WO2012166870A1

WO2012166870A1 - Thick film pressure sensitive adhesive and laminated structure made therefrom

Info

Publication number: WO2012166870A1
Application number: PCT/US2012/040139
Authority: WO
Inventors: Robert A. EKELAND; Min Hee Mini KWON; Youngsoo WOO
Original assignee: Dow Corning Corporation; Dow Corning Korea Ltd.
Priority date: 2011-06-02
Filing date: 2012-05-31
Publication date: 2012-12-06
Also published as: KR20140037886A; TW201319198A; JP2014522436A; CN103764784A

Abstract

A pressure sensitive adhesive (PSA) formulation that can be formed and cured into a thick film without sacrificing performance is provided. The PSA formulation exhibits optical transmittance that is at least 80% in both uncured and cured states. A PSA laminated structure in which the PSA formulation has a Si-H:vinyl ratio and coating thickness that provides for a very stable and low release force from a fluorosilicone release coating applied to a backing sheet or liner.

Description

THICK FILM PRESSURE SENSITIVE ADHESIVE AND LAMINATED STRUCTURE MADE

THEREFROM

FIELD

[0001] This disclosure relates generally to a pressure sensitive adhesive (PSA) formulaton that can be formed and cured into a thick film without sacrificing performance. This disclosure further relates to a PSA laminated structure in which the PSA has a Si- H:vinyl ratio and coating thickness that provides for a very stable and low release force from a fluorosilicone release coating present on a liner sheet.

BACKGROUND

[0002] Silicone compositions suitable for forming pressure sensitive adhesives are known in the art. Many of these compositions contain solvent and thus have drawbacks associated with use, handling and the emission of flammable or volatile organic compounds. Low solvent and solventless compositions are also known, however their performance, such as adhesive strength, optical transmittance, and consistency of release force, among others, is deficient for some applications.

[0003] U.S. Patent No. 5,082,706 describes addition-curable silicone pressure sensitive adhesives that can be applied to the surface of an addition-cured fluorosilicone release coating to provide a releasable laminate. The release force of the laminate has a low to moderate value, while the adhesion and tack associated with the adhesive is high with all three values being stable with time. The laminate is prepared by contacting the release coating with a cured adhesive or by curing the adhesive while in contact with the release coating.

[0004] Japanese Kokai No. 2001-200221 describes a silicone gel adhesive sheet characterized by laminating in the following order: a separator, an adhesive layer, a substrate sheet, a silicone gel layer, and a second separator. The silicone gel adhesive sheet is used in a liquid crystal display.

[0005] Japanese Kokai No. 2006-290960 and No. 2004-225005 also provide a light transmitting pressure sensitive adhesive sheet installed between a liquid display panel and a transparent protection plate. The adhesive sheet renders the display with high visibility, shock absorption, and productivity. The light transmitting pressure sensitive adhesive sheet is composed of a transparent silica gel having a ball tack number of 5-30 (angle of inclination: 30 degree).

[0006] U.S. Patent No. 6,798,467 discloses a liquid crystal display device in which a non-tacky silicone sheet having rubber elasticity is provided between the display panel and an external transparent protection plate.

[0007] U.S. Patent No. 6,703, 120 describes a pressure sensitive adhesive (PSA) formulation used in making articles, such as cover tapes for analytical receptacles. The PSA formulation comprises two different polydiorganosiloxanes having at least two alkenyl groups, an organopolysiloxane MQ resin, an organohydrogenpolysiloxane, and a group VIIB-containing catalyst. The PSA formulation is applied to an ethylene/propylene backing at a coating weight of 0.8 grams/154.8 cm² and adhered to a polypropylene plate.

[0008] U.S. Patent No. 7,592,070 discloses an adhesive silicone elastomer sheet prepared by curing a hydrosilylation curable silicone elastomer composition comprising: an organopolysiloxane that contains at least one diorganosiloxane unit and at least two silicon- bonded alkenyl groups; an organopolysiloxane MQ resin; an organopolysiloxane that contains at least two silicon-bonded hydrogen atoms, and (D) a hydrosilylation catalyst.

[0009] U.S. Patent No. 7,659,003 provides a pressure sensitive adhesive film comprising a substrate film and a pressure sensitive adhesive layer formed on a surface of the substrate film. The pressure sensitive adhesive layer is prepared from a silicone composition comprising a diorganopolysiloxane having at least two alkenyl groups per molecule and a polyorganosiloxane having an Si-H bond. The alkenyl groups are present in an amount ranging from 0.0007 to 0.05 mole per 100 g of the diorganopolysiloxane. The molar ratio of Si-H bonds in the polyorganosiloxane to the alkenyl group(s) in the diorganopolysiloxane ranges from 0.5 to 20.

[0010] U.S. Patent No. 7,728,080 discloses a solvent-less silicone pressure sensitive adhesive composition that comprises a polyorganosiloxane with a polymerization degree of 300 to 2,000 and having at least two alkenyl group-containing organic groups, a polyorganohydrosiloxane having at least three silicon-bonded hydrogen atoms, a polydiorganosiloxane having alkenyl groups at both terminals, a polydiorganosiloxane having Si-H groups at both terminals, a MQ polyorganosiloxane resin, and a platinum-based catalyst. The composition enables the prevention of problems caused by residual or volatilized organic substances, such as the absorption of ultraviolet radiation or the like.

