Before the 1970s, most of the signs were made of metal materials. Today, plastic signs have been widely used in household appliances, instruments, meters, office equipment, etc., and have become an indispensable part of mechanical and electrical products, not only Trademark identification specifications, function indications, etc., and become a bright spot in the appearance of the product.
With the continuous use of new materials and new processes, the surface of plastic signage is constantly improving, and the degree of color is increasing. It has become the crystallization of comprehensive surface treatment, processing and Screen-printing technology.
Plastic signs can be divided into two categories according to their material processing methods and objects of use: one is the injection type main plastic sign, which is injection molded by ABSPC, and then subjected to secondary surface decoration processing such as spraying, plastic plating or hot stamping. A dazzling metal texture. It is usually processed with opaque materials and used for trademark labeling of household appliances. Plastic stamps processed by transparent materials such as PMMA are processed by vapor deposition, coating, and reverse-faced screen printing. The display window: the other category is the focus of this article, namely the plastic (sheet) label. This type of signage uses a variety of color, texture, texture of engineering plastic sheets through a series of mechanical processing and screen-printing process.
The film touch Switch is a new type of electronic control system developed on the basis of the plastic (sheet) label processing technology. It is a plastic (sheet) sign with electronic switch function, which is used for the whole machine panel. Called the panel switch. The Membrane Switch has been widely used due to its aesthetics, small size, light weight, long life and convenient installation to meet the requirements of digitalization, intelligence and self-service of electronic products.
Most of the Membrane Switches use the processing method of plastic (sheet) label, but because the membrane switch is a functional print, the gas-pass design and processing of the conductive silver paste printing and drying isolation layer, the design and processing technology of the main Keyboard in terms of the stricter workmanship and technical requirements and requirements.
Material plastic (sheet) signs generally use PVCPC, PETPMA and other engineering plastic sheets, thickness. 1~2.0, the color has high light and matt, the color has white, black and white, transparent, the texture has matte surface, matte surface, etc., can be selected according to the requirements of different effect signs.
Process flow (see below) Film design and production of the whole machine appearance and sign appearance and color separation film calculation of the film screen processing stretch net cloth to oil rough coating photosensitive film (glue) low temperature drying plate machine exposure - "development ―"Drying seal inspection" quality inspection qualified screen printing ink color sample test printing combined batch printing (4) mold design and manufacturing sign structure line cutting small size design sample processing machine trial and correction size punching Material composite mold design and manufacture of film punching and positioning pre-hole composite mold punching blanking inspection qualified into the library has now adopted computer-aided design, laser photo-array and output, its processing speed and film quality is also non-tone ratio, It should be noted that the graphic structure size and characters of the film must conform to the CAD design of the whole structural part, and it must conform to the screen printing process. Generally, the line (including characters) must have a competition of 0.2. If there is a transition color dot, it must be large. 100 lines.
Characters should be represented by hollowing out as much as possible, that is, the characters are printed according to the color requirements, and the lines are more than doubled than the hollowed-out character lines, and the "bleeding" margin is reserved for the line. Then, the cover is printed with the hollowed-out film characters, so that even if the color registration printing has a slight positioning error, the color registration accuracy is not affected, and since it is a hollowed-out character, there is no disadvantage such as cross-coloring caused by ink overprinting.
The hollowing method is generally dark color, light color, that is, the color block is pressed with light color characters, the line color block, the line competition is generally a3mn, and the color block can have 20.15nn "bleeding" on each side to compensate for the color printing.
Each color separation film and positioning reference of the color printing must be uniform and accurate, and consistent with the size of the mold guiding positioning. The printing position is outside the punching line, and the signage needs to be punched to locate the pre-hole. The center of the "Ten" word positioning line must be drawn. There is a positioning hole, the line is less than 0.3, the punching of the punching die (punch) diameter of the pre-hole circle, such as the pre-hole circle line is 0.3, the outer diameter is 4.6nm, the inner diameter is 4nm the diameter of the punch should be designed by 4nm. After the pre-punching, there is still a circle of the circle on the side of the slit left on the printed part, which can verify the accuracy of the punching position and facilitate the next processing.
