EP1807367A1

EP1807367A1 - Process for the production of glazes comprising components in the form of particle of various size and the glazes thus obtained

Info

Publication number: EP1807367A1
Application number: EP05794605A
Authority: EP
Inventors: Guido Bitossi; Marco Bitossi; Gabriele Montanari; Laura Niccolai
Original assignee: Colorobbia SpA
Current assignee: Colorobbia SpA
Priority date: 2004-09-16
Filing date: 2005-09-16
Publication date: 2007-07-18
Also published as: ITFI20040191A1; WO2006030026A1; RU2007114048A

Abstract

A process is described that enables the preparation of glazes comprising components in the form of particles of selectively controlled size, in which said components are ground separately under dry or wet conditions. Also described are glazes which are useful in the aforesaid fields of application.

Description

PROCESS FOR THE PRODUCTION OF GLAZES COMPRISING COMPONENTS IN THE FORM OF PARTICLE OF VARIOUS SIZE AND THE GLAZES THUS OBTAINED Field of the invention The invention relates to glazes for industrial and artistic use at all the temperature ranges of application, from glass to porcelain, and to their production processes. State of the art

As is well-known in the ceramics industry, glazes are a product of special interest in view of the characteristics of brightness, mechanical strength and coloration that can be imparted to finished products by their application to the semi-finished article. Essentially, glazes normally consist of:

- ground vitreous material (frit) (consisting of mixtures of oxides in suitable percentages which are melted in suitable kilns followed by rapid cooling of the formed vitreous mass);

- materials of mineral origin for the purpose of opacifying, plasticizing, etc.

- pigments.

Ceramic factories and ceramic colour manufacturers who produce glazes in the ground form, purchase the aforesaid components separately, mix them according to in-house recipes which provide for differing percentages of the various components and then wet grind these mixtures based on well-established traditional methods used in ceramics, or dry grind them in accordance with more recent and innovative methodology. The mixtures are ground to a residual particle size which varies depending on the application, from about 0 to 5 wt% at 45μ for glazes and industrial silk-screen printing and from 0 to 1 wt% at 20μ for glazes and colours for specific applications such as glass, third firing etc. and in any case always depending on requirements for later use. The grinding systems for the mixtures involve the use of mills, for example, or other grinding systems depending on the particular requirements of the user and hence the glaze to be obtained.

Grinding technology, whether wet or dry, therefore provides for a single grinding of all the necessary components, pre-mixed, at the end of which the residue and particle size distribution curve for the glaze are obtained but not the residue and particle size distribution curve for each individual component. Up to the present time it has been considered impossible to grind the individual components separately, store them, and reconstitute the desired ground glaze when required, as it was believed that by proceeding in this manner the rheological parameters would be altered to such an extent to render the glaze completely unsuitable for its intended final applications. For wet application in particular, there would be a spontaneous sedimenting and cementing of the solid part, suspoended in the solution applied to the article to be glazed; the cause of this being the lack of intimate binding of the individual components during the process. The aforesaid glaze production process presents the following disadvantages:

- the mills have to be emptied and carefully cleaned every time the mixture is changed - additionally, in the case of wet grinding, the water used for washing must either be recycled or discharged

- discontinuous processes have to be mainly used, with consequent requirement for storage warehouses in order to guarantee an immediate supply of the market. In view of the foregoing, it is evident the importance of developing processes that enable the required glazes to be prepared by mixing, in the required quantities, pre-ground raw materials at the time of use. Detailed description of the invention

The present invention enables the aforesaid disadvantages to be overcome and the desired glazes to be prepared by mixing the necessary components already pre-ground in the required amounts and form.

In accordance with the invention the various components are ground separately until powders are obtained with dimensions aimed at the final technical result and application, and varying, depending on the application, from about 0 to 5 wt% at 45μ for glazes and industrial silk-screen printing and from 0 to 1 wt% at 20μ for glazes and colours for particular applications such as glass, third firing etc. and in any case always depending on the requirements for later use. The aforestated grinding can be undertaken using any grinding instrument suitable for the purpose (mills, pressure roller pulverizers, jet mills, track mills and other systems etc.) and can be undertaken under dry or wet conditions. Pressure roller pulverizers have proved to be particularly advantageous for grinding as they possess a system of in-line high pressure mills with a wind separator. Grinding is conducted by means of a semi-continuous system i.e. continuous for every type of raw material and with stop and change on changing the component.

Grinding is continued as aforesaid until powders are obtained with dimensions less than 45μ. In accordance with a particular embodiment of the process, grinding can proceed until powders with dimensions less than 20μ are obtained.

The components in powder form thus obtained can be stored in suitable storage locations and then mixed in the required amounts with possible addition of pigments (which are generally already available in a suitable form or in a form that can be adapted to the required dimensions using other grinding systems).

