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Analysis of the causes affecting the quality of silk screen printing

release date: Source: China paper

I. preface

silk screen printing (later referred to as silk screen printing) is a classification other than offset printing, relief printing and gravure printing, and this category is particularly widely used. It is used in paper, plastic, leather, wood products, glass, ceramics, textiles and other industries. At present, silk screen printing is widely used to serve the electronic and 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 that has been developed again in 30 years. Therefore, people only have a preliminary understanding of silk screen printing, but they do not know much about the impact of 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. Today, we are going to introduce the related reasons in detail

II. Silk printing template and its quality

technological process of two methods of silk printing template manufacturing

1 Direct method

preparation of silk frame stretching - silk cleaning - multiple scraping of photosensitive adhesive - drying and covering with photographic plate after printing - Development - drying - Revision - sealing

precautions during operation: (1) the oil stain on the silk must be completely removed before applying the photosensitive adhesive; (2) the times of applying and scraping the photosensitive adhesive shall be determined according to the accuracy of the printed pattern and the number of silk meshes; (3) When printing, make sure that the photographic plate and the photosensitive adhesive layer are closely covered; (4) The silk shall be used immediately after cleaning, and shall not be touched by hands

2. Direct photosensitive film method (coating fine soft film method)

wetting the film or applying photosensitive glue - drying - stripping the film base - Printing - developing - revision, etc

precautions: (1) keep the film away from light or yellow light; (2) Apply the corresponding photosensitive adhesive back film

material. The properties of common materials are compared according to the requirements of HRH quality

a. nylon yarn:

(1) it has certain wear 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 using, pay attention to increasing the tension on the wire, and fine products can be printed

b. polyester filament:

(1) vanilon filament has all the advantages:

(2) strong acid resistance and chemical resistance

(3) because the moisture absorption is lower than that of nylon, the dimensional stability is better

(4) the strength decrease of polyester filament after exposure 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 monofilament diameter is larger than that of nylon filament. Therefore, under the same through-hole ratio as nylon, the ink passing performance of polyester is worse than that of nylon

mesh number refers to the number of inner holes per centimeter of length. Inch system refers to the number of holes per inch

through hole rate refers to the percentage of the hole part in the whole wire area

hole width refers to the side length of the square hole

thickness refers to the thickness of the wire

wire diameter refers to the diameter of the single wire of the braided wire

3. Tension requirements

in the silk screen printing process, the wire must also be fixed on the frame, so that after the wire is stressed in the scraping process, the blade edge of the scraper contacts the wire and the substrate in a line. Once the pressure disappears, the wire will leave the substrate immediately. Otherwise, the required clear pattern will not be printed. Therefore, the silk itself must have a certain elasticity, and it is not appropriate to be too large or too small. In order to make the silk elastic, the silk must be stretched on the frame. Therefore, people believe that in order to obtain an ideal template, the stretching must be:

(1) the tension at all parts of the silk must be uniform

(2) the wire hole area is basically close to the square

(3) the stretched wire ensures stable tension during the service life. Before stretching, the wires and frames must be subjected to stress treatment to stabilize their cold deformation

(4) in the stretching process, the force applied to the wire should be uniform at the same speed. As far as possible, the tension of the wire should be increased in stages and at intervals to promote a stable "aging" process of the wire. (the company sells all kinds of silk, sizes and sizes, from 80 mesh to 420 mesh)

in order to achieve the above ideal conditions:

it is best to use a special stretching equipment with a tension test table. It must be noted that it is not possible to stretch at one time. It should be increased for 2-3 times within a certain period of time and then placed for 2-4 hours for natural "aging". After the silk deformation is stable, the tension should be measured, The wire can be fixed on the frame only after reaching the standard

II. For the silk plate with Overprint requirements, the silk texture, cutting direction and tension must be consistent

the feedback quantity is that the longitude and latitude lines of the wires are perpendicular to each other as far as possible under the force when the current is stretched for three times

the frame shall be stressed before four stretching. If you do the above, you can stretch a satisfactory silk

4 requirements for black-and-white manuscript

drawing black self manuscript is the basic preparation process for photographic plate making and the necessary process equipment before silk screen printing. The quality of black-and-white manuscript directly affects the accuracy and beauty of the finished product. Therefore, the black-and-white manuscript is required to be accurate in size, with smooth scribed edges, large manuscript contrast, clear and beautiful characters and symbols, symmetrical stroke arrangement, etc. In order to improve the accuracy of black-and-white manuscripts, it is suggested that the paper used should be considered when drawing manuscripts. Relying on the scalability of Hexin casting, Dongfang Yunda and other enterprises, manuscripts should be stored and kept. Therefore, the following requirements are put forward

requirements for black-and-white painting and its tools, materials and equipment paper: heavy weight Daolin paper or coated paper with no reflection above 250g, with no impurities, stains, etc. on the surface, and absolutely flat... The painting method and requirements for black-and-white manuscript:

the proportion depends on the equipment, and is generally drawn as 2:1 and 4:1

for the workpieces requiring front and back silk screen printing, if the position is required, they shall be drawn on both sides of the same paper, such as double-sided printing plate, etc

for the black-and-white manuscript used for multiple overprinting, it should be considered that the lines of several sheets of paper should be consistent when drawing the manuscript, the selected positioning datum should be consistent, and the environmental and climatic conditions should be basically consistent as far as possible. If necessary, it should 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 plate)

in recent years, due to the extensive use of screen printing, the materials providing screen printing are also increasing. On the contrary, there are new requirements for screen printing quality. Therefore, the requirements for screen printing die should be stable in size, high in printing precision and high in printing resistance. Therefore, the manufacturing of screen printing die occupies a very important position in the whole screen printing process. Here, the main problems of silk impression are briefly discussed

(1) jagged line edge:

due to insufficient exposure, the photosensitive material crosslinked by absorbing light is not fully crosslinked, resulting in swelling and partial dissolution of the photosensitive adhesive during development. During the development process, the pattern is pulled off by external forces, such as wiping. High precision pattern but low mesh silk will also produce burrs. If the above situation occurs, the solution is to overcome it one by one, but the key point is to select the correct exposure time

(2) when the exposure time is appropriate. The parts that should not be removed in the version fall off or there is residual glue in the parts that should be removed. Check the following problems. Whether the contrast of the photographic plate is accurate, whether there is contamination, etc. Whether the drying temperature of the photosensitive film before exposure on the silk is too high, which causes the thermal crosslinking of the film to be invisible, or the film is not dried sufficiently, and the development falls off. 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 well adjusted, resulting in overexposure and underexposure. The position between the light source and the plate is incorrect, resulting in unequal exposure within the same time. The photosensitive adhesive (film) is uneven, and the quality is different at different positions on the same plate

(3) collapsing and die collapsing

1 after the plate is made, the drying temperature is too high, especially the large deformation of the wooden frame (distortion, bending, irregular expansion) causes die collapsing

2 due to the change of weather, the tension of silk changes, resulting in film collapse, especially after repeated application and cleaning

3 improper wire treatment, especially incomplete cleaning before pasting (coating) photosensitive film, which is easy to collapse in use

(4) the photosensitive film (glue) is not firmly combined with the silk

① the silk is not thoroughly decontaminated and degreased

② insufficient exposure, check the lighting system

③ the selected wire is incorrect, the hole is too thick or the development and washing are not suitable

④ drying too fast after film or photosensitive adhesive coating, which will make the film or adhesive disappear quickly

⑤ poor performance of photosensitive materials

(5) pinholes and pockmarks appear on the template

① check the photographic plate

② dust causes pollution of silk and photosensitive film (glue) and unclean printing glass

③ insufficient exposure, poor control, light source, distance and time

④ development, so each load can only reach a certain load, and the flushing is excessive

⑤ the film is too thin and the uniformity of the dissolution of photosensitive colloid and sensitizer is poor

in a word, sometimes the quality problems of the die are caused by many factors. Therefore, it is necessary to analyze and check each process and solve them accordingly

6. To measure the quality of a piece of silk template, the following aspects should be examined:

first, the resilience of the silk is relatively stable during the silk screen printing process. During the silk screen printing process, the mold is close to the original tension before the silk screen printing

second, the printing material has good passing performance

third, the lines and edges of the pattern are flat without sawtooth and pockmarks

fourth, during the screen printing process, the original screen printing accuracy and resolution of the screen printing front die shall be maintained

fifth, the mold has a long service life, that is, it is resistant to printing, wear, cleaning and can be reused

the first four points meet the requirements of the fifth point according to the requirements of manufacturing die, so that the wire die can achieve the maximum economic benefits. How to meet? The discussion is as follows:

(1) the stretched silk must be thoroughly degreased and decontaminated to maximize the bonding strength between the silk and the glue

① degreasing and decontamination treatment methods generally use organic solvent, 120 aviation gasoline or acetone to wipe the front and back of the silk

② for the silk used in single piece production, it can be boiled in boiling water for half an hour and then removed. It can still be wiped with organic solvent before applying the photosensitive film

(2) select the appropriate method of making mold

(3) on the premise of not affecting the requirements of the workpiece, the photosensitive film (adhesive) shall be as thick as possible so as to (4) optimize the correct exposure time to make the film (adhesive) of the light receiving part cross-linked completely

(5) reasonably select the photosensitive adhesive (film) layer matching the printing material performance

(6) after development, the photosensitive adhesive film is cured by light and heat to make it thoroughly cross-linked

III. selection of printing materials

due to the development of silk screen printing technology with the national economy. Need and development, and the printing material in silk is an indispensable part of the whole screen printing. Screen printing must be based on plate (template) and printing material

currently, there are many printing materials used in silk screen printing, which can be divided into three categories

1. Water based printing materials

2 Solvent based printing

(1) physical drying

(2) oxidation drying

(3) chemical drying

3 UV solid printing materials

due to the applicability, there is no kind of printing materials

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