Textile color screen printing technology (on)

Abstract This paper introduces the characteristics of spot color screening printing technology and the difference between it and four-color printing technology. The requirements for manuscripts for spot color screen printing, the color separation technology for spot color screen printing, the ink used and the requirements for equipment, etc. Made a detailed explanation. It is pointed out that spot color screen printing technology has attracted more attention from people in the industry due to its advantages of high quality, high efficiency, and high profit.

Keywords: spot color; textiles; screen printing.

Spot color screen printing and CMYK four-color printing

 Spot color screen printing is currently mainly used in textile screen printing. Why develop spot color screen printing technology? What are the differences and technical advantages of spot color screen printing and CMYK four-color printing?

 1. The fundamental difference between four-color printing and spot color screen printing is the transparency of the ink. Four-color printing technology requires the higher transparency of the ink the better (see Figure 1 A, B, C). In Figure 1A, the ink has a transparency of 100%. No matter which color is printed first, its composite color (overlapping portion) is emerald green (100% C+100% Y). If the transparency of the ink is only 50%, it is printed yellow ( Yellow is covered by darkness by fifty percent), and its composite color is bluish; first cyan, then its composite color is yellowish (see Figure 1B, C). This is the color cast often heard in four-color printing.

The spot color screen printing technology requires the lower the transparency of the ink, the better, that is, the higher the hiding power of the ink the better, preferably 100% hiding power, the printing effect is shown in Figure 1D, E. Why spot color screen printing technology requires the higher the hiding power of ink? Because, spot color screen printing technology is developed for the printing of colored textile fabrics. Obviously, when printing on colored textile fabrics, the hiding power of the ink is certainly better. It is like printing a white pattern on a black textile fabric. If the hiding power of white ink is not enough, it may be necessary to print three or four times to achieve the whiteness requirement. If the white ink's hiding power reaches 100%, it is enough.

So, what about using four-color printing on color substrates? Since four-color inks are highly transparent, the printing effect is, of course, confusing after the underlying color of the substrate has penetrated. The only way is to print a layer of white, and then print a layer of CMYK four colors. However, if textile fabrics are printed in this way, there will be two major problems: First, the ink is thick, and the hand feels bad; second, it is like a patch plaster. Therefore, printing on colored textile fabrics is not desirable. Only spot color screen printing technology is used.

2. Spot color screen printing technology has the following characteristics compared to CMYK four-color printing:
a. Color images can be printed on any color (including white) substrates.

b. The color of the image can be adjusted arbitrarily. For example, in the orange color of a spot color screen pattern, we can not only adjust the color depth of orange, but also replace it with red, rose, gold, etc. without affecting other colors.

c. Brightness is much better than four-color printing. In the four-color printing, the grayscale problem in the color is difficult to solve, especially green, purple, orange, etc., always bright, and the brightness is not enough. This is because there are several problems that are difficult to solve in four-color printing: the three-primary inks for color separation are difficult to match with the three-primary inks for printing; the three-primary inks are difficult to achieve 100% purity and 100% transparency. The spot color screen printing not only does not exist these problems, and the color is more abundant, you can use metal ink (gold, silver, etc.), fluorescent ink, color ink, etc., so that the color screen printing pattern is far more than four-color printing Beautiful, strange.

d. Spot color screen printing is usually more than four colors.

It can be seen that spot color screen printing technology is a new technology developed specifically for garments and T-shirt printing. This technology is also applied to other textile products and other substrates. Spot color screen printing technology is developed on the basis of four-color printing.

Spot color screen printing manuscript requirements and revision

The design of the spot color screen printing pattern gives the designer more freedom and design space than the traditional spot color printing pattern. Whether it is painting: Chinese paintings, oil paintings, watercolors, etc., or photographic works, computer 3D images or physical scanning can be used as originals for printing patterns.

However, spot color screen printing requires much more image clarity (ie, the resolution of images) than traditional prints. The traditional manuscript print can be a plain paper with a sharp color, or it can be a monochrome manuscript with the color of the color of the block, and it can be copied, faxed, or drafted. Because the color blocks and the simple transition color pattern outline the outline of the excellent block, add solid color (black) to the outline or set the direction and density of the gradation, the computer can add color in seconds. Color blocks and simple transition color patterns generally use vector drawing software. Vector drawing software does not require resolution for far manuscripts, and no resolution is set in drawing. The majority of spot color screen printing manuscripts are paintings, photographic works, computer 3D images, etc. The color gradient is not regular at all. Therefore, it is impossible to draw and separate such manuscripts with vector drawing software. Use bitmap drawing software to draw and separate the far drafts. The resolution of the scan determines the sharpness of the image. If the resolution set when scanning the original is low, the quality of the image is definitely not good.

In actual production, many customers have received low-quality manuscripts, a T-shirt, a floppy disk, a low-quality print, or a small-sized color draft. How to do? There is only one way: painting! Repaint! Or use bitmap drawing software to draw, or draw on paper by hand. Whether using bitmap drawing software to draw on a computer or drawing on paper by hand, the painters are required to have a higher level of professional painting, which is not something that ordinary computer drafters can do.

