Patent Application
20220195205
This application makes reference to and claims the benefit of priority of an application for “Durable Anti-Reflection Anti-Fog Single Layer Coating” filed on 18 Mar. 2019 with the Intellectual Property Office of Singapore, and duly assigned application number 10201902396V. The content of the above application filed on 18 Mar. 2019 is incorporated herein by reference for all purposes, including an incorporation of any element or part of the description, claims or drawings not contained herein.
The present invention generally relates to a multi-layered coating. The multi-layered coating may have anti-reflection, anti-fog and abrasion resistance properties. The present invention also relates to a process for forming such multi-layered coatings, an article comprising the same and uses thereof.
Optically clear substrate, such as glass or certain plastics, finds applications in eyewear (which can include spectacle lenses, visors or goggles), windows (which can include automotive windshields or architectural glass), optical instruments, and digital displays. For different applications, one or more surface properties, such as abrasion resistance, anti-fog, and anti-reflection are highly attractive and practical to have because they enhance the usability of the transparent material.
In cases where the substrate is used in a high humidity place or at a boundary of a large temperature/humidity difference, fogging or condensation of water vapor may occur on the surface of the substrate, which reduces its transparency. In cases where the substrate is exposed to elements, abrasion resistance is a critical property of the substrate to ensure that the durability and transparency of the substrate surface are maintained. In cases where the substrate is used in a medium where the reflective index is different from that of the substrate, reflection caused light loss may reduce the transmittance of a transparent substrate. Accordingly, there has been no lack of attempts in the past to provide coatings to protect and increase the surface properties of the optically clear substrate.
There is previously described a coating composition comprising a porous silica nanoparticles, one or more organic soluble polymer resins, one or more UV-cross linkable resins, one or more UV cross linkable reactive diluents, solvents, and a UV-initiator system. However, the coating here is not abrasion resistant.
While coatings having properties of superhydrophilicity, high transparency, and antireflection exist, such coatings appear not to be abrasion resistant.
Hitherto, it has not been possible to combine all three properties of anti-reflection, anti-fog, and abrasion resistance in the same coating and achieve a high level of performance in a satisfactory manner.
Thus, there is a need to provide a multi-layered coating that overcomes, or at least ameliorates, one or more of the disadvantages described above. The multi-layered coating is preferably one that has anti-reflection, anti-fog and abrasion resistance properties.
There is also a need to provide a process for forming such multi-layered coatings.
According to a first aspect, there is provided a multi-layered coating having a plurality of cavities therein, the multi-layered coating comprises a first layer comprising an oxide-containing polymer; and a second layer disposed on the first layer, the second layer comprising an oxide.
Advantageously, the multi-layered coating may have anti-reflection, anti-fog and abrasion resistance properties. The multi-layered coating may also be optically clear or transparent so as to allow light to substantially pass through the multi-layered coating from one side of the coating to another (usually opposite) side, so as to allow a user to look through the multi-layered coating with minimal optical interference or impediment.
Advantageously, by having more than one property in one coating, this negates the need for a number of individual coatings to be used. Therefore, this not only reduces the number of individual coatings required, but is also able to reduce the need of layering the coating to achieve different properties.
According to a second aspect, there is provided a process of forming a multi-layered coating having a plurality of cavities therein, the process comprising the steps of:
a. applying an oxide-containing polymer onto a substrate to form a first layer;
b. contacting the oxide-containing polymer with a mold to imprint a plurality of cavities therein the first layer;
c. polymerizing the oxide-containing polymer while in contact with the mold; and
d. oxidizing the first layer to form a second layer disposed on the first layer, the second layer comprising an oxide.
Advantageously, the process may be a simple process in order to form a multi-layered coating having at least the above properties of anti-reflection, anti-fog and abrasion resistance. The process may be scalable depending on the size of the mold.
Advantageously, the second layer may be formed in situ and does not require a separate layer to be applied into the first layer. The second layer is formed as a result of a chemical reaction and does not require adhesion or physical means to adhere to the first layer. Therefore, the process optionally does not require an adhering step or a physical placement of the second layer onto the first layer.
According to a third aspect, there is provided an article comprising a multi-layered coating thereon, the multi-layered coating having a plurality of cavities therein and comprises a first layer comprising an oxide-containing polymer; and a second layer disposed on the first layer, the second layer comprising an oxide.
The following words and terms used herein shall have the meaning indicated:
The term ‘cavity’ is to be interpreted broadly to include a recess or a hole that extends from the surface of the coating into the body or bulk material of the coating. This is opposed to a projection or a protrusion that extends outward from the surface of the coating.
The term ‘curable’ is to be interpreted broadly to refer to the ability of a resin/monomer to be hardened or toughened by covalent cross-linking to each other, brought about by chemical additives, ultraviolet radiation, electron beam or heat.
