PAPER BOARD – WEIGHT (GSM ) vs THICKNESS (CALIPER)

All Paperboard tests are to be done after conditioning the samples. The steps in conditioning are :

1.    Pre dry the samples at 60°C for 30 minutes in a drying chamber with air circulation.

2.    Condition the samples at 23°C ± 10C and 50% ± 2% relative humidity for at least 3 hours.

Grammage:

Weight per unit area expressed in g/m2. The standard procedures are laid out in ISO 536, Tappi T 410.

How to calculate GSM:

Formula for calculating GSM ( cm2)

In order to calculate the GSM accurately, there is a requirement of a cutting a piece of sample to be measured with the dimensions of 10cm X 10cm. This gives you a piece of 100 sq. cm. of the sample. Measure the weight of the pieces cut from the sample. Now the weight obtained is the weight of sample per 100 sq. centimetres. In order to convert it to per square meter, you need to multiply the obtained weight of the specimen with 100. This will give you the weight of the sample per sq. meter. This gives you the GSM of the sample easily.

Convert this 10cmx10cm =100mm x 100mm = 10000mm

Convert paper board size to mm (20” x 28” = 508mm x 711mm

GSM IN MM

Is sample weight is 60gms

60 x 10000/ 361289 x 100 = 166GSM

The total weight of paper in SQM is 166GSM.

PAPER Thickness ( CALIPER) :

Measuring Paper Thickness with a Micrometer

Thickness (Caliper):

The perpendicular distance between the two surfaces of the board / paper, expressed in mm or microns measured with a micrometer. The standard procedures are explained in Tappi T 411.

The second and most accurate way to measure paper thickness is to use a micrometer. This is at least twice as accurate as a standard caliper, so it is probably the best option you can go for.

Set up the Micrometer

There aren’t many types of micrometer. You will only need to pick between those that use inches and the ones that use millimeters.

Set up the micrometer following this:

  • Make sure you can open and close the jaws of the micrometer. Do this by moving the dial, so the measuring shaft moves up and down accordingly.
  • Try to look for the shaft and see that it gives accurate measurements. Try measuring anything around so you can find out whether it works well or not. At the same time, make sure it is readable.

After setting up the micrometer and making sure it works, you are ready to start measuring the paper.

Measure the Paper

Once you have a micrometer, it is time to measure the paper. This is not an easy thing to do, as micrometers are extra-accurate, so you will have to be as careful as possible.

Here’s how to measure with a micrometer:

  • Start by considering whether you want to measure a few pages (20 pages will suffice), or an entire stack/ream (from 100 to 200 pages). You can measure both ways with a micrometer.
  • Then proceed by setting up the micrometer at the ideal thickness of the paper. Move the thimble/dial accordingly, so the claws open to fit the paper. You will see how the shaft moves depending on how much you open the jaws.
  • If the stack is small (20 pages or so), then you will probably adjust the jaws accordingly. This usually starts at about 0.1 inches and goes on from there. Remember that these tools can go really low in inches, so you need to place the micrometer as accurately as possible.
  • Then, get the marks on the shaft gauge or sleeve. This is a small set of lines that usually go from 0 to 25. And this measure should go perfectly with the lines on the tube shaft, not the same for the first measurement, but the ones on the other face.

To explain this, you will get the first measurement by adjusting the jaws to the paper. This starts at 0.1-inches. Then you’ll get the second by looking at which lines on the gauge fit well with the opposite lines on the shaft tube. These usually go from 0 to 11 – with 1 meaning 0.005 inches.

The lines/marks will tell you how thick the paper is. Write or type these two measurements, so you don’t lose it. 

Calculate the Thickness

You have two measurements nowThe one given from the shaft starts at about 0.1-inches. Then you have the measurement from the gauge with the other face of the gauge, which goes from 0 to 11.

So, what can you do with these measurements? Follow these steps:

  • Let’s say the first measurement ended up in the number 1 (0.1-inches). Then the second (gauge with shaft) gave you 5 (0.005-inches). Well, now you need to add them up. This should give you a total thickness of about 0.105 inches.
  • If you measured a sheet alone, then this would be the final thickness. But if you measured an entire stack, then you need to dive that number by the number of sheets. For example: 0.105 / 20 = 0.00525 per sheet.

As you can see, this process may take a few more time and effort than you think. But it is the most accurate out there – so we recommend it if you need the exact measure.

End……

You can invest in GSM and Micrometer through this link.

Testing Equipments for Printing industry

Published by Panthala Selvan

Authorised partner for Kodak prepress workflow, Techkon Spectrodensitometers, cip3 solutions, colour management, packaging development etc

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