Silicone pressure sensitive adhesives having enhanced adhesion to low energy substrates

• US 5,248,739 A
• Filed: 10/14/1992
• Issued: 09/28/1993
• Est. Priority Date: 10/18/1991
• Status: Expired due to Fees

• Current Assignee: Dow Corning Corporation (Dow, Inc.)
• Original Assignee: Dow Corning Corporation (Dow, Inc.)
• Inventors: Chung, Kyuha, Vincent, Gary A., Schmidt, Randall G., Brady, William P.
• Primary Examiner(s): Marquis, Melvyn I.
• Assistant Examiner(s): MOORE, MARGARET G
• Application Number:
  US07/960,634
• Time in Patent Office: 349 Days
• Field of Search: 525/477, 525/478, 428/447
• US Class Current: 525/477
• CPC Class Codes: C08L 83/00 Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon only; Compositions of derivatives of such polymers
• CPC Class Codes: C09J 183/04 Polysiloxanes
• CPC Class Codes: Y10T 428/31663 As siloxane, silicone or silane

Abstract

There is disclosed a pressure-sensitive adhesive composition based on a silicone resin and a polydiorganosiloxane polymer wherein the resin component has a number average molecular weight of about 950 to 1,600 and consists essentially of triorganosiloxy (M) units and silicate (Q) units wherein the molar ratio M/Q is in the range 1.1/1 to 1.4/1, inclusive. The adhesives of the invention exhibit improved adhesion to low energy substrates such as polyethylene and polytetrafluoroethylene.

Claims

1. A silicone pressure sensitive adhesive composition consisting essentially of:

(A) 60 to 90 parts by weight of a soluble organopolysiloxane having a M_n value of about 950 to 1,600 and consisting essentially of R₃ SiO_1/2 siloxane units and SiO_4/2 siloxane units wherein each R denotes a monovalent radical selected from the group consisting of hydrocarbon and halogenated hydrocarbon radicals, at least 1/3 of all R radicals being methyl and the mole ratio of R₃ SiO_1/2 siloxane units to SiO_4/2 siloxane units in the soluble organopolysiloxane having a value of from 1.1/1 to 1.4/1; and

(B) 10 to 40 parts by weight of a polydiorganosiloxane having the general formula R¹ R²₂ SiO(R²₂ SiO)_n SiR²₂ R¹ wherein each R² denotes a monovalent radical selected from the group consisting of hydrocarbon and halogenated hydrocarbon radicals, at least 1/2 of all R² radicals being methyl, each R¹ denotes a radical selected from the group consisting of R² radicals and OH radicals and the subscript n is a number having an average value of at least 50.

2. The composition according to claim 1, further containing an effective amount of a nonreactive solvent.

3. The composition according to claim 2, wherein the non-reactive solvent is selected from the group consisting of hydrocarbons, volatile siloxanes, halohydrocarbons, alcohols, esters, ketones and mixtures thereof.

4. The composition according to claim 1, wherein component (A) consists essentially of (CH₃)₃ SiO_1/2 siloxane units and SiO_4/2 siloxane units and component (B) is a polydiorganosiloxane having the general formula R"R'"'"'₂ SiO(R'"'"'₂ SiO)_n SiR'"'"'₂ R" wherein each R'"'"' denotes methyl, phenyl or alkenyl, at least 85 percent of which are methyl radicals, each R" denotes a radical selected from the group consisting of R'"'"' radicals and OH radicals and the subscript n is a number having an average value of greater than 200.

5. The composition of claim 4, further comprising an effective amount of a crosslinking agent.

6. The composition of claim 5, wherein the crosslinking agent is an organic peroxide.

7. The composition of claim 6, wherein the organic peroxide is benzoyl peroxide.

8. The composition according to claim 1, wherein at least two of the R² radicals of said polydiorganosiloxane (B) are alkenyl radicals, said composition further containing (C) an effective amount of an organohydrogenpolysiloxane crosslinking agent having an average of at least 2 silicon-bonded hydrogen atoms in each molecule and (D) a catalytic amount of a platinum group metal-containing catalyst for the addition reaction of alkenyl radicals with silicon-bonded hydrogen atoms.

9. The composition according to claim 8, wherein said component (A) consists essentially of (CH₃)₃ SiO_1/2 siloxane units and SiO_4/2 siloxane units and at least 85 percent of the R² radicals of said polydiorganosiloxane (B) are methyl radicals.

10. The composition of claim 9, wherein said organohydrogenpolysiloxane is a methylhydrogenpolysiloxane.

11. The composition of claim 10, wherein said methylhydrogenpolysiloxane is a linear methylhydrogenpolysiloxane.

12. The composition according to claim 9, further containing an effective amount of a nonreactive solvent.

13. The composition of claim 9, wherein said platinum group metal-containing catalyst is a chloroplatinic acid-vinylsiloxane complex.

