TWI441854B - Silica coating for enhanced hydrophilicity/transmittivity - Google Patents

Description

Ceria coating for improving hydrophilicity/transmittance

The present invention relates to a coating of cerium oxide (SiO ₂ ) nanoparticle, in particular to an article having a coating of nanoparticle cerium oxide thereon, such as an optical device or graphic medium, and for preparing such an article The method.

A variety of applications require articles having a surface that can spread water and thus prevent the formation of water droplets on the surface of the article. For example, transparent plastics used in foggy or humid environments, such as windows in greenhouses, should avoid the formation of water droplets that reflect light, which can reduce light transmission. The water spreading surface on these materials helps to maintain its transparency and minimize undesirable streaking.

For traffic signs using reflective films, water spreading properties are also required. The retroreflective film has the ability to return a large amount of incident light to the source. Adhesion of raindrops and/or dew can impair the transmission of light into and reflection from the retroreflective film.

The main form of water affecting light transmission is the formation of dew. Because dew mainly occurs during the night when the reflective film is working, it is especially problematic. When present in the form of bead-like water droplets on a traffic sign, the dew destroys the path of the incident and reflected light. This makes it very difficult for passers-by to identify the information on the sign. Conversely, when the dew spreads smoothly into a transparent layer on the surface of the reflective traffic sign, the information on the sign is easier to identify because the thin, smooth water layer formed does not significantly mislead the incident and reflected light path to a strong degree.

The problem of water spreading surface coatings, especially cerium oxide based coatings, is colloidal oxygen The high degree of surface chemistry, reaction chemistry and solution chemistry of ruthenium and colloidal ruthenium dioxide films. For example, despite intensive research, the interaction of ions with the surface of cerium oxide is not fully understood (see Iler, "The Chemistry of Silica," John Wiley, 1979 p. 656). Despite such difficulties, according to the present invention described below, a ceria-based water-spreading film having improved durability is provided.

In view of the above problems, it is an object of the present invention to provide a coating composition comprising a dispersion containing ceria nanoparticles having an average primary particle size of 40 nanometers (nm) or less and an acid having a pKa < 3.5, and A method for coating a substrate comprising coating a substrate with a coating composition and drying the coating.

To achieve the above object, according to the invention, a coated article comprising a matrix, in particular a polymeric matrix, has a coating of cerium oxide nanoparticles thereon. The coating comprises a continuous coating of agglomerated cerium oxide nanoparticles having an average primary particle size of 40 nanometers or less. The thickness of the coating is substantially uniform and adheres permanently to the substrate.

The adhesion of the coating to the various substrates is very good, especially for polymer matrices, and can provide excellent average specular reflectance reduction for such substrates, for example at least 2%. When the substrate is transparent, the coating can provide an increase in the transmittance of normal incident light in the wavelength range of 400 to 700 nm than in the substrate of the same material transmitted through the uncoated layer, wherein it is preferably increased by at least 2%, and Up to 10% or higher. As used herein, "transparent" means that the incident light is transmitted at least 85% in the visible portion of the selected portion (about 400 to 700 nm wavelength). Transparency to the UV zone and the near IR zone can also be mentioned high. For light of any selected wavelength, the corresponding anti-reflective layer will also have an optimum thickness.

The coating may further provide a hydrophilic surface to the substrate, and is particularly useful for providing a hydrophilic surface to the hydrophobic polymer matrix. The coating can also provide anti-fog properties and provide antistatic properties to polymer films and sheets that are electrostatically deposited. Additionally, the coating is preferably a polymeric material such as a film and sheet that provides abrasion resistance, thereby enhancing its handling properties.

Coatings produced from these acidified nanoparticle compositions can further provide water-repellent and mechanically durable hydrophilic surfaces for surfaces such as glass and polyethylene terephthalate (PET) substrates, and at various temperatures and high humidity conditions. Good anti-fog properties. In addition, the coating can provide a protective layer and exhibit rinsing to remove organic contaminants, including food and oil, paint, dust and dirt, as the nanoporous structure of the coating tends to prevent penetration of the oligomerized polymeric molecules.

As stated above, the process according to the invention does not require a solvent or surfactant for coating on the substrate, so the hazard is less and no volatile organic compounds (VOCs) are added to the air. Other advantages include a more uniform coating, better adhesion to the substrate, better durability of the coating, higher anti-reflectivity and improved transmission, and an easy-to-clean surface where contaminants can be rinsed away.

Hereinafter, a ceria coating for improving hydrophilicity/transmittance according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings, wherein the same elements will be described with the same reference numerals.

A method for coating a substrate comprising using pKa (H ₂ O) 3.5. A solution coating substrate preferably having a pKa < 2.5, preferably an acid having a pKa of less than 1 and an average primary particle size of 40 nm or less of cerium oxide nanoparticles, and a dried coating.

Unexpectedly, these cerium oxide coating compositions, when acidified, can be applied directly to hydrophobic organic and inorganic substrates without the use of organic solvents or surfactants. The wetting properties of these aqueous inorganic nanoparticle dispersions on hydrophobic surfaces such as polyethylene terephthalate or polycarbonate (PC) are a function of the pH of the dispersion and the pKa of the acid. When acidified to pH = 2 to 3 with hydrogen chloride (HCl), and even in some embodiments, the pH is up to 5, the coating composition can be applied to a hydrophobic organic substrate. Conversely, the coating composition will unite into beads on the organic substrate at neutral or alkaline pH.

Without wishing to be bound by theory, we believe that the agglomerates of cerium oxide nanoparticles are formed by the bonding of acid-catalyzed oxiranes to protonated stanol groups on the surface of nanoparticles, which are explained in The coatability on hydrophobic organic surfaces, as these groups are easily bonded, adsorbed or otherwise permanently attached by hydrophobic surfaces.

Although an aqueous organic solvent-based coating of a nanoparticle cerium oxide dispersion is described, such a mixture of water and an organic solvent typically undergoes a different evaporation rate, resulting in a continuous change in the composition of the liquid phase, which in turn changes the coating. Nature; resulting in poor uniformity and defects. Although surfactants can contribute to the wetting properties of the dispersion, they can interfere with matrix adhesion between the particles and between the interfaces, often resulting in uneven and defect-containing coatings.

