JPH04330966A - Drying method - Google Patents

Abstract

PURPOSE:To prevent foaming, blistering and run generating when drying a coating film with the conventional hot air furnace or far infrared furnace immediately after coating. CONSTITUTION:A material to be coated is coated in the coating booth 51. The drying method consists of a preliminary drying process in the preliminary drying furnace 52 drying the coating film formed on the surface of the base material with near infrared rays which are within a region high in transmissivity of infrared rays to the coating film applied on the surface of a base material and high in absorptivity by the base material, and a final drying process finally drying in the regular drying furnace 53.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention is designed to improve the infrared transmittance of a paint film applied to the surface of a base material before drying it in a conventional drying oven such as a conventional hot-air oven or a far-infrared drying oven after painting. The present invention relates to a drying method in which a coating film formed on the surface of a base material is preheated in a drying oven using infrared rays in a region where the absorption rate is high and the absorption rate of the base material is high.

0002

[Prior Art] Conventionally, as a drying method for drying objects coated with various paints, so-called hot air ovens,
A drying method using a drying oven that utilizes far infrared rays is known. The drying mechanisms of these drying methods are understood as follows.

That is, first, an object to be dried, such as a metal plate or the like, whose surface is coated with a paint made of a solvent or a resin such as acrylic resin, is carried into a furnace. Next, hot air is blown or far infrared rays are irradiated. Then, the solvent on the surface of the paint applied to the object to be dried is first evaporated, and the surface loses fluidity and solidifies. When heat such as hot air propagates inside, that is, to the base material side, the coating film solidifies due to heating. Then, the solvent inside the surface breaks through the already solidified coating surface and evaporates. This leaves traces of foaming on the surface and creates pinholes. Therefore, in conventional hot air ovens or drying ovens that use far infrared rays, the solvent is evaporated in a setting room without rapid heating, and then far infrared rays are irradiated with a small temperature gradient and hot air is blown.

However, the conventional drying methods using these drying ovens have the problem that drying takes a long time because drying is carried out while maintaining a low temperature that does not cause foaming.

[0005] In particular, in a heating furnace that uses a combination of hot air and infrared rays for short-time drying, the surface of the paint film becomes higher temperature, and a temperature difference between the surface of the paint film and the metal surface at the interface between the paint film causes foaming. There were problems that could easily arise.

On the other hand, "Near-infrared liquids, powders, coatings, and stoves" (Utility Model Application Publication No. 1-151873), "Light plate exclusively for paint baking ovens" (Utility Model Application Publication No. 2-43217), US Pat.
P4,863,375 “BAKING METHOD F
OR USE WITH LIQUID OR POW
DER VARNISHING FURNACE” (Baking Method for Youth with
liquid or powder vanishing
Furnace) etc. are known. These conventional examples include “
There is a description of ``a type of near-infrared liquid, powder, coating, stove baking method'', and ``Using near-infrared rays' rapid high temperature and strong penetrating properties, the stove baking method has been improved and paints can be baked. A device that dries quickly and strengthens its adhesion, that is, ``
``A coating method in which powder, liquid paint, gas, or fluid in a powder-liquid state is applied as a transport medium to the surface of an object, and then heated and melted to coat it evenly, as in so-called liquid or powder-liquid coating.'' There is a description of.

Alternatively, “a drying oven using near-infrared rays,”
Alternatively, a drying method in which a high-temperature section and a low-temperature section are sequentially formed in a drying oven, or a ceramic reflector is installed behind the near-infrared lamp, and a heater is installed inside the ceramic reflector.'' There is a description of.

[0008] Also, in the October issue of Painting Technology Special Issue, there is a description about ``medium wavelength infrared radiator'' (October 1990).
Published by Riko Publishing Co., Ltd., pp. 211-213). In other words, ``Some of the radiant energy that reaches the paint film is absorbed, some of it is reflected, and some of it is transmitted.The absorbed energy turns into heat, heating and drying the paint film.Painting In the case of , there is a base material and a body, so the radiant energy that passes through the paint film heats the base material, and heat conduction heats the paint film from the inside.

■Near infrared: Temperature 2000-2200°C
Maximum energy wavelength approximately 1.2 μm, high energy density, large reflected and transmitted energy, fast rise speed (
(1 to 2 seconds), and the lifespan is short at about 5,000 hours.

■Mid-infrared: Temperature 850-900°C, maximum energy wavelength approximately 2.5 μm, energy density medium, absorption. The transmitted energy is balanced and the energy penetrates into the coating film, resulting in a long life.

■Far infrared rays: Temperature 500-600°C, maximum energy wavelength approximately 3.5 μm, energy density low, well absorbed but tends to be absorbed and heated on the coating surface, long rise time (5-15 minutes) , convection loss is large. ”.

