JP2003340361A - Method for drying coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for drying a coating film outstandingly shortening a drying time, generating no foam and not deteriorating an appearance of the coating film. <P>SOLUTION: In the method for drying a coating film including a coating process for coating a surface of an object to be coated with a water base coating; a setting process for allowing the object to be coated to stand at ordinary temperature; a pre-heat process for heating the coated substance until the temperature of the coated substance becomes 35-60°C; and a drying process for heating the coated substance until a nonvolatile content of the coating film becomes 97% or higher, the heating of the pre-heat process is carried out at a condition satisfying a relationship of equation I: ΔNV/Δt=2-5.5 (%/min) (wherein ΔNV represents a variation of unvolatile content in the pre-heat process and Δt represents a time of the pre-heat process). <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for drying a coating film, and more particularly to a method for drying a coating film coated with a normal-drying type or forced-drying type aqueous coating material.

[0002]

2. Description of the Related Art For coating industrial products having a large heat capacity, parts thereof such as engine blocks of automobiles, axles and the like, normally dry type or forced dry type water-based paints and solvent-based lacquer paints are usually used. For parts with large heat capacity,
This is because it is difficult to raise the temperature to a temperature sufficient to cure the thermosetting coating material within the time allowed in the manufacturing process and then cool it.

When coating is carried out with a normal-drying type or forced-drying type water-based paint, the coating film is in a liquid state immediately after the application, and the coated article cannot be handled. Therefore, it is necessary to leave or heat the coated parts for a certain period of time and wait for the coating film to dry before performing subsequent steps such as assembly. Since waiting time in the manufacturing process of the industrial product lowers the manufacturing efficiency of the product, it is preferable that the drying time of the coating film is as short as possible.

The waiting time for drying the coating film can be shortened by heating the coated article to a high temperature during the drying. However, when the drying temperature is raised, volatile components such as water are vaporized in the coating film, and a bubble-like film defect generally called "armpit" is likely to occur. On the other hand, when the drying temperature is low, no cracking occurs and the appearance of the coating film improves, but the drying time becomes long.

At present, in the coating process of industrial parts, as a harmony point between the appearance of the coating film and the drying time, a setting process of leaving at room temperature (3 to 5 minutes) and a drying process of heating in a drying furnace (about 25 minutes) , And a cooling process (2 to 5 minutes) of cooling to a temperature that can be handled by hand are combined to dry the coating film.
It takes 40 minutes.

[0006]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to drastically reduce the drying time of a coating film formed by a normal-drying type or forced-drying type aqueous coating material. It is an object of the present invention to provide a coating film drying method which can be shortened and which does not cause cracking and does not deteriorate the appearance of the coating film.

[0007]

SUMMARY OF THE INVENTION The present invention is a coating step of coating a surface of an article to be coated with a normally-drying type or forced-drying type aqueous coating material;
A setting step of leaving the coated object as it is at room temperature; a preheating step of heating the coated object until the temperature of the coated object reaches 35 to 60 ° C .; and a drying step of heating the coated object until the coating film nonvolatile content becomes 97% or more; In the method for drying a coating film including:

[0008]

[Equation 2] ΔNV / Δt = 2-5.5 (% / min) I

[Wherein ΔNV is the change in the nonvolatile content during the preheating step, and Δt is the time of the preheating step. The present invention provides a method for drying a coating film, which is carried out under the condition of satisfying the relationship [1].

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a technique for forming a coating film on the surface of an article to be coated with a water-based coating composition and then evaporating water so that the coated article can be handled in a short time. A normally-drying type or a forced-drying type water-based paint is used as the material. The water-based paint is mainly composed of components such as a binder resin, a pigment and water.

[0012] Specifically, the normal-drying type or forced-drying type water-based coating material is, specifically, an oxidative polymerization-type water-based coating material (“Aude Recycle F-1000” manufactured by Nippon Paint Co., Ltd.) which is polymerized by the action of oxygen in the air several days after coating and drying. , "Ode Recycle F-2000" manufactured by the same company).

As the article to be coated, an industrial product having a large heat capacity and a temperature that does not easily rise itself, a component for assembling the industrial product, for example, an engine block of an automobile, an axle and the like are used. This is because an object to be coated having a large heat capacity requires time for heating and cooling, and it is difficult to use the thermosetting coating material in the manufacturing process.

The normal dry type or forced dry type aqueous coating material may be applied to the article by a method well known to those skilled in the art. For example, a spray coating method, a dip coating method, a shower coat method and the like can be mentioned. The amount of coating is 15-
The amount is 50 μm, preferably 20 to 40 μm. If the coating amount is less than this range, the film formation will be incomplete and the appearance and quality of the coating film will be poor. When the coating amount is more than this range, the drying property is deteriorated, and cracking or sagging occurs and the appearance of the coating film becomes poor.

