A Release liner is a paper or plastic based carrier web material, which is coated

Coating

Coating is a covering that is applied to the surface of an object, usually referred to as the substrate. In many cases coatings are applied to improve surface properties of the substrate, such as appearance, adhesion, wetability, corrosion resistance, wear resistance, and scratch resistance...

 on one or two sides with a release agent

Release agent

A release agent is a chemical used to get a slip effect. It can provide a solution in processes involving mold release, die-cast release, plastic release, and tire and web release.-Concrete:...

, which provides a release effect against any type of a sticky material such as an adhesive

Adhesive

An adhesive, or glue, is a mixture in a liquid or semi-liquid state that adheres or bonds items together. Adhesives may come from either natural or synthetic sources. The types of materials that can be bonded are vast but they are especially useful for bonding thin materials...

 or a mastic

Mastic (plant resin)

Mastic is a resin obtained from the mastic tree . In pharmacies and Nature shops it is called "arabic gum" and "Yemen gum". In Greece it is known as the "tears of Chios," being traditionally produced on that Greek island, and, like other natural resins is produced in "tears" or droplets...

. Release liner are available in different colors, with or without printing under the silicone or on the backside of the liner. Release is separation of the liner from a sticky material. a liner is the carrier for the release agent.

Industry segmentation

Globally there are between 400 and 500 companies involved in making or dealing with release liner products on an industrial scale. In general there are two types of companies which are manufacturing release liner.

Liner producer

Commercial coating companies, deal with a lot of different end uses of this industry. They provide unique solutions to their customers, based on a wide variety of substrates and an endless combination of release agents with specialized properties. Commercial coaters usually make no finished products, but just the release liner itself and then their customers will coat a sticky material on this liner and then apply the end product to it.

In-house producer

In-house producer make release liner and use it internally to manufacturer the final product. In-house producer are typically focused on a very narrow rage of products e.g. Labels or Tapes. They use a limited amount of substrates and release materials, specialized for their end applications.

Liner materials

As "Liner" material, the industry is using a wide variety of so called substrates, which are the carrier materials of the release agent and which is needed to transport a sticky material from the manufacturer to an industrial or private end user. Typical liner materials are:

Paper

Paper

Paper

Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....

1. SCK = Super Calandered Kraft paper, typically used for Labels in the USA
2. Glassine= Is also a SCK paper but typically with a PVOH Polyvinyl alcohol
   Polyvinyl alcohol
   Polyvinyl alcohol is a water-soluble synthetic polymer .-Properties:...
   
    top coat, typically used for Labels in Europe
3. CCK = Clay Coated Kraft paper or also just called coated paper
   Coated paper
   Coated paper is paper which has been coated by a compound to impart certain qualities to the paper, including weight, surface gloss, smoothness or reduced ink absorbency. Kaolinite or calcium carbonate are used to coat paper for high quality printing used in packaging industry and in magazines...
   
   
4. MFK = Machine Finished Kraft paper, which is the paper as it comes from a standard paper machine
5. MG = Machine Glazed paper which is a paper which has been glazed e.g. on a yankee cylinder of a paper machine.

Plastic film

1. BO-PET: a PET film (biaxially oriented)
   PET film (biaxially oriented)
   BoPET is a polyester film made from stretched polyethylene terephthalate and is used for its high tensile strength, chemical and dimensional stability, transparency, reflectivity, gas and aroma barrier properties and electrical insulation.A variety of companies manufacture boPET and other...
   
    is a very high temperature resistant and tough film liner.
2. BOPP: a biaxially oriented PP film
3. Other Polyolefin
   Polyolefin
   A polyolefin is a polymer produced from a simple olefin as a monomer. For example, polyethylene is the polyolefin produced by polymerizing the olefin ethylene. An equivalent term is polyalkene; this is a more modern term, although polyolefin is still used in the petrochemical industry...
   
   s: typically made out of HDPE, LDPE, PP plastic resins

Plastic films in general are made by plastics extrusion

Plastics extrusion

Plastics extrusion is a high volume manufacturing process in which raw plastic material is melted and formed into a continuous profile. Extrusion produces items such as pipe/tubing, weather stripping, fence, deck railing, window frames, adhesive tape and wire insulation.-Process:In the extrusion of...

 process out of plastic resins and can be made out of one single type of plastic material, a blend of different plastic materials or a multilayered coextrusions. Providing them with unique and adjusted features for the application that they are targeted for.

Others

• Poly coated Kraft papers, which are typically MFK papers which have a one one or both sides a poly olefin coating, to make them very smooth, moisture resistant and dimensionally stable
• A poly coated BO-PET film, which has been like a paper coated on both sides with a polyolefin material. This way the tough and dimensionally stable PET film is combined with cheap polyolefin resin which makes the fill a better carrier web for specialty applications.

Release agents

Commonly used release agents for release liner can be crosslinkable silicone

Silicone

Silicones are inert, synthetic compounds with a variety of forms and uses. Typically heat-resistant and rubber-like, they are used in sealants, adhesives, lubricants, medical applications , cookware, and insulation....

, other coatings, and materials that have a low surface energy

Surface energy

Surface energy quantifies the disruption of intermolecular bonds that occur when a surface is created. In the physics of solids, surfaces must be intrinsically less energetically favorable than the bulk of a material, otherwise there would be a driving force for surfaces to be created, removing...

.

Applications

There are probably hundreds of different applications, where release liner materials are being used. Such as

1. pressure-sensitive label
   Label
   A label is a piece of paper, polymer, cloth, metal, or other material affixed to a container or article, on which is printed a legend, information concerning the product, addresses, etc. A label may also be printed directly on the container or article....
   
   s
2. Pressure sensitive tape
   Pressure sensitive tape
   Pressure-sensitive tape, known also in various countries as PSA tape, adhesive tape, self-stick tape, sticky tape, or just tape, is an adhesive tape that will stick with application pressure, without the need for solvent, heat, or water for activation...
   
   
3. Hygienic application e.g. for FemHygiene pads
4. Building and construction materials, e.g. window films, roofing underlayment, air barriers
5. Composites e.g. Air plane construction, Wind mill blades, Golf clubs, soldier helmets
6. Medical applications e.g. wound care