JP7491655B2 - Silicone pressure sensitive adhesive composition and uses thereof - Google Patents

Description

The present invention relates to a silicone pressure-sensitive adhesive composition. The present invention also relates to applications of the composition, such as an adhesive layer or elastic adhesive member obtained by curing the composition, and a laminate including an adhesive layer obtained by curing the composition.

Compared to acrylic and rubber-based pressure-sensitive adhesive compositions, polysiloxane-based pressure-sensitive adhesive compositions have excellent electrical insulation, heat resistance, cold resistance, and adhesion to various substrates, and are therefore used in heat-resistant adhesive tapes, electrically insulating adhesive tapes, heat seal tapes, plating masking tapes, etc. These polysiloxane-based pressure-sensitive adhesive compositions are classified into addition reaction curing types, condensation reaction curing types, peroxide curing types, etc., depending on their curing mechanism. Addition reaction curing type pressure-sensitive adhesive compositions are widely used because they cure quickly when left at room temperature or when heated, and do not produce by-products.

Taking advantage of the above-mentioned properties of polysiloxane-based pressure-sensitive adhesives and their ability to achieve high transparency when necessary, their application in advanced electronics materials and display element fields such as smart devices has been considered in recent years. Such devices have a structure in which a film consisting of multiple layers including an electrode layer and a display layer is sandwiched between transparent substrates, and it is expected that polysiloxane-based pressure-sensitive adhesives, which have excellent heat and cold resistance, will be effective in protecting the electrode layer and display layer and improving the adhesion between the layers.

However, polysiloxane-based pressure-sensitive adhesives are generally commercialized dissolved in organic solvents, so their applications are limited. In particular, in recent years, with countries around the world moving toward stricter environmental regulations, there has been a strong demand for the development of solvent-free polysiloxane-based pressure-sensitive adhesives. For example, Patent Documents 1 to 4 disclose solvent-free polysiloxane-based pressure-sensitive adhesives, but improvements in various properties are desired compared to solvent-based polysiloxane-based pressure-sensitive adhesives.

Japanese Patent Publication No. 6-84494 JP 2006-160923 A Patent No. 5130995 JP 2012-41505 A

The present invention has been made to solve the above problems, and aims to provide a silicone pressure-sensitive adhesive composition that has a viscosity that can be applied even if it contains almost no solvent as a low-solvent or solvent-free composition, has excellent curing properties, and the polyorganosiloxane-based pressure-sensitive adhesive formed by the curing reaction forms a pressure-sensitive adhesive layer that has a good balance of adhesive strength, tack, and high-temperature retention. Here, the high-temperature retention of the pressure-sensitive adhesive refers to the property that when two substrates are bonded using the pressure-sensitive adhesive, the adhesive strength can be maintained even at high temperatures without causing the substrates to shift in the bonding position or the two substrates to separate. Furthermore, the present invention aims to provide the use of the cured product of the silicone pressure-sensitive adhesive composition as a pressure-sensitive adhesive layer, the use of the composition as an elastic adhesive member in a wide range of applications, and an apparatus or device equipped with them.

As a result of intensive research into the above-mentioned problems, the present inventors have arrived at the present invention.
[1] (A) a linear or branched organopolysiloxane having at least two aliphatic unsaturated carbon-carbon bond-containing groups in one molecule and having a degree of siloxane polymerization in the range of 5 to 250;
(B) a linear organohydrogenpolysiloxane having silicon-bonded hydrogen atoms only at both molecular chain terminals;
(C) an organopolysiloxane resin containing, in the molecule, siloxane units (M units) represented by R ₃ SiO _1/2 (wherein R each independently represents a monovalent organic group) and siloxane units (Q units) represented by SiO _4/2 ;
(D) an organohydrogenpolysiloxane having at least three silicon-bonded hydrogen atoms in the molecule; and (E) a hydrosilylation reaction catalyst,
the ratio of the number of moles of silicon-bonded hydrogen atoms in component (B) to the number of moles of aliphatic unsaturated carbon-carbon bond-containing groups in component (A) is in the range of 0.90 to 1.30;
the ratio of the number of moles of silicon-bonded hydrogen atoms in components (B) and (D) combined to the number of moles of aliphatic unsaturated carbon-carbon bond-containing groups in component (A) is in the range of 0.95 to 1.35;
The viscosity of the entire composition at 25°C is in the range of 1,000 to 300,000 mPa·s, and
The content of the organic solvent is less than 20% by mass of the total composition.
This is accomplished by the silicone pressure sensitive adhesive composition.

The object of the present invention can also be advantageously achieved by the following silicone pressure-sensitive adhesive composition.
[2] When the total amount of components (A) to (D) is 100 parts by mass,
The total amount of the (A) component and the (B) component is in the range of 10 to 80 parts by mass,
The amount of component (C) is in the range of 10 to 80 parts by mass,
The amount of the (D) component is in the range of 0.01 to 10 parts by mass.
The silicone pressure-sensitive adhesive composition according to [1].
[3] The component (D) is
(D1) at least one selected from the group consisting of cyclic organohydrogenpolysiloxanes having at least three silicon-bonded hydrogen atoms in the molecule, and (D2) linear or branched organohydrogenpolysiloxanes having no silicon-bonded hydrogen atoms at the molecular chain terminals and having at least three silicon-bonded hydrogen atoms in the molecule.
The silicone pressure-sensitive adhesive composition according to [1] or [2].
[4] The silicone pressure-sensitive adhesive composition according to any one of [1] to [3], wherein the adhesive strength of a 40 μm-thick pressure-sensitive adhesive layer obtained by curing the composition to a SUS substrate is in the range of 100 to 2,500 gf/inch, as measured at a tensile speed of 300 mm/min using the 180° peel test method in accordance with JIS Z 0237.
[5] The silicone pressure-sensitive adhesive composition according to any one of items [1] to [4], wherein the content of the organic solvent is in the range of 0 to 5 mass % of the total composition, and the composition is a solvent-free or low-solvent composition.

Similarly, the object of the present invention can be suitably achieved by the following pressure-sensitive adhesive layer, laminate, and elastic adhesive member, and by using the same for the following applications.
[6] A pressure-sensitive adhesive layer obtained by curing the silicone pressure-sensitive adhesive composition according to any one of [1] to [5].
[7] A laminate comprising a film-like substrate and a pressure-sensitive adhesive layer formed by curing the silicone pressure-sensitive adhesive composition according to any one of [1] to [5].
[8] The laminate according to [7], comprising one or more film-like substrates, on which a release layer for the pressure-sensitive adhesive layer is provided.
[9] A film-like substrate,
a first release layer formed on the film-like substrate;
The laminate of [7] or [8], comprising: a pressure-sensitive adhesive layer formed by applying the silicone pressure-sensitive adhesive composition according to any one of [1] to [5] onto the release layer and curing the applied pressure-sensitive adhesive layer; and a second release layer laminated onto the pressure-sensitive adhesive layer.
[10] An elastic pressure-sensitive adhesive material obtained by curing the silicone pressure-sensitive adhesive composition according to any one of [1] to [5].
[11] An electronic device or electrical device comprising the elastic adhesive member according to [10].

The silicone pressure-sensitive adhesive composition of the present invention is a low-solvent or solvent-free composition that has a viscosity that can be applied even if it contains almost no solvent, has excellent curing properties due to a hydrosilylation reaction, and can form a pressure-sensitive adhesive layer that has sufficient adhesive strength, tack, and high-temperature retention when cured, and has excellent mechanical strength and elongation of the adhesive layer after curing, and has sufficient adhesiveness for practical use. Furthermore, the cured product of the silicone pressure-sensitive adhesive composition can be suitably used as a pressure-sensitive adhesive layer, electronic material, or display device member, and electric/electronic parts or display devices equipped with them have sufficient viscoelasticity of the adhesive layer over a wide temperature range, so that a pressure-sensitive adhesive layer that is unlikely to cause problems with poor adhesion to substrates such as electronic parts can be formed in a temperature range including low temperatures to room temperature, which makes it easy to industrialize electronic parts, etc., and is expected to improve the performance of the resulting electronic parts, etc.

[Silicone Pressure Sensitive Adhesive Composition]
First, the silicone pressure-sensitive adhesive composition according to the present invention will be described. The composition, as a low-solvent or solvent-free composition, has practically sufficient coatability even if it is a composition that does not substantially contain an organic solvent, cures quickly by a curing reaction including a hydrosilylation reaction, has practically sufficient adhesive strength, and forms a pressure-sensitive adhesive layer that is excellent in mechanical strength and elongation. Below, each of the components, the range of organopolysiloxanes that are technical features, the mass ratio of the organopolysiloxane resin to the linear organopolysiloxane, and the properties of the pressure-sensitive adhesive layer will be described.

