Coating processes – Applying superposed diverse coating or coating a coated base – Synthetic resin coating
Reexamination Certificate
2002-02-25
2004-08-24
Beck, Shive P. (Department: 1762)
Coating processes
Applying superposed diverse coating or coating a coated base
Synthetic resin coating
Reexamination Certificate
active
06780473
ABSTRACT:
The present invention relates to a process for the preparation of multi-layer plastics composites.
Fluoropolymers have a plurality of advantageous properties. They are resistant to most chemicals. They are resistant to environmental influences such as, e.g., weathering and UV radiation. Fluoropolymers are therefore used for numerous purposes, specially as a protective layer against the action of chemicals or as a UV-resistant protective layer against environmental influences of other kinds. Fluoropolymers have the disadvantage, however, of being very expensive. Moreover, their mechanical properties, e.g., impact resistance, do not meet the requirements of all applications. Consequently, fluoropolymers are used in some cases as a layer in multi-layer plastics composites. The other layers contribute further advantageous properties, such as, for example, good mechanical properties or low costs or functional properties such as, for example, ease of melting-on, as a result of which the plastics composite may be further processed to laminates.
U.S. Pat. No. 4,659,625 discloses plastics composites of three layers, the first layer comprising polyvinyl fluoride or polyvinylidene fluoride, the second, middle layer comprising a vinyl acetate polymer, for example, an ethylene-vinyl acetate copolymer, and the third layer comprising a polar polymer, for example, polycarbonate. The middle layer of vinyl acetate polymer is used, according to the teaching of U.S. Pat. No. 4,659,625, as a coupling agent to bond the two outer layers. Accordingly, the method of preparation given in U.S. Pat. No. 4,659,625 is that of bonding the solid layers of polyvinyl fluoride or polyvinylidene fluoride and the polar polymer by means of vinyl acetate polymer. According to the teaching of U.S. Pat. No. 4,659,625, bonding takes place either at room temperature, in which case the vinyl acetate polymer is used as a solution, or by heating to above the softening point of the vinyl acetate polymer, in which case the outer layers remain solid. Moreover, the coextrusion of the three polymer layers is mentioned in U.S. Pat. No. 4,659,625 as a possible method of preparation. It is expressly pointed out in U.S. Pat. No. 4,659,625 that the method of preparation must be selected in accordance with the special properties of the polymers used for the three layers.
Coextrusion is a particularly advantageous process for the preparation of multi-layer plastics composites. In coextrusion, the layers of the composite are brought together in a coextrusion block as melt layers and then extruded together through a die. In order to produce sheets or films, a slot die, for example, is used during extrusion.
The preparation of plastics composites of several layers, wherein one layer comprises an ethylene-vinyl acetate copolymer and one layer comprises polycarbonate is not possible by coextrusion because sufficiently low-viscosity polycarbonate melts have such a high temperature, typically 280° C. to 320° C., that the properties of the ethylene-vinyl acetate copolymers are impaired, e.g., due to crosslinking. A deterioration in the optical properties such as, e.g., discolouration and a deterioration in the mechanical properties such as, e.g., strength and elasticity occurs. Such a deterioration is undesirable in terms of the use of the plastics composites, particularly, e.g., in the use in photovoltaic modules.
Plastics composites of three layers, wherein the first layer comprises a fluoropolymer (particularly polyvinyl fluoride, hereinafter abbreviated to PVF), the second, middle layer comprises polycarbonate (hereinafter abbreviated to PC) and the third layer comprises ethylene-vinyl acetate copolymer (hereinafter abbreviated to EVA) are required, for example, for the manufacture of photovoltaic modules. Their preparation by coextrusion is not, however, possible for the intended application mentioned, for the reasons already given.
Fluoropolymers and polycarbonate adhere very poorly to one another. For this reason, a coupling agent is normally used between the layer of fluoropolymer and the layer of polycarbonate.
The object of the present invention is, therefore, to provide a process for the preparation of plastics composites of three layers wherein the first layer comprises a fluoropolymer, the second, middle layer comprises polycarbonate, and the third layer comprises ethylene-vinyl acetate copolymer, which does not have the disadvantages of the prior art.
The object according to the invention is achieved by a process for the preparation of plastics composites of three layers, wherein the first layer comprises a fluoropolymer, the second, middle layer comprises polycarbonate and the third layer comprises ethylene-vinyl acetate copolymer, characterised by the following steps to be executed one after the other:
a) Preparation of a plastics composite of two layers, wherein the first layer comprises the fluoropolymer and the second layer comprises the polycarbonate,
b) Application of the third layer of ethylene-vinyl acetate copolymer to the polycarbonate layer of the plastics composite of two layers.
The present invention thus provides the process mentioned.
The process according to the invention has numerous advantages. The required plastics composites of three layers, wherein the first layer comprises a fluoropolymer, the second, middle layer comprises polycarbonate and the third layer comprises ethylene-vinyl acetate copolymer, can be prepared according to the process of the invention in a simple and inexpensive manner without the ethylene-vinyl acetate copolymer being damaged by heat, e.g., due to crosslinking.
The process is solvent-free and therefore advantageous from an economic and ecological standpoint. The process according to the invention permits the continuous preparation of endless plastics composites and, e.g., during a later manufacture of photovoltaic modules, obviates the separate insertion and polishing of the individual layers in each case (films or sheets).
The plastics composites according to the invention have good mechanical properties such as, e.g., high strength, high toughness and high elasticity. They have good optical properties such as, e.g., high transparency and high gloss and low production-related discolouration. They have good resistance to chemicals and environmental influences such as weathering and UV radiation. This is particularly the case when at least one of the three layers has been provided with further additives, such as, e.g., UV stabilisers, absorbers, heat stabilisers, colorants, catalysts, hydrolysis stabilisers, mineral substances, nanoparticles etc. The fluoropolymer layer (optionally also the PC layer) is preferably provided with a sufficient amount of an adequate UV absorber. Moreover, the PC layer is preferably protected by coextrusion, coating or laminating with a UV absorber-containing material (for example, 2 to 20 wt. % of UV absorber), whether or not the PVF layer contains UV absorber. The layers of the plastics composite adhere well to one another.
The process steps a) and b) of the process according to the invention may be carried out one immediately after the other or with an interval of time between them and/or at a distance from one another, e.g., in order to store the two-layer plastics composite on an interim basis. It is preferable to carry out said steps one immediately after the other. In this case, a heating or cooling of the two-layer plastics composite may take place between process steps a) and b).
A preferred embodiment of the process according to the invention is that in which a coupling agent layer is applied to the polycarbonate layer on the two-layer plastics composite which is prepared in process step a), prior to the application of the third layer in process step b).
Suitable coupling agents are, for example, those based on acrylate.
A further preferred embodiment of the process according to the invention is that in which the two-layer plastics composite in process step b) has a temperature at which the ethylene-vinyl acetate copolymer does not undergo the
Gorny Rüdiger
Roelofs Marco
Röhner Jürgen
Zander Klaus
Bayer Aktiengesellschaft
Beck Shive P.
Fletcher, III William Phillip
Gil Joseph C.
Preis Aron
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