WO2020036564A2

WO2020036564A2 - Hydrophilic anti-reflective coating which can be tempered and has high corrosion resistance

Info

Publication number: WO2020036564A2
Application number: PCT/TR2019/050479
Authority: WO
Inventors: Refika BUDAKOGLU; Aref CEVAHIR; Yalcin KURU
Original assignee: Turkiye Sise Ve Cam Fabrikalari Anonim Sirketi
Priority date: 2018-06-28
Filing date: 2019-06-20
Publication date: 2020-02-20
Also published as: WO2020036564A3

Abstract

The present invention relates to hydrophilic anti-reflective coating solution, which can be tempered and whose corrosion resistance is high and obtained by using sol-gel method so as to be compliant to the roll coating method, the production method of said solution and the glass where said method is applied.

Description

HYDROPHILIC ANTI-REFLECTIVE COATING WHICH CAN BE TEMPERED AND HAS

HIGH CORROSION RESISTANCE

TECHNICAL FIELD

The present invention relates to the production of anti-reflective coatings, applied onto flat and patterned glass surfaces by means of roll coating method and prepared by means of wet method for providing transmittance increase in photovoltaic (FV), automotive glasses and architectural applications, coating thereof onto glass and anti-reflective coated glass.

PRIOR ART

Anti-reflective coatings, which provide low reflection or high transmittance in a wide wavelenth range, are preferred in various applications like solar panels, showcase glasses and screen glasses. In case anti-reflective coatings are applied to glass surfaces as single layer, the refraction index of the coating shall be lower than the refraction index (n - 1 .5) of glass. Such coatings generally exist in the literature and patents as coatings produced by means of dip coating in solutions with high acid ingredient. Dip coating method is an off-line application method and leads to extra cost particularly in mass production conditions. By means of the roll coating method which has become frequent in the last five years, even if homogeneous coatings cannot be obtained as in the coatings produced by means of dip coating method, sufficient optic performance is provided particularly in case of patterned glasses used in solar panels. If the solutions with high acid ingredient and suitable for dip coating method are used in roll coating system, roll system and equipment have the risk of being subjected to corrosion rapidly. Thus, for the roll coating system coating solutions are needed which do not include strong acid. Anti-reflective coatings used on photovoltaic cover glasses and on screens are coatings are in general present as single layer and their refraction index dependon pore ingredient which decreases the refraction index and increase the transmittance. The porous areas present on the surface of the coating layer are affected in an unfavorable manner by the humidity or corrosive gases, existing in the atmosphere, in time and transmittance losses are occur. Various methods related to increasethe corrosion resistance are provided by means of application of hydrophobic (water repellent) or hydrophilic (high water distribution) coatings onto the coating. In the known state of the art, even if the corrosion resistance of closed pore single layer anti- reflective coatings is high, in rainy weathers, rain droplets accummulate on the coating surfaces and lead to decrease in the coating transmittance. Another application, which is the application of hydrophobic or hydrophilic coating onto anti-reflective coating, leads to a secondary process and secondary cost since coating is realized onto a coating.

As a result, because of all of the abovementioned problems, an improvement is required in the related technical field.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to production of anti-reflective coatings applied onto glass surface by means of roll coating method and prepared by means of wet method for providing transmittance increase in photovoltaic (FV), automotive glasses and architectural applications, coating thereof onto glass and anti-reflective coated glass, for eliminating the above mentioned disadvantages and for bringing new advantages to the related technical field.

An object of the present invention is to provide an anti-reflective coating solution which does not comprise corrosive acid.

An object of the present invention is to provide an anti-reflective coating solution whose pH value is close to neutral.

An object of the present invention is to provide an anti-reflective coated glass whose liquid distribution on the surface, where it is applied, is increased.

An object of the present invention is to provide an anti-reflective coated glass whose thermal process resistance is increased.

An object of the present invention is to provide an anti-reflective coated glass whose corrosion resistance is increased.

In order to realize all of the abovementioned objects and the objects which are to be deducted from the detailed description below, the present invention is production of hydrophilic anti-reflective coating which can be tempered and whose corrosion resistance is high. Accordingly, said coating solution comprises components which will form pore at temper conditions and chemicals which will provide resistance against corrosion.

