Solventless silicone compositions for release paper

A solventless silicone composition for release paper containing a partially branched organopolysiloxane as a vinyl base polysiloxane to be cured, which may be applied without containing any organic solvents, and which gives a cured film having excellent slip properties and releasability without using any slip-imparting materials.

BACKGROUND OF THE INVENTION 
The present invention relates to silicone compositions for release paper 
which provides excellent releasability and slip properties with 
substrates, more particularly to a solventless silicone composition for 
release paper which may be applied without containing organic solvents. 
Conventionally, silicone compositions have been used as release agents to 
prevent the adhesion and fixing between substrates such as paper or 
plastics and adhesive substances, or to improve the slip between paper and 
paper, paper and plastics, a plastic film and a plastic film, paper and 
human fingers, plastics and human fingers, or plastics and metals. 
These release agent silicone compositions have been widely used as organic 
solvent solutions or as aqueous emulsions (see, for example, Japanese 
Patent Publication Nos. Sho 35-13709, Sho 36-1397, and Sho 46-26798). 
Since the organic solvent solution-type silicone release agents contain, 
as a main constituent, gum-like diorganopolysiloxanes of a high molecular 
weight or of a high polymerization degree, they need large volumes of 
solvents in their use, and thus inevitably cause air pollution if the 
solvents are vented into the atmosphere, and they require a substantial 
cost in the solvent recovery system. In contrast, the aqueous 
emulsion-type silicone release agents cause no serious air pollution; 
however, they might cause some environmental pollution from the use of 
emulsifying agents, and they are required to be heated for a longer time 
at a high temperature for film formation. 
To solve these problems, solventless-type release agent silicone 
compositions have been proposed which contain virtually no water or 
organic solvents. Examples of these silicone compositions may be found, 
for example, in U.S. Pat. Nos. 3,922,443, 4,057,596, and 4,071,644, and 
Japanese Patent Publication No. Sho. 52-39791. However, the cured film 
obtained from these compositions has a low polymerization degree, because 
these compositions use a vinylsiloxane or hydrogensiloxane having a 
viscosity between 50 and 5,000cSt at 25.degree. C., as a main constituent, 
and as a result it is inferior in mechanical strength in comparison to 
that obtained from the conventional organic solvent solution-type silicone 
compositions stated above. In addition to this disadvantage, it is 
unsatisfactory in slip properties, and thus the conventional solventless 
silicone compositions have limited applications. 
For example, if the conventional solventless release agent silicone 
compositions are used for release agents for a kraft tape with a 
pressure-sensitive adhesive, the application of the kraft tape to 
corrugated boards is not smoothly done, since the cured film formed on the 
back side of the kraft tape is poor in slip properties, and the slip 
between hands and the release surface is not good. Sometimes workers hurt 
their hands. If this happens, workers cannot apply sufficient force to the 
kraft tape, and thus the pressure sensitive adhesive does not 
satisfactorily adhere to the corrugated board, and thus the peeling of the 
tape from the corrugated board sometimes happens. It has also been pointed 
out that in case the conventional solventless release agent silicone 
compositions are applied to paper or a plastic film to make a slip sheet 
for a cassette tape, a magnetic tape is sometimes damaged, or troubles 
occur in tape rotation, because the slip between the tape and the slip 
sheet is not good. 
It has further been pointed out that if release paper is manufactured by 
applying and curing the conventional solventless release agent silicone 
compositions to paper or a plastic film, the cured silicone film thus 
obtained contacts a metal or plastic roll before the release paper is 
wound up. The poor slip properties of the cured film might cause damages 
to the silicone surface, and this becomes a cause of scattering in release 
performance of the release paper thus manufactured. The poor slip 
properties also might make the wind-up of the coated paper or plastic film 
unsmooth, and thereby cause processing troubles. 
To solve these problems in the conventional solventless release agent 
silicone compositions, various slip-imparting materials, such as 
dimethylsiloxane oils, polyether modified oils, surfactants, waxes, and 
metal soaps, have been added. However, satisfactory results have not yet 
been obtained. Since virtually none of these slip-imparting materials are 
very compatible with the silicone compositions, the coating fluid thus 
obtained becomes unstable, and curing often fails to occur. The most 
serious problem is that almost all of these slip-imparting materials tend 
to migrate onto the surface of the silicone cured film, and this causes a 
decrease in the adhesive force between the cured film and the adhesive. 
