JP2012072294A - Powder coating for cast iron pipe and cast iron pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a powder coating for a cast iron pipe improved in both a pinhole property and a leveling property (surface smoothness), and excellent in corrosion resistance and adhesion even with a temperature difference, and to provide the cast iron pipe.SOLUTION: The powder coating contains an epoxy resin (A), a curing agent (B), and a filler (C), wherein the filler (C) contains a Cirrus balloon (C1) which is porous and spheroidal as an essential component, and contains one or more of other fillers (C2) selected from barium sulfate, talc, calcium carbonate, barium carbonate, silica, titanium oxide, alumina, and mica. The cast iron pipe is also provided with the powder coating for the cast iron pipe applied on an inner surface thereof.

Description

  The present invention relates to a powder paint for cast iron pipe and a cast iron pipe.

  Epoxy powder coatings using epoxy resins have excellent properties such as corrosion resistance, adhesion, water resistance, chemical resistance, and mechanical properties. Widely used in civil engineering and construction fields such as pipes, industrial water pipes and gas pipes.

Among these various uses, bisphenol A type (BPA type) epoxy resins are generally used for cast iron pipes used in the civil engineering / architecture field because of a good balance of physical properties. However, in order to ensure sufficient anti-corrosion properties and long-term reliability, it is necessary to make the film thicker than ordinary powder coatings, so the appearance (pinhole property / surface smoothness) of the coating film deteriorates. There were problems such as being easy to invite, and deterioration of coating film adhesion under different temperature differences due to climate change (seasonal temperature).
In particular, recently, there is a problem of environmental hormones of bisphenol A, and there are increasing cases of using bisphenol F type (BPF type) epoxy resins for further safety (see Patent Document 1 below).

  In addition, various improvements have been proposed for forming a coating film using a powder coating material, based on factors that reduce the coating film performance. For example, in powder coatings using conventional solid bisphenol F type epoxy resins, improvements from resin design such as epoxy equivalent of epoxy resin, molecular weight, purity of binuclear component, and spherical inorganic filler as filler Improvement techniques such as use have been proposed (see Patent Document 2 below).

Japanese Patent No. 2813986 Japanese Patent Application Laid-Open No. 9-100500

However, unlike the BPA type epoxy resin, the BPF type epoxy resin has a polyfunctional component in the raw material BPF itself, and thus has a structure having not only a linear molecule but also a branched structure. .
For this reason, the BPF type epoxy resin differs from the BPA type epoxy resin in both curability and physical properties of the coating film, and is difficult to control. Therefore, it is desired to construct a more optimal paint design / curing system.

Conventionally, since cast iron pipes are centrifugally cast, shrinkage nests, dross (impurities such as metals), wrinkles (convex), etc. are generated on the inner surface of the pipe. For this reason, the cast iron pipe surface is treated by grinder polishing or the like to remove sink marks, dross, wrinkles (convex), etc. as much as possible. However, it is difficult to completely remove them, and fine scratches (irregularities) remain on the inner surface of the cast iron pipe due to polishing, which inevitably results in poor appearance of the paint film (pinhole and leveling properties) and paint film. This is a factor that causes a decrease in adhesion. However, the properties of the coating film by the conventional improvement are not fully satisfied, and further improvement is desired.
Furthermore, cast iron pipes are sometimes buried in the ground, and it is necessary to maintain the adhesion of the coating film that can withstand harsh environments such as seasonal differences in temperature and humidity. There is a strong desire for improvement.

  The problem to be solved by the present invention is to improve both pinhole property and leveling property (surface smoothness), and to have excellent adhesion to temperature differences due to climate change, and cast iron tube powder coating and cast iron tube Is to provide.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor has used a spherical porous shirasu balloon as a filler, so that the coating film appearance (leveling property, pinhole property) and anticorrosion in a powder coating for cast iron pipes can be obtained. To obtain a paint coating for cast iron pipes that has a high degree of coating adhesion (temperature difference adhesion test) that can withstand changes in temperature (salt spray test, etc.) and climatic conditions (temperature difference / humidity change) The headline and the present invention were completed.

That is, the powder coating for cast iron pipe of the present invention is a powder coating for cast iron pipe containing an epoxy resin (A), a curing agent (B), and a filler (C), and the filler (C) is porous. A spherical Shirasu balloon (C1) is an essential component.
Moreover, the cast iron pipe of the present invention is characterized in that the powder paint for cast iron pipe of the present invention is applied to the inner surface.

