Anti-Static Coated Paperboard or Similar Rigid Material

FIG. 1 is a perspective view of a corrugated container, with a plurality of packaging cells partially defined therein by transverse and longitudinal dividers of the multiple-ply anti-static paperboard of this invention.

FIG. 2 is a cross-sectional view taken on lines 2--2 of FIG. 1.

FIG. 3 is a cross-sectional view of the preferred embodiment of a multiple-ply anti-static paperboard of this invention.

FIG. 4 is a diagrammatic illustration of a method of forming the paperboard of FIG. 3.

FIG. 5 is a cross-sectional view of an alternative embodiment of the multiple-ply anti-static paperboard of this invention.

Many of the terms used throughout this application have recently been redefined by the American National Standard Institute in their new Packaging Material Standards for ESD Sensitive Items ElA-541, published in June of 1988. In these new standards, packaging materials are defined as being in the "conductive" range if they have a measurable surface resistivity of less than 10.sup.4 ohms per square. Until the standards were changed in June, 1988, "conductive materials" were defined as those having measurable surface resistivity of less than 10.sup.5 ohms per square. Similarly, the new standard, ANSI/EIA-541-1988, defines "Static-Dissipative materials" (formerly known as static-dissipative or anti-static materials) as those having a surface resistivity greater than 10.sup.5 ohms/square, but less than 10.sup.12 ohms/square. And, these same standards now define "Insulative materials" as those having surface resistivity equal to or greater than 10.sup.12 ohms/square. "Anti-static materials" are now defined by these new standards as those materials which minimize electrostatic charge when rubbed against or separated from themselves or other similar materials. For purposes of this application, and when used in this application, the terms "anti-static," "static-dissipative," "conductive" and "insulative" shall be used as defined in the new definitions contained in ANSI/EIA-514-1988.

With reference first to FIG. 1, there is illustrated a container 10 embodying the invention of this application. This container 10 is fitted therein with transverse dividers or partitions 12 and longitudinal dividers or partitions 13 which define the side walls of a plurality of cells 14. Each cell 14 is designed to hold an article 15 to be shipped. Both the transverse dividers 12 and the longitudinal dividers 13 have some excess portion 16 which extends beyond an adjacent cell 14 and into contact with side panels 17 of the container 10, thereby defining a plurality of voids 18 or empty spaces which remain unused. As known in the container industry, the transverse dividers 12 have vertically, downwardly extending slits, and the longitudinal dividers 13 have corresponding vertically, upwardly extending slits, to enable interfitting of the dividers within the container 10 to partially define the cells 14. Alternately, the vertical slits in the transverse divider 12 may be upwardly extending and the vertical slits in the longitudinal dividers 13 may extend downwardly.

As shown in FIG. 2, a lower pad 23 resides beneath the dividers, and an upper pad 22 overlays the dividers to completely enclose the cells 14. According to the invention, the transverse dividers 12, the longitudinal dividers 13, and the top 22 and bottom 23 pads are comprised of a multiple-ply anti-static paperboard 25, which is shown in FIG. 3.

The multiple-ply anti-static paperboard 25 comprises a layer of insulative paperboard or fiberboard 26 which is preferably sandwiched between two layers of low-density, anti-static polyethylene 27, as shown in FIG. 3. The interior paperboard ply 26 is electrically insulative, having a surface resistivity equal to or greater than 10.sup.12 ohms per square.

The preferred insulative inner layer 26 is a relatively rigid ply of paperboard formed by a conventional paper making slurry process to create a fiberboard or paperboard sheet having a surface resistivity equal to or greater than 10.sup.12 ohms per square. The insulative property of the paperboard is not critical to the practice of this invention. It is only critical that the inner layer 26 be relatively rigid such that it may be self-standing and provide physical protection to articles contained in the cells of the container.

