WO1998051416A1

WO1998051416A1 - Process for phosphating a substrate surface and product therefrom

Info

Publication number: WO1998051416A1
Application number: PCT/US1998/009215
Authority: WO
Inventors: Kenichi Fukuya; Ryuji Kojima; Eiji Hirai
Original assignee: Henkel Corporation
Priority date: 1997-05-14
Filing date: 1998-05-14
Publication date: 1998-11-19
Also published as: JPH10315137A

Abstract

An adherent coating that contains phosphate anions and is predominantly barbosalite with an approximate chemical formula of Fe(III)2Fe(PO4)2(OH)2 is formed on a substrate surface by vigorous physical impingement of a finely divided solid material that is predominantly barbosalite onto the substrate surface that is to be coated. The required barbosalite may be made by the hydrothermal treatment of a solid that is predominantly ferric phosphate. This solid advantageously may be the sludge from a conventional phosphate conversion coating process and may contain zinc, nickel, sodium, and nitrate ions in addition to its predominant content of ferric phosphate. The substrate need not be cleaned before contacting it with the solid phosphate particulate in a process according to this invention, as would be required to obtain good results in many conventional chemical phosphating processes, because the impinging action of the solid phosphate particulate polishes any soil away form the substrate surface.

Description

PROCESS FOR PHOSPHATING A SUBSTRATE SURFACE AND PRODUCT

THEREFROM

FIELD OF THE INVENTION

This invention pertains to a process for treating a substrate surface, which may be metallic or non-metallic, to form thereon by physical or combined physical and chemical means a phosphate coating that imparts superior coating adherence and corrosion resistance to the phosphate coated surface, and to articles of manufacture that include a surface coated by such a process RELATED ART

Conventionally, when the surface of a metal or nonmetal is being phosphatized, foreign matter such as fats and oils, rust, and contaminants was removed from said sur- face by means such as alkaline cleaning, acid cleaning, neutralization, and water washing, and then the clean surface was coated with a phosphate by means such as immersion and/or electrodeposition Thus, the process involved two steps pre-treatment and phosphatization However, the removal of foreign matter such as fats and oils, rust, and contaminants, and treatment with a phosphate was not usually conducted simultane- ously in a single step conventionally, and the pre-treatment process usually could not be omitted, in order to achieve rapid and simple treatment, while still obtaining satisfactory results

Furthermore, the surface of a metal or nonmetal substrate previously was sometimes polished by blowing a polishing agent such as silica, silicon carbide, alumina, pig iron, or steel onto the surface at high pressure in order to remove foreign matter such as fats and oils, rust, and contaminants, and create an appropriate surface as a coating base A substrate treated in this manner may be phosphated without further treatment However, immediately after polishing, the pure metal or nonmetal itself of the substrate is exposed Although there are no problems associated with coating a recently polished substrate, if it is allowed to stand for a long period of time after polishing, it may rust or otherwise spontaneously change by chemical interaction with the environment, so that if the substrate is coated after being allowed to stand after polishing for a long period of time, the coating adherence and corrosion resistance imparted by the phosphate coating formed often are lower than desirable Thus, there were practical problems associated with the use of metals and nonmetals whose surface had been treated only with a polishing agent PROBLEMS TO BE SOLVED BY THE INVENTION

This invention was developed to solve the aforementioned problems associated with the prior art, and aims to provide a process for treating the surface of a metal or nonmetal in which the removal of foreign matter such as fats and oils, rust, and contam- inants, and treatment with a phosphate are conducted simultaneously in a single step, omitting any separate pre-treatment process to achieve rapid and simple treatment This invention also provides a metal or nonmetal article whose surface has been treated in the aforementioned manner Another concurrent or alternative objective is to reduce environmental pollution associated with formation of phosphate coatings SUMMARY OF THE INVENTION

As a result of earnest investigation into a means to solve the aforementioned problems associated with the prior art, the inventors discovered that when the surface of a metal or nonmetal is polished by physical means such as dry blasting, wet blasting, abrading, and electrostatic coating using a solid phosphate, the phosphate itself be- comes embedded in the material and adheres strongly, thus coating said surface and forming a film In other words, by such physical means, the surface of the metal or non- metal is polished by the phosphate while simultaneously being coated by the phosphate that forms a film Furthermore, the inventors determined that during the stage in which the substrate is coated by the phosphate film, the coating process was facilitated by em- ploying physical means rather than the conventional phosphatization process, and perfected this invention

