GB754823A - Improvements in or relating to core binders - Google Patents

Abstract

A core-sand composition comprises a particulate mixture of sand and, as a binder therefor, a powder comprising a particulate water-soluble cellulose ether or ester and a resinous component which is a rosin and/or one or more thermosetting synthetic resins. The powder may consist of a mixture of particles of the cellulose derivative with particles of the resinous component and/or of composite particles in which the cellulose derivative and the resinous component are present together. The rosin may be tall oil rosin or a rosin derivative such as a saponified or esterified rosin, e.g. sodium, potassium or calcium rosinate, ammonium rosinate or a hydroxyalkyl rosinate. Rosincontaining substances such as tall oil, tall oil distillation products or tall oil pitch may also be employed. A plasticizer such as dibutyl or dioctyl phthalate, or a minor amount of a synthetic resin, such as polyvinyl acetate or a sulphamide resin, may be added, to prevent the rosin from causing the formation of fine dust during the grinding of the finished core binder. Examples of thermo-setting synthetic resins which may be used are urea-formaldehyde, phenol - formaldehyde, melamine, polyvinyl, sulphamide and acrylic resins. Synthetic resins which evolve formaldehyde when setting are preferred. Suitable cellulose ethers or esters include water-soluble methyl cellulose, ethyl cellulose, methyl ethyl cellulose, hydroxy-ethyl cellulose, methyl and ethyl hydroxy-ethyl cellulose, water-soluble salts of cellulose ether carboxylic acids, sodium salts of cellulose sulphuric acid esters, cyanoethyl cellulose and sulphoethyl cellulose. There may be added to the cellulose ether or ester a surface-active agent such as a salt of a higher fatty acid with an organic or inorganic base, an alkyl aryl sulphonate, a fatty alcohol or other alkyl sulphate, a sulphosuccinate; a polyalkylene glycol, a polyalkylene glycol ether of an aliphatic alcohol such as lauryl or cetyl alcohol or of a phenol such as butyl- or octyl-phenol, or a condensation product of a polyalkylene oxide with tall oil fatty acids, oleic acid or lauric acid. In an example 5 parts by weight of tall oil rosin partially saponified with soda to an acid number of 100 are melted, heated to about 120 DEG C., and 0.5 part of a polyvinyl acetate melting at 100-110 DEG C. is added; 4.5 parts of ethyl hydroxy-ethyl cellulose are moistened with 1.5 parts of 95 per cent ethyl alcohol, heated to 70 DEG C. and mechanically mixed with the resinous component. The fibrous product is allowed to cool and ground to a fine powder, which is homogenized in a drum mixer. The 10 parts of core binder thus obtained are mixed with 30 parts of water at 50-70 DEG C., and the resultant paste is allowed to swell for a few minutes, whereafter 5 to 8 litres of the core binder paste are mixed for 5-10 minutes in an edge-runner mill with 100 litres of sea sand having a moisture content of 2 per cent. Swedish Specification 112,609 is referred to.