This invention relates to a method for coating a work object in two tones, particularly for coating surfaces of a work object such as a vehicle body or the like in two tones.
Generally speaking, coating machines which are currently in use in the art are largely constituted by a coating action mechanism like a coating robot which is located in a coating booth, and a paint sprayer unit which is adapted to spray atomized paint particles toward a work object. In the case of coating vehicle bodies, for instance, when a work object is delivered to a coating booth by means of a work object transfer system, paint is sprayed toward the work object from a sprayer unit which is mounted on an arm distal end portion of a coating robot to move the sprayer unit along coating surfaces of the work object, keeping a predetermined distance from the latter.
In this connection, as is well known in the art, in addition to coating in one and single color, the so-called two-tone coating is often resorted to in painting vehicle bodies, for example, coating an upper half of a vehicle body in one color and a lower half in a different color.
More specifically, according to a prior art two-tone coating method, as shown in the block diagram of FIG. 35, an upper half of a vehicle body is coated with a first color, for example, by the use of paint of color A (Step 1), a clear paint is coated on the surface of the coating of color A (Step 2), and the vehicle body is put in a baking furnace to cure the coated films (Step 3). In the next place, masking tapes are put on the vehicle body along borders of the coated area, masking the coated area of color A to prevent deposition of a second color,
namely, to prevent deposition of paint of color B on the color A area (Step 4). After masking the color A area, the color B is coated on the lower half of the vehicle body in such a way as that upper portions of the color B area partly overlaps the color A area (Step 5). A clear paint is then coated on the coated color A (Step 6), and the vehicle body is put in the baking furnace again to cure the coated films (Step 7), followed by removal of the masking tapes (Step 8). The removal of masking tapes reveals two coated areas of different colors (two tones) which are clearly separated from each other by a border line.
In the case of the above-described two-tone coating method, however, coated films of the second color B are forcibly stripped off together with the masking tapes at the time of removal of the latter, leaving a stepped surface along border lines between the color A and color B areas. In addition, upon peeling off masking tapes, fine sawtooth-like notches appear continuously along bordering edges of the color B area to degrade the quality of finish coating to a considerable degree.
The masking involves the jobs of sticking masking tapes and sheet on and over a masking area and peeling off the masking tapes and sheets afterwards. Because of the difficulty of performing these jobs by automation, it has been the usual practice to rely on manual labors in masking and unmasking particular coating areas despite a conspicuous drop in production efficiency.
Further, in the case of the two-tone coating method using masking tapes, it is a paramount requisite to bake and cure the coating films of the color A area into a dried state before adhering masking tapes on the surfaces of the color A or of the clear paint. For this purpose, the coating process should include a step of coating a color paint, a step for coating clear paint and steps of baking coating films separately for each one of the colors A and B, which is obviously disadvantageous in view of degradations in productivity and increases in production cost.
In an attempt to improve the productivity of the two-tone coating process by aborting the masking step or by aborting the use of masking tapes, there have been developed a number of coating methods as disclosed, for example, in Laid-Open Japanese Patent No. S58-58168 and Laid-Open Japanese Patent No. H11-57606.
Firstly, above-mentioned Laid-Open Japanese Patent No. S58-58168 discloses a method for coating heavy anti-rust or corrosion-proof paint, (hereinafter referred to simply as xe2x80x9cthe first prior artxe2x80x9d for brevity), by the use of a coating robot having a sprayer unit and a masking device in the form of a masking plate on a fore distal end portion of a robot arm. According to this coating method, a fore end portion of the masking plate is abutted against a vehicle body at the time of a heavy anti-rust coating operation thereby covering the vehicle body on the upper side of the masking plate. In this state, lower portions of the vehicle body are coated with a heavy corrosion-proof paint which is sprayed from the sprayer unit.
