JP2882730B2 - Aqueous coating composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous coating composition having both excellent water resistance and excellent pigment dispersibility.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of the environment, the needs of aqueous coating compositions have been greatly increased, and various types of coating compositions have been developed.

[0003] Emulsions, dispersions, and the like, because polymers are dispersed in water, do not cause a significant increase in viscosity even when the molecular weight increases, so that a high molecular weight polymer can be used. . For this reason, there is an advantage that an aqueous coating composition having very good physical properties of a coated film after coating can be prepared, and a great many have been developed so far.

[0004] However, when it is necessary to disperse the pigment at a high concentration, it is essential that the polymer wraps the pigment to prevent reaggregation of the pigment. , Dispersion, etc.,
Re-aggregation of the pigment could not be prevented, and sufficient pigment dispersibility could not be obtained. That is, in order to enclose the pigment and prevent re-aggregation of the pigment, it is necessary that the polymer is dissolved in water and exists. For this reason, various developments of water-soluble polymers have been conventionally made. Typical examples thereof include polyvinyl alcohol and a soda salt of polyacrylic acid.

However, since these water-soluble polymers tend to remain soluble in water even after the formation of the coating film, the coating film is re-dissolved due to trivial effects such as dropping of water droplets. However, there were many disadvantages in practical use due to damage.

In order to solve this problem, a polymer having an acid group such as sulfonic acid and carboxylic acid is neutralized with a volatile base to form a salt, so that the polymer is solubilized in water and dried after coating. In recent years, many developments of aqueous coating compositions based on a technique of insolubilizing in water due to volatilization of a volatile base have been introduced in recent years.

[0007] For example, Japanese Patent Application Laid-Open No. 60-215007 discloses a method for producing a low molecular weight acrylic polymer having a narrow molecular weight distribution by supplying a monomer or the like to a continuous mixing reaction zone by a specific method and polymerizing the monomer. It has been disclosed. However, in this method, when a monomer containing an acid group is copolymerized to an extent that it can be dissolved in water after neutralization with a base, pigment dispersibility is very good, but water resistance is reduced.

As described above, in the aqueous coating composition thus far developed, the acid value has to be increased in order to increase the solubility in water. For this reason, when a water droplet is dropped on the surface of the coating film and rubbed five times with a finger, the coating film does not have a low level of water resistance such as dissolving, but the water is not immersed in water.
When subjected to a severe water resistance test such as being left for 0 hours, deterioration such as clouding of the coating film was unavoidable.

The deterioration of the coating film such as cloudiness can be improved by lowering the acid value of the polymer. However, when the acid value of the polymer is reduced, the solubility of the polymer in water is rapidly reduced, and the polymer is dispersed in water, and the dispersibility of the pigment is reduced. Some polymer dispersions with good water resistance, such as emulsions, are also being studied for blending with aqueous polymer solutions.However, when it is necessary to disperse the pigment at a high concentration, It was impossible to balance. Accordingly, there has been a demand for an aqueous coating composition which has a low acid value and good water resistance, and which is well dissolved in water and exhibits excellent pigment dispersibility.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide an aqueous coating composition having excellent water resistance and excellent pigment dispersibility.

[0011]

That is, the present invention provides:
(A) 30 to 90% by weight of methyl methacrylate, (b)
A secondary transition temperature comprising 0 to 30% by weight of an aromatic vinyl compound, 4 to 15% by weight of (c) an acid group-containing vinyl compound and 0 to 66% by weight of (d) another copolymerizable vinyl monomer. Is 30 to 100 ° C, and the weight average molecular weight is 7,000 to 3
000 and an acid value of 30 to 90 mgKOH / g.
Vinyl polymer (I) polymerized by a suspension polymerization method
Is a vinyl polymer (I) with a base having a boiling point of 200 ° C. or less.
Aqueous coating composition obtained by neutralizing 70 to 100% of the acid groups of the above and dissolving in water.

[0012]

The vinyl polymer (I) used in the present invention comprises:
(A) 30 to 90% by weight of methyl methacrylate, (b)
It is composed of 0 to 30% by weight of an aromatic vinyl compound, 4 to 15% by weight of (c) an acid group-containing vinyl compound, and 0 to 66% by weight of another copolymerizable vinyl monomer.

[0013] Methyl methacrylate (a) is an essential component for imparting hardness to the vinyl polymer.
It is used in a proportion of 90% by weight. If the amount is less than 30% by weight, the hardness decreases, while if it exceeds 90% by weight, the water solubility decreases.

