HK1119194A

HK1119194A - Self-adhesive addition cross linking silicon-rubber blends, method for the production thereof, method for producing composite moulded parts and the use thereof

Info

Publication number: HK1119194A
Application number: HK08110408.7A
Authority: HK
Inventors: Stephan Bosshammer
Original assignee: Ge Bayer Silicones Gmbh & Co. Kg
Priority date: 2005-03-24
Filing date: 2006-03-24
Publication date: 2009-02-27

Description

Self-adhesive addition-crosslinking silicone rubber mixtures, method for the production thereof, method for the production of composite molded parts, and use thereof

The invention relates to addition-crosslinking silicone rubber mixtures, to a method for the production thereof, to a method for the production of composite molded parts, and to the use thereof.

The self-adhesive addition-crosslinking silicone rubber mixtures of the invention are characterized by good adhesion to substrates, while the molds (Form) used for producing the molded parts do not require special treatment, so that the addition-crosslinking silicone rubber mixtures can be released from the molds. In addition, post-annealing of the composite mouldings is not generally required.

A series of methods have been proposed for achieving adhesive bonding between addition-crosslinked silicone elastomers and different substrates. One possible method is the use of so-called primers, which are used to pretreat the substrate surface. This requires additional processing steps and treatment with solvents at the time of treatment. Both of which are disadvantageous. Another possibility consists in bonding the addition-crosslinked silicone elastomer to the substrate by adding one or more additives to the uncrosslinked silicone rubber mixture.

Another variant provides a process for preparing thermoplastic-silicone blends, in which various silicones are mixed into the thermoplastic matrix before shaping and the surface of moldings prepared from the thermoplastic blends is bonded to addition-crosslinked silicone rubbers. US 5366806 claims hydrogen siloxanes having additional alkenyl groups in a thermoplastic matrix which is adhesively bonded to an addition-crosslinking polyorganosiloxane rubber which may preferably contain a further organofunctional SiH binder.

US 5366805 discloses a polycarbonate containing a copolymer or terpolymer of a hydrosiloxane and a siloxane having an epoxy group or an aromatic group. The US 5418065 recommends using instead of silicone-containing thermoplastics polypropylene terpolymers containing addition-crosslinking polyorganosiloxane rubbers and SiH siloxanes containing epoxy groups, which polypropylene terpolymers achieve adhesion upon crosslinking. The bonding is effected, for example, at 120 ℃ for 8 minutes. The thermoplastic part is injected just before the silicone rubber is applied. The system allows the composite part to be demolded from a metal mold.

Another solution is to provide addition-crosslinking polyorganosiloxane rubbers which, depending on the type of thermoplastic substrate, contain one or more additives and can adhere to such thermoplastics under various conditions during crosslinking. It is desirable that a particular thermoplastic with a high softening temperature adheres to silicone rubber, as opposed to the metal mold material (i.e., typically steel) which remains as little as possible.

According to US 4087585, good adhesion to aluminum is achieved, for example, by adding two additives, one being a short-chain siloxane having at least one SiOH group and one being a silane having at least one epoxy group and an alkoxy group bonded to Si. Good adhesion to different metals and plastics was achieved by adding a combination of epoxy silanes and homopolymer cross-linking agents according to J.Adhesion Sci.Technol. Vol.3, No.6, pp.463-473 (1989). In EP-A875536, improved adhesion to different plastics is achieved by using alkoxysilanes having epoxy groups and hydrosilanes having at least 20 SiH functions per molecule, the mixtures also being distinguished by improved reactivity.

EP 350951 describes the use of a combination of acryloyl or methacryloyloxysilanes with epoxy-functional silanes and partial allyl ethers of polyols as additives to achieve durable adhesion of addition-crosslinked silicone elastomers to glass and metals.

The disadvantage of this mixture is that it also has good adhesion to metals and therefore causes problems when working with uncoated metal molds.

EP-A2-1085053 discloses that good adhesion to polyamide and polybutylene terephthalate is achieved by the addition of a combination of glycidoxypropyltrimethoxysilane and methacryloxypropyltrimethoxysilane and by post-annealing of the composite while the mold is readily released from an uncoated steel mold. However, relatively high amounts of silane are used and post-annealing of the composite mouldings is generally recommended in order to achieve good final adhesion, which means an additional processing step.

US 4082726 discloses the use of terpolymers, i.e. siloxanes consisting of at least three different siloxy groups. It may contain, in addition to Si-epoxy groups, Si-phenyl, SiH and other siloxy units. Such epoxysiloxanes use hydrogensiloxanes B) in addition to almost any alkenylsiloxanes A) to provide adhesion between the thermoplastic substrate and the addition-crosslinking polyorganosiloxane rubber. It does not disclose a preferred concentration for organofunctional units on silicon. The presence of epoxy-containing terpolymers adheres both to thermoplastics and to metals.

US 5405896 discloses the use of copolymers or terpolymers having at least one oxyphenylene group and at least one SiH group instead of ethoxy-containing silicone terpolymers. The silicone rubber is adhesively cured on the thermoplastic surface, for example at 120 ℃ for 8 minutes. The release was successful in an uncoated metal mold.

US 6127503 recommends the use of terpolymers having at least one phenyl or phenylene unit, at least one nitrogen-containing unit and at least one SiH group instead of oxygen-containing siloxane copolymers or terpolymers. The silicone rubber is adhesively cured on the thermoplastic surface within 10 minutes, for example at 120 ℃.

EP 686671 (U.S. Pat. No. 3, 5536803) describes the use of organohydrogenpolysiloxanes in which at least 12 mol% of the Si-bonded monovalent organic residues are aromatic groups as additives. Although adhesion to ABS that has not been quaternized and easy release from metal surfaces are ensured, no evaluation of typical industrial thermoplastics such as polyamides, polybutylene terephthalate or polyphenylene sulfide has been carried out. No specific task has been proposed for these thermoplastics. Likewise, no preferred ranges for the SiH content of the corresponding alkoxy component are disclosed. Silicone rubbers adhere to thermoplastic surfaces, for example, during crosslinking at 60 to 100 ℃ within 100 seconds to 8 minutes. The SiH content given is typically more than 2 hydrogen atoms per molecule. In specific embodiments there is no hydrogen content exceeding six hydrogensiloxy units per molecule.

