DE2820721A1 - Plasticising ceramic masses with microbial polysaccharide - for higher plasticity and dry flexural strength - Google Patents

Abstract

The plasticity and/or dry flexural strength of ceramic masses are improved by using as plasticizer a water-soluble or colloidally-soluble microbial polysaccharide (I) of mean mol. wt. >2 x 105, at 0.005-0.5% based on the material to be plasticized. Pref. (I) is Xanthomonas polysaccharide and may be added to one component of the mixt. of raw materials, or to a complete blend either as slurry, partly-dewatered material or as dry substance. Esp. it is added to a ceramic spray-granulate before or during conversion of the granulate to a processable form. Used. esp. for porcelain and earthenware mfr. No undesirable materials are produced from (I) during sintering and starting materials of poor plasticity can now be used.

Description

Title of the invention

Process for increasing plasticity (malleability) and / or dry flexural strength ceramic masses Field of application of the invention The invention relates to a method to improve the processing properties of ceramic masses, in particular to increase the plasticity (malleability) (in the following are malleability and plasticity used synonymously) and / or dry flexural strength and can be used especially with conventional Use offset for hard, electrical, sanitary ware and earthenware.

Characteristics of the known technical solutions for manufacture The basic materials of ceramic goods are kaolins, clays, feldspars, and sands processed into pourable, plastic or molding compounds. For the shaping of the plastic masses are sufficient plasticity and dry flexural strength, for crack-free deformation and fast drying as well as for further treatment To ensure the desired strength is a prerequisite.

In general, the plasticity of ceramic bodies is due to the use highly plastic kaolins and / or clays are guaranteed, but these are becoming increasingly scarce, In addition, highly plastic kaolins and / or clays are usually rich in pollutants, i.e. a high proportion of coloring oxides is introduced into the backfill. To the Manufacturing products with a high degree of whiteness is therefore not feasible.

There are already many suggestions in the literature for increasing plasticity have been made, see e.g. F. Singer, Industrielle Keramik, Bd. 1, Berlin - Göttingen -Heidelberg - New York: Springer, 1964, p. 155 - 157, whereby the raw materials resp. Appropriate substances are added to the masses.

Additions of hydrophobic substances, such as e.g.

Emulsions or suspensions of dispersible plastics, also in Combination with hydrophilic, soluble components (equivalent e.g. DT-OS 1 927 019) Disadvantage that they do not meet the requirements of a mass circuit because they suffer irreversible changes on drying, emulsions also show when Use in casting compounds due to the differences in density, cream phenomena or

agglomerations can occur because the stability areas of Emulsion and casting compound usually do not match.

The use of water-soluble or colloid-soluble substances, such as F starch, starch derivatives (cf. z, B, DT-AS 1 098 430), casein (SU - P 98 285), esters of macromolecular uronic acid esters (GB 824 143) permitted if one is selected corresponding concentration to increase the plasticity of ceramic masses, however, the amounts of these compounds used are so high that the production a casting compound with the known liquefiers (soda, water glass, derived substances, Humic acid derivatives) due to the thickening effect of these substances is possible. A drastic reduction in the proportion of plasticizer is possible the production of a casting compound, however, there is then no improvement in plasticity more verifiable. For example, there was a significant increase in plasticity for cold-soluble starch detectable at a use concentration of 1%, while the production of Casting compound possible with a concentration of the same strength of less than 0.05% is, but an increase in plasticity is then no longer detectable.

Low-molecular substances as plasticizers are the decisive ones Disadvantage that they are with the filtrate water leave their place of work, because they can be filtered and penetrate into mold materials and their function affect.

Object of the invention There is thus no known method of ceramic Manufacture masses by adding suitable substances in their plastic Properties are significantly improved and with the same content of these substances optionally according to the usual processes, such as extrusion, injection molding, pressing, Turning, casting, workable. Also, it is currently not possible already at the raw material manufacturer in the course of the preparation process the kaolins and / or To treat clays with substances and to move, since then the amount used the Determines the processing method.

