WO2000000855A1

WO2000000855A1 - Coating composition for reducing reflection and fogging

Info

Publication number: WO2000000855A1
Application number: PCT/US1999/014740
Authority: WO
Inventors: Walter R. Blackwell; Mike Zamora
Original assignee: Kimberly-Clark Worldwide, Inc.
Priority date: 1998-06-30
Filing date: 1999-06-29
Publication date: 2000-01-06
Also published as: AU4844999A

Abstract

A coating composition which when applied to a substrate imparts anti-fogging and anti-reflective properties is described. The coating composition is prepared by mixing at least two types of inorganic oxide particles in combination with a nonionic surfactant. The coating compositions are especially useful in the field of disposable surgical masks and face shields.

Description

COATING COMPOSITION FOR REDUCING REFLECTION AND FOGGING TECHNICAL FIELD OF THE INVENTION

This invention relates generally to coating compositions and methods for producing articles with anti-glare and anti-fogging properties for use with any variety of substrate. Such properties are desirable in articles such as face shields used for personal protection, ophthalmic lenses, architectural glazes, windows, automotive windshields and windows, decorative glass and the like.

BACKGROUND OF THE INVENTION Wearing protective face masks and eye shields has become standard procedure for many health care and other related activities. The use of a face mask and eye shield is important, for example, to lab technicians while conducting tests, to nurses during the care of patients, to physicians during surgery and other medical treatment, to dentists working in a patient's mouth, etc.

Many industrial applications also require the wearing of protective equipment, including face shields, to protect the workers from possibly hazardous chemicals and the like. An ever present problem attendant with the use of protective face masks and eye shields in both medical and industrial applications is the warm moist air exhaled by the wearer. Exhaled air has a tendency to fog or cloud eye shields, as well as glasses and eye pieces used for scientific equipment such as endoscopes and microscopes. In general, fog formation occurs under conditions of high humidity and high temperature or at interfacial boundaries where there is a large temperature or humidity difference. This fogging or clouding often results when a high concentration of moisture vapor contained within the protective mask passes through or around the mask and condenses on a cooler eye shield in the proximity of the face mask.

Various patents have reportedly addressed problems with fogging through the use of coatings (i.e. "anti-fogging coatings"). For example, U.S.

Patent 4,235,638 to Beck et al. discloses sulfonate-organosilanol compounds which are used for imparting hydrophobicity and anti-fogging properties to siliceous surfaces such as glass. Various other types of anti-fogging coatings are disclosed in U.S. Patents 3,212,909; 3,075,228; 3,819,522; 4,478,909; 2,803,552; 3,022,178 and 3,897,356; Japanese Patent Kokai No. Hei 6[1994]-41335; "Anti-fog Antistat Eases Processing Problems," Modern Plastics, October 1988, and by American Cyanamid Industrial Chemical

Division who markets "Aerosol OT Surface Active Agent" which is advertised as useful to prepare an anti-fog composition for direct application.

Personnel working in clean rooms for extended periods of time and medical personnel performing lengthy, complex surgery often report eye strain and eye fatigue from reflections and glare after wearing a face mask and eye shield for extended periods of time. Glare is the undesirable reflection of light from a surface upon which the light is incident. In general, glare may be reduced by increasing the amount of light transmitted by the article, thereby reducing the amount of light available for reflection. Alternatively, the article surface can be modified (e.g. roughened, embossed, etc.) to cause the light to be reflected more randomly and, therefore, with less glare.

Eye fatigue from glare is particularly noticeable when using precision scientific equipment such as microscopes and endoscopes while wearing a face mask or other protective equipment to shield the wearer's face. U.S.

Patent No. 5,020,533 entitled "Face Mask with Liquid and Glare Resistant Visor", incorporated herein by reference, addresses some of these problems.

Anti-reflective coatings which increase percent transmission of light and provide articles having very low reflection (i.e. reduced "glare") are purported in the art. For example, U.S. Patent 4,816,333 issued to Lange et al. and incorporated by reference herein, discloses anti-reflective coatings of silica particles. The coating solution contains colloidal silica particles and optionally a surfactant, such as Triton X-100 or Tergitol TMN-6, to improve the wettability of the coating solution. U.S. Patent 4,374,158, issued to Taniguchi et al., discloses an anti-reflective coating using a gas phase treatment technique. The coating may optionally contain additives as surface controlling agents, such as silicone type surfactants. U.S. Patent 4,409,285 issued to Swerdlow, et al. and incorporated herein by reference, discloses the use of silica and alumina particles to increase light transmission and subjectively to decrease surface misting.

