JP2554921B2 - Protective coating method for concrete storage tanks - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a protective coating method for a concrete storage tank,
More specifically, it relates to a method for efficiently spraying a protective coating agent for a concrete storage tank containing no solvent on the surface of a concrete storage tank to form a protective coating excellent in chemical resistance and crack followability.

[Conventional technology]

Conventionally, in order to prevent concrete storage tanks for storing chemicals from deteriorating due to chemicals and leakage of chemicals from cracks in concrete, various materials have been painted or lined on the concrete surface. There is. For example, glass fiber reinforced unsaturated polyester resin (hereinafter referred to as FRP) is lined with a trowel or roller. In addition, a method of applying an epoxy resin paint typified by tar epoxy with a spray or roller is also used.

[Problems to be Solved by the Invention]

Since FRP contains an ester bond in its molecular structure, the ester bond is decomposed by the action of chemicals, particularly acids and alkalis, and the resin itself is depolymerized and deteriorates. For this reason, in the case of a storage tank lined with FRP,
There is a problem that FRP gradually dissolves from the surface and the protective layer disappears during use.

In addition, since FRP and epoxy resin have a small elongation of the cured coating film, when a crack occurs in concrete, the coating film will crack at the crack occurrence point. The so-called crack followability is poor. Therefore, there is a problem that chemicals leak from cracks in concrete. The larger the capacity of the concrete storage tank, the more likely it is that cracks will occur due to hardening of the concrete. Also,
Recently, various additives have been studied to prevent the generation of cracks, but it is essentially impossible to prevent concrete cracks at this stage.

Furthermore, there is no efficient construction method for the FRP lining,
It is often the case that the concrete surface is lined by hand, which requires skill and takes a long time. In addition, there are many variations in the coating film thickness, and coating defects are likely to occur in the thin portion of the coating film.

In the case of epoxy resin, both the base resin and the curing agent must be coated with a highly viscous and flammable solvent. The use of such flammable solvents in a closed room such as a storage tank is unsuitable due to the risk of explosion.

The inventors of the present invention have conducted earnest research for the purpose of solving the above problems. That is, the coating film is not deteriorated by chemicals, and even if concrete cracks, the coating film does not crack, and in addition, it is possible to efficiently spray the concrete surface without using a flammable solvent. The method was studied and the present invention was completed.

[Means and Actions for Solving the Problems]

That is, the present invention provides a protective coating agent comprising a mixture of a compound having two or more active hydrogen groups and an inorganic powder as a main agent, and a compound having two or more isocyanate groups as a curing agent in a concrete storage tank. In a protective coating method for a concrete storage tank to be sprayed, (1) a compound having two or more active hydrogen groups is a hydroxyl-terminated liquid polybutadiene having a 1,4-bond content of 50% or more and a viscosity of 5 to 100 poise. 30% by weight or more, (2) the inorganic powder contains silica, aluminum silicate or magnesium silicate alone or a mixture thereof, (3) the main agent and The curing agent is liquid and the viscosity of each is
Provided is a protective coating method for a concrete storage tank which is adjusted to 0.1 to 60 stokes.

The concrete protective coating method of the concrete storage tank of the present invention will be described below.

The "compound having two or more active hydrogen groups" as referred to in the specification is a compound containing two or more hydroxyl groups and / or amino groups in the molecule.

Compounds having a relatively large molecular weight include polyolefin polyols, polyether polyols and polyester polyols.

As the polyolefin polyol, a polybutadiene polyol (referred to as a hydroxyl group-terminated liquid polybutadiene) obtained by polymerizing a diene such as butadiene and isoprene with an initiator of hydrogen peroxide, and polyisoprene polyol can be used.

Specific examples of the polyether polyol include polyoxypropylene polyol, polyoxyethylene polyoxypropylene polyol, and tetrahydrofuran obtained by polymerizing propylene oxide or ethylene oxide in the presence of an alkali catalyst with a compound having two or more active hydrogens as an initiator. Polytetramethylene ether glycol obtained by ring-opening polymerization of can be used.

Polyester adipate, polybutylene adipate, polyhexylene adipate, polycaprolactone and castor oil can be used as the polyester polyol. However, the polyester polyol is decomposed by chemicals such as acid and alkali, and the coating film deteriorates. Should be as small as possible. In particular, polyester polyols having a high ester group concentration are likely to cause ester bond decomposition.

