JPS5813662A - Preventing method of foaming in coating of coating composition - Google Patents

Abstract

PURPOSE:To prevent the foaming in coating, particularly the foaming in the resource saving and anti-pollution high-solid coating, without changing the coating conditions or addition of an antifoaming agent, by using a specific melamine- formaldehyde resin as a vehicular component. CONSTITUTION:A composition containing a melamine-formaldehyde resin, preferably a resin etherified with any one of methyl alcohol, butyl alcohol and a mixture thereof, having a solubility parameter >=10.5(cal/cc)<1/2> and a viscosity <=5 poises at 25 deg.C in a 60% solution (containing the solvent substituted by 70pts.wt. n-butanol and 30pts.wt. xylol, in the resin) as a vehicular component. The resultant composition is coated by the air spray or electrostatic coating method.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing foaming during application of a coating composition containing the melamine-formaldehyde tree Qli.

In recent years, air-len painting, electrostatic airless painting, rotary electrostatic atomization painting, etc. have been increasingly adopted for the purpose of saving resources, preventing pollution, and improving painting efficiency. This often causes bubbles to form in the paint film, causing problems. Foaming may also be a problem with other spray coating machines, roll coaters, etc.

Conventional countermeasures have been to reduce the discharge amount, change coating conditions such as thinner coating, extremely low viscosity coating, or add antifoaming agents to the paint. It has drawbacks such as defects, insufficient film thickness, too much time for painting, and consumption of a large amount of solvent, which is a problem in terms of resource conservation and pollution control. Although the method of adding antifoaming agents to paint can prevent foaming, it has the disadvantage of causing new defects such as dents and repellents in the paint film, and no satisfactory method has been found to prevent foaming during conventional painting. Ta.

The present inventors improved the resin itself, which is a vehicle component, and set the solubility 1/2 parameter of melamine-formaldehyde resin, which is relatively easy to foam, to 10.5 (7/cC) or more, and the viscosity (in the resin) The solvent was replaced with a mixed solvent of 70 parts of n-butanol and 30 parts of kijirole, and the non-volatile content was 6.
By setting the viscosity of the 0% solution (hereinafter simply referred to as viscosity (60% solution)) to 5 voids / 25 ° C or less,
It has been found that foaming during painting can be prevented. Therefore, various drawbacks of the prior art such as changing coating conditions and adding an antifoaming agent can be overcome, and it is possible to prevent foaming in high solid coating, which is particularly desirable from the viewpoint of resource saving and pollution prevention.

"Solubility parameter" is defined by W. Sue et al., J. A. P. S. ■, 2359-2370.
(1968), and the details are described in the paper. However, the solubility parameters of resins have never been discussed in relation to their foaming properties.There is also a theory that the foaming phenomenon is mainly related to the surface tension of the resin solution, but there have been no experimental studies. Often there is no correlation.

Foaming of paint is caused by the dispersion of air into the paint and its atomized particles during painting. The ease with which bubbles form and their stability are said to be related to the surface viscosity, surface elasticity, surface charge, and evaporation phenomenon from the surface of the paint film that forms the bubbles.

In general, the ease of foaming and the difficulty of defoaming tend to be proportional; those that are easy to foam are difficult to defoam, and conversely, those that are difficult to foam are easy to defoam. Although it is not possible to explain in detail why the value of the solubility parameter greatly contributes to foaming during coating, in a coating composition containing a melamine-formaldehyde resin with a high solubility parameter and low viscosity, the above-mentioned paint The physical properties of the membrane are such that it is difficult to foam and is easily defoamed.

Further, the conditions that can prevent foaming again are also the conditions that maintain a good level of coating performance in helisolid coating, which is preferable from the standpoint of resource conservation and pollution control. That is, if the viscosity of the melamine-formaldehyde resin is too high, high solids coating becomes difficult.

The melamine-formaldehyde resin used in the present invention is a hexakisalkoxymethylol melamine resin modified with a single or mixed alcohol having 1 to 5 carbon atoms, or a part thereof is substituted with an imino group or an N-methylol group, The solubility parameter is to, s (7/cc) and the viscosity (60% solution) is 5 voids/25° C. or less.

