GB1583103A

GB1583103A - Method for the treatment of metal surfaces

Info

Publication number: GB1583103A
Application number: GB1844677A
Authority: GB
Original assignee: Nippon Paint Co Ltd
Current assignee: Nippon Paint Co Ltd
Priority date: 1976-05-04
Filing date: 1977-05-03
Publication date: 1981-01-21
Also published as: JPS5524506B2; FR2350386A1; BE854260A; FR2350386B1; JPS52133837A; DE2719558A1; DE2719558C2

Description

(54) METHOD FOR THE TREATMENT OF METAL SURFACES (71) We, NIPPON PAINT CO. LTD., No. 1-2, Oyodo Kita 2-chome, Oyodo-ku, Osaka-shi, Osaka-fu, Japan, a body corporate organised under the laws of Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a method for the treatment of a metal surface for the purpose of preparing it to receive a coating finish.More particularly. it relates to a method for the treatment of a metal surface which comprises applying a treatment liquid comprising (a) an emulsion prepared by emulsion-polymerizing an a.P-monoethylenical ly unsaturated monomer in the presence of a specific water-soluble polymer as an emulsifier and (b) a water-soluble chromium compound containing trivalent and hexavalent chromium and optionally (c) a water-insoluble "white carbon" (as herein defined). the treatment liquid containing substantially no alkali metal ion. Bv "white carbon" is meant a material selected from silicic acid anhydrides and silicic acid hydrates.

The treatment of a metal surface for the purpose of preparing it to receive a coating finish. i.e.. the primary treatment of a metal surface. is essential in order to improve the corrosion resistance thereof and the adhesion of the coating film subsequently applied thereto. The conventional methods of treatment of a metal surface are chemical conversion treatments such as a zinc phosphate conversion treatment or an iron phosphate conversion treatment or a chromate treatment. These are coating film methods of the so-called chemical conversion type wherein a coating film is formed by the reaction of a treatment liquid and the metal. In these methods, it is necessary to remove the unreacted treatment liquid and the reaction by-products bv washing the metal thus treated after the film-forming reaction.

The chemical conversion treatment of the surfaces of metals. such as iron. galvanized steel, aluminium, or the like is usually carried out in the following steps: degreasing # rinsing with water # rinsing with water or surface preparation # chemical conversion treatmentwashing with wateroafter-treatment with diluted chromium compound aqueous solution # drying.

According to this method. however. in order to achieve a film-forming reaction giving a film of high quality. it is necessary to control each step strictly. for instance. the temperature and concentration of the components (e.g. free acids. total acidity. zinc. etc.) in the degreasing bath. and the conversion coating treatment bath. or the like. to remove constantly the sludges deposited in the baths during the treatment for a long time. to make clean the nozzle or other devices. and further. to remove a large amount of the waste water which is drained in the washing with water after the convention coating treatment.

Moreover. it is occasionally necessary to abandon the baths in which a large amount of nitrate ions. sodium ions. chloride ions or the like have accumulated.

In order to eliminate these defects in the above-mentioned coating film forming methods of the chemical conversion type. certain film forming methods have been proposed which comprise coating the metal surface with a treatment liquid comprising an emulsion prepared bv emulsion-polymerizing an cr.(-l-monoethylenicallv unsaturated monomer and a water-soluble chromium compound (Japanese Patent Publication (As laid open without examination) No. 57931/1975 and Japanese Patent Publications Nos. 31(126/1974. 4(11(65/ 1974 and 1889/1975).However. the above-mentioned defects are not necessarily sufficiently eliminated even by these methods. That is, the most important point in the above film-forming method using an emulsion is that the emulsion should be chemically stable.

From this viewpoint, a non-ionic surfactant or an anionic surfactant is used to stabilize the emulsion in these known methods (Japanese Patent Publication (As laid open without examination) No. 57931/1975 and Japanese Patent Publications Nos. 40865/1974 and 1889/1975), but this causes a significant deterioration of the adhesion, corrosion resistance and moisture resistance of the coating film which is subsequently applied to the metal.

Moreover, the method described in Japanese Patent Publication No. 31026/1974 requires cooling of the treating liquid at a temperature below 20"C in order to prevent the deterioration of the resin which occurs when the emulsion is admixed with the chromium compound.

We have sought to find an improved emulsion which can give a stable treatment liquid without using any surfactant and any specific treatment, and we have found that the desired emulsion can be prepared by emulsion-polymerizing the a,ss-monoethylenically unsaturated monomer in the presence of a specific water-soluble polymer, and that the emulsion thus prepared can be 'admixed with the water-soluble chromium compound containing trivalent and hexavalent chromium without the occurrence of an undesirable destruction of the emulsion, of gelation or of precipitates, and can give an excellent stable treatment liquid admixed with the water-soluble chromium compound and optionally with a water-insoluble white carbon which shows excellent adhesion, corrosion resistance and moisture resistance of the coating film subsequently applied thereto, and further that the treatment liquid containing substantially no alkali metal ion can afford a painted metal having an improved corrosion resistance.

Furthermore, according to the method of metal surface treatment of the present invention, the desired coating film can be easily formed merely by supplementing intermittently the consumed amount of the treatment liquid at a fixed period without the strict control of the steps. and the steps such as the rinsing with water. the treatment of the water and further the after-treatment of the metal as in the conventional coating film forming method of the chemical conversion type.

An object of the present invention is to provide an improved method for the treatment of a metal surface in order to prepare the metal surface for receiving a coating finish.

Another object of the invention is to provide a treatment liquid useful for the treatment of a metal surface, which comprises a stable emulsion and a water-soluble chromium compound containing trivalent and hexavalent chromium and optionally a water-insoluble white carbon and contains substantially no alkali metal ion.

A further object of the invention is to provide an improved method for preparing the emulsion bv emulsion-polymerizing an a.i3-monoethylenically unsaturated monomer in the presence of a specific water-soluble polymer.

These and other features of the present invention will be apparent from the following description.

