FR2715407A1 - Elastomeric material for making moulds for moulding radiation curable plastics - Google Patents

Abstract

An elastomeric material for making moulds for moulding plastics materials that are curable by activation with electromagnetic radiation having a frequency in the high frequency (HF), very high frequency (VHF) or ultra high frequency (UHF) band, comprises (i) a cold curing silicone rubber compsn. of the type that crosslinks by hydrosilylation (or polyaddition) and (ii) a mineral filler comprising at least one ceramic compsn.

Description

 The invention relates to the technology of molds or dies, useful in reproducing identically forms of plastics and curable by activation, by means of electromagnetic radiation whose frequency belongs to one of the following areas - high frequencies, - very high frequencies, - ultra high frequencies.

 More specifically, the present invention relates to a novel elastomeric material particularly suitable for producing such molds. It also relates to the manufacture of the latter, the high frequency molding processes by applying, as well as the molds, in themselves, made from the new elastomeric material.

 Conventionally, the casting techniques considered are those in which plastic material is injected into a mold at a temperature where it is in the liquid state, at a pressure of the order of a few bars, this plastic material being then heated and hardened by electromagnetic radiation. The resulting shape is then cooled before demolding.

 High frequency molding has been used for a very long time in many industrial sectors and, in particular, in the automotive industry in particular, for the manufacture of polyvinyl chloride (PVC) gaskets.

 In this regard, patent applications EP 0 333 538 and 0 436 438 are known which describe the encapsulation of automobile windows by polyvinyl chloride or polyurethane e seals. g.

 In this high-frequency molding technique, the mold is obviously a determining element, which must respect a certain number of constraints.

 In the first place, it must be made of a material as much as possible transparent to electromagnetic waves, which may be high frequency (HF), very high frequency (THF) or ultra high frequency (UHF or microwave) waves. . This transparency is necessary to prevent heating of the mold by consuming electromagnetic waves, to the detriment of the activation and hardening phenomenon of the plastic material to be molded. The reflection of this essential property of the mold material is given by: e. more preferably at 5.0 at 27 MHz.

 It is also necessary to take into account the heat dissipation (tangent 6) of the material. This variable should tend, preferably, to low values (tg a <10-3) and also be associated with a good thermal conductivity (> 0.5 W.m.K), so as to allow faster demolding.

 Secondly, it is also important that the mold material has a sufficiently high hardness, for example between 50 and 90 SHORE hardness, to have a correct mechanical strength.

 In addition to the hardness, the material must, advantageously, possess suitable mechanical characteristics, namely, in particular: an elongation at break, preferably greater than or equal to 70%, a breaking strength, preferably greater than or equal to 2 MPa.

 In practice, it is preferable for the mold material to retain a certain flexibility, while being sufficiently hard to guarantee dimensional stability of the impression, this flexibility facilitating, among other things, demolding. In addition, it should be noted that the fact of presenting surface lubricating properties is certainly not a handicap in the perspective of demolding the formed part.

 It is also interesting that this material is easily machinable, to achieve various shapes when shaped in solid form. The mold may, optionally, be obtained from a precursor system in liquid form, so as to allow its shaping impression before hardening. To this end, it is clear that these liquid forms must meet certain requirements in terms of rheology.

 Finally, it is advantageous for the mold material to be of such a nature that it makes it possible to obtain a tight closure after meeting and bringing into contact the two half-cavities which generally constitute the mold.

 In view of these constraints, certain silicone elastomer compositions have thus been imposed as constituent materials of the matrices used in HF molding, of curable plastics. However, it has proved necessary to compensate for the relative weakness of these silicone materials as regards the dielectric permittivity, by adding mineral fillers, in particular ceramics.

In this respect, we can mention the book "Physics of Dielectrics" by BUNGET and
POPESCU, (1984), which discloses the combination of inorganic fillers based on titanium or mixed titanium of barium or strontium, with polymeric materials in general and elastomeric silicones in particular, to increase the dielectric permittivity.

 Similarly, US patent 4412 029 relates to dielectric materials, elastic and intended to influence the electric fields in high voltage and power current systems, for which a high dielectric constant (permittivity) is sought. This document discusses combinations of elastomer compositions with fillers, such as titanium dioxide, barium titanate. It also recalls the possibility of precisely adjusting the permittivity of the material by modifying the volume fraction of barium titanate. It does not omit to mention the disadvantage that the excess of mineral charges represents with respect to the mechanical properties and, in particular, of the elasticity.

