TECHNICAL FIELD

The present invention relates to a transparent coating composition which provides protection against ultraviolet rays and which has high mechanical strength surfaces to which this coating composition is applied, and the preparation and application method of said composition.

PRIOR ART As the transparent glass is light-transparent in the UV-A region, the energy of the light in this region leads to the decomposition of many organic compounds. Thus, transparent glass delimits the usage areas of transparent package products which include foodstuff.

The coating solutions are easily prepared by means of dissolving the UV protective organic compounds in polymer resins like acrylic, alkyd. However, since the polymers used have poor resistance to UV rays, alternatively mixtures of functional silane derivatives whose UV resistance is better when compared with organic polymers are used. Since, the amount of UV protective organic compounds in the coating has been found to decrease over time, the organic coating loses its UV protection function in time.

Since the compositions of food and beverages consist of various organic substances, they are easily affected by UV light. As a result of being subject to UV light, changes occur in their chemical structures and they lose their nutritive values and original tastes. The oxygen in the medium changes the structure of the food and beverages and it increases the undesired effect of the UV light. Therefore, in order for the foodstuff and drinks to preserve their freshness, they shall be kept in packages which do not transmit UV light and oxygen. In order for the foodstuff and drinks to preserve their freshness for a long time, Tetrapak package and aluminum boxes are used. Although Tetrapak packages provide UV protection and although their oxygen transmittance is low, the aluminum layer is coated with a plastic film in order to prevent foodstuff contamination and taste change which results from contact with used aluminum. At the same time, this plastic film prevents corrosion of aluminum. It is known that the plasticizers and Bisfenol A existing in plastic film have unfavorable effects on human health. This leads to contamination of the foodstuff and beverage, put into aluminum boxes, in time and may change the taste of the foodstuff or beverage. Since said boxes are easily subject to corrosion, the usage areas of these boxes are limited. Glass is a fairly healthy packaging material because it does not interact with the food or beverage it contains and does not allow gas input from the outside since its oxygen permeability is low. However, since transparent glass transmits UV rays, the usage of glass for food and beverages as a package is limited. In order to reduce UV transmittance of glass, color is provided to glass from batch material and thermal process is applied at high temperature. Thus, since special raw materials are used for providing UV protection to the glass from the batch, this method is an expensive method, and moreover, transparency of the glass is compromised and the glass has to be colored as green, bronze, etc.

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 a transparent coating composition which provides protection against ultraviolet rays and of which the mechanical resistance is high, and the surfaces where said coating composition is applied, for eliminating the above mentioned disadvantages and for bringing new advantages to the related technical field.

The main object of the present invention is to provide a UV coated glass package where protection against ultraviolet rays is provided.

Another object of the present invention is to provide a UV coated glass package which transmits daylight. Another object of the present invention is to provide a UV coated glass package of which the mechanical resistance is high.

Another object of the present invention is to provide a UV coated glass package of which the chemical resistance is high.

Another object of the present invention is to provide a UV coating composition which completely adsorbs onto the glass surface. Another object of the present invention is to provide a UV coating composition obtained by means of sol-gel method.

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 UV protective coating composition which is in colloidal form and developed by means of sol-gel method in order to be applied onto a glass package. Accordingly, said invention is characterized by comprising at least one type of anorganic nano-particle therein, at least one type of silan embodiment wherein said anorganic nano-particles are doped, at least one type of solvent and at least one type of surface active substance which provides homogeneous distribution on the surface where the composition is applied.

In a preferred embodiment of the invention, the anorganic nano-particle is at least one of Ti0 ₂ , ZnO and Ce0 ₂ .

In a preferred embodiment of the invention, the subject matter composition is a composition applied by means of spraying method onto the glass surface.

In a preferred embodiment of the invention, as the anorganic nano-particle source, it comprises at least one of titanium (IV) etoxide, titanium (IV) isopropoxide, titanium (IV) butoxide, titanium (IV) chloride, titanium based alkoxides or salts, zinc sulphate, zinc acetate, zinc chloride, zinc based slats, cerium oxide aqueous dispersion.

In a preferred embodiment of the invention, as the Ti0 ₂ nano-particle source, the subject matter composition comprises titanium (IV) isopropoxide.

