CA1088296A - Semi-conductive silicone elastomers - Google Patents
Semi-conductive silicone elastomersInfo
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- CA1088296A CA1088296A CA272,583A CA272583A CA1088296A CA 1088296 A CA1088296 A CA 1088296A CA 272583 A CA272583 A CA 272583A CA 1088296 A CA1088296 A CA 1088296A
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Abstract
ABSTRACT OF THE DISCLOSURE
Conductive silicone elastomer compositions which cure under hot air vulcanization conditions are provided by formulating a vinylorganopolysiloxane gum, an organo-hydrogenpolysiloxane fluid, a conductive carbon black filler, a peroxide catalyst which is not normally capable of causing the composition to vulcanize in hot air and a small, effective amount of a catalyst comprising platinum or a platinum compound, in an amount which is less than that which will cause cross-linking in up to 24 hours at about 23°C. but at least an amount sufficient to cause the composition to cure hot air vulcanization conditions.
Conductive silicone elastomer compositions which cure under hot air vulcanization conditions are provided by formulating a vinylorganopolysiloxane gum, an organo-hydrogenpolysiloxane fluid, a conductive carbon black filler, a peroxide catalyst which is not normally capable of causing the composition to vulcanize in hot air and a small, effective amount of a catalyst comprising platinum or a platinum compound, in an amount which is less than that which will cause cross-linking in up to 24 hours at about 23°C. but at least an amount sufficient to cause the composition to cure hot air vulcanization conditions.
Description
This invention relates to improvements in silicone elastomer compo~itions. More particularly, it i9 concernsd with providing electrically conductive silicone elastomers by formulating vinyl containing organopoly~iloxanes, a liquid ~ilicone having silicon-hydrogen bonds, conductive carbon black fillers, an organic peroxide catalyst, and a small amount, æufficient to catalyze vulcanization under hot air conditions, of a catalyst comprising platinum or a platinum compound.
Silicone rubber can be made electrically conductiv~
by u~ing conductive carbon black as the filler. Acetylene blacks are found to be v~ry useful for this purpose. Conductive silicone rubber gives the typical benefits of heat resistance, weather resi~tance, low temperature flexibility, and the like, of ordinary silicone rubber~ Such rubber i8 finding increasing usefulness as an elastic heating medium (heat results from current flow), as well as in any electrical application where low electrical resistance is required. In general, a broad range of conductivities may be obtained in silicone rubber in incorporating varying amounts of the conductive carbon black into the formulation. The higher the carbon black content of the compound, the greater will be the conductivity, or the lower will be the volume resistivity.
In the present state of the art, the most desirable conductive compositions will exhibit a volume resistivity of not more than about 10,000 ohm-cm., a Shore A hardness of at least 50, a tensile strength of greater than 450 pounds per s~uare inch and elongation of greater than lOOX at break.
The specific requirements needed by conductive silicone rubber make it difficult to qxtend conventional silicone elastomer technology to this field of u~e. For example, the material must contain a type of carbon black '~
1~88zg6 60SI-21 that will conduct electricity, but all conductive blacks so far investigated can be cured only with peroxides, using compression molding or ~team vulcanization, both of which require expensive eguipment and high energy requirements.
q~le catalyst which i3 normally used to vulcanize ~ilicone elastomers with hot air, which is a cheaper, less energy and equipment intensive means of curing, is 2,4-dichlorobenzoyl peroxide. Unfortunately, however, silicone rubber compositions containing conductive blacks react with and deplete the
Silicone rubber can be made electrically conductiv~
by u~ing conductive carbon black as the filler. Acetylene blacks are found to be v~ry useful for this purpose. Conductive silicone rubber gives the typical benefits of heat resistance, weather resi~tance, low temperature flexibility, and the like, of ordinary silicone rubber~ Such rubber i8 finding increasing usefulness as an elastic heating medium (heat results from current flow), as well as in any electrical application where low electrical resistance is required. In general, a broad range of conductivities may be obtained in silicone rubber in incorporating varying amounts of the conductive carbon black into the formulation. The higher the carbon black content of the compound, the greater will be the conductivity, or the lower will be the volume resistivity.
In the present state of the art, the most desirable conductive compositions will exhibit a volume resistivity of not more than about 10,000 ohm-cm., a Shore A hardness of at least 50, a tensile strength of greater than 450 pounds per s~uare inch and elongation of greater than lOOX at break.
