DE2328841A1 - Dry pressing ceramic powders esp. high-purity alumina - using powder particles coated with polyisobutylene soln - Google Patents

Abstract

The polyisobutylene (PIB) has an average mol. wt. obtd. by viscosity measurements of 95,000-5,000,000 (pref. 1.3.106), and is used either as a 1-10, pref. 2-6 wt.% soln. in an organic solvent, or an aq. dispersion, to coat the ceramic powder, which is then granulated to particle size 0.1-1.5mm (pref. 0.2-0.5mm), pressed to shape at 100-1500kp/cm2 and fired in air to remove the PIB. The powder which can be coated include BeO, BeTiO3, steatite, cordierite, silicate, titanate, ferrite, spinel, carbide, boride, nitride, silicide, sulphide, cermet, garnet, porcelain, refractories, or other ceramic powders. Pref. solvents for the PIB are toluene, benzene, isoctane, CCl4. The cold flow of the PIB helps pressing of ceramics for electronic use.

Description

DRY COMPRESSING PROCESS FOR THE FORMING OF ONE OR MORE COMPONENTS EXISTING CERAMIC POWDERS, PREFERABLY OF ALUMINUM OXYDE, object of the invention is a dry pressing process using polyisobutylene as a pre-aid for the formation of one or more components, such as 3e0, BeTiO3, steatite, Cordierite, silicate, titanate, ferrite, spinel, carbide, boride, nitride, silicide, sulfide, Cermet, existing garnet powders, fine porcelain mixes, refractory mixes or other ceramic powders, mainly for molding high purity Alumina powders for the production of aluminum oxide panels. These plates serve as carriers of high frequency electronic and electrotechnical components, preferably as a carrier of integrated Circuits.

One of the most common molding processes in ceramic production technology is the pressing of powders under high i) pressure. In this process the shape becomes of the irofilament body to be sintered. The dry pressing of a little Using binders, water or other solvents practically at all non-containing powders at room temperature is widely used. The advantage This method consists in that when eating little binder containing fit profile bodies of high dimensional accuracy can be produced, so are add Example according to the communication from J.E.

Fernstermaxcer, "Dimension control of dry-pressed electrical ceramics" in Bull. Ceram. Soc. 48/8. 1969 dimensional deviations of +1% achievable. To eat Higher pressure is required for material with a low binder content. When dry For example, aluminum oxide presses generally use 5-10% binder and a pressure of 500-1500 kgf / cm2 is used. Panels whose thickness is less than 1-2 mm, however, due to their low rigidity and fragility difficult to produce by pressing. For the production of such plates rather a thicker block pressed and this cut into plates, or else the panels are formed using another shaping process, for example by casting or calendering. Drilling the necessary holes requires subsequent processing, which is why these processes are less economical. The .iahl of the pressing auxiliaries is also very important. Regarding these auxiliaries there is an indispensable requirement that it be used as a binding plasticizer and lubricant do not work and, according to the standard, must be completely removable and combustible. There It is difficult to address all of these problems with a single excipient To meet, various auxiliary materials are used together, what the F @ brikationsgang however difficult.

The method according to British Patent No. 1,142,684 known, worked according to the injection molding process and beforehand dried polyethylene emulsion on the surface of the dust, then melted aluminum stearate or butyl stearate at a temperature of 93-190 ° C will. The amount of polyethylene is 8-12.0, that of plasticizing Stearate 11-22%. For further work-up, the mixture is used in the above named temperature a granulate is produced, in which the mixture through an extruder-like, Threads producing spray head is pressed, and the threads into small pieces be dismembered.

The granules formed in this way are fed into a machine that is based on the works the same way as the injection molding machines for plastic. In this machine the granulate is molded into injection molded articles at a temperature of 93-232 ° below I) processed. The disadvantage of this method is that injection molding involves high temperatures requires what is expensive. In order for the mass to become liquid, both auxiliary substances are used Applied in considerable amounts, which according to the porosity of the finished product the burnout increases. Such porous products are for electrical engineering purposes not suitable. The dimensional accuracy of the finished product in the case of smooth, A few millimeters thick profiles at most +2.0.

