What Is a Release Liner?

2021/03/24

Blue release liner for double sided foam tape
The relationship between release and bonding is completely opposite. Bonding is to stick the two interfaces with adhesive, and it is not easy to separate. Release is the phenomenon that the two interfaces are temporarily connected, and it is easy to separate when peeling off and the contact interface will not be broken. The release liner structure can be divided into three parts: backing, barrier (release paper) and release layer.

  • Release Liner Backing Materials:
    • Polymer Film:
      Transparent PET silicone release liner used as carrier tape
      Release Film
      PET, OPP, PE. It is smoother than the paper substrate, and its gloss, transparency, cleanliness, water resistance, strength and thickness are better than paper, but its heat resistance is worse than paper.
    • Release Paper:
      1. Polyethylene Laminate Type: The base paper is wood-free paper and kraft paper. If the release agent is directly coated on the base paper, the release agent may penetrate into the paper layer, it is difficult to form a continuous and uniform coating on the paper surface, and it cannot have good release performance. Therefore, a polyethylene film was used as a barrier layer. Polyethylene laminated release paper has good surface gloss and smoothness, good water resistance and solvent resistance. The disadvantage is that polyethylene film has poor heat resistance and is not recycled.

      2. Glassine Type: The base paper
      Yellow silicone release paper for medical adhesive tape
      Release Paper
      is glassine paper, which has a higher density than wood-free paper and kraft paper. The surface has a fine structure, and the release agent can be directly coated on it. The advantage is good heat resistance and high transmittance, but the disadvantage is that the density of the paper is high, which causes the paper to warp easily after moisture absorption and drying.

      3. Supercalendered Type: The base paper is high density. It is processed by calendering to make the surface denser, and the release agent can be directly coated. The advantage is good heat resistance, the disadvantage is that the paper is easy to warp after moisture absorption and drying.

      4. Clay Coated Type: White clay is coated on the surface of wood-free paper or kraft paper as a barrier layer, and then coated with a release agent. The advantages are that the base paper with good heat resistance and low density, the base paper is not easy to warp after moisture absorption and drying, and the paper can be recycled.

  • Release Agent:
    • Silicone Release Agent: For light peeling force, generally 1-200 g (tested by Tesa 7475)
    • Non-Silicone Release Agent: The release force is above 200 g (tested by Tesa 7475) or even higher. Non-silicone release agent molecules do not contain silicone, fluorosilicone and heavy metal harmful substances. There is no silicone migrate the product and it is an environmentally friendly product.
    • Fluorosilicone Release Agent: High temperature resistance, no silicone migrates, high subsequent adhesion.

     

    Related Products: Fluorosilicone Release Liner

  • Release Liner Functions
    • Different Release Force
      The release film should be matched with the most suitable release force according to the application. If the release force is too small, the release film cannot be attached and easily falls off. If the release force is too large, the release film will not be easily peeled off. The required release force is also different depending on the adhesive used. Choose a light release force for high adhesion, a medium release force for medium adhesion, and a heavy release force for low adhesion.
      There is a relationship between the release force and speed. As the tearing speed becomes faster, the release force will also tend to increase. Based on Horaetape’s rich experience, we propose a release film with a low correlation between release force and speed.

    • Release Liner with Good Subsequent Adhesion
      After the adhesive is in contact with the release liner, the adhesion will be reduced due to the migration of the release agent or the influence of the unevenness on the surface of the release liner. The influence of the release film on the release force is as small as possible. The adhesion after contact with the release liner is called ” subsequent adhesion “, and this value can be used to evaluate the degree of influence on the release force, that is, the higher the subsequent adhesion rate, the better.

      subsequent adhesion rate (%) =Adhesion force after contact with release paper / Adhesion force before contact with release paper x 100

      In addition, the smaller the unevenness on the surface of the release paper, the higher the sub-sequent adhesion rate. ESCA (Electron Spectroscopy for Chemical Analysis System) is an analytical method to measure the migration amount of release agent.
    Analysis of Release Agent Migration of Release Liner by ESCA
    • Unwarped Release Paper
      Most release liners are required to have low warpage, since adhesive products require cutting. The base material of the tape is a polymer film, which is particularly prone to warpage. When the tape is warped, it will affect printing and cutting. The cause of warping is the difference in tension between the two materials. After the paper absorbs moisture or dries, the dimensions of the paper change. The moisture absorption of the paper causes the paper to stretch, but the polymer film of the tape base material does not stretch, and thus warps occur. Conversely, when paper is dehumidified, it shrinks and causes warping. The warpage caused by moisture absorption and dehumidification mainly occurs in the transverse direction (TD) of the paper, and the transverse direction (TD) of the paper is more significant than the machine direction (MD). There are several ways to prevent this warping:

      1. Adjust the moisture content of the paper.

      2. Choose the base paper with small hygroscopic dimensional change, such as base paper with low density or glass fiber, etc.

      3. Add dimensional stabilizer during paper processing.

      4. Add a warpage prevention layer such as polyethylene (PE), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC) to the inner side of the paper.

      In addition to the warpage caused by the moisture absorption and dehumidification of the paper, there is also the warpage caused by rolling. This warpage is different from moisture warpage and occurs in the longitudinal direction. To prevent such warpage, the tension can be adjusted during rolling, the diameter of the die can be increased, or an elastic release paper can be used.

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