JP2000336286A - Low temperature curing type powder coating composition and method for fornming coating film on inner surface of metallic pipe using the same powder coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide low temperature curable epoxy resin based powder coating compositions which can be cured at a temperature of lower than the curing temperature of the conventional epoxy resin based powder coatings and give coating films with inhibited occurrence of pinholes and coating film properties excellent in long-term reliability, and a method for coating the inner surface of a metallic pipe by using these compositions. SOLUTION: In the powder coating composition comprising, as the essential components, (A) an epoxy resin having an epoxy equivalent weight of 500-2,500 g/eq and a softening point of 65-130 deg.C, (B) a curing agent, and (C) a filler, the epoxy resin (A) is a bisphenol type epoxy resin, and the curing agent (B) is a basic nitrogen-containing heterocyclic compound. Further, this powder coating can give a coating film with inhibited occurrence of pinholes and excellent in long-term reliability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-temperature curable epoxy resin-based powder coating composition and a method for coating the inner surface of a metal tube with the powder coating composition. The body paint cures at a lower temperature than the curing temperature of conventional epoxy resin-based powder paints, and the resulting coating has reduced pinholes and is a low-temperature curable epoxy resin-based powder with excellent long-term reliability. TECHNICAL FIELD The present invention relates to a body coating composition and a method for coating an inner surface of a metal tube using the same. Furthermore, in the coating process of the metal pipe to be coated, a low-temperature curable epoxy resin that can be applied to both curing conditions, including a post-curing furnace after preheating coating and natural cooling after preheating coating The present invention relates to providing a powder-based coating composition.

[0002]

2. Description of the Related Art In recent years, powder coating which can improve the working environment without pollution has been adopted as a method for preventing corrosion of metals. BACKGROUND ART Epoxy resin-based powder coatings have obtained many achievements as corrosion-resistant powder coating materials because of their excellent mechanical properties and corrosion resistance. BACKGROUND ART Cast iron pipes used for water pipes or sewer pipes are provided with anticorrosion coating on inner and outer surfaces to protect the pipes from being buried in the soil and from being corroded by external fluids and corroded by fluid flowing in the pipes. Epoxy resin powder coatings are often used as coating materials, but it is necessary to prevent coating film defects such as unevenness of the coating film and generation of pinholes remaining in the coating film. In addition, if the coating itself does not have long-term corrosion resistance with excellent properties such as impact resistance, flexibility (appropriate Erichsen value), corrosion resistance, water resistance, abrasion resistance, temperature gradient resistance, etc. No. In the industrial field, the ability to automate the coating process, increase the yield, and reduce energy costs are important issues.Therefore, there is a need for a powder coating that can be applied with an economical coating method. ing.

Conventionally, many epoxy resin powder coatings have been generally proposed and put into practical use. There are proposals for these powder coatings in Japanese Patent Publication Nos. 62-28194 and 62-28193, which, although satisfying long-term corrosion resistance, require preheating the cast iron pipe to be coated to around 230 ° C. , And a large amount of energy is required in the heating step, which is very disadvantageous economically. Therefore, even if the preheating temperature of the cast iron pipe is lowered by lowering the temperature of the heating step, the curing reaction of the coating film proceeds, and the coating film has good flowability and has a poor coating appearance such as unevenness and pinholes of the coating film. There has been a demand for a low-temperature curable powder coating material which does not generate and has excellent long-term corrosion resistance and a coating method thereof. Such low temperature curable powder coatings with excellent long-term corrosion resistance are applied to various types of cast iron pipes to be coated,
The pipe is 100 mm from a small diameter pipe with a diameter of 250 mmφ or less.
There are medium-diameter pipes having a diameter of 0 mmφ or less, and large-diameter pipes having a diameter of 1100 mmφ or more, and straight pipes and deformed pipes.
When these tubes are powder-coated and cured, small tubes such as small-diameter tubes and deformed tubes have a rapid cooling rate by natural cooling after preheating. The curing reaction must be terminated by heating. In addition, when a large-diameter pipe or a long straight pipe is used, a heating furnace for covering the entire pipe is required. The curing reaction must be completed while painting and allowing to cool naturally. However, in the case of heating each part locally and hardening by natural cooling as described above, even if the pipes have the same diameter, the pipe thickness differs at the receiving end at the end of the pipe, the outlet, and the straight path at the center. Therefore, the speed of temperature rise and temperature drop at the site differs, and the temperature varies at the site, so that the curing conditions of the coated paint also differ. In other words, the portion having a small thickness is preheated to a higher degree, but the cooling rate is increased. Conversely, a thick part is difficult to cool and hard to cool, so that a distribution occurs in the coating start temperature for each local part. For this reason, it is necessary to adjust the preheating temperature for each part in order to prevent poor curing of the paint at any part and to cure the paint uniformly, but it has been substantially difficult. For this reason, the parts that are easy to cool down (thin parts) can be preheated to a higher degree, and only the treatment that increases the coating start temperature can be performed. The temperature of the object to be coated at the start of coating varies depending on each part. Therefore, the low-temperature-curable powder coating used under these conditions is, of course, excellent in low-temperature curability, but in a locally heated state of a thin-walled portion that is easy to cool. Even if it is applied to a certain part, a coating film having excellent performance must be formed. Painting start temperature is 140 ~
Even in the case of a low-temperature-curable powder coating material that can form an excellent coating film in a low-temperature region of 150 ° C., under high-temperature heating coating conditions under which it is allowed to cool naturally (a high-temperature region where the temperature immediately after coating is locally around 230 ° C.) It is necessary that the coating finishes the curing reaction without any problem even if exposed to water, and that the coating film be excellent without deterioration.

