Pad Printing Tips – Increase Efficiency AND Profitability

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 it’s 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. Don’t 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 won’t 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, it’s 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 you’ll 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 doesn’t 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.

Publish by: Plastics Decorating. If you would like to continue reading, click here.

Multi-color Pad Printing with Automation

At some point, every pad printing operation must rise to the next level of difficulty by taking on jobs that demand technical expertise beyond the single-color, manual-load comfort zone. The risks are significant but the benefits to your customers can be substantial. Surely you would like to be considered for those high-volume, automated projects that come along– especially multi-color ones. But how can you conquer the technical pitfalls, be competitive with other methods, and still show a decent profit on your bottom line? Here are a few guidelines to consider.

Fast, Good, Cheap; Choose Any Two
Of course, choosing a fully automated system versus a semi-automatic, or even versus a manual one, all depends on your customer’s application and goals. If the volume is high enough and speed is critical, full automation is in order. With a production run in several millions of units within a few months time, a manual operation is out of the question. Feeding blank parts into a machine, pad printing each with one or more colors, and then outfeeding the finished parts would be impossible without at least some form of mechanical assistance – if those high production goals must be met. So the choice is driven by the numbers: total run times cost per unit equals production budget. And, don’t forget the time factor. You may find a way to produce the job with just as good quality and cheaper, but if you blow your deadline, the result won’t be acceptable to your customer.

When is a Manual-Load Perfect and When is it just too Slow?
Before moving forward, consider carefully whether you should stick with a manual operation or move up to an automated pad printing system. If the part is too large or irregular to be sorted and oriented by a feeder bowl or conveyor, or if a pick-and-place robot cannot easily grasp the part, manual is the preferred method, at least for the part-loading section.

Another consideration when pad printing larger parts that are continually lifted and pushed into a fixture is operator fatigue and repetitive physical stress. These ergonomic questions also may impact your decision to keep a manual load and unload situation versus seeking an automated alternative. Finally, the key factor is speed. If your production goal is beyond what can be humanly achieved under normal working conditions, it may be time to look into adding some form of mechanical device to boost that piece rate to a more profitable level.

 

Published By: Plastics Decorating. If you would like to continue reading, click here.

UV Curable Inks and Special Effect Decorative Pigments

Question: UV-curable Inks
We are considering changing from heat curing inks to UV to speed up our printing process lines. Will UV ink stick to polyethylene, and how does the process work?

UV inks can achieve excellent adhesion to polyethylene using a surface pretreatment such as corona discharge or flame treatment. Note that some pigment colors may be more difficult to print than others, but your ink supplier can assist you. Basically, the application of ultraviolet (UV) inks is a photopolymerization process or formation of molecular chains by fusion. Various chemical accelerators or catalysts are dormant in the ink until acted upon by ultraviolet light. UV inks generally consist of liquid oligomers (polyester resins are very common and cost effective), monomers (generally acrylates as dilution agents), photoinitiators, and various additives and pigments as required. UV “A” electromagnetic radiation, approximately 300-450 nanometers in wavelength, is a very efficient range for curing most applications.

The chemical photoinitiators are sensitive to UV light, which changes the chemical bond structure of the photoinitiators, forming free-radical groups that trigger resin cross-linking. Curing happens in a 2-step sequence; first a photoinitiator absorbs UV rays and forms free radicals. These interact with resin molecules to form resin free radicals, then the small amount of heat from the infrared (IR) component in UV lamps accelerates the polymerization crosslinking reactions of the resin molecule free radicals. This IR heat is minimal due to the brief dwell time of parts in the UV cure zone, but it is enough to give a fully-cured coating. Some radicals often remain for a brief time (1-2 minutes) after UV exposure, which gives a minor degree of added post-curing to the ink.

Question: Special-effect Decorative Pigments
What’s the difference between pearlescent and metallic effect pigments?

