IMPROVED METHOD FOR PURGING PAINT CIRCUITS AND WATERBORNE PURGE CLEANER

Abstract

Described herein is a method for purging paint circuits coated with a non-cured paint with improved cleaning efficiency and a reduced COD (Chemical Oxygen Demand) in the wastewater, where a paint circuit is brought into contact with a waterborne purge cleaner solution including at least one glycolether and which additionally includes at least one water-soluble amine having at least 7 carbon atoms. Also described herein is a waterborne purge cleaner solution with improved cleaning efficiency and reduced VOC (Volatile Organic Compound) content as well as a concentrate for producing the purge cleaner solution.

Claims

1. A method for purging a paint circuit coated with a non-cured paint, comprising bringing the paint circuit into contact with a waterborne purge cleaner solution comprising at least one glycolether characterized in that it additionally comprises at least one water-soluble amine having at least 7 carbon atoms.

2. The method according to claim 1 characterized in that the at least one glycolether comprises hexylglycol and/or hexyldiglycol.

3. The method according to claim 1 characterized in that the at least one water-soluble amine comprises at least one amine having 7 to 15 carbon atoms.

4. The method according to claim 1 characterized in that the purge cleaner solution comprises a) 0.05 to 0.50% (w/w) of at least one water-soluble amine having 7 to 15 carbon atoms calculated as N-methyldiisopropanolamine, b) 0.3 to 1.0% (w/w) of hexylglycol and c) 0.3 to 1.0% (w/w) of hexyldiglycol.

5. The method according to claim 1 characterized in that the at least one amine comprises at least one amine having a conjugated acid with a pKa of at least 8.0.

6. The method according to claim 1 characterized in that the at least one amine comprises at least one tertiary amine having at least one hydroxyalkyl group.

7. The method according to claim 6 characterized in that the at least one tertiary amine has one to three hydroxyalkyl groups.

8. The method according to claim 7 characterized in that the at least one amine comprises at least one amine selected from the group consisting of N-methyldiisopropanolamine, N-octyl di ethanol amine, triisopropanolamine and N,N-dibutylethanolamine.

9. The method according to claim 1 characterized in that the purge cleaner solution does not contain any surfactants.

10. The method according to claim 1 characterized in that the purge cleaner solution does not contain any organic solvents selected from the group consisting of benzylalcohol and butylglycol.

11. A waterborne purge cleaner solution comprising at least one glycolether characterized in that it additionally comprises at least one water-soluble amine having at least 7 carbon atoms.

12. A concentrate for producing the waterborne purge cleaner solution according to claim 11 characterized in that the purge cleaner solution is obtainable by diluting the concentrate with water, and adjusting the pH value, if required, with at least one acid or base.

13. The concentrate according to claim 12 characterized in that it comprises a) 1 to 40% (w/w) of at least one amine having 7 to 15 carbon atoms calculated as N-methyldiisopropanolamine b) 40 to 60% (w/w) of hexylglycol and c) 40 to 60% (w/w) of hexyldiglycol.

14. The method according to claim 1 characterized in that the at least one glycolether comprises hexyldiglycol.

15. The method according to claim 1 characterized in that the at least one water-soluble amine comprises at least one amine having 7 to 12 carbon atoms.

16. The method according to claim 1 characterized in that the at least one amine comprises at least one amine having a conjugated acid with a pKa of at least 8.3.

17. The method according to claim 6 characterized in that the at least one tertiary amine has one to three hydroxyalkyl groups selected from the group consisting of 2-hydroxyethyl and 2-hydroxypropyl and zero to two alkyl groups, with the proviso that the sum of the hydroxyalkyl groups and the alkyl groups is three.

18. The method according to claim 7 characterized in that the at least one amine comprises at least one amine selected from the group consisting of N-methyldiisopropanolamine, triisopropanolamine and N,N-dibutylethanolamine.

19. The method according to claim 1 characterized in that the purge cleaner solution does not contain any organic solvents selected from the group consisting of benzylalcohol and glycolethers having 6 to 10 carbon atoms except hexylglycol and hexyldiglycol.

