JP3814738B2 - High corrosion resistance electrodeposition coating - Google Patents

Description

【００３９】
表１からわかるように、比較例１と実施例４を比較すると、主体樹脂、ＰＶＣおよびＰＷＣは同じであるが、実施例４は反応速度のおそい硬化剤IIを使用しているためＲａが０．４μｍ以下になっている。比較例２を実施例３と比較すると、実施例３は顔料ペーストＩの配合量を少し、そのためＰＶＣおよびＰＷＣが小さくなっているためＲａが０．４μｍ以下になっている。実施例１および２は比較例３より顔料ペーストの配合量が少なく、ＰＶＣおよびＰＷＣが小さくなっているためＲａが０．４μｍ以下にとどまっている。
【００４０】
評価方法
１）耐食性
素地に達するように電着塗膜にナイフでクロスカットキズをいれ、塩水噴霧試験（３％食塩水、３５℃×８００ｈｒ）を行い、粘着テープによってカット部からの最大剥離幅を測定した。
○：＜３ｍｍ △：３〜６ｍｍ ×：＞６ｍｍ
２）ガスピンホール
２６０Ｖで電着した時の硬化塗膜５０ｃｍ² あたりのピンホールの数
○：ピンホールなし
△：１０個未満
×：１０個以上
３）つきまわり性
日本ペイント株式会社発行テクノコスモス１９９３，Ｖｏｌ．３，４４−５１頁記載の４ボックスつきまわり性測定装置を使用して測定した。特開平７−２８６２９７参照。単位μｍ[0001]
Background of the present invention The present invention relates to an electrodeposition coating film coating made of a metal and having sufficient corrosion resistance even though the film thickness is thinner than usual.
[0002]
Electrodeposition paints have excellent corrosion resistance and throwing power, and are widely used as corrosion resistant primer coatings on metal materials such as automobile bodies and parts in order to form a uniform coating film. By the way, in the conventional methods, a film thickness of 20 μm or more is usually required to ensure sufficient corrosion resistance. If sufficient corrosion resistance can be secured even if this film thickness is reduced to about 1/2 of the conventional film thickness, not only can the paint consumption be greatly saved, but also the current consumption and time can be saved, making resources and energy more efficient. Can be used for
[0003]
However, if the film thickness is reduced according to the conventional method, the corrosion resistance is significantly lowered as the coating film becomes thinner. According to the inventors, the cause of the decrease in corrosion resistance is closely related to the surface roughness of the coating film, that is, if the surface roughness is large, the distance from the substrate to the point where the coating film is recessed ( It has been found that the minimum film thickness point) becomes smaller, and at this point, the corrosion-promoting substance passes through the coating film and reaches the interface with the substrate, which is likely to cause corrosion. Therefore, if the surface roughness is small, a film thickness sufficient to prevent the passage of the corrosion promoting substance can be secured even at the minimum film thickness point, so that the film thickness can be reduced as a whole. The present invention is based on such knowledge.
[0004]
DISCLOSURE OF THE INVENTION Accordingly, the present invention provides an electrodeposition coating film having a thickness of 5 to 12 μm and a center line surface roughness Ra of 0.4 μm or less, particularly to a metal material to be protected, Provided is a highly corrosion-resistant coating formed by coating a cationic electrodeposition coating film.
[0005]
Detailed discussion A method for measuring Ra using a stylus type surface roughness measuring instrument is defined in JIS B 0651. Ra here is based on this test method.
[0006]
As described above, it is difficult to reduce Ra to 0.4 μm or less according to the conventional method. Thus, special measures are required to make Ra 0.4 μm or less. Ra can generally be improved by increasing the heat flow during baking. However, other performances should not be adversely affected by changing the paint composition to enhance heat flow. For this purpose, the following method was found to be effective.
