Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-03-11
2001-03-13
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S588000, C525S478000
Reexamination Certificate
active
06201055
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a silicone composition for preparing a silicone pressure sensitive adhesive and more particularly to an addition-curable silicone composition containing a certain concentration of a silica filler having a low surface area. The present invention also relates to a silicone pressure sensitive adhesive produced from such composition.
BACKGROUND OF THE INVENTION
Silicone pressure sensitive adhesives, hereinafter also referred to as silicone PSAs, are useful in a variety of applications by virtue of their unique properties, including excellent adhesive and cohesive strength, high tack, very low alpha particle emissions, good moisture resistance, good electrical properties, high ionic purity, and good adhesion to low energy substrates. For example, silicone PSAs are widely used in adhesive tapes, bandages, low-temperature backings, transfer films, and labels. Moreover, silicone PSAs are used in the assembly of automotive parts, toys, electronic circuits, and keyboards.
Addition-curable silicone compositions useful for preparing silicone pressure sensitive adhesives are known in the art. For example, silicone compositions containing an alkenyl-containing polydiorganosiloxane, an organopolysiloxane resin, an organohydrogenpolysiloxane, and a hydrosilylation catalyst are disclosed in U.S. Pat. No. 5,290,885 to Vincent et al.; U.S. Pat. No. 5,366,809 to Schmidt et al.; U.S. Pat. No. 3,983,298 to Hahn et al.; U.S. Pat. No. 5,399,614 to Lin et al.; U.S. Pat. No. 5,100,976 to Hamada et al.; U.S. Pat. No. 5,446,532 to Wengrovius et al.; U.S. Pat. No. 4,774,297 to Murakami et al.; U.S. Pat. No. 4,988,779 to Medford et al.; and U.S. Pat. No. 5,292,586 to Lin et al. The above-cited references disclose adding only small amounts of additional ingredients, including fillers, to the addition-curable silicone compositions. However, these references do not teach the silica filler of the present invention or the concentration of such filler.
However, conventional addition-curable silicone compositions, including the aforementioned, cure to form silicone pressure sensitive adhesives having relatively high coefficients of thermal expansion, rendering them unsatisfactory for certain applications, such as attachment of heat sinks to semiconductor chips and semiconductor chips to substrates. During thermal cycling, stresses develop in the silicone pressure sensitive adhesive due to differences in the coefficients of thermal expansion between the substrate materials and the adhesive. Thermally-induced stresses can weaken or fracture the pressure sensitive bond, limiting the useful service life of a device.
While inorganic fillers such as silica and alumina are typically added to silicone rubber compositions to reduce the coefficient of thermal expansion of cured products, silicone compositions for preparing silicone pressure sensitive adhesives are usually unfilled or contain only low concentrations, for example, less than about 5 percent by weight, of filler. Fillers are generally considered undesirable in the later silicone compositions because moderate to high amounts of filler can cause and increase in viscosity of a given composition and also significantly reduce the tack of the silicone PSA produced therefrom.
Therefore, there is a need for an addition-curable silicone composition that cures to form a silicone pressure sensitive adhesive having a low coefficient of thermal expansion and high tack.
SUMMARY OF THE INVENTION
The present inventors have discovered that a silicone composition containing a certain concentration of a silica filler having a low surface area cures to form a silicone pressure sensitive adhesive having a low coefficient of thermal expansion and unexpectedly high tack.
Specifically, the present invention is directed to a silicone composition for preparing a silicone pressure sensitive adhesive, the composition comprising (A) 20 to 55 parts by weight of a polydiorganosiloxane containing an average of at least two silicon-bonded alkenyl groups per molecule; (B) 45 to 80 parts by weight of an organopolysiloxane resin consisting essentially of R
3
3
SiO
1/2
units and SiO
4/2
units, wherein the total amount of components (A) and (B) is 100 parts by weight; (C) an organohydrogenpolysiloxane having an average of at least two silicon-bonded hydrogen atoms per molecule in an amount sufficient to cure the composition; (D) 25 to 200 parts by weight of a silica filler having an average surface area less than 25 m
2
/g; and (E) a catalytic amount of a hydrosilylation catalyst. In the above formula for the organopolysiloxane resin, each R
3
is independently selected from the group consisting of monovalent hydrocarbon and monovalent halogenated hydrocarbon groups. The mole ratio of R
3
3
SiO,
1/2
units to SiO
4/2
units in the organopolysiloxane resin is from 0.6:1 to 1.5:1 and the resin contains less than about 2 mole percent of alkenyl groups. The sum of the average number of silicon-bonded alkenyl groups per molecule in component (A) and the average number of silicon-bonded hydrogen atoms per molecule in component (C) is greater than 4.
The present invention is also directed to a silicone pressure sensitive adhesive comprising a reaction product of the above-described composition.
The present invention is further directed to a multi-part silicone composition for preparing a silicone pressure sensitive adhesive, the composition comprising components (A) through (E) in two or more parts, provided neither component (A) nor component (B), when component (B) contains alkenyl groups, are present with components (C) and (E) in the same part.
The silicone composition of the present invention has numerous advantages, including good flow, low VOC (volatile organic compound) content, and rapid low. Moreover, the present silicone composition cures to form a silicone pressure sensitive adhesive having good adhesion, a low coefficient of thermal expansion, and unexpectedly high tack.
The silicone composition of the present invention is useful for preparing a silicone pressure sensitive adhesive. The silicone PSA of the present invention has numerous uses, including adhesive tapes, bandages, and labels. The present silicone PSA composition is also useful for bonding a variety of materials, particularly electronic components to flexible or rigid substrates.
These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, a silicone composition for preparing a silicone pressure sensitive adhesive, comprises:
(A) 20 to 55 parts by weight of a polydiorganosiloxane containing an average of at least two silicon-bonded alkenyl groups per molecule;
(B) 45 to 80 parts by weight of an organopolysiloxane resin consisting essentially of R
3
3
SiO
1/2
units and SiO
4/2
units wherein each R
3
is independently selected from the group consisting of monovalent hydrocarbon and monovalent halogenated hydrocarbon groups, the mole ratio of R
3
3
SiO
1/2
units to SiO
4/2
units is from 0.6:1 to 1.5:1, the resin contains less than about 2 mole percent of alkenyl groups, and the total amount of components (A) and (B) is 100 parts by weight;
(C) an organohydrogenpolysiloxane having an average of at least two silicon-bonded hydrogen atoms per molecule in an amount sufficient to cure the composition;
(D) 25 to 200 parts by weight of a silica filler having an average surface area less than 25 m
2
/g; and
(E) a catalytic amount of a hydrosilylation catalyst; wherein the sum of the average number of silicon-bonded alkenyl groups per molecule in component (A) and the average number of silicon-bonded hydrogen atoms per molecule in component (C) is greater than 4.
Component (A) of the present invention is a polydiorganosiloxane containing an average of at least two silicon-bonded alkenyl groups per molecule. The structure of component (A) is typically linear, however it may contain some branching due
Lutz Michael Andrew
Mojica Andrew Anthony
Watson Michael John
Dow Corning Corporation
Milco Larry A.
Moore Margaret G.
LandOfFree
Silicone composition and silicone pressure sensitive adhesive does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Silicone composition and silicone pressure sensitive adhesive, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Silicone composition and silicone pressure sensitive adhesive will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2466793