The method of treatment of a metal surface of the present invention comprises applying a treatment liquid comprising: (a) an emulsion prepared by emulsion-polymerizing an a.ji-monoethylenically unsaturated monomer. and (b) a water-soluble chromium compound containing 30 to 9.)% by weight of hexavalent chromium and also trivalent chromium and optionally (c) a water-insoluble white carbon.

and containing substantially no alkali metal ion. said emulsion being prepared by emulsion-polymerizing at least one a.ss-monoethylenically unsaturated monomer in the presence of an emulsifier consisting of a polyacrylic acid or a copolymer of acrylic acid and at least one monomer consisting of methacrylic acid. acrylamide or methacrylamide or a hydrophilic monomer of the formula:

wherein A is hydrogen or methyl. R is a substituted or unsubstituted alkylene group having 2 to 4 cirbon atoms and X is a functional group having at least one of oxygen, phosphorus and sulphur. or any combination thereof.

said emulsifier being used in an amount of 2d parts by weight or more (in solid content) relative to 1()() paits by weight of the cr.r-i-monoethylenically unsaturated monomer or monomers.

The emulsifier (i.e. the water-soluble polymer) is polyacrylic acid and a copolymer of acrylic acid and at least one compound consisting of methacrylic acid, an acrylamide (e.g.

acrylamide or N-methylol-acrylamide), a methacrylamide (e.g. methacrylamide or Nmethylolmethacrylamide) or a hydrophilic monomer of the above formula (I), or any combination thereof, [specific examples of the monomers in the case where X is a functional group containing oxygen being 2-hydroxyethyl acrylate, hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, 3-hydroxybutyl acrylate, 2,2-bis (hydroxymethyl) -ethyl acrylate, 2,3-dihydroxypropyl methacrylate, 3-hydroxybutyl methacrylate, etc.; specific examples of the monomers in the case where X is a functional group containing phosphorus being (a) mono-(2-hydroxyethylmethacrylate) acid phosphate.

of the formula:

and (b) mono-(3-chloro-2-hydroxypropylmethacrylat,e) acid phosphate of the formula:

and a specific example of the monomer in the case where X is a functional group containing sulphur beirig sulphonylethyl methacrylate, which are used alone or in a mixture of two or more thereof].

The proportion of the acrylic acid relative to the other hydrophilic monomer or monomers in the above copolymer may be appropriately chosen so as to make the content of the acrylic acid in the whole monomer in the range of 50% by weight or more, preferably 60% by weight or more, from the viewpoints of the stability of the emulsion, the adhesion property relative to the metal substrate, etc.

The preparation of such water-soluble polymers may be carried out in accordance with conventional methods (e.g. polymerization in an aqueous solution, block polymerization, polymerization in an organic solvent, etc.) Thus, for instance, in the case of the polymerization in an aqueous solution, the polymerization may be carried out by adding dropwise simultaneously acrylic acid or a mixture of acrylic acid and at least one other hydrophilic monomer and water (preferably deionized water) containing a water-soluble free radical catalyst other than an alkali metal salt (e.g. ammonium persulphate) from separate dropping funnels to water (preferably deionized water) which is kept at a temperature suitable for the reaction, and reacting the mixture with agitation at a temperature within the range of from 70 to 90"C. The reaction period of time including the time for adding the reactants is usually 3 to 5 hours.

The a,ss-monoethylenically unsaturated monomers used in the present invention include acrylic esters (e.g. methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, isooctyl acrylate, 2-ethylbutyl acrylate, octyl acrylate, methoxyethyl acrylate, ethoxyethyl acrylate, 3-ethoxypropyl acrylate, etc.); methacrylic esters (e.g. methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, lauryl methacrylate, decyl methacrylate, octyl methacrylate, stearyl methacrylate, 2-methylhexyl methacrylate, glycidyl methacrylate, 2-ethoxyethyl methacrylate, cetyl methacrylate, benzyl methacrylate, 3-methoxybutyl methacrylate, etc.); acrylonitrile; methacrylonitrile; vinyl acetate; vinyl chloride; vinyl ketone; vinyltoluene; and styrene, which may be used alone or in a mixture of two or more thereof. In addition to these monomers, there may also be used a small amount of the monomers constituting the above water-soluble polymer, such as acrylamides, methacrylamides and the hydrophilic monomers of the above formula (I). In particular, when a hydroxy group-containing monomer (e.g. 2-hydroxyethyl methacrylate) is added, the polymer has a structure crosslinked with the COOH group in the emulsion, and hence, the coating film formed can afford a very much improved paint adhesion to the metal substrate.

Emulsion-polymerization of the a,ss-monoethylenically unsaturated monomer can be carried . out by conventional emulsion-polymerization methods except that the abovementioned specific water-soluble polymer is used as the emulsifier, and the catalyst is a water-soluble catalyst containing substantially no alkali metal ion which gives a bad influence (e.g. decrease of corrosion resistance and moisture resistance) on the coating film.

Thus, for instance, the emulsion-polymerization may be carried out by adding dropwise simultaneously the a,ss-monoethylenically unsaturated monomer and water (preferably a deionized water) containing an alkali metal-free water-soluble catalyst (e.g. ammonium persulphate) and optionally a part of the emulsifier from the separate dropping funnels to water (preferably a deionized water) containing the whole or the remaining part of the emulsifier which is kept at a temperature suitable for the reaction, and then reacting the mixture with agitation at a temperature of from 50 to 700C, preferably 55 to 650C. The reaction period of time including the time for adding the reactants is usually from 3 to 7 hours.

The emulsifier is used in an amount of from 20 parts by weight or more, preferably 20 to 50 parts by weight (in solid content), relative to 100 parts by weight of the a,ss- monoethylenically unsaturated monomer. When the amount of the emulsifier is less than 20 parts by weight, the emulsion has an inferior storage stability and hence cannot be used.

The use of the emulsifier in excess of 50 parts by weight does not specifically provide an improvement to the storage of the emulsion or to its chemical stability to water-soluble chromium compounds but conversely causes problems such as the foaming of the emulsion.

