DE2363650A1 - COMPOSITE HEATING ELEMENTS AND PROCESS FOR THEIR PRODUCTION - Google Patents

Description

Composite heating elements and processes for their manufacture

Priority:

2O.12. 1972, Japan 147 139/72,
26.12. 1972, Japan 001 831/73,
April 15, 1973, Japan- O42 541/73

The invention relates to composite heating elements, in particular plate-shaped Composite heating elements.

Laminated heating elements are already known in which the heating layer applied to a carrier layer consists of a mixture of finely divided carbon, for example carbon black, and a binder. These heating elements have the disadvantage that the heating layer formed from the finely divided carbon is relatively uneven, which brings about irregularities with regard to the electrical resistance and thus also with regard to the heating power. Furthermore, heating elements are known in which the heating layer is produced by vapor deposition of a metal layer in a vacuum on a carrier layer
These heating elements are unsuitable for larger areas, since vacuum evaporation becomes difficult as the area increases

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thus the already relatively high costs continued to rise v / earth. Furthermore, heating elements are known in which the heating is provided by fine metal wires located on the carrier layer is effected. The production of these heating elements also causes relatively high costs, which are essentially determined by that the metal is first drawn into fine wire, the wires are then braided or braided and finally in plate-shaped Be brought into shape.

Recently, electrically conductive paints or binders have come onto the market, the electrical conductivity of which is based on the content of silver or other noble metals, the metals being present as a powder in the form of a mixture with vitreous masses. By applying the mixture to a carrier layer and stoving it, an electrically conductive layer is formed on the carrier layer. Those metals are selected that are resistant to oxidation with respect to the stoving process. These include, in particular, silver and others. Precious metals are suitable, which is why this process is very expensive. In order to overcome this disadvantage, US Pat. No. 3,647,532 proposes a method in which an electrically conductive metal layer is produced on the carrier layer in such a way that a mass containing metal powder, for example copper powder , which together with vitreous Compounds in thermally destructible or volatile organic binders, preferably together with reducing compounds, are dispersed, applied to a refractory carrier layer and then burned in. The use of this method avoids the need to use noble metals. The oxidation can be achieved by working in a inert V 409826/0889

Atmosphere can be prevented, thereby preventing the use "cheaper metals such as copper, nickel or cobalt will be possible.

Based on the aforementioned prior art, it was found. the task of producing improved composite heating elements, in particular plate-shaped composite heating elements, wherein a or several important technical properties, such as easy manufacturing, low manufacturing cost, durability, versatile Usability, heat storage capacity or heat regeneration capacity, are improved. This object is achieved by the invention.

The invention thus relates to composite heating elements that are characterized by

(I) an insulating backing layer,

(II) a heating layer, consisting of the stoving product of · (Ha) one or more metals or of

(lib) one or more metals and glass, the components (Ha) and (lib) optionally being metal oxides included, as well as ^

(III) an insulating cover layer.

The invention also relates to a method for producing the composite heating elements, which is characterized in that one a stoving mixture of (Ha) metal powder or (lib) metal powder and glass powder on an insulating carrier layer, where (Ha) and (lib) optionally contain metal oxides, with (lic) a organic dispersant and after stoving

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the resulting heating layer applies an insulating cover layer, or the top layer is applied before the stoving stage and subjected to the stoving process together with the stoving ring mixture.

The invention is based on the idea that it should be possible could produce new heating layers from mixtures of the aforementioned metals and vitreous masses by baking without using metals that are difficult to oxidize and / or without that the baking process can be carried out in a special, inert atmosphere undertakes. Here one deliberately leaves one to a certain extent Oxidation of the metals occur. This oxidation impairs the advantageous properties of the heating layers produced in this way not, since these must have a certain resistance anyway, depending on the desired heating power. In this way Composite heating elements with excellent properties can be produced very easily and at low cost.

The composite heating elements of the invention are both for heating

/ suitable for the formation of larger as well as smaller surfaces, since the risk / interruptions are lower and since they are easier to manufacture than other band-shaped heating elements.

An excellent material for the insulating backing layer (I) is an enamelled metal plate which is an excellent

Has strength and durability. The term "metal plate" here also means sheet metal and foil material.

