JPH0688621A - Heat resistant coating material and oven range door using it - Google Patents

Abstract

PURPOSE:To ensure a heat resistant coating material capable of preventing a part from clogging by dispersing in an organic solvent a material taking as chief components silicon resin with a weight average molecular weight of a specific number are lower, fluorine resin powder with a particle diameter of a specific value or less, and mica powder with a maximum particle diameter of a specific value or less. CONSTITUTION:A heat resistant coating material is ensured, which is yielded by dispersing in an organic solvent a material taking as chief components 30-70wt.% silicon resin with a weight-average molecular weight of 300,000 or less, 5-15wt.% fluororesin powder with a particle diameter of 20mum or less, 10-40wt.% black pigment, and mica powder 5-40wt.% with a maximum particle diameter of 20mum or less and with an average thickness of 1mum or less. The heat resistant coating material is applied on a surface having fine holes for prevention of electric radiation leakage from a window 16 in a door 14 of a heating chamber 12 as a curing film by 50-70mum, and is heated and cured at 250-400 deg.C to obtain a mirror surface brightness of 60 degree with the arrangement, the coating material has satisfactory fluidity and hence does not cause any clogging to result in its performance excellent in corrosion resistance and heat resistant crack property.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant coating material used for coating a screen having a large number of pores, and a microwave oven door using the screen coated with the heat-resistant coating material.

[0002]

2. Description of the Related Art FIG. 1 is an external perspective view of an oven microwave oven 11. Reference numeral 12 is a heating chamber, 13 is an opening of the heating chamber, 14 is an openable / closable door, 15 is an operation panel, and 16 is a heating chamber 12 so that the cooked state can be visually observed from the outside while cooking an object to be cooked. It is a window provided for the purpose. The window 16 is usually provided with two heat-resistant glasses on the heating chamber 12 side and outside of the door 14, and a punching metal 17 is provided as a screen between the two heat-resistant glasses. The punching metal 17 prevents high frequency radio waves from leaking to the outside from the window 16 during high frequency heating. As shown in FIG. 2 (a), the plate thickness is 0.8 mm and is about 1.4 mm.
A large number of φ holes are opened. Punching metal corrodes during use, and when it is damaged and a large hole is opened, radio waves leak and seriously affect the human body. In order to prevent this, the punching metal base material has been subjected to enamel processing and coating mainly composed of acrylic resin, epoxy resin, phenol resin, polyester resin and silicone resin.

[0003]

However, in the above configuration, it is difficult to see the state of the object being heated from the outside. There is a method of increasing the output of a lamp that irradiates the heating chamber in order to make the inside visible from the outside, and by adopting this method, it became easier to see. However, the holes for punching and the non-transparent portions of the holes cast shadows and the object to be heated could not be clearly seen. If the hole diameter is increased, the width of the light non-transmissive portion between the holes is increased due to a manufacturing technology problem, and the above phenomenon is promoted. Therefore, a method is conceivable in which the hole diameter is reduced and the width of the light non-transmissive portion between the holes is reduced. Aperture ratio (area of light transmitting part per unit area) using punching metal as the screen
Fig. 2 shows the current manufacturable values for punching metal 17 when the hole diameter is as large as possible and the hole diameter is as small as possible.
The hole diameter shown in (b) is 0.7 mm, and the plate thickness at this time is 0.2 mm.
Is. By using the punching metal 17 having a large number of holes having a hole diameter of 0.7 mm, the object to be heated inside the heating chamber 12 can be seen considerably better than the outside. In order to use the punching metal 17 having a hole diameter of 0.7 mm, it is necessary to treat the surface of the punching metal base material with anti-corrosion treatment as described above. The above-mentioned enamel processing as this anti-corrosion treatment has a problem that the punch holes are clogged because of the large particle size. Also,
Since the surface temperature of acrylic resin, epoxy resin, phenol resin, and polyester resin paints rises, fogging of the door glass occurs due to the generation of decomposed gas and water vapor of the resin, and the effect of viscosity and surface tension affects the appearance of the glass during coating. There are things that get stuck. On the other hand, the silicone resin paint has a low hardness, so that the film is easily scratched when the door is opened and closed, and punched holes may be clogged with the one having a high weight average molecular weight.

The present invention is to solve the above-mentioned problems.
The purpose of is to provide a heat-resistant coating material which has heat resistance, corrosion resistance and impact resistance, and does not cause clogging even when coated, and the second purpose is to provide pores coated with the coating composition. It is to provide a highly reliable microwave oven where the inside can be clearly seen by using the punching metal for shielding the radio wave.