Furthermore, "2. Maximum efficiency medium wavelength infrared rays"
In order to dry faster and obtain better paint film quality, that is, to heat and dry with maximum efficiency, the following two conditions must be met at the same time.

(2) The radiant energy of the infrared radiator is proportional to the fourth power of the absolute temperature (T) of the radiator.

[0014]Eb∝T4

[0015] The higher the temperature, the greater the radiant energy.

■The maximum energy wavelength is somewhat shorter than the peak absorption rate of the paint.

The maximum peak wavelength that can be used for industrial infrared heating of paints is around 3 μm without exception. Therefore 2.5
The infrared radiator, which has a maximum energy wavelength around μm, has good absorption and transmission, heating the base material and heating it from within.

Related to the above, the temperature of the infrared radiator (T
) and the maximum energy wavelength (λm), Wien's displacement law,

From λm=2897/T

T=(t+273)=2897/2.5

[
t=880°C

[0021] Medium wavelength infrared rays satisfy this condition, have large effective energy, and have maximum efficiency. ”.

However, Utility Model Application Publication No. 1-151873,
Utility Model Application Publication No. 2-43217, US Pat. However, there is no description of the optimum range of infrared rays to be irradiated and selection based on the relationship between near-infrared rays and the coating film applied to the metal surface.

On the other hand, far-infrared rays and mid-infrared rays conventionally used for drying paint films select and use areas where the paint film has a high absorption rate, that is, areas where the paint film has a good infrared absorption rate. This is for the purpose of heating the coating film surface. However, the use of infrared rays, which have a high absorption rate in coatings, inherently poses the problem of pinhole formation. Therefore, there was a problem in that it took a long time to dry because the temperature was maintained at a low temperature that did not cause foaming.

[0024] Also, in the above-mentioned "Painting Technology Special Issue October Issue", there is no mention of selection of infrared rays based on the relationship between infrared rays and the absorption rate of the base material, or selection of infrared rays based on the cause of pinhole generation. And when it comes to drying paint, they conclude that ``an infrared radiator with a maximum energy wavelength of around 2.5 μm has good absorption and transmission, heating the base material and heating it from within.''

On the other hand, in the process of drying the paint film applied to the surface of the base material using near infrared rays, the inventors discovered that rather than selecting a region where the applied paint film has a high infrared absorption rate, the infrared transmission of the paint film We found that selecting near-infrared rays in a highly sensitive region can suppress the generation of pinholes. It is speculated that this is because the paint film is dried not from the paint film surface, but by directly heating the base material surface located at the interface with the paint film on the coated object, and the paint film is dried from the base material surface. be done.

That is, in general, when a metal is used as a base material, the longer the wavelength of infrared rays, the higher the reflectance of the metal, and the shorter the wavelength, the higher the heat absorption rate of the metal. Regarding the paint film, when drying the paint film using near-infrared rays, it is rather difficult to dry the paint film by using near-infrared rays that have a high transmittance to the paint film, that is, the absorption rate of the paint film is low. It is assumed that the heat is generated without any formation of .

Therefore, the inventor first filed Japanese Patent Application No. 2-3109.
16 ``Method for drying a paint film'', ``Drying method for drying a paint film applied to the surface of a base material using infrared rays in a region where the infrared transmittance of the paint film applied to the surface of the base material is high and the absorption rate of the base material is high is used. A method for drying a paint film characterized by drying the paint film.

On the other hand, it is known to install an air curtain at the opening to the outside air of a drying oven such as a tunnel oven. The air curtain is required to maintain the temperature inside the furnace and prevent the heat inside the tunnel furnace from leaking to the outside air. The higher the speed of the air used in the air curtain, the more effective it is. In order to maintain the temperature, the air used in the air curtain was circulated, and cooling the air curtain installed at the opening of the tunnel furnace was not used because it caused temperature loss. .

[0029]

[Problem to be Solved by the Invention] The inventor has proposed that, after painting, before drying in a conventional drying oven such as a conventional hot-air oven or a far-infrared drying oven, When we preliminarily dried the coating film formed on the surface of the base material using infrared rays in the region of high transmittance and high absorption rate of the base material in a drying oven, we found that it could be dried immediately using only a conventional drying oven. It was found that the adhesion between the base material and the coating film was improved compared to when it was dried, and the surface smoothness and gloss were improved.

[0030]

[Means for Solving the Problems] The present invention is based on these findings. That is,

0031
]The process of applying a coating to the object to be coated, then forming the coating on the surface of the base material using infrared rays in the region where the infrared transmittance of the coating film of the paint applied to the surface of the base material is high and the absorption rate of the base material is high. A drying method characterized by comprising the steps of preheating the coated film in a drying oven, followed by main heating.