On the other hand, disclosed in above-mentioned Laid-Open Japanese Patent No. H11-57606 (hereinafter referred to simply as xe2x80x9cthe second prior artxe2x80x9d for brevity) is a two-tone coating method employing, for the purpose of demarcating a border line on a work object 101, a sprayer unit which employs a binary fluid nozzle spray gun (or the so-called air brush gun) 102 with straight directionability, namely, with a narrow spray pattern which is smaller than 30 degrees in diverging angle xcex8 as shown in FIG. 36. An air gun (not shown) is located over the spray gun 102 thereby to spurt air toward a border line of a coating area. In addition, according to the coating method of the second prior art, the spray gun 102 is tilted with respect to a work object 101 by an angle which is greater than half the diverging angle xcex8 of the spray pattern ( greater than xc2xdxcex8). Namely, a border line of a coating area is demarcated on the work object 101 by spraying paint from the spray gun 102 in the tilted position. During a coating operation, air is spurted toward the border line from the air gun to prevent deposition, for example, of a color B paint on an adjoining coating area which was coated with a color A paint in a preceding stage.
In the case of the coating method according to the first prior art, that is, in the case of the coating method according to Laid-Open Japanese Patent No. S58-58168, the masking plate is adapted to cover surface areas other than a target coating area. Therefore, a large mount of paint inevitably deposits on the masking plate during a coating operation, necessitating the provision of a paint scraper in association with the masking plate to scrape deposited paint off and as a consequence requiring larger and more complicated equipment. Besides, the fore end of the masking plate which is held in abutting engagement with a vehicle body during a coating operation always has the possibility of damaging or bruising coating surfaces. For this reason, the coating method according to the first prior art may be applicable to undercoatings like heavy anti-corrosive coatings which would not require a quality finish, but does not suit for application to finish coatings.
Further, in the case of the coating method according to the above-mentioned second prior art, disclosed in Laid-Open Japanese Patent No. H11-57606, a binary fluid nozzle spray gun 102 (an air brush gun) is employed as a sprayer unit for demarcating a border line. The spray gun 102 of this sort is adapted to spurt paint under the pressure of jet air. That is, paint is vigorously spurted out from the spray gun 102 together with jet air. Therefore, there is always a problem that, while demarcating a border line by the use of a color B paint, splashes of color B paint particles rebounding on the surfaces of the work object 101 tend to scatter around and deposit on surfaces of the coating film in the adjoining color A area.
Further, according to the coating method of the abovementioned second prior art, air is spurted toward the position of the border line from an air gun. A problem with an air gun of this sort is that, because of the difficulty of controlling the direction of an air jet precisely toward an aimed position, the spray of paint from the spray gun 102 is often blown off and broken up by air jets, resulting in disturbances of the border line.
Furthermore, generally the binary fluid nozzle spray gun 102 has been used as a brush in artistic work, for example, for spraying a color on a painting, poster or craft work. In addition, the binary fluid nozzle spray gun 102 is suited for spraying a relatively small amount of a low viscosity dye color or a laquer type paint, and low in capacity of atomizing paint which is used for coating vehicle bodies or the like. Namely, the binary fluid nozzle spray gun 102 is suited for drawing a thin line by means of a small spray pattern, but not suited for coating broad surface areas of a vehicle body or the like. Even if used for coating vehicle bodies, it would take a considerably long coating time and fail to yield high quality finish coatings.
In view of the above-discussed problems with the prior art, it is an object of the present invention to provide a method for coating a work object in two tones, which can paint a border line in a clearly defined form to distinguish one coating area from an adjacent coating area of a different color, while permitting a reduction of the number of steps for a two-tone coating operation, improve the reliability of operation, and cut the cost of two-tone coating operations.
According to the present invention, in order to achieve the above-stated objectives, there is provided a method for coating a work object in two tones, comprising: a first color coating stage for coating a first color area on a coating surface of said work object with first color paint; a border zone coating stage for coating a border zone with second color paint, by (1) positioning a rotary atomizing head of a sprayer unit at a distance to said work object that is well within the range of the sprayer and in an inclined state tilted toward said border zone, (2) supplying mist blocking air in a direction forward of said rotary atomizing head to block mist of said second color paint from scattering and flying toward a first color coating on said first color area, (3) without supplying other shaping air to shape a spray pattern, (4) applying no high voltage to paint, and (5) coating a border zone with said second color paint to paint a border line bounding on said first color area; and a belt zone coating stage for coating a belt zone with said second color paint, by (1) positioning a rotary atomizing head of a sprayer unit at a distance to said work object that is well within the range of the sprayer and in an inclined state tilted toward belt zone, (2) supplying mist blocking air in a direction forward of said rotary atomizing head to block mist of said second color paint from scattering and flying toward a first color coating on said first color area, (3) applying no high voltage to paint, and (4) coating said second color paint on said belt zone continuously from said border zone coating on said border zone by putting said rotary atomizing head in a reciprocating pattern.
