JP5269405B2 - Flame retardant silicone rubber composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flame-retardant silicone rubber composition which is excellent in flame retardance and maintains physical properties inherent in silicone rubber as they are. <P>SOLUTION: The flame-retardant silicone rubber composition is obtained by adding a platinum complex in an amount of 0.1-1,000 ppm expressed in terms of platinum element based on 100 pts.wt. of a thermosetting polyorganosiloxane composition, wherein the platinum complex is solid at ordinary temperature and pressure, and the temperature at which the weight loss rate becomes higher than 50 wt.% is &ge;300&deg;C, as measured with a thermogravimetric analyzer. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a silicone rubber composition having excellent flame retardancy.

Conventionally, silicone compositions that cure to become silicone rubbers are well known, and their excellent properties such as weather resistance, heat resistance, and electrical insulation make use of potting materials and coating materials for electrical and electronic parts. It is widely used for molding materials such as molds and wire materials. In addition, by adding various additives to this silicone composition, it is generally performed to impart properties according to the application, for example, flame retardancy. As a technique for imparting flame retardancy to the silicone rubber composition, many reports have been made conventionally. For example, a method of blending a platinum compound as a flame retardancy imparting agent (see Patent Document 1), or a platinum compound There are known a method in which a metal oxide or the like is used in combination (see Patent Document 2), and a method in which a platinum compound and carbon black or the like are used in combination (see Patent Document 3). As a technique for imparting flame retardancy without using a platinum-based compound, a method of blending an organic halogen compound (see Patent Document 4) is known. However, if it is possible to color and obtain UL94V0 grade flame retardancy, there are conditions such as the influence of the color tone of the flame retardant aid and the need to reduce the amount of low molecular siloxane in the methyl siloxane used for the base. there were. Moreover, there was nothing which showed favorable flame retardance irrespective of the thickness of the test body.
Japanese Patent Publication No. 44-2591 JP 48-96650 A JP-A-53-130753 JP 55-108454 A

  The present invention has been devised in view of such problems of the prior art, and provides a flame retardant silicone rubber composition which is excellent in flame retardancy and maintains the original physical properties of silicone rubber. With the goal.

As a result of intensive studies to achieve the above-mentioned object, the present inventors have tested a thermosetting polyorganosiloxane composition by blending a certain amount of a platinum complex that is solid under normal temperature and pressure as a flame retardant imparting agent. It has been found that it has effective flame retardancy regardless of the thickness of the body, and has completed the present invention.
That is, the present invention
(A) With respect to 100 parts by weight of the thermosetting polyorganosiloxane composition,
(B) 0.1 to 1000 ppm as a platinum element amount of a platinum complex that is solid under normal temperature and normal pressure and has a temperature of 300 ° C. or higher when the weight loss rate exceeds 50 wt% in a thermogravimetric analyzer.
It is a flame retardant silicone rubber composition added.

  ADVANTAGE OF THE INVENTION According to this invention, the flame-retardant silicone rubber composition which can be colored without conditions, such as having to reduce the amount of low molecular siloxanes of the methylsiloxane used for a base, can be provided. The flame-retardant silicone rubber composition of the present invention is excellent in flame retardancy and maintains the excellent physical properties of silicone rubber as it is, so it can be used in cables, packings, connectors, etc. that require UL flame retardant certification. It is suitably used for electric parts to be provided, and is also suitably used for building members (gaskets, packing, sealing materials) that are essentially required to be flame retardant against heat and flame.

