Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2002-01-18
2004-12-07
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S148000, C522S172000, C522S060000, C522S024000, C522S066000, C522S071000, C522S081000, C525S280000, C525S281000, C525S282000, C525S410000, C525S411000, C525S437000, C525S445000
Reexamination Certificate
active
06828355
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to resin-reinforced silicone compositions curable upon exposure to radiation in the electromagnetic spectrum, which compositions when cured demonstrate improved elastomeric properties, such as tensile strength, modulus and elongation. The inventive resin-reinforced silicone compositions may alternatively be rendered curable by exposure to moisture. In addition, the inventive composition may be rendered curable by exposure to radiation in the electromagnetic spectrum, and exposure to moisture. The inventive silicone compositions are particularly well suited for use in electronic conformal coating and potting applications, as well as in automotive gasketing applications, pressure sensitive adhesive applications and the like.
2. Brief Description of Related Technology
Silicone elastomers have been used for potting and encapsulating electrical devices, such as integrated circuits, because of their excellent thermal stability, low temperature flexibility and high dielectric strength. They typically provide shock, vibrational and thermal stress protection on fragile electronic components. [See U.S. Pat. Nos. 3,933,712; 4,072,635; 4,087,585; 4,271,425; 4,374,967; and D. Dickson, Jr.,
Proc. Electric/Electronic Intel. Conf
., 12, 92 (1975). See also U.S. Pat. No. 4,374,967.]
Certain silicones containing (meth)acrylate functional groups may be cured by ultraviolet light (“UV light”). See U.S. Pat. Nos. 4,201,808 and 4,348,454, and U.K. Patent Application GB 2039287A, which, though not producing elastomeric materials, describe UV light curing compositions of silicones containing (meth)acrylates for paper release coatings.
Room temperature vulcanization (“RTV”) (also called moisture curable) silicone compositions are well known, such as those sold under the ULTRA tradename.
Loctite Corporation has for a number of years sold under the “NUVASIL” tradename a variety of UV and UV/moisture curable silicone compositions—that is, silicone compositions curable upon exposure to UV light or UV light, followed by exposure to moisture. These compositions generally provide a reactive polyorganosiloxane component, and a photoinitiator component. Where moisture cure capabilities are also desirable, a moisture cure catalyst is also included. The viscosity of the composition, as well as the physical properties of the cured elastomer, may be modified by the inclusion of a non-reactive silicone fluid, such as a polydimethyl siloxane, for instance one terminated with alkyl silyl groups (e.g., trimethyl silyl, hydroxyl dimethyl silyl, alkoxy dimethyl silyl and the like). See U.S. Pat. No. 4,528,081 (Lien), the disclosure of which is hereby expressly incorporated herein by reference. See also U.S. Pat. No. 5,179,134 (Chu) and U.S. Pat. No. 5,300,608 (Chu), the disclosure of each of which is hereby expressly incorporated herein by reference.
Other UV and UV/moisture curable silicone compositions are also known. [See U.S. Pat. No. 5,489,622 (Hara) and U.S. Pat. No. 5,384,340 (Hara).]
Silicone elastomers, however, are inherently very weak materials due to weak intermolecular van der Waals forces between the siloxane chains. In the past, improved strength has been imparted to certain of these compositions by including a fumed silica as a reinforcing filler. See U.S. Pat. No. 4,675,346 (Nakos), the disclosure of which is expressly hereby incorporated herein by reference. One drawback to this approach in some instances is that dispensability may become difficult, as oftentimes even a small amount of fumed silica tends to increase viscosity.
In addition, inclusion of such reinforcing filler tends to confer a translucent or “milky” appearance to the silicone compositions. Such an appearance can be disadvantageous in many applications, particularly where cure is to occur through exposure to radiation in the electromagnetic spectrum and/or where clarity of the cured elastomer is a desirable property. Radiation cure may become impeded when the composition has a translucent appearance because the radiation pathway through the composition may become blocked.
Recently, Loctite Corporation made an advance in the field of anaerobically-curable silicone compositions by providing compositions including (a) a silicone fluid formed as the reaction product of a first silane having at least one hydrolyzable functional group, and a second silane having a (meth)acrylic functional group and at least one hydrolyzable meth)acrylic functional group and at least one hydrolyzable functional group. (b) a (meth)acrylate monomer; and (c) polymerization initiator. See U.S. Pat. No. 5,605,999 (Chu) and U.S. Pat. No. 5,635,546 (Rich), the disclosures of each of which are hereby expressly incorporated herein by reference.
Silicone products of the type noted above (sometimes referred to as “MQ” resins) have been used to impart reinforcement properties to cured elastomers of heat-curable silicone compositions without increasing the viscosity of the composition, and while maintaining the clarity of the composition.
MQ resins generally are copolymers of siloxanes formed from reactive trialkylsilyl (“M”) and tetra functional silicate (“Q”) structures that can be prepared by either cohydrolyzing silanes containing M and Q units or by silylating inorganic silicates with a trialkylsilyl containing silanes.
Vinyl- or hydride-containing silanes have been added during preparation to yield MQ resins suitable for use in heat-cure silicone compositions. During heat cure, the vinyl groups on the MQ resin and the silicone fluid polymerize in a crosslinked network with the MQ resin incorporated in the network for reinforcement.
MQ resins have been used to impart reinforcement properties to room temperature vulcanization (“RTV”) silicone compositions, as well. See U.S. Pat. No. 5,340,887 and European Patent Document EP 767 216. Here, the use of a resin-polymer system is described where both resin and polymer contain hydroxl groups and may be crosslinked with the addition of an oxime crosslinker.
One drawback to the use of MQ resins to reinforce reaction products of silicone-based compositions is their compatibility with the remaining components of the composition—that is, phase separation is oftentimes seen to occur. This results in a compromised shelf life stabiliity for certain one-part silicone-based compositions.
Notwithstanding the state-of-the-technology, it would be desirable to provide resin-reinforced radiation and radiation/moisture curable silicone compositions. Such compositions could advantageously be used in a variety of commercial applications and would benefit from the enhanced strength imparted by the resin reinforcement.
SUMMARY OF THE INVENTION
The present invention meets the desires discussed above by providing resin-reinforced silicone compositions capable of curing upon exposure to radiation in the electromagnetic spectrum, such as UV light, and exposure to moisture, such as is found under atmospheric conditions, and a combination thereof:
The compositions include:
(a) a polyorganosiloxane, having photocurable groups, such as (meth)acrylate or glycidoxyl functionality, like methacryloxypropyl, vinyl ether groups and the like and/or moisture curable groups, such as alkoxy or aryloxy groups, like methoxy, acetoxy groups, oximino groups, enyloxy groups, imido groups, amino groups, and the like;
(b) a silicone resin selected from
(i) those formed from at least one silane within the formula R
1
m
R
2
p
Si(X)
4−(m+p)
I, where R
1
is a (meth)acrylate functional group or a hydrolyzable group, and R
2
may be the same or different and may be selected from monovalent ethylenically unsaturated radicals, hydrogen, C
1-12
alkyl, C
6-12
aryl, C
7-18
alkylaryl, or a hydrolyzable group, X is a hydrolyzable group, m is an integer from 1 to 3, and m+p is an integer from 1 to 3;
(ii) those formed from at least one silane within the formula R
3
q
Si(X)
4−q
II, where R
3
may be the same as or different from R
2
above and may be selected
Bauman Steven C.
Henkel Corporation
McClendon Sanza
Seidleck James J.
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