Pressure activated siloxane-based adhesive article with fluorocarbon-free release liner

Abstract

A pressure activated adhesive article includes a substrate, a pressure activated adhesive layer disposed on the substrate, and a hydrocarbyl release liner. The pressure activated adhesive layer is a cross-linked adhesive composition having a cross-linked siloxane polymer and at least one siloxane tackifying resin. The pressure activated adhesive is non-tacky at room temperature, has a Tg of at least 50 DEG C as measured by DMA (Dynamic Mechanical Analysis), but adheres to the substrate upon application of pressure to the adhesive layer.

Description

Summary of the Invention

[0001] This document discloses a pressure-activated adhesive, a pressure-activated adhesive composition, and an adhesive construct prepared from a pressure-activated adhesive article. The pressure-activated adhesive article includes a first substrate having a first main surface and a second main surface, a pressure-activated adhesive layer disposed on at least a portion of the second main surface of the first substrate, and a fluorocarbon-free release liner. 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 tackifying resin. The adhesive composition is a pressure-activated adhesive that is non-tacky at room temperature and has a Tg of at least 50°C as measured by DMA (Dynamic Mechanical Analysis), but adheres to the substrate when pressure is applied to the adhesive layer.

[0002] A method for forming an adhesive article is also disclosed, the method comprising: providing a substrate having a first primary surface and a second primary surface; providing an adhesive coating composition comprising at least one siloxane polymer and at least one siloxane tackifying resin; providing a fluorocarbon-free release liner having a first primary surface and a second primary surface, wherein at least the first primary surface is a release surface; disposing the adhesive coating composition on at least a portion of the second primary surface of the substrate to form a layer; drying the layer if necessary; crosslinking the at least one siloxane polymer by applying heat, UV radiation, or ionizing radiation to form a crosslinked layer, the crosslinked layer being a pressure-activated adhesive layer; and disposing the first surface of the hydrocarbon-based release liner on the surface of the adhesive layer. The pressure-activated adhesive layer is non-adhesive at room temperature and has a Tg of at least 50°C as measured by DMA (Dynamic Mechanical Analysis), but the adhesive layer adheres to the substrate when pressure is applied to the adhesive layer. In some embodiments, the method further includes removing the fluorocarbon-free release liner from the adhesive layer; contacting the adhesive layer with the surface; and applying pressure to a portion or all of the adhesive layer to form an adhesive bond with a portion or all of the surface. Detailed Implementation

[0003] Adhesives are used for a variety of marking, retaining, protecting, sealing, and masking purposes. Tapes typically consist of a backing or substrate and an adhesive. One type of adhesive (pressure-sensitive adhesive) is particularly useful in many applications.

[0004] Pressure-sensitive adhesives (PSAs) are well known to those skilled in the art and possess specific properties at room temperature including: (1) strong and persistent tack; (2) adhesion not exceeding finger pressure; (3) sufficient ability to hold onto the adhesive; and (4) sufficient cohesive strength for clean removal from the adhesive. While PSAs require no more than finger pressure to form a contact, their adhesive response hardly changes if pressure is applied above finger pressure. Materials that have been found to function well as pressure-sensitive adhesives are polymers designed and formulated to exhibit the necessary viscoelastic properties that achieve a desired balance of tack, peel adhesion, and shear strength. The most commonly used polymers for preparing pressure-sensitive adhesives are natural rubber, synthetic rubber (e.g., styrene / butadiene copolymers (SBR) and styrene / isoprene / styrene (SIS) block copolymers), various (meth)acrylates (e.g., acrylate and methacrylate copolymers), and siloxanes. Each of these categories of materials has its advantages and disadvantages.

[0005] A wide range of adhesive articles involve placing an adhesive article on a surface to provide protection and seal that surface, typically for a limited amount of time, and then removing the article. Examples of such articles include protective films, sealing tapes, and the like. Increasingly popular applications for sealing articles are cover tapes for medical diagnostic devices (microplates or microcards). These applications present particular challenges because many medical diagnostic microplates have contoured surface areas with arrays of microchannels and microcavities, and the adhesive article must conform to the specific shape of the surface when mechanically applied. Mechanically applying the adhesive article and achieving a perfect seal on the device surface can be difficult. There are several reasons for this difficulty. In some cases, the adhesive may briefly touch other surfaces before adhering to the surface of the adhesive. In this case, the adhesive article bonds prematurely to an unwanted surface and therefore fails to seal the diagnostic device. Additionally, if the adhesive article is misaligned when it comes into contact with the surface, properly removing and re-adhering the adhesive article to the surface can be difficult and time-consuming. This process is known as “repositionability.”

[0006] Various techniques have been developed to produce adhesive articles with easy-to-apply characteristics. Typically, these techniques involve modifying the adhesive surface by imparting a microstructured surface or incorporating non-adhesive elements to prevent premature contact and adhesion of the adhesive surface to the substrate. This allows the adhesive article to be positioned correctly aligned with the surface to which it is to be adhered, and the adhesive is subsequently typically pressed onto the substrate surface to form an adhesive bond. An example of this technique is described in PCT Publication WO 03 / 05019, which describes an "on-demand adhesive" where spacers (such as beads) are spaced apart on the adhesive surface. The spacers provide a barrier between the substrate surface and the adhesive layer to provide repositionability, and upon application of pressure, the adhesive surface contacts the substrate surface and forms an adhesive bond.

[0007] While this technology is effective in some applications, it also has drawbacks. Because these elements are non-adhesive, the areas they occupy on the adhesive surface are non-adhesive points, and when attached to a substrate surface, areas of adhesive failure or seal failure may form. Adhesive failure may cause the adhesive article to detach from the substrate surface, or may lead to leakage, wrinkles, and / or other unevenness in the attached adhesive article. Furthermore, setting non-adhesive elements onto the adhesive surface can be a very complex process. Additionally, adhesive articles are often supplied in either the form of a release liner or in rolls, where the adhesive surface contacts the back surface of the adhesive article during roll formation. Positioning protrusions or other spacers on the surface of the adhesive layer typically requires a specialized liner with recesses to accommodate spacers on the adhesive surface. Therefore, there is a desire to develop novel and different adhesive articles with repositioning capabilities.

[0008] Another desired feature for adhesives is the ability to selectively adhere to surfaces, meaning that a portion of the adhesive layer adheres without the entire layer, or that a portion of the adhesive layer adheres more effectively than other portions. Recently, Deneke et al. published in *Advanced Materials*... Adv. Mater. An article in the journal *[Journal Name]*, 2023, 35, 2207337, describes what they call “pressure-adjustable adhesives” (PTA). These adhesives contrast with pressure-sensitive adhesives (PSA) because PSA adheres at very low pressure, but additional pressure does not increase adhesion, while PTA exhibits increased adhesion with increasing pressure. They introduce a highly adjustable, scalable, and versatile PTA based on the self-assembly of rigid microscale roughnesses on an elastomer substrate via film dewetting. Thus, the PTA has a physically modified adhesive layer, where the roughnesses alter the physical properties of the adhesive surface.

[0009] Another complicating feature (especially in medical applications) is that the many surfaces to which the adhesive article is to be attached are expected to be made of inert, non-reactive, and therefore low-surface-energy materials. However, since medical adhesive articles are expected to be attached to a wide variety of surfaces, the adhesive article should be able to adhere to a wide variety of surfaces.

[0010] Siloxane pressure-sensitive adhesives are widely used due to the desirable properties of siloxane materials, such as strong adhesion to a wide range of surfaces, including low surface energy surfaces. Pressure-sensitive adhesive products require a release liner or release surface on the back of the tape backing (called a LAB or low-adhesion adhesive) for processing or use. A challenge with siloxane pressure-sensitive adhesives is that many types of release liner or release surface are unsuitable. Many release liners use silicone release layers, but as is well known in the adhesives industry, they bond well with their counterparts; therefore, siloxane pressure-sensitive adhesives typically bond well to silicone release layers to form a relatively strong adhesive bond and thus cannot peel well from the release surface. Similarly, siloxane pressure-sensitive adhesives generally adhere well to low surface energy surfaces. Because hydrocarbon-based release liners rely on low surface energy materials to create non-adhesive surfaces, hydrocarbon-based release liners are generally not suitable for siloxane pressure-sensitive adhesives. Therefore, fluorinated release liners are often required for siloxane pressure-sensitive adhesives.

