DE1007593B - Mica puelpe and process for the electrophoretic production of mica layers - Google Patents

Description

It is known to turn mica into a condition by calcination and subsequent treatment with acid to move that he converted into a mica pulp by adding appropriate liquid which can then be processed into sheets, plates, moldings, etc. in a similar way to paper pulp leaves. For example, the mica pulp is applied to sieves in thinner or thicker layers, so that the liquid can drain or evaporate, as is the case in the paper industry is common. But they can also be used in a similar way to the porcelain paste used in porcelain production Process with the help of absorbent molds, but with all these and similar processes comes but in the end the stratification would result that the liquid of the pulp migrates through pores or holes in some substrate and so on the fine mica particles remain. On metallic, non-porous and non-sieve-shaped bodies it was not previously possible to achieve a sufficiently tight mica layer in this way.

It is also known to electrophoretically isolate layers from a suspension of ground mica to manufacture on wires. Such layers are easy to chalk off because they do not have a sufficiently strong cohesion show after drying .. Only through special additives to the suspension, special After treatment of the dry layer, etc., it can be sufficiently solidified.

The invention is based on mica layers. to produce that already without special additives and After-treatment become so firm that they do not chalk off after drying, even as self-supporting Sleeves, foils can be peeled off the base. Whereas we used to go to electrophoretic Manufacture of mica layers has used a dispersion of ground mica, a dispersion of calcined mica (mica pulp) is used according to the invention. Naturally the calcined mica is appropriately finely comminuted beforehand. During the subsequent drying process the deposited layer is so firm that nothing chalked off when wiped over it.

The invention is to be explained in more detail below. When electrophoresing the mica pulp, it is best to work with a DC voltage of around 200 to 300VoIt or more, depending on the shape and size of the body on which the mica is to be produced, and at a current density of around 20 to 50 mA / cm ² . A thin, well-connected mica layer of mica pulp and process is then obtained in about 10 to 30 seconds, depending on the nature of the dispersant and depending on the amount of the additives specified below

for electrophoretic production

of mica layers

Applicant:

Siemens-Schuckertwerke

Corporation,

Berlin and Erlangen,

Erlangen, Werner-von-Siemens-Str. 50

Dipl.-Met. Hans Werner Rotter, Nuremberg,
has been named as the inventor

from Vs to ¹ Zt mm, for example. This layer is sufficient for many purposes, for example for the electrical insulation of conductors. _{The mica pulp is best adjusted to a Pj 1} of 5 to 6 by additives or in another known manner. It is advisable to work with aqueous pulp and aqueous additives, but alcohols or ketones can also be used as dispersants. Aqueous mixtures of these substances, for example with 30% water, are generally more favorable than pure alcohols or ketones. This addition of alcohol or ketone is intended primarily to increase the conductivity of the dispersant, e.g. B. of water, and to eliminate troublesome electrolytic side effects.

The partial replacement of water by volatile alcohols also has the advantage that the precipitates dry faster and, as a result, the time of the liquid's action on the Metal is shortened. This is particularly favorable for metals that have been attacked by the liquid will. The processing time is of course also shortened due to the faster drying.

The deposited mica particles adhere well to one another, but it may be advantageous to to increase the adhesion by adding binding agents. These binders are added to the dispersant to. They must be such that they do not impair the stability of the dispersion. If the deposited mica layers are to withstand higher temperatures later, then will appropriately temperature-resistant binders

709 507/371

use, ζ. B. an aqueous emulsion of silicone resins or an alcoholic suspension of silicone rubber. Of course, instead of silicone, you can also use appropriate silicic acid esters or emulsions of fluorine compounds, as are known for electrical insulation purposes with high thermal resistance. Colloidal silica may also be suitable as a binder. The quantitative ratio of mica flakes to dispersants and binders can be changed within relatively wide limits as required and depending on the desired nature of the precipitate. So you can z. , 50 'use as a mixture% aqueous Glimmerpülpe and 50% aqueous resin emulsion ,, where the quantitative proportion of pulp and resin emulsion is essentially given by the fact that the _pH value in the range of. about 5 to 6 remains. Since the bath becomes more and more depleted in mica particles and binding agent after the production of larger amounts of precipitation, it must be renewed at certain intervals, or these substances must be added in appropriate amounts from time to time.

The precipitate thus obtained is for different people Purposes already suitable, especially if a varnish or an impregnating agent is applied afterwards or if the body coated with a mica layer is in casting, injection molding, molding or injection molding is embedded or if bodies provided with such layers are packed tightly on top of one another, as is common with capacitors, for example. However, it will mostly be better for strength and To increase the adhesion of the precipitation layer through a special heat treatment. Sintering separates with such mica layers. For this one can use the heat treatment in the presence of substances perform that attach themselves to the surfaces of the mica particles cling and chemically combine them colloidally or superficially, without going into the depth of the mica particles to act. So · you can z. B. the Precipitation for about 1 hour at 500 ° C. and with simultaneous action of 10% phosphoric acid or heat-treat phosphoric acid vapors.

