KR20050081285A - Chromium-free coating system, method of producing steel plate and coated steel plate - Google Patents

Abstract

The present invention relates to a coating system for coating an embossed pattern or flat plate (cold rolled steel sheet, hot-dip galvanized steel sheet, galvanized steel sheet, galvanium steel sheet, molten aluminum plated steel sheet, molten stainless steel plate, etc.) Specifically, it relates to a coating system comprising a pretreatment free of chromium, a paint coating free of chromium and a topcoat coating free of chromium. According to the chromium-free coating system of the present invention, it is possible to secure the work environment and the health stability of the worker, and to give the coating film adhesion, workability, corrosion resistance after painting or more equivalent to the existing chromium-treated steel sheet.

Description

Chromium-free Coating System, Method of Producing Steel Plate and Coated Steel Plate

The present invention relates to a coating system for coating an emboss pattern or flat plate, more specifically a pretreatment that does not contain chromium (hereinafter also referred to as 'chromium-free'). The present invention relates to a coating system including a paint coat and a paint coat.

Conventionally, a pretreatment agent containing chromic acid on a base steel sheet such as a cold rolled steel sheet, a hot dip galvanized steel sheet, an electrogalvanized steel sheet, a galvanium steel sheet, a molten aluminum plated steel sheet, a molten stainless steel plated steel sheet, etc. Various coating steel sheets are manufactured by coating a top coat on it one by one. It is true that the use of chromium as a component of the coating material is effective in improving the physical properties and quality of the product.

However, the pretreatment and paint containing chromium, which is a heavy metal, was not only harmful to the environment due to the toxicity of chromium, but also caused various diseases such as lung cancer. Nevertheless, there is no research and development in the prior art regarding the importance of chromium in the coating material and excluding its use.

The present inventor has started from research and development of a coating system that can avoid the use of chromium and keep the physical properties and quality of the coating product at a high level while eliminating the use of chromium, and after numerous tests and trials and errors, The invention has been completed.

An object of the present invention is to provide a coating system that provides physical properties such as corrosion resistance, workability, adhesion, and the like of a coated steel sheet of a chromium system without using chromium from a pretreatment agent to a bottom coat and a top coat on a substrate.

The chromium-free coating system of the present invention is a water-based pretreatment agent for metal surface treatment that does not contain chromium, which can be dried at a low temperature of PMT 60 to 130 ° C., which is a treatment condition for a pretreatment agent, and a coating material that does not contain chromium, and It also contains a top coat that does not contain chromium.

The chromium-free pretreatment used in the chromium-free system of the present invention is based on the solids weight of the pretreatment agent, 5 to 30% by weight of the water-soluble organic resin dissolved in water, 10 to 40 corrosion-resistant rust inhibitor of phosphate-based metal oxide 1 wt% to 20 wt% of the compound constituting the organometallic chelate, and 1 to 10 wt% of the coupling agent for imparting adhesion and corrosion resistance between the base and the top coat layer provided thereon.

As corrosion-resistant antirust additives, phosphate solutions, such as (1) aluminum, aluminum phosphate, manganese, zinc, molybdenum, and fluorine, (2) phosphate aqueous solution of hexaammonium hepta molybdate tetrahydrate, and (3) soda.

If the content of the anti-rust additive of the metal salt component exceeds 40% by weight, it exceeds the ratio of stably reacting with the water-soluble organic resin and the organic metal material, which may cause side effects on the long-term stability of the solution.

The organometallic materials include organic titanates, organic zirconates, and other organic silanes, which are coupling agents and chelating agents, and these compounds are used in polymers such as water-soluble acryl, alkyd, polyester polymers, epoxy, urethane, and the like. It improves the adhesion of the polymer and the bonding force between the polymer and the inorganic sol used to strengthen the coating film.

If the amount of the organometallic material is more than 20% by weight, the price is very expensive, so the economic effect is greatly reduced, the stability of the solution may be weak, and the improvement of physical properties is very slight, so do not use more than 20% by weight.

The pretreatment has a solid content in the range of 2 to 20% by weight, and in order to obtain the desired physical properties, the dry adhesion amount of the pretreatment should be 20 to 1,000 mg / m 2.

