Introduction:silkscreen printinginCosmetic PackagingVery common in manufacturing, screen printing is a relatively simple process thatHowever, the entire screen printing process there are many factors affecting the variation of product quality, directly affecting the quality of the final product, such as equipment, printing plates, inks, post-processing, as well as operating skills, such as inappropriate will cause printing failures, and mostly due to a variety of factors cross-influence the results.This article shares the quality control of silkscreen printing for the reference of friends:

Screen printing process is the ink through some of the mesh of the screen plate after the leakage of printing on the substrate, the rest of the mesh of the screen plate is blocked, the ink can not come through. Printing ink poured on the screen, in the absence of external force, the ink will not leak through the mesh to the substrate, and when the squeegee to a certain pressure and tilt angle of the ink when scraping, it will be transferred to the substrate through the screen below so as to realize the image of the reproduction.

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01Pre-Press Selection

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Generally speaking, most of the screen frames used for screen printing and packaging are aluminum alloy screen frames, which are praised by users for their resistance to stretching, strength, good quality, light weight and ease of use. The size and material of the frame play an important role in the quality of the screen.

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Wire mesh is divided into polyester wire mesh, nylon wire mesh and stainless steel wire mesh, which is also divided into multi-filament mesh and monofilament mesh. Depending on the precision of the print pattern, the quality of the print and the customer's requirements, usually, fine products should use monofilament mesh.

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Aluminum mesh frames are usually tautened using a pneumatic tautening machine to ensure that the tension of the stencil is maintained. In order to achieve the best printing quality, the tension of the screen must be uniform. If the tension is too high, it will cause damage to the screen, which is not resistant to printing; if the tension is too low, it will lead to low printing quality and inaccurate overprinting. The tension of the screen depends on the screen printing pressure, printing accuracy and screen stretch resistance.

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1) first taut screen should be degreased and roughened to enhance the affinity of the photopolymer and screen.

2) in order to improve the quality of the screen plate of the solarization, screen printing required for the solarization of the film requirements for the Yangtu positive characters, photographic materials depending on the substrate to choose, the thickness of the photographic adhesive depending on the requirements of the printed matter.

3) Exposure time: exposure time depends on the quality of the film, screen mesh, photopolymer thickness and the power of the exposure light source. The correct exposure time can improve the quality of the screen plate tanning.

4) overhaul and secondary exposure: the first exposure after the drying of the screen, the need to check the quality of the screen tanning and do trimming, to determine the correctness of the second exposure to enhance the screen printing resistance.

5) Substrate: According to the product and customer requirements to determine the required substrate material, if the substrate provided by the customer, to check the substrate material, color, thickness uniformity, surface texture, etc., in order to select the appropriate printing ink according to its different requirements.

6) ink: the physical properties of printing ink mainly includes density, fineness, fluidity and light resistance, etc., they have a great impact on the quality of printed products and special effects. If the density is moderate, the fineness meets the requirements, the deployment of the ink fluidity is ideal, good light resistance, printed products to achieve the desired effect. Ink is divided into solvent-based ink (natural drying) and UV light-curing ink, according to the requirements of the equipment and printing methods, select the matching ink.

02 Printing controls the variables

Printing is the last process. During the printing process, if it is found that the printing results do not meet the requirements, adjustments can be made to remedy the problems that have arisen. Obviously, if you use a defective printing plate, squeegee or other equipment, certainly not achieve the desired printing results. The end of printing, usually using drying equipment for drying, screen printing commonly used two kinds of dryers, one is the use of IR heat source drying; the other is the use of UV light source curing. On the printing and drying part, there are eight main variables.

1) Mesh spacing

Non-contact printing is a prominent feature of screen printing, that is, the screen printing plate and the substrate above to maintain a small distance, this distance is called net distance. Screen printing relies on the pressure of the squeegee to make the printing plate and the substrate contact, complete the transfer of graphics. Mesh distance should be maintained properly, otherwise, the printing effect is not good.

2) Stripping distance (off-grid distance)

The stripping distance is the distance between the screen plate and the substrate after the squeegee has scraped the ink across an area of the plate image. Ideally the stripping distance does not need to be adjusted, and the screen distance can be utilized so that the plate and the substrate can be easily separated. However, if the ink is too thick or printing a large area of the field, etc., the plate and the substrate may not be quickly separated, resulting in blurred images. In these cases, it is necessary to fine-tune the distance from the screen, but the amount of adjustment must not be too large, otherwise it will cause image distortion.

3) Flatness of the printing table

The flatness of the printing plate table is important for consistent print quality. Any dips and bumps in the table surface will have a negative effect on the print quality.

4) Parallelism of the printing table and stencil

The distance between the stencil and the entire surface of the printing plate table must be consistent. When measuring the mesh distance before printing, be sure to measure at multiple points.

5) Color Sequence

In multicolor printing, color sequence is a key variable. The order in which an image is printed has a significant impact on the quality of the final print. The color sequence of printing depends on the accuracy of the print, the material of the substrate and the saturation of the pattern.

6) Curing temperature

For solvent-based inks or water-based inks, increasing the drying temperature reduces the drying time. However, if the temperature is set too high, the dimensional stability of the substrate will be affected.

7) UV light intensity

UV ink to use UV light drying. UV light intensity is high, the curing speed is fast, low intensity, the curing speed is slow. Thus, to choose the appropriate light intensity, the spectral distribution of the UV light source should be used with the characteristics of UV ink corresponds to, otherwise, the drying time is longer, the ink layer will not be completely dry.

8) Curing time

The curing speed of the ink affects the quality of the ink after curing, and must be adjusted according to the curing temperature and the light intensity of the UV lamp in order to fully cure the ink film. The curing quality of the finished printed product depends on the curing speed, curing temperature and power regulation of the UV lamp.

03 Environment

The working environment of screen printing has a direct impact on the printing results, especially high-quality prints must be in a stable temperature and humidity environment to complete the printing and drying. If constant temperature and humidity can not be guaranteed, it is necessary to take the approach of monitoring environmental changes and compensation. Variable factors affecting the printing environment are the following two.

1) Airborne pollutants

Screen printing shops have a variety of contaminants, such as dust and lint, which all have an impact on print quality. A clean environment eliminates these problems

2) Ambient temperature and humidity

In the plate making workshop and printing workshop, any change in temperature and humidity will have an impact on the printing quality. If constant temperature and humidity cannot be achieved, other variables have to be flexibly adjusted according to changes in temperature and humidity, which is cumbersome but saves money.

In addition to effectively control and deal with the many factors affecting the quality of screen printing described in this paper, cultivate high-quality operators, the establishment of perfect process management procedures, quantitative control of the variables in order to effectively improve the quality of prints, and bring economic benefits to the enterprise.