JP2002332310A - Aqueous resin dispersion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare an aqueous resin dispersion which excels in polymerization stability and storage stability and has low thixotropic properties and excellent alkali thickening properties. SOLUTION: This aqueous resin dispersion comprises a polymer having an acid value of 50-400 mgKOH/g and a weight average molecular weight of 20,000-200,000, and has a viscosity of 20 mass% the above polymer present at 25 deg.C of <=1,000 mPas, an increase in viscosity at the time of neutralization by 10-100 times, and simultaneously, a viscosity ratio (pH=9/pH=7) at pH=7 and pH=9 in the range of 1 to 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkali-thickening aqueous resin dispersion having excellent production stability and storage stability and low thixotropy, and is suitable for use as a thickener for aqueous paints. What can be used.

[0002]

2. Description of the Related Art As a dispersant or a thickener for an aqueous paint, for example, an aqueous dispersion of an alkali-soluble oligomer is used. This utilizes the property that the polymer in the aqueous dispersion partially or completely dissolves in water according to the amount of the basic substance to be added, that is, the pH of water as the dispersion medium.

[0003] In particular, when this is used as a thickener, the thickening behavior at the time of dissolving the polymer is important. It is required that the change in the viscous behavior is small, the thixotropy is low, and the like.

[0004] For example, JP-A-4-7309 describes an aqueous dispersion of an oligomer obtained by emulsion-polymerizing a polymerizable carboxylic acid or the like in an aqueous medium. However, when the amount of the polymerizable carboxylic acid used in the emulsion polymerization is increased in order to increase the viscosity, there is a problem that the polymerization stability is reduced.

[0005] In order to solve this problem, Japanese Patent Application Laid-Open No. Hei 6-271779 proposes that an aqueous dispersion of an alkali-soluble oligomer be obtained by emulsion polymerization in the presence of a polymerizable emulsifier. ing. This aqueous dispersion has characteristics such as low thixotropy.

[0006]

However, Japanese Patent Laid-Open No. 6-2 / 1994
The aqueous dispersion of an alkali-soluble oligomer described in Japanese Patent No. 71779 has a problem that the viscosity is insufficient. When this aqueous dispersion is added to increase the viscosity of the aqueous paint to a required level, the water resistance of the resulting coating film tends to decrease.

The present invention has been made to solve the above-mentioned problems, and an aqueous resin dispersion having excellent polymerization stability and storage stability, low thixotropy, and excellent alkali thickening is provided. It is intended to provide.

[0008]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that an aqueous resin dispersion containing a polymer having a specific acid value and a weight average molecular weight and having a specific viscosity characteristic has the above problem. And have completed the present invention.

[0009] That is, the aqueous resin dispersion of the present invention contains a polymer having an acid value of 50 to 400 mgKOH / g and a weight average molecular weight of 20,000 to 200,000. Has a viscosity at 25 ° C. of not more than 1000 mPas, the viscosity increases by 10 to 100 times during neutralization, and the viscosity ratio at pH = 7 and pH = 9 (pH = 9 / p
H = 7) is in the range of 1 to 10.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The acid value of a polymer as a component of the aqueous resin dispersion of the present invention is 50 to 400 mgKOH / g.
Must be in the range It has an acid value of 50 mg KO
If it is less than H / g, it tends to be difficult to impart sufficient alkali thickening to the aqueous resin dispersion. It is preferably at least 50 mgKOH / g. Also,
If the acid value exceeds 400 mgKOH / g, the polymer becomes water-soluble irrespective of its molecular weight, so that the viscosity of the dispersion becomes high and the handleability as a thickener is reduced (for example, when the water-based paint, Viscosity adjustment becomes difficult). Preferably it is 300 mgKOH / g or less.

