For starters, though, the screen printer must first conduct a market analysis. The screen printer must identify which market segments will be entered, what market share can be expected, what additional returns the investment will generate, and then calculate if the return on the investment is satisfactory. If the result of this exercise is a positive one, then one can proceed with confidence knowing which direction to take.

This section covers: 

(a) The system, its function, its background and what it offers

(b) The equipment required, including:

 
Dryers

Reflectors

Chillers

Presses

(c) The consumables required, including:
 
Inks

Coatings

Stencils & meshes

Squeegees

(d) Other aspects, such as safety, terminology and the future

(e) Summary
 
 

Most screen printers have at least one production specialty. Each specialty requires a unique marketing strategy and each requires a unique drying system for the manufacture of these products. The drying system of today and future is UV curing as it provides the screen printer with a distinct production and marketing advantage over conventional drying competitors.

UV inks contain liquid prepolymers, photoinitiators and pigments and when the inks are exposed to UV radiation they polymerize almost instantaneously into hard, dry films. UV radiation is supplied by special lamps that emit radiation in the UV range of 240-400nm.

These lamps are available with bulbs and reflectors housed in separate modules for easy replacement and repair. By replacing drying with instant curing, screen printers significantly increase efficiency and productivity. Many printers find that after installing a UV curing system they can increase production which allows return on their equipment investment within a year or less. Others find they can manufacture entirely new products that were previously impossible. The marketing advantages are very significant and can lead to substantial profit increases.

UV inks and coatings were first used as an improvement over solvent-based products. As conventional heat and air drying evaporates solvents and reduces the initial ink or coating film 50%, it also emits pollutants. Rather than driving off solvents with heat or high velocity air drying, UV cures instantly. As they are a 100% solids formulation, there is no loss of coating thickness and nothing to evaporate. The entire amount put down as a liquid remains in the final dried product. This enables screen printers to lay down thinner film weights which in turn leads to sharper prints. Screen printers are now able to print four color process (up to 150 line per inch) giving final results equivalent to offset quality.

- Many printers rushed into UV without first taking the time to thoroughly research their market and identify the real opportunities that existed or could be created.

- Ignorance of the process itself retarded its progress. Little or no training was available, and learning was a matter of trial and error.

- Some of the early UV inks had shortcomings such as printing properties, short shelf life and viscosity instability. Since the range of inks was limited, inks for certain substrates such as glass and some plastics were not yet available.

- Squeegees were not totally satisfactory as the rubbers would often swell, become soft and then distort. These rubbers usually had the wrong durometer rating.

- Screen mesh was not suitable for UV printing and ink thickness was difficult to control.

- Photo emulsion would not stand up to long runs.

- Some of the early UV curing systems were far too hot, and light control and shielding were inadequate. There were, therefore, problems of stock distortion curing and registration.

- Insufficient research and development had been undertaken to select the best materials and application methods for each printing project.

- Little or no safety procedures were known or observed.

- Inks

- Coatings

- Meshes

- Squeegees

- Lamps

- Coating equipment

- Curing equipment

As time progressed, however, cooperation between suppliers and printers blossomed, and their joint know-how expanded greatly. It is to those pioneers that today's industry owes its gratitude for the progress made.

- Release coatings for paper and film

- Pressure sensitive adhesive

- Antistatic coating

- Leather finishes

- Abrasives

- Decorative Paper

- Timber lamination

- Ceramics

- Ink jet printing

- Metal decorating

- Screen printing

- Offset printing and coating

- 3D coating automotive industry

The following questionnaire provides a few of the answers why: 

Q. Is it possible to print opaque inks?

A. Yes. Previously, printing opaque UV inks was very difficult. Because of new developments in the UV formulations, we can print whites, blacks and metallics that compare favorably with solvent inks.

Q. Can UV inks be used for vacuum forming?

A. New developments are beginning to make this possible. This was not so in the past as UV inks are not thermoplastic and are normally of a brittle nature. The ink would crack if there are deep depressions in vacuum forming.

Q. Can plastic bottles be printed UV?

A. Yes, if the bottles are made of normal bottle type plastics (i.e. polyethylene, polystyrene, polypropylene or PVC etc.) 

Q. Is UV ink adhesion good on all substrates?

A. Yes, if the surface tension of the substrate is above 38 dynes minimum. However, with surface tensions under 38 dynes, adhesion would be questionable. Therefore, corona or flame treating may be required.