The above emulsion-polymerization can give an even and stable emulsion having substantially 30% by weight of solid content. When the emulsion is incorporated into the treatment liquid, an epoxy resin such as a bisphenol-type epoxy resin (e.g. Epicoat 828 and Epicoat 1001, trade marks of Shell Chemical) may optionally be used as a hardening agent.

The epoxy resin may be incorporated in the preparation of the emulsion by dissolving it in a,(3-monoethylenically unsaturated monomer and adding the mixture dropwise to the emulsion-polymerization system. The use of the epoxy resin can afford a coating film having superior paint adhesion properties.

The water-soluble chromium compound used in the present invention includes any conventional chromium compounds containing 30 to 90% by weight of hexavalent chromium, but chromates are not necessarily preferred because the treatment liquid should contain substantially no metallic ion or anionic ion which has a bad influence on the corrosion resistance of the coating film. The most suitable example of the chromium compound is chromic anhydride (CrO3). It is important that the chromium compound should contain 30 to 90% by weight, preferably 40 to 60% by weight, of hexavalent chromium based on the total chromium content. When the content of the hexavalent chromium is less than 30% by weight, not only is the corrosion resistance of the coated plate lowered, but the processing characteristics of the product in the forming step thereof also deteriorate.On the other hand, when the content of the hexavalent chromium is more than 90% by weight, the chromium compound tends to effuse out of the coating film, which results in inferior corrosion resistance and moisture resistance. Besides, the chromium other than hexavalent chromium in the chromium compound is predominantly trivalent chromium. It is known that, when the trivalent chromium is contained, the coating film shows an improved corrosion resistance and adhesion properties, but on the other hand, the stability of the treatment liquid is unfavourably lowered. However, when the emulsion of the present invention is used, a suitably stable treatment liquid can be obtained even if trivalent chromium is present.Besides, when the solution of the chromium compound is prepared, the hexavalent chromium is partially reduced to trivalent chromium by using a reducing agent such as formaldehyde, hydrogen peroxide or the like.

The following fine grain compounds are examples of the water-insoluble white carbon which may be used in the present invention: (i) fine grain silicic acid annydnde, which has 98% by weight or more of SiO2 content and contains little adhesive moisture and bound water, for example, a fumed silica prepared by a gaseous phase method (e.g. Aerosil, trade mark of Degussa Co.; or Carb-O-Sil, trade mark of Cabot Co.), a silica prepared by an arc method (e.g. Fransil, trade mark of Fransol Co.; or ArcSilica, trade mark of PPG Industries Inc.); (ii) fine grain silicic acid hydrate, which has 80 to 98% by weight of SiO2 and contains a large amount of adhesive moisture and bound water, for example, a silica prepared by a wet process, i.e. by hydrolysing a silicate with an acid and purifying the resulting silicic acid hydrate (e.g. Hi-Sil, trade mark of PPG Industries Inc.; Ultrasil, trade mark of Degussa Co.; Tokusil, trade mark of Tokuyama Soda Co. Ltd., or Carplex, trade mark of Shionogi Pharmaceutical Co.), and (iii) fine grain silicate. such as calcium silicate or aluminium silicate.

Among these, preferred white carbons are (a) a water-insoluble white carbon having primary particles or ().1 to 3 IL in particle size which is mostly present in the form of primary particles without aggregation in the treating liquid, and (b) a water-insoluble white carbon wherein the primary particles have .large aggregation properties and the particles are present in the form of aggregated particles of 0.1 to 3 11 in particle size in the treatment liquid.

The water-insoluble white carbon (a) includes the silicates mentioned above. Suitable examples of the aluminium silicates are Kaolin and calcined Kaolin (e.g. ASP &num; 100 - 105, ASP &num; 600, Satentone No. 1 or Satentone No. 3, trade mark of Engelhardt Mineral & BR< Chemicals Inc.(; However, many silicates contain an alkali and show an alkaline pH in the treatment liquid, which is not suitable because the alkali ion or metal ion has a bad influence on the moisture resistance of the coating film. Accordingly, we prefer to use the silicate white carbon which shows a pH value of less than 7 when it is suspended in water in a concentration of substantially 5% by weight. Besides, while they are usually not classified as a white carbon, there may also be used other water-insoluble silicates such as zirconium silicate.Moreover, there may also be used the pulverized product of silica gel which is prepared by gelating silicicacid, for example, Syloid &num;244, &num;65 or &num;978 (trade marks of Fuji-Davison Chemical Ltd.) or Silnex (trade mark.of Mizusawa Kagaku Kogyo K.K.).

The water-insoluble white carbon (b) is selected from silicic acid anhydrides and silicic acid hydrates. As silicic acid anhydrides, a suitable example of a fumed silica prepared by a gaseous phase method is Aerosil TT 600 (trade mark of Degussa Co.), a suitable example of silica prepared by the arc method is TK 800 (trade mark of Degussa Co.), and a suitable example of a silicic acid hydrate is HK 125 (trade mark of Degussa Co.). These white carbons are present in the form of aggregated secondary particles having a particle size of micron order. The silica prepared by a wet process may also be used because it is present in the form of aggregated particles having a particle size of the micron order.The silica prepared by a wet process. contains occasionally in accordance with the process or the grade thereof, alkali metal.ions which have a bad influence on the corrosion resistance and moisture resistance of the coating film. Accordingly, the suitable silica should show a pH value of less than 7 when it is suspended in water in a concentration of 5% by weight', 'f6r instance, the content of sodium ions should be less than 0.1% by weight in the entire silica.

The treatment liquid may be prepared by mixing the emulsion and the water-soluble chromium compound in water (preferably a deionized water) in an appropriate concentra- tion; and, where the.water-insoluble white carbon is also incorporated, by thoroughly dispersing the water-insoluble white carbon into water (preferably deionized water), admixing the dispersion with the emulsion and the water-soluble chromium compound, and optionally diluting the mixture with water (preferably a deionized water) so that the solid content falls in an appropriate range, for example, substantially 0.5 to 10% by weight.