Various other types of anti-reflective coatings are disclosed in U.S. Patents 2,336,516; 3,301 ,701 ; 3,833,368; 4,190,321 ; 4,273,826; and

4,346,131 ; by Cathro et al. in "Silica Low-Reflection Coatings for Collector Covers by a Dye-Coating Process," Solar Energy, Vol. 32, No. 5, 573-579 (1984); and by J.D. Masso in "Evaluation of Scratch Resistant and Anti- Reflective Coating for Plastic Lenses," Proceedings of the 32nd Annual Technical Conference of the Society of Vacuum Coaters, Vol. 32, p. 237-240

(1989).

Coating compositions which are described as having both anti- reflective and anti-fogging properties are known. For example, U.S. Patent 5,585,186, incorporated by reference for all purposes within this application, discloses a coating composition comprising a porous inorganic metal oxide and a silane or siloxane oligomer on a substrate.

A face mask described as having anti-fog and anti-glare properties is described in U.S. Patent 4,944,294 issued to Borek. The hospital face mask is described as including a transparent plastic eye shield coated with any suitable anti-fogging, anti-glare silicone agent, such as dimethylsiloxane polymer.

World Patent Application No. 89/10106 by Russell discloses a surgical mask/face shield combination. The face shield is coated with an anti-fog coating, such as that described in U.S. Patent 4,467,073. OBJECTS AND SUMMARY OF THE INVENTION

It is a principal object of the present invention to provide an improved coating for substrates having anti-fogging and anti-glare characteristics.

It is a further object of the present invention to provide a face shield having anti-fog and anti-glare characteristics. Additional objects and advantages of the invention will be set forth in the following description, or may be obvious from the description, or may be learned through practice of the invention. The present invention provides coating compositions which impart both anti-reflective and anti-fog properties to substrates coated therewith. By "anti- reflective" it is meant that the percent transmission of a light transmissive substrate coated with the present coating is increased by at least three percent [3%] over the uncoated substrate.

The coating composition uses at least two types of inorganic oxides in combination with a nonionic surfactant which are present in a concentration that imparts a durable anti-fog property to the coated substrate yet does not destroy the anti-reflective properties provided by the porous interlinked network of inorganic oxides.

The present invention provides a coating composition comprising: at least two types of inorganic oxide particles selected from groups consisting of silica, tin oxides, antimony oxides, and titanium oxides, as well as, mixtures and combinations thereof; and at least one nonionic surfactant; wherein the coating composition when coated on at least one side of a light transmissive substrate exhibits anti-reflective and anti-fogging characteristics as described herein.

The composition may optionally contain a volatilizing agent (e.g. an alcohol) and/or a polymeric binder that improves adhesion of the dried coating to the substrate, although a unique feature of the invention is the fact that such a binder is not necessary.

Preferred coating compositions applied to at least one side of a light transmissive substrate increase the percent transmission by at least 5 percent at a wavelength of 550 nm and most preferably by at least 10 percent, while resisting fogging.

The compositions may be applied to a wide variety of substrates using a variety of coating methods.

The invention advantageously relates to protective eyewear, such as surgical masks and face shields, as well as ophthalmic lenses, windows, and windshields which have anti-reflective and anti-fog properties. BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following written description taken in conjunction with the accompanying drawings, in which: Figure 1 is a schematic drawing showing a perspective view of a face mask and visor incorporating teachings of the present invention illustrated on the head of a wearer;

Figure 2 is a schematic drawing showing a view of the front or exterior of a face mask and visor incorporating teachings of the present invention; Figures 3a and 3b are high resolution images of a substrate with the present coating composition; and

Figures 4a through 4c are three-dimensional images of a coated substrate according to the invention.

DETAILED DESCRIPTION OF THE INVENTION The preferred embodiments of the present invention and its advantages are best understood by referring to FIGURES 1 through 3 of the drawings, like numerals being used for like and corresponding parts of the various drawings.