Q. Are UV inks and conventional inks compatible?

A. In theory, they do not like each other; however, there is no reason why you could not combine the two systems to obtain a desired effect. Tests would have to be done to check adhesion between the two inks. When in doubt, consult your ink supplier.

Q. Can UV inks be used on all types of screen printing presses?

A. There are no problems in using UV ink on all types of screen printing presses. However, UV printing requires finer, even deposits of ink lay down. As such, finer meshes and the purchase of a UV dryer are required.

Q. How does UV differ from conventional drying?

A. UV drying is UV curing. As UV inks are 100% solids, there are no solvents present. Therefore, everything will polymerize. When UV inks are exposed to ultraviolet light, a reaction takes place which causes the total ink film to become a solid mass.

Q. Can UV be printed onto most substrates?

A. Yes. With the evolution of inks and dryers, UV printing on the most difficult substrates, such as metal, aluminum, polyethylene, mylar, foil, polystyrene, polypropylene, A.B.S., PVC, ceramic and glass, offers excellent printability.
 
 

• Although UV inks and coatings cost more per gallon than conventional products, remember that UV inks have great mileage. Therefore, in most instances, UV inks are actually less expensive.
• UV lamps in a curing unit must be replaced after a certain number of hours use. Some lamps do last up to 3,000 hours, but replacement and running costs are a consideration.
• UV printing requires knowledge of the complete system, including: inks, curing units, and application methods. Therefore, training and retraining of personnel will be necessary to obtain maximum benefit of the process.
• Attention to safety procedures and practices are greater with UV.

Do I have to develop a market for my products?

Have I lost customers because I do not use UV?

Does my market warrant conversion to UV?

Do I have the market for faster production speeds?

Do my customers want UV inks and coatings?

Do I need a process which provides sharp fine printing detail?

Do I need product that will be more durable to chemicals, abrasion, solvents, weather and moisture?

Do I need special effects, i.e. matte, gloss, frost, textured and spot UV varnishes?

Do I have enough factory space?

Do I need a cooling section for heat sensitive substrates?

Who is going to maintain a UV curing system?

Do I have a press that will print with UV ink?

Is my press fast enough for UV printing?

Should I install a full UV line or go for add-on unit?

Should I eliminate racks and large dryers to open more floor space?

Would I clean my factory environment?

What factory alterations have to be made (power, air, water, space)?

Can I obtain UV knowledge from other printers?

How long will it take to convert to UV, i.e. equipment, installation and full production capabilities?

Is training available; how long will it take?

Do I understand the technology of UV inks?

Is financing available for my UV system?

How long will it take to get a return on my investment?

Do I know what costs are involved to start up a UV system?

Should I retain my current drying system or replace it?

What safety needs have to be met?

Are my printers ready for UV curing?

After answering these questions, do not overlook performance characteristics that might convince you to obtain a UV system: 

• Faster printing speed 
• Reduction of plant space 
• Sharper and finer detail in print 
• Cleaner plant environment 
• High gloss finish on jobs 
• Market requirement and customer demand 
• Durability of printed material 
• Economy of operation 
• Inks do not dry in the screen 
• Requires less energy 
• High speed multicolor printing 
• Minimal substrate shrinkage 
• Excellent intercoat adhesion 
• No rewetting or blocking 
•  

It is now assumed the decision has been made to adopt the UV process. The following information is therefore presented to assist in selecting the best curing equipment, reflectors, dryers, chillers and presses.
 

When choosing what type of UV curing unit to purchase, consideration must be given to the following: 

Intensity of the UV lamp: 300, 400, 600 or 750w.

Number of UV lamps (this will depend on the speed of your press).

Heat filtration unit. Controlling temperature. (If printing heat sensitive substrates, this is very important.)

Conveyor speeds. How slow and how fast your conveyor will run so you have proper control of drying on all substrates.

Control of wattage on your UV lamp. Some 300w dryers have four different settings: 300w, 200w, 150w and 100w. Newer systems offer infinite variable control. This is very important when drying sensitive substrates.

Equipment selection is quite varied. The selection process can be extensive, as well as expensive, if not thoroughly researched. For example, maximum substrate width and substrate thickness is critical when purchasing a fixed parabolic focused unit.

