JPH03181372A - Method for coating metal body with powder - Google Patents

Abstract

PURPOSE:To make a stuck layer uniform by sticking powdery resin having low melt viscosity on a heated metal body as a lower layer and powdery resin having high melt viscosity on the molten lower layer as an upper layer. CONSTITUTION:A metal body is heated to the m.p. of powdery resin or above to be stuck. While the temp. of the metal body is >= m.p. the powdery resin having low melt viscosity is stuck on the metal surface to form a molten film as a lower layer. Powdery resin having high melt viscosity is then stuck on the molten lower layer. The resin having low melt viscosity may be polyphenylene sulfide resin having 100-1,500P. The resin having high melt viscosity may be polyphenylene sulfide resin having 1,600-10,000P. Coating free of pinhoks is enabled.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a method for powder coating a metal body.

<Prior art> Among the resin coating methods for metal objects, the powder coating method uses air instead of a solvent, so there is no danger of fire or toxicity due to solvents, there is no solvent loss, and there is no IR It has advantages such as being able to be reused by recovery and being able to use resins that are difficult to melt in solvents, and its range of application is wide-ranging.For example, it is used for the inner lining of metal pipes, etc. . For the resin lining of metal objects, especially the inner lining of metal pipes, it is essential to make the resin thick and uniform in thickness, and to paint it without pinholes in order to guarantee blister resistance. . In other words, even if the resin itself applied to the inner surface of the metal tube has excellent heat resistance, if the film thickness is less than 500 μm, hot water will permeate through the film and the adhesion between the film and the metal surface will deteriorate. Therefore, blistering phenomenon is likely to occur. In particular, if a pinhole exists between the membrane and the metal surface, the pinhole becomes a starting point for blistering and accelerates the onset of the blister phenomenon. Further, if the film has irregularities, even if the average thickness of the film is thick, the film is thin in the concave parts, and this thin part tends to cause a blister phenomenon.

In the powder coating method for metal objects, the metal object is heated above the melting point of the powder resin, and while the metal object is heated above the melting point, the powder resin is coated on the metal surface. It is necessary to form a coating film by adhering to the molten film and then cooling and solidifying it, but it is necessary to heat the metal body to a sufficiently high temperature and complete the melting of the above-mentioned adhesion layer with this amount of preheating heat. This is required from the viewpoints of work efficiency, blistering on the surface of the film (if unmelted material is melted by reheating, the voids between the powders become air bubbles), etc. However, it is difficult to form a resin film of the thickness required for preventing blisters on the inner surface of a metal tube by melting only by the amount of heat used to preheat the metal tube, without using vinyl poles, and without unevenness or skin roughness.

In other words, in order to increase the thickness of the film, it is necessary to use a resin powder with a high melt viscosity that does not easily cause sag, but it is not possible to form the vinyl poles on the inner surface of the metal pipe with such a high viscosity resin. If this happens, the pinhole will likely remain. In addition, when the viscosity becomes high, the η1 flow decreases, and the
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Since the bonding speed of the resin particles is also slow, it is difficult to form a smooth "111Q" without skin roughness.On the other hand, if a resin powder with a low melt viscosity is used, pinholes may remain, concave 1'-11 faces, Although skin roughness etc. can be prevented, it is difficult to increase the thickness, and unevenness in IId thickness due to sagging is unavoidable.

In this way, in the conventional powder coating method for the inner surface of a metal tube, a thick powder non-adhesive layer (500 to 55
Completed melting of 0 μm), thick and pole-less,
Moreover, it is difficult to form a coating film with a smooth inner surface without causing skin irritation. As a result of intensive study of the current situation, the present inventors decided to attach a powdered resin with a low melt viscosity as a lower layer,
If a powder resin with high melt viscosity is attached as an upper layer to the bottom of the molten Jr41-, and the upper and lower layers of resin are melted and diffused, the J7-type can be made to a sufficient thickness <(500~
550μ River) I learned that it is pinhole-free and has a smooth inner surface that is coated with a resin film that does not cause skin irritation.

