JP4121364B2 - Coating method of metallic paint in metallic coating of automobile - Google Patents

Description

【００２７】
ＮＶ値が５５％未満であると、塗料の流動性が過多であり、寝ていたアルミ片が起きる可能性がある。この結果、色差が発生する。また、磁力線などにより筋むらが発生する。
【００２８】
ＮＶ値が６５％を超えると、塗料の流動性が過少となり、膜厚が均一になる前に固まるなどの理由により、乾燥むらが発生する。
【００２９】
この点、ＮＶ値が５５〜６５％の範囲にあれば、流動性が適度であり、色差が発生せず、筋むらが発生せず、且つ乾燥むら発生しない。
従って、ＮＶ値が５５〜６５％の範囲になるように制御する技術が必要となる。
【００３０】
図４はベルの回転速度とＮＶ値の関係を調べたグラフであり、通常の速度である３×１０^４ｒｐｍでは、ＮＶ値（８０秒）は５０％より遙かに小さかった。
回転速度を増加して４×１０^４ｒｐｍにすると、ＮＶ値（８０秒）は５０％程度であった。
回転速度をさらに増加して５×１０^４ｒｐｍにすると、ＮＶ値（８０秒）は５３％程度まで増加した。
【００３１】
回転速度を増加すると、塗料の粒子が小径化するとともに粒の数が増加する。すると、塗粒の表面積総和が増加し、そこに含まれる溶剤がより蒸発する。その結果、回転速度に比例してＮＶ値が増加する。
【００３２】
しかし、目標とするＮＶ値には至らないため、更なる工夫が必要となる。本発明者らは、塗粒の飛行時間が長ければ、この時間に比例して溶剤の蒸発が進むのではないかと考え、塗装距離（塗装面と塗装ガンとの間の距離）を増加することを試した。その結果を、次図で示す。
【００３３】
図５は塗装距離とＮＶ値の関係を調べたグラフであり、ベルの回転速度は、一律、４×１０^４ｒｐｍとした。
通常の塗装距離である２００ｍｍでは、ＮＶ値（８０秒）は５５％より遙かに小さかった。
塗装距離を増加して２５０ｍｍにすると、ＮＶ値（８０秒）は５４％程度であった。
【００３４】
塗装距離をさらに増加して３００ｍｍにすると、ＮＶ値（８０秒）は５８％程度まで増加した。
従って、塗装距離を増加すれば、ＮＶ値を高めることができることが確認できた。
【００３５】
ところで、メタリック塗料は、顔料に鋭いアルミ片を混ぜ、溶剤で薄めたものであるから、顔料の濃さによりアルミ片の目立ち方が大きく異なる。これを表２にまとめる。
【００３６】
【表２】

【００３７】
濃色であれば、アルミ片は比較的目立たなくなり、アルミ片の姿勢は気にする必要がないため、ＮＶ値はそれほど重要ではない。
逆に、淡色は、アルミ片が目立つため、ＮＶ値は極めて重要となる。
中間色は、それらの中間であって、ＮＶ値の管理はやや重要になる。
【００３８】
上記のことから、色別に制御パラメータを決めることができる。その一例を表３で説明する。
【００３９】
【表３】

【００４０】
表の最も右欄に淡色の制御パラメータを示すが、ＮＶ値を５５〜６５に管理する必要があり、そのためにはシェーピングエアを７００Ｎｌ／分とし、塗装距離を３００ｍｍとし、ベル回転速度を５×１０^４ｒｐｍとすればよい。
【００４１】
濃色はＮＶ値を殆ど管理する必要がないので、シェーピングエアを４５０Ｎｌ／分とし、塗装距離を２００ｍｍとし、ベル回転速度を３×１０^４ｒｐｍとする。
【００４２】
中間色は、両者の中間であるから、シェーピングエアを６００Ｎｌ／分とし、塗装距離を２５０ｍｍとし、ベル回転速度を４×１０^４ｒｐｍとすればよい。
【００４３】
以上の塗装制御を前提とした本発明の作用を次に説明する。
図６は側面から見た塗装要領図であり、ワークとしての車両ボディ２０に塗装ロボット２１で塗装するときに、塗料が濃色であれば、第１軌跡Ｔ１（塗装距離＝２００ｍｍ）に沿って塗装ガン１０を相対移動させる。
塗料が中間色であれば、第２軌跡Ｔ２（塗装距離＝２５０ｍｍ）に沿って塗装ガン１０を相対移動させる。塗料が淡色であれば、第３軌跡Ｔ３（塗装距離＝３００ｍｍ）に沿って塗装ガン１０を相対移動させる。
【００４４】
図７は背面から見た塗装要領図であり、ワークとしての車両ボディ２０に塗装ロボット２１で塗装するときに、塗料が濃色であれば、第１軌跡Ｔ１（塗装距離＝２００ｍｍ）に沿って塗装ガン１０を相対移動させる。
塗料が中間色であれば、第２軌跡Ｔ２（塗装距離＝２５０ｍｍ）に沿って塗装ガン１０を相対移動させる。塗料が淡色であれば、第３軌跡Ｔ３（塗装距離＝３００ｍｍ）に沿って塗装ガン１０を相対移動させる。
【００４５】
図６、図７を実施する際に、前記の表３で述べた制御ファクターを選択することは勿論のこと、塗装ガン１０の軸２３を常に曲面（塗装面）の法線２４に沿わせることが重要である。
【００４６】
次に、本発明に係る２回塗り塗装方法について説明する。