The specific requirements needed by conductive silicone rubber make it difficult to qxtend conventional silicone elastomer technology to this field of u~e. For example, the material must contain a type of carbon black '~
1~88zg6 60SI-21 that will conduct electricity, but all conductive blacks so far investigated can be cured only with peroxides, using compression molding or ~team vulcanization, both of which require expensive eguipment and high energy requirements.
q~le catalyst which i3 normally used to vulcanize ~ilicone elastomers with hot air, which is a cheaper, less energy and equipment intensive means of curing, is 2,4-dichlorobenzoyl peroxide. Unfortunately, however, silicone rubber compositions containing conductive blacks react with and deplete the
2,4-dichlorobenzoyl peroxide catalyst, and hot air vulcanization does not occur.
Many approaches to overcoming these problems and providing a hot air ~ulcanizing composition containing con-ductive blacks have been tried, but without success. These approaches have included substituting cross-linking agents, variou~ other conductive blacks and catalyst compositions, and the substitution of platinum addition catalysts for the `~
peroxide.
It has now been surprisingly discovered that if a peroxide catalyst different from the preferred prior art hot ~-air vulcanization catalyst is substituted, there i8 obtained a composition which cures with compression molding or steam, but not with hot air. Mbreover, if this composition is then treated wlth a small amount of a platinum addition catalyst, not sufficient to cause cross-linking within about 24 hours at room temperature, 23~C., there will be obtained a u~eful conductive compound which will permit the materials to be mixed with a reasonable sh~lf age and still provide an extrudable product which, surprisinyly, hot air cures. I~
too much of the platinum addition catalyst is used, such as a conventional amount, the rubber composition will tend to cross-link and become unusable in a ~hort period of time, ~ 88296 60S~-21 e.g., of the order of 2-4 hours. Using the platinum catalyst alone at a lower concentration ext~nds the shelf age, but only provides a semi-cured rubber after hot air vulcanization.
The foregoing indicates the need for using a combination of peroxide and platinum catalyst in a relatively narrow u~e ..
range.
According to the pre~ent invention, there are .
provided in compositions vulcanizable to an electrically conductive silicone elastomer, said compo~ition compri~ing: :.
(i) a vinylorganopolysiloxane gum~ :
(ii) an organohydrogenpolysiloxane7 .,., ~, : .
(iii) an electrically conductive carbon black filler in an amount capable of rendering the cured composition electrically conductive;
I and (iv) a small, effective amount, sufficient to cure the composition with steam or under com~
pression molding conditions, of a peroxide catalyst which is not normally capable of curing.~he compo- ~`.
sitLon on exposure to hot air, the improvement whLch ~;.
comprLses including in saLd composition (~) a cataly~t comprising platinum or a platinum compound in a small amount, at least effective to render the composition vulcanizable upon exposure to hot air but less than an amount whLch wLll cause any substantial cros~ linking of the composition wi~hin 24 hours at a temperature of about 23C.
Within the invention as broadly de~crLbed above, a preferred family of composLtions will be those in which the organohydrogenpolysiloxane (ii) compri~es from about 0.1 to about 1.0 parts by weight, the filler (iii) comprises from about 20 to about 50 parts by weight, the peroxide catalyst 1~88296 60SI-21 (iv) comprises from about 0~2 to about 2.0 parts by weight, and ~he c~talyst ~v) comprising platlnum or a platinum ~ompound comprises from about 0.0001 to about 0.005 parts by weight per 100 parts by weight of the gum ~i).
The present invention also in its broadest a~pects contemplates in a proceqs for preparing an electrically conductive vulcanized silicone elastomer comprising:
~A) ~orming a composition of:
(i) a vinylorganopolysiloxane gum: -(ii) an organohydrogenpolysiloxane fluid: -(iii) an electrically conductive carbon black filler in an amount capable of rendering the cured composition electrically conduetive:
and (iv) a small, effective amount, sufficient to cure the compo~ition with steam or under compre~sion molding con~
ditions, of a peroxide catalyst which i~
not normally capable of curing the compo- -sition on expo3ure to hot air, and 1B) heating the composition under vulcanizing conditions until it is substantially eured, the improvement whieh comprises adding to said composition before vulcanization a catalyst comprising platinum or a platinum compound in a small amount, at least suf~icient to render the composition vulcanizable upon exposure to hot air but less than an amount which will cause any substantial cross-linking of the compo~ition within 24 hours at a temperature of about 23C., shaping to form, and thereafter heating the compo~ition in hot air until it has been substantially completely vulcanized.
