Choosing a pad printing machine

Pad printing applications tend to fall into three main categories, listed in descending order of application quality:

• Printing involves the precise application of ink to the substrate. Images usually contain letters or symbols and can be monochrome or multicolor.
• They are decorated so that the design or effect is applied to the product to enhance the look of the product. The design is exclusively artistic, without a functional purpose, which can be monochromatic or multicolored. Effects include unusual patterns, simulated wooden branches, etc.
• Coding involves printing information that must be legible, but not necessarily of high quality. An example is a date printed on a can and other packaging. Coding should not be confused with barcode, where quality is very important, especially with contrast and edge definition. Barcode is considered as a separate printed application.

Some machine requirements are consistent for all pad printing applications. The machine should transfer the color from the image carrier (cliché) over a flexible (silicone) substrate to the substrate to be printed. It must be able to carry out this process as accurately as possible, ideally in the range of +0.025 mm. It should work without problems, without unwanted vibrations at production speeds.

The print should be designed in such a way that the operator simply regulates the color condition and drying rate (amount of color solvent). The ability to maintain color, and thus the printing conditions, is of primary importance and many machines lack it. Although well-designed, some machines use large ink holes (troughs) that degrade ink quality control.

There are basic requirements for pad printing. To get the right printing for your business, you need to understand the differences in the types of machines currently available.

Manual pad printing machine

Figure 1 - Manual pad printing machine

Except in cases where pad printing will be used on a very small scale, machine instructions are no longer even entry-level. However, some may be useful for testing purposes.

The first buffer machines were manual (Figure 1). Very high-quality watches and instruments with keys have been printed over the years by hand tampon machine. Now the only reason to buy them is the low purchase price. The cost of prints is extremely low, and maintaining quality compared to continuous operation is extremely difficult. Well-designed units can be useful for testing clichés, tampons, colors, and designs as an alternative to producing machines outside the production line.

Open system (paint application mechanism placed above the cliché)

Figure 2 - Open system

Many machines of this type (Figure 2) are in the field. This is the original semi-automatic system, dating from the late 1960s and early 1970s, and was the basis of many clones. Original machines that work mechanically, give little opportunity to adjust the individual printing because the mechanism for color and pad are located on the same carrier. Print speed is controlled by the speed setting of the main drive motor. Later, more sophisticated mechanical machines gave more flexibility in adaptation. This is a very robust system with a smooth print that is not affected by fluctuations in manual movement through the air. In these original semi-automatic machines, the paint application mechanism is placed above the cliché. Although many modern models have better options, color condition control fluctuates.

Over the years, this style has continued to develop, and the basis of machines in production are electromechanical, and even machines with servo power. Also, PLCs are common, providing a wide range of order options.

No matter how sophisticated these presses are, color control is problematic due to the high exposure of the paint surface to the atmosphere.

This can be improved in a variety of ways. Some manufacturers help reduce evaporation by concealing the paint mechanism and the paint container. Other manufacturers use paint pumps and evaporation compensation systems.

Changing the paint and cliché can be done relatively quickly by removing the paint tray, paint applicator, including the cliché and replacing it with another that has already been prepared. You have to consider the price of spare paint tubs, which can be quite expensive. The paint container (tub) can be designed to capture the paint that spills over the edges of the cliché, so that the maintenance of the machine is cleaner.

Partially covered container with paint

Figure 3 - Partially covered container with paint

In these machines, the color stays behind the cliché. The paint is pulled forward with a paint applicator located on a horizontal stroke together with a knife that removes the paint from the cliché. While the paint covers the clichés, the applicator covers the paint and reduces the evaporation of the solvent. When it returns to the back position, the paint is drawn from the cliché into the tub, which reduces further evaporation.

I have to admit prejudices: this is my favorite way of printing if it is well designed. The paint is placed in a tub located behind the cliche, as shown in Figure 3. The paint is applied to the cliche with a paint applicator mounted on a horizontal bracket together with a paint stripper. (Imagine a squeegee on a screen printing machine) While the ink is applied to the cliches, the horizontal applicator applies it from the tub and reduces solvent evaporation. When it comes back, the mechanism covers over the paint. To clarify, this system does not close the paint as we have with a closed system, but it does not lead to a large amount of solvent evaporation. The mixture of paint and solvent will remain stable longer than in a fully open system.