[0011] Fluorinated release liner is very useful, but also very expensive. Furthermore, as industry moves away from the use of fluorinated materials, fluorinated release liner will become even scarcer and more expensive, thus creating an expectation for alternative release liner options for use with siloxane adhesives.

[0012] This disclosure describes adhesive articles capable of repositioning not by surface modification of the adhesive so that it does not contact the substrate surface when applied, but by modification of the adhesive to make it "pressure-activated". The adhesives currently described have very low or no initial wetting of the substrate surface to achieve repositionability, but form an adhesive bond with the substrate surface under pressure. Surprisingly, fluorocarbon-free release liner can be used with these pressure-activated adhesives, providing easy and stable release. Fluorocarbon-free release liner includes hydrocarbon-based release liner and siloxane-based release liner. Articles comprising a substrate, a pressure-activated adhesive, and a fluorocarbon-free release liner are disclosed herein.

[0013] A surprising result is that the hydrocarbon-based release liner provides easy and stable release for siloxane adhesives, as, as mentioned above, conventional siloxane PSAs adhere firmly to typically hydrocarbon-based low surface energy surfaces. Even more surprisingly, the siloxane release liner provides easy and stable release for siloxane adhesives because, as noted above, "like attracts like" is well-known in the chemical field, and siloxane adhesives typically adhere firmly to siloxane release liners.

[0014] When the terms "hydrocarbon-based" and "siloxane-based" are used to describe release liner, they refer to the release layer of the liner, not the entire liner. For example, siloxane-based release liner typically has a thin layer of siloxane release agent coated on at least one surface. The base substrate used for the release liner can be any suitable material, polymer, paper, etc.

[0015] The term “fluorocarbon-free” used to describe a release liner refers to the release layer of the release liner, wherein the release layer does not contain fluorine groups. As used herein, “fluorine-” (e.g., in relation to a group or portion, such as in the cases of “fluoroalkylene” or “fluoroalkyl” or “fluorocarbon”) or “fluorination” means (i) partial fluorination, wherein at least some of the hydrogen atoms of the bonded carbon are replaced by fluorine atoms such that at least one hydrogen atom of the bonded carbon is present, or (ii) perfluorination, wherein all the hydrogen atoms of the bonded carbon are replaced by fluorine atoms.

[0016] As used herein, the term "adhesive" refers to a polymer composition that can be used to attach two adhesives together. Examples of adhesives include pressure-sensitive adhesives, heat-activated adhesives, and pressure-activated adhesives.

[0017] 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 cohesive 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.

[0018] Heat-activated adhesives are not tacky at room temperature, but become tacky and able to bond to the substrate at elevated temperatures. These adhesives typically have a T0 value above room temperature. g (glass transition temperature) or melting point (T) m When the temperature rises above T g or T m At this time, the energy storage modulus usually decreases and the adhesive becomes sticky.

[0019] Pressure-activated adhesives (PAAs) are adhesives that differ from pressure-sensitive adhesives or heat-activated adhesives because they are non-tacky at room temperature, or have very low tack. PAAs can have a Young's modulus equal to or greater than 1.0 MPa (above the Dalquist criterion for tackiness above 0.3 MPa) as measured by DMA (Dynamic Mechanical Analysis), are not self-wetting, and have a Tg above 50°C as measured by DMA. Although PAAs are not heat-activated, 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 considerable pressure is applied; rather, it forms an adhesive bond with the substrate upon application of pressure. Pressure-sensitive adhesives are defined as adhesives that adhere with finger pressure (in other words, very light pressure). Pressure-activated adhesives, on the other hand, require pressure greater than finger pressure.

[0020] The adhesive properties used herein include "self-wetting" and "repositionability." The term "self-wetting" refers to the ability of an adhesive layer to spontaneously wet the substrate surface it contacts. Self-wetting is generally a characteristic 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 placed on a surface and easily removed from and reattached to that surface. Repositionability is generally not a characteristic of pressure-sensitive adhesives (especially self-wetting ones), but it is a characteristic of the pressure-activated adhesives of this disclosure.

[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] As used herein, the term "crosslinked" refers to polymers that are chemically or physically crosslinked. Chemical crosslinking involves chemical bonds between polymer chains. Physical crosslinking involves interactions between polymer chains without forming chemical bonds. Examples of physical crosslinking interactions between polymer chains include "hydrogen interactions." Hydrogen interactions, sometimes called "hydrogen bonding," are not actually chemical bonds, but rather involve the interaction of an electron-depleted hydrogen atom on one polymer chain with an electron-rich atom (such as an oxygen atom) on another polymer chain. This phenomenon is observed, for example, in polymers containing urethane, urea, or polyethylene glycol bonds. For instance, in the presence of a urea bond: -NH-C(O)-NH-, where C(O) is a carbonyl group C=O, an electron-depleted hydrogen atom of a nitrogen atom attached to a urea bond in one polymer can interact with an oxygen atom of a carbonyl group in another polymer chain to form a hydrogen interaction. While each individual hydrogen interaction is not strong, the combined interactions can be quite strong when many such interactions are present between polymer chains. The cumulative effect of hydrogen interactions provides the physically crosslinked polymer matrix. In this disclosure, the siloxane block copolymer is physically crosslinked, but may also contain chemical crosslinks.

[0023] As used herein, the term "siloxane" refers to a polymer or polymer unit containing a siloxane unit. The terms organosilicon or siloxane are used interchangeably and refer to a unit having a repeating dialkyl or diarylsiloxane (-SiR2O-) unit.

[0024] As used herein, the term "hydrocarbon group" refers to a polymer containing hydrocarbon units, typically aliphatic (i.e., saturated) hydrocarbon units.

[0025] The terms “room temperature” and “ambient temperature” are used interchangeably to refer to temperatures in the range of 20°C to 25°C.

[0026] The terms "Tg" and "glass transition temperature" are used interchangeably. If measured, unless otherwise specified, the Tg value is determined by differential scanning calorimetry (DSC) at a scan rate of 10 °C / min. Typically, the Tg value of copolymers is not measured, but rather calculated using the well-known Fox formula with the Tg value of the homopolymer provided by the monomer supplier, as understood by those skilled in the art.

[0027] 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., laminated together), or there may be an intervening floor.

[0028] The terms “polymer” and “macromolecule” as used herein are consistent with their common usage in chemistry. Polymers and macromolecules are composed 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] Unless otherwise specified, the terms "optically transparent" and "visible light transmittance" are used interchangeably and refer to articles, films, or adhesives that have high light transmittance over at least a portion of the visible spectrum (about 400 nm to about 700 nm). Typically, optically transparent articles have at least 90% visible light transmittance and less than 10% haze.

[0033] Unless otherwise specified, "optically clear" means an adhesive or article that has high light transmittance over at least a portion of the visible spectrum (about 400 nm to about 700 nm) and exhibits low haze, typically less than about 5%, or even less than about 2%. In some embodiments, the optically clear article exhibits less than 1% haze at a thickness of 50 micrometers, or even 0.5% haze at a thickness of 50 micrometers. Typically, the optically clear article has at least 95%, and often higher, such as 97%, 98%, or even 99% or higher visible light transmittance.

[0034] As used herein, when referring to coating compositions, the term "solvent-free" means that the coating composition is substantially free of solvents. "Substantially solvent-free" means that no solvent is added to the composition, making the coating composition substantially 100% solids, and that the coating composition is applied and cured without providing solvent removal.

[0035] When referring to coating compositions, the term "free of heavy metals" as used herein means that the coating composition is substantially free of silicone curing catalysts containing heavy metals such as tin, platinum, and / or rhodium. "Substantially free of heavy metals" means that no silicone curing catalyst is added to the composition, because curing is carried out without the need for a catalyst containing heavy metals.