The term ‘UV-curable’ is to be interpreted broadly to refer to the ability of a resin/monomer to be hardened or toughened by covalent cross-linking to each other, brought about by ultraviolet radiation.
The term ‘cross-linking’ is to be interpreted broadly to refer to forming covalent bonds or crosslinks between monomers to form polymers, or between polymers, for example, linear polymers, branched polymers, dendrimers, or macromolecular molecules. Here, the cross-linking may also refer to covalent bonds or crosslinks between a molecule and a polymer. The term ‘cross-linker’ or ‘cross-linking agent’ refers to a compound or a mixture of compounds capable of forming crosslinks in such a context.
The term ‘nanoimprint process’ is to be interpreted broadly to refer to a process to make coatings comprising imprinted surface structures in the nano-sized range.
The term “optically clear” is to be interpreted broadly to refer to a property of the coating whereby the coating is substantially transparent and allows light to pass through the coating from one side to another (usually opposite) side of the coating. This is opposed to translucent or opaque. Optically clear coatings are usually colorless and remain that way.
The word “substantially” does not exclude “completely” e.g. a composition which is “substantially free” from Y may be completely free from Y. Where necessary, the word “substantially” may be omitted from the definition of the invention.
Unless specified otherwise, the terms “comprising” and “comprise”, and grammatical variants thereof, are intended to represent “open” or “inclusive” language such that they include recited elements but also permit inclusion of additional, unrecited elements.
As used herein, the term “about”, in the context of concentrations of components of the formulations, typically means +/−5% of the stated value, more typically +/−4% of the stated value, more typically +/−3% of the stated value, more typically, +/−2% of the stated value, even more typically +/−1% of the stated value, and even more typically +/−0.5% of the stated value.
Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.
Certain embodiments may also be described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the disclosure. This includes the generic description of the embodiments with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.
Exemplary, non-limiting embodiments of a multi-layered coating will now be disclosed.
The multi-layered coating has a plurality of cavities therein, the multi-layered coating comprises a first layer comprising an oxide-containing polymer; and a second layer disposed on the first layer, the second layer comprising an oxide.
The size of the cavities may be in the nanometer scale. The size of the cavities may be regarded as being smaller than the wavelength of visible light. The size of the cavities may be in the range of about 100 nm to about 380 nm, about 150 nm to about 380 nm, about 200 nm to about 380 nm, about 250 nm to about 380 nm, about 300 nm to about 380, about 350 nm to about 380 nm, about 100 nm to about 350 nm, about 100 nm to about 300 nm, about 100 nm to about 250 nm, about 100 nm to about 200 nm, or about 100 nm to about 150 nm.
The size of the cavity may be regarded as a dimension of the cavity when measured at the surface of the coating. The dimension may depend on the shape of the cavity when viewed from the top of the coating. Where the cavity is viewed as one having a circular shape, the dimension may be regarded as the diameter and depth of the circular shape. Where the plurality of cavities is viewed as an array, the dimension may be regarded as the period of the array, which is the distance from one point of a cavity to the same point but of a neighbouring cavity.
The cavity may have a shape selected from a dimple shape, a cylindrical shape, a conical shape, or a conical frustum shape. Therefore, the sides of the cavity may form a perpendicular angle with the surface of the coating or may be angled relative to the surface of the coating. The base of the cavity (that is present within the coating) may be substantially straight or curved.
The plurality of cavities may form a honeycomb-like structure where the cavities are circular-shaped when viewed from the top of the coating.
Due to the presence of cavities that are dimensioned smaller than the wavelength of visible light, this may lead to the anti-reflection property of the multi-layered coating. While projections that extend from the surface of a coating can also confer an anti-reflection property, this is not desirable in the present application as such projections can be brittle and can be damaged easily when a shear force is applied onto the coating, leading to the removal of the projections when a shear force is applied. Having cavities in the coating ensure that the cavities are undamaged and intact in the presence of a shear force, thereby maintaining the anti-reflection property of the coating.
The size of the cavities being in a range smaller than the wavelength of visible light may form a gradient of refractive index (GRIN) which is required for the anti-reflective effect. This gradient of refractive buffers the transition of light as it passes from air to solid medium, resulting in less reflection and thus higher transmission.
In the multi-layered coating, the oxide of the oxide-containing polymer and the oxide in the second layer is the same. The oxide of the second layer may be formed when oxidizing the first layer in order to retain the oxide and remove the organic components. Therefore, the oxide has to be part of the material used to form the first layer. The oxide of the second layer may confer the anti-fogging property to the multi-layered coating due to the ability of the oxide to create a superhydrophilic surface. Therefore, any exposure of the multi-layered coating to water vapour results in the formation of a water film on the surface which helps to avoid the negative appearance of fog. Any oxide that is able to form a superhydrophilic surface may be used. Exemplary types of oxides include silica (SiO2), titanium oxide (TiO2) and zinc oxide (ZnO).
