Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2001-05-16
2003-09-30
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...
C522S018000, C522S028000, C522S038000, C522S064000, C522S172000, C522S148000, C522S182000, C528S030000, C528S032000, C528S033000
Reexamination Certificate
active
06627672
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to dual curing silicone compositions. More specifically, this invention relates to dual curing silicone compositions that achieve an improved depth of cure through the incorporation of photoinitiators which have heretofore not been compatible with silicones.
2. Brief Description of Related Technology
A variety of silicone compositions have been developed that may be used as sealants, conformal coatings, potting compounds, and the like. Among the numerous silicone compositions that have evolved, some depend on atmospheric humidity and/or moisture to be present on the substrate to which the composition is applied, for their cure. Although such moisture-curing silicone systems provide good physical properties and performance when fully cured, they suffer the disadvantage that the moisture curing process is relatively slow.
In consequence, silicone compositions that depend on other curing processes have been developed which are significantly faster than the moisture-curing process. In particular, photo-curable (e.g., UV-curable) silicones have been developed which offer a fast curing speed, far superior to conventional moisture-curing silicone. These silicone compositions may include a photoinitiator that provides a faster and more effective cure. Silicone compositions that are both moisture-curable and photo-curable have also been developed that provide a rapid cure. Examples of these are described in U.S. Pat. No. 5,663,269 to Chu, et al. (Chu); U.S. Pat. No. 6,140,444 to Levandoski, et al., (Levandoski); U.S. Pat. No. 4,528,081 to Lien et al. (Lien) and U.S. Pat. No. 4,699,802 to Nakos et al. (Nakos), all of which are hereby expressly incorporated herein by reference.
Conventional photo- and/or dual curing silicones have shown only limited depth of cure. Many applications, such as potting and gap filling of electronic components require compositions which can effectively cure through relatively large depths or volumes. Also, many conventional photoinitiators, such as 2,2-diethoxyacetophenone, are UV curable, but not curable by visible light.
While a variety of different photoinitiators are generally known as being useful for curing silicones, none are known to have produced a substantial increase in cure-through-volume (CTV) or depth of cure. Successful increases in depth of cure have been reported for non-silicone compositions. For example, U.S. Pat. No. 6,207,727 to Beck et al. discloses a photoinitiator combination of an acyl- or diacylphosphine oxide and a benzophenone in non-silicone ethylenically unsaturated compounds, such as C
1
-C
20
-alkyl(meth)acrylates, vinylaromatic compounds having up to 20 carbons, vinylesters of carboxylic acids containing up to 20 carbons, vinylesters of carboxylic acids containing up to 20 carbons, ethylenically unsaturated nitrites, vinyl ethers of C
1
-C
10
-alcohols, and aliphatic hydrocarbons having 2 to 8 carbons and 1 or 2 double bonds. While this patent alleges improved depth of cure for these materials, the acyl- or diacylphosphine oxide photoinitiators used therein are not normally compatible with silicones.
There is a need for silicone compositions that have improved depth of cure. There is further a need for a photoinitiator composition that is compatible with silicones and provides for enhanced depth of cure.
SUMMARY OF THE INVENTION
For purposes of this invention, cure-through-volume (CTV), cure-through-depth (CTD) and depth of cure will be used interchangeably.
One aspect of the present invention relates to a photocurable silicone composition having enhanced cure-through-volume/depth that includes a photocurable silicone component, at least one of an acylphosphine oxide, a diacylphosphine oxide or a combination thereof, and at least one polar carrier. A second photoinitiator may also be added to the composition. Desirably, the silicone composition is a dual photo- and moisture curing composition.
Another aspect of the present invention relates to a photocurable or dual photo/moisture curable silicone composition that is the reaction product of a photocurable silicone component, an acylphosphine oxide, a diacylphosphine oxide or a combination thereof, and at least one polar carrier. A second photoinitiator may also be added to the composition.
The present invention also provides a photoinitiator composition that includes at least two different photoinitiators. The first photoinitiator includes an acylphosphine oxide, a diacylphosphine oxide or a combination thereof, and the second photoinitiator may include conventional UV and visible light initiators. Examples are acetophenones, substituted acetophenones, benzoin and its alkyl esters, xanthone, substituted xanthones, camphoroquinone peroxyester initiators, 9-fluorene carboxylic acid peroxyester initiators and alkyl thioxanthones, such as isopropyl thioxanthone, and combinations thereof.
A further aspect of the present invention provides a photoinitiator composition compatible with silicones that includes an acylphosphine oxide or a diacylphosphine oxide, a second photoinitiator different from the first, and a polar carrier.
A method of preparing a photocuring or dual photo/moisture curing silicone composition is also provided. The method includes first preparing a premix of an acylphosphine oxide or a diacylphosphine oxide or a combination thereof and a polar carrier; and optionally adding thereto a second photoinitiator that is different than the first photoinitiator. The premix is then added to a photocurable silicone component.
In a still further aspect of the present invention there is provided a method of producing a silicone which cures through a cure-through-depth of about 4.0 mm or greater. The method includes first preparing a premix of an acylphosphine oxide or a diacylphosphine oxide or a combination thereof and a polar carrier. The premix is then added to a curable silicone component.
In a still further aspect of the present invention there is provided a dual curing silicone potting composition that includes a dual photo/moisture curable silicone component, at least two different photoinitiators, one of which is either an acylphosphine oxide or a diacylphosphine oxide or a combination thereof, a polar carrier, and a moisture cure catalyst.
DETAILED DESCRIPTION OF THE INVENTION
For purposes of this invention, the term (meth)acryl or (meth)acrylate will refer to both methacrylate and acrylate species.
The present invention is directed to a curable silicone composition that demonstrates an enhanced cure-through-depth capability upon cure. The composition includes a curable silicone component, an acylphosphine oxide photoinitiator and a polar carrier. The acylphosphine oxide may be an acylphosphine oxide or a diacylphosphine oxide, such as diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide, or a combination thereof.
The curable silicone component of the present invention may be any suitable curable silicone component. These may include the silicones described in the aforementioned Chu and Levandoski patents such as those with the general formula I as shown below:
where A represents a polymer or copolymer backbone, which can be any number of combinations of polyurethane, silicone, polyamide, polyether, polyester and the like; R
1
and R
2
may be the same or different and are monovalent hydrocarbyl groups having up to 10 carbon atoms (C
1
-
10
), or halo- or cyano-substituted hydrocarbyl groups; R
3
and R
4
may be the same or different monovalent groups and may contain an ethylenically unsaturated polymerizable double bond; R
5
is a methyl, ethyl, isopropyl or —CH
2
CH
2
OCH
3
; a is 0, 1 or 2; b is 0, 1 or 2; a+b is 1 or 2; and R
6
is a monovalent hydrocarbyl group or
Most desirable silicones are those which have moisture and photocuring capabilities. Such desirable silicones conform to the formula.
where MA is a methacryloxyalkyl group such as methacryloxypropyl, R
1
and R
2
are described as above, and n is from 1 to 1,200. While the curable silicone component may be made a variety
Angus, Jr. Richard Oliver
Lim Thomas Fay-Oy
Lin Chiu-Sing
Bauman Steven C.
Henkel Loctite Corporation
McClendon Sanza L.
Seidleck James J.
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