DE2549027A1 - METHOD OF MANUFACTURING SILICONE RUBBER - Google Patents

Description

Process for making silicone rubber

The present invention provided a method of making a silicone rubber composition in which a
powdered composition of a silicone polymer and a
Filler is produced and continuously fed to a device for intensive mixing, in which the powdered composition is formed into a mass and softened, then the device for intensive mixing takes the mass-formed and softened product and gives it a
discrete shape or a variety of discrete shapes.

Silicone rubber compositions that are effective at both high and low levels
are also known to be curable at low temperatures. For the production of these rubbery compositions, longer mixing cycles have been used with the application of heat in order to incorporate additional materials which are necessary, among other things, to make a product.

that has a commercially acceptable appearance and physical properties. These processes have been carried out in various types of devices, requiring the transfer of the viscous sticky materials from one device to another.

For example, in the past it was heat-vulcanized during manufacture common silicone rubber compositions to produce a highly viscous polymer or such a rubber, which was the basic component of the composition mentioned and generally a diorganopolysiloxane polymer or rubber with a viscosity of 100,000 to 200,000,000 centipoise at 25 ° C comprised "

The rubber was then transported to a batter mixer. In the dough mixer, the required amounts of reinforcing and / or stretch fillers, heat stabilizers, flame retardant additives were added _s processing aids and other types of materials to your rubber which usually curable heat-in the current silicone rubber compositions are used "

The dough mixer includes a large tank with two large mixing paddles which move the rubber and other materials and process them into a uniform mixture. Normally it takes from a minimum of 6 hours to a maximum of * 18 hours to produce a uniform, homogeneous mass of diorganopolysiloxane rubber, Filler and the other components of the silicone rubber compositions. A normal approach in a dough mixer comprises about 2500 kg of rubber, filler and other ingredients of the above-mentioned kind. Those for the formation of a homogeneous mass of diorganophysi-doxane-Ka.utschuk, filler

required time

and the other ingredients / is independent of whether the Approach only includes 200 kg or 2500 kg.

After the cycle in the pastry maker is complete, this will be blended material removed from the batter mixer. Usually the dough mixer has to be scraped out to get the formed

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homogeneous mass of diorganopolysiloxane rubber, filler and remove the other ingredients from it. The resulting mass is then transported to a cart and removed from the batter mixer conveyed to an extruder. During the extrusion, the cut plates conveyed through a sieve, thereby removing foreign matter — particles to remove from the mass. The extruder forms packable sheets weighing around 25 kg, which are then packaged and can be shipped, or you can still extrude the sheets in other and shaping machines before shipping.

In some cases the 25 kg panels are still on a roller machined to add an adhesion catalyst and the rolled Mass can then be extruded or extruded into the desired shape and then shipped in that shape. In the first case, the consumer receives an uncatalyzed mass in which he adds the required amount of catalyst; roll in and then the mass will harden at an elevated temperature to form the thermoset silicone rubber mass. In the second case receives the consumer a catalyzed molded mass which he will use according to his needs.

The most time consuming part of this procedure is the formation of the desired homogeneous mass of rubber and filler in the dough mixer. They are therefore powdered silicone compositions has been developed, which allows the use of a dough mixer to produce a homogeneous mixture of diorganopolysiloxane chewing cheeses, a filler and the other ingredients of a silicone rubber composition. The pulverized ones Compositions facilitate the addition of extenders, pigments and catalysts. One method of making powdered compositions is described in U.S. Patent 3,824,208.

The methods described in the aforementioned patent specification "are batch-wise or discontinuous processes, which are analogous to the batch process used in a dough mixer.

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In contrast, the present invention creates a new method for preparing a curable silicone rubber composition comprising the following steps:

(a) preparing a free flowing particulate mixture made of a viscous, sticky and cohesive silicone polymer and a filler,

(b) continuously feeding the mixture (a) into an apparatus for intensive mixing in which the free flowing particulate Mixture is shaped into a mass and softened,

(c) continuously removing the mass-molded and softened product from the device for intensive Mix and

(d) processing the mass molded and plasticized ^: product into a discrete shape or a plurality of discrete shapes.

The term used in the context of the present application "Free flowing particulate mixture" describes a material composed of a viscous, sticky and cohesive silicone polymer and a filler by the following process steps has been received:

(1) crushing the polymer into particles in the size range of 0.1 to 25, ^ mm,

(2) mixing the polymer particles thus obtained with at least 15 parts of filler per 100 parts of the polymer and

(3) Recovering the resulting free flowing particulate Mixture.

The silicone polymer may be a triorganosilyl-stopped diorganopolysiloxane rubber or a silanol terminated diorganopolysiloxane base liquid for cold-curing silicone rubber compositions, said method at a temperature of 0 to 100 C and is preferably carried out from 25 to 60 ⁰ C.

