JPH02145774A - Organic coated multilayered steel sheet excellent in weldability and corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain the title org. coated multilayered steel sheet excellent in weldability and corrosion resistance by depositing a specified amt. of Cr on a galvanized steel sheet having specified surface roughness to form the lower film, and further forming the upper film of a specified resin having specified thickness thereon. CONSTITUTION:A partially reduced chromic acid-based chromating soln. is applied on a steel sheet plated with zinc or a zinc-based alloy, and baked to form the lower film contg. 10-150mg/m<2> Cr. A resin soln. is applied on the lower film, and baked at 80-300 deg.C to form the upper film having 0.2-4mum thickness. The resin soln. consists of an epoxy resin or a modified epoxy resin, and contains a cross-linking agent in such an amt. as to control the molar ratio of the functional group to the total amt. of the epoxy group and hydroxyl group to 0.1-0.2. In this case, the maximum height Rmax of the ruggedness of the base material of the plated steel sheet and the thickness (d) of the upper film fulfil Rmax>=12d, and the parameter PPI of the surface roughness (the number of peaks per inch, and the threshold value is 30% of Rmax) is controlled to >=30. By this method, an org. coated multilayered steel sheet excellent in spot welding, working adhesion, and suitability for electrodeposition coating is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention consists of 4. This invention relates to organic composite coated steel sheets with excellent weldability and corrosion resistance for automobiles.

(Prior art) Steel plates capable of S-resistance welding are gradually being used in Japan, for example, to prevent automobiles from rusting due to salt sprayed as a snow-melting agent on roads in snow-covered areas. It's coming.

Conventional weldable painted steel sheets include Synchrometal (
There is a rope board coated with zinc-rich brimer, which is represented by the product name Diamond Jam (USA). Synchrometal uses a base chromate layer (Dacromethod) containing zinc powder and chromic acid as the main ingredients on the steel sheet.
A zinc chloride primer layer (zinchromet) made of an epoxy resin containing a large amount of zinc is formed, and exhibits significantly superior corrosion resistance compared to cold-rolled button 1 treatment.

Generally, anti-corrosion coated steel sheets for automobiles and the like are required to have formability, weldability, and corrosion resistance, but the above-mentioned Synchrometal does not particularly have sufficient formability and corrosion resistance. This is because the zinc-rich brimer used in these steel plates contains approximately 50% zinc powder by volume and 85-90% heavy arsenic to ensure weldability. Is the formed coating film dangerous to your ears? ,l+
This is because separation is likely to occur. As a result, corrosion resistance deteriorates, and the fallen coating film hits the press die and causes scratches, which increases the frequency of cleaning the die and deteriorates workability. In addition, Zinc 11-notch braimer has a high permeability into the paint film, which also tends to reduce corrosion resistance. It is effective to reduce the amount of zinc dust in order to reduce the peeling of the coating film 741 and the decrease in corrosion resistance.
Since the electrical resistance of 1 is increased, 6-connection (resistance) becomes disadvantageous or impossible.

In addition, conventional Synchrometal requires high temperatures of 150 to 180°C to bake the chromate film and 250 to 280°C to bake the zinc-rich brimer, so it has the disadvantage that the bake hardenability of the steel sheet becomes tH. Ta. Here, the term "bake hardenability" refers to the property that the temporary yield stress of fF4 increases when the user performs processing such as pressing and bakes with electrodeposition coating or the like.

(Problems to be Solved by the Invention) As a result of studies to eliminate the two consecutive drawbacks of zinc clinch and brimer, the inventors of the present invention used a plated steel plate as a base material, and applied colloidal chromic acid as a base layer on top of the base material. After coating and baking an aqueous suspension containing chromate to form a chromate film, the upper layer is coated and baked with a polyhydroxypolyether resin solution containing no pigment or containing a chromate pigment. We would like to first propose that by forming a clear film, it is possible to obtain a coated steel sheet that can be resistance welded and has excellent corrosion resistance and formability.
-211964). Since this steel plate can be baked at a relatively low temperature that does not affect bake hardenability, the obtained coated steel plate stably maintains bake hardenability.

Furthermore, in the present invention, the upper coating film can be formed from a general-purpose epoxy resin or a modified epoxy resin by blending at least one of various inorganic fillers and crosslinking agents into the resin liquid for forming the upper layer T film. Moreover, we have proposed an organic 71 coated steel sheet that can obtain excellent edibility without containing chromate pigments (Japanese Patent Application No. 62-239669).
), L Kashi, -Recently, users such as automobile manufacturers have been demanding a high level of welding workability, and the conventional )8
It may be difficult to respond at the level of contact. In particular, if we investigate the continuous dot performance by combining the welding electrode knob so that it touches the resin-coated surface, the results may be unsatisfactory. There is a method of incorporating conductive powder, but there are problems with corrosion resistance and press workability. Another method is to reduce the thickness of the upper layer film, but in the second case, a decrease in corrosion resistance is unavoidable.

