JP3386714B2 - Corrosion protection method for cast iron tubes - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cast iron pipe anticorrosion method applied to a water pipe or the like.

[0002]

2. Description of the Related Art Conventionally, as a method for preventing corrosion of cast iron pipes, the following steps are performed: a step of forming a zinc sprayed coating layer on the outer surface of the cast iron tube, a step of forming an acrylic resin emulsion primer layer on the surface of the sprayed coating layer, A method including a step of forming a cement mortar lining layer on the inner surface of a cast iron pipe, a curing step, and a step of forming an overcoat coating layer on the surface of the primer layer has been widely adopted. However, this conventional method has a problem that the cement mortar lining layer greatly increases the weight of the cast iron pipe and the durability is slightly inferior. In addition, due to the curing step, white rust is likely to occur even if there is a primer layer, and when a top coat film is formed on the primer layer where white rust has occurred, the top coat film tends to peel off. Therefore, a method of coating the inner surface of the pipe with a powder paint instead of cement mortar has been attracting attention because it is excellent in terms of weight reduction and durability.

However, in the method of coating powder paint,
Since it is necessary to preheat the tubular body to a high temperature in advance, there is a problem that the primer layer is deteriorated by the heat and peeled off easily. Furthermore, after forming the primer layer, cast iron pipes coated with powder paint generally cannot avoid temporary placement outdoors due to storage space etc., and if the temporary placement period is long, white rust will occur during that period. However, there is a problem in that the adhesion of the top coating film is deteriorated due to the occurrence.

[0004]

SUMMARY OF THE INVENTION Therefore, the present invention makes use of the characteristics of weight reduction and durability due to powder coating, while the primer layer is not deteriorated by the preheating of the tubular body, and it is temporarily outdoor. It is an object of the present invention to provide a method for preventing corrosion of cast iron pipes in which white rust is unlikely to occur even when placed and therefore has good adhesion of the top coating film.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve the above problems, and as a result, formed a specific primer layer containing an epoxy resin powder to solve the above problems. Therefore, it was found that a cast iron pipe excellent in corrosion resistance is manufactured. The present invention has been completed based on such findings. That is, the present invention includes (A) a step of spraying zinc, a zinc-aluminum alloy, or zinc and aluminum on the outer surface of a cast iron pipe to form a sprayed coating layer,
(B) a step of coating an acrylic resin emulsion primer containing an epoxy resin powder on the surface of the sprayed coating layer to form a primer layer, (C) a step of preheating the cast iron pipe, (D) the cast iron pipe A step of applying an epoxy resin-based powder coating on the inner surface of the above, and curing by preheating to form a powder coating layer, and (E) applying a top coating on the surface of the primer layer to form a top coating layer. The present invention relates to a method for preventing corrosion of a cast iron pipe, which comprises each step of forming.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. In the step A of the present invention, after the outer surface of the cast iron pipe is subjected to blast treatment, substrate adjustment such as cleaning, etc., if necessary, by a gas spraying method, an arc spraying method, a plasma spraying method, or the like, zinc is applied. , Zinc-aluminum alloy, or zinc and aluminum are sprayed to form a sprayed coating layer of zinc or a zinc-aluminum alloy or a pseudo-alloy of zinc and aluminum on the outer surface of the cast iron pipe. Regarding the zinc-aluminum alloy used in the step A, for example, the weight ratio of zinc and aluminum is (95: 5 to
40:60) is suitable from the viewpoints of anticorrosion properties, white rust occurrence prevention properties, and the like. Further, the pseudo alloy composed of zinc and aluminum means a state in which the sprayed zinc and aluminum irregularly overlap with each other to form a zinc-aluminum alloy in appearance. Also in this case, the weight ratio of zinc and aluminum is the same as that of the zinc-aluminum alloy.