 US Pat. No. 4,441,876 discloses an imprint for the high-frequency molding of plastics, made of a cold-vulcanizable silicone elastomer by polycondensation of a dihydroxylated polysiloxane reagent with organosilane crosslinking agents, said elastomer being supplemented with calcium titanate. for purposes of adjusting the dielectric constant.

Finally, patent applications EP 0 333 538 and O 436 438 describe high frequency molds made from a silicone elastomer (RTV 3110 +
RTV 3112 + Corning Catalyst S) cold vulcanizable by polycondensation.

 However, all matrices for high frequency molding, made from these known silicone elastomer compositions, possibly loaded with ceramic, always suffer from a serious defect. Indeed, being subjected to relatively high temperatures (60-120 ° C) during high-frequency molding, and for a large number of reproductions, the molds are subject to a phenomenon of thermal degradation, which is observed after relatively few reproductions (30) and results in a clear softening of the mold, which makes it unsuitable for longer use, except to accept a significant decrease in quality.

 In this state of the art, one of the essential objectives of the present invention is to provide an elastomeric material intended, in particular, for producing molds for the HF molding of hardenable plastics, remedying, in particular, the disadvantages above deficiency or lack of stability of mechanical properties in the cured state or not.

 Another object of the invention is to provide an elastomeric material for the construction of HF molds, which constitutes, in addition, a good technical compromise with regard to: - transparency to high frequency electromagnetic radiation, - the evacuation capacity of heat, - and appropriate mechanical properties.

 Another object of the invention is to provide an elastomeric material that can be moldable in all forms of fingerprints desired and allows quick and easy demolding, while remaining relatively economical.

 Another object of the invention is to provide an elastomeric material which retains its physical properties for a very large number of cycles of reproduction by HF molding.

 Another object of the invention is to provide a process for molding high-frequency activation hardenable plastics, as well as a mold for carrying out said method, which benefit from all the advantages inherent to the elastomeric material, the specification of which is charges is exposed supra.

These and other objects are achieved by the present invention which relates, first of all, to an elastomeric material for producing molds for molding plastics curable by activation by means of electromagnetic radiation whose frequency belongs to one of the following fields: high frequencies, very high frequencies, ultra high frequencies, comprising at least one cold vulcanizable silicone elastomer composition (EVF) and a mineral filler, characterized:
in that the silicone elastomer composition is of the type of
those crosslinkable by hydrosilylation (or polyaddition)
and in that the charge comprises at least one compound
ceramic.

It is the merit of the Applicant - to have selected a silicone composition, mono or two-component, type
cold-hardening polyaddition by catalytic hydrosilylation reactions; and having associated it with a filler comprising at least one ceramic compound.

According to a preferred arrangement of the invention, the ceramic compound is selected from
ferrites and / or complex salts of formula Mit203
in which
M1 is an alkaline earth metal,
M2 is a metal selected in column 4b of the
periodic classification, as published in the
64th edition of the "HANDBOOK OF CHEMISTRY",
and / or mixtures of these ceramics.

 By way of examples of ceramic compounds that are more particularly suitable, mention may be made of barium titanate (BaTiO 3), calcium (CaTiO 3) or strontium (SrTiO 3) or else magnesium zirconate (Mg 2 O 3). As examples of other possible ceramic compounds and belonging to the ferrite species, mention may be made of the compounds of formula: MFqO, with M = Mn, Cu, Ni or Zn.

 All mixtures of the above compounds are also to be considered.

 It should be emphasized that barium titanate is more particularly preferred.

 Quantitatively, the ceramic compound is present in an amount of 10 to 200, preferably 30 to 150 parts by weight per 100 parts by weight of the silicone elastomer composition.

In a preferred manner, the silicone elastomer composition comprises
(I) - at least one organopolysiloxane having, per molecule,
at least two alkenyl groups, preferably vinyls,
related to silicon,
(H) - at least one organopolysiloxane having, per molecule,
at least three silicon-bonded hydrogen atoms,
(III) - a catalytically effective amount of at least one
catalyst, which is a compound of at least one metal
belonging to the platinum group, the crosslinking of this composition being effected by the addition (hydrosilylation) of at least one vinyl group of (I) to at least one hydride functional group of (II) and being catalyzed by (III).