In the case of the arrangements just described above, in the first color area coating stage, first color paint is applied on a coating surface of a work object to form a first color coating thereon.
In the next border zone coating stage, the rotary atomizing head which is located at a distance to the work object that is well within the range of the sprayer, is tilted toward the border zone on the coating surface, while mist blocking air is supplied forward of the rotary atomizing head to prevent mist, i.e., fine particles of second color paint, from scattering and flying toward the first color coating. In this stage, no other shaping air is supplied to shape the spray pattern. A high voltage is not applied to the paint, and paint is sprayed by high speed rotation of the rotary atomizing head.
Accordingly, the second color paint is pulled toward a negative pressure region which is formed forward of the rotary atomizing head by high speed rotation of the latter, and at the same time urged to fly radially outward under the influence of centrifugal force. In this case, however, since the rotary atomizing head is positioned at a distance from a work object that is well within the range of the sprayer, second color paint is allowed to reach and deposit on the work object before it is atomized and scattered around by pneumatic resistance. Therefore, a clear border line can be painted on the work object. Besides, since the rotary atomizing head is tilted with respect to a coating surface of the work object, second color paint can be sprayed solely by centrifugal force without resorting to jet air, so that paint particles are allowed to deposit and settle on a coating surface without scattering and rebounding off the coating surface. In addition, the mist blocking air which is supplied forward of the rotary atomizing head blocks paint particles from scattering and flying toward the first color coating, ensuring to finish the coating in favorable conditions.
In the next belt zone coating stage, the rotary atomizing head which is located at a distance from the work object that is well within the range of the sprayer, is tilted toward the belt zone on the coating surface, while mist blocking air is supplied in a direction forward of the rotary atomizing head. In this stage, either no voltage is applied or a low voltage is applied if necessary, while coating a wide belt zone (belt-like surface area) on the coating surface of the work object with second color paint continuously from the border line by the rotary atomizing head which is put in a reciprocating pattern.
As a consequence, scattering of paint particles is blocked substantially in the same maimer as in the above-described border zone coating stage as second color paint is coated on the work object continuously under the border zone coating. At this time, since the rotary atomizing head is put in a reciprocating pattern, second color paint can be coated over a wide surface area of the work object continuously from the border zone coating.
According to the present invention, there is also provided a method for coating a work object in two tones, which comprises: a first color coating stage for coating a first color area on a coating surface of said work object with first color paint; a border zone coating stage for coating a border zone with second color paint, by (1) positioning a rotary atomizing head of a sprayer unit at a distance to said work object that is well within the range of the sprayer and in an inclined state tilted toward said border zone, (2) supplying mist blocking air in a direction forward of said rotary atomizing head to block mist of said second color paint from scattering and flying toward a first color coating formed on said first color area, (3) without supplying any other shaping air to shape a spray pattern, (4) applying no high voltage to the paint, and (5) coating a border zone with said second color paint to paint a border line bounding on said first color area; a belt zone coating stage for coating a belt zone with said second color paint, by (1) positioning a rotary atomizing head of a sprayer unit at a distance to said work object that is well within the range of the sprayer and with the sprayer in an inclined state tilted toward said belt zone, (2) supplying mist blocking air in a direction forward of said rotary atomizing head to block mist of said second color paint from scattering and flying toward a first color coating on said first color area, (3) applying no high voltage to the paint, and (4) coating said second color paint on said belt zone continuously from said border zone coating on said border zone by putting said rotary atomizing head in a reciprocating pattern of movements; and a remainder area coating stage for coating said second color paint on remainder areas of said work object left subsequent to said belt zone coating stage.
In this instance, in the first color area coating stage, first color paint is applied on a coating surface of a work object to form a first color coating thereon.
