Abstract:
A double-sided, slip resistant material is produced using a blown film process which produces a film having an interior heat sealable layer, a core layer of flexible polyolefin and an exterior polyolefin elastomer layer in combination with a blowing agent and optionally grit to produce a double-sided slip resistant material. A number of rollers are provided after nip rollers have fused the film together, and which form part of a machine direction orienter (MDO) that is used in line in the manufacturing process to heat, and then cool and condition (anneal and relieve any stresses and/or thickness inconsistencies in the film) prior to the film being wound onto a roll for storage.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application No. 61/150,405 filed on Feb. 6, 2009 entitled “Double-Sided Slip-Resistant Material and Method of Making Same” which is incorporated fully herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to slip resistant material and more particularly, relates to a slip resistant, lightweight cloth-like material useful for products such as, but not limited to, a drop cloth for the moving and painting industry. 
     BACKGROUND INFORMATION 
     There is often a need for lightweight protective material such as drop cloths to cover floors and furniture during moving, construction or other activities such as painting and decorating. One problem that has consistently been struggled with for such material is the need of the material to be relatively impervious to liquids such as water and paint. 
     The prior art has dealt with the problem of waterproofing lightweight cloth materials by placing a plastic coating on one or both sides of a paper or cloth material. Unfortunately, although this makes the product waterproof, it also makes it very slippery. If a painter cannot place a ladder on the material without fear that it will slip out from under him or her, they are not apt to use it. 
     There have been some prior art attempts at making non-slip surfaces but this relates mostly to roofing materials or more permanent material such as floor tapes and the like. 
     Accordingly, what is needed is a lightweight, reusable, puncture resistant, cloth like material that is generally impervious to water and other liquids while providing at least one surface that is a non-slip surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the present invention will be better understood by reading the following detailed description, taken together with the drawings wherein: 
         FIG. 1  is a perspective schematic view of a portion of a system for making the slip resistant material according to the present invention; and 
         FIG. 2  is a schematic diagram of the travel path of the double-sided slip resistant material of the present invention after the material has been blown showing incorporation of a machine direction orienter (MDO) in-line in the manufacturing process. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention features a two-sided slip resistant material made by the blown film process, which process is well known in the industry, comprising the co-extrusion of multiple layers to produce a finished film composite having the desired characteristics described herein. 
     As illustrated in  FIG. 1 , a film blowing machine (not shown but well known in the art) produces a film “bubble”  10  comprising, in the preferred embodiment and without limiting the present invention, 3 layers or films: A, B and C. In the preferred embodiment, layer A, (the inside most layer of the bubble) is a heat sealable thermoplastic layer of approximately 0.2-2 mils in thickness having a softening point in the range of 110° to 200° F. which facilitates gluing of the two “A” layers together at a low temperature, as will be described below. Layer A may be an EVA, EMA, LDPE or POP resin based layer. An advantage of using an Ethyl Vinyl Acetate (EVA) layer is that the VA (vinyl acetate) content may be adjusted to achieve the desired softening point of the layer to facilitate its gluing to an adjacent similar layer. 
     Layer B, the central or center layer, is preferably a flexible polyolefin layer having a thickness of approximately 0.5-2 mils. Suitable material for the center “B” layer include, LDPE, LLDPE, TPO, and POE. In addition to the resin this layer may also include a colorant, UV stabilizer, UV absorber and antioxidant, which will be exposed during the manufacturing process after the formation of the collapsed bubbles in the C layer. An example of a potential UV Stabilizer is Chimassorb 994™; examples of potential antioxidants include Irganox 1010™, Irganox 1076™ and Irgafos 168™; and an example of a potential UV Stabilizer is Cyasorb UV-531™. 
     The C layer (the outermost layer of the film which forms the top and bottom of the finished film product) is also a flexible polyolefin layer. This layer, however, contains a “blowing” agent that causes the film to form many small “bubbles” on the exterior surface  12  of the C layer. The blowing agent creates a gas in the extruder during the melting process and this gas is distributed throughout the “C” layer and is soluble in the molten plastic due to the high extruder pressure. When the film exits the blown film die, there is a drop in pressure, and bubbles form in the “C” layer. By, stretching and cooling the film, the bubbles collapse forming a rough, nonslip open celled surface  12 . 
     The blowing agent can be either a physical blowing agent (PBA) such as carbon dioxide or butane, or an exothermic or endothermic chemical blowing agent (CBA) such as a sodium bicarbonate and citric acid mixture, which decomposes under heat during the extrusion process and produces a gas. 
     In the preferred embodiment, the preferred flexible polyolefin is a polyolefin elastomer (POE) such as Dow Chemical&#39;s “Engage” product preferably, Engage grade 8003. After considerable experimentation, it has been determined that not all polyolefin elastomers are suitable for the skid resistance application. A resin with appropriate melting point, and softness to create bubbles that are very rubbery, flexible and have a high Coefficient of Friction (COF) creating a surface with significant “slip” resistance is required. These characteristics, which can be found in the Engage 8003 product include: flexural modulus less than 200 MPa, and Durometer hardness (Shore A) less than 100. 
     In addition to the polyolefin elastomer, layer C may also include a coloring agent, to color the finished product, a UV stabilizer, UV absorber and antioxidant, as well as a grit material such as ultra-high molecular weight polyolefin which will adhere to the outside of the bubbles formed by the blowing agent and add additional slip resistance to the finished film. 
     Near the top of the bubble  14 , two rollers  16 ,  18  (top nip rollers) are utilized to “collapse” the bubble  14  causing both sides of the bubble to come together. In the preferred embodiment, one of the rollers is a rubber roller while the other is a metal nip roller, which is heated. The temperature of the nip is such that it is above the softening point of the resin in the “A” layer. This causes the two inside “A” layers to fuse together forming a single film structure. 
     The processing of the fused film layer  20  is shown schematically in  FIG. 2 . After the film  20  leaves the nip rollers  16 / 18 , the film enters a set of in-line rollers  24 - 30 , which serve as a Machine Direction Orienter (MDO)  22 . The MDO rollers  22  serve as a post treatment of the film, annealing or conditioning the film to take any stresses out of the film and to remove any variation in film thickness. The MDO section consists of 2 sets of 2 rollers each. The first two rollers  24 / 26  are heated to above the glass transition temperature of the resin of the inside A layer of the film  20 . These rollers operate at a speed, which is the same as the speed at which the blown film  20  is manufactured. 
     The next two rollers  28 / 30  are cooling rollers operated at a temperature in the range of 80-100° F. In addition, the cooling rollers  28 / 30  are operated at a speed of 2% to 10% faster than the line or manufacturing speed at which the first 2 rollers  24 / 26  operate, thus causing the now fused, double-sided film to stretch in the region and direction indicated generally by arrow  32 . The MDO section anneals the film, gives it a second heat treatment annealing the film and relieving it of any stresses. 
     The pair of cooling rollers  28 / 30  serve to cool the film down before it is wound into a roll for later use. Although the use of an MDO is known in the art, it is not known to place such a device “in line” in the manufacturing process. Typically, in the prior art, a film is blown, wound onto a roll, subsequently unwound into an MDO for stretching, and then rewound before use. Accordingly, the present invention provides a double-sided non-slip, waterproof, plastic film which is easy and relatively inexpensive to manufacture and which is very slip resistant on both sides, and can be used for numerous applications such as painter&#39;s drop cloths, non-slip protective coverings, moving cloths and the like. 
     Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention, which is not to be limited except by the allowed claims and their legal equivalents.