In order to realize all of the abovementioned objects and the objects which are to be deducted from the detailed description below, the present invention is a hydrophilic anti- reflective coating solution which can be tempered and whose corrosion resistance is high and obtained by using sol-gel method so as to be compliant to the roll coating method. Accordingly, said coating solution is characterized by comprising:

- predetermined amount of tetra-ethyl-ortho-silicate (TEOS) as the hydrolizable silica source,

- at least one of or mixtures at specific proportions of propylene glycol mono-methyl ether acetate, ethanole, buthanole, n-propanole, 2-propanole for providing dissolving and controlled evaporation,

- predetermined proportion of dibuthyl tin diacetate which provides hydrophilic characteristic and anti-static characteristic to the coating and bonded crosswise by means of its Glycidoxypropyltrimethoxysilane (GLYMO) componentto increase the corrosion resistance of the coating,

- porosity agent in chain structure of poly-ethylene-glycol poly-propylene-glycol polyethylene-glycol (hereafter, it will be called PE-PO-PE) with predetermined proportion and

- at least one of or mixtures at specific proportions of acetic acid, glacial acetic acid, formic acid, ascorbic acid, citric acid.

In a preferred embodiment of the present invention, the amount of said dibuthyl tin diacetate amount is between 2% and 5% by weight.

In another preferred embodiment of the present invention, said TEOS amount is between 5% and 10% by weight, GLYMO amount is between 1 % and 3% by weight, the amount of organic acid is between 3% and 5% by weight, the amount of propylene glycol mono-methyl ether acetate is between 3% and 5% by weight, the amount of ethanol is between 7% and 10% by weight, the amount of 2-propanol is between 60% and 70% by weight and the amount of porosity agent is between 10% and 30% by weight.

In order to realize all of the above mentioned objects and the objects which are to be deducted from the detailed description below, the present invention is the production method of said anti-reflective coating solution. Accordingly, said production method of the coating solution is characterized by comprising the following steps respectively: (i) adding a mixture comprising predetermined proportions of propylene glycol methyl ether acetate, ethanol, 2-propanol, water and TEOS to another mixture comprising predetermined proportions of propylene glycol methyl ether acetate, ethanol, 2- propanol and acetic acid,

(ii) applying thermal process at a temperature between 50°C and 70°C for a duration between 200 minutes and 280 minutes in order to provide rapid wetting of the solution obtained in step (i),

(iii) waiting of the solution until room temperature after step (ii), and in addition to isopropyl alcohol and in addition to GLYMO for increasing corrosion resistance of the coating, adding predetermined proportion of dibuthyl-tin-acetate bonded crosswise to the GLYMO structure and which provides anti-static characteristic to the coating and at the same time, which provides hydrophilic characteristic to the coating,

(iv) adding a surfactant having high molecular weight and PE-PO-PE chain structure as the porosity agent into the solution obtained after step (iii).

In order to realize all of the above mentioned objects and the objects which are to be deducted from the detailed description below, the present invention is the anti-reflective coated glass where said anti-reflective coating solution is applied. Accordingly, said glass is characterized in that the anti-reflective coating has hydrophilic structure and its contact angle is 20° and lower.

In another preferred embodiment of the present invention, in order to increase resistance of the coating against humidity, the pores, provided in the body of the coating, have gradually reduced pore size from the glass towards the surface.

In order to realize all of the abovementioned objects and the objects which are to be deducted from the detailed description below, the present invention is the method of application of said coating to the glass. Accordingly, said method is characterized in that the solution is applied onto the glass surface by means of the roll method and afterwards, pre- thermal process is applied for 1 -2 minutes between 80°C and 120°C and thermal process is applied for 2-5 minutes between 650°C and 750°C respectively.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows the spectrum of the patterned glass without anti-reflective coating. Figure 2 shows the SEM surface morphology of the anti-reflective coatings comprising 5% porosity agent.

Figure 3 shows the SEM surface morpohology of the anti-reflective coatings comprising 15% porosity agent.

Figure 4 shows the TEM cross section morphology of the anti-reflective coatings comprising 5% porosity agent.

