Defect Analysis And Solution Of Flat Screen Printing

- Dec 28, 2020-

The defects of flat screen printing are ever-changing. People classify them into several types and distinguish them in the inspection of finished products. They are named according to the phenomenon. As a matter of fact, there are few recurring defects. Although there are the same phenomena, they are not necessarily caused by the same reason. This paper mainly analyzes the most common defects, analyzes the possibility of defects, and provides a way to analyze defects for reference.

1. Press paste

The phenomenon is that the contour of the pattern is not clear, the polychromatic contact surface is fuzzy or the edge is pressed. According to the principle of pressure will paste, wet cover wet printing, the latter version will be pressed to the previous version, then the plate mouth pressure times, press paste serious.

To overcome this situation, we must first select the appropriate scraper (hardness), scraping and printing paste to be clean; when conditions permit, the distance between the plate and the plate, if necessary, heating and blowing in the middle; correctly arrange the position of the pattern plate, printing the thin stem first and then printing the block surface; when the pattern is open, we should try to avoid too much extrusion of the plate position; we should make appropriate filler treatment on the edge of the pattern frame to reduce the pressure Less imprint contact area.

2. Paste edge

The fabric is pressed on the edge. Due to the uneven width of the gray cloth door, first narrow and then wide, or the cloth is not in the same line, the paste at both ends of the flat screen plate is printed on the guide belt, and then stuck to the back of the next screen plate, and then printed to the cloth edge of the next plate, resulting in paste edge; the edge absorber fails, and the cloth edge is not in the same line; the width of the flat screen after sealing is greater than the gray cloth door width.

Solution: the gray cloth with different door width must be rearranged, and the door width of machine printed cloth must be consistent. The distance between the two ends of the screen plate and the width of the cloth cover and the edge of the printing position shall be sealed, so as to avoid unnecessary patterns and printing the color paste on the guide belt; the edge absorber shall be in good condition, and it shall be equidistant from the side of the guide belt when pasting the cloth without drifting; the scraping width of the scraper shall be at least 5cm larger than each side of the cloth cover.

3. Huakai

The shape of the flower is indistinct, and the color of the pattern penetrates into the direction of the fiber.

Causes: after cleaning, the guide belt does not wipe dry, and there is a watermark on the gray cloth after the guide belt with water, resulting in the penetration of the color paste after printing; low viscosity of the color paste, extremely strong dye concentration, excessive amount of printing pulp absorption, or excessive amount of hygroscopic agent, as well as poor water holding capacity of the original paste will cause the opening of the printed pattern; printing before the pattern is dry after washing, resulting in the opening of the previous versions, all of which need attention I mean it.

Solution: check whether the wiper device of the guide belt washing box is in good condition; select the paste with good water holding capacity. Check that the amount of process prescription is reasonable (the saturation amount of dye and the amount of auxiliaries for different grey fabrics), the slurry should not be left for too long, and it can only be used after the pattern is washed and dried.

4. Scrape in

The different color paste is scraped in to form the wrong color light, or the light color pattern is mixed with the dark color.

Causes: the dark color block surface is large, with more pulp; the border of the flower frame is not good; the pulp is brought into the pattern from the guide band. Add wrong color when adding pulp.

Solution: block the pattern position according to the fabric width. When printing, the pulp should be collected, less and more. When changing the color, the scraper should be cleaned to prevent the residual pulp from being brought into the new color matching pattern. Change the position of the pattern without affecting the multicolor.

5. Frame seal

There are abnormal streaks in the shape of pattern frame near the plate mouth. This is due to improper screen caused. The frame is not installed well, or the gap between the screen and the guide belt is too small.

Solution: the net frame can be slightly raised or leveled, the correct open circuit of the pattern can be handled, and the distance between the pattern and the edge of the net frame should be kept.

6. Color difference in one plate (uneven scuffing or a certain interval in the transverse direction of the fabric)

Causes: screen inherent deficiencies, photosensitive glue uneven thickness, uneven pattern exposure, and affect the difference in the amount of pulp. Second, the net frame is not on the same plane, or the installation is poor. Third, the scraper is loose, the scraper mouth is uneven or when scraping is caused by jumping.

Solution: screen defects caused by the need to make a new screen, if it is film sensitive, you must also check the quality of the film. Press the screen frame flat, but observe whether the pattern is out of shape when printing. The height of the two ends of the screen installation is the same. The thickness and height of the blade are consistent, and the blade is installed in place.

