JPH06226187A - Drying oven - Google Patents

Abstract

PURPOSE:To dry a one component urethane coating film efficiently by emitting near infrared rays with peaks of specified wavelength to a material to be dried obtained by coating a matrix composed of metal with a coating material provided with a block material near an inlet of a hot air oven. CONSTITUTION:A material 11 to be dried obtained by coating a metal surface with a coating material containing a block material is introduced from a feed line 33 into a hot air oven 31 for heating the material 11 to be dried by hot air. Near infrared rays having with peaks of wavelength in the vicinity of 1.2-1.5mum are emitted from an infrared ray generating device 21 disposed near an inlet of a heat effecting section 32. As the infrared ray transmittance for a thin film and absorptivity for metal of the near infrared rays are high, the metal surface is heated directly, and the film is heated by the metal surface to raise the interface temperature rapidly, break the block material and expose reactive groups. Then the material 11 is moved away from the emission zone of near infrared rays, and the reactive groups are successively reacted in progress by being dried by the hot air.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drying furnace, and more particularly, to a drying furnace in which the inside of the furnace is heated to a high temperature.

[0002]

2. Description of the Related Art So-called one-component urethane paints have been known as paints. With the same paint, temporarily about 16
It is said that it is necessary to destroy the block material by heating it to 0 ° C to expose the reactive group.

On the other hand, "near-infrared liquid, powder, coating, stove" (actual flat 1-151873), "light plate for paint baking oven" (real flat 2-43217), USP 4,863,375 "BA
KINGMETHOD FOR USE WITH LIQUID OR POWDER VARNISHIN
G FURNACE "(Baking Method for Youth
With liquid or powder varnishing
Furnace) and the like are known. In these conventional examples,
There is a description of "a kind of near-infrared liquid, powder, coating, stove baking method", "Using the fast high temperature and strong penetration characteristics of near-infrared rays, improving the method of baking products of stove, paint To quickly dry and enhance its adhesive force ", that is," the powder, powder paint, liquid paint, gas or fluid in the powder liquid state is adhered to the surface of the object as a transportation medium, just as the so-called liquid or powder liquid is coated. Then, the method of coating the coat evenly by heating and melting is described.

Alternatively, "drying oven using near infrared rays,
Or a drying method in which a high temperature part and a low temperature part are sequentially formed in a drying oven to dry, or a ceramic reflector is provided behind the near infrared lamp, and a heater is provided in the ceramic reflector. " There is a description of.

In addition, the October issue of the coating technology special issue has a description of "medium wavelength infrared radiator" (October 20, 1990, Riko Publishing Co., Ltd., pages 211-213). That is, "The radiant energy that reaches the coating film is partially absorbed, partially reflected, and partially transmitted. The absorbed energy is converted into heat to heat and dry the coating film. In the case of 1, since there is a base material and a body, the radiant energy transmitted through the coating film heats the base material, and the coating film is heated from the inside by heat conduction.

Near-infrared: Temperature 2000 to 2200 ° C. Maximum energy wavelength about 1.2 μm, large energy density, large reflected and transmitted energy, fast rising speed (1 to 2 seconds), and short life of about 5000 hours.

Mid-infrared: temperature 850-900 ° C, maximum energy wavelength about 2.5 μm, absorption in energy density. The transmitted energy is balanced, the energy penetrates into the coating film, and the life is long.

Far-infrared: temperature 500 to 600 ° C., maximum energy wavelength about 3.5 μm, energy density small, well absorbed, but tends to be absorbed and heated on the surface of the coating film, long rise time (5 to 15 minutes), convection The loss is large. It is said that.

Furthermore, in order to "2. Maximum efficiency medium-wave infrared rays" dry faster and obtain better coating quality ", that is, to heat and dry at maximum efficiency, the following two conditions are simultaneously satisfied. Need to be

Radiant energy with a high temperature of the infrared radiator is proportional to the fourth power of the absolute temperature (T) of the radiator.

