Pressure swirl atomizing nozzle for spraying a curable composition and associated method and use

#The present invention relates to a pressure swirl atomizing nozzle as defined in the preamble of claim 1 for spraying a curable composition onto a surface to produce a polymeric layer thereon. The invention also relates to a method for spraying the curable composition onto a surface, in which method use is made of the nozzle according to the invention.

#The curable composition is in particular a polyurethane reaction mixture which is sprayed onto a mould surface to produce for example interior trim parts or panels for automobiles such as dashboards, door panels, glove compartment covers, consoles, etc. Such polyurethane reaction mixtures usually have a relatively high viscosity and hence are quite difficult to atomize.

#A pressure swirl atomizing nozzle for spraying a layer of a polyurethane reaction mixture onto a mould surface as defined in the preamble of claim 1 is already disclosed in EP-B-0 303 305 and EP-B-0 389 014. The nozzles disclosed in these patents comprise an orifice piece that defines a funnel-shaped cavity ending in the exit orifice of the nozzle. At its upstream extremity, the funnel-shaped cavity is closed off by an injector piece so that a swirl chamber is formed between the front side of the injector piece and the exit orifice. The injector piece comprises two or more swirl ports through which the curable composition is injected into the swirl chamber. Due to the obtained swirling motion, the curable composition is sprayed out of the exit orifice in the form of a hollow spray cone.

#Other particularities and advantages of the invention will become apparent from the following description of some particular embodiments of the nozzle and of the method according to the present invention. The reference numerals used in this description relate to the annexed drawings wherein:

#FIG. 1 is a schematic diagram showing the principle of spraying a polyurethane reaction mixture onto a mould surface with a nozzle according to the present invention;

#FIG. 2 shows a schematic side view of a spray pattern which can be achieved by a nozzle according to the present invention, the reaction mixture being sprayed in the form of a hollow cone;

#The present invention relates to a pressure swirl atomizing nozzle, and to a method for spraying method a curable composition by means of this nozzle onto a surface to produce a polymeric layer thereon. The nozzle is a so-called airless spray nozzle, i.e. a nozzle wherein no gas is added in order to influence the spray pattern. The curable composition is in particular a reactive mixture of components producing polyurethane, called herein a polyurethane reaction mixture. The curable composition may optionally contain a physical or chemical blowing agent which provides for a foaming of the layer of curable composition deposited on the surface. Although other curable compositions such as silicone resins, epoxy resins and phenolic resins can also be sprayed, the further detailed description will be made with reference to the spraying of polyurethane reaction mixtures. Such mixtures are usually obtained by mixing two components, namely an isocyanate component and a polyol component, although it is possible to use more than two component streams. The sprayed polyurethane reaction mixture preferably comprises no solvents (including water), or only a small amount of solvents, in particular less than 10% by weight, more particularly less than 5% by weight, so that the reaction mixture, when being sprayed, has a relatively high viscosity.

#The sprayed polyurethane layer has usually an average density higher than 300 g/l, preferably higher than 400 g/l and most preferably higher than 600 g/l. The polyurethane layer may be a rigid polyurethane layer but it is preferably a flexible elastomeric polyurethane layer, in particular a so-called polyurethane skin having preferably an average thickness (determined by dividing the volume of the skin by its surface area) in the range of 0.1 to 3 mm, preferably 0.3 to 2 mm. In practice, especially in order to produce an interior trim part for automotive vehicles such as a dash board, a door panel, a console, etc., a rigid backing layer is applied behind such skin layer and, between both layers preferably an intermediate foam layer.

#Reaction mixtures for spraying a polyurethane skin are disclosed for example in EP-B-0 379 246. These reaction mixtures are composed by mixing an isocyanate component and a polyol component just before spraying the reaction mixture. The isocyanate component may be based on aliphatic isocyanates in order to achieve a light-stable polyurethane skin. In practice, it is however also possible to spray a polyurethane skin which is not light-stable. In the reaction mixture for such skins, use is made of more reactive aromatic polyisocyanates. In this case a paint layer is preferably applied onto such skins either after having produced the skin or by applying the paint layer onto the mould surface as an in-mould coating before spraying the reaction mixture for the skin onto the mould surface, in order to render the skins light-stable.