Release Liners - Films
The main film types for silicone coating are low density and high density polyethylene (LDPE/HDPE), cast polypropylene (CPP), oriented polypropylene (mOPP and bOPP), amorphous polyester (APET), biaxially oriented polyester (PET), polystyrene, and polyvinyl chloride (PVC).
Films have some obvious differences compared to paper. Paper is normally not extensible to any degree, and is relatively heat resistant, but films can be transparent , opaque or self coloured, some are easily deformed or conformable, tear resistance can be very high, or very low, some will shrink extensively some temperature resistant.
LDPE and HDPE can be very tear resistant and can be cut with a hot wire, so they have uses for making tapes and used in making sealable PE packaging bags for items of clothing or magazines. Because of their high tear resistance HDPE is often used for producing bitumen tapes for anticorrosion pipeline wrapping, and for flashing tapes where removal of the liner without tearing is a requisite function.
Cast and oriented PP are made from the same resin but have different characteristics because of the orientation during manufacture. mOPP is extruding in a similar manner but the rewind is running much faster than the extruder so the film is stretched (oriented) in the machine direction. This gives very high tensile strength in the machine direction, (but very low tear strength) and high tear strength in the cross direction. mOPP is use for making tear tapes for packaging, and also for high specification tapes where the resistance to CD tear is very important.
bOPP is made in a similar way to mOPP but the film edges can be gripped on a stenter frame which stretches the film in the cross direction as well. This produces the normal OPP film you see for flower wrapping, packaging cigarettes CDs etc.
Amorphous PET or APET follows the cast PP route and gives a polyester film that is thermoformable at low temperatures, normal PET is produced in the cast stenter route and has good heat resistance and low shrinkage.
APET silicone release liners are used when the liner is expected to the thermoformed into a 3D shape for the production of electrodes for heart activity monitoring and the conductive gel adhesive needs to be contained in an indentation to retard any tendency for drying out.
PET and bOPP films are commonly used for high clarity labels (clear on clear) where the face material is printed and a clear adhesive used to mimic a container with direct print. It is normal that a PET liner would be used with a PET face material and bOPP with a PP face. The thinness, (with good profile) and high tensile strength of these liners allow more labels per reel and faster labeling speeds to be achieved. Filmic liners also allow use in high humidity conditions such as a bottling line without the possibility that condensation and splashing could cause paper breaks.
Filmic liners do not normally suffer from dust production during slitting and have an advantage for use in clean rooms and for laminate where dust could build up on the adhesive edges. The main drawback for films is static electricity generation, and invisibility because of the high clarity, meaning that it can be difficult to see where the liner is in order to remove it and once removed it can stick to surfaces rather than being easily disposed. In order to mitigate these effects we can colour filmic liners either with ink under the silicone or adding pigment direct to the silicone to make it visible, and additives are available to reduce static generation slightly.
To find out more about the range of release liners we manufacture using films please contact us with your specific enquiry contact us page