The importance of ceramic decal printing
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There are many types of decal paper printing, and ceramic decal printing is an important part of decal printing. Ceramic decal paper printing can be divided into large-film glaze paper (standard four-open specification) printing and small-film glaze flower printing according to the order of decal and glazing and the sintering method. Compared with small-film underglaze printing, although the printing quality of large-film underglaze printing is not as good as that of small-film underglaze printing, its price is relatively low, and the overall printing effect is also ideal, while the small-film glaze is suitable. Although the quality of printing is better than that of large-film glaze, the price is higher. Therefore, from the current domestic ceramic decal paper industry, most manufacturers use large-film glaze paper. Early ceramic decal printing mainly consisted of both lithographic and screen printing. However, with the continuous development of screen printing technology and the low production cost of screen printing, the screen can be reused without being restricted by the size and shape of the substrate. The ink layer is thick (up to 2 to 4 microns), the color is bright, the reproducibility is good, and the stereoscopic effect is fully reflected. The screen printing ceramic decal paper technology has become the leading printing technology in this field. Nowadays, it has basically replaced all the printing technology of lithographic ceramic decals.
First, the principle and process of ceramic decal paper screen printing
Ceramic decal paper screen printing is a classification of screen printing. Its basic principle is: after the plate making, the pattern part on the screen is permeable, the non-pattern part is non-permeable, and it is attached to the screen cloth. On the upper side, the screen is in contact with the paper when printing, and the ink is immediately printed on the paper through the mesh of the pattern portion to complete a color printing. Ceramic applique screen printing differs from other types of screen printing and color packaging printing in the principle of color stacking. Generally, color printing is produced by overprinting of three primary colors, and the ceramic decal special pigment is an oily powdery organic pigment composed of metal oxide, which has the characteristics of dullness after printing, color change without discoloration, and discoloration after grilling. Therefore, the ceramic decal paper screen printing uses a step printing method. Generally speaking, it is necessary to make a plurality of pieces or even more than ten screen printing plates according to the original requirements in order to meet the original requirements.
The process of ceramic decal paper screen printing is generally: firstly according to the user's manuscript or self-design, the photographic color separation, according to the characteristics of the ceramic pigment color does not change color, in general, the main flower red, blue, green to be separated, red It should be divided into three times (light, medium and deep), blue and green divided into two times (light, deep), and finally black or gray lines (be now designed and produced using the desktop system, the quality and progress are greatly improved) . After the good color is checked and the requirements are met, the positive small piece (single spell) is made, and the small version is used for manual proofing. After the barbecue, the sample is adjusted in various aspects until it meets the requirements, and the porcelain factory is tested, and the user approves and orders. After the machine is mass-produced.
Second, the technical problems that should be paid attention to in each process
1. Screening and imposition
The dot of the ceramic applique color screen printing is generally 1/3 of the minimum screened line/mesh ratio during printing. In addition, the particle thickness of the ceramic decal ink should be fully considered, whether the mesh is smooth, and the generation of the moiré is controlled. A variety of comprehensive factors. For the phenomenon of moiré generated at the dot of color printing, it can generally be controlled and eliminated by changing the mesh number, screen angle or stretch angle, dot type and dot arrangement.
The imposition can be carried out according to the user's requirements and the standard of the backing paper, but the layout must meet the national standard, that is, not less than 43 cm × 34 cm. The hand-stamping is simple and the color is less. However, due to the influence of technology and other factors, the accuracy of overprinting is often not high enough, especially in the case of more colors, sometimes even less than multi-color overprinting. The quality requirements, and the ceramic flower paper color is generally more than 5 colors, and even more than 10 colors. Therefore, it is best to use the imported continuous drying machine for continuous drying, so as to ensure the overprint quality requirements.