[0007]
A. The pigment concentration adjusting paint contains various pigments for the purpose of coloring and corrosion protection. In electrodeposition paints, in order to reduce the occurrence of craters due to self-repellency and oil repellency, a relatively large amount of extender pigment such as clay is added to rather suppress flowability. Therefore, it is possible to increase the flow property rather by keeping the pigment ratio in the coating film as low as possible within a range in which a satisfactory repellency preventing effect is ensured. This includes a method of reducing the weight ratio (PWC) of the entire pigment to the coating film and a method of reducing the volume ratio (PVC) of the entire pigment to the coating film. PVC can be lowered by using a large amount of pigment having a large specific gravity while keeping PWC constant. Of course, both can be used together. In this case, the range in which flowability can be improved without adversely affecting the securing of other performances, particularly repellency resistance, is generally 1 to 25%, preferably 5 to 15% for PWC, and 0. It is 2 to 15%, preferably 1.5 to 7%.
[0008]
B. Use of flow improver or surface smoothness improver In epoxy-based cationic electrodeposition paints, a part of the epoxy ring is opened with a hydroxyl compound such as 2-ethylhexanol, nonylphenol, ethylene glycol mono-2-ethylhexyl ether. It is known to obtain a cationic resin with improved heat flow. Further, Japanese Patent Application Laid-Open No. 5-287223 and Japanese Patent Application Laid-Open No. 7-126557 of the present applicant disclose cationic resins that improve acrylic and epoxy surface smoothness, respectively. It is also an effective means to add these components that can improve flowability or flatness to the paint. In particular, a cationic resin derived from a t-alkylphenol novolac epoxy resin disclosed in JP-A-7-126557 is particularly preferable because it can improve surface smoothness without adversely affecting other properties, particularly topcoat adhesion.
[0009]
C. Use of low-viscosity main resin It is natural that low-viscosity resin has good flowability, but since viscosity increases in proportion to molecular weight, lowering the molecular weight of main resin generally reduces the mechanical strength of the coating film, so it is commonly used. It is practically not applicable to other cationic resins. Japanese Patent Application Laid-Open No. 5-306327 filed by the present applicant discloses a cationic resin for electrodeposition coatings derived from an epoxy resin whose resin skeleton contains an oxolidon ring. Since this resin has a lower viscosity than conventional epoxy cationic resins when compared at the same molecular weight level, using this resin as the main resin can improve flowability without adversely affecting the other performance of the coating film. it can.
[0010]
D. Use of slow-reacting or low-viscosity curing agents In cationic electrodeposition coatings, blocked polyisocyanates are mainly used as curing agents, but they blocked free and inherently slow polyisocyanates such as crude MDI (diphenylmethane diisocyanate). It is also effective to select one having a slow dissociation reaction rate or a blocking agent such as furfuryl alcohol or ethylene glycol monobutyl ether.
[0011]
It is also an effective method to select a blocked product of a polyisocyanate compound having a low viscosity when mixed with the main resin, for example, a blocked product of hexamethylene diisocyanate monomer. However, whichever method is used, the amount of the curing agent depends on the active hydrogen of the main resin and the functional group of the curing agent (the functional group of the curing agent (since the cured coating must have sufficient crosslinking density to exhibit satisfactory performance). The ratio should be such that the ratio of blocked NCO groups is in the range of 1: 0.3 to 1: 2, preferably 1: 0.8 to 1: 1.5.
[0012]
The methods A to D described above are effective even when used alone, but some of them can be used in combination. Further, the method of controlling Ra to 0.4 μm or less is not limited to these methods, and it is needless to say that the present invention can employ other methods effective for that purpose.
[0013]
As is clear from the above description, the subject of the present invention is not the electrodeposition paint itself or its composition. Therefore, the type of electrodeposition paint to be used is not questioned, but what is used for automobiles today is an epoxy-based cationic electrodeposition paint having excellent anticorrosion properties, and will be described below. However, the present invention is also applicable to anionic electrodeposition paints and cationic electrodeposition paints other than epoxy-based paints, such as acrylic and polybutadiene-based electrodeposition paints, and corresponding effects can be obtained.
[0014]
Cationic epoxy resins Cationic modified epoxy resins which are the main component of the film-forming resin component of the cationic electrodeposition coating composition are described in JP-A Nos. 54-4978 and 56-34186. Well-known resin is mentioned.