[0032] and

[0033] In the process of applying a coating to the object to be coated, the surface of the base material is coated using infrared rays in a region that has a high infrared transmittance to the coating film of the paint applied to the surface of the base material and a high absorption rate of the base material. A drying method characterized by comprising the steps of preheating in a drying oven to dry the coating film formed on the coating, then further applying the coating to the object to be coated, and then main heating.

[0034] and

[0035] In the step of applying a coating to the object to be coated, the surface of the base material is coated using infrared rays in a region where the infrared transmittance of the paint applied to the surface of the base material is high and the absorption rate of the base material is high. The process of preheating in a drying oven to dry the coating film formed on the surface of the base material, and then the process of applying the coating to the object to be coated. Using infrared light in the high rate area,
A drying method comprising the steps of preheating the coating film formed on the surface of the base material in a drying oven, followed by main heating.

[0036] is provided.

[0037]

[Operation] In the painting process, paint is applied to the surface of the object to be painted. Next, in a preheating step, the surface of the object to be coated is irradiated with infrared rays in a region where the infrared transmittance of the coating film of the paint applied to the surface of the base material is high and the absorption rate of the base material is high. Then, the infrared rays that have passed through the coating film are absorbed by the base material on which the coating film is formed, and the surface of the base material is heated. By heating the base material, the coating film is heated from the base material side and the solvent contained in the paint is evaporated. Next, further heating is applied in the main heating furnace. Heating in this heating furnace is done from the surface side of the coating film, but since the solvent in the coating film is released from the base material side during the preheating process, even if the coating surface begins to solidify, the solvent in the coating film is No foaming occurs due to further divergence.

[0038] A step of further applying coating to the object to be coated after preheating, a step of applying main heating, or a step of further applying coating to the object to be coated after preheating, and a step of applying coating to the object to be coated on the surface of the base material. A case consisting of a step of preheating in a drying oven to dry the coating film formed on the surface of the base material using infrared rays in a region with high infrared transmittance and high absorption rate of the base material, and then a step of performing main heating. Even if additional coatings are applied after the first coating, the infrared rays that have passed through the coating film during the preheating process are absorbed by the base material on which the coating film is formed, and the base material surface is heated. The paint film is heated from the base material side and the solvent contained in the paint is evaporated and then applied and dried, so even if it is applied thickly, the paint film will not sag.

Furthermore, in the step of further coating the object to be coated after preheating, using infrared rays in a region where the infrared transmittance of the paint film applied to the surface of the base material is high and the absorption rate of the base material is high. If the process consists of a step of preheating the coating film formed on the surface of the base material in a drying oven, and then a step of main heating, the coating film formed on the surface of the base material will be absorbed by the additional preheating. The surface of the base material is heated, and the coating film is heated from the base material side by heating the base material, and the solvent contained in the paint is evaporated.The paint film is applied from above and dried, so even if it is coated thickly, it will not be possible to coat it further. Does not cause sagging on the film.

[0040]

[Example] When a metal plate is used as the base material on which the coating film is formed, the metal plate may be iron, aluminum, copper, brass, gold, beryllium, molybdenum, nickel, lead,
It consists of rhodium, silver, tankel, antimony, cadmium, chromium, iridium, cobalt, magnesium, tungsten and other metals, with copper, aluminum and iron being particularly preferred. As the paint forming the coating film applied to the metal surface, acrylic resin paint, urethane resin paint, epoxy resin paint, melamine resin paint, and other paints can be used. The coating film is a so-called powder coating film (
A coating film obtained by melting polyester-based, epoxy-based, acrylic-based, etc.) may also be used.

Tables 1 to 4 show the reflectance of each metal at each wavelength (AMERICAN INSTITUTE
OF PHYSICS HANDBOOK, American Institute of Physics Handbook 6-120). The higher the reflectance, the lower the absorption, and the lower the reflectance, the higher the absorption.

FIG. 1 is an infrared absorption curve of a butylated urea-butylated melamine resin. Figure 2 shows bisphenol A
This is an infrared absorption curve of type epoxy resin. Figure 3 shows the MMA
This is an infrared absorption curve of homopolymer (acrylic). FIG. 4 is an EMA homopolymer (acrylic) infrared absorption curve. FIG. 5 is an infrared absorption curve of unsaturated polyester resin. FIG. 6 shows the characteristic curve of the near-infrared lamp used in this example and the characteristic curve of the far-infrared lamp used in the comparative example. The peak wavelength of a near-infrared lamp is 1.
4 μm, and the peak wavelength of the far infrared lamp is 3.5 μm.

