US-12624264-B2 - Solventless pressure sensitive adhesive composition

US12624264B2US 12624264 B2US12624264 B2US 12624264B2US-12624264-B2

Abstract

A process for preparing a solventless pressure sensitive adhesive composition comprising mixing (A) a solid polyorganosilicate resin component with (B) an aliphatically unsaturated polydiorganosiloxane (B-1), a branched polyorganosiloxane (B-2), or a mixture of (B-1) and (B-2), at certain temperatures, followed by cooling. The solventless pressure sensitive adhesive composition prepared by the process has a low viscosity and can be cured to form pressure sensitive adhesives. The pressure sensitive adhesives are suitable for protective film applications.

Inventors

Rongrong Fan
Zhihua Liu
Qing Cao
Xiaocong XU
Jiayin Zhu

Assignees

DOW SILICONES CORPORATION

Dates

Publication Date: 20260512
Application Date: 20210209

Claims (14)

1 . A process for preparing a solventless pressure sensitive adhesive composition comprising: (i) providing starting material (A) a solid polyorganosilicate resin component comprising: (A-1) more than 30% to 100% by weight, based on the weight of starting material (A), of a solid capped resin of unit formula (I-1): where each R M is independently a monovalent hydrocarbon group of from 1 to 20 carbon atoms; each Z is independently a hydrolyzable group selected from the group consisting of alkoxy, hydroxyl, or mixtures thereof; c is from 0 to a value sufficient to give the capped resin a hydrolyzable group content up to 2% by weight based on the weight of the capped resin; and a and b have values such that a>4, b>0, and the value of (a+b) is sufficient to give the capped resin a number average molecular weight of from 500 to 8,000 g/mol; and (A-2) zero to less than 70% by weight, based on the weight of starting material (A), of a solid uncapped resin of unit formula of (I-2): ( R M 3 ⁢ SiO 1 / 2 ) a ′ ⁢ ( SiO 4 / 2 ) b ′ ⁢ Z c ′ where R M and Z are as described above; a′ and b′ have values such that a′>4, b′>0, and the value of (a′+b′) is sufficient to give the uncapped resin a number average molecular weight of from 500 to 8,000 g/mol; and c′ has a value sufficient to give the uncapped resin a hydrolyzable group content of >2% to 10% by weight based on the weight of the uncapped resin; (ii) mixing starting material (A) with starting material (B) and optionally starting material (C) at a temperature of 100° C. or higher; wherein starting material (B) is an aliphatically unsaturated polydiorganosiloxane (B-1), a branched polyorganosiloxane (B-2), or a mixture of (B-1) and (B-2), wherein the aliphatically unsaturated polydiorganosiloxane (B-1) comprises unit formula (II-1): where each R 1 is independently a monovalent hydrocarbon group of from 1 to 20 carbon atoms that is free of aliphatic unsaturation; each R 2 is independently a monovalent aliphatically unsaturated hydrocarbon group of from 2 to 20 carbon atoms; x, y, z, and w have values such that x>0, y≥0, (x+y)=2, z≥0, w≥0, (w+z)>0, and the value of (x+y+z+w) is sufficient to give the aliphatically unsaturated polydiorganosiloxane a number average molecular weight of from 5,000 to 50,000 g/mol; wherein the branched polyorganosiloxane (B-2) comprises unit formula (II-2): where R 1 and R 2 are as described above, and g, h, and i have values such that 2≥g ≥0, 4≥h≥0, 995≥i≥4, (g+h)=4, and the value of (g+h+i) is sufficient to give the branched polyorganosiloxane a number average molecular weight of from 5,000 to 50,000 g/mol; wherein starting material (C) is a polydiorganosiloxane gum of unit formula (III): where R 1 is as described above; each R G is independently a monovalent aliphatically unsaturated hydrocarbon group of from 2 to 20 carbon atoms, hydroxyl, or combinations thereof; and d has a value sufficient to give the polydiorganosiloxane gum a number average molecular weight of 300,000 g/mol or more; wherein starting materials (A), (B), and (C) are present in amounts to provide a weight ratio of the amount of starting material (A) to combined amounts of starting materials (B) and (C) if present of from 0.1 to 1.2; (iii) cooling the mixture obtained from step (ii) to form a silicone base part with a viscosity of less than 5,000 mPas at room temperature; and (iv) admixing the silicone base part obtained from step (iii) with starting material (D) a polyorganohydrogensiloxane, starting material (E) a hydrosilylation reaction catalyst, optionally starting material (F) a hydrosilylation reaction inhibitor, and optionally starting material (G) an anchorage additive; thus forming the solventless pressure sensitive adhesive composition, wherein the process is conducted in the substantial absence of a solvent.
2 . The process of claim 1 , wherein each R 1 is independently an alkyl group of from 1 to 6 carbon atoms and each R 2 is independently an alkenyl group of from 2 to 6 carbon atoms.
3 . The process of claim 1 , wherein the aliphatically unsaturated polydiorganosiloxane (B-1) and the branched polyorganosiloxane (B-2) each independently has a number average molecular weight of 5,500 to 20,000 g/mol.
4 . The process of claim 1 , wherein mixing in step (ii) is conducted at a temperature of from 120 to 230° C.
5 . The process of claim 1 , wherein starting material (B) has a viscosity of 3,000 mPa·s or less at room temperature.
