T-shirt has played a very special role in the history of human clothing development. It is different from other clothing because of its important cultural value. Now, it has broken through the concept of clothing, representing a spiritual culture and social consciousness. A unique reflection of form. The soul of a T-shirt lies in the pattern printed on the surface of the T-shirt”. The type of T-shirt pattern and the demand for printing volume are different, and the processing technology is also different. The printing volume is 1~5 pieces, suitable for digital inkjet technology, and the original manuscript can be a color block , it can also be a continuous tone pattern. The disadvantage of its process is that the cost of a single print is high. The printing volume is 5~100 pieces, which is suitable for the thermal transfer process. The original can be a color block or a continuous tone pattern. The disadvantage of the process The cost of a single printed piece is high, and the ink layer and the underlying fabric do not adhere well. The printing volume is more than 100 pieces, and the original is a color block, which is suitable for dye printing process. This process is a common printing process, with high color fastness and migration resistance. Good, the cost per piece is low. The disadvantage of the process is that the post-press processing is complicated, and the ratio of the color paste is difficult to master. The printed parts are more than 100, and the original is a continuous tone pattern, which is suitable for the paint printing process. The biggest feature of this process is that it can be used on textiles. Printing the mesh tone pattern, the color paste is attached to the fabric, and has high color fastness. The disadvantage of this process is that the color separation process is complicated, and moiré is easy to produce after printing. The purpose of this test is to test the continuous tone pattern printing volume of more than 100 pieces. Screen printing process parameters.
Experimental conditions
Requirements for environmental parameters
Since there are many factors that affect the printing quality, in order to ensure the accuracy of the experimental results, the consistency of parameters such as screen distance, ambient temperature and humidity, and ink should be maintained during the experiment.
Selection of plate-making parameters
The silk screen used in the screen printing plate for printing mesh tone has stricter requirements on its texture, tensile strength, mesh number and other parameters.
1. Selection of screen mesh
The selection of the mesh number has a lot to do with the customer’s requirements and the quality of the pattern. The mesh number of wire mesh can generally be selected from 300 mesh, 350 mesh, 380 mesh, and 420 mesh. The fundamental principle for selecting the four meshes is the required image clarity. The mesh number of the screen is generally more than four times the number of added screen lines, which will avoid moiré. However, considering the amount of ink, the screen mesh should not be selected too high. Generally, the screen mesh used for T-shirt printing is 300 mesh.
2. Determination of Tension of Stretching Net
The measurement method of fine mesh tension is five-point measurement method, using yellow dyed wire mesh, aluminum mesh frame, mesh angle of 90°, using 30min stretching method, the tension reaches 22Ncm, and the tension of each plate is consistent.
Fine mesh method:
①Tighten the warp and weft tension to half of the specified value at the same time;
②Stable for 60s;
③ Increase the tension by 2~4N/cm and pause for 60s;
④Increase the tension by 2~4Ncm, and then operate to the tension value;
⑤ Stable for 15 minutes and stretch again to the standard tension value, but the tension of the 30-minute stretching method may lose 6%~10% after 24 hours, which mainly occurs within the first 4 hours, so it should be stabilized for at least 4~8 hours before drying Version.
3. Determination of film thickness
The thickness of the plate film is closely related to the amount of ink passing. If the thickness of the plate film is too thin and the amount of ink passing is small, the subtle parts of the image may not be displayed, the small lines are easy to break, and the small dots are not easy to transfer to the substrate; plate; If the film thickness is too thick and the amount of ink is too large, it will cause a slope on the cross section of the ink on the substrate, which will affect the accuracy of graphics and text.
The principles for determining the film thickness are as follows: ① coating and drying time; ② image accuracy; ③ printing time; ④ printing durability. The relationship between the thickness of the plate film and the above-mentioned items in the experiment is shown in the following table: It can be seen from the above data that the thicker the plate film coating is, the longer the working hours are, and the more difficult it is to dry. And the drying time is long, it is easy to cause the hardening of the photosensitive adhesive due to heat, resulting in the dots not appearing. Based on the performance of printing durability and dot restoration, the film thickness is set at 154m.
4. Determination of exposure time
The exposure time is determined by means of an exposure time test chart. This test card consists of five parts, namely the bottom card part, the 0.7 coefficient part, the 0.5 coefficient part, the 0.33 coefficient part, and the 0.25 coefficient part. The use of the test card is very simple, avoiding the complicated process of the traditional five-stage test method. The usage method is as follows: First, set a basic exposure value with reference to other plate-making processes. The basic exposure value is 2 to 3 times the usual exposure time. After exposure and development of the screen plate, observe the color of the plate film where the four parts are located. Darker colors indicate less exposure. Find two consecutive color blocks with the same color, and select the coefficient of the color block with the smaller value. After finding the coefficient, multiply the exposure time by the coefficient to get the optimal exposure time.