2. Plate making
Plate making includes multiple processes such as printing, development, revision, and film removal. Each process has its technical requirements and skills. The first is to make a screen printing plate. The diazo photosensitive adhesive can be used. The blade of the rubberizing blade has a 45 degree angle. The smaller the blade angle, the thinner the photosensitive liquid left on the screen. Apply the photoresist, apply on both sides and pay attention to the coating. The coated screen plate is dried at an appropriate temperature, and the dried screen can be delivered to the plate.
(1) Printing plate. Ceramic glaze flower paper screen printing generally uses solvent-resistant screen printing, oily photosensitive gel or capillary film, or water-oil two-color photosensitive adhesive plate, and the glaze flower paper printing screen is water-resistant screen, water sexy Light glue or water oil two sexy light glue plate. Before printing, you should first wash the plate with detergent or washing powder, remove the dust, fingerprint and residual glue on the plate. Finally, rinse it with a high-pressure water gun to apply the photoresist.
Photosensitive adhesives should use special denitrifying photoresist for ceramic decals. One or two components may be used as needed. The one-component photoresist has been prepared with sensitizer and glue and can be used directly. The two-component photosensitive adhesive is separately packaged by the sensitizer and the glue, and is prepared by the user. The method is as follows: 10 g of the sensitizer is fully dissolved with 50 ml of distilled water or water, added to 950 g of the glue, stirred evenly and then allowed to stand for air bubbles. Can disappear after use, can not use metal products to stir, so as not to affect the stability, the matching photosensitive glue should be stored at low temperature (not less than 5 degrees Celsius) in the dark. When applying the photoresist, avoid direct sunlight. Use a special glue applicator to apply the photoresist to the mesh at about 45 degrees Celsius. Generally, the front and back sides are coated twice, and can be coated by wet or wet pressure. Then it is put into the screen oven for drying (currently, a fully automatic photosensitive glue coating machine has been produced abroad, and the coating quality is quite satisfactory). The coating quality requires uniform coating, uniform service, and uniform thickness. The coated screen should be stored away from light.
The most important thing is to master the proper exposure time. According to the practical experience, the general exposure time is controlled at 3 to 7 minutes. During the specific operation, you can try some samples first, adjust the exposure time according to the actual situation, and get the best. The exposure data of the printing effect is printed in large quantities. In addition, we must master the light source and the distance between the lamps. The light source can generally be used with 10 to 15 40-watt fluorescent lamps. The distance between the lamps is 25-30 cm. It can also be washed with water using a screen source exposed by a point source. . When printing the plate, you should also pay attention to the "Ten" rule line when you design the color of the design. When you print the plate, you should use the rule line as the benchmark for the screen printing.
(2) Development and scouring. After developing the water, put the dried screen into the clear water, shake for several tens of seconds, check whether the pattern is visible, and then use a high-pressure water gun to flush the net. When the net is not washed, the photosensitive part is washed away by water and the photosensitive part is washed away. (Non-pattern part) is retained by photohardening, which is a screen version. When the net is flushed, the water pressure of the water gun should be consistent (about 4 MPa) to master the time of the net and the distance of the net. After flushing, rinse off the residual glue on the plate with clean water, and carefully check the transparency of the screen pattern on the light. If there is any problem, you should punch it for this part.
After checking the qualified screen, immediately absorb the residual moisture on the screen with a water-absorbent paper or sponge to avoid forming a watermark, and then put it into the screen oven for drying. The oven temperature is controlled at 30 to 45 degrees Celsius, and the temperature is too high to cause deformation of the screen.
(3) Revision. In the printing and development, due to the influence of materials, technology, environment and other factors, some of the produced screens are defective and cannot fully meet the quality requirements. If you encounter minor common defects, you can make repairs to make up for the defects. When revising the plate, you can put the screen on the revision table. First check the deformation degree of the screen with film. If the deformation is too large, it should not be put into use, and find the reason and re-dry. The masking glue can be added with a small amount of white latex (speeding up the drying speed) or the sealing gel with the original photosensitive glue. Carefully check the blisters and the parts of the non-patterned part, and finally use the brush to evenly apply the photosensitive glue on the non-pattern part. It is placed in an oven for low-temperature drying (if the screen is not urgently used, it is better to dry naturally), and finally, the second exposure can be performed according to the amount of printing, and the printing durability of the screen is increased. The finished screen printing plate can be delivered to the printing process for decal screen printing.