[0011] The weight average molecular weight of the polymer must be in the range of 20,000 to 200,000. This is because if the weight average molecular weight is less than 20,000, it tends to be difficult to impart sufficient viscosity to the aqueous resin dispersion. Preferably it is 40,000 or more. Further, when the weight average molecular weight is 20
If it exceeds 10,000, the pH at the time of alkali thickening of the aqueous resin dispersion is
The change in viscosity with respect to the change is remarkably large, and the handleability as a thickener tends to decrease (it becomes difficult to mix and adjust the viscosity of a water-based paint or the like). Preferably it is 150,000 or less.

[0012] The aqueous resin dispersion of the present invention comprises the polymer
Viscosity at 25 ° C. in the presence of 0 mass% is 1000 mPa
s or less. It has a viscosity of 1000 mP
If it exceeds as, it is difficult to mix the water-based paint or the like and adjust the viscosity thereof, and the handleability tends to be impaired. Preferably it is 500 mPas or less.

[0013] The aqueous resin dispersion of the present invention can be neutralized (pH =
The viscosity of 7) needs to be increased by 10 to 100 times.

[0014] This is because if the viscosity increase during the neutralization is less than 10 times, it tends to be difficult to impart a sufficient viscosity to the aqueous resin dispersion. Preferably it is 15 times or more. On the other hand, if the increase in viscosity during neutralization exceeds 100 times, the viscosity of the compound tends to be extremely high. Preferably it is 50 times or less.

Further, the aqueous resin dispersion of the present invention has a pH of 7
And the viscosity ratio at pH = 9 (pH = 9 / pH = 7) is 1
It must be in the range of 10 to 10. This is because pH = 7 and p
If the viscosity ratio at H = 9 is less than 1, the viscosity of the composition tends to be difficult to adjust. Preferably 2
That is all. On the other hand, when the viscosity ratio exceeds 10, the change in the viscosity of the aqueous resin dispersion with respect to the change in the pH during alkali thickening becomes large, and the handleability as a thickener is reduced. Harder). Preferably it is 5 or less.

The polymer used in the present invention preferably comprises an ethylenically unsaturated carboxylic acid and a compound copolymerizable therewith from the viewpoint of alkali thickening performance.

Examples of the ethylenically unsaturated carboxylic acid usable as a component of the polymer used in the present invention include, for example, (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and succinic acid. -(Meth) acryloyloxyethyl, 2- (meth) acryloyloxyethyl phthalate, 2- (meth) acryloyloxyethyl hexahydrophthalate, and the like. One or more of these can be appropriately selected and used as necessary, and among them, acrylic acid is preferred from the viewpoints of polymerization stability, alkali thickening and the like.

Further, the constituent components of the polymer used in the present invention include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, (meth)
I-butyl acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (meth)
Lauryl acrylate, stearyl (meth) acrylate,
Cyclohexyl (meth) acrylate, glycidyl (meth) acrylate, tetrafurfuryl (meth) acrylate,
2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, ethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, 2- (meth) acryloyloxyethyl succinate, (Meth) acrylic acid esters such as 2- (meth) acryloyloxyethyl maleate, hexahydrophthalic acid- (meth) acryloyloxyethyl and diethylaminoethyl (meth) acrylate, and vinyl cyanide such as (meth) acrylonitrile Compound, furthermore styrene,
Examples thereof include aromatic vinyl compounds such as vinyltoluene, vinyl esters of ethylenically unsaturated carboxylic acids, and conjugated diene compounds such as 1,3-butadiene, isoprene, and 2-chloro-1,3-butadiene. One or more of these can be appropriately selected and used as needed.

As a polymerization method of the polymer used in the present invention, a solution polymerization method, a suspension polymerization method, an emulsion polymerization method, or the like can be employed. In addition, as a polymerization method, a batch polymerization method in which raw materials excluding an initiator and a polymerization catalyst are initially charged all at once and polymerization is started by adding an initiator and a polymerization catalyst, and a drop polymerization method in which raw materials are added dropwise over several hours. Alternatively, a partial drop polymerization method in which a part of the raw materials are charged in advance and the rest is added dropwise may be employed.

