Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
2002-10-11
2003-12-30
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C523S212000, C524S864000
Reexamination Certificate
active
06670439
ABSTRACT:
This invention relates to a room temperature curable organopolysiloxane composition of the ketone-removal type for use in a clean room where the emission of low-molecular-weight siloxanes is troublesome, especially as a sealant or adhesive in a semiconductor clean room or on electrical and electronic parts.
BACKGROUND OF THE INVENTION
For seals at joints, air-tight seals on ducts and piping, and seals around filters used in the construction and utility installation of clean rooms, seals to fittings installed in semiconductor facilities such as semiconductor manufacturing apparatus, seals on utility piping for electricity and gas feed to such facilities, seals and adhesives on electric and electronic parts, frequent use is made of room temperature curable organopolysiloxane compositions because of their weather resistance, heat resistance, electrical properties and ease of working. The room temperature curable organopolysiloxane compositions generally comprise an organopolysiloxane which contains low-molecular-weight siloxanes as a base polymer, and low-boiling silane compounds as curing agents or additives. With the passage of time after curing, cured compositions (silicone rubber) give off volatile low-molecular-weight siloxanes, unreacted silane compounds, as well as low-molecular-weight siloxanes arising from cracking of the cured polymer. Such emissions are undesired when the compositions are used in the above-described applications. More particularly, undesired emissions have a detrimental influence on equipment in a clean room. When the compositions are applied to electric and electronic parts, low-molecular-weight siloxanes or low-boiling silane compounds volatilize at contacts and similar sites where heat accumulates, and are ignited with sparks that can generate at the contacts and thus burned into silicon dioxide, which in turn, deposit on the contacts. As a consequence, the contacts become electrically insulated, resulting in a contact failure that motor circuits, relay circuits or other circuits fail to correctly function.
Known in the prior art are a room temperature curable organopolysiloxane composition in which the content of low-molecular-weight organopolysiloxane having a vapor pressure of at least 10
−2
mmHg is 0.3% by weight or lower (JP-A 61-209266) and a room temperature curable organopoly-siloxane composition in which the content of low-molecular-weight organopolysiloxane having a vapor pressure of at least 10
−3
mmHg is 0.7% by weight or lower (Japanese Patent No. 2,565,333). These compositions are still insufficient in the above-described applications, typically joint seals in a clean room.
Many countermeasures have been taken to these problems. With respect to the base polymer, recent improvements in such techniques as stripping and solvent washing made it possible to produce polymers having a minimized content of low-molecular-weight organopoly-siloxanes. It has become possible to clear even the very strict requirement that the content of low-molecular-weight organopolysiloxane having a vapor pressure of at least 10
−12
mmHg is 0.1% by weight or lower as called for in the above-described applications.
With respect to the curing agent, a composition using a high-boiling &agr;-silyl ester compound was proposed as eliminating the contact failure (JP-A 7-331076). With respect to the additive, the present inventors proposed the addition of an organic compound capable of coordinating with a metal (JP-A 3-56564).
The Japan Air Cleaning Association prescribes the substrate surface adsorption-thermal desorption method (adsorption test on silicon wafer) under JACA No. 34 as a standard for selecting a sealing material for use in a clean room, especially a semiconductor clean room. In view of this standard, silicone-base sealing materials comprising a base polymer, a curing agent and additives which have taken in the above-mentioned countermeasures fail to achieve satisfactory performance, and undesirable low-molecular-weight siloxanes are detected. It is noted that this test is to ascertain, after the sealing material is cured, whether or not low-molecular-weight siloxanes and organic compounds migrate therefrom to silicon wafers. It is a very important test upon selection of a material for use in a clean room where KrF excimer lasers and the like are used.
Whether or not low-molecular-weight siloxanes and organic compounds evolved with the passage of time after curing was ascertained by two methods: (1) a method for the analysis (purge and trap analysis) of volatile components from a cured material and (2) a method for the selection of a sealing material for use in a semiconductor clean room, that is, the substrate surface adsorption-thermal desorption method (the adsorption test on silicon wafer, JACA No. 34). It was found with the analysis method (1) that low-molecular-weight siloxanes, despite the absence prior to curing, are created, though in a minor amount, after curing and with the passage of time or by heating. It was found with the analysis method (2) that for all the existing silicone-base sealants, low-molecular-weight siloxanes and organic matter were detected.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a room temperature curable organopolysiloxane composition which is suitable for use in a clean room and as a sealant or adhesive on electrical and electronic parts in that the cured composition does emit essentially no low-molecular-weight siloxanes with the passage of time.
It has been found that a room temperature curable organopolysiloxane composition of the ketone removal type comprising a diorganopolysiloxane having a significantly reduced content of low-molecular-weight organopolysiloxanes as a base polymer and an alkenoxysilane as a crosslinking agent, after curing, does produce essentially no low-molecular-weight siloxanes and organic matter with the passage of time, when examined by the above analysis methods. The composition is then suitable for use as a sealant in a clean room, especially in a semiconductor clean room, and as a sealant or adhesive on electrical and electronic parts.
Accordingly, the present invention provides a room temperature curable organopolysiloxane composition comprising
(A) 100 parts by weight of a diorganopolysiloxane end-capped with a hydroxyl, alkoxy or alkenoxy radical and containing up to 0.1% by weight of low-molecular-weight organopolysiloxanes having a vapor pressure of at least 10
−12
mmHg at 20° C., and
(B) 0.5 to 30 parts by weight of a silane compound having a radical of the following general formula (1):
wherein R
1
and R
2
are independently hydrogen or a substituted or unsubstituted monovalent hydrocarbon radical, or a partial hydrolytic condensate thereof.
Preferably, the composition further comprises (C) 0.01 to 10 parts by weight of an organosilicon compound having a monovalent radical of the following general formula (2):
wherein R
3
and R
4
are independently hydrogen or a monovalent hydrocarbon radical, or a partial hydrolytic condensate thereof.
It is recommended that upon measurement by the substrate surface adsorption-thermal desorption method (the adsorption test on silicon wafer, JACA No. 34), a quantity of low-molecular-weight siloxanes and organic matter arising from the cured composition is up to 1.0 (ngC
16
eq./cm
2
).
DESCRIPTION OF THE PREFERRED EMBODIMENT
Component (A) in the room temperature curable organopolysiloxane composition of the invention is a diorganopolysiloxane serving as a base polymer. Any desired diorganopolysiloxane may be used as long as it is end-capped with a hydroxyl, C
1
-C
6
alkoxy or C
2
-C
6
alkenoxy radical. The preferred diorganopolysiloxane has the average compositional formula: R
5
SiO
(4−c)/2
wherein R
5
is a substituted or unsubstituted monovalent hydrocarbon radical and c is 1.90 to 2.05 and is end-capped with a hydroxyl, alkoxy or alkenoxy radical. The hydrocarbon radicals represented by R
5
are preferably those of 1 to 10 carbon atoms, especially 1 to 8 carbon atoms, for
Kimura Tsuneo
Sakamoto Takafumi
Wakayama Yoshihide
Birch & Stewart Kolasch & Birch, LLP
Moore Margaret G.
Taisei Corporation
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