The aromatic vinyl compound (b) has an effect of imparting water resistance to the coating film, and is copolymerized in a range of up to 30% by weight, preferably in a range of 0 to 25% by weight. However, if it exceeds 30 % by weight, the water solubility is lowered, so that it is not suitable. Specific examples of the aromatic vinyl compound include styrene, α-methylstyrene, p-methylstyrene, and benzyl (meth) acrylate, among which styrene is particularly preferred.

The acid group-containing vinyl compound (c) imparts an acid group to the vinyl polymer and is a compound having an acidic group such as carboxylic acid or sulfonic acid. The acid value of the vinyl polymer (I) obtained in the range of 4 to 15% by weight is 30 to 90 mgKOH / g.
It is used so that Specific examples of the acid group-containing vinyl compound include monobasic acids such as acrylic acid, methacrylic acid and crotonic acid; dibasic acids such as fumaric acid, maleic acid and itaconic acid; and partial esters thereof. These can be used as a mixture of two or more kinds. In particular, when a vinyl compound having a carboxylic acid is copolymerized, a copolymer having good water solubility, water resistance and pigment dispersibility can be obtained. In particular, when methacrylic acid is copolymerized, water solubility, water resistance and pigment dispersibility are all very good.

The other vinyl monomer (d) copolymerizable with the monomers (a) to (c) is used in an amount of 0 to 66% by weight, and at least one polymerizable monomer is used. It can be arbitrarily selected from those having a suitable vinyl group according to the purpose. Specific examples of the vinyl monomer (d) include ethyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, t-butyl (meth) acrylate, cyclohexyl (meth) acrylate, (Meth) having an alkyl group having 1 to 18 carbon atoms, such as 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, and stearyl (meth) acrylate
Alkyl acrylate; hydroxyalkyl (meth) acrylate such as 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate; glycol di (meth) acrylate such as ethylene glycol di (meth) acrylate and butylene glycol (meth) acrylate Meth) acrylates; alkylamino (meth) acrylates such as dimethylaminoethyl (meth) acrylate; and dimethylaminoethyl (meth) acrylate methyl chloride salt, cyclohexyl (meth) acrylate, allyl (meth) acrylate, trimethylolpropanetri (meth) acrylate ) Acrylate, glycidyl (meth) acrylate, vinyl acetate, vinyl propionate, (meth) acrylonitrile and the like.

The secondary transition temperature of the vinyl polymer (I) is as follows:
The temperature must be 30 to 100 ° C. as measured by the DSC method, and preferably 35 to 80 ° C. If the temperature is lower than 30 ° C., the stain resistance is insufficient or the blocking resistance is reduced. On the other hand, when the temperature exceeds 100 ° C., the coating film becomes brittle. The weight average molecular weight of the vinyl polymer measured by the GPC method is 7,000 to 30,000.
And preferably 8,000 to 25,000.
0. If it is less than 7,000, the coating film becomes brittle. On the other hand, when it exceeds 30,000, the water solubility decreases. The acid value was determined by adding KOH dissolved in ethanol dropwise to an aqueous solution of a vinyl polymer based on the discoloration point of phenolphthalein, and titrating the vinyl polymer.
When expressed in mg of KOH required to neutralize
９０90 mg KOH / g, preferably 4
0-70 mgKOH / g. If it is less than 35 mgKOH / g, the solubility in water will decrease, and if it exceeds 90 mgKOH / g, the water resistance will be insufficient.

As the polymerization method for producing the vinyl polymer (I), a suspension polymerization method, a solution polymerization method, a bulk polymerization method and the like can be applied . Because it has excellent pigment dispersibility as well as excellent water resistance,
In the present invention, those produced by a suspension polymerization method are used.
In addition, rather than a method in which the monomer is divided into several degrees while the polymerization is proceeding and charged into the system or a method in which the monomer is dropped into the system over a period of several hours while the polymerization is proceeding, a method in which the monomer is produced is used. Those produced by a monomer batch charging method in which polymerization is started after the batch charging into the system are preferable. This is believed to be effective in terms of copolymerizability.