If the solid content of the pretreatment agent is less than 2% by weight, the adhesion amount of the pretreatment agent is so small that the ability to impart corrosion resistance to the base is weak. This is difficult.

The pretreatment may further include an appropriate amount of a diluent for controlling the drying conditions and spreadability to the base material, as a diluent may be used mixed with water and a low boiling alcohol.

Alcohols include methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, etc. Low boiling alcohol is used, and its amount is used in a mixture of 3 to 20% by weight of the total diluent.

The use of such low boiling alcohols contributes to the stability of the water-soluble resin and organometallics contained therein, and may also contribute to the stable wetting of the treatment agent. This amount can be reduced to less than 5% by weight of the total ratio of the solution if the drying conditions of the steel sheet after PMT 120 ℃ and good spreadability after the treatment agent is applied.

The chromium-free undercoat used in the chromium-free coating system of the present invention includes resins, hardeners, pigments, additives and solvents, and is coated with a relatively thick film on an embossed pattern, so that adhesion, processability, corrosion resistance, It should have popping stability due to the difference in coating thickness.

The resin used in the present invention is an epoxy component of 15 to 30% by weight of a polymer linear polyester resin having an average molecular weight of 10,000 to 16,000 for imparting high processability as a main resin and an average molecular weight of 4,000 to 10,000 for imparting corrosion resistance as an auxiliary resin. It contains 10-20 weight% of containing polyester resin.

When the main resin and the auxiliary resin have a weight average molecular weight of more than 16,000, the coating film properties after the crosslinking reaction with a curing agent and the dryness of the coating film are poor. If the main resin and the auxiliary resin are lower than 4,000, cracking of the deep processing portion of the embossed material occurs.

On the other hand, the glass transition temperature (Tg) of the main resin which determines workability and the auxiliary resin which determines adhesiveness is 0-70 degreeC, and 5-45 degreeC is more suitable. When the glass transition temperature is lower than 0 ° C, the cured coating film exhibits a sticky phenomenon, poor workability and dryness, and when higher than 70 ° C, the coating film is too hard to secure workability and adhesion.

As the crosslinking agent, an organic amino resin which is excellent in reactivity with the main resin, the reaction rate can be controlled by the catalyst, and the coating property on the base is stable can be used. Specific examples thereof include methoxy melamine, butoxy melamine, methoxy-butoxy melamine, blocked isocyanates, urea resins, and the like, and particularly, organic amino resins having easy reactivity can be used.

In the paint coating of the present invention, a catalyst for controlling the curing density and the reaction rate of the main resin and the curing agent is used. Representative examples of the catalyst which can be used include dinonylnaphthalene disulfonic acid (DNNDSA) and dinonylnaphthalene sulfonic acid (DSSNA). ), Dodecylbenzene sulfonic acid (DDBSA), p-toluene sulfonic acid (p-TSA), alkyl acid phosphate (AAP), phenyl acid phosphate (PAP) and the like or derivatives thereof. Their selection is very important, and it is important to use derivatives reacted with relatively large molecules to satisfy the workability of topcoats and bottomcoats.

Solvents are also a very important factor in embossed plated steel sheets. If the solvent of the paint coating is applied a lot of solvents having a too high boiling point, the non-volatile solvent causes a popping occurs when drying the top coating, so in the present invention, the mixing ratio according to the boiling point of the solvent (130 ℃ ~ 220 ℃) In consideration of the above, hydrocarbon-based, ester-based, ketone-based and alcohol-based solvents may be appropriately mixed. By using 0.5 to 1.0% by weight of an acrylic anti-popping agent in consideration of surface hardening delay effect and bubble prevention in the coating film, it is possible to suppress the popping of the coating film even when the thick film is embossed on the intaglio surface.

In addition, the pigment is pre-treatment agent and, like chromium, lead, and used as components of heavy metals is not at all contained, such as cadmium, high hiding power and heat, acid, alkali, stable TiO ₂ with an organic pigment in a chemical solvent and silica gel Since the whiteness is high by using a non-toxic white rust preventive pigment substituted with calcium ions, the color stability is excellent when developing a top coat color compared to the existing chromium-based yellow rust preventive pigments.