Examples of the alcohol having 1 to 5 carbon atoms include methyl alcohol, ethyl alcohol, isopropyl alcohol, normal phthyl alcohol, and isobutyl alcohol.

The melamine-formaldehyde resin can be used as a crosslinking agent for acrylic resins, polyester resins, oil-free polyester resins, and other resins that can be used as paint binders, like ordinary melamine-formaldehyde resins.

When combining acrylic resins, it is desirable that the solubility parameter of the acrylic resins to be combined is 10.5 (1/2 d/CC) or less.

Further, conventional pigments, additives, solvents, other modified resins, etc. can be added to the coating composition used in the present invention by conventional methods.

A melamine-formaldehyde resin solution having characteristic values suitable for the purpose of the present invention is prepared into a coating composition by a conventional method, and when this is applied, no antifoaming agent is used and the coating conditions are changed. It is possible to perform airless painting or electrostatic painting without any problems, prevent foaming during painting, and obtain a coating that has a clean finish and excellent film performance even when high solid coating is applied. I can ride.

The invention is illustrated below with examples and comparative examples.

In the text, "parts" and "%" are by weight.

The solubility parameter is indicated by "SP" and its unit is 1/2 ha (oaa/CC). The viscosity of melamine-formaldehyde resin was measured by the following method: rV I
It is indicated as SJ, and its unit is poise/25°C.

Since the non-volatile content and solvent of the melamine-formaldehyde resins used were different, in order to obtain accurate viscosity, the solvent in each melamine-formaldehyde resin was mixed at 40°C x 48 hours.
3ymH? After drying and evaporating under reduced pressure under the conditions of
The viscosity of the mixture was measured by replacing the solvent with a mixed solvent consisting of 70 parts of n-butanol and 30 parts of Kijirole to adjust the non-volatile content to 60%. The measurement method is a converted value of the measured value using a Gardner viscometer.

Example 1 Xylene 268 and P+n-butanol 32y were charged into a 117 flask equipped with a stirrer, a cooler, a thermometer, a nitrogen inlet tube, and a dropping funnel, and heated and stirred at 125° C. under a nitrogen stream. To this, styrene 120y, methacrylic acid n
-butyl 172p, n-butyl acrylate 48y, 2-hydroxyethyl methacrylate 52y, acrylic acid s,
A solution containing 8.0 y of azobisisobutyronitrile was added dropwise over 3 hours. 3'0 minutes after the completion of the dropwise addition, a solution of 2,0 y of t-butylperoxy-2-ethylhexanoate and 20 y of xylene was added dropwise over a period of 0 minutes. After the dropwise addition was completed, stirring was continued for an additional 90 minutes at 125°C.

The obtained acrylic resin solution is colorless and transparent with a non-volatile solid content of 5.
5.0%, and the viscosity was 7725°C (Gardner viscometer). The SP of the resin is 10.02. Number average molecular weight (high performance liquid chromatography, Shimabara Seisakusho LC-83)
Polystyrene equivalent value measured by type 0) is 7,400
Met.

Example 2 Xylene 268Pan-butanol 32Y was charged into a flask No. 11 equipped with a stirrer, a cooler, a thermometer, a nitrogen introduction tube, and a dropping rotor, and the mixture was heated and stirred at 125° C. under a nitrogen stream. To this, 802 y of styrene, 127.2 y of methyl methacrylate, 128.8 y of n-butyl acrylate, 52 y of 2-hydroxyethyl methacrylate, 1 y of acrylic acid.
2.1', azobisisobutyronitrile8. A solution containing Oy was added dropwise over 3 hours. 30 minutes after the dropwise addition was completed, a solution of t-butylperoxy 1,2-ethylhexanoate 2,09 and xylene 20y was further added dropwise over 30 minutes. After the dropwise addition, stirring was continued for an additional 90 minutes at 125°C. Ta.

The obtained acrylic resin solution is colorless and transparent with a non-volatile solid content of 5.
At 5.0%, the viscosity is V-W/25℃ (Gardner viscometer)
The SP of the resin was 10.70° and the number average molecular weight was 6.
,900.

