PRIMER COMPOSITION FOR PRESSURE-SENSITIVE SILICONE ADHESIVE, AND ARTICLE

Abstract

A primer composition for pressure-sensitive silicone adhesives which comprises (A) an organopolysiloxane including at least two alkenyl-containing organic groups in the molecule and having an alkenyl group content of 0.001-0.008 mol per 100 g of the organopolysiloxane, (B) an organopolysiloxane including at least two alkenyl-containing organic groups in the molecule and having an alkenyl group content of 0.15-1.3 mol per 100 g of the organopolysiloxane, (C) an organohydrogenpolysiloxane having at least three SiH groups in the molecule but containing neither any alkoxy group nor any epoxy group, and (D) a platinum-group metal catalyst. The primer composition cures satisfactorily while sufficiently exhibiting adhesiveness to pressure-sensitive silicone adhesives. Even after having cured sufficiently, the primer composition can retain the satisfactory adhesiveness.

Claims

1. A primer composition for silicone pressure-sensitive adhesives, comprising: (A) 100 parts by weight of an organopolysiloxane containing at least two alkenyl-containing organic groups in the molecule and having an alkenyl content of 0.001 to 0.008 mole per 100 g of the organopolysiloxane, represented by the average compositional formula (1): ##STR00037## wherein R.sup.1 which may be the same or different is a hydroxyl group, C.sub.1-C.sub.3 alkoxy group, substituted or unsubstituted C.sub.1-C.sub.10 monovalent hydrocarbon group free of aliphatic unsaturation, or C.sub.2-C.sub.10 alkenyl-containing organic group, at least two of R.sup.1 being C.sub.2-C.sub.10 alkenyl-containing organic groups, a is an integer of at least 2, b is an integer of at least 1, c and d each are an integer of at least 0, and 400a+b+c+d2,000, (B) 1 to 20 parts by weight of an organopolysiloxane containing at least two alkenyl-containing organic groups in the molecule and having an alkenyl content of 0.15 to 1.3 moles per 100 g of the organopolysiloxane, represented by the average compositional formula (2): ##STR00038## wherein R.sup.2 which may be the same or different is a hydroxyl group, C.sub.1-C.sub.3 alkoxy group, substituted or unsubstituted C.sub.1-C.sub.10 monovalent hydrocarbon group free of aliphatic unsaturation, or C.sub.2-C.sub.10 alkenyl-containing organic group, at least two of R.sup.2 being C.sub.2-C.sub.10 alkenyl-containing organic groups, e to h each are an integer of at least 0, and 2e+f+g+h20, (C) an organohydrogenpolysiloxane containing at least three SiH groups in the molecule, but not alkoxy and epoxy groups, in such an amount that a molar ratio of SiH groups to the total of alkenyl groups in components (A) and (B) ranges from 0.5/1 to 30/1, and (D) a platinum group metal based catalyst for promoting hydrosilylation addition reaction between alkenyl groups in components (A) and (B) and SiH groups in component (C) for curing, in such an amount as to give 1 to 500 ppm of metal based on the weight of component (A).

2. The primer composition of claim 1, further comprising (E) 0.01 to 5 parts by weight of a reaction regulator per 100 parts by weight of components (A) to (C) combined.

3. The primer composition of claim 1 or 2, further comprising (F) 0.5 to 10 parts by weight of a silane coupling agent per 100 parts by weight of component (A).

4. The primer composition of claim 3 wherein component (F) is a silane coupling agent having the general formula (3):
R.sup.3.sub.iSi(OR.sup.4).sub.4-i (3) wherein R.sup.3 is a monovalent organic group free of nitrogen, sulfur, phosphor and tin elements, R.sup.4 is C.sub.1-C.sub.4 alkyl, and i is a number 1i3.

5. The primer composition of claim 1, further comprising (G) 0.1 to 10 parts by weight of a compound having the general formula (4) or (5) per 100 parts by weight of component (A), ##STR00039## wherein R.sup.5 which may be the same or different is a substituted or unsubstituted C.sub.1-C.sub.10 monovalent hydrocarbon group free of aliphatic unsaturation, R.sup.6 is hydrogen or R.sup.5, R.sup.7 is an epoxy-containing organic group, R.sup.8 is an alkoxysilyl-containing organic group, j and n each are an integer of at least l, k and o each are an integer of at least 0, l, m, p and q each are an integer of at least 0, l+m and p+q each are an integer of at least 1.

