JP4232649B2 - Electrodeposition coating method for aluminum or aluminum alloy - Google Patents
Electrodeposition coating method for aluminum or aluminum alloy Download PDFInfo
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- 238000000576 coating method Methods 0.000 title claims description 61
- 238000004070 electrodeposition Methods 0.000 title claims description 28
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 title claims description 17
- 229910052782 aluminium Inorganic materials 0.000 title claims description 17
- 229910000838 Al alloy Inorganic materials 0.000 title claims description 8
- 239000011248 coating agent Substances 0.000 claims description 56
- 239000003973 paint Substances 0.000 claims description 14
- 229920000877 Melamine resin Polymers 0.000 claims description 10
- 238000000034 method Methods 0.000 claims description 6
- NIXOWILDQLNWCW-UHFFFAOYSA-N acrylic acid group Chemical group C(C=C)(=O)O NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 claims description 3
- JDSHMPZPIAZGSV-UHFFFAOYSA-N melamine Chemical compound NC1=NC(N)=NC(N)=N1 JDSHMPZPIAZGSV-UHFFFAOYSA-N 0.000 claims description 3
- 238000001035 drying Methods 0.000 description 16
- 238000011156 evaluation Methods 0.000 description 15
- 230000000052 comparative effect Effects 0.000 description 14
- 238000012360 testing method Methods 0.000 description 10
- 239000002253 acid Substances 0.000 description 8
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 8
- 230000005856 abnormality Effects 0.000 description 7
- 239000000126 substance Substances 0.000 description 7
- 238000006243 chemical reaction Methods 0.000 description 6
- JOYRKODLDBILNP-UHFFFAOYSA-N Ethyl urethane Chemical compound CCOC(N)=O JOYRKODLDBILNP-UHFFFAOYSA-N 0.000 description 5
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 5
- 239000000243 solution Substances 0.000 description 5
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 125000001033 ether group Chemical group 0.000 description 4
- 239000004640 Melamine resin Substances 0.000 description 3
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- LSNNMFCWUKXFEE-UHFFFAOYSA-N Sulfurous acid Chemical compound OS(O)=O LSNNMFCWUKXFEE-UHFFFAOYSA-N 0.000 description 3
- 239000007864 aqueous solution Substances 0.000 description 3
- 238000004132 cross linking Methods 0.000 description 3
- 238000006460 hydrolysis reaction Methods 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 229910017604 nitric acid Inorganic materials 0.000 description 3
- 238000012643 polycondensation polymerization Methods 0.000 description 3
- 230000000007 visual effect Effects 0.000 description 3
- 0 CN(C)c1nc(N(C)*)nc(N(C)C)n1 Chemical compound CN(C)c1nc(N(C)*)nc(N(C)C)n1 0.000 description 2
- RTZKZFJDLAIYFH-UHFFFAOYSA-N Diethyl ether Chemical compound CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 description 2
- 239000000853 adhesive Substances 0.000 description 2
- 230000001070 adhesive effect Effects 0.000 description 2
- 125000003178 carboxy group Chemical group [H]OC(*)=O 0.000 description 2
- 239000003054 catalyst Substances 0.000 description 2
- 238000009833 condensation Methods 0.000 description 2
- 238000006482 condensation reaction Methods 0.000 description 2
- 238000001723 curing Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000011056 performance test Methods 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 230000002159 abnormal effect Effects 0.000 description 1
- 239000003377 acid catalyst Substances 0.000 description 1
- 239000010407 anodic oxide Substances 0.000 description 1
- 238000002048 anodisation reaction Methods 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 230000005494 condensation Effects 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 229910021641 deionized water Inorganic materials 0.000 description 1
- 230000032798 delamination Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000002845 discoloration Methods 0.000 description 1
- 238000005868 electrolysis reaction Methods 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 238000004299 exfoliation Methods 0.000 description 1
- 238000011049 filling Methods 0.000 description 1
- 238000013007 heat curing Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000007062 hydrolysis Effects 0.000 description 1
- 238000010030 laminating Methods 0.000 description 1
- 238000006116 polymerization reaction Methods 0.000 description 1
- 229920000098 polyolefin Polymers 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000000197 pyrolysis Methods 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 239000003566 sealing material Substances 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 238000005979 thermal decomposition reaction Methods 0.000 description 1
- 229920001187 thermosetting polymer Polymers 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- 239000002023 wood Substances 0.000 description 1
- 230000037303 wrinkles Effects 0.000 description 1
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Description
本発明は、アルミニウム又はアルミニウム合金の電着塗装方法、とりわけ電着塗膜表面の接着性を改善するのに好適な焼付硬化方法に関するものである。 The present invention relates to an electrodeposition coating method of aluminum or an aluminum alloy, and more particularly to a bake hardening method suitable for improving the adhesion of the electrodeposition coating film surface.
