U.S. patent number RE31,727 [Application Number 06/434,399] was granted by the patent office on 1984-11-06 for vinyl gum cure accelerators for addition-cure silicone.
This patent grant is currently assigned to General Electric Company. Invention is credited to Richard P. Eckberg.
United States Patent |
RE31,727 |
Eckberg |
November 6, 1984 |
Vinyl gum cure accelerators for addition-cure silicone
Abstract
There are provided addition-curable silicone release
compositions comprised of a vinyl or silanol functional polymer
base, a crosslinker containing silanic hydrogen, a precious metal
catalyst such as platinum or rhodium, an optional carboxylic ester
inhgibitor and silicone vinyl gum cure accelerations effective for
allowing thermal cure at relatively lower temperatures while
minimizing the necessity of excess metal catalyst.
Inventors: |
Eckberg; Richard P. (Round
Lake, NY) |
Assignee: |
General Electric Company
(Pittsfield, MA)
|
Family
ID: |
26952209 |
Appl.
No.: |
06/434,399 |
Filed: |
October 14, 1982 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
267091 |
May 22, 1981 |
04340647 |
Jul 20, 1982 |
|
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Current U.S.
Class: |
428/429; 427/387;
427/391; 428/344; 428/438; 525/477; 525/478; 525/479; 528/15;
528/31; 528/32 |
Current CPC
Class: |
C08K
5/11 (20130101); D21H 19/32 (20130101); C08L
83/04 (20130101); C08K 5/11 (20130101); C08L
83/04 (20130101); C08L 83/04 (20130101); C08L
83/00 (20130101); C08G 77/12 (20130101); C08G
77/16 (20130101); C08G 77/20 (20130101); Y10T
428/31612 (20150401); Y10T 428/2804 (20150115); Y10T
428/31634 (20150401); C08L 2666/28 (20130101) |
Current International
Class: |
C08K
5/00 (20060101); C08K 5/11 (20060101); C08L
83/04 (20060101); C08L 83/00 (20060101); D21H
19/32 (20060101); D21H 19/00 (20060101); B32B
009/00 () |
Field of
Search: |
;528/15,31,32
;525/477,478,479 ;428/429,344,438 ;427/387,391 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Marquis; Melvyn I.
Attorney, Agent or Firm: Hedman, Gibson, Costigan &
Hoare
Claims
What is claimed as new and desired to be protected by Letters
Patent of the United States is:
1. A silicone release coating composition comprising:
A. A solventless addition curable composition comprised of:
(i) a diorganopolysiloxane base polymer having up to approximately
20% by weight alkenyl or silanol functional groups and having a
viscosity ranging from approximately 50 to approximately 100,000
centipoise at 25.degree. C.;
(ii) a polymethylhydrogen siloxane fluid crosslinking agent having
up to approximately 100% by weight SiH-containing siloxy groups and
having a viscosity in the range of approximately 25 to
approximately 1000 centipoise at 25.degree. C.;
(iii) an effective amount of precious metal catalyst for
facilitating an addition cure hydrosilation reaction between said
base polymer and said crosslinking agent at temperatures between,
approximately, 90.degree. C. to 300.degree. C.;
(iv) an amount of dialkyl carboxylic ester containing carbon to
carbon unsaturation effective to inhibit the precious metal
catalyzed hydrosilation cure reaction of said silicone composition
at temperatures below the heat cure temperature of said silicone
composition, and
B. an amount of dimethylvinyl chainstopped
polydimethylmethylvinylsiloxane polymer gum effective for
accelerating the cure of said addition curable composition wherein
said gum has an average molecular weight of, approximately, 200,000
to 400,000.
2. A composition as in claim 1 wherein said gum is present in an
amount of at least 0.5 weight percent of said addition curable
composition.
3. A composition as in claim 1 wherein said gum has a methyl-vinyl
siloxy unit content .[.if.]. .Iadd.of .Iaddend.0 to 5 mole % of
said gum.
4. A silicone release coating composition comprising:
A. a solvent based addition curable composition comprised of:
(i) a diorganopolysiloxane base polymer having up to approximately
20% by weight alkenyl or silanol functional groups and having a
viscosity ranging from approximately 50 to approximately 100,000
centipoise at 25.degree. C.;
(ii) a polymethylhydrogen siloxane fluid crosslinking agent having
up to approximately 100% by weight SiH-containing siloxy groups and
having a viscosity in the range of approximately 25 to
approximately 100 centipoise at 25.degree. C.;
(iii) an effective amount of precious metal catalyst for
facilitating an addition cure hydrosilation reaction between said
base polymer and said crosslinking agent at temperatures between
approximately, 90.degree. to 300.degree. C.;
(iv) an amount of hydrocarbon solvent effective for dispersing said
addition curable composition; and
B. an amount of dimethylvinyl chainstopped
polydimethylmethylvinylsiloxane polymer gum effective for
accelerating the cure of said addition curable composition wherein
said gum has an average molecular weight of, approximately, 200,000
to 400,000.