The thickness of the sprayed coating layer is usually 70 to 300 g.
/ M ² , preferably 100 to 260 g / m ² is suitable from the viewpoint of long-term corrosion resistance and adhesion. As the thermal spraying method, for example, zinc, zinc-aluminum alloy, or zinc and aluminum from a fixed spraying gun to a cast iron pipe that is transferred in the axial direction while rotating (hereinafter, the three are simply referred to as “zinc”). The method of spraying zinc on the rotated cast iron pipe while moving the spray gun to the rotated cast iron pipe is suitable, but the method is not limited to these and various known methods can be used. It is also possible to spray zinc. In the step B, a primer is applied to the surface of the zinc sprayed coating formed on the outer surface of the cast iron pipe in order to prevent white rust from being generated from the sprayed coating and to improve the adhesion of the overcoat coating film described later. Before applying the primer, the cast iron pipe is dried by applying the primer in a state where the cast iron pipe is heated by, for example, immersing the cast iron pipe in a warm water tank so as to have a temperature of about 50 to 80 ° C in advance. Is desirable because it will be faster.

The primer used in the present invention is a conventionally known acrylic resin emulsion paint comprising an acrylic resin emulsion, a pigment, and various additives such as a surfactant, a pigment dispersant and an antifoaming agent, and an epoxy resin. It is a mixture of resin powder. The acrylic resin emulsion can be obtained by emulsion polymerization of one or more radically polymerizable monomers in water in the presence or absence of an emulsifier by a conventional method. Examples of the radical-polymerizable monomer include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate,
(Meth) acrylates such as hexyl (meth) acrylate and 2-ethylhexyl (meth) acrylate; aromatic monomers such as styrene and vinyltoluene; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, glycidyl ( Functional group-containing monomers such as (meth) acrylate, (meth) acrylic acid, crotonic acid and itaconic acid; and various monomers such as (meth) acrylonitrile, butadiene, vinyl chloride and vinyl acetate.

The glass transition temperature of the acrylic resin is, for example, -20 ° C to 60 ° C, preferably 0 ° C to 30 ° C. Examples of the pigment include color pigments such as carbon black and titanium oxide; extender pigments such as talc, precipitated barium sulfate, calcium carbonate, and silica. The epoxy resin powder is composed of an epoxy resin, a curing agent, and if necessary, a pigment, an additive, etc., for example, an average particle size of 5 to 150 μm, preferably 15 to 80 μm.
m thermosetting epoxy resin-based powder is preferred. Specific examples of the epoxy resin include bisphenol A.
For normal powder coatings that are solid at room temperature, such as glycidyl ether type resins typified by condensates of vinyl chloride and epichlorohydrin, glycidyl ester type resins, glycidyl amine type resins, cycloaliphatic epoxy resins, linear aliphatic epoxy resins, etc. Epoxy resin can be used. However, the epoxy resin has, for example, a softening point of 60 to 150 ° C. and an epoxy equivalent of 400 to 30.
00 is suitable.

The mixing ratio of each component of the primer used in the present invention is usually 10 to 100 parts by weight of epoxy resin powder to 100 parts by weight of acrylic resin (solid content),
Preferably 30 to 70 parts by weight, 100 to 300 parts by weight of pigment, preferably 130 to 250 parts by weight, and 0.
5 to 20 parts by weight, preferably 3 to 18 parts by weight is suitable, and the solid content of the primer is usually 40 to 8 parts by weight.
0% by weight, preferably 50 to 70% by weight is suitable.
If the amount of the epoxy resin powder blended is less than the above range, the primer layer is likely to deteriorate due to preheating of the pipe body before coating with the powder coating material, which will be described later, and the white rust generation preventing effect is likely to decrease. On the other hand, when the blending amount is excessively larger than the above range, the storage stability and the like of the primer tend to be lowered. Further, if the amount of the pigment blended is less than the above range, the hardness of the primer layer is lowered, and the primer layer is easily damaged,
On the contrary, if it is more than the above range, the physical properties of the primer layer,
The chemical strength tends to decrease. On the other hand, if the solid content of the primer is less than the above range, the storage stability tends to decrease due to a decrease in viscosity, and if it is more than the above range, the workability of coating tends to deteriorate.

