Abstract:
A curable silicone composition cures to form a silicone cured product with improved fire-retarding, properties. The composition comprises a hydrosilylation-reaction curable silicone composition. Fire-retarding properties are imparted to the composition by using an additive comprising tetrafunctional and monofunctional siloxane units and a diamine compound. The silicone cured product is preferably a silicone gel.

Description:
FIELD OF THE INVENTION 
     This invention relates to a curable silicone composition. More specifically, this invention relates to a curable silicone composition that forms a silicone cured product of superior flame resistance. 
     BACKGROUND OF THE INVENTION 
     Curable silicone compositions are used as sealants, fillers or coatings for electric or electronic parts. On curing, they form silicone gels, silicone rubbers, or silicone resins of superior electrical characteristics, heat resistance, weatherability, and the like. For example, Japanese Patent JP-C-48-017847 discloses a curable silicone composition comprising a diorcanopolysiloxane with silicon bonded vinyl groups at the molecular chain terminals and in the side chains of the molecular chain, a diorganopolysiloxane having silicon-bonded hydrogen atoms at the molecular chain terminals or in the side chains of the molecular chain, or both, and a platinum-based catalyst. 
     U.S. Pat. No. 4,374,867 to Brown, et al. discloses a curable silicone composition comprising a branched dimethylpolysiloxane having silicon-bonded vinyl groups at the terminal ends of the molecular chain, an organopolysiloxane having silicon-bonded hydrogen atoms, and a platinum-based catalyst. 
     Japanese Patent Application JP-A-05-209127 discloses a curable silicone composition comprising a diorganopolysiloxane having two or more silicon-bonded alkenyl groups in each molecule, with a cyclic diorganosiloxane content of not more than 0.5 wt %, an organopolysiloxane resin having silicon-bonded alkenyl groups, a diorganopolysiloxane having silicon-bonded hydrogen atoms at both terminal ends of the molecular chain, and a platinum-based catalyst. 
     Diamine compounds have been suggested for improving the storage stability of such curable silicone compositions in U.S. Pat. No. 4,801,642 and 4,791,186 to Buentello et al. and U.S. Pat. No. 5,334,687 to Ikeno. 
     However, when these curable silicone compositions were cured, the cured products had insufficient flame resistance. This problem was particularly conspicuous in silicone gels. For this reason, it was impossible to seal or fill electric or electronic parts exposed to elevated temperatures over an extended period of time using these curable silicone compositions, especially silicone gel compositions. 
     Various inorganic flame resistance-imparting agents have been compounded with curable silicone compositions to improve flame resistance. For example, Japanese Patent JP-C-61-069865 discloses a curable silicone composition comprising an organopolysiloxane having two or more silicon-bonded alkenyl groups in each molecule, an organopolysiloxane having two or more silicon-bonded hydrogen atoms in each molecule, a reinforcing silica powder, an aluminum hydroxide powder, a clayey mineral powder, a triazole compound, and a platinum-based catalyst. 
     Japanese Patent No. JP-C-06-016937 discloses a curable silicone composition comprising an organopolysiloxane having, on the average, 0.1 to about 2.0 silicon-bonded vinyl groups in each molecule; an organopolysiloxane having, on the average, more than two silicon-bonded hydrogen atoms in each molecule; an inorganic filler selected from the group consisting of ground quartz, metallic carbonate, and carbon black; and a platinum-based catalyst. 
     However, sufficient flame resistance could not be obtained without compounding large quantities of inorganic flame resistance-imparting agents in these curable silicone compositions. As a result, the curable silicone compositions had insufficient flowability and handling properties, the external appearance of the resultant silicone cured products was non-transparent and was limited to white, black, or gray colors. Furthermore, when curable silicone compositions containing the inorganic flame resistance-imparting agents are stored, the flame retardants can precipitate. 
     The object of the present invention is to produce a curable silicone composition that forms a silicone cured product with superior flame resistance. 
