Printing with Purpose The Official Blog of Lithographics

The Science Behind Testing Paper

Posted by Lori Slovik, Technology Manager Printing Papers, Domtar on September 26, 2018 at 2:40 PM

Screen Shot 2018-09-26 at 2.31.06 PM

This is 1 of a multi-series blog about the science behind testing paper.  We will share some insights to how Domtar Paper Geeks test paper and how it affects your print projects. 

When you think about paper, what comes to mind is that it’s white, it’s rectangular, I print on it or it’s something that shows up in my mail.

As a paper manufacturer, it’s more than just paper to us.  It’s a magazine meant to inspire or educate, a book written to take us away into another dimension for a period of time, a diploma that reminds us of our accomplishments, a wedding invitation for the biggest moment of our life, a folding carton designed to hold a new product, a shopping bag, a cupcake wrapper, and so many other things.  Each of these end-uses has different requirements that allow for the functionality necessary for that specific product.

Even though you can’t always see differences, the recipes used to manufacture the various paper types are all unique. Different applications require different functionality.  To ensure that these needs are met, we test our products to meet your requirements!

Basic Paper Properties and So Much More

When specifying paper for a print job, there are some basic properties that are generally used to direct that decision.  Generally, these are basis weight, caliper (or thickness) and brightness.  The basis weight and caliper will impact the functionality of the end product, but there are many other “features” that are built into your paper choice.

Let’s say you are planning to make a pocket folder for your brand. Other components of your brand will be contained within, but the folder itself will create the first impression.  The key features will include aesthetic qualities as well as tactile attributes.

Aesthetic properties of the pocket folder will include the brightness and, uniformity of the printing and vibrancy of the printed images. Tactile attributes will include the smoothness/roughness of the substrate, stiffness of the folder, and enhancements like embossing and foil stamping.

How do we make sure your paper will produce the results you need?  We TEST it!

Testing for Functionality

The basic properties are pretty straightforward. When testing paper basis weight, we use a paper scale.  When testing paper caliper (thickness), we use a paper micrometer.  Both of these properties, however, will impact many of the other attributes of the paper and its ability to perform in the desired end use application.

For projects that require embossing, you will want to consider the thickness of the paper. Embossing the paper will create texture with raised detail.  It can be as simple as making your brand logo stand above the rest of the folder or it can be intricate and create an all over texture.

Regardless, it is important to make sure that the paper has sufficient bulk to handle embossing. A thicker substrate will be able to handle a more detailed emboss than a thinner one.  It is important to consider this in your paper selection to avoid cutting the paper surface during embossing.

Critical to the pocket folder is the stiffness of the paper.  We do not want the finished product to feel “flimsy”.  When testing paper for stiffness, we use a device that flexes a paper strip and measures the force required to flex the paper. At a given basis weight, higher caliper will generally produce higher stiffness. Therefore, an 80# cover with caliper of 10.9 will be stiffer than an 80# cover with caliper of 10.1.

science behind testing paper

Pictured: Paper Stiffness Testing Devices, Gurley Stiffness Tester and Tabor Stiffness Tester

While paper basis weight and caliper is important when it comes to scoring, the type of fiber that is specified is also a critical component to prevent cracking when opening and closing the folder.  The score provides a hinge that allows the paper fibers to “flex” around and fold without cracking.  As thickness of the stock increases, appropriate scoring becomes critical to this mechanism.  The width and depth of the score should be matched to the specific stock used in the job.

Many paper variables, including the type of fiber, surface treatments, and moisture levels will impact your score and subsequent folding ability.  For this reason, it is important to test your specified stock with the selected scoring rule and channel matrix prior to converting the entire job.   This will not be a lab test, but a test that is done on-site during the converting stage of your process.

Testing before committing to a score design can prevent failure at the final stage of the print job. On heavy weight covers scores need to be deeper and wider than on lighter weight stock.  Slight adjustments may be required to optimize a score, prevent cracking on the fold, and achieving expected performance.

We’ll talk about specific paper attributes and testing on other paper grades over the next few months. As a confessed Paper Geek, hope this interests you as much as it does me!

Topics: Print Budget, Domtar, Paper Stock, paper specification, Paper formation, Printing Techniques