[0043] As the metal plate, iron, aluminum, copper, brass, gold, beryllium, molybdenum, nickel, lead,
Metal plates made of rhodium, silver, tankel, antimony, cadmium, chromium, iridium, cobalt, magnesium, and tungsten are used, and acrylic resin paint, urethane resin paint, epoxy resin paint, and melamine resin paint are used as paints. If the wavelength peak is 2
An infrared lamp of 1.2 μm or less, preferably 1.2 μm to 1.5 μm.
It is preferable to use a so-called near-infrared lamp of 5 μm.

Example 1

Near-infrared lamp (output peak 1.4 μm)

Metal plate Bonded steel plate (plate thickness 1mm,
Dimensions: 100mm x 100mm)

Paint: Melamine resin (Amilac No. 1531, white, alkyd melamine resin paint, manufactured by Kansai Paint Co., Ltd., viscosity 20 sec, Iwata Cup NK-2 viscometer)

Comparative example 1

[0049] Far-infrared lamp (output peak 3.5 μm)

Metal plate Bonded steel plate (plate thickness 1 mm,
Dimensions: 100mm x 100mm)

Paint: Melamine resin (Amilac No1531, white, alkyd melamine resin paint, manufactured by Kansai Paint Co., Ltd., viscosity 20 sec, Iwata Cup NK-2 viscometer)

Example 2

[0053] Near-infrared lamp (output peak 1.4 μm)

Metal plate Bonded steel plate (plate thickness 1mm,
Dimensions: 100mm x 100mm)

Paint: Acrylic resin (Magicron No. 1531 manufactured by Kansai Paint Co., Ltd., white, acrylic/melamine/epoxy resin paint, viscosity 20 sec, Iwata Cup NK-2 viscometer)

Comparative example 2

[0057] Far-infrared lamp (output peak 3.5 μm)

Metal plate Bonded steel plate (plate thickness 1mm,
Dimensions: 100mm x 100mm)

Paint Acrylic resin (Magicron No. 1531 manufactured by Kansai Paint Co., Ltd., white, acrylic/melamine/epoxy resin paint, viscosity 20 sec, Iwata Cup NK-2 viscometer)

Example 1, Example 2, Comparative Example 1, Comparative Example 2
For each film thickness: 30 μm, 40 μm, 50 μm
The ambient temperature and irradiation time were 130°C x 12
min, 140°C x 10 min, 150°C x 8 min, 160°
Table 5 (Example 1), Table 6 (Comparative Example 1), Table 7 (Example 2) ), shown in Table 8 (Comparative Example 2).

The embodiments illustrated in FIGS. 7, 8, and 9 are based on the following findings. In other words, ``the paint film formed on the surface of the base material is dried using infrared rays in a region where the infrared transmittance of the paint film applied to the base material surface is high and the absorption rate of the base material is high. A unique method for drying paint films.A conventional simple circulation type air curtain is installed at the opening to the outside air of the furnace, and the paint film applied to the base material is dried in the furnace. It was found that many pinholes were generated.

Compared to conventional drying ovens such as hot air ovens, this method uses infrared rays in the region where the infrared transmittance of the coating film of the paint applied to the surface of the base material is high and the absorption rate of the base material is high. A method for drying a coating film formed on the surface of a material, characterized by drying the coating film formed on the surface of the material." Furnaces that use this method are highly efficient. Therefore, the heat radiation from the furnace opening is large, and the temperature of the air supplied to the air curtain is gradually raised. When sprayed on the material to be dried in advance, the hot air heats the surface of the coating film without heating it from the base material side, resulting in surface drying (surface hardening), a thin diaphragm is formed on the surface, and then the surface of the material is heated. When heated from the material side, the solvent inside the surface breaks through the already solidified diaphragm surface and evaporates. It is presumed that then, traces of foaming remain on the surface, causing pinholes. In other words, it has been found that outside the effective range of infrared irradiation, it is more effective not to allow the workpiece to be affected by the air heated by infrared irradiation.

In FIGS. 7, 8, and 9, 11 is a tunnel furnace, and W is a workpiece whose surface is coated with paint. The work W consists of a metal plate as a base material, and as a metal plate,
Consisting of iron, aluminum, copper, brass, gold, beryllium, molybdenum, nickel, lead, rhodium, silver, tankel, antimony, cadmium, chromium, iridium, cobalt, magnesium, and tungsten. On the base material of the work W, acrylic resin paint, urethane resin paint,
Epoxy resin paint and melamine resin paint are applied.