     SUMMARY OF THE INVENTION 
     This invention pertains to a silicone composition comprising: an organopolysiloxane with at least 2 silicon-bonded alkenyl groups per molecule, an organopolysiloxane flame resistance imparting agent, an organopolysiloxane curing agent, a hydrosilylation catalyst, and a diamine compound. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The curable silicone composition comprises: 
     (A) an organopolysiloxane with at least 2 silicon-bonded alkenyl groups per molecule and no SiO4/2 units, 
     (B) an organopolysiloxane with an average unit formula (R 1   3  SiO l/2 ) a  (RSiO 4/2 ) 1 .0, where R 1  is a substituted or non-substituted monovalent hydrocarbon group and a is 0.5 to 4.0. 
     (C) an organopolysiloxane curing agent having at least 2 silicon-bonded hydrogen atoms per molecule, 
     (D) a hydrosilylation catalyst, and 
     (E) a diamine compound. 
     Component (A) is an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule. Suitable alkenyl groups are exemplified by vinyl, allyl, butenyl, pentenyl, and hexenyl groups. Vinyl groups are preferred. 
     Component (A) preferably comprises at least two units selected from the group consisting of R 3  SiO 1/2 , R 2  SiO 2/2 , and RSiO 3/2  units, where R is a substituted or non-substituted monovalent hydrocarbon group. Component (A) does not have any SiO 4/2  units. 
     Examples of suitable non-substituted monovalent hydrocarbon groups for R include alkyl such as methyl, ethyl, propyl, butyl, pentyl, and hexyl; cycloalkyl such as cyclopentyl and cyclohexyl; aryl such as phenyl, tolyl, and xylyl; and aralkyl such as benzyl and phenethyl. Examples of suitable substituted monovalent hydrocarbon groups for R include halogenated alkyl groups such as 3,3,3-trifluoropropyl and 3-chloropropyl. Methyl and phenyl groups are preferred. 
     Component (A) can have a straight chain, a partially branched straight chain, or a branched chain molecular structure. However, straight chain and partially branched straight chain are preferred. 
     The viscosity of component (A) is not critical. However, the viscosity at 25° C. is preferably in the range of 50 to 100,000 mPa s. When the viscosity at 25° C. is less than 50 mPa s, the physical characteristics of the resultant silicone cured product might deteriorate. On the other hand, when viscosity exceeds 100,000 mPa s, the flowability and handling properties of the resultant composition may deteriorate. 
     Component (B) is an organopolysiloxane of the formula (R 1   3  SiO 1/2 ) a  (SiO 4/2 ) 1 .0, where R 1  is a substituted or non-substituted monovalent hydrocarbon group, and a is a number between 0.5 and 4.0. Preferably, a is within the range of 0.5 to 2.0, and more preferably within the range of 0.5 to 1.5. A mixture of components (B) and (E), imparts flame-retarding properties to the curable composition. 
     R 1  may be a substituted or non-substituted monovalent hydrocarbon group. Examples of suitable non-substituted monovalent hydrocarbon groups include alkyl such as methyl, ethyl, propyl, butyl, pentyl, and hexyl; cycloalkyl such as cyclopentyl and cyclohexyl; alkenyl such as vinyl, allyl, butenyl, and hexenyl, aryl such as phenyl, tolyl, and xylyl; and aralkyl such as benzyl and phenethyl. Examples of suitable substituted monovalent hydrocarbon groups include halogenated alkyl groups such as 3,3,3-trifluoropropyl and 3-chloropropyl. R 1  is preferably a methyl group. Preferably, the total amount of R 1  in component (B) is not less than 95 mole % methyl groups. 
     Component (B) contains a small amount of silicon-bonded hydroxyl or alkoxy group, such as methoxy and ethoxy groups. Bonding to hydroxyl groups is preferable. Preferably, the amount of hydroxyl groups bonded to silicon atoms in component (B) is 4.0 wt % ,or less; preferably 3.5 wt %, or less. This is because the silicon-bonded hydroxyl groups impart improved flame-retardation properties to silicone bodies obtained by curing the composition. 
     Component (B) is readily soluble in component (A). It is the solubility of component (B) in component (A) that improves flame-retardation properties of the cured substance. 
     Component (B) is present in an amount in the range of 0.01 to 20 parts by weight; preferably, in the range of 0.01 to 10 parts by weight; and especially preferably, in the range of from 0.01 to 5.0 parts by weight, per 100 parts by weight of component (A). When the amount of component (B) per 100 parts by weight of component (A) is below this range, the flame resistance of the resultant cured product tends to decrease. On the other hand, when the amount exceeds this range, the viscosity of the resultant composition increases, its flowability and handling, properties decrease, and transparency tends to decrease. 