Eb ∝ T ⁴

The higher the temperature, the greater the radiant energy.

The maximum energy wavelength is slightly shorter than the peak absorption of the paint

The maximum peak wavelength that can be used for industrial infrared heating of paint is around 3 μm without exception. Therefore, the infrared radiator, which has the maximum energy wavelength around 2.5 μm, is well absorbed and transmitted, and the base material can be heated and heated from the inside.

The above relation, the Vienna displacement law, which represents the relationship between the temperature (T) of the infrared radiator and the maximum energy wavelength (λm),

From λm = 2897 / T

T = (t + 273) = 2897 / 2.5

T = 880 ° C.

The medium-wavelength infrared ray satisfies this condition, has a large effective energy, and has maximum efficiency. It is said that.

[0020]

[Problems to be Solved by the Invention] However, in the actual Kaihei 1-151873, the actual Kaihei 2-43217, USP 4,863,375, etc.,
Although there is a description that the coating film is dried using near-infrared rays, the properties of the near-infrared rays used are generally described but the relationship between the coating film applied to the metal surface and the near-infrared rays There is no description about the optimum range and selection of infrared rays to be irradiated by.

In addition, in the above-mentioned "Painting Technology Special Issue October issue", the selection of infrared rays based on the relationship between infrared rays and the absorption rate of the base material, or the selection of infrared rays based on the cause of pinholes It is concluded that in coating drying, "the infrared radiator having the maximum energy wavelength around 2.5 μm has good absorption and transmission, and the base material can be heated from the inside as well."

On the other hand, in hot air drying in which hot air is blown onto a material to be dried using a conventional tunnel furnace or mountain furnace, the temperature is raised to the interface between the base material and the coating film because it is heated from the surface. Was difficult. Therefore, it takes a long time to raise the interface to the required temperature, and there is a problem that the furnace length becomes long.

Further, in order to raise the temperature in a short time, there is a problem that yellowing (burning) occurs when a high temperature is suddenly applied. In order to avoid yellowing, it was necessary to provide two hot-air stoves heated to a temperature higher than the temperature at which the block material was removed and a low-temperature hot-air stove having a temperature required to promote the reaction of the reaction group.

When the far infrared rays are used for heating, there is a problem that the heating efficiency is poor and it takes a long time to dry.

On the other hand, it is known that so-called near-infrared rays having a wavelength peak of 1.2 μm to 1.5 μm have a high infrared ray transmittance with respect to a plastic thin film and a high metal absorption rate.

[0026]

Means for Solving the Problems

Near infrared rays having a wavelength of 1.2 μm and 1.5 μm near the entrance of a hot-air stove for heating an object to be dried by hot air, a base material made of metal is coated with a coating material having a block material. A drying oven characterized by irradiating a dried product,

Is provided.

[0029]

The object to be dried, in which the coating material containing the block material is applied to the metal surface, is introduced into the hot air oven. Next, near-infrared rays are irradiated from above the coating film near the entrance. Near-infrared rays have a high infrared transmittance with respect to a thin film and a high metal absorptivity,
The metal surface is directly heated and the coating film is heated from the metal surface side, the temperature of the interface rises rapidly, the block material is destroyed, and the reactive group is exposed.

Next, the material to be dried is dried by hot air when it leaves the irradiation region of near-infrared rays, and the reactive groups sequentially proceed the reaction.

[0031]

Examples Metals used as the base material of the object W to be heated include iron, aluminum, copper, brass, gold, beryllium, molybdenum, nickel, lead, rhodium, silver, tanker, antimony, cadmium, chromium, iridium, It consists of cobalt, magnesium, tungsten and other metals, with copper, aluminum and iron being especially preferred.

7 to 10 show the reflectance of each metal at each wavelength (AMERICAN INSTITUTE OF PHYSICS HANDBOO).
K, American Institute of Physics Handbook 6-120). The higher the reflectance, the lower the absorptivity, and the lower the reflectance, the higher the absorptance.

