Four-color screen printing color and original production process

As we all know, the basic process of screen printing is: using a wire mesh, a frame to make a stencil carrier, and creating an image on the carrier, and then using the pressure of the squeegee to force the ink to transfer through the opening of the image area and attach to the printing. Things. This process is not difficult to understand, especially the screen printing of color blocks, it should be said that there has been a wealth of experience.

However, the screen printing of such color blocks is increasingly unable to meet the demand for the fine screen printing market, especially the demand for the halftone screen printing market.

Because halftone screen printing can be used in many fields, such as advertising paintings, textile printing, T-shirts, ceramic glass printing, ceramic decal printing, CD printing, and the like. Half-tone screen printing can even be used in unexpected areas such as surface decoration of aerospace, aerospace and electrical products.

In recent years, the screen printing industry has generated a great interest in performing color halftone reproduction on different substrates. The ability of screen printing to perform color reproduction on substrates of different shapes and materials has been recognized by many graphic designers, advertising manufacturers, packaging and decorators, and printers, and has received more and more attention. Its market is very competitive. force.

At present, in China, halftone screen printing technology can be used not only for small-format screen printing, but also for half-tone screen printing of large-scale outdoor advertising, showing screen printing-specific functions, such as: for printing bus stop cards and The screen printing of subway advertisements and outdoor advertisements has gradually become popular, and the application field is expanding. As a result, half-tone screen printing is also attracting textiles, plastics, glass, metal printers, and large-scale advertising and decoration companies. They have conducted research and explorations in terms of process, technology and materials. There are also many fine-printing half-tone printing products available.

However, it is not easy to grasp the process of halftone screen printing. Because when you look deep into the halftone screen printing process, you will find that the process itself is much more complicated than expected. There are many variables in the overall halftone screen printing process, and each variable factor affects the quality of the final screen printing product.

Halftone screen printing should consider the question: In short, what is the final product? What is printed on the substrate? What kind of ink is used? How many colors should be printed? Determine, requirements for positive drawing base, selection of screen, determination of stretching tension, quality requirements for templates, requirements and control of exposure, such as requirements and control of screens in screen printing, templates Variable control, the control of the amount of ink transfer, and the impact of printing materials on the accuracy of the ship and the prevention of static electricity, half-tone screen printing and color registration order and registration requirements. This chapter analyzes and discusses the factors affecting quality in the above-mentioned halftone screen printing, so as to arouse the attention of screen printers and improve the quality of halftone screen printing products.

One, four color screen printing tone

There are many ways to express levels in printing. There are two common methods: one is continuous halo staining and hierarchical expression; the other is halftone hierarchical expression.

The image of the reflected manuscript, from the highlights to the shades of the color shades, is formed continuously and uninterruptedly from deep to shallow or from shallow to deep even density, and is called continuous tone. For example, the colorless shade diagram baseplate without the net, the black and white photographs of the bottom edition and the drafts and photographs are continuously adjusted. Regardless of whether the image of the negative or positive image is from the highlight to the shadow, the shades of the image are represented by halftones, which are called halftones.

Second, four-color screen printing level representation method

The representation of the halftone gradation is to divide the continuous halo staining into different lines, such as coarse, short, and short, or small dots of varying sizes. There are three main methods of general expression:

The first is the line representation, which is the high, medium, and low tone levels of the manuscript. It is expressed in terms of thickness, density, and length. The lines are thick and dense, and the lines are thin and sparse. The disadvantage of this method of expression is that it is relatively rough, and the expression of the tone levels of the continuous blooming is not fine. Moreover, it can only appear in black and white or a single color, there is no color change, and the rich colors of the original cannot be reflected by the overlap color.

The second is the AM representation. The shades of the manuscript are represented by small dots and regular dots.

The third is the FM network representation. This method is rather special, with some irregularly arranged fine points to express the level of color, dense performance of dark and deep levels, point evacuation performance light and bright level.

Screen printing, in addition to the field color block patterns, text, lines, are halftone dot size, reproduction shades of gray tone level, instead of the original continuous blooming color, to complete the copy of the original image.

What is commonly used now is the amplitude modulation point. This kind of dot is the basic unit that constitutes an image on a screen printing plate. It is a real point of a regular arrangement with an equal center distance and an unequal area. Dots are the basis of the screen printing reproduction process. The correct transmission of screen dots in screen printing and printing is the most basic requirement for halftone screen printing. In screen printing, the dots play the following roles:

(1) The task of presenting hue, brightness, and saturation is imposed on the printing effect.

(2) In the printing process, it is the basic element of image transmission.

(3) In color synthesis is the organizer of image color, gradation, and outline.

As we all know, the halftone screen printing graphic is done by the dot. After coating the sensitized film, printing plate, and other series of treatments on the screen, the dots are made into the image part, and the remaining part of the image part except the screen dots penetrates the mesh and seals the ink.