[0004] As an epoxy resin powder coating for coating the inner surface of cast iron pipes buried in the ground such as water pipes or sewer pipes, the amount of α-glycol obtained by reacting a liquid bisphenol A type epoxy resin with bisphenol A is known. A test piece prepared by mixing a solid bisphenol A type epoxy resin having an amount of 0.03 to 0.07 meq / g and a hydrolyzable chlorine of 200 ppm or less and a curing agent (imidazoline compound) and heating to 180 to 210 ° C. There is a proposal of a powder paint (Japanese Patent Application Laid-Open No. 10-95928) capable of forming a coating film having a thickness of 250 to 350 μm after spray coating the surface and then allowing it to cool. However, in this proposal, in order to obtain the performance of the coating film, the preheating temperature of the ductile cast iron pipe is set to 180 to 210.
It requires a relatively high temperature of ℃ and a narrow temperature control range, and an effective powder coating has not yet been obtained in terms of energy cost and process control of a heating furnace.

[0005] From the viewpoint of long-term reliability, the powder coating on the inner surface of cast iron pipes buried underground such as water pipes or sewer pipes is required to have a uniform coating appearance and high corrosion resistance. For this reason, in order to secure sufficient corrosion resistance, baking is performed at a high temperature of 180 ° C. or more using an epoxy resin-based powder coating, and several hundred μm.
m is applied. When coating on a metal tube, the object to be coated must be preliminarily heated to a curing temperature or higher through a preheating step before coating. At this time, gas may be generated due to expansion of volatile components on the surface of the metal tube or moisture contained in the cast iron tube due to heating,
It is necessary to evaporate this volatile component while the powder coating is melting or during the crosslinking reaction. In order to increase the thickness of the coating film for this application, the coating material will harden when the volatile components are hard to evaporate and partially evaporate. There is also. Furthermore, due to high temperature baking, the retention time of the fluid state after painting is very short,
It causes poor appearance of the coating film, and it has been very difficult to cure at low temperature with the conventional techniques.

As a method for preventing the appearance of the coating film from being defective, there is a method in which the object to be coated is kept at a curing temperature for a long time and preheated, but the productivity of a metal pipe or a cast iron pipe is extremely reduced. The result is. Further, JP-A-50-92941
Although there is a method of increasing the preheating of the object to be coated to a high temperature equal to or higher than the curing temperature as described in the above, this method causes a significant increase in production cost. In addition, a method of improving the flowability of the powder coating at the time of melting by reducing the molecular weight of the epoxy resin as the main component is also considered. However, it is specified by JIS K 5400 which is a test indicating the long-term reliability of the coating film. Performance in corrosion tests. In addition, blocking occurs due to heat and its own weight during storage, which results in the inability to paint. In order to bake at a low temperature, there is a method of increasing the amount of a curing accelerator in the composition, but if the amount is increased, the coating film lacks water resistance and corrosion resistance, and also causes a problem in storage stability of the powder coating. I have.

