JPS603110B2 - Method for producing calcium carbonate water slurry for paper coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a water slurry for coating paper made of calcium carbonate with little secondary agglomeration.

When using calcium carbonate as a pigment for paper coating,
In order to obtain printing paper with excellent whiteness, opacity, gloss, and printability, calcium carbonate particles are required to have less agglomeration and a sharp particle size distribution.

Conventionally, a known method for producing a calcium carbonate aqueous slurry for paper coating is to add a certain amount of acrylic acid or methacrylic acid to calcium carbonate powder or press cake, and then vigorously heat the mixture to form a slurry. However, calcium carbonate slurries produced by these methods tend to have a wide particle size distribution because secondary aggregation of calcium carbonate particles easily occurs and it is difficult to redisperse them. Moreover, since the acrylic acid or methacrylic acid polymer required for slurrying is expensive, it has been desired to reduce the required amount from economic considerations.

Therefore, as a result of various studies in order to remove these momme points, the present inventors have developed a polymer of acrylic acid or methacrylic acid, which was previously used simply as a viscosity modifier for a highly concentrated aqueous slurry of Sameki mineral powder. As shown in the examples, by pre-treating about half of the total amount used as a surface treatment agent for calcium carbonate with an aqueous suspension containing about 10% of calcium carbonate immediately after the carbonation reaction. It has been found that the quality and economic problems mentioned above can be solved.

Regarding calcium carbonate particles as a base material, if the average particle size used for coating fibers is less than 2,
There are no particular restrictions.

Further, as the polymer of acrylic acid or methacrylic acid, commonly used sodium polyacrylate, sodium polymethacrylate, etc. having a degree of polymerization of 1000 or less can be used without any problem. If the amount of acrylic acid or methacrylic acid polymer added to a low concentration calcium carbonate aqueous suspension is 0.3% or less based on calcium carbonate, it is insufficient to prevent secondary aggregation of calcium carbonate particles. On the other hand, if 1.0% or more is added, a dehydrated cake will be produced when a water suspension containing approximately 10% calcium carbonate is used in a dehydrator such as a filter press to raise the calcium carbonate content to 50 to 65% in the subsequent process. is not practical as it would be difficult to obtain.

The reason is that the acrylic acid or methacrylic acid polymer added to the aqueous suspension of calcium carbonate is adsorbed on the surface of calcium carbonate, and this acts as a viscosity reducing agent.
This is because even if the concentration of calcium carbonate increases during the dehydration process, it is still in a slurry or similar state, making it difficult to obtain it in the form of a dehydrated cake. In addition, as described in the examples, the solid content after dehydration using a centrifuge is approximately 55%.
An acrylic acid or methacrylic polymer, which is post-added (post-treated) as a cake slurry agent, is added to the cake at a slurry viscosity required in the paper coating process, that is, B
It is added so that the ratio is about 10 at 6 PM using a type viscometer, and then mixed, dispersed, and pulverized.

This completes the product of the present invention, which has practical utility as a highly concentrated calcium carbonate slurry for coating paper. Next, the method of implementing the present invention will be explained in detail by giving an example.

Example 1 Milk of lime containing 740 grams of calcium hydroxide, concentration 2
Blow 0 to 30% carbon dioxide gas at 10,000 Z'h,
Even after the axis of the suspension reached 7, the above carbon dioxide gas was continued to be blown into the suspension for 5 minutes to sufficiently carbonate the calcium hydroxide. An aqueous suspension containing calcium lk9 is produced.

Next, the above calcium carbonate aqueous suspension was added with a polymerization degree of about 7.
After adding a 20% solution of 00 sodium polyacrylate for 25 days and stirring it vigorously, leave it for a day and night so that the sodium polyacrylate was completely adsorbed on the surface of the calcium carbonate particles, and then dehydrate it with a centrifuge. to make a cake with a solids content of about 55%.

Transfer this cake to a first-class kneader and knead it while adding 35% of the 20% solution of the above PoIJ sodium acrylic acid salt.
and slurry. The viscosity of the slurry at the end of the addition is approximately 10 ratio p when measured with a B-type viscometer at 6 ratio pm.
This slurry was processed with a sand grinder for about 5 minutes to obtain the product of Example 1 (solids content %).

Example 2 The same procedure as in Example 1 was carried out except that the polyacrylic acid sodium salt described in Example 1 was replaced with polymethacrylic acid sodium salt, and the product of Example 2 (solid separation %)
I got it.

Test results table Particle size distribution (%) (according to hydrometer method)
Table 2 Viscosity (CP〆60 rpm) (Measured with a B-type viscometer) Example 1 for untreated
The same amount of polyacrylic acid sodium salt as the total amount of the polyacrylic acid sodium salt used in was added to make the solid content 54% o
※※Polymethacrylic acid used in Example 2 was added to a calcium carbonate aqueous suspension without the addition of sodium polymethacrylic acid salt in a dehydration furnace to achieve a solid content of 55%, that is, without pretreatment. The same amount of polymethacrylic acid sodium salt as the total amount of soda salt was added to make the solid content 54%.

Table 1 shows that the product of Example 1 has a narrower particle size distribution than Control Product 1, and the product of Example 2 has a narrower particle size distribution than Control Product 2. It shows a value close to the particle diameter. In addition, from the results in Tables 1 and 2, the products of each Example compared with each control product showed that the amount of acrylic acid or methacrylic acid polymer required to form a slurry with a ratio of about 10 p required in the paper coating process was Rather than adding the amount all at once, for example, it is better to add the calcium carbonate particles in pre-treatment and post-treatment in order to improve the dispersibility of calcium carbonate particles in the resulting calcium carbonate slurry and reduce the viscosity of the calcium carbonate slurry. , is clearly effective.

Claims (1)

[Claims] 1. To an aqueous suspension of calcium carbonate with an average particle size of 2 μm or less, as a pretreatment, add an alkali metal salt polymer of acrylic acid or methacrylic acid with a degree of polymerization of 1000 or less to 100 parts of calcium carbonate in a proportion of 0.3 to 1. The cake obtained by filtering 0 part of the added material was further treated with a polymerization degree of 10 as a post-treatment.
0.00 or less alkali metal salt polymer of acrylic acid or methacrylic acid, per 100 parts of calcium carbonate, 0.5
A method for producing an aqueous slurry of calcium carbonate for coating paper, which comprises adding from 1 to 1.5 parts, followed by stirring, mixing, dispersing and pulverizing.