WO2007132029A1

WO2007132029A1 - Ceramic paste whose formulation incorporates raw materials with a low melting point in order to increase the mechanical strength of the dried, shaped pieces

Info

Publication number: WO2007132029A1
Application number: PCT/ES2006/000253
Authority: WO
Inventors: Joaquín PIQUER MARTÍ
Original assignee: Neos Cerámica E Investigación, Sl
Priority date: 2006-05-16
Filing date: 2006-05-16
Publication date: 2007-11-22

Abstract

The subject matter of the invention is the incorporation of raw materials that are either natural or prepared from phosphorus and that have low melting points. The purpose of the invention is to increase the mechanical strength of the ceramic pieces by means of the partial melting of said raw materials in the process of drying the ceramic slabs. The incorporation of these raw materials into the formulation of the ceramic pastes allows greater complexity in the decoration of the pieces, reducing the dips associated with the lack of mechanical strength that result between the steps of drying and firing the ceramic products.

Description

Ceramic paste that incorporates in its formulation raw materials with a low melting point to increase the mechanical resistance of the shaped and dried pieces.

Description Sector of the technique

The invention relates, in general, to the manufacture of ceramic products and, in particular, relates to a ceramic paste comprising a raw material with a low melting cost, giving the assembly a greater mechanical resistance with respect to that achieved using compositions of traditional ceramic pastes. Background of the invention

The elaboration of traditional ceramics has been based on the use of clay minerals, as the main! component of ceramic pastes. However, in recent years and due to a greater market trend towards more sophisticated products, the globalization in ceramic production and the development of equipment for forming ceramic pieces with a greater capacity (large tonnage presses), has given place to the development of ceramic pastes with a lower content of clay ore.

This decrease in the percentage of clay minerals has been compensated with an increase in other types of more degreasing materials, which give the ceramic paste better physical-chemical properties (flux, whiteness), greater economic profitability or greater availability of materials. premiums in the vicinity of production centers.

These substitute raw materials for clay minerals are, among others: feldspars, feldspathic sands, silicon sands, talc, zirconium silicate,

Alumina, fried or glass, dolomite, pegmatite, etc. and its use depends of the availability of the same in the areas of ceramic production, as well as the final physical-chemical result that you want to obtain from the ceramic piece (low water absorption, high mechanical resistance, whiteness, etc.).

This tendency within the traditional ceramics to develop products with better technical performance, is reflected in the strong increase in the production of porcelain stoneware. Said product has as its main characteristics: a low water absorption (less than 0.5%) and the whiteness of the ceramic support. For its formulation, clay minerals (clays and kaolins) have been replaced by: melting material with a low content of chromophores oxides (iron and titanium oxides): feldspars, talc, dolomite, fried, etc. materials with a low economic cost: feldspathic sands, quartz, etc. - materials that confer greater whiteness to the ceramic support: zirconium silicate or alumina.

However, the reduction of the clay content or its replacement by clays with a lower plasticity in the porcelain stoneware formulations has been associated, in some cases, with a decrease in the mechanical strength of the formed and dried piece. To improve this mechanical resistance, presses of greater capacity have been installed in the production system, or materials that act as binders have been introduced into the porcelain stoneware formulations. These materials are added in a small percentage, generally less than 1% and are mainly organic in nature (hydroxypropyl methyl cellulose, polyvinyl alcohol, polyvinyl acetate, cellulose, hydroxypropyl cellulose, lignosulfates, gum arabic, etc.), although it also fits The possibility of introducing boron compounds that facilitate the shaping of the ceramic piece and have low melting points. Below is a usual composition of a ceramic paste used for the production of glazed porcelain stoneware: Clay 20-40%

Feldspar 30-60%

Feldspathic Arena 0-10%

0-20% kaolin

0.5% de-flocculants

If it is intended to generalize, it can be said that there is no single formulation in traditional ceramics, but if a range of compositions that encompass most formulations can be established, this range would be:

Plastic raw materials 5-100% Degreasing raw materials 0.1-95%

For formulations of red pastes for flooring or cladding, 99.7% of its composition in the wet way and 100% in the dry way are formulated with plastic materials. However, for formulations of materials similar to porcelain stoneware or porcelain, the content of plastic material decreases significantly to low percentages.