In a preferred embodiment of the invention, as the ZnO nano-particle source, the subject matter composition comprises zinc chloride. In a preferred embodiment of the invention, as the silan embodiment where the anorganic nano-particles are to be doped, it comprises at least one of 3-glycidoxypropyltrietoxysilane, 3-glycidoxypropyltrimetoxysilane, 3-metacryloxypropylmetoxysilane, 3- metacryloxypropyltrietoxysilane, epoxy and/or acrylate functional cross binding silane. In a preferred embodiment of the invention, as the silan embodiment whereto the anorganic nano-particles are doped, the subject matter composition comprises 3- glycidoxypropyltriethoxysilan. In a preferred embodiment of the invention, as the solvent, the subject matter composition comprises at least one of 1 -methoxy-2-propanol and butyl glycol. In a preferred embodiment of the invention, as the surface active substance, the subject matter composition comprises poly-ether modified polydimethylsilan.

In a preferred embodiment of the invention, the amount of surface active substance in the total UV protective coating composition is between 0.20 and 0.80% by weight.

In a preferred embodiment of the invention, the particle dimension of the Ti0 ₂ nano-particle provided in the subject matter composition is between 2 and 20 nm.

In a preferred embodiment of the invention, the particle dimension of the Ce0 ₂ nano-particle provided in the subject matter composition is between 2 and 20 nm.

In a preferred embodiment of the invention, the particle dimension of the ZnO nano-particle provided in the subject matter composition is between 15 and 50 nm. In a preferred embodiment of the invention, the amount of the anorganic nano-particle amount doped into the silan embodiment is 5-35% of the total weight.

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 coated glass package to whose surface a UV protective coating composition, given in Claim 1 and which is in colloidal structure, is applied. Accordingly, said Tuv value is at most 30%.

In another preferred embodiment of the invention, Tv value is at least 85%. In another preferred embodiment of the invention, Te value is at least 81 %.

In a preferred embodiment of the invention, the coating thickness is between 1 .0 and 1 .5 micrometers. In a preferred embodiment of the invention, the pencil hardness value of the coating is between 6H and 9H. In a preferred embodiment of the invention, the adhesion of the coating to the glass surface is 5B.

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 UV protective coating composition production method which is in colloidal structure given above. Accordingly, said method is characterized by comprising the steps of:

(a) Synthesizing/preparing at least one type of anorganic nano-particle selected from Ti0 ₂ or ZnO or Ce0 ₂ ,

(b) Adding the synthesized anorganic nano-particles into the silane binding system comprising Si0 ₂ nano-particles,

(c) Diluting UV protective coating composition by means of solvents,

(d) Adding surface active substance to the UV protective coating composition. In a preferred embodiment of the invention, in step (a), as the nano-particle source, at least one of titanium (IV) etoxide, titanium (IV) isopropoxide, titanium (IV) butoxide, titanium (IV) chloride, titanium based alkoxides or salts, zinc sulphate, zinc acetate, zinc chloride, zinc based salts, cerium oxide aqueous dispersion is used. In a preferred embodiment of the invention, in step (b), as the silan embodiment where the anorganic nano-particles are to be doped, it comprises at least one of 3- glycidoxypropyltrietoxysilane, 3-glycidoxypropyltrimetoxysilane, 3-metacryloxypropylmetoxy- silane, 3-metacryloxypropyltrietoxysilane, epoxy and/or acrylate functional cross binding silane.

In a preferred embodiment of the invention, in step (c), as the solvent, it comprises at least one of 1 -metoxy-2-propanol and butyl glycol.

In a preferred embodiment of the invention, in step (d), as the surface active substance, polyether modified poly-dimethyl-silan based materials are used.

In a preferred embodiment of the invention, in step (a), at least one of Ti0 ₂ or ZnO or Ce0 ₂ is mixed and diluted with at least one type of alcohol and completely dissolved. In a preferred embodiment of the invention, in step (a), the diluted anorganic nano-particle is waited in a back-cooler in at least 60 ^S C and for at least 1 hour. In a preferred embodiment of the invention, in step (a), acid and water is added into the solution after diluting for obtaining Ti0 ₂ nano-particle.

In a preferred embodiment of the invention, the proportion of mole acid/mole titanium used is between 0.30 - 0.70%.

