DE1921207A1 - Fireproof protective coating for electrical film resistors - Google Patents

Description

PATENT ADVOCATE

Dr. ERNST STURM 8 Munich 23, de “April 25, 1969

UOPOLDSTR. 20 / IV - '• τ · J ^ J DeuUche Bank AG. Munich Account No. 21/34120 _ (Concordiahaus)

Postal checking account: Munich 91707 1921207 Telephone 39Ä451

Telegram address: Ijarpatont -Dl * H.

Applicant: Corning Glass Works

GOEMIFG

C orning. ITew York U830 / V.St.A.

Fireproof protective coating compound for electrical

Film resistors

The invention relates to fire retardant protective coating compositions for electrical film resistors, containing at least partially hydrolyzed tetra-alkyl-orthosilicate, Aluminum oxidej a suspending agent and possibly fillers, and / or inorganic pigment colors and their use.

Recently, a wide range of uses has been opened up for film electrical resistors. Usually exist these film resistors consist of a substrate such as glass covered with a thin film of a resistor material, such as zinc oxide. It is known to cover these film resistors with a protective layer. However, there is the problem that these protective coatings burn very often and due to the heat which the film-

903348/0986

resistance arises, is destroyed. The burning of the resistive coatings leads not only to the destruction of the resistor itself, but also very often to damage to the adjacent ones Elements in the system in which it is used. The damage caused by the burning of the resistive coatings The electrical parts and systems has to be an intensive search for non-flammable. Covers led - which withstand the heat generated by sudden heavy overloads on the resistors.

The film resistors, which come with the well-known protective coatings are provided, have the further disadvantage that the protective coatings not only burn due to the overload, but also favor external arcing and in some cases short-circuiting the circuit in which they are are built-in tend. There has therefore been an intensive search for a protective coating composition for resistors, which with heavier Overcharge does not burn, avoids external arcing and makes it easier to open the overcharged circuit.

3s it was proposed to use protective coatings for film resistors add various conventional flame retardant additives. However, this was unsuccessful. Many of the conventional flame retardant additives could burn at extremely high temperatures (400 - 600 ° G), which occurred during high overloads, do not prevent it.

908843/0988

Recently, a protective coating composition for resistors has been proposed, which is a tetraalkyl ortliosilicate, alumina, a suspending agent and various fillers and Pigments, including titanium dioxide. Although this composition provides a non-flammable coating, it has the ! • laughed at that the coating during and after application and tends to break as it cures, thereby exposing the substrate.

Although the "use of coatings containing TiOp as a filler contain a slightly larger flame retardant than other known ones Coatings, it was found that the life of the coating composition was greatly reduced.

By using "clad" material, i. H. of material, which is dispersed in a carrier liquid at high speed and high shear to form a "! particle To avoid separation, the active surface area of the titanium dioxide and the suspending agent is due to the small Particle size (in the submicron range) of the suspended material significantly increased, adding to its catalytic effect contributes to the weathering of the coating mass.

It is also known that the presence of alkali metal ions has an unfavorable influence on the composition exerts the moisture resistance of the coatings and on the other hand contributes to the weathering of the coating. the

0008 - ^ / 096.6 _r .

conventional suspending agents normally found in the Industry used often contain a relatively honing Percentage of alkali metal ions. The "use of relatively large amounts of suspension agents and other coating components, which have a high content of allcalimetal ions, adversely affects the moisture resistance of the coating.

The object of the invention is therefore to provide an improved, difficult to create flammable protective coating material for electrical film resistors, which results in a break-free coating, Has improved moisture resistance and increased service life, prevents external arcing from their chemical or dielectric properties not significantly changed and in particular also splinter and abrasion resistant is.

This object is achieved according to the invention in that the Mass silicon dioxide as crystalline SiOp with a grain

2
size of 0.044-0.149 mm is added.

It has also been found that it is advantageous to add TiO _p and the suspension medium in a certain, critical and larger grain size than before, in particular as dry solid particles with agglomerates larger than 1 μl.

It has unexpectedly been found that this particle size is critical. 9 0 9 (U 8 / Ö § 8 6

The "silicon dioxide" that is used as an additive to coating compounds which has been proposed to the present invention is an amorphous, fine-grained "silicon dioxide" and is added to the mixture for its ability to act as a suspending agent or a thixotropic agent. These "silicon dioxide" mixtures have a particle size in the submicron or kollddalen Area and are amorphous. Surprisingly, these "silicon dioxide" mixtures have a structure and particle size which render them ineffective for the purposes of the present invention; these coating mixtures tend to during and after Application in the resistances and the hardening for breaking, while the crystalline silicon dioxide with the proposed Surprisingly, grain size has the unique ability to break the coating composition described above impede.

