JPH0522741B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a powder coating composition for reinforcing bars. Generally, in concrete structures, reinforcing rods, particularly deformed reinforcing rods having convex portions on the outer periphery, are inserted to provide strength. Conventionally, since the concrete of these reinforcing bars is in an alkaline environment, a thin film of hydrated oxide called a passive film is formed on the surface of the reinforcing bars, so corrosion of reinforcing bars has rarely been a problem. However, in recent years, due to the use of sea sand and the spraying of ice melting agents due to the depletion of aggregate resources, reinforcing rods in concrete come into contact with corrosive substances such as chlorine ions, and the passive film may be destroyed. Alternatively, the formation of a passive film is inhibited, resulting in corrosion of reinforcing bars, which has become a problem. Therefore, a method was proposed to protect reinforcing bars from corrosion by coating them with an epoxy resin powder coating that has excellent corrosion resistance and durability. However, since painted reinforcing steel bars are often used after being deformed into a "C" shape, etc., such powder coatings must not only be corrosion resistant, but also be able to withstand the deformation to the extent that the coating film does not deteriorate. It is required to have good bending workability and good ability to maintain the shape of the deformed reinforcing bar, but no conventional epoxy resin powder coating that satisfies these conditions is known yet. In view of the above-mentioned current situation, the inventors of the present invention have developed a coating film with excellent bending workability and shape retention while taking advantage of the excellent performance of epoxy resin powder coatings such as corrosion resistance and chemical resistance. The present invention was developed as a result of extensive research into an epoxy resin powder coating for reinforcing bars that can be formed, has excellent storage stability, and can be cured quickly. That is, the present invention provides (A)(i) an epichlorohydrin-bisphenol type epoxy resin having at least two or more epoxy groups in one molecule and having a melting point of 50 to 140°C...50 to 95% by weight; (ii) General formula: (However, m is an integer from 4 to 18, and n is from 2 to
5 to 50% by weight of a polyacid polyanhydride with a melting point of 50°C or higher, represented by (an integer of 20), and the ratio of the acid anhydride equivalent of the polyacid polyanhydride to the epoxy equivalent of the epoxy resin The ratio (acid anhydride equivalent/epoxy equivalent) is
A mixture of 0.6 to 1.0...
...100 parts by weight, (B) triphenylphosphine...0.1 to 4 parts by weight, and (C) ultrafine anhydrous silica with an average particle size of 30 mμ or less...0.1 to 2 parts by weight. relating to things. The epichlorohydrin-bisphenol type epoxy resin which is one component of the powder coating composition of the present invention includes epichlorohydrin-bisphenol A
Epichlorohydrin-bisphenol F type epoxy resin is used, but one having at least two or more epoxy groups in one molecule is suitable. When the number of epoxy groups decreases, coating film strength, adhesion, etc. decrease, which is not preferable. Moreover, the melting point of the epoxy resin is suitably 50 to 140°C. If the melting point is less than 50°C, it is not preferable because the powder state required for a powder coating at room temperature cannot be maintained and storage stability deteriorates. On the other hand, if the temperature exceeds 140°C, it is generally necessary to keep the temperature below 140°C in the melting and kneading process of powder coating production, so the powder coating composition of the present invention, which is a fast-curing powder coating, Part of the reaction proceeds during the kneading step, which is undesirable because it has an adverse effect on coating performance, storage stability, and the like. As the epichlorohydrin-bisphenol type epoxy resin, those obtained by modifying the above-mentioned epoxy resin with dimer acid, polybutadiene, acrylonitrile rubber, novolak resin, etc. can also be used. Specifically, the commercially available Epotote YD-011, Epotote YD-012, Epotote YD-013, Epotote YD-014, Epotote YD-017, Epotote YDF-1701, Epotote YDF-1704, Epotote YDF-1707 (the above Toto Kasei company product name);
AER661, AER664, AER667 (product names manufactured by Asahi Kasei Industries, Ltd.); Epicron 1000, Epicron
1010, Epicron 3010, Epicron 3050 (all product names manufactured by Dainippon Ink and Chemicals); EPOMIK R
-301, EPOMIK R-302, EPOMIK R-304,
EPOMIK SR-33, EPOMIK R-304E,
EPOMIK R-304P, EPOMIK R-307 (trade names manufactured by Mitsui Petrochemical Epoxy Co., Ltd.); Epicote
1001, Epicote 1001FR, Epicote 1002, Epicote 1004, Epicote 1004K, Epicote
