JPH0531442A - Method for hardening aqueous alkali silicate-based inorganic coating material - Google Patents

Abstract

PURPOSE:To prevent cracking and film exfoliation and to improve resistance to water, chemicals, corrosion and contamination by specifying the relation between the thickness of a coating film and the temp. of a coated plate and the wavelength of IR having short wavelength for irradiation when the coating material is hardened in a hot stove, and by specifying the temp. of the coated plate at the time of the subsequent concluding hardening. CONSTITUTION:A plate is coated with a coating material and this coating material is hardened in a hot stove irradiation with IR having short wavelength of 0.7-3mum. This irradiation is carried out until the temp. of the coated plate attains to 100-180 deg.C in case of <25mum thickness of the resulting coating film and to 100-130'C in case of 25-45mum. Thereafter, hardening is carried out at 200-300 deg. temp. of the coated plate. Since a change in film thickness due to complex shape can easily be controlled by a wide range of work conditions, the coating film does not crack or exfoliate and performance peculiar to the coating material can be satisfactorily brought out. A coating film having especially excellent resistance to water, chemicals, corrosion and contamination is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to various metal products and ceramic products such as crows, ceramics, tiles and slate, which are free from cracks and film peeling, and have water resistance, chemical resistance, corrosion resistance and stain resistance. The present invention relates to a curing method for forming an excellent coating film.

[0002]

2. Description of the Related Art Water-based alkali silicate inorganic coatings have improved water resistance and chemical resistance as the silicate molar ratio increases, but at the same time cracks occur in the coating film. It is known that the adhesion between the material and the paint deteriorates. This is largely due to the setting temperature after coating, the setting time, the temperature rising rate during curing, the strength of the hot air in the curing oven, etc., so the curing conditions had to be set within an extremely narrow range. ..

A method of baking an aqueous inorganic coating (see Japanese Patent Application Laid-Open No. 3-30875) partially eliminates this drawback, but this method requires a setting time of 10 minutes.
Keep it within a minute, and keep the temperature of the coated plate at 15
Strict setting conditions such as keeping the temperature below 0 ° C. and increasing the temperature rising rate at 10 ° C./min or more, preferably 50 ° C./min or more are required. To satisfy all these conditions, the properties of the coated plate ( It is necessary to finely control the irradiation distance and the irradiation output according to the weight, size, material, etc.), and it is not easy to perform such control.

The object of the present invention is to provide a water-based alkali silicate-based inorganic coating material which does not require strict curing conditions, does not cause cracks and film peeling, and is excellent in water resistance, chemical resistance, corrosion resistance and stain resistance. Another object of the present invention is to provide a method for curing a water-based alkali silicate-based inorganic coating material for forming the above coating film.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to cure the above-mentioned problems when curing an aqueous alkaline silicate inorganic coating material, and as a result, have a wavelength of 0.7 to 3 μm. The inventors have found that the irradiation of infrared rays makes it possible to form a coating film of an excellent water-based alkali silicate-based inorganic coating under simpler operating conditions, and completed the present invention.

That is, according to the present invention, in a method of curing after coating a water-based alkaline silicate-based inorganic coating material, the coating plate temperature is 100 to 180 ° C. until the coating material is cured in a hot air oven if the coating film thickness is less than 25 μm. Until the film thickness reaches 25-4
At 5 μm, a short-wave infrared ray with a wavelength of 0.7 to 3 μm is irradiated until the temperature of the coated plate reaches 100 to 130 ° C., and then main curing is performed at the temperature of the coated plate of 200 to 300 ° C. The present invention provides a method for curing a silicate-based inorganic coating material.

The basic concept of the present invention will be described below.

The present inventors have considered that the presence of "hot air" is the most important factor in curing an aqueous alkaline silicate inorganic coating material. That is, when the coating film is dried and hardened in the presence of hot air, the gelation of the coating film surface proceeds much faster than that of the coating layer below that. Further, in the hot-air curing furnace, the heat conduction to the lower layer is even worse because the material is heated mainly by convection energy. On the other hand, since the volume contraction due to gelation of the alkali silicate is extremely large, a significant difference in volume contraction occurs between the coating layers.
When this difference becomes large, it progresses to fine cracks and further to large cracks. In addition, at the interface between the base material and the coating film, the respective silanol groups react to complete the adhesion, but due to the above reason, the upper layer is heated by hot air and convection without sufficient heat supply and gelation occurs. It is thought that this will lead to peeling of the coating as it progresses and shrinks.