It was also surprising that a non- "disguised" Titanium dioxide filler and suspending agent, with grain agglomerate sizes larger than approx. 1 micron, the life of the non-flammable Coating compounds based on tetraalkyl orthosilicate, which they are admitted to increase substantially.

Furthermore, it has been found that, by adjusting the alkali metal ion content of the coating composition such that a cured coating made from the coating composition, less than about 0.05 $ sodium, less than about 0.05 7 " Potassium, less than about 0.01 fo lithium, less than 0.001 fo cesium above

9 0 9 0 ^ 9/0986

and contains less than about 0.001 fo rubidium (by weight on an oxide basis), the moisture resistance and overall stability of the coating composition is significantly increased.

Another advantageous use of the inventive Protective coating compound "consists in that they are used to Production of an intermediate, second layer of film resistor is used, which * a first layer, containing a largely inorganic silicone resin, an inorganic resin and a filler, and a third Layer containing an at least partially hydrolyzed Tetraalkyl orthosilicate, a largely inorganic silicone resin, suspended resin particles and a contract with the mass- «· Liches solvent.

According to the invention it has been found that the above-described three coating compositions, when applied to an electrical resistor, a mutual synergistic one Have an effect by making the resistance non-flammable, moisture-resistant, flame-arc-resistant, Give abrasion and splinter-resistant properties, in other words, while one of the coating compounds, if they used alone, the resistor has high moisture resistance imparts, however, this is very sensitive to burning or producing flammable rauoheee Reason for severe overload. However, when the crowd is in touch used with one or both of the other coatings

ilire sensitivity to burning is avoided, however gels their ability to be a moisture-sensitive protective layer to "form. While either or both of the other coating compositions, when in conjunction with the / first Coatings are used, which improve their non-flammable properties, they themselves have a low moisture resistance. The third coating mass acts. B. in a synergistic manner with a view to improvement the moisture resistance of the second coating composition.

In general, any tetraalkyl orthosilicate can be used for the purpose of the invention. Preferably di ^{': i} lower tetraalkyl orthosilicates such as Me.thyl, ethyl, propyl, butyl, etc., esters used. In particular, it is advantageous to use partially hydrolyzed tetraethyl orthosilicates. The degree of hydrolysis of the orosilicates is not very important. In general, the degree of hydrolysis may vary up to about $ 90 from about 10 io. In general, approx. 5 ⁰ to approx. 55 $>0r1fc> silicates, based on the total mixture, could be used. It should be mentioned at this point that "partially hydrolyzed" also means the in situ hydrolysis of the tetraalkyl orthosilicates during the coating or curing operation.

The amount of aluminum oxide is not always critical. In ■ general amounts can be used up to approximately 95 ° i of about 4 $ "

903648/0986

Any conventional suspending agent can be used for the purpose of the present invention. Examples of suitable suspending agents are the organic derivatives of the various Hontmorillonites, et., Which are generally known as B ^ -ntones. Additional suspending agents contain amorphous silicon dioxide, clays, e.g. B. the montmorillonites themselves and diatomaceous earths, e.g. B. Kieselguhr. In general, alkylammonium montmorillonites are preferred; they can be used in an amount of 0.1 to 2.0 ¹ P.

Any conventional inorganic filler and / or pigment material can be added to the "coating masses of the present composition. A preferred?" Filler and a preferred pigment material is titanium dioxide. TiO ₀ acts as a "functional: filler and functional · pigment color", ie, besides acting as a filler and pigment color, it aids preparation and handling of the mixture by acting as a suspending agent. In general, amounts of titanium dioxide from about 1 to about 45 ° can be used. Any additional conventional pigment colors, such as cobalt aluminate, Cr ₀ O- ,, Fe ₀ O ,, Fe ^ O. ',

>;' c 3 3 4

-Lamp black, etc., can be added. In general, amounts of pigment and / or filler can be added which correspond to the difference between the other constituents and approx. 100%.

The nature of the solvent used is not very special

909848/0986

BAD ORfGlNAL

_ Q _ ■

decisive. The only requirement for the solvent is that it be inert to the other coating components. . A preferred solvent is isopropanol. However, other conventional solvents can also be used, e.g. the lower alkanols such as ethanol, propanol etc., ketones such as ketylethyl ketone, dimethylformamide, diacetone alcohol, dimethyl sulfoxide, pyridine, furan, furfuryl alcohol, trichloroethane, H-methyl- pyrrolidone, isooctane, hexane, etc. Solvent amounts from 0 to 20 ^e / x can be used.

The amount of silicon dioxide that is necessary to break one To prevent the coating is generally from approx. 1 to approx. 48 / °. It should be mentioned, however, that an addition any amount of silicon dioxide to that according to the invention Coating mixtures have some effect on the tendency to break the coating.

As stated above, it was found according to the invention that the tendency of the coating compositions described, during and After curing, the only way to prevent silicon dioxide from breaking is that it is in certain forms and specified Grain sizes is added.

