JPH07242790A - Pigment dispersant for coated paper - Google Patents

Abstract

PURPOSE:To provide a pigment dispersant which is excellent in the capability of dispersing a pigment for coated paper. CONSTITUTION:This dispersant contains a water-sol. polymer which is a salt of a copolymer of maleic anhydride with an alkyl vinyl ether of the general formula: CH2=CHOR (wherein R is 1-4C alkyl) and has a wt.-average mol.wt. (in terms of polyethylene glycol) of 10,000-100,000.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dispersant for pigments for coated paper, and more particularly to a dispersant exhibiting excellent dispersibility which gives a dispersion having low viscosity even when added in a small amount.

[0002]

2. Description of the Related Art In the coated paper industry, coated paper has conventionally been manufactured using various pigments such as calcium carbonate, clay, kaolin, satin white, titanium oxide, zinc oxide and aluminum hydroxide. There is. Coated paper is generally prepared by adding a dispersant of a certain kind to a pigment as described above to disperse it in water, and adding casein, starch, vinyl-based synthetic latex or the like as a binder to this, alone or as a mixture. Is coated and dried on the base paper, and if necessary, mechanical treatment such as super calendering is applied to produce.

Coated papers have been considered in various respects so as to exert the best printing effect under the conditions for producing coating liquids which are relatively inexpensive. For example, various kinds of pigment dispersion liquids are prepared. There are increasing demands that different pigments can be dispersed as a mixture, that a higher concentration pigment dispersion can be prepared, and that finely divided pigments and highly hydrophobic pigments can be dispersed. Therefore, the conditions that the pigment dispersant for coated paper should have are that it is effective for a wide range of various pigments, and that it is effective for pigments having a finer particle diameter and strongly hydrophobic pigments, etc. From the standpoints of economy and quality of coated paper, conditions such as the ability to prepare a high-concentration pigment dispersion with a small amount are required. Incidentally, when a coating liquid having a poor pigment dispersion state is used, not only the coating suitability is remarkably lowered due to increase in viscosity, poor fluidity, etc., but also the smoothness of the obtained coated paper is impaired, which should be satisfied. The printability cannot be obtained.

Suitable dispersants for coated paper pigments include condensed phosphates such as sodium tripolyphosphate and sodium hexametaphosphate, condensates of naphthalene / formalin, and nonionic surfactants such as polyalkylene glycol surfactants. Activators and other organic polymer dispersants such as poly (meth)
Sodium acrylate, (meth) acrylic acid / polyalkylene glycol mono (meth) acrylate copolymer (JP-A-59-193126, JP-B-5-61398),
(Meth) acrylic acid / polyethylene glycol monoallyl ether copolymer (JP-A-57-192469),
(Meth) acrylic acid / hydroxyalkyl (meth) acrylate copolymer (JP-A-55-71758), copolymer with (meth) acrylic acid / unsaturated dicarboxylic acid / phosphoric acid ester group-containing monomer 60-60288
No.) etc. are known. Alkali metal salts or ammonium salts of acrylic acid / maleic anhydride copolymer, olefin (eg isobutylene) / maleic anhydride copolymer, copolymer with acrylic acid / sulfone group-containing monomer (eg styrene sulfonic acid), etc. Etc. have been generally adopted. However, these dispersants are not at a level satisfying the above requirements.

On the other hand, among the alkyl vinyl ether / maleic anhydride copolymers, especially methyl vinyl ether /
Maleic anhydride copolymers are generally commercially available and used for patches, adhesives and the like. Further, the lower alcohol ester form thereof is used for hair styling agents and the like. Further, Na salt of methyl vinyl ether / maleic acid copolymer is also sold. However, these are inferior in performance when used as a dispersant for coated paper, and there is a practical problem.
That is, the conventional salt of an alkyl vinyl ether / maleic anhydride copolymer or a lower alcohol ester does not satisfy the performance as a dispersant for coated paper.
Also, JP-A-64-4227 and JP-A-64-4228
The publication discloses, as a non-aqueous dispersant, an inclusion or esterified product of an alkyl vinyl ether / maleic anhydride copolymer and a polyether polyol. However, since the alkyl group of the alkyl vinyl ether used has 4 or more carbon atoms, the lipophilicity becomes strong, and there is a problem in performance as a dispersant for a water-based pigment for coated paper.

[0006]

SUMMARY OF THE INVENTION In view of the above situation, an object of the present invention is to provide a dispersant having excellent dispersibility of a pigment for coated paper.

