CA1129270A - Method for coating a substrate using a curable silicone release composition - Google Patents
Method for coating a substrate using a curable silicone release compositionInfo
- Publication number
- CA1129270A CA1129270A CA342,133A CA342133A CA1129270A CA 1129270 A CA1129270 A CA 1129270A CA 342133 A CA342133 A CA 342133A CA 1129270 A CA1129270 A CA 1129270A
- Authority
- CA
- Canada
- Prior art keywords
- radicals
- curable silicone
- composition
- silicone release
- silicon
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D5/00—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures
- B05D5/08—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain an anti-friction or anti-adhesive surface
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L83/00—Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon only; Compositions of derivatives of such polymers
- C08L83/04—Polysiloxanes
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D183/00—Coating compositions based on macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon, with or without sulfur, nitrogen, oxygen, or carbon only; Coating compositions based on derivatives of such polymers
- C09D183/04—Polysiloxanes
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
- C08G77/04—Polysiloxanes
- C08G77/12—Polysiloxanes containing silicon bound to hydrogen
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
- C08G77/04—Polysiloxanes
- C08G77/20—Polysiloxanes containing silicon bound to unsaturated aliphatic groups
Abstract
ABSTRACT OF THE DISCLOSURE
An improved coating process is provided which comprises applying to a substrate certain curable silicone release compositions which have a high ratio of silicon-bonded hydrogen radicals to silicon-bonded vinyl radicals. The curable silicone release composition further comprises a vinyl-containing, xylene-soluble siloxane resin copolymer. The high SiH/SiVi ratio oermits the effective lowering of the otherwise high viscosity of the composition, thereby improving its application to flexible substrates, such as paper, by roller coating methods.
An improved coating process is provided which comprises applying to a substrate certain curable silicone release compositions which have a high ratio of silicon-bonded hydrogen radicals to silicon-bonded vinyl radicals. The curable silicone release composition further comprises a vinyl-containing, xylene-soluble siloxane resin copolymer. The high SiH/SiVi ratio oermits the effective lowering of the otherwise high viscosity of the composition, thereby improving its application to flexible substrates, such as paper, by roller coating methods.
Description
This invention relates to an improved process for treating substrates to aid in the release of adhesive materials therefrom. .~ore specifically, this invention relates to a new substrate-coating process which uses a silicone release composition which cures rapidly, has improved resistance to abrasion and rub-off in the cured form and yet has a viscosity at room temperature that permits its application to the substrate by standard coating methods, without the necessity of using a volatile thinning medium, such as a solvent or a dispersant.
The term "adhesive materials" as employed herein means materials having a lasting sticky nature, such as pressure sensitive adhesives, foodstuffs, asphalt, pitch and raw rubber, in contrast to temporary sticky materials which become non-sticky, such as cements and moldin~ compositions.
The application of curable silicone release compositions to substrates to aid in the release of adhesive materials therefrom is old and well known in the coatings art. However, most, if not all, curable silicone compositions that have been used in the release coatings art suffer from a property trade-off which affects the viscosity of the curable composition, the release behavior of the cured coating and the abrasion resistance of the cured coating.
Specifically, with respect to the silicone compositions which cure by way of a catalyzed reaction of silicon-bonded vinyl radicals with silicon-bonded hydrogen radicals, this proper~y trade-off can be summarized in the following manner. Solventless, low-viscosity coating compositions, such as those disclosed by Chandra et al., U.S. Patent No. 3,928,629 and Grenoble, U.S.
Patent No. 4,071,644 are based on low-molecular weight, vinyl-containing polymers and, therefore, frequently lac~ the - . -.
~ J~
necessary strength, in the cured state, to sur~ive vigorous abrasion and flexing forces. Using a higher molecular weight polymer, instead of the low molecular weight polymer, such as is disclosed in U.K. Patent ~o. 1,240,523, is ~nown to provide increased strength to the cured coatins; however, the viscosity of the uncured composition is correspondingly increased, resulting in difficulty in applying the curable composition to a substrate.
Low viscosity is thereby traded for increased strength~ Cured silicone release compositions, whether based on high or low molecular weight polymer, have excellent release characteristics and are desired as abhesive, i.e., non-stick, coatings. ~owever, in many instances, such as in the preparation of a release backing for pressure-sensitive adhesive labels, easy release is not desired. To control the adhesive release behavior of a silicone composition and to provide additional strength, it has been taught by Sandford, U.S. Patent No. 4,123,604 to mix a vinyl-containing resin with the curable silicone composition. ~hether this resin is mixed with a low molecular weight polymer or a high molecular weight polymer, a considerable increase in the viscosity of the composition results. To obtain a solventless, low-vlscosity curable release composition from such a resin-containing mixture, a very low molecular weight, vinyl-containing polymer, including vinyl-containing cyclopolysiloxanes, must be used, thereby trading abrasion resistance for controlled release.
Of course, an obvious way to decrease the viscosity of a curable silicone release composition is to dissolve or disperse the composition in a volatile thinning medium; however, this expedient is undesirable from at least two aspects. First, environmental considerations suggest that it may be undesirable to vent a solvent to the atmosphere during the preparation and/or use 7C~
of the release composition. Second, recovery of a solvent from a release composition may be a prohibitively expensive process for the manufacturer and/or user o~ the release composition.
It is an object of this invention to provide an improved process for coating substrates which provides abrasion-resistant, adhesive-releasing coatings from solventless coating compositions.
This object and others are realized by applying to a surface of a substrate, ~rom which adhesive release is desired, certain fast-curing, tough silicone compositions having a high ratio of silicon-bonded hydrogen radicals to silicon-bonded vinyl radicals. Certain of the curable silicone compositions which are useful in the process of this invention have been disclosed as a marking ink composition and as a repair composition for surface imperfections on translucent silicone rubber articles. Others useful herein appear to be new.
This invention relates to an improved process for coating a substrate to provide release of adhesive materials therefrom, said process comprising applying a curable silicone release composition to a surface of the substrate and thereafter curing the applied composition, the improvement comprising applying, as the curable silicone release c~mposition, a composition obtained by mixing components consisting essentially of (I) a polydiorgano-siloxane having the general formula ViR2Sio(R2SiO)x~RViSiO)ySiR2Vi wherein x and y are integers whose sum has an average value sufficient to provide the polydiorganosiloxane with a viscosity at 25C. of at least 1.0 pascal-second, Vi denotes a vinyl radical and each R denotes, independently, a monovalent radical selected from the group consisting of methyl, phenyl and saturated hydrocarbon radicals having from 2 to 6 carbon atoms, the total number of organic radicals in the polydiorganosiloxane consisting
The term "adhesive materials" as employed herein means materials having a lasting sticky nature, such as pressure sensitive adhesives, foodstuffs, asphalt, pitch and raw rubber, in contrast to temporary sticky materials which become non-sticky, such as cements and moldin~ compositions.
The application of curable silicone release compositions to substrates to aid in the release of adhesive materials therefrom is old and well known in the coatings art. However, most, if not all, curable silicone compositions that have been used in the release coatings art suffer from a property trade-off which affects the viscosity of the curable composition, the release behavior of the cured coating and the abrasion resistance of the cured coating.
Specifically, with respect to the silicone compositions which cure by way of a catalyzed reaction of silicon-bonded vinyl radicals with silicon-bonded hydrogen radicals, this proper~y trade-off can be summarized in the following manner. Solventless, low-viscosity coating compositions, such as those disclosed by Chandra et al., U.S. Patent No. 3,928,629 and Grenoble, U.S.
Patent No. 4,071,644 are based on low-molecular weight, vinyl-containing polymers and, therefore, frequently lac~ the - . -.
~ J~
necessary strength, in the cured state, to sur~ive vigorous abrasion and flexing forces. Using a higher molecular weight polymer, instead of the low molecular weight polymer, such as is disclosed in U.K. Patent ~o. 1,240,523, is ~nown to provide increased strength to the cured coatins; however, the viscosity of the uncured composition is correspondingly increased, resulting in difficulty in applying the curable composition to a substrate.
Low viscosity is thereby traded for increased strength~ Cured silicone release compositions, whether based on high or low molecular weight polymer, have excellent release characteristics and are desired as abhesive, i.e., non-stick, coatings. ~owever, in many instances, such as in the preparation of a release backing for pressure-sensitive adhesive labels, easy release is not desired. To control the adhesive release behavior of a silicone composition and to provide additional strength, it has been taught by Sandford, U.S. Patent No. 4,123,604 to mix a vinyl-containing resin with the curable silicone composition. ~hether this resin is mixed with a low molecular weight polymer or a high molecular weight polymer, a considerable increase in the viscosity of the composition results. To obtain a solventless, low-vlscosity curable release composition from such a resin-containing mixture, a very low molecular weight, vinyl-containing polymer, including vinyl-containing cyclopolysiloxanes, must be used, thereby trading abrasion resistance for controlled release.
