Opaque, white film with low transparency made from a crystallizable thermoplastic

Abstract

The invention relates to an opaque