[0005]

In order to solve the first object of the present invention, 30 to 70 wt% of a silicone resin having a weight average molecular weight of 300,000 or less and 5 to 15 wt% of a fluororesin powder having a particle diameter of 20 μm or less, Black pigment 10-50w
A heat-resistant coating material was prepared by dispersing, in an organic solvent, t% and 5 to 40 wt% of mica powder having a maximum particle diameter of 20 μm or less and an average thickness of 1 μm or less.

Further, in order to achieve the second object, a screen having a large number of pores provided for preventing electric wave leakage from a window of a door attached to a heating chamber for heating an object to be heated is provided. The heat-resistant coating material described is used as a cured coating 5
It was applied so as to have a thickness of ˜70 μm, and was heated and cured at 250 to 400 ° C. to have a mirror gloss of 1 to 50 at 60 degrees.

[0007]

With the above construction, the heat-resistant coating material of the present invention has good flowability, so that it does not cause clogging even with a screen having pores, and the finished coating is not easily scratched, and has excellent corrosion resistance and heat crack resistance. Have performance.

Further, since it is finished to have a 60-degree specular gloss of 1 to 50, it is possible to provide a door in which the specular reflection of light is small and the inside can be easily seen.

[0009]

EXAMPLES Examples of the present invention will be described below.

Example 1 A heat-resistant coating material according to an example of the present invention is a silicone resin paint having the following composition.

Component Content (wt%) Silicone resin (* Note 1) 51.9 Fluororesin powder (* Note 2) 7.7 Black pigment (* Note 3) 15.4 Mica powder (* 4) 21.2 Additive (* 5) 3.8 * Note 1 ··· Weight average molecular weight 300,000 or less * Note 2 ··· Particle diameter 20 μm or less * Note 3 ··· Fe or Cu with particle diameter 20 μm or less Mn
Oxide * Note 4 ··· Average particle size 1μ with maximum particle size 20μm or less
* Note 5 ... Leveling agent: Modified silicone oil Dispersant: Fluorosurfactant Anti-settling agent: Bentonite Curing catalyst: Cobalt naphthenate A mixture of the above substances, xylene or alcohol, alone or mixed. Dissolve in solvent to make paint. Furthermore, dilution is performed with an organic solvent such as alcohol, ether, ketone, aromatic hydrocarbon or the like. In this case, the viscosity is Ford Cup N
o. It is desirable to adjust the electric resistance of the coating material to 8 to 12 seconds at 4 and to 5 to 50 MΩ / cm ² · cm by a Landsberg tester. This is coated on a screen made of punching metal by an electrostatic coating method. Since the coating agent uses a silicone resin having a fine particle diameter and a low surface tension and having a weight average molecular weight of 300,000 or less, it can be coated in a film thickness range of 5 to 70 μm without clogging the punch holes. Further, since the mica powder is scaly, cracks and peeling do not occur even after heating at a temperature of 280 ° C., and the heat crack resistance is excellent.

The silicone resin used in the present invention is 25
By heat-curing at a temperature of 0 ° C. to 400 ° C. for 10 to 30 minutes, there is no problem that decomposed gas or water vapor, which itself causes fogging of the glass surface, is generated by heat.

1 and 2 are cross-sections of a heat-resistant coating material and a coating film of a conventional semi-gloss paint, 1 is a base, 2 is a clear layer, 3 is a fluororesin powder, 4 is a color pigment and other It is a pigment. Since the heat-resistant coating material of the present invention exists in a state in which the fluororesin powder floats in the upper layer portion, even if the clear layer increases or decreases depending on the film thickness, there is little variation in gloss as normally seen in semi-gloss paints, and , Finishes with a film with small specular reflection. Moreover, since the fluororesin powder has a low coefficient of friction, the scratch resistance is improved, and the coating is less likely to be scratched. The gloss can be used in the range of 60 degree specular gloss 1 to 50,
It is desirable that the specular reflection is 20 or less, which is small. In addition, since a clear layer of silicone resin is present in the middle layer, penetration of corrosive substances (eg water, corrosive gas), which are usually found in semi-gloss paints, hardly occurs, resulting in excellent corrosion resistance.

Test Example Next, the present invention will be described in more detail based on a test example. The description of the test items in each table is shown in Table-11.

Test Example 1 Table 1 shows the results of evaluation of clogging of punch holes during coating with coating material resin, adhesion of coating material, and cloudiness of the glass portion.