Anti-reflective and anti-fogging properties of the coating of this invention are provided by an interlinked network of at least two types of inorganic oxide particles of different particle size and at least one nonionic surfactant. The surfactant is preferably hydrophobic, but may be hydrophillic as well. More particularly, the coating composition, when coated on a substrate and dried, provides a continuous interlinked network of at least two different size inorganic oxide particles. As used herein the term "continuous" refers to a coating having no visible discontinuities or gaps. The term "network" as used herein refers to a three-dimensional structure, preferably formed by an aggregation of the various inorganic particles described herein, wherein the particles define an upper surface of defined varying "peaks and valleys" resulting from the homogeneous dispersion of the different sized particles. The particle network is held together and adhered to the substrate without a binder, although a binder may be used, providing a coating having integrity which does not flake off and that is not easily abraded off of the substrate with normal use of the coated article. This is a significant advantage of the present coating. Silicosis (a disease of the lungs caused by inhaling siliceous particles) has become an increasing concern and face masks or other articles using a silicon coating for anti-reflective purposes may contribute to the condition if the silicon particles are easily abraded from the substrate under normal operating conditions.

As a result of the packing or network of oxide particles, the coating according to the invention defines voids between the various inorganic oxide particles. As discussed in detail in U.S. Patent No. 5,586,186 (incorporated herein by reference in its entirety), for single layer coatings, it is known that in order to maximize light transmission in air through an optically transparent substrate, the refractive index of the coating should equal as closely as possible the square root of the refractive index of the substrate and that the thickness of the coating should be one-fourth (1/4) of the optical wavelength of the incident light. The presence of voids in the coating provides a plurality of subwavelength interstices between the inorganic oxide particles where the index of refraction is that of air (IR=1). Each type of inorganic oxide will also possess a unique index of refraction (e.g., silica has an IR of 1.44 and tin oxide has an IR of 1.997). By adjusting the types of inorganic oxides, the sizes of the inorganic oxide particles, the concentrations of each inorganic oxide, and the porosity of the coating, a coating having a calculated index of refraction (as shown in U.S. Patent 4,816,333 issued to Lange, et al., incorporated herein by reference) very close to the square root of the refractive index can be created. By utilizing coatings having optimal indices of refraction, at coating thicknesses equal to approximately one-quarter (1/4) of the optical wavelength of the incident light, the percent transmission of light through the coated substrate is maximized and reflection is minimized. It is believed that the coating of the present invention contains substantially more voids throughout its three-dimensional structure due to the network of different sized oxide particles. The coating may actually vary in density due to disposition of the particles and voids (e.g., the coating may have a gradient density where the coating becomes more porous moving away from the substrate). It is believed that such a gradient density might enhance the anti-reflective property of the coating. When the inorganic oxides are silicon dioxide and tin oxide, these components provide a coating having an index of refraction of about 1.71 to 1.76, which is capable of providing a highly anti-reflective surface when coated on a polyethylene terephthalate substrate (IR=1.64) at a thickness of 100 to 200 nm.

In this specification, average particle sizes are expressed as the average size of the individual primary particles determined in their greatest dimension.

The inorganic oxide is most conveniently coated on the substrate as a colloidal dispersion ("sol"), which comprises finely divided solid inorganic oxide particles in an aqueous or an organic liquid. The sol may be acid or base stabilized. Preferred sols are a silica dioxide sol referred to as "NALCO 2326" commercially available from NALCO Chemical Co., and a tin oxide sol commercially known as ALFA AESAR 40127 from Alfa Aesar Co.

In the present invention at least two different inorganic oxide components are selected from the following group consisting of silica (essentially silicon dioxide with or without other additives or impurities), tin oxides (with or without other additives or impurities), titanium oxides (with or without other additives or impurities), and antimony oxides (with or without other additives or impurities), as well as mixtures and combinations thereof. Preferably, the two selected components are colloidal silica and colloidal tin oxide. The metal oxide particles should be less than about 200 nm in diameter in order to provide effective anti-reflective properties. Preferably the average particle diameter is less than 70 nm. Although the particles are preferably spherical, other shapes are possible including irregular and fibrous shapes. In this specification proportions expressed as % weight/volume are based upon amounts in grams of the respective component compared to the total volume of the composition in milliliters. The weight/volume percentages of the oxide particles are based on the weight of the colloidal dispersion added to the composition with a known concentration of the particulate oxide particles in the aqueous solution.

