JP5014762B2 - Antirust pigment and antirust paint composition containing the same - Google Patents

Description

  The present invention relates to a pollution-free rust preventive pigment that imparts excellent rust preventive properties to a metal material, and a rust preventive coating composition containing the same.

  Conventionally, chromate (strontium chromate, basic zinc chromate, basic potassium zinc chromate, etc.) and lead compounds (lead red, lead suboxide, cyanamide lead, calcium leadate, etc.) have been used as rust preventive pigments. It was used. Although these rust preventive pigments exhibit excellent rust prevention performance against metals, there are concerns about toxicity. Therefore, chromium and lead have been regulated as environmental pollutants, and provision of new rust preventive pigments that can replace these materials is expected.

Non-lead and non-chromium rust preventive pigments currently on the market include, for example, metal phosphates, phosphites, phosphosilicates, borosilicates, borates, metaborates, molybdates, For example, calcium, strontium, barium, zinc, aluminum, magnesium, etc. are used as these metal cations. Further, silica subjected to ion exchange, for example, silica subjected to calcium exchange, is also commercially available. Further, the following Patent Document 1 discloses a rust preventive pigment containing a phosphonic acid having chelating ability, and the following Patent Document 2 discloses an anti-rust pigment containing an organo-substituted phosphonic acid or a polyvalent metal salt of phosphonocarboxylic acid. Rust pigments are disclosed.
Japanese National Patent Publication No. 11-512126 JP-A-7-207182

  Among these rust preventive pigments, the most widely used rust preventive pigments are mainly composed of aluminum tripolyphosphate or zinc phosphate. However, anti-corrosion pigments such as aluminum tripolyphosphate and zinc phosphate do not necessarily reach the same level in terms of performance compared to chromium-based and lead-based anti-rust pigments, and further improvements in anti-rust performance Is required.

  Accordingly, an object of the present invention is to provide a pollution-free rust preventive pigment capable of imparting excellent rust preventive properties to a metal material, and a rust preventive coating composition containing the same.

As a result of intensive studies in view of the above circumstances, the present inventors have found that a rust preventive pigment comprising an amorphous inorganic composition containing P ₂ O ₅ , CaO, SiO ₂ , and MgO is a pigment. When the coating composition containing the anti-corrosion pigment is applied to the surface of the metal material, the paint containing the conventional chromium-based or lead-based anti-corrosion pigment is dissolved in water. It has been found that excellent rust preventive properties comparable to the composition can be imparted, and the present invention has been completed.

That is, the first invention to be provided by the present invention is an amorphous material containing 10 to 30% by mass of P ₂ O ₅ , 20 to 40% by mass of CaO, 10 to 30% by mass of SiO _{2, and} 10 to 20% by mass of MgO. It is an antirust pigment characterized by comprising an inorganic composition.

  In addition, a second invention to be provided by the present invention is a rust preventive coating composition comprising the rust preventive pigment of the first invention.

  ADVANTAGE OF THE INVENTION According to this invention, the pollution-free rust preventive pigment which can provide the metal material with the outstanding rust prevention property, and the rust preventive coating composition containing this can be provided.

Hereinafter, the present invention will be described based on preferred embodiments.
The rust preventive pigment of the present invention contains P ₂ O ₅ , CaO, SiO ₂ , and MgO, and its preferred composition is
(1) _P 2 _O 5 10~30 wt% as a phosphoric acid component, preferably 15 to 25 wt%,
(2) CaO 20-40% by mass as a calcium component, preferably 25-35% by mass,
(3) 10-30% by mass of SiO ₂ as a silicic acid component, preferably 15-25% by mass,
(4) 10-20 mass% MgO as a magnesium component, 12-17 mass%,
It is characterized by comprising an amorphous inorganic composition that exhibits amorphousness in X-ray diffraction analysis.

  The rust preventive pigment of the present invention comprising the amorphous inorganic composition has a stable pigment characteristic while each component elutes slightly, and a coating composition containing the rust preventive pigment is applied to the surface of a metal material. In this case, it is possible to impart excellent rust preventive properties comparable to conventional coating compositions containing chromium-based or lead-based anticorrosive pigments.

  In the rust preventive pigment of the present invention, if the proportion of each component is out of the range of the composition, the inorganic composition is likely to be crystallized, and the elution of the component from the pigment tends to be lost. As a result, it becomes difficult to obtain the effect of the present invention.