従来、塗膜表面を改質するためのアルミニウム又はアルミニウム合金の電着塗装方法として、例えば、特許文献１では電着塗装後、水蒸気雰囲気中で焼付を行いシーリング用プライマーの接着性を改善するようにしたものが開示されている。また、特許文献２では熱硬化型塗料を被塗物に塗装後、該被塗物表面への酸性ガスの接触・非接触を制御し、酸性ガスに接触した表面部分の硬化を塗膜内部より促進させることによって酸性ガスとの接触部にチリメン模様状等の粗面塗膜を形成する方法が開示されている。
ところが、上記した従来のアルミニウム又はアルミニウム合金の電着塗装方法において、例えば特許文献１の方法はシーリング材のように充填部分での接着性を問題にする場合は僅かな表面改質でも改善効果が現れるので適用できるが、例えばウレタン系塗料を上塗り塗装する場合やラミネートシートを貼り付ける場合など、塗膜表面での層間剥離防止のための接着性改善のためには効果が十分でなく、適用できないという問題があった。
また、特許文献２の方法は酸性ガスとの接触部にチリメン模様状等の粗面塗膜を形成することを目的とするものであり、接着性改善のための表面改質効果は十分であるが、表面外観も変化してしまうという問題があり、こうした問題点を解決することが従来の課題となっていた。
However, in the above-described conventional electrodeposition coating method of aluminum or aluminum alloy, for example, the method of Patent Document 1 has an improvement effect even with a slight surface modification when the adhesiveness at the filling portion is a problem as in a sealing material. Appears and can be applied, but is not sufficient for improving adhesion to prevent delamination on the surface of the paint film, such as when applying a urethane-based paint or applying a laminate sheet. There was a problem.
Moreover, the method of patent document 2 aims at forming a rough surface coating film, such as a chirimene pattern, in a contact part with acid gas, and the surface modification effect for adhesiveness improvement is enough. However, there is a problem that the surface appearance also changes, and it has been a conventional problem to solve such problems.
請求項１に記載の発明は、アルミニウム又はアルミニウム合金にアクリルメラミン系塗料による電着塗装を行った後、ＳＯ２濃度が５０〜２００ｐｐｍの雰囲気中で、焼付温度１７０〜２００℃、焼付時間２０〜４０分で塗膜の焼付乾燥を行う構成を前述した従来の課題を解決するための手段としている。 In the first aspect of the present invention, after electrodeposition coating with an acrylic melamine-based paint is applied to aluminum or an aluminum alloy, a baking temperature of 170 to 200 ° C. and a baking time of 20 to 20 in an atmosphere having an SO 2 concentration of 50 to 200 ppm are provided. The structure in which the coating film is baked and dried in 40 minutes is used as a means for solving the above-described conventional problems.