[0036] This document discloses a pressure-activated adhesive article. The pressure-activated adhesive article includes a substrate having a first main surface and a second main surface; a pressure-activated adhesive layer having the first main surface and the second main surface, wherein the first main surface of the pressure-activated adhesive layer is disposed on at least a portion of the second main surface of the substrate; and a fluorocarbon-free release liner disposed on the second main surface of the pressure-activated adhesive layer. The pressure-activated adhesive layer comprises a crosslinked adhesive composition, wherein the crosslinked adhesive composition comprises at least one chemically or physically crosslinked siloxane polymer and at least one siloxane tackifying resin. The adhesive composition is a pressure-activated adhesive that is non-tacky at room temperature and has a Tg of at least 50°C as measured by DMA (Dynamic Mechanical Analysis), but adheres to the substrate when pressure is applied to the adhesive layer.

[0037] As described above, pressure-activated adhesives are those that do not form a strong adhesive bond when light pressure is applied, but form a strong adhesive bond when significant pressure (such as greater than finger pressure) is applied. A useful method for measuring this pressure-activated characteristic is by using probe tack measurement. Probe tack measurement is well-known in the adhesives industry. A particularly suitable method for use with pressure-activated adhesives is to press the probe onto the adhesive surface with relatively low pressure and measure the adhesion force when the probe is removed from the adhesive surface. Subsequently, the probe is pressed onto the adhesive surface with higher pressure, and the adhesion force is measured again when the probe is removed from the adhesive surface. The adhesion force values ​​at different pressures can be ratioed according to the following formula: Ratio = (Adhesion force under high pressure) / (Adhesion force under low pressure).

[0038] Probe tackiness can be measured for both pressure-activated adhesive surfaces and pressure-sensitive adhesive surfaces. Since various probes can be used at various pressures, the absolute values ​​of the aforementioned ratios can vary, but generally, when testing PAA surfaces in the same manner as PSA, the ratio is much lower for PSA. Similarly, depending on the specific test conditions, the ratio can be 20 or greater for PAA, and less than 5 for PSA. This is one of many indicators showing the difference between pressure-activated adhesives and pressure-sensitive adhesives. Pressure-sensitive adhesives, by definition, are persistently and strongly tacky, and therefore produce high probe tack values ​​even at low pressures when in contact with a probe. On the other hand, pressure-activated adhesives not only feel non-tacky to the touch, but also produce low probe tack values ​​at low pressures. However, at higher pressures, pressure-activated adhesives produce high probe tack values. It should also be noted that the pressure-activated adhesives of this disclosure differ not only from PSA but also from PTA (pressure-adjustable adhesive), because additional pressure increases the adhesion of PTA to the substrate. The PAA disclosed herein reaches its maximum adhesion level to the substrate when pressure is applied, and the adhesion level does not increase when increasingly higher pressure is applied.

[0039] Pressure-activated adhesive articles include a substrate. Examples of suitable substrates are release liner and tape backing. Release liner is well known in the adhesive industry and is a film from which an adhesive composition or coating can be easily removed. Exemplary release liner includes 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). In some embodiments, the substrate may be a release liner. While release liners free of fluorocarbons are particularly desirable and are described in more detail below, in some cases, the substrate may be a fluorinated release liner. Fluorinated release liners are coated with a layer of release agent (such as a fluorinated silicone material or a fluorocarbon material). If the substrate is a release liner, a silicone PAA transfer tape can be prepared. Transfer tape is well understood in the adhesive industry as a self-standing adhesive layer disposed between two release liners. As described above, if the substrate is a release liner, it is generally desirable that the release liner be a fluorocarbon-free release liner. Thus, both the substrate release liner and the article release liner are fluorocarbon-free release liners. The fluorocarbon-free release liner may be the same as, or different from, the fluorocarbon-free release liner located on another main surface of the adhesive layer.

[0040] As mentioned above, the release liner that does not contain fluorocarbon compounds can be a hydrocarbon-based release liner or a siloxane-based release liner. Each of these types of release liners is described below.

[0041] Hydrocarbon-based release liner is a liner coated with a layer of hydrocarbon release agent, such as those described in US 7,816,477 or those commercially available from Toray Industries, Inc. as PJ271. The fact that current siloxane-based PAAs can peel off from release liner coated with a layer of hydrocarbon release agent is surprising, as siloxane-based adhesives typically do not peel off from release liner coated with a layer of hydrocarbon release agent.

[0042] Siloxane release liner is a liner coated with a layer of siloxane release agent. Examples of suitable siloxane release liners include silicone release liners as 78B purchased from Laufenberg, and those as 30065 and 30076 purchased from SilicoNature.

[0043] Examples of suitable tape backings include polymer films, modified polymer films, nonwovens, nonwovens with inorganic fillers, textiles, glass fabrics, foams, metal foils, paper, or combinations thereof.

[0044] In some embodiments, the polymer film comprises polyester, polycarbonate, polyimide, PEEK (polyether ether ketone), PTFE (polytetrafluoroethylene), PS (polystyrene), CBC (cyclic block copolymer), and polyolefin or combinations thereof, wherein the polyolefin is selected from BOPP (biaxially oriented polypropylene), COP (cyclic olefin polymer), COC (cyclic olefin copolymer), and polypentene.

[0045] The pressure-activated adhesive article disclosed herein further includes a pressure-activated adhesive layer disposed on at least a portion of a second primary surface of a substrate. The pressure-activated adhesive layer comprises a crosslinked adhesive composition, wherein the crosslinked adhesive composition comprises at least one crosslinked siloxane polymer and at least one siloxane tackifying resin.

[0046] Pressure-activated adhesive layers can have a wide range of thicknesses. Typically, the adhesive layer has a thickness of at least 10 micrometers and at most 2 millimeters, and in some embodiments, the thickness will be at least 20 micrometers and at most 1 millimeter. A wide range of intermediate thicknesses are also suitable, such as 25 micrometers to 500 micrometers, 200 micrometers to 400 micrometers, etc.

[0047] A variety of siloxane polymers are suitable for preparing pressure-activated adhesive layers. Siloxane polymers can be functionalized siloxane polymers, non-functionalized siloxanes, organosilicon thermoplastic polymers, or combinations thereof. Each of these types of siloxane polymers is described in detail below.

[0048] Functionalized siloxane polymers contain functional groups selected from alkoxysilane groups, terminal silanol groups, olefin groups, hydride groups, epoxy groups, vinyl ether groups, (meth)acrylate groups, thiol groups, or combinations thereof. Unless otherwise specified, these functional groups can be terminal or side-chain. Reactions for forming crosslinks with these functionalized siloxane polymers are described below.

[0049] As used herein, the term "curing" refers to polymerization that may or may not result in crosslinking. Functionalized siloxane polymers are cured, meaning they polymerize via functional groups, thereby creating interconnected networks. The cured polymer may be a crosslinked adhesive composition, or the cured polymer may be subjected to ionizing radiation to further crosslink the cured polymer.

[0050] Various siloxane materials are suitable for forming the crosslinked siloxane compounds of this disclosure. Typically, the siloxane materials are fluids as described in Formula 1:

[0051] 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 functional group or a non-functional group, and n and m are integers, and at least one of m or n is not zero.