  The powder coating for cast iron pipes of the present invention uses a spherical and porous shirasu balloon as an essential component of the filler, so that the appearance of the coating film (pinhole and leveling properties) and various coating film performance (salt spray test [ Corrosion resistance], temperature difference adhesion test, etc.) are improved.

  Although the epoxy resin (A) used for this invention is not specifically limited, Specifically, bisphenol A type epoxy resin, bisphenol F type epoxy resin, tetramethylbisphenol F type epoxy resin, or these React with one or two or more dihydric phenols such as hydroquinone, trimethylhydroquinone, 2-tertiarybutylhydroquinone, resorcin, catechol, biphenol, bisphenols (bisphenol A, bisphenol AD, bisphenol F), tetramethylbisphenol F, etc. The epoxy resin obtained by making it contain is mentioned. In the present invention, considering the balance between pinhole properties and leveling properties, bisphenol A type epoxy resins, bisphenol F type epoxy resins, or epoxy resins obtained by reacting these with dihydric phenols are preferred.

  In the present invention, in addition to the above, other epoxy resins (A ′) may be used in combination as part of the epoxy resin (A) within a range not impairing the effects of the present invention. Examples of other epoxy resins (A ′) that can be used here include bifunctional epoxy resins such as bisphenol S type epoxy resins, bisphenol AD type epoxy resins, bisphenol type epoxy resins, naphthalene type epoxy resins, and biphenyl type epoxy resins. Resin, phenol novolac type epoxy resin, brominated phenol novolak type epoxy resin, orthocresol novolak type epoxy resin, bisphenol A novolak type epoxy resin, bisphenol AD novolak resin and other novolak type epoxy resins; epoxy resin having tricyclodecene oxide group Cycloaliphatic epoxy resins such as epoxidized products of dicyclopentadiene type phenol resins; glycidyl ester type epoxies such as dimer acid glycidyl ester and triglycidyl ester Resin; Glycidylamine type epoxy resin such as tetraglycidylaminodiphenylmethane, triglycidyl p-aminophenol, triglycidyl-p-aminophenol, tetraglycidylmetaxylylenediamine, tetraglycidylbisaminomethylcyclohexane, etc .; complex such as triglycidyl isocyanurate Cyclic epoxy resin; phloroglicinol triglycidyl ether, trihydroxybiphenyl triglycidyl ether, trihydroxyphenylmethane triglycidyl ether, glycerin triglycidyl ether, 2- [4- (2,3-epoxypropoxy) phenyl] -2- [4- [1,1-bis [4- (2,3-epoxypropoxy) phenyl] ethyl] phenyl] propane, 1,3-bis [4- [1- [4- (2,3- Poxypropoxy) phenyl] -1- [4- [1- [4- (2,3-epoxypropoxy) phenyl] -1-methylethyl] phenyl] ethyl] phenoxy] -2-propanol Tetrafunctional phenyl epoxy resins such as tetrahydroxyphenyl ethane tetraglycidyl ether, tetraglycidyl benzophenone, bisresorcinol tetraglycidyl ether, tetraglycidoxybiphenyl; n-butyl glycidyl ether, allyl glycidyl ether, 2-ethylhexyl glycidyl ether, styrene oxide Monofunctional epoxies such as phenyl glycidyl ether, cresyl glycidyl ether, p-sec-butylphenyl glycidyl ether, glycidyl methacrylate, vinylcyclohexene monoepoxide Xyoxy compounds are mentioned.

  When other epoxy resin (A ′) described above is used in combination, it is preferable to blend such that the other epoxy resin (A ′) is within the range of 1 to 20% with respect to the entire epoxy resin (A) component. . Even when one kind of epoxy resin is used alone or when two or more kinds of epoxy resins are used in combination, the epoxy equivalent of the epoxy resin (A) as a whole is 600 to 1,500, and the softening point is 70. It is preferable that it is -130 degreeC from the point which is excellent in the storage stability of a coating material in addition to fluidity | liquidity and sclerosis | hardenability.

  Next, the curing agent (B) used in the present invention is not particularly limited, but examples thereof include imidazole compounds, imidazoline compounds, dicyandiamide, acid anhydrides, polycarboxylic acid hydrazides and derivatives thereof, phenols. Examples thereof include resins and derivatives thereof. Of these, the use of an imidazole compound, an imidazoline compound, a polycarboxylic acid hydrazide, or a derivative thereof alone or in combination is preferable from the viewpoint that the corrosion resistance, flexibility, adhesion, and strength of the coating film are remarkably improved.