[0011] U.S. Patent No. 7,687,591 discloses solvent-less curable pressure sensitive adhesive (PSA) compositions exhibiting improved high temperature cohesive strength while maintaining good tack and adhesive properties. The PSA compositions comprise at least one organosiloxane polymer having on average at least two aliphatic unsaturations per molecule; at least one MQ resin; at least one reactive diluent that includes at least one hydrocarbon compound and at least one aliphatic unsaturation; at least one Si-H containing crosslinker having on average at least two silicon bonded hydrogen atoms per molecule; at least one hydrosilylation catalyst; and optionally at least one inhibitor.

SUMMARY

[0012] In overcoming the enumerated drawbacks and other limitations of the related art, the present disclosure provides a pressure sensitive adhesive (PSA) formulation capable of being formed and cured into a thick film without sacrificing overall performance. The PSA formulation generally comprises at least one MQ resin; at least one vinyl functional organosiloxane polymer; at least one organohydrogensilicon compound; a hydrosilyation catalyst; and at least one inhibitor. The PSA formulation has an uncured and a cured state with the PSA formulation capable of forming a film in the uncured state that has a thickness of about 100 micrometers or more in the cured state. The optical transmittance of the PSA formulation is at least 80% in both the uncured and cured states.

[0013] According to another aspect of the present disclosure, the PSA formulation may further comprise at least one of a high molecular weight dimethylmethylvinylsiloxane copolymer having dimethylvinyl endblocking moieties; a solvent; an olefin diluent; and an epoxy functional trimethoxysilane. Alternatively, the PSA formulation may also comprise at least two MQ resins; the second MQ resin containing a predetermined amount of vinyl functionality and an alkyl group. The PSA formulation has a ratio of Si-H bonds in the organohydrogensilicon compound to Si-vinyl bonds in the vinyl functional organosiloxane polymer that ranges between 1 :1 to 40:1 and alternatively between 1 :1 to 10:1 when desirable.

[0014] The MQ resin in the PSA formulation, which is a combination of R₃SiOi_/2 (M units) and Si0_4/2 (Q units), with the R group being an alkyl group has an M to Q ratio range of 0.6 to 1.2 and up to 5 weight percent of a silanol functionality. The vinyl functional organosiloxane polymer in the PSA formulation exhibits either a weight average molecular weight greater than about 400,000 amu or a weight average molecular weight that is less than 400,000 amu with a lower limit that is about 12,000 amu; and an amount of vinyl functionality that is in the range of about 0.01 wt.% to 0.4 wt.%.

[0015] According to another aspect of the present disclosure, a thick fjm _presSure sensitive ad_hesi e (PSA) laminate that exhibits high optical transmittance is provided. This laminate generally comprises: a backing sheet; a fluorosilicone release coating in contact with the backing sheet; and a PSA film in contact with the release coating, the PSA film comprising the PSA formulation as described above and hereafter. The PSA laminate has a wet-side and a dry-side when applied to the backing sheet or liner in the uncured state and then allowed to cure. The applied PSA film in its cured state exhibits a release force on the wet-side and on the dry-side that ranges from about 6 to 45 g/2.5 cm and about 5 to 37 g/2.5 cm, respectively, when pulled at a rate of 3 meters/minute. Alternatively, the PSA film exhibits a release force on the wet-side that ranges from about 25 to 45 g/2.5 cm and on the dry-side a release force that ranges from about 5 to 12 g/2.5 cm, when pulled at a rate of 3 meters/minute.

[0016] The release coating in the PSA laminate generally comprises: about 13 to 17 wt. % of an addition curable, fluoro-functional silicone polymer; about 80 wt. % of an alkane solvent; and about 0.5 wt. % of a Si-H functional cross-linker. [0017] Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

[0019] Figure 1A is a cross-sectional view of a PSA laminate prepared according to the teachings of the present disclosure; and

[0020] Figure 1 B is a cross-sectional view of a PSA laminate prepared according to another aspect of the present disclosure.

DETAILED DESCRIPTION

[0021] The following description is merely exemplary in nature and is in no way intended to limit the present disclosure or its application or uses. It should be understood that throughout the description and drawings, corresponding reference numerals indicate like or corresponding parts and features.

[0022] The present disclosure generally provides an addition curable, silicone pressure sensitive adhesive (PSA) formulation comprising at least one MQ resin [Component A]; at least one organosiloxane polymer having vinyl functionality [Components B - C]; at least one organohydrogensilicon compound [Component D]; a hydrosilyation catalyst [component E]; and at least one inhibitor [Component F]. The present disclosure also provides a fluorosilicone release coating that is optimized in terms of Si-H:vinyl ratio and can be applied to a backing sheet or release liner with an adhesive coating weight that provides for a very stable and low release force associated with the release of a PSA film (i.e., cured PSA formulation) from the liner. The PSA formulation and fluorosilicone release coating may be used, for example, in the construction and application of a touch screen or flat panel display. [0023] Optionally, the silicone PSA formulation may further comprise a high molecular weight dimethylmethylvinylsiloxane copolymer having dimethylvinyl end-blocking moieties [Component G]; a solvent [Component H], a second MQ resin containing a predetermined amount of vinyl functionality along with an alkyl R group [Component I]; an olefin diluent [Component J]; and/or an epoxy functional trimethoxysilane [Component K].

