Technology | How to effectively improve the accuracy of printed products
In the past ten years, China printing and dyeing industry has made considerable progress. In 2001, the total output of printing and dyeing cloth in the country was 17.9 billion meters, and in 2010 it reached nearly 60 billion meters. Relatively speaking, the development speed of printed products is relatively slow. Due to the high technical content of printing, many factors are affected. Many customers report that there are many good printing lists, but few printing and dyeing factories that do well. There are technical problems here. There are also management issues. As far as printing processing is concerned, the idea and spirit of pattern design can be better expressed as the goal pursued by printing workers, and the key is how to improve the accuracy of the sample.
The accuracy rate of the printed product and the original sample
Textile printing is a combination of artistic creation and production technology. A well-designed printing pattern, after a certain technical processing process of printing production, becomes a colorful printed fabric. Whether the printing effect of the printed product meets the original design requirements is an important factor in determining the appearance quality of the printed product. The standard sample rate can be considered from three aspects.
1. The original conformity rate
To express the patterns on paper or fabric to the maximum extent on the processed fabric, first of all, it must conform to the original spirit. To reflect the spirit of the original, not only the pursuit of copying the original, but also the characteristics of different patterns, striving to achieve and surpass the printing effect of the sample. The printing process is also an artistic creation process.
Realistic patterns: generally flowers are the main body. Pay attention to the liveliness of the flowers, their natural shapes, supporting small flowers, flexible interspersed branches and leaves, full of vitality, and can be used to avoid joint blocking.
Regular patterns: generally represented by geometric patterns and imitated yarn-dyed stripes. It is usually composed of many points, lines, and surfaces of the same size and shape and arranged regularly. This type of pattern strives for smooth, fine lines, reasonable distribution, and attention to vertical printing. This type of pattern requires high weaving quality of the fabric itself.
Exaggerated patterns: Generally, cartoon animals and characters are the mainstay, supplemented by various object shapes. In order to increase the artistic appeal, the pattern has been exaggerated. When testing this kind of pattern, pay attention to whether it reflects the boldness and flexibility of the pattern.
Hazy pattern: Generally abstract hazy pattern, such as imitation tie-dye, imitation batik, imitation water stain, and the colors are all superimposed on each other. This kind of pattern focuses on testing whether the overlapping effect is uniform, rich, and layered.
The color combination of the pattern also reflects the design spirit of the pattern, and the original conformity rate includes the color accuracy. The color light must be accurate, there are two aspects: the color difference from the original and its own color difference. Generally speaking, printing pays more attention to the overall effect. The individual color requirements are lower than dyeing, but the main color must be accurate. Large areas can be inspected by computer color measurement, but it is still mainly based on visual judgments.
2. Printing level
From the perspective of printing production, the printing level can generally be measured by the amount of surface color, the uniformity of the block surface, the sharpness of the contour, the smoothness of the lines, the sense of layering, etc.
Surface color amount: Printing is surface coloring, so the coloring effect can often be measured by the level of surface color. The color level refers to the depth of surface color obtained after the same component of dye is printed on the fabric. There are many factors that affect the amount of color on the surface, including dye properties, paste rheology, fabric structure, quality of pre-treatment such as wool effect, smoothness, etc., printing machine operation, etc. It can be quantitatively expressed by measuring the K/S value of the printing surface with a spectrophotometer with a reflecting device. Due to the small print pattern area, it is difficult to determine the K/S value. This test method is mainly used to select dyes, pastes or printing processes as a basis for comparison experiments. The evaluation of the apparent color amount of printed fabrics is mainly based on visual inspection, the color is full, the color is bright, and the surface color effect is good, otherwise it is poor.
The uniformity of the surface refers to the uniform color of the large surface on the ground, without blooming. Because the printing is surface coloring, for the dark printing of tighter fabrics, the uniformity of the block surface is an important indicator to measure the level of printing. It mainly depends on the quality of fabric pretreatment and the choice of paste. Since the uniformity of dyeing is much better than that of printing, the anti-discharge printing process is adopted for the denser fabrics and the dark and all-over printed fabrics, and the printing effect is better.
Contour definition: refers to the degree of accurately showing patterns on the fabric. The pattern has no bleeding phenomenon, and there is no third color between the opposite colors such as red and blue, yellow and blue. In order to obtain a good printing outline definition, the choice of paste has good rheology and water holding capacity, and the color separation between opposite colors should be reasonable when making plates. If the equipment is limited, it is difficult to solve the flower. ) Dyeing process.
Line smoothness: The lines (including straight lines, diagonal lines, horizontal lines, and envelope lines) are smooth and not imaginary, and there is no zigzag in the screen printing. The smoothness of the lines largely depends on the plate-making (engraving) technology, such as screen printing, the number of meshes must be high. Secondly, it is closely related to the rheology of the selected paste. The paste should have good shear thinning and permeability, and finally it is also related to the printing operation.
