JPS5835937B2 - Method for producing pigments or fillers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates primarily to a process for treating pigments and/or fillers, especially calcium sulfate, by purification and/or bleaching.

Calcium sulfate, or gypsum, is a natural material found in several countries, such as the Mediterranean countries.

Its common form is the dihydrate with the composition CaSO42H20.

However, gypsum also exists as a waste product produced during the production of phosphoric acid, and in this case is often referred to as "chemical gypsum 11".

The term calcium sulfate according to the present invention is to be understood to mean lucium sulfate in all its forms, ie intact calcium sulfate and its dihydrates and hemihydrates.

The use of gypsum as a pigment in paper coatings has already been proposed.

The reason such proposals have not been successful in practical application is probably that the special prerequisites necessary to obtain good results were not understood.

It is an object of the present invention to provide a method for pre-treating calcium sulfate to make it suitable for use as a pigment and/or filler.

According to the invention, said object is achieved by treating calcium sulfate with an oxidizing bleach.

According to a particularly suitable embodiment, the treatment is carried out by bleaching with chlorine, hypochlorous acid, hypochlorites, chlorine dioxide and/or chlorine peroxide.

In this case, it is advantageous to carry out the treatment on calcium sulfate in the form of an aqueous suspension.

Dry content in the slurry is up to 60% by weight, preferably up to 5%
Particularly good results are obtained when well over 0 weight is reached.

When carrying out bleaching with chlorine, hypochlorous acid or hypochlorite, it is of essential importance that the value in the slurry is maintained between 1.5 and 6, preferably between 2 and 4. It was discovered.

Bleaching may be carried out over a period of 5 minutes to 1 hour, preferably 20 to 30 minutes.

When treating with chlorine or chlorine compounds, it is important to add the required amount for maximum effectiveness.

0.1-1% based on the amount of calcium sulfate, preferably 0
．． It has been found through practical experience that it is necessary to add active chlorine in a calculated amount of 3 to 0.5%.

According to another embodiment, the calcium sulfate is purified by fractionation, preferably in a cyclone, before or after bleaching to remove undesirable particles.

After bleaching, the calcium sulfate must be washed with water, for example on a filter or in a column, to remove residual chlorine, chloride and oxidizing compounds.

The invention will be explained in more detail below on the basis of a non-limiting example of the accompanying drawing, which shows a block diagram of the implementation steps of the method according to the invention.

EXAMPLE In this example, waste stone obtained from phosphoric acid production was used as a raw material.

At No. 1, the material was suspended in water to a dry weight of approximately 15% by weight, and the slurry value was adjusted to a value of 3%.

The above value is a critical value since at higher values the discoloring impurities stick to the gypsum particles.

The gypsum used here contains as impurities, in addition to organic matter, silicates produced by the previous treatment, calcium fluoride, and extremely discolored gypsum.

When the pH value is higher than 3, it is preferable to carry out an acidification treatment with sulfuric acid.

The resulting slurry was then fractionated in hydrocyclone 2, whereby fractions with particle sizes ranging from 25 to 100 microns were recovered.

The particle size should not be less than 25μ, as this makes dewatering in the next processing step substantially more difficult.

A portion of the partition containing particles larger than 100μ consists of dark particles and a portion of the dark particles consists of tomaline (tourmaline).

However, the phosphate rock that constitutes the starting material for the production of phosphoric acid exists in many different qualities, and therefore there are various types of impurities.

Fractionation was carried out in two stages 3 and 4 respectively.

In the first stage, the coarse fraction was removed, and in the second stage, the fine fraction was removed and removed from the treatment process as waste.

Performing the separation in this way is not affected by the operating conditions of the phosphate plant where the gypsum was collected.

The resulting slurry has a dry weight of approximately 45%.

The recovered fractions were then bleached in a continuous bleaching plant 5 by adding chlorine water 6.

By adding chlorine water, the dry content decreased to about 20% by weight.

