JP4582875B2 - Coating film forming method and article to be coated - Google Patents

Description

【００７６】
外観評価
塗装した塗板の外観を、ビッグケミー社製ウエーブスキャンのＳＷの値で評価した。結果を表２に示した。数値の小さいもの程良好な結果が得られたことを表す。
【００７７】
塗着ＮＶ（不揮発分）測定方法
中塗り塗装、ベース塗装及びクリヤー塗装について別々に操作を行って、下記方法に従って計算した。
器具：重量（ｗ１）を測定したアルミ箔を、５ｃｍ×１０ｃｍの四角い穴をあけた紙で覆ったものをマスキングテープで鉄板にはりつける。
操作：この鉄板を上記塗装時に塗板に隣接するように移動板に付着させ、塗料塗布後、アルミ箔を鉄板から剥がす。
ＮＶ測定：塗料の付着したアルミ箔の重量（ｗ２）を測定後、１４０℃で３０分間乾燥後の重量（ｗ３）を測定する。
計算：下記の式より塗着ＮＶ（％）を計算する。
塗着ＮＶ（％）＝（ｗ３−ｗ１）／（ｗ２−ｗ１）×１００
得られた結果を表２に示した。
【００７８】
体積収縮率計算方法
体積収縮率（％）を下記式に従って計算する。
体積収縮率（％）＝｛（１００−塗着ＮＶ）／溶剤比重｝／［｛（１００−塗着ＮＶ）／溶剤比重｝＋（塗着ＮＶ／乾燥塗膜比重）｝×１００
溶剤比重：塗料中の溶剤組成から、中塗り塗料は０．８７、ベース塗料は０．８６とした。
乾燥塗膜比重：各塗料組成から、中塗り塗料１．６４、ベース塗料１．２３とした。
得られた結果を表２に示した。
【００７９】
粘度測定方法
中塗り塗料をブリキ板にスプレー塗装し、８０℃で約５分間加熱後、不揮発分９０％近傍の塗料を掻き取った。このサンプルの粘度を、以下の条件にて測定した。
測定機種：ＵＢＭ社製レオゾルＧ−３０００
測定法：動的粘弾性率測定（正弦波）
測定モード：温度依存性
チャックコーンプレート
コーン直径／角：１８．９６ｍｍ／１．９７４ｄｅｇ
加振条件：連続加振（周波数１．０Ｈｚ／ひずみ ０．５ｄｅｇ）
開始／終了温度：４０／１５０℃
昇温ステップ：２℃／分
トルク／ロードセル：２ｋｇ・ｃｍ／５ｋｇ
得られた粘度の結果を曲線で結んだグラフを図１に示し、６０℃、９０℃及び１２０℃での粘度を表２に示した。図１より読み取った最低粘度及び硬化開始温度を表２に示した。
中塗り塗料と同様にして、ベース塗料及びクリヤー塗料についてもそれぞれ粘度を測定し、最低粘度及び硬化開始温度を読み取った。結果を表２及び図１に示した。
【００８０】
耐溶剤性試験方法
中塗り塗料及びベース塗料をそれぞれブリキ板上に塗装後（２０μｍ）、８０℃×１０分乾燥してＮＶを上げたものを作成し、これに、代表的な塗料溶剤であるＳ−１５０、キシロール、ＥＥＰを１滴スポットし、３０秒静置後約４５度傾斜して状態を観察した。
○：変化なし
△：膨潤
×：溶解
得られた結果を表２に示した。
【００８１】
比較例１
固形分比が表２の通りになるように、樹脂、非水ディスパージョン樹脂及び硬化剤を配合したこと以外は、実施例１と同様にして、中塗り塗料及びベース塗料を調製して塗装を行い、測定及び評価を行った。
結果を表２及び図２に示した。
【００８２】
【表２】

【００８３】
表２中、サイメル２５４はメチル・ブチル混合型メラミン樹脂（三井サイテック社製）である。
実施例１は、中塗り塗料、ベース塗料及びクリヤー塗料の焼き付け過程における最低粘度及び硬化開始温度の関係が適正なものであること、更に、実施例１で使用した中塗り塗料及びベース塗料は、体積収縮率が小さいものであり、非水ディスパージョン樹脂を含むことより耐溶剤性にも優れるものであったことより、３コート１ベーク法で塗装し焼き付け硬化させた場合の仕上がり外観に優れるものであった。
比較例１は、中塗り塗料、ベース塗料及びクリヤー塗料の焼き付け過程における最低粘度が、中塗り塗料よりもベース塗料の方が高くなっていること、また、ベース塗料の体積収縮率が大きく、非水ディスパージョン樹脂を含まない中塗り塗料は耐溶剤性に劣るものであったので溶剤により膨潤すると考えられることより、良好な仕上がり外観は得られなかった。
【００８４】
【発明の効果】
本発明の塗膜形成方法により、自動車車体等を３コート１ベーク法で塗装した場合に、優れた仕上がり外観の塗膜を得ることができる。
【図面の簡単な説明】
【図１】実施例１における、中塗り塗料、ベース塗料及びクリヤー塗料それぞれについての温度に対する粘度の測定結果を示したグラフである。
【図２】比較例１における、中塗り塗料、ベース塗料及びクリヤー塗料それぞれについての温度に対する粘度の測定結果を示したグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming a multilayer coating film on an electrodeposition-coated material such as an automobile body, and more specifically, an intermediate coating is applied to an automobile body and the like, and wet-on-wet is applied thereon. The present invention relates to a method of forming a multilayer coating film by a so-called three-coat one-bake coating system in which a base paint and a clear paint are applied by a method and baking and curing is performed at once.
[0002]
[Prior art]
For automobile bodies, etc., the surface of the steel sheet, which is the object to be coated, is subjected to chemical conversion treatment with zinc phosphate as the coating base, followed by undercoating, intermediate coating, and topcoating to form a multilayer coating film Has been.
Of these, the coating process is usually after the undercoat is applied by electrodeposition and baked and cured to form an undercoat, and then the intermediate coat is applied and baked and cured to form the intermediate coat. The top coating is performed, and the undercoating, intermediate coating and top coating are baked and cured separately after each coating.
[0003]
When using the base paint and clear paint as the top coat, apply the intermediate paint and bake and cure, then apply the base paint and clear paint by the wet-on-wet method, and then bake and cure at once. This is performed by the so-called 3-coat 2-bake method.
[0004]
Such a 3-coat 2-bake method has a problem that the total cost is high because of a long painting process and a large energy consumption.
Japanese Examined Patent Publication No. 59-33033 discloses a metallic coating method in which an undercoat is applied by electrodeposition coating and baking is performed, and then an intermediate coating and a metallic coating are applied and baking is performed simultaneously.
However, when this method is carried out using conventional intermediate coating and metallic coating, the intermediate coating and metallic coating are mixed at the interface of the coating, and after baking the intermediate coating, it is once baked and cured. There was a problem that the finished appearance was inferior compared with the coat 2 baking method.
[0005]
By the way, non-aqueous dispersion resin (NAD) is used for metallic coating of equipment, automobiles, etc. because of its low pollution, resource saving, and excellent workability and durability due to its fluidity. I came.
Japanese Patent Application Laid-Open No. 57-177068 discloses a non-aqueous dispersible resin coating composition containing dispersed particles obtained by graft polymerization of a monomer component in the presence of an acrylic copolymer. This is because the dispersed particles are dispersed in the coating film even after curing to form a non-uniform structure, whereby a coating film having excellent surface hardness and impact resistance can be obtained.
[0006]
[Problems to be solved by the invention]
The present invention applies an intermediate coating when applying an electrodeposition-coated material such as an automobile body, and applies a base coating and a clear coating by a wet-on-wet method. An object of the present invention is to provide a method of forming a coating film by simultaneously baking and curing three layers of a clear paint, and capable of obtaining an excellent finished appearance equal to or higher than that of a conventional three-coat two-bake method. It is what.
