BOROSILICATE GLASS WITH SNOW VISUAL EFFECT AND THE PRODUCTION

METHOD THEREOF

TECHNICAL FIELD

The present invention relates to opalescent glasses; particularly relates to opalescent borosilicate glasses with snow visual effect and which have lower thermal expansion coefficient in order to be used as glass household good.

PRIOR ART

For glass household goods, in applications requiring thermal resistance during usage like cooking, borosilicate glasses including boron are indispensable goods.

In the present art, in cases where opal and/or colored borosilicate glass is/are desired to be produced, colorants are added to the glass through batch. The added colorants are mixed homogeneously in the batch, and in the glass household good obtained, the obtained color and/or opacity is/are homogeneous. In the present art, even if colored/opal borosilicate glass can be obtained, pattern and/or effect cannot be applied to the body of the glass without coating thereon.

High proportion (equal to or greater than 10%) of colorant/nucleating material is added to most of the opal glasses in furnaces requiring special production method, and a homogeneous structure is obtained. In the present art, for nucleation in order to provide opacity, Ti0 ₂ is added to the batch. Ti0 ₂ addition increases melting temperature. Thus, cost increases and production becomes difficult. The coloring of glass household goods, which include soda-lime, can be applied from batch or through the forehearth. In case coloring is applied through the furnace, the same color of glass is taken from all shaping machines. This leads to limitations in production.

The patent US7737062B2 provides an opalescent forehearth color concentrate comprising a non-smelted agglomerated interspersion of particles for use in coloring glass, said concentrate comprising by weight from about 10% to about 70% of a glass component and from about 30% to about 90% of one or more opalescent pigments, the glass component comprising by weight from about 10% to about 50% ZnO and about 15 to about 60% Si0 ₂ . The invention also provides a method of using the color concentrate.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to opal glasses, particularly, borosilicate glasses, for bringing new advantages to the related technical field.

The main object of the present invention is to provide an opalescent borosilicate glass.

Another object of the present invention is to provide a borosilicate glass with snow visual effect.

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 borosilicate glass household good whose thermal shock resistance is high. Accordingly, said borosilicate glass is characterized by comprising non-melted and crystallized particles forming a snow-like visual effect having point and lineal appearance in borosilicate glass body. In a preferred embodiment of the present invention, it has an opalescent appearance.

In another preferred embodiment of the present invention, it has a heterogeneous structure.

In another preferred embodiment of the present invention, the point and lineal structures forming the heterogeneous structure are distributed in a homogeneous manner in the glass body.

In a preferred embodiment of the present invention, the point and lineal structures provided in the glass body have a proportion of 99% - 77% in the whole glass.

In a preferred embodiment of the present invention, thermal expansion coefficient a is smaller than or equal to 45 x 10 ^"7 /°K.

In a preferred embodiment of the present invention, light transmittance is prevented partially. In a preferred embodiment of the present invention, light transmittance is at most 10%. In a preferred embodiment of the present invention, light transmittance is at most 8.8%.

In a preferred embodiment of the present invention, the main glass comprises 76-81 % Si0 ₂ by weight, 4-6% Na ₂ 0 and/or K ₂ 0 by weight; 12-15% B ₂ 0 ₃ by weight and 2-4% Al ₂ 0 ₃ by weight.

In a preferred embodiment of the present invention, it comprises colorant/nucleating components providing an opalescent appearance and whose proportions by weight are given below:

In a preferred embodiment of the present invention, nucleating is at a proportion of 1 -5% 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 a production method for a borosilicate glass household good whose thermal shock resistance is high. Accordingly, the subject matter method is characterized by comprising the steps of: a) Feeding the glass components to the furnace and melting

b) Feeding colorants/nucleating in the open type forehearth section in the glass flow direction into the borosilicate glass coming from the furnace in molten form and stirring thereof

c) Cooling the borosilicate glass in a controlled manner in the muffle type forehearth section provided at the continuation of the open type forehearth

d) Shaping and heat treatment of borosilicate glass. In another preferred embodiment of the present invention, in step (b), the time duration for the colorants/nucleating to reach the first stirrers from the feeding point is between 10 and 50 minutes.

