DE961831C - Process for curing silicone resins, especially silicone resin varnishes - Google Patents

Description

ISSUED APRIL 11, 1957

D 16585 IVc / 22h

The invention relates to a method for curing silicone resins, especially silicone resin lacquers, especially for preventing the formation of bubbles when curing silicone resins and for improvement the thermal stability of the cured products by adding certain carboxylic acids.

More recently, silicone resins are used for electrical Insulation is increasingly used, especially in cases where resistance to high Temperatures is required. In electrical engineering, such as B. in the insulation of electric motors, the silicone resins are generally in the form of a layer material made of resin and glass fabric and / or or used as impregnation varnish.

Although the silicone resins are excellent for this, it is quite cumbersome to use a solid silicone-fiberglass sheet material and to impregnate the coils of electric motors and the like, since the resin bubbles during curing.

The appearance of bubbles is important both in the impregnation of electric motors and in the Production of layer materials from silicone resin

and glass cloth poses a serious problem. Electric motors or parts thereof are generally used impregnated by dipping the motor in the resin solution. After the impregnation, the engine will start air dried to allow the solvent to evaporate and then to elevated temperatures heated until the resin is hardened. The appearance of bubbles or voids in the resin coating results often to a failure of the engine, so that despite ίο their otherwise excellent properties such Insulation often becomes unusable.

Laminates of silicone resin and glass cloth are generally made by adding individual sheets of glass cloth immersed in the resin solution, then the foils air-dry and individually heated moderately, in order to prevent the resin from flowing away when the layers are subsequently united. However caused even this weak heating of the individual impregnated foils, which cannot be avoided, a multitude of bubbles inside and on the surface of the resin film. The surface vesicles cause already before the production of the layer material cracks and a flaking of the resin, whereby up to 30% resin can be lost. This makes these materials very expensive to manufacture, and it is also difficult to make laminates with a specific resin content. Also can Due to the many bubbles inside, the dielectric properties of the product also seriously especially if the individual layers are very thin.

So far it was therefore necessary to avoid the formation of bubbles, after the impregnation of the electrical device or the glass fabric to air dry this for a long time and the subsequent Carry out hardening in stages as the temperature rises. For these reasons, the Processing of silicone resins is much more laborious than that of purely organic synthetic resins for Insulation purposes.

It has now been found, surprisingly, that this long curing time is avoided and thereby the cost of silicone resin insulation can be matched to that of insulation with organic resins can, making a significant advance in the insulation of electric motors and layered materials for high temperatures is achieved if the silicone resins or their solutions before they harden an unsaturated aliphatic and / or alicyclic carboxylic acid with at least 10 carbon atoms in one Amount from 1 to 18 percent by weight, based on the total weight of silicone resin and acid, clogs.

Previously impregnated stator and wound thereon motors 6 to 8 hours at 70 °, 4 to 6 hours at 149 ^0, and finally 4 to 6 hours, with silicone coatings after impregnation for 3 hours, air dried, cured at 205 °. This gives a total curing time of 17 to 23 hours. In the process according to the invention, satisfactory results are achieved if a wound motor is impregnated, ^{air-dried for 1} Z ₂ hours and cured at 205 ° for 2 to 6 hours.

Accordingly, in the method according to the invention, the total hardening time is 2 ¹ J ₂ to 6 ¹ Z ₂ hours or a third to a ninth of the previous hardening time. The total curing times mentioned represent average values, which of course vary depending on the type of object to be impregnated.

It is known to add small amounts of silicones to unsaturated oils, such as linseed and wood oil, to modify them; however, a change in the properties of the silicone will occur in the presence of Such a predominant amount of oil is neither intended nor can it be achieved.

According to the invention, any unsaturated aliphatic or alicyclic carboxylic acids which have at least 10 carbon atoms or any combinations of such acids can be used as additives. Suitable acids are e.g. B ₀ aliphatic acids, such as laurolic acid, myristolic acid, palmitoleic acid, oleic acid, gadolic acid, erucic acid, ricinoleic acid, linoleic acid, linolenic acid, eleostearic acid, licanic acid, arachidic acid and clupanodonic acid, and alicyclic acids, such as abietic acid, diabetic acid, dextropic acid, isoabietic acid, dehydropic acid, isoabietic acid, iso-dextimaric acid, isoabietic acid. Mixtures of acids from drying oils such as linseed oil, wood oil and castor oil are particularly beneficial.

Any silicone resin can be used for the present method. " Silicone resin " is to be understood as meaning siloxane polymers or copolymers whose polymer units mainly have Si - O - Si bonds. These polymer units have the general formula

wherein R is a hydrocarbon radical and η has an average value of 0.9 to 1.75. The silicone resin can also consist of siloxane polymers and siloxane copolymers in which a small proportion of the polymer units have other bonds, such as Si - CH ₂ - Si and Si - Si bonds. In the above formula, R can be any hydrocarbon radical, such as e.g. B. an alkyl, alkenyl, aralkyl, alkaryl, cycloalkyl or aryl radical. It is expedient to use silicone resins with polymer units in which R is a methyl and / or phenyl radical, since these have the best thermal stability and are easily available commercially.