 
 
 

A mercury vapor lamp consists of a quartz tube that measures about an inch in diameter. It contains a precisely calculated amount of mercury (Hg) and an inert gas, either argon (Ar) or xenon (Xe). Before the unit is activated, almost all the mercury is in its normal liquid state (quicksilver). When the unit is turned on, the electrodes of each end generate an arc between them. This arc conducts electricity, increasing the temperature in the bulb and evaporating the mercury into a vapor. This evaporation usually requires two to five minutes (the unit's warm-up period).

A mercury vapor lamp's output lessens with length of use. A regular output of 200 watts results in a 15% decrease in energy emission after 1,000 hours. Of course, lower power settings slow this deterioration.

Proper maintenance of the bulb can increase the lamp's life. Clean the bulb with unadulterated solvent before turning the unit on. This keeps fingerprints and other handling marks from being etched onto the quartz when the bulb gets hot.
 
 

(a) It is very important to prevent mercury vapor lamps from overheating.

(b) Some printed substrates are sensitive to heat; they can distort during curing. Cooling systems can minimize or prevent this.

1. Air cooling:

One or more circulating fans are positioned on or within the unit to ventilate the irradiator and conveyor.

2. Water cooling:

An insulated water jacket surrounds either the conveyor, the reflector, the electrodes, or a combination of these components.

3. Combination air/water:

Some units combine air and water with a heat filter. The latter is placed between the lamp and conveyor and allows ultraviolet light to pass through to the print while absorbing most of the heat and protecting the substrate.

Another test for UV output is a light sensitive tape which can measure the level of absorbed UV when passed under a UV source. These tapes change color depending on the intensity of lamp and speed of the conveyor, and are then checked against a calibration chart.
 
 

(a) Conventional, hot-air knife tower dryers.

(b) UV curing units.

(c) Infra-red dryers.

There are two types of multicolor UV printing systems that are affordable:

1. In-line multicolor presses.

2. Carousel multicolor presses.

Multicolor screen printing will replace the repetitive time consuming and labor intensive efforts of conventional single-color screen printing. It replaces the tedious steps of printing, drying and stacking one color at a time. 
 
 
 
 

In this section, the main consumable products used in screen printing are discussed. These include:

Inks and Coatings

Stencils

Squeegees

Meshes
 
 

Screen inks are required to be much more than decorative. Product demands include resistance to chemicals, abrasion, prolonged exterior exposure as well as withstanding the rigors of die-cutting, welding, bending and forming. Furthermore, these properties must be manifested on the widest range of substrates. Without question, UV inks and coatings outperform conventional systems in these requirements.

In order to understand this process, it is necessary to understand the compositionof UV ink. Typical UV inks consist of the following major components: 

- Oligomers

- Monomers

- Photoinitators

Oligomers and monomers are very reactive chemically. During exposure to UV light, and in the presence of photoinitators, they undergo a fast polymerization reaction (fast cure). The photoinitators serve as a UV light antenna which is capable of absorbing UV energy mainly in the wavelength range of 200-400nm. Upon absorption of UV radiation, the photoinitiator undergoes a chemical reaction which leads to the production of reactive molecules known as radicals. The radicals cause a polymerization reaction which then proceeds with great speed. Upon completion, the oligomers and monomer have formed a solid crosslinked network of cured coating. Contrary to the drying mechanism of conventional solvent inks, this transformation is a change of condition without any loss of molecular weight or film thickness.

The ultraviolet range of the electromagnetic spectrum can be divided into three main groups: 

Near UV (UV-A band) wavelength range 315 - 400 nm

Middle UV (UV-B band) wavelength range 280 - 315 nm

Far UV (UV-C band) wavelength range 100 - 280 nm

The UV-B band is mainly used for therapeutic purposes (sunlamps). It is also called erythemal band.

The UV-C band features rays that have strong germicidal effect. This band is used for destroying harmful bacteria. It is also called bacterial band.

The combination of UV wavelengths from UV-A and UV-B (240 - 400 nm) initiates photochemical reactions in some materials to produce rapid curing. This is the region of the spectrum used for the UV cure of inks and coatings.

In the final analysis, however, it is the printer who must ultimately decide because only the printer has the full knowledge of what is required to complete the work. Only the printer knows the capabilities of his equipment, the conditions in his plant, and the standards of the client. For instance, there may be three or four inks which will adhere satisfactorily to a difficult substrate but only one which can print at the equipment speeds which make the job profitable.