Other methods for improving slip properties have been proposed, as for 
example, in Japanese Patent Laid-open Publication Nos. Sho. 61-159480 and 
Sho. 63-101453. However, these methods are still unsatisfactory. 
SUMMARY OF THE INVENTION 
The object of the invention is to provide a solventless silicone 
composition for release paper which produces a cured film having excellent 
slip properties, releasability, and subsequent adhesion. In the present 
invention, release paper may be composed of any substrate, such as paper, 
plastic film, or metal foil, and should not be limited to release paper 
composed of paper. 
It has now been found by the inventors that the foregoing object is 
attained by employing as the vinyl base siloxane to be cured a partially 
branched one, since a cured film produced from the silicone composition of 
the invention has a similar level of slip properties to that produced from 
a conventional solvent-borne release agent silicone composition, and thus 
it does not require the use of slip imparting materials which tend to 
migrate onto the surface of a cured film. 
The foregoing object, feature and advantages of the invention will be 
apparent from the following detailed description thereof. 
The solventless composition of the invention comprises: 
(a) 100 parts by weight of an organopolysiloxane having per molecule at 
least two silicon-bonded alkenyl radicals, and at least one silicon-bonded 
radical of the formula: 
##STR1## 
wherein R.sup.1 is the same or a different monovalent hydrocarbon radical, 
n is an integer of 5 to 100, and m is an integer of 2 to 8; 
(b) 1 to 100 parts by weight of methylhydrogenpolysiloxane having per 
molecule at least two silicon-bonded hydrogen atoms; and 
(c) A catalytically effective amount of a platinum catalyst; and the sum of 
the number of the alkenyl radicals per molecule in component (a) and that 
of SiH radical per molecule in component (b) is at least five.

DETAILED DESCRIPTION 
Each component of the composition of the invention will be explained in 
detail. 
The organopolysiloxane employed as component (a) in the invention has at 
least two silicone-bonded alkenyl radicals in a molecule. This 
organopolysiloxane has a comb-like structure, and is represented by, for 
example, the following formulae: 
##STR2## 
In these formulae, A is a linear polysiloxane radical represented by the 
formula: 
##STR3## 
The substituents R.sup.1 and R.sup.3 are alkyl radicals, e.g., methyl, 
ethyl, propyl, butyl, etc., aryl radicals, e.g., phenyl, tryl, etc., 
cycloalkyl radicals, e.g. cyclohexyl, etc., or the same or different, or, 
substituted or non-substituted monovalent hydrocarbon radicals wherein all 
or some of the hydrogen atoms bonded to the carbon atoms in the radicals 
are substituted with halogen atoms, cyano atoms, etc. The most preferable 
R.sup.1 is methyl radical. 
The substituent R.sup.2 is an alkyl radical, e.g., methyl, ethyl, propyl, 
butyl, etc., an alkenyl radical, e.g., vinyl, allyl, etc., an aryl 
radical, e.g., phenyl, tryl, etc., a cyclo alkyl radical, e g., cyclo 
alkyl, etc., the same or different, or, substituted or non-substituted 
monovalent hydrocarbon radicals wherein all or some of the hydrogen atoms 
bonded to the carbon atoms in the radicals are substituted with halogen 
atoms, cyano radicals, etc. 
The most preferable alkenyl radical as R.sup.2 is a vinyl radical or allyl 
radical, and m is an integer of 2 to 8, n is an integer of 5 to 100, a, b, 
or c is an integer greater than or equal to 1. The most preferable m is 2 
or 3. 
From the standpoint of practical use, eighty mole percent (80 mole %) of 
R.sup.1, R.sup.2, and R.sup.3 preferably are methyl groups. By changing 
the ratio b/(a+b), it is possible to control the level of the slip 
properties of a cured film produced from the compositions, and the 
preferable range of this ratio is 0.001 to 0.1. 