The preparation of a free flowing particulate mixture can be done by adding all of the ingredients already

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Beginning the process by adding it or you can add the filler and add the other ingredients to the polymer during this is crushed into free flowing particles, i.e. simultaneously while the polymer is formed into free flowing particles you can add filler and the other ingredients. Crushing the polymer into a free flowing particulate form is preferably carried out with a shear device, which may preferably be some type of stirrer. The present However, the invention is not limited to such mechanical stirring devices. The crushing of the mixture of polymer and filler and the other ingredients for particulate form can be made using any means that are suitable Making polymer into small particles, such as dissolving the polymer and filler in a solvent and removing the solvent according to different procedures.

The shearing devices that can be used to crush the polymer are not limited to mechanical cutting devices, but rather any kind of safety device or means can be used which is suitable for producing a finely powdered product. For example, an impingement of a polymer stream at high speed can occur on a solid surface in a chamber that contains a dense cloud of filler so that the polymer particles immediately coated with filler can be used for this purpose. Another method of making a powdery! Silicone composition is described in U.S. Patent No. 5,691,328.

In general, up to 900 parts by weight of FtDl st off per 100 Parts by weight of the silicone polymer are used. Preferably 20 to 900 parts by weight of filler and more preferably 20 up to 400 parts by weight of filler per 100 parts by weight of the organopolysiloxane polymer used.

A useful embodiment of a free flowing particulate Mixture of a silicone polymer, a hardening agent and a filler containing an organopolysiloxane polymer having a viscosity of from ICO,000 to 200,000,000 centipoise 25 ° C, where the OrganopoIysiIoxaη has the following formula:

wherein R is selected from optionally halogen-substituted monovalent ones Hydrocarbon radicals and cyanoalkyl radicals and η one Has a value of 1.95 to 2.1.

The radical R in the above formula I can be used, for example, for monovalent hydrocarbon radicals such as alkyl radicals, e.g. methyl, ethyl, propyl, octyl, octadecyl etc., aryl radicals, e.g. phenyl, tolyl, XyIyI etc., aralkyl radicals, e.g. benzyl, phenylethyl etc., Cycloalkyl and cycloalkenyl radicals, for example cyclohexyl, cycloheptyl, cyclohexenyl etc., alkenyl radicals, for example vinyl, allyl etc., alkaryl radicals, cyanoalkyl and haloalkyl-j halalkenyl and haloaryl radicals, eg chloromethyl, chlorophenyl, dibroyanophenyl, etc., preferably trifluoromethylethyl at least 50 % of the radicals R in formula I are methyl radicals and the remainder are phenyl radicals. Furthermore, 0.1 to 1 % of the radicals R in formula I are preferably vinyl radicals.

In the context of the above formula I ['all also polydiorganosiloxanes, the copolymers of two or more different diurganosiloxane units can be and copolymers of dimethylsiloxane units and methylphenylsiloxane units or copolymers Methylphenylsiloxane units, Dipheriylsiloxane units, dimethylsiloxane units and methylvinylsiloxane units as well as copolymers of dimethylsloxane units, methylvinylsiloxane units and diphenylsiloxane units.

The preparation of the Üiorganopolysiloxane of the formula I with a Viscosity from 100,000 to 200,000,000 centipoise at 25 ° C, the may contain both saturated and olefinically unsaturated hydrocarbon radicals, can according to any of the known for this purpose Procedure. Such polysiloxanes are made by hydrolyzing one or more hydrocarbon-substituted ones Dicilorsilanes, where one of the substituents is a saturated one Is a hydrocarbon radical, a crude hydrolyzate being obtained from a mixture of linear and cyclic polysiloxanes. Further

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one or more hydrocarbon-substituted DLchlorosilanes hydrolyzed, their hydrocarbon substituents or comprise several olefinically unsaturated hydrocarbon radicals and a crude hydrolyzate of a mixture of linear and cyclic polysiloxanes is also obtained. The two crude hydrolyzates are depolyinerized by treatment with KOII and thereby Mixtures of low boiling, low molecular weight cyclic polymer and undesirable material such as the monofunctional and trifunctional chlorosilanes, that were present in the source material. The compositions obtained are fractionally distilled and two pure products collected showing the low boiling, low molecular weight cyclic polymers free of notable Contain amounts of monofunctional and trifunctional groups.

A catalyst is added to the depolymerization of the crude hydrolyzates and the mixture is heated to a temperature above 150 ° C. for the preparation and recovery by evaporation of a product which consists of low molecular weight cyclic polysiloxanes and, for example, about 85 % of the tetra and 15 % of the mixed trimer and Includes pentamers. If the hydrocarbon residues on the silicon atom are methyl, then the remainder of the materials remain in the distillation vessel or tower, which result from the presence of monomethyltrichlorosilane in this product made from dimethyldichlorosilane.