The introduction of the deflocculant is necessary when grinding the ceramic paste is carried out wet. Deflocculants are products that decrease the viscosity and thixotropy of the slip, and allow greater effectiveness in grinding, as well as a shorter discharge time of the mill. The deflocculants used for the preparation of ceramic pastes by grinding in liquid are: polyacrylates, sodium metasilicates, sodium hexametaphosphate, sodium tripolyphosphate or phosphonates. Generally, and to obtain greater effectiveness, a mixture of two or more types of deflocculants is used. To perform the forming of the ceramic pieces, the ceramic paste must first be adapted to the necessary conditions for each forming technology (pressing, extrusion or casting). This preparation of the ceramic paste is usually carried out in two ways: - Dry track, where once the dry milling of the different components that make up the ceramic paste is made, they are wetted or kneaded to a moisture that allows the forming of the piece.

- Wet track, where the grinding is carried out in a liquid medium with the aim of achieving a better distribution of particles. This liquid paste, called slip, is dried, usually by atomization, to a suitable humidity for the forming of the piece. To facilitate the grinding and unloading of the slip of the mills, additives (deflocculants) are incorporated, which modify the rheology of the slip.

Finally, it should be mentioned that phosphorus compounds have been widely used in traditional ceramics, their function has been, mainly, as:

Preparation of bone ceramics by incorporating ashes from bone calcination. - Defloculants, with the aim of adapting the Theological conditions of the slippers. Within this typology of phosphorus compounds are: sodium tripolyphosphate, sodium hexametaphosphate and phosphonates. As opacifiers in the production of frits or glasses.

In addition, phosphates, especially phosphoric acid, monoammonium phosphates and alumina, magnesium or calcium phosphates, are used in Ia advanced ceramic and refractory industry, as binders. Such an effect is described, for example, in patents: US 4,417,925 "Refractory mixture with ceramic fiber", US 4,770,943 "Method for creating a rigid film of a calcium phosphate compound", US 6,013,321 "Method for manufacturing phosphate bonded ceramics ", US 5328879" Binding and plasticizing agent for preparing carbon-containing, refractory, ceramic materials and material prepared therewith "or US3888687" Refractory

Alumina-Chrome "

Also in the patent ES 2,193,864 A1 "Ceramic pastes with unconventional formulation with phosphorus contents greater than 2%. Procedure for its elaboration and advantages", the formulation of a ceramic paste using as binders and plasticizers, the compounds is described of monovalent phosphorus, as substitutes for clay in traditional ceramic formulations, especially in the elaboration of ceramic tiles with low water absorption.

In the present invention the percentage of phosphate introduced is not sufficient to act as a binder and plasticizer. Therefore, the natural or synthetic plastic material necessary for the preparation of traditional ceramic pastes must be incorporated.

On the other hand, the typology and the percentage of phosphates necessary for the present invention, are not intended to seal the pores of the ceramic piece in its cooking process. For this purpose, in the formulation of the ceramic paste, materials will be incorporated which, in the cooking temperatures of the ceramic products, melt totally or partially. These raw materials are among others: all types of feldspar, fried, boron compounds, phosphates with melting points higher than those described in the present invention, clays, etc. Description of the invention

It is an object of the present invention to provide a ceramic paste that incorporates in its formulation raw materials with a melting point equal to or less than 500 ⁰ C, which has the following dry weight formulation: - Plastic raw materials in a range between 5 - 99.9%;

Degreasing raw materials in a range between 0.1-94.9%; and Raw materials with a melting point equal to or less than 500 ⁰ C in a range between 0.1-7%.