[0024] Component A comprises a resin having R₃SiOi_/2 (M units) and Si0_4/2 (Q units), where each R is a predetermined alkyl group, such as a methyl group. One skilled-in- the-art will understand that other aliphatic groups having up to about 20 carbon atoms may be used instead of a methyl group without exceeding the scope of the present disclosure. The molar ratio of M:Q units may range from about 0.6:1 to 4:1 (Component A1 ). According to another aspect of the present disclosure, the molar ratio of M:Q units may be about 0.92:1. Alternatively, the M:Q ratio can be about 0.98 (Component A2) or when desired the M:Q ratio may be greater than or equal to 1.0 (Component A3). Component A may also comprise up to 5 weight percent of silanol functionality with less than about 1 weight percent being alternatively used. Component A is present in the PSA composition in an amount greater than about 55 weight percent. Alternatively, Component A may range from 60 to 75 weight percent based on total resin solids or from 62 to 70 weight percent when desired. Component A may be prepared by any method known to one skilled-in-the-art and may include any resins known to be commercially available. Examples of Component A may include, but are not limited to, DC 2-7066 MQ resin, DC 2-7366 Resin, DC 2-7466 Resin, and mixtures thereof (Dow Corning Corporation, Midland, Michigan).

[0025] Components B and C are organosiloxane polymers end-blocked with vinyl functionality. According to another aspect of the present disclosure, these components may also include additional vinyl functionality. These two components differ from one another in that one of the organosiloxane polymers exhibits a high molecular weight, while the other polymer exhibits a medium to low molecular weight. Component B may exhibit a weight average molecular weight that is greater than about 400,000, while Component C exhibits a weight average molecular weight that is less than 400,000 amu with a lower limit of about 12,000 amu. The amount of vinyl functionality in Component B and Component C may range between about 0.01 % to 0.4%. The overall amount of Components B and C in the PSA formulation may be greater than 24 weight percent. Alternatively, the amount of Components B and C in the PSA formulation may range between 24 wt. % and about 32 wt. %.

[0026] One specific example, among many examples, for Component B is DC 4-

7009 Polymer (MF Vi gum, Dow Corning Corp., Midland, Michigan), which is a vinyl end- blocked polydimethylsiloxane (Vi-eb-PDMS) polymer having about 0.0014% vinyl functionality and a number average molecular weight on the order of 390,000 amu. Several specific examples for Component C include SFD 128 (Component C1 ) and SFD 1 19 (Component C2) available from Dow Corning Corp., Midland, Michigan. Component C1 is a vinyl end-blocked polydimethylsiloxane (Vi-eb-PDMS) polymer exhibiting a weight average molecular weight of 66,700 amu, a viscosity of 39,400 mPa-sec, a vinyl concentration of 0.081 %, and a volatility of 0.47%. Component C2 also is a vinyl end-blocked polydimethylsiloxane (Vi-eb-PDMS) polymer having a weight average molecular weight of 11 ,700 amu, a viscosity of 357 mPa-sec, a vinyl concentration of 0.47%, and a volatility of 0.43%. One skilled-in-the-art will understand that other vinyl end-blocked polydimethylsiloxane (Vi-eb-PDMS) polymers may be used, such as a polymer (Component C3) exhibiting a weight average molecular weight of 62,200 amu, a viscosity of 43,300 mPa- sec, a vinyl concentration of 0.087%, and a volatility of 0.05%.

[0027] Component D comprises at least one crosslinking organohydrogensiloxane compound having on average at least two Si-H bonds per molecule. The organohydrogensiloxane compounds that are suitable for use as Component D can be linear, branched, or cyclic molecules, and any mixtures or combination thereof. The amount of Component D added to the PSA formulation of the present disclosure will depend on the amount of Si-H groups present in this component and the total amount of alkenyl groups present in the PSA formulation arising from Components B and/or C, as well as any optional components containing reactive vinyl functionality. Generally, the ratio of Si-H:Si-vinyl ratio is between 1 :1 to 40:1 or alternatively between 1 :1 to 10:1 when desired.

[0028] Component D may include, but not be limited to, one or more organohydrogensiloxanes described as trimethylsiloxy-terminated polydimethyl- siloxanepolymethylhydrogensiloxane copolymers (Component D1 ), a mixture of dimethylhydrogensiloxy-terminated polydimethylsiloxane homopolymers and trimethylsiloxy-terminated polymethylhydrogensiloxane homopolymers (Component D2), or trimethylsiloxy-terminated polymethylhydrogensiloxane homopolymers (Component D3), among others, such as SL-2 type crosslinking polymers that have less than about 0.5% SiH. Each organohydrogensiloxane has between about 0.5% to 2.0% Si-H functionality and a viscosity at 25°C between 5 to 200 mPa-sec. The overall amount of Component D present in the PSA formulation may be greater than0.3 wt. %. Alternatively, Component D is present in the PSA formulation in a range between 0.5 wt. % and 5.5 wt. %.