In this sense, halftone screen printing is called dot printing. Then, why can the outlets realistically reproduce the continuous tone level on the original? This is because once the original image is screened, the original image is divided into countless mesh dots, that is, the continuous tone image information is converted into a dot image. information. When the color is synthesized, since the dots of different sizes are printed at different angles or close together, the ink on the dots selectively absorbs and reflects the light under the action of light. The reflected part of the light passes through the light. Space mixing, acting on human eyes (colored nerves), creating illusions in people's eyes, looks like continuous tone. In fact, the space occupied by each dot on screen printing products is equal. The difference in color tone seen by people is due to the difference in the size of the space occupied by each dot, and the depth of tone is caused by The dot space reflects the reflected light intensity. $Page break $

Third, four-color screen printing manuscript requirements

The main goal of half-tone screen printing is to control the ink deposition, so that the amount of printing ink is extremely accurate, and people seem to feel that the brightness, darkness, and subtle levels of the image colors can faithfully reproduce the originals. In the operation, this effect must always be consistent between the printed sheet and the printed sheet, and any change in the process will cause differences in the color and level of the image, and the variable factors must be strictly controlled throughout the process. Only print qualified products. However, to control the entire process, the original must first be controlled and selected. The original is the basis.

Originals are provided by customers, and some are also called originals. Strictly speaking, only original works can be called originals, while a Chinese painting is original. Color reversal films taken with originals, black and white or color photos cannot be called originals but are called manuscripts. The form, color, and structure of the manuscript are very different and can be clearly categorized.

1. Divided by type of original

(1) Photographic originals - color reversal film (natural color film), color copy positive film (color positive film copied with color negative film), color photos, and black-and-white photos.

(2) Original artwork - Chinese painting, gouache, watercolors, prints, and pencil drawings.

(3) The second manuscript—generally refers to a color reversal film or color photo that is a copy of an original artwork.

(4) Printed manuscripts—refers to the use of prints as manuscripts.

(5) Line manuscript—refers to black-and-white line drawings and manuscripts consisting of patterned fields, art characters, and text.

2. Divided by light

It can be divided into two categories: transmissive and reflective.

(1) Transparency. The original is transparent. When the color is separated, the light source shines on the back of the original and the transmitted light is used for color separation.

(2) Reflection draft. In color separation, the light source illuminates the front surface of the original and is a manuscript that uses the reflected light of the original for color separation. Reflections include original paintings, color photos, black-and-white photos, and prints.

The quality of direct color separation is best with the original. This type of manuscript has a small contrast, generally only about 1.4, and the brightness density is 0.1, 0.3. Shadow density 1.5-1.7.

Color photographic paper is a kind of color multi-layer photosensitive material, and its structure and coloring principle are similar to those of reversal film. The color photo image is enlarged and printed on the color photo paper by the color negative film, so the light and dark contrast is intense and the color is vivid and real. Only because of the reflection of the original, but not contrasting contrast of the reversal film, but also because it is a color negative film copy or amplified, so the level of loss, the color has color cast, it is appropriate for the original large or reduced copy.

3. Applicable and non-applicable

The manuscript is the basis of screen printing and copying. The quality of the manuscript is directly related to the quality of the plate making and printing products. Therefore, when the manuscripts and process design are to be carried out, the manuscript submitted by the customer must first be carefully examined and confirmed to determine whether the screen printing process is suitable. Platemaking requirements.

4. Suitable for screen printing manuscripts

Applicable manuscripts are often referred to as qualified manuscripts, that is, in accordance with the requirements of the screen printing process for making a master plate, and it is not necessary to make a manuscript that can be copied by processing correction. The standards are: 1 image, good resolution; 2 fine particles, clean and clean the map; 3 moderate contrast, high and low-key levels rich; 4 hue is correct, colorful, sense of color balance; 5 copy, the magnification does not exceed 3-4 times; 6 originals such as reflections and drawings should be flat and free from damage and dirt.

5. Unsuitable for screen printing manuscripts

Non-applicable originals, ie originals that do not meet the copying requirements. Although this type of manuscript can be copied, it requires a lot of processing adjustments and corrections, and the final copying effect is also unsatisfactory. Such as: 1 image is false and false, there are double shadows, poor clarity; 2 coarse particles, surface pollution, dirty spots, more than road; 3 contrast is too large, too stressed or too thin tone; 4 color cast, old color ;5 Magnification more than 10 times.

6. Uncopyable manuscript

Some manuscripts cannot be copied and should be returned. Such as: 1 serious image imaginary, unclear outline; 2 particles are too rough, magnification is too large; 3 graphics serious wrinkles, pollution. The main part of the image has obvious dirt spots, roads, molds, etc.; 4 serious color cast, the tone is completely distorted.

Whether it is a physical manuscript or an artwork, or a positive edition, these manuscripts determine the quality of future prints. Therefore, the most important thing is that the printer should be able to check and identify the quality of the manuscript, even if the user provides user satisfaction. The manuscript should also be able to correctly identify the quality of the manuscript. Why are you not satisfied with the manuscript? What are the defects and deficiencies in the manuscript? These must be given to the user in advance so that they know the consequences of these defects. If the manuscript was received without prior explanation, it would be too late to say it was rejected by the customer when handing over the screen print. The screen printer was responsible for this. $Page break $

Fourth, select the original to consider factors

1. Original color

It is also commonly known as "hue." When selecting originals, you should pay attention to selecting those originals with a large range of colors or “hues”. The range of tones is large, and the eyes look like a rainbow. Various blue, green, red, and other colors make people interested and dizzying.

2. Original tone value