The one proposed in British Patent Specification No. 1 081 730, Auxiliary material for dry pressing consisting of 1-2% sodium lignosulphate and paraffin wax proved unsuitable for the purposes that led to the present invention, as that with the binder some brought the high-purity alkali, for example 99.99 % -ige Aluminum oxide extremely contaminated. When trying with organic solvents gave 6 ç paraffin, which from the well-known Gasoline solution has been applied, does not have the required raw strength; also claimed the dewaxing of the paraffinic moldings, which soften at 55 ° C., takes a long time Heat treatment.

When using "Buna gum" also dissolved in gasoline, on aluminum oxide an extraordinarily poor one, in the order of magnitude of 10-2 Loss factor measured, primarily due to the sodium content of the binder is due.

Another important aspect is the choice of the pressing pressure, since the sintering speed of profiles with greater bulk density is greater, their linear Shrinkage during firing is smaller than that of the profiles with less density Structure. It follows that the ceramic powder using a minimal Amount of binder must be pressed as tightly as possible, this is more brittle ceramic powders, such as aluminum oxide, are difficult to achieve, since the hardness of the diamond depends on the Mohs' hard scale 9, the hardness of the diamond (10) is therefore closer than, for example, that of otatite (7.5 degrees Mohs), of beryllium oxide (8 degrees Mohs) or magnesia (6 degrees Mohs). In the interest of a larger one Bulk density and better ventilation of the powder introduced into the press tool the powders treated with the auxiliary pressing agents are usually pre-pressed, then broken into granules again and shaped into the desired shape. In the Communication from ALCOA Product Data from October 1967 is for the purpose of better granulation In addition to the powder provided with a binder, a granulating aid is also proposed. The grain size of the granulate influences the quality of the ceramic: Coarse-grained granulate results in less smooth surfaces, but the air can use too fine PreBpulver difficult to remove the product is given a layer structure. The best compression is achieved with granules with a grain size of 0.2-0.6 mm.

In British Patent No. 1,057,235, dry pressing is used of A miniumoxide the use of 0.5-2% of a combination of stearic acid and Suggested fatty acid. On the basis of pressing tests, with the endlese substances through dry grinding applied to the surface of the powder could be determined that the greatest raw strength at the recommended pressure of 350 kp / cm2 However, the production of panels less than 15 2 mm thick was not obtained was possible because the plates separated in layers with increased pressure.

Even in pressing tests in which the pre-pressed bodies are granulated again an appropriate result could not be obtained.

In tests according to USP 3,377,176 with a ceramic powder of 0.3 2% oleic acid applied around the grain size as a binder and 270 kp / cm2 pressure Similar results were obtained.

The application disclosed in British Patent No. 1,027,939 of aqueous binder containing 10% ethylene glycol (Carbowax 4000) and At least 1000 kpiom2 pressure produced corundum, siliconized at high temperature showed a high loss factor and a low dielectric constant.

iLuf was able to establish these unsatisfactory results that in the production of high requirements, for electrotechnical and high-frequency purposes ceramic water-containing binder is not suitable is. The reason for this is the hydration of the over a large specific surface area available powder or the bad ones resulting from hydration Eristal properties.

The aim of the invention is to eliminate the listed defects and difficulties in devising an economical dry pressing process the ceramic powder, preferably aluminum oxide powder for electrical engineering, using a minimal amount and, if possible, a single amount removable binder without pre-pressing to any shape, for example drilled thin, suitable for supporting integrated circuits and angular profile bodies can be formed.

That which fulfills the enumerated conditions, the subject matter of the invention Formative dry pressing process To standardize BeO, BeTiO3, steatite, cordierite, silicate, Titanate, ferrite, spinel, carbide, boride, nitride, silicide, sulfide, cermet, garnet, fine porcelain, mixtures of refractory materials or other ceramic materials Powder, preferably aluminum oxide, can be characterized in that as Compression aid polyisobutylene with an average determined by viscosity measurements Molecular weight of 95,000-5,000,000, preferably 1,300,000-4,700,000 in the form one prepared with an organic solvent, 1-10% by weight, preferably 2-6% strength by weight solution or in the form of an aqueous dispersion, preferably through Drying applied to the surface of the powder with the auxiliary molding agent provided powder preferably by means of vibration granulation to granules of the grain size 0.1-1.5 mm, preferably 0.2-0.5 mm, the granules processed under a pressure of 100-1500 kg / cm2, preferably 300-600 kg / cm2 and the polyisobutylene from the crude product by firing in an oxidizing atmosphere, for example on the Air, is removed.