FIG. 1 is an infrared absorption curve of a butylated urea-butylated melamine resin. Figure 2 shows bisphenol A
It is an infrared absorption curve of a type epoxy resin. Figure 3 shows MMA
It is an infrared absorption curve of a homopolymer (acrylic type). 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. Near infrared lamp has a peak wavelength of 1.4
The peak wavelength of the far infrared lamp is 3.5 μm.

As the base material of the material to be dried W, iron, aluminum, copper, brass, gold, beryllium, molybdenum, nickel, lead, rhodium, silver, tanker, antimony, cadmium, chromium, iridium, cobalt, magnesium, tungsten are selected. When using a one-part urethane coating containing a so-called block material as a coating, the infrared lamp with a wavelength peak of 3 μm or less and the mid-infrared lamp with a wavelength peak of 2.5 μ are also used. Effective, but preferably 1.2 μm to 1.5 μm
It is desirable to use a so-called near-infrared lamp having infrared rays having a high infrared transmittance with respect to the plastic thin film 12 and a high absorptivity of the metal 11.

In FIG. 11, reference numeral 21 is an infrared ray generator, which is an infrared lamp in this embodiment. Reference numeral 31 is a mountain furnace in which the infrared generator 21 is installed. The infrared mountain furnace 31 has a carry-in path 33 that is tilted to carry the object to be heated 21 into the furnace, a tilted carry-out path 34 that carries out the heated metal round pipe 11 to the outside of the furnace, and a carry-in path 33 and carry-out. The heating effective portion 32 is provided horizontally at a high position with respect to the passage 34. The infrared generator 11 has a heating effective portion 32.
Install near the entrance of. Gas outlet 13, gas inlet 14
Are installed on both side surfaces of the heating effective portion 32, or on the ceiling surface and the floor surface, respectively. Although the temperature of the heated atmosphere rises, since the heating effective portion 32 is located at the uppermost part of the furnace, heat does not escape to the other parts, and the inside of the heating effective portion 32 is thermally cut off from the outside to form an effective heating atmosphere. To do. Reference numeral 35 is a conveyor. In this embodiment, the drying furnace is a mountain furnace, but it may be a tunnel furnace.

Infrared lamp 21 which is an infrared generator
Is a metal of the object W to be heated, such as iron, aluminum, copper,
Brass, gold, beryllium, molybdenum, nickel,
When a metal plate made of lead, rhodium, silver, tantalum, antimony, cadmium, chromium, iridium, cobalt, magnesium, and tungsten is used and a one-component urethane resin coating film is used as a thin film, the wavelength peak is 3 μm. The following infrared lamps, preferably 1.2μm-1.5μ
Although it is composed of a so-called near-infrared lamp of m, a mid-infrared lamp having a wavelength peak of 2.5 μ is also effective. The distance from the surface of the infrared lamp 21 to the surface of the workpiece 11 to be heated, which is a workpiece, was set at about 250 to 300 mm. A plurality of infrared lamps 21 are installed horizontally. A bank including a plurality of infrared lamps 21 is installed on both sides of the heating target 11 in the conveying direction so as to face the inner surface of the mountain furnace 31 with the heating target 11 interposed therebetween. The mountain furnace 31 is hermetically sealed except for both entrances and exits. A is a work carry-in port, and B is a work carry-out port.

Reference numeral 23 is a gas discharge port, and 24 is a gas suction port. The heated gas is discharged from the gas discharge port 23 to the mountain furnace 31.
The inside of the mountain furnace is heated by discharging the gas inside and sucking it through the gas suction port 24 and circulating it.

Infrared irradiation and hot air blowing are performed simultaneously.

