equipment used, and those skilled in the art can define dose calibration models for specific equipment, geometry, and line speed, as well as other well-understood process parameters.

[0075] Commercially available electron beam generators are readily available. In the examples described herein, radiation treatment was performed using a Model CB-300 electron beam generator (available from Energy Sciences, Inc. (Wilmington, MA)). Generally, a support film (e.g., polyester terephthalate support film) passes through the chamber. In some embodiments, a sample of uncured material having liners (e.g., fluorosilicone release liners) on both sides ("closed side") may be attached to the support film and transported at a desired speed. In some embodiments, the support film is transported at a fixed speed of about 6.1 meters / min (20 feet / min). In some embodiments, the sample of uncured material may be applied to one liner and the opposite surface may not have a liner ("open side"). Generally, the chamber is deactivated (e.g., oxygen-containing chamber air is replaced with an inert gas, e.g., nitrogen), and the sample is E-beam cured, especially in the case of open-side curing.

[0076] Commercially available gamma irradiation equipment includes equipment often used for gamma irradiation sterilization of products for medical use. Such equipment can be used to crosslink the polysiloxane layer of this disclosure.

[0077] The adhesive layer also contains at least one siloxane tackifier. A wide range of siloxane tackifiers are preferred. Examples of preferred siloxane tackifiers are described above. Mixtures of siloxane tackifiers are preferred. Particularly preferred siloxane tackifiers are MQ resins. Typically, the siloxane tackifier is added in large quantities relative to the total weight of the adhesive composition. In some embodiments, the siloxane tackifier is present in an amount of 52% to 72% by weight based on the total weight of the adhesive composition, particularly when MQ end-cap siloxane polymers are used. In some embodiments, this amount may be at least 54%, at least 56%, at least 58%, at least 60%, or at least 62%.

[0078] The pressure-activated adhesive layer can have a wide range of thicknesses. Typically, the adhesive layer has a thickness of at least 10 micrometers and a maximum of 2 millimeters, and in some embodiments, the thickness is at least 15 micrometers and a maximum of 1 millimeter. A wide range of intermediate thicknesses, such as 25 to 500 micrometers and 30 to 100 micrometers, are also preferred.

[0079] The pressure-activated adhesive articles of this disclosure possess a variety of desirable properties in addition to the repositionability characteristic conferred by the pressure-activated ability of the adhesive. Due to their low tackiness, it may be expected that the adhesive will only weakly bond to the substrate surface. Furthermore, it may be expected that such adhesives will have insufficient adhesion to surfaces with low surface energy. However, this has been found not to be the case. In some embodiments, it has been found that pressure-activated adhesive articles can bond to surfaces containing moderate surface energy of 36 to 300 dynes / cm (0.036 to 0.30 N / m) or low surface energy of less than 36 dynes / cm (0.36 N / m). This is particularly useful because many medical surfaces that we want to bond, for example, to provide a protective cover layer, have low or moderate surface energy. Pressure-activated adhesive articles can also form selective adhesive bonds by applying selective pressure. Selective pressure means that pressure can be applied to some areas of the pressure-activated adhesive article to form a bond, while other areas are not pressured and therefore do not form a bond in those areas. Furthermore, applying stronger pressure to certain areas can create stronger bonds, while applying weaker pressure to other areas can create weaker bonds in those areas. There are several reasons why this may be useful, for example, to make it easier to adhere articles to a surface and then remove them.

[0080] Examples of bonding surfaces having a low surface energy include films or rigid plates made of PE (polyethylene), PS (polystyrene), PC (polycarbonate), PET (polyethylene terephthalate), PP (polypropylene), COC (cyclic olefin copolymer), COP (cyclic olefin polymer), PDMS (polydimethylsiloxane), or combinations thereof.

[0081] The desirable combination of properties for pressure-activated adhesive articles can be demonstrated by low peel strength from the release liner, low initial adhesion to the surface before pressure is applied, and high peel strength to the low surface energy surface after pressure is applied. In some embodiments, the pressure-activated adhesive has a low peel strength from the release liner of less than 250 grams / inch (9.6 N / dm). Also in some embodiments, the initial adhesion to the surface is low, less than 100 grams / inch (3.8 N / dm). However, when pressure is applied, in some embodiments, the peel strength from PP exceeds 50 ounces / inch (55 N / dm).

