Covestro barrier coating resins help us to create a better environment

Protection for beverages

Water absorption and humidity

The amount of water and moisture the surface of a material can take up in a certain time is measured by two different tests.

WVTR / MVTR

Water vapor transmission rate (WVTR) tells us how much moisture is able to pass from a material’s interior surface to the outside.

This is determined at specified conditions of temperature and relative humidity, and expressed as grams per square meter per day: g/m2 /24hr (ASTM F 1249 at 38°C and 90% RH, BS 3177 at 25°C and 75% RH, DIN 53122 at 23°C and 85% RH).

All our MVTR / WVTR tests are conducted using MOCON technology which delivers extremely accurate results by combining precision temperature and humidity control with highly-sensitive sensors.

Cobb testing: Measuring water absorption

Cobb Sizing Tester determines the amount of water absorbed by paper, cardboard, corrugated fiberboard, paperboard, in a specified time under standardized conditions. The levels of water absorption help evaluate various characteristics of paper (such as sizing, porosity, etc.).

A sample of water is placed on the top of a beaker containing water. Then the beaker is flipped so the water comes in contact with the material. At specific time intervals, the sample’s weight is determined.

Results from the Cobb test show that board (especially boxboard made from recycled fiber) is extremely sensitive to atmospheric humidity and must be stored at a maximum of 50% relative humidity, which often means using air-conditioned warehouses. This is because water-damaged board will bend and become unsuitable for printing or box manufacture.

Recycling and repulping combined

Recyclability

Reworkability is a combination of recyclability and repulpability. And recyclability refers to the capability of used paper and paperboard, including in-plant waste, and post-consumer waste, to be processed into new paper or paperboard.

Repulpability

This refers to the capability of material to be re-wetted and fiberized to form new sheets.

The parameters that determine an effective heat seal

Seal limit

Is the minimum temperature needed for a proper seal at given times and pressures. This is normally expressed in °C and may refer to the machinery used to carry out this test e.g. Otto Brugger.

Seal window

These are the maximum and minimum temperatures between which proper seals can be formed on packaging. The window is expressed as a range of °C. Optimal seal windows often refer to the running speed of the film on the production line. This range normally becomes narrower – and seal temperatures higher – as line speed increases. You may see seal windows described in terms of branded machinery.

Seal strength

The seal strength is the maximum force needed to tear a specified width of a seal. It is expressed as force per width e.g. N/25mm.

Keep the good in and bad out

Grease leakage typically causes dark spots to form on the outer layer of the paper or board. Grease resistance can be improved by the degree of grinding of the fibers, and coatings used.

There are several tests that will determine the grease resistance of the board. One of these is the Kit test. In this test, a drop of fluid is put on one side of the board. The composition of the fluid corresponds to a certain Kit value. The time it takes for any spots to appear on the other side of the board can be measured, and subsequently correlated into a measurement of a material’s grease resistance.

Kit test data and results are available for all of our resins.

Food odors: as intended Foods that are sensitive to odor issues will require the correct packaging. If these foods are not suitably packaged, they can represent an economic and health challenge to the manufacturer.

We have reduced the residual monomer levels used in our resins to some of the lowest levels, in order to make any odors present in packaging as neutral as possible.

This means the end consumer can enjoy the food or beverage experience as the manufacturer intended.