The emulsion and the water-soluble chromium compound are preferably admixed in the ratio of 100 1 to 1: 10 by weight, more preferably 10: to 1: 5 by weight (in the solid content). When the mixed ratio of the water-soluble chromium compound is smaller than the above lower limit, the corrosion resistance of the coated plate is decreased, and the adhesion properties of the coating film onto the metal surface are also decreased. On the other hand, when the mixed ratio of the chromium compound is larger than the upper limit, the adhesion properties of.the coated plate are unfavourably decreased.

The water-insoluble white carbon is preferably admixed in the ratio of 10 1 to 1:10 by weight, more preferably 2:1 to 1: 2 by weight (the emulsion : the white carbon, in the solid content). When the mixed ratio of the white carbon is smaller than the lower limit, the adhesion properties and corrosion resistance of the coating film are not improved, and on the other hand, when it is larger than the upper limit, the moisture resistance of the coating film deteriorates.

The treatment liquid of the present invention may also be incorporated with some inorganic compounds which can release an inorganic ion other than an alkali metal ion, such as Zn2+, Co2+, Ni2+, Fe2+, Fe3+, PO43-, F-, BF4-, SiF62-, or the like. Incorporation of the inorganic ion-releasing compound can afford a still better, more even and more adhesive coating film on the metal surface.

The treatment liquid comprising the emulsion and the water-soluble chromium compound and optionally the water-insoluble white carbon is applied to the surface of metals (e.g. iron, galvanized steel, aluminium, etc.) by conventional methods such as roll coating, mist spraying or dipping and followed by the drying thereof to.form a coating film on the metal surface. The coating film is usually formed in an amount of from 10 mg/m to g f/m2, preferably from 50 mg/m2 to 700 mg/m-, in the dry state. When the coating film is formed in an amount outside the above range, the processability of the coated plate is liable to be adversely affected.

Drying.of the coating film is carried out under the condition that the moisture included in the coating film can be removed but the resin is not molten, for instance, at a temperature of the metal plate not higher than 1200C, preferably 80 to 110 C, for from 1 second to 60 seconds. In practice, the metal to be dried is kept at an atmosphere of a little higher temperature than the above temperature of the metal plate.For instance, when a treatment liquid containing the solid content of 2 to 5% by weight is applied to the metal surface to form a coating film in an amount of from 500 mg/m2 to 1 g/m2, the drying is carried out at an atmospheric temperature of 100"C for from 30 to 60 seconds or at an atmospheric temperature of 200"C for 7 to 8 seconds. When the drying temperature is too high, the resin is molten and the coating film loses the rough surface, which results in deterioration of the adhesion properties and scratch resistance of the coating subsequently applied thereto.

Since the treatment liquid of the present invention is incorporated into the emulsion prepared by using no surfactant and contains substantially no alkali metal ions, the coated plate shows excellent corrosion resistance and moisture resistance, and further highly improved processability and adhesion properties such as scratch resistance.

According to the present invention, the maintenance of the treatment liquid is not required and hence the formation of the coating film on the metal surface can be continuously effected merely by supplementing intermittently the consumed amount of the treatment liquid having the same components as used firstly at a fixed period. Furthermore, since the steps of rinsing and other after-treatment are not required, the process can be shortened and further no specific apparatus for treating the waste water is required.

The present invention is illustrated by the following examples but is not limited thereto.

In the examples, "part" and "%" mean "part by weight" and "% by weight", respectively, unless specified otherwise.

EXAMPLE 1 Into a flask provided with a stirrer, a reflux condenser, a thermometer and two dropping funnels, there are charged 150 parts of deionized water and 120 parts of a water-soluble copolymer obtained by copolymerizing acrylic acid and 2-hydroxyethyl methacrylate in the ratio of 8 : 2 by weight (25% aqueous solution, molecular weight (Mw) : 66000), and the resulting mixture is heated to 60 - 650C with stirring. Then, a monomer mixture consisting of 35 parts of methyl methacrylate, 15 parts of styrene, 10 parts of 2-hydroxyethyl methacrylate and 40 parts of n-butyl acrylate and a catalyst solution consisting of 2 parts of ammonium persulphate and 50 parts of deionized water are separately but simultaneously added dropwise from separate dropping funnels over a period of 8 hours.After completion of the dropwise addition, the resulting mixture is kept at 60 to 65"C for about 2 hours to complete the polymerization reaction and to give an emulsion having a 30.1% solids content.

Preparation of treatment liquid: 8.1 parts of the above emulsion, 7.4 parts of the aqueous solution of chromium compound (solid content: 16.5 %) which is obtained by reducing about 50% of the amount of the hexavalent chromium to trivalent chromium by adding 5 parts of formalin (37% aqueous solution) to 95 parts of 17% aqueous solution of chromic anhydride and 20 parts of a dispersion (solid content 10%) of fine grain silicic acid anhydride (Aerosil TT 600, trade mark of Degussa Co.) in dionized water are mixed at room temperature, to which deionized water is added to prepare a treatment liquid having a 2.3% solids content.

Metal surface treatment and coating: The above treatment liquid is applied with a roll coater to the surface of a galvanized steel plate (GALVANYL plate, thickness: 0.35 mm) degreased with an alkali degreasing agent ("RIDOLINE No. 72", trade mark of Nippon Paint Co., Ltd.), and the product is immediately dried at 100"C for 40 seconds to give an even coating film having a film weight of 293 mg/m2.Thereafter, the surface-treated galvanized steel is coated with a coating formulation for galvanized steel, i.e. with a primer formulation (Superlac DIF-TX-1, trade mark of Nippon Paint Co., Ltd.), (baking: at a furnace temperature of 220 to 240"C for 45 seconds, film thickness: 3 ) and then with a topcoating formulation (Superlac DIF-A-55, trade mark of Nippon Paint Co., Ltd.). (baking: at a furnace temperature of 210 to 230"C for 60 seconds, film thickness: 11 Il) to give a coated plate.

