JP2010188235A - Electrostatic coating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic coating method which is capable of upgrading the smoothness of a surface to be coated. <P>SOLUTION: This electrostatic coating method is to make the electrostatic coating of a body 20 using a coating gun 30. That is, the particle diameter of coating material particles is changed by varying the supply of the coating material to a rotary atomizing head of the coating gun 30, while rotating the rotary atomizing head. Further, a solvent is added to the coating material so as to allow the NV value of a coat to fall within a specified range. Consequently, it is possible to lessen the unevenness of the surface to be coated of the body 20 which is caused by the build-up of the coating material particles, and further, secure the fluidity of the coating material deposited on the surface to be coated to such an extent that the coating material can be levelled off. Therefore, the smoothness of the coated surface can be enhanced beyond the level achieved by the conventional method. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrostatic coating method. Specifically, the present invention relates to an electrostatic coating method for electrostatically coating a surface to be coated.

2. Description of the Related Art Conventionally, a 3-coat 3-bake method is known as a method for painting a car body. The 3-coat 3-bake method is a method in which electrodeposition coating, baking, intermediate coating, baking, base coating, clear coating, and baking are performed in this order.
In the above coating process, for example, a rotary atomizing coating apparatus is used as a coating apparatus. The rotary atomizing coating apparatus rotates while applying a high voltage to the rotary atomizing head, and supplies liquid paint to the rotary atomizing head in this state. As a result, the liquid paint is charged and atomized, and sprayed from the leading edge of the rotary atomizing head to perform electrostatic coating.

  By the way, high-grade vehicles are required to have high smoothness in the appearance of the vehicle. For this reason, when painting the body of a luxury car, it is common to perform a water sharpening process after the intermediate coating process. This water sharpening step is a step of manually polishing with a sander or the like while applying water to the vehicle body (see Patent Documents 1 and 2).

However, when the water sharpening process is carried out, it takes time for the worker to become proficient, and there is a problem that the cost for arranging the worker is increased and the manufacturing cost of the automobile is increased.
Therefore, a method for maintaining the smoothness of the surface to be coated constant has been proposed. That is, by detecting the smoothness of the surface to be coated and comparing the detected smoothness with a reference value, the coating conditions such as the amount of paint discharged are corrected according to the change in the detected smoothness value, The smoothness of the surface is kept constant (see Patent Document 3). Thus, by changing the discharge amount of the paint, for example, by reducing the discharge amount, the paint particles are atomized, so that when the paint particles are applied to the surface to be coated, the unevenness due to the lamination of the particles is reduced. Therefore, the smoothness improvement of the surface to be coated is expected.

JP 58-124571 A Japanese Patent Laid-Open No. 4-159479 JP-A-6-269704

  However, in the above-described method of changing the discharge amount of the paint and atomizing the paint particles, the specific surface area (ratio of the surface area to the volume) of the paint particles increases due to the atomization of the paint particles. The amount of volatilization of the solvent increases. Therefore, the paint particles may be dried before they are sufficiently adapted to the surface to be coated, and unevenness may remain on the painted surface.

  In particular, this problem becomes significant when the side surfaces of the vehicle body are painted. In other words, when painting the upper surface of a vehicle body such as a bonnet or roof, even if paint particles are applied to the surface to be coated and unevenness occurs, gravity acts perpendicularly to the surface to be coated. Thus, the paint particles are easily adapted to the shape of the surface to be coated. However, when painting the side of a vehicle body such as a fender or a door panel, if the paint particles are applied to the surface to be coated and unevenness occurs, gravity acts along the surface to be coated. However, it becomes difficult to adapt to the shape of the surface to be painted.

  An object of this invention is to provide the electrostatic coating method which can improve the smoothness of a coating surface more.

  The electrostatic coating method of the present invention is an electrostatic coating method in which a surface to be coated (for example, a body 20 to be described later) is electrostatically coated using a rotary atomizing type coating apparatus (for example, a coating gun 30 to be described later). Then, while rotating the rotary atomizing head, the supply amount of the paint to the rotary atomizing head (for example, the rotary atomizing head 32 described later) of the rotary atomizing coating apparatus is changed, so that the particle size of the paint particles While changing the diameter, the solvent is added to the paint so that the NV value of the coating film falls within a predetermined range.

Here, the NV (Non Volatile: non-volatile content of paint) value is represented by the following formula, for example.
NV = (mass of paint after drying) / (mass of paint before drying) × 100
As the solvent to be added, a high boiling point solvent is preferable because the amount added may be small.

