Patent GB-966624-A (GB)
Title: Siliceous pigments and their production
IPC: C08K3/34
Filed: 1962-03-20
Abstract: A finely divided pigment containing at least 50% SiO2 is composed of porous flocs of ultimate particles, said particles having an average diameter below 0.5 microns and being in the form of an outer shell structure of water-insoluble siliceous material enclosing an interior volume which is free of water-insoluble siliceous material and has a lower optical density than the shell which is discontinuous and has a thickness between 1/20 and 1/4 of the diameter of the particle, i.e. from 0.001 to 0.15 microns. The pigments contain one or more metals or metal oxides, e.g. CaO in amount 3-15%, and can be represented as MO(SiO2)n where n is from 5-25 including fractional values. Other metals, e.g. Fe, Al, Na may be present in amount 0.1-6%. The pigments are prepared by inducing precipitation (in the presence of a slurry of a finely-divided water-insoluble salt) of a water insoluble siliceous material from an aqueous solution which itself would precipitate siliceous material on standing. The water insoluble salt which may be CaCO3 of particle size 0.01 to 0.25 microns may be formed in situ by adding Na2CO3 to CaCl2 or other source of CO3=ions to another soluble calcium salt, is then removed by converting to a water soluble salt by adding HCI.  The precipitation may be induced by a water-soluble metal salt, e.g. CaCl2, NaCl, BaCl2, SrCl2, ZnCl2, CaBr2, NaI or metal salts of strong acids, e.g. Ca(NO3)2, NaNO3 or Na2SO4. The precipitation which may be at atmospheric sub or superatmospheric pressure is effected by adding CaCl2 to an alkali metal silicate solution having a mol. ratio of SiO2 to metal oxide greater than that of water-soluble alkali metal silicates, usually greater than 6.  The silicate may be Na2SiO3 having a mol. ratio of 2-4 or Li2SiO3, NaKSiO3 of ratio 1-5.  To the silicate solution acid, e.g. HCl, H2SO4, HNO3, CH3CO2H, H2SO3, H3PO4, H2CO3 or their anhydrides, or NaHCO3, KHCO3, NaHSO3 or Na2SO3 and HCl may be added under conditions of high turbulence preferably at 0-40 DEG  C., and the CaCl2 is added simultaneously or just after neutralization. After precipitation, acid, e.g. HCl is added to the slurry and agitated, followed by alkali, e.g. NaOH, heated, filtered, dried and milled.  The streams of the three solutions may be fed into a precipitation tank at points equidistant from the wall and the axis of the propeller, e.g. partly neutralized Na2SiO3 may be added at a position 180 degrees from the point where the CaCl2 is added and 90 degrees from where the Na2CO3 is added. Alternatively the Na2CO3 and CaCl2 are added adjacent one another and spaced 180 degrees from where the aqueous silicate solution was added. The pigments may be compounded with GR-S-1000 rubber, S, ZnO, phenylbeta naphthylamine, dibenzothioxyl disulphide, tetramethyl thiuram disulphide, coumarin-indene resin, diethylene glycel and cured at 280 DEG  F. Paper is prepared by adding to a beaten pulp containing, e.g. 0.5-5% pigment, sufficient Al2(SO4)3.18H2O to adjust pH to 5 and sheeting the product.  TiO2 may be added. Specification 942,263 is referred to.ALSO:A rubber composition comprises GR-S-1000 rubber and a pigment containing at least 50% SiO2 and composed of porous flocs of ultimate particles, said particles having an average diameter below 0.5 microns and being in the form of an outer shell structure of siliccous material enclosing an interior volume.  The shell has a thickness between 1/20 and 1/4 of the diameter of the particle i.e. from 0.001 to 0.15 microns.  The pigment may contain one or more metals or metal oxides e.g. CaO in amount 3-15% or Al, Fe or Na in amount 0.1-6%. Specification 942,263 is referred to.ALSO:A finely divided pigment containing at least 50% SiO2 is composed of porous flocs of ultimate particles, said particles having an average diameter below 0.5 microns and being in the form of an outer shell structure of water-insoluble silicious material enclosing an interior volume which is free of water-insoluble siliceous material and has a lower optical density than the shell which is discontinuous and has a thickness between 1/20 and 1/4 of the diameter of the particle i.e. from 0.001 to 0.15 microns. The pigments contain one or more metal oxides e.g. CaO in amount 3-15% and can be represented by the formula MO(SiO2)n, where n is from 5-25 including fractional values.  Other metals, e.g. Al, Na Fe may be present in amount 0.1-6%.  The pigments are prepared by inducing precipitation (in the presence of a slurry of a finely divided water-insoluble salt) of a water-insoluble siliceous material from an aqueous solution which itself would precipitate siliceous material on starting. The water-insoluble salt which may be CaCO3 of particle size 0.01 to 0.25 microns may be formed in situ by adding Na2CO3 or other source of CO3 ions to CaCl2 or other soluble calcium salt is then removed by adding HCl. The precipitation may be induced by a water-soluble metal salt, e.g. CaCl2 NaCl BaCl2, SrCl2, ZnCl2, CaBr2, NaI or metal salts of strong acids, e.g. Ca(NO3)2, NaNO3 or Na2SO4.  The precipitation which may be at atmospheric, sub- or super-atmospheric pressure is effected by adding CaCl2 to an alkali metal silicate solution having a mole ratio of SiO2 to metal oxide greater than that of water-soluble alkali metal silicates, usually greater than 6.  The silicate may be Na2SiO3 having a mole ratio of 2-4, or Li2SiO3, NaKSiO3 of ratio 1-5.  To the silicate solution acid, e.g. HCl, H2SO4, HNO3, CH3CO2H H2SO3, H3PO4, H2CO3 or their anhydrides, or NaHCO3, KHCO3, NaHSO3 or Na2SO3 and HCl may be added under conditions of high turbulence, preferably at 0-40 DEG  C., and the CaCl2 is added simultaneously or just after neutralization.  After precipitation, acid, e.g. HCl, is added to the slurry followed by agitation and alkali, e.g. NaOH, heated, filtered, dried and milled.  Specification 942,263 is referred to.ALSO:Paper is prepared by adding 0.5-5% of a siliceous pigment to an aqueous pulp slurry followed by sufficient Al2(SO4)3. 18H2O to adjust the pH to 5 and sheeting on a Nobel-Wood machine.  The pigment contains at least 50% S1O2 and is composed of porous flocs of ultimate particles, said particles having an average diameter below 0.5 micron and being in the form of an outer shell structure of silicous material enclosing an interior volume.  The shell which is discontinuous has a thickness between 1/20 and 1/4 of the diameter of the particle i.e. from 0.001 to 0.15 micron. The pigment contains one or more metals or metal oxides e.g. CaO in amount 3-15%, and other metals e.g. Fe, Al, Na may be present in amount 0.1-6%.  The pigment enhances the opacity and brightness of the paper.  TiO2 may also be added.  (For preparation of pigment see Division C1).  Specification 942,263 is referred to.