The silicone pressure sensitive adhesive composition of the present invention comprises
(A) a linear or branched organopolysiloxane having at least two aliphatic unsaturated carbon-carbon bond-containing groups in one molecule and having a degree of siloxane polymerization in the range of 5 to 250;
(B) a linear organohydrogenpolysiloxane having silicon-bonded hydrogen atoms only at both molecular chain terminals;
(C) an organopolysiloxane resin containing, in the molecule, siloxane units (M units) represented by R ₃ SiO _1/2 (wherein R each independently represents a monovalent organic group) and siloxane units (Q units) represented by SiO _4/2 ;
The composition contains (D) an organohydrogenpolysiloxane having at least three silicon-bonded hydrogen atoms in the molecule, and (E) a hydrosilylation reaction catalyst, the content of the organic solvent is less than 20 mass% of the total composition, and from the viewpoint of handling and workability, may further contain (F) a cure retarder if desired, and may contain other additives within the scope of the object of the present invention. Each component will be described below.

[Component (A)]
Component (A) is a linear or branched organopolysiloxane having at least two aliphatic unsaturated carbon-carbon bond-containing groups in one molecule and a siloxane polymerization degree in the range of 5 to 250, and is the main component (base polymer) of the composition. By using component (A) having a siloxane polymerization degree in the range of 5 to 250, the overall viscosity of the composition can be reduced, and a low-solvent or solvent-free composition can be designed, and even if the composition does not substantially contain an organic solvent, the composition as a whole can achieve sufficient coatability for practical use. Component (A) may be a single organopolysiloxane or a mixture of two or more organopolysiloxanes.

The siloxane polymerization degree of the organopolysiloxane of component (A) is in the range of 5 to 250, preferably 5 to 200, and more preferably 5 to 180. Component (A) may be (A1) an organopolysiloxane having a siloxane polymerization degree in the range of 5 to 50, or may be a mixture of component (A1) and (A2) an organopolysiloxane having a siloxane polymerization degree in the range of 51 to 250, preferably 51 to 200. If the siloxane polymerization degree of component (A) exceeds the upper limit, the viscosity of the entire composition tends to increase, and coating may become difficult unless a large amount of organic solvent is used. On the other hand, if the siloxane polymerization degree of component (A) is less than the lower limit, the curability and adhesive performance of the composition may decrease. From the standpoint of the technical effects of the present invention, it is preferred that 50 mass % or more of component (A) be organopolysiloxane (A1) having a siloxane polymerization degree in the range of 5 to 50, which has the advantage that the overall viscosity of the composition can be reduced.

Component (A) has at least two aliphatically unsaturated carbon-carbon bond-containing groups in the molecule. Examples of such aliphatically unsaturated carbon-carbon bond-containing groups include alkenyl groups, alkenyloxyalkyl groups, acryloxyalkyl groups, and methacryloxyalkyl groups, with alkenyl groups being particularly preferred. Specifically, the alkenyl groups include vinyl groups, allyl groups, propenyl groups, butenyl groups, pentenyl groups, and hexenyl groups, with vinyl groups and hexenyl groups being particularly preferred. In addition, it is preferable that these aliphatically unsaturated carbon-carbon bond-containing groups are bonded to silicon atoms.

The aliphatic unsaturated carbon-carbon bond-containing groups may be present either at the ends of the siloxane molecular chain or on the side chains of the molecular chain, or may be present in both.

The content of the aliphatic unsaturated carbon-carbon bond-containing group is preferably 0.001 to 10 mass%, more preferably 0.005 to 8.50 mass%, and more preferably 0.01 to 7.5 mass%, relative to the mass of component (A). In particular, the content of the vinyl (CH ₂ ═CH—) moiety in the aliphatic unsaturated carbon-carbon bond-containing group (hereinafter referred to as the “vinyl content”) is preferably in the range of 0.005 to 10.0 mass%, and particularly preferably in the range of 0.005 to 8.50 mass%.

Component (A) may contain, as organic groups other than the aliphatic unsaturated carbon-carbon bond-containing group, alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, and heptyl; aryl groups such as phenyl, tolyl, xylyl, and naphthyl; aralkyl groups such as benzyl and phenethyl; and halogenated alkyl groups such as chloromethyl, 3-chloropropyl, and 3,3,3-trifluoropropyl. From an industrial standpoint, it is particularly preferable for the group to contain a methyl or phenyl group.

Examples of such component (A) include compounds represented by the general formula:
R ¹ ₃ SiO(R ¹ ₂ SiO) _m1 SiR ¹ ₃
However, component (A) may also contain an average of 0 to 5 units per molecule selected from the group consisting of branched siloxane units represented by R ¹ SiO _3/2 and branched siloxane units represented by SiO _4/2 , and therefore may be a branched organopolysiloxane.

In the formula, each R ¹ is independently a substituted or unsubstituted monovalent hydrocarbon group, and examples of the monovalent hydrocarbon group include the aliphatic unsaturated carbon-carbon bond-containing group and other organic groups described above. However, in one molecule, at least two R ¹ are aliphatic unsaturated carbon-carbon bond-containing groups, preferably alkenyl groups, more preferably vinyl groups or hexenyl groups. In addition, in the formula, the siloxane polymerization degree "m1+2" is preferably a number in the range of 5 to 230, more preferably a number in the range of 5 to 200, and particularly preferably a number in the range of 5 to 190. Note that "+2" is the sum of the siloxane units at both ends of the linear molecule, and may further include units selected from branched siloxane units represented by R ¹ SiO _3/2 and branched siloxane units represented by SiO _4/2 in the range of 0 to 5. In addition, one R 1 SiO 3/2 unit is added to the molecule for the branched siloxane unit represented by R ¹ SiO _3/2 , and two R ¹ ₃ SiO _1/2 units are added to the molecule for the branched siloxane unit represented by SiO _4/2 , forming a molecular chain end corresponding to the branched siloxane unit.

In the above general formula, R ¹ in the R ¹ ₃ SiO _1/2 units at both ends is preferably an organic group other than an aliphatic unsaturated carbon-carbon bond-containing group, and R ¹ at both ends is preferably an alkyl group, and from an industrial viewpoint, a methyl group is particularly preferred.

The properties of component (A) at room temperature are oily, and it is preferable that component (A) has a viscosity of 1 mPa·s or more at 25°C. In particular, when the silicone pressure-sensitive adhesive composition of the present invention is designed as a low-solvent or solvent-free composition, from the standpoint of coatability, it is preferable that component (A) has a viscosity of 1 mPa·s or more and 100,000 mPa·s or less at 25°C.

From the standpoint of preventing contact failure, it is preferable that these alkenyl group-containing organopolysiloxanes have reduced or removed volatile or low molecular weight siloxane oligomers (octamethyltetrasiloxane (D4), decamethylpentasiloxane (D5), etc.). The extent of this can be designed as desired, but may be less than 1 mass% of the entire component (A) or less than 0.1 mass% for each siloxane oligomer, or may be reduced to near the detection limit by gas chromatography, if necessary.

Component (B) is a linear organohydrogenpolysiloxane that has silicon-bonded hydrogen atoms only at both ends of the molecular chain, and functions mainly as a chain extender for component (A) in the hydrosilylation reaction, improving the elongation and flexibility of the cured reaction product (adhesive layer). By using a specific amount of component (B) relative to the aliphatic unsaturated carbon-carbon bond-containing groups in component (A), the cured reaction product obtained by curing the composition contains a certain amount of structure with an extended molecular chain length, significantly improving the adhesion and holding power of the elastic adhesive material.

Such component (B) may be a polyorganosiloxane containing SiH groups at both ends of the molecular chain as shown in the following formula:

式中、Ｒ^２は、アルケニル基を除く炭素数１～１０の一価炭化水素基である。nは０～５０の範囲の数である。アルケニル基以外のケイ素原子に結合した炭素数１～１０の一価炭化水素基としては、例えば、メチル基、エチル基、プロピル基、ブチル基、ペンチル基、ヘキシル基、ヘプチル基等のアルキル基；フェニル基、トリル基、キシリル基、ナフチル基等のアリール基；ベンジル基、フェネチル基等のアラルキル基；クロロメチル基、３－クロロプロピル基、３，３，３－トリフロロプロピル基等のハロゲン化アルキル基などが挙げられ、特に、メチル基、フェニル基であることが好ましい。

In the formula, ^R2 is a monovalent hydrocarbon group having 1 to 10 carbon atoms, excluding alkenyl groups. n is a number ranging from 0 to 50. Examples of monovalent hydrocarbon groups having 1 to 10 carbon atoms bonded to a silicon atom, other than alkenyl groups, include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, and heptyl groups; aryl groups such as phenyl, tolyl, xylyl, and naphthyl groups; aralkyl groups such as benzyl and phenethyl groups; and halogenated alkyl groups such as chloromethyl, 3-chloropropyl, and 3,3,3-trifluoropropyl groups, with methyl and phenyl groups being particularly preferred.

Specific examples of component (B) include 1,1,3,3-tetramethyldisiloxane, 1,1,3,3,5,5-hexamethyltrisiloxane, dimethylpolysiloxane terminated at both molecular chain ends with dimethylhydrogensiloxy groups, dimethylsiloxane-methylphenylsiloxane copolymer terminated at both molecular chain ends with dimethylhydrogensiloxy groups, dimethylsiloxane-diphenylsiloxane copolymer terminated at both molecular chain ends with dimethylhydrogensiloxy groups, and mixtures of two or more of these organopolysiloxanes.