5. A composition as in claim 4 wherein said gum is present in an
amount of at least 0.5 weight percent of said addition curable
composition.
6. A composition as in claim 4 wherein said solvent is selected
from the group consisting of hexane, toluene, naptha, xylene, and
benzene and mixtures thereof.
7. A composition as in claim 4 wherein said gum has a methyl-vinyl
siloxy content of 0 to 5 mole % of said gum.
8. A composition as in claim 2 or 5 wherein said gum is present in
an amount of, approximately, 5 to 10 weight percent of said
addition curable composition.
9. The cured product of claim 1 or 4.
10. An article of manufacture comprising a paper substrate coated
with the composition of claim 1 or 4.
11. A method for rendering substrates relatively nonadherent to
substances that would normally adhere thereto, comprising the steps
of:
A. combining
(a) a diorganopolysiloxane base polymer having up to approximately
20% by weight alkenyl or silanol functional groups and having a
viscosity ranging from approximately 50 to approximately 100,000
centipoise at 25.degree. C.;
(b) a polymethylhydrogen siloxane fluid crosslinking agent having
up to approximately 100% by weight SiH-containing siloxy groups and
having a viscosity in the range of approximately 25 to
approximately 1000 centipoise at 25.degree. C.;
(c) an effective amount of precious metal catalyst for facilitating
an addition cure hydrosilation reaction between said base polymer
and said crosslinking agent at temperatures between, approximately,
90.degree. to 300.degree. C.; and
(d) an amount of dimethylvinyl chainstopped polydimethylmethylvinyl
siloxane polymer gum effective for accelerating the cure of an
addition curable composition wherein said gum has an average
molecular weight of, approximately, 200,000 to 400,000 and a
methyl-vinyl siloxy unit content of, approximately, 0 to 5.0 mole
%.
12. A method as in claim 11 further comprising the step of coating
said composition upon a substrate.
13. A method as in claim 12 further comprising the step of curing
said composition.
14. A process as in claim 12 wherein said substrate is paper.
15. A process in claim 11 wherein said addition curable composition
is further comprised of an amount of dialkyl carboxylic ester
containing carbon to carbon unsaturation effective to inhibit the
precious metal catalyzed hydrosilation cure reaction of said
silicone composition at temperatures below the heat cure
temperature of said silicone composition.
16. A process as in claim 11 wherein said addition curable
composition is dispersed in a solvent.
17. A process as in claim 11 wherein said gum is present in an
amount of at least 0.5 weight percent of said addition curable
composition.
18. A product made by the process of claim 11.
19. A silicone composition capable of low temperature crosslinking
to a nonadherent film when combined with a methyl hydrogen siloxy
crosslinking fluid, comprised of:
(a) a diorganopolysiloxane base polymer having up to approximately
20% by weight alkenyl and silanol functional groups and a viscosity
of, approximately, 50 to 100,000 centipoise at 25.degree. C.;
(b) an effective amount of precious metal catalyst for facilitating
an addition cure hydrosilation reaction at temperatures between
90.degree. to 300.degree. C.;
(c) an amount of dialkyl carboxylic ester effective to inhibit said
hydrosilation cure reaction at temperatures below the heat cure
temperature of said composition; and
(d) an amount of dimethylvinyl chainstopped
polydimethylvinylsiloxane gum effective for accelerating the cure
of said composition. .Iadd.
