Antistatic coating

An antistatic article including a substrate having a first surface, a sputtered conductive layer arranged on the first surface and having a thickness ranging from approximately 0.5 nanometers to approximately 10 nanometers, and an outer layer or a series of layers arranged atop the sputtered conductive layer, wherein, the antistatic article exhibits a surface resistivity of less than approximately 1012 ohms/square. A method of making an antistatic article includes pretreating a surface of the substrate, sputtering the conductive layer onto the surface to a thickness ranging from approximately 0.5 nanometers to approximately 10 nanometers, and sputtering the outer layer and one or more additional layers atop the conductive layer, wherein, the antistatic article exhibits a surface resistivity of less than approximately 1012 ohms/square.

FIELD OF THE INVENTION

The present application relates to coatings adapted to control static on substrates made of glass, acrylic, fiberglass, and other materials. More particularly, the present application relates to coatings on substrates such as glazing for framing or shadow boxing specimens such as artwork, memorabilia, documents or other types of specimens for display.

BACKGROUND

Combined anti-static and anti-reflective coatings are sometimes used on glazing such as glass, acrylic, or other materials that are used for framing a specimen for display. The anti-static effect of the coating may help to reduce the attraction of dust or other particulate to the glazing during the framing process and, thus, introduction of these foreign materials into the framed assembly can be reduced or eliminated. In addition, the antistatic effect may help to preserve the integrity of the specimen by reducing tendencies to attract pigments in the specimen. The anti-reflective coating may be helpful for viewing of the specimen by reducing reflections and allowing for clearer viewing of the specimen by onlookers such as patrons to a museum, an art studio, conference, or other place of display. The combined anti-static and anti-reflective coating can be relatively expensive to produce and an anti-static coating alone may be desired.

SUMMARY

In one embodiment, an antistatic article is provided. The article may include a substrate having a first surface. A sputtered conductive layer may be arranged on the first surface and may have a thickness ranging from approximately 0.5 nanometers to approximately 10 nanometers. An outer layer or series of outer layers may be arranged atop the sputtered conductive layer and the antistatic article may exhibit a surface resistivity of less than approximately 1012ohms/square.

In another embodiment, a method of making an antistatic article is provided. The antistatic article may include a substrate, a conductive layer, and an outer layer or series of outer layers and the method may include pretreating a surface of the substrate. The method may also include sputtering the conductive layer onto the surface to a thickness ranging from approximately 0.5 nanometers to approximately 10 nanometers. The method may also include sputtering an outer layer or series of layers atop the conductive layer and the resulting antistatic article may exhibits a surface resistivity of less than approximately 1012ohms/square.

In another embodiment, an antistatic article having a substrate with a first surface, a conductive layer arranged on the first surface and having a thickness ranging from approximately 0.5 nanometers to approximately 10 nanometers, and an outer layer or series of outer layers arranged atop the conductive layer, wherein the antistatic article exhibits a surface resistivity of less than approximately 1012 ohms/square is formed by the following method. A surface of the substrate may be pretreated, a conductive layer may be sputtered onto the surface, and an outer layer or series of layers (e.g., outer layers) may be sputtered atop the conductive layer.

DETAILED DESCRIPTION

The present application, in some embodiments, relates to an antistatic glazing for framing of artwork, documents, memorabilia, or other specimens. The antistatic glazing may include a coating similar to that used to produce antistatic and antireflective coatings, but with a largely reduced thicknesses. That is, it may include a conductive film and an overlying outer layer and may also include an additional one or more layers arranged between the outer layer and the conductive film. The conductive layer, for example tin oxide, may be largely reduced in thickness relative to antistatic and antireflective coatings. While the thickness or thicknesses are largely reduced, the resulting glazing may surprisingly remain antistatic and may be offered at a reduced cost when compared to antistatic and antireflective coated articles.

In one embodiment, the coating may be applied to a substrate with a sputtering process and the antistatic property of the reduced thickness coating described herein may be maintained at least in part due to the particular parameters used in the sputtering process. For example, in some embodiments, the oxygen provided during the sputtering process may be particularly controlled to eliminate or reduce free oxygen that may be present in the coating without such control. The eliminated or reduced free oxygen may allow the reduced thickness coating to provide an antistatic effect.