Further examples of component (B) include the following organopolysiloxanes: In the formula, Me and Ph represent a methyl group and a phenyl group, respectively, m2 is an integer from 1 to 100, and n2 is an integer from 1 to 50.
_HMe2SiO ( _{Me2SiO ) m2SiMe2H
HMe2SiO} ( _{Ph2SiO ) m2SiMe2H}
HMePhSiO( _Ph2SiO ) _m2SiMePhH
HMePhSiO( _Ph2SiO ) _m2 (MePhSiO) _n2SiMePhH
HMePhSiO( _Ph2SiO ) _m2 ( _Me2SiO ) _n2SiMePhH

From the standpoint of preventing contact failure, it is preferable that volatile or low molecular weight siloxane oligomers (octamethyltetrasiloxane (D4), decamethylpentasiloxane (D5), etc.) are reduced or removed from these (B) components. The extent of this can be designed as desired, but it may be less than 1 mass% of the entire (B) component, less than 0.1 mass% for each siloxane oligomer, or may be reduced to near the detection limit as necessary.

The content of silicon-bonded hydrogen atoms in component (B) is not particularly limited, but from the standpoint of the technical effects of the present invention, the H content in the SiH groups is preferably in the range of 0.01 to 3.0 mass%, and particularly preferably in the range of 0.05 to 2.00 mass%.

[SiH/Vi ratio of component (A) and component (B)]
As described above, component (B) is a linear siloxane having silicon-bonded hydrogen atoms capable of hydrosilylation only at both ends of the molecular chain, and functions as a chain extender in the cured product, improving the elongation and flexibility of the cured product. To achieve this technical effect, the ratio (substance amount ratio) of the number of moles of silicon-bonded hydrogen atoms in component (B) to the number of moles of aliphatic unsaturated carbon-carbon bond-containing groups such as alkenyl groups in component (A) must be in the range of 0.90 to 1.30, and it is particularly preferable for it to be in the range of 0.90 to 1.10, or 0.90 to 1.00. If it is less than the lower limit, it may cause adhesive residue, and if it exceeds the upper limit, the adhesive strength may be insufficient.

[Component (C)]
Component (C) is an organopolysiloxane resin, and is a tackifier that imparts adhesion to a substrate. Depending on the amount of this component used, it is possible to adjust the adhesive strength and pressure-sensitive adhesive performance of the cured product of the composition from weak to strong adhesion.

Component (C) is an organopolysiloxane resin containing within its molecule (a) siloxane units (M units) represented by R ₃ SiO _1/2 (wherein R each independently represents a monovalent organic group) and (b) siloxane units (Q units) represented by SiO _4/2 . The molar ratio of M units to Q units is preferably 0.5 to 2.0 (M units/Q units). If this molar ratio is less than 0.5, the adhesive strength to the substrate may decrease, and if it is more than 2.0, the cohesive strength of the material constituting the adhesive layer decreases.

In particular, the molar ratio of (a) M units to (b) Q units is preferably in the range of 0.50:1.00 to 1.50:1.00, more preferably in the range of 0.55:1.00 to 1.20:1.00, and even more preferably in the range of 0.60:1.00 to 1.10:1.00. The molar ratio can be easily measured by ^29Si nuclear magnetic resonance.

Component (C) is preferably an organopolysiloxane resin represented by the general formula: ( _{RSiO1 /2} ) _a (SiO4 _/2 ) _b , where R is each independently a monovalent organic group, a and b are each positive numbers, a+b=1, and a/b=0.5 to 1.5.

The (C) component may be composed of only (a) M units and (b) Q units, but may also contain R ₂ SiO _2/2 units (D units) and/or RSiO _3/2 units (T units). In the formula, R each independently represents a monovalent organic group. The total content of (a) M units and (b) Q units in the (C) component is preferably 50% by weight or more, more preferably 80% by weight or more, and particularly preferably 100% by weight.

The monovalent organic groups are not particularly limited, but can be divided, for example, into aliphatic unsaturated carbon-carbon bond-containing groups and aliphatic unsaturated carbon-carbon bond-free groups, and the monovalent organic groups of component (C) can each independently be either of these.

The aliphatic unsaturated carbon-carbon bond-containing groups and the aliphatic unsaturated carbon-carbon bond-free groups include monovalent unsaturated hydrocarbon groups and oxygen atom-containing monovalent unsaturated hydrocarbon groups, as well as monovalent saturated hydrocarbon groups and oxygen atom-containing monovalent saturated hydrocarbon groups, respectively.

Examples of monovalent unsaturated or saturated hydrocarbon groups include substituted or unsubstituted monovalent unsaturated hydrocarbon groups having 2 to 12 carbon atoms, preferably 2 to 8 carbon atoms, and more preferably 2 to 6 carbon atoms, as well as substituted or unsubstituted monovalent saturated hydrocarbon groups having 1 to 12 carbon atoms.

Examples of unsubstituted monovalent unsaturated hydrocarbon groups having 2 to 12 carbon atoms, preferably 2 to 8 carbon atoms, and more preferably 2 to 6 carbon atoms, include alkenyl groups such as vinyl, allyl, propenyl, butenyl, pentenyl, and hexenyl. Examples of substituted monovalent unsaturated hydrocarbon groups having 2 to 12 carbon atoms, preferably 2 to 8 carbon atoms, and more preferably 2 to 6 carbon atoms, include those in which some of the hydrogen atoms of these monovalent unsaturated hydrocarbon groups have been substituted with halogen atoms (fluorine, chlorine, bromine, or iodine) or the like.

Examples of unsubstituted monovalent saturated hydrocarbon groups having 1 to 12 carbon atoms include alkyl groups such as methyl, ethyl, propyl, pentyl, hexyl, and octyl; cycloalkyl groups such as cyclohexyl and cycloheptyl; aryl groups such as phenyl, tolyl, and xylyl; and aralkyl groups such as benzyl, α-methylstyryl, and 2-phenylethyl. Examples of substituted monovalent saturated hydrocarbon groups having 1 to 12 carbon atoms include those in which some of the hydrogen atoms of these monovalent unsaturated hydrocarbon groups have been substituted with halogen atoms (fluorine, chlorine, bromine, or iodine). Specific examples of fluorinated monovalent saturated hydrocarbon groups include perfluoroalkyl groups such as 3,3,3-trifluoropropyl, 4,4,5,5,5-pentafluorobutyl, and 3,3,4,4,5,5,6,6,6-nonafluorohexyl; chlorinated monovalent saturated hydrocarbon groups include chloroalkyl groups such as 3-chloropropyl, and chlorophenyl groups such as dichlorophenyl.

As the monovalent saturated hydrocarbon group, a substituted or unsubstituted alkyl group having 1 to 12 carbon atoms is preferred. As the substituted or unsubstituted alkyl group having 1 to 12 carbon atoms, a methyl group is preferred. As the monovalent unsaturated hydrocarbon group, a substituted or unsubstituted alkenyl group having 2 to 12 carbon atoms is preferred. As the substituted or unsubstituted alkenyl group having 2 to 12 carbon atoms, a vinyl group is preferred.

Examples of oxygen-containing monovalent unsaturated or saturated hydrocarbon groups include substituted or unsubstituted oxygen-containing monovalent unsaturated hydrocarbon groups having 2 to 12 carbon atoms, and substituted or unsubstituted oxygen-containing monovalent saturated hydrocarbon groups having 1 to 12 carbon atoms.

Examples of substituted or unsubstituted oxygen-containing monovalent unsaturated hydrocarbon groups having 2 to 12 carbon atoms include alkenyloxyalkyl groups, acryloxyalkyl groups, and methacryloxyalkyl groups.

Examples of alkenyloxyalkyl groups include allyloxymethyl groups and 3-allyloxypropyl groups. Examples of acryloxyalkyl groups include acryloxymethyl groups and 3-acryloxypropyl groups. Examples of methacryloxyalkyl groups include methacryloxymethyl groups and 3-methacryloxypropyl groups.

Examples of substituted or unsubstituted monovalent saturated hydrocarbon groups containing an oxygen atom and having 1 to 12 carbon atoms include alkoxy groups having 1 to 12 carbon atoms.

Examples of alkoxy groups having 1 to 12 carbon atoms include methoxy groups, ethoxy groups, propoxy groups, butoxy groups, and isopropoxy groups.

[Reduction of Hydroxyl Groups or Hydrolyzable Groups]
Hydrolyzable groups such as hydroxyl groups or alkoxy groups in component (C) are directly bonded to silicon atoms such as T units or Q units in the siloxane units in the resin structure, and are groups derived from the raw material silane or generated as a result of hydrolysis of the silane, so the content of hydroxyl groups or hydrolyzable groups can be reduced by hydrolyzing the synthesized organopolysiloxane resin with a silylating agent such as trimethylsilane. This can suppress the formation of organopolysiloxane resin structures with large molecular weights in the cured product, and can further improve the curability of the composition at low temperatures and the storage modulus of the resulting pressure-sensitive adhesive layer.