(4) Stripping: Stripping is a major advantage of screen printing. As long as the screen cloth is not damaged, the original film can be removed by using the stripping solution. After the coating is applied, the other screens can be dried. If used properly, a screen can be reused dozens of times.
3. Screen selection and stretching
The ceramic decal net generally adopts polyester or other color polyester mesh (or nylon mesh). The common product mesh is controlled by 180 to 300 mesh (for example, 250 mesh), and the flower surface is 220 to 250 mesh, which can produce relief effect. Small text can be used 340 ~ 400 mesh, ordinary products can be achieved as long as the use of domestically produced, so the price will be relatively low, but for the printing of fine products, in order to ensure quality, you can choose to import high mesh (300 mesh or more) Wire mesh, but the price is high. The frame is preferably made of aluminum alloy, which is not easily deformed, light and durable. Stretching the net is to cut the mesh according to the size of the frame and glue the mesh to the frame. Before the stretcher, the four sides of the frame should be flattened with a file to increase the adhesion between the mesh and the frame. The stretcher should use a pneumatic stretcher or a mechanical (adhesive) stretcher. When stretching the net, pay attention to the fact that the tension around the belt is basically the same, the elasticity is uniform, and the conditional tension meter can be used for testing. The stretch net glue can be selected with DS series adhesive mesh glue or glued firmly. The air pressure of the stretch net is kept at 0.4-0.5 MPa. After the stretched mesh glue is dried, the plate can be taken, and the excess mesh cloth around the frame is bonded to the frame. Increase the durability of the mesh.
4. Film on the bottom paper
The film on the bottom paper can be divided into two processes of filming and filming.
(1) Film distribution. The ratio of the film is generally: polyvinyl butyral resin: methanol (ethanol) = 1:5. For example, when the membrane is used, about 16 to 18 grams of butyral can be used. The methanol (ethanol) is firstly pumped into the reaction pot, and the butyral is uniformly introduced while stirring, and the heating switch is turned on (the temperature is controlled at 50 to 60). Stirring for 3 hours, after the butyral is completely dissolved, it can be discharged for later use. The quality of the film must be completely melted, no block, no impurities, and slightly concentrated. In the film, methanol can be added appropriately. Ethanol) is adjusted for concentration.
(2) Upper film. As the paper for the backing paper, use the decal-dedicated base paper (wood pulp paper). Before use, use a paper cutter to flatten the four sides of the paper to ensure that the specifications meet the requirements. The upper film is generally a special film machine (the principle is similar to that of the glazing machine). Adjust the gap between the feed roller and the printing roller to apply the film evenly and evenly to the base paper. Generally, it is required to apply the film twice (do not need to turn the head) and then go to the second time after the first dry, but each time you need to open the paper (can be cooled by the fan), the thickness of the film is 0.01±0.001 mm, which can be slightly thicker. It can be adjusted without the use of a micrometer.
The film drying tunnel should be kept at 70~80 degrees Celsius. If the temperature is too high, the film will not be bright, and the bottom paper will be burnt. If it is too low, it will foam and dry, and it will cause adhesion failure. All in all, the film layer needs to be bright, the thickness is up to standard, uniform, and there is no residual film on the edge, no adhesion, no damage. The dried bottom paper can be stacked neatly after the number of shuttles to prevent dust. After the film is good, it should be stored for a period of time to make it flat and set before use. According to the practice, it is generally better to master it in 15~20 days. Since the backing paper is composed of paper, plastic film and butyral film, the amount of deformation of the three materials is different after hot air drying, so the pre-printing process of the backing paper must be performed. Before the official printing, the bottom paper is not loaded with the printing plate, and the squeegee or manual conveying method is used to enter the oven for shaping, that is, the empty car, but at this time, the temperature of the oven must be controlled and officially printed. The temperature is basically the same. By shaping, the deformation of the backing paper in the future multi-color printing can be minimized to ensure the overprint quality of the product.
