WO2025088387A1 - Pressure activated siloxane-based adhesive articles with fluorocarbon-free release liners - Google Patents

Abstract

Pressure activated adhesive articles include a substrate, a pressure activated adhesive layer disposed on the substrate, and a hydrocarbon-based release liner. The pressure activated adhesive layer is a crosslinked adhesive composition, with a siloxane polymer that has been crosslinked, and at least one siloxane tackifying resin. The pressure activated adhesive is non-adhesive at room temperature having a Tg of at least 50°C as measured by DMA (Dynamic Mechanical Analysis), but upon application of pressure to the adhesive layer the adhesive layer adheres to a substrate.

Description

PRESSURE ACTIVATED SILOXANE-BASED ADHESIVE ARTICLES WITH FLUOROCARBON-FREE RELEASE LINERS

Summary

Disclosed herein are pressure activated adhesives, pressure activated adhesive compositions, and adhesive constructions prepared from pressure activated adhesive articles. Pressure activated adhesive articles comprise a first substrate with a first major surface and a second major surface, a pressure activated adhesive layer disposed on at least of a portion of the second major 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 siloxane polymer that has been crosslinked, and at least one siloxane tackifying resin. The adhesive composition is a pressure activated adhesive that is nonadhesive at room temperature having a Tg of at least 50°C as measured by DMA (Dynamic Mechanical Analysis), but upon application of pressure to the adhesive layer the adhesive layer adheres to a substrate.

Also disclosed are methods of forming an adhesive article comprising providing a substrate with a first major surface and a second major 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 with a first major surface and a second major surface, where at least the first major surface is a release surface, disposing the adhesive coating composition on at least a portion of the second major surface of the substrate to form a layer, drying the layer if necessary, crosslinking the at least one siloxane polymer by the application of heat, UV radiation, or ionizing radiation to form a crosslinked layer that is 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 having a Tg of at least 50°C as measured by DMA (Dynamic Mechanical Analysis), but upon application of pressure to the adhesive layer the adhesive layer adheres to a substrate. In some embodiments, the method further comprises removing the fluorocarbon-carbon-free release liner from the adhesive layer, contacting the adhesive layer to a surface, and applying pressure to a portion or the whole of the adhesive layer to form an adhesive bond to a portion or the whole of the surface. Detailed Description

Adhesives have been used for a variety of marking, holding, protecting, sealing and masking purposes. Adhesive tapes generally comprise a backing, or substrate, and an adhesive. One type of adhesive, a pressure sensitive adhesive, is particularly useful for many applications.

Pressure sensitive adhesives are well known to one of ordinary skill in the art to possess certain properties at room temperature including the following: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength to be removed cleanly from the adherend. While PSAs require no more than finger pressure for contact formation, there is little to no change in their adhesion response if the applied pressure is above the finger pressure. Materials that have been found to function well as pressure sensitive adhesives are polymers designed and formulated to exhibit the requisite viscoelastic properties resulting in a desired balance of tack, peel adhesion, and shear strength. The most commonly used polymers for preparation of pressure sensitive adhesives are natural rubber, synthetic rubbers (e.g., styrene/butadiene copolymers (SBR) and styrene/isoprene/styrene (SIS) block copolymers), various (meth)acrylate (e.g., acrylate and methacrylate) copolymers and siloxanes. Each of these classes of materials has advantages and disadvantages.

A wide range of adhesive articles involve the placement of the adhesive article onto a surface to provide protection of the surface and to seal the surface, typically for a limited amount of time and then the article is removed. Examples of this include protection films, sealing tapes, and the like. Among the uses for article sealing that are becoming more prevalent are cover tapes of medical diagnostic devices (microplates or microcards). These uses provide particular problems because many medical diagnostic microplates have a contoured surface area with an array of micro channels and microcavities and the adhesive article has to conform to a specifically shaped surface when mechanically applied. Mechanical application of the adhesive article and achieving perfect sealing to the device surface can be difficult. There are a number of reasons for this difficulty. In some instances, the adhesives may touch other surfaces briefly before being adhered to the adherend surface. In this event, the adhesive article is bonded to unwanted surfaces prematurely, and therefore fails to seal of the diagnostic device. Additionally, if the adhesive article is misaligned upon contacting of the adhesive article to the surface, it can be difficult and time consuming to remove and re-adhere the adhesive article correctly to the surface. This process is referred to as “repositionability”.

A number of techniques have been developed to produce adhesive articles with ease of application features. Typically, these techniques involve modifying the adhesive surface by imparting a microstructured surface to the adhesive surface or disposing non-adhesive elements to the adhesive to prevent the adhesive surface from contacting and adhering to the surface prematurely. In this way the adhesive article can be placed in the proper alignment with the surface that it is to be adhered to and then the adhesive is typically pressed onto the substrate surface to form the adhesive bond. An example of such a technique is described in PCT Publication No. WO 03/05019, which describes “tack-on-demand” adhesives where spacers (such as beads) are placed on the adhesive surface at intervals. The spacers provide a barrier between the substrate surface and the adhesive layer to provide repositionability, and upon the application of pressure, the adhesive surface contacts the substrate surface, and an adhesive bond is formed.

While this technique has been effective in some applications, it also has drawbacks. Because these elements are non-adhesive, the regions where they are located on the adhesive surface are spots of non-adhesion and when attached to a substrate surface can form regions of adhesive or seal failure. Adhesive failure can cause the adhesive article to lift off of the substrate surface or can cause leaking, wrinkles and/or other non-uniformities in adhered adhesive articles. Additionally, disposing the non-adhesive elements to the adhesive surface can be a very complicated process. Additionally, frequently adhesive articles are supplied either disposed on a release liner or in the form of a roll, where the adhesive surface contacts the back surface of the adhesive article upon formation of the roll. Having protrusions or other spacers located on the surface of the adhesive layer generally requires a specialized liner with depressions to accommodate the spacers on the adhesive surface. Therefore, it is desirable to develop new and different adhesive articles capable of repositionability.

Another desirable feature for adhesives is being able to selectively adhere to surfaces, by which it is meant to have a portion of the adhesive layer adhere without having the entire adhesive layer adhere or having portions of an adhesive layer adhere more strongly than other portions of the adhesive layer. Recently a journal article by Deneke et al. in Adv. Mater. 2023, 35, 2207337 describes what they term “Pressure-Tunable Adhesives” (PTAs). These adhesives are contrasted with pressure sensitive adhesives because PSAs adhere with very little pressure, but additional pressure does not increase the level of adhesion, whereas the PTAs demonstrate increased adhesion with increased pressure. They present a highly tunable, scalable, and versatile PTA that is based on the self-assembly of stiff microscale asperities on an elastomeric substrate via thin film dewetting. In this way, PTAs have physically altered adhesive layers, where the asperities alter the physical properties of the adhesive surface.

Another complicating feature, especially in medical applications, is that many of the surfaces to which it is desired to attach adhesive articles are prepared from inert, non-reactive and thus low surface energy materials. However, since it is desired to adhere medical adhesive articles to a wide range of surfaces, the adhesive articles should be able to adhere to a wide range of surfaces. Siloxane pressure sensitive adhesives have found wide use 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 articles require a release liner or release surface on of the back side of the tape backing (referred to as an LAB or Low Adhesion Backsize) in order to be handled or used. The difficulty with siloxane pressure sensitive adhesives is that many classes of release liners or release surfaces are not suitable. Many release liners use silicone release layers, but as is well understood in the adhesive arts, likes bond well with likes, therefore, siloxane pressure sensitive adhesives typically bond well with siloxane release layers to form relatively strong adhesive bonds, and thus does not release well from the release surface. Similarly, siloxane pressure sensitive adhesives typically adhere well to low surface energy surfaces. Since hydrocarbon-based release liners rely upon low surface energy materials to produce a non-adhesive surface, hydrocarbon-based release liners are also generally unsuitable for siloxane pressure sensitive adhesives. Therefore, siloxane pressure sensitive adhesives typically require fluorinated release liners.