In particular, it has been found that when using crystalline silicon dioxide with a grain size of approximately 0.044 to approx. 0.149 mm of coatings are obtained during use and will not break during or after curing.

9O9048 / Ö98S

- ίο -

When using silicon dioxide with grain sizes of

2
less than about 0.044 mm coatings are obtained, which

2 have cracks. Grain sizes larger than approx. 0.149 mm can be used Coatings result which are not easily processable.

Crystalline silica is known to the pachmann as "molten" Silicon dioxide "," silicon dioxide flour "," ground Silicon dioxide "," powdered silicon dioxide "," sand "etc. are known.

As stated above, adding the titanium dioxide filler lengthens and the suspension medium in non-disguised form, i.e. with an agglomerate * particle size of the additives of more than approx. 1 micron, the service life of the entire Coating mass considerably. Generally they are agglomerate particles with a size between about 1 and about 150 microns are suitable. Agglomerate sizes in this range combine the best properties in terms of easier preprocessing the coating mass and increased service life. By "agglomerates" is a group or bundle of particles which exist in the mixture as discrete units, meant.

If desired, the. Protective coating composition can also be added to a solvent. Suitable solvents include lower alkanols, methyl ethyl ketone, dimethylformamide, diac et on alcohol, dimethyl sulfoxide, toluene, xylene, trichlorethylene, Tetrachlorethylene, trichloroethane, IT ~ Methy! Pyrrolidon ^

9 0 9848/0986

Isooctane, hexane, benzene, dioxane etc. Isopropanol is that preferably solvents. In general, solvent masses can be used from approx. O "to approx. 20? ί can be used.

The elimination of the "disguise" step "in processing the titanium dioxide and the suspending agent continue to save Time and cost.

It should be mentioned again at this point that one can "disguise" the titanium dioxide and the conventional suspending agents deemed necessary to the contribution into other systems to facilitate and exit or Avoid "sedimentation" of the particles. Although the use of non-clad materials, as mentioned above, Provided favorable results are adverse results which are normally obtained with "non-disguised" materials are connected, in connection with the inventive No coating compounds based on tetraalkyl orthosilicate. That means even if not in disguise Titanium dioxide and suspending agents are used, surprisingly no problems such as incomplete mixing, separation, etc. occur.

To provide a moisture-resistant coating that protects the meets the requirements set by the electrical industry, too obtained, it is advantageous to reduce the alkali metal! ones content of the Adjust the coating compound in such a way that hardened

909846/0986

• - 12 -

eyes made from these blends are not have more than the maximum percentages given above. Conventional suspending agents generally contain fairly high percentages of alkali metal ions. A reduction in the amount of suspending agent therefore leads to a corresponding reduction in the alkali metal ion content. However, it should be understood that the amount of any ingredient can be used the coating mass with regard to the required alkali metal ion concentrations are adjusted.

On the other hand, the constituents of the invention Coating mass can also be cleaned from the start to reduce their alkali metal ion content before it is introduced into the coating mass to zoom out. This cleaning can be carried out in the form of cold water or hot water leaching, since most alkali metal compounds are water soluble. Those compounds that are not water-soluble train you far less influence on moisture resistance of the coating. Of course, any cleaning method can be used to reduce the alkali metal ion. Salary will be applied.

The exact mechanism by which alkali metals on the one hand affect the moisture resistance and on the other hand to the weathering of the coatings according to the invention contribute has not yet been clarified in detail. As a first approximation, however, it is assumed that a high alkali

909848/0986

metal ions content the coating at high temperatures like them generated during overcharging, makes it electrically conductive. Furthermore, free alkalis cause high humidity an electrolysis of the tin oxide film. When the resistance is conductive it will not open the circuit, which is heavily overloaded, and thereby short circuits and damage the other components in the circuit.

These problems can arise when the alkali metal is in salt form and in the presence of water in the open Ions disassociated. When the alkali metals e.g. B. are chemically bound in complexes insoluble silicates, there is a less risk of destruction of the coatings in the presence of moisture. These complex alkali metal compounds can however, if severely overloaded, they decompose and release alkali metals in salt form. It is therefore consistently recommended to free the components of the coating compound from all alkali metal compounds.

The moisture resistance of the coated resistors is tested according to the standard method MIL-STD-2O2B. Method 106A (May 31, 1957). The results of these tests are usually reported as ΖΛ R percent. The maximum UA R allowed in each case depends on the magnitude of the resistance. In general, LA. R percentages below approx. 1 # accepted if they meet the MII-STD

909848/0986 _ ^ __ ^

-H- requirements for moisture resistance

The coating compositions according to the invention can be applied to the resistance can be applied by any of the conventional methods: e.g. B. by dipping, spraying, brushing, Rolling, etc. In general, an amount of material sufficient to produce a final cured coating of 5 to 10 mils, preferably 5 to 7 mils thick. In particular, although not absolutely necessary, two protective coatings are recommended to muster up the resistance. The coating is made by heat treatment at elevated temperatures, usually at up to approx. 250 ° C, hardened.