All of the el~ments in the above-mentioned 1088Z9~ 60SI-21 formulations and processes are well known to tho~e of ordlnary skill in the art of silicone elastomer formulation. :~ ~
The vinylorganopoly~iloxane gum i8 .a conventional ~ -ingredient which is available from a number of commercial -~ :
sources on an readily be made by following the teachings of the prior art. ~y way of illustration, the gum can be one of a formula - :
R R' R
CH2 ~ SiO ~ Si ~ Si - CH - CH2 (I) . ~.
R R~ R
wherein R and R' may be the same or different and are mono-valent hydrocarbon group~ free of aliphatic unsaturation, with at lea~t 50 mole percent of R~ being methyl and where : -n ha~ a value ~ufficient to provide a gum-like con~istency at room temperature. The~e vinyl- topped diorganopolysiloxane~
are also well known, as evidenced by U.S. Patent No. 3,425,967, Mbdic, is~ued February 4, 1969.
The monovalent hydrocarbon groups repre~ented by ::, R and R' include alkyl, such a~ me~hyl, ethyl, propyl, isopropyl, butyl, octyl, dodecyl, and the like; cycloalkyl such a~ cyclopentyl, cyclohexyl, cycloheptyl, and the like:
aryl, such as phenyl, naphthyl, tolyl, xylyl, and the like;
aralkyl, such as benzyl, phenyethyl, phenylpropyl, and the ~-like; halogenated derivatives of the afore~aid.radicals ..
including chloromethyl, trifluoromethyl, chloropropyl, chloro-phenyl, dibromophenyl, tetrachlorophenyl, difluorophenyl and the like; cyanoalkyl, such as beta-cyanoethyl, gamma-cyanopropyl, beta-cyanopropyl and the like.
Preferably, R and R' are selected from among . .
_ ~ _ 10~829~ 60SI-21 methyl and phenyl and most preferably, R and R~ are methyl.
It i9 to be under~tood, of cour~e, that the above formula iQ intended to include organopolysiloxanes which are vinyl terminated, or contain the vinyl groups along the chain or which are vinyl terminated and also contain vinyl groups along the chain.
The organohydrogenpoly~iloxanes employed in the compositions of this invention are those which have structural units represented by the formula, Ra ~ SiO ~4-a-b/2) wherein R is a~ defined above, a is from about 0.5 to 2, inclu~ive, b is from about 0.05 to 2, inclusive, and the sum of a and b i8 from about 1 to 3, inclusive. Preferably R is methyl.
The organohydrogenpolysiloxanes of the composition are fluids which are preferably, but not necessarily, free of olefinic unsaturation. These are well known in th~ art and are described in detail in U.S. Patent 3,344,111 to Chalk, issued September 26, 1967.
A broad range of conductivities may be obtained in the present ~ilicone compositions by incorporating various amount~ of carbon black fille~ (iii~ into the organopoly-~iloxane. For this purpo~e, any of the carbon blacks conventionally employed ~or imparting electrical conductivity to silicones may be used, such as acetylene black. A
preferred conductive carbon black is Shawinigan Black.
Generally, the higher the amount of carbon black which is added, ~he greater will be the conductivity and, correspondingly, the lower will be the volume resistivity.
The organopoly~iloxane compositions of the present invention may also comprise, in addition to the conductive carbon black, other conventional additives, such as reinforcing ~ 60SI-21 1~88Z9~ .
fillers commonly used in connection with organopoly-iloxanes.
Inorganic reinforcing fillers, such as silica fillors, are especially advantageous. These may include silica aerogel, fumed silica, precipitated silica, and the like. Especially preferred is Cab-0-Sil, commercially available from Cabot Corporation, Massachusetts, U.S.A. By adjusting the carbon to reinforcing filler ratio, a broad range of conductivities can be obtained.
