The Coating Options.
Off-line UV and Aqueous Coating over Dried Ink Films. 
Markets for Radiation Cure. 

THE COATING OPTIONS

In this section we will discuss the options available for improving efficiency and appearance of litho print production through the use of coating and varnishes, especially UV. In the past, only two options were available: litho print with varnish or without varnish. 

Typically, litho overprint varnishes are applied in-line, but they can also be applied as a separate operation on a single colour press. While in-line litho varnish is still being used extensively with very acceptable results, drying and setting times are slow and spray powder must be used to avoid sheets sticking in the stack. The process requires considerable expertise on the part of the printer to avoid set-off and to avoid producing sheets of sandpaper. As modern litho press speeds increase, this factor becomes more critical and can be a limitation of achieving full production potential. 

Off-line coating with solvent-based spirit varnishes has been a popular means to achieving good gloss and print protection. However, the process is relatively slow, requires a completely separate operation, and, with the inclusion of flammable solvent, can be hazardous to employee health and safety. 
Film laminating should be mentioned, but costs are high and a spray-free receptive print surface is still required. Another coating option is calendering.  While results are very good, the process is slow and requires a special heat press. 

Three convergent technologies meet these needs: the development of in-line coating hardware, the introduction of UV cure inks, and the development of UV and aqueous coatings. Aqueous in-line coatings have paralleled the development of press in-line coaters. All the major press manufacturers supply multicolour printing machinery with dedicated in-line coaters or convertible dampening systems. 

To put the options into perspective, let us examine the applications, features, benefits and limitations of the following: 
1. Conventional ink/litho varnish. 
2. Conventional ink/aqueous varnish. 
3. Conventional ink/UV varnish. 
4. UV ink/UV varnish. 

Litho overprint varnishes are generally solutions of solid resins in vegetable drying oils. They dry partially by absorption into the paper or board, but mainly by oxidation which cross links the vegetable oil component to a tough flexible film. Litho overprint has been around the longest and is still the most widely used means of improving gloss and print protection. Material unit costs are lower than any of the other processes by a factor of 2. Gloss level and scuff resistance is lower than UV, and, depending on substrate, is generally similar to aqueous. Although considerable progress has been made over the years, litho varnishes have a tendency to yellow and, although mild, do have a distinctive odour on dried print. Litho overprint varnishing does not offer an instantly dry print at delivery in contrast with UV and aqueous. The resultant necessity to use spray powder sometimes causes the characteristic “rough” feel. However, litho varnishing provides the ideal means of “spot” or pattern varnishing at high speed. 
The higher viscosity reduces the amount of penetration and “greying” of lower quality boards. Maximum film weights of litho varnish which can be applied are as low as 0.8-1.5 Wm2 and, coupled with the flexibility of the resin/oil combination, ensures that cracking on carton and cover creases or folds is not a problem. 

Aqueous coatings
Glossy aqueous in-line coatings are relative newcomers compared to litho varnishes. Most recently, acrylic dispersions have replaced the old emulsions, offering improvements in application, and storage stability, and wetting characteristics. The aqueous coatings of today are quite different from those available even five years ago. The in-line coaters as optional extras to multicolour litho presses have kept pace with, or perhaps even led, the development of these aqueous coatings. 
The advantages and benefits of aqueous coatings are: 
1. Almost instant drying at the delivery; printed stocks can be immediately processed. 
2. Little or no spray powder imparts improved feel and a cleaner environment. 
3. The dried coating film is tougher and generally more scuff resistant than a litho varnish. 
4. Gloss on quality coated paper can be expected to be superior to litho varnish, but on more absorbent carton boards, gloss is reduced and similar results can be anticipated. 
5. Aqueous coatings are water white, and, once dried, are odourless. 
Suitable for food packaging. 
6. Specially formulated aqueous coatings can provide an ideal base for subsequent processes, e.g. film lamination, UV roller coat or screen gloss varnishing, foil blocking, gluing, etc. 

