JPS6014971A - Powder coating method of reinforcing bar - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION A certain O generally contains conc. In REIT structures, reinforcing bars, particularly deformed reinforcing bars having convex portions on the outer periphery, are usually inserted in order to provide strength. Conventionally, this reinforcing bar is made of concrete in an alkaline environment, so a thin film of hydrated oxide called a passive film is formed on the surface.
Corrosion of the reinforcing bars was therefore hardly a problem.

However, in recent years, due to the depletion of aggregate resources, the use of sea sand and the spraying of ice melting agents have made the reinforcing rods in concrete
When it comes into contact with corrosive substances such as chlorine ions, the passive film is destroyed or the formation of the passive film is inhibited,
As a result, corrosion of the reinforcing bars has become a problem.

Therefore, a method has been proposed in which reinforcing bars are coated with an epoxy resin powder coating that has excellent corrosion resistance and durability to protect them from corrosion.

However, since painted reinforcing rods are often used after being deformed into a shape such as a square, the pipe paint must not only be corrosion resistant, but also be able to withstand the deformation to the extent that the coating film does not deteriorate. Good bending workability is required,
No conventional epoxy resin powder coating that satisfies these conditions is known yet.

In view of the above-mentioned current situation, the present inventors have discovered that they can form a coating film with excellent bending workability 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-based powder coating for reinforcing bars that has excellent storage stability and can be cured at low temperatures.

That is, the present invention provides (A)(1) epichlorohydrin-bisphenol type having at least two or more epoxy groups in the /molecule and having a melting point of 3θ to /'10°C to a reinforcing bar preheated to /gO or above. Epoxy resin······
・・・・・・・・・・・・・・・・・・・・・・・・
... Polymer with a weight coefficient of 50 to 93 and a melting point of 5 occ or more represented by the general formula (where m id must be an integer of g to /g, and n is an integer of a to 0) Acid polyanhydride...
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・5-40% by weight・・・・・・・・・・・・・70
0 parts by weight and (B))! J phenylphosphine.../~
The present invention relates to a powder coating method for reinforcing steel bars, which is characterized by coating a powder coating composition consisting of 4=xi parts.

As the epichlorohydrin-bisphenol type epoxy resin which is one component of the powder coating composition used in the present invention, epichlorohydrin-bisphenol A type and epichlorohydrin-bisphenol F type epoxy resin are used. Those having more than 3 epoxy groups are suitable. When the number of epoxy groups decreases, coating film strength, adhesion, etc. decrease, which is not preferable.

Further, the melting point of the epoxy resin is suitably 50 to 4tO°C. If the melting point is less than 0°C, the powder state required for a powder coating at room temperature cannot be maintained and the storage stability becomes poor, which is not preferable. On the other hand, when /daθ0C is exceeded, the temperature must generally be kept above /lθ0C in the melting and kneading process of powder coating production, so this powder coating composition, which is a low-temperature, fast-curing powder coating, Part of the reaction proceeds during the id melt-kneading process, which is not preferable because it does not adversely affect the coating film performance, especially the smoothness of the coating film.

As the epichlorohydrin-bisphenol type epoxy resin, the above-mentioned epoxy resins modified with dimer acid, polybutadiene, acrylonitrile, etc. can also be used.

Specifically, commercially available F3? Tote YD-0//, engineering
issue? TOTO YD-0/, 2, EPOTO
- YD-073, epot -) YD-77
/l', epot YD-θ/7
, Epot YDF-2007, Eng.
I? To-to YDF-ko θ o 4t,
EPOTO-TO YDF-KO θθ7 (all trade names manufactured by Tobu Kasei Co., Ltd.); A, E, R.

66/, A, E, R, A
o, Epicron 1010, Ebicuron 301θ, Ebicuron 30j3-θ (all trade names manufactured by Dainippon Ink and Chemicals); EPOMIK R-, 70/, EPOMIK
R-,? θko, EPOMIK R-, 301I, EP
OMIK 5R-33, EPOMIK R-3011E
% EPOMIK R-30gP.