The method according to the invention and the use of said binder cannot be separated from each other. With the help of the procedure, the cold flow properties of polyisobutylene used. By drying the polyisobutylene from the solvent on the Surface of the ceramic powder particles - being the solution medium wets the surface of the powder - an elastic film is formed, which during the pressing process ensures that the particles roll and slide on one another and at the same time acts as a plasticizing and binding agent.

The ability of polyisobutylene to flow cold is also dated point of view of the permanent deformation and the high degree of dimensional stability of the pressed product of importance.

The other properties of the binder also influence this Product cheap; the saturated chain molecules make it resistant to aging, causes resistance to atmospheric oxygen, ozone and other substances. Metal oxides harmful from the point of view of ceramic production, for example stabilizers, are not included in the binder. The polyisobutylene is pressed dry fine ceramics in aliphatic and / or aromatic and / or chlorinated hydrocarbons, for example dissolved in toluene, gasoline, isooctane, carbon tetrachloride, to dryness press less demanding ceramics in the form of an aqueous dispersion.

It was found through experiments that the polyisobutylene It can be used as the sole pressing aid, but also in combination with in organic Solution with soluble binders and additives, for example pareffins, Wax, polypropylene, as well as with water-soluble additives such as rolyvinyl alcohol, Polyethylene glycol, ethyl cellulose or mixtures thereof have an advantageous effect retains.

Werner was found that you ch in the appropriate way dispersed or dissolved polyisobutylene also has effects, which cannot be achieved with the known binders or their mixtures are. Such an advantage is, for example, the possibility of denser grouting, whereby the sintering speed grows significantly.

Experiments have shown that when using polyisobutylene Products pressed from aluminum oxide as a pressing aid were 0.18 g / cm3 denser As those under the same conditions with ethylene glycol or paraffin in the dry pressing process manufactured.

The molecular weights given in the working examples were determined by viscosity measurements.

Example 1 0.1% BeO-Y2O3 sintered oxide powder with 1000 g 99.8-99.9 Grind% A1203 powder containing a maximum of 0.01% alkalis, which over has a grain size of 0.5-1 / µm and was calcined with 0.1% MgO.

11 g of tolyisobutylene with an average molecular weight of 1,3,106 and 45 g of polyisobutylene with an average molecular weight of 4.7.106 are dissolved in 1000 g of analytically pure toluene. The 5.3% solution after the polyisobutylene has completely dissolved, through a sieve with the mesh size 0.05 x 0.05mm sieved. 752 g of this solution are added to the one described above, Powder mixture with a specific surface area of 5-7 m2 / g was added and the whole thing intimately mixed.

The resulting thick cup is placed in a suction device Mixing chamber introduced and mixed again every hour. After 12 hours it will the mass is brought into a drying cabinet equipped with a suction device and dried at 50-60 ° C. After complete drying, the material is cooled down and sieved through a sieve with a mesh size of 0.5 x 0.5 mm.

The sieved powder containing approximately 5% polyisobutylene is compacted by vibratory shaking for 12 hours. After that it will be again sifted through a sieve with a mesh size of 0.5 x 0.5 mm, the granules falling through are collected. With what remained powder becomes the process compressing, sieving and reading out repeatedly. The granulate obtained is under Based on a linear shrinkage of 12.5% at a pressure of 500-600 kp / cm2 to 25 x 25 x 2 mm plates, with the 'height of the filling opening should be 2-3 times the press thickness. The density of the pressed profiles is 2.52-2.58 g / cm3. The approximately 5% binder is maintained by holding for one hour a temperature of at least 800 ° C in an oxidizing, for example in air atmosphere burned out and the pre-burned profiles in a known manner by 30-60 minute heat treatment at 1740 0C. The specific weight of the finished Plates are 3.94-3.96 g / cm3, their loss factor 2-5. 10-4.

