Screen printing of glass (top)

Glass screen printing is the use of screen printing plates, the use of glass glaze, decorative printing on glass products. Glass glaze is also called glass ink and glass printing material. It is a paste-like printing material that is mixed and stirred by coloring material and linking material. The coloring material consists of inorganic pigments and low-melting fluxes (lead glass powder); the linking material is commonly referred to as linoleum oil in the glass screen printing industry. After printing, the glass products are placed in a stove and fired at a temperature of 520 to 600°C. The glaze printed on the glass surface can be consolidated on the glass to form a colorful decorative pattern.

If you use silk screen printing with other processing methods, you will get better results. For example, by polishing, engraving, etching, etc., the glass surface is processed before or after printing, and the printing effect can be doubled.

First, plate making

The screen printing plate for glass printing is exactly the same as the ordinary screen printing plate.

Glass screen printing plates are generally made of stainless steel, natural or synthetic fiber screens, and the specific use of the materials depends on the purpose of printing. When the glass surface is to be printed with gold or silver, synthetic fiber mesh should be used, and it should be as thin as possible to improve the printing quality. If stainless steel wire mesh is used when printing gold, stainless steel and gold ink will chemically react, causing various problems.

If printing high-grade goods and high-precision glass products, generally use 300 to 360 mesh nylon mesh. This synthetic fiber screen can be used for infrared thermal printing glaze printing. This type of printing is widely used because it is economical for a large number of substrates.

Stainless steel wire mesh has good adaptability to hot-printing color glaze. It is suitable for single-species, large-volume printing. The commonly used stainless steel wire mesh is 165-200 mesh.

Glass printing usually uses thick-film printing plates, but it is only necessary to use thin-film printing plates when printing gold.

Second, glass glaze

As previously mentioned, the glass glaze is prepared by mixing a colorant with a low-melting glass powdery flux and then stirring it with a scraper oil to form a paste.

1. Colorant. The colorant is fired at a temperature of at least 500°C with the participation of the fluxing agent. Therefore, the colorant should not be a low-temperature decomposer, and should be a substance that does not easily undergo a chemical reaction with the fluxing agent. There are roughly the following general colorants.

Green: Chromium oxide, or copper oxide dissolved in the flux, gives a green co-solvent.
Blue: Diamond blue or dissolved in the flux into the oxide drill, cobalt blue flux.
Yellow: uranium salt, vulcanized steel, etc.
Brown: Iron oxide, manganese salt, etc.
Red: silver red.
Black: Mixed iron chromate or drilled salt and manganese salt, or yttrium oxide.
White: tin oxide, ashes, zirconia, high manganese oxide, etc.

2. Flux. The glass frit in the flux is generally lead oxide and shed acid-based glass having good water resistance at low temperatures. The raw material having the above-mentioned properties is put in an ancestor vortex, melted, and then allowed to flow into water to form glass fragments. These pieces of glass are called glass frits, which are mixed with a coloring agent in a glass frit to form a powder and then used as a printing glaze.

The most important property of the flux is the coefficient of temperature and thermal expansion melted on the printed glass. If the coefficient of expansion of the flux is not much different from that of the printed glass, and if the gap between the flux and the printed glass is large, peeling will occur after firing. The relationship between the increase and decrease of the flux composition and the semi-melting temperature and expansion coefficient is shown in Table 4-28.

Table 4-28 Relationship between increase and decrease in flux composition and semi-melting temperature and linear expansion coefficient Lead oxide glass (%) Boric acid glass (%) Semi-melting temperature (°C) Linear expansion coefficient (×10-7) State
90 10 340 116 slightly transparent yellow
80 20 400 90 yellow slightly transparent
70 30 460 75 Slightly transparent yellow
60 40 520 65 slightly transparent yellow
50 50 560 58 slightly transparent yellow
40 60 570 65 Transparent and slightly poor
30 70 560 75 Less water resistance
20 80 520 90 Less water resistant

Note: Semi-melting means that the flux particles soften as the temperature rises, and begin to produce blocking between the particles. The temperature of the whole body is in a German shape, and the actual firing temperature is higher than that.

The composition of flux for glass glazes is actually not just two components. In order to improve performance, silicon dioxide (SiO2), zinc oxide (ZnO), aluminum oxide (Al2O3), and lithium oxide (Li2O) are also added. Adding these substances will increase the coefficient of expansion. Ordinary glass (sodium glass) has a coefficient of expansion of about 95-105 x 10-7.

