How to perform COBB testing on non-absorbent paper and cardboard?

What is water absorption?

Water absorption (also known as Cobb value) is a function or method of determining the properties of paper, paperboard and corrugated board, including porosity, sizing and fiber composition. In order to determine the relative permeation rates of aqueous solutions such as water or other solutions, the procedure is carried out on various sheets or non-absorbent or highly absorbent paper or cardboard. It indicates the degree of surface and internal sizing. This method was neither designed for water resistance testing nor to measure resistance to trace amounts of liquid, but it was introduced to test how much water a material can absorb in a given period of time, thereby checking the penetration strength of a material. the material. If the specimen absorbs more water,

Suitable method for testing water absorption of paper and board

A suitable method for conducting Cobb size testing is a Cobb size Tester. The design of the instrument allows for immediate firm wetting of one side of the sample from the start of the immersion phase and immediate removal of excess moisture from the sample at the end of the test.

Presto Stantest manufactures high quality Cobb Dimensional Testers which are designed in compliance with various National and International Standards such as TAPPI T 441, ISO – 1060 (Part 1) – 1966. This instrument helps to calculate the Cobb value, which is the amount of water absorbed by 1 square meter (i.e. 10.76 square feet) of paper, cardboard or corrugated board in 1 centimeter of water in a specific time.

According to standard instrument specifications

specimen holder

Type: Metal ring bracket with machined lower surface,

Internal diameter of holder: 28 ± 0.02 cm (4.44 inches). {Reporter 2 to 100 cm cross-sectional area, 2.5 cm high and approximately 0.6 cm thick.

Clamp the bracket snugly onto the flat bottom plate above the rubber pad (which is larger than the outer dimension of the ring).

Metal Roller – It is solid brass or stainless steel (corrosion resistant material) with a smooth surface, 20 cm wide and 10.0 ± 0.5 kg wide.

Timer – A stopwatch is used to measure test duration.

A graduated cylinder of 100 ml is fixed to the device.

GSM Balances – Accuracy to 0.01 grams or better.

Standard test area of ​​the instrument – ​​100cm² (devices with test areas of 25 cm 2 and 10 cm 2 are also available upon request)

 Meets testing requirements and standard specifications for materials

Reagents – Deionized or distilled water.

Specimen Size – Square specimen measuring 5 x 12.5 cm (4.9 x 4.9 in) 

Specimen Type – Unwrinkled and Uncreased Specimens\

Test Duration – Typically 60 seconds or 120 seconds (for paper) for very stiff paper and board, and 4 minutes and 45 seconds or 5 minutes.