A preferred embodiment of the multiple-ply anti-static paperboard 25 is illustrated in FIG. 3. In this embodiment, precast, permanently anti-static/static-dissipative plastic layers 27 are laminated onto the opposite sides of the conductive paperboard 26. The preferred precast, permanently anti-static/static-dissipative plastic layers 27 are layers of low-density, polyethylene film which have been coated and subjected to high-energy, electron-beam radiation so as to render the film permanently anti-static and permanently static dissipative. A complete description of the process for manufacturing such a polyethylene film may be found in U.S. Pat. No. 4,623,594. This polyethylene film is characterized by a surface resistivity of more than 10.sup.5 but less than 10.sup.12 ohms per square. One preferred precast, polyethylene film having this permanent anti-static/static-dissipative surface resistivity is manufactured by MPI Metallized Products, Inc. of Winchester, Massachusetts and is identified by that company as its "Staticure" product. This "Staticure+ product is particularly advantageous for use in this application because it is a permanently anti-static and static dissipative, i.e., it does not lose its anti-static and static-dissipative qualities or change its surface resistivity over prolonged periods of time.

With reference to FIG. 4, there is illustrated schematically the manner in which the paperboard product 25 of FIG. 3 is manufactured. As there illustrated, a roll 30 of paperboard 26 is unwound at a first level 31. The paperboard 26 may be electrically conductive, high-carbon content paperboard or it may alternatively be nonconductive or insulative paperboard. At a first extruding station 32, a thin film 33 of low-density, molten, polyethylene is extruded onto the top side of the paperboard 26. Before the polyethylene film solidifies, a first ply of the precast permanently anti-static/static-dissipative plastic film 27 is unwound from a roll 34 and applied over the top surface of the molten polyethylene film 33. Rollers 34 then direct the paperboard 26, having one ply of precast anti-static plastic film 27 applied thereto, to a second level 35. As the paperboard 26 moves along the second level 35, the paperboard 26 passes beneath a second extruding station 56 at which a second thin film 33 of molten, low-density polyethylene is applied to the now top surface (formerly the undersurface) of the paperboard 26. While this second film 33 of molten polyethylene is still in the molten state, a second ply 27 of precast permanently anti-static/static-dissipative plastic film is unrolled from a roll 37 onto the top surface of the molten polyethylene film 33. When the polyethylene films 33 are solidified, they permanently secure the top and bottom plies or laminates 27 to the paperboard 26 which is now sandwiched therebetween. The multiple-ply, anti-static paperboard 25 is now ready to be cut for use.

Thus, according to one preferred embodiment of the invention, a layer of paperboard 26 or other relatively rigid ply of material is sandwiched by layers of permanently anti-static/static-dissipative material. The anti-static layer adjacent the article prevents sloughing or abrading of the paperboard material onto articles packaged in the material, which could cause circuit damage. It also prevents generation of static electricity resulting from relative movement of the protected articles and the packaging paperboard.

The multiple-ply anti-static/static-dissipative paperboard also provides sufficient rigidity to physically protect packaged articles. This physical protection is achieved with a savings in material and labor, as compared to packaging requiring a bag.

The multiple-ply anti-static/static-dissipative paperboard of this invention has the advantage of being permanently anti-static and of permanently maintaining its static-dissipative quality. Otherwise expressed, the invention of this application, because of this permanence, has no shelf life. Heretofore, all anti-static and/or static-dissipative coatings or materials have been produced by doping polypropylene or other plastic materials with an amine so as to impart the anti-static property to the polypropylene plastic. That amine, though, was solely dissipated or gassified from the polypropylene plastic over a period of time with the result that the polypropylene plastic lost its anti-static property over a period of time. Consequently, such material had a limited shelf life.

Because the multiple-ply anti-static/static-dissipative paperboard of this invention is amine free, the material does not cause amine corrosion of metal packaged within such amine-free material. Additionally, many printed electrical circuits are imprinted on polycarbonate plastic, which plastic is subject to stress cracking when subjected or exposed to amines. The invention of this application, because it contains no amines, does not have this adverse effect upon polycarbonate boards. Anti-static plastics which contain amines are also humidity sensitive, i.e., they are only operative and only maintain their anti-static properties so long as there is some minimal humidity level maintained in the atmosphere. The amine-containing anti-static plastics therefore are not operative in very dry atmospheres to which such anti-static materials are often exposed. The invention of this application is not humidity dependent.