     Component (C) is an organopolysiloxane with at least two silicon-bonded hydrogen atoms per molecule. Component (C) may also contain substituted or non-substituted monovalent hydrocarbon groups. Examples of suitable non-substituted monovalent hydrocarbon groups include alkyl such as methyl, ethyl, propyl, butyl, pentyl, and hexyl; cycloalkyl such as cyclopentyl and cyclohexyl; aryl such as phenyl, tolyl, and xylyl; and aralkyl such as benzyl and phenethyl. Examples of suitable substituted monovalent hydrocarbon groups include halogenated alkyl groups such as 3,3,3-trifluoropropyl and 3-chloropropyl. Methyl and phenyl groups are preferred. 
     Component (C) can have a straight chain, a partially branched straight chain, or a branched chain molecular structure. However, straight chain and partially branched straight chain are preferred. 
     The viscosity of component (C) is preferably in the range of 1 mPa s to 100,000 mPa s at 25° C. If the viscosity of component (C) is less than 1 mPa s, the component could easily volatilize and render the composition unstable. On the other hand, when viscosity exceeds 100,000 mPa s, the flowability and handling properties of the resultant composition might deteriorate. 
     The amount of component (C) is 0.1 to about 5 moles of silicon-bonded hydrogen atoms in component (C) per 1 mole of the silicon-bonded alkenyl groups in component (A). When there is less than 0.1 mole of silicon-bonded hydrogen atoms in component (C) per 1 mole of the silicon-bonded alkenyl groups in component (A), the composition is difficult to cure completely. On the other hand, the flame resistance becomes insufficient when the cured product is obtained from a composition in which the quantity of the silicon-bonded hydrogen atoms in component (C) per 1 mole of the silicon-bonded alkenyl groups in component (A) exceeds 5. 
     Component (D) is a hydrosilylation catalyst used to cure the composition. Suitable hydrosilylation catalysts include platinum catalysts such as chloroplatinic acid, alcohol solutions of chloroplatinic acid, olefin complexes of platinum, 1,3-divinyl-1,1,3,3-tetramethyldisiloxane complexes of platinum, and diketone complexes of platinum; palladium catalysts such as palladium black and tetrakis(triphenylphosphine) palladium; and rhodium catalysts. Platinum catalysts are preferable. 
     The amount of component (D) is a catalytic amount. When a platinum catalyst is used as component (D), the amount is preferably selected such that the content of platinum metal contained in the platinum catalyst is 0.01 to about 1,000 ppm based on the weight of component (A). The amount is more preferably in the range of 0.1 to 500 ppm. Compositions, in which the amount of platinum metal contained in the catalyst is below this range, tend become difficult to cure completely. On the other hand, when the amount of platinum metal exceeds this range, the cured products obtained from compositions can assume a brown color when heated. 
     Component (E) is a diamine compound represented by the general formula: 
     
         R.sup.3.sub.2 N--R.sup.2 --NR.sup.3.sub.2 
    
     Each R 3  is independently selected from the group consisting of alkyl groups of 1 to about 4 carbon atoms and hydrogen atoms. Suitable alkyl groups are exemplified by methyl, ethyl, propyl, and butyl groups. 
     R 2  is an alkylene group with 2 to about 4 carbon atoms. Suitable alkylene groups are exemplified by ethylene, propylene, and butylene groups. Ethylene is preferred. 
     Component (E) was known in the art as an agent for improving the storage stability of curable silicone compositions cured by hydrosilylation reaction, however, component (E) could not impart flame resistance to the cured product by itself. However, it has been found that component (E) could impart flame resistance to the cured product when added together with component (B). 
     Suitable diamine compounds for component (E) include N,N,N&#39;,N&#39;-tetramethylethylenediamine, N,N-dimethylethylenediarnine, N,N-diethylethylenediamine, N,N-dibutylethylenediarnine, and N,N,N&#39;,N&#39;-tetraethylethylenediamine. N,N,N&#39;,N&#39;tetramethylethylenediamine is preferred. 