The tunnel furnace 11 has two openings, a workpiece loading port A and a workpiece loading port B. 12 is an infrared lamp. In this embodiment, the infrared lamp 12 is an infrared lamp with a peak wavelength of 2 μm or less, preferably 1 μm.
．． A so-called near-infrared lamp of 2 μm to 1.5 μm is used. Figures 1 to 6 and Tables 1 to 6 show the infrared rays in the region where the infrared transmittance of the coating film of the paint applied to the surface of the workpiece W is high and the absorption rate of the base material is high, depending on the base material and the type of paint. Select based on Table 8 and install it at the required location in the furnace. 13 is an air curtain. The air curtain 13 is the tunnel furnace 1
They are installed at the workpiece loading port A and the workpiece loading port B of No. 1, respectively. 14 is an air outlet of the air curtain, and 15 is an air inlet. 16 is a fan, 17 is an air outlet 14
, a circulation duct that connects the air intake port 15. 18
is a filter installed closer to the air outlet 14 than the fan 16 of the circulation duct 17. 21 is a cooling device. The fan 16 circulates the air so that the air taken in through the air intake port 15 is blown out from the air outlet 14.

22 and 23 are modustrol motors, 2
4 is a damper installed upstream of the fan 16 in the circulation duct 17 and operated by the Modustrol motor 22; 25 is a damper driven by the Modustrol motor 23; 26 is an exhaust fan; 27 is the air outlet 14.
A modustrol motor 22 installed in the
This is a temperature controller that controls the operation of 23. These constitute an air curtain and also constitute a cooling device 21.

In the embodiment shown in FIG. 8, the infrared lamp 12 is also installed at the air curtain 13 installation location. In FIG. 9, 31 is the effective irradiation range of the infrared lamp 12. In the effective irradiation range 31, the workpiece W is heated from the base material side using an infrared lamp to dry the coating film. 32 is an air blowing range. In this embodiment, there is a slight overlap between the effective irradiation range 31 and the air blowing range.

Next, the operation of the embodiment shown in FIGS. 7, 8, and 9 will be explained. Workpiece W coated with paint
are carried into the tunnel furnace 11 from the workpiece carrying entrance A. Then, air passes through the air curtain 13 and is blown at the air outlet 14, but the air supplied by the air curtain is cooled by the cooling device 21 and the temperature rise is suppressed, so that the air does not reach the surface of the workpiece W. Even if they come into contact, they will not act on the surface of the coating to form a coating. That is,
While using the air curtain, the temperature controller 27 detects that the temperature of the air outlet 14 is 110 degrees, for example, and the temperature inside the tunnel furnace 11 is 160 degrees.
If the set temperature of the air blown from 4 is 80 degrees, 30
Modustrol motor 22 to correct the temperature difference in degrees;
23 is activated. Note that in this state, the air intake port 15
So it is 130°C. Then, the modustrol motor 22 opens the damper 24 and introduces outside air into the circulation duct 17. The modustrol motor 23 is
The damper 25 is opened and the exhaust fan 26 is operated to exhaust the air inside the circulation duct 17 to the outside of the circulation duct 17. When the temperature controller 27 detects that the temperature of the air blown out from the air outlet 14 has fallen below the set temperature, each damper 24, 25 is held at its opening degree to maintain the temperature of the air curtain 13. .

Next, in the tunnel furnace 11, an infrared lamp 1 is applied to the surface of the base material of the workpiece W, which emits infrared rays in a region where the infrared transmittance is high for the coating film and the absorbance of the base material is high.
Irradiate 2. Then, the infrared rays that have passed through the coating film are absorbed by the base material on which the coating film is formed, and the surface of the base material is heated. Therefore, the coating film is heated and solidified from the back surface of the coating film, which is close to the surface of the base material. Since no surface coating film is formed by the air curtain 13, even if the solvent in the coating film evaporates, the solidified coating film surface will not be broken and pinholes will not be formed.

As shown in FIG. 8, the air curtain 1
If the infrared lamp 12 that irradiates infrared rays in a region where the infrared transmittance to the coating film of the paint applied to the surface of the base material is high and the absorption rate of the base material is high is installed at the installation location of 3, the air curtain 13 At the installation location, the surface of the base material on which the coating film is formed is irradiated with infrared rays in a region where the infrared transmittance is high for the coating film and the absorption rate of the base material is high. Then, the infrared rays that have passed through the coating film are absorbed by the base material on which the coating film is formed, and the surface of the base material is heated. Therefore, the coating film is heated and solidified from the back surface of the coating film close to the surface of the base material, and the coating film is dried from the position where the air curtain 13 is installed.

Table 9 shows the example illustrated in FIG.
The figure shows the state of pinhole occurrence in the coating film at different air curtain wind speeds and temperatures in a comparative example using an air curtain without a cooling device. In order to prevent the occurrence of pinholes, it is desirable to maintain the temperature at approximately 80°C or less.