In the present invention, the reason why the deterioration of the primer layer due to the preheating of the tubular body before the powder coating is effectively prevented can be effectively prevented by adding the epoxy resin powder to the primer.
Although it is not certain, the epoxy resin powder is probably melted by preheating, the endothermic effect at that time, the cross-linking reaction between the epoxy resin powders, or the functional groups of the acrylic resin and the epoxy resin powder that are emulsion resins (for example, the former carboxyl group and It is presumed that thermal degradation is suppressed by the polymerizing effect due to the reaction between the latter (hydroxyl group). As a coating method of the primer, for example, while rotating the cast iron pipe,
The method of spray coating with a fixed or reciprocating spray gun is suitable, but it is also possible to use various known methods such as brush coating and roller coating. The painted primer is cured by heat heated in the hot water tank or natural drying.

The film thickness of the primer layer is, for example, 40 to 120 μm, preferably 50 to 100 μm, and particularly preferably 50 to 70 μm as a dry film thickness. The cast iron pipe having the primer layer thus formed is usually temporarily stored indoors or outdoors due to the storage space and the manufacturing line.
However, it is of course possible to immediately proceed to the next step. In the C step of the present invention, first, before performing the C step,
It is desirable to adjust the base material by means such as polishing or cleaning the inner surface of the cast iron pipe as necessary. The step C is a step of preheating the cast iron pipe in advance for curing the powder coating material applied in the step D. Examples of means for preheating include known heating furnaces such as gas furnaces and electric furnaces, but are not limited to these means.

The preheating temperature is arbitrarily determined according to the type of epoxy resin powder coating used in the step D, the curing time, etc., but the tube temperature is usually (220 ° C. ± 50 ° C.). The degree is appropriate, and the epoxy resin-based powder coating material melts in this temperature range, and a crosslinking reaction occurs between the epoxy resin and the curing agent. In step D, an epoxy resin powder coating material is applied to the inner surface of the preheated cast iron pipe. The epoxy resin-based powder coating material used in the present invention is composed of an epoxy resin which is solid at room temperature, a curing agent for the epoxy resin, and various pigments and additives as required. As the epoxy resin, those conventionally used in epoxy resin powder paints can be used without particular limitation. Examples of such an epoxy resin include a glycidyl ether type resin represented by a condensate of bisphenol A and epichlorohydrin, a glycidyl ester type resin, a glycidyl amine type resin, an alicyclic epoxy resin, and a linear aliphatic epoxy resin. Ordinary epoxy resin for powder coating that is solid at room temperature can be used.

The epoxy resin has a softening point of 60 to 60.
150 ° C., an epoxy equivalent of 400 to 3000 is suitable. If the softening point is lower than 60 ° C., or if the epoxy group equivalent is less than 400, the powder coating material is likely to solidify during storage, while the softening point is higher than 150 ° C. If it is high or the epoxy equivalent is more than 3000, the melt viscosity becomes high, so that it becomes difficult to obtain a smooth coated surface, and pinholes and the like tend to occur easily. The curing agent for the epoxy resin is not particularly limited as long as it has been conventionally used in epoxy resin powder coatings, and various curing agents can be used. As such a curing agent, for example, acid anhydride-based, dicyandiamide-based, aromatic amine-based, organic acid dihydrazide-based, BF ₃ -amine complex salt-based, imidazole-based, polyhydric phenol-based curing agents are typical curing agents. As.