     The amount of component (E) in this composition ranges from 0.0001 to 1.0 parts by weight, preferably 0.001 to 0.1 parts by weight, per 100 parts by weight of component (A). When amount of component (E) per 100 parts by weight of component (A) is below this range, it becomes difficult to impart sufficient flame resistance to the resultant cured product. On the other hand, the curability of compositions, in which the amount exceeds this range, tends to decrease. 
     The curable silicone composition is prepared by mixing components (A), (B), (C), (D), and (E). The composition cures to a flame resistant cured silicone product. The silicone cured product obtained by curing this composition can be colorless and transparent or colorless and semi-transparent. Alternatively, colored transparent, or colored semi-transparent, silicone cured products possessing flame resistance can be formed by adding various optional dyes and fluorescent dyes to the composition. When the transparency of the resultant silicone cured product is not important, various optional pigments and inorganic fillers can be compounded therewith. 
     Furthermore, other optional additives may be used in this composition, as long as long as this does not negate the purpose of the present invention. For example, acetylene compounds, ene-yne compounds, hydrazine compounds, phosphine compounds, mercaptan compounds and other addition reaction suppressants can be used. Heat-resistant additives, inorganic flame resistance-imparting agents, plasticizers, and adhesive property-imparting agents can be added to the present composition. 
     Silicone gels, silicone rubbers, and silicone resins are suggested as examples of silicone cured products obtained by curing the curable silicone composition of the present invention. In a preferred embodiment of the invention, silicone gels obtained by curing the present composition possess a relatively good flame resistance. Preferably, the 1/4 consistency, as specified in JIS K 2220, of these silicone gels should be in the range of from 20 to 200. This is due to the fact that when their 1/4 consistency is less than 20, stress relaxation properties of the silicone gels deteriorate, and when they are used for sealing or filling electric or electronic parts, the silicone gels used for filling or sealing are prone to crack, and, on the other hand, when it exceeds 200, the silicone gels are prone to become fluid on exposure to vibration. 
     The process for curing the curable silicone composition of this invention is not critical. For example, the composition can be cured by allowing the composition to stand at room temperature, or it can be heated to 50 to about 200° C. 
     Although the silicone cured product obtained in this manner can be handled as is, it is commonly handled by applying it to a substrate, for example, it is preferable to handle it in a state, in which it seals or fills electric or electronic parts, and it is especially preferable to handle it as sealant or filler for power modules and the like. 
    
    
     EXAMPLES 
     These examples are intended to illustrate the invention to those skilled in the art and should not be interpreted as limiting the scope of the invention set forth in the claims. 
     Viscosity in these examples is measured at 25° C. The 1/4 consistency was measured as follows: A silicone cured product was formed by placing 40 g of the curable silicone composition in a 50 ml beaker and then heating it for 1 hour at 125° C. After cooling the silicone cured product to 25° C., measurements were performed using a 1/4-inch cone in accordance with the method specified in JIS K 2220. The cone is positioned in a dropping device, perpendicular to the sample. The cone is dropped and allowed to penetrate the sample for 5 seconds, and penetration is measured. 
     Flame resistance of the cured product was measured as follows: Test samples, which were 12.7 mm wide, 127 mm long, and 3 mm thick, were prepared by placing the curable silicone composition in a Teflon® container and then heating it for 30 min to 1 hour at 120 to 125° C. A test sample was secured in a vertical position and the bottom portion of the test sample was placed in the center of a 20 mm flame (blue flame: 10 mm) of a gas burner, whose main ingredient was methane gas, for about 10 seconds, after which the gas burner was taken away and the time to extinction of the flame on the test sample was measured. Also, immediately after extinction of the flame on the test sample the above described operation was performed again, and the time to extinction of the flame (combustion time) was measured. This operation was repeated twice on each of the five test samples, obtaining a total combustion time based on ten measurements. 
     Example 1 
     Four curable silicone gel compositions were prepared and cured. The components and amounts in each sample (expressed in parts by weight) are listed as Examples, samples 1-1, 1-2, 1-3, and 1-4 in Table 1-1. The curable silicone gel compositions were prepared by uniformly mixing the components. 
