Common defects in printing products--Cylindrical printing (2)

(b) Common rashes in printing

1. Knife line (1) Form: In the longitude and width of a certain part of the printed fabric, a wide strip of knife lines is presented. The probability of a knife line appearing in the cloth is large.
(2) Cause:
1 The quality of the printing squeegee is not good, and the blade is not resistant to wear, bending, or being crushed.
2 The bad contact of the scraper in the circular net causes uneven color paste.
3 The inner surface of the inner wall of the circular net is not smooth enough to damage the blade and feed the slurry unevenly.
4 In the paste, the paste is not fully puffed, hard materials are mixed in, or the binder in the paint paste is not properly used. The film is attached at room temperature and adheres to the knife edge. When insoluble azo dyestuffs are stably printed, the squeegee rubs against the wire mesh to generate heat and friction, and it often sticks to the knife edge, creating a knife line or clogging the mesh.
(3) Preventive measures:
1 According to the type of fabric, the size of the pattern area, the performance of the color paste to determine the blade blade specifications, pressure and angle, in order to reduce the friction between the blade and the rotary screen.
Stork's innovative PTFE blade (with PTFE inserts on the outside of the blade to reduce the friction between the blade and the rotary screen) is more suitable for rotary screen printing, but it requires the use of low viscosity, rheologically good materials. paste.
2 It is better to choose the paste with low viscosity, high paste-forming rate and near Newtonian fluid. Avoid the mixing of impurities, paste expansion should be sufficient.
3 Before photosensitivity, the clarity of the mesh and the finish of the inner wall should be carefully checked to control the thickness of the glue during the squeegee and prevent the glue from penetrating into the inner wall.

2. Enclosed Circular Mesh Hole (1) Form: Partial pattern exposed on the printed fabric.
(2) Cause:
1 The surface of the fabric is not cleaned by fiber linters or yarns.
2 Color paste contains impurities.
(3) Preventive measures:
1 Install bristles and dust suction devices at the entrance of the rotary screen printing machine, and do a good job of cleaning the cloth.
2 Before using the color paste on the machine, use a high-mesh (above-mesh) screen filter.

3. Exposed bottom (1) Form: Some patterns on printed fabrics are light or uneven in shade and even white.
(2) Cause: Mainly due to the lack of proper colorant on the pattern of the fabric. The reasons are:
1 Scraper selection and pressure are not suitable for squeegee printing requirements.
2 The circular mesh hole is not clear, the mesh hole is too small or the mesh hole is blocked.
3 When the fabric semi-finished product is pretreated, the capillary effect is poor and the mercerization is insufficient. Affect the permeability of the fabric, easy to produce uneven color or light color.
(3) Preventive measures:
1 When printing thick fabrics and large-faced flowers, use a 50mm×0.15mm scraper to adjust the pressure and angle to increase the amount of color and reduce the exposed bottom.
2 Use low-viscosity sodium alginate, high etherification vegetable gum paste, or mix sodium alginate with emulsified paste.
3 Strengthen fabric quality control.

4. Permeation (1) Morphology: The colorant oozes out from the edge of the outline of the pattern, and the outer edge of the pattern is unclear.
(2) Cause:
1 Use a syrup with poor viscosity or decomposed dehydration.
2 Improper amount of auxiliary agent in the color paste causes the color-holding property of the color paste to decrease. For example, the amount of acid-releasing agent and reducing agent in printing ink paste is excessive.
(3) Preventive measures:
1 Strictly control the thickness of color paste, must not have dehydration, deterioration occurs.
2 The amount of the anti-dye agent should be reasonably determined according to the resistance of the dye to be dyed and the resistance of the original paste to the anti-dye agent.

5. Color transfer (1) Morphology: The color paste printed on the fabric by the rotary screen will reach the position of the next rotary screen printing position as the fabric is transferred. The residual slurry on the surface of the screen is transferred to the screen mesh, causing the color of the pattern to be inconsistent with the color of the original. .
(2) Cause:
1 Excess slurry.
2 When multiple sets of flower prints overlap each other, the layout order is unreasonable. For example, dark dark patterns are printed first, then bright and bright patterns are overprinted. 3 The printing scraper, feeding tube and feeding pump are printed in dark color paste after printing dark color paste. It is used for printing of light color paste, causing full or partial printing. Color transfer.
4 The patch is not correct, but one side of the guide belt, and the color paste printed on the guide belt, can be easily transferred to the surface of the latter circular net, resulting in color transfer.
(3) Preventive measures:
1 For the pattern with serious color transmission, the circular net can be arranged according to the principle of shallow depth first.
2 When a reasonable scraper is selected and a dark pattern is printed, a hard scraper (small height and large thickness) should be used to increase the pressure of the scraper, increase the penetration of the color paste, and reduce the amount of residual pulp remaining on the fabric. When printing light-colored patterns, soft scrapers (high-height, small-thickness) should be used to reduce the pressure of the scraper so that the deep-colored residual slurry does not reach the light-colored circular mesh openings.
3 The fabric semi-finished products are tentered to a width slightly larger than the printing width of the circular screen. Generally, 1 cm margin is reserved on both sides of the fabric.

6. Pressing light printing (1) Form: A regular light-colored scar appears on the surface of the printed fabric. The distance between the marks is the same as the circumference of the circle.
(2) Reasons: The non-pattern of the rotary screen has fiber fluff and impurities sticking to the pattern on which the color paste has been printed so that the original uniform color becomes lighter in the local color.
(3) Preventive measures:
1 Improve the surface finish of semi-finished products. Such as singeing, shearing, cutting nep and so on.
2 Install a brush and a vacuum cleaner at the place where the rotary screen printing machine is installed to ensure the surface of the printed fabric is clean.