The pexoxide catalyst (iv) of the present compositions should be selected from among the alkyl peroxides or aralkyl peroxides commonly employed in the curing of silicones. Especially preferred are di-t-butylperoxide and dicumyl peroxide. Benzoyl peroxides and halobenzoyl peroxides, ~ -.
such as 2,4-dichlorobenzoyl peroxide, should be avoided inasmuch as the catalytic activity of these materials is inhibited by the presence of conductive carbon black.
The platinum catalyst (v) may be selected from among any of the platinum addition catalysts which are-known ;~
to be effective in curing silicone gums at room temperature.
These materials include, for example, finely divided elemental platinum catalysts, ~uch as those described in U.S. Patent 2,970,150 to Bailey, issued January 31, 1961, the chloroplatinic acid catalysts described In U.S. Patent No. 2,823,218 to Speier, issued February 11, 1958, the platinum hydroaarbon complexes shown in U.S. Patent No. 3,159,601 to Asbby,-~issued December 1, 1964 and U.S. Patent No. 3,159,662 to Ashby, issued December 1, 1964, as well as the platinum alcoholate catalysts described in U.S. Patent No. 3,220,972 to Lamoreaux, issued November 30, 1965. ~oreover, the platinum chloride-oIefin complexes described in U.S. Patent No. 3,516,946 to Modic, issued 3une 23, 1970 are also useful herein. Mixtures of these compounds may also be usefully employed~
. ...
1~88296 60SI-21 The present compositions are preferably prepared in two parts which are combined prior to hot air vulcanization.
Preferably one part will comprise a carbon black-filled organopolysiloxane gum, an organohydrogenpolysiloxane, and a peroxide catalyst, and the other part will comprise a carbon black-filled organopolysiloxane gum and a platinum or platinum compound catalyst. The two portions can be combined by rubber milling or dough mixing. Amounts of the peroxide catalyst and the platinum catalyst are used which allow the two parts to be combined and yet stored for up to 24 hours at room temperature without the occurrence of substantial cross-linking. An extrudable product that hot air cures is obtained even after such storage.
In general, the compositions of the present invention are cured at elevated temperatures in the range of from about 400 to about 750F. Complete cure time can vary considerably, e.g., from less than a minute to 10 minutes or more, e.g., from about 2 to about 15 minutes, depending on factors such as the thickness of the extruded product, the relative proportions of ingredients, and other operating conditions. These and other details concerning the curing of the compositions are readily ascertainable by those skilled in the` art.
The following examples are presented in order to provide a better understanding of how the present invention is practiced. It will be understood, however, that these examples are provided by way of illustration and are not intended to be limiting.
This example illustrates the preparation of a 3Q cured, semi-conductive silicone rubber, according to the method of the present invention.
A two-part package is prepared having the following 108~329~
formulation:
P~T A:
Com~onents Amounts (Parts by Weight) Methylvinyl polysiloxane gum 100 Methyl hydrogen-containing polysiloxane fluid 0.7 Acetylene black (Shawinigan Black) 40 Dicumyl peroxide catalyst 2.0 PART B:
Components Amounts IPart~ by Weight) Methylvinyl poly~iloxane gum 100 Acetylene Black (Shawinigan Black) 40 Platinum alcoholate catalyst .0075 Prior to use, the two parts are combined by milling 95 parts of A with 5 parts of B, No cross-linking will occur even after storage for 24 hours at 23C.
To use, the composition i8 extruded to the shape of a tape of 75 mils thickness, then it is vulcanized by curing in a hot air tunnel oven at 700F. for 30 seconds.
The electrical conductivity of the cured composition is measurea, and the Volume Resistivity i5 100 ohm-cm. Other properties of the cured composition are as followss Tensile Strength (ASTM D-412 500 psi Elongation at break ~ASTM D-414) 140%
Hardne~s, Shore A (ASTM D-676) 60 Other modifications of the compositions of the invention illustrated above are possible. For in~tance, the two parts of the composition can be blended in various other ratios. A 50/50 blend of Parts A and B is particularly suitable for commercial preparations. Instead of dicumyl peroxide as a catalyst, other peroxide catalysts can be employed, eOg., di-t-butyl peroxide. Instead of a platinum _ g _ 1~88zgG 60SI-21 alcoholate catalyst, finely divided elemental platinum, chloroplatinic acid and platinum-hydrocarbon compl~xe~ can be used. In addition to carbon black, reinforcing filler can be used such as colloidal silica, it being understood, however, that as larger amounts of such reinforcing fillers are added at the expense of the carbon black filler, the elec~rical conductivity of the composition can be adver~ely affected.