  According to the present invention, for example, the rotational speed of the rotary atomizing head is made constant, and in this state, the NV value of the coating film (ratio of non-volatile content in the coating film) is managed so as not to exceed a predetermined range. While reducing the amount of paint supplied to the rotary atomizing head, the paint particles are atomized.

If the amount of paint supplied to the rotary atomizing head is reduced while the rotational speed of the rotary atomizing head is constant, the paint particle diameter is reduced, and the unevenness caused by the coating of the paint particles on the surface to be coated is reduced.
However, when the paint particle diameter is reduced, the NV value of the coating film increases, and the proportion of non-volatile components in the coating film increases (that is, the solvent content in the coating film decreases). As a result, the fluidity of the coating film is lost, and the paint applied to the surface to be coated loses the fluidity with insufficient leveling. Therefore, the fluidity of the applied paint is ensured by adding an appropriate amount of solvent, preferably a high boiling point solvent.

  In this way, the unevenness caused by the lamination of paint particles on the surface to be coated can be reduced, and the fluidity to the level that the paint applied to the surface to be coated can be leveled can be ensured. Can be improved more.

  According to the present invention, the unevenness due to the lamination of the paint particles on the surface to be coated can be reduced and the fluidity to the extent that the paint applied to the surface to be coated can be leveled can be ensured. Smoothness can be further improved.

1 is a plan view of a part of a coating line to which an electrostatic coating method according to an embodiment of the present invention is applied. It is a perspective view of the clear coating equipment which comprises the coating line which concerns on the said embodiment. It is a schematic diagram which shows the path | route of the coating material and solvent of the clear coating equipment which concerns on the said embodiment. It is a 1st schematic diagram for demonstrating operation | movement of a clear painting installation. It is a 2nd schematic diagram for demonstrating operation | movement of a clear painting installation. It is a 3rd schematic diagram for demonstrating operation | movement of a clear painting installation. It is a 4th schematic diagram for demonstrating operation | movement of a clear painting installation. It is a 5th schematic diagram for demonstrating operation | movement of a clear painting installation. It is a 6th schematic diagram for demonstrating operation | movement of a clear painting installation. It is a figure which shows the relationship between the discharge amount of a rotary atomization head, and NV value. It is a figure which shows the relationship between the discharge amount of a rotary atomization head, and LW value. It is a schematic diagram which shows the path | route of the coating material and solvent of the clear coating equipment which concerns on the modification of this invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a plan view showing an outline of a part of a coating line 1 to which an electrostatic coating method according to an embodiment of the present invention is applied.
The painting line 1 performs top coating (base coating and clear coating).
FIG. 1 shows a part of the painting line 1, and the painting line 1 includes a base painting facility 3, a flash-off facility 4, and a clear coating along a conveyance path 2 through which a vehicle body 20 is conveyed. Equipment 10 and baking equipment 5 are provided in this order.

  The base coating facility 3 is a facility that performs base coating on the intermediate coating on the body 20 as a painted surface, and the flash-off facility 4 is a facility that performs flash-off after the base coating. The clear coating facility 10 is a facility that performs clear coating on the body 20 after performing flash-off, and the baking facility 5 is a facility that performs baking of top coating (base coating and clear coating).

FIG. 2 is a perspective view of the clear painting facility 10.
The clear painting facility 10 includes six painting robots 11 to 16 provided on both sides of the conveyance path 2, a paint supply pipe 41 that supplies paint to each of the painting robots 11 to 16, and the paint supply pipes 41. Among them, a solvent supply pipe 42 that supplies a solvent to those connected to the painting robots 13 to 16 is provided (see FIG. 1).
The painting robots 11 and 12 are upper surface painting robots that are disposed on the most upstream side with the conveyance path 2 interposed therebetween and paint the upper surface of the body 20.
The painting robots 13 and 14 are side painting robots that are arranged on the downstream side of the painting robots 11 and 12 with the conveyance path 2 interposed therebetween and paint the side surface of the body 20.
The painting robots 15 and 16 are side painting robots that are disposed on the downstream side of the painting robots 13 and 14 with the conveyance path 2 interposed therebetween and paint the side surface of the body 20.

  Each of the coating robots 11 to 16 includes a coating gun 30 as a rotary atomizing coating apparatus that sprays paint, and a robot arm 40 that adjusts the position of the coating gun 30 in a three-dimensional space.