  The thermosetting polyorganosiloxane composition of the component (A) is obtained by uniformly dispersing (a) a polyorganosiloxane base polymer, (b) a curing agent, and various additives as required. is there. Of the various components used in such a composition, (a) the silicone base polymer and (b) the curing agent are appropriately selected according to the reaction mechanism for obtaining a rubber elastic body. As the reaction mechanism, (1) a crosslinking method using an organic peroxide vulcanizing agent, (2) a condensation reaction method, (3) an addition reaction method, etc. are known. It is well known that the preferred combination of component and component (b), ie a curing catalyst or crosslinker, is determined. First, in the case of applying the crosslinking method of (1), usually, as the base polymer of the component (a), at least two of organic groups bonded to silicon atoms in one molecule are vinyl, propenyl, Polyorganosiloxanes that are alkenyl groups such as butenyl and hexenyl are used. Of these groups, vinyl groups are frequently used because of the ease of synthesis and the availability of raw materials. In addition, as the curing agent for component (b), benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dicumyl peroxide, cumyl-t-butyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxy Various organic peroxide vulcanizing agents such as hexane and di-t-butyl peroxide are used and give particularly low compression set. Therefore, dicumyl peroxide, cumyl-t-butyl peroxide, 2,5-dimethyl- 2,5-Di-t-butylperoxyhexane and di-t-butylperoxide are preferred. These organic peroxide vulcanizing agents are used as one kind or a mixture of two or more kinds. The blending amount of the organic peroxide which is the curing agent of the component (b) is preferably in the range of 0.05 to 15 parts by weight with respect to 100 parts by weight of the silicone base polymer of the component (a). If the amount of organic peroxide is less than 0.05 parts by weight, vulcanization will not be performed sufficiently, and if it exceeds 15 parts by weight, there will be no particular effect, and the physical properties of the resulting silicone rubber will be reduced. This is because it may have an adverse effect.

  When the condensation reaction (2) is applied, a polydiorganosiloxane having hydroxyl groups at both ends is used as the base polymer of the component (a). As the curing agent for component (b), first, as a crosslinking agent, ethyl silicate, propyl silicate, methyltrimethoxysilane, vinyltrimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, methyltris (methoxyethoxy) silane, vinyltris ( Alkoxy type such as methoxyethoxy) silane and methyltripropenoxysilane; acetoxy type such as methyltriacetoxysilane and vinyltriacetoxysilane; methyltri (acetoneoxime) silane, vinyltri (acetoneoxime) silane, methyltri (methylethylketoxime) silane, Examples thereof include vinyltri (methylethylketoxime) silane and the like, and partial hydrolysates thereof. Hexamethyl-bis (diethylaminoxy) cyclotetrasiloxane, tetramethyldibutyl-bis (diethylaminoxy) cyclotetrasiloxane, heptamethyl (diethylaminoxy) cyclotetrasiloxane, pentamethyl-tris (diethylaminoxy) cyclotetrasiloxane, hexamethyl-bis ( Examples thereof include cyclic siloxanes such as methylethylaminoxy) cyclotetrasiloxane and tetramethyl-bis (diethylaminoxy) -mono (methylethylaminoxy) cyclotetrasiloxane. Thus, the cross-linking agent may be either a silane or siloxane structure, and the siloxane structure may be linear, branched or cyclic. Furthermore, when using these, it is not necessary to be limited to one type, and two or more types can be used together. Among the curing agents of component (b), examples of the curing catalyst include metal carboxylic acid salts such as iron octoate, cobalt octoate, manganese octoate, tin naphthenate, tin caprylate, and tin oleate; dimethyltin dioleate; Organotin compounds such as dimethyltin dilaurate, dibutyltin diacetate, dibutyltin dioctoate, dibutyltin dilaurate, dibutyltin dioleate, diphenyltin diacetate, dibutyltin oxide, dibutyltin dimethoxide, dibutylbis (triethoxysiloxy) tin, dioctyltin dilaurate Used. Of the curing agent (b), the amount of the crosslinking agent is preferably 0.1 to 20 parts by weight per 100 parts by weight of the base polymer (a). If the amount of the crosslinking agent used is less than 0.1 parts by weight, sufficient strength cannot be obtained in the rubber after curing, and if it exceeds 20 parts by weight, the resulting rubber becomes brittle, both of which are difficult to withstand practical use. Moreover, the compounding amount of the curing catalyst is preferably 0.01 to 5 parts by weight with respect to 100 parts by weight of the base polymer of the component (a). If the amount is less than this, it is insufficient as a curing catalyst, and it takes a long time for curing, and curing in the interior far from the contact surface with air becomes poor. On the other hand, when it is more than this, the storage stability is lowered. A more preferable range of the blending amount is 0.1 to 3 parts by weight.