In a preferred embodiment of the invention, in step (a), for obtaining ZnO nano-particle, aqueous sodium hydroxide solution is added into the solution after dilution. In a preferred embodiment of the invention, the silan binding system, comprising Si0 ₂ nano- particles used in step (b), has 43-48% solid ingredient.

In a preferred embodiment of the invention, in step (b), the doping amount of at least one of Ti0 ₂ or Ce0 ₂ or ZnO nano-particles into the silane binding system solution comprising Si0 ₂ nano-particles is between 5 and 35% by weight.

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 application method of the coating composition, obtained by means of the abovementioned method, onto a glass package. Accordingly, spraying is realized such that the gun vertical speed is 50 mm/second onto the glass package surface and such that the glass package rotation speed is 90 rev/minutes.

BRIEF DESCRIPTION OF THE FIGURES

In Figure 1 , the UV-Vis spectrums of the coatings comprising 5-35% Ti0 ₂ by weight are given.

In Figure 2, the UV-Vis spectrums of the coatings comprising 5-35% Ce0 ₂ by weight are given.

In Figure 3, the UV-Vis spectrums of the coatings comprising 5-20% ZnO by weight are given.

DETAILED DESCRIPTION OF THE INVENTION In this detailed description, the subject matter transparent coating composition, which provides protection against ultraviolet rays and of which the mechanical resistance is high, and, the UV coated glass package are explained with references to examples without forming any restrictive effect only in order to make the subject more understandable.

UV protective coating solution, which is to be applied onto the glass package, is obtained by means of sol-gel method, and said UV protective coating solution comprises anorganic nano- particles. By means of the UV protective coating solution comprising the obtained anorganic nano-particle, glass, ceramic, etc. structures can be coated by using methods like immersion, spraying, sputtering, etc. In the preferred application, spraying method is used.

The subject matter UV protective coating solution comprises at least one type of anorganic nano-particle, at least one type of silan embodiment which is the sol medium where said anorganic nano-particles are to be doped and at least one type of solvent. Preferably, at least one type of surface active substance can be added into the coating solution in order to provide dispersion in a homogeneous manner on the surface where preferably the UV protective coating solution is applied. As the surface active substance, preferably polyether modified poly-dimethyl-silan is used. As the solvent, at least one of 1 -methoxy-2-propanol (PM) and butyl-glycol or a mixture of these with the pre-calculated proportion is used.

In the UV protective coating solution, at least one of Ti0 ₂ , ZnO and Ce0 ₂ nano-particles is used as the anorganic substance. In case Ti0 ₂ nano-particles are used as anorganic substance, at least one of titanium-based alcoxides or salts like titanium (IV) etoxide, titanium (IV) isopropoxide, titanium (IV) butoxide, titanium (IV) chloride is used or the mixture of some of them at a pre-calculated proportion for synthesis of the Ti0 ₂ nano-particles is used. In the preferred application, preferably titanium (IV) isopropoxide is used.

In case ZnO nano-particles are used as the anorganic substance, at least one of zinc salts like zinc sulphate, zinc acetate, zinc chloride is used for the synthesis of the ZnO nano- particles or the mixture of some of them at a pre-calculated proportion is used. In the preferred application, zinc chloride is used.

In case Ce0 ₂ nano-particles are used as the anorganic substance, at least one of Ce0 ₂ dispersions is used for the synthesis of Ce0 ₂ nano-particles.

As the silan embodiment where anorganic nano-particles are to be doped, at least one of epoxy or acrylate functional cross binding silane like 3-glycidoxy-propyl-tri-etoxy-silane (GLYEO), 3-glycidoxypropyltrimetoxysilane (GLYMO), 3-metacryloxypropyltrimetoxysilane (MPTS), 3-metacryloxypropyltrietoxysilane (MPTES) is used or the mixture of some of them at a pre-calculated proportion is used. In the preferred application, 3- glycidoxypropyltrietoxysilane (GLYEO), which is an epoxy functional silan, is used. Si0 ₂ nano-particle mixtures are used for increasing mechanical resistance of the system.

In order to prepare UV protective coating solution, first of all, the nano-particle selected from Ti0 ₂ or ZnO or Ce0 ₂ is synthesized/prepared, and afterwards, the particles are added to the silan binding system comprising Si0 ₂ nano-particles and they are diluted by means of solvents in a compliant manner to the coating method.