The requirements for manuscripts for general spot color screen printing are as follows: Drawings are as 1:1 as possible, and color printing requires higher printing quality and larger size; computer design manuscripts have a resolution of 200-300 dpi.

Spot color screen printing separation technology

 Spot color screen printing color separation technology is much more complicated than color block color separation and four color separation. The color separation of the color blocks can be either color-separated by computer or color separation by hand-painting; the general four-color separation can also be performed by setting the color mode of the image to CMYK mode in any set of bitmap drawing software. Complete the color separation (in the CMYK mode channel, there are four color channels: cyan, magenta, black, and yellow. Screens are screened separately to make a screen). However, spot color screen printing technology is far from simple.

It is not possible to use manual drawing separation for spot color screen printing. Only computer digital technology can be used. There are two main methods to use computer digital methods for spot color screening. The first is to directly use bitmap drawing software (most commonly used for photoshop software) to perform color separation, and the other is to use professional printing spot color separation software to automatically perform color separation. Separation.

A. Direct use of photoshop software for color separation, also known as computer manual color separation. This is the only way without the printing spot color separation software.
If you design your own design, you can use the photoshop software's "layers" to set different color layers directly for design. After finalizing the design, each color layer can be individually screened out to each spot color separation sheet.
 If you are working on a draft or using a color draft, first open the image file in photoshop and select the “color range” command in the “select” menu to open the color dialog box. as shown in picture 2. Use the dropper to select the appropriate color. After “OK”, the selected color is stored in the channel, which completes the separation of the spot color.
 Direct use of photoshop software for color separation not only requires the accumulation of rich separation printing experience, but also takes time and effort.

B. Use color separation software for color separation.
Under normal circumstances, the printing software is used as a photoshop plug-in. Open the color separation software and follow the prompts to turn on the black background image and the white background image (as shown in Figure 3). After that, the color separation will be automatically performed to completion. Finally, appropriate adjustments must be made for each channel.
 Here we must explain that even the best color separation software can not be consistent with the original 100% color separation, because the original color is always between 50-255 colors, but with a limited number of special Color to represent rich original artwork can only achieve similar results.
Clothing printing spot color software can currently be seen in the United States (fast films, spot process, Wei Feishi color separation software), Guangzhou Wantongda version. Domestic agents are mainly Guangzhou Lixin, Shanghai Yarn Union and Tongli Company. These agents provide corresponding technical guidance. Suzhou Chenggong Company also provides guidance on color separation screening technology of FM network.
In addition to the above two methods, the following describes a new spot color separation method that has been developed in recent years in the world - color tone network plus color separation.

The traditional screening technologies are amplitude modulation network points, which are milestones in the development of human printing technology. The characteristic of the amplitude modulation network point is to use the size change of the network point to reflect the grayscale image, and the network points are arranged linearly. The characteristic of the FM network is to use the density change of the dot to reflect the gray image. The size of the dot is the same according to the density value of the image. There is no law at all (see Figure 4). According to its simulation principle, FM dot printing is closer to grayscale original image than amplitude modulation dot printing.

In practical printing projects, FM dot printing has the following advantages over AM dot printing:
a. Cut out the moire phenomenon that can not be overcome by the amplitude modulation network point.
b. Plate making is easier, and the resulting screen is closer to the film. We know that highlights (15% or less density) and shadowing (above 85% density) in the AM sites appear as extremely small black or transparent dots, which are unavoidable losses in platemaking and printing. What can be done is to reduce this part of the loss as much as possible. Moreover, taking care of the highlights in the actual operation (increasing the exposure value) will lose the dark tone part of the network, take care of the dark tone (reducing the exposure value), and will lose the high-light part of the network. Because all network outlets are the same size in FM network outlets, as long as the exposure value of one outlet is determined, then all outlets can be exposed without loss.
c. The printed ink layer is thinner than the AM screen printing, which not only saves ink, but also the softness of the printed textile.
 d. AM printing can be performed after the original color image is divided into grayscale images. The original color image can be converted to the index color mode, and then color separation can be performed. The latter method has the advantage that multiple colors can be specified to form a new FM image. Of course, there will be some differences from the original color image unless you specify enough colors. This advantage is even more pronounced when the original color is not much.

During the first two years, we had seen a South African friend bring a T-shirt with a picture of Mandela and a dragon with an image printed on it, which was beautifully printed and richly detailed. Especially the image of the dragon, at first glance, only three colors, yellow, gray and white. They can see the printed video they brought with them before they had to believe that it was printed in twelve sections: three whites, four grays, four yellows and one black. Why is this so? Please look at Figure 5. The original in Fig. 5 is a gradient from red to white on the yellow bottom; Fig. 5a is a single-tone red-red tone dot printing effect; Fig. 5b is a big red, a pink two-color printing; Fig. 5c, and Fig. 5d are respectively Four, six different shades of red printed effect.

Because of this