MXPA96004543A - Compositions that form elastomer - Google Patents

Abstract

The present invention relates to a composition forming siloxane-based elastomers, characterized in that it comprises (A) a first alpha, w-dihydroxyl polydiorganosiloxane, (B) a second alpha-w-dihydroxyl polydiorganosiloxane, (C) a third alpha, w-dihydroxyl polydiorganosiloxane, (D) an organosilicon compound having at least three hydrogen or alkoxy groups attached to the silicon and (E) a condensation catalyst, characterized in that the ratio of the average molecular weight of A / B is in the range of 20 to 80, the ratio of the average molecular weight number of B / C is in the range of 1 to 6, the ratio of A / B is in the range of 0.01 to 0.15 and the molar ratio of B / C is in the range of 0.2. to

Description

COMPOSITIONS THAT FORM ELASTOMEROS DESCRIPTION OF THE INVENTION The present invention relates to elastomer forming compositions, more specifically to compositions forming siloxane-based elastomers, which are substantially free of organic solvents and which exhibit improved strength, without the use of reinforcing filler particles. In some applications it is important that elastomeric siloxane materials are provided, which have a good mechanical strength, but do not have a high viscosity before curing to the elastoeric phase. Systems have been provided that have a relatively low viscosity before curing, and which give a high strength when cured to the elastomeric form, but tend to use organic solvent materials to reduce the inherent viscosity of elastomer-forming siloxane compositions, which have been formulated with reinforcing filler particles. There is a need to provide compositions that achieve a low viscosity before curing to an elastomeric form, without the use of organic solvents, which are REF: 23221 environmentally undesirable, but that retain good mechanical properties. Some systems have been suggested by Madkour and Mark in Poymer Bulletin 31, 615-621, 1994 and in Macromolecular Reports A31, 153-160, 1994. Suggested systems include those known as bimodal systems, in which a mixture of functionally terminated polydimethyl siloxanes and attached at the ends. Trimodal systems were also prepared and tested (using three siloxane polymers of different specified molecular weights), but the authors state that although the "change from a unimodal distribution to a bimodal distribution significantly improves the mechanical properties, the change from a bimodal distribution to a trimodal distribution does not give an additional improvement in the properties and can really be harmful. " Now we have found that by carefully selecting the components of a trimodal distribution «And their relationships, substantial improvements can be obtained. According to the invention there is provided a siloxane-based elastomer composition, which comprises (A) a first a,? -dihydroxyl polydiorganosiloxane, (B) a second a,? -dihydroxyl polydiorganosiloxane, (C) a third a,? -dihydroxyl polydiorganosiloxane, (D) an organosilicon compound having at least three hydrogens or alkoxy groups attached to the silicon and (E) a condensation catalyst, which is characterized in that the ratio of the average molecular weight index of A / B is in the range of 20 to 80, the ratio of the average molecular weight Index of B / C is in the range of 1 to 6, the molar ratio of A / B is in the range of 0.01 to 0.15 and the molar ratio of B / C is in the range of 0.2 to 2. Each of the components of the compositions according to the invention is known and commercially available, and will be described with greater detail later. Components (A), (B) and (C) are a,? - dihydroxyl polydiorganosiloxanes, which are substantially linear materials having an average general formula (I) HO - [Si - 0] "- H (I) wherein R denotes an organic group, preferably a hydrocarbon group, more preferably an alkyl group or an aryl group, for example, methyl, ethyl, n-propyl, isobutyl, n-hexyl, n-octodecyl, and n is a whole number R may be saturated or unsaturated, aliphatic or aromatic, but is preferably a group having up to 8 carbon atoms, more preferably not more than 3 carbon atoms. It is particularly preferred that at least 80% of all R groups are alkyl groups, preferably methyl groups. The most preferred are a, β-dihydroxyl polydimethyl siloxanes. Such siloxane materials are well known and commercially available with a wide range of chain lengths and molecular weights. The actual molecular weight of the materials used is not very important. The ratio of the molecular weight of the different components (A), (B) and (C) is, however, very important. The ratio of the average molecular weight index of A / B is from 20 to 80, preferably from 30 to 50, and from B / C is from 1 to 6, preferably from 2 to 4. From the conditions indicated above, it is of course, component (A) will have the highest molecular weight, and component (C) will be lowest, thus making (A) the longest polymer and (C) the shortest. However, it is preferred that component (A) have an average molecular weight index of 20,000 to 500,000, preferably 50,000 to 200,000, and that component (C) have an average molecular weight index of 200 to 3000, preferably 500 to 2500.