The polymerization method and the polymerization method can be appropriately selected as necessary. As the polymerization method, the obtained polymer dispersion can be used as it is as the aqueous resin dispersion of the present invention. Therefore, an emulsion polymerization method is preferable. As the polymerization method, a known method such as a batch method or drop polymerization can be used.

The emulsifier used in the emulsion polymerization is not particularly limited, and commonly used anionic, cationic and nonionic surfactants, polymer emulsifiers and the like can be used. Among them, a reactive emulsifier having an ethylenically unsaturated group capable of undergoing radical polymerization is preferable because it tends to improve the polymerization stability of the polymer and the storage stability of the aqueous resin dispersion of the present invention.

Examples of the reactive emulsifier include Eleminol JS-2 manufactured by Sanyo Kasei Co., Ltd., Latemul S-120, S-180, S-180A manufactured by Kao Corporation, and Adecaria manufactured by Asahi Denka Kogyo Co., Ltd. Soap SE-10N, an anionic emulsifier such as Aqualon HS series manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Adecaria Soap NE series manufactured by Asahi Denka Kogyo Co., Ltd., Aqualon RN series manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Blemmer PE and PEP series manufactured by Rhodia Nika Co., Ltd.
Nonionic emulsifiers, such as SEM-25, can be mentioned. One or more of these can be appropriately selected and used as needed.

The amount of the emulsifier used in the emulsion polymerization is preferably in the range of 0.1 to 10 parts by mass in solid content based on 100 parts by mass of the above-mentioned polymer constituents. This is because the use of the emulsifier in an amount of 0.1 parts by mass or more tends to improve the polymerization stability of the polymer and the storage stability of the aqueous resin dispersion of the present invention. It is more preferably at least 0.5 part by mass. Also, when the amount is 10 parts by mass or less, the water resistance of a coating film formed from a water-based paint or a coating material containing the water-based resin dispersion of the present invention tends to be excellent. More preferably 5
Not more than parts by mass.

The initiator used in the production of the polymer used in the present invention is not particularly limited.
Persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate, t-butyl hydroperoxide, benzoyl peroxide, cumene hydroperoxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxide Peroxides such as oxyisobutyrate, azobisisobutyronitrile, 2,2-azobis (2,4-dimethylvaleronitrile), 2,2-azobis (4-methoxy-2,4-dimethylvaleronitrile) ) And azo compounds such as 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile. One or more of these can be appropriately selected and used as needed. Further, for the purpose of accelerating the polymerization or performing the polymerization at a low temperature, an oxidizing or reducing agent such as sodium bisulfite, ferrous sulfate, ascorbate, pyrophosphate, Rongalit, ethylenediaminetetraacetate and the like can be used.

In the production of the polymer, the molecular weight can be adjusted by using a chain transfer agent during the polymerization in order to keep the weight average molecular weight of the obtained polymer in the range of 20,000 to 200,000. Examples of the chain transfer agent include mercaptans such as n-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, α-methylstyrene dimer, 1-methyl-4-isopropylidene-1-
Cyclohexene and the like can be mentioned. The type and amount of the chain transfer agent to be used can be appropriately selected according to the polymerization temperature and the target molecular weight.

The aqueous resin dispersion of the present invention has a p
H is preferably in the range of 2 to 5. This is 25 ° C
This is because, by setting the pH in the above to 2, the polymerization stability and the storage stability of the obtained aqueous resin dispersion tend to be improved. More preferably, it is 3 or more. Further, by setting the pH at 25 ° C. to 5 or less,
There is a tendency that stability during polymerization and productivity are improved. More preferably, it is 4 or less.

The aqueous resin dispersion of the present invention may contain an appropriate amount of a basic substance in order to adjust the pH and viscosity of the dispersion. The basic substance may be added to the dispersion or may be added during the production of the aqueous resin dispersion.

