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Optical properties for optimized experience

Published 01/04/2016

What does packaging actually signify? It depends on everything from the manufacturer’s message to the recipient’s final experience. One of the keys is the optical properties of the paper, which form the basis for numerous sales points. Here we explain what they represent – and about the importance of a common standard for measuring and reporting correctly.

Reflectance, whiteness, brightness and opacity – these are all examples of the optical properties of paper. Together or individually, they send a message, whether or not that is intentional.

Some choose glossy board for their perfume for a touch of luxury, while others choose unbleached paper or board for a more down-to-earth message. What you want to communicate depends, of course, on what you are selling and to which segments. 

The optical properties are thus the foundation for numerous sales points. And this is true of all industries, all over the world. It is important, therefore, to decide what you want to communicate – and to do it with as uniform quality as possible. Packaging should ideally maintain the same performance, whether the customer buys it in the spring or the autumn. Likewise if the raw material comes from different mills. 

In an ideal world, there would be a single source, but reality, notoriously, involves a mix. Some raw material comes mainly from spruce, while another may contain more birch, which also leads to differing shades. This affects the colour reproduction, which is important to the overall experience. For example, a logo should look the same, regardless of the background.

So how do you achieve the desired result in those circumstances? The answer is correct instrument calibration, for customised and uniform production. If, for instance, you intend to bleach your product, you want to do it at exactly the right level, using as low amount of chemicals as possible. 

The paper industry has, therefore, agreed common standards for measuring and reporting correctly. The standardisation is about various aspects of measurement, e.g. specification of measurement apparatus, preparation of the measured samples, the angles of  illumination and measurement. Anyone who has paid attention to paper has probably noticed that it looks different in different circumstances: for example, from the side, from the front, in UV light, under direct sunlight  or in the shadow. 

Li Yang

The ISO standardization has a hierarchical structure. Li Yang, Technical Manager, Optical Calibration Laboratory at Innventia, explaines: 

“The laboratory providing ISO level 2 standards, to which everyone refers back, is in Canada. The laboratories providing ISO level 3 reference standards are located in France, Canada, Sweden and the United States. All laboratories are authorized according to the ISO standards, which are regularly reviewed and evaluated.”

When it comes to optical properties, the lab can assist in various ways. Anita Teleman, Research Manager of Innventia’s laboratory, explains:

Anita TelemanThrough the calibration service, the laboratory helps customers to calibrate their instruments, for correct measurement of optical properties. The laboratory then produces a reference paper that is provided along with assigned data.” 

In addition, a service is offered for dealing with questions, including complaints. A user  may suspect that a paper contains optical brighteners, while the manufacturer denies. The laboratory can then sort out the issue by carrying out impartial measurement and analysis.

Optical simulation is another service. A customer may want to change something in their paper, such as a chemical or paper structure. With help of simulation, one can have a fairly good prediction on the possible outcome in term of the optical properties. Simulations can therefore be a useful tool in reducing cost of full-scale trials. 

We have previously looked at the issue of how the future may look for the paper industry here on the blog when we presented our latest Global Outlook Report. Increasing digitalisation is common knowledge, and this is also one of the industry’s greatest challenges. But the world is also moving more towards a bioeconomy with an increased focus on sustainability. 

By calibrating equipment for optical properties, you are also doing something for the environment: As few chemicals as possible need to be added and the level of optical brighteners can be kept to a minimum.

What will happen in the future for Innventia? Most immediately, in June, we are expecting an inspection by Swedac, Sweden’s national accreditation body – something that happens every eighteen months. Then, in August, the OPAL group meeting will be hosted at Innventia, in which the technical managers of the Authorized Laboratories participate.

“This is an important and vital process for ensuring that we are measuring correctly,” concludes Anita Teleman. “Therefore we need to undertake regular critical evaluations and ask ourselves: ‘How are things going?’ and ‘How can we reduce the measurement uncertainty?’”

Ongoing discussion is a prerequisite for remaining accredited and certified – and for living up to our promises.

Read more about the optical properties of paper » 

Read more about optical calibration » 

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