[0029] One specific example of Component D1 is provided as DC 6-3570 (Dow

Corning Corp., Midland, Michigan). This particular example (DC 6-3570) is a trimethylsiloxy- terminated polydimethylsiloxane polymethylhydrogensiloxane copolymer having a viscosity of 5 mPa-sec and a Si-H concentration of 0.76%. Similarly, an example of Component D2 is DC 7049 (Dow Corning Corp.); a mixture of homopolymers containing 75 parts dimethylhydrogensiloxy-terminated polydimethylsiloxane and 25 parts trimethylsiloxy- terminated polymethylhydrogensiloxane. In this example, the dimethylhydrogensiloxy- terminated polydimethylsiloxane homopolymer exhibits a viscosity of 10 mPa-sec and a Si-H concentration of about 0.16%, while the trimethylsiloxy-terminated polymethylhydrogensiloxane homopolymer exhibits a viscosity of 200 mPa-sec and a Si-H concentration of about 1.61 %. An example of Component D3 is DC 7048 Crosslinker (Dow Corning Corp.); a trimethylsiloxy-terminated polymethylhydrogensiloxane homopolymer having a viscosity of 20 mPa-sec and a Si-H concentration of about 1.57%.

[0030] Component E may comprise any catalyst known to one skilled-in-the-art to be useful in catalyzing a hydrosilylation reaction. Component E may be a platinum group metal- containing catalyst. By definition, a platinum group metal refers to ruthenium, rhodium, palladium, osmium, iridium and platinum metals, as well as any mixtures or complexes thereof. The platinum group metal may comprise solid or hollow particles, a layer deposited on a carrier such as silica gel or powdered charcoal, or an organometallic compound or complex. Several examples of platinum-containing catalysts include chloroplatinic acid, either in hexahydrate form or anhydrous form, and a platinum-containing catalyst obtained by reacting chloroplatinic acid or platinum dichoride with an aliphatically unsaturated organosilicon compound. One specific example of Component E, among many examples, is Pt 4000 Catalyst (Dow Corning Corp., Midland, Michigan), which is described as a vinyl end- blocked polymer diluted platinum complex of 1 ,3 diethenyl-1 ,1 ,2,2-tetramethyldisililoxane having a platinum concentration of about 5,200 ppm.

[0031] The appropriate amount of the catalyst used in the PSA formulation is predetermined by the specific catalyst used. The platinum catalyst is present in an amount sufficient to provide at least 2 parts per million (ppm) of platinum in the PSA formulation. Typically, Component E is present in the PSA formulation in an amount that is greater than about 0.7 wt. %. Alternatively, the amount of Component E present in the PSA formulation may range from 0.7 wt. % to 1.5 wt. %. The catalyst may be added as a single species or as a mixture of two or more different species.

[0032] Component F comprises an inhibitor, which can be any material that is known to one skilled-in-the-art capable of being used at ambient temperatures to inhibit the catalytic activity of a platinum group metal catalyst. In other words, Component F is a material that retards activity of the catalyst (Component E) at room temperature but does not interfere with the properties of the catalyst at elevated temperatures. Component F may include, but not be limited to, ethylenically or aromatically unsaturated amides, acetylenic compounds, silylated acetylenic compounds, ethylenically unsaturated isocyanates, olefinic siloxanes, unsaturated hydrocarbon monoesters and diesters, hydroperoxides, nitriles, and diaziridines. Generally, Component F will be added to the PSA formulation in an amount ranging from 0.05 to 1 wt. %. Several specific examples, among many examples, of Component F include diallyl maleate (Component F1 ), ethynyl cyclohexanol (Component F2), and bis-2- methoxy-1-methylethylmaleate (Component F3).

[0033] According to another aspect of the present disclosure, the PSA formulation may optionally comprise one or more of Components G-K. Component G is a high molecular weight dimethylmethylvinylsiloxane copolymer having dimethylvinyl end-blocking moieties. The weight average molecular weight of Component G is greater than 400,000 amu and the vinyl concentration greater than 0.4%. Component G is a dimethylvinyl end- blocked dimethylmethylvinylsiloxane copolymer having a number average molecular weight of about 254,000 amu and a vinyl concentration of about 0.7%. Component H is an optional solvent, such as xylene, among others. Component I is a second MQ resin containing a predetermined amount of vinyl functionality along with an alkyl R group, such as a methyl group. A specific example of Component I is DC 2-7286 Resin (Dow Corning Corp.), a vinyl MQ resin. Components J and K represent an olefin diluent and an epoxy functional trimethoxysilane, respectively. Several specific examples of Component K include Z-6040 epoxysilane (Dow Corning Corp.), glycidoxypropyl trimethoxysilane (Syl-Off^® SL-9250, Dow Corning Corp.), or dimethyl, methylvinyl siloxane with epoxide (Syl-Off^® SL-9176, Dow Corning Corp.). Components G, H, I, and K may be added to the PSA formulation in an amount ranging from about 1.5 wt. % to 2.5 wt. %; less than 10 wt. %; 5 wt. %; and 1 wt. %, respectively. Alternatively, Component H may be present in the PSA formulation in an amount ranging between about 1 wt. % to 5 wt. %.

[0034] Component J is a reactive diluent that comprises at least one hydrocarbon compound having between about 8 to 18 carbon atoms with some degree of aliphatic unsaturation. Component J may be either linear or branched with the aliphatic unsaturation being either pendant or terminal. Several examples of useful reactive diluents include dodecene, tetradecene, hexadecene, and octadecene, among others. Component J may be added to the PSA formulation in an amount ranging from about 1 to 7 wt%.

[0035] The mixing of the different Components A-K can be done using any equipment known to one skilled-in-the-art. The temperature that such mixing is done is also not critical as long as the solvent stripping procedure is accomplished and the integrity of the ingredients is not compromised. For example, the solvent may be stripped under reduced pressure while increasing the temperature to 150°C when desirable. The mixing of the different components is preferably performed at a temperature that is below the flashpoint of the components present in the PSA formulation. For example, a temperature of 90 to 100°C is desirable when using tetradecene as Component J.