[0052] Formula 1 can be used to describe terminally functionalized polysiloxanes as well as side-functionalized polysiloxanes. The X group is usually referred to as the "terminal" group, and the R1, R2, R3, and R4 groups are referred to as "side-functionalized" groups, and they can also be functional groups. Functionalized polysiloxanes described by Formula 1 include: alkoxysilane-functionalized polysiloxanes (alkoxysilane groups); hydroxyl-functionalized polysiloxanes (silanol groups); vinyl-functionalized or allyl-functionalized polysiloxanes (terminal olefin groups); hydride-functionalized polysiloxanes (hydroxysilane groups); epoxy-functionalized polysiloxanes (epoxy groups); vinyl ether-functionalized polysiloxanes (vinyl ether groups); (meth)acrylate-functionalized polysiloxanes ((meth)acrylate groups); mercapto-functionalized polysiloxanes (thiol groups); or combinations thereof. When Formula 1 is a polysiloxane with terminal functional groups, it can be used to describe: alkoxysilane-functionalized polysiloxanes, each X being -OR, and one or more R5 groups may additionally be -OR groups, wherein R is an alkyl or aryl group; when Formula 1 is a hydroxyl-functionalized polysiloxane, each X is -OH; when Formula 1 is a vinyl-functionalized polysiloxane, each X is a vinyl group (-HC=CH2); when Formula 1 is an allyl-functionalized polysiloxane, each X is an allyl group (-CH2-CH=CH2); when Formula 1 is a hydride... In the case of functionalized polysiloxanes, each X is -H; when Formula 1 is an epoxy-functionalized polysiloxane, each X contains a terminal ethylene oxide ring; when Formula 1 is a vinyl ether-functionalized polysiloxane, each X is a vinyl ether group (-O-CH=CH2); when Formula 1 is a (meth)acrylate-functionalized polysiloxane, each X is a (meth)acrylate group of the general formula (-(CO)CR=CH2, where (CO) is a carbonyl group C=O, and R is H or a methyl group); when Formula 1 is a mercapto-functionalized polysiloxane, each X is -SH. As described above, in the case of functionalized polysiloxanes, each R1, R2, R3, and R4 is independently selected from the group consisting of alkyl groups, aryl groups, and functional groups, in addition to or as a substitute for the X group, so that these groups can also provide functionality. For example, a variety of siloxanes having side-chain functional groups are commercially available.

[0053] In some embodiments, R1 and R2 are alkyl groups, and n is zero, 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, R2 is an aryl group, and n is zero, 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 embodiments, R1 and R2 are methyl groups, and R3 and R4 are phenyl groups, i.e., the material is poly(dimethyldiphenylsiloxane). In some embodiments, the polydiorganosiloxane material may be branched. For example, one or more of the R1, R2, R3 and / or R4 groups may be linear or branched siloxanes having alkyl or aryl (including haloalkyl or aryl) substituents and a terminal R5 group.

[0054] In some commercially available embodiments, R1, R2, R3, R4, and R5 are all methyl groups, making the material a polydimethylsiloxane or PDMS material. In other embodiments, at least some of R1, R2, R3, and R4 are aryl groups.

[0055] Functionalized siloxane polymers are crosslinked by moisture curing, condensation curing, addition curing, epoxy curing, free radical polymerization, thiol-ene reaction, or a combination thereof.

[0056] One curing method is condensation curing. This involves two related reaction types as condensation reactions. The first is the condensation reaction itself, and the second is wet curing, which is a two-step condensation curing reaction. The difference between these two condensation reactions lies in the starting materials used. In the condensation reaction, the reactants contain silanol groups (-SiOH), while in the wet curing reaction, the reactive groups are precursor groups that react with water to form silanol groups. These formed silanol groups then undergo a condensation reaction.

[0057] The condensation reaction involves the formation of a -Si-O-Si- bond between two silanol groups and a water molecule. As described above, if the reactants contain silanol groups, the condensation reaction proceeds to form a cured matrix. In wet-curing reactions, the reactants are silanol precursors, typically alkoxy or acetoxysilanes (-SiOR). These precursor groups react with water to form silanol groups and an alcohol molecule. The formed silanol groups then undergo a condensation reaction to form a -Si-O-Si- bond. This sequence is summarized in reaction scheme 1 below:

[0058] In this reaction scheme, the first step is the reaction of the precursor with water to form a silanol group, and the second step is a condensation reaction. Typically, a catalyst is used to promote the wet curing reaction. Examples of suitable curing catalysts for this wet curing reaction include alkyl tin derivatives (e.g., dibutyltin dilaurate, dibutyltin diacetate, and dibutyltin dioctanoate, commercially available as “T-series catalysts” from Air Products and Chemicals, Inc., Allentown, Pa.) and alkyl titanate esters (e.g., tetraisobutyl titanate, titanium acetylacetonate, and acetoacetate titanate, commercially available under the trade name “TYZOR” from DuPont). Other catalysts that can be used for the wet curing reaction include acids, acid anhydrides, and their lower alkylammonium salts.

[0059] Another curing reaction is hydrosilylation. Hydrosilylation (also known as catalytic hydrosilylation) describes the addition of Si-H bonds across unsaturated bonds. When hydrosilylation is used for curing, both the Si-H and the unsaturated bonds are typically present on the siloxane molecule, either on the same molecule or on different molecules. Hydrosilylation reactions are typically catalyzed by platinum or rhodium catalysts and usually require heat to achieve the curing reaction. In this reaction, Si-H adds across the double bond to form new CH and Si-C bonds. This method is described, for example, in PCT Publication WO 2000 / 068336 (Ko et al.) and PCT Publication WO 2004 / 111151 and WO 2006 / 003853 (Nakamura).

[0060] Epoxy curing can be achieved by homopolymerizing the epoxy resin using a catalyst or by reacting it with a curing agent. Typically, epoxy siloxanes are cured by homopolymerization, eliminating the need for a curing agent. Epoxy homopolymerization is usually carried out using acid or base catalysts. Examples of suitable base catalysts include tertiary amine or imidazole catalysts. This curing typically requires the addition of heat to achieve complete curing. Examples of acid catalysts include Lewis acid catalysts such as BF3, ZnCl2, SnCl4, FeCl3, and AlCl3. These acid catalysts typically react very rapidly at room temperature. A particularly suitable class of catalysts is UV-activated salts. These salts are latent, meaning they are inert before being subjected to UV light treatment, at which point the catalyst becomes active and initiates polymerization. Representative examples include onium salts diphenyliodonium hexafluorophosphate and triphenylsulfonium hexafluorophosphate.

[0061] Any polysiloxane material containing olefinically 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 radiation 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 various conditions using a variety of different types of free radical initiators. Photoinitiators have been found to be particularly suitable, as described in U.S. Patent No. 5,514,730 (Mazurek).

[0062] Another curing mechanism is the thiol-alkene reaction. In this reaction, the alkene-bonded unsaturated group (“alkene”) reacts with the thiol group -SH, causing the -S and H groups to add to the alkene group to form a thioether bond. The thiol-alkene reaction is usually a radical-initiated reaction and therefore includes photoinitiators, such as those mentioned above, or a Michael addition reaction catalyzed by a base or nucleophile.

[0063] The siloxane polymer may be a nonfunctionalized siloxane polymer. In this context, a nonfunctionalized siloxane polymer is one that does not contain any functional groups involved in the reaction that form the crosslinked adhesive composition of this disclosure. The crosslinked adhesive composition is formed by crosslinking using a peroxide initiator or by treating the nonfunctionalized siloxane polymer with ionizing radiation to form crosslinks, wherein the ionizing radiation is electron beam radiation, gamma radiation, or a combination thereof. Nonfunctionalized siloxane polymers include siloxane block copolymers, nonfunctionalized siloxane polymers capable of curing with ionizing radiation, or combinations thereof.

[0064] Examples of nonfunctionalized siloxane polymers include: silanol-functionalized siloxane polymers that have been capped with siloxane tackifying resins; silanol-capped siloxanes; alkyl-capped siloxanes; or siloxane block copolymers.

[0065] Examples of silanol-functionalized siloxane polymers end-capped with siloxane tackifying resins are described in PCT Publication WO 2020 / 099999. The silanol groups present on the silanol-functionalized siloxane polymer condense with the hydroxyl groups on the siloxane tackifying resin to form the end-capped polymer.

[0066] Typically, silanol-functionalized siloxane polymers are fluids as described in Formula 1A:

[0067] R1, R2, R3, and R4 are independently selected from the group consisting of alkyl or aryl groups, each R5 is an alkyl group, each X is a hydroxyl group, and n and m are integers, with at least one of m or n being non-zero. In some embodiments, R1 and R2 are alkyl groups, and n is zero, 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, R2 is an aryl group, and n is zero, 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, making the material a polydimethylsiloxane or PDMS material. In other embodiments, at least some of R1, R2, R3, and R4 are aryl groups.