DX-55X, Epicote 1007 (product names manufactured by Ciel Chemical Co., Ltd.); DER661, DER662, DER663U,
DER664, DER664U, DER667 (and above)
(trade name manufactured by Chemical Co., Ltd.) is a typical example. In addition, the polyacid polyanhydride, which is one component of the powder coating composition of the present invention, is used as a curing agent for epoxy resin and has the general formula (However, m is an integer of 4 to 18, and n is an integer of 2 to 20.) Compounds having a melting point of 50°C or higher and mixtures of these compounds. In addition, in the general formula, the smaller the m value, the more difficult it is to obtain a coating film with elongation, that is, the flexibility, and the bending workability tends to deteriorate, so it is 4 or more, particularly preferably 8 or more. It is preferable that If the m value exceeds 18, the hardness of the coating film decreases, which is not preferable. Furthermore, if the n value is less than 2, the coating film performance during high-temperature, short-time curing (230°C, 3 minutes) will not be fully demonstrated, and if it exceeds 20, reactivity will increase, resulting in the melt-kneading process of powder coating manufacturing. Both are unfavorable because the reaction partially proceeds and has an adverse effect on coating performance and storage stability. Further, it is desirable that the polyacid polyanhydride has a linear (-CH ₂ ) _-n as shown in the formula. others,
Polyacid polyanhydrides having some side chains may also be used. Furthermore, it is essential that the melting point of the polyacid polyanhydride is 50°C or higher. If the melting point is less than 50°C, it is not preferable because the powder cannot be maintained at room temperature. Specifically, commercially available OSK-DA-SL-20AH,
OSK-DA-SL-12AH, OSK-DA-SL-
20ADAH (product name manufactured by Okamura Oil Co., Ltd.), DSPA
(trade name manufactured by ACI Japan Limited) etc. are listed as representative examples. Furthermore, triphenylphosphine, which is one of the components of the powder coating composition of the present invention, has excellent coating film performance even under baking conditions of 230°C for 3 minutes, which is considered a tentative standard for high-temperature, short-curing powder coatings. used to demonstrate. Further, the ultrafine anhydrous silica, which is a component of the powder coating composition of the present invention, usually has an average particle size of 30 mμ or less and a surface area of 100 m ² /g or more, and is used in the deformed reinforcing bar of the present invention. When a powder coating composition is applied, the shape of the convex portion is not impaired, that is, it is used to improve shape retention. Examples of the ultrafine anhydrous silica include
AEROSIL130 (average particle size 16 mμ, surface area 130 m ² /
g), AEROSIL200 (average particle size 12mmμ, surface area 200
m ² /g), AEROSIL300 (average particle size 7 mμ, surface area 300 m ² /g), AEROSIL380 (average particle size 7 mμ,
surface area 380 m ² /g), AEROSIL R972 (average particle size 16
mμ, surface area 110 m ² /g) [the above are trade names manufactured by Nippon Aerosil Co., Ltd.], and the like. The powder coating composition of the present invention contains the above-mentioned epoxy resin, polyacid polyanhydride, triphenylphosphine, and ultrafine anhydrous silica as essential components. The appropriate blending ratio of the epoxy resin and the polyacid polyanhydride as a curing agent is (50-95):(50-5) [by weight]. This is because the original resin properties are exhibited within this range. Further, it is necessary to blend the epoxy resin and the polyacid polyanhydride so that the ratio of the acid anhydride equivalent of the polyacid polyanhydride to the epoxy equivalent of the epoxy resin (acid anhydride equivalent/epoxy) is 0.6 to 1.0. If the ratio exceeds 1.0, the storage stability of the powder coating becomes poor, and as a result, the paint film obtained using the powder coating after being stored for 7 days under conditions of 40°C, especially at low temperatures. Bending workability deteriorates significantly in this region. Similarly, if the ratio is less than 0.6, the bending workability, particularly in the low temperature range, will deteriorate significantly, which is not preferable. The appropriate amount of triphenylphosphine to be used is 0.1 to 4 parts by weight based on 100 parts by weight of the total amount of the epoxy resin and polyacid polyanhydride. If the amount of triphenylphosphine used is less than 0.1 part by weight, the coating film performance during high temperature short-time curing (230°C, 30 minutes) will not be fully demonstrated, and if it exceeds 4 parts by weight, corrosion resistance etc. will decrease. Therefore, neither is preferable. The amount of ultrafine anhydrous silica used is suitably 0.1 to 2 parts by weight based on 100 parts by weight of the total amount of epoxy resin and polyacid polyanhydride. If the amount of ultrafine anhydrous silica used is less than 0.1 part by weight, the above-mentioned effect of addition will not be observed, and if it exceeds 2 parts by weight,