Aqueous coating applied as a sealer over conventional inks will enhance the appearance of any subsequent UV coating application and reduce UV coating usage. 
Aqueous coatings have been developed to achieve a number of specialized purposes such as: 
In-line heat seal (blister-pack) coatings. 
Grease resistant barrier coats (for food contact). 
In-line calendering coating. 
Completely matte finish coatings. 
Prime coats, clear, opaque and pearlescent to upgrade low quality board. 
Tie coats (sealers) to enhance gluing, film lamination and UV varnishing over conventional inks, either in-line or dried. Special “Tie-Coats” are available for in-line web heatset coating. 
Acrylic aqueous coatings are compatible with most glues, including PVA’s and EVA’s. This has been confirmed in tests carried out with National Adhesives and N.B. Love. However, as the application of aqueous coatings reduces the absorbency of the board, gluing performance will be affected, but not necessarily adversely. 

The two advantages perceived with aqueous coatings are:
1. Economics: Although unit costs are similar to conventional litho varnishes, usage is 2-1/2 times as much. The reason for this is that aqueous coatings are only 40-45% solids and more wet coating must be applied to achieve the same dry film weight. This is an added cost when viewed in isolation, but when savings due to quicker turn-around, less spray-related damage and improved product are considered, the extra material costs are negligible. 
2. The perceived drawback is of coating as a “too hard” process and being problematic. However, once the operators have mastered the technique they are reluctant to forego the security of running aqueous on almost every job. 

These negative and positive factors need to be weighed against the product being produced and the advantages gained 
 
 

UV cure
UV inks and coatings do produce the ultimate gloss and film hardness, plus instant curing at the press delivery. They are 100% solids systems which cross link to form a hard plastic film. This ability to apply heavy film weights of a hard glossy film when cured is also responsible for one of the disadvantages of UV coatings. That is, if not correctly formulated, the film may crack on folds and may not adhere to unsuitable substrates. 

The advantages of UV cure systems are therefore:
Highest gloss results for very acceptable print appearance. 
Excellent abrasion resistance. 
Good product resistance. 
Immediate cure. 
No spray powder required. 
Fast turn-around with in-line processing possible.  Being solvent free, taint problems are reduced although UV does have a characteristic odor. 

The disadvantages are:
Higher unit costs, but these are partially cancelled out by better mileage. 
Film flexibility has been a problem, although this is being constantly improved. 
Substrate or dried ink surface has to have sufficiently high surface energy levels to be UV receptive. 
UV curing has established a firm niche in the high quality packaging field and for printing on non-absorbent substrates. As mentioned earlier, all these options in practice prove to be complementary rather than competitive. In fact, if we consider the number of combinations, the permutations may seem infinite. Possibly the most relevant way to explore the alternatives is from the viewpoint of the practical print application. 

For instance: 
For a medium to long run catalogue or magazine print run, at high speed, conventional heat-set inks remain the obvious choice.  However, for short run, high quality publications, such as prospectuses and annual reports, various alternatives are available, including: 
1. Conventional ink, litho spot varnish (gloss or matte). 
2. Conventional ink, UV coating (e.g. screen). 
3. Conventional ink, aqueous gloss coating. 
4. Conventional ink, aqueous matte tie-coat and off-line spot UV gloss roller coat; or, for optimal result, UV screen coating applied off-line over an aqueous in-line tie-coat (prime coat). 
5. A proven process is UV gloss coating over UV ink. 

Outstanding results can be achieved by litho pattern printing UV matte varnish over the gloss coating. 
For printing on non-absorbent substrates, like polyolefins such as Yupo, Phase 3 and Tyvek, or PVC’s, metallized films, etc., UV ink, with or without a protective UV varnish, is a logical choice. But caution is required. Surfaces which have low treatment levels will have adhesion problems. 

Conventional hard drying inks can be considered but sticking and set-off is a real threat. Racking small stacks is often required.  Unfortunately, application of aqueous in-line coatings is not recommended as some substrate absorbency is necessary for the drying process to function efficiently. 
Similar alternatives apply to the packaging field, ranging from low cost, high volume paper labels to high quality, low volume cosmetic cartons. 
As with most real life situations, performance and product quality must be weighed against cost and economics. 
 

