Application areas of pad printing machines
Pad printing is far more tolerant of product shapes than screen printing. Therefore, the application areas of pad printing are not inferior to screen printing.
In terms of printing the following products, pad printing has unique advantages:
1) Spheres
Spheres that will not be significantly deformed: such as basketballs, footballs, table tennis balls, some decorative balls, and plastic products similar to spheres.
2) Special-shaped bodies
Bowls, plates, dishes, spoons, ladles, gourds, and daily necessities with irregular shapes used in the tableware industry.
3) Smooth transition surfaces
Chamfered parts of some plastic products, arc parts, and the joint surfaces of the bottom and edges of some containers.
4) Concave parts of products
The printing surface area is small, and in the concave parts of the products, the inner walls of some containers, such as the bottom and inner side of rice cookers.
5) Soft and small products
Medical catheters, infusion tubes, needle-shaped products, small diameter products, and products with an outer size of less than 5mm.
6) Products with complex structures
Some resistors, capacitors, cable connectors, small dimensions, and structures such as elbows and steps, which can only be avoided by pad printing rubber heads.
7) Some large products on the assembly line
Some large product assembly lines such as washing machines, refrigerators, and cars, the surface that needs to be printed during the conveying process is located on the side or bottom of the product.
8) Auto parts
Steering wheels, some tapered knobs, the inside of handles, seat armrests, etc.
9) Toy industry
Some soft and easily deformed silicone dolls, gloves, car models, irregular surfaces of airplane models.
10) Daily necessities
The handles of cups, toothbrush handles, decorations and jewelry, brushes, hair dryers, scissors, etc. in daily necessities.
The above products can basically only be printed with pad printing machines, and pad printing machines need to be specially upgraded in structure and take more complex actions to achieve this.
Structure of pad printer
1. Loading method of pad printer
Vibration plate loading mechanism
• The vibration plate arranges the materials in order along a specific track and transports them to the designated position one by one through vibration. Regular products will be fixed at a specific position of the workbench by the positioning block for pad printing, and irregular products can be clamped into the fixture by the robot. Whether it is a linear automatic pad printer or a turntable automatic pad printer, the loading mechanism will accurately transport the products to a position that meets the printing process.
Robot automatic loading and unloading mechanism
• It is composed of robot arms, suction cups or grippers and other components. The robot's movements are controlled by programming, and the materials to be printed can be accurately grabbed from the material stacking place and placed in the loading station of the pad printer. After the pad printing is completed, the finished product is removed and placed in the designated position, realizing unmanned automatic operation.
Push plate loading mechanism:
Some products, such as paper, regular plastic plates, cards, etc., can be stored in a stacked manner first, and then the push plate is used to separate the products one by one from the stacked state and push them to the printing position.
2. Pre-press device of pad printer
• Flame treatment device: The surface of the substrate is instantly heated by flame to change the molecular structure of the surface, increase the surface energy, and enhance the adhesion of the ink. It is mostly used for substrates such as polyolefin plastics and rubber. For example, the fully automatic beverage bottle cap pad printer adopts this device.
• Plasma treatment device: The high-energy particles in the plasma react physically and chemically with the surface of the substrate to clean the surface, remove oil and impurities, increase the surface roughness and activity, and improve the ink adsorption. It has the advantages of good treatment effect and no pollution. It is suitable for substrates of various materials, especially for some materials with low surface energy.
• Electrostatic dust removal device: By generating an electrostatic field to adsorb dust and impurities on the surface of the substrate, keep the surface clean, and prevent dust particles from affecting the printing quality, it can effectively improve the clarity and integrity of the printed pattern. It is often used in occasions with high requirements for printing quality.
• Pre-coating device: Before printing, a layer of primer or pre-treatment agent is applied to the surface of the substrate to improve the surface properties of the substrate, so that the ink can adhere and dry better, and the printing quality and durability are improved. It is suitable for some special materials or substrates with special requirements for printing effects. For example, PP water wiping device.
3. Printing system of pad printer:
1) Control interface
• Operation panel: Usually a microcomputer panel with buttons and knobs. The buttons are used to realize basic operating functions, such as start, stop, reset, etc.