Referring toFIG. 1, a specimen display device100is shown including a frame102, a specimen104, and a glazing106. InFIG. 2, the specimen display device100is shown in an exploded view revealing the backing108in addition to the frame102, specimen104, and glazing106ofFIG. 1. In the embodiment shown inFIGS. 1 and 2, the glazing106may be in the form of a coated substrate106. While the specimen display device100is shown as a piece of framed artwork, the specimen display device100may include other types of displays such as shadow boxes, display cases, display counters, display tables, and other specimen display systems or devices100. It is also noted that while the presently described coated substrate106is described with respect to glazing106for display specimen devices100, the coated substrate106may also be useful for television or computer display screens, overhead projectors, handheld device screens, and other applications where static is not desirable.

The frame102of the specimen display device100may include four side members110or another number of side members110may be provided. The frame102and associated side members102may include a depth suitable for the specimen104to be displayed therein. The frame side members110may have a substantially rectangular cross-section and may be joined at intersections with adjacent side members110. The side members110may be miter cut at the intersections to form corners or angular transitions. Internal or external connectors such as biscuits, brackets, and the like may be used. The side members110may also have alternative cross-sections and may intersect with butt joints or other intersecting arrangements. The cross-section of the side members may include a keeper lip extending inward toward opposing side members110and may be generally aligned with a front surface of the side members110. The keeper lip may allow the glazing106, specimen104, and backing108to be inserted into the frame102from the rear of the frame102and the glazing106, specimen104, and backing108may be secured in the frame102with operable tabs, flaps, rotating hands, or other devices commonly used in framing. Alternatively, a more permanent backing108may be provided. The side members110may also include one or more additional stepped keeper lips for setting the specimen104back from the backside of the glazing106, for example. Still other arrangements and specimen display devices100may be used.

The specimen104may be anything that is desired to be placed on display including artwork, documents, memorabilia, and other types of specimens104. In some embodiments, the specimen104may be high-end artwork and the antistatic glazing106may be desirable to reduce a tendency for the glazing106to attract pigments from the specimen104and, as such, damage or otherwise modify the specimen104. In some cases, the specimen104may include pastel coloring, or charcoal or chalk based artwork. In still other embodiments, the specimen104may be documents and may be old or historical documents or newer documents that are desired to be kept for extended periods of time. In still other embodiments, the specimen104may be photos, certificates, awards, portraits, diplomas, or any other type of specimen104that is desired to be displayed and/or generally protected.

Referring toFIG. 3, a cross-sectional view of the glazing106ofFIGS. 1 and 2is shown. As shown, the glazing106may be in the form of a coated substrate106that may be sized, shaped, and oriented for arrangement on or in the specimen display device100. The coated substrate106may be configured to protect the specimen104arranged in the specimen display device100and allow for viewing of the specimen104. The coating on the coated substrate106may cause the coated substrate106to have antistatic properties. The coated substrate106may include a substrate112having a conductive film114arranged on a surface thereof and an outer film116arranged atop the conductive film114and one or more additional films or layers117, may also be provided.

The substrate112may include a body portion118having an inner surface120and an outer surface122. For purposes of discussion, the inner surface120may be defined as the surface having the coating applied thereto and the outer surface122may be the surface opposite to the inner surface120. This description is selected because, in one embodiment, the coated side may face the specimen104in the specimen viewing device100leaving the opposite side to face outward, for example. However, other uses and arrangements may be provided such that the coated surface faces outward and the present application should not be limited in this respect.

The body portion118of the substrate112may be generally flat and plate-like such that the inner surface120and the outer surface122are generally parallel to one another. In other embodiments, the body portion112may be curved similar to a lens, for example, and the inner and outer surfaces120,122may be concave and convex, respectively, or convex and concave, respectively. In still other embodiments both inner and outer surfaces120,122may be concave or both inner and outer surfaces120,122may be convex. Still further, the degree of curvature of the inner and outer surfaces120,122may be the same or different from one another. In still other embodiments, one of the inner and the outer surface120,122may be generally flat and the other surface may be curved. Still other surface arrangements may include wavy surfaces or cross-sections, textured surfaces, and the like.