[0007]
In the case of the conventional three-coat two-bake method in which baking curing is performed after applying the intermediate coating, the present inventors have a high base concealing property, that is, the electrodeposition coating film formed by the electrodeposition coating. Surface roughening has little effect on the base and clear coatings after the intermediate coating has been applied and cured, but it does not bake and cure after applying the intermediate coating. In the case of the 3-coat 1-bake method, in which the base paint and clear paint are applied by the wet method and the three layers are baked and cured simultaneously, the surface concealment is low and the surface of the electrodeposition coating film formed by the electrodeposition paint is rough. However, it was found that the final appearance was greatly affected, and the skin was developed. In order to improve the base concealing property for this electrodeposition coating film, (1) In the process of baking and curing the intermediate coating, base coating and clear coating, the viscosity initially decreases as the temperature rises. When the curing starts, the viscosity starts to rise, but the relationship between the minimum viscosity of each layer and the curing start temperature in this baking process is appropriate, that is, in the baking process, the minimum viscosity of the upper layer of the three layers is The present inventors have found that it is important that the viscosity is lower than the lowest viscosity of the lower layer and that the upper layer has a higher curing start temperature than the lower layer.
[0008]
The present inventors also (2) reduce the solvent swelling rate of the intermediate coating and base paint when the base coating and the clear coating are applied by the wet-on-wet method after the intermediate coating is applied.
(3) In the process of baking and curing the intermediate coating, base coating and clear coating, the solvent volatilizes and the volume of the coating decreases, but this volume shrinkage should be reduced.
It has also been found that a coating film having an excellent finished appearance can be obtained by further improving the base concealing property for the electrodeposition coating film.
[0009]
[Means for Solving the Problems]
The present invention relates to a coating film forming method comprising a step of sequentially applying an intermediate coating, a base coating and a clear coating on an electrodeposited material, and a step of baking and curing the three coated layers at once. The intermediate coating, the base coating, and the clear coating have a minimum viscosity when the viscosity is measured with respect to temperature at a nonvolatile content of 90% by weight.
Intermediate paint ≥ Base paint ≥ Clear paint
And the curing start temperature is
Intermediate paint ≤ Base paint ≤ Clear paint
It is the coating-film formation method characterized by satisfy | filling the relationship of these.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
The method for forming a coating film according to the present invention includes a step of sequentially applying an intermediate coating, a base coating, and a clear coating on an electrodeposited material, and a step of baking and curing the three coated layers at a time. It will be.
[0011]
In the present invention, the intermediate coating, the base coating, and the clear coating have a minimum viscosity when the viscosity is measured with respect to temperature at a nonvolatile content of 90% by weight.
Intermediate paint ≥ Base paint ≥ Clear paint
And the curing start temperature is
Intermediate paint ≤ Base paint ≤ Clear paint
It satisfies the relationship. By satisfying the above relationship, in the baking and curing process, among the three coated layers, the lowest viscosity is lower as the upper layer and the curing start temperature is higher as the upper layer. As a result, the upper layer has flowability even when the lower layer begins to cure. Then, since the curing starts later than the lower layer, the base concealing property can be improved, and the appearance of the obtained coating film becomes excellent.
[0012]
In the present invention, the minimum viscosity and the curing start temperature are measured at various temperatures at a nonvolatile content of 90% by weight of the paint, and the minimum viscosity and the temperature at the minimum viscosity are read from the measured values. It is a thing. This measurement is performed separately for the intermediate coating, base coating, and clear coating. Examples of the temperature to be measured include a range of 40 to 150 ° C.
In the present invention, the viscosity at a nonvolatile content of 90% by weight means a viscosity at a nonvolatile content of 90 ± 2% by weight.
Moreover, in this invention, a viscosity means what is measured as a dynamic viscoelastic modulus with respect to a sine wave stress, For example, it can measure using the Resol G-3000 made from UBM.
[0013]
In the case of a solution type, the non-volatile content of the intermediate coating material, base coating material and clear coating material of the present invention is preferably 40 to 70% by weight, 30 to 60% by weight and 40 to 70% by weight at the time of coating. If the value falls below the lower limit, a high solid paint cannot be obtained, and not only the minimum viscosity and the curing start temperature satisfying the above-mentioned relationship cannot be obtained at a nonvolatile content of 90% by weight. In some cases, the viscosity value measured at 90% by weight has no lowest point, and furthermore, the volume shrinkage during bake-curing increases, so that the finished appearance of the resulting coating film is inferior. When the value exceeds the upper limit, the viscosity is too high, so that the appearance of the coating film may be inferior or workability may be lowered. More preferably, the intermediate coating material is 45 to 60% by weight, the base coating material is 40 to 50% by weight, and the clear coating material is 45 to 60% by weight.
[0014]
The intermediate coating, base coating and clear coating preferably have a volume shrinkage of 45% or less when cured at 140 ° C. for 30 minutes after coating. If it exceeds 45%, the electrodeposition coating film may be inferior in the base concealing property, and as a result, a coating film having a good finished appearance may not be obtained. More preferably, it is 40% or less.
In the present invention, the volume shrinkage when cured at 140 ° C. for 30 minutes can be determined by the following equation.
Volume shrinkage (%) = {(100-coating NV) / solvent specific gravity} / [{(100-coating NV) / solvent specific gravity} + (coating NV / dry coating specific gravity)} × 100
(In the formula, the coating NV is W1 when the weight of the object to be coated is W1, the weight of the object to which the paint is attached is W2, and the weight after drying at 140 ° C. for 30 minutes is W3.
Coating NV (%) = (W3-W1) / (W2-W1) × 100
Represents the value of the non-volatile content obtained by. The solvent specific gravity represents the specific gravity of the solvent contained in each paint. The dry film specific gravity is the specific gravity of the non-volatile content in each paint, and is a value obtained by calculation from the specific gravity of each component and its ratio. )
[0015]
Intermediate coating
In the present invention, the intermediate coating has a viscosity Vis (60 ° C.) at 60 ° C. of 10 to 1000 poise and a viscosity Vis (90 ° C.) at 90 ° C. of 1 to 500 poise at a nonvolatile content of 90% by weight. The viscosity Vis (120 ° C.) at 120 ° C. is preferably 100 to 10,000 poise.
By using a non-volatile component of 90% by weight with Vis (90 ° C.) of 1 to 500 poise, the minimum viscosity of the intermediate coating in the baking process is small. Thus, the base concealing property for the electrodeposition coating film is improved, and a coating film having an excellent finished appearance can be obtained. Therefore, when Vis (90 ° C.) exceeds 500 poise, the minimum viscosity of the intermediate coating in the baking process is large, and a coating film having an excellent finished appearance cannot be obtained. Preferably, Vis (90 ° C.) is 1 to 300 poise, more preferably 1 to 200 poise.
[0016]
A paint having a non-volatile content of 90% by weight having a Vis (60 ° C.) of less than 10 poise, a paint having a Vis (90 ° C.) of less than 1 poise, and a paint having a Vis (120 ° C.) of less than 100 poise have poor coating appearance. Or the basic performance of the coating film may not be maintained. Those whose Vis (60 ° C.) exceeds 1000 poise and those whose Vis (120 ° C.) exceeds 10,000 poise cannot be made into a high-solid-type intermediate coating at the time of coating preparation. The coating film having an excellent finished appearance cannot be obtained.
[0017]
The intermediate coating composition of the present invention has a ratio of the viscosity Vis (60 ° C.) at 60 ° C. to the viscosity Vis (90 ° C.) at 90 ° C. [Vis (60 ° C.) / Vis (90 ° C. )] Is 1.5 to 10, and the ratio of the viscosity Vis (120 ° C.) at 120 ° C. to the viscosity Vis (90 ° C.) at 90 ° C. [Vis (120 ° C.) / Vis (90 ° C.)] is 2 It is preferably ~ 30.