Light scattering measurements of these acidified dispersion solutions indicate that these cerium oxide nanoparticles are readily agglomerated, providing (after coating and drying) cerium oxide nanoparticles A three-dimensional porous network in which each nanoparticle appears to be firmly bonded to adjacent nanoparticles. The photomicrographs reveal that this combination is a "neck junction" between adjacent ceria particles which is produced by the acid in the absence of a source of cerium oxide such as tetraalkoxy decane. Its formation is attributed to the catalysis of strong acids in the production and cleavage of the siloxane linkages. Surprisingly, the acidified dispersion exhibits stability when the pH is in the range of 2 to 4. Light scattering measurements showed that these coagulated acidified 5 nm or 4 nm cerium oxide nanoparticles remained the same at pH = 2 to 3 and at a concentration of 10 wt.% after more than one week or even more than one month. size. Such acidified cerium oxide nanoparticle dispersions are expected to remain stable for even longer periods of time at lower dispersion concentrations.

The cerium oxide nanoparticles used in the composition are dispersions of submicron sized cerium oxide nanoparticles in water or in a water/organic solvent mixture having an average primary particle size of 40 nm or less. Preferably, it is 20 nm or less, more preferably 10 nm or less. The average particle size can be determined using a transmission electron microscope (TEM). The cerium oxide nanoparticles are preferably cerium oxide nanoparticles which have not been surface-modified.

Smaller nanoparticles, those of 20 nm or less, typically do not require additives such as tetraalkoxy decane, surfactants or organic solvents to provide a better coating upon acidification. Further, the specific surface area of the nanoparticles generally has a surface area greater than about 150 square meters per gram (m ² /g), preferably greater than 200 square meters per gram, more preferably greater than 400 square meters per gram. . The nanoparticles preferably have a narrow particle size distribution, i.e., a polydispersity of 2.0 or less, and preferably 1.5 or less. If desired, larger cerium oxide particles may be added in an amount that does not detract from the coatability of the composition on the selected substrate without reducing transmission and/or hydrophilicity.

Inorganic cerium oxide sols in aqueous media are well known in the art and are commercially available. The cerium oxide sol in water or water-alcohol solution can be traded under the trade names LUDOX (manufactured by EI duPont de Nemours and Co., Inc., Wilmington, Del. USA), NYACOL (available from Nyacol Co., Ashland, MA) or NALCO (prepared by Ondea Nalco Chemical Co., Oak Brook, Ill. USA) is commercially available. A useful cerium oxide sol is NALCO 2326, which is available as a cerium oxide sol having an average particle size of 5 nm, a pH of 10.5 and a solids content of 15 wt.%. Other commercially available cerium oxide nanoparticles include "NALCO 1115" and "NALCO 1130" available from NALCO Chemical Co., "Remasol SP30" available from Remet Corp. and available from EI DuPont de Nemours Co. , "LUDOX SM" of Inc..

It is also possible to use a non-aqueous cerium oxide sol (also referred to as cerium oxide organosol) which is a cerium oxide sol dispersion in which the liquid phase is an organic solvent or an aqueous organic solvent. In the practice of the invention, the cerium oxide sol is selected such that its liquid phase is compatible with the emulsion and its liquid phase is typically water or an aqueous organic solvent. However, it has been observed that sodium stabilized cerium oxide nanoparticles should be first acidified prior to dilution with an organic solvent such as ethanol. Dilution prior to acidification may result in a poor or uneven coating. The ammonium stabilized cerium oxide nanoparticles can generally be diluted and acidified in any order.

If desired, larger cerium oxide particles may be added in an amount that does not reduce the transmittance value and/or the anti-fog property. These additional cerium oxide particles typically have greater than 40 to 100 nm, of which an average primary particle size of 50 to 100 nm is preferred, and is used in a ratio of 0.2:99.8 to 99.8:0.2 with respect to the weight of the ceria nanoparticle of less than 40 nm. Larger particles are preferably used in a ratio of 1:9 to 9:1. Typically, the total weight of the cerium oxide particles (i.e., the sum of <40 nm and larger cerium oxide particles) in the composition is from 0.1 to 40 wt.%, preferably from 1 to 10 wt.%, most preferably It is 2~7 wt.%.

The coating composition contains pKa(H ₂ O) 3.5, wherein preferably an acid having a pKa < 2.5, most preferably a pKa of less than 1. Useful acids include organic acids and inorganic acids, examples of which may be oxalic acid, citric acid, H ₂ SO ₃ , H ₃ PO ₄ , CF ₃ CO ₂ H, HCl, HBr, HI, HBrO ₃ , HNO ₃ , HClO ₄ , H ₂ SO ₄ , CH ₃ SO ₃ H, CF ₃ SO ₃ H, CF ₃ CO ₂ H and CH ₃ SO ₂ OH. The most preferred acids include HCl, HNO ₃ , H ₂ SO ₄ and H ₃ PO ₄ . In some embodiments, it is desirable to provide a mixture of an organic acid and a mineral acid. In some embodiments, a pKa can be used An acid mixture of 3.5 (preferably pKa < 2.5, preferably pKa less than 1) and a small amount of other acids having a pKa > It has been found that a weak acid having a pKa > 4, such as acetic acid, does not provide a uniform coating with the desired transmission, cleanability and/or durability properties. In particular, coating compositions containing a weak acid such as acetic acid typically unite into beads on the surface of the substrate.

The coating composition typically contains a sufficient amount of acid to provide a pH of less than 5, with a pH of less than 4 being preferred, and a pH of less than 3 being preferred. In some embodiments, it has been found that the pH of the coating composition can be adjusted to a pH of 5-6 after the pH is lowered to less than 5. This makes it possible to coat substrates which are more sensitive to pH.