Self-adhesive addition-crosslinking silicone elastomer compositions are known from EP-A2-1106662, which use polyorganohydrogensiloxanes having an average of less than 20 SiH groups in the molecule. The use of less than 20 SiH groups per molecule of such polyorganohydrogensiloxanes is described as being necessary because the storage stability of the addition-crosslinked silicone rubber mixtures is increased, i.e.the flowability is greatly impaired.

Addition-crosslinking silicone elastomer compositions containing polyorganohydrogensiloxanes and special adhesion promoters based on diphenyl compounds are likewise known from EP-B1-1375622. However, the use of such diphenyl compounds is disadvantageous because of their relatively high price.

Addition-crosslinking silicone elastomer compositions are likewise known from WO 03/066736, which contain relatively SiH-group-rich, phenyl-free organohydrogenpolysiloxanes and phenyl-containing organohydrogenpolysiloxanes. The phenylorganohydrogenpolysiloxanes used are relatively SiH-deficient.

The inventors of the present patent application have surprisingly found that self-adhesive, addition-crosslinked silicone elastomer compositions having an SiH content of more than an average of 20 SiH groups per molecule are stable at relatively low aromatic group content, adhere better to most substrates, ensure high crosslinking rates, and nevertheless release from injection molds filled therewith.

The object of the present invention is to provide addition-crosslinking silicone rubber mixtures having good adhesion to different substrates, in particular industrial thermoplastics such as polyamides, polybutylene terephthalate or polyphenylene sulfide having a high softening temperature, without the need for coating the mold for processing on an automatic injection molding machine (spritziae β automatic) or for treatment with a mold release agent to avoid mold adhesion and without the need for conventional back annealing of the composite. For this reason, simple and inexpensive producible additive components for silicone rubbers are sought which can be added separately as separate components to the commercially known, preferably two-component rubbers.

The subject matter of the invention is therefore addition-crosslinking silicone rubber mixtures comprising:

a) at least one linear or branched organopolysiloxane having at least two alkenyl groups and a viscosity of 0.01 to 30000Pa.s (25 ℃),

b1) at least one organohydrogensiloxane having an average of at least 20 SiH units per molecule in each case having at least one organic residue containing at least one member selected from the group consisting of aromatic groups, halogen atoms, pseudohalogen groups, polyether groups, aminoalkyl groups and ammonioalkyl groups,

b2) optionally one or more organohydrogenpolysiloxanes having an average of at least two SiH groups per molecule and wherein the organic residue is selected from saturated and unsaturated aliphatic hydrocarbon groups,

c) at least one hydrosilylation reaction catalyst,

d) at least one component selected from the group consisting of acryloxyalkyltrialkoxysilanes and methacryloxyalkyltrialkoxysilanes, alkoxysilanes and/or alkoxysiloxanes each having at least one epoxy group, and condensation products of the above-mentioned compounds with water, alcohols, silanols and/or siloxane diols,

e) optionally at least one inhibitor selected from the group consisting of,

f) optionally at least one optionally surface-modified filler,

g) optionally at least one auxiliary agent.

The addition-crosslinking silicone rubber mixtures of the invention preferably have the following composition (parts by weight):

100 parts of polyorganosiloxane a)

0.2-60 parts of organohydrogensiloxane b)

1-1000ppm of metal content based on catalyst c) and silicone rubber

Total amount of mixture

0.01 to 10 parts of an epoxyalkoxysilane or epoxyalkoxysiloxane d)

0-2 parts of inhibitor e)

0 to 300 parts of an optionally surface-modified filler f)

0 to 15 parts of auxiliary g)

The addition-crosslinking silicone rubber mixtures according to the invention contain a) at least one linear or branched organopolysiloxane having at least two alkenyl groups and a viscosity of 0.01 to 30000Pa.s (25 ℃).

The organopolysiloxanes a) may be branched polysiloxanes. The term "branched polysiloxane" includes macrocyclic or spirocyclic structures, i.e. they are molten solids having a melt viscosity in the stated viscosity range at 90 ℃ or solids soluble in conventional solvents or silicone polymers.

Component a) is substantially free of Si-H groups.

The organopolysiloxanes a) are preferably linear or branched polysiloxanes which may have the following siloxy units:

wherein the substituents R, which may be the same or different, are selected from the following:

a linear, branched or cyclic alkyl group of up to 12 carbon atoms, which may optionally be substituted by at least one substituent selected from phenyl and halogen, in particular fluorine,

-a linear, branched or cyclic alkenyl group of up to 12 carbon atoms,

-a phenyl group,

-a hydroxyl group, and

-a linear, branched or cyclic alkoxy group of up to 6 carbon atoms,

or two substituents R from different alkoxy units together form a linear, branched or cyclic alkylene group of 2 to 12 carbon atoms between two silicon atoms,

with the proviso that at least two substituents R per molecule represent the abovementioned alkenyl radicals, which may be identical or different.

The alkoxy units mentioned may be present in random distribution or in block arrangement with respect to one another.

Preferred straight, branched or cyclic alkyl groups of up to 12 carbon atoms are methyl groups.

Preferred alkyl groups substituted with phenyl groups include, for example, styryl (phenylethyl).

Preferred alkyl groups substituted with halogen include, for example, fluoroalkyl groups having at least one fluorine atom, such as a perfluoroalkylethyl group (e.g., preferably 3, 3, 3-trifluoropropyl group) or a perfluoroalkyl ether or an epoxy-perfluoroalkyl ether.

Straight-chain or branched alkenyl groups of 2 to 8 carbon atoms include, for example: vinyl, allyl, hexenyl, octenyl, vinylphenylethyl, cyclohexenylethyl, ethylidenenorbornyl or norbornenylethyl or limonyl. Vinyl groups are particularly preferred.

Preferred linear, branched or cyclic epoxy groups of up to 6 carbon atoms are, for example, methoxy and ethoxy.

Preferred radicals R are therefore methyl, phenyl, vinyl and 3, 3, 3-trifluoropropyl.

Preferred siloxy units are, for example, alkenyl units such as dimethylvinylsiloxy, methylvinylsiloxy, vinylsiloxy units, alkyl units such as trimethylsiloxy, dimethylsiloxy and methylsiloxy units, phenylsiloxy units such as triphenylsiloxy, dimethylphenylsiloxy, diphenylsiloxy, phenylmethylsiloxy and phenylsiloxy units, phenyl-substituted alkylsiloxy units such as (methyl) (styryl) siloxy units.

Preferably, the organopolysiloxanes a) have a siloxy unit number of from 100 to 10000, particularly preferably from 300 to 1000.