Therefore, long-wavelength far-infrared irradiation works extremely effectively against evaporation of water and vaporization of reaction product water, but because of its good heating efficiency, the thicker the material, the more The temperature of the coating film rises in a short time, the temperature of the material is not kept up, and the upper layer gels and shrinks before the reaction between the coating material interface and the material proceeds, which hinders adhesion. If the setting is not done within 10 minutes, cracks and peeling will occur because the gelation of the surface is progressing during the setting, and highly efficient far-infrared irradiation accelerates there, causing a large volume shrinkage of the surface. Due to the occurrence of
If it is 0 minutes or more, cracking and peeling proceed, and a good coating film cannot be obtained. Further, since the efficiency is high, the temperature rising heating rate becomes too fast and the coating film swells unless fine control of the irradiation distance or the like is always performed with respect to changes in the shape (weight, size, material) of the coated plate. Due to this control, it is necessary to increase the furnace length and furnace width of the far infrared furnace, which is uneconomical, the work efficiency is reduced, and the installation area is large. I want to.

The short-wavelength near-infrared irradiation used in the present invention is inefficient as compared with far-infrared irradiation in terms of heating temperature of a coating film of a water-based alkali silicate-based inorganic coating, but excessively rapid temperature rise is caused. Since it does not occur, it progresses from the surface of the coating film to the interface of the substrate without causing a large difference in gelation degree, so that the coating film is formed without cracks or peeling. It proved to be a very suitable preheating method for paints. Moreover, it was found that the control range of the irradiation distance was wide and, as a result, the work could be performed without increasing the length and width of the irradiation furnace.

As described above, it has been found that the infrared irradiation is most suitable for the heating method that does not cause a remarkable difference in gelation degree from the surface layer of the coating film to the interface of the substrate, and especially from Experiment 1, silanol at the substrate and the interface is found. It was found that a good coating film free from cracks and peeling can be obtained if the reaction between the bases is allowed to proceed.

Experiment 1. Application of water-based alkaline silicate inorganic coating on heat-coated plate, hot air curing Material Degreased stainless steel SUS304 (0.4 x
70 × 150 mm) Coating Water-based alkaline silicate-based inorganic coating CRM-700S (Okuno Pharmaceutical Co., Ltd.) 20 μm (cured film thickness) Spray coating Curing 25-100 ° C. 20 minutes temperature increase 100-150 ° C. 10 minutes temperature increase 150-230 ℃ 12 minutes temperature increase 230 ℃ 20 minutes curing

[0013]

[Table 1]

Fine cracks: observed with a metallurgical microscope × 150 times Peeling off: visual observation In Experiment 2, the relationship between the infrared irradiation temperature rising rate and the swelling of the coating film was determined. The results are shown in Figure 1.

The materials and the coating film were formed under the same conditions as in Experiment 1. The cured film thickness was 45 μm.

In order to obtain a cured film thickness of 26 to 45 μm in short wavelength infrared irradiation (near infrared) and the subsequent hot air curing furnace, the temperature rising rate during infrared irradiation is about 30 ° C./minute. It is necessary to be below, and when the temperature is raised at a speed higher than that, swelling of the coating film occurs. Furthermore, the final temperature rise in the infrared is 100 to 1
It is necessary to set the temperature to 30 ° C, and below that, coating film cracks,
Above that, swelling of the coating film occurs.

On the other hand, when the cured film thickness is 25 μm or less,
The irradiation temperature rise is 100 ° C./min or less, and the final temperature rise is 100 to 1
By performing the heating up to 80 ° C., the finish is completed without cracks and swelling.

Even with far-infrared irradiation, it is not impossible to raise the temperature by 30 ° C./min. However, if the temperature is raised below 10 ° C./minute, cracks and peeling will occur, and the control of irradiation conditions will become strict.