Preferred metals for the hot layer are more practical for reasons Stoving temperatures of metals that have a melting point

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point below 11OO ° C,

Because the top layer makes contact with the heating layer. the air and thus the oxidation of those contained in the heating layer To prevent metals, plastics are preferred or vitreous masses used as materials for the top layer. Silicone resins and melamine resins are particularly preferred or low-melting glass masses or soft porcelain masses. When a porous layer is applied directly to the heating layer, the heat storage capacity and the heat regenerative capacity are increased the plate-shaped heating layer is significantly improved.

The method of the invention for making the composite heating elements can be done in different ways.

The process is preferably carried out in such a way that first a paste by grinding a mixture of metal powder, glass powder and the organic dispersant (lic.) produces the paste obtained on the carrier layer. applies film-like, the PiIm burns in, so that a heating layer is created on the carrier layer, and.

a
either / applying paint over the heating layer or (if necessary before baking) applying an insulating film to the heating layer, so that an insulating cover layer is created.

To produce the paste film on the carrier layer, one can

kt on the Trägei 409826/0889

• either apply the paste directly to the carrier layer. Man

Abzieh.-Nap.ier can, however, first apply the paste to a backing paper) and from there to the carrier layer. According to the second method below. Using a printing paper, a uniform !: ¹ egg can be produced in a simple V / eise especially when the surface of the carrier layer is not flat. but is more or less curved. It is important that the film ₉ is flexible so that it can be 'closely matched the profile of the support layer. From the same Gz ^ and those synthetic polymers are preferably used in the organic dispersant (lic) which have a glass temperature (T) below

20 ° C.

The invention is explained below with reference to the drawings.

Show it; ,

Fig.1.a longitudinal section through an inventive, plate-shaped Composite heating element,

2 shows a partially sectioned plan view of the plate-shaped Composite heating element,

3 is a partially sectioned plan view of another embodiment a heating element according to the invention and FIG. 4 shows an example of the current flow in the heating element according to the invention plate-shaped composite heating elements.

In Figures 1 and 2 there is the plate-shaped composite heating element 10 from a carrier layer 11, a heating layer 12 located thereon and a cover layer 13 for protecting the heating layer 12. Both ends of the heating layer 12 are equipped with flat electrodes 14, which in turn are connected with lead wires 15 are. The heating layer 12 can be arranged in strips,

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as shown in FIG.

For the carrier layer 11, such insulating materials can be used that the stoving temperatures for the formation of the Resist heating layer 12. Examples of suitable materials are earthenware, glass, and burnt clays, such as those in bricks present, ceramic, plaster of paris, calcium carbonate, calcium silicate or asbestos. The support layer 11 is generally plate-shaped or in some other convenient form, e.g. in disc, cup or tube form. Fiber can also be used made of ceramic "or glass, be it in a knotted or otherwise bound form, can also be used Carrier layers 11 are used, which are only on one side, namely

Borrowed are insulated on the side where the heating layer 12 is located. Here, an ordinary enameled metal plate, for example with a glass or ceramic enamel layer, is particularly preferred; since glass or ceramic layers can be reinforced by a base metal, whereby the heating layer 12 obtained on the enamel layer gets a very good adhesion. Thermal stresses cannot be ~ in the composite heating elements

always avoid. In this case, the glass or ceramic layers work as a buffer, between the heating layer 12 and the base metal. The use of enamelled metal plates as a support layer thus provides composite heating elements with good durability, high mechanical strength and insensitivity to rapid Heating and cooling.

To produce the heating layer 12, stoving mixtures are used

applies, the metal powder or a mixture of metal powder and

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Contain glass powder,

Any metals can be used as long as they are electrically conductive. Preferably, such metals are used which have a melting point below ⁰ 110o C, whereby metals are particularly preferably having a melting point around 400 C as this, the baking process is greatly facilitated. Examples of preferred metals are, for example, copper, silver, gold, zinc, cadmium, aluminum, indium, talliuni, tin, lead, antimony or bismuth. Metals with a melting point of over 1100 ° C. can also be used, provided that these metals in a mixture with other metals have a melting point of not over 1100 ^° C. Although the invention is also applicable when using burn-in temperatures

O
Temperatures of over 1100 C can still be carried out, but such high temperatures are less preferred for practical and economic reasons.

