JPH01257044A - Iron parts plated with zinc - Google Patents

Abstract

PURPOSE:To obtain iron parts plated with corrosion-resistant zinc by a method wherein the title parts possess composite coating comprised by laminating in order a chromate film whose deposition quantity of chromium is specific and an organic silicate resin film whose thickness is specific on a zinc plated layer formed on an iron base material. CONSTITUTION:A zinc plated layer and chromate film are formed on an iron base material. Chromium deposition quantity is made 20-800mg/m<2>, in a chromate film. An organic resin silicate film of 0.5-30mum in thickness is formed on the chromate film. An organic silicate resin film is formed by applying a mixture aqueous solution comprised by heating 1-50 pts. natural aqueous high-molecular compound possessing carboxyl group such as shellac, rosin and alginic acid as a terminal part structure to 100 pts.wt. aqueous organic/inorganic composits resin having aqueous colloidal silica for its inevitable ingredient. When the natural aqueous high-molecular compound is 1 pt. or less, it does not show effective function upon corrosion resistance, oil resistance, film hardness, wear resistance and moisture resistance of the film. When loading exceeds 50 pts., it becomes unfavorable economically and film characteristics is deteriorated unexpectedly.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a zinc plating process in which an organic silicate resin coating film is formed on a chromate film of an iron base material, which is formed by successively laminating a zinc plating film and a chromate film. This invention is particularly suitable for iron parts for automobiles, such as bolt nuts and leaf spring clips.

<Conventional technology> Conventionally, bolts and nuts used as steel parts for automobiles are usually galvanized (including zinc alloy plating), and in order to improve the corrosion resistance of the zinc plating, chemical conversion of chromate coating is applied. I was using what I had done.

<Problems to be solved by the invention> In recent years, with the increasing popularity of marine leisure activities (fishing, windsurfing, sailing, etc.), cars are being left on the coast for long periods of time, and antifreeze agents are being used on expressways in winter. Steel parts of automobiles (particularly fasteners such as bolts and nuts) are increasingly being exposed to harsh corrosive environments due to the dispersion of corrosive substances. For this reason, corrosion resistance standards for steel parts for automobiles are becoming more stringent than ever. However, as far as the present inventors are aware, no material has yet been developed that satisfies the requirements of these strict corrosion resistance standards.

Means for Solving the Problems In order to solve the above problems, the inventors of the present invention made earnest efforts in development, and as a result, they were able to come up with a galvanized iron part having the following structure.

The present invention is an iron part having a composite film in which a chromate film with a specific chromium adhesion amount and an organic silicate resin film with a specific film thickness are sequentially laminated on a galvanized layer formed on an iron base material. In the presence of a specific colloidal silica, the organosilicate resin film emulsifies a vinyl group-containing silane coupling agent and a polymerizable monomer consisting of α,β monoethylenically unsaturated carboxylic acid alkyl ester and alkenylbenzene. An aqueous composite resin dispersion obtained by polymerization, or a water-soluble composite resin dispersion in which an aqueous solution of an acrylic acid/styrene resin block copolymer of a fatty acid esterified epoxy resin and colloidal silica are combined in the presence of a silane coupling agent. 1 in terms of solid content of a single substance or a mixture of an aqueous resin dispersion in which carboxylated polyolefin resin and colloidal silica are combined in the presence of a vinyl group-containing silane coupling agent.
00 parts by weight and a natural aqueous polymer compound having a carboxyl group as a terminal structure such as shellac, rosin, alginic acid, etc., in a specific ratio of 1 to 50 parts by weight in terms of solid matter. It is characterized by being

<Implementation mode> Hereinafter, embodiments of the present invention will be described.

In addition, unless otherwise specified, the number of blended parts and blending ratio are as follows:
It is a unit of weight.

(1) The material of the iron base material also includes an iron alloy of steel.

(2) The galvanized layer and chromate film are formed by conventional methods.

Here, the zinc plating includes zinc alloy plating such as zinc-tin, zinc-iron, and zinc-nickel. The thickness of the galvanized layer is usually 1 to 15 μm. however,
In cases where particularly scratch resistance is required, such as a nut for fixing a driven wheel wheel that frequently interferes with other members, the plating thickness may be set to 40 to 50 μm.