6 . The process of claim 1 , wherein each R M is independently an alkyl group of from 1 to 6 carbon atoms.
7 . The process of claim 1 , wherein starting materials are present in amounts to provide a molar ratio of silicon bonded hydrogen atoms to aliphatically unsaturated groups in the solventless pressure sensitive adhesive composition of from 1 to 10.
8 . The process of claim 1 , wherein the weight ratio of the amount of starting material (A) to combined amounts of starting materials (B) and (C) if present is in the range of from 0.3 to 0.8.
9 . The process of claim 1 , wherein the solventless pressure sensitive adhesive composition has a viscosity of less than 5,000 mPa·s at room temperature.
10 . The process of claim 1 , wherein the hydrosilylation reaction catalyst comprises platinum.
11 . The process of claim 1 , wherein starting material (C) is present in an amount of from zero to 6%, by weight based on the total weight of starting materials in the solventless pressure sensitive adhesive composition.
12 . The process of claim 1 , wherein the polyorganohydrogensiloxane comprises unit formula (IV): (R 1 3 SiO 1/2 ) 2 (R 1 2 SiO 2/2 ) e (HR 1 2 SiO 2/2 ) f , where R 1 is as described above, e≥0, f≥3, and (e+f) is from 4 to 500.
13 . The process of claim 1 , wherein the process is conducted with 80 ppm by weight or less of a solvent, based on total weight of starting materials in the solventless pressure sensitive adhesive composition.
14 . A method of making an adhesive article comprising: preparing a solventless pressure sensitive adhesive composition by a process comprising: (i) providing starting material (A) a solid polyorganosilicate resin component comprising: (A-1) more than 30% to 100% by weight, based on the weight of starting material (A), of a solid capped resin of unit formula (1-1): where each R M is independently a monovalent hydrocarbon group of from 1 to 20 carbon atoms; each Z is independently a hydrolyzable group selected from the group consisting of alkoxy, hydroxyl, or mixtures thereof; c is from 0 to a value sufficient to give the capped resin a hydrolyzable group content up to 2% by weight, based on the weight of the capped resin; and a and b have values such that a>4, b>0, and the value of (a+b) is sufficient to give the capped resin a number average molecular weight of from 500 to 8,000 g/mol; and (A-2) zero to less than 70% by weight, based on the weight of starting material (A), of a solid uncapped resin of unit formula of (1-2): where R M and Z are as described above; a′ and b′ have values such that a′>4, b′>0, and the value of (a′+b′) is sufficient to give the uncapped resin a number average molecular weight of from 500 to 8,000 g/mol; and c′ has a value sufficient to give the uncapped resin a hydrolyzable group content of >2% to 10% by weight, based on the weight of the uncapped resin; (ii) mixing starting material (A) with starting material (B) and optionally starting material (C) at a temperature of 100° C. or higher; wherein starting material (B) is an aliphatically unsaturated polydiorganosiloxane (B-1), a branched polyorganosiloxane (B-2), or a mixture of (B-1) and (B-2), wherein the aliphatically unsaturated polydiorganosiloxane (B-1) comprises unit formula (11-1): where each R 1 is independently a monovalent hydrocarbon group of from 1 to 20 carbon atoms that is free of aliphatic unsaturation; each R 2 is independently a monovalent aliphatically unsaturated hydrocarbon group of from 2 to 20 carbon atoms; x, y, z, and w have values such that x>0, y≥0, (x+y)=2, z≥0, w≥0, (w+z)>0, and the value of (x+y+z+w) is sufficient to give the aliphatically unsaturated polydiorganosiloxane a number average molecular weight of from 5,000 to 50,000 g/mol; wherein the branched polyorganosiloxane (B-2) comprises unit formula (II-2): where R 1 and R 2 are as described above, and g, h, and i have values such that 2≥g≥0, 4≥h ≥0, 995≥i≥4, (g+h)=4, and the value of (g+h+i) is sufficient to give the branched polyorganosiloxane a number average molecular weight of from 5,000 to 50,000 g/mol; wherein starting material (C) is a polydiorganosiloxane gum of unit formula (III): where R 1 is as described above; each R G is independently a monovalent aliphatically unsaturated hydrocarbon group of from 2 to 20 carbon atoms, hydroxyl, or combinations thereof; and d has a value sufficient to give the polydiorganosiloxane gum a number average molecular weight of 300,000 g/mol or more; wherein starting materials (A), (B), and (C) are present in amounts to provide a weight ratio of the amount of starting material (A) to combined amounts of starting materials (B) and (C) if present of from 0.1 to 1.2; (iii) cooling the mixture obtained from step (ii) to form a silicone base part with a viscosity of less than 5,000 mPa·s at room temperature; and (iv) admixing the silicone base part obtained from step (iii) with starting material (D) a polyorganohydrogensiloxane, starting material (E) a hydrosilylation reaction catalyst, optionally starting material (F) a hydrosilylation reaction inhibitor, and optionally starting material (G) an anchorage additive; thus forming the solventless pressure sensitive adhesive composition, wherein the process is conducted in the substantial absence of a solvent, thereby preparing the solventless pressure sensitive adhesive composition, optionally (1) treating a surface of a substrate, (2) coating the solventless pressure sensitive adhesive composition on the surface of the substrate, and (3) curing the solventless pressure sensitive adhesive composition.