JP2000239376A - Production of pigment dispersant for aqueous paint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject pigment dispersant having no negative effect on waterproofness of coatings and little selectivity for pigments and capable of forming coatings excellent in glossiness and the like by reacting a polyester resin with a polybasic acid anhydride and the resultant with a polyamine compound. SOLUTION: This method comprises reacting a polyester resin having 25-250 mgKOH/g hydroxy number with a polybasic acid anhydride to obtain a modified polyester resin having 40-300 mgKOH/g acid value. The modified polyester resin is reacted with a polyamine compound (e.g. ethylenediamine) having >=2 amino groups in a molecle to obtain a polyesterpolyamide resin having 15-150 mgKOH/g acid value and 3,000-8,000 weight-average molecular weight. The pigment dispersant is obtained by neutralization of the polyesterpolyamide resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a resin for a pigment dispersant, which is preferably used for improving the dispersibility of a pigment when preparing an aqueous paint, a pigment dispersant using the resin, The present invention relates to a method for producing the pigment dispersant.

[0002]

2. Description of the Related Art Conventionally, an aqueous paint containing a pigment is prepared by dispersing a pigment in a high concentration in an aqueous medium in advance in the presence of a pigment dispersant in a stable manner from the viewpoint of dispersion efficiency. A paint is prepared by mixing and dispersing with an aqueous paint component excluding a pigment component.

On the other hand, a pigment dispersant is blended to prevent agglomeration and precipitation of the pigment in the coating material, and to prevent defects in the appearance of the coating film such as reduction in gloss and color separation of the coating film caused by the aggregation and precipitation. .

Heretofore, low molecular weight surfactants have been mainly used as pigment dispersants. However, since the molecular weight is low, not only the dispersion stability of the pigment is insufficient but also the pigment remains in the coating film. However, there is a problem that it is eluted and adversely affects water resistance, corrosion resistance and the like.

Therefore, recently, a pigment dispersant using a high molecular weight resin has been used. As such a pigment dispersant, a resin liquid in which a part of a binder resin used in an aqueous paint is dissolved in an organic solvent is generally used. Therefore, a relatively large amount of organic solvent is contained in the water-based paint, and there is a problem from the viewpoint of environmental pollution and resource saving. Pigment dispersants using high molecular weight resins are also being developed, but all have problems in the selectivity of pigments, and pigment dispersants that improve the dispersibility of pigments for a wide range of pigments The fact is that the agent has not yet been developed.

[0006]

Accordingly, the present invention overcomes the problems of the conventional pigment dispersants, does not adversely affect the water resistance of the coating film, and uses no or no organic solvent. It is an object of the present invention to provide a pigment dispersing agent which can be used in a small amount, and has a low selectivity to a pigment, and can be suitably applied to an aqueous paint.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, have found that high-molecular-weight polyester polyamide resins containing an ester group and an amide group in the main chain. It has been found that the use of a hydrate as a pigment dispersant can form an excellent coating film having low pigment selectivity and high gloss. The present invention has been completed based on such findings.

That is, the present invention relates to the following inventions. (1) A resin for a pigment dispersant, comprising a polyester polyamide resin containing an ester group and an amide group in the main chain. (2) The polyester polyamide resin has two or more amide groups in one molecule, and has an acid value of 15 to 150 mg.
The resin for a pigment dispersant according to the above (1), having a KOH / g and a weight average molecular weight of 3,000 to 80,000. (3) A pigment dispersant for an aqueous paint, comprising a neutralized product of the polyester polyamide resin described in (2). (4) A method for producing a pigment dispersant for a water-based paint, comprising the following steps: (a) a hydroxyl value of 25 to 250 mgKOH / g;
Reacting the polyester resin with an acid anhydride of a polybasic acid to produce a modified polyester resin having an acid value of 40 to 300 mgKOH / g, (b) two or more modified polyester resins and two or more per molecule. By reacting with an amino group-containing polyamine compound, a polyester polyamide resin having two or more amide groups in one molecule, and having an acid value of 15 to 150 mgKOH / g and a weight average molecular weight of 3,000 to 80,000 is produced. And c) a step of neutralizing the polyester polyamide resin.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The resin for a pigment dispersant of the present invention comprises a polyester polyamide resin containing an ester group and an amide group in the main chain, and is suitably 2 or more, preferably 5 to 150 in one molecule. More preferably, it has 10 to 50 amide groups and has an acid value, for example, 15 to 150 m
gKOH / g, preferably 25-100 mgKOH / g
g and weight average molecular weight, for example, 3000-8000
It is a resin having 0, preferably 8,000 to 30,000.

