Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1989-12-15
1992-05-05
Michl, Paul R.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
523351, 523353, 26421123, 4253812, C08K 1300, C08J 320, B29C 4760, A01J 2102
Patent
active
051108461
DESCRIPTION:
BRIEF SUMMARY
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.
ADDITOL XL 432
Blocked aliphatic isocyanic prepolymer produced and marketed by Hoechst.
ADDITOL XL 496
Masterbatch--spreading additive marketed by Hoechst, containing 15% of active substance.
ALFTALAT 01918
Experimental polyester resin with hydroxyl end radicals.
BECKOPOX EH 694
Polyanhydride, produced and marketed by Hoechst.
ALFTALAT AN 721
Polyester resin with carboxyl end radicals--produced and marketed by Hoechst.
ARALDIT PT 810
Triglycidyl isocyanurate
REFERENCES:
patent: 2540146 (1951-02-01), Stober
patent: 4405547 (1983-09-01), Koch et al.
Farronato Silvestro
Gazzea Sergio
Hoechst Sara S.p.A.
Michl Paul R.
Niland Patrick
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