JPH0561291B2 - - Google Patents

Description

[Detailed description of the invention]

BACKGROUND OF THE INVENTION This invention relates to a method of densifying or consolidating fillers and compositions made by the method. More particularly, the present invention provides reinforcing fillers, such as fumed silica and precipitated silica, or extending fillers, such as quartz powder and calcium carbonate, by blending such fillers with silicone polymers.
The present invention relates to a method of densification by creating free-flowing powders with higher densities than are obtainable with current densification methods. Reinforcing fillers such as fumed silica and precipitated silica are well known in the art. Basically, these fillers are silicon dioxide particles in very finely divided form and have a particle size of less than 1 μm, preferably less than 500 mμ, and most preferably less than 100 mμ. The specific surface area of these materials is therefore between a few m ² /g and several hundred m ² /g, for example between 10 and 400 m ² /g, depending on the particle size. Similarly, its density is correspondingly in the range of about 3 to 5 pounds per cubic foot. Generally, such reinforcing fillers are added to silicone compositions to provide high tensile strength and hardness. One method of producing finely divided silica involves subjecting a volatile silicon halide, preferably a chlorosilane, to exothermic hydrolysis to form an oxide in the gas phase according to the following reaction equation (for silicon tetrachloride): do. SiCl ₄ +2H ₂ +O ₂ →SiO ₂ +4HCl Such exothermic hydrolysis methods are well known in the art and are disclosed, for example, in US Pat. . Another known method of producing finely divided silicon dioxide particles involves precipitating silica from an alkali metal silicate solution with an acid, such as carbonic acid or sulfuric acid. The gel thus obtained is filtered, washed, dried and, if necessary, ground to obtain a precipitated silica filler having a surface area of about 10 to several hundred m ² /g. Furthermore, the oxide and carbon mixture is subjected to reduction treatment in an electric arc furnace to obtain a gas mixture of carbon monoxide and metal oxide, and then the temperature is adjusted to ensure complete combustion and avoid agglomeration. It is known to combust such mixtures, taking care to ensure that the temperature is sufficiently low. Such methods are described, for example, in US Pat. No. 2,862,792 and US Pat. No. 3,311,451. Those skilled in the art will be familiar with the methods of manufacturing reinforcing fillers described above as well as other suitable methods. Extending fillers such as quartz powder, diatomaceous earth, zinc oxide, titanium dioxide, zinc oxide, calcium carbonate,
Iron oxides and the like are also well known in the art. Extending fillers are usually included in the composition not only to reduce cost, but also to increase (durometer) hardness and reduce elongation. Reinforcing fillers are usually critical in formulating silicone compositions suitable for a particular purpose, but their low density makes them somewhat uneconomical to transport and store. There is a drawback. Formulators and compounders who require large quantities of filler must pay a premium for transportation, for example by railcar. This is because freight cars cannot carry a large amount of filler based on weight. moreover,
Once the compounder receives the fill material, he must now pay for suitable storage space, e.g. warehouses, silos, etc., which further adds to the cost, which is ultimately transferred to the end customer or end use. be passed on to someone else. Therefore, it would be highly desirable to provide a means to increase the density of fillers to reduce shipping costs. Additionally, it would be highly desirable to provide an increased density reinforcing or bulking filler that can be easily and quickly incorporated into other silicone polymers to increase efficiency and productivity. Equipment for increasing density and granulating powder materials
As disclosed in Oldham et al., US Pat. No. 3,114,930. The device of Oldham et al. uses a vacuum to remove air from the aerated powder material, thereby reducing volume. Loffler US Pat. No. 3,632,247 is an evolution of Oldham's US patent. A plurality of vacuum cylinders are arranged in groups requiring different degrees of vacuum, connected to a common vacuum line, and powder is compressed and degassed between these vacuum cylinders. Valve control means in the vacuum line automatically and continuously adjust the vacuum pressure in each group of cylinders. In Carter, US Pat. No. 3,664,385, a rotating screw feeder is used to compress finely ground particulate material. The particulate material is advanced axially along the sleeve. At this time, the air in the gaps between the particles in the sleeve is at the internal pressure of the sleeve. Compression is achieved by applying a suction pressure to the outside of the sleeve, which is lower than the internal pressure of the sleeve, to draw air from between the particles of the material. In the silica powder compaction method disclosed in Kongsgaarden, US Pat. No. 4,126,423, silica powder is placed in a drum with closed ends and tumbled there.