[0011] Such a polyester polyamide resin is
Typically, it is manufactured by a method comprising the steps described below. (First step) The hydroxyl value is 25 to 250 mgKOH /
g, preferably 40 to 180 mg KOH / g, of a polyester resin is reacted with a polybasic acid anhydride to produce a modified polyester resin.

The polyester resin as a starting material before being modified with an acid anhydride has a hydroxyl value of 25 mgKOH /
g, it is difficult to obtain the modified polyester resin having a high acid value, and conversely, the hydroxyl value is 250 mgKOH / g.
When the ratio exceeds the above range, it becomes difficult to increase the molecular weight, and the pigment dispersing agent obtained by the reaction with a polyamine compound described below tends to have insufficient pigment dispersing performance.

The polyester resin as a starting material is prepared by dehydration-condensing a polyol and a polybasic acid or an acid anhydride thereof and, if necessary, a monobasic acid as a molecular weight modifier according to a conventional method. It is obtained by reacting.

As the polyol, various aliphatic, alicyclic and aromatic alcohols usually used for the synthesis of polyester resins for paints can be used without any particular limitation. Specifically, ethylene glycol, diethylene glycol, neopentyl glycol, 1,6-
Hexanediol, dimethylolpropane, trimethylolpropane, cyclohexanedimethanol, dihydromethylbenzene, dimethylolpropanoic acid, dimethylolbutanoic acid, polycaprolactonediol, bisphenol A, bisphenol-dihydroxyethyl ether, and the like are typical examples. . As the polybasic acid or acid anhydride thereof, various polybasic acids or acid anhydrides which are generally used for synthesizing a polyester resin for paints can be used without any particular limitation. Specifically, saturated polybasic acids such as succinic acid, adipic acid, azelaic acid, and sebacic acid or anhydrides thereof; phthalic acid, pyromellitic acid, trimellitic acid, maleic acid, citraconic acid, itaconic acid, fumaric acid Typical examples thereof include unsaturated polybasic acids such as acids and acid anhydrides thereof. The weight average molecular weight of the starting material polyester resin is
For example, 350 to 5000, preferably 450 to 20
00 is preferred.

As the acid anhydride of the polybasic acid which modifies the polyester resin as the starting material, the acid anhydride of the polybasic acid used in the synthesis of the polyester resin described above can be similarly used. The modified polyester resin formed by the reaction between the polyester resin and the acid anhydride of the polybasic acid can be obtained, for example, by heating and reacting both at 120 to 200 ° C. for 10 to 90 minutes. Polyester resin modified with acid anhydride of polybasic acid has an acid value of, for example, 40 to 300.
mgKOH / g, preferably 60-200 mgKOH
/ G is appropriate.

If the acid value is less than 40 mgKOH / g, the amount of amide groups introduced into the resin for a dispersant of the present invention is reduced, so that the function as a pigment dispersant is liable to decrease. / G tends to lower the water resistance and the like of the obtained coating film. (Second Step) In the second step, the polyester resin modified with the acid anhydride of the polybasic acid obtained in the first step is reacted with a polyamine compound containing two or more amino groups in one molecule. Thus, a polyester polyamide resin containing an ester group and an amide group in the main chain is produced.

The polyamine compound containing two or more amino groups in one molecule includes ethylenediamine, trimethylenediamine, tetramethylenediamine, and the like.
Aliphatic polyamines such as pentamethylenediamine and triaminopropane; aromatic polyamines such as phenylenediamine, xylenediamine and diaminodiphenylmethane;
Other typical examples include polyoxyethylene diamine, polyoxypropylene diamine, triethylene glycol diamine, and tripropylene glycol diamine.

The polyester polyamide resin is obtained by reacting the above-mentioned modified polyester resin with a polyamine compound to form two or more amide groups in one molecule, preferably 5 to 5 amide groups.
150, more preferably 10 to 50, and the acid value is, for example, 15 to 150 mgKOH / g, preferably 25 to 100 mgKOH / g, and the weight average molecular weight is, for example, 3000 to 80,000, preferably Is 8
A polyester polyamide resin having a molecular weight of 000 to 30,000 is suitable.

