Materials

How do you reduce the weight of a pack without reducing its strength or branding? For many, the answer lies in flexible plastic, in the form of films, shrink wrapping and pouches. To take full advantage of this format, brands are emblazoning logos, images and information across the flexible surfaces. However, printing on to these substrates requires specialist knowledge.

It comes down to the stability of the substrate, explains Simon Balderson, managing director at Telford-based plastic packaging specialist Sirane. It’s about whether the substrate stretches or shrinks; stability is key.

Sirane manufactures a range of packaging, including biodegradable and compostable products. Although his firm outsources the printing, Balderson has a good idea which flexible substrates work best for the right job. Flexible plastics pose different challenges to printing on other substrates.

Shrink sleeves provide a challenge, he says. These tend not to be stable before they are shrunk. You therefore have to make sure that your design is straightforward. When the sleeve shrinks, you get an improved density of colour. But some parts will shrink more than others, which results in a distortion of the image.

European first
Packaging manufacturer Linpac has what it believes is an innovative approach to printing on this substrate. The company claims to be the first in Europe to print on flexible plastic using water-based inks. The ink provides sufficient adhesion to the film, explains Manuella Cheny, product manager for printed film. The other advantages are that the inks have no solvent emissions, which is better for our employers. There’s also no solvent residue, and no solvent emissions when cutting the film.

On top of that, the substrate itself has to be dealt with in a certain way. On flexible stretch film, it is very important to have the correct tension, she adds. This makes it vital to iron out any potential problems at the design stage, as once the design goes on to the press there’s no going back. Sirane’s work is mainly produced on CPP. This is a cast polypropylene film, which is heat sealable and often used as a heatseal layer in retortable packaging. But it isn’t always easy to find the right plastic film for the job.

The selection of plastic films is so vast and we are tasked with finding the best ink for that job, says Barry Ferne, Sun Chemical business development director for its UK packaging division.

Adding value
Sun Chemical has unveiled several new products in the sector. It has developed lacquers which feel rough or smooth and can be overprinted on to standard packs. The aim is to help stimulate the senses, and is a technique used by Amcor Flexibles to produce Hovis crustless bread packs; the soft-touch lacquer allows the packaging to feel even softer – inviting the consumer to think about the softness of the bread inside.

There are a plethora of effects, says Ferne. If you go back 20 years, then there was less choice. But today there are many ways in which brands are trying to get their product to stand out.

Ferne adds that brands are becoming ever more demanding. There are challenges in the industry, he says. One factor is the films that are being printed on. Coated products are now considered expensive but the construction of films is important; there is now a move to treated materials.

Take muesli bags, for example. These are thick and made up of different layers. The challenge is to make them thinner but also to make them sturdy. There is pressure to reduce excess packaging and to reduce costs. The problem facing manufacturers is that clever does not always come cheap.

What also doesn’t come cheap is the investment in new equipment for packaging printers. The dominant technology is flexo, just ahead of gravure printing. The method involves printing on a web press using rubber or plastic plates with raised images. In contrast, gravure involves the printing of an image that has been etched on the surface of a metal plate, and is noted for its high quality at long runs.

One of the big spenders on flexo technology is VMB, part of British Polythene Industries (BPI), a manufacturer of polythene films. The company has invested in two 10-colour Comexi Flexographic printing presses, complementing the Worcester firm’s existing eight-colour presses.

This ability to print using 10 rather than eight colours on almost any substrate, including polythene and polypropylene, will enable even better brand representation on packaging, says a BPI spokesman. It also has major implications in terms of speed and efficiency. More can be done on a single pass of substrate, whether that’s printing in CMYK plus five spot colours and the application of a specialist lacquer, or printing in all 10 colours to maximise the colour gamut.

Sirane’s Balderson adds that flexo has come on a lot over the past few years and is edging up to gravure in terms of quality. If we wanted to go to high quality printing then we would still use flexo, he adds. I’ve seen an increasing number of fancy effects on flexo presses.