[0015]
Typically, all of the epoxy rings of the bisphenol type epoxy resin are opened with an active hydrogen compound capable of introducing a cationic group, or some of the epoxy rings are opened with another active hydrogen compound, and the rest It is produced by opening an epoxy ring with an active hydrogen compound capable of introducing a cationic group.
[0016]
A typical example of the bisphenol type epoxy resin is a bisphenol A type or bisphenol F type epoxy resin. As the former commercial products, there are Epicoat 828 (Oilized Shell Epoxy Co., Ltd., Epoxy Equivalent 180-190), Epicoat 1001 (Same, Epoxy Equivalent 450-500), Epicoat 1010 (Same, Epoxy Equivalent 3000-4000), etc. As the latter commercially available product, there is Epicoat 807, (epoxy equivalent 170). As disclosed in Japanese Patent Application Laid-Open No. 5-306327 by the present applicant, an epoxy resin containing an oxadoridone ring in the chain may be used. As described above, this resin has a low viscosity and is effective in improving flowability. These epoxy resins are desirably ring-opened with an active hydrogen compound so that an amine equivalent of 0.3 to 4.0 meq / g is obtained after ring opening.
[0017]
Examples of the active hydrogen compound capable of introducing a cationic group include a primary amine, a secondary amine, a tertiary amine acid salt, or a sulfide / acid mixture. Examples include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine hydrochloride, N, N-dimethylethanolamine acetate, diethyl disulfide / acetic acid mixture, etc. In addition, there are secondary amines in which primary amines such as aminoethylethanolamine ketimine and diethylenetriamine diketimine are blocked. A plurality of amines may be used in combination.
[0018]
Other active hydrogen compounds that can be used to open the epoxy ring include monophenols such as phenol, cresol, nonylphenol, nitrophenol; hexyl alcohol, 2-ethylhexanol, stearyl alcohol, ethylene glycol or propylene glycol. Monoalcohols such as monobutyl- or monohexyl ether; aliphatic monocarboxylic acids such as stearic acid and acetic acid; aliphatic hydroxycarboxylic acids such as glycolic acid, dimethylolpropionic acid, hydroxypivalic acid, lactic acid, citric acid; and mercapto Examples include mercaptoalkanols such as ethanol.
[0019]
Curing agent As the curing agent, melamine resins and block polyisocyanate compounds can be used, but block polyisocyanate compounds are preferred.
[0020]
Each of the block polyisocyanate compounds is an addition reaction product of a theoretical amount of a polyisocyanate compound and an isocyanate blocking agent, and is a curing agent for the main resin. Examples of the polyisocyanate compound include tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate (MDI), phenylene diisocyanate, bis (isocyanate methyl) cyclohexane, tetramethylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, isophorone diisocyanate, and these diisocyanate compounds. Aromatic, cycloaliphatic, and aliphatic polyisocyanate compounds such as dimers or trimers, and low amounts of ethylene glycol, propylene glycol, trimethylolpropane, hexanetriol, castor oil, etc. in excess of these isocyanate compounds Examples include terminal isocyanate-containing prepolymers obtained by reacting molecularly active hydrogen-containing compounds. That. Further, the isocyanate blocking agent is added to the isocyanate group of the polyisocyanate compound and blocked. It is important that the block polyisocyanate compound produced by addition is stable at room temperature and can regenerate free isocyanate groups by dissociating the blocking agent when heated above the dissociation temperature.
[0021]
Specifically, phenol-based blocking agents such as phenol, cresol, xylenol, chlorophenol and ethylphenol; lactam-based blocking agents such as ε-caprolactam, δ-parerolactam, γ-butyrolactam and β-propiolactam; ethyl acetoacetate And active methylene blocking agents such as acetylacetone; methanol, ethanol, propanol, butanol, amyl alcohol, furfuryl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, propylene glycol monomethyl ether, Benzyl alcohol, methyl glycolate, butyl glycolate, diacetone alcohol, milk Alcohol-based blocking agents such as methyl and ethyl lactate; oxime-based blocking agents such as formaldoxime, acetoaldoxime, acetoxime, methylethylketoxime, diacetylmonooxime, cyclohexaneoxime; butyl mercaptan, hexyl mercaptan, t-butyl mercaptan, thiophenol , Methylthiophenol, ethylthiophenol and other mercaptan blocking agents; acetic acid amide, benzamide and other acid amide blocking agents; succinimide and maleic imide imide blocking agents; xylidine, aniline, butylamine, dibutylamine, etc. Amine-based blocking agents; Imidazole-based blocking agents such as imidazole and 2-ethylimidazole; Imines such as ethyleneimine and propyleneimine Blocking agent; Of these, oxime blocking agents such as methyl ethyl ketoxime are particularly suitable.
