Abstract:
The method consists of the separate simultaneous extrusion, by means of two or more contiguous extruders or one extruder with two or more separate homogenization chambers, of two or more paints in powder form and the union of the extrusions in the molten state or still hot and then subsequent cooling as a single extrusion.

Description:
BACKGROUND OF THE INVENTION 
     Various methods are currently used to obtain matt or satin powder paints but, to a greater or lesser extent, all of them have limitations. 
     Some methods have recourse to overpigmentation or the addition of polymers which are incompatible with the binder system in intimate homogenization but this leads to a diminution in the chemical and mechanical resistance of the paints. 
     Other methods use intimate homogenization of additives or special catalysts which, however, can only be used with specific systems of binders. 
     Other methods, always with intimate homogenization, are based on the difference in reactivity between resins of the same type of reactive group in a single binder system. 
     Still other methods do not use intimate homogenization but cold physical mixing of one or more paints extruded separately and with different viscosity or reactivity or systems of binders as described in international patent application PCT/EP 89/00022 in the name of the same applicant, published under number WO 89/06674. 
     These last methods are much less limiting than the preceding ones because they can employ practically all the systems of binders as long as they have different viscosities or different types of cross linking. However they are less practical because, with cold mixing methods, manufactures of powder paints normally extrude the paints separately, cool the extrusions, crush or grind them, sieve them and then weigh them out in the various pre-established ratios and mix them in a mixing machine. This means that the process is discontinuous and thus more time, space, materials and manpower are required. 
     There is also the danger of partial separation of the two paints during the various stages of grinding and sieving because of the difference in their specific weights or a different conformation of the granules of powder. Finally, at the spraying stage, the two paints can be deposited non-uniformly because of the different charges accumulated by the two binders. 
     SUMMARY OF THE INVENTION 
     According to this invention, surprisingly it has been found that there is no need to cool the extruded paints separately and then cold mix them, working discontinuously, but, as long as there is no intimate homogenization, they can be put together or roughly mixed in the molten state or still hot in the pre-established ratios and then cooled, crushed etc. as if they came from a single extrusion. 
     Therefore, according to this invention, two or more extruders side by side or one extruder with two or more separate homogenization chambers and a single output nozzle can be used, regulating the inflow ratio to comply with the pre-established ratio. The paints extruded separately still in the molten state or hot from the nozzles of the extruders or the intimate homogenization chambers are put in contact with one another and then drawn through a single calender or cooling body as if they were a single extrusion. 
     The advantage of this invention is obvious since the regulation of the ratio of the input into the homogenization chambers eliminates the need to weigh the paints and there is no longer any need for a mixer because the paints are put into contact before they are cooled. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This invention will be more clearly understood from an examination of the following descriptive and non-limiting examples of the scope of the invention. 
     Description of the polymers and additives used in the illustrative examples of the invention: 
     ALFTALAT 01844 
     Experimental polyester resin with hydroxyl end radicals. 
     Hydroxyl number=30 mg KOH/g resin 
     Viscosity at 200° C. C&amp;P=4500-600 mPa.s 
     Glass transition temperature T g  =50° C. 
     ADDITOL XL 432 
     Blocked aliphatic isocyanic prepolymer produced and marketed by Hoechst. 
     Total contents of NCO=9.50%. 
     ADDITOL XL 496 
     Masterbatch--spreading additive marketed by Hoechst, containing 15% of active substance. 
     ALFTALAT 01918 
     Experimental polyester resin with hydroxyl end radicals. 
     Hydroxyl number=100 mg KOH/g resin 
     Viscosity at 200° C. C&amp;P=4000-6000 mPa.s. 
     T g  =approx 57° C. 
     BECKOPOX EH 694 
     Polyanhydride, produced and marketed by Hoechst. 
     Acid value=260-280 mg KOH/g 
     Melting point=approx 60° C. 
     ALFTALAT AN 721 
     Polyester resin with carboxyl end radicals--produced and marketed by Hoechst. 
     Acid value: 35-45 mg KOH/g. 
     Viscosity at 200° C. C&amp;P=4000-6000 mPa.s. 
     T g  =approx 52° C. 
     ARALDIT PT 810 
     Triglycidyl isocyanuratete (TGIC) produced and marketed by CIBA-GEIGY. 
     EXAMPLE I 
     Paint A (aliphatic polyurethane paint) composed of: 
     