  As the base polymer of the component (a) in the case of applying the addition reaction of (3) above, the same base polymer as in the above (1) is used. In addition, as the curing agent of component (b), platinum catalysts such as chloroplatinic acid, platinum olefin complexes, platinum vinylsiloxane complexes, platinum black, platinum, etc. are used as curing catalysts. A polydiorganosiloxane having an average of more than at least two bonded hydrogen atoms per molecule is used. Of the curing agent of component (b), the blending amount of the curing catalyst is preferably in the range of 1 to 1000 ppm in terms of platinum element relative to the base polymer of component (a). If the amount of the curing catalyst is less than 1 ppm as the amount of platinum element, curing will not proceed sufficiently, and if it exceeds 1000 ppm, no improvement in the curing rate can be expected. The blending amount of the cross-linking agent is preferably such that 0.5 to 4.0 hydrogen atoms bonded to silicon atoms in the cross-linking agent per alkenyl group in component (a), more preferably The amount is 1.0 to 3.0. If the amount of hydrogen atoms is less than 0.5, curing of the composition does not proceed sufficiently, resulting in a low hardness of the composition after curing, and if the amount of hydrogen atoms exceeds 4.0, The physical properties and heat resistance of the composition are reduced.

  The organic group in the polyorganosiloxane as the base polymer of the component (a) used in the various reaction mechanisms as described above is a monovalent substituted or unsubstituted hydrocarbon group, such as a methyl group, an ethyl group, or a propyl group. An unsubstituted hydrocarbon group such as an alkyl group such as a butyl group, a hexyl group or a dodecyl group, an aryl group such as a phenyl group, an aralkyl group such as a β-phenylethyl group or a β-phenylpropyl group, Examples thereof include substituted hydrocarbon groups such as a methyl group and 3,3,3-trifluoropropyl group. In general, methyl groups are frequently used because of their ease of synthesis.

The platinum complex of component (B) used in the present invention must be a solid at normal temperature and pressure. It is difficult to impart sufficient flame retardancy with a liquid platinum complex alone. Further, a thermogravimetric analyzer having a weight reduction rate exceeding 50% by weight at 300 ° C. or higher is particularly preferable.
A preferable component (B) is a compound complex containing a platinum-phosphorus element, and a platinum-phosphite complex is particularly preferable.
Examples of the phosphorus compound used here include tris (2,4-di-tert-butylphenyl) phosphite, 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy]- 2, 4, 8, 10-Tetra-tert-butyldibenz [d, f,] [1.3.2] A compound exemplified by dioxaphosphepine, etc., which is a solid phosphite compound at room temperature and normal pressure. Some are preferred.
The blending amount of the (B) platinum complex is within a range of 0.01 to 1000 ppm, preferably 0.5 to 200 ppm, in terms of the elemental amount of platinum with respect to 100 parts by weight of the thermosetting silicone rubber composition of the component (A). Range. If the compounding amount of these platinum elements is less than 0.01 ppm, the effect of imparting flame retardancy is insufficient. On the other hand, platinum compounds contain precious metals and are generally expensive, so adding a large amount is economically disadvantageous, and even if it exceeds 1000 ppm, there is no particular meaning and the heat resistance deteriorates. Is defined.

  Furthermore, it is preferable to use a liquid platinum complex in combination with the solid platinum complex used in the present invention. The liquid platinum complex may be the same as the platinum compound used as the curing catalyst in the polyorganosiloxane addition reaction described above. For example, alcohol-modified chloroplatinic acid, a complex of platinum and olefin, platinum and ketones And platinum-based compounds exemplified by complexes with platinum, complexes of platinum and vinylsiloxane, and the like. By using such a platinum compound in combination with the aforementioned component (B), it is possible to obtain a silicone rubber that is excellent in flame retardancy and does not hinder the inherent properties of the silicone rubber. The compounding amount of the liquid platinum compound used in combination is in the range of 0.01 to 1000 ppm, preferably 0.5 to 200 ppm, in terms of the amount of platinum metal element, per 100 parts by weight of the silicone rubber composition (A). Range. When the compounding amount of these platinum compounds is less than 0.01 ppm, the effect of imparting flame retardancy is insufficient. On the other hand, platinum compounds are generally expensive, so adding a large amount is economically disadvantageous, and there is no particular meaning even if the amount exceeds 1000 ppm, and the heat resistance deteriorates, so such a range is defined. .

  The flame retardant silicone rubber composition of the present invention may additionally contain various additives such as reinforcing fillers, heat resistance improvers and flame retardants other than those described above. As such, usually, fumed silica, precipitated silica, diatomaceous earth and other reinforcing fillers, graphite, aluminum oxide, titanium dioxide, cerium hydroxide, mica, clay, glass beads, polydimethylsiloxane, Examples thereof include heat resistance improvers such as alkenyl group-containing polysiloxane.

  Examples of the present invention will be described below. In addition, the part in an Example shows a weight part.