Here, the imidazole compound used as the curing agent (B) is not particularly limited. For example, imidazole, methylimidazole, dodecylimidazole, heptadecylimidazole, phenylimidazole, etc., and 1-cyanoethylated products thereof. Examples include 1-cyanoethylated product / trimellitic acid mixture, isocyanuric acid adduct and the like.
Examples of the imidazoline compound include methyl imidazoline, dodecyl imidazoline, heptadecyl imidazoline, phenyl imidazoline, and the like.
These can be used alone or in combination of two or more.

  The acid anhydride is not particularly limited, and examples thereof include tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylbutenyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, and succinic anhydride. .

  The polycarboxylic acid hydrazide and its derivatives are not particularly limited, and examples of the polycarboxylic acid hydrazide include succinic acid dihydrazide, adipic acid dihydrazide, sebacic acid dihydrazide, and isophthalic acid dihydrazide. Examples of the derivatives include N-cyclohexyl-β-aminopropion hydrazide, N-phenyl-β-aminopropion hydrazide, N-butyl-β-aminopropion hydrazide, N-benzyl-β-aminopropion hydrazide and the like. Substituted -β-aminopropion hydrazides are mentioned.

  In addition, the phenol resin and its derivative are not particularly limited as long as they are solid at room temperature. For example, phenol formaldehyde resin, cresol formaldehyde resin, reaction product with bisphenol A formaldehyde resin or triazine, bisphenol and bisphenol type epoxy resin These reactants can be mentioned.

The filler (C) used in the present invention is not particularly limited except that a porous spherical Shirasu balloon (C1) is an essential component, but the present invention is not limited to Shirasu. The balloon (C1) can be used alone or in combination with other fillers (C2).
Examples of other fillers (C2) used in combination include barium sulfate, talc, calcium carbonate, barium carbonate, silica (silicon oxide), titanium oxide, alumina (aluminum oxide), and mica. These can be used alone or in combination of two or more.

Shirasu balloon (C1) preferably has a mean particle size of 10 to 300 μm, more preferably 30 to 100 μm from the viewpoint of fluidity.
Further, the thermal conductivity of the shirasu balloon (C1) is 0.01 to 0.20 kcal / mh- ° C., and further 0.05 to 0 in order to maintain the coating film adhesion due to the influence of temperature difference. A range of 10 kcal / mh- ° C. is preferable.
Further, if the bulk specific gravity (apparent specific gravity) of the shirasu balloon (C1) is 0.05 to 0.50, and more preferably 0.10 to 0.40, it is possible to achieve an effect in a low usage amount. The bulk specific gravity can be determined, for example, as a numerical value expressed in units of g / cm ³ of an apparent density measured according to Part 12 (apparent density or apparent specific volume) of JIS K 5101 (pigment test method).

  Since the shirasu balloon used in the present invention has a spherical shape, the fluidity of the paint is better than that of a normal pigment (filler), and a gas generated from a cast iron pipe sink or the like or a gas generated from the paint is applied. Before the film is cured, it can be quickly discharged out of the paint film to reduce the occurrence of pinholes, and the fluidity improves over time, improving the smoothness (leveling) of the paint film. A coating film having a good appearance can be obtained.

In addition, by controlling the particle size of the shirasu balloon, the paint can easily penetrate even on the inner surface (scratch / defect portion) of fine irregularities, and as a result, the decrease in coating film adhesion can be suppressed.
By improving the adhesion and fluidity, it is possible to suppress and reduce coating film peeling at the time of cutting when casting a cast iron pipe or at the time of drilling for sending water to a home, and as a result, it is possible to maintain corrosion resistance. Furthermore, cast iron pipes buried in the ground have a temperature difference between the outer surface and the inner surface (water temperature) of the pipe depending on the temperature of the water to be passed between summer and winter. Adhesion by test is listed as an important item. In conventional paints, it has been pointed out that this temperature difference affects the coating film and is likely to cause swelling, peeling, etc. of the coating film. Since Shirasu balloons have low thermal conductivity, the temperature difference between the inside and outside of the coating film can be relaxed and the adhesion of the coating film can be maintained by including the Shirasu balloon in the coating film. .
Further, since the shirasu balloon is hollow and has a small bulk specific gravity, there is also an advantage that a lightweight and sufficient coating film performance can be obtained with a low addition amount.