These printing machines must be strongly designed. During the time the knife flies over the cliché, a significant rotation occurs in the bearings at the rear of the tub. Inadequate bearings will quickly fail, and the tub will become unstable, resulting in poor paint removal and uneven application. Even ideal systems must remain clean, not cluttered with paint. Do not allow the paint float, which is floating normally, to be flooded with paint or get stuck up or down.

Closed system

Figure 4 - Closed system

The diagram shows piston clichés for printing here, but other closed systems are also available. These systems are designed to contain ink in a cup that is turned upside down and pressed onto clichés, moving across the paint. The dish contains paint and also acts as a knife that removes it. The advantage of this system is that evaporation is minimized.

This system (Figure 4) is considered to be the cure for all diseases of the tampon press. What is surprising is that this "new" development has been present for many years. The Swiss manufacturer of pad printing machines had this system 30 years ago! 

The concept of these machines is to contain the paint in a container that is turned upside down. The vessel is turned to press the clichés and move across the paint over it. The dish not only has paint but also acts as a knife to remove it. He goes back and forth over the cliché, leaving the color only in the engraved areas. The obvious advantage of this system is that solvent evaporation is minimized. This allows for much better color control, which leads to reduced ingredients and partial cessation of production.

"But," he will tell you, "the salesman told me he would work 24 hours a day, seven days a week, 52 weeks a year." Did he say what the quality of the print will be, how often you should add colors, how many clichés it can last, or how long the dish will last? Did he mention that you can't ignore the fact that color does not degrade clichés over time, that the use of two-component colors is not recommended, that clichés must be twice as big as a normal image that is printed? You should ask yourself this question when ordering a system like this: "How much does it cost to replace a container?" The answer may come as a surprise: 500e is not a surprise at all. Fortunately, but the damage to the vessel is very small, it can be repaired carefully honed on a fine surface of carborundum stone. Some containers can be refurbished for a quarter of the replacement cost.

The paint container comes in a variety of designs. The simplest is a machine made of solid metal, usually hardened steel. The other type has a ribbon-steel surface that can be replaced when worn. The third is a metal vessel with a ceramic contact surface that has passed over the metal. This ensures a long service life of the vessel. But it is much more expensive than a conventional cup.

In order to achieve maximum efficiency with any of these cups, a minimum pressure is applied and it should be ensured that stable bearings are mounted on the vessel. Any attempt to damage the container will lead to uneven application and will leave irregularities on the logo that will be reflected on the tampon. Some systems use a magnet to hold the glass to the cliché, which has proven to be a very good solution. Clichés and vessels with a magnet can be smaller than in a vertical arrangement, which allows you to change from one cliché to another without moving the vessel as if they were tied in a pair.

Figure 4 shows clichéd printing clichés. In many closed systems today, the cliché stands and the vessel crosses the cliché. Multicolor machines are now common, and some manufacturers offer a choice of a sealed cup or an open system on the same basic machine.

There is no doubt that closed systems will be further improved. They were only available in limited container sizes, but changing the container size changed this. Another interesting variation of the closed type is where the clichés are mounted in the paint container vertically instead of horizontally. The cliché is lifted upright from the bowl, using a knife to remove the paint from the top where there is no picture. The buffer is moved horizontally to pick up the image from the cliché and depending on the application and design of the buffer machine, rotates either 90 ° or 180 ° to deposit the image on the substrate. The mixture of ink and thinner is almost as stable as in a closed system, but larger surfaces can be printed as e.g. 12.7 x 45.7cm. 

 The only additional benefit of a closed system: They reduce the level of solvents that are released into the atmosphere in the working environment. 

 Piston clichés

Figure 5 - Piston clichés

Sometimes, machine manufacturers will decide to keep the tampon on the same vertical plane before moving it back and forth from the cliché in the conventional way. For this to happen, the cliché must be moved out of the way. Manufacturers have achieved this by using piston cliches (Figure 5) that work the same as piston tables of screen printing machines. This press boot is available with a closed and open system. In these models, instead of the pad moving back and forth from the printing plate, the plate moves forward, while the pad remains stationary in place. This type of machine results in less pad vibration and a faster number of prints.