20. The concentrate for producing the waterborne purge cleaner solution according to claim 11 characterized in that the purge cleaner solution is obtainable by diluting the concentrate with water by 5:1,000 to 30:1,000 and adjusting the pH value, if required, with at least one acid or base.

Description

EXAMPLES

Test 1: Quantitative 9 Drops Test on Wet Paint 5 Min. at RT:

[0056] A waterborne paint layer with a thickness between 40 to 60 μm was extended on a glass panel (200×200 mm). The layer was then partially dried for 4 minutes at room temperature (RT) and placed at a slope of 45°. At a rate of 1 drop per second and from a height of 12 cm, 9 drops of the purge cleaner solution to be tested were added onto the panel.

[0057] After 5 minutes at room temperature, the width of the paint-free spot where the drops had hit the panel (“open head”), in cm was measured. The larger the width, the better the stripping effect, i.e. the cleaning efficiency, of the tested solution.

Test 2: Spray on Wet Paint Test 10 Min. at RT:

[0058] A waterborne paint layer with a thickness of approx. 60 μm was extended on a glass panel (100×200 mm). The layer was then partially dried for 4 minutes at room temperature and placed at a slope of 45°. From 30 cm distance, 10 ml of the purge cleaner solution to be tested were sprayed on the panel.

[0059] After 10 minutes at room temperature, the stripping effect, i.e. the cleaning efficiency, was evaluated according to the following categories: Bad (−), regular (+), good (++) and very good (+++).

Test 3: Quantitative N Drops Test on Dried Paint:

[0060] A waterborne paint layer with a thickness between 40 to 60 μm was extended on a glass panel (200×200 mm). The layer was then dried for 24 h at room temperature and placed at a slope of 45°. At a rate of 1 drop per second and from a height of 12 cm, drops of the purge cleaner solution to be tested were added onto the panel until the layer was opened, i.e. until there was a paint-free spot where the drops had hit the panel.

[0061] The number of drops (n) added was determined. The lower the number, the better the stripping effect, i.e. the cleaning efficiency, of the tested solution.

Purge Cleaner Solutions and Test Results:

[0062] For every amine A, B and C (see below), a mixture of 95 wt.-% of hexyldiglycol and 5 wt.-% of amine was prepared.

[0063] Amine A: Triethanolamine (6 carbon atoms) (comparative example)

[0064] Amine B: N-methyldiisopropanolamine) (7 carbon atoms) (inventive example)

[0065] Amine C: N,N-dibutylethanolamine (10 carbon atoms) (inventive example)

[0066] The mixtures were diluted with deionized water to 2 wt.-%.

[0067] The Quantitative 9 Drops Test was performed as described above (Test 1) on the wet paint “Füller Red” (Hemmelrath, Germany).

[0068] The results are summarized in the following table wherein the cleaning efficiency was calculated compared to the one with triethanolamine (amine A) which was considered as reference.

TABLE-US-00001 Amine Width of open head in cm Cleaning efficiency in % A 1.45 100 B 1.51 104 C 1.48 102

[0069] The Spray Test was conducted as described above (Test 2) on the wet paint “Füller Red” (Hemmelrath, Germany) as well and showed the following results:

TABLE-US-00002 Amine Cleaning efficiency A + B + to ++ C ++

[0070] For amines A and B, the Quantitative N Drops Test was performed as described above (Test 3) on the dried paint “Füller Red” (Hemmelrath, Germany). The results are summarized in the following table. The cleaning efficiency was calculated compared to the one with triethanolamine (amine A) as a reference.

TABLE-US-00003 Amine Number of drops (n) Cleaning efficiency in % A 20 100 B 9 222

[0071] Surprisingly, all tests revealed an improved cleaning efficiency of the inventive purge cleaner solutions containing a water-soluble amine with at least 7 carbon atoms (amines B and C) compared to a purge cleaner solution which contains an amine having 6 carbon atoms (amine A).