Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2001-11-19
2004-08-31
Moore, Margaret G. (Department: 1712)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C428S447000, C524S266000, C524S268000, C528S015000, C528S031000, C528S032000, C528S034000
Reexamination Certificate
active
06783858
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates both to a method for improving the primeness adhesion of cured silicone elastomers and to curable (and cured) high strength, organopolysiloxane molding compositions useful to produce cured silicone rubber articles that exhibit excellent adhesion to thermoplastic resins such as, but not limited to, PBT and PPA, while not significantly adhering to metal substrates.
BACKGROUND OF THE INVENTION
Moldable primerless organopolysiloxane compositions are known and used. One problem with all such compositions is that due to the adhesion additives in the compositions they also adhere to metal surfaces. In molding processes, the typical mold is metal. It is difficult to selectively adhere to thermoplastic substrates without deleterious effects. Additionally, the kinetics and thermochemistry of the molding process and the compositions used in such processes are such that only small lightweight composite plastic and silicone elastomer articles of manufacture can be made by molding techniques because of the difficulty of removing the article from the metal mold.
Organopolysiloxane compositions useful for molding typically contain alkenyl polymers, fillers, and other additives. The compositions contain a platinum catalyst, a hydride crosslinker and cure inhibitors. These can be one or two component systems that are mixed prior to the molding process. These heat cured (i.e. high consistency or millable rubber) or liquid injection molded silicone rubbers are commonly available without additives that improve adhesion.
Typical molding compositions generally include the following ingredients:
1) 100 parts by weight of a vinyl stopped polydimethylsiloxane having a viscosity ranging from 10,000 to 1,000,000 centipoises at 25° C. and a vinyl content ranging from about 0.01 to 0.25 mole per cent;
2) up to 10 parts by weight of a low molecular weight vinyl stopped vinyl on chain hydroxyl end blocked polyorganosiloxane having a viscosity ranging from 50 to 10,000 centipoises at 25° C. and a vinyl content of 0.3 to 30 mole per cent;
3) up to 10 parts by weight of a low molecular weight hydroxy end blocked polyorganosiloxane having a viscosity ranging from 500 to 2,000 centipoises at 25° C.;
4) from 5 to 50 parts by weight of a fumed or pyrogenic silica having a surface area ranging from 150 to 450 square m/gm;
5) up to 40 parts by weight of an organohydrogenpolysiloxane crosslinker containing at least two silicon-bonded hydrogens per molecule and having a viscosity ranging from 80 to 1,000 centipoises at 25° C.;
6) from 2 to 500 wppm of a platinum hydrosilylation catalyst;
7) from 0.01 to 3.0 parts by weight of an inhibitor compound; and
8) from 100 to 1,000 wppm of silyl hydrides.
Additional components may include extending fillers, coloring agents, and additives to impart increased performance with respect to certain physical properties such as oil resistance, heat aging, abrasion resistance and the like.
The functional properties of the resulting rubber elastomer depend not only on the levels of components but also on the properties of the filler, additives, and type of curing catalyst. Consequently, the elastomer property profile is highly dependent on the chemical nature of the various constituent components as well as the relative proportions of those components. For example, a heat additive increases the temperature range of the resulting rubber. Such improvements however, do not necessarily increase the adhesion stability and some times fail to adhere after heat soak.
In seeking to increase the selective adhesion of silicone compositions to thermoplastic and thermoset substrates, it is frequently desirable to increase the ability of the silicone to be released from a mating part or surface for which the molded composite may come in contact. These two properties collide in that adhesion of the silicone to a thermoplastic or thermoset substrate is desired but ready release from another substrate is necessary for the device to function. For example, the fabrication of connecters requires adhesion of the grommet and facial seal to a thermoplastic closure and also requires that the silicone surface have sufficient lubricity to allow mating sides to fasten and unfasten with ease.
A typical method of improving the lubricity of a silicone composition is simply to add a liquid component to the formulation that has limited solubility in the elastomer and thus the compound bleeds out over time. Ideally such a material itself also has a lubricating quality. These components are typically selected from the group of compounds consisting of phenyl containing siloxanes such as copolymers of polydimethylsiloxanes, diphenylsiloxane or methylphenylsiloxane, and fluorosiloxanes such as silicones containing trifluoropropyl substituted siloxanes.
SUMMARY OF THE PREFERRED EMBODIMENTS
Accomplishment of this selective adhesion is by the addition to a diorganopolysiloxane composition of soluble polydiorganosiloxanes, polycycloorganosiloxanes (linear and cyclic) and/or hydroxy end blocked hydrocarbons (glycols) of a specific molecular distribution preferably having a viscosity of 10 to 1,000 centipoises at 25° C.; and an epoxy functional compound, thus giving release characteristics to metal substrates while maintaining adhesion to the thermoplastic substrate.
In general, the preferred embodiment of the present invention provides for a curable silicone elastomer composition comprising:
1) a silicone elastomer;
2) an epoxy functional compound; and
3) a linear and/or cyclic diorganopolysiloxane and/or hydroxy end blocked hydrocarbons (glycols). Examples of such glycols include polyethylene glycol (e.g., PEG 400) and 1,3 butylene glycol PEG 400 is preferred.
The foregoing composition may also include a silicone soluble in the curable elastomer composition. Preferably, the silicone is less soluble in the curable elastomer composition when the curable composition has been cured. As a result, the silicone bleeds out of cured composition to improve lubricity.
The present invention provides a composition that selectively adheres to a substrate that may be a thermoset or a thermoplastic, but not to a metal such as aluminum or steel. The thermoset or thermoplastic substrates may be filled polymers with glass or clays. The silicone compositions of the present invention release readily from metal substrates after they have been overmolded, transfer molded or injection molded. The present invention further provides for the incorporation of an adhesion promoter and a self-bleed additive that allows lubrication of the surfaces of the cured silicone simultaneously with adhesion to the overmolded, transfer molded or injection molded substrate. The formulations of the present invention demonstrate that compositions containing both an adhesion promoter and a self-bleed additive for lubricity can simultaneously achieve the contradictory goals of adhesion to a substrate used in overmolding, transfer or injection molding and release from a second substrate where the silicone was not bonded to the substrate by the action of the adhesion promoter and the co-molding process of overmolding, transfer molding or injection molding.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
This invention utilizes the release characteristics of soluble polydiorganosiloxanes, polycycloorganosiloxanes (linear and cyclic), and/or hydroxy end blocked hydrocarbons (glycols) of specific molecular distribution preferably having viscosity of 10 to 1,000 centipoises at 25° C. The two (2) additives that provide the selective adhesion properties are:
1) generally from 0.01 to 30, preferably from 0.01 to 10, more preferably from 0.05 to 1.0 and even more preferably from 0.10 to 0.50, parts by weight of an epoxy function compound; and
2) generally from 0.01 to 10, preferably from 0.5 to 5 and more preferably from 1 to 3, parts by weight of soluble polydiorganosiloxanes and/or polycycloorganosiloxanes (linear and/or cyclic) and/or hydroxy end blocked hydrocarbons (glycols), or mixtures thereof.
Generally, it has been foun
Bryant Rubber Corporation
Jeffer Mangels Butler & Marmaro LLP
Moore Margaret G.
Zimmer Marc S
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