従来は、厚塗りを達成するためなどを目的として２回塗りを実施してきたが、本発明方法によれば、別の目的を達成することができる。
【００４７】
図８は２回塗り塗装ラインの平面図であり、塗装ライン３０は、１回目の上塗り塗装を行う第１ステージ３１と、その上に２回目の上塗り塗装を行う第２ステージ３２とからなる。
【００４８】
第１ステージ３１には、左側面塗り用の１番塗装ロボット２１Ａ（位置を区別するためにＡを添えたが、図２の塗装ロボット２１と同一物である。以下、同じ）と、右側面塗り用の２番塗装ロボット２１Ｂと、右上面塗り用の３番塗装ロボット２１Ｃと、左上面塗り用の４番塗装ロボット２１Ｄとを備える。
【００４９】
同様に第２ステージ３１にも、左側面塗り用の１番塗装ロボット２１Ｅと、右側面塗り用の２番塗装ロボット２１Ｆと、右上面塗り用の３番塗装ロボット２１Ｇと、左上面塗り用の４番塗装ロボット２１Ｈとを備える。
【００５０】
本発明では、第１ステージ３１の塗装ロボット２１Ａ〜２１Ｄによる１回目の上塗り条件と、第２ステージ３２の塗装ロボット２１Ｅ〜２１Ｈによる２回目の上塗り条件とに、大きく差を付けたことを特徴とする。条件の一例を次表に示す。
【００５１】
【表４】

【００５２】
濃色の場合、１回目は、シェーピングエアを４５０Ｎｌ／分とし、塗装距離を２００ｍｍとし、ベル回転速度を３×１０^４ｒｐｍとした。
ベルの回転速度が比較的低速であるため、得られる塗粒の径は比較的大径となる。そして、シェーピングエアの量が比較的少量であるため塗粒の噴射角は比較的大きくなる。
この結果、大径の塗粒を効率よく塗装面に付着させることができ、塗着効率を高めることができる。
【００５３】
濃色の場合の２回目は、シェーピングエアを６００Ｎｌ／分とし、塗装距離を２５０ｍｍとし、ベル回転速度を５×１０^４ｒｐｍとした。
ベルの回転速度が高速であるため、得られる塗粒の径は小径になる。この小径化によりＮＶ値が高まる。
そして、シェーピングエアの量が多量であるためアルミ片を寝かせることができると共に塗粒の噴射角は比較的小さくなる。加えて、塗装距離が長くなったために塗粒の飛行時間が増し、これに比例して溶剤が蒸発してＮＶ値が高まる。
この結果、色差や色むらのない光沢のある上塗り塗膜を得ることができる。
【００５４】
すなわち、本発明の２回塗り方法では、１回目は塗着効率を重視し、２回目は仕上がり品質を重視した。この結果、生産性と品質の双方を達成することができた。
【００５５】
淡色の場合、１回目は、シェーピングエアを３５０Ｎｌ／分とし、塗装距離を３００ｍｍとし、ベル回転速度を４×１０^４ｒｐｍとた。
ベルの回転速度が比較的低速であるため、得られる塗粒の径は比較的大径となる。そして、シェーピングエアの量が比較的少量であるため塗粒の噴射角は比較的大きくなる。
この結果、大径の塗粒を効率よく塗装面に付着させることができ、塗着効率を高めることができる。
【００５６】
淡色の場合の２回目は、シェーピングエアを７００Ｎｌ／分とし、塗装距離を３００ｍｍとし、ベル回転速度を５×１０^４ｒｐｍとた。
ベルの回転速度が高速であるため、得られる塗粒の径は小径になる。この小径化によりＮＶ値が高まる。
そして、シェーピングエアの量が多量であるためアルミ片を寝かせることができると共に塗粒の噴射角は比較的小さくなる。
この結果、色差や色むらのない光沢のある上塗り塗膜を得ることができる。
【００５７】
すなわち、本発明の２回塗り方法では、１回目は塗着効率を重視し、２回目は仕上がり品質を重視した。この結果、生産性と品質の双方を達成することができた。
【００５８】
濃色の塗装条件と淡色の塗装条件とを比較すると、濃色に対して淡色は、シェーピングエアを増量し、且つベル回転速度を大きく設定する。
これは、ＮＶ値の管理などを厳しく行う必要がある淡色と、ＮＶ値の管理などを厳しく行う必要がない濃色とに差を付けたことを意味する。
【００５９】
中間色については、濃色を淡色の中間であるため、説明は省略する。
【００６０】
表４の条件で塗装を実施したところ、目的とする塗装品質を得ることができた。そこで、表４を考察すると、１回目より２回目に、シェーピングエアを増量したのでアルミ片をより寝かせることことができ、塗装距離及びベル回転速度を増加したのでＮＶ値を高めることができたと考えられる。
【００６１】
従って、塗装品質を高める上では、シェービングエアの増量、塗装距離の増加、ベル回転速度の増加の３つが有効である。しかし、塗装距離とベル回転速度との一方を増加することでもＮＶ値を高めることができることなどを考慮すれば、少なくとも、シェービングエアの増量、塗装距離の増加の３つのうち２つが達成できれば塗装品質を高めることができると言える。
【００６２】