If the content of the filler (C) is too large, the fluidity of the coating deteriorates, so 5 to 50% is preferable in terms of the weight percentage with respect to the whole powder coating, and the range of 5 to 30% optimizes the coating film performance. Is more preferable.
The present invention is effective not only when the shirasu balloon (C1) is used alone but also with other fillers (C2). This is because, in powder coating by rotating a cast iron tube, centrifugal force works due to the difference in specific gravity, and when the viscosity of the melted powder coating is low, a low specific gravity shirasu balloon is selectively applied to the coating surface. This is because the specific gravity of the low specific gravity shirasu balloon and the high specific gravity other fillers is averaged, and consequently the other fillers are uniformly dispersed.
The specific gravity of the other filler (C2) mentioned above (in the case of two or more types, the average value obtained from the total weight and the total volume) is the dispersibility when the powder coating is melted and the bulk specific gravity of the shirasu balloon (C1). For example, a range of 2.0 to 4.5 is preferable.
When the shirasu balloon (C1) is used in combination with another filler (C2), the content of the shirasu balloon (C1) with respect to the entire paint is preferably within the range of the content of the filler (C) described above. Further, since the other filler (C2) generally has higher thermal conductivity than the resin, if the amount of the shirasu balloon (C1) is too small, it becomes difficult to obtain the effect of lowering the thermal conductivity. In contrast, the Shirasu balloon (C1) is preferably in the range of 5 to 100% by weight.

Additives such as a hardening accelerator, a pigment, a coloring agent, a spreading agent, an anti-waxing agent, and aerosil can be blended with the powder coating for cast iron pipes of the present invention as necessary.
Although it does not specifically limit as a hardening accelerator, For example, organic acids, such as a succinic acid, adipic acid, salicylic acid, and sebacic acid, are mentioned.
In addition, as the pigment, since the filler (C) functions as an extender, it is not necessary to use other pigments, but other pigments may be used in combination depending on circumstances.
Examples of the colorant include iron oxide, bengara, carbon black, phthalocyanine green, phthalocyanine blue, and quinacridone red. Although the usage-amount of these pigments or coloring agents is not specifically limited, It is preferable that it is the range used as 10 to 50 weight% in a powder coating material.

  Production (painting) of the powder coating material of the present invention requires an epoxy resin (A), a curing agent (B), a filler (C) having a porous spherical Shirasu balloon (C1) as essential components, and further necessary. Depending on the condition, other additives are roughly pulverized and blended, and this blend is uniformly pulverized and mixed using a Henschel mixer, etc., then melt kneaded using a heated kneader or extruder, pulverized after cooling, The classification method is mentioned.

  The powder coating for cast iron pipes of the present invention thus obtained has an average particle diameter of 10 μm or more from the viewpoint of good coating efficiency, and is 20 to 150 μm from the viewpoint of good smoothness of the coating surface. It is preferable.

  Moreover, it does not specifically limit as a cast iron pipe which is a to-be-coated object, A straight pipe, a deformed pipe, its accessories, etc. are mentioned.

  The application to the inner surface of the cast iron pipe is preferably performed by a method suitable for the paint to be used after removing rust and other deposits on the inner and outer surfaces of the cast iron pipe before application. Although it does not specifically limit as a coating method, Methods, such as spray coating, electrostatic spray coating, a centrifugal projection method, and fluidized immersion coating, are mentioned. Among the above methods, spray coating is particularly preferable. Specific examples of the method include preheating a cast iron pipe to 200 ° C. or higher and spraying the inner surface while rotating at about 500 rpm (the number of rotations per minute). Moreover, it is preferable from the point of anticorrosive property and pinhole prevention that the film thickness of a coating film is 0.1-1.0 mm.

  Hereinafter, the present invention will be described by way of examples, but the present invention is not limited thereto.

[Synthesis Example 1]
In a 2 liter four-necked flask equipped with a stirrer, thermometer, and cooler, 700 g of bisphenol F type epoxy resin (EPICLON 830 manufactured by DIC Corporation, epoxy equivalent 172 g / eq.), 300 g of bisphenol F, and 50% tetramethylammonium 0.22 g of chloride was added and stirred, the temperature was raised to 140 ° C. over about 2 hours, and further stirred at 140 ° C. for 5 hours to obtain an epoxy resin (1). The obtained epoxy resin (1) has an epoxy equivalent of 1050 g / eq. The softening point was 89 ° C.