[0007]

In view of the above-mentioned problems, the problem to be solved by the present invention is that a coating film is cured in a low temperature region maintained at 200 ° C. or lower, preferably 150 ° C. or lower. A powder coating that can be cured at a low temperature under natural cooling with a non-uniform temperature distribution in which the temperature range at the start of coating of an object to be coated having a different shape or a heating and cooling state is 230 to 150 ° C., An object of the present invention is to provide a powder coating composition having performance excellent in appearance and long-term reliability of a coating film, and a method for coating the same.

[0008]

Means for Solving the Problems As a result of intensive studies in view of solving the problems, it has been found that a specific epoxy resin, a specific curing agent and a filler can be used at a temperature of 200 ° C. or lower, preferably 150 ° C.
Curing can be carried out in a low temperature range kept at a temperature of not more than ℃. We have now found an epoxy resin powder coating composition which is curable under standing cooling and has excellent long-term corrosion resistance. That is, the gist of the present invention is that the epoxy equivalent is 500 to 2,500 g / eq.
A powder coating composition comprising, as essential components, an epoxy resin (A) having a softening point of 65 to 130 ° C., a curing agent (B) and a filler (C), wherein the epoxy resin (A) is a bisphenol-type epoxy resin. A curing agent (B) comprising a basic nitrogen-containing heterocyclic compound, wherein the curing agent (B) is a low-temperature curable powder coating composition. By performing electrostatic coating or preheating spray coating under the curing conditions in which the preheating temperature of the cast iron pipe is maintained at 140 to 150 ° C. using the powder coating, unevenness and pinholes can be obtained without deteriorating the coating film performance. Deterioration of coating film was suppressed, and inner coating became possible. Further, the coating start temperature range of the object to be coated in the case where the shape is different and the heating and cooling state is different, such as a receiving portion, an outlet portion, etc., such as a straight tube or a different diameter tube, is 23.
Even under the curing conditions with non-uniform temperature distribution of 0 to 150 ° C, even if the coating is performed by electrostatic coating or preheating spray coating and cured under natural cooling, the coating film defect is not reduced without lowering the productivity and curability. This makes it possible to apply a powder coating having excellent performance in terms of appearance, water resistance and long-term reliability to the inner surface of the object to be coated.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail.
The epoxy resin powder coating composition of the present invention has an epoxy equivalent of 500 to 2,500 g / eq and a softening point of 65 to 1
A powder coating composition comprising, as essential components, an epoxy resin (A), a curing agent (B), and a filler (C) at 30 ° C.
A preferable mixing ratio is 100 parts by weight of the bisphenol type epoxy resin (A) and the curing agent (B).
0.1 to 5.0 parts by weight, and filler (C) 0 to 150
Parts by weight. The epoxy resin (A) is not particularly limited as long as it is a bisphenol type epoxy resin. Specific examples include bisphenol A type epoxy resin, bisphenol F type epoxy resin, and tetrabromobisphenol A type epoxy resin.
Among these, bisphenol A epoxy resin is particularly preferable for obtaining uniform coating properties such as impact resistance, flexibility and long-term corrosion resistance required for the present application.

The epoxy resin may be a so-called direct synthesis epoxy resin obtained by a polyaddition reaction between a bisphenol and epihalohydrin, or a so-called indirect synthesis method obtained by a polyaddition reaction between a bisphenol type epoxy resin and a bisphenol. Epoxy resins can also be used. Examples of the former epoxy resin include Epotote YD-012, Epotote YD-014, and Epotote YDF-2004 manufactured by Toto Kasei Co., Ltd. Bisphenol A, bisphenol F, and tetrabromobisphenol A are used as phenols.
And the like. As epihalohydrin, epichlorohydrin is usually used industrially. Examples of the latter are Epototo YD-902 and Epototo Y
D-903 and Epotote YDF-803.
Such a bisphenol type epoxy resin has an epoxy equivalent of 500 to 2500 g / eq and a softening point of 65 to 1.
If the epoxy equivalent is less than 500 g / eq, it is easy to block even if it is solid at room temperature, and the obtained coating film has flexibility (appropriate Erichsen value) and impact resistance. Chip. Conversely, the epoxy equivalent is 2500
If the ratio is g / eq or more, the softening point becomes high, and the kneading in the coating process is insufficient, which is not preferable. If the softening point of the solid epoxy resin (A) of the present invention is less than 65 ° C., a powder coating having no good storage stability cannot be obtained, and the blocking resistance is remarkably lowered, which is not preferable. On the other hand, if the softening point exceeds 130 ° C., it becomes difficult to maintain fluidity during coating, and traces of spraying remain helically, making it impossible to form a smooth coating film, resulting in poor appearance of the coating film. Furthermore, pinholes are generated in the coating film due to poor fluidity during coating, and corrosion resistance cannot be obtained.