7. Plate printing

There are deep and light embossing or overlapping or separation in the printing pattern. Causes: printing guide belt running back setting is not accurate; scraper left and right pressure is not adjusted properly; the screen frame is too high from the guide belt, the screen on the edge is found to be off during scraping; the open circuit size of flower shape is too large, resulting in large pressure area of plate opening.

Solution: according to the flower shaped return, set the guide belt running back, or check whether the guide belt runs normally; adjust the pressure of scraper to just the right size; adjust the height of screen plate; the back of screen plate can be partially set off by large gap fine screen; modify the unreasonable open circuit.

8. Ding Hua Edition

The color of the flower is uneven with chrysanthemum like hair. Causes: the paste is pulled up when the pattern is lifted, and the paste is stained on the reverse side of the pattern, which affects the next printing; the paste viscosity is too thick or insufficient expansion; the amount of certain dyes is too high.

Solutions: adjust the viscosity of the paste or the expansion time of the paste; filter the old paste and then use or replace it with new paste; adjust the prescription and wash the plate in time.

9. Blooming

The gray cloth color or poor permeability appeared at the flower position, which was similar to the skin shape of sand fish. Causes: there is no curing agent after making the pattern: it is washed clean, or the pattern is used for a long time, and its pulp makes the mesh smaller, leading to blocking; the scraper is not selected properly or the pressure is too small, and the sizing is not enough; the paste viscosity is too thick, and it is difficult to scratch; there are oil stains and wax on the grey cloth: the front pattern is not dry, and it is absorbed by the back of the back pattern.

Solution: check whether the plate hole is in good condition after patterning; clean the screen after each printing; select the scraper with appropriate force; test the capillary effect for the gray cloth to be printed, and re refine the gray cloth if necessary; test the paste viscosity every time; select the mesh number corresponding to the pattern.

10. Thick and thin stem

The causes of the uneven thickness of the thin stem are as follows: there are thickness defects in screen plate making; the left and right magnetic sizes of the magnetic table are different, resulting in different printing pressure; the screen plate is placed unevenly; the left and right pressure of the scraper is inconsistent, the blade edge is uneven, and the thickness of the blade edge is inconsistent; the scraping pulp is not clean.

Solutions: carefully check whether the fine stem of each return position of the pattern is the same; check the magnetic force of the magnetic table; lay flat when installing the screen; select a good scraper and adjust the loading pressure; the blade should be consistent when changing the scraper; adjust the height of the screen cylinder according to the fabric thickness.

11. The flower shape is askew

The pattern is inclined or curved to the warp and weft yarns of the fabric. Causes: printing fabric (silk) itself has weft skew or poor sewing head: stick skew.

Solution: the printing grey fabric (especially the printed geometric pattern) needs to be weft adjusted and inspected before it can enter the mass production; the sewing head is sewed in the parallel direction of the weft thread; and the machine sticking cloth is kept straight.

12. Trachoma

The printed fabric has sand like color spots. Causes: the screen has been used for a long time, exceeding its service life, resulting in local photosensitive adhesive falling off and water permeability; poor plate making quality, unstable adhesive film, and film falling off after scraping and printing by scraper.

Solution: often observe the screen, sand holes found immediately fill; on the screen before the strict inspection.

13. Slurry leakage

Color appears in the non flower shape. Causes: pattern off film or pattern welt is not good.

Solution: screen on the machine before inspection, midway appear timely repair.

14. Plug net

The flower shape is incomplete or partial with color spots, white spots or partial lack of flowers or few mud spots. Causes: impurities in the slurry block the mesh, especially in pigment printing: the edge of the mesh is starched after a long time of printing; the surface of the cloth is invaded by impurities, such as thread head, etc.; the photosensitive adhesive film is not washed out during screen making; the fabric is covered with fluff or thread head, etc.

Solutions: frequently observe when printing, and immediately wipe the garbage if the plug net is found; immediately stop to clean the screen plate if large area plug net is found; filter the color paste; if the small surface is obviously impurity outside the screen or on the back of the screen plate, scrape it with tools.

15. Loose print (moire)There are ripples on the printed pattern. Causes: the mesh of the screen and the yarn of the printed fabric overlap and interfere with each other; the frame tension yarn is too loose; the mesh number is not suitable.

