Improved paint circuit purging method and aqueous purge cleaner

Abstract

The present invention relates to a method for purging a paint circuit covered with uncured paint with improved cleaning efficiency and reduced COD (chemical oxygen demand) in the wastewater, in which the paint circuit is contacted with an aqueous purge cleaner solution containing at least one glycol ether and at least one water-soluble amine having at least 7 carbon atoms. The present invention also relates to an aqueous purge cleaner solution with improved cleaning efficiency and reduced VOC (volatile organic compound) content, and a concentrate for producing the purge cleaner solution.

Description

[Technical field]

[0001] The present invention relates to a method for purging a paint circuit covered with uncured paint, which method shows improved cleaning efficiency and reduced COD (Chemical Oxygen Demand) in the wastewater.Furthermore, the present invention relates to an aqueous purge cleaner solution with improved cleaning efficiency and reduced VOC (Volatile Organic Compound) content, and a concentrate for producing the purge cleaner solution. [Background technology]

[0002] In water-based painting workshops, purge cleaners, so-called paint removers, are used to clean the paint circuit, which is a closed circuit between the paint mixing chamber and the paint booth where the car body is painted manually or robotically. The paint circuit includes pumps, hoses, nozzles, tanks and tubes, the latter made for example of stainless steel or polyethylene. The purge cleaners must clean efficiently in the shortest possible time to avoid contamination when changing paint colors in the paint booth.

[0003] Purge cleaners are sold in concentrated form, i.e. as a concentrate, which is then diluted by the customer before cleaning the paint circuit, but they may also be sold in an RTU (Ready to Use) form, which does not require dilution.

[0004] Aqueous purge cleaners containing water-soluble organic solvents, such as glycol ethers, and certain amines, such as diethanolamine or triethanolamine, are known from the prior art. Summary of the Invention [Problem to be solved by the invention]

[0005] However, there remains a need to improve the cleaning efficiency while reducing the VOC content of said cleaning agents.

[0006] VOCs (volatile organic compounds) such as organic solvents must be avoided as much as possible because of their impact on health and the environment. For wastewater generated when purging the paint circuit, the COD (chemical oxygen demand), a measure of the amount of organic matter, must be as low as possible.

[0007] SUMMARY OF THE PRESENTLY PREFERRED EMBODIMENTS It is therefore an object of the present invention to provide a method for purging a paint circuit coated with uncured paint, which improves cleaning efficiency and reduces COD in the wastewater. [Means for solving the problem]

[0008] This object is solved by a method according to the invention for purging a paint circuit covered with uncured paint, in which the paint circuit is contacted with an aqueous purge cleaner solution comprising at least one glycol ether and further comprising at least one water-soluble amine having at least 7 carbon atoms. Definition: In the sense of the present invention, "aqueous purge cleaner solution" means that the corresponding purge cleaner solution, ie in RTU form, is 50% or more (w / w) water.

[0009] By "water-soluble amine" is meant that at least 1 g / l, preferably at least 100 g / l, particularly preferably at least 1,000 g / l of the corresponding amine is completely soluble in deionized water at room temperature (25° C.) and atmospheric pressure (1,013 mbar).

[0010] According to the present invention, a "VOC" or "volatile organic compound" is an organic compound having a vapour pressure of at least 0.01 kPa at 20° C., as defined by Council Decree 1999 / 13 / EC of 11 March 1999.

[0011] According to the present invention, "COD" or "Chemical Oxygen Demand" means the amount of oxygen that can be consumed by the reactions in a measured solution. It is usually expressed as the mass of oxygen consumed relative to the volume of the solution, in SI units milligrams per liter (mg / l).

[0012] "% (w / w)" means wt.-%, i.e. mass %.

[0013] Preferably, the at least one glycol ether in the aqueous purge cleaner solution comprises at least one glycol ether having an alkyl group having from 6 to 10 carbon atoms.

[0014] More preferably, the at least one glycol ether in the purge cleaner solution comprises hexyl glycol and / or hexyl diglycol, even more preferably comprises hexyl diglycol. Even more preferably, it comprises or is a mixture of hexyl glycol and hexyl diglycol. Preferably, the at least one water-soluble amine having at least 7 carbon atoms comprises at least one amine having 7 to 15 carbon atoms, more preferably an amine having 7 to 12 carbon atoms.

[0015] In the purge cleaner solution, the at least one amine preferably comprises at least one amine having a conjugate acid with a pKa of at least 8.0, preferably at least 8.3, more preferably at least 8.6. Due to their high basicity, such amines improve the cleaning efficiency of the purge cleaner, especially for dried paint. For example, the conjugate acid of N-methyldiisopropylpropanolamine (MDIPOA) has a pKa of 8.71, whereas triethanolamine (TEA) has a pKa of only 7.86, resulting in a reduced cleaning efficiency.

