KR890004337B1 - Process for the treatment of particulate the talc mineral for paper coating - Google Patents

Abstract

A process for treating a particulate talc mineral comprises forming an aq. suspension of the talc mineral, and mixing a hydroxy polymer having a positive electric charge with the aq. suspension to give pH 6-10 of the suspension. The suspension contains 5-30 wt.% talc mineral and the hydroxy polymer of bi- or multi-valency metal. The particulate talc mineral is used as a paper coating pigment.

Description

Method of Treating Particulate Talc Minerals for Use as Paper Coating Pigments

The present invention relates to the preparation of an aqueous suspension of a particulate solid material, and more particularly to a method for treating talc minerals such that the talc minerals are susceptible to suspension and dispersion in water or an aqueous medium.

The term "talc mineral" here means at least 60% by weight, preferably at least 80% by weight, of pure mineral talc, ie minerals consisting of hydrous magnesium silicate having a theoretical molecular composition of 3MgO, 4SiO ₂ , H ₂ O. References ["Industrial Minerals and Rocks", published by The American Institute of Mining, Metallrugy and Petroleum Engineers, 1960, New York, pages 835-836).

Talc has a water-repellent or hydrophobic crystal surface. This property makes it very difficult to wet the talc with water, so making an aqueous suspension containing about 50% or more pure mineral talc is uneconomical in terms of time and energy.

The use of talc as a paper coating pigment has been very limited until now because paper coating compositions were typically in the form of an aqueous suspension of one or more pigments or adhesives. The solid concentration of such a composition must be fluid enough to contain a minimum amount of water so that the composition can be spread evenly on the surface of the paper web by the coating machine and since the water must be removed from the coated paper later by thermal evaporation. It depends on your needs.

Problems caused by the hydrophobicity of talc surfaces have so far been solved by adding humectants to the water normally used to suspend the talc. However, currently known humectants or surfactants are expensive and therefore use talc as a paper coating pigment. Increase the cost in practice. Also, since they tend to generate bubbles, antifoaming agents often have to be used with them.

British Patent No. 2022566A discloses a method of reacting a basic polyaluminum salt with an acid or its salt together in the presence of a solid substance in powder or granule form to make the surface of the substance more hydrophilic or lipophilic. It is describing. If the acid is inorganic, the material surface becomes more hydrophilic. Talc is included among the solid materials that can be treated by the method described in British Patent 2022566A. The patent also states that the reaction is usually carried out in a solvent and the amount of basic polyaluminium salt used is usually used in an amount of 0.01 to 1 parts by weight relative to 1 part by weight of the solid material to be treated. Example 12 of British Patent 2022566A relates to a method of making a surface of talc hydrophilic and it can be calculated that the amount of added basic polyaluminum corresponds to 108 milligrams of aluminum per gram of talc.

It is an object of the present invention to ensure that treated talc minerals are dry in nature for shipment and storage, and that they are reproduced in an aqueous medium with minimal time and energy expense upon receipt of the actual talc minerals by the customer. The talc surface of the talc mineral becomes even more hydrophilic such that it can be suspended to form, for example, a relatively low viscosity paper coating composition for a given solid material content.

According to the present invention, after forming an aqueous suspension of particulate particulate active minerals, the aqueous suspension containing a mixture of a talc mineral and a hydroxy polymer of a divalent or polyvalent metal is subjected to particulate talc under conditions such that it has a pH of 6 to 10. Particulate form, consisting of mixing a substantially water-soluble and slightly positively charged hydroxypolymer of a divalent or polyvalent metal in an amount such that 0.5 to 20 mg of a divalent or polyvalent metal is provided per gram of talc in the mineral with the aqueous suspension formed above. A method of treating talc minerals is provided.

The aqueous suspension of the particulate talc mineral should preferably contain from 5 to 30% by weight, more preferably from 15 to 20% by weight of the particulate talc mineral. The hydroxypolymer may be mixed with the aqueous suspension of the particulate talc mineral by precipitating the hydroxypolymer in the aqueous suspension in situ or by separately preparing the hydroxypolymer and mixing the previously prepared hydroxypolymer with the aqueous suspension.

Preferably, the divalent or polyvalent metal has a colorless cation. Zinc, magnesium and aluminum are examples of divalent or polyvalent metals that form hydroxypolymers and have colorless cations.

In the case of in situ precipitation of a hydroxypolymer, a solution of a salt of a divalent or polyvalent metal is added to the suspension of the particulate talc at a pH such that the hydroxypolymer does not precipitate immediately, and the pH of the suspension is such that the hydroxypolymer is the talc mineral. It is adjusted to a value in the range of pH 6-10, which causes it to precipitate on the surface of the particles. Preferably, the amount of salt added is such that 2 to 10 milligrams of divalent or polyvalent metal is provided per gram of talc in the dry talc mineral.

