Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1993-12-30
2002-11-05
Woodward, Michael P. (Department: 1631)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S227000, C525S067000, C428S337000
Reexamination Certificate
active
06476148
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to matte-finished polymethacrylate (PMA) films.
BACKGROUND OF THE INVENTION
It has been found to be advantageous to protect materials against mechanical wear and the like, and against weathering, by coating the materials with a transparent polymethyl methacrylate (PMMA) film. Such films have a smooth, high gloss surface. However, there are a number of potential applications for which a matte finish of low reflectance is desired.
Matte finishes of thermoplastic plastic substrates, particularly films, are generally produced with the aid of a special matte-finish roll or a rubber-coated roll. In Jap. Pat. 90-28,239, for example, the manufacture of a film or sheet with a matte finish is described. The material comprises vinylidene fluoride resin and methacrylic acid ester resin, and the method comprises extrusion and passage of the extrudate through an embossing roll. A disadvantage of films produced by this method is that when stretched to a minor degree, as occurs for example when the film is wrapped over an edge, or is subjected to pressing in a laminating process (see, e.g., Winnacker-Kuechler, 1982, 4th Ed., Vol. 6, pub. Carl Hanser Verlag, p. 471), the film loses its embossed structure and thus its matte finish.
Matte effects can also be produced on a surface by means of polymer mixtures with a certain heterogeneous mixed phase morphology, possibly stabilized by additional additives. An example of this approach is EP-A 188,123, in which films are described which are comprised of an inherently incompatible polymer mixture of nylon-6 and polypropylene, with the phase morphology stabilized by an ethylene-methacrylate copolymer. Similarly, in EP-A 348,115, polyethylene films are described which contain an ethylehe-methyl methacrylate copolymer as the second phase, with the polyethylene functioning as the disperse phase.
The amounts of the disperse phases which produce the matte effect by their characteristic light dispersion is dependent, in such systems, on the thermodynamic equilibrium in the polymer mixture, and thus is very sensitive to the processing conditions of the film. Accordingly, it is very difficult in a laminating process to establish thermodynamic and therefore thermal conditions which are appropriate for the manufacturing conditions and which at the same time allow the amounts of the disperse phases to be unaffected. However, if these phases are not dimensionally stabile, the result is nonuniform light-dispersive behavior and thereby, at least in some places, loss of the matte effect on the surface.
Certain inorganic pigments, as set forth, e.g., in Jap. Pat. 89-234,427, are dimensionally stabile matte-finish agents (deglossing agents). According to the said patent, a matte surface is produced on polyester films at the time of extrusion, by addition of CaCO
3
or BaSO
4
together with microspheres of acrylic polymers such as PMMA. However, the high index of refraction of the inorganic pigments results in low transparency of the film, due to high losses of dispersed light.
Another disadvantage is the wear on roll surfaces in the film extrusion process, attributable to the inorganic pigments.
Consequently, a number of applications have proposed crosslinked polymer particles as light-dispersive pigments to produce a matte effect. Thus, Jap. Pat. 84-89,344 describes a weather-resistant protective film having a matte surface comprised of mixtures of polymers of fluorinated ethylenically unsaturated monomers, a crosslinked (meth) acrylate polymer prepared in several stages, and a matte-finish agent comprising crosslinked particles with mean diameter between 1 and 500 microns, comprised of a copolymer of (meth)acrylates, vinyl aromatics, additional &agr;,&bgr;-unsaturated compounds, and crosslinking agent(s). Another example is described in U.S. Pat. No. 3,992,486, wherein translucent plates or coatings having variable gloss can be produced using acrylic resin as the continuous phase which contains particles of crosslinked styrene copolymer(s) which copolymers may also contain methacrylic monomer units, wherewith the particles are uniformly dispersed in the continuous phase. These dispersed particles are produced in polymerization in the presence of polyfunctional unsaturated monomers, wherewith the continuous acrylic resin phase is first present as a dissolved polymer in the monomer mixture. During the polymerization the two polymer phases (acrylic resin and crosslinked styrene copolymer) separate, wherewith due to the poor miscibility of the polymers the styrene copolymer takes the form of small spherical particles with mean diameter between 0.5 and 30 micron.
The light dispersion capabilities of the particles described in the last two mentioned patents depends on the size of the particles and on the difference in index of refraction between the particles and the matrix. The incompatibility between the particles and the matrix is a disadvantage; it leads to substantial degradation of the mechanical properties of the matrix material.
Ger. Pat. 1,554,781 claims a method of manufacturing molded bodies comprised of thermoplastic plastics having a diamond shaped pattern on the surface, said method being characterized in that a mixture of two thermoplastic materials having substantially different flow properties is extruded. Extrudates of this type, when thin, e.g. in the form of films, may display inhomogeneous mechanical behavior, due to flow anomalies during extrusion and thereby variations in thickness of the extrudate.
In a number of practical applications, e.g. protection of articles subject to weathering, it is necessary to coat the articles with a film which provides protection against weathering effects such as the effect of moisture, wind, and sunlight, particularly radiation in the ultraviolet range, and in addition has high impact-strength and a matte-finished surface. The problem presented is to produce a film which has high inherent weather resistance and which protects weather-damageable articles against the above-mentioned weathering influences, and further has high impact strength and a matte-finished surface, so that articles coated with the film have high extensibility and low light reflection.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a composition having high extensibility, and which does not degrade or roll surfaces in a film extrusion process. In addition it is an object of the invention to provide a film which resists weathering (moisture, wind, sunlight), and in a preferred embodiment provides protection from UV radiation. Further, it is an object of the invention to provide a film with a matte-finish surface, which does not degrade upon cooling or heating. It is an additional object of the invention to provide a film having high impact strength, low incidence of white fracture when buckled or folded, and which maintains the matte-finish when stretched (e.g., wrapped over an edge) or subjected to pressing in a laminating process. Furthermore it is an object of the invention to provide a film which has reduced gloss, high light transmission, and which provides diffused light dispersion.
The inventive film is comprised of:
A. A thermoplastic polymer matrix A, in the amount of 30-099.9 wt. %, preferably 50-95%, more preferably 75-85% comprised of:
a1) 10-95 wt. %, preferably 50-90%, more preferably 70-80%, of a coherent hard phase with glass transition temperature >70° C., preferably >85° C., comprised of units as follows:
a11) 80-100 wt. % (of a1), preferably 85-95% of methyl methacrylate; and
a12) 0-20 wt. %, preferably 5-15%, of one or more other ethylenically unsaturated, radically polymerizable monomers; and
a2) 5-90 wt. %, preferably 10-50%, more preferably 20-30%, of a tough phase distributed in the hard phase and having glass transition temperature <−10° C., preferably <−30° C., comprised of units as follows:
a21) 50-99.5 wt. % (of a2), preferably >80% to 99.5%, more preferably 95-99.5%, of an alkyl acrylate wherein the alkyl group h
Roehm GmbH & Co. KG
Woodward Michael P.
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