This consists essentially of low molecular weight cyclic dimethyl polymers existing distillate, which is free of appreciable amounts of inonofunctional and trifunctional groups, is in one Vessel collected. The then dried cyclic siloxane contains less than 5 ppm water. The cyclic methylvinyl and diphenylsiloxanes are made in the same way. The pure cyclic siloxanes are in the desired proportions in a Given reaction vessel and subjected to equilibration there, so that they form the polysiloxanes of formula I. About 2.5 to 17 mol-yi cyclic diphenylsiloxane can add up to 83 to 97.5 mol-55 cyclic dirnethylsiloxanes are added. If so desired is and depending on the type of to be produced

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Connection can with the cyclic dimethyl and diphenylsiloxanes or other desired proportions of the cyclic siloxanes 0.1 to 1 mol /? Methylvinylsiloxane are mixed. To the above A polymerization catalyst is added to the mixture of the pure cyclic siloxanes like KOH ^ added. The KOH breaks the ring of the cyclic siloxanes to form a potassium i lan o la ts the following Formula ow! ':

K-O -SiO- K

This potassium silanolate can then break open the other rings attack and thus increase the chain length of the siloxanes formed. An amount of one is further added to the reaction mixture or more monofunctional compounds are added, the amount of which is calculated so that they can be used as chain terminators for restriction of the degree of polymerization act and thus limit the lengths and molecular weights of the linear polysiloxane chains and stabilize the polymers, usually a low Amount of monofunctional compounds added as chain terminators to regulate the chain length of the polymers. Preferably a compound of the following formula is used for this:

SiO SiO-SiO-Si

II
CH ₃ CH

Other monofunctional compounds that are more satisfactory Ways to control polymer growth are, for example, hexamethyldisiloxane, tetramethyldiäthoxydisiloxan, diethyltetraäthoxydisiloxan and Divinyl tetraethoxydisiloxane.

The equilibration reaction is carried out about 2 to l \ hours to 'about 85% of cyclic diorganosiloxanes converted into polymers

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those with monofunctional groups as chain termination links have been converted are provided. When this point of 85 conversion is reached, just as many polymers will be converted into cyclic siloxanes converted as cyclic siloxanes are converted into the polymer. At this point it will be too drr Mixture a sufficient amount of an acid, such as phosphoric acid, added, which neutralizes the KOH catalyst and the Polymerization reaction ended. The cyclic diorganosiloxanes of the reaction mixture are then left behind with the polydiorganosiloxane rubber, which is useful in the context of the present invention is distilled off.

The polydiorganosiluxan mixture can also continue with the cyclic siloxanes contained therein are reacted and the remaining cyclic siloxanes can during the mixing the mixture with processing aids and fillers by means of Gas purging must be removed.

The polydiorganosiloxane is preferably prepared so that it has a penetration of 50 to ^ 1000 mm / minute on a standard penetrometer. Further, the polymer preferably has a molecular weight in the range of 10,000 to 2,000,000 and a viscosity of 100,000 to 200,000,000 centipoise or more, and preferably a viscosity of 3,00,000 to 1O, 000,000 at 25 ° C.

Hydrocarbon-substituted polysiloxanes, their side groups consist mainly of groups other than methyl, namely such as ethyl or other saturated hydrocarbon groups and olefinically unsaturated hydrocarbon groups other than vinyl groups or those other in addition to vinyl groups can be produced by similar processes with modification according to the known properties of the various hydrocarbon groups used.

The polydiorganosiloxari chewing school is preferred among such Conditions established that the incorporation of significant amounts of trifunctional compounds, groups or molecules avoided is to allow a crosslinking of the linear polysiloxane chains over

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Si.Iicium- and oxygen atoms is avoided and the process is continued so that only such monofunctional compounds or residues are present that are specific as Ketteri terminators intended to limit the degree of polymerization are . For this purpose, the polydiorganosiloxane rubber used as the starting material contains 2.0 hydrocarbon residues per silicon atom. Deviations from one 2 to 1 ratio, e.g. ratios from 1.98 to 2.01 are for all practical purposes are irrelevant as they imply the presence of other hydrocarbon groups compared to the total number the hydrocarbon groups bonded to silicon atoms of the linear polysiloxane contribute only insignificantly.

In a more preferred embodiment of the present invention 15 to 400 parts by weight of a filler are selected from reinforcing, stretching fillers and their mixtures pro 100 parts by weight of a diorganopolysiloxane polymer having terminal silanol groups with a viscosity of 1,000 to 10,000 Centipoise at 25 ° C and the following formula:

(ΓΙ)

used, where R in the above formula IL is selected from optionally halogen-substituted monovalent hydrocarbon radicals and Cyanalkylresteii and t varies from 300 to 5-00.

The diorganopolysiloxanes of the formula containing silanol end groups They are produced in a manner similar to that of diorganopolysiloxane rubber of formula I, i.e. cyclic polysiloxanes are equilibrated with an alkali metal hydroxide. lot, however, it is desirable To prepare the diorganopolysiloxanes of the formula II containing silanol end groups, a certain amount of water is then used as a chain terminator for the silanol terminated Diorganopolysiloxane of formula II added. The amount of the added Water is calculated so that the polymer of formula II

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with the desired viscosity is obtained.

