JPS5948671B2 - HUNTAITRIYOOTOSOUSURUHOHO - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a powder coating method, and more specifically, the present invention relates to a powder coating method, and more specifically, the present invention relates to a powder coating method. It relates to the method by which powder coatings are applied while in a state, the so-called wet-on-dry application method.

[Conventional technology]

In the manufacturing process of automobiles, sealers are applied at key points to prevent water leakage from welded parts of the body and to prevent dust from entering the interior of the vehicle.

Then, in order to improve the appearance etc., an organic solvent type paint is painted on this bare body. In the car body painting process, a sealer such as body sealer or drip sealer is applied to the loop trip area, the hemmed parts of the steel plate inside the door and trunk lid, and the joints of the outer skin of the car body. . For example, in the case of a passenger car, which consists of three layers of painting: undercoat, intermediate coat, and top coat, this coating process is usually carried out between the undercoat and intermediate coat, while in the case of trucks, the undercoat and top coat are applied. When the coating consists of only two layers, it is applied between the undercoat and topcoat. Therefore, in the former case, the intermediate coat paint and in the latter case, the top coat paint is applied with a solvent on the sealer coating surface, and heat is applied inside a drying oven to bake both coats at the same time. It is being done. Conventionally, so-called solution-type paints using organic solvents have been used as intermediate coats or top coats for such purposes.

When such a paint is used, no particular problems occur during or after painting, and a good paint film is generally obtained. However, as it is well known, pollution countermeasures are currently attracting a lot of attention, and new coating methods are attracting attention in this industry as well.

That is, it is a so-called powder coating coating method that does not use a solvent from the viewpoint of being non-polluting and is advantageous in terms of both cost and equipment used. There are many recent documents related to "powder coatings", such as "Painting Technology" December 1969 Special Issue (Vol. 8, No. 1).
No. 4), pp. 223-226, "Epoxy Powder Coating" by Tatsube Ito. As such powder coating,
Acrylic and polyester powder paints will be used as top coats, and epoxy powder paints will be used as intermediate coats. However, undesirably, various disadvantages occur when powder coatings, particularly thermosetting powder coatings, are used. Among these, a particularly important one is so-called ``bleeding'', and when this occurs, the appearance of the resulting coating film is significantly deteriorated, and the commercial value of the coated product is also significantly reduced. In extreme cases, for example in the case of automobile doors, the seeped sealer may flow out from the back side and wrap around the front side, resulting in a noticeable appearance defect. To explain ``bleeding'' in more detail, there is no particular problem when applying a sealer, curing it, then applying a powder coating, and then curing it. When a powder coating is applied onto a sealer and then heated to simultaneously cure these coatings, the molten sealer oozes out from the coated surface and surrounding areas. I'm here.

In fact, when a powder coating is applied in place of a known solution-based coating using substantially the same technique, significant "bleeding" (dissolution and flow of the coating film) occurs on the sealer coating surface and its surrounding areas. Although ``bleed'' does not occur as much when acrylic or polyester powder paints are used, it occurs particularly when epoxy powder paints are used. Problems to be Solved by the Invention] As can be understood from the above explanation, oozing'' has become a serious problem in the conventional wet-on-dry powder coating method.

Therefore, without changing the working order currently employed in the conventional painting process, the powder coating is applied on the sealer coating surface while it is still wet, following the same order as before. It would be desirable to provide an improved powder coating method that does not involve sealer bleed during application and subsequent simultaneous baking of the two. [Means for Solving the Problems] According to the present invention, the above-mentioned problems can be solved by wet powder coating on the sealer applied to the joints of steel plates of automobile bodies, etc.
For on-dry painting, in detail, the first step is to apply a sealer to the joints of steel plates of an automobile body, and then an epoxy powder is applied onto the applied sealer before the sealer is cured. A method for applying a powder coating, the method comprising: a second step of applying the paint; and a third step of simultaneously heating and curing the applied sealer and the applied epoxy powder coating film. The powder coating applied in the second step is a powder until the viscosity of the sealer applied in the first step reaches 350 voids in the curing process of the third step in the third step. Alternatively, the problem can be solved by a method of applying a powder coating, which is characterized by being an epoxy powder coating exhibiting a viscosity of 350 poise or more during the process of lowering the melt viscosity.

〔Effect of the invention〕

According to the method of the present invention, when performing powder coating on the coated layer of sealer, the conventional epoxy powder, which has not been able to be used until now for bleeding, can be applied without changing the conventional coating procedure. Paint can be used.