Fluorinated release liners, while very useful, are also very expensive. Additionally, as the industry begins to move away from the use of fluorinated materials, fluorinated release liners are going to become scarcer and more expensive, so it is desirable to find alternative release liners for use with siloxane adhesives.

In this disclosure, adhesive articles are described that are repositionable, not by modifying the surface of the adhesive so that the adhesive does not contact the substrate surface upon application of the adhesive article to the substrate surface, but rather by modifying the adhesive to make it “pressure activatable”. The currently described adhesives have very low or no initial wet out on the substrate surface to permit repositionability, but upon application of pressure the adhesive forms an adhesive bond to the substrate surface. Surprisingly, the fluorocarbon-free release liners can be used with these pressure activated adhesives providing easy and stable release. The fluorocarbon-free release liners include hydrocarbon-based release liners and siloxane-based release liners. Articles that contain a substrate, a pressure activated adhesive, and fluorocarbon-free release liner are disclosed herein.

It is a surprising result that hydrocarbon-based release liners are able to provide easy and stable release to siloxane-based adhesives since, as stated above, conventional siloxane-based PSAs can adhere strongly to low surface energy surfaces which often are hydrocarbon-based. It is even more surprising that siloxane-based release liners can provide easy and stable release to siloxane- based adhesives, since as pointed out above, it is well understood in the chemical arts that “likes attract likes” and typically siloxane-based adhesives adhere strongly to siloxane-based release liners. When the terms “hydrocarbon-based” and “siloxane -based” are used to describe release liners, it is meant that the release layer of the liners, and not the entire liner. For example, a siloxane- based release liner generally has a thin layer of siloxane release agent coated on at least one surface. The base substrate for the release liner can be any suitable material, polymer, paper, etc.

The term “fluorocarbon-free: as used to describe release liners, refers to the release layer of release liner where the release layer is free from fluoro groups. As used herein, "fluoro-" (for example, in reference to a group or moiety, such as in the case of "fluoroalkylene" or "fluoroalkyl" or "fluorocarbon") or "fluorinated" means (i) partially fluorinated wherein at least some of the carbon-bonded hydrogen atoms are replace by fluorine atoms such that there is at least one carbon- bonded hydrogen atom, or (ii) perfluorinated such that all carbon-bonded hydrogen atoms are replaced by fluorine atoms..

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

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

Heat activated adhesives are non-tacky at room temperature but become tacky and capable of bonding to a substrate at elevated temperatures. These adhesives usually have a T_g (glass transition temperature) or melting point (T_m) above room temperature. When the temperature is elevated above the T_g or T_m, the storage modulus usually decreases and the adhesive becomes tacky.

Pressure Activated Adhesive (PAA), the term pressure activated adhesive refers to an adhesive that is different from a Pressure Sensitive Adhesive or a Heat Activated Adhesive in that it is non-adhesive at room temperature, being non-tacky or having extremely low tack at room temperature. PAAs can have a Young’s Modulus as measured by DMA (Dynamic Mechanical Analysis) at room temperature that is equal to or greater than 1.0 MPa, above the Dahlquist Criterion for tack of 0.3 MPa, is not self-wetting, and has a Tg above 50°C as measured by as measured by DMA (Dynamic Mechanical Analysis). While the PAAs are not activated by heat, layers of the adhesive, upon the application of pressure, adhere to a substrate. In other words, a layer of the adhesive does not adhere to a substrate surface until substantial pressure is applied to the adhesive layer, and upon the application of pressure the adhesive layer forms an adhesive bond to the substrate. The definition of pressure sensitive adhesives states that the adhesive adheres with finger pressure, in other words a very light pressure. Pressure activated adhesives on the other hand require the application of a pressure that is greater than finger pressure.

Adhesive properties used herein include “self-wetting” and “repositionable”, the term selfwetting refers to the ability of an adhesive layer to spontaneously wet a substrate surface to which the adhesive layer is contacted. Self-wetting is often a property of pressure sensitive adhesives but is not a property of the pressure activated adhesives of this disclosure. Repositionability refers to the ability of an adhesive layer to be placed on a surface and be easily removed from the surface and re-attached to the surface. Repositionability is often not a property of pressure sensitive adhesives, especially those that are self-wetting, but it is a property of the pressure activated adhesives of this disclosure.

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

The term “crosslinked” as used herein refers to polymers that chemically or physically crosslinked. Chemical crosslinks are those that involve chemical bonds between polymer chains. Physical crosslinks involve interactions between polymer chains without the formation of chemical bonds. Examples of physical crosslinking interactions between polymer chains include “hydrogen interactions”. Hydrogen interactions, sometimes called “hydrogen bonding”, is not in fact chemical bonding but involves the interaction of an electron-poor hydrogen atom on one polymer chain, with an electron-rich atom on another polymer chain, such as an oxygen atom. This phenomenon is observed for example in polymers that contain urethane, urea or polyoxamide linkages. For example, when a urea linkage is present: -NH-C(O)-NH-, where C(O) is a carbonyl group C=O. the electron-poor hydrogen atoms attached to the nitrogen atoms on the urea linkage of one polymer can interact with the oxygen atom of the carbonyl on another polymer chain to form a hydrogen interaction. While each individual hydrogen interaction is not strong, when many of such interactions are present between polymer chains the combined interaction can be quite strong. The cumulative effect of the hydrogen interactions provides a physically crosslinked polymeric matrix. In this disclosure, siloxane block copolymers are physically crosslinked, but may also contain chemical crosslinks.

The term “siloxane -based” as used herein refer to polymers or units of polymers that contain siloxane units. The terms silicone or siloxane are used interchangeably and refer to units with dialkyl or diaryl siloxane (-SiRzO-) repeating units. The term “hydrocarbon-based” as used herein refer to polymers that contain hydrocarbon units, typically aliphatic (that is to say saturated) hydrocarbon units.

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

The terms “Tg” and “glass transition temperature” are used interchangeably. If measured, Tg values are determined by Differential Scanning Calorimetry (DSC) at a scan rate of 10°C/minnte, unless otherwise indicated. Typically, Tg values for copolymers are not measured but are calculated using the well-known Fox Equation, using the homopolymer Tg values provided by the monomer supplier, as is understood by one of skill in the art.

The term “adjacent” as used herein when referring to two layers means that the two layers are in proximity with one another with no intervening open space between them. They may be in direct contact with one another (e.g. laminated together) or there may be intervening layers.

The terms “polymer” and “macromolecule” are used herein consistent with their common usage in chemistry. Polymers and macromolecules are composed of many repeated subunits. As used herein, the term “macromolecule” is used to describe a group attached to a monomer that has multiple repeating units. The term “polymer” is used to describe the resultant material formed from a polymerization reaction.

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

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

The terms “free radically polymerizable” and “ethylenically unsaturated” are used interchangeably and refer to a reactive group which contains a carbon-carbon double bond which is able to be polymerized via a free radical polymerization mechanism.

Unless otherwise indicated, the terms “optically transparent”, and “visible light transmissive” are used interchangeably, and refer to an article, fdm or adhesive that has a high light transmittance over at least a portion of the visible light spectrum (about 400 to about 700 nm). Typically, optically transparent articles have a visible light transmittance of at least 90% and a haze of less than 10%.

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

The term “solvent-free” as used herein when referring to coating compositions means that the coating composition is essentially free of solvent. By essentially free of solvent, it is meant that no solvent is added to the composition so that the coating composition is essentially 100% solids and the coating composition is coated and cured with no provision for the removal of solvent.

The term “heavy metal free” as used herein when referring to coating compositions means that the coating composition is essential free of silicone curing catalysts comprising heavy metals, such as tin, platinum, and/or rhodium. By essentially free of heavy metals, it is meant that no silicone curing catalyst is added to the composition, as curing is carried out without the need for a catalyst that contains heavy metals.