20. A silicone composition, capable of low temperature crosslinking
to a nonadherent film when combined with a methyl hydrogen siloxy
crosslinking fluid, and a precious metal catalyst, said composition
comprising:
(a) a diorganopolysiloxane base polymer having up to approximately
20% by weight alkenyl or silanol functional groups and a viscosity
of, approximately, 50 to 100,000 centipoise at 25.degree. C.;
and
(b) an amount of dimethylvinyl chainstopped polydimethylmethylvinyl
siloxane gum effective for accelerating the cure of said
composition. .Iaddend. .Iadd.21. A silicone composition as defined
in claim 20 wherein the dimethylvinyl chainstopped
polydimethylmethylvinylsiloxane polymer gum effective for
accelerating the cure of the composition has an average molecular
weight of approximately 200,000 to 400,000. .Iaddend. .Iadd.22. A
silicone composition as defined in claim 21 wherein the
diorganopolysiloxane base polymer has up to 20% by weight vinyl
groups. .Iaddend. .Iadd.23. A silicone composition as defined in
claim 21 wherein the dimethylvinyl chainstopped
polydimethylmethylvinylsiloxane gum has a molecular weight of
approximately 300,000. .Iaddend. .Iadd.24. A silicone composition,
capable of low temperature crosslinking to a nonadherent film when
combined with a methyl hydrogen siloxy crosslinking fluid, said
composition comprising:
(a) a diorganopolysiloxane base polymer having up to approximately
20% by weight alkenyl or silanol functional groups and a viscosity
of, approximately, 50 to 100,000 centipoise at 25.degree. C.;
(b) an effective amount of precious metal catalyst for facilitating
an addition cure hydrosilation reaction at temperatures between
90.degree. C. to 300.degree. C.; and
(c) an amount of dimethylvinyl chainstopped polydimethylmethylvinyl
siloxane gum effective for accelerating the cure of said
composition. .Iaddend. .Iadd.25. A silicone composition as defined
in claim 24 wherein the dimethylvinyl chainstopped
polydimethylmethylvinylsiloxane polymer gum has an average
molecular weight of approximately 200,000 to 400,000. .Iaddend.
.Iadd.26. A silicone composition as defined in claim 24 wherein the
diorganopolysiloxane base polymer has up to 20% by weight vinyl
groups. .Iaddend. .Iadd.27. A silicone composition as defined in
claim 24 wherein the precious metal catalyst is a platinum
catalyst. .Iaddend. .Iadd.28. A silicone composition as defined in
claim 26 wherein the precious metal catalyst is a platinum
catalyst. .Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates to addition cure polysiloxane
compositions with vinyl gum cure accelerators which are
particularly well suited for coating applications and are
especially useful in the manufacture of paper and other articles
having release coatings.
Silicone compositions have long been used for rendering surfaces
nonadherent to materials which would normally adhere thereto. For a
long time, it was necessary that these silicone coatings be applied
as a dispersion within a solvent in order to control the viscosity
of the coating material so as to be suitable for coating
applications. However, although the solvent aids in the application
of the coating, it is a highly inefficient process inasmuch as the
solvent must thereafter be evaporated. The evaporation of solvents
requires large expenditures of energy and pollution control
requirements mandate that solvent vapors be prevented from escaping
into the air. Removal and recovery of all the solvent entail
considerable expenditure for apparatus and energy.
Thus, it has been noted that there is a need to provide a
solventless coating composition which will, however, remain easy to
apply to the substrate. Such solventless coating compositions are
sometimes referred to as "100% solids" compositions. The absence of
solvent in such compositions both lowers the amount of energy
required to effect a cure and eliminates the need for expensive
pollution abatement equipment. It is noted that even previous
solventless coatings are limited to certain applications because
oven cure temperatures must still be in the neighborhood of
300.degree. F. minimum, at which temperature many substrates are
thermally degraded. Although cure time can be shortened with
solventless grades, high temperatures can require that only
high-density paper or high-melting point plastics and the like be
utilized, so that the substrate will not char, melt or otherwise
degrade during cure. The composition of the present invention is a
low viscosity polydiorganosiloxane fluid which can readily be
coated onto a substrate with or without solvent by standard methods
such as blade, press, brush or gravure and which will thermally
cure onto the substrate to form a nonadherent surface at lower
temperatures than previously necessary.
Silicone release coating compositions made in accordance with U.S.
Pat. No. 4,256,870 (Eckberg) can be cured at temperatures as low as
200.degree. F. thereby enabling coating upon a wider range of
substrates than formerly possible. However, to effect an acceptable
cure at reduced temperatures a large amount of platinum catalyst is
required. For example, as much as eight times the amount of
platinum might be necessary for low temperature cure compared to
the composition in the Eckberg patent undergoing conventional high
temperature cure.
Since the high platinum concentration (e.g. 200 ppm instead of 25
ppm) adds a large cost to such grades, there was considerable
interest in efforts to limit the level of required platinum without
sacrificing low temperature cure performance. As a result of the
present invention, it has been discovered that certain vinyl
functional siloxane gums will act as cure accelerators allowing
lower temperature cure with levels of platinum much lower than
would be required in the absence of the vinyl gums.
Release coatings are useful for many applications whenever it is
necessary to provide a surface or material which is relatively
nonadherent to other materials which would normally adhere thereto.
Silicone paper release compositions are widely used as coatings
which release pressure-sensitive adhesives for labels, decorative
laminates, transfer tapes, etc. Silicone release coatings on paper,
polyethylene, Mylar, and other such substrates are also useful as
non-stick surfaces for food handling and industrial packaging
applications.