[0068] The dynamic viscosity of linear organopolysiloxanes with silanol end groups is typically around 500 mmHg at 25°C. 2 / sec or greater, approximately 1000mm 2 / sec or greater or approximately 2000mm 2 / sec or greater and approximately 10,000,000 mm 2 / sec or less, approximately 1,000,000 mm 2 / sec or less or about 500,000 mm 2 / sec or less.

[0069] Silanol-functionalized siloxane polymers are end-capped with siloxane tackifying resins. Siloxane tackifying resins were formerly referred to as tackifying "silicate" resins, but this designation has been replaced by the term "siloxane tackifying resin." In this disclosure, the terms "silicate" and "siloxane" are used interchangeably when referring to tackifying resins.

[0070] Suitable siloxane tackifying resins include those composed of the following structural units: M (i.e., monovalent R'3SiO) 1 / 2 unit), D (i.e., divalent R'2SiO), 2 / 2 Unit), T (i.e., trivalent R'SiO), 3 / 2 Unit) and Q (i.e., quaternary SiO) 4 / 2(units) and combinations thereof. Typical exemplary siloxane resins include MQ siloxane tackifying resin, MQD siloxane tackifying resin, and MQT siloxane tackifying resin. These siloxane tackifying resins typically have a number average molecular weight in the range of 100 gm / mol to 50,000 gm / mol, for example, 500 gm / mol to 15,000 gm / mol, and typically the R' group is a methyl group.

[0071] MQ siloxane tackifying resin is a copolymer resin 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, producing HOSiO 3 / 2 Unit (i.e., "T") OH "unit"), thereby obtaining the content of some silicon-bonded hydroxyl groups in the siloxane tackifying resin.

[0072] Based on the molecular weight of the MQ resin and the weight of the silicate tackifying resin, the content of silicon-bonded hydroxyl groups (i.e., silanols) on the MQ resin can be 10% by weight, 5% by weight, 1.0% by weight, or 0.5% by weight.

[0073] Suitable siloxane tackifying resins are commercially available from sources such as Dow Corning (e.g., DC 2-7066), Momentive Performance Materials (e.g., SR545 and SR1000), and Wacker Chemie AG (e.g., BELSIL TMS-803).

[0074] Terminally capped linear organopolysiloxanes with silicate resins can be prepared by a condensation reaction of a linear organopolysiloxane containing silanol end groups and a silicate resin. The condensation reaction is typically carried out using a catalyst. Examples of catalysts include: metal hydroxides, including lithium hydroxide, sodium hydroxide, potassium hydroxide, and calcium hydroxide; carbonates, including sodium carbonate and potassium carbonate; bicarbonates, including sodium bicarbonate; metal alkoxides, including sodium methoxide or potassium butoxide; organometallic compounds, including butyllithium; complexes of potassium hydroxide and siloxanes; and nitrogen compounds, including ammonia, aqueous ammonia solution, methylamine, trimethylamine, and triethylamine. Ammonia or aqueous ammonia solution is advantageously used as a catalyst because the catalyst can be readily removed by back-extraction under reduced pressure.

[0075] Condensation reactions can be carried out in the presence of a solvent or in the absence of a solvent. Examples of solvents include aromatic hydrocarbons, including toluene and xylene; linear or branched aliphatic hydrocarbons, including hexane, heptane, octane, isooctane, decane, cyclohexane, methylcyclohexane, and isoalkanes; hydrocarbon-based solvents, including industrial gasoline, petroleum ether, and solvent naphtha; ketones, including acetone, methyl ethyl ketone, 2-pentanone, 3-pentanone, 2-hexanone, 2-heptanone, 4-heptanone, methyl isobutyl ketone, diisobutyl ketone, acetone-based acetone, and cyclohexanone; 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 mixture of a linear or branched aliphatic hydrocarbon with an ether, ester, or substituted acetate solvent.

[0076] The condensation reaction can typically be carried out at temperatures of 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 solvent.

[0077] The condensation reaction can proceed until about 50% or more, about 70% or more, or about 90% or more of the silanol groups in the linear organopolysiloxane containing silanol end groups are reacted. In some embodiments, by using an excess molar equivalent of silicate, substantially all the silanol groups in the linear organopolysiloxane containing silanol end groups are consumed by the condensation reaction with the silicate resin.

[0078] Although there is no particular limitation on the time of the condensation reaction, it can typically be about 0.5 hours or more, or about 1 hour or more, or about 48 hours or less, or about 24 hours or less.

[0079] Following the condensation reaction, a neutralizing agent may be added as needed to neutralize the base catalyst. Examples of neutralizing agents include: acidic gases, including hydrogen chloride and carbon dioxide; organic acids, including octanoic acid and citric acid; and inorganic acids, including hydrochloric acid, sulfuric acid, and phosphoric acid. In addition to neutralization, or as a substitute for neutralization, the base catalyst can be removed by vacuum stripping or washing with water.

[0080] In some implementations, the silanol condensation end-capping reaction with the siloxane tackifying resin is carried out in situ during the adhesive compounding process, for example, in the absence of solvents in a hot melt twin-screw compounding process.

[0081] Examples of suitable MQ-modified siloxane polymers are described in co-pending application No. 63 / 457,842, filed on the same day as this disclosure.

[0082] In some embodiments, the nonfunctionalized siloxane is a silanol-terminated siloxane fluid. Various silanol-terminated siloxane fluids are suitable. Typically, the silanol-terminated siloxane fluid is a linear material described by the following formula 1:

[0083] 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 hydroxyl group, and n and m are integers, and at least one of m or n is not zero.

[0084] In some commercially available embodiments, R1, R2, R3, R4, and R5 are all methyl groups, making the material a polydimethylsiloxane or PDMS material. In other embodiments, at least some of R1, R2, R3, and R4 are aryl groups.

[0085] Many suitable silanol-terminated siloxane fluids are commercially available. Numerous examples of materials are available, for example, from Gelest, Inc. Morrisville, PA; Dow Corning, Midland MI, Michigan; and Wacker Chemie AG, Munich, Germany. Particularly suitable examples include silanol-terminated PDMS (polydimethylsiloxane), available as XIAMETER OHX-4070 from Dow Corning, Midland, Michigan; and hydroxyl-functionalized PDMS, available as 350N from Wacker Chemie AG, Munich, Germany.

[0086] Another class of suitable siloxane polymers includes, for example, urea-based siloxane copolymers, oxamido-based siloxane copolymers, amide-based siloxane copolymers, urethane-based siloxane copolymers, and mixtures thereof.

[0087] Available siloxane polyurea block copolymers are disclosed, for example, in U.S. Patent Nos. 5,512,650, 5,214,119, 5,461,134 and 7,153,924 and PCT Publications Nos. WO 96 / 35458, WO 98 / 17726, WO 96 / 34028, WO 96 / 34030 and WO 97 / 40103.

[0088] Another class of available siloxane polymers are oxalamide-based polymers, such as polydiorganosiloxane-polyethylene amide block copolymers. Examples of polydiorganosiloxane-polyethylene amide block copolymers are presented, for example, in U.S. Patent Publication No. 2007-0148475.

[0089] Another available class of siloxane polymers is amide-based siloxane polymers. These polymers are similar to urea-based polymers, but contain amide bonds (-N(D)-C(O)-) instead of urea bonds (-N(D)-C(O)-N(D)-), where C(O) represents a carbonyl group and D is a hydrogen or alkyl group.

[0090] Another class of available siloxane polymers is urethane-based siloxane polymers, such as siloxane polyurea-urethane block copolymers. Siloxane polyurea-urethane block copolymers comprise the reaction product of polydiorganosiloxane diamine (also known as siloxane diamine), diisocyanate, and organic polyol. Examples of such polymers are presented, for example, in U.S. Patent No. 5,214,119.