The alkenyl content of the organopolysiloxanes a) is preferably from 0.003mmol/g to 11.6mmol/g, based on the vinyl-substituted polydimethylsiloxane, which is correspondingly applied equimolar to other radicals R having a formula weight different therefrom.

The organopolysiloxanes a) have a viscosity of from 0.001 to 30kPa.s, very particularly preferably from 5 to 200 Pa.s. The viscosity is determined according to DIN 53019 at 25 ℃.

In a preferred embodiment of the invention, the organopolysiloxanes a) comprise mixtures of different organopolysiloxanes having different alkenyl groups, preferably vinyl groups, which differ in alkenyl or vinyl content preferably by a factor of at least 1.5 to 3.

Preferred mixtures of organopolysiloxanes a) are mixtures which comprise organopolysiloxanes which are rich in alkenyl groups, preferably vinyl groups, and at least one, preferably at least two, particularly preferably two, organopolysiloxanes which are poor in alkenyl groups, preferably poor in vinyl groups.

The alkenyl-group-rich, preferably vinyl-group-rich, organopolysiloxanes preferably contain an alkenyl content of more than 0.4mmol/g to 11.6mmol/g, based on the vinyl-substituted polydimethylsiloxane, which is correspondingly equimolar to the other radicals R.

These siloxane polymers may preferably represent branched polysiloxanes as defined above, i.e. solids which melt at 90 ℃ or solids which are soluble in conventional solvents or siloxane polymers.

The alkenyl group-poor (preferably vinyl group-poor) organopolysiloxane preferably has an alkenyl group content of less than 0.4mmol/g, more preferably 0.02-0.4 mmol/g.

The alkenyl content is determined here by 1H-NMR, see a.l Smith (Ed.): the analytical Chemistry of Silicones, J.Wiley & Sons 1991, volume 112, from page 356, edited in Chemical Analysis, J.D. Winefordner.

Preferably, the alkenyl content is adjusted by alkenyldimethylsiloxy units. In addition to different alkenyl contents, different chain lengths and thus different viscosities are thereby obtained.

The use of the above-described mixtures having different alkenyl, preferably vinyl, contents makes it possible to optimize the mechanical properties, such as elongation and re-tensile strength, of the crosslinked silicone rubbers of the invention.

The mixing ratio of the alkenyl-rich organopolysiloxanes a) is preferably from 0.5 to 30% by weight, based on the total amount of organopolysiloxanes a). The total alkenyl content of the mixture of different organopolysiloxanes having various alkenyl, preferably vinyl, contents should preferably be less than 0.9 mmol/g.

The organopolysiloxanes a) can be prepared according to known methods, for example by means of basic or acidic catalysts, as described, for example, in US 5536803.

The amount of organopolysiloxane a) can preferably be from about 20.5 to 99.8% by weight, based on the total amount of the silicone rubber mixture.

The alkenyl group-rich organopolysiloxanes include in particular solid or liquid resins which are soluble in solvents, these resins preferably consisting of trialkylsiloxy (M-units) and silicate units (Q-units) and preferably containing vinyldimethylsiloxy units in such an amount that a vinyl content of at least 2mmol/g is obtained. Furthermore, these resins can also have up to 10 mol% of alkoxy groups or OH groups on the Si atom.

Component b1) of the addition-crosslinking silicone rubber mixtures according to the invention is an organohydrogensiloxane having an average of at least 20 SiH units per molecule in each case. If the organohydrogensiloxane contains less than 20 SiH units per molecule, the adhesion to the substrate (e.g., particularly a thermoplastic) is reduced. The organohydrogensiloxanes b1) used according to the invention preferably contain an average of at least 23 SiH groups in the molecule, more preferably at least 30 SiH groups in the molecule.

Furthermore, the organohydrogensiloxane b1) has at least one organic residue which contains at least one component selected from the group consisting of aromatic groups, halogen atoms, pseudohalogen groups, polyether groups, aminoalkyl groups and ammonioalkyl groups. Preferably, the organohydrogensiloxanes b1) preferably contain at least one organic residue containing on average at least one aromatic group.

The organohydrogensiloxanes b1) are preferably selected from linear, branched or cyclic polysiloxanes which may have the following siloxy units:

wherein R is¹May be the same or different and is selected from the following groups:

-hydrogen, and (C) hydrogen,

-a linear, branched or cyclic alkyl group of up to 12 carbon atoms, which may optionally be substituted by at least one substituent selected from phenyl, naphthyl, biphenyl, diphenyl ether and halogen, in particular fluorine,

-a linear, branched or cyclic alkenyl group of up to 12 carbon atoms,

-an aromatic group, and

-a linear, branched or cyclic alkoxy group of up to 6 carbon atoms,

or two radicals R from different alkoxy units¹Together form a linear, branched or cyclic alkylene group of 2 to 12 carbon atoms between the two silicon atoms.

In a first embodiment, the organohydrogensiloxane b1) has a Si-H content of greater than 36 mol%, which is defined as the ratio of the H atoms bonded to silicon to the sum of the H atoms bonded to silicon and the organic groups bonded to silicon.

Particularly preferred are organohydrogensiloxanes b1) having at least one optionally substituted aromatic group, particularly preferably a phenyl, naphthyl, biphenyl or diphenyl ether group. Preferred aromatic units as substituents R1 include, for example, aromatic units in which the aromatic group is directly bonded to the silicon atom, such as phenyl, C1-C10 alkylphenyl, C2-C10 alkylenephenyl, C1-C10 alkoxyphenyl, C2-C10 alkyleneoxyphenyl, halophenyl and naphthyl; and aromatic groups in which the aromatic group is attached to the silicon atom via an alkyl group, such as phenyl (C1-C12) alkyl. Preference is given to aromatic radicals, in particular phenyl radicals, which are bonded directly to the silicon atom.

The content of aromatic group-containing organic residues in the organohydrogenpolysiloxane b1) is preferably less than 12 mol%, more preferably less than 8 mol%, and still more preferably less than 7.4 mol%, based on all residues bonded to silicon atoms (except for Si-O-Si oxygen atoms), that is, including hydrogen atoms and organic residues. Preferably, the minimum amount of aromatic groups is 0.5 mol%, more preferably 1 mol%.