When the above-described composition is advantageously used as an intermediate layer on a film resistor, the The first coating mass is a largely inorganic silicone resin, an inorganic filler and a solvent. These Composition results in an inner, very moisture-resistant protective coating on an electrical resistor. This protective coating also has good dielectric strength and is resistant to arcing.

The largely inorganic silicone resin component can be any silicone resin that has relatively few organic substituents Has. In general, these silicones are derived from di- and trifunctional silanes, which are the following Structural formula has:

90884 6/09 8 6

R-, - O -Si - O - R 'J

A.

f ¹

o -Si - O

0-L

These silanes react (via hydrolysis) to silicone resins, which have the following repeating units:

Si

R ^ and Rp saturate the valences on the Si atom in the resin, where the starting silane is a di-functional silane (with 2 alkoxy groups). R ^ and, to a large extent, a cross or A bridge bond with another silicone resin chain saturates the valences on the Si atom, where the starting silane is is tri-functional silane. Mixtures of di- and tri-functional silanes can of course be used for the production the silicone resins can be used.

A "largely inorganic" silicone resin means a silicone resin in which the silicon and oxygen content is at least about 50% by weight (as SiO ₂ ) of the resin.

In the functional alkoxy groups of the structural formulas above, R 1, R and R _{5 can be the} same or different lower alkyl groups, such as methyl, ethyl, propyl groups, etc.

9098A8 / 0986

R ₁ . and Rp, which lead to "leaded" as the main organic constituents in the silicone resin, are selected in such a way that the Si and O content of the resin of at least 50% by weight (as SiOp) is maintained. R ₁ and R ₂ can be the same or various substituents, and are preferably lower alkyl groups, such as methyl, ethyl, n- or iso-propyl, n- or iso-butyl and phenyl groups.

In order to carry out the invention, it is essential that the silicone resin be "largely inorganic". Silicone resins were used before as components of coating compounds for resistors etc. However, it is believed that because of her high organic material content and their organic structure, their decomposition products have a low flash point and so after being exposed to elevated temperatures (approximately 600 0 'caused by severe overcharging of the resistors tend to ignite or burn and thus cause the disadvantages described above.

Apparently the "according to the invention" largely decompose inorganic "silicone resins at elevated temperatures iäTigsaiH "to relatively small amounts of decomposing brittle" which have a high flash point and which at temperatures * the ' if severe overloads occur, neither ignite nor burn.

The polymethyl-pheriylsiloxanes are preferably silicone resins ;

9Ö984S / Ö986

ORIGINAL INSPECTED

which either consist of the di-functional silanes described above, where R _{1 is} a methyl group and Rp is a phenyl group, or from two tri-functional silanes, where R. is a methyl group in one and a phenyl group in the other silane, It has been found that this resin, due to its mixed organic content, slowly decomposes over a wide temperature range, while the amount of "decomposition products present, which is available for" potential ignition during the decomposition process, is kept low. In other words: the methyl and phenyl components each decompose at different temperatures and thus produce fewer decomposition products at a certain temperature and at a certain point in the decomposition cycle than if R- and R _{2 were} identical.

Another disadvantage associated with the presence of relatively large amounts of organic decomposition products is that these materials make the partially decomposed coating electrically conductive at elevated temperatures. Polly Resistors coated with these products will not open the circuit in the event of severe overcharging.

The amount of silicone resin in the first coating composition can vary from approx. 5 to approx. 65 #. Using less than about $ 5 results in a protective coating that is low in weight has moisture resistance. The usage

909843/0986

More than 65 ⁰ A silicone resin results in a mixture which is difficult to handle.

The inorganic filler can be any conventional filler. In general, the silicates are preferable. The amount of silicate filler can vary from about 1 to about 10 ^c / o . The amount of silicate influences the adhesion to the first coating layer of the subsequently used coating materials. The use of too little silicate causes cracks in the subsequently applied coating layer. The use of more than 10 tfo of silicate reduces the moisture resistance of the entire system.

The silicate filler material is powdered

2 turns. The particles can have a grain size of approximately 0.16 mm (80 mesh) to sub-micron size .

The mica are preferably silicate fillers. Mica particles are in the form of narrow platelets. _R E according to the invention it was found that these platelets align themselves in the products manufactured from the novel mixtures coatings and as an effective, dense, form an impenetrable protective layer. Although "other conventional inorganic fillers can also improve the temperature resistance, adhesion, etc. of the coating compounds, the mica is particularly effective due to the platelet shape of its particles.

