EP2470308A1

EP2470308A1 - Method and device for the production of a spray application consisting of reactive plastic

Info

Publication number: EP2470308A1
Application number: EP10743048A
Authority: EP
Inventors: Hans-Guido Wirtz; Stephan Schleiermacher; Roger Scholz; Frithjof Hannig; Dirk Steinmeister; Frank Grimberg; Andreas Frahm
Original assignee: Bayer MaterialScience AG
Current assignee: Covestro Deutschland AG
Priority date: 2009-08-26
Filing date: 2010-08-13
Publication date: 2012-07-04
Also published as: JP2013503052A; CN102574140A; MX2012002239A; US20120178895A1; KR20120053503A; WO2011023302A1

Abstract

The present invention relates to a method for the production of layers and moulded parts consisting of reactive plastic, the reactive components being intermixed on a plurality of planes with the aid of mixed gases. The invention further relates to a device which allows a corresponding method.

Description

Method and device for producing a spray application

Reactive plastic

The present invention relates to a process for the production of layers and moldings from reactive plastic wherein the reactive components are mixed in a spray channel in several levels with the aid of mixed gases. The invention further relates to a device with which a corresponding method is made possible.

The use of different reactive plastics for the production of molded parts is well known from the prior art. When it comes to apply a reactive plastic on a substrate, usually the spraying has prevailed as application technique. As a reactive plastic polyurethanes are often used, the described techniques are also applicable to other reactive plastics.

The Kunststoffhandbuch Volume 7 Polyurethanes / Carl Hanser Verlag describes various application examples with regard to such spraying techniques.

The mixing of the liquid reaction components takes place during polyurethane processing in a mixing head, it being possible to distinguish between high-pressure and low-pressure mixing. The spray application is realized in both cases via downstream atomizer systems. In the low-pressure mixing process, the mixing energy necessary for mixing the reaction components is introduced via dynamic stirrers or static mixing elements. The volume of the mixing chambers are relatively large compared to mixing heads of high-pressure mixing and must be cleaned after completion of the mixing process with suitable detergents or compressed air. In particular, in the processing of highly reactive polyurethane systems such low-pressure mixing heads tend by design to Mischkammerablagerungen and thus after prolonged operation for clogging.

In the high-pressure mixing process, the pressure energy of the

Reaction components converted into kinetic energy via nozzles. By injecting the components into a comparatively small mixing chamber, the kinetic energy is spatially concentrated and used for mixing. The cleaning of the mixing chamber is carried out by mechanical plunger, whereby short-term interruptions of the spraying process are possible. This advantage is a feature of the high-pressure mixing heads and crucial for the formation of constant layer thicknesses in robot-controlled spraying processes, since the traverse speeds are reduced immediately before the turning points of the robot paths and thus the area / discharge ratio changes. The possibility of a brief interruption of the spray application allows the laying of the inflection points on the outer areas of the surfaces to be sprayed

The sprayer systems downstream of the mixing process serve to break down the reaction mixture into individual drops. For the Atomization are single-fluid nozzles (airless high-pressure atomization) as well as with two substance nozzles outer and inner mixture (compressed gas atomization) used. The advantage of dual-fluid nozzles internal mixture is that they have relatively large flow cross-sections, so that even coarse particle-containing liquids can be sprayed. Another advantage is that viscosity or volumetric flow changes have less of an impact on the geometry of the spray jet. This property is of great importance for the processing of solid-state polyurethane systems according to the method described below since the possibility of variably settable solid parts results in large changes in viscosity.

Different atomizer systems are also described in the prior art. Corresponding air and / or gas inlet openings in the flow channel are known, for example, from US Pat. No. 3,923,253, DE 10 2007 016 785 A1 or US Pat. No. 6,131,823.

DE 27 00 488 A1 discloses a device in which, if appropriate, reactants are passed from two supply lines into a mixing tube. The mixing tube has a series of nozzles Bl, Dl, B2 and D2, which are introduced into the tube by a high-pressure medium, for example a gas, but also components of the main liquid flow, which are mixed with the main liquid flow. The nozzles are mounted in opposite directions, so that a turbulence takes place in the mixing tube.

