Screen printing (later called silk screen printing) is a classification outside offset printing, letterpress printing and gravure printing. This kind of printing is particularly widely used. At present, it should be widely used in the paper industry.Several Factors Leading To Paper Printing Deformation
It is used in paper, plastic, leather, wood products, glass, ceramics, textile and other industries. At present, silk screen printing is widely used to serve the electronic telecommunications industry, such as manufacturing printed circuits and nameplate labels. Although silk screen printing is widely used, it is only an old and young industry developed again in 30 years.Several Factors Leading To Paper Printing Deformation
Therefore, people only have a preliminary understanding of silk screen printing, but they don’t know much about the impact on silk screen printing quality. How to ensure silk screen printing quality has become the scope of our current discussion. This paper mainly discusses some quality problems in silk screen printing from the aspect of process requirements and how to control them, so as to further improve the level of silk screen printing and better decorate the products.Several Factors Leading To Paper Printing Deformation
Screen printing template and its quality
Technological process of two methods of silk screen template manufacturing
1. Direct method
Preparation of screen frame stretching – > cleaning of screen – > scraping photosensitive adhesive for many times – > covering and printing with photographic plate after drying – > development – > drying – > revision – > screen closure.
Precautions during operation: (1) the oil stain on the screen must be completely removed before applying the photosensitive adhesive;
(2) the number of times of applying and scraping the photosensitive adhesive shall take into account the accuracy of the printed pattern and the number of screen mesh; (3) When printing, make sure that the photographic plate is closely covered with the photosensitive adhesive layer; (4) The wire mesh shall be used immediately after cleaning, and shall not be contaminated by hand.Several Factors Leading To Paper Printing Deformation
2. Direct photosensitive film method (wool thin film method)
Wet the film or apply photosensitive adhesive – > dry – > strip the film base – > Print – > develop – > repair, etc.
(1) keep the film away from light or yellow light;
(2) Apply the corresponding photosensitive adhesive to the rear film.
Mesh. From the quality requirements, the properties of common mesh materials are compared.
A. Nylon mesh:
(1) It has certain wear resistance and tensile strength;
(2) Good resilience and printing material permeability;
(3) Not resistant to acid solution;
(4) Large moisture absorption, so the dimensional stability is poor;
(5) When in use, pay attention to increasing the tension on the screen to print fine products.
B. Polyester mesh:
(1) All the advantages of nylon mesh are:
(2) Strong acid resistance and chemical resistance;
(3) Because the moisture absorption is lower than that of nylon fiber, the dimensional stability is better.
(4) The strength decrease of polyester filament exposed to sunlight is smaller than that of nylon filament;
(5) Disadvantages: the binding force with the currently used photosensitive adhesive (film) is slightly poor, and the diameter of single wire is thicker than that of nylon wire. Therefore, compared with the same through-hole rate of nylon wire, the ink passing through the wire mesh of polyester wire mesh is worse than that of nylon wire mesh.
Mesh – refers to the number of mesh holes per centimeter of length. English system refers to the number of meshes per inch;
Through hole rate refers to the percentage of the mesh part in the whole screen area.
Mesh width refers to the side length of square mesh;
Thickness – refers to the thickness of the wire mesh;
Wire diameter – refers to the diameter of the single wire of the woven wire mesh.
3. Net stretching requirements
In the silk screen printing process, the screen must also be fixed on the frame, so that after the screen is stressed in the scraping process, the blade edge of the scraper is in line contact with the screen and the substrate. Once the pressurized force disappears, the screen will leave the substrate immediately. Otherwise, the required clear pattern will not be printed. Therefore, the screen itself must have a certain elasticity, and it is inappropriate to be too large or too small. In order to make the screen elastic, the screen must be stretched on the frame. Several Factors Leading To Paper Printing Deformation
Therefore, people believe that in order to obtain an ideal template, the stretched screen must be:
(1) The tension throughout the wire mesh must be uniform.
(2) The mesh hole area is basically square
(3) The stretched wire mesh ensures stable tension during the service life. Before stretching the mesh, the mesh and mesh frame must be subjected to stress treatment to stabilize their cold deformation.
(4) In the process of stretching the wire mesh, the force applied to the wire mesh shall be uniform at the same speed, and the tension of the wire mesh shall be increased in stages and intervals as far as possible, so as to promote a stable “aging” process of the wire mesh. (the company sells all kinds of wire mesh, with sizes ranging from 80 mesh to 420 mesh)
In order to achieve the above ideal conditions:
It is better to use a special stretching equipment with a tension test table. It must be noted that the stretching can not be completed at one time. The tension should be increased for 2-3 times within a certain time, and then placed for 2-4 hours for natural “aging”. After the deformation of the screen is stable, the tension can be measured again, and the screen can be fixed on the screen frame only after reaching the standard.
For the screen version with Overprint requirements, the grain, cutting direction and tension of the screen must be consistent.
When three nets are stretched, the longitude and latitude lines of the screen shall be perpendicular to each other as far as possible under stress.
Four, before stretching the net, give the net frame a certain stress treatment. Do the above points, you can stretch a satisfactory screen.
4 requirements for black and white manuscripts
Drawing black self draft is the basic preparation process for photographic plate making. It is the necessary process equipment before silk screen printing. The quality of black-and-white draft directly affects the accuracy and beauty of finished products. Therefore, the size of black-and-white manuscript is required to be accurate, the scribed edge is smooth and the manuscript contrast is required
Large, clear and beautiful characters and symbols, symmetrical stroke arrangement, etc. In order to improve the accuracy of black-and-white manuscripts, the flexibility of the paper used, the storage and safekeeping of manuscripts should be considered when drawing manuscripts. Therefore, the following requirements are put forward;Several Factors Leading To Paper Printing Deformation
Requirements for black-and-white painting and its tools, materials and equipment paper: more than 250g non reflective heavy forest paper or coated paper, the surface is free of impurities, stains, etc., and is absolutely flat… Drawing methods and requirements for black-and-white manuscripts:
The scale depends on the equipment. Generally, it is drawn as 2:1 and 4:1.