In the multi-layered coating, the polymer is formed by UV-curable resins. The UV-curable resin may contain monomers with multiple reactive groups to facilitate cross-linking of the cured polymer chains, which is the process to harden the cured polymer and therefore to confer the abrasion resistance property of the multi-layered coating.
The UV-curable resin may be polymerized by monomers selected from the group consisting of (meth)acrylates, esters, epoxy resins, urethanes, silicones, ethers and vinyl ethers. The UV-cured resin may be epoxy (meth)acrylates, acrylated polyesters, acrylate modified urethanes or acrylated silicones. Some examples of UV-cured resins are, but not limited to, diglycidyl ether of bisphenol A (DGEBA), hexanediol diacrylate (HDDA), dipentaeryth ritol hexaacrylate (DPHA), tripropylene glycol diacrylate (TPGDA), pentaerythritol triacrylate (PETA), or derivatives thereof. The photo-initiator used in the polymerization process is 2-Hydroxy-2-methylpropiophenone.
The first layer may have a thickness in the range of about 1 μm to about 100 μm, about to about 90 μm, about 1 μm to about 80 μm, about 1 μm to about 70 μm, about 1 μm to about 60 μm, about 1 μm to about 50 μm, about 1 μm to about 40 μm, about 1 μm to about 30 μm, about 1 μm to about 20 μm, about 1 μm to about 10 μm, about 10 μm to about 100 μm, about 20 μm to about 100 μm, about 30 μm to about 100 μm, about 40 μm to about 100 μm, about 50 μm to 100 μm, about 60 μm to about 100 μm, about 70 μm to about 100 μm, about 80 μm to about 100 μm, or about 90 μm to about 100 μm. The second layer may have a thickness in the range of about 1 nm to about 50 nm, about 1 nm to about 40 nm, about 1 nm to about 30 nm, about 1 nm to about 20 nm, about 1 nm to about 10 nm, about 10 nm to about 50 nm, about 10 nm to about 50 nm, about 20 nm to about 50 nm, about 30 nm to about 50 nm, or about 40 nm to 50 nm.
The multi-layered coating may be substantially optically clear.
Exemplary, non-limiting embodiments of a process of forming a multi-layered coating having a plurality of cavities therein will now be disclosed.
The process comprises the steps of:
a. applying an oxide-containing UV-curable resin onto a substrate to form a first layer;
b. contacting the oxide-containing UV-curable resin with a mold to imprint a plurality of cavities therein the first layer;
c. polymerizing the oxide-containing UV-curable resin while in contact with the mold; and
d. oxidizing the first layer to form a second layer disposed on the first layer, the second layer comprising an oxide.
The second layer may be formed in situ on the first layer and therefore, an additional layering step is not required. The second layer adopts the shape and conformation of the first layer easily (including those of the cavities) due to the in situ formation of the second layer on the first layer. Since additional layering steps are not used (which can be difficult to ensure that the added layer conforms exactly to the shape and conformation of the first layer), this process avoids the need for such conformity and ensures that the integrity of the cavities is maintained.
The oxide-containing polymer may be an oxide-containing UV-cured resin. The UV-cured resin may be polymerized by UV-curable resins which comprise monomers selected from the group consisting of (meth)acrylates, esters, epoxy resins, urethanes, silicones, ethers and vinyl ethers. The UV-curable resin may be epoxy (meth)acrylates, acrylated polyesters, acrylate modified urethanes or acrylated silicones. Some examples of UV-curable resins are, but not limited to, diglycidyl ether of bisphenol A (DGEBA), hexanediol diacrylate (HDDA), dipentaeryth ritol hexaacrylate (DPHA), tripropylene glycol diacrylate (TPGDA), pentaerythritol triacrylate (PETA), or derivatives thereof. The UV-cured resin may be polymerized in the presence of a photo-initiator that is activated by UV-light may cause the UV-curable resin to polymerise and thereby cure, forming a UV-cured resin. The UV-curable resin may contain additives as required.
The oxide-containing polymer may be polymerized when in contact with the mold. The mold may have a plurality of projections that form corresponding cavities when applied onto the first layer such that upon polymerizing, the plurality of cavities is imprinted into the first layer. The plurality of cavities may be imprinted via nanoimprinting lithography.
The contacting step may be undertaken at a room temperature and pressure in the range of about 5 bars to about 20 bars, about 5 bars to about 15 bars, about 5 bars to about 10 bars, about 10 bars to about 20 bars, or about 15 bars to about 20 bars.
The polymerizing step may be undertaken at a room temperature and pressure in the range of about 5 bars to about 20 bars, about 5 bars to about 15 bars, about 5 bars to about 10 bars, about 10 bars to about 20 bars, or about 15 bars to about 20 bars.