But there are other challengers. Sheetfed offset manufacturers such as Heidelberg and Manroland have set their sights firmly on the packaging market with the launch of several large-format presses. Web offset manufacturer Drent Goebel is also eyeing growth in packaging. Marketing manager Rob Meij explains that printing on flexible plastic is not a stumbling block.

In offset, you can print on any kind of substrate that is common for flexo and gravure, he says. There is only one exception: monolayer PE thin quality. Web offset needs a higher web tension in comparison to flexo. But in web offset, you can print on the same substrates as common sheetfed offset.

Breaking it down
While Meij says he hasn’t experienced much demand for biodegradable films, such as PLA, it has the same features as OPP, OPA, CPP and PET in terms of printing – meaning there should be no problems printing on biodegradable substrates. He adds that it is important to follow developments in these materials.

Offset, Meij says, also has the edge when printing on shrink sleeves. The features of shrink sleeves [PVC or PETG] mean that when they are printed in offset they have an advantage over flexo or gravure; this is because of the thinner ink layer of offset ink, explains Meij. The shrink ability is much better; this part of the market is growing very fast.

Web offset manufacturers may have good cause to be optimistic in this area with print runs getting shorter. While gravure is considered the superior quality process, it is more expensive, making it more suited to longer runs. Flexo has well and truly eaten into that market with offset following. But there is another process: digital.

Sure, digital printing could fill a gap for ultra-short print runs and one-off promotional jobs, argues Meij. But it will never replace the common print technologies for flexible packaging.

New kids on the block
But Sirane’s Balderson is less dismissive of the emerging technology. You can go from design to print quite quickly and changes can be made easily. It is very niche but digital will develop; there are all sorts of drivers. But for high volume printing there would be no point going down the digital route.

Another breakthrough technology is UV curing. Curing systems are starting to emerge, observes Sun Chemical’s Ferne. This is mainly coming from the narrow web side of the market. Narrow web is predominantly used for label printing.

Sun Chemical has been busy in this area and recently launched Wetflex, a partnership with electron beam supplier Energy Sciences and flexo press manufacturer Comexi. The product made its debut in May and provides wet-on-wet flexo printing. Wetflex also uses UniQure curable inks, which do not contain any alcohols, organic solvents or volatile compounds.

The manufacturer says that this is breakthrough stuff; the UniQure inks are wet trapped using a common impression cylinder press and cured instantly by exposure to an inline electron beam at the end of the press. Ink trapping is achieved without inter-station drying.

It would seem that putting ink on flexible plastic is not as straightforward as putting ink on paper. However, while brands are searching for lightweight, fully-branded packaging, it is a demand that is sure to grow.

COMPOSTABLE LABELLING
Welsh flour producer Bacheldre Watermill wanted to put its flour in biodegradable packaging, in keeping with its organic and traditional image. The bags being used were compostable, but the foil-based labels were not. Berkshire Labels provided its BioTak labels, the first self-adhesive labels to meet standard EN13432 for biodegradable and compostable materials.

The labels were printed in five colours using a standard flexo press and UV flexo ink. There are currently no specialist biodegradable UV flexo inks. In order to still be classed as biodegradable under standard EN13432, the ink must make up less than 5% of the weight of the label, and metallic inks, foils or varnishes cannot be used.

The BioTak range is produced by applying a biodegradable adhesive to Innovia Film’s NatureFlex film. The cellulose-based film is available in white, clear and metallised and is the only metallised film on the market that is suitable for home composting because the level of metal is so small – less than 0.02%. A modified coating achieves excellent metal lay down and adhesion, providing a high moisture barrier with a transmission rate of less than 10g per square metre per day. The metal slows the film’s degradation by a few days, but does not interfere in any other way.

Bacheldre Watermill co-owner and founder Matt Scott says: Our packaging is now fully sustainable and compostable and certainly stands out as something special in the flour category.