Layering: It mainly refers to the uniform and full gradation of moiré or halftone (HalfTone), without hard mouth or moiré, reflecting a good three-dimensional effect, that is, a sense of layering, giving people a beautiful enjoyment. To achieve the moiré effect, plate making (engraving) is the key, the depth of roller engraving (roller printing, transfer paper printing) is reasonable, the number of meshes selected for screen printing is reasonably matched with the added dots, and the saturation, brightness, Contrast and other tools. In addition, the color paste viscosity control and the pressure of the printing squeegee directly affect the layering of the pattern.
The textile printing process is a systematic project, and it is affected by many factors. If any technology or management is not in place, printing defects may occur, which directly affects the printing effect. For any printing defects, we must carefully analyze, find out the reasons for improvement, and improve the printing effect of the product and the rate of authenticity. There are three main types of printing defects in the production process. One is caused by improper plate-making (engraving); the other is directly produced in the printing process; the third is the weaving defects of the original fabric itself and the defects caused by improper fabric pretreatment. disease.
Now the common defects are described as follows:
Inaccurate pattern registration: When printing patterns with more than two sets of colors, all or part of the patterns on the fabric are not printed on the fabric where they should be printed. Inaccurate pattern is a common defect in the production of multi-color printing. The reasons are many and complicated. It is closely related to the plate-making (engraving) technology, the accuracy of the printing equipment, the proficiency of the operation technology, and the specifications of the printed fabric. If the inaccuracy of the pattern is regular and is related to the circumference of the rotary screen or the length of the screen frame, it may be a problem with the plate-making or net-making, or it may be a problem with the net frame or the circular net is not round or the frame is deformed; Inaccurate patterning is irregular, and time difference is good. Generally, the color matching between color and color is small during plate making, and the accuracy of printing equipment is poor. It may also be caused by weak patching. It is caused by the relative movement of the belt; if the flower is not allowed to be in one direction, it can be adjusted because the operation is not in place.
Printing and color transfer: The pattern on the fabric has a color change. Screen printing mainly occurs when the dark area of the front sleeve is large, and the dark paste is easily scraped into the back sleeve when the light color is printed. The printing scraper, the slurry feeding pipe, and the slurry feeding are not printed after the darker color is printed. Clean and change the light color, it will produce overall or partial discoloration; in rotary screen printing, when the fabric is attached to one side of the printing belt, the color paste of the previous rotary screen is scraped and printed on the printing belt, and When the subsequent round net pattern overlaps the previous round net pattern, the color paste is easily transferred to the subsequent round net and enters the mesh, resulting in color transfer.
Printing bleed: The color paste on the fabric spreads outward from the edge of the pattern contour, and the contour of the anti-printing and anti-dyeing (discharge) printing pattern appears white halo, commonly known as eye circles. The main reasons are: poor water retention of the paste; improper preparation of the color paste; low viscosity of the color paste and slow scraping and incomplete paste recovery; steaming before drying; too high humidity during steaming; ) Too much anti-discharge agent in the dyeing paste.
Printed color spots: irregularly darker small color spots of the same color appear in the colored patterns on the fabric. The reasons are: the dye is not fully dissolved or the color paste is placed for too long, sedimentation or skinning; the colored patterns on the fabric show irregularities The small color spots of different colors (that is, the dyes that do not have this shade in the color paste prescription) may be caused by other dye powder particles flying into the color paste when the color paste is prepared, or the color paste tank was not cleaned last time; Small colored dots are regular, appearing in the pattern or even on the white ground, it is the degumming of the flower net or pattern or trachoma.
Pattern depth: The pattern on the fabric presents irregular color depth or regular horizontal and vertical blocks. The main reasons: the fabric pre-treatment desizing is not complete or the scouring is uneven; the patch paste is not evenly scratched; the printing belt is uneven, with longitudinal streaks or joint marks.
Printing knife line: single, double or multiple linear color marks appear on the fabric. Mainly due to small gaps on the printing squeegee or adhesion of garbage impurities, uneven scratching will occur during printing, resulting in the depth of the target pattern and linear color marks. The position of the rotary screen printing knife line occurs in the warp direction, and the flat screen printing Then in the weft direction. If the squeegee blade of the patch paste is uneven or has impurities adhered to it, it will cause a continuous strip of color marks, also known as the patch line.
Printing blocking: It is a common defect of screen printing. Because the mesh of the screen pattern is partially blocked, the color paste cannot pass through during scraping, resulting in regular incomplete patterns or intermittent lines or white spots on the fabric. The main reasons: the flower net or pattern is not cleaned; the garbage on the fabric sticks to the net: the paste dissolves unevenly; the color paste is not filtered well; the pigment printing adhesive is selected or operated improperly, and the conjunctiva speed is too fast.