本発明の請求項１に係わる電着塗装方法では、電着塗膜をＳＯ２ガス雰囲気中で焼付乾燥するものであるから、加熱によるアクリル−メラミンの縮合重合反応及びメラミンの自己縮合反応の進行による塗膜の架橋硬化の進行と並行して、塗膜表面においてＳＯ２ガスの触媒作用によるエーテル基の加水分解反応を進行させることによって塗膜表面にＯＨ基を増加させ、表面の濡れ性を高めることで、例えばウレタン系塗料などを上塗り塗装する場合やラミネートシートを貼り付ける場合などにおいて充分な接着性を付与できる。また、電着塗膜の表面外観を変化させないのでクリヤー塗膜を上塗りすることも可能であるという優れた効果を有するものである。 In the electrodeposition coating method according to claim 1 of the present invention, the electrodeposition coating film is baked and dried in an SO2 gas atmosphere, and therefore, by the progress of an acrylic-melamine condensation polymerization reaction and a melamine self-condensation reaction by heating. In parallel with the progress of cross-linking and curing of the paint film, the OH group is increased on the paint film surface by advancing the hydrolysis reaction of ether groups by the catalytic action of SO2 gas on the paint film surface, thereby improving the surface wettability. Thus, sufficient adhesion can be imparted, for example, in the case of overcoating with a urethane-based paint or the like, or in the case of attaching a laminate sheet. In addition, since the surface appearance of the electrodeposition coating film is not changed, the clear coating film can be overcoated.
以下、本発明の実施例及び比較例について、データを添えて詳細に説明する。 Hereinafter, examples and comparative examples of the present invention will be described in detail with data.
先ず、アルミニウム合金押出形材Ａ６０６３Ｓ−Ｔ５（以下、アルミ形材という）に、通常実施している電着塗装前処理を行なった。即ち、アルミ形材を１３０ｇ／ｌの硫酸水溶液に２５℃で５分間浸漬して脱脂洗浄を行なった後、５０ｇ／ｌの水酸化ナトリウム水溶液に５０℃で５分間浸漬してエッチング処理を行ない、次いで、このアルミ形材を４０ｇ／ｌの硝酸に２０℃で２分間浸漬してスマット除去を行なった後、１２０ｇ／ｌ硫酸水溶液中でアルミ形材を陽極として電流密度１００Ａ／ｍ2で３４分間の電解処理を行ない、表面に９μｍの陽極酸化皮膜を生成させた。
続いてこのアルミ形材を８０℃の脱イオン水で８分間の湯洗処理を行ない、これを冷却後、次の通りの電着塗装処理を施した。電着塗料は艶消しタイプのアクリル−メラミン系アニオン電着塗料（神東塗料株式会社製エスビアＥＤ＃５０２０）を使用し、電着塗料浴中でアルミ形材を陽極として１６０Ｖで２．５分間の通電を行ない、形材表面に７μｍの電着塗膜を形成させた後、室温雰囲気中で１５分間のセッティングを行った。
続いて焼付乾燥処理を行なったが、この焼付乾燥処理に際しては焼付乾燥炉内に亜硫酸を投入し、熱分解によって発生するＳＯ２ガスを５０〜２００ｐｐｍの雰囲気となるように調整して焼付温度１７０〜２００℃、焼付時間２０〜４０分の条件範囲で実施例１〜実施例６の電着塗装アルミ形材を作製した。
First, an aluminum alloy extruded profile A6063S-T5 (hereinafter referred to as an aluminum profile) was subjected to a conventional electrodeposition coating pretreatment. That is, after the aluminum profile was degreased and washed by immersing it in a 130 g / l sulfuric acid aqueous solution at 25 ° C. for 5 minutes, it was immersed in a 50 g / l aqueous sodium hydroxide solution at 50 ° C. for 5 minutes for etching treatment. Next, the aluminum shape was immersed in 40 g / l nitric acid at 20 ° C. for 2 minutes to remove smut, and then the aluminum shape was used as an anode in a 120 g / l sulfuric acid aqueous solution at a current density of 100 A / m 2 for 34 minutes. The electrolysis treatment was performed to produce a 9 μm anodic oxide film on the surface.