Example 3 Methylated melamine-formaldehyde resin (Sumimar M40-8,5P=12.60.V) was added to 114.5 parts (solid content 55%) of the acrylic resin solution obtained in Example 1.
IS=0.06. Manufactured by Jumin Kagaku ■) 225 parts (solid content 8
0%) was added to prepare a clear paint.

Example 4 114.5 parts of the acrylic resin solution obtained in Example 1 (@
methyl isobutyl mixed etherified melamine-formaldehyde resin (Cyme #325-10)
1,5P=11.78. VIS=0.65. 22.5 parts (solid content: 80%) (manufactured by Mitsui Cyanamid Co., Ltd.) were added to prepare a clear paint.

Example 5 114.5 parts (solid content 55%) of the acrylic resin solution obtained in Example 1 was added with n-butylated melamine-formaldehyde resin d resin (Super Beckamine 14-559.5P=
11.08. VIS=1.40. 30.0 parts (solid content: 60%) (manufactured by Dainippon Ink Chemical ■) was added to prepare a clear paint.

Comparative Example 1 Isobutylated melamine-formaldehyde resin (Super Beckamine L121-60,5P=1
1.05. VIS=6.30. Manufactured by Inu Nippon Ink Chemical Company)
A clear paint was prepared by adding 30.0 parts (solid content: 60%).

Comparative Example 2 N-butylated melamine-formaldehyde resin (Cymer 1156,5P=10.03.VI
S=0.02. (manufactured by Mitsui Cyanamid Co., Ltd.) 18.0 parts (
(solid content 100%) was added to prepare a clear paint.

Comparative Example 3 114.5 parts (solid content 55%) of the acrylic resin solution obtained in Example 1 was added with n-butylated melamine-formaldehyde resin (Kneepan 220,5P=9°90, VIS=5
．． 5. Manufactured by Mitsui Toatsu Chemical Co., Ltd.) 30.0 parts (solid content 60%)
was added to prepare a clear paint.

Comparative Example 4 114.5 parts (solid content 55%) of the acrylic resin solution obtained in Example 1 was added with n-butylated melamine-formaldehyde resin (Kneepan 125.5P=9°78, VIS
=14.2. manufactured by Mitsui Toatsu Chemical Co., Ltd.) 36.0 parts (solid content 5
0%) was added to prepare a clear paint.

Example 6 To 114.5 parts of the acrylic resin solution (solid content 55%) obtained in Example 2, methylated melamine-formaldehyde resin (Sumimaru M40-5.SP=12.60.V
IS=0.06. A clear paint was prepared by adding 22.5 parts (solid content: 80%) of Sumitomo Chemical Co., Ltd.).

Example 7 To 114.5 parts of the acrylic resin solution (solid content 55%) obtained in Example 2, methyl and isobutyl mixed etherified melamine-formaldehyde resin (Cymer 325-10
1,5P=11.78. VIS=0.65. 22.5 parts (solid content: 80%) (manufactured by Mitsui Cyanamid Co., Ltd.) were added to prepare a clear paint.

Example 8 To 114.5 parts of the acrylic resin solution obtained in Example 2 (solid content 55%) was added n-butylated melamine-formaldehyde 41 fat (K-Pervecamine 14-559.5P=1
1.08. VIS=1.40. Dainippon Ink Chemical (Japanese)
A clear paint was prepared by adding 30.0 parts (solid content: 60%).

Example 9 114.5 parts of the acrylic resin solution obtained in Example 2 ([
Methylated melamine-formaldehyde resin (Sumimail 325,5P = 13゜8
5, VIS=0.70. (manufactured by Mitsui Cyanamitsu Co., Ltd.) 22
．． A clear paint was prepared by adding 5 parts (solid content: 80%).

Comparative Example 5 Isobutylated melamine-formaldehyde resin (Super Beckamine L121-60,5P=1
1.05. VIS=6.3. Dainippon Ink Kagakuwa) 3
0.0 part (solid content: 60%) was added to prepare a clear paint.

Comparative Example 6 N-butylated melamine-formaldehyde resin (Cymer 1156,5P=10.03.VI
S=0.02. (manufactured by Mitsui Cyanamid Co., Ltd.) 18.0 parts (
(solid content: 100%) to prepare a clear paint.