[0082] As described above, pressure-activated adhesives do not form strong adhesive bonds when light pressure is applied, but rather when considerable pressure (such as pressure greater than finger pressure) is applied. One useful method for measuring such pressure-activated properties is by using probe tack measurement. Probe tack measurement is well known in the field of adhesives. One method particularly suitable for use with pressure-activated adhesives is to press the probe against the adhesive surface at a relatively low pressure and measure the adhesive strength when the probe is removed from the adhesive surface. Then, press the probe against the adhesive surface at a higher pressure and measure the adhesive strength again when the probe is removed from the adhesive surface. The adhesive values ​​at different pressures can be calculated as a ratio according to the following formula. Ratio = (Adhesion at high pressure) / (Adhesion at low pressure).

[0083] Probe tack can be measured for pressure-activated adhesive surfaces as well as pressure-sensitive adhesive surfaces. Since various probes can be used at various pressures, the absolute values ​​of the above ratios can vary, but generally, when PAA surfaces are tested in the same way as PSA, the ratio for PSA is lower, often much lower. Even in this case, depending on the specific test conditions, in some embodiments, when the high pressure is 30 times greater than the low pressure, the ratio can be at least 3 or 4 for PAA and less than 3 for PSA. This is one of many indicators showing the difference between pressure-activated adhesives and pressure-sensitive adhesives. Pressure-sensitive adhesives are, by definition, permanently and strongly tacky, and therefore, when in contact with a probe, still give high probe tack values ​​even at low pressure. Pressure-activated adhesives, on the other hand, not only do not feel tacky to the touch, but also give low probe tack values ​​at low pressure. However, when higher pressure is applied, pressure-activated adhesives give high probe tack values. The pressure-activated adhesives of this disclosure differ not only from PSAs but also from PTAs (pressure-adjustable adhesives), where additional pressure increases the adhesion of PTAs to the substrate. The PAAs of this disclosure reach their maximum level of adhesion to the substrate when pressure is applied, and the level of adhesion does not increase even with increasingly higher pressure.

[0084] Adhesive compositions are also disclosed herein. In some embodiments, the adhesive composition comprises at least one crosslinked siloxane polymer and at least one siloxane tackifier in an amount of at least 52% to a maximum of 72% by weight, based on the total weight of the adhesive composition. The adhesive composition is a pressure-activated adhesive that is non-adhesive at room temperature and has a Tg of at least 50°C as measured by DMA (dynamic mechanical analysis). In some embodiments, the adhesive composition has a Young's modulus of at least 1.0 MPa at room temperature as measured by DMA and is intrinsically non-adhesive, but when pressure is applied to the adhesive layer, the adhesive layer adheres to the substrate surface. Suitable siloxane polymers, siloxane tackifiers, and crosslinking methods are described in detail above.

[0085] Methods for forming adhesive structures are also disclosed. In some embodiments, the method includes providing a surface to be bonded, providing a pressure-activated adhesive article having an exposed pressure-activated adhesive surface, bringing the exposed pressure-activated adhesive surface of the pressure-activated adhesive article into contact with the surface to be bonded, and applying pressure to bond the adhesive article to the surface to be bonded. The exposed pressure-activated adhesive surface comprises a pressure-activated adhesive. The pressure-activated adhesive comprises a layer of a crosslinked adhesive composition comprising at least one siloxane polymer and at least one siloxane tackifier. The pressure-activated adhesive composition is described above. The pressure-activated adhesive is non-adhesive at room temperature and has a Tg of at least 50°C as measured by DMA (dynamic mechanical analysis). In some embodiments, the adhesive composition has a Young's modulus of at least 1.0 MPa at room temperature as measured by DMA and is not inherently self-wetting.

[0086] A pressure-activated adhesive article, as described above, comprises a substrate having a first main surface and a second main surface, and including a release liner or tape backing, and a pressure-activated adhesive layer disposed on at least a portion of the second main surface of the substrate. Suitable substrates include those described above as the first and second substrates. A pressure-activated adhesive composition is described above, comprising at least one crosslinked siloxane polymer and at least 52% to a maximum of 72% by weight of at least one siloxane tackifier based on the total weight of the adhesive composition. Suitable siloxane polymers, siloxane tackifiers, and crosslinking methods are described in detail above.

