Most of the decoration on porcelain enamel products for daily use in China is a hand-painted process. As the enamel color enamel for decoration contains a lot of rare metals such as aluminum, selenium, and cadmium, a large amount of glaze dust enters the air when spraying. The process not only wastes a lot of raw materials, but also seriously pollutes the air. The effluent rinsing in production also causes pollution, and more seriously harms the health of sprayers.
In foreign countries, the spray flower decoration process has long been eliminated, and screen printing is commonly used to decorate enamel products. Such as tableware, kitchen utensils, household appliances and other enamel products, and even enamel boxes and other miscellaneous items are printed with enamel flowers to decorate.
In the 1970s, domestically used lithographic enamel decals were used in China. However, due to the small proportion of enamel in the color enamel and high pigment content, the surface color of the pattern after high-temperature firing is not brilliant and the gloss is poor. Less than the decorative effect. Finally in the 1980s it was gradually replaced by screen-printed enamel decals.
First, screen printing enamel decal paper technology silk screen enamel floral decoration, multi-color enamel glaze is overprinted on the paper base pre-coated with water-soluble glue through the screen printing, the pattern is transferred to the enamel products through the organic polymer film , and then quickly burned at 800-840 °C high temperature, and made enamel decorative effect. The effect of this decoration process is bright colors, good glossiness, clear and delicate patterns, and strong realism. Compared with screen printing enamel decals and spray printing, the former uses mechanical printing, which has high utilization of raw materials, high labor productivity, greatly reduced labor intensity, and significantly reduced environmental pollution. Therefore, the screen printing process has a strong vitality in the decoration of enamel products, and its development prospects are broad. In the future, besides special styling, it will gradually replace the spray flower process. The process flow is as follows:
Negative-drawing bottom plate production (design, color separation, screening, revision) → Production of screen printing plate → Preparation of color glaze → Screen printing →
Film preparation → film → film decal → dry → product fired screen printing process of enamel decals and other screen printing products production is basically the same, but the main difference is ink and printing paper and other special materials.
Second, the printed decals paper 1 domestic production silk screen enamel decals more than the use of bicycles, sewing machine logo decals printing paper. Its structure consists of four layers of three parts, specifications for the four open (about 540mm × 390mm). The decal printing paper, 130g offset paper for the paper-based, paper base coated with a layer of hydrosol, while rolling a layer of copy paper for the liner, and then coated with a layer of water-soluble adhesive on the liner. This decal printing paper is disposable and cannot be used repeatedly. After printing a pattern, a thin film is applied. When the decal is applied, each pattern is cut or cut, immersed in water, and the paper base is detached and adhered to the porcelain surface.
2 Foreign production silk screen enamel decals, widely used for decals printing has a very good absorbent paper base. The paper base is coated with a very soluble water-soluble glue that can be used for printing. This paper has the advantages of fast water absorption, fast film release, and easy printing. At present, the domestic market has started to print paper with water-soluble adhesive, but the water absorption of the paper base has not been fully passed.
Third, the enamel with printing materials (a) enamel glaze 1. There are many kinds of enamel, there are several classification methods, according to the composition of enamel silicate enamel and non-silicate enamel, according to the function of enamel, can be divided for:
(1) Bottom glaze This is a enamel that is used as a transitional layer of glaze and metal.
(2) Face Glaze This is a enamel coated on the transition layer, which gives the product a smooth and beautiful surface and a series of excellent physical and chemical properties;
(3) Color Glaze This is a colored glaze as a decorative item. Can also be used as colored enamel glaze and decorative flower glaze;
(4) Special glaze This is to meet the special application of high temperature, high pressure, light, absorption or emission of infrared, insulation and other special applications.
2. The components of the enamel glaze The main components of the enamel glaze are a matrix, a flux, an opacifying agent, an adhesion agent, an oxidizing agent, a colorant, and an auxiliary agent, as shown in the following Table 4-7.