[0091] As mentioned above, siloxane block copolymers are physically crosslinked polymers. In addition to this physical crosslinking formed through hydrogen interactions, chemical crosslinking can also be formed between polymers using the crosslinking techniques described herein.

[0092] The aforementioned nonfunctional siloxanes are crosslinked via peroxide curing, radiation curing, or a combination thereof to form polymeric siloxane compounds. In peroxide curing, a peroxide initiator is added to the non-crosslinked siloxane composition. Upon heating, the peroxide decomposes to form free radicals, which react with the siloxane to form polymeric free radicals. These polymeric free radicals combine to form the crosslinked portion. Several peroxides have been found to be suitable, such as diacid peroxides and peroxide esters.

[0093] A particularly suitable curing mechanism for forming the crosslinked siloxane compounds of this disclosure is radiation curing using ionizing radiation. Various ionizing radiation sources are suitable, especially E-beams (electron beams) and gamma-ray radiation, as described in PCT Publication WO2010 / 056543. The advantage of electron beam and gamma-ray radiation is that nonfunctional siloxane materials can be cured in this manner without the need for initiators or catalysts, particularly heavy metal-based catalysts. Furthermore, the desired level of crosslinking can be controlled by adjusting the level of electron beam or gamma-ray radiation used. Moreover, unlike thermal crosslinking chemistry, electron beam crosslinking allows for the hot-melt processing of high-viscosity solvent-free siloxane formulations without concern for premature crosslinking during siloxane compounding and thickening processes.

[0094] While peroxide curing can be used to form cross-linked polymeric siloxane layers, in many embodiments, electron beams, gamma-ray radiation, or combinations thereof are used to form cross-linked polymeric siloxane layers.

[0095] The various processes used for electron beam curing 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 the specific equipment, geometry, and linear velocity, as well as other well-known process parameters.

[0096] Commercially available electron beam generation equipment is readily available. For the example described herein, the radiation treatment was performed on a CB-300 electron beam generation device (available from Energy Sciences, Inc., Wilmington, MA).

[0097] Commercially available gamma radiation equipment includes equipment commonly used for gamma radiation sterilization of products intended for medical applications. Such equipment can be used to crosslink the polysiloxane layers of this disclosure.

[0098] The adhesive compositions disclosed herein also comprise at least one siloxane tackifying resin. Siloxane tackifying resins have historically been referred to as tackifying "silicate" resins, but this designation has been replaced by the term "siloxane tackifying resin." In this disclosure, the terms "silicate" and "siloxane" are used interchangeably when referring to tackifying resins.

[0099] Particularly suitable are MQ siloxane tackifying resins as described above. Suitable siloxane tackifying resins are commercially available from sources such as Dow Corning (e.g., DC 2-7066), Momentive Performance Materials (e.g., SR545 and SR1000), and Wacker Chemie AG (e.g., BELSIL TMS-803).

[0100] The amount of siloxane tackifying resin present in the composition can vary depending on the composition of the crosslinked siloxane polymer. In some embodiments, the content of siloxane tackifying resin is relatively high, at least 62% by weight, and in some embodiments at least 64% by weight, based on the total weight of the crosslinked adhesive composition. In other embodiments, particularly with MQ-modified siloxane polymers, the content of siloxane tackifying resin can be low, at 54% by weight or more.

[0101] The pressure-activated adhesive articles disclosed herein possess a wide range of desirable properties, including repositionability as described above. One of the most surprising properties is the availability of fluorocarbon-free release liner (such as hydrocarbon release liner or siloxane release liner) in these articles. Perhaps even more surprising is that, despite being removable from hydrocarbon or siloxane release liner, the pressure-activated adhesive articles are capable of bonding firmly to a wide range of surfaces upon pressure activation, including medium and even low surface energy substrates. Typically, medium surface energy substrates are those with a surface energy of 36 dynes / cm to 300 dynes / cm (0.036 N / m to 0.30 N / m), and low surface energy substrates are those with a surface energy less than 36 dynes / cm (0.36 N / m). Examples of low surface energy surfaces include films or rigid sheets 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.

[0102] In some embodiments, it may be desirable for the pressure-activated adhesive article to be optically transparent or even optically clear. In these embodiments, both the substrate and the pressure-activated adhesive layer are optically transparent.

[0103] This document also discloses a method for forming an adhesive article. In some embodiments, the method includes providing a substrate having a first main surface and a second main surface; providing an adhesive coating composition comprising at least one siloxane polymer and at least one siloxane tackifying resin; disposing the adhesive coating composition on at least a portion of the second main surface of the substrate to form a layer; drying the layer if necessary; crosslinking the at least one siloxane polymer by applying heat, UV radiation, or ionizing radiation to form a crosslinked layer, the crosslinked layer being a pressure-activated adhesive layer; providing a fluorocarbon-free release liner having a first main surface and a second main surface, wherein at least the first main surface is a release surface; and disposing the first surface of the fluorocarbon-free release liner on the surface of the pressure-activated adhesive layer. The substrate, the pressure-activated adhesive layer, and the fluorocarbon-free release liner are described in detail above.

[0104] In some embodiments, the substrate is a fluorocarbon-free release liner. In these embodiments, the siloxane pressure-activated adhesive tape is a siloxane transfer tape.

[0105] The adhesive coating composition may be solvent-free, i.e., 100% solids, or the composition may contain one or more solvents. The siloxane polymer of the coating composition is a functionalized siloxane polymer, a non-functionalized siloxane, or a combination thereof as described above. The siloxane tackifying resin of the adhesive coating composition is typically an MQ resin as described above.

[0106] In some embodiments, when crosslinking at least one siloxane polymer includes applying heat or UV radiation, the siloxane polymer is a functionalized siloxane polymer, and the solvent-free coating composition further comprises at least one curing catalyst or free radical initiator.

[0107] In other embodiments, when crosslinking at least one siloxane polymer includes applying ionizing radiation, the siloxane polymer is a nonfunctionalized siloxane polymer, and the ionizing radiation includes electron beam radiation, gamma radiation, or a combination thereof.

[0108] In some embodiments, the method further includes removing a fluorocarbon-free release liner from the adhesive layer, bringing the adhesive layer into contact with the surface, and applying pressure to the adhesive layer to form an adhesive bond with the surface. As described above, pressure activates the adhesive layer to bond to a wide range of surfaces, including low and medium surface energy surfaces.

[0109] Example

[0110] These examples are for illustrative purposes only and are not intended to limit the scope of the appended claims. Unless otherwise stated, all parts, percentages, ratios, etc., in the examples and the remainder of the specification are by weight. Unless otherwise indicated, the solvents and other reagents used were obtained from Fujifilm WakoPure Chemical Corp. or Sigma-Aldrich Chemical Company (Milwaukee, Wisconsin). The following abbreviations are used: mm = millimeter; in = inch; g = gram; kg = kilogram; lb = pound; Hz = Hertz; kV = kilovolt; mA = milliampere; Mrd = megarad; mpm = meter / minute; Pa = Pascal; kPa = kilopascal; MPa = megapascal; psi = pound / square inch; sec = second; min = minute; hrs = hour; N = newton; SP = synthetic polymer.

[0111]

[0112] Example Set II. Examples of Non-MQ Resin End-Capping

[0113] Test methods

[0114] Viscosity – Probe viscosity test

[0115] The probe tackiness test was evaluated using a texture analyzer. A 5-inch long and 1-inch wide test strip was mounted on the underside of a steel plate with multiple holes, where the probe was lowered to contact the adhesive for a specified duration. This steel plate, along with the adhesive construct, was then placed on a stage with the probe directly above one of the holes. The probe was lowered and attached to the adhesive side of the sample. Based on the target force and contact time, the probe was pulled away from the adhesive, and the force required to pull the probe away from the adhesive side was measured as the adhesive force.

[0116] The details of the test conditions are as follows.