Generally, the salts added to the aqueous suspension of particulate talc minerals have divalent or polyvalent metals as cations, for example sulfates, hydrochlorides or nitrates of the metals. In this case, the pH can be adjusted to a value in the pH range of 6 to 10 by adding an alkali such as carbonate or hydroxide of sodium, potassium, ammonium or lithium. Otherwise, it may be added to particulate talc minerals of salts with divalent or polyvalent metals present as anions such as sodium aluminate or sodium zincate. In this case the pH can be adjusted to a value in the pH range of 6 to 10, for example by adding an acid such as sulfuric acid, hydrochloric acid or nitric acid.

Preferably, before adjusting the pH of the suspension to a value in the range of 6 to 10, the salt solution is stirred for 5-30 minutes with the suspension of particulate talc to distribute the salt substantially uniformly in the suspension. Thereafter, the pH is adjusted to a value in the range of 6 to 10 by addition of an appropriate alkali or acid to precipitate the hydroxypolymer. Preferably, the suspension of the particulate talc mineral having hydroxypolymer deposited thereon is stirred again for 5 to 30 minutes. The treated particulate talc mineral is then separated from the suspension, for example by filtration, washed with clean water (ie river water, tap water or demineralized water containing low levels of dissolved salts) to remove dissolved cations and anions. This can be accomplished by passing clean water through a filtered cake of treated particulate talcum mineral or by resuspending the filter cake in clean water and filtering the resulting suspension once or several times. Thereafter, the filtergake can be dried to the required moisture content, typically 0-15% by weight, for transport and storage.

When a hydroxypolymer is prepared separately and mixed with a suspension of particulate talc, the hydroxypolymer adjusts the pH of an aqueous solution of a divalent or polyvalent metal salt with a suitable alkali or acid to a value in the range of pH 6 to 10. Is precipitated first. The precipitate of hydroxypolymer is then separated by filtration and washed with clean water.

For future use the hydroxypolymer can be stored in the form of a wet filter cake or as a suspension of known concentration dissolved in clean water. The cleaning can be done by sending clean water through the gage on the filter or by resuspending the cake in clean water and filtering again. This operation can be repeated once or several times.

Preferably, sufficient hydroxypolymers prepared separately are mixed with an aqueous suspension of the particulate talc mineral to provide 2 to 10 milligrams of divalent or polyvalent metal per gram of talc in the dry talc mineral, the mixture of which is a hydroxypolymer in particulate form. Stir for 5-30 minutes to ensure complete dispersion in the talc mineral suspension. Thereafter, the suspension of the treated talc mineral is filtered and the filter cake is dried to the required moisture content, generally 0-15% by weight, for transport and storage. In this case, the filtration gasket of the treated particulate talc mineral no longer needs to be ironed out.

The dry particulate talc minerals prepared by one of the two methods described above will only form aqueous suspensions having a relatively low viscosity with a high content of solids for use in, for example, paper coating compositions, with the aid of dispersants alone. Can be. There is no need to add organic wetting agents such as those conventionally used to prepare aqueous suspensions of fluid, high talc-containing particulate solids. The invention is illustrated by the following examples.

Example 1

Commercial talc minerals used in the paper industry were found to have the following mineralogy by X-ray diffraction analysis.

Mineral weight%

Talc 93

Magnesite 3

Chlorite 4

The reflectance of light at 457 nm wavelength was measured by the "ELREPHO" brightness meter according to ISO standards 2469, 2470 and 2471, and found to be 84.6. The particle size distribution consists of particles having a spherical diameter of more than 10 microns by 9% by weight. 35% by weight consisted of particles with a spherical diameter of less than 2 microns. 100 g of talc mineral was stirred in 40 ml of water to form a suspension containing 20% by weight solids. While continuing stirring, 5.58 ml of a molar solution of aluminum sulfate octadecahydrate was added to the suspension. This amount of aluminum sulfate solution was such that 2.8 milligrams of aluminum were provided per gram of talc in the dry talc mineral. Stirring was continued for 10 minutes after the addition of aluminum sulfate was completed, after which 0.5 mol of caustic soda solution was added until the pH was raised to 9.5. The suspension was further stirred for 10 minutes, then filtered and washed by passing 1.5 liters of clean water through the filter cake. The filter cake was then placed in an oven at 105 ° C. and dried overnight. Thereafter, the dried filter cake was ground into balls and mortar.

The treated dry talcum mineral was then mixed in a high speed laboratory mixer by mixing water in a high speed laboratory mixer with 0.5% by weight of water containing an average molecular weight of 1560 sodium polyacrylate dispersant and 0.1% by weight of caustic soda (but no wetting agent). A suspension containing weight percent solids was formed. The suspension was found to have a viscosity of 170 cps as measured by a Brookfield viscometer using spindle 3 at a rotational speed of 100 r.p.m.