Of course, an obvious way to decrease the viscosity of a curable silicone release composition is to dissolve or disperse the composition in a volatile thinning medium; however, this expedient is undesirable from at least two aspects. First, environmental considerations suggest that it may be undesirable to vent a solvent to the atmosphere during the preparation and/or use 7C~
of the release composition. Second, recovery of a solvent from a release composition may be a prohibitively expensive process for the manufacturer and/or user o~ the release composition.
It is an object of this invention to provide an improved process for coating substrates which provides abrasion-resistant, adhesive-releasing coatings from solventless coating compositions.
This object and others are realized by applying to a surface of a substrate, ~rom which adhesive release is desired, certain fast-curing, tough silicone compositions having a high ratio of silicon-bonded hydrogen radicals to silicon-bonded vinyl radicals. Certain of the curable silicone compositions which are useful in the process of this invention have been disclosed as a marking ink composition and as a repair composition for surface imperfections on translucent silicone rubber articles. Others useful herein appear to be new.
This invention relates to an improved process for coating a substrate to provide release of adhesive materials therefrom, said process comprising applying a curable silicone release composition to a surface of the substrate and thereafter curing the applied composition, the improvement comprising applying, as the curable silicone release c~mposition, a composition obtained by mixing components consisting essentially of (I) a polydiorgano-siloxane having the general formula ViR2Sio(R2SiO)x~RViSiO)ySiR2Vi wherein x and y are integers whose sum has an average value sufficient to provide the polydiorganosiloxane with a viscosity at 25C. of at least 1.0 pascal-second, Vi denotes a vinyl radical and each R denotes, independently, a monovalent radical selected from the group consisting of methyl, phenyl and saturated hydrocarbon radicals having from 2 to 6 carbon atoms, the total number of organic radicals in the polydiorganosiloxane consisting
2~'0 of at least 95 percent rneth~l radicals and no more than 1 percent vinyl radicals, (II) a xylene-soluble copolymer of (CH3)3SiO1/2, (CH3)2(CH2=C~)SiOl/2 and SiO4/2 siloxane units, said copolymer having from 1 to 5 percent by weight of vinyl radisals, based on the weight of the copolymer, and a total of from 0.6 to 1.1 of said (CH3)3siOl/2 plus (CH3)2(CH2=CH)SiOl/2 siloxane units for every said SiO4/2 siloxane unit, (III) a methylhydrogenpoly-siloxane, soluble in the mixture of (I) plus ~II), and having an average of at least three silicon-bonded hydrogen radicals per molecule, said hydrogen radicals being bonded to separate silicon atoms, and (IV) a catalytic amount of a hydrosilylation catalyst, said components being mixed in sufficient amounts to provide, in the curable silicone release composition, from 10 to 70 parts by weight of (II) for every 100 parts by weight of (I) plus (II) and from 2 to 10 silicon-bonded hydrogen radicals for every silicon-bonded vinyl radical.
The four essential components, i.e., polydiorganosiloxane (I), xylene-soluble copolymer (II), methylhydrogenpolysiloxane (III) and hydrosilylation catalyst (IV), which are mixed to form 2~ the curable silicone composition which is used as a curable release agent in the improved process of this invention are all known, broadly, in the organopolysiloxane art.
Polydiorganosiloxane (I) is a vinyl-endblocked linear polymer having the general formula ViR2SiO(R2SiO)X(RViSiO)ySiR2Vi.
Each R denotes, independently, a methyl radical, a phenyl radical or a saturated hydrocarbon radical having 2 to 6, inclusive; carbon atoms such as alkyl radicals, such as ethyl, propyl, isopropyl, ~utyl and hexyl and cycloaliphatic radica's, such as cyclohexyl. At least 9S persent of all organic radicals
The four essential components, i.e., polydiorganosiloxane (I), xylene-soluble copolymer (II), methylhydrogenpolysiloxane (III) and hydrosilylation catalyst (IV), which are mixed to form 2~ the curable silicone composition which is used as a curable release agent in the improved process of this invention are all known, broadly, in the organopolysiloxane art.
Polydiorganosiloxane (I) is a vinyl-endblocked linear polymer having the general formula ViR2SiO(R2SiO)X(RViSiO)ySiR2Vi.
Each R denotes, independently, a methyl radical, a phenyl radical or a saturated hydrocarbon radical having 2 to 6, inclusive; carbon atoms such as alkyl radicals, such as ethyl, propyl, isopropyl, ~utyl and hexyl and cycloaliphatic radica's, such as cyclohexyl. At least 9S persent of all organic radicals
3(; in (I) are the methyi radical. Preferably, each termir.al silicon ~ 3 Z~t~
atom o~ poiydiorganosiloxane (I) bears at least one methyl radical. To avoid overcuring of the release composition, the total number of vinyl radicals in polydiorganosiloxane (I) should not exceed 1 percent of all of the silicon-bonded organic radicals therein.
Examples of preferred siloxane units which form polydiorganosiloxane (I) include ViMe2SiOl/2, Phl~eViSiOl/2, Me2SiO2/2 and MeViSiO2/2. Examples of other siloxane units suitable for use in polydiorganosiloxane (I) include PhViSiO2/2, Ph2SiO2/2, PhMeSiO2/2, ViEtSiO2/2 and ~eEtSiO2/2 siloxane units.
Herein the symbols ~e, Et, Ph and Vi denote, respectively, the methyl, ethyl, phenyl and vinyl radical.
Examples of preferred polydiorganosiloxanes (I) to be used in the process of this invention include ViMe2SiO(~e2SiO)xSiMe2Vi, ViPhMeSiO(Me2SiO)xSiMePhVi, ViMe2SiO(Me2SiO)x(ViMeSiO)ySiMe2Vi and ViPh~eSiO(Me2SiO)x(ViMeSiO)ySiMePhVi.
The average value of the sum of x plus y in the above formulae is such that the viscosity of the resulting polydiorgano-siloxane is at least 1.0 pascal-seconds (1000 centipoise) at 25C.
Preferred results, such as rapid cure rate of the curable composition and high abrasion resistance of the cured release coating, are obtained when said viscosity of the vinyl-endblocked polydiorganosiloxane is at least 25 pascal-seconds. There is no known upper limit to the viscosity of polydiorganosiloxane (I) unless a solventless coating composition is desired, in which case an upper viscosity limit is approximately 100 pascal-seconds.
The exact average value for the sum of x plus ~ which will produce a desired viscosity at 25C. for polydiorganosilox~ne (I) depends upon the amounts and types of R radicals present Ji~
therein and is difficult to predict. However, for the above-delineat~d preferred vinyl-endblocked polydiorganosiloxanes, an average value for x plus y of approximately 225 will provide a viscosity of 1.0 pascal-seconds and an average value of approximately 695 will provide a viscosity of 25 pascal-seconds, both measured at 25C.
Polydiorganosiloxanes (I) are well known in the organosilicon polymer art and may be prepared by any suitable method. While the preparation of polydiorganosiloxane (I) needs no further elaboration here, it should be noted that, depending upon the particular polydiorganosiloxane (I) that is prepared and the particular method for its preparation that is used, there may be coproduced therewith approximately 0 to 15 percent by weight of cyclopolydiorganosiloxanes. A large portion of said cyclopolydi-organosiloxanes may be volatile at temperatures up to 150C. It is to be noted that the suitability of vinyl-endblocked polydiorganosiloxane (I) for use in the process of this invention is determined by its viscosity at 25C., as delineated above, and does not depend upon the presence or absence therein of the above-described amounts of coproduced cyclopolydiorganosiloxanes.
That is to say, vinyl-endblocked polydiorganosiloxane (I) may be optionally freed of any volatile cyclopolydiorganosiloxanes, if desired, without having a detrimental effect on the process of this invention.
For the purposes of this invention, however, the viscosity and the amount of vinyl-endblocked polydiorganosiloxane (I) that is used, and which is further delineated belo~, are based on polydiorganosiloxane which has been devolatilized at 1~0C. for 1 hour.
~3 i~hile ~olydior~anosiloxane (I) is stated to be linear and to ~ear only hydrocar~on radicals on silicon, it is within the scope anà spirit of this invention to permit the presence therein of small amounts of non-linear siloxane units, i.e. SiO4/2, ViSiO3/2 and RSiO3/2 siloxane units wherein ~ is as denoted above, and trace amounts of other sillcon-bonded radicals, such as hydroxyl and alkoxyl, which are normally incidentally present in commercial polydiorganosiloxanes. Preferably, polydiorgano-siloxane ~I) is free of said non-linear siloxane units and said other radicals.
The xylene-soluble copolymer (II) of (CH3)3SiOl/2 siloxane units, (CH3)2(CH2=CH)SiOl/2 siloxane units and SiO4/2 siloxane units is ~ell known in the organosilicon polymer art~
Said copolymer is a solid, resinous material which is prepared as, and usually, but not necessarily, used as, a solution in an organic solvent. Typical solvents that are used with copolymer (II) include benzene, toluene, xylene, methylene chloride, perchloroethylene and naphtha mineral spirits.