The objective of this invention is to improve the mechanical strength of the shaped and dry ceramic piece, by incorporating into the formulation in said ceramic paste raw materials with a low melting point. These raw materials are basically: ammonium phosphates, phosphates or hydrogen phosphates of monovalent elements with valence +1, or mixtures of phosphates or hydrogen phosphate of ammonium and monovalent elements with valence +1. These compounds generally have melting temperatures below 500 ⁰ C. An example of the above mentioned would be monoammonium phosphate whose melting point according to the literature is 19 ⁰ C, however, in the laboratory, and previously dissolving the salt in water, it presents a beginning of the fusion at a lower temperature. Other examples of this type of materials would be: Monobasic potassium phosphate whose melting temperature is 253 ⁰ C and dibasic potassium phosphate that has a melting temperature of 465 ⁰ C.

The total or partial melting temperature of these raw materials is reached in the drying process of the shaped part. This total or partial fusion and the subsequent solidification of the molten material during the cooling of the dry piece, produces an increase in the mechanical resistance of the tile, facilitating the subsequent processes to which the ceramic products are subjected until their final firing. These processes are: the enamelling, the decoration of the ceramic pieces, the transfer from the dryer to the oven, the raw grinding of the pieces, etc.

The increase in mechanical resistance reduces the chances of breaking ceramic pieces in said processes, which implies an increase in the percentage of quality of the finished material and a decrease in production costs.

The incorporation of these raw materials with a low melting point is carried out in the processes of adaptation of ceramic pastes before forming them. Said compounds, which exclude the current deflocculants (tripolyphosphate or sodium hexametaphosphate), are generally added during the preparation of the composition. The incorporation of said compounds does not modify the current preparation processes of the ceramic paste for subsequent shaping. Mode of a preferred embodiment

The paste used in this embodiment consists of a porcelain stoneware paste with a high flux, where 1% monoammonium phosphates are incorporated. Said paste is with the following formulation in% weight:

Clay 30

Sodium Feldspar 68.15 Monoammonium Phosphate 1

0.5 sodium carbonate

Defloculant (sodium hexametaphosphate) 0.35

Subsequently, said paste is mixed with a sufficient amount of water, and ground in a planetary laboratory mill, obtaining a slip that has the following characteristics:

Viscosity in 4mm Ford Cup: 25 seconds Density: 1670 Kg / m ³

Rejection on a sieve of 63 microns: 1%

Then, said slippery is dried in an oven at a temperature of 150 ° C for a period of 24 hours, for its subsequent wetting and pressing in a laboratory press. The pressure exerted on the powder moistened at a humidity of 5.5% was approximately 106 bars, obtaining a rectangular platelet with dimensions of 110x50x12 mm. Said platelets are, again, dried in the laboratory oven, at a temperature of 150 ° C, for 24 hours, where the partial fusion of the monoammonium phosphate occurs. Subsequently, the specimens were characterized, measuring the apparent density and the mechanical resistance of the dry piece: Bulk density: 1928 Kg / m ³ Breaking load: 34.5 N / cm ² Finally, the material was cooked in a flask at a maximum temperature of 114O ⁰ C, for 15 minutes, and a total cooking cycle of 60 minutes, obtaining the following values of the ceramic piece: Water absorption, according to UNE-EN ISO 10545-3: 0 method , 00% Apparent density of the cooked piece: 2401 Kg / m ³ Linear Contraction: 8.39%

Chromatic coordinates: L = 67.60 a = 1.69 b = 11, 94

The incorporation of phosphates or hydrogen phosphates of ammonium or monovalent elements, gives the ceramic pastes a greater mechanical resistance in crude, mainly due to the partial fusion of the phosphorus compounds. This increase of the mechanical resistance of approximately 50% with respect to the same formula with the absence of this type of phosphorus compound. Other examples made with different types of raw materials, and especially clays, are:

1) Incorporation of phosphorus compounds into the production of porcelain stoneware pastes with raw materials from Europe. Breaking load (N / cm ² )

TRADITIONAL porcelain base paste 25

TRADITIONAL porcelain base paste + 0.5% monoammonium phosphate 54

Super white TRADITIONAL porcelain paste 30 Super white porcelain paste + 1.5%

50 monoammonium phosphate

2) Formulation of porcelain pastes with clays and raw materials from South America. Breaking load (N / cm ² )

- Standard 7 super white porcelain paste

- Super white porcelain paste + 1.5% monoammonium phosphate 15

The advantages that this greater resistance incorporates are: - Reduction of the losses due to the breaks that occur in the line during the transfer of the tiles between its forming until its cooking.