At the coating site, as the coated object becomes more complicated in shape, it is more difficult to keep the cured film thickness constant at 25 μm or less. Therefore, if the irradiation control is strict, it is a work problem. I can't.

The wavelength range and emissivity of infrared irradiation used in the experiment are as shown in FIG.

In the present invention, as a first step, the coated plate after coating is irradiated with short-wave infrared rays (near red irradiation) to reach a predetermined temperature, and then, as a second step, the temperature is raised in a hot air curing oven. 2
It cures at 00 to 300 ° C.

The short-wave infrared rays (hereinafter, abbreviated as near infrared rays) used in the present invention is mainly composed of light having a wavelength of 0.7 to 3 μm. As a near infrared light source, tungsten, Filaments such as carbon and tantalum are used. The water-based alkaline silicate inorganic coating used in the present invention,
For example, CRM-700S and CRM-300S (above, Okuno Pharmaceutical Industry Co., Ltd. make) are mentioned.

When the coating thickness is less than 25 μm, the temperature of the coated plate reaches 100 to 180 ° C., preferably 120 to 120 ° C.
It is preferable to perform short-wave infrared irradiation until the temperature reaches 150 ° C. When the coating film thickness is 25 to 45 μm, the temperature of the coated plate reaches 100 to 130 ° C., preferably 100 to 130 ° C.
It is preferable to perform short-wave infrared irradiation until the temperature reaches 120 ° C. Further, when the coating film thickness is around 25 μm, it is preferable to irradiate short wavelength infrared rays until the temperature of the coated plate reaches 100 to 130 ° C.

The temperature at the time of main curing of the coating film after irradiation with near-infrared rays is in the range of 200 to 300 ° C, preferably 200 to 300 ° C.

[0025]

EFFECTS OF THE INVENTION The curing method of the present invention can sufficiently cope with changes in atmosphere and changes in temperature rising rate during the setting time after coating, one temperature, and further during the main curing thereof, and against changes in film thickness due to a complicated shape. However, since it can be easily controlled by its wide range of workability, there is no cracking or peeling of the coating film, and the performance that the paint originally has can be fully exploited, and water resistance, chemical resistance, corrosion resistance, and It is more preferable because a coating film having particularly excellent stain resistance is obtained, which leads to further improvement.

[0026]

EXAMPLES The present invention will be described in detail below with reference to examples.

Example 1. Alkaline degreased SUS30
4 (0.4 × 70 × 150 mm, weight 48 g) was coated with a water-based alkaline silicate inorganic coating CRM-700S (white) (manufactured by Okuno Chemical Industries Co., Ltd.) so that a cured film thickness was 40 μm. After setting under the condition of 1,
Using the same hot-air curing furnace as in Experiment-1, curing under the same temperature rising curing conditions (No. 1), far infrared irradiation in the wavelength range shown in Fig. 2 (No. 2), or near infrared irradiation (No. 3,
4, 5) and then No. It was hot-air cured in the same manner as 1 and each was subjected to the test. The results are shown in Table 2.

[0028]

[Table 2]

Cured coating film test: Presence of cracks; observation with a metallurgical microscope (× 150).

Oily black magic stain: Apply oily black magic on the surface of the coating film, and after 24 hours, wipe with water.

Boiling resistance: Observation of changes in coating film after immersion in boiling water for 10 hours.

Alkali resistance: 5% sodium hydroxide was observed at room temperature for 240 hours to observe changes in the coating film.

Acid resistance: 5% sulfuric acid, room temperature,
Observe the change in the coating after dipping for 240 hours.

Corrosion resistance: Cass test (JI
SH8681) Observation of coating film after 720 hours.

Test evaluation ◯: No change or abnormality in the coating film in each test.

X: Change in coating film in each test,
Something abnormal.

From the results shown in Table 2, those cured only with hot air (No. 1) were found to have cracks and peeling, and the original performance of the coating could not be brought out. Far-infrared irradiation (No. 2) shows swelling at the time of irradiation, and near-infrared irradiation can obtain a good coating film regardless of setting time and temperature, and bring out the original performance of the coating material. found.