After addition of chlorine water, the value was adjusted to 3 and bleaching was carried out by stirring in two tanks connected in series to extend the residence time.

The amount of added chlorine was 0.5 weight φ relative to the amount of dry gypsum.

After bleaching, the slurry was concentrated in a settling thickener to a dry weight of approximately 35%.

The plaster was then washed in the next step 1 to remove blowing agents, chlorides, organics and other impurities.

Cleaning was carried out continuously with water 8 flowing in a countercurrent direction in a vertical pipe.

The gypsum is removed by a screw at the bottom of the pipe.

Simultaneously with washing, concentration to a dry mass of approximately 45% was carried out.

Clarification of the slurry obtained from the washing step was then carried out on a rotary vacuum filter 9.

The filter was simultaneously sprayed with water primarily to remove chloride residues.

The filter yielded a clean bleach product weighing approximately 75 lbs. dry.

The effluents 10, 11 from the washing stage I and the filter 9 can be drawn off together at 22.

The main components in coating compositions, whether used for paper and cardboard coatings or as pigments, are pigments, binders and liquid phases.

The addition of dispersants is also usually necessary to achieve good pigment distribution.

This makes it possible to reduce the viscosity of the composition at the same time.

This means that it is possible to increase the dry matter without reducing the applicability.

Kaolin, titanium dioxide or chalk are conventionally used as pigments for application to paper, cardboard or similar materials.

However, it was also proposed to use plaster.

The reason gypsum was not put into practical use was probably because it was thought to require a higher amount of dispersant.

Conventional binders used for coating compositions consist, for example, of water-soluble substances such as starch and casein or aqueous dispersions of various polymers such as polyacrylates, polymethacrylates and polyvinyl alcohol.

However, it is also known per se to use certain cellulose derivatives, such as methylcellulose, ethylcellulose, hydroxyethylcellulose or carboxymethylcellulose.

A large number of agents are commercially available for use as dispersants.

Incomparably more frequently used are the various types of phosphates, especially sodium hexametaphosphate.

However, this dispersant, like some other dispersants, has some drawbacks.

For example, the binding strength of the binder used is often reduced.

Additionally, when these dispersants are used to coat printing papers in offset printing, they can in some cases cause emulsification of the ink in the offset water, resulting in undesirable coloration of the print. In view of the foregoing, the process of the invention essentially uses a dispersing agent, ie a polysaccharide substituted with carboxyl groups, which itself acts as a binder.

In this case, it has been found that it is essentially important that the gypsum is beaten in the presence of the carboxyl-substituted polysaccharide.

According to a particularly preferred method, the beating is carried out in the presence of water.

In various experiments conducted in connection with the development of the present invention, commonly known as C
Beating was carried out with carboxymethyl cellulose of MC, and the average molecular weight of CMC was i o, o o .

~500,000 preferably 20,000~150,0
It has been found that particularly good results are obtained when 0.00.

When using CMC, the amount of CMC added is 0.5 to 3 weight more than the amount of dry calcium sulfate.

The particle size of the calcium sulfate is important in this connection.

For example, when it is desired to prepare a coating composition for producing matte paper, the gypsum must have a particle size distribution such that 30% has a size smaller than 2μ.

In the case of coating compositions for the production of glossy paper, 95% of the material is 2μ
It must have a smaller particle size.

Regarding pigments for fillers, the particle size of calcium sulfate is
The grain size must be such that 50 weight units of material have dimensions smaller than 5μ.

The particle size distribution as described above is similar to that of Kebo Grape.

Andreassen (AJldr), marketed in Sweden with reference number 111,904 by the company Grave
The test sample is prepared by weighing approximately 11 g of gypsum slip, to which is added 1% CMC, and then mixing and stirring the slip with approximately 40 rIL of water.

Transfer the samples to a sedimentation device and pipette out 10 rILl samples each using the method described below.

