# The hottest halftone screen printing technology

2022-10-20
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Halftone silk printing technology

template control is particularly important when printing with three primary colors. Because the inks have a certain degree of transparency (especially UV inks), coupled with the template deviation, the thickness of the printing ink film changes, resulting in a significant shift in the printing color

this color shift can be described by the absorption of light (i.e. optical density) by the ink film. The optical density can be obtained by measuring the printing color with a densimeter. The measurement results are displayed in logarithmic form. It can also be said that this number represents the ratio of the light absorbed by the "absolute" white material to the light absorbed by the tested ink

"normal ink volume" is a term used to describe the correct optical density printed with a specific ink and substrate. The printing materials with relatively accurate ink volume (the color is visually correct) measured by densitometer can be used as a reference for printing or proofing under the same ink and substrate conditions. Using this method, we can detect the change of color and ensure that the printing quality is maintained within an acceptable tolerance range through immediate adjustment

the color we feel is not only related to the size of the printing point, but also related to the thickness of the ink layer. Eye opening size, wire diameter, 4 If the heating sample is placed in the box, the thickness of the template, the type of ink and the viscosity of the ink will affect the thickness of the ink layer

we know that the wet thickness of the ink layer is equal to the theoretical color value of the silk fabric, which is usually provided by the manufacturer. For example, a theoretical color value of 20 cc/m2 will form a wet ink layer thickness of about 20 microns. The ink layer thickness can be calculated simply by dividing the color value by the hole area according to the following method: ((20 in China cubic centimeters ÷ (100 cm × 100 cm)) × 10000 microns/cm) = 20 microns

the thickness of the template film also affects the thickness of the ink layer, and the thickness must be increased according to the silk color value. Therefore, on a wire, using a template with a thickness of 10 microns and a theoretical color value of 20 cubic centimeters/square meter, a wet ink film thickness of approximately 30 microns will be formed, which is 10 microns more than the above calculation results. In order to print fine halftones, choosing silk fabrics with low theoretical color value is as important as using thin film

before establishing quality control parameters, it is also necessary to measure template characteristics, such as thickness, surface roughness, etc. Once accurate and acceptable values based on printing are determined, a standard plate making process should be established to ensure that the same template characteristics can be obtained constantly

under the condition that there is no same benchmark for silk printing, many enterprises have established production standards and their deviations without considering their respective conditions. Because there is no objective quality control conditions, it makes many silk workshops produce inaccurate and unpredictable printing colors in printing. In fact, this can be completely avoided, because the silk printing process can be controlled by a series of measurable parameters. You can measure these parameters and get the desired color reproduction standard

in addition, it can help you obtain accurate and consistent colors, help you improve the overall quality of printing, and enhance the stability of product reproduction in printing. When establishing the standard, the following parameters should be mainly considered:

1. printing point and tone range

2. Ink layer thickness

3. Optical density of printing color

4. Point expansion and loss

5. Ink overprint

the first two parameters are mainly affected by the quality of silk fabrics. Choosing the right silk diameter is as important as using the right silk fabric and mesh. In addition, in order to ensure the consistency of printing quality standards, you should learn how to calculate the deviation values of these parameters

other parameters are affected by the fact that some measurable factors in plate making and printing will eventually realize the closed loop of the whole lithium battery industry chain. The above five parameters will be briefly described in subsequent issues

although some factories establish standards and tolerances to guide production in specific production processes, the same standards do not exist for the silk printing industry. As a result, some silk printing plants tried to print halftone products without objective quality control. The result is that the accuracy is not enough to achieve the expected color. However, this is not the reason, because the silk printing process is controlled by a measurable range of changes, and you can improve your own color reproduction standards through measurement and use

in addition to helping you achieve accurate colors on a constant basis, establishing quality control standards can also help manufacturers comprehensively improve printing quality, improve the reproduction stability of the whole printing process, and ensure the repeatability of the same or similar work. In the process of improving the standard, the most basic variables that need to be considered include the following:

* printing point size and gradient range

* ink layer thickness

* optical density of printing color

* point increase and point loss

* ink overprint control

the first two variables are mainly affected by the screen fabric used, and you will see that choosing the correct fiber diameter is as important as using the correct fabric and hole number. You can also learn the calculation method of tolerance related to these variables to ensure consistency with quality standards. The remaining variables are affected by other measurable features of screen production and printing. You will find out how to better evaluate these variables

understand halftone point and tone range

before evaluating point size and tone range, you need to understand the skills and screen parameters that affect them. The best starting point is halftone image

halftone is defined by the number of lines and the range of tones following the completion of the new Darmstadt production base two years ago. The number of lines refers to the number of points per line inch or centimeter (line/inch, or line/centimeter). The higher the number of lines, the more points of each measurement unit, and the better the resolution of the image

the gradient range is determined by the halftone dot size used to represent different degrees of image density or ink range. For reproduction, the image is decomposed into yin and Yang dots of different sizes to represent brighter and darker areas. Each dot size represents the percentage of coverage from 0 to 100% (the ratio of printed to non printed areas)