REFERENCE EXAMPLE 1 Preparatioti of emulsion: Into the same flask as used in Example 1, there are charged 100 parts of deionized water and 7 parts of a non-ionic surfactant (Emulgen 950, trade mark of Kao Atlas Co.) and the resulting mixture is kept to 60 to 650C with stirring. Then, the same monomer mixture as used in Example 1 and a catalyst solution consisting of 2 parts of ammonium persulphate and 20 parts of deionized water are separately and simultaneously added dropwise from separate dropping funnels over a period of 3 hours. After the completion of the dropwise addition, the resulting mixture is heated at 60 to 650C for about 1 hour to complete the polymerization reaction and to give an emulsion having a 46.3% solids content.

Preparation of treatment liquid: To 5.3 parts of the above emulsion are added 7.4 parts of the same' aqueous solution (solid content: 16.5%) of chromium compound as used in Example 1 and 20 parts of the same dispersion of white carbon (solid content: 10%) as used in Example 1, and deionized water is added thereto to give a treatment liquid having a 2.4% solids content.

Metal surface treatment and coating: In the same manner as described in Example 1 except that the treatment liquid obtained above is used, there is obtained a coated plate (the film weight of the coating film: 305 mg/m2).

REFERENCE EXAMPLE 2 In the same manner as described in Reference Example 1 except that 5 parts of an anionic surfactant (Levenol WX, trade mark of Kao Atlas Co., 25% aqueous solution) are used instead of 7 parts of the non-ionic surfactant, an emulsion (solid content: 45.5%) is obtained. 5.4 parts of the emulsion are admixed with 7.4 parts of the same aqueous solution of chromium compound (solid content: 16.5%) as that used in Example 1 and 20 parts of the same dispersion of white carbon (solid content: 10.) as used in Example 1. As a result, the mixture is wholly instantaneously aggregated, and the supernatant liquid has the colour of an aqueous solution of a chromium compound.

EXAMPLE 2 Preparation of treatment liquid: 8.1 parts of the emulsion prepared in Example 1 are admixed with 20 parts of the same aqueous solution of chromium compound (solid content: 16.5%) as used in Example 1 and 20 parts of a dispersion (solid content: 10%) of ultra-fine grain silica gel (Silnex P-526, trade mark of Mizusawa Kagaku Kogyo K.K.) in deionized water at room temperature, and deionized water is added thereto to give a treatment liquid having a 2.4% solids content.

Metal surface treatment and coating: In the same manner as described in Example 1 except that the treatment liquid as obtained above is used, there is obtained a coating plate (the film weight of the coating film: 288 mg/m2).

EXAMPLE 3 Preparation of emulsion: In the same manner as described in Example 1 except that 200 parts of polyacrylic acid (25% aqueous solution, molecular weight (Mw): 59000) are used instead of 120 parts of acrylic acid/2-hydroxyethyl methacrylate copolymer and the monomer mixture consists of 35 parts of methyl methacrylate. 15 parts of styrene, 10 parts of ethyl methacrylate and 40 parts of n-butyl acrylate, an emulsion-polymerization is carried out to yield an emulsion having a 30.8% solids content.

Preparation of treatment liquid: 7.9 parts of the above emulsion are admixed with 7.4 parts of the same aqueous solution of chromium compound (solid content: 16.5%) as used in Example l and 20 parts of the same dispersion of white carbon (solid content: 1OC/o) as used in Example 1 and deionized water is added thereto to give a treatment liquid having a 2.3C/c solids content.

Metal surface treatment and coating: In the same manner as described in Example 1 except that the above treatment liquid is used. there is obtained a coated plate (the film weight of the coating film: 27Smg/m2).

EXAMPLE 4 Preparation of emitlsioii: In the same manner as described in Example 1 except that 120 parts of the polyacrylic acid used in Example 3 are used instead of 120 parts of the acrylic acid/2-hydroxyethyl methacrylate copolymer, the emulsion-polymerization is carried out to give an emulsion having 29.4% solids content.

Preparatiosl of treannent liqltifi: 5.1 parts of the above emulsion are admixed with 18 parts of an aqueous solution of chromium compound (solid content: 16.2%) which is prepared at room temperature by reducing substantially 70% of the amount of hexavalent chromium to trivalent chromium by adding 7 parts of formalin (37% aqueous solution) to 95 parts of 17% chromic anhydride aqueous solution and 15 parts of the same dispersion of white carbon (solid content: 10%) as used in Example 1, and deionized water is added thereto to give a treatment liquid having a 2.4% solids content.

Metal surface treatment and coating: In the same manner as described in Example 1 except that the above treatment liquid is used, there is obtained a coating plate (the film weight of the coating film: 308 mg/m2).

EXAMPLE 5 Prepnratiosl of emulsion: In the same manner as described in Example 1 except that 120 parts of a water-soluble copolymer (25% aqueous solution, molecular weight (Mw): 34000) which is prepared by copolymerizing acrylic acid and acrylamide in a ratio of 8 : 2 by weight is used instead of 120 parts of the acrylic acid/2-hydroxyethyl methacrylate copolymer. the emulsionpolymerization is carried out to give an emulsion having a 31.5% solids content.

Preparation of treatment liquid: 5.1 parts of the above emulsion are admmixed with 18 parts of the same aqueous solution of chromium compound (solid content: 16.5%) as used in Example 1 and 15 parts of a dispersion of fine grain silicic acid anhydride (Aerosil 200, trade mark of Degussa Co.) in deionized water (solid content: 10%), and deionized water is added thereto to give a treatment liquid having a 3.1% solids content.

Metal surface treatment and coating: The above treatment liquid is applied with a roll coater to a galvanized steel previously degresed as in Example 1 and the product is immediately dried at 100 C for 60 seconds to form an even coating film (film weight: 520 mg/m). The surface-treated galvanized steel is coated with coating formulations for galvanized steel as in Example 1 to give a coated plate.