EPOMIK R-307 (product name manufactured by Mitsui Petrochemical Eposhi Co., Ltd.); Epicort 1008 Epicort 10
0/FR, Epicor) 100, Epicor 100
'l.

Epicort 1004tK, Epicort) DX-3jX,
Epicote 10θ7 (trade name manufactured by Shell Chemical Co., Ltd.); D
, E, R, l, A /, D, E, R, A4, D
,E,R,t43U.

D, E, R, A/l, D, E, R, AA da U, D.
Typical examples include E, R, and Otsu67 (all trade names manufactured by Dow Chemical Company).

Polyacid tetraanhydride, which is a component of the powder coating composition, is used as a curing agent for epoxy resin and has the general formula (where In is an integer of g~/g, and n is 2~ It is a compound with a melting point of 3086 or higher, which is an integer of 0.

In addition, in the general formula, when the m value is less than g, the elongation of the coating film,
That is, a flexible coating film cannot be obtained and bending workability deteriorates, and conversely, if the bending angle is exceeded, the hardness of the coating film decreases, which is not preferable. Also, if the n value is less than -, the coating film performance will be sufficiently developed when cured at low temperature (it will not be blotted, and on the contrary,
Exceeding this is not preferable because the reactivity increases and some reactions proceed during the melt-kneading step of powder coating production, which adversely affects the viability of the coating film and the storage stability.

In addition, polyacid polyanhydride is a linear 1+-
Those having CH2-)-7- are desirable. In addition, polyacid polyanhydrides partially having side chains can also be used.

Further, it is essential that the melting point of the polyacid polyanhydride is 5060 or higher. If the melting point is less than 5oOc, it is not preferable because the powder cannot be maintained at room temperature.

Specifically, commercially available 08K-DA-8L-=OAH1O8
K-DA7SL-/2AHS, 08K-DA-8L-
, 20AH-G (trade name manufactured by Interzai Seishi Co., Ltd.) and the like are representative examples.

Triphenylphosphine, which is one of the components of the powder coating composition, is used to exhibit excellent coating film performance even under igoOc and SO sorting baking conditions, which is considered a rough guideline for low-temperature, fast-curing powder coatings. used for.

The powder coating used in the present invention contains the above-mentioned epoxy resin, polyacid polyanhydride, and triphenylphosphine as essential components.

The appropriate blending ratio of the epoxy resin and the polyacid polyanhydride as a curing agent is (,5-θ~9.5-):(JO~S) [by weight]. This is because the original resin properties are exhibited within this range.

The appropriate amount of triphenylphosphine to be used is about 100 parts by weight of the total amount of epoxy resin and polyanhydride. If the amount of triphenylphosphine used is less than 7 parts by weight, the coating film performance during low-temperature curing will not be sufficiently exhibited, and if it exceeds 1 part by weight, corrosion resistance etc. will deteriorate, so both are not preferred.

The powder coating composition used in the present invention may contain, if necessary, surface conditioners, anti-sagging agents, etc., which are usually used in powder coatings.
Additives such as antistatic agents; Coloring pigments such as titanium dioxide, single wave iron, carbon black, zinc powder, and aluminum powder; Barium sulfate, calcium carbonate,
Extender pigments such as talc, silica, glass fiber; novolac resin, phenoxy resin, butyral resin,
Modified resins such as ketone resins and polyester resins; epoxidized oils, plasticizers such as dioctyl phthalate, etc. can be appropriately added in effective amounts.

A typical method for producing the powder coating composition used in the present invention is to roughly mix the above three components and optional additives, pigments, resins, etc. A method may be used in which the mixture is melted and mixed using a heating roll, an extruder, etc. at a temperature of about 70 to 0.0 C, and then pulverized after cooling. The average particle size of the powder coating material obtained in this manner is suitably 3θ to /SOμ.

The powder coating composition used in the present invention, which contains the above-described epichlorohydrin-bisphenol type resin, polyacid polyanhydride, and triphenylphosphine as essential components, has a coating film with excellent bending properties. It also has a short dulling time after melting, and therefore has low reflow properties, so when applied to deformed reinforcing bars,
It is suitable as a powder coating for reinforcing bars because the shape of the convex part is not lost, it has good shape retention, it has excellent storage stability even at high temperatures, and it can be cured quickly at low temperatures. Ruru.