Example 2. Example 1. Similarly to the above, the paint was replaced and a test was conducted according to the conditions of Table-2, and the results are shown in Table 3.

Material: SUS304 0.4 × 70 × 15
0 mm Weight 48 g Cured film thickness; 20 μm Paint; Water-based alkaline silicate inorganic paint CRM-300
S (Made by Okuno Pharmaceutical Co., Ltd.)

[0040]

[Table 3]

From the results of Table 3, regarding the setting time after coating, from the comparison of far-red irradiation (No. 6, 8) and near-red irradiation (No. 7, 9, 10), the former is within a certain range. I knew I had to.

Example 3. Example 1 except that the material was changed. The test was carried out under the same conditions as described above. The results are shown in Table 4.

Material: Cold rolled steel plate SPCC 2 × 50 ×
150 mm Weight 128 g Cured film thickness; 45 μm Paint; CRM-700S

[0044]

[Table 4]

From the results of Table 4, when the weight of the coated plate was 128 g and the temperature increase of far red and near red was compared at the same irradiation distance, as the weight increased, the temperature increase rate was clearly apparent in near red. Although there was a large difference (Nos. 13 and 14), it was found that a large difference did not occur with far-infrared rays. (No. 11,
12).

The temperature rising time in the case of far infrared irradiation is (30 to 1)
(20 ° C.) About 1 minute and the coating film swelled. With far-infrared irradiation, the temperature rise of the coating film is extremely fast due to the high efficiency, and it is considered that the water vaporized all at once bursts through the thick film and swells when released to the outside.

Example 4. Example 1 except that the paint and materials are changed. The test was carried out under the same conditions as described above.
The results are shown in Table 5.

Material: Alumite (6 μm) Aluminum JH4000 (1 × 70 × 150 mm) Weight 28
g Cured film thickness; 25 μm Paint; CRM-300S

[0049]

[Table 5]

From the results shown in Table 5, when the temperature reached at the time of temperature increase by far-infrared and near-red irradiation is less than 100 ° C., cracks and peeling occur in the coating film, and (No. 15 and 16) coating film thickness. 25
It was found that when the particle size is μm, the irradiation temperature reaches 180 ° C. without blistering. (No. 20, 21) Example 5. Example 4 except that the cured film thickness was 45 μm
The test was carried out under the same conditions as in. The results are shown in Table 6.

[0051]

[Table 6]

From the results shown in Table 6, when the cured film thickness was 45 μm and the temperature reached by the infrared irradiation was less than 130 ° C., the product was not swollen and finished (No. 22, 23).
It was found that swelling occurred at 0 ° C. (No. 2
4).

Example 6. Example 1 except that only the cured film thickness was 20 μm. The test was carried out under the same conditions as in. The results are shown in Table 7. The temperature of the coating plate for curing initiation is 28 ° C.

[0054]

[Table 7]

From the results in Table 7, the temperature rising rate in infrared irradiation and the presence or absence of cracks were examined. In far infrared irradiation, cracks were generated at a temperature increase of about 5 ° C./1 minute (No. Two
5), with near red irradiation, approximately 5 ° C / 1 minute and 2 ° C / 1
It was revealed that no crack was found even in minutes. (No. 26, 27).

[Brief description of drawings]

FIG. 1 shows the relationship between the temperature rising rate and the swelling of a paint film.

FIG. 2 shows the emissivity and wavelength of the heater used in the experiment.

Claims (1)

Claims: 1. After coating with a water-based alkali silicate inorganic coating,
In the curing method, when the coating film thickness is less than 25 μm, the temperature of the coated plate is 100 to 1 before the coating material is cured in a hot air oven.
When the coating film thickness is 25 to 45 μm until the temperature reaches 80 ° C., the wavelength is 0.7 to 100 ° C. until the temperature of the coated plate reaches 100 to 130 ° C.
Irradiate short wavelength infrared rays of 3μm, then 200 ~ 3
A method for curing an aqueous alkali silicate inorganic coating material, which comprises performing main curing at a temperature of a coated plate of 00 ° C.