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Cobb Value Of Packaging Materials

What is Cobb Testing?

Cobb Sizing Tester determines the amount of water absorbed by the paper, cardboard, corrugated fiberboard, paperboard, in a specified time under standardized conditions. Various characteristics of paper such as sizing, porosity, etc. are evaluated by the water absorptiveness.

  • If the COBB value is high, means substrate has the ability to absorb and retain moisture.
  • If the COBB value is low, means the substrate can resist penetration and retention of moisture.

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The COBB value has to be maintained as per the need of paper or board. This test procedure includes a quantity of water absorbed in a specified time by no bibulous paper and paperboard with a minimum 0.1 mm thickness.

Features and Equipment

  • A cylindrical panel which is clamped to a flat base along with a flexible backing to place Key features
  • The machine has strong sample mounting and rugged construction.
  • The instrument requires minimum maintenance and low wear and tear of components
  • A Standard weight roller provided along with the equipment.
  • Manual clamping and sample placement

Procedures for Cobb Testing

Cobb sizing tester is a significant instrument that evaluates the water-absorptive quality of the packaging materials and prevents the damaged caused to the products. The testing procedure is simple and easy providing a precise result.

  • Take a piece of sample of a cardboard and cut in circular shape more than the diameter of the rubber Weight the sample using digital weighing balance.
  • Place the sample between cylinder and rubber pad and support. Tighten sample manually with the screw
  • Ensure sample has no crush while clamping and then invert the cylinder back to its position.
  • When the sample is clamped, add 100 or 250 ml water up to the marking in the cylinder as required for the test. Start the stop water for 1 to 10 minutes for single to multilayered board
  • Remove water from the cylinder when the test completes and takes out the sample. Drain excessive amount of water with the help of hand roller by moving one time forward and one time backward.
  • Weight the sample again with digital weighing machine
  • To determine the Cobb Value, subtract the weight of the sample before testing from the weight of the sample after testing.

Purpose of Cobb Testing

The Cobb Sizing Tester is used to check the water resistance ability of box and measures the weight increase of specimen when exposed to water for a given time. Paper and fiberboard attract and hold the water molecules from the surrounding environment because these materials are hygroscopic. Water absorption is a purpose of various paper such as porosity. The Cobb test is essential as it tests the ability of paper to resist the penetration of water and quantity of water absorbed by the surface of cardboard evaluates the quality of paper over a given time. The device is best suited to perform the corrugated testing, paper testing, and tissue Testing. The accurate Cobb value assists the manufacturer to use the right materials for packaging before supplying to the consumers.


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