Anticorrosive pigment of the present invention, in addition to the component (1) to (4), required by the _B 2 _{O 3} 5 wt% or less, can be contained MnO in a range of 5 mass% or less, further Fe ₂ Components such as O ₃ , Al ₂ O ₃ , and Na ₂ O can be contained in the range of 5% by mass or less.

The amorphous inorganic composition used for the rust preventive pigment of the present invention preferably has a water content measured in accordance with JIS K5101-16-1 in the range of 0.1 to 1% by mass. More preferably, it is in the range of 0.1 to 0.6% by mass. If the water content is less than the above range, the rust preventive effect on the surface of the metal material due to the component eluted in water becomes insufficient, and if the water content exceeds the above range, the component elution is too fast and the rust preventive effect lasts long. No longer. Further, from 0.001 to 1 mass% phosphoric acid fraction elutes as _P 2 _{O 5,} preferably particularly preferred in that it can be improved further anticorrosive performance to be 0.002 mass%.

  The amorphous inorganic composition used in the rust preventive pigment of the present invention preferably has a volume average particle size determined by measurement by a laser diffraction scattering method in the range of 0.5 to 15 μm, and in the range of 1 to 5 μm. It is more preferable that If the volume average particle size of the amorphous inorganic composition is in the range of 0.5 to 15 μm, the appearance of the coating film applied to the surface of the metal material when the antirust coating composition is prepared using this pigment , Strength and durability are good.

  The amorphous inorganic composition used for the rust preventive pigment of the present invention preferably has a sieve residue of 1.0% by mass or less measured according to JIS K5101-14-1, and 0.5% by mass. % Or less is more preferable. In the present invention, the sieve residue measured according to JIS K5101-14-1 is a sieve residue measured using a mesh having a mesh size of 45 μm, and the content of particles having a particle size of 45 μm or more. Is a value corresponding to. If the sieve residue exceeds 1.0% by mass, the appearance, strength, and durability of the coating film applied to the surface of the metal material deteriorate when a rust-proof coating composition is prepared using this pigment.

  The amorphous inorganic composition used for the rust preventive pigment of the present invention is produced by heating and melting a mixture containing a magnesium source, a calcium source, a phosphoric acid source and a silicic acid source, and then rapidly cooling the mixture. However, it is preferable in that crystallization (mainly apatite formation) can be prevented and elution of components such as phosphoric acid can be within the above range when contacted with water.

  The mixture containing the magnesium source, calcium source, phosphoric acid source, and silicic acid source may be a mixture of the compounds containing these components, or a compound or mineral containing two or more of these components. May be used.

In the present invention, a particularly preferable amorphous inorganic composition has a molar composition of xMgO.yCaO.P ₂ O ₅ .zSiO ₂ (where x is in the range of 2.9 to 3.1, and y is 3.9. in the range of ～4.1, z is an amorphous inorganic composition of a is) the range of 2.9 to 3.1, are particularly represented by _{3MgO · 4CaO · P 2 O 5} · 3SiO 2 This is so-called molten phosphorus fertilizer.

  The amorphous inorganic composition used for the rust preventive pigment of the present invention can be produced by using a typical production method of molten phosphorus fertilizer, such as JP-A-57-92588 and JP-A-57. -149885, JP 57-200209, JP 58-69794, JP 58-89939, JP 58-145681, JP 60-65785, It can be produced using the methods described in JP-A-62-270484, JP-A-8-295584 and the like.

  That is, this amorphous inorganic composition can be produced by mixing and melting the raw materials containing each component, then rapidly cooling, and if necessary, pulverizing and classifying. Examples of the raw material containing each component include industrial raw materials such as calcium phosphate, magnesium phosphate, silica (natural products and synthetic products), calcium silicate, and natural raw materials (silica stone, quartz sand, phosphate rock, serpentinite, peridotite) Etc.).

