JPS5845904B2 - Treatment method for galvanized coating surface - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a treatment method for corrosion protection and coloring of galvanized coatings, particularly hot-dip galvanized coatings.

Conventionally, galvanizing has been applied as a long-term corrosion protection method for steel materials or steel products, and it is well known that large structures such as power transmission towers are coated with hot-dip galvanizing.

This corrosion prevention method is far superior to the commonly used coating method, but recently,
Due to the progress of air pollution, the consumption of zinc has become significant, and the current situation is that it is no longer possible to expect long-term corrosion prevention effects as before.

In order to make the long-term corrosion protection inherent in galvanizing effective, it has become necessary to interpose an organic coating film on the galvanized surface to prevent contact with corrosive factors such as water and the atmosphere.

Furthermore, with the recent increase in the size of structures, the need for air signs has increased.
Alternatively, from the aesthetic point of view of harmonizing with the environment, there is a strong demand for colored and beautiful structures.

Due to the above-mentioned reasons, it is necessary to paint the galvanized surface, so various paints such as oil-based paints or synthetic resin-based paints are currently applied.

However, this type of paint is not always in a satisfactory condition,
The paint film peels off and separates from the surface of the galvanized layer at an early stage.

Furthermore, as structures become larger, repainting for maintenance becomes difficult, so synthetic resin paints such as epoxy resin enamel and polyurethane resin enamel are used as top coats for long-term durability and color retention. is considered and N
However, there is currently a lack of a definitive method for treating galvanized surfaces to improve the adhesion of these top coats.

The present invention seeks to solve the current problems as described above by applying a specific coating composition to galvanized surfaces.

That is, in the present invention, an oxyacid salt and/or The present invention relates to a method for treating the surface of a galvanized film, which comprises applying a coating composition containing 1 to 350 parts by weight of a metal oxide and drying it to form a coating layer.

The epoxy resin used in the present invention consists of a mixture of an epoxy resin containing at least two or more epoxy groups at the end and a crosslinking agent that chemically reacts with the epoxy resin.

Examples of the epoxy resin include linear bisphenol type epoxy resin, phenol novolak type epoxy resin, cresol type epoxy resin, polyphenol type epoxy resin, aliphatic type epoxy resin, aromatic type epoxy resin, cycloaliphatic type epoxy resin, There are ether ester type epoxy resins, etc., and commercially available product names include Epicoat (trade name manufactured by Shell Chemical Co., Ltd.) and Epiclon (product name manufactured by Shell Chemical Co., Ltd.).
Typical examples include Inu Nippon Ink (trade name manufactured by Kagaku Kogyo) and Araldite (trade name manufactured by Ciba Geigy).

These are not limited to the use of only one type, but two types.
It is also possible to use more than one species in combination to bring out the characteristics of each.

The crosslinking agent used in the method of the present invention is one that has a group that reacts with the epoxy group or hydroxyl group contained in the epoxy resin molecule, and is commonly used as a crosslinking agent for epoxy resins. Either is fine.

For example, diethylenetriamine, triethylenetetramine, metaxylylene cyanide, metaphenylenediamine,
Aliphatic or aromatic polyamines such as heterocyclic diamines, secondary and tertiary polyamines such as dimethyl azmethylphenol, tris(dimethylaminomethyl)phenol, piperidine, etc.
grade amines, polyamide resins, amine adducts (generally
In addition to amine compounds such as amine compounds (known under the name of adduct), incyanate compounds (including blocked isocyanates) such as tolylene diisocyanate and hexamethylene diisocyanate, phenolic resins, acid anhydrides, melamine resins, urea resins, etc. However, since the object of the present invention is generally large steel materials and large steel products, the chemical reaction between the epoxy resin and the crosslinking agent proceeds at normal humidity or forced drying, and it is accompanied by a chemical reaction with the epoxy group. Most preferred are amino compounds.

As will be described later, the present invention is characterized in that the oxyacid salt and/or metal oxide contained in the composition chemically reacts with the galvanized surface to impart adhesion to the coating film. However, especially when phosphates are used in combination with other oxysaccharides and/or metal oxides, chelate bonds can be formed between phosphoric acid and hydroxyl groups in epoxy resins and polyvinyl butyral resins via metal ions. When formed, the effect of imparting strong adhesion can be obtained.

Therefore, when mixing a crosslinking agent into the mixture of the epoxy resin and polyvinyl butyral resin of the present invention, if the crosslinking agent has a property that involves a chemical reaction with the hydroxyl group in the resin composition, It is preferable to adjust the amount of the crosslinking agent to an equivalent amount or less so that hydroxyl groups in the resin composition molecules remain.

The polyvinyl butyral resin used in the present invention has an average degree of polymerization of 250 to 2,000, preferably 250 to 1.
000 and a degree of butyralization of 57 to 75 mol%, preferably 57 to 70 mol%.

The mixing ratio of the epoxy resin and polyvinyl butyral resin is preferably 99 to 60% by weight of the epoxy resin and 1 to 40% by weight of the polyvinyl butyral resin, with the former being 95 to 80% by weight.
% by weight, the latter being 5-20% by weight.