Kongsgaarden, US Pat. No. 4,126,424, discloses an alternative method for compressing silica powder in which the silica powder is placed in a hopper and then pressurized air is injected into the hopper. The pressurized air has sufficient strength to fluidize the silica powder in the hopper and maintain the silica powder in an agitated state. Once the air treatment was completed, the bulk density of the material increased by up to 300%. The powder densification apparatus disclosed in Leon et al., U.S. Pat. Demarcate the densification area. The gas permeable belt is driven at a substantially constant speed toward the convergent end of the densification zone, and the powder material to be densified is fed at a sufficient rate to the divergent end of the densification zone to form a substantially complete powder. Maintain filling condition. US Pat. No. 4,326,852 to Kratel et al. discloses a method for increasing the bulk weight of silicon dioxide having a surface area of 50 m ² /g or more by applying reduced pressure to the filter surface. Here, the silicon dioxide is moved by a screw conveyor, and the longitudinal axis of the screw conveyor is arranged parallel to the filter surface. Screws with decreasing thread pitch along the feed direction are preferred. Although fillers prepared according to the above-mentioned patents are significantly denser than those without the densification process, incorporating such fillers into viscous, sticky silicone polymers remains difficult and time consuming. It's expensive, and if anything, it's expensive. Moreover, the density is not high enough to allow significant savings in transportation and storage. Accordingly, it would be highly desirable to provide a means for producing highly dense reinforcing and bulking fillers. Additionally, it would be desirable to provide a dense filler that can be easily and quickly mixed with other silicone polymers. SUMMARY OF THE INVENTION It is a primary object of the present invention to provide a method of increasing the density of reinforcing and extending fillers by compounding them with silicone polymers or mixtures thereof. A second object of the present invention is to provide a method for producing free-flowing mixtures of silicone polymers and fillers that can be easily and quickly incorporated into silicone compositions intended for further processing to form silicone rubbers or silicone elastomers. It is about providing. According to the present invention, (A) in a suitable mixing vessel (i) 100 parts by weight of a silicone polymer or silicone polymer mixture having a viscosity in the range of about 1000 to 200 million centipoise at 25°C, and (ii) ( a) Per 100 parts by weight of the above silicone polymer
50 to 500 parts by weight of reinforcing filler; (b) 400 parts by weight per 100 parts by weight of the above silicone polymer;
~5000 parts by weight of an extender filler and (c) a filler selected from a mixture of (a) and (b) above; (B) mixing the silicone polymer and the filler for a sufficient period of time; A method of making a polymer densified filler is provided comprising obtaining a flowable densified particulate mixture. Please note that Link and Scarbel's U.S. patent no.
No. 3,824,208 defines a similar method for solving a very different problem, namely forming free-flowing particulate polymers from viscous sticky polymers. Link and
Scarbel also mixes fillers and polymers. Broadly speaking, the method disclosed in Link and Scarbel for making free-flowing particulate mixtures from viscous, sticky, cohesive polymers involves (a)
(b) mixing the polymer particles with at least 15 parts, preferably between 20 and 900 parts of filler per 100 parts of polymer; (c) the resulting free-flowing The process consists of the step of recovering the sexual mixture. The patent further states that step (a)
It is taught that (b) can be done simultaneously. The objective of Link and Scarbel was to provide a process for producing free-flowing particulate mixtures from viscous sticky polymers to provide a continuous process for producing thermoset rubbers. In addition to diorganopolysiloxanes and fillers, Link and Scarbel consider including processing aids, binders, heat stabilizers, catalysts, flame retardants, and other additives. According to the Link and Scarbel disclosure, the resulting free-flowing mixture can be formulated to form thermoset or room temperature curable compositions. According to the teachings of Link and Scarbel, the polymer and filler should be mixed for only a period of time effective to render the polymer-filler mixture free-flowing. The density of the mixture is not important except as regards equipment selection. There is no disclosure or suggestion of obtaining a polymer densified filler by mixing for longer than the time taught in Link and Scarbel. In fact, Link and Scarbel teach that mixing for longer than the time required to obtain a homogeneous, free-flowing mixture is undesirable because the heat generated by such mixing causes the mixture to coagulate. Quite contrary to the teachings of Link and Scarbel, discussed above, the present inventors have surprisingly found that mixing the filler and polymer for longer than the time required to form a free-flowing mixture does not result in processing. It has been found that the result is a mixture of increased density rather than a solid polymer mass. DETAILED DESCRIPTION OF THE INVENTION The process for making the polymer densified reinforcing and extending filler of the present invention consists essentially of (A) placing in a suitable mixing vessel (i) 100 parts by weight of about 1,000 to 2,000,000 at 25°C; a silicone polymer or mixture of silicone polymers having a viscosity in the range of centipoise; and (ii) (a) per 100 parts by weight of the above silicone polymer.