For example, when labels are coated with an adhesive it is
desirable that the paper backing be easily peeled away from the
label when it is ready for use, yet the adhesive quality of the
label should not be derogated by the fact that it has been peeled
away from the substrate upon which it was stored. The same
principle applies to certain types of adhesive tapes which come in
rolls. It is necessary that the tape unroll easily and still
maintain its adhesive characteristics. This can be accomplished by
coating the nonadhesive side of the tape with a silicone release
composition which will come into contact with the adhesive as the
roll of tape is manufactured.
Two other problems previously encountered with silicone
compositions of the above-described type are related to premature
gelation of the composition. Inasmuch as a typical composition can
be made up of a vinyl chainstopped base polymer, and a platinum
metal catalyst, premature curing may occur over a length of time
resulting in a product with unsatisfactory shelf-life. Furthermore,
when the composition is ready for use, at which time a reactive
crosslinking agent is introduced, it is desirable that the
catalyzed polymer composition have a sufficiently long pot-life to
enable one skilled in the art to carry out the coating
application.
These additional problems were solved in U.S. Pat. No. 4,256,870
(Eckberg) which is hereby incorporated by reference, which provided
solventless addition cure silicone release coating compositions
which contained effective inhibitor components which provided
stable products. These compositions were thermally cured at
elevated temperatures to obtain release coatings. As noted, it is
necessary that increased amounts of precious metal catalysts such
as platinum or rhodium be utilized in order to effectively lower
the cure temperature of these coatings, but at significantly
increased cost.
Therefore, a primary objective of the present invention is to
provide a solventless composition which will render surfaces
nonadherent to materials which would normally adhere thereto.
Another object of the present invention is to provide a solventless
coating composition with a satisfactory shelf-life which will cure
at relatively low temperatures.
Another object of the present invention is to provide a solventless
coating composition utilizing novel vinyl siloxane gum cure
accelerators.
Another object of the present invention is to provide a method of
rendering materials nonadherent to other materials which would
normally adhere thereto.
Another object is to provide articles of manufacture having
nonadherent surfaces by coating the articles with the release
compositions of the present invention.
Another object of the present invention is to provide a solventless
silicone composition which is particularly well suited for paper
release applications.
SUMMARY OF THE INVENTION
The present invention involves a silicone release coating
composition comprising a base polymer such as a vinyl chainstopped
polydialkyl-alkylvinyl polysiloxane base copolymer and a
methylhydrogen crosslinking fluid. This composition is catalyzed by
platinum or a platinum metal which will initiate an addition cure
reaction. Ordinarily the crosslinking compound is added at the time
of use to the other ingredients. Generally, any silicone base
polymer having alkenyl or silanol functionality will lend itself to
a precious metal catalyzed hydrosilation or condensation cure
reaction of the present invention. An inhibitor such as
diallylmaleate or dimethylmaleate can be added to the composition
in order to selectively retard the cure reaction so as to provide
adequate shelf-life and workable pot-life for the coating
composition. There is also added a dimethylvinyl chainstopped
polydimethylmethylvinylsiloxane polymer gum which will accelerate
the hydrosilation cure reaction at a relatively low temperature
without sacrificing performance. It is believed that excesses of
platinum catalyst can be avoided since the vinyl gum raises the
efficiency of the crosslinking reaction thereby reducing the
required amount of catalyst for a given temperature and cure time
polymer. In a sense the highly polymerized gum reduces the amount
of crosslinking required of the catalyst and facilitates a
reduction in amount of catalyst at any given temperature. This
vinyl gum will ordinarily be contained in the crosslinkable polymer
base along with the catalyst and optional inhibitor. Addition of
the crosslinking agent at the time of use provides the coating
composition.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention provides silicone release coating
compositions which may be utilized in solventless form if a
catalyst inhibitor is also used, or they may be provided in a
solvent dispersion without the necessity of such an inhibitor.
The addition curable compositions will ordinarily be comprised of a
mixture of several ingredients which can be coated upon a substrate
such as paper and when cured thereon will form a coating which is
relatively nonadherent towards materials which would normally
adhere thereto, such as organic adhesives.
The major ingredient in such a composition will ordinarily be a
diorganopolysiloxane base polymer which will preferably have up to
approximately 20% by weight of alkenyl or silanol functional groups
and a viscosity of, approximately, 50 to 100,000 centipoise at
25.degree. C. The preferred alkenyl group for such polymers is
vinyl, while the remainder of the organic groups are preferably
methyl.
The second major ingredient in the release composition is a
polymethylhydrogen siloxane fluid crosslinking agent, having up to,
approximately, 100% by weight SiH-containing groups and a viscosity
of, approximately, 25 to 1000 centipoise at 25.degree. C.