Tetraalkoxy coupling agents such as tetraethoxydecane (TEOS), and oligomeric forms For example, an alkyl polyphthalate such as poly(diethoxyoxane) can also effectively increase the bonding between the cerium oxide nanoparticles. The amount of coupling agent included in the coating composition should be limited to prevent damage to the coating's anti-reflective or anti-fogging properties. The optimum level of coupling agent is determined in the assay, which depends on the identity, molecular weight and refractive index of the coupling agent. The coupling agent, if present, is typically added to the composition at a level of from 0.1 to 20 wt.% of the cerium oxide nanoparticle concentration, more preferably from about 1 to 15 wt.% of the cerium oxide nanoparticle.

The article of the present disclosure is a matrix of a continuous network structure with cerium oxide nanoparticle agglomerates. Nanoparticles, preferably having an average primary particle size of 40 nm and less. The average particle size can be determined using a transmission electron microscope. The term "continuous" as used herein means that the surface of the substrate is covered with almost no interruptions and gaps in the area where the colloidal network is coated. The term "mesh structure" refers to aggregates and agglomerates of nanoparticles that are joined together to form a porous three-dimensional network. The term "secondary particle size" refers to the average diameter of individual particles of uncondensed cerium oxide.

Figure 1 shows a coated article of the invention from Example 78. It can be seen that the monomeric cerium oxide nanoparticles are connected to adjacent cerium oxide nanoparticles. The coating is uniform. In contrast, Figure 2 shows a coating containing ethanol at an alkaline pH which is non-uniform and the monomer particles are not connected to adjacent particles.

The term "porous" refers to the voids present between the cerium oxide nanoparticles when the nanoparticles form a continuous coating. For single layer coatings, it is known that in order to maximize the transmission of light through the optically transparent substrate in air and to minimize substrate reflection, the refractive index of the coating should be as close as possible to the square root of the refractive index of the substrate, the thickness of the coating. should It is a quarter (1/4) of the wavelength of the incident light. The voids in the coating provide a plurality of sub-wavelength gaps between the cerium oxide nanoparticles, wherein the refractive index (RI) suddenly changes from the refractive index of air (RI = 1) to the refractive index of the metal oxide particles ( For example, for cerium oxide RI = 1.44). By adjusting the void fraction, it is possible to produce a coating having a calculated refractive index that is very close to the square root of the refractive index of the substrate (as shown in U.S. Patent No. 4,816,333 (Lange et al), incorporated herein by reference). By using a coating having an optimum refractive index, the percentage of transmission through the coated substrate is maximized at a coating thickness approximately equal to a quarter of the wavelength of the incident light, and reflection is minimized.

Preferably, when dried, the network has a porosity of from about 25 to 45 volume percent, more preferably from about 30 to 40 volume percent. In some embodiments, the porosity may be higher. Porosity can be calculated from the refractive index of the coating according to published methods, for example, WLBragg, ABPippard, Acta Crystallographica, Vol. 6, p. 865 (1953), which is incorporated herein by reference. Using cerium oxide nanoparticles, the porosity provides a coating having a refractive index of 1.2 to 1.4, preferably a coating having a refractive index of 1.25 to 1.36, which is approximately equal to polyester, polycarbonate, and polymethyl The square root of the refractive index of the methyl acrylate matrix. For example, a porous cerium oxide nanoparticle coating having a refractive index of 1.25 to 1.36 is 1000 to 2000. The thickness of the coating on the polyethylene terephthalate matrix (RI = 1.64) provides a highly anti-reflective surface. The coating thickness can be higher, up to a few microns or mils thick, depending on the application, for example to facilitate cleaning to remove unwanted particles rather than anti-reflection. As the thickness of the coating increases, it is expected that its mechanical properties may be improved.

In some embodiments, the articles of the present invention comprise a substrate that can be substantially any structure, transparent to opaque, polymeric, glass, ceramic or metallic, having a flat, curved or complex shape, and on which A continuous network of agglomerated cerium oxide nanoparticles is formed. When the coating is applied to a transparent substrate to achieve an increase in light transmission, the coated article preferably produces normal incident light depending on the substrate of the coating, in the breadth of the wavelength range between at least 400 and 700 nm. The total transmittance is increased by at least 2% on average and up to 10% or higher. An increase in transmittance can also be observed at wavelengths entering the ultraviolet and/or infrared portions of the spectrum. Preferably, when applied to at least one side of the light transmissive substrate, the coating composition increases the percent transmission of the substrate by at least 5%, preferably 10%, when measured at 550 nm.

In addition to providing anti-reflective properties to the substrate coated therewith, the coating compositions of the present invention also provide hydrophilicity to the substrate, facilitating the introduction of anti-fogging properties. After the direct repeated artificial blowing on the article and/or after the article is held on the "steam" nozzle, if the substrate of the coating resists the formation of small condensed water droplets, the density is sufficient to significantly reduce the transparency of the coating matrix, such that Can not fully see through, then think that the coating is anti-fog. Even if a uniform water film or a small amount of large water droplets are formed on the coating substrate, the coating composition can be considered to be anti-fog as long as the transparency of the coating substrate is not significantly lowered so that it is not easily seen. In many cases, the water film that does not significantly reduce the transparency of the substrate remains after the substrate contacts the "steam" nozzle.

In many cases, the value of an optically transparent article will increase if the article produces light scattering or glare or fog formation on the surface of the article, which may reduce the tendency to blur. For example, protective glasses (goggles, masks, helmets) Etc., lenses, architectural glazing, decorative glazing, motor vehicle windows and windshields scatter light in a manner that causes interference and destructive glare. The use of such articles can also be detrimental to the formation of water vapor mist on the surface of the article. Desirably, in a preferred embodiment, the coated articles of the present invention have outstanding anti-fog properties while additionally having a light transmission of greater than 90% of 550 nm.

The polymeric matrix can include polymeric sheets, films or molding materials. In some embodiments, where it is desired to increase the transmittance, the substrate is transparent. The term "transparent" refers to the transmission of incident light through at least 85% of the visible spectrum (about 400-700 nm wavelength). The transparent substrate can be colored or colorless.

