Registered in England No. 1725990
Q & A / Advice - Coatings:
A coating is basically a solution which is applied onto the surface of a substrate
to enhance, protect or give added performance. The most obvious benefits are
an enrichment of the optical effect, combined with protection of the material’s
surface during both the finishing process and final use. In addition, coatings are
available which will affect the way in which the substrate will perform under
certain conditions, i.e. when being subjected to possible oil or water
contamination, low or high temperatures and when being used on converting
and packaging machines. Finally, and a factor which is often underestimated, a
coating will enhance the feel or tactile effect of a product, increasing its
perceived substance or value when being handled.
Primarily, there are three main types of coating currently available:
•
Oil based varnish.
•
UV cured.
•
Water based.
The use of oil based varnishes is slowly declining, with the market now being
split largely between UV and water based coatings, with the latter steadily
gaining in popularity due to the many benefits that it offers.
The factor that currently has the greatest influence on coatings is environmental
legislation.
Despite the increasing use of water based coatings, UV coatings still prove
popular, due to their durable finish and high reflective values, typically in the
region of 93%. In addition, modern UV coatings are much safer to use; those
produced by Vegra, for example, have a reduced skin irritancy factor.
Nevertheless, water based coatings are catching up fast. Although the reflective
values of Vegra water based production coatings range from 75 to 80%,
depending on the substrate used, laboratory tests have shown that figures of
around 90% can be achieved.
The extra performance offered by UV coating has, however, a cost. The coating
itself is more expensive than water based materials, while to utilise UV coatings
a large investment in pressroom equipment is required.
The factor which now has the greatest influence, on both the formulation and
use of coatings, is environmental and health and safety legislation. This is
becoming tougher, making it increasingly difficult both to use and dispose of UV
materials, while the emissions from UV coating systems now have to be safely
ducted away from the work area, requiring additional capital expenditure.
Water based coatings that can be applied through the ink train are now
available.
Vegra Print Coat 1501:
Aside from the impact of legislation, the most significant development
was the introduction of coatings which can be applied through the ink
train without difficulty. For both UV and water based materials, the cost of
the specialised coating and drying units has been high and many printers
have found it difficult to justify the extra investment. In responce, Vegra
and Pomeroy have carried out a major research and development
programme into products which could be applied and dried without
special equipment. One of the first results of this programme was Vegra
Print Coat 1501.
Factors to be considered:
The following is a checklist of factors which need to be considered before
purchasing coatings:
o
The substrate.
o
The final use of the product.
o
The application method.
o
The finish required.
o
The inks being used.
o
The slip factor.
o
The rub resistance.
o
The finishing or converting process.
o
The environmental implications.
o
The viscosity of the coating.
Of course, the printer is unlikely to have the time or inclination to consider
all of these factors for every job and, to an extent, will need to rely on the
coatings supplier for guidance.
Apart from the substrate to which the coating is to be applied, the most
obvious factor in choosing a coating is the finish required. This can range
from matt to satin and from gloss to high gloss, plus sealers. Next to be
considered is the final use to which the coated product will be put; this is
where factors such as rub resistance, scratch resistance, slip factors,
stability, toughness, flexibility, adhesion and product performance come
into the equation. For example, the production of food wrappings and
cartons, where coatings will often come into contact with the food or drink
being packaged, can be refrigerated, or may need to be water or grease
resistant. Equally, point of sale material will often be exposed to sunlight
for long periods of time and will require a coating that is resistant to
ultraviolet light.
The finishing or converting process can have a significant impact on the
choice of coating.
An area which is often forgotten, but which can have a significant impact
on the choice of coating, is any finishing or converting process that is
used. Materials subjected to automated finishing processes can be very
harshly treated, so the coating must be both tough and durable; similarly,
the slip factor may also need to be taken into consideration.
Water based coatings applied directly through the ink train allow high
press speeds to be used without the need for extended delivery or any
other ancillary equipment. Consequently, materials such as Vegra Print
Coat 1501 can be applied wet on wet as, remarkably, the inks can
breathe through the coating emulsion to dry. Results have shown that
only the bare minimum of spray powder needs to be applied and, as
oppsed to other forms of coating, where the powder sits on top of the
coating, it is absorbed within and surrounded by the coating to leave a
smooth finish. Also, the job can be backed-up straight away.
Vegra Print Coat 1501 is run with the dampening unit off. No special
rollers are required and, unlike other methods of coating, there is no build
up on the rollers enabling the inking unit to be easily cleaned after use.
In partnership with Vegra, we can offer our customers a wealth of coating
knowledge. At our manufacturing plant in Gloucestershire, we produce a
wide range of Vegra coatings. In many instances the coatings are
formulated for each customer’s particular requirements. A laboratory
service is available for analysis and research and the development of
coatings to solve specific problems.
© Pomeroy Pressroom Products Ltd 2010
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