Table 4-7 Main constituents of enamel
La2P3 PrO2 NdO2 Sm2O3
MgSO4 MaCO3 Organic Plastic
(1) The network forming agent of the enamel network forming agent is the main body of the hanging enamel, and it is the basis of forming a complete enamel. Generally, SiO2, B2O3, and P2O3 are used as enamel network forming agents. Because Si4+, B3+, and P5+ have small cation radii, the charge is relatively large; the bonds of these oxides are strong, in which Si4+ is 106 kcal/mol, B3+ is 89-119 kcal/mol, and P5+ is 88-111 kcal/mol; both are polar covalent. Bond oxides.
(2) Flux The flux is referred to as flux, which is to accelerate the high-temperature chemical reaction during the melting process of enamel, that is, to accelerate the structural bond breaking process of the high-melting crystalline substance (such as SiO2, etc.) in the composition and make the enamel appear together. The oxide of the melting point becomes a compound. The flux simultaneously functions to adjust the physical and chemical properties of the enamel, such as the coefficient of expansion, chemical resistance, and the like. The size of the adjustment depends on the size of the cation and the way and quantity of the enamel structure. The typical oxides and compounds belonging to the flux are as follows: Li2O, Na2O, B2O3, K2O, PbO, V26, CaF2 and the like.
(3) Opacifying Opacifying agent is to ensure that the enamel has sufficient hiding power, that is, to ensure that the glass phase precipitates out of various gases and solid ligands when firing is ensured, resulting in a difference in refractive index and causing light scattering. Muddy components. The enamel opaque compound commonly used for emulsification is arranged as follows: TiO2>ZrO2>SnO2>Sb2O3>Na3AlF6>Na2SiF6>CaF2
(4) Adhesives Adhesives are compounds that ensure firm bonding with the enamel and metal surfaces. Typical adhesives are arranged as follows: CoO>NiO>MoO3>MnO2>Fe2O3>As2O3
(5) Oxidizing agent Oxidizing agent is raw material that can provide oxygen during the melting process of enamel to prevent the reduction of certain oxides and ensure whiteness during the melting process. Typical enamel oxidizers are arranged as follows:
NaNO3>KNO3>Ba(NO3)>(NH4)NO3>kMnO4 The process of supplying oxygen to the oxidant raw material is to release oxygen first and then decompose into oxides and gases.
The Na2O in the oxidant raw material enters the enamel structure as an excellent additive for enamel and a modifier for enamel properties (such as expansion coefficient, etc.). Nitric oxide gas volatilizes during melting. Oxygen supplies the oxidizing effect of the enamel melt.
Practice has proved that enamels without oxidants, especially enamel glazes, generally do not become good whiteness and strong luster
category
Agent
Easy to form a network or a compound that has a strong effect on the properties
Compounds that are not easily networked or have a weaker effect on properties
Abrasive components
1
Matrix
SiO2 B2O3 P2O3 GeO2 As2O3
ZrO2 Sb2O3 Al2O3
2
Fused
Li2O Na2 K2O PbO SrO V26
CaF2 Na3AlF Na2SiF6
3
Emulsion
TiO2 ZrO2 Sb2O3 SnO2
CeO2 Na3AlA6 Na2SiF6 ZnO CaF2
TiO2 NaSbO3 SnO2 Sb2O2
4
Closely
CoO NiO MoOO3 Sb2O3 Mixing Adhesive
Fe2O3 V2O5 MnO
BaMoO3 Sb2O3 NaSbO3
5
Oxidation
O2
NaClO3 KClO3
6
Coloring
CoO NiO Cr2O3 CuO Na2Cr2O·6H2O
MnO2 Fe2O3 AuCl3
Various colors
7
Aid
Al2O3 MgO CaO BaO ZnO
Na2SiF6 Na3AlF6
Clay, urea, KCL BaCl2 CaCl2