Then, the metal on which the urethane thin film is installed is carried into the mountain furnace 31. Then, near-infrared rays are irradiated from above the urethane thin film in the furnace. Near-infrared rays have a high infrared transmittance to the urethane thin film and a high metal absorption rate, so the metal surface is heated directly to heat the urethane coating film from the metal surface side, and the urethane coating film applied to the surface is heated. In the initial stage, the material is rapidly decreased from the interface side of the base material and is heated to about 160 ° C., so that the block material is destroyed and the reactive groups are exposed. Then, the reactive group is heated and reacted only by heating with hot air. Since the hot air temperature is lower than that of infrared heating, the reaction of the reactive groups proceeds and yellowing does not occur.

As the one-component polyurethane coating material, (skeleton resin) polyol (polyether diol, polyoxypropylene etc.) and diisocyanate (diphenylmethane diisocyanate, bis (4-isocyanate cyclohexyl) methane etc.), butanone as a blocking agent Oxime, dibutyl tin dilaurate as a urethane reaction catalyst, other, polyethyl methacrylate,
A paint containing a styrene acrylonitrile copolymer and acetyl butyl cellulose is known.

The blocking agent comes off at about 140 ° C. in a hot air oven.

Solvents for these one-component polyurethane paints include ethyl acetate as an ester-based solvent, MEK and cyclohexanone as a ketone-based solvent, tetrahydrofuran as an ether-based solvent, and white spirit, toluene, glycol ether acetate-based solvent as a hydrocarbon-based solvent. Butyl oxitol acetate is used as a mixture.

The material to be dried coated with these one-component polyurethane paints has a lead hardness of 4H when dried in a hot air oven heated to 160 ° C. for 20 minutes. 2 at 130 ° C
Hardness B is obtained by heating for 0 minutes. The same applies when heated at 130 ° C. for 30 minutes.

A so-called near infrared ray having a wavelength peak in the vicinity of 1.2 μm to 1.5 μm is irradiated for 10 seconds near the entrance of the hot air stove, and then heated in a hot air stove at 130 ° C. for 20 minutes to obtain a hardness of 4H. The same applies to irradiation for 20 seconds. However, when the irradiation time is less than 10 seconds, the hardness decreases. When the atmospheric temperature is 140 ° C., the drying time can be shortened.

When a near infrared ray was irradiated for 10 seconds in the middle of heating for 20 minutes in a hot air oven at 130 ° C., a hardness of 2H was obtained.

When a near infrared ray was irradiated for 10 seconds at the exit of heating for 20 minutes in the same hot air oven, hardness B was obtained.

When the coating film is dried in a hot air oven, if the coating material is changed from a urethane type to a melamine type, it is necessary to lower the heating temperature from 160 ° C to 140 ° C. Takes time. This is because the hardness temperature differs depending on the paint.

According to the present invention, by selecting the ON state and the OFF state of the infrared ray generator, it becomes possible to easily correspond to the coating film to be dried. Therefore, it becomes possible to continuously dry objects to be dried having different types of coating films.

[0049]

Therefore, the present invention efficiently
It is possible to dry the one-pack type urethane coating film.

[Brief description of drawings]

[Figure 1] Infrared absorption curve of each resin

[Figure 2] Infrared absorption curve of each resin

[Figure 3] Infrared absorption curve of each resin

[Figure 4] Infrared absorption curve of each resin

FIG. 5: Infrared absorption curve of each resin

FIG. 6 is a characteristic curve diagram of an infrared lamp.

FIG. 7: Reflectivity of metal at each wavelength

FIG. 8: Reflectivity of metal at each wavelength

FIG. 9: Reflectivity of metal at each wavelength

FIG. 10: Reflectivity of metal at each wavelength

FIG. 11 is a central cross-sectional view of a metal and plastic thin film heated in a mountain furnace.

[Explanation of symbols]

 21 Infrared generator 31 Hot stove

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[Procedure amendment]

[Submission date] August 12, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

Claims (1)

[Claims] 1. A coating material having a block material is applied to a base material made of metal with near-infrared rays having a wavelength of 1.2 μm to 1.5 μm near the entrance of a hot air oven for heating an object to be dried with hot air. A drying furnace for irradiating the dried material.