 This crosslinked material may have been shaped in the shape of the impression before hardening and / or machined, shaped by any appropriate means, to obtain, in fine, the target mold.

 The adjustment of the crosslinking density is important with regard to the ideal hardness that one wishes to achieve for the mold. According to an advantageous arrangement of the invention, this adjustment is done through the proportions of (I) and (II), which are such that the molar ratio of silicon-bonded hydrogen atoms in (II) on the vinyl radicals related to silicon in (I) is between 0.4 and 10, preferably between 0.6 and 5.

 The alkenyl, preferably vinyl, groups of (I) and the hydrogen atoms of (II) are generally bonded to different silicon atoms.

Within the meaning of the invention, the elastomer material considered is constituted - as well by the crosslink obtained after the hydrosilylation reaction (addition) of
polyorganosiloxane (I) bearing alkenyl unsaturated groups, preferably
vinyl, with organopolysiloxanes (II) carrying hydride functions, in
presence of platinum complexes, - that precursor systems in the uncrosslinked state.

According to a preferred characteristic of the invention, the organopolysiloxane (I) has units of formula in which
YaZbSiO4 - (a + b) (1)
2 - Y is a vinyl group, - Z is a monovalent hydrocarbon group, free from unfavorable action on
the activity of the catalyst and preferably selected from alkyl groups having
1 to 8 carbon atoms, advantageously, among the methyl groups,
ethyl, propyl and 3,3,3-trifluoropropyl and as well as aryl groups and,
advantageously, among the radicals xylyl and totyl and phenyl, - a is 1 or 2, b is 0, 1 or 2 and a + b is between 1 and 3, - optionally at least a part of the other units are units of formula
average:
ZSiO4 - c (2)
T
in which Z has the same meaning as above and ca a value included
between 0 and 3.

 The organopolysiloxane (I) may be formed only of units of formula (1) or may further contain units of formula (2). Likewise, it may have a cyclic linear or branched linear structure. Its degree of polymerization is preferably between 2 and 5,000.

 Z is generally chosen from methyl, ethyl and phenyl radicals, at least 60 mol% of Z radicals being methyl radicals.

 Examples of siloxyl units of formula (1) are the vinyldimethylsiloxane unit, the vinylphenylmethylsiloxane unit and the vinylsiloxane unit.

 Examples of siloxyl units of formula (2) are the units Six4,2, dimethylsiloxane, methylphenylsiloxane, diphenylsiloxane, methylsiloxane and phenylsiloxane.

 Examples of organopolysiloxanes (I) are dimethylvinylsilyl-terminated dimethylpolysiloxanes, trimethylsilyl-terminated methylvinyldimethylpolysiloxane copolymers, dimethylvinylsilyl-terminated methylvinyldimethylpolysiloxane copolymers and cyclic methylvinylpolysiloxanes.

According to another preferred feature of the invention, the organopolysiloxane (II) comprises siloxyl units of formula
HdWeSIO4- (d + c) (3)
2 in which - W is a monovalent hydrocarbon group, free from unfavorable action on
the activity of the catalyst and preferably selected from alkyl groups having
1 to 8 carbon atoms inclusive and, advantageously, among the methyl groups,
ethyl, propyl and 3,3,3-trifluoropropyl and as well as aryl groups and,
advantageously, among the radicals xylyl and totyl and phenyl, - d is 1 or 2, e is 0, 1 or 2, d + ea a value between 1 and 3, - optionally, at least a part of the other reasons being patterns Formula
average:
Wz4 - 8 (4)
2
where W has the same meaning as above and g has a value included
between 0 and 3.

 The organopolysiloxane (II) may be formed only of units of formula (3) or in addition comprises units of formula (4).

 The organopolysiloxane (II) may have a cyclic linear or branched structure. The degree of polymerization is greater than or equal to 2. More generally, it is less than 5,000.

 The group W has the same meaning as the group Z above.

Examples of units of formula (3) are H (CH 3) 2 SiO 2, HCH 3 SiO 2 .2 H (C 6 H 5) SiO 2, 2
The examples of units of formula (4) are the same as those given above for the units of formula (2).

Examples of organopolysiloxanes (II) are dimethylpolysiloxanes with hydrogenodimethylsilyl ends, and dimethylhydrogenomethylpolysiloxane copolymers with ends.
trimethylsilyl, - dimethylhydrogenomethylpolysiloxane copolymers with hydrogenodimethylsilyl ends, - trimethylsilyl-terminated hydrogenomethylpolysiloxanes, - cyclic hydrogenomethylpolysiloxanes.

