SE125490C1 - - Google Patents

Description

Inventor: E. L. Warrick.

Priority was given on 25 July 1945 (United States of America).

The present invention relates to a process for the preparation of surface coatings, which consists in applying to a substrate a mixture of an organosiloxane and a heat-resistant filler in such relative proportions that in the absence of solvent a paste is formed, and which can be characterized By applying a mixture in which a minor content of a dialyl peroxide has been incorporated, on the substrate in such an amount as to form a coating of between about 0.0525 mm and 0.175 mm thickness, the coating temperature rises to at least 180 ° C but not more than 400 ° C within two minutes and the temperature within one, of 180-400 ° C, until the coating hardens, the organic substituents in the organosiloxanes mainly consisting of monovalent hydrocarbon radicals bound to silicon by carbon-silicon links , and the siloxane contains at least 60 mol% of a structural unit corresponding to the formula R, SiO, where R is an alkyl radical, and the diacyl peroxide contains at least one aromatic ac ylradikal.

The process described above completely eliminates the need to take steps to exclude oxygen from the atmosphere in which the curing takes place. The resulting films are heat-resistant, oil-resistant, electrically insulating, water-resistant, flexible and elastic. They are particularly suitable for use as coatings for metallic conductors, as liners for containers and as protective coatings for silicon-containing surfaces & WA 'as metal surfaces.

The organosilicon compositions which, according to the present process, are to be paloras which are prepared as follows. An organopolysiloxane is thoroughly mixed with a heat-resistant filler until a smooth, homogeneous, non-separating paste is obtained. The mixture is suitably carried out in a color mill to ensure complete homogeneity of the paste. A minor content of a diacyl peroxide is incorporated into the paste either simultaneously with the above mixture or afterwards, as desired.

The organopolysiloxanes (commonly referred to as "silicones") used in the manufacture of the aforementioned products are compositions comprising mainly silicas connected to each other. Through oxygen atoms through silicon-oxygen moieties, thus - Si - 0 - Si -, and with an average of 1 , 75 to 2.25 monovalent organic radicals bound by carbon-silicon anchors at the usual silicon atom. They are preferred but not necessarily of high molecular weight, but they should not have attained a degree of polymerization at which they are no longer soluble in common hydrocarbon solvents, such as toluene. They must contain a recurring structural unit, which corresponds to the empirical formula RR'SiO, where R and R 'are alkyl radicals. Preferably, the number of units of this formula present in the siloxanes is at least GO% of the total number of silicon units in the siloxane. By silicon unit is meant any heist unit corresponding to one of the following empirical formulas, SiO 2, R 5 SiO 3, 2, R 2 SiO and R 3 SiO = where R is a monovalent organic radical which binds to silicon through carbon-silicon chains.

These organopolysiloxanes can be prepared by hydrolysis of a hydrolyzable dialkylsilane, followed by condensation (partial or complete) of the hydrolysis product. They can also be prepared by hydrolysis and condensation of mixtures of different hydrolysable organomonosilanes, containing at least 60 mol% of a hydrolysable dialkylsilane. In the latter case, hydrolyzable silanes which do not contain any organic radicals bound to silicon by such as silicon tetrachloride or ethyl orthosilicate, none of the organosilanes. By mixing such mixtures of silanes with the correct proportions, it is possible to produce organosiloxanes, which contain on average between 1.75 and 2.25 organic radicals per silicon atom. It is understood that the siloxanes may contain some uncondensed hydroxyl groups as well as some remaining unhydrolyzed hydrolyzable radicals.

Hydrolyzable organosilanes are derivatives of Sill4 of the general formula RySiX (), where R represents an organic radical, such as Sr bonded to silicon by carbon-silicon links, X represents a readily hydrolyzable radical, which Sr is selected from a class consisting of halogens, amino groups, alkoxy, aroxy and acyloxy radicals, and y is an integer from 1 to 3. Examples of organic radicals, represented by the symbol R, are as follows: aliphatic radicals, such as methyl, ethyl propyl, isopropyl, butyl, amyl, hexyl, heptyl to octadecyl and higher, alicyclic radicals, such as cyclopentyl and cyclohexyl, aryl and alkary radicals, such as phenyl, mono- and polyalkylphenyl, such as tolyl, xylyl, mesityl, mono-, di- and triethylphenyls , di- and tripropylphenyls, naphthyl, mono- and polyalkylnaphthyls, such as methylnaphthyl, diethylnaphthyls, tripropylnaphthyl, tetrahydronaphthyl and anthracyl, aralkyl, such as benzyl, phenylethyl, alkenyl, sasona metal! and allyl, as well as heterocyclic radicals. The above-mentioned organic radicals may also contain inorganic substituents, such as halogens.