The total inorganic oxides concentration is preferably from about 15 to 25% weight/volume of the coating composition or solution, more preferably from about 17 to 22% weight/volume. Above about 25% weight/volume total for all inorganic oxides, the coating becomes difficult to apply in the desired thickness range, and at below about 15% weight/volume, excessive time periods are required for the coating to dry after application to the substrate. The term "solution" as used herein includes dispersions or suspensions of finely divided inorganic oxide particles in a liquid medium.

The use of at least two sizes of particles in the coating composition can be effective in improving anti-fogging properties and increasing light transmission. Preferably, the invention consists of a small particle size and large particle size. More preferably, the invention consists of two inorganic oxide components wherein one inorganic oxide component corresponds to the small particle size and the other inorganic oxide component corresponds to the large particle size.

Preferably, the small particles are present in the coating composition in an amount in the range of about 18.0% to about 20.0% weight/volume, the most preferred range being about 14.0% to about 14.75% weight/volume, wherein the small particles are added to the coating composition as a sol having a concentration of about 15% of the small oxide particles in an aqueous solution. Average particle size in the range of about 4 to 8 nm are preferred. A colloidal silica suitable for inclusion as the small particle component is commercially available under the trade name "NALCO 2326" with an average particle size of 6 nm, and a stated concentration of 15% silica particles in aqueous solution and a particle weight of 16.5 grams per 100 ml of the colloidal solution. In general, amounts of the large particles less than about 0.2% weight/volume have no significant modifying effect upon anti-fogging properties and amounts greater than about 1.0% weight/volume introduce optical haziness.

The large particles are preferably present in an amount significantly less than the small silica oxide particles, generally in a range of about 0.2% to about 1.0% weight/volume, and especially in an amount of about 0.40% to about 0.50% weight/volume, with a preferred particle size in the range of about 10 to 15 nm. The large particles are preferably colloidal tin oxide, a suitable material commercially available under the trade name "ALFA AESAR 40127" and which comprises 17.314 grams of tin oxide particles per 100 ml of aqueous colloid and a stated concentration of about 15% tin oxide particles in the colloidal solution. The average particle size of the tin oxide particles in ALFA AESAR 40127 is between 12 and 15 nm. The coating solution also contains at least one non-ionic block copolymer surfactant, preferably a polyethoxylated alkyl alcohol, to improve the wettability of the solution on the substrate. Inclusion of an excessive amount of surfactant may, however, reduce the adhesion properties of the coating. These surfactants or the surfactant residues are primarily responsible for the anti-fogging properties of the present coating. Examples of suitable polyethoxylated alkyl alcohol surfactants as described in The Merck Index, 10th edition, Monograph No. 7449, incorporated herein by reference, include the preferred surfactants

Tergitol TMN-6 from Union Carbide Co. and Marklear AFL-3, from Witco Co. The coating can contain the TMN-6 surfactant in a range of about 0.05% to about 0.20% weight/volume, and preferably in the range of about 0.1% to about 0.15% weight/volume. The AFL-3 surfactant can be in the range of about 0.75% to about 1.50% weight/volume, and preferably in the range of about 1.0% to about 1.2% weight/volume.

Optionally, the coating composition may include a volatile liquid medium drying agent. Suitable volatilizing agents include methanol, ethanol, acetone, diacetone alcohol, and 2-methoxy ethanol. Applicants have found that the present coating forms a strong bond with the substrate without the use of a polymeric binder even though a surfactant is added to the coating, which would conventionally tend to decrease adhesion of the coating to the substrate. The coating adheres well to the substrate and will not rub off or flake off in a normal operating environment. Although not wishing to be held to any particular theory, applicants believe that the inclusion of tin oxide in the coating is primarily responsible for adhesion of the coating to the substrate. The tin oxide may possibly react with the non-ionic block copolymer surfactant and/or with the substrate. The tin oxide particles may also cause a mechanical entrapment of the oxide particles, which may also include a matrix between the surfactant. The preferred embodiment of the coating without tin oxide is rubbed off the substrate with relative ease if a binder is not also used in the solution. With the tin oxide included, the coating adheres quite well to the substrate and is not rubbed off or abraded in normal environmental or operating conditions. Applicants do not believe that the liquid component of the tin oxide colloidal dispersion plays any role in the adhesion properties since, with the preferred tin oxide sol (Alfa Aesar 40127), the aqueous colloid is water.