 The ratio of the number of silicon-bonded hydrogen atoms in the organopolysiloxane (I) to the number of alkenyl unsaturation groups of the organopolysiloxane (H) is between 0.4 and 10, preferably between 0.6 and and 5.

 The organopolysiloxane (I) and / or the organopolysiloxane (II) can be diluted in a non-toxic organic solvent compatible with silicones.

 Organopolysiloxanes (I) and (II) in a network are commonly known as silicone resins.

 The bases of silicone polyaddition compositions may comprise only linear organopolysiloxanes (I) and (II) such as, for example, those described in US Pat. Nos. 3,220,972, 3,679,473 and US Pat. A4 340 709 or comprise both branched or networked organopolysiloxanes (I) and (Ir), such as, for example, those described in US Pat. Nos. 3,284,406 and 3,434,366.

 Catalysts (III) are also well known.

 The platinum and rhodium compounds are preferably used.

 In particular, platinum complexes and an organic product described in US-A-3 159 601, US-A-3 159 602, US-A-3,220,972 and European patents can be used. A-0 057 459, EP-A-0 188 978 and EP-A-0 190 530, the complexes of platinum and vinyl organosiloxanes described in US-A-3,419,593, US-A-3 715 334, US-A-3. 377,432 and US-A-3,814,730.

 The most preferred catalyst is platinum.

 In this case, the weight amount of catalyst (III), calculated as weight of platinum-metal, is generally between 2 and 400 ppm, preferably between 5 and 200 ppm based on the total weight of the organopolysiloxanes (') and (it ).

 To optimize the performance of the elastomeric material according to the invention, the filler (preferably mineral) is completed by at least one other reinforcing agent selected from siliceous materials, preferably from the following list of products: amorphous silicas (pyrogenic silica ) or crystalline (quartz), advantageously in crushed form, diatoms ... and mixtures thereof.

 In a practical but nonlimiting manner, the reinforcing agent employed is a mixture of quartz and diatoms.

 In terms of weight, it is preferred to use, for 100 parts by weight of silicone elastomer compositions, an amount of reinforcing agent of less than or equal to 120 parts by weight, preferably 100 parts by weight.

Ideally, but not exclusively, this amount is between 20 and 90, preferably between 40 and 60 parts by weight. It is, for example, of the order of 50 parts by weight.

 Advantageously, the silicone elastomer composition comprises at least one retarder of the addition reaction, chosen from polyorganosiloxanes, advantageously cyclic and substituted with at least one alkenyl, tetramethylvinyltetrasiloxane being particularly preferred.

 Such a retarder is present at a maximum of 3000 ppm, preferably at 100 to 2000 ppm relative to the total weight of organopolysiloxanes (I) and (II).

 In the case where the silicone elastomer composition is of the two-component cold-vulcanizable type, the elastomer material according to the invention may be in the form of an uncured precursor system and in two parts A and B, which are separate and of a different nature, one of which of these parts A or B comprising the catalyst (III) and / or a single species (I) or (II) of polyorganosiloxane.

 In this case, the mold is frozen in a form of a donkey impression by placing the parts A and B in contact with each other. For this purpose, the composition of the parts A and B should be established so that their intrinsic viscosities allow their mixing and shaping, in the form of impression targeted for the molds before hardening.

 An example of an elastomer material according to the invention is given below from a bicomponent silicone elastomer composition crosslinking at room temperature or with heat by addition reactions, a filler, a catalyst. and a retarder, without distinguishing the two-component A and B parts of the precursor system.