The purpose of the present invention is to significantly improve the resistance welding workability of the coated steel plate previously proposed by the above-mentioned inventor -φ.
It is an object of the present invention to provide an organic coated steel sheet having improved heat resistance and good i7 eating properties.

(Means for solving !ili!II) The present inventors 1. As a result of studies aimed at achieving the above objectives, we found that it is better to provide appropriate projections on the surface of the zinc plating or zinc alloy plating used for organic composite coated button eyes according to the thickness of the upper layer clear film) It has been found that it is possible to obtain an organic composite corrugated steel sheet having 8-joint workability and good corrosion resistance.

In other words, the lower chromate film and the upper resin film provided on a plated steel sheet with a certain surface roughness have non-uniform film thickness when viewed microscopically, and the thickness of the coating is uneven at the protrusions of the plating. It is slightly thinner and forms a slightly thicker film in the recessed areas of the plating.

The thinner part of the film is more likely to have contact (
1 (it is thought that the resistance becomes lower and the weldability improves by -12v).

As a result of detailed studies, the inventors determined that the base material, zinc plating
The maximum height Rmax of the plate surface and the I height d of the upper 13 coating satisfy the relationship 17Hax≧12d, and the guard length of the base plated steel plate (
It has been found that when the surface roughness parameter PPI, which indicates the number of protrusions of a certain height or more per inch, is between 30 and 1, excellent contact resistance can be obtained, leading to the present invention.

Here, the gist of the present invention is to apply a partially reduced chromic acid-based chromate-F treatment solution to a zinc or zinc-based alloy coated steel sheet and bake it.
It consists of a lower layer film with an adhesion of 10 to 150 mg/m'' and an epoxy resin or modified epoxy resin, and the molar ratio of functional groups to the total of epoxy groups and hydroxyl groups in the resin is 0.1 to 2. It has an upper layer film with a thickness of 0.2 to 4/] formed by applying a resin liquid containing a crosslinking agent of Y to 0 and then baking at a temperature of 80 to 300°C, and serves as a base material. The maximum height Rmax of the plated steel plate satisfies the relationship R+l1ax≧12d with the thickness d of the upper layer coating, and the following surface roughness parameter PP of the plated steel plate
These are four organic 7M composite coated plates with excellent weldability and corrosion resistance, characterized by an I of 30 or more.

Here, PPI: Number of peaks per inch. However, the threshold (direction is assumed to be 30% of R+++ax).

In the preferred B4X of the present invention, the chromate treatment; at night, (colloidal chromic acid with a weight of 0.1 to 2 times that of the total chromic acid star) cylindrical purifying agent, ta) polyhydric alcohol and/or polyhydric carboxylic acid and/or oxycarboxylic acid in an amount of 0.01 to 2.0 times the mole of unreduced chromic acid;
iron phosphide weighing 0.1-20 times as much as ft1t total chromic acid, and one or two of fe) metal chromates.
It may further contain more than one species. Further, the resin liquid further contains an inorganic filler other than metal chromate in an amount of 1 to 30% by weight based on the resin solid content and/or a resin other than epoxy resin in an amount of 1 to 50% by weight. Good too.

(Function) Next, in the present invention G, the reason why the surface thickness of the plated steel sheet and the composition of each film-forming treatment liquid were limited as described above, and the effect of each component will be explained in detail.

T! ′! The plated steel sheet used in the present invention is a zinc or zinc-based alloy plated button I plate, which is manufactured by conventional methods such as hot-dip plating and electroplating, and is not particularly limited to plated steel sheets generally used for automobiles. The surface roughness of the maximum height Rmax is 4~
However, in the present invention, a film having Rmax of 12 times or more as rl depth d of the upper layer film is used. Since the top coating has a thickness of 0.2 to 4μ, Rmax must be higher than a value in the range of 2.4μ to 48μ.
If Rmax is less than 12 times d, the effect of improving weldability is not significant. However, if the appearance of the product is required, Rma
It is desirable that x is 30 or less.

Surface roughness parameter PPI (Peak per Inc.
h) shall be 30 or more. Note that the threshold value at this time is R
Approximately 30% of max. If this PPT is less than 30, the surface will not be sufficiently rough, making it difficult to ensure weldability.

Examples of methods for imparting the above-mentioned surface roughness to a plated steel plate include a method of rolling the steel plate with rolls such as a sikotodal or laser duller, and a method such as Scotch grinding.

Chromate film is formed by reduction of chromic acid and evaporation of water, but in order to reduce and form the film efficiently at low temperature, the following method was used.

(1) Partially reduce the chromic acid in the chromic acid aqueous solution. By performing partial reduction, the amount of chromic acid reduced during heat drying is reduced and film formation is effectively achieved.