Next, the powder coating method for reinforcing bars will be explained.

The reinforcing bars are subjected to surface treatments such as shot blasting and grid blasting, and then preheated in a heating furnace. In addition, in the present invention, it is possible to use the so-called post-heating method in which heating is performed after powder coating is applied without preheating, but it is not suitable because it tends to cause detritus in the coating film and causes corrosion of the reinforcing bar. do not have.

The preheating temperature is such that the powder coating composition used in the present invention is /7θ
Because it fully reacts and hardens at a low temperature of about OC, / or OOC
It may be a certain degree, but considering the temperature drop of the reinforcing bar, 1108
Sθ0C of 0 or more, preferably 200 to 0C is appropriate.

Next, the powder coating composition is applied to the reinforcing rod using an electrostatic powder spray coating machine or the like commonly used for powder coating to a film thickness of approximately gO to 2Sθμ. Note that post-heating after coating is not particularly necessary, but there is no problem with post-heating to an appropriate temperature.

The first factor shows a 1 m diagram of a typical painted state of the present invention. Hereinafter, the above coating method will be explained in more detail with reference to this figure.

The deformed reinforcing bar 1 preheated by a heating furnace (not shown) is heated by rotating rolls 2 constituting a competition "γ-".
; it is installed by an electrostatic powder spray coating machine 4 surrounded by a shielding plate 3. Na 2, overflow 0
The collection device 5 installed under the conveyor is used for collecting powder.
recovered by.

The deformed reinforcing bar 1 is rotated by the four mounting means shown in FIG.
Since the coating is applied in the space between the tiles 2 and 2', there is no uncoated area, making it suitable for the coating method of the present invention. Also, the electrostatic powder spray coating machine 4 is located in front (left side in the drawing).
It is further preferable that heating means be installed inside the rotating roll 2 so that the preheating temperature of the deformed reinforcing bar 1 does not decrease.

Note that by the time the deformed reinforcing bar 1 coated by the electrostatic powder spray coating machine 4 reaches the rotating roll 2' with which it comes into contact for the first time, the coating film must have been cured by a factor of about DA θ or more. 2' may have a paint film attached or damage to the paint film may occur. Therefore, it is necessary to adjust the moving speed of the deformed reinforcing bar, that is, the rotational speed of the rotating rolls 2 or the distance between the rotating rolls. That is, the time it takes for the coated deformed reinforcing bar 1 to reach the rotating roll 2' varies depending on the preheating temperature, the blending ratio of the powder coating composition, etc., but is usually about 30 seconds.

As described above, in the coating method of the present invention, the powder coating composition has excellent storage stability and can be cured quickly at low temperatures, so it has very good coating workability, and is not only corrosion resistant but also bendable. It has the characteristic of being able to form a coating with excellent workability and shape retention.

Therefore, the powder coating method for reinforcing bars of the present invention has great practical value in this industry.

Hereinafter, the present invention will be explained in more detail with reference to Examples. In the examples, "1 part" and "%" are based on heavy chain.

The powder coating composition used is obtained by roughly mixing the formulations shown in Table 7 in a Henschel mixer, then melt-kneading in a twin-screw extruder, cooling it with a cooling roll, and then finely mixing it in a pulverizer. It was prepared by grinding to obtain a powder coating of /O mesh pass.

