Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2000-01-11
2003-02-25
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C524S404000
Reexamination Certificate
active
06524694
ABSTRACT:
BACKGROUND OF THE INVENTION
Transparent thermoplastic polymers are widely used in place of glass in the manufacture of a variety of products because of their light weight, their resemblance to glass, their economical use, and their excellent impact resistance and other physical properties. For example, transparent blow-molded containers, such as vials, cosmetic bottles, liquid flavoring containers and beverage bottles made of polyethylene terephthalate (PET), are increasingly in demand because they are easily molded and relatively inexpensive. Transparent thermoplastic polymers are used for a variety of other molded, extruded or formed products, such as drinking cups, cooking and eating utensils, food containers, refrigerator storage containers, medical and pharmaceutical tubing and extruded parts, packaging films, extruded sheets and toys. In addition to PET, the transparent polymers commonly used in the manufacture of these products include, for example, styrene acrylonitrile copolymers (SAN), polycarbonates, acrylics, ionomers, polystyrenes, and the like.
Although most transparent plastics have excellent clarity and resemblance to glass, it is desirable in many cases to improve the aesthetic appearance of transparent plastic products by making them translucent, i.e. “frosted”. In the context of the invention, the terms “translucent” and “frosted” are intended to encompass all gradations of translucency, from almost transparent to almost opaque. Such treatment is intended to impart a softer, more elegant and high grade visual textured appearance to the plastic. Containers and other products having a frosted glass appearance are in demand particularly in the packaging of cosmetics, health, beauty and personal hygiene goods, foods and beverages, as well as for household products, such as frozen food trays, tableware (dishes, cups, plates) and other decorative and utilitarian housewares, and other products, such as cigarette lighters. The frosted glass appearance can be visual only (a smooth surface) or can be both visual and tactile (a rough surface).
Conventional methods for making transparent plastic products translucent include spraying the smooth outer surface of the plastic product with a coating to form a matte surface layer. The plastic article appears frosted because the rough surface diffusely reflects light. Such matte coatings, however, tend to be easily separated from or scratched off the smooth polymer surface due to friction with other articles, and they require an extra production step which adds to production costs. Another method employs a mold with an inner surface that has been roughened to impart a rough or textured matte finish to the molded product. However, the roughened mold may be more expensive to manufacture than a standard mold and, because it is permanent, the mold is limited to producing finished products having a matte surface. Moreover, rough matte surfaces that are designed to resemble ground or frosted glass have tiny projections and recesses that reflect light but may be unpleasant to the touch and easily soiled due to dust and oils transferred from the hands. Oils, in particular, fill recesses and add shine to these rough surfaces. Thus, the amount of diffused light is decreased and any original lustrous appearance may be readily lost.
Other reported methods for achieving a frosted effect in blow-molded bottles and other containers include injection molding of a preformed piece, followed by sandblasting and then heat-crystallizing of the outer surface to roughen and opacify the surface layer prior to the blow molding step. A ground glass effect has been produced in plastic containers by using a blend of olefin resins in which one resin comprises a continuous phase in which another resin is dispersed. Frosted surfaces on bottles have been achieved by heat-crystallizing the outer surface while leaving the inner surface transparent, to form a milky white or translucent effect. Chemical flatting agents have also been employed to opacify acrylic.
Although the above methods produce various types of frosted glass effects, there is still a need for simple and inexpensive methods and compositions for imparting a translucent frosted glass effect to transparent thermoplastic polymers.
SUMMARY OF THE INVENTION
The invention provides inexpensive compositions and one-step and two-step methods for imparting a variety of individual translucent optical effects to transparent thermoplastic polymers. The methods and compositions of the invention are particularly useful for imparting a lustrous and rich translucent optical effect to packaging products, such as blow-molded and injection molded products manufactured from polyethylene terephthalate (PET) and styrene acrylonitrile copolymer (SAN), which have traditionally been left transparent because of their excellent clarity and resemblance to glass. Although the invention is herein described with respect to transparent polymers, a translucent effect may also be obtained by the compositions and methods of the invention in polymers that are “near transparent”, such as high density polyethylene and polypropylene. The term “transparent”, as used herein below, is intended to encompass all grades of thermoplastic polymers that are “near transparent” as well as transparent.
The desired translucent optical effect is selectable from a continuum of visual effects from very smooth to very grainy, and is accomplished by selecting an appropriate invention composition and method. Transparent or semitransparent color compounds, pigments and dyes may also be added to the invention compositions to produce colored translucent products.
The invention employs conventional molding, extruding and forming techniques with existing tooling. Thus, the methods do not require expensive extra production steps; nor do they require specialized tools. By the method, a translucent visual frosted glass effect can be imparted to virtually any transparent or near transparent thermoplastic polymer used in the production of molded, extruded or formed products, including films.
In one embodiment of the invention, a one-step method comprises forming a composition comprising (i) 0.01 to 15 parts by weight of at least one particulate, light-diffusing material having an average maximum particle size of about 0.1 micron to about 200 microns, preferably about 1 micron to about 100 microns, and (ii) 85 to 99.99 parts by weight of at least one transparent thermoplastic polymer. The mixture may be molded, extruded or formed by conventional means to form a translucent polymer product.
The particulate material may be in the form of, for example, powders, flakes, platelets, fibers, whiskers, aggregates, agglomerates and mixtures of these. Preferably, the particulate material is selected from the group consisting essentially of calcium sulfates, talc, silicates, kaolin, silicas, mica flakes, mica platelets, mica pearls, titanates, metal sulfates, metal carbonates, sulfides, metal oxides, borides, wollastonite, basalt, boron, boron nitrides, ceramics, naturally occurring calcium carbonates, and mixtures of the foregoing. If the particulate material is boron nitride, it is preferably in the form of for example, powders, aggregates, agglomerates, and the like, or mixtures of these.
In another embodiment of the invention, a two-step method is employed that comprises the steps of forming a concentrate composition which comprises a mixture of (i) 40 to 90 parts by weight of a carrier agent selected from the group consisting of a first transparent thermoplastic polymer, a dispersing agent, and mixtures of these, and (ii) 10 to 60 parts by weight of at least one particulate, light-diffusing material having an average maximum particle size of about 0.1 to 200 microns, preferably about 1 to about 100 microns, as described above. If a mixture of the first polymer and the dispersing agent is employed, the mixture preferably comprises 80 to 98 parts by weight of the first polymer and 2 to 20 parts by weight of the dispersing agent. The carrier agent is preferably finely gro
Jones Day Reavis & Pogue
PolyOne Corporation
Thibodeau Paul
Zacharia Ramsey
LandOfFree
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