Compounds containing two or more active hydrogen groups with a relatively small molecular weight, and compounds containing two or more hydroxyl groups in the molecule include ethylene glycol, propylene glycol, 1,4-butanediol, 1,3-butanediol, 1 , 6-hexanediol, neopentyl glycol, octanediol, bisphenol A, trimethylolpropane, glycerin, pentaerythritol, triethanolamine, bis (2
-Hydroxypropylaniline) and compounds having two or more hydroxyl groups of these alkylene oxide adducts, and examples of the compound having two or more amino groups in the molecule include diaminodiphenylmethane, methylenebis (orthochloroaniline) ( MOCA), phenylenediamine, tolylenediamine, ethylenediamine and piperazine. Further, as compounds having a hydroxyl group and an amino group in the molecule, there are monoethanolamine, diethanolamine, aminoethylethanolamine, and compounds obtained by adding an alkylene oxide to a part of the amino groups of the compound having two or more amino groups. .

Among the compounds having two or more active hydrogen groups, polyolefin polyol is most preferable. In particular, hydroxyl-terminated liquid polybutadiene, preferably 50% or more of 1,4-bonds,
Hydroxyl-terminated liquid polybutadiene with a viscosity of 5-100 poise / 30 ° C has a relatively low viscosity, is ready for spraying, and the resulting coating film has good crack followability and other properties. Has excellent chemical resistance. Therefore, in order to achieve the object of the present invention, it is necessary to adjust such that 30% by weight or more of the compound having two or more active hydrogen groups is hydroxyl group-terminated liquid polybutadiene.

Examples of the inorganic powder used as the main agent include silica, aluminum silicate, magnesium silicate alone or a mixture thereof. Specific examples include clay, kaolin clay,
There are talc and mica. Inorganic powders that do not chemically react with chemicals and that do not undergo changes such as swelling due to chemicals should be used. Since the inorganic powder contains a small amount of water or is basic, if added to the curing agent, it may cause deterioration of the curing agent, so it should be added to the main agent. By adding inorganic powder, the chemical resistance of the coating film can be improved, and the permeability of chemicals, water, etc. can be reduced, making it difficult for the chemicals to permeate the coating film and reach the concrete surface. effective. Also, the addition of inorganic powder has the effect of improving the paintability of the paint when spraying with a two-liquid internal mixing type airless coating machine, so inorganic powder should be blended into the paint for coating. Is. The inorganic powder is usually 10 to 250 parts by weight, preferably 20 to 100 parts by weight per 100 parts by weight of the compound having two or more active hydrogen containing machines.
Used in 150 parts by weight, the average particle size of the powder is usually 0.1 ~
It can be 50 microns, preferably 0.5-10 microns.

The curing agent used in the present invention is a compound having two or more isocyanate groups in the molecule. For example, 2,4
-Tolylene diisocyanate, 2,6-tolylene diisocyanate and mixtures thereof (hereinafter collectively referred to as TDI),
Diphenylmethane diisocyanate (hereinafter referred to as MDI), liquid MDI, polymethylene polyphenyl polyisocyanate (hereinafter referred to as crude MDI), hexamethylene diisocyanate, xylylene diisocyanate, cisophorone diisocyanate, etc., and compounds having two or more isocyanate groups and the above There is an isocyanate-terminated prepolymer obtained by reacting a compound having two or more active hydrogen groups with an excess of isocyanate groups. When selecting a curing agent, the curing reaction proceeds from low temperature to high temperature, its reactivity is optimal for spraying, and the vapor pressure is low so as not to volatilize during spraying, and the cured coating film It should be selected so that it will not easily decompose due to chemicals. Liquid MDI and crude MDI are the most suitable for these conditions. In particular, since crude MDI is liquid even at low temperatures, the curing reaction proceeds even at low temperatures, the vapor pressure is low, and the resulting coating film has excellent chemical resistance, crude MDI is used for the purpose of the present invention. Is preferred.