The base polymer and crosslinker are catalyzed by an effective
amount of precious metal catalyst for facilitating a well known
addition cure hydrosilation reaction between these materials.
Particularly preferred catalysts will be complexes of platinum and
rhodium which will be described below. Those skilled in the art
will be able to vary the amount of catalyst to effect the rate of
cure. For example, as taught in U.S. Pat. No. 4,256,870,
satisfactory cure can be obtained at approximately 150.degree. C.
by utilizing approximately 25 ppm platinum metal. As will be seen,
the present invention allows satisfactory cure at as low as
90.degree. C. without requiring excessive amounts of platinum
catalyst. Of course, thermal cures of 300.degree. C. or more could
still be utilized as long as the substrate does not deform.
To prevent premature gellation of the composition, U.S. Pat. No.
4,256,870 also teaches that a dialkyl carboxylic ester will
effectively inhibit the addition cure reaction until thermal cure
is desired. Suitable inhibitors include dimethylmaleate, and
diallylmaleate. Of course the amount needed will vary according to
the amount of catalyst which must be inhibited. It is to be noted
that such inhibitors are not essential in a solvent based system
but may be used if desired.
The silicone compositions of the present invention also contain a
so-called vinyl gum accelerator which facilitates or enhances the
rate of cure at as little as 90.degree. C. such that satisfactory
cure times can be obtained with reduced amounts of catalyst.
Heretofore, if satisfactory cure time was required at 90.degree. or
100.degree. C. for example, the coating required at least 200 ppm
platinum or rhodium catalyst generally in the form of a
silicone-soluble complex, which required at least, at least 1.25
weight percent dimethylmaleate (DMM) to effectively inhibit cure at
ambient conditions. But by utilizing an effective amount of the
vinyl gum accelerator, the same satisfactory cure could be obtained
with only 150 ppm platinum and 0.9% DMM. This represents a 25%
reduction in the amount of platinum required in this example which
is a significant cost savings.
As little as 0.5 weight percent of this vinyl gum will exhibit some
effect, and ordinarily up to 10 weight percent based upon the total
weight of the base polymer will be used. Greater than 10 weight
percent of the vinyl gum can also be used, but since it is quite
viscous it is relatively more difficult to get it into solution in
the silicone base polymer, especially for coating applications.
The particularly preferred vinyl gums for use as cure accelerators
in the present invention are essentially linear dimethylvinyl
chainstopped polydimethylmethylvinyl siloxane polymers having an
average molecular weight of, approximately, 200,000 to 400,000.
This material can be obtained by well known means by using
appropriate amounts of dimethylvinylsilyl chainstoppers,
methyltetramer and methylvinyl tetramer. Such polymers can also
have from 0 to 5 mole % methylvinylsiloxy content but vinyl ion the
chain does not have the same advantageous effect as does the vinyl
chainstopper in such gums.
The release composition of the present invention is particularly
well suited for rendering materials nonadherent to other normally
adherent materials such as glue and adhesives. Additionally, the
composition can be applied directly to a substrate without the need
for a solvent, thus avoiding all of the problems associated with
coating solvents as described above.
The composition is a polysiloxane made up of several ingredients
which will thermally cure on the substrate upon which it is coated,
and render the substrate nonadherent. A major proportion of the
composition is typically a vinyl chainstopped polysiloxane having
the formula ##STR1## wherein R is a monovalent hydrocarbon radical
free of unsaturation. Suitable radicals for R include, for example,
methyl, ethyl, proply, butyl, and other similar saturated
hydrocarbons, but ordinarily would not include phenyl groups for
paper release purposes. R' is a hydrocarbon radical having alkenyl
unsaturation. Typically, R' represents vinyl groups but may also
represent allylic or cyclo-alkenyl unsaturated groups. X and Y are
positive integers so that the vinyl chain-stopped polysiloxane has
up to approximately 20% by weight of R' groups. The viscosity of
such a polysiloxane ranges from approximately 50 to approximately
100,000 centipoise at 25.degree. C. Preferably, the vinyl
chainstopped polysiloxane has up to approximately 20% by weight of
vinyl groups represented by R' and the viscosity of this polymer
ranges from approximately 300 to approximately 550 centipoise at
25.degree. C. The preferred vinyl chainstopped polysiloxane has the
formula ##STR2## wherein X and Y are as described above.
Methylhydrogen fluid is often used by those skilled in the silicone
art as a crosslinking agent for addition-cured silicone systems.
Particularly useful as a crosslinking agent for the present
invention is a trimethyl chainstopped polymethylhydrogen siloxane
fluid having from approximately 10% to approximately 100%
SiH-containing siloxy groups and having a viscosity in the range of
approximately 25 to approximately 1,000 centipoise at 25.degree.