Based on this knowledge, it is an object of the present invention to coat a metal tube with a resin coating having a thickness that is sufficiently thick, no vinyl poles, and no skin irritation, using only the T-ripe amount of the metal tube. An object of the present invention is to provide a powder coating method for a metal body that can be applied to the inner surface.

<Means for Solving the Problems> The powder coating method for a metal body according to the present invention involves heating a metal body, attaching a powder resin with a low melt viscosity as lower R4 to the heated metal body, and applying a powder resin to a molten state. By depositing a powder resin with high melt viscosity as an upper layer on the lower layer of , and melting and diffusing the resin of upper f-' 34, a dense, vinyl-free coating film of almost uniform thickness is formed. This is a configuration characterized by the following.

<Function> For such an introduction, (1) the pinholes on the inner surface of the metal tube are filled with a powder resin of low melt viscosity to achieve pinhole-free performance; The lower layer has enough Jv to fill pinholes.
Just say it. This will prevent the bottom layer from sagging. ■By melting and diffusing the upper and lower layers, the overall viscosity can be made uniform, even the uneven powder adhesion layer, and sag! 7j, +I-1 as well as the viscosity suitable for preventing skin irritation (densification), resulting in a dense coating without unevenness within the thickness.

In the present invention, the melt viscosity of the low melt viscosity resin is, for example, 1[)O~ in the case of polyphenylene sulfide.
It is effective to use 1500 poise, preferably 300 to 1300 poise. The reason for this is that if the number of voids exceeds 1500, it becomes difficult to fill the bottle pole, and if the number of voids falls below 100 voids, it becomes difficult to hold the resin inside the bottle pole. In addition, the thickness of the adhesion is 2 to prevent sagging.
It is effective to set the thickness to 50 μm or less. It is necessary to select a high melt viscosity resin for the upper layer that does not cause sagging by melting and diffusing with the lower layer, and has viscoelasticity suitable for uniformly adhering resin thickness and densification of the coating film. . for example,
In the case of polyphenylene sulfide resin, the melt viscosity is 16
00-1oooo boys, preferably 1900-500
You can use one with 0 voise.

In the present invention, any suitable method can be used to attach the lower layer and the upper layer as long as the upper layer powder does not adhere to the metal surface before the lower layer powder is attached to the metal surface. For example, in the case of coating the inner surface of a metal pipe, a spray gun for low melt viscosity resin powder is run into the metal pipe to coat the entire inner surface of the metal pipe, and then a high melt viscosity resin powder is coated on the entire inner surface of the metal pipe. A method in which a spray gun for molten viscosity resin powder is run inside a metal pipe, a spray gun for low molten viscosity resin powder is placed in advance, and both spray guns are isolated to the extent that mixing of both powders does not occur. A method in which both guns are run at the same time, the spray gun is fed into a metal pipe while supplying low melt viscosity resin powder to adhere the low melt viscosity resin powder to the entire surface of the pipe, and then the resin powder is supplied to the same spray can. A method such as switching the resin powder to a high melt viscosity resin powder can be used.

<Description of Examples> Examples of the present invention will be described below in comparison with comparative examples.

The resin powder used was a polyphenylene sulfide resin powder having a melt viscosity as shown in Table 1.

However, the melt viscosity can be measured using a flow tester (Co., Ltd.;
Temperature: 300" C1 width: 20, die diameter: 1 m
m, and the die length was measured under the conditions of 101111n.

The results of applying each of these resin powders to the inner surface of a metal tube using a spray gun are shown in Table 2.

However, the metal tube used had an inner diameter of 100 mm, a length of 2.5 m, and had been subjected to alkali degreasing and sandblasting, and the preheating conditions were 380° C. and 90 minutes.