Of the aforementioned metals, zinc, tin and. Lead is particularly preferred both because of its favorable baking temperatures and because of its price. During the baking process, these metals are partially oxidized. If the degree of oxidation is not sufficient to achieve the desired electrical resistance of the heating layer, it is preferred to mix the metals with a certain amount of metal oxide before the baking process.

According to the invention, all glass can be used in the stoving mixtures . Ordinary types of glass are used, provided they are basic components (Skeletal components) ρ such as silica, phosphoric acid odor Boric acid, as well as certain elements such as alkali, alkaline earth, lead or containing zinc

L "' J

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In the aforementioned stoving mixtures, the metals represent the electrically conductive component and the metal oxides and the glass represent the insulating component. To the desired specific To achieve resistance, which is generally a few ohms to a few kilo-ohms (here and in the following "is the specific Resistance based on an area of 1 cm), the content of non-oxidized metal (Me °) in the stoving mixture or in the stoved mixture is preferably 97 to 20 percent by weight. If the metal content is above the upper limit, the Resistance too low, so that it is difficult to achieve a good heating output. On the other hand, if the value falls below the lower limit, the resistance is so high that the current flow is too low to achieve a good heating output.

In view of the usual mains voltages of about 100 to 220 volts, it is generally preferred to have an Me content of in the stoving mixtures or the stoved mixtures about 95 to 40 percent by weight, in particular about 90 to 70 percent by weight, to be used. The metal oxide content is preferably at most 80, in particular 10 to 70 percent by weight.

Of course, the resistance is also related to the

12 ^ /

Thickness of the heating layer formed from the stoving mixture / taking into account the ease of manufacture and durability of the composite heating elements is the thickness of the stoving layer

12th
or the heating layer / preferably a few 10 to a few 100 u.

In accordance with this fourth, the aforementioned desired resistance values are for the composite heating elements.

the cover layer 13 can use the same insulating material as for the carrier layer 11. Since the cover layer 13 is preferably applied after the formation of the heating layer 11,

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ordered x ^ eder the need to bake the top layer 13 to subject, nor is it necessary for the cover layer 13 fire-resistant materials as in the Pail of the carrier layer 11 to use. Thus, all heat-resistant plastics, such as polytetrafluoroethylene, are used as materials for the cover layer 13 Silicone resins, aminoplasts, epoxy resins, polyurethanes, polyamides, polyimides, polyphenylene oxides, as well as copper, boron, titanium or aluminum-containing polymeric substances in question. For heat storage of

Composite heating elements that are only to be heated up to temperatures of at most 100 G, v / ground, can also not particularly temperature-resistant plastics such as polyvinyl chloride, polyvinylidene chloride, polyamides, acrylic polymers, synthetic rubbers or natural rubbers can be used. '

In addition, from the point of view of the heat storage capacity and other thermal properties the use of expanded inorganic substances, e.g. as ceramic, glass, plaster, CaI- calcium carbonate, calcium silicate, "shirasu" (volcanic ash from

material

see volcano Aso), some of which are commercially available in the form of plates / are, or the use of inorganic, heat-resistant, porous materials, such as knotted from glass or ceramic fibers or otherwise obtained fabrics or mats, an advantage.

As far as economic aspects and heat resistance Aminoplasts, such as melamine resins, will play a role, urea resins or benzoguanamine resins are preferred. '.

U -J

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A preferred embodiment for the production of the invention, plate-shaped composite heating elements is described below.

First , the metal powder or a mixture of metal powder

thoroughly and glass powder mixed with the organic dispersant / that e.g. from the solution of a synthetic resin or polymeric substance consists. Here, the metal powders preferably have a particle size of about 10 to 50 µm, and the glass powder preferably a particle size of about 10 to 30 η. Is the particle size too small, the grinding operation becomes difficult; at the same time, it becomes difficult to achieve a uniform film.