For example,
(A) Phosphorous ore as a phosphorus-containing component is blended with serpentinite, peridotite, quartzite, nickel slag containing both components, etc. as a main raw material, and if necessary, a small amount of additive components such as manganese or boron After mixing, heat and melt at 1200 ° C. or higher, preferably 1400 to 1500 ° C. in a melting furnace such as an electric furnace or a flat furnace, and then the molten product is granulated and dried, and further pulverized and classified as necessary. How to get,
(B) A mixture of a predetermined amount of magnesium oxide, quicklime, phosphoric acid and silicic acid and, if necessary, a small amount of additive components such as manganese or boron are mixed, and then 1200 ° C. or higher in a melting furnace such as an electric furnace or a flat furnace. , Preferably 1400-1500 ° C., and then melted and granulated, dried, and further pulverized and classified as required to obtain a fine powder product,
(C) A mixture composed of a predetermined amount of magnesium silicate, calcium phosphate and quick lime, and after adding a small amount of an additive component such as manganese or boron as necessary, in a melting furnace such as an electric furnace or a flat furnace, 1200 ° C or higher, preferably Can be heated and melted at 1400 to 1500 ° C., and then the melted product is crushed and dried, and further pulverized and classified as necessary to obtain a fine powder product.

  In addition to the amorphous inorganic composition, the rust preventive pigment according to the present invention is used in combination with a metal compound containing one or more metal elements selected from the group consisting of Ca, Mg, Zn and Si. The rust prevention performance can be improved.

  As the metal compound that can be used, these metal powders, oxides, carbonates, hydroxides, phosphates, and phosphites of these metals can be used. May be. Among these, metal powders, metal oxides, and carbonates are preferably used because of their high synergistic effect, and particularly preferably zinc powder, zinc oxide, calcium carbonate, magnesium phosphite, and amorphous silicic acid. It is 1 type, or 2 or more types selected from the group which consists of. The physical properties and the like of the metal compound are not particularly limited, but the volume average particle size obtained by measurement by a laser diffraction scattering method is preferably in the range of 0.5 to 15 μm, and in the range of 1 to 5 μm. It is more preferable. If the volume average particle size is in the range of 0.5 to 15 μm, when a rust preventive coating composition is prepared using this metal compound and the rust preventive pigment, the coating film applied to the surface of the metal material. Appearance, strength and durability are good.

  The metal compound to be used in combination may be prepared in advance as a uniform mixture with the rust preventive pigment. In the case of the coating composition described later, it can also be added separately to the coating composition.

  The rust preventive pigment and the metal compound may be surface-treated with an organic phosphate compound selected from acidic phosphate esters and / or phosphonic acids having chelating ability, or derivatives thereof as desired. Acid phosphate esters include, for example, methyl acid phosphate, dimethyl acid phosphate, ethyl acid phosphate, diethyl acid phosphate, methyl ethyl acid phosphate, normal- or iso-propyl acid phosphate, positive- or iso-dipropyl acid phosphate, methyl Butyl acid phosphate, ethyl butyl acid phosphate, propyl butyl acid phosphate, positive- or iso-octyl acid phosphate, positive- or iso-dioctyl acid phosphate, positive-decyl acid phosphate, positive-didecyl acid phosphate, positive-lauryl acid phosphate , Positive-dilauryl acid phosphate, positive- or iso-ceyl acid phosphate, positive- or Iso-disesyl acid phosphate, normal-stearyl acid phosphate, positive- or iso-distearyl acid phosphate, allyl acid phosphate, diallyl acid phosphate, and the like, from these compounds Mg, Ca, Sr, Ba, Zn or Al One or two or more selected metal salts, amine salts and the like can be mentioned.

  Typical examples of the phosphonic acid compound having chelating ability include aminoalkylenephosphonic acid, ethylenediaminetetraalkylenephosphonic acid, alkylmethane-1-hydroxy-1,1-diphosphonic acid, and 2-hydroxyphosphonoacetic acid. As a compound. Among these, examples of the aminoalkylenephosphonic acid include nitrilotristyrenephosphonic acid, nitrilotripropylenephosphonic acid, nitrilodiethylmethylenephosphonic acid, nitrilopropylbismethylenephosphonic acid, and the like. Examples of the ethylenediaminetetraalkylenephosphonic acid include ethylenediaminetetramethylenephosphonic acid, ethylenediaminetetraethylenephosphonic acid, ethylenediaminetetrapropylenephosphonic acid, and the like. Examples of the alkylene-1-hydroxy-1,1-diphosphonic acid include methane-1-hydroxy-1,1-diphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid, and propane-1-hydroxy-1 , 1-diphosphonic acid, and the like. These compounds may be one or two or more complex salts selected from Mg, Ca, Sr, Ba, Zn, or Al, but are limited to these compounds. It is not a thing. Moreover, you may use 1 type or in combination of 2 or more types of the compound of said phosphoric acid which has chelate ability with acidic phosphate ester. The amount of acidic phosphate ester and / or phosphonic acid having chelating ability relative to the oxyacid salt of phosphorus is not uniform depending on the physical properties and type of the compound used, but is usually 0.1 to 30% by mass, preferably 1 to 10% by mass.