Both are unfavorable because the smoothness of the coating film deteriorates and pinholes are likely to occur in the coating film. The powder coating composition of the present invention may contain, if necessary, additives such as surface conditioners, anti-sagging agents, and antistatic agents that are normally used in powder coatings; titanium dioxide, iron oxide, carbon black, and zinc powder. , coloring pigments such as aluminum powder; extender pigments such as barium sulfate, calcium carbonate, talc, glass fiber; modified resins such as novolac resin, phenoxy resin, butyral resin, ketone resin, polyester resin; epoxidized oil, dioctyl phthalate, etc. An effective amount of a plasticizer or the like can be appropriately added. A typical method for producing the powder coating composition of the present invention includes adding the above-mentioned epoxy resin, polyacid polyanhydride, triphenylphosphine, and, if necessary, the above-mentioned additives, pigments, resins, etc. After rough mixing, a method may be used in which the mixture is melt-kneaded using a heating kneader, heating roll, extruder, etc., usually at about 70 to 140°C, and after cooling, the ultrafine anhydrous silica is dry blended and pulverized. It should be noted that if ultrafine particulate anhydrous silica is melt-kneaded at the same time as other components, the above effects of addition cannot be obtained, which is not preferable. The average particle size of the powder coating obtained in this way is
A suitable thickness is 30 to 150μ. Next, the method after powder coating the reinforcing bar will be explained.
The reinforcing bars are subjected to surface treatments such as shot blasting and grit blasting, and then preheated in a heating furnace. In the present invention, it is possible to use a so-called post-heating method in which powder coating is applied and heated without preheating, but this is not appropriate because it tends to cause voids in the coating film and causes corrosion of the reinforcing bars. The preheating temperature is 170°C for the powder coating composition of the present invention.
In order to sufficiently react and harden at a low temperature of about 170℃, a temperature of about 170℃ is sufficient, but in consideration of the temperature drop of the reinforcing bar, it is recommended to set the temperature at 180℃.
℃ or higher, preferably 200 to 250℃. Next, the powder coating composition is coated to a film thickness of approximately 180 mm using an electrostatic powder spray coating machine commonly used for powder coatings.
Paint the above reinforcing bar to a thickness of ~250μ. In addition,
Post-heating after painting is not particularly necessary, but there is no problem with post-heating to an appropriate temperature. The powder coating composition of the present invention, which contains the above-described epichlorohydrin-bisphenol type epoxy resin, polyacid polyanhydride, rifenylphosphine, and ultrafine anhydrous silica as essential components, has excellent bending workability. It is possible to form a coating film, and the gelation time after melting is short, so reflowability is low, so when applied to deformed reinforcing bars, the shape of the convex part is not impaired, that is, the deformation retention is good. Furthermore, it has the characteristics of excellent storage stability even at high temperatures and rapid curing. Therefore, the powder coating composition for reinforcing bars of the present invention is as follows:
It has great practical value in this industry. Hereinafter, the present invention will be explained in more detail with reference to Examples. In addition, "part" and "%" in the examples are based on weight. Examples 1 to 9 and Comparative Examples 1 to 9 The compositions shown in Table 1, excluding ultrafine anhydrous silica, were roughly mixed in a Henschel mixer, then melt-kneaded in a twin-screw extruder, and cooled. Then, unground pellets were produced. Next, ultrafine anhydrous silica particles were mixed uniformly into the pellets, and the pellets were pulverized into fine particles using a pulverizer to prepare a 150-mesh pass powder coating. The obtained powder coating was applied to a shot-blasted deformed reinforcing rod (JISG3112,
Name D19) Paint the surface with an electrostatic powder spray coating machine to a dry film thickness of 200μ, then 230μ
Baked at ℃ for 3 minutes. Table 2 shows the results of a performance test of the resulting coating film. Further, the powder coating was placed in a polyethylene bag, sealed, and stored in a thermostat at 40°C for 7 days, and then painted and baked in the same manner. The results of the performance test of the obtained coating film are shown in the lower column of Table 2.