Subsequently, the treated talc mineral was used to make paper coating compositions by adding 9.6 g of a self-thickening acrylic latex produced by BASF under the trade name "ST 4250". The latex comprises 50% by weight solid material. The pH of the coating was adjusted to 9, and the measured composition was measured using Brooks viscometer at 3 rs at 100 r.pm at a final solids content of 53.1% by weight. The viscosity of the coating composition was 520 cps. The Ferranti-Shirley viscometer was measured at a shear rate of 10,20S- ¹ and found to be 213 cps.

Example 2

Samples of talc minerals as used in Example 1 were treated in the same manner as described in Example 1, but only in each case the amount of aluminum sulfate octadecahydrate solution used was different.

In each case, the treated dry talcum mineral was mixed with water containing sodium polyacrylate and caustic soda to form a high solids suspension. The above suspension was used to prepare a paper coating composition containing the same latex as used in Example 1 per 100 g of dry active mineral. In each case, the high shear viscosity of the paper coating composition was measured at a shear rate of 10,120 S ⁻¹ with a Ferranti-Shirley viscometer, and the weight percentage of solids contained in the composition was measured.

As a comparison, 100 grams of untreated talc minerals were used as in Example 1 at 0.5 wt% based on the weight of the talc mineral, a proprietary wetting agent known as " PLURONIC L62 " Another paper coating composition was prepared by adding to 50 ml of water containing a sodium polyacrylate dispersant ("PLURONIC L62" is believed to have a hydrophilic moiety consisting of a polyoxypropylene base having a molecular weight of about 1750 and is a polyethylene oxide group Is about 20% by weight based on the weight of poly oxypropylene). 9.6 grams of the same acrylic acid latex were added and the pH was raised to 9 by adding caustic soda solution.

As described above, the solid content and high shear viscosity of the paper coating component were measured.

The results are shown in Table 1 below.

Table I

In each case, the above results indicate that the treatment according to the present invention is a paper coating composition having a high shear viscosity and a solid content which are not significantly different from a paper coating composition prepared using a talc mineral treated with an organic wetting agent according to a conventional method. Shows that it calculated. The amount of aluminum hydroxypolymer containing 3 milligrams of aluminum per gram of dry talc mineral seems to adequately cover the talc surface, and the ratio of 7.5 milligrams of aluminum per gram of dry fossil mineral seems to be the optimal amount of hydroxypolymer.

Example 3

The following mixture was prepared with reference to Example 12 of British Patent Specification 2022566A.

100.0 grams of talc

(Na PO ₃ ) _n 10.0 grams

196 milliliters of basic polyaluminum

Chloride

The talc used was the same as the talc mineral used in Example 1. The basic polyaluminum chloride has the following molecular formula [Al (OH) _1.5 Cl _1.5 ] and 2.02 moles (55 milligrams of Al per milliliter) of aluminum per liter of solution. Had content. Thus, as in Example 12 of British Patent Specification 2022566A, the amount of basic polyaluminum yields 108 milligrams of aluminum per gram of talc. Talc was completely dispersed in 2 liters of water at 80 ° C. and then added thereto a suspension of 10.0 grams of sodium phosphate dissolved in 200 milliliters of water. 196 milliliters of basic polyaluminum chloride was then slowly added to the suspension with stirring. The resulting mixture was stirred at 60 ° C.-80 ° C. for 15 minutes, then cooled and the pH of the mixture was 4.5. The treated talc was then recovered by filtration, washed with 2 liters of water and dried.

A portion of the dry treated talc mineral is intended to be mixed in a high speed experimental mixer containing 0.5% by weight sodium polyacrylate dispersant as in Example 1 by weight of dry talc mineral and 0.1% by weight of caustic soda by weight of dry active mineral. An attempt was made. However, it has been found that talc is not hydrophilic enough to be completely wet with water.

Another portion of the treated dry talc mineral was added to water containing 1.5 wt% sodium polyacrylate dispersant and 0.1 wt% caustic soda based on the talc mineral weight. In this case, it was possible to completely wet the talc and produce a homogeneous suspension, but found that the Brookfield viscometer can only measure the viscosity if the suspension is diluted to a level that is very unsuitable for use in papercoating compositions. .

Two other mixtures of talc, sodium phosphate and basic polyaluminum chloride were prepared according to the formulation, with the amount of basic polyaluminium chloride used in the two mixtures providing 54 milligrams and 5 milligrams per gram of talc in the dry talc mineral, respectively. Manufactured in the manner described above, with the exception of the degree to which it is intended.