However, for many applications it is necessary to add additional components to the reactive plastic. These can be fibers be, which allow a higher stability of the product. Other possible additives include fire retardants, anti-aging agents, UV protectants and others. The admixture of solid, liquid and / or gaseous components in the reactive mixture is described in different ways in the prior art. In WO 03/037528 A2, the polyol and the isocyanate component are mixed together with a filler in a mixing head. This allows mixing not only of the polyurethane components with each other but also with the filler. The disadvantage here, however, that the mixing head can be damaged by the filler. Also may be damaged by any shear forces in the mixing head, the fillers themselves.

As an alternative to this, a corresponding additive can also be added to the reactive mixture after mixing. This is often done by mixing the spray of the reactive plastic with a spray of the appropriate filler. This is known, for example, from DE 25 17 864 A1, US Pat. No. 3,302,891, WO 2009/052990 A1 or EP 1 458 494 B1. In the methods described here, the mixing head is no longer damaged by the fillers. Also, there is no damage to the fillers themselves. However, the wetting of the fillers with the reactive mixture is often insufficient here.

In the not yet published patent application PCT / EP 2009/001007 a newly developed method for introducing solids into a compressed gas atomized polyurethane spray is described. The introduction of the solid particles takes place by means of a spray gas as a particle carrier in the still located in the spray attachment liquid reaction mixture (reaction jet). A device with which a corresponding method is possible, for example, in the not yet published PCT application PCT / EP 2009/003545 described. About a mixing head downstream header with an integrated mixing level, the gas-solid mixture is fed tangentially to the liquid reaction mixture, mixed by means of the resulting Rotationsdralls and then discharged as a multi-phase mixture through a nebulizer as a spray.

Prior to this process development, feeding and mixing of solids via the gas flow supply of two-substance nozzles of internal mixing was not intended in the case of polyurethane spray processes. The spray devices had only the function of a compressed gas atomizer, with short residence times of the reaction mixtures in the spray attachment as well as barrier or dead space free channel geometries were preferred for reasons of cleanliness.

In tests according to the method described in PCT / EP2009 / 001007 and using the spray device described therein, however, it has been found in the processing of higher solids contents that the wetting of the particles may be partially insufficient.

High solids contents with small particle sizes provide the reaction mixture with a large surface area which, due to the short residence time in the mixing zone, can not be sufficiently mixed and wetted with the reaction mixture. Solid particles with high specific gravity are also concentrated due to of centrifugal forces on the wall region of the flow channel and can be mixed by the compression only conditionally with the reaction mixture. At a mixture discharge of, for example, 100 g / s and a solids content of 70 percent by weight (barium sulfate), this effect on mixture discharge was an annular formation of unwanted solid particles.

Another indication of insufficient mixing, for example, for the local concentration of solids by centrifugal forces are swirling leaching on the walls of the flow channel. In the case of turbulent flow and homogeneous distribution of the solid particles, uniform surface wear should also be achieved when using an uncured spray attachment.

The object of the present invention is therefore to develop a process and a device for producing layers and moldings from reactive plastic, in particular polyurethane, in particular by spray application, with which higher solids contents can be processed while at the same time ensuring uniform wetting of these solids ,

As known from DE 10 2005 058 292 A1, a lightweight and small design for the spray process via robots is advantageous. Robot-guided mixing heads experience extremely fast motion changes; with hand-held mixing heads, the advantage of a light and small design is self-explanatory. A further object of the present invention is therefore to provide a device which is small and lightweight. It should be possible with her be able to bring a high solids content in the reactive mixture. It should continue to wear, spray and be easy to clean. In particular, a device according to the invention allows short order intervals; In addition, it is adaptable with commercially available casting mixheads.

The object underlying the invention could be achieved by a method in which the mixing section was extended, and in this several mixing levels were introduced.

In a first embodiment, a reaction mixture, in particular a polyurethane reaction mixture, was passed from a mixing head into a device according to the invention. Over inlet was added a solid-gas mixture. The individual mixing levels consist of at least one gas channel opening into the spray channel, through which a gas stream flows. The direction of flow of the gas stream entering the spray channel according to the invention extends outside the center of the spray channel. Due to the tangential arrangement, a radial flow component is impressed on the axial flow. By means of this radial flow component, the components, in this case the reactive mixture and the solid, are thoroughly mixed with one another. The gas channels and the inlet openings in the respective mixing planes are arranged so that opposing swirl directions are impressed on the mixture via the flow path in the mixing chamber. The twisting direction of one plane is opposite to the twisting direction of the following mixing plane. Here, the first mixing level, ie the first at least one gas channel above the inlet openings for the solid-gas mixture. Fig. Ia shows a cross section of a device according to the invention. For reasons of a simplified functional representation, the mixed gas ducts opening into the mixing chamber were not drawn tangentially in this and the subsequent sectional drawings.

