MXPA01000067A - Process for preparing heat-vulcanizable silicone compositions - Google Patents

Abstract

Untreated filler and a high viscosity silicone polymer premix is charged into a compounding apparatus. Treating agent and additional silicone polymer are added to the premix and the premix, treating agent and additional silicone polymer are compounded to produce a heat vulcanizable filled silicone composition.

Description

COMPOSITIONS OF THERMOVULCANIZABLE SILICON FROM A PREMIX BACKGROUND OF THE INVENTION The invention relates to a process for preparing thermovulcanizable silicone compositions. Particularly, the invention relates to a process for preparing thermovulcanizable silicone compositions from a premix of an untreated filler and a silicone polymer. A thermovulcanizable silicone composition comprises a high viscosity silicone polymer, an inorganic reinforcing filler and various additives that help to process or impart the desired final properties to the composition. A vulcanizing agent can be added and the composition can be solidified with heat to make a silicone rubber molding such as gaskets, medical tubes and computer keyboards. The thermovulcanizable silicone composition can be prepared from a concentrate called premix. A premix is an extrudable composition formed of a mixture of a polymer and a finely divided filler, prepared by combining the materials under conditions of high stress, shear force in the presence of a liquid processing aid. The liquid processing aid treats the silanol filling groups. The remaining silanol groups on the surface of the filler can regulate the strength of the hydrogen bonds between the silica and the hydroxyl or the oxygen groups in the silicone polymer chain. The high concentrations of silanols remaining in a filler cause "structuring" or "crepe hardening" of the final product in storage. This effect causes difficulties in processing the material after it has been stored for long periods. Typically, a treatment agent is added to reduce the silanol functional groups to a required concentration. Large free interfacial forces develop between the silicone polymer and the unreacted, free, silanol groups present in the filler. The treatment agent must be propagated in a mass of the high molecular weight silicone polymer and penetrate a rigid interface of silicone polymer / filler to reach reactive silanol groups. Therefore, the treatment agent is added directly to the silica before the premix formation step or during the premix formation step under the conditions of high shear mixing. A treated premix is a wet composition that is harder to store or transport than a dry mix. That is why the treated premix is prepared and loaded immediately in a subsequent extrusion step. For example, Kasahara et al., In the U.S. Patent. 5,198,171, shows the preparation of a premixture of an inorganic polydiorganosiloxane filler substance and liquid treatment agents in a high speed mechanical cutting mixer. The resulting premix is combined in a twin screw extruder of the same direction. The difficulties in storing and transporting a treated wet premix poses limitations in the use of the premix and its commercial value. There is a need for a filling and premixing substance of silicone polymer with widely used properties.

BRIEF DESCRIPTION OF THE INVENTION The invention provides a process using an untreated filler substance having widely used properties. In the process, the premix of an untreated filler and a high viscosity silicone polymer is loaded into a mixing apparatus. The treatment agent and the additional silicone polymer are added to the premix and the premix, treatment agent and additional silicone polymer are combined to produce a thermoformable silicone filler composition. In another embodiment, a premix of a filler and a high viscosity silicone polymer is formed in the absence of a treatment agent. The untreated filler premix and high viscosity silicone polymer is loaded into a mixing apparatus in which the treating agent and the silicone polymer are added. The premix, treatment agent and additional silicone polymer are combined in the apparatus to produce a thermovulcanizable silicone filler composition.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic representation of a process for preparing an untreated filler premix and silicone polymer and preparing a heat-vulcanizable filler silicone composition from the premix.