Comparative Example 7 114.5 parts (solid content 55%) of the acrylic resin solution obtained in Example 2 was added with n-butylated melamine-formaldehyde resin (Niepan 220, 5P=9.90VIS=5
．． 5. Manufactured by Mitsui Toatsu Chemical Co., Ltd.) 30.0 parts (solid content 60%)
was added to prepare a clear paint.

Comparative Example 8 114.5 parts (solid content 55%) of the acrylic resin solution obtained in Example 2 was added with n-butylated melamine-formaldehyde 41 fat (Kneepan 125.5P=9°78, VIS=
14.2. manufactured by Mitsui Toatsu Chemical Co., Ltd.) 36.0 parts (solid content 50
%) to prepare a clear paint.

The clear paints obtained in Examples 3 to 9 and Comparisons 8 to 8 were treated with a thinner consisting of 20 parts of isobutanol, 30 parts of xylene, and 50 parts of Nurubetsun 150 (mixed solvent manufactured by Esso Standard) in 7 ord cups & 4.
A diluted paint was prepared by diluting it at 0°C for 20 seconds, and the nonvolatile content of this diluted paint was measured.

There are two methods for determining the ease with which paint foams: one is to apply it directly, and the other is to stir diluted paint and measure the ease with which paint foam disappears.The latter method is explained below. We conducted a test.

The diluted paint was stirred with a small dispenser for 5 minutes to foam the paint. Immediately after the stirring stops, the paint is dropped into a 200CC graduated cylinder, and the time until the surface of the liquid in the graduated cylinder is exposed is measured to determine the defoaming property.

Regarding the former, diluted paint was applied using an electrostatic coating machine or an Ares coating machine at a discharge rate of 3QQcc/min, with a dry film thickness of 40 to 50%.
/I on the steel plate, setting for 10 minutes,
After prebaking at 100° C. for XIO minutes, the coating was baked at 160° C. for 20 minutes to form a coating film, and the foaming state of the coating film and other abnormalities in the appearance of the coating film were evaluated with the naked eye. The reason why preliminary baking is performed at this time is to prevent pinholes (flanks) from occurring during baking, and if pinholes (flanks) occur, it will be difficult to distinguish them from bubbles.

These results are shown in Table 1. Table 1 shows that paints using melamine resins with solubility parameters of IO, 5 (7/cc) 1/2 or higher and viscosity (60% solution) of 5 poise/25°C or lower, Compared to resins that do not satisfy the above-mentioned conditions in terms of at least one of laminator and viscosity, this shows that the antifoaming properties are excellent and that no bubbles are generated in the dried coating film.

Focusing on the non-volatile content of the paint during painting, as shown in Table 1, Examples 3 to 9, in which no bubbles occur in the dried paint film, have a high non-volatile content of 42% or more; In most of the comparative examples, the non-volatile content is as low as 41% or less. This indicates that the viscosity of the melamine-formaldehyde resin used in the non-foaming paint is low, so the non-volatile content of the paint during painting is high.

Based on the above facts, the present invention can prevent foaming during coating, and also enables high solid coating, contributing to resource saving, pollution control, and improvement in coating efficiency.

Next, in order to test the coating performance of the coating composition to which the present invention was applied, the diluted coatings prepared in Examples 3 to 9 and Comparative Coatings to 8 were spray-painted on a thin film type zinc phosphate treated steel plate. The evaluation was performed by baking at 160° C. for 20 minutes. The results are shown in Table 2.

(The following is a blank space) As seen in Table 2, the coating film performance of Examples 3 to 9 was all satisfactory.

Patent applicant: Nippon Paint Co., Ltd. Agent: Patent attorney Takuya Akaoka, 7. Fortress -

Claims (3)

[Claims] (1) The solubility parameter as a vehicle component is 1.
Foaming during coating of a coating composition characterized by using a melamine-formaldehyde resin having a viscosity of 0.5 (7!/CC) of 172 or higher and a viscosity of 5 mm or less at 25°C in a 60% solution. How to prevent it. (2) The method of claim 1, wherein the PM fat is etherified with any one of melamine-formaldehyde alcohol, butyl alcohol, and mixtures thereof. (3) The method according to claim 1, wherein the coating method is an airless spray method or an electrostatic coating method.