The blending ratio of the epoxy resin and the curing agent may vary depending on the characteristics of each curing agent, but may be determined within a known range where the original coating performance of the epoxy resin can be exhibited. . For example, when using a polyhydric phenol-based curing agent, the equivalent ratio of the hydroxyl groups in the curing agent to the epoxy groups in the epoxy resin is appropriately in the range of (0.7 to 1.3: 1). Epoxy resin powder coating materials include titanium oxide, iron oxide, carbon black, phthalocyanine blue, calcium carbonate, precipitated barium sulfate, silica,
If desired, various coloring pigments such as talc, extender pigments, fillers such as glass fibers, and various additives such as dispersants and surface modifiers may be added. It is desirable that the total amount of the pigment and the filler is, for example, 20 to 50% by weight in the powder coating in order to obtain a thick film.

The particle size of the epoxy resin powder coating is, for example, 5 to 150 μm in average particle size, preferably 15 to 80 μm. The manufacturing method of the powder coating material is not particularly limited, and various conventionally known manufacturing methods can be adopted, for example, the dry blending method and the hot melt kneading method. The epoxy resin-based powder coating material can be used as the epoxy resin powder blended in the primer as described above. As a method for coating the epoxy resin powder coating on the inner surface of the cast iron pipe, for example, a method of inserting the spray nozzle into the rotating cast iron pipe and coating while moving in the axial direction of the pipe, or powder coating with gas It is possible to apply the powder coating material by various well-known methods such as a method in which a large excess amount is fed into a rotating cast iron pipe, the pipe inner wall is fused and the surplus powder coating material is removed.

The thickness of the powder coating layer formed is, for example,
300 μm or more, preferably 400 to 700 μm is suitable. In the step E of the present invention, an overcoat paint is applied to the outer surface of the cast iron pipe provided with the thermal spray coating layer and the primer layer to form an overcoat coating layer. Since the top coat film is inferior in gloss, durability and the like only with the primer layer, it is formed for the purpose of imparting a glossy appearance and improving weather resistance and durability.
The topcoat paint used in the present invention can be used without any particular limitation, and various paints that have been conventionally used as topcoat paints for cast iron pipe outer surfaces, specifically, fluororesin, polyester resin, alkyd resin. Examples include organic solvent-based or water-dilutable coatings using acrylic resin, urethane resin, epoxy resin, silicone resin, or the like as a binder.

The top coating composition can be applied by the same coating method as the above-mentioned primer coating, and can be cured by natural drying or forced drying. The film thickness of the top coating film layer is, for example, 10 to 60 μm, preferably 20 to 40 μm, as a dry film thickness.

[0019]

EXAMPLES The present invention will now be described in more detail with reference to examples. In the examples, "parts" and "%" are shown by weight. <Preparation of epoxy resin powder coating A> (reference) Epoxy resin (epoxy equivalent 780, softening point 95 ° C) 95 parts adipic acid dihydrazide 5 parts calcium carbonate 10 parts silica 15 parts titanium dioxide 15 parts carbon black 0.2 parts Flow control agent 0.5 parts After mixing the above ingredients with a Henschel mixer, about 11
The mixture was melt-kneaded in an extruder under a temperature condition of 0 ° C., cooled, and then pulverized with a bantam mill and sieved with a wire mesh of 150 mesh (corresponding to a particle size of 105 μm) to prepare a powder coating material A.

<Preparation of Epoxy Resin Powder Coating B> Epoxy resin (epoxy equivalent 920, softening point 97 ° C.) 78 parts Polyphenol (hydroxyl equivalent 250, molecular weight 500) 22 parts Silica 25 parts Titanium dioxide 20 parts Carbon black 0.2 part Flow control agent 0.5 part The above components were mixed, kneaded and pulverized in the same manner as the powder coating material A to prepare a powder coating material B. <Preparation of primer A> Acrylic / styrene / butadiene copolymer Emulsion resin varnish Note ¹⁾ 45 parts Talc 37.5 parts Carbon black 2.5 parts Ammonia water (28%) 1.2 parts Thickener 1 part Defoaming Agent 1 part Pigment dispersant 0.5 part Nonionic surfactant 0.5 part Water 10.8 part Note ¹⁾ "Luck Star 3700D" (trade name of Dainippon Ink and Chemicals, Inc.), resin solid content 40%, resin Glass transition temperature of 10 ° C. A primer A, which is a black acrylic resin emulsion paint comprising the above components, was prepared.