For the workpieces requiring front and back silk screen printing, if the position is required, the drawings on the front and back sides of the same paper, such as double-sided printing plate, etc.
For the black-and-white manuscript used for multiple overprint, it shall be considered that the lines of several sheets of paper shall be consistent when drawing the manuscript, the selected positioning datum shall be consistent, and the environmental and climatic conditions shall be basically consistent as far as possible.Several Factors Leading To Paper Printing Deformation
If necessary, it shall be drawn and photographed under the condition of constant temperature and humidity. Nowadays, computer drawings and films are generally used.
5. Quality of screen printing die (also known as screen printing)
In recent years, due to the wide use of silk screen printing, the materials providing silk screen printing are also increasing. On the contrary, there are new requirements for silk screen printing quality. Therefore, the requirements for silk screen printing template should be stable in size, high printing accuracy and high printing resistance of screen. Therefore, the manufacturing of silk screen printing template occupies a very important position in the whole silk screen printing process. The main problems of wire impression are briefly discussed here.
(1) Jagged line edges:
Due to insufficient exposure, the photosensitive material crosslinked by absorbing light is not completely crosslinked, resulting in swelling and partial dissolution of the photosensitive adhesive. During the development process, the pattern is pulled off by external forces, such as wiping. High precision pattern but low mesh screen will also produce burrs. If the above situation occurs, the solutions should be overcome one by one, but the key point is to select the correct exposure time.
(2) When the exposure time is suitable. If the part that should not be displayed in the screen falls off or there is residual glue in the part that should be displayed, the following problems should be checked. Whether the contrast of the photographic plate is accurate, whether there is contamination, etc. Whether the drying temperature of the photosensitive film pasted on the screen before exposure is too high, which causes the thermal crosslinking of the adhesive film and does not show, or the development falls off due to insufficient drying of the adhesive film. Photographic plate and photosensitive film are not close to each other, which has refractive effect. The relationship between the distance between the light source and the workpiece and the exposure time is not adjusted well, resulting in overexposure and underexposure. The position between the light source and the screen is incorrect, resulting in unequal exposure within the same time. Uneven photosensitive adhesive (film), the quality difference at different positions on the same screen.
(3) Broken mesh and broken mesh mold
1 after the screen plate is made, the drying temperature is too high, especially the large deformation of the wooden screen frame (distortion, bending and irregular expansion) causes the screen die to collapse.
2. Due to the change of weather and the change of wire mesh tension, the mesh and film collapse are caused, especially the film that has been repeatedly applied and cleaned for many times.
3. Improper screen treatment, especially incomplete cleaning before pasting (coating) photosensitive adhesive film, which is easy to collapse in use.Several Factors Leading To Paper Printing Deformation
(4) The photosensitive film (glue) is not firmly combined with the screen.
① Screen decontamination and degreasing are not complete.
② Insufficient exposure, check the lighting system.
③ The screen selected is incorrect, the mesh is too thick or the development is not suitable.
④ Drying too fast after pasting film or coating photosensitive adhesive will make the film or adhesive disappear soon.
⑤ Poor performance of photosensitive materials.
(5) There are pinholes, pits, etc. in the template.
① Check the photographic plate.
② Dust causes pollution of screen and photosensitive film (glue) and uncleanness on printing glass.
③ Insufficient exposure, poor control, light source, distance and time.
④ Develop and rinse too much.
⑤ The film is too thin and the uniformity of the dissolution of photosensitive colloid and sensitizer is poor.
In short, the quality problems of mesh formwork are sometimes caused by many factors. Therefore, each process should be analyzed and checked and solved accordingly.
6. To measure the quality of a screen template, the following aspects shall be assessed:
First, in the process of silk screen printing, the resilience of the screen remains relatively stable. In the process of silk screen printing, the screen mold is close to the original tension before silk screen printing.
Second, the printing material has good passing performance.
Third, the pattern line edge is flat without sawtooth and pitting;
Fourth, in the process of silk screen printing, maintain the original silk screen printing accuracy and resolution of the screen mold before silk screen printing.Several Factors Leading To Paper Printing Deformation
Fifth, the screen mold has a long service life, that is, it is resistant to printing, wear, cleaning, and can be reused.
The first four points are carried out according to the requirements of manufacturing mesh mold, which meets the requirements of the fifth point, so that the mesh mold can achieve the maximum economic benefits. How to meet? The discussion is as follows:
(1) The stretched wire mesh must be thoroughly degreased and decontaminated to maximize the bonding strength between the wire mesh and the glue.
① The degreasing and decontamination treatment method generally uses organic solvent, 120 aviation gasoline or acetone to wipe the front and back of the screen.
② For the screen used in single piece production, it can be boiled in boiling water for half an hour, then the screen can be stretched, and it can still be wiped with organic solvent before applying photosensitive adhesive film.
(2) Select the appropriate method of making mesh mold.
(3) On the premise of not affecting the requirements of the workpiece, the photosensitive film (glue) shall be as thick as possible, so as to (4) optimize the correct exposure time to completely crosslink the film (glue) of the light receiving part.
(5) Reasonably select the photosensitive adhesive (film) layer matching the printing material performance.
(6) After developing the photosensitive film, it is cured by light and heat to make it completely cross-linked.