Copolymer (II) contains from 1 to 5, preferably 1.5 to 3.5, percent by weight of vinyl radicals, based on the weight of the copolymer, ancl from 0.6 to 1.1 of the siloxane units bearing organic radicals for every SiO4~2 siloxane units. Thus, in copolymer (II), for every SiO4/2 unit there is a total of from 0.6 to 1-1 (CH3)3SiOl/2 units plus (cH3)2(cH2=cH)siol/2 units.
Copolymer (II) is preferably prepared by an adaptation of the procedure described by Daudt et al. in U.S. Patent Mo.
2,676,182 whereby a silica hydrosol is treated ~t lo~ pH with a source of trimethylsiloxane units, such as hexamethyldisiloxane or trimethylchlorosilane and a source of dimethylvinylsiioxane units, such as divinyltetramethyldisiloxane or dimethylvinylchlorosilane.
.~lternativeiv, a suitable mixture of hydrolyzable trimethyl-substituted, dimethyl-~inyl-substituted and organic radical free silanes t such as chlorosilanes and/or alkoxysilanes, may be cohydrolyzed. In this alternate procedure, the resulting cohydrolyzate is preferably subsequently treated with a suitable silylating agent, such as hexamethyldisilazane or divinyltetra-methyldisilazane, to reduce the hydroxyl content of the resulting resinous copolymer to less than 1 percent by weightA Minor amounts of diorganosiloxane units may be present in the copolymer (II).
Methylhydrogenpolysiloxane (III) operates as a curing agent for the mixture of polydiorganosiloxane (I) and xylene-soluble copolymer (II) and therefore must be soluble therein and must contain an average of at least three, preferably more than three, silicon-bonded hydrogen radicals per molecule.
The term "methylhydrogenpolysiloxane" means that at least three, but preferably all, silicon atoms therein which bear the hydrogen radicals also bear at least one methyl radical. For efficient curing of the mixture of (I) plus (II), it is preferred that no silicon atom in IIII) bear more than one silicon-bonded hydrogen radical. Methylhydrogenpolysiloxane (III) may also contain silicon-bonded phenyl radicals and silicon-bonded alkyl radicals having from 2 to 6 carbon atoms, provided that it is soluble in the mixture of (I) plus (II).
Methylhydrogenpolysiloxane (III) is preferably a fluid having a low viscosity, such as less than 0.1 pascal-seconds at 25C., thereby considerably and desirably decreasing the initial, i.e., uncatalyzed, viscosity of the mixture of polydiorgano-siloxane (I) and copolymer (II) when mixed therewith. It is desirable to decrease the viscosity of the mixture of (I) plus 1~2~3~, ~
(II) because application of the resulting curable composition onto, and adhesion of the suhsequently cured composition to, a substrate is aided thereby. The viscosity of the mixture of (I) 2Ius (II) can be considerably decreased by the use of a low viscosity methylhydrogenpolysiloxane as component (III) because the curable silicone compositions which are uni~uely operative in the process of this invention have an unusually high ratio of silicon-bonded hydrogen radicals to silicon-bonded vinyl radicals, further delineated below, thereby permitting the use of relatively large amounts of any particular methylhydrogenpolysiloxane (III).
Preferred siloxane units which form the methylhydrogen-polysiloxane (III) include Me3Sil/2~ Me2HSiOl/2~ Me2Si2~2~
MeHSiO2/2, MeSiO3/2, and SiO4/2. Methylhydrogenpolysiloxane (III) may also further comprise other siloxane units, such as HSiO3/2, PhHSiO2/2, PhMeHSiOl/2, PhMeSiO2/2 and PhSiO3/2, provided that the resulting methylhydrogenpolysiloxane is soluble in the mixture of (I) plus (II).
Examples of methylhydrogenpolysiloxane (III) whicA are operative in the process of this invention include, but are not limited to, siloxanes consisting of Me3SiOl/2 units and MeHSiO2/2 units, siloxanes consisting of Me3siol/2 units, Me2SiO2/2 units and MeHSiO2/2 UllitS, siloxanes consisting of HMe2SiOl/2 units, Me2SiO2/2 units and MeHSiO2/2 units, siloxanes consisting of SiO4/2 units, Me3SiOl~2 units and HMe2SiOl/2 units, siloxanes consisting of SiO4/2 units and HMe2SiOl/2 units, siloxanes consisting of HMeSiO2/2 units and siloxanes consisting of HMeSiO2/2 units and Me2SiO2/2 units.
Specific examples of sultable methylhydrogenpolysiloxanes that may be used as component (III) in the process of this 33 invention include (HMe2sio~4si~ (.YeHSiO)4, MeSi(OSiMe2H~, 2'~
PhSi(OSiMe2H)3 and, preferably, higher molecular weight fluid siloxanes having t~e average formulae ~e3SiO(MeHSiO)35SiMe3, Me3SiO(~e2SiO)3(1~eHSiO)5Sii~e3 and HMe2SiO(Me2SiO)3(.~eHSiO)5Si~e2H.
The higher molecular weight methylhydrogenpolysiloxanes are preferred as a curing component for a silicone release composition because said higher molecular weight methylhydrogenpolysiloxanes have a low volatility and will remain with and more effectively cure the silicon release composition at elevated temperatures.
I~ethylhydrogenpolysiloxanes are well known in the organosilicon polymer art; their preparation therefore needs no further elaboration here. As in the case of the preparation of vinyl-endblocked polydiorganosiloxanes, it should be noted that the preparation of methylhydrogenpolysiloxanes comprising diorganosiloxane units may produce small amounts of cyclopolydi-organosiloxanes. The presence or absence of these cyclopolydi-organosiloxane species in the methylhydrogenpolysiloxane is of no importance to this invention as long as the methylhydrogenpolysiloxane has an average of at least 3 silicon-bonded hydrogens per molecule.
Component (IV) is any hydrosilylation catalyst that is effective to catalyze the addition reaction of silicon-bonded hydrogen radicals with silicon-bonded vinyl radicals in the well known manner. Typically, component (IV) is an active metal containing composition such as a platinum-containing compound or a rhodium-containing compound. Examples of these active metal compositions include chloroplatinic acid, platinum deposited on a substrate, platinum complexed with organic liquids, such as ketones, vinylsiloxanes and ethylene, and complexes of rhodium halides. Preferably, the hydrosilylation catalyst is soluble in the curable silicone release composition.
3~t~l~3 The platinum-containing catalysts may also contain an inhibitor to ~oderate its catalytic activity at room temperature, in the well ~nown manner, if desired. ~hodium-containing catalysts do not need room temperature inhibiting.
Hydrosilylation catalysts and their inhibitors are well known in the organosilicon art and need no further delineation herein. For further details, if needed, the reader is directed to the teachings of Speier et al., U.S. Patent No. 2,823,218;
Willing, U.S. Patent No. 3,419,593; Xookootsedes et al., U.S.
Patent No. 3,445,~20; Chandra, U.S. Patent No. 3,890,359;
Polmanteer et al., UOS. Patent No. 3,697,473; Nitzsche et al., U.S. Patent ~7O. 3,814,731; and Sandford, U.S. Patent No.
atom o~ poiydiorganosiloxane (I) bears at least one methyl radical. To avoid overcuring of the release composition, the total number of vinyl radicals in polydiorganosiloxane (I) should not exceed 1 percent of all of the silicon-bonded organic radicals therein.
Examples of preferred siloxane units which form polydiorganosiloxane (I) include ViMe2SiOl/2, Phl~eViSiOl/2, Me2SiO2/2 and MeViSiO2/2. Examples of other siloxane units suitable for use in polydiorganosiloxane (I) include PhViSiO2/2, Ph2SiO2/2, PhMeSiO2/2, ViEtSiO2/2 and ~eEtSiO2/2 siloxane units.
Herein the symbols ~e, Et, Ph and Vi denote, respectively, the methyl, ethyl, phenyl and vinyl radical.
Examples of preferred polydiorganosiloxanes (I) to be used in the process of this invention include ViMe2SiO(~e2SiO)xSiMe2Vi, ViPhMeSiO(Me2SiO)xSiMePhVi, ViMe2SiO(Me2SiO)x(ViMeSiO)ySiMe2Vi and ViPh~eSiO(Me2SiO)x(ViMeSiO)ySiMePhVi.
The average value of the sum of x plus y in the above formulae is such that the viscosity of the resulting polydiorgano-siloxane is at least 1.0 pascal-seconds (1000 centipoise) at 25C.
Preferred results, such as rapid cure rate of the curable composition and high abrasion resistance of the cured release coating, are obtained when said viscosity of the vinyl-endblocked polydiorganosiloxane is at least 25 pascal-seconds. There is no known upper limit to the viscosity of polydiorganosiloxane (I) unless a solventless coating composition is desired, in which case an upper viscosity limit is approximately 100 pascal-seconds.