The substrate112may be made of one of several materials or a combination of materials may be used. In one embodiment, the substrate112is an acrylic material. In other embodiments, the substrate112may be a glass, plastic, fiberglass, plexiglass, or polymer, for example. Still other materials may be used and the a suitable material may be selected based on the nature of the specimen104, the desired viewing of the specimen104, and the exposure conditions anticipated for the specimen104.

The conductive film114may be configured to provide an antistatic property to the coated substrate106and may thus help to reduce the entrance of dust, debris, or other foreign matter when assembling the specimen display device100. Moreover, the antistatic property may help to reduce damage to specimens104by reducing or eliminating the charge on the glazing106that may otherwise attract pigments, for example. The conductive film114may be arranged on the inner surface120of the body portion118of the substrate112and may be adapted to provide the coated substrate106with antistatic properties. The conductive film114may include tin oxide (SnO2), zinc oxide (ZnO), or indium tin oxide (ITO), for example. In some embodiments, the conductive film may be a transparent conductive oxide and in other embodiments, a less transparent and more opaque or fully opaque film may be used. Other conductive film materials may also be used and combination of materials may also be provided.

In one embodiment, the conductive film114may include tin oxide (SnO2) having a thickness ranging from approximately 0.25 nanometer to approximately 12 nanometers, for example. In another embodiment, the tin oxide may have a thickness ranging from approximately 1 nanometer to approximately 8 nanometers. In still other embodiments, the tin oxide may have a thickness ranging from approximately 2 nanometers to approximately 6 nanometers. In still other embodiments, the tin oxide may have a thickness of about 3, 4 or 5 nanometers or a thickness of about 7, 9, 10, or 11 nanometers. Thicknesses of a fraction of a nanometer or fractional values between the integer values mentioned may also be used. Where conductive film materials are provided other than tin oxide, similar thicknesses may be provided. Still further, other conductive film thicknesses outside the ranges provided may also be used. In some implementations, conductive film layers having a thickness of about 4 nanometers may meet specifications for optical properties (reflection level, transmission level, transmitted color).

The outer film116may be configured to protect the conductive film114and may allow for the conductive film114to maintain its antistatic property. With respect to protecting the conductive film114, the outer film116may prevent or reduce scratching or marring of the conductive film114, for example, or may help to make the coated substrate106more hydrophobic. With respect to maintaining the antistatic property of the conductive film114, the outer film116may protect the conductive film114from exposure to moisture, for example, which may affect the resistivity of the conductive film114. In other embodiments, the outer film or layer116may be configured to enhance the product. The outer film116may be arranged on the conductive film114. The outer film may include silicon dioxide (SiO2), titanium dioxide (TiO2), or zirconium dioxide (ZrO2), for example. Other outer films may also be used.

In one embodiment, the outer film116may include silicon dioxide (SiO2) having a thickness ranging from approximately 1 nanometer to approximately 60 nanometers, for example. In another embodiment, the silicon dioxide may have a thickness ranging from approximately 2.5 nanometer to approximately 55 nanometers. In still other embodiments, the silicon dioxide may have a thickness ranging from approximately 5 nanometers to approximately 30 or to approximately 50 nanometers. In still other embodiments, the silicon dioxide may have a thickness ranging from 30 nanometers to approximately 50 nanometers or from 40 nanometers to approximately 50 nanometers. Thicknesses of a fraction of a nanometer or fractional values between the integer values mentioned may also be used. Where other outer film116materials are provided other than silicon dioxide, similar thicknesses may be provided.

In addition to the outer film116, one or more additional layers117may also be provided. For example, an additional layer of titanium dioxide (TiO2) with a thickness ranging from approximately 0.25 nanometers to approximately 2 nanometers or from approximately 0.5 nanometers to approximately 1.5 nanometers or from approximately 0.75 nanometers to 1.25 nanometers, for example, may be provided. Other thicknesses and materials of additional layers may also be provided. More than one additional layer may also be provided. WhileFIG. 3shows the one or more additional layers117provided between the conductive layer114and the outer film116, the additional layers117may be provided atop the outer film116. A suitable number and type of additional layers may be selected based on several factors including resistance to salt and humidity, making the coated substrate106more hydrophobic, and other factors. The one or more additional layers may be provided generally to enhance and protect the product with an effort to avoid adding significant cost, avoid increasing the reflection level, or negatively influencing the reflected and transmitted color.