[Examples 1 to 5 and Comparative Examples 1 to 3]
A curing agent and a filler were blended at a ratio shown in Table 1 with respect to 100 parts of the epoxy resin (1) obtained in Synthesis Example 1, and were sufficiently pulverized and mixed using a Henschel mixer. Thereafter, using “Konaida PCS-30” manufactured by Buss as an extruder, melt-kneaded, extruded, cooled, ground and classified to obtain a powder coating material having a particle size of 20 to 100 μm.
Using the obtained powder coating, the appearance (pinhole property / leveling property), anticorrosion property (salt water spray test), and adhesion (temperature difference adhesion test) of each example and comparative example were evaluated. The following criteria were used.

[Evaluation of pinhole properties]
Test pieces using the powder coating materials produced in Examples 1 to 5 and Comparative Examples 1 to 3, respectively, preheat a ductile cast iron pipe having a diameter of 100 mm and a length of 50 cm at 200 to 220 ° C., and rotate the cast iron pipe at 500 rpm. The coating was made by spraying on the inner surface and allowing to cool to form a coating film having a thickness of 250 to 350 μm.
The pinhole property of the powder coating was evaluated based on the following criteria by visually observing the appearance of the coating surface of each test piece. The results are shown in Table 1.
○: No pinhole ×: With pinhole

[Evaluation of leveling]
Test pieces using the powder coating materials produced in Examples 1 to 5 and Comparative Examples 1 to 3, respectively, preheat a ductile cast iron pipe having a diameter of 100 mm and a length of 50 cm at 200 to 220 ° C., and rotate the cast iron pipe at 500 rpm. The coating was made by spraying on the inner surface and allowing to cool to form a coating film having a thickness of 400 to 500 μm.
The leveling property of the powder coating was evaluated by visually observing the appearance of the coating film surface of each test piece and by the following criteria. The results are shown in Table 1.
○: Glossy, no roughness △: Glossy, no roughness ×: Glossy, no roughness

[Salt spray test]
The test pieces using the powder coatings produced in Examples 1 to 5 and Comparative Examples 1 to 3 were each a 150 mm × 70 mm × 7.0 mm ductile cast iron piece from which the oxidized scale was removed by shot blasting at 200 to 220 ° C. It was prepared by heating, spraying a powder paint on the surface of the cast iron piece, allowing to cool, and forming a coating film having a thickness of about 300 μm.
In the salt spray test of powder coating, salt water spray on each test piece is performed according to JIS K 5600-7-1, the state of the coating after 1000 hours is visually observed, and a knife is put in the wound. The creep peel width was confirmed. The results are shown in Table 1.
○: No abnormality such as blister, peeling width is small ×: Abnormality such as blister, peeling width is large

[Temperature difference test]
Using a test piece prepared in the same manner as in the salt spray test, a heat cycle with a humidity of 90% and a unit of 24 hours from −10 ° C. to 50 ° C. (8 hours at −10 ° C., 8 hours for temperature rise) It was left in a thermostatic chamber that can take 8 hours at 50 ° C. and 8 hours to drop in temperature), and the swelling of the coating film (peeling from the cast iron piece) after one month (30 days) was visually confirmed. .
In the temperature difference test of the powder coating, the adhesion was evaluated according to the following criteria. The results are shown in Table 1.
○: No swelling ×: With swelling

In Table 1, “parts” is parts by weight.
Moreover, the shirasu balloon used for the filler is as follows.
Shirasu balloon (1): average particle size 80 μm, thermal conductivity 0.06 kcal / m-hr- ° C., bulk specific gravity 0.18.
Shirasu balloon (2): average particle size 40 μm, thermal conductivity 0.05 kcal / m-hr- ° C., bulk specific gravity 0.35.

Claims (6)

  A powder coating for cast iron pipe containing an epoxy resin (A), a curing agent (B), and a filler (C), wherein the filler (C) is a porous spherical Shirasu balloon (C1) as an essential component A powder paint for cast iron pipe, characterized by:   The powder paint for cast iron pipes according to claim 1, wherein the filler (C) comprises a shirasu balloon (C1).   The powder coating material for cast iron pipes according to claim 2, wherein the bulk specific gravity of the shirasu balloon (C1) is 0.05 to 0.50.   As the filler (C), one or more other fillers (C2) selected from the group consisting of barium sulfate, talc, calcium carbonate, barium carbonate, silica, titanium oxide, alumina and mica are used as shirasu balloon (C1 The powder coating material for cast iron pipes according to claim 1 comprising   The powder paint for cast iron pipes according to claim 4, wherein the specific gravity of the other filler (C2) is 2.0 to 4.5.   6. A cast iron pipe, wherein the powder coating material for cast iron pipe according to claim 1 is applied to an inner surface.