[0117] stainless steel probe : Equipment: Texture analyzer Probe label: TA-57R Probe size (diameter): 7mm Probe shape: Circular 7mm-1'' R (Stabilized Microsystem) Probe material: Stainless steel Trigger force: 1g Target strength: 5g, 150g Velocity before test from trigger force to target force: 0.05 mm / sec Contact time: 1 second Test speed: 10mm / sec Proportional-Integral-Derivative (PID): 10 (P) 5 (I) 15 (D) Test atmosphere: 23℃ / 50%RH Number of repeated trials: N5 Polypropylene probe : Equipment: Texture analyzer Probe size (diameter): 7mm Probe shape: Circular 7mm-1'' R (Stabilized Microsystem) Probe material: Polypropylene Trigger force: 1g Target strength: 10g, 2000g Velocity before test from trigger force to target force: 0.05 mm / sec Contact time: 0.1 sec Test speed: 10mm / sec Proportional-Integral-Derivative (PID): 10 (P) 5 (I) 15 (D) Test atmosphere: 23℃ / 50%RH Number of repeated trials: N5 Record the area under the curve as the probe viscous force, and record the average value as n5.

[0118] Gasket peel force

[0119] The liner peel strength was evaluated using an IMASS Model SP-2300 tester. An 8-inch × 1-inch (20 cm × 2.5 cm) test piece was applied to the measuring stage with the liner side using double-coated adhesive tape, and the edges of the adhesive construct were clamped with suction cups to perform the measurement. Test speeds were 12 in / min (30 cm / min) or 90 in / min (229 cm / min), and results were the average of three tests. Results are presented in N / 25 mm.

[0120] In this disclosure, a peeling liner force of 0.3 N / 25 mm or less is defined as a good liner peeling level.

[0121] Peel adhesion

[0122] Peel adhesion was measured using an 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 rolled back and forth on a 2 kg roller for one cycle. The sample was allowed to remain on the panel for 5 min or 30 min before testing. Another set of tests involved placing the test strip on the polypropylene panel and laminating and expelling air pockets using very light finger pressure instead of the 2 kg roller. The test strip was then allowed to remain on the panel for 5 min before testing. The 180° peel test was run at 0 in / min (229 cm / min), and the reported value is the average of three tests in N / 25 mm. The fracture mode was also recorded as PO: bursting (meaning complete peeling) or AN: anchorage failure.

[0123] Tensile strength and elongation at break

[0124] Tensile force and elongation at break are measured using the Instron 5900 series. Dog-bone shaped test specimens are cut using a die-cutting machine and clamped in the Instron's jaws / grippers to generate tensile force and elongation at break. The force at which the material breaks is called tensile strength (psi), and the distance the test specimen is stretched is called elongation at break (%).

[0125] Example

[0126] Preparation of Comparative Examples CE1-CE4

[0127] For Comparative Example CE1, the provided tape-1 was used. For Comparative Examples CE2-CE4, silicone-1 and tackifier-1 were mixed in a twin-screw extruder at the ratios shown in Table 1 below, and coated onto backing-1 at a thickness of 51 micrometers (2 mils) through a rotary die, and cured using electron beam radiation at 300 keV and the doses shown in Table 1. The prepared samples were tested, and the results are shown in Table 2.

[0128]

[0129] Preparation of Examples E1-E9

[0130] For Example E1, silicone adhesive-1 (SA-1) was coated onto the backing 3, dried and cured at 70°C for 15 min to obtain an adhesive layer with a thickness of 51 micrometers (2 mils), and then laminated onto the backing 3.

[0131] For Examples E2-E7; silicone-1 and tackifier-1 were mixed in a twin-screw extruder at the ratios according to Table 3, coated onto the backings listed in Table 3 to the thickness shown in Table 3 through a rotary die, and cured using electron beam radiation at 200 keV (except for E3, 300 keV) and the doses shown in Table 3. Examples E5-E6 were coated and cured onto liner-4, and subsequently laminated onto the backing.

[0132] For Examples E8-E9, silicone-2 (silicone-polyethylene glycol copolymer) and tackifier-2 were mixed in THF at 35% solids according to the ratio in Table 3. The solution was applied to pad-3 using a doctor blade with a 178-micron (7-mil) gap and dried at 70°C for 15 minutes to a thickness of 25 microns (1 mil).

[0133] The prepared samples were tested, and the results are shown in Tables 4 and 5.

[0134]

[0135] Examples E10-E20

[0136] For Example E10; silicone-5 (silicone polyurea copolymer) and tackifier-3 were mixed at a ratio of 45:55 in a mixed solvent of 30.3% IPA, 56.2% toluene, and 13.5% xylene (added by addition of Dow 2-7066 MQ resin) to a solids content of 28%. The solution was applied to a pad according to Table 6 using a doctor blade with a 178-micrometer (7-mil) gap and dried at 70°C for 15 minutes to a thickness of 25 micrometers (1 mil).

[0137] The prepared samples were tested, and the results are shown in Table 6.

[0138]

[0139] For Example E11; silicone adhesive-1 (SA1) was applied to the pad according to Table 7 using a scraper with a gap of 178 micrometers (7 mils) and dried at 70°C for 15 minutes to a thickness of 25 micrometers (1 mil).

[0140] The prepared samples were tested, and the results are shown in Table 7.

[0141]

[0142] For Examples E12-E20; silicone 6-8 and tackifier-1 were mixed in a twin-screw extruder at the ratios shown in Table 8, coated onto 3 mil (75 μm) BOPP through a rotary die, cured using electron beam radiation at 200 keV and the doses shown in Table 8, and laminated onto liner-5 according to Table 8. The prepared samples were tested, and the results are shown in Table 8.

[0143]

[0144] Example Set II. Examples of MQ Resin End-Capping

[0145] Test methods

[0146] Viscosity – Probe viscosity test

[0147] A texture analyzer was used to evaluate the probe viscosity test.

[0148] The details of the test conditions are as follows.

[0149]

[0150] The peak value at the test speed is recorded as the probe viscous force, and the average value is recorded at n6. In this disclosure, 25g or less is defined as low viscosity for lower loads (target force, in the case of 5g), or 40g or less is defined as low viscosity for medium loads (target force, in the case of 20g).

[0151] Gasket peel force

[0152] The liner peel force was evaluated using an IMASS Model SP-2100 tester. An 8-inch × 1-inch (20 cm × 2.5 cm) test sheet with the polyester film backing-5 side applied via double-coated adhesive tape was placed on the measuring stage, and the edges of the peel film were clamped using suction cups to perform the measurement. The test speed was 12 in / min (30 cm / min), and the result is the average of three tests. Results are presented in N / 25 mm.

[0153] In this disclosure, a peeling liner force of 0.3 N / 25 mm or less is defined as a good liner peeling level.

[0154] Peel adhesion

[0155] Peel adhesion was measured using a TENSILON RTG-1250 (A&D Company, Limited).

[0156] The details of the test conditions are as follows.

[0157]

[0158] In this disclosure, 7 N / 25 mm or greater is defined as good adhesive strength.

[0159] Gel fraction ratio

[0160] The gel fraction ratio was calculated using the initial sample weight (A) and the residual sample weight (B) after immersion in sufficient solvent solution and drying.

[0161]

[0162] Gel fraction ratio = (A) – (B) / (A)%

[0163] Rheological properties (dynamic mechanical analysis)

[0164] Rheological property data, such as G' (storage modulus) and G'' (loss modulus), and tanδ (=G'' / G'), are measured through dynamic mechanical analysis. The Tg value is extracted from the peak value of tanδ.

[0165]

[0166] Synthesis Examples

[0167] Condensation examples of hydroxyl-functionalized siloxanes with MQ resin: MMS1-MMS3 and comparative synthesis example: MMCS1

[0168] A series of condensation polymers were prepared by reacting organosilicon and tackifier-1 in a toluene solution with added catalyst-1 at 70°C for 1 day, adding a capping agent, and then reacting at 70°C for 12 hours (the synthesis for MQ modification is labeled MMS or the comparative synthesis for MQ modification is labeled MMCS).

