JPH01104335A - Dispersing agent for pigment - Google Patents

Abstract

PURPOSE:To decrease viscosity of a dispersion liquid of pigment of high viscosity, by producing dispersing agents for use in pigment by combining polystyrene sulfonates having weight-average mol.wt. of 5,000-100,000 and sulfonation rate of 60-95%. CONSTITUTION:Polystyrene is directly sulfonated by the use of sulfonation agents such as sulfuric acid, sulfuric acid anhydride, fuming sulfuric acid, etc. by a normal method, from which unreacted polystyrene is filtered to be separated and the remainder is neutralized by sodium hydroxide, calcium hydroxide, etc. to obtain polystyrene sulfonates having a weight-average molecular weight of 5,000-100,000 and sulfonation rate of 60-95%. By adding the polystyrene sulfonates to dispersion liquids of pigments, particularly, inorganic pigments such as heavy calcium carbonate, kaoline, etc., the viscosity thereof is decreased, in which the quantity of added polystyrene sulfonates is preferably 0.05-1wt.% per inorganic pigments.

Description

Detailed Description of the Invention The present invention relates to a dispersant for pigments used in coating liquids, etc. Coated papers such as art paper and coated paper contain calcium carbonate, kaolin, clay, etc. It is obtained by applying a coating liquid in which pigments such as , titanium oxide, satin white, and various resins are dissolved or dispersed in water onto the paper surface using a high-speed coating machine. Therefore, if the dispersibility of the pigment is poor, the apparent viscosity of the coating liquid will increase and the fluidity will deteriorate, making it difficult to apply well, and the resulting coated paper will have poor printability and other properties. As a result, the initial objective cannot be achieved. Therefore, attempts have been made to add a dispersant to improve the properties of the coating liquid.From the viewpoint of the properties and economics of the resulting coating liquid, adding a small amount of dispersant can improve the viscosity. It is desirable to have a pigment dispersion with a low pigment dispersion and a stable preparation of a pigment dispersion with a high concentration.

Conventionally, dispersants for this purpose include sodium hexametaphosphate, sodium pyrophosphate, and sodium polyacrylate. -33055 Publication)
, a water-soluble copolymer of acrylic acid and maleic acid (Japanese Patent Publication No. 54-36166), and a salt of a copolymer of acrylic acid and styrene sulfonic acid (Japanese Unexamined Patent Publication No. 57-95396) have been proposed. There is. Furthermore, the above-mentioned Japanese Patent Application Publication No. 57-9
The comparative example in Japanese Patent No. 5396 shows viscosity characteristics when a homopolymer of sodium styrene sulfonate is used as a dispersant.

However, when sodium phosphates are used as a dispersant in a coating solution, they do not have a sufficient dispersing effect on pigments such as calcium carbonate and satin white.

Moreover, the stability of the viscosity of the obtained dispersion over time is poor, and although sodium acrylate and its copolymers have excellent storage stability, they are not necessarily satisfactory in terms of dispersibility.

The present invention provides a pigment dispersant that allows the preparation of a good coating liquid when used as a low-viscosity, high-concentration pigment dispersion.

The pigment dispersant of the present invention has a weight average molecular weight of 5,000 to 5,000.
100,000 and a polystyrene sulfonate with a sulfonation rate of 60 to 95%.

The present invention will be explained in more detail below.

The weight average molecular weight of polystyrene sulfonate is 5.0
It needs to be 00 to ioo, ooo.

When the molecular weight is less than 5,000, the amount of adsorption is small, and when it is more than 100,000, sufficient dispersion performance cannot be obtained in either case due to aggregation effect. Further, the sulfonation rate needs to be 60 to 95%. When the sulfonation rate is lower than 60%, the hydrophobicity increases, and when it is higher than 95%, the hydrophilicity is too strong.
In either case, sufficient dispersion performance cannot be obtained.

As the counter ion for polystyrene sulfonate, sodium, potassium, ammonium, alkanolamine, etc. are preferable, and calcium and magnesium can also be used.

The polystyrene sulfonate of the present invention can be prepared, for example, by adding polystyrene to sulfuric acid or sulfuric anhydride in a conventional manner.

It can be obtained by directly sulfonating using a sulfonating agent such as fuming sulfuric acid, followed by separating the unreacted polystyrene from P, and neutralizing it with sodium hydroxide, calcium hydroxide, etc.

By adding polystyrene sulfonate to a dispersion of a pigment, especially an inorganic pigment such as ground calcium carbonate or kaolin, the viscosity is reduced. The amount of polystyrene sulfonate to be added is suitably in the range of O,OS to 1 weight relative to the inorganic pigment.

The dispersant of the present invention may be added and blended in any form such as solid, powder, or aqueous solution.

Further, there is no particular restriction on the mixing order of water, dispersant, and inorganic pigment. Furthermore, the dispersant of the present invention can be used in combination with other conventionally known dispersants.

According to the present invention, the viscosity of a highly concentrated pigment dispersion can be reduced by using polystyrene sulfonate as a dispersant. Further, by applying such a pigment dispersion as a coating liquid for coated paper, excellent coating properties can be obtained.

Example 1 Polystyrene sulfonate was dissolved in a predetermined amount of water, and heavy calcium carbonate was mixed with Drex #80 and Nitto Funka Kogyo.
ml) and stirred for 2 minutes at 1100 Orp with a TK Auto Homo Mixer (manufactured by Tokushu Kika Kogyo ■).
The mixture was further stirred at 00 rpm for 2 minutes to prepare a dispersion with a pigment concentration of 70% by weight.

Polystyrene sulfonates with various molecular weights, sulfonation rates, and counterions were used, and the viscosity at 25° C. was measured using a Brookfield viscometer for various addition amounts.

The results are shown in Table-1. The amounts added in the table are based on the solid content (weight) of the dispersant relative to the pigment. It can be seen that the viscosity of all pigment dispersions using the dispersant of the present invention is low.

Example 2 Kaolin clay (Ultra White 90,
A 70% by weight dispersion of Hngelhard II) was prepared, and the viscosity at 25° C. was measured in the same manner as in Example 1.

The results are shown in Table-2.

Example 3 A 60% by weight pigment dispersion of heavy calcium carbonate/kaolin clay (30/70) was prepared in the same manner as in Example 1 using 0.4% by weight of sodium polystyrene sulfonate based on the pigment. .

A coating liquid was prepared by mixing starch, latex, etc. in the blending ratio shown in Table 3 below. The coating liquid concentration was 60.2% by weight.

(Left below) Polyepoxy water resistant agent 0.36 parts Stearin Calcium 0.75 The resulting coating solution was applied to the surface of high-quality paper using a suitable coach-in-blonde and dried at 105°C for 3 minutes. After that, 25℃
-75% R)I for 5 hours.

Then, finishing was performed by calendering to obtain coated paper.

Experiments were conducted using several types of sodium polystyrene sulfonate with different properties as dispersants, and the various properties of the resulting coated paper are shown in Table 4.

Claims (1)

[Claims] 1. A pigment dispersant characterized by containing a polystyrene sulfonate having a weight average molecular weight of 5,000 to 100,000 and a sulfonation rate of 60 to 95%.