In addition, when forming a chromate film, an acidic bath is usually used, and a pure chromate bath or a chromic acid/phosphoric acid mixed bath is used. (“Revised 3rd edition, Chemistry Handbook/Advanced Edition” No. 1162-1
(See page 163). And, this chromate film has a chromium adhesion amount of 20 to 800 mg/rr? shall be. 20mg
If the amount is less than 800 mg, it is difficult to obtain the desired corrosion resistance, and 800 mg is the limit value that can be used to form a film by chemical conversion treatment, and even if the amount is more than 800 mg, there is no adhesion and the film will peel off.

(3) 0, 5 to 30μ formed on the above chromate film
The organic resin silicate film of m is formed by applying an aqueous solution containing the following composition.

■A water-soluble composite resin dispersion obtained by emulsion polymerization of a vinyl group-containing silane coupling agent, an α,β monoethylenically unsaturated carboxylic acid alkyl ester, and a polymerizable monomer consisting of alkenylbenzene in the presence of colloidal silica; A water-soluble composite resin dispersion made by combining an aqueous solution of acrylic acid/styrene resin block copolymer of fatty acid esterified epoxy resin and colloidal silica in the presence of a silane coupling agent. A water-soluble composite resin dispersion composited in the presence of a silane coupling agent.

Here, the colloidal silica is water-dispersible silica with a particle size of 4 to 20 nm, and is usually commercially available stable silica sol (S
i02 concentration 20-40%).

Examples of the vinyl group-containing silane coupling agent include 7-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, vinyltrimethoxysilane, and vinyltriethoxysilane. Further, the coupling agent exhibits its effect in a blending ratio of 0.3 to 5 parts with respect to the water-dispersible resin.

If it is less than 0.3 parts, sufficient effects will not be obtained, and if it exceeds 5 parts, it will be economically disadvantageous.

A simple substance of the water-soluble composite resin of ■, ■, ■ above, or
1 to 50 parts of a natural aqueous polymer compound having a carboxyl group as a terminal structure such as shellac, rosin, alginic acid and its salt as a second component is added to the mixture as a second component per 1 part by weight of resin. If the amount is less than 1 part, it will not have an effective effect on the desired corrosion resistance of the film, oil resistance, film hardness, abrasion resistance, moisture resistance, etc. of the film. Addition of more than 50 parts will be economically disadvantageous and will even deteriorate the film properties. It is desirable to adjust the amount of water or add a thickener to the aqueous solution of this composition so that a corrosion-resistant coating film of the required thickness can be obtained by one dip coating. If the thickness of this corrosion-resistant coating film is less than 0.5 μm, the required corrosion resistance cannot be obtained, and even if it exceeds 30 μm, the corrosion resistance will hardly improve and the material will become uneconomical. In addition, as the above-mentioned thickener,
- Examples include acrylic polymers, polyvinyl alcohol, CMC, and methyl cellulose, which are commonly used in paints.

<Operations and Effects of the Invention> As described above, the present invention provides a chromate film defined by specific chromium adhesion 1 and an organic silicate resin film with a specific thickness on a galvanized layer formed on an iron base material. An iron part having a composite film formed by sequentially laminating layers,
The above organic silicate resin film is produced by emulsion polymerization of a vinyl group-containing silane coupling agent, an α,β monoethylenically unsaturated carboxylic acid alkyl ester, and a polymerizable monomer consisting of alkylbenzene in the presence of colloidal silica. Water-soluble composite resin dispersion, ■Modified epoxy resin (typical aqueous solution of acrylic acid/styrene resin block of fatty acid esterified epoxy resin)
A water-soluble composite resin dispersion in which a carboxylated polyolefin resin and colloidal silica are combined in the presence of a silane coupling agent, ■A water-soluble composite resin dispersion in which a carboxylated polyolefin resin and colloidal silica are combined in the presence of a vinyl group-containing silane coupling agent .

Add 100 parts by weight of a natural water-based polymer compound having a carboxyl group as a terminal structure such as cera-tsuk, rosin, or alginic acid as a second component to the above water-soluble composite resin (■, ■, or ■) alone or as a mixture. By applying a mixed aqueous solution containing 1 to 50 parts of
This makes it possible to provide galvanized iron parts with corrosion resistance that has not been available in the past.

Although the corrosion prevention mechanism of the composite film of the present invention cannot be determined, it is presumed to be as follows.

■Strong water repellency due to the hydrophobic moiety contained in the organic silicate resin film, ■Dispersion effect on corrosion current due to the porosity of water-dispersible silica, ■Due to the mobility of chromate ions eluted from the chromate film. Effect of sustaining passive state on zinc and iron surfaces; ■ Corrosion inhibition effect by capturing eluted zinc ions with water-dispersible silica; ■ Corrosion inhibition by capturing zinc and iron ions with a water-based natural polymer compound having a carboxyl group at the terminal functional group. It is presumed that the effects work together to impart great corrosion resistance to galvanized iron parts.

