Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
2001-11-05
2004-10-19
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C528S031000, C528S032000, C524S588000, C524S862000
Reexamination Certificate
active
06806339
ABSTRACT:
This invention relates to a novel branched siloxane and also to silicone based release coating compositions and release modifier compositions containing the aforementioned branched siloxane.
Silicone based release coatings are useful in applications where relatively non-adhesive surfaces are required. Single sided liners, for example, backing papers for pressure sensitive adhesive labels, are usually adapted to temporarily retain the labels without affecting the adhesive properties of the labels. Double sided liners for example, interleaving papers for double sided and transfer tapes, are utilised to ensure the protection and desired unwind characteristics of a double sided self-adhesive tape or adhesive film.
A substrate, for example a single sided liner, is coated by applying a silicone based release coating composition onto the substrate and subsequently curing the composition, by, for example, thermally initiated hydrosilylation.
The basic constituents of silicone based release coating compositions which are cured by hydrosilylation are:
1) an alkenylated polydiorganosiloxane, typically a linear polymer with terminal alkenyl groups,
2) a polyorganohydrogensiloxane cross-linking agent, designed to cross-link the alkenylated polydiorganosiloxane and
3) a catalyst, to catalyse the aforementioned cross-linking reaction.
Often a fourth constituent, an inhibitor designed to prevent the commencement of curing below a prerequisite cure temperature, is also included in the composition.
Silicone based release coating compositions consisting of the three essential constituents and optionally the inhibitor are generally referred to as premium release coating compositions.
In order to control the level of release force from a release coating it has become common practice for a silicone based release coating composition to contain an additive, generally known as a release modifier. The release modifier usually replaces a proportion of the alkenylated polydiorganosiloxane in a premium release coating composition.
Improvements in the performance of release coatings are continuously being sought with respect to, for example, ease of cure, i.e. the decrease in cure times at relatively low temperatures, anchorage of coatings to a substrate and release performance. One factor which particularly necessitates continued development of release coatings is the use of an ever increasing number of substrates, for example, polypropylene, polyethylene and polyester onto which release coating compositions are applied and cured.
U.S. Pat. No. 4,772,515 describes a silicone release coating composition having the three essential constituents discussed above, wherein the polydiorganosiloxane must have in a single molecule at least two groups of the following general formula:
R
c
(R
f
)
2
SiO
1/2
((R
g
)
2
SiO
2/2
)
h
R
j
SiO
3/2
where R
c
is an alkenyl group; each R
f
, R
g
and R
j
are independently hydrogen, hydroxyl or a monovalent organic group and h is 0 or an integer between 1 and 300 inclusive. The resultant release coating composition is made by merely mixing the three constituents together.
U.S. Pat. No. 4,774,111 describes a silicone based release coating composition comprising an organosilicon compound having on average one to three silicon bonded monovalent hydrocarbon or halohydrocarbon radicals per silicon atom. An average of at least two of these groups being olefinic groups and the remaining silicon vacancies being satisfied by divalent radicals free of aliphatic unsaturation which link the silicon atoms together.
EP-A-559575 describes a silicone based release composition containing the three essential constituents and an additional constituent comprising a silicone containing a plurality of ethylenically unsaturated groups having from four to twelve carbon atoms wherein from 25 to 90 mole % of the total number of siloxane groups are T units.
For the sake of clarification M, D, T and Q units represent units of the empirical formulae R
3
SiO
1/2
, R
2
SiO
2/2
, RSiO
3/2
and SiO
4/2
respectively, wherein each R group is a monovalent substituent.
U.S. Pat. No. 5,616,672 describes the use of a substantially branched curable alkenyl silicone consisting of M, D and T groups and having on average at least two branching points per molecule. These compounds are said to be useful in release coating compositions.
U.S. Pat. No. 5,063,254 describes a polysiloxane comprising a linear polydiorganosiloxane chain having 25 to 1000 repeating units joined at one end to an acrylic end group and at its other end to a crosslinked MTQ moiety wherein the ratio of M units to T and Q units M/(T+Q) is 0.55-0.75. The M and/or T units may also contain (meth)acrylate groups. The polysiloxane has utility in potting and conformal coating.
A branched siloxane according to a first aspect of the present invention consists of:
i) one or more Q units of the formula(SiO
4/2
) and
ii) from 15 to 995 D units of the formula R
b
2
SiO
2/2
which units (i) and (ii) may be inter-linked in any appropriate combination, and
iii) M units of the formula R
a
R
b
2
SiO
1/2
, wherein each R
a
substituent is selected from the group consisting of an alkyl group having from 1 to 6 carbon atoms, an alkenyl group having from 1 to 6 carbon atoms and an alkynyl group having from 1 to 6 carbon atoms, at least three Ra substituents in the branched siloxane being alkenyl or alkynyl units, and each R
b
substituent is selected from the group consisting of an alkyl group having from 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an aryl group, an alkoxy group, an acrylate group and a methacrylate group.
The branched siloxane preferably contains at least two polydiorganosiloxane chains of the formula (R
b
2
SiO
2/2
)n where each n is independently from 2 to 100.
A branched siloxane according to a second aspect of the invention contains at least three aliphatically unsaturated hydrocarbon groups, terminated by units of the formula R
a
R
b
2
SiO
1/2
and otherwise consists of:
i) one or more units of the formula(SiO
4/2
); and
ii) at least two polydiorganosiloxane chains of the formula (R
b
2
SiO
2/2
)n, where each n is independently from 2 to 100, the total R
b
2
SiO
2/2
units in the branched siloxane being from 15 to 995 units, wherein each R
a
substituent is selected from the group consisting of an alkyl group having from 1 to 6 carbon atoms, an alkenyl group having from 1 to 6 carbon atoms and an alkynyl group having from 1 to 6 carbon atoms and each R
b
substituent is selected from the group consisting of an alkyl group having from 1 to 6 carbon atoms, an aryl group, an alkoxy group, an acrylate group and a methacrylate group.
Preferably the aliphatically unsaturated hydrocarbon groups are either alkenyl or alkynyl groups.
Preferably at least 50% of R
a
substituents are alkenyl groups. Most preferably each R
a
substituent is an alkenyl group.
Each alkenyl group may be selected from vinyl, allyl, butenyl, pentenyl and hexenyl groups but is preferably selected from a vinyl (vi) and a hexenyl (hex) group.
The branched siloxane most preferably comprises at least one Q unit bonded to four (R
b
2
SiO
2/2
)n chains and for example can have the formula
where each n is independently from 1 to 100.
Preferably each R
b
substituent is an alkyl groups for example, a methyl, ethyl, propyl, isopropyl, butyl, pentyl or hexyl group; preferred are methyl and ethyl groups but the most preferred is a methyl group. Hence, in the case when there is only a single unit of the formula SiO
4/2
present in the branched siloxane according to the first aspect of the present invention, the branched siloxane may have substantially the following formula wherein each n is independently from 1 to 100 when each R
a
substituent is a vinyl group and each R
b
group is a methyl group.
It is to be appreciated that in view of the size of the branched siloxane, it is possible that a very small number of the siloxane units present in the branched siloxane (preferably less than 1%) may be units of the formula R
b
SiO
3/2
, where R
b
is as previousl
Cray Stephen Edward
Francis John
Dow Corning Limited
Moore Margaret G.
Scaduto Patricia M.
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