For use in the organic dispersant are practical all s yn the ti see resins or polymeric substances suitable. Preferred polymeric substances are polymers of vinyl monomers, acrylic 'monomers, methacrylic monomers, vinyl acetate, styrene, vinyl ether ,. Vinyl chloride, vinylidene chloride, vinyl pyrrolidone, ethylene or propylene, polyvinyl alcohol, polyacetals or polybutyrals, poly- > condensates such as phenolic resins, alkyd resins, melamine resins, polyamides or polyurethanes, cellulose derivatives such as methyl, hydroxyethyl, Carboxy / ethyl or ethyl cellulose, cellulose nitrate, cellulose acetate or CeUulosebutyrat, rubbers such as styrene-butadiene, Acrylonitrile-butadiene, isoprene, butyl, butadiene, chloroprene, i-ethylene-prop7 / len or thiokol rubber as well as natural rubbers and their subsequent products, polymers obtained from petroleum, Cunaron resins, turmeric resins, resins of rosin or its derivatives, starch, denatured starch, proteins or denatured Proteins. ·

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The aforementioned polymeric substances can either be used alone or in a mixture of two or more polymeric substances; possibly can add additives, such as plasticizers, the thermal Decomposition "favoring substances or reducing agents" are used.

When using the aforementioned synthetic resins or polymers Substances may contribute to tackiness when a transfer method using a printing paper is applied the heating layer come what uti advantages in handling brings with it. To overcome this disadvantage, the use of such synthetic resins or. polymeric substances. preferred that have a glass temperature

ture (T) about a Zersetzungstemperattir of having at 60O ⁰ C of about -50 ⁰ C and given the baking and Oxydationstemperaturen the metals addition. Of course, the invention can also be carried out using other synthetic resins or polymeric substances which do not meet the aforementioned conditions. For example, “the tack even with synthetic resins or. handle polymeric substances with a glass temperature of -30 ⁰ C also by crosslinking. ι _

The aforementioned synthetic resins bzv /. polymeric substances is commercially available in a wide variety of forms, e.g. as organic solutions, aqueous solutions or emulsions, whereby as Solvents or dispersants z "B = toluene, xylene, ethyl acetate,

c äthylätherac etat butyl acetate, ethylene glycol monobutyl ether, ethylene glycol ·? » Acetone,

Use methyl ethyl ketone, naphtha or turpentine oil. These

a solutions or suspensions or /. Emulsions v / iron in general /

Solids content of about 30 to 60 percent by weight.

The .- 'aorgenanriten mixtures and the aforementioned organic dispersant are mixed with each other, e.g. using a ball mill, a mixing roller, a mortar or other comminution devices, ground into a paste.

The composition of the paste can be adjusted in accordance with the electrical resistance desired for a particular heating layer. In particular, under unchanged stoving conditions, the electrical resistance of a paste that contains a larger proportion of metal powder decreases. Nevertheless it can too
With higher metal contents in the paste, there is a greater increase in the electrical resistance, if the oxidation of the metal also increases with increasingly harsher stoving conditions.
So that a heating layer ", which has been produced under baking conditions customary in practice, ie 1 hour heating at about 100 ° C., is sufficient to achieve the desired specific resistance within the aforementioned range from a few ohms to
If the required metal content has a few kilohms, the content of glass powder in the mixture of metal powder and glass powder is preferably set below 60 percent by weight, whereby it does not matter if there is practically no glass powder but only metal powder.

The ratio of organic dispersant to metal
or a mixture of metal and glass depends, among other things, on the thickness of the heating layer and the properties of the carrier layer. In general, about 10 to 60 parts by weight of organic dispersant are used per 100 parts by weight of the aforementioned mixtures.

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This quantitative ratio influences the processing conditions when the stoving mixture is applied. If the proportion of organic dispersant is above the upper limit given, the stoving mixture is too strong due to the low viscosity during application organic dispersant, the viscosity of the stoving mixture is so high that it is difficult to apply.

The paste-like stoving mixture obtained can be applied to the carrier layer 11, ζ.Β, applied by means of screen printing will. However, if the carrier layer is not flat but curved, a so-called peel-off transfer method is preferably used. This consists in spreading the paste on a printing paper to form a PiIm, which is used to ensure good processing properties should be flexible in the transfer. For this "is the glass temperature (T) in the organic dispersing

medium synthetic resins used or polymeric materials preferably below 2O ⁰ C, otherwise, the flexibility of the printing layer to be not sufficiently erv) / iron (at glass temperatures of about 2O ⁰ C), as light AASS "cracks occur and no good adaptation takes place on the surface profile of the carrier layer.

