JP3212355B2 - Surface treatment method for polyethylene powder lining - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preparing a surface of a polyethylene powder lining used for piping and equipment of various devices made of carbon steel.

[0002]

2. Description of the Related Art Conventionally, a polyethylene powder lining has been subjected to degreasing and washing of the surface of a lining material made of carbon steel, blasting or acid washing, and then forming a chemical conversion film of phosphate, and then to 200 to 300 ° C. Preliminarily heating the lining material, supplying polyethylene powder and heat-melting the polyethylene powder by the retained heat of the lining material or the heat supplied from the opposite side of the lining surface to form a continuous polyethylene coating. A method of forming has been performed.

[0003]

Hitherto, polyethylene powder lining has been frequently used in an environment where it is in contact with a liquid having a relatively low temperature (30 ° C. or less) such as a water supply pipe or a seawater intake pipe, and has a reasonable durability. Has a track record. However, when the polyethylene powder lining material constructed by the conventional method is used in a chemical plant, a power plant, or the like, the liquid temperature is 50-6.
When used in an environment at 0 ° C., there are many accidents in which the polyethylene coating peels off or blisters are formed. Inspection of the lining surface of the exfoliation and blister parts always shows that the lining surface is corroded.Therefore, the conventional polyethylene powder lining material is used in a temperature gradient environment where the liquid temperature is high and the transmission of water vapor and oxygen is accelerated. In this case, it can be seen that the base surface is easily corroded.

[0004] Conventional polyethylene powder lining method
Treatment to form a chemical conversion coating with phosphate in water
Is the diffusion of corrosive substances and the metals contained in the coating
In general, with the aim of the electrochemical rust prevention effect of salt,
This is a method applied to the mounting base treatment. However
Phosphate conversion coatings are Zn, Mn, Fe, Ca
A tertiary phosphate such as_Three(PO_Four)
_Two・ 2MnPO_Four・ 4H_TwoO and FeHPO_Four・ 4H_TwoO
Mixed crystal of Zn or Zn_Three(PO_Four)_Two・ 4H _TwoO and F
eHPO_Four・ 2-4H_TwoO mixed crystal or γFe_Two
O_Three・ FePO _Four・ 2H_TwoO or FeHPO_Four・ 4 ~
8H_TwoO or Zn_Three(PO_Four)_Two・ NH_TwoO, Zn
_TwoCa (PO_Four)_Two・ 2H_TwoO etc. This
These crystals release water of crystallization at 100-240 ° C.
In the case of a manganese phosphate coating,
In the case of zinc, oxidative decomposition starts at 130 ° C. Therefore, 2
Polyethylene powder line that is heated and melted at 00-300 ° C
In the case of polishing, the porous body is formed by dehydration,
Cracking of acid coating and decrease in adhesion of conversion coating
Not by oxidation of Mn, Zn, etc. in the phosphoric acid coating
The anticorrosion effect has been reduced and the oxidation of these salts has progressed.
In such cases, reversal of the corrosion potential may lead to accelerated corrosion.
And the same level of protection as commonly applied paint
No rust effect can be expected, due to porous formation and crack generation
Due to the decrease in rust prevention, the adhesion decreases and the polyethylene coating
Peeling and blisters easily occur in a short time.

[0005] Therefore, in order to expand the application to a high-temperature environment, which is more problematic in terms of blister resistance than a conventionally used environment near normal temperature, polyethylene lining having excellent corrosion resistance, adhesion, and abrasion resistance is required. Development or improvement of a base treatment method having excellent corrosion resistance and excellent corrosion resistance has become a technical issue.

The present invention has been made in view of the above-mentioned technical level, and has as its object to provide an undercoating method capable of performing excellent polyethylene lining even in a high-temperature environment.

[0007]

According to the present invention, a polyethylene powder is supplied to a lining material made of carbon steel which has been preheated to a melting temperature of the polyethylene powder or higher, and the powder is melted by the heat of the lining material. In the lining method of forming a continuous polyethylene film on the surface of the material to be lined, the surface of the material to be lined is acid-washed with hydrochloric acid,
After washing with water, a chemical conversion treatment was performed using a zinc phosphate-calcium-based solution, and then pH 4.5 to 6.0,
This is a method for preparing a polyethylene powder lining, which is characterized in that it is brought into contact with a 0.5 to 0.05 wt% chromic acid aqueous solution at a liquid temperature of 50 ° C. or lower and then dried.

[0008] The base treatment of the present invention is an acid washing with hydrochloric acid, water washing,
A chemical conversion treatment for forming a zinc-calcium phosphate film is performed by a conventional method, and immediately or within several days, a solution of 50 to 50% by weight of chromic acid in aqueous solution of 0.005 to 0.05 wt% is used.
This is a base treatment method in which contact is made at a temperature of not more than ℃. In the undercoating treatment of the present invention, as the polyethylene powder lining, the chromic acid concentration at which long-term durability is obtained is 0.005 to 0.0
It is 5 wt%, preferably 0.01 to 0.03 wt%, and the liquid temperature is 50 ° C or lower.

In the present invention, the chemical conversion treatment using a zinc calcium phosphate solution refers to a treatment with Zn (H
₂ PO ₄ ) ₂ , Ca (H ₂ PO ₄ ) ₂ as a main component and a lining material made of degreased and pickled carbon steel
By immersing for up to 5 minutes, Zn ₃ (P
O ₄ ) refers to a chemical conversion treatment for forming a mixed crystal film of ₂ · nH ₂ O and CaPO ₄ · mH ₂ O.