• Touch screen interface: More advanced pad printers are equipped with touch screens. Various parameters can be set intuitively on the touch screen. At the same time, the touch screen can also display the operating status of the equipment, including the current printing mode, fault alarm information, etc.
The operation panel is used to control the pad printer, realize the action of the pad printer according to the pad printing process, and set different parameters at the same time to ensure perfect pad printing quality.
• Program storage function: Different printing task settings can be stored as programs. For example, for a task that requires printing complex color patterns, the corresponding parameters such as print head speed, pressure, ink supply, etc. are stored as a program.
• Multi-task management: Supports simultaneous storage of multiple different printing programs, facilitating quick switching between different printing tasks. For example, if the logos of product A and product B need to be printed alternately on the production line, the printing programs of product A and product B can be stored in the operating system respectively, and then called at any time according to the production schedule.
• Fault monitoring: The operating system can monitor the status of key components of the pad printer in real time, such as whether the motor is overloaded, whether the sensor is working properly, etc. Once an abnormal situation is found, an alarm signal is immediately issued.
• Alarm method: The operator is reminded through sound alarms (such as buzzers) and visual alarms (such as flashing fault indicator lights on the operation panel). At the same time, the specific fault code and simple fault description are displayed on the touch screen or operation panel to help the operator quickly locate and solve the problem.
2) Ink supply and scraping system
Ink tray ink supply system
• Structural features:
The ink supply system of the oil basin is mainly composed of an ink basin (trough) and a scraper. The ink basin is a relatively large container for holding ink. It is usually located below the printing plate, and part of the printing plate will be immersed in the ink basin. The scraper is installed above the printing plate, and its position and angle can be adjusted.
Ink cup ink supply system
• Structural features:
The ink cup ink supply system mainly includes an oil cup and a push cylinder. The oil cup is a closed or semi-closed container for holding ink, with an opening at the bottom to contact the printing plate. The sliding of the oil cup on the steel plate plays the role of supplying ink to the image area of the printing plate and scraping ink from the non-image area. The oil cup seals the ink in a small space, which can effectively reduce the volatilization of the solvent, thereby reducing the amount of ink used, and has a certain effect on environmental protection. Therefore, it is often sold to developed countries in Europe and the United States.
3) Pad cleaning device
The pad printing machine pad cleaning device is mainly used to clean the pad printing machine's pad to ensure printing quality.
The most commonly used cleaning device is to install a tape pulled by a motor in the area where the pad moves. The pad printing pad passes over the tape and is pressed down on the tape by the command of the operation panel to simulate the printing action. The ink remaining on the surface of the pad will be removed by the tape, which plays the role of cleaning the pad.
4. Drying device of pad printing machine:
Hot air drying device
• Working principle: The air is heated by the heating element to form hot air, and then the hot air is blown to the surface of the printed matter by the fan to make the solvent in the ink evaporate quickly.
Infrared drying device
• Working principle: The infrared rays emitted by the infrared radiator are directly irradiated to the ink on the surface of the printed matter, so that the ink molecules absorb the energy of the infrared rays, generate thermal vibrations, accelerate the volatilization of the solvent in the ink, and achieve drying.
Ultraviolet drying device
• Working principle: The ultraviolet drying device is mainly composed of ultraviolet lamps, reflectors and power supplies. When the ultraviolet lamp emits ultraviolet rays, the photoinitiator in the ink absorbs the energy of ultraviolet rays, generates free radicals, triggers the polymerization reaction of the monomers in the ink, and makes the ink quickly solidify and dry. When using UV pad printing ink and UVLED pad printing ink, an ultraviolet drying device should be configured.
5.Unloading method of pad printing machine:
Unloading by conveyor belt
• Description of method: The pad printing machine is connected to the conveyor belt, and the printed products are conveyed to the designated location through the conveyor belt. The speed of the conveyor belt can be adjusted according to the working efficiency of the pad printing machine, and the conveying process is relatively smooth.
Unloading by robotic arm
• Description of method: Use the robotic arm to grab the printed product and place it in the designated unloading area. The movement of the robotic arm can be precisely programmed to adapt to different product shapes and placement requirements.