Incidentally, the steel parts for automobiles to which the present invention can be applied include:
In addition to the above, examples include washer plackets, coil springs, joint hinges, latch strikers, radiator caps, engine hooks, and the like. Furthermore, if a pigment or the like is added to the composition that forms the organic silicate resin film, it becomes possible to provide galvanized iron parts with excellent design. In such a case, the result will be a colored iron part that has unprecedented colored coating properties (a property that cannot be obtained with conventional colored paints, such as not accelerating corrosion of the base material even if scratched).

<Examples> Examples carried out to confirm the effects of the present invention will be described below along with comparative examples and reference examples.

(1) On a 2-thick steel plate (SPCC-D) test piece (70x150 punch)
Each base material was prepared by subjecting it to zinc plating of μm (λ, roughness), and performing a chromate coating treatment using the chromate bath described below.

Zinc plating bath Zinc chloride 40g/l Ammonium chloride 200g/l Brightener 31.5ml/IPH5,5 Temperature 25°C 'tim, density 2 A/d rr1'' Chromate bath Chromic anhydride 12g/l Phosphoric acid 2.5g/l l nitric acid
Q, 5g/l Sulfuric acid 2.0g/l Temperature Room temperature immersion time 1 minute (2) Organosilicate resin film 1'! , in the implementation fl+ and comparative examples, coating materials A and B having the compositions shown below,
C, D, E, F, G, H, I, J, K in the reference examples, JP-A-59-71316 and JP-A-60-501.
The following ar b+ C+ described in Publication No. 79
A coating of d*e+'r gr was used. The following formulations are expressed in terms of solid content unless otherwise specified.

(Coating agent A) 2-ethylhexyl acrylate 40 parts methyl methacrylate 59 parts acrylic acid
1 part γ-methacryloxypropyltrimethoxysilane 0.5 part Sodium lauryl sulfonate 3 parts Colloidal silica (solid content 3
0%) 15 parts ion-exchanged water 150 parts ammonium persulfate 0.5 parts sodium bisulfite 0.2 parts A polymerization initiator was added thereto, and the monomer was then added dropwise over a period of 3 hours. The reaction temperature at this time is maintained in the range of 60 to 70°C,
After dropping, maintain the same temperature for 2 hours and then cool down to about 1
A stable dispersion was obtained by adjusting the pH to 8 to 9 and the solid content to 40% with 4% aqueous ammonia. This is 1
A coating agent prepared by dissolving and mixing io parts by weight of shellac as an ammonium salt to 00 parts by weight.

(Coating agent B) 10% of the same aqueous composite resin dispersion as above.
A coating agent in which 1 part by weight of shellac is dissolved as an ammonium salt per 0 parts by weight, and mixed with a composite resin.

(Coating agent C) 10% of the same aqueous composite resin dispersion as above.
A coating agent in which 50 parts by weight of shellac as an ammonium salt is dissolved in 0 parts by weight and mixed with a composite resin.

(Coating agent D) A water-soluble material obtained by emulsion polymerization of a vinyl group-containing silane coupling agent, an α,β monoethylenically unsaturated carboxylic acid alkyl ester, and a polymerizable monomer consisting of alikenylbenzene in the presence of colloidal silica. Composite resin dispersion (
Manufactured by Dainippon Ink and Chemicals Co., Ltd., product name [Boncoat D]
A coating material prepared by dissolving and mixing 100 parts by weight of V-759J) and 1.0 parts by weight of shellac as an ammonium salt.

(Coating material E) Same silica-containing water-based composite acrylic resin as above (manufactured by Dainippon Ink and Chemicals Co., Ltd., trade name [Bonko 1-DV-75]
A coating material prepared by dissolving and mixing 100 parts by weight of 9J) and 20 parts by weight of shellac as an ammonium salt.

(Coating agent F) The same silica-containing water-based composite acrylic resin (manufactured by Inu Nippon Ink Chemical Co., Ltd., trade name: "Bonko 1-DV-75")
A coating agent prepared by dissolving and mixing 100 parts by weight of 9J) and 50 parts by weight of shellac as an ammonium salt.

(Coating agent G) Colloidal silica-containing modified epoxy ester resin (manufactured by Dainippon Ink and Chemicals Co., Ltd., trade name: "T9-7'E")
A coating agent prepared by dissolving and mixing 100 ffiffi parts of C3-18J) with 5 parts by weight of shellac as an ammonium salt.

