DE2041274A1 - Process for improving the raw breaking strength of porcelain bodies - Google Patents

Description

WACKER-G HEM I E Munich, August 18, 1970

Dr.RÖ / .Sch * ^{UH I £ /} V

Wa 7004

"Process to improve the raw fracture strength of

• porcelain masses "

The present invention relates to improving the Raw breaking strength of porcelain bodies before the first firing. Stoneware masses should also be included under Porsellan masses be understood, i.e. all masses made of clays, quartz or quartz-containing minerals and fluxes (for example Calcite or feldspar) are produced. These mixtures show a before the first firing poor raw breaking strength. Therefore some of the moldings made from the masses break and it has to a sizeable reject can be expected.

A method has now been found for improving the raw breaking strength of porcelain masses. The method is characterized in that 0.5 to 5% by weight, preferably 1 to 3% by weight, based on the total mass, of polyvinyl acetate or copolymer of vinyl acetate and up to 50 % by weight of ethylenically unsaturated monomers are added to the porcelain mass before the first firing will.

The raw breaking strength is increased by the additives according to the invention by at least 20%, mostly by 30%, improved. In addition, the surface smoothness of the

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The moldings produced by the masses improved and the tendency for cracks to form is reduced.

The addition of the polymers to the porcelain masses takes place mostly in the form of dispersions or solutions. It has proven to be beneficial to use polyvinyl acetate or copolymers of vinyl acetate and ethylenically unsaturated monomers in the form of aqueous dispersions in which at least 80 % of the polymer particles have a size of 0.01 to 1 ^ i, preferably 0.1 to 0.5 ^ i to add. It is also possible to use dispersions which have been produced from redispersible powders.

It may be advantageous to add anti-foaming agents, for example based on silicone.

The copolymers can contain up to 50% by weight, preferably 20% by weight, of ethylenically unsaturated monomers. Examples of such conomers are vinyl esters of carboxylic acids with J> - Λ8 carbon atoms such as vinyl propionate, vinyl butyrate, vinyl 2-ethylhexoate, vinyl laurate, vinyl versataate (Versatic acid, trade name of Shell), vinyl halides such as vinyl chloride and vinylidene chloride; Acrylic - methacrylic, -Croton, - maleic and fumaric acid esters with mono- or dialcohols and ^oil-e ^ i ^{ne w} i ^e, for example, ethylene, propylene, isobutylene. Terpolymers such as vinyl acetate, vinyl laurate, vinyl chloride and graft polymers such as vinyl chloride grafted onto ethylene-vinyl acetate polymer emulsions are also suitable.

In some cases, the powders prepared from the dispersions can be added. It is there cheap to use redispersible powders that

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distribute well in the aqueous porcelain slip and don't clump.

The addition of copolymers is also preferred of vinyl acetate and up to 20% by weight, preferably 8% by weight, of unsaturated carboxylic acids in the form of aqueous Solution. Examples of unsaturated carboxylic acids are Acrylic, methacrylic, crotonic, maleic and fumaric acid into consideration. The aqueous solutions are through Dissolving the copolymer powder in a basic medium e.g. made in ammoniacal or alkaline solution * Polymer solutions with up to 20% by weight of solid substances can be used achieve and add.

The vinyl acetate polymers used according to the invention can be used as protective colloids, ionic and / or nonionic emulsifiers, which are usually produced by their production are present in such polymers, included.

Examples of protective colloids are polyvinyl alcohol, which optionally contains up to 40 mol percent acyl groups, in particular Contains acetyl groups, gelatin and cellulose derivatives, such as water-soluble methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxyethylmethyl cellulose and Hydroxypropyl cellulose, copolymers of maleic acid or its half-esters and styrene, also starch, dextrin derivatives, Polyvinyl pyrrolidone and polyacrylic acid amides.