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a U.S. national stage filing under 35 U.S.C. § 371 of PCT Application No. PCT/CN2021/076335 filed on 9 Feb. 2021. PCT Application No. PCT/CN2021/076335 is hereby incorporated by reference. FIELD OF THE INVENTION The present invention is a solventless pressure sensitive adhesive composition and a process for preparing the pressure sensitive adhesive composition. INTRODUCTION A polyorganosilicate resin is solid at room temperature. Without solvent, the polyorganosilicate resin typically has a powder or flake form, which makes it difficult to blend with other ingredients homogeneously when preparing silicone pressure sensitive adhesive (PSA) compositions. Attempts to manufacture solventless PSA compositions typically include dissolving the polyorganosilicate resin in a solvent or combining the polyorganosilicate resin and other silicone components in a solvent and thereafter removing the solvent. The step of solvent removal (e.g., stripping) results in increased manufacturing and equipment cost and the resulting composition inherently typically contains residual solvent in an amount of more than 1,000 part per million (ppm). Moreover, relatively low viscosity is desirable for certain applications such as for protective films, e.g., a viscosity of less than 5,000 millipascal-seconds (mPa·s) at room temperature. However, commercially available solventless PSA compositions usually have high viscosities which make it difficult to directly coat such solventless PSA compositions onto substrates. In this case, customers still need to dilute the PSA compositions using solvents after receipt and before use. It is desirable to discover a process for preparing a solventless PSA composition suitable for use in protective films for electronics applications without the aforementioned problems. SUMMARY OF THE INVENTION The present invention solves the problem of discovering a solventless pressure sensitive adhesive (PSA) composition without the aforementioned problems. The present invention provides a novel process for preparing the solventless PSA composition comprising preparation of a silicone base part with a viscosity of less than 5,000 millipascal-seconds (mPa·s) at room temperature. The resulting solventless PSA composition of the present invention can be directly applied to a substrate and cured to form pressure sensitive adhesives (PSAs). The PSAs can provide desired coating appearance and adhesion strength particularly suitable for protective film applications, for example, peel adhesion of 20 grams per inch (g/in) or less. Viscosity and adhesion properties can be measured according to the test methods described in the Examples section below. In a first aspect, the present invention provides a process for preparing a solventless pressure sensitive adhesive composition. The process comprises: (i) providing starting material (A) a solid polyorganosilicate component comprising:(A-1) more than 30% to 100% by weight, based on the weight of starting material (A), of a solid capped resin of unit formula (I-1): where each RM is independently a monovalent hydrocarbon group of from 1 to 20 carbon atoms; each Z is independently a hydrolyzable group selected from the group consisting of alkoxy, hydroxyl, or mixtures thereof; c is from 0 to a value sufficient to give the capped resin a hydrolyzable group content up to 2%, by weight based on the weight of the capped resin; and a and b have values such that a>4, b>0, and the value of (a+b) is sufficient to give the capped resin a number average molecular weight of from 500 to 8,000 g/mol; and (A-2) zero to less than 70% by weight, based on the weight of starting material (A), of a solid uncapped resin of unit formula of (I-2): where RM and Z are as described above; a′ and b′ have values such that a′>4, b′>0, and the value of (a′+b′) is sufficient to give the uncapped resin a number average molecular weight of from 500 to 8,000 g/mol; and c′ has a value sufficient to give the uncapped resin a hydrolyzable group content of >2% to 10% by weight based on the weight of the uncapped resin;(ii) mixing starting material (A) with starting material (B) and optionally starting material (C) at a temperature of 100° C. or higher;wherein starting material (B) is an aliphatically unsaturated polydiorganosiloxane (B-1), a branched polyorganosiloxane (B-2), or a mixture of (B-1) and (B-2),wherein the aliphatically unsaturated polydiorganosiloxane (B-1) comprises unit formula (II-1): where each R1 is independently a monovalent hydrocarbon group of from 1 to 20 carbon atoms that is free of aliphatic unsaturation; each R2 is independently a monovalent aliphatically unsaturated hydrocarbon group of from 2 to 20 carbon atoms; x, y, z, and w have values such that x>0, y≥0, (x+=2, z≥0, w≥0, (w+z)>0, and the value of (x+y+z+w) is sufficient to give the aliphatically unsaturated polydiorganosiloxane a number average molecular weight of from 5,000