Next, a method for mixing the paint and the solvent will be described.
There are three types of mixing methods of paint and solvent: premix, static mixer mixing and bell tip mixing.
The premix is a method in which a stirrer is provided closer to the paint tank than the coating robot, and the paint and the solvent are mixed by the stirrer. In this premix, when the color is changed, the flow path from the stirrer to the coating gun is washed.
The static mixer mixing is a method in which a static mixer is provided in the vicinity of the robot body, and the paint and solvent are mixed by the static mixer. In this static mixer mixing, when the color is changed, it is only necessary to clean the static mixer to the coating gun. Therefore, compared with the premix, the cleaning route is shortened, the time required for switching the paint color can be shortened, and the paint loss can be reduced.

Bell tip mixing is a method in which paint and solvent are mixed inside the coating gun. In this bell tip mixing, when changing colors, it is only necessary to clean the inside of the paint gun, so compared to static mixer mixing, the cleaning route is further shortened, and the time required for switching the paint color can be further shortened. Paint loss can be further reduced.
In the present embodiment, bell tip mixing is adopted among the above three types of mixing methods.

FIG. 3 is a schematic diagram showing the paint and solvent paths of the clear coating facility 10.
The clear coating facility 10 employs bell-end mixing as described above. That is, the paint supply pipe 41 and the solvent supply pipe 42 are connected to the painting gun 30 of the painting robots 13 to 16. A gear pump 43 is provided in the middle of the paint supply pipe 41.

A solvent extrusion device 44 is provided in the middle of the solvent supply pipe 42, and valves 421 and 422 are provided on the upstream side and the downstream side of the solvent supply device 42 of the solvent supply pipe 42.
The coating gun 30 mixes and sprays the paint supplied through the paint supply pipe 41 and the solvent supplied through the solvent supply pipe 42.

  The coating gun 30 includes a main body (not shown) and a rotary atomizing head 32 that is rotatably provided on the main body.

The main body has a cylindrical shape, and in addition to a paint supply pipe 41 for supplying paint to the rotary atomizing head 32 and a solvent supply pipe 42 for supplying solvent, the rotary atomizing head 32 is rotated by air pumped from a compressor. It includes an air motor that does not, and a high voltage generator (not shown) that charges the paint.
The rotary atomizing head 32 is formed with an expanded surface 321 that expands in the injection direction.
The paint supply pipe 41 extends along the central axis of the rotary atomizing head 32 and reaches the center of the spread surface 321.

The solvent extrusion device 44 includes a cylindrical cylinder 441, a piston 442 slidably provided in the cylinder 441, and a servo motor 443 that moves the piston 442 in the axial direction of the cylinder 441.
The piston 442 includes a disk-shaped piston main body 444 that contacts the inner peripheral surface of the cylinder 441, and a rod-shaped piston rod 445 provided on the piston main body 444 and connected to the servo motor 443.
The piston 442 is a feed screw mechanism, and the servo motor 443 is driven to rotate so that the position of the piston 442 in the cylinder 441 can be adjusted with high accuracy.

Next, an operation in the case where electrostatic coating is performed without diluting the paint of the coating robots 11 to 16 with a solvent will be described.
First, the valve 422 is closed by the control device 50. Then, the gear pump 43 is driven while rotating the rotary atomizing head 32 of the coating gun 30, and the paint is supplied to the coating gun 30 through the paint supply pipe 41.

  Then, since the rotary atomizing head 32 is rotating, centrifugal force acts on the discharged paint, and the paint moves toward the peripheral edge along the surface of the spread surface 321. As the paint approaches the peripheral edge of the spread surface 321, the centrifugal force acting on the paint increases, and the paint is separated into a large number of fine droplets to form a mist. This mist-like paint scatters from the periphery of the spread surface 321 and is applied to the surface of the body 20.

Next, an operation in the case where electrostatic coating is performed by diluting the paint of the coating robots 13 to 16 with a solvent will be described.
First, the control device 50 closes the valve 422 and opens the valve 421. In this state, the solvent is supplied from a solvent supply source (not shown) to the solvent supply pipe 42, and the cylinder 441 of the solvent extrusion device 44 is filled with the solvent. To do.
Next, the gear pump 43 is driven while rotating the rotary atomizing head 32 of the coating gun 30, and a small amount of coating material is supplied to the coating gun 30 through the coating material supply pipe 41 than the standard coating conditions.

