High-grade ceramic decal paper fine screen printing technology (4)

The screen printing process for ceramic decals is usually spot color printing. An exquisite picture with rich layers and full color generally requires more than 10 color blocks, which has many processes, low efficiency, and large waste. At the same time, a series of problems such as poor misregistration due to paper stretching can occur. Based on this, in the production practice, the manuscript that simulates the effect of oil painting is printed using a four-color screen printing process. The ink layer is thick, and the three-dimensional effect is strong. After firing, the ceramic vessel exhibits strong color rendering ability, bright colors, and sharpness. high.

A high-quality screen print—ceramic decals, in addition to the fidelity reproduction of the tone levels and colors on the originals, it is also required to test whether the color rendering of the pigments after high-temperature baking is satisfactory. Whether the amount of cadmium eluted meets the national standard or the US FDA standard (export) can only be regarded as a qualified print when it satisfies the above three factors at the same time.

With the rapid development of printing technology, the bottom plate making of ceramic decals replaced the traditional photoengraving process with a high-end networked color desktop system.

1. Making positive negatives

First analyze the manuscript, the principle of screen printing manuscript is not much different from the manuscript used for letterpress and lithographic printing. It is only slightly different in detail. Since the ink layer of screen printing is thick and does not show subtle levels, it is necessary to have a finer level of image. With appropriate adjustments and compensations, the general network level is increased by 1%~2% to compensate for the loss of 1%~5% high-light network level in the printing process. Letters and lines must be bolded in half. If they are too thin, the printed lines will be broken due to the loss of the fine level in the process of printing. If it is too thick, it will be blurred due to the extrusion and diffusion of the ink. Therefore, grasping the original document level as a whole and at the same time grasping the accurate judgment of the partial color cast and the percentage of the main color halftone dots and the influence on the post-processes are crucial to the quality of the printed matter.

2. Printing plate production

The bottom plate will be closely attached to the screen plate coated with the photosensitive resin. After being exposed to ultraviolet light, it will be developed with water under the automatic developing machine. After the hair dryer is dried, the dirty spots and the sand spot on the screen plate will be trimmed and dried. Printing on the machine.

(1) Four-color screen printing, due to the high precision requirements, so the performance requirements of the screen are as follows: 1 large tensile strength; 2 small elongation; 3 appropriate resilience; 4 good ink permeability; Good resistance (temperature and humidity resistance, friction resistance, aging resistance, acid and alkali resistance, organic solvents, and UV resistance).

Available 270 ~ 300T yellow polyester mesh, its good dimensional stability, suitable for high-precision screen printing. The higher the number of screen meshes, the clearer the level of prints obtained and the softer the color, but the higher the cost.

(2) In actual operation, serious loss of images is often encountered. This is mainly due to the following reasons: (1) poor positive contact with the emulsion when exposed; (2) insufficient positive blackness; (3) overexposure; 4 Insufficient development; 5 Inadequate sensitization of the emulsion; 6 Inverse emulsion side of the picture; 7 Insufficient screen pretreatment.

Sometimes the urgent need for spot color and livelihood, out of the high cost of the original version, and some manufacturers often use sulfuric acid paper instead of film, but need to shorten the exposure time, while increasing the development time, can also be more satisfied with the bottom plate.

3. print

Due to the poor transparency of ceramic pigments, there are still many insurmountable defects in terms of hue, lightness, and saturation. Therefore, most of the color light produced by the three primary colors of ceramic pigments (Y, M, and C) is the dot surface of the pigment ink. Reflected directly out of the color subtractive method.

M (Magenta) + C (Cyan) Blue (B)

M (Magenta) + Y (Yellow) Red (R)

C (Cyan) + Y (Yellow) Green (G)

The same amount of ceramic three-color ink overprinting can not obtain neutral gray, but there is a color cast, only the change of the three primary colors of the ceramic dot network synthesis ratio and ink volume can use the three primary colors to show most of the levels and colors to meet the copy requirements.

Different printing sequences, after overprinting the diffuse reflection and refraction are different, then the overprinting after the trial of the color effect is also different, according to the characteristics of the original and customer requirements, a reasonable arrangement of color order in order to obtain a rich layer, bright color ideal product .

(1) In the production, the color sequence shall be selected based on the color reproduction, and the main color of the screen shall also be considered. Since the decal paper itself cannot visually recognize the color rendering effect, only the ceramic pigment penetrates into the glaze after high-temperature baking. Layers and glazes undergo a series of changes to achieve coloration. Therefore, the screen angle is 90° in yellow, 75° in red, 15° in blue, and 45° in black. The color sequence of printing is first shallow and then deep, that is, yellow (Y), magenta (M), and then blue (C). ), and finally printed black (BK).

(2) Small areas of text or lines are printed first. Large areas of ink are printed on the back to prevent large areas from being scratched or stained.

(3) When overprinting, the network cable superimposed on the top is printed afterwards, so that the level is clear, and the sense of three-dimensionality and space are strong.

Pigments will absorb the moisture in the air in long-term storage, especially in the high humidity environment. Therefore, the ink should be dried in an oven at 120-130°C before the ink is rolled, and the ink should be hot rolled to ensure the ink. Moderate viscosity, good thixotropy. Otherwise, due to the low viscosity of the ink, the ink is pulled out along the direction of the force of the squeegee, so that the printed pattern is roughened, the dot is enlarged, and the image clarity is reduced.

The ways to improve are: 1 increase the ink viscosity; 2 reduce the printing pressure; 3 replace the harder squeegee; 4 increase the squeegee angle.

(4) Conversely, if the viscosity of the ink is too high, the performance of the ink through the mesh is poor, the obtained ink layer is thin, the ink color is light, and the surface of the printed material may also have a moire or orange peel, affecting the surface of the ink film. Gloss, the improvement approach is: 1 add solvent, reduce viscosity; 2 increase the printing pressure; 3 properly reduce the screen mesh; 4 use a softer scraper;

During printing, the thickness of the ink film is controlled at 15 to 25 μm, generally about 20 μm. If the ink layer is too thin, the color is not full; if it is too thick, it will cause a block or popping.

After the paper print is qualified, the process can be processed. As a ceramic decal, only after the high-temperature baking, the coloring effect is satisfactory, no fading, no popping, no pinholes, high gloss, lead and cadmium elution in line with international or U.S. FDA standards can be unpacked. If not, think of a remedy. If the individual fades, the temperature may be high, the temperature test burns still fade, and the pigments need to be changed to make up the printing; the lead and cadmium exceeding the standard may print a layer of cover oil on the paper, which can improve the gloss of the screen and reduce lead. The amount of cadmium dissolved is suitable for export requirements and is beneficial to people's health.

Source: Coinprint