Solution: oblique tension is adopted for the mesh, and the angle between the mesh and the fabric should be kept at 10 to 15 degrees; the mesh should be changed properly; the tension of the mesh should be the same everywhere.

16. Fuzzing

The shape of the flower is blurred, and there is a sense of shifting double shadow. The screen is too loose; the operation of the screen is not synchronized with the operation of the bandage.

Solutions: slow or oblique plate lifting; safety standard requires frame stretching; check the synchronization of printing machine screen and guide belt.

17. Pultrusion printing

Similar to tadpole print. Causes: too thin color paste, too much paste, too fast pulp collection.

The solution: select the right slurry; adjust the required viscosity.

18. Slurry splashing

Color dot or paste drag caused by splash of color paste. Causes: the printing operation is too fierce, the plate action is not appropriate; the paste viscosity is not appropriate; too much paste is added in the sizing tank.

Solution: adjust the viscosity of the color paste; operate with appropriate force; add less force.

19. Flying point, color point

Irregular dye spots are sprinkled on the cloth surface to form small spot like color stains. Or the same color flowers contain a color matching monochrome point. Causes: the printing paste is too sticky; after printing, the paste is not clean, the plate is too fast, and the force is strong; there are undissolved dyes or impurities in the paste, which form spots after printing to the cloth.

Solution: the original paste should be placed for enough time, and the paste is good: improve the printing start-up operation, one side of the screen plate should be tilted, and the slurry should be collected gently, and the scraping speed should be adjusted; for the dye that can not be dissolved completely, the high mesh screen can be used to filter the color paste, if there is any, the color paste should be adjusted again, and the chemical operation should be paid attention to.

20, crepe print

There are white wrinkles on the calico surface. Cause: The cloth surface is not flat, there is a zou print, the color paste fails to penetrate into the crease during printing: the grey cloth is not fastened, and it is taken up when the plate is lifted, and the printing is changed when the next set of plates is pressed down again The position of the white blank side is wide and sharp, and creases occur when the cloth is applied: uneven seam heads produce wrinkles or uneven tension in the silk; the resin of the conductive belt is not flat, making the scratches uneven.

Solution: The cloth should be smooth and the tension of the cloth should be adjusted; check the resin viscosity on the surface of the guide belt or the viscosity of the patch paste, check the temperature of the hot roller or the pressure of the patch pressure roller, and make the patch paste Or re-apply the resin; the seam head should be flat and not affect the effect of the patch.

21, Lu Bai

A part of the warp or weft is turned or moved to the front and back of the fabric. Causes: poor permeability of the color paste, the dye cannot penetrate into the fiber; too small scraping force, insufficient sizing, resulting in insufficient dyes of the actual color; the grey fabric is water-repellent and does not absorb the color paste; Silk, the fabric structure is relatively loose, and a small amount of fiber is turned over, revealing the white bottom.

Solution: Ensure the swelling time of the original paste, mix the color paste evenly, make the color paste penetrate two-thirds of the thickness of the cloth when printing: For water-repellent fabrics, the grey fabric needs to be reprocessed; pay attention to uniform tension when processing after printing, especially It is a twill and satin weave type.

22. Printing depth

The same color or the color at the back of the flower has shades, and the mud spots have sizes. Causes: The resin on the conduction belt is uneven; the color paste is too high in viscosity and the grey cloth has poor moisture absorption; the force of the scraper is uneven; the thickness of the screen is inconsistent, and the screen is not on the same level.

Solution: Check the surface of the patch resin to be flat, like a mirror: check the viscosity of the color paste and make adjustments; test the capillary effect of the grey cloth. If it fails, it will be repaired before printing; the shades are reproduced in the same pattern. Plate or scraper problem. The blades of the scraper are the same, the pressure on the left and right of the scraper is the same, and the penetration rate of the net cylinder at the flower position is the same.

23, left, middle and right depth

The hue and depth of the two sides and the middle of the cloth are different. Causes: poor fabric scouring and bleaching; poor installation of the screen frame; insufficient scraper stroke: too thick resin on the edge of the printing belt.

Solution: When fabric scouring and bleaching, the pH of the cloth surface is uniform; the screen frame is at the same level as the guide belt; the scraping distance of the scraper exceeds the cloth edge by more than 5cm to prevent the deceleration effect when the scraper is turned over; to print different widths of gray fabric, change the patch position.