for a specific halftone line number, the full frequency point size will produce the halftone tone tone range. This range includes highlights, intermediate and dark points. For% of the tone, use the positive printing point, which continues to increase, and the second tone continues to decrease from% of the negative printing point. (Figure 1) in silk printing, points less than 5% and more than 95% are usually discarded

note that as the number of halftone lines increases, the dot size also increases (Table 1). This is an important basic principle, because points below a certain size will be lost, so it cannot be reproduced in silk printing

as shown in Figure 2, the minimum highlight size that can be uniformly printed is limited by the hole fiber diameter. Because the dot ink cannot be guaranteed to fall on the open area of the hole, when the highlight is equal to or less than the fiber diameter, it cannot be printed. The printing ability of dark dots is also affected by the width of hole opening. When the dim dot is smaller than the hole width, the template area containing the dim dot will not adhere to the hole, and the dot will not be printed. (Figure 3)

the point size can be calculated at a specific tone value (f) based on the number of halftone lines. Simply use the following formula:

1 When the halftone line is given in centimeters, the point size = ((1.1284 × Square root of F) ÷ number of lines/cm) × 1000 for example: calculate the size of a 48l/cm halftone point 5% - point size = ((1.1284 × Square root of 5) ÷ 48) × 1000=52.6 μ m

2 When halftone lines are given in inches, point size = ((1.1284 × Square root of F) ÷ number of lines/inch) × 2540 for example: calculate a 120l/in Halftone point of 5% point size - --- point size = ((1.1284 × Square root of 5) ÷ 120) × 2540=53.4 μ m

the hole fiber diameter relative to the hole width also affects the printing performance of the image. However, the fiber diameter listed in the technical data sheets of most silk manufacturers is a normal value, which represents the measured value before fiber weaving. In the process of weaving and perfecting, the circular cross-section of the fiber is deformed into flat and oval, and the fiber diameter increases along the plane direction of the screen (Fig. 4). For the purpose of this article, I will call this wider fiber diameter the transverse fiber diameter

if the silk supplier provides relevant hole (MO) size data for a specific fabric, this information can be used to calculate the approximate transverse hole diameter using one of the following formulas:

a. if the mesh is given in cm (mc/cm), the transverse fiber diameter = (10000 ÷ mc/cm) -mo

b. if the mesh is given in inches (mc/in.), Transverse fiber diameter = (10000 × 2.54÷Mc/in.）- Mo

for example, if you want to calculate the actual diameter of the fiber, 305 Wires/inch, a low draw rate wire with a normal diameter of 31 microns and a hole size (MO) of 48 microns, the formula will be expressed as follows: transverse fiber diameter = (10000 × 2.54 ÷ 305) -48=35.3 or 35 microns

when selecting wires, the ratio of hole to transverse fiber diameter should be as high as possible. Screen fabrics with holes much larger than the transverse fiber diameter have less silk interference and easier ink circulation than those with smaller holes and thicker fibers. Therefore, they are more suitable for printing small dots

however, some work requirements may limit the fabric, where the hole width is less than or equal to the transverse fiber diameter. Regardless of the environment, the minimum highlight point of a given fabric can be calculated

1. When the hole is larger than the transverse fiber diameter, the minimum point size = hole width + transverse fiber diameter

2 When the hole is equal to the fiber diameter, the minimum point size = (2 × Hole width) + transverse fiber diameter

3 When the hole is smaller than the fiber diameter, the minimum point size =2 × (hole width + transverse fiber diameter)

in all cases, the printable darkening point must be equal to or greater than hole width + fiber diameter

because the smallest fiber diameter of silk fabrics that play a leading role today is about 30 microns, the minimum highlight point that can be printed will be greater than or equal to 85 microns. Too small dot size has an impact on the printing quality and the consistency between printing and printing. Table 2 shows the minimum highlight and dim point sizes within a certain range of hole numbers and fiber diameters

once the minimum highlight and dim dot size supported by the screen fabric is determined, the maximum and minimum tone values that the main fabric will produce under a specific number of halftone lines can be calculated. The following formula can be used, where lc= number of halftone lines, mo= blank area, thd= transverse fiber diameter: 1 Minimum order value of printing highlight = π × 100% × (printable point size × Lc）÷2）＾2

2. Maximum step value of printing dark tone point =100- (π) × 100% × （（Mo+Thd) × LC) ÷ 2) ＾ 2)

for example, suppose you want to know the maximum and minimum tone values that can be reproduced by printing on a 305 silk/inch fabric with a half tone value of 85 threads/inch. Because in the previous example, the manufacturer provided a hole size of 48 microns and a normal fiber diameter of 31 microns

first, calculate the transverse fiber diameter (THD) as described above, which is approximately equal to 35 microns. Next, determine the minimum point size. Since the hole is larger than the fiber diameter, the point size is equal to the sum of the hole and the transverse fiber diameter (35 microns +48 microns =83 microns). Note that this value also represents the minimum dim point size. Finally, in order

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