FI72770B - KALCIUMSULFATUPPSLAMNING. - Google Patents

Description

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calcium sulphate

The invention relates to a slurry containing calcium sulphate pigment and up to 35% by weight of water and to its use in the preparation of a coating paste for paper or board.

The manufacture of paper and board involves a step in which they are coated with a paste to improve printability. The components of the coating paste can be e.g. various pigment slurries such as kaolin and gypsum slurries, and suitable binders therefor. In addition to the actual pigment, the sludges also contain its grinding and dispersing aids.

The following are known pigment slurries of calcium sulphate, i.e. gypsum, containing two aqueous crystals and their excipients: patent application FI 750 387 discloses a process in which gypsum is dispersed with an anionic polycarboxylic acid such as sodium or amine acrylate and / or inorganic dispersant compounds such as EDTA, or compounds precipitating Ca ions such as oxalates, ferrocyanides, citrates, fluorosilicates, bi-fluorides, fluorides, tartrates and silicates. In addition to the substances mentioned, it is possible to use a small amount of a cellulose-based protective colloid. According to the application FI 750 387, the use of gypsum as the main pigment in paper coating paste is sought. Thus, the above-mentioned substances have provided slurries in which the calcium sulphate pigment is suitable for mixing with kaolin only if the gypsum content is at least 40% by weight.

- In Paper and Wood, 1976: 9, 558-570, Na-polyacrylate or Na-hexametaphosphate together with NaOH or carboxymethylcellulose are used as excipients.

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Finnish publication 64 208 mentions the excipients carboxymethylcellulose and NaOH

- in Finnish patent application 810 311 the excipients are de-polymerized and optionally substituted starch together with carboxymethylcellulose.

In Finnish patent application 822 708, in addition to the usual dispersants which may be used, the excipients are at least two polymeric compounds, the first of which is a polysaccharide derivative and the second a polysaccharide or polysaccharide derivative, polyvinyl alcohol or polyethylene glycol.

according to ES 498 334, a protective colloid and / or an anionic or nonionic surfactant is used as excipients.

A pigment slurry of calcium sulphate or hemihydrate containing half water of crystallisation is known from ES 445 985. To stabilize the pigment, phosphoric acid ester of starch is used as an excipient, which at the same time acts as a binder for the coating paste.

The use of anhydrous calcium sulphate or anhydrite as a paper coating pigment is disclosed in German application 310 6631 A1 without mentioning the method of slurrying.

Using known excipients, calcium sulphate slurries are formed which have good properties e.g. in terms of the printability of paper and board. However, the disadvantage of these pigments is that they lead to a reduced gloss of the paper compared to a conventional kaolin pigment. In order to achieve a better gloss, it would be desirable to be able to use mixtures of calcium sulphate and kaolin in the preparation of the coating paste. However, mixing the known calcium sulfate pigments and kaolin 3,72770 is difficult. The result is high viscosity, a significantly increased need for dispersants, and instability of the coating paste. Thus, it has proved particularly difficult to prepare a paste for blade coating with a pigment content of more than 60% by weight of kaolin and a calcium sulphate pigment content of less than 40% by weight without having to significantly reduce the dry matter content of the paste to less than 60% by weight.

It has now surprisingly been found that the stability and miscibility of the calcium sulphate slurries which are the subject of the invention with kaolin have been improved by the new slurry composition. The slurry according to the invention is characterized by what is stated in the appended claims.

In one embodiment, the slurry of the invention contains ammonia or ammonium salts as the amino compound, either alone or in combination with potassium compounds or other amino compounds.

In another preferred embodiment, the slurry contains a C 1 -C 8 amino alcohol, preferably ethanolamine, isopropanolamine, or 2-amino-2-methylpropanol, either alone or preferably in combination with ammonia or ammonium salts, calculated as nitrogen in a mixture ratio of 1: 1 to 1: 4.

The calcium sulphate slurries according to the invention can increase the ratio of kaolin to calcium sulphate pigment in the coating pastes from about 60:40 to about 70-80: 30-20 by the known ones, while the composition of the paste in other respects and also the dry matter content and viscosity are kept constant.

The calcium sulphate slurries according to the invention can also be utilized by making the coating paste with a higher proportion of calcium sulphate pigment, but with a higher dry matter content than previously known. The calcium sulphate slurry according to the invention has also proved to be excellently useful as 4,72770 as the sole pigment in the paste. Among other things, the moisture resistance of coated paper or board has been found to be good.

The invention is illustrated by the following examples in which the calcium sulphate is acid gypsum from the preparation of phosphoric acid. The principles of the invention are equally applicable to other grades of calcium sulphate, in dihydrate, hemihydrate and anhydrous forms, since the nitrogen and potassium compounds used according to the invention have been found not only to promote CaSO dispersion but also to have a particularly active effect on kaolin surface properties. that the viscosity-increasing effect of calcium ion is reduced. The percentages of the examples are% by weight.

