TILE TO BE FELT WARM WHEN TOUCHED AND ITS METHOD OF PRODUCTION Subject of the Invention

The present invention relates to the tiles having lower thermal conductivity and proper water absorption value and to the method of production thereof.

Present State of the Art

The thermal conductivity value of a ceramic tile which has been produced depending on the conventional methods is quite high to the extent that it will cause the tile to be felt cold when somebody touches it.

The amount of the heat that the human-beings lost when they touch any object having less temperature than himself (Qi _os t) is in direct proportion to the thermal conductivity coefficient (k) of the touched object and temperature difference (ΔΤ: the difference between the body temperature and the object temperature). The equation showing the heat loss has been provided below. Here "Δχ" expresses the thickness of the object on the x axis. When somebody touches two different objects of the same temperature and thickness, the object having higher thermal conductivity is felt colder as the heat that is lost from the body is higher when touched this object.

For instance, when we compare a metal object and a wooden object which are available in the same room and which have reached to the same temperature, the metal object is felt colder than the wooden object. The reason of this situation is that the thermal conductivity coefficient of the metals is much higher than that of the wooden objects.

Q _l0St =k.(AT/Ax)

The tile production process is comprised of tile shaping (pressing), drying and firing processes following the raw material preparing processes (grinding, enabling the moisture content to reach to a certain value in the spray drier and generating spherical particles). The main structure excluding the layers that the surface treatments like glazing have generated in the tile is called as body. In the tile production, there are many different processes enabling the surface and the whole body to have an aesthetic outlook. Some of the processes making the surface and the whole body to have an aesthetic outlook are the processes that are applied during the pressing process; however some of the processes can be applied on the fired product before or after the firing. The most important one of these processes is the glazing process. In the production of glazed tiles with single-firing, the glaze is applied onto the surface by means of various techniques before firing. The difference between the ceramic and porcelain tiles is based on the differences in the raw materials and firing temperature; and while the water absorption value of the porcelain tiles is lower, its strength is higher.

In order to obtain the desired strength and water absorption values in the tile, it is needed that the sintering process has been carried out in the desired level. As the firing time in the ceramic tile production is about 35-50 minutes, the sintering speed is required to be high so that the sintering process can be carried out. In the case that micro-pores are generated due to foaming during the sintering process, it becomes more important to provide a good sintering. If a good sintering is not provided, the generated micro-pores grow too much and the water absorption value of the tile increases too much. This problem can be eliminated to some extent by increasing the firing time, but it is not preferred to increase the firing time too much as it will reduce the production capacity.

When somebody touches a tile under room conditions, in order for the tile to be felt warm, it is needed to decrease the thermal conductivity coefficient of the tile to an important extent. In many researches that have been carried out for this purpose, it is provided that the body or the glaze has more air bubbles by adding various additives to the body and glaze formula. As the thermal conductivity coefficient of the air is quite low, the thermal conductivity coefficient of the body or glaze decreases thanks to the air bubbles. In the studies that have been carried out so far, two different methods have been made use of in order to create air bubbles in the body or glaze. In the first method, the air bubbles are created by providing the gas discharge as a result of the decomposition of the additives during firing that have been added to the body or the glaze, which is called as the foaming process. In this method, in order for the micro-pores, which are created in the tile depending on the gas discharge, not to close up during firing as a result of the vitrification in the body or glaze, it is needed for the additives such as silicon carbide and nitride to make gas discharge during sintering process. However, in this case, the water absorption value and the thermal insulation effect is not stable, wherein the said effect emerges because of the fact that the number and the size of the pores that come into being by using a different additive for foaming or by using only silicon carbide is not stable as well. In the second method, on the other hand, it is provided that the body or the glaze is produced in a way that they comprise air bubbles by using additives already containing air bubbles. In the said method, by making use of the air bubbles in the additives, the tile body or the glaze are made porous. It is needed for these air bubbles not to be deformed/closed under firing temperatures. However, under tile firing temperature, many porous additives such as hollow glass beads, sepiolite, silicon beads, quartz glass beads are deformed depending on the volumetric expansion under high temperature.