[0169] The composition is shown in Table S1

[0170] Example

[0171] Preparation and testing of adhesive compositions E21-E23 and comparative examples CE5-CE6

[0172] A series of adhesive compositions were prepared using synthetic polymers (SPs) corresponding to the MMCS or MMS polymers described above as shown in Table 6. For Comparative Example CE6, silicone adhesive-2 was used.

[0173] For Examples CE5, CE6, and E1-E3, the composition solution was applied to backing-5 and dried at 70°C for 10 minutes to form a layer with a thickness of 0.05 mm. An electron beam was irradiated from the adhesive surface side opposite to the surface of backing-5. Pad-2 was laminated onto the irradiated surface side, and the adhesion properties on the opposite side were evaluated.

[0174] Electron beam radiation was treated under the following conditions:

[0175] The pad peel strength, tack, peel adhesion and DMA of the adhesive structure formed were tested, and the data are presented in Table 10.

[0176]

Claims

1. A pressure-activated adhesive article, the pressure-activated adhesive article comprising: The substrate has a first main surface and a second main surface. A pressure-activated adhesive layer having a first main surface and a second main surface, wherein the first main surface of the pressure-activated adhesive layer is disposed on at least a portion of the second main surface of the substrate; as well as A fluorocarbon-free release liner is disposed on the second main surface of the pressure-activated adhesive layer, wherein the pressure-activated adhesive layer comprises a crosslinked adhesive composition, wherein the crosslinked adhesive composition comprises: At least one cross-linked siloxane polymer; and At least one siloxane tackifying resin; The adhesive composition thereof is a pressure-activated adhesive, which is non-sticky at room temperature and has a Tg of at least 50°C as measured by DMA (Dynamic Mechanical Analysis), but the adhesive layer adheres to the adhesion surface when pressure is applied to the adhesive layer.

2. The article of claim 1, wherein the fluorocarbon-free release liner comprises a liner having a hydrocarbon-based release coating or a siloxane-based release coating.

3. The article of claim 1, wherein the substrate comprises a release liner free of fluorocarbon compounds, the release liner free of fluorocarbon compounds comprising a hydrocarbon-based release coating or a siloxane-based release coating.

4. The article of claim 1, wherein the siloxane polymer is a functionalized siloxane polymer, a non-functionalized siloxane, or a combination thereof; The functionalized siloxane polymer comprises a functional group selected from alkoxysilane groups, terminal silanol groups, olefin groups, hydride groups, epoxy groups, vinyl ether groups, (meth)acrylate groups, thiol groups, or combinations thereof, wherein the functional group may be terminal or side-chain, and is thermosetting or UV-curable in the presence of a catalyst or initiator; and The nonfunctionalized siloxane polymers include siloxane block copolymers, nonfunctionalized siloxane polymers that can be cured by ionizing radiation, or combinations thereof.

5. The article of claim 4, wherein the siloxane polymer comprises a functionalized siloxane polymer cured by thermosetting or UV curing, wherein thermosetting or UV curing includes wet curing, condensation curing, addition curing, cationic curing, free radical curing, or a combination thereof.

6. The article of claim 4, wherein the siloxane polymer is a nonfunctionalized siloxane polymer that has been crosslinked or cured by treatment with ionizing radiation, wherein the nonfunctionalized siloxane polymer comprises a silanol-functionalized siloxane polymer that has been terminated with a siloxane tackifying resin, a silanol-terminated siloxane, an alkyl-terminated siloxane, or a siloxane block copolymer, wherein the ionizing radiation is electron beam radiation, gamma radiation, or a combination thereof.

7. The article of claim 1, wherein the pressure activation of the adhesive results in an adhesion energy of less than 4 N·mm when tested with a 10 g contact force for a 180-second contact time using a polypropylene probe via probe adhesion measurement, but an adhesion energy of at least 40 N·mm when tested with a 2,000 g contact force for a 180-second contact time.

8. The article of claim 1, wherein, based on the total weight of the crosslinked adhesive composition, the at least one siloxane tackifying resin comprises MQ resin present in an amount of at least 62% by weight.

9. The article of claim 1, wherein the substrate comprises a release liner or an adhesive tape backing.

10. The article of claim 8, wherein the tape backing comprises a tape backing containing: a polymer film, a modified polymer film, a nonwoven fabric, a nonwoven fabric having inorganic fillers, textiles, glass fabrics, foams, metal foils, paper, or combinations thereof, wherein the polymer film comprises polyester, polycarbonate, polyimide, PEEK (polyether ether ketone), PTFE (polytetrafluoroethylene), PS (polystyrene), CBC (cyclic block copolymer), and polyolefins or combinations thereof, wherein the polyolefin is selected from BOPP (biaxially oriented polypropylene), COP (cyclic olefin polymer), COC (cyclic olefin copolymer), and polypentene.

11. The article of claim 1, wherein the pressure-activated adhesive article is capable of bonding to an adhesive surface having a medium surface energy of 36 dynes / cm to 300 dynes / cm (0.036 N / m to 0.30 N / m) or a low surface energy of less than 36 dynes / cm (0.36 N / m).

12. The article of claim 11, wherein the adhesive surface comprises a low surface energy surface, the low surface energy surface comprising a film or rigid sheet 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.

13. The article of claim 1, wherein the substrate and the pressure-activated adhesive layer are optically transparent.

14. A method of forming an adhesive article, the method comprising: A substrate having a first main surface and a second main surface is provided; Provides an adhesive coating composition comprising At least one siloxane polymer; and At least one siloxane tackifying resin; A fluorocarbon-free release liner is provided having a first primary surface and a second primary surface, the fluorocarbon-free release liner comprising a hydrocarbon-based release liner or a siloxane-based release liner, wherein at least the first primary surface is a release surface. The adhesive coating composition is disposed on at least a portion of the second primary surface of the substrate to form a layer; Dry the layer if necessary; The at least one siloxane polymer is crosslinked by applying heat, UV radiation or ionizing radiation to form a crosslinked layer, the crosslinked layer being a pressure-activated adhesive layer that is non-adhesive at room temperature and has a Tg of at least 50°C as measured by DMA (Dynamic Mechanical Analysis), but adheres to the adhesive surface when pressure is applied to the adhesive layer. as well as The first surface of the fluorocarbon-free release liner is disposed on the surface of the adhesive layer.

15. The method of claim 14, wherein the siloxane polymer is a functionalized siloxane polymer, a non-functionalized siloxane, or a combination thereof; The functionalized siloxane polymer comprises a functional group selected from alkoxysilane groups, terminal silanol groups, olefin groups, hydride groups, epoxy groups, vinyl ether groups, (meth)acrylate groups, thiol groups, or combinations thereof, wherein the functional group may be terminal or side-chain, and is thermosetting or UV-curable in the presence of a catalyst or initiator; and The nonfunctionalized siloxane polymers comprise siloxane block copolymers and nonfunctional siloxane polymers or combinations thereof that can be cured by ionizing radiation.

16. The method of claim 15, wherein crosslinking the at least one siloxane polymer comprises applying heat or UV radiation, the siloxane polymer being a functionalized siloxane polymer, and the solvent-free coating composition further comprises at least one curing catalyst or free radical initiator.

17. The method of claim 15, wherein crosslinking the at least one siloxane polymer comprises applying ionizing radiation, the siloxane polymer being a nonfunctionalized siloxane polymer, and the ionizing radiation comprising electron beam radiation, gamma radiation, or a combination thereof.

18. The method of claim 14, wherein, based on the total weight of the crosslinked adhesive composition, the at least one siloxane tackifying resin comprises an MQ resin present in an amount of at least 62% by weight.

19. The method of claim 14, wherein the substrate comprises a release liner or an adhesive tape backing.

20. The method of claim 19, wherein the tape backing comprises a polymer film, a modified polymer film, a nonwoven fabric, a nonwoven fabric having inorganic fillers, a textile, a glass fabric, a foam, a metal foil, paper, or a combination thereof.

21. The method according to claim 14, further comprising: Remove the fluorocarbon-free release liner from the adhesive layer; Make the adhesive layer contact the adhesion surface; as well as Pressure is applied to the adhesive layer to form an adhesive bond with the adhesive surface.

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