Example 1 A (Comparative Example)

Gypsum from the production of phosphoric acid, i.e., phosphogypsum at pH 2.3, was slurried in water to a slurry containing 68% dry matter, the pH was raised to about 9 with NaOH, and dispersed 1: 1: 1 with a combination of Na polyphosphate, Na polyacrylate, and low viscosity carboxymethylcellulose. The viscosity of the slurry was 600 mPas. It was ground in a mill equipped with microminer pieces with the aim of matt pigment for coating paper or board. The mill was filled with water at the beginning of the experiment. Grinding was started by pumping gypsum slurry into a mill, at which point grinding began at a low dry matter content and as the grinding progressed, the dry matter content increased. After about 20 minutes, the grinding had to be stopped when the viscosity in the mill became too high. The dry matter content of the ground gypsum did not reach the level of 68%.

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Example 1 B (according to the invention) The grinding test of Example A was repeated with the difference that ammonia was used to raise the pH of the gypsum. It was needed for about 0.3 to 0.3% of the amount of gypsum. The viscosity of the slurry was 500 mPas. The grinding test could now be carried out without difficulty and took about 2 hours.

Example 2

Slurries containing 67% dry matter were prepared from acid gypsum using 1.1% of the polymer combination according to Finnish patent application 822,708 and 0.2% of ethanolamine as dispersants. The pH of the first slurry was adjusted to 9.5 with sodium hydroxide to give a viscosity of 1100 mPas. The slurry was ground in a mill equipped with microminer pieces to a coating pigment having 60% of the particles smaller than 2 μm and 40% less than 1 μm.

The pH of the second sample was adjusted to 9.5 with ammonia, which required about 0.2% of the gypsum, calculated as 100%. The viscosity now became 1000 mPas. The slurry was ground under exactly the same conditions as the first slurry. Of the pigment particles now obtained, 65% were less than 2 μm and 45% were less than 1 μm. Thus, the combination of ethanolamine and ammonia was a more effective dispersing and pH adjusting aid than the corresponding combination of ethanolamine and sodium hydroxide.

Example 3

A slurry was made of acidic phosphogypsum containing 0.5% low viscosity carboxymethylcellulose, 0.5% polyethylene glycol PEG 400 and 0.2% sodium polyacrylate as dispersants based on gypsum. The pH of the slurry was adjusted with NaOH to 10 teas (= reference slurry). A slurry according to the invention was made by replacing polyethylene glycol with ethanolamine. Both gypsum slurries were ground to paper coating pigments in a mill equipped with microminer pieces under the same conditions. The pigments were made into paper coating pastes by adding 0.1 parts of Na polyacrylate, 0.7 parts of low viscosity carboxymethylcellulose, 0.5 parts of calcium stearate, 9 parts of styrene-butadiene latex and 0.1 parts of glyoxal per 100 gypsum to 100. . The dry matter content of the pastas was about 66%. The stability of the pasta samples was monitored for viscosities n 100 (Brookfield, 100 rpm mPas) (Table I): η 100

Pasta Room stored stored temperature 1 day 6 days o o _______45 C; in__45 ° C

Comparison 1220 1680 6200

According to the invention. 1080 1400 2070

0.2 parts of high-viscosity carboxymethylcellulose was added to the pastes to give a dry matter content of about 64.5%, and a wood-based base paper coating test was performed on a Dixon tester with similar results.

Example 4

The acidic phosphogypsum was slurried in water to a slurry containing 67% gypsum, the pH was adjusted to 9.0 with NaOH, and dispersed using 0.4% Na polyacrylate and 1.5% low viscosity carboxymethylcellulose (CMC). The slurry was ground in a mill equipped with microminer pieces. A coating pigment with a pH of 7.8 and a viscosity of 27,000 mPas was obtained. To reduce the viscosity, the pigment was dispersed with CMC and amino compounds. The results are shown in Table II.

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Table II__________________

Dispersant Dosage Viscosity, Tinn __% gypsum __ (mPas) ____ ---- ---- 27,000 CMC (reference) 0.4 16,500 CMC --- "--- 1.0 11,000 ethanolamine 0.4 7,800 N, N-diethylethanolamine 0.4 7 600 2-amino-2-methyl-1-propanol 0.4 8 800 1 (dimethylamino) -2-propanol 0.4 9 700 benzylamine 0.4 11 400 diethylaminoethanol 0, 4 10,000 triethanolamine 0.4 14,000 N, N-diethylethylenediamine 0.4 5,500 N, N-dimethylethylenediamine _____ 0.4__6 100________

5-Amino-1-pentanol, monoisopropanolamine and 2-amino-2-methylpropanol were compared to ethanolamine at various times. These were all found to be more effective than ethanolamine.

