JP2005232460A - Water-borne rust preventive coating - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-borne rust preventive coating by formulating a nonpolluting rust preventive pigment composition which is excellent in rust preventing performance and not imparting an adverse effect on storage stability when formulated to a water-borne coating. <P>SOLUTION: The invention relates to the water-borne rust preventive coating comprising a vehicle for the water-borne coating formulated with a reaction product of sodium tripolyphosphate and a water-soluble zinc salt, to improve storage stability of the water-borne rust preventive coating, wherein the mole ratio of the water-soluble zinc salt to the sodium tripolyphosphate in the reaction product is 0.5-10. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a water-based rust-preventing paint containing a rust-preventing pigment composition that is pollution-free and has excellent rust-preventing ability and does not adversely affect the storage stability of the paint even when blended in a water-based paint.

  Conventional anti-corrosion pigments include lead-based pigments such as red lead, lead oxide, cyanamide lead, calcium leadate, basic lead sulfate, basic lead chromate, zinc chromate, strontium chromate, barium chromate, calcium chromate, etc. Chrome pigments, zinc phosphate, calcium phosphate, aluminum phosphate, titanium phosphate, phosphite, hypophosphite and other phosphate pigments, zinc molybdate, calcium molybdate, zinc phosphomolybdate, etc. Molybdate pigments and other borate pigments such as barium metaborate have been used.

 In recent years, pollution regulations on heavy metal elements such as lead and chromium have been strengthened, and accordingly, the use amount of non-polluting phosphate pigments has been greatly increased. In particular, the rust preventive pigment composition blended with aluminum dihydrogen tripolyphosphate, which is a layered phosphate, has excellent rust preventive properties, and is a pollution-free rust preventive pigment that does not contain heavy metals. It is widely used in various paint systems such as powder systems (Japanese Patent Laid-Open No. 55-160059).

Examples of the layered phosphate widely used as an antirust pigment include aluminum dihydrogen phosphate [AlH ₂ P ₃ O ₁₀ .nH ₂ O (n = 0 or 2)], titanium phosphate [Ti (HPO _{4 2} ) nH ₂ O (n = 0 or 2)], zirconium phosphate [Zr (HPO ₄ ) ₂ .nH ₂ O (n = 0 or 2)], cerium phosphate [Ce (HPO ₄ ) ₂ .nH ₂ O (n = 1.33 or 2)] and the like. In particular, when aluminum dihydrogen tripolyphosphate is used as a rust preventive pigment, tripolyphosphate ions (P ₃ O ₁₀ ⁵⁻ ) are eluted in a corrosive environment, and orthophosphate ions (PO ₄ ) eluted from other layered phosphates. Compared with ^3- ), the chelating power against iron ions, which are rust components, is very large, which is preferable as a rust preventive pigment.

In addition to the above-mentioned layered phosphate, there is zinc phosphate [Zn ₃ (PO ₄ ) ₂ .nH ₂ O (n = 2 or 4)] as a pollution-free rust preventive pigment, but it exhibits rust prevention properties. The component orthophosphate anion (PO ₄ ³⁻ ) has a lower chelating ability against iron than the tripolyphosphate ion (P ₃ O ₁₀ ⁵⁻ ), which is an elution component from aluminum tripolyphosphate. I can't.

  Reducing VOC volatilization into the atmosphere for environmental conservation is a social issue today. Therefore, the use of water-based paints is increasing more and more in the field of paints. Conventional layered phosphate anticorrosive pigments, particularly aluminum dihydrogen phosphate, are excellent in anticorrosive performance, but have the drawback of reducing the storage stability of the paint when used in water-based paints. Accordingly, a pollution-free rust preventive pigment that is equivalent to or better than the conventional rust preventive pigment and that does not adversely affect the storage stability of the paint when used in an aqueous paint is desired.

  The present invention satisfies the above-mentioned demands by providing a water-based anticorrosive paint comprising a poorly water-soluble reaction product of sodium tripolyphosphate and a water-soluble zinc salt in an aqueous solution.