Disclosed herein are pressure activated adhesive articles. The pressure activated adhesive article comprises a substrate with a first major surface and a second major surface, a pressure activated adhesive layer with a first major surface and a second major surface, where the first major surface of the pressure activated adhesive layer is disposed on at least of a portion of the second major surface of the substrate, and a fluorocarbon-free release liner disposed on the second major surface of the pressure activated adhesive layer. The pressure activated adhesive layer comprises a crosslinked adhesive composition, where the crosslinked adhesive composition comprises at least one siloxane polymer that has been crosslinked, either chemically or physically, and at least one siloxane tackifying resin. The adhesive composition is a pressure activated adhesive that is nonadhesive at room temperature having a Tg of at least 50°C as measured by DMA (Dynamic Mechanical Analysis), but upon application of pressure to the adhesive layer the adhesive layer adheres to a substrate.

As described above, a pressure activated adhesive is one that upon application of light pressure does not form a strong adhesive bond but rather upon the application of substantial pressure (such as more than finger pressure) forms a strong adhesive bond. One useful method for measuring such a pressure activation property is through the use of probe tack measurements. Probe tack measurements are well known in the adhesive arts. One particularly suitable method for use with pressure activated adhesives, is to press the probe to the adhesive surface at a relatively low pressure and measure the adhesion when the probe is removed from the adhesive surface. The probe is subsequently pressed to the adhesive surface at a higher pressure and again the adhesion is measured when the probe is removed from the adhesive surface. The adhesion values at different pressures can be ratioed according to the equation:

Ratio = (Adhesion at high pressure)/( Adhesion at low pressure).

The probe tack can be measured for pressure activated adhesive surfaces as well as for pressure sensitive adhesive surfaces. Since a variety of probes can be used at a variety of pressures, the absolute values of the ratios described above can vary, but in general when a PAA surface is tested the same way as a PSA, the ratio is much lower for the PSA. Again, depending upon the specific conditions of testing, the ratio can be 20 or greater for a PAA and less than 5 for a PSA. This is one of the many indicators that show the difference between a pressure activated adhesive and a pressure sensitive adhesive. A pressure sensitive adhesive is by definition permanently and aggressively tacky and thus when contacted with the probe even at low pressure still gives a high probe tack value. The pressure activated adhesives on the other hand, not only do not feel tacky to the touch, but also at low pressures give a low probe tack value. Upon application of higher pressure, however, the pressure activated adhesives give a high probe tack value. It should also be noted that the pressure activated adhesives of this disclosure are not only different from PSAs but also are different from the PTAs (Pressure-Tunable Adhesives) were additional pressure increases the adhesion of PTA to a substrate. The PAAs of this disclosure reach a maximum level of adhesion to a substrate upon the application of pressure and the adhesion level does not increase upon the application of higher and higher pressures.

The pressure activated adhesive articles comprise a substrate. Examples of suitable substrates are release liners and tape backings. Release liners are well known in the adhesive arts and are films from which adhesive compositions or coatings can be readily removed. Exemplary release liners include those prepared from paper (e.g., Kraft paper) or polymeric material (e.g., polyolefins such as polyethylene or polypropylene, ethylene vinyl acetate, polyurethanes, polyesters such as polyethylene terephthalate, and the like, and combinations thereof). In some embodiments, the substrate may be a release liner. Although fluorocarbon-free release liners are particularly desirable and are described in greater detail below, in some instances the substrate may be a fluorinated release liner. Fluorinated release liners are coated with a layer of a release agent such as a fluorosilicone-containing material or a fluorocarbon-containing material. If the substrate is a release liner, a silicone PAA transfer tape could be made. Transfer tapes are well understood in the adhesive arts as being a free-standing adhesive layer provided between two release liners. As mentioned above, if the substrate is a release liner, it is often desirable that the release liner be a fluorocarbon-free release liner, In this way, both the substrate release liner and the release liner of the article are both fluorocarbon free release liners. The fluorocarbon-free release liner may be the same as the fluorocarbon-free release liner located on the other major surface of the adhesive layer or it may be different.

As mentioned above, the fluorocarbon-free release liner may be a hydrocarbon-based release liner or a siloxane-based release liner. Each of these types of release liners are described below.

The hydrocarbon-based release liners are liners that are coated with a layer of hydrocarbon release agents, such as those described in US 7,816,477 or are commercially available from Toray as PJ271. The fact that the current siloxane-based PAAs release from release liners coated with a layer of hydrocarbon release agents is surprising, since siloxane-based adhesives typically do not release from release liners coated with a layer of hydrocarbon release agents.

The siloxane-based release liners are liners that are coated with a layer of siloxane release agents. Examples of suitable siloxane release liners include a silicone release liner available from Laufenberg as 78B and those available from SilicoNature as 30065 and 30076.

Examples of suitable tape backings include a polymeric film, a modified polymeric film, a non-woven, a non-woven with inorganic fillers, a textile, a glass fabric, a foam, a metal foil, a paper, or a combination thereof.

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

The pressure activated adhesive articles of this disclosure also comprise a pressure activated adhesive layer disposed on at least of a portion of the second major surface of the substrate. The pressure activated adhesive layer comprises a crosslinked adhesive composition, wherein the crosslinked adhesive composition comprises at least one siloxane polymer that has been crosslinked, and at least one siloxane tackifying resin.

The pressure activated adhesive layer can have a wide range of thicknesses. Typically, the adhesive layer has a thickness of at least 10 micrometers, up to 2 millimeters, and in some embodiments the thickness will be at least 20 micrometers up to 1 millimeter thick. A wide range of intermediate thicknesses are also suitable, such as 25-500 micrometers, 200-400 micrometers, and the like.

A wide range of siloxane polymers are suitable for preparing the pressure activated adhesive layer. The siloxane polymer may be a functionalized siloxane polymer, a non-functionalized siloxane, silicone thermoplastic polymer, or a combination thereof. Each of these types of siloxane polymers are described in detail below. Functionalized siloxane polymers comprise functional groups selected from alkoxysilane groups, terminal silanol groups, alkene groups, silicon hydride groups, epoxy groups, vinylether groups, (meth)acrylate groups, thiol groups, or a combination thereof. Those functional groups could be either terminal or pendant, unless otherwise indicated. The reactions that are used to form crosslinks with these functionalized siloxane polymers are described below.

As used herein, the term “curing” refers to polymerization which may or may not result in crosslinking. The functionalized siloxane polymers are cured, meaning that they are polymerized through the functional groups, resulting in interconnected networks. This cured polymer may be the crosslinked adhesive composition, or the cured polymer may be exposed to ionizing radiation to further crosslink the cured polymer.

A wide variety of siloxane materials are suitable to form the crosslinked siloxane matrices of this disclosure. Generally, the siloxane materials are fluids that are described by Formula 1 below:

Formula 1 wherein Rl, R2, R3, and R4 are independently selected from the group consisting of an alkyl group, an aryl group and a functional group, each R5 is an alkyl group, each X is a functional or a nonfunctional group, and n and m are integers, and at least one of m or n is not zero.