Setting conditions

0072 Paint Melamine resin

Object to be painted Bonded steel plate 1.2t

0074: Coating film thickness: 30 microns

[0075] Indoor temperature 30°C

Furnace temperature: 160°C

Air curtain height (air outlet to air intake) 2m

0078 Air curtain wind speed

When the air speed is 10 m/s at the air outlet, the air intake speed is 4 m/s. When the air speed is 7 m/s at the air outlet, the air intake speed is 2.8 m/s. When the air speed is 4 m/s at the air outlet, the air intake speed is 4 m/s. At the mouth, it was 1.2 m/s.

Next, the embodiments shown in FIGS. 10, 11, and 12 will be described. 51 is the first painting booth, 5
4 is the second painting booth. 1st painting booth 51, 2nd
In the painting booth 54, steel,
For example, a work W made of aluminum, copper, brass, gold, beryllium, molybdenum, nickel, lead, rhodium, silver, tankel, antimony, cadmium, chromium, iridium, cobalt, magnesium, tungsten, etc. has a thickness of 30 μm. A coating film made of acrylic resin paint, urethane resin paint, epoxy resin paint, or melamine resin paint is formed on the material. Figure 1
In the embodiment illustrated at 0, the paint booth consists of only a first paint booth. The second coating booth 54 has the same structure as the first coating booth 51, and further forms a coating film with a thickness of, for example, 30 μm on the workpiece W that has been dried in the preheating furnace 52, thereby applying so-called thick coating.

52 is a preheating furnace. Preheating furnace 52
consists of a tunnel furnace or a mountain-shaped furnace, and in this embodiment, the infrared lamp 12 uses an infrared lamp with a peak wavelength of 2 μm or less, preferably a so-called near-infrared lamp with a peak wavelength of 1.2 μm to 1.5 μm. Furthermore, a preheating furnace 52
The furnace shown in FIGS. 7 and 8 may be used. Figures 1 to 6 and Tables 1 to 6 show the infrared rays in the region where the infrared transmittance of the coating film of the paint applied to the surface of the workpiece W is high and the absorption rate of the base material is high, depending on the base material and the type of paint. Select based on Table 8 and install it at the required location in the furnace. In the embodiment shown in FIG. 10, the preliminary heating furnace 52 maintains the ambient temperature at 140 to 160°C, heats the workpiece W for 3 to 4 minutes, and raises the object temperature of the workpiece W to 40 to 60°C. °C. In the embodiment illustrated in FIGS. 11 and 12,
Heat is applied to the workpiece W for 2 to 3 minutes to bring the temperature of the workpiece W to 50 to 70°C. The preheating furnace 52 has a
, an air curtain 13 as shown in FIG. 8 may be installed.

53 is the main heating furnace. Figure 10, Figure 11
In the embodiment shown in FIG. 12, a conventional hot blast furnace, a tunnel furnace, a far-infrared furnace, or a mountain-shaped furnace is used. Furthermore, the furnace illustrated in FIGS. 7 and 8 may be used as the present heating furnace. In the embodiment illustrated in FIG. 10, the heating furnace 53 heats the workpiece W for 20 to 30 minutes while maintaining the atmosphere at 130 to 150°C. In the embodiment shown in FIGS. 11 and 12, the ambient temperature is maintained at 200 to 220° C., and the workpiece W is heated for 30 to 50 minutes.

Next, the operation of the embodiment will be explained. Figure 1
0, as shown in FIGS. 11 and 12, a paint is applied to the surface of a workpiece W, which is an object to be painted, in a first painting booth 51, which is a painting process. Next, in a preheating furnace 52, which is a preheating step, the surface of the workpiece W is irradiated with infrared rays in a region where the infrared transmittance of the paint film applied to the base material surface is high and the base material has a high absorption rate. Then, the infrared rays that have passed through the coating film are absorbed by the base material on which the coating film is formed, and the surface of the base material is heated. By heating the base material, the coating film is heated from the base material side and the solvent contained in the paint is evaporated. Next, further heating is applied in the main heating furnace 53. Heating in the main heating furnace 53 is carried out from the surface side of the coating film, but since the solvent in the coating film is released from the base metal side in the preheating process, even if the surface of the coating film begins to solidify, the solvent in the coating film is heated. Foaming due to further divergence does not occur.

As shown in FIG. 11, in the first painting booth 51, which is the painting process, paint is applied to the surface of the workpiece W, which is the object to be painted, and then, after preheating, the workpiece W is further painted. step, then a step of main heating in the main heating furnace 53, or a step of preheating in the preheating furnace 52 and then applying secondary coating to the workpiece W in the second coating booth, as shown in FIG. 2 in a preheating furnace 52 that dries the coating film formed on the surface of the base material using infrared rays in a region where the infrared transmittance of the paint film applied to the material surface is high and the absorption rate of the base material is high. If the process consists of a second preheating process and then a main heating process, even if a second coat is applied after the first coat, the infrared rays that have passed through the coating film during the preheating process will not cause a coating film to form on the surface. It is absorbed by the base material and heats the surface of the base material, and the heating of the base material heats the paint film from the base material side and evaporates the solvent contained in the paint.As it is applied from above and dried, it is not coated thickly. No sagging occurs on the paint film.