[0036] The silicone PSA formulation of the present disclosure may be used in a variety of applications by virtue of its unique properties, including but not limited to, excellent adhesive and cohesive strength, high transparency, high tack, very low alpha particle emissions, high moisture resistance, resistance to hot or cold environments, good electrical properties, high ionic purity, and good adhesion to low energy substrates, such as polyethylene terephthalate (PET). For example, these silicone PSA formulations may be used in adhesive tapes, bandages, low-temperature backings, transfer films, labels, emblems and decorative or informative signs. In addition, these silicone PSA formulations may be used in the assembly of automotive parts, toys, electronic circuits, or keyboards. Alternatively, the silicone PSA formulations may be used in the construction and application of a laminated touch screen or flat panel display.

[0037] The properties exhibited by the silicone PSA formulation of the present disclosure provides an enhancement in the workability of the formulation and the ability of a laminate prepared using the PSA formulation to undergo subsequent convertability processes and operations. Convertability is a term that generally refers to a number of post- coating processes associated with using an adhesive laminate. These processes include, but are not limited to, die cutting, stripping, slitting or perforating, weaving or sewing, sheeting, guillotining, and printing. Die-cutting refers to cutting through the laminate to the surface of the release liner, while guillotining, slitting, and perforating refers to cutting cleanly through the laminate. Since the cost of converting an adhesive laminate into a finished product is a function of the speed and efficiency at which it undergoes the various convertability operations, the properties associated with the PSA formulation of the present disclosure provides a manufacturer with the benefits of lower manufacturing costs and increased productivity.

[0038] The various properties exhibited by the PSA formulations of the present disclosure may be measured using multiple techniques and methods known to one skilled- in-the-art. For example, a Polyken Probe Tack instrument may be used to obtain tack measurements from samples coated onto a 2 mil polyester film. In this test, a dwell time of 1.0 second and a probe speed of 0.5 cm/sec are commonly used. Adhesion testing may be performed using a conventional Instron tester or the like. Such a tester typically pulls a 1 inch (2.5 cm) wide strip of the PSA formulation coated and cured onto a 2 mil polyester film from a clean stainless steel panel at a rate of 7.5 m/min. The release properties of the PSA formulations from both wet cast and dry sides may be measured using a peel tester, such as a 3M90 or ZPE-1000 peel tester (Instrumentors, Inc., Ohio). In this test, a predetermined amount of the PSA formulation is coated onto a PET backing (e.g., 50 micrometers thick) using a shimmed bar to yield a PSA layer or film that exhibits a thickness of 175 micrometers after curing. Curing of the PSA formulation is achieved by heating the formulation to an elevated temperature, e.g., 120°C, for several minutes in a forced air oven. The viscosity exhibited by the PSA formulations at ambient or elevated temperatures may be measured using a conventional stress-controlled or shear-controlled rheometer equipped with a parallel plate cell or the like. Finally, the optical properties associated with the PSA formulation, such as percent transmittance, may be measured using a 1 cm cuvette on an UV-Vi spectrophotometer at a predetermined wavelength (i.e. ,550 nm).

[0039] Several PSA Compounds 1-7 were prepared according to the teachings of the present disclosure by mixing together various amounts of Components A-D and F-K with the corresponding amount of Component E (Platinum hydrosilation catalyst) as shown in Table 1. A The values in Table 1 are provided in weight percentages of each Component A- K used in Compounds 1-7. The weight percentage listed for Components A-D and F-K represent the amount of each of these base components used to prepare Compounds 1-7. Thus the weight percentages listed for Components A-D and F-K in Table 1 for each Compound 1-7 are equivalent to 100 wt. % of the base PSA formulation (minus Component E). The weight percentage indicated for Component E is considered to be in addition to the weight percentage listed for Components A-D and F-K. The weight percentage of Component E is derived from the overall sum of all components contained within the PSA formulation including the various base components A-D and F-K, as well as Component E. Each catalyzed Compound 1-7 was then coated using a shimmed bar onto a fluorosilicone coated PET backing sheet (50 micrometer thickness).

[0041] Table 1

[0042] Each of the PSA Compounds 1-7 after being applied to the PET backing sheet exhibited a consistent thickness on the order of 175 microns after curing. Cure was achieved by heating the PSA formulation coated on the PET backing sheet to 120°C for 2 minutes in a forced air oven.

