Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2002-09-25
2004-11-09
Moore, Margaret G. (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S447000, C428S450000, C524S323000, C524S324000, C524S330000, C524S331000, C524S333000, C524S334000, C524S335000, C524S339000, C524S342000, C524S343000, C524S344000, C524S349000, C524S588000, C528S015000, C528S031000, C528S032000
Reexamination Certificate
active
06815076
ABSTRACT:
This invention relates to a silicone pressure-sensitive adhesive composition and a pressure-sensitive adhesive tape which when is effectively attached to metals such as copper and leaves no adhesive residues after peeling off.
BACKGROUND OF THE INVENTION
Pressure-sensitive adhesive tapes and labels using silicone pressure-sensitive adhesive compositions are utilized under rigorous environments where conventional pressure-sensitive adhesive compositions such as acrylic, rubber, urethane and epoxy base compositions can be altered or degraded. This is because silicone pressure-sensitive adhesive composition layers have excellent heat resistance, freeze resistance, weather resistance, electrical insulation and chemical resistance.
Such pressure-sensitive adhesive tapes are generally prepared by applying silicone pressure-sensitive adhesive compositions to plastic films or suitable supports and effecting crosslinking reaction to cure the compositions for improving tackiness.
Typical forms of pressure-sensitive adhesive tape include heat resistant pressure-sensitive adhesive tape and heat resistant masking tape in which pressure-sensitive adhesive compositions are applied to heat resistant supports, and chemical resistant masking tape.
In the manufacture of printed circuit boards, the heat resistant masking tape and chemical resistant masking tape are used during etching, plating and soldering steps for preventing the processing solution (e.g., etching solution, plating solution) and solder from contacting unnecessary areas of electronic parts. While it should be avoided that when the adhesive tape is contacted with or immersed in the processing fluid or held under processing temperature conditions, the adhesive tape peels off or partially separates away allowing the area to be protected to be contaminated, it is also required that at the end of processing, the adhesive tape be smoothly peeled from the part without allowing residues of the adhesive to transfer to or remain on the part. If the adhesive transfers to or remains on the part, it can cause troubles in the ensuing manufacture of printed circuit boards.
The above-mentioned tape is also used during the manufacture of semiconductor devices for protecting lead frames or securing lead pins of lead frames. Even when the tape is exposed to elevated temperatures of 150 to 250° C. in the steps of securing and bonding, wire bonding, and resin encapsulating of semiconductor chips, the adhesive layer should not peel off or partially separate away. Once the operation is completed, the tape must be peeled without allowing the adhesive to transfer to or remain on the adherend.
Regrettably, if a conventional pressure-sensitive adhesive tape using silicone adhesive is exposed to elevated temperatures of 150 to 250° C. after attachment to a metal portion, especially of copper, copper alloy or iron, for bonding or masking purposes, the pressure-sensitive adhesive layer undergoes cohesive failure upon removal of the pressure-sensitive adhesive tape by peeling. Then some adhesive is left on the metal portion, or the adhesive layer transfers from the tape support to the metal portion. This is generally referred to as adhesive residue.
SUMMARY OF THE INVENTION
An object of the invention is to provide a silicone pressure-sensitive adhesive composition which even after exposed to elevated temperatures of 150 to 250° C. during the attachment to adherends of metals such as copper, copper alloys and iron for bonding or masking purposes, can be smoothly peeled from the adherend without leaving any adhesive residue; and a pressure-sensitive adhesive tape using the same.
