GB2112409A

GB2112409A - Phenolic compounds and their use in metal finishing processes

Info

Publication number: GB2112409A
Application number: GB08138529A
Authority: GB
Inventors: Andreas Lindert
Original assignee: Pyrene Chemical Services Ltd
Current assignee: Pyrene Chemical Services Ltd
Priority date: 1981-12-22
Filing date: 1981-12-22
Publication date: 1983-07-20
Also published as: GB2112409B

Abstract

Solutions that can be used for post-treating conversion coated metal surfaces are based on polymers formed of recurring groups of the formula <IMAGE> wherein each X is hydrogen or CRR1OH and each of R and R1 is hydrogen or an aliphatic or aromatic organic moiety having 1 to 12 carbon atoms, or a salt of such a polymer.

Description

SPECIFICATION Phenolic compounds and their use in metal finishing processes This invention relates to the post-treatment of conversion coated metal surfaces, for instance to improve their corrosion resistance and paint adhesion characteristics, and in particular to phenolic compounds suitable for use in such processes.

It is well known to form conversion coatings on metals, for instance by application of an acidic solution containing phosphate ions to form a corrosion resistant, non-reactive, phosphate complex coating. It is also known that the corrosion resistance of conversion coatings can be enhanced by posttreatment of the coating, generally after an aqueous rinse. The traditional post-treatment has involved application of a dilute aqueous acidic solution containing hexavalent chromium. Although this gives effective results the use of hexavalent chromium can result in environmental difficulties. Accordingly efforts have been made in recent years to deveiop effective and simple to operate post-treatments that do not involve the use of hexavalent chromium.

In the invention a conversion coating is formed on a metal surface and is post-treated by contacting the surface with a compound which is a polymer formed of recurring groups of the formula

or a metal salt thereof, wherein each X is H or CRR10H and each of R and R1 is hydrogen or an aliphatic or aromatic organic moiety having from 1 to 12 carbon atoms. It will be appreciated that the groups X may be the same or different and the groups R and R1 may be the same or different.

The compounds used in the invention can be regarded as poly-4-vinyl phenols and derivatives thereof. The polymer is preferably formed substantially only of the said groups and thus should be a homopolymer, although it may contain minor amounts of non-interfering other groups. The polymer will generally contain from 5 to 100 of the recurring groups defined above. The terminal end groups of the polymer can be hydrogen or other moiety depending upon the particular initiator employed in polymerising the polymer.

It is preferred that at least one group X is of the formula CRR,OH and such compounds can be made by reacting poly-4-vinyl phenol with a suitable aldehyde or ketone. A preferred compound is a poly-4-vinyl phenolformaldehyde derivative, wherein X is CH2OH, and this can be made by dissolving poly-4-vinyl phenol in ethanol at 70% solids, neutralising 20% of the phenolic moieties with sodium hydroxide, then diluting the solution with water and reacting with formaldehyde for six hours at 600 C.

Formaldehyde and poly-4-vinyl phenol can be reacted in a 1:1 or other molar ratio although at ratios above 1:1 the reaction solution becomes so viscous as to react with difficulty.

The compounds are soluble in organic solvents, for example ethanol, and so can be provided as solutions in such solvents. Preferably solutions are aqueous and the compounds can be made water soluble by neutralising 1 5 to 100% of the phenolic groups, for instance with a metal hydroxide such as sodium or potassium hydroxide, to provide a water soluble metal salt. Any such solution will normally have a pH of at least about 8, in order to avoid precipitation of the compound from the solution, and generally the pH should be between 8 and 12.

The solutions can initially be formulated as concentrates having a concentration up to about 30% by weight, typically 5 to 30% by weight. The solutions that are used for post-treatment are normally much more dilute, typically having a concentration of 0.01 to 5% by weight, preferably 0.1 to 1% by weight.

The invention includes not only methods of post-treatment but also the novel solutions, especially those of compounds in which at least one group X is CRR10H.

The metals that are treated by the invention can include any of the metals traditionally treated with conversion coatings, for instance zinc, iron and aluminium, including alloys thereof such as coldrolled, ground, pickled or hot rolled steel and galvanised steel.

Before formation of the conversion coating the metal is generally initially cleaned by a chemical or physical process to remove grease and dirt from the surface and it may then be rinsed. The conversion coating may then be formed in conventional manner.

Processes and solutions for forming conversion coatings on metal surfaces are well known and have been described, for example, in Metal Handbook, Volume li, 8th Edition, pages 529-547 of the American Society for Metals and in Metal Finishing Guidebook and Directory, pages 590-603 (1972). Although the coating may be formed by application of chromate or other conversion coating compositions preferably the coating is of a phosphate formed by application of an acidic phosphate solution. Examples of conversion coating solutions include solutions comprising iron phosphate, magnesium phosphate, zinc phosphate, and zinc phosphate modified with calcium or magnesium ions.

The conversion coated surface may then be rinsed with water and the post-treatment solution is then generally applied immediately.

Application of the post-treatment solution can be carried out by any conventional method. For example, the post-treatment solution can be applied by spray coating, roller coating, or dipping. The temperature of the solution applied can vary over a wide range, but is preferably from 21 OC to 71 OC.

After application of the post-treatment solution to the metal surface, the surface can optionally be rinsed, although good results can be obtained without rinsing after post-treatment. For some end uses, however, rinsing may be preferred.

The post-treated metal surface is generally then dried. Drying can be carried out by, for example, circulating air or oven drying. While room temperature drying can be employed, it istpreferable to use elevated temperatures to decrease the amount of drying time required.