In addition to the importance of the average molecular weight number relationships of the polymers used as components (A) to (C), it is also important that the components (A, (B) and (C) are used in the correct molar proportions The number of moles used should reflect the A / B ratio from 0.01 to 0.15, preferably from 0.01 to 0.1, more preferably from 0.02 to 0.06, and a B / C ratio from 0.2 to 2, preferably from 0.5 to 1.5. Values outside the specified ratios tend to give elastomeric siloxane materials that have lower mechanical strength Component (D) is an organosilicon compound, which functions as a crosslinker for components (A) to (C) during the curing process, causing a three-dimensional network to form after curing the compositions according to the invention.To be active as a crosslinker, it is important that the component (D) has at least three sites per molecule in which it can react with any of the components (A) to (C). The curing mechanism of the elastomer forming compositions comprise a, β-dihydroxyl polydiorganosiloxanes, it is preferably a condensation reaction, in which the silanol group of the components (A) to (C) reacts with the hydrogen atoms attached to the silicon , releasing gaseous hydrogens, or with the alkoxy groups attached to the silicon, releasing alcohols. Consequently component (D) has either at least three hydrogen atoms attached to the silicon per molecule or three alkoxy groups attached to the silicon. The component (D) can be silanes or siloxanes and can be a linear, branched or resinous compound. Where the component (D) has hydrogen atoms attached to the silicon, it is preferably that component (D) having the average formula (II) R 'R' R 'I I I R "- [Yes - 0] a" [Yes - 0] b - Yes - R "(II) I I I R' R" R ' wherein R 'denotes a hydrocarbon group having up to 8 carbon atoms, R "denotes a hydrogen atom or a group R', provided that at least three R" groups are hydrogen atoms, a has a value of 0 or an integer and b is an integer with a value of minus 1. It is more preferred that the component (D) has at least three alkoxy groups attached to the silicon. The most preferred components (D) are either silanes or small resinous siloxanes. Preferred silanes have the general formula R'Si (OR ') 3 or Si (OR') 4, in which R 'is as defined above, preferably the alkyl has up to 4 carbon atoms. Examples of suitable silanes include methyltrimethoxy silane, phenyl trimethoxy silane, ethyl tripropoxy silane, hexyl trimethoxy silane, tetra ethoxy silane and tetra n-propoxy silane. Alternatively, but less preferred than silanes, component (D) can be a resinous siloxane, preferably consisting of monovalent siloxane units of the formula R "3 SiO? / 2 and tetravalent siloxane units of the formula Si04 / 2, preferably in a ratio of 0.6 / 1 to 1.5 / 1. The amount of component (D) used must be sufficient to provide sufficient crosslinking to give the elastomer formed sufficient mechanical strength, while having sufficient flexibility. It is preferred that the ratio of hydrogen or alkoxy groups attached to the silicon of component (D) to silanol groups in the combined components (A), (B) and (C) be in the range of 1/1 to 10/1. For compositions wherein the component (D) is a compound containing hydrogen bonded to the silicon, the ratio is preferably 1/1 to 5/1, more preferably 1/1 to 3/1. For compositions wherein the component (D) has alkoxy groups attached to the silicon, the ratio is preferably 2/1 to 10/1. The component (D) may also comprise more than one organosilicon compound useful as a crosslinker for the compositions according to