14. The composition of claim 9, further comprising a platinum catalyst inhibitor.

15. The composition of claim 14, wherein said platinum catalyst inhibitor is selected from the group consisting of 3,5-dimethyl-1-hexyne-3-ene, a dialkyl fumerate, a dialkyl maleate and benzyl alcohol.

16. The composition according to claim 1, wherein said soluble organopolysiloxane (A) has a silicon-bonded hydroxyl content of less than 1 percent by weight, based on the weight of soluble organopolysiloxane.

17. The composition according to claim 4, wherein said soluble organopolysiloxane (A) has a silicon-bonded hydroxyl content of less than 1 percent by weight, based on the weight of soluble organopolysiloxane.

18. The composition according to claim 8, wherein said soluble organopolysiloxane (A) has a silicon-bonded hydroxyl content of less than 1 percent by weight, based on the weight of soluble organopolysiloxane.

19. The composition according to claim 9, wherein said soluble organopolysiloxane (A) has a silicon-bonded hydroxyl content of less than 1 percent by weight, based on the weight of soluble organopolysiloxane.

20. An article coated with the cured composition of claim 1.

21. An article coated with the cured composition of claim 4.

22. An article coated with the cured composition of claim 8.

23. An article coated with the cured composition of claim 9.

24. An article coated with the cured composition of claim 16.

25. An article coated with the cured composition of claim 17.

26. An article coated with the cured composition of claim 18.

27. An article coated with the cured composition of claim 19.

28. A solventless silicone pressure sensitive adhesive composition consisting essentially of:

(A) 60 to 90 parts by weight of a soluble organopolysiloxane having a M_n value of about 950 to 1,600 and consisting essentially of R₃ SiO_1/2 siloxane units and SiO_4/2 siloxane units wherein each R denotes a monovalent radical selected from the group consisting of hydrocarbon and halogenated hydrocarbon radicals, at least 1/3 of all R radicals being methyl and the mole ratio of R₃ SiO_1/2 siloxane units to SiO_4/2 siloxane units in the soluble organopolysiloxane having a value of from 1.1/1 to 1.4/1; and

(B) 10 to 40 parts by weight of a polydiorganosiloxane having the general formula R¹₂ R² SiO(R¹ R² SiO)_n SiR² R¹₂ wherein each R¹ individually is a radical selected from the group consisting of methyl, ethyl, propyl and phenyl, each R² individually is an olefinic radical or any R¹ as defined above with the proviso that at least two R² radicals per molecule must be olefinic and n has an average value of 50 to 200;

(C) an organohydrogenpolysiloxane compatible with the mixture of (A) and (B) and having an average of at least 2 silicon-bonded hydrogen atoms per molecule, the amount of (C) present in the adhesive composition being sufficient to provide from 1 to 30 silicon bonded hydrogen atoms for every olefinic radical in (B); and

(D) a platinum containing catalyst in sufficient quantity to provide at least 0.1 part by weight platinum for every one million parts by weight of the combined weight of (A), (B) and (C).

30. The composition of claim 28, wherein substantially all R radicals in component (A) are methyl.

31. The composition of claim 28, wherein R² in component (B) is an olefinic radical containing two to six carbon atoms.

32. The composition of claim 28, wherein the organohydrogenpolysiloxane, component (C), is a linear liquid polysiloxane which contains an average of at least three methylhydrogensiloxy groups.

34. The composition of claim 28, which comprises from 65 to 75 parts by weight of a soluble organopolysiloxane (A) and from 25 to 35 parts of polydiorganosiloxane (B).

36. The composition of claim 28, further comprising a platinum catalyst inhibitor.

38. The composition of claim 36, wherein the platinum catalyst inhibitor is diethyl fumerate.

39. The composition of claim 36, wherein the platinum catalyst inhibitor is bis-(methoxymethyl)ethyl maleate.

40. The composition of claim 28, further comprising less than one percent by weight of a solvent.

46. An article having on at least one surface thereof the cured composition of claim 28.

48. An article having on at least one surface thereof the cured composition of claim 36.

49. A pressure sensitive adhesive tape comprising a flexible support having on at least one surface thereof the cured composition of claim 28.

51. A pressure sensitive adhesive tape comprising a flexible support having on at least one surface thereof the cured composition of claim 36.