[0016] Preferably, the at least one amine comprises at least one tertiary amine having at least one hydroxyalkyl group, wherein the at least one tertiary amine has 1 to 3 hydroxyalkyl groups, preferably selected from the group consisting of 2-hydroxyethyl and 2-hydroxypropyl, and 0 to 2 alkyl groups, preferably selected from the group consisting of linear alkyl groups having 1 to 8 carbon atoms, with the proviso that the sum of the hydroxyalkyl groups and the alkyl groups is 3.

[0017] More preferably, the at least one amine is selected from the group consisting of N-methyldiisopropanolamine, N-octyldiethanolamine, triisopropanolamine and N,N-dibutylethanolamine (DBEOA), preferably selected from the group consisting of N-methyldiisopropanolamine, triisopropanolamine and N,N-dibutylethanolamine, more preferably comprising at least one amine comprising N-methyldiisopropanolamine.

[0018] logP of at least one amine oct / wat The value preferably ranges from -0.5 to +3.0 at a temperature of 25°C and a pH value of 10.3. The value refers to the HLB (hydrophilic-lipophilic balance) of the amine and is defined as follows:

number

[0019] where at least one amine is a non-ionized solute. The cleaning efficiency achieved with such amines is particularly high. In the case of N-methyldiisopropanolamine, logP oct / wat The value is -0.03.

[0020] The purge cleaner solution comprises at least one water-soluble amine having at least 7 carbon atoms. This is advantageous because, compared to amines with fewer carbon atoms, such as triethanolamine, the at least one amine exhibits lower surface tension and can therefore act like a surfactant. As a result, there is no need to add surfactants, such as traditional anionic, cationic, zwitterionic or nonionic surfactants, to the purge cleaner solution, and therefore the purge cleaner solution is preferably surfactant-free. Thus, the concentrate from which the purge cleaner solution can be obtained by dilution is preferably surfactant-free.

[0021] Preferably, the purge cleaner solution does not contain diethanolamine, dimethylethanolamine, or triethanolamine, and more preferably does not contain amines having less than 7 carbon atoms.

[0022] Since organic solvents, especially benzyl alcohol and butyl glycol, are considered VOCs, as well as surfactants, and contribute to high COD in wastewater, it is desirable to reduce the organic solvent content in the purge cleaner solution and corresponding concentrates.

[0023] Therefore, the purge cleaner solution preferably does not contain an organic solvent selected from the group consisting of benzyl alcohol and butyl glycol, more preferably an organic solvent selected from the group consisting of benzyl alcohol, butyl glycol and butyl diglycol, even more preferably an organic solvent selected from the group consisting of benzyl alcohol and butyl glycol having 6 to 10 carbon atoms except for hexyl glycol and hexyl diglycol, and most preferably does not contain an organic solvent except for hexyl glycol and hexyl diglycol.

[0024] When the purge cleaner solution contains at least one alcohol, it is preferred that it does not contain alcohols containing less than 5, more preferably less than 6, even more preferably less than 7 carbon atoms, since these alcohols exhibit high vapor pressure. In particular, the purge cleaner solution contains only benzyl alcohol, which has 7 carbon atoms, as the alcohol.

[0025] If the purge cleaner solution contains at least one glycol ether other than hexyl glycol and hexyl diglycol, it is preferred not to contain glycol ethers having alkyl groups with less than 5, more preferably less than 6 carbon atoms, since these glycol ethers exhibit high vapor pressures. In particular, the purge cleaner solution contains only hexyl glycol and / or hexyl diglycol.

[0026] The aqueous purge cleaner solution does not require a chelating agent to effectively purge the paint circuit, therefore the purge cleaner solution is preferably free of any chelating agents.

[0027] Furthermore, the method according to the invention does not require a post-rinsing step, for example with water, to effectively purge the paint circuit, and therefore the method preferably does not include a post-rinsing step following the step of contacting the paint circuit to be purged with a purge cleaner solution.

[0028] The present invention also relates to a solution that provides improved cleaning efficiency and reduced VOC content, namely, an aqueous purge cleaner solution in RTU form.

[0029] Preferably, the at least one glycol ether in the purge cleaner solution comprises hexyl glycol and / or hexyl diglycol, more preferably comprises hexyl diglycol. Even more preferably, it is or comprises a mixture of hexyl glycol and hexyl diglycol. Preferably, the at least one water-soluble amine having at least 7 carbon atoms is at least one amine having 7 to 15 carbon atoms, more preferably 7 to 12 carbon atoms.