Moreover, according to the present invention, there is no need to use solvents, which are a source of pollution, which greatly contributes to environmental conservation, and furthermore, it is possible to reduce necessary costs. In addition, the present invention is useful not only for improving the painting process in the automobile manufacturing process, but also for related fields, for example, the field of manufacturing products whose constituent elements include a sealer and a powder coating applied thereon. Can be applied effectively. [Explanation of Terms] Next, some of the terms used in this specification will be briefly explained.

As used herein, the term "gelation temperature" refers to the temperature at which gelation begins. "Geling temperature" is
For example, it can be determined as follows: Attachment 2
The graph shown in the figure is based on the sealer B described in detail below.
This is a graph showing the relationship between temperature and viscosity per hour for (fast curing sealer), and from this graph, it can be seen that the temperature T of the sample is 81
Since the viscosity V rapidly increases around 0.degree. C., it can be seen that gelation begins around this temperature. The temperature at which gelation begins in this manner is generally referred to as the "gelation temperature." In this example, the experimental conditions were set so that the heating rate was as shown in the figure, and heating was performed, and the temperature at which the sample was set in the viscosity measuring device was always room temperature. Although the viscosity measurement started at about 22°C (room temperature), when the temperature is initially constant, the viscosity is almost constant regardless of the elapsed time (at a temperature of about 22°C for 2.5 minutes). Approximately 232 poise). Furthermore, the term "melt viscosity lowering process" used in this specification refers to a process in which a thermosetting powder coating, although initially in powder form, gradually melts and lowers its viscosity by heating. It refers to the process of

In other words; taking the graph viscosity curve PP-A (powder coating A) shown in attached FIG. 1, which will be explained in detail below, as an example, approximately 1
The viscosity of paint A heated to a temperature of 10°C is about 750 poise, but this viscosity decreases rapidly as the temperature rises, and after about 8 minutes (at a temperature of about 16°C)
The sample exhibits a minimum viscosity value of about 50 poise, and as the temperature increases, it exhibits a thickening phenomenon due to a curing reaction, and eventually gels, making it impossible to measure the viscosity of the sample.
The process (time) from when the sample starts melting until it reaches the lowest viscosity is generally referred to herein as the "melt viscosity decreasing process." In addition, the expression "exhibits a viscosity of 350 poise or more during the melt viscosity decreasing process", which is often used in the specification of the present application, refers to the expression "exhibits a viscosity of 350 poise or more in the melt viscosity decreasing process" as defined above. It refers to the part that displays the

〔Example〕

Below, in order to make this invention easier to understand,
The present invention will be explained in detail by giving specific examples.

Here, the following sealer and powder coating were used as samples. The curing speed of Sealer 1 was adjusted by changing the amount of low-temperature melting resin in its main component, vinyl chloride resin.

Here, three types of sealers with different curing speeds were used: Sealer A (slow-curing sealer), vinyl chloride resin, phthalate plasticizer, and calcium carbonate (as a filler). ), heat stabilizers and other additives.

The amount of low temperature melting range in vinyl chloride resin is 2.7 parts (
The total amount was 100 parts). This Sealer-A is commercially available from Aisin Chemical Co., Ltd. as Sealneeds 516T. Sealer 1 B (fast curing sealer 1) consists of vinyl chloride resin, phthalate plasticizer, calcium carbonate (as a filler), heat stabilizer and other additives.

The amount of low temperature melting resin in the vinyl chloride resin was 14.7 parts (total amount: 100 parts) in order to increase the curing speed.
This Sealer 1B was prototyped by the present inventors with reference to the Sealer 1A described above. Sealer-C (standard, ie, intermediate-cure sealer-1) consists of vinyl chloride resin, phthalate and polyester plasticizers, calcium carbonate (as a filler), heat stabilizers, and other additives.

The amount of low melting resin in the vinyl chloride resin was 4.8 parts (total amount: 100 parts) in order to place the curing speed between those of the sealers A and B. This sealer 1C was prototyped by the present inventors with reference to the sealers 1A and B described above. These sealers are in the form of plastisol, similar to conventional sealers, and contain (1) thermoplastic vinyl chloride resin powder, (2) phthalate ester plasticizer, and (3) similar materials such as calcium carbonate. (4) other additives, and does not contain any reactive components.