When mixing synthetic resins or polymeric substances it is sufficient if only the glass transition temperature of the GemiseheS is below 20 G lies. To determine the glass temperature of the . Mixture T "serves the following equation:

. gA A gB B φ -

L. _ί

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in the

T. the glass transition temperature of component A, T -η the glass transition temperature of component B, M is the mole fraction of component A and Mg is the oil fraction. of component B.

Conventional methods can even be used to transfer the paste to the carrier layer Paper can be used, but paper is preferably used that allows easy removal of the paste, e.g. an art print paper.

For printing the transfer paper with the aforementioned paste.

screen printing is usually used.

After printing with the paste, a protective varnish can be applied to protect the printing layer. to use a protective varnish based on a binder made of the same synthetic resins or. polymeric substances, i.e. with a glass transition temperature below 20 C, such as

) those used according to the invention in the organic dispersant synthetic resins or polymeric substances.

The printing layer obtained in this way is then transferred to the carrier layer, which is insulated on at least one side, with as an insulating layer e.g. ceramic, steatite, forsterite, - with one Oxide film coated aluminum, glass or ceramic enamel is used. To achieve adhesion when transferring the print layer on the carrier layer one uses, for example, the adhesion under the influence of pressure, the effect of yaemia (melt adhesion), under application_j

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of adhesion determinants (primers) or according to the so-called water slide.

procedure (see example 3).

then the baking takes place, / generally about 1 hour

de at temperatures of around 600 to 1000 C in ordinary

you are led /

Atmosphere (air) / without the use of an inert atmosphere would be required.

As a result of the heating during stoving, the synthetic ones decompose Resins or polymeric substances in the print layer and volatilize while the metals melt and partially are oxidized, so that a heating layer with a specific

r
see resistance of a few ohms to a few kilo ohms

(here and in the following, the specified values for .den

f specific resistance is the resistance value over an area of

1 related).

In the event that the aforementioned plastics are used to produce the cover layer to insulate the heating layer, this is done either by applying an appropriate paint from a solution of the plastic on the heating layer or by using a plastic film Adhesives or by the hot melt adhesive process on the heating layer. WeDn e.g. glass or a glaze for the production the top layer is used, the film of the stoving paste can be mixed with a dispersion of the top layer before stoving chtmate rials are coated, then the stoving mixture and subjecting the cover material together to the baking process. Even if the aforementioned inorganic Porous material is used, this can be done with the heating.

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layer can be connected by means of adhesives. In addition, e.g. glass, ceramics, polytetrafluoroethylene or silica, which are accessible to evaporation are applied by means of vacuum evaporation.

The plate-shaped composite heating element 10 is connected to a stream, for example connected to the circuit (as shown in Fig. 4, for example). In the circuit there is a variable resistor 16 and a switch 17. By actuating the switch 17 flows a current that heats the heating element 10. As an alternative to this, for heating the composite heating element 10, a High frequency induction heating can be applied.

The composite heating elements according to the invention can be used in the use in a wide variety of fields of application. Special application examples are electrical heating, baking and grilling devices as well as other electrically heatable devices for kitchen, household and medical purposes, heated furniture and, sanitary facilities as well as heating elements for technical purposes, e.g. for ceiling and street heating.

The examples illustrate the invention.

example 1

■ A burnt mixture of barium carbonate is used as glass powder

and boric acid used in a weight ratio of 1: 1. Zinc powder with a particle size of less than 50 μ is used as the metal powder.

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The organic dispersant used is a 50 percent Solution of polymethyl acrylate in high-boiling gasoline used.

The aforementioned ingredients are ground in the following proportions using a mixing roller

Component parts by weight

Glass powder 20 -

Zinc powder .80 dispersant 12 "

By grinding, a paste is obtained that can be used with

an enamelled metal / screen printing process (silk screen process) on / plate as

Carrier layer is applied in a thickness of about 150 P.

'After application and drying, the coated carrier layer 1 hour to a maximum temperature of 600 to -700 C. After baking and cooling, the Heating layer connected at both ends with strips of aluminum foil as electrodes. ·

The surface of the resulting heating layer is 57 percent Solution of melamine j? Ormaldehyde resin etherified with butanol coated in a mixture of butanol and xylene, then

the coating is baked for 30 minutes at 150 ° C * " 'The thickness of the paint film is about 100 yes »The obtained Composite heating element is referred to as heating element A »

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Example. 1a

Amounts- /

By changing the / ratio of glass powder to zinc powder in the paste used in Example 1, those in Table I specified pastes 1 to 5 produced. ·. ·. ·

Table I.