<Preparation of Primer B> To 100 parts of the black acrylic resin emulsion paint, 7 parts of powder paint A were dispersed and mixed, and further 10 parts of water was mixed to prepare primer B. <Preparation of Primer C> 12 parts of powder coating material B was dispersed and mixed with 100 parts of the black acrylic resin emulsion coating material, and further 10 parts of water was mixed to prepare primer C.

Example 1 Cut to a size of 70 × 150 mm, a thickness of 7 mm and a diameter of 150
mm of cast iron pipe piece is blasted and cleaned, and zinc wire is sprayed on the outer surface of the cast iron pipe piece by arc spraying method, 150 g
A sprayed coating layer of / m2 was formed. Then, the cast iron pipe piece coated with the thermal spray coating is immersed in a hot water tank, and the temperature of the cast iron pipe piece is set to about 60.
After heating to 0 ° C., the primer B was spray-coated on the surface of the sprayed coating layer to form a primer layer having a dry film thickness of about 60 μm. In this way, cast iron pipe pieces coated only on the outer surface
It was temporarily stored outdoors for a week. Then, after polishing and cleaning the inner surface of the cast iron pipe piece, the cast iron pipe piece was placed in a hot air heating furnace at 250 ° C.
After staying for a while and raising the temperature of the cast iron pipe piece to 250 ° C., it was taken out of the heating furnace, and immediately the inner surface of the cast iron pipe piece was sprayed with the powder coating material A to form a powder coating film layer having a thickness of about 500 μm. . The cast iron pipe piece coated with the powder paint on the inner surface in this manner was temporarily stored outdoors for one week, and then the organic solvent type acrylic resin paint ["Kurimoto Coat AC" (trade name, manufactured by Kurimoto Iron Works Co., Ltd.) ] Was spray-coated on the outer surface side of a cast iron pipe piece and naturally dried to form a top coating film layer having a dry film thickness of about 30 μm. Example 2 In Example 1, the primer C was used instead of the primer B.
Except that the powder coating material B is used instead of the powder coating material A, a spray coating layer, a primer layer, and a top coating film layer are formed on the outer surface side of the cast iron pipe piece in the same manner. A powder coating layer was formed on the.

Comparative Example 1 In Example 1, instead of the primer B, the primer A was used.
In the same manner as above except for using, the thermal spray coating layer, the primer layer and the top coating film layer were formed on the outer surface side of the cast iron pipe piece, and the powder coating film layer was formed on the inner surface side of the cast iron pipe piece. Comparative Example 2 In Example 2, instead of the primer C, the primer A was used.
In the same manner as above, except that the above was used, a sprayed coating layer, a primer layer, and a top coating film layer were formed on the outer surface side of the cast iron pipe piece, and a powder coating film layer was formed on the inner surface side of the cast iron pipe piece. Example 3 In the same manner as in Example 1, except that instead of zinc, a zinc / aluminum alloy wire consisting of (87:13) [weight] of zinc and aluminum was sprayed, the same procedure was performed on the outer surface of the cast iron pipe piece. A primer layer and a top coating film layer were formed, and a powder coating film layer was formed on the inner surface side of the cast iron pipe piece. Comparative Example 3 The same procedure as in Comparative Example 1 was repeated except that a zinc / aluminum alloy wire consisting of (87:13) [weight] of zinc and aluminum was sprayed instead of zinc. A primer layer and a top coating film layer were formed, and a powder coating film layer was formed on the inner surface side of the cast iron pipe piece. The test pieces obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were tested by the following method in order to test the adhesion and the easiness of white rust generation, and the results are shown in Table 1. It was As is clear from Table 1,
In all of Examples 1 to 3 according to the method of the present invention, the adhesion was good and white rust did not occur. On the other hand, in Comparative Examples 1 to 3 in which the epoxy resin powder was not mixed with the primer, the adhesion was poor due to deterioration of the primer layer, and white rust occurred. In addition, on the side on which the powder coating film layer was formed, there was no abnormality in any of Examples 1 to 3 and Comparative Examples 1 to 3 in the test for occurrence of white rust.