Moving just one part in this machine saves for the manufacturer's machines because there is one less activation on the machine. From the user's point of view, since the buffer moves in a vertical plane, it vibrates less, and the cycle of the machine can be much faster. Automatic product insertions can take advantage of this accelerated cycle.

One application for this system is high-speed coding machines, which some manufacturers claim work at speeds of up to 10,000 cycles / hour. Here, a small cliché is used with a closed system. Larger machines with cliché dimensions of 20.3 x 45.7 cm were produced using this method, but the name requires very significant bearings to support the cliché in the front position because too much pressure is applied if a large pad is needed.

The manufacturers claim that since the pad is printed under the work surface, the working space has increased. The downside of this is that the machine must be well guarded, because moving the cliché forward can be a serious danger if it gets stuck.

Rotating machine

​Figure 6 - Rotary printing operation

The rotary printing system (Figure 6) evolved directly from engraving printing. They are very suitable for cylindrical parts and continuously flat prints. These machines use a rotary type of tampon, usually in conjunction with a steel cylinder in which the design is engraved. The paint is poured into the clichés from or through the channels, and the knife removes excess paint. As the cylinder rotates, the silicone rotating swab buys the paint from the engraved part of the cliché and transfers it to the substrate. One advantage of this system is speed - small things can sometimes be printed at speeds of 120,000 parts/hour. 

These machines use a rotating silicone pad in conjunction with a cylindrical steel cliché. The design is engraved on steel clichés, and the color flows through it or channels. The knife removes excess ink. As the cylinder rotates, the silicone rubber takes on color and transfers it to the substrate.

One of the advantages of this system is its speed. With small components such as bottle caps or lids, 120,000 parts per hour can be achieved. Printing one of these components in a conventional way, assuming a diameter of 2.54 cm, can achieve about 3000 parts per hour. Another advantage is the very fine details that can be printed with rotary presses.

Ink storage tends to be smaller compared to conventional pad printing, especially at higher speeds that are achievable. Also, the paint must be started with a high level of solvent. Paint manufacturers recommend 20% solvent, but I once used 30% on a multicolor application. Each color may require a special mixture that is determined at the beginning of the work and maintained during the work. Balance control is necessary. We recommend using a paint pump to maintain the same level of balance. Some pumps have viscosity measuring devices, but I have not yet found them to be successful. Keep in mind that changing the color requires cleaning the system, so we do not recommend rotary systems for short series.

An alternative to cylindrical rotating steel is available. Steel foil and even photopolymer clichés can be mounted on a modified cylinder, but their efficiency is debatable, because the pressure of the knife causes them to wear out very quickly. Although steel cylinders are by no means cheap, the investment pays off by reducing production downtime.

The capital costs of a rotating system are relatively high because the addition system almost always requires a complete use of the technique. The quality should be as good as, if not better than, conventional pad printing.

Although most major suppliers produce some variations of this equipment, availability is limited. Never accept a printing press if you do not see it working with your requirements at the manufacturer's premises.

Total color system transfer

Figure 7 - Total color system transfer

This technique, developed for printing on ceramic objects, uses a mixture of pad printing and screen printing technologies, as shown in Figure 7. These systems do not use an image that is pre-engraved on clichés. Instead, the paint or ceramic paint is transferred by screen printing to a flat, silicone-coated plate. The paint remains on top of this plate, and then it is transferred to the base with the help of a tampon. This technique is used almost exclusively in ceramic decorations, combining pad and screen printing. As you can see from the diagram, the image on the sieve is printed on a special plate, and then the tampon buys the image and transfers it to the substrate.

When this process was first developed in the 1950s, the color was cool. This did not allow complete transfer, so thermoplastic paint was used. This paint is solid like wax at room temperature, which is then heated on a metal grid via electricity. This raises the ink temperature to 35-40 ° C lower than the printing ink. The tampon lifts the paint from the silicone surface and transfers it to the ceramic product, which cools the paint and causes complete paint transfer.