It is, however, within the realm of the invention to use a polymeric binder even with the tin oxide. Useful polymeric binders include polyvinyl alcohol, polyvinyl acetate, polyesters, polyamides, polyvinyl pyrrolidone, copolyesters, copolymers of acrylic acid, copolymers of methylacrylic acid, copolymers of acrylic acid and methylacrylic acid, and copolymers of styrene. Useful amounts of the polymeric binder are generally in the range of about 0.5% to about 10.0% weight/volume. If a binder is to be included, one suitable colloidal silica dispersion including a PVA binder is "LUDOX" commercially available from E.I. Du Pont de Nemours Co., Inc.

Substrates to which the coating compositions of the invention can be applied are preferably transparent or translucent to visible light. Preferred substrates are made of polyester (e.g., polyethylene terephthaiate, polybutylene terephthaiate), polycarbonate, allyldiglycolcarbonate, polyacrylates, such as polymethacrylate, polystyrene, polysulfone, polyethersulfone, cellulose acetate butyrate, glass and the like, including blends and laminates thereof. Typically the substrate is in the form of a film, sheet, panel, or pane of material and is part of an article such as ophthalmic lenses, architectural glazings, decorative glass frames, motor vehicle windows and windshields, and protective eyewear, such as surgical masks and face shields. The coatings may, optionally if desired, cover only a portion of the article, e.g., only the section immediately adjacent the eyes in a face shield may be coated. The substrate may be produced by blowing, casting, extrusion, or injection molding. A preferred substrate particularly for use as a face shield is a clear polyester or polyethylene film, such as Mylar® film, from Dupont. Examples of face masks with eye shields and face shields incorporating the preferred embodiment of this invention are shown in FIGURES 1-2. In FIGURE 1 , a transparent eye shield 10 is used to protect the eyes 18 and face of the wearer 26. The coating composition of the present invention has been applied to both the inside 14 and outside 16 of transparent substrate 12 of the eye shield 10. Figure 2 illustrates an alternative embodiment of a face shield incorporating coating 10 on the inside surface 14 of the clear substrate 12. Other eye shields, also known as visors, satisfactory for use with the present invention are known and described in U.S. Patent 5,020,533 incorporated by reference herein. It should be appreciated that the present coating can be used on any conventional face mask, visor, or the like, wherein anti-reflective and/or anti-fogging characteristics are desired.

Figures 3a and 3b are images of a Mylar film substrate coated with the coating composition according to the invention taken with a Hibachi S4500 field emission microscope at the magnification indicated on the images. The specimen was sputtered coated with about 10nm of chromium to obtain the high resolution electron images. It is apparent from these images that the coating composition forms a rough or "gritty" upper surface on the substrate. Applicants believe that this rough surface, due primarily to the presence of the tin oxide particles, prevents the silicon particles, and coating in general, from being easily abraded or rubbed off of the substrate. Figures 4a through 4c are three-dimensional images taken with a Park CP-M atomic force microscope using an Ultralever® tip in contact mode with the specimen. Figure 4a is a top or frontal topography image with the difference in shade indicating the roughness of the upper surface of the coating according to the scale indicated. Figure 4b is an alternate topography image generated at an angle to show the relative "gritty" nature of the upper surface of the coating. Figure 4c is an image similar to Figure 4b taken where a line was scratched on the specimen with a needle to present a cross- sectional view of the coating composition. Height measurements show that the coating composition on the tested specimen was about 150nm.

Applicants have also found that conventional face masks coated primarily with a silicon coating have a tendency to smear easily and must be frequently cleaned, which leads to premature abrasion or removal of the silicon from the substrate. Face masks coated with the present inventive coating exhibit a significant resistance to smearing, possibly due to the gritty upper texture of the coating.

