Silicone composition and a pressure sensitive adhesive film having a pressure sensitive adhesive layer made from the composition

1. A pressure sensitive adhesive film comprising:

a substrate film; and

a pressure sensitive adhesive layer formed on a surface of the substrate film, said pressure sensitive adhesive layer being prepared from a silicone composition comprising:

(A) a diorganopolysiloxane having at least two alkenyl groups per molecule;

(B) a polyorganosiloxane comprising an R 1 3 SiO 0.5 unit and an SiO 2 unit in a molar ratio of the R 1 3 SiO 0.5 unit to the SiO 2 unit of from 0.6 to 1.7, wherein R 1 is a monovalent hydrocarbon group having 1 to 10 carbon atoms;

(C) a polyorganosiloxane having an SiH bond,

characterized in that

the diorganopolysiloxane (A) contains alkenyl groups in an amount of from 0.002 to 0.05 mole per 100 g of the diorganopolysiloxane (A),

the polyorganosiloxane (C) is contained in such an amount that a molar ratio of the SiH bond to the alkenyl group of the diorganopolysiloxane (A) ranges from 0.5 to 20,

a mass ratio of the diorganopolysiloxane (A) to the polyorganosiloxane (B) comprising an R 1 3 SiO 0.5 unit and an SiO 2 unit ranges from 95/5 to 55/45, and

the adhesive layer has an adhesion strength ranging from 0.01 to 0.5 N/10 mm measured according to the 180-degree peel test specified in the Japanese Industrial Standard Z 0237 on a film composed of a polyethylene terephthalate film having a thickness of 25 μm and the adhesive layer having a thickness of 30 μm provided on the polyethylene terephthalate film, wherein said pressure sensitive adhesive film is transparent and is suitable to apply on a surface of a flat panel display.

2. The pressure sensitive adhesive film according to claim 1 , further comprising:

0 to 8.0 parts by mass, based on a total of (A) and (B) of 100 parts by mass, of a retarder (D);

5 to 2,000 ppm, calculated as platinum, based on a total of (A) and (B) of 100 parts by mass, of a platinum catalyst (E); and

25 to 900 parts by mass, based on a total of (A) and (B) of 100 parts by mass, of an organic solvent (F).

3. The pressure sensitive adhesive film according to claim 1 , wherein a mass ratio of the diorganopolysiloxane (A) to the polyorganosiloxane (B) is 55/45 and the alkenyl group is contained in an amount of from 0.005 to 0.05 mole per 100 g of the diorganopolysiloxane (A).

4. The pressure sensitive adhesive film according to claim 1 , wherein a part or all of the components (A) and (B) is contained as a product prepared by reacting the part or all of the components (A) and (B) in the presence of a basic catalyst.

5. The pressure sensitive adhesive film according to claim 1 or claim 2 , wherein the alkenyl group of the diorganopolysiloxane (A) is a vinyl group.

6. The pressure sensitive adhesive film according to claim 1 , wherein the diorganopolysiloxane (A) is represented by the following formula:

wherein R 2 is a substituted or unsubstituted monovalent hydrocarbon group which does not have an aliphatic unsaturated bond, R 3 is an organic group having an alkenyl group, “a” is an integer of from 0 to 2, “m” is an integer of 0 or larger, provided that “in” is 2 or larger when “a” is zero, “n” is an integer of 10 or larger, with a sum of “m” and “n” being such that the diorganopolysiloxane has a viscosity of 10 mPa·s or larger.

7. The pressure sensitive adhesive film according to claim 1 , wherein the film has a primer layer between the substrate film and the pressure sensitive adhesive layer.

8. The pressure sensitive adhesive film according to claim 7 , wherein a surface of the substrate film has been corona-treated and the primer layer is placed on the corona-treated surface.

9. The pressure sensitive adhesive film according to claim 1 , wherein the silicone composition consists of the aforesaid components (A), (B), and (C) and at least one component selected from non-reactive polyorganosiloxanes having no alkenyl group, antioxidants, photostabilizers, flame retardants and antistatic agents.

10. The pressure sensitive adhesive film according to claim 2 , wherein the silicone composition consists of the aforesaid components (A), (B), (C), (D), (E), and (F) and at least one component selected from non-reactive polyorganosiloxanes having no alkenyl group, antioxidants, photostabilizers, flame retardants, and antistatic agents.