  At this time, the control device 50 closes the valve 421 and opens the valve 422 so that the NV value of the coating film falls within a predetermined range, and drives the solvent extrusion device 44 to supply the solvent to the solvent supply pipe 42. Then, the paint and the solvent are mixed inside the coating gun 30, and further, centrifugal force acts on the discharged paint and solvent mixture, and this mixture is further mixed by the rotation of the rotary atomizing head 32. , And moves toward the peripheral edge along the surface of the expanded surface 321. When the mixed paint approaches the peripheral edge of the spread surface 321, the rotary atomizing head 32 rotates at a high speed, so that the centrifugal force acting on the mixed paint becomes considerably large. The liquid droplets are separated into mists. This mist-like paint scatters from the periphery of the spread surface 321 and is applied to the surface of the body 20.

Hereinafter, the operation of the clear painting facility 10 will be described with reference to FIGS.
In this clear coating facility 10, two types of bodies 20A and 20B are mixed and conveyed from upstream. The body 20B is required to have higher smoothness than the body 20A.
First, as shown in FIG. 4, the clear coating facility 10 performs coating of the bodies 20A and 20B. Specifically, the side surfaces of the body 20A are painted by the painting robots 13-16. Further, the upper surface of the front side of the body 20B is painted by the painting robots 11 and 12. Here, only the paint is supplied to the painting robots 11 to 16.

  When proceeding one tact from the state shown in FIG. 4, the clear painting facility 10 paints the rear side surface of the body 20 </ b> A by the painting robots 15 and 16 as shown in FIG. 5. Further, the painting robots 11 to 14 paint the upper surface on the rear side and the side surface on the front side of the body 20B. Here, since the front side surface of the body 20B is painted by the painting robots 13 and 14, the amount of paint supplied to the rotary atomizing head 32 of the painting gun 30 of the painting robots 13 and 14 is the same as the side surface of the body 20A. The coating robots 13 and 14 are simultaneously supplied with a solvent in addition to the paint.

  When one tact progresses from the state shown in FIG. 5, as shown in FIG. 6, the body 20 </ b> A is carried out from the clear coating facility 10, and the body 20 </ b> B is newly carried into the clear coating facility 10. Then, the painting robots 13 to 16 paint the side surface of the downstream body 20B already carried in, and the painting robots 11 and 12 coat the front side upper surface of the newly carried upstream body 20B. . Here, since the side surfaces of the body 20B are painted by the painting robots 13 to 16, the amount of paint supplied to the rotary atomizing head 32 of the painting gun 30 of the painting robots 13 to 16 is painting the side surfaces of the body 20A. The amount is smaller than the case, and simultaneously, the coating robots 13 to 16 are supplied with a solvent in addition to the paint.

  When proceeding one tact from the state shown in FIG. 6, as shown in FIG. 7, the clear painting facility 10 paints the rear side surface of the downstream body 20 </ b> B by the painting robots 15 and 16. Also, the painting robots 11 to 14 paint the rear upper surface and the front side surface of the upstream body 20B. Here, since the side surfaces of the body 20B are painted by the painting robots 13 to 16, the amount of paint supplied to the rotary atomizing head 32 of the painting gun 30 of the painting robots 13 to 16 is painting the side surfaces of the body 20A. The amount is smaller than the case, and simultaneously, the coating robots 13 to 16 are supplied with a solvent in addition to the paint.

  When one tact progresses from the state shown in FIG. 7, as shown in FIG. 8, the body 20 </ b> B is carried out from the clear coating facility 10, and the body 20 </ b> A is newly carried into the clear coating facility 10. Then, the painting robots 13 to 16 paint the side surface of the body 20B already carried in, and the painting robots 11 and 12 coat the front side upper surface of the newly carried body 20A. Here, since the painting robots 13 to 16 paint the side surfaces of the body 20B, the amount of paint supplied to the rotary atomizing head 32 of the painting gun 30 of the painting robots 13 to 16 is painting the side surfaces of the body 20A. At the same time, the coating robots 13 to 16 are supplied with a solvent in addition to the paint.

  When proceeding one tact from the state shown in FIG. 8, the clear painting facility 10 paints the rear side surface of the body 20B already carried in by the painting robots 15 and 16, as shown in FIG. In addition, the painting robots 11 to 14 paint the rear upper surface and the front side surface of the newly loaded body 20A. Here, since the painting robots 15 and 16 paint the side surfaces of the body 20B, the amount of paint supplied to the rotary atomizing head 32 of the painting gun 30 of the painting robots 15 and 16 is painting the side surfaces of the body 20A. The coating robots 15 and 16 are simultaneously supplied with a solvent in addition to the paint.