[0022]
The method of controlling Ra to 0.4 or less by selecting the block polyisocyanate curing agent has been described above.
[0023]
After adding a half-block polyisocyanate compound to the secondary hydroxyl group in the chain of the polyepoxy resin, the self-crosslinking amine-modified epoxy resin obtained by opening the terminal epoxy ring with an amine or the like is used as the main resin and the crosslinking agent. Or it may be used as a part. After self-crosslinking type amine-modified epoxy resin blocks a part of the isocyanate group of the polyisocyanate compound with the above-mentioned blocking agent, and performs an addition reaction between the remaining free isocyanate group and the secondary hydroxyl group of the epoxy resin Similarly to the main resin, it can be produced by opening an epoxy ring with an active hydrogen compound capable of introducing a cationic group such as amine.
[0024]
Electrodeposition coating composition The electrodeposition coating composition is prepared by dispersing a main resin, a curing agent, and, if used, a surface smoothness control resin in an aqueous medium containing a neutralizing agent. The surface smoothness control resin is dispersed in an aqueous medium containing a main resin and a cross-linking agent and a neutralizing agent in one place, or dispersed with an appropriate cationic resin separately from the main resin and then into a dispersion of the main resin. It can be added and blended. Neutralizing agents are inorganic or organic acids such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, lactic acid.
[0025]
The amount of cross-linking agent must be sufficient to react with functional groups such as hydroxyl groups in the resin upon curing to give a good cured coating, generally 5-50% by weight of resin solids is used. The The amount of neutralizing agent is an amount sufficient to neutralize at least 20%, preferably 30-60% of the amino groups of the resin.
[0026]
The amount of the surface smoothness control resin used is 0.05 to 30% by weight, preferably 0.5 to 20% by weight, based on the total solid content of the main resin and the curing agent. When this amount is less than 0.05% by weight, there is no effect of improving the surface smoothness, and when it exceeds 30% by weight, the surface smoothness is rather lowered.
[0027]
The electrodeposition paint can contain a tin compound such as dibutyltin dilaurate and dibutyltin oxide and a usual urethane cleavage catalyst in a system containing a block polyisocyanate. The amount is usually 0.1 to 5% by weight of the blocked polyisocyanate compound.
[0028]
Electrodeposition paints include colored pigments such as titanium dioxide, carbon black, and bengara, rust preventive pigments such as basic lead silicate and aluminum phosphomolybdate, and extender pigments such as kaolin, clay, and talc, as well as water-miscible organic solvents. Conventional paint additives such as surfactants, antioxidants and ultraviolet absorbers can be included. The specific method for controlling the surface smoothness by PWC and PVC has been described above.
[0029]
Production Example 1
Synthesis of main resin Epoxy equivalent: 285 parts by weight of epoxy resin synthesized from flask bisphenol A and epichlorohydrin equipped with stirrer, cooler, nitrogen injection tube, thermometer and dropping funnel and epoxy equivalent: 950 epoxy 380 parts by weight of resin, 77 parts by weight of P-nonylphenol and 82 parts by weight of methyl isobutyl ketone were respectively weighed, heated up, dissolved uniformly, added with 3.0 g of benzyldimethylamine, and reacted at a reaction temperature of 150 ° C. to obtain an epoxy equivalent The reaction was continued until 1140. Thereafter, the mixture was cooled, 19 parts by weight of diethanolamine, 27 parts by weight of N-methylethanolamine and 31 parts by weight of a ketimine product of aminoethylethanolamine (79% methyl isobutyl ketone solution) were added, and the reaction was continued at 110 ° C. for 2 hours. Then, it diluted with methyl isobutyl ketone until it became 80% of non volatile matters, and main resin I was obtained.
