JPS59117565A - Water-based coating composition - Google Patents

Abstract

PURPOSE:To prepare a water-based coating cmposition having excellent dispersion stability of fine powder and storage stability, by using a varnish of a specific resin having carboxyl group and fine powder of similar resin as a film- forming component. CONSTITUTION:The objective composition contains (A) a varnish of a carboxyl- containing resin and (B) fine powder of a carboxyl-containing resin at a weight ratio (A:B) of 45:55-98:2 (in terms of the solid component of the resin). The acid strength of the carboxyl group of the resin of the component (A) is equal to or higher than that of the carboxyl group in the component B (preferably higher than that of the component B by >=20mV in terms of half equivalent point potential in nonaqueous potentiometric titration).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an aqueous coating composition containing an aqueous resin varnish and a fine resin powder as substantial film-forming components, and which has particularly excellent dispersion stability and storage stability of the fine powder.

Water-based paints containing as a resin vehicle a water-based resin varnish obtained by dissolving or dispersing a resin in water are increasingly replacing organic solvent-based paints because of their safety, low pollution, and ease of operation.

However, in general, with water-based paints, it is necessary to introduce a large amount of hydrophilic groups into the molecule in order to dissolve the resin in water, or to use a material whose molecular weight is not very high. It is rough, and it is difficult to adjust the nonvolatile content to a high concentration, resulting in poor coating workability and problems in terms of pigment dispersibility. In order to improve this problem, various slurry-like water-dispersed paints have been proposed in which water-insoluble resin fine powder is mixed and dispersed in the above-mentioned water-based paint (for example, JP-A-50-65531). However, with this type of paint, it is difficult to disperse the resin fine powder well in the system, and using a dispersant inevitably causes problems in terms of water resistance. I haven't seen it.

The present inventors have found that if this paint system is used in combination with an aqueous resin having acid groups and a fine resin powder, it will have relatively excellent dispersibility, and it will also be possible to create a bake-hardening type using melamine or the like, which will improve film performance. However, we found that a significant improvement could be obtained. However, in actual combinations, it has often been found that the stability of aqueous resins is impaired due to the adverse effects of fine resin powders containing acid groups, and the use of surfactants as a solution to this problem can reduce membrane performance. It has also been found that if measures such as adjusting the amount of the neutralizing agent are used, the workability is reduced and the characteristics of the composition cannot be fully utilized.

The type of carboxyl group that expresses the acid value in the aqueous resin or resin fine powder can be arbitrarily designed depending on the usage, blending of the resin material, and synthesis technology (Patent Application No. 154209/1989)
(see issue). Water solubilization of aqueous resins having carboxyl groups,
Water dispersion is usually achieved by neutralizing the carboxyl group with an amine, and according to acid-base theory, it is known that the stronger the acid, the stronger the bond with the amine. The present inventors found that in the combination of an aqueous resin having an acid group and a resin fine powder having an acid group, the reason why the stability of the aqueous resin is impaired is due to the bonding with the carboxyl group during the aqueousization of the aqueous resin. It was found that the neutralized amine was carried away by the resin when mixed with resin fine powder, and in combination with the above knowledge, the present invention was completed.

That is, according to the present invention, as a substantial film-forming component, an aqueous varnish (1) of a resin having a carboxyl group,
The fine powder (n) of a resin having a carboxyl group is (I): (II) = 45: 55 to 98 in terms of resin solid content.
: Regarding the acid strength of the carboxyl group included in the weight ratio of 2 and expressing the resin acid value, the acid strength of the carboxyl group of the resin (I) is substantially equal to the acid strength of the carboxyl group of the resin of (I[). Aqueous coating compositions are provided that are characterized in that they are equal to or greater than

One of the substantial film-forming components in the aqueous coating composition of the present invention is an aqueous varnish (
Examples of such resins include those that inherently have carboxyl groups such as polyester resins, alkyd resins, acrylic resins, and modified acrylic resins, or those that directly have carboxyl groups such as epoxy resins, animal and vegetable oils, and polybutadiene. However, those that can easily introduce carboxyl groups by addition reaction etc. are used, and these usually have an acid value of 5 to 300 and a number average molecular weight of 1,500 to 20.
It is about 000.

