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
1999-01-27
2001-04-10
Dawson, Robert (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, C524S860000, C524S425000, C524S433000, C524S445000, C524S493000, C525S474000, C525S477000, C528S033000, C528S034000, C528S038000, C528S901000
Reexamination Certificate
active
06214930
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for producing one-package room temperature curable organopolysiloxane compositions having improved extrusion and slump properties in the compound or uncured state, curable in the presence of moisture, and suitable as sealants.
2. Prior Art
RTV organopolysiloxane compositions of the one-package type are well known in the art which cure into silicone rubber at room temperature in the presence of moisture. They are widely used in a variety of industrial fields including mechanical, electrical and building fields as sealing agents, adhesives, potting agents, framing materials, automotive FIPG, etc.
When sealants of RTV compositions in the uncured state are applied in practice, such factors as ease of discharge or extrusion and sag-control are important. It is then a common practice to add thixotropy control agents for the sag-control purpose.
Illustratively, U.S. Pat. Nos. 4,261,758 and 4,100,129 disclose RTV compositions having polyoxyalkylenes added as the sag-control agent, and U.S. Pat. No. 4,301,269 discloses an RTV composition having the reaction product between a polyoxyalkylene and a functional silane added as the sag-control agent.
These RTV compositions are generally prepared by mixing a base polymer, filler, sag-control agent, and plasticizer, finally blending a crosslinking agent, and dispersing the ingredients uniformly, or by previously reacting a functional silane with a base polymer at its end and thereafter, mixing a filler and sag-control agent with the base polymer.
However, the RTV compositions prepared by the above procedures have the problem that the sag-control agent, which is essentially a parting component, adversely affects the adhesion and if blended in larger amounts, can adversely affect the ease of extrusion of the composition. The addition of the sag-control agent leads to the complication of the manufacturing process, adding to the cost of manufacture and adversely affecting the sealant properties. As a countermeasure, JP-A 41361/1990 discloses a process for preparing an RTV polyorganosiloxane composition by mixing a hydroxyl group-bearing polyorganosiloxane with a ketoxime group-bearing organosilane as the crosslinking agent, and thereafter, mixing finely divided silica and a curing catalyst therewith. This composition is insufficient in anti-slump or sag-control properties and ease of extrusion when a filler having a relatively high specific gravity, typically calcium carbonate is used, or in the case of a different crosslinking system.
Therefore, an object of the present invention is to provide a process for preparing a one-package RTV organo-polysiloxane composition having sag-control, ease of extrusion, and improved sealing properties, through simple steps and at a low cost.
SUMMARY OF THE INVENTION
The invention provides a process for preparing a one-package RTV organopolysiloxane composition comprising (A) an organopolysiloxane containing at least two Si—OH groups or hydrolyzable groups in a molecule and having a viscosity of at least 100 centistokes at 25° C., (B) an organosilane having at least two hydrolyzable groups in a molecule or a partial hydrolyzate thereof, and (C) an inorganic filler. According to the invention, components (A) and (B) are premixed in a substantially anhydrous state (i.e., in a state which is substantially free of moisture), and component (C) is then added to the premix. Despite the absence of sag-control agents, the resulting organopolysiloxane composition in the uncured state has a sufficient viscosity to achieve a significant improvement in sag, ease of extrusion or discharging, and improved slump properties. This is also true even when the inorganic filler used has a relatively high specific gravity. Therefore, a one-package RTV organo-polysiloxane composition of quality suited as sealants can be prepared through simple steps and at a low cost.
Specifically, in a process for preparing a one-package room temperature curable organopolysiloxane composition having improved slump properties, comprising (A) 100 parts by weight of an organopolysiloxane containing at least two Si—OH groups or hydrolyzable groups in a molecule and having a viscosity of at least 100 centistokes at 25° C., (B) 1 to 20 parts by weight of an organosilane having at least two hydrolyzable groups in a molecule or a partial hydrolyzate thereof, and (C) 2 to 200 parts by weight of an inorganic filler, the invention is characterized by comprising the steps of premixing components (A) and (B) in a substantially anhydrous state, and adding component (C) to the premix.
REFERENCES:
patent: 3438930 (1969-04-01), Beers
patent: 4100129 (1978-07-01), Beers
patent: 4261758 (1981-04-01), Wright et al.
patent: 4301269 (1981-11-01), Hashimoto et al.
patent: 4888380 (1989-12-01), Kamis et al.
patent: 5780543 (1998-07-01), Adachi et al.
patent: 5789480 (1998-08-01), Adachi et al.
patent: 5939487 (1999-08-01), Kimura et al.
patent: 2-41361 (1990-02-01), None
Kimura Tsuneo
Miyake Masatoshi
Suzuki Kazuyuki
Teshigawara Mamoru
Dawson Robert
Robertson Jeffrey B.
Shin-Etsu Chemical Col, Ltd.
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