the invention. It has been found that some combinations of different compounds can confer improvements to the mechanical properties, particularly the resistance to tearing or tearing. One such combination is the use of a tetra-alkoxy silane with a trialkoxy silane in a 2: 1 to 1: 2 ratio, for example, tetraethoxy silane and phenyl trimethoxy silane. The component (E) is a catalyst that causes the condensation of the components (A), (B) and (C) cotí (D). Any suitable condensation catalyst can be used, preferably the metal salts of carboxylic acid, for example, tin or lead salts. Particularly suitable condensation catalysts are the tin or lead salts of octoates or acetates, for example, dibutyltin dioctoate, dibutyltin dilaurate, dibutyltin di-ethyl-haxonate, dibutyltin diacetate, lead octoate, piorne ethyl hexoate. and lead acetate. The catalysts can be provided as 100% solid materials or can be diluted in suitable solvents or dispersed in suitable dispersion media. It is preferred to use from 1 to 4% by weight of the catalyst, based on the weight of the total composition%, preferably from 1.2 to 2%, or from 0.001 to 0.1 molar parts by weight of the present metal per 100 g of the composition, preferably from 0.002 to 0.05 molar parts. The levels indicated will ensure good curing, and will at the same time preserve a reasonable shelf life of the compositions according to the invention. Particularly preferred to improve the shelf life are mixtures of tin and lead salts, preferably in a weight ratio of 50/50 of the active catalyst species. Additional optional ingredients according to the invention may also be incorporated into the compositions. One such ingredient is (F) an organosilicon compound having at least three hydrogen atoms attached to the silicon. Although such an ingredient is suitable as a crosslinking component (D), the component (D) can also be added at a level of 1 to 2% by weight based on the total weight of the components (A) to (D). The organosilicon component (F) will act as a curing accelerator, whatever the crosslinking component (D) used. Preferably, the organosilicon compound (F) is added where the component (D) is an organosilicon compound having at least three alkoxy groups attached to the silicon. Where component (D) has alkoxy groups attached to silicon, it is also beneficial to add component (G), which is an organosilicon resin consisting solely of monovalent siloxane units of the formula Ra3SiO? 2 and tetravalent siloxane units of the formula SIO4 / 2 in a ratio of 0.4 / 1 to 1.2 / 1, preferably from 0.6 / 1 to 0.9 / 1, where Ra is an alkyl group, preferably having up to 6 carbon atoms, more preferably methyl , or a hydroxyl group, provided that no more than 5% by weight of hydroxyl groups are present on the resin molecule, preferably 2 to 3% by weight. Component (G) is usually a solid material, and is preferably provided in a suitable solvent, for example xylene or toluene, for example as a solids solution of 5"0 to 80% Where this component (G) is used at high levels, ie above 10% by weight based on the total weight of the components (A) to (D), preferably above 15%, an improvement in tear or tear strength was also observed Other optional ingredients include adhesion promoters, for example, amino functional or epoxy functional organosilicon compounds, colorants, dyes, preservatives, curing inhibitors, fillers, which may be reinforcing or non-reinforcing fillers or solvents. it prefers to leave out the reinforcing solvents or fillers, since the invention is particularly related to compositions without such ingredients.