Preferred organohydrogensiloxanes b1) are linear triorganosiloxy and/or diorganohydrogensiloxy terminated organohydrogensiloxanes in which the triorganosiloxy end groups are selected from the group consisting of trimethylsiloxy, triphenylsiloxy, diphenylmethylsiloxy, phenyldimethylsiloxy, phenylethyldimethylsiloxy and phenylpropyldimethylsiloxy; the diorganohydrogensiloxy end group is preferably a dimethylhydrogensiloxy group and has an average of from 20 to 1000 methylhydrosiloxy units, an average of from 0 to 500 dimethylsiloxy units, an average of less than 360 (methyl) (phenyl) siloxy units and/or an average of less than 180 diphenylsiloxy units, preferably less than 111 or 222 diphenylsiloxy units.

The molar ratio of dimethylsiloxy to methylhydrosiloxy units is preferably less than 0.1.

Preferably, the organohydrogensiloxane b1) contains more than 2mmol SiH/g to about 16mmol SiH/g. Particularly preferably, the organohydrogensiloxanes b1) contain more than 7mmol SiH/g, based on polymethylhydrogensiloxane, which correspondingly applies equally well in the presence of radicals R1 having other formula weights.

The organohydrogensiloxane b1) has, for example, a viscosity of from 10 to 100Pa.s, preferably from 15 to 10Pa.s (25 ℃).

In this case, the SiH content is determined by¹H-NMR determination, see a.l. smith (Ed.): the analytical Chemistry of Silicones, J.Wiley&Sons 1991, volume 112, edited by j.d. wineforder in Chemical Analysis, from page 356. Si phenyl content was likewise determined by 1H-NMR or 29Si-NMR, see A.L. Smith (Ed.); ebd.

The addition-crosslinking silicone rubber mixtures according to the invention optionally additionally contain one or more organohydrogensiloxanes b2), the organic residues of which are selected from saturated or unsaturated hydrocarbon residues, i.e.contain no aromatic groups. Furthermore, the organohydrogenpolysiloxane b2) contains an average of at least two SiH groups per molecule.

It is particularly preferred that both component b1) and component b2) are present. Furthermore, it is preferred that both component b1) and component b2) are selected from at least one triorganosiloxy or diorganohydrogensiloxy terminated polyorganohydrogensiloxane having more than 20 SiH units.

The organohydrogensiloxanes b2) are preferably linear, branched or cyclic polysiloxanes which may contain the following siloxy units:

wherein, the substituent R²May be the same or different and is selected from the following groups:

-hydrogen, and (C) hydrogen,

-a linear, branched or cyclic alkyl group of up to 12 carbon atoms,

-a linear, branched or cyclic alkenyl group of up to 12 carbon atoms,

-a linear, branched or cyclic alkoxy group of up to 6 carbon atoms,

or two substituents R from different alkoxy units¹Together form a linear, branched or cyclic alkylene group of 2 to 12 carbon atoms between the two silicon atoms.

Optionally with organohydrogensiloxanes b 2). They are particularly suitable where the crosslinking speed, the mechanical properties of the rubber, for example the re-tensile strength, or the ageing properties, for example the hot air stability, have to be optimized.

The optional component b2) has an SiH content of 0.2 to 16mmol/g, preferably 4 to 16mmol/g, based on polymethylhydrogensiloxane, which is correspondingly suitable for the presence of residues R of other formula weights²The case (1).

In the case of organohydrogensiloxanes b2), the number of siloxy units is preferably from 5 to 1000, more preferably from 10 to 500, and still more preferably from 10 to 200.

b2) The siloxy units in (a) are preferably adjusted in such a way that liquid or siloxane-soluble hydrosiloxanes having a viscosity of from 0.5 to 50000mPa.s are obtained at 25 ℃. The siloxane b2) also includes solids having a melt viscosity in the above-mentioned range and melting at 90 ℃ or solids soluble in conventional solvents or siloxane polymers.

Preferred representatives are trimethylsiloxy or hydrogendimethylsiloxy-terminated polymethylhydrogendiorganosiloxanes.

Organohydrogensiloxanes b2) were prepared in a manner known per se (for example in US 5536803), with the SiH content being adjusted by selecting a suitable weight ratio of hydroorganosilyloxy units to organosilyloxy units and monofunctional end groups (for example trimethylsiloxy groups).

Preferred amounts of organohydrogensiloxy b2) are from 0 to 30 parts by weight, based on 100 parts by weight of component a).

The addition-crosslinking silicone rubber mixtures according to the invention contain c) at least one Pt-Ru catalyst and/or Rh catalyst for the crosslinking reaction and/or hydrosilylation reaction. Platinum catalysts are preferred. Particularly preferred catalysts c) are preferably Pt (0) complexes, Pt (II) complexes or salts thereof or Pt (IV) complexes or salts thereof with ligands which are complex formers, for example alkenylsiloxanes, cycloalkyldienes, olefins, halogens or pseudohalogens, carboxyl groups, ligands containing S-N-or P groups, in amounts of from 1 to 1000ppm, preferably from 1 to 100ppm, particularly preferably from 1 to 20ppm, based on the metal. Ru and/or Rh catalysts include, for example: rh complexes or Ru complexes and salts, for example, di μ, μ' -dichloro-bis (1, 5-cyclooctadiene) dirhodium. As Rh compounds, the compounds described in J.Appl.Polym.Sci 30, 1837-1846(1985) can likewise be used.

The addition-crosslinking silicone rubber mixtures of the invention optionally contain at least one inhibitor. Inhibitors within the scope of the present invention are all customary inhibitors which have hitherto been used for slowing down or inhibiting hydrosilylation reactions. Examples of such preferred inhibitors are vinylmethylsiloxanes such as 1, 3-divinyltetramethyldisiloxane, 1, 3, 5, 7-tetravinyl-1, 3, 5, 7-tetramethylcyclotetrasiloxane, alkynols such as 2-methylbutynol- (2) or 1-ethynylcyclohexanol (US 3445420), in amounts of from 50 to 10000ppm, and all other known S-, N-or P-containing inhibitors (DE-A3635236), which make it possible to retard the hydrosilylation reaction promoted by component c) pure Pt, Ru or Rh catalysts.