First of all, preferably titanium (IV) isopropoxide, used for the synthesis of Ti0 ₂ nano- particles, is diluted in an alcohol medium like dehydrated ethyl alcohol. After the dilution process, the titanium (IV) isopropoxide, existing in ethyl alcohol, is stirred in a strong manner in the magnetic stirrer, and meanwhile, acid catalyst and water needed for hydrolysis are respectively added thereon, and the water is preferably added drop by drop. As the acid catalyst, at least one of an acid with anorganic properties like HN0 ₃ , HCI is used. The prepared solution is fixed back to the cooler mechanism and it is held for 12-20 hours in the temperature range of 75 and 1 10 ^S C, and particle formation is provided. In the preferred application, the prepared solution is subjected to the back cooler mechanism in the temperature range of 80 and 105 ^S C. More preferably, the prepared solution is subjected to back cooler mechanism in the temperature range of 85 and 95 ^S C.

The mole proportion of the used anorganic acids like nitric and/or hydrochloric acid to the used titanium compound; the proportion of the mole acid/mole titanium compound is between 0.30 and 0.70. In the preferred application, the proportion of mole acid/mole titanium compound is between 0.35 and 0.65. More preferably, the proportion of mole acid/mole titanium compound is between 0.40 and 0.60. The mole proportion of the used water to the used titanium compound; the mole water/mole titanium compound proportion is between 0.50 and 3.00. In the preferred application, mole water/mole titanium compound proportion is between 1 .00 and 2.80. More preferably, mole water/mole titanium compound proportion is between 1 .50 and 2.50. The mole alcohol/mole titanium compound proportion is between 0.60 and 2.80. In the preferred application, mole alcohol/mole titanium compound proportion is between 1 .20 and 2.50. More preferably, mole alcohol/mole titanium compound proportion is between 1 .80 and 2.20. At least one of mineral acids like hydrochloric acid, nitric acid or mixtures with pre-calculated proportion can be used as the abovementioned acid catalyst. Preferably, hydrochloric acid is used as the acid catalyst.

For the synthesis of ZnO nano-particles, preferably zinc chloride is diluted in ethylene glycol medium. The diluted zinc chloride solution is fixed to the back cooler mechanism, and zinc chloride is completely dissolved in the temperature range of 30 and 70 ^S C. Aqueous sodium hydroxide solution is prepared in a separate vessel and it is added drop by drop onto the zinc solution completely dissolved which is stirred in the magnetic stirrer and it is mechanically stirred. The pH of the solution is adjusted to the range of 7.8 and 13.0 by adding sodium hydroxide. In the preferred application, the pH of the solution is adjusted to the range of 8.2 and 12.0. More preferably, the pH of the solution is adjusted to the range of 8.5 and 1 1 .0. The prepared solution is fixed again to the back cooler mechanism and it is kept for time range of 1 and 4 hours in the temperature range of 60 and 100 ^S C, and formation of the ZnO nano-particles is provided. In the preferred application, the prepared solution is subjected to back cooling mechanism in the temperature range between 75 and 85 ^S C.

20% Ce0 ₂ dispersions are used which comprise 2.5% acetic acid for the synthesis of Ce0 ₂ nano-particles. The used Ce0 ₂ dispersions are obtained from the company Sigma-Aldrich. In the synthesis process of the nano-particles, the changes, which occur in the particle dimension depending on the hydrolysis and condensation duration and depending on the used acid/base catalyst amount, are monitored by means of the particle dimension analyzer. The particle dimensions of the particles to be used in coating systems are between 2 nm and 20 nm for Ti0 ₂ and Ce0 ₂ . In the preferred application, the particle dimensions for Ti0 ₂ and Ce0 ₂ are between 5 nm and 15 nm. More preferably, the particle dimensions for Ti0 ₂ and Ce0 ₂ are between 8 nm and 12 nm. The particle dimension for ZnO is between 15 and 50 nm. In the preferred application, the particle dimension for ZnO is preferably between 22 and 40 nm. More preferably, the particle dimension for ZnO is between 28 and 35 nm. Preferably 3-glycidoxypropyltrietoxysilane (hereafter, it will be called GLYEO), which is preferably an epoxy functional silan, is used for preparing the binding system where the nano-particles are to be doped. GLYEO is mixed with aqueous dispersion of acidic Si0 ₂ nano-particle for increasing the mechanical characteristic of the coating. As the acidic Si0 ₂ nano-particle aqueous dispersion, Levasil 200S/30 coded product of the Obermeier Company is used which has 200 m ² /g of surface area on the average with proportion of 30% by weight in acidic aqueous medium and which is in 15 nm particle dimension on the average. In order to prepare the mixture of this, suitable amount of Levasil 200S/30 product is added on GLYEO weighed in a glass vessel, and the mixture is mixed in a strong manner in a mechanical stirrer for at least 6 hours. The mixture is adjusted such that 70% of the mixture is GLYEO and 30% of the mixture is Levasil. More preferably, the mixture is adjusted such that it comprises 50% of GLYEO and 50% of Levasil.