Subsequently, this aluminum profile was subjected to a hot water washing treatment with deionized water at 80 ° C. for 8 minutes. After cooling, the aluminum electrode was subjected to the following electrodeposition coating treatment. The electrodeposition paint uses a matte type acrylic-melamine anion electrodeposition paint (Esvia ED # 5020 manufactured by Shinto Paint Co., Ltd.), and the aluminum shape is used as an anode in an electrodeposition paint bath at 160V for 2.5 minutes. Then, a 7 μm electrodeposition coating film was formed on the surface of the profile, and then setting was performed for 15 minutes in a room temperature atmosphere.
Subsequently, the baking and drying treatment was performed. In this baking and drying treatment, sulfurous acid was introduced into the baking and drying furnace, the SO 2 gas generated by thermal decomposition was adjusted to an atmosphere of 50 to 200 ppm, and the baking temperature was 170. The electrodeposition-coated aluminum profiles of Examples 1 to 6 were produced in a condition range of ˜200 ° C. and baking time of 20 to 40 minutes.
しかる後に上記した本発明の実施例１〜実施例６の処理を施した電着塗膜の表面接着性の改善効果を評価するために、これらを焼付乾燥後４８時間以上室温で放置した後、上塗り塗装及びラミネート処理（貼り付け）を施し、上塗り塗装の付着性の評価としては碁盤目試験を、ラミネートシートの接着性の評価としてはラミネートシートの剥離強度の測定を行った。上塗り塗装の付着性の評価用には所定条件で調製した常温硬化型アクリルウレタン系塗料（藤倉化成株式会社製アクレタンＭ、グレー色）を用い、塗膜厚さが４０〜６０μｍとなるように塗布して、８０℃、３０分の条件で強制乾燥を行なった後、室温で２４時間以上放置した試料を用いた。
また、ラミネートシートの剥離強度の測定用には上記した電着塗装を施したアルミ形材に二液型ウレタン系接着剤を所定量塗布し、木目柄のポリオレフィンシートを用いて所定条件でラミネート処理を施した後、これを室温で4日間放置した試料を用いた。また、上塗り塗装をしてない電着塗膜について、目視外観評価、鉛筆硬度試験、耐酸性試験及び耐候性試験を行った。
Thereafter, in order to evaluate the effect of improving the surface adhesion of the electrodeposition coating film subjected to the treatment of Examples 1 to 6 of the present invention described above, after leaving them at room temperature for 48 hours or more after baking and drying, Top coating and laminating treatment (attaching) were performed, and a cross-cut test was performed as an evaluation of the adhesion of the top coating, and a peel strength of the laminate sheet was measured as an evaluation of the adhesion of the laminate sheet. For the evaluation of the adhesion of the top coat, a room temperature curable acrylic urethane paint prepared under predetermined conditions (Acretan M manufactured by Fujikura Kasei Co., Ltd., gray color) is used so that the coating thickness is 40-60 μm. Then, after forced drying at 80 ° C. for 30 minutes, a sample that was allowed to stand at room temperature for 24 hours or more was used.
For measuring the peel strength of laminate sheets, a predetermined amount of two-component urethane adhesive is applied to the above-mentioned electrodeposited aluminum profile, and laminate processing is performed under specified conditions using a wood grain patterned polyolefin sheet. Then, a sample was used which was allowed to stand at room temperature for 4 days. Further, visual appearance evaluation, pencil hardness test, acid resistance test, and weather resistance test were performed on the electrodeposition coating film that was not overcoated.
