Process for making a polymeric film

A process for the manufacturing of an ultrahigh molecular weight polyethylene (UHMWPE) film, comprising in sequence the steps of:

• (a) providing a bed of UHMWPE powder;
• (b) applying a compression pressure on the bed of UHMWPE powder at a compression temperature below a melting temperature of the UHMWPE powder to obtain a compressed bed;
• (c) forming a film by compacting the compressed bed in a smoothing unit comprising two compacting surfaces providing a non-constant line of pressure and a gap having a gap-thickness dimension and a gap length dimension between the two compacting surfaces, at a compacting temperature below the melting temperature of the UHMWPE powder, the non-constant line of pressure being achieved by establishing a substantially constant gap-thickness dimension which has a variation over time between a minimum gap thickness and a maximum gap-thickness (Δcompaction) of at most 20%, and wherein
• the film formed by step (c) exhibits a reduced variation in thickness along its width and/or length as determined by a plurality of tapes slit from the film each having an average thickness (T) such that a plurality of the tapes has a coefficient of variation in thickness (CVthickness) of less than 2% as determined by the following formula using the average thickness (T) of a number of five representative tape lengths each corresponding to a different randomly chosen tape from the plurality of tapes slit from the film:
• CV
• THICKNESS
• =
• ∑
• i
• =
• 1
• n
• ⁢
• (
• x
• i
• -
• x
• _
• )
• 2
• n
• -
• 1
• ×
• 1
• x
• _
• ×
• 100
• ,
• wherein
• xi is the average thickness of any one of the representative tape lengths and x is the averaged value over the n=5 measured average thicknesses, where each measured average thickness is an average of at least 10 thickness measurements carried out at randomly chosen locations of the representative tape lengths.