WO2020007598A1

WO2020007598A1 - Use of polyurethanes in water-based carrier media for separation of paint overspray

Info

Publication number: WO2020007598A1
Application number: PCT/EP2019/065923
Authority: WO
Inventors: Christian KOLT; Sebastian SINNWELL
Original assignee: Henkel Ag & Co. Kgaa
Priority date: 2018-07-03
Filing date: 2019-06-18
Publication date: 2020-01-09

Abstract

The invention relates to the use of a water-based agent, containing at least one polyurethane thickener and at least one nonionic surfactant, as carrier medium for separation of paint overspray from paint booths. The invention further relates to a method for separating paint overspray from the ambient air using the described water-based agent.

Description

Use of polyurethanes in water-based carrier media for the separation of paint overspray

The present invention relates to the use of a water-based agent, comprising at least one polyurethane thickener and at least one non-ionic surfactant, as a carrier medium for separating paint overspray from paint booths. Furthermore, the present invention relates to a method for separating paint overspray from the ambient air using the water-based agent described.

In lacquer technology, lacquer overspray or lacquer mist is the portion of the lacquer that does not get onto the workpiece to be lacquered, but into the environment. The paint overspray can be caused, for example, by spraying past or flowing off the workpiece. In addition to the geometry of the workpiece, the spray technology used and its handling in particular have an influence on the amount of losses caused by paint overspray, which can account for up to 90% of the paint used. In order to protect the environment, the paint overspray that has got into the environment must be separated and disposed of or disposed of in a controlled manner. This is done using various technologies of paint deposition.

One possible way of removing the paint overspray from the ambient air is classic wet washing, in which the paint overspray is separated from the air stream with the aid of a washing medium. Large-scale painting systems are often equipped with wet separators, whose task is to intensely interact with the air laden with paint mist drops with the washout medium. The paint sludge created during the washout process is separated from the washing medium and then disposed of or processed. The washing medium is processed and can be made available again for the washing process.

DE 10 2008 046 409 A1 describes a method for removing solids from the overspray formed when painting objects, in which the overspray is taken up by an air stream and transported to a separation surface over which a separation liquid flows, where a large part of at least the solids is in the separation liquid passes over, is transported away from this and is removed from the liquid by separation. A separation liquid is used which comprises a detackifying medium and optionally a carrier fluid, with paint overspray particles being detackled by the detackifying medium.

EP 2 365 037 A1 describes an aqueous separating liquid for collecting paint overspray from a gas stream, which contains at least 49.95% by weight of water, at least one nonionic surface-active agent and 5 to 50% by weight of an organic water-soluble film-supporting component which is selected from monomeric polyols with at least three hydroxyl groups in the polymer and polymeric polyols selected from poly (ethylene glycols), polyester polyols, acrylic polyols and polyurethane polyols, the aqueous separating solution having a viscosity expressed as a flow time in the range from 1 1 s to 25 s, measured according to DIN 53 21 1 using a 4 mm flow cup at 23 ° C. The separation liquid described can be used in a process in which a gas stream is passed through the painting booth and the paint overspray is brought into contact with the gas stream. The gas stream is passed over a surface on which an essentially continuous liquid film of the separating liquid is formed, as a result of which paint particles or droplets from the gas stream are transferred into the separating liquid.

EP 3 165 577 describes an aqueous carrier medium for washing out paint overspray which contains at least 40% by weight of a polyfunctional organic oxo compound. The carrier medium is characterized in that its viscosity lies over a range of shear stresses in a predetermined corridor, so that a homogeneous, laminar flow of the carrier medium from the separating surfaces is ensured over time.

A variant of wet scrubbing has recently become established in the field of paint separation, in which the paint overspray is electrically charged in the circulating air, then ionized with high voltage and moved to a separation area in the electric field and bound with release agents. With such a method, when selecting the release agent, particular care must be taken to ensure that the dilution properties can be kept stable when flowing around the separation surfaces. Another problem that occurs with processes with electrostatically assisted wet washing is the accumulation of ozone due to the ionization of the paint overspray, which can lead to a chemical degradation of rheological additives that may be contained in the release agent, which further influences its flow behavior.

In this regard, the carrier media known in the prior art have the disadvantage that they are susceptible to degradations induced by oxidation and have a turbulent flow behavior, which can lead to a disturbance in the electrical field, as a result of which the separation rate deteriorates significantly.