The rust preventive pigment and metal compound may be further surface-treated with a higher fatty acid or a derivative thereof, a surfactant, or a silane coupling agent for the purpose of improving dispersibility.
In addition, the rust preventive pigment may include an inorganic anion exchanger having a chlorine ion scavenging ability such as hydrocalumite and hydrotalcite, and a nitrite such as an alkali metal nitrite and an alkaline earth metal nitrite. It can contain with the addition amount of the range which does not impair the effect of this invention.

  The rust preventive coating composition of the present invention contains the rust preventive pigment and a paint vehicle. A paint vehicle refers to a medium in which paint components are dispersed. That is, a polymer material that is a coating film forming component, a natural or synthetic resin, an inorganic binder, a high-molecular substance such as a fiber or rubber derivative, or the like is dissolved in a solvent.

  Examples of the synthetic resin include phenol resin, alkyd resin, melamine resin, guanazine resin, vinyl resin, epoxy resin, polyamine resin, acrylic resin, polybutadiene resin, polyester resin, urethane resin, silicon resin, and fluorine-containing resin. These may be mixed systems or modified resins as required.

  Examples of the inorganic binder include water-soluble silicate, modified aqueous silicate, alkyl silicate, alkoxy silicate, coupling agent, colloidal silica, and the like.

The water-soluble silicate is represented by a general formula M ₂ O · xSiO ₂ · yH ₂ O, where M is an alkali metal such as sodium, lithium, potassium, N (C ₂ H ₄ OH) ₂ , N (CH ₂ OH) ₄ , N (C ₂ H ₄ OH) ₄ , C (NH ₂ ) ₃ NH, wherein x and y represent integers, and specific compounds include, for example, sodium silicate, potassium silicate, silicic acid Examples thereof include alkali metal silicates such as lithium, triethanolamine silicate, tetramethanol ammonium silicate, tetraethanol ammonium silicate and the like.

  As the modified water-soluble silicate, the water-soluble silicate is selected from the group consisting of oxides, hydroxides, fluorides, and silicon fluorides of metals selected from aluminum, magnesium, calcium, barium, strontium, zinc, zirconium, and vanadium. Modified with seeds or two or more, or modified with sodium silicofluoride, potassium trisilicofluoride zincate, fluoroaluminum complex salt, fluorozinc complex salt, etc. (see JP-A-53-18636) Etc.

The alkyl silicate is represented by the general formula; SiR ₄ or SiXR ₃ , wherein R represents an alkyl group, and X represents an alkoxy group, a vinyl group, an epoxy group, an amino group, a methacryl group, or a mercapto group. Examples of the alkyl group include linear or branched alkyl groups having 1 to 5 carbon atoms such as a methyl group, an ethyl group, a propyl group, and a butyl group. Specific examples of the alkyl group include tetramethyl Examples thereof include silicate, tetraethyl silicate, tetrapropyl silicate, tetrabutyl silicate and the like.

The alkoxysilane is represented by the general formula; Si (OR) ₄ or SiX (OR) ₃ , SiR (OR) ₃ , wherein R represents an alkyl group, and X represents a vinyl group, an epoxy group, or an amino group. , A methacryl group and a mercapto group. Examples of the alkyl group include linear or branched alkyl groups having 1 to 5 carbon atoms such as a methyl group, an ethyl group, a propyl group, and a butyl group. Specific examples of the alkyl group include tetramethyl Examples thereof include xyl silicate, tetraethoxy silicate, tetrapropoxy silicate, tetrabutoxy silicate and the like.

  Examples of the coupling agent include γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, and vinyltriethoxysilane. Silane coupling agents such as γ-methacryloxytrimethoxysilane and γ-mercaptopropyltrimethoxysilane, isopropyltriisostearoyl titanate, tetraoctylbis (didodecyl) phosphite titanate, isopropyltrioctanoyl titanate, isopropyltridodecyl Examples include titanium coupling agents such as benzenesulfonyl titanate, aluminum coupling agents, and zirconium coupling agents.