Formula 1 can be used to describe both terminal-functional polysiloxanes as well pendentfunctional poly siloxanes. The X groups are frequently referred to as “terminal” groups and the Rl, R2, R3, and R4 groups are referred to as “pendant” groups and they can be functional groups as well. Functional polysiloxanes that are described by Formula 1 include: an alkoxysilane-functional polysiloxane (alkoxysilane groups); a hydroxyl-functional polysiloxane (silanol groups); a vinylfunctional or allyl-functional polysiloxane (terminal alkene groups), a hydride-functional polysiloxane (silicon hydride groups); an epoxy-functional polysiloxane (epoxy groups); a vinyl ether-functional polysiloxane (vinyl ether groups); a (meth)acrylate-functional polysiloxane ((meth) acrylate groups), a mercapto-functional polysiloxane (thiol groups); or a combination thereof. When Formula 1 is a polysiloxane with terminal functionality, it can be used to describe: an alkoxysilane-functional polysiloxane each X is -OR and one or more R5 groups may additionally be an -OR group, where R is an alkyl or aryl group; when Formula 1 is a hydroxyl-functional polysiloxane each X is -OH; when Formula 1 is a vinyl-functional polysiloxane, each X is a vinyl group (-HC^CHz); when Formula 1 is an allyl-functional polysiloxane each X is an allyl group (- CH2-CH=CH2); when Formula 1 is a hydride-functional polysiloxane each X is -H; when Formula 1 is an epoxy-functional polysiloxane, each X contains an terminal oxirane ring; when Formula 1 is a vinyl ether-functional polysiloxane each X is an vinyl ether group (-0-CH=CH2);when Formula 1 is a (meth)acrylate-functional polysiloxane each X is a (meth) acrylate group of the general formula (-(C0)CR=CH2, where (CO) is a carbonyl group C=O, and R is an H or a methyl group); when Formula 1 is a mercapto-functional polysiloxane each X is -SH. As described above, in the case of functional polysiloxanes, in addition to or in the alternative to the X groups, each Rl, R2, R3, and R4 is independently selected from the group consisting of an alkyl group, an aryl group and a functional group, so these groups can also provide functionality. For example, a wide variety of siloxanes with pendant functional groups are commercially available.

In some embodiments, Rl and R2 are alkyl groups and n is zero, i.e., the material is a poly (dialkylsiloxane). In some embodiments, the alkyl group is a methyl group, i.e., poly(dimethylsiloxane) (“PDMS”). In some embodiments, Rl is an alkyl group, R2 is an aryl group, and n is zero, i.e., the material is a poly(alkylarylsiloxane). In some embodiments, Rl is methyl group and R2 is a phenyl group, i.e., the material is poly (methylphenylsiloxane). In some embodiments, Rl and R2 are alkyl groups and R3 and R4 are aryl groups, i.e., the material is a poly (dialkyldiarylsiloxane). In some embodiments, Rl and R2 are methyl groups, and R3 and R4 are phenyl groups, i.e., the material is poly(dimethyldiphenylsiloxane). In some embodiments, the poly diorganosiloxane materials may be branched. For example, one or more of the Rl, R2, R3, and/or R4 groups may be a linear or branched siloxane with alkyl or aryl (including halogenated alkyl or aryl) substituents and terminal R5 groups.

In some commercially available embodiments, Rl, R2, R3, R4, and R5 are all methyl groups, making the material a polydimethyl siloxane or PDMS material. In other embodiments, at least some of the Rl, R2, R3, and R4 are aryl groups.

The functionalized siloxane polymer is crosslinked by moisture curing, condensation curing, addition curing, epoxy curing, free radical polymerization, thiol-ene reactions or a combination thereof.

One method of curing is condensation curing. Two related reaction types are included as condensation reactions. The first is the condensation reaction itself, the second is moisture curing, which is a 2-step condensation curing reaction. The difference between these two condensation reactions is the starting materials used. In the condensation reaction silanol groups (-SiOH) are present in the reactants, whereas in the moisture curing reaction, the reactive groups are precursor groups that react with water to form silanol groups. These formed silanol groups then undergo the condensation reaction. Condensation reactions involve the reaction of two silanol groups to form a -Si-O-Si- linkage and a molecule of water. As mentioned above, if the reactants contain silanol groups, this condensation reaction proceeds to form the cured matrix. In the moisture curing reaction, the reactants are precursors to silanols, typically alkoxy or acetoxy silanes (-SiOR). These precursor groups react with water to form silanol groups and a molecule of alcohol. The formed silanol groups then react by condensation to form a -Si-O-Si- linkage. This sequence is summarized in Reaction Scheme 1 below:

Reaction Scheme 1

In this reaction scheme, the first step is the reaction of the precursor with water to form silanol groups, and the second step is the condensation reaction. Typically, the moisture curing reaction is facilitated by a catalyst. Examples of suitable curing catalysts for this moisture curing reaction include alkyl tin derivatives (e.g., dibutyltindilaurate, dibutyltindiacetate, and dibutyltindioctoate commercially available as "T-series Catalysts" from Air Products and Chemicals, Inc. of Allentown, Pa.), and alkyl titanates (e.g., tetraisobutylorthotitanate, titanium acetylacetonate, and acetoacetic ester titanate commercially available from DuPont under the designation "TYZOR"). Other catalysts useful for the moisture curing reaction include acids, anhydrides, and lower alkyl ammonium salts thereof.

Another curing reaction is hydrosilylation. Hydrosilylation, also called catalytic hydrosilation, describes the addition of Si-H bonds across unsaturated bonds. When hydrosilylation is used for curing, typically both the Si-H and unsaturated bonds are present on siloxane molecules, either the same molecule or on different molecules. The hydrosilylation reaction is typically catalyzed by a platinum or rhodium catalyst, and generally heat is applied to effect the curing reaction. In this reaction, the Si-H adds across the double bond to form new C-H and Si-C bonds. This process in described, for example, in PCT Publication No. WO 2000/068336 (Ko et al.), and PCT Publication Nos. WO 2004/111151 and WO 2006/003853 (Nakamura).

Epoxy curing can be carried out by homopolymerization of the epoxy through the use of a catalyst or by reaction with a curing agent. Typically, the epoxy siloxanes are cured by hompolymerization so that no added curing agent is necessary. Epoxy homopolymerization is generally carried out with an acid or a base catalyst. Examples of suitable base catalysts include tertiary amine or imidazole catalysts. Typically, this curing requires the addition of heat to give complete curing. Examples of acid catalysts include Lewis Acid catalysts such as BF3, ZnCl₂, SnCL, FeCls, and AICI3. These acid catalysts typically react very quickly at room temperature. One particularly suitable class of catalysts are UV-activated salts. These salts are latent, meaning that they are inert until exposed to UV light, at which point the catalysts become active and initiate polymerization. Representative examples include the onium salts diphenyliodonium hexafluorophosphate, and triphenylsulfonium hexafluorophosphate.

Any of the polysiloxane materials that contain 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 radically 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. The free radical polymerization can be carried out under a variety of conditions using a variety of different types of free radical initiators. Photoinitiators have been found to be particularly suitable as describe in US Patent No. 5,514,730 (Mazurek).

Another curing mechanism is the thiol-ene reaction. In this reaction an ethylenically unsaturated group (an “ene”) reacts with a thiol group -SH, such that the -S and H groups add across the ene group to form a thioether linkage. The thiol-ene reaction is typically either a free radical initiated reaction and therefore includes a photoinitiator such as those described above or is a Michael Addition reaction catalyzed by either a base or a nucleophile.

The siloxane polymer may be a non-functionalized siloxane polymer. In this context, nonfunctionalized siloxane polymers are those that do not contain any functional groups that participate in a reaction to form the crosslinked adhesive compositions of this disclosure. The crosslinked adhesive composition is formed by crosslinking through the use of peroxide initiators or by exposing the non-functionalized siloxane polymer to ionizing radiation to form crosslinks, where ionizing radiation is E-beam radiation, gamma radiation, or a combination thereof. Non-functionalized siloxane polymers comprise a siloxane block copolymer, a nonfunctional siloxane polymer curable with ionization radiation, or a combination thereof.

Examples of non-functionalized siloxane polymers include: a silanol-functional siloxane polymer that has been end-capped with a siloxane tackifying resin; a silanol-terminated siloxane; an alkyl-terminated siloxane; or a siloxane block copolymer.