The following list of typical flux components is provided for reference:

19.82% SiO2 2.13% As2O3 0.46% MgO
62.10% PbO 0. 27% CaO 1. 83% K2O
10.75% B2O3 1.63% Al2O3 1.76% Na2O

When adding a coloring agent to the flux for firing, some white color should be added in order to make it vivid. This is because most of the glass is transparent, and the glass of the colored glaze that has been fired is also transparent.

When using cadmium red or yellow as a colorant, a small amount of oxidation must be added to the flux.

3. Scraper oil. Because the glass glaze is powdery, it must be mixed with a scraper oil to make it into a paste-like color glaze before it can be printed. In order to make printing easy, and to avoid the phenomenon of line disorder after printing, it is necessary to use as little as possible suet. A part of the sulphur must be evaporated before the printed glassware stove is fired, and the other part should be completely evaporated before reaching the firing temperature.

4. Glass glaze. Glaze firing temperature can be divided into high temperature, medium temperature, low temperature three. In Japan, the high temperature is 600°C, the medium temperature is 580°C, and the low temperature is 550°C. The imported glass glaze has a high temperature of 600°C, an intermediate temperature of 560°C, and a low temperature of 520°C.

Low-temperature color glaze is used for thin glassware and glass that must be fired at low temperature. Medium-temperature color glaze is widely used in large glasses, cutlery, cosmetic bottles and other general glass printing. It is more resistant than low-temperature glaze. Strong. High-temperature color glaze has stronger acid, alkali, hydrogen sulfide resistance, so it is most suitable for printing beverage bottles. In common sense, the more lead-based it is, the lower the lead content should be. However, in fact, some medium-temperature glazes have less lead than high-temperature glazes. In the increasingly serious pollution problem today, excellent quality glazes must be selected for printing.

Other glass glazes are powdery glazes, paste glazes, thermal glazes, gold (platinum) gloss glazes, lacquer gloss glazes, transparent glazes, matt glazes, and many others. When using a powdered glaze it can be turned into a paste for blown printing. The lake-like glaze will precipitate and solidify when it is stored for a long time and cannot be used. The powdery glaze can overcome this disadvantage. Since the amount and color tone of the powdery glaze can be freely adjusted, waste can be avoided, and it can be very easily modulated for a small amount of colored glaze and intermediate colors that the manufacturer does not produce.

The heating glaze is a waxy solid at room temperature, and it becomes a paste after heating to 75-85°C, and can be cured immediately at the time of printing. Even if 2-color or 3-color overprinting is performed, no drying time is required. Printing The efficiency is high and the printing surface is also very beautiful. It can print fine lines. This is because the thermal glaze is printed while heating and melting. In practice, it is placed in a separate container, melted at a temperature of 75°C, and injected into the platen, where it is heated to 80°C while printing. This kind of heating is generally used as a transformer to reduce the voltage, and then the current is passed to the stainless steel wire mesh for heating, which requires the screen plate to have good insulation properties. In addition, there are infrared heating method and hot air blowing heating method. These methods are simple to operate and can also be used for synthetic fiber screens, especially when the printing volume is small. When using this type of thermal glaze, special attention must be paid to humidity and exhaust during heating. The lacquer gloss glaze, also known as icing enamel, can produce the same effect as ice cubes on the screen. This color glaze is a fine particle, firing temperature is divided into two kinds of 540 °C and 560 °C. When using this color glaze to print patterns on the glass, after about ten minutes, the color glaze is shaken under the condition that the colored glaze is not completely dry, so that the vibrated paint can be completely dropped, leaving only the pigment of the pattern part. Then put it in the stove and make sure that you do not touch the printed part before firing it in the oven. If it touches it will cause a scar and it will not be repaired. In addition, if the firing temperature is too high, the icing body becomes a large solid. Because the temperature is too low, the pigment will fall off, so it is necessary to strengthen the temperature management.

When glass glazes are not in use, they should be kept in a closed container. It is necessary to prevent the mixing of dirt, moisture, and dirty air.

Third, glass screen printing machine

There are two domestic and imported printing presses for printing glassware. Each has its own advantages and disadvantages, and the right type can be selected according to the application.

The main machines used today are improved semi-automatic machines and fully automatic machines. The full-automatic printer has a multi-color overlay application and is equipped with an automatic stop device controlled by a photocell. Fully automatic machines are ideal for printing single-product glass products such as beverage bottles.

Semi-automatic printing presses are not as efficient as automatic machines in terms of work efficiency, but the replacement of upper editions and accessories is very simple, and its accuracy is much better than that of today's fully automatic machines, so it is still widely used today.

Manual printers vary from complex machines to simple racks. These machines, which have a variety of properties, are compatible with the user's experience and technology and can be used for exquisite printing. They are simple to operate and are used for the printing of a wide variety of glass products.