Patent Application
20160244230
Disclosed is an improved printed film, and an associated method of production, that achieves the dissipation of static electricity typically built up during the processing, handling and use of such films. One embodiment includes the selective application of material(s), for example by overprinting, that are electrically dissipative and/or conductive. More specifically static electricity on the film is discharged or equalized through a coating that is selectively applied to electrically interconnected regions to provide a dissipative path.
In manufacturing and packaging industries static electricity can interfere with the handling of parts and materials. Arcs and sparks produced by static discharge can also create dangerous explosions in a variety of hazardous environments. Accordingly countermeasures have been developed to control and mitigate the counterproductive effects of electrostatic energy and its discharge (e.g., electrostatic discharge or ESD). However, in the general manufacturing environment personnel, as well, are all too often subjected to static discharges that can be uncomfortable and in some cases hazardous. While the physiological effects are negligible the psychological consequences from receiving an ESD microshock can have a negative effect on an operator. A person will begin to feel an effect from a discharge of as little as 1 kV and will typically experience an unpleasant consequence from discharges at a level of 2 kV and higher. Notably voltages in the range of 10-25 kV can be encountered under certain conditions. And, while not generally lethal, due to the low current level, such a shock can induce muscular contractions, or may at least cause the personnel to be distracted from the task(s) being performed because of such shocks or in anticipation of such shocks.
Static charge generally arises from an imbalance of charges within, or on, a surface that is created when two surfaces come into contact and then are separated—particularly when one of the surfaces has a high resistance to electrical current, such as in packaging films. Minimization of the potential for shocking is achieved by dissipating or equalizing the charge with that on adjacent objects or surfaces. The unbalanced charge remains “static” until it is capable of being discharged or neutralized by direct current flow to a point (or person) providing a different voltage potential. It is also known that surfaces may be treated with antistatic agents to, at least temporarily, dissipate the charge.
Typical polymer-based materials are known in the packaging and printing industry as being electrically non-conductive and, in fact, such materials are used as dielectrics because of their resistance to electron flow. Attempts at imparting electrically conductive properties to polymers generally require the inclusion of conductive materials, such as carbon or graphite, as a filler. While the inclusion of a uniformly dispersed material, such as carbon, provides an effective electrical pathway it also imparts a predominately black color to any polymeric material into which it is incorporated. Therefore, there is a requirement in the printing and packaging industry for materials which are more practical and aesthetically pleasing.
One method for creating a conductive polymer is either by laminating or coating a conducting layer onto the polymer sheet. Typical coatings consist of oxides such as indium tin, aluminum, zinc, as well as carbon tubes, graphene and polythiophenes. The development of an electrically conductive coating on a sheet is particularly important in the field of packaging where static may be created or induced as the film is being manufactured and transported over, and through rollers during the manufacturing processes, and is further created during a coating or lamination process as well as during the slitting or finishing procedures. Accordingly, films such as biaxially oriented polypropylene (OPP), which come into contact with an operator during the aforementioned processes, have the potential for causing an ESD and associated shock, particularly during operations such as splicing, roll handling including changeover, etc.
Static electricity is a common occurrence in web converting operations. Some materials tend to have a higher potency to build static charge. In accordance with an embodiment disclosed herein one such film material is biaxially oriented polypropylene (OPP), and an application in which such a material is used includes use as a printed overwrap film for tobacco cigarette cartons.
At a manufacturing facility where the OPP film is used to wrap cigarette cartons on high speed converting lines, ESD or static electric shock, is experienced by line operators. The electrostatic discharge often occurs at the point where an operator is preparing a roll of printed OPP film for a splice over onto a new roll of OPP near the running roll of unwinding OPP film. This electrostatic discharge is strong enough to cause employee complaints.
Referring to
Therefore it is an object of the disclosed embodiments to combine a substrate and a conductive composition, applied in a plurality of separately patterned regions on a surface of said film, to dissipate any acquired static charge.
Another object of the disclosed embodiments is to provide a conductive trace or similar path that interconnects the patterned regions so as to increase the static dissipative area on the film surface.
Disclosed in embodiments herein is a packaging film, including: a film substrate (e.g., biaxially oriented polypropylene (OPP)); and a conductive lacquer applied in a plurality of separately patterned regions on a surface of said film to dissipate static created during the handling (e.g., moving, rolling, “transporting,” etc.) of said film at its manufacture and further induced through the handling (e.g., moving, rolling, “transporting,” etc.) of the film during its converting (e.g., printing, slitting).
Further disclosed in embodiments herein is a method of producing a packaging film, including: providing a film substrate (e.g., OPP); and applying to a surface of said film substrate, a patterned conductive lacquer to dissipate static created by handling (e.g., moving, rolling, transporting, etc.) of the film.