[(C1) Curable reactive organopolysiloxane resin]
In one embodiment of the present invention, at least a portion of component (C) may be a curable reactive organopolysiloxane resin that contains at least siloxane units (M units) represented by (Alk)R' ₂ SiO _1/2 (wherein each Alk is independently an aliphatic unsaturated carbon-carbon bond-containing group, and each R' is independently an aliphatic unsaturated carbon-carbon bond-free group) and siloxane units (Q units) represented by SiO _4/2 in the (C1) molecule.

In the above embodiment, the aliphatic unsaturated carbon-carbon bond-containing group Alk is preferably a group independently selected from the group consisting of alkenyl groups, alkenyloxyalkyl groups, acryloxyalkyl groups, and methacryloxyalkyl groups, as described above. The aliphatic unsaturated carbon-carbon bond-free group R' is preferably a group independently selected from the group consisting of alkyl groups, aryl groups, and aralkyl groups, as described above. Some of these groups may be substituted with halogen atoms, etc. From an industrial point of view, the aliphatic unsaturated carbon-carbon bond-containing group Alk may be a vinyl group, an allyl group, or a hexenyl group, and the aliphatic unsaturated carbon-carbon bond-free group R' is preferably independently a methyl group, a phenyl group, or the like.

In the above embodiment, when a component (C) other than the curing-reactive organopolysiloxane resin (C1) is present, it is preferable that the component (C) is non-curing-reactive. In this case, R of the non-curing-reactive component (C) is preferably the aliphatic unsaturated carbon-carbon bond-free group described above, and more preferably is independently an alkyl group, an aryl group, or an aralkyl group. In addition, some of these groups may be substituted with halogen atoms, etc. From an industrial point of view, it is preferable that the aliphatic unsaturated carbon-carbon bond-free group that is R is independently a methyl group, a phenyl group, etc.

The proportion of the curable reactive organopolysiloxane resin (C1) in the component (C) is not particularly limited, but in order to achieve an appropriate hardness as a pressure-sensitive adhesive in the composition of the present invention or its cured product, the proportion of the curable reactive organopolysiloxane resin (C1) is preferably 50% by weight or less, more preferably 30% by weight or less, and even more preferably 20% by weight or less, when the entire component (C) is taken as 100% by weight. Preferably, the content of the component (C1) in the component (C) is in the range of 0 to 20% by weight, and particularly preferably in the range of 0 to 15% by weight, so that the pressure-sensitive adhesive made of the composition of the present invention or its cured product can have appropriate hardness and flexibility as an adhesive layer for a display device, a solar cell module, etc.

In the present invention, component (C) is an organopolysiloxane resin represented by the general unit formula: ( _{R3SiO1 /2} ) _a (SiO4 _/2 ) _b , in which R are each independently a monovalent organic group, a and b are each positive numbers, a+b=1, and a/b=0.5 to 1.5, in which preferably 90 mol % or more of R are independently alkyl groups having 1 to 6 carbon atoms or phenyl groups, and particularly preferably 95 to 100 mol % of R are independently methyl groups or phenyl groups, and it is most preferable to use a resin (also called MQ resin) in which the content of hydroxyl groups or hydrolyzable groups in component (C) is in the range of 0 to 7 mol % (0.0 to 1.50 mass % as hydroxyl groups) based on the total silicon.

Examples of such component (C) include:
(Me3SiO1 _{/2 ) 0.45} (SiO4 _/2 ) _0.55 (HO1 _/2 ) _0.05
(Me3SiO1 _{/2 ) 0.40} (SiO4 _/2 ) _0.60 (HO1 _/2 ) _0.10
(Me3SiO1 _{/2 ) 0.52} (SiO4 _/2 ) _0.48 (HO1 _/2 ) _0.01
( _{Me3SiO1 /2} ) _0.40 (Me2ViSiO1 _{/ 2} ) _0.05 (SiO4 _/2 ) _0.55 (HO1 _/2 ) _0.05
(Me3SiO1 _{/2 ) 0.45} (SiO4 _/2 ) _0.55 (MeO1 _/2 ) _0.10
( _{Me3SiO1 /2} ) _0.25 (Me2PhSiO1 _{/ 2} ) _0.20 (SiO4 _/2 ) _0.55 (HO1 _/2 ) _0.05
( _{Me3SiO1 /2} ) _0.40 ( _{Me2SiO2/2 ) 0.05} (SiO4 _/2 ) _0.55 (HO1 _/2 ) _0.05
( _{Me3SiO1 /2} ) _0.40 (MeSiO3 _/2 ) _0.05 (SiO4 _/2 ) _0.55 (HO1 _/2 ) _0.05
( _{Me3SiO1 /2} ) _0.40 (Me2SiO2 _{/2 ) 0.05} (MeSiO3 _/2 ) _0.05 (SiO4 _/2 ) _0.50 (HO1 _/2 ) _0.05
(Me: methyl group, Ph: phenyl group, Vi: vinyl group, MeO: methoxy group, HO: silicon-bonded hydroxyl group. In order to express the relative amount of hydroxyl groups to silicon atoms, the sum of the subscripts of the silicon-containing units is set to 1, and the subscript of the (HO) _1/2 unit indicates the relative amount.)
From the standpoint of preventing contact failure, etc., the amount of low molecular weight siloxane oligomers in component (C) may be reduced or eliminated.

Since component (C) is a component that imparts adhesive strength to the silicone pressure-sensitive adhesive composition of the present invention, its amount is preferably in the range of 10 to 80 parts by mass, assuming that the sum of the masses of components (A) to (D) of the composition is 100 parts by mass. If the amount of component (C) is less than the lower limit, sufficient adhesive strength may not be imparted to the silicone pressure-sensitive adhesive composition of the present invention. On the other hand, if the amount of component (C) exceeds the upper limit, the silicone pressure-sensitive adhesive composition of the present invention may become too hard, and therefore may not be particularly suitable for use as a pressure-sensitive adhesive. However, if a composition design with low adhesive strength is required, the content of component (C) may be suppressed to 10 parts by mass or less.

[Component (D)]
Unlike the (B) component, the (D) component is an organohydrogenpolysiloxane having at least three silicon-bonded hydrogen atoms in one molecule, and functions as a crosslinking agent in the hydrosilylation reaction with the (A) component/(D) component, and adjusts the hardness of the cured product according to the amount added. In general, each of the three silicon-bonded hydrogen atoms is bonded to a different silicon atom. By using such a (D) component in a certain quantitative range relative to the (A) component, the curing reactivity of the entire composition is improved, good curing characteristics and appropriate hardness (crosslinking density) are realized, and the adhesive strength of the cured product and the surface tack after curing can be designed to be in a practically good range.

Such component (D) may be at least one selected from the group consisting of (D1) cyclic organohydrogenpolysiloxanes having at least three silicon-bonded hydrogen atoms in the molecule and (D2) linear or branched organohydrogenpolysiloxanes having no silicon-bonded hydrogen atoms at the molecular chain terminals and having at least three silicon-bonded hydrogen atoms in the molecule. Component (D) may also be a mixture of two or more organohydrogenpolysiloxanes belonging only to the category of either component (D1) or (D2).

The cyclic organohydrogenpolysiloxane of component (D1) is, for example, a compound represented by the following formula:
[( ^R3HSiO ) _{m3 (} ^R32SiO ) _m4 ]
Here, m3+m4 is a number in the range of 3 to 20, m3 is a number equal to or greater than 3, and m4 is a number equal to or greater than 0. ^R3 is a monovalent hydrocarbon group having 1 to 10 carbon atoms excluding alkenyl groups, and can be exemplified by the same groups as ^R2 , and is preferably a group independently selected from a methyl group and a phenyl group.

The linear or branched organohydrogenpolysiloxane (D2) that has no silicon-bonded hydrogen atoms at the molecular chain terminals and has at least three silicon-bonded hydrogen atoms in the molecule is an organohydrogenpolysiloxane such as a polyorganohydrogensiloxane or an organohydrogensiloxane-diorganosiloxane copolymer that has at least three silicon-bonded hydrogen atoms in the side chain portion and whose molecular chain terminals are blocked with trialkylsiloxy groups, aryldialkylsiloxy groups, or the like. The degree of polymerization of the siloxane is in the range of 5 to 500, and preferably in the range of 5 to 200.