The addition-crosslinking silicone rubber mixtures according to the invention additionally contain at least one component selected from the following: acryloxyalkyltrialkoxysilanes and methacryloxyalkyltrialkoxysilanes, alkoxysilanes and/or alkoxysiloxanes, in each case containing at least one epoxy group, and also condensation products of the above-mentioned compounds obtained by reaction with water, alcohols, silanols and/or silanediols. The epoxy group is suitably an epoxy group linked to Si via an alkylene group (epoxy group- (CH2) x-Si). Preferred are those having up to 5 carbon atoms in the alkoxy functionality, and typically having 2, but preferably 3, alkoxy groups per molecule. Epoxysilanes and epoxysiloxanes belonging to this class are described in EP 691364.

The alkoxysilanes d) also include glycidoxypropyltrialkoxysilanes and dialkoxysilanes or 2- (3, 4-epoxycyclohexyl) ethyltrialkoxysilanes, epoxylimonyltrialkoxysilanes, epoxidized norbornenylethyltrialkoxysilanes or ethylidenenorbornenyltrialkoxysilanes and other C₃-C₁₄Epoxidized alkenyl or alkenylaryltrialkoxysilanes, epoxidized trialkoxysilylpropylallylcyanurates or isocyanurates and in each case their dialkoxy derivatives, acryloxypropyltrialkoxysilanes or methacryloxypropyltrialkoxysilanes and their condensation products after reaction with water, alcohols or silanols or siloxane diols.

Preference is given to mono (epoxyorgano) trialkoxysilanes, such as glycidoxypropyltrimethoxysilane, 2- (3, 4-epoxycyclohexyl) ethyltrialkoxysilane or methacryloxypropyltrimethoxysilane and/or siloxanes thereof, particular preference being given to mixtures of glycidoxypropyltrimethoxysilane and methacryloxypropyltrimethoxysilane, in amounts of from 0.01 to 10 parts, based on 100 parts of component a), or from 0.002 to 9.1% by weight, based on the total amount of the addition-crosslinked silicone rubber mixture.

As described in component b1), it is also possible to use reaction products of d) with a) and b) by hydrosilylation or d) with b) by condensation.

The addition-crosslinking silicone rubber mixtures of the invention additionally optionally contain one or more optionally surface-modified fillers (f). These include, for example: all finely divided fillers (i.e.particles smaller than 100 μm) which do not interfere with the Pt-catalyzed crosslinking reaction make it possible to obtain elastomeric coatings, moldings or extrudates.

The filler may be a mineral filler such as a silicate, carbonate, nitride, oxide, carbon black or silica. Preferably, it is a filler which enhances the mechanical properties of the rubber,for example BET surface areas of 50 to 400m²A/g pyrogenic or precipitated silica, which may be surface-treated, in an amount of from 0 to 300 parts by weight, preferably from 10 to 50 parts by weight, based on 100 parts by weight of component a).

BET surface area of more than 50m²The fillers/g allow the preparation of silicone elastomers having improved mechanical properties of the rubber. In the case of, for example, pyrogenic silica, such as highly dispersed silica gel, HDK, Cab-O-Sil, the mechanical strength and transparency of the rubber are increased by its surface area.

Furthermore, BET surface areas of 1 to 50m²Additional or alternative so-called extender fillers per gram, such as quartz flour, diatomaceous earth, cristobalite powder, mica, alumina, titanium oxide, iron oxide, zinc oxide, chalk or carbon black.

The term filler f) means a filler comprising a hydrophobic agent or dispersant or processing aid adhering to its surface, which influences the interaction of the filler with the polymer, for example to effect thickening. The surface treatment of the filler preferably involves hydrophobization with silanes or siloxanes. They can be carried out, for example, "in situ", by adding silazanes, for example hexamethylsilazane and/or divinyltetramethyldisilazane, and water, hydrophobicization "in situ" being preferred. It is also possible to carry out the treatment with the aid of other customary filler surface treatment agents, for example vinylalkoxysilanes, such as vinyltrimethoxysilane, organosiloxane diols having chain lengths of from 2 to 50, to provide the reaction sites required for the crosslinking reaction, and also with fatty acids or fatty alcohol derivatives.

The addition-crosslinking silicone rubber mixtures according to the invention additionally optionally contain at least one auxiliary g), for example a phenylsiloxane oil, a vulcanized rubber which provides self-lubrication, for example a copolymer from dimethylsiloxy and diphenylsiloxy or methylphenylsiloxy groups, and also a polysiloxane having a viscosity of preferably from 0.1 to 10Pa.s (25 ℃) and containing methylphenylsiloxy groups or as a colorant or color pigment for pigmented pastes, additional mold release agents, for example fatty acids or fatty alcohol derivatives, extrusion aids, for example boric acid or PTFE pastes, biocides, for example fungicides, and hot-air stabilizers, for example Fe-, Ti-, Ce-, Ni-, Ce-compounds. The amount of auxiliaries is preferably from 0 to 15 parts by weight, based on 100 parts by weight of component a), and preferably less than 13% by weight, based on the total weight of the rubber mixture.

Furthermore, the present invention relates to an organohydrogenpolysiloxane characterized in that it has an average of at least 20 hydrogensiloxy units in a molecule, it contains a Si-bonded monovalent organic residue having an aromatic group, and the content of the aromatic group-containing monovalent organic residue is at least 12 mol%. For these organohydrogenpolysiloxanes the aforementioned preferred ranges for component b1) apply.

The addition-crosslinking silicone rubber mixtures of the invention preferably contain no separate, Si-containing biphenyl adhesion promoter component. These include compounds in which both phenyl groups are substituted by divalent radicals, e.g. optionally substituted alkylene, SO_2--SO-, -CO-, -O-or-O-Si (CH)₃)₂-O-is connected. Particular preference is given to the absence of diphenyl adhesion promoters as defined according to component (C) of EP 1375622, which is incorporated by reference in its entirety.

The invention also relates to a method for producing addition-crosslinking silicone rubber mixtures, comprising mixtures of components a) to d) and optionally components e) to g).

The mixing is preferably carried out by means of mixers suitable for high-viscosity pastes, such as kneaders, high-speed dispersers or planetary mixers under an inert atmosphere.

In a preferred embodiment, so-called reinforcing fillers are incorporated in such a way that the BET surface area is greater than 50m²Those of/g such that they are hydrophobized "in situ" during mixing.

Of these, organopolysiloxanes a), fillers and hydrophobicizing agents, preferably hexamethyldisilazane and/or divinyltetramethyldisilazane, are preferably stirred with water in the presence of silica component f), preferably at temperatures of 90 to 100 ℃ for at least 20 minutes in mixing devices suitable for high-viscosity materials, such as kneaders, high-speed dispersers or planetary mixers, and the remaining hydrophobicizing agent and water are then removed at 150-160 ℃ first by evaporation at atmospheric pressure and then under vacuum at pressures of 100 to 20 mbar. Subsequently, the other components are mixed in, suitably over a period of 10-30 minutes.