Broadly speaking, future efforts are being directed in three major areas: 
1. Improved user friendliness in regards to ease of handling and improved health and safety. 
2. Improved product appearance. 
3. Products which offer better value for the money. 

Examples are:
Epoxy cationic UV cure systems which have a different mechanism of cross linking and curing which improves adhesion, flexibility and water resistance. 
“Aqueous” UV systems which are water washable.  Improved UV ink formulations which allow press performance similar to conventional inks at all press speeds, and Glossier aqueous in-line coatings which do not sacrifice any blocking resistance or film hardness. 

Finally, the health and safety, or physiological, effects of the various options should be briefly discussed. Conventional inks, because of the many years of experience, are considered to be low in toxicity and have very low skin irritancy levels. Conventional litho inks and varnishes, however, are not suitable for direct food contact. 
Some of the earlier monomers used in UV cure products had high draize values and were fairly irritant on skin contact. However, most responsible UV producers now use materials with much lower irritancy levels below the limits set by some regulatory agencies. Although food taint levels are low, having almost no volatiles, UV has the characteristic acrylic “new carpet” odour which, to some people, is unpleasant. It must be emphasized that this is only a typical acrylic odor and does not necessarily signify the presence of any harmful vapors, particularly in dried film. 
UV inks and varnishes are not suitable for direct food contact. Aqueous coatings, being water based, are the safest of any of the products covered.  No solvents are used to present a fire risk or to pollute the atmosphere, and many aqueous coatings are approved for direct food contact. 

OFF-LINE UV AND AQUEOUS COATING OVER DRIED INK FILMS

Successful application of UV or aqueous coatings over dried inks is controlled by a physical effect known as surface tension. Surface tension, or energy level, can be explained by the understanding that a liquid with high surface tension levels has a greater degree of cohesive force and intermolecular attraction and less adhesion to or wetting of another material. 

For example, water has a surface energy level of around 80 dynes/cm2. The molecules of water have a great internal attraction for each other and readily form a bead, or droplet. Non-polar solvents can have energy levels varying from 10-20 dynes and therefore have much greater wetting ability and less tendency to bead. UV monomers and oligomers lie between these two extremes, at around 30-36 dynes/cm2. 
Plastic or printed substrates have particular dyne or treatment levels. This is simply a measure of the “wettability” of the substrate. A substrate that can be wetted by a liquid of high surface energy obviously has a friendlier surface than one which can only be wetted by low energy level liquids. The surface tension of the substrate is measured by comparing the wetting of liquids of varying surface energy levels. The treatment level, or surface tension/energy level, is rated as the lowest energy level liquid which will wet that film or substrate, and is quoted in dynes/cm2. This is why we say that a substrate must have a high surface treatment or dyne level before it can be successfully printed or coated. 

The treatment or dyne level of the paper or film must be higher than the surface tension of the ink or coating. The higher the dyne level of the substrate, the better the wetting and adhesion of the coating or ink. UV and aqueous coatings, by their physical nature, have fairly high energy levels or surface tension. They therefore require a substrate or film with a high treatment or dyne level. 

Usually a dried film of conventional ink will accept UV or aqueous coating quite adequately. However, there are a number of factors which can reduce the dyne level of the printed film, creating problems with wetting or adhesion of UV or aqueous coating. These include: 
1. Ink not fully dried. 
2. Ink containing excessive wax or lubricant. 
3. Ink containing slip or release additives. 
4. Excessive or incorrect spray powders (water soluble powders should be avoided.) 
5. Excessive ink film weight. 
6. Board with low absorbency. 
7. Ink has entrained excessive water from fountain. 