6. The primer composition of claim 1, further comprising (H) 5 to 2,000 parts by weight of an organic solvent per 100 parts by weight of component (A).

7. An article comprising a substrate and a cured coating of the primer composition of claim 1 thereon.

8. A pressure-sensitive adhesive article comprising the article of claim 7 and a cured product of a silicone pressure-sensitive adhesive composition on the surface of the cured coating of the primer composition.

9. The pressure-sensitive adhesive article of claim 8 wherein the silicone pressure-sensitive adhesive composition is curable through hydrosilylation.

Description

EXAMPLES

[0137] Examples and Comparative Examples are given below for further illustrating the invention although the invention is not limited thereto. In Examples, Me stands for methyl, Vi for vinyl, Et for ethyl, and Ph for phenyl.

<Primer Cure>

[0138] A primer composition for silicone PSA was coated onto a polyethylene terephthalate (PET) of 25 m thick and 25 mm wide by means of a wire bar so as to give a solid weight of 0.5 g/m.sup.2 after curing, and air dried at 130 C. for 1 minute. The primer-treated substrate was evaluated for cure by touching the silicone coated surface with the finger.

[0139] : no finger marks left

[0140] x: finger marks left

<Adhesion>

[0141] A tape sample was prepared by coating a silicone PSA composition on the primer-treated substrate (prepared as above) by means of an applicator so as to give a thickness of 30 m after curing, and curing at 130 C. for 1 minute. Lateral portions of 2 mm were cut off from the tape sample. After the tape sample was torn and pulled from the opposite ends, it was visually observed whether or not the PSA layer was separated apart from the substrate, and evaluated as follows.

[0142] : not separated

[0143] x: separated apart

<Elongation>

[0144] In the adhesion test, the tape sample was torn, after which the tape sample with the substrate separated was further pulled. The distance (mm) by which the PSA layer was elongated was measured. A smaller distance indicates better adhesion.

[0145] It is noted that the tape sample was evaluated for adhesion and elongation at two levels where the primer composition was cured for 1 minute and 5 minutes.

Example 1

Preparation of Primer Composition for Silicone PSA

[0146] A primer composition 1 for silicone PSA was prepared by mixing 100 parts by weight of a dimethylpolysiloxane containing 0.00245 mole/100 g of vinyl and having the average compositional formula (a-1):

##STR00020##

as component (A), 3 parts by weight of a dimethylpolysiloxane containing 0.2160 mole/100 g of vinyl and having the average compositional formula (b-1):

##STR00021##

as component (B), 0.97 part by weight of a methylhydrogenpolysiloxane having the average compositional formula (c-1):

##STR00022##

as component (C), 0.60 part by weight of ethynylcyclohexanol as component (E), and 242.00 parts by weight of rubber solvent as component (H), to form a liquid mixture containing 30 wt % of solids, adding 0.5 part by weight of a toluene solution of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum(0) complex containing 0.5 wt % of platinum to the mixture, and diluting the mixture with a solvent of hexane and methyl ethyl ketone in a weight ratio of 1:1 so as to give 5 wt % of solids. The molar ratio of SiH groups in component (C) to the total of vinyl groups in components (A) and (B) was 1.7/1.

Preparation of Silicone PSA Composition

[0147] A composition was prepared by mixing 35 parts by weight of dimethylpolysiloxane (containing 0.00091 mole/100 g of vinyl) having the average compositional formula (i-1):

##STR00023##

as component (I), 65 parts by weight (calculated as nonvolatile) of a 60 wt % toluene solution of methylpolysiloxane consisting of Me.sub.3SiO.sub.1/2 units and SiO.sub.2 units in a molar ratio (Me.sub.3SiO.sub.1/2/SiO.sub.2) of 0.85 as component (J), 0.23 part by weight of methylhydrogenpolysiloxane having formula (c-1) as component (C), and 0.25 part by weight of ethynylcyclohexanol as component (E) and diluting with toluene so that the composition had a solid content of 60 wt %. A silicone PSA composition was prepared by adding 50 parts by weight of toluene to 100 parts by weight of the resulting composition, and further adding 0.5 part by weight of a toluene solution of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum(0) complex containing 0.5 wt % of platinum as component (D) thereto. The molar ratio of SiH groups in component (C) to vinyl groups in component (I) was 11.4/1.

