NO863443L - HARDENABLE SILICONE COATS. - Google Patents

Description

The invention relates to room temperature curable, hereinafter referred to briefly as RTV, silicone rubber compounds and the like, which harden when an elevated temperature is used.

Such silicones have been known for a long time (compare, for example, W. Noll, Chemie und Technologie der Silicone, Verlag Chemie GmbH., 1969, p. 391).

These pastes vulcanize when exposed to the humidity of the air or after mixing a second component to an elastomer. Corresponding to the majority of applications, formulations have been proposed in the literature which should optimally correspond to the respective application area.

The invention also relates to one-component RTV formulations

which, while maintaining the silicone-typical climate stability, enables the production of cost-effective pastes with improved transparency or good extrudability from a storage container as well as addition cross-linked silicone rubber masses.

When it comes to the production of one-component RTV pastes with particularly good light permeability, the previous state of the art as a polymer block copolymer of dimethyl and diphenylsiloxane units is used.

However, when a "glass-clear" transparency is not required, such formulations are too expensive to be marketed on a large scale. Additions have therefore previously been described with which a sufficiently good transparency is achieved for many conditions of use. Moreover, these formulations have the advantage that they are more affordable than those without these additives.

However, these additives all have some disadvantages, e.g.

are they only compatible with silicone polymers in relatively small amounts, reduce adhesion or the tendency to discolouration under climatic conditions or already under

storage conditions of the uncured paste. Such additives include substances, e.g. disclosed in DE-OS 1,286,246, 2,346,856, 2,457,816, 2,908,036, 3,221,655 and FR 2,405,984.

The invention relates to new, transparently improved silicone formulations, obtained by mixing polydiorganosiloxanes with reactive end groups, resp. possibly reactive side groups, reinforcing fillers and possibly mixtures of reactive silanes with the general formula R a Si Y4. —a, wherein R independently means alkyl, haloalkyl, aminoalkyl, aryl or aralkyl and Y independently means

Groups with a 0 0 to 3 and 4-a in sum > 2 resp. with the partial hydrolysis resp. condensation products, hydrogenated oligomers of 2-methylpropene with 2 to approx. 10 monomer units and catalysts and other state-of-the-art additives such as anti-ageing agents, biologically active substances and possibly a,w-triorgano-siloxy-polydiorgano-siloxanes and other silanes as adhesives.

The invention relates to formulations that result from mixing 100 parts by weight of polydiorganosiloxanes with a-

and deployed and possibly side-located reactive groups of viscosity from 0.1 to 500,000 Pa.s at 20°C, 8 to 100 parts by weight of reinforcing active fillers, 1 to 30 parts by weight of reactive silanes resp. siloxanes and 10 to 100 parts by weight of hydrogenated products of an oligomerization from 2-methylpropene, preferably of 2 to 6 monomer units, particularly preferred with 5 monomer units, possibly catalysts and further per se known fillers such as a,aj-trimethylsiloxypolydimethylsiloxanes of viscosity 0, 01

to 10 Pa.s at 20°C. The 2-methylpropene derivatives must have a

molecular weight up to approx. 600, preferably between 200 and 500.

As polydiorganosiloxanes, due to their easy availability, preferably polydimethylsiloxanes with end-placed hydroxy- or vinyl groups, which may optionally be: side-spaced, with at least part of the methyl groups being replaced by longer-chain alkyl groups. A certain amount of branching-acting organosiloxy groups may be present.

The hydroxydimethylsiloxy end groups can be replaced with hydrolytically cleavable end groups, such as e.g. by tri-acetoxysiloxy groups.

The viscosity of the polymers for RTV silicones is preferably between 5,000 mPa.s to achieve a satisfactory extensibility and 500,000 mPa.s to ensure good handling of the otherwise too viscous material. Another component of the paste according to the invention can be a polydioirganosiloxane end-capped by trimethylsiloxy groups, whose organogroups can normally be methyl groups but also

at least in part, vinyl or phenyl groups. Also in this polymer, instead of the diorganosiloxy building group, quantities of branching active groups may be present.

Finely divided silicic acid is used as a reinforcing filler, which can optionally be surface modified or optionally treated using modifiers such as fvex. hexamethyldisilazane and divinyltetramethyldisilazane during the mixing process in the presence of water.

The amount of filler is thereby adjusted to the area of application, for which the corresponding formulation is prescribed. The simultaneous use of other fillers or the use of other reinforcing fillers is thereby not excluded. Cross-linked in the formulation according to the invention are siloxanes with Si-H proportions or hydrolysis-stable silicon compounds, preferably those whose cleavage products do not adversely affect the transparency of the formulation such as some oximes, carboxylic acids, partially esterified multiply functional carboxylic acids, alcohols, amines, amides or hydroxylamines and especially preferred acetic acid and butanone oxime.