Furthermore, as shown in FIG. 12, in the first coating booth 51, which is a coating process, paint is applied to the surface of the workpiece W, which is the object to be painted, and after preheating in the preheating furnace 52, the object to be painted is further heated. The process of applying secondary coating to the surface of the base material, a coating film formed on the surface of the base material using infrared rays in the region where the infrared transmittance of the paint applied to the surface of the base material is high and the absorption rate of the base material is high. If the process consists of a step of performing secondary preheating in a preheating furnace for drying, and then a step of performing main heating in the main heating furnace 53, the second preheating process further absorbs into the base material on which a coating film has been formed on the surface. The surface of the base material is heated, and the coating film is heated from the base material side by heating the base material and the solvent contained in the paint is evaporated.
Even when applied thickly, the coating film does not sag. Since the solvent evaporates further, it becomes possible to further increase the temperature of the hot air oven and shorten the drying time.

FIGS. 13 and 14 are center sectional views of each embodiment in which preheating and main heating are performed in the same furnace, and the preheating is performed near the workpiece entrance A of the same furnace. 13 relates to a mountain-shaped furnace 61, and FIG. 14 relates to a tunnel furnace 62. Both furnaces perform main heating using hot air as a whole, but Figure 1
In the mountain-shaped furnace 61 shown in FIG. 3, an infrared lamp 12 is installed in the elevation part 63 continuous to the workpiece loading port A, and in the tunnel furnace shown in FIG. do. And infrared lamp 12
or by using the action of the infrared lamp 12 in combination with hot air. When hot air is used in combination, the preheating time can be shortened. Furthermore, preheating is applied to the effective irradiation range of the infrared lamps using multiple infrared lamps that emit infrared rays in areas where the infrared transmittance of the paint film applied to the surface of the base material is high and the absorption rate of the base material is high. Consists of hot air.

Therefore, the surface of the object to be coated is irradiated with infrared rays in a region where the infrared transmittance of the coating film of the paint applied to the surface of the base material is high and the absorption rate of the base material is high.
Hot air is blown into the effective range of infrared radiation. Then, in the irradiation range of the infrared rays, the temperature is maintained at a certain level or higher by the hot air, and the infrared rays pass through the coating film and are heated from between the base material and the coating film. The hot air blowing point on the surface of the object to be coated is not only irradiated with hot air but also infrared rays in the region where the infrared transmittance of the paint film applied to the surface of the base material is high and the base material has a high absorption rate. Therefore, preheating can be performed without pinholes or bubbles occurring when the solvent evaporates and evaporates as the coating surface dries.

Next, in the mountain-shaped furnace 61 shown in FIG. 13, main heating is performed using hot air at the center of the furnace, and in the tunnel furnace 62 shown in FIG. 14, main heating is performed using hot air after the center.

Next, an example in which preheating and main heating using a hot air oven are performed after coating, and a comparative example where drying is performed directly after coating using a hot air oven will be shown.

Example 3

[0091] In the painting booth, a bonded steel plate (plate thickness 1 mm,
30 μm of acrylic paint (Acrylite 100 manufactured by Chiyoda Paint Co., Ltd.) was applied to a surface (size: 100 mm x 100 mm). Next, a near-infrared lamp with an output peak of 1.4 μm is introduced into a tunnel furnace. The ambient temperature is 1
The temperature of the workpiece was 50°C, the passage time in the furnace was 3 minutes and 30 seconds, and the temperature of the workpiece was 50°C. Then, the ambient temperature is 140°
It was placed in a hot air oven of C for 25 minutes.

The obtained workpiece had a pencil hardness of 2H, a density of 100/100, and no foaming or swelling was observed.

Comparative example 3

[0094] In the painting booth, bonded steel plate (plate thickness 1 mm,
30 μm of acrylic paint (Acrylite 100 manufactured by Chiyoda Paint Co., Ltd.) was applied to a surface (size: 100 mm x 100 mm). Then, it was placed in a hot air oven at an ambient temperature of 140°C for 25 minutes.
Installed for minutes.

[0095] The obtained workpiece has a pencil hardness of H, a density of 100/100, and foaming and blistering of 20 pieces/100c.
It was m2.

Next, an example will be shown in which after painting, preliminary heating, secondary painting, and main heating with a hot air oven are performed, and a comparative example where after the primary painting, the secondary coating is directly dried in a hot air oven.