  The rust preventive pigment composition of the present invention is rather superior in rust preventive power compared to known layered phosphate rust preventive pigments, and when used in water-based paints, the storage stability of the paint is reduced to the extent that it is practically unusable. I won't let you.

Sodium tripolyphosphate used in the present invention has the formula Na ₅ P ₃ O ₁₀ and is readily soluble in water having uses such as sequestering agents, dyeing assistants, detergents, synthetic detergent builders and food additives. Compound.

  The zinc salt as the other raw material needs to be soluble in water.

  For this purpose, it is selected from zinc sulfate, nitrate or chloride.

  As described above, the tripolyphosphate metal salt exhibits excellent performance as a rust-preventive pigment for water-based paints, but does not exist in nature, and thus is produced by synthesis.

  In a conventional method for producing a conventional tripolyphosphate metal salt, (for example, 85%) phosphoric acid and a metal compound (for example, (water) aluminum oxide if producing an aluminum salt) are mixed and reacted, The rust preventive pigment of the present invention starts with a sodium tripolyphosphate aqueous solution and a soluble zinc salt aqueous solution, adds a soluble zinc salt to the sodium tripolyphosphate aqueous solution, and adjusts the pH as necessary. It is obtained by thoroughly washing and drying the precipitate formed.

  That is, a sodium tripolyphosphate aqueous solution and a zinc salt aqueous solution are prepared in advance, and these are mixed and stirred at a molar ratio (M / 3P, M: metal ion, 3P: tripolyphosphate ion) capable of forming a precipitate. The precipitate is separated by filtration, washed with water, dried and then pulverized. As a procedure for forming a precipitate, an aqueous solution of a water-soluble metal salt may be added to the aqueous solution of sodium tripolyphosphate, and conversely, an aqueous solution of sodium tripolyphosphate may be added to the aqueous solution of the water-soluble metal salt.

  The molar ratio (M / 3P) and pH at which precipitation is generated may be adjusted in the range of M / 3P = 0.5 to 10, preferably in the range of M / 3P = 1 to 7.5.

  For example, in the case of a sodium tripolyphosphate aqueous solution and a zinc chloride aqueous solution, it is preferable to obtain a precipitate in the range of M / 3P = 1 to 7.5, and the pH of the aqueous solution at that time is 2.5 to 4.5. Range. Alternatively, using sodium hydroxide, sulfuric acid, hydrochloric acid, or the like, the precipitate may be formed while adding the aqueous sodium tripolyphosphate and the aqueous water-soluble metal salt solution while keeping the pH of the aqueous solution at around 4-9.

  Since the composition of the present invention does not have the active hydrogen that the layered phosphate such as aluminum tripolyphosphate has, the storage stability of the paint is excellent even when blended with an aqueous paint, and the rust prevention performance is excellent. Yes.

  All layered phosphates have an active hydrogen atom and are known to react with various basic substances and to intercalate guest molecules between layers.

  In general, water-based paints are maintained at a weakly basic pH using ammonia or amines in order to stabilize the resin.

  Therefore, when these layered phosphates having active hydrogen are used as a rust preventive pigment in water-based paints, they react with ammonia and amines and are taken in between the layers. It leads to poor storage stability.

  In that respect, since the rust preventive pigment composition according to the present invention does not have these active hydrogens, it does not take in ammonia or amine, and the stability of the paint is inhibited even when used as a rust preventive pigment in a water-based paint. Never happen.

  The rust preventive pigment composition of the present invention may be used in combination with zinc oxide, or an alkaline earth metal oxide or hydroxide for the purpose of further improving the rust prevention property. As zinc oxide, a special one is not required, and one that is usually used for industrial purposes may be used. As the alkaline earth metal oxide or hydroxide, for example, magnesium oxide, magnesium hydroxide, magnesium carbonate, calcium oxide, calcium hydroxide, calcium carbonate and the like may be used. Calcium oxide is preferred.