[0087] In some embodiments, applying pressure to bond an adhesive article to a surface to be bonded includes applying uniform pressure to the adhesive article to form a uniform adhesive bond, or applying selective pressure to selective regions of the adhesive article to form a selective adhesive bond. Selective pressure means that pressure can be applied to some regions of the pressure-activated adhesive article to form a bond, while other regions are not pressured and therefore do not form a bond. Alternatively, stronger pressure can be applied to some regions to form a stronger bond, while weaker pressure can be applied to other regions to form weaker bonds in those regions.

[0088] In some embodiments, a method for forming a pressure-activated adhesive article includes providing a substrate having a first main surface and a second main surface, wherein the first substrate includes a release liner or tape backing; forming a layer by arranging a coating composition on the second main surface of the first substrate, wherein the coating composition includes at least one siloxane polymer and at least one siloxane tackifying resin; and crosslinking the layer by exposure to heat or ionizing radiation to form a pressure-activated adhesive layer arranged on at least a portion of the second main surface of the first substrate. The coating composition may or may not contain a solvent. Suitable solvents include aromatic solvents such as toluene, ketones such as MEK (methyl ethyl ketone), and esters such as ethyl acetate. If in a solvent, the coating layer may be dried before crosslinking if necessary or desired.

[0089] As described above, at least one siloxane polymer includes a silanol-functionalized siloxane polymer end-capped with a siloxane tackifier, a silanol-functionalized siloxane polymer end-capped with a siloxane tackifier and also containing at least one functional group, a non-functionalized siloxane polymer, or a siloxane block copolymer.

[0090] As described above, crosslinking of at least one siloxane polymer can be carried out in various ways depending on the properties of the at least one siloxane polymer. Crosslinking of at least one siloxane polymer includes free radical polymerization, thiol-ene reaction, exposure to ionizing radiation including e-beam, gamma ray, or a combination thereof, peroxide curing, or a combination thereof.

[0091] A wide range of surfaces to be bonded are suitable for use with this method. In some embodiments, the surfaces to be bonded include moderate surface energies of 36 to 300 dynes / cm (0.036 to 0.30 N / m) or low surface energies of less than 36 dynes / cm (0.36 N / m).

[0092] In many embodiments, the formed adhesive structure is designed to be temporary, and it is desirable that the adhesive structure be dismantled. For example, if the adhesive article is designed to protect the surface of a device or article, it is desirable to attach the pressure-activated adhesive article to the surface of the device or article and then remove and discard the pressure-activated adhesive article afterward. [Examples]

[0093] These examples are for illustrative purposes only and are not intended to limit the scope of the appended claims. All parts, percentages, ratios, etc., in the examples and the remainder of the specification are by weight unless otherwise noted. The solvents and other reagents used were obtained from Fujifilm Wako Pure Chemical Corporation or Sigma-Aldrich Chemical Company; Milwaukee, Wisconsin unless otherwise noted. The following abbreviations are used: mm = millimeter, in = inch, g = gram, kg = kilogram, lb = pound, Hz = hertz, kV = kilovolt, mA = milliampere, Mrad = megarad, mpm = meters per minute, Pa = pascal, MPa = megapascal, sec = second, min = minute, hrs = hour, N = newton, SP = synthetic polymer.

[0094] Table of Abbreviations [Table 1]

[0095] Example Set I. MQ Resin Cap Example Test method Adhesion - Probe Tack Test Probe tack testing was evaluated using a texture analyzer.

[0096] The details of the test conditions are as follows: Probe size (diameter): 7mm Probe shape: Round (R 1 / 2 inch curvature, P / 7D, Stable Micro Systems) Probe material: Stainless steel Trigger load: 1g Target load: 5, 20, 150g Pre-test speed from trigger to target load: 0.05 mm / second Contact time: 1 second Test speed: 10 mm / second Proportional-integral-derivative (PID): 40(P)20(I)5(D) Test environment: 23℃ / 50%RH Number of repeated tests: N6

[0097] The peak top value at the test speed was recorded as the probe tack force, and the average value using n6 was recorded. In this disclosure, low tack is defined as 25g or less for lower loads (target load 5g), or 40g or less for intermediate loads (target load 20g).

[0098] Liner peeling force Liner peel strength was evaluated using an IMASS Model SP-2100 tester. An 8-inch x 1-inch (20cm x 2.5cm) test specimen was attached to the measurement stage with double-sided tape on the polyester film backing-1 side, and the edge of the release film was clamped with a chuck for measurement. The test speed was 12 in / min (30cm / min), and the results are the average of three tests. Results are presented in N / 25mm units.