The compositions according to the present invention can be prepared by any convenient method, for example, by mixing all the ingredients until a homogeneous mixture is obtained. To improve a storage stable composition, it is preferred that the ingredients are mixed in two parts, whereby the catalyst (E) is kept separate from the crosslinking component (D), preferably in sealed containers, which do not allow moisture to enter. . A suitable way of packaging the compositions according to the invention is incorporating part of the mixture of the components (A), (B) and (C) with the component (E) in a first part and the rest of the mixture of ( A), (B) and (C) with the component (D) in a second part, since the mixing of the parts 1 and 2 in the ratio of 1/1 will provide a composition forming elastomers according to the invention. Alternatively the component (E) is kept separate and is added as a second part in the desired ratio to the rest of the composition in a first part. The compositions according to the invention can be cured to elastomers by exposing them to moisture, for example, to air at ambient temperatures.

The curing of the compositions can be accelerated by heating the compositions when applied to appropriate substrates. The compositions according to the present invention are particularly useful as sealing compounds, for example, formable coatings for electronic applications or complicated or intricate molded materials. Those uses are of particular interest, since the initial viscosity of the compositions can be kept relatively low, allowing easy flow of uncured materials. The viscosities could be as low as 100 mPa.s at 25 ° C, and preferably remain below 50,000 mPa.s. Particularly useful viscosities are in the range of 500 to 10,000 mPa.s at 25 ° C. A number of examples and comparative examples now follow that demonstrate the benefits of the compositions according to the invention. All parts and percentages are by weight, unless otherwise indicated. The viscosities are given at 25 ° C. In the examples, the following compounds were used as ingredients of the compositions. The ingredient (1) was a,? - high viscosity dihydroxy polydimethyl siloxane having an average molecular weight of 100,000 and a viscosity of 50,000 mPa.s. Ingredient (2) was a high viscosity α, β-dihydroxy polydimethyl siloxane having an average molecular weight index of 146,000 and a viscosity of 360,000 mPa.s. The ingredient (3) was a high viscosity α, β-dihydroxy polydimethyl siloxane having an average molecular weight index of 71,000 and a viscosity of 13,500 mPa.s. Ingredient (4) was a high viscosity α, β-dihydroxy polydimethyl siloxane having an average molecular weight of 62,000 and a viscosity of 10,000 mPa.s. The ingredient (5) was an α, β-dihydroxy polydimethyl siloxane having an average molecular weight index of 4,600 and a viscosity of 70 mPa.s. The ingredient (6) was an α, β-dihydroxy polydimethyl siloxane having an average molecular weight index of 38,500 and a viscosity of 2000 mPa.s. The ingredient (7) was an α, β-dihydroxy polydimethyl siloxane having an average molecular weight index of 2000 and a viscosity of 40 mPa.s. The ingredient (8) was an α, β-dihydroxy polydimethyl siloxane having an average molecular weight index of 400 and a viscosity of 20 mPa.s. The ingredient (9) was a tetraethoxy silane. The ingredient (10) was phenyltri ethoxy silane. The ingredient (11) was a polymethylhydroxy siloxane blocked at the end with trimethylsiloxane having a viscosity of about 30 mPa.s. The ingredient (12) was a copolymer of polydimethyl siloxane. and polymethylhydroxy siloxane blocked at the end with trimethyl siloxane having a viscosity of about 5 mPa.s and 0.7% hydrogen. Ingredient (13) was a 50/50 mixture of dibutyltin di-2-ethylhexoate and lead 2-ethylhexoate with some organic solvent. The ingredient (14) is an organosilicon resin consisting solely of monovalent siloxane units of the formula Me3SiO? / 2 and tetravalent siloxane units of the formula SIOO / 2 in a ratio of 0.6 / 1 to 0.9 / 1, wherein It denotes a methyl group.

Examples 1 to 22 The compositions according to the invention were prepared by mixing, together, the ingredients according to Table I, wherein the components (A), (B) etc. they have the same meaning as the specification in the relationships as specified in Table II (where PM means the ratio of the average molecular weight index and Mol means molar ratio).

TABLE I Components A B C D E F G Example Ingredients 1 2 5 7 9 13 2 2 5 7 9 13 - - 3 2 5 7 9 13 - - 4 1 5 7 9 13 - - 5 1 5 7 9 + 10 13 - - 6 1 5 7 9 13 - - 7 1 5 7 9 + 10 13 - - 8 1 5 7 9 13 - - 9 3 7 8 9 13 - - 10 3 7 8 9 13 - - 11 4 7 8 9 13 - - 12 1 5 7 11 13 - - 13 1 5 7 11 13 - - 14 1 5 7 11 13 - - 15 1 5 7 11 13 - - 16 1 5 7 12 13 - - 17 1 5 7 9 + 10 13 11 - 18 1 5 7 9 + 10 13 11 - 19 1 5 7 9 + 10 13 11 - 20 3 7 8 9 13 '- 14 21 3 7 8 9 13 - 14 22 3 7 8 9 13 - 14 TABLE II Example Relationship PM PM Mol Mol Mol Mol A / B B / C A / B B / C SiH / SiOH SiOR / SiOH 1 56 3 0.04 0.35 - 4 2 56 3 0.02 0.35 - 4 3 56 3 0.02 0.54 - 4 4 40 3 0.04 0.70 - 4 5 40 3 0.04 0.70 - 4 6 40 3 0.03 0.35 - 4 7 40 3 0.04 0.52 - 4 40 3 0.04 0.70 - 4 9 80 3 0.05 0.54 - 3 80 3 0.04 0.54 - 3 11 57 3 -0.04 0.54 - 3 12 40 3 0.13 0.18 2 - 13 40 3 0.06 0.35 2 - 14 40 3 0.05 0.35 2 - 15 40 3 0.04 0.70 2 - 16 40 3 0.04 0.70 2 - 17 40 3 0.07 0.65 - 8 18 40 3 0.07 0.65 - 2 19 40 3 0.07 0.65 - 8 20 80 3 0.07 0.90 - 14 21 80 3 0.05 0.54 - 28 22 80 3 0.04 2.00 - 27 All the examples were tested to determine the Shore A hardness and viscosity (using a durometer according to DIN 53,505). They were also tested to determine elongation (%), tensile strength (Mpa) and mechanical strength (H = high, M = medium, L = low) according to DIN 53,504, Matrix S2. The results are given below in Table III.