50 to 500 parts by weight of reinforcing filler; (b) 400 parts by weight per 100 parts by weight of the above silicone polymer;
~5000 parts by weight of an extender filler and (c) a filler selected from a mixture of (a) and (b) above; (B) mixing the silicone polymer and the filler for a sufficient period of time; It consists essentially of obtaining a flowable, densified granular mixture. Generally, silicone polymers have a temperature of about 1000 ~
It is an organopolysiloxane with a viscosity in the range of 200 million centipoise. Such polymers have the general formula: It is expressed as wherein R is selected from the group consisting of monovalent hydrocarbon groups, monovalent halogenated hydrocarbon groups and cyanoalkyl groups, and n varies from 1.95 to 2.1. The viscosity of silicone polymer is approx.
More preferably, the viscosity is in the range of 100,000 to 5,000,000 centipoise, and even more preferably, the viscosity is in the range of 1,00,000 to 4,000,000 centipoise at 25°C. Suitable R groups include alkyl groups such as methyl, ethyl, propyl and butyl; aryl groups such as phenyl, tolyl and xylyl; aralkyl groups such as benzyl and phenylethyl; cycloalkyl and cycloalkenyl groups,
Examples include cyclohexyl, cycloheptyl, cyclopentenyl and cyclohexenyl; alkenyl groups such as vinyl, allyl and butenyl; alkaryl group; cyanoalkyl group: haloalkyl group; haloalkenyl group and haloaryl group. Preferably, the silicone polymer contains methyl groups, vinyl groups, or both. Silicone polymers considered within the scope of this invention are well known to those skilled in the art. However, readers interested in a more detailed explanation may refer to the Link and
See US Pat. No. 3,824,208 to Scarbel. Within the scope of the polymers of the above formula are the general formula: Also included are mixtures of polymers of and copolymers containing two or more different diorganosiloxane units. Additionally, it is not important whether such copolymers are block copolymers or random copolymers. Examples of copolymers within the scope of the invention include copolymers of dimethylsiloxane units and methylphenylsiloxane units, copolymers of methylphenylsiloxane units, diphenylsiloxane units, dimethylsiloxane units and methylvinylsiloxane units. There are copolymers of methylvinylsiloxane units, dimethylsiloxane units and diphenylsiloxane units. Copolymers of this type are also well known to those skilled in the art. Reinforcing fillers of the present invention are well known in the art, such as fumed silica, treated fumed silica, precipitated silica, treated precipitated silica, silica aerogel and treated silica aerogel. Preferably, the reinforcing filler is selected from fumed silica and treated fumed silica, most preferably untreated fumed silica. These fillers can be manufactured by known methods, such as those described in the aforementioned patents. Additionally, the reinforcing fillers used in the present invention can be treated as described in Lucas, US Pat. No. 2,938,009. In the method of this patent, a silica filler is treated with a cyclic siloxane, such as octamethylcyclotetrasiloxane, to attach, substitute, or bond an amount of diorganosiloxane groups to the hydroxyl groups of the silica filler. Reinforcing fillers, such as fumed silica or precipitated silica, can also be treated with silicon-nitrogen compounds, such as silicon-amine compounds, as disclosed in US Pat. No. 3,024,126.