[0030] According to a preferred embodiment, 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) hexyl glycol; c) 0.3 to 1.0% (w / w) hexyl diglycol; Includes.

[0031] According to a particularly preferred embodiment, 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) hexyl glycol; c) 0.3 to 1.0% (w / w) hexyl diglycol; d) 0 to 0.2% (w / w) of at least one low foaming surfactant; e) 0 to 0.4% (w / w) benzyl alcohol; f) 0-80% (w / w) of at least one other glycol ether having 6-10 carbon atoms, including butyl glycol and butyl diglycol; where the sum of the % (w / w) of all ingredients a) through f) and water equals 100% (w / w).

[0032] Further preferred embodiments of the purge cleaner solution correspond to the preferred embodiments of the method according to the invention described above.

[0033] The present invention further relates to a concentrate for producing the aqueous purge cleaner solution according to the present invention, which can be obtained by diluting the concentrate according to the present invention with water, preferably at 5:1,000 to 50:1,000 (5 to 50 g of concentrate per 1,000 g of cleaner solution), more preferably at 5:1,000 to 30:1,000 (5 to 30 g of concentrate per 1,000 g of cleaner solution), particularly preferably at 14:1,000 to 26:1,000 (14 to 26 g of concentrate per 1,000 g of cleaner solution), and adjusting the pH value using at least one acid or base as necessary.

[0034] According to the present invention, the amount of concentrate required to produce the purge cleaner solution is less than that of the prior art concentrates (usually diluted 35:1,000 to 100:1,000), thereby helping to reduce the VOC content of the purge cleaner solution and the COD in the resulting wastewater. This can be explained by the higher cleaning efficiency achieved by the at least one water-soluble amine having at least 7 carbon atoms.

[0035] According to a preferred embodiment, the concentrate comprises: a) 1 to 40% (w / w) of at least one water-soluble amine having 7 to 15 carbon atoms, calculated as N-methyldiisopropanolamine; b) 40-60% (w / w) hexyl glycol; c) 40-60% (w / w) hexyl diglycol; Includes.

[0036] According to a particularly preferred embodiment, the concentrate comprises a) 1 to 40% (w / w) of at least one water-soluble amine having 7 to 15 carbon atoms, calculated as N-methyldiisopropanolamine; b) 40-60% (w / w) hexyl glycol; c) 40-60% (w / w) hexyl diglycol; d) 0-10% (w / w) of at least one low foaming surfactant; e) 0 to 30% (w / w) benzyl alcohol; f) 0-80% (w / w) of at least one other glycol ether having 6-10 carbon atoms, including butyl glycol and butyl diglycol; where the sum of the % (w / w) of all components a) through f) equals 100% (w / w).

[0037] The present invention is illustrated by the following invention and comparative examples, which, however, are not meant to limit the scope of the present invention. EXAMPLES

[0038] Test 1: 9-drop test on wet paint - room temperature for 5 minutes A layer of water-based paint with a thickness of 40-60 μm was drawn onto a glass panel (200 × 200 mm). The layer was then partially dried at room temperature (RT) for 4 min and placed at a 45° inclination. Nine drops of the purge cleaner solution to be tested were applied onto the panel from a height of 12 cm at a rate of one drop per second.

[0039] After 5 minutes at room temperature, the width of the paint-free spot ("open head") where the drop hit the panel was measured in centimetres - the greater the width, the more effective the stripping, i.e. cleaning efficiency, of the test solution. Test 2: Wet paint spray test - room temperature for 10 minutes A layer of water-based paint approximately 60 μm thick was drawn onto a glass panel (100×200 mm). The layer was then partially dried at room temperature for 4 minutes and placed at a 45° incline. From a distance of 30 cm, 10 ml of the purge cleaner solution to be tested was sprayed onto the panel.

[0040] After 10 minutes at room temperature, the stripping effect, i.e. cleaning efficiency, was rated according to the following categories: poor (-), fair (+), good (++), very good (+++). Test 3: Quantitative N-drop test on dried paint A layer of water-based paint with a thickness of 40-60 μm was drawn onto a glass panel (200 × 200 mm). The layer was then dried for 24 hours at room temperature and placed at a 45° inclination. Drops of the purge cleaner solution to be tested were applied onto the panel from a height of 12 cm at a rate of 1 drop per second until the layer opened, i.e. until there was a paint-free spot where the drop had hit the panel.

[0041] The number of drops (n) applied was determined: the smaller this number, the greater the stripping effect, i.e., cleaning efficiency, of the test solution.