  The combined proportion of the antirust pigment composition and zinc oxide or alkaline earth metal oxide or hydroxide is preferably 10/1 to 1/10, particularly preferably 10/1 to 10/10, by weight. . When the proportion of the rust preventive pigment composition of the present invention is less than the above range, there is no combined effect, and conversely when it increases, the dissolved metal ions of zinc and alkaline earth metal increase, so that the storage stability in the water-based paint is improved. Be inhibited. About the mixing method for combined use, it can carry out by any of dry mixing and wet mixing. Alternatively, before being dispersed in the paint resin, they may not be mixed in advance but added separately to the paint resin so that they are mixed in the resin. However, when used for water-based paints where storage stability is likely to be a problem, it is preferable to perform wet mixing in advance before being dispersed in the paint resin.

  The above-described wet mixing can be either batch type or continuous type, and any order of the components to be added in the mixing may be added first. The mixing temperature is suitably in the range from room temperature to 80 ° C., and the time is usually preferably 30 minutes to 3 hours. After mixing, the slurry is filtered and dried, and the resulting dried product is pulverized to obtain the target product.

  In addition, the wet mixing can be performed after filtering the precipitate of the metal tripolyphosphate and before drying. That is, the water-containing filter cake may be dispersed again in the aqueous solution, and zinc oxide or an alkaline earth metal oxide may be added and mixed under the above conditions.

  The rust preventive pigment composition of the present invention can have excellent storage stability even when used particularly in water-based paints. However, with regard to coating, water-soluble resins, dispersion resins, emulsion resins (cationic electrodeposition paints) Water-based resins including emulsion resins for coatings and emulsion resins for anionic electrodeposition coatings), as well as those used in coating resins, can be used without particular limitation. For example, boil oil, oily varnish, phenolic resin, amino resin, epoxy resin, urethane resin, vinyl resin, acrylic resin, fluororesin, silicone resin, polyester resin and other various synthetic resins for coatings, chlorinated rubber, cyclized rubber, etc. Rubber derivatives and other fiber derivatives can be used alone or in combination.

  Next, the present invention will be described more specifically with reference to examples. However, this invention is not limited only to those Examples. In the following, the number of parts indicating the amount and% indicating the concentration are based on weight.

Example 1. (Molar ratio Zn / 3P = 2.5)
50 g of sodium tripolyphosphate was charged and stirred with respect to 500 g of water, and completely dissolved to prepare a sodium tripolyphosphate aqueous solution. In addition, 46 g of zinc chloride (ZnCl ₂ ) was added to 200 g of water and stirred to completely dissolve it, thereby preparing a zinc chloride aqueous solution. An aqueous zinc chloride solution was added to an aqueous sodium tripolyphosphate solution and stirred for 30 minutes to form a precipitate. The resulting precipitate was dehydrated and filtered, then poured into 500 g of water again, heated to 60 ° C., and stirred for 1 hour. The slurry solution after stirring was dehydrated, filtered, dried at 90 ° C. for 36 hours, and then pulverized to obtain a rust preventive pigment composition.

Comparative Example 1 Blank (talc)

Comparative Example 2 T-100 K-100P (calcined aluminum tripolyphosphate)

Comparative Example 3 K-105 manufactured by Teika (calcined aluminum tripolyphosphate / zinc-treated product)

Comparative Example 4 Zinc phosphate

  Table 1 shows the pH of the water slurries of Example 1 and Comparative Examples 1 to 4.

  The pH of the water slurry was measured according to the pigment test method of JIS K5101. That is, 5 g of the sample was added to 100 ml of water, boiled for 5 minutes, cooled to room temperature, and then the pH was measured.

  Using the rust preventive pigment composition of Example 1 and the pigment compositions of Comparative Examples 1 to 4, as test examples, each of the normally dry emulsion resin coatings was adjusted, and after the coating was formed, a salt spray test was performed. It was. In addition, the storage stability test of the paint was conducted separately.