Alternative methods of making treated silica fillers within the scope of this invention include treating the filler separately with hydroxylamine and silazane compounds, or cyclically treating the filler with hydroxylamine and silazane compounds, as described in U.S. Pat. No. 3,635,743. Treatment with siloxane and silazane compounds.
The disclosures of the above-mentioned patents are shown for reference as prior art to the present invention. Of course, it is also within the scope of the invention to use suitable reinforcing fillers or mixtures of treated reinforcing fillers. In practicing the present invention, the reinforcing filler is generally a silicone polymer and a silicone polymer.
Mix at a ratio of about 50 to 400 parts by weight of filler per 100 parts by weight. 100~ per 100 parts by weight of polysiloxane
Preferably, 250 parts by weight of filler are added, and even more preferably 100 parts by weight of reinforcing filler per 100 parts by weight of silicone polymer. The reinforcing silica filler used in the present invention must have a surface area of 20 m ² /g or more, preferably
Must be 50m ² /g or more. 100, 200,
It is also preferred that the reinforcing filler has a surface area of 300 m ² /g or more. The density of reinforcing fillers densified with free-flowing polymers will, of course, vary depending on the filler to polymer ratio, the type of filler and polymer used, blade speed and mixing time. For example, if a mixture is formed from one part fumed silica and one part polymer with a viscosity of 2,000,000 centipoise, the density of the reinforcing filler densified with the free-flowing polymer will be between 25 and 30 centipoise.
Approximately pounds per cubic foot. On the other hand, if the mixture is formed from 5 parts filler and 1 part polymer, the density will be on the order of 6-8 pounds per cubic foot. Preferred free-flowing polymer densified reinforcing fillers within the scope of this invention have densities and mixing times as set forth in Table I.

[Table] Generally, the density of the free-flowing, polymer-densified reinforcing filler should be at least 10% higher than when the mixture was initially reduced to free-flowing particles. Preferably, the density increases by about 100% or more, and even more preferably by about 500%. The mixing time required to obtain such a density increase will, of course, depend on the blade speed, mixer type, polymer type and viscosity, polymer to filler ratio, and the desired density of the free-flowing composition. It changes accordingly. Typically, the mixing time will be 50% or more longer than the time required to initially form a free-flowing mixture. However, typically the mixing time is about twice the time required to form a free-flowing mixture.
It will be twice as long. Regardless of the filler-to-polymer ratio, all reinforcing fillers densified with the polymers of the present invention have a very good consistency, quite similar to, for example, talc. Past experience has shown that
A 1:1 ratio provides several advantages, such as the mixture exhibiting optimal flow, as well as the ability to easily and quickly mix the mixture with other silicone polymers. Another advantage of using a 1:1 mixture of filler and polymer to produce reinforcing fillers densified with the polymers of the present invention is that a maximum weight of filler per unit volume is obtained, thus reducing the fill Transportation and storage of materials will be relatively inexpensive. On the other hand, polymer 1
A ratio of about 2.5 parts reinforcing filler to about 2.5 parts reinforcing filler occupies only about twice the volume of the 1:1 ratio mixture. It will therefore be obvious to those skilled in the art that the most advantageous ratio of reinforcing filler to silicone polymer will depend on the specific objectives of the end user. If the end user's interest is primarily in obtaining a reinforcing filler, a ratio of 3 parts filler per part silicone polymer is preferred. On the other hand, if the end user requires significant amounts of both reinforcing filler and silicone polymer, a ratio of about 1:1 may be appropriate. Extending fillers such as titanium oxide, lithopone, zinc oxide, zirconium silicate, iron oxide, diatomaceous earth, calcium carbonate, glass fiber, magnesium oxide,
Also included within the scope of this invention are chromic oxide, zirconium oxide, aluminum oxide, quartz powder, calcined clay, asbestos, carbon, graphite and cork.
Because extender fillers have different physical properties than reinforcing fillers, relatively high levels of extender fillers must be incorporated to obtain densified extender fillers with free-flowing polymers. . Generally, the extending filler is mixed with the silicone polymer in proportions ranging from about 4 parts filler per part silicone polymer to about 50 parts filler per part silicone polymer, by weight. In a preferred embodiment, 9 parts per part of polymer.