In the next border zone coating stage, the rotary atomizing head, which is located at a distance to the work object that is well within the range of the sprayer, is tilted toward the border zone on the coating surface, while mist blocking air is supplied forward of the rotary atomizing head to prevent mist, i.e., fine particles of second color paint, from scattering and flying toward the first color coating. In this stage, no other shaping air is supplied to shape the spray pattern. A high voltage is not applied to the paint, and paint is sprayed by high speed rotation of the rotary atomizing head.
Accordingly, second color paint is pulled toward a negative pressure region which is formed forward of the rotary atomizing head by high speed rotation of the latter, and at the same time urged to fly radially outward under the influence of centrifugal force. In this case, however, since the rotary atomizing head is positioned at a distance from a work object that is well within the range of the sprayer, second color paint is allowed to reach and deposit on the work object before it is atomized and scattered around by pneumatic resistance. Therefore, a clear border line can be painted on the work object. Besides, since the rotary atomizing head is tilted with respect to a coating surface of the work object, second color paint can be sprayed solely by centrifugal force without resorting to jet air, so that paint particles are allowed to deposit and settle on a coating surface without scattering and rebounding off the coating surface. In addition, the mist blocking air which is supplied forward of the rotary atomizing head blocks paint particles from scattering and flying toward the first color coating, ensuring that the coating will be finished in favorable conditions.
In the next belt zone coating stage, the rotary atomizing head, which is located at a distance from the work object that is well within the range of the sprayer, is tilted toward the belt zone on the coating surface, while mist blocking air is supplied in a direction forward of the rotary atomizing head. In this stage, a high voltage is not applied, while coating a wide belt zone on the coating surface of the work object with second color paint continuously from the border line by the rotary atomizing head which is put in a reciprocating pattern.
As a consequence, scattering of paint particles is suppressed substantially in the same manner as in the above-described border zone coating stage as second color paint is coated on the work object continuously under the border zone coating. Further, a broad belt zone (a belt-like area) is coated by a reciprocating pattern of the rotary atomizing head in the belt zone coating stage, so that, in coating second color paint in the succeeding remainder area coating stage, the rotary atomizing head can be located at a large distance from the first color coating to prevent particles of second color paint from depositing on the first color coating.
In the remainder area coating stage, second color paint is coated on remaining areas of the coating surface continuously from the belt zone coating. At this time, the border zone coating and the belt zone coating of second color paint intervene between the first color coating and the remainder areas to be painted in the remainder area coating stage, so that particles of second color paint can be prevented from scattering and flying toward the first color coating even under normal coating conditions.
According to the present invention, coating is formed on the work object in the border zone coating stage, by (1) reducing a coating distance between a confronting marginal edge of the rotary atomizing head and the work object to a minimal value when the rotary atomizing head is in a coating position for painting the border line bounding on a first color coating on the first color coating area, and (2) increasing the coating distance between the marginal edge of the rotary atomizing head and the work object when the rotary atomizing head is moved in a direction away from the border line, (3) while moving the rotary atomizing head in a reciprocating pattern toward and away from the border line in a direction of intersecting the latter.
In this instance, in relation with the reciprocating coating action, the marginal edge of the rotary atomizing head is positioned closer to a coating surface on the side of a border line bounding on the first color coating, thereby forming the border line with thick and clear coating. On the other hand, when in a position away from the first color coating and the border line, the rotary atomizing head is located at a greater distance from the work object to spray paint particles over a broader area. Accordingly, flat and thinner coating is formed on a surface area distant from the border line.
According to the present invention, the rotary atomizing head is moved substantially parallel with the border line while painting a border zone area in the border zone coating stage.
In this case, by moving the rotary atomizing head parallel with the border line, a smooth (rectilinear) border line can be painted on the surface of the work object.
According to the present invention, coating is applied on a surface area of the work object in the belt zone coating stage, by (1) reducing the coating distance between a confronting marginal edge of the rotary atomizing head and work object to a minimal value on the side of a border zone coating, (2) increasing the coating distance between the marginal edge of the rotary atomizing head and the work object when the rotary atomizing head is moved in a direction away from the border zone coating, (3) while the rotary atomizing head moves in a reciprocating pattern toward and away from the border line in a direction of intersecting the latter.