In particular, non-toxic anti-rust pigments include zinc phosphate, zinc / aluminum phosphate, modified zinc phosphate, silicates and aluminum-zn-triphosphate with silicate, potassium-strontium-zinc phospho-silicate, calcium-barium phosphosilicate, zinc phosphosilicate, calcium borosilicate borosilicate, silica ion exchanged gel type in silica gel, modified barium metaborate, zinc borate, zinc phosphate / zinc molybdate ), Basic calcium-zinc-molybdate, etc. can be used. The potassium ions substituted in the system (calcium ion exchanged gel type) that was shown to the right.

The use of non-toxic rust preventive pigment should be used in 2 ~ 15% by weight, if less than 2% can not secure the corrosion resistance and moisture resistance, when using more than 15% may be rather boiling water resistance or processability.

Looking at the reaction mechanism, the first step is an adsorption action step, in which the Ca ²⁺ ions are separated as the hydrogen ions of the aggressive and active ions penetrating into the coating film are adsorbed and exchanged on the non-toxic rust preventive pigment. The second step is the formation of a molecular barrier, which is released from the surface of non-toxic anti-rust pigments, and the dissociated Ca ²⁺ ions form a hard protective layer on the surface of the material to penetrate moisture, pollutants and salts in the air. Equipped with the ability to withstand rust. In the third step, the composite oxide layer continuously maintains anticorrosion ability of the bottom.

It is important to properly mix and use a polyester resin having two or more molecular weight ranges in consideration of workability, processability, and reactivity with a curing agent in the topcoat paint for emboss or flat plate containing no chromium of the present invention.

In order to increase the compactness of a coating film, the polyester resin which is the subject used at this time is 20-40 weight% of linear polymeric polyester with a weight average molecular weight of 10,000-12,000, and an OH value of 20 or less, and a weight average molecular weight of 6,000- A linear polymer polyester resin of 8,000 and a relatively low Tg value of 20 or less is used in a mixture of 5 to 20% by weight. Mixing and using the linear polymer having a large molecular weight may further impart strength, fouling resistance, etc., in addition to physical properties such as processability and chemical resistance of the coating film.

As a crosslinking agent used in top coat, it is an organic amino resin that has excellent reactivity with main resin, can control reaction rate by catalyst, and has stable coating property on base. It is methoxy melamine, butoxy melamine, methoxy-butoxy melamine. , Blocked isocyanates, urea resins and the like can be used. In particular, it is preferable to use the organic amino resin etc. which are easy to control reactivity.

In the top coat of the present invention, the catalyst component prevents the popping of the coating film and selects an appropriate reaction rate. The coating component has excellent storage properties and two kinds of dissociation temperature ranges of 140 to 160 ° C and 180 to 200 ° C. It is effective to use

Representative examples of catalysts that can be used include, as illustrated above, dinonylnaphthalene disulfonic acid (DNNDSA), dinonylnaphthalene sulfonic acid (DSSNA), dodecylbenzene sulfonic acid (DDBSA), p-toluene sulfonic acid (p-TSA ), Alkyl acid phosphate (AAP), phenyl acid phosphate (PAP), or derivatives thereof, and a catalyst such as blocked-DNNSA having a dissociation temperature of 140 to 200 ° C.

Topcoat paint solvent is a very important factor in embossed plated steel sheet. It uses a lot of solvents that have a relatively high boiling point than the solvent of the paint, and a solvent having a boiling point of about 200 to 216 ° C. is used relatively much. In order to solve the problem of popping, hydrocarbon, ester, ketone, and alcohol solvents are properly mixed and used, and such mixed solvents can complement the wettability and flowability of the paint, and the coating property of the embossed engraved part.

In addition, the pigment uses components containing no heavy metals such as chromium, lead, and cadmium, and mainly uses TiO ₂ , which is an inorganic pigment that is high in hiding power and stable to chemicals such as heat, acid, alkali, solvent, etc. Some used.