(Coating material H) Carboxylated polyethylene (carboxylation rate 20%
, Mn=80000), 15 parts of colloidal silica, 2 parts of γ-methacryloxypropyltrimethoxysilane, and 250 parts of water.
A coating agent in which 20 parts by weight of shellac and 1 part by weight of shellac as an ammonium salt are dissolved and mixed.

(Coating agent I) Colloidal silica-containing, water-based composite acrylic resin (manufactured by Dainippon Ink and Chemicals Co., Ltd., trade name [Boncoat DV-7])
59J) to 100 parts by weight, 5 parts by weight of rosin,
Coating agent dissolved and mixed as ammonium salt.

(Coating agent J) Colloidal silica-containing modified epoxy ester resin (manufactured by Dainippon Ink and Chemicals Co., Ltd., trade name [T9-Sol Ec
s-108J) (7) A coating material prepared by dissolving and mixing 10 tlfffi parts of alginic acid as an ammonium salt to 100 parts by weight.

(Coating agent K) Water-based composite acrylic resin containing colloidal silica (manufactured by Dainippon Ink and Chemicals Co., Ltd., trade name [Boncoat DV-7]
Coating prepared by dissolving and mixing 10 parts by weight of shellac as an ammonium salt with 85 parts by weight of colloidal silica-containing modified epoxy ester resin (manufactured by Dainippon Ink & Chemicals Co., Ltd., trade name "Watersol EC3-18J"). agent.

(Coating agent a) A silica-complexed acrylic resin dispersion prepared by the synthesis method shown in the above-mentioned publication, JP-A-59-71316, page 5.

(Coating agent b) Acrylic composite silicate prepared by the synthesis method shown in the above publication, JP-A-60-50179, page 6. However, the blending ratio of organic resin and colloidal silica is 60/40 in solid content ratio.

(Coating agent C) An epoxy composite silicate resin prepared by the synthesis method disclosed in the same published publication, JP-A No. 60-50179, page 6. However, the blending ratio of organic resin and colloidal silica is 6
The solid content ratio is 0/40.

(Coating agent d) Water-based composite acrylic resin containing colloidal silica (manufactured by Dainippon Ink and Chemicals Co., Ltd., trade name: “Boncoat D”)
V-759J) (Coating agent e) Colloidal silica-containing modified epoxy ester resin (manufactured by Dainippon Ink and Chemicals Co., Ltd., trade name [Watersol EC
3-18J) (Coating material f) Carboxylated polyethylene (carboxylation rate 20%
, M n = 80000), 15 parts of colloidal silica, 2 parts of γ-methacryloxypropyltrimethoxysilane, and 250 parts of water.

(Coating agent g) Colloidal silica-containing, water-based composite acrylic resin (manufactured by Dainippon Ink and Chemicals Co., Ltd., trade name: "Boncoat PV-7")
594) Dispersion 85 weight 1 part, colloidal silica-containing modified epoxy ester resin (Dainippon Ink & Chemicals Co., Ltd.)
manufactured by Co., Ltd., trade name [Watersol EC3-18J) Dispersion 15
Mixture parts by weight.

Then, using each coating agent, an organic silicate resin film of the indicated thickness was formed on each base material by a dipping method.
The test piece was prepared. Each specimen was scratched to reach the iron substrate, and a combined cycle corrosion test (salt spray test NaCl3
%, 35℃, 18h-70℃ drying 2h-Na015%,
50'C, salt water immersion test for 2 hours - room temperature standing for 2 hours (one cycle), and the time until red rust appeared was measured. The measurement results are shown in Tables 1 and 2. It can be seen from the measurement results that the test pieces of each Example have significantly improved corrosion resistance compared to each Comparative Example. Note that the number of red rust occurrence cycles was 5 when no corrosion-resistant film was formed.

Table 1

Claims (1)

[Claims] A galvanized iron part comprising a composite film having the following structure. (a) Galvanized layer formed on an iron base material. (b) Amount of chromium deposited on the galvanized layer: 20
~800mg/m^2 chromate film. (c) A film thickness of 0.5 to 0.5 to be formed on the chromate film.
30μm organic silicate resin film. (d) The organic silicate resin film is formed by applying an aqueous solution containing the following composition. I, aqueous organic/inorganic composite resin containing aqueous colloidal silica as an essential component...100 parts by weight. II, natural water-based polymer compounds that have a carboxyl group as a partial structure at the end, such as shellac, rosin, and alginic acid. ...1 to 50 parts by weight.