In this instance, at a position on the side of the border zone coating, the coating distance between an opposing marginal edge of the rotary atomizing head and a coating surface is reduced to a minimum value to prevent particles of second color paint from depositing on the first color coating across the border zone coating. Besides, at the time of forming second color coating continuously under the belt zone coating, flat and thinner coating can be formed in overlapping portions of second color paint, namely, on surface areas away from the border line.
According to the present invention, the rotary atomizing head is moved substantially parallel with the border line while painting the belt zone in the belt zone coating stage.
In this instance, second color paint which is sprayed by the rotary atomizing head is coated on substantially parallel with the border line, and particles of second color paint are prevented from flying toward the first color coating across the border zone coating and the belt zone coating.
According to the present invention, in the belt zone coating stage, in addition to the mist blocking air, shaping air is either not supplied at all or supplied in a suppressed amount which will not disturb the mist blocking air.
In this instance, second color paint which is sprayed from the rotary atomizing head by centrifugal force is allowed to deposit on the work object free of possibilities of disturbance by shaping air, and particles of second color paint are prevented from flying toward and depositing on the first color coating.
According to the present invention, the rotary atomizing head of the sprayer unit is provided with an air nozzle adapted to spurt mist blocking air in a direction forward of the rotary atomizing head, the air nozzle being turned on to supply mist blocking air forward of the rotary atomizing head in the border zone coating stage and the belt zone coating stage.
In this instance, when mist blocking air is supplied in a direction forward of the rotary atomizing head, the mist blocking air prevents particles of second color paint from flying toward and depositing on the first color coating.
According to the present invention, the rotary atomizing head of the sprayer unit is provided with an air nozzle adapted to spurt mist blocking air in a forward direction toward the rotary atomizing head and a flow rectification plate for guiding mist blocking air from the air nozzle in a direction forward of the rotary atomizing head, the air nozzle being turned on to spurt out mist blocking air and supply same forward of the rotary atomizing head under the guidance of the flow rectification plate in the border zone coating stage and the belt zone coating stage.
In this instance, the mist blocking air which is supplied from the air nozzle toward the rotary atomizing head is hit on the flow rectification plate and thereby turned toward the rotary atomizing head. By the mist blocking air which is controlled by the flow rectification plate, particles of second color paint are prevented from flying toward the first color coating across the border line in a reliable manner.
According to the present invention, in the border zone coating stage and the belt zone coating stage, the rotary atomizing head is tilted through an angle in the range between 50 degrees and 80 degrees with respect to a straight line normal to the coating surface of the work object.
In this instance, paint particles which are sprayed by the rotary atomizing head under the influence of centrifugal force are allowed to deposit and settle on a coating surface of the work object without scattering in the direction of the first color coating.
According to the present invention, there is also provided a method for coating a work object in two tones, which comprises: a first color coating stage for coating a first color area on a coating surface of said work object with first color paint; a bordering belt zone coating stage for coating a bordering belt zone with second color paint, by (1) positioning a rotary atomizing head of a sprayer unit at a distance to said work object that is well within the range of the sprayer and in an inclined state tilted toward said bordering belt zone, (2) supplying mist blocking air in a direction forward of said rotary atomizing head to block mist of said second color paint from scattering and flying toward a first color coating on said first color area, (3) without supplying any additional shaping air to shape a spray pattern, (4) applying no high voltage to paint, and (5) coating said bordering belt zone with said second color paint to paint a border line bounding on said first color area by putting said rotary atomizing head in a reciprocating pattern of movements; and a remainder area coating stage for coating said second color paint on remainder area of said work object subsequent to said bordering belt zone coating stage.
In this instance, in the first color area coating stage, first color paint is applied on a coating surface of a work object to form a first color coating thereon.
In the next bordering belt zone coating stage, the rotary atomizing head, which is located at a distance from the work object that is well within the range of the sprayer, is tilted toward a bordering belt zone on the coating surface, while mist blocking air is supplied forward of the rotary atomizing head to prevent mist, i.e., fine particles of second color paint, from scattering and flying toward the first color coating. In this stage, no other shaping air is supplied to shape the spray pattern. A high voltage is not applied to the paint, and paint is sprayed by high speed rotation of the rotary atomizing head.