When making such a resin into an aqueous varnish, the carboxyl group is replaced with a basic substance such as monomethylamine,
Dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monoisopropylamine, diisopropylamine, diethylenetriamine, triethylenetetramine, monoethanolamine,
Neutralized with jetanolamine, triethanolamine, monoisopropanolamine, diisopropanazine, dimethylethanolamine, morpholine, methyl 5-morpholine, piperazine, ammonia, sodium hydroxide, potassium hydroxide, lithium hydroxide, etc. do it. Although not particularly critical in the present invention, the resin acid value of the aqueous varnish is usually selected within the range of 5 to 300. This is because if the acid value is less than 5, the dispersion stability of fine resin powder and pigments in the paint will be poor, and if the acid value exceeds 300, the viscosity of the water-based varnish will tend to increase and the paint will become solid. This is because the concentration has to be lowered, which has an adverse effect on workability, etc.

In the present invention, a fine powder of a resin having a carboxyl group (
IT) is used. Such resins can be used as water-based varnishes (I
As mentioned above, it can be made from various resins having carboxyl groups, but any resin that is solid at room temperature, water-insoluble or sparingly soluble, and can be dispersed and suspended in the aqueous varnish (I) may be used. Particularly preferred fine resin powders having carboxyl groups are fine powders of polyester, epoxy, and acrylic resins and/or mixtures thereof, the average particle size of which is about 5 to 200 μm, which is used in ordinary powder coating systems.
It is within the range of degree. The acid value of fine powder resin is usually 1 to 1.
It is about 150.

In this way, in the present invention, both the aqueous varnish (I) and the fine powder resin having a carboxyl group that expresses an acid value are used in combination, but the most important feature is that the resin exhibits an acid value. Regarding the acid strength of the carboxyl group, the resin of I) is substantially equal to that of the resin of (II), or (I) is better than (IF).
It is pointed out that it must be larger than that of . In the specification III and claims of the present application, the acid strength of the carboxyl group is defined as "the half-equivalent point potential when a non-aqueous potentiometric titration is performed on a pyridine solution of the resin using n-tetrabutylammonium hydroxide as a titration reagent. ] shall mean the strength of the indicated carboxyl group.

Only by selecting the acid strengths of the carboxyl groups of the resins of the aqueous varnish (I) and the fine powder (II) as described above, can the objects of the present invention of dispersion stability and storage stability be fully achieved.

Taking polyester obtained from a polybasic acid and a polyhydric alcohol as an example, if two or more polybasic acids are added to the reaction system, the reactivity will differ depending on the acid, so the one with the highest reactivity will be the ester first. Carboxyl groups that are involved in the chemical reaction and are derived from weakly reactive acids remain selectively. However, the esterification reaction is first carried out using a polybasic acid and a polyhydric alcohol with low reactivity, and then a highly reactive polybasic acid with relatively high acidity is added later to continue the esterification reaction. If this is done, a carboxyl group derived from an acid with high acidity is introduced depending on the amount of acid added later, and therefore it is possible to arbitrarily control the carboxyl group that expresses the resin acid value (Japanese Patent Application No. 1983-1999). 154.209
issue). When polyester is produced using various polybasic acids, the acid strength of the carboxyl group that expresses the resin acid value is expressed as shown in Table 1 at the half-equivalent point potential of these resins determined by non-aqueous potentiometric titration. become.

Table 1 In the present invention, the acid strength shown by the half-equivalent point potential in the non-aqueous potentiometric titration of the carboxyl group that expresses the resin acid value is that of the resin of the aqueous varnish (■) and that of the fine powder (II).
) When compared with the resin one, the former must be substantially the same, or the former must be larger. If the acid strength of the carboxyl group of the fine powder resin is higher, when the fine powder is mixed into the water-based varnish, the amine will be transferred from the water-based varnish-forming resin to the fine powder resin, and the stability of the water-based varnish will be significantly reduced. The purpose of the invention cannot be achieved without harm.