REFERENCE EXAMPLE 3 Preparation of treatment liquid: In the same manner as described in Example 1 except that no chromium compound is incorporated, there is obtained a treatment liquid having a 2.3% solids content.

Metal surface treatment and coating: In the same manner as described in Example 1 except that the above treatment liquid is used, there is obtained a contend plate (the film weight of the coating film: 28() mg/m2).

REFERENCE EXAMPLE 4 Preparation of treatment liquid: In the same manner as described in Example 1 except that no emulsion is incorporated, there is obtained a treatment liquid having a 2.3% solids content.

Metal surface treatment and coating: In the same manner as described in Example 1 except that the above treatment liquid is used. thete is obtained a coated plate (the film weight of the coating film: 3()3 mg/m2).

REFERENCE EXAMPLE 5 Preparation of treatment liquid: In the same manner as described in Example 1 except that 0.6 part of sodium hydroxide is additionally incorporated, there is obtained a treatment liquid having a 2.3% solids content.

Metal surface treatment and coating: In the same manner as described in Example 1 except that the above treatment liquid is used. there is obtained a coated plate (the film weight of the coating film: 21(0 mg/m-).

REFERENCE EXAMPLE 6 A commercially available zinc phosphate treatment liquid for a chemical conversion treatment is applied by a spray coating for 2 minutes to a galvanized steel previously degreased as in Example 1. The products is immediately washed with a large amount of water, dipped in an aftertreatment liquid, and then dried at 100 C for 1 minute to form an even phosphate coating film (film weight: 1500 mg/m). The thus-treated galvanized steel is subjected to a coating finish as in Example 1 to give a coated plate.

The coated plates prepared in the above Examples and Reference Examples are subjected to the following tests. The results are shown in Table 1 below.

(1) Scratch resistance The surface of the coated plate is scratched with a coin and the degree of injury of the surface is observed. The results are evaluated as follows: Oo : Superior (not injured) o : Good (little injured) A: A little bad (injured) x : Inferior (significantly injured) (2) Bending resistance The coated plate (width: 5 cm) is bent at an angle of 1800 and vised, and a pressure-sensitive adhesive tape is adhered onto the bent surface and is then peeled off. The results are evaluated by a 10 point method ranging from Point 10 (no trouble) to Point 1 (fully peeled off).

(3) Resistance to saline solution A 5% saline solution is sprayed onto the coated plate which is scribed with a knife at 35 + 1"C for 1000 hours, and the width of blistered paint film from the scribe line is measured.

The results are evaluated as follows: Point 5: No trouble " 4: 0.5 mm > " 3: 0.5 - 1.5 mm " 2: 1.5 - 2.5 mm " 1: 2.5 mm < (4) Moisture resistance The coated plate is kept under an atmosphere of a humidity of 98 + 2 % and a temperature of 50 + 1"C for 1000 hours, and then the blister density is measured (cf. ASTM D714-56). The results are evaluated as follows: Point 5: No trouble " 4: Few " 3: Medium " 2: Medium dense " 1: Dense TABLE 1 Test Example No. Reference Example No.

1 2 3 4 5 1 3 4 5 6 Scratch resistance # # # # # x # # # # Bending resistance 10 10 10 10 10 4 6 8 8 8 Resistance to saline solution 5 5 5 4.5 5 1 1 4 2 4 Moisture resistance 5 5 5 5 5 1 1 2 1 4 EXAMPLE 6 Into a flask provided with a stirrer, a reflux condenser, a thermometer and two dropping funnels, there are charged 150 parts of dionized water and 120 parts of water-soluble copolymer obtained by copolymerizing acrylic acid and 2-hydroxyethvl methacrylate in a ratio of 8 : 2 by weight (25% aqueous solution, molecular weight (Mw) : 66000), and the resulting mixture is heated to 60 - 650C with stirring.Then, a monomer mixture consisting of 35 parts of methyl methacrylate, 15 parts of styrene, 10 parts of 2-hydroxyethyl methacrylate and 40 parts of n-butyl acrylate and a catalyst solution consisting of 2 parts of ammonium persulphate and 50 parts of deionized water are separately but simultaneously added dropwise from separate dropping funnels over a period of 8 hours. After completion of the dropwise addition, the resulting mixture is kept at 60 to 650C for about 2 hours to complete the polymerization reaction and to give an emulsion having a 30.1% solids content.

Preparation of treatment liquid: 8.1 parts of the above emulsion and 7.4 parts of an aqueous solution of chromium compound (solid content: 16.5%) which is obtained by reducing about 50% of the amount of the hexavalent chromium to trivalent chromium by adding 5 parts of formalin (37% aqueous solution) to 95 parts of 17% aqueous solution of chromic anhydride are mixed at room temperature, deionized water being added to yield a treatment liquid having a 2.3% solids content.

Metal surface treatment and coating: The above treatment liquid is applied with a roll coater to the surface of a galvanized steel plate (GALVANYL plate, thickness: 0.35 mm) degreased with an alkali degreasing agent ("RIDOLINE No. 72", trade mark of Nippon Paint Co., Ltd.) and the product is immediately dried at 1000C for 40 seconds to give an even coating film having a film weight of 293 mg/m2. Thereafter, the thus surface-treated galvanized steel is coated with a coating formulation for galvanized steel (a melamine-alkyd resin formulation: Orga 100, trade 'mark of Nippon Paint Co., Ltd.) (baking: at a furnace temperature of about 200"C fof 45 seconds, film thickness: about 8 > ) to give a coated plate.

REFERENCE EXAMPLE 7 Preparation of Emulsion Iiito the same flask as used in Example 6, there are charged 100 parts of deionized water and 7 parts of a non-idnic surfactant (Emulgen 950, trade mark of Kao Atlas Co.), and the mixture is kept to 60 to 65"C with stirring. The same monomer mixture as used in Example 6 and a catalyst solution consisting of 2 parts of ammonium persulphate and 20 parts of deionized water are separately but simultaneously added drop-wise from separate dropping funnels over a period of 3 hours. After completion of the dropwise addition, the resulting mixture is heated at 60 to 650C for about 1 hour to complete the polymerization reaction and to give an emulsion having a 46.3% solids- content.