In the first experiment, a screen plate with a film thickness of 15Hm was used, and the exposure time was set to 280s. After exposure, it was found that the position with a coefficient of 0.5 was the same as 0.7 and the color of the base plate, so it can be determined that the optimal exposure time is 280*0.5= 140 (s), if you want to make a more accurate measurement, you can set the exposure time to 200s. After exposure, it is found that the position with a coefficient of 0.7 is the same as the color of the base plate, so the best exposure time is 200*0.7=140(s ), it can be concluded from two experiments that the optimal exposure time of the screen is 140s.
Determination of the number of screen lines
The quality of the printing effect has a lot to do with the number of screen lines. The method of determining the number of screen lines for T-shirt printing is to use the same pattern, use different screen lines for printing and keep other process parameters unchanged.
20 lines/in, 30 lines/in, 35 lines/in, 40 lines/in. 50 lines/in, 60 lines/in, 70 lines/in, 80 lines/in. 90 lines/in. . 100 lines/in. The comparison of the same pattern shows the optimal number of screen lines. The optimum number of screen lines is 40 in. At the same time of screening, it should be noted that the screening angle is different from that of offset printing. Because screen printing has the effect of a screen mesh, moiré is more likely to appear.
Some experience in avoiding moiré is as follows: When printing halftone patterns, first ensure the consistency of all production variables; the number of meshes that should be used and the same diameter of mesh each time the same type of product is printed ; Make sure that the mesh tension is in the range of 1~2Ncm; if you change the working parameters at will, it will be easy to make mistakes. Therefore, standardization is the key to screen printing, it helps to determine the scope of the moiré problem.
This is a very common problem in the printing process. Since most of the raw materials used for printing have “accurate” specifications and characteristics, most of the printing work is operated with the characteristics, but the actual situation is often not the case. For example, the stated mesh value is actually based on the weave metric conversion and then rounded to the nearest 5 threads/inch. Again, the halftone line values are only obtained when the halftone angle is 0° or 90°, and for all other halftone angles
It is said that due to the small number of dots per inch, the number of lines is very small, so it is not specified. In addition, on the equipment, the relative angular range has been set in many RIP (image processor) software that drives imagesetters and inkjet printers according to many design procedures. Therefore, in the application, great attention should be paid to the real specifications of the materials used and the accuracy of the equipment and meters, and cannot be taken for granted.
The wreath pattern is actually a moiré pattern too, but it’s a harmless moiré. A wreath is formed when the angles are at 30° and 60° and face each other. This pattern consists of halftone patterns that are beautiful and pleasing to the eye. If the two corners are separated by 45°, it is very likely that the dots will be accurately formed, resulting in harmful moiré. Thus, simply by separating the three main contrasting colors (cyan, magenta, and black) at 30° angles to each other, a garland pattern can be created. Yellow is a non-contrasting color and can be inserted at 15° in any other color.
Rotate the lithography angle by 4~8°. In lithography, generally start with yellow and set it to 0°, then rotate 15° to set cyan, 45° to black, and 75° to magenta. Alternatively, often tint cyan to 105° (exactly 15°+90°) and magenta to 165° (75°+90°). For screen printing and flexographic printing, rotating these angles by 4~8° has been used for many years.
practiced and very successful method. Of course, before rotating the setting angle, you should consult the relevant prepress supplier and RIP (image processor) software manufacturer to determine what angle is suitable for the number of halftone lines to be used.
Here are two sets of the most common angles: one is 5° for yellow, 20° for cyan, 50° for black, and 80° for magenta; the other is 7.5° for yellow, 22.5° for cyan, and 52.5° for black °, magenta is 82.5°. Both sets of angles are suitable for contrasting color printing. But when the color separation is produced, be sure to remember to first verify the angular position of the calibration rotation with a protractor or goniometer. Mesh-dot-ratio is the ratio of the number of screen lines to the halftone dots. Over the years, the industry has compared this
For example, the theory is debated, and it is generally believed that it should be 4:1 or 3.5:1. It should be said that this ratio is only suitable for individual prints, and cannot be used to point to surface. The mesh-dot ratio relationship is only for guidance, because the ratio is affected by many factors. For example, the number of screen lines affected by its tension is a continuous variable. The higher the tension, the fewer threads per inch. For halftone dots, the number of halftone lines is only accurate to 50% of the tone value, that is – - one fully formed dot and one
Fully formed spatial coexistence. For all other values, the halftone dot coverage is much less than the actual number of lines marked. The quality of the mesh selection determines the size of the halftone dot interference between the screen mesh and the mesh line. Theoretically: the thinner the network cable, the less chance of interference. However, in actual operation, if the screen wire is too thin, the printing tension of the screen will be reduced. Generally speaking, when choosing a mesh, it is best to choose a smaller diameter with a given number of mesh lines.