7. Take apart or mop (1) Form: The fabric has a certain shape of the photocopy.
(2) Cause:
1 The large-area pattern fabrics are not fully dried, and they are stacked in the cloth for too long. The colorants absorb the moisture in the air and cause regular patterns to overlap.
2 After the squeegee fabric is improperly routed in the drying room, or the circulation air pressure in the drying room is improperly controlled, the fabric flutters, and the dry color paste does not adhere to the guide roller or the air outlet, causing the color to shift, causing no The rule is to open or drag.
(3) Preventive measures:
1 Control drying room temperature and printing locomotive according to the area of ​​the flower pattern to ensure the fabric is fully dried.
2 The path of the fabrics in the drying room should be correct. Pay attention to the inspection and cleaning of the parts (such as guide rollers, tuyere, blankets, etc.) that often appear defects.

8. Paste-stencil printing (1) Morphology: Light-colored patches or strips appear on the fabric.
(2) Causes: There are dents on the blanket, and the application paste is not evenly painted. The application of more paste will affect the penetration of the printing paste, resulting in a stain.
(3) Preventive measures:
1 The paste should be fully stirred and used after filtration.
2 The sizing blade should be straight.

9. Paste edge and white edge (1) Morphology: On one or both edges of the fabric, there is a pattern that is blurred or exceeds the allowable range.
(2) Cause:
1 The screen printing width exceeds the width of the fabric.
2 The fabric is biased toward one side when it enters the blanket.
(3) Preventive measures:
1 The width of the semi-finished product is greater than the width of the screen printing, and the margins on both sides are controlled within the allowable range, so as to effectively avoid the occurrence of edging.
2 Control the feeding device of the printing machine to ensure that the fabric is positively put into the conduction band.

10. Incorrect flowers (1) Form: In multi-color printing, one or more colors in all or part of the fabric are not in the proper positions.
(2) Cause: There are mainly the following aspects:
1 During the printing process, intermittent irregularities in the fabric occurred. That is, when every round of the round net, there is a phenomenon that the flowers are not in the same pattern at the same distance.
2 Platemaking:
The description of the black and white manuscript is improper, such as the use of the borrow line to use the line, the line is too large or too small and so on.
The accuracy of the circle size of the circle network is not uniform or the allowable error of the size of the circle network is not on the same side.
The entire set of polyester film used for the drafting or even the dry film shrinks in different directions. When the photosensitive film is misplaced, the circular net itself is not correct.
3 printing machine:
In the squeegee printing process, due to the shaking of the rotary screen or the printing blade, the flowers are not properly formed.
The gap caused by the wear of the driving gear of the rotary screen is large, and the oscillation of the tooth tip causes the improper flowering.
Due to the inertia of the printing machine after start-up, the conduction band is not tightened, and it is easy to make it slip on the driving roller, which causes the warp to be misaligned. This will also lead to deviation of the conduction band around the phenomenon, so that the incidence of zonal and oblique flowering.
4 Patching: Fabrics appear to have a section of uneven flower, and are not equidistantly spaced, so that the adhesive force of the thermoplastic patch chamber is poor, the printed fabric is wetted by the color paste and then shrinks, and relative displacement occurs on the conduction belt.
(3) Preventive measures:
1 When there are intermittent irregularities, you should first check the marks on the circle and check if the circle pattern is misaligned.
2 According to the production technology requirements, seriously complete each process of plate making.
3 Check whether the running of the printing rubber belt is correct, and whether the position of the leading roller is smooth, so as to prevent the warp and weft of the flower from being wrong.
4 Reasonable selection of paste, timely stripping thermoplastic adhesive that has lost its adhesion, and improve its adhesion to the fabric.

11. Multi-flowering (blister)
(1) Form: The same color spots with the same circumference and the same circumference are present on the printed fabric.
(2) Reasons: Due to the poor adhesion or poor mechanical strength of the rotary screen, the printing blade rubs against the rotary screen and the adhesive peels off the mesh.
(3) Preventive method: Apply sand with no repair glue. Conscientiously carry out the process technology requirements for photo-resist, exposure, development and inspection in the plate making operation to improve the plate making quality and avoid the occurrence of trachoma in the production process.

12. Cylinder Wrinkles (1) Morphology: The surface of the fabric presents a regular, horizontal, or blocky shade of light with the same pitch and circumference as the shape of the circle.
(2) Causes: The surface of the circular net has creases. When printing, the circular net and the fabric do not make good contact, resulting in non-uniformity of the slurry, resulting in vertical and horizontal dark creases.
1 The loading and unloading scraper inadvertently inspects the round net.
2 Artificial pinching caused creases.
(3) Preventive measures:
1 When the rotary screen is placed on the bracket, the height of the support roller is adjusted so that the distance between the rotary screen and the printing guide belt is constant at 0.3 mm, so as to prevent the rotary screen from being deformed by the pressure of the doctor blade to generate wrinkles.
2 Before the operation of the rotary screen, the circular net should be tensioned evenly to keep the rotary net with sufficient rigidity and elasticity to prevent the single-side drive from being distorted under the pressure of the printing scraper.
3 The sharp corners of the contact between the two ends of the printing blade and the rotary screen must be cut into an arc shape and polished to avoid excessive resistance, resulting in damage to the rotary screen.

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