Section V Glass Printing - 2

(3) Shaped glassware Screen-printing decals for printing daily-use glassware, such as tableware, tea sets, coffee sets, cups, ashtrays, fruit plates, vases, etc., belong to special-shaped vessels, and common printing equipment and techniques cannot be used. The decorative printing methods of this type often include air gun spray, direct screen printing, manual drawing, transfer printing decals and the like. Among them, the screen-printing decal paper method has been recognized by most manufacturers because of its advantages such as large printing format, high production efficiency, fine pattern, good decorative effect, and wide adaptability to shaped containers.
1. Ordinary daily glassware decals. Ordinary daily glassware decals are generally used for molding glassware decoration. For this vessel, it takes two stages of molding process and applique firing process. Only after the color is burned can the decorative effect of the pattern be achieved.
Since the flower paper is attached to the surface of the molded glassware, in order to prevent deformation of the utensils during the coloring of the grill, the coloring temperature of the pigment used in the printed tissue paper cannot be higher than the softening temperature of the glassware, and is generally 550-600°C. The requirements of this temperature range for different types of glass are as low as 480°C. When printing decals, special glass pigments or low-temperature series ceramic pigments that meet the glass temperature range should be selected.
The glassware has a transparent texture, and when the decal paper printing ink film is thin, the color effect is poor. The ink layer is thick and real-time, colorful, eye-catching and bright. Glass decals produced with the screen printing process have this feature. Thickness of the screen printing ink layer is relatively large, and pigment components that play a role in color development are correspondingly large; in the screen printing ink preparation, the proportion of the varnish is small and the proportion of the pigment is large. In addition, the adhesion of the screen printing pigment is good, and the glass body formed after the color burning is formed. The structure is tight, so the screen printed decals are bright and shiny.
The choice of silk screen depends on the decorative requirements of the pattern and the type of pigment used. Under normal circumstances, on-site flat-coated block surface printing, screen mesh is about 180-270 mesh; halftone dot printing selects 270-350 mesh mesh; coarse mesh halftone available 270 mesh mesh, thin mesh halftone Use 350 mesh or more. Coarse-grained pigments may have a lower mesh size. In the case of pigments consisting of selenium sulfide and cadmium sulphide, sulfur is easily sublimed in high-temperature environments where color burns, and when selenium sulfide and cadmium sulfide are low in sulfur content, the color is dark and pale, and coarse mesh screen printing is used. Print ink film thickness to ensure bright and bright colors.
Ordinary daily glassware decals production process shown in Figure 3-49.
Ink preparation
Manuscript design → plate making → copy printing → printing → printing → inspection → packaging into storage
Paper Processing Figure 3-49 Production Flow Chart of Ordinary Daily-use Glassware Decal Sheets The general-purpose glassware decals of daily-use glassware are first decaled and then baked into the oven.
Take polyvinyl butyral film decals as an example: first, cut off the patterns on the decals and cut them out. Use a paste on the row of brushes to evenly brush on the parts of the glassware to be decorated. After the film is slightly soft, use a squeegee to gently squeegee the stencil sheet to remove the excess paste and bubbles beneath the stencil. Paste liquid alcohol and clear water. Jiuqing content is 20%-30% in summer and 30%-40% in winter. After the glassware for daily use is decaled, it can be boxed into the oven and baked at the required temperature. During the preheating carbonization stage during baking, the temperature should not be increased too quickly.
2. Special daily-use glassware decals The special daily-use glassware decals are used for unformed flat glass sheets. The color-burning process of pattern patterns is synchronized with the molding process of the glassware, and molding and color-burning are completed once. When the glass is formed into a certain shape of a vessel from a plate shape, which is softened at a high temperature and softened into the mold, the coloring of the decorative pattern of the vessel is completed. Different from common glassware decals, the color firing temperature of the pigment should be consistent with the softening temperature of the glass. Some dishes, fruit plates, ashtrays, etc. are decorated in this way, with a temperature of 650-700°C. At the same time, in the screen printing pigments currently used in the production of ceramic decals, with the exception of a few varieties with a narrow firing temperature range and a high temperature requirement, most ceramic screen printing pigments can also be used for the production of special glassware decals. For a small number of ceramic pigments with high temperature requirements, as long as the pigment in the pigment composition is modified, the color firing temperature is lowered to suit the molding conditions of glassware, and it can also be used for decals production of special glassware. This will increase the production area for ceramic decals manufacturers and increase the product variety.
Special glassware decals are also produced using a screen printing process. The production process of floral paper is the same as that of ordinary daily-use glassware decals.
The process of applique, molding and coloring of special daily-use glassware decals is as follows:
1 According to the requirements of the shape of the vessel, it is cut into circular or elliptical, round and other shapes of flat glass, and edging. As shown in Figure 3-50.
2 Place the cut single decal paper film on top, apply it on the flat glass sheet with adhesive solution, scrape flat, and drain the excess adhesive liquid and the gas coating under the paper. As shown in Figure 3-51.
3 After the decaled flat glass has been dried, the paper-coated side faces down and faces the mold and is placed flat on the mold. The mold has a stainless steel mold or a cast iron mold. Since the pattern faces the mold, after the molding, the paper is decorated on the bottom of the vessel. The pattern of the flower paper is reflected in our eyes through the glass. It appears particularly bright and bright, and the decorative effect is unique.