Next, the curing agent (B) used in the present invention will be described. In the present invention, a specific basic nitrogen-containing heterocyclic compound represented by the general formula (1) can be used as the curing agent (B). Further, the basic nitrogen-containing heterocyclic compound represented by the general formula (2) can be used as a mixture with a specific basic nitrogen-containing heterocyclic compound represented by the general formula (1).

Embedded image R = H, C _n H _{(2n + 1)} , phenyl group However, in the case of R = CH ₃ and isocyanuric acid adduct, crystallization water nH ₂ O is attached (n is an integer)

Embedded image However, when R = H, C _n H _{(2n + 1)} , a phenyl group and a basic nitrogen-containing heterocyclic compound as an example,
Curesol 2MZ-OK, Curesol 2PZ-OK, Curesol 2MZ-A, etc., manufactured by Shikoku Chemical Industry Co., Ltd. The compound names and structural formulas are as follows.

Embedded image The amount of the curing agent added to the epoxy resin is 0.1 to 5.0 parts by weight, preferably 1.0 to 4.0 parts by weight, per 100 parts by weight of the epoxy resin. If the amount is less than 0.1 part by weight, the curability at a low temperature will be impaired, and 5.0 will result.
When the amount is more than the weight part, the curability is too fast, so that an armpit or a pinhole is formed, or a trace of spraying at the time of coating remains, often resulting in an unevenly painted surface. As a result, the evaluation based on the corrosion test and the temperature resistance test becomes insufficient. In addition, since the curability is too fast, the physical properties change during storage, causing a problem. When the basic nitrogen-containing heterocyclic compound represented by the general formula (2), which is a raw material of the basic nitrogen-containing heterocyclic compound represented by the general formula (1), is used alone, the curability is low. The same problem occurs too fast.

Further, when a performance based on a more severe corrosion resistance test or temperature gradient test is required, an aromatic amine or an aromatic amine is added to the basic nitrogen-containing heterocyclic compound represented by the general formula (1). This can be achieved by using an adduct together. A specific example of the aromatic amine is Mitsui MDA-150 manufactured by Mitsui Chemicals, Inc., and an aromatic amine adduct is tote amine TH-10 manufactured by Toto Kasei Co., Ltd.
00 (modified aromatic amine adduct). In these cases, the amount of the basic nitrogen-containing heterocyclic compound represented by the general formula (1) may be smaller than that described above,
0.1 to 4.0 parts by weight, preferably 0.5 to 3.0 parts by weight, but the proportion of the basic nitrogen-containing heterocyclic compound represented by the general formula (1) is 50 parts by weight in the curing agent. % Is required.