This material is therefore composed of: (a) - 100 parts by weight of at least one linear diorganopolysiloxane oil
blocked at each end of its chain by a vinyldiorganosilyl motif,
whose organic radicals linked to the silicon atoms are chosen
among the methyl, ethyl and phenyl radicals, at least 60 mol%
of these radicals being methyl radicals and having a viscosity
ranging from 400 to 10,000 mPa.s at 25 ° C, (a ') - to 80 parts, preferably 5 to 50 parts by weight of at least one
vinylated oil of nature (a), but having a viscosity ranging from 5 to
400 mPa.s at 25 ° C., (b) at least one organohydrogenpolysiloxane chosen from
homopolymers and linear or network copolymers having, for
molecule, at least three hydrogen atoms bonded to atoms of
different silicon and whose organic radicals, bonded to the atoms of
silicon, are selected from methyl, ethyl and 60%
less of these radicals being methyl radicals and having a
viscosity ranging from 5 to 500 mPa.s at 25 ° C., the product (b) being used in
such as the molar ratio of the hydride functions to the
vinyl groups brought by the oils (a) and (a ') is between 1
and 4, (c) - a catalytically effective amount of a platinum catalyst, (d) - 20 to 200 parts by weight, preferably 50 to 150 parts by weight of
ceramic compound per 100 parts by weight of all
organopolysiloxanes (a) + (a ') + (b), (e) - 0 to 100 parts by weight, preferably 20 to 60 parts by weight
reinforcing fillers (crushed quartz, diatomaceous, etc.)
as defined above) per 100 parts by weight of all
organopolysiloxanes (a) + (a ') + (b), (f) - 0 to 3000 ppm, preferably 100 to 2000 ppm, retarder (s)
defined above, based on the weight of all organosiloxanes
(a) + (a ') + (b).

 The amount by weight of catalyst (c) is between 2 and 400 ppm, preferably between 5 and 200 ppm based on the weight of the set (a) + (a ') + (b).

 The viscosity referred to herein is the so-called "Newtonian" dynamic viscosity at 25 ° C., ie the dynamic viscosity which is measured, in a manner known per se, at a shear rate gradient. sufficiently low for the measured viscosity to be independent of the velocity gradient.

According to the invention, the elastomeric material can be prepared from a two-component silicone elastomer composition AB, by proceeding as follows: the part A of the two-component is prepared by mixing a feed containing at least one
least one ceramic compound according to the invention and, optionally, one or more
reinforcing fillers and / or one or more crosslinking retarders, with
at least a part of the alkenyl unsaturated polyorganosiloxanes (t) (said
part corresponding, for example, to 60 to 99% by weight of said
polyorganosiloxanes) with all the hydride-functional polyorganosiloxanes (II), the part B of the bicomponent is prepared by combining the catalyst (hui)
with the remainder of the unsaturated polyorganosiloxanes (I), of the order of 10 to 40% by weight, and finally the part A and part B thus obtained are homogeneously mixed.

 The elastomeric materials according to the invention are characterized by a dielectric permittivity E 'measured at 27 MHz of greater than 4.0, preferably 4.5, and more preferably still 5. The measurement of this variable is carried out from classical way, according to the indications of the techniques, e. g. AFNOR Standards NFC 26230 and IEC250.

 With regard to their ability to evacuate heat, it should be noted that the materials according to the invention have a tangent a less than 1 2 2.

The tangent a corresponds to the loss angle e "/ e '.

 The hardness, which is an equally important parameter for these constituent materials of the HF mold, is between 50 and 80 hardness units SHORE A (DSA), measured 96 hours after the crosslinking.

 With regard to their mechanical properties, these materials have an elongation at break greater than 70%, preferably 100% and, more preferably, 105%, while their tensile strength is greater than or equal to 2 MPa. .

 The present invention also relates to a method for manufacturing molds for molding curable plastics, by activation by means of electromagnetic radiation, the frequency of which belongs to one of the following fields: high frequencies, very high frequencies, ultra high frequencies , characterized in that it consists in implementing the elastomeric material of the invention described above.

 In the case where said material is in the form of a precursor, two-component liquid system, it is then necessary to cure it by mixing its parts A and B and developing the hydrosilylation between the alkenyl (vinyl) unsaturation groups. and the hydride functions belonging respectively to the two types of polyorganosiloxanes present, this reaction taking place in the presence of a catalytic amount of platinum or an analogue.

 This hardening can be carried out by imposing an impression form on the mixture AB during crosslinking.

 This form of impression can also be obtained on the hardened material by machining using any suitable tool, milling cutter, press, etc.

 The mold thus obtained may be a car seal mold or any other article that can be manufactured by high frequency molding of curable plastics such as PVC, polyurethane or the like.

 This mold, which constitutes another object of the invention, has a remarkable conformational and dimensional stability. I1 thus makes it possible to carry out at least 900 reproduction cycles by molding, without the appearance of signs of early wear. In particular, no softening is observed as on the molds of elastomeric materials of the prior art. It is moreover a very permissive material for electromagnetic radiation and has, moreover, a good ability to evacuate heat. Its silicone nature gives it lubricating properties, particularly appreciable when demolding.