Pearlescent pigments used in paint, inks, and plastic are based on mica flakes coated with titanium dioxide. As the coating thickness increases, the color varies from silvery white to yellow, red, blue, and green. Different colors can be achieved by adding a second coating of iron oxide (gold and beige) or chrome oxide (green), and a range of metallic colors (bronze and copper) is achieved by replacing the titanium dioxide with iron oxide. Pearl-like appearances can be “tuned” by adjusting the size of the flakes. Small flakes (about 5 microns) give rise to a satiny appearance with good opacity. Larger flakes (about 25 microns) give a lustrous effect with lower hiding power. Typically you would blend different particle sizes to achieve a desired combination of luster and opacity.

 

Published By: Plastics Decorating. If you would like to continue reading, click here. 

Cliché Choices Not So Cut and Dried

Not long ago, the only real choice for creating a pad printing cliché was to chemically etch a steel plate. However, new innovations and advancements with photopolymer technology and laser-based CTP systems have created more choices for pad printing operations to consider.

Steel Clichés
Steel clichés for pad printing continue to be the mainstay for very large runs, especially for automotive, medical, or consumer electronic applications. Steel clichés are chemically etched and are available in either 10 mm (3/8”) or 0.5 mm (0.02) thickness. Thinner plates are used for runs up to 500,000 and the thicker plates are most commonly used for runs over 500,000.

The number one advantage of properly manufactured steel clichés is that they can last as long as one million impressions or more. Again, this can be important for very long runs, where eliminating machine downtime to change out the cliché can make a substantial difference in production efficiency.

The disadvantage of steel clichés is the high cost and extended lead times to manufacture them. Because steel clichés are chemically etched, most are not manufactured in-house and are created by a supplier specializing in this service. In addition, the chemicals create an environmental issue to consider. However, it is important to keep in mind that the most common applications for steel clichés involve very large runs where pre-planning is necessary so lead times and overall costs are not main factors.

Laser-etched Computer-to-plate Systems
Computer-to-plate (CTP) laser systems are the newest technology on the market for creating pad printing clichés. “This technology provides a great advantage for pad printing companies who want to improve efficiencies, reduce plate making time, and standardize the pad printing process,” stated Ben Adner, president of Inkcups Now. “It can be an excellent choice for manufacturing clichés for both short-run and long-run applications.”

Many potential advantages exist when considering a CTP laser system. Because it is computer-to-plate, graphics are first generation, with no loss of resolution – unlike photopolymer or steel clichés where film is first needed to create the image. There are no film, developing, or etching material costs. And, a main advantage is time. Laser-etched clichés can be made in three to five minutes.

The disadvantage of a CTP laser system is the upfront costs involved with setting up the system. A laser etching system can run several times the cost of setting up photopolymer cliché exposure, development, and post-exposure/drying equipment. Another issue to consider is that it is imperative to have a capable operator to laser-etch the clichés. Although the software is not overly difficult to understand, knowledge in the area of computer graphic software is necessary to properly create laser-etched plates. “The key to creating consistent, laser-etched clichés is having proper training and a good operator running the system,” stated Michael Chaney, vice president of Diversified Printing Techniques. “It is important that the supplier of the laser system provides training and service at the time of purchase.”

 

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Greener Solutions for Pad Printing

Advancements in the pad printing industry have helped companies reduce their environmental footprint in a number of ways. The utilization of electro-mechanical drive systems in modern pad printing machines and accessories has significantly reduced utility costs. Advancements in laser-engraved cliché materials have largely replaced older, chemically-intensive film and cliché developing processes. UV (ultraviolet)-cure inks are rapidly gaining popularity over conventional, solvent-based ink systems in a number of industries due to their lack of an operational pot-life. This article will discuss the impact of electro-mechanical drive systems, laser engraved cliché materials and UV-curable inks.

Electromechanical Drive Benefits
The majority of pad printing machines feature electronically controlled pneumatic drive systems. Because compressed air is one of the most expensive sources of mechanical energy in the industrial setting, it is more energy efficient, and therefore less expensive, to use pad printing machines that feature an electromechanical drive.