The coated substrate106may be made using one or a combination of several processes.FIG. 4shows one embodiment of how a substrate112may be coated with an antistatic coating. The substrate may be pretreated (124), a conductive layer114may be applied to the substrate112(126), and an outer layer116and optionally one or more additional layers117may be applied over the top of the conductive layer114(128). In some embodiments, the coated substrate106may be placed in a specimen viewing device (130). While the operations are shown in the form of a flow chart, it is to be appreciated that one or more of the operations may be performed in another order and the invention should not be limited to the particular order shown.

The pretreatment process (124) may be adapted to ready the surface120of the substrate112to receive the conductive layer114. In one embodiment, the pretreatment process (124) may include treating the surface120of the substrate112with a linear ion source. This process may include using permanent magnets to create a magnetic field around a cathode arranged in front of an anode. Gas, such as oxygen and/or argon may be fed through a manifold and electrons that are confined by the magnetic field may collide with the gas and ionize the gas. The positively biased anode may accelerate the ions to create an ion beam. The beam may be used to bombard the surface120of the substrate112to clean off contaminants and promote bonding of the conductive layer114to the substrate112, for example. In one embodiment, the system used to provide the linear ion source is made by Advanced Energy, for example. Other linear ion source systems may also be used and methods other than linear ion source may also be used to pretreat the substrate112. In some embodiments, for example, the surface120of the substrate112may be chemically cleaned using cleaning agents, such as cerium oxide, nickel oxide, or commercially available detergents. In other embodiments, the surface120of the substrate112may be pretreated by corona treatment (air plasma), glow discharge, or vacuum plasma treatment.

The conductive layer114may be applied to the pretreated surface120of the substrate112using a sputtering process (126). The sputtering process (126) may include arranging the substrate112in a chamber with a sputtering target having a negatively charged target surface. The negatively charged target surface may be bombarded with argon ions, for example, which ejects atoms from the target. The sputtering process (126) may also include the addition of a reactive gas for combining with the ejected atoms to form a compound. The formed compound may then be deposited on the surface120of the substrate112.

In one embodiment, where the conductive layer114is tin oxide, the sputtering target may be a tin material and the reactive gas may be oxygen. As such, the bombarded tin sputtering target may eject tin atoms that combine with the oxygen gas to form tin oxide which is then deposited on the substrate112. In some embodiments, the flow of oxygen gas may be controlled. For example, on a small scale development coater, the oxygen gas may range from approximately 20 standard cubic centimeters per minute (SCCM) to approximately 40 SCCM. In other embodiments, the flow of oxygen gas may range from approximately 25 SCCM to approximately 35 SCCM. In still other embodiments, the flow of oxygen may range from approximately 28 SCCM to approximately 30 SCCM. In still other embodiments, the flow of oxygen may be approximately 29 SCCM. On a larger scale production coater, relatively higher oxygen flows may be used. For example, the flow of oxygen gas may range from approximately 200 SCCM to approximately 400 SCCM or from approximately 250 SCCM to approximately 350 SCCM. In still other embodiments, the flow of oxygen may range from approximately 280 SCCM to approximately 300 SCCM. In still other embodiments, the flow of oxygen may be approximately 290 SCCM. In further embodiments, the total oxygen flow to the conductive layer may be about 175 SCCM. In some implementations, further reductions in oxygen flow in the production coater below 175 SCCM may result in a tin oxide layer with a suitable thickness and surface resistivity. Other integer values, and fractions thereof, of oxygen flow may also be provided within the mentioned ranges or outside the ranges.

Other factors associated with sputtering may also be considered to achieve a suitable coating thickness with the desired properties. For example, the pump efficiency may require that the flow be adjusted upward when efficiency is low, for example. In addition, for maintaining a substantially uniform coating the oxygen gas used in the sputtering process may be routed to particular areas of the chamber and the flow of oxygen to a given area may vary based on the size and location of the area. Still further, the replacement of sputtering targets may indicate that the oxygen flow be adjusted.

