Method of coating packaging material with anti-static composition

A rigid packaging material having a coating of heat-sealable, anti-static plastic. A fiberboard sheet substrate is coated with a lamina of polyethylene made electrostatic-free by the addition of an organic anti-static compound. When skin-packaged with a film of heat sealable, anti-static plastic material, a static-sensitive item is completely enclosed by a static-free barrier package.

BACKGROUND OF THE INVENTION 
The present invention relates to anti-static packaging material and to 
methods of producing such materials, and more particularly to a laminated 
packaging material having a semi-rigid substrate sheet of packaging 
material which is coated with a layer of heat-sealable, anti-static 
plastic material. The structure provides both mechanical support for a 
static-sensitive item to be packaged and a continuous electrostatic shield 
to protect the item from static buildup while it is being packaged. 
Furthermore, the heat-sealable plastic coating permits a flexible 
anti-static skin film to be heat sealed to the material so that it may be 
employed in skin-packaging systems. 
Heat-sealable, anti-static packaging materials which are intended to 
protect static-sensitive items from damage due to triboelectric charging 
are known in the art. Such a material is disclosed, for example, in U.S. 
Pat. No. 3,572,499 to Mondano which discloses the fabrication of a 
laminate material consisting of a layer of metal foil which is sandwiched 
between an electrically conductive, heat-sealable, synthetic plastic. The 
material disclosed in the Mondano patent is intended to be used as a wrap 
or fabricated into a bag, and is not practical for use in skin-packaging 
operations, either as a skin-packaging film or as a relatively rigid 
material which can support the item being packaged. A laminated 
heat-sealable packaging material which is provided in sheet form and which 
is resistant to the penetration of grease or oil is taught in U.S. Pat. 
No. 3,775,239 to Snow. This packaging material, although excellent in 
resistance to certain specified compounds, does not provide an anti-static 
protection to static-sensitive components. A method of coating various 
surfaces with a plastic coating material to which a metallic powder has 
been added is taught in U.S. Pat. No. 3,085,025 to Eaton. The method of 
the Eaton patent includes applying a thermoplastic material to the surface 
to be coated followed by applying a powdered metallic matter to the 
thermoplastic material, and then heating the film to a viscous liquid into 
which the powdered matter migrates. The liquid is then cooled so that it 
is returned to its solid state with the powder bonded thereto. However, 
the object of the Eaton process is to utilize the suspended powdered metal 
to provide a surface appearance to the coated object, not to impart 
electrical characteristics such as a resistance to static discharge. 
U.S. Pat. No. 3,104,985 discloses compositions of cured polyolifin which 
are suitable for producing conductive films by adding fillers such as 
carbon black to solutions of plastic. Carbon black is an unacceptable 
material for use in many packaging operations since it sloughs off of the 
plastic in which it is dissolved and contaminates the packaged items. U.S. 
Pat. No. 2,405,104 teaches the construction of an anti-static ordnance bag 
having a layer of combustible material which is inappropriate for use in 
skin packaging operations. A method for encapsulating rigid items in 
molten plastic is described in U.S. Pat. No. 3,313,089; however, no 
reference or teaching is made of providing anti-static material in my 
method step to prevent the buildup of static charges. 
Other examples of various coating, packaging, or bagging techniques or 
materials are found in the following U.S. Pat. Nos.: 3,373,918; 3,143,364; 
3,078,201; 3,057,539; 2,845,962; 2,817,604; and 2,551,087. However, such 
techniques and materials are not adapted for use in skin packaging 
operations of the type already owned and maintained by many packaging 
enterprises. 
Therefore, a need exists for a material which is suitable for packaging 
static-sensitive items which combines protection of the item from exposure 
to electrostatic charge, mechanical support of the item while it is being 
packaged and handled in packaged form, and adaptability to 
state-of-the-art packaging techniques. 
It is therefore a principle object of the present invention to provide an 
improved material for packaging static-sensitive items. 
It is a further object of the invention to provide an anti-static packaging 
material which can be utilized in a heat-sealable, skin-packaging process. 
Another object of the invention is to provide an anti-static, heat-sealable 
packaging material which provides mechanical support to the item being 
packaged. 
Another object of the invention is to provide an anti-static heat-sealable 
package which is constructed from such a material. 
A further object of the invention is the provision of a method for making 
such a material. 
These and other objects of the invention will become readily apparent from 
the ensuing description when it is taken together with the following 
drawings.