91 In a preferred member of the present invention, water-based varnish (I)
For both resins and fine powder (If), those having an acid strength of the carboxyl group that expresses an acid value of 1450 mV or more at the half-equivalent point potential of non-aqueous potentiometric titration are selected, and the half-equivalent of these resins is The point potential difference is set to O or positive. The difference in half-equivalent point potential in non-aqueous potentiometric titration of each resin between aqueous varnish (I> and fine powder (II)) is usually 0 to 1
0n+■, preferably 10 mV or more, more preferably 2
It is selected to be 0 mV or more.

In this way, in the present invention, in a coating system consisting of a combination of an aqueous varnish and a fine resin powder, the aqueous varnish and the fine powder resin both have a carboxyl group that expresses an acid value. A water-based coating composition with excellent dispersibility of powder and markedly improved dispersion stability and storage stability by specifying the acid strength of the carboxyl group that expresses the acid value of the water-based varnish and fine powder resin. is provided.

In addition, the aqueous varnish (I) having a carboxyl group (10-) and the fine powder of a resin having a carboxyl group (π) have a resin solid content of 45 to 98% by weight, preferably 50 to 90% by weight, and 55 to 2% by weight of the latter. %, preferably 50 to 10% by weight. If the former amount is too small, the dispersion stability of the fine resin powder will deteriorate and the smoothness of the coating film will be impaired, while if it is excessive, the viscosity of the coating will increase, causing problems such as water resistance of the coating film. This is because it causes

Although the present invention uses water (preferably deionized water) as a medium,
If necessary, alcohols, cellosolves, ketones, esters, ethers, etc., which are both resin-soluble and water-miscible, are used. In addition, a hydrophobic organic solvent that is not water-miscible can also be used in combination in a small amount.

The aqueous coating composition of the present invention contains resin hydroxyl groups and carboxyl groups as film-forming components, and can be formed into a tough three-dimensional coating film with a curing agent such as melamine, urea, isocyanate block, dicyandiamide, or epoxy. It is possible to add various pigments and additives (modifiers, dispersants, surface conditioners) to the composition of the present invention as necessary, and the paint can be manufactured according to ordinary paint manufacturing techniques. It will be done.

The thus obtained water-based paint composition of the present invention provides excellent coating workability, adhesion, and finished appearance that cannot be obtained with conventional slurry-type paints, improves the drawbacks of water-based paints and powder paints, and has stable dispersion. To provide extremely useful paints with excellent properties and storage stability.

The present invention will be explained below with reference to Production Examples, Examples, and Comparative Examples. Note that % in the example text represents weight %.

Production example 1 Production of water-based resin varnish (1) Patent application 1987-1
According to the resin design technology of No. 54209, tall oil fatty acid 480 (], neopentyl glycol 336 (+), trimethylol propane 73 g, 45 g of non-phophthalic acid, 60 g of xylene, and 2.49 g of dibutyltin oxide were charged, the temperature was raised to 210°C, and the dehydration and esterification reaction was continued until the acid value reached 5 or less.

Then, after cooling to 140°C or less, trimellitic anhydride 37
(l) was added and the temperature was raised to 190°C to cause a dehydration esterification reaction, and the reaction was terminated when the acid value reached 60. After cooling to 120°C, ethylene glycol monobutyl ether 246
σ was added and stirred for 30 minutes to uniformly dissolve. 7.6 dimethylaminoethanol per 100 g of resin obtained
01 and water 1420 were added, stirred and held at 30 to 50°C for 1 hour, and then water-based resin varnish (1
) was obtained. The obtained fatty acid-modified alkyd resin has an oil length of 40, an acid value of 60, and a number average molecular weight of about 1300, and the half-equivalent point potential of the carboxylic acid that expresses the resin acid value is -240 m.
It showed V.