In each case, the dry treated talc mixture was mixed with water containing sodium polyacrylate dispersant and caustic soda to form a high solids suspension. A series of suspension clay measurements were performed at different solids contents using a Brookfield viscometer and the solids content of suspensions with a viscosity of 500 cps at 22 ° C. was interpolated. The results obtained are shown in Table II below.

For comparison, another two specimens of talc minerals, such as those used in Example 1, were substituted with the basic polyaluminum chloride described above in an amount that provides 5 milligrams of aluminum per gram of talc in the dry talc mineral instead of aluminum sulfate. Treatment was conducted in the same manner as described in Example 1 except for the use. In each case, the suspension was stirred for 10 minutes after the addition of the basic polyaluminum chloride was complete, after which a 0.5 molar solution of caustic soda was added until the pH rose to 9.5. The suspension was then stirred for 10 minutes and filtered. In one case the filter cake was washed by passing 1.5 liters of clean water and in other cases the washing step was omitted. In each case, the filter cake was dried overnight in an oven at 80 ° C. to crush the dried filter cake into mortar and balls. In each case the solids content of the treated dry talcum suspension with a viscosity of 500 cps at 22 ° C. was determined by the method described above and the results are shown in Table II below.

For another comparison, Example 1, a sample of talc minerals as used in Example 1, except that the amount of aluminum sulfate used is such that it provides 5 milligrams of aluminum per gram of talc in the talc mineral. The same process as described in The solids content of the suspension of the treated dry talcum having a viscosity of 500 cps at 22 ° C. was determined by the above method and the results are shown in Table II below.

TABLE II

Note: A and B-basic polyaluminum chloride and sodium phosphate pH 4.5-5.0, C-basic polyaluminum chloride, pH9.5, unwashed, D-basic polyaluminum chloride, pH9.5, washed, E-aluminum sulfate, pH9.5, wash.

These results show that the use of British Patent Specification 2022566A yields a talc suspension of much higher viscosity than the present method for a given solid matter content. Although the amount of aluminum compound is reduced within the preferred range of the present invention, the rheological properties of the obtained talc suspension are obtained by the method of the present invention which adjusts the pH of the mixture of talc and aluminum hydroxypolymer to a value in the range of 6 to 10. Inferior to the rheological properties of talc suspension.

Claims (12)

After the aqueous suspension of the particulate talc mineral is formed, the aqueous suspension containing the mixture of the particulate talc mineral and the hydroxypolymer of the divalent or polyvalent metal has a pH in the range of 6 to 10, in the particulate talc mineral. Characterized by mixing a substantially water-soluble, slightly positively charged hydroxypolymer of divalent or polyvalent metal in an amount such that 0.5 to 20 milligrams of divalent or polyvalent metal is provided per gram of talc. A method of treating particulate talc minerals for use as a paper coating pigment. The method of claim 1 wherein the aqueous suspension contains 5 to 30 weight percent particulate talc mineral. The method of claim 2 wherein the aqueous suspension contains 15 to 20 weight percent particulate talc mineral. The method of claim 1 wherein the divalent or polyvalent metal has a colorless cation. The method of claim 1, wherein between 2 and 10 milligrams of divalent or polyvalent metal are provided per gram of talc in the particulate talc mineral. The method of claim 1 wherein the hydroxypolymer is mixed with the aqueous suspension of the particulate talc mineral by in situ precipitation of the hydroxy polymer in the aqueous suspension. 7. A solution according to claim 6, wherein a solution of a salt of divalent or polyvalent metal is added to the suspension of the particulate talc mineral at a pH such that the hydroxypolymer does not precipitate immediately, so that the hydroxypolymer precipitates on the surface of the particles of the particulate talc mineral. Wherein the hydroxypolymer is precipitated in situ by adjusting the pH of the suspension to a value of 6 to 10. 8. A salt solution according to claim 7, wherein the salt solution is mixed with an aqueous suspension of particulate talc to substantially uniformly disperse the salt throughout the suspension, before adjusting the pH to a value in the range of 6 to 10 so as to precipitate the hydroxy polymer. Method for stirring for 5 to 30 minutes together. A process according to claim 1, wherein the hydroxypolymer of divalent or polyvalent metal is prepared separately before mixing with the aqueous suspension of the particulate talc mineral. The method of claim 1 wherein the aqueous suspension containing the particulate talc mineral and the hydroxypolymer is stirred for 5 to 30 minutes. The method of claim 1, wherein the particulate talc and hydroxypolymer are separated from the aqueous suspension by filtration, washed with clean water and dried to a water content of 0 to 15% by weight. 12. The process of claim 11, wherein the dried particulate talc and hydroxypolymer are formed of an aqueous suspension of relatively low viscosity with a high solids content with only the aid of a dispersant.