To accelerate or effect vulcanization, metal catalysts such as e.g. platinum or tin connectors. If necessary, an inhibitor can also be used which delays curing at room temperature. The additive according to the invention is a hydrogenated oligomer of 2-methylpropene which, depending on the manufacturing conditions, consists of only two or more monomer units and is hydrogenated after manufacturing. Corresponding manufacturing conditions, the additive does not consist of a uniform product, but of a mixture of compounds of different degrees of oligomerization with a center of gravity at a certain number of monomer units. The presence of other alkenes at oligo- or the polymerization is possible corresponding to the purification conditions (e.g. distillation) of the monomer. For the manufacture of these products see e.g. Kunststoff-Fandbuch, Volume IV, Hrgb. R. Vieweg, A. Schley, A. Schley, A. Schwarz, Carl Hanser Verlag, Munich, 1969, DE-OS 1 194 398 and DE-OS 3 010 720. The additive is processed in liquid form with the other ingredients of the formulation with usual evacuable mixing units.

The following examples refer to the Shore-A values

on the measurement according to DIN 53 505, bcud expansion, tensile strength and tension values to DIN 53 504, the indications on UV stability for storage of vulcanizates under a

300 W UV lamp (Osram UltraVitalux). The compatibility of the plasticizer is distributed visually, tactilely and with a placement test. Thereby, a cured sample (2 mm layer thickness, 11 mm diameter) is placed between absorbent paper, be-

is loaded with a wall and after 7 days the diameter of the formed oil spot is measured. The compatibility of the emollient in the caut disease resp. the vulcanizate is assessed as good, when the above-mentioned samples are similarly favorable as in the comparison test. The viscosity was measured at 20°C.

The invention shall be explained by means of some examples.

Example_l

61.6 g a,co-dihydroxypolydimethylsiloxane of viscosity 50,000 mPa.s are mixed under moisture exclusion with 12.1 g a,w-bis-trimethylsiloxypolydimethylsiloxane of viscosity 100 mPa.s, 12.0 g hydrogenated 2-methylpropenepentamer, 4.0 g ethyltriacetoxysilane, 0, 9 g of dibutoxydiacetoxysilane, 9.5 g of fumed silicic acid with an average BET surface area of 130 m 2 /g and 0.01 g of dibutyltin diacetate.

After seven days, the paste vulcanizes in air to an elastomer, after which the following values were measured:

This vulcanizate does not change after 7 days of UV storage. Plasticizer compatibility is good.

Example_el_2_

The mixture corresponding to Example 1 is repeated, however, instead of 12.0 g of hydrogenated 2-methylpropenepentamer, 24.1 g and no α,β-bistrimethylsiloxypolydimethylsiloxane were used.

The highly transparent paste vulcanized after seven days into an elastomer with the following measured values:

The compatibility of the plasticizer with the silicone mass is good. After 7 days of storage under UV exposure, no color change is observed.

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Example 2 is repeated with the change that instead of the hydrogenated pentamer, 24.1 g of a,w-bis-trimethyl-siloxypolydimethylsiloxane of viscosity 1000 mPa.s is used.

After 7 days, the values are measured on a vulcanizate of this paste:

The transparency compared to example 2 is clearly worse.

Example_4

55.6 g of a, co-dihydroxypolydimethylsiloxane of viscosity 50,000 mPa.s are mixed under moisture exclusion with 30.0 g of hydrogenated 2-methylpropenepentamer, 4.0 g of ethyltriacetoxysilane, 0.9 g of dibutoxydiacetoxysilane, 9.5 g of fumed silicic acid with a mean surface area of 150 m 2 /g according to BET and 0.01 g of dibutyltin diacetate. After 7 days, the stable paste is vulcanized into an excellent transparent elastomer with

the following mechanical properties:

UV storage causes no change to the vulcanizate, the compatibility of the plasticizer is good.

Example_5

55.9 g of a, two-dihydroxypolydimethylsiloxane of viscosity 50,000 mPa.s are mixed under exclusion of air with 30.0 g of hydrogenated 2-methylpropene pentamer, 6.0 g of methyl tributanone oxime silane, 8.1 g of fumed silicic acid with an average BET surface area of 110 m 2 /g, 0.7 g of yaninopropyltriethoxysilane and 0.3 g of dibutyltin dilaurate and then vulcanized for 7 days in the air. The following mechanical values are measured on the elastomer:

UV storage causes no change to the vulcanizate, the compatibility of the plasticizer is good.

Example_6

55.6 g of ot, io-dihydroxypolydimethylsiloxane of viscosity 50,000 mPa.s are mixed under moisture exclusion with 30.0 g of hydrogenated 2-methylpropenetetramer, 4.0 g of ethyltriacetoxysilane, 0.9 g of dibutoxydiacetoxysilane, 9.5 g of fumed silicic acid with medium BET surface area of 150 m 2 /g and 0.01 g of dibutyltin diacetate. After 7 days of curing, a slightly cloudy rubber (less transparent than the rubber according to example 4) with the following mechanical data results:

Example_7

55.6 g of a, io-dihydroxypolydimethylsiloxane of viscosity 50,000 mPa.s are mixed under moisture exclusion with 30.0 g of hydrogenated 2-methylpropene trimer, 4.0 g of ethyltriacetoxysilane, 0.9 g of dibutoxydiacetoxysilane, 9.5 g of fumed silicic acid with a mean surface area of 150 g /g according to BET and 0.01 g of dibutyltin diacetate. After curing, a transparent rubber appears, which becomes slightly cloudy after 3 days of UV illumination.