         ______________________________________ALFATALAT 01844      500ADDITOL XL 432       110ADDITOL XL 496       30BENZOIN              5TITANIUM DIOXIDE (rutile)                345                1000      parts______________________________________ 
    
     dry mixed in a mixer and then homogenized in an extruder at 90°-100° C. and cooled, crushed, ground and sieved through a 110 micron sieve. The powder obtained in this way was sprayed onto a sheet with a spraygun for electrostatic painting at a voltage of approx. 60 KV at 30-60 microns of thickness and hardened in a oven for 30 minutes at a temperature of 180° C., providing an elastic film with good chemical and mechanical resistance, good adherence to the support and a brilliance of 90 gloss, determined with a glossmeter at an angle of incidence of 60°. 
     Composition B (polyanhydride hydroxylated paint) composed of: 
     
         ______________________________________ALFTALAT 01918     456BECKOPOX EH 694    164ADDITOL XL 496     30BENZOIN            5TITANIUM DIOXIDE   345              1000       parts______________________________________ 
    
     treated in the same way as composition A, producing a film with good mechanical resistance and a brilliance of 92 gloss. 
     Various ratios of paints obtained from compositions A and B were weighed and then the ratios were cold mixed. These mixtures were then applied to a Unichim sheet and baked under the same conditions used for the paint from composition A, producing films with good chemical and mechanical resistance with the gloss values shown in table I. 
     
                       TABLE I______________________________________Ratios Part A/Part B             Gloss 60°______________________________________20/80             4330/70             2350/50              760/40             1970/30             4180/20             69______________________________________ 
    
     In conformity with the present invention, two extruders were placed side by side, one was loaded with the A composition and the second with the B composition. 
     Extrusion was then started simultaneously, regulating the delivery of the extruded material to the same value. The extruded material exiting from the nozzles was still hot and was mixed together and then conveyed to the cooling calender. 
     The extrusion obtained in this way was cooled, crushed, ground and sieved through a 100 micron sieve. 
     This powder paint obtained in conformity with the invention of the hot union of paints A and B, applied and baked in the same conditions used for paint A, produced a film with a gloss of 7, thus with exactly the same value as that obtained with a 50/50 ratio of the cold mixture of Table I. 
     Separate and simultaneous extrusion of paints A and B in conformity with the invention was then repeated, varying the delivery ratios of the two extruders in order to obtain as output from the nozzles a union of the hot extrusions in the ratios shown in table I. 
     The gloss values of the paint films produced in this way are identical to those of table I. 
     
         ______________________________________EXAMPLE 2______________________________________Composition A (anhydride hydroxylated paint) composed of:ALFTALAT 01918     456BECKOPOX EH 644    164ADDITOL XL 496     30BENZOIN            5TITANIUM DIOXIDE   345              1000       partsComposition B (glycidylic carboxylicated paint) composed of:ALFTALAT AN 721    574ARALDIT PT 810     45ADDITOL XL 496     30BENZOIN            4BLANC FIXE         47TITANIUM DIOXIDE   300              1000       parts______________________________________ 
    
     Compositions A and B were extruded separately in the conditions of example 1A, and the resulting paints were applied and baked in the same way, producing a 92 gloss film for A and an 89 gloss for B. 
     In conformity with the invention, two extruders were positioned facing one another with the nozzles almost touching so that the molten material which was extruded combined together and dropped together into a cooling calender. 
     Composition A was loaded into one extruder and composition B into the other. The two paints were then extruded simultaneously and the delivery ratio of the two extruders was varied to obtain combinations of different ratios of the molten paints. 
     After cooling, the paints were flaked, ground, sieved and a layer of 30-40 microns was applied to the sheet and then baked for 30 minutes at 180° C. 
     The gloss values of the paints obtained in this way are given in table 2. 
     
                       TABLE 2______________________________________Ratios Part A/Part B             Gloss 60°______________________________________90/10             7380/20             4370/30             3260/40             2350/50             2240/60             2330/70             3420/80             44______________________________________