JPH05214292A - Water-base coating composition - Google Patents

Abstract

PURPOSE:To prevent separation and coagulation when recovering by condensation from washing water in a coating booth without deterioration of the performance of the coating film. CONSTITUTION:The title composition is obtained by mixing a principal constituent comprising a water-soluble alkyd or acrylic resin having an acid value of 25 to 100, a hydroxyl number of 35 to 200 and an SP value of 10.0 to 11.0 with a curing agent having an SP value higher than that of the resin by 0.5 to 3.0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-based coating composition suitable for recovery from washing water in a coating booth and reuse.

[0002]

2. Description of the Related Art When spray coating paint in a coating booth, a large amount of paint dust that does not adhere to the object to be coated is generated, and this paint dust is dissolved or dispersed in the wash water in the coating booth and collected. It Since a large amount of paint dust is collected in the wash water as described above, discarding the paint dust as it is leads to a loss of paint and also leads to a problem of environmental pollution.

Therefore, it has been studied to recover and reuse the coating material collected in the washing water, and a recovery method as disclosed in, for example, Japanese Patent Application Laid-Open No. 49-51324 is provided. There is. That is, this is a water-based coating composition, which is obtained by collecting sprayed water in a coating solution, and diluting water obtained by filtering the water through a reverse osmosis filtration membrane, an ultrafiltration membrane, etc. The concentration of non-volatile components such as water-soluble resin such as water-soluble alkyd resin and water-soluble acrylic resin for forming a coating film and pigment is reduced to the original aqueous concentration by concentrating in this way. It is designed to be reusable in a manner similar to that of a coating composition.

[0004]

However, the water-based coating composition contains a few% of a water-soluble organic solvent for dispersing a water-soluble resin in water, and if the water is filtered for recovery. This water-soluble organic solvent is also filtered together with water, and the content of the water-soluble organic solvent in the recovered aqueous coating composition becomes small. As a result, the water-soluble resin or pigment may be separated or aggregated in the water-based coating composition in the process of concentrating, so that the paint film may be glossed.

For this reason, a water-soluble alkyd resin or a water-soluble acrylic resin, which has a high acid value or a high hydroxyl value, is used in the water-based coating composition to increase the degree of water-solubilization, so that separation in the concentration process or It has been studied to prevent aggregation and improve paint stability. However, when a water-soluble alkyd resin or a water-soluble acrylic resin having a high acid value or a high hydroxyl value is used as described above, the moisture resistance and the boiling water resistance are lowered in the coating performance of the water-based coating composition, and the impact resistance is also high. The problem was that it would decrease.

The present invention has been made in view of the above points, and provides an aqueous coating composition capable of preventing separation and agglomeration when concentrated and recovered from washing water without deteriorating coating film performance. It is intended to be provided.

[0007]

The aqueous coating composition according to the present invention has an acid value of 25 to 100 and a hydroxyl value of 35 to 20.
0, a SP value of 10.0 to 11.0 is a water-soluble alkyd resin or water-soluble acrylic resin as a main component, and the SP value of the water-soluble alkyd resin or water-soluble acrylic resin is 0.
It is characterized by containing a curing agent having a high SP value of 5 to 3.0.

The present invention will be described in detail below. In the present invention, as the water-soluble resin for forming the coating film, a water-soluble alkyd resin or a water-soluble acrylic resin is used, and either one can be used or both can be used together.
In the present invention, the water-soluble alkyd resin or water-soluble acrylic resin has an acid value (AV) of 25 to 100, a hydroxyl value (OHV) of 35 to 200, and an SP value of 1
The thing of 0.0-11.0 is used. Acid value is 2
If it is less than 5, a hydroxyl value is less than 35, and an SP value is less than 10.0, the water solubility (hydrophilicity) of the water-soluble alkyd resin or water-soluble acrylic resin is low and separation or the like may occur during the concentration process. There is. On the contrary, when the acid value exceeds 100, the hydroxyl value exceeds 200, and the SP value exceeds 11.0, the water-solubility (hydrophilicity) of the water-soluble alkyd resin or water-soluble acrylic resin becomes too high, Problems will occur in the water resistance of the coating film. The acid value of the water-soluble alkyd resin or water-soluble acrylic resin is in the range of 40 to 70, and the hydroxyl value is 60 to 1.
A range of 50 is more preferable. When a water-soluble alkyd resin is used, its oil length is preferably 45 or less.