Figure 5 shows the TEM cross sectionl morphology of the anti-reflective coatings comprising 15% porosity agent.

DETAILED DESCRIPTION OF THE INVENTION

In this detailed description, the subject matter anti-reflective coating is explained with references to examples without forming any restrictive effect only in order to make the subject more understandable.

By means of the subject matter anti-reflective coating solution, a hybrid coating solution is obtained. By means of the obtained anti-reflective coating solution, structures like glass, ceramic, etc. can be coated by using methods like dip coating, spraying, roll coating, sputtering, etc. In the preferred application, method of roll coating onto glass is used.

The subject matter anti-reflective coating solution comprises at least one organic acid and at least one solvent, at least one silane and at least one organo-metal.

After the thermal process, a solution is accumulated on the glass surface so as to form a coating including at least one of anorganic oxides like Al₂0₃, Ti0₂, Si0₂ and Sn0₂ whose refraction index is lower than the refraction index of glass. In this solution, preferably silica source is used, in other words, at least one of alkoxy-silane derivatives comprising Si and O and which can be hydrolized preferably by means of sol-gel method is used. As the alkoxy- silane, at least one of or mixtures at specific proportions of tetra-metoxy-silane (TMOS), tetra-ethyl-ortho-silicate (TEOS), tetra-propoxy-silane, trietoxy-silane, methyl-trietoxy-silane (MTEOS), methyl-trimetoxy-silane, methyl-propoxy-silane, tetra-isopropoxy-silane is/are used. Preferably, tetra-ethyl-ortho-silicate (hereafter, it will be called TEOS) is used. The TEOS amount in the solution is between 5% and 10% by weight. The TEOS amount in the solution is one of 5%, 6%, 7%, 8%, 9% or 10% by weight. The TEOS inside the solution forms the frame structure in the anti-reflective thin film and as the TEOS% amount increases, and since the coating thickness increases, it shall be used at proportions which can give the optimum coating thickness.

The solvents inside the coating solution are used for providing controlled evaporation. As the solvent, at least one of or mixtures at specific proportions of propylene glycol mono-methyl ether acetate, ethanol, buthanol, n-propanol, 2-propanol is/are used.

The amount of propylene glycol mono-methyl ether acetate is between 3% and 5% by weight. The amount of propylene glycol mono-methyl ether acetate is between 3%, 3.5%, 4%, 4.5% or 5%. Since propylene glycol mono-methyl ether acetate has high boiling point, in case the usage amount is lower than the mentioned low value, the surface tension increases and in case the usage amount is higher than the mentioned value, it becomes difficult for it to diverge from the surface, whereon it is coated, during the pre-thermal process.

The amount of ethanol in the solution is between 7% and 10% by weight. The amount of ethanol can be 7%, 8%, 9% or 10% by weight. In case the ethanol amount is greater than the mentioned upper value, the surface tension of the coating increases, and the surface distribution of the coating is affected in an unfavorable manner. In case the ethanol amount is lower than the mentioned low value, it becomes difficult for the solvents to diverge from the surface during the pre-thermal process.

The amount of 2-propanol inside the solution is between 60% and 70% by weight. The amount of 2-propanol can be 61 %, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69% or 70% by weight. The usage of 2-propanol amount outside the values mentioned by weight decreases the effect of other solvents and thus, the surface distribution is affected in an unfavorable manner.

In order to increase corrosion resistance of the coating, at least one of or mixtures at specific proportions of cross binding silanes with epoxy or acrylate function like 3-glycidoxy-propyl- triethoxy-silane (GLYEO), 3-glycidoxy-propyl-trimethoxy-silane (GLYMO), 3-metacryl-oxy- propyl-trimethoxy-silane (MPTS), 3-metacryl-oxy-propyl-triethoxy-silane (MPTES) is/are used. In the preferred application, 3-glycidoxy-propyl-trimethoxy-silane (hereafter, it will be called GLYMO) is used. The GLYMO amount inside the solution is between 1 % and 3%. The amount of GYLMO inside the solution is at least one of 1 %, 1 .5%, 2%, 2.5% or 3%. GLYMO is used for making bonds and for providing corrosion resistance and in case GLYMO is used above these percents, the transmittance values of the coating decreases and in case GLYMO is used lower than these percents, the corrosion resistance of the coating weakens.