The coating of this invention is not known to suffer loss of anti-fogging properties due to the use of other materials for packaging. Articles such as disposable surgical face masks and face shields which are coated with the anti-reflective, anti-fog compositions of this invention may be stored in single use packages which reduce environmental exposure. Reusable articles are preferably used in combination with a package that protects or completely seals the product from environmental exposure when not in use. Preferably, the material used to form the packages should be comprised of a noncontaminating materials including paper and bleached paper products, such as bleached white bond paper, cardboard, and clay coated solid white bleached sulfate boxboard, and/or films or laminates made from polyester, high density polyethylene, or polystyrene.

The coating of the present invention is preferably coated on articles or substrates using conventional techniques, such as bar, roll, curtain, rotogravure, spray, or dip coating techniques. It is believed that rotogravure coating techniques will be most efficient in commercial production of articles incorporating the coating. In order to ensure uniform coating and wetting of the film or substrate, it is convenient to oxidize the substrate surface prior to coating using corona discharge or flame treatment methods. Other applicable methods capable of increasing the surface energy of the article include the use of primers such as polyvinylidene chloride PVDC). The optimal average dry coating thickness is dependent upon the particular coating composition, but in general the average thickness of the coating is between 50 and 250 nm, preferably between 75 and 200 nm, and more preferably between 100 and 150 nm. Above and below this range the anti-reflective properties of the coating may be significantly diminished. It should be noted, however, that although the average coating thickness is preferably uniform, the actual coating thickness may vary considerably from one particular point on the coating to another. Such variation in thickness, when correlated over a visibly distinct region, may actually be beneficial by contributing to the broad band anti-reflective properties of the coating. The coating of the present invention is preferably coated on both sides of the substrate. Alternatively, the coatings of the present invention may be coated on one side of the substrate. The opposite side of the substrate may be uncoated, coated with other surfactants or polymeric anti-fogging compositions, or coated with other anti-reflective coatings.

Once coated, the article should be typically dried at temperatures between 20°C and 150°C in any conventional hot air drying apparatus, such as an oven or forced hot air drying chamber. The temperature may be increased further to speed the drying process, but care must be taken to avoid degradation of the substrate. The preferred coating compositions are preferably dried at between 50°C and 130°C and more preferably between 115°C and 125°C.

When the coating composition of the invention is applied to the substrate to provide anti-reflection properties, glare is reduced by increasing the light transmission of the coated substrate. Preferably the coated substrate exhibits an increase in transmission of normal incident light of at least 3 percentage points and as great as 10 percentage points or more, when compared to the uncoated substrate, at a wavelength of approximately 550 nm, as determined using the ASTM test method D1003-92, entitled "Haze and Luminous Transmittance of Transparent Plastics," incorporated herein by reference. The coating compositions of the invention provide anti-fog as well as anti-reflective properties to surfaces coated therewith. The anti-fog property is demonstrated by the tendency of the coating to resist the formation of water droplets which tend to significantly reduce the transparency of the coated substrate. Water vapor from, for example, human breathing, tends to condense upon the coated substrate in the form of a thin uniform water film, rather than as a water droplets. Such a uniform film does not significantly reduce the clarity or transparency of the substrate.

The coating compositions of the present invention are durable and have a relatively long shelf life. Samples exposed to air at temperatures of 70° to 75° F and 50-79% relative humidity for periods of thirty and ninety days showed no significant deterioration or degradation of the coating. Samples sealed in air tight containers during the same periods also showed no significant deterioration.

The following specific, but non-limiting, examples will serve to illustrate the invention.

EXAMPLES A coating solution (total volume of 504.75 ml and total weight of 417.1 grams) was prepared by adding 73.8 ml (80.3 grams) of a colloidal silica (NALCO 2326 colloidal silica comprising a concentration of about 15% silica particles and 16.5 grams of silica dioxide per 100 ml of aqueous colloid with an average particle size of about 6nm) and 0.20 ml(2.0 grams) of a colloidal tin oxide (ALFA AESAR 40127 colloidal tin oxide comprising a concentration of about 15% tin oxide particles and 17.31 grams of tin oxide per 100 ml of colloid with an average particle size of about 15 nm) to 430 ml (330 grams) of Methanol (MeOH). 0.4 ml (0.5 grams) of the nonionic surfactant TERGITOL

TMN-6 (Union Carbide Corp.) and 0.35 ml (4.3 grams) of the nonionic surfactant Marklear AFL-3 (Witco Co.) were then added to the solution. The coating solution was then coated on a 5 mil thick polyester Mylar® film from Dupont using the slot die method whereby the coating solution was uniformly deposited from the slot die onto the film by surface tension. The coated film was then dried by continuous movement through a three foot cylindrical drying oven set at 120°F.