In the present invention, the purpose of using polyvinyl butyral resin is to further promote the chelate bond with the phosphate contained in the composition, thereby imparting long-term flexibility to the coating film, and adhesion to the galvanized surface. This is to strengthen the relationship.

The adhesion of paint films to active non-ferrous metal surfaces such as galvanized metal surfaces is not as good as that to steel surfaces, and the hardness of the paint film increases as the crosslink density increases due to the progression of chemical reactions, especially with epoxy resins. On the other hand, the flexibility decreases and the adhesion strength gradually decreases, but the combination of polyvinyl butyral resin, which is a polymeric and thermoplastic resin, as in the present invention, is extremely effective in alleviating the aforementioned coating film deterioration. It is.

The effect of adding polyvinyl butyral resin as described above increases as the amount added increases, but if the amount exceeds the range for the epoxy resin, it may cause a decrease in the fire resistance of the coating film, deterioration of painting workability, etc. Undesirable.

The oxyacids used in the present invention include chromic acid, phosphoric acid (including condensed phosphoric acid), boric acid, molybdic acid, phosphomolybdic acid, silicomolybdic acid, tungstic acid, phosphotungstic acid, and silicotungstic acid. It is a salt consisting of various metals.

For example, strontium chromate, calcium chromate, lead chromate, zinc chromate, zinc chromate, zinc molybdate, calcium molybdate, zinc tungstate, calcium tungstate, magnesium tungstate, zinc phosphate, lead pyrophosphate, lead orthophosphate, metallin. Acid lead, aluminum phosphate, silver orthophosphate, silver pyrophosphate, silver oxyphosphate, zinc tetraborate, zinc metaborate, lead metaborate, lead tetraborate, etc. can be used.

The metal oxides used in the present invention include chromium, molybdenum,
These are oxides of tungsten, manganese, etc.

For example, chromium trioxide, molybdenum trioxide, tungsten trioxide, manganese dioxide, etc. can be used.

These oxyacid salts and metal oxides described above can be used alone or in a mixture in any proportion.

In particular, when the above-mentioned phosphate is used as an oxysalt component in combination with other oxysalts and/or metal oxides, the phosphoric acid generated by its hydrolysis can be used as an oxysalt component and/or the metal in the metal oxides. Since it is thought that a chelate compound is formed between the hydroxyl groups in the epoxy resin and the polyvinyl butyral resin via ions, its use is most preferable.

The amounts of the oxyacid salts and/or metal oxides used in the present invention vary greatly in their reactivity to the galvanized surface, corrosion resistance, etc., so the amounts added are as follows:
1 to 350 parts by weight per 100 parts by weight of a resin composition formed by mixing an epoxy resin and a polyvinyl butyral resin,
Preferably it is 1 to 200 parts by weight.

As mentioned above, in the present invention, when phosphate is used as an essential component in combination with other oxysaccharides and/or metal oxides other than phosphate, the effects of the present invention can be made more effective. However, phosphates and other oxylates and/or
Or the mixing ratio of metal oxide is 95-30% by weight: 5-7
About 0% by weight is preferable.

In the above, if the amount of the oxyacid salt and/or metal oxide is less than 1 part by weight, no effect of forming a chemical conversion film or forming a chelate on the galvanized surface can be expected.

On the other hand, if the amount is more than 350 parts by weight, it is not preferable because it tends to impair the adhesion of the coating film to the zinc plating.

As described above, the present invention uses a resin composition consisting of an epoxy resin and a polyvinyl butyral resin as well as an oxyacid salt and/or a metal oxide as essential components, thereby making it more durable against galvanized surfaces due to their synergistic effect. It imparts adhesion resistance.

In the present invention, the above-described components are essential, but other resins that are compatible with the coating composition may also be added within a range that does not impair the object of the present invention.

Furthermore, if desired, zinc powder, anti-rust pigments such as lead compounds, extender pigments such as talc and silica, coloring pigments such as iron oxide, carbon black, titanium oxide, anti-settling agents, anti-sagging agents,
Additives such as surfactants and surface conditioners, coupling agents, chelate compounds, solvents, etc. for further promoting the adhesion of the coating film can also be added.

When the optional solvent is an organic solvent other than hydrate, at least one alcohol-based solvent is used to assist in the elution or hydrolysis of the metal ion of the oxyacid salt and/or metal oxide in the composition. Preferably, the composition contains a solvent or 3% by weight or less of water.

In the method of the present invention, a coating composition consisting of the above-mentioned components is adjusted and applied to a galvanized surface by a known method such as brushing, spraying, or rolling so as to obtain a dry film thickness of about 10 to 3,300 microns, and then an epoxy resin is applied. The crosslinking agent and the crosslinking agent undergo a chemical reaction, and the coating film is cured under conditions necessary for drying the coating film.

Furthermore, if it is difficult to obtain the desired hue with the above coating composition, various colors such as polyurethane resin paint, epoxy resin paint, chlorinated rubber paint, vinyl chloride resin paint, etc. may be applied to the surface of the coating film obtained by the present invention as necessary. Optionally, paint may be applied over and over again.