[Examples and Comparative Examples]
The paint and solvent were supplied to the above-mentioned clear coating equipment, and the relationship between the ratio of the solvent to the paint and the NV value and LW value was examined.

FIG. 10 is a diagram illustrating a relationship between the discharge amount of the rotary atomizing head and the NV value when the rotational speed of the rotary atomizing head is constant. FIG. 11 is a diagram showing the relationship between the discharge amount of the rotary atomizing head and the LW value when the rotational speed of the rotary atomizing head is constant.
In FIG. 11, LW (Long Wave) is an index representing the smoothness of the coating film measured by a measuring instrument called Wavescan (manufactured by BYK Gardner). Specifically, the surface of the coating film is irradiated with laser light from this measuring device, the reflected light intensity on the coating film surface is detected, and the optical profile on the coating film surface is detected. Then, the optical file is subjected to a mathematical filter, the structure of the coating film surface is separated for each wavelength, and the measured wavelength is extracted to a certain extent and digitized. It can be said that the lower the LW value, the smoother the surface and the better the appearance.

In the case of normal coating that does not reduce the amount of paint supplied to the rotary atomizing head (standard conditions), the NV value increases as the discharge rate is reduced from l ₄ to l ₁ . Here, when the discharge amount is l ₃ , the NV value falls within a predetermined range (range from t ₁ to t _{2 in} FIG. 10), but even in this case, the LW value is only slightly reduced.
That is, when the supply amount of the paint to the rotary atomizing head is reduced, the paint particles are atomized, so that the specific surface area of the paint particles increases and the NV value of the coating film increases. Therefore, the effect of atomization of the paint particles is halved, and the LW value is not greatly reduced.

On the other hand, in addition to the reduction in the amount of paint supplied to the rotary atomizing head, when a solvent is added to the paint so that the NV value is within a predetermined range, the LW value is significantly reduced.
That is, when the supply amount of the paint to the rotary atomizing head is reduced, the paint particles are refined and the specific surface area of the paint particles is increased, but since the solvent is added, the solvent volatilization amount of the paint is suppressed, The ratio of the volatile component in the coating film is not so high, and the increase in NV value can be suppressed. Therefore, the fluidity of the paint applied to the surface to be coated is ensured and the leveling of the coating film is promoted, so that the unevenness of the coating film surface is suppressed and the LW value is remarkably lowered.

  As described above, the amount of paint discharged from the rotary atomizing head 32 is reduced while the NV value of the coating film is controlled so as not to increase beyond a predetermined range while the rotational speed of the rotary atomizing head 32 is constant. Then, it can be seen that the fine appearance of the paint particles can reduce the LW value and improve the appearance.

According to this embodiment, there are the following effects.
(1) The rotational speed of the rotary atomizing head 32 is constant, and in this state, the coating value is discharged from the rotary atomizing head 32 while managing the NV value of the coating film so as not to exceed a predetermined range. To reduce paint particles. Thereby, the unevenness due to the lamination of the paint particles in the body 20 can be reduced, and the fluidity of the paint applied to the body 20 can be secured, so that the smoothness of the body 20 can be further improved as compared with the conventional case.

It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.
For example, in the present embodiment, the electrostatic coating method is applied to the clear coating facility 10, but the present invention is not limited to this. In other words, it may be applied to intermediate coating equipment, or it may be applied to equipment other than the base coating equipment, such as overcoat clear painting equipment (premium clear painting applied over clear painting). You may apply. Moreover, you may apply to one of these facilities, and may apply to multiple.

Further, in the present embodiment, the bell tip mixing is adopted for the clear coating facility 10, but not limited to this, the above-described static mixer mixing may be adopted.
That is, as shown in FIG. 12, the paint supply pipe 41 is provided with a static mixer 45 in addition to the gear pump 43, and the solvent supply pipe 42 is connected to the static mixer 45 instead of the coating gun 30. The static mixer 45 mixes the paint supplied from the gear pump 43 with the solvent supplied from the solvent extrusion device 44. Even if it does in this way, there exists an effect similar to the above-mentioned (1).

30 coating gun (rotary atomization coating equipment)
32 Rotating atomizing head 20 Body (surface to be painted)

Claims (1)

An electrostatic coating method in which a surface to be coated is electrostatically coated using a rotary atomizing coating device,
While rotating the rotary atomizing head, changing the amount of paint supplied to the rotary atomizing head of the rotary atomizing coating device, and changing the particle size of the paint particles,
An electrostatic coating method comprising adding a solvent to a paint so that the NV value of the coating film falls within a predetermined range.

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