[0030]
Production Example 2
Synthesis of main resin 54 parts by weight of 2.4 / 2.6-tolylene diisocyanate (80/20 wt ratio) and methyl isobutyl in a flask equipped with a stirrer, cooler, nitrogen injection tube, thermometer and dropping funnel 136 parts by weight of ketone and 0.5 parts by weight of dibutyltin dilaurate were weighed and 11 parts by weight of methanol was added dropwise from a dropping funnel over 30 minutes while stirring. The temperature was raised from room temperature to 60 ° C. Thereafter, the reaction was continued for 30 minutes, and then 54 parts by weight of ethylene glycol mono-2-ethylhexyl ether was dropped from the dropping funnel over 1 hour. The reaction was carried out while maintaining mainly in the range of 60 ° C to 65 ° C. The reaction was continued until the isocyanate group disappeared with an infrared spectrometer. Thereafter, 285 parts by weight of an epoxy resin with an epoxy equivalent of 475 synthesized from bisphenol F and epichlorohydrin and 380 parts by weight of an epoxy resin with an epoxy equivalent of 950 are added to a reaction vessel, mixed uniformly, heated to 120 ° C., and benzyldimethyl 0.62 parts by weight of amine was added, and the reaction was continued until the epoxy equivalent was 1120 while distilling off the by-produced methanol using a decanter. After cooling, 29 parts by weight of diethanolamine, 22 parts by weight of N-methylethanolamine and 33 parts by weight of ketimine product of aminoethylethanolamine (79% methyl isobutyl ketone solution) were then added. The reaction was performed at 110 ° C. and allowed to react for 2 hours. Diluted with methyl isobutyl ketone to a non-volatile content of 80% to obtain the main resin II.
[0031]
Production Example 3
Synthesis of curing agent I 199 g of hexamethylene diisocyanate trimer (Coronate HX: manufactured by Nippon Polyurethane) and 32 g of methyl isobutyl ketone in a flask equipped with a stirrer, a cooler, a nitrogen injection tube, a thermometer and a dropping funnel While weighing 0.1 g of dibutyltin dilaurate and stirring and nitrogen bubbling, 87.0 g of methyl ethyl ketoxime was dropped from the dropping funnel over 1 hour. The temperature was raised from 70 ° C. to 70 ° C. The reaction was continued, and the reaction was continued until the absorption of the NCO group disappeared with an infrared spectrometer.
[0032]
Production Example 4
Synthesis of curing agent II 199 g of crude MDI (Coronate 1104: made by Nippon Polyurethane), 32 g of methyl isobutyl ketone and dibutyltin dilaurate in a flask equipped with a stirrer, cooler, nitrogen injection tube, thermometer and dropping funnel. While weighing 1 g, stirring and nitrogen bubbling, 8 g of furfuryl alcohol was dropped from the dropping funnel over 1 hour. The temperature was raised from 70 ° C. to 70 ° C. The reaction was continued, and the reaction was continued until the absorption of the NCO group disappeared with an infrared spectrometer.
[0033]
Production Example 5
Synthesis of surface smoothness control resin A flask equipped with a stirrer, a cooler, a nitrogen injection tube, a thermometer, and a dropping funnel was attached to a P-alkyl-substituted phenol novolac type epoxy resin (manufactured by Tohto Kasei Co., Ltd .: epoxy equivalent: 311). , Alkyl = t-butyl group, number average molecular weight: 1160) 311 parts by weight and 96 parts by weight of methyl isobutyl ketone were weighed and heated to 80 ° C. to be uniformly dissolved. After cooling to 40 ° C., 74 parts by weight of N-methylethanolamine was added to the reaction vessel while paying attention to heat generation. Thereafter, the reaction was continued at 80 ° C., and the reaction was continued until the epoxy group disappeared (epoxy equivalent measurement, reaction tracking with an infrared spectrometer). Further, 114 parts by weight of ε-caprolactone was weighed and continuously heated to 120 ° C., 1.141 parts by weight of dibutyltin oxide was added to the reaction vessel, reacted at a reaction temperature of 140 ° C., and ε- This was continued until the absorption based on caprolactone (690 cm ⁻¹ ) disappeared. Thereafter, the mixture was cooled and 29 parts by weight of methyl isobutyl ketone was added to obtain a surface smoothness control resin. Nonvolatile content: 80.1%.