The solvent used can be any liquid

909848/0986

which is inert towards the components of the mixture and is compatible with the entire coating system. As suitable Solvents are mentioned here: ketones, such as acetone, methyl ethyl ketone etc., aliphatic alcohols such as ethanol, propanol, isopropanol, diacetone alcohol, et., halogenated hydrocarbons such as tri- and tetrachlorethylene, etc .; Hydrocarbons, such as toluene, xylene, benzene, isooctane, hexane, etc .; Dimethylformamide, Dimethyl sulfoxide, N-methylpyrrolidone, dioxane ect. The "preferred solvent is isopropanol".

In general, the amount of solvent may 70 <'■> vary from about 20 ms approx. The amount of solvent used depends, of course, in each particular case to a large extent on the amounts of silicone resin and silicate filler used.

The second coating has the composition according to the invention which has already been described above.

The hydrolyzed tetraalkyl orthosilicate component and the silicone resin of the third coating composition can be the same as or different from those in the second composition. The amount of hydrolyzed tetraalkyl orthosilicate katin in the third protective coating composition can vary from about 1 to about 95 $. The amount of silicone resin can vary from about $ 1 to about $ 90.

The resin material can be any resin which has a low coefficient of friction. Where, however, a high degree at

909848/0986

Flame, heat and flame arc resistance required, it is preferable to use suspensions of the fluorocarbon resins to use, such as those made from tetrafluoroethylene, trifluorochloroethylene, fluorinated ethylene-propylene resins, Vinylidene fluoride, copolymers of tetrafluoroethylene and hexafluoropropylene, vinyl fluoride and telomers of tetrafluoroethylene.

Where a. high degree of flame, flame arc and heat resistance is not required, any resin material with a (static) coefficient of friction of approx. 0.04 Ms approx. 1.00 used v / earth. Suitable non-fluorinated resins are e.g. B. polyethylene and polypropylene.

The resin particles are preferably suspended in a carrier liquid before they are introduced into the third coating composition; however, the resin material can be suspended in the solvent used in the third mass. The only requirement for the carrier liquid is that it be a liquid in which the resin is insoluble and that it be compatible with the other ingredients of the mixture. Suitable carrier liquids are aromatics, such as toluene, benzene, xylene, etc. In general, the amount of resin suspension can range from about 1 to about 75 ^c / o . If a prepared suspension of the resin in a carrier liquid is used, the amount of resin in the suspension can

909848/0986

1921? N7

vary from 0.1 "to 52 °.

The solvent used in the third mass can be any. Be liquid, which is inert to the system, with the other components of the preparation is compatible and does not exert a solvation effect on the resin particles. Suitable Solvents are e.g. B. the solvents of the first coating composition, see above.

Isopropanol is the preferred solvent. In general, the amount of solvent used can vary up to about 80 i * of about 1 ".

The protective coating compositions described above are in in the order given, successively separated on the electrical Resistance applied. The individual layers can • be hardened before the next subsequent coating operation or partially hardened. If necessary, everyone can three coating compounds applied individually and partially cured and then subjected to total hardening.

Any conventional one can be used for the coating mixtures according to the invention Coating process, such as rolling ?! Dipping, spraying etc. can be used.

The curing of the individual layers can preferably take place in several stages be performed. In other words: the

90984 9/098 6

1921201

"The applied coating is first heated to approx. 80 ° C for a few minutes, to drive off the corresponding solvents. Then the temperature is gradually increased to approx. 250 ° C and used for Completion of curing cooled.

Den of the first or covering compound will be so much on / resistance is applied to provide a final cured layer 1/2 to 5 mils, preferably 1 to 2 mils thick.

So much of the second or insulating layer is applied to the resistor that a cured layer of 5 to 10 mils, preferably 5 to 7 mils, in thickness. Preferably two layers of the second mixture are used, wherein each having the thickness described is applied.

Since the third coating composition penetrates the second coating composition, it does not contribute significantly to the thickness of the overall coating at. In general, amounts increasing the thickness to about 2 mils, preferably 1 mil, will suffice.

In the following, the invention is illustrated by means of exemplary embodiments explained in more detail.

example 1

A coating composition according to the invention was produced by mixing the following ingredients and quantities:

909848/0986

Alumina '4540 g

Silica (crystalline, 200 mesli) 46O g

Titanium dioxide 635 g

Prehydrolyzed tetraethyl

orthosilicate 9OO g

Suspending agent (Benton ilr. 27-

allcyl-ammonium-montmorillonite) 90 g

Anhydrous isopropanol 472 g

Pigment paint (cobalt aluminate + Cr ₂ O-,) 300 g

The mixture obtained was a homogeneous and stable liquid.

example

A glass-tin oxide film 1 K resistor to an estimated power of 4 watts was "coated" with the mixture according to example 1 twice cured at 250 ^p G to yield a combined coating of 10 mils thickness.