Statement of the essence of the invention It has been found possible to do so is, the plasticity and / or dry flexural strength of ceramic masses through addition of high molecular weight water-soluble microbial polysaccharides, especially Xanthomonas polysaccharides, and mixtures thereof, the use concentration of the same so it is chosen that the usual methods of shaping and further processing are optional Can find application. With the additive found, it is still possible to use raw materials already in the preparation stage by adding the above-mentioned substances to plasticize and to bring on the market without the kind of further ceramic To negatively influence the use. This also makes it possible to produce coarse-grained, low-pollutant To make kaolins and / or clays generally ceramically processable, as well as those for the material properties of the products, such as optical properties (whiteness, Transparency), mechanical strength and tendency to deform during sintering, cheapest raw materials regardless of their original processing properties, the Plasticization of kaolins / clays or ceramic masses takes place according to the invention in that the aqueous solutions of the microbial polysaccharides in suspensions or in partially dehydrated suspensions of kaolins and / or clays respectively ceramic masses are introduced by mixing. These so plasticized Substances can then be further processed accordingly, in particular the following are Process steps without noticeable influence on the plasticization: dewatering of Suspensions on filter presses, drying up to a maximum of 1200C, dry and wet grinding of the plasticized material.

In the case of raw materials or masses that are dewatered by spray drying the plasticizers have to be added after this stage, only a part will be the offset raw materials or the mass plasticized according to the above process, so can this part before further processing as a suspension, as partially dehydrated Material or as a dry substance can be incorporated into the overall backfill.

The amount required to achieve plasticization the above substances is surprisingly low and is below 0.5 percent by mass, based on the dry mass of ceramic substance, in general are already 0.01 to 0.05% is sufficient. With these small amounts used, no harmful effects occur Influences due to the burning out of the substances introduced during the sintering of the substances treated masses on. Are the raw materials plasticized with the above substances or masses stored in a moist state for a long time, it is advisable to to prevent biodegradation antibacterial and antifungal Adding additives.

Exemplary embodiment The invention is based on the following exemplary embodiments explained in more detail: 1. A suspension with 45 0 water content of a little plastic, Coarse-grained but low-pollutant kaolin was made with 0.1 jó of a Xanthomonas polysaccharide based on its dry matter.

The Xanthomonas polysaccharide had an average molecular weight of 1.2 Million daltons.

After a contact time of 3 hours, the kaolin plasticized in this way was pressed out. The quotient was used as the degree of plasticization for the partially dehydrated kaolin determined from the tensile and shear strength of a strand of material.

The test results are summarized in the following overview: Kaolin plasticity index for the same processing consistency. Less plastic kaolin a) without addition 0.047 b) with 0.1 S Xanthomonas polysaccharide 0.069 highly plastic Kaolin Zettlitz Ia (for comparison) 0.070 2. It was made in a hard-paste porcelain batch a highly plastic kaolin exchanged for a less plastic kaolin in such a way, that the rational analysis of the offset did not change, whereby for the hochplasti between kaolin, the less plastic kaolin and non-plastic hard materials in the offset were recorded.

For the plasticization of the less plastic kaolin Offset 0.014 t> '% of a Xanthomonas polysaccharide was obtained applied to dry matter. The procedure was once so that the total offset was dated in suspension before pressing on filter presses and the offset when wet was used, on the other hand it was little plastic kaolin doped with 0.1% Xanthomonas polysaccharide in suspension, was then dried and stored for 2 months, in the dried state used in the production of offset.

The overview shows the plasticity indicators for a screw-in mass as well as some characteristics for the casting compounds produced from the above batches cited.

Offset 1 2 3 4 Offset with highly plastic kaolin 0.039 4.2 180 28 Backing with a little plastic kaolin 0.027 4.2 170 27 Backing with 0.014% Xanthomonas polysaccharide a) total mass doped 0.044 3.2 220 -b) little plastic kaolin doped separately 0.042 3.6 260 32 The meanings are: Column 1: Plasticity numbers Column 2: Body thickness after 10 minutes in mm column 3: Apparent toughness in cP at a shear rate of 170 s 1 and a slip density of 1.68 g / cm3 Column 4: Dry flexural strength in kp / cm2

Claims (2)

Invention claim 1. A method for increasing the plasticity and / or Dry flexural strength of ceramic masses, characterized in that as a plasticizer soluble in water or colloid-soluble, microbial polysaccharides with medium molecular weights greater than 200,000 and in proportions by mass of 0.005 to 0.5 i, based on the to plasticizing material. 2. The method according to item 1, characterized in that as a microbial Polysaccharide preferably Xanthomonas polysaccharides are used. 3, the method according to item 1 to 2, characterized in that the plasticizer is added either to the entire mass displacement or to individual components and that the raw materials treated with the plasticizer are added to the total batch as a slurry, be supplied as partially dehydrated material or as a dried substance. 4, method according to items 1 to 3, characterized in that the addition of the plasticizer to a ceramic spray granulate before or during the transfer the granulate is processed into the processing form, 5, procedure according to points 1 to 4, characterized in that low-pollutant raw materials with low plasticity and Raw breaking strength used for the production of technologically processable masses will.