At this time, 20 parts of mica powder, 15 parts of oxides of Fe, Cu and Mn as colorants, and 2 parts of anti-settling agent were mixed with 50 parts of resin, and a diluent was added to the mixture to adjust the viscosity of Ford Cup No. It was adjusted to 4 seconds for 12 seconds and applied to the punching metal using a general hand electrostatic coating gun. As conditions for heat curing, an electric oven was used for preliminary drying at 80 ° C. and then heating at 300 ° C. for 10 minutes.

[0017]

[Table 1]

<Evaluation of Test Results> From Table-1, the clogging of punch holes at the time of coating, the adhesion after heating at 280 ° C. and the cloudiness of glass are confirmed by silicone resins (9) and (11).
It can be seen that, while the ones used were good, those using other resins (50 parts in each case) were not good.

Test Example 2 Table 2 shows the evaluation results of the scratch resistance and heat crack resistance of the coating material raw material pigment. At this time, 50 parts of the silicone resin (9) of Test Example 1, 15 parts of the coating material raw material pigment, 15 parts of the black pigment, and 2 parts of the anti-settling agent were mixed, and a diluent was added thereto to adjust the viscosity to Ford Cup No. ． It was adjusted to 4 seconds for 12 seconds and applied to the substrate by using a general air slagan. The conditions for heat curing are the same as in Test Example 1. Also,
As the base material for this evaluation, a hot-dip aluminum-plated steel sheet (made by Ulster 40DD Nisshin Steel Co., Ltd.) was used.

[0020]

[Table 2]

<Evaluation of Test Results> From Table 2, it is found that fluororesin powder is a good anti-scratch material and mica powder is a good anti-heat cracking material.
It can be seen that the one using (part) is not good.

Test Example 3 Table 3 shows the results of examining the blending amounts of the fluororesin powder and the mica powder in Test Example 2 using the silicone resin (9) in Test Example 1. When the scratch resistance, heat crack resistance and corrosion resistance of the coating material composed of the non-volatile components shown in the formulation example were examined, the results shown in Table 4 were obtained. At this time, the coating conditions, the heat curing conditions and the substrate were the same as in Test Example 2.

[0023]

[Table 3]

[0024]

[Table 4]

<Evaluation of Test Results> From Table 4 (1), the compounding amount of the fluororesin powder is 5 to 15 w in the cured film.
It can be seen that, while t% is good, scratch resistance is poor at 3 wt% and hardness is poor at 20 wt%.

From Table 4 (2), the content of mica powder in the cured film is preferably 5 to 40 wt%, while
It can be seen that the heat crack resistance is poor at 3 wt% and the corrosion resistance is poor at 50 wt%.

Test Example 4 Table 5 shows the results of examining the particle size of the coating material. 50 parts of the silicone resin (9) in Test Example 1, 15 parts of mica powder having different maximum particle sizes, 20 parts of black pigment,
It is the result of evaluation under the same conditions as in Test Example 1 by mixing 2 parts of the anti-settling agent into a paint.

[0028]

[Table 5]

<Evaluation of Test Results> From Table 5, those using mica powder having a maximum particle size of 20 μm or less and an average thickness of 1 μm or less are good, while those having a maximum particle size of 30 μm or more have punch holes. You can see it gets stuck.

Test Example 5 Table 6 shows the results of examination on the visibility of the inside of the door after coating with the coating material. Silicone resin (9) in Test Example 1, fluororesin powder in Test Example 2, mica powder (2) in Test Example 4, black pigment and additives (leveling agent, dispersant, anti-settling agent) were used in the formulation examples. A comprehensive evaluation was performed on the coating material composed of the nonvolatile components shown in Table 7, and the results shown in Table 7 were obtained. At this time, the coating conditions, heat curing conditions and equipment were the same as in Test Example 1.

[0031]

[Table 6]

[0032]

[Table 7]

<Evaluation of Test Results> From Table 7, it is easy to see the ones having a 60-degree specular gloss of 1 to 50 because the specular reflection is small, whereas the ones having a 60-degree specular gloss of 70 have a large specular reflection. Therefore, it is difficult to see.

The silicone resin content in the cured coating is preferably 30 to 70% by weight, while
It can be seen that the corrosion resistance is not good at 20 wt% and the heat crack resistance is not good at 80 wt%.

Test Example 6 Table-8 shows the results of the examination of the blending amount of the black pigment and the film thickness of the coating material. Using the materials in Test Example 5,
When the coating material shown in the formulation example was evaluated under the same conditions as in Test Example 2, the results shown in Table 9 were obtained.