Neither during application nor during hardening or the following hardening was observed to break the layer,

The coated resistor became a 100-fold overload exposed. As a result, the resistance did not burn or smoke. No external arcing was observed either; the Circuit. Containing the resistor opened by overcharging.

90 9848/0986

- 24 - Example 3 one Coating G in both one Not at all By Hisclien the following ingredients was G game 2 coated. The layer broke neither before nor after opened mass divided by: i54O G the hardening after various manipulations. Alumina ' 460 G Silicon dioxide (crystalline, 300 mesh) 635 G While exposed to a 100-fold overcharge, became Protection- Titanium dioxide 900 G watch out for burning or smoking of the cover. Prehydrolyzed tetraethyl orthosilicate 90 G external arching became evident; the resistances OaI-O- ¹ SiI (amorphous silicon dioxide 'Sus
pension funds Cabot Corp.) 200 g ' the circuit. Anhydrous ethanol 272 ^ appreciated Example 4 Propanol anhydrous 300 how By mixing the following ingredients was made Pigment color (cobalt aluminate + Cr ₂ O-) coating mass produced: 1 K Güaj tin oxide film resistors with an abf 909SAS / 0986 Power of 1 watt were used with the above mixture

BAD ORSGiNAL

700 G 635 G 500 G 500 G 90 G 472 G 300 G

Alumina 4300 g

Silicon dioxide (crystalline, 0.149 mm = 100 mesh.)

Titanium dioxide

Prehydrolyzed tetrapropyl orthosilicate. Prehydrolyzed tetraethyl orthosilicate Suspending agent- (Benton 27-alkyl-ammonium-Hontmorillonit)

Anhydrous isopropanol pigment paint (cobalt aluminate + Cr ₂ O ₇ )

5K glass tin oxide film resistors with an estimated performance of 3 watts were coated with the Hasse according to Example 2. No coating breakage was observed during or after curing.

During the resistance exposed to a 100-fold overcharge there was neither flame formation nor smoking nor external arcing observed and the resistors opened the circuit during the overcharge.

Example 5 below demonstrates the undesirable fracturing that occurs when using blends that do not contain silica contain.

Example 5

A mixture was made from the following ingredients:

909848/0986

Alumina 4800 g

Titanium dioxide 835 g

Prehydrolyzed tetraethyl orthosilicate 900 g Suspending agent (Cal-0-Sil. Amorphous Silica - Cabot Corp.) 90 g

Anhydrous isopropanol 472 g

Pigment paint (cobalt aluminate + Cr ₂ O ₅ ) 300 g

The composition was applied to 1K glass-tin oxide film resistors with an estimated power of 4 watts, as in Example 2. During and after hardening, cracks appeared in the layer.

Example 6

Three coating compositions were prepared as follows:

A. Cover layer (first coat) Components

Polymethyl-phenyl-siloxane anhydrous isopropanol mica, white, water -ground (160 mesh)

Parts by weight 40 50

7.5

B. Insulation layer (second coating)

Components Parts by weight of aluminum oxide 72

Silica (crystalline, 200 mesh) 18

Titanium dioxide (not clad, 0.044 mm = 325 mesh agglomerates)

909848/0986

1.5

- 27 - 0.8 ' Minutes 8th Benton 27 (alkyl-ammonium-Hontmoril-
lonit, not clad, 200 meoii-
Agglomeratec) 6.6 1. Coated with A.
Solvent driven off
at 80-90 ° G 4
hardened at 150 ° C 4
hardened at 250 C 4
chilled to <100 ° G 5 Anhydrous lüopropanol 7.5 2. Coated with B.
Solvent driven off
at 100 - 140 ° C 4
hot cured 150 ° C '4
haem ^ V? - ⁵ 250 ° C .-- 4
chilled i v. <10000 C 5 Cyan dye jfe 157b
(Cobalt aluminate and ohromoxide dye) 30.5 90 9 848/098 6 .-- 6th oilnotid IT-6 (pre-hydrolyzed tetra-
ethyl crthosilicate) valued performance C. Iinprägiiicrscliiclit (third excess) Components weight percentages Scheme with Silbond H-4 (pre-hydrolyzed tetra-
ätliyl-ortlio silicate) Teflon-Süsponsion (KS-142C, Killor-
Steplienson Co., 2-3 5 ° Teflon in toluene) thickness
(HiI) Polymethyl-plienyl-siloxane 2 Water-free isopropanol • V. '=. -6 ·. ...- ■, '"." G-las tin oxide 1 K pilm resistors with a output of 1 watt were according to the following standing mixtures "coated:

BATH ORIGINAL

- 26 -

Minutes

Thickness (mil)

again "coated with B. Solvent driven out at 100 - HO ⁰ G
hardened at 150 ° C

hardened at 250 ° C, cooled to <100 ° C

4 4 4

4. Coated with 0.

solvent driven off at 90 -110 ° 0
hardened at 150 ° G

hardened at 250 C, cooled to <100 ° G

4 4 4

The resistors coated in this way were built into a circuit and subjected to a 10O-fold overcharge. Neither flaming nor burning was found. The resistances opened the circuit; there was no evidence of external arcing or conduction through the layer. '

The "coated resistors" were subjected to the standardized 10-day humidity test (MIL-STD 202B, Method 106A, May 31, 1957). It was found that the resistors met the requirements for the maximum permitted / \ R.