Preparation of treatment liquid: To 5.3 parts of the above emulsion are added 7.4 parts of the same aqueous solution (solids content: 16.5%) of chromium compound as used in Example 1, and deionized water is added to give a treatment liquid having a 2.4% solids content.

Metal surface treatment and coating: In the same manner as described in Example 6 except that the treatment liquid obtained above is used, there is obtained a coated plate (film weight of the coating film: 305 mg/m2).

EXAMPLE 7 Preparation of treating liquid: 8.1 parts of the emulsion prepared in Example 6 are admixed with 6.7 parts of a mixture (solids content: 18.2 %) of 100 parts of the same aqueous solution of chromium compound as used in Example 6 and 3 parts of phosphoric acid (75%) at room temperature, and deionized water is added to give a treatment liquid having a 2.4% solids content.

Metal surface treatment and coating: In the same manner as described in Example 6 except that the treatment liquid as obtained above is used, there is a coating plate (film weight of the coating film: 288 mg/m2).

EXAMPLE 8 Preparation of emulsion: In the same manner as described in Example 6 except that 200 parts of polycacrylic acid (25% aqueous solution, molecular weight (Mw): 59000) are used instead of 120 parts of acrylic acid/2-hydroxyethyl methacrylate copolymer and the monomer mixture consists of 35 parts of methyl methacrylate, 15 parts of styrene, 10 parts of ethyl methacrylate and 40 parts of n-butyl acrylate, the emulsion-polymerization is carried out to give an emulsion having a 30.8% solids content.

Preparation of treatment liquid: 7.9 parts of the above emulsion are admixed with 4.9 parts of the same aqueous solution of chromium compound (solids content: 16.5%) as used in Example 6 and deionized water is added to give a treatment liquid having a 2.3% solids content.

Metal surface treatment and coating: In the same manner as described in Example 6 except that the above treatment liquid is used, there is obtained a coated plate (film weight of the coating film: 278 mg/m2).

EXAMPLE 9 Preparation of emulsion: In the same manner as described in Example 1 except that 120 parts of the polyacrylic acid as used in Example 3 are used instead of 120 parts of the acrylic acid/2-hydroxyethyl methacrylate copolymer, the emulsion-polymerization is carried out to give an emulsion having a 29.4% solids content.

Preparation of treatment liquid: 8.3 parts of the above emulsion are admixed with 5 parts of an aqueous solution of chromium compound (solids content: 16.2%) which is prepared by reducing about 70% of the amount of hexavalent chromium to trivalent chromium by adding 7 parts of formalin (37% aqueous solution) to 95 parts of 17% chromic anhydride aqueous solution at room temperature, and deionized water is added to give a treatment liquid having a 2.4% solids content.

Metal surface treatment and coasting: In the same manner as described in Example 6 except that the above treatment liquid is used, there is obtained a coated plate (film weight of the coating plate: 308 mg/m2).

EXAMPLE 10 Preparation of emulsion: In the same manner as described in Example 6 except that 120 parts of a water-soluble copolymer (25% aqueous solution, molecular weight (Mw): 34000) which is prepared by copolymerizing acrylic acid and acrylamide in the ratio of 8 : 2 by weight is used instead of 120 parts of the acrylic acid/2-hydroxyethyl methacrylate copolymer, the emulsionpolymerization is carried out to give an emulsion having a 31.5% solids content.

Preparation of treatment liquid: 7.7 parts of the above emulsion are admixed with 4.9 parts of the same aqueous solution of chromium compound (solid content: 16.5%) as used in Example 6 and deionized water is added to give a treatment liquid having a 3.1% solids content.

Metal surface treatment and coating: The above treatment liquid is applied to a galvanized steel previously degreased as in Example 6 with a roll coater and product is immediately dried at 100"C for 60 seconds to form an even coating film (film weight: 520 mg/m2). The thus surface-treated galvanized steel is coated with a coating formulation for galvanized steel as in Example 6 to give a coated plate.

The coated plates prepared in the above Examples 6 to 10 and Reference Example 7 are subjected to the following tests. The results are shown in Table 2.

(1) Scratch resistance The surface of the coated plate is scratched with a coin and the degree of injury of the surface is observed. The results are evaluated as follows: o : Good (little injured) A : A little bad (injured) x : Inferior (significantly injured) (2) Bending resistance The coated plate (width: 5 cm) is bent at an angle of 1800, between which two plates having the same thickness as that of the plate to be tested are inserted, and vised, and a pressure-sensitive adhesive tape is caused to adhere to the bent surface and is then peeled off. The results are evaluated by a 10 point method ranging from Point 10 (no trouble) to Point 1 (fully peeled off).

(3) Resistance to saline solution A 5% saline solution is sprayed onto the coated plate which is scribed with a knife at 35 1 1 C for 500 hours, and the width of blistered paint film from the scribe line is measured. The results are evaluated as follows: Point 5: No trouble " 4: 0.5 mm > " 3: 0.5 - 1.5 mm 2: 1.5 - 2.5 mm " 1: 2.5 mm < (4) Moisture resistance The coated plate is kept under an atmosphere with a humidity of 98 + 2% and a temperature of 50 + 1"C for 1000 hours, and the blister density is then measured (cf. ASTM D714-56). The results are evaluated as follows: Point 5: No trouble " 4: Few " 3: Medium 2: 2: Medium dense 1: Dense TABLE 2 Test Example No. Ref.