Examples of silanol-functional siloxane polymers that has been end-capped with a siloxane tackifying resin are described in PCT Publication No. WO 2020/099999. The silanol groups present on the silanol-functional siloxane polymers condense with hydroxyl groups on siloxane tackifying resin to form the end-capped polymers.

Generally, the silanol-functional siloxane polymers are fluids that are described by Formula 1A below:

Formula 1A where Rl, R2, R3, and R4 are independently selected from the group consisting of an alkyl group, or an aryl group, 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. In some embodiments, Rl and R2 are alkyl groups and n is zero, i.e., the material is a poly (dialkylsiloxane). In some embodiments, the alkyl group is a methyl group, i.e., poly(dimethylsiloxane) (“PDMS”). In some embodiments, Rl is an alkyl group, R2 is an aryl group, and n is zero, i.e., the material is a poly (alkylarylsiloxane). In some embodiments, Rl is a methyl group and R2 is a phenyl group, i.e., the material is poly (methylphenylsiloxane). In some embodiments, Rl and R2 are alkyl groups and R3 and R4 are aryl groups, i.e., the material is a poly (dialkyldiarylsiloxane). In some commercially available embodiments, Rl, R2, R3, R4, and R5 are all methyl groups, making the material a polydimethyl siloxane or PDMS material. In other embodiments, at least some of the Rl, R2, R3, and R4 are aryl groups.

The dynamic viscosity of the silanol end group-containing linear organopolysiloxane at 25 °C can be generally about 500 mm²/sec or greater, about 1000 mm²/sec or greater, or about 2000 mm²/sec or greater, and about 10,000,000 mm²/sec or less, about 1,000,000 mm²/sec or less, or about 500,000 mm²/sec or less.

The silanol-functional siloxane polymers are end-capped with siloxane tackifying resins. Siloxane tackifying resins have in the past been referred to as “silicate” tackifying resins, but that nomenclature has been replaced with the term “siloxane tackifying resin”. In this disclosure, the terms “silicate” and “siloxane” when referring to tackifying resins are used interchangeably.

Suitable siloxane tackifying resins include those resins composed of the following structural units M (i.e., monovalent R ^SiOj^ units), D (i.e., divalent R'2SiC>2/2 units), T (i.e., trivalent R'SiC>3/2 units), and Q (i.e., quaternary SiOq/2 units), and combinations thereof. Typical exemplary siloxane resins include MQ siloxane tackifying resins, MQD siloxane tackifying resins, and MQT siloxane tackifying resins. These siloxane tackifying resins usually have a number average molecular weight in the range of 100 to 50,000- gm/mole, e.g., 500 to 15,000 gm/mole and generally R' groups are methyl groups. MQ siloxane tackifying resins are copolymeric resins where each M unit is bonded to a Q unit, and each Q unit is bonded to at least one other Q unit. Some of the Q units are bonded to only other Q units. However, some Q units are bonded to hydroxyl radicals resulting in HOSiC>3/2 units (i.e., "TOH" units), thereby accounting for some silicon-bonded hydroxyl content of the siloxane tackifying resin.

According to the molecular weight of MQ resin, the level of silicon bonded hydroxyl groups (i.e., silanol) on the MQ resin may be 10 weight percent, 5 weight percent, 1.0 weight percent, or 0.5 weight percent based on the weight of the silicate tackifying resin.

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).

The end-capped linear organopolysiloxane with the silicate resin may be produced by the condensation reaction of the silanol end group-containing linear organopolysiloxane and the silicate resin. The condensation reaction can be generally carried out by using a catalyst. Examples of catalysts include a metal hydroxide including lithium hydroxide, sodium hydroxide, potassium hydroxide, and calcium hydroxide; a carbonate salt including sodium carbonate and potassium carbonate; a bicarbonate salt including sodium bicarbonate; a metal alkoxide including sodium methoxide or potassium butoxide; an organic metal including butyl lithium; a complex of potassium hydroxide and a siloxane; a nitrogen compound including ammonia gas, aqueous ammonia solution, methylamine, trimethylamine, and triethylamine. Since the catalyst can be easily removed by using reduced pressure stripping, ammonia gas or aqueous ammonia solution is advantageously used as the catalyst.

The condensation reaction may be carried out in the presence of a solvent or in the absence of a solvent. Examples of the solvent include an aromatic hydrocarbon including toluene and xylene; a linear or branched aliphatic hydrocarbon including hexane, heptane, octane, isooctane, decane, cyclohexane, methylcyclohexane, and isoparaffin; a hydrocarbon-based solvent including industrial gasoline, petroleum benzine, and solvent naphtha; a ketone including acetone, methyl ethyl ketone, 2-pentanone, 3-pentanone, 2-hexanone, 2-heptanone, 4-heptanone, methyl isobutyl ketone, diisobutyl ketone, acetonyl acetone, and cyclohexanone; an ester including ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, and isobutyl acetate; an ether including diethylether, dipropylether, diisopropylether, dibutylether, 1,2 -dimethoxy ethane, and 1,4-dioxane; a substituted acetate solvent including 2 -methy oxyethyl acetate, 2-ethyoxyethyl acetate, propylene glycol monomethylether acatate, and 2-butoxyethyl acetate; and mixtures thereof. In some embodiment, the solvent is an aromatic hydrocarbon, a linear or branched alphatic hydrocarbon, or a mixture of linear or branched alphatic hydrocarbon and ether, ester, or substituted acetate solvent. The temperature of the condensation reaction can be generally 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 may be carried out at the reflux temperature of the optional solvent.

The condensation reaction can be carried out until the about 50% or greater, about 70% or greater, or about 90% or greater of the silanol group in the silanol end group -containing linear organopolysiloxane is reacted. In some embodiments, substantially all of the silanol groups of the silanol end group-containing linear organopolysiloxane is consumed by the condensation reaction with the silicate resin by using an excess molar equivalent of the silicate.

Although the time of the condensation reaction is not particularly limited, the time can be generally about 0.5 hour or more, or about 1 hour or more, and about 48 hours or less, or about 24 hours or less.

After the condensation reaction, a neutralizer for neutralizing the base catalyst may be added, as needed. Examples of the neutralizer include an acidic gas including hydrogen chloride and carbon dioxide; an organic acid including octylic acid and citric acid; a mineral acid including hydrochloric acid, sulfuric acid and phosphoric acid. In addition to the neutralization, or instead of the neutralization, the base catalyst can be removed by reduced pressure stripping or washing with water.

In some embodiments, the silanol condensation end-capping reaction with siloxane tackifying resins are carried out in-situ during adhesive compounding process, e.g. hotmelt twin screw compounding in the absence of solvent.

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

In some embodiments, the non-functionalized siloxane is a silanol-terminated siloxane fluid. A wide variety of silanol-terminated siloxane fluids are suitable. Generally, the silanol-terminated siloxane fluids are linear materials described by Formula 1 below:

Formula 1 wherein Rl, R2, R3, and R4 are independently selected from the group consisting of an alkyl group, an aryl group and a functional group, 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.

In some commercially available embodiments, Rl, R2, R3, R4, and R5 are all methyl groups, making the material a polydimethyl siloxane or PDMS material. In other embodiments, at least some of the Rl, R2, R3, and R4 are aryl groups.

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

Another class of suitable siloxane polymers include for example, urea-based siloxane copolymers, oxamide-based siloxane copolymers, amide-based siloxane copolymers, urethane- based siloxane copolymers, and mixtures thereof.

Useful siloxane polyurea block copolymers are disclosed in, e.g., U.S. Patent Nos. 5,512,650, 5,214,119, 5,461,134, and 7,153,924 and PCT Publication Nos. WO 96/35458, WO 98/17726, WO 96/34028, WO 96/34030 and WO 97/40103.

Another useful class of siloxane polymers are oxamide-based polymers such as polydiorganosiloxane poly oxamide block copolymers. Examples of polydiorganosiloxane polyoxamide block copolymers are presented, for example, in US Patent Publication No. 2007- 0148475.