The multiple-ply anti-static paperboard of this invention may be made to provide chemical protection for packaged articles. For example, a corrosion inhibitor commonly referred to as Cobra Tech, manufactured by PMC Specialty and formerly made by Sherwin Williams, may be mixed into the outer layers 27 prior to application of these outer layers to the interior layer 26 in order to protect copper or copper alloyed articles. This substance dissipates off the outer layer to attach itself to the copper or copper alloy, thereby shielding the article from sulfuric compounds in the paper. Similarly, other corrosion inhibitors could be used with other types of articles, depending upon the metal that is required to be protected. Because the low-density anti-static/static-dissipative polyethylene layers of the preferred embodiment are chemically inert, they will physically shield the packaged article from chemical corrosion. Thus, the addition of a corrosion inhibitor for this embodiment would not be necessary, but would provide added protection against chemical corrosion.

While I have heretofore described one preferred embodiment of the multiple-ply anti-static/static-dissipative material of this invention as embodying a single ply of paperboard or other relatively rigid material sandwiched between two plies of anti-static/static-dissipative material, the invention of this application contemplates that such multiple-ply material may comprise only a single ply or coating 27 on one side of the base material 26 as illustrated in FIG. 5. Such a multiple-ply product is particularly useful in many packaging applications wherein only a single side of the material may be exposed to electrical components or static-sensitive articles. One such application for single-side coated, multiple-ply anti-static/static-dissipative material is in the production of corrugated paperboard material used in the manufacture of boxes or containers within which static-sensitive electrical components or articles may be packaged. When used to produce permanently anti-static/static-dissipative corrugated paperboard, the base ply of paperboard is first laminated or coated with a single ply of anti-static/static-dissipative material, and then that coated or laminated material is subjected to a corrugating process in which it is converted into corrugated paperboard.

As yet another alternative to the practice of this invention, the base ply of material 26, rather than being electrically insulative paperboard, may be a relatively rigid sheet of extruded plastic material to which the coating or ply of anti-static/static-dissipative material may be applied.

In the description of this invention, the preferred practice of this invention has been described as having the exterior ply of anti-static/ static-dissipative material laminated to the base ply of paperboard or other material. It is contemplated, though, that exterior ply may be applied to the base ply 26 by extrusion of the permanently anti-static/static-dissipative material onto the base ply.

The preferred embodiment of the invention described hereinabove employs "Staticure," a polyethylene material which has been chemically coated and subjected to high energy electron beam radiation as the anti-static/static-dissipative material in the multiple-ply product. The process by which such "Staticure" material is created is completely described in U.S. Pat. No. 4,623,594 issued Nov. 18, 1986 to MPI Metallized Products, Inc. This material has been found to be very satisfactory in the practice of this invention. It is contemplated, though, that such polyethylene material prior to being treated so as to render it anti-static/static-dissipative may have compounded therein conventional materials to render the polyethylene material biodegradable either by chemical breakdown of the material or by ultraviolet light breakdown.

It is also contemplated, and within the scope of this invention, that in lieu of polyethylene film material being utilized in the practice of this invention as the permanently anti-static/static-dissipative material, polyethylene foam may be treated and used as the permanently anti-static/static-dissipative ply of material. The polyethylene foam would otherwise be treated the same as the film in order to impart to the foam the permanent anti-static/static-dissipative quality. After formation of the foam and anti-static agent and treatment by exposure to electron beam radiation to render the foam permanently anti-static/static-dissipative, the foam would be adhered to the paperboard or other relatively rigid substrate in exactly the same manner that the polyethylene film is described hereinabove as being laminated to the paperboard or other substrate. The advantage of the foam-coated product is, of course, that it provides additional physical protection of any products packaged with the multiple-ply foam-coated product.

While I have described only a limited number of embodiments of the multiple-ply anti-static paperboard of this invention, it is to be understood that the invention is not to be limited solely to these embodiments. Various other alternative embodiments will be readily apparent to persons skilled in this art. Accordingly, it is to be understood that changes may be made without departing from the scope of the invention as particularly set forth and described.