In some of the conventional embodiments, both the glaze and the body are enabled to comprise air bubbles. However, as the thickness of the glaze layer is much lower compared to that of body, any thermal conductivity decrease in the glaze layer is not enough for the ceramic/porcelain tile to be felt warm. Moreover, no matter how carefully the air bubbles are generated inside the glaze layer by means of any method, the porous additives added into the glaze layer are deformed under the firing temperature and also they cause the glaze layer to be deformed aesthetically during the production process.

In the methods according to the state of art, the thermal conductivity coefficient cannot be decreased down to the desired extent by means of micro-pores that could not have been generated in a controlled and homogeneous manner; as well as the proper water absorption value cannot be obtained, and surface deformation occurs (Figure 1).

Description of the Figures:

Figure 1: is the view of the micro pores that have not been generated in a controlled and homogeneous manner by using the methods according to the state of the art in the body Figure 2a, 2b, 2c: is the pore structure that is obtained by the additive that is added to the body according to the present invention. The pore structures that are shown in Figure 2a, 2b and 2c, respectively, are obtained by gradually making the particle size of the additive smaller according to the present invention. References:

1: The pore structure that is obtained by means of the methods according to the state of the art

2a, 2b, 2c: The pore structure that is obtained by means of the method according to the present invention. The pore structures that are shown in Figure 2a, 2b and 2c, respectively, are obtained by gradually making the particle size of the additive smaller according to the present invention.

Description of the Invention:

The present invention relates to tiles having lower thermal conductivity and proper water absorption value and to their method of production.

The tiles that are produced according to the present invention will be felt warm when touched, and the places will become more comfortable by using these tiles.

No matter how controlled the air bubbles generation process is carried out inside the glaze layer of the tiles by means of any method, as it is probable for the glaze layer to be aesthetically deformed during the production and as the porous additives that are added to the glaze or body are deformed under firing temperature, it is provided in the present invention that only the body is made porous by means of foaming and by doing so, the thermal conductivity coefficient is made to decrease. Moreover, by means of the method according to the present invention, the problem that the micro pores generated by means of foaming according to the state of the art expand if the sintering process cannot be carried out well and therefore the problem that the water absorption value of the tile increases are eliminated.

The thermal conductivity value of a tile which has been produced conventionally, is high to extent that it will be felt cold when touched, which is approximately 1,3 W/m.K. In the method according to the present invention, the tile is produced in a way that it will have lower thermal conductivity and proper water absorption value without making any change in the tile production process. In other words, the tiles which are felt warm when touched on the surface can be produced in a conventional production line as well.

In order for the micro pores, which have been produced by means of the method according to the present invention, to be smaller and more in number, it has been detected that the particle size of the added additive should be small; and the pore structures (2a, 2b, 2c) that have been obtained when the particle size of the additive become smaller accordingly are shown in figure 2a, 2b and 2c, respectively.

In addition to the additives such as silicon carbide and silicon nitride which are added to the body for foaming in the tile structure of the present invention, some other additives containing Mg such as MgOCI ₂ , magnesite or magnesium clays are also added, and therefore a proper water absorption value is obtained by providing a good sintering speed in the medium where there is foaming. Thanks to these added additives, the viscosity of the liquid phase decreases, and therefore the pressure that is applied to the emerging air bubbles decreases and the air bubbles are prevented from getting deformed. The pore structure that is obtained by means of the methods used in the present state of art and without using such kind of additives is shown in Figure 1. As shown in Figure 1, in the methods according to the state of the art, micro pores can't be obtained in desired sizes and homogeneous structure, which causes the surface to be deformed.

By adding additives to the body of tile according to the present invention, which generating air bubbles depending on foaming, increasing sintering speed and decreasing liquid phase viscosity; the thermal conductivity coefficient of the tile is decreased. The used production process is same as the conventional tile production process. Therefore the tiles that have been developed according to the present invention, which will be felt warm when touched on the surface, can also be produced in a conventional production line. It is possible for the tiles that are mentioned in the present invention to be ceramic or porcelain.

In the Table 1 below, the additives that are used in the present invention, their ratios, and the thermal conductivity coefficient obtained depending on their particle size and their water absorption values are shown.

Table 1