[0007]

The present invention comprises a salt of a copolymer of maleic anhydride and an alkyl vinyl ether represented by the following general formula (I), wherein the weight average molecular weight of the salt of the copolymer is 10,0 in terms of polyethylene glycol
It is a dispersant for pigments for coated paper, which contains a water-soluble polymer compound of 100 to 100,000 as an active ingredient. General formula (I) CH2 = CHOR (In the formula, R is an alkyl group having 1 to 4 carbon atoms.)

The maleic anhydride used in the present invention includes
A maleic anhydride derivative or another α, β-unsaturated carboxylic acid such as citraconic anhydride or itaconic anhydride may be contained.

Specific examples of the alkyl vinyl ether used in the present invention include methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, and one or two of them. It may be a mixture of the above. The number of carbon atoms of the alkyl group of this alkyl vinyl ether is preferably 4 or less from the viewpoint of hydrophilicity, and among them, methyl vinyl ether is most preferable because it is water-soluble and has excellent dispersibility of the pigment for coated paper.

Any conventional polymerization method and polymer reaction method may be applied to the method for producing the copolymer used in the present invention. Here, the charging ratio of maleic anhydride / alkyl vinyl ether can be arbitrarily selected, but is preferably selected from 30/70 to 70/30 (molar ratio). As the polymerization method, a radical catalyst such as benzoyl peroxide or azobisisobutyronitrile is usually used, and benzene derivatives such as benzene, toluene and ethylbenzene, organic acid esters such as ethyl acetate and isopropyl acetate, and methyl ethyl ketone. Radical copolymerization is performed at a temperature of 5 to 150 ° C. in a solvent such as ketones such as methyl isobutyl ketone, carbon tetrachloride, and organic halides such as chloroform. For controlling the molecular weight, a usual chain transfer agent such as a thiol chain transfer agent or an alkylaldehyde chain transfer agent can be used. Further, as a technique for controlling the molecular weight, there is also used a method in which maleic anhydride and a radical catalyst are added to a solvent and then an alkyl vinyl ether is added and fed over a specific period of time. Incidentally, within a range that does not change the characteristics of the obtained copolymer,
It is also possible to copolymerize monomers such as styrene and α-olefin.

In the present invention, in order to obtain a high degree of pigment dispersibility, the weight average molecular weight of the copolymer of maleic anhydride and alkyl vinyl ether is from 10,000 to 10.
It is in the range of 10,000, more preferably 10,000.
Is in the range of -60,000. If it is less than 10,000, the dispersibility will be poor, and if it exceeds 100,000, the cohesive force will be increased, which is not preferable.

The cation moiety forming the salt of the copolymer in the present invention includes alkali metal ions such as lithium, sodium and potassium, alkaline earth metal ions such as calcium and magnesium, aluminum, iron and the like. Examples include trivalent metal ions, ions from organic amines such as ammonium, triethanolamine, and triethylamine.

The dispersant thus obtained is usually 1
Used as an aqueous solution of 0 to 60% by weight, after adding a predetermined amount of pigment for coated paper to the aqueous solution, stirring and mixing with a stirrer equipped with stirring blades such as paddle type blades and turbine blades, a homomixer, etc. To give a 40-80 wt% pigment aqueous dispersion.

The pigment for coated paper referred to in the present invention is a pigment which is widely used in the coated paper industry, and includes, for example, kaolin, talc, satin white, titanium dioxide, hydrohaloysite, clay, ground calcium carbonate, Light calcium carbonate, barium sulfate, aluminum hydroxide, zinc sulfate, calcium sulfite and the like. The dispersant of the present invention exhibits an excellent dispersing effect on these pigments. still,
The amount of the dispersant used is preferably 0.01 to 3.0% by weight based on the pigment solid content.

The present invention will be specifically described below with reference to Examples and Comparative Examples. Copolymerization Example 1 A 1.5 liter glass autoclave equipped with a stirrer was used as a polymerization vessel, and a vacuum conduit and a nitrogen conduit were connected so that the reaction could be carried out under air interruption. The polymerization vessel was heated on a water bath. First, maleic anhydride 5
0.4 g was added, the autoclave was closed, and after vacuum replacement, nitrogen was introduced and the pressure was returned to normal pressure. Then, 370 g of n-butyraldehyde and 35.8 g of methyl vinyl ether were added, and the mixture was stirred for about 15 minutes until maleic anhydride was dissolved. The mixture was heated to 60 ° C., 80 ml of an initiator solution consisting of 1 g of lauroyl peroxide and 100 g of n-butyraldehyde was added, and the mixture was reacted for 8 hours to complete the polymerization. The weight average molecular weight of the obtained copolymer is G
As a result of PC analysis (eluent: sodium chloride aqueous solution, converted to polyethylene glycol), it was 6,200. (Dispersant 5)