Next, in a coating line which is not equipped with a post-curing furnace, it is necessary to cure during natural cooling after pre-heating coating, and the coated material having a different shape and a different heating and cooling state. The temperature range at the start of painting the object is 230 to 150
The curing agent (B) of the present invention is required when curing performance under natural cooling with an uneven temperature distribution of
It is necessary to use a mixture of the compounds represented by the general formulas (1) and (2). As the coating composition, the curing agent (B) was added in an amount of 0.1 to 100 parts by weight of the epoxy resin (A).
To 5.0 parts by weight in the curing agent (B).
And the compounding ratio of the compound represented by the general formula (2) (general formula (1) / general formula (2)) is 99/1 to 30/70, and the amount of the filler (C) added to the epoxy resin for,
It must be a powder coating composition blended from 0 to 150 parts by weight. In the case where the surface temperature of the object to be coated is partially exposed to 200 ° C. or more, if the curing agent (B) is based only on the general formula (1), the temperature is 200 ° C.
The properties of the coating film applied to the above sites are unsatisfactory. In the case where the curing agent (B) is a coating composition based on the general formula (1), particularly excellent coating film performance can be exhibited if the curing conditions are controlled in a low temperature range of 200 ° C. or less. The object of the present invention can be achieved. However, it has been found that when there is a portion where the surface temperature of the object to be coated is 200 ° C. or more even partially, this cannot be ignored. In such a case, it has been found that the curing reaction proceeds even at a high temperature of the object to be coated, and it is necessary to improve the high-temperature characteristics, and the curing agent (2) works effectively. When the curing agent (B) is used together with the general formula (1) and the general formula (2) in a limited range,
Surprisingly, despite the fact that most of the curing conditions are in the low-temperature region of 200 ° C. or less, even if there is a locally high temperature portion of 200 ° C. or more, the properties of the coating film can guarantee excellent performance as a whole. . In particular, portions having different heating and cooling rates, such as a receiving portion and an outlet portion, are locally 230 to 150 ° C. at the start of coating.
It is particularly effective under the pre-heated curing conditions under natural cooling with an uneven temperature distribution. The general formula (2) which is a component of the curing agent (B) is exemplified by Curesol 2MZ, Curesol 2PZ, manufactured by Shikoku Chemical Industry Co., Ltd.
Curesol 2PZL and the like. The chemical names and structural formulas are as follows.

Embedded image

Further, the filler (C) will be described. Coloring pigments, extenders and additives can be added as the filler (C). In each case, known materials can be used.
Examples of the coloring pigment include titanium oxide, carbon black, and iron oxide. Examples of the extender include calcium carbonate, silica, and barium sulfate.
As an additive, an acrylic oligomer (flow control agent) or finely divided silica (powder flow improver) can be used. Further, if necessary, known auxiliary materials such as a curing accelerator, a surface conditioner and an antifoaming agent can be added, but this does not impair the effects of the present invention.

As a typical example of the epoxy resin powder coating of the present invention, the bisphenol type epoxy resin (A) 10
0 parts by weight, 0.1 to 5.0 parts by weight of the curing agent (B) represented by the general formula (1) with respect to the epoxy resin, and 0 to 5 parts by weight of silica as the filler (C) with respect to the epoxy resin. Fifteen
One compounded with 0 parts by weight is exemplified. In the case where curing under natural cooling is required in a coating line not equipped with a post-curing furnace, the epoxy resin (A) 100
The curing agent (B), which is a mixture of the compounds represented by the general formulas (1) and (2), is used in an amount of 0.1 to 5.0 parts by weight.
The mixing ratio (general formula (1) / general formula (2)) is 9 in parts by weight.
9/1 to 30/70, and examples of the filler (C) in which silica is added to the epoxy resin in an amount of 0 to 150 parts by weight. The present invention was developed as a powder coating for the inner surface of cast iron pipes for water pipes. The bisphenol-type epoxy resin (A), which enables low-temperature curing, which is a feature of the present invention, and a specific curing agent (B) As long as it does not deviate from the composition combination of (1), the effect is exhibited, and it can be applied not only to the inner surface of cast iron pipes for water pipes but also to all powder coatings that can lower the curing temperature in the heating process. It is.

As a method for producing a powder coating of the present invention, a general method for producing a powder coating can be applied. Although it can be produced by simply mixing the above-mentioned materials at room temperature, it is preferable to produce it by a commonly used melt mixing method. That is, after premixing each raw material,
If it is necessary to adjust the particle size distribution after melt-mixing at 100 to 130 ° C. and pulverization, classification may be performed to obtain a powder coating.

With respect to the powder coatings obtained as described above, the state of coating film formation was evaluated while observing the coating film appearance. When a conventional powder coating is electrostatically applied, the softening point and the curing temperature of the resin are very close, and the induction time and the curing time until the resin reaches a temperature at which the resin can melt and flow can be very long. It was in a state where curing was completed at the same time as melting, and it was difficult to smooth the coating film. On the other hand, by using the powder coating according to the present invention, the coating film can be cured even in a low temperature region maintained at 150 ° C. or lower, and a high temperature portion of 200 ° C. or higher is locally formed. Even when it was present, it was found that, at the time of coating, no evaporation path or trace of evaporation of volatile components remained in the coating film, and no trace of spraying was observed, and a smooth coating film could be formed. When various tests were performed using the powder coating obtained as described above, storage stability, curability, low-temperature baking properties and various cured physical properties,
It has been confirmed that there is no inferiority to a conventionally used high temperature cured coating film of a powder coating.