When the number of amide groups is one or less per molecule, the pigment dispersing performance is poor, and when the number exceeds 150, water resistance, weather resistance and the like tend to decrease. The acid value is 15m
When the acid value is less than gKOH / g, it is difficult to stably disperse in the water-based paint, and when the acid value exceeds 150 mgKOH / g, the water resistance and the like tend to decrease.

When the weight average molecular weight is less than 3,000, the pigment dispersion stability is reduced, and the weight average molecular weight is less than 80.
If it exceeds 000, the water dispersibility tends to decrease.

As the resin for a pigment dispersant of the present invention, a polyester polyamide resin produced from the first step and the second step described above is preferable.

In the present invention, when such a polyester polyamide resin is used as a pigment dispersant for an aqueous paint, it is preferable to neutralize the polyester polyamide resin with a neutralizing agent so as to be dissolved or stably dispersed in water. .

Examples of the neutralizing agent include primary amines such as ethanolamine and secondary amines such as diethanolamine.
Representative amines; tertiary amines such as triethanolamine and dimethylethanolamine; hydroxides of alkali metals such as potassium hydroxide and sodium hydroxide; and ammonia.

The neutralization treatment can be easily carried out by adding a neutralizing agent or an aqueous solution thereof to the above-mentioned polyester polyamide resin or a solution thereof according to a conventional method. The neutralizer is
For example, 0.2 to 2.0 with respect to 1 equivalent of the acid group in the resin.
An equivalent amount, preferably a used amount of 0.5 to 1.5 equivalent is appropriate.

When the pigment dispersant of the present invention comprising a neutralized polyester polyamide resin is used for an aqueous coating, it is diluted with water to have a solid content of, for example, 20 to 60% by weight, preferably 30 to 45% by weight. Preferably, it is used as an aqueous dispersion of a pigment dispersant by weight.

The aqueous pigment dispersion for an aqueous paint using the pigment dispersant of the present invention is an aqueous dispersion of a pigment and a pigment dispersant,
Further, if necessary, water, a small amount of a surfactant, a protective colloid, etc. are added, and the mixture is ball milled, roll milled,
It can be prepared by dispersing with a dispersing device such as an attritor or a paint shaker.

The mixing ratio of the pigment and the pigment dispersant is
The optimum ratio may be arbitrarily determined depending on the type of the pigment, the type of the water-based paint, and the like, but usually, for example, 1 to 2000 parts by weight, preferably 3 to 500 parts by weight, per 100 parts by weight of the pigment is appropriate. The content of the pigment in the aqueous pigment dispersion is, for example, 2 to 90% by weight, preferably 1 to 90% by weight.
0-60% by weight is suitable.

As the pigment to be used, pigments usually used for paints can be used without any particular limitation. Specifically, inorganic pigments such as titanium oxide, iron oxide, carbon black, ultramarine, graphite, zinc sulfide, cobalt blue, barium sulfate, and calcium carbonate; metal powder pigments such as aluminum powder, bronze powder, and zinc powder; Typical examples thereof include organic pigments such as nitroso, nitro, phthalocyanine, azo, and condensed polycyclic compounds.

The aqueous pigment dispersion containing the pigment at a high concentration obtained in this manner can be made of a conventionally known water-soluble resin such as a polyester resin, an acrylic resin, a fluororesin, an epoxy resin, a urethane resin or a polybutadiene resin. It has good miscibility with water-dispersible resins and emulsion resins, and can be widely used for coloring aqueous paints composed of any of these resins. The mixing ratio of the aqueous pigment dispersion to the aqueous paint can be changed in a wide range depending on the kind of the pigment and the required degree of coloring, etc., but is generally 100 parts by weight of the resin component of the aqueous paint. On the other hand, the aqueous pigment dispersion is, for example,
It is appropriate to mix in the range of 10 to 1000 parts by weight.