Applicants believe that all of the aqueous liquid from the tin and silica oxide colloids evaporates off. Thus, with the above volumes and concentrations, about 12.18 grams of silica dioxide and about 0.035 grams of tin oxide are actually added to the coating composition. Assuming that the particles are homogeneously distributed in the composition when dried, the large tin oxide particles are present in a weight ratio of about 1 :350 with the smaller silica oxide particles.

New film samples coated as described above were created in a laboratory environment of approximately 20° C and a relative humidity of 60%, and were tested the same day. These samples are referred to in the tables below as "New" samples. Samples referred to in the tables as "30 day samples" were stored for over thirty days in an open air environment of approximately 23° C and a relative humidity of 65%. Samples referred to in the tables as "90 day samples" were stored for over ninety days in an open air environment of approximately 22° C and a relative humidity of 45%.

ANTI-FOGGING CHARACTERISTICS The samples described above were tested for anti-fogging characteristics in accordance with the "Wetting Test" set forth in U.S. Patent No. 5,585,186 (which has been incorporated herein by reference). A 3 microliter drop of deionized water was placed from an accurate pipette onto each of the samples and allowed to spread to the maximum diameter. The maximum diameter of the drop was measured by placing the sample over a paper printed with pre-measured circles of varying diameter. The results are set forth in Table 1 : TABLE 1

New samples 30-day samples 90-day samples

Samples: 1) 11 mm 2) 10 mm 3) 10 mm Samples: 4) 11 mm 5) 10.5 mm 6) 10 mm Samples: 7) 9.5 mm 8) 9 mm 10) 9mm

The coated films exhibited improved anti-fogging properties based on U.S. Patent 5,585,186 which suggests that wetting values below about 4.1 mm indicate that the coating will experience an unacceptable degree of fogging when used in surgical mask applications. The results also indicate that the anti-fogging properties do not degrade over time.

Fogging characteristics were also evaluated in accordance with the steam test set forth in U.S. Patent No. 5,585,186 by holding the individual samples above a source of steam (water vapor) for approximately 2 to 3 seconds. The steam source was a beaker of deionized water which was equipped with an inverted polypropylene funnel so that the steam was allowed to exit 14 to 15 cm above the liquid level through an opening which was approximately 8 mm in diameter. The steam temperature was 63° C. The results were rated using the following scale: "0" means no fog; "1" means minimal slight haze; "2" means medium fog; and "3" means heavy fog. The results are reported in Table 2:

TABLE 2

New samples 30-day samples 90-day samples

Samples: 1) 0 2) 0 3) 0 Samples: 4) 0 5) 0 6) 0 SSaammpplleess:: 7 7)) 00 8) 0 10) 0

There was no observable degree of fogging in any of the samples regardless of the age of the samples.

ANTI-GLARE CHARACTERISTICS The anti-glare or light transmission properties of the coated films were measured using a spectrophotometer at a wavelength of approximately 550 nm. An uncoated sample of the film was used for comparison. The results are reported in Table 3 below: TABLE 3

(percentage of light transmission)

New samples 30-day samples 90-day samples

Samples: 1) 96% 2) 97% 3) 98.3%

Samples: 4) 96% 5) 97% 6) 98.3%

Samples: 7) 96% 8) 97% 10) 98.3%

Uncoated samples: 88.2%

The New samples exhibited an increase in light transmission of almost 8% as compared to the uncoated sample. The 30-day and 90-day samples exhibited increases of greater than 9% and 10% respectively. These results are a significant increase in light transmission of films coated according to the present invention, resulting in substantial anti-reflective properties of the coated films as compared to uncoated films.