If Vis (60 ° C.) / Vis (90 ° C.) is less than 1.5 or Vis (120 ° C.) / Vis (90 ° C.) is less than 2, the minimum viscosity of the intermediate coating in the baking process Since it cannot be made small, a coating film having an excellent finished appearance cannot be obtained. If Vis (60 ° C.) / Vis (90 ° C.) exceeds 10, or Vis (120 ° C.) / Vis (90 ° C.) exceeds 30, it is actually difficult to prepare.
[0018]
In the present invention, as the intermediate coating material, a resin comprising a hydroxyl group-containing resin (a), a curing agent (b) capable of reacting with a hydroxyl group, and a non-aqueous dispersion resin (c) can be preferably used.
By using the intermediate coating material containing the non-aqueous dispersion resin (c), the solvent swelling rate of the intermediate coating material due to the solvent contained in the base coating material is reduced, and the intermediate coating material and the base coating material are coated. Since mixing at the interface can be prevented, a coating film having a more excellent finished appearance can be obtained.
[0019]
The hydroxyl group-containing resin (a) means a hydroxyl group-containing resin that dissolves in a medium used for an intermediate coating, and examples thereof include an acrylic resin and / or a polyester resin. It is preferable to use an acrylic resin from the viewpoint that the SP value can be designed high.
As said polyester resin, what consists of a polyol and polycarboxylic acid or its anhydride can be used.
[0020]
The hydroxyl group-containing resin (a) preferably has a hydroxyl value of 50 to 250, an acid value of 1 to 50 mgKOH / g, and an SP value of 9.5 to 12. If the hydroxyl value, acid value, and SP value exceed the upper limits of these ranges, the water resistance in the case of coating is reduced. When the hydroxyl value and the acid value are less than the lower limit, the curability of the paint is lowered, and when the SP value is less than the lower limit, familiarity with the base paint occurs.
As for the number average molecular weight of the said hydroxyl-containing resin (a), 1000-10000 are mentioned, However, 1100-5000 are preferable, More preferably, it is 1200-3000. By using a material having a number average molecular weight within this range, the intermediate coating can be made into a high solid system, so that it is possible not only to obtain an intermediate coating having the above viscosity range, but also bake hardening. The volume shrinkage when it is made small, and the finished appearance of the coating film can be improved.
[0021]
In the present specification, the SP value is called a solubility parameter and indicates a measure of solubility. SP values are reported by SUH, CLARKE, J.A. Polymer Science, A-1, Vol. 5, pages 1671-1681 (1967) can be used for calculation.
That is, at a measurement temperature of 20 ° C., 0.5 g of resin as a sample is weighed into a 100 mL beaker, 10 mL of a good solvent is added using a whole pipette, and dissolved with a magnetic stirrer. Dioxane and acetone are used as good solvents, and n-hexane and ion-exchanged water are used as poor solvents. In the cloud point measurement, a poor solvent is dropped using a 50 mL burette, and the point at which turbidity is generated is defined as a drop amount. The SP value δ of the resin can be calculated 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 = V₁ V₂ / (Φ₁ V₂ + Φ₂ V₁ )
δ_m = Φ₁ δ₁ + Φ₂ δ₂
V_i : Molecular volume of solvent (mL / mol)
φ_i : Volume fraction of each solvent at cloud point
δ_i : SP value of solvent
ml: Low SP value poor solvent mixed system
mh: high SP value poor solvent mixed system
[0022]
It is preferable that the said hydroxyl-containing resin (a) is contained 10 to 70weight% with solid content with respect to the resin solid content total amount. If it is less than 10% by weight, the resulting coating film becomes brittle or the appearance of the coating film deteriorates, resulting in poor basic performance of the coating film. If it exceeds 70% by weight, the blending ratio of the non-aqueous dispersion resin (c) decreases, and as a result, the finished appearance of the coating film decreases. Preferably, it is 10 to 50% by weight, more preferably 20 to 50% by weight.
[0023]
The intermediate coating material contains a curing agent (b) that can react with a hydroxyl group.
It does not specifically limit as said hardening | curing agent (b), For example, a melamine resin and / or block isocyanate resin etc. are mentioned.
It is preferable that the said hardening | curing agent (b) is 10-70 weight% in solid content with respect to resin solid content total amount. If it is less than 10% by weight, curing may be insufficient and the physical properties of the coating film are poor. Even if it exceeds 70% by weight, it is uneconomical, and the finished appearance of the coating film is deteriorated. More preferably, it is 20 to 50% by weight.
The combination of the hydroxyl group-containing resin (a) and the curing agent (b) capable of reacting with a hydroxyl group is not particularly limited, but an acrylic resin and / or a polyester resin and a melamine resin are combined from the viewpoint of pigment dispersibility and workability. It is preferable.
[0024]
The intermediate coating material contains a non-aqueous dispersion resin (c).
The non-aqueous dispersion resin (c) is composed of a core portion having a high SP value and a shell portion having a low SP value. Since the core part has a high SP value, it is insoluble in the solvent in the paint. As a result, the swelling rate due to the solvent can also be reduced, and color reversion caused by delicate mixing with the base coating film. Can be prevented. The shell portion having a low SP value serves as a dispersion stabilizer. Furthermore, since this non-aqueous dispersion resin (c) is non-crosslinked particles, the minimum viscosity at the time of baking can be reduced. Further, the particles themselves can also be crosslinked by the curing agent (b) capable of reacting with the hydroxyl group, and in this case, it can be a coating film forming component, so that the addition amount can be increased. Therefore, the non-aqueous dispersion resin (c) can provide a coating film appearance that has a large background concealing property of the electrodeposited coating film, can suppress uneven skin, and has high definition and glossiness.
[0025]
The non-aqueous dispersion resin (c) preferably has an SP value of 11 to 14, and a difference in SP value between the core portion and the shell portion of 0.5 to 3. If the difference in SP value is less than 0.5, the non-volatile content of the paint cannot be reduced, so that it will swell and swell, and the viscosity control effect of the core part will be low. In addition, a familiarity with the base paint occurs, and a coating film having an excellent finished appearance cannot be obtained. When the SP value difference exceeds 3, dispersion may become unstable and separation may occur, or the intermediate coating material and the base coating material may be mixed to cause inversion or cracking. Preferably, the difference in SP value is 1 to 3.
The relationship between the SP value of the hydroxyl group-containing resin (a) and the SP value of the non-aqueous dispersion resin (c) is that the compatibility with the base paint can be suppressed, so that the non-aqueous dispersion resin (c) A higher SP value is preferred.
[0026]
The non-aqueous dispersion resin (c) has a hydroxyl value of 100 to 400, preferably 130 to 300. If it is less than 100, the curability of the coating is lowered, and if it exceeds 400, the water resistance may be lowered.
As an acid value, it is 0-200 mgKOH / g, Preferably it is 0-50 mgKOH / g. When it exceeds 200 mgKOH / g, the water resistance when formed into a coating film is lowered.
Average particle size (D₅₀) Is 0.05 to 5 μm, preferably 0.05 to 1 μm.
If it is less than 0.05 μm, the non-volatile content of the paint is reduced, and if it exceeds 5 μm, the viscosity control effect is inferior and the appearance is poor.
The dispersion stabilizing resin preferably has a Tg of 30 ° C. or lower. When it exceeds 30 degreeC, it is inferior to the coating-film external appearance, and chipping resistance will fall.
[0027]
The non-aqueous dispersion resin (c) is prepared as non-crosslinked resin particles insoluble in the mixed solution by copolymerizing a polymerizable monomer in the mixed solution of the dispersion stabilizing resin and the organic solvent. Can do. The dispersion-stable resin constitutes the shell portion, and the copolymerized polymerizable monomer constitutes the core portion.