     COMPONENT A-1 is an organopolysiloxane with a viscosity of 800 mPa s comprising 93.8 mol % (CH 3 ) 2  SiO 2/2  units, 3.1 mol % CH 3  SiO 3/2 , 2.5 mol % (CH 3 ) 3  SiO 1/2  units, and 0.6 mol % (CH 3 ) 2  (CH 2  ═CH)SiO 1/2  units (vinyl content=0.22 wt %). 
     COMPONENT A-2 is a dimethylpolysiloxane with a viscosity of 2,000 mPa s having both ends of the molecular chain blocked with dimethylvinylsiloxy groups (vinyl content=0.22 wt %). 
     COMPONENT B is an organopolysiloxane with the average unit formula: ((CH 3 ) 3  SiO 1/2 ) 0 .7 (SiO 4/2 ) 1 .0 and is soluble in components A-1 and A-2 (silicon-bonded hydroxyl content=0.5 wt %). 
     COMPONENT C is a dimethylpolysiloxane with a viscosity of 10 mPa s having both ends of the molecular chain blocked with dimethylhydrogensiloxy groups (silicon-bonded hydrogen content=0.13 wt %). 
     COMPONENT D is a complex of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane with platinum, in which the concentration of platinum was 0.5 wt %. 
     COMPONENT E-1 is N,N,N&#39;,N&#39;-tetramethylethylenediamine. 
     Colorless transparent silicone gels were formed by curing these silicone gel compositions by heating, them for 1 hour at 125° C. in an oven. The 1/4 consistency and flame resistance of the silicone gels was evaluated and the results are listed in Table 1-1. SiH/SiCH═CH 2  in Table 1-1 shows the molar number of the silicon-bonded hydrogen atoms contained in the or-anopolysiloxane used as component (C) per 1 mole of the silicon-bonded alkenyl groups contained in the organopolysiloxanes used as components (A-1), (A-2), and (B). 
     Comparative Example 1 
     Five curable silicone gel compositions were prepared and cured. The components of each sample (expressed in parts by weight) are listed as Comparative Examples, samples 1-5, 1-6, 1-7, 1-8, and 1-9 in Table 1-2. The curable silicone gel compositions were prepared by uniformly mixing the following components. 
     COMPONENTS A-1, B. C, D, and E-1 are as defined in Example 1. 
     COMPONENT E-2 is N-methylaniline. 
     COMPONENT E-3 is N-N&#39;-diisopropylamine. 
     COMPONENT E-4 is N,N,N&#39;,N&#39;-tetramethyl hexamethylene diamine. 
     Colorless transparent silicone gels were formed by curing these silicone gel compositions as in Example 1. The 1/4 consistency and flame resistance of the silicone gels were evaluated as in Example 1, and the results are listed in Table 1-2. 
     Example 2 
     Four curable silicone gel compositions were prepared by uniformly mixing the components (parts by weight) listed in Table 2-1. 
     COMPONENT A-3 is an organopolysiloxane with a viscosity of 800 n-pa s comprising 95.7 mol % (CH 3 ) 2  SiO 2/2  units, 1.8 mol % CH 3  SiO 3/2 , 1.8 mol % (CH 3 ) 3  SiO 1/2  units, and 0.7 mol % (CH 3 ) 2  (CH 2  ═CH)SiO 1/2  units (content of vinyl groups=0.25 wt %). 
     COMPONENT A-4 is a dimethylpolysiloxane with a viscosity of 1,000 mPa s having both ends of the molecular chain blocked with dimethylvinylsiloxy groups (vinyl content=0.22 wt %). 
     COMPONENTS B, C, D, E-1, E-2, E-3, and E-4 are the same as defined in Example 1. 
     Colorless transparent silicone gels were formed by curing these silicone gel compositions by heating them for 1 hour at 125° C. in an oven. The 1/4 consistency and flame resistance of the silicone gels was evaluated and the results were listed in Table 2-1. In addition, SiH/SiCH═CH 2  in Table 2-1 shows the molar number of the silicon-bonded hydrogen atoms contained in the organopolysiloxane used as component (C) per 1 mole of the silicon-bonded alkenyl groups contained in the organopolysiloxanes used as components (A-3), (A-4), and (B). 