Extended fillers densified with polymers are prepared from mixtures ranging from 1 part filler to 35 parts filler per part polymer. In a most preferred embodiment, the ratio of extending filler to silicone polymer is from 10:1.
It is in the range of up to 20:1. Among the extending fillers of the invention are quartz powder, e.g.
Minusil is also preferred, and such bulking filler has a surface area of about 2 to 50 m ² /g. Of course, the surface area will vary over a wide range due to the large variety of materials that can be used as extender fillers. As in the case of polymer-densified reinforcing fillers, the density of polymer-densified extended fillers is
It will vary depending on the filler to polymer ratio and the particular filler and polymer used. In the case of extended fillers, the filler to polymer ratio is generally slightly higher, as discussed above, in order to obtain a suitably densified extended filler. Thus, for example, if a mixture is formed from 8 parts filler per part polymer, the density of the polymer densified extended filler will be on the order of 40-50 pounds per cubic foot. per part of polymer
Forming a mixture from 16 parts of filler, the density is 38
It would be on the order of ~45 lbs/ft3, and when 32 parts of bulk filler is combined with 1 part silicone polymer, the density would be in the range of about 36-42 lbs/ft3. The densities and recommended mixing times for quartz powder extended fillers densified with free-flowing polymers within the scope of this invention are shown in Table 1.

[Table] R○
Pure Minusil − 36
Experience to date has shown that a ratio of extending filler to silicone polymer of from 9:1 to 35:1 is preferred, and even more preferably from 10:1 to 20:1. In practicing the present invention, the silicone polymer and an effective amount of reinforcing filler, extender filler, or mixture thereof are placed in a suitable mixing vessel or device, such as a Henschel mixer.
Stirring means, usually one or more blades, are operated to mix or compound the polymer and filler to form free-flowing, generally spherical particles about 1 to 100 micrometers in diameter. Preferably, the particle diameter is in the range of 10 to 75 μm, and even more preferably in the range of 20 to 50 μm. It is also within the scope of this invention to initially place the polymer in a mixing vessel or apparatus and to add filler to the mixing vessel continuously or batchwise while mixing. The blades of a suitable mixing device are typically 1
~108 inches or more radius giblets. The only prerequisite is a proper combination of blade size and blade speed of the mixing means. Generally, this combination varies from 40 revolutions per minute for a 108 inch blade to about 25,000 revolutions per minute for a 1 inch blade. As can be readily appreciated, the larger the blade radius, the lower the blade speed can be tolerated. That is, it is the blade tip speed that is critical. Those interested in more detailed information regarding agitators or mixing means may refer to the links and links above.
See US Pat. No. 3,824,208 to Scarbel.
However, those skilled in the art will be able to determine appropriate mixing conditions without undue experimentation. The time required to achieve proper blending of the polymer and filler may be any number of minutes from about 10 to 90 minutes, but preferably from 15 to 30 minutes. As previously mentioned, mixing time is important to the process of the present invention and will vary depending on the type of filler and polymer used and the filler to polymer ratio. The table lists typical mixing times for various reinforcing and extending filler to silicone polymer ratios, length of time required to initially obtain free-flowing polymer-filler, and optimal consolidation. Indicates the time required to obtain the filler.

Table of Contents Of course, the length of time that the polymer and filler are combined in carrying out the method of the present invention can be longer or shorter than that required to obtain optimal properties.
By optimal properties is meant the properties at which the density does not increase significantly during the additional mixing time required to obtain the increase in density. Similarly, in some cases it may be unnecessary or undesirable to consolidate or densify the filler material to the maximum extent possible. Table 1 therefore reveals the surprising discovery that the continued mixing of silicone polymers with reinforcing or bulking fillers provides a means of making the filler more dense, resulting in lower transportation and storage costs. be interpreted as merely illustrating.