The coating system containing the chromium free pretreatment agent, the undercoat paint, and the top coat as described above is coated on the substrate in the order shown in FIG. 1. Specifically, first, a dry coating amount is applied to a pretreatment agent on a substrate using a roll coater, and the coating amount is 20 to 1,000 mg / m 2, and the coated film is dried using a drying furnace so that the surface temperature of the steel sheet is 60 to 150 ° C., followed by After coating the paints 4 ~ 15㎛ and top coat 8 ~ 35㎛ in order and drying them to 205 ~ 249 ℃ respectively, it is possible to produce a coated steel sheet having coating film adhesion, processability and corrosion resistance comparable to the existing chromium-containing coated steel sheet. have.

Example

The following is intended to explain the present invention in more detail by examples, but the present invention is not limited thereto.

Preparation of Chromium Free Pretreatment

Preparation Example 1

30 parts by weight of a water-soluble acrylic modified epoxy resin synthesized to have a solid content of 30% by weight using 50 parts of an acrylic resin and 50 parts of an epoxy equivalent of 450-500 bisphenol A type epoxy resin, and an aqueous solution of molybdenum trioxide phosphate A metal pretreatment having a solid content of 5% by weight was prepared by mixing 26 parts by weight, 13 parts by weight of 2-glycidoxypropyl trimethoxysilane, and 11 parts by weight of carboxyzirco aluminate. Isopropyl alcohol (IPA), a low boiling alcohol, was mixed and used to be 6% by weight of the diluent. The prepared pretreatment agent was applied to the substrate and dried at 75 ° C. to prepare a coated steel sheet having an adhesion amount of 65 mg / m ² .

Preparation Example 2

5 parts by weight of a water-soluble acrylic modified epoxy resin synthesized so that the solid content is 30% by weight using 70 parts of acrylic resin and 30 parts of bisphenol A type epoxy resin having an epoxy equivalent of 450-500, and hexaammonium heptamolybate 48 parts by weight of aqueous tetraphosphate solution and 22 parts by weight of tetraethyl titanate were mixed to prepare a metal pretreatment having a solid content of 10% by weight. IPA, a low-boiling alcoholic solvent, was mixed to be 10% of the diluent to improve dryness and spreadability. The prepared pretreatment was applied to the substrate and dried at 75 ° C. to prepare a coated steel sheet having an adhesion amount of 130 mg / m ² .

Preparation of chrome-free paint and topcoat

Preparation Example 3

The chromium free undercoat paint and topcoat of the present invention were prepared using the components in Table 1 below.

Composition of chrome-free paint and top coat for embossed steel sheet division ingredient Undercoat paint (% by weight) Top coat (wt%) Remarks Suzy Linear polyester-1 15-30 20-40 Molecular Weight 10,000 ~ 16,000 Linear polyester-2 - 5-20 Molecular Weight 6,000 ~ 8,000 High Corrosion Resistant Polyester 10-20 - Molecular Weight 4,000 ~ 10,000 Hardener Methoxy melamine 1-5 1-5 Butoxy Melamine - 1-5 Isocyanate - - Pigment Inorganic pigments 3-30 3-30 Non-toxic antirust pigment 2-15 - Cr-free Organic pigment 2-10 2-10 additive Anti-popping agents 0.1-2 0.1-2 Antifoam 0.1-1.0 0.1-1.0 Leveling agent 0.5-3.0 0.5-3.0 solvent Hydrocarbon 10-20 15-30 Ester 5-10 5-10 Ketone 1-5 1-5 Alcohol 5-10 1-5

Examples 1 to 3 and Comparative Examples 1 and 2

Using the chromium-free pretreatment agent, the bottom coat and the top coat of the present invention prepared in the above production example, and the existing chromium-containing pretreatment, the bottom coat and the top coat were coated with the embossed and flat plate, The coating film properties were measured. The results are as shown in Table 2 below.

division Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Applied Material Possession of emboss Reputation Possession of emboss Reputation Pretreatment Preparation Example 1 Preparation Example 2 Preparation Example 1 Chrome pretreatment Undercoat Chrome-free undercoat of the composition Chromium-containing conventional paint Topcoat Chrome-free top coat of the above composition Original topcoat Work stability Great Great Great Great Great Primary adhesion 5 5 5 5 5 2nd adhesion 4 4 5 4 5 Boiling water resistance 5 5 5 5 5 Corrosion resistance 5 4 5 5 5 Moisture resistance 5 5 5 5 5 * Score: 5 (excellent) <----------> 1 (bad)

The evaluation method of each physical property of the said Example and a comparative example was evaluated by the following method and reference | standard.