[0018]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which, however, are not intended to restrict the scope of the present invention. In the examples and comparative examples, the number of parts by weight of each component indicates parts by weight unless otherwise specified.

First, an evaluation was made of a case where a curing furnace was provided after coating and reheating was performed to terminate the curing reaction. 2
The case where post-curing was provided in a low temperature region maintained at 00 ° C or lower, preferably 150 ° C or lower was evaluated. The formulation is shown in Table 1.

Example 1 A basic nitrogen-containing heterocyclic compound derived from 2-phenylimidazole (Shikoku) as an epoxy resin (A), 100 parts of Epototo YD-903 manufactured by Toto Kasei Co., Ltd. as a curing agent (B) Kasei Kogyo Co., Ltd., Curesol 2PZ
-OK: 2 parts of curing agent A), titanium oxide (Ishihara Sangyo Co., Ltd.)
, CR-50), 50 parts of silica (Crystalite-A, manufactured by Tatsumori Co., Ltd.), and 1 part of a flow control agent (Modaflow III, manufactured by Monsanto Co., Ltd.). Melt mixed. After cooling, the mixture was pulverized and classified with a 100-mesh wire net to obtain a powder coating material I. The obtained powder coating was baked on a cold-rolled steel sheet specified in JIS G 3141 under the coating conditions shown in Table 2b. Table 2a and Table 2b show the physical properties of the paint, the flexibility of the paint, the impact resistance of the paint, the adhesion of the paint, the corrosion resistance of the paint, and the temperature resistance of the paint. Gradient comparisons were made.

Example 2 The same test as in Example 1 was performed. However, a method similar to that of Example 1 was used except that 1 part of TH-1000 (Totoamine TH-1000: curing agent E) and 3 parts of curing agent A were used as the curing agent (B). Powder coating II was obtained. Further, the same evaluation as in Example 1 was performed.

Example 3 The same test as in Example 1 was performed. However, the epoxy resin (A) used was Epototo YDF-803 manufactured by Toto Kasei Co., Ltd.
To 100 parts, and 4 parts of a basic nitrogen-containing heterocyclic compound derived from 2-methylimidazole (Curesol 2MZ-A: curing agent B, manufactured by Shikoku Chemicals Co., Ltd.) as the curing agent (B) used. , Powder paint in the same manner as in Example 1
III was obtained. Further, the same evaluation as in Example 1 was performed.

Comparative Example 1 The same test as in Example 1 was performed. However, a powder coating material IV was obtained in the same manner as in Example 1, except that 2 parts of dicyandiamide was used as a curing agent (B) and 1 part of a curing agent C was used as a curing accelerator. Further, the same evaluation as in Example 1 was performed.

Comparative Example 2 The same test as in Example 1 was performed. However, in place of the 2-methylimidazole / isocyanuric acid adduct, 4-part of unadducted 2-methylimidazole (Curesol 2MZ: curing agent C, manufactured by Shikoku Chemicals Co., Ltd.) was used instead of the 2-methylimidazole / isocyanuric acid adduct. A powder coating V was obtained in the same manner as in Example 1 except for the above. Further, the same evaluation as in Example 1 was performed.

Comparative Example 3 Powder coating VI was prepared in the same manner as in Example 1 except that 2 parts of curing agent A of the curing agent (B) used in Example 1 were replaced with 6 parts outside the scope of the claims. Obtained. Further, the same evaluation as in Example 1 was performed. The formulation is shown in Table 1. In addition, Examples 4 and 5 and Comparative Examples 4 and 5 described later are also described.

[0026]

[Table 1]