[0043] The PSA formulations of the present disclosure may be applied and cured as thick films or layers without sacrificing performance. More specifically, the PSA formulations are applied in layers at least 100 micrometers in thickness. Alternatively, the PSA formulations may be applied in layers that are at least 150 micrometers thick or in layers that are 175 micrometers thick or more when desirable. The properties, such as adhesion, peel (release), tack, viscosity, and percent transmittance measured for Compounds 1-7 are summarized in Table 2. The overall percent solids of Compounds 1-6 prepared according to the teachings of the present disclosure range from 70 to 100 percent with a resin/polymer ratio greater than 1.3. Conventional PSA formulations normally exhibit a percent solid less than 65% and a resin/polymer ratio less than 1.3. The viscosity exhibited by Compounds 1- 7 ranges between 2,000 and 30,000 mPa-sec. Alternatively, the viscosity of the PSA prepared according the present disclosure may range between 2,000 and 3,000 mPa-sec as shown for Compounds 2-6. [0044] Still referring to Table 2, the PSA formulations prepared, applied, and cured according to the present disclosure as a 175 micrometer thick film exhibit very consistent measurements in regards to adhesion and probe tack. More specifically, Compounds 1-7 exhibit adhesion to steel values that range from 1500 to 2500 g/2.5 cm and probe tack values that are between 150 g and 1050 g. In addition, Compounds 1-7 exhibit a very stable and low release force. On the wet-side of the applied and cured PSA formulation, the release force exhibited by Compounds 1-7 range from 6 to 45 g/2.5 cm when pulled at a rate of 3 meters/minute. On the dry-side of the applied and cured PSA formulation, the release force exhibited by Compounds 1-7 range from 5 to 37 g/2.5 cm when pulled at a rate of 3 meters/minute. Alternatively, the wet- and dry-side release force values may range between 7 to 35 g/2.5 cm @ 3 meters/minute and from 5 to 12 g/2.5 cm @ 3 meters/minute, respectively.

[0045] The transparency of the PSA formulations in the liquid state and after application and curing remains substantially unchanged. As shown in Table 2, the percent transmittance measured for Compounds 1-7 at 550 nm in the liquid state range from 30% to about 96%. After application and curing of Compounds 1-7 in thick film form, the percent transmittance values exhibited by these films at 550 nm exhibits very little change with some films exhibiting greater transparency. The percent transmittance exhibited by Compounds 1-7 after application and curing of the resulting thick film range between 83% to 96%.

[0046] According to another aspect of the present disclosure, a fluorosilicone release coating is provided that has a Si-H:vinyl ratio and coating thickness optimized to provide for a very stable and low release force when used with the previously described PSA formulations to form a laminated structure. More specifically, the PSA formulations, which are used in conjunction with a fluorosilicone release liner, exhibits a very stable release force and a high level of initial adhesion to the surface of the release coating on the liner. Referring now to Figure 1A, a laminated structure 1 is shown in which the release coating 5 is applied to the surface of a backing sheet or release liner 10. The PSA formulation is then applied and cured to form a coating or film 15 on the surface of the release coating 5. The laminated structure 1 may comprise one backing sheet or release liner 10 as shown in Figure 1A. Alternatively, the laminated structure 1 may also utilize a second backing sheet or liner 10 having a release coating 5 applied to its surface as shown in Figure 1 B. In this scenario (Figure 1 B), the PSA film 15 is sandwiched between backing sheets or release liners 10. The backing sheets or liners 10 may be identical or different depending upon the application and desired properties.

[0047] Table 2

Compound Compound Compound Compound Compound Compound Compound

% Solids

Resin/Polymer

Viscosity, m Pa-sec

Adhesion to Steel (wet side)

g/2.5 cm @ 0.3 m/min

Probe Tack (wet side)

0.5 sec dwell, 5 g, 0.5 cm²

Release Force (wet side)

g/2.5 cm @ 3m/min

Release Force (dry side)

g/2.5 cm @ 3m/min

Film % Transmittance

150 microns @ 550nm

Liquid % Transmittance

1 cm@550 nm

[0048] The fluorosilicone release coating 5 is comprised of an addition curable, fluoro-functional silicone polymer (Component L); a small amount of a vinyl functional siloxane polymer (Component M); an alkane solvent (Component N), such as heptane; and a cross-linker (Component O). The release coating 5 may also contain a small amount of a platinum catalyst used in the cure of the coating. The vinyl functional siloxane may be tetramethyldivinyldisiloxane, methylvinylcyclosiloxanes, and mixtures thereof. The cross- linker (Component O) may be a Si-H functional siloxane, including but not limited to methylperfluorobutylethyl methylhydrogensiloxane. The amount of polymers present in the release coating 5 is on the order of 20 weight percent. These polymers include about 13 to

17 wt. % of Component L and between about 3 to about 7 percent of Component M. The amount of the alkane solvent (Component N) present in the liquid release coating 5 is 80 wt. %. Only a small amount, i.e., 0.5% of Component O in the release coating 5 is desirable. An example of the fluorosilicone release coating 5 may include but not be limited to a mixture of Syl-Off^® Q2-7785 and Q2-7560 (Dow Corning Corp., Midland, Michigan).

[0049] The following specific examples are given to illustrate the invention and should not be construed to limit the scope of the invention. A summary of Components A-K as described above and utilized in preparing Compounds 1-7 in the following examples is provided in Table 3.