Accordingly, the second color paint is pulled toward a negative pressure re is formed forward of the rotary atomizing head by high speed rotation of the latter, and at the same time urged to fly radially outward under the influence of centrifugal force. In this case, however, since the rotary atomizing head is positioned at a distance from a work object that is well within the range of the sprayer, second color paint is allowed to reach and deposit on the work object before it is atomized and scattered around by pneumatic resistance. Therefore, a clear border line can be painted on the work object. Besides, since the rotary atomizing head is tilted with respect to a coating surface of the work object, second color paint can be sprayed solely by centrifugal force without resorting to jet air, so that paint particles are allowed to deposit and settle on a coating surface without scattering and rebounding off the coating surface. In addition, the mist blocking air which is supplied forward of the rotary atomizing head blocks paint particles from scattering and flying toward the first color coating, ensuring that the coating will be finished in favorable conditions.
In the remainder area coating stage, remainder areas of the coating surface on the work object are coated with second color paint continuously from the bordering belt zone. At this time, the broad bordering belt zone coating of second color paint intervenes between the first color coating and the remainder surface areas to be painted in the remainder area coating stage, so that particles of second color paint can be prevented from scattering and flying toward the first color coating even under normal coating conditions.
According to the present invention, a coating is applied in the bordering belt zone coating stage, by (1) reducing the coating distance between the confronting marginal edge of the rotary atomizing head and the work object to a minimal value when the rotary atomizing head is in a coating position for painting the border line bounding on a first color coating on the first color coating area, and (2) increasing the coating distance between the marginal edge of the rotary atomizing head and the work object when the rotary atomizing head is moved in a direction away from the border line, (3) while moving the rotary atomizing head in a reciprocating pattern toward and away from the border line in a direction of intersecting the latter.
In this instance, in relation with the reciprocating coating action, the marginal edge of the rotary atomizing head is positioned closer to a coating surface on the side of a border line bounding on the first color coating, thereby forming the border line with thick and clear coating. on the other hand, when in a position away from the first color coating and the border line, the rotary atomizing head is located at a greater distance from the work object to spray paint particles over a broader area. Accordingly, flat and thinner coating is formed on a surface area distant from the border line.
According to the present invention, the rotary atomizing head is moved substantially parallel with the border line while painting a border zone area in the bordering belt zone coating stage.
In this instance, by moving the rotary atomizing head parallel with the border line, a smooth (rectilinear) border line can be painted on the surface of the work object.
According to the present invention, the rotary atomizing head of the sprayer unit is provided with an air nozzle adapted to spurt mist blocking air in a direction forward of the rotary atomizing head, the air nozzle being turned on to supply mist blocking air forward of the rotary atomizing head in the bordering belt zone coating stage.
According to the present invention, the rotary atomizing head of the sprayer unit is provided with an air nozzle adapted to spurt mist blocking air in a forward direction toward the rotary atomizing head and a flow rectification plate for guiding mist blocking air from the air nozzle in a direction forward of the rotary atomizing head, the air nozzle being turned on to spurt out mist blocking air and supply same forward of the rotary atomizing head under the guidance of the flow rectification plate in the bordering belt zone coating stage.
According to the present invention, in the bordering belt zone coating stage, the rotary atomizing head is tilted through an angle in the range between 50 degrees and 80 degrees with respect to a straight line normal to the coating surface of the work object.
In this instance, paint particles which are sprayed by the rotary atomizing head under the influence of centrifugal force are allowed to deposit and settle on a coating surface of the work object without scattering in the direction of the first color coating.
According to the present invention, the coating method further comprises a baking stage for baking coatings of the first and second color paint simultaneously after completing coating operations of the respective coating stages.
In this instance, after coating first color paint, second color paint is coated on before baking and curing first color coating into a dried state, namely, when first color coating is still in a wet state, by the so-called wet-on-wet process. Therefore, it becomes possible to omit a baking stage subsequent to a first color area coating stage, which is inevitably required in the above-described prior art for masking purposes thereby simplifying the coating process.