Pad printing silicone rubber is two-component rtv silicone (room temperature vulcanization), includes tin curing silicone type and platinum cure silicone type. It can be colored with pigments and softened by silicone fluid. Pad printing silicone rubber material is an ideal material for making pad printing rubber heads, rubber head is a carrier which transfers the patterns on the steel plate onto the substrate surface in the pad printing process.
In pad printing, transfer pads made from silicone rubber are used almost exclusively since the silicone materials are the best known release agents for this printing process. Also there has been some pad printing done using Polyurethane pads, for specialized applications.
Principle of Pad Printing
Pad printing, also called tampography or tampo printing, is an indirect offset (gravure) printing process, where an image is transferred via a soft silicone pad onto the surface to be printed.
Pad printing is accomplished by transferring an image onto your product using a silicone pad and ink. an offset press is used for 2 steps in the pad printing process. First, to press the silicone printing pad into an inset plate to pick up the ink for your design. Next, it's issued to “stamp” your logo or design onto the surface of your product.
- Antistatic, does not produce static electricity, prevent the silicone pad's surface from dust.
- Excellent printing effect, good oil absorption effect, very efficient ink transfer on any substrate.
- The unique properties enable it to pick the image up from a flat plane and transfer it to flat, cylindrical, spherical, compound angles shapes.
- Easy demoulding.
- Good purity without impurities.
- Outstanding solvent resistance even in diluted state.
- Soft and stretchy.
- Low viscosity, Outstanding flowability.
- Variety of Shore hardness.
- Mechanical properties with long-term consistency.
- High tear resistance.
- Very low shrinkage and good dimensional stability.
Pad printing operations are used in a wide variety of industries, pad printing silicone rubber can print all colors and all graphics on all surfaces of all shapes. For example, toymakers use pad printing silicone rubber to imprint very fine details on everything from plastic dolls to metal models. Cosmetics makers need to reproduce their logos on everything from sophisticated perfume bottles to curved plastic tubes via ceramic cream jars.
Popular pad printing applications:
- Pens, garment tags, flash drives, silicone items, and watch faces.
- Irregular picture printing and badge printing, etc.
- Electronics' printing, for example, mobile phone screen, electronic components, chips, circuit boards and so on.
- Industrial Buttons and Keys as found on calculators, telephones and computer keyboards.
- Electrical Household Appliances such as iron, VCR, TV, coffee pots, telephones, etc..
- Large Industrial Appliance panels such as on dishwashers, washing machines and dryers.
- Sporting Goods such as golf balls, baseballs, tennis rackets, footballs.
Pad printing pads are made of a rtv silicone rubber material. The type of silicone and hardness (durometer) of the pad depend upon the application. The following are the basic steps for making pad printing pads for you to learn:
Step 1: Mold Preparation: The surface of the molds in which the print pads are being cast should be clean and free of loose material.
Step 2: Mixing: Mix rtv-2 silicone rubber part A and part B according to the correct weight ratio, The mixing must be carried out thoroughly and evenly, otherwise it will cause partial non-curing. Hand or mechanical mixing can be used.
Step 3: Add silicone oil (optional) : Usually the original hardness of the silicone pad is around 15-25 shore A , but adding silicone fluid to adjust the hardness is available, please note that working time and cure time will be prolonged with silicone fluid addition. Note that silicone oil will destroy the molecular chain of silicone rubber, so the addition ratio of silicone oil should not exceed 30%.
Step 4: Vacuum pumping: Although not necessary, vacuum degassing helps eliminate any entrapped air in pourable silicone rubber. After mixing parts A and B, vacuum material for 3-5 minutes at 29 inches of mercury, making sure that you leave enough room in container for product expansion.
Step 5: Pouring: Pour the mixed Pad printing liquid silicone rubbber as soon as possible into the mold.
Step 6: Curing: Follow the principle that the higher the temperature, the faster the curing. The catalyzed rtv-2 liquid silicone material will cure to a flexible rubber within 24 hours at room temperature and the pad can then be removed.
Q: Why the silicon pad is non-durable?
A: Silicon oil can change the hardness and the viscosity of the liquid silicone rubber, at the same time, silicone oil will also break the molecular chain of the silicone rubber. More silicone oil added, softer the pad printing will be, meanwhile nondurable and easy ageing it will also turn to be.
Q: Why the printed pattern is incomplete or not clear?
A: If the silicon pad is too hard while the pattern is very delicate or small, the printing patterns will be incomplete or not very clear, for in that way the silicon pad could not adsorb the printing ink from the steel plate well. If your pattern is very delicate or small, please use soft silicon pad for pad printing. In addition, if the percentage of water in the ink is very high, the printing pattern also will be incomplete, and spot may appeared. For this situation, please clean your ink box, or change the printing ink.
Q: Why the silicon pad did not absorb the ink?
A: usually, silicone pad or liquid silicone rubber could absorb ink well. If large patterns or big letters need to print, the printing pad will for sure absorb ink well. For small letters, please do not use hard silicon pad, as it could not absorb the printing ink thoroughly from the steel plate.