Mechanical data:

Example_8

55.6 g of a,co-dihydroxypolydimethylsiloxane of viscosity 50,000 mPa.s are mixed under moisture exclusion with 30.0 g of hydrogenated 2-methylpropendimer, 4.0 g of ethyltriacetoxysilane, 0.9 g of dibutoxydiacetoxysilane, 9.5 g of fumed silicic acid with an average BET surface of 150 m 2 /g and 0.01 g of dibutyltin diacetate. The rubber formed after curing at room temperature is transparent and has a dry surface.

After 3 days of UV lighting, no color change occurs.

The following mechanical values were determined:

Example_9_|Comparison_to^

55.6 g of a, two-dihydroxypolydimethylsiloxane of viscosity 50,000 mPa.s are mixed under moisture exclusion with 3 0.0 g of unhydrogenated 2-methylpropenepentamer, 4.0 g of ethyltriacetoxysilane, 0.9 g of dibutoxydiacetoxysilane, 9.5 fumed silicic acid with a medium surface according to BET of 150 m 2 /g and 0.01 g of dibutyltin diacetate. After 7 days of curing the paste at room temperature, the rubber showed a slightly sticky surface.

After 3 days of UV lighting, a strong yellowing of the rubber occurred as well as a strong sweating on the surface. The following mechanical values were measured:

Example_10

In a kneader, 140 parts of vinyl end-stopped polydimethylsiloxane with a viscosity of 65,000 mPa.s are kneaded with 10 parts of hexamethyldisilazane and 6 parts of water then with 46 parts of pyrogenically produced silicic acid with a specific BET surface area of 300 m 2 /g to a homogeneous mass (incorporation of fillers according to DE-OS 2 535 334). The mixture is first heated to 130°C and stirred for 1.5 hours in a closed vessel and then freed from water and excess hexamethyldisilazane at 160°C under vacuum. After cooling the mixture, the mixture is mixed with 60 parts of hydrogenated 2-methylpropenepentamer, 2.2 parts of trimethylsiloxy end-capped polydimethylsiloxane with 30 mol% SiH groups and a viscosity of 100 mPa.s at 20°C and 0.01 parts of a complex compound -ation of platinum and tetramethyltetravinylcyclotetrasiloxane and cured for 10 minutes at 175°C. The compatibility of the plasticizer is good.

Exemgel_ll

Example 10 was repeated with trimethylsiloxy-terminated polydimethylsiloxane having a viscosity of 1000 mPa.s instead of hydrogenated 2-methylpropene pentamer.

Example<p>el_12

Example 10 was also repeated with the modification that instead of hydrogenated, non-hydrogenated 2-methylpropenepentamer was used. The sample did not vulcanize into an elastomer, but only gelled.

Claims (6)

1. Curable silicone composition obtained by mixing polydiorganosiloxanes with reactive end groups or optionally reactive side groups, reinforcing optionally surface-modified fillers, cross-linking acting silanes or silane mixtures, RaSi Y^_where R independently means alkyl, haloalkyl, aminoalkyl, aryl or aralkyl and Y means independently -H, -OR-OCOR, -N(R)-C(R)=0, -NRR, -ONRR, -0N=CRR, -0-C(R)=CHR with a = 0 to 3 and 4-a in sum greater than 2 resp. of which can be produced siloxanes and possibly catalysts, characterized in that hydrogenated oligomers of 2-methylpropene with a molecular weight of up to approx. 600. 2. Curable silicone composition according to claim 1 obtained by mixing 100 parts by weight polydimethylsiloxane of viscosity from 0.1 to 500,000 mPa.s with reactive end groups resp. possibly reactive side groups with 0 to 100 parts by weight of a, two-trimethylsiloxypolydimethylsiloxane, 8 to 100 parts by weight of reinforcing fillers, 1 to 30 parts by weight of cross-linking active silanes or siloxanes and possibly 0.003 to 1 part by weight of curing catalyst, characterized in that 10 to 100 parts by weight of hydrogenated 2-methylpropene oligomers are also used. 3. Composition according to claim 1 or 2, characterized in that dimers, trimers, tetramers, pentamers and/or hexamers are used as hydrogenated 2-methylpropene oligomers. 4. Composition according to claim 1 or 2, characterized in that a,w-divinylpolydimethylsiloxane is used as polydimethylsiloxane with optionally side-located vinyl groups and as cross-linking acting silanes resp. siloxanes hydrogen-containing siloxanes and possibly an inhibitor that delays curing at room temperature. 5. Composition according to one of claims 1-4, characterized in that a, two-dihydroxypolydimethylsiloxane is used as polydimethylsiloxane and acyloxysilanes as cross-linking silanes. 6. Composition according to one of claims 1-4, characterized in that ketoxime silanes are used as cross-linked acting silanes.