[0030]

The present invention will be described below in more detail with reference to examples and comparative examples. In the examples and comparative examples, “parts” and “%” are shown on a weight basis. Example 1 In a vessel equipped with a stirrer, thermometer and water separator, 1,6-
330.4 parts of hexanediol, 72.8 parts of neopentyl glycol, 98 parts of dimethylolpropanoic acid, 282.8 parts of sebacic acid, and 232.4 parts of isophthalic acid were charged, and the temperature was raised to 150 ° C. over 1 hour. After, 230 ° C
The temperature was raised while removing the produced water over 5 hours. At the same temperature, the dehydration-condensation reaction is continued until the acid value (measured based on JIS K 6901 4.3) becomes 50 mgKOH / g, and a polyester resin having a hydroxyl value (measured based on JIS K00707) of 180 mgKOH / g (weight) An average molecular weight (measured according to ASTM D3536-91) of 1000) was produced. Next, after cooling to 150 ° C., 200 parts of succinic anhydride was added. Reaction temperature 1
The temperature was raised to 70 ° C. over 1 hour, and the acid value was 120 m
The reaction was continued until gKOH / g was reached to produce a modified polyester resin.

Next, after cooling to 130 ° C., 135 parts of triethylene glycol diamine was added. After the addition, the temperature was raised to 220 ° C. over 3 hours while removing generated water, and the mixture was further reacted at the same temperature for 2 hours. The number of amide groups in one molecule (theoretical calculation value) was 12, the acid value was 40 mg KOH / g, and A polyester polyamide resin having a weight average molecular weight (measured based on ASTM D3536-91) of 20,000 was produced. The resin solution was cooled to 150 ° C., diluted with 100 parts of ethylene glycol monobutyl ether, and further diluted with 80 parts.
After adding 50 parts of n-butanol at a temperature of 68 ° C., 68 parts of N, N-dimethylethanolamine as a neutralizing agent and 2200 parts of deionized water are added, and a pigment dispersant containing a neutralized polyester polyamide resin is added. Was obtained. The aqueous dispersion was a transparent liquid having a pH of 7.3 and having a nonvolatile content of 35%.

Example 2 In a vessel equipped with a stirrer, thermometer and water separator, 1,6-
After charging 177 parts of hexanediol, 104 parts of neopentyl glycol, 85 parts of dimethylolpropanoic acid, 560 parts of dimer acid, and 166 parts of isophthalic acid, the temperature was raised to 150 ° C. over 1 hour, and then to 230 ° C. over 5 hours. The temperature was raised while removing generated water. Acid value 40m at the same temperature
The dehydration condensation reaction was continued until gKOH / g was reached to produce a polyester resin having a hydroxyl value of 130 mgKOH / g (weight average molecular weight 1200). Next, after cooling to 150 ° C., 180 parts of succinic anhydride was added. Reaction temperature 1
The temperature was raised to 70 ° C. over 1 hour, and the acid value was 110 m.
The reaction was continued until gKOH / g, to produce a modified polyester resin. Next, after cooling to 130 ° C., 110 parts of metaxylenediamine were added. After addition, 220
The temperature was raised to 3 ° C. over 3 hours while removing generated water, and the reaction was further continued at the same temperature for 2 hours. The number of amide groups in one molecule was 15, the acid value was 35 mg KOH / g, and the weight average molecular weight was 30,000.
Was produced. The resin solution was cooled to 150 ° C., diluted with 120 parts of ethylene glycol monobutyl ether, and further added with 100 parts of n-butanol at 80 ° C., followed by 60 parts of N, N-dimethylethanolamine as a neutralizing agent. 2,000 parts of deionized water was added to obtain an aqueous dispersion of a pigment dispersant consisting of a neutralized polyester polyamide resin. The aqueous dispersion had a pH of 7.3.
And a transparent liquid having a nonvolatile content of 36%. Example 3 In a container equipped with a stirrer, a thermometer and a water separator, 530 parts of polycaprolactone diol ("Placcel 205U": trade name of Daicel Chemical Industries, Ltd.), 104 parts of neopentyl glycol, and 67 parts of dimethylolpropanoic acid Then, 146 parts of adipic acid and 83 parts of isophthalic acid were charged, and the temperature was raised to 150 ° C over 1 hour, and then raised to 230 ° C over 5 hours while removing generated water. 37m acid value at the same temperature
The dehydration condensation reaction was continued until gKOH / g was reached to produce a polyester resin having a hydroxyl value of 125 mgKOH / g (weight average molecular weight 1300). Next, after cooling to 150 ° C., 150 parts of succinic anhydride was added. Reaction temperature 170
The temperature was raised to 1 ° C over 1 hour, and the acid value was 110 mgK.
The reaction was continued until OH / g was reached to produce a modified polyester resin. Next, after cooling to 130 ° C., 150 parts of tripropylene glycol diamine was added. After the addition, the temperature was raised to 220 ° C over 3 hours while removing generated water, and the reaction was further performed at 220 ° C for 2 hours. The number of amide groups in one molecule was 10, the acid value was 40 mgKOH / g, and the weight average molecular weight was 25,000. Was produced. The resin solution was cooled to 150 ° C., diluted with 150 parts of ethylene glycol monobutyl ether, further added with 50 parts of n-butanol at 80 ° C., and mixed with 65 parts of N, N-dimethylethanolamine as a neutralizing agent. 1500 parts of deionized water was added to obtain an aqueous dispersion of a pigment dispersant consisting of a neutralized polyester polyamide resin.
The aqueous dispersion was a transparent liquid having a pH of 8.2 and a nonvolatile content of 40%.