After the coating material is applied to the coating object, the coating material is set to be left at room temperature for a while. Without setting, the appearance of the coating film will be poor due to armpits and lack of leveling. The setting process takes less than 5 minutes,
It is preferably 3 minutes or less. This is because it is difficult to shorten the drying time if the setting time is 5 minutes or more.

After setting, the coated article is preheated. Preheating refers to preliminary heating of the coated article at a temperature lower than the ambient temperature used in the conventional drying process. The preheating can be performed by putting the coated object in a drying oven whose temperature is adjusted to a predetermined temperature. It may be performed using air blowing, hot air drying, or far infrared heating. Moreover, you may use these heating methods in combination.

The preheating step is carried out until the temperature of the coated article reaches a temperature 10 to 80 ° C., preferably 20 to 60 ° C. lower than the ambient temperature used in the drying step. For example, when the ambient temperature used in the drying step is 80 to 120 ° C,
The preheating process is performed until the temperature of the coated product reaches 35 to 60 ° C. If the temperature of the coated article at the end of the preheating step is lower than 35 ° C., the drying step causes cracking and the appearance of the coating film deteriorates. If this temperature exceeds 60 ° C., cracking occurs in the preheating step and the drying step, and the film thickness that makes the appearance good is reduced.

In the preheating step, it is necessary to carry out heating under conditions satisfying the relation of the formula I. If the value of the formula I is less than 2% / min, the shortening of the drying time becomes insufficient, and if it exceeds 6% / min, cracking occurs and the appearance of the coating film deteriorates.

The preheating step time is preferably 3 to 5 minutes. If this time is less than 3 minutes, cracking occurs and the appearance of the coating film deteriorates, and if it exceeds 5 minutes, the shortening of the drying time becomes insufficient.

After preheating, the coated article is subsequently dried by heating. This drying step is carried out until the volatile solvent (water) evaporates from the coating film to such an extent that the coated object can be handled. Usually, the heating may be terminated when the nonvolatile content of the coating film is about 97% by weight, preferably 98% by weight.

In the drying step, it is preferable to heat at a high temperature unless the object to be coated or the coating film deteriorates. This is because the drying time can be shortened. For example, when heating in an ambient temperature, that is, in a drying oven, the set temperature may be raised by 10 to 80 ° C., preferably 20 to 60 ° C. higher than in the preheating step, and heating may be continued. Further, in order to accelerate drying, air blowing or heating with medium to infrared rays may be used together.

In the method for drying a coating film according to the present invention, one example of changes in the nonvolatile content of the coating film is 65 to 80% by weight, preferably 70 to 80% 5 to 7 minutes after the start of heating after setting.
% By weight, 80 to 95% by weight after 8 to 10 minutes, 12 to
It is 97% by weight or more after 15 minutes.

An example of a drying condition satisfying the above-mentioned change in non-volatile content is a water-based paint having an initial non-volatile content of 50% by weight, and an SPCC of 0.8 cm × 10 cm × 30 cm as an object to be coated.
-Using SD steel plate, the coating amount is 30-35μ after drying
When setting m, set for 1 to 3 minutes, and 40 to
Preheat for 5 minutes in a drying oven set at 60 ° C, and
Further heat and dry for 10 minutes in a drying oven set to -100 ° C.

As a result, within 15 minutes, preferably 12 to
The non-volatile content of the coating film can be increased to 97% or more in a heating time of 15 minutes. On the other hand, during the heating step, the coating film is free from cracking and the appearance of the coating film is kept good.

After the heating step is completed, the coated article may be naturally cooled, but it may be forcibly cooled in order to cool it in the shortest possible time. Cooling is performed at a temperature at which the drying property does not substantially matter, for example, when the surface temperature of the coated product is 30 to 60 ° C.
Until. In order to shorten the cooling time, it is preferable to perform air blowing, cold air cooling, water cooling and the like. When water cooling is performed, it is preferable to spray mist-like water on the coated object. Then, the cooling process can be completed in 1 to 3 minutes.

Particularly, it is more effective to concentrate the cooling only on a part of the place where the drying property becomes a problem.

[0026]

As described above, according to the method of the present invention, it takes about 15 minutes from the application of the paint to the object to be dried and cooled so that the object can be handled. Compared with the required 30 minutes, it is greatly shortened. On the other hand,
The appearance of the coating film is good with no cracking in the coating film.

[0027]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Example 1 SPC of 0.8 cm × 10 cm × 30 cm as an object to be coated
A C-SD steel plate was prepared. "Aude Recycle F-2000TMS Black" (nonvolatile content: 50% by weight) manufactured by Nippon Paint Co., Ltd. was applied to one surface of this steel plate in an amount such that the film thickness after drying was 25 to 50 μm using a Wider 88 hand-blown cup gun. .