In other embodiments, where it is desired to increase hydrophilicity, the matrix may initially be hydrophobic. The composition can be applied to a wide variety of substrates by a variety of coating methods. As used herein, "hydrophilic" is used merely to mean the surface properties of a thermoplastic polymer layer, i.e., it is wetted by an aqueous solution and does not indicate whether the layer absorbs an aqueous solution. Thus, regardless of whether the layer is impermeable or permeable to the aqueous solution, the thermoplastic polymer layer can be represented as hydrophilic. A surface in which a droplet of water or an aqueous solution exhibits a static water contact angle of less than 50 Å is said to be "hydrophilic". The hydrophobic matrix has a water contact angle of 50 Å or more. The coatings described herein can increase the hydrophilicity of the substrate by at least 10 Torr, with a preferred increase of at least 20 Torr.

The coating composition of the present invention can be applied to a substrate wherein it is preferably transparent or translucent to visible light. Among the preferred substrates are made of polyester (e.g., polyethylene terephthalate, polybutylene terephthalate), polycarbonate, polyallyl diethylene glycol carbonate, Polyacrylates such as polymethyl methacrylate, polyphenylene Ethylene, polyfluorene, polyether oxime, homopolyepoxy polymer, epoxy adduct with polydiamine, polydithiol, polyethylene copolymer, fluorinated surface, cellulose ester such as acetate and butyl Acid esters, glass, ceramics, organic and inorganic composite surfaces, and the like, including blends and laminates thereof.

Typically the substrate is in the form of a film, sheet, sheet or long square of material which may be part of the article, such as lenses, architectural glazing, decorative glazing, motor vehicle windows and windshields, and protective spectacles such as surgery. Mask and face screen. Optionally, if desired, the coating may only cover a portion of the article, such as only the portion of the mask that is directly adjacent to the eye. The substrate can be flat, curved or shaped. The article to be coated can be prepared by blow molding, casting, extrusion or injection molding.

Articles coated with the anti-reflective, anti-fog compositions of the present invention, such as disposable surgical masks and masks, are preferably stored in separate use packages that reduce environmental exposure and prevent contamination to prevent degradation of anti-fog properties. Reusable articles are preferably used in combination with packaging that protects and completely seals the product from exposure to the environment when not in use. The material used to make up the package should consist of a non-contaminating material. Certain materials have been found to cause partial or complete loss of anti-fog properties. Although not bound by any theory, it is currently believed that materials containing plasticizers, catalysts, and other low molecular weight species that will volatilize upon aging will be absorbed into the coating and result in reduced anti-fog properties.

Accordingly, the present invention provides protective eyewear such as surgical masks and face shields, as well as lenses, windows and windshields having anti-reflective and anti-fogging properties.

In other embodiments, the substrate does not have to be transparent. Compositions have been found to provide an easy to clean surface for substrates such as flexible films for drawing and signage. The flexible film may be made of a polyester such as polyethylene terephthalate or a polyolefin such as polypropylene (PP), and polyethylene (PE) and polyvinyl chloride (PVC) are particularly preferred. The substrate can be formed into a film using conventional film forming techniques, such as extruding a matrix resin into a film and optionally uniaxially or biaxially orienting the extruded film. The substrate can be treated to increase the adhesion between the substrate and the hard coat layer using, for example, chemical treatment, corona treatment such as air or nitrogen corona, plasma, flame or actinic radiation. If desired, an optional tie layer can also be applied between the substrate and the coating composition to improve interlayer adhesion. It is also possible to treat the other side of the substrate using the above treatment method to improve the adhesion between the substrate and the adhesive. The substrate may be provided with a pattern, such as a word or symbol, as is known in the art.

In some embodiments, the coating composition provides improved cleanability and provides a solid abrasion resistant layer that protects the substrate and underlying graphics from damage such as scratches, abrasion, and solvents. "Cleanable" means that the coating composition provides oil and stain resistance after curing to help protect the coated article from exposure to contaminants such as oil or foreign soils. The coating composition also allows the hardcoat to be easier to clean if soiled, so it is only necessary to simply rinse in water to remove contaminants.

In order to uniformly apply the composition from the aqueous system to the hydrophobic substrate, it may be desirable to increase the surface energy of the substrate and/or reduce the surface tension of the coating composition. The surface energy can be increased by oxidizing the surface of the substrate using a corona discharge or a flame treatment method prior to coating. These methods also improve the adhesion of the coating to the substrate. Other methods that increase the surface energy of the article include the use of an undercoat such as a thin coating of polyvinylidene chloride (PVDC). Alternatively, the surface tension of the coating composition can be lowered by adding a lower alcohol (C ₁ to C ₈ ). However, in some cases, it may be beneficial to add a wetting agent to enhance the hydrophilicity of the coating and to ensure a uniform coating of the article from an aqueous or hydroalcoholic solution, which is typically a surfactant.

The term "surfactant" as used herein refers to a molecule comprising hydrophilic (polar) and hydrophobic (non-polar) regions in the same molecule which is capable of reducing the surface tension of the coating solution. Useful surfactants can include those disclosed in U.S. Patent No. 6,040,053 (Scholz et al.) incorporated herein by reference.

For typical concentrations of cerium oxide nanoparticles (e.g., about 0.2 to 15 wt.% relative to the total coating composition), most surfactant levels are less than about 0.1 wt.% of the coating composition, preferably about 0.003. ~0.05 wt.% to maintain the anti-reflective properties of the coating. It should be noted that for some surfactants, a more spotted coating will be obtained at concentrations that are more than necessary to achieve anti-fog properties.

Anionic surfactants in the coating composition are preferred when added to increase the uniformity of the coating formed. Useful anionic surfactants include, but are not limited to those having the following molecular structure comprising: (1) at least one hydrophobic moiety, for example, about from about C ₆ ~ C ₂₀ alkyl group, an alkylaryl group and / or alkenyl group, (2 At least one anionic group, such as a sulfate, a sulfonate, a phosphate, a polyethylene oxide sulfate, a polyoxyethylene sulfonate, a polyoxyethylene phosphate, etc., and/or (3) a salt of such an anionic group, The salt includes an alkali metal salt, an ammonium salt, a tertiary amino salt and the like. Representative commercial examples of useful anionic surfactants include sodium lauryl sulfate available from Henkel Inc., Wilmington, Del., under the trade name TEXAPON L-100, or from Stepan Chemical Co., Northfield, under the trade POLYSTEP B-3. Ill.; sodium lauryl ether sulfate, available from Stepan Chemical Co., Northfield, Ill., commercially available as POLYSTEP B-12; ammonium lauryl sulfate, available from Henkel Inc., Wilmington, Del.; and dodecane under the trade name STANDAPOL A; Sodium benzenesulfonate, available from Rhone-Poulenc, Inc., Cranberry, NJ, under the trade name SIPNATE DS-10.