【table】

【table】

【table】

[Epoxy equivalent: 950, melting point: 100℃]

Examples 7 to 9 Comparative example of a (1:1) mixture of Epicote #1004 and Epicote #1007 (product name manufactured by Ciel Chemical Co., Ltd.) [epoxy equivalent: 1950, melting point 127°C] 5 Epicote #1009 (product name manufactured by Ciel Chemical Co., Ltd.) Name) [Epoxy equivalent: 2950, melting point: 150°C] (Note 2) Examples 1, 3 to 4 OSK-DA-SL-20AH (trade name, manufactured by Okamura Oil Co., Ltd.) [m = 14 in the above general formula is approximately 10%, m=18 is about 90%
Example 2 OSK-DA-SL-20AH-4 (trade name manufactured by Okamura Oil Co., Ltd.) [A compound of the general formula m=14 is about 10%, m=18 is about 90%
Example 5 and Comparative Examples 1 to 5, 8 to 9 OSK-DA-SL-20ADAH (manufactured by Okamura Oil Co., Ltd.) Product name) [In the above general formula, m = 4 is approximately 30%, m = 14 is approximately 7
%, m=18 is a mixture of about 63%, n=3.2 (average value)
A compound with an acid anhydride equivalent of 180 and a melting point of 86°C] Examples 6 to 9 OSK-DA-SL-12AH (trade name manufactured by Okamura Oil Co., Ltd.) [m = 10, n = 3.2 (average value) in the general formula A compound with an acid anhydride equivalent of 170 and a melting point of 84°C] Comparative Example 6 Dicyandiamide Comparative Example 7 Adipic acid dihydrazide (Note 3) AEROSIL 200 (trade name manufactured by Nippon Aerosil Co., Ltd.) (Note 4) Visual judgment of coating film condition ○: Good ×: Defective (Note 5) Visually judge the protrusions [protrusions in the axial direction (ribs) and protrusions in other than the axial direction (knots)] of the deformed reinforcing bar. ○: The irregularity of the deformed reinforcing bar is maintained (deformed shape retained). In other words, a coating film with a uniform film thickness is formed on the entire deformed reinforcing bar according to the shape of the uneven parts, and the uneven state of the deformed reinforcing bar is reproduced as is. ×: The irregularity of the deformed reinforcing bar is In other words, the thickness of the paint film on the top of the convex part in the uneven part is relatively thin, and the paint film is relatively thick on the concave part, centering on the base of the convex part, and the unevenness Condition in which the shape of the part disappears (Note 6) A deformed reinforcing bar is bent and the coating condition of the part is visually judged [Bending conditions: Temperature 5℃; 4D (bending diameter) x 180°
(Angle)] ○: No abnormalities ×: Abnormalities such as clutches (Note 7) Visually judge the state of the paint film after immersion in 10% caustic soda solution (20℃) for 100 hours ○: No abnormalities ×: Fading, etc. As is clear from Table 2, the powder coating composition of the present invention had excellent coating film performance. On the other hand, in Comparative Example 1 in which the ratio (acid anhydride equivalent/epoxy equivalent) exceeded 1, the bending workability after storage was poor. On the contrary, in Comparative Example 2 in which the ratio was less than 0.6, the bending workability and alkali resistance were poor. Furthermore, in Comparative Example 3 in which ultrafine anhydrous silica was contained in excess, the smoothness and bending workability were poor. On the contrary, in Comparative Example 4 in which ultrafine anhydrous silica was not added, the shape retention was poor. Further, in Comparative Examples 6 and 7 in which a curing agent other than the polyacid polyanhydride of the present invention was used, the bending workability was poor. Comparative Example 8, in which a small amount of triphenylphosphine was added, had poor shape retention, bending workability, and alkali resistance; conversely, Comparative Example 9, in which an excessive amount of triphenylphosphine was added, had poor alkali resistance and bending workability after storage. .

Claims (1)

[Scope of Claims] 1 (A)(i) Epichlorohydrin-bisphenol type epoxy resin having two or more epoxy groups in one molecule and having a melting point of 50 to 140°C...50
~95% by weight; (ii) General formula: (However, m is an integer from 4 to 18, and n is from 2 to
5 to 50% by weight of a polyacid polyanhydride with a melting point of 50°C or higher, represented by (an integer of 20), and the ratio of the acid anhydride equivalent of the polyacid polyanhydride to the epoxy of the epoxy resin Equivalent ratio (acid anhydride equivalent/epoxy equivalent) is 0.6
A mixture that is blended so that it becomes ~1.0...
100 parts by weight, (B) triphenylphosphine...0.1 to 4 parts by weight,
and (C) ultrafine anhydrous silica particles with an average particle size of 30 mμ or less...
...0.1 to 2 parts by weight of a powder coating composition for reinforcing bars.