The various embodiments described herein are not intended to limit the disclosure to those embodiments described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the various embodiments and equivalents set forth. For a general understanding, reference is made to the drawings. In the drawings, like references have been used throughout to designate identical or similar elements. It is also noted that the drawings may not have been drawn to scale and that certain regions may have been purposely drawn disproportionately so that the features and aspects could be properly depicted.
As noted above, static electricity, by description, is an imbalance of electric charges that build up within or on the surface of a material (see e.g.,
Even when utilizing equipment described in Table 1, electrostatic discharge can be experienced by individuals handling materials that have a potential to acquire electrostatic charge. Another factor that is important to the potency (potential) of electrostatic charge build-up is humidity in an environment. Humidifiers can be used to raise the moisture level in a room and create a semi-conductive environment that minimizes the build-up of charge, or that dissipates charge that is built-up. More specifically, the humidity in a room creates an avenue for the excess charge to escape through water's naturally occurring conductivity. The humidification of an environment, though potentially useful in lowering electrostatic discharge, can be a prohibitively expensive investment for a large space.
The embodiments disclosed herein include a conductive material applied to a biaxially oriented polypropylene (OPP) film to create a dissipative region on the surface of the film (e.g., conductive) and which thereby provides a path so that the electrostatic charge can escape the film material that is acting as an insulator and holding the excessive charge. The disclosed embodiments include applying a material (e.g., a lacquer) that serves to dissipate the electrostatic charge. Other components in a film processing system or line, dependent upon the particular product or packaging requirements, could include a grounded machine as well as optional equipment such as described in Table 1, an application method, an applicator tool, as well as a device to measure the electrostatic charge.
Lacquer Coating Material
In one embodiment a film product may include a strategically coated over lacquer. The primary purpose of such a lacquer is to act as a transparent coating to build-up material in an area of the web where zero print coverage occurs. Without the lacquer, in the final roll, this area with zero print coverage would be soft in comparison to the area with print causing a poor roll profile.
Referring to
As
To create an electrical current path to discharge excess electrostatic charge built up on the film, a coating with a certain conductivity level may be applied on the OPP film 100 to help dissipate or equalize the charge. There are many conductive coatings in the printing and electronics industry, and the disclosed embodiments are not specifically limited to one material, but may include several materials or a combination of such coating materials.
Nonetheless, there are certain criteria that are necessary to make the coating function in accordance with the disclosed embodiment. One that is paramount is that the coating lacquer or material must be transparent so as to enable or allow underlying printing, graphics, etc. to be seen through the coating. The second characteristic is that the material, when applied to and dried on the surface of film 100, must be conductive or at least dissipative for static charge. Based on the specific application, there are a number of generic requirements for a coating on a film that is conductive. Foremost is that the coating must provide the OPP film with a static dissipative property such as a surface resistance that may be less than conductive yet in the dissipative range, for example, a surface resistance greater than 10 kilohms but less than 100 gigohms when tested according to ANSI/ESD STM11.11 or a volume resistivity greater than 1.0×105 ohm-cm but less than or equal to 1.0×1012 ohm-cm when tested according to the methods of ANSI/ESD STM11.12 may provide the appropriate dissipative response to a static charge.
Additionally the coating should have a viscosity and drying time that is compatible with the required coating process (e.g., gravure roll printing). In certain applications the coating needs to be non-toxic in order to meet product integrity guidelines dictated by the products being packaged. The list below includes several transparent conductive coatings, which may be used individually or in combination with one another or other coatings:
Indium Tin Oxide;
Aluminum Oxide;
Silver Nanowires;
Carbon Tubes;
Doped Zinc Oxide;
Graphene; and
Polythiophenes.
To prove the concept that a conductive coating could facilitate electrostatic dissipation, an experiment was conducted using a conductive silver ink pen, printed OPP film, a field static meter, and a grounded rewinding machine.
Pens containing silver ink (a conductive ink), manufactured by ITW Chemtronics (CircuitWorks® Conductive Pen) were considered. Two styles of pens were selected, one with a fine tip and the other with a thicker, standard tip. Tests were conducted to determine the conductivity of each pen style and predicted process parameters for production. The charts in
With the fine tip pen, the experiment continues to show how a trace of conductive ink can be employed to create an electric current path to dissipate or conduct the electrostatic charge. In this case ink containing a certain concentration of silver is confirmed to be suitable to dissipate static charge.
The following addition was made to an OPP film to test the dissipation effect of silver traces from the conductive ink pens of Example A, again using silver traces. More specifically traces were drawn in varying frequencies (separation distances), across the film web having a width of approximately 5.3 inches. Traces were drawn at:
100 feet;
Every pattern repeat—approximately 6.653 inches;
Every cylinder repeat—approximately 26.612 inches; and
Control—no silver ink traces.