In another process for the preparation of the polymers of the formula II, a diorganopolysiloxane rubber of the formula I is used equilibrated with a little water until the compound of formula II is obtained with the desired viscosity, what with is determined by the amount of water used.

Yet another method of making the silanol end groups having diorgatiopolysiloxane of the formula II is to steam for a sufficiently long time over the surface or through the To blow through polymer of formula I with a high molecular weight, to produce a desired product with the desired silanol content.

It is therefore desirable to use a diorganopolysiloxane of the formula II low molecular weight from a high molecular weight diorganopolysiloxane by the above water treatment, which is known per se to those skilled in the art.

In preparing the free flowing particulate mixture the shear device is preferably a mechanical shear device having a mixer blade radius of about 2.5 to about 270 cm (corresponding to 1 to 108 inches) and this mechanical shear device can have a blade speed in the range of 400 to 25,000 revolutions per minute. Stirring with the shear device is carried out until a free flowing particulate mixture has formed, including a time on the order of 60 seconds up to 60 minutes and more preferably 60 seconds to 30 minutes required can be. The blade radius of the mechanical shearing device can advantageously be from about 7.5 to about 43 cm (corresponding to 3 to 17 inches) and the blade speed can advantageously be between 400 and 8000 revolutions per minute vary. The fillers can be reinforcing or extending fillers and they are added to the vessel in which the mechanical shear device is working.

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The extending fillers, or simply fillers, can make up 20 to 400 parts by weight of the filler and the remainder is one reinforcing filler or a mixture of reinforcing fillers, The various fillers can be treated or untreated Be fillers, wherein stretching fillers are usually not treated with a special process before they are used in vulcanizable silicone rubber compositions. In general there is no upper limit on that Amount of filler that can be used, other than the amounts and types of fillers that are used in conjunction with the diorganopolysiloxane polymer are desired to have the desired final silicone rubber composition to give, i.e. such a composition which has the desired properties in view of the amount and type of filler used to make this composition.

The reinforcing agents that can be used in the context of the present invention Fillers are untreated, deposited from the gas phase Silicon dioxide (in English "fumed silica"), untreated, Precipitated silica, silica airgel, treated silica airgel, treated, deposited from the gas phase Silicaumdioxyd, regardless of the process used to manufacture the filler and its treatment. Reinforcing Fillers, such as deposited and precipitated from the gas phase Silica, can be used in vulcanizable silicone rubber compositions be treated, such as in the. U.S. Patent No. 2,938,009 according to which the silica filler is treated with a cyclic siloxane so that a certain amount of diorganosiloxy groups with the hydroxyl groups in the silica -Filler is connected or put in its place. Reinforcing fillers, such as precipitated or gas deposited Silicon dioxide, can also be used with a silicon nitrogen -Compound treated as a silicone amine compound, as disclosed in U.S. Patent 3,024,126. There are other known methods of treating such reinforcing fillers, which are also useful in connection with the present invention. These other procedures include treating the si- silicon dioxide fillers with a hydroxylamine and a silazane

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connection as disclosed in US Pat. No. 3,63,57 ^{J l3.}

The elongating fillers used in heat-vulcanizable silicone rubber compositions can be used are known. These materials can be used to form free flowing silicone powder be used. Such expanding fillers are e.g. titanium dioxide, lithopone, zinc oxide, zirconium silicate, iron oxide, Diatomaceous earth, calcium carbonate, glass fibers, magnesium oxide, chromium oxide, zirconium oxide, aluminum oxide, crushed quartz, calcined Clay, asbestos, carbon, graphite, cork, cotton, synthetic fibers, etc. Some of the aforementioned stretching fillers are sometimes ... also referred to as semi-reinforcing fillers, in the context of the present application, these fillers however collectively referred to as extending fillers. It can be any of these fillers, both reinforcing and reinforcing the stretching, used in the method according to the invention will.

The filler comprises more than about 4 wt -.% Absorbed water or hydroxyl groups, then it is too wet and leads to the formation of lumps during the mixing process of the invention. More preferred are the above fillers with a content of hydroxyl groups and / or absorbed water in the range from 0.2 to 2% by weight . It is also important that the filler is one

2
Has a surface area of at least 10 nm / g and more preferably

P.
is a surface area of 25 to 500 m / g or more. The larger the surface area of the filler, the finer the filler particles will be and the more easily they can be dispersed in the silicone polymer to form the free flowing silicone particles. Most preferred are therefore within the scope of the present-

p the invention fillers with a surface area of 100 to 300 m / g,

The free flowing particulate mixture of silicone polymer, curing agent, and filler should have a bulk density of about 0.03 to 1.6 g / cm x ⁵ (corresponding to 2 to 100 uS pounds / US foot ^) and a particle size in the range of 0. 1 to 7000 um. Most preferred is a powder with a bulk density in the range

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Ranging from about 0.05 to about 1.1 g / cm (equivalent to 3 to 70 US pounds / US foot ^) and a particle size of 0.1 to 100 µm.