After designing the pre-hole punching die and the blanking punching die, the die can be punched directly with the backup film to detect the correctness. It can also be used to pre-align the pre-holes on the film according to the process procedure. Holes are blanked. This can achieve two purposes: First, the mold performance can be tested (such as wool, concave and convex mold with clearance); second, the detectable structure fit size is correct, can also be sent to the customer through the machine to test, confirm, confirm the qualified You can proceed to the next step.
350 mesh polyester yellow net production screen version, if it is four-color dot printing, the ratio of the amount of mesh to the number of dot lines is i5:1 (100 mesh uses 350 mesh mesh), the angle of the mesh is 22 mesh KeTutai mill net grinding (to be polished), to achieve the purpose of decontamination of the mesh. The sanding qualified screen will have a uniform water film after being washed by water, and the mesh has a fine layer of fluff. This process can greatly improve the bridge bonding of the photosensitive film (glue) and the mesh. The printing durability of force and screen.
When using the straight film method, it is preferable to use the capillary film photosensitive film, the photosensitive film and the mesh cloth have good bonding fastness, the film is flat, and the thickness is uniform. If you want to further improve the printing durability of the screen, you can use a high-sensitivity photosensitive adhesive (such as 20 photographic adhesives) to apply a back and forth on the scraping surface.
Note: When the capillary film is attached to the surface, the photoresist can be applied to the surface of the scraping surface. After drying at a low temperature, the capillary film base can be removed. The degree of dryness should be such that there is no resistance and no tearing when tearing off the screen from the corner of the sheet. Otherwise, it should be dried. After the base is removed, the screen still needs to be dried 1~2nhn to completely remove the residual water under the base.
There are two important factors in the exposure of the screen-printing industry to the screen printing: one is that the moisture content of the photosensitive adhesive (film) must be small, and it should be dry; the other one is the exposure time, because the commercially available photosensitive adhesive (film) The sensitivity varies from lamp to lamp, so the correct exposure time must be determined in advance.
Different test charts, each of which has an exposure index above it. Using the test piece, use different preset exposure times to develop the screen exposure, and then select the picture with the best development effect, press the top of the picture. Multiply the exposure index by the exposure time to get an accurate halftone exposure time. If there is no exposure test piece, you can use a finer line of film, different exposure time to test, in order to obtain accurate exposure time.
Indirect printing can be used to print particularly fine, non-serrated, smooth and clean lines. At present, the Ketutai five-star red film membrane is mainly used, because the film is first exposed hardened, developed, and then attached to the mesh. The combination of the film and the mesh is mainly the adhesion of the incomplete photosensitive layer on the film (commonly known as "soft top"), so the bridging property with the mesh is the worst, the printing durability is also the lowest, and the soft top is formed. In addition to strict operation according to the process, the degree of exposure determines the adhesion of the soft top. If the exposure is insufficient, it cannot be properly developed. If the exposure is excessive, the all-light curing "soft top" disappears and there is no adhesion, so the exposure is the key. In addition to requiring extremely high signage, the plate making method is generally not used.
After the screen is developed, the transparency must be checked by light to prevent the residual glue from clogging the mesh. If the sand hole is repaired with the photoresist or the sealing glue, the non-leakage parts are sealed and dried with the sealing glue. Label the model number, plate making parameters and flood period on the side of the frame for storage.
The size of the blank should be in accordance with the standard to save raw material costs. The more the number of signs printed on a single blank, the higher the material utilization rate and work efficiency, but the overprinting error also increases accordingly, so the trade-offs should be made according to the actual requirements of the sign. Cutting should ensure that the shape and size are the same, and the edges are smooth and burr-free to meet the requirements of color registration printing. After the blank is cut, the side to be printed is facing up and stacked neatly. Do not mistake the front and back of the sheet.
Plastic signage, a few are monochrome printing, such as TV back cover signs, but most plastic signs are multi-color printing, multi-color printing generally pastes the positioning piece on the printing table, using 3-point positioning method, the positioning piece thickness is slightly lower than the thickness of the sheet to be printed.