The base and curing agent must be liquid at the temperatures used. When the main agent and the curing agent are solid, they can be made into a liquid state by heating, but it is preferable that they are in a liquid state without heating. The viscosities of the base and curing agents should be adjusted to be 0.1 to 60 Stokes at the temperature of the coating material during application. If the viscosity becomes higher than this range, it should be heated to adjust the viscosity to this range before use. If the viscosity is lower than 0.1 Stokes, it will cause pulsation in the airless coating machine when spraying, causing defective coating. If the viscosity is higher than 60 Stokes, spraying with an airless coating machine will not be possible. The temperature of the coating material during construction is 20-80 ℃
Is preferred. If the viscosity of the coating agent does not fall within the above range unless the temperature is lower than 20 ° C, it must be cooled in the summer and the surface of the sprayed surface will be condensed due to the condensation caused by the reaction between water and isocyanate. The film may be defective. If the temperature of the coating material does not reach the above range unless the temperature is higher than 80 ° C, if the pot life is constant during spraying, the temperature of the coating material will decrease after application, and the curing speed will increase. Not only does the workability of spraying work become extremely poor, but it is also difficult to maintain the heat when the paint is transported over a long distance with a hose. Therefore, the viscosity is 0 when the temperature of the coating material is adjusted to 20-80 ° C.
Spraying should be performed after adjusting the coating agent so that it becomes 1 to 60 stokes.

The protective coating agent for the concrete storage tank of the present invention should be applied and the cured coating film must have an elongation at break of 30% or more in the tensile test of JIS K 7113. 30% elongation at break
If it is lower, when the concrete cracks, the coating film also cracks, causing chemical leakage from the storage tank.

If desired, a catalyst, a colorant, an antifoaming agent, an antioxidant, an antiaging agent, and other additives and auxiliaries can be added to the protective coating agent used in the present invention.

Next, the spraying method of the present invention is a method of coating a protective coating agent with a two-liquid internal mixing type airless coating machine. This construction method is a method (airless spray method) in which the main agent and the curing agent are sent to a two-liquid internal mixing type airless coating machine by a high-pressure metering pump and atomized by the pressure (airless spray method). The airless spray method does not scatter the coating agent during spraying and hardly entraps air bubbles in the coating film. Therefore, it is the most suitable protective coating method for concrete storage tanks. When coating by the airless spray method according to the present invention, the main agent and the curing agent should be uniformly mixed in the coating machine with a static mixer or a power mixer so as not to entrap air bubbles. There is an external mixing method in which the main agent and the curing agent are separately sprayed to cure, but in this case, a coating film with sufficient performance cannot be obtained due to poor mixing of the main agent and the curing agent.

Other methods include a hand-painting method and an air spray method, but they are not preferable due to the following drawbacks. The hand-coating method is a method in which the main agent and the curing agent are mixed in a suitable container such as a vat and applied with a trowel, etc. It takes a long time from mixing to construction, so the pot life must be extended, so curing It takes a long time. Furthermore, not only does it require skill, but the coating film tends to be uneven.

The air spray method is a method in which the main agent and the curing agent are sent by a low-pressure metering pump and atomized with air pressure to apply the coating. Since the coating agent is atomized with a large amount of air during spraying, the coating agent scatters. However, the coating workability is poor, and the coating film obtained also entraps a large amount of air, so the performance of the coating film deteriorates.

Prior to spraying with the two-liquid internal mixing type airless coating machine of the present invention, it is preferable to pretreat the surface of the concrete to be worked by sandblasting, shot blasting, skelton, etc. If dirt, dust, dry chemicals, concrete grits or deteriorated materials adhere to the surface of concrete, it may cause troubles such as poor adhesion of the coating film. In addition, if the chemicals or water in the storage tank are impregnated in the concrete, it may cause foaming of the coating film, so the surface to be constructed should be dried sufficiently.

The chemicals stored in the concrete storage tank of the present invention include alkalis such as sodium hydroxide, potassium hydroxide and calcium hydroxide, inorganic acids such as sulfuric acid, hydrochloric acid and nitric acid, salts such as sodium carbonate, sodium sulfate and salt, and the above. There are water, sewage, seawater and industrial waste liquid.

Specific examples include chemical tanks and reservoirs at water treatment plants, chemical tanks and sewage treatment tanks at sewage treatment plants, waste liquid treatment tanks at factories, and concrete structures constructed near the coastline.

[Examples] Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. In the examples and comparative examples, “parts” means parts by weight.

Examples and Comparative Examples The base resin and curing agent shown in Table 1 were coated on a release paper and mortar by a two-liquid internal mixing type airless coating (manufactured by Asahi Osumi Sangyo Co., Ltd.) so that the thickness was 3 mm. The obtained coating film was cured at room temperature for 7 days and then subjected to the test.

Polybutadiene R-15HT: 1,4-bond 80% viscosity 13 poise
Hydroxyl-terminated liquid polybutadiene at / 30 ℃, Idemitsu Arco Co., Ltd., hydroxyl value 118 mgKOH / g.