Note/) Powder coating A, C, D, E, F, G, H, I Epicoat φ/θO+ (Product name manufactured by Shell Chemical Co., Ltd.) [Epoxy backstitch 9 left O, melting point 10θ0C] Powder coating B Epicoat + 10θ7 (trade name manufactured by Shell Chemical Co., Ltd.) [Epoxy weight M:/qso, melting point/core °C] Powder coating J Epicoat Φ1009 (trade name manufactured by Shell Chemical Co., Ltd.) [Epoxy weight J4. Ko9SO9 melting point/! ;O0C] Note 2) Powder coating A, B, C, F, G, JO8K-DA-8L-20
AH (product name manufactured by Mazai Oil Co., Ltd.) [m=/'l in the above general formula
is about /θchi2m=/zaga is about? A mixture of O, n-3-
, 2<average value), acid anhydride equivalent weight 23g, melting point 9riQ
Compound C] Powder coating D O8K-DA-8L-/CoAH (trade name manufactured by Mazashi Oil Co., Ltd.)
[In the general formula m-10, roux 3.2 (average value),
M anhydride equivalent -4/7/, melting point glI0C] Powder coating E O8K-DA-8L-ko θAH-1I (trade name manufactured by Interzai Oil Co., Ltd.) [m=/'l in the above general formula is approximately 10% , rrL
A mixture with =/l of about qθ% and an acid anhydride equivalent weight of n=//(average value) of 300. Compounds with melting point/θ0°C] Powder coating H Dicyandiamide powder coating I Tetrahydro-7-talic anhydride Note 3) No? Lac resin (D, E, N, 1 g (product name manufactured by Dow Chemical Company) Note 4") Mota 70- (product name manufactured by Monsando Chemical Company) Example / Surface treated with shot blasting Diameter / 9 m irregular shape Preheat the reinforcing bar in a heating furnace so that the temperature when it is moved to the bottom of the electrostatic powder spray coating is approximately 2'100C, and apply powder coating A to a dry film thickness of approximately 1SOμ. The moving speed of the deformed reinforcing bar 1 was adjusted so that the time from when the powder coating A was applied until it first contacted the rotating roll 2' was 30 seconds, and the deformed reinforcing bar 1 was continuously applied. The coating was carried out while moving the rod 1. The performance test results of the obtained coating film are shown in the upper column of Table 2.

Also, put powder paint A in a polyethylene bag and seal it.
After being stored in a constant temperature chamber at °C for 1s days, it was painted in the same manner, and the performance test results of the obtained coating film are shown in the lower column of Table 2. The body paints B, C, D, E, F, G, H, I, and J were coated in the same manner as in Examples, and the performance test results of the resulting paint films are shown in Table 2.

Table C Note 5) Visual judgment ○: Good
1, D (bending diameter) x 1g0o (angle)] Visual judgment of coating film condition O: No abnormality in coating film, X: Abnormality such as cracks in coating film 7) Deformed reinforcing bar after bending workability test Stick @,
,>00:1: Salt water spray test was conducted.

○: No abnormality, ×: Rust occurred at bent portions As is clear from Table 2, the coating film obtained by the method of the present invention has excellent coating performance and is stable in storage as a powder coating. Her sex was also excellent.

on the other hand,)! JComparative example using a powder coating with low phenylphosphine melting/Comparative example using a powder coating with an excessive amount of triphenylphosphine, using the conventionally commonly used dicyandiamide and tetrahydrophthalic anhydride as curing agents Comparative example 3 using powder paint. Both the bending workability and corrosion resistance were poor. Furthermore, Comparative Example S, which used a powder coating made of an epoxy resin with a high melting point, failed in terms of the smoothness of the coated surface, poor bending workability, and poor corrosion resistance.

[Brief explanation of the drawing]

The figure is a front view showing a typical coating state of the present invention. In the figure, 1 is a deformed reinforcing bar, 2 and 2' are rotating rolls,
3 is a shielding plate, 4 is an electrostatic powder spray coating machine, and 5 is a collection device.

Claims (1)

[Claims] (A) (+) / Epichlorohydrin-bisphenol type epoxy resin having at least one epoxy group in the molecule and having a melting point of SO to /1IOoC on a reinforcing bar preheated to /'gOcC or more・・・・・・
...30 to 95% by weight and a melting point of 3000 or more, represented by the general formula (11) (where m is an integer of g to /g and n is an integer of λ to -〇) Polyacid polyanhydride...
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・ A mixture consisting of 5 to 50% by weight...
・・・・・・・・・・・・ 100 parts by weight and (B) triphenylphosphine.../~4' iJI amount tll
1. A method for powder coating a reinforcing bar, the method comprising coating a reinforcing bar with a powder coating composition consisting of s.