上記した各種性能試験の結果を表１に示す。表１は左側欄から順に実施例の番号（Ｎｏ．）、焼付乾燥炉に投入する薬液の名称（投入薬液）、炉中ガス濃度測定対象成分（測定ガス）、炉中ガス濃度測定結果（ガス濃度）、焼付温度、焼付時間を記し、続いて右側欄に各評価結果（電着塗膜の表面接着性、上塗り塗装或いはラミネート加工をしていない塗膜の目視外観、鉛筆硬度、耐酸性、耐候性）を記してあり、表１において各性能の評価方法は次のとおりである。
上塗り塗装の付着性はＪＩＳ−Ｋ５６００．５．６に規定された１ｍｍ桝の碁盤目試験を行って『○＝１００／１００（剥離なし）、×＝剥離発生』として評価し、ラミネートの剥離強度は２５ｍｍ幅の９０°剥離試験による剥離強度の測定を行って『○＝３０Ｎ以上、×＝３０Ｎ未満』として各々評価したものであるが、表１の表面接着性の評価欄では『○＝上塗り塗装の付着性及びラミネートの剥離強度の評価が共に○のもの、△＝上塗り塗装の付着性またはラミネートの剥離強度の評価のいずれか一方が×のもの、×＝上塗り塗装の付着性及びラミネートの剥離強度の評価が共に×のもの』として纏めて表記した。
目視外観の評価は『○＝異常なし、×＝縮み、シワ等の外観異常発生』を表わしている。
鉛筆硬度試験はＪＩＳ−Ｋ５６００．５．４によって試験し、評価結果は『○＝３Ｈ以上、×＝２Ｈ以下』として表記した。
耐酸性の評価は５％Ｈ２ＳＯ４水溶液に７２時間浸漬後の外観評価で『○＝異常なし、×＝腐食ピット発生』を表している。
耐候性の評価はＪＩＳ−Ｈ８６０２．５．１２に規定された促進耐候性試験による２５０時間後の外観評価で『○＝異常なし、×＝変色、肌荒れ、艶ムラなどの外観異常発生』を表している。
Table 1 shows the results of the various performance tests described above. Table 1 shows the example number (No.) in order from the left column, the name of the chemical solution to be fed into the baking / drying furnace (input chemical solution), the gas concentration measurement target component (measurement gas), and the gas concentration measurement result in the furnace (gas). (Concentration), baking temperature, baking time, and each evaluation result (surface adhesion of electrodeposition coating film, visual appearance of coating film not overcoated or laminated, pencil hardness, acid resistance, Weather resistance) is described, and in Table 1, the evaluation method of each performance is as follows.
The adhesion of the top coat is evaluated as “◯ = 100/100 (no peeling), x = exfoliation occurs” by conducting a 1 mm square cross-cut test specified in JIS-K5600.55.6, and the peel strength of the laminate Is a peel strength measured by a 90 ° peel test with a width of 25 mm, and evaluated as “◯ = 30N or more, x = less than 30N”, but in the surface adhesive evaluation column of Table 1, “◯ = top coating” The evaluation of the adhesion of the coating and the peel strength of the laminate are both ○, △ = either the adhesion of the top coating or the evaluation of the peeling strength of the laminate is ×, × = the adhesion of the top coating and the laminate The peel strength is evaluated as “x”.
The visual appearance evaluation represents “◯ = no abnormality, x = abnormal appearance of shrinkage, wrinkles, etc.”.
The pencil hardness test was conducted according to JIS-K5600.5.5.4, and the evaluation result was expressed as “◯ = 3H or more, x = 2H or less”.
The evaluation of acid resistance is an appearance evaluation after being immersed in a 5% H 2 SO 4 aqueous solution for 72 hours.
The evaluation of weather resistance is an appearance evaluation after 250 hours according to the accelerated weather resistance test stipulated in JIS-H8602.5.12, indicating “○ = no abnormality, × = occurrence of appearance abnormality such as discoloration, rough skin, gloss unevenness”. ing.