Example 4

[0098] In the painting booth, bonded steel plate (plate thickness 1 mm,
30 μm of acrylic paint (Acrylite 100 manufactured by Chiyoda Paint Co., Ltd.) was applied to a surface (size: 100 mm x 100 mm). Next, a near-infrared lamp with an output peak of 1.4 μm is introduced into a tunnel furnace. The ambient temperature is 1
The temperature of the workpiece was 50°C, the passage time in the furnace was 2 minutes and 30 seconds, and the temperature of the workpiece was 60°C. Next, apply 30μ of acrylic paint (Acrylite 100 manufactured by Chiyoda Paint Co., Ltd.) again.
Apply. Then, it was placed in a hot air oven at an ambient temperature of 210°C for 40 minutes.

[0099] Sagging and foaming of the coating film was hardly observed, and accounted for less than 1% of the produced workpiece.

Comparative Example 4

[0101] In the painting booth, bonded steel plate (plate thickness 1mm,
30 μm of acrylic paint (Acrylite 100 manufactured by Chiyoda Paint Co., Ltd.) was applied to a surface (size: 100 mm x 100 mm). Then, 30μ of acrylic paint (Acrylite 100 manufactured by Chiyoda Paint Co., Ltd.) was applied again. Then,
It was placed in a hot air oven at an ambient temperature of 210°C for 40 minutes.

Approximately 10% of the manufactured workpieces required product cleaning due to the occurrence of sag and foaming.

Therefore, in these Examples, the adhesion of the coating film is improved, which is presumed to be because the solvent evaporation and the crosslinking reaction take place immediately in the preheating furnace. In addition, the fluidity between the coating film and the metal surface is increased, and this is presumed to be due to good secondary leveling during the crosslinking reaction, and the coating film becomes smooth and the visual gloss of the surface improves.

[0104]

[Effects of the Invention] Therefore, in this invention, even if the solvent in the coating film evaporates, the surface of the solidified coating film will not be broken and pinholes will not be formed.

[Brief explanation of drawings]

[Figure 1] Infrared absorption curve diagram of each resin

[Figure 2] Infrared absorption curve diagram of each resin

[Figure 3] Infrared absorption curve diagram of each resin

[Figure 4] Infrared absorption curve diagram of each resin

[Figure 5] Infrared absorption curve diagram of each resin

[Figure 6] Characteristic curve diagram of infrared lamp

[Fig. 7] A central sectional view of an embodiment of the present invention.

[Fig. 8] Central sectional view of an embodiment of the invention

[Figure 9] Partially enlarged view of Figure 7

FIG. 10 is a schematic diagram of an embodiment of the present invention.

FIG. 11: Schematic diagram of an embodiment of the invention

FIG. 12: Schematic diagram of an embodiment of the invention.

FIG. 13 is a central sectional view of another embodiment of the invention.

[Figure 14
] Central sectional view of another embodiment of this invention

[Table 1] Reflectance of metal at each wavelength

[Table 2] Reflectance of metal at each wavelength

[Table 3] Reflectance of metal at each wavelength

[Table 4] Reflectance of metal at each wavelength

[Table 5] Number of pinholes in Example 1

[Table 6] Number of pinholes in Comparative Example 1

[Table 7] Number of pinholes in Example 2

[Table 8] Number of pinholes in Comparative Example 2

[Table 9] Pinhole occurrence state in the coating film at different air curtain wind speeds and temperatures in Examples and Comparative Examples using air curtains without a cooling device

[Explanation of symbols]

51 1st painting booth 52 Preheating furnace 53 Main heating furnace 54 Second painting booth

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[Table 5]

[Table 6]

[Table 7]

[Table 8]

[Table 9]

Claims (3)

[Claims] [Claim 1] A step of applying a coating to an object to be coated;
Preheating in a drying oven to dry the paint film formed on the surface of the base material using infrared rays in the region where the infrared transmittance of the paint film applied to the surface of the base material is high and the absorption rate of the base material is high. A drying method characterized by comprising a step of heating, followed by a step of performing main heating. [Claim 2] A step of applying a coating to an object to be coated;
Preheating in a drying oven to dry the paint film formed on the surface of the base material using infrared rays in the region where the infrared transmittance of the paint film applied to the surface of the base material is high and the absorption rate of the base material is high. A drying method comprising the following steps: a step of coating the object to be coated, and then a step of main heating. [Claim 3] A step of applying a coating to an object to be coated;
Preheating in a drying oven to dry the paint film formed on the surface of the base material using infrared rays in the region where the infrared transmittance of the paint film applied to the surface of the base material is high and the absorption rate of the base material is high. The process of coating the object to be coated uses infrared rays in the region where the infrared transmittance of the coating film of the paint applied to the surface of the base material is high and the absorption rate of the base material is high. A drying method comprising the steps of preheating the coating film formed in a drying oven in a drying oven, and then performing main heating.