DETAILED DESCRIPTION OF THE INVENTION In accordance with the invention, high viscosity thermovulcanizable silicone compositions are prepared directly from untreated premixes. An untreated premix is a combined mixture of a filler with unreacted silanol surface groups, with a treatment agent and a high viscosity silicone polymer, surprisingly, the silica silanol groups of the premix can be treated properly with a treatment agent during a subsequent mixing step with polymeric rubber in a high-speed mixer or extruder. The filler that can be used in the invention is any inorganic filler with silanol surface groups that can be used in blends with silicone polymers. Some examples of inorganic fillers are reinforcing silica such as fuming silica or precipitated silica. A simple filler or a combination of fillers can be used to reinforce the silicone polymer. The amount of filler in the premix can be from about 20 to about 150 parts by weight, preferably from about 30 to about 100 parts by weight and preferably from about 40 to about 70 parts by weight, per 100 parts by weight of the silicone polymer of high viscosity. During the mixing phase, the addition of more silicone polymer reduces the proportion of silica in the final silicone composition to about 10 to about 100 parts by weight, preferably and about 15 to about 90 parts by weight and preferably about 25 parts by weight. to about 70 parts by weight, per 100 parts by weight of the total high viscosity silicone polymer. The high viscosity silicone polymer used in the compositions of the present invention is typically referred to as "rubber" or "rubber silicone." The polymer has a viscosity greater than 1, 500,000 cps at 25 ° C. The viscosity may be greater than 4,000,000 cps and preferably greater than 8,000,000 at 25 ° C. The polymer can be represented by the recurring units of the formula I: Formula I wherein, R1 independently represents at each occurrence a C1-4alkyl, or alkylene of C2.t; R2 independently represents at each occurrence a C? -4 alquilo alkyl, a C hal haloalkyl; Or C2-4 alkylene; R3 independently represents at each occurrence an H, CMO alkyl, C2-4 alkylene, C4-6 cycloalkyl, OH or C1-C4 haloalkyl; and n represents an integer from 1, 000 to 20,000. Another preferred composition comprises a silicone polymer wherein CH 3 or CH = CH 2; R2 independently represents at each occurrence a CH3, CH = CH2 or CH2CH2CF3; R3 independently represents at each occurrence a CH3, CH = CH2, OH or CH2CH2CF3; and n represents an integer of approximately 4,000 to 10,000. Another embodiment provides a composition wherein the vinyl content of the silicone polymer is on the scale of about 0.05% to about 0.5% by weight of the silicone polymer. The treatment agent is a silanol or silicone fluid blocked by methoxy which reacts with the surface hydroxyl filler or silanol groups to avoid a condensation reaction between the particles of the filler or between the filler and the rubber molecules that otherwise leads to stiffness and loss of elastomeric properties. The treatment agent reduces the silanol filler groups and reduces the time necessary for the maturation of the silicone, to avoid crepe hardening and / or regulate plasticity. The treatment agent may be an organylosane, a low viscosity polysiloxane or a silicone resin, having a silanol group and / or an alkoxy group having from 1 to 6 carbon atoms. Some examples are diphenylsilandiol, dimethylsilanediol, methyltriethoxysilane and phenyltrimethoxysilane. The low viscosity polysiloxane may contain one or more types of organic groups selected from a methyl group, a phenyl group, a vinyl group and a 3,3,3-trifluoropropyl group. Preferred reactive silanol treatment agents include