[0099] In this disclosure, a peel liner force of 0.3 N / 25 mm or less is defined as a good liner peel level.

[0100] Peel adhesive strength The peel adhesion strength was measured using TENSILON RTG-1250 (A&D Company, Limited).

[0101] The details of the test conditions are as follows: Test mode: 180° peeling direction Sample size: 25mm x 100mm Base material: Polypropylene (PP) Surface treatment of the substrate: Wiping with IPA / heptane Pressure conditions: 2kg rubber roller - 1 reciprocating motion at 50mm / second Delay time: 20 minutes after pressurization Test environment: 23℃ / 50%RH Test speed: 300 mm / min Number of repeated tests: N3

[0102] The destruction mode was also recorded as follows: PO: Pop-off (meaning clean peeling) AN: Anchor failure

[0103] In this invention, a good adhesive strength is defined as 7 N / 25 mm or higher.

[0104] Gel fraction The gel fraction was calculated using the initial sample weight (A) and the residual sample weight (B) after immersion in a sufficient solvent solution and drying. Sample size: Approximately 25 x 25 mm Immersion solvent: Toluene Immersion time: 24 hours at room temperature Drying conditions: 2 hours at 130°C Gel fraction = (A) - (B) / (A)%

[0105] Rheology (dynamic mechanical analysis) Rheological data such as G' (storage modulus), G'' (loss modulus), and tanδ (=G'' / G') were measured by dynamic mechanical analysis. The Tg value was extracted from the Tanδ peak. Sample preparation: PSA layers with a thickness of 0.05 mm were stacked to a thickness of over 2.0 mm, and then the test specimens were punched out to a thickness of 8 mm. Equipment: ARES-G2 (TA Instruments) Test mode: Temperature scan Frequency: 1Hz Temperature rise rate: 5°C / min Measurement temperature: -20℃ or 0℃ to 160℃

[0106] Synthesis example Examples S4-S23 of condensation between hydroxyl-functionalized siloxane and MQ resin, and comparative synthesis examples CS1, CS2, and CS4-CS6. The series of condensed polymers were prepared by reacting silicone and tackifier-1 in a toluene solution with catalyst-1 at 40°C for 1 day, followed by reaction at room temperature for 3 days.

[0107] Condensation examples S1-S3 of hydroxyl-functionalized siloxane and MQ resin, and comparative synthesis example CS3. The series of condensed polymers were prepared by reacting silicone and tackifier-1 in a toluene solution with catalyst-2 at 70°C for 1 day, adding end caps, and then reacting at 70°C for 12 hours.

[0108] The composition is shown in Tables S1 to S4.

[0109] [Table 2]

[0110] [Table 3]

[0111] [Table 4]

[0112] [Table 5] N / A = Not applicable

[0113] Examples Preparation and testing of adhesive compositions E1-E23 and comparative examples CE1-CE7 As shown in Tables 1-4, a series of adhesive compositions were prepared using synthetic polymers (SP) corresponding to the CS or S polymers described above.

[0114] For Examples CE1, CE2, CE4-6, and E4-18, the composition solution was applied to liner-1 and dried at 70°C for 10 minutes to form a layer with a thickness of 0.05 mm. An electron beam (E beam) was irradiated from the adhesive surface side opposite to the liner surface. Backing material-1 was laminated on the irradiated side, and the adhesive properties on the opposite side were evaluated.

[0115] For Examples CE3, 7, and E1-3, the composition solution was applied to backing material-1, dried at 70°C for 10 minutes to form a 0.05 mm thick layer, and irradiated with an E-beam from the adhesive surface side opposite to the surface of backing material-1. Liner-2 was laminated on the irradiated side, and the adhesive properties on the opposite side were evaluated. For rheology (dynamic mechanical analysis), the composition solution was applied to liner-2, dried at 70°C for 10 minutes to form a 0.05 mm thick layer, and irradiated with an E-beam from the adhesive surface side. The rheology was then evaluated.