In a preferred embodiment of the process for preparing addition-crosslinked silicone rubber mixtures, at least one partial mixture is first prepared which comprises more than one, but not all, of the components a) to g).

This partition in the partial mixing serves to improve the handling of the reactive mixture from the components a) to d) and, if desired, e) to g). In particular, for storage, the components b1) -b2) should preferably be kept separate from the catalyst c). Component d) and inhibitor e) may be present more or less advantageously in the individual components, provided that components a), b1)/b2) and c) which react with one another are not placed beforehand one another at the same time.

In a preferred embodiment of the process according to the invention for producing addition-crosslinked silicone rubber mixtures, the following first-part mixtures are first prepared by combining:

at least one organopolysiloxane a)

Optionally at least one filler f)

Optionally at least one auxiliary g)

At least one catalyst c), and

optionally at least one alkoxysilane and/or alkoxysiloxane d),

and preparing a second part mixture by combining:

-optionally an organopolysiloxane a),

at least one organohydrogensiloxane b1),

optionally one or more organohydrogenpolysiloxanes b2),

optionally at least one filler f),

optionally at least one alkoxysilane and/or alkoxysiloxane d),

optionally at least one inhibitor e), and

optionally at least one auxiliary g),

the two partial mixtures are subsequently mixed.

In a further preferred embodiment of the process according to the invention for preparing addition-crosslinking silicone rubber mixtures, component b2) is used, the following first-part mixtures are first prepared by combining:

at least one organopolysiloxane a),

optionally at least one filler f),

optionally at least one auxiliary g),

at least one catalyst c), and

optionally at least one alkoxysilane and/or alkoxysiloxane d), if not accommodated in the second or third part mixture,

preparing a second part mixture by combining:

at least one organohydrogensiloxane b2),

optionally at least one organopolysiloxane a),

optionally at least one filler f),

optionally at least one alkoxysilane or alkoxysiloxane d), if not accommodated in the first or third part mixture,

optionally at least one inhibitor e) and

optionally at least one auxiliary g),

the following third part mixture was prepared by combining,

at least one organohydrogensiloxane b1) containing aromatic groups and/or

At least one alkoxysilane and/or alkoxysiloxane d),

optionally at least one organopolysiloxane a),

optionally at least one filler f), and

optionally at least one auxiliary g),

and then mixing the three part mixtures.

The term "partial mixture" or "reactive component" includes the case where the partial mixture contains only one component.

The invention also relates to addition-crosslinking silicone rubber mixtures which are obtained by crosslinking or vulcanizing the addition-crosslinking silicone rubber mixtures according to the invention. The crosslinking or vulcanization is carried out in a temperature range of 0 to 300 ℃ depending on the reactivity of the addition-crosslinked silicone rubber mixture.

The crosslinking can be carried out, if desired, under normal pressure, under a vacuum of up to 20 mbar or in the presence of an overpressure of ambient air. The injection molding and crosslinking are carried out under injection conditions (i.e.up to 300 bar per surface unit of the molding) on the substrate surface under an overpressure in the presence of ambient air.

Addition-crosslinking silicone rubber mixtures are generally referred to as elastomeric moldings.

The invention also relates to a method for producing a composite molded part, which is characterized in that at least one addition-crosslinking silicone rubber mixture according to the invention is applied to a mineral, metal, hard plastic and/or thermoplastic substrate in order to achieve crosslinking.

Preferred substrates are thermoplastic substrates, particularly preferred are substrates made of polybutylene terephthalate, polyamide or polyphenylene sulfide.

In a preferred embodiment of the process according to the invention for producing composite mouldings, the addition-crosslinking silicone rubber mixtures according to the invention are applied to the surface of previously produced thermoplastic mouldings, optionally under spreading, casting, calendering, knife coating and roller coating conditions, preferably under normal pressure, and subsequently crosslinked at temperatures of from 0 to 300 ℃, preferably from 50 to 250 ℃, and adhesion is achieved thereby.

Particularly preferably, the production of the preferred thermoplastic moldings takes place immediately before the application of the addition-crosslinking silicone rubber mixture.

In a further preferred embodiment of the process according to the invention for producing composite mouldings, the addition-crosslinking silicone rubber mixtures according to the invention are crosslinked or vulcanized, preferably on the surface of the thermoplastic mouldings injected in an injection mould, at temperatures of from 50 to 300 ℃ and adhesion is achieved thereby.

In the above-described process for producing composite mouldings, the addition-crosslinking silicone rubber mixture is generally applied to the substrate by injection into a vulcanization chamber in which the surface of the substrate is placed. The addition-crosslinked silicone rubber mixtures are thus preferably prepared immediately before by mixing the components a) to g). It is particularly preferred to prepare the above-mentioned reactive partial mixture beforehand and then to mix these partial mixtures. The reactive partial mixture can be injected directly onto the substrate to be coated and subsequently crosslinked.

Substrates coated with the crosslinked silicone rubber mixtures according to the invention additionally include, for example: glass, optionally pretreated metal or preferably optionally pretreated plastic. Preferred thermoplastics are, for example, polyethylene terephthalate, polybutylene terephthalate, wholly aromatic polyesters, liquid-crystalline polyesters, polycyclohexylene terephthalate, polytrimethylene terephthalate, aliphatic polyamides, polyphthalamides, partially aromatic polyamides, polyphenylamides, polyamideimides, polyetherimides, polyphenylene ethers, polysulfones, polyether sulfones, aromatic polyether ketones, PMMA, polycarbonates, ABS polymers, fluoropolymers, syndiotactic polystyrene, ethylene-carbon monoxide copolymers, polyphenylene sulfones, polyarylene sulfides and polyphenylene sulfoxides. Hard plastic type plastics include, for example: melamine resins, urethane resins, epoxy resins, phenylene oxide resins or phenolic resins.

During the crosslinking process and/or the vulcanization process, the substrate surfaces are caused to adhere to at least one addition-crosslinkable and/or crosslinked silicone rubber mixture according to the invention.