In the prepared GLYEO/Levasil binding system, the proportion of the section, described as solid section and which is not evaporative and which may form film on the surface after thermal processes, is between 43 and 48%. At least one of Ti0 ₂ or Ce0 ₂ or ZnO nano- particles in the range of 5 and 35% by weight is doped into the binding system solution having solid ingredient between 43 and 48%. In the preferred application, at least one of Ti0 ₂ or Ce0 ₂ or ZnO nano-particles in the range of 10 and 30% by weight is doped into the binding system solution. More preferably, at least one of Ti0 ₂ or Ce0 ₂ or ZnO nano-particles in the range of 15 and 25% by weight is doped into the binding system solution. The obtained UV protective transparent coating solution whose mechanical resistance is high is diluted by means of solvents having different boiling points in a compliant manner to the coating method by means of spraying. As solvent, 1 -metoxy-2-propanol (PM) and butyl glycol (BG) solvents whose boiling points are respectively 120°C and 171 °C are used. The solvents are added such that the total solid amount of the silan binding system, where at least one of Ti0 ₂ or Ce0 ₂ or ZnO nano-particles is doped, is obtained as 15%.

After the diluting process, in order to provide more homogeneous dispersion of UV protective coating composition on the surface where it is applied during coating with spraying, poly- ether modified polydimethylsilane surface active agent BYK 306 is added such that its amount in the total composition is between 0.20 and 0.80% by weight, and thus, the UV protective coating composition becomes ready for being applied onto the surface. In the preferred application, polyether modified polydimethylsilane surface active agent BYK 306 is added such that its weight in the total solution is between 0.30 and 0.70%. In the more preferred application, polyether modified polydimethylsilane surface active agent BYK 306 is added such that its weight in the total solution is between 0.40 and 0.60%. The UV protective composition, which is the final product, is in homogeneous colloidal structure.

The obtained UV protective coating composition is applied onto the glass package by means of spraying method. Optimum UV protective coating thickness and optimum performance are obtained by means of 50 mm/second gun vertical speed of spraying onto the glass surface of the UV protective coating composition and by means of single direction spraying settings. During spraying of UV protective coating composition onto the glass package, the glass package rotates with speed 90 rev/minute. The thickness of the UV coatings on the glass package is between 1 .0 and 1 .5 micrometers.

As a result of the applications of UV protective coating composition, comprising cerium oxide, onto the glass package, the glass transmittance values are given in Table 1 and Table 2. The results of application of UV protective coating composition comprising cerium oxide onto a glass bottle is given in Table 1 and application of UV protective coating composition comprising cerium oxide onto a glass bell is given in Table 2. According to the obtained results, transparent and homogeneous coatings have been obtained on the glass package surfaces.

Table 1 : Optical measurements for uncoated glass bottle and UV protective coated glass bottle comprising cerium oxide with proportion of 20%

Table 2: Optical measurements for uncoated glass jar and UV protective coated glass jar comprising cerium oxide with proportion of 20%

In order to measure mechanical resistance values of the coatings, the hardness measurements of glass packages where UV protective coating solution, comprising 5 and 35% particle amount, is applied have been realized according to ASTM D 3363 test standard. The results are given in Table 3. The increase in the amount of nano-particles according to the values obtained as a result of hardness measurements shows a small decrease in the hardness value in coatings comprising Ti0 ₂ and ZnO. Besides, in the UV protective coating comprising Ce0 ₂ , the increase in the nano-particle amount does not have an effect on the hardness. In accordance with the obtained measurement results, it cannot be said that the increase in the amount of nano-particle has strong unfavorable effect on hardness for UV protective coatings comprising Ce0 ₂ and for UV protective coatings comprising Ti0 ₂ and ZnO. At the same time, in accordance with the obtained measurement results, the hardness value of the UV protective coating comprising Ce0 ₂ or Ti0 ₂ or ZnO is high. Particularly, when the nano-particle amount is between 5 and 15%, UV protective coating is at the highest hardness value for all of the three components.