As a filler for the paste, heat-resistant inorganic materials which melt above 350 ° C, such as silicate and polyvalent metal wires, are preferred. Among the materials used are the following: asbestos, clay 188 (a non-swelling clay), silene (hydrated calcium silicate), zinc sulphide, silica aerogel, Buca-clay (a swelling clay), barium titanate, fiberglass flock, iron oxide (Wyomingb), a Wyoming b State of Wyoming, AFS, recovered bentonite), lithopone, zinc oxide, titanium dioxide, magnesium oxide, finely divided graphite, finely divided shale, finely divided mica, celite (diatomaceous earth with 95% SiO2), calcine T (fait calcium carbonate containing 2% of a water-soluble coating) ), Pb02, Pb0, hlâ pencil, dehydrated alumina and hydrated alumina. The social choice of filler depends to a large extent on the desired property or properties. If strength, toughness and high tension are desired, aro zinc oxide, titanium oxide and hydrated alumina bast. If small weight loss and insignificant change of dimensions after prolonged impact of advanced temperatures are desired, asbestos is an excellent filler. Oni. short solidification time Desired, Sr iron oxide is the best filler.

In general, any called diacyl peroxide, which contains hrinstinstone an aromatic acyl radical, is effective in the process. Examples of such peroxides are benzoyl peroxide, benzoylacetyl peroxide, dinaphthoyl peroxide and benzoyl lauroyl peroxide. The acyl radical can in-. nehalla inorganic substituents, such as halogens and nitro groups.

The relative proportions of organosiloxane, filler and peroxide can be varied quite considerably with the sole general limitation that the mixture of organosiloxane and filler must essentially have a paste consistency and that it must contain a sufficient amount of peroxide to promote curing of the siloxane to a tack free condition. In general, measure the amount of peroxide used as possible due to the responsibility to maintain control over its decomposition. In the case of benzoyl peroxide, the amount is preferably less than about 8% by weight of the siloxane.

The paste composed of the organosiloxane, the filler and the peroxide is then pafores the forearm intended for coating with some suitable aid, such as a knife blade, a brush or even by spraying, if its consistency is sufficiently thin. The thickness of the coating is important if a carefully cured film is to be obtained without deliberately excluding oxygen. The cover should not be less than 0.00 frames thick and not more than 0.175 mm thick. The optimum range may even Tara be more limited, depending on the amount of peroxide present and the filler pineapple and Sven it for vulcanization any other time, but is determined la.tt by previous tests.

When a film or a Cover of the right dimension has palorts p5. the substrate, the resulting coated form is subjected to sufficient heat to raise the temperature of the coating to at least 180 ° C for a minute. When the supply of heat is effected by placing the coated form in an oven, it is obviously necessary to keep the oven at a temperature above 180 ° C, if the coating is to reach 180 ° C in two minutes. How much higher depends, of course, on. many factors, the size and shape of the sasoni form, as well as the specific heat of, the material from which it is made. However, the temperature of the coating should not be allowed to reach 400 ° C, while the elastic properties of the resulting film are severely impaired, especially if the temperature is measured at 400 ° C for a considerable period of time.

For such materials, which can not withstand high temperatures for a long time, such as - --3 cotton or paper, it is advisable that after the coating with the organosilicon composition they are exposed to a temperature much better than 180 ° C for a few seconds. hardening. A higher temperature, i.e. 250 ° C or more, does not damage the cellulosic material if it is maintained for only one moment and the breath is sufficient to effect the desired cure of the organosilicon film.

For many applications, it is undesirable to apply a film to the organosilicon composition described above, which not only has the required dimensions, but which is uniform with respect to the pH thickness throughout. It is black to obtain a uniform coating in industrial practice using a paste. Therefore, a modification of the above procedure can be used. Instead of a paste, a solution of the organopolysiloxane and the peroxide is prepared in a volatile solvent in which an appropriate amount of filler is suspended by thorough mixing. The foremales intended for coating can be dipped in the suspension a sufficient number of times to precipitate the desired coating or they can also be sprayed with the liquid.

When curing coatings obtained by inhaling solutions, it has been found customary to substantially completely remove the solvent at a temperature below 50 ° C before the rapid treatment at high temperature is carried out. The removal of the solvent can be accomplished by passing an air stream therethrough or by subjecting the coated vacuum. In general, any heist organic solvent with a boiling point equal to or lower than the boiling point of toluene. Carbon tetrachloride is a release agent that is often used for the above mentioned purposes. At higher temperatures boiling solvents can be used, but their long time is required to deposit them at temperatures below 50 ° C, that their respiration is not economically possible.