In the actual printing process, especially when printing large blocks or background colors, the printed matter easily adheres to the screen-printing surface to cause waste. In order to avoid this, it is possible to use the offset glue to assist the printing. The viscosity of common plate glue is high, medium and low. It can be selected according to the actual situation. Generally, it is suitable for low viscosity.
The coated plate glue must be thin and even, and it should be 8~101 cloth in advance. It is best to apply it before work. When it is used to work the next day, dry it as much as possible. Dry it with a hair dryer when it is urgent.
When the initial application of the plate glue is milky white, it will be transparent after drying. It should be noted that it is necessary to check whether there is any residual plate glue on the reverse side. If it is, the plate glue is not dry or coated too thick, or the plate version Poor combination of glue and screen.
Before the batch printing, the label should be printed in color sequence, and check whether the line, pattern, character, size and color are consistent with the customer's requirements or samples. The customer can confirm the batch printing.
Ink printing inks are generally not directly used for printing but should be color-matched against swatches or PANTONE color system color cards. Toning should be adjusted with ink of the same grade and different colors to ensure ink printability. When grading, first determine whether the hue of the color block is reddish (warm) or bluish (cold), then the main color is dominant, and the auxiliary color is added a small amount multiple time. To join, half, observe, adjust, and pay attention to the color difference of the ink in wet and dry state, generally, light color, dry when it is lighter than wet, dark tone, dry when deeper than wet.
In the printing process, the most common fault is the plugging net. The reasons are as follows: First, the ink particles are too thick, and the ink brand needs to be replaced. Second, the solvent component in the ink is too fast. At this time, the slow drying agent can be added for adjustment. Here, the author introduces an effective method for adding extra slow drying agents in production practice. After the ink is purchased, it is opened and opened in the warehouse. During the period, the mixture is properly stirred to prevent the film from conjunctiva. The quick-drying agent volatilizes and the viscosity of the ink increases. When printing, a large amount of extra slow drying agent can be added to adjust the viscosity to moderate viscosity. The ink is printed with good adaptability and is not easy to plug the net.
After printing for each color in the color printing, the printing must be dry, and the background color or color block is the most likely to occur.
In order to prevent adhesion when stacking, resulting in scrap, especially the printing method of large plastic signs is generally 2W: "The type is front printing, printing in the light order of the first shallow and deep, in order to prevent the product from scratching before use, generally It is necessary to cover the low-viscosity protective film, and because the plastic signage is mostly assembled with pressure-sensitive adhesive, the composite pressing tape is needed on the reverse side of the label; the other is to use the transparent material to print from the reverse side, the light color in the first and the lower. Imported transparent materials are generally protected by a protective film on both sides. After tearing one side of the printing, only the composite pressure sensitive tape can be used on this side. The sign is double-sided, the face is covered, and it needs to be determined according to the actual brother.
The film can be applied by hand to form a split on the stone surface. Now, one-sided or double-sided coating is generally used with an automatic laminator.
Plastic label printing will be stamped and formed after being divided by double-sided or single-sided lamination. In order to ensure the accuracy of the plastic label shape, hole position and relative position of the pattern, it is generally necessary to punch the positioning pre-hole before final molding. Also known as the process hole), the signage has only accurate pre-hole positioning to ensure the final molding quality. The pre-hole punching is generally carried out on a foot punch, and the punching is visually observed.
The material of the final punching and blanking of the plastic sign is soft and thin, and the forming precision is high. Generally, the composite die is used for punching. The gap of the mold is small, the manufacturing precision is high, and the burrs and burrs of the punching piece are large, and the punching piece is easy to adhere to the film without being easily peeled off. In order to avoid this phenomenon, the punch can be quenched to increase the hardness (Rc60 degrees) during the heat treatment of the mold, and the hardness of the die is reduced by quenching (Rc4 (degrees). In the actual test, the hand is used to tap the concave The method of deforming the die edge adjusts the gap of the die to the optimum state.