The inventors also determined that barbosalite, which is a crystalline basic iron phosphate with the approximate chemical formula Fe(lll)₂Fe(ll)(P0₄)₂(OH)₂, is particularly desirable as the solid phosphate to be used in this invention, and that when barbosalite that has been synthesized by hydrothermal reaction treatment of the sludge generated during the phosphatization process is used, the sludge is recycled, thereby ameliorating environmental problems from industrial waste

In other words, this invention provides a process for treating the surface of a metal or nonmetal that is characterized by the fact that the surface of the metal or non- metal is physically polished using a solid phosphate, while a film is simultaneously formed on said surface by coating said surface with the aforementioned phosphate

In addition, it is particularly desirable with respect to this invention that the aforementioned physical means of polishing is dry blasting, and that the aforementioned phosphate is barbosalite Furthermore, this invention provides a surface-treated metal or nonmetal that is characterized by the fact that its surface has been coated with a film of a phosphate, preferably barbosalite, by at least partially physical means. DETAILED DESCRIPTION OF THE INVENTION

The metal or nonmetal that is the substrate of this invention is not narrowly limited; the invention is applicable to a wide range of materials as long as they can be polished in the manner described. For example, with respect to metals, this invention is advantageous in treating materials such as stainless steel, titanium, titanium alloys, copper, and copper alloys, for which a chemical conversion treatment, such as phosphatization and chromating, that provides a film coating is difficult to achieve. In addition, nonmetals such as plastics cannot undergo a chemical conversion treatment, so that the use of this invention is particularly desirable for these substrates, for which there are fewer other options for improving coating adherence. This invention can also be applied to metals for which chemical conversion treatment is possible, such as iron and steel, aluminum, aluminum alloys, magnesium, magnesium alloys, zinc, and zinc alloys. In this invention, if the surface of a metal or nonmetal is treated by physical means using a phosphate, the surface of said metal or nonmetal is polished while simultaneously being coated with the phosphate, forming a film.

Physical means suitable to be used in this invention for achieving contact with and coating of the substrate by the solid phosphate used include dry blasting, wet blasting, abrading, or electrostatic coating; dry blasting is particularly preferable.

In dry blasting, a polishing device with a spray nozzle is used. A polishing agent (a phosphate) is sprayed from the nozzle of the polishing device to blast the substrate, thereby surface-treating the substrate. Efficient spraying requires appropriate adjustment of the spraying distance, spraying angle, spraying pressure, polishing agent and air pressure. The spraying distance is also affected by the specific gravity of the polishing agent; in this invention, the spraying distance between the nozzle outlet and the substrate is preferred to be 100 to 120 millimeters (hereinafter usually abbreviated as "mm") and the spraying pressure is independently preferred to be 4 to 5 kilograms per square centimeter (hereinafter usually abbreviated as "kg/cm²"). A spraying angle of 30 to 60 degrees is generally preferred, but values outside this range can also be used.

The mixing ratio of air and the polishing agent is affected by the roughness and weight of the polishing agent as well as by air pressure; in this invention, the mixing ratio was set at approximately 0.5. Polishing devices that fulfill these conditions are conven- tional. In the above, a phosphate is used as the polishing agent, but the polishing agent also functions as a coating material.

While there are no narrow limitations with respect to the phosphate to be used in this invention, an isomorphic phosphate is preferably used, and barbosalite is particu- larly desirable. There are no narrow limitations with respect to the purity of the barbosalite to be used. For example, a reagent grade of barbosalite can be used, and barbosalite synthesized from the phosphate sludge, or other ferric phosphate-containing by-products, produced by generation of household electricity, processes of manufacturing and cold working iron and steel, automobile factories and the like, can also be used. In general, the barbosalite that is used preferably, primarily for reasons of economy, is synthesized from the aforementioned sludge by employing a hydrothermal reaction. This method is described in detail in Japanese Laid-Open Patent Application Hei] 5-320938 and Japanese Laid-Open Patent Application Hei] 8-53771 , so that only a brief explanation will be given here.

Phosphate film is widely used as a coating base or in forming metals such as iron and steel, and through chemical conversion coating, a sludge in which the primary component is Fe(lll) phosphate and which has a composition such as that indicated in Table 1 precipitates from the liquid phosphating composition for chemical conversion coating.