Most litho inks contain 10-30% of solvent to control tack and viscosity. This solvent is actually a very thin paraffinic mineral oil. Inks are formulated so that the solvent component will be absorbed into the board or paper.  However, if a heavy coverage of ink is applied and the board has limited absorbency, not all the solvent is absorbed. As the solvent does not dry, it has nowhere else to go but to form a thin film on top of the dried ink surface.  This “oily” solvent film prevents good UV or aqueous coating adhesion. That is why, very often, merely wiping the printed film with a dry cloth improves lay and adhesion dramatically, as the solvent is removed. 
“Patchy” reticulation and adhesion across a sheet can sometimes be observed due to slight variations in absorbency of the paper coating.  However, there are a number of solutions which can be tried. 

1. Passing the printed sheets under the UV lamps before coating can occasionally “burn off” oil or surface contamination. Coating must be applied immediately after this operation. 
2. Corona treatment of the printed sheet is more effective and will solve most problems by “burning off” contamination and providing more satisfactory bonding sites. In most cases, corona treatment is carried out in-line with coating. 
3. If spray powder is the cause of the problem (often recognized by “spotty” reticulation), spray powder can be removed or crushed by running sheets through a dry printing unit under impression. 
4. A bridging or key coat can be printed or coated over the ink to provide a more suitable surface for the UV or aqueous coating. 
5. A coating with lower surface tension can assist. This is achieved by adding a flow agent or solvent to the coating to reduce surface tension. However, caution must be observed, as foaming tendencies are increased when some silicones are added. 

Isopropyl alcohol can be added to aqueous and UV coatings to reduce surface tension. 
However, these problems are best avoided by following a few simple rules: 
1. Avoid excessive ink film weights. 
2. Use full strength inks. 
3. Avoid superimposition of more than 200%. 
4. Do not apply excess spray powder and avoid water soluble grades. 
5. Do not use inks with high levels of lubricant or release agents. 
6. Inks should not be coated within 24 hours of printing. 
7. Excess damp and inks which emulsify can cause problems. Alcohol dampening tends to give more consistent coating lay and adhesion. 
8. Avoid very hard surfaced boards with low porosity or “chalky” coating. 
9. Select a coating or varnish which is specifically formulated for off-line coating. Hard curing coatings tend to have inferior lay and adhesion. 
10. Do not apply excessive coating or varnish film weights. 
 

 MARKETS FOR RADIATION CURING

Introduction

The utilization of Ultraviolet (UV) curing for a variety of coating (and other) applications has become a fact of life for a number of industries, although it is most popular with the graphic arts (printing), timber (finishing) and electronics (coatings) industries. And while the growth rate is currently believed to be 15% per annum, the reason for such growth is attributed to a variety of environmental, economic and technical advantages. 

TABLE1: Advantages and limitations of UV/EB curing.
 

Advantages:
Solvent free. 
Low energy consumption.
Low temperature requirements. 
Small space requirement. 
Lower material costs. 
Rapid dry. 
Totally controllable reaction. 
Advantageous physical properties. 
Higher productivity. 
Less waste. 
Novel products. 

Limitations:
Higher cost of materials. 
Line of sight curing. 
UV-photon penetration. 
High cost of equipment (EB only). 
Skin irritation/sensitization. 
No FDA approval. 

However, UV curing still only represents a small portion of the total market for coatings. This has been largely due to the major limitations and constraints of the technology. Recent research has become increasingly successful at overcoming these limitations by various aspects of chemistry and/or equipment design. Some of these innovations will be discussed later. 

This should be compared with reference 2 which places the global market for1985 at 51,000 tons. Reference 3 projects the US and Japanese markets for 1990 at 51,000 tons and 50,000 tons respectively. 
 
 

Formulator markets
Formulators of radiation curing products manufacture coatings, inks and adhesives for a variety of end uses. The ‘split” of application uses in the US is estimated at approximately 75% coatings, 35% printing inks and 25% adhesives. 
Since some users employ more than one application system, the total of the split exceeds 100           Introduction 

Current end user markets
A comprehensive list of applications of UV is presented in  It is not possible to discuss all of these applications in detail and only industries where acceptance is wholesale will be considered in the following discussion. 