Assessment Methods

(1) Primary adhesion: 3 layers of test plates are sandwiched between spacers (3TT processing) in an environment of 20 ° C, and 180 ^° bending is performed. Then, the bending portion is peeled three times and the peeling degree is 20 times loupe (loupe). ), And evaluated according to the following criteria.

5 points: no crack

4 points | pieces: The crack generate | occur | produces in the whole area of a process part.

3 points | pieces: Peeling area is less than 20% of a process part.

2 points | pieces: Peeling area is 20% or more and less than 80% of a process part.

1 point | piece: The peeling area is 80% or more of a process part.

(2) Secondary adhesiveness: After the test plate was immersed in boiling water for 1 hour, the test plate was cooled to room temperature, and then subjected to the bending process by the same method as the primary adhesiveness and evaluated by the same criteria.

(3) Boiling water resistance: 3TT, 180 ℃ After molding process, immerse in boiling water for 1 hour and visually observe the occurrence of blisters and cracks on the surface.

(4) Corrosion resistance: The test plate was scratched with an X character, and the swollen width of one side of the cut part after 500 hours of salt spray test was measured according to ASTM B117 standard, and evaluated according to the following criteria.

5 points: Puffed width 0 mm

4 points: Swollen width less than 1 mm

3 points: Swollen width more than 1 mm, less than 3 mm

2 points: bulge width more than 3 mm, less than 5 mm

1 point: puffy width 5 mm or more

(5) Moisture resistance: After the specimens were tested at 98% R.H, 50 ° C for 500 hours, the occurrence of surface blisters and changes in color difference were observed and evaluated according to the following criteria.

5 points: No blister occurrence. Color difference 0.2 or less

4 points: blister occurrence 5% or less, color difference 0.2 or less

3 points: blister occurrence 20% or less, color difference 0.5 or less

2 points | pieces: 20% or more and less than 80% of blister occurrence, 1 or less color differences

1 point: blister occurrence 80% or more, color difference 1 or more

According to the chromium-free coating system of the present invention, it is possible to secure the working environment and the health stability of the worker, and to impart physical properties such as coating film adhesion, workability, corrosion resistance after painting and more than the existing chromium-treated steel sheet.

1 is a cross-sectional view of a coated steel sheet coated using the coating system of the present invention.

Claims (5)

Chrome for painting steel plate containing pretreatment without chromium, undercoat containing 2 ~ 15% by weight of nontoxic rustproof pigments containing no chromium and silica ions substituted on silica gel and topcoat without chromium As the pre-coating system, the pretreatment agent is 5 to 30% by weight of water-soluble organic resin, 1 to 20% by weight of phosphate-based metal oxide rust-preventing agent, and 1 to 20% by weight of organometallic chelate compound, based on the solid content weight of the pretreatment agent. And 1 to 10% by weight of a metal coupling agent. The method of claim 1, wherein the chromium-free coating material comprises a main resin and an auxiliary resin, the main resin is a linear polyester having a weight average molecular weight of 10,000 to 16,000 and the auxiliary resin has a weight average molecular weight of 4,000 to 10,000 Chrome-free coating system using a high corrosion resistant polyester. The chromium-free coating according to claim 1, wherein the topcoat without chromium comprises, as main resin, a linear polyester having a weight average molecular weight of 10,000 to 20,000 and a linear polyester having a weight average molecular weight of 6,000 to 8,000. system. The base steel sheet is coated using the chrome-free coating system in any one of Claims 1-3, The coating method of the steel plate characterized by the above-mentioned. Steel plate coated by the method of Claim 4.