[0028]
As the polymerizable monomer, a monomer having a functional group is preferable. The monomer having a functional group can react with the curing agent (b) capable of reacting with the above hydroxyl group to form a coating film that is three-dimensionally crosslinked.
Typical examples of the polymerizable monomer having the functional group are as follows. Examples of those having a hydroxyl group include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxymethyl (meth) acrylate, allyl alcohol, and hydroxyethyl (meth) acrylate. And an adduct of ε-caprolactone.
[0029]
On the other hand, those having an acid group include those having a carboxyl group, a sulfonic acid group, etc. Examples of those having a carboxyl group include (meth) acrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, Examples include isopropylacrylic acid, itaconic acid, maleic anhydride, fumaric acid and the like. Examples of those having a sulfonic acid group include t-butylacrylamide sulfonic acid. When using the polymerizable monomer which has an acid group, it is preferable that a part of acid group is a carboxyl group.
Furthermore, glycidyl group-containing unsaturated monomers such as glycidyl (meth) acrylate, isocyanate group-containing unsaturated monomers such as m-isopropenyl-α, α-dimethylbenzyl isocyanate, isocyanatoethyl acrylate, etc. It is done.
[0030]
Other polymerizable monomers include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, and n-butyl (meth) acrylate. , T-butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, methacryl (Meth) acrylic acid alkyl esters such as tridecyl acid; addition reaction product of oil fatty acid and acrylic acid or methacrylic acid ester monomer having oxirane structure (for example, addition reaction product of stearic acid and glycidyl methacrylate); C_Three Addition reaction product of oxirane compound containing alkyl group and acrylic acid or methacrylic acid; styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, pt-butylstyrene; Methacrylic acid benzyl; itaconic acid ester (dimethyl itaconate, etc.); maleic acid ester (dimethyl maleate, etc.); fumarate ester (dimethyl fumarate, etc.); acrylonitrile, methacrylonitrile; methyl isopropenyl ketone; Vinyl acetate; Veova monomer (trade name, manufactured by Shell Chemical Co., Ltd.), vinyl propionate, vinyl pivalate, vinyl propionate; ethylene, propylene, butadiene, N, N-dimethylaminoethyl acrylate, N, N-dimethylaminoethyl methacrylate, acrylic Ruamido, vinylpyridine, and the like.
The polymerizable monomer may be used alone or in combination of two or more from among those having a functional group and other monomers.
[0031]
The polymerizable monomer is preferably copolymerized in the presence of a radical polymerization initiator. Examples of radical polymerization initiators include azo initiators such as 2,2′-azobisisobutyronitrile and 2,2′-azobis (2,4-dimethylvaleronitrile); benzoyl peroxide, lauryl peroxide And peroxide initiators such as t-butyl peroctoate. The amount of these initiators used is preferably 0.2 to 10 parts by weight, preferably 0.5 to 5 parts by weight per 100 parts by weight of the total polymerizable monomers. In general, the polymerization reaction in the organic solvent containing the dispersion-stable resin is preferably performed in a temperature range of about 60 to 160 ° C. for about 1 to 15 hours.
[0032]
The dispersion stable resin that is present when copolymerizing the polymerizable monomer is not particularly limited as long as it can stably synthesize a non-aqueous dispersion resin in an organic solvent. Specifically, the hydroxyl value is 10 to 250, preferably 20 to 180. If it is less than 10, curability, adhesion, stability and the like are lowered, and if it exceeds 250, dispersion becomes unstable.
An acid value is 0-100 mgKOH / g, Preferably it is 0-50 mgKOH / g. When it exceeds 100 mgKOH / g, the water resistance in the case of coating is lowered.
As a number average molecular weight, 2000-10000 are preferable. If it is less than 2000, the dispersion becomes unstable, and if it exceeds 10,000, the non-volatile content of the paint decreases.
[0033]
The method for producing the dispersion stable resin is not particularly limited, and preferable examples include a method obtained by radical polymerization in the presence of a radical polymerizable initiator, a method obtained by a condensation reaction or an addition reaction, and the like.
As the dispersion stabilizing resin, acrylic resin, polyester resin, polyether resin, polycarbonate resin, polyurethane resin, or the like can be used.
The monomer used to obtain the dispersion-stable resin can be appropriately selected according to the characteristics of the resin, and has a functional group such as a hydroxyl group or an acid group used for the polymerizable monomer. Monomers are preferably used, and those having a functional group such as a glycidyl group or an isocyanate group may be used as necessary. The monomer having a functional group can form a three-dimensionally crosslinked coating film by reacting the obtained non-aqueous dispersion resin with the curing agent (b).
[0034]
The monomer used for obtaining the dispersion-stable resin preferably has a side chain having 10 or more carbon atoms and is contained in an amount of 10 to 50% by weight based on the total amount of the monomer.
When the amount is less than 10% by weight, familiarity with the base paint occurs. If it exceeds 50% by weight, separation may occur in the intermediate coating, or the intermediate coating and the base coating may be mixed to cause inversion or cracking.
[0035]
Furthermore, it is preferable that the monomer has a hydrophilic group in an amount of 20 to 50% by weight based on the total amount of the polymerizable monomer. If it is less than 20% by weight, the curability, adhesion and stability may be inferior. If it exceeds 50% by weight, the dispersibility may become unstable.
Examples of the hydrophilic group include a hydroxyl group, a carboxyl group, an amide group, and an ether group.
[0036]
The ratio of the dispersion stabilizer and the polymerizable monomer can be arbitrarily selected according to the purpose. For example, the dispersion stabilizing resin is 3 to 80% by weight based on the total weight of both components, Preferably it is 5 to 60% by weight, and the polymerizable monomer is 97 to 20% by weight, preferably 95 to 40% by weight. Furthermore, the total concentration of the dispersion stabilizer and the polymerizable monomer in the organic solvent is 30 to 80% by weight, preferably 40 to 60% by weight, based on the total weight.
[0037]
The non-aqueous dispersion resin (c) thus obtained is preferably contained in a solid content of 18 to 50% by weight with respect to the total resin solid content. If it is less than 18% by weight or exceeds 50% by weight, the appearance of the resulting coating film is deteriorated. More preferably, it is 23 to 45% by weight.
[0038]
The intermediate coating paint usually contains a pigment.
It is preferable that the said pigment is contained by 10 to 70 weight% with respect to the total amount of a pigment and resin solid content. In the present specification, the resin solid content means the total amount of the solid content of the hydroxyl group-containing resin (a), the curing agent (b) capable of reacting with a hydroxyl group, and the non-aqueous dispersion resin (c). If it is less than 10% by weight, the resulting intermediate coating cannot be made into a high solid type, and when it is baked and cured, the volume shrinkage becomes large and the finished appearance may be inferior. When it exceeds 70% by weight, the appearance of the coating film is deteriorated because of too much pigment.
[0039]
The pigment is not particularly limited, and examples thereof include those used in conventional intermediate coatings. For example, azo chelate pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene Organic pigments such as pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments; inorganic pigments such as chrome yellow, yellow iron oxide, red iron oxide, carbon black, titanium dioxide, etc. . Furthermore, extender pigments such as calcium carbonate, barium sulfate, clay and talc; flat pigments such as aluminum powder and mica powder may be used in combination.
As the above pigment, a standard gray-based intermediate coating with carbon black and titanium dioxide as main pigments can be used, or a so-called color that combines a top coating with a set gray that combines lightness or hue, and various colored pigments. An intermediate coating can also be used.
[0040]
The intermediate coating material can be added with conventionally known additives such as a viscosity control agent, an anti-waxing agent, a dilution solvent, and the like.
Examples of the viscosity control agent include fatty acid amide swelling dispersions, amide fatty acids, polyamides such as long chain polyaminoamide phosphates; polyethylenes such as colloidal swelling dispersions of oxidized polyethylene; organic acids Organic bentonite type materials such as smectite clay and montmorillonite; inorganic pigments such as aluminum silicate and barium sulfate; and flat pigments that develop viscosity depending on the shape of the pigment.