Complex preparation example 1
5 g of chloroplatinic acid (H ₂ PtCl ₆ ) (platinum content 37 wt%), 90 g of THF (tetrahydrofuran), 12.3 g of tris (2,4, -di-tert-butylphenyl) phosphite were mixed, The mixture was heated to reflux for 6 hours under a nitrogen atmosphere. Then, it was concentrated under reduced pressure. 200 g of ethanol was added to obtain a white precipitate. The resulting precipitate was filtered off and washed with ethanol. However, the temperature exceeding the 50% weight reduction rate in a thermogravimetric analyzer (in the air atmosphere, at a temperature rising rate of 10 ° C./min) was 395 ° C. A paste 1 (platinum content 1 wt%) was prepared by diluting at 25 ° C. with a vinyldimethylsiloxy group-blocked linear dimethylpolysiloxane having a viscosity of 10 Pa · s at both ends.

Complex preparation example 2
5 g chloroplatinic acid (H ₂ PtCl ₆ ) (platinum content 37 wt%), 90 g THF, 12.2 g 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2, 4, 8, 10-Tetra-tert-butyldibenz [d, f,] [1.3.2] dioxaphosphine was mixed and heated to reflux in a nitrogen atmosphere for 6 hours. Then, it was concentrated under reduced pressure. 200 g of ethanol was added to obtain a white precipitate. The obtained precipitate was separated by filtration and then washed with a large amount of ethanol. However, the temperature at which the weight loss rate exceeded 50% was 436 ° C. in a thermogravimetric analyzer (in the air atmosphere, at a temperature rising rate of 10 ° C./min). A paste 2 (platinum content 1 wt%) was prepared by diluting with a linear dimethylpolysiloxane blocked with vinyldimethylsiloxy group-blocked linear dimethylpolysiloxane having a viscosity of 10 Pa · s.

Comparative complex preparation example 1
5 g of chloroplatinic acid (H ₂ PtCl ₆ ) (platinum content 37 wt%), 80 g of ethanol, 13 g of trisnonylphenyl phosphite and 34 g of sodium hydrogen carbonate were mixed and heated to reflux for 4 hours. Next, the produced salt was filtered and further washed with 20 g of ethanol to obtain an ethanol solution of a platinum complex. Excess ethanol was removed under reduced pressure. However, the temperature at which the weight loss rate exceeded 50% was 286 ° C. in a thermogravimetric analyzer (in the air atmosphere, at a temperature rising rate of 10 ° C./min). Next, the paste 3 was prepared by diluting with a linear dimethylpolysiloxane blocked at both ends with a vinyldimethylsiloxy group having a viscosity of 10 Pa · s so that the platinum content was 1% at 25 ° C.

Comparative complex preparation example 2
5 g of chloroplatinic acid (H ₂ PtCl ₆ ) (platinum content 37 wt%), 80 g of ethanol, 13 g of 2-ethylhexyl acid phosphate and 34 g of sodium hydrogen carbonate were mixed and heated to reflux for 4 hours. Next, the produced salt was filtered and further washed with 20 g of ethanol to obtain an ethanol solution of a platinum complex. Excess ethanol was removed under reduced pressure, and the precipitated salt was further filtered. However, the temperature exceeding the 50% weight reduction rate by a thermogravimetric analyzer (under an air atmosphere at a temperature rising rate of 10 ° C./min) was 207 ° C. Next, the paste 4 was prepared by diluting with a linear dimethylpolysiloxane blocked at both ends with a vinyldimethylsiloxy group having a viscosity of 10 Pa · s so that the platinum content was 1% at 25 ° C.

Example 1
After uniformly kneading 100 parts of polydimethylsiloxane (degree of polymerization about 5500) containing 0.13 mol% of methylvinylsiloxane unit and 30 parts of fumed silica (Aerosil 130, Nippon Aerosil Co., Ltd.) using a kneader This was treated at a temperature of 150 ° C. for 2 hours. After cooling to room temperature, 60 parts of crystalline silica (Crystalite VX-S, manufactured by Tatsumori Co., Ltd.), 5 parts of titanium oxide (P-25, manufactured by Nippon Aerosil Co., Ltd.), cerium hydroxide (first rare element) 10 parts by Chemical Industry Co., Ltd. and the paste prepared in Complex Preparation Example 1 (platinum content 1 wt%) were mixed and stirred to obtain a compound.
After adding a vulcanizing agent (2,5-dimethyl-2,5-di-t-butylperoxyhexane) to this compound, press it at 170 ° C for 10 minutes, and then perform hot air vulcanization at 200 ° C for 4 hours. The rubber sheet of 3 types (0.5, 1.0, 2.0 mm) was produced.