Furthermore, the method of the present invention has the additional advantage that the time required to mix the polymer densified filler with the silicone composition is significantly reduced, thus allowing the formulator or compounder to increase productivity. You can also get Another important advantage, especially with respect to silicosis-causing fillers, such as α-quartz IMinusil, is that polymer-densified expanded fillers are less "dusty" than pure expanded fillers. The aim is to reduce the risk of harm to health when handling these materials. The temperature at which the method of the invention is carried out is generally between 0°C and 100°C;
Preferably the temperature is 25-60°C, particularly preferably about 25°C. Furthermore, the method can be carried out either under reduced pressure, atmospheric pressure or elevated pressure. The following examples of the invention are given by way of illustration and not by way of limitation. All parts are by weight unless otherwise specified. Example 1 In a Henschel mixer with a capacity of 0.2 cubic feet.
30000000 at 25℃ of 550g surface-treated fumed silica (1/2 of total fumed silica) and 1100g
A silicone polymer with a viscosity of centipoise was introduced. Mixing blade with a radius of approximately 4 inches at approximately 3800 rpm
It rotated at a speed of (revolutions per minute). After mixing for 5 minutes,
The temperature was 52°C and the density of the mixture was 16.6 pounds per cubic foot. After an additional 5 minutes of mixing, the density increased further to 26.2 pounds per cubic foot and the temperature remained approximately the same. After a total of 15 minutes of mixing, the density of the mixture was found to have decreased slightly to 23.3 pounds per cubic foot. At this point an additional 355g (total = 905g) of treated silica filler was added to the mixture. The mixture was blended for an additional 5 minutes, the density was 25.8 pounds per cubic foot, and the temperature rose to about 70°C. The final 195 g needed to achieve a 1:1 filler to polymer ratio was added and mixing was resumed for an additional 5 minutes. At this point (25 minutes of total mixing), the density of the polymer densified filler had reached its maximum value of 30.8 pounds per cubic foot. The temperature remained around 70°C. An additional 5 minutes of mixing resulted in a polymer densified fill with a density of 30.0 pounds per cubic foot.
This example demonstrates that the density of filler material is significantly increased by practicing the present invention.
This example also shows that it is more effective to add the filler in small portions rather than adding the entire amount of filler to the polymer at the beginning. Example 2 This example is similar to Example 1, except that the fumed silica and silicone polymer are initially added to the Henschel mixer in a 1:1 mixing ratio.
550 g of the same silicone polymer was mixed with 550 g of treated fumed silica. After mixing for 5 minutes, the density was 5.0 pounds per cubic foot and the temperature was 33°C. Mixing for an additional 5 minutes increased the density by 50% to 7.5 lbs/ft3, and mixing for an additional 5 minutes achieved a nearly 100% increase to 14.6 lbs/ft3. In 20 minutes, the temperature rises to about 40℃, and the density of the compacted filler increases.
It reached 19.0 lb/ft. Two additional 5 minutes of mixing resulted in little increase in density. That is, the density after 25 minutes of mixing is 20.0 pounds per cubic foot and the density after 30 minutes of mixing is 21.5.
It was in pounds/cubic foot. This indicates that although the present invention achieves a density increase of approximately 537% (21.5/4.0 x 100), it is not as effective as adding the filler to the polymer in portions. Example 3 This example illustrates the criticality of blade tip speed in practicing the present invention. 2 capacities 0.2
To a cubic foot Henschel mixer was added 550 g of fumed silica and 275 g of silicone polymer. Both components were mixed for 30 minutes, during which time samples were taken at 5 minute intervals to measure density and temperature. However, the difference between the two mixers is that the first mixer is 1800
Run at 3800 rev/min and the second mixer at 3800 rev/min.
It worked in minutes. The results are shown in Tables 1 and 2.

【table】

TABLES As can be seen from Tables 1 and 1, the increase in density cannot be achieved unless the mixing of polymer and filler occurs at or near the critical blade tip speed. Example 4 The mixture of Example 3 was not cooled to lower the processing temperature. Therefore, this example shows that some increase in density can be achieved by performing the mixing process at a relatively low temperature. The experimental conditions were the same as in Example 3, and the following results were obtained.

EXAMPLE 5 This example shows that fillers densified according to the invention can be easily and quickly incorporated into other silicone polymers. A Henschel mixer was charged with 80 parts of 5 micron Minusil (quartz powder) and 10 parts of 850 penetration silicone gum (viscosity 2.35 million cps). A second mixture was made with 80 parts of Minusil and 5 parts of the same polymer. A mixed product was made using the following formulation specifications.

