DE1769088A1 - Non-flammable resin mixture - Google Patents

Description

Western Electric Company Incorporated Sharp - Jan.

Non-flammable resin mixture

The invention relates to non-flammable epoxy resin coating compositions, which are suitable as dielectric encapsulation agents for electrical components, as well as with such compositions coated electrical components.

Electrical resistances are usually made by coating a ceramic body with carbon particles and fixing it made of metallic connections on it. The resistors are then covered with an organic encapsulation material coated, which serves as an insulator and also protects the resistor from atmospheric and moisture influences. If such Resistors are heavily loaded during operation, they get quite hot, sometimes even glowing, and so do the encapsulation material often breaks through and catches fire.

According to the invention, a non-flammable, for encapsulation Dielectric resin mixture suitable for components, consisting of 40-60 percent by volume epoxy resin, 5-25 percent by volume halo mixed Epoxy resin, 20-30 percent by volume glass beads, 5-25% antimony

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trioxide or antimony trioxide zinc borate and a hydrazide hardener from Föxxnel R (CONHNH), with η being 1, 2 or 3;

/ i η

and the invention is characterized in that both epoxy resins have on average more than one, 2-epoxy group per average molecular weight, that the glass beads have an average Have a diameter of 0.008 cm (0.003 inches) or less, and that the amount of hardener equal to 0.25 to 0.5 moles of hydrazide per epoxy equivalent which is epoxy resins.

In a preferred embodiment, mixtures of five components form a desired encapsulation material that is to be applied to electrical components in the form of thin films. These mixtures contain an epoxy resin, a hydrazide curing agent, a halogenated epoxy resin, an inorganic filler material made of fine glass particles which can be combined with mica, silica and the like, and antimony trioxide - the combination of antimony trioxide and zinc borate. The proportions of the various components in the mixture can be varied over fairly wide ranges, but it is preferred to have about three volume units of epoxy resin per volume unit of halogenated epoxy resin, although proportions down to equal volumes of these two resins can be used. The inorganic filler from about 20 to about 50 percent by volume of the resin mixture

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to take. It is preferred to use as much filler material as possible without deleteriously influencing the film-forming properties of the resin mixture to use. The amount of curing agent is controlled by the amount of epoxy resins in the mixture; usually 0.25 to 0.5 moles of hydrazide per epoxy equivalent are required.

The antimony trioxide component can contain 5 - 30% of the volume of the Resin. The antimony trioxide serves as an

medium (flame retardant booster) in combination with the halo ™

mixed epoxy resin.

The epoxy resin component of the encapsulation material can be any of the well-known, commercially available epoxy resins having on average more than one 1,2-epoxy group per average Has molecular weight. Preferred are epoxy resins obtained from epichlorohydrin and a bisphenol such as bisphenol-A. Such resins are described in U.S. Patent 2,847,395, and in "Plastics Materials" by J.A. Brydson, D. Van Nostrand Company, Inc., 1966, pp. 451-483.

The halogenated epoxy resin component can be as above correspond to the epoxy resin mentioned, the bisphenol being halogenated is. The bisphenol has the following general formula:

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XX RXX

OH

Here, X is chlorine or bromine, R and R ^{1 are} hydrogen or lower alkyls, and the number of "Xs" can range from 4 to 8. For example, it can be tetrachlorobisphenol-A or tetrabromobisphenol-A of the following formula:

CH

OH

where X is chlorine or bromine. Other halogenated aromatic dihydrate compounds can also be used to make the halogenated epoxy resin, such as chlorinated bisphenol-C and chlorinated bisphenol-F of the following formulas:

Cl

CH

OH

Cl

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CH ₁ , Cl CH _Q Cl CH _q

I «J I J" > I «J

HO

Cl

LJ

C / \ _OH

CH,

Cl

The hydrazide curing agent can be represented by the formula R (CONHNH ₀ ), where R is an organic radical and η is 1, 2 or 3. The dihydrazides with η equal to 2 are preferred. The radical R can also carry substituents such as amino, hydroxyl, nitro and halogen. Typical hardening agents are the dihydrazides of two basic acids, such as sebacic, adipic, azelaic, succinic, halon, oxal, terephthalic, hexahydroterephthalic, isophthalic, 5-nitroisophthalic, 5-aminoisophthalic, hexahydroisophthalic and m-Benzene bisoxyacetic acid. The preferred dihydrazides have the general formula H ₀ NNH-CO-R-CO-NHNH, where R is a divalent hydrocarbon radical of 1 to 20 carbon atoms. Further suitable hydrazides are those obtained from p-aminobenzoic, p-hydroxybenzoic, 2,4-dihydroxybenzoic, 3,5-diamino · benzoic and citrus acids. Such hydrazides are described in U.S. Patent 2,847,395.

The inorganic filler material is a finely powdered glass and can

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Contain materials such as silica, mica, sand and the like. The average particle size of this material should be no greater than 0 008 cm (0 003 inch) in diameter, preferably about 0, 005 cm (002 inches _O1), his.

The antimony trioxide component is preferably antimony trioxide (technical grade), although mixtures of antimony trioxide and zinc borate can be used.