The coated article was set at room temperature for 1 minute.
The nonvolatile content of the coating film after the setting was 56% by weight. This coated article was placed in a drying oven whose temperature was adjusted to 40 ° C. and preheated for 5 minutes. The non-volatile content of the coating film after the completion of preheating was 69% by weight. ΔNV / Δt during the preheating process
Was calculated to be 2.6% / min.

After that, the temperature of the drying furnace was raised to 80 ° C. and set, and further heated for 10 minutes to complete the drying. The graph of FIG. 1 shows the change in the temperature (° C.) of the coated article with respect to the time (minutes) immediately after the application of the coating material. Further, the change in nonvolatile content (%) of the coating film with respect to the time (minutes) immediately after the coating of the coating material is shown in the graph of FIG. When observing the dried coating film surface,
No cracking occurred and the appearance of the coating film was good.

When drying was performed under these conditions, the armpit limit film thickness was 37 μm, and the appearance determination time immediately after coating was 9 minutes. The armpit limit film thickness is a film thickness at which armpits do not occur, and means a film thickness at which armpits are generated when the armpit limit film thickness is exceeded.

The armpit limit film thickness is determined by actually varying the film thickness of the coating film and drying the film to measure the limit value.

Example 2 The coating film was dried in the same manner as in Example 1 except that the heating conditions were changed as shown in Table 1 and a cooling step was further performed after the drying step. Cooling was performed by spraying a water mist and air blowing on the dried coating film for 2 minutes. After cooling
The temperature of the coated article was 40 ° C. The obtained results are shown in Table 1. Further, changes in the temperature (° C.) of the coating material and the nonvolatile content (%) of the coating film with respect to the time immediately after the coating of the coating material are shown in FIGS. 1 and 2, respectively.

Examples 3 and 4 The coating film was dried in the same manner as in Example 1 except that the heating conditions were changed as shown in Table 1. The results obtained are also shown in Table 1.
It was shown to. Further, changes in the temperature (° C.) of the coating material and the nonvolatile content (%) of the coating film with respect to the time immediately after the coating of the coating material are shown in FIGS. 1 and 2, respectively.

[0035]

[Table 1] In Table 1, the armpit property is × when the armpit limit film thickness is 20 μm or less, Δ when the armpit limit film thickness is 20 to 24 μm, and 25 μm.
When it was m or more, it was evaluated as ◯.

Comparative Examples 1 to 3 The coating film was dried in the same manner as in Example 1 except that the heating conditions were changed as shown in Table 2. The results obtained are also shown in Table 2.
It was shown to. Further, changes in the temperature (° C.) of the coating material and the nonvolatile content (%) of the coating film with respect to the time immediately after the coating of the coating material are shown in FIGS. 1 and 2, respectively.

[0037]

[Table 2]

[Brief description of drawings]

FIG. 1 is a graph showing changes in the temperature of a coated article with respect to time immediately after coating, for the coated articles of Examples and Comparative Examples.

FIG. 2 is a graph showing changes in the non-volatile content of the coating film with respect to the time immediately after coating for the coated articles of Examples and Comparative Examples.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshiro Miyajima             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. F-term (reference) 3L113 AC10 BA33 DA10                 4D075 BB18Z BB24Z BB25Y BB33Z                       BB37Z BB38Z BB57Z BB79Z                       BB91Z BB93Z BB95Z CA47                       DA06 DA23 DB01 DC13 DC16                       EA06 EA24

Claims (7)

[Claims] 1. A coating step of applying a normally-drying or forced-drying water-based coating material to the surface of an article to be coated; a setting step of leaving the article to be coated at room temperature as it is; coating until the temperature of the article to be coated reaches 35 to 60 ° C. In a method for drying a coating film, which includes a preheating step of heating the coating material; and a drying step of heating the coating material until the coating nonvolatile content is 97% or more, the heating in the preheating step is represented by the formula: [Formula 1] ΔNV / Δt = 2 to 5.5 (% / min) I [wherein ΔNV is a change in non-volatile content during the preheating process, and Δt is a time period of the preheating process. ] The coating film drying method performed on the conditions satisfy | filling the relationship of these. 2. The method according to claim 1, wherein the drying step is performed at an ambient temperature which is 10 to 80 ° C. higher than the ambient temperature at the end of the preheating step. 3. The nonvolatile content of the coating film at the end of the coating step is 5
The method according to claim 1, wherein 0 to 55% by weight, and the nonvolatile content of the coating film at the end of the preheating step is 70 to 80% by weight. 4. The method according to claim 1, wherein the time of the setting step is 5 minutes or less, and the time of the preheating step is 3 to 5 minutes. 5. The method according to claim 1, wherein the preheating step is performed using air blowing, hot air drying, or far infrared heating. 6. The method of claim 1, further comprising a cooling step of cooling the coated article to a hand-handleable temperature after the drying step. 7. The method according to claim 1, wherein the cooling step is performed by using air blow, cold air cooling, or spraying of water mist.