Specifically, the following compounds are used as component (D): 1,3,5,7-tetramethylcyclotetrasiloxane, tris(dimethylhydrogensiloxy)methylsilane, tris(dimethylhydrogensiloxy)phenylsilane, 1-(3-glycidoxypropyl)-1,3,5,7-tetramethylcyclotetrasiloxane, 1,5-di(3-glycidoxypropyl)-1,3,5,7-tetramethylcyclotetrasiloxane, 1-(3-glycidoxypropyl)-5-trimethoxysilylethyl-1,3,5,7-tetramethylcyclotetrasiloxane, methylhydrogenpolysiloxane terminated at both ends with trimethylsiloxy groups, dimethylsiloxane-methyl terminated at both ends with trimethylsiloxy groups, Examples of such copolymers include methylhydrogensiloxane copolymers, methylhydrogensiloxane-diphenylsiloxane copolymers capped at both molecular chain terminals with trimethylsiloxy groups, methylhydrogensiloxane-diphenylsiloxane-dimethylsiloxane copolymers capped at both molecular chain terminals with trimethylsiloxy groups, methyltris(dimethylsiloxy)silane, tetrakis(dimethylsiloxysilane), methylhydrogenpolysiloxane capped at both molecular chain terminals with trimethylsiloxy groups, methylhydrogensiloxane-dimethylsiloxane copolymers capped at both molecular chain terminals with trimethylsiloxy groups, and methylhydrogensiloxane-methylphenylsiloxane copolymers capped at both molecular chain terminals with trimethylsiloxy groups.

[SiH/Vi ratio in components (B) and (D) relative to component (A)]
In addition to the SiH/Vi ratio of the (B) component and the (A) component, the composition of the present invention requires that the ratio (amount of substance ratio) of the number of moles of silicon-bonded hydrogen atoms in the (B) component and the (D) component in the entire composition to the number of moles of aliphatic unsaturated carbon-carbon bond-containing groups such as alkenyl groups in the (A) component is in the range of 0.95 to 1.35. Within this range, the overall crosslink density is appropriately adjusted, and an adhesive layer that has excellent elongation and viscoelasticity in relation to the (B) component, has appropriate hardness in relation to the (D) component, and has a suitable range of surface tack after curing can be realized. If the SiH/Vi ratio (number of moles of silicon-bonded hydrogen atoms/number of moles of aliphatic unsaturated carbon-carbon bond-containing groups) is less than the lower limit, it may cause adhesive residue, and if it exceeds the upper limit, the adhesive strength may be insufficient.

[Component (E)]
The solventless or low-solvent silicone pressure-sensitive adhesive composition of the present invention contains a hydrosilylation catalyst as component (E). Examples of hydrosilylation catalysts include platinum-based catalysts, rhodium-based catalysts, and palladium-based catalysts, with platinum-based catalysts being preferred because they can significantly accelerate the curing of the composition. Examples of platinum-based catalysts include platinum fine powder, chloroplatinic acid, alcohol solutions of chloroplatinic acid, platinum-alkenylsiloxane complexes, platinum-olefin complexes, and platinum-carbonyl complexes, with platinum-alkenylsiloxane complexes being particularly preferred. Examples of this alkenylsiloxane include 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, alkenylsiloxanes in which a portion of the methyl groups of these alkenylsiloxanes have been substituted with a group selected from the group consisting of nitriles, amides, dioxolanes, and sulfolanes, ethyl groups, phenyl groups, etc., and alkenylsiloxanes in which the vinyl groups of these alkenylsiloxanes have been substituted with allyl groups, hexenyl groups, etc. In particular, 1,3-divinyl-1,1,3,3-tetramethyldisiloxane is preferred because this platinum-alkenylsiloxane complex has good stability, and it is preferred to add this in the form of an alkenylsiloxane solution. In addition, from the viewpoint of improving the handling and workability and the pot life of the composition, these hydrosilylation catalysts may be hydrosilylation catalyst-containing thermoplastic resin fine particles, particularly thermoplastic resin fine particles containing a platinum-containing hydrosilylation catalyst, which are catalysts dispersed or encapsulated in a thermoplastic resin such as a silicone resin, a polycarbonate resin, an acrylic resin, etc. Note that non-platinum metal catalysts such as iron, ruthenium, and iron/cobalt may also be used as catalysts that promote the hydrosilylation reaction.

In the present invention, the content of the hydrosilylation reaction catalyst is not particularly limited, but is in a range in which the amount of the above-mentioned metals, particularly platinum-based metals, is in the range of 0.1 to 200 ppm relative to the total amount of solids in the composition, and may be in the range of 0.1 to 150 ppm, 0.1 to 100 ppm, or may be in the range of 0.1 to 50 ppm. Here, the platinum-based metals are metal elements of Group VIII consisting of platinum, rhodium, palladium, ruthenium, and iridium, and in practical use, it is preferable that the content of the platinum-based metals excluding the ligands of the hydrosilylation reaction catalyst is in the above range. The solid content refers to the components (mainly the base agent, adhesion-imparting component, crosslinking agent, catalyst, and other non-volatile components) that form a cured layer when the silicone pressure-sensitive adhesive composition according to the present invention is cured, and does not include volatile components such as solvents that volatilize during and, in some cases, after curing by heating.

When the content of platinum-based metals in the silicone pressure-sensitive adhesive composition of the present invention is 50 ppm or less (45 ppm or less, 35 ppm or less, 30 ppm or less, 25 ppm or less, or 20 ppm or less), discoloration or coloring of the transparent pressure-sensitive adhesive layer may be suppressed after curing or when exposed to high-energy rays such as heating or ultraviolet light. On the other hand, from the viewpoint of the curing property of the organopolysiloxane composition, the content of platinum-based metals is 0.1 ppm or more, and if it is below this lower limit, it may cause poor curing.

[Component (F)]
Component (F) is a cure retarder that is incorporated in order to inhibit the crosslinking reaction between the aliphatic unsaturated carbon-carbon bond-containing groups and silicon-bonded hydrogen atoms in the composition, thereby extending the pot life at room temperature and improving storage stability. The cure retarder is preferably used when it is desired to extend the pot life of the curable silicone pressure-sensitive adhesive composition of the present invention. In particular, from a practical standpoint, it is generally preferable to use a cure retarder in the solventless or low-solvent silicone pressure-sensitive adhesive composition of the present invention.

Specific examples of component (F) include acetylene compounds, enyne compounds, organic nitrogen compounds, organic phosphorus compounds, oxime compounds, and phosphorus compounds.Specific examples include alkyne alcohols such as 3-methyl-1-butyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, 3-methyl-1-pentyn-3-ol, 1-ethynyl-1-cyclohexanol, and phenylbutynol; enyne compounds such as 3-methyl-3-penten-1-yne and 3,5-dimethyl-1-hexyn-3-yne; methylalkenylcyclosiloxanes such as 2-ethynyl-4-methyl-2-pentene, 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, and 1,3,5,7-tetramethyl-1,3,5,7-tetrahexenylcyclotetrasiloxane; and benzotriazole.

From the viewpoint of the curing behavior of the composition, it is preferable that the silicone pressure-sensitive adhesive composition of the present invention has a viscosity increase of no more than 1.5 times 8 hours after preparation of the composition at room temperature, and is curable at 80 to 200°C. Suppressing viscosity increase is important from the viewpoints of handling, pot life, and post-curing properties, and curing at a certain high temperature (80 to 200°C) or higher can ensure curability. Such a composition can be realized by selecting an appropriate combination and blending amount of each of the above components, the hydrosilylation catalyst, and component (F).

[Low-solvent/solvent-free composition]
The silicone pressure-sensitive adhesive composition according to the present invention has a relatively low viscosity of its constituent components, so that it is possible to design a low-solvent or solvent-free composition, and even if the composition contains a small amount of organic solvent or contains substantially no organic solvent, it is possible to achieve sufficient coatability for practical use. Specifically, the content of the organic solvent is less than 20% by mass of the entire composition, and is particularly preferably less than 15% by mass, and is substantially within the range of 0 to 5% by mass. On the other hand, when the purpose is to improve the wettability of the composition to the substrate, or when the organic solvent is inevitably contained in the component (B) as a solvent accompanying the component (B), it is possible to contain a small amount of organic solvent, particularly within the above-mentioned range. The type and amount of organic solvent are adjusted taking into consideration the coating workability, etc., but from the viewpoint of composition design of a solvent-free or low-solvent silicone pressure-sensitive adhesive, it is preferable to use as little organic solvent as possible. Examples of the organic solvent include aromatic hydrocarbon solvents such as toluene, xylene, and benzene; aliphatic hydrocarbon solvents such as heptane, hexane, octane, and isoparaffin; ester solvents such as ethyl acetate and isobutyl acetate; ether solvents such as diisopropyl ether and 1,4-dioxane; chlorinated aliphatic hydrocarbon solvents such as trichloroethylene, perchloroethylene, and methylene chloride; and volatile oils. One or more types selected from these can be used, and two or more types may be combined depending on the wettability of the sheet-like substrate.

The silicone pressure-sensitive adhesive composition of the present invention may optionally contain components other than the above components, provided that the technical effects of the present invention are not impaired. For example, the composition may contain adhesion promoters; non-reactive organopolysiloxanes such as polydimethylsiloxane or polydimethyldiphenylsiloxane; antioxidants such as phenols, quinones, amines, phosphorus, phosphite, sulfur, or thioethers; light stabilizers such as triazoles or benzophenones; flame retardants such as phosphate esters, halogens, phosphorus, or antimony; one or more antistatic agents such as cationic surfactants, anionic surfactants, or nonionic surfactants. In addition to these components, pigments, dyes, inorganic fine particles (reinforcing fillers, dielectric fillers, conductive fillers, thermally conductive fillers), etc. may also be optionally blended.