Although this process is used exclusively in the ceramics industry, it shows a happy marriage of two processes. Its advantages are the following:

• Stencils can be printed on certain parts and surfaces (eg, two curved surfaces), which cannot be printed directly by screen printing.
• Fine lines and complicated markings can be applied at the same time as the main template in one pass of the machine.
• Heavy paint deposits can be applied to complex shapes. Previously, this was possible only by using screen printing, which could only print on a limited space of the form.
• Screen printing, not pad printing, determines the amount of color applied. Therefore, it can still be deposited in relation to conventional pad printing. This ensures high-quality print consistency. The design can have a full range of effects from full lines to halftones.
• Many users have the production of screen printing at home, where the cliché often has to be done at the seller.

Carousel pad printing machine

Figure 8 - Carousel pad printing machine

This machine (Figure 8) is a multi-color pad printing system designed around a rotary table. It uses a combination of two rotating tables and a rotating carousel buffer. Substrates are mounted on one table, the cliché code can be adjusted in X, Y, and rotary axis, which allows precise positioning of the image. This multicolor pad printing uses a combination of two rotating tables and a rotating carousel pad. The bases are mounted on one table, while the cliché is mounted on the other. Above the cliché is a closed color system so that it passes over the engraved image. After raising the image, the pad and the cliché board rotate so that the pad is placed over the base. The pad then transfers the image to the substrate to be printed.

Above the cliché is a closed color system that passes over the engraved image on the cliché and then returns to its original position. The clichés were painted shortly before the tampon was soaked. After the tampon takes the image, the tampon and clichés rotate so that the tampon carries the image over the substrate while the other tampon is positioned over the second already colored cliché. The wrapped tampon is then lowered and transferred part of the image to the substrate. At the same time, another tampon lowers and raises the image from the other plate. This sequence continues until multicolor images are printed. The printed part has been replaced with a new substrate that is being printed.

The cam control system is completely mechanical, allowing up to 750 cycles per hour. Printing 250 prints in four colors per hour is achievable. This makes the machine ideal for short and medium series. The printing machine is designed so that adjustment is easy and fast, and different shapes of tampons can be placed on the carousel of the appropriate design. Photopolymer cliches can be used, but as with conventional machines, steel cliches give a longer life cycle.

Carousel printing is a very useful tool, especially for contracted prints of shorter series in several colors. For longer distances, conventional linear, rotating, and oval systems are more economical due to the larger series.

Print on a non-horizontal plane

Figure 9 - Vertical pad printing machine

A machine like this is suitable for printing on surfaces that are vertical or angled. All standards of the paint application mechanism are used with these machines, but in general, they tend to use smaller clichés.

You will rarely have applications that you will print on vertical surfaces or at an angle. However, machines are available for such work (Figure 9).

This equipment is often used in combination with a vertical-stroke printing machine from the side of the object, while conventional machines print at the top. The printing angle can be variable up to 90 °; some machines even print up. All paint application standards are used with these machines, but as a rule, they tend to use smaller clichés.

Numerical control via computer

Figure 10 - Machines with computer numerical control

In computer numerical control (CNC) printing, the substrate is standing and the tampons are programmed to print one image per substrate. The CNC control system can actually be built into standard machines or modular assemblies such as this one to suit almost any application.

In addition to all other printing styles up to this point, the printing station is stationary and parts are supplemented from one station to the next until multicolor printing is achieved. Not so with machines that use computer numerical control (CNC). Here the substrate stands and the tampons are programmed to print one image per unit time on the object, as shown in Figure 10.

Although the robotic actions of these printing machines seem complicated, CNC allows easy adjustment of the procedure and allows several adjustments for machine programming. All activations are controlled by servo drive, giving a very smooth, highly controlled print action. The stroke length varies continuously depending on the dimensions of the machine. The manufacturers claim significant energy savings during pneumatically active machines, plus CNC machines do not affect fluctuations in air pressure changes.

The CNC control and activation system can be installed in standard machines or modular upgrades (as in Figure 10) that can be manufactured to suit any printing application. The degree of complexity refers exclusively to the designer and the color of the module to be used. All elements can be combined by manipulating components with several closed color systems, cleaning tampons, different lengths of tampon prints, alternative forms of tampons, etc. This system is often used when things have to be printed in accordance with other upgrade processes, or complex multicolor printing on different substrates.