[0041]
In the present invention, as the coating form of the intermediate coating, a solution type is preferably used. As the solution type, an organic solvent type, an aqueous type (water-soluble, water-dispersible, emulsion), and a non-aqueous dispersion type are used. Is mentioned.
The intermediate coating material is prepared by kneading a hydroxyl group-containing resin (a), a curing agent (b) capable of reacting with a hydroxyl group and a non-aqueous dispersion resin (c), a pigment and other components using a kneader, a roll, or the like. , And the like can be obtained by methods well known to those skilled in the art.
[0042]
Base paint
In the present invention, the base paint has a non-volatile content of 90% by weight, a viscosity Vis (60 ° C.) at 60 ° C. of 10 to 1000 poise, a viscosity Vis at 90 ° C. (90 ° C.) of 1 to 500 poise, and 120 Viscosity Vis (120 ° C.) at 100 ° C. is 100 to 10000 poise, Vis (60 ° C.) / Vis (90 ° C.) is 1.5 to 10, Vis (120 ° C.) / Vis (90 ° C.) is 2 It is preferably ~ 20.
By using a non-volatile content of 90% by weight with Vis (90 ° C.) of 1 to 500 poise, the minimum viscosity of the base paint in the baking process is small, and as a result, the coating has flowability even if the volume shrinks. Thus, the base concealing property for the electrodeposition coating film is improved, and a coating film having an excellent finished appearance can be obtained. Therefore, when Vis (90 ° C.) exceeds 500 poise, the minimum viscosity of the base paint in the baking process is large, and a coating film having an excellent finished appearance cannot be obtained. Preferably, Vis (90 ° C.) is 1 to 300 poise, more preferably 1 to 200 poise.
[0043]
A paint having a non-volatile content of 90% by weight having a Vis (60 ° C.) of less than 10 poise, a paint having a Vis (90 ° C.) of less than 1 poise, and a paint having a Vis (120 ° C.) of less than 100 poise have poor coating appearance. Or the basic performance of the coating film may not be maintained. When Vis (60 ° C.) exceeds 1000 poise and Vis (120 ° C.) exceeds 10,000 poise, it cannot be used as a high solid base paint at the time of coating preparation. It becomes large and a coating film having an excellent finished appearance cannot be obtained.
[0044]
The base paint has a ratio [Vis (60 ° C.) / Vis (90 ° C.)] of the viscosity Vis (60 ° C.) at 60 ° C. and the viscosity Vis (90 ° C.) at 90 ° C. at a nonvolatile content of 90% by weight. The ratio of the viscosity Vis (120 ° C.) at 120 ° C. to the viscosity Vis (90 ° C.) at 90 ° C. (Vis (120 ° C.) / Vis (90 ° C.)) is 2 to 20 Preferably there is.
When Vis (60 ° C.) / Vis (90 ° C.) is less than 1.5 or Vis (120 ° C.) / Vis (90 ° C.) is less than 2, the minimum viscosity of the base paint in the baking process is reduced. Therefore, it is impossible to obtain a coating film having an excellent finished appearance. If Vis (60 ° C.) / Vis (90 ° C.) exceeds 10, or Vis (120 ° C.) / Vis (90 ° C.) exceeds 20, it is actually difficult to prepare.
[0045]
In the present invention, as the base paint, one containing a non-aqueous dispersion resin and / or one containing crosslinkable polymer fine particles (microgel) can be suitably used.
Both the non-aqueous dispersion resin and the cross-linkable polymer fine particles function as a viscosity imparting agent, and prevent the familiarity and inversion between the layers from occurring to obtain a coating film appearance with high definition and gloss. It is intended. However, since the cross-linkable polymer fine particles are cross-linked and cannot be a coating film forming component, the addition amount is limited to 5% by weight or less, and as a result, contributes to a decrease in swelling rate due to the solvent. The ratio is small. On the other hand, the non-aqueous dispersion resin is a non-crosslinked particle having a core portion having a high SP value, and the amount added can be increased, so that not only a large proportion of the solvent contributes to a decrease in swelling rate. In the present invention, it is preferable to use one containing a non-aqueous dispersion resin from the viewpoint that the minimum viscosity at the time of baking can be reduced, and thus a coating film having an excellent finished appearance can be obtained.
[0046]
Examples of the non-aqueous dispersion resin include the non-aqueous dispersion resin (c) described in the above-mentioned intermediate coating, and the resin and curing agent used together with the non-aqueous dispersion resin are also described above. The materials described in the intermediate coating material can be mentioned.
In the base paint, the blending amount of the non-aqueous dispersion resin is preferably 5 to 50% by weight based on the total solid content of the resin. When the amount is less than 5% by weight or exceeds 50% by weight, the appearance of the obtained coating film is deteriorated. More preferably, it is 18 to 45% by weight.
[0047]
As the cross-linkable polymer fine particles, those described in JP-A-10-5680 can be used. Specifically, it is made of a polymer that is insoluble in organic solvents for paints and is crosslinked to some extent, and is preferably microparticles having an average particle size of 0.01 to 10 μm, and has a property of being stably dispersed in the paint. It is provided.
When the average particle size is less than 0.01 μm, the difficulty in production facilities is high, and it is difficult to maintain the particle shape. When it exceeds 10 μm, the stability is lowered. Preferably, it is 0.01-1 micrometer.
[0048]
As a method for producing the crosslinkable polymer fine particles, an ethylenically unsaturated monomer is emulsion-polymerized in a crosslinkable monomer and an aqueous medium to form a fine particle copolymer, and solvent substitution, azeotropic distillation, and centrifugal separation are performed. , A method of removing water by means such as filtration and drying; a monomer having an ethylenically unsaturated group is crosslinkable in a non-aqueous organic solvent in which a monomer such as a fatty acid hydrocarbon is dissolved but a polymer is not dissolved Various methods are known, such as a method of reacting with the above monomer and dispersing the resulting fine particle copolymer (NAD method). In the present invention, any method can be used as long as it has the above-mentioned characteristics. It may be due to.
In the present invention, the former method obtained by emulsion polymerization is preferred. Among them, emulsification of alkyd resin or polyester resin synthesized with a monomer having a zwitterionic group in the molecule as one of the polyhydric alcohol components. Those obtained by emulsion polymerization of a polymerizable monomer in an aqueous medium in the presence of a resin having a function and a polymerization initiator are more preferred.
[0049]
The above zwitterionic group is -N⁺ -R-COO^- Or -N⁺ -R-SO_Three ^- Where R is C₁ ~ C₆ As the monomer having this in the molecule, one having two or more hydroxyl groups can be used. As such a monomer, a hydroxyl group-containing aminosulfone-type zwitterionic compound is preferable for resin synthesis. Specific examples include bishydroxyethyl taurine.
[0050]
The resin having an emulsifying ability zwitterionic group synthesized using the above monomer in the molecule has an acid value of 30 to 150 mgKOH / g, preferably 40 to 150 mgKOH / g, and a number average molecular weight of 500. A polyester resin of ˜5000, preferably 700 to 3,000 can be suitably used. If the upper limit is exceeded, the handling properties of the resin will be reduced, and if it is lower than the lower limit, the resin having emulsifying ability will be detached or the solvent resistance will be reduced.
[0051]
As the polymerizable monomer to be emulsion polymerized in the presence of the resin, it is necessary to contain a monomer having two or more radically polymerizable ethylenically unsaturated groups in the molecule. The monomer having two or more radically polymerizable ethylenically unsaturated groups in the molecule is preferably contained in the range of 0.1 to 70% by weight in the total monomers. This amount is selected to the extent that sufficient crosslinking is provided so that the particulate polymer does not dissolve in the solvent.