Polybutadiene R-45HT: 1,4-bond 80% viscosity 50 poise
Hydroxyl-terminated liquid polybutadiene at / 30 ℃, manufactured by Idemitsu Arco Co., Ltd., hydroxyl value 46.5mgKOH / g.

Castor oil modified polyol: Ito Oil Co., Ltd., hydroxyl value
167 mg KOH / g.

Polyhardener D-200: polypropylene glycol, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., hydroxyl value 56 mg KOH / g.

Polyhardener PA-400: Aromatic amine polyol, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., hydroxyl value 430 mgKOH / g.

Inorganic powder: All have an average particle size of 1 to 10 microns.

Hardness: According to JIS K 6301.

Tensile strength: According to JIS K 7113.

Elongation at break: According to JIS K 7113.

Crack followability: According to the method of salt damage countermeasure guideline for road bridges (Japan Road Association).

Adhesion strength: According to the guideline for salt damage of road bridges (Japan Road Association).

Chemical resistance: According to JIS K 7114.

As is clear from the examples, the protective coating method of the concrete storage tank of the present invention has good coatability, and the crack followability of the obtained coating film is 0.
It is far superior to 4 mm and has excellent chemical resistance.

Comparative Example 1 has good coatability, but contains castor oil as a main component, and ester bonds are decomposed to reduce the film thickness and soften the coating film. Even when a castor oil or a castor oil-modified polyol is used as in Examples 2 and 3, when the polybutadiene polyol is the main component, the chemical resistance is excellent and the coating film is not dissolved or the film thickness is not reduced.

When polypropylene glycol is used as the main component as in Comparative Example 2, the viscosity is low and the coatability is good, but polypropylene glycol has a high water absorption, so the coating film softens. Further, since barium sulfate is used as the inorganic powder in Comparative Example 2, the inorganic powder is eluted by decomposing it into sodium sulfate and barium hydroxide by the reaction of barium sulfate with an alkali such as sodium hydroxide.

In Comparative Example 3, since no inorganic powder is used, chemicals are likely to permeate and the coating film tends to be slightly softened. In addition, the paintability is poor when coated with a two-liquid internal mixing type airless coating machine.

In Comparative Example 4, even if the main component was heated to 80 ° C., the viscosity was as high as 120 Stokes, and coating could not be performed.

In Comparative Example 5, the strength of the obtained coating film is high, but the crack followability is poor because there is no elongation.

As described above, the method of the present invention is extremely excellent as a protective coating method for concrete storage tanks.

〔The invention's effect〕

Since the protective coating film obtained by the protective coating method for a concrete storage tank of the present invention is not only resistant to chemicals, particularly acid, alkali and salt, but also the coating film has elongation. ， Has more crack followability than conventional FRP and epoxy resin and does not leak chemicals. Furthermore, according to the protective coating method of the present invention, the coating workability is good, and the resulting coating film has excellent performance with less entrainment of bubbles.

 ─────────────────────────────────────────────────── ─── Continued front page (72) Hiromitsu Togashi Hiromitsu Togashi 1-2-7 Moto-Akasaka Minato-ku, Tokyo Kashima Construction Co., Ltd. (72) Inventor Saburo Nomura 3-2750-10750 Motohachioji-cho, Hachioji-shi, Tokyo No. (72) Inventor Takashi Sano 25-3 Inabadai, Otsu City, Shiga Prefecture (72) Inventor Katsuo Matsuzaki 2-10-9 Akasaka, Minato-ku, Tokyo Japan Maritime Construction Co., Ltd. (56) References 50-161530 (JP, A) JP-A-57-11883 (JP, A) JP-A-53-33237 (JP, A) JP-A-63-285181 (JP, A)

Claims (1)

(57) [Claims] 1. A mixture comprising an inorganic powder and a compound having two or more active hydrogen groups as a main agent, and an isocyanate group of 2 or more.
In a protective coating method for a concrete storage tank, which comprises spraying a protective coating agent comprising a compound having two or more compounds as a curing agent onto a concrete storage tank, (1) the compound having two or more active hydrogen groups is 1,4 −
30% by weight or more of hydroxyl-terminated liquid polybutadiene having a bond of 50% or more and a viscosity of 5 to 100 poise, (2) The inorganic powder is silica, aluminum silicate, or magnesium silicate alone, Or a mixture containing them as a main component, and (3) the main agent and the curing agent are liquid, and the viscosity of each is adjusted to 0.1 to 60 Stokes. Protective coating method.