The partial reduction rate is Cr”/(Cr” + Cr”)
= preferably 0.1 to 0.6, more preferably 0.3
~0.6. If it is less than 0.1, the reduction efficiency will be poor;
If it exceeds 6, the stability of the liquid may be impaired due to the large amount of Cr.

The following (2) to (7) are explanations of optional components that can be added to the chromate treatment liquid as desired in the present invention.

(2) Colloidal silica The action of colloidal silica increases the wettability of the chromic acid aqueous solution, assists in forming the chromate film, and also contributes to corrosion resistance and adhesion between the upper layer film and the lower layer film. The amount of colloidal silica added is 0.1 to 2 times the weight of the total chromic acid. If it is less than 0.1 times, the effect of addition will not appear, and if it exceeds 2 times, the coating will become brittle and weldability will further deteriorate.

(3) Silane Coupling Agent The silane coupling agent is hydrolyzed to produce polyroxane, thereby strengthening the chromate coating containing colloidal silica and improving the adhesion with the upper layer coating. The alcohol liberated by hydrolysis acts as a reducing agent for chromic acid.

Examples of silane coupling agents that can be used include vinyltriethoxosilane, vinyl-tris(β-nodoxyethoxy)silane, and γ-methacryloquinophyl
Rimethoxysilane, T-glycidoniF-knopropyltrimethoxysilane, γ-aminopropyltriethoxinolane, N-β-(aminoethyl)-T-aminopropyltrimethoxinlan, β-(3,4- Evoquine cyclohequine) ethyltrimethoxinelan, etc. When the silane coupling agent is added, it is used in a molar amount of 0401 times or more relative to unreduced chromic acid. 0.01
If it is less than twice the molar amount, the effect will be small. However, it is economically disadvantageous to add too much. (4) Polyhydric alcohol, polycarboxylic acid, oxycarboxylic acid In order to increase the reduction efficiency of chromic acid at low temperatures, polyhydric One or more of alcohol, polyhydric carboxylic acid, and oxycarboxylic acid may be added.

Examples of polyhydric alcohols include ethylene glycol,
Examples include propylene glycol and glycerin. Examples of polyhydric carboxylic acids include succinic acid, glutaric acid, and adipic acid. Examples of oxycarboxylic acids include citric acid and lactic acid.

Furthermore, it is also possible to partially replace the above reducing agent with #Ns.

The amount added is preferably within the range of 0.01 to 2.0 times the mole of unreduced chromic acid. If it is less than 0.01 times the mole, the reducing effect is small, and if it exceeds 2.0 times the mole, the action of the reducing agent not only becomes saturated, but also remains in the chromate film, impairing the water resistance of the film.

(5) Iron phosphide When iron phosphide coexists in the chromate treatment solution, the iron phosphide reacts with free hexavalent chromium in the chromate film and reduces the number of stars, so water that has passed through the paint The amount of easily soluble components is reduced, which maintains the adhesion of the coating in corrosive environments. Further, since iron phosphide has tetraelectricity, electrodeposition coating and resistance welding of the resulting coated steel sheet are facilitated without the presence of zinc powder, and welding workability is also improved.

Therefore, for coated steel sheets for electrodeposition coating and resistance welding, it is very preferable to add iron phosphide, especially when the top N coating film is thick.

Iron phosphide is water-insoluble and in a localized state in an aqueous chromic acid solution, so in order to react efficiently with hexavalent chromium, it must be present in a small amount (both 0.1 times as much) as compared to the total chromic acid. On the other hand, if a large amount of iron phosphide is added, the iron phosphide will not be firmly adhered to the chromate coating, causing the coating to peel off during processing, resulting in a decrease in processability and corrosion resistance.

In addition, iron phosphide has electrical conductivity as described above, so
If added in excess, current will easily flow between the base material and the coating surface, impairing its role as a corrosion barrier. These phenomena become noticeable when the weight of iron phosphide exceeds 20 times that of total chromic acid. For the following reason, when iron phosphide is added, the amount added should be 0.1 to 10% of the total chromic acid by weight.
20 times, preferably 1 to 10 times.

In addition to the typical FezP, iron phosphides include FeP, F
Those having compositions such as e, P, and FePz are also known, and any of these can be used. Further, it is preferable to use iron phosphide having a fine particle size with an average particle size of less than 5 mm.

(6) The aqueous suspension containing chromic acid and colloidal silica used to form the metal chromate underlayer coating preferably further contains metal chromate. When metal chromate is present in the chromate coating, it acts as a rust-preventing pigment that enhances the rust-preventing power. That is, since the metal chromate passivates zinc and iron in the base plated steel sheet, their dissolution in a corrosive environment is suppressed, contributing to further improvement in the corrosion resistance of the RGL steel sheet. Examples of metal chromates include zinc and strontium salts of chromic acid, and instead of the metal chromates, zinc or strontium oxides or hydroxides may be used as precursors thereof. Such oxides or hydroxides are converted to metal chromates by reacting with chrono-acid ions in a chromic acid-containing liquid.