TABLE III Example Viscosity Durometer Lengthening Traction Mechanical Resistance PPaa..ss S ihnoorree A a% MPa 1 5 5,, 666600 4444 185 4.7 H 2 1 1,, 770000 4 455 200 5.3 H 3 3 3,, 550000 4 444 200 5.6 H 4 2 2,, 553300 4 455 185 4.5 H 2 2,, 770000 4 422 200 5.2 H 6 1 1,, 000000 4 488 130 3.7 H 7 1 1,, 990000 4 488 180 5.2 H 8 1 1,, 553300 4 488 185 3.9 H 9 1 1 ,, 664400 4 400 200 3.6 H 1 1,, 000000 4 455 180 4.5 H 11 7 75500 4 488 170 3.7 H 12 2 211,, 440000 3 311 220 2.1 H 13 1 133,, 000000 3 388 200 2.2 H 14 7 7,, 667700 3 388 170 2.4 H 6 6,, 550000 3 355 140 1.4 M 16 3 3,, 660000 3 333 190 2.3 H 17 1 1,, 998800 4 411 190 4.2 H 18 2 2,, 002200 4 400 200 4.5 H 19 1 1,, 885500 4 444 185 4.0 H 1 1,, 000000 4 488 150 4.0 H 21 3 36600 5 566 150 4.2 H 22 4 46600 5 566 150 4.9 H In addition to the results given above, Examples 17, 18 and 19 (using component F) showed an improved curing time. Examples 20, 21 and 22 using component (G) were also tested for tear or tear resistance and showed a greater improvement (as a result of approximately 10 kN / m) over the examples in which the component was not used (G) Comparative Examples Cl to C15 The comparative examples were prepared in the same manner as the previous Examples, with the details of the compositions and ratios given in Tables IV and V and the test results in Table VI, where NA means not applicable.

TABLE IV Components A B Example Ingredients Cl 2 6 5 9 13 C2 1 5 8 9 13 C3 1 5 - 11 13 C4 3 5 - 11 13 C5 6 5 - 11 13 C6 2 5 - 9 13 C7 1 7 - 9 13 C8 3 8 - 9 13 C9 1 - - 11 13 CIO 3 - - 11 13 CU 6 - - 11 13 C12 5 - - 11 13 C13 3 - - 9 13 C14 3 - - 9 13 C15 3 - - 9 13 TABLE V Example Relationship PM PM Mol Mol Mol Mol A / B B / C A / B B / C SiH / SiOH SiOR / SiOH Cl 4 14 0.04 0.35 4 C2 40 8 0.04 0.38 - 4 C3 40 NA 0.03 NA 1 - C4 28 NA 0.03 NA 1 - C5 14 NA 0.03 NA 1 C6 56 NA 0.04 NA - 4 C7 114 NA 0.04 NA - 4 C8 180 NA 0.04 NA - 4 C9 NA NA NA NA 1 - CIO NA NA NA NA 1 - CU NA NA NA NA 1 - C12 NA NA NA NA 1 - C13 NA NA NA NA - 20 C14 NA NA NA NA - 40 C15 NA NA NA NA - 60 TABLE VI Example Viscosity Durometer elongation Traction ResistETKia Map¡tn.ca mPa.s Shore A% MPa Cl 1,160 28 120 0.85 L C2 1,780 39 80 1.00 L C3 9,200 39 90 0.70 L C4 1,700 42 50 0.40 L C5 360 44 30 0.40 L C6 57,000 27 180 1.20 L C7 22,000 30 180 1.60 L C8 4,000 23 225 1.50 L C9 50,000 6 1,200 0.25 L CIO 13,800 8 330 0.21 L CU 2,700 20 150 0.20 L C12 90 28 40 0.28 L C13 13,000 20 100 0.30 L C14 11,000 40 110 0.33 L C15 9,400 17 100 0.23 L The comparative results for the prior art systems require the use of polymers similar to gums of extremely high viscosity and large amounts of solvents (up to 70% toluene). Where lower viscosity polymers were used, and thus less solvent was required, the remaining mechanical and elastomeric properties tended to be less desirable (eg very low elongation). It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it refers. Having described the invention as above, the content of the following is claimed as property: '.