It may be beneficial to add another wetting agent, including those that do not impart durable anti-fog properties, in order to ensure that the article is from water or if the coating composition does not contain a surfactant or where it is desired to improve coating uniformity. A uniform coating of the hydroalcoholic solution. Examples of useful wetting agents include polyethoxylated alkyl alcohols (e.g., available from ICI Americas, Inc commercially available "Brjj ^TM 30" and "Brjj ^TM 35", and available from Union Carbide Chemical and Plastics Co. commercially available "Tergitol ^TM TMN-6 ^TM Specialty Surfactant"), polyethoxylated alkylphenols (e.g., "Triton ^TM X-100" from Union Carbide Chemicals and Plastics Co., and "from BASF Corp. of Iconol ^TM NP-70") and polyethylene glycol/polypropylene glycol block copolymer (can be used as "Tcstronic ^TM 1502 block copolymer surfactant", "Tcstronic ^TM 908 block copolymer surfactant" and "pluronic ^TM F38 Block copolymer surfactants are commercially available from BASF, Corp.). Of course, any added wetting agent must include levels that do not compromise the antireflective and antifogging properties of the coating. Typically, the wetting agent is present in an amount of less than about 0.1 wt.% of the coating composition, preferably between about 0.003 and 0.05 wt.% of the coating composition, based on the amount of the cerium oxide nanoparticles. The coated article can be rinsed or soaked in water to remove excess surfactant or wetting agent.

The composition, wherein it is preferably applied to the article using conventional techniques, such as bar coating, roll coating, curtain coating, rotogravure coating, spray coating or dip coating techniques. Preferred ways include Bar coating and roller coating, or air knife coating to adjust the thickness. To ensure uniform coating and wetting of the film, it may be desirable to oxidize the surface of the substrate using a corona discharge or flame treatment prior to coating. Other methods that increase the surface energy of the article include the use of an undercoat such as polyvinylidene chloride.

The coating of the present invention, wherein it is preferably applied in a uniform average thickness with a variation of less than about 200 More preferably less than 100 To avoid visible interference color changes in the coating. The optimum average dry coating thickness depends on the particular coating composition, but the average thickness of the coating is typically 500 to 2500, as determined by using an ellipsometry spectrometer such as Gaertner Scientific Corp Model No. L115C. Which is preferably 750~2000 More preferably 1000~1500 . Above and below the range, the anti-reflective properties of the coating are significantly reduced. However, it should be noted that despite the average coating thickness, which is preferably uniform, the actual coating thickness can vary significantly from one particular point on the coating to the other. This change in thickness, when associated with a visually sensitive area, is actually beneficial to the broadband anti-reflective properties of the coating.

The coating of the present invention is preferably coated on both sides of the substrate. Alternatively, the coating of the invention may be applied to one side of the substrate. The opposite side of the substrate may be uncoated, or coated with conventional surfactants or polymeric anti-fogging compositions such as those disclosed in U.S. Patent Nos. 2,803,552, 3,075,228, 3,819, 522, 4, 467, 073, or 4,944, 294, each incorporated herein by reference. Or coated with an anti-reflective composition such as the anti-reflective composition disclosed in U.S. Patent No. 4,816,333 or JDMasso in "Evaluation of Scratch Resistant and Anti-reflective Coatings for Plastic Lenses," (supra), both Introduce this by reference At the office. Preferably, the anti-fog coating surface should be oriented in the direction of higher humidity, for example the side with the anti-fog coating on the mask should face the wearer. The opposite side may have a transparent elastic and/or tough coating to combat particle wear, and/or wind blown.

Once coated, the article is typically dried in a circulating oven at a temperature of 20 to 150 °C. The inert gas can be looped back. The temperature can be further increased to speed up the drying process, but care must be taken to avoid damage to the substrate. After the coating composition is applied to the substrate and dried, the coating preferably comprises from about 60 to 95 wt.% (more preferably from about 70 to 92 wt.%) of cerium oxide nanoparticles (usually agglomerated) ), about 0.1 to 20 wt.% (more preferably about 10 to 25 wt.%) of tetraalkoxy decane and optionally about 0 to 5 wt.% (more preferably about 0.5 to 2 wt.%) a surfactant, and up to about 5 wt.% (preferably 0.1 to 2 wt.%) of a wetting agent.

When the coating composition of the present invention is applied to a substrate to provide anti-reflective properties, glare is reduced by increasing the light transmittance of the coated substrate. Preferably, the coated substrate exhibits at 550 millimeters (mm) when compared to an uncoated substrate (eg, at this wavelength the human eye exhibits a light-visual peak response), normal incident light transmission The rate is increased by at least 3 percentage points and as much as 10 percentage points or higher. The percent transmission depends on the angle of incidence and the wavelength of the light, as determined using ASTM Test Method D 1003-92 entitled "Haze and Luminous Transmittance of Transparent Plastics", which is incorporated herein by reference. Preferably, using 550 nm light, the coated substrate exhibits a percent increase in transmission greater than 3%, more preferably greater than 5%, most preferably greater than 8% when compared to an uncoated substrate. When the desired use involves significant "off-axis" (ie, illegal incident) viewing or unwanted reflections, especially when the reflection approaches or exceeds the observation In the case of the brightness of the object in the case, greater visibility can be obtained.

The coating composition of the present invention as discussed above provides antifogging and anti-reflective properties to the surface 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 coating matrix. Water vapor from, for example, human breathing tends to condense on the coating substrate in the form of a thin uniform water film rather than as water droplets. This uniform film does not significantly reduce the clarity or transparency of the substrate.