It i9, therefore, to be understood that changes may be made in the particular embodiments of the invention described above whic}l are within the full intended scope of the invention as defined in the appended claims.
Many approaches to overcoming these problems and providing a hot air ~ulcanizing composition containing con-ductive blacks have been tried, but without success. These approaches have included substituting cross-linking agents, variou~ other conductive blacks and catalyst compositions, and the substitution of platinum addition catalysts for the `~
peroxide.
It has now been surprisingly discovered that if a peroxide catalyst different from the preferred prior art hot ~-air vulcanization catalyst is substituted, there i8 obtained a composition which cures with compression molding or steam, but not with hot air. Mbreover, if this composition is then treated wlth a small amount of a platinum addition catalyst, not sufficient to cause cross-linking within about 24 hours at room temperature, 23~C., there will be obtained a u~eful conductive compound which will permit the materials to be mixed with a reasonable sh~lf age and still provide an extrudable product which, surprisinyly, hot air cures. I~
too much of the platinum addition catalyst is used, such as a conventional amount, the rubber composition will tend to cross-link and become unusable in a ~hort period of time, ~ 88296 60S~-21 e.g., of the order of 2-4 hours. Using the platinum catalyst alone at a lower concentration ext~nds the shelf age, but only provides a semi-cured rubber after hot air vulcanization.
The foregoing indicates the need for using a combination of peroxide and platinum catalyst in a relatively narrow u~e ..
range.
According to the pre~ent invention, there are .
provided in compositions vulcanizable to an electrically conductive silicone elastomer, said compo~ition compri~ing: :.
(i) a vinylorganopolysiloxane gum~ :
(ii) an organohydrogenpolysiloxane7 .,., ~, : .
(iii) an electrically conductive carbon black filler in an amount capable of rendering the cured composition electrically conductive;
I and (iv) a small, effective amount, sufficient to cure the composition with steam or under com~
pression molding conditions, of a peroxide catalyst which is not normally capable of curing.~he compo- ~`.
sitLon on exposure to hot air, the improvement whLch ~;.
comprLses including in saLd composition (~) a cataly~t comprising platinum or a platinum compound in a small amount, at least effective to render the composition vulcanizable upon exposure to hot air but less than an amount whLch wLll cause any substantial cros~ linking of the composition wi~hin 24 hours at a temperature of about 23C.
Within the invention as broadly de~crLbed above, a preferred family of composLtions will be those in which the organohydrogenpolysiloxane (ii) compri~es from about 0.1 to about 1.0 parts by weight, the filler (iii) comprises from about 20 to about 50 parts by weight, the peroxide catalyst 1~88296 60SI-21 (iv) comprises from about 0~2 to about 2.0 parts by weight, and ~he c~talyst ~v) comprising platlnum or a platinum ~ompound comprises from about 0.0001 to about 0.005 parts by weight per 100 parts by weight of the gum ~i).
The present invention also in its broadest a~pects contemplates in a proceqs for preparing an electrically conductive vulcanized silicone elastomer comprising:
~A) ~orming a composition of:
(i) a vinylorganopolysiloxane gum: -(ii) an organohydrogenpolysiloxane fluid: -(iii) an electrically conductive carbon black filler in an amount capable of rendering the cured composition electrically conduetive:
and (iv) a small, effective amount, sufficient to cure the compo~ition with steam or under compre~sion molding con~
ditions, of a peroxide catalyst which i~
not normally capable of curing the compo- -sition on expo3ure to hot air, and 1B) heating the composition under vulcanizing conditions until it is substantially eured, the improvement whieh comprises adding to said composition before vulcanization a catalyst comprising platinum or a platinum compound in a small amount, at least suf~icient to render the composition vulcanizable upon exposure to hot air but less than an amount which will cause any substantial cross-linking of the compo~ition within 24 hours at a temperature of about 23C., shaping to form, and thereafter heating the compo~ition in hot air until it has been substantially completely vulcanized.