The organopolysiloxane may be prepared, for example, by reacting an 
organopolysiloxane represented by, for example, formula [I]: 
##STR4## 
wherein R.sup.2, R.sup.3, a, b, and c are the same as hereinabove 
described, and d is b plus c; with an organopolysiloxane having a hydrogen 
at one end of, for example, formula [II ]: 
##STR5## 
wherein n is an integer of 5 to 100, in a solvent such as toluene, or 
tetrahydrofuran in the presence of a catalyst for a hydrosilyl reaction 
such as chloroplatinic acid at 40.degree. to 120.degree. C. 
The organopolysiloxane having a hydrogen at one end may be prepared by, for 
example, the following known method: A trialkylsilanol (R.sub.3 SiOH) is 
copolymerized with hexaorganotrisiloxane in an acetonitrile solvent in the 
presence of a penta-coordinate catalyst such as one represented by 
formulae [III] and [IV], whereby an organopolysiloxane having a silanol 
radical represented by formula [V ] at one end is produced. The 
thus-produced organopolysiloxane is reacted with a dialkylchlorosilane in 
the presence of a hydrochloric acid-uptaking agent (e.g., triethylamine, 
pyridine, etc.). 
##STR6## 
(wherein R.sup.1 and n are the same as described in formula [II ] above) 
An example of the alkenyl group in the organopolysiloxane of component (a) 
is a vinyl radical, allyl radical, or propenyl radical, and the most 
preferable alkenyl radical is a vinyl radical. If the amount of the 
alkenyl radical in the organopolysiloxane is lower than or equal to 0.5 
mole %, the silicone compositions do not cure well. If the amount is 
higher than or equal to 10.0 mole %, the peel resistance of a cured film 
produced from the silicone compositions becomes too high, and the adhesion 
of adhesives to the cured film becomes instable from the standpoint of 
practical use. Thus, the amount of the alkenyl group should be within the 
range of 0.5 to 10.0 mole %, and preferably of 1.0 to 8.0 mole %. 
The organohydrogen polysiloxane which is component (b) of the silicone 
composition of the invention may be chosen from known 
organohydrogenpolysiloxanes which contain per molecule at least two, and 
preferably at least three, hydrogen atoms, which may undergo an addition 
reaction with an alkenyl radical. At least 90 mole % of the organic 
radicals other than hydrogen atoms should preferably are methyl groups. 
Examples of this kind of polysiloxane are homopolymers or copolymers with 
siloxyl units such as (CH.sub.3)HSiO, HSiO.sub.1.5, (CH.sub.3).sub.2 SiO, 
CH.sub.3 SiO.sub.1.5, (CH.sub.3).sub.2,HSiO.sub.0.5, and (CH.sub.3).sub.3 
SiO.sub.0.5. The structure of this polysiloxane may be linear, branched or 
cyclic, and a polysiloxane having a viscosity of 10 to 500cSt at 
25.degree. C. is preferable. The amount of the polysiloxanes may be that 
in proportion to the amount of the alkenyl radicals contained in component 
(a), and is generally 1 to 100 parts by weight per 100 parts by weight of 
the amount of the alkenyl radicals contained in component (a), from the 
standpoint of the formation of film and peel properties. 
The third component (Composition (c)) of the silicone composition of the 
invention is a catalyst for an addition reaction of components (a) and 
(b), and may be selected from among such catalysts conventionally used for 
this kind of reaction as chloroplatinic acid, an alcohol, or an aldehyde 
solution of chloroplatinic acid, or complexes of chloroplatinic acid and 
various olefines. Platinum black and various carriers on which platinum is 
placed may also be used. The catalyst may be present in an amount which is 
catalytically effective, and the amount should usually be 1 to 1,000 ppm 
based on component (a), to obtain a good cured film, and from an economic 
standpoint. 
The sum of the number of the alkenyl radicals in component (a) and that of 
SiH radicals in component (b) should be at least five, to make a 
crosslinked polymer structure, and to make the thus-copolymerized silicone 
composition insoluble to solvents. 