C.
The curing reaction which takes place between the vinylfunctional
polysiloxane and the polymethylhydrogensiloxane fluid crosslinking
agent is an addition cure reaction, also known as a hydrosilation.
The composition of the present invention may be thermally cured by
means of a platinum metal catalyzed crosslinking reaction between
the pendant vinyl groups of a dialkylvinyl chainstopped
polydialkyl-alkylvinylsiloxane copolymer and the H-Si groups of a
trimethyl chainstopped polymethylhydrogen fluid.
A useful catalyst for facilitating the hydrosilation curing
reaction is the Lamoreaux catalyst as described in U.S. Pat. No.
3,220,972 issued Nov. 30, 1965, and assigned to the same assignee
as the present invention. Another is the catalyst proposed by Ashby
in U.S. Pat. No. 3,159,601. Other Group VIII-metal catalysts can
also be utilized in practicing the present invention and their
selection depends upon such factors as speed of the reaction
required as well as expense, useful shelf-life, useful pot-life and
the temperature at which the cure reaction is to take place. Such
precious-metal catalysts include those which utilize the metals
ruthenium, rhodium, palladium, osmium, iridium and platinum, and
complexes of these metals. In U.S. Pat. No. 4,262,107 the present
inventor proposed several rhodium catalysts useful in silicone
rubber compositions. It is believed that these catalysts should
also be useful in the addition cure release composition of the
present invention. All of the patents mentioned in this paragraph
are hereby incorporated by reference. For coating compositions as
described above, the amount of catalyst ranges from approximately
10 to approximately 500 ppm of metal, again depending upon the
factors of speed of reaction and cost. Preferably, the amount of
catalyst is approximately 10 to 50 ppm of precious metal.
EXAMPLE 1
Prior art silicone release coatings can be prepared in accordance
with U.S. Pat. No. 4,256,870 (Eckberg) and may be comprised
oflinear dimethylvinyl chainstopped polydimethylmethylvinyl
siloxane fluid having a viscosity of approximately 300 to 600
centipoise and a vinyl on the chain (V.O.C.) content of
approximately 3.7 weight percent (D.sup.vi). An amount of a
chloroplatinic acid-octyl alcohol complex catalyst prepared as
instructed by Lameroux in U.S. Pat. No. 3,220,972 which was
sufficient toprovide approximately 25 ppm platinum (as Pt metal)
along with 0.25 weight percent diallylmaleate inhibitor was used to
complete the prior art composition. This composition requires a
minimum oven temperature of 150.degree. C. to effect cure at useful
rates. For low temperature curing, approximately 200 ppm platinum
catalyst is utilized as described in U.S. Pat. No. 3,159,601
(Ashby) is utilized rather than the 25 ppm Lameroux catalyst. This
catalyst is a complex of chloroplatinic acid and
tetravinyltetramethyl cyclotetrasiloxane. Dimethyl maleate (DMM) is
used as an inhibitor at a rate of 1.25 weight percent DMM based
upon the weight of polymer. The coating composition is completed
upon addition of 4 parts methylhydrogen siloxane crosslinking
fluid, per 100 parts of the catalyst-containing polymer-inhibitor
mixture.
Initial experiments were performed in which test batches of the
prior art-type compositions were prepared in the fashion described
above, except for varying the amount of the platinum catalyst and
changing the dimethylmaleate concentration according to such
changes in platinum level. The following cure profiles demonstrate
the effect of lower platinum levels on cure performance in these
solventless compositions.
______________________________________ Cure Profile A Cure Profile
B Cure Profile C (200 ppm Pt) (175 ppm Pt) (150 ppm Pt) T. .degree.
F. cure T. .degree. F. Cure T. .degree. F. Cure time. sec. time.
sec. time. sec. ______________________________________ 200 25 200
35 200 60 250 15 250 20 250 30 300 5 300 5 300 10
______________________________________
It is apparent that small reductions in platinum content result in
unacceptable loss of cure, particularly at lower temperatures.
However, it was found that the addition of a small amount of a soft
vinyl-functional gum to the solventless compositions containing 150
ppm platinum (representing a 25% reduction in platinum usage from
the prior art composition) restored the low-temperature cure
performance otherwise lost. The vinyl gum is a soft (3000 to 7000
penetration) dimethyl vinyl-stopped siloxane gum with 0.2 mole %
methylvinyl D' units on the linear polymer chains. The molecular
structure of the gum is analogous to that of the vinyl base polymer
in the prior art composition save for a much higher molecular
weight of approximately 300,000. The effect of gum increments on
the cure performance of the experimental blend can be seen in the
table below.
