What are the right tensions for laminating two webs together?

The number one rule of laminating is to match the machine direction strains of the two webs. Strains are a function of the web’s tension force divided by width, thickness, and modulus.

If two webs have equal widths, thicknesses, and moduli, then they should be laminated with matching tensions.

However, if any of these values are higher in one web over the other, it should have a proportionally higher tension than the lesser web.

If the first web is twice as thick as the second web, it should get twice the tension.
If the first web is twice as wide as the second web, it should get twice the tension (in units of force, not force per width).
If the first web has twice the elastic modulus of the second web, it should get twice the tension.

If the first web is twice as thick and twice the modulus, it should get four times as much tension as the second web as they are laminated.
The tension ratio that will match MD strain is the product of the thickness, width, and modulus ratios.

lam tension ratio

Example 1: In laminating 25 micron polyester(modulus of 3500 MPa) to 100 micron polyethylene (modulus of 700 MPa) of equal width, the laminating tension ratio should be (25/100)(1/1)(3500/700) = 1.25:1

Example 2: In laminating 1-mil polyester(modulus of 500 kpsi) to 4-mil polyethylene (modulus of 100 kpsi) of equal width, the laminating tension ratio should be (1/4)(1/1)(500/100) = 1.25:1