polydimethylsiloxane, octamethylcyclotetrasiloxane (D4) and hexamethyldisilazane (HMDZ) blocked by silanol. The viscosity of the polysiloxane measured at 25 ° C is on the scale from about 1 to about 300 cp, preferably from about 5 to about 100 cp. The treatment agent may be added in the mixing phase in a weight ratio of from about 0.1 to about 100 parts of fluid to 100 parts of filler, preferably from about 0.5 to about 75 parts of fluid to 100 parts of filler and preferably from about 1.0 to about 50 parts of fluid to 100 parts of filling. The treating agent may be reacted to reduce the available groups of the filler to a concentration of from about 8 to about 2 hydroxyl groups / (nanometer) 2 of filler, preferably from about 7 to about 3 hydroxyl groups / (nanometer) 2 of filler . In one embodiment, the treatment agent may be a combination of HMDZ and water. This combination may comprise a weight ratio of HMDZ / water of between about 1 / 0.1 to about 1/10 or between about 1 / 0.5 and about 1/5 or between about 1/1 and about 1/3. The thermovulcanizable silicone composition may also include other additives such as thermal resistance enhancers such as oxides, hydroxides and fatty acid salts of metals, vulcanization reversal inhibitors, flame retardants, such as platinum compounds, agents that prevent discoloration, plasticizers such as silicone oil, internal release agents such as metal soaps, pigments and dyes. The drawing of Figure 1 is a schematic representation of a process for preparing a premix of an untreated filler and silicone polymer and preparing a thermoformable silicone filler composition of the premix. In Figure 1, the untreated filler and silicone polymer 12 and 14 are supplied in the first mixer 16, where an untreated premix is formed. The untreated premix 18 is discharged directly to the feeder 20 or sent 22 to a storage receptacle or area 24 and then charged to the feeder 20 or other process 28 carried out elsewhere. The feeder 20 supplies the untreated premix and the feeder 32 supplies the treatment agent to the second mixing apparatus 36, wherein the premix is treated and combined with an additional silicone polymer 38 to produce a thermo-vulcanizable silicone polymeric composition. The first mixer 16 can be any suitable mixer. However, in one embodiment of the invention, the mixer 16 is a continuous annular layer mixer comprising a cylindrical mixing trough wherein the material to be mixed is thrown along a helical path along the axis of the trough in the form of a ring adjacent to the wall of the cylindrical mixer. A typical continuous annular layer mixer is shown by Erich et al., U.S. Pat. 5,018,673 wherein a mixer comprising a horizontally arranged cylindrical recess is disclosed, which is provided at a first end with a material supply tube for the continuous supply of material and at a second end with a material discharge tube for the continuous extraction of material. The cylindrical hollow encloses a mixing apparatus, which is arranged coaxially in the hollow. The mixing apparatus can be operated at high speeds. The apparatus comprises mixing tools, which project essentially radially of the apparatus to the vicinity of the inner wall of the gap. The second mixing apparatus 36 is illustrated as a mixer. Nevertheless, the apparatus 36 can be any suitable mixing apparatus. A co-rotating constant-take extruder, a constant-feed rotary-extruder extruder or not, a single-screw reciprocal or non-reciprocal extruder and a self-cleaning, corrotative extruder are examples of the apparatus 36. These and other features will be apparent with the following detailed discussion, which by way of example and without limitation describes the preferred embodiments of the present invention.