While compressed air is a versatile tool, running air compressors uses more energy than any other equipment. Air compressor efficiency is the ratio of energy input to energy output. Many air compressors may be running at efficiencies as low as 10 percent.

Consider the cost of the electricity used to generate the compressed air. The average cost for electricity in the United States in 2009 was $ 0.1002 per kWh1. This example utilizes a Tampoprint Model SIC 90 machine with a compressed air consumption of 2.7 NL (normal liters) per cycle. If the machine is working at an average rate of 1,000 cycles per hour, it will require 2,700 NL (about 950 cubic feet per hour) at 6 bar (90 p.s.i).

Maintaining that pressure at the machine with an oil injected rotary screw compressor would require, on average2, about 15 kW. By comparison, an electromechanically driven machine (such as the Tampoprint Model Hermetic 911) consumes a mere 1 kW in performing the same amount of work.

If the air delivery system was 100-percent efficient, and cost was calculated using the average industrial cost of electricity, the electromechanical machine would save $2,024.00 per year. If the air delivery system is only 25-percent efficient, the electromechanical machine becomes $ 3,650.00 less expensive to operate annually.

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Polymer Clichés for Pad Printing

Q: What purpose does the line screen serve in cliché making?
The line screen serves three purposes: to support the ink cup’s doctor ring, to control the volume of ink and to give the ink some resistance.

To support the ink cup’s doctor ring so that it doesn’t “dip” ink out as it passes over the image area.
Most manufacturers use magnets to create the hermetic seal between the ink cup and cliché. When the magnet force is too great, the cliché can be pulled off the base plate, causing defection and ultimately resulting in uneven doctoring and inconsistent ink film thickness. The line screen helps minimize this by supporting the doctor ring as it passes over the image area.

To control the volume of ink within the etched image.
It is not advisable to alter exposure times in an attempt to make the etch deeper or hold more ink.

The proper way to adjust ink volume is to alter the lineage of the screen. Typically, 120 line/cm is used for the vast majority of images. For large text and images, 100 line/cm is used. 80 line/cm screen is used on extremely rare occasions, such as when the operator is printing over an extremely rough or porous texture.

 

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Pad Printing Trends Today and in the Future

The pad printing process began in Switzerland when a small gelatin pad was used to transfer ink onto a watch. The first industrial machines were invented in the 1960s, and that was the start of a full-fledged decorating industry that took off and has never looked back.

The essentials of the pad printing process have basically stayed the same over the last century, but the technology has obviously seen many changes over the years. Innovations with pads and clichés, as well as completely automated pad printing systems, have kept pad printing on top as one of the most popular choices for plastics part decorating.

New applications offer opportunities

Although new decorating technologies are replacing pad printing for certain types of applications, there are additional opportunities for the process. “We have seen pad printing replacing industrial labels, especially when short-run, quick-change labels are required,” stated Inkcups Now President Ben Adner. “Customers are seeing that applying the printed information directly to the product saves both time and money. This is especially cost-effective for one- or two-color applications.”

Julian Joffe, CEO of Pad Print Machinery of Vermont, said pad printing continues to be the “method of choice” whenever difficult shapes must be decorated. “With the flexibility of pad printing, product designers can focus on part function and aesthetics,” stated Joffe. He also sees opportunity for growth in anti-counterfeiting applications. “Pad printing and other wet ink systems are more forgiving versus inkjet systems for these types of applications,” explained Joffe. With the continued increase in counterfeit parts and products, there will be many opportunities to use specialized pad printing inks for security applications.

Another trend that is sparking growth in the United States is the on-shoring of pad printing for existing applications. “Many US manufacturers that had off-shored now are re-tooling American facilities with updated technologies,” explained Innovative Marking Systems President Trent Pepicelli. “More plastic processors are taking the time to learn how to do industrial pad printing correctly and investing in automated systems.”

 

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