It is a peculiarity of the electric field to concentrate on edges and tips. Consequently will turn out to be angular or pointed. Bodies on sharp projections a denser precipitation than in other places. On the other hand, in the production of mica layers by means of absorbent Make the suction less at the vocals than at other places., And consequently arises from. the projections a smaller layer thickness. One therefore becomes · with bodies with Use both methods by making an absorbent anode for example on uneven surfaces porous metal or made of a metal sieve, the cavity of which is under negative pressure. So z. B. the Interior of a hollow cylindrical screen can be placed on the suction side of a pump.

Should the precipitate be firmly on the electrode, e.g. B. on a ladder, stick, then you will ensure that there are no easily removable or colloidal oxides or Form hydroxide layers. This can be achieved by appropriate adjustment of the dispersant. A layer of oxide that may be formed adheres firmly to iron and nickel, and as a result it becomes also the mica layer firmly on these. Adhere to metals. But if the ladder should be made of other metals, z. B. copper exist, then you have to prevent or limit the formation of oxide layers, but You can also use a thin iron or iron layer before depositing the mica with these other metals Plating a nickel layer, but if self-supporting, thin-walled mica bodies are produced on the other hand, there will be the formation of an easily removable or colloidal oxide layer Od. Like. Favor and choose metals that are particularly suitable for such purposes. The precipitation can then be easily detached from the metal body before or after the heat treatment.

example 1

In an aqueous Glimmerpülpe with p _H = 5.8 a cylindrical cathode of iron with 20 mm diameter and a is. Iron wire with a diameter of 0.5 mm was introduced as an anode. If direct current with a voltage of 200 Volts and a current density of 30 mA / cm ^{2 are allowed to} act for 10 seconds, a 0.5 mm thick layer of mica results on the wire, which after drying forms a solid coating.

Example 2

In a 50% aqueous Glimmerpülpe with an addition of a 50% aqueous silicone resin emulsion in such an amount that results in a p _H = 5.4, is allowed to given on copper electrodes from above. Dimensions and shapes. For 15 seconds, a DC voltage of 200 voit ¹ at a current density of 80 mA / cm ^2. On the anode there is again a 0.5 mm thick, well-adhering coating.

Example 3

If you add mica powder, which is suitable for pulp production, in 70% di acetone alcohol and leave 300 volts DC voltage at 70 ^{mA / cm 2 to} act for 30 seconds with the above-mentioned electrode arrangement, a 0.2 mm thick layer is obtained. After the solvent, i.e. the alcohol, has evaporated, this is coated with 10% phosphoric acid and then. Treated for 1 hour at 500 ° C heat.

Claims (11)

PATENT APPROACH: 1. Mica pulp for the electrophoretic production of mica layers, characterized in, that it consists of a dispersion of calcined mica. 2. Mica pulp according to claim 1, characterized by an addition of alcohol or ketones, especially when mixed with water as a dispersant. 3. mica pulp according to claim 1 and 2, characterized in that it contains binders, which increase the cohesion of the precipitate or its adhesion, without its stability the dispersion, affecting, 4. mica pulp according to claim 1 to 3, characterized in that it is an aqueous binder Contains emulsion of silicone resins or an alcoholic suspension of silicone rubber. 5. mica pulp according to claim 1 to 4, characterized in that it consists of 50% aqueous mica pulp consists in 50% aqueous silicone resin emulsion. In that it comprises 6 Glimmerpülpe according to claim 1 to 5, characterized in that a _pH value of about 5 to. 6 7. The method using a mica pulp according to claim 1 to 6, characterized in that a direct voltage of about 200 to 300 volts at a current density of about 30 to 50 mA / cm ² is used. 8. The method according to claim 7, characterized in that that an absorbent anode, the cavity of which is under negative pressure, is used. 9. The method according to claim 7 and 8, characterized in that the precipitate is about 1 hour at about 500 ° C heat is treated with simultaneous action of a Binder for the mica particles. 10. The method according to claim 9, characterized in that that 10% phosphoric acid or phosphoric acid vapors are used as a binder will. 11. The method according to claim 7 to 10 ¹ , characterized in that the mica deposit is withdrawn from the electrode before or after a heat treatment. Considered publications:
British Patent Nos. 655 763, 587 039;
U.S. Patent No. 2,530,546.