Paste No. 1 2 3 4 5

Glass powder 30 40 50 '60 70

(Weight steep)

Zinc powder

(Weight-. 70. 60 5 O 40 JO parts) ·

Using pastes 1 to 5, according to Example 1 Composite heating elements manufactured.

Table II shows the resistance values and the contents metallic zinc for heating element A and heating elements Nos. 1 to 5. In Table II and below mean dip specified resistance values the specific resistance in

Ohms / 1 cm.

Table II

'' Heating element A No. Λ No. 2 No. 3 No. 4 No.

werr ^StandS "-5 100"& 0 1800 ₅ · ^ 1-10 ⁶ % by weight metal- nc cc. co ,,, -, / κ λο'lic zinc ^{7 & 65 52} ^ ^ - ¹³

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From Table II it can be seen that in practice heating elements with a glass powder content in the paste of more than 60 percent by weight and a metal content in the paste

approximately

of less than 20 percent by weight because of their relatively large resistance are less suitable.

Example 2

This example is carried out using ground quartz glass, silver powder and a mixture of JO parts by weight of ethyl cellulose, 70 parts by weight of Pineoil and 10 parts by weight of dioctyl phthalate as the organic dispersant. The aforementioned ingredients are ground in a mortar in the following proportions:.

Component · part by weight e

Glass powder 5 -

Silver powder 25

Dispersants - .10

The paste obtained in this way is applied with a squeegee to a ceramic plate as a carrier layer with a thickness of about 200 μm . After the paste has dried,

Corn paste is applied in the form of a tape at both ends of the dried paste film. The entire arrangement is then baked for 1 hour at a maximum temperature of 850 C. This gives a plate-shaped heating layer which has _L band-shaped electrodes at both ends. - _j

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On the surface of the heating layer obtained is using an epoxy adhesive, a polyvinyl chloride film with a thickness of 0.5 mm is stuck on. A plate-shaped one is obtained here Composite heating element referred to as heating element B.

Comparative play

Amounts,
The pastes 6 to 10 listed in Table III are produced by changing the / ratio of glass powder to silver X> powder in the paste used in Example 2.

Table III '

Paste no. 6th 7th 8th- 9 10 Glass powder
(Weight
parts) O 1 2 3 15th Silver powder
(Weight
parts) 30th 29 28 27 15th

Using pastes 6 to 10, according to Example 2 various composite heating elements are produced, but the Burning-in is carried out in a nitrogen atmosphere, utri an To avoid oxidation of the silver.

The Ivlderstandswerke and the contents of metallic silver of the Heinelements β and the heating elements made from pastes 6 to 10 are listed in Table IV.

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BAD ÖHKäiNAL

Table IV

Hot element B. No. 6 No.7 ' No. 8 No. 9 Wr. 10 Resistance
value 2500 0 0.5 0.7 1 Wt .-% metal
lish silver 20.3 100 97 93 90 50

From Table IV it can be seen that when the metal content is exceeded of 97 percent by weight, due to the very low resistance resulting therefrom, none that are advantageous in practice Heating elements can be manufactured.

example

In this example, a phosphate glass powder, a metal powder mixture made of tin, copper and silver

(2: 4: 4-) and as a dispersant a 40 per cent solution; from "Tufprene", a styrene-butadiene rubber in "Solvesso 150" (commercial mixed hydrocarbon solvent) - used as an organic dispersant.

> The aforementioned components are in a grinding device, in the following Quantity ratio ground:

U 0 9 8 2 67 0 8

BATH ORIGINAL

Ingredient parts by weight glass powder 15

Metal powder 85

Dispersant JO

The paste obtained in this way is applied by means of the screen printing process to a cardboard which has previously been coated with water-soluble dextrin. The applied paste is then allowed to air-dry. The dried print layer has a thickness of about 100 to 150 μm The transfer board (or transfer paper) obtained in this way has a flexible printing layer and is easy to store and handle.

