Development of screen printing technology and its application in metal packaging
Yang Wenliang
ã€Abstract】This paper lists the progress of screen printing technology in the past ten years, and gives a detailed introduction to some domestic printing materials. It is pointed out that only the innovation of screen printing materials, equipment and processes can broaden it into more fields and have an advantage in the metal packaging industry.
[Keywords] screen printing metal packaging ink process
1 Introduction
Screen printing technology is an ancient and unique printing technique. The characteristics of this technology show many of its advantages, and with the innovation of screen printing materials, equipment and processes and its integration with other technologies, screen printing technology has broad market prospects. In particular, the development of functional inks has made the field of screen printing more diverse and has been expanded.
2 About screen printing
Screen printing is the printing of a stencil with a pattern or pattern attached to a screen. Usually the screen is made of nylon, polyester, silk or metal mesh. When the substrate is placed directly under the screen with the template, the screen printing ink or paint is passed through the mesh in the middle of the screen under the squeeze of the doctor blade and printed onto the substrate (the doctor blade has manual and Automatic two). The stencil on the screen seals a portion of the screen aperture so that the pigment does not pass through the screen, and only the image portion can pass through, so that only the image portion is imprinted on the substrate. In other words, screen printing is actually printed by using ink to penetrate the plate.
3 About printed metal packaging
Printing of metal packaging, generally using large-scale tinplate printing, using four-color overprinting and other printing machines for printing. However, such printing requires a certain amount of batches, and small-volume printing has higher printing costs due to higher plate making costs and slotting costs, and is not economical. In small batches of printing, screen printing is currently preferred. Due to the low cost of plate making, the cost can be greatly reduced and the production cycle can be reduced. For example, small-volume metal can printing, printing of steel drum surface patterns, metal cover, small-size printing of signs, etc. Practice has proved that due to the low cost and easy implementation of screen printing, it has been widely used in the field of metal packaging in small batches.
4 Screen printing applications in metal packaging
Screen printing has been used in the manufacturing technology of metal packaging. In the past, the screen printing in the metal packaging manufacturing technology is "dark and bright", which is extremely popular. Why is the change so big before and after? It is to continue the wolf ambition new. Innovative new metal packaging screen printing, new metal packaging screen printing process, new metal packaging screen printing and testing equipment. Until today, screen printing has a great situation in the metal packaging industry. Today's screen printing can already complete multi-color overprinting, non-planar printing and other technical processes.
The development in recent years has made screen printing a good process adaptability and a controllable and easy to control production process. Below we briefly introduce the progress of screen printing materials:
4.1 Screen printing screen
Screens are the most important part of screen printing. This is because it controls the fluidity and ink consumption of the ink, and it also determines the durability and quality of the screen, which determines the quality of the print. Now, people can see high-performance screen printing screens with good performance on the market, especially high-bonding, high-tension, monofilament, plain woven polyester (PET) screens. The introduction of flat woven screens up to 27 μm and up to 150 lines per cm has changed the understanding of some of the important factors in printing, which has been confirmed in the technical aspects of precision screen printing. In addition, the excellent cross-linking properties of the screen and screen photoresist or photosensitive film are also an important factor in the production of high-quality screen printing plates.
4.2 Screen photosensitive material
Today, we can purchase many high-resolution screen photoresists or photosensitive films on the market, especially water-based photosensitive film (direct drying film), which is easy to use and has a thin film thickness. Uniform, controllable, especially water-based photosensitive film with a film thickness of 80~140μm, can be used in some special applications. At the same time, it also provides a reliable material basis for the development of new fields of screen printing.
4.3 Screen printing (ink)
The advancement of screen printing, especially the development of functional inks, not only benefits ordinary screen printing (such as UV inks never block), but it also directly leads to screen printing technology and products. High-tech. There are many characteristics of screen printing. The most fundamental point is that printing is highly adaptable. It is called printing except for air and water. It can be printed on all the different materials and different surface shapes.