Table 3. Pencil hardness test results of the UV protective coatings comprising Ti0 ₂ , Ce0 ₂ and ZnO

In order to measure the values of adsorption onto the surface where the coatings are applied, the adsorption measurements of the glass packages have been realized, where UV protective coating solution comprising particle amount in the range between 5 and 35% is applied. The results are given in Table 4. In accordance with the values obtained as a result of surface adsorption test measurements realized in accordance with ASTM D 3359 test standard, the increase in the nano-particle amount does not affect adsorption of the UV protective coating solution onto the glass.

Table 4. Adsorption test results of the UV protective coatings comprising Ti0 ₂ , Ce0 ₂ and

ZnO

Adsorption Test (ASTM D 3359)

Amount of

Coatings Coatings Coatings nano-particle

comprising Ti0 ₂ comprising Ce0 ₂ comprising ZnO by weight %

5% 5 B 5 B 5 B 10% 5 B 5 B 5 B

15% 5 B 5 B 5 B

20% 5 B 5 B 5 B

25% 5 B 5 B -

30% 5 B 5 B -

35% 5 B 5 B -

In order to measure the values of chemical resistance to the surface where the coatings are applied, the glass packages where UV protective coating solution, comprising particle amount in the range of 5 and 35%, is applied have been subjected to base resistance test. The base resistance test has been realized by using 0.5% Sodium Hydroxide solution by weight by means of waiting for five each minutes in stove at 65°C. The results are given in Table 5. In accordance with the values obtained as a result of chemical resistance measurements, the increase in the nano-particle amount decreases the chemical resistance of the UV protective coating solution.

Table 5. Base resistance test results of the UV protective coatings comprising Ti0 ₂ , Ce0 ₂ and ZnO

The UV protection performances of the glass packages coated by means of coating composition have been realized by using bacteria. In the test, the UV protection is directly proportional with the surviving bacteria proportion. In other words, as UV protection increases, the survival percent of the bacteria also increases.

In order to measure the UV protection performance of the surface where coatings are applied, in glass packages where UV protective coating solution, comprising particle amount in the range of 5 and 10% at 3 and 6 times, is applied, the survival proportions of bacteria have been determined. The results are given in Table 6. In accordance with the values obtained as a result of anti-bacterial measurements, the increase in the application coefficient of the UV protective coating solution increases the survival percent values of micro-organisms. At the same time, by means of the increase of the % amount of the nano- particles, the survival percent values of the micro-organisms increase. According to the test results, it is shown that an effective UV protection is obtained by means of the subject matter coating.

Table 6. The survival percents of the micro-organisms thanks to the coatings comprising

Ti0 ₂ , Ce0 ₂ and ZnO

Survival

Spraying

Irradiation Bacteria percents of

Sample coating

with UV colony microcoefficient

organisms

Control - - 320 100%

Uncoated

+ - 167 52%

glass

Control

Coating not

Group

comprising

+ 6 181 57%

nano- particles

5% Ce0 ₂ + 3 215 67%

5% Ce0 ₂ + 6 219 68%

Samples

7.5% Ce0 ₂ + 3 201 63% doped

7.5% Ce0 ₂ + 6 267 83% with Ce0 ₂

10% CeO ₂ + 3 210 66%

10% CeO ₂ + 6 313 98%

5% Ti0 ₂ + 3 130 16%

5% Ti0 ₂ + 6 128 17%

Samples

7.5% Ti0 ₂ + 3 150 39% doped

7.5% Ti0 ₂ + 6 170 49% with Ti0 ₂

10% TiO ₂ + 3 224 72%

10% TiO ₂ + 6 240 77%

Samples 5% ZnO + 3 220 11 % doped 5% ZnO + 6 1 10 — with ZnO 7.5% ZnO + 3 147 27%

7.5% ZnO + 6 251 28%

10% ZnO + 3 180 43%

10% ZnO + 6 200 55%

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.