From the foregoing it becomes readily apparent new and useful anti- reflective and anti-fogging coatings have been herein described and illustrated which fulfill all of the aforestated objectives. It is of course understood that such modifications, alterations and adaptations as will readily occur to one skilled in the art confronted with this disclosure are intended within the scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. A coating composition which imparts anti-reflective and anti- fogging properties to a substrate coated therewith, the coating composition comprising: first inorganic oxide particles selected from the group consisting of silica, tin oxides, antimony oxides, titanium oxides, and combinations thereof; second inorganic oxide particles having a size different than that of said first inorganic oxide particles and selected from the group consisting of silica, tin oxides, antimony oxides, titanium oxides, and combinations thereof; a nonionic surfactant; said coating composition adhering to a substrate without a polymeric binder such that said inorganic oxide particles are not readily abraded or rubbed off of the substrate; and wherein the coating composition when coated on at least one side of a light transmissive substrate imparts anti-reflective and anti-fogging characteristics to the substrate.

2. The coating composition of claim 1 , wherein said first inorganic oxide particles comprise silica and said second inorganic oxide particles comprise tin oxide.

3. The coating composition of claim 1 , wherein at least one of the inorganic oxide particles are provided as a colloidal solution.

4. The coating composition of claim 1 , wherein the nonionic surfactant is a polyethoxylated alkyl alcohol.

5. The coating composition of claim 2, wherein the nonionic surfactant is a polyethoxylated alkyl alcohol.

6. The coating composition of claim 1 , further comprising at least one volatilizing agent.

7. The coating composition of claim 6, wherein the volatilizing agent is selected from the group consisting of methanol, ethanol, acetone, diacetone alcohol, and 2-methoxy ethanol.

8. The coating composition of claim 1 , wherein said first inorganic oxide particles are silica and said second inorganic oxide particles are tin oxide, said silica particles having an average particle size of about 4 to 8 nm.

9. The coating composition of claim 8, wherein said tin oxide particles have an average particle size of about 10 to 15 nm.

10. An article comprising a substrate having a surface and a layer of a coating composition according to claim 1 deposited on said surface, wherein said coating composition has been dried on said surface.

11. An article according to claim 11 , wherein said substrate is plastic or glass.

12. An article according to claim 12, wherein said substrate is transparent or translucent to visible light incident thereon.

13. An article according to claim 12, wherein said substrate is selected from the group consisting of polyester, polycarbonate, allyldigycolcarbonate, polyacrylates, polystyrene, poysulfone, polyethersulfone, cellulose acetate butyrate, glass, blends and laminates thereof.

14. An article according to claim 12, wherein said layer of coating composition has a thickness in the range of about 50 to 250 nm.

15. An article according to claim 12, wherein said layer of coating composition defines a continuous network of said inorganic metal oxide particles.

16. An eye shield comprising a substrate which is transparent or translucent to visible light, said substrate coated with a layer of coating composition comprising at least two types of different sized inorganic oxide particles, each of said oxide particles selected from the group consisting of silica, tin oxides, antimony oxides, titanium oxides, and combinations thereof, and at least one nonionic surfactant or nonionic surfactant residue, said coating composition adhered to said substrate without a polymeric binder such that said inorganic oxide particles are not readily abraded or rubbed off of said substrate.

17. The eye shield of claim 17, wherein said nonionic surfactant is a polyethoxylated alkyl alcohol.

18. The eye shield of claim 17, wherein said inorganic oxide particles are silica and tin oxide.

19. The eye shield of claim 17, further comprising a face mask configured therewith.

20. A coating composition which imparts anti-reflective and anti- fogging properties to a substrate coated therewith, the coating composition consisting essentially of: silica dioxide particles having a particle size in a range of about 4 to 8 nm; tin oxide particles having a particle size in a range of about 10 to 15 nm; at least one nonionic surfactant of less than about 1.5% weight/volume of said composition; and wherein the coating composition when coated on at least one side of a light transmissive substrate imparts anti-reflective and anti-fogging characteristics to the substrate while adhering to the substrate so as not to be abraded or rubbed off in a normal operating environment.

21. The coating composition as in claim 20, wherein said silica dioxide and said tin oxide are added to said composition as aqueous colloidal solutions of oxide particles having a concentration of about 15% particles and about 85% aqueous liquid.

22. The coating composition as in claim 21 , wherein when said composition is dried on the substrate, said tin oxide particles and said silica dioxide particles are present in a weight ratio of about 1 :350.