It is therefore an object of the present invention to provide a carrier medium which overcomes the disadvantages mentioned above. It is in particular the object of the present invention to provide a carrier medium which is stable with respect to oxidation and which can be used in electrostatically assisted wet washings. In this context, it has proven to be particularly advantageous to use carrier media which have a linear viscous (Newtonian) flow behavior. It has surprisingly been found that this object is achieved by using a water-based agent which comprises a special thickener selected from the group of polyurethanes and at least one nonionic surfactant.

A first subject of the present invention is therefore the use of a water-based agent comprising a) at least 0.2% by weight of at least one thickener selected from those polyurethanes which are in the form of a 1.5% by weight solution in water and in the presence of 0.2% by weight of 12-fold ethoxylated coconut amine at a temperature of 20 ° C. and a shear rate of 10 reciprocal seconds have a viscosity of at least 10 mPas, and b) at least one nonionic surfactant in an amount of less than 5 % By weight as a carrier medium for separating paint overspray from paint booths.

The weight specifications of the at least one thickener and the at least one nonionic surfactant each relate to the total weight of the water-based agent.

In the context of the present invention, the carrier medium is understood to be the liquid medium which is carried out in the cycle of wet washing and which absorbs the paint overspray. Accordingly, the carrier medium can by definition contain the paint overspray, but is not composed of this.

In the context of the present invention, paint overspray of a paint booth is understood to mean the paint components and particles which are not immobilized on the surface to be painted and which are carried out of the paint booth with the cabin air. The paint overspray therefore consists of gaseous or liquid paint components such as solvents and leveling agents as well as the pigmented or unpigmented particulate paint components.

In the context of the present invention, the viscosity is defined as the first derivative of the shear stress after the shear rate and can be determined as such by means of a Coulette rotary viscometer with a cone and plate construction of the measuring head and a temperature of 20 ° C.

In the case of electrostatically assisted wet washing, the carrier medium is generally passed over a passive separating plate, the paint overspray being charged by building up an electric field and being introduced into the carrier medium in this way. It has surprisingly been found that the use of a water-based agent as described above leads to the formation of a stable film on the passive deposition plate. This ensures on the one hand that the paint particles always are absorbed and transported away by sufficient carrier medium and in this way the contamination of the separating plates is prevented. Furthermore, the flow of a homogeneous film of the carrier medium ensures that the electrical voltage required for the separation of the paint particles is not subject to any fluctuations, and thus the separation performance remains largely constant.

In a preferred embodiment, the water-based agent has the at least one thickener in an amount of at least 1% by weight, but preferably less than 10% by weight, based on the total weight of the water-based agent. In a further preferred embodiment, the proportion of thickener in the water-based agent is 0.2 to 8.0% by weight, preferably 0.4 to 6.0% by weight, in each case based on the total weight of the water-based agent ,

In a further preferred embodiment, the water-based agent contains the at least one nonionic surfactant in an amount of at least 0.05% by weight, preferably at least 0.1% by weight, particularly preferably at least 0.3% by weight. %, but preferably less than 3% by weight, particularly preferably less than 2% by weight and in particular less than 1% by weight, in each case based on the total weight of the water-based agent.

The thickener is preferably selected from polyurethanes which are at least partially end group-capped. The polyurethanes from which the thickener is selected preferably have a hydroxyl number of less than 10 mg KOH / g, preferably less than 5 mg KOH / g, particularly preferably less than 2 mg KOH / g and in particular less than 1 mg KOH / g on. The hydroxyl number is understood as a measure of the hydroxyl groups in the thickener and can be determined, for example, by titration.

In a further preferred embodiment, the thickener is selected from polyurethanes which at least partially result from an addition reaction of polyols with diisocyanates. The polyols are preferably those selected from polyether glycols. Examples of suitable diisocyanates are toluene-2,4-diisocyanate, hexamethylene diisocyanate and isophorone diisocyanate. The diisocyanates are preferably at least partially selected from aliphatic diisocyanates with secondary and / or tertiary carbon atoms and a shortest carbon chain of 5-8 carbon atoms connecting the cyanate groups, particularly preferably from hexamethylene diisocyanate and isophorone diisocyanate. In particular, the diisocyanate is at least partially isophorone diisocyanate. A thickener, which is obtained by reacting a polyether glycol with isophorone diisocyanate, has proven to be particularly advantageous. It was surprisingly found that on this A carrier medium is obtained which holds the paint overspray in a stable suspension.