Copolymerization Example 2 Using a 5 liter SUS autoclave equipped with a stirrer, a vacuum conduit and a nitrogen conduit were connected so that the reaction could be carried out under air exclusion. The polymerization vessel was heated on a water bath. First, add 401.8 g of maleic anhydride,
The autoclave was closed, the atmosphere was replaced with vacuum, and then nitrogen was introduced to return the pressure to normal pressure. Then, 2437 g of toluene, 285.7 g of methyl vinyl ether, and 75 g of thioglycolic acid as a chain transfer agent were added, and the mixture was stirred for about 15 minutes until maleic anhydride was dissolved. The mixture was heated to 60 ° C., 80 ml of an initiator solution consisting of 1 g of lauroyl peroxide and 100 g of toluene was added, and the mixture was reacted for 6 hours to complete the polymerization. The weight average molecular weight of the obtained copolymer is
As a result of GPC analysis (eluent: sodium chloride aqueous solution, converted to polyethylene glycol), it was 12,800.
(Dispersant 1)

Copolymerization Examples 3 to 6 Samples having different molecular weights (dispersing agents 2, 3, 6) were prepared by varying the amount of thioglycolic acid, which is a chain transfer agent, according to the above-mentioned copolymer example 2. An isobutyl vinyl ether / maleic anhydride copolymer was prepared by replacing methyl vinyl ether with isobutyl vinyl ether (dispersant 4).

[Pigment dispersant for coated paper] The obtained copolymer is dissolved or dispersed in water, neutralized with NaOH, and PH = 7.
Used as an aqueous solution dispersant. The dispersant examples are summarized in Table 1.

[Measurement of Molecular Weight] Water is further added to the above aqueous solution to prepare a 0.3% aqueous solution, and the molecular weight is calculated based on polyethylene glycol and polyethylene oxide-equivalent molecular weight using a GPC device manufactured by Tosoh Corporation under the following conditions. did. Column: GPWP + G5000PW + G3000P
W Column temperature: 40 ° C Eluent: 0.1 N-NaCl solution Solvent flow rate: 1.02 ml / min Detection unit: RI

[Method of Evaluating Dispersant Performance] Using the various dispersants obtained above, as a heavy calcium carbonate, Sunlite SL-700 (average particle size: 4.5, manufactured by Takehara Chemical Co., Ltd.)
μ) was used as fine particle heavy calcium carbonate, Nanox # 30 (average particle diameter 0.7 μm) manufactured by Maruo Calcium Co., Ltd. In addition, an evaluation test of dispersibility with respect to these pigments was carried out by using Ultra Coat manufactured by Engelhard Co. as kaolin. The pigment dispersion was prepared by the following method.

As shown in Table 2, a predetermined amount of deionized water and a dispersant as shown in Table 1 were placed in a 1-liter stainless steel container in an amount of 0.01-3.
The pigment was added at a rate of 0% by weight, the pigment was added under stirring with an auto homomixer, and stirring was continued for 20 minutes after the addition was completed to prepare a pigment slurry. The viscosity of each slurry was measured using a B-type viscometer at 12 rpm and 25 ° C. As is clear from the results of Table 2, the dispersant of the present invention (NO.1 to 4)
When used, the contrast dispersants (NO.5-8)
An excellent pigment slurry having a lower viscosity was obtained with a small addition amount as compared with the case of using.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

INDUSTRIAL APPLICABILITY The pigment dispersant for coated paper of the present invention exhibits an excellent dispersing effect on heavy calcium carbonate, kaolin and other pigments which are widely used in the papermaking industry and has a low viscosity even when added in a small amount. Give a dispersion. Therefore, coated paper having excellent smoothness, glossiness, printability, etc. can be produced extremely efficiently.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C09D 135/08 PFY D21H 19/44 // C08F 216/18 MKY 222/06 MLT (72) Inventor Ryo Kobayashi 2209 Aomi, Omi-cho, Aomi-cho, Nishikubiki-gun, Niigata Prefecture Aomi Plant of Denki Kagaku Kogyo Co., Ltd.

Claims (1)

[Claims] 1. A salt of a copolymer of maleic anhydride and an alkyl vinyl ether represented by the following general formula (I), wherein the weight average molecular weight of the salt of the copolymer is 10,000 to 100 in terms of polyethylene glycol. A pigment dispersant for coated paper containing 100,000 water-soluble polymer compounds as an active ingredient. General formula (I) CH2 = CHOR (In the formula, R is an alkyl group having 1 to 4 carbon atoms.)