Here, the SP value (solubility parameter) is a measure of solubility and is measured as follows. References SUH, CLARKE [J. P. S. A
-1,5,1671-1681 (1967)]-Measurement temperature 20 ° C-Sample 0.5 g of resin is weighed in a 100 ml beaker, 10 ml of a good solvent is added using a whole pipette, and dissolved by a magnetic stirrer. -Solvent Good solvent: dioxane, acetone Poor solvent: n-hexane, ion-exchanged water-Mudging point measurement Poor solvent is dropped using a 50 ml buret, and the point at which turbidity occurs is the dropping amount. -Calculation The SP value δ of the resin is given by the following equation.

Δ = (V _ml ^1/2 δ _ml + V _mh ^1/2 δ _mh ) /
^{_{(V ml 1/2 + V mh 1/2}} ) V m = V 1 V 2 / (φ 1 V 2 + φ 2 V 1) δ m = φ 1 δ 1 + φ 2 δ 2 V i: solvent molecular volume (ml / Mol) φ _i : volume fraction of each solvent at the turbidity point δ _i : SP value of solvent ml: low SP poor solvent mixed system mh: high SP poor solvent mixed system Further, as the curing agent (crosslinking agent) in the present invention, Although amino resins such as melamine resin and benzoguanamine resin can be used, the SP value was adjusted to be higher than the SP value of the water-soluble alkyd resin or water-soluble acrylic resin in the range of 0.5 to 3.0. It uses things.
By using a curing agent having a SP value within this range for a water-soluble alkyd resin or a water-soluble acrylic resin, it can be applied when the water-soluble alkyd resin or water-soluble acrylic resin is cured during coating to form a coating film. The film can be hydrophobized, and coating film performance such as moisture absorption resistance and boiling water resistance can be enhanced. When the difference in SP value between the curing agent and the water-soluble alkyd resin or water-soluble acrylic resin is less than 0.5 (including the case where the SP value of the curing agent is lower than the SP value of the water-soluble alkyd resin or water-soluble acrylic resin) If so, the stability of the water-based coating composition may deteriorate and separation or the like may occur. On the contrary, if the difference in SP value exceeds 3.0, coating performance such as moisture absorption resistance and boiling water resistance may be increased. It will not be possible to obtain the effect of increasing.

The water-based coating composition according to the present invention can be obtained by blending the above-mentioned water-soluble alkyd resin or water-soluble acrylic resin, a curing agent, a pigment and a water-soluble organic solvent. This pigment includes titanium dioxide,
Coloring pigments such as carbon and quinacridone-based pigments and extender pigments such as calcium carbonate can be used, and the blending amount thereof is preferably PVC = 0 to 35%. Further, butyl cellosolve or the like can be used as the water-soluble organic solvent. Here, the mixing ratio of the curing agent to the water-soluble alkyd resin or the water-soluble acrylic resin is preferably set in the range of 50:50 to 95: 5 in terms of solid content.

The aqueous coating composition thus prepared can be used for coating by diluting it with water. And after the paint dust generated during spray painting of this paint is dissolved or dispersed in the wash water in the paint booth and collected,
According to the method provided in the above-mentioned JP-A-49-51324, the collected washing water is subjected to ultrafiltration or the like to filter the water so that the solid content concentration of the aqueous coating composition is returned to the original state. It can be reused by concentrating to Here, as described above, the SP value of the water-soluble alkyd resin or water-soluble acrylic resin is 0.5 to
By using 3.0 high one, the coating film is made hydrophobic to enhance the coating performance such as moisture absorption resistance and boiling water resistance. Therefore, as the water-soluble alkyd resin or water-soluble acrylic resin, Thus, those having a relatively high degree of water solubilization can be used. Therefore, even if the water-soluble organic solvent is filtered in the process of concentration to reduce its content, it is possible to prevent the separation of the water-soluble alkyd resin or the water-soluble acrylic resin and prevent the aggregation of the pigment, and thus the coating film It is possible to prevent the occurrence of gloss and the like.

[0013]

The invention will now be illustrated by the examples. (Example 1) A raw material having the following composition was charged into a container equipped with a stirrer, a temperature controller, and a decanter, and heated with stirring.