In order to increase the corrosion resistance of the coating, at least one of or mixtures at specific proportions of dibuthyl-tin-diacetate, mono-buthyl-tin-chloride, titanium-isopropoxide, aluminium-trisec-butoxide is/are used as the organo-metal. In the preferred application, dibuthyl-tin-diacetate (hereafter, it will be called DBTDA) is used as organo-metal. DBTDA also increases the hydrophilic characteristic of the coating. The amount of DBTDA inside the solution is between 2% and 5%. The DBTDA amount inside the solution is at least one of 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%. DBTDA is used for providing corrosion resistance together with GLYMO and in case DBTDA is used above these percents, the transmittance values of the coating decreases and in case DBTDA is used lower than these percents, the corrosion resistance of the coating weakens.

GLYMO and DBTDA are bonded in a crosswise manner and increase the chemical resistance of the coating. Moreover, thanks to the bond made by tin with silicon in the coating composition, the contact angle of the coating decreases to 20° and lower, and thus, hydrophilic characteristic is provided to the coating. By means of this, on the surfaces where the coating is used, the liquid is distributed without accummulating on the surface and it is cleaned from the surface.

At least one organic acid is used for accelerating hydrolysis of alkoxy-silane. As the organic acid, at least one of or mixtures at specific proportions of acetic acid, glacial acedic acid, formic acid, ascorbic acid, sitric acid is/are used. In the preferred application, acetic acid is used. The amount of acetic acid inside the solution is between 3% and 5% by weight. The amount of acetic acid in the solution is at least one of 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%. In case said amount is above this value, the shelf lifetime of the solution decreases and instability occurs during usage. In case said amount is lower than this value, the preparation step of the coating extends.

In practice, the steps of obtaining anti-reflective solution including the above mentioned components and applying thereof to glass are as follows; a) Preparing the solvent mixtures: In order to obtain the main solvent mixture, first of all, propylene glycol methyl ether acetate, ethanol and 2-propanol are stirred. The obtained solvent is separated into two, and TEOS and water are added to one of them as alkoxy-silane and acetic acid is added to the other one as organic acid. The solution including TEOS is mixed with water for 5 minutes on the average for hydrolysis. The amount of water inside the solution is between 1 % and 5%. The amount of water inside the solution is at least one of 1 %, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%. In case the amount of water in the solution is greater than the mentioned upper value, wetting occurs on the coating and in case the amount of water in the solution is lower than the mentioned upper value, the targeted reaction cannot start.

The solution including acetic acid is stirred for 5 minutes for homogeneous distribution and it is combined with the other solution including TEOS and water. The solution obtained after combining the two solutions is stirred for 25-30 minutes for obtaining homogeneity. b) Thermal process step: In order to provide wetting of the solution obtained in step (a) and thus, in order to shorten the production duration, the solution is waited at a predetermined temperature for a predetermined duration. The solution waiting temperature is between 50°C and 70°C. The solution waiting temperature can be 50^SC, 52^SC, 54^SC, 56^SC, 58^SC, 60^SC, 62^SC, 64^SC, 66^SC, 68^SC, 70^SC. In the preferred application, it can be between 56°C and 64°C. Most preferably, it is between 58°C and 62°C. The solution waiting duration is between 200 minutes and 280 minutes. The solution waiting duration can be 200 minutes, 210 minutes, 220 minutes, 230 minutes, 240 minutes, 250 minutes, 260 minutes, 270 minutes and 280 minutes. In the preferred application, it is between 220 minutes and 260 minutes. Most preferably, it is between 230 minutes and 250 minutes. In case the mentioned temperature and durations are worked on, the solution polymerization is accelerated in an uncontrolled manner and instability may occur in the coating solution. c) Adding reactives: The solution is waited until room temperature after step (b), and isopropyl alcohol is added therein in order for the reactions to continue. Optionally, acetic acid mixture can be added together with isopropyl alcohol. Afterwards, GLYMO is added after stirring for 10 minutes and the solution is stirred for 20 minutes for homogeneous distribution. After the stirring process, DBTDA and isopropyl alcohol mixture is added to the solution and stirred for 30 minutes. d) Adding additives: A surfactant, having high molecular weight and having PE-PO-PE chain structure, is added as the porosity agent and stirred into the solution obtained after step (c). The stirring duration is between 20 minutes and 40 minutes. The stirring duration can be preferably 20 minutes, 22 minutes, 24 minutes, 26 minutes, 28 minutes, 30 minutes, 32 minutes, 34 minutes, 36 minutes, 38 minutes and 40 minutes. Stirring more than the mentioned duration leads to oxygen entry from the medium into the coating solution and this leads to wetting of the coating solution more than desired. Thus, it is important that the coating solution is stirred for optimum duration and stored in an insulated manner.