Excessive addition of the metal chromate inhibits the film-forming action of the Chronaut coating, thereby reducing the adhesion between the steel sheet and the coating. Therefore, when adding metal chromate, the amount added should be equal to or less than chromic acid, and when added as an oxide or hydroxide, it will react with chromic acid and cause chromic acid to react with chromic acid. Therefore, it is preferable to keep the amount to a small amount of 0.5 times the mole of chromic acid or less.

(7) In addition, in order to further improve the adhesion between the chromate film and the zinc-plated steel sheet, the aqueous G3 liquid containing chromic acid contains phosphoric acid in an amount equal to or less than the molar amount of chromic acid. You can.

In the organic composite coated steel sheet of the present invention, the amount of the aqueous suspension deposited is 10 to 150 .mu./m, preferably 30 to 100 .mu./m in terms of Cr content. However, in this specification, this Cr amount means only those derived from chromic acid, and excludes those derived from metal chromates. Cri is 10■
, ·'d, the corrosion resistance will be insufficient. On the other hand, Cr
If the amount exceeds 100 mg/d, severe damage to the 1,000-knob may occur during welding.
A chromate film thicker than /m is likely to cause peeling of the coating film 711 during post-coating processing. Coating can be carried out by conventional means such as a bar coater or a roll coater.

The above aqueous 'J! The eight zinc-based plated plates coated with the suspension are then baked, that is, heated and dried to insolubilize the coating film.

This baking is preferably carried out at a temperature of about 60 to 200°C4, more preferably 100 to 150°C. Seizure, low grade 2
If the temperature exceeds 00°C, bake hardenability is inhibited as described above.

In the organic composite coated plate of the present invention, the epoxy group and hydroxyl group in the resin are added to the 1Ml-coated epoxy resin or modified epoxy resin on the chromate-i coating, which is the lower layer coating formed as described above. A resin solution containing a star crosslinking agent with a molar ratio of functional groups to total density of O11 to 2.0 is applied, and then baked at a temperature of 80 to 300°C to form a film with a film thickness of 0.2 to 4)bn. An upper layer of coating is formed. This resin liquid may further contain 1 to 30% by weight of a star inorganic filler and/or 1 to 50% by weight of a resin other than the star epoxy resin based on the resin solid content.

(1) Resin type As the epoxy resin, any grindyl ether type epoxy resin such as bisphenol A type, novolac type, bisphenol F type, brominated epoxy, etc. can be used. In addition, the epoxy groups and hydroxyl groups in the epoxy resin can be added to t! It can be used in modified epoxy resins such as epoxy ester resins reacted with carboxyl groups in jj acids and urethane modified epoxy resins obtained by reacting with isocyanates. These resins desirably have a molecular weight of 11,000 or more so that the coating film dries to a touch-dry state even when no curing reaction occurs due to low-temperature baking.

In the present invention, a polyhydroxy polyether resin is preferably used as one type of epoxy resin.

This resin is obtained by polycondensing mononuclear or dinuclear dihydric phenol or a mixed dihydric phenol of mononuclear and dinuclear type with approximately equimolar amount of shrimp halohydrin in the presence of an alkaline catalyst. It is a polymer. Examples of i-karyotype dihydric phenols are resorcinol, hydroquinone and catechol, and an example of di-karyotype phenol is bisphenol A, which may be used alone or in combination with two scrapers. A typical example of shrimp halohydrin is shrimp chlorohydrin. When the dihydric phenol is a mixture of resorcinol and bisphenol at a molar ratio of 1/1, the polyhydroxypolyether resin is composed of repeating units represented by the following structural formula.

C11° Also, when the dihydric phenol is resolun alone, the anti-1y position of the resin is shown by the following structural formula.

Since OHO polyhydroxypolyether resins are manufactured from the same raw materials as epoxy resins, they are included in epoxy resins in the present invention. However, unlike epoxy resins, this resin does not have terminal epoxy groups, and is a thermoplastic resin with a number average molecular weight of approximately 3.000 to 20,000, which is considerably larger than ordinary epoxy resins. Polyhydroquine polyether resin (phenoquino resin) manufactured from bisphenol A and shrimp chlorohydrin is commercially available from Union Carbide Company in the United States (product name: PKIH).
).