[0052]
Examples of the monomer having two or more radically polymerizable ethylenically unsaturated groups in the molecule include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, and trimethylolpropane di (meth) acrylate. , Trimethylolpropane tri (meth) acrylate, glycerin di (meth) acrylate, and the like.
[0053]
The addition amount of the crosslinkable polymer fine particles obtained as described above is preferably 0.5 to 5% by weight based on the solid content of the base paint. If it is less than 0.5% by weight, the effect of adding the crosslinkable polymer fine particles cannot be obtained, and if it exceeds 5% by weight, the smoothness of the resulting coating film is easily lost and pinholes are also likely to occur. .
[0054]
The film-forming resin used together with the crosslinkable polymer fine particles is not particularly limited, and examples thereof include phenol resins, acrylic resins, alkyd resins, epoxy resins, polyester resins, fluororesins, and among these, acrylic resins Polyester resins, alkyd resins, epoxy resin alkyd resins and the like are preferably used.
If necessary, the coating film-forming resin can contain an amino resin such as a melamine resin; and a crosslinking agent such as a (block) polyisocyanate compound.
[0055]
In the present invention, the base paint can be used as a metallic base paint by blending a bright pigment, or a colored pigment such as red, blue or black and / or an extender pigment without blending a bright pigment. It can also be used as a solid-type base paint.
The glitter pigment is not particularly limited, and examples thereof include non-colored or colored metallic glitter materials such as metals or alloys and mixtures thereof, interference mica powder, colored mica powder, white mica powder, graphite, or colorless colored flat pigment. Etc.
Since it is excellent in dispersibility and can form a highly transparent coating film, non-colored or colored metallic glitter materials such as metals or alloys and mixtures thereof are preferred. Specific examples of the metal include aluminum, aluminum oxide, copper, zinc, iron, nickel, tin and the like.
[0056]
The shape of the glitter pigment is not particularly limited, and may be further colored. For example, the average particle diameter (D₅₀) Is 2 to 50 μm, and a scale-like one having a thickness of 0.1 to 5 μm is preferable. Those having an average particle size in the range of 10 to 35 μm are more preferable because of excellent glitter.
The pigment concentration (PWC) in the base paint of the glitter pigment is generally 23% by weight or less. When it exceeds 23% by weight, the appearance of the coating film is deteriorated. Preferably, it is 0.01-20 weight%, More preferably, it is 0.01-18 weight%.
[0057]
As the pigment other than the glitter pigment, the color pigments and extender pigments described in the intermediate coating can be used.
As said pigment, it can be used 1 type or in combination of 2 or more types among a luster pigment, a coloring pigment, and an extender pigment.
The pigment concentration (PWC) in the base paint including the glitter pigment and all other pigments is generally 0.1 to 50% by weight, preferably 0.5 to 40% by weight, More preferably, it is 1 to 30% by weight. When it exceeds 50% by weight, the appearance of the coating film is deteriorated.
[0058]
In the present invention, the paint form of the base paint is preferably a solution type, and as the solution type, there are an organic solvent type, an aqueous type (water-soluble, water-dispersible, emulsion), and a non-aqueous dispersion type. Can be mentioned.
Examples of other additives used in the base coating material and the method for preparing the base coating material include those exemplified in the intermediate coating material.
[0059]
Clear paint
The clear coating is used to smooth the unevenness and flickering of the base coating caused by the bright pigment when the metallic base coating containing the bright pigment is used as the base coating, and to protect the base coating. Is formed.
In the present invention, the clear coating is not particularly limited as long as it satisfies the relationship between the minimum viscosity and the curing start temperature, and examples thereof include those composed of a film-forming resin, a curing agent, and other additives. Can do.
[0060]
The film-forming resin is not particularly limited, and examples thereof include acrylic resins, polyester resins, epoxy resins, urethane resins, and the like. These are used in combination with a curing agent such as an amino resin and / or a blocked isocyanate resin. . From the viewpoint of transparency or acid etching resistance, it is preferable to use a combination of an acrylic resin and / or a polyester resin and an amino resin, or an acrylic resin and / or a polyester resin having a carboxylic acid / epoxy curing system.
[0061]
As the clear paint, since the base paint described above is applied in an uncured state, it is preferable to contain a viscosity control agent as an additive in order to prevent familiarity, reversal or sagging between layers. . The addition amount of the viscosity control agent is 0.01 to 10 parts by weight, preferably 0.02 to 8 parts by weight, more preferably 0.03 to 6 parts by weight, based on 100 parts by weight of the resin solid content of the clear paint. Part. When the amount exceeds 10 parts by weight, the appearance is deteriorated, and when the amount is less than 0.1 parts by weight, the viscosity control effect cannot be obtained, causing problems such as sagging.
The clear coating composition may be any of organic solvent type, aqueous type (water-soluble, water-dispersible, emulsion), non-aqueous dispersion type, and powder type. If necessary, a curing catalyst, a surface conditioner, etc. Can be used.
Examples of the method for preparing the clear coating include the methods exemplified in the intermediate coating.
[0062]
Base material
The coating film forming method of the present invention is applied to an electrodeposition-coated material.
As the electrodeposition paint used for the electrodeposition coating, a cation type and an anion type can be used. From the viewpoint that a coating film excellent in corrosion resistance can be obtained, a cationic type is preferable.
It does not specifically limit as a raw material which performs electrodeposition coating, For example, iron, copper, aluminum, tin, zinc, etc .; The alloy and casting containing these metals are mentioned. Specific examples include automobile bodies and parts such as passenger cars, trucks, motorcycles, and buses. These metals are particularly preferably those that have been previously subjected to chemical conversion treatment with phosphate, chromate or the like before electrodeposition coating.
[0063]
Painting method
The coating film forming method of the present invention includes a step of sequentially applying an intermediate coating, a base coating, and a clear coating on the above-mentioned electrodeposition-coated material.
The coating method is not particularly limited, and for example, an air electrostatic spray commonly called “react gun”; commonly called “micro / micro (μμ) bell”, “micro (μ) bell”, “metabell”, etc. This can be done by using a rotary atomizing electrostatic coating machine or the like. A method using a rotary atomizing electrostatic coating machine or the like is preferable.
When the base paint is applied to an automobile body or the like, in order to improve the design, multi-stage painting by air electrostatic spray, preferably two stages, or air electrostatic spray and the above-mentioned It is preferable to carry out by a coating method in combination with a rotary atomizing electrostatic coating machine.
[0064]
The dry film thickness of the intermediate coating, base coating, and clear coating varies depending on the application, but is 5 to 40 μm for the intermediate coating, 5 to 35 μm for the base coating, and 10 to 70 μm for the clear coating, respectively. . If this dry film thickness exceeds the upper limit, sharpness may deteriorate, or defects such as unevenness and flow may occur during painting. If the lower film thickness is less than the lower limit, the substrate cannot be concealed and film breakage may occur. .
In the present invention, the intermediate coating, the base coating and the clear coating are sequentially applied means that the intermediate coating, the base coating and the clear coating are applied in this order by wet-on-wet. The coating film, the base coating film, and the clear coating film may be any one that does not include a step of baking and curing at 100 ° C. or more. Therefore, before applying the base paint and / or before applying the clear paint, it is allowed to stand at room temperature for a certain period of time, or to dry the coating film in advance by, for example, heating at 60 to less than 100 ° C. for 2 to 10 minutes. Such a method is also one aspect of the present invention. In particular, when the base paint is used as a water-based paint, it is preferable to dry the coating film before applying the clear paint because a good finished appearance can be obtained.
[0065]
The coating film forming method of the present invention includes a step of baking and curing three layers of the intermediate coating material, the base coating material, and the clear coating material coated as described above at a time.
By performing the baking and curing at 110 to 180 ° C, preferably 120 to 160 ° C, a cured coating film having a high degree of crosslinking can be obtained. If it exceeds 180 ° C, the coating film becomes hard and brittle, and if it is less than 110 ° C, curing is not sufficient. The curing time varies depending on the curing temperature, but is suitably from 120 to 160 ° C. for 10 to 60 minutes.