5. Rolling ink
Ink rolling is to add the baked pigment to the binder in proportion to heat, and the mixture is uniformly stirred and then rolled by a three-roll mill. Generally, each color is rolled 2 to 3 times, the first rough rolling, and the second fine rolling (adjusting the roller gap). The rolled pigment should be rolled and used now. The remaining pigment after printing can not be discarded. It can be rolled. Screen printing pigments dry quickly without adding any desiccant. Ceramic decals are available in lithographic and screen printing pigments. Currently, there are a variety of pigments, each with its own characteristics. For example, four-color pigment: the same principle as color printing, good reductivity, quality has reached international level; high-temperature fast-burning pigment: barbecue temperature 1006 ~ 1200 ° C, 3 minutes baked; lead-free cadmium-free pigment: pigment does not contain lead, Cadmium, this series of pigments is powdered before unmixed, 90% of the particle size is greater than 5 microns. There are more than 10 basic colors, which can basically meet the color requirements of various flower surfaces. With baking pigments: according to the pigment ratio and the amount of printing determined by the proofing, the pigments should be put into the ratio of 90-100 degrees Celsius. Barbecue in the oven for half an hour, do not allow moisture in the pigment (not more than 0.5%), otherwise it will cause the product to burst, resulting in waste. Due to the different properties of different pigments (high temperature resistance), the range of use is also different. Therefore, it is necessary to select suitable screen printing pigments for different equipment and printing objects. In addition, it is necessary to pay special attention to the fact that due to the poor miscibility of the screen printing pigment and the porcelain ink, improper mixing, chemical reaction occurs during sintering, and the color is deteriorated or even bursting, so the screen printing pigment with good mutual compatibility should be selected. And porcelain ink, it is best to use the same manufacturer and the same brand of products. For lithographic, screen printing, high temperature, low temperature and screen printing pigments and porcelain inks produced by different manufacturers and different brands, it is not allowed to mix and use at will, so as not to affect the quality.
6. Printing
Screen printing equipment should use a roller flat screen printer. The dryer uses a paper feed hot air dryer. There are also related auxiliary equipment. Such as grinding ink knife machine, vertical drying rack, and so on. In addition, because different ceramic decorative processes use different ceramic decals, the different ceramic decals have different printing processes and materials such as reticulated plates and inks used. Therefore, before printing ceramic decals, it is necessary to first understand the specific ceramic decoration process and the printing process of the decals and the use of materials, so as to avoid unnecessary rework and waste, quality and efficiency.