Ex. 7 6 7 8 9 10 Scratch resistance 0 0 0 0 O x Bending resistance 8 9 10 9 8 4 Resistance to saline solution 5 5 5 5 5 1 Moisture resistance 5 5 5 5 5 1 WHAT WE CLAIM IS: 1. A method for the treatment of a metal surface, which comprises applying to the surface a treatment liquid comprising an emulsion and a water-soluble chromium compound containing 30 to 90% by weight of hexavalent chromium and drying the resulting product, the treatment liquid containing substantially no alkali metal ions, the emulsion being the product bf the emulsion-polymerization of at least one a,ss-monoethylenically unsaturated monomer in the presence of an emulsifier consisting of a polyacrylic acid or a copolymer of acrylic acid and at least one monomer consisting of methacrylic acid, an acrylamide, a methacrylamide or a hydrophilic monomer of the formula: :

wherein A is hydrogen or methyl; R is a substituted or unsubstituted alkylene having 2 to 4 carbon atoms; and X is a functional group containing at least one of oxygen, phosphorus and sulphur, or any combination thereof, and the emulsifier being used in an amount of 20 parts by weight or more (in the solid content) relative to 100 parts by weight of the a,ss- monoethylenically unsaturated monomer.

2. A method according to claim 1, wherein the mixed ratio of the emulsion and the water-soluble chromium compound is in the range of from 100:1 to 1:10 by weight (in the solid content).

3. A method according to claim 1 or 2, wherein the chromium compound contains from

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

(2) Bending resistance The coated plate (width: 5 cm) is bent at an angle of 1800, between which two plates having the same thickness as that of the plate to be tested are inserted, and vised, and a pressure-sensitive adhesive tape is caused to adhere to the bent surface and is then peeled off. The results are evaluated by a 10 point method ranging from Point 10 (no trouble) to Point 1 (fully peeled off).

(3) Resistance to saline solution A 5% saline solution is sprayed onto the coated plate which is scribed with a knife at 35 1 1 C for 500 hours, and the width of blistered paint film from the scribe line is measured. The results are evaluated as follows: Point 5: No trouble " 4: 0.5 mm > " 3: 0.5 - 1.5 mm 2: 1.5 - 2.5 mm " 1: 2.5 mm < (4) Moisture resistance The coated plate is kept under an atmosphere with a humidity of 98 + 2% and a temperature of 50 + 1"C for 1000 hours, and the blister density is then measured (cf. ASTM D714-56). The results are evaluated as follows: Point 5: No trouble " 4: Few " 3: Medium 2: 2: Medium dense 1: Dense TABLE 2 Test Example No. Ref.

Ex. 7

6 7 8 9 10 Scratch resistance 0 0 0 0 O x Bending resistance 8 9 10 9 8 4 Resistance to saline solution 5 5 5 5 5 1 Moisture resistance 5 5 5 5 5 1 WHAT WE CLAIM IS: 1. A method for the treatment of a metal surface, which comprises applying to the surface a treatment liquid comprising an emulsion and a water-soluble chromium compound containing 30 to 90% by weight of hexavalent chromium and drying the resulting product, the treatment liquid containing substantially no alkali metal ions, the emulsion being the product bf the emulsion-polymerization of at least one a,ss-monoethylenically unsaturated monomer in the presence of an emulsifier consisting of a polyacrylic acid or a copolymer of acrylic acid and at least one monomer consisting of methacrylic acid, an acrylamide, a methacrylamide or a hydrophilic monomer of the formula::

wherein A is hydrogen or methyl; R is a substituted or unsubstituted alkylene having 2 to

4 carbon atoms; and X is a functional group containing at least one of oxygen, phosphorus and sulphur, or any combination thereof, and the emulsifier being used in an amount of 20 parts by weight or more (in the solid content) relative to 100 parts by weight of the a,ss- monoethylenically unsaturated monomer.
2. A method according to claim 1, wherein the mixed ratio of the emulsion and the water-soluble chromium compound is in the range of from 100:1 to 1:10 by weight (in the solid content).
3. A method according to claim 1 or 2, wherein the chromium compound contains from

40 to 60% by weight of hexavalent chromium.
4. A method according to any of claims 1 to 3, wherein the emulsifier is a polyacrylic acid.
5. A method according to any of claims 1 to 3, wherein the emulsifier is a water-soluble acrylic acid/acrylamide copolymer.
6. A method according to any of claims 1 to 3, wherein the emulsifier is a water-soluble acrylic acid/methacrylamide copolymer.
7. A method according to any of claims 1 to 3, wherein the emulsifier is a water-soluble acrylic acid/2-hydroxyethyl methacrylate copolymer.
8. A method according to any of claims 1 to 3, wherein the emulsifier is a water-soluble acrylic acid/mono-(2-hydroxyethyl methacrylate)-acid phosphate copolymer.
9. A method according to any of claims 1 to 3, wherein the emulsifier is a water-soluble acrylic acid/2-hydroxyethyl methacrylate/mono-(2-hydroxyethyl methacrylate)-acid phosphate copolymer.
10. A method according to any of claims 1 to 3, wherein the emulsifier is a water-soluble acrylic acid/methacrylic acid copolymer.
11. A method according to any of claims 1 to 10, wherein the treatment liquid comprises the emulsion and the water-soluble chromium compound and a water-insoluble "white carbon", said "white carbon" being a material selected from silicic acid anhydrides and silicic acid hydrates.
12. A method according to claim 11, wherein the water-insoluble white carbon is incorporated in the emulsion in the ratio of white carbon to emulsion of 10 1 to 1:10 by weight (in solid content).
13. A method according to claim 11 or 12, wherein the water-insoluble white carbon consists of primary particles of 0.1 to 3 11 in particle size which are mostly present in the form of primary particles without aggregation in the treatment liquid, or the primary particles having large aggregation properties which are present in the form of aggregated particles of 0.1 to 3 F in particle size in the treatment liquid.
14. A method according to any of claims 1 to 13, wherein the drying is carried out at a temperature of the metal plate not higher than 1200C.
15. A method for the treatment of a metal surface according to claim 1, substantially as herein described with reference to any of the specific examples.
16. Metal surfaces treated by a method as claimed in any of claims 1 to 15.
17. Metal surfaces as claimed in claim 17 and subsequently provided with at least one paint and/or coating film.