[0042] Purge Cleaning Solution and Test Results For every amine A, B, C (see below), a mixture of 95% by weight hexyl diglycol and 5% by weight of the amine was prepared.

[0043] Amine A: Triethanolamine (6 carbon atoms) (Comparative Example) Amine B: N-methyldiisopropanolamine (7 carbon atoms) (Example of the present invention) Amine C: N,N-dibutylethanolamine (10 carbon atoms) (Example of the present invention) The mixture was diluted to 2% by weight with deionized water.

[0044] The 9-drop test was carried out as described above (Test 1) using the wet paint "Fuhler Red" (Hemmerlath, Germany).

[0045] The results are summarized in the table below and cleaning efficiency was calculated relative to that using the benchmark triethanolamine (Amine A).

[0046] [Table 1]

[0047] A spray test was also carried out as above (Test 2) using the wet paint "Fuhler Red" (Hemmerlath, Germany) with the following results:

[0048] [Table 2]

[0049] For amines A and B, the quantitative N drop test was carried out as described above (Test 3) using the dry paint "Fuhler Red" (Hemmerlath, Germany).

[0050] The results are summarized in the table below, and cleaning efficiency was calculated relative to the use of a benchmark triethanolamine (amine A).

[0051] [Table 3]

[0052] Surprisingly, all tests revealed improved cleaning efficiency of the purge cleaner solutions of the present invention containing water-soluble amines having at least seven carbon atoms (Amine B and C) compared to the purge cleaner solutions containing an amine containing six carbon atoms (Amine A).

Claims

1. A method for purging a paint circuit covered with uncured paint, comprising contacting the paint circuit with an aqueous purge cleaner solution comprising at least one glycol ether, the glycol ether further comprising at least one water-soluble amine having from 7 to 15 carbon atoms; The purge cleaner solution comprises: a) 0.05-0.50% (w / w) of at least one water soluble amine having from 7 to 15 carbon atoms; b) 0.3-1.0% (w / w) hexyl glycol; c) 0.3-1.0% (w / w) hexyl diglycol; A method comprising:

2. 2. The method of claim 1, wherein the at least one glycol ether comprises hexyl glycol and / or hexyl diglycol.

3. 3. The method of claim 1, wherein the at least one water-soluble amine comprises at least one amine having from 7 to 12 carbon atoms.

4. 4. The method of claim 1, wherein the at least one amine comprises at least one amine having a conjugate acid with a pKa of at least 8.

5. 5. The method of claim 1, wherein the at least one amine comprises at least one tertiary amine having at least one hydroxyalkyl group.

6. 6. The method of claim 5, wherein the at least one tertiary amine has 1 to 3 hydroxyalkyl groups and 0 to 2 alkyl groups, the total of the hydroxyalkyl groups and alkyl groups being 3.

7. 7. The method of claim 6, wherein the at least one amine comprises at least one amine selected from the group consisting of N-methyldiisopropanolamine, N-octyldiethanolamine, triisopropanolamine, and N,N-dibutylethanolamine.

8. The method of any one of claims 1 to 7, characterized in that the purge cleaner solution is surfactant-free.

9. 9. The method according to claim 1, wherein the purge cleaner solution does not contain any organic solvent selected from the group consisting of benzyl alcohol and butyl glycol, except for hexyl glycol and hexyl diglycol.

10. An aqueous purge cleaner solution comprising at least one glycol ether and further comprising at least one water soluble amine having from 7 to 15 carbon atoms, comprising:

1. The aqueous purge cleaner solution of claim 1, wherein the at least one glycol ether comprises hexyl glycol and / or hexyl diglycol, the solution comprises only hexyl glycol and / or hexyl diglycol as the at least one glycol ether, and the at least one water soluble amine having from 7 to 15 carbon atoms is selected from the group consisting of N-methyldiisopropanolamine, N-octyldiethanolamine, triisopropanolamine, and N,N-dibutylethanolamine.

11. 11. The concentrate for producing the aqueous purge cleaner solution according to claim 10, characterized in that the purge cleaner solution can be obtained by diluting it with water and adjusting the pH value, if necessary, with at least one acid or base.

12. a) 1-40% (w / w) of at least one amine having 7-15 carbon atoms; b) 40-60% (w / w) hexyl glycol; c) 40-60% (w / w) hexyl diglycol; The concentrate according to claim 11, characterized in that it comprises:

13. 2. The method of claim 1, wherein the at least one glycol ether comprises at least one glycol ether having an alkyl group having from 6 to 10 carbon atoms.

14. 10. The method of claim 1, wherein the aqueous purge cleaner solution does not contain amines having less than 7 carbon atoms. 。

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