The glaze decal paper printing generally uses a high-temperature solvent ink, and its main component is a binder (ie, a film-forming material, mainly using a solid resin and an organic solvent for dissolving the resin), and a coloring agent (which determines the color hue of the ceramic after firing). , mainly a series of metal oxides), additives (the role is to increase the brightness of the pigment, so that the silk screen porcelain ink is baked with the ceramic glaze, generally lead glass, low melting point boron, etc.). The ink printed on the underglaze decal is a high-temperature aqueous ink, that is, a water-soluble material is used as a binder. Screen printing ceramic decals generally require a temperature of 22 to 26 ° C for the environment in the workplace, and the relative humidity is maintained at 65% to 70%; For the decals used for enamel color printing, before the screen printing, the paper should be placed in the screen printing place for a period of time (usually several days) according to the weather and other environmental factors, so that the expansion of the decal paper is stable to facilitate printing. Registration. For the colored decals, each color should be dried for a certain period of time, check whether it is dry, and wait until it is dry to restore the water content of the paper to the next color, such as drying after drying. If it is not transparent or takes a long time to dry, it is necessary to find the cause and solve it. If you encounter a large area of printed color that is not transparent, you need to erect the paper to dry it. In short, you must dry it before you can print the next color. In addition, due to the large color sequence of screen printing porcelain paper, the machine equipment should be carefully checked before starting the machine. Do the fueling and maintenance work, check whether all the plates are deformed, whether the overprinting is accurate, and whether the angle of the doctor blade is reasonable and flat. . In the production process, we will achieve three diligences (diligence, diligent ink, diligent grinding and squeegee) to keep the pigments with certain fluidity. The whole batch of products has the same ink color, uniform thickness, clear layers and accurate overprinting. In the process of screen printing, the oven temperature should generally be maintained between 30 and 40 degrees Celsius, or be flexibly controlled according to the local temperature changes. The principle of keeping the product out of the oven is to keep the whole batch of products in the same temperature during the printing process. Avoid multiple fluctuations in temperature and cause multiple deformations of the paper. In addition, in the screen printing, the angle of the squeegee, the flatness, the mesh distance, and the height of the ink return knives have a great relationship with the product quality. The angle of the squeegee (15 to 30 degrees) should be adjusted according to product requirements. Generally, the same angle is applied to the same batch of products to avoid unevenness of the ink layer caused by adjusting the angle during the printing process. The working surface of the squeegee must be carefully leveled and kept at 90 degrees. The mesh distance can be adjusted from 4 to 10 mm, preferably from 5 to 7 mm. It is better to apply the ink to the screen evenly when the ink is returned to the ink. If the ink is too high, the ink will be uneven, and if it is too low, the screen will be scratched.
7. Test burn
Before the proofing and mass production is completed, the test piece should be taken for a thousandths of the test. First, use a blade to gently draw down the pattern of the test burn (note that no force is available to avoid scratching the base film), and apply the pattern on the porcelain with methanol (ethanol) to water (1:3), requiring no wrinkles or no wraps. Blisters, bubbles, and then use cotton to lightly wipe the pattern, remove excess water, air bubbles, make the flower paper and porcelain compact, and put it into the resistance furnace to heat up.
According to the selected pigment (high temperature, low temperature, etc.), the test firing temperature is set. First, the furnace door is not closed. When the temperature rises to about 200 degrees Celsius, the base film is turned black and then closed (base film carbonization). When the temperature rises to the set temperature and the power is automatically turned off, the furnace door is not opened, the heat is kept for about 15 minutes, and finally the furnace door is opened. When the furnace temperature drops to room temperature in about 2 hours, the sample can be taken out. If it meets the requirements, you can proceed to the next process.
8. Uncover film and inspection
Film uncovering and inspection can be carried out simultaneously. When uncovering the film, first use a knife to pick out the film opening (the whistle should be picked up instead of the mouth), then take the film with a smooth piece of bamboo, and use a copy of each paper pad as a pad to avoid Sticky. The liner and the film are required to be flat and wrinkle-free, stacked neatly, and the printed cross paper is basically aligned. For the inspection at the time of uncovering the film, if the whole unqualified product is rejected, if a flower fails in a sheet, the red pen is used to mark the lining paper, and the number of sheets is folded according to the actual number of flowers. If it is not one, it will be supplemented by the whole sheet. The exposed film is embossed with 80 grams of kraft paper per 100 sheets, rolled into a roll, and a piece of thick-lining paper (also available in a paper tube or plastic bag) is affixed with a certificate. The certificate is for every ten volumes. The box is shipped from the factory. In addition, the amount of lead and cadmium should be checked to ensure that the product meets the requirements of hygiene and environmental protection. According to international standards, the amount of lead dissolved out is 7×10-6 or less, and the cadmium dissolution is less than 0.5×10-6. For the inspection of lead and cadmium, it is generally required to send. Go to a special inspection agency.
Finally, use a single-sided scraper to clear the film, remove the residual film, dust, oil traces on the base film, pay attention to not scratch the bottom paper, in order to repeat the use of the paper.