[Table] As shown in the table, the densified expanded filler produced in accordance with the present invention
can be incorporated into the base polymer much more quickly. Furthermore, the amount of filler not incorporated into the base polymer upon initial addition is negligible compared to the amount of Minusil remaining on the pan in Experiment A. As can be seen from the data in Table 1, the time required to incorporate the polymer densified extender filler into the base silicone polymer is reduced by a factor of 4 to 6.

Claims (1)

Claims: 1(A) In a suitable mixing vessel: (i) 100 parts by weight of a silicone polymer or mixture of silicone polymers having a viscosity in the range of about 1000 to 200 million centipoise at 25°C; and (ii) (a) Per 100 parts by weight of the above silicone polymer
50 to 500 parts by weight of reinforcing filler or/and (b) 400 parts by weight per 100 parts by weight of the above silicone polymer.
filler consisting of ~5000 parts by weight of bulking filler and (B) initially until the silicone polymer and filler give a free-flowing particulate mixture with a density that is at least 100% higher than when the silicone polymer and filler initially became the free-flowing particles. (C) mixing said silicone polymer and said filler for a time that is at least 100% longer than the time required to form a free-flowing mixture; (C) an effective amount of said free-flowing polymer-densified filler; (D) combining the filler densified by the polymer with the base silicone composition by any suitable means. 2. The method of claim 1, wherein the means for combining the polymer densified filler and the base silicone composition is a milband. 3 The above silicone polymer has the general formula (R in the formula is a monovalent hydrocarbon group, a monovalent halogenated hydrocarbon group, or a cyanoalkyl group,
2. The method according to claim 1, wherein n varies between 1.95 and 2.1. 4 The viscosity of the above silicone polymer at 25°C is approximately
The method of claim 1 in the range of 100,000 to 5,000,000 centipoise. 5 The viscosity of the above silicone polymer is 25°C.
The method of claim 1 in the range of 1,000,000 to 4,000,000 centipoise. 6. The method of claim 1, wherein the reinforcing filler is fumed silica, precipitated silica or silica aerogel. 7. The method of claim 6, wherein the fumed silica, precipitated silica and silica aerogel are treated. 8 Approximately 100 to 250 per 100 parts of the above silicone polymer
2. A method according to claim 1, in which a reinforcing filler is added. 9. The method of claim 1 in which about 100 parts of reinforcing filler is added per 100 parts of said silicone polymer. 10. The method of claim 1, wherein the reinforcing filler has a surface area of about 50 m ² /g or more. 11. The method of claim 1, wherein the reinforcing filler has a surface area of about 100 m ² /g or more. 12. The method of claim 1, wherein the free-flowing polymer densified filler particles have a diameter in the range of about 1 to 100 microns. 13. The method of claim 1, wherein the free-flowing polymer densified filler particles have a diameter in the range of about 10 to 75 microns. 14. The method of claim 1, wherein the free-flowing polymer densified filler particles have a diameter in the range of about 20-50 microns. 15 The above-mentioned bulk filler is titanium oxide, lithopone,
Zinc oxide, zirconium silicate, iron oxide, diatomaceous earth,
2. The method of claim 1, wherein the material is selected from the group consisting of calcium carbonate, glass fibers, magnesium oxide, dichromic oxide, aluminum oxide, quartz powder, calcined clay, asbestos, carbon, graphite, and cork. 16. The method of claim 1, wherein said bulking filler is diatomaceous earth, calcium carbonate or quartz powder. 17. The method of claim 1, wherein said bulking filler is quartz powder. 18 Approximately 900 to 100 parts of the above silicone polymer
Claim 1 adding 3500 parts of bulking filler
The method described in section. 19 Approximately 1000 to 100 parts of the above silicone polymer
Claim 1 adding 2000 parts of bulking filler
The method described in section. 20. The method of claim 1, wherein the polymer is first added to a mixing vessel and the filler is added to the polymer while mixing. 21. The method according to claim 20, wherein the filler is added batchwise. 22. The method of claim 20, wherein the filler is added continuously.