[0116] The E-beam was processed under the following conditions: Equipment: BROADBEAM (PCT Engineered Systems, LLC) Acceleration voltage: 200kV Current values: 3, 5, 7mA (3mA: 3Mrad, 5mA: 6Mrad, 7mA: 80Mrad) Line speed: 5 mpm Irradiation atmosphere: Room temperature, under nitrogen atmosphere

[0117] For Examples E19-21 (thermosetting), the coating solution was applied to release liner-1 and dried and cured at 70°C for 5 minutes and then at 180°C for 3 minutes to form a layer with a thickness of 0.05 mm. Backing material-1 was laminated to the adhesive surface side, and the adhesive properties on the opposite side were evaluated.

[0118] For Examples E22-E23 (gamma ray curing), the coating solution was applied to release liner-1 and dried at 70°C for 10 minutes to form a 0.05 mm thick layer. Then, release liner-1 was laminated onto the adhesive layer. With both sides sandwiched between the release liners, gamma rays were irradiated under the following conditions: (0.6 Mrad (61.4-63.2 kGy)). Backing material-1 was laminated on the coated side, and the adhesive properties on the opposite side were evaluated.

[0119] [Table 6] * = Synthetic polymer

[0120] [Table 7] * = Synthetic polymer

[0121] [Table 8] * = Synthetic polymer

[0122] [Table 9] * =Synthetic polymer, N / A=Not applicable

[0123] The formed adhesive structure was tested for liner release, tackiness, peel adhesion, and DMA, and the data are presented in Tables 5-8.

[0124] [Table 10] NT = Not tested N / A = Not applicable * =N / 25mm

[0125] [Table 11] * =N / 25mm

[0126] [Table 12] N / A = Not applicable. * =N / 25mm

[0127] [Table 13] NT = Untested * =N / 25mm

[0128] Example Set II. Non-MQ Resin Cap Example Test method Adhesion - Probe Tack Test The probe tack test was evaluated using a texture analyzer. A 5-in long, 1-in wide specimen was attached to the underside of a steel plate having multiple holes into which the probe was lowered to contact the adhesive for a predetermined time. This steel plate and adhesive structure were placed on a stage so that the probe was directly above one of the holes. The probe was lowered and bonded to the adhesive side of the specimen. Depending on the target load and contact time, the probe was pulled away from the adhesive, and the force required to pull the probe away from the adhesive surface was measured as the adhesive force.

[0129] The details of the test conditions are as follows:

[0130] Stainless steel probe: Device: Texture analyzer Probe label: TA-57R Probe size (diameter): 7mm Probe shape: Round 7mm-1”R (Stable Micro Systems) Probe material: Stainless steel Trigger load: 1g Target load: 5g, 150g Pre-test speed from trigger to target load: 0.05 mm / second Contact time: 1 second Test speed: 10 mm / second Proportional-integral-derivative (PID): 10(P)5(I)15(D) Test environment: 23℃ / 50%RH Number of repeated tests: N5

[0131] Polypropylene probe: Device: Texture analyzer Probe size (diameter): 7mm Probe shape: Round 7mm-1”R (Stable Micro Systems) Probe material: Polypropylene Trigger load: 1g Target load: 10g, 2000g Pre-test speed from trigger to target load: 0.05 mm / second Contact time: 0.1 seconds Test speed: 10 mm / second Proportional-integral-derivative (PID): 10(P)5(I)15(D) Test environment: 23℃ / 50%RH Number of repeated tests: N5

[0132] The area under the curve was recorded as the probe tack force, and the average value using n5 was recorded.

[0133] Liner peeling force Liner peel strength was evaluated using an IMASS Model SP-2300 tester. An 8-inch x 1-inch (20cm x 2.5cm) test specimen was attached to the measurement stage with double-sided tape on the liner side, and the end of the adhesive structure was clamped with a chuck for measurement. The test speed was 12 in / min (30cm / min) or 90 in / min (229cm / min), and the results are the average of three tests. Results are presented in N / 25mm units.

[0134] In this disclosure, a peel liner force of 0.3 N / 25 mm or less is defined as a good liner peel level.

[0135] Peel adhesive strength Peel strength was measured using IMASS SP-2300. Each test strip was applied to a clean polypropylene panel at 23°C / 50%RH. Each test strip was 6 inches (15 cm) × 1 inch (2.5 cm). The test strip was placed on the polypropylene panel and a 2 kg roller was rolled over the entire length of the test strip in one down and back cycle. The sample was left on the panel for 5 or 30 minutes before testing. Another test set had the test strip placed on the polypropylene panel and laminated using very light finger pressure instead of a 2 kg roller to push out air pockets. This was then left on the panel for 5 minutes before testing. 180° peel tests were performed at 90 in / min (229 cm / min), and reported values ​​are the average of three tests in N / 25 mm units. The failure mode was also recorded as PO: pop-off (meaning clean peel) or AN: anchor failure.