[(A') Chain organopolysiloxane containing no carbon-carbon double bond-containing reactive group in the molecule]
The silicone pressure-sensitive adhesive composition of the present invention can be blended with a non-reactive organopolysiloxane such as polydimethylsiloxane or polydimethyldiphenylsiloxane that does not contain any silicon-bonded hydrogen atoms or any carbon-carbon double bond-containing reactive groups such as alkenyl groups, acrylic groups or methacrylic groups, which may improve the loss factor (tan δ), storage modulus (G') and loss modulus (G'') of the pressure-sensitive adhesive layer, as described below. For example, the loss factor of the pressure-sensitive adhesive layer can be increased by using a polydimethylsiloxane or polydimethyldiphenylsiloxane that has a hydroxyl group terminal, and such compositions are within the scope of the present invention.

[Total Viscosity of Composition]
The silicone pressure-sensitive adhesive composition of the present invention has a viscosity of the entire composition at 25° C. in the range of 1,000 to 300,000 mPa·s, and preferably in the range of 1,000 to 250,000 mPa·s. In particular, when the content of the organic solvent is less than 20 mass % of the entire composition, it is preferable that the viscosity of the entire composition be in the range of 1,000 to 100,000 mPa·s.

The method for preparing the silicone pressure-sensitive adhesive composition of the present invention is not particularly limited, and is carried out by mixing the respective components homogeneously. If necessary, a small amount of organic solvent may be added within the above-mentioned range, and the composition may be prepared by mixing at a temperature of 0 to 200°C using a known stirrer or kneader.

The organopolysiloxane composition of the present invention is applied to a substrate to form a coating film, and then heated at a temperature of 80 to 200° C., preferably at a temperature of 90 to 190° C., to form a cured product. Examples of coating methods include gravure coating, offset coating, offset gravure, roll coating, reverse roll coating, air knife coating, curtain coating, and comma coating.

Pressure-sensitive adhesive and adhesion ranges
The silicone pressure-sensitive adhesive composition of the present invention is characterized in that the cured layer formed by curing the composition through a hydrosilylation reaction has pressure-sensitive adhesive properties. The pressure-sensitive adhesive layer of the present invention has the above-mentioned structure and exhibits sufficient adhesive strength for practical use, so that it can be used as a replacement for known silicone pressure-sensitive adhesives as desired.

Specifically, it is possible to design a 40 μm thick pressure-sensitive adhesive layer formed by curing the silicone pressure-sensitive adhesive composition of the present invention, with the adhesive strength against a SUS base measured using a 180° peel test method according to JIS Z 0237 at a tensile speed of 300 mm/min, in the range of 100 to 2500 gf/inch, with a pressure-sensitive adhesive layer in the range of 500 to 2250 gf/inch being preferred. Note that the above thickness (40 μm) is the thickness of the cured layer itself, which serves as a standard for objectively defining the adhesive strength of the cured layer according to the present invention, and it goes without saying that the organopolysiloxane composition of the present invention can be used as a cured layer or pressure-sensitive adhesive layer of any thickness, not limited to 40 μm.

[Use as a pressure-sensitive adhesive layer]
The cured product of the present invention can be used as a pressure-sensitive adhesive layer. In addition, in order to improve adhesion to an adherend, the surface of the pressure-sensitive adhesive layer or the substrate may be subjected to surface treatment such as primer treatment, corona treatment, etching treatment, plasma treatment, etc. However, since the pressure-sensitive adhesive layer of the present invention has excellent adhesion to substrates such as display devices as described above, these steps may be added as necessary to further improve adhesion to the adherend, and these steps may be omitted to achieve higher production efficiency.

The silicone pressure-sensitive adhesive composition according to the present invention can be applied to a release liner, cured by heating under the above-mentioned temperature conditions, and the release liner can be peeled off and the composition can be attached to a film-like substrate, a tape-like substrate, or a sheet-like substrate (hereinafter referred to as a "film-like substrate"), or the composition can be applied to a film-like substrate and cured by heating under the above-mentioned temperature conditions to form a pressure-sensitive adhesive layer on the surface of the substrate. A laminate having a cured layer, particularly a film-like pressure-sensitive adhesive layer, formed by curing the organopolysiloxane composition according to the present invention on these film-like substrates may be used for adhesive tapes, bandages, low-temperature supports, transfer films, labels, emblems, and decorative or explanatory signs. Furthermore, the cured layer formed by curing the organopolysiloxane composition according to the present invention may be used in the assembly of automobile parts, toys, electronic circuits, or keyboards. Alternatively, the cured layer formed by curing the organopolysiloxane composition according to the present invention, particularly a film-like pressure-sensitive adhesive layer, may be used in the construction of a laminated touch screen or flat panel display.

Examples of substrates include paperboard, corrugated cardboard, clay-coated paper, polyolefin-laminated paper, especially polyethylene-laminated paper, synthetic resin film/sheet, natural fiber cloth, synthetic fiber cloth, artificial leather cloth, and metal foil. In particular, synthetic resin film/sheet is preferred, and examples of synthetic resin include polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polycarbonate, polyethylene terephthalate, cyclopolyolefin, and nylon (registered trademark). When heat resistance is particularly required, films of heat-resistant synthetic resins such as polyimide, polyether ether ketone, polyethylene naphthalate (PEN), liquid crystal polyarylate, polyamide imide, and polyether sulfone are suitable. On the other hand, in applications requiring visibility such as display devices, transparent substrates, specifically transparent materials such as polypropylene, polystyrene, polyvinylidene chloride, polycarbonate, polyethylene terephthalate, and PEN are suitable.

The substrate is preferably in the form of a film or sheet. There is no particular restriction on the thickness, and the desired thickness can be designed depending on the application. Furthermore, in order to improve the adhesion between the support film and the pressure-sensitive adhesive layer, a support film that has been subjected to a primer treatment, a corona treatment, an etching treatment, or a plasma treatment may be used. In addition, the surface opposite to the pressure-sensitive adhesive layer of the film-like substrate may be surface-treated to prevent scratches, stains, fingerprints, glare, reflection, static electricity, etc.

Methods for applying the silicone pressure-sensitive adhesive composition to a substrate include, without limitation, gravure coating, offset coating, offset gravure, roll coating using an offset transfer roll coater, reverse roll coating, air knife coating, curtain coating using a curtain flow coater, comma coating, Mayer bar, and other known methods used for forming a cured layer.

The amount of silicone pressure-sensitive adhesive composition applied to the substrate can be designed to the desired thickness depending on the application, such as a display device. As an example, the thickness of the pressure-sensitive adhesive layer after curing is 1 to 1,000 μm, may be 5 to 900 μm, or may be 10 to 800 μm, but is not limited to these.

The pressure-sensitive adhesive layer according to the present invention may be a single layer or a multilayer formed by laminating two or more pressure-sensitive adhesive layers depending on the required characteristics. A multilayer pressure-sensitive adhesive layer may be formed by laminating pressure-sensitive adhesive films prepared one by one, or a process of applying and curing a pressure-sensitive adhesive layer-forming organopolysiloxane composition onto a film substrate provided with a release layer may be carried out multiple times.

The pressure-sensitive adhesive layer of the present invention may be given the role of other functional layers selected from a dielectric layer, a conductive layer, a heat dissipation layer, an insulating layer, a reinforcing layer, etc., in addition to the adhesive or cohesive function between components.

When the cured layer obtained by curing the solventless or low-solvent silicone pressure-sensitive adhesive composition of the present invention is a pressure-sensitive adhesive layer, particularly a pressure-sensitive adhesive film, it is preferable to handle the cured layer as a laminate film that is peelably attached to a film substrate having a release layer having a release coating function. The release layer is sometimes called a release liner, separator, release layer, or release coating layer, and is preferably a release layer having a release coating function such as a silicone release agent, a fluorine release agent, an alkyd release agent, or a fluorosilicone release agent. Alternatively, without a release layer, a pressure-sensitive adhesive layer may be formed on a substrate having a physically fine uneven surface on the substrate surface or on a substrate itself made of a material that is difficult to adhere to the pressure-sensitive adhesive layer of the present invention. In particular, in the laminate according to the present invention, it is preferable to use a release layer obtained by curing a curable fluorosilicone release agent as the release layer.

The cured product obtained by curing the solvent-free or low-solvent silicone pressure-sensitive adhesive composition of the present invention has both the viscoelasticity and adhesive strength as described above, and is therefore useful as an elastic adhesive member for various electronic devices or electrical devices. In particular, it is useful as an electronic material, a display device member, or a transducer member (including sensors, speakers, actuators, and generators), and the preferred use of the cured product is as a member of an electronic component or display device. The cured product of the present invention may be transparent or opaque, but a film-shaped cured product, particularly a substantially transparent pressure-sensitive adhesive film, is suitable as a member for a display panel or display, and is particularly useful for so-called touch panel applications in which equipment, particularly electronic devices, can be operated by touching the screen with a fingertip or the like. In addition, the opaque elastic adhesive layer is particularly useful for applications as a film- or sheet-shaped member used in sensors, speakers, actuators, etc., where transparency is not required and the adhesive layer itself is required to have a certain degree of elasticity or flexibility.