Example 2 To 975 g of powder of average particle size of 1-2 µm, a specific surface of 2-4 m2 / g and an aluminum oxide content of 99.55%, 25 g of metal oxide additives with a particle size of 1-2 / µm are used Example frit with the composition ZrO2 + CeO2 + SiO2, given and both powders together grind. Milling is continued until the millbase has a particle size of 70-80 l has less than 2 Xux. 56 g of polyisobutylene with an average molecular weight of 4.7. 106 are dissolved in 1000 g of analytically pure toluene and the 5.3% strength obtained Sieve the solution through a sieve with a mesh size of 0.05 x 0.05 mm. 470 g of the thus obtained Auxiliaries are added to the millbase, as described in Example 1 below worked. The granules, which contain approximately 2.5% polyisobutylene, are used in one Pressure of 300-800 kp / cm2, preferably 600 kp / cm2 for plates of the size 25 x 25 x 0.8 mm pressed. The density of the pressed profiles is 2.42-2.46 g / cm3. That obtained crude product is for one hour at a temperature of 1200 0C in oxidizing, for example in air atmosphere maintained, deburred after cooling and then sintered by a known method. The specific weight of the product is 3.86 g / cm3, its loss factor is less than 6. 10 4.

Example 3 To 1000 g of 85-95% Al203 with an average Particle size of 1-5 / µm and a specific surface of 1-2 m2 / g is the aqueous, approximately 60% suspension of 50 g of polyisobutylene with the average Molecular weight of 9.5, 104 or 3.8. 105 given.

The fabrics are ground together for 4-8 hours.

After the number, the water is at 50-60 0C by stirring or spray drying removed the powder obtained in this way, which is approximately 3% polyisobutylene contains, processed into granules according to Example 1 and pressed.

The pressure is for profiles with a thickness of 0.6 - 1 mm 300 kp / cm2, for profiles with greater thickness, depending on the shape and size a pressure of 800-1500 kp / cm2 was applied to the profile. The raw profiles obtained from the Density 2.3 g / cm3 are burned out in an oxidizing atmosphere, for example in air and then sintered at 1650 ° C in a known manner. The specific weight of the product is 3.75 - 3.85 g / cm3.

Example 4 For the production of a ceramic dielectric 1000 g of a 90% barium titanate powder with a grain size of 0.5-15 µm 752 g of the polyisobutylene solution described in Example 1 and the whole thing stirred with a mechanical stirrer for 2 wounds. Then the mixture is in Porcelain or aluminum bowls with a large surface are poured and the solvent removed under strong suction. If necessary, the removal of the solvent Accelerated in a drying cabinet with a suction device at 50-60 ° C. The completely dried material is passed through a mesh size sieve Sieved 0.5 x 0.5 mm.

The barium titanate, which contains about 5, J binder, is compacted by vibratory shaking for 8-10 hours, again through a sieve the mesh size 0.5 x 0.5 mm sieved and then pressed. For the production of panels 1-2 mm thick, a press with a movable punch is sufficient, with the specific Pressure is 200-400 kp / cm2.

For the production of profiles with a thickness of more than 2 mm a press acting on both sides is necessary, the pressure applied may be lower be than the one given above. The pressed profiles are in the air at 800-900 ° C pre-fired, deburred after cooling and then the final one in a familiar journey subject to bintering.

Example 5 For the production of ferrite or garnet for electrotechnical Purposes are to 1000 g of ceramic powder, which to 90-100 (, J from particles of under 1 In addition, 800-1000 g of the polyisobutylene solution described in Example 1 are added. The mixture is ground in a ball mill for 4-8 hours, then the Dispersion consisting of binding agent and ceramic powder, prepared at room temperature, then dried at 50-60 ° C. with strong suction. Further processing takes place as described in example 1. The pressing pressure depends on the type of preparation of the ceramic Powder and is 500-700 kp, 'cm2.

The pressed profile bodies are burned out in an oxidizing atmosphere, then deburred and, for example in an oxidizing atmosphere, using known methods sintered.

Example 6 For the production of steatite, cordierite or forsterite For electrotechnical purposes, the prepared basic material is based on that in the example 3 described manner mixed with aqueous polyisobutylene emulsion ceramic powder on steatite, cordierite or Forsterite base, which consists of 80-90% of particles 2-4 / µm in size, with 50 g of approximately Grind the polyisobutylene emulsion containing 60% dry matter for 4-8 hours. After grinding, the water is spray dried, in simpler cases removed from the mass by evaporation with stirring. The material obtained will dried at 80 ° C for 4 hours. That dehydrated by spray drying Material can be pressed without further treatment, while that by evaporation sifted dried powder through a sieve of mesh size 0.4 x 0.4 mm, 8-12 hours long compacted by vibration shaking, again through the sieve with the mesh size 0.4 x 0.4 mm is sieved and then pressed. The specific pressure is in the case of spray-dried material 250-400 kp / cm2, in the case of the powder dried by evaporation, 300-500 kp / cm2.