Generally speaking, UV inks and coatings are formulated to print on and adhere to a wide variety of substrates. They are also designed to provide the optimum in film properties, i.e. gloss, flexibility, opacity, abrasion resistance and durability. It follows, therefore, that any change to composition will change properties and disturb the fine balance provided by the ink maker. As such, the ink has to be used as it comes from the factory though it is possible to alter the performance of the ink without significantly affecting the properties. For example: 

- Reducers are available to adjust viscosity

- Opacity can be lowered by adding extender base

- Photoinitators can increase cure rate

- Halftone bases can be added to assist in four-color process printing.

Mixing by weight rather than by volume is the recommended method as the specific gravity of each ink will vary. Do not attempt to color mix and match without a basic (by weight) formula. Random, intuitive matching may well be color accurate, but it may also result in producing too much ink for the job (waste/inventory loss).
 
 

The chart below compares the mileage of a 40% solids conventional product with that of a 100% solids UV product.
 

Film thickness Mils.	Spread rate Square feet/gallon
	UV	Conventional
0.6	2650	1050
0.4	4000	1600
0.2	8000	3200

In this example, UV mileage is more than double. So even if UV is priced twice as much per gallon, it is still more cost effective. When factored with the improved print quality, the benefit is even more pronounced.

Ink advantages include: 

- Non-drying in the screen

- No solvent emission

- Stability of viscosity because of 100% solids; no solvent loss during cure

- Better mileage

- Reduction in process time

- Reduction in working space

- Improved print quality

- Productivity gain is minimally 25%

- A clean working environment

- Wider range of substrates can be printed/coated

- Some dark and opaque colors are harder to cure

- The process requires more maintenance

 
 
 

Adhesion of a solvent-based ink is usually aided by wetting - the physical or chemical interaction between the substrate and the ink. Since UV inks cure so fast, there is very little opportunity for wetting to occur. Thus, it cannot be depended on as an adhesion-promoting factor.

With flame treating, plastic substrates are momentarily passed in front of a flame jet prior to being printed. The fire slightly rearranges the plastic surface's molecular structure to ensure proper ink adhesion.

Using an X-Acto knife or similar tool, cut a crosshatch pattern in the cured ink film. Then stick a portion of transparent plastic tape over the crosshatch. Rub it down well.

Now grasp the tape firmly between your thumb and forefinger and abruptly pull it off. Some of the cured ink film may come with it. The less ink is picked up by the tape, the better the adhesion.
 
 

1. Surface tack: If the ink film feels sticky, it is not completely cured.

2. Scuff resistance: If the ink film is easily damaged by rubbing or abrading, the cure may be incomplete.

3. Wet ink beneath the surface: Press your thumb into the ink film, then twist it to one side. If there is wet, uncured ink beneath the cured outer surface, this force should break through the outer layer to expose it.

4. Easy-peel softness: If the cured ink film is soft enough to be peeled from the substrate's surface, it means the ink either is not fully cured or is incompatible with the substrate.
 
 

Screen printing's one great advantage is that it is not profitable for the litho printer to gear-up for short runs. Further, the litho printer cannot readily handle very large or very small sizes, thick or very thin materials, nor materials that are too rigid or too flexible.

It must be remembered, however, that coating and varnishing over inks or over virgin substrates should be tested before full production is undertaken. When UV screen coatings are to be applied over litho printed stock, please note: 

- The litho ink should be thoroughly dry.

- The litho ink be free of waxes and lubricants to ensure maximum adhesion and to avoid reticulation.

- Avoid litho inks containing alkaline pigments. Examples of these are rhodamine red and Pantone reflex blue and purple. Most UV clears when used over these colors will cause some color bleaching.

- Only a minimum of spray powder has been used.

- Coated stocks are used - uncoated stocks are generally too absorbent.

As cooperation develops between the litho and screen printer, and mutual knowledge develops, all over-coating problems should be eliminated

- The direct.

- The indirect.

- The direct/indirect.

- The capillary film.

Although the cost of capillary film is higher than the cost of an equivalent amount of direct emulsion, the advantages of capillary film outweighs the extra cost of the film itself. These advantages include high quality stencil and savings in press time. The film's durability handles print runs up to 50,000, saving more time and money. Yet again, contact your UV ink suppliers to choose a stencil to suit your production procedures.
 
 

- Type of ink: is it a water-based, or standard UV ink or coating?