Metal packaging screen printing inks generally include resist ink, anti-electroplating ink, two-liquid (two-component) reactive ink, thermosetting ink, and the like.
(1) Resist ink
The screen printing is used to screen the corrosion-resistant ink on the surface of the metal packaging to protect the parts that do not need to be etched, and then the surface of the metal packaging is chemically converted by a special etching solution to achieve the desired marks and patterns on the surface of the metal packaging. It is currently the most widely used in the production of metal signs.
Corrosion-resistant inks can be broadly classified into four categories: solvent-based resist inks, alkali-soluble resist inks, ultraviolet light-resistant inks, and infrared heat-curing and corrosion-resistant inks.
(2) Anti-electroplating ink
The anti-electroplating ink is mainly applied to the three-dimensional relief process on the surface of the metal packaging, that is, the screen printing negative image and the relief embossed pattern are formed by electroplating to produce a "stereo relief" effect. This ink is often used to process cap designs in metal-clad caps.
Anti-electroplating ink, in addition to the same properties as the anti-etching ink, should also consider the ink thixotropy should be appropriate, the negative printing can not cause the ink to spread; there should be no conductive material in the ink; the ink can not be dissolved into the plating solution.
(3) Thermosetting ink
Heat drying and curing screen printing ink is the main ink type of metal screen printing, which can be directly used to print graphic information on the surface of metal packaging. It is often used in the production of small batches of tinplate printing cans, caps, barrels, etc.
4.4 Screen printing process for metal packaging
The screen printing process for metal packaging products is as follows:
Screen printing, substrate pretreatment → screen printing → drying → punch forming → inspection → packaging → factory.
(1) Production of printing plates
(2) Positioning
The rules on the screen printing metal packaging plate are the means to ensure the accurate position of the graphic on the surface of the same printed workpiece and uniformly meet the requirements of color overprinting precision. According to the material and shape of the substrate, the positioning method of the silk screen metal packaging is also different, usually the following.
(a) Positioning by edge: Suitable for straight-sided packaging workpieces, such as plaques before signing, metal packaging, etc., and positioning the two right-angle sides of the workpiece in the silk screen.
(b) Flange positioning: It is suitable for silk screen printing of workpieces with different forming packages. The outer frame of the packaging material can be processed. After trimming the gap, the outer frame is attached to the required position of the platform after the trimming method. Simply place the shaped package workpiece into the blanking frame.
(c) Hole positioning: The hole positioning is suitable for the imprinting silk screen of the same figure, that is, the positioning hole is punched out on the plate first, and the hole is positioned when the silk screen is printed, and finally the mold blanking forming is performed on the package workpiece by the positioning hole. Hole positioning methods are often used for printing and machining of steel drum closures.
(3) Ink mixing
The requirements for screen printing inks for metal packaging are strong adhesion, good abrasion resistance, clear graphics after printing, fast drying and no sealing. The metal packaging screen printing ink is generally made of a synthetic resin such as alkyd or phenolic as a side material, and a special ink made by adding a part of a pigment or an auxiliary agent. The ink has good printing performance, and is dried naturally after printing or baked at 120 ° C for 2 hours. The surface of the ink film is bright, has a sense of body, and has excellent adhesion to metal and wear resistance. The ink film of this ink was tested with a JM-1 type paint film abrasion tester, and the rubber grinding wheel with a load of 750 g can be ground more than 500 times, and the cloth wheel can be ground up to 5000 times or more.
If the silk screen color pattern, you can refer to the relevant color printing ink color sample to add ink, and adjust the amount of varnish and desiccant. The amount of the ink desiccant added is about 5% to 8% of the total amount of the ink, and the addition is less difficult to dry, and the addition of the ink affects the adhesion of the ink.
(4) Quality requirements for silk screen metal packaging
The text, graphics and color of the silk screen metal packaging shall conform to the requirements of the drawings. The surface of the finished product shall be free from obvious scratches and smudges. The adhesion of the ink film shall meet the requirements.