[0028] The basic substance is not particularly limited and can be appropriately selected and used as necessary. Among them, hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide and the like can be used. Alkali metal salts such as sodium carbonate, sodium hydrogencarbonate, and amines such as ammonia, methylamine, ethylamine, dimethylamine, triethylamine, dimethylethanolamine, 2-amino-2-methyl-1-propanol, and triethanolamine. When used, the aqueous resin dispersion of the present invention tends to have good storage stability, which is preferable.

When the aqueous resin dispersion of the present invention is used as a thickener, for example, it is added little by little to an aqueous paint or the like, and if necessary, an appropriate amount of a basic substance is added to adjust the pH. Thereby, the viscosity of the water-based paint or the like increases, and the viscosity can be adjusted to a desired value.

[0030]

EXAMPLES The present invention will be described in detail with reference to examples. All “parts” in the examples are “parts by mass”. The evaluation of the performance in Examples and Comparative Examples was performed using the following method.

(1) Solid content 3 g of the aqueous resin dispersion liquid was weighed on an aluminum dish and placed in a thermostat (1
The mass change (mass after drying / mass before drying (mass%)) after drying for 4 hours in the temperature of 50 ° C.) was determined.

(2) Viscosity The aqueous resin dispersion (25 ° C.) was mixed with a B-type viscometer (Toki Sangyo,
It was measured using an R100 type viscometer, rotation speed = 6 rpm).

(3) Weight average molecular weight Measured using gel permeation chromatography (GPC) (in terms of standard polystyrene).

(4) Acid value 1 g of the aqueous resin dispersion was weighed and dissolved by adding 50 ml of dimethylformamide. Then, phenolphthalein was added as an indicator, and a 0.2N potassium hydroxide / ethanol solution was used. Neutralization titration was performed to determine the number of mg of potassium hydroxide required to neutralize the carboxyl group contained in 1 g of the polymer.

(5) Storage stability The aqueous resin dispersion was put into a glass bottle with a lid, left in a constant temperature bath at 50 ° C., and observed one month later, and evaluated according to the following criteria. ◎: No aggregates were generated, the change in pH was less than 0.5, and the change in viscosity was less than 10% of the initial value. ：: The change in pH was less than 1 and the change in viscosity was 20% of the initial value. Less than Δ: Change in pH is less than 2, change in viscosity is less than 30% of initial value ×: What appears to be agglomerates or gelation at the bottom of glass bottle

(6) Thixotropic index (TI
Value) Pure water and dimethylethanolamine are added to the aqueous resin dispersion, and the dilution is adjusted so that the solid content concentration of the polymer is 20% by mass and pH = 9, and the viscosity after standing at 25 ° C. for 24 hours (m
Pas) was measured by measuring the rotor rotation speed of a B-type viscometer (R100 type viscometer, manufactured by Toki Sangyo) at 6 rpm and 60 rpm, and expressed as a value obtained by dividing the viscosity value at 6 rpm by the viscosity value at 60 rpm.

(7) Dependence on viscosity and pH Pure water and dimethylethanolamine are added to the aqueous resin dispersion, and the dilution is adjusted so that the solid content concentration of the polymer is 20% by mass, pH = 7, or pH = 9. Viscosities (mPas) after standing at 25 ° C. for 24 hours were measured using a B-type viscometer (R
100 type viscometer, rotation speed = 6 rpm), pH =
The value obtained by dividing the viscosity value at pH 7 by the viscosity value of the aqueous dispersion before neutralization (pH → 7) and the viscosity value at pH = 9 were calculated as pH =
7 (pH = 7 → 9).