[0136] Tensile strength and elongation at break Tensile force and elongation at break were measured using the Instron 5900 series. Dogbone-shaped test specimens were cut with a die cutter and clamped to the Instron jaws / grip to generate tensile force and elongation at break. The force at which the material breaks is known as tensile strength (psi), and the distance the test specimen stretches is known as elongation at break (%).

[0137] Examples Preparation of Comparative Examples CE8-CE11 For Comparative Example CE8, Tape-1 was used as supplied. For Comparative Examples CE9 to CE11, Silicone-5 and tackifier-1 were mixed in a twin-screw extruder in the ratios shown in Table 9 below, coated onto backing material-3 to a thickness of 51 micrometers (2 mils) through a rotating rod die, and cured by E-beam irradiation at 300 keV and the doses shown in Table 9. The prepared samples were tested, and the results are shown in Table 10.

[0138] [Table 14]

[0139] [Table 15] NT = Untested

[0140] Preparation of Examples E24-E32 For Example E24, silicone adhesive 1(SA) was coated onto liner-4, dried and cured at 70°C for 15 minutes to obtain an adhesive layer with a thickness of 51 micrometers (2 mils), and laminated onto backing material-4.

[0141] For Examples E25 to E30, silicone-5 and tackifier-1 were mixed in a twin-screw extruder in the ratios shown in Table 11, coated onto the backing materials listed in Table 11 to the thickness shown in Table 11 through a rotating rod die, and cured with E-beam irradiation at 200 kev (except for E25 at 300 kev) and the doses shown in Table 11. Examples E28 to E29 were coated onto liner 5, cured, and then laminated onto backing material 4.

[0142] For Examples E31-E32, Silicone-8 (silicone polyoxamide copolymer) and tackifier-2 were mixed in THF at a ratio according to Table 11, with 35% solid content. The solution was coated onto liner-4 with a knife, leaving a gap of 178 micrometers (7 mils), and dried at 70°C for 15 minutes to a thickness of 25 micrometers (1 mil).

[0143] The prepared samples were tested, and the results are shown in Tables 12 and 13.

[0144] [Table 16]

[0145] [Table 17]

[0146] [Table 18]

Claims

1. A first substrate having a first main surface and a second main surface, The invention comprises a pressure-activated adhesive layer disposed on at least a portion of the second main surface of the first substrate, wherein the pressure-activated adhesive layer comprises a crosslinked adhesive composition, and the crosslinked adhesive composition is as follows: A crosslinked siloxane polymer and A pressure-activated adhesive article comprising at least one siloxane tackifying resin, The adhesive composition has a Tg of at least 50°C as measured by DMA (dynamic mechanical analysis), is non-adhesive at room temperature, but when pressure is applied to the adhesive layer, the adhesive layer adheres to the substrate; this is a pressure-activated adhesive article.

2. The article according to claim 1, wherein the first substrate includes a release liner or a tape backing material.

3. The article according to claim 1, wherein the first substrate includes a tape backing, the tape backing being optically transparent and comprising a polyolefin selected from polyester, polycarbonate, PS (polystyrene), CBC (cyclic block copolymer), and BOPP (biaxially oriented polypropylene), COP (cyclic olefin polymer), COC (cyclic olefin copolymer), polypentene, a glass film, or a combination thereof.

4. The article according to claim 1, wherein the first substrate includes a release liner, further includes a second substrate having a first main surface and a second main surface, the first main surface of the second substrate is disposed on the adhesive layer, and the second substrate includes a release liner or tape backing material.

5. The article according to claim 1, wherein the at least one siloxane polymer comprises a silanol-functionalized siloxane polymer end-capped with a siloxane tackifying resin.

6. The article according to claim 5, wherein the at least one siloxane polymer further comprises at least one functional group selected from an alkene, a (meth)acrylate, a thiol, or a combination thereof.

7. The article according to claim 1, wherein the at least one siloxane polymer comprises a non-functional siloxane polymer or a siloxane block copolymer.