Finally, the invention also relates to a molding process according to which plastic curable material, preferably in a fluid state, is injected into a mold made of elastomer material according to the invention, and then activated, then , this plastic material by electromagnetic radiation whose frequency belongs to one of the following fields
- high frequencies,
- very high frequencies,
- ultra high frequencies.

For more details, refer to the patent application
EP 0 333 538.

 The present invention will be better understood, its advantages as well as its variants will emerge from the following examples of preparation of elastomeric materials according to the invention.

EXAMPLE
PREPARATION OF ELASTOMTIC MATERIAL FOR THE PREPARATION OF
MOLD
FOR HIGH FREQUENCY MOLDINGS, FROM A SILICONE SYSTIE
BICOMPONENTS, VULCANIZABLE BY HYDROSILYLATION
IN THE PRESENCE OF A PLASTER COMPLEX 1 - PREPARATION OF PART A OF THE BICOMPONENT:
In a melan
600 mPa. s and containing 1.5 mol% of groupings
(CH3) 2 (CH2 = CH) SiO1n, ii - crushed quartz fillers (marketed by SIFRACO under
the denomination C 600) and diatoms (marketed by the JOHNS group
MANVILLE under the name CEIlite SF), the introduction of the charges is done slowly, with gentle agitation (60 revolutions / min).

The mixture is then heated at 120 ° C. for 2 hours with vigorous stirring (250 rpm).

Loads of FqO or TiO3Ba type are then introduced slowly with gentle agitation (60 rpm).

The mixture is maintained for 1 hour at 120 ° C. with vigorous stirring (250 rpm).

The mixture is then brought to ambient temperature and the following oils are added thereto: poly (dimethylsiloxy) (methylhydrogensiloxy) a, dimethylhydrogenosiloxy oil of low viscosity 25 mPa.s and containing 0.25 mol% of H and the polydimethylsiloxane oil a. , X (dimethylvinylsiloxy) viscosity 20 mPa.s and containing 7.70 mol% of groups (CH3) 2 (CH2 = CH) SiOln.

The composition is then filtered.

2 - PREPARATION OF PART B OF THE BICOMPONENT
In a reactor, at room temperature, the high viscosity polydimethylsiloxane a, X (dimethylvinylsiloxy) oil is mixed in the proportions indicated in Table I below.
Approximately 600 mPa.s, α, s (dimethylvinylsiloxy) polydimethylsiloxane oil of medium viscosity
About 200 mPa.s and containing 2.8 mole% of groups
(CH3) 2 (CH2 = CH) SiO1n, - Pt metal, crosslinking catalyst introduced in the form of a complex
organometallic, KARSTEDT type, and tetramethylvinyltetrasiloxane for adjusting the kinetics of crosslinking.

3 - PREPARATION OF THE BICOMPONENT
The two-component is obtained by mixing, at room temperature, 100 parts by weight of Part A and 10 parts by weight of Part B.

TABLE I

<tb> A <SEP> B <SEP> A + B <SEP>
<tb><SEP> 100 <SEP> parts <SEP> in <SEP> 10 <SEP> parts <SEP> 110 <SEP> parts <SEP> in <SEP>
<tb><SEP> weight <SEP> weight <SEP> weight <SEP>
<tb><SEP> a) <SEP> Oil <SEP> SiVi <SEP> high <SEP> viscosity <SEP> 28,00 <SEP> 1,790 <SEP> 29,790
<tb><SEP> a ') <SEP> Oils <SEP> SiVi <SEP> medium <SEP> and <SEP> low <SEP> viscosity <SEP> 2.00 <SEP> 8,170 <SEP> 10,170
<tb><SEP> b) <SEP> Oil <SEP> SiH <SEP> 4.7 <SEP> 4,700
<tb><SEP> c) <SEP> Catalyst <SEP> 0.001 <SEP> 0.001
<tb><SEP> d) <SEP> TiBaO3 <SEP> 43.6 <SEP> 43,600
<tb><SEP> e) <SEP> Loads <SEP> of <SEP> reinforcement <SEP> 21.7 <SEP> 21,700
<tb><SEP> (quartz <SEP> + <SEP> diatoms)
<tb><SEP> f) <SEP> Retarder <SEP> 0.029 <SEP> 0.029
<tb><SEP> TOTAL <SEP> 100.00 <SEP> 9.990 <SEP> 109.99
<tb> 4- RESULTS
The following Table II gives a comparative example of an elastomer material composition according to the invention (test) and a negative control (control), as well as the physical and dielectric properties peculiar to this test and to this control.