The oxidizing step may be undertaken by a manner of deep reactive-ion etching (DRIE), using oxygen gas under high oxygen pressure with low power at a room temperature. The oxygen pressure is about less than 1 mbar, such as in the range of about 0.1 mbar to about 0.9 mbr, about 0.1 to about 0.8 mbar, about 0.1 mbar to about 0.7 mbar, about 0.1 mbar to about 0.6 mbr, about 0.1 mbar to about 0.5 mbar, about 0.2 mbar to about 0.9 mbar, about 0.3 mbr to about 0.9 mbr, about 0.4 mbr to about 0.9 mbr, or about 0.5 mbr to about 0.9 mbr.
The multi-layered coating may be applied onto an article in order to confer desirable properties to the article. Therefore, there is also provided an article comprising a multi-layered coating thereon, the multi-layered coating having a plurality of cavities therein and comprises a first layer comprising an oxide-containing polymer; and a second layer disposed on the first layer, the second layer comprising an oxide.
The multi-layered coatings can be used in a number of applications such as those mentioned below.
The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.
Referring to
Non-limiting examples of the invention will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.
A multi-layered coating with an array of dimples was formed by the method of nanoimprint lithography. Here, a UV-curable resin was made from a mixture of the following chemicals: MA0736—Acrylo POSS Cage Mixture (Hybrid Plastics, Mississippi, USA), 1,6-hexanediol diacrylate (Sigma-Aldrich, Missouri, USA), Pentaerythritol tetrakis(3-mercaptopropionate) (Sigma-Aldrich, Missouri, USA), isobornyl acrylate (Sigma-Aldrich, Missouri, USA), 3-(Trimethoxysilyl)propyl methacrylate (Sigma-Aldrich, Missouri, USA) and 2-Hydroxy-2-methylpropiophenone (Sigma-Aldrich, Missouri, USA). Among the above, MA0736—Acrylo POSS Cage Mixture (Hybrid Plastics, Mississippi, USA) and 1,6-hexanediol diacrylate (Sigma-Aldrich, Missouri, USA) were used for providing the coating. Pentaerythritol tetrakis(3-mercaptopropionate) (Sigma-Aldrich, Missouri, USA) is a monomer used to increase cross-linking and to reduce oxygen inhibition of the polymerization. Isobornyl acrylate (Sigma-Aldrich, Missouri, USA) is a monomer which increases adhesion of the cured polymer to the substrate. 3-(Trimethoxysilyl)propyl methacrylate (Sigma-Aldrich, Missouri, USA) is a silicon containing chemical, which increases the concentration of silicon at the surface of the polymer and it can increase adhesion to oxide substrates. 2-Hydroxy-2-methylpropiophenone is the photo-initiator. The as-prepared UV curable resin was applied onto a substrate 4, as shown in
The formed multi-layered coating is then subjected to a number of characterization processes.
In order to show that cavities were more resistant to shearing as compared to projections, the multi-layered coating with the plurality of cavities was subjected to a shear force test. Conventionally, arrays of pillar type projections were used to confer the anti-reflection properties to the coating. However, such pillar type structures cannot cope with abrasive forces because the pillars were brittle and fragile to shear forces. Here, it can be seen that cavity structures 10 on nanostructured coating 11 were much less susceptible to damage by shear force 8 as compared to pillar type structures 12 as illustrated in
The anti-reflection properties were acquired using an array of structures with dimensions smaller than the wavelength of visible light. As show in
Anti-fogging properties can be obtained by creating a superhydrophilic surface that will facilitate the immediate formation of a water film of the surface, avoiding the negative appearance of fog. As seen in
XPS characterization of the coating surface taking (a) before and (b) after oxidation treatment, and a control surface (non-silicon containing coating) taken (c) before and (d) after oxidation treatment is shown in
To demonstrate the anti-fogging properties, samples were exposed to a flow of steam to simulate a fogging environment.
Therefore, this shows that the coating of the present application is able to have anti-fogging properties that remain even after a period of time.
The multi-layered coating may be used in optical applications such as eyewear (which can include spectacle lenses, visors or goggles) as well as in digital displays, camera lenses or photovoltaics. This may be due to the advantageous properties of the multi-layered coating such as anti-reflective, anti-fogging and abrasion resistant. Depending on the application required, the multi-layered coating may be optically clear or transparent so that where the multi-layered coating is used on devices, this does not impede the eyesight or vision of a user using such devices.
The multi-layered coating may find application in various optoelectronic equipment, aeronotical displays and sensors, automotive displays and sensors, space technologies and head-up display (HUD) devices as emitters and in displays.
The multi-layered coating may also be applied to soft substrates, creating a hard, non-scratch surface on softer polymer substrates.
It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10201902396V | Mar 2019 | SG | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SG2020/050143 | 3/18/2020 | WO | 00 |