The silicone rubber mixtures, which are divided into two or three reactive partial mixtures, are mixed prior to vulcanization by means of an automatic injection molding machine or together by means of an upstream-connected mixing head and, if appropriate, a subsequent static mixer and then crosslinked and brought to adhesion at 0 to 300 ℃. Preferably, the components are mixed and injected into the mold at an elevated temperature of 50-250 ℃. The mold cavity of the mold containing the silicone rubber mixture need not be coated or treated with a release agent to keep the adhesion of the mold surface sufficiently small for demolding. For the constructive structure of the mould, it is preferable to coat it successively with a hard plastic type or with a thermoplastic and an elastomeric material, see Schwarz; ebeling; furth; kunststoffverarbeitung, Vogel-Verlag, ISBN: 3-8023-1803-X.

Walter Michaeli：Einführung in die Kunststoffverarbeitung，Hanser-Verlag，ISBN 3-446-15635-6。

To allow for forming and maintaining the seal, it is preferred to choose a material having a thickness greater than 3000N/cm²Automatic injection molding machine for closure force of molded part surfaces.

The process of the invention can be used with all customary automatic injection molding machines. The technical choice is determined by the viscosity of the silicone rubber mixture and the dimensions of the molded parts.

The quantitative ratios of the reactive partial mixtures used correspond to those given for the mixing of the silicone rubber mixtures described according to the invention. It is determined by the desired Si-alkenyl to SiH ratio and the desired amounts of adhesion-promoting constituents of component b1) and optionally b 2).

The invention also relates to the use of the addition-crosslinking silicone rubber mixtures according to the invention for producing composite mouldings, for example sealing and/or damping fastening elements, handles, keyboards, switches, shower heads, socket boards with elastomer seals, lamp holders or other fastening means, which may contain both a thermoplastic part and a silicone part.

Detailed Description

Example 1 (comparative experiment)

Preparation of the base mixture BM 1

9.1 parts of dimethylvinylsiloxy-terminated polydimethylsiloxane a1) having a viscosity of 10Pa.s (25 ℃ C.) and 16.5 parts of dimethylvinylsiloxy-terminated polydimethylsiloxane a2) having a viscosity of 65Pa.s (25 ℃ C.) were mixed in a high-speed disperser with 2.9 parts of hexamethyldisilazane and 1.0 part of water, 11.1 parts of a mixture having a BET surface area of 300m being then admixed²/g (Aerosil 300 — Degussa) fumed silica f), the mixture is heated to about 100 ℃, stirred for about 1 hour, and then the water and the remaining hydrophobicization application residue are removed at 150-. The base mixture BM 1 is obtained.

After cooling, approximately 200 parts of base mixture BM 1 are mixed with 6 parts of dimethylvinylsiloxy-terminated polydimethylsiloxane a1 having a viscosity of 10Pa.s (25 ℃), 0.6 part of dimethylvinylsiloxy-terminated polydimethylsiloxane a3) which contains methylvinylsiloxy groups and has a vinyl content of 2mmol/g and a viscosity of 0.2Pa.s, 1.5 parts of epoxyvinylsiloxy-terminated polydimethylsiloxane a3)Propoxypropyltrimethoxysilane, 1.8 parts of methacryloxypropyltrimethoxysilane, and 0.1 part of ethynylcyclohexanol as an inhibitor and 0.0145 part of Pt complex compound c of tetramethyltetravinylcyclotetrasiloxane with alkenylsiloxane as a ligand (Pt content: 15% by weight) and also 1.1 part of trimethylsilyl-terminated methylhydrogensiloxane b2) having an average SiH content of 15mmol/g and component b2) containing an average of 30 MeHSiO groups per molecule, 2.0 parts of trimethylsilyl-terminated diphenylmethylhydrodimethylpolysiloxane b1) M having an average SiH content of 4.9mmol/g₂D₇D^H ₆D^Phe2 _0.9Mixing the two phases. Component b1) produces an anionic equilibrium.

The reactive mixing was carried out in moulds with a mould cavity, each containing a built-in thermoplastic part as listed in table 1, cured or vulcanized under the conditions given. Good adhesion results were achieved with all elastomer-thermoplastic composites tested.

Example 2 (according to the invention)

After cooling, approximately 200 parts of base mixture BM 1 were mixed with 6 parts of dimethylvinylsiloxy-terminated polydimethylsiloxane a1 having a viscosity of 10Pa.s (25 ℃), 0.6 part of dimethylvinylsiloxy-terminated polydimethylsiloxane a3 containing methylvinylsiloxy groups and having a vinyl content of 2mmol/g and a viscosity of 0.2Pa.s (25 ℃), 1.5 parts of glycidoxypropyltrimethoxysilane, 1.8 parts of methacryloxypropyltrimethoxysilane and also 0.1 part of ethynylcyclohexanol as inhibitor and 0.0145 part of Pt complex compound c of tetramethyltetravinylcyclotetrasiloxane with alkenylsiloxane as ligand (Pt content: 15% by weight) and also 0.34 part of trimethylsilyl-terminated methylhydrogensiloxane b2) having an average SiH content of 15mmol/g and a component b2) containing an average of 30 MeHSiO groups per molecule, 2.0 parts of trimethylsilyl-terminated diphenylmethylhydrodimethylpolysiloxane M having an average SiH content of 10.8mmol/g as component b1)₂D₂D^H ₂₄D^Phe2 ₂Mixing the two phases. Component b1) produces an anionic equilibrium.

The reactive mixing was carried out in moulds with a mould cavity, each containing a built-in thermoplastic part as listed in table 1, cured or vulcanized under the conditions given. Excellent adhesion results were achieved with all elastomer-thermoplastic composites tested, which were several times higher than the results of comparative example 1.

TABLE 1

Base material	Comparative example 1[ N/mm]	Example 2[ N/mm ] of the invention]
Base material	Comparative example 1[ N/mm]	Example 2[ N/mm ] of the invention]	PA 6.6	2.6	4.0
PA 6	3.5	2.9	PA 6.6	2.6	4.0
PA 6	3.5	2.9	PBT	2.5	3.5
PPS	2.0	3.2	PBT	2.5	3.5
PPS	2.0	3.2	Sum of	10.6	13.6

Preparation and evaluation of composite parts

The composite was prepared as follows: after placing the approximately 3 mm-thick thermoplastic moldings, the respective silicone rubber mixtures were vulcanized on the surface of the respective thermoplastic moldings in a laboratory press mold at 175 ℃ for 10 minutes.