Example 4 In a container equipped with a stirrer, a thermometer and a water separator, 150 parts of "Placcel 205U" and 50 parts of dimethylolbutanoic acid were added.
Part, adipic acid 219 parts, neopentyl glycol 10
4 parts, 59 parts of 1,6-hexanediol, 15
After the temperature was raised to 0 ° C. over 1 hour, the temperature was raised to 230 ° C. over 5 hours while removing generated water. The dehydration reaction was continued at the same temperature until the acid value became 37 mgKOH / g, to produce a polyester resin having a hydroxyl value of 125 mgKOH / g (weight average molecular weight 1300). Next, after cooling to 150 ° C., 150 parts of phthalic anhydride were added. The reaction temperature was raised to 180 ° C. over 1 hour to obtain an acid value of 115.
The reaction was continued until the concentration reached mg KOH / g to produce a modified polyester resin. Then, after cooling to 130 ° C,
112 parts of tripropylene glycol diamine were added. After the addition, the temperature was raised to 220 ° C. over 3 hours while removing generated water, and the reaction was further performed at 220 ° C. for 2 hours. The number of amide groups in one molecule was 11, the acid value was 40 mg KOH / g, and the weight average molecular weight was 15,000. Was produced. The resin was cooled to 150 ° C, diluted with 55 parts of ethylene glycol monobutyl ether, further added with 30 parts of n-butanol at 80 ° C, and dehydrated with 43 parts of N, N-dimethylethanolamine as a neutralizing agent. 1300 parts of ionic water was added to obtain an aqueous dispersion of a pigment dispersant consisting of a neutralized polyester polyamide resin. The aqueous dispersion was a transparent liquid having a pH of 8.0 and a nonvolatile content of 35%.

Comparative Example 1 To a reactor equipped with a reflux condenser and a stirrer, 45 parts of butyl cellosolve was added, and the mixture was heated to 100 ° C. while stirring.
Next, 20 parts of methyl methacrylate, 25 parts of butyl acrylate, and 2.5 parts of hydroxyethyl methacrylate
, 2.5 parts of acrylic acid and 1.5 parts of t-butylperoxy-2-ethylhexanoate were added dropwise at the same temperature over 3 hours, and then the temperature was raised to 105 ° C and maintained for 2 hours. The reaction was terminated. Next, after cooling to 60 ° C,
A mixture of 1.8 parts of N, N-dimethylethanolamine and 85 parts of deionized water was added at 60 ° C. for 1 hour.

The obtained acrylic resin (acid value: 47 mg KO)
H / g) The aqueous dispersion was a clear liquid having a pH of 8.0 and a non-volatile content of 50%. Comparative Example 2 In a container equipped with a stirrer, a thermometer, and a water separator, 1,6-
177 parts of hexanediol and neopentyl glycol 1
04 parts, dimethylolpropanoic acid 40 parts, dimer acid 5
60 parts and 166 parts of isophthalic acid were charged, and the temperature was raised to 150 ° C. over 1 hour, and then raised to 230 ° C. over 5 hours while removing generated water. Acid value 20mgK at the same temperature
The dehydration condensation reaction was continued until OH / g was reached to produce a polyester resin (weight average molecular weight 3500). Then 1
After cooling to 50 ° C., 65 parts of succinic anhydride were added.
Raise the reaction temperature to 170 ° C. over 1 hour,
The reaction was continued until the acid value reached 35 mgKOH / g to produce a modified polyester resin. Next, the mixture was cooled to 80 ° C, diluted with 120 parts of ethylene glycol monobutyl ether, and further added with 60 parts of n-butanol at 80 ° C.
N, N-dimethylethanolamine 45 as a neutralizing agent
And 1700 parts of deionized water were added to obtain an aqueous dispersion comprising a polyester resin neutralizing agent. The aqueous dispersion has a pH
It was a transparent liquid having 7.3 and a nonvolatile content of 40%.