______________________________________ Additional Vinyl Gum, %
200.degree. F. Cure 250.degree. F. Cure 300.degree. F. Cure
______________________________________ 0 60 sec. 30 sec. 10 sec.
2.5 45 sec. 30 sec. 5 sec. 3 40 sec. 20 sec. 5 sec. 3.5 35 sec. 15
sec. 5 sec. 4 30 sec. 15 sec. 5 sec. 5 25 sec. 12 sec. 5 sec.
______________________________________
The addition of 5 weight % vinyl gum provides essentially identical
cure performance in the experimental grade as is generally observed
for the prior art compositions, the advantage being the lower level
of platinum catalyst required in the gum-containing
composition.
EXAMPLE 2
While it is theoretically possible to blend higher amounts of gums
into the solventless base polymer, the high viscosity (e.g. 2000
cps.) of resulting compositions renders them difficult to coat via
standard offset gravure techniques so that incremental gum
adjustments are limited to approximately 5% for solventless paper
release grades. The use of vinyl gum in solventless paper release
grades intended for low temperature applications is illustrated by
a composition, the preparation of which is summarized as
follows.
A base polymer was prepared by blending 95.2 parts
dimethyltetramer, 1.8 parts methylvinyltetramer, and 3 parts
dimethylvinyl chainstopper, then polymerizing the mixture with
standard KOH/H.sub.3 PO.sub.4 equilibration/neutralization
techniques. After removal of lite ends, a vinyl-stopped
dimethylmethylvinyl copolymer base polymer fluid of 118 cps.
viscosity was obtained. 5 parts of the vinyl stopped polydimethyl
methylvinylsiloxane gum described in Example 1 was blended with 100
parts of the base polymer fluid to afford a fluid mixture of 410
cps. viscosity. Sufficient platinum catalyst was added to the fluid
mixture to provide 150 ppm platinum, plus 0.9 weight %
dimethylmaleate inhibitor. The cure profile obtained for this
composition was essentially identical to the cure profile typically
noted for the prior art composition (see Cure Profile A), despite
the 25% reduction in platinum level.
EXAMPLE 3
A composition was prepared by KOH-catalyzed equilibration of 97
parts octamethyltetracyclosiloxane and 3 parts
sym-divinyltetramethyldisiloxane. A dimethylvinyl chainstopped
linear polydimethylsiloxane polymer fluid was obtained having 132
cps. viscosity. 100 parts of the polymer fluid was then mixed with
5 parts of a 5200 penetration (approximately 300,000 MW) linear
dimethylvinyl-stopped polydimethylmethylvinylsiloxane copolymer gum
including approximately 0.2 mole % vinyl D groups on the linear
chains. This mixture was agitated at 150.degree. C. for 4 hours to
yield a smooth, free-flowing dispersion of gum in fluid, 440 cps.
viscosity. This blend was cooled to 80.degree. C. and sufficient
trichloro-rhodium (III) tris (dibutylsulfide) (dissolvedin
methanol) was added to provide 75 ppm rhodium in the composition,
the methanol being removed in vacuo. The solventless product was
completed with the addition of 0.33 weight percent dimethylmaleate
inhibitor. The rhodium compound used was prepared as described by
Fergusson et al., J. Chem. Soc. 1965, 2627. A control material was
also prepared consisting of a 400 cps. dimethylvinyl-stopped
polymethylsiloxane fluid but with no gum and with precisely the
same concentration of rhodium catalyst and dimethylmaleate
inhibitor present in Example 3.
Coating baths were prepared by mixing 10 parts of Example 3 (or the
control) with 0.4 parts of a trimethylsilyl-stopped
polymethylhydrosiloxane fluid crosslinker. This material is
available from General Electric Company as SS-4300c. The cure
performance of these coating baths was ascertained as described
above, with the following results observed on (SCK) super
calendared Kraft paper substrates:
______________________________________ Minimum Cure Time, seconds
Composition 250.degree. F. 350.degree. F.
______________________________________ Example 3 30 5 Control No
Cure* 15 ______________________________________ *Migration and
ruboff was noted on cured films, even after 90 min. at
250.degree..
It is thus clear that vinyl gum cure accelerators of the present
invention are also effective for hydrosilation catalysts other than
standard platinum-containing catalysts.
EXAMPLES 4 to 7
Two experimental compositions were prepared via standard
KOH-catalyzed equilibration of D.sub.4, and M.sup.vi M.sup.vi
siloxanes. Example 4 included 97.5 parts of D.sub.4, 1 part of
D.sub.4.sup.vi and 1.5 parts of M.sup.vi M.sup.vi chainstopper.