Production Example 2 Production of Water-Based Resin Varnish (2) Using the same equipment as in Production Example 1, tall oil fatty acid 480 (+, neopentyl glycol 197 (1), pentaerythritol 136 (
+, 4750 g of phthalic anhydride, 60 g of xylene, and 2.40 g of dibutyltin oxide were charged, and the temperature was raised to 210° C. to cause a dehydration esterification reaction, and the reaction was terminated when the acid value reached 50. After cooling to 120°C, 246 g of ethylene glycol monobutyl ether was added and stirred for 30 minutes to uniformly dissolve. Dimethylaminoethanol 6.4 (1) and water 93Q per 1000 of the obtained resin
was added and the same procedure as in Production Example 1 was carried out to obtain an aqueous resin varnish (2) having a resin solid content of 40%. The obtained fatty acid-modified alkyd resin has an oil length of 40°, an acid value of 50, and a number average molecular weight of about 1.
100, and the half-equivalent point potential of the carboxylic acid that develops the resin acid value was -290 mV.

Production Example 3 Production of aqueous resin varnish (3) Using the same equipment as Production Example 1, safflower oil 5650, neopentyl glycol 131g, trimethylolpropane 12. M,
and 2.4g of dibutyltin oxide, 195
The temperature was raised to ℃ and the transesterification reaction was carried out for 1 hour. Next, after cooling to 140° C. or lower, 484 g of isophthalic acid was added, and the temperature was raised to 220° C. to cause a dehydration esterification reaction, and the reaction was terminated when the acid value reached 60. After cooling to 120℃,
Ethylene glycol monobutyl ether 307 (I was added and stirred for 30 minutes to uniformly dissolve. Resin 1 obtained.
00(+), 7.6 g of dimethy14-aminoethanol and 121 g of water were added, and the following procedure was repeated in the same manner as in Production Example 1 to obtain an aqueous resin varnish (3) with a resin solid content of 35%. The oil-modified alkyd resin has an oil length of 45, an acid value of 60, and a number average molecular weight of about 1000, and the half-equivalent point potential of the carboxylic acid that develops the resin acid value is 13.
It showed 10mV.

Production Example 4 Production of water-based resin varnish (4) Using the same equipment as in Production Example 1, Neopentyl Glycol 169! II,
Hydrogenated bisphenol A 191g, trimethylolethane 217 (1, hexahydrophthalanhydride M705 ()
1 xylene 60a1 and dibutyltin oxide 2.4
0 was charged, the temperature was raised to 230'C, a dehydration esterification reaction was carried out, and the reaction was terminated when the acid value reached 55. 120℃
After cooling to ethylene glycol monobutyl ether 24
6(+) was added and stirred for 30 minutes to uniformly dissolve.

Dimethylaminoethanol 7, Oo and 160 g of water were added to 100 (l) of the obtained resin, and the following procedure was repeated in the same manner as in Production Example 1 to obtain an aqueous resin varnish (4) with a resin solid content of 30%. The oil-free polyester resin is
The acid value was 55, the number average molecular weight was about 1500, and the half-equivalent point potential of the carboxylic acid that developed the resin acid value was -400 mV.

Production Example 5 Production of Fine Resin Powder (A>) In a 2-liter fourth container equipped with a thermometer, nitrogen gas blowing tube, reflux device, and stirring blade, 245Ω of ethylene glycol, 183 g of trimethylolethane, 384 g of dimethyl terephthalate, and 2.40 g of dibutyltin oxide, heated to 200°C, and subjected to demethanolization reaction for about 3 hours. After cooling to 140°C, 658 g of isophthalic acid was added, and the temperature was raised to 230°C to reach an acid value of 40. The dehydration esterification reaction was continued until the resin was removed from the reaction vessel and cooled, and the solid resin was crushed to obtain a fine resin powder (A).The number average molecular weight of the obtained polyester resin was approx. 3500, with an average particle size of 50 to 60μ, and as a result of dissolving this fine resin powder in pyridine and performing potentiometric titration in a non-aqueous system, the half-equivalent point potential of the carboxylic acid that expresses the resin acid value was -310 mV. Indicated.

Production Example 6 Production of fine resin powder (B) Using the same equipment as Production Example 5, ethylene glycol 25
7 g, trimethylolethane 169 g'.

Dimethyl terephthalate 522 (+) and dibutyltin oxide 2.4 g were charged, the temperature was raised to 200°C, and a demethanol reaction was carried out for about 3 hours. Then, after cooling to 140°C, isophthalic acid IU 425 (l) was added, and the temperature was raised to 220°C. The mixture was dehydrated and esterified, and the reaction was continued until the acid value reached 4.