The rheological properties of the carrier medium can be adapted, for example, by the choice of the thickener. In a preferred embodiment, the thickener is selected from polyurethanes which have a molecular weight of 10,000 to 60,000 daltons, preferably 15,000 to 50,000 daltons. The molar mass is determined in the respective peak maximum on the basis of a polydispersity of less than 1.5 from molar mass distribution curves, which are recorded by means of gel permeation chromatography against polystyrene molar equivalents with elution with tetrahydrofuran, the M _p value (peak molecular weight) of the respective molar equivalent - standards is calibrated.

In addition to the thickener, the water-based agent for use as a carrier medium comprises a nonionic surfactant. This nonionic surfactant is preferably selected from alkoxylated fatty alcohols or fatty amines, which in turn are preferably selected from alkoxylated saturated or unsaturated aliphatic alcohols or amines with an aliphatic chain length of at least 8, preferably at least 10 and particularly preferably at least 12, but preferably not more more than 20, particularly preferably not more than 18 and particularly preferably not more than 16 carbon atoms.

The alkoxylated fatty alcohols and fatty amines are preferably with at least 3, preferably with at least 6, particularly preferably with at least 8, in particular with at least 10, but preferably not more than 16, particularly preferably not more than 14, ethylene oxide and / or propylene units, preferably ethylene oxide units. Units, alkoxylated.

In a preferred embodiment, the water-based agent for use as a carrier medium is distinguished in that it additionally contains less than 40% by weight, preferably less than 25% by weight, particularly preferably less than 15% by weight, but preferably at least 5 wt .-% of polyfunctional organic oxo compounds with no more than 12 carbon atoms, preferably with no more than 9 carbon atoms, particularly preferably with no more than 6 carbon atoms, particularly preferably with less than 6 carbon atoms, each based on the total weight of the Water-based agent. In the context of the present invention, polyfunctional organic oxo compounds are understood to mean compounds which have at least three functional groups selected from hydroxyl, ester and / or ether groups, at least one hydroxyl group always being present, in a preferred embodiment no heteroatom other than oxygen is contained. It is further preferred that the polyfunctional organic oxo compounds are selected from compounds with at least three functional groups, the functional groups being hydroxyl and / or ether groups. The polyfunctional organic oxo compounds are preferably selected from compounds with at least two hydroxyl groups, particularly preferably from compounds with at least three hydroxyl groups. Preferred representatives of the polyfunctional organic compounds are 1, 2,3-propanetriol, 1, 1, 1-tris (hydroxymethyl) ethane, threitol, erythritol, pentaerythritol, pentites such as xylitol, adonite and arabitol, hexites such as sorbitol and mannitol, aldotetrosis such as erythrose , Aldopentoses such as ribose and xylose, aldohexoses such as glucose and mannose and its simple ethers each having no more than 4 carbon atoms or a total of four ethylene oxide and / or propylene oxide units in the ether group. In a particularly preferred embodiment, the polyfunctional organic oxo compound is 1, 2,3-propanetriol.

The presence of the polyfunctional organic oxo compounds supports the detackification of the paint particles in the carrier medium and prevents greater coagulation of the paint particles contained in the carrier medium, which is disadvantageous in particular for the flow behavior on the separating plates and also promotes their soiling. Likewise, a relatively low water vapor partial pressure in the cabin air can be set via the hygroscopic properties of the polyfunctional organic oxo compounds.

In order to be able to be used as a carrier medium for separating paint overspray, the water-based agent should have a suitable viscosity. Too high a viscosity can, for example, result in the drainage of the carrier medium from the separation surfaces or plates being slowed down, so that, while maintaining a volume flow specified in the process flow, a critical wet film build-up is formed on the separation surfaces, in which the wet film of the carrier medium under the action gravitationally sagging and, analogous to the runner formation, no drainage in homogeneous wet film thickness can be achieved over the entire drainage surface. Therefore, when used as a carrier medium, the water-based agent preferably has a viscosity at shear rates in the range from 10 to 1000 s ^-1 , which is always above 10 mPas, particularly preferably above 20 mPas. Furthermore, the ratio of rest viscosity hio to process viscosity h-ioo is preferably not greater than 10: 1. In this way, a homogeneous drainage of the carrier medium can be achieved at the separation surfaces.

In the context of the present invention, the process viscosity h-ioo denotes the viscosity determined in this way at a shear rate of 100 s ⁻¹ , which is approximately the Corresponds to shear stress when the carrier medium runs off the separation surfaces of a system for separating paint overspray by means of wet washing. Analogously, the rest viscosity h-io is the viscosity determined in this way at a shear rate of 10 S ¹ .