Test Example A normally dry emulsion resin paint having the composition shown in Table 2 was prepared, and after forming a coating film, a salt spray test and a storage stability test were conducted.

1-1 Adjustment of paint 11 kinds of normally dry emulsion resin paints were prepared according to the formulation shown in Table 2.

1-2 Coating and coating conditions The above-mentioned 11 types of normally dry emulsion resin-based paints were each coated on a coated plate under the following conditions, and dried at room temperature to form a coating film.
Coating: Bar coater coating Substrate: Degreasing mild steel JIS G 3141 (SPCC-SB)
Nippon Test Panel Industrial Co., Ltd. Film thickness: 38-42 μm
Drying: normal temperature, 7 days

1-3 Salt spray test A test plate prepared by forming a coating film on a coated plate as described above is placed in a salt spray test machine maintained at 35 ° C., and 5% sodium chloride aqueous solution is added at 1 kg / The coating film was sprayed at cm ² for 10 days, and the occurrence of rust on the test plate and the swelling of the coating film were observed.

1-4 Results of salt spray test The results of the salt spray test are shown in Table 3 for each type of rust preventive pigment. The rust prevention effect is evaluated by the effect of preventing the occurrence of rust on the test plate and the effect of preventing the occurrence of swelling of the coating film. The evaluation criteria are as follows. In addition, the evaluation standard of the rust generation prevention effect is based on ASTM D610-68 (1970), and the evaluation standard of the swelling generation prevention effect is based on ASTM D714-59 (1965). As is clear from the following evaluation criteria, the higher the evaluation value, the better the rust generation prevention effect and the blister generation prevention effect.

Evaluation criteria for rust generation prevention effect 5: Rust generation area less than 0.1% 4: Rust generation area 0.1% to less than 1% 3: Rust generation area 1% to less than 10% 2: Rust generation area 10% More than less than 33% 1: Rust generation area 33% or more

Evaluation criteria for swelling prevention effect 5: 8F or more 4: 8M, 6F, 4F
3: 8MD, 6M
2: 8D, 6MD, 4M, 2F
1: 6D, 4MD or more, 2M or more

1-5 Storage Stability Test of Paints Paints containing various rust preventive pigments with the above composition were prepared. This paint was left in a constant temperature room at 40 ° C., and the viscosity of each paint was measured with a B-type viscometer every week for one month.

1-6 Storage Stability Test Results of Paint The results of the above storage stability test are shown in Table 4 for each type of rust preventive pigment. As an evaluation, it is preferable that the viscosity change is small with time, and when the viscosity change is extremely large, the coating may gel and become unusable. The unit of the numbers in Table 4 is cps.

  As shown in Table 3, the rust preventive pigment composition of Example 1 was high in both the evaluation values of the rust generation preventing effect and the blister generation preventing effect, and was excellent in the rust preventing effect. Moreover, as shown in Table 4, the rust preventive pigment compositions of Examples 1 to 7 had a small increase in viscosity due to storage, and were excellent in storage stability in water-based paints.

  In contrast, Comparative Example 1. The blank (in which the rust preventive pigment component was replaced with talc having no rust preventive effect) and the zinc phosphate of Comparative Example 4 had good storage stability but had a low rust preventive effect. The solid acidic aluminum tripolyphosphate produced by the firing method of Comparative Example 2 has poor storage stability and rust resistance, and the composition is obtained by treating the solid acidic aluminum tripolyphosphate produced by the firing method of Comparative Example 3 with zinc oxide as the main component. Although the thing was excellent in the antirust effect, the storage stability of the paint was bad.

Claims (2)

  In order to enhance the storage stability of water-based anticorrosive paints, water-based anticorrosive paints comprising a reaction product of sodium tripolyphosphate and a water-soluble zinc salt in an aqueous paint vehicle.   The water-based anticorrosive paint according to claim 1, wherein the reaction product has a reaction molar ratio of a water-soluble zinc salt to sodium tripolyphosphate of 0.5 to 10.