The precipitated sludge is currently being disposed of for the most part as industrial waste. By applying heat and pressure to the sludge in a sealed container in the presence of water but in the absence of metallic iron (for example, by treating a 20 % by weight suspension of the sludge for 6 hours at 180 °C), most of the sludge is converted to a water-insoluble, green-blue, barbosalite-containing solid with the composition also indicated in Table 1 , in which the oxidation state of part of the iron is reduced. (The quantity of Fe indicated in Table 1 is the sum of the quantities of Fe(ll) and Fe(lll).) The product is then washed in water, filtered, and dried, and is used as the polishing agent in this invention. In this hydrothermal reduction in the absence of added metallic iron, three Fe(lll) phosphate molecules, which contain three iron atoms, are required to form each molecule of barbosalite, which, as indicated by its chemical formula given above, also contains three iron atoms. By adding metallic iron and/or steel during the reaction in sufficient quantity to provide one atom of elemental iron for each two molecules of ferric phosphate in the sludge, the yield of crude barbosalite suitable for use in this invention from a given quantity of sludge can be increased.

The barbosalite obtained in the manner described above for use in this invention is in the form of spherical granules with a diameter of approximately 10 micrometres (a unit hereinafter usually abbreviated as "μm"). Although the hardness of the product obtained in this manner is uncertain because it is changed when melted, whether in an inert or a reducing atmosphere, it is harder than stainless steel plates, so that it is ideal for use as a polishing agent and conforms approximately in size to Japanese Industrial Standard (hereinafter usually abbreviated as "JIS") R6001 grit sizes 1000 or 1200.

When a material is polished by barbosalite that is the polishing and filming agent in this invention, the surface is initially cleaned and finely scratched. The size of the scratches is approximately 3 μm wide and 20 μm deep, and the coating adherence improves as a result of the anchoring effect of these polishing scratches, because the part of the coating formed in them is continuous with the part of the coating that covers and conforms in shape to the entire surface being coated.

In addition, when a material is polished by barbosalite that is the polishing and filming agent in this invention, the barbosalite itself becomes embedded in the material and adheres so strongly that it cannot be released, even by pressing ordinary adhesive tape against it and then peeling off the tape. The quantity of barbosalite adhered varies depending on the polishing conditions, but it is preferable for the mass per unit area of phosphorus in the adherent barbosalite to be in a range from 5 to 100 milligrams of phosphorus per square meter of the surface covered (a unit hereinafter usually abbreviated as "mg/m²"), or more preferably to be in a range from 10 to 50 mg/m² Outside of these ranges, the coating adherence and corrosion resistance are normally less than those of a conventionally conversion coated phosphate film As shown in Table 2, barbosalite has superior acid resistance and alkali resistance, because, although not shown in Table 2, barbosalite is also more resistant to strong acids, this film can protect the surface of the substrate from corrosion, so the corrosion resistance is improved as well

Table 2 STABILITY OF BARBOSALITE AND PHOSPHATE SLUDGE AT VARIOUS PH VALUES

Abbreviations for Table 2 "Brbslt " means "Barbosalite", "Subst " means "substantial"

The effect of this invention is explained in further detail below with the use of working examples In these examples, the surface roughness, coating adherence, sec- ιo ondary adherence, and corrosion resistance were evaluated as follows Surface roughness was measured by a direct surface roughness measuring device (from Tokyo Precision Instruments) Coating adherence was evaluated by the cellophane tape releasing method according to the JIS K5400 visual substrate test The materials were rated on a scale of 1 to 10, and the larger the number, the better the coating adherence Secon- 15 dary adherence was evaluated by the cellophane tape releasing method according to the JIS K5400 visual substrate test after the coated plate had been immersed in boiling water for 60 minutes The materials were rated on a scale of 1 to 10, and the larger the number, the better the secondary adherence Corrosion resistance was evaluated by 60 days of the JIS Z2371 salt water spray test, by adding a cross cut after immersing the 20 coated plate in boiling water for 60 minutes The evaluation standards were as follows

OO absolutely no rust

O hardly any rust

Δ some rust

X much rust CONVERSION OF PHOSPHATING SLUDGE TO BARBOSALITE

A volume of 100 liters of water was added to a mass of 100 kilograms (hereinafter usually abbreviated as "kg") of a phosphate sludge, with a water content of 60 % by weight, that had been collected from the zinc phosphate conversion coating tank of an automobile body pre-painting treatment line. The solids content of this sludge was analyzed as 52.7 % of P0₄^, 24.6 % of Fe, 3.1 % of Zn, 0.23 % of Ni, 2.4 % of Na, and 2.5 % of N0₃ ^~. The mixture of this sludge and water was placed in a steel plate- lined 200 liter capacity autoclave and subjected to hydrothermal reaction treatment for 6 hours at 180 °C. After cooling and depressurizing, the autoclave was opened, the synthesized solid barbosalite separated from the liquid content of the autoclave, and then was washed three times with 100 liters of water each time, air-dried, and then dried at 105 °C. A yield of 26 kg of crude barbosalite, which was analyzed to contain 50.5 % of P0₄ ^3", 28.4 % of Fe, 7.6 % of Zn, 0.77 % of Ni, 0.59 % of Na, and 0.08 % of N0₃ ^~, was obtained. This polishing and filming agent was used as the solid phosphate in the processing described below.