[0010]

According to the present invention, as a base treatment for polyethylene powder lining, zinc phosphate by acid washing, water washing and chemical conversion treatment is used.
PH 4.5 to 6.0 after the formation of the calcium film,
Liquid temperature 5 in 0.005-0.05 wt% chromic acid aqueous solution
By contacting at 0 ° C. or lower, an appropriate amount of chromic acid penetrates into the pores existing on the entire surface of the coating formed of the aggregate of crystal particles of zinc phosphate-calcium salt, and is in contact with the zinc phosphate-calcium salt. By forming a chromic acid film on the free surface of the material to be lined, the corrosion of the material to be lined is greatly suppressed compared to the conventional undercoating with a zinc phosphate-calcium salt film alone. The present invention can provide a polyethylene powder lining material that can withstand long-term use without causing cracks.

When the pH is higher than 6.0 and the chromic acid concentration is less than 0.005 wt%, the amount of chromium for coating the free surface of the lining material in the pores is insufficient, and the pH is insufficient.
Is less than 4.5 and the chromic acid concentration is higher than 0.05 wt%, the hydrogen ion concentration increases with the excess of chromic acid or the chromic acid concentration increases, and the free surface of the lining material is corroded. And lowers the durability of the underlayer treatment.

[0012]

EXAMPLE A 6 mm thick carbon steel sheet having a thickness of 3 mm and a diameter of 120 mm was prepared.
It was immersed in a 3 wt% solution of sodium orthosilicate at 0 ° C. for 5 minutes, degreased and washed, washed with warm water, and dried sufficiently. The steel sheet is immersed in a 5 wt% solution of hydrochloric acid at 50 ° C. for 5 minutes, washed with water, and then Zn (H ₂ PO ₄ ) ₂ , Ca at 80 ° C.
A zinc phosphate-calcium chemical conversion treatment solution (Hostex F, manufactured by Kowa Chemical Industry Co., Ltd.) containing (H ₂ PO ₄ ) ₂ as a main component.
-125) for 20 minutes, and Zn ₃ (PO ₄ ) ₂ .n
A zinc phosphate-calcium chemical conversion coating of a mixed crystal of H ₂ O, CaPO ₄ .mH ₂ O was formed. After being pulled up from the chemical conversion treatment solution, it was washed with water, subjected to various chromic acid treatments having different concentrations and temperatures of a chromic acid aqueous solution as shown in Table 1, and dried to prepare a base treatment specimen.

The test material subjected to the undercoating treatment is 250
Put in an electric furnace adjusted to ± 10 ° C, and set the surface temperature to 250 ° C.
℃, melt flow rate 3.0g / 10m
In, polyethylene powder having an average particle size of 90 μm was evenly sprayed on the surface subjected to the base treatment to form a lining film having a thickness of 0.5 mm.

Using these lining materials as test materials, a DuPont type lining tester is used to apply p
A sulfuric acid solution of H0.5 was added, heated to 60 ° C., and the time until blistering was measured under the condition that the unlined steel plate side was cooled with cooling water at 20 ° C. as a result,
As shown in Table 1, the time required for blister generation is 20 times or more that of the test material prepared under the base treatment conditions of the present invention as compared with the reference material obtained by lining a polyethylene powder on the conventional chemical conversion only surface. However, when the chromic acid concentration in the chromic acid treatment was 0.005 or less or 0.05 or more and the temperature was 50 ° C. or more, the concentration was 1 or less.

[0015]

[Table 1]

[0016]

By applying the undercoating treatment of the present invention, it has become possible to apply the polyethylene powder lining to an environment of 50 to 60 ° C., which has conventionally been difficult to use because peeling and blistering occur in a short time. Polyethylene powder lining is another resin (thermosetting resin) used for the above environmental conditions
The production cost is lower than that of rubber lining, and there is also an advantage that it can be applied to the inner surface of small-diameter pipes that cannot be applied with resin lining or rubber lining.Because the present invention is expected to expand the application range of polyethylene lining, The industrial effect is great, and the effect of improving reliability by securing a long life is also great.

Continuation of the front page (51) Int.Cl. ⁷ Identification code FI C23C 22/00 C23C 22/00 Z 22/78 22/78 22/83 22/83 (56) References JP-A-61-274771 (JP, A) JP-A-52-132085 (JP, A) JP-A-63-27248 (JP, A) JP-A-3-234527 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) ) B05D 1/00-7/26 C23C 22/00 C23C 22/78 C23C 22/83

Claims (1)

(57) [Claims] 1. The polyethylene powder is supplied to a lining material made of carbon steel which has been preheated to a melting temperature of the polyethylene powder or higher, and the powder is melted by the heat of the lining material and is continuously formed on the surface of the lining material. In the lining method of forming a polyethylene film, the surface of the material to be lined is acid-washed with hydrochloric acid, washed with water, and then subjected to a chemical conversion treatment using a zinc phosphate-calcium solution,
4.5-6.0, 0.005-0.05wt%
A method for treating a surface of a polyethylene powder lining, comprising: contacting a chromic acid aqueous solution at a liquid temperature of 50 ° C. or lower, followed by drying.