In many embodiments, the coating compositions of the present invention are shelf-stable, for example, they do not gel, become opaque, or significantly degrade. Moreover, in many embodiments, the coated articles are durable and abrasion resistant using the test methods described herein.

Example

The material cerium oxide nanoparticle dispersion is Nalco 1115 ^TM (4 nm), 2326 ^TM (5 nm), 1030 ^TM (13 nm), 1050 ^TM (20 nm), 2327 ^TM (20 nm) 45 nm and 93 nm, available from Nalco Company, Naperville, IL.

Tetraethoxydecane (TEOS, 99.9%) was obtained from Alfa Aesar, Ward Hill, MA.

The polyethylene terephthalate film was obtained from E. I. DuPont de Nemours, Wilmington, DE under the trade designation "Melinex 618" having a thickness of 5.0 mils and a primed surface.

Polycarbonate films were obtained from GE Advanced Materials Specialty Film and Sheet, Pittsfield, MA, under the trade names LEXAN 8010 (0.381-mm), 8010 SHC (1.0-mm), and QQ92.

Bynel-3101 ^TM is a polyethylene copolymer available from EIDuPont de Nemours & Co., Wilmington, Del.

Pellathene 2363 ^TM is a polyether-based polyurethane, available from Dow Chemical, Midland, MI.

Polyvinyl chloride film is ^{3M (TM) Scotchcal TM Luster Overlaminate} 8519,1.25 mil, available from 3M Company, St.Paul, MN.

Polycarbonate coated with perfluoropolyether (PFPE) (Example 84) refers to a polycarbonate matrix having a perfluoropolyether coating thereon, in accordance with 11/828566 (Klun et al., incorporated herein by reference) For the preparation of Example 1, a solution containing 0.5 wt.% of SHC-1200 of the perfluoropolyether obtained in Preparation 2 was used as a top coat.

Sample Preparation: The cerium oxide nanoparticle dispersion (dimensions shown in the examples) was diluted to 5 wt.% with deionized water and acidified to the stated pH (usually 2-3) with a concentrated aqueous solution of HCL. For some embodiments, tetraethoxy decane or an organic solvent is mixed with the acidified cerium oxide nanoparticle dispersion (5 wt.%) in the proportions indicated in the table.

The substrate is coated with a 1 mil gap and a 5 wt.% cerium oxide dispersion (total cerium oxide weight) using a blocked coater or Meyer rod to provide a thickness of 100 to 200 nm. Dry coating in the range. The coated sample is heated to 80 to 100 ° C for 5 to 10 minutes to achieve drying.

Transmittance Transmission and reflection tests were performed at 20% relative humidity using a Varian Cary 5E spectrophotometer. Use a nanoscope ranging from 500 nm to 5 microns (μm) IIIa, Dimension 5000 Atomic Force Microscope (AFM) (Digital Instruments, Santa Barbara), collects atomic force microscope height and phase images. The coating on polyethylene terephthalate or glass was measured by a multi-angle ellipsometry spectrometer (M2000). Measurements of 300 to 900 nm were made at an incident angle of 70 。. The film thickness was measured in the range, and the refractive index value was measured at 555 nm.

Contact angle measurement The dried coating was applied to the video contact angle analyzer of product number VCA-2500XE from AST Products (Billerica, MA) using the original deionized water filtered through a filtration system obtained from Millipore Corporation (Billerica, MA). The sample was subjected to static water contact angle measurement. The reported values are the measured average of at least three droplets measured on the right and left sides of the droplet, as shown in the table. For static measurements, the droplet volume was 1 μL.

Anti-fog test Anti-fog properties were evaluated by immediate appearance changes to the coated side of the breath-blowing toward the non-alcoholic evaluator. The anti-fog property rating is as follows: 5=Excellent 4=good 3=poor

Durability test was evaluated by mechanical durability as shown in the examples, dry and wet Kimwipe ^TM tissue wipe hard coating surface. The values reported in the table represent the number of wipes required to visually remove the coating. Light transmission is used to determine if the coating is retained or removed.

An easy cleaning test applies dirty diesel, vegetable oil or soap to the surface of the coating for a period of time (2 minutes to overnight). The contaminated area is then rinsed with water until the dirty oil or vegetable oil is completely removed. The time consumed was recorded when the applied flow rate was set to 750 ml per minute (750 mL/min). Typically, the water rinse time is within 1 minute. Then repeat 4~5 cleaning loops. The cleanability was evaluated by the cleaning speed (time) and residual oil on the surface. To evaluate the surface mechanical durability and easy to clean by wiping hard surfaces with a wet Kimwipe ^TM coated tissue.

In the following comparative examples and Examples 1-5, the 5 wt.% nanoparticle ceria composition was coated with a coating thickness of pH 2 to 3 and 1 mil (~25 μm). The halo treated polyethylene terephthalate substrate is dried at 80 to 100 ° C for 5 to 10 minutes. The mechanical durability and transmittance of the coated samples were tested using the aforementioned test methods. The results are shown in Table 1. For the purpose of comparison, a sample using 93 nm of cerium oxide was also tested. It is concluded from the test results that the smaller particle size shows improved durability.

In the following Examples 6-8, the untreated polyethylene terephthalate matrix was coated and tested as before. It is not easy to apply an aqueous acidified dispersion having a particle size of 45 nm or more on the substrate.

In the following Examples 9-20, corona was applied with a 5 wt.% nanoparticle ceria composition as shown at pH 2 to 3 and 1 mil (~25 μm) coating thickness. The treated polyethylene terephthalate substrate is dried at 110 to 120 ° C for 5 to 10 minutes. Some embodiments further comprise the tetraethoxydecane in the ratios indicated. Test the coating sample as before. It is concluded from the test results that the addition of tetraethoxydecane improves the durability of the coating.

In the following Examples 21-28, the coated 5 wt.% nanoparticle ceria composition was applied at a coating thickness of pH 2 to 3 and 1 mil (~25 microns). The corona treated polyethylene terephthalate substrate was dried at 110 to 120 ° C for 5 to 10 minutes. Some embodiments further comprise the tetraethoxydecane in the ratios indicated. Test the coating sample as before. From the test results, it is concluded that tetraethoxy decane improves the durability of the mixed particle system.