24. Water stains

Blots or spots caused by water droplets. Causes: the conduction belt is not cleaned or the drying room is dripping; the semi-products are not properly protected for a period of time before the end of the steaming after printing, dripping on condensed water or splashing water droplets, dripping on the top of the steaming machine.

Solution: Check the flatness of the wiper blade of the water tank of the washing and guiding belt, and repair it in time; protect the semi-finished product and wrap it in cloth: stop steaming, check the cause of dripping from the steaming machine, and steam after the solution.

25. Hole

The strength of the fabric is damaged at the printing area, and the warp or weft is broken. Cause: The content of the reducing agent (whiteness) in the discharge printing color paste is too high; after the discharge printing, the steaming and washing is not timely.

Solution: Adjust the whiteness of the carving to make the carving and hair color just right; arrange the printing shape to be steamed and washed in time after printing.

26. Relief

Occurs in anti-printing (paint-proof) and engraving, the ground color around the flower has irregular displacement. Causes: Too much reducing agent is used, and it is not completely decomposed during the steaming process, and continues to destroy the ground color under the damp and hot state; the back of the screen is stained during printing and the pattern is inaccurate; the tension of the screen is too loose when the screen is stretched.

Solution: According to the amount of dye and the depth of the printing ground color, correctly control the amount of reducing agent and test it before use; pay attention to the operation during printing, and do not frequent debugging; the screen tension is uniform and appropriate.

27. The color is not clean or the anti-dyeing effect is poor

Causes: insufficient amount of reducing agent or problem with the amount of auxiliary agent: too little amount of sizing during scraping; too long exposure to air after printing drying, premature oxidation; improper steaming conditions; poor extraction of ground dyes.

Solution: Before printing, a whitening test must be carried out on the ground color cloth of each car to prevent the non-extractable cloth from entering the printing; the actual effective composition of the reducing agent in the color paste is measured before printing; the scraping and printing paste is moderate and sufficient Pulp is on the cloth surface; after printing and drying, the fabric is wrapped in cloth to prevent premature oxidation due to oxygen in the air, and steam in time, and maintain the steam pressure during steaming.

28, friction stains drag away

Fuzz in one direction at the edge of the pattern. Cause: When printing is drying, the temperature in the drying room is low, and the cloth is not dried in time, and the cloth on the car rubs and drags apart when moving; when the printing pattern is not fully dried, it touches foreign objects and stains other parts; Drag the fabric when the printed fabric is not fully dried.

Solution: After printing, enter the drying room should be level, and the drying room temperature should ensure the drying conditions; the drying temperature is determined according to the thickness of the fabric and the speed of the car; after the cloth is out, do not load the car too full and squeeze or drag it down.

29. When printing, the fabric partially rises, and the fabric in the printed part swells away from the guide belt, similar to seersucker form, such as thin polyester fabric printing, nylon umbrella silk printing

Cause: The fabric stretches when wet.

Solution: Set the fabric to an extended state before printing, so that it loses the space for extension after being wet (wet patching is used to solve this problem when printing on the platen).

30. Printed flower-shaped arch

The cloth surface is uneven, showing that the paint printing part on stretch cloth or knitted cloth is prominent. Cause: Stretch cloth or knitted cloth has a certain degree of elasticity, and it is stretched when the cloth is attached. After printing, the printed paint part of the fabric is fixed in the state of fabric extension, and the printed part will return to its original state. As the printed and non-printed parts shrink differently, the cloth surface is arched.

Solution: Overfeed the fabric before printing, even exceed the shrinkage of the finished product, and apply tension without tension.

31. After finishing the color fastness decreases, the color fastness index after washing meets the standard, but after softening or some finishing, the color fastness of the finished product (especially the rubbing fastness) drops by half or even one level

Cause: The addition of a certain softening agent forms a film on the surface of the fabric, which binds to a part of the dye when it is combined with the fiber, so the dye is brought out during friction. Especially the combination of disperse dye and fiber is that the electron donating group and electron withdrawing group on the dye molecule dipolarize the dye molecule, and form a dipole moment with the =C=O group on the fiber to form a hydrogen bond. At high temperatures, a small amount of unbound or unstable disperse dyes are easily precipitated.

Solution: For reactive dye printing, choose a suitable softener. For disperse dye printing, the most convenient solution is to bake at high temperature and then enter a new simple water wash.