Applications of UV curing
Particle board filler 
Photopolymer print plates 
Photoresists 
Printed circuit board 
Large scale integrated circuits 
Conformal coatings 
Floor tile / hardwood coatings 
Offset inks 
Overprint coatings 
Dental bonding 
Screen print inks and coatings 
Narrow web printing (flexo offset letterpress) 
Vinyl and paper laminates 
Vinyl flooring 
Metal decorating 
Metal and plastic name plates 
Galvanized metal tubing 
Fiber optic coatings 
Clear hard coats 
Metallized plastic coatings 
Adhesives 
Lens bonding 
Wire bonding 
Flat wood finishing 
3D wood finishing 
Silicone release coatings 
Electrical encapsulation 
Discs: CD/DVD/optical 
Plastic tube coating 
Wire marking 
Plastic bottle coating 
Solar reflective films 
Abrasive binders 
Optical lenses 

In addition to the known applications listed, many companies, until recently, have been very secretive about their uses of UV/EB curing. It has only been very recently that the use of EB processing (in a number of countries world-wide) for curing of inks and varnish in fruit juice packs has been made public. The radiation-processing activities of another major multi-national company is indicated by the number of patents it has lodged in the areas of adhesives, coated abrasives and photographic processes. 

The Printing and Graphics Arts industry has been the first to fully embrace UV/EB curing technology as a viable solution to solvent emissions and low cure speeds. UV cured inks and varnishes are now used in many medium to large printing houses for application to almost every type of substrate from paper to plastics to metals. 
The timber industry has for a long time been using UV (and EB) curing for flat panel processing to produce scuff, - solvent - and stain-resistant high gloss coatings. More recently, the range of applications has increased rapidly as new coatings have become available. 
Although a later starter, UV/EB curing for electronics applications is growing very rapidly as the advantages of solvent-free rapid curing have become apparent for sensitive components and production-line processing. 

Cellulosic substrates (paper and board)
In the Graphic Arts industry, the initial attraction of UV curing for printers was the excellent gloss and rapid dry characteristics of both inks and varnishes.  Many of the other unique properties of UV coatings (e.g. scuff and solvent resistance) have subsequently been utilized in a variety of printing applications. Indeed, there have been a number of developments in the industry which rely on UV as the only viable high speed curing source (e.g.  rotary letterpress). 

Table 6 summarizes the range of coatings currently offered by various suppliers. These are available for application via roller coater, gravure, screen, flexographic, lithographic or letterpress print methods. 
Coatings other than varnishes and inks have been developed for a variety of applications including adhesion primers, release coatings, adhesives and adhesive desensitizers. 
 

Currently offered commercial coatings for printing and packaging: 
Coating type 
Application 
Varnish 
Matte 
Gloss 
Gluable 
Foil stamping 
Abrasion resistant 
Acid resistant 
Solvent resistant 
Stain resistant 
Water and freeze resistant Food products (indirect contact) 
High slip 
Inks 
Process and PMS colors 
Fluorescent 
Scratch off 
Release coatings 
Tight release 
Easy release 
Controlled release 
Differential release 
Adhesives 
Laminating 
Pressure sensitive 
Reverse 
Piggy back 
Desensitizers 

Coating formulators have responded to printers’ needs by expanding the range of coatings offered to satisfy requirements for faster cure speeds (or fewer lamps), in-line wet-on-wet over conventional inks and new printing substrates. Equipment manufacturers have contributed to the technology with innovations such as higher intensity lamps, cooler operation, interdeck curing, doped lamps for specific curing requirements, instantaneous on-off and special geometries to reduce gripper shadow cure problems. 
The early fears of the printing industry for UV and EB curing have largely been allayed by the excellent track record of the technology. Initial concerns about the irritancy of the coatings and UV exposure hazards have been overcome with better chemistry and better shielding techniques. 

Wood
The increasingly stringent restrictions on volatile organic compounds is putting more and more pressure on the wood finishing industry to remove solvents from their operations. With a proven track record in flat panel processing, 100% solids UV or EB processes are becoming the logical and favored alternative. 