Soybean oil fatty acid 34 parts by weight Isophthalic acid 25 parts by weight Trimellitic anhydride 9 parts by weight Trimethylolpropane 31 parts by weight Xylene 1 part by weight Dibutyltin oxide 0.02 parts by weight Water produced along with reaction proceeds together with xylene. The mixture was boiled and removed, and heating was continued until the acid value became 50 and the hydroxyl value became 125, and the reaction was terminated. The obtained resin was diluted with butyl cellosolve to a nonvolatile content of 73% by weight to obtain an alkyd resin varnish. This resin varnish has a Gardner viscosity Z
_{It was 2} , and SP value was 10.37. This resin varnish was theoretically 100% neutralized with dimethylethanolamine and adjusted to a nonvolatile content of 40% by weight with deionized water to obtain a water-soluble alkyd resin varnish A.

Titanium dioxide was dispersed in this water-soluble alkyd resin varnish A using a lab mixer, and methanol / ethanol modified benzoguanamine resin (SP value = 11.47) was used as a curing agent to obtain the composition ratio shown in Table 1. A stainless steel container was weighed and blended to prepare an aqueous coating composition. (Example 2) An aqueous coating composition was prepared in the same manner as in Example 1 except that a melamine resin modified with methanol / butanol (SP value = 11.90) was used as a curing agent.

Example 3 A reaction vessel equipped with a stirrer, a temperature controller and a cooling tube was charged with 76 parts by weight of ethylene glycol monobutyl ether, 122 parts by weight of styrene, 66 parts by weight of lauryl methacrylate and 66 parts of 2-hydroxyethyl methacrylate. Parts by weight, methacrylic acid 23
61 parts by weight of a monomer solution consisting of 3 parts by weight of azobisisobutyronitrile was added, and the temperature was raised to 12 with stirring.
The temperature was adjusted to 0 ° C. Further, 245 parts by weight of this monomer solution was added dropwise over 3 hours, and stirring was continued for 1 hour. Then, by adding 24 parts by weight of dimethylethanolamine and 200 parts by weight of deionized water, a water-soluble acrylic resin varnish B having a volatile content of 50% by weight and a resin number average molecular weight of 6000 was obtained. This resin has an acid value of 50 and a hydroxyl value of 9
5, SP value was 10.5.

Titanium dioxide was dispersed in this water-soluble acrylic resin varnish A using a lab mixer, and a benzoguanamine resin modified with methanol / ethanol (SP value = 11.47) was used as a curing agent to obtain the composition ratio shown in Table 1. A stainless steel container was weighed and blended to prepare an aqueous coating composition. (Comparative Examples 1 to 3) Using the water-soluble alkyd resin varnish A obtained in Example 1, titanium dioxide was dispersed using a lab mixer, and the curing agent shown in Table 2 was used.
A water-based coating composition was prepared by weighing and blending in a stainless steel container so as to have the composition ratio shown in.

(Comparative Example 4) A raw material having the following composition was charged in a container equipped with a stirrer, a temperature controller and a decanter, and heated while stirring. Isophthalic acid 30 parts by weight Trimellitic anhydride 5 parts by weight Harthol FA-1 * 1 27 parts by weight Trimethylolpropane 15 parts by weight Neopentyl glycol 11 parts by weight BAP8Glycol * 2 5 parts by weight PPG1000 * 3 5 parts by weight xylene 2 parts by weight dibutyltin Oxide 0.02 parts by weight * 1 ... Tall oil fatty acid manufactured by Harima Kasei Co., Ltd. * 2 ... Propylene oxide adduct of bisphenol A manufactured by Nippon Emulsifier Co., Ltd. * 3 ... Polypropylene glycol manufactured by Sanyo Chemical Co., Ltd. (molecular weight of about 1000) Produced as the reaction progresses The water was removed by azeotroping xylene with water, and heating was continued until the acid value became 30 and the hydroxyl value became 40, and the reaction was terminated. The obtained resin is added to the nonvolatile content 73
An alkyd resin varnish was obtained by diluting with butyl cellosolve so as to be a weight%. The resin varnish had a Gardner viscosity of Z _{2 to} Z ₃ and an SP value of 10.50. This resin varnish was theoretically 100% neutralized with triethylamine and adjusted to a nonvolatile content of 40% by weight with deionized water to obtain a water-soluble alkyd resin varnish C.

Using this water-soluble alkyd resin varnish C,
Thereafter, water-based coating compositions were prepared in the same manner as in Comparative Examples 1 to 3 above.