Another useful class of siloxane polymer is amide-based siloxane polymers. Such polymers are similar to the urea-based polymers, containing amide linkages (-N(D)-C(O)-) instead of urea linkages (-N(D)-C(O)-N(D)-), where C(O) represents a carbonyl group and D is a hydrogen or alkyl group.

Another useful class of siloxane polymer is urethane-based siloxane polymers such as siloxane polyurea-urethane block copolymers. Siloxane polyurea-urethane block copolymers include the reaction product of a polydiorganosiloxane diamine (also referred to as siloxane diamine), a diisocyanate, and an organic polyol. Examples are such polymers are presented, for example, in US Patent No. 5,214,119.

As was mentioned above, the siloxane block copolymers are physically crosslinked polymers. In addition to this physical crosslinking that is formed by hydrogen interactions, chemical crosslinks can also be formed between the polymers using the crosslinking techniques described herein. The above-described non-functionalized siloxanes are crosslinked to form a polymeric siloxane matrix by peroxide curing, radiation curing, or a combination thereof. In peroxide curing, a peroxide initiator is added to an uncrosslinked siloxane composition. Upon heating the peroxide decomposes to form radicals which react with siloxane to form polymeric radicals. The polymeric radicals combine to form crosslinks. A wide variety of peroxides have been found to be suitable, such as di-acyl peroxides and peroxy esters.

A particularly suitable curing mechanism for forming the crosslinked siloxane matrix of this disclosure is radiation curing using ionizing radiation. A variety of ionizing radiation sources are suitable, especially E-beam (electron beam), and gamma ray radiation, as described in PCT Publication No. WO 2010/056543. An advantage of E-beam and gamma ray radiation is that nonfunctional siloxane materials are curable in this way and no initiators or catalysts, especially heavy metal-based catalysts, are required. Additionally, the level of crosslinking desired can be controlled by controlling the level of E-beam or gamma ray radiation used. Further, unlike thermal crosslinking chemistries, E-beam crosslinking allows high viscosity solventless siloxane formulations to be hotmelt processed without concerns about pre-mature crosslinking in the siloxane compounding and bodying processes.

While peroxide curing can be used to form the crosslinked polymeric siloxane layer, in many embodiments an electron beam, gamma ray radiation, or a combination thereof is used to form the crosslinked polymeric siloxane layer.

A variety of procedures for E-beam and gamma ray curing are well-known. The cure depends on the specific equipment used, and those skilled in the art can define a dose calibration model for the specific equipment, geometry, and line speed, as well as other well understood process parameters.

Commercially available electron beam generating equipment is readily available. For the examples described herein, the radiation processing was performed on a Model CB-300 electron beam generating apparatus (available from Energy Sciences, Inc. (Wilmington, MA).

Commercially available gamma irradiation equipment includes equipment often used for gamma irradiation sterilization of products for medical applications. Such equipment may be used to crosslink the polysiloxane layers of the present disclosure.

The adhesive compositions of this disclosure also comprise at least one siloxane tackifying resin. Siloxane tackifying resins have in the past been referred to as “silicate” tackifying resins, but that nomenclature has been replaced with the term “siloxane tackifying resin”. In this disclosure, the terms “silicate” and “siloxane” when referring to tackifying resins are used interchangeably.

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).

The amount of siloxane tackifying resin present in the composition can vary depending upon the composition of crosslinked siloxane matrix. In some embodiments, the level siloxane tackifying resin is relatively high, being present in an amount of at least 62 weight %, based on the total weight of the crosslinked adhesive composition, in some embodiments at least 64% by weight. In other embodiments, particularly the MQ-modified siloxane polymers, the level of siloxane tackifying resin can be lower, being present in an amount 54 weight % or greater.

The pressure activated adhesive articles of the present disclosure have a wide range of desirable properties including repositionability as described above. One of the most surprising properties is that fluorocarbon-free release liner, such as a hydrocarbon-based release liner or siloxane-based release liner, can be used in these articles. Perhaps even more surprising is that despite the removability from a hydrocarbon-based or siloxane-based release liner, the pressure activated adhesive articles, when pressure activated, are capable of strong bonding to wide range of surfaces, including medium and even low surface energy substrates. Generally, medium surface energy substrates are those with a surface energy of from 36-300 dynes/cm (0.036-0.30 N/m), and low surface energy substrates are those with a surface energy of less than 36 dynes/cm (0.36 N/m). Examples of low surface energy surfaces include films or rigid plates of PE (polyethylene), PS (polystyrene), PC (polycarbonate), PET (polyethylene terephthalate), PP (polypropylene), COC (cyclic olefin copolymer), COP (cyclic olefin polymer), PDMS (poly dimethylsiloxane), or combinations thereof.

In some embodiments, it may be desirable that the pressure activated adhesive articles be optically transparent or even optically clear. In these embodiments, the substrate and the pressure activated adhesive layer are optically transparent.

Also disclosed herein are methods of forming adhesive articles. In some embodiments, the method comprises providing a substrate with a first major surface and a second major 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 major surface of the substrate to form a layer, drying the layer if necessary, crosslinking the at least one siloxane polymer by the application of heat, UV radiation, or ionizing radiation to form a crosslinked layer that is a pressure activated adhesive layer, providing a fluorocarbon-free release liner with a first major surface and a second major surface, where at least the first major 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 substrates, pressure activated adhesive layers, and fluorocarbon-free release liners are described in detail above. 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.

The adhesive coating composition may be solventless, that is to say 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.

In some embodiments, when crosslinking the at least one siloxane polymer comprises the application of 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.

In other embodiments, when crosslinking the at least one siloxane polymer comprises the application of ionizing radiation, the siloxane polymer is a non-functionalized siloxane polymer, and the ionizing radiation comprises E-beam radiation, gamma radiation, or a combination thereof.

In some embodiments, the method further comprises removing the fluorocarbon-free release liner from the adhesive layer, contacting the adhesive layer to a surface, and applying pressure to the adhesive layer to form an adhesive bond to the surface. As mentioned above, the pressure activated adhesive layers bond to a wide range of surfaces including low and medium surface energy surfaces.

Examples

These examples are merely for illustrative purposes only and are not meant to be limiting on the scope of the appended claims. All parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight, unless noted otherwise. Solvents and other reagents used were obtained from FUJIFILM Wako Pure Chemical Corp, or Sigma-Aldrich Chemical Company; Milwaukee, Wisconsin unless otherwise noted. The following abbreviations are used: mm = millimeters; in = inches; g = grams; kg = kilograms; lb = pounds; Hz = Hertz; kV = kilo Volts; mA - milliAmps; Mrad - Megarads; mpm - meters per minute; Pa - Pascals; kPa - kiloPascals; MPa = MegaPascals; psi = pounds per square inch; sec = seconds; min = minutes; hrs = hours; N = Newtons; SP = Synthetic Polymer.

Table of Abbreviations

Example Set II. Non-MQ-resin Capped Examples

Test Methods

Tack- Probe Tack test

The probe tack test was evaluated by using a Texture analyzer. A testing strip of 5 in long and 1 in wide is mounted onto the underside of a steel plate that has multiple holes where the probe will be lowered to touch the adhesive for an allotted amount of time. This steel plate plus adhesive construction is then placed onto a stage with the probe directly above one of the holes. The probe is lowered and adheres to the samples adhesive side. Depending on the target force and the contact time, the probe will pull away from the adhesive, and the force required to pull the probe from the adhesive face is measured as adhesive force.

The details of the test conditions are as follows.