Another object of the present invention is a method for separating paint overspray from the ambient air, which is characterized in that i) the paint overspray is guided with the ambient air onto a separation surface wetted by a carrier medium, and ii) part of the Carrier medium that has taken up paint overspray from the ambient air, is removed from the separating surface and at the same time is replaced by another part of the same carrier medium that differs from the removed part only in that less paint overspray is contained in the same volume, whereby , the carrier medium in addition to water, at least one non-ionic surfactant and at least one thickener selected from such polyurethanes, which as a 1.5% by weight solution in water and in the presence of 0.2% by weight of 12-fold ethoxylated coconut amine a viscosity of at least 10 mPas at a temperature of 20 ° C and a shear rate of ten reciprocal seconds contains, the proportion of the non-ionic surfactant being less than 5% by weight and the proportion of the thickeners being less than 10% by weight, in each case based on the carrier medium.

In a preferred embodiment of the method, the deposition surface is continuously washed around by the carrier medium, the carrier medium preferably flowing off the deposition surface following gravity. The flow around the deposition surface is preferably laminar. A laminar flow of the carrier medium on the separating surfaces is defined in the context of the present invention in such a way that the carrier medium flows outside of a laminar boundary layer following gravity almost parallel to the separating surface and the flow neither breaks off nor swirls, so that with a constant volume flow of the flushing carrier medium largely stationary flow along the separation surface results.

It has surprisingly been found that with the aid of the method according to the invention, a homogeneous wetting of the deposition surfaces can be achieved using the specified carrier medium. The film that forms on the separating surface should also have a sufficient thickness in order to prevent paint overspray from striking or damaging the separating surface. An embodiment is therefore preferred in which Separation area a wet film coverage of at least 0.5 l / m ² , but preferably less than 2 l / m ² , each based on the volume of carrier medium, is realized.

It was also surprisingly found that the use of the specified carrier medium or the water-based agent allows a very small spacing of the separation surfaces without there being a risk of electrical flashovers, for example caused by an inhomogeneous drainage of the carrier medium. This is particularly advantageous if the deposition process is supported electrostatically. An embodiment is therefore preferred in which the paint overspray is electrostatically charged in the ambient air under the action of an electrical voltage and transported to the separation surface in the electrical field. For this purpose, it is preferred that the separating surface is made from a flat metallic material and the electrical voltage is preferably applied between the separating surface and a metallic electrode which is in direct contact with the ambient air.

Exemplary recipes are listed below which are suitable as water-based agents for use according to the invention as a carrier medium for separating paint overspray. However, these recipes are by no means to be understood as a restriction, but merely as an illustration of the inventive concept.

The selection of polyurethanes suitable according to the invention is illustrated in FIG. 1, in which the corresponding viscosity-shear rate profile for 1.5% by weight aqueous solutions of a thickener based on various commercially available polyurethanes in the presence of 0.5% by weight. -% of the non-ionic surfactant Lutensol ^® FA 12K (coconut amine with 12 EO available from BASF SE) is reproduced. The polyurethanes used are:

PU1: Tafigel PUR 44, available from Münzing Chemie GmbH

PU2: Tafigel PUR 40, available from Münzing Chemie GmbH

PU3: PU 1 191, available from BASF SE

PU4: BYK-425, available from ALTANA AG

PU5: Tafigel PUR 85, available from Münzing Chemie GmbH

PU6: Tafigel PUR 45, available from Münzing Chemie GmbH

Only the polyurethanes PU1 and PU2 have the special thickening properties to in combination with Lutensol ^® FA 12K or other non-ionic surfactant used in the invention to be able to. The viscosity over the specified shear rate range of 0.01-100 reciprocal seconds was determined using a plate / cone viscometer (Haake Mars 60, Thermo Fisher Scientific Inc.) with a cone diameter of 35 mm at 20 ° C. when going through a shear rate staircase of 0.01 - 100 s ^{1 determined} with 45 measured values per decade, whereby the first cycle is shown.

Claims

Expectations

1. Use of a water-based agent containing a) more than 0.2% by weight of at least one thickener selected from those polyurethanes which are used as a 1.5% by weight solution in water and in the presence of 0.2% by weight. % of 12-fold ethoxylated coconut amine at a temperature of 20 ° C. and a shear rate of ten reciprocal seconds have a viscosity of at least 10 mPas, and b) at least one non-ionic surfactant in an amount of less than 5% by weight as carrier medium for separating paint overspray from paint booths.