In another preferred embodiment of the present invention, in step (b), the feeding proportion of the colorant/nucleating to the glass is between 1 -5%.

In another preferred embodiment of the present invention, in step (b), the feeding proportion of the colorant/nucleating to the glass is 3%.

In another preferred embodiment of the present invention, in step (b), the temperature of the region where the colorant/nucleating is fed to the glass is greater than 1290°C. BRIEF DESCRIPTION OF THE FIGURES

In Figure 1 , the view of the dense crystal structured product is given. In Figure 2, the view of the sparse crystal structured product is given.

DETAILED DESCRIPTION OF THE INVENTION

In this detailed description, the subject matter opalescent borosilicate glass with snow visual effect and the production method thereof are explained with references to examples without forming any restrictive effect only in order to make the subject more understandable.

Borosilicate glasses are colored by means of from batch in the present art. In our subject matter study, the coloring process is realized through forehearth for obtaining flexibility in production.

Coloring process through forehearth is realized for the produced glasses in passages/channels which are named forehearth and which are placed between the conditioning section and shaping machine after the working end. It is very difficult to shape glass which is in substantially fluidized form at high temperatures. Therefore, fluidized glass is homogeneously cooled down to temperatures which are suitable for the production processes for shaping. Conditioning is cooling the glass to a temperature which is suitable for shaping the glass in a successful and efficient manner. The coloring method of borosilicate glass through forehearth is realized by bringing two separate technologies together. One of them is the closed and electrically heated muffle type forehearth and the other one is the open type forehearth application. In the present invention, open type forehearth is used in the section from the working end to the end of the stirrers, and muffle type forehearth is used from the end of the stirrers to the forehearth end. Evaporation is reduced by means of muffle type forehearth and thus, the scum is eliminated.

In this study, in Table 1 , borosilicate glass, whose component proportions are given, is used. The components forming the borosilicate glass are fed to the furnace. In order for the melting and affining to be realized in the desired manner, raw materials are heated up to high temperatures and they are brought into molten form. In the glass batch given in Table 1 , Ti0 ₂ is not used and thereby, melting temperature is reduced.

Table 1

During production, in the method of coloring the borosilicate glass through forehearth, first of all, colorant/nucleating is added to the clear glass glass, which comes in fluid form from the furnace, in the first section of the forehearth which is in open type. These colorants/nucleating react in the main glass composition, and partially melted. Finally, they are mixed with the main glass in a homogeneous manner with the help of stirrers. Thus, the glass is colored in the desired color.

In the muffle type forehearth region provided at the continuation of the open type forehearth region, the colored borosilicate glass is brought in a controlled manner to the required temperature for shaping. Moreover, here, the homogenization of the glass mixture is provided before it enters into the shaping process.

Since the boron oxide evaporates from the molten borosilicate glass surface, a silica-rich layer, having lower density than the molten glass, is formed on the glass surface. Since the second section of the forehearth is made as muffle type forehearths, in the final step of production, the formation of this silica-rich layer, which is observed as an optic fault on glass, is prevented. In the preferred application, opalescent glass which is colored in white tones is produced. In order to obtain the opalescent appearance, frit, whose component proportions are given in Table 2 and whose melting temperature is low when compared with the borosilicate glass and whose colorant/nucleating proportion is high, is added to the molten glass coming from the furnace in the open type forehearth region. Afterwards, the glass, which is in fluid structure, is mixed with the help of stirrers in order to obtain a structure with homogeneous appearance.