[0051] Table 3

Description of Component

Component Al MQ resin with MW = 15,000 and SiOH < 1%; 76% solids

Component A2 MQ resin with MW = 13,000 and SiOH < 1%; 72% solids

Component A3 MQ resin with MW = 10,000 and SiOH < 1%; 72% solids

Component B Vinyl EB PDMS polymer with Mn = 274,000 amu and Vinyl % = 0.014%

Vinyl EB polymer with MW = 66,700 amu; viscosity = 39,400 mPa-sec;

Component CI

Vinyl % = 0.081%; and volatility = 0.47%

Vinyl EB Polymer with MW = 11,700 amu; viscosity = 357 mPs; Vinyl% = Component C2

0.47%; and volatility = 0.43%

Vinyl EB Polymer with MW = 62,200 amu; viscosity = 43,300 mPa-sec; Component C3

Vinyl % = 0.087%; and Volatility = 0.05%

Me₃ end blocked Me₂,MeH Copolymer with viscosity = 5 mPa-sec; and Component Dl

Si-H% = 0.76%

75 parts SiMe₂H end blocked PDMS homopolymer with viscosity = 10 mPa-sec

Component D2 and Si-H% = 0.16%; and 25 parts Me₃Si endblocked MeH homopolymer with viscosity = 200 mPa-sec and Si-H% = 1.61%

Me₃Si end blocked MeH homopoymer with viscosity = 20 mPa-sec and

Component D3

Si-H% = 1.57%

Vinyl endblocked polymer comprising a diluted Platinum complex of 1,3

Component E

diethenyl-l,l,2,2-tetramethyldisililoxane with a Pt% = 5,200 ppm

Component Fl Diallyl Maleate

Component F2 EtCH (Ethynyl cyclohexanol)

Component F3 Bis-2methoxy-l-methylethylmaleate

Vinyl end blocked dimethylmethylvinylsiloxane with a Mn = 254,000 and

Component G

Vinyl % = 0.7%

Component H xylene

Component I Vinyl MQ resin

Component J 1-tetradecene

epoxy silane, glycidoxypropyl trimethoxysilane, or dimethyl, methylvinyl

Component K

siloxane with epoxide

[0052] Example 1 - Preparation of Compound 1

[0053] Compound 1 is a solvent-less silicone PSA formulation that can be prepared by two different methods. The first method involves mixing together 24.3 parts of component C3 and 66.8 parts of component A2 and then devolatilizing the mixture under vacuum at 130°C in a sigma blade mixer. After the volatiles are removed from the mixture, the mixture is cooled to 80°C and 0.24 parts of component F1 , 3.4 parts of component J and 5.48 parts of component D1 are blended into the mixture to form a PSA base only lacking component E. Alternately, Compound 1 can be formulated by mixing together component C3 and A2 in the body of a twin screw extruder at the above described ratios. These components are simultaneously mixed, heated to 200°C and vacuum devolatilized in the first ¾ of the extruder. Then, the above mentioned ratios for components F1 , J, and D1 are pumped into the body of the extruder at the ¾ point and mixed into the devolatilized resin/polymer mixture for the final ¼ of the length. The output PSA base of this continuous process is substantially similar to the PSA prepared in the first process described above. The weight percentage of each component used in preparing Component 1 is described in Table 1.

[0054] Example 2 - Preparation of Compounds 2-7

[0055] Compounds 2-7 are all solvent-based PSAs. The preparation of these compounds requires a reactor set-up capable of mixing relatively high viscosity liquids under an inert atmosphere (e.g., a N₂ blanket). Such a reactor set-up may include a 3-necked round bottom flask equipped with a mechanical paddle stirrer, a nitrogen gas inlet and a vapor condenser. In the preparation of each compound, the weight percentage of each component present in the compound as described in Table 1 was added to the flask. The mixture of components was then blended until the mixture was homogeneous. The resulting PSA Compound 2-7 was filtered through a 0.5 micrometer filter yielding a water white clear liquid.

[0056] Example 3 - Preparation of Component E (Release Coating)

[0057] A total of 100 parts of Components L and M were mixed with 400 parts of

Component N and 2.6 parts of Component O. This release coating mixture was applied via a wire wound rod to a 50-250 micrometer thick polyethylene terephthalate (PET) sheet and cured at 150°C for 30 seconds. The final coating weight as determined by XRF analysis was determined to be approximately 1.2 g/m². The coated side of this PET sheet can be used as the surface upon which the PSA formulation (Compounds 1-7) may be applied.

[0058] A person skilled in the art will recognize that the measurements described are standard measurements that can be obtained by a variety of different test methods. The test methods described in the examples represents only one available method to obtain each of the required measurements.

[0059] The foregoing description of various embodiments of the present disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the present disclosure to the precise embodiments disclosed. Numerous modifications or variations are possible in light of the above teachings. The embodiments discussed were chosen and described to provide the best illustration of the principles included in the present disclosure and its practical application to thereby enable one of ordinary skill in the art to utilize the teachings of the present disclosure in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the present disclosure as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

Claims

CLAIMS What is claimed is

1. A pressure sensitive adhesive (PSA) formulation capable of being formed and cured into a thick film without sacrificing overall performance, the PSA formulation comprising:

at least one MQ resin [Component A];

at least one vinyl functional organosiloxane polymer [Components B, C]; at least one organohydrogensilicon compound [Component D]; a hydrosilyation catalyst [component E]; and

at least one inhibitor [Component F];

wherein the PSA formulation has an uncured and a cured state; the PSA formulation capable of forming a film in the uncured state that has a thickness of 100 micrometers or more in the cured state; the PSA formulation exhibiting optical transmittance that is at least 80% in the cured state.

2. The PSA formulation of Claim 1 , wherein the PSA formulation further comprises at least one selected from the group of:

a high molecular weight dimethylmethylvinylsiloxane copolymer having dimethylvinyl endblocking moieties [Component G];

a solvent [Component H],

an olefin diluent [Component J]; and

an epoxy functional trimethoxysilane [Component K].

3. The PSA formulation of Claim 1 , wherein the PSA formulation comprises at least two MQ resins; the second MQ resin containing a predetermined amount of vinyl functionality and an alkyl group [Component I].