TABLE ll
COMPOSITIONS OF ELASTOMERIC MATERIALS FOR HIGH FREQUENCY MOLDING

<tb><SEP> PARTS <SEP> A <SEP> (parts <SEP> into <SEP> weight)
<tb><SEP> WITNESS <SEP> TRIAL
<tb> a) <SEP> Oil <SEP> SiVi <SEP> High <SEP> Viscosity <SEP> 442 <SEP> 280
<tb> a ') <SEP> Oil <SEP> SiVi <SEP> Low <SEP> Viscosity <SEP> 20
<tb> e) <SEP> SIFRACO <SEP> C <SEP> 600 <SEP> (quartz) <SEP> 320 <SEP> 99
<tb> e) <SEP> CELITE <SEP> SUPERFLOSS <SEP> (Diatoms) <SEP> 195 <SEP> 118
<tb> d) <SEP> TiBaO3 <SEP> - <SEP> 436
<tb> b) <SEP> Oil <SEP> SiH <SEP> 43- <SEP> 47
<Tb>
B-SHARES (part weight)

<tb> a) <SEP> Oil <SEP> SiVi <SEP> high <SEP> viscosity <SEP> 18 <SEP> 18
<tb> a ') <SEP> Oil <SEP> SiVi <SEP> medium <SEP> viscosity <SEP> 82 <SEP> 82
<tb> c) <SEP> Catalyst <SEP> 105 <SEP> ppm <SEP> 105 <SEP> ppm
<tb><SEP> Pt <SEP> Pt <SEP>
<tb> f) <SEP> Retarder <SEP> (0.3) <SEP> (0.3) <SEP>
<tb> Ratio <SEP> A / B <SEP> (parts <SEP> in <SEP> weight) <SEP> 10011Q <SEP> 100110 <SEP>
<Tb>
PHYSICAL AND DIELECTRIC PROPERTIES

<tb> Hardness <SEP> SHORE <SEP> at <SEP> 24 <SEP> h <SEP> (DSA) <SEP> 64 <SEP> 64
<tb> Hardness <SEP> SHORE <SEP> to <SEP> 96 <SEP> h <SEP> (DSA) <SEP> 66 <SEP> 65
<tb> Resistance <SEP> rupture, <SEP> MPa <SEP> 2,3 <SEP> 2,3
<tb> Lengthening <SEP> breaking, <SEP>% <SEP> 147 <SEP> 109
<tb> Permittivity <SEP> dielectric <SEP> 3.9 <SEP> 5.5
<tb> Tg <SEP> Delta <SEP><<SEP> 10-2 <SEP><<SEP> 10-2
<Tb>

Claims (11)

