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Method of improving the performance of organic coatings for corrosion resistance

a technology of organic coatings and corrosion resistance, applied in the field of polymer resins, can solve the problems of weak bonding between the paint and the steel substrate, and achieve the effect of eliminating the chromation step and simplifying the process

Inactive Publication Date: 2005-08-25
POHANG IRON & STEEL CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0010] The instant invention describes a method of improving the performance of organic conversion coatings for metals by modifying the compositions of the organic resins by adding an organosulfur compounds. The improved performance of the modified resin compositions can protect metal substrates from corrosion without chromation. Several possible mechanisms may operate to enhance the properties of the coating:
[0011] i) The sulfur-containing surfactants disclosed in the instant invention chemisorb on the surfaces of the metallic substrates, and give rise to improved adhesion of the organic resins on the substrates.
[0012] ii) The surface free energies of the metallic substrates are reduced and, therefore, render the substrates less susceptible to corrosion.
[0013] iii) The small organosulfur compounds as compared to the molecules of the resins can readily fill the pores of polymer matrix, thereby increasing the barrier effect for corrosion protection.
[0017] A distinguishing feature of the instant invention is the simplicity in coating a metal surface with the modified-resins. There are no needs to add additional steps or equipment. A mixture of the resin and organosulfur compounds can be directly applied to a metal surface by any means that is usually employed for the original resin. Also, there are no needs to modify the procedures or equipment involved in curing the coated surface. In fact, the process as disclosed in the instant invention simplifies the process by eliminating the chromation step.

Problems solved by technology

According to van Ooij (U.S. Pat. No. 5,455,080), this method suffers from the weak bonding between the paint and steel substrate.

Method used

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  • Method of improving the performance of organic coatings for corrosion resistance
  • Method of improving the performance of organic coatings for corrosion resistance
  • Method of improving the performance of organic coatings for corrosion resistance

Examples

Experimental program
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Effect test

example 1

[0034] A 0.1-M ODT solution was prepared in ethanol. The resin solution was prepared by mixing 99 parts of polymer solution and 1 part of inorganic hardener solution, both of which were provided by a chemical company. The ODT solution and resin solution were subsequently mixed together in the ratio of 30:70 by volume. The resultant mixture solution was applied to a test panel of 12×7.5 cm by means of a No. 5 bar coater. The panel was an electrogalvanized (EG) CRS sheet from Pohang Iron and Steel Company (POSCO). The coated panel was then cured in an oven at a temperature of 150° C. for 5 minutes. As a result, a uniform, lightly gray-colored coating was formed on the steel panel with thicknesses in the range of 1-2 μm. For comparison, another EG steel panel was coated with the aforesaid resin solution without ODT. The test panels coated with the resins with and without ODT were subjected to salt spray test (SST) by following the test procedures of ASMT B117. Also subjected to SST was...

example 2

[0036] This example illustrates the optimization of the concentration of ODT as a modifier in the resin. The coatings of ODT-modified resins were prepared in the same manner as described in Example 1, but the mixing ratio between resin solution and ODT solution (0.1M in ethanol) was varied in the range of 90:10 to 40:60 by volume.

[0037] The EG steel panels coated with the ODT-modified resins were subjected to salt spray tests.

[0038] For comparison, two other EG steel panels were also subjected to salt spray tests. One was without any treatment, and the other was coated with the unmodified resin. Still another panel was treated with chromate rinsing prior to coating it with the unmodified resin.

[0039] The results of the salt spray tests are given in Table 1. As shown, even a small amount of ODT added to the resin increased corrosion resistance considerably. As the ODT dosage was increased, the corrosion resistance was further increased. At very high dosages of ODT, the resistance ...

example 3

[0042] In this example, a 16-mercaptohexadecenoic acid (MCA, HS(CH2)15COOH) was used instead of ODT as a resin modifier. This reagent was different from ODT in that it was a bi-functional sulfur-containing compound. A 0.025 M MCA solution was prepared with ethanol and then mixed with the resin solution at a ratio of 1:1 by volume, which was not necessarily the optimal mixing ratio. At this ratio, the resin-organosulfur mixture contained 0.0125 M MCA. The modified resin was used to coat an EG steel panel with a No. 5 bar coater. The coated panel was cured at 150° C. for 5 minutes. Under this condition, the coating thickness would be approximately 1-2 μm. The EG steel panel coated with the modified resin was subjected to salt spray test. For comparison, salt spray tests were also conducted on an uncoated EG steel panel and an EG steel panel that had been coated with the unmodified resin.

[0043] After 144 hours of salt spray tests, the untreated EG steel panel showed red rusts, while t...

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Abstract

This invention pertains to a method of modifying polymeric coating materials by adding organosulfur compounds, so that the metallic substrates coated with the modified polymeric materials become more resistant to corrosion. The organosufur compounds are alkane thiols with a general formula R(CH2)nSH, where R represents H, NH2, HOOC, and HO groups and n is in the range of 10 to 21. The reagents are designed to increase the adhesion between the polymeric coating materials and the metallic substrates, which may be conducive to increased corrosion resistance.

Description

FIELD OF THE INVENTION [0001] This invention applies to polymeric resins that are used to coat metallic substrates for corrosion protection, and to a method of modifying the resins with organosulfur compounds for improved corrosion resistance. In particular, the invention pertains to preparing a homogeneous mixture of the resin and the organosulfur compound. BACKGROUND OF THE INVENTION [0002] Metals that are exposed to the ambient for prolonged periods of time require coatings to protect the exposed surface from corrosion. Steel producers use various organic and inorganic coatings to protect cold-rolled steel (CRS) sheets from corrosion during shipment and storage. The common practice in providing temporary corrosion protection for steel sheets is to apply a conversion coating. Traditionally, conversion coatings are produced by exposing untreated or galvanized CRS sheets to phosphoric acid or chromic acid treatment or both. The latter provides the most effective corrosion protection...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): B05D7/24B05D1/28C09D5/08C09D181/00
CPCC09D5/086C09D5/08C09D181/00
Inventor KIM, HYUNG-JOONZHANG, JINMINGGANDOUR, RICHARD D.YOON, ROE-HOAN
Owner POHANG IRON & STEEL CO LTD
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