Examples of ionic emulsifiers are anionic emulsifiers, such as alkali and ammonium salts of 8 to 18 carbon atoms containing straight-chain or branched monocarboxylic acids, e.g. sodium laurate or sodium stearate, of acidic esters of alkanols containing 9 to 18 carbon atoms and sulfuric acid, e.g. sodium lauryl sulfate,

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of secondary sulfonic acids of 10 to 18 carbon atoms ^ containing alkanes, of alkylarylsulfonic acids and of "sulfosuccinic acid dialkyl esters, partial phosphoric acid esters and cationic emulsifiers such as stearamidopropyldimethyl-ß-hydroxyethylammonium dihydrogen phosphate.

Examples of non-ionic emulsifiers are partial fatty acid esters of polyhydric alcohols such as sorbitol monopalmitate, Fatty alcohol sulfuric acid esters, partially etherified polyalcohols, block copolymers of ethylene oxide and propylene oxide e.g. from 10 moles of ethylene oxide and 30 moles of propylene oxide as well Reaction products of at least 4 moles of ethylene oxide and organic compounds containing active hydrogen atoms, i.e. substances that form gaseous during the reaction according to Zerewitinoff Form hydrogen with at least 8 carbon atoms, whereby these are fatty acids, alcohols, alkylphenols, Qxycarboxylic acids, carboxamides or primary or secondary Amines can act, e.g. reaction products of 1 mole of nonylphenol and 8 to 50 moles of ethylene oxide or of 1 mole of oleyl alcohol and 20 moles of ethylene oxide. Reaction products of alcohols and / or alkylphenols and ethylene oxide or propylene oxide are preferred. Mixtures of different classes of dispersants as well as different types within the above mentioned can be used Classes of dispersants are used.

The aqueous dispersions preferably contain 1 to 3% by weight, based on the polymer content, of anionic and / or cationic emulsifiers and are free of protective colloids.

The processes suitable for producing the additives according to the invention are generally known. However, the suitability of these substances for the purpose according to the invention is surprising.

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Example 1 .

To 10 kg porcelain slip with 70.8% dry residue

are 0.6 kg of 50% aqueous polyvinyl acetate dispersion ■

with a maximum particle size of 0.5 ~ p (SO % of the particles below 0.4 ^ j) added and mixed. After filtering off the water, the mass was dried and moldings were made from it. The roll breaking strength has improved by 25% compared to moldings that do not contain polyvinyl acetate.

Example 2

1 l of a 15% strength ammoniacal aqueous solution of a copolymer of 95% by weight of vinyl acetate and 5% by weight of crotonic acid was added to 5 kg of porcelain slip with 75 % dry residue. After mixing, suction was carried out on the porcelain groove. The mass was dried and moldings were made from it, which have a raw breaking strength improved by 30%.

Example 3 '

10 kg of porcelain slip with 68 % dry matter were mixed with a copolymer dispersion of ethylene vinyl acetate with 15% by weight of ethylene. The dispersion containing no protective colloid and 1.5 wt.% Nonionic emulsifier. The particle size is 80 % between 0.1 and 0.5 JU. The mass was treated as described in Example 1, and moldings were made from it. They show an approx. 35 % improved raw breaking strength.

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Claims (1)

Claim / 1 Process for improving the raw breaking strength of Porcelain mass, characterized in that the porcelain mass before the first firing 0.5 "to 5 wt.%, preferably 1 to 3% by weight, based on the total mass, of polyvinyl acetate or mixed polymers of vinyl acetate and up to 50% by weight Ethylenically unsaturated monomers are added. Claim 2 Process according to claim 1, characterized in that polyvinyl acetate or copolymers of vinyl acetate and ethylenically unsaturated monomers in the form of aqueous dispersions in which at least 80 % of the polymer particles are from 0.01 to 1 ^ μ, preferably 0.1 to 0.5 ) i exist, are added. claim Process according to claim 2, characterized in that the aqueous dispersion is 1 to 3% by weight, based on polymer content, anionic and / or cationic Contains emulsifiers and is free of protective colloids. Claim 4- Method according to claim 1, characterized that copolymers of vinyl acetate and up to 20% by weight, preferably up to 8% by weight, of unsaturated Carboxylic acids are admixed in aqueous solutions. 209809/0844