アルミ形材に上記した実施例と同様の前処理〜陽極酸化〜電着塗装を行い、室温雰囲気中で１５分間のセッティングを行った。しかる後に焼付乾燥処理を行うに際して、亜硫酸などの薬液を投入しない場合（＝従来法）（比較例１）、焼付乾燥炉内に投入する亜硫酸の量を加減してＳＯ２ガス濃度のより低い場合（比較例２〜比較例６）、より高い場合（比較例２３〜比較例２７）、ＳＯ２ガス濃度は上記した実施例と同等として焼付乾燥の温度又は時間の条件を変化させた場合（比較例７〜比較例２２）、焼付乾燥炉への別の投入薬液として硝酸又は塩酸を用いた場合（この場合に熱分解などで発生するガスの種類（炉中濃度を測定したガスの種類）は硝酸の場合ＮＯ及びＮＯ２（ＮＯＸと総称）であり、塩酸の場合は揮散するＨＣｌである。）（比較例２８、比較例２９）について各々上記した実施例と同様の性能試験を行った結果を表２に示す。
尚、比較例においてはいずれかの試験で何らかの異常発生が認められた条件の試料については残る試験は中止した。
The same pretreatment, anodization, and electrodeposition coating as in the above-described example were performed on the aluminum profile, and setting was performed for 15 minutes in a room temperature atmosphere. After that, when performing baking and drying treatment, when no chemical solution such as sulfurous acid is added (= conventional method) (Comparative Example 1), when the amount of sulfurous acid charged into the baking and drying furnace is adjusted to lower the SO 2 gas concentration (Comparative Example 2 to Comparative Example 6), when higher (Comparative Example 23 to Comparative Example 27), when the SO 2 gas concentration is equivalent to that of the above-described Example, and the baking or drying temperature or time conditions are changed (Comparison Example 7 to Comparative Example 22), when nitric acid or hydrochloric acid is used as another chemical solution to be baked and dried (in this case, the type of gas generated by pyrolysis or the like (the type of gas whose concentration in the furnace is measured) is In the case of nitric acid, it is NO and NO 2 (generally referred to as NO X ), and in the case of hydrochloric acid, it is HCl that volatilizes.) (Comparative Example 28 and Comparative Example 29) were subjected to the same performance tests as the above-described examples. The results are shown in Table 2.
In the comparative example, the remaining test was stopped for the sample in which any abnormality was observed in any test.
本発明に用いているアクリル−メラミン系電着塗料の主成分であるアクリル−メラミン樹脂の加熱硬化（焼付乾燥）時における縮合重合の反応式は一般に次に示す化１によって表わされ、同時並行的に進行するメラミン樹脂の自己縮合の反応式は化２によって表わされる。 The reaction formula of the condensation polymerization at the time of heat curing (baking and drying) of the acrylic-melamine resin which is the main component of the acrylic-melamine-based electrodeposition coating used in the present invention is generally represented by the following chemical formula 1 and simultaneously The reaction formula of self-condensation of a melamine resin that progresses automatically is represented by Formula 2.
本発明における電着塗膜表面の化学変化の状況を確認するために、上記した実施例及び比較例のいくつかについて顕微ＡＴＲ法によるＩＲ分析を実施した結果、図１の分光スペクトルが得られた。図１において、ピーク（１）（３３５０ｃｍ−１）は水酸基（−ＯＨ）の伸縮振動によるものであり、ピーク（２）（１７５０ｃｍ−１）はカルボキシル基（−Ｃ＝Ｏ）の伸縮振動によるものであり、ピーク（３）（１１００ｃｍ−１）はエーテル基（Ｃ−Ｏ−Ｃ）の逆対称伸縮振動によるものである。 In order to confirm the state of chemical change on the surface of the electrodeposition coating film in the present invention, IR analysis by micro ATR method was performed on some of the examples and comparative examples described above, and as a result, the spectrum shown in FIG. 1 was obtained. . In FIG. 1, peak (1) (3350 cm-1) is due to stretching vibration of hydroxyl group (-OH), and peak (2) (1750 cm-1) is due to stretching vibration of carboxyl group (-C = O). And peak (3) (1100 cm −1) is due to the inversely symmetric stretching vibration of the ether group (C—O—C).