[Use as adhesive tape]
An article containing a pressure-sensitive adhesive made of the silicone pressure-sensitive adhesive composition of the present invention may be an adhesive tape, characterized in that it comprises the above-mentioned adhesive layer and a sheet-like member made of a textile product such as the above-mentioned synthetic resin film/sheet, metal foil, woven fabric, nonwoven fabric, paper, etc. The type of such adhesive tape is not particularly limited, and examples thereof include insulating tape, heat-resistant tape, solder masking tape, mica tape binder, temporary fixing tape (particularly including temporary fixing tape for silicone rubber parts, etc.), and splicing tape (particularly including splicing tape for silicone release paper).

In particular, the pressure-sensitive adhesive layer obtained by curing the silicone pressure-sensitive adhesive composition of the present invention can achieve pressure-sensitive adhesive properties equivalent to those of conventional silicone pressure-sensitive adhesive layers, and can improve adhesion to substrates such as display devices without causing problems of poor curing or reduced curing properties.

[Laminate and pressure-sensitive adhesive sheet]
Next, the laminate according to the present invention and the pressure-sensitive adhesive sheet, which is one type of the pressure-sensitive adhesive layer, will be described.

The laminate of the present invention is a laminate comprising the above-mentioned film-like substrate and a pressure-sensitive adhesive layer formed by curing the above-mentioned silicone pressure-sensitive adhesive composition, and preferably, these film-like substrates are provided with a release layer for the pressure-sensitive adhesive layer.

In the laminate of the present invention, it is preferable that the sheet-like substrate has at least one release layer, and that the release layer is in contact with the pressure-sensitive adhesive layer. This allows the pressure-sensitive adhesive layer to be easily peeled off from the sheet-like substrate. The release agent contained in the release layer is not particularly limited, and as described above, examples of the release agent include silicone-based release agents, fluorine-based release agents, alkyd-based release agents, and fluorosilicone-based release agents.

In particular, the laminate of the present invention may be capable of handling the pressure-sensitive adhesive layer alone separated from the film-like substrate, or may have two film-like substrates.
in particular,
Film-like substrate,
a first release layer formed on the film-like substrate;
The adhesive may comprise a pressure-sensitive adhesive layer formed by applying the above-mentioned silicone pressure-sensitive adhesive composition onto the release layer and curing the composition, and a second release layer laminated onto the pressure-sensitive adhesive layer.

Similarly, the laminate of the above form may be formed, for example, by applying the above silicone pressure-sensitive adhesive composition onto one release layer formed on a film-like substrate and curing it to form a pressure-sensitive adhesive layer, and then laminating another release layer onto the pressure-sensitive adhesive layer.

The laminate of the above form may also be produced, for example, by sandwiching the silicone pressure-sensitive adhesive composition between a first film-like substrate and a second film-like substrate, heating and molding the composition to a certain thickness using a press or roll, and then curing the composition.

The first sheet substrate may have a first release layer, or the first sheet substrate itself may have a release property. Similarly, the second sheet substrate may have a second release layer, or the second sheet substrate itself may have a release property. When the first sheet substrate and/or the second sheet substrate have a first release layer and/or a second release layer, it is preferred that the pressure-sensitive adhesive layer contacts the first release layer and/or the second release layer.

Examples of sheet substrates with release properties include sheet substrates made of materials with release properties, such as fluororesin films, and sheet substrates made of materials with no or low release properties, such as polyolefin films, to which a release agent, such as silicone or fluororesin, has been added. On the other hand, examples of sheet substrates with a release layer include polyolefin films coated with a release agent, such as silicone or fluororesin.

The laminate of the present invention can be used, for example, by applying the pressure-sensitive adhesive layer to an adherend and then peeling the pressure-sensitive adhesive layer from the film-like substrate adhered to the adherend.

The thickness of the pressure-sensitive adhesive layer is preferably 5 to 10,000 μm, more preferably 10 μm or more or 8,000 μm or less, and particularly preferably 20 μm or more or 5,000 μm or less.

[Display panel or display member]
The cured product obtained by curing the composition of the present invention can be used to construct a laminated touch screen or flat panel display, and the specific method of use can be any known method for using a pressure-sensitive adhesive layer (particularly a silicone PSA (pressure-sensitive adhesive)) without any particular restriction.

For example, the cured product obtained by curing the composition of the present invention can be used in the manufacture of display devices such as touch panels as the optically transparent silicone pressure-sensitive adhesive film or adhesive layer disclosed in the above-mentioned JP-T No. 2014-522436 or JP-T No. 2013-512326, etc. Specifically, the cured product obtained by curing the composition of the present invention can be used without particular restriction as the adhesive layer or adhesive film described in JP-T No. 2013-512326.

As an example, the touch panel according to the present invention may be a touch panel including a substrate such as a conductive plastic film having a conductive layer formed on one surface thereof, and a cured layer formed by curing the composition of the present invention attached to the side on which the conductive layer is formed or the surface opposite thereto. The substrate is preferably a sheet-like or film-like substrate, and examples thereof include a resin film or a glass plate. The substrate on which the conductive layer is formed may be a resin film or a glass plate, particularly a polyethylene terephthalate film, having an ITO layer formed on one surface thereof. These are disclosed in the above-mentioned JP2013-512326 and the like.

In addition, the cured product obtained by curing the silicone pressure-sensitive adhesive composition of the present invention may be used as an adhesive film for polarizing plates used in the manufacture of display devices such as touch panels, or as a pressure-sensitive adhesive layer used for bonding between a touch panel and a display module as described in JP 2013-065009 A.

The silicone pressure-sensitive adhesive composition of the present invention and the cured product obtained by curing the composition are not subject to any restrictions other than those disclosed above, and the pressure-sensitive adhesive film comprising the cured product obtained by curing the composition can be used in various display devices for displaying characters, symbols, and images, such as television receivers, computer monitors, monitors for portable information terminals, surveillance monitors, video cameras, digital cameras, mobile phones, portable information terminals, dashboard displays for automobiles, dashboard displays for various facilities, devices, and equipment, automatic ticket vending machines, automated teller machines, in-vehicle display devices, and in-vehicle transmissive screens. The surface shape of such display devices may be curved or curved rather than flat, and examples thereof include various flat panel displays (FPDs) as well as curved displays or curved transmissive screens used in automobiles (including electric vehicles) and aircraft. Furthermore, these display devices can display icons for executing functions or programs on a screen or display, notification displays for e-mails and programs, and operation buttons for various devices such as car navigation devices, membranes for speakers, audio devices, and air conditioners, and may be provided with a touch panel function that allows input operations by touching these icons, notification displays, and operation buttons with a finger. As devices, the composition can be applied to display devices such as CRT displays, liquid crystal displays, plasma displays, organic EL displays, inorganic EL displays, LED displays, surface electrolytic displays (SEDs), and field emission displays (FEDs), as well as touch panels using these displays. In addition, the cured product obtained by curing the composition has excellent adhesiveness and viscoelastic properties, and can be used as a film or sheet-like member that is a transducer member (including for sensors, speakers, actuators, and generators) such as a membrane for speakers, and can also be used as a sealing layer or adhesive layer for use in secondary batteries, fuel cells, or solar cell modules.

The pressure-sensitive adhesive layer obtained by curing the silicone pressure-sensitive adhesive composition of the present invention may be substantially transparent, does not cause problems of poor curing or reduced curing properties, and has excellent adhesion to substrates such as various display devices, so that it can be suitably used in vehicle display devices that have good visibility and operability of the displayed content over a long period of time, particularly vehicle display devices equipped with a curved screen or curved display and optionally with a touch panel function. For example, JP 2017-047767 A, JP 2014-182335 A, JP 2014-063064 A, JP 2013-233852 A, etc. disclose vehicle display devices equipped with curved display surfaces, and the pressure-sensitive adhesive layer according to the present invention can be suitably applied or replaced as part or all of the adhesive layer or pressure-sensitive layer in these documents that require transparency. Furthermore, it goes without saying that the silicone pressure-sensitive adhesive composition of the present invention can also be used in other known curved display devices to replace currently used adhesive or pressure-sensitive layers that require transparency, and it is preferable to adjust the design of the display device and the thickness of the components by known techniques in order to further utilize the advantages of the pressure-sensitive adhesive of the present invention.

Furthermore, the transparent film-like substrate having the pressure-sensitive adhesive layer of the present invention may be used for purposes such as preventing the display surface from being scratched, stained, fingerprints, static electricity, reflection, and peeking.

(Examples 1 to 11, Comparative Examples 1 to 3)
Examples and comparative examples of the present invention are described below. In each example and comparative example, the term "cured" means that each composition was completely cured under each curing condition.

(Preparation of Silicone Pressure Sensitive Adhesive Composition)
The silicone pressure-sensitive adhesive compositions shown in each Example and Comparative Example were prepared using the components shown in Table 1 (Examples 1 to 11) and Table 2 (Comparative Examples 1 to 3). Note that all percentages in Tables 1 and 2 are by mass, and in each component, Me represents a methyl group and Vi represents a vinyl group. Furthermore, the compositions are substantially solvent-free compositions.