The device for intensive mixing for the process stage (b) of the process according to the invention is preferably a two-roll rubber mill, although other types of mixing devices which shape the composition into a mass and soften it, Can be used, such as twin-screw mixers or extruders. The mixing device should be arranged so that the one Bulky molded and plasticized product is continuously removed from the device and conveyed to a device, with the das.Product into foils, pellets, rods or other discrete Forms is processed. The device for forming can be a roller for producing foils and for producing lellets an extruder and a chopper.

The preferred embodiment of the method according to the invention refers to a continuous production of one-component heat-vulcanizable Silicone rubber compositions. These compositions contain a chemical vulcanization or curing agent as commonly used. These Embodiment of the method according to the invention comprises the following stages:

(a) preparing a cold, free flowing, particulate mixture of a silicone polymer, a curing agent and a filler,

(b) continuously feeding the mixture according to (a) to a two-roll rubber mill, on which the free flowing particulate mixture of (a) is shaped into a mass and softened will,

(c) continuously removing the formed into a mass and softened product from the two-roll mill,

(d) passing the mass molded and softened Product through an operating extruder that contains cooling devices in its mixing section,

(e) removing the composition of (d) by a tool in the. Extruder, this tool having at least one opening

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has and thereby produces at least one strand of the extrudate,

(f) Feeding the strand into one with a cloud of dust from one dry coating agent-filled chamber to prevent that the discrete forms of uncured silicone rubber adhere to one another,

(g) chopping the extrudate strand into a plurality in the chamber of shapes and sleeves of discrete shapes with the dry coating agent and

(h) removing the coated discrete shapes from the chamber

The hardening agents preferably roll to the cold, free-flowing one added particulate mixture of the silicone polymer. However, the hardener can also be added later in the mixing cycle will.

The cold, free-flowing particle-shaped mixture of silicone polymer, The hardener and filler are prepared by means of suitable intensive mixing equipment such as those above has been described. Forming into a mass and plasticizing is preferably carried out on a two-roll mill, but can other mass molding and plasticizing devices can also be used. These other devices include continuous ones FarreIHVIischer, the Stewart-Bolling-Mixtrumat and the twin-screw extruder from Werner-Pfleiderer. The free flowing particulate mixture is continuously fed to the massaging and softening device, including suitable ones Facilities such as hoppers, conveyor belts and the like are used. If a two-roller mill is used, the rollers can a distance of about 3 to 12 mm or more.

The product formed into a mass and softened is con- continuously removed from the two-roll mill and passed through a suitable extruder. The tool of the extruder can iine Have a plurality of openings, but it is usually suitable to use a tool that has several 100 openings. The extrudate is preferably closed with a rotating knife Chopped up pellets. The pellets are then with a dry

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Coating agent covers according to the method described above.

The speed for the extrusion and the rotation of the knife is adjusted so that coated pellets in the form are formed by cylinders that are about 3 to 10 mm in diameter and about 3 to 12 mm in length. These dimensions are ideal to avoid clogging in extruder funnels later. If the length is increased to about 18 mm, then stay the pellets will hang slightly later. Thus this length of about 12 mm appears to be about the optimum for this purpose. if There are narrower or wider holes in the tool plates, then corresponding thinner or thicker cylinders are obtained. Generally, the diameters will be between about 3 and 15 mm and the lengths between about 3 and 28 mm.

The previously used term "cold" is intended to describe a temperature at which the silicone rubber composition provided with the catalyst does not yet harden to form a silicone rubber. This temperature is to avoid the activation of the Perοxyd curing usually in the range of 0 to 100 ⁰ C and preferably from 25 to 60 ⁰ C and more preferably still between 25 and 40 C. The method of the invention also includes the preparation of a cold composition by working in a suitably cooled chamber large enough to contain the necessary processing equipment and the use of an apparatus which is provided with cooling means or the inlet. set of inert solid or liquid coolants. These cooling agents may liquefied or solidified gas, such as liquid nitrogen, solid carbon dioxide, and the like include the particulate directly to the free flowing silicone rubber composition may be added during the mixing cycle portions.

Solid carbon dioxide can be present in an amount of from about 1 to 10 kg per 50 kg of the polymer, and preferably from about 2.5 to 7.5 kg per about 50 kg of the polymer, and more preferably from about 4 to 6 kg per about 50 kg of the polymer can be used.

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R ¹ 1 and 1 R ¹ - CR
ι I.
O I.
O R ¹ - C-R Jl

The preferred inhibitors are organic peroxides like them
usually used for curing silicone elastomers. Particularly suitable are dimethylperoxycfe, which have the following
Structural formula can have:

R ¹ R ¹

1 ' ¹ I.