例えば、機構的にベル回転速度を高めることに限界があるときには、ベル回転速度は据え置き、シェービングエアを増量し塗装距離を増加させるとよい。また、設備的に塗装距離を増加することに制約がある場合には、塗装距離は据え置き、シェービングエアを増量し、ベル回転速度を増加させるとよい。
【００６３】
尚、本実施例では、ワークは車両ボディとしたが、ワークはこれに限定するものではなく、筐体、平板、曲板などの塗装に、本発明を適用することは差し支えない。
【００６４】
【発明の効果】
本発明は上記構成により次の効果を発揮する。
自動車のメタリック塗装において、メタリック塗料を回転霧化式塗装ガンで霧化するとともに高電圧で帯電させ、これと反対電位のワークに塗装する第１ステージ、並びに第２ステージを準備し、第１ステージで１回目の塗装を施し、その上に第２ステージで２回目の塗装を施す塗装方法においてメタリック塗料の塗装方法において、第１回目の塗装では、濃色の場合は、シェーピングエアを４５０Ｎｌ／分とし、塗装距離を２００ｍｍとし、ベル回転速度を３×１０^４ｒｐｍとしたので、ベルの回転速度が比較的低速であるため、得られる塗粒の径は比較的大径となる。そして、シェーピングエアの量が比較的少量であるため塗粒の噴射角は比較的大きくなる。この結果、大径の塗粒を効率よく塗装面に付着させることができ、塗着効率を高めることができる。
又第１回目の塗装で淡色の場合は、シェーピングエアを３５０Ｎｌ／分とし、塗装距離を３００ｍｍとし、ベル回転速度を４×１０^４ｒｐｍとしたので、ベルの回転速度が比較的低速であるため、得られる塗粒の径は比較的大径となる。そして、シェーピングエアの量が比較的少量であるため塗粒の噴射角は比較的大きくなる。この結果、大径の塗粒を効率よく塗装面に付着させることができ、塗着効率を高めることができる。
このように第１ステージでは、上記のように塗装ガンでのシェーピングエアの量と、塗装ガンと塗装面との距離と、塗装ガンのベル回転速度とを抑えるため、大きな噴射角で、安定して大きな径の塗粒を塗装面に当てることができる。この結果、自動車のメタリック塗装における塗着効率を向上させることができる。
【００６５】
一方、第２回目の塗装では、濃色の場合は、シェーピングエアを６００Ｎｌ／分とし、塗装距離を２５０ｍｍとし、ベル回転速度を５×１０^４ｒｐｍとしたので、ベルの回転速度が高速であるため、得られる塗粒の径は小径になる。この小径化によりＮＶ値が高まる。
そして、シェーピングエアの量が多量であるためアルミ片を寝かせることができると共に塗粒の噴射角は比較的小さくなる。加えて、塗装距離が長くなったために塗粒の飛行時間が増し、これに比例して溶剤が蒸発してＮＶ値が高まる。
この結果、色差や色むらのない光沢のある上塗り塗膜を得ることができる。
又第２回目の塗装で淡色の場合は、シェーピングエアを７００Ｎｌ／分とし、塗装距離を３００ｍｍとし、ベル回転速度を５×１０^４ｒｐｍとしたので、ベルの回転速度が高速であるため、得られる塗粒の径は小径になり、この小径化によりＮＶ値が高まる。
そして、シェーピングエアの量が多量であるためアルミ片を寝かせることができると共に塗粒の噴射角は比較的小さくなる。
この結果、色差や色むらのない光沢のある上塗り塗膜を得ることができる。
各ステージでは、塗装ガンでのシェーピングエアの量と、塗装ガンと塗装面との距離と、塗装ガンのベル回転速度との全て若しくは少なくも２つを増加させるため、適度な噴射角で、適度な流動性の小さな径の塗粒を塗装面に当てることができる。この結果、自動車のメタリック塗装における塗装品質を向上させることができる。
【００６６】
すなわち、請求項１による自動車のメタリック塗装における２回塗り方法によれば、１回目は塗着効率を重視し、２回目は仕上がり品質を重視し、この結果、自動車のメタリック塗装において塗着効率の向上並びに塗装品質の向上の２つを達成することができ、メタリック塗料の自動車のメタリック塗装方法において、自動車のメタリック塗装における生産性と品質の双方を達成することができる。
【図面の簡単な説明】
【図１】本発明で採用した回転霧化式塗装ガンの要部断面図
【図２】塗装ロボットの配置図
【図３】アルミ片の姿勢とシェーピングエアの関係を調べたグラフ
【図４】ベルの回転速度とＮＶ値の関係を調べたグラフ
【図５】塗装距離とＮＶ値の関係を調べたグラフ
【図６】側面から見た塗装要領図
【図７】背面から見た塗装要領図
【図８】２回塗り塗装ラインの平面図
【符号の説明】
１０…回転霧化式塗装ガン、２０…ワークとしての車両ボディ、２１，２１Ａ〜２１Ｈ…塗装ロボット、３０…塗装ライン、３１…第１ステージ、３２…第２ステージ。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for applying a metallic paint suitable for top coating of automobiles .