The flexibility of CNC comes close to the ideal production of machines for a particular application, but it is significantly more expensive than conventional pneumatic machines. If the business can withstand a certain increase in investment, CNC machines are worth considering.

The price of printing with CNC machines does not mean that it will be higher, but the delay and obfuscation should be significantly reduced. The ability to store and retrieve details for the next job offers more uniform print quality. Of course, some pneumatic machines allow easy control of card production (when filled correctly) will help with any machine. 

Print options

Most manufacturers provide different data for printing machines. I'm not talking about handling and inserting substrates into the system or treating the equipment before or after printing, but a device that improves the quality of printing.

Cleaning tampons

These systems use adhesive tapes that are placed on the platform. At programmed intervals, the platform is placed under the tampon. When the tampon comes down on the tape, any paint or debris from the tampon is removed. The tape platform is retracted and printing continues. The system cleaning board is used mainly for machines without human control, although operators who insert the product are sometimes installed. The machine operator uses it only when necessary. 

Automatic tampon cleaning is generally considered a useful addition. But even though the surfaces are clean, the environmental conditions are under control, and the color is properly mixed, automatic cleaning is more of a luxury than a necessity.

Paint pumps

The concept is to have a tank with paint in a closed container. The paint is pumped from the tank into the tub, then back again. In some cases, the solvent is introduced into the tank as regulated by the automatic viscosity instrument. These devices are notoriously unreliable, so it is better to mix a certain amount of solvent at the beginning and add a certain amount during operation.

Even if the paint never changes, the whole assembly must be cleaned regularly because the paint has a period of life (the period of time during which the paint remains usable) after which it tends to clog the equipment. Two-component paints can only be used with great care and must be changed regularly. Leaving one color for more than 24 hours would be a very costly mistake.

One of the simplest paint injection systems is the peristaltic pump. This system beautifies the color by compressing the pipes through which it moves. The advantage of this is that the pump never comes into contact with the paint, only outside the pipe. The flow is infinitely variable, and the pipes are available to withstand aggressive solvents.

Thinner dispensary

This is a simple alternative to paint pumps when the amount of paint used is low. This system excludes a certain amount of solvent at a given interval. Both the quantity and the time can be adjusted to suit the printing conditions. In general, adding thinner regularly is a great concept. As long as the application system is firmly designed, it will take a long time to reduce one of the main variables in the process.

Use special care when choosing a solvent application system to ensure that it will withstand the solvent components. Also, the paint applicator must be slightly modified to ensure that the solvent is mixed immediately in the system, slowly moving the cylinder through the paint in the tub keeping the color disturbed so that the solvent mixes well with the paint.

This technique is also used with some closed systems. Great care must be taken in regulating the flow, because the amount of color is much smaller, and it is possible to dilute the color too much.

Air blower

The goal here is to help the paint solvent evaporate when etched, on a tampon, or on a substrate. This can be achieved by directing air from either a compressed air device or a hot air fan. Such blowers can be mounted on the machine, but they must be used with care and only when environmental conditions require them.

Charge eliminators (static eliminators)

By its very nature, pad printing generates a significant amount of static electricity. Silicone rubber is an excellent insulator and the continuous mechanical action of the tampon can generate thousands of volts of static charge. Add to that the static charge inherent in the mold of a plastic object - especially when stored in plastic bags and brought to print immediately after shaping - and you have a static cocktail that can cause a real printing problem. A common effect of static electricity is detachment. There the ink tries to stay back on the pad when it is lifted from the substrate on which it is printed.

Before diagnosing static electricity, make sure that the engraved image on the cliché is not too deep or that the color is not too thick. If statics is the definitive culprit, you must eliminate it. You can do this by releasing ionized air over the tampon and / or conducting static electricity away from the substrate. Equipment for such static elimination is usually through electrodes in a stream of air that are usually high voltage (20,000 - 40,000 volts). These electrodes emit charged ions that give the air the property of static elimination.