All of the el~ments in the above-mentioned 1088Z9~ 60SI-21 formulations and processes are well known to tho~e of ordlnary skill in the art of silicone elastomer formulation. :~ ~
The vinylorganopoly~iloxane gum i8 .a conventional ~ -ingredient which is available from a number of commercial -~ :
sources on an readily be made by following the teachings of the prior art. ~y way of illustration, the gum can be one of a formula - :
R R' R
CH2 ~ SiO ~ Si ~ Si - CH - CH2 (I) . ~.
R R~ R
wherein R and R' may be the same or different and are mono-valent hydrocarbon group~ free of aliphatic unsaturation, with at lea~t 50 mole percent of R~ being methyl and where : -n ha~ a value ~ufficient to provide a gum-like con~istency at room temperature. The~e vinyl- topped diorganopolysiloxane~
are also well known, as evidenced by U.S. Patent No. 3,425,967, Mbdic, is~ued February 4, 1969.
The monovalent hydrocarbon groups repre~ented by ::, R and R' include alkyl, such a~ me~hyl, ethyl, propyl, isopropyl, butyl, octyl, dodecyl, and the like; cycloalkyl such a~ cyclopentyl, cyclohexyl, cycloheptyl, and the like:
aryl, such as phenyl, naphthyl, tolyl, xylyl, and the like;
aralkyl, such as benzyl, phenyethyl, phenylpropyl, and the ~-like; halogenated derivatives of the afore~aid.radicals ..
including chloromethyl, trifluoromethyl, chloropropyl, chloro-phenyl, dibromophenyl, tetrachlorophenyl, difluorophenyl and the like; cyanoalkyl, such as beta-cyanoethyl, gamma-cyanopropyl, beta-cyanopropyl and the like.
Preferably, R and R' are selected from among . .
_ ~ _ 10~829~ 60SI-21 methyl and phenyl and most preferably, R and R~ are methyl.
It i9 to be under~tood, of cour~e, that the above formula iQ intended to include organopolysiloxanes which are vinyl terminated, or contain the vinyl groups along the chain or which are vinyl terminated and also contain vinyl groups along the chain.
The organohydrogenpoly~iloxanes employed in the compositions of this invention are those which have structural units represented by the formula, Ra ~ SiO ~4-a-b/2) wherein R is a~ defined above, a is from about 0.5 to 2, inclu~ive, b is from about 0.05 to 2, inclusive, and the sum of a and b i8 from about 1 to 3, inclusive. Preferably R is methyl.
The organohydrogenpolysiloxanes of the composition are fluids which are preferably, but not necessarily, free of olefinic unsaturation. These are well known in th~ art and are described in detail in U.S. Patent 3,344,111 to Chalk, issued September 26, 1967.
A broad range of conductivities may be obtained in the present ~ilicone compositions by incorporating various amount~ of carbon black fille~ (iii~ into the organopoly-~iloxane. For this purpo~e, any of the carbon blacks conventionally employed ~or imparting electrical conductivity to silicones may be used, such as acetylene black. A
preferred conductive carbon black is Shawinigan Black.
Generally, the higher the amount of carbon black which is added, ~he greater will be the conductivity and, correspondingly, the lower will be the volume resistivity.
The organopoly~iloxane compositions of the present invention may also comprise, in addition to the conductive carbon black, other conventional additives, such as reinforcing ~ 60SI-21 1~88Z9~ .
fillers commonly used in connection with organopoly-iloxanes.
Inorganic reinforcing fillers, such as silica fillors, are especially advantageous. These may include silica aerogel, fumed silica, precipitated silica, and the like. Especially preferred is Cab-0-Sil, commercially available from Cabot Corporation, Massachusetts, U.S.A. By adjusting the carbon to reinforcing filler ratio, a broad range of conductivities can be obtained.
The pexoxide catalyst (iv) of the present compositions should be selected from among the alkyl peroxides or aralkyl peroxides commonly employed in the curing of silicones. Especially preferred are di-t-butylperoxide and dicumyl peroxide. Benzoyl peroxides and halobenzoyl peroxides, ~ -.
such as 2,4-dichlorobenzoyl peroxide, should be avoided inasmuch as the catalytic activity of these materials is inhibited by the presence of conductive carbon black.
The platinum catalyst (v) may be selected from among any of the platinum addition catalysts which are-known ;~
to be effective in curing silicone gums at room temperature.