2. Use according to claim 1, characterized in that the thickener is selected from polyurethanes which are at least partially end group capped and preferably have a hydroxyl number of less than 10 mg KOH / g, particularly preferably less than 5 mg KOH / g and particularly preferably less have than 2 mg KOH / g.

3. Use according to one or both of the preceding claims, characterized in that the thickener is selected from polyurethanes which at least partially result from an addition reaction of polyols, which in turn are preferably at least partially selected from polyethylene glycols, with diisocyanates, the diisocyanates in turn preferably are at least partially selected from aliphatic diisocyanates with secondary and / or tertiary carbon atoms and a shortest carbon chain of 5-8 carbon atoms connecting the cyanate groups, particularly preferably from hexamethylene diisocyanate and isophorone diisocyanate, particularly preferably from isophorone diisocyanate.

4. Use according to one or more of the preceding claims, characterized in that the thickener is selected from polyurethanes, the one

Have molecular weight in the range of 10,000 - 60,000 daltons.

5. Use according to one or more of the preceding claims, characterized in that the proportion of the thickener is at least 1% by weight, but preferably less than 10% by weight, particularly preferably less than 5% by weight, particularly preferably less than 3 wt .-% based on the water-based agent.

6. Use according to one or more of the preceding claims, characterized in that the non-ionic surfactant is selected from alkoxylated fatty alcohols or fatty amines, which in turn are preferably selected from alkoxylated saturated or unsaturated aliphatic alcohols or amines with an aliphatic chain length of at least 8, preferably of at least 10 and particularly preferably of at least 12, but preferably not more than 20, particularly preferably not more than 18 and particularly preferably not more than 16 carbon atoms.

7. Use according to claim 6, characterized in that the alkoxylated fatty alcohols or fatty amines with at least 3, preferably with at least 6, particularly preferably with at least 8, particularly preferably with at least 10, but preferably not with more than 16, particularly preferably not with more alkoxylated as 14 ethylene oxide and / or propylene oxide units, preferably ethylene oxide units.

8. Use according to one or more of the preceding claims, characterized in that the proportion of the non-ionic surfactant is at least 0.05% by weight, preferably at least 0.1% by weight, particularly preferably at least 0.3% by weight. %, but preferably less than 3% by weight, particularly preferably less than 2% by weight and particularly preferably less than 1% by weight, based on the water-based agent.

9. Use according to one or more of the preceding claims, characterized in that the water-based agent additionally less than 40 wt .-%, preferably less than 25 wt .-%, particularly preferably less than 15 wt .-%, but preferably contains at least 5% by weight of polyfunctional organic oxo compounds having no more than 12 carbon atoms.

10. Use according to one or more of the preceding claims, characterized in that water-based agents at shear rates in the range from 10 to 1000 s ^{_1 have} a viscosity which is always above 10 mPas and the ratio of rest viscosity h-io to process viscosity hioo is not greater than 10: 1.

1 1. Method for separating paint overspray from the ambient air, characterized in that i) the paint overspray is guided with the ambient air onto a separation surface wetted by a carrier medium, and ii) a part of the carrier medium which has received paint overspray from the ambient air is removed from the separation surface and at the same time is replaced by another part of the same carrier medium which differs from the removed part only in that in the same volume less paint Overspray is included, characterized in that the carrier medium in addition to water, at least one non-ionic surfactant and at least one thickener selected from such polyurethanes as a 1.5 wt .-% solution in water and in the presence of 0.2 wt. -% of 12-fold ethoxylated coconut amine at a temperature of 20 ° C and a shear rate of ten reciprocal seconds have a viscosity of at least 10 mPas, the proportion of non-ionic surfactants being less than 5% by weight and the proportion of thickeners is less than 10 wt .-% each based on the carrier medium.

12. The method according to claim 11, characterized in that the separating surface is continuously washed around by the carrier medium and the carrier medium flows away from the gravitational force thereof, the washing around the separating surface preferably being laminar.

13. The method according to one or both of claims 11 and 12, characterized in that a wet film coating of at least 0.5 l / m ² , but preferably less than 2 l / m ² , in each case based on the carrier medium volume, is realized on the deposition surface is.

14. The method according to one or more of claims 1 1 to 13, characterized in that the paint overspray in the ambient air under the influence of an electrical voltage is electrostatically charged and transported in the electrical field to the separation surface.