4.5 Computerized plate making
Screen printing production, the most common is the computer equipment → laser photoplotter screen printing film (photographic film). Another approach is to image directly on a screen coated with a screen photographic material using computer inkjet technology (a digital plate-making system). Using this technology directly challenges the plate-making film (photographic film), not only eliminates the camera in the screen-making technology, but also eliminates the darkroom process and the silver salt base (plate-making film). This new technology from computer to screen has been used. Commercialized, its complete sets of equipment have been put on the market. Currently, the only drawback of this technology is that the system is extremely expensive. However, it is foreseeable that the high price of such screen printing high-tech equipment is impossible to maintain for a long time. Price cuts, a substantial price cut is inevitable. This point can be seen from the reality that computers and other information products are greatly reduced in price every year. Even more gratifying is the introduction of new technologies for more advanced direct exposure production screen printing.
4.6 Parameterization procedure for screen production control
With the introduction of new technologies, automation of control of screen printing prepress parameters has become possible, and because of this, modern screen printing will completely or maximally bid farewell to the production mode of the former workshop. Screen printing will become a controllable and easy to control production process. So, how are the production and production parameters controlled during the screen printing production of metal packaging?
Screen tension is a very important factor in ensuring the quality of screen printing production. If we only pay attention to the high-tech of the pre-press equipment and printing equipment and the post-process in the production process and ignore the importance of the tension of the screen, then all the efforts we have made will be futile. According to experts, the tension of the screen will directly affect the consistency of the thickness of the screen, the uniformity of the exposure, the durability of the screen, the stability of the screen spacing, positioning, size, the pressure of the blade, the speed of the blade, the flow of the ink. Sex, ink consumption, energy consumption. The following are factors that affect tension.
(1) Stretching equipment and stretching method
The final tension of the screen is largely influenced by the equipment used in the stretcher (pneumatic, mechanical or self-tensioning). It is important to choose a device that ensures the uniformity of the stretcher every time. It is not affected by the skill of the operator. Stretching the net should not be in place at one time; before applying the adhesive to the mesh, the screen should be loosened by 15~20mm first, which will help stabilize the tension of the screen. The tension on the screen is preferably slightly above the circumference, and the pressure distribution of the blade when moving on such a screen is relatively uniform. In order to ensure the ultimate stability of the tension, the mesh frame of the stretched net should stay on the stretcher for more than 48 hours. It should be noted that non-standard operation can not only achieve the desired tension, but also cause accidental tearing of the wire mesh.
(2) Frame
The material of the frame and the shape of the section are very important. Relative to a certain size of the frame, if the strength of the frame is not enough, the consistency of the tension cannot be guaranteed. For mesh models for screen printing of metal packaging, wooden frames are not suitable, and metal mesh frames are recommended.
(3) Tensiometer
The tension meter is an indispensable tool for stretching the net and controlling the tension of the screen. It is an effective way to ensure the quality of the screen printing by monitoring the tension condition before the screen printing and the tension loss during the printing process. The same tensiometer should be used when checking or comparing the tension of the set of screens.
5 Conclusion
In summary, the new screen printing production mode of metal packaging is not only an excellent development opportunity for modern metal packaging to give screen printing, but also a serious challenge to the screen printing industry. At present, the most important thing in the metal packaging industry is to act. This action is to innovate new screen printing materials, equipment and processes to meet the needs of future metal packaging. Innovation is the soul of screen printing progress! With the development of screen printing technology, screen printing technology has become more and more important in the printed circuit manufacturing industry. Its application not only improves the production efficiency of metal packaging printing, but also reduces the production cost of printing. The quality of the processing. On the other hand, due to the research, development and application of screen printing materials, especially the development of functional inks, the application fields of screen printing have become more diverse and have been expanded. (This article Source: "Metal Packaging")
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