After 0 minutes First sample after 60 minutes Second sample after 120 minutes Third sample after 1080 minutes Fourth sample after 1560 minutes Fifth sample According to special embodiments, a binder, for example latex or starch, is added.

It is preferable that the above-mentioned addition is carried out after beating.

As mentioned above, a high dry content is extremely important for an effective and economical coating.

Using the selected binder/dispersant and the method of the invention, the dry matter of the coating for producing matte paper is between 60 and 8
It can be as high as 0 weight reward.

Dry contents of 55 to 80 weight φ have been achieved with coatings for producing glossy paper.

According to a special embodiment, the refining is carried out at elevated temperatures, preferably at temperatures below 130°C.

Specifically, the coating agent can be manufactured as follows based on the drawings.

The product obtained from the example is fed to a dispersion device 12,
At the same time, 1.6 wt. of carboxymethyl cellulose (CMC) in the form of a 1.4% solution was added to the dry gypsum at step 13. In this case, the gypsum contained a small amount of phosphoric acid. So sodium hydroxide was added to raise the pH value to 12.

The phosphoric acid is liberated in a subsequent refining step.

Furthermore, conventional polishing agents, defoamers, fluorescent bleaches, coloring substances and preservatives can be added to the mixture if desired.

The various components are continuously fed into the mixing vessel so that a flow rate of approximately 4 m8/h is obtained.

A dispersing effect is created by the rapidly rotating stirrer.

The material is continuously transported from the dispersion stage 12 to a vacuum deaerator 14 to remove entrained air.

After degassing, the dispersion was beaten in one step in a pearl beater 15 at a temperature of about 50° C., then cooled in 16 and sorted in a self-cleaning screen 11.

The final product 18 was a slurry that could withstand storage of 71 dry strips.

The product is dispensed by a pump discharge to fill a tank or barrel.

The present invention is not limited to the specific examples described, but can be modified within the scope of the gist of the invention.

[Brief explanation of drawings]

The figure is a block diagram of the implementation steps of the method of the present invention. 2...Hydrocyclone, 3.4...
・Separation stage, 5... Bleaching plant, 6...
...Chlorinated water, 1...Cleaning stage, 8...
Water, 9...Filter, 12...Dispersion device, 14...Deaerator, 15...Bar beater-11γ...Screen.

Claims (1)

[Claims] 1 Calcium sulfate is purified by fractionation to remove undesirable particles, and then an aqueous suspension of calcium sulfate having a dry content of up to 60% by weight is mixed with chlorine and hypochlorous acid. A method for producing pigments or fillers for use in coating compositions comprising bleaching with an oxidizing bleach selected from chlorite, chlorine dioxide, chlorine peroxide and mixtures thereof, the bleaching being carried out at a pH of 1. , 5 to 6. 2. Process according to claim 1, characterized in that the dry content in the slurry is at most 50% by weight. 3. The method according to claim 1 or 2, wherein the pH is 2 to 4. Claim 3, characterized in that 4pH is 3.
The method described in section. 5. The method according to any one of claims 1 to 4, characterized in that bleaching is carried out for 5 minutes to 1 hour. 6. The method according to claim 5, characterized in that bleaching is carried out for 20 to 30 minutes. 1. The method according to any one of claims 1 to 6, characterized in that chlorine or a chlorine compound is added in an amount of 0.1 to 1 part of active chlorine relative to the amount of calcium sulfate. Method. 8. Process according to claim 7, characterized in that chlorine or chlorine compounds are added in an amount of 0.3 to 0.5% of active chlorine relative to the amount of calcium sulfate. 9. The method according to any one of claims 1 to 8, characterized in that calcium sulfate is purified in a cyclone. 10. The method according to any one of claims 1 to 9, characterized in that after bleaching, the calcium sulfate is washed with water to remove residual chlorine, chloride, and oxidizing compounds. 11. The method according to claim 10, characterized in that a filter or column is used in washing the calcium sulfate.