As the dispersant in the suspension polymerization, 70 to
Known water-soluble polymers such as poval having a saponification degree in the range of 100% and a soda salt of polymethacrylic acid can be used. The solvent in the solution polymerization is not particularly limited as long as it dissolves the monomer and the polymer used in the present invention. However, alcohols such as methanol, ethanol, isopropyl alcohol and n-butanol, ethyl cellosolve, Examples thereof include glycols such as cellosolve acetate, butyl carbitol, and propylene glycol methyl ether; acetates such as ethyl acetate and butyl acetate; and ketones such as methyl ethyl ketone and methyl isobutyl ketone.

As the polymerization catalyst, conventionally known initiators such as azo initiators such as azobisisobutyronitrile and peroxide initiators such as benzoyl peroxide may be optionally used according to the purpose. Can be.

If necessary, a chain transfer agent such as n-dodecyl mercaptan or α-methylstyrene dimer may be added to the above vinyl monomer mixture for controlling the molecular weight of the vinyl polymer (I). can do.

The vinyl polymer (I) thus obtained is neutralized with 70 to 100% of the acid groups in the vinyl polymer (I) using a base having a boiling point of 200 ° C. or less. By forming a salt, water solubility is imparted and the compound is dissolved in water. If less than 70% of the acid groups of the vinyl polymer are neutralized, the polymer will disperse in water, resulting in insufficient pigment dispersibility.

The base used for the neutralization has a boiling point of 200 ° C. or less, and if it exceeds 200 ° C., the water resistance decreases. Examples of the base having a boiling point of 200 ° C. or lower include ammonia, triethylamine, propylamine, diethylamine, tripropylamine, dibutylamine, amylamine, 1-aminooctane, 2-dimethylaminoethanol, ethylaminoethanol, 2-diethylaminoethanol, -Amino-2-propanol, 2-amino-
1-propanol, 3-amino-1-propanol, 1
-Dimethylamino-2-propanol, 3-dimethylamino-1-propanol, 2-propylaminoethanol, ethoxypropylamine, aminobenzyl alcohol, morpholine and the like.

The aqueous coating composition of the present invention is used as a solution in which the neutralized product of the vinyl polymer (I) is dissolved in water at a concentration of usually 20 to 30% by weight. In addition, the aqueous coating composition of the present invention can be used by adding additives such as an antifoaming agent, a pigment dispersant, and a preservative in order to express high performance as a paint and an ink. .

The coating method for forming a coating on the surface of various materials using the aqueous coating composition of the present invention includes spray coating, roller coating, bar coating, air knife coating, and casting. Method, brush coating method, dipping method and the like, but are not particularly limited.

When the aqueous coating composition of the present invention is used as a coating, it is dried usually at room temperature to 200 ° C. for 10 seconds to 10 hours to form a coating film.

[0027]

The present invention will be described below in detail with reference to examples. In the examples, “parts” and “%” indicate “parts by weight” and “% by weight”, respectively. (1) Production of vinyl polymer I-1 In a polymerization apparatus equipped with a stirrer, a thermometer, and a reflux condenser and capable of both heating and cooling, 200 parts of deionized water was mixed with polyvinyl alcohol (degree of saponification). 80%, degree of polymerization 1,70
0) After adding 0.6 part and stirring to completely dissolve the polyvinyl alcohol, the stirring was stopped once, and 70 parts of methyl methacrylate (hereinafter abbreviated as MMA), 10 parts of styrene (hereinafter abbreviated as St), n-butyl acrylate (hereinafter abbreviated as n-BA) 10 parts, methacrylic acid (hereinafter MA)
A) (10 parts) was added and stirring was started again, and 0.5 parts of azobisisobutyronitrile (hereinafter abbreviated as AIBN) and 4 parts of n-dodecylmercaptan (hereinafter abbreviated as n-DM) were added and added. C., and the reaction was carried out for 3 hours so that the reaction temperature was maintained at 75 to 80.degree. C., and then the temperature was raised to 95.degree. C. and maintained for 1 hour to terminate the reaction. The obtained polymer had a molecular weight of 12,000, an acid value of 65 mgKOH / g, and a secondary transition temperature of 87 ° C. (2) Production of vinyl polymers I-2 to I-9 Table 1 was prepared in the same manner as in the production method of vinyl polymer I-1.
Are polymerized using the radical initiator and the chain transfer agent shown in Table 1, respectively, and the characteristic values of the obtained polymer are shown in Table 2.