Grinding is preferably undertaken with an intensive mixer, making suitable adjustments with the purpose of optimising the applicative result. These adjustments are of the same type as those normally undertaken in wet and dry grinding operations of complete mixtures and depend on the particular requirements of the manufacturer.

The technology of the present invention presents the following advantages:

- from the technological and processing viewpoint the selective control of particle size enables the technical contribution of each individual component to be optimised - from the economic and operational viewpoint it enables the amount of energy used for grinding each individual component to be selected, thus optimizing the quality to price ratio

- high flexibility in dispatching orders as these can be made up immediately from ready-to-use stored material - greater diversification of formulations for the same number of starting components

- more precise planning of the chemico-physical surface characteristics of the finished glaze by the targeted selection of the particle size of individual components or different particle size of the raw material itself.

The invention will be better understood in the light of the following examples.

EXAMPLE 1 A matt glaze was prepared, typical for applying to industrial tiles, consisting of: 1 frit, calcium carbonate, kaolin, sodium feldspar, quartz, wollastonite, alumina, corundum, zinc oxide, micronized zirconium.

The frit used was obtained by melting and then rapidly cooling, in accordance with conventional techniques, a mixture of oxides consisting of: Frit 1 : CaO 8.7%, MgO 1.9 %, PbO 2.7%, K₂O 5.3 %, Na₂O 0.5%, ZnO 8.4%, AI₂O₃

8.6%, B₂O₃5.5%, SiO₂52.9%, ZrO₂ 5.5%.

The aforesaid components were dry ground under the following conditions. (The percentages are expressed by weight:)

Frit 1 quantity 39.6% hourly throughput 3.5 t/h final powder size 0.7% residue at 45 micron

Calcium carbonate quantity 9.4% hourly throughput 3.6 t/h final powder size 0.5% residue at 45 micron

Kaolin lumps quantity 4.6% hourly throughput 4.1 t/h final powder size 0.1 % residue at 45 micron

Feldspate quantity 5.7% hourly throughput 4.1 t/h final powder size 0.6% residue at 45 micron Quartz quantity 5.7% hourly throughput 3.4 t/h final powder size 0.9% residue at 45 micron

Wollastonite quantity 9.4% hourly throughput 3.9 t/h final powder size 0.7% residue at 45 micron

Alumina quantity 7.6% hourly throughput 3.6 t/h final powder size 0.9% residue at 45 micron Corundum quantity 7.6% hourly throughput 3.2 t/h final powder size 0.9% residue at 45 micron

The various components in the form obtained by grinding as aforedescribed were mixed, together with zinc (3.8%) and micronized zirconium (6.6%) which are already available in a suitable form for mixing, using an intensive mixer (Eirich) and making adjustments as previously indicated, to obtain the ground glaze ready for either dry or wet application.

The mixture was applied by disc application for single-firing at a density of 1650 g/L on a white paste support and fired with a cycle of 118O⁰C for 45 minutes.

Characterization of the glaze obtained

A glaze mixture identical to the aforesaid one was prepared by simultaneously grinding together the various components in accordance with the usual techniques. The mixture was then applied in a similar manner to that described in example 1 ; the glaze obtained had visually the same surface coating and colour characteristics as that obtained with the process of the invention.

EXAMPLE 2

A glossy glaze was prepared consisting of: 3 frits, kaolin and micronized zirconium.

The frits used were obtained by melting and then rapidly cooling, in accordance with conventional techniques, a mixture of oxides consisting of: Frit 1 : CaO 4.8%, K₂O 2.5 %, Na₂O 18.5 %, AI₂O₃ 10.1%, B₂O₃ 12.5 %, Fe₂O₃ 0.1%,

SiO₂ 51.5%.

Frit 2 : CaO 5.3%, MgO 0.3 %, K₂O 2.5 %, Na₂O 5.0%, ZnO 6.3%, AI₂O₃ 6.1% , B₂O₃

12.4 %, SiO₂52.6%, ZrO₂9.5%. Frit 3 : CaO 4.3%, K₂O 1.0 %, Na₂O 5.2%, ZnO 1.1%, AI₂O₃7.5%, B₂O₃ 12.4 %, BaO

3.5%, SiO₂55.1%, ZrO₂9.9%.

The aforesaid components were dry ground under the following conditions:

Frit 1 : quantity 15.7% by weight hourly throughput 3.5 t/h final powder size 1.9% residue at 45 micron

Frit 2: quantity 50.7% by weight hourly throughput 3.5 t/h final powder size 2.1% residue at 45 micron

Frit 3 quantity 29.1 % by weight hourly throughput 3.5 t/h final powder size 2.0% residue at 45 micron Kaolin quantity 3.4% by weight hourly throughput 4.0 t/h final powder size 0.1% residue at 45 micron

The various components in the form obtained by grinding as aforedescribed were mixed together with the micronized zirconium (1.1 %), which is already available in a suitable form for mixing, using an Eirich intensive mixer to obtain the glaze ready for either dry or wet application.