When a solvent-free coating is obtained, the curing process is the same as described above in the case of a film which phorts frail a paste. The release agent only serves as a suitable aid to obtain a uniform film thickness and does not affect the pH of the resulting cure, provided that it is substantially deposited before the temperature of the film is raised to the desired high temperature.

The coated foremalt should be kept at a temperature Over 180 ° G or dal-Over, until the coating has been completely hardened. This takes a maximum of ten minutes and often less. If the temperature is above 180 ° C, less time is required for complete curing as indicated above in the case of heat curing of coated cotton or paper. In order that the invention may be more readily understood, it shall be described in connection with the following examples, which are left for explanation and not for limitation.

Example 1. 100 parts by weight of liquid dimethylsiloxane having a viscosity of 2600 centistokes, 100 parts of Titanox A (titanium dioxide) and 8 parts of benzoyl perexide were mixed on a 3-roll paint mill. A paste was obtained which consisted of an even, homogeneous, non-separating and highly viscous material. This paste was brushed on a cadmium copper lid at a thickness of about 0.00s mm. The coated disk was then placed in an oven and its temperature was raised to 180 ° C for 120 seconds and then kept at about 200 ° C for four minutes. The temperature was determined by means of a thermocouple in direct contact with the Transfer. After four minutes, the ph disc formed a non-stick completely hardened film.

Example 2. 100 parts of liquid dimethylsiloxane having a viscosity of 2300 centistokes, 100 parts of Titanox A and 8 parts of benzoyl peroxide were ground in a 3-roll paint mill. Carbon tetrachloride was added while stirring, until the amount of solvent was 80% by weight of the whole mixture. A sheet of cadmium-plated copper was dipped in the resulting paint composition and air-dried at room temperature. The thickness of the film was about 0.0075 ram. The air-dried disk was then heated to a minimum of two minutes to 250 ° C and kept there for 30 minutes without any attempt to exclude oxygen. A smooth, non-stick coating is applied which adheres securely to the metal surface. Similar coatings are obtained when applied to ceramic surfaces and glass surfaces.

It is generally preferred to use as organosilicon component in the coating composition such organosiloxanes, the organic substituents of which are lower layers, alkyl radicals and which consist essentially entirely of dialkylsiloxanes of the formula R, SiO2, such as dimethylsiloxane, diethylsiloxane, diethylsiloxane. After curing by peroxide treatment, these have a high resistance to repeated thermal shock, i.e. sudden temperature change, e.g. when immersing a strongly heated form in cold water, bite at high and low temperatures. This is particularly advantageous in applications where electrical conductors are sought to be protected from the effects of moisture when these conductors are cooled or heated repeatedly and rapidly.

The invention relates to coatings which can be used as electrically insulating coatings for metallic conductors and the like, which adhere securely to textile wraps such as cotton to form a water-impermeable and water-repellent film darph, and to adhesives in silicon-containing materials, such as porcelain, glass °. eh similar. The coating resists local, strong and repeated fluctuations in temperature without separating Iran from the treated surface.

Claims (6)

Patent claim: Procedure for preparing surface coatings. which consists in applying to a substrate a mixture of an organosiloxane and a heat-resistant filler in such relative proportions, that in the absence of a solvent a paste is formed, it may be claimed that a mixture in which a minor content of a diacyl peroxide, ph the substrate in such a way as to drip Midas a coating ay between about 0.0025 mm and 0.17mm thickness, raises the coating temperature to at least 180 ° C but not above 4000 C mom two minutes and hailer the temperature mom one (miracle of 180-400 ° C, until the coating hardens, the organic substituents in the organosiloxanes consisting essentially of monovalent hydrocarbon radicals bound to silicon by carbon-silicon anchors, and the siloxane containing at least 60 mole percent of a structure with the corresponding formula R 2 SiO, where R is an alkyl radical, the saint diacyl peroxide contains at least one aromatic acyl radical. Loss according to claim 1, characterized in that the organic substituents in the organosiloxanes consist essentially of higher alkyl and phenyl radicals bound to silicon by carbon-silicon strands. 3. Process according to claims 1 and 2, characterized in & tray, that a soluble dialkylsiloxane is mixed with the heat-resistant filler and that the alkyl substituents in the siloxane have from 1 to 5 carbon atoms. 4. A process according to claim 1 or 2, characterized in that a soluble dimethylsiloxane is mixed with the heat-resistant filler and a small amount of benzoyl peroxide is incorporated into the paste. Process according to Claim 1 or 2, characterized in that a high-molecular-weight dimethylsiloxane is mixed with the heat-resistant filler. 6. A process according to claim 5, characterized in that titanium dioxide is introduced into the mixture. 7. Coated product prepared according to the method according to any one of the patent claims 1 - 6. Stockholm 1949. Kungl. Bohr. P. A .. Norstedt & SOnec 400080