RC- (CII ₀ ) CR ¹

0 0

1 I 0 0

1 '1 1' 1

R-C-R R-C-R

R ^ A ¹ A ¹

where R is always the same or two or more different
Types of alkyl groups and η 0 is odex 'an integer.

Preferred peroxide curing catalysts include
tertiary butyltriethylethyl peroxide, tertiary butyl peroxide, tertiary triphenyl peroxide and a di-tertiary alkyl peroxide such as dicumyl peroxide. Other suitable peroxide catalysts that promote curing
Aryl peroxides, including benzoyl peroxides, mixed alkyl aryl peroxides, such as tert-butyl perbenzoate, chloroalkyl peroxides, such as 1, il-dichlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, monochlorobenzoyl peroxide, etc., are in general benzoyl peroxide , 5 to 10 % of the peroxide, based on the weight of the polydiorganosiloxane rubber, used for curing the silicone rubber composition and preferably 0.5 to 5% by weight , based on 100 parts of rubber.

In the process according to the invention, 1 to 25 and preferably 5 to 15 wt .- ^, based on the polydiorganosioxane rubber, of a processing aid for silicone can be used to prevent the mixture of rubber and
Textured filler before hardening. The processing aid becomes the stirrer along with the polysiloxane and filler
added. An example of such a processing aid is a compound of the following formula:

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ο R ² / r ² \ r ² ο

XC (CH ₀ ) Si O Si O Si (CII ₀ ) CX

I ₂ II ₂ / I ₂

FT \ R / b R

ρ
wherein R is selected from methyl and phenyl, X is selected from -OH, -NH ₂ or -OR, where R is methyl or ethyl, η has a value from 2 to 4 inclusive and b is an integer from 0 to IO inclusive . Details of the preparation of these types of compounds are contained in U.S. Patent 3,464,945.

The processing aid can also be a dihydrocarbyl-substituted polysiloxane oil which has a ratio of hydrocarbyl substituents to silicon atoms of 1.6 to 2 and whose hydrocarbyl substituents include at least one selected from methyl, ethyl, vinyl, allyl, cyclohexenyl and phenyl, wherein the polysiloxane oil comprises polysiloxane molecules containing an average of 1 to 2 lower alkoxy groups attached to each of the terminal silicon atoms, the alkoxy groups being selected from methoxy, ethoxy, propoxy and butoxy.

The preparation of the alkoxy-containing hydrocarbon-substituted polysiloxane oils, which can be used as processing aids in the process according to the invention, can be carried out by converting one or more types of cyclic dicohydrocarbon-substituted polysiloxanes from one or more types of dicohydrocarbon-substituted dichlorosilanes and dialkoxysilanes under Manufactures using hydrolysis, depolymerization and fractional distillation, as they were used to prepare the rubber of the formula I. One or more types of cyclic siloxanes so produced are then mixed with a dihydrocarbyl substituted 'predetermined amounts dialkoxysilane and the mixture under controlled Bedin equilibrated -gungen ^5, having to afford the desired alkoxy-hydrocarbon-substituted linear polysiloxane to "obtain.

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The appropriate for use in the present invention, alkoxy-having hydrocarbon-substituted polysiloxane oils are relatively low molecular weight _{polysiloxanes)}} le having its polymer chains and between H 35 or more Dikohlenwasserstoffsiloxy units per molecule. The polysiloxane oils preferably have an average of at least one and no more than two alkoxy groups attached to each of the terminal silicon atoms of the molecule. A more detailed description of this type of processing aid and its preparation is contained in US Pat. No. 2,954,357.

Hydroxylated organosilanes can also be used as processing auxiliaries, which contain from one silicon-bonded hydroxyl group per 70 silicon atoms to two silicon-bonded hydroxyl groups per silicon atom and have 1.9 to 2.1 hydrocarbon radicals per silicon atom. The other valences of the silicon atom are saturated by oxygen atoms. The hydroxylated materials contain both monomers, such as diphenylsilanediol, and polymers that contain two silicon-bonded OH groups in the molecule. The hydroxylated organosilane can also be a mixture of hydroxyl-containing siloxanes and completely condensed siloxanes. Regardless of the particular composition of the hydroxylated organosiloxane, it is necessary that 1 to ^v 70 silicon atoms are present in the organosiloxane and up to two OH groups per silicon atom.

The hydroxylated siloxanes can be prepared by any suitable method, such as by heating said siloxanes with steam under pressure at a temperature of 120 ^° C. or by hydrolyzing silanes of the formula R Si X, wherein X is any hydrolyzable group, such as Cl. OR, H, -OOR, and R is a monovalent hydrocarbon radical as defined above. The former method is preferred for the preparation of those hydroxylated materials in which the hydrocarbyl groups are alkyl, while the latter method is best for the siloxanes in which the hydrocarbyl groups are monocyclic aryl groups. For more information on the hydroxylated organosiloxanes used as processing aids

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Agents which can be used are contained in US Pat. No. 2,890,188.