The colloidal silica usually has a particle size of about 2 to 100 nm, contains about 20 to 40% solids and contains 0.7% or less Na ₂ O, and is particularly preferably stable at pH 8 to 10 with alkali. Colloidal silica can be used.

  The coating film components can be used alone or in combination of two or more. As diluents, water, alcohols, ketones, benzenes, aromatic hydrocarbons such as toluene and xylene, and aliphatic hydrocarbons such as liquefied paraffin are generally used in the field of paints. Can be applied.

  The blending amount of the rust preventive pigment of the present invention with respect to the paint vehicle is usually 2 to 50% by mass, preferably 5 to 20% by mass. When the blending amount is less than 2% by mass, the rust preventive power is lowered, and when it is greater than 50% by mass, preferable coating film characteristics cannot be obtained.

  The anticorrosive coating composition of the present invention can be used by containing various additives generally used in the coating field as components other than those described above. In particular, the rust preventive coating composition of the present invention improves the rust preventive performance by using in combination with a metal compound containing one or more of the metal elements selected from Ca, Mg, Zn and Si described above. It is preferable at the point which can do.

  The rust preventive coating composition according to the present invention can be used for brush, roller coating, spray coating, electrostatic coating, powder coating, roll coater, curtain flow coater, dipping coating, electrodeposition coating, and the like.

  Although the rust prevention mechanism of the rust preventive pigment according to the present invention is complicated and has not yet been elucidated, a strong passive film formed by reacting slightly eluted phosphate ions and silicate ions with iron or zinc of metal materials It is presumed that magnesium ions and calcium ions stabilize the metal material.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these. In the following examples, the amorphous inorganic composition as the main component of the rust preventive pigment of the present invention is referred to as “amorphous inorganic powder sample”.

<Preparation of amorphous inorganic powder sample>
Powder adjusted and mixed to a ratio of 4517 parts magnesium silicate (MgSiO ₃ ), 3102 parts calcium phosphate (Ca ₃ (PO ₄ ) ₂ ) and 841 parts quicklime (CaO) was melted in an electric furnace set at 1500 ° C. for 2 hours. Next, the melt was subjected to water pulverization and drying, and then pulverized for 2 hours using a dynamic mill (made by Mitsui Mining Co., Ltd.). As a result, the average particle diameter determined by the laser diffraction scattering method using a microtrack particle size distribution measuring apparatus manufactured by Nikkiso Co., Ltd. was 2.5 μm, and the sieve residue was measured according to JIS K5101-14-1. Inorganic powder sample containing 0.2% by mass of P ₂ O _5, 21.3% by mass, CaO 33.6% by mass, SiO ₂ 27.0% by mass, and MgO 18.1% by mass. (3MgO · 4CaO · P ₂ O ₅ · 3SiO ₂ ) was obtained.

  The obtained inorganic composition sample was confirmed to be amorphous by X-ray diffraction, and this was used as an amorphous inorganic powder sample.

Moreover, as a result of measuring the water content of the obtained amorphous inorganic powder sample according to JIS K5101-16-1, the water content was 0.31% by mass. Furthermore, as a result of analyzing the water-soluble component, the water-soluble component mainly contains phosphate ions of 0.005% by mass as P ₂ O ₅ , silicate ions at 0.16% by mass as SiO ₂ , and calcium ions at 0% as CaO. It was confirmed that 0.08 mass% and magnesium ions contained 0.012 mass% as MgO.

{Examples 1 to 4}
As shown in Table 1, an antirust pigment was prepared by operating the amorphous inorganic powder sample prepared above and the metal compound at 2000 rpm for 5 minutes using a high speed mixer.

{Comparative Examples 1 to 4}
As shown in Table 1, strontium chromate or an antirust pigment was prepared in the same manner as described above.

  In Table 1, zinc oxide having an average particle diameter of 1 μm, calcium carbonate having an average particle diameter of 1 μm, strontium chromate having an average particle diameter of 1 μm, and zinc phosphate having an average particle diameter of 5 μm were used.

<Evaluation of rust prevention performance>
1) The following two types of steel plates were used as test steel plates.
JIS G3141 SPCC-SD steel plate (hereinafter referred to as “steel plate”)
JIS G3302 SGCC hot-dip galvanized steel sheet (hereinafter referred to as “zinc steel sheet”)
2) Test paint A paint conditioner comprising a rust preventive paint composition containing the rust preventive pigment obtained in Examples 1 to 4 and Comparative Examples 1 to 4, and a paint composition containing no rust preventive pigment (Comparative Example 5). Prepared by the method. The blending ratio of each test paint is as follows.