The pressed profile bodies are pre-burnt in the air and deburred and finally sintered in a known manner.

The loss factors of the finished profile body amount to one Frequency of 1 megahertz for steatite about 6-12. 10-4, for cordierite 8-13. 10-4 and for forsterite 3-8. 10-4. The values vary greatly from the preparation of the Basic material, its chemical purity, etc.

away.

Example 7 For the production of profile bodies for electrotechnical or thermal purposes are 1000 g beryllium oxide, magnesium spinel or Titanium dioxide, 90-100% of which consists of particles 0.5-1.5 µm in size, 752-800 g of one from 1000 g of reagent grade toluene and 56 g of polyisobutylene of the average Molecular weight of 2.7. 106 prepared in the manner described in Example 1 given a sieved solution. The mixture is ball milled for 2-5 hours ground, after which the dispersion containing organic solvent is made under dried with strong suction. The material is passed through a sieve with the mesh size sieved from 0.5 x 0.5 mm and then further dried at 120 ° C. for another 3-4 hours.

After drying, the material is granulated, with a vibratory compaction is used, the duration of which is 10 hours for beryllium oxide and 10 hours for magnesium spinel and titanium dioxide is 12 hours, the powder is through before dry pressing sieved a sieve with a mesh size of 0.3 x 0.3 mm. The pressure is for beryllium oxide 400-650 kp / cm2, for magnesium spinel and titanium dioxide 50-700 kp / cm2.

For profiles with a thickness of 5-20 mm, double the specified Press prints estimated. The pressed profile bodies are in an oxidizing atmosphere Pre-fired at 900-1200 ° C, deburred, possibly mechanically processed and finally sintered in the known manner.

Example 8 11 g of polyisobutylene are added to 1000 g of analytically pure toluene the average molecular weight 9.5 20 g polyisobutylene of the average Molecular weight 3.8. 105 and 32 g of polyisobutylene of average molecular weight 2.7. 106 dissolved. after the polyisobutylene has completely dissolved, is sieved the 5.9% solution through a sieve with a mesh size of 0.05 x 0.05 mm. To the Production of tight pressed bodies intended for thermal engineering purposes Carbide, boride, mitride or silicide base are based on the surface of 1000 g of the corresponding base material, which consists of 70-80% particles of size 3-5 / um consists, 500-600 g of the described polyisobutylene solution dried up. in the Further work is carried out as indicated in Example 1. From the thickness of the profiles The pressure for oilicium carbide was 600-800 kp / cm2, for titanium boride 800-1200 kp / cm2.

For the production of porous profile bodies, the fine-grained Base material depending on the desired porosity 10-40 percent by volume a burn-out Component, for example graphite, naphthalene or polyethylene powder added. At the same time, preferably with a mechanical one Stirrer, in the manner described in Example 3, 50-110 g of polyisobutylene in the form a 60% aqueous emulsion mixed. After stirring for 6-20 hours, the Material dried on the tracks described in Example 3. To the one with binders provided, dry powder can, if the application of aluminum oxide is necessary is, by grinding or melting, aluminum stearate in an amount of 2-6 % By weight are given.

The vibration compaction and pressing are based on the example 3 made manner described. The type and amount of pressure applied is strong depends on the burn-out component and must be determined on a case-by-case basis but approximately the same as the pressure values given in the first part of this example. The pressed profile bodies are pre-burned in an oxidizing atmosphere, with the upper temperature limit is 900-1460 oC. In the further the product is known according to Procedures dealt with.

Example 9 For the production of cermet for structural purposes, a Mixture of metal powder, for example chromium, which is 90-100 * io from 4-8 µm in size Particle consists, and a ceramic powder, for example aluminum oxide, its 90% particle size is about 1 / µm with a 60% aqueous polyisobutylene emulsion mill in an aqueous medium. The amount of chromium is 30% by weight the aluminum oxide is 70% by weight, the dry content of polyisobutylene is 10% by weight. The latter is made by grinding and drying 100 g of an aqueous emulsion to 1000 g of metal-ceramic powder. In the following, according to the example 3 described technology worked. It is ground for 8-15 hours, then by means of Spray drying or evaporation dried.