It has been found that when a phenolic antioxidant is contained in a silicone pressure-sensitive adhesive composition, especially when a phenolic antioxidant is contained in a silicone pressure-sensitive adhesive composition of the addition reaction curing type comprising a linear polydiorganosiloxane in which vinyl-bearing backbone is composed of R
1
2
SiO units, a polyorganosiloxane of three-dimensional structure composed of R
1
3
SiO
0.5
units and SiO
2
units, and a polyorganohydrosiloxane or platinum compound as a curing catalyst, as disclosed in JP-B 54-37907, there is obtained a silicone pressure-sensitive adhesive composition which is effectively attached to metals such as copper and does leave no adhesive residue after removal from the metal. The preferred phenolic antioxidant is a phenolic compound having in a molecule a structure of the following formula:
wherein R is a monovalent hydrocarbon group having 1 to 6 carbon atoms, preferably tert-butyl. The use of such a phenolic antioxidant enhances the benefit of the invention that when the pressure-sensitive adhesive is attached to a copper board or copper wiring, heat aged at 150 to 250° C., and thereafter, peeled therefrom, it leaves no adhesive residue on the copper.
Therefor, the present invention provides a silicone pressure-sensitive adhesive composition comprising a phenolic antioxidant.
In one preferred embodiment, a silicone pressure-sensitive adhesive composition comprising the following components (A) to (F) is provided.
(A) 20 to 80 parts by weight of an alkenyl group-containing polydiorganosiloxane,
(B) 80 to 20 parts by weight of a polyorganosiloxane containing R
1
3
SiO
0.5
units and SiO
2
units in a molar ratio between 0.6 and 1.7 wherein R
1
is a monovalent hydrocarbon group having 1 to 10 carbon atoms,
(C) a SiH group-containing polyorganosiloxane in an amount to provide 0.5 to 20 mol of SiH groups per mol of alkenyl groups in component (A),
(D) 0 to 5.0 parts by weight per 100 parts by weight of components (A) and (B) combined of a retarder,
(E) a platinum catalyst in an amount to give 1 to 5,000 ppm of platinum based on the weight of components (A) and (B) combined, and
(F) 0.1 to 10 parts by weight per 100 parts by weight of components (A) and (B) combined of a phenolic antioxidant in the form of a phenolic compound having in a molecule a structure of the following formula:
wherein R is a monovalent hydrocarbon group having 1 to 6 carbon atoms, typically tert-butyl.
Also contemplated herein is a pressure-sensitive adhesive tape comprising a cured layer of the silicone pressure-sensitive adhesive composition lying on at least one surface of plastic film.
The silicone pressure-sensitive adhesive composition and tape are useful as masking tape intended for electrical and electronic parts comprising copper or copper alloy.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the present invention, a silicone pressure-sensitive adhesive composition comprising a phenolic antioxidant is provided. The phenolic antioxidant used herein is preferably a phenolic compound having in a molecule a structure of the following formula:
wherein R is a monovalent hydrocarbon group having 1 to 6 carbon atoms, typically alkyl group, most preferably tert-butyl.
Illustrative examples of the phenolic antioxidant are shown below. Note that
t
Bu is tert-butyl.
The phenolic antioxidant is blended in an amount of 0.05 to 20%, especially 0.1 to 10% by weight of the entire silicone pressure-sensitive adhesive composition.
As used herein, the silicone pressure-sensitive adhesive composition may be selected from various compositions of well-known formulation and curing type, preferably silicone pressure-sensitive adhesive compositions of the addition reaction curing type.
Preferred silicone pressure-sensitive adhesive compositions contain the following components:
(A) an alkenyl group-containing polydiorganosiloxane,
(B) a polyorganosiloxane containing R
1
3
SiO
0.5
units and SiO
2
units,
(C) a SiH group-containing polyorganosiloxane (i.e., polyorganohydrogensiloxane),
(D) a retarder,
(E) a platinum catalyst, and
(F) the phenolic antioxidant defined above.
They are described in detail. First, component (A) is an alkenyl group-containing polydiorganosiloxane, which is preferably represented by either of the formulae below;
R
1
(3-a)
X
a
SiO—(R
1
XSiO)
m
—(R
1
2
SiO)
n
—SiR
1
(3-a)
X
a
R
1
2
(HO)SiO—(R
1
XSiO)
p
—(R
1
2
SiO)
q
—S
Birch & Stewart Kolasch & Birch, LLP
Moore Margaret G.
Shin-Etsu Chemical Co. , Ltd.
Zimmer Marc S
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