It is expedient to use largely condensed silicones which are only relatively small Contain quantities of uncondensed hydroxyl residues. They generally contain no more than 2 percent by weight, expediently 0.1 to 1 percent by weight Hydroxyl groups on silicon. The main candidates for the procedure, im Commercially available silicone resins contain about 0.2 to 0.9 percent by weight of hydroxyl radicals and are by condensation of the hydrolyzates obtained by hydrolysis of various hydrolyzable organosilanes

won. These silicone resins are well known and are commercially available.

In order to cure the silicone resins in a relatively short time, curing catalysts are generally used used. All curing catalysts commonly used in silicone resins, such as. B. the metal salts of organic acids such as cobalt naphthenate and zinc 2-ethylhexoate or amines and amine derivatives can be used. Although the method according to the invention in particular in the manufacture of layered materials from

ίο is of particular value, it can also be anywhere there Find application where the problem of blistering occurs with silicone resins, e.g. B. when pulling over of wires with silicone resins, and wherever there is an improvement in the thermal stability of silicone resins is desired. The inventive method can, for. B. in the production of improved Siloxane resin foams are used. These foam masses are expediently according to the method the German patent specification 927830

ao posed.

The improved silicone resins can be made by simply mixing the silicone resin with the acid. In general, it is advantageous to mix the substances in a mutual solvent such as toluene, xylene or petroleum benzine. The best results are achieved by adding enough acid that it makes up 2 to 12 percent by weight, calculated on the total weight of the composition. If the content of acid above 18 ° / _0, the properties of the products are adversely affected. After mixing, the composition is ready to use without further treatment. The mixture can, however, optionally be heated before it is used in order to increase the viscosity, ie be thickened. A possible thickening is expediently carried out before adding the curing catalyst.

example 1

Containing a silicone resin having 35 mole percent of phenylmethylsiloxane units, 25 mole percent of monomethylsiloxane units, 30 mole percent monophenylsiloxane units and 10 mole percent Dimethylsüoxaneinheiten, was prepared toluene solution of a ₀ ° 5o /. The silicone resin contained 0.6 percent by weight of hydroxyl radicals on the silicon. 0.03 percent by weight, calculated on the weight of the silicone resin, of cobalt in the form of the 2-ethylhexanoic acid salt was added to the mixture.

With the 50% toluene solution of the silicone resin, linseed oil fatty acid (a mixture of oleic, linolenic, linoleic and arachidic acid) was mixed in the proportions given in the table. Thereupon 0.15 mm-thick aluminum plates were dipped in the varnish and the film obtained at 150 ⁰ to a tack-free cured. The thickness of the cured films was measured and the plates were alternately heated to 300 ° for 24 hours and then cooled to room temperature until the film broke at room temperature. The number of hours at 300 ° until cracking occurs characterizes the life of the film.

Tabel

Weight Weight Film thickness lifespan share
Silicone resin share
linseed oil in mm of the film
at 300 ⁰ fatty acid 0.045 in hours 100 0.05 220 100 2 0.055 44O 100 4th 0.057 44O 100 6th O, o6 415 100 8th 38O

The paint was also subjected to the following test to determine its tendency to blister during curing: Bundles of 12.5 ^cm long, glass cloth-covered copper wire were thus converted into a 7.5 cm double, extra thick 1.25 cm Iron pipe with an inner diameter of 0.625 cm was introduced so that it practically filled the pipe. The whole thing was then immersed in the resin solution until the bundled copper wires inside the tube were completely impregnated. The impregnation was carried out until no more air bubbles appeared. After the impregnation, the tube was removed from the resin solution, ^{air-dried for 1} Z ₂ hours and immersed again. After the second impregnation, the sample was cured again ¹ Z ₂ hours in air and then dried for 1 hour at 150 ⁰ in an oven. If whole or cracked resin bubbles were present at the point where the copper wires protruded from the pipe when it was removed from the furnace, the impregnation was considered defective. This test method was chosen because it corresponds to the conditions that occur when electric motors are impregnated by immersion in resin solutions.

If the paints described above were subjected to this test, it was found that the mixtures silicone resin and linseed oil fatty acid resulted in bubble-free impregnations, while those with silicone resins had a multitude of bubbles obtained alone. Also were the dielectric properties of the mixtures after curing is much better than that of the unmodified silicone resin.

Example 2

The life of a film made from the silicone resin of Example 1 was determined by addition extended from 4 parts of abietic acid to 96 parts of resin. This addition also stopped bubbling decreased during the curing of the silicone resin.

Claims (3)

PATENT CLAIMS: i. Process for hardening silicone resins, especially silicone resin varnishes, characterized in that that the resins or their solutions are 1 to 18 percent by weight before their hardening, calculated on the total weight of the composition, an unsaturated aliphatic and / or alicyclic Carboxylic acid with at least 10 carbon atoms is added. 2. The method according to claim i, characterized in that that linseed oil fatty acid is added as the carboxylic acid. 3. The method according to claim χ and 2, characterized in that silicone resins with 0.1 to ι Weight percent of hydroxyl residues on silicon hardens. References considered: U.S. Patent Nos. 2,258,218 to 2,258,222.10 © «09 658/459 10.56 (609 855 4. 57)