The outer layer116and the one or more additional layers117may also be applied using a sputtering process (128). In the case of a silicon dioxide outer layer116/117, the sputtering target may be a silicon material and the reactive gas may be oxygen. As such, the bombarded silicon sputtering target may eject silicon atoms that combine with the oxygen gas to form silicon dioxide which is then deposited on the substrate112. The flow of oxygen for the outer layer116or additional layers117formed atop the conductive layer114, may be the same or different than the flows used for the conductive film layer. In some embodiments, the similar flows may be used and in other embodiments, much larger flows of oxygen may be used. In some implementations, the resulting silicon dioxide outer layer116or series of layers atop the conductive layer114may have a thickness of approximately 3 nanometers.

While the application of the conductive layer114, the outer layer116and the one or more additional layers117have been described as being applied with a sputtering process, other methods of applying the layers114,116,117may also be used. In some embodiments, chemical vapor deposition may be used. In other embodiments ion assisted deposition may be used. In still other embodiments, high power impulse magnetron sputtering may be used. Still other methods of applying the layers114,116,117to the substrate may be provided.

Where the coated substrate106is to be used in a specimen display device100as described, the coated substrate106may be placed in the frame102, the specimen104may be arranged behind the coated substrate106and may be placed against or spaced away from the coated surface120of the coated substrate106. A backing material108may be applied to secure the specimen104in the frame102.

As applicants developed the current coated substrate106and the process for making the coated substrate106, several advantages were realized. First, previous antistatic and antireflective coatings included a substrate with a tin oxide coating having a thickness of approximately 35-45 nanometers overlaid with a silicon dioxide coating having a thickness of approximately 110-140 nanometers. At the time of the invention, those of skill in the art understood that the tin oxide layer provided the antistatic property and the combination of the tin oxide and silicon dioxide (or additional layers beyond the two) provided the antireflective property. In setting out to produce a less expensive antistatic product, applicants expected that the silicon dioxide layer could be omitted since there was no longer a need for an antireflective property. Still further, since similar antistatic properties were desired, applicants expected that a similar tin oxide thickness would be needed. Both of these expectations turned out not to be true.

First, a surprising result of applicant's development of the antistatic coated substrate106is that the tin oxide layer tends to lose its antistatic property after time (e.g., several days) without the silicon dioxide layer. As such, while an antireflective property may not be desired, an outer coating may still be provided. Second, an additional surprising result of applicant's development included that the thickness of the conductive layer114could be reduced in thickness considerably in the absence of a requirement to make the coated substrate antireflective. Even with the reduced thickness of the conductive layer114(e.g., from 35-45 nanometers down to approximately 5 nanometers or approximately 10-15% as thick), the coated substrate106would still exhibit suitable antistatic properties of below 1012ohms/square. In this regard, applicants also found that the control of the oxygen in the process of sputtering the conductive layer114affected the antistatic properties of the coated substrate106and, as such, may be at least one reason why such a thin layer of conductive material provides the desired antistatic effect. For example, in one embodiment on a development coater, the oxygen flow of 29 SCCM provides a surface resistivity of approximately 108ohms/square while oxygen flow of 28 SCCM provides a surface resistivity of 1011ohms/square and 30 SCCM provides a surface resistivity of 1010ohms/square. On the production coater, oxygen flows of approximately 300 SCCM may provide suitable surface resistivity. In another example, a reduction of oxygen flows to approximately 175 SCCM on the production coater may provide suitable surface resistivity. In comparison to oxygen flows of approximately 750 to 1000 SCCM for previous sputtering processes for applying conductive film layers, these flows are considerably less. In addition to oxygen flows affecting surface resistivity, the base pressure of a coating environment may affect surface resistivity. Accordingly, in some implementations, the substrate may be provided in a vacuum or in a low pressure environment prior to coating in order to yield the coated substrate106with the desirable surface resistivity.FIG. 5is a graph showing the how changes in base pressure affects surface resistivity in an environment where gas flow, power and line speed are held constant. In some implementations, sputter coating surfaces at a base pressure of 5.5−5to 6.0−5may provide coatings, e.g., conductive layer114, outer layer116, the one or more additional layers117or each thereof, with a conductivity that falls in the 108ohms/square range.

In the foregoing description various embodiments of the present disclosure have been presented for the purpose of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise form disclosed. Other modifications or variations are possible in light of the above teachings. The embodiments were chosen and described to provide the best illustration of the principals of the invention and its practical application, and to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth they are fairly, legally, and equitably entitled.