The relative proportions of the five components of the resin composition can be varied over moderate ranges. The epoxy resin makes up 40 to 60 volume percent of the total composition off, and the halogenated epoxy resin 5 to 25 volume percent. The glass beads make up 20 to 30 percent by volume of the total composition. Other inert filler materials can range from 0 to Make up 20 percent by volume of the total composition. The amount of hydrazide hardener added is between 0.25 and 0.5 mol Hydrazide per epoxy equivalent of resin. The antimony trioxide component makes up 5 - 25% of the volume of the total composition.

The epoxy resin / inorganic filler combination described here has excellent adhesion properties to carbon -

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stands, good meltability and requires only one relative short cure cycle, like this one in a high speed production in an automatic treatment oven at 204 ° C (400 ° F). The curing time can be reduced at higher temperatures.

The inorganic filler sets the required amount of epoxy resin per 0.0025 cm (0.001 inch) film thickness, and thus the flammable «: · Amount of material per unit volume. It is desirable to use as high a percentage of inorganic filler material as possible in the mixture, so high that just barely sufficient adhesion and impact resistance can be achieved.

The non-flammable dielectric coating for electrical Components are made by applying the epoxy resin mixture as a thin, smooth film that does not exceed 0.0125 to /

0.026 cm (0.005-0.01 in) thick. The flammability of the resin is a function of the film thickness. The higher the temperature and the faster it is reached, the thinner the resin coating must be in order not to ignite. 0.0125 cm (0.005 inches) is a thickness for a coating that is required for the highest loads. For example, a 0.0125 cm resisted (0.005 inch) thick film of the described epoxy resin mixture

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on a carbon resistor (0.5 watt resistor with a vapor-deposited carbon layer of the type Western Electric 221) an ignition, when the resistor was made to glow by overloading 64 times its rated power, and also fulfilled also all other electrical and mechanical requirements.

The preferred method by which the epoxy resin mixture is applied to carbon resistors is a multi-step process. The resistors are 218 - preheated in a tunnel furnace which is composed of upper and lower permanent quartz lamps, the radiation is concentrated in turn by elliptical reflectors - 232 ° C (450 ⁰ F 425). After the pre-heated resistors have absorbed plenty of resin powder, they are sent through another tunnel oven to liquefy all of the resin. The resistors coated with liquid resin are rolled mechanically. By this rolling treatment, the resin is pressed and molded into a film of suitable thickness and shape.

The present resin mixtures can be used in all insulation or encapsulation processes in which powdered epoxy resins are used, including those in which liquid resins are used.

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An example is given below. The material quantities and working conditions can be within the range given here Boundaries are changed.

48 parts by volume epoxy resin (SK-262 from Minnesota Mining and Manufacturing Company), 20 parts by volume of chlorinated epoxy resin (SK-609 from Minnesota Mining and Manufacturing Company) and 32 parts by volume f

part No. 660 glass beads (mean diameter of 0.005 cm (0.002 inches)) were carefully mixed with 20 parts by volume of antimony trioxide and 15 parts by volume of isophthalic acid dihydrazide. Carbon resistors were coated with an approximately 0.0125 cm (0.005 inch) thick film of this resin composition. After 3 minutes long cure at 204 C (400 F) this resin had good film strength and dielectric properties. To obtain a maximum Moisture protection s the curing cycle was 10 minutes expanded at 204 C (400 F). The resin coating showed im Compared to other, known epoxy-synthetic resin mixtures, a greatly increased ability to withstand ignition.

It is therefore an advantage of the invention that the encapsulation materials does not ignite even at high temperatures. Furthermore, it is an advantage that the encapsulation materials in their Use for carbon resistors and similar electrical construction

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parts can easily be applied in the form of thin films and are stable even under heavy load conditions. Mixtures of Epoxy resins and inorganic fillers can be made which are highly effective dielectric encapsulation materials

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Claims (4)

Claims 1. Non-flammable dielectric resin mixture, which is suitable for the encapsulation of components, made of 40-CO volume percent epoxy resin, 5-25 volume percent halogenated epoxy resin, 20-30 volume percent glass beads, 5-25 °, Ό antimony trioxide or antimony triuxide zinc burate and a hydrazide hardener of the formula f H (CONHNH ,,) with η equal to 1, 2 or 3, characterized in that that both epoxy resins have on average more than one 1,2-epoxy group per average molecular weight that the glass beads have an average diameter of at most 0.008 cm (0.003 Inches) and that the amount of hardener equals 0.25 to 0.5 mol Is hydrazide per epoxy equivalent of epoxy resins. 2. Mixture according to claim 1, characterized by 0-20 volume I percent additional inert filler materials. 3. Mixture according to claim 1 or 2, characterized in that as the hardener NH_NH-CO-R-CO-NHNH_ is provided, where R is a divalent hydrocarbon radical having 1 to 20 carbon atoms. 009849/1805 ^BAD 4. Carbon resistance created by a film of a Resin mixture according to one or more of Claims 1 to 3 is encapsulated, characterized in that the film is approximately 0.0125 to 0.026 cm (0.005-0.010 inches) thick. 00 9849 / 180S