After drying, the conversion coated and post-treated metal surface is then ready for painting. The paint may be a conventional paint or other protective coating and can be applied by conventional techniques, such as brush painting, spray painting, electrostatic coating, dip, roller coating, as well as electro-coating.

As a result of the post-treatment step of the present invention, the conversion coated surface has improved paint adhesion and corrosion resistance characteristics.

In the following examples several panels were treated and tested. The following procedures were used for each panel.

Each panel comprised cold rolled steel and was first cleaned with a strong alkaline cleaner followed by thorough rinsing with hot water. An iron phosphate conversion coating (Bonderite *1000 made by Parker Co., Bonderite being a trade mark) was applied to the clean panel surface at 60 to 71 OC by spray application to form a conversion coating thereon, followed by rinsing with cold water.

Then a post-treatment solution identified below was immediately applied to the conversion coated surface at 60 to 71 OC. The treated panel was then rinsed with deionised water and baked in a 1 700C oven for 5 minutes. Each panel was then painted with a thermosetting baking enamel.

Salt spray corrosion resistance was measured in accordance with ASTMB1 17-61. The paint was scribed from corner to corner with an "X", using a sharp knife scribing all the way to the bare metal.

Then the panel was placed in a salt spray cabinet containing a 5% aerated sodium chloride solution at 350C. Each panel was placed above the solution and the salt solution was continuously misted into the air by a spray nozzle. The panels were tested in salt spray for 504 hours. As is set forth below, each panel was rated in terms of the amount of paint loss from the scribe in 1/1 6 inch increments (N for no loss of paint at any point). The numbers represent the general range of the creepage from the scribe along its length in inches. Thus, 0--1 represents creepage varied from 0 to 1/16 inches (1.6 mm).

Humidity corrsion resistance was measured in accordance with the procedure of ASTM 224764T. As set forth below, the panels were rated in terms of the number size of blisters: from 9 for a very small size to 1 for very large. Ten represents no blisters.

Examples 504 hours salt Humidity Example Post-treatment Concentration spray resistance 1. Parcolene 60 - N 10 Chromate Control 2. Deionised Water (264 hours) Failure Failure 3. Poly-4-vinylphenol .33% N 10 formaldehyde sodium salt 20% neutralized 1:1 phenolformaldehyde ratio 4. ,, .1% N 10 5. ,, .05% N 10 6. Poly-4-vinylphenol 1% 0-1 10 in Ethanol 7. ,, .1% 0-1 10 8. ,, .05% 0-2 10 The results of the above examples show that after-treatment of a phosphatised metal surface in accordance with the present invention provides good salt spray and humidity resistance to the material, even though the post-treatment is free of hexavalent chromium. As will be observed, best results are obtained with compounds in which X is CRR,OH.

Claims

Claims

1. A process in which a conversion coating is formed on a metal surface and is post-treated by contacting the surface with a compound which is a polymer formed of recurring groups of the formula

or a salt thereof, wherein each X is H or CRR1OH and each of R and R, is hydrogen or an aliphatic or aromatic organic moiety having from 1 to 12 carbon atoms.

2. A process according to claim 1 in which the polymer is formed substantially only of the said groups and is formed from 5 to 1 00 of the said groups.

3. A process according to claim 1 or claim 2 in which at least one group X is CRR,OH.

4. A process according to claim 1 or claim 2 in which at least on group X is CH2OH.

5. A process according to any preceding claim in which the polymer is the reaction product of poly-4-vinylphenol with an aldehyde or ketone.

6. A process according to any of claims 1 to 4 in which the polymer is the reaction product of poly-4-vinylphenol and formaldehyde.

7. A process according to any preceding claim in which the polymer is applied to the conversion coating in the form of an aqueous solution of a metal salt.

8. A process according to claim 7 in which the solution has pH of from 8 to 12.

9. A process according to any of claims 1 to 6 in which the polymer is applied to the conversion coating in the form of an organic solution.

10. A process according to any of claims 7 to 9 in which the solution contains from 0.01 to 5% by weight of the polymer.

1 A composition for use or suitable for use in a process according to claim 1 and which is a solution of a polymer formed of recurring groups of the formula

or a salt thereof, wherein each group X is H or CRR,OH and each of R and R, is hydrogen or an aliphatic or aromatic organic moiety having from 1 to 12 carbon atoms.

1 2. A solution according to claim 11 in which the polymer is formed substantially only of the said groups and is formed from 5 to 100 of the said groups.

13. A solution according to claim 11 or claim 12 in which at least one group X is CRR,OH.

14. A solution according to claim 11 or claim 12 in which at least one group X is CH2OH.

1 5. A solution according to any of claims 11 to 14 in which the polymer is the reaction product of poly-4-vinylphenol with an aldehyde or ketone.

1 6. A solution according to any of claims 11 to 14 in which the polymer is the reaction product of poly-4-vinylphenol and formaldehyde.

1 7. A solution according to any of claims 11 to 1 6 which is an aqueous solution of a metal salt of the polymer.

18. A solution according to claim 17 having a pH of from 8 to 12.

19. A solution according to any of claims 11 to 16 in which the polymer is dissolved in an organic solvent.

20. A solution according to any of claims 11 to 19 containing from 0.01 to 5% by weight of the polymer.

21. A solution according to any of claims 11 to 19 and which contains from 5 to 30% by weight of the polymer.

22. A process in which a paint coating is applied over a conversion coating that has been posttreated by a process according to any of claims 1 to 10.