The first major application of UV curing was to the curing of polyester/styrene wood coatings in the early to mid sixties. Since then, the application of UV curing to wood coatings has grown considerably. With the increase in line speeds to above 80ft/min., acrylate chemistry has become more prevalent even though it is more expensive. In general, cure performance is better and lower film thicknesses are required to achieve a given level of performance. 
Typical coating types include: 
? Reverse roll coat fillers (paste filler for chipboard, 60-100 gsm) 
? Forward roll coat sealers (low viscosity for wood, wood veneer or hardboard, 25 gsm) 
? Curtain topcoat (for wood, wood veneer, 200-300 gsm - polyester 70-200 gsm - acrylate) 
? Roll coat topcoat (for wood, open grain, 10 gsm, gloss or matte) 

The first semi-commercial EB curing line was installed in 1967 in the US. The plant, which was designed to apply and cure paint on wood was not in use for very long due to a number of teething problems. The next commercial installation for wood coating was in Holland in 1973, closely followed by three other European operations which coated products such as furniture, doors and timber panels. More recently, lines have been set up also in Japan, the US and South America. 
US operations use EB curing to achieve a bond of wood grain paper impregnates to the substrate via a timber filler/laminating adhesive. The adhesive is applied and pre-gelled using UV to create cohesive tack, the paper impregnated (in-line) and laminated, a tie coat and one or two curtain coats applied, and then all coatings are EB cured simultaneously at speeds up to 50 m/minute. 
The products produced by EB are superior in all respects to low pressure melamine laminates and have equivalent properties to high pressure laminates (better than some grades) with the exception of wear resistance. 
The most recent developments in the wood finishing industry involve 3-D processing and opaque “wet-look” finishes. Equipment is now available to satisfactorily cure large objects with difficult geometries. Using a combination of specialized lamps and coatings it is possible to finish wood surfaces to a high gloss pigmented and opaque “wet-look” appearance. 

Electronics
UV curing is receiving considerable attention for its application in the electronic industry. Commercial applications include: 
Photoresists 
Through-hole plugs for PC boards 
Photoimageable solder masks 
Conformal coatings 
Encapsulants and potting compounds 
Membrane switch 
 
 
 

Metals
Metal surfaces are routinely coated using UV inks and varnish formulated for metal decorative applications. Because of the high shrinkage and generally poor adhesion of acrylate coatings to metals, a solvent based primer coat is usually employed as the primary coating. More recent advances in types of materials available have allowed acrylate coatings to be used in direct contact with metals in all but the most demanding of applications (formability). 
(a) Special substrates: metals or foils. 

Metallized papers and foils are being produced by UV techniques, and are designed for a variety of decorative and functional purposes including label stock and microwave packaging. In this direct coating process, a UV primer coat is applied to the substrate of interest using a roller coater and then UV cured. The roll is then transferred to a metallizing facility for vacuum deposition of aluminum. Finally a protective top-coat is applied and UV cured. An alternative more complicated indirect transfer process requires that the coatings be released from a carrier web as part of the process. UV is also being used for the production of these materials and is an ideal process for printing to this substrate. 
(b) Coil coatings. 

The use of UV in coil coatings is finishing coats and adhesives for film laminations. Work has been done in the use of UV cured coatings as anti-corrosive primer coats. 
A great deal of research is currently being undertaken into cationically cured systems. These have shown the potential to solve problems previously unachievable with free radical systems. In particular, low irritancy, fast cure response, shadow zone curing and low shrinkage (i.e. good adhesion to metals and glass) characteristics have shown enormous potential. 

Plastics
The use of plastics as printable substrates and as part of laminates in labels for graphic arts applications is rapidly increasing. Substrates commonly used include PVC, polypropylene and polyethylene. The use of UV inks, varnishes and adhesives are ideal for these non-porous substrates. 
More novel innovations in plastic applications include radiation polymerization of ethylene and commercial utilization of radiation grafting processes e.g. grafting of meth acrylic acid to PVC has been used to improve salt spray resistance of PVC precoated steel. In addition, the grafting of acrylic acid on polyethylene has been reported. 