     Comparative Example 2 
     Five curable silicone gel compositions were prepared and cured as in Example 2. The components and amounts in each sample (expressed in parts by weight) are listed as Comparative Examples, samples 2-5, 2-6, 2-7, 2-8, and 2-9 in Table 2-2. The curable silicone gel compositions were prepared by uniformly mixing, the components. All components are the same as defined in Example 2. 
     Colorless transparent silicone gels were formed by curing these silicone gel compositions as in Example 2. The 1/4 consistency and flame resistance of the silicone gels was evaluated and the results were listed in Table 2-2. 
     
                                           TABLE 1-1__________________________________________________________________________       ExamplesComponent   1-1   1-2   1-3   1-4__________________________________________________________________________Composition A-1   100   100   50    100 A-2   0     0     50    0 B     0.5   2     0.5   2 C     6.8   8.2   6.7   6.8 D     0.2   0.2   0.2   0.2 E-1   0.002 0.002 0.002 0.004 E-2   0     0     0     0 E-3   0     0     0     0 E-4   0     0     0     0SiH/SiCH═CH.sub.2       1.1   1.3   1.1   1.1Viscosity (mPa s)       800   850   1400  850Appearance  Colorless             Colorless                   Colorless                         Colorless       transparent             transparent                   transparent                         transparent1/4 consistency       80    122   105   80Flame-Retarding (sec)       161   150   130   165__________________________________________________________________________ 
    
     
                                           TABLE 1-2__________________________________________________________________________Comparative Examples with Different Diamine Compounds     Comparative Examples     1-5   1-6   1-7   1-8   1-9__________________________________________________________________________Composition A-1 100   100   100   100   100(parts by A-2 0     0     0     0     0weight) B   0     0.5   0.5   0.5   0.5 C   6.8   6.8   6.8   6.8   6.8 D   0.2   0.2   0.2   0.2   0.2 E-1 0.002 0     0     0     0 E-2 0     0     0.002 0     0 E-3 0     0     0     0.002 0 E-4 0     0     0     0     0.002SiH/SiCH═CH.sub.2     1.1   1.1   1.1   1.1   1.1Viscosity (mPa s)     750   800   800   800   800Appearance     Colorless           Colorless                 Colorless                       Colorless                             Colorless     transparent           transparent                 transparent                       transparent                             transparent1/4 consistency     80    80    80    80    80Flame-Retarding (sec)     340   1030  980   665   420__________________________________________________________________________ 
    
     
                                           TABLE 2-1__________________________________________________________________________     Examples     2-1   2-2    2-3    2-4__________________________________________________________________________Component A-3 100   100    50     100 A-4 0     0      50     0 B   0.5   2      0.5    2 C   6.8   8.2    6.7    6.8 D   0.2   0.2    0.2    0.2 E-1 0.002 0.002  0.002  0.004 E-2 0     0      0      0 E-3 0     0      0      0 E-4 0     0      0      0SiH/SiCH═CH.sub.2     0.9   1.1    1.0    0.9Viscosity (mPa s)     800   850    900    850Appearance     Colorless,           Colorless,                  Colorless,                         Colorless,     transparent           transparent                  transparent                         transparent1/4 consistency     80    122    105    80Flame Resist (sec)     161   150    130    165__________________________________________________________________________ 
    
     
                                           TABLE 2-2__________________________________________________________________________Comparative Examples with Different Diamine Compounds    Comparative Examples    2-5   2-6   2-7   2-8   2-9__________________________________________________________________________Component A-3    100   100   100   100   100 B  0     0.5   0.5   0.5   0.5 C  6.8   6.8   6.8   6.8   6.8 D  0.2   0.2   0.2   0.2   0.2 E-1    0.002 0     0     0     0 E-2    0     0     0.002 0     0 E-3    0     0     0     0.002 0 E-4    0     0     0     0     0.002SiH/SiCH═CH.sub.2    0.9   0.9   0.9   0.9   0.9Viscosity (mPa s)    750   800   800   800   800Appearance    Colorless          Colorless                Colorless                      Colorless                            Colorless    transparent          transparent                transparent                      transparent                            transparent1/4 consistency    80    80    80    80    80Flame Resist (sec)    340   1030  980   665   420__________________________________________________________________________