CLAIMS:  An elastomeric material intended for producing molds for molding curable plastics, by activation by means of an electromagnetic radiation whose frequency belongs to one of the following domains: high frequencies, very high frequencies, ultra high frequencies, comprising at least one cold-vulcanizable silicone elastomer composition (EVF) and a mineral filler,  characterized:  in that the silicone elastomer composition is of the type of  those crosslinkable by hydrosilylation (or polyaddition,),  and in that the charge comprises at least one compound  ceramic.  2 - Material according to claim 1, characterized in that the ceramic compound is chosen from  ferrites and / or complex salts of formula  M'M203  in which  M1 is an alkaline earth metal,  M2 is a metal selected in column 4b of the  periodic classification, as published in the  64th edition of the "HANDBOOK OF CHEMISTRY",  and / or mixtures of these ceramics.  3 - Material according to claim 2, characterized in that the ceramic compound is barium titanate (BaTiO3), calcium (CaTiO3), strontium (SrTiO3), magnesium zirconate (MgZrO3) or a mixture thereof , barium titanate being more particularly preferred.  4 - Material according to any one of claims 1 to 3, characterized in that the ceramic compound is present in a proportion of 10 to 200, preferably 30 to 150 parts by weight, per 100 parts by weight of the silicone elastomer composition .  5 - Material according to any one of claims 1 to 4, characterized in that the silicone elastomer composition comprises  (I) - at least one organopolysiloxane having, per molecule,  at least two alkenyl groups, preferably vinyls,  related to silicon,  (II) - at least one organopolysiloxane having, per molecule,  at least three silicon-bonded hydrogen atoms,  (III) - a catalytically effective amount of at least one  catalyst, which is composed of at least one metal  belonging to the platinum group, the crosslinking of this composition taking place by addition (hydrosilylation) of at least one vinyl group of (1) to at least one hydride functional group of (II) and being catalyzed by (III).  6 - Material according to claim 5, characterized in that the organopolysiloxane (I) has units of formula  YaZSiO4 - (b) (1)  2 in which: Y is a vinyl group, Z is a monovalent hydrocarbon group, free from unfavorable action on  the activity of the catalyst and preferably selected from alkyl groups having  1 to 8 carbon atoms, advantageously, among the methyl groups,  ethyl, propyl and 3,3,3-trifluoropropyl and as well as aryl groups and,  advantageously, among the radicals xylyl and totyl and phenyl, - a is 1 or 2, b is 0, 1 or 2 and a + b is between 1 and 3, - optionally at least a part of the other units are units of formula  average: Z1O4 - c (2)  2  in which Z has the same meaning as above and c has a value  between 0 and 3.  7 - Material according to claim 5 or claim 6, characterized in that the organopolysiloxane (II) comprises siloxyl units of formula  HdWeSIO4- (d + e) (3)  2 in which - W is a monovalent hydrocarbon group, free from unfavorable action on  the activity of the catalyst and preferably selected from alkyl groups having  1 to 8 carbon atoms inclusive and, advantageously, among the methyl groups,  ethyl, propyl and 3,3,3-trifluoropropyl and as well as aryl groups and,  advantageously, among the radicals xylyl and totyl and phenyl, - d is 1 or 2, e is 0, 1 or 2, d + ea a value between 1 and 3, - optionally, at least a part of the other reasons being patterns Formula  average (4):  W8St04-8 (4)  2  where W has the same meaning as above and g has a value  between 0 and 3.  8 - Material according to any one of claims 5 to 7, characterized in that the proportions of (I) and (11) are such that the molar ratio of silicon-bonded hydrogen atoms in (11) on the radicals silicon-bonded vinyls in (I) is between 0.4 and 10, preferably between 0.6 and 5.  9 - Material according to any one of claims 1 to 8, characterized in that the filler comprises, in addition, at least one other reinforcing agent selected from siliceous materials, preferably from the following list of products: silica (quartz ), advantageously in milled form, diatoms and their mixtures.  10 - Material according to claim 9, characterized in that, for  100 parts by weight of silicone elastomer composition, the amount of reinforcing agent is less than or equal to 120 parts by weight, preferably 100 parts by weight, said quantity being, more preferably still, between 20 and 90 parts by weight .  II - Material according to any one of claims 1 to 10, characterized in that the silicone elastomer composition comprises at least one retarder of the addition reaction, chosen from polyorganosiloxanes, advantageously cyclic and substituted by at least one alkenyl, the tetramethylvinyltetrasiloxane being particularly preferred.  12 - Material according to any one of claims 1 to 11, characterized:  in that the silicone elastomer composition is of the type  two-component system,  and in that the material is in the form of a system  uncured precursor and in two separate parts A and B and  different nature, one of those parts A and B including the  catalyst (hui) and a single species (I) or (II) of  polyorganosiloxane.  13 - Material according to claim 12, characterized in that the composition of the parts A and B is established so that their intrinsic viscosities allow their mixing and shaping in the form of impression targeted for the molds, before hardening.  14 - Method for producing molds for molding plastics that can be activated by activation by means of electromagnetic radiation whose frequency belongs to one of the following fields: high frequencies, very high frequencies, ultra high frequencies,  characterized in that the material according to any one of claims 1 to 13 is used, cured as necessary and shaped into the desired impression shape, which shaping may be effected beforehand. during or after hardening of the material.  15 - A method of molding curable plastics, characterized in that it consists in injecting the curable plastic material in the fluid state into a mold consisting of material according to any one of claims 1 to 13, and then to activate this plastic material by electromagnetic radiation whose frequency belongs to one of the following areas: high frequencies, very high frequencies, ultra high frequencies.