Example 5

The phosphogypsum was ground without dispersants to a particle size of about 60% to less than 2 microns at a dry matter content of about 50% and water was removed by centrifugation until a dry matter content of about 65% was obtained. The solid gypsum was dispersed using 1% low viscosity carbox-β 72770 cimethylcellulose, 0.25% Na polyacrylate and 0.25% Na polyphosphate based on the gypsum, and the pH was adjusted to neutral. The slurry was divided into six portions, with the following additions, in which the amount of anion in the polyacrylates is equal in each case: 1 0.35% NH polyacrylate + NH OH ---> pH 9.0 4 4 2 0.35% NH polyacrylate + KOH ---> pH 9.0 4 *) 3 0.38% Na polyacrylate + NaOH ---> pH 9.0 0.38% Na SO 2 4 4 0.38% Na polyacrylate + NaOH - -> pH 9,0 0,38% K SO 2 4 *) 5 0,38% Na polyacrylate + NaOH ---> pH 9,0 6 0,29% polyacrylic acid + monoisopropanolamine - ---> pH 9 , 0 *) = comparative test Using these gypsum pigment slurries, paper coating pastes were made by mixing the following ingredients, calculated as dry matter: gypsum 20, carboxymethylcellulose 1.2, styrene-butadiene latex 10 and kaolin (as finished pigment slurry) 80. The dry matter content of the pastes was about 60. 5% and pH 7.5. The viscosities were: pasta n, mPas - -100-- 1 - 3430 2 3280 3 (comparison) 4290 4 2940 5 (comparison) 4220 6 3260 9 72770

Example 6

Phospho gypsum was slurried in water together with dispersants and a base to form a slurry with a dry matter content of 67%. The pH was about 3 before base addition and about 9.5 after base addition. The dispersants used in this experiment were 0.5% sodium polyacrylate and 1% of a polymer composition according to Finnish patent application 822,708 of the protective colloid type. Sodium hydroxide was used as the base in the first experiment and ammonia in the second. After dispersion, the resulting gypsum slurries were ground in a mill equipped with micromills to about 65% fineness.

Using both gypsum pigment slurries, coating pastes were made by adding styrene-butadiene latex and carboxymethylcellulose as binders to the gypsum pigment slurry, as well as separately dispersed kaolin slurry as CMC, each containing 1.5 parts of kaolin and 60 parts, 40 parts of kaolin. Pigment dispersants are included in the pigment amounts. The paste had a dry matter content of 60% and the pH was adjusted to 7.5 with lye solution.

It was found that the ammonia neutralized gypsum pigment achieved a significantly lower viscosity of the paste than the lye neutralized. The gypsum pigment contained about 0.14% ammonia, calculated as nitrogen, based on the amount of calcium sulfate, CaSO.

4

In gypsum pigment production experiments, it was found that by using a combination of ammonia and amino alcohol in a ratio of about 4: 1 to 1: 1 (N: CaSO), the proportion of the protective colloid-type polymer compound-4 could also be reduced between 0.2 and 0.8% by weight of the gypsum. At the same time, by adding a corresponding amount of conventional organic or inorganic dispersants as sodium salts, the dry matter content of the gypsum pigment could be increased to 69% without changing the other properties of the pigment.

When the invention is applied to neutral or basic calcium sulphate sources, it is preferred to replace at least some of the ammonia and Na salts of dispersants with ammonium salts and potassium salts of dispersants and / or other acids in order to obtain a sufficiently high amount of N + K / CaSO.

Claims (6)

11 72770 Slurry containing calcium sulphate pigment and up to 35% by weight of water, characterized in that it contains at least about 0.05% by weight and preferably at most about 2% by weight of calcium sulphate, based on the sum of nitrogen and potassium, of amino and / or potassium compounds. Slurry according to Claim 1, characterized in that ammonia or ammonium salts are used as the amino compound, either alone or in combination with potassium or other amino compounds. Slurry according to Claim 1 or 2, characterized in that it contains a C 1 -C 6 amino alcohol, preferably 2 8 ethanolamine, isopropanolamine, or 2-amino-2-methylpropanol, either alone or preferably in combination with ammonia or ammonium salts calculated as nitrogen in a mixture ratio of 1: 1 to 1: 4. Use of a slurry containing calcium sulphate pigment and up to 35% by weight of water for the preparation of a coating paste for paper or board, characterized in that the slurry contains at least about 0.05% by weight and preferably at most about 2% by weight of amino and / or potassium compounds % of calcium sulphate. Use according to Claim 4, characterized in that ammonia or ammonium salts are used as the amino compound, either alone or in combination with potassium or other amino compounds. Use according to Claim 4 or 5, characterized in that the slurry contains a C-amino alcohol, preferably ethanolamine, isopropanolamine, or 2-amino-2-methylpropanol, either alone or preferably in combination with ammonia or with ammonium salts calculated as nitrogen in a mixture ratio of 1: 1 to 1: 4.