As is clear from the above structural formula, the polyhydroxy polyether resin contains many OH groups and 10-groups in the chain. Ordinary epoxy resins also have a similar structure at the end, so they also have many OH groups and 10-groups in the chain. Since the OH group forms a hydrogen bond with the substrate, it contributes to an increase in adhesion, and the -0- group easily causes intramolecular rotation, so it contributes to an increase in the flexibility of the resin. These functional groups have a lower molecular weight when the dihydric phenol is a mononuclear type like resorcinol than a dihydric phenol like bisphenol A, because the molecular weight of the dihydric phenol is smaller. The number of functional groups per unit increases. for example,
The molar ratio of resorcinol and bisphenol A is 0/1.1/
The number of functional groups per 100 molecular weight of polyhydroxy polyether resin when the molecular weight is 1.110 is shown in Table 1 below.

LL table 0/I OO,350,701/
1 23 0.44 0.
89110 66 0.60
1.20 Therefore, the higher the content of dihydric phenol such as L/zorcin, the higher the content of difunctional groups in the chain7, which improves the adhesion and flexibility of the resulting coating film. tends to increase. In this sense, when using a polyhydroxy polyether resin, the divalent fluorol preferably contains 50% or more of a mononuclear type such as resorcin, and may be 100% resorcin, as well. Even when using other epoxy resins, it is generally more advantageous to use one with a large number of ○H groups and 10-groups in the resin.

Furthermore, epoxy resin can be modified with acrylic acid, methacrylic acid, etc. to produce epoxy acrylate.

One of the above-mentioned epoxy resins including modified epoxy resins and polyhydroxypolyether resins or H1 or higher is used, and this is mixed with an appropriate resin selected by considering the required properties such as drying speed and smoothness. Yes R? A resin liquid for coating can be prepared by dissolving it in 8 agents. Suitable solvents include those used in the preparation of epoxy resin coatings, such as cellosolves, ketones, esters, hydrocarbons, halogenated hydrocarbons, or mixtures thereof. In the case of polyhyperoxybolyether resin, ketones, cellosolves, mixed solvents thereof, etc. can be used.

(2) - The inorganic filler is 1. It is added as desired for the purpose of improving the corrosion resistance of the coating film.

Examples of inorganic fillers useful in the present invention include calcium carbonate, alumina, various silicate minerals, zinc phosphate,
Examples include calcium phosphate, zinc phosphomolybdate, aluminum phosphomolybdate, silica powder, and colloidal silica. The particle size of colloidal silica ranges from several mF to several dozen! Examples of commercially available products include LudO from Tibon, Nalcoag from Nalco, 5yton from Monsanto, Snow Latex from Nichiso Kagaku, Cataroid from Catalysts, and Asahi. There are those manufactured by Denka Co., Ltd., and the one used in the present invention is preferably an alcohol type with an organophilic surface.

Although it is possible to use metal chromate-based rust preventive pigments such as strontium chromate and curved lead chromate, which are known to have a high effect of improving corrosion resistance, as an inorganic filler, During processing, chromium content is released into the degreasing solution or chemical conversion solution, causing contamination of the solution, so the use of chromate-based rust preventive pigments should be avoided.

The amount of these inorganic fillers added is 1% based on the solid content of the resin.
-40% by volume, preferably 1-20% by volume. If the amount of inorganic filler I3 is less than 1%, the improvement in corrosion resistance will be small; if it exceeds 40%, the adhesion and corrosion resistance of the coating will decrease, and the electrical resistance of the coating will become too high, resulting in electrodeposition coating,
Spot welding becomes difficult.

When colloidal silica is used as an inorganic filler, a small amount of the silane coupling agent mentioned above can be added to increase the adhesion between the silica and the resin.
The corrosion resistance of the film can be further improved.

(3) View 4M A crosslinking agent is also added for the purpose of improving corrosion resistance, and it is thought that the corrosion resistance is improved by strengthening the coating due to crosslinking.

As the crosslinking agent, those known as epoxy resin paint curing agents and (7) can be used. Specific examples include phenol resins, amine resins, polyamides, amines, isocyanates, ), acid anhydrides, etc. Preferred crosslinking agents are isocyanates.

The amount of crosslinking agent added is such that the molar ratio of the functional groups in the crosslinking agent to the total of epoxy groups and hydroxyl groups in the resin is 0.
．． The amount is within the range of 1 to 2.0.

When this molar ratio is less than 0.1, the effect is small, and when it exceeds 2.0, the coating loses its flexibility and cracks during processing, resulting in low F corrosion resistance.

Both the above-mentioned inorganic filler and crosslinking agent are added to improve corrosion resistance.

(4) (Φ system) In addition to the above-mentioned components, epoxy resin is Various additives such as other resins, conductive pigments, lubricating agents, and plasticizers may also be added.

For example, for the purpose of imparting flexibility to the film, a flexible resin such as butyral resin can be added as a type of plasticizer.

However, if this is added too quickly, it may bleed out depending on the temperature and time. This phenomenon can be prevented by further adding (meth)acrylic acid ester as a reactive plasticizer. That is, the unsaturated bonds contained in C in this ester are cleaved over time, and are then crosslinked and fixed. Furthermore, if the material is further heated during painting or baking after processing, the plasticizer will quickly become fixed. Furthermore, a water-soluble resin can be added for the purpose of improving electrodeposition coating properties. Examples of water-soluble resins include polyvinyl alcohol, polyacrylic acid, polyacrylamide, and the like.