For special-shaped signs with large area and low precision requirements, the steel wire cutter for printing and rolling boxes can be used to manufacture stamping dies. The method 6 is as follows: on the multi-layer board or the bad oxygen board, manual or steel wire knives are used automatically. The grooving machine processes the steel wire sipe, and then bends the steel wire knives into the groove by manual or steel wire cutter automatic molding machine. The mold is mounted on the creasing machine, and the rubber cavity of the mold cavity is glued to the height of the knife edge. When stamping, the sponge is firstly elastically pressed to stabilize the punching piece, and then the blade is cut downward to cut the punching piece. After the knife edge is withdrawn, the sponge ejects the workpiece and cuts it into a punching cut.
In order to prevent the size of the composite mold design mistakes, before the manufacture, it is advisable to use a metal sheet (copper sheet or aluminum sheet) for the shallow cutting machine. Firstly, the mold is installed according to the preset size of the mold. If there is a dimensional error, it can be corrected to confirm. After the error is correct, the mold manufacturing can be started to ensure the success rate of the mold.
The membrane switch can be regarded as a plastic with electronic switch function (the chip r material, named after the switch circuit, is printed on the sheet substrate, and has the dual function of the sign and the switch. The membrane switch power S1W is a touch The switch is responsible for the transmission of the whole electromechanical signal. According to its material and the method of use, it can be divided into two categories: soft and rigid. The flexible membrane switch is mainly used. The structure is generally composed of panel, Button and liner. Instructional key graphic text symbol.
The button is the main part of the switch, generally consists of three pieces: the upper layer is the moving piece, as a contact of the button, the lower layer is the fixed piece, which is the other contact of the button; the moving piece and the fixed piece are double-snidely covered The separator of the pressure sensitive adhesive with good insulation performance has a total thickness of about 25 to a 35 nm, and the spacer has a window at the corresponding key position and is provided with a gas groove to ensure the conduction of the circuit between the movable piece and the fixed piece.
The membrane switch adopts a polyester sheet with excellent elasticity and conductivity as a carrier of the switch circuit pattern and is printed by using a low temperature curing conductive ink (silver paste, carbon paste, etc.).
In addition to the correct switching circuit design, the quality and printing thickness of the conductive ink will directly affect the switching performance. The silver content of the silver paste must be 265% (weight ratio), and the printing thickness of 12~13un silver paste is an important production of the membrane switch. Process, the general silver paste drying temperature is 80~120C, the time is 20~30nin. In the specific production process, it must be strictly in accordance with the detailed technical description and operation process of different grades of conductive silver paste. In order to avoid the oxidation corrosion of the silver layer, it can be protected by carbon paste coating. The carbon paste is not oxidized by non-metal, and the carbon is self-lubricating material. The friction is small. The protection with carbon paste can improve the contact reliability and switch use. life.
In order to improve the recognition and finger touch of the membrane switch keyboard, the panel layer is processed by the mold at the contact position of the switch keyboard, so that the button in the plane state forms a stereo key body.
The bubbling is divided into two types: spherical and basin shaped. When the spherical bubbling touch is heard, the obvious rebound sound can be heard. With the touch of the keyboard, the bubbling and the contact conduction are synchronized, and the action is quick and reliable. However, due to the large stress at the intersection of the spherical bubbling root and the plane, a circular arc transition should be adopted. The ratio of the spherical crown diameter to the spherical crown height should be 10:1, the height is S2 times the material thickness; the basin bubbling is touched back. The bomb is small, no obvious sound, but because of the small operating force, the hand feels good, and the processing is convenient because of the cold processing method.
In order to make the keyboard in the turbulent state, the sealed air in the isolation layer is discharged in time, and the rotor and the stator switch circuit are turned on. The spacer must be designed with a reasonable airflow channel, generally in the associated two or more keys. An air flow channel is set up between the airflows, and the airflow can be shunted to other key positions. After the turbulence action is completed, the airflow returns, and the top support plastic sheet rebounds to restore the open state of the switch.
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