[0148] These compositions prepared as above were evaluated for primer cure, adhesion and elongation by the above methods. The results are shown in Table 1.

Example 2

[0149] A primer composition 2 for silicone PSA was prepared as in Example 1 aside from using 5 parts by weight of dimethylpolysiloxane having formula (b-1) as component (B), 1.44 parts by weight of methylhydrogenpolysiloxane having formula (c-1) as component (C), and 247.76 parts by weight of rubber solvent as component (H). The molar ratio of SiH groups in component (C) to the total of vinyl groups in components (A) and (B) was 1.7/1.

[0150] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 2. The results are shown in Table 1.

Example 3

[0151] A primer composition 3 for silicone PSA was prepared as in Example 1 aside from using 10 parts by weight of dimethylpolysiloxane having formula (b-1) as component (B), 2.62 parts by weight of methylhydrogenpolysiloxane having formula (c-1) as component (C), and 262.18 parts by weight of rubber solvent as component (H). The molar ratio of SiH groups in component (C) to the total of vinyl groups in components (A) and (B) was 1.7/1.

[0152] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 3. The results are shown in Table 1.

Example 4

[0153] A primer composition 4 for silicone PSA was prepared as in Example 1 aside from using 3 parts by weight of a dimethylpolysiloxane (containing 0.4190 mole/100 g of vinyl) having the average compositional formula (b-2):

##STR00024##

as component (B), 1.64 parts by weight of methylhydrogenpolysiloxane having formula (c-1) as component (C), and 243.56 parts by weight of rubber solvent as component (H). The molar ratio of SiH groups in component (C) to the total of vinyl groups in components (A) and (B) was 1.7/1.

[0154] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 4. The results are shown in Table 1.

Example 5

[0155] A primer composition 5 for silicone PSA was prepared as in Example 1 aside from using 3 parts by weight of a dimethylpolysiloxane (containing 1.1628 mole/100 g of vinyl) having the average compositional formula (b-3):

##STR00025##

as component (B), 4.07 parts by weight of methylhydrogenpolysiloxane having formula (c-1) as component (C), and 249.23 parts by weight of rubber solvent as component (H). The molar ratio of SiH groups in component (C) to the total of vinyl groups in components (A) and (B) was 1.7/1.

[0156] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 5. The results are shown in Table 1.

Example 6

[0157] A primer composition 6 for silicone PSA was prepared as in Example 1 aside from using 100 parts by weight of a dimethylpolysiloxane (containing 0.00364 mole/100 g of vinyl) having the average compositional formula (a-2):

##STR00026##

as component (A), 1.10 parts by weight of methylhydrogenpolysiloxane having formula (c-1) as component (C), and 242.30 parts by weight of rubber solvent as component (H). The molar ratio of SiH groups in component (C) to the total of vinyl groups in components (A) and (B) was 1.7/1.

[0158] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 6. The results are shown in Table 1.

Example 7

[0159] A primer composition 7 for silicone PSA was prepared as in Example 1 aside from using 100 parts by weight of a dimethylpolysiloxane (containing 0.00527 mole/100 g of vinyl) having the average compositional formula (a-3):

##STR00027##

as component (A), 1.28 parts by weight of methylhydrogenpolysiloxane having formula (c-1) as component (C), and 242.72 parts by weight of rubber solvent as component (H). The molar ratio of SiH groups in component (C) to the total of vinyl groups in components (A) and (B) was 1.7/1.

[0160] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 7. The results are shown in Table 1.

Example 8

[0161] A primer composition 8 for silicone PSA was prepared as in Example 1 aside from further adding 1.0 part by weight of a compound having the following formula (f-1) as component (F). The molar ratio of SiH groups in component (C) to the total of vinyl groups in components (A) and (B) was 1.7/1.

##STR00028##

[0162] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 8. The results are shown in Table 1.

Example 9

[0163] A primer composition 9 for silicone PSA was prepared as in Example 1 aside from further adding 1.0 part by weight of a compound having the following formula (f-2) as component (F). The molar ratio of SiH groups in component (C) to the total of vinyl groups in components (A) and (B) was 1.7/1.

##STR00029##

[0164] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 9. The results are shown in Table 1.