29. A solventless silicone pressure sensitive adhesive composition comprising:

(A) 60 to 90 parts by weight of a soluble organopolysiloxane having a M_n value of about 950 to 1,600 and consisting essentially of Me₃ SiO_1/2 siloxane units and SiO_4/2 siloxane units in a mole ratio of 1.1/1 to 1.4/1, wherein Me denotes a methyl radical;

(B) 10 to 40 parts by weight of a polydiorganosiloxane having the general formula CH² ═

CH(R¹₂ SiO)_n R¹₂ SiCH═

CH₂ wherein each R¹ individually is a radical selected from the group consisting of methyl, ethyl, propyl and phenyl, and m has an average value of 50 to 200;

(C) an organohydrogenpolysiloxane compatible with the mixture of (A) and (B) and having an average of at least 3 silicon-bonded hydrogen atoms per molecule, the amount of (C) present in the adhesive composition being sufficient to provide from 1 to 30 silicon bonded hydrogen atoms for every olefinically unsaturated radical in the total of (A) plus (B); and

(D) a platinum containing catalyst in sufficient quantity to provide at least 0.1 part by weight platinum for every one million parts by weight of the combined weight of (A), (B) and (C).

33. The composition of claim 29, wherein the organohydrogenpolysiloxane, component (C), is a linear liquid polysiloxane which contains an average of at least three methylhydrogensiloxy groups.

35. The composition of claim 29, which comprises from 65 to 75 parts by weight of a soluble organopolysiloxane (A) and from 25 to 35 parts of polydiorganosiloxane (B).

37. The composition of claim 29 further comprising a platinum catalyst inhibitor.

41. The composition of claim 29, further comprising less than one percent by weight of a solvent.

47. An article having on at least one surface thereof the cured composition of claim 29.

50. A pressure sensitive adhesive tape comprising a flexible support having on at least one surface thereof the cured composition of claim 29.

42. A process for preparing a solventless silicone pressure sensitive adhesive composition comprising:

(I) preparing an organic solvent solution of

(A) 60 to 90 parts by weight of a soluble organopolysiloxane having a M_n value of about 950 to 1,600 and consisting essentially of Me₃ SiO_1/2 siloxane units and SiO_4/2 siloxane units in a mole ratio of 1.1/1 to 1.4/1, in which Me denotes a methyl radical;

(B) 10 to 40 parts by weight of a polydiorganosiloxane having the general formula R² (R¹₂ SiO)_n SiR¹₂ R² wherein R¹ is independently selected from the group consisting of methyl, ethyl, propyl and phenyl, R² is an olefinically unsaturated radical and m has an average value of 50 to 200; and

(C) an organohydrogenpolysiloxane compatible with the mixture of (A) and (B) and having an average of at least 3 silicon-bonded hydrogen atoms per molecule, the amount of (C) present in the adhesive composition being sufficient to provide from 1 to 30 silicon bonded hydrogen atoms for every olefinically unsaturated radical in the total of (A) plus (B);

(II) removing organic solvent from the solution to obtain a devolatilized mixture containing less than one percent by weight, based on the total weight of devolatilized mixture, of volatiles; and

(III) mixing the devolatilized mixture with

(D) a platinum containing catalyst in sufficient quantity to provide at least 0.1 part by weight platinum for every one million parts by weight of the combined weight of (A), (B) and (C).

44. The process of claim 42, wherein organic solvent is added to produce a composition with less than one percent by weight of said organic solvent.

43. A process for preparing a solventless silicone pressure sensitive adhesive composition comprising;

(I) preparing an organic solvent solution of

(A) 60 to 90 parts by weight of a soluble organopolysiloxane having a M_n value of about 950 to 1,600 and consisting essentially of Me₃ SiO_1/2 siloxane units and SiO_4/2 siloxane units in a mole ratio of 1.1/1 to 1.4/1, in which Me denotes a methyl radical, and

(B) 10 to 40 parts by weight of a polydiorganosiloxane having the general formula R² (R¹₂ SiO)_n SiR¹₂ R² wherein R¹ is independently selected from the group consisting of methyl, ethyl, propyl and phenyl, R¹ is an olefinically unsaturated radical and m has an average value of 50 to 200;

(II) removing organic solvent from the solution to obtain a devolatilized mixture containing less than one percent of volatiles based on the total weight of devolatilized mixture; and

(III) mixing the devolatilized mixture with

(C) an organohydrogenpolysiloxane compatible with the mixture of (A) and (B) and having an average of at least 3 silicon-bonded hydrogen atoms per molecule, the amount of (C) present in the adhesive composition being sufficient to provide from 1 to 30 silicon bonded hydrogen atoms for every olefinically unsaturated radical in the total of (A) plus (B) and

(D) a platinum containing catalyst in sufficient quantity to provide at least 0.1 part by weight platinum for every one million parts by weight of the combined weight of (A), (B) and (C).

45. The process of claim 43, wherein organic solvent is added to produce a composition with less than one percent by weight of said organic solvent.