The silicone composition of the invention may be obtained by blending 
specific amount of three components (a), (b) and (c). Component (c) is 
preferably added after obtaining the uniform blend of components (a) and 
(b). If necessary, reaction retardants such as various organic nitrogen 
compounds, organic phosphate compounds, acetylene compounds, oxim 
compounds, and organic chloro compounds, may be added as the fourth 
component to control the activity of platinum catalysts. The viscosity of 
the composition of the invention is preferably 50 to 20.000 cSt from the 
standpoint of the workability in its coating process. The viscosity may be 
chosen dependent on the amount to be coated, coating methods, or materials 
of the substrates to be coated. For example, lower or moderate 
viscosities, of 50 to 3,000 cSt, are used if the amount of coating on 
substrates is chosen to be in the range of 0.3 to 3.0g/m.sup.2, in the 
coating of metal foils or plastics such as polyethylene-laminated papers 
by means of known coating machines such as roll coaters, gravure coaters, 
air-knife coaters, curtain-flow coaters, offset-transfer roll coaters, 
etc. Higher viscosities than those in this range are preferred in the 
coating of substrates such as glassine papers, kraft papers, and 
clay-undercoated papers into which release agent compositions are readily 
absorbed. 
Substrates on which the composition of the invention is coated are heated 
for 5 to 60 seconds at a temperature of 80.degree. to 200.degree. C., or 
are irradiated for more than 0.2 seconds with a UV radiator of a power of 
about 80 w/cm, and a cured film is formed on the surface of the 
substrates. The thus-formed cured film imparts slip properties to the 
substrate, and coated substrates such as paper, plastic films, and metal 
foils become useful as release paper. The manual application of an 
adhesive tape is then smoothly done, because the slip properties of the 
cured silicone surface is good. In addition, since the cured silicone 
surface has a light release force and good slip properties, the scope of 
uses of this release silicone composition may be broadened in comparison 
with that of the conventional solventless release agent silicone 
compositions. 
As stated above, since the silicone composition of the invention employs a 
partially branched vinyl-base siloxane as a vinyl-base siloxane to be 
cured, it may be applied without the use of organic solvents. Thus, it is 
excellent in the points of energy savings, safety, and environmental 
pollution. It may also impart a good level of slip properties which has 
never been attained by the conventional solventless silicone compositions. 
In addition, the subsequent adhesion is excellent, and the release force 
is light and constant. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The release agent silicone composition of the invention is illustrated in 
more detail by reference to the following examples, wherein the term 
"parts" means "parts by weight," and the values of viscosity were all 
measured at 25.degree. C. These examples are illustrative and the claims 
are not to be construed as limited to them. 
EXAMPLE 1 
To a solution of 100 g of toluene and 100 g of dimethylpolysiloxane (vinyl 
value: 7.2.times.10.sup.-4 mole/g) containing 4.5 mole % of vinyl 
radicals, having dimethylsilyl radicals at its molecular ends, and of a 
viscosity of 800 cSt at 25.degree. C., 1 g of a 1% isopropanol solution of 
chloroplatinic acid was added, and the mixture was heated up to 80.degree. 
C. To this mixture 160 g of dimethylpolysiloxane (polymerization degree 
60) having a SiH radical at one end was dropped, and the reaction was 
initiated. After the drop of dimethylpolysiloxane, the reaction mixture 
stood for two hours at 80.degree. to 100.degree. C. Thereafter, 1 g of 
active carbon was added to this reaction mixture to adsorb the catalyst in 
the reaction mixture, and the reaction mixture was filtered. 
From the thus-obtained filtrate toluene was distilled off, and an oil (oil 
A) having a vinyl value of 1.4.times.10.sup.-4 mole/g and a viscosity of 
18,000 cSt was obtained. 
To 100 g of oil A was added 3 g of methylhydrogenpolysiloxane, both of 
whose end groups are trimethylsilyl having a viscosity of 20 cSt at 
25.degree. C., and 1 g of 3-methyl-1-butyne-3-ol of the formula [V ] was 
further added. This mixture was uniformly mixed and then 2 g of a complex 
salt of platinum and vinylsiloxane (200ppm in terms of platinum content) 
was added, and then these components were sufficiently mixed to prepare 
product 1. 
##STR7## 
Curability of product 1, peel resistance, slip properties, and the 
subsequent adhesion of a cured film from product 1 were measured by the 
methods described below, and the results of these measurements are shown 
in Table 1. 
Measurement of Curability 
Product 1 was coated on the surface of polyethylene laminated fine paper in 
a coated amount of 0.8 g per 1 m.sup.2 of the surface area, and the coated 
paper was then heated for 20 seconds at 120.degree. C. in a hot air 
circulation-type drying oven. The cured surface was rubbed with a finger 
and the curability was judged by the dropping-off of the cured composition 
from the cured surface, and the haze of the cured surface was estimated. 