4. The PSA formulation of Claim 1 , wherein the MQ resin comprises a mixture of R3S1O1/2 (M units) and Si0₄/2 (Q units), the R group being an alkyl group;

wherein the MQ resin has a M to Q ratio range of 0.6 to 1.2 and up to 5 weight percent of a silanol functionality.

5. The PSA formulation of Claim 1 , wherein the vinyl functional organosiloxane polymer comprises:

a polymer that exhibits either a weight average molecular weight greater than 400,000 amu (Component B) or a weight average molecular weight less than 400,000 amu with a lower limit of 12,000 amu (Component C); and an amount of vinyl functionality that is in the range of 0.01 wt.% to 0.4 wt.%.

6. The PSA formulation of Claim 1 , wherein the PSA formulation has a ratio of Si-H bonds in the organohydrogensilicon compound to Si-vinyl bonds in the vinyl functional organosiloxane polymer that ranges between 1 :1 to 10:1.

7. The PSA formulation of Claim 1 , wherein the PSA formulation has a wet-side and a dry-side when applied to a release liner in the uncured state and then allowed to cure;

wherein the applied PSA formulation in the cured state exhibits a release force on the wet-side and on the dry-side that ranges from 6 to 44 g/2.5 cm and 5 to 33 g/2.5 cm, respectively, when pulled at a rate of 3 meters/minute.

8. A thick film pressure sensitive adhesive (PSA) laminate that exhibits high optical transmittance, the laminate comprising:

at least one backing sheet;

a fluorosilicone release coating in contact with the backing sheet; and a PSA film in contact with the release coating, the PSA film having an uncured state and a cured state, the PSA film comprising:

at least one MQ resin [Component A]; at least one vinyl-functional organosiloxane polymer [Components

B, C];

at least one organohydrogensilicon compound [Component D]; a hydrosilyation catalyst [component E]; and

at least one inhibitor [Component F];

wherein the PSA film is applied to the liner in the uncured state and has a thickness of 100 micrometers or more in the cured state; the PSA film exhibiting optical transmittance that is at least 80% in the cured state.

9. The PSA laminate of Claim 8, wherein the PSA film has a wet-side and a dry- side when applied to the release liner in the uncured state and then allowed to cure;

wherein the applied PSA film in the cured state exhibits a release force on the wet-side and on the dry-side that ranges from 6 to 45 g/2.5 cm and 5 to 37 g/2.5 cm, respectively, when pulled at a rate of 3 meters/minute.

10. The PSA laminate of Claim 9, wherein the wet-side release force ranges between 7 to 35 g/2.5 cm and the dry-side release force ranges from 5 to 12 g/2.5 cm, when pulled at a rate of 3 meters/minute.

11. The PSA laminate of Claim 8, wherein the PSA film further comprises at least one selected from the group of:

a solvent [Component H],

an olefin diluent [Component J]; and

an epoxy functional trimethoxysilane [Component K].

12. The PSA laminate of Claims 8-1 1 , wherein the MQ resin comprises a mixture of R3S1O1/2 (M units) and S1O4/2 (Q units), the R group being an alkyl group; wherein the MQ resin has a M to Q ratio range of 0.6 to 1.2 and up to 5 weight percent of a silanol functionality.

13. The PSA laminate of Claim 8, wherein the vinyl-functional organosiloxane polymer in the PSA film comprises:

a polymer that exhibits either a weight average molecular weight greater than 400,000 amu (Component B) or a weight average molecular weight less than 400,000 amu with a lower limit of 12,000 amu (Component C); and an amount of vinyl functionality that is in the range of about 0.01 wt.% to about 0.4 wt.%.

14. The PSA laminate of Claim 8, wherein the PSA film has a ratio of Si-H bonds in the organohydrogensilicon compound to the Si-vinyl bonds in the vinyl functional organosiloxane polymer that ranges between 1 :1 to 10:1.

15. The PSA laminate of Claim 8, wherein the release coating comprises:

between 13 to 17 wt. % of an addition curable, fluoro-functional silicone polymer (Component L);

between 3 to 7 wt. % of a vinyl-functional siloxane polymer (Component M);

80 wt. % of an alkane solvent (Component N); and

0.5 wt. % of a Si-H functional cross-linker (Component O).

16. A thick film pressure sensitive adhesive (PSA) laminate that exhibits properties amenable to undergoing convertibility operations, the laminate comprising:

at least one backing sheet;

a fluorosilicone release coating in contact with the backing sheet; and a PSA film in contact with the release coating, the PSA film having an uncured state and a cured state, the PSA film in the cured state having a wet-side and a dry- side, the PSA film comprising:

B, C];

at least one organohydrogensilicon compound [Component D]; a hydrosilyation catalyst [component E]; and at least one inhibitor [Component F];

wherein the PSA film is applied to the liner in the uncured state at a viscosity between 2,000 and 30,000 mPa-sec and has a thickness of 100 micrometers or more in the cured state;

wherein the PSA film exhibits a wet-side adhesion to steel value between 1500 and 2500 g/2.5 cm, a probe tack value between 150 g and 1050 g; and a release force between 6 and 45 g/2.5 cm when pulled at a rate of 3 meters/minute;

wherein the PSA film exhibits a dry-side release force between 5 to 37 g/2.5 cm when pulled at a rate of 3 meters/minute.