[0024]

[Table 1]                                 Table 1 Test item Example Comparative example 1 2 3 1 2 3 Adhesiveness 25/25 25/25/25/25 0/25 0/25/0/25 White rust occurrence No white rust No white rust No white rust Many white rust Many white rust Little white rust Occurrence Occurrence Occurrence <Adhesion test> 2 x 2 m reaching the substrate with a cutter knife
Make 25 pieces of m-shaped mesh, and use cellophane adhesive tape on the surface.
And then peel it off, leaving the top coat layer on the cast iron pipe piece.
Count the number of scoring spots and evaluate the adhesiveness by the number of remaining / 25
did. <White rust occurrence test> In Examples 1 to 3 and Comparative Examples 1 to 3.
Test as above, except that the top coat layer is not formed.
Make a piece and set it to JISK5400.9.2.2
The test piece was hung in a moist box for 24 hours, taken out, and then
Then, it was left standing for 24 hours, and the state of occurrence of white rust was visually evaluated.

[0025]

EFFECTS OF THE INVENTION In the method of anticorrosion for cast iron pipes of the present invention, the inner surface of the pipe is coated with an epoxy resin powder coating instead of the cement mortar lining, so that the weight can be reduced and the durability is excellent. Further, as the primer on the outer surface of the cast iron pipe, since the acrylic resin emulsion primer containing the epoxy resin powder is coated, it does not deteriorate even in preheating for curing the powder coating material, and white rust hardly occurs, As a result, there is a feature that a cast iron pipe excellent in corrosion resistance can be obtained.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshisada Michiura 1-12-19 Kitahori, Nishi-ku, Osaka City, Osaka Prefecture Kurimoto Iron Works Co., Ltd. (72) Inventor Yoshio Yamada 37-3 Aobadai, Izumi City, Osaka ( 72) Inventor Tadahiko Nishijima 613-62 Sakurai, Sakurai City, Nara (56) Reference JP-A-7-247446 (JP, A) JP-A-10-34080 (JP, A) JP-A-3-252465 (JP, A) JP-A-58-133878 (JP, A) JP-A-58-67765 (JP, A) JP-A-49-8529 (JP, A) Actual development Sho-59-5333 (JP, U) JP-B 6 -7000 (JP, B2) Special Table 8-505929 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F16L 58/02 C09D 5/02 C23C 4/08 C23F 15/00

Claims (2)

(57) [Claims] 1. A process of spraying zinc, a zinc-aluminum alloy, or zinc and aluminum onto the outer surface of a cast iron pipe to form a sprayed coating layer, and (B) an acrylic resin on the surface of the sprayed coating layer. (solid
Min) 100 to 10 parts by weight of epoxy resin powder 10 to 10
Coating acrylic resin emulsion primer containing 0 parts by weight to form a primer layer; (C) preheating the cast iron pipe; (D) coating epoxy resin powder coating on the inner surface of the cast iron pipe. A step of forming a powder coating layer by curing with the preheating, and (E) applying an overcoat paint on the surface of the primer layer,
A method for preventing corrosion of a cast iron pipe, which comprises the steps of forming an overcoat coating layer. 2. The epoxy resin powder contained in the primer is a thermosetting epoxy resin powder coating material.
The method for preventing corrosion of a cast iron pipe according to claim 1.