Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2002-05-14
2004-09-14
Robertson, Jeffrey B. (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C427S387000, C524S437000, C524S492000, C524S493000, C524S588000, C528S031000, C528S032000, C528S034000, C528S042000, C528S043000
Reexamination Certificate
active
06790533
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to self-adhesive, thermally crosslinkable 1-component silicone compositions having a long shelf-life, to silicone elastomers obtainable therefrom, and to their use in manufacturing composite moldings.
2. Background Art
The adhesion of crosslinked silicone elastomers to numerous substrates, such as plastics, metals and glasses, is known to be low, i.e. if an addition-crosslinking silicone elastomer material is applied to a substrate and then crosslinked, the resulting silicone elastomer can, as a rule, be peeled away from the substrate surface without difficulty, i.e. by application of but slight tensile forces. Frequently, spontaneous delamination of the silicone elastomer from the substrate may occur. However, since strong and permanent adhesion of the silicone elastomer to the substrate is of decisive importance in numerous applications, a large number of special measures have been proposed for obtaining a strong bond between substrate and silicone elastomer.
In principle, the adhesive strength of the silicone elastomer/substrate laminate can be increased by suitably modifying the chemical and/or physical characteristics of the substrate or of the substrate surface prior to application of the crosslinking silicone elastomer composition. Modification can be effected, for example, by pretreating the substrate surface with adhesion-promoting additives (i.e. primers), by plasma treatment of the substrate surface, by mixing special additives into the substrate, by controlling the morphology of the substrate, by increasing the surface roughness, etc. These measures have, inter alia, the disadvantage that additional process steps are required or the characteristics of the substrate have to meet special requirements.
In the case of high temperature-crosslinking systems, the adhesive strength of the silicone elastomer/substrate composite can be increased by changing the chemical and/or physical characteristics of the addition-crosslinking silicone elastomer material in a controlled manner. Numerous adhesion-promoting additives are known which when mixed with the uncrosslinked silicone material, give rise to self-adhesion of the resulting silicone elastomer on various substrates. These include compounds which contain highly reactive functional groups, such as alkoxy, epoxy, carboxyl, amino, etc., these groups generally being chosen such that the adhesion promoter is capable of reacting both with the substrate and with a silicone elastomer constituent. Although such adhesion promoters may make it possible to dispense with pretreatment of the substrate, the adhesive strength obtained frequently is not satisfactory. Furthermore, the adhesive strength can be increased only to a limited extent by higher adhesion promoter content since the highly reactive groups contained in the adhesion promoter have an increasingly adverse effect on performance characteristics such as shelf-life, crosslinking characteristics (inhibition), toxicology, etc. For these reasons, interest tends to be focused on keeping the content of adhesion promoters as low as possible.
EP-A-686 671 describes a self-adhesive addition-crosslinking material which manages without special adhesion promoters due to the presence of unique reactive polymer constituents. The adhesion-promoting constituent is either an organohydrogenpolysiloxane with minimally two SiH groups on average and whose monovalent Si-bonded radicals consist of at least 12 mol % of hydrocarbon radicals having an aromatic ring, or is a compound with at least one SiH group on average and which contains a group consisting of two aromatic rings, the two aromatic rings being separated from one another by —R
13
R
14
Si—, —R
13
R
14
SiO—, —OR
13
R
14
SiO— or —R
13
R
14
SiOR
13
R
14
Si— and the radicals R
13
and R
14
being monovalent hydrocarbon radicals. The adhesion-promoting constituent can thus simultaneously be the crosslinking agent of the silicone elastomer material. Good adhesion to organic plastics (especially ABS) is achieved with this composition, while at the same time easy demoldability is exhibited from metallic vulcanization molds, i.e. chromium- or nickel-plated steel molds or mold produced from aluminum alloy.
The high content of 12 mol % or more of radicals containing aromatic rings in the SiH-containing, adhesion-promoting constituent of the compositions of EP-A-686 671, however, results in considerable incompatibility with the other constituents of the addition-crosslinking silicone elastomer material, leading on the one hand, to partial separation (exudation) during storage, necessitating repeated homogenization of the constituent-containing component before use. This incompatibility, which is evident simply from a milky haze in the uncrosslinked material, also manifests itself in substantially reduced transparency of the silicone elastomer parts produced therefrom. If the adhesion-promoting constituent simultaneously acts as a crosslinking agent of the silicone elastomer composition, the incompatibility leads to vulcanization disturbances which result in inhomogeneous network formation and poor mechanical vulcanization properties. In order to overcome these vulcanization disturbances, an SiH-containing crosslinking agent completely compatible with the silicone elastomer material must be used in addition to the adhesion-promoting SiH-containing constituent, which however results in other disadvantages, for example higher compression set, and higher tendency to exude the adhesion-promoting constituent. The high content of aromatic radicals in the SiH-containing, adhesion-promoting constituent also causes a considerable structural viscosity and thixotropy of the silicone elastomer material, which is undesirable in numerous applications for example in injection molding and in liquid silicone rubber. Moreover, the curable silicone mixture of EP-A-686 671 has a very limited shelf-life, so that metering of the platinum catalyst or mixing with the H-siloxane component must occur only a few minutes to hours prior to vulcanization. Finally, the adhesion of this composition to metals is also insufficient.
EP-A-875 536 describes a self-adhesive addition-crosslinking silicone rubber blend which is distinguished in that the SiH crosslinking agent contains at least 20 SiH groups, the remaining radicals being aliphatically saturated; the composition contains an epoxy-functional alkoxysilane and/or alkoxysiloxane; and further optionally a peroxide. The use of glycidyloxypropyltrimethoxysilane (Glymo) is particularly preferred. The silicone rubber blend described in EP-A-875 536 is suitable in particular for the production of composite moldings which consist of the silicone elastomer and an organic plastic. However, the composition described in EP-A-875 536 has the disadvantage that sufficient adhesive strength can be achieved only with the use of very Si-rich crosslinking agents having on average at least 20 SiH groups per molecule. For instance, the crosslinking agents exemplified in the examples have 30 SiH groups per molecule. The use of such high-functionality crosslinking agents reduces the shelf-life of addition-crosslinking silicone rubber blends considerably, i.e. the flowability is greatly impaired, which can lead to stiffening of the material. As a result, proper processing of the material, for example by injection molding, is no longer possible. In addition, relatively large amounts of epoxy-functional alkoxysilane/alkoxysiloxane have to be used in order to achieve a high adhesive strength, with the result that the crosslinking rate is considerably reduced. Although this can partly be compensated by employing a peroxide, as described in EP-A-875 536, only peroxides having a low initiation temperature, such as the disclosed 2,4-dichlorobenzyl peroxide, are suitable for this purpose owing to the necessarily low crosslinking temperature (softening of the organic plastic). These peroxides are both toxicologically suspect owing to the cleavage and secondary products liberated (PC
Mueller Philipp
Reitmeier Rudolf
Vogl Guenter
Winter Hans-Joerg
Brooks & Kushman P.C.
Robertson Jeffrey B.
Wacker-Chemie GmbH
LandOfFree
Self-adhesive thermally crosslinkable 1-component silicone... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Self-adhesive thermally crosslinkable 1-component silicone..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Self-adhesive thermally crosslinkable 1-component silicone... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3235326