The amount of the resin other than the xylene resin added to Step 2 is preferably within the range of about 1 to 50% by weight of the total resin solid content in the resin liquid, since too much will cause a decrease in corrosion resistance.

The resin liquid for forming the upper layer film can also be applied by a φ means such as a bar coater or a roll coke, and after drying, the resin liquid can be applied so as to obtain a film with a film thickness of 0.3 to 10-1, preferably 062 to 2/j11. Apply. If the film thickness is less than 0.3 degrees, corrosion resistance and coating during processing will be poor! ! Alff1 quality is poor, 2/
If it exceeds Jl, resistance welding becomes difficult or impossible, so in the case of welding, the film thickness should be 2 or less. Film thickness is 1
If it exceeds 0μ, the manufacturing cost increases.

The coating film is dried by baking at a temperature above 80°C and below 300°C. The reason why such a baking temperature was adopted was to not only dry the two-layer coating, but also to promote the reduction of the chromate coating, which is the lower layer coating, and make this coating tougher. be.

Regarding the baking temperature, it is desirable to set the temperature above the boiling point of the 7-pack agent for product quality and to prevent kinging, but if the dry coating film is 5 degrees or less, the baking temperature should be below the boiling point of the 18-pack agent. Also, blocking does not occur. Therefore, more specifically, it is heated to 80 to 300°C.

Naturally, if the baking temperature is high, a uniform film will be formed and corrosion resistance will be improved.
Although workability improves, the bake hardenability of the steel plate disappears when heated to 200°C or higher, so if the base material is a steel plate with bake hardenability, heating
It is preferable to set the temperature to 00°C or less.

The organic composite coated steel sheet thus obtained has a cross-sectional structure in which a zinc-based plating layer on a tA plate body, a lower chromate coating layer, and an upper epoxy resin coating layer are laminated in this order. For automobiles, such coating is usually applied only to one side of the steel plate, but depending on the application, the composite coated FI plate of the present invention may be coated on both sides.

Next, the present invention will be explained by examples. In the examples, % and parts are by weight unless otherwise specified.

(Example) A cold rolled steel plate with a thickness of 0.8 mm was coated with various surface shapes (j
- rolled using a shot dull roll, and then
One side with eyes! An alloy zinc electroplated steel sheet electroplated with 12% Ni-Zn at 20 g/m was used as the base material. This plated steel plate should be cleaned with Fine Cleaner 43 before use.
36 (manufactured by Nihon Bariki Rising Co., Ltd.) to clean the surface before use.

An aqueous solution of ethylene glycol as a reducing agent was added to 8 liquids (chloroacid water containing 120 g/1 of b137Q-mate solution Crys) and heated at 80°C for 6 hours. After the reaction is completed, Cr
Cr (h 40 g
/l of an aqueous solution. Water was further added to this to prepare 8 liquids of partially reduced chromic acid water with a concentration of 40 g/l (=0.4 mol/l) in terms of CrO* in two layers.

Colloidal silica (Aerosil 200 manufactured by Nippon Aerosil Co., Ltd., average particle size 12m7<) was added to this chromic acid aqueous solution.
0 g/l was added. In addition to this, the following ingredients: ■Glycerin 11.5g/7 as a polyhydric alcohol! , ■ Citric M6.5 g/e as oxycarboxylic acid, ■ T-glycidoxypropyltrimethoxysilane 15 g// as silane coupling agent, ■ Predetermined amount of iron phosphide (manufactured by Hooker Chemical, HMS- 2132, average particle size 3/1), and optionally further add a predetermined amount of strontium chromate as a metal chromate, stir with a high-speed disper U7, and use the resulting water ↑± suspension. provided.

In a flask equipped with FCI U conventional cooling H, digrindyl ether to bisphenol (Ebiko 828, manufactured by Yuka Shell Co., Ltd.)
230 parts, 55 parts of resorcinol, 20 parts of methyl ethyl ketone
Add 0 parts, 4 parts of 5N NaOH aqueous solution, and return it.
The reaction was allowed to proceed for 18 hours at temperature. The obtained resinous substance was put into water in a ff1l↑ vessel, stirred 17, and reprecipitated in water to recover a water-insoluble resin.

This was dried under reduced pressure to obtain a powdered polyhydroxypolyether resin whose dihydric phenols were resolnon and bisphenol A (1/1).

The obtained 15) powder resin was dissolved in a mixed solvent of cellosolve acetate/cyclohequinone (volume ratio) of 171 parts (volume ratio) to obtain a resin solution having a resin solid content of 20% by volume.