PROCESS CONDITIONS FOR ALL WORKING EXAMPLES AND COMPARISON EXAMPLES

The substrate specified below for each instance was treated by using a polishing device with the polishing and filming agent described in the immediately preceding paragraph, for working examples, or grit size 220 alumina, for comparison examples, at a fluid to polishing agent mixing ratio of 0.5, a spraying pressure of 4.5 kg/cm², spraying distance of 100 mm, spraying angle of 60 degrees, and polishing time of 1 minute per square decimeter. The polishing device used was a Model 3LD Pneuma-Blaster manufactured by Fuji Seisakusho (Ltd.). Some of the substrates as thus prepared were subjected to physical testing. Others of the substrates as thus prepared were, within a time interval of 2 to 3 hours after the polishing treatment was completed, further spray-coated with Aery #150 White Coating manufactured by Yuukousha Ltd. to produce a coating that was 20 to 30 μm thick. The plate was then baked for 20 minutes at 150 °C. The treated substrate obtained in this manner was then evaluated with respect to coating adherence, secondary adherence, and corrosion resistance. Still others of the substrates as polished were allowed to stand indoors for one month after polishing, and then coated with the Aery #150 White Coating exactly as described above, in order to test for any deterioration of the protective value of the coating over time after polishing.

The example numbers and substrates used in them are shown in Table 3. The results of physical testing of the substrates as polished are shown in Table 4, and the results of physical testing of the substrates as further coated are shown in Table 5. Table 3 CORRELATION BETWEEN EXAMPLE NUMBERS AND SUBSTRATES USED

Additional Abbreviation for Table ^L-

'n a " means "not applicable" Table 5: PHYSICAL PROPERTIES AFTER SHORT AND LONG DELAYED PAINTING AFTER POLISHING

Judging from the evaluation results of Working Examples 1 through 5 and Comparison Examples 1 through 5 above, the following statements can be made:

(1) With respect to all substrates, there was no difference in the initial paint adherence when the substrate had been coated within a short time after polishing. In two of the comparison examples, there was a small diminution of initial paint adherence when there was a one month interval between polishing. The remaining comparison examples and all of the working examples showed just as good initial paint adhesion even when the paint was applied after one month rather than within a few hours after polishing.

10 (2) For the comparison examples, the secondary adherence was much more strongly affected by the delay in applying paint; all of the comparison examples showed inferior secondary adherence when the paint was applied one month after polishing. In contrast, for all of the working examples according to the invention and for the comparison examples in which the substrates were painted within a few hours after

15 polishing, secondary adherence received the highest rating, just as initial paint adherence did. Thus, using barbosalite as the polishing and film forming material produces a conversion coating to which paint can adhere well even after the conversion coated surface is thoroughly dry, so that the secondary adherence and corrosion resistance were better than when a non-phosphate-containing solid was used as the polishing material. BENEFIT OF THE INVENTION

This invention allows the removal of foreign matter such as fats and oils, rust, and contaminants and treatment with a phosphate to be conducted simultaneously in a single step, omitting the pre-treatment process in order to allow rapid and simple treatment compared to the conventional treatment method. In addition, in the step of coating the substrate with a phosphate film, the physical method allows for easier coating than the conventional phosphatization process. Furthermore, when barbosalite that has been synthesized from the sludge generated as a waste product of the phosphatization process is used as the phosphate in this invention, the invention is useful as a means of recycling industrial waste.

Claims

1. A process for forming a phosphate ions-containing coating on a substrate surface by physically contacting said substrate surface with a solid, phosphate ions- containing material that at least partially adheres to the substrate surface after said contacting.

2. A process according to claim 1 , wherein the contacting is accomplished by dry blasting, wet blasting, electrostatic coating, or abrading.

3. A process according to claim 1 or 2 wherein the solid, phosphate ions-containing material is predominantly barbosalite.

4. A process according to claim 3, wherein the solid, phosphate ions-containing material has been made by hydrothermal treatment of a solid that is predominantly ferric phosphate.

5. A process according to any of claims 1 , 2, or 4, wherein the contacting is accomplished by dry blasting.

6. A process according to claim 3, wherein the contacting is accomplished by dry blasting.

7. An article of manufacture comprising a substrate having at least a portion of its surface covered with a solid, phosphate ions-containing coating that is constituted predominantly of barbosalite.