4 Place the plate glass mold into the furnace for baking according to temperature requirements.
There is also a roasting method is: the mold is first sent to the furnace heated to the required temperature, with the suction nozzle with a decal of the plate glass is placed on the hot mold, placed 6-7min, the plate glass is heated soften the recessed Mold. As shown in Figure 3-52 (a), (b), (c). In order to prevent the glass from bursting on the hot mold, the edge of the mold is slightly larger than the edge of the glass, and only the edge of the glass is supported on the mold, as shown in Figure 3-53(a). If the curvature of the vessel is large, it can be divided into two shapes, as shown in Figure 3-53(b). When the size of the vessel is too large, press molding with the male mold can be performed, as shown in Figure 3-53(c). In order to avoid indentation on the glassware, a glass fiber cloth coated with chalk powder is put on the punch, and the glass sheet on the hot mold starts to press immediately when it starts to bend and deform.
The size and thickness of the flat glass sheet and the heat capacity of the mold affect the length of the vessel molding time. The larger the area of ​​the glass sheet, the thinner, the easier it will bend and sink into the mold; the thicker the glass sheet, the smaller the area, the deeper the curvature of the vessel, the higher the required molding temperature, or the longer the molding time some.
After the special glassware decal paper is formed and burned, the decorative pattern is prone to defects such as air bubbles, pinholes, linear cracks, and popping flowers. There are a few issues to be aware of in the production of paper and the formation of color burning.
1 The same part of the decorative pattern of flower paper should not overlap too much. In the formation of color burning, pattern paper ink layer is located between the glass and the mold. During molding, the glass gradually softens and sticks to the mold. Too much overlap, the ink layer will be too thick. It is difficult for the carbonized gas such as the oil in the ink layer to be completely discharged from the gap between the glass and the mold in time. Decorative patterns appear bubbles, cracks, popping and other phenomena;
2 The temperature rise during baking cannot be too fast. If the temperature rises too fast, the pigment will begin to melt before it fully burns, carbonizes, and volatilizes in the paper-cut film and varnish, and the carbon will be entrapped in the paint to form bubbles. The bubbles encountered and rubbed, and the paint was dropped, exposing the glass, and a hole, pinhole, etc. appeared on both sides of the decorative pattern.
3 Flower pattern is decorated at the bottom of the glassware. After the pattern is burned, the pattern pigments are required to have good friction resistance so as to prevent the pattern from falling off due to friction during use.

Fifth, sintering
Where glass pigment inks or other sintering inks are used to print glass products, post-processing—sintering work—is required after printing. For the automatic curved screen printing machine, an automatic output device should be set up after printing. The printing is transferred to a sintering furnace for sintering to form a printing-sintering automatic production line.
(1) Sintering furnace (1) The heat source used in the heat source sintering furnace is mainly urban gas or liquefied petroleum gas. In some special occasions, the heat source is used.
In the past, diesel or kerosene was used as a heat source. Although the fuel consumption cost was low, considering the pollution of the product and the structure of the sintering furnace, the comprehensive cost would not be very low. Therefore, such a heat source is rarely used.
(2) The composition of the sintering furnace The size of the sintering furnace is the main factor that determines the output. Under normal circumstances, the size of the sintering furnace, that is, the capacity should be greater than the printing capacity of the printing press. Of course, the production capacity of the sintering furnace is related to the shape of the glass product, the ink layer thickness, and the external dimensions. The structure of the sintering furnace is shown in Figure 3-54.
Glass sintering furnace is generally composed of heat source, gas control valve, heating sintering chamber, automatic temperature control device and product conveyor belt, etc. The temperature of the sintering chamber is detected by the temperature detection device (sensor), and then the automatic temperature control device Issue a temperature adjustment command to adjust the valve of the gas control valve to output different gas volumes.
(b) temperature - time curve In the sintering process, if the choice of glass pigment ink does not meet the basic requirements of glass substrates, it will cause the failure of the sintering process, so the printing ink should be properly selected. Similarly, if the selected printing ink is completely correct and reasonable, if it cannot be properly sintered according to the sintering temperature-time curve, the printing and sintering process will also fail. Therefore, a reasonable control of the temperature-time curve is the key to ensuring the quality of glass products in the sintering process.
The so-called temperature-time curve refers to the sintering furnace temperature in the sintering furnace with the curve of the relationship between the time, that is, the heating furnace and cooling rate control procedures.
When the sintering temperature reaches the softening temperature (500°C) of the glass pigment, the temperature-time curve in the sintering furnace is shown in Figure 3-55.
Practice shows that if the sintering temperature-time curve is controlled according to the curve 1 in the figure, that is, the sintering temperature is about 550° C. (above the glass softening temperature) in 10 min, and then the rapid cooling, the desired effect can be obtained. The initial sintering causes the glass surface layer to soften quickly. As a result, a thin intermediate glass layer is formed between the glass and the glass powder in the vicinity of the contact surface between the glass and the ink layer, so that the ink adheres firmly to the glass surface, as shown in Figure 3-56 As shown.
If the sintering temperature-time curve is controlled according to the curve 2 in Figure 3-55, the sintering temperature is about 550°C in 10 minutes, and then slow cooling is performed at room temperature. This increases the high-temperature sintering time and increases the surface softening layer of the glass substrate. Thickness will not only cause deformation of glass products, reduce the value of commodities, but also cause the stress concentration due to the difference in the linear expansion coefficient of the components of the middle glass layer. This is the main cause of the phenomenon of ink layer peeling caused by excessive sintering. .
If the sintering temperature-time curve is controlled according to the curve 3 in Figure 3-55, the sintering temperature is too low to reach the glass softening temperature, and the heating rate is too slow.