The result was very good, and the mark ".circleincircle." in Table 1 means 
good curability. 
Measurement of Peel Resistance 
Product 1 was coated on the surface of a polyethylene laminated fine paper 
in an amount of 0.8 g per 1 m.sup.2 of surface area, and heated for 30 
seconds at 140.degree. C. in the drying oven, whereby a cured film was 
formed on the laminated paper. On the surface ORIBAIN BPS-5127 (a product 
name for an acrylic-type solventborne adhesive manufactured by Toyo Ink 
Manufacturing Co., Ltd.) or ORIBAIN BPS-2411 (a product name for a 
rubber-type solventborne adhesive manufactured by the same company) was 
coated, and heated for 3 minutes at 100.degree. C. Thereafter, a piece of 
paper having a weight of 40 g per 1 m, was applied to this treated 
surface, and a pressure of 20 g/cm.sup.2 was applied to this paper and 
kept for a certain time at 25.degree. C. Thereafter, this paper, together 
with the adhesive, the cured film, and the laminated paper, was cut into 
strips having a width of 5 cm, to get test pieces. The 180-degree release 
test was conducted by peeling the applied paper from the test pieces at a 
rate of 0.3 m/min, 30 m/min, and 60 m/min by using a tensile strength 
tester, and the peel force(g) required to peel was measured for each test 
piece. 
Measurement of Slip Properties 
A cured film of product 1 was formed on the surface of a sheet-like 
substrate by the same method used in the peel resistance test above. On 
its surface was placed a piece of urethane rubber or styrene-butadiene 
rubber. A weight of 200 g was placed on the rubber, and then the rubber 
was pulled in a direction parallel to the cured silicone surface at a rate 
of 0.3 m/min, and the kinetic frictional force was obtained by dividing 
the force(g) required to pull the rubber by 200 g. This procedure employed 
is similar to that described in ASTM D 1894-63. Slip properties were also 
evaluated by sliding a finger on a cured film surface, and the results 
were estimated in terms of the following standards, and the results are 
shown in Table 1 using the following marks: 
.circleincircle.: slided very well 
.largecircle.: slided well 
x: did not slide 
x x: did not slide at all 
Measurement of Subsequent Adhesion 
A cured film of product 1 was formed on the surface of a sheet-like 
substrate by the same method as used in the peel strength test given 
above. On its surface was applied a polyester adhesive tape No. 31B (a 
product name for a polyester pressure sensitive adhesive tape manufactured 
by Nitto Denko Corporation), and heated for 20 hours at 70.degree. C. 
under a pressure of 20 g/cm.sup.2, and then the applied polyester tape was 
peeled. Thereafter, the peeled polyester tape was applied to a 
stainless-steel sheet, and the 180-degree release test was conducted at a 
rate of 0.3 m/min, and force 1 required to peel the tape from the 
stainless-steel surface was measured. 
To make a comparison, tape No. 31B was applied to a polytetrafluoroethylene 
sheet, then heated for 20 hours at 70.degree. C. under a pressure of 20 
g/cm.sup.2, and then peeled from the sheet. This 180-degree release test 
was also conducted by applying the peeled tape to a stainless-steel 
surface, and force 2 required to peel the tape from the stainless-steel 
surface was measured. The subsequent adhesion was expressed in % by 
dividing force 1 by force 2. 
EXAMPLE 2 
Oil B, having a vinyl value of 8.2.times.10.sup.-5 mole/g, and having a 
viscosity of 12,000 cSt, was prepared by repeating the same process as 
that used to prepare oil A in Example 1, but by replacing 160 g of the 
dimethylpolysiloxane having a SiH radical at one end and having a 
polymerization degree of 60 used in Example 1 with 120 g of the same 
dimethylpolysiloxane, but having a polymerization degree of 30. 
Thereafter, composition was prepared by repeating the same process as that 
used to obtain composition I in Example 1, but by replacing 100 g of oil A 
with 100 g of oil B. By using composition II, the same physical properties 
were measured by using the same methods as those described in Example 1, 
and the results obtained are also shown in Table 1. 