Test method (1) Gel time Place the powder coating on a hot plate kept at 150 ° C. and stir with a needle. Measure the time until the paint gradually thickens and the paint no longer pulls. (2) Gel fraction The obtained coating film is peeled off and finely ground to obtain a sample. This is subjected to chloroform extraction for 24 hours using a Soxhlet extractor, and the ratio of paint not extracted is determined. (3) Storage stability Evaluation of coating workability and coating film appearance after storage at 40 ° C. × 1 month. No abnormalities ○, problematic × (4) Blocking property Whether blocking occurred after storage at 40 ° C for 1 month. No abnormalities ○, problems × (5) Appearance of coating film Follow the test method of JIS G 5528 6.2. The smoothness of the coating film is visually observed, and the presence or absence of a pinhole is determined by applying 1000 V with a holiday detector. No abnormality ○, problematic × (6) Flexibility of coating film JIS G 5528 5.4.
Follow the provisions of 4. Erichsen test (JIS Z224)
According to 7). 3 mm or more ○, less than 3 mm × (7) Impact resistance JIS G 5528 5.4.3
Follow the provisions of DuPont impact test (JIS K54
00 8.3.2). The shooter drops a 1/4 inch radius, 500 g weight from a height of 50 cm. No abnormality ○, problematic × (8) Adhesion JIS G 5528 5.4.2
Follow the provisions of It complies with the provisions of JIS K 5400 8.5. Make a 1 mm square cross cut, and remove 5
% Is evaluated as 8 points. 8 points or more ○, less than 8 points × (9) Corrosion resistance JIS G 5528 5.4.6
Follow the provisions of Salt spray test (JIS K 5400
According to 9.1). The test time is 500 hours. No abnormality ○, problem ×

(10) Resistance to Temperature Gradient
The back surface (coated surface) was immersed in water with a temperature gradient of 25 ° C., and the appearance of the coating film was evaluated 14 days later. Japan Paint Inspection Association Visual judgment using coating film evaluation criteria (11) Actual pipe coating Each powder coating is electrostatically coated on the inner surface of a ductile cast iron pipe having a diameter of 100 mm and a length of 500 mm, and the appearance is investigated. The coating film appearance is evaluated in accordance with JIS G 5528 6.2 by cutting the object to be coated in half in the longitudinal direction after coating. Construction conditions Pipe rotation speed: 320 rpm Construction temperature: Preheating After preheating to the heating temperature, paint. Curing method: Apply at each temperature in Tables 2 and 3 and allow to cool. Number of constructions: 10 each Evaluation ○: No abnormality △: Somewhat problematic (pinholes or bubbles generated in 1 to 4 / 10s) ×: Problematic (pinholes or bubbles in 5 or more / 10s) Occurrence) The measurement results for Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Tables 2a and 2b.

[0029]

[Table 2a]

[0030]

[Table 2b]

Next, the temperature range at the start of coating is from 230 to 1
An evaluation was made of a case where curing under natural cooling with a non-uniform temperature distribution of 50 ° C. was required. Example 4 The same test as in Example 1 was performed. However, 2 parts of a basic nitrogen-containing heterocyclic compound (Curesol 2PZ-OK: curing agent A, manufactured by Shikoku Chemicals Co., Ltd.) derived from 2-phenylimidazole as the curing agent (B), and 2-methyl Using 1 part of imidazole (manufactured by Shikoku Chemicals Co., Ltd., Curezol 2MZ: curing agent C), a powder coating VII was obtained in the same manner as in Example 1. About the obtained powder coating, J
Table 3b for the cold-rolled steel sheet specified in IS G 3141
The baking was performed under the coating conditions shown in. In addition, regarding the obtained coating film, the physical properties of the coating material shown in Tables 3a and 3b, the flexibility of the coating film,
The impact resistance of the coating, the adhesion of the coating, the corrosion resistance of the coating, and the temperature gradient of the coating were compared. In addition, as an evaluation in actual pipe coating, in order to determine the appearance after coating and the state of occurrence of pinholes, the powder obtained on the inner surface while rotating a ductile cast iron pipe of φ = 100 mm L = 500 mm at 320 rpm was used. The paint was applied under various coating conditions shown in Table 3b, and the performance was evaluated. The test method is as described above.

Example 5 The same test as in Example 1 was performed. However, 2 parts of curing agent B and 2 parts of 2-phenylimidazole (Curesol 2PZL: curing agent D, manufactured by Shikoku Chemicals Co., Ltd.), which is a raw material of 2-phenylimidazole, were used as the curing agent (B). Except for the above, a powder coating VIII was obtained in the same manner as in Example 1. Further, the same comparative evaluation as in Example 1 was performed.

Comparative Example 4 The same test as in Example 1 was performed. However, a powder coating IX was obtained in the same manner as in Example 1, except that 1 part of the curing agent A and 3 parts of the curing agent C were used as the curing agent (B).