Since the shelf lifetime is long by means of the form thereof obtained after step (b) according to the solution usage time, it can be wailted as half-product and the continuing application steps can be continued when the solution is to be applied to the surface. In order to increase the tolerance of the solution against medium temperature and humidity, the solution has been diluted with isopropyl alcohol.

The obtained anti-reflective solution is coated to the glass surface by using the roll coating method. After the coating application, pre-thermal process has been applied to the coated glasses in the range of 80°C and 120°C for duration of 1 -2 minutes and afterwards, thermal process has been applied in the range of 650°C and 750°C for duration of 2-5 minutes and tempered. The pre-thermal process temperature can be one of 80°C, 90°C, 100°C, 1 10°C or 120°C. The thermal process temperature can be one of 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C and 720°C. Cracks can occur on the coatings over these temperatures and the targeted reaction cannot be completed on the coating under these temperatures.

With reference to Figure 1 , the visible region transmittance value of the subject matter anti- reflective coated glass has been increased from 91 .70% to 94.85%, and according to AM1 .5, the transmittance has been increased from 91 .64% to 94.41 %. Thus, an average transmittance increase of 2.8% is provided.

By means of the subject matter anti-reflective coating solution, coating solution at values which are close to the neutral has been developed without using corrosive acid, and the types and proportions of solvent used in the solution have been optimized according to the roll coating method. The resistance of the coating against corrosion is provided by means of the optimization of the types and proportions the porosity generating chemicals besides the chemicals added to the coating solution. The performances of the coatings against the related tests are given in Table 1 .

Table 1 : Coating performance

The porous structure in the anti-reflective coating is provided by means of porosity agents provided as PE-PO-PE chain structure. The type of the porosity agents and their additional amount determine the final coating structure. The porosity agents are polymers where the polar and apolar structures are provided together.

Studies which include porosity agents with different proportions have been tried. In Figure 2, the SEM (scanned electron microscope) surface morphology of the anti-reflective coatings comprising 5% porosity agent is given, and in Figure 3, the SEM surface morphology of the anti-reflective coatings comprising 15% porosity agent is given. In Figure 4, the STEM (scanned transmittance electron microscope) cross section morphology of the anti-reflective coatings comprising 5% porosity agent is given, and in Figure 5, the TEM cross sectionmorphology of the anti-reflective coatings comprising 15% porosity agent is given. The anti-corrosion resistance of the porous surfaces is low because of their humidity adsorbance behaviour. In the subject matter anti-reflective coating, the wide pores are positioned at the bottom so as to be close to the glass. Thus, in the subject matter anti- reflective coating, resistance against corrosion is also obtained together with anti-reflective characteristic.

Table 2: The thickness and refraction index measurement values of the coatings at controlled temperature and in humid media

Humidity T: Medium Temperature n: Refraction Index VISE: Square of Average Fault

Humidity increase according to the obtained values (Table 2) by means of spectral ellipsometer in controlled temperature and humidity medium and the refraction index increase together are the most important evidences that porous structure is obtained in the coating. By using the data in Table 2 and the data in Table 3 and when calculation is realized according to Kelvin equation, the pore diameter in the structure including 5% porosity agent is 5.1 nm ± 0.3; the total pore volume is 21 %. The pore diameter in the coating including 15% porosity is 13 nm ± 0.3; total pore volume is 31 %.