The coating film obtained by the treatment method of the present invention exhibits strong durability against long-term exposure, and has stable adhesion over a long period of time without peeling or detaching in a short period of time as in conventional methods. It is.

Next, specific effects of the present invention will be illustrated by examples.

In Examples and Comparative Examples, "part" or "%" means "part by weight" or "% by weight."

Example 1 Epoxy equivalent weight 450-500 and epoxy equivalent weight 230-2
Epoxy obtained by mixing the epoxy resin and crosslinking agent in an equivalent ratio using a linear bisphenol type epoxy resin consisting of a 1:1 mixture of 70% epoxy resin and a polyamide resin with an active hydrogen equivalent of 130% as a crosslinking agent. A coating composition having the composition shown in Table 1 was prepared by combining a resin composition and a polyvinyl butyral resin having an average degree of polymerization of about 2601 and a degree of butyralization of 60 mol%.

For comparison, a coating composition other than the one according to the invention was also prepared in the same manner.

The resulting composition was coated on the surface of a hot-dip galvanized steel plate to a dry film thickness of 80 microns, and dried under conditions of 20° C. and 75% RH for 7 days to prepare a test piece.

Example 2 An epoxy resin obtained by mixing the epoxy resin and the crosslinking agent in an equivalent ratio using a linear bisphenol type epoxy resin with an epoxy equivalent of 900 to 1000 and a boria □ resin with an active hydrogen equivalent of 150 as a crosslinking agent. The composition was combined with a polyvinyl butyral resin having an average degree of polymerization of about 600 and a degree of butyralization of 72 mol% to prepare a coating composition having the composition shown in Table 2.

For comparison, a coating composition other than the one according to the invention was also prepared in the same manner.

Each of the obtained compositions was coated on the surface of a hot-dip galvanized steel sheet in a rice-like manner with a dry film thickness of 50 □, and heated at 20°C and 75% R.
It was left to dry under H conditions for 24 hours.

Next, acrylic resin [Acrydic A] was applied to the surface of the coating film.
-801: Dainippon Ink Chemical Industry ■Product name) 60 copies,
A polyurethane resin enamel consisting of 13 parts of polyisocyanate (Takenate D-11ON: trade name manufactured by Takeda Pharmaceutical Co., Ltd.), 15 parts of titanium oxide, and 12 parts of butyl acetate was coated over and over to a dry film thickness of 30 microns, and heated at 20°C and 75°C. %
A test piece was obtained by leaving it to dry under RH conditions for 7 days.

Separately, the same polyurethane resin enamel used in Example 2 was applied directly to the surface of a hot-dip galvanized steel sheet to a dry film thickness of 50.
Painted to make it micron and heated at 20℃.

Comparative sample A1 was dried for 7 days under the condition of 75% RH.
No. 3 test piece was used.

Comparative Experiment 1 Using the specimens of the invention samples A1 to 13 and comparative samples A1 to 13 obtained as described above, a cutter knife was used to test the adhesion of the coating film to the initial galvanized surface. Width II for the coating film! 11 vertical and 11 horizontal cutting lines that cross at right angles are inserted to reach the galvanized surface at one interval to form 100 squares.

Next, a piece of tape was pressed onto the square, and the tape was instantly peeled off, and the number of remaining squares was expressed as a percentage.

On the other hand, using another specimen, two cutting lines reaching the galvanized surface diagonally crossing each other at the center of the specimen were made, and the specimen was subjected to outdoor exposure for 5 years.

After 5 years have passed, the paint film surface is observed to confirm the presence or absence of paint film defects and abnormalities, and then the paint film is subjected to a long-term test using the same procedure and evaluation method as the initial adhesion test. Determine whether the adhesion is good or bad after exposure.

The results are shown in Table-3.

Comparative Experiment 2 The test pieces of the present invention samples A1-13 and comparative samples A1-13 obtained as described above were immersed in 3% saline solution for 6 months, and then the test pieces were taken out and kept at room temperature for 24 hours. Leave it for a while to allow the moisture in the paint film to evaporate.

Next, 11 vertical and 11 horizontal cutting lines were cut at right angles to the galvanized surface at 1-width intervals on the coating film of the test piece to form 100 squares, and cellophane tape was applied to the squares. After pressing and instantly peeling off the cellophane tape, the number of remaining squares is expressed as a percentage to judge whether the adhesion is good or bad.

The test results obtained are shown in Table 4.

It is clear from the comparative test results Tables 3 and 4 that the film obtained by the present invention had excellent long-term adhesion to the galvanized surface.

Claims (1)

[Scope of Claims] 1. An oxyacid salt based on 100 parts by weight of a resin composition consisting of 99 to 60% by weight of a epoxy resin containing at least two or more epoxy groups at the end and 1 to 40% by weight of a polyvinyl butyral resin. A method for treating the surface of a galvanized coating, which comprises applying a coating composition prepared by mixing 1 to 350 parts by weight of a metal oxide and/or a metal oxide and drying the coating composition to form a coating layer. 2. The method for treating the surface of a galvanized coating according to claim 1, wherein the oxysaccharide and/or metal oxide is a phosphate and another oxysaccharide and/or metal oxide.