<Alkyd paint>
Alkyd resin 21.3 parts Anticorrosive pigment 5.3 parts Titanium oxide 13.3 parts Calcium carbonate 24.0 parts Mineral spirit 8.0 parts Dryer 0.37 parts Alkyd resin: Beccosol P-470-70 (Dainippon Ink Chemical Co., Ltd.) (Manufactured by Kogyo)
Dryer: Dick Nate (Dainippon Ink Chemical Co., Ltd.)

<Epoxy paint>
Epoxy resin 34.0 parts Anticorrosive pigment 5.4 parts Titanium oxide 6.5 parts Xylene / Methyl ethyl ketone 17.0 parts Curing agent 41.3 parts Xylene / butanol 7.7 parts Epoxy resin: Epicoat 1001X75 (Japan Poxy Resin Co., Ltd.) Made)
Curing agent: Tomide 410N (Fuji Kasei Kogyo Co., Ltd.)

3) Test coating plate Each steel plate of 0.8 mm x 70 mm x 150 mm is degreased with a solvent, and each test paint is applied with a bar coater having a dry coating thickness set to 30 microns, and left to dry at room temperature for 1 week. After drying, seal the back and end surfaces of the coated steel sheet with masking tape and make a crosscut on the test painted surface.

4) Salt spray test A 5% NaCl aqueous solution is spray-tested on a test coating plate for 240 hours under conditions of a salt spray tester internal temperature of 35 ° C. and a spray pressure of 1 kg / cm ² .

5) Test result Rust prevention performance was judged by the following five-step evaluation method from the salt spray test result. The results are shown in Table 2.
Evaluation 5: There is no rust and no blisters other than the crosscut portion.
Evaluation 4: Rust and blister are generated within 2 mm on one side from the cross cut part.
Evaluation 3: Rust and blister occurred within 6 mm on one side from the cross cut part.
Evaluation 2: Rust or blister occurs within 12 mm on one side from the crosscut part.
Evaluation 1: Rust or blister occurs at 12 mm or more on one side from the cross cut part.

  From the results of Table 2, it was demonstrated that the anticorrosive coating composition containing the anticorrosive pigments of Examples 1 to 4 according to the present invention exhibits an excellent antirust effect when applied to each steel plate. .

Claims (10)

P ₂ O ₅ 10 to 30 wt%, CaO20～40 _wt%, SiO 2 10 to 30 wt%, antirust pigment, characterized in that it consists of amorphous inorganic composition containing MgO10~20 mass%. The water content of the amorphous inorganic composition measured in accordance with JIS K5101-16-1 is in the range of 0.1 to 1% by mass, and the eluted phosphoric acid content is 0.001 as P ₂ O _5. The rust preventive pigment according to claim 1, which is not less than wt%. The rust preventive pigment according to claim 1 or 2 , wherein the amorphous inorganic composition is produced by heating and melting a mixture containing a magnesium source, a calcium source, a phosphoric acid source and a silicic acid source and then rapidly cooling the mixture. . The amorphous inorganic composition has a molar composition of xMgO.yCaO.P ₂ O ₅ .zSiO ₂ (where x is in the range of 2.9 to 3.1 and y is in the range of 3.9 to 4.1). The rust preventive pigment according to any one of claims 1 to 3 , wherein z is a range of 2.9 to 3.1. The rust preventive pigment according to any one of claims 1 to 4 , wherein the volume average particle diameter is in a range of 0.5 to 15 µm. The rust preventive pigment according to claim 5 , wherein a sieve residue measured in accordance with JIS K5101-14-1 is 1.0 mass% or less. A rust preventive coating composition comprising the rust preventive pigment according to any one of claims 1 to 6 . The rust preventive coating composition according to claim 7 , comprising a metal compound containing one or more metal elements selected from the group consisting of Ca, Mg, Zn and Si together with the rust preventive pigment. The rust preventive coating composition according to claim 8 , wherein the metal compound is one or more selected from the group consisting of zinc powder, zinc oxide, calcium carbonate, magnesium phosphite, and amorphous silicic acid. The rust preventive coating composition according to claim 8 or 9 , wherein a blending ratio of the metal compound is in a range of 5 to 100 parts by mass with respect to 100 parts by mass of the amorphous inorganic composition .