The exact average value for the sum of x plus ~ which will produce a desired viscosity at 25C. for polydiorganosilox~ne (I) depends upon the amounts and types of R radicals present Ji~
therein and is difficult to predict. However, for the above-delineat~d preferred vinyl-endblocked polydiorganosiloxanes, an average value for x plus y of approximately 225 will provide a viscosity of 1.0 pascal-seconds and an average value of approximately 695 will provide a viscosity of 25 pascal-seconds, both measured at 25C.
Polydiorganosiloxanes (I) are well known in the organosilicon polymer art and may be prepared by any suitable method. While the preparation of polydiorganosiloxane (I) needs no further elaboration here, it should be noted that, depending upon the particular polydiorganosiloxane (I) that is prepared and the particular method for its preparation that is used, there may be coproduced therewith approximately 0 to 15 percent by weight of cyclopolydiorganosiloxanes. A large portion of said cyclopolydi-organosiloxanes may be volatile at temperatures up to 150C. It is to be noted that the suitability of vinyl-endblocked polydiorganosiloxane (I) for use in the process of this invention is determined by its viscosity at 25C., as delineated above, and does not depend upon the presence or absence therein of the above-described amounts of coproduced cyclopolydiorganosiloxanes.
That is to say, vinyl-endblocked polydiorganosiloxane (I) may be optionally freed of any volatile cyclopolydiorganosiloxanes, if desired, without having a detrimental effect on the process of this invention.
For the purposes of this invention, however, the viscosity and the amount of vinyl-endblocked polydiorganosiloxane (I) that is used, and which is further delineated belo~, are based on polydiorganosiloxane which has been devolatilized at 1~0C. for 1 hour.
~3 i~hile ~olydior~anosiloxane (I) is stated to be linear and to ~ear only hydrocar~on radicals on silicon, it is within the scope anà spirit of this invention to permit the presence therein of small amounts of non-linear siloxane units, i.e. SiO4/2, ViSiO3/2 and RSiO3/2 siloxane units wherein ~ is as denoted above, and trace amounts of other sillcon-bonded radicals, such as hydroxyl and alkoxyl, which are normally incidentally present in commercial polydiorganosiloxanes. Preferably, polydiorgano-siloxane ~I) is free of said non-linear siloxane units and said other radicals.
The xylene-soluble copolymer (II) of (CH3)3SiOl/2 siloxane units, (CH3)2(CH2=CH)SiOl/2 siloxane units and SiO4/2 siloxane units is ~ell known in the organosilicon polymer art~
Said copolymer is a solid, resinous material which is prepared as, and usually, but not necessarily, used as, a solution in an organic solvent. Typical solvents that are used with copolymer (II) include benzene, toluene, xylene, methylene chloride, perchloroethylene and naphtha mineral spirits.
Copolymer (II) contains from 1 to 5, preferably 1.5 to 3.5, percent by weight of vinyl radicals, based on the weight of the copolymer, ancl from 0.6 to 1.1 of the siloxane units bearing organic radicals for every SiO4~2 siloxane units. Thus, in copolymer (II), for every SiO4/2 unit there is a total of from 0.6 to 1-1 (CH3)3SiOl/2 units plus (cH3)2(cH2=cH)siol/2 units.
Copolymer (II) is preferably prepared by an adaptation of the procedure described by Daudt et al. in U.S. Patent Mo.
2,676,182 whereby a silica hydrosol is treated ~t lo~ pH with a source of trimethylsiloxane units, such as hexamethyldisiloxane or trimethylchlorosilane and a source of dimethylvinylsiioxane units, such as divinyltetramethyldisiloxane or dimethylvinylchlorosilane.
.~lternativeiv, a suitable mixture of hydrolyzable trimethyl-substituted, dimethyl-~inyl-substituted and organic radical free silanes t such as chlorosilanes and/or alkoxysilanes, may be cohydrolyzed. In this alternate procedure, the resulting cohydrolyzate is preferably subsequently treated with a suitable silylating agent, such as hexamethyldisilazane or divinyltetra-methyldisilazane, to reduce the hydroxyl content of the resulting resinous copolymer to less than 1 percent by weightA Minor amounts of diorganosiloxane units may be present in the copolymer (II).
Methylhydrogenpolysiloxane (III) operates as a curing agent for the mixture of polydiorganosiloxane (I) and xylene-soluble copolymer (II) and therefore must be soluble therein and must contain an average of at least three, preferably more than three, silicon-bonded hydrogen radicals per molecule.
The term "methylhydrogenpolysiloxane" means that at least three, but preferably all, silicon atoms therein which bear the hydrogen radicals also bear at least one methyl radical. For efficient curing of the mixture of (I) plus (II), it is preferred that no silicon atom in IIII) bear more than one silicon-bonded hydrogen radical. Methylhydrogenpolysiloxane (III) may also contain silicon-bonded phenyl radicals and silicon-bonded alkyl radicals having from 2 to 6 carbon atoms, provided that it is soluble in the mixture of (I) plus (II).
Methylhydrogenpolysiloxane (III) is preferably a fluid having a low viscosity, such as less than 0.1 pascal-seconds at 25C., thereby considerably and desirably decreasing the initial, i.e., uncatalyzed, viscosity of the mixture of polydiorgano-siloxane (I) and copolymer (II) when mixed therewith. It is desirable to decrease the viscosity of the mixture of (I) plus 1~2~3~, ~
(II) because application of the resulting curable composition onto, and adhesion of the suhsequently cured composition to, a substrate is aided thereby. The viscosity of the mixture of (I) 2Ius (II) can be considerably decreased by the use of a low viscosity methylhydrogenpolysiloxane as component (III) because the curable silicone compositions which are uni~uely operative in the process of this invention have an unusually high ratio of silicon-bonded hydrogen radicals to silicon-bonded vinyl radicals, further delineated below, thereby permitting the use of relatively large amounts of any particular methylhydrogenpolysiloxane (III).
Preferred siloxane units which form the methylhydrogen-polysiloxane (III) include Me3Sil/2~ Me2HSiOl/2~ Me2Si2~2~
MeHSiO2/2, MeSiO3/2, and SiO4/2. Methylhydrogenpolysiloxane (III) may also further comprise other siloxane units, such as HSiO3/2, PhHSiO2/2, PhMeHSiOl/2, PhMeSiO2/2 and PhSiO3/2, provided that the resulting methylhydrogenpolysiloxane is soluble in the mixture of (I) plus (II).
Examples of methylhydrogenpolysiloxane (III) whicA are operative in the process of this invention include, but are not limited to, siloxanes consisting of Me3SiOl/2 units and MeHSiO2/2 units, siloxanes consisting of Me3siol/2 units, Me2SiO2/2 units and MeHSiO2/2 UllitS, siloxanes consisting of HMe2SiOl/2 units, Me2SiO2/2 units and MeHSiO2/2 units, siloxanes consisting of SiO4/2 units, Me3SiOl~2 units and HMe2SiOl/2 units, siloxanes consisting of SiO4/2 units and HMe2SiOl/2 units, siloxanes consisting of HMeSiO2/2 units and siloxanes consisting of HMeSiO2/2 units and Me2SiO2/2 units.
Specific examples of sultable methylhydrogenpolysiloxanes that may be used as component (III) in the process of this 33 invention include (HMe2sio~4si~ (.YeHSiO)4, MeSi(OSiMe2H~, 2'~
PhSi(OSiMe2H)3 and, preferably, higher molecular weight fluid siloxanes having t~e average formulae ~e3SiO(MeHSiO)35SiMe3, Me3SiO(~e2SiO)3(1~eHSiO)5Sii~e3 and HMe2SiO(Me2SiO)3(.~eHSiO)5Si~e2H.
The higher molecular weight methylhydrogenpolysiloxanes are preferred as a curing component for a silicone release composition because said higher molecular weight methylhydrogenpolysiloxanes have a low volatility and will remain with and more effectively cure the silicon release composition at elevated temperatures.
I~ethylhydrogenpolysiloxanes are well known in the organosilicon polymer art; their preparation therefore needs no further elaboration here. As in the case of the preparation of vinyl-endblocked polydiorganosiloxanes, it should be noted that the preparation of methylhydrogenpolysiloxanes comprising diorganosiloxane units may produce small amounts of cyclopolydi-organosiloxanes. The presence or absence of these cyclopolydi-organosiloxane species in the methylhydrogenpolysiloxane is of no importance to this invention as long as the methylhydrogenpolysiloxane has an average of at least 3 silicon-bonded hydrogens per molecule.
Component (IV) is any hydrosilylation catalyst that is effective to catalyze the addition reaction of silicon-bonded hydrogen radicals with silicon-bonded vinyl radicals in the well known manner. Typically, component (IV) is an active metal containing composition such as a platinum-containing compound or a rhodium-containing compound. Examples of these active metal compositions include chloroplatinic acid, platinum deposited on a substrate, platinum complexed with organic liquids, such as ketones, vinylsiloxanes and ethylene, and complexes of rhodium halides. Preferably, the hydrosilylation catalyst is soluble in the curable silicone release composition.