Resin powders A and B had 1500 voids or less and were able to fill pinballs without pinholes, but they sagged and left traces of sagging, giving a poor appearance and having a thickness of 500 μm.
It was not possible to reach m. Resin powders C11) and E did not cause sagging due to their high melt viscosity, but they were not pinhole-free and caused skin roughness due to their slow melting speeds. Furthermore, although the coating thickness could be thickened, the J-elasticity due to the non-uniform adhesion thickness was insufficient and unevenness occurred on the coating surface.

Furthermore, resin powder A and 13. When a mixture of A, A, E-B, C, and B and D (former/latter ratio is approximately %) was applied under the same conditions as above, the results were as shown in Table 3. .The mixtures of A and B, A and A, and A and E were made without pinholes, but sagging occurred, and the mixtures of A and I3 and A and D were 500 μm.
The average thickness of mixtures A and E could be increased to 500 μm or more, but sagging occurred and the minimum and maximum thicknesses were between 400 μm and 700 μm. On the other hand, the mixtures of B and C and B and D could not be made pinhole-free, but there was little sagging and the film surface was dense, and the film thickness could be reduced to 500 μm.
As a result, uniformity of non-uniform powder adhesion is well achieved.
The film surface was sufficiently smooth.

Next, the coating results of Examples and Comparative Examples are as shown in Table 4. The metal tube used was the same as above, with a diameter of 100 m.
2.5 m in length, and after alkaline degreasing, the inner surface was treated with sandblasting. Preheating conditions were 380° C. and heating for 90 minutes. As the lower layer, a resin powder as shown in Table 4 was applied using a spray gun at a rate of about 200 It mJ'7, and the molten debris of the lower layer was removed by preheating the metal tube.
Apply the resin powder for the upper layer as shown in the table using another spray gun, aiming for a total thickness of 500 μm or more for the upper and lower layers, preheat the metal tube to melt and diffuse the lower L layer, and after natural cooling to room temperature, apply the coating. I checked the condition.

In Table 4, regarding the evaluation item pinholes, when low melt viscosity resin powder A or B was used as the lower layer, no pinholes were achieved, but when C or D high melt viscosity resin powder was used. , pinholes occurred. Regarding sag, when the lower layer/upper layer is 8/B, A/C, A/D, and A/E, even if the upper and lower layers melt and diffuse, the melt viscosity is still low and sag occurs, and in other cases ( B/C, B/D, B
/E, C/D, C/E and D/E), no sagging occurred. Furthermore, regarding the uniformity of uneven adhesion of powder due to viscosity (smoothness) and the denseness of the film surface (skin roughness) due to the powder coagulation rate, A/B, A/C, A/D, A
/E, B/C, B/D, whether it was good or B/E
, C/D, and C/E, skin irritation occurred and the results were poor.

The skin roughness of B/E, C/D, and C/E is due to the high melt viscosity and slow condensation rate, and the reason why B/C and B/D are good is as shown in Table 3. This is clear from the results. Fourth
The film thicknesses in the table indicate the minimum film J7 and the maximum film thickness.

As is clear from Table 4, in Example 1.2,
No pinholes, no sag, surface is sufficiently smooth, the film surface is dense and beautiful, and the film thickness is 500 μm.
That's all.

<Effects of the Invention> As described above, according to the present invention, by preheating the metal tube, the lower melting viscosity powdered resin layer and the higher melting viscosity powdered resin upper layer are melted and diffused, thereby preventing sagging, preventing skin irritation, The melt viscosity can be made suitable for smoothing, and the pinholes can be filled with a lower layer of low melt viscosity, so the powder coating method can be used to coat the metal tube within -3 times, without the need for bottle balls, and smooth. Can line dense coatings on film surfaces.

Table 1 Table 2

Claims (1)

[Claims] A metal body is heated, a powder resin with a low melt viscosity is deposited as a lower layer on the heated metal body, a powder resin with a high melt viscosity is deposited as an upper layer on the molten lower layer, and the resins in the upper and lower layers are melted. A powder coating method for metal objects that is characterized by forming a dense, pinhole-free, and uniformly thick coating film by diffusion.