[0002]
[Prior art]
Conventionally, a two-time coating method in which metallic coating is performed in two steps for various reasons is known (for example, Patent Document 1).
[0003]
[Patent Document 1]
JP 62-132572 A (2nd page)
[0004]
The second page, lower left column, lines 9 to 12 of Patent Document 1, “In such a separate coating method, the same metallic paint is used, and the first color coating condition and the second color coating condition are changed. In the lower right column of the same page, lines 1 to 5 indicate that “the coating film of the first color and the second color are different in the light receiving angle of light entering the sight. In spite of being coated with the same metallic paint, a different color tone, that is, a different color tone is obtained due to the different brightness.
[0005]
[Problems to be solved by the invention]
When the present inventors tried the method of patent document 1, it turned out that there exists the following subject.
In Patent Document 1, the efficiency of the painting operation, that is, the coating efficiency is not guaranteed because it is simply for the purpose of painting.
Further, in Patent Document 1, the finished quality of the painted surface is not guaranteed because it is simply for the purpose of painting.
[0006]
In recent years, two factors have been demanded at the same time: reduction of production costs by improving coating efficiency and improvement of the finished quality of the painted surface. However, Patent Document 1 is not a technology that can achieve these two elements.
[0007]
[Means for Solving the Problems]
The present inventors have entrusted the improvement of the coating efficiency to the first time if the top coating is divided into two in the research of the coating method that can achieve the improvement of the coating efficiency and the improvement of the coating quality. I came to think that the improvement of coating quality could be entrusted for the second time.
[0008]
That is, since it is covered with the second coating film, the quality of the first coating film is not so much of a problem. If so, the first time can be set to a coating condition that places importance on improving the coating efficiency.
Based on the above knowledge, as a result of accumulating experiments, we have succeeded in establishing a painting method that can achieve two things: improvement of coating efficiency and improvement of coating quality.
[0009]
That is, claim 1 is a metallic coating of an automobile, wherein the metallic paint is atomized with a rotary atomizing paint gun, charged at a high voltage, and applied to a workpiece having a potential opposite thereto, and the first stage In the coating method in which two stages are prepared, the first coating is performed on the first stage, and the second coating is performed on the second stage. In the first coating, in the first coating, the dark paint is applied to the painted surface. The coating distance between the rotary atomizing paint gun is 200 mm, the amount of shaping air is 450 Nl / min, the bell rotation speed is 3 × 10 ⁴ rpm, and the light paint is applied to the painted surface and the rotary atomizing type. painting distance between the spray gun and 300 mm, to and the amount of the shaping air is 350Nl / min, the bell speed and 4 × 10 4 ^rpm, the second round of paint, dark paint, and painted surfaces Painting distance between Utatekiri-expression spray gun and 250 mm, and to the amount of the shaping air is 600 Nl / min, the bell speed and 5 × 10 4 ^rpm, pale paint, painted surfaces and rotary atomization The coating distance to the coating gun is 300 mm, the amount of shaping air is 700 Nl / min, and the bell rotation speed is 5 × 10 ⁴ rpm.
[0010]
If the amount of shaping air is small, the spray angle of the paint sprayed from the paint gun is widened.
Conversely, if the amount of shaping air is large, the spray angle of the paint sprayed from the paint gun is narrowed, the paint particles strongly hit the paint surface, and the aluminum pieces lie down.
[0011]
If the paint distance is small, the paint will stably strike the paint surface.
When the coating distance is increased, the flight time of the paint grains is extended, and the solvent contained in the paint grains is evaporated in proportion to the increase of the flight time. The paint becomes difficult to fluidize due to evaporation of the solvent, which suppresses the movement of the aluminum piece and the deterioration of the coating quality.
[0012]
When the rotation speed of the bell is low, the coating grain has a large diameter.