These materials include, for example, finely divided elemental platinum catalysts, ~uch as those described in U.S. Patent 2,970,150 to Bailey, issued January 31, 1961, the chloroplatinic acid catalysts described In U.S. Patent No. 2,823,218 to Speier, issued February 11, 1958, the platinum hydroaarbon complexes shown in U.S. Patent No. 3,159,601 to Asbby,-~issued December 1, 1964 and U.S. Patent No. 3,159,662 to Ashby, issued December 1, 1964, as well as the platinum alcoholate catalysts described in U.S. Patent No. 3,220,972 to Lamoreaux, issued November 30, 1965. ~oreover, the platinum chloride-oIefin complexes described in U.S. Patent No. 3,516,946 to Modic, issued 3une 23, 1970 are also useful herein. Mixtures of these compounds may also be usefully employed~
. ...
1~88296 60SI-21 The present compositions are preferably prepared in two parts which are combined prior to hot air vulcanization.
Preferably one part will comprise a carbon black-filled organopolysiloxane gum, an organohydrogenpolysiloxane, and a peroxide catalyst, and the other part will comprise a carbon black-filled organopolysiloxane gum and a platinum or platinum compound catalyst. The two portions can be combined by rubber milling or dough mixing. Amounts of the peroxide catalyst and the platinum catalyst are used which allow the two parts to be combined and yet stored for up to 24 hours at room temperature without the occurrence of substantial cross-linking. An extrudable product that hot air cures is obtained even after such storage.
In general, the compositions of the present invention are cured at elevated temperatures in the range of from about 400 to about 750F. Complete cure time can vary considerably, e.g., from less than a minute to 10 minutes or more, e.g., from about 2 to about 15 minutes, depending on factors such as the thickness of the extruded product, the relative proportions of ingredients, and other operating conditions. These and other details concerning the curing of the compositions are readily ascertainable by those skilled in the` art.
The following examples are presented in order to provide a better understanding of how the present invention is practiced. It will be understood, however, that these examples are provided by way of illustration and are not intended to be limiting.
This example illustrates the preparation of a 3Q cured, semi-conductive silicone rubber, according to the method of the present invention.
A two-part package is prepared having the following 108~329~
formulation:
P~T A:
Com~onents Amounts (Parts by Weight) Methylvinyl polysiloxane gum 100 Methyl hydrogen-containing polysiloxane fluid 0.7 Acetylene black (Shawinigan Black) 40 Dicumyl peroxide catalyst 2.0 PART B:
Components Amounts IPart~ by Weight) Methylvinyl poly~iloxane gum 100 Acetylene Black (Shawinigan Black) 40 Platinum alcoholate catalyst .0075 Prior to use, the two parts are combined by milling 95 parts of A with 5 parts of B, No cross-linking will occur even after storage for 24 hours at 23C.
To use, the composition i8 extruded to the shape of a tape of 75 mils thickness, then it is vulcanized by curing in a hot air tunnel oven at 700F. for 30 seconds.
The electrical conductivity of the cured composition is measurea, and the Volume Resistivity i5 100 ohm-cm. Other properties of the cured composition are as followss Tensile Strength (ASTM D-412 500 psi Elongation at break ~ASTM D-414) 140%
Hardne~s, Shore A (ASTM D-676) 60 Other modifications of the compositions of the invention illustrated above are possible. For in~tance, the two parts of the composition can be blended in various other ratios. A 50/50 blend of Parts A and B is particularly suitable for commercial preparations. Instead of dicumyl peroxide as a catalyst, other peroxide catalysts can be employed, eOg., di-t-butyl peroxide. Instead of a platinum _ g _ 1~88zgG 60SI-21 alcoholate catalyst, finely divided elemental platinum, chloroplatinic acid and platinum-hydrocarbon compl~xe~ can be used. In addition to carbon black, reinforcing filler can be used such as colloidal silica, it being understood, however, that as larger amounts of such reinforcing fillers are added at the expense of the carbon black filler, the elec~rical conductivity of the composition can be adver~ely affected.
It i9, therefore, to be understood that changes may be made in the particular embodiments of the invention described above whic}l are within the full intended scope of the invention as defined in the appended claims.
