A look inside our label lab: Measuring moisture resistance with the Cobb test
The Hally Labels purpose-built laboratory is dedicated to testing, analysing and understanding labels across all industries and challenges. Based at our Christchurch factory, the Hally lab uses specialist and customised equipment to perform a wide range of tests.
One of the many procedures our lab performs is the Cobb test which is an industry-standard method for measuring the moisture absorbency of paper and board materials. We specifically use this test for our paper-based label materials and it is particularly relevant for the wine and beverage markets where the label is regularly subject to condensation, water and ice.
Read on to learn more about the Cobb test including what it is, why we perform it, the test method, and what it tells us.
What is the Cobb test?
The Cobb test is used to determine the quantity of water that can be absorbed by the surface of a paper label and the effectiveness of the paper to repel the water in a given time under standardised conditions. This certified method for measuring water absorption is used globally.
The test is used predominantly for the wine and beverage industry where a label is exposed to large amounts of moisture or water such as in ice buckets.
The Cobb test allows us to rate and compare different paper label materials:
- If the Cobb value is high, it means the label substrate can absorb and retain moisture
- If the Cobb value is low, it means the label substrate can resist penetration and retention of moisture
For the wine and beverage markets, a low Cobb value is desired. We categorise our paper label materials into Gold, Silver and Bronze Cobb ratings for easy comparison – you might see these ratings on some of our documentation.
The key test method steps we follow against the internationally recognised standard are:
- The test piece of label paper is weighed.
- The dry piece of label paper is placed under a metal cylinder and 100ml of water is poured over it.
- After a specified time the water is poured off and the test piece is placed on standardised blotting paper. Another blotting paper is placed on top of the test piece and the excess water is removed by the roller.
- The test piece is then weighed again and the results are calculated and reported as absorption in grams per m2.
Why do we perform Cobb tests?
When it comes to label materials, there are many many options available. It pays to determine if your current label material meets all label performance expectations for your specific application or requirements. The Cobb test is an essential part of our in-house testing regime and together with other analysis can proficiently evaluate what material will be best for your specific application.
We use the Cobb test when conducting comparative and quality control tests on all new materials. The test is also useful when a client is considering changing materials such as moving to a more environmentally sustainable substrate. Evaluation of any alternative material is essential to ensuring product and branding consistency.
Another way to add moisture resistance is via a barrier coating or laminate to provide optimum moisture or scuff resistance. Uncoated materials, such as natural kraft or sugar cane paper tend to be more affected by moisture than coated stocks due to their fibrous or textured nature. We would be happy to advise you on the right material type to meet your needs.
What does a Cobb test tell us?
Extreme environments, such as high moisture or humidity, damp, or cold, may affect the label’s moisture resistance. Accurate Cobb values assist us in selecting the right materials for the right applications, and help our customers determine the best fit-for-purpose solution.
Our experienced technologist can perform a Cobb test immediately, along with a vast range of other tests, to ensure you have the optimum solution for your labelling needs.
Our team of label experts are available at any time to advise the right material for your application. Book a free expert consultation to discuss your labelling requirements where we will develop a solution specifically for you.