（図１）
図１より明らかなように、焼付乾燥時に炉内のＳＯ２ガス濃度を変化させてもピーク（２）即ち１７５０ｃｍ−１のカルボキシル基（−Ｃ＝Ｏ）の伸縮振動強度はほぼ一定の値を示している一方、焼付乾燥時に炉内のＳＯ２ガス濃度が高くなるほどピーク（１）即ち３３５０ｃｍ−１における水酸基（−ＯＨ）の伸縮振動強度が大きくなり、逆にピーク（３）即ち１１００ｃｍ−１におけるエーテル基（Ｃ−Ｏ−Ｃ）の逆対称伸縮振動が小さくなっている、すなわち、電着塗膜表面では焼付乾燥炉内のＳＯ２ガス濃度が高くなるほどエーテル基が減少して、水酸基が増加していることを示している。 As is clear from FIG. 1, even when the SO2 gas concentration in the furnace is changed during baking and drying, the stretching vibration intensity of the peak (2), that is, the carboxyl group (-C = O) of 1750 cm <-1> shows a substantially constant value. On the other hand, the higher the SO2 gas concentration in the furnace during baking and drying, the higher the stretching vibration strength of the hydroxyl group (—OH) at peak (1), ie 3350 cm−1, and the ether at peak (3), ie 1100 cm−1. The reverse symmetrical stretching vibration of the group (C—O—C) is small, that is, the ether group decreases and the hydroxyl group increases on the surface of the electrodeposition coating film as the SO2 gas concentration in the baking and drying furnace increases. It shows that.
本発明に用いているアクリル−メラミン系の加熱硬化型塗料中には酸触媒が添加されて塗膜の架橋反応の促進に作用するようにしてある。また、焼付炉内に酸性ガスが存在して未硬化の塗膜表面に接触するとこれが触媒となって表面の硬化が促進され、遅れて塗膜内部の縮合重合が進行すると内部容積の収縮を引き起こして塗膜表面に縮み模様の外観異常が生成される現象はガスチェッキングとして知られており、本発明に用いたＳＯ２ガスもこのような性質を持つ触媒として働いて塗膜の表面硬化反応が促進されると考えられている。表２の比較例７〜比較例２２において鉛筆硬度が２Ｈ以下のもの（塗膜の硬化（架橋重合反応）がまだ十分進行していないもの）では外観異常が発生していないのに対して、鉛筆硬度が３Ｈ以上のもの（塗膜の硬化が十分進行したもの）では縮み現象による外観異常が発生しているという事実はこのことを裏付けるものである。 An acid catalyst is added to the acrylic-melamine heat-curable coating used in the present invention so as to act to promote the crosslinking reaction of the coating film. In addition, when acid gas is present in the baking oven and contacts the surface of the uncured coating, it acts as a catalyst to accelerate the curing of the surface, and when the condensation polymerization inside the coating progresses, the internal volume shrinks. The phenomenon that shrinkage pattern appearance abnormality is generated on the surface of the coating film is known as gas checking, and the SO 2 gas used in the present invention also acts as a catalyst having such properties to react with the surface hardening reaction of the coating film. Is believed to be promoted. In Comparative Examples 7 to 22 in Table 2, the pencil hardness was 2H or less (the coating film was not sufficiently cured (crosslinking polymerization reaction)), whereas no appearance abnormality occurred. The fact that the appearance abnormality due to the shrinkage phenomenon occurs in the case where the pencil hardness is 3H or more (the coating film has sufficiently hardened) supports this fact.