Glass
The use of “primary” and secondary” coatings for optical fibers is well documented. 
Inks and varnishes are readily available for screen printing onto glass bottles. More recently, UV coatings have been proposed for use in glass laminates and to reduce the weight of glass bottles. 
 
 

Novel applications 
(a) Special substrates - MONO-WEB used for the label making process. 
Here, UV is used to cure the silicone that is directly applied to ink printed on a plastic support. This allows the label to be rewound without the use of a throw-away silicone backing sheet. Products in this area also include the UV cured PSA. 

(b) Special substrates - static dissipative coatings are being cured by EB for protection of electronic components. 

(c) UV-coated polycarbonate is being utilized for touch panel overlays (reference 21). 

In addition, other areas of growing utilization of UV curing are: 
Binders for magnetic media. 
3-Dimensional modeling (stereolithography). 
Pressure sensitive adhesives. 
Textile and leather coating. 
Staple cements 
Pre-preg composites. 
Optical fibers. 
Sealer for fiber reinforced plastics. 
Microencapsulation. 
Wire markings. 
 

Future market applications 

1. Upgrading of paper and other substrates 

Many chrome-coated and clay-coated print stocks will, in the future, be manufactured utilizing EB and UV curing processes. Such coatings are ideally suited to UV inks and varnishes, but currently do not print well using oil based inks. Such stocks may be designed with such high gloss levels that UV varnish may no longer be required. 
Adhesion to metals and metal foils has been a continual problem for UV cured coatings. The use of primers and/or thermal “post cure” is currently employed to reduce problems associated with the very significant shrinkage of these coatings. More recently, developments in alternative curing mechanisms indicate that coatings with excellent adhesion to metals and other non-reactive substrates will soon become commercially available. 

2. Lamination of films (adhesives) 

(a) Release coatings - The current generation of UV silicone acrylate release coatings work reasonably well for hot melt and (non-acrylic) water-borne adhesives. However, crosslinking (reactive) adhesives are a problem because of their attack (crosslinking) on residual acrylates in the silicone release coating. This is particularly a problem where the (acrylic) adhesive is applied and dried in contact with the release liner. 

Recent developments in cationically cured silicone epoxides have demonstrated their ability to overcome many of the above difficulties in easy-release applications. No need for moisturization, less curl and the ability to use thinner films or heat sensitive substrates are the incentives to use such processes for preparation of release coatings.
(b) Pressure sensitive adhesives - The initial development of UV curable PSA’s was fairly slow. The types of polymers required to achieve these properties were not readily synthesized and the current status of these coatings has progressed tremendously. 
(c) Laminating adhesives - UV cured laminating adhesives are available for cellulose-polyolefin or polyolefin-polyolefin laminating. The critical requirement is that one substrate be transparent to UV light. In the future these coatings will be extended in application to a wider range of substrates and/or substantially higher peel strength requirements. 
 

3. Novel end uses 

(a) Special substrates - barrier layers. 
Considerable research is being conducted also into the use of UV curing to produce coatings with barrier properties built in so that a barrier substrate may be produced “insitu” rather than by film lamination. This could be readily extended to include multi-layer compositions. 

(b) Special substrates - free films 
The possibility that EB or UV may be used as a replacement for extrusion in the manufacture of free films is of great interest. 

(c) Security coatings - The use of UV cured coatings to produce 3D or holographic effects. 
Coatings which are transparent (or opaque) to optical or magnetic reading devices. 

(d) Conductive coatings - for the printing of integrated circuits and printed circuit boards. 

(e) Lottery tickets-base for scratch-off. 

4. Novel properties 

Coatings could be made print receptive or unreceptive, or heat-sealable (i.e.  thermoplastic). 
Membranes could be manufactured by incorporation of pores into the film using controlled elimination of solvent by the curing process. 

UV Curing systems are now being manufactured in India, Technical data sheets pertaining on the application can be obtained from