On the other hand, when the rotation speed of the bell is increased, the diameter of the coated grains becomes smaller and the number thereof increases. Thereby, the surface area of the coating grain per weight can be increased. If the surface area is large, the contact area with the atmosphere increases, and the solvent contained in the coating particles can be further evaporated. The paint becomes difficult to fluidize due to evaporation of the solvent, which suppresses the movement of the aluminum piece and the deterioration of the coating quality.
[0013]
In the first stage, in order to reduce the amount of shaping air in the painting gun, the distance between the painting gun and the painting surface, and the bell rotation speed of the painting gun, a large spray angle and a stable large-diameter particle are applied. It can be applied to the painted surface. As a result, the coating efficiency can be improved.
[0014]
On the other hand, in the second stage, all or at least two of the amount of shaping air in the paint gun, the distance between the paint gun and the paint surface, and the bell rotation speed of the paint gun are increased. Thus, small-diameter coating particles with appropriate fluidity can be applied to the painted surface. As a result, the coating quality can be improved.
[0015]
That is, according to the first aspect, it is possible to achieve two of the improvement of the coating efficiency and the improvement of the coating quality.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The features of the present invention are shown in FIG. 8 and Table 4. These prerequisite technologies will be described first with reference to FIGS. 1 to 7 and Tables 1 to 3.
Embodiments of the present invention will be described below with reference to the accompanying drawings. The drawings are viewed in the direction of the reference numerals.
[0017]
FIG. 1 is a cross-sectional view of a main part of a rotary atomizing paint gun employed in the present invention. A rotary atomizing paint gun 10 includes a bell 11 that rotates at several tens of thousands of revolutions per minute and a gun body that surrounds the bell 11. 12, and an air passage 13 and an air nozzle 14 provided in the gun body 12. The rotary atomizing paint gun 10 is charged with -50000V static electricity.
[0018]
When the paint is supplied to the bell 11 as indicated by the white arrow, the paint 15 spreads along the bell 11 rotating at high speed and jumps out from the outer edge of the bell 11. That is, the centrifugal force imparted by the bell 11 pops out and becomes fine particles. Therefore, this type of paint gun is called a rotary atomizing paint gun.
[0019]
The air 15 blown out from the air nozzle 14 surrounds the coating particle 16. Therefore, when the amount of air 15 is increased, the flight speed of the coated particles 16 can be increased while suppressing the spread of the coated particles 16. On the other hand, when the amount is reduced, the flying speed of the coating particles 16 can be lowered while promoting the spreading of the coating particles 16. Therefore, this air 15 is called shaping air.
[0020]
Since the centrifugal force is directly proportional to the diameter and rotation speed of the bell 11, the diameter of the coating particle 16 becomes smaller by increasing the diameter and / or rotation speed.
[0021]
FIG. 2 is a layout diagram of the painting robot. A painting robot 21 is installed on the side of the vehicle body 20 as a workpiece, and a rotary atomizing painting gun 10 is attached to the tip of an arm 22 of the painting robot 21, and a first locus is shown. The rotary atomizing paint gun 10 is relatively moved along the vehicle body 20 as shown in T1. The first trajectory T1 can be achieved by teaching.
[0022]
The painting robot 21 is controlled to follow the three-dimensional shape so that the shaft 23 of the rotary atomizing paint gun 10 matches the normal 24 of the curved surface of the vehicle body 20.
[0023]
After various painting operations, the following were found. That is, the posture of the aluminum piece immediately after painting is described with reference to FIG. 3, and the form of the aluminum piece after a certain time has passed since immediately after painting is described with reference to Table 1.
[0024]
FIG. 3 is a graph showing the relationship between the posture of the aluminum piece and the shaping air, and the vertical axis shows the amount of shaping air Nl (normal liters) / minute. The numerical value in parentheses attached to the vertical scale indicates the flow velocity.
It has been found that when the amount of shaping air exceeds 650 Nl / min, the aluminum piece preferably sleeps (falls down). It was also found that standing aluminum pieces were included when the amount of shaping air dropped below 450 Nl / min.
[0025]
Table 1 shows the form of the aluminum pieces at a certain time from immediately after painting, organized by NV value. This NV value means the ratio (%) of solid content in the paint, and is an index that can be calculated by NV = 100 × solid content / paint.
However, the NV value is a value when a certain time (60 to 80 seconds) elapses after application from the coating gun.
This certain time indicates the time until the next work (work such as the next overcoating) becomes possible.
[0026]
[Table 1]

[0027]
If the NV value is less than 55%, the fluidity of the paint is excessive, and there is a possibility that a sleeping aluminum piece will occur. As a result, a color difference occurs. In addition, streaks occur due to lines of magnetic force.
[0028]
If the NV value exceeds 65%, the fluidity of the coating becomes too low, and drying unevenness occurs due to reasons such as hardening before the film thickness becomes uniform.