SUMMARY OF THE INVENTION 
The present invention provides an improvement over existing anti-static 
packaging materials by utilizing a sheet of stiff substrate material on at 
least one surface of which a sheet of heat-sealable organic plastic 
material is formed which has been made electrostatic-free by the addition 
of an organic anti-static compound. The resulting packaging material can 
then be formed into a six-sided anti-static container for the packaging of 
static-sensitive items, or a sheet of the material may provide 
electrostatic protection and mechanical support to an item which is to be 
skin-packaged with a heat-sealable plastic sheet. 
The present invention also provides a method for producing such a material. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
As is known in the packaging art, certain techniques are used to package 
static-sensitive items for storage or shipment. One packaging technique 
involves the construction or assembly of a six-sided container, such as a 
box, in which the item to be packaged is enclosed. Another, more modern 
method, called "skin-packaging", consists of drawing a vacuum between the 
item and a semi-molten plastic film. The heated, semi-molten film bonds to 
itself and around the item during cooling, thereby forming a seal which 
maintains the vacuum between itself and the enclosed item. Typically, when 
being skin-packaged, the item will be carried on a piece of stiff material 
which provides support for the item during the packaging procedure. A 
packaging material which is useful with either packaging technique and 
which provides protection from static buildup for static-sensitive items 
such as electronic components or modules is illustrated in FIG. 1. 
As shown in FIG. 1, the material of the invention, indicated generally by 
10, consists of a substrate sheet of packaging material 12. The substrate 
material preferably comprises a standard packaging material which 
possesses sufficient stiffness or rigidity to provide support to an item 
to be packaged, yet which is deformable so that it can be shaped into the 
form of a package. Such a material can comprise, for example, cardboard or 
fiberboard, either of which is commonly used to construct six-sided 
enclosures such as boxes for packaging electronic items. 
A second layer 13 is formed on, and is co-extensive with a surface 14 of 
the substrate sheet 12. The material layer 13 possesses a high surface 
resistivity to prevent the buildup and discharge of static electricity 
between an item which is to be packaged and the surface of the packaging 
material 12 which encloses the item. The material layer 13 is composed of 
a thermoplastic resin to which an organic anti-static compound has been 
added to provide the resulting material with the level of electrical 
resistivity which is necessary to prevent the buildup of static charges. 
The material layer 13 also possesses the characteristic of being able to 
bond to a semi-molten plastic film which is used in a skin-packaging 
process. A thermoplastic ionomer resin material which is commercially 
available from E. I. du-Pont de Nemours and Company under the trademark 
"Surlyn D" is useful as the basis material from which the material layer 
13 may be formed. 
In composing the layer 13, a solution can be made which consists of the 
materials listed in Table I. The materials are listed in Table I together 
with the portion which they contribute to the total volume of the 
solution. For example, the polyethylene compound constitutes between 31% 
and 34% of the solution volume. 
TABLE I 
______________________________________ 
PORTION OF 
MATERIAL SOLUTION VOLUME 
______________________________________ 
Polyethylene Compound 
31-34% 
Deionized Water 30-34% 
Isopropynol Alcohol 
30-34% 
Organic Anti-Static Compound 
&gt;2% 
______________________________________ 
The organic anti-static compound can comprise a tertiary animal fatty amine 
plus any number of available proprietary compounds. One such compound is 
used by Gemini Plastics, Los Angeles, Calif. to manufacture an antistatic 
film distributed under the trade name of GPAS 1400. 
A solution having a composition as specified in Table I is heated to 
approximately 200.degree. F. in order to make it viscous so that it can be 
mixed to a homogeneous composition and applied by any known technique to 
the substrate sheet 12. For example, the heated solution may be applied by 
any known laminating technique. Once the solution is applied to the 
surface of the substrate sheet 12, it is metered to any desired thickness 
and then cooled and dried. Once the material layer 13 has been applied to 
the surface of the substrate sheet 12, the uniformly distributed organic 
anti-static compound will provide the packaging material 10 with the 
resistance to the formation of surface static charges which is required 
for the packaging of static-sensitive items. 
One type of anti-static package which may be formed from a sheet of 
material having the structure illustrated in FIG. 1 and explained 
hereinabove can be understood with reference to FIGS. 2 and 3. FIG. 2 
illustrates a sheet of anti-static material 15 which is fabricated 
according to the above-described procedure and which has the shape of a 
cross. The cross includes a pair of opposing arms 16 and 18 and another 
pair of opposing arms 20 and 21. The arm 20 has a tab 22 along one edge 
and the arm 21 has a slot 23 which extends through the arm 21. A printed 
circuit card 24 is placed on the area 25 which is formed by the 
intersection of the arms of the cross. The surface 26 of the sheet 15 upon 
which the circuit card 24 rests has been coated with a static-resistive 
layer according to the procedure disclosed above. 
The sheet 15 having the shape illustrated in FIG. 2 can be closed to hold 
the printed circuit board 24 in a six-sided container illustrated in FIG. 
3. The coating of the surface 26 with the anti-static layer prevents the 
buildup of a static charges which may accumulate while the sheet 15 and 
the circuit board 24 are being handled during the packaging procedure. 
As illustrated in FIG. 3, the sheet 15 can be formed into a six-sided 
container by folding the opposing arms 16 and 18 over the circuit board 24 
and then folding first the arm 21 and then the arm 22 over the circuit 
board and the arms 16 and 18. To keep the package closed, the tab 22 is 
inserted through the slot 23. 
FIG. 4 illustrates the use of material fabricated according to the method 
of the invention in a skin-packaging procedure. In the procedure, a sheet 
of material 30 which is fabricated according to the above-disclosed method 
supports a printed circuit board 32 on a layer 33 of anti-static material. 
Preferably, the sheet 30 is cut so that a continuous border of the layer 
33 surrounds the circuit board 32. The sheet 30 with the circuit board 32 
resting thereon is then sealed by any typical skin-packaging technique 
with a film of flexible plastic packaging material 34. During the 
packaging operation, the material 34 will bond to itself and to the layer 
33 of anti-static material. This will enhance the quality of the completed 
package by increasing the total area of the completed bond. An apparatus 
which can form the skin-packaged container illustrated in FIG. 4 is 
available from Ampack Corporation under the Model Name "Poly-Tite, 
Port-A-Vac 300 Series". 
During packaging operations, the package illustrated in FIG. 4 prevents the 
buildup of static charges between the material sheet 30 and the circuit 
card 32 by the provision of the anti-static layer 33. It should be evident 
that use of an anti-static material for the flexible plastic sheet 34 will 
enhance the static prevention qualities of the FIG. 4 package. Moreover, 
it should be evident that the circuit card 32 can be packaged between two 
sheets of material fabricated according to the above-disclosed method with 
the coated surface of each sheet contacting the surface board. 
Obviously, many modifications and variations of the present invention are 
possible in light of the above teachings, and it is therefore to be 
understood that the invention may be practiced otherwise than as 
specifically described.