In the following Examples 29-32, the coating was applied at a coating thickness of pH 2 to 3 and 1 mil (~25 μm) using the 5 wt.% nanoparticle ceria composition shown. The treated polyethylene terephthalate substrate is dried at 110 to 120 ° C for 5 to 10 minutes. The composition further comprises tetraethoxynonane in the indicated proportions. Test the coating sample as before. From the test results, it was concluded that tetraethoxy decane improved the durability of the coating on untreated polyethylene terephthalate.

In the following Examples 33-40, a 5 wt.% mixed nanoparticle ceria composition (containing mixtures of different sizes) was shown at pH 2~3 and 1 mil (~25 microns) coating. Coating untreated polyethylene terephthalate based on thickness Body, dry at 80~100 °C for 5~10 minutes. The composition further comprises tetraethoxynonane in the indicated proportions. Test the coating sample as before. It is concluded from the test results that tetraethoxy decane improves the coating durability of the mixed particle composition on untreated polyethylene terephthalate.

In the following Examples 41-42, the coating of the 5 wt.% mixed nanoparticle ceria composition was applied at a coating thickness of pH 2 to 3 and 1 mil (~25 μm). The treated polyethylene terephthalate substrate is dried at 80 to 100 ° C for 5 to 10 minutes. The examples compare the properties of aqueous dispersions and ethanol dispersions. Mechanical durability was tested only with wet Kimwipe. When the ethanol was not acidified, the comparative examples showed poor performance.

In the following examples and comparative examples, the pH dependence of coating properties was investigated. In the comparative example, the nanoparticles were coated as an alkaline dispersion. The coating properties were then compared to a dispersion in which the pH was adjusted to 2 to 3, and then compared to a dispersion in which the pH of the acidic dispersion was adjusted again to pH 5-6 prior to coating. As shown in Table 8, each dispersion had 5 wt.% nanoparticles. The substrate is untreated polyethylene terephthalate. The dispersion providing a visually uniform coating was named "coatable". The paint that is formed into beads and/or provides a visually uneven coating is named "beading". Embodiments of nanoparticle emulsions having mixed sizes are also provided. These implementation examples The effect of coatability on the coatability and the re-adjusted pH is maintained.

In Examples 58-63 and Comparative Examples 7-8, the 5 wt.% nanoparticle ceria composition is shown at a pH of 1 mil (~25 microns) coating thickness as indicated. The untreated polyethylene terephthalate substrate was coated and dried at 110 to 120 ° C for 5 to 10 minutes. 59,60,62 and 63 Example 98: silicon dioxide 2: The ratio of the surfactant, comprising Rhone-Poulenc, Inc of surfactant SIPONATE ^TM DS-10. Static water contact angle, transmittance, and anti-fog performance are reported. These examples show the effect of pH on coatability and on coating properties.

In the following Examples 64-82 and Comparative Examples 9-14, the 5 wt.% nanoparticle ceria composition shown, at a pH of 1 mil (~25 microns) coating thickness as indicated. Next, the untreated polyethylene terephthalate substrate is coated and dried at 110 to 120 ° C for 5 to 10 minutes. Water advancement and receding contact angles are reported. In Example 84, the substrate was a polycarbonate having a perfluoropolyether coating, prepared in accordance with Example 1 of 11/828566 (Klum et al., incorporated herein by reference), using Preparation 2 containing 0.5 wt.%. A solution of perfluoropolyether SHC-1200 was applied as a top coat. In Example 85, the acid anhydride modified product of the matrix is polyethylene polymer sold Bynel ^TM, available from EIDuPont de Nemours & Co., Wilmington, Del .. Stable means that there is no gel for at least 2 months. These examples demonstrate that dispersion stability and coatability are related to pH and particle size.

In the following Examples 86-89, the 5 wt.% nanoparticle ceria shown is used. The composition is coated with an untreated polyethylene terephthalate substrate at a coating thickness of pH 2 to 3 and 1 mil (~25 μm) and dried at 110 to 120 ° C for 5 to 10 minutes. . The initial transmittance was measured, and then the sample was subjected to "wet rubbing" by 100 rubs of the wet tissue to measure the durability, and the transmittance was measured again. Anti-fog properties were also tested. In Examples 87 and 89, a DS-10 surfactant was added. The antifogging property was further evaluated by aging at 50 ° C and 95% humidity for at least 11 days. The examples show that the surfactant does not significantly impair the coating properties and improves the anti-fog properties.

In the following Examples 90-93 and Comparative Examples 15-16, the 5 wt.% nanoparticle ceria composition shown, at the pH values shown, and 1 mil (~25 nm) were used. Under the coating thickness, the tile is coated and dried at 110~120 °C for 5~10 minutes. Rinsing is easily removed by immersing in soap scum and then successfully rinsing the soap with water. The durability of the coating was evaluated by wiping with a wet wipe or alternating with a dry paper towel; measuring the light transmission to determine whether the coating was retained or removed. If pinholes appear or if the interference color is intense and uneven, the coating quality is poor.

In the following Example 94 and Comparative Example 17, the 5 wt.% nanoparticle ceria composition shown was coated at a pH of 1 mil (~25 microns) coating thickness as indicated. The untreated polyethylene terephthalate matrix is dried at 110 to 120 ° C for 5 to 10 minutes. An easy degreasing rinse is performed by applying several oil droplets to the coating sample and then successfully rinsing off the oil droplets with a narrow water flow of 750 mL/min. The durability of the coating was evaluated by wiping with a wet wipe or alternating with a dry paper towel; the measurement of light transmission was used to determine whether the coating was retained or removed.

In Figures 3 to 5, the transmittance of the coated article was tested. The article was prepared primarily in accordance with Example 1, using a polyethylene terephthalate film substrate.