EXAMPLES A pre-mix was prepared in a 10L Henschel mixer by loading 66.6 parts of a silicone rubber (800, 0.2m% penetration), 33.3 parts of a silicone rubber (800, 0.5m% penetration) and 53.5 parts of gas of silica with a surface area of 200 m2 / (gram surface (Agus 200 Degussa filler) The mixer was rotated for 20 minutes at 3500 RPM The resulting premix had a talc appearance with a bulk density of 0.42 to 0.46. This premix was used in formulations shown in Table 1. Formulations 1001, 1002, 1004 and 1005 of Table 1 were prepared by adding the premix to a Henschel mixer together with a silanol fluid plasticizer, a methoxy blocked fluid plasticizer. and a vinyl triethoxy silane crosslinker HMDZ was added in the preparation of formulations 1002 and 1005 and the HNDZ and the premix were mixed for 5 minutes in the Henschel mixer before adding other additives. They were mixed to make a dough.

Each charge was heated between 70 ° C to 80 ° C and maintained on this temperature scale for half an hour with a nitrogen purge. The load was heated to 150 ° C and cooked for 30 minutes. Formulations 1003 and 1006 were made by mixing a silicone gum (800, 0.2m% penetration) and a different gum (800, 0.5m% penetration) in the mixer for 10 minutes followed by the addition of HMDZ and mixing continued for 5 minutes. Twenty percent (20) of the filler was added and continued mixing for 15 to 20 minutes. A vinyltriethoxy silane crosslinker was added and the mixture was continued for 5 minutes. 20 percent of the filler was added and continued mixing for 15 to 20 minutes. A plasticizer of fluid blocked by methoxy was then added and mixing was continued for 5 minutes. Twenty percent (20) or more of filler was added and mixing was continued for 15 to 20 minutes after which the charge was heated to 120 ° C with a nitrogen purge. Fifteen percent (15) more of the filling was added and continued mixing for 15 to 20 minutes. Half of a plasticizer amount of silanol fluid was added and mixing was continued for 25 minutes. Then a final 15 percent of the filler was added and mixed for 10 to 15 minutes after which the remaining plasticizer was added, and the load was mixed for 10 minutes after which it was heated to 150 ° C and cooked for 30 minutes. The formulations were catalyzed using 1.5 parts of 2,4-cyclobenzoyl peroxide, per 100 g of formulation. The catalyzed formulation was solidified in press for 12 minutes at 260 ° C in a cold mold. The press-solidified formulations were further solidified at 200 ° C for 4 hours in an oven. The physical properties were evaluated after balancing the post-solidified leaves in a controlled humidity environment for 3 hours. The formulations were reported in the following table 1 TABLE 1 Formulation (g) / sample 1001 1002 1003 1004 1005 1006 Premix 921 921 1427 1415 Treatment agent 24.6 24.6. 24.6 38.1 37.8 37.8 silanol fluid Fluid treatment agent 15.6 15.6 15.6 24.2 23.9 23.9 methoxy Vinyl silane crosslinker 4.9 4.9 4.9 7.5 7.5 7.5 trietoxy HMDZ 6.8 6.8 10.4 10.4 DL water 5.2 5.2 Silicone polymer (800, 399.6 614) 0. 2m%) Silicone polymer (800, 200.4 307.9 0. 5m%) fumed silica 321 493.2 The properties for the formulations in Table 1 are reported in Table 2. In Table 2, Williams plasticity was measured in a 100-gram sample. The thickness of narrowing was between .952 + .317 cm. Fifteen (15) runs were made from end to end and the sample rested for 10 minutes. All times listed were taken from an initial pass of three minutes with a Williams plasticity meter. The Shore A hardness was measured with three lifting weights, stacked at not less than 0.533 cm high. Three measurements were taken and the average was reported in table 2. Tension, elongation and coefficient were measured in samples cut in accordance with ASTM D412-87. Weights were pulled to fail. The percentages are reported in Table 2. Rip resistance was measured in samples cut as for ASTM D624-86. A 0.0508 + 0.0508 mm slot was made in each sample. The samples were pulled until they were torn. The percentages are reported in table 2. Specific gravity was measured using a ratio of sample weight in air and sample weight in water. The compression fit was determined by measuring the thickness of the samples by heating them in an oven at 176.6 ° C for 22 hours. The volatile compounds were determined (C-9%) by weight loss of the samples measured at 135 ° + 5 ° C for 45 minutes in a vacuum of 20 mm Hg + 5 mm Hg.

TABLE 2 Property / Sample 1001 1002 1003 1004 1005 1006 Specific gravity 1, 194 1 .18 1, 191 1, 189 1, 191 1.19 Edge hardness A (Durometer) 70.8 63.9 73.2 70.4 63.5 70.3 Tension force (psi) 1 154 1364 1249 1389.6 1519.2 1405.2 Elongation (%) 231 292 241 266.4 308.8 312.4 Coefficient 100% 425 326 491 478.8 332.8 395.5 Rip B (ppi) 78 80 80 81.2 85.6 94.5 C / S 22hr, 176.6 ° C (%) 61.7 52.2 57.8 49 43.6 16.8 C-9 (%) 27.23 35.33 34.40 Williams plasticity 10 min. 251 276 406 332 306 372 24 hr 341 340 593 478 358 414 2 days 505 385 635 518 389 444 3 days 534 387 701 577 405 451 1 week 727 457 777 674 456 482 2 weeks 871 495 827 790 489 525 3 weeks 875 510 853 860 503 552 4 weeks 982 542 972 907 524 570 2 months 1042 605 743 TRAN 77.4 78.2 80 Y1 14.5 12.8 13.3 HAZE 58.4 57.8 37.8 L 88.1 88.6 89.6 A 0 0.4 -0.4 B 7.2 6.2 Shrinkage L (%) 3.5 3.1 3.6 W (%) 0.9 1.1 0.8 Suitable thermo-vulcanizable silicone polymeric composns meet the following standards of physical properties: Williams plasticity greater than 100, Shore A hardness greater than 20, hardness greater than 52.72 kg / cm2, elongation at rest of at least 100% , Razgadura B of at least 10 ppi and specific gravity of at least 1.05. Formulations 1002 and 1005 show less structuring and plasticity over time. The lowest durometer and excellent plasticity show that the 1002 and 1005 underwent an adequate filling treatment. Formulation 1005 shows the importance of adding distilled water to vary treatment levels. Although preferred embodiments of the invention have been described, the present invention is capable of variation and modification and therefore should not be limited to the precise details of the examples. The invention includes changes of alterations that fall within the scope of the following claims.