3~t~l~3 The platinum-containing catalysts may also contain an inhibitor to ~oderate its catalytic activity at room temperature, in the well ~nown manner, if desired. ~hodium-containing catalysts do not need room temperature inhibiting.
Hydrosilylation catalysts and their inhibitors are well known in the organosilicon art and need no further delineation herein. For further details, if needed, the reader is directed to the teachings of Speier et al., U.S. Patent No. 2,823,218;
Willing, U.S. Patent No. 3,419,593; Xookootsedes et al., U.S.
Patent No. 3,445,~20; Chandra, U.S. Patent No. 3,890,359;
Polmanteer et al., UOS. Patent No. 3,697,473; Nitzsche et al., U.S. Patent ~7O. 3,814,731; and Sandford, U.S. Patent No.
4,123,604.
The vinyl-containing components of the curable silicone release composition are mixed in amounts sufficient to provide from 10 to 70 parts by weight of the xylene-soluble copolymer (II) for every 100 parts by weight of the mixture of vinyl-endblocked polydiorganosiloxane (I) plus copolymer (II). A preferred combination of properties, for the cured release agent, such as premium release of aggressive acrylic adhesives and high film strength, is obtained when the curable composition contains a mixture of (I) and (II) which is from 20 to 60 percent by weight ccmponent (II).
The desired amounts of (I) and (II) are used on a non-~olatile basis. This is easily achieved by subjecting samples of the polydiorganosiloxane, which frequently contains volatile cyclopolydiorganosiloxanes, and xylene-soluble copolymer, which is usually prepared and handled in xylene, to a devolatilization procedure at 150C. for 1 hour to determine the non-volatile ~0 content of each and using a sufficient quantity of each material v to ob_ain the desired amount of the vinyl-elldblocked polydiorgano-siloxane (I) and :~ylene-soluble copolymer (II) in the curable composition.
The amount of methylhydrogenpolysiloxane (III) to be mi~ed when preparing the curable silicone release composition is merely the amount that will provide from 2 to 10 silicon-bonded hydrogen radicals for every siiicon-bonded vinyl radical in the composition and the desired viscosity for the silicone release composition. For any given resin concentration in the resin plus polymer mixture, the amount of methylhydrogenpolysiloxane (III) that is needed to obtain a suitable coating viscosity for the curable composition is related to the viscosity of the polymer (I). Thus, a curable composition comprising a polydiorgano-siloxane (I) having a viscosity of 5 pascal-seconds may have a suitable coating viscosity when the SiH/SiVi ratio is 2.0; whereas a curable composition containing the same amount of resin but comprising a polydiorganosiloxane (I) having a viscosity of 100 pascal-seconds may require a Si~/SiVi ratio of 10.0 to provide a suitable coating viscosity for the curable composition. A
preferred value for this ratio of hydrogen radicals to vinyl radicals is from 2 to 5 wherein the hydrogen gassing, sometimes observed at higher ratios, is usually avoided.
The number of said silicon-bonded hydrogen radicals and said silicon-bonded vinyl radicals should be measured by suitable analytical techniques.
The amount of hydrosilylation catalyst to be used in the curable silicone release composition is merely that amount that will catalyze the addition of silicon-bonded hydrogen to silicon-bonded vinyl and provide the desired cure time at a ~articular curing temperature for the curable silicone release 1~L2~Z~7~
compositions. ~ suitable catalytic amount of hydrosilylation catalyst can be determined by simple experimentation. A
composition soluble, platinum-containing catalyst is typically used in sufficient amount to provide from 0.5 to 20 parts by weight of platinum for every one million parts by weight of components (I) plus (II) plus (III). A composition soluble, rhodium-containing catalyst is typically used in sufficient amount to provide from 5 to 40 parts per million of rhodium, on the same weight basis.
The curable silicone release composition may further contain up to 95 percent by weight, based on the weight of the curable composition, of a volatile thinning medium having a normal boiling point of less than 150C., such as a dispersant or a solvent, to aid in mixing and using said composition, if desired.
A volatile thinning medium is advantageously employed when further reduc~ion in the viscosity of the curable silicone composition, beyond that conferred by the methylhydrogenpolysiloxane, is desired.
Conveniently, said thinning medium is the solvent in which the xylene-soluble copolymer (II) is normally prepared and handled.
Organic thinning media should be free of aliphatic ~nsaturation.
The curable silicone release composition may further contain additional components which do not adversely interfere with the curing of the composition or its use as a release agent, such as pigments, rheology-control additives, substrate-adhesion promoters and adjuvants to control substrate penetration by the release composition.
The curable silicone release composition is prepared by mixing the desired amounts of the four essential components and any additional components in any suitable manner such as by stirringl blending and/or tumbling and in any suitable order.
t~
Prefera~ly, the methylhydrogenpolysiloxane (III) and the hydrosilylatior. c~talyst ~IV) are brought together in a final mixing step.
For example, the curable silicone release composition can be conveniently prepared by preparing two non-curing compositions which, when blended in proper proportions, will give rise to the curable silicone release composition. Typically, one of said non-curing compositions comprises a portion of the polydiorgano-siloxane (I), the xylene-soluble copolymer (II), optionally containing its processing solvent such as xylene, and the methyl-hydrogenpolysiloxane (III) and another of said non-curing compositions comprises the balance of the polydiorganosiloxane (I) and the hydrosilylation catalyst (IV) and any inhibitor.
Alternately, one of said non-curing compositions may comprise all of the ccmponents except the methylhydrogenpolysiloxane, which constitutes another non-curing composition to be mixed with the first non-curing composition at the proper time.
Any solid substrate may be treated by the process of this invention to provide release of adhesive materials therefrom.
Examples of suitable substrates include cellulosic materials, such as paper, cardboard, and wood; metals, such as aluminum, iron and steel; siliceous materials, such as ceramics, glass and concrete;
and synthetics, such as polyester and polyepoxide. To assure proper curing and adhesion of the curable silicone release composition, the substrate to which it is applied should be clean and free of materials which undesirably inhibit the cure of the release composition, such as materials containing amines, mercaptans and phosphines.
The process of this invention is particularly useful for coating flexible substrates, such as paper, aluminum foil, and tapes to provide controlled release of pressure-sensitive adhesive materials, such as aggressive acrylic adhesives. The curable silicone release composition may be applied in a thin layer to the surface of the flexible substrate to provide a coating with a mass of approximately one gram per square metre of coated surface. In the cured state, ~any of these coatings will release aggressive acrylic adhesives with a force of no more than 38.61 newtons/metre as measured by the method described in the examples. It is to be understood that thinner or thicker coatings of release composition may be applied to the substrate, if desired. In the paper coating art, the amoun' of release coating will generally be applied in an amount between 0.1 and 2.0 grams per square metre of surface.
In the process of the invention, the curable silicone release compositions may be applied to a substrate by any suitable means, such as by brushing, dipping, spraying, rolling and spreading. Flexible substrates, such as paper, may also be coated by any of the well known rolling methods, such as by a trailing blade coater, kiss rolls, gravure rolls and offset printing rolls as desired.
For general applications, a practical upper limit for the viscosity of the curable silicone release composition is ap2roximately lO0 pascal-seconds; however, for coating flexible substrates by rolling methods, a practical upper limit for said viscosity is approximately 50 pascal-seconds, preferably 10 pascal-seconds at 25C. In many instances, the release compositions used in the process of this invention have a viscosity which is useful in said roller methods of coating without comprising a significant amount; for example, less than 5 percent by weight, of a volatile thinning medium.
9;2~
After application to a substrate r the curable silicone release composition is allowed to cure and any volatile thinning medium is allowed to evaporate. Preferably, said curing and evaporating are accelerated by the application of heat to the applied composition. Heating, usually limited to temperatures less than 300C., preferably less than 200C., may be accomplished by any suitable means; however, the curable silicone release composition should not be heated much above room temperature before it is applied because it will rapidly gel and become unusable.
The invention having been fully described, it will now be exemplified, but not limited, by the following examples, which also include the best mode for practicing the invention.
For this disclosure, all viscosities were measured in centipoise at 25C. and were converted to pascal-seconds by multiplying by 0.0001 and rounding off. Adhesive release was measured in grams/inch and was converted to newtons/metre by multiplying by 0.3860885 and rounding off. Tensile strength was measured in pounds/square inch and was converted to mega-pascals by multiplying by 6.894757 x 10-3 and rounding off. All parts, percentages and ratios are by weight unless otherwise indicated.
These examples illustrate the viscosity-lowering that is obtained by using a high SiH/SiVi ratio in a curable, vinyl resin-containing silicone release composition.
Examples Release agents, designated by letters A through L in the Table, were prepared by mixing sufficient poiydiorganosiloxane and resin copolymer solution to provide the indicated ratio of non-volatile polydiorganosiloxane to non-volatile resin copoiymer.