Such sealers are therefore thermoplastic in nature and at the time of their application (not yet heated, of course)
It is paste-like or paste-like. Furthermore, two types of powder coatings were used here: as mentioned above;
Although the viscosity characteristics of the sealer and powder coating are important in this invention, the viscosity change was measured as follows.

Using a commercially available rotating cone and disk viscometer, the viscosity was measured while the temperature was continuously raised from room temperature, and the relationship between time, temperature, and viscosity was determined.

The details of the rotational viscometer and the viscosity measurement conditions are as follows: Measurement conditions: Temperature increase rate: The temperature was continuously increased at a rate of 11 to 15° C./min (sample was set at room temperature).

However, as understood from the temperature curve TEMP in Figure 1,
Although a constant temperature increase, ie, a straight line, was intended, a gentle curve was obtained due to experimental precision. In addition,
Here, the temperature increase rate was set at 11 to 15°C/min for the following reason: Powder coatings have a high temperature increase rate due to their heat-melting characteristics and curing mechanism. The higher the value, the lower the minimum melt viscosity, and therefore the better the smoothness of the coating film.

It is usually desirable for the temperature increase rate to be 10°C/min or more (Special Publication No. 51-45606 Akane Mitsho) (Ii) When actually designing equipment for a paint drying oven in an automobile body painting factory , a temperature increase of 10 minutes and a holding time of 20 minutes are standard.

In the examples described below, therefore, a bake hardening time of 30 minutes at a temperature of 170° C. (heating up for 10 minutes and holding for 20 minutes) was adopted. When the body temperature is 20°C and the temperature is raised to 170°C in 10 minutes, the rate of temperature rise is calculated as α70-20)/10=15°C/min. As understood from the above, the temperature increase rate of 11 to 15° C./min is a set value to approximate the heat curing conditions in an actual body painting line.

Shear rate: 189.1 sec-1 Temperature measurement was carried out using a C-C (copper-constantan) thermocouple and cold junction, and the obtained values were continuously measured using a tabletop recorder. (Hitachi Model 056).

The viscosity was calculated according to the formula below.

Standard viscosity Prior to measuring the liquid viscosity, the viscosity of the following standard viscosity liquid (officially referred to as a standard solution for viscosity meter calibration) was measured.

The viscosity measurement conditions were as described above. Manufactured by Showa Sekiyu Co., Ltd. (2-7-3 Marunouchi, Chiyoda-ku, Tokyo) Prepared at Showa Sekiyu Co., Ltd.'s Central Research Laboratory Tested by the Institute of Metrology, Agency of Industrial Science and Technology The viscosity of this standard viscosity liquid was measured under the viscosity measurement conditions above. When measured, its absolute viscosity was 832.4 cp (
30°C).

Comparative example cold rolled steel plate (dimensions 100 x 300 x 0.8 m/m; J
IS-G-3141, SPCC) was degreased and then treated with zinc phosphate coating (chemical conversion treatment).

The obtained treated steel plate was drained and dried at a temperature of 80° C. for 10 minutes, and then a polybutadiene-based electrodeposition paint was applied to a thickness of 25 μm. This electrodeposited coating was cured by baking at a temperature of 160° C. for 30 minutes. The above-mentioned Sealer-A was applied in the form of a rod to the obtained panel, and the above-mentioned powder coating A was electrostatically applied on the uncured coated surface of this Sealer-A, and both coatings were heated at a temperature of 170°C for 30 minutes. Bake hardening took place for 1 minute. In this case, dissolution and spreading of the coating film was observed on the sealer-applied surface and its surrounding areas. This suggests a decline in coating quality. Next, the above results were repeated in the laboratory.

From the obtained data, the relationship between temperature, hour, and viscosity of Sealer A and powder coating A is shown in the graph in Figure 1 (Sealer A = curve S-A, powder coating A = curve PP-A). become that way. To obtain this graph, the ``viscosity measurement''
The changes in viscosity of the sealer and powder coating were measured by applying the conditions detailed in section 1, and the obtained measured values were combined to obtain 1.
It was made into two graphs. As is clear from this graph, Sealer A and Powder Coating A each exhibit viscosity curves that intersect at a viscosity of about 270 poise at a temperature of about 130°C. That is, these sealers and powder coatings have a period of time in which they coexist at relatively low viscosities. In the heat curing step, the sealer A undergoes gelation and increases in viscosity as the temperature rises.