[0029]
In this regard, if the NV value is in the range of 55 to 65%, the fluidity is moderate, no color difference occurs, no stripe unevenness occurs, and no dry unevenness occurs.
Therefore, a technique for controlling the NV value to be in the range of 55 to 65% is required.
[0030]
FIG. 4 is a graph showing the relationship between the rotational speed of the bell and the NV value. At a normal speed of 3 × 10 ⁴ rpm, the NV value (80 seconds) was much smaller than 50%.
When the rotation speed was increased to 4 × 10 ⁴ rpm, the NV value (80 seconds) was about 50%.
When the rotational speed was further increased to 5 × 10 ⁴ rpm, the NV value (80 seconds) increased to about 53%.
[0031]
When the rotation speed is increased, the particle size of the coating material is reduced and the number of particles is increased. Then, the total surface area of the coated grains increases, and the solvent contained therein evaporates more. As a result, the NV value increases in proportion to the rotation speed.
[0032]
However, since the target NV value is not reached, further ingenuity is required. The present inventors consider that if the flying time of the coating grains is long, the evaporation of the solvent proceeds in proportion to this time, and the coating distance (distance between the coating surface and the coating gun) is increased. Tried. The result is shown in the following figure.
[0033]
FIG. 5 is a graph in which the relationship between the coating distance and the NV value is examined. The rotation speed of the bell is uniformly 4 × 10 ⁴ rpm.
At the normal coating distance of 200 mm, the NV value (80 seconds) was much smaller than 55%.
When the coating distance was increased to 250 mm, the NV value (80 seconds) was about 54%.
[0034]
When the coating distance was further increased to 300 mm, the NV value (80 seconds) increased to about 58%.
Therefore, it was confirmed that the NV value can be increased by increasing the coating distance.
[0035]
By the way, the metallic paint is obtained by mixing a sharp aluminum piece into a pigment and thinning it with a solvent. Therefore, the noticeability of the aluminum piece varies greatly depending on the density of the pigment. This is summarized in Table 2.
[0036]
[Table 2]

[0037]
If the color is dark, the aluminum piece becomes relatively inconspicuous, and there is no need to worry about the posture of the aluminum piece, so the NV value is not so important.
On the contrary, since the aluminum piece is conspicuous in the light color, the NV value is extremely important.
The intermediate colors are intermediate between them, and the management of the NV value becomes somewhat important.
[0038]
From the above, control parameters can be determined for each color. One example is described in Table 3.
[0039]
[Table 3]

[0040]
The light color control parameter is shown in the rightmost column of the table, and it is necessary to manage the NV value from 55 to 65. For that purpose, the shaping air is set to 700 Nl / min, the coating distance is set to 300 mm, and the bell rotation speed is set to 5 ×. It may be 10 ⁴ rpm.
[0041]
Since it is unnecessary to manage the NV value for dark colors, the shaping air is 450 Nl / min, the coating distance is 200 mm, and the bell rotation speed is 3 × 10 ⁴ rpm.
[0042]
Since the intermediate color is between the two, the shaping air may be 600 Nl / min, the coating distance may be 250 mm, and the bell rotation speed may be 4 × 10 ⁴ rpm.
[0043]
The operation of the present invention based on the above coating control will be described next.
FIG. 6 is a side view of the painting procedure, and when the paint is applied to the vehicle body 20 as a workpiece by the painting robot 21, if the paint is dark, it follows the first trajectory T1 (painting distance = 200 mm). The paint gun 10 is moved relatively.
If the paint is an intermediate color, the paint gun 10 is relatively moved along the second locus T2 (painting distance = 250 mm). If the paint is light, the paint gun 10 is relatively moved along the third locus T3 (painting distance = 300 mm).
[0044]
FIG. 7 is a drawing of a painting procedure as viewed from the back. When the paint is applied to the vehicle body 20 as a work by the painting robot 21, if the paint is dark, it follows the first locus T1 (painting distance = 200 mm). The paint gun 10 is moved relatively.
If the paint is an intermediate color, the paint gun 10 is relatively moved along the second locus T2 (painting distance = 250 mm). If the paint is light, the paint gun 10 is relatively moved along the third locus T3 (painting distance = 300 mm).
[0045]
6 and 7, the control factor described in Table 3 is selected, and the shaft 23 of the coating gun 10 is always along the normal 24 of the curved surface (painted surface). is important.
[0046]
Next, the two-time coating method according to the present invention will be described.
Conventionally, coating has been performed twice for the purpose of achieving thick coating, but according to the method of the present invention, another object can be achieved.
[0047]
FIG. 8 is a plan view of a two-time coating line. The coating line 30 includes a first stage 31 that performs the first overcoating and a second stage 32 that performs the second overcoating on the first stage 31.