Example 1 In a reaction vessel equipped with a stirrer and a dropping funnel, 5 parts of ethyl acrylate and 4 parts of ABEX-JKB (a non-polymerizable anionic emulsifier manufactured by Rhodia Co., Ltd.)
After charging 52 parts of pure water and purging with nitrogen, the inside of the reaction vessel was heated to 80 ° C. while stirring, and 2 parts of a 3% aqueous sodium persulfate solution was added to the reaction vessel and reacted for 30 minutes. Was. Thereafter, 87 parts of ethyl acrylate and 8 parts of acrylic acid, 0.2 part of n-octyl mercaptan, AB
EX-JKB 4 parts, dimethylethanolamine 2.3
Parts, a premixed dispersion of 35 parts of pure water, and 12 parts of a 10% aqueous sodium persulfate solution were separately added dropwise to the reaction vessel over 3 hours to allow the polymerization to proceed. After completion of the dropwise addition, the internal temperature of the reaction vessel was raised to 85 ° C., and the mixture was further polymerized for 1 hour to obtain an aqueous resin dispersion. Table 1 shows the evaluation results of the aqueous resin dispersion.

(Examples 2 to 5) An aqueous resin dispersion having the composition shown in Table 1 was produced in the same manner as in Example 1 except for the initiator and the polymerization temperature. Table 1 shows the evaluation results of these aqueous resin dispersions.

(Comparative Examples 1 to 4) An aqueous resin dispersion having the composition shown in Table 2 was produced in the same manner as in Example 1 except for the initiator and the polymerization temperature. In Comparative Example 4, an aqueous resin dispersion was produced by carrying out a total amount drop polymerization using the dropping compositions shown in Table 2 and 12 parts of a 10% aqueous sodium persulfate solution at a polymerization temperature of 80 ° C. Table 2 shows the evaluation results of these aqueous resin dispersions. In Comparative Example 1, the polymerization was interrupted because a remarkably large amount of cullet was generated during the polymerization.

[0041]

[Table 1]

[0042]

[Table 2]

As is clear from the examples, the aqueous resin dispersion of the present invention was excellent in storage stability, had low thixotropy, and had viscosity-pH dependence suitable as a thickener. On the other hand, the comparative examples which do not satisfy the requirements of the present invention were inferior in performance as compared with the examples, and there were cases where the polymerization could not be carried out stably.

[0044]

The aqueous resin dispersion of the present invention has excellent polymerization stability and storage stability, has low thixotropy, and has an excellent alkali thickening property, and is extremely useful in industry.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masatoshi Ura 4-160 Sunadabashi, Higashi-ku, Nagoya-shi, Aichi F-term in the Mitsubishi Rayon Co., Ltd. Product Development Laboratory (reference) 4J011 KA06 KB04 KB05 KB07 KB29 4J100 AB02Q AB04Q AJ01P AJ02P AJ08P AJ09P AL03Q AL04Q AL05Q AL08P AL08Q AL10Q AL62Q AL66Q AM02Q AS02Q AS03Q AS07Q BA05Q BA06Q BA08Q BA16P BA16Q BA31Q BC04P BC04Q BC43P CA04 CA31 DA01 DA09 DA29 DA38 EA07 FA02 FA20 HC37 HC43 HC43 HC43 HC37 HCB

Claims (4)

[Claims] 1. A polymer having an acid value of 50 to 400 mg KOH / g and a weight average molecular weight of 20,000 to 200,000, and having a viscosity at 25 ° C. of 1000 mPas or less when 20% by mass of the polymer is present. Yes, viscosity is 10-1 when neutralized
An aqueous resin dispersion having a 00-fold increase and a viscosity ratio at pH = 7 and pH = 9 (pH = 9 / pH = 7) in the range of 1-10. 2. The aqueous resin dispersion according to claim 1, wherein the pH at 25 ° C. is in the range of 2 to 5. 3. The aqueous resin dispersion according to claim 1, wherein the polymer is produced by emulsion polymerization. 4. The aqueous resin dispersion according to claim 3, wherein the polymer is produced using an emulsifier having radical polymerizability.