Example 7 '

The procedure was as in Example 6 with the exception that Dow-Oorning ^ 991 lacquer (a 50 $ silicone resin in xylene dispersion, the silicone resin having a total silicone and oxygen content (as SiO ₂ ) of over 50% by weight Resin)

909848/0986

ORIGIMAL BATHROOM

Replaced in the covering and impregnating compounds duroh Glasharz 100 became.

1 K glass-tin oxide resistors with an estimated power of 4 watts were coated as in Example 1 and in a similar way Way exposed to 100-fold overloads and moisture-resistant tested.

Neither flame formation nor burning was observed during overcharging; the resistors opened the circuit.

Furthermore, the resistances corresponded to the requirements for the maximum permitted l \ R.

Example 8

The procedure was as in Example 6 with the exception that Dow-Corning R-447I (a silicone resin which contains less than about 50 $ Si (as SiO ₂ ) and 0) was replaced by glass resin 100.

5K glass-tin oxide 3-film resistors with an estimated power of 3 watts were coated as in Example 1 and one
lOOfacheu exposed to overcharging

Flame formation and burning of the coating occurred. «Des white * External arcing was observed j the resistance never opened the electricity price

"809848/0688

Example 9

The procedure was as in Example 6 with the exception that the following mixture was used instead of B, the insulating or second coating compound.

Ingredients aluminum oxide silicon dioxide (crystalline, 200 mesh) Titanium dioxide (unclad, 300 mesh agglomerates) Aerosil (amorphous silicon dioxide Pigment color (cobalt aluminate + chromium oxide) Prehydrolyzed tetrapropyl orthosilicate isopropanol

Parts by weight 2160 540

453 10 225 915 204

The resistors coated with the three compounds were subjected to overcharge and moisture resistance tests as in Example 6 and were satisfactory.

Example 10

The procedure was as described in Example 6 with the exception that that pre-hydrolyzed tetramethyl orthosilicate instead Tetraethyl ester was used.

Those coated with the three coating compositions. Resistors were satisfactorily non-flammable and fire-resistant. . ^:

§09848 / 0986 "^^

Example 11

Lg The procedure was as described in Example 6 except that instead of polyethylene Polytetrafluorätli3 ^r len was used in the impregnation layer.

The v / ids provided with the serving system were fulfilled the Kil-ÜTD requirements for moisture resistance,

B is ν i el 12

It became a vain protective coating composition of the following composition manufactured:

Components Parts by weight of aluminum oxide d 2160

Silica 54O

Titanium dioxide 4.53

Suspending agent (Benton 27 - alkylammonium montmorillonite) 24

Pigment paint (cobalt aluminate + chromium oxide) 225 Prehydrolyzed tetraethyl orthosilicate 915 Anhydrous isopropanol 204

One for each of those included in the measures described above Components, a spectrographic analysis was carried out to determine its alkali metal content, with the following Values - in percent by weight based on oxide - were obtained:

909848/0986

BATH ORIGINAL

1921.20?

component - jji lia I. 3 & - .Gs Orthosilicate HB * • HB KB HB. HB jfLluniiniuniöxid 0.005 0.03 0.01 HB HB Silicon dioxide Ό, ΟΟΐ 0.01 O »01 HB- HB Titanium dioxide. 0.001 0.05 0.05 HB - HB B-.ntos. 27 1.0 0.25. O, 1 HB HB Pigment dye 0.01 0.15 Ό, 05 HB HB

* HB - not

Bas ämgegeftene Titandio3-: id lay in mieM-disguised form and. i had an agglomerate particle size of approx. 50 microns (325 "

Bas Suspen # i © mti »ittel C ^ ston 2?) W ^ rde efeenfallö ± ή iiter Foa? M veywenaet and- Mtte an A ¥ © ii ^ a * 50 Miföron (325 Mesa) * .-

Ms

one

tqu meferals

The Itesge wiaa * i, e in gwei SeüiGliteii Suf

Filed with a Gesöitafeten ielstiang vqu 4 at 25Ö ^Ö ß> wodarok a to Mil BiMie was eriaalten »Dea? Geliiertete tfeerzmg had a GeSit-4Ik & liaetäil- & eMlt (as oxides) v © n ännaherttd 1> Ö2 g odei ¹ O-, Ö4 fo * Öie t) esöiaieB.te1; e: n resistances were ■: on ^; ! "euGiitigke its -Wists tandsfäMgk © it according to the ΗΙΙί» - &! Γ1) -202Β '.... ■ Method 1QA tested uad result in a BurGhBclmittö Ü4. k - -. "

903848/0988

During the resistance exposed to a 100-fold overcharge he opened the circuit without burning or inflaming. Flames. There was no evidence of an external arch-r "formation; the coating was non-conductive during overcharge.