[0028]

[Table 1] Explanation of symbols BPO: benzoyl peroxide n-BMA: normal butyl methacrylate EHA: ethylhexyl acrylate MeSt: α-methylstyrene dimer AA: acrylic acid

[0029]

[Table 2] (3) Production of Vinyl Polymer I-10 Isopropyl alcohol (hereinafter abbreviated as i-PA) 100 in a polymerization apparatus equipped with a stirrer, a thermometer, and a reflux condenser and capable of both heating and cooling. Part, MMA 65 parts, St
10 parts, 12 parts of n-BA, 13 parts of MAA, 2 parts of AIBN and 3 parts of n-DM were added, stirring was started, the temperature was raised to 80 ° C., polymerization was started, and 0.2 parts of AIBN was added every one hour. The temperature was maintained for a time to complete the polymerization, and the solid content was 51%.
An i-PA solution of a vinyl polymer having a viscosity of 10,000 cps was obtained. Thereafter, the solution was put into a vat, and i-PA was evaporated in a dryer heated to 50 ° C. to obtain a solid content of 99.5.
% Of a vinyl polymer solid. The obtained polymer had a molecular weight of 13,000, an acid value of 85.5 mgKOH / g, and a secondary transition temperature of 84 ° C. (4) Production of Vinyl Polymer I-11 100 parts of i-PA was added to a polymerization apparatus equipped with a stirrer, a thermometer, and a reflux condenser and capable of heating and cooling, and stirring was started. ℃ 65, MMA 65 parts, St10
, 12 parts of n-BA, 13 parts of MAA, and 3 parts of AIBN were added dropwise over 4 hours.
The polymerization was terminated by maintaining the temperature for 4 hours while adding 0.1 part of N to obtain an i-PA solution of a vinyl polymer having a solid content of 50% and a viscosity of 2,000 cps. Thereafter, the solution was put in a vat, and i-PA was evaporated in a dryer heated to 50 ° C. to obtain a vinyl polymer solid having a solid content of 99.5%. The resulting polymer had a molecular weight of 11,000 and an acid value of 85.
The secondary transition temperature was 5 mgKOH / g and the second transition temperature was 84 ° C. (5) Dissolution of vinyl polymer in water [5-1] Using ammonia as a base,
% Neutralization 50 g of vinyl polymer I-1 and 147.5 g of deionized water are charged into a 300 ml flask equipped with a stirrer, a thermometer, and a reflux condenser and capable of both heating and cooling. Stirring was started, and 3.5 g of 28% aqueous ammonia was gradually added. Thereafter, the temperature was raised to 50 ° C., and the temperature was maintained for 2 hours to complete the dissolution, thereby obtaining an aqueous solution of vinyl polymer I-1. .
The obtained aqueous solution has a solid content of 25% and a viscosity of 500 cpS.
Met. For the vinyl polymers I-3 to I-11, the addition amounts of 28% ammonia water and deionized water were calculated according to the following calculation method, and the dissolution operation was performed in the same manner. However, the vinyl polymers I-6, I-8 and I-9 could not be dissolved. Required ammonia water (g) = A ÷ 56.1 ÷ 1000 × 5
0 × 17 ÷ 0.28 (where A represents the acid value of the polymer (mg KOH / g).) Required deionized water (g) = 150−Necessary ammonia water (g) × 0.72 [5- 2] When 2-dimethylaminoethanol is used as the base and the acid groups are neutralized by 100% In the same flask as in [5-1], the vinyl polymer I-3 is placed.
Of 50 g of deionized water and 150 g of deionized water, and stirring was started. Then, 7.9 g of 2-dimethylaminoethanol was gradually added. An aqueous solution of coalescence I-3 was obtained. The obtained aqueous solution had a solid content of 25% and a viscosity of 70 cps. [5-3] When diethanolamine is used as a base and the acid group is neutralized by 100% The vinyl polymer I-1 is placed in the same flask as in [5-1].
And 50 g of deionized water were added thereto, stirring was started, and 7 g of diethanolamine was gradually added.
The temperature was raised to 0 ° C., and the temperature was maintained for 2 hours to complete the dissolution, thereby obtaining an aqueous solution of the vinyl polymer I-1. The obtained aqueous solution had a solid content of 25% and a viscosity of 100 CpS. [5-4] Using ammonia as a base and reducing acid groups by 74%
Neutralization In the same flask as in [5-1], place the vinyl polymer I-2 in the same flask.
Was added, and 508.8 g of deionized water and 148.8 g of deionized water were added thereto, stirring was started, and 1.8 g of 28% ammonia water was gradually added.
Thereafter, the temperature was raised to 50 ° C., and the temperature was maintained for 2 hours to complete the dissolution, thereby obtaining an aqueous solution of the vinyl polymer I-2. The resulting aqueous melt had a solids content of 25% and a viscosity of 90 cps. [5-5] When the base neutralizes ammonia and acid by 60% The vinyl polymer I-1 is placed in the same flask as in [5-1].
Was added, 50 g of deionized water and 148.5 g of deionized water were added, stirring was started, and 2.1 g of 28% ammonia water was gradually added.
Thereafter, the temperature was raised to 50 ° C., and the temperature was maintained for 2 hours to complete the dissolution, thereby obtaining an aqueous solution of the vinyl polymer I-1. The obtained aqueous solution had a solid content of 25% and a viscosity of 150 cps.