The film thickness of the multilayer coating film obtained by the coating film forming method of the present invention is usually 30 to 300 μm, preferably 50 to 250 μm. When it exceeds 300 μm, film physical properties such as a cooling / heating cycle deteriorate, and when it is less than 30 μm, the strength of the film itself decreases.
[0066]
The coating film forming method of the present invention is excellent in the base concealing property and can provide a coating film having a good finished appearance. Furthermore, compared to the conventional 3-coat 2-bake method, the intermediate coating paint baking process can be omitted, so that the painting process can be shortened and the energy consumption can be reduced. Can be greatly reduced.
[0067]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples. In the examples, “parts” represents parts by weight.
Synthesis Example 1 Synthesis of acrylic resin 1
In a vessel equipped with a stirrer, temperature controller and reflux condenser, 82 parts of xylene are charged, and then a solution having the following composition:
Methacrylic acid 4.5 parts
Ethyl acrylate 26.0 parts
PLACCEL FM-1 64.5 parts
(Hydroxyl-containing monomer manufactured by Daicel Chemical Industries)
MSD-100 5.0 parts
(Mitsui Toatsu Chemical Co., Ltd. methylstyrene dimer)
Azoisobutyronitrile 13.0 parts
Of these, 20 parts were added and heated with stirring to raise the temperature. While refluxing, the remaining 93.0 parts of the mixed solution was added dropwise over 3 hours, and then a solution consisting of 1.0 part of azoisobutyronitrile and 12 parts of xylene was added dropwise over 30 minutes. The reaction solution was further stirred and refluxed for 1 hour, and then 63 parts of the solvent was distilled off under reduced pressure to complete the reaction. An acrylic resin varnish 1 having a solid content of 75% and a number average molecular weight of 2000 was obtained.
[0068]
Synthesis example 2 Synthesis of acrylic resin 2
In a vessel equipped with a stirrer, a temperature controller, and a reflux condenser, 300 parts of toluene and 100 parts of methyl isobutyl ketone (MIBK) were charged and heated while stirring to raise the temperature. When the temperature rose to 105 ° C., a solution having the following composition was added dropwise at a constant rate over 3 hours while refluxing.
Styrene 50.0 parts
Methyl methacrylate 300.0 parts
Ethyl methacrylate 79.0 parts
Ethyl acrylate 444.0 parts
2-hydroxyethyl methacrylate 104.0 parts
Methacrylic acid 23.0 parts
400.0 parts of toluene
7.0 parts of t-butylperoxy-2-ethylhexanoate
After aging for 30 minutes, a solution consisting of 200 parts of toluene and 3 parts of t-butylperoxy-2-ethylhexanoate was added dropwise at a constant rate over 30 minutes. The reaction solution was further stirred and refluxed for 1 hour to increase the rate of conversion to resin, and then the reaction was terminated to obtain an acrylic resin varnish 2 having a solid content of 50% and a number average molecular weight of 21,000.
[0069]
Synthesis Example 3 Synthesis of non-aqueous dispersion resin
(A) Production of dispersion stable resin
A container equipped with a stirrer, a temperature controller, and a reflux condenser is charged with 90 parts of butyl acetate, and then a solution having the following composition:
Methyl methacrylate 38.9 parts
Stearyl methacrylate 38.8 parts
2-Hydroxyethyl acrylate 22.3 parts
Azoisobutyronitrile 5.0 parts
Of these, 20 parts were added and heated with stirring to raise the temperature. The remaining 85 parts of the above mixed solution was added dropwise at 110 ° C. over 3 hours, and then a solution consisting of 0.5 parts of azoisobutyronitrile and 10 parts of butyl acetate was added dropwise over 30 minutes. The reaction solution was further stirred and refluxed for 2 hours to increase the rate of conversion to resin, and the reaction was terminated to obtain an acrylic resin having a solid content of 50%, a number average molecular weight of 5600, and an SP value of 9.5.
[0070]
(B) Production of non-aqueous dispersion resin
In a container equipped with a stirrer, a temperature controller, and a cooler, 35 parts of butyl acetate was charged, and 60 parts of the acrylic resin obtained in the production of (a) the dispersion stable resin was charged. Next, a solution having the following composition:
7.0 parts of styrene
Methacrylic acid 1.8 parts
Methyl methacrylate 12.0 parts
8.5 parts of ethyl acrylate
2-Hydroxyethyl acrylate 40.7 parts
Azoisobutyronitrile 1.4 parts
Was added dropwise at 100 ° C. over 3 hours, and then a solution comprising 0.1 part of azoisobutyronitrile and 1 part of butyl acetate was added dropwise over 30 minutes. When the reaction solution was further stirred for 1 hour, an emulsion having a solid content of 60% and a particle size of 0.18 μm was obtained. This emulsion was diluted with butyl acetate to obtain a butyl acetate dispersion having a viscosity of 300 cps (25 ° C.) and a particle size of 0.18 μm and a non-aqueous dispersion resin content of 40% by weight. The non-aqueous dispersion resin had a Tg of 23 ° C. and a hydroxyl value of 162. The SP value was 11.8, and the difference in SP value between the shell portion and the core portion, which is a dispersion stable resin, was 2.3.
[0071]
Example 1
Preparation of intermediate coating
Into a 2 L vessel, 328 parts of the acrylic resin varnish 1 obtained in Synthesis Example 1 was added, followed by 973 parts of CR-93 (titanium oxide manufactured by Ishihara Sangyo Co., Ltd.) and 10 parts of FW-200P (carbon black manufactured by Degussa). Further, 159 parts of butyl acetate and 82 parts of xylene were added in this order. Thereafter, glass beads (product name GB503M, particle size 1.6 mm) of the same amount as the total weight charged were charged and dispersed for 3 hours with a desktop SG mill. The particle size at the end of dispersion by a grind gauge was 5 μm or less. Finally, 81.8 parts of xylene was added and stirred for about 10 minutes, and the glass beads were filtered to obtain a pigment paste.
A resin, a non-aqueous dispersion resin, and a curing agent were blended in the prepared paste so that the solid content ratio was as shown in Table 2, to prepare an intermediate coating material.
[0072]
Preparation of base paint
Into a 2 L vessel, 500 parts of the acrylic resin varnish 1 obtained in Synthesis Example 1 and 320 parts of DISPERBYK161 (manufactured by Big Chemie; dispersion aid) were added, followed by 10 parts of Monarch 1400 (carbon black manufactured by Cabot). Furthermore, 31 parts of butyl acetate and 31 parts of xylene were put in order. Thereafter, glass beads (product name GB503M, particle size 1.6 mm) of the same amount as the total weight charged were charged and dispersed for 3 hours with a desktop SG mill. The particle size at the end of dispersion by a grind gauge was 5 μm or less.
After the dispersion was completed, the glass beads were filtered to obtain a pigment paste.
A resin, a non-aqueous dispersion resin, and a curing agent were blended in the prepared paste so that the solid content ratio was as shown in Table 2 to prepare a base paint.
[0073]
Clear paint
As the clear paint, MAC O-1330 (manufactured by Nippon Paint Co., Ltd.) having a nonvolatile content of 48% was used.
Dilution conditions
Each paint was diluted and painted under the following conditions.
