by Steve Smith, Diversified Printing Technologies
Pad printing has had the reputation of being a tough process to nail. Consistency is even more difficult to achieve. This is still true if you think pad printing is an art form or that its success depends on some secret recipe. Instead, pad printing is a scientific procedure. Many variables exist that can affect the outcome, but there are new tricks that can help stabilize the decorating process and give an expected outcome or proven result. It’s not good enough anymore to have any significant rejection rate – a printer must have repeatability. Even in markets and industries where cycle time and speed are more critical than cosmetic appearance, it is advantageous to have a process that gives identical print image and the ability to repeat that process at set-up. At the end of the day, these elements will produce good part rate increases!
1 – Surface Tension Testing
The first piece of information the printer needs to capture and control is the surface tension of the material or product to be decorated. It is important to know the immediate surface to which the ink is going to adhere. Many times ink is specified on a sample part, only to find out that the part is going to have a painted or coated surface. Forget the base material in that case ink needs to adhere to the coating.
How many printers have a dyne test (surface tension) kit? Would you be surprised to hear that very few decorators use one? However, if the dyne (or surface tension) is less than 35, it is difficult, if not impossible, to get adhesion. These kits are inexpensive and its a smart move for any decorating project to know how compatible the product is to available ink systems. There are also materials that require pre-treatment, such as corona electrical discharge, chemical primer, or open flame. These can significantly change the surface tension of the material. Dont get caught up with the notion that surface tension testing is only for those assumed materials like polypropylene or polyethylene. It may also work on substrates like metal, ceramic, wood, and others. All of these can have oils, varnishes, or coatings that could benefit from pre-treatment or a changed surface tension. You wont know without a way to test!
A surface tension test also will tell a printer how to set up pre-treatment. What dyne number should be achieved? Dyne number can be controlled by how long, how close, what type of pre-treat, and the intensity of the system. But the practical way to know quickly is test it! This easy test will save set-up time and collect factual data that will make future set-ups smooth and consistent. Please note that a plethora of formulations exists within a material category, particularly with so many parts and products coming from emerging industrial countries. For instance, there are literally hundreds, if not thousands, of different compositions of polypropylene. Add different re-grind percentages and it becomes clear that printers should not have a preconceived notion of surface tension. Products from different material manufacturers and different lots of manufactured parts should be independently tested so there is a degree of certainty in the decorating process.
2 – Cliché Purchased or In-House?
This next tip is for printers using polymer plate making equipment. First, if a printer purchases 10 or more clichés a month, its time to start producing them in-house. The direct ROI on this type of equipment is just one year when compared to the price of just the 10 mentioned above. After the initial equipment investment, yearly costs will be insignificant. The old method of exposing a cliché and then using a hand brush to remove the unexposed image area is no longer an accepted procedure. A good photopolymer cliché is only 1 mil deep and should have a dot pattern in the image area to hold the cup or doctor blade level across the surface of the image. Imagine hand sanding a piece of wood without any backing and youll see the analogy of hand scrubbing to wash out a cliché. The same characteristics are true in the plate making process. Hand brushing the cliché gives an uneven surface across the face and, at the same time, can damage the dot pattern. This compounds the unevenness and it is a slight miracle to produce a cliché that has consistent depth, image, and color. Now before those of you who have hand washed for years start writing me letters yes, I believe you are good! But can everyone in your department make a good cliché and then a second one exactly the same?
A washout station will take the human element out of cliché making. Anyone who is capable of setting a timer will produce good quality plates. There are savings in time and money when a good plate is produced the first and every time, particularly on multi-color setups. A washout station will improve the quality and attitude of any print making area.
The washout station concept assumes that there is a good vacuum bed exposure unit involved. On a regular basis, the bulbs should be checked and replaced if UV output has diminished. Any unlit or low intensity bulb will expose inconsistently and could cause print problems and/or soft plates that wear quickly.
3 – Maintenance
This next suggestion is a maintenance item. Any type of sealed ink cup must have a parallel and sharp edge with a minimum flat on the edge free from nicks and chips. Even if the cup edge doesnt have any visible imperfections, it may not clean neatly and an edge touch-up can improve this condition. A lapping kit is a honing plate and a diamond dressing paste. A few figure eights every four to six weeks will help the cut perform in a repeatable, consistent fashion, as well as increasing the life of the ring and printing plate. A lapping kit may be the difference in getting a rush project out the door.
4 – Set-Up
How long does it take to set-up a pad printer? The time given to registration often takes too long to be productive. Its now a proven concept to register the artwork on the cliché instead of registering the equipment to the artwork. The technique means doing the color separation using registration marks on the film positive and then using a dead-on light box to place the film precisely on the cliché. Pad printers using this technique have been known to complete 4-color changes in as little as three minutes. Worst-case scenarios are still substantially faster than the old method of shooting the plate and then registering the image. This process of pre-registering the image on the plate works as long as the platform isnt moved, limiting this application to photopolymer and thin steel clichés. Thick steel clichés usually function as a platform and so must be registered. Final Food for Thought
The last two tricks are accomplished with auxiliary equipment pieces that organize and speed up the printing department. The first is a printers trolley. Most print rooms incorporate some version of a cart, but a moveable work station with enough storage space and work surface keeps all the tricks of the trade at hand. Inventory the trolley every morning so that tools, solvents and cleaners, splash cans, and even the inks needed for the day go with the tech to the print equipment. It may not seem essential until the amount of time it takes the technician to go back and forth getting everything he needs is monitored!
The final item to mention is a cup washer. This may seem like a luxury item in most print shops but again, its a time saver that quickly pays for itself. The washer is pneumatically operated for safetys sake and is as easy to use as the dishwasher at home minus the detergent. This is one of those housekeeping items that is usually messy and hard to accomplish sufficiently. How many set-ups have started with cleaning what should have been done already? Clean up is a much tougher job the next morning.
These are just a few ideas and concepts that will help a print department function more smoothly, rapidly, professionally, and profitably. Just remember: customers love to see proficiency in any facility and it can be a wonderful marketing tool as well!
Steve Smith has been the sales manager for Diversified Printing Technologies for 2 1/2 years. Prior to that, he served as president of Plastic Provisions Inc., in Michigan, for ten years, representing Diversified for much of that time. He can be contacted at (704) 583-9433.