Table 2

In order to provide a snow-like visual effect, which is in point and lineal structure, to the borosilicate glass which is the final product in production, crystallization is provided in the glass body and/or melting of some particles is prevented. In order to provide crystallization and/or in order to prevent melting of some particles, a specific temperature value is not exceeded during production. By means of this, in the preferred application, the colorants/ nucleating, the Ca-P including particles, provided in the frit, are provided in crystallized form without melting in the glass melt. Rapid crystallization is provided in the places where energy is high, for instance in the regions having boron and the sections having faults, glass surface, kernel, Ca in P in the borosilicate glass. In other words, the non-melted particles and crystallization support each other. Moreover, the fluor (F), provided in the frit, also accelerates crystallization. In said application, the increase of the temperature over a specific limit, preferably increase of the temperature over 1500°C reduces crystallization. The crystallization begins from the fore hearth, and it continues during cooling.

In order to provide opalescent characteristic to the glass, the feeding proportion of the colorant/nucleating, added from the fore hearth to the main glass, in the preferred application, the feeding proportion of the frit to the main glass is between 1 -5%. In a more preferred application, the feeding proportion of the frit to the main glass is 3%. The increase of the feeding proportion provides reduction of the transparent characteristic. The time duration for the colorant/nucleating to reach the first stirrers from feeding point shall be between 10<x<50 minutes. The temperature in the feeding point shall be greater than 1290°C. The products are passed through annealing or tempering furnace after shaping.

The color and optic performance values of the opalescent borosilicate glass with white colored snow visual effect and with thickness of 3 mm are given in Table 3.

Table 3: The color and optical performance values of the white glass with snow visual effect

(standard thickness 3 mm)

In the alternative embodiments, colorant material is added from the forehearth or the furnace, and various colored borosilicate glass can be produced in the snow visual effect. In case colorant is added to said production, the color and optical values of the glass, obtained in accordance with the colorant and the proportion thereof, also change. In the opalescent borosilicate glass with snow visual effect, the local light transmittance is provided by means of preventing via the snow visual effect. In the preferred application, the light transmittance % is lower than 10. More preferably, the light transmittance % is equal to 8.8. In the white colored opalescent borosilicate glass with snow visual effect taken as example, the proportion of the sections, with snow visual effect in crystal structure, in the main glass is within about 99% - 77%. The optic microscope images of the measured samples are given in Figure 1 and 2. In Figure 1 , the density of the crystal structure has been measured as 99.7%. In Figure 2, the density of the crystal structure has been measured as 77.8%.

The thermal expansion coefficient of the opalescent borosilicate glass with snow visual effect after production is preferably as follows: a = < 45 x 10 ⁷ /°K

More preferably, the measured thermal expansion coefficient of the borosilicate glasses after production is equal to 39 x 10 ^"7 /°K. The microwave tests have been realized in accordance with EN 15284 standard, and the opalescent borosilicate glasses with snow visual effect are kept for 2 minutes at 56°C for a short term at 600 Watt, and it is kept for 13 minutes at 80°C for a long term. After the test, crack formation and breaks have not been observed in the opalescent borosilicate glasses with snow visual effect.

The particles, which are crystallized and/or which are non-melted, prevent passage of light. In the final product, there is a heterogeneous structure. In the opalescent borosilicate glasses with snow visual effect, the product surface is not glassy as different from the opal glass. The distribution of snow visual effect in the opalescent borosilicate glass structure is homogeneous.

The advantages of opalescent borosilicate glasses with snow visual effect when compared with the other opal glasses can be given as follows:

- It does not comprise heavy metals like Cd and Pb

- Cost advantage is obtained by not using Bi element

- There is no cord fault resulting from refractory dissolving in the glass since the Bi element is effective on the refractory corrosion

- V ₂ 0 ₅ is not used

- It does not lead to harmful or pollutant vapor, emission and dust

In case coloring is provided to the glass from the forehearth, colored glass can be produced only by means of the machine connected to that channel/forehearth. Thus, flexibility is provided to production when compared with coloring of the glass from the furnace.

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.