Statics is, to a large extent, influenced by environmental conditions. Very high humidity is the biggest problem. In some printing houses, aerosols can be used instead of a static eliminator to minimize the effect.

Image recognition

More and more companies are using buffer machines automated without operators, and the need for image recognition equipment has increased. These systems can detect fingerprint changes by only 0.0127 mm. They can also detect discoloration. Image recognition equipment can be set to operator alerts, component rejection, or machine downtime. Costs continue to fall. The CD industry uses this technology to a great extent and shows its advantages.

How to decide which machine to buy

In order to enable you to correctly estimate which machine to buy, you will need answers from the "Procurement Review" list. Most are obvious, but incorrect assumptions can be very costly. When you are satisfied with your own printing needs, look at the following 20 factors from suppliers and their equipment:

• Good technical support
• Solid machine construction
• Ease of setting up all printing functions
• Sufficient distance between the tampon and the cliché to accept sufficient tampon depth
• Knife holder to be able to accept both flexible as well as hard, with the provision that flexible knives can be adjusted with a softer angle
• A big enough cliché that the tampon can be completely extended beyond the frame of the image.
• Acceptable quality output rate (not machine cycle time)
• Tampon retention, which allows you to adjust the precise speed of taking and giving the impression, as well as the speed of falling of the tampon
• Adjust the workbench and paint retrieval parts so that they can move back and forth and left and right
• Quick adjustment and disassembly
• Costs of spare tubs, paint applicators, knife holders, tampon holders, etc.
• For multicolor machines, X, Y, and rotary adjustment for each cliché
• X, Y, rotary, and height adjustment
• Easy to clean
• Easy access to all operating parts of the machine
• Standard pneumatic, electrical and electronic components
• Instructions for use or customer service
• The cost of replacing ceramic cups
• Ability to re-machine ceramic dishes
• Good technical support (I repeated this on purpose)

And finally...

Before you buy a machine, always have a few experienced people who will decide together with you. Unless you are an expert, never accept "it will give better results in production". Talk to other people who bought from the same seller.

Lastly, don't think of printing as a separate machine. It doesn't have to fit into your whole production process. The product must pass smoothly to and from the machine. Cleaning, adjustment, changes, and all other factors of proper use of the machine in your shop must be taken into account. If you follow these guidelines and recommendations from the previous texts, you will have a print sound in your shop that will provide efficient, repeatable results.

Procurement consideration

Are you trying to decide which tampon machine to buy? Start by answering the following questions. These answers will help you identify and understand your printing needs so you can choose the equipment that suits you best when you buy it.

• What range of components will the machine be able to print? Item size? Fingerprint size?
• Are objects flat, cylindrical, curved, or rounded?
• What is the best line that can be printed?
• What is the largest surface on which one color is printed?
• Treatment of the surface of the object after printing?
• Print position?
• Positioning tolerance?
• Material specification, additives, filters, etc.?
• Material color (s)?
• One or more color printing?
• Color (s) to be printed, Pantone, BS, DIN, etc.?
• Are things cleaned before printing?
• Is it needed before treatment? If so, which process is most appropriate?
• Is it necessary after printing? If so, which process is most appropriate?
• Packaging in and out of the printing press?
• How soon after printing can an object be used?
• Tolerance of object dimensions?
• An image of an object?
• Test requirements?
• Environmental conditions?
• Batch size?
• Frequency per series? Series frequency?
• Overall annual quality?
• Need print speed?
• Manual insertion / removal?
• Automatic insertion / removal?
• What are the quality requirements (distance, color matching, etc.)?
• Visual inspection system?
• What is the allowable loss?
• Are samples available for printing?
• If not, are the models available?
• Are the final holdings available?
• When will the pre-production sample be printed be available?
• When will eligible products be available?
• Providing capital for the purchase of equipment?
• The price of the print?
• Is the production space available, and is it clean? Does the ambiance have stable conditions? Is it well lit?
• What service is available?
• Storage and removal of paint, solvents, and chemicals to consider?
• Are the employees ready to start the equipment and do they have enough experience?
• What training do we need?
• Who will have managerial responsibility for the press?
• Who will be involved in the purchase decision?
• What is the dynamics of equipment delivery?
• When is the first batch requested by the client?