Each of the above processing aids can be used either alone or in admixture within the above concentration the processing aids being added to the stirrer. Other suitable processing aids, which are useful for making heat-vulcanizable silicone rubber compositions in which Methods of the present invention find use.

Schnitzel When a product is made in pellet or / form then it is preferred to extrude the curable silicone rubber composition through a cloud of dust in a chamber, in which the extrudate is cut into pellets. A rotating drum may be used to create the dust cloud, however, any other suitable stirring device can also be used for this purpose will. The dry powder, e.g. buzzer, can be mixed with a Air jet can be swirled against the surface of the extruder. This effectively coats the pelletized product. The dust cloud is a means of coating the pellets or 7 so * that they during during storage and before they are brought into the final shape, do not adhere to one another.

These materials are then easier to shape and extrude manageable.

The dust cloud can be formed from any material, which does not adversely affect the physical and / or electrical properties of the rubber and that with the increased Temperatures that occur during further processing is stable. The particulate materials that can be used the formation of the dust cloud includes mica, talc and diatomaceous earth of the known particle sizes or so far comminuted that the particles only have a diameter of a few / µm, further silicon dioxide produced and precipitated in the gas phase, grinds quartz and metal carbonates, sulfates, and silicates Oxides as well as soot and finely divided pigments.

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The powder-coated pellets were removed from the chamber, preferably fully automatically, such as with a conveyor belt, and in suitable Packed in containers.

With the help of a large mixer titensi did a powder mixture from 100 parts by weight of a dimethylpolysiloxane rubber having a viscosity of 10,000,000 centipoise, 80 parts by weight silica deposited from the gas phase, 6 parts by weight of a processing aid, as described in US Pat. No. 3 82H 208, Example I, is described, 5 parts by weight of precipitated silicon dioxide, 50 parts by weight of ground quartz and 3 parts by weight of 2,4-dichlorobenzoyl peroxide are produced. During the 30 minute By mixing, solid carbon dioxide is added in portions of about 1 kg until a total of about 5 kg has been added.

The cold particulate silicone composition thus obtained is continuously fed to a two-roll rubber mill (dimensions 22 22 χ 60 inches) where the mixture is formed into a mass and softened. The distance between the rollers can vary between about 3 and about 12 mm or more. The one Mass molded composition is fed continuously from the two-roll rubber mill removed and fed to an extruder that operates at 10 revolutions / minute, the extruder having a cooling device and the composition is extruded through a tool. The extruded strand is made through a tool removed and cut into pellets in a fixed dust chamber attached to the head of the extruder. The dust cloud is created by introducing dry powder into a stream of air and blowing the stream against the extruder surface. The pellets are removed from the dust in a vibrating pan-type feed screen device separated. The excess dust flows back into a dust silo to be added to the air flow again. The pellets are then fed to a second screening device to remove excess dust, which is also is returned again.

609819/0393

-22- 2549077

Various other variations in methodology and materials can be made within the scope of the present invention will. For example, instead of strongly crushed mica, talc or diatomaceous earth can be used as dust particles to to prevent the pellets from sticking together, and instead of Polydimethylsiloxane polymers, other silicone polymers can be used e.g. those containing methylphenylsiloxane units.

809819/0399

Claims (2)