Example 10

[0165] A primer composition 10 for silicone PSA was prepared as in Example 1 aside from further adding 1.0 part by weight of a compound having the following formula (f-3) as component (F). The molar ratio of SiH groups in component (C) to the total of vinyl groups in components (A) and (B) was 1.7/1.

##STR00030##

[0166] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 10. The results are shown in Table 1.

Example 11

[0167] A primer composition 11 for silicone PSA was prepared as in Example 1 aside from further adding 1.0 part by weight of a compound having the following formula (f-4) as component (F). The molar ratio of SiH groups in component (C) to the total of vinyl groups in components (A) and (B) was 1.7/1.

##STR00031##

[0168] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 11. The results are shown in Table 1.

Example 12

[0169] A primer composition 12 for silicone PSA was prepared as in Example 1 aside from further adding 1.0 part by weight of a compound having the following formula (f-5) as component (F). The molar ratio of SiH groups in component (C) to the total of vinyl groups in components (A) and (B) was 1.7/1.

##STR00032##

[0170] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 12. The results are shown in Table 1.

Example 13

[0171] A primer composition 13 for silicone PSA was prepared as in Example 8 aside from using 3.0 parts by weight of the compound having formula (f-1) as component (F). The molar ratio of SiH groups in component (C) to the total of vinyl groups in components (A) and (B) was 1.7/1.

[0172] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 13. The results are shown in Table 1.

Example 14

[0173] A primer composition 14 for silicone PSA was prepared as in Example 8 aside from using 5.0 parts by weight of the compound having formula (f-1) as component (F). The molar ratio of SiH groups in component (C) to the total of vinyl groups in components (A) and (B) was 1.7/1.

[0174] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 14. The results are shown in Table 1.

Example 15

[0175] A primer composition 15 for silicone PSA was prepared as in Example 4 aside from using 1.0 part by weight of the compound having formula (f-1) as component (F). The molar ratio of SiH groups in component (C) to the total of vinyl groups in components (A) and (B) was 1.7/1.

[0176] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 15. The results are shown in Table 1.

Example 16

[0177] A primer composition 16 for silicone PSA was prepared as in Example 5 aside from using 1.0 part by weight of the compound having formula (f-1) as component (F). The molar ratio of SiH groups in component (C) to the total of vinyl groups in components (A) and (B) was 1.7/1.

[0178] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 16. The results are shown in Table 1.

Example 17

[0179] A primer composition 17 for silicone PSA was prepared as in Example 6 aside from using 1.0 part by weight of the compound having formula (f-1) as component (F). The molar ratio of SiH groups in component (C) to the total of vinyl groups in components (A) and (B) was 1.7/1.

[0180] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 17. The results are shown in Table 1.

Example 18

[0181] A primer composition 18 for silicone PSA was prepared as in Example 7 aside from using 1.0 part by weight of the compound having formula (f-1) as component (F). The molar ratio of SiH groups in component (C) to the total of vinyl groups in components (A) and (B) was 1.7/1.

[0182] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 18. The results are shown in Table 1.

Example 19

[0183] A primer composition 19 for silicone PSA was prepared as in Example 8 aside from further adding 0.60 part by weight of a siloxane compound having the following formula (g-1) as component (G) and using 243.40 parts by weight of rubber solvent as component (H). The molar ratio of SiH groups in component (C) to the total of vinyl groups in components (A) and (B) was 1.7/1.

##STR00033##

[0184] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 19. The results are shown in Table 1.

Example 20

[0185] A primer composition 20 for silicone PSA was prepared as in Example 8 aside from further adding 0.60 part by weight of a siloxane compound having the following formula (g-2) as component (G) and using 243.40 parts by weight of rubber solvent as component (H). The molar ratio of SiH groups in component (C) to the total of vinyl groups in components (A) and (B) was 1.7/1.

##STR00034##

[0186] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 20. The results are shown in Table 1.