EXAMPLE 3 
Oil C, having a vinyl value of 1.29.times.10.sup.-4 mole/g and having a 
viscosity of 1,500 cSt, was prepared by repeating the same process as that 
used to prepare oil A in Example 1 by replacing 160 g of the 
dimethylpolysiloxane having a SiH radical at one end and having a 
polymerization degree of 60 as used in Example 1 with 40 g of the same 
dimethylpolysiloxane but having a polymerization degree of 10. Thereafter, 
composition III was prepared by repeating the same process as that used to 
prepare oil A in Example 1, but by replacing 100 g of oil A with 100 g of 
oil C. 
By using composition III, the same physical properties were measured by the 
same methods as those described in Example 1, and the results obtained are 
also shown in Table 1. 
COMATIVE EXAMPLE 1 
To 100 g of vinyldimethylpolysiloxane having a vinyl radical only at one 
end, and having a viscosity of 1,000 cSt at 25.degree. C. which replaces 
the vinyl radical containing dimethylpolysiloxane used in Example 1, 2 g 
of the methylhydrogenpolysiloxane, both of whose and groups are 
trimethylsilyl having a viscosity of 20 cSt at 25.degree. C., and 1 g of 
3-methyl-1-butyne-3-ol, were added, and these compounds were uniformly 
mixed. Thereafter, 2 g of a complex salt of platinum and vinylsiloxane 
(200 ppm in terms of platinum content) was added, and these components 
were sufficiently mixed. Composition V was thus prepared. 
By using composition the same physical properties were measured by the same 
methods as those described in Example 1, and the results obtained are also 
shown in Table 1. 
COMATIVE EXAMPLE 2 
To 100 g of dimethylpolysiloxane containing 4.5 mole % of a vinyl radical, 
both of whose end radicals are dimethylvinylsilyl groups having a 
viscosity of 800 cSt at 25.degree. C., 3 g of methylhydrogenpolysiloxane 
both of whose end radicals are trimethylsilyl having a a viscosity of 20 
cSt at 25.degree. C. and lg of 3-methyl-1-butyne-3-ol, were added, and 
these components were uniformly mixed. To this mixture 2 g of a complex 
salt of platinum and vinylsiloxane (200ppm in terms of platinum content ) 
was added, and these components were sufficiently mixed. Composition V was 
thus prepared. 
By using composition V, the physical properties were measured by the same 
methods as described in Example 1, and the results are shown in Table 1. 
EXAMPLE 4 
To composition 1 in Example 1, 4 parts of 4-methoxybenzophenone, a 
photosensitizer, was added. The thus-prepared composition was coated on 
polyethylene laminated fine paper in an amount of 0.8 g/m.sup.2. The 
coated substrate was irradiated for 3 seconds with a low-pressure mercury 
vapor lamp of 80 w/cm placed 8 cm from the coated substrate. The 
curability, peel resistance, slip properties, and residual adhesive rate, 
were measured. The results are shown in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Slip properties 
Kinetic 
Friction Co- Peel 
efficiency Resistance 
Ure- 
SBR Subsequent 
(g/5 cm) 
thane 
Rub- Cur- 
Adhesion 
BPS- 
BPS- 
Com. Rubber 
ber Touch 
ability 
(%) 5127 
2411 
__________________________________________________________________________ 
Ex. 1 
I 0.16 
0.66 
.circleincircle. 
.circleincircle. 
95 41 73 
Ex. 2 
II 0.16 
0.64 
.circleincircle. 
.circleincircle. 
96 35 57 
Ex. 3 
III 0.18 
0.65 
.circleincircle. 
.circleincircle. 
96 32 47 
C. Ex. 1 
IV 0.27 
0.85 
X .circleincircle. 
98 63 135 
C. Ex. 2 
V 0.34 
0.95 
XX .circleincircle. 
98 60 140 
Ex. 4 
VI 0.16 
0.64 
.circleincircle. 
.circleincircle. 
96 45 70 
__________________________________________________________________________ 
As is apparent from the results in Table 1, the release agent silicone 
composition of the invention may form a cured film which has good slip 
properties, a good subsequent adhesion, and a light release force. 
From the foregoing description one skilled in the art can easily ascertain 
the essential characteristics of this invention, and without departing 
from the spirit and scope thereof, can make various changes and 
modifications of the invention to adapt it to various uses and conditions.