- What image is to be printed e.g. solids, fine lines or four color process?

- The substrate: is it absorbent or non-absorbent, smooth or irregular, flat or three dimensional?
 
 

This defines how much of the ink is allowed to pass through the screen mesh. For example, a screen with 40% open print area blocks 60% of the ink passage and permits 40% to go through. Open print area influences how thick the ink deposit will be.

Color volume

This refers to the color holding capacities of all the mesh openings in one square meter. Calendered fabrics are reduced in thickness for minimum ink deposit, thus their color volume is 20-40% lower. Printing or coating on non-absorbent substrates becomes much easier when you use a calendered fabric.

Calendered mesh

The calendered mesh is a commonly used mesh for UV screen printing. This is due to the following reasons: 

(a) Calendered mesh is designed for printing specifically with ultraviolet curable inks and varnishes.

(b) Every square inch is heat processed through a precise roll arrangement to uniformly flatten one side. This reduces the fabric's overall thickness and gives more strength to the monofilament weave.

(c) This mesh enables you to get a very sharp print as well as faster drying.

(d) You have more exact control of the print and 20% less deposit.

(e) Calendered mesh is normally used with the flat side of the fabric inside the screen or squeegee side. To get an even lower deposit, you can reverse the mesh so that the flat side is on the substrate side.

Soft, low durometer squeegees easily conform to irregularities in the substrate and various tension levels in the screen. Harder, more rigid, high durometer squeegees accurately flood and force the ink through the mesh while maintaining uniform off-contact release. The most widely used squeegee for UV screen printing must have the highest durometer possible (80+) that will still retain flexibility and adapt to both the screen and the surface of the substrate. The harder the durometer, the sharper the print, and the thinner the ink deposit. The blade profile of a UV squeegee should be square edged and sharp, as the ultimate aim is to get an even and very thin film weight of ink.

There are many types of squeegee blade formulations available with different levels of strength and chemical resistance. UV squeegee blade composition is an important factor in maintaining durometer, color consistency and the sharpest result. UV blades are cast from a combination of polyurethane and slip agents for extra resistance to the UV chemicals. The slip agent also ensures a low degree of friction for excellent ink flow across the screen.

All workers should thoroughly clean hands with soap and water after printing with UV inks. All foods, beverages, and smoking materials should be kept out of the workshop.

If ink comes into contact with skin, wash the affected area right away with lukewarm water and soap or cleansing compound, but not with a cleaning agent that contains lanolin.

Do not try to remove UV inks from the skin by using the ink's wash-up solvent or thinner. This can increase the health risk.
 
 

If ink comes into contact with eyes, generously flush the eyes with water for 15 minutes and get medical care. Consult your ink's material safety data sheet for explicit first aid instructions.
 
 

Impervious aprons, footwear, etc., may be wiped clean with small amounts of the ink's wash-up solvent. Make sure this is done in a well-ventilated area, preferably the same area used for cleaning screens with this solvent.

Keep containers tightly closed when not in use. Allow at least 10% air space between the surface of the ink and the container lid; this air pocket extends the ink's shelf life.

Never subject a UV ink to high temperatures or bright light. Keep the ink container away from the light emitted by your curing unit. Keep inked screens away from direct sunlight.

Avoid contaminating the ink with foreign chemicals - especially strong acids, strong alkalis, reactive metals, metal salts, and peroxides.

Finally, make sure your disposal procedure for unused UV inks, contaminated clothing, used tools, and soiled rags complies with any regulations (local, state, or federal) that apply to waste material management in your area.
 
 
 
 

• Inks and coatings will improve.
• Curing and printing equipment will continue to advance.

• More opaque inks 
• Faster curing inks/coatings 
• Water-based systems of ink and coating for less pollution. 
• Exterior durability extending to 7 or 10 years. 
• A universal, more flexible ink/coating for every substrate. 
• Surface treatment will be eliminated.

• Cure faster 
• Run cooler 
• Become less expensive 
• Print faster 
• Occupy less space 
• Be less labor intensive

UV screen printing is a proven and successful process. As printing equipment, consumables and substrates have all improved dramatically, the implementation of correct process procedures now have yielded a trouble-free process. Those contemplating UV as an addition to their business can do so with confidence. By following the guidelines set forth here, and having established that there is sufficient need and sufficient market share available, moving into the process should be relatively simple.

Based on current performance and emerging developments, UV screen's viability is assured.