Stainless Steel Probe:

Device : Texture Analyzer

Probe label : TA-57R

Probe size (diameter) : 7mm

Probe shape : Round type 7mm- 1” R (Stable Micro Systems)

Probe material : Stainless steel

Trigger force : 1 g

Target force : 5g, 150g

Pre-test speed from trigger to target force : 0.05 mm/sec

Contact time : 1 sec

Test speed : 10 mm/sec

Proportional-Integral-Differential (PID) : 10 (P) 5 (I) 15 (D)

Test atmosphere : 23°C/50%RH

Repeat test number : N5

Polypropylene Probe:

Device : Texture Analyzer

Probe size (diameter) : 7mm

Probe shape : Round type 7mm- 1” R (Stable Micro Systems)

Probe material : Polypropylene

Trigger force : 1 g

Target force : 10g, 2000g

Pre-test speed from trigger to target force : 0.05 mm/sec

Contact time : 0.1 sec

Test speed : 10 mm/sec Proportional-Integral-Differential (PID) : 10 (P) 5 (I) 15 (D)

Test atmosphere : 23°C/50%RH

Repeat test number : N5

The area under the curve was recorded as the probe tack force, and the average value by n5 noted.

Liner Release Force

Liner release force was evaluated with an IMASS Model SP-2300 tester. The liner side of a test piece of 8 inches x 1 inch (20 cm x 2.5 cm) was applied on the measurement stage by double coated tape and the edge of the adhesive construction was pinched with a chuck to perform the measurement. Test speed was 12 in/min (30 cm/min) or 90 in/min (229 cm/min) and the result is an average of 3 tests. The results are presented in N/25mm.

In this disclosure, a release liner force of 0.3N/25mm or less was defined as good liner release level.

Peel Adhesion Force

Peel adhesion force was measured by IMASS SP-2300. Each testing strip was applied to a clean polypropylene panel at 23°C/50%RH. Each testing strip was 6 inch (15 cm) x 1 inch (2.5 cm). The testing strips were laid down on the polypropylene panel and a 2Kg roller was rolled across the testing strip for one down and back cycle. The samples dwelled on the panel for either 5 min or 30 min before testing. Another set of testing was putting the testing strip down onto the polypropylene panel and instead of a 2 Kg roller, very light finger pressure was used to laminate and push the air pockets out. This then dwelled for 5 min before testing. The 180° Peel tests were run at 0 in/min (229 cm/min) and the reported value is the average of 3 tests in N/25mm. The fracture mode was also recorded as PO: Pop off (it means clean peel) or AN: Anchor failure.

Tensile strength and elongation at break

Tensile force and elongation at break were measured by an Instron 5900 Series. Dog bone shaped testing samples were cut with a die cutter and clamped into the jaws/grips of the Instron to produce the tensile force and elongation at break. The force at material rupture is known as the tensile strength (psi), and the distance the test sample stretch is known as the elongation at break (%).

Examples

For Comparative Example CE1, Tape-1 was used as supplied. For Comparative Examples CE2-CE4, Silicone- 1 and Tackifier- 1 -were mixed in a twin screw extruder at the ratios according to the Table 1 below and coated on Backing-1 through a rotary rod die at 51 micrometer (2mil) thickness and cured with E-beam radiation with 300kev and the doses shown in Table 1. The prepared samples were tested and the results are shown in Table 2.

Table 1

NA = Not Applicable

Table 2

Preparation of Examples E1-E9

For example El, Silicone Adhesive-1 (SA-1) was coated on liner 3, dried and cured at 70°C for 15min, to give an adhesive layer with a thickness of 51 micrometers (2 mils), and laminated to Backing-3

For examples E2-E7; Silicone- 1 and Tackifier- 1 -were mixed in a twin screw extruder at the ratios according to Table 3, coated on the Backing listed in Table 3 through a rotary rod die to the thickness shown in Table 3, and cured with E-beam radiation with 200kev (except for E3 300kev) and doses shown in Table 3. Examples E5-E6 were coated and cured on Liner-4 and then laminated to the Backing.

For Examples E8-E9 Silicone-2 (silicone polyoxamide copolymer) and Tackifier-2 were mixed at the ratio according to the Table 3 in THF at 35% solids. The solution was coated onto Liner-3 through a knife coated with a 178 micrometer (7 mil) gap and dried at 70°C for 15 minutes to a thickness of 25 micrometers (1 mil).

The prepared samples were tested and the results are shown in Tables 4 and 5.

Table 3

Table 4

Table 5

Examples E10-E20

For Example E10; Silicone-5 (silicone polyurea copolymer) and Tackifier-3 were mixed at the ratio of 45:55 in the mixed solvent of (30.3% IPA, 56.2% toluene, and 13.5% xylenes (added from addition of Dow 2-7066 MQ Resin)) at 28% solid. The solution was coated onto liners according to Table 6 with a knife coated with a 178 micrometer (7 mil) gap and dried at 70°C for 15 minutes to a thickness of 25 micrometers (1 mil).

The prepared samples were tested and the results are shown in Tables 6.

Table 6

For Example El l; Silicone Adhesive-1 (SAI) was coated onto liners according to the Table 7 through a knife coated with a 178 micrometer (7 mil) gap and dried at 70°C for 15 minutes to a thickness of 25 micrometers (1 mil).

The prepared samples were tested and the results are shown in Tables 7.

Table 7

For examples E12-E20; Silicone 6-8 and Tackifier-1 were mixed in a twin screw extruder at the ratios according to Table 8, coated on 3mil (75 micrometer) BOPP through a rotary rod die, cured with E-beam radiation with 200kev and doses shown in Table 8, and laminated to liner-5 according to Table 8. The prepared samples were tested and the results are shown in Tables 8. Table 8

Example Set II. MQ-Resin Capped Examples Test Methods

Tack- Probe Tack test

The probe tack test was evaluated using a Texture analyzer.

The details of the test conditions are as follows.

Probe size (diameter) : 7mm

Probe shape : Round type (Rl/2inch curvature, P/7D, Stable Micro Systems)

Probe material : Stainless steel or Polypropylene

Trigger force : 1 g

Target force : 5, 10, 20, 150, 2000 g

Pre-test speed from trigger to target force : 0.05 mm/sec

Contact time : 1 sec and 0.1 sec

Test speed : 10 mm/sec

Proportional-Integral-Differential (PID) : 40 (P) 20 (I) 5 (D)

Test atmosphere : 23°C/50%RH

Repeat test number : N6

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

Liner Release Force

Liner release force was evaluated with an IMASS Model SP-2100 tester. Polyester film Backing-5 side of a test piece of 8 inches x 1 inch (20 cm x 2.5 cm) was applied on the measurement stage by double coated tape and the edge of the release film was pinched with a chuck to perform the measurement. Test speed was 12 in/min (30 cm/min) and the result is an average of 3 tests. The results are presented in N/25mm.

In this disclosure, a release liner force of 0.3N/25mm or less was defined as good liner release level.

Peel Adhesion Force

Peel adhesion force was measured by TENSILON RTG-1250 (A&D Company, Limited)

The details of the test conditions are as follows.

Test mode : 180°peel direction

Sample size : 25mm x 100mm

Substrate : Polypropylene (PP)

Surface treatment of substrate : Wipe by IPA/heptane

Pressure condition : 2kg rubber roller- Iround trip at 50mm/sec

Delay time : 20 min after pressure Test atmosphere : 23°C/50%RH

Test speed : 300 mm/min

Repeat test number : N3

The fracture mode was also recorded as follows:

PO : Pop off (it means clean peel)

AN : Anchor failure

In this disclosure, 7 N/25mm or more was defined as good adhesive strength.

Gel Fraction ratio

The gel fraction ratio was calculated by initial sample weight (A) and residue sample weight (B) after soaking into enough solvent solution and drying.

Sample size : about 25 x 25 mm

Soaking solvent : Toluene

Soaking time : 24hrs at room temperature

Drying condition : 130°C for 2hrs

Gel fraction ratio = (A) - (B) / (A) %

Rheology (Dynamic Mechanical Analysis)

Rheology data such as G’ (storage elastic modulus) and G” (loss modulus), tan5 (= G’7G’) were measured by Dynamic Mechanical Analysis. Tg values were extracted by the peak of Tan5.