Comparative Example 5 The powder coating material I obtained in Example 1 was used. Example 1
The same comparative evaluation was performed.

[0035]

[Table 3a]

[0036]

[Table 3b]

[0037]

As described above, according to the present invention, by blending a bisphenol-type epoxy resin as an epoxy resin with a specific curing agent and a filler, it is possible to obtain excellent storage stability and blocking properties, and the conventional powder. This powder coating cures at a low temperature compared to the body coating, and cures without any problem even when it needs to be cured under natural cooling with a temperature distribution at the start of coating that is not uniform. The film obtained from is flexible (proper Erichsen value), impact resistance,
It has excellent properties of adhesion, corrosion resistance and temperature gradient resistance.

Continued on the front page (72) Inventor Goro Funabashi 2-26-Ohama-cho, Amagasaki-shi, Hyogo Prefecture Inside Kubota Mukogawa Works Co., Ltd. Inside the Mukogawa Works (72) Inventor Hiroshi Nakanishi 10 at Techno Park, Mita City, Hyogo Prefecture Inside the Tokyo Metropolitan Resin Chemical Co., Ltd.Mita Plant (72) Inventor Masayoshi Kashino 1 at 10 Techno Park, Mita City, Hyogo Prefecture In the Mita Plant of Kako Co., Ltd. (72) Inventor Tsutomu Hamada 1 of 10 Techno Park, Mita City, Hyogo Prefecture F-term in the Mita Plant of Tokyo Resin Chemical Co., Ltd. F term (reference) 4D075 BB23X BB93X CA47 DA15 DA19 DB01 EA02 EB34 EB53 EB55 EC37 EC54 4J036 AD08 AD09 DC41 DC45 FA05 JA03 4J038 DB001 DB061 GA07 HA446 JB32 JB36 KA03 KA08 MA02 MA13 PC02

Claims (8)

[Claims] 1. An epoxy equivalent of 500 to 2,500 g
/ Eq, in a powder coating composition comprising an epoxy resin (A) having a softening point of 65 to 130 ° C., a curing agent (B) and a filler (C) as essential components, the epoxy resin (A) is bisphenol Epoxy resin, and the curing agent (B)
A low temperature-curable powder coating composition comprising a basic nitrogen-containing heterocyclic compound. 2. The curing agent (B) is a basic nitrogen-containing heterocyclic compound represented by the general formula (1).
A powder coating composition which can be cured at a low temperature as described above. Embedded image R = H, C _n H _{(2n + 1)} , phenyl group However, in the case of R = CH ₃ and isocyanuric acid adduct, crystallization water nH ₂ O is attached. 3. A mixture of the basic nitrogen-containing heterocyclic compound represented by the general formula (1) and the basic nitrogen-containing heterocyclic compound represented by the general formula (2), wherein the curing agent (B) is a mixture. The powder coating composition capable of being cured at a low temperature according to claim 1. Embedded image Where R = H, C _n H _{(2n + 1)} , phenyl group 4. The method according to claim 1, wherein the filler (C) is silica.
4. The powder coating composition capable of being cured at a low temperature according to 2, 3. 5. The curing agent (B) is a basic nitrogen-containing heterocyclic compound represented by the general formula (1) in an amount of 0.1 to 5.0 parts by weight based on 100 parts by weight of the epoxy resin (A). And
The amount of the filler (C) added is 0 to the epoxy resin.
The low-temperature curable powder coating composition according to claim 1, wherein the amount is 150 parts by weight. 6. The curing agent (B) is used in an amount of 0.1 to 5.0 parts by weight based on 100 parts by weight of the epoxy resin (A). When the compounding ratio (general formula (1) / general formula (2)) of the compound represented by (2) is 99
The low-temperature curable powder coating composition according to claim 1, wherein the amount of the filler (C) is 0 to 150 parts by weight based on the epoxy resin. . 7. A method for coating an inner surface of a metal tube using the powder coating material according to claim 1, wherein the curing temperature at the time of coating the previously heated metal tube is 200 ° C. The following is a method for forming a coating film having excellent corrosion resistance. 8. A method for coating an inner surface of a metal tube using the powder coating material according to claim 1, wherein the coating start temperature at the time of coating the previously heated metal tube is 230. ~ 1
A method of forming a coating film having excellent corrosion resistance on a metal tube having a non-uniform temperature distribution in the range of 50 ° C.