With reference to Figure 4 and 5, as the amount of the used porosity agent increases, the pores are combined and they form bigger pores. As the pores are combined inside the coating, a stepped pore structure is formed which reduces towards the outer surface along the coating cross section. Bigger pores are formed on the coating base and smaller pores are formed on the coating ceiling. Thanks to this structure, the humidity adsorption of the coating in medium conditions decreases and thus, the resistance against humidity (corrosion) increases.

Table 3: Measurement results for contact angle of the coatings

After sintering, since the contact angle of the coatings with porosity agent and without porosity agent is lower than 20°, this shows that the coating has hydrophilic characteristic. The contact angle of the sintered coating without porosity agent is 14° although there is no porosity agent therein.

In the sintered coating with agent and porosity 5%, although there is porosity agent, its hydrophilic characteristic is almost the same as the coating without porosity agent. Even in the sintered coating with porosity agent 15%, even if a partial porosity occurs on the surface, the contact angle is lower than 20°. This is an indicator showing that even if the porosity agent is used at the value of 15%, the hydrophilic characteristic is preserved as the subject matter coating is obtained at the mentioned ingredients and by means of the mentioned method.

According to AFM results, the surface porosity value of the coating including 15% porosity agent is 1 .9 nm and the surface porosity value of the coating including 5% porosity agent is 0.4 nm. Within the frame of these results, as the porosity agent amount increases, porosity on the coating surface increases. However, even if the surface porosity increases in case of 15% porosity agent usage, the coating has hydrophilic structure since the contact angle is lower than 20°. Thanks to the hydrophilic characteristic, liquid distribution on the coating surface is high. Thus, liquid is not kept on the surface where it is coated, and liquid residue, lime, chemical, dirt, etc. on the surface are prevented.

The protection scope of the present invention is set forth in the annexed claims and cannot be restricted to the illustrative disclosures given above, under the detailed description. It is because a person skilled in the relevant art can obviously produce similar embodiments under the light of the foregoing disclosures, without departing from the main principles of the present invention.

Claims

1. A hydrophilic anti-reflective coating solution which can be tempered and whose corrosion resistance is high and obtained by using sol-gel method so as to be compliant to the roll coating method, said coating solution is characterized by comprising:

- at least one of or mixtures at specific proportions of propylene glycol mono-methyl ether acetate, ethanol, buthanol, n-propanol, 2-propanol for providing dissolving and controlled evaporation,

- predetermined proportion of dibuthyl tin diacetate which provides hydrophilic characteristic and anti-static characteristic to the coating and bonded crosswise by means of its GLYMO structure in addition to GLYMO for increasing corrosion resistance of the coating,

2. The anti-reflective coating solution according to claim 1 , wherein the amount of said dibuthyl tin diacetate amount is between 2% and 5% by weight.

3. The anti-reflective coating solution according to claim 1 , wherein said TEOS amount is between 5% and 10% by weight, GLYMO amount is between 1 % and 3% by weight, the amount of organic acid is between 3% and 5% by weight, the amount of propylene glycol mono-methyl ether acetate is between 3% and 5% by weight, the amount of ethanol is between 7% and 10% by weight, the amount of 2-propanole is between 60% and 70% by weight and the amount of porosity agent is between 10% and 30% by weight.

4. The production method of the anti-reflective coating solution according to claim 1 , characterized by comprising the following steps respectively:

(i) adding a mixture comprising predetermined proportions of propylene glycol methyl ether acetate, ethanol, 2-propanol, water and TEOS to another mixture comprising predetermined proportions of propylene glycol methyl ether acetate, ethanole, 2-propanol and acetic acid,

5. An anti-reflective coated glass where said anti-reflective coating solution, given in claim 4, is applied, characterized in that the anti-reflective coating has hydrophilic structure and its contact angle is 20° and lower.

6. The anti-reflective coated glass according to claim 5, wherein in order to increase resistance of the coating against humidity, the pores, provided in the body of the coating, have gradually reducing geometry from the glass towards the surface.

7. A method of application of said anti-reflective coating solution to glass given in claim

1 , characterized in that the solution is applied onto the glass surface by means of the roll method and afterwards, pre-thermal process is applied for 1 -2 minutes between 80°C and 120°C and thermal process is applied for 2-5 minutes between 650°C and 750°C respectively.