Comparative Example 1

[0187] A primer composition 21 for silicone PSA was prepared by mixing 100 parts by weight of dimethylpolysiloxane containing 0.00245 mole/100 g of vinyl and having formula (a-1) as component (A), 0.27 part by weight of methylhydrogenpolysiloxane having formula (c-1) as component (C), 0.60 part by weight of ethynylcyclohexanol as component (E), and 233.36 parts by weight of rubber solvent as component (H), to form a liquid mixture containing 30 wt % of solids, adding 0.5 part by weight of a toluene solution of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum(0) complex containing 0.5 wt % of platinum to the mixture, and diluting the mixture with a solvent of hexane and methyl ethyl ketone in a weight ratio of 1:1 so as to give a solid content of 5 wt %. The molar ratio of SiH groups in component (C) to vinyl groups in component (A) was 1.7/1.

[0188] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 21. The results are shown in Table 1.

Comparative Example 2

[0189] A primer composition 22 for silicone PSA was prepared as in Comparative Example 1 aside from using 100 parts by weight of dimethylpolysiloxane having formula (a-2) as component (A), 0.40 part by weight of methylhydrogenpolysiloxane having formula (c-1) as component (C), and 233.67 parts by weight of rubber solvent as component (H). The molar ratio of SiH groups in component (C) to vinyl groups in component (A) was 1.7/1.

[0190] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 22. The results are shown in Table 1.

Comparative Example 3

[0191] A primer composition 23 for silicone PSA was prepared as in Comparative Example 1 aside from using 100 parts by weight of dimethylpolysiloxane having formula (a-3) as component (A), 0.57 part by weight of methylhydrogenpolysiloxane having formula (c-1) as component (C), and 234.06 parts by weight of rubber solvent as component (H). The molar ratio of SiH groups in component (C) to vinyl groups in component (A) was 1.7/1.

[0192] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 23. The results are shown in Table 1.

Comparative Example 4

[0193] A primer composition 24 for silicone PSA was prepared as in Comparative Example 1 aside from using 100 parts by weight of a dimethylpolysiloxane (containing 0.00213 mole/100 g of vinyl) having the following average compositional formula (a-4):

##STR00035##

as component (A), 0.23 part by weight of methylhydrogenpolysiloxane having formula (c-1) as component (C), and 233.27 parts by weight of rubber solvent as component (H). The molar ratio of SiH groups in component (C) to vinyl groups in component (A) was 1.7/1.

[0194] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 24. The results are shown in Table 1.

Comparative Example 5

[0195] A primer composition 25 for silicone PSA was prepared as in Comparative Example 1 aside from using 100 parts by weight of a dimethylpolysiloxane (containing 0.01772 mole/100 g of vinyl) having the following average compositional formula (a-5):

##STR00036##

as component (A), 1.93 parts by weight of methylhydrogenpolysiloxane having formula (c-1) as component (C), and 237.24 parts by weight of rubber solvent as component (H). The molar ratio of SiH groups in component (C) to vinyl groups in component (A) was 1.7/1.

[0196] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 25. The results are shown in Table 1.

Comparative Example 6

[0197] A primer composition 26 for silicone PSA was prepared by mixing 100 parts by weight of dimethylpolysiloxane having formula (b-1) as component (B), 23.54 parts by weight of methylhydrogenpolysiloxane having formula (c-1) as component (C), 0.60 part by weight of ethynylcyclohexanol as component (E), and 287.66 parts by weight of rubber solvent as component (H), to form a liquid mixture containing 30 wt % of solids, adding 0.5 part by weight of a toluene solution of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum(0) complex containing 0.5 wt % of platinum to the mixture, and diluting the mixture with a solvent of hexane and methyl ethyl ketone in a weight ratio of 1:1 so as to give a solid content of 5 wt %. The molar ratio of SiH groups in component (C) to vinyl groups in component (B) was 1.7/1.

[0198] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 26. The results are shown in Table 1.

Comparative Example 7

[0199] A primer composition 27 for silicone PSA was prepared as in Comparative Example 6 aside from using 100 parts by weight of dimethylpolysiloxane having formula (b-2) as component (B), 45.66 parts by weight of methylhydrogenpolysiloxane having formula (c-1) as component (C), and 339.27 parts by weight of rubber solvent as component (H). The molar ratio of SiH groups in component (C) to vinyl groups in component (B) was 1.7/1.

[0200] The primer cure, adhesion and elongation were evaluated as in Example 1 aside from using primer composition 27. The results are shown in Table 1.