[0034]
Production Example 6
Preparation of pigment dispersion pastes I and II The components were mixed in the following composition and pulverized with a sand grind mill to a particle size of 10 µm or less to prepare pigment dispersion pastes I and II.
[0035]
Component I II
Pigment-dispersed resin ^* 125.0 g 125.0 g
Ion exchange water 400.0g 400.0g
Carbon black 8.5g 3.5g
Kaolin 172.0g 22.0g
Titanium oxide 245.0g 400.0g
Aluminum phosphomolybdate 75.0 g 75.0 g
* Sulphonium salt type, Nippon Paint Co., Ltd., resin solid content 75%
[0036]
Examples 1-6
Main resin / curing agent / surface smoothness control resin is mixed at a solid content ratio in the composition shown in Table 1, and 2 wt% of ethylene glycol monohexyl ether is added to the solid content. After neutralization to a sum of 42.5%, it was slowly diluted with ion-exchanged water. Methyl isobutyl ketone was removed under reduced pressure so that the solid content was 36.0%. The obtained main elmagion, pigment dispersion paste, and ion-exchanged water were added in the number of parts by weight shown in Table 1 to prepare a cationic electrodeposition paint having a solid content of 20.0%. The prepared paint was electrodeposited on a cold-rolled steel sheet treated with zinc phosphate so as to have a dry film thickness of 8 μm, and baked at 160 ° C. for 10 minutes. Thereafter, various coating film evaluations were performed. The obtained results are shown in Table 1.
[0037]
Comparative Examples 1-3
A coating material was prepared in the same manner as in Examples 1 to 6 with the blending components shown in Table 1, and electrodeposition was baked to evaluate the coating film. The obtained results are shown in Table 1.
[0038]
[Table 1]

[0039]
As can be seen from Table 1, when Comparative Example 1 and Example 4 are compared, the main resin, PVC and PWC are the same, but since Example 4 uses slow curing agent II with a slow reaction rate, Ra is 0. .4 μm or less. Comparing Comparative Example 2 with Example 3, Example 3 has a small amount of pigment paste I, and accordingly, PVC and PWC are small, so Ra is 0.4 μm or less. In Examples 1 and 2, the amount of pigment paste is smaller than that in Comparative Example 3, and PVC and PWC are small, so Ra is 0.4 μm or less.
[0040]
Evaluation method 1) The electrodeposition coating film is cross-cut with a knife so as to reach the corrosion-resistant substrate, subjected to a salt spray test (3% salt solution, 35 ° C. × 800 hr), and the maximum peel width from the cut portion with an adhesive tape Was measured.
○: <3 mm Δ: 3-6 mm ×:> 6 mm
2) the number of pinholes per cured coating film 50cm ² at the time of electrodeposition in the gas pinhole 260V ○: No pin hole △: less than 10 ×: 10 or more 3) throwing power Nippon Paint Co., Ltd. issued Techno Cosmos 1993, Vol. It was measured using a 4-box throwing power measuring device described on pages 3,44-51. See JP-A-7-286297. Unit μm

Claims (4)

  A cationic electrodeposition coating material containing a slow-acting curing agent or a low-viscosity curing agent and having a pigment weight concentration PWC and a pigment volume concentration PVC adjusted to 1 to 25% and 0.2 to 15%, respectively, is applied to a metal material. A highly corrosion-resistant coating formed by electrodeposition and forming an electrodeposition coating film having a film thickness of 5 to 12 μm and a centerline average surface roughness Ra of 0.4 μm or less.   The coating of claim 1, wherein the slow-acting hardener is a blocked product of crude MDI.   The coating according to claim 1, wherein the low viscosity curing agent is a blocked product of hexamethylene diisocyanate.   2. The coating according to claim 1, wherein the cationic electrodeposition paint contains a coating film flowability improving component.