その一方で上記した通り、図１のＩＲ分析チャートからはＳＯ２ガス濃度の高い雰囲気中で焼付乾燥を行ったほうが塗膜表面の水酸基（−ＯＨ）が増加し、エーテル基（Ｃ−Ｏ−Ｃ）が減少している事実がわかることから、ＳＯ２ガス雰囲気中では塗膜表面にＳＯ２が作用して上記した化２のメラミン樹脂の自己縮合反応の逆反応として縮合部分の加水分解反応が並行的に進行しており、それによって塗膜表面の水酸基（−ＯＨ）を増加させているものと考えられる。このように塗膜表面の水酸基（−ＯＨ）を増加せしめていることが塗膜の表面の濡れ性を高めるとともに、表面接着性の改善効果を付与しているものであることは表１及び表２のデータによって明らかである。 On the other hand, as described above, from the IR analysis chart of FIG. 1, the surface of the coating film surface has increased hydroxyl groups (—OH) when subjected to baking and drying in an atmosphere with a high SO 2 gas concentration, and ether groups (C—O—C). ) Is reduced, SO2 acts on the coating surface in the SO2 gas atmosphere, and the hydrolysis reaction of the condensation portion is performed in parallel as the reverse reaction of the self-condensation reaction of the melamine resin of Chemical Formula 2 described above. It is considered that the hydroxyl group (—OH) on the surface of the coating film is thereby increased. It is shown in Table 1 and Table 1 that increasing the hydroxyl group (—OH) on the surface of the coating film as described above increases the wettability of the surface of the coating film and provides an effect of improving the surface adhesion. It is clear from the data of 2.
また上記した通り、焼付乾燥炉中のＳＯ２ガス濃度を高くするほど塗膜表面に生成される水酸基（−ＯＨ）の量が増加することによって塗膜の表面接着性が良くなる一方で、表２の比較例２３〜比較例２７に見られるようにＳＯ２ガス濃度が高すぎると塗膜への加水分解が進行することによる塗膜性能の劣化が認められるようになることも表１及び表２のデータによって明らかであり、従ってこれらの結果から塗膜外観及び塗膜性能を十分満足しつつ塗膜の表面接着性を向上させることのできる最適な焼付乾燥条件範囲としては表１の実施例１〜実施例６に示した通り、ＳＯ２濃度が５０〜２００ｐｐｍの雰囲気中で、焼付温度１７０〜２００℃、焼付時間２０〜４０分の条件で塗膜の焼付乾燥を行うことが最も好ましいものである。このようにして表面改質された電着塗膜は、例えばウレタン系塗料などを上塗り塗装する場合やラミネートシートを貼り付ける場合などにおいて充分な接着性を付与できる。また、電着塗膜の表面外観を変化させないのでクリヤー塗膜を上塗りすることも可能であるという優れた効果を有するものである。 Further, as described above, the surface adhesiveness of the coating film is improved by increasing the amount of hydroxyl group (—OH) generated on the surface of the coating film as the SO2 gas concentration in the baking and drying furnace is increased. As shown in Comparative Examples 23 to 27, when the SO2 gas concentration is too high, deterioration of the coating film performance due to the progress of hydrolysis to the coating film is also observed in Tables 1 and 2. It is apparent from the data, and therefore, from these results, the optimum baking and drying condition range capable of improving the surface adhesiveness of the coating film while sufficiently satisfying the coating film appearance and coating film performance is shown in Examples 1 to 1 in Table 1. As shown in Example 6, it is most preferable to bake and dry the coating film in an atmosphere having an SO2 concentration of 50 to 200 ppm under conditions of a baking temperature of 170 to 200 ° C. and a baking time of 20 to 40 minutes. The electrodeposition coating film thus surface-modified can provide sufficient adhesiveness, for example, when a urethane-based paint or the like is applied by overcoating or when a laminate sheet is applied. In addition, since the surface appearance of the electrodeposition coating film is not changed, the clear coating film can be overcoated.
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