The following example clearly shows the results obtained when using a coating mix which has a high alkali metal ion content:

Example 13

It became a coating mixture of the following composition manufactured:

Ingredients Parts by weight aluminum oxide 2160

Silicon dioxide 54-0

Titanium dioxide 453

Suspending agent (Benton 27)
Alkyl ammonium montmorillonite 24

Pigment (cobalt aluminate + chromium oxide) 225

Prehydrolyzed tetraethyl ofthosilicate 915 Anhydrous isopropanol 204

The ingredients were not as in Example 1 in terms of selected for low alkali content. The TiOp and suspending agent were the same as in Example 1.

909848/0986. ..

BATH ORIGINAL

H-

The coating mass produced in this way was applied to the same resistors as in Example 1 under the same conditions. The cured coating such as ε has an alkali metal ion content (as oxides) of 10.0 g or 0.4 ^C A.

The moisture resistance test showed an average JL \ R of ^ 3 »0 fo and thereby proved that an increased alkali metal ion content in the hat has an unfavorable effect on its moisture resistance.

During the resistance exposed to a 100-fold overcharge v / urde, the coating was found to be conductive; in addition, there was a slight external arcing, whereby the un- ' The favorable effects of high alkali metal contents on the dielectric properties of the coating become evident.

The following example shows the results obtained when using a coating composition which is a disguised suspension medium and TiOp contains:

Example H

A protective coating was made from the following ingredients manufactured:

8/0986

BAD ORSQINAL

192120? ^: Components .Ge \ iiGlit sant e ile α 1 \ ΐΐ31 & 3. ttffio you are 2T € 0
540! TitandiOirid (disguised)
■ 453: I.
I suspending agent - (Btntoa 27) Pigsientfa ^ Btoff (Ko% altml «.aini 90 silicate * "- QfS ■. ■ - 204 i : The Koa? NgfüS.se des Suspensiönst was &&. * 0.1 'micron ^ -! walirend daa T'iO ^ a dttretasotir
'Oj 05 micron .atiifwies » yh / e So ^ ngifÖsse from ca * The approved Ma.s.ee liatte is'biens duration ΎΌή only © £ u 1 week. _s | ^; and then decomposed into a diekei ; the unfavorable influence i ^ srkXs Titanium dioxide on the Lefeensdauea ? of* ! . In del Besölia? Eii3ung M.nd in the .g'eliold the tiTseizugsmassen 3esi _: indicated - in weight percent, ¹ OQi 55- 3 _Si iriscous gel ₄ ws.s. 1 ? SuspendionSMittel and icii & n ai & d, all i2? oEent- JIe - if not different ^[ sucked on the whole rthO " littli'c

BATH ORIGINAL

Claims (8)

- 36 claims M. J Fire-proof protective coating compound for electrical film resistors, containing at least partially hydrolyzed tetraalkyl orthosilicate, aluminum oxide, a suspension agent and possibly fillers and / or inorganic pigment colors, characterized in that the compound contains silicon dioxide as crystalline SiO ₂ with a grain size of 2
0.04-4-0.149 mm is added. 2. Protective coating composition according to claim 1, characterized in that TiO _{2 is} used as filler and pigment color. 3. Protective coating mass according to claims 1 and 2, characterized in that the mass TiO ₂ and suspending agent as dry pesticide particles with agglomerates of more than 1 u in size are added 4. Protective coating composition according to claims 1 to 3, characterized in that it has an alkali content - determined after the hardening of the composition, in percent by weight based on oxide - of less than 0.05 f <> Ua, less than 0.05 $ K, less than 0.01 fo Li, less than 0.001 <fo Cs, less than 0.001 io Eb. 5 .. protective coating composition according to claims 1 to 4, characterized marked that they also contain a solvent holds. 8 48/098 6 • · - 37 - 6. protective coating according to claim 5, characterized in that that the amount of solvent is $ 0.5 to $ 20 ". 7. Use of the fireproof protective coating compound according to the Claims 1-6 for coatings on resistors, consisting of a glass substrate and a tin oxide pilm. 8. Use of the fireproof protective coating compound according to the Claims 1-7 as an intermediate second layer of film resistor comprising a first coating containing a substantially inorganic silicone resin, an inorganic resin and a filler, and a third coating an at least partially hydrolyzed tetraalkylene / orthosilicate, a largely inorganic silicone resin, suspended resin particles and one that is compatible with the mass Solvent. 9098Afl / ng-fifi