The mixture was applied by artistic ceramic immersion at a density of 1600 g/L on a red paste support and fired with a cycle of 950⁰C for 8 hours Characterisation of the glaze obtained

A glaze mixture, identical to the aforesaid one, was prepared by simultaneously grinding together the various components in accordance with the usual techniques.

The mixture was then applied in a similar manner to that described in example 2; the glaze obtained had visually the same surface coating, colour and brightness characteristics as that obtained with the process of the invention. EXAMPLE 3

This glaze has better hardness and stain resistance surface characteristics than known glazes, such characteristics being achieved, as described in the invention, precisely by using raw materials of different particle size distribution targeted for this purpose, A matt glaze was prepared consisting of: 2 frits, clay, dolomite, wollastonite, nepheline, zinc oxide, quartz and corundum in three different particle sizes

(indicated as a, b and c which correspond respectively to 100, 150 and 220 μ).

The frits used were obtained by melting and then by rapidly cooling, in accordance with conventional techniques, a mixture of oxides consisting of: Frit 1 : CaO 12.4%, K₂O 0.4 %, Na₂O 5.4%, ZnO 10.0%, AI₂O₃ 14.2%, Fe₂O₃ 0.2%,

SiO₂ 57.4 %.

Frit 2 : CaO 8.0%, MgO 1.2 %, PbO 2.8%, K₂O 4.1%, Na₂O 2.0%, ZnO 5.0%, AI₂O₃

9.1%, B₂O₃ 9.0 %, BaO 1.4 %, SiO₂ 57.4%.

Frit 1 quantity 30.0% by weight hourly throughput 3.4 t/h final powder size 0.9% residue at 45 micron

Frit 2 quantity 17.0% by weight hourly throughput 3.8 t/h final powder size 1.2% residue at 45 micron

Dolomite quantity 3.0% by weight hourly throughput 3.7% t/h final powder size 0.1 % residue at 45 micron

Wollastonite quantity 9.0% by weight hourly throughput 3.1 t/h final powder size 0.1% residue at 45 micron

Nepheline quantity 10.0% by weight hourly throughput 4.1 t/h final powder size 0.2% residue at 45 micron

Quartz quantity 3.0% by weight hourly throughput 3.3 t/h final powder size 0.7% residue at 45 micron

Corundum of particle size a quantity 5.0% by weight hourly throughput 5.7 t/h final powder size 0.1% residue at 75 micron

Corundum of particle size b quantity 6.0% by weight hourly throughput 3.0 t/h final powder size 0.1% residue at 45 micron

Corundum of particle size c quantity 8.0% by weight hourly throughput 1.7 t/h final powder size 0.1% residue at 25 micron The various components, in the form obtained by grinding as aforedescribed, were mixed together with zinc oxide (5.0%) and air dry clay (4.0%), which are already available in a suitable form for mixing, then using an Eirich intensive mixer to obtain the glaze ready for wet application.

The mixture was applied by disc application at a density of 1680 g/L on a white paste support for single-firing and fired with a cycle of 1170-118O⁰C for 45 minutes. Characterization of the glaze obtained

The glaze has better abrasion and staining resistance characteristics than glazes of similar chemical composition due to the use of components chosen with targeted differentiated particle size distribution. Abrasion resistance is >PEI 4 and in the stain resistance test no visible traces of stains were found according to the standard UNI EN ISO 1045/14.

Claims

1. Process for preparing glazes whose components consist of powders, each having a given residual particle size.

2. Process as claimed in claim 1 wherein the various components of said glazes are individually ground and subsequently mixed by intensive mixing possibly in the presence of the usual pigments and additives.

3. Process as claimed in claim 1 wherein said components are individually dry or wet ground.

4. Process as claimed in claims 1-3 wherein said individually ground components are in the form of powders with dimensions having a 0 to 5 wt% residue at 45μ.

5. Process as claimed in claim 4 wherein the glaze obtained is suitable for industrial applications.

6. Process as claimed in claims 1-3 wherein said individually ground components are in the form of powders with dimensions having a 0 to 5 wt% residue at 20μ.

7. Process as claimed in claim 6 wherein the glaze obtained is suitable for artistic and decorative applications.

8. Process as claimed in claims 1-7 wherein grinding is undertaken by means of pressure roller pulverizers possessing a system of in-line high pressure mills with a wind separator.

9. Process as claimed in claims 1-7 wherein the intensive mixing is undertaken with the usual industrial mixers.

10. Ground glazes obtained with the processes claimed in claims 1-9.