The polydiorganosiloxane consis~ed of 91 percent of a non-volatile ~ethylpn~nylvinylsilo~rle-endbloc1~ed ~lydimethylsilox~ne having a viscosity of approximately 65 pascal seconds at 25C. and 9 percent o~ volatile cyclic polydimethylsiloxanes.
The r~sin copolymer solution consisted of 34.5 percent xylene and 65.5 percent o~ a non-volatile resin copolymer having (CH3)3SiOl~2, (CH3)2(CH2=CH)SiOl~2 and SiO4/2 siloxane units wherein the mol ratio of the sum of the methyl- and vinyl-bearing siloxane units to the SiO4/2 siloxane units had a value of 0.7 and the vinyl content was 1.7 percent. The resulting mixtures were devolatilized for 3 hours under reduced pressure and at steam temperatures and, after being cooled, were mixed with sufficient methylhydrogenpolysiloxane to provide the indicated ratio of silicon-bonded hydrogen radicals to silicon-bonded vinyl radicals and 0.004 percent methylbutynol as a platinum-catalyzed cure control additive. The methylhydrogenpolysiloxane had the average formula l~e3SiO(Me2SiO)3(i~eHSiO)5SiMe3.
The viscosities of these mixtures were then measured with a rotating spindle viscometer at 25C. and are recorded in the Table. The percent viscosity decrease is based on the viscosity of the corresponding comparative composition (A, E or I).
Samples were prepared for tensile strengtA and elongation measurements by catalyzing the devolatilized mixture of vinyl-containing polymer, vinyl-containing resin copolymer, methylhydrogenpolysiloxane and cure control additive with 0.012 percent of the platinum-containing catalyst containing 0.6 percent platinum. The platinum-containing catalyst was a complex of PtCl6-6H2O and divinyltetramethyldisiloxane, prepared according to U.S. Patent No. 3,419,593. The catalyzed compositions were poured into 7.6 cm. x 12.7 cm. x ~0 mil chases and were heated at 70C. for 15 minutes and at 177C. for 5 minutes. The cured samples, after being cooled, were cut into "dog-bone" samples.
Tensile strength and elongation were measured according to ASTM
D-~12, using these "dog-~one" samples, and are recorded in the Table.
Adhesi~Je release was measured on compositions A, C, E and G, except that the mixtures of polydiorganosiloxane and resin copolymer solution were not devolatilized before being mixed with methylhydrogenpolysiloxane and catalyst and applied to a substrate.
Catalyzed formulations A, C, E and G were coated onto 40 pound supercalendared kraft paper uslng a blade coater at 35 p.s.i. pressure to give approximately 0.8 grams of coating per square metre of surface. The applied coatings were heated at 163C. for 60 seconds to cause curlng. A coating was considered to be cured if a piece of adhesive tape would stic~ to itself after having first been adhered to the coating and then removed and its adhesive-bearing surface doubled back on itself. A11 coatings passed this cure test. The abrasion resistance of each cured formulation was determined by rubbing the cured coating with the index finger to see if rub-off occurred. No rub-off occurred.
~11 coatings therefore passed this test for abrasion resistance.
Each cured release coating was prepared for release testing according to the following procedure. The cured release coating was coated with adhesive using a solution of a commercial acrylic adhesive. The acrylic adhesive solution was applied to the cured coating at a wet thickness of 3 mils (76.2 um) using a Bird Bar. The applied adhesive was air dried at room temperature for one minute, heated at 70C. for 30 seconds and then cooled to room temperature again for 1 minute. A sheet of 60 pound matte litho was applied to the dried adhesive and the resulting laminate 3~
lP~9.~t3~
was rolled with 3 4 . 5 Dound rubber-coated roller and aged for 20 hours at 70C.
Release testing of the laminates was accomplished by cooling the aged laminates to room temperature, cutting the cooled laminates into 1 inch (25.4 mm) wide strips and pulling the matte/adhesive lamina from the kraft paper/coating lamina at an angle of 180 (~ radians) at 400 inches/minute (0.17 m/s). The force, in grams per inch, that was required to separate the laminae was noted. A composition that results in a release value of no more than 38.61 N/m using this test is considered to display premium release.
The Table summarizes the release values (converted from grams/inch to newtons/metre) that were obtained.
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The vinyl-containing components of the curable silicone release composition are mixed in amounts sufficient to provide from 10 to 70 parts by weight of the xylene-soluble copolymer (II) for every 100 parts by weight of the mixture of vinyl-endblocked polydiorganosiloxane (I) plus copolymer (II). A preferred combination of properties, for the cured release agent, such as premium release of aggressive acrylic adhesives and high film strength, is obtained when the curable composition contains a mixture of (I) and (II) which is from 20 to 60 percent by weight ccmponent (II).
The desired amounts of (I) and (II) are used on a non-~olatile basis. This is easily achieved by subjecting samples of the polydiorganosiloxane, which frequently contains volatile cyclopolydiorganosiloxanes, and xylene-soluble copolymer, which is usually prepared and handled in xylene, to a devolatilization procedure at 150C. for 1 hour to determine the non-volatile ~0 content of each and using a sufficient quantity of each material v to ob_ain the desired amount of the vinyl-elldblocked polydiorgano-siloxane (I) and :~ylene-soluble copolymer (II) in the curable composition.
The amount of methylhydrogenpolysiloxane (III) to be mi~ed when preparing the curable silicone release composition is merely the amount that will provide from 2 to 10 silicon-bonded hydrogen radicals for every siiicon-bonded vinyl radical in the composition and the desired viscosity for the silicone release composition. For any given resin concentration in the resin plus polymer mixture, the amount of methylhydrogenpolysiloxane (III) that is needed to obtain a suitable coating viscosity for the curable composition is related to the viscosity of the polymer (I). Thus, a curable composition comprising a polydiorgano-siloxane (I) having a viscosity of 5 pascal-seconds may have a suitable coating viscosity when the SiH/SiVi ratio is 2.0; whereas a curable composition containing the same amount of resin but comprising a polydiorganosiloxane (I) having a viscosity of 100 pascal-seconds may require a Si~/SiVi ratio of 10.0 to provide a suitable coating viscosity for the curable composition. A
preferred value for this ratio of hydrogen radicals to vinyl radicals is from 2 to 5 wherein the hydrogen gassing, sometimes observed at higher ratios, is usually avoided.
The number of said silicon-bonded hydrogen radicals and said silicon-bonded vinyl radicals should be measured by suitable analytical techniques.
The amount of hydrosilylation catalyst to be used in the curable silicone release composition is merely that amount that will catalyze the addition of silicon-bonded hydrogen to silicon-bonded vinyl and provide the desired cure time at a ~articular curing temperature for the curable silicone release 1~L2~Z~7~
compositions. ~ suitable catalytic amount of hydrosilylation catalyst can be determined by simple experimentation. A
composition soluble, platinum-containing catalyst is typically used in sufficient amount to provide from 0.5 to 20 parts by weight of platinum for every one million parts by weight of components (I) plus (II) plus (III). A composition soluble, rhodium-containing catalyst is typically used in sufficient amount to provide from 5 to 40 parts per million of rhodium, on the same weight basis.
The curable silicone release composition may further contain up to 95 percent by weight, based on the weight of the curable composition, of a volatile thinning medium having a normal boiling point of less than 150C., such as a dispersant or a solvent, to aid in mixing and using said composition, if desired.
A volatile thinning medium is advantageously employed when further reduc~ion in the viscosity of the curable silicone composition, beyond that conferred by the methylhydrogenpolysiloxane, is desired.
Conveniently, said thinning medium is the solvent in which the xylene-soluble copolymer (II) is normally prepared and handled.
Organic thinning media should be free of aliphatic ~nsaturation.
The curable silicone release composition may further contain additional components which do not adversely interfere with the curing of the composition or its use as a release agent, such as pigments, rheology-control additives, substrate-adhesion promoters and adjuvants to control substrate penetration by the release composition.
The curable silicone release composition is prepared by mixing the desired amounts of the four essential components and any additional components in any suitable manner such as by stirringl blending and/or tumbling and in any suitable order.
t~
Prefera~ly, the methylhydrogenpolysiloxane (III) and the hydrosilylatior. c~talyst ~IV) are brought together in a final mixing step.
For example, the curable silicone release composition can be conveniently prepared by preparing two non-curing compositions which, when blended in proper proportions, will give rise to the curable silicone release composition. Typically, one of said non-curing compositions comprises a portion of the polydiorgano-siloxane (I), the xylene-soluble copolymer (II), optionally containing its processing solvent such as xylene, and the methyl-hydrogenpolysiloxane (III) and another of said non-curing compositions comprises the balance of the polydiorganosiloxane (I) and the hydrosilylation catalyst (IV) and any inhibitor.
Alternately, one of said non-curing compositions may comprise all of the ccmponents except the methylhydrogenpolysiloxane, which constitutes another non-curing composition to be mixed with the first non-curing composition at the proper time.