[0020]

[Table 1]

[0021]

[Table 2]

The aqueous coating compositions of Examples 1 to 3 and Comparative Examples 1 to 4 obtained as described above were mixed with 5 cups of NK # 2.
It was diluted with water until 0 seconds, and this was sprayed onto a zinc phosphate-treated plate (manufactured by Nippon Test Panel Co., Ltd., thickness 0.8 mm) so that the dry coating film thickness was 25 to 30 μm.
Baking at 60 ° C. for 20 minutes. With respect to this coating film, boiling water resistance (0.5 hours) and impact resistance (DuPont type impact tester, 1 / 2φ inch 500 g × 30 cm or more pass) were measured, and stability of each aqueous coating composition (40 ℃ x 30
Days). The results are shown in Tables 3 and 4.

Further, spray coating was carried out by a sprayer 2 using each of the above aqueous coating compositions in a coating booth 1 shown in FIG. Then, the paint dust is dispersed or dissolved in the wash water 6, and the concentration of the nonvolatile components in the wash water 6 is 15% by weight.
When the temperature reaches, the cleaning water 6 in which the paint is diluted is transferred from the coating booth 1 to the paint concentration tank 3 and is used as an ultrafiltration membrane to desalination systems (DESARLINA).
The washing water 6 was filtered and concentrated through an ultrafiltration device 4 using "EW4026" manufactured by TION SYSTEMS), and the filtrate 8 was collected in the filtrate tank 5 and returned to the coating booth 1. Thus, the regenerated aqueous coating composition 7 containing 55% by weight of non-volatile components obtained by concentrating with the ultrafiltration device 4 was supplied from the coating concentrate tank 3 to the sprayer 2 and reused.
A coating obtained by observing the state of the coating in the process of concentrating the coating thus diluted by being dispersed or dissolved in the washing water 6 by ultrafiltration and reusing the regenerated aqueous coating composition 7 was obtained. The appearance of the film was observed. The results are shown in Tables 3 and 4.

[0024]

[Table 3]

[0025]

[Table 4]

As shown in Tables 3 and 4, it was confirmed that the water-based coating compositions of the respective examples had excellent coating film performance and coating stability, and were further concentrated from the coating booth. It is confirmed that the paint does not cause separation or the like when recycled and the state of the coating film is good. On the other hand, the paint of Comparative Example 1 in which the SP value of the water-soluble alkyd resin is smaller than that of the water-soluble alkyd resin is used as the curing agent, the stability of the paint is poor and the paint is separated during the concentration even when it is concentrated and recycled. In addition, gloss was generated in the coating film, and in Comparative Example 2 in which the SP value of the water-soluble alkyd resin was 3.0 or more higher than that of the water-soluble alkyd resin, the coating performance was deteriorated. .. Further, in Comparative Example 3 in which a water-soluble curing agent was used, the coating film performance deteriorated, and in Comparative Example 4, the coating material separated and was separated at the time of concentration when it was concentrated and reused. Shiny marks were generated on the film.

[0027]

As described above, the present invention has an acid value of 25 to 1
00, hydroxyl value 35-200, SP value 10.0-1
A water-soluble alkyd resin or water-soluble acrylic resin of 1.0 as a main component and a hardener having a SP value of 0.5 to 3.0 higher than the SP value of the water-soluble alkyd resin or water-soluble acrylic resin The coating composition is prepared so that separation and aggregation can be prevented when the coating composition is concentrated and recovered from the wash water of the coating booth without degrading the coating film performance.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a system for reusing paint.

[Explanation of symbols]

 1 Coating booth 2 Sprayer 3 Paint concentrate tank 4 Ultrafiltration device 5 Filtrate tank 6 Wash water 7 Regenerated water-based paint composition 8 Filtrate

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Masahiro Nagasaki 19-17 Ikedanaka-cho, Neyagawa-shi, Osaka Japan Paint Co., Ltd. (72) Inventor Tetsuro Fusano 19-17 Ikedanaka-cho, Neyagawa-shi, Osaka Japan Into Inc.

Claims (2)

[Claims] 1. An acid value of 25 to 100 and a hydroxyl value of 35 to 35.
200, SP value is mainly composed of a water-soluble alkyd resin or a water-soluble acrylic resin having an SP value of 10.0 to 11.0, and an SP value 0.5 to 3.0 higher than the SP value of the water-soluble alkyd resin or water-soluble acrylic resin. A water-based coating composition comprising a curing agent having 2. The aqueous coating composition according to claim 1, wherein an amino resin is used as a curing agent.