Claims (23)

NOVELTY OF THE INVENTION CLAIMS

1. - A process for preparing a thermofusible filling silicone composition comprising: loading an untreated filler and a high viscosity silicone polymer premix in a mixing apparatus; adding a treatment agent and an additional silicone polymer to the premix and combining the premix, the treating agent and the additional silicone polymer to produce a thermofusible silicone filler composition.

2. The method according to claim 1, further characterized in that the treatment agent is HMDZ.

3. The process according to claim 1, further characterized in that the treatment agent is a combination of HMDZ and water in a weight ratio of HMDZ / water of between about 1 / 0.1 to about 1/10.

4. The process according to claim 1, further characterized in that the treatment agent is a combination of HMDZ and water in a weight ratio of HMDZ / water of between about 1/1 to about 1/3.

5. The process according to claim 1, further characterized in that the treatment agent is a combination of HMDZ and water in a weight ratio of HMDZ / water of between about 1/1 to about 1/3.

6. The process according to claim 1, further characterized in that the silicone polymer has a viscosity greater than 1, 5000,000 cps at 25 ° C.

7. The process according to claim 1, further characterized in that the silicone polymer has a viscosity greater than 4,000,000 cps at 25 ° C.

8. The process according to claim 1, further characterized in that the silicone polymer has a viscosity greater than 8,000,000 cps at 25 ° C

9. The method according to claim 1, further characterized in that the premix comprises approximately 20 to about 150 parts by weight of filler per 100 parts by weight of high viscosity silicone polymer.

10. The process according to claim 1, further characterized in that the premix comprises about 30 to about 100 parts by weight of filler per 100 parts by weight of high viscosity silicone polymer.

11. The process according to claim 1, further characterized in that the premix contains about 40 to about 70 parts by weight of filler per 100 parts by weight of high viscosity silicone polymer.

12. - A process for preparing thermofusible silicone filler compositions, consisting of: forming a filler premix and high viscosity silicone polymer in the absence of a treatment agent; load the untreated filler premix and high viscosity silicone polymer in a mixing apparatus; add a treatment agent and silicone polymer to the premix; and combining the premix, treatment agent and silicone polymer to produce a thermovulcanizable silicone filler composition.

13. The method according to claim 12, further characterized in that it comprises storing the premix for at least 24 hours before loading it into the mixing apparatus.

14. The method according to claim 12, further characterized in that the treatment agent is HMDZ.

15. The process according to claim 12, further characterized in that the treatment agent is a combination of HMDZ and water in a weight ratio of HMDZ / water of between about 1 / 0.1 to about 1/10.

16. The process according to claim 12, further characterized in that the treatment agent is a combination of HMDZ and water in a weight ratio of HMDZ / water of between about 1 / 0.5 to about 1/5.

17. The method according to claim 12, further characterized in that the treatment agent is a combination of HMDZ and water in a weight ratio of HMDZ / water of between about 1/1 to about 1/3.

18. The process according to claim 12, further characterized in that the premix comprises from about 20 to about 150 parts by weight of filler per 100 parts by weight of high viscosity silicone polymer.

19. The process according to claim 12, further characterized in that the premix comprises about 30 to about 100 parts by weight of filler per 100 parts by weight of high viscosity silicone polymer.

20. The process according to claim 12, further characterized in that the premix comprises about 40 to about 70 parts by weight of filler per 100 parts by weight of high viscosity silicone polymer.

21. The process according to claim 12, further characterized in that the silicone polymer has a viscosity greater than 1, 500,000 cps at 25 ° C.

22. The process according to claim 12, further characterized in that the silicone polymer has a viscosity greater than 4,000,000 cps at 25 ° C.

23. The process according to claim 12, further characterized in that the silicone polymer has a viscosity greater than 8,000,000 cps at 25 ° C.