- Increase the number of decorative applications that can be made on

The piece formed and dried, due to its greater resistance to breakage. So far, the different decoration processes are based on a transfer of enamel or silkscreen base from the decoration system to the tile through a physical contact. Said transfer subjects the tile to a pressure that can cause the breakage thereof, with the consequent economic loss. The increase of the mechanical resistance allows a greater number of applications in the decoration of the ceramic piece.

The greater mechanical resistance of the tile allows the elaboration of tiles with more pronounced reliefs. The incorporation of the phosphorus compounds of the present invention have a low melting temperature, facilitating, together with the rest of the melting materials that are incorporated in the production of the ceramic pieces, the total or partial sintering of said products.

Claims

1.- Ceramic paste that incorporates in its formulation raw materials with a melting point equal to or less than 500 ⁰ C, characterized in that it presents the following dry weight formulation: - Plastic raw materials in a range between 5 - 99.9% ;

2. Pasta ceramic according to claim 1, wherein said raw materials with low melting point exceeding 500 ⁰ C are phosphorus compounds, more specifically a salt or a combination of different salts consisting of phosphates or hydrogen phosphates of ammonium, phosphates or hydrogen phosphates of elements with valence +1, or a mixture of different phosphates or hydrogen phosphates of ammonium and elements with valence +1.

3. Ceramic paste according to claims 1 and 2, characterized in that between the forming of the ceramic pieces and their final cooking, said ceramic pieces must be subjected to a heat treatment with temperatures below 500 ⁰ C.

4. Ceramic paste according to claim 1, characterized in that the rest of plastic materials or degreasers, consist of natural or synthetic raw materials essential for the elaboration of the ceramic paste.

5. Ceramic paste according to claim 4, characterized in that it comprises between 0-15% of monovalent elements with valence -1 or elements with multiple valences that include valence -1.

6. Ceramic paste according to claim 4, characterized in that it comprises between 0-90% of an oxide of a monovalent element that responds to the general formula [1]: Me (I) ₂ O [1] where Me (I) is a monovalent element, or an element with multiple valences that include the valence +1, or a mixture of different oxides of monovalent elements that respond to said general formulation [1], or a mixture of different oxides of elements with multiple valences that include the valence +1.

7. Ceramic paste according to claim 4, characterized in that it comprises between 0-70% of an oxide of a divalent element that responds to the general formula [2]: Me (II) O [2] where Me (Il) is a divalent element or an element with multiple valences that include the valence +2, or of a mixture of different oxides of divalent elements that respond to said general formulation [2], or a mixture of different oxides of elements with multiple valences that include the valence +2.

8. Ceramic paste according to claim 4, characterized in that it comprises between 0-100% of an oxide of a trivalent element of general formula [3]: Me (HI) ₂ O ₃ [3] where Me (III) is an element trivalent or an element with multiple valences that includes the valence +3, or a mixture of different oxides of trivalent elements that respond to said general formula [3], or a mixture of different oxides of elements with multiple valences that include the valence + 3.

9. Ceramic paste according to claim 4, characterized in that it comprises between 0-100% of an oxide of a tetravalent element of general formula [4]: Me (IV) O ₂ [4] wherein Me (IV) is a tetravalent element or an element with multiple valences that include the valence +4, or of a mixture of different oxides of tetravalent elements that respond to said general formula [4] or a mixture of different oxides of elements with multiple valences that include the valence +4; where all the percentages are referred to the total elements or oxides provided by the combination of all the materials that make up the partially or totally sintered ceramic paste together with the phosphorus compounds.

10. Ceramic paste according to claim 1, characterized in that it is suitable for the manufacture of traditional ceramics, partially or fully gresified ceramic paste, enameled as not enameled, ceramic paste suitable for the manufacture of bricks, tiles, tiles, sanitary ware, earthenware , porcelain, stoneware and porcelain, and ceramic paste suitable for the manufacture of ceramics for electrical insulators.