Claims (10)

1. A composition forming siloxane-based elastomers, characterized in that it comprises (A) a first α, β-dihydroxyl polydiorganosiloxane, (B) a second α, α-dihydroxyl polydiorganosiloxane, (C) a third α, β-dihydroxyl polydiorganosiloxane, ( D) an organosilicon compound having at least three hydrogens or alkoxy groups attached to the silicon and (E) a condensation catalyst, characterized in that the ratio of the average molecular weight index of A / B is in the range of 20 to 80, the ratio of the average molecular weight number of B / C is in the range of 1 to 6, the ratio of A / B is in the range of 0.01 to 0.15 and the molar ratio of B / C is in the range of 0.2 to 2.

2. A composition according to claim 1, characterized in that the components (A), (B) and (C) are substantially linear α, β-dihydroxyl polydiorganosiloxanes having an average general formula R I HO - [Si - 0] "- H I in which R is a hydrocarbon group and n is an integer.

3. A composition according to claim 2, characterized in that R is an alkyl group having up to 8 carbon atoms or an aryl group having up to 8 carbon atoms.

4. The composition according to any of the preceding claims, characterized in that in addition the component (A) has a number average molecular weight in the range of 20,000 to 500,000 and the component (C) has a number of the average molecular weight in the range of 200 to 3000.

5. The composition according to any of the preceding claims, characterized in that also the component (D) has the average formula R 'R' R 'I I I R "- [Yes - 0] a - [Yes - 0] b - Yes - R" I I R' R '' R ' wherein R 'is a hydrocarbon group having up to 8 carbon atoms, R "is a hydrogen atom or R', with the proviso that at least three R" groups are hydrogen or alkyl groups, a is a integer greater than or equal to 0 and b is an integer greater than 0.

6. The composition according to any of the preceding claims, characterized in that in addition the component (D) has the general formula R'Si (OR ') 3 or Si (0R), in which R' is a hydrocarbon group having up to 8 carbon atoms.

7. A composition according to any of the preceding claims, characterized in that in addition the component (D) is a resinous siloxane consisting of monovalent siloxane units of the formula R''3SiO? / 2 and tetravalent siloxane units of the formula SiO 2 and the ratio of monovalent siloxane units to tetravalent siloxane units is in the range of 0.6 / 1 to 1.5 / 1.

8. The composition according to any of the preceding claims, characterized in that in addition the component (E) is a condensation catalyst based on the metal salts of a carboxylic acid.

9. The composition according to any of the preceding claims, characterized in that in addition the component (D) is an organosilicon compound having alkoxy groups attached to the silicon and wherein the composition also comprises an organosilicon compound (F) having at least three hydrogen atoms attached to the silicon, wherein the component (F) is present in a concentration of 1 to 2% by weight based on the total weight of "the components (A), (B) , (C) and (D).

10. The composition according to any of the preceding claims, characterized in that in addition the component (D) is an organosilicon compound having alkoxy groups attached to the silicon and wherein the composition also comprises an organosilicon resin. (G) consisting of monovalent siloxane units of the formula Ra3SiO? / 2 and tetravalent siloxane units of the formula siO? /, In a ratio of 0.4 / 1 to 1.2 / 1, wherein Ra is an alkyl group having up to 6 carbon atoms or a hydroxyl group, with the proviso that not more than about 5% by weight of hydroxyl groups are present on the resin (G) and wherein the component (G) is present in a ratio greater than 10. % by weight based on the total weight of the components (A), (B), (C) and (D).