Printed ground: The pattern on the fabric or the white ground or ground color is partially exposed. The main reasons: the scraper Kawaguchi is too Pu, and the scraping pressure is low; the color paste is too thick or the paste has poor permeability; the permeability of the paste does not match the mesh number of the screen; the fabric pretreatment wool effect is too low.
Printing color difference: the difference in color depth or hue on the left and right, side or between the patterns on the fabric. The main reasons for the color difference between the left and right sides: the left and right pressure of the printing scraper is uneven or the left, middle and right of the scraper is uneven; the left, middle and right of the pulp feeding is uneven; the effect of fabric pretreatment is different. The color difference between the horses mainly occurs when the batch is large. The main reasons are: poor dye stability or poor color matching compatibility; different color paste concentration or viscosity in each barrel; gray fabrics from different manufacturers or inconsistent pre-treatment process conditions; printing operations are not consistent Standardization, the pulp position, speed, pressure, and drying temperature in the network are unstable or even change randomly; the humidity changes greatly during steaming.
White ground stain: The white ground or white pattern stained on the fabric causes the white not to be white, which directly affects the overall printing effect. Main reasons: low fixation rate of the dye itself or too high dye concentration (such as turquoise, scarlet, black, etc.); hydrolysis of the dye after a long time: insufficient steaming time and insufficient fixation of the dye; unreasonable post-treatment washing process; Did not choose the right detergent.
Many of the anomalies of printed fabrics are related to the plate-making method and process. Although traditional manual color separation has been basically eliminated, there is a big gap in the level of practitioners mastering computer color separation software, especially in dealing with some complex patterns; and Abnormalities caused by improper plate making operations also often occur. The reasons for poor printing results and the corresponding adjustments are as follows.
Inaccurate patterning is not only related to the operation technology and the accuracy of printing equipment, but also directly related to the color separation plate making. For example, the patterning inaccuracy is regular and is related to the circumference of the cylinder or the length of the screen frame, which may be plate making. Or the problem of making the net, it may also be the problem of the net frame or the round net or the deformation of the frame; if there is no regular pattern in the pattern, the time difference is usually caused by the small color matching between the colors during plate making.
Adjustment measures: increase the temperature or extend the time when the rotary screen is restored; a set of patterns should be selected from the blank net of the same manufacturer; the rotary screen should be used after the bulkhead is corrected; often check whether the flat screen frame is degenerate; when making the screen, it is accurate and aligned Cross: The relationship between color and color should be handled reasonably according to the rheology of the color paste and the tissue specifications of the fabric.
Poor definition of pattern edges
When flat screen printing (exposure), the film and the screen printing plate are not in solid contact or the distance between the printing light source and the screen is large; the mesh number of the screen is low; the photosensitive adhesive is unevenly coated and the drying is insufficient.
Adjustment measures: When printing, increase the vacuum pressure value, increase the adhesion between the film and the screen, and reduce the distance between the exposure light source and the screen; use a high-mesh screen; improve coating quality and coating uniformity ; Increase the development time and carry out sufficient cleaning.
The pattern lines are not smooth, resulting in a sawtooth phenomenon
Inappropriate selection of the screen mesh or underexposure, light diffraction occurs during exposure; the thickness of the photosensitive film is not enough; the tension of the flat screen is uneven; the water pressure is too large when the screen is developed.
Adjustment measures: According to the accuracy of the pattern, select a screen with an appropriate mesh. It is best to use a colored screen to prevent light diffraction during exposure; use a method of uniformly coating photosensitive glue multiple times to increase the thickness of the glue layer, but too thick will also Influencing the finish, some studies suggest that the thickness of the film is greater than 25% of the wire diameter, and the edge finish of the pattern is better; increase the tension and uniformity of the stretched screen; reduce the flushing pressure during development.
Moire patterns are produced during plate making
When the flat screen is stretched, the color printing plate adopts a positive stretched screen; when making a plate, the direction of the screen line and the angle between the warp and weft of the screen are not correct; the number of screen meshes and the number of screen lines do not match; the screen of each color plate The angle difference does not meet the requirements.
Adjustment measures: In general, oblique stretched screens should be used for color printing; correctly grasp the direction of screen dots and the angle between the screen warp and weft wires; the number of screen meshes and the number of screen lines should match appropriately, and the flat screen should control the screen mesh number 4-6 times larger than the number of screen lines, and 1. 5-2 times larger than the round screen is more appropriate; the screen angle of each color version is 45º for the monochrome version, 45º for the main color and 45º for the secondary color. It is 15º.