Any solid substrate may be treated by the process of this invention to provide release of adhesive materials therefrom.
Examples of suitable substrates include cellulosic materials, such as paper, cardboard, and wood; metals, such as aluminum, iron and steel; siliceous materials, such as ceramics, glass and concrete;
and synthetics, such as polyester and polyepoxide. To assure proper curing and adhesion of the curable silicone release composition, the substrate to which it is applied should be clean and free of materials which undesirably inhibit the cure of the release composition, such as materials containing amines, mercaptans and phosphines.
The process of this invention is particularly useful for coating flexible substrates, such as paper, aluminum foil, and tapes to provide controlled release of pressure-sensitive adhesive materials, such as aggressive acrylic adhesives. The curable silicone release composition may be applied in a thin layer to the surface of the flexible substrate to provide a coating with a mass of approximately one gram per square metre of coated surface. In the cured state, ~any of these coatings will release aggressive acrylic adhesives with a force of no more than 38.61 newtons/metre as measured by the method described in the examples. It is to be understood that thinner or thicker coatings of release composition may be applied to the substrate, if desired. In the paper coating art, the amoun' of release coating will generally be applied in an amount between 0.1 and 2.0 grams per square metre of surface.
In the process of the invention, the curable silicone release compositions may be applied to a substrate by any suitable means, such as by brushing, dipping, spraying, rolling and spreading. Flexible substrates, such as paper, may also be coated by any of the well known rolling methods, such as by a trailing blade coater, kiss rolls, gravure rolls and offset printing rolls as desired.
For general applications, a practical upper limit for the viscosity of the curable silicone release composition is ap2roximately lO0 pascal-seconds; however, for coating flexible substrates by rolling methods, a practical upper limit for said viscosity is approximately 50 pascal-seconds, preferably 10 pascal-seconds at 25C. In many instances, the release compositions used in the process of this invention have a viscosity which is useful in said roller methods of coating without comprising a significant amount; for example, less than 5 percent by weight, of a volatile thinning medium.
9;2~
After application to a substrate r the curable silicone release composition is allowed to cure and any volatile thinning medium is allowed to evaporate. Preferably, said curing and evaporating are accelerated by the application of heat to the applied composition. Heating, usually limited to temperatures less than 300C., preferably less than 200C., may be accomplished by any suitable means; however, the curable silicone release composition should not be heated much above room temperature before it is applied because it will rapidly gel and become unusable.
The invention having been fully described, it will now be exemplified, but not limited, by the following examples, which also include the best mode for practicing the invention.
For this disclosure, all viscosities were measured in centipoise at 25C. and were converted to pascal-seconds by multiplying by 0.0001 and rounding off. Adhesive release was measured in grams/inch and was converted to newtons/metre by multiplying by 0.3860885 and rounding off. Tensile strength was measured in pounds/square inch and was converted to mega-pascals by multiplying by 6.894757 x 10-3 and rounding off. All parts, percentages and ratios are by weight unless otherwise indicated.
These examples illustrate the viscosity-lowering that is obtained by using a high SiH/SiVi ratio in a curable, vinyl resin-containing silicone release composition.
Examples Release agents, designated by letters A through L in the Table, were prepared by mixing sufficient poiydiorganosiloxane and resin copolymer solution to provide the indicated ratio of non-volatile polydiorganosiloxane to non-volatile resin copoiymer.
The polydiorganosiloxane consis~ed of 91 percent of a non-volatile ~ethylpn~nylvinylsilo~rle-endbloc1~ed ~lydimethylsilox~ne having a viscosity of approximately 65 pascal seconds at 25C. and 9 percent o~ volatile cyclic polydimethylsiloxanes.
The r~sin copolymer solution consisted of 34.5 percent xylene and 65.5 percent o~ a non-volatile resin copolymer having (CH3)3SiOl~2, (CH3)2(CH2=CH)SiOl~2 and SiO4/2 siloxane units wherein the mol ratio of the sum of the methyl- and vinyl-bearing siloxane units to the SiO4/2 siloxane units had a value of 0.7 and the vinyl content was 1.7 percent. The resulting mixtures were devolatilized for 3 hours under reduced pressure and at steam temperatures and, after being cooled, were mixed with sufficient methylhydrogenpolysiloxane to provide the indicated ratio of silicon-bonded hydrogen radicals to silicon-bonded vinyl radicals and 0.004 percent methylbutynol as a platinum-catalyzed cure control additive. The methylhydrogenpolysiloxane had the average formula l~e3SiO(Me2SiO)3(i~eHSiO)5SiMe3.
The viscosities of these mixtures were then measured with a rotating spindle viscometer at 25C. and are recorded in the Table. The percent viscosity decrease is based on the viscosity of the corresponding comparative composition (A, E or I).
Samples were prepared for tensile strengtA and elongation measurements by catalyzing the devolatilized mixture of vinyl-containing polymer, vinyl-containing resin copolymer, methylhydrogenpolysiloxane and cure control additive with 0.012 percent of the platinum-containing catalyst containing 0.6 percent platinum. The platinum-containing catalyst was a complex of PtCl6-6H2O and divinyltetramethyldisiloxane, prepared according to U.S. Patent No. 3,419,593. The catalyzed compositions were poured into 7.6 cm. x 12.7 cm. x ~0 mil chases and were heated at 70C. for 15 minutes and at 177C. for 5 minutes. The cured samples, after being cooled, were cut into "dog-bone" samples.
Tensile strength and elongation were measured according to ASTM
D-~12, using these "dog-~one" samples, and are recorded in the Table.
Adhesi~Je release was measured on compositions A, C, E and G, except that the mixtures of polydiorganosiloxane and resin copolymer solution were not devolatilized before being mixed with methylhydrogenpolysiloxane and catalyst and applied to a substrate.
Catalyzed formulations A, C, E and G were coated onto 40 pound supercalendared kraft paper uslng a blade coater at 35 p.s.i. pressure to give approximately 0.8 grams of coating per square metre of surface. The applied coatings were heated at 163C. for 60 seconds to cause curlng. A coating was considered to be cured if a piece of adhesive tape would stic~ to itself after having first been adhered to the coating and then removed and its adhesive-bearing surface doubled back on itself. A11 coatings passed this cure test. The abrasion resistance of each cured formulation was determined by rubbing the cured coating with the index finger to see if rub-off occurred. No rub-off occurred.
~11 coatings therefore passed this test for abrasion resistance.
Each cured release coating was prepared for release testing according to the following procedure. The cured release coating was coated with adhesive using a solution of a commercial acrylic adhesive. The acrylic adhesive solution was applied to the cured coating at a wet thickness of 3 mils (76.2 um) using a Bird Bar. The applied adhesive was air dried at room temperature for one minute, heated at 70C. for 30 seconds and then cooled to room temperature again for 1 minute. A sheet of 60 pound matte litho was applied to the dried adhesive and the resulting laminate 3~
lP~9.~t3~
was rolled with 3 4 . 5 Dound rubber-coated roller and aged for 20 hours at 70C.
Release testing of the laminates was accomplished by cooling the aged laminates to room temperature, cutting the cooled laminates into 1 inch (25.4 mm) wide strips and pulling the matte/adhesive lamina from the kraft paper/coating lamina at an angle of 180 (~ radians) at 400 inches/minute (0.17 m/s). The force, in grams per inch, that was required to separate the laminae was noted. A composition that results in a release value of no more than 38.61 N/m using this test is considered to display premium release.
The Table summarizes the release values (converted from grams/inch to newtons/metre) that were obtained.
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Claims (3)
1. In a process for coating a substrate to provide release of adhesive materials therefrom, said process comprising applying a curable silicone release composition to a surface of the substrate and thereafter curing the applied composition, the improvement comprising applying as the curable silicone release composition, a composition obtained by mixing components consisting essentially of (I) a polydiorganosiloxane having the general formula ViR2SiO(R2Sio)x(RViSiO)ySiR2Vi wherein x and y are integers whose sum has an average value sufficient to provide the polydiorganosiloxane with a viscosity at 25°C. of at least 1.0 pascal-seconds, Vi denotes a vinyl radical and each R denotes, independently, a monovalent radical selected from the group consisting of methyl, phenyl and saturated hydrocarbon radicals having from 2 to 6 carbon atoms, at least 95% of the total number of organic radicals in the polydiorganosiloxane being methyl radicals and no more than 1 percent being vinyl radicals, (II) a xylene-soluble copolymer of (CH3)3SiO1/2, (CH3)2(CH2=CH)SiO1/2 and SiO4/2 siloxane units, said copolymer having from 1 to 5 percent by weight of vinyl radicals, based on the weight of the copolymer, and a total of from 0.6 to 1.1 of said (CH3)3SiOl/2 plus (CH3)2(CH2=CH)SiO1/2 siloxane units for every said SiO4/2 siloxane unit, (III) a methylhydrogenpolysiloxane, soluble in the mixture of (I) plus (II), and having an average of at least three silicon-bonded hydrogen radicals per molecule, said hydrogen radicals being bonded to separate silicon atoms, and (IV) a catalytic amount of a hydrosilylation catalyst, said components being mixed in sufficient amounts to provide, in the curable silicone release composition, from 10 to 70 parts by weight of (II) for every 100 parts by weight of (I) plus (II) and from 2 to 10 silicon-bonded hydrogen radicals for every silicon-bonded vinyl radical.