(Measurement of Molecular Weight of Organopolysiloxane Component)
The weight average molecular weight (Mw) and number average molecular weight (Mn) of organopolysiloxane components such as organopolysiloxane resins were determined in terms of standard polystyrene using a Waters gel permeation chromatography (GPC) with tetrahydrofuran (THF) as a solvent.

(Adhesive strength measurement, film surface)
Each composition was applied to a PET film (manufactured by Toray Industries, Inc., product name Lumirror (registered trademark) S10, thickness 50 μm) so that the thickness after curing was 40 μm, and cured at 150 ° C for 3 minutes. After leaving it for 1 day, the sample was cut to a width of 20 mm, and the adhesive layer surface was attached to a SUS plate (manufactured by Paltec) using a roller to prepare a test piece. The test piece was measured for adhesive strength (measurement at a width of 20 mm converted to gf / inch) at a pulling speed of 300 mm / min using a 180 ° peel test method according to JIS Z0237 using an Orientec RTC-1210 tensile tester. In addition, the film surface was observed when peeled, and compositions where the adhesive remained on the SUS plate were judged to have adhesive residue.

(High temperature retention)
The silicone pressure-sensitive adhesive composition was applied to a polyimide resin film to a thickness of 40 μm, and then dried at 150° C. for 3 minutes to produce an adhesive film. The pressure-sensitive adhesive side was attached to a SUS plate, a 200 g weight was hung from the bottom of the SUS plate, and the plate was aged in an oven at 200° C. for 30 minutes. After aging, the distance the SUS plate had moved relative to the polyimide resin film was measured.

(Overall Viscosity of Composition)
[viscosity]
The viscosity (mPa·s) is a value measured using a rotational viscometer in accordance with JIS K7117-1, and the kinetic viscosity (mm ² /s) is a value measured using an Ubbelohde viscometer in accordance with JIS Z8803.

(Ball tuck)
[Adhesive strength: ball tack value] The adhesive sheet prepared in the same manner as above was placed on a slope at an angle of 30° from the horizontal, and a specified stainless steel ball was rolled three times from above. Among the ball numbers that rolled within 10 cm on the adhesive sheet in at least two out of three times, the largest was recorded as the ball tack value.

The materials of the solventless silicone pressure-sensitive adhesive composition are shown in Table 1. The viscosity of each component was measured at room temperature (25° C.) by the following method.
[viscosity]
The viscosity (mPa·s) is a value measured using a rotational viscometer in accordance with JIS K7117-1.

The following silicones were used as the components in Table 1. Components (A) and (B) were mixed in advance, to which was added a xylene solution of silicone resin (C), and the xylene was then distilled off under reduced pressure.

(A1 component)
Alkenyl group-containing polysiloxane represented by the following formula (vinyl group content: 6.3% by mass)

(Component A2)
Alkenyl group-containing polysiloxane represented by the following formula (vinyl group content: 0.44% by mass)

(B1 component)
A SiH group-containing polysiloxane represented by the following formula (content of silicon-bonded hydrogen atoms: 0.124% by mass)

(B2 component)
A SiH group-containing polysiloxane represented by the following formula (content of silicon-bonded hydrogen atoms: 0.072% by mass)

(C1 component)
MQ silicone resin consisting of (CH ₃ ) ₃ SiO _1/2 units, SiO _4/2 units and hydroxyl groups, weight average molecular weight (Mw) calculated as polystyrene of 6,500, OH content of 4.5 mol % (1.0 mass %), xylene solution (solid content 70 mass %)

(C2 component)
MQ silicone resin consisting of (CH ₃ ) ₃ SiO _1/2 units, SiO _4/2 units and hydroxyl groups, Mw 3300, OH content 3.5 mol % (0.8 mass %), xylene solution (solid content 75.5 mass %)

(D1 component)
Methylhydrogensiloxane copolymer with both molecular chain ends blocked with trimethylsiloxy groups, silicon-bonded hydrogen atom content: 1.58% by mass

(D2 component)
Dimethylsiloxane-methylhydrogensiloxane copolymer with both molecular chain ends blocked with trimethylsiloxy groups, silicon-bonded hydrogen atom content: 0.70% by mass

(D3 component)
Dimethylsiloxane-methylhydrogensiloxane copolymer with both molecular chain ends blocked with trimethylsiloxy groups, weight average molecular weight (Mw) calculated as polystyrene: 1600, silicon-bonded hydrogen atom content: 0.73% by mass

[Summary]
The silicone pressure-sensitive adhesive compositions of Examples 1 to 11 were substantially solvent-free, but had a viscosity within a range that allowed practical application, and the curing and adhesive properties of the resulting adhesive layer were sufficiently excellent for practical use. On the other hand, in Comparative Examples 1 and 2, in which the SiH/Vi ratio of component (B) was below the lower limit of the present invention, adhesive residue was generated in the cured product on the adherend. Furthermore, in Comparative Example 3, in which the SiH/Vi ratio of the entire composition exceeded the upper limit of the present invention, sufficient adhesive strength could not be achieved.

Claims (11)

(A) a linear or branched organopolysiloxane having at least two aliphatic unsaturated carbon-carbon bond-containing groups in one molecule and having a degree of siloxane polymerization in the range of 5 to 250;
(B) a linear organohydrogenpolysiloxane having silicon-bonded hydrogen atoms only at both molecular chain terminals;
(C) an organopolysiloxane resin containing, in the molecule, siloxane units (M units) represented by R ₃ SiO _1/2 (wherein R each independently represents a monovalent organic group) and siloxane units (Q units) represented by SiO _4/2 ;
(D) an organohydrogenpolysiloxane having at least three silicon-bonded hydrogen atoms in the molecule, and (E) a hydrosilylation reaction catalyst (excluding those containing a linear or branched organopolysiloxane having at least two aliphatic unsaturated carbon-carbon bond-containing groups in one molecule and a siloxane polymerization degree of greater than 250);
the ratio of the number of moles of silicon-bonded hydrogen atoms in component (B) to the number of moles of aliphatic unsaturated carbon-carbon bond-containing groups in component (A) is in the range of 0.90 to 0.95;
the ratio of the number of moles of silicon-bonded hydrogen atoms in components (B) and (D) combined to the number of moles of aliphatic unsaturated carbon-carbon bond-containing groups in component (A) is in the range of 0.95 to 1.34;
The viscosity of the entire composition at 25°C is in the range of 1,000 to 300,000 mPa·s, and
The content of the organic solvent is less than 20% by mass of the total composition.
Silicone pressure sensitive adhesive compositions. The silicone pressure-sensitive adhesive composition according to claim 1, wherein component (A) is a mixture of (A1) an organopolysiloxane having a siloxane polymerization degree in the range of 5 to 50 and (A2) an organopolysiloxane having a siloxane polymerization degree in the range of 51 to 250. When the total amount of components (A) to (D) is 100 parts by mass,
The total amount of the (A) component and the (B) component is in the range of 10 to 80 parts by mass,
The amount of component (C) is in the range of 10 to 80 parts by mass,
The amount of the (D) component is in the range of 0.01 to 10 parts by mass.
The silicone pressure sensitive adhesive composition of claim 1 or claim 2. The component (D) is
(D1) at least one selected from the group consisting of cyclic organohydrogenpolysiloxanes having at least three silicon-bonded hydrogen atoms in the molecule, and (D2) linear or branched organohydrogenpolysiloxanes having no silicon-bonded hydrogen atoms at the molecular chain terminals and having at least three silicon-bonded hydrogen atoms in the molecule.
The silicone pressure sensitive adhesive composition of any one of claims 1 to 3. The silicone pressure-sensitive adhesive composition according to any one of claims 1 to 4, characterized in that the adhesive strength of a 40 μm thick pressure-sensitive adhesive layer obtained by curing the composition against a SUS substrate is in the range of 100 to 2500 gf/inch, as measured at a tensile speed of 300 mm/min using a 180° peel test method according to JIS Z 0237. A pressure-sensitive adhesive layer obtained by curing the silicone pressure-sensitive adhesive composition according to any one of claims 1 to 5. A laminate comprising a pressure-sensitive adhesive layer formed by curing the silicone pressure-sensitive adhesive composition according to any one of claims 1 to 5 on a film-like substrate. The laminate according to claim 7, comprising one or more film-like substrates, on which a release layer for the pressure-sensitive adhesive layer is provided. Film-like substrate,
a first release layer formed on the film-like substrate;
9. The laminate according to claim 8, further comprising a pressure-sensitive adhesive layer formed by applying the silicone pressure-sensitive adhesive composition according to any one of claims 1 to 5 onto the release layer and curing the composition, and a second release layer laminated onto the pressure-sensitive adhesive layer. An elastic adhesive member obtained by curing the silicone pressure-sensitive adhesive composition according to any one of claims 1 to 5. An electronic device or electrical device comprising the elastic adhesive member according to claim 10.