Example 1 20 parts of carbon black # 100 manufactured by Degussa was added to 100 parts of the aqueous solution of the vinyl polymer I-1, and the mixture was mixed with a planetary ball mill manufactured by FRITSCH for 2 hours to disperse the pigment. Thereafter, when the mixture was left at room temperature for 100 days, no sedimentation of the pigment was observed. Immediately after the pigment was dispersed, the composition was applied to a glass plate so as to have a solid film thickness of 80 μm, dried in a drying oven at 50 ° C. for 20 minutes, and then left in warm water at 20 ° C. for 10 days. No damage such as whitening was observed.

Examples 2 to 5 and Comparative Examples 1 to 8 Table 3 shows the results of tests performed in the same manner as in Example 1. The evaluation of each test was based on the following criteria. [Water solubility] The vinyl polymer was dissolved in water in the same manner as in (5) above. Good: no layer separation or precipitation occurs after 10 hours. Poor: Layer separation or precipitation occurs after 10 hours. [Pigment dispersibility] Carbon black # 1 manufactured by Degussa
00 with respect to 100 parts of the aqueous solution of the vinyl polymer.
0 parts were added and mixed for 2 hours with a FRITSCH planetary ball mill to disperse the pigment. Then, it was left at room temperature for 100 days. Good: No sedimentation of the pigment was observed. Moderately good: pigment sedimentation is observed after 100 days. Normal: pigment settling is observed after 30 days. (Usable range) Poor: Settling of pigment is observed after 3 days. [Water resistance] Solid film thickness of 80 on glass plate immediately after pigment dispersion
It was applied to a thickness of μm, dried in a drying oven at 50 ° C. for 20 minutes, and then left in warm water at 20 ° C. for 10 days. Good: No damage such as whitening is observed. Slightly good: Damage such as whitening and blistering is observed after 10 days. Normal: Damage such as whitening and blistering is observed after 3 days.
(Practically usable range) Poor: Damage such as whitening and blistering is observed after 5 hours.

[0032]

[Table 3]

[0033]

Industrial Applicability The aqueous coating composition of the present invention is excellent in water resistance and pigment dispersibility, and is used in an aqueous coating composition containing no organic solvent, which has heretofore been incompatible with both. The effect is extremely remarkable.

Continuation of front page (56) References JP-A-4-153276 (JP, A) JP-A-50-122528 (JP, A) JP-A-4-57856 (JP, A) JP-A-51-7033 (JP, A) JP-A-53-37733 (JP, A) JP-A-3-192172 (JP, A) JP-A-62-135575 (JP, A) JP-A-3-504138 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) C09D 133/04-133/14 C09D 5/00, 11/10 C08L 33/04-33/14

Claims (2)

(57) [Claims] (A) methyl methacrylate 30 to 90
% By weight, (b) 0 to 30% by weight of an aromatic vinyl compound,
(C) 4 to 15% by weight of an acid group-containing vinyl compound and (d) 0 to 66% by weight of another copolymerizable vinyl monomer.
Having a secondary transition temperature of 30 to 100 ° C, a weight average molecular weight of 7,000 to 30,000, and an acid value of 30 to 9
0 mgKOH / g der is, polymerized <br/> vinyl polymer by suspension polymerization (I), a boiling point of 200 ° C. or less of the base of the acid groups of the vinyl polymer (I) 70 to 100 % Of an aqueous coating composition which is neutralized and dissolved in water. 2. The aqueous coating composition according to claim 1, wherein the acid group-containing vinyl compound (c) contains methacrylic acid.