Sample preparation : 0.05 mm thickness PSA was laminated until over 2.0 mm, and then test piece was punched out to 8mm.

Device : ARES-G2 (TA Instruments)

Test mode : Temperature scan

Frequency : 1 Hz

Temp, rising speed : 5°C/min

Measurement temp. : from -20 or 0°C to 160°C

Synthesis Examples

Condensation of Hydroxyl-functional Siloxanes with MQ Resin Examples MMS1-MMS3 and Comparative Synthesis Example MMCS1

A series of condensation polymers (labeled MMS for MQ-Modified Synthesis or MMCS for MQ-Modified Comparative Synthesis) were prepared by reacting Silicones and Tackifier- 1 in a toluene solution with added Catalyst- 1, for 1 day at 70°C, end capping agent was added followed by 12 hrs at 70°C.

The compositions are shown in Table SI Table SI

Examples

Preparation and Testing of Adhesive Compositions E21-E23 and Comparative Examples CE5-CE6

A series of adhesive compositions were prepared using the Synthesis Polymers (SP) corresponding to the MMCS or MMS polymers described above as shown in Table 6. For Comparative Example CE6 Silicone Adhesive-2 was used.

For Examples CE5, CE6, and El-3 the composition solutions were applied to Backing-5 and dried at 70°C for 10 minutes to form a layer of 0.05 mm thickness, E-beams were irradiated from the adhesive surface side opposite to the Backing-5 surface. Liner-2 was laminated on the irradiation surface side and adhesion characteristics on the opposite side were evaluated.

The E-beam radiation was treated under the following conditions:

Device : BROADBEAM (PCT Engineered Systems, LLC)

Accelerated voltage : 200 kV

Current value : 3, 5, 7 mA (3mA : 3Mrad, 5mA : 6 Mrad, 7mA : 80 Mrad)

Line speed : 5 mpm

Irradiated atmosphere : At room temperature, in a nitrogen atmosphere

Table 9

ND = Not Determined

The formed adhesive constructions were tested for Liner Release, Tack, Peel Adhesion, and DMA, the data are presented in Table 10.

Table 10

* - N/25mm

Claims

What is claimed is:

1. A pressure activated adhesive article comprising: a substrate with a first major surface and a second major surface, a pressure activated adhesive layer with a first major surface and a second major surface, wherein the first major surface of the pressure activated adhesive layer is disposed on at least of a portion of the second major surface of the substrate; and a fluorocarbon-free release liner disposed on the second major surface of the pressure activated adhesive layer, wherein the pressure activated adhesive layer comprising a crosslinked adhesive composition, wherein the crosslinked adhesive composition comprises: at least one siloxane polymer that has been crosslinked; and at least one siloxane tackifying resin; wherein the adhesive composition is a pressure activated adhesive that is nonadhesive at room temperature having a Tg of at least 50°C as measured by DMA (Dynamic Mechanical Analysis), but upon application of pressure to the adhesive layer the adhesive layer adheres to an adherent surface.

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

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

4. The article of claim 1 , wherein the siloxane polymer is a functionalized siloxane polymer, a nonfunctionalized siloxane, or a combination thereof; wherein the functionalized siloxane polymer comprises functional groups selected from alkoxysilane groups, terminal silanol groups, alkene groups, silicon hydride groups, epoxy groups, vinylether groups, (meth)acrylate groups, thiol groups, or a combination thereof, wherein the functional groups may be terminal or pendant, and capable of thermal or UV curing in the presence of catalysts or initiators; and the non-functionalized siloxane polymer comprises a siloxane block copolymer, a nonfunctional siloxane polymer curable with ionization radiation, or a combination thereof.

5. The article of claim 4, wherein the siloxane polymer comprises a functionalized siloxane polymer cured by thermal or UV curing, wherein thermal or UV curing comprises moisture 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 non-functionalized siloxane polymer that is crosslinked or cured by exposure to ionizing radiation, wherein the non-functionalized siloxane polymer comprises a silanol-functional siloxane polymer that has been end-capped with a siloxane tackifying resin, a silanol-terminated siloxane, an alkyl-terminated siloxane, or a siloxane block copolymer, wherein ionizing radiation is E-beam radiation, gamma radiation, or a combination thereof.

7. The article of claim 1, wherein the pressure activation of the adhesive is such that when measured by probe tack using a polypropylene probe, has an adhesion energy of less than 4 N.mm when tested by 10 grams of contact force with 180 seconds contact time, but has an adhesion energy of at least 40 N.mm when tested by 2,000 grams of contact force with 180 seconds contact time.

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

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

10. The article of claim 8, wherein the tape backing comprises a tape backing comprising a polymeric film, a modified polymeric film, a non-woven, a non-woven with inorganic fillers, a textile, a glass fabric, a foam, a metal foil, a paper, or a combination thereof, wherein the polymeric film comprises polyester, polycarbonate, polyimide, PEEK (poly ether ether ketone), PTFE (polytetrafluoroethylene), PS (polystyrene), CBC (cyclic block copolymers), and polyolefin selected from BOPP (biaxially oriented polypropylene, COP (cyclic olefin polymer), COC (cyclic olefin copolymer), and polypentene, or a combination thereof.

11. The article of claim 1, wherein the pressure activated adhesive article is capable of bonding to an adherent surface comprising a medium surface energy of from 36-300 dynes/cm (0.036-0.30 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 adherent surface comprises a low surface energy surface comprising 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 (poly dimethylsiloxane), 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 comprising: providing a substrate with a first major surface and a second major 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 comprising a hydrocarbon-based release liner or a siloxane-based release liner, with a first major surface and a second major surface, where at least the first major surface is a release surface; disposing the adhesive coating composition on at least a portion of the second major surface of the substrate to form a layer; drying the layer if necessary; crosslinking the at least one siloxane polymer by the application of heat,

UV radiation, or ionizing radiation to form a crosslinked layer that is a pressure activated adhesive layer that is non-adhesive at room temperature having a Tg of at least 50°C as measured by DMA (Dynamic Mechanical Analysis), but upon application of pressure to the adhesive layer the adhesive layer adheres to an adherent surface; and disposing the first surface of the fluorocarbon-free release liner on the surface of the adhesive layer.

15. The method of claim 14, wherein siloxane polymer is a functionalized siloxane polymer, a nonfunctionalized siloxane, or a combination thereof; wherein the functionalized siloxane polymer comprises functional groups selected from alkoxysilane groups, terminal silanol groups, alkene groups, silicon hydride groups, epoxy groups, vinylether groups, (meth)acrylate groups, thiol groups, or a combination thereof, wherein the functional groups may be terminal or pendant, and capable of thermal or UV curing in the presence of catalysts or initiators; and the non-functionalized siloxane polymer comprises a siloxane block copolymer and a nonfunctional siloxane polymer curable with ionization radiation, or a combination thereof.

16. The method of claim 15, wherein crosslinking the at least one siloxane polymer comprises the application of 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.

17. The method of claim 15, wherein crosslinking the at least one siloxane polymer comprises the application of ionizing radiation, the siloxane polymer is a non-functionalized siloxane polymer, and the ionizing radiation comprises E-beam radiation, gamma radiation, or a combination thereof.

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

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

20. The method of claim 19, wherein the tape backing comprises a polymeric film, a modified polymeric film, a non-woven, a non-woven with inorganic fillers, a textile, a glass fabric, a foam, a metal foil, a paper, or a combination thereof.

21. The method of claim 14, further comprising: removing the fluorocarbon-free release liner from the adhesive layer; contacting the adhesive layer to an adherent surface; and applying pressure to the adhesive layer to form an adhesive bond to the adherent surface.