8. The article according to claim 1, wherein the at least one siloxane tackifying resin comprises 52 to 72% by weight of MQ resin based on the total weight of the crosslinked adhesive composition.

9. The article according to claim 6, wherein the at least one siloxane polymer is crosslinked by free radical polymerization, thiol-ene reaction, or a combination thereof.

10. The article according to claim 1, wherein the at least one siloxane polymer is crosslinked by peroxide curing, ionizing radiation, or a combination thereof, and the ionizing radiation includes e-beam radiation or gamma rays.

11. The article according to claim 1, wherein the pressure-activated adhesive article can bond to a surface having a moderate surface energy of 36 to 300 dynes / cm (0.036 to 0.30 N / m) or a low surface energy of less than 36 dynes / cm (0.36 N / m), and the low surface energy surface includes a film or rigid plate of PE (polyethylene), PS (polystyrene), PC (polycarbonate), PET (polyethylene terephthalate), PP (polypropylene), COC (cyclic olefin copolymer), COP (cyclic olefin polymer), PDMS (polydimethylsiloxane), or a combination thereof.

12. The article according to claim 1, wherein the pressure-activated adhesive article is optically transparent.

13. A crosslinked siloxane polymer and An adhesive composition comprising 52 to 72% by weight of at least one siloxane tackifying resin based on the total weight of the adhesive composition, An adhesive composition that is non-adhesive at room temperature and has a Tg of at least 50°C as measured by DMA (dynamic mechanical analysis), but is a pressure-activated adhesive in which, when pressure is applied to the adhesive layer after it has been formed into a layer, the adhesive layer adheres to the substrate.

14. The adhesive composition according to claim 13, wherein the at least one siloxane polymer comprises a silanol-functionalized siloxane polymer end-capped with a siloxane tackifying resin.

15. The adhesive composition according to claim 14, wherein the at least one siloxane polymer further comprises at least one functional group selected from alkenes, hydrides, vinyl ethers, (meth)acrylates, thiols, or combinations thereof.

16. The adhesive composition according to claim 13, wherein the at least one siloxane polymer comprises a non-functional siloxane polymer or a siloxane block copolymer.

17. A method for forming an adhesive structure, To provide a surface to be bonded, To provide an adhesive article having an exposed adhesive surface, wherein the exposed adhesive surface contains a pressure-activated adhesive, and the pressure-activated adhesive is At least one siloxane polymer, The adhesive composition comprises a layer of crosslinked adhesive composition containing at least 62% by weight of at least one siloxane tackifying resin based on the total weight of the adhesive composition, The adhesive composition is a pressure-activated adhesive, and the pressure-activated adhesive, which is non-adhesive at room temperature, has a Tg of at least 50°C as measured by DMA (dynamic mechanical analysis), to provide an adhesive article. The exposed adhesive surface of the adhesive article is brought into contact with the surface to be bonded, A method comprising applying pressure to bond the adhesive article to the surface to be bonded.

18. The method according to claim 17, wherein applying pressure to bond the adhesive article to the surface to be bonded includes applying uniform pressure to the adhesive article to form a uniform adhesive bond, or applying selective pressure to a selective region of the adhesive article to form a selective adhesive bond.

19. To provide the aforementioned adhesive article, To provide a first substrate having a first main surface and a second main surface, The first substrate is provided, which includes a release liner or tape backing material. The coating composition is placed on the second main surface of the first substrate to form a layer, wherein the coating composition is At least one siloxane polymer, At least one siloxane tackifying resin, Forming a layer containing a solvent of any choice, If present, the solvent is dried, The method according to claim 17, comprising crosslinking the layer by exposure to heat or ionizing radiation to form a pressure-activated adhesive layer disposed on at least a portion of the second main surface of the first substrate.

20. The method according to claim 17, wherein the at least one siloxane polymer includes a silanol-functionalized siloxane polymer end-capped with a siloxane tackifying resin, a silanol-functionalized siloxane polymer end-capped with a siloxane tackifying resin and also containing at least one functional group, a non-functionalized siloxane polymer, or a siloxane block copolymer.

21. The method according to claim 20, wherein crosslinking the at least one siloxane polymer includes exposure to ionizing radiation, including free radical polymerization, thiol-ene reaction, electron beam, gamma ray, or a combination thereof, peroxide curing, or a combination thereof.

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