Once the traces were applied to each roll in the spacing (frequency) indicated above, the rolls of film were placed on a rewinding machine. Also note that the beginning and end of the rolls do not have conductive traces in order to measure a “control” static level. While running the rewinding machine, static was measured with a field static meter. At the beginning of the roll, where no conductive trace was applied, the measurements demonstrated a higher level of electrostatic charge. As the film on the roll material transitioned to the portion where conductive trace material was present, the field static meter was able to measure a change in electrostatic charge. Furthermore, the roll or web does contact idle rollers on the machine, which is in turn grounded through the floor.
Static changes were measured with a field static meter measuring in the kilovolt (kV) range. The results indicate that when the conductive traces pass over the idler roller, the static charge drops in comparison to where the web does not contain conductive traces (see
The modified film and process described above was indicative of a strong likelihood of success in scaling up to a production environment, particularly where the conductive ink can be implemented by substituting a transparent, conductive lacquer coating for a lacquer coating currently applied to the OPP film. Factors that may be key to the selection of a transparent conductive coating suitable to be employed as a lacquer include:
A packaging film incorporating the properties proposed herein, includes a film substrate or web 100 such as biaxially oriented polypropylene, and a conductive lacquer applied in a plurality of separately patterned regions on at least one surface of the film to dissipate static created during the processing and handling (e.g., printing, moving, slitting, rerolling, transporting) of the film during its manufacture and converting, and subsequent handling during its use as a packaging material. Moreover, in one of the disclosed embodiments the conductive lacquer regions are electrically interconnected to one another by traces 202 to provide a path to dissipate the static charges and thereby remove or at least equalize such charges across surfaces—including personnel coming into contact. While various materials are contemplated for producing the conductive pattern regions and traces, such materials should be suitable for use with conventional film printing techniques and may include components such as: Indium Tin Oxide; Aluminum Oxide; Silver Nanowires; Carbon Tubes (including nanotubes); Doped Zinc Oxide; Graphene; Polythiophenes as well as other organic or inorganic materials that either have conductive properties, or at least demonstrate the ability to lower the resistance of the dried material and produce a dissipative coating. In one embodiment, the film with the dried coating or lacquer thereon exhibits a surface resistance in the static dissipative range (e.g., a surface resistance greater than 10 kilohms but less than 100 gigohms).
In one embodiment, a coating available from Sun Chemical may be utilized to meet the above criteria. The coating may be a specifically formulated coating for this application or may be a known lacquer including one or more of the conductive materials noted above. It is understood that the material and application may be unique or customized to meet the requirements for a particular industry (e.g., tobacco) and for the targeted application of dissipating electrostatic charge.
Application Process
The conductive lacquer is applied via a gravure printing method, although other registered printing methods may be used as well. A gravure cylinder which has an engraving to collect and deposit the liquid to form the lacquer areas on the film will be the deposition tool that applies the lacquer to the substrate/OPP packaging material. The engraving layout may or may not need to have modifications, including interconnections between adjacent regions. It is believed that interconnecting lacquer patches, for example using traces 202, as illustrated in
The functionality of the unique combination of the transparent, conductive lacquer and application method can be actualized as the OPP web passes over and in contact with idle rollers on a printing machine, a slitting machine, and a packaging line. The diagrams of
The disclosed embodiments result in one or more of the following advantages:
In summary the process generally described above for producing a packaging film, includes: providing a film substrate (e.g., OPP) and applying to a surface of the film substrate, a patterned conductive lacquer to dissipate static created by handling of the film (e.g., moving, rolling, transporting, etc.). The desired dissipation of electrostatic charge may be accomplished by placing a grounded conductor into proximity or direct contact with the patterned lacquer regions and/or traces. Furthermore, the patterned lacquer is applied using a gravure printing method, or at least an alternative method that enables the accurate registration of the material being deposited. Such a method further contemplates providing an interconnection (e.g., by traces) of the conductive lacquer between the patterned lacquer regions, thereby providing a continuous dissipation path for at least a substantial length of the film roll.
It should be understood that various changes and modifications to the embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present disclosure and without diminishing its intended advantages. It is therefore anticipated that all such changes and modifications be covered by the instant application.
This application claims priority under 35 U.S.C. §119(e) from U.S. Provisional Patent Appl. No. 62/119,993 for DISSIPATION OF STATIC ELECTRICITY ON A PRINTED FILM, filed Feb. 24, 2015 by John L. Muehlbauer, which is also hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62119993 | Feb 2015 | US |