TABLE-US-00001 TABLE 1 Primer composition for silicone PSA Adhesion after Elongation (mm) after Component Component Component Component Component Primer 1 min heating/ 1 min heating/ (A) (B) (C) (F) (G) cure 5 min heating 5 min heating Example 1 (a-1) (b-1) (c-1) /X 1/25 Example 2 (a-1) (b-1) (c-1) /X 1/30 Example 3 (a-1) (b-1) (c-1) /X 2/25 Example 4 (a-1) (b-2) (c-1) /X 2/15 Example 5 (a-1) (b-3) (c-1) /X 2/30 Example 6 (a-2) (b-1) (c-1) /X 3/30 Example 7 (a-3) (b-1) (c-1) /X 2/30 Example 8 (a-1) (b-1) (c-1) (f-1) / 1/1 Example 9 (a-1) (b-1) (c-1) (f-2) / 1/2 Example 10 (a-1) (b-1) (c-1) (f-3) / 2/1 Example 11 (a-1) (b-1) (c-1) (f-4) / 3/3 Example 12 (a-1) (b-1) (c-1) (f-5) / 1/3 Example 13 (a-1) (b-1) (c-1) (f-1) / 1/1 Example 14 (a-1) (b-1) (c-1) (f-1) / 1/2 Example 15 (a-1) (b-2) (c-1) (f-1) / 2/5 Example 16 (a-1) (b-3) (c-1) (f-1) / 1/3 Example 17 (a-2) (b-1) (c-1) (f-1) / 1/1 Example 18 (a-3) (b-1) (c-1) (f-1) / 2/2 Example 19 (a-1) (b-1) (c-1) (f-1) (g-1) / 0/2 Example 20 (a-1) (b-1) (c-1) (f-1) (g-2) / 1/1 Comparative (a-1) (c-1) X / 2/3 Example 1 Comparative (a-2) (c-1) X X/X 20/25 Example 2 Comparative (a-3) (c-1) X X/X 30/30 Example 3 Comparative (a-4) (c-1) X X/X 20/20 Example 4 Comparative (a-5) (c-1) X/X 50/65 Example 5 Comparative (b-1) (c-1) X X/X 80/120 Example 6 Comparative (b-2) (c-1) X X/X 110/160 Example 7

[0201] As is evident from the results in Table 1, Examples 1 to 7 showed satisfactory cure and adhesion in a compatible way. It is presumed that since the relatively long-chain siloxane as component (A) affords flexibility for effective bond to the silicone PSA layer, and the highly reactive low-molecular-weight siloxane as component (B) supplements the rate of crosslink formation of component (A), the adhesion to the silicone PSA (i.e., cured silicone PSA composition) and cure are met in a compatible way.

[0202] It is noted that when the curing time of the primer composition is extended, the adhesion is exacerbated, but improved by using a silane coupling agent as component (F) in combination, as seen from Examples 8 to 20. It is empirically known that when a primer composition is over-cured, the adhesion between the cured composition (primer layer) and the silicone PSA is exacerbated. This is probably because the primer layer is weakened in anchoring force. It is believed as one hypothesis that the primer composition in under-cured or semi-cured state is wettable to the silicone PSA composition and develops a stronger anchoring force. It is believed that since a silane coupling agent plays the role of a wetter when added to a primer composition, the primer composition maintains the adhesion to the silicone PSA even after the primer composition is fully cured.

[0203] Comparative Example 1 fails to meet both adhesion and cure in that the adhesion to the silicone PSA is good, but the primer composition is less curable. It is surmised that since component (B) is omitted, the primer composition is based on a siloxane of greater chain length which is low reactive. Comparative Examples 2 to 4, which do not contain component (B), exhibit poor adhesion to the silicone PSA. In Comparative Examples 2 and 3, because the crosslinking density is increased over Comparative Example 1, a cured coating of the primer composition becomes slightly harder so as to restrain the primer from developing an anchoring force. In Comparative Example 4 wherein the base of the primer composition has a too long molecule (has a higher degree of polymerization than component (A) according to the invention), the progress of cure is retarded so that the primer composition itself does not fully act on the substrate. In Comparative Example 5 using a siloxane outside components (A) and (B) as the base polymer, the primer composition is fully curable, but the adhesion to silicone PSA is insufficient because the crosslinking density is increased as in Comparative Examples 2 and 3, and a cured product of the primer composition becomes a hard coating. In Comparative Examples 6 and 7 which do not contain component (A), it is believed that many reactive sites are available so that the primer composition is less curable.