However, since Sealer A requires a high temperature to start gelling, as is clear from the graph, it is still uncured even when the melt viscosity of powder coating A has decreased considerably. It is in the low viscosity range. Therefore, these sealers and powder coatings exhibit compatibility in a low viscosity range, resulting in oozing, that is, dissolution and spreading of the coating film. Example 1 The procedure described in the comparative example above was repeated, but in this example powder coating B (see above) was used instead of powder coating A.

In this case, no seepage of the sealer 1 was observed on or around the surface coated with the sealer 1. In this example as well, changes in viscosity were measured in the laboratory in the same manner as in the comparative example.

The obtained results are shown in the graph of Figure 1 (Sheila-A=Curve S-
A, Powder coating B: As shown in curve PP-B).
As is clear from this graph, Sealer A and Powder Coating B each intersect at a viscosity of about 450 poise at a temperature of about 135°C. That is, until the sealer A heats and hardens and reaches a viscosity of 350 poise, the powder coating B remains in the powder state and is in the process of decreasing its melt viscosity (however, above 350 poise). In the heat curing process, when both the sealer A and the powder coating B coexist in a relatively high viscosity range, no particular abnormality occurs in the coating film. That is, in the process where the powder coating B shows a decrease in melt viscosity, the sealer A is already in the high viscosity range and gelation is progressing, so that dissolution and spreading of the coating film does not occur. Example 2 The procedure described in the comparative example above was repeated, but in this example Sealer 1B (see above) was used in place of Sealer 1A.

In this case, the sealer rapidly gelled, and at the time gelation was completed, the powder coating was still powder. No oozing of the sealer 1 was observed on or around the surface coated with the sealer 1. In this example as well, changes in viscosity were measured in the laboratory in the same manner as in the comparative example.

The obtained results are shown in the graph of Figure 1 (Sheila-B = Curve S-
B, Powder coating A=as shown in curve PP-A).
As is clear from this graph, Sheila-B is approximately 100
It completely gels and exhibits a high viscosity at temperatures below .degree. C., while powder coating A is still in an unmelted state, that is, a powder state, at such temperatures and times. Of course, Sealer-B remains a powder until its viscosity reaches 350 poise. In the heat curing process, if the powder coating is in an unmolten state or in a high viscosity state and the sealer is in a gel state, that is, if it exhibits a high viscosity, special No abnormalities occur.

That is, in such a case, dissolution and spreading of the coating film will not occur. Example 3 The procedure described in the Comparative Example above was repeated, but in this example, Sealer 1C (Sansho, above) was used in place of Sealer 1A.

In this case, although a slight tendency for paint film abnormalities was observed on the sealer-applied surface and its surrounding areas, the paint film obtained in this way was sufficiently satisfactory in terms of coating quality, especially in terms of appearance properties. It was acceptable. In this example as well, changes in viscosity were measured in the laboratory in the same manner as in the comparative example. The obtained results are as shown in the graph of FIG. 1 (Sealer-C=curve S-C, powder coating A-PP-A). As is clear from this graph, after the start of heat curing, Sealer 1C and Powder Coating A have viscosity curves that intersect at a viscosity of about 400 poise at a temperature of about 123°C. Similarly, repeating the above experiment using more than 20 different sealer compositions with similar viscosity properties as Sealer 1C yielded essentially the same results, i.e., acceptable coatings in terms of coating quality. Obtained.

To summarize the above, when applying a powder coating on an uncured sealer that has been applied and then heating and curing both,
In other words, if the powder coating is unmelted or in the process of decreasing melt viscosity (more than 350 poise) until the sealer thickens and reaches a viscosity of 350 poise, then in other words, the sealer and powder coating have a viscosity of about 350 poise. It is clear that coatings with acceptable coating quality can be obtained if they coexist in a viscosity range of 350 poise or higher.

Although this invention has been described in detail with reference to particularly preferred embodiments, it should be understood that various changes and modifications may be made within the spirit and scope of the invention.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between Sealer A-C and powder coatings A and B during the heat curing process in terms of time-temperature and viscosity.

Claims (1)

[Claims] 1. A first step of applying a sealer to the joints of steel plates of an automobile body, and a second step of applying an epoxy powder coating on the applied sealer before curing the sealer.
and a third step of simultaneously heating and curing the applied sealer and the applied epoxy powder coating film, the method comprising the steps of:
In the third step, the powder coating to be applied in the step is powder or has a reduced melt viscosity until the viscosity of the sealer applied in the first step reaches 350 poise in the curing process of the third step. A method for applying a powder coating, characterized in that it is an epoxy powder coating exhibiting a viscosity of 350 poise or more during the process.