In addition, as another polyhydroquine polyether resin, commercially available Bakelite (registered trademark) phenoxy resin PKHH (molecular weight 30.000) manufactured by Union Carbide
Also, it was used in the form of a resin solution similar to -L as a Heath resin for the upper coating film.

The crosslinking agent (isocyanate) and plasticizer (butyral resin) were added by adding predetermined amounts to the resin i8 liquid and stirring. The inorganic filler dispersion has a diameter of approximately 2fiI
The process was carried out using a sand mill using glass beads as follows. That is, a predetermined amount of inorganic filler was added to the resin solution of No. 80, glass beads were added, and the mixture was stirred for 10 to 30 minutes. 5. Using a crush gauge. The dispersion was intended to be completed at the time when particles of IJ111 or higher were no longer visible.

+ di length equipment handling - Φ lesson] - Apply chromate solution (
1)) is coated with various Cr-attached stars using a bar coater,
The plate was heated for 30 seconds to a temperature of 120 to 140°C to form a chromate film. Next, after cooling to room temperature, resin 'ate+ was applied to the chromate film in various thicknesses using a bar coater, and heated to a predetermined plate temperature for 6 to 6 hours.
Baking was performed by heating for 0 seconds to form a resin coating film. The obtained organic composite coated steel sheet was subjected to the following tests to evaluate corrosion resistance, workability, paintability 2, weldability, and chromium elution property.

1elj&! Ekata ■Corrosion resistance test: The test pieces used for the corrosion resistance test were flat plates and cylindrical drawings with a diameter of 50 cm. The die eyebrows of the cylindrical aperture were cleaned with Triclean and polished with No. 120 Emery each time so that the surface roughness was always constant. These test pieces were immersed in degreasing liquid FC-4357 manufactured by Roki Vercalizing Co., Ltd. for 2 minutes at 60°C, washed with water, and then baked at 165°C for 25 minutes. Each specimen was then subjected to salt spray 4 at 35°C.
We conducted a dry-wet cycle test with one cycle of 2 hours of hot air drying at 60°C and 2 hours of humid atmosphere at 50°C and a relative humidity of 95% or higher for 200 cycles (test time 1
Corrosion resistance was evaluated by the area ratio (%) of red rust generated after 600 hours).

■Working adhesion test: In order to evaluate the workability of painted steel sheets, a beaded U-bending ironing test as shown in Figure 1 was conducted (
Because it is symmetrical, only one side is shown in Figure 1). A test piece 2 is placed on the die 1 shown in FIG. 1 with the coating film 3 facing the die side, and the test piece is supported by a plate holder 5 via a smoother 4.

Next, the punch 6 is pushed in the direction of the arrow at a constant speed to squeeze the test piece between the die and the punch to perform a U-bend of E+N.Evaluation is performed on the coating that has been squeezed by the die as shown in Figure 2. Membrane? , the area of the female part 7 is used, and the p1 separation area is determined by the following formula.

r Note that only one side is shown in Figures 1 and 2, but 7J
The I-separation area is calculated using the formula 1 based on the results on both sides of the U-bending test piece. In addition, to ensure that the surface roughness of the die eyebrows is always constant, each measurement (cleaning with clean water and
Polishing was performed using No. 20 emery paper.

■Electrodeposition coating property test: After degreasing the test month in the same manner as the corrosion resistance test, using F1 paint system U-100, the conditions were to adhere 20p+a to the chemically treated cold-rolled steel sheet (il!l always 20
Electrodeposition coating was performed at 0V (3 minutes) and baked at 165°C for 25 minutes. The appearance of the coating was evaluated based on the following criteria: △: Severely rough skin; X: Cratered or not electrodepositable. Further, secondary adhesion was evaluated by a square stitch/tape 'f11 release test after immersion in 40°C warm water for 10 days.

■Weldability test: Using an AC 5/Ngursboso welder, welded an electrode with a tip diameter of 6.0 ml to a test piece made by stacking two Q-coated steel plates so that the two coated and unpainted surfaces were in contact with each other. Under the conditions of a welding current of 10,000 A, a current application time of 12 cycles, and a pressure load of 200 kg, surface welding was carried out. Weldability was evaluated using the following criteria: 9A, conductivity stability:
After 1000 dots, 100 samples were taken, and the number of samples with unstable indentation diameters was evaluated.

FIG. 3 shows a schematic diagram of a good impression and a bad impression. A good indentation has a clean circular shape, but an unstable indentation has
In the figure, a localized portion where the electron N is observed can be seen as shown by the hatched area.

B Electrode diameter after continuous dots: The diameter of the electrode after continuous dots after 1ooo dots was measured using 1-square paper, and the following evaluations were made.