[0036]

[Table 8]

[0037]

[Table 9]

<Evaluation of Test Results> As shown in Table 9, the compounding amount of the black pigment is preferably 5 to 50% by weight in the cured coating, while 3% by weight gives an appearance of 60 w when coated with a thin film.
It can be seen that at t%, the corrosion resistance after heating is not good. Further, the coating thickness of the coating is preferably 5 to 70 μm, while the coating thickness of 3 μm is excellent in the appearance at the time of coating, heat crack resistance and corrosion resistance.
It can be seen that when 90 μm, the heat crack resistance after heating is not good.

Test Example 7 Table 10 shows the results of examining the heat curing conditions of the coating material using the formulation (3) of Test Example 6.

The sheath lure was coated under the conditions of Test Example 1, pre-dried at 80 ° C., and then heat-cured at a predetermined temperature to examine the adhesion, hardness, and haze of glass.

[0041]

[Table 10]

<Evaluation of Test Results> From Table-10, bake-hardening conditions of 250 ° C. to 400 ° C. for 20 minutes each are good, whereas at 200 ° C. or less, decomposition gas is generated after heating at 450 ° C. or more. Then, it can be seen that the adhesion is not good.

[0043]

[Table 11]

Example 2 The heat resistant coating material obtained in Example 1 was applied to a hot-dip aluminum plated steel sheet having a thickness of 0.7 mm as shown in FIG.
It was applied to punching metal for radio wave shielding having a large number of 7 mm holes. Then heated at 350 ℃ and cured film 20μm
A coating film of The specular gloss of this coating film was 20.

When the punching metal having the above coating film was used in an oven microwave oven, the inside of the heating chamber could be clearly seen because the gap between the holes was very narrow and the specular gloss was small.

As described above, when the coating composition of the present invention is used, a practical coating film can be obtained without clogging pores having a pore diameter of 0.7 mm. The same effect can be obtained even when this coating composition is used in a conventional punching metal having pores having a diameter of 1.4 mm or more. Further, in the embodiment of the present invention, the case where the punching metal is used as the screen has been described, but the same effect can be obtained even when the punching metal is used as the base material in which the pores are obtained by a method such as etching.

[0047]

As described above, according to the present invention, the following effects can be obtained. (1) When the coating composition of the present invention is used for a substrate having pores, a coating film having excellent heat resistance, corrosion resistance and impact resistance can be obtained without clogging. (2) When a punching metal having a large number of pores is coated with the coating composition of the present invention, a highly reliable coating film free from clogging can be obtained. Therefore, when this punching metal is used in an oven microwave oven, the inside can be clearly seen due to the large number of small holes and the low 60-degree specular gloss.

[Brief description of drawings]

FIG. 1A is a sectional view of a coating film made of a heat-resistant coating material of the present invention. FIG. 1B is a sectional view of a coating film made of a conventional semi-gloss paint.

FIG. 2 (a) is a sectional view of a coating film made of the heat-resistant coating material of the present invention. (B) is a sectional view of a coating film made of a conventional semi-gloss paint.

FIG. 3 is an external perspective view of an oven microwave oven.

FIG. 4A is a configuration diagram of a punching portion of punching metal having a hole diameter of 1.4 mm, and FIG. 4B is a configuration diagram of a punching portion of punching metal having a hole diameter of 0.7 mm.

[Explanation of symbols]

 2 Clear layer (silicone resin) 3 Fluororesin powder 4 Coloring pigment 11 Oven microwave oven 12 Heating chamber 14 Door 16 Window 17 Punching metal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazumasa Okita No. 1109, Shibaide, Kuramochi-cho, Nabari-shi, Mie Prefecture No. 7 at 1109, Okitsumo Co., Ltd. Okitsumo Co., Ltd.

Claims (2)

[Claims] 1. A silicone resin having a weight average molecular weight of 300,000 or less, 30 to 70 wt%, a fluororesin powder having a particle diameter of 20 μm or less, 5 to 15 wt%, and a color pigment, 10 to 50 wt%.
And a heat resistant coating material obtained by dispersing, in an organic solvent, 5 to 40 wt% of mica powder having a maximum particle size of 20 μm or less and an average thickness of 1 μm or less. 2. A heat-resistant coating material according to claim 1, which is cured on a screen having a large number of pores provided to prevent electric wave leakage from a window of a door attached to a heating chamber for heating an object to be heated. Coating to 5 to 70 μm
Heat-cured at 50-400 ℃, 60 degree specular gloss 1-5
A microwave oven door finished to 0.