(Intermediate paint)
Thinner: EEP (ethoxyethyl propionate) / xylene = 9/11
19 seconds / No. 4 Ford Cup / 20 ° C
(Base paint)
Thinner: EEP / S-100 (Aromatic hydrocarbon solvent manufactured by Exxon) / ethyl acetate = 8/7/5
20 seconds / No. 4 Ford Cup / 20 ° C
(Clear paint)
Thinner: EEP / S-150 (Aromatic hydrocarbon solvent manufactured by Exxon) = 1/122 sec / No. 4 Ford Cup / 20 ° C
[0074]
Painting method
Cations obtained by electrodeposition-coating Power Top V-6 (Cation Electrodeposition Paint manufactured by Nippon Paint Co., Ltd.) on a SPC dull steel plate (20 cm × 30 cm × 0.8 mm) under the coating conditions shown in Table 1 to a dry film thickness of 20 μm. While the electrodeposition coating plate is attached to the moving plate and moved, the intermediate coating is applied, the base coating is applied after 10 minutes, the base coating is applied again after 2.5 minutes (two-stage coating), and then 20 minutes Later, a clear paint was applied. The applied intermediate coating film, base coating film and clear coating film were baked and cured at 140 ° C. for 30 minutes.
[0075]
[Table 1]

[0076]
Appearance evaluation
The appearance of the coated plate was evaluated by the SW value of a wave scan manufactured by Big Chemie. The results are shown in Table 2. The smaller the value, the better the result.
[0077]
Coating NV (non-volatile) measurement method
The intermediate coating, the base coating, and the clear coating were operated separately and calculated according to the following method.
Apparatus: An aluminum foil whose weight (w1) is measured is covered with a paper having a square hole of 5 cm × 10 cm and attached to an iron plate with a masking tape.
Operation: This iron plate is attached to the moving plate so as to be adjacent to the coating plate at the time of painting, and after coating the aluminum foil is peeled off from the iron plate.
NV measurement: The weight (w3) after drying for 30 minutes at 140 ° C. is measured after measuring the weight (w2) of the aluminum foil to which the paint has adhered.
Calculation: The coating NV (%) is calculated from the following formula.
Coating NV (%) = (w3-w1) / (w2-w1) × 100
The obtained results are shown in Table 2.
[0078]
Volume shrinkage calculation method
The volume shrinkage (%) is calculated according to the following formula.
Volume shrinkage (%) = {(100-coating NV) / solvent specific gravity} / [{(100-coating NV) / solvent specific gravity} + (coating NV / dry coating specific gravity)} × 100
Solvent specific gravity: Due to the solvent composition in the paint, the intermediate paint was 0.87 and the base paint was 0.86.
Dry coating specific gravity: From each paint composition, it was set as intermediate coating 1.64 and base paint 1.23.
The obtained results are shown in Table 2.
[0079]
Viscosity measurement method
The intermediate coating was spray-coated on a tin plate, heated for about 5 minutes at 80 ° C., and then the coating with a non-volatile content of 90% was scraped off. The viscosity of this sample was measured under the following conditions.
Measurement model: Reosol G-3000 manufactured by UBM
Measurement method: Dynamic viscoelasticity measurement (sine wave)
Measurement mode: Temperature dependence
Chuck cone plate
Cone diameter / angle: 18.96 mm / 1.974 deg
Excitation conditions: Continuous excitation (frequency 1.0 Hz / strain 0.5 deg)
Start / end temperature: 40/150 ° C
Temperature increase step: 2 ° C / min
Torque / load cell: 2kg ・ cm / 5kg
A graph obtained by connecting the obtained viscosity results with a curve is shown in FIG. The minimum viscosity and curing start temperature read from FIG. 1 are shown in Table 2.
In the same manner as the intermediate coating, the viscosity of each of the base coating and the clear coating was measured, and the minimum viscosity and the curing start temperature were read. The results are shown in Table 2 and FIG.
[0080]
Solvent resistance test method
After coating the intermediate coating and base coating on a tin plate (20 μm), they were dried at 80 ° C. for 10 minutes to increase the NV, and the typical coating solvent S-150, xylol A drop of EEP was spotted, and after standing for 30 seconds, the state was tilted about 45 degrees and the state was observed.
Y: No change
Δ: swelling
×: dissolution
The obtained results are shown in Table 2.
[0081]
Comparative Example 1
The intermediate coating material and the base coating material were prepared and applied in the same manner as in Example 1 except that the resin, the non-aqueous dispersion resin and the curing agent were blended so that the solid content ratio was as shown in Table 2. Measured and evaluated.
The results are shown in Table 2 and FIG.
[0082]
[Table 2]

[0083]
In Table 2, Cymel 254 is a methyl / butyl mixed melamine resin (manufactured by Mitsui Cytec).
In Example 1, the relationship between the minimum viscosity and the curing start temperature in the baking process of the intermediate coating, base coating, and clear coating is appropriate, and the intermediate coating and base coating used in Example 1 are It has a small volumetric shrinkage, and it has excellent solvent resistance compared to containing a non-aqueous dispersion resin. Therefore, it has excellent finished appearance when it is painted and baked and cured by the 3-coat 1-bake method. Met.
In Comparative Example 1, the minimum viscosity in the baking process of the intermediate coating, base coating, and clear coating is higher in the base coating than in the intermediate coating, and the volume shrinkage of the base coating is large. Since the intermediate coating material containing no water dispersion resin was poor in solvent resistance, it was considered that it was swollen by the solvent, so that a good finished appearance could not be obtained.
[0084]
【The invention's effect】
According to the coating film forming method of the present invention, a coating film having an excellent finished appearance can be obtained when an automobile body or the like is coated by a three-coat one-bake method.
[Brief description of the drawings]
1 is a graph showing viscosity measurement results with respect to temperature for each of an intermediate coating, a base coating, and a clear coating in Example 1. FIG.
2 is a graph showing the measurement results of viscosity with respect to temperature for each of an intermediate coating, a base coating, and a clear coating in Comparative Example 1. FIG.

Claims (3)

A method of forming a coating film comprising a step of sequentially applying an intermediate coating, a base coating, and a clear coating on an electrodeposited material, and a step of baking and curing the three coated layers at once.
The intermediate coating, the base coating, and the clear coating have a minimum viscosity when the viscosity is measured with respect to temperature at a nonvolatile content of 90% by weight.
It satisfies the relationship of intermediate coating ≧ base coating ≧ clear coating, and the curing start temperature is
All SANYO satisfies the relationship intermediate coating ≦ base coating ≦ clear coating,
The intermediate coating is composed of a hydroxyl group-containing resin (a) having a hydroxyl value of 50 to 250, an acid value of 1 to 50 mgKOH / g, and a number average molecular weight of 1000 to 10,000; a curing agent (b) capable of reacting with a hydroxyl group; 100 to 400 and a non-aqueous dispersion resin (c) having an average particle diameter (D ₅₀ ) of 0.05 to 5 μm ;
The intermediate coating, base coating and clear coating have a volume shrinkage of 45% or less when cured at 140 ° C. for 30 minutes after coating,
The intermediate coating has a non-volatile content of 90% by weight, a viscosity Vis (60 ° C.) at 60 ° C. of 10 to 1000 poise, a viscosity Vis at 90 ° C. (90 ° C.) of 1 to 500 poise, and 120 ° C. The viscosity Vis (120 ° C.) is 100 to 10,000 poise,
Vis (60 ° C.) / Vis (90 ° C.) is 1.5-10, Vis (120 ° C.) / Vis (90 ° C.) is 2-30, and
The base paint has a non-volatile content of 90% by weight, a viscosity Vis (60 ° C.) at 60 ° C. of 10 to 1000 poise, a viscosity Vis at 90 ° C. (90 ° C.) of 1 to 500 poise, and 120 ° C. Viscosity Vis (120 ° C.) is 100 to 10000 poise,
Vis (60 ° C.) / Vis (90 ° C.) is 1.5 to 10,
Vis (120 ° C.) / Vis (90 ° C.) is 2 to 20,
Coating film forming method. The non-volatile content at the time of applying the intermediate coating is 40 to 70% by weight, the non-volatile content at the time of applying the base coating is 30 to 60% by weight, and the non-volatile content at the time of applying the clear coating is 40 to 70% by weight. method of forming a coating film is claimed in claim 1. Claim 1 or 2 coating forming a coated product obtained by the method described.

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