Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2000-12-05
2003-01-21
Ahmad, Nasser (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C015S215000, C296S039100, C296S039200, C296S039300, C428S143000, C428S147000, C428S409000
Reexamination Certificate
active
06509084
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to thermoplastic products having slip resistant surface properties. The invention particularly applies to thermoformed pickup truck bed liners having an increased coefficient of friction on load bearing and cargo carrying surfaces thereof. The invention further relates to a variety of other practical and industrial applications such as pallets, totes and trays for packaging and shipping, sport and recreational products, and walking surfaces such as marine docks and decks, swimming pool surfaces, showers, bathtubs, walks, stairs, and floor mats.
BACKGROUND INFORMATION
Thermoplastic materials are being used to manufacture a growing variety of products. Thermoplastics can be conveniently and economically formed by various methods including thermoforming, injection molding, blow molding, compression molding, rotational molding, and extruding, for example. Products made of thermoplastics are durable, economical, and adaptable to many different applications. One disadvantage that has plagued many thermoplastic products is a relatively low surface coefficient of friction. In other words, the thermoplastic surfaces are too slippery to be acceptable in some applications. The thermoplastic surfaces become especially slippery when wet, and thus may present dangerous conditions when thermoplastic products are used in an outside environment, e.g. pickup truck bed liners, or used in typically wet conditions, e.g. swimming pool or spa areas and marine docks and the like, and especially when the thermoplastic materials form walking surfaces, e.g. steps, floor mats, runners, and the like.
A particular thermoplastic material that has been proved economical and suitable for making many different products is high density polyethylene (HDPE). However, high density polyethylene exhibits a rather low coefficient of friction, especially when wet, so it particularly suffers the disadvantages of slipperiness mentioned above. This problem is well recognized in the field, and various attempts have been made to correct it. One approach for increasing the surface coefficient of friction involves mechanically forming a rough surface texture on the thermoplastic material, for example by embossing the surface of the product as it is being molded. Disadvantages of this approach are that the embossing increases the cost and complexity of the molding or other forming operation, the embossed surface textures have been found to perform inadequately when wet, and the embossed surface textures can wear down with use, whereby the coefficient of friction is again reduced to that of the smooth ordinary HDPE.
Another approach for trying to improve the surface coefficient of friction is to apply a surface coating onto the polyethylene material. The difficulty with such an approach is that the HDPE is rather inert and molecularly non-active, so that conventional antislip coating materials do not adhere sufficiently to the HDPE surface. Thus, the durability and wearability of the surface is inadequate, because the coating materials peel or flake off of the HDPE. In order to provide sufficient adhesion, prior efforts have involved forming a continuous film of an antislip material onto the HDPE surface, for example by coextruding or coforming the antislip film with the HDPE material. By providing such a continuous film of antislip material, the surface area of contact adhesion is maximized, and the locations at which peeling, separation, or abrasion of the antislip material from the underlying HDPE material are minimized. Unfortunately, the use of a continuous film of an antislip material increases the cost of the product, limits the types of forming or molding processes that can be used to manufacture the product, and also increases the cost and complexity of carrying out the forming method.
An example of the above discussed attempts to use a continuous film of nonslip material on an HDPE base material is represented by conventional bedliners for pickup truck cargo carrying areas. Essentially all truck bed liners are thermoformed from high density polyethylene (HDPE) sheets. Other materials such as ABS, synthetic rubber plastic, and other thermoplastic polymers are sometimes used. The thermoplastic sheets are heated to a thermoforming temperature in a thermoforming oven and are deformed by ambient air pressure after application of vacuum on one side in a thermoforming mold to produce the desired product. Many products other than truck bed liners are also manufactured by this process.
U.S. Pat. No. 4,693,507 (Dresen et al.) describes a truck bed liner with antislip surface properties. The disclosure of U.S. Pat. No. 4,693,507 is incorporated herein by reference. An increased coefficient of friction on the liner surface is achieved by applying a continuous film or layer of elastomeric material over the HDPE sheet. The thickness of the integral elastomeric layer or film is typically in the range of 25 mils-30 mils (625&mgr;-750&mgr;). The elastomeric film is preferably coextruded over the HDPE sheet which is typically 180 mils-250 mils (4.5 mm-6.2 mm) in thickness. The elastomeric film layer can alternatively be applied to the HDPE sheet by lamination, by an adhesive, or by heat application.
According to the Dresen et al. scheme, an increased frictional force is achieved primarily by the “plowing effect” or embedding effect of harder cargo pieces pressing into the softer continuous elastomer film layer. This antislip plowing effect is attributable to the continuous film or layer of the softer elastomer. A disadvantage of the Dresen et al. scheme however, is that the frictional force attributable to the integral elastomeric layer is reduced, and the layer also becomes slippery, when it is wet. Another disadvantage of the Dresen et al. method is the increase in cost of adding and applying the integral and continuous film layer of elastomeric material by coextrusion, lamination, adhesion, or heat application. The elastomer film of Dresen et al. generally extends across the entire substrate plastic sheet. The Dresen et al. film also does not allow different antislip characteristics to be achieved at different locations, namely the film has a uniform antislip characteristic over the entire area to which it is applied.
OBJECTS OF THE INVENTION
In view of the above discussion, it is an object of the present invention to provide thermoplastic products that have more effective antislip surface properties in a manner that is more economical and adaptable to a greater variety of products. More specifically, the invention aims to avoid the disadvantages in the prior art, namely to provide a thermoplastic product having an antislip surface that retains its antislip surface properties even when wet, that avoids the use of a continuous film of antislip material, and that provides good adhesion, durability and wearability of the antislip material on the thermoplastic base material of the product.
It is a further object of the invention to provide methods of imparting antislip properties to thermoplastic surfaces, which increase frictional forces and the coefficient of friction for wet as well as dry surfaces. The different methods are respectively suitable for achieving different characteristics of the antislip surface, and for application to different products formed by different techniques. A first method is especially suited to form an antislip surface be fore and during the thermoforming of the product, and a second method is particularly suited to provide an antislip surface on a product that has been previously molded or otherwise formed.
Another object of the invention is to increase the practical coefficient of friction and frictional force on thermoplastic surfaces by means of increased three dimensional macroscopic surface relief, asperities, and roughness. This is to be accomplished with hard and tough antislip materials preferably having viscoelastic or elastomeric properties and a hardness that is not brittle or sharp. It is thus an object of the invention to specify particular materi
Cullivan Edward E.
Sturtevant Thomas M.
Ahmad Nasser
Custom Plastics Molding, Inc.
Fasse W. F.
Fasse W. G.
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