In Figure 3, the sample is as follows: A polyethylene terephthalate film, as a control 5 wt.% aqueous dispersion of 5 nm cerium oxide with a pH of 2 5 wt.% ethanol dispersion of 5 nm cerium oxide with a pH of 2 5 wt.% ethanol dispersion of 5 nm cerium oxide with a pH of 10

As can be seen in Figure 3, samples B and C exhibited much higher transmission than uncoated polyethylene terephthalate sample A. Sample D coated at an alkaline pH did not exhibit an increase in either of samples B and C at a wavelength of 350-600 nm.

In Figure 4, the sample is as follows: A polyethylene terephthalate film, as a control 5 wt.% aqueous dispersion with a pH of 2 at 5 nm/45 nm mixture (10:90) 5 wt.% ethanol dispersion with a F pH of 2 at 5 nm/45 nm mixture (10:90) 5 wt.% aqueous dispersion of a 5 nm/90 nm mixture (10:90) with a pH of 2 5 wt.% ethanol dispersion with a H pH of 2 5 nm / 90 nm mixture (10:90) I pH 5 of 5 nm / 90 nm mixture (10:90) of 5 wt.% ethanol Dispersions 5 wt.% ethanol dispersion with a pH of 2 to 90 nm 5 wt.% ethanol dispersion with a K pH of 10 to 90 nm 5 wt.% ethanol dispersion with a pH of 2 at 45 nm

In Figure 5, the sample is as follows: A polyethylene terephthalate film, as a control 5 wt.% aqueous dispersion of 4 pH/45 nm mixture (50/50 by weight) with a pH of 2, one-side coating 5 wt.% aqueous dispersion with N pH of 4 to 4 nm, single-sided coating 5 wt.% aqueous dispersion of 4 pH/45 nm mixture (50/50 by weight) with a pH of 2, double coated 5 wt.% aqueous dispersion with a pH of 2 to 4 nm, double coated

From the comparison of the samples M and O, or N and P, it can be seen that by double-coating the base film, the transmittance of the substrate can be greatly improved.

The above is intended to be illustrative only and not limiting. Any equivalent modifications or alterations to the spirit and scope of the invention are intended to be included in the scope of the appended claims.

1 is a transmission electron micrograph of the article prepared in Example 78; FIG. 2 is a transmission electron micrograph of the article of Comparative Example 12; and FIGS. 3 to 5 are transmission diagrams of the article of the present invention.

Claims (20)

A method of providing a coating to a substrate, the method comprising contacting a substrate with a coating composition and drying to provide a coating of cerium oxide nanoparticle, the coating composition comprising: a) 0.5 to 99 wt.% water; 0.1 to 20 wt.% of cerium oxide nanoparticles having an average particle diameter of 40 nm or less; c) 0 to 20 wt.% of cerium oxide nanoparticles having an average particle diameter of 50 nm or more Wherein the sum of b) and c) is 0.1 to 20 wt.%; d) an acid having a pKa value of < 3.5 sufficient to lower the pH to less than 5; and e) 0.1 to 20 wt% relative to the amount of cerium oxide nanoparticles .% tetraalkoxydecane. The method of claim 1, wherein the concentration of the cerium oxide nanoparticles in the coating composition is from 0.1 to 20 wt.%. The method of claim 1, wherein the substrate is a hydrophobic matrix having a static water contact angle greater than 50°. The method of claim 1, wherein the aqueous dispersion of the cerium oxide nanoparticles further comprises cerium oxide nanoparticles having an average particle diameter of more than 40 nm. The method of claim 1, wherein the acid is selected from the group consisting of oxalic acid, citric acid, H ₃ PO ₄ , HCl, HBr, HI, HBrO ₃ , HNO ₃ , HClO ₄ , H ₂ SO ₄ , CH ₃ SO ₃ H, CF ₃ SO ₃ H, CF ₃ CO ₂ H and CH ₃ SO ₂ OH. The method of claim 1, wherein the cerium oxide nanoparticle It has an average particle diameter of 20 nm or less. The method of claim 1, wherein the cerium oxide nanoparticles have an average particle diameter of 10 nm or less. The method of claim 1, wherein the substrate has a static water contact angle of less than 50° after coating. The method of claim 1, wherein the coating composition has a pH of less than 3. The method of claim 1, comprising the steps of: adding a sufficient amount of acid to adjust the pH of the coating composition to less than 5, and then adding a sufficient amount of base to adjust the pH to a range of 5-6. Inside. A hydrophilic article prepared by the method of claim 1 of the patent application. A coated article comprising a substrate and a coating thereon obtained by the method of claim 1, wherein the coating is cerium oxide having an average particle diameter of 40 nm or less An agglomerate of particles comprising a three-dimensional porous network of cerium oxide nanoparticles, and the cerium oxide nanoparticles are combined with adjacent cerium oxide nanoparticles. The coated article of claim 12, having less than 50. Water contact angle. The coated article of claim 12, wherein the coating has a thickness of about 500 to 2500 Å. The coated article of claim 12, wherein the substrate is transparent. The coated article of claim 15 wherein the transmission of normal incident light in the wavelength range of 400 to 700 nm is improved as compared to the uncoated substrate. The coated article of claim 16 wherein the average transmission is increased by at least 2%. The coated article of claim 12, wherein the coating has a refractive index between about 1.2 and 1.4. The coated article of claim 12, wherein the coating comprises: a. 60 to 95 wt.% of condensed cerium oxide nanoparticles, b. about 0.1 to 20 wt.% of tetradecane. Oxydecane, c. optionally from about 0 to 5 wt.% of a surfactant; and from d to 0 to about 5 wt.% of a wetting agent. A coating composition comprising: a) 0.5 to 99 wt.% water; b) 0.1 to 20 wt.% of cerium oxide nanoparticles having an average particle diameter of 40 nm or less; c) 0 to 20 wt.% An cerium oxide nanoparticle having an average particle diameter of more than 50 nm, wherein the sum of b) and c) is 0.1 to 20 wt.%; d) an acid having an amount sufficient to lower the pH to less than 5, pKa < 3.5; Between 0.1 and 20 wt.% of tetraalkoxyquinone relative to the amount of cerium oxide nanoparticles alkyl.