The mold used in the examples for preparing the composite moldings was a steel mold with a teflon-prepared surface coating. Without additional heat treatment of the composite samples, the adhesion of the fully cured silicone rubber mixtures to different thermoplastic substrates was tested in accordance with DIN 53289 (Floating roll Peel test (Rollenschel) for 24 hours after preparation at a tensile speed of 100mm/min for at least 2 samples each. The results of the dancer roll peel test are summarized in table 1.

Claims

1. An addition-crosslinked silicone rubber mixture comprising:

c) at least one hydrosilylation reaction catalyst,

e) optionally at least one inhibitor selected from the group consisting of,

f) optionally at least one optionally surface-modified filler,

g) optionally at least one auxiliary agent.

2. The addition-crosslinking silicone rubber mixture of claim 1, characterized in that,

the organopolysiloxanes a) are linear or branched polysiloxanes which may have the following siloxane units:

-a linear, branched or cyclic alkenyl group of up to 12 carbon atoms,

-a phenyl group,

-a hydroxyl group, and

-a linear, branched or cyclic alkoxy group of up to 6 carbon atoms,

3. The addition-crosslinking silicone rubber mixture as claimed in claim 1 or 2, wherein component b1) is selected from linear, branched or cyclic polysiloxanes which may have the following siloxy units:

-hydrogen, and (C) hydrogen,

-a linear, branched or cyclic alkenyl group of up to 12 carbon atoms,

-an aromatic group, and

-a linear, branched or cyclic alkoxy group of up to 6 carbon atoms,

4. The addition-crosslinking silicone rubber mixture as claimed in one or more of claims 1 to 3, wherein the organohydrogensiloxanes b1) contain an average of at least 23 SiH units per molecule.

5. The addition-crosslinking silicone rubber mixture as claimed in one or more of claims 1 to 4, wherein the organohydrogensiloxane b1) has a Si-H content of more than 36 mol%, said Si-H being defined as the ratio of the H atoms bound to silicon to the sum of the H atoms bound to silicon and the organic groups bound to silicon.

6. The addition-crosslinking silicone rubber mixture as claimed in one or more of claims 1 to 5, wherein the organohydrogensiloxanes b1) have at least one optionally substituted aromatic group.

7. The addition-crosslinking silicone rubber mixture as claimed in one or more of claims 1 to 6, wherein the organohydrogensiloxanes b1) are linear triorganosiloxy and/or diorganohydrogensiloxy-terminated organohydrogensiloxanes in which the triorganosiloxy end groups are selected from the group consisting of trimethylsiloxy, triphenylsiloxy, diphenylmethylsiloxy, phenyldimethylsiloxy, phenylethyldimethylsiloxy and phenylpropyldimethylsiloxy; the diorganohydrogensiloxy end group is preferably a dimethylhydrogensiloxy group and has an average of 20 to 1000 methylhydrosiloxy units, an average of less than 500 dimethylsiloxy units, an average of less than 360 (methyl) (phenyl) siloxy units and an average of less than 180 diphenylsiloxy units.

8. The addition-crosslinking silicone rubber mixture as claimed in one or more of claims 1 to 7, characterized in that the alkoxysilane according to component d) is selected from the group consisting of glycidoxytrialkoxysilanes, 2- (3, 4-epoxycyclohexyl) ethyltrialkoxysilanes, or methacryloxypropyltrialkoxysilanes

9. Process for preparing addition-crosslinking silicone rubber mixtures according to one or more of claims 1 to 8, characterized in that the process comprises mixing components a) to d) and optionally components e) to g).

10. The process of claim 9, characterized in that it comprises preparing at least one partial mixture comprising more than one but not all of components a) to g).

11. The method of claim 9 or 10, characterized in that,

preparing a first part mixture of the following by combining:

at least one organopolysiloxane a)

Optionally at least one filler f)

Optionally at least one auxiliary g)

At least one catalyst c), and

optionally at least one alkoxysilane and/or alkoxysiloxane d),

and preparing a second part mixture by combining:

-optionally an organopolysiloxane a),

at least one organohydrogensiloxane b1),

optionally at least one organohydrogenpolysiloxane b2),

optionally at least one filler f),

optionally at least one alkoxysilane and/or alkoxysiloxane d),

optionally at least one inhibitor e), and

optionally at least one auxiliary g),

the two partial mixtures are subsequently mixed.

12. An addition-crosslinked silicone rubber mixture obtainable by crosslinking a composition as claimed in any of claims 1 to 8.

13. Method for producing composite mouldings, characterized in that at least one addition-crosslinking silicone rubber mixture according to one or more of claims 1 to 8 is applied to a substrate for crosslinking.

14. The method of claim 13, wherein the substrate is selected from the group consisting of mineral, metal, hard plastic, or thermoplastic substrates.

15. The method according to claim 13 or 14, characterized in that the silicone rubber mixture is applied to the surface of a previously produced hard plastic or thermoplastic molding, optionally under spreading, casting, calendering, knife coating and roller coating conditions, and subsequently crosslinked at a temperature of 0 to 300 ℃ and adhesion is achieved thereby.

16. A method according to one of claims 13 to 15, characterised in that the silicone rubber mixture is vulcanised at a temperature of 50 to 300 ℃ on the surface of a hard plastic or thermoplastic moulding which has been previously injection moulded in an injection mould and thereby brought into adhesion.

17. Process according to one of claims 13 to 16, characterized in that the thermoplastic material is selected from polybutylene terephthalate, polyamide or polyphenylene sulfide.

18. The process as claimed in one of claims 13 to 17, wherein the preparation of the addition-crosslinking silicone rubber mixture is carried out by mixing parts of the mixture as described in one of claims 10 or 11.

19. Component batch consisting of at least two storage-stable components which, when combined, give an addition-crosslinking composition according to one of claims 1 to 8.

20. Composite mouldings composed of a mineral, metal, hard plastic and/or thermoplastic substrate and the addition-crosslinking silicone rubber mixture as claimed in claim 12.

21. The composite molding of claim 19 wherein said composite molding relates to a sealing and/or shock absorbing fastening element, a handle, a keyboard, a patch panel with elastomeric seal, a switch, a shower head, a lamp holder or other fastening.

22. Organohydrogenpolysiloxane b1), characterized in that it has an average of at least 20 hydrogensiloxy units in the molecule, said hydrogensiloxy units containing an aromatic group-containing monovalent organic residue bonded to Si, and the content of said aromatic group-containing monovalent organic residue is less than 12 mol%.