A ceramic plate is used as the carrier layer. The print layer is transferred using the so-called water slip process. Here, the transfer board is immersed in water with the print layer facing up, the water dissolving the dextrin and thus removes the print layer from the base. The detached pressure layer * floats to the surface of the water and becomes there either taken up by the carrier layer itself or transferred to the carrier layer by means of tweezers.

The coated support layer thus obtained is heated to a tem-5 .. temperature of 600 to 700 ⁰ C. After cooling, the heating layer formed is connected to strip-shaped aluminum foils as electrodes.

Then, using a urethane adhesive, a

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Fiberglass mat connected to the surface of the heating layer. In this way, a plate-shaped composite heating element C is obtained which has a metal content (Me ) of 48 percent by weight and a resistance value of 30. This heating element has good storage capacity.

Example 4-

In this example an organic dispersant is used, by mixing 5 parts by weight of ethylene glycol and 20 G-svi-teDen of a hydroxyethyl cellulose solution with 100 parts by weight of a copolymer emulsion of butyl acrylate and butyl methacrylate has been produced in a molar ratio of 1: 3 '.

Zinc powder as metal powder and barium oxide powder as glass powder are used as further components.

The aforementioned ingredients are ground using a ball mill in the following proportions:

Component parts by weight

Zinc powder 90

Barium oxide 10

Dispersant 40

The paste obtained is applied to a release paper by means of a roller upset. The dried paste film has a thickness

_L of 50 left . .

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Metal plate / an enamelled / cylindrical shape serves as the carrier layer.

The release paper with the paste film is carefully adapted to the surrounding wall of the cylinder , the film remains. adhere under pressure. After the release paper is peeled off, the film adheres firmly to the outer wall. Electrically conductive paste is then applied in strips to the top and bottom of the film. Thereafter, the surface of the film is coated with a glaze. After drying, the Gunze is heated to a temperature of 700 to 800 ° C. This gives a vessel covered with a glaze, which is referred to as the Yerbund heating element D.

(Me ⁰ "

The heating element D has a metal content Y of 84 wt. ° β> and a resistance value of S-I / cm.

Claims

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Claims (12)

Claims .Jcompound heating elements, characterized by (I) an insulating carrier layer (11),
(II) a heating layer (l2) , ■ consisting of the stoving product from (Ha) one or more metals or from (lib)
one or more metals and glass, the components (Ha) and (lib) optionally containing metal oxides, as well as
(III) an insulating cover layer (13). 2. Composite heating elements according to claim 1, characterized in that that the metal content (Me °) in the heating layer (12) is 97 to 20 percent by weight amounts to. . . 3. Composite heating elements according to claim 1, characterized in that the carrier layer (11) consists of an enamelled metal plate
consists. . "' 4. Composite heating elements according to claim 1, characterized in that the cover layer (13) consists mainly of a melamine resin. 5. composite heating elements according to claim 1, characterized in that the cover layer (13) is porous. 6. A method for producing the composite heating elements according to claim 1 to 5, characterized in that a stoving mixture of (Ha) metal powder is applied to an insulating carrier layer (11) J 409826/0889 ver or (lib) metal powder and glass powder where (Ha) and. (lib) possibly contain metal oxides, with (lic) an organic one Applies dispersant and, after stoving, applies an insulating cover layer (13) to the resulting heating layer (12), or the top layer (13) is applied before the stoving stage and subjected to the stoving process together with the stoving mixture. 7. The method according to claim 6, characterized in that there is a film as the cover layer (13), optionally using Adhesives, applied directly to the heating layer (12) or the top layer (13) by coating with a paint and subsequent drying of the paint produces. 8. The method according to claim 7, characterized in that as Paint used a solution of a plastic. 9. The method according to claim B _f, characterized in that a melamine resin is used as the plastic. 10. The method according to claim 6, characterized in that first a film of the stoving mixture on a release paper or a peel-off cardboard, then peel off the film and transfer it to the carrier layer (11). . 11. The method according to claim 6, characterized in that one a stoving mixture is used, the 10 to 75 parts by weight of organic dispersant (lic) 100 parts by weight of a Geraisches from 0 to 60 percent by weight of glass powder and 100 to 40 409826/0889 contains weight percent metal powder. 12. The method according to claim 11, characterized in that one a dispersant used which is a synthetic resin or a polymeric substance with a glass transition temperature below 20 ° C contains. A0 9826/0889