2. A process according to claim 1 wherein the curable silicone release composition contains from 20 to 60 parts by weight of xylene-soluble copolymer for every 100 parts by weight of the mixture of polydiorganosiloxane (I) and xylene-soluble copolymer (II).
3. A process according to claim 1 wherein the curable silicone release composition further contains a volatile thinning medium.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US1722879A | 1979-03-05 | 1979-03-05 | |
| US17,228 | 1979-03-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1129270A true CA1129270A (en) | 1982-08-10 |
Family
ID=21781441
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA342,133A Expired CA1129270A (en) | 1979-03-05 | 1979-12-18 | Method for coating a substrate using a curable silicone release composition |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS55139452A (en) |
| CA (1) | CA1129270A (en) |
| DE (1) | DE3005742C2 (en) |
| FR (1) | FR2450642B1 (en) |
| GB (1) | GB2045788B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10155883B2 (en) | 2014-06-27 | 2018-12-18 | Dow Silicones Corporation | Silicone release coating composition and low release force emulsion silicone release coating for films and papers having cured release coating |
Families Citing this family (29)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4322518A (en) * | 1980-12-02 | 1982-03-30 | Dow Corning Corporation | Curable silicone compositions comprising liquid resin and uses thereof |
| ATE66008T1 (en) * | 1982-09-10 | 1991-08-15 | Gen Electric | METHOD FOR PREPARING AN ANTIADH|SIVEN DIORGANOPOLYSILOXA COMPOSITION. |
| US4500584A (en) * | 1983-07-07 | 1985-02-19 | General Electric Company | Transparent membrane structures |
| US4537829A (en) * | 1984-09-20 | 1985-08-27 | Dow Corning Corporation | Curable silicone compositions comprising resins |
| JPS61197448A (en) * | 1985-02-22 | 1986-09-01 | Toray Silicone Co Ltd | Coating agent for optical fiber for optical communication |
| JPH0641562B2 (en) * | 1985-05-16 | 1994-06-01 | 東レ・ダウコーニング・シリコーン株式会社 | Curable organopolysiloxane composition |
| US4611042A (en) * | 1985-10-03 | 1986-09-09 | Dow Corning Corporation | Resinous copolymeric siloxanes containing alkenyldimethylsiloxanes |
| JPH0637614B2 (en) * | 1986-07-15 | 1994-05-18 | 東レ・ダウコ−ニング・シリコ−ン株式会社 | Silicone pressure sensitive adhesive composition |
| US5110882A (en) * | 1986-11-28 | 1992-05-05 | Dow Corning Toray Silicone Company, Ltd. | Silicone pressure-sensitive adhesive composition |
| US4861670A (en) * | 1987-12-15 | 1989-08-29 | General Electric Company | Marine foulant release coating |
| US4882398A (en) * | 1988-08-26 | 1989-11-21 | Dow Corning Corporation | Optically clear reinforced organosiloxane compositions |
| US5082706A (en) * | 1988-11-23 | 1992-01-21 | Dow Corning Corporation | Pressure sensitive adhesive/release liner laminate |
| US5281656A (en) * | 1992-12-30 | 1994-01-25 | Dow Corning Corporation | Composition to increase the release force of silicone paper release coatings |
| GB9322793D0 (en) * | 1993-11-05 | 1993-12-22 | Dow Corning | Silicone release compositions |
| GB9322794D0 (en) * | 1993-11-05 | 1993-12-22 | Dow Corning | Silicone release compositions |
| JP2004359756A (en) * | 2003-06-03 | 2004-12-24 | Wacker Asahikasei Silicone Co Ltd | Sealant composition for led |
| FR2894591A1 (en) * | 2005-12-09 | 2007-06-15 | Rhodia Recherches & Tech | ANTI-SOILING POLYADDITION SILICONE VARNISH, APPLICATION OF THIS VARNISH ON A SUBSTRATE AND SUBSTRATE THUS TREATED |
| FR2901800B1 (en) * | 2006-05-31 | 2008-08-29 | Rhodia Recherches & Tech | CROSS-LINKABLE SILICONE COMPOSITION FOR THE PRODUCTION OF ANTI-ADHERENT COATINGS FOR POLYMERIC FILMS |
| KR101620123B1 (en) | 2008-07-30 | 2016-05-12 | 블루스타 실리콘즈 프랑스 에스에이에스 | Silicone composition for coating a flexible support intended to form a crosslinked coating having increased attachment, mechanical strength and reactivity |
| FR2946981A1 (en) | 2009-06-19 | 2010-12-24 | Bluestar Silicones France | SILICONE COMPOSITION RETICULABLE BY DEHYDROGENOCONDENSATION IN THE PRESENCE OF A METAL CATALYST |
| JP5470454B2 (en) | 2009-06-19 | 2014-04-16 | ブルースター・シリコーンズ・フランス・エスアエス | Silicone compositions suitable for crosslinking by dehydrogenative condensation in the presence of non-metallic catalysts |
| KR101346478B1 (en) | 2009-06-19 | 2014-01-02 | 블루스타 실리콘즈 프랑스 에스에이에스 | Silicone composition which is cross-linkable by dehydrogenative condensation in the presence of a non-metal catalyst |
| EP2443177B1 (en) | 2009-06-19 | 2014-04-02 | Bluestar Silicones France | Silicone composition which is cross-linkable by dehydrogenative condensation in the presence of a metal catalyst |
| FR2957604A1 (en) | 2010-03-22 | 2011-09-23 | Bluestar Silicones France | CROSS-LINKABLE SILICONE COMPOSITION FOR THE PRODUCTION OF ANTI-ADHERENT COATINGS FOR FLEXIBLE SUPPORTS AND ADDITIVE PROMOTER FOR HITCHING CONTAINED IN THIS COMPOSITION |
| US9150755B2 (en) | 2011-07-07 | 2015-10-06 | Bluestar Silicones France Sas | Silicone composition that can be cross-linked by means of dehydrogenative condensation in the presence of a carbene-type catalyst |
| CN104136543A (en) * | 2011-11-08 | 2014-11-05 | 道康宁公司 | Organopolysiloxane compositions and surface modification of cured silicone elastomers |
| US9487677B2 (en) | 2014-05-27 | 2016-11-08 | Momentive Performance Materials, Inc. | Release modifier composition |
| EP3353252B1 (en) | 2015-09-25 | 2019-09-11 | ELKEM SILICONES France SAS | Crosslinkable silicone composition for the production of non-stick coatings for flexible substrates and an attachment-promoting additive contained in this composition |
| CN114058290B (en) * | 2021-11-18 | 2023-08-08 | 成都富彩新材料有限公司 | Solvent-free organosilicon release agent with ultralow release force and preparation method thereof |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1476314A (en) * | 1973-06-23 | 1977-06-10 | Dow Corning Ltd | Coating process |
| US3900617A (en) * | 1973-11-27 | 1975-08-19 | Gen Electric | Method of rendering flexible sheet material non-adherent and article produced thereby |
| CA1064640A (en) * | 1975-08-18 | 1979-10-16 | Robert W. Sandford (Jr.) | Polysiloxane release coating of a substrate |
| DE2736499C2 (en) * | 1977-08-12 | 1990-03-29 | Wacker-Chemie GmbH, 8000 München | Process for the production of coatings which repel tacky substances |
| JPS55110155A (en) * | 1979-02-16 | 1980-08-25 | Toray Silicone Co Ltd | Organopolysiloxane composition forming releasable film |
-
1979
- 1979-12-18 CA CA342,133A patent/CA1129270A/en not_active Expired
-
1980
- 1980-02-15 DE DE3005742A patent/DE3005742C2/en not_active Expired
- 1980-02-18 GB GB8005377A patent/GB2045788B/en not_active Expired
- 1980-02-18 JP JP1895180A patent/JPS55139452A/en active Pending
- 1980-03-03 FR FR8004705A patent/FR2450642B1/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10155883B2 (en) | 2014-06-27 | 2018-12-18 | Dow Silicones Corporation | Silicone release coating composition and low release force emulsion silicone release coating for films and papers having cured release coating |
Also Published As
| Publication number | Publication date |
|---|---|
| DE3005742C2 (en) | 1982-04-15 |
| GB2045788B (en) | 1983-05-11 |
| FR2450642A1 (en) | 1980-10-03 |
| JPS55139452A (en) | 1980-10-31 |
| GB2045788A (en) | 1980-11-05 |
| FR2450642B1 (en) | 1985-07-19 |
| DE3005742A1 (en) | 1980-09-11 |
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