[0048]
The first stage 31 has a first painting robot 21A for painting the left side surface (A is added to distinguish the position, but it is the same as the painting robot 21 in FIG. 2. The same applies hereinafter) and the right side surface. A second painting robot 21B for painting, a third painting robot 21C for painting the right upper surface, and a fourth painting robot 21D for painting the left upper surface.
[0049]
Similarly, on the second stage 31, the first painting robot 21E for left side painting, the second painting robot 21F for right side painting, the third painting robot 21G for right top painting, and the left painting 4th painting robot 21H.
[0050]
In the present invention, the first overcoating conditions by the painting robots 21A to 21D in the first stage 31 and the second overcoating conditions by the painting robots 21E to 21H in the second stage 32 are greatly different. To do. An example of the conditions is shown in the following table.
[0051]
[Table 4]

[0052]
In the case of a dark color, the first time, the shaping air was 450 Nl / min, the coating distance was 200 mm, and the bell rotation speed was 3 × 10 ⁴ rpm.
Since the rotation speed of the bell is relatively low, the diameter of the obtained coating grain is relatively large. And since the quantity of shaping air is comparatively small, the spray angle of a coating grain becomes comparatively large.
As a result, large-diameter coating grains can be efficiently attached to the painted surface, and the coating efficiency can be increased.
[0053]
In the second case of dark color, the shaping air was 600 Nl / min, the coating distance was 250 mm, and the bell rotation speed was 5 × 10 ⁴ rpm.
Since the rotation speed of the bell is high, the diameter of the obtained coating grain is small. This smaller diameter increases the NV value.
And since the quantity of shaping air is large, an aluminum piece can be laid down and the spray angle of a coating grain becomes comparatively small. In addition, since the coating distance is increased, the flying time of the coating grains is increased, and the solvent is evaporated in proportion to this, so that the NV value is increased.
As a result, it is possible to obtain a glossy topcoat film having no color difference or color unevenness.
[0054]
That is, in the two-time coating method of the present invention, the first time emphasized the coating efficiency, and the second time emphasized the finished quality. As a result, both productivity and quality could be achieved.
[0055]
In the case of the light color, the first time, the shaping air was 350 Nl / min, the coating distance was 300 mm, and the bell rotation speed was 4 × 10 ⁴ rpm.
Since the rotation speed of the bell is relatively low, the diameter of the obtained coating grain is relatively large. And since the quantity of shaping air is comparatively small, the spray angle of a coating grain becomes comparatively large.
As a result, large-diameter coating grains can be efficiently attached to the painted surface, and the coating efficiency can be increased.
[0056]
For the second time in the case of light color, the shaping air was 700 Nl / min, the coating distance was 300 mm, and the bell rotation speed was 5 × 10 ⁴ rpm.
Since the rotation speed of the bell is high, the diameter of the obtained coating grain is small. This smaller diameter increases the NV value.
And since the quantity of shaping air is large, an aluminum piece can be laid down and the spray angle of a coating grain becomes comparatively small.
As a result, it is possible to obtain a glossy topcoat film having no color difference or color unevenness.
[0057]
That is, in the two-time coating method of the present invention, the first time emphasized the coating efficiency, and the second time emphasized the finished quality. As a result, both productivity and quality could be achieved.
[0058]
Comparing the dark color coating conditions with the light color coating conditions, the light color increases the shaping air and the bell rotation speed is set larger than the dark color.
This means that there is a difference between a light color that requires strict management of NV values and a dark color that does not require strict management of NV values.
[0059]
Regarding the intermediate color, since the dark color is intermediate between the light colors, the description is omitted.
[0060]
When coating was performed under the conditions shown in Table 4, the intended coating quality could be obtained. Thus, considering Table 4, the shape air was increased from the first time to the second time, so that the aluminum piece could be laid more and the painting distance and the bell rotation speed were increased, so the NV value could be increased. It is done.
[0061]
Therefore, in order to improve the coating quality, three methods are effective: increasing the amount of shaving air, increasing the coating distance, and increasing the bell rotation speed. However, considering that the NV value can be increased by increasing one of the painting distance and the bell rotation speed, at least two of the three effects of increasing shaving air and increasing painting distance can be achieved. It can be said that it can raise.
[0062]
For example, when there is a limit to increase the bell rotation speed mechanically, the bell rotation speed may be left unchanged, and the painting distance may be increased by increasing the shaving air. In addition, when there is a restriction on increasing the painting distance in terms of equipment, the painting distance may be left unchanged, the shaving air increased, and the bell rotation speed increased.
[0063]
In the present embodiment, the workpiece is a vehicle body, but the workpiece is not limited to this, and the present invention may be applied to the coating of a casing, a flat plate, a curved plate, and the like.
[0064]
【The invention's effect】
The present invention exhibits the following effects by the above configuration.