Examples 2-4, Comparative Examples 1-4
As shown in Table 1, Table 1 shows pastes 1 to 4 prepared in Complex Preparation Examples 1 and 2, Comparative Complex Preparation Examples 1 and 2, and platinum-triphenylphosphite complex (platinum content: 6.3 wt%). A rubber sheet was prepared in the same manner as in Example 1 except that the amount shown in (1) was added.

Comparative Examples 5-7
As shown in Table 1, a rubber sheet was prepared in the same manner as in Example 1 except that instead of paste 1, a mixture of vinyl complex and phosphine was added in the amount shown in Table 1.

Example 5
100 parts of dimethylpolysiloxane having both ends of a molecular chain with a viscosity of 10 Pa · s blocked with vinyldimethylsiloxy groups, 27 parts of fumed silica (Aerosil 130, manufactured by Nippon Aerosil Co., Ltd.), 4 parts of hexamethylsilazane The mixture was uniformly kneaded using a universal kneader, and then subjected to reduced pressure treatment at a temperature of 150 ° C. for 2 hours. After cooling to room temperature, 60 parts of crystalline silica (Crystalite VX-S, manufactured by Tatsumori Co., Ltd.), 60 parts of titanium oxide (P-25, manufactured by Nippon Aerosil Co., Ltd.), paste prepared in Complex Preparation Example 1 (Platinum content 1 wt%) and platinum-phosphorous triphenyl complex (platinum content 6.3 wt%) were mixed and stirred to obtain a compound. Thereto was added 5 parts of methyl hydrogen polysiloxane having a viscosity of 0.04 Pa · s and mixed uniformly to obtain a flame retardant silicone composition.
This composition was pressed at 170 ° C. × 10 minutes and then hot-air vulcanized at 200 ° C. × 4 hours to prepare rubber sheets having three thicknesses (0.5, 1.0, 2.0 mm).

Examples 6-8, Comparative Examples 8-10
As shown in Table 2, pastes 1 to 4 prepared in Complex Preparation Examples 1 and 2 and Comparative Complex Preparation Examples 1 to 2, and these and a platinum-triphenylphosphite complex (platinum content 6.3 wt%) are shown in Table 2. A rubber sheet was prepared in the same manner as in Example 1 except that the amount shown in (1) was added.
Comparative Examples 11-13
As shown in Table 2, a rubber sheet was prepared in the same manner as in Example 5 except that instead of paste 1, a mixture of a vinyl complex and a phosphine was added in the amount shown in Table 2.

(Evaluation of flame retardancy)
The flame retardancy of the cured product was evaluated according to the flame retardancy test method of UL-94 as follows. In the open blue flame with a height of 20 mm that is generated upward from the top of the Bunsen burner (inner diameter 9.5 mm), the test piece is positioned so that the end of the test piece is at a height of 10 mm from the top of the Bunsen burner. Was fixed vertically. They were then exposed for 10 seconds in an open blue flame. Thereafter, the test piece was taken out from the open blue flame, and the time (seconds) until the test piece was completely extinguished was measured (operation 1). This operation 1 was repeated twice for the same sample. The above operation was performed on five samples, and the total value of the maximum burning time of operation 1 and a total of 10 measurement values (time until the sample was completely extinguished after flame release) was obtained. The total value of each thickness was also obtained. The results are shown in the flame retardancy column of Tables 1 and 2.

Claims (3)

(A) (a) Thermosetting poly , comprising a polyorganosiloxane base polymer in which at least two of the organic groups bonded to silicon atoms in one molecule are vinyl groups, and (b) an organic peroxide vulcanizing agent. For 100 parts by weight of the organosiloxane composition,
(B) 0.1 to 1000 ppm as a platinum element amount of platinum complex that is solid under normal temperature and normal pressure, and the temperature when the weight reduction rate exceeds 50% by weight in a thermogravimetric analyzer is 300 ° C. or more.
A flame retardant silicone rubber composition added.   The flame retardant silicone rubber composition according to claim 1, wherein the component (B) is a compound complex containing a platinum-phosphorus element. The flame retardant silicone rubber composition according to claim 1, wherein the component (B) is a platinum-phosphite complex.