Reference Examples 1 to 12 The aqueous dispersions and pigments obtained in the above Examples and Comparative Examples were
The mixture was mixed at the blending ratio (unit “parts”) described in 2, water was added, and the mixture was dispersed for 2 hours using a paint shaker disperser to obtain an aqueous pigment dispersion. The properties of the aqueous pigment dispersion are shown in Tables 1 and 2. Next, the pigment dispersion was mixed with a commercially available water-based acrylic-melamine resin clear paint in the mixing ratio (unit “parts”) shown in Tables 1 and 2, and then applied to a glass plate with a 6 mil applicator. And heated at 150 ° C. for 20 minutes to obtain a colored coating film. Table 1 shows the surface gloss of the coating film.
2 is shown.

Table 1

Table 2

Note 1) Based on JIS K 5400A method.

Note 2) After standing at room temperature for 2 weeks, the dispersion state of the aqueous pigment dispersion was compared with the initial dispersion state, and the presence or absence of sedimentation separation was observed.

Note 3) The aqueous pigment dispersions of Reference Examples 1 and 2 were each diluted with deionized water until the pigment concentration reached 1% by volume, and then the volume ratio of titanium oxide white to carbon black was 8%.
/ 2, put this in a test tube, let stand at room temperature for 2 days, and observe the color separation. The aqueous pigment dispersions of Reference Examples 8 and 9 were mixed in the same manner, and the color separation was observed. Note 4) 60-degree specular reflectance As is clear from Tables 1 and 2, each of the aqueous pigment dispersions of Reference Examples 1 to 7 using the pigment dispersant of the present invention has good pigment dispersion stability. There was no color separation. Further, the coating film of the paint produced by blending these pigment aqueous dispersions had high gloss.

On the other hand, Reference Examples 8 to 10 using a conventional acrylic resin-based pigment dispersant, and Reference Examples 11 and 12 using a polyester-based pigment dispersant containing no amide group, all show pigment selectivity. was there.

[0043]

The pigment dispersant of the present invention requires a small amount of an organic solvent, has excellent pigment dispersibility, has low selectivity to pigments, and can be suitably used for water-based paints.

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[Procedure amendment]

[Submission date] June 2, 2000 (2006.2)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Name of invention

[Correction method] Change

[Correction contents]

Patent application title: Method for producing pigment dispersant for water-based paint

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Teiichi Tomura 1-10-7 Kusanagi, Yamato-shi, Kanagawa F-term (reference) 4J001 DA03 EB75 EC04 EC05 EC07 EC45 EC46 EC47 EC48 EC54 EC77 EC86 GD06 JA17 JA20 JB01 JB16 4J037 AA02 AA05 AA06 AA08 AA09 AA10 AA11 AA13 AA15 AA17 AA22 AA30 CC24 CC27 DD04 DD24 EE08 EE28 EE43 FF15

Claims (4)

[Claims] 1. A pigment dispersant resin comprising a polyester polyamide resin having an ester group and an amide group in the main chain. 2. The polyester polyamide resin has two or more amide groups in one molecule, and has an acid value of 15 to 150.
mgKOH / g and weight average molecular weight 3000-8000
The resin for a pigment dispersant according to claim 1, which has 0. 3. A pigment dispersant for a water-based paint, comprising a neutralized product of the polyester polyamide resin according to claim 2. 4. A method for producing a pigment dispersant for an aqueous paint, comprising the steps of: (1) reacting a polyester resin having a hydroxyl value of 25 to 250 mg KOH / g with an acid anhydride of a polybasic acid. Producing a modified polyester resin having an acid value of 40 to 300 mg KOH / g, (2) reacting the modified polyester resin with a polyamine compound having two or more amino groups in one molecule to obtain 1 Having two or more amide groups in the molecule and having an acid value of 1
5-150 mgKOH / g and weight average molecular weight 3000
A method of producing a polyester polyamide resin of 〜80,000, and (3) a step of neutralizing the polyester polyamide resin.