Color matching algorithms in ceramic tile production

doi:10.1016/j.jeurceramsoc.2004.11.012

Journal of the European Ceramic Society

Volume 26, Issue 3, 2006, Pages 311-316

https://doi.org/10.1016/j.jeurceramsoc.2004.11.012 Get rights and content

Abstract

In the present work, the possibility of transferring in the ceramic tiles production the know-how developed in the field of the paints by using the Kubelka–Munk theory, in the form used for opaque surface coatings, have been evaluated. Five different target colors have been chosen as target and tried to reproduce with an industrial glaze in a cycle for fine porcelain stoneware tiles. Four industrial pigments have been chosen as basic stains for the formulations. The results show a good efficiency of the color matching algorithm applied to pigments for glazes for fine porcelain stoneware tiles. All the formulations, in fact, have allowed to obtain a value of ΔE^* lower to the accepted limit.

Introduction

The utilization of algorithms in the formulation of colors is not a new idea in the industry. It has been approximately 50 years since the first colorant formulation algorithm was reported introducing the color matching concept. By color matching, we mean the ability to reproduce, through mixing few fundamental pigments, whatever type of color experimentally measured by using algorithms of calculus. In activities such as printing, the textile industry, plastics or cold paints,¹ this technique represents a working tool, long consolidated and efficient in supplying rapid solutions to many of the chromatic problems of the production process, both those of a formulating and qualitative nature. The advantages are the possibility to have an elevated number of colors using a low number of pigments, the rejects elimination in the pigment production because the color matching equipment can prepare in real time the required volume of mixtures, the possibility to replicate colors also if it is not available the pigment with the target color, the possibility to adjust errors in the preparation of the color, etc. These aspects should be certainly advantageous also in the ceramic field where many producers now use different typology of applicators (flat, drum, rotary with photoincisive rollers serigraphic machines) that in many plants frequently cohabit. All these factors normally leads to use a wide range of decorating materials (often a question of hundreds of colored products) that make up a complex system to manage both at a warehouse and production level. However, despite various attempts (studies intended to predict the color of a ceramic glaze can be found with interesting results in literature),2, 3, 4, 5 in ceramic tiles sector the technology of colorant formulation via software has not found a fertile field. For the final result, in fact, some specific limitations, characteristics of a ceramic material that develops its color during firing, have to be considered. The most important is connected with the thermal and chemical stability that pigments must have towards the molten glass (frits or sintering aids) developed during the firing cycle at high temperatures: the same pigment, in fact, can develop slightly different colors depending on both firing temperature and chemical composition of glaze or ceramic body to color. Aspects such as the grain size distribution, the chemical and physical interaction between pigments and glazes, variations during the firing process, the final appearance of the ceramic tile surface, make up a series of elements that influence in a determining way not easily controllable the development of colors.

In the present work, the possibility of transferring in the ceramic tiles production the know-how developed in the field of the paints by using the Kubelka–Munk theory, in the form used for opaque surface coatings, have been evaluated. Five different target colors have been chosen as target and tried to reproduce with an industrial glaze in a cycle for fine porcelain stoneware tiles. Four industrial pigments have been chosen as basic stains for the formulations. Moreover, the influence of the temperature on the efficiency of the algorithm has been evaluated.

Section snippets

Kubelka–Munk theory

All the most modern formulation softwares are essentially based on the application of the Kubelka–Munk theory (1931),⁶ the most widely used in most industrial sectors. In measuring reflected color the values obtained for every wavelength are function both of absorbed light and scattered light by pigment particles.7, 8 This means that for every frequency of the visible spectrum, every component of a formulation possesses a coefficient of absorption, K, and a coefficient of scatter, S. In

Experimental

Four industrial pigments have been chosen as basic stains for the formulations (Table 1). The pigments have been chosen according to their intensity, tone purity, stability to both the firing temperature and chemical aggression exerted by the chosen glaze. A white industrial zirconium silicate has been used as opacifier, while the black pigment is a commercially available iron–chromium pigment. The base glass has been an industrial frit for high temperature (Table 2).

Results and discussion

In the present work, the term “masstone” is used for the mixture: pigments (10 wt.%), glass (88 wt.%) and sodium bentonite (2 wt.%). The K and S parameters have been determined for the system “masstone” and likewise the formulation to reproduce the NCS standards have been determined considering the mixtures. In this way, we have tried to avoid the correction suggested by some authors³ due to the solubility of the pigment in the glass that determines a reduction of the pigment tint strength.

The

Conclusion

The results show a good efficiency of the color matching algorithm applied to pigments for glazes for fine porcelain stoneware tiles. The decisive steps have been the introduction of a base glass in the formulations and the characterization of the colored glazes after firing. The color matching experiments have been conducted on five target colors and the determined formulations have allowed to obtain, after firing, results very close to the targets. All the measured ΔE^*, in fact, are lower to

Acknowledgment

Authors are grateful to CPS Color Equipment S.p.a for the collaboration to define the color matching procedure.

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View full text

Color matching algorithms in ceramic tile production

Abstract

Introduction

Section snippets

Kubelka–Munk theory

Experimental

Results and discussion

Conclusion

Acknowledgment

Computer-aided design and manufacturing of the color of decorative and protective coatings

J Coat. Tech.

Predicting the color of a ceramic glaze

Am. Ceram. Soc. Bull.

Measurement and interpretation of color in glazes

Ceram. Eng. Sci. Proc.

Blending of pigments in ceramic glazes

Ceram. Eng. Sci. Proc.

Calculating glaze color from pigment and opacifier standards

Ceram. Eng. Sci. Proc.

Ein beitrag zur optik der farbanstriche

Z. Tech. Phys.