_ 23-2549077 claims 1. A method for producing a curable silicone rubber composition, characterized by the following levels: (a) Forming a free flowing particulate mixture from a viscous, tacky and adherent silicone polymer and a filler, (b) continuously supplying the free flowing, particulate Mixing of (a) to an intensive mixing device in which the free flowing, particulate mixture is molded into a mass and softened, (c) continuously removing the mass-formed and plasticized product from the device for intensive Mix, (d) making a discrete shape or a plurality of discrete shapes from the mass molded and plasticized Product. 2. The method according to claim 1, characterized that the intensive mixing device is a two roll rubber mill. 3. The method according to claim 2, characterized that the multitude of discrete shapes are sheets / sheets of curable silicone rubber, which are directly from the Two-roller rubber mill can be removed. l \. A method according to claims 1 to 3, characterized in that the mass molded and plasticized product is in a plurality of discrete shapes man
is processed by continuously passing the product through a working extruder and removing at least one strand of the composition through a tool in the extruder and then cutting each strand of extrudate to form a plurality of discrete shapes. 609819/0399 2549077 5. The method according to claim 4, d a d u i * c h characterized that the multitude of discrete shapes are pellets. 6. The method according to claims 1 to 5, characterized ge indicates that the free-flowing, particulate Mixing with the help of solid carbon dioxide and a mechanical one Shear device is formed. 7. The method according to claim 6, characterized that the mechanical shear device has a mixer blade radius that is from about 2.5 to about 270 cm (corresponding to 1 to 108 inches) and wherein the mechanical shear means have a blade speed in the range of 400 to 25,000 revolutions / minute can have. 8. The method according to claims 1 to Y _3, characterized in that the silicone polymer is an organopolysiloxane polymer with a viscosity of 100,000 to 200,000,000 centipoise at 25 ⁰ C and the following formula is: wherein R is an optionally halogen-substituted monovalent hydrocarbon radical or a cyanoalkyl radical and η varies from 1.95 to 2.01. 9. The method according to claims 1 to 7, characterized that the silicone polymer is an organopolysiloxane polymer having a viscosity of 1,000 to 10,000 Centipoise is at 25 ° G and has the following formula: 609819/0399 ? 5 4 9 Π? 7th where K is an optionally halogen-substituted monovalent hydrocarbon radical or a cyanoalkyl radical and t is an integer from 300 to 5200. 10. The method according to claims: 1 to 9, characterized characterized in that the filler is a reinforcing material Filler made of treated silicon dioxide deposited from the gas phase, precipitated silicon dioxide, treated, precipitated silica, silica airgel, treated Silica airgel or mixtures thereof. 11. The method according to claims 1 to 9, characterized in that the I ¹ TiJ Istoff is a stretching filler made of titanium oxide, lithopone, zinc oxide or mixtures thereof. J 2. The method according to claims 1 to 11, dad u r c h characterized in that the silicone particles a Have a size in the range of 0.1 µm to 25.4 mm. 13. The method according to claim 9, characterized in that step (a) is carried out at a Temperature in the range of 25 to ^) O C and the hardening agent included in the free-flowing, particle-free mixture is. 1 ^ 1. Process according to Claim 13, characterized in that the temperature is kept at 25 to 40 ⁰ C by adding solid carbon dioxide during the formation of the free-flowing, particulate mixture. 15. A method for producing a curable silicone rubber composition, characterized by the following stages:
(a) preparing a cold, free flowing, particulate mixture of silicone polymer, a curing agent and a filler, 609819/0399 . ■■■■■ - - 26 -? 5 4 9 η? 7th (h) continuously supplying the free flowing, particulate Mixture according to (a) to a two-roll rubber mill, in which the free-flowing, particulate mixture is added a mass is molded and softened,. (c) continuously removing the mass molded and plasticized product from the two-roll rubber mill, (d) Passing the molded and plasticized product through a working extruder, which is in its Mixing part contains a cooling device, (e) conveying the composition out through a die in the extruder, the die having at least one opening has and thus produced at least one strand of the extrudate, (f) conveying each extrudate strand into a chamber filled with a cloud of dust from a dry coating agent, to prevent the discrete forms of uncured silicone rubber from sticking to one another, (g) cutting the extrudate strand into a plurality of discrete shapes in this chamber and coating each of the discrete ones Shapes with the dry coating agent and (h) removing the coated discrete shapes from the chamber, . Method according to Claim 15, characterized that step (d) is carried out in an extruder which has a device for deforming the plasticized Has silicone rubber composition. 17. The method according to claim 15 or i6, characterized in that the discrete shapes of the Stage (f) are pellets. 18, method according to claims 15 to 17, characterized characterized that the cold, free, flowing, particulate mixture is formed with the aid of solid carbon dioxide and a mechanical shear device. 609819/0399 - 27 - 2549077 19. The method according to claim 18, characterized that the solid carbon dioxide is added in the form of fine particles. 20. The method according to claims l8 or 19, characterized characterized in that the mechanical shear device has a mixer blade radius that can vary from about 2.5 to about 270 cm (corresponding to 1 to 108 inches) and that the mechanical shearing device has a blade speed which has from 400 to about 25,000 revolutions / minute can vary. 21. The method according to claims 15 to 20, characterized characterized in that the silicone polymer is an organosiloxane polymer having a viscosity of 100,000 to Is 200,000,000 centipoise at 25 ° C and has the following formula: (R) Si O ₁₁
^v η ^ J -η T " wherein R is an optionally halogen-substituted monovalent hydrocarbon off rest or a cyanoalkyl radical and η from 1.95 up to and including 2.01 varies. 22. The method according to claim 21, characterized that the silicone polymer is an organopolysiloxane polymer having a viscosity of 1,000 to 10,000,000 centipoise at 25 ° C and having the following formula: wherein R is an optionally halogen-substituted monovalent hydrocarbon radical or a cyanoalkyl radical and t is an integer from 300 to 5200. 609819/0399 2549077 23. The method according to claims 15 to 22, characterized in that the filler is a reinforcing filler selected from treated or unbehändeltem _s from the gas phase deposited silicon dioxide, gefaltem silica, silica airgel or mixtures thereof, 24. The method according to claims 15 to 22, characterized characterized in that the filler is an expanding filler selected from titanium dioxide, lithopone, Zinc oxide or mixtures thereof. 25. The method according to claim 15 to 24, characterized that the silicone particles have a size in the range of 0.1 µm to 25.4 mm. 609819/8399