Claims (10)
1. In a composition vulcanizable to an electrically conductive silicone elastomer, said composition comprising:
(i) a vinylorganopolysiloxane gum;
(ii) an organohydrogenpolysiloxane:
(iii) an electrically conductive carbon black filler in an amount capable of rendering the cured composition electrically conductive; and (iv) a small, effective amount, sufficient to cume the composition with steam or under compression molding conditions, of a peroxide catalyst which is not normally capable of curing the composition on exposure to hot air, the improvement which comprises including in said composition (v) a catalyst comprising platinum or a platinum compound in a small amount, at least effective to render the composition vulcanizable upon exposure to hot air but less than anamount which will cause any substantial cross-linking of the composition within 24 hours at a temperature of about 23°C.
(i) a vinylorganopolysiloxane gum;
(ii) an organohydrogenpolysiloxane:
(iii) an electrically conductive carbon black filler in an amount capable of rendering the cured composition electrically conductive; and (iv) a small, effective amount, sufficient to cume the composition with steam or under compression molding conditions, of a peroxide catalyst which is not normally capable of curing the composition on exposure to hot air, the improvement which comprises including in said composition (v) a catalyst comprising platinum or a platinum compound in a small amount, at least effective to render the composition vulcanizable upon exposure to hot air but less than anamount which will cause any substantial cross-linking of the composition within 24 hours at a temperature of about 23°C.
2. A composition as defined in claim 1 wherein said organohydrogenpolysiloxane (ii) comprises from about 0.1 to about 1.0 parts by weight, said filler (iii) comprises from about 20 to about 50 parts by weight, said peroxide catalyst (iv) comprises from about 0.2 to about 2.0 parts by weight, and said catalyst comprising platinum or a platinum compound (v) comprises from about 0.0001 to about 0.005 parts by weight per 100 parts by weight of said gum (i).
3. A composition as defined in claim 1 wherein the vinylorganopolysiloxane gum (i) is of the formula wherein R and R' may be the same or different and are mono-valent hydrocarbon groups free of aliphatic unsaturation, with at least 50 mole percent of R' being methyl and where n has a value sufficient to provide a gum-like consistency at room temperature.
4. A composition as defined in claim 1 wherein the organohydrogenpolysiloxane (ii) is comprised of structural units of the formula RaHb Si O (4-a-b/2) wherein R is a monovalent hydrocarbon free of aliphatic unsaturation, a is from about 0.5 to 2, inclusive, b is from about 0.05 to 2, inclusive, and the sum of a and b is from about 1 to 3, inclusive.
5. A composition as defined in claim 1 wherein said vinylorganopolysiloxane gum is a methylvinylpolysiloxane gum.
6. A composition as defined in claim 5 wherein said methylvinylpolysiloxane gum is a dimethylvinyl chain-stopped dimethylpolysiloxane gum.
7. A composition as defined in claim 1 wherein said carbon black filler (iii) is an acetylene black.
8. A composition as defined in claim 1 wherein said peroxide is dicumyl peroxide, di-t-butyl peroxide or a mixture thereof.
9. A composition as defined in claim 1 wherein said catalyst (v) comprises finely divided elemental platinum, chloroplatinic acid, a platinum hydrocarbon complex, a platinum alcoholate, a platinum chloride-olefin complex or a mixture of any of the foregoing.
10. A composition as defined in claim 1 which, after vulcanization, exhibits a volume resistivity of less than
10. A composition as defined in claim 1 which, after vulcanization, exhibits a volume resistivity of less than
Claim 10 continued:
10,000 ohm-cm., a Shore A hardness of at least 50, a tensile strength of greater than 450 pounds per square inch and an elongation of greater than 100 percent at break.
10,000 ohm-cm., a Shore A hardness of at least 50, a tensile strength of greater than 450 pounds per square inch and an elongation of greater than 100 percent at break.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA272,583A CA1088296A (en) | 1977-02-24 | 1977-02-24 | Semi-conductive silicone elastomers |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA272,583A CA1088296A (en) | 1977-02-24 | 1977-02-24 | Semi-conductive silicone elastomers |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1088296A true CA1088296A (en) | 1980-10-28 |
Family
ID=4108012
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA272,583A Expired CA1088296A (en) | 1977-02-24 | 1977-02-24 | Semi-conductive silicone elastomers |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1088296A (en) |
-
1977
- 1977-02-24 CA CA272,583A patent/CA1088296A/en not_active Expired
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