The material is passed through a sieve with a wire spacing from Sifted 0.8-1.0 mm, then compacted by vibration for 10-14 hours. That Compressed Prod kt is subjected to a sieve fractionation, the fraction of Grain size 0.7-1.2 mm is collected. The granulated powder is at the temperature of the tinmer pressed, the specific pressure depending on the type of cermet and the strength of the Profile body is depending on 800-1500 kp / cm2. The binder will be at the lowest possible temperature burned out in an oxidizing flame, then the profile body sintered in a known journey in a neutral or slightly acidic medium.

For pressing cermet, it is advisable to use a double-sided press to use.

The PreL method according to the invention using polyisobutylene In contrast to the previously known processes for pressing, it is harder and harder less hard ceramic powder equally applicable. The pre-auxiliary polyisobutylene -IEt easy to process with any ceramic powder. The solution or the aqueous one Dispersion of polyisobutylene is open to others, for example with paraffins, Wax emulsions, stearic acid, ceresin, etc. compatible. The accompanying substances influence the applicability of polyisobutylene is not. That in less tight on the surface The polyisobutylene contained in the powder is guaranteed even without pre-pressing, that the particles of the powder adhere well to one another and, at the same time, that the powder does not adhere to the walls of the press tool.

The disadvantageous property of polyisobutylene for other areas of application, to flow cold is of crucial importance for the method according to the invention. this property means that the ceramic masses are relatively low Compression pressure easily malleable, permanent deformation already occurs at room temperature, and products with high bulk strength and bulk density are obtained. The pressed ones Profile bodies have a certain elasticity, by virtue of them in the case of Zui, for example, during drying or placing in the kiln occurring smaller mechanical forces, allow example impacts, without Resist deformation. They are tear and break resistant, which makes the fabrication practical Works without waste and can be automated. Reached by the leg presses high bulk density becomes the rate of compaction occurring during sintering increased, which, in addition to the advantages mentioned, is a significant reduction in the Manufacturing costs jit itself.

With the method according to the invention, thin- and thick-walled plates that serve as supports for integrated circuits, transistor supports and caps are molded. The method is also suitable for production from structural elements for heat and electrical engineering, to the manufacture of very hard ones and abrasion-resistant profile bodies, of grindstones, cutting edges, insulating elements of antennas, of capacitor dielectric, of norial, miniature and cermet potentiometer bodies, Transmitter tube ceramics, also for shaping BeO, Al2O3, BaTiO3, steatite, cordierite, Silicate, titanate, perite, spinel, carbide, boride, nitride, silicide, sulfide, cermet, Garnet, fine porcelain mixes as well as for further processing, for example Small amounts of high-frequency forming before turning Ceramic materials containing binding agents made from refractory materials or their Mix.

Claims (4)

Claims 1. Dry pressing process for the formation of one or more 1 Components of existing powders, the BeO, BeTiO3, steatite, cordierite, silicate, titanate, Contains ferrite, spinel, carbide, boride, nitride, silicide, sulfide, cermet, garnet as well as fine porcelain mixtures, mixtures of refractory materials or other ceramic powders, in particular for the formation of aluminum oxide powder, d u r.c h e k e n n n z e i c h n e t that polyisobutylene as a pressing aid with a viscosity measurements certain average molecular weight of 95,000 - 5,000,000 in the form of a 1-10% strength by weight, preferably 2-6%, prepared with organic solvent Solid solutions or in the form of an aqueous dispersion, preferably by drying applied to the surface of the powder provided with the auxiliary molding agent Powder processed into granules with a grain size of 0.1-1.5 mm, the granules under one Pressure of 100-1500 kp / cm2 molded and the polyisobutylene from the raw product through Burning in an oxidizing atmosphere, preferably in air, is removed. 6. The method according to claim 1, characterized in that the polyisobutylene in aliphatic and / or aromatic among chlorinated hydrocarbons, preferably dissolved in toluene, gasoline, isooctane, carbon tetrachloride or to one aqueous dispersion is processed. 3. The method according to claim 1, characterized in that the molecular weight of the polyisobutylene is between 1,300,000 and 1,4,700,000. 4. The method according to claim 1, characterized in that the with the powder provided with the auxiliary molding agent processed into granules with a grain size of 0.2 to 0.5 mm will.