0, M rod diameter 7.0 mm or less △: Electrode diameter 7.0 to 8. On+mX: 'WPii 8. Omm or more
When immersed in L4410 at 43°C for 2 minutes and 30 seconds, and further in zinc phosphate chemical conversion treatment liquid PB-L3020,
The amount of chromium eluted in each case when immersed at 3° C. for 2 minutes was calculated from the amount of chromium deposited on the coated steel sheet before and after immersion, which was measured by X-ray fluorescence analysis.

Table 2 below summarizes the test results along with the details of each coating under L.

As is clear from the results in Table 2:1, the organic composite coated steel sheet of the present invention not only has excellent weldability and corrosion resistance, but also excellent adhesion and electrodeposition coating properties, and The amount of elution is also small.

FIG. 4 summarizes the relationship between the upper layer film Wd and Rn+ax of the plated U74 plate with poor spot weldability.

The white circles in the figure indicate that the Subov [8 contact properties are good, and the black circles indicate that the bonding properties are poor. From this figure, R
It can be seen that spot weldability is good when the relationship max≧12a is not satisfied.

082 Table continued) Umbrella Molar ratio of functional groups in the crosslinking agent to the total amount of hydroxyl groups and epoxy groups in the salt 1LD resin to total chromic acid (excluding SrCr04) as a DC buffer outside the scope of the invention (invention Effects) As detailed above, according to the present invention, processing adhesion,
It is possible to obtain a steel plate that has excellent electrodeposition coating properties and particularly low groove weldability, and has great practical significance at present when there is a strong demand for improvement in spot weldability from knee 9°.

[Brief explanation of the drawing]

Fig. 1 is a schematic explanatory diagram showing an example of a beaded 0-bending ironing test; Fig. 2 is a schematic explanatory diagram showing a method for evaluating the ironing area; A schematic diagram of an unstable indentation diameter with current concentration; and FIG. 4 are graphs showing the relationship between the upper layer film thickness d and Rmax of the plated steel sheet on spot weldability. I: Dice, 2: Test piece, 3: Paint film, 4 Varnish spacer, 5: Plate holder, 6: Punch, 7: Peeling part Fig. 1 Fig. 2

Claims (10)

[Claims] (1) The amount of Cr deposited on a zinc or zinc-based alloy coated steel sheet by applying and baking a partially reduced chromic acid-based chromate treatment solution is 10 to 150 mg/m
It consists of a lower layer film of ^2 and an epoxy resin or a modified epoxy resin, and contains a crosslinking agent in an amount such that the molar ratio of functional groups to the total amount of epoxy groups and hydroxyl groups in the resin is 0.1 to 2.0. Application of resin liquid and subsequent 80-30
Film thickness 0.2-4μ formed by baking at a temperature of 0℃
m upper layer coating, and the maximum height Rmax of the plated steel sheet serving as the base material is the thickness d of the upper layer coating, and Rmax≧12d.
An organic composite coated steel sheet with excellent weldability and corrosion resistance, which satisfies the following relationship and further has a surface roughness parameter PPI of 30 or more as described below. PPI: Number of peaks per inch. However, if the threshold value is R
30% of max. (2) The chromate treatment solution contains 0.1 of the total amount of chromic acid.
The organic composite coated steel sheet according to claim 1, which contains up to twice the weight of colloidal silica. (3) The chromate treatment solution contains 0.0% of unreduced chromic acid.
The organic composite coated steel sheet according to claim 1 or 2, further comprising a silane coupling agent in an amount of 0.01 times the mole or more. (4) The chromate treatment solution contains 0.0% of unreduced chromic acid.
The organic composite coating according to any one of claims (1) to (3), further containing 01 to 2.0 times the mole of polyhydric alcohol and/or polycarboxylic acid and/or oxycarboxylic acid. steel plate. (5) The chromate treatment solution contains 0.1 to 0.1 of total chromic acid.
The organic composite coated steel sheet according to any one of claims (1) to (4), further containing 20 times the weight of iron phosphide. (6) The organic composite coated steel sheet according to any one of claims (1) to (5), wherein the chromate treatment liquid further contains a metal chromate. (7) The amount of the epoxy resin is 1 to 3 based on the solid content of the resin.
Organic composite coated steel sheet according to any one of claims (1) to (6), further comprising an inorganic filler other than metal chromate in an amount of 0% by weight. (8) The epoxy resin is a polyhydroxy polyether resin obtained by polycondensation of epihalohydrin and one or more dihydric phenols selected from mononuclear and dinuclear dihydric phenols. , claim (1)
The organic composite coated steel sheet according to any one of (7) to (7). (9) The organic composite coating according to any one of claims (1) to (8), wherein the resin liquid further contains a resin other than epoxy resin in an amount of 1 to 50% by weight based on the resin solid content. steel plate. (10) The plated steel sheet is a steel sheet having baking hardenability, and the baking temperature of the lower layer film and the upper layer film is 200°C.
The organic composite coated steel sheet according to any one of claims (1) to (9), which is as follows.