After further cooling to 140'C, tetrahydrophthalic anhydride 10
4() was added and subjected to a halfesterization reaction at 160°C for 2 hours to obtain a resin with an acid value of 35.The same operation as in Production Example 5 was then carried out to obtain a fine resin powder (B).The obtained polyester The number average molecular weight of the resin is approximately 3500, and the average particle size is 5.
The half-equivalent point potential of the carboxylic acid, which has a value of 0 to 60μ and exhibits a resin acid value, was -380 mV.

Production Example 7 Production of fine resin powder (C) Using the same equipment as Production Example 5, ethylene glycol 34
0g, trimethyloleethane, 94g, dimethylte17-phthalate, 902g, and 2.4g of dibutyltin oxide were charged, the temperature was raised to 200°C, and a demethanol reaction was carried out for about 3 hours.Then, after cooling to 140°C, anhydrous trimethyl 198 g of mellitic acid was added, the temperature was raised to 210°C, and the dehydration and esterification reaction was continued until the acid value reached 40.Hereinafter,
The same operation as in Production Example 5 was performed to obtain a fine resin powder (C). The number average molecular weight of the obtained polyester resin is approximately 3.
The half-equivalent point potential of the carboxylic acid exhibiting a resin acid value with a 2001 average particle size of about 50 μm was -240111V.

Production Example 8 Production of Fine Resin Powder <D) Add 70 xylene to a 2-liter fourth container equipped with a thermometer, nitrogen gas blowing pipe, dropping funnel, and stirring blade.
0 (+), methacrylic acid 45 (+, 2 hydroxyl methacrylate 80 g, methyl methacrylate 213 (], ] n-butyl methacrylate 1620
The mixture was added dropwise at 135° C. for 3 hours from a dropping funnel containing tertiary-butyl peroxide 15Q, and then polymerized for 3 hours while maintaining the same temperature. Next, the solvent was removed under reduced pressure, and the same operations as in Production Example 5 were performed to obtain a fine resin powder (D) with an acid value of 59. The number average molecular weight of the obtained acrylic resin is about 4800, the average particle size is about 50μ, and the half-equivalent point potential of the carboxylic acid that develops the resin acid value is -400+1.
It showed 1V.

Examples 1 to 7 and Comparative Examples 1 to 3 34 parts of the resin fine powder in each of the above Ill preparation examples and 46 parts of the water-soluble resin composition (non-volatile fraction) were mixed with melamine resin (Cymail 303J manufactured by Mitsui Toatsu Co., Ltd.). ) and 80 parts (based on resin solid content) of a pigment (Titanium R820J manufactured by 6 Gen Titan Co., Ltd.) to obtain a stomer viscosity value of 80 Ku (25
°C) was adjusted with water before and after to obtain a paste. This was placed in a paint agitator and dispersed until the particle size became 5 microns or less.

Water was further added to this paste to obtain a predetermined viscosity (stormer viscosity value of 70 to 72 KU/25°C) to prepare an aqueous coating composition for testing.

After putting these paint compositions in a mayonnaise bottle and sealing it,
It was stored at 40°C for 2 months, and the dispersion state and viscosity change before and after storage were examined, and the results are shown in Table 2 below.

The criteria for evaluating the dispersion state (separation, aggregation, etc.) was as follows.

◎ Dispersion state Invasion (no change observed at all) O Good (Hatondo )

Claims (2)

[Claims] (1) As substantial film-forming components, an aqueous varnish (I) of a resin having a carboxyl group and a fine powder (I[) of a resin having a carboxyl group are used as (I) in terms of resin solid content.
: Included in the weight ratio of (It) = 45:55 to 98:2,
In addition, regarding the acid strength of the carboxyl group that expresses the resin acid value, the acid strength of the carboxyl group of the resin (■) is substantially equal to or greater than the acid strength of the carboxyl group of the resin (T[). A water-based paint composition characterized in that: (2) The acid strength of the carboxyl group in the resin (I) is 20 mV or more greater than the acid strength of the carboxyl group in the resin i), expressed as a half-equivalent point potential in non-aqueous potentiometric titration. Composition according to item 1.