After equilibration, neutralization, and removal of polymer lite
ends, a 350 cps. fluid product was obtained. A second composition,
Example 5, included 98 parts D.sub.4, 0.5 parts D.sub.4.sup.vi and
1.5 parts M.sup.vi M.sup.vi chainstopper, and, following
conventional processing techniques, yielded a 360 cps. fluid
product which was indistinguishable from Example 4 except for the
amount of vinylsiloxane D.sup.vi units on the linear chains. Both
of these fluids were then treated with sufficient platinum catalyst
(Lameroux, U.S. Pat. No. 3,220,972) to furnish 25 ppm Pt plus 0.25%
diallylmaleate inhibitor (Eckberg, U.S. Pat. No. 4,256,870). It
should be noted that no vinyl gum was included in these
compositions.
Two other experimental compositions were prepared as described
above. A fluid was prepared by equilibration of 96 parts D.sub.4, 1
part D.sub.4.sup.vi, and 3 parts M.sup.vi M.sup.vi chainstopper.
After neutralization and stripping off lite ends, the fluid
viscosity was 125 cps. To 100 parts of this fluid was added 5 parts
of a dimethylvinyl-stopped polydimethyl-methylvinylsiloxane gum
having a molecular weight of approximately 300,000. Agitation of
this mixture at 150.degree. C. for 4 hours completely dissolved the
gum in the fluid thereby affording a 400 cps mixture which was
designated Example 6. A fourth fluid mixture, Example 7, was
prepared (including the vinyl gum) in an identical fashion as
Example 6, except for incorporation of 0.5 parts D.sub.4.sup.vi
rather than 1.0 parts D.sub.4.sup.vi in theoriginal charge.
Platinum catalyst and diallylmaleate inhibitor were added to these
two fluids precisely as described for the previous two examples to
complete the processing.
All four compositions were than qualitatively checked for cure on
40 lb. supercalendered Kraft substrates in this fashion: 10 parts
of the test fluid were combined with 0.3 parts crosslinker (MeH
fluid, grade SS-4300c described above) and this blend was manually
coated onto the paper substrate with a doctor blade. The coated
paper was then hung in a forced-air oven at 350.degree. F. until a
cured migration-free nonadherent adhesive surface was obtained.
Results are tabulated below:
______________________________________ Blend Minimum Cure Time,
350.degree. F. ______________________________________ Example 4 60
sec.* Example 5 60 sec.* Example 6 30 sec. Example 7 30 sec.
______________________________________ *Some migration still poured
after 60 sec. at 350.degree. F.
Clearly, the presence of 5 weight percent vinyl gum in these
compositions provides a significant improvement in the cure
performance when all other components of the blends are held
constant.
EXAMPLE 8
The practice of this invention not only provides for faster cure
than would otherwise be observed but, equally important, a
relatively more complete cure is also obtained. An incomplete cure
of the release agent results in significant amounts of uncured free
silicone on the abhesive (or nonadherent) coating. When laminated
against pressure-sensitive adhesive over normal storage periods,
the uncured silicone will slowly migrate into the adhesive layer.
The result of such a process is an undesirable loss of adhesive
tack as the laminate ages. Therefore, the more complete the cure of
the solventless release coating, the better the aging
characteristics of laminated articles manufactured with the
silicone release liner.
Experiments were run to determine the relative degree of cure for
solventless release coatings. Silicone coatings on SCK substrate
were applied and cured as described above. Exactly 32 in.sup.2 of
the coated paper was then treated with 15 grams of hexane at
60.degree. C. for 120 seconds. The hexane was then placed in tared
aluminum weighing cups and evaporated to dryness in an oven.
Uncured silicone extracted from the coated paper was left as a
residue in the aluminum vessels. The weight of extracted silicone
serves as a relative measure of degree of cure; i.e. the more
residue detected, the poorer the degree of cure. Tests were
conducted with the standard solventless grade described as the high
temperature prior art material in Example 1 (which contains no
vinyl gum) and on the experimental grade of Example 7 described
above. Each sample was blended with 3 weight percent crosslinker
prior to coating and curing at 350.degree. F. for 30 seconds. It
should be pointed out that these tested materials have identical
amounts of the Lameroux platinum catalyst and diallylmaleate
inhibitor. 5 hexane extractions were performed on each composition,
with these results:
______________________________________ Grade Extractibles, mg
______________________________________ Prior Art 4.2 .+-. 0.6
Example 7 1.9 .+-. 0.3 ______________________________________
Thus it can be seen that inclusion of 5 weight percent vinyl gum in
solventless silicone release products provides not only a faster,
but a more complete, and therefore superior cure.
* * * * *