the network cable (sometimes called the S cable). The best combination of mesh count and wire diameter is: 300 threads/inch mesh with 34 μm diameter mesh; 380 threads/inch mesh with 30 μm diameter mesh; 420 threads/inch Mesh and wire with a diameter of 27 μm. It is emphasized here that the mesh for printing must be plain weave.
The key to printing is that the silk screen and the positive picture must be integrated and exposed in a full vacuum state. Under full vacuum conditions, Newton’s rings are formed on the surface of the positive sheet. This clearly visible rainbow-like texture indicates that the positive image and the screen printing plate are closely attached, and the positive image is completely adhered to the photosensitive emulsion layer of the screen plate. Full vacuum can ensure sufficient exposure, and the screen photosensitive layer receives even light. The biggest danger of photocopying exposure is overexposure. Overexposure will cause vignetting or poor light scattering, resulting in uneven edges and incomplete dot formation. In addition, overexposure can cause the screen plate to change the size of the dots or even lose fine dots, making it difficult to determine the dot or tone ratio produced by moiré.
Experimental results
This experiment takes the screen printing plate process parameters as the research object, and analyzes the screen angle, screen line number, plate film thickness, exposure time, screen and other parameters that affect the quality of the printing plate according to the screen printing process principle. The paper uses the exposure time test card to determine the optimal sea light time to ensure the printing quality, and eliminates the influence of the printing quality problem on the accuracy of the subsequent experimental results. A test version suitable for the study of the process parameters of the screen printing with mesh tone is designed, and the relationship between the screen parameters and the tone reproduction is obtained. The unavoidable moiré problem in the process of screen printing is studied, and the configuration of the screen angle and the reasonable range of mesh/line ratio are obtained.
main conclusion:
1. The optimal exposure time of Taipingqiao DS-1 type two-component diazo photoresist is 140s. At present, the exposure calculator method and the hierarchical exposure method can be used to determine the optimal exposure time. If screen printing companies want to save time and improve production efficiency, they can use the exposure calculator method to determine the optimal exposure time of the photoresist used.
2. Screen parameters determine the minimum light tone and minimum dark tone dots that can be reproduced by screen printing. Each screen with different geometric parameters has its own range of tones that can be reproduced. When selecting the screen parameters, the enterprise can calculate the minimum bright-tone dots to be copied according to the number of screen lines and the tone range of the film, and then determine whether the selected screen meets the requirements according to the screen printing resolution.
3. Selection of the number of added screen lines: The higher the number of added screen lines, the more serious the expansion of the dots, and the smaller the dot size under the same dot percentage, the easier the dot loss phenomenon occurs, which affects the tone reproduction. Therefore, under the premise of satisfying the viewing distance, the smaller the number of screen lines in screen printing, the better.
4. Selection of mesh/line ratio: It can be comprehensively selected in the range of 3.5 ~ 4.7, which is mainly related to the tone range to be copied. To ensure the transfer of extremely fine dots, a larger mesh/line ratio can be used. As long as the screen angle is selected correctly, there will be no obvious moiré, and the final printing effect is shown in Figure 8.
Through this experiment it was found that:
1. The application of modern special printing technology to the design and output of textile patterns has greatly promoted the digital development of the textile printing and dyeing industry, opened up a new way to highlight individuality for textile pattern design and output, and greatly promoted textile printing and dyeing. industry development. The application of pigment printing technology in the textile industry will bring unlimited development possibilities to T-shirt printing. The application of pigment printing technology is becoming a new bright spot in the economic growth of the textile printing and dyeing industry.
2. Digital output technology and digital pre-press design technology effectively combine the pigment printing technology with the design of textile patterns, enabling the production of textiles to achieve a personalized, small-batch, data-variable production mode.
3. The development of digital technology improves the design efficiency and production efficiency of paint printing, embodies the new characteristics and new concepts of textile technology and pattern art design, innovates the traditional textile pattern design method, and enriches the design content and design materials.