In the metallic coating of automobiles, the first stage and the second stage are prepared, in which the metallic paint is atomized with a rotary atomizing paint gun and charged with a high voltage, and is applied to a workpiece having the opposite potential. In the coating method of metallic paint in the coating method in which the first coating is performed on the second stage and then the second coating on the second stage, the shaping air is 450 Nl / min in the first coating when the color is dark. Since the coating distance is 200 mm and the bell rotation speed is 3 × 10 ⁴ rpm, since the rotation speed of the bell is relatively low, the diameter of the resulting coated grains is relatively large. And since the quantity of shaping air is comparatively small, the spray angle of a coating grain becomes comparatively large. As a result, large-diameter coating grains can be efficiently attached to the painted surface, and the coating efficiency can be increased.
When the first coating is light, the shaping air is 350 Nl / min, the coating distance is 300 mm, and the bell rotation speed is 4 × 10 ⁴ rpm, so the bell rotation speed is relatively low. The diameter of the obtained coated grains is relatively large. And since the quantity of shaping air is comparatively small, the spray angle of a coating grain becomes comparatively large. As a result, large-diameter coating grains can be efficiently attached to the painted surface, and the coating efficiency can be increased.
Thus, in the first stage, as described above, the amount of shaping air in the painting gun, the distance between the painting gun and the painting surface, and the bell rotation speed of the painting gun are suppressed. Large diameter particles can be applied to the painted surface. As a result , the coating efficiency in metallic coating of automobiles can be improved.
[0065]
On the other hand, in the second painting, in the case of a dark color, the shaping air is 600 Nl / min, the painting distance is 250 mm, and the bell rotation speed is 5 × 10 ⁴ rpm, so the bell rotation speed is high. For this reason, the diameter of the obtained coated grains is small. This smaller diameter increases the NV value.
And since the quantity of shaping air is large, an aluminum piece can be laid down and the spray angle of a coating grain becomes comparatively small. In addition, since the coating distance is increased, the flying time of the coating grains is increased, and the solvent is evaporated in proportion to this, so that the NV value is increased.
As a result, it is possible to obtain a glossy topcoat film having no color difference or color unevenness.
If the second coating is light, the shaping air is set to 700 Nl / min, the coating distance is set to 300 mm, and the bell rotation speed is set to 5 × 10 ⁴ rpm. The diameter of the coated particles is small, and the NV value is increased by reducing the diameter.
And since the quantity of shaping air is large, an aluminum piece can be laid down and the spray angle of a coating grain becomes comparatively small.
As a result, it is possible to obtain a glossy topcoat film having no color difference or color unevenness.
Each stage increases the amount of shaping air in the paint gun, the distance between the paint gun and the paint surface, and all or at least two of the bell speed of the paint gun. It is possible to apply a small-diameter coating particle having a small fluidity to the painted surface. As a result, the coating quality in the metallic coating of the automobile can be improved.
[0066]
That is, according to the two-time coating method in the metallic coating of the automobile according to claim 1, the first time places importance on the coating efficiency, and the second time places importance on the finished quality. As a result, the coating efficiency in the metallic coating of the automobile is improved . The improvement and the improvement of the coating quality can be achieved, and both the productivity and the quality in the metallic coating of the automobile can be achieved in the metallic coating method of the automobile of the metallic paint .
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of the main part of a rotary atomizing paint gun employed in the present invention. FIG. 2 is a layout diagram of a painting robot. FIG. 3 is a graph showing the relationship between the posture of an aluminum piece and shaping air. Graph of the relationship between the rotation speed of the bell and the NV value [Fig. 5] Graph of the relationship between the coating distance and the NV value [Fig. 6] The coating procedure seen from the side [Fig. 7] The coating procedure seen from the rear [Figure 8] Plan view of the two-time coating line [Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Rotary atomization type painting gun, 20 ... Vehicle body as work, 21, 21A-21H ... Painting robot, 30 ... Painting line, 31 ... First stage, 32 ... Second stage.

Claims (1)

Prepare the first stage and the second stage to paint the metallic paint with a rotary atomizing paint gun and charge it with a high voltage, and apply it to the workpiece of the opposite potential. In the painting method of applying the second coating on the second stage on it,
In the first painting,
For the dark paint, the paint distance between the paint surface and the rotary atomizing paint gun is 200 mm, the amount of shaping air is 450 Nl / min, the bell rotation speed is 3 × 10 ⁴ rpm,
For the light paint, the coating distance between the painted surface and the rotary atomizing paint gun is 300 mm, the amount of shaping air is 350 Nl / min, the bell rotation speed is 4 × 10 ⁴ rpm,
In the second painting,
For dark paint, the paint distance between the paint surface and the rotary atomizing paint gun is 250 mm, the amount of shaping air is 600 Nl / min, the bell rotation speed is 5 × 10 ⁴ rpm,
For the light paint, the coating distance between the painted surface and the rotary atomizing paint gun was 300 mm, the amount of shaping air was 700 Nl / min, and the bell rotation speed was 5 × 10 ⁴ rpm.
A method of painting a metallic paint in a metallic paint of an automobile .

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