Fig. Ib shows the mixing principle in a device according to the invention. In a nozzle according to the invention, a radial flow component is impressed into the spray channel, in which the reactive mixture flows axially, by the mixed gas. This leads to a renewed turbulence of the reactive mixture. In a next mixing level, the solid-gas mixture is introduced through appropriate inlets. The inlets are arranged tangentially, so that there is a further mixing. The twisting direction caused by the solid-gas mixture is opposite to the twisting direction caused by the mixed gas in a first mixing plane. In a further mixing level, a mixed gas is again introduced via corresponding gas channels.

Due to the tangential introduction, a radial disturbance of the axial flow of the reactive mixture takes place here again. The swirl direction of the reactive mixture produced here is now again in the opposite direction to the swirl direction generated by the introduced solid-gas mixture. By the opposite directions of twist mixing is ensured between solid and reactive mixture. The reactive mixture itself is thoroughly mixed. For this it is crucial that there is a gas inlet for a mixed gas before the inputs for the solid-gas mixture. An inventive Device therefore has at least two levels each at least one gas inlet, namely one before the inlet for example, the solid-gas mixture and after this intake.

According to the invention, not only a solid-gas mixture can be introduced into the reactive stream via the inlets. It is also possible to initiate the individual components of the reactive mixture via this. It is also possible to add solid, liquid and / or gaseous additives to the reactive mixture. However, it should always be borne in mind that a mixing plane is located in front of these inlet openings, ie that a mixed gas is introduced into the flow channel.

It is preferred that a device according to the invention has further mixing levels. As shown in FIG. 1b, in each of the further mixing planes, the at least one gas inlet is arranged in such a way that the twisting direction initiated by the mixed gas is different, namely opposite, from that of the overlying mixing plane. In particular, a device according to the invention has more than two, in particular more than four, in particular more than 6 mixing levels with at least one gas inlet.

The vectors of the gas streams thus replace the function of a static mixer or an agitator. According to the invention, a mixing plane has at least one, in particular two, gas inlets.

Surprisingly, tests with a device according to the invention have shown that, due to the counter-rotating swirl directions in the mixing channel and the pronounced shear forces, a qualitatively so Good mixing effect is generated, that can be dispensed with a mixing of the reaction components via an upstream PUR mixing head.

Fig. 2a shows a modular mixer assembly according to the invention without an upstream PUR mixing head, in which the mixing levels can be combined as required, for example mixing elements in disc shape depending on the mixing requirement. The original inlet bores are used here to initiate reaction components A and B of the reactive plastic. Fig. 2 b shows the corresponding mixing principle. Shown here are two inlet openings. According to the invention, however, further inlet openings can also be located in the same plane.

Accordingly, in a method according to the invention, at least two components are introduced individually via the at least two inlets from the outside into the spray channel in a nozzle and these are mixed there. This spray channel has at least two mixing planes into which at least one mixed gas is introduced through at least one tangentially arranged gas channel and at least one of these mixing planes is prior to the admission of the components, the other thereafter. "Before" and "after" are to be understood here according to the flow direction of the reactive current.

The mixing head function is thus taken over exclusively by the device according to the invention, the mixing / spraying, whereby very small and lightweight designs without moving parts and Waterproofing can be realized inexpensively. Furthermore, according to the invention, cost-intensive high-pressure doses can be dispensed with.

In a device according to the invention, the spray channel is located inside the mixing nozzle. This is separated via a wall from a gas space surrounding it, wherein from the gas space in the spray channel in at least two mixing levels via at least one gas channel, a mixed gas can be introduced into the spray channel. As a result, only a gas connection of the nozzle according to the invention is needed. The mixed gas flows at the same pressure over all existing gas channels in the interior of the spray channel. Within a plane is at least one gas channel which directs the mixed gas from the gas space in the spray channel. Preferably, however, there are more than one gas channel in one plane, preferably there are two gas channels in one plane, these being opposite one another.

In a preferred embodiment, the cylindrical mixing area has a tapered nozzle exit. Such a design is the simplest design of a spray mixing nozzle according to the invention.

The principle of compressed gas mixing creates a gas loading of the mixture, which causes a density reduction of the later polyurethane matrix and is undesirable for certain applications. For example, in functional layers for sound reduction after the spring / Mass principle densities in the mass layer of significantly> 2 are sought. The addition of solids with simultaneous gas loading introduced by the mixing process would be counterproductive in such a case.

Therefore, in a further embodiment, the object underlying the present invention is achieved by a spray mixing nozzle, in which a hollow cylinder is mounted in the interior of the spray channel, in the center of which a gas distributor is located, via which gas streams, which lead into the spray channel, tangentially mixed gas streams be initiated. In Fig. 3a, a cross section of a device according to the invention is shown. In Fig. 3b, the associated mixing principle is shown. The introduced mixed gas streams are introduced tangentially and in opposite directions. In the now external spray channel corresponding reactive components, but also solid, liquid and / or gaseous additives can be introduced from the outside. The inlets for the reactive components and the additives are on two distinct levels, with the reactive components introduced in one plane and the additives in a different plane. Between these levels is at least one mixing level into which a mixed gas is introduced.

Such a mixing space geometry ensures the mixture between the individual reactive components and the additives, in particular of solids. Due to the outflow of the gas from the inside to the outside, a sufficient mixing is made possible even with a reduced amount of compressed gas and thus reduced gas loading. The mixing becomes tangential through opposite directions introduced mixed gases, and thus by opposite direction of twist in the individual mixing levels allows. The introduction of the reactive components and the additive is carried out so that the twisting direction is changed within the nozzle.

The geometry of the mixing chamber consists of a hollow cylinder, in the center of which there is a gas distributor. By forming a ring flow with a small gap size, it can be ruled out in comparison to a cylindrical mixing space that the mixing effect of the compressed gas streams in the center of the mixing space (in the center of the flow channel) is lost. Furthermore, the mixing effect of the gas flows is not affected by centrifugal forces.

The keeping clean of the compressed gas channels is advantageously designed in the arrangement described in FIG. 3a, since the mixing chamber wall bounding to the outside is completely closed after the solids have been introduced and thus the entry of wetted solid particles through centrifugal forces into the gas channels can be ruled out. With the corresponding gas flow, a mixture entry into the mixed gas channels by return flow is not possible.

With an appropriate design, the gas distributor located in the center can be axially displaced in its position, whereby the volume and thus the flow velocity in the mixing chamber can be adjusted immediately before the outlet opening. This effect can be used inter alia to influence the spray pattern. If required, a mixing spray nozzle described in FIG. 3a can also be combined with conventional polyurethane mixing plants and thus enables the further use of existing machine technology.

The cleaning of a mixing spray nozzle according to the invention can be accomplished according to the prior art via compressed gas. By switching off the component streams and maintaining or increasing the supply of compressed gas, the cleaning process is initiated. This procedure also makes short-term firing interruptions analogous to high-pressure technology possible, which, as already mentioned, is advantageous for example for robot-controlled spray application for the formation of uniform spray layer thicknesses.

In a particular embodiment, the entry angles of the gas channels below the component plane were arranged tangentially and obliquely in the direction of component flow, whereby the mixing effect is increased again. However, this inlet geometry of the gas streams is only possible using increased gas throughputs or high flow velocities since the inclination in the flow direction of the mixture promotes a mixture entry into the gas channels.

In addition to the number of mixing levels, the gas flow rate, the direction of rotation and the inlet angle of the gas flows, it is also possible to influence the mixing via pulsating gas flows. With pulsating gas supply, it is advantageous to supply the respective mixing levels independently and, if necessary, alternately with high-frequency discharge gas. The outside Compressed gas supply of the devices of Fig. Ia and Fig. 2a offer ideal conditions for this process variant.

With the aid of a device according to the invention not only solid-gas mixtures can be introduced into a reactive mixture. It is also possible that reaction components are introduced as pre-atomized aerosols by means of a compressed gas stream in the nozzle. By adjusting the volume flows and the particle sizes, mass differences in the mixing ratio of the reactants can be compensated. Mixing ratios of up to 100 to 1, which are usually not miscible via high-pressure mixer, can be successfully mixed or processed, for example, up to a discharge rate of 50 g / s.

In a further embodiment, it is also possible to introduce hot gas into the reactive mixture via the existing inlets. This allows the thermal activation of the reactants. Due to the short mixture residence times, in a process according to the invention with gas temperatures of up to 600 ⁰ C is used.

The influence of the reaction courses of reactive plastics over heated mold surfaces or tempered mixture components is a common procedure. The method of hot air spraying allows similar effects, but can be varied over the duration of Gemischaustrags if necessary. This makes it possible, for example, to adapt the reaction course of the mixture over the entire duration of spraying in the case of large-area components, thereby increasing the productivity of such processes can be. In addition, the flow of reaction mixtures on inclined surfaces can be positively influenced.

According to the invention, the reactive plastic is preferably polyurethane. The reactive components used are therefore in particular polyol and isocyanate components. It is possible to use components which are well known from the prior art.

Fibers are preferably introduced into the reactive mixture via the inlets according to the invention. Other possible solids which may be added include, for example, flame retardants, stabilizers or anti-aging agents. The same functions can also have the possibly supplied liquid aids.

Claims

claims

1. A process for the production of layers and moldings from reactive plastics, characterized in that initiating at least two components individually via an inlet from the outside into a spray channel of a nozzle and these are mixed there, said spray channel has at least two mixing planes, in which by at least one at least one mixed gas is introduced tangentially arranged gas channel, and at least one of these mixing levels is upstream of the inlet for the components.

2. The method according to claim 1, characterized in that one introduces the mixed gas into the spray channel, that the flow direction of the gas stream when entering the spray channel runs outside the center of the spray channel.

3. The method according to claim 1 or 2, characterized in that initiating a polyol component and an isocyanate component in the nozzle.

4. The method according to any one of claims 1 to 3, characterized in that the nozzle at a mixing head, from which a reactive mixture, in particular a polyurethane reactive mixture, flows axially into the spray channel, connected and admixed via the inlet of this reactive stream further components.

5. The method according to claim 4, characterized in that one supplies the reactive stream solid, liquid and / or gaseous components via the inlets.

6. The method according to any one of claims 1 to 5, characterized in that the gas channels are arranged so that by introducing the mixed gas in the planes of the axial flow of the reactive mixture, a radial flow component is impressed and this radial flow component in one of the planes in one direction and pointing in the opposite direction in the following plane, whereby also the registration of the components via the inlets is considered to be a plane.

7. The method according to claim 1, characterized in that introducing a mixed gas in at least three planes via at least one gas channel tangentially into the nozzle via a hollow cylinder located inside the nozzle, wherein the nozzle further inlet for different components in at least two different levels having.

8. The method according to claim 7, characterized in that the gas channels are arranged so that by introducing the mixed gas in the planes of the axial flow of the reactive mixture, a radial flow component is impressed and the directions of the radial flow component in a plane from the direction in the following Level is opposite, whereby the inlays for components are considered as levels.

9. A device for producing layers and moldings from a reactive plastic according to claim 1, characterized in that the nozzle has in the interior a spray channel which is separated via a wall of a gas space surrounding it, wherein the Gas space in the spray channel in at least two mixing levels via at least one gas channel, a mixed gas is introduced into the spray channel.

10. The device according to claim 9, characterized in that the gas channels are arranged so that the flow direction of the gas stream when entering the spray channel outside the center of the spray channel and is impressed by this tangential arrangement of the actual axial flow in the spray passage, a radial flow component.

11. The device according to any one of claims 9 or 10, characterized in that the gas channels and inlets are arranged so that the mixture over the flow path in the spray channel different swirl directions are impressed, wherein the swirl direction is in a plane opposite to the subsequent level.

12. Device according to one of claims 9 to 11, characterized in that the spray channel is connected to a mixing head and solids are introduced via the inlet solids, liquids, reactive gases and / or mixed gases in the axially flowing from the mixing head reactive flow, wherein above this Include at least one gas channel for mixed gas.

13. Device according to one of claims 9 to 12, characterized in that opposite one another in a plane two gas channels.

14. An apparatus for producing layers and moldings from a reactive plastic according to claim 1, characterized in that the interior of the spray channel has a hollow cylinder, in the center of which there is a gas distributor, via the gas channels, which lead into the spray channel, the mixed gas streams tangentially be initiated.

15. The apparatus according to claim 14, characterized in that in the spray channel from the outside in at least two mutually different levels rich inlets through which reactive components and at least one liquid, solid and / or gaseous additive can be added.

16. Device according to one of claims 14 or 15, characterized in that the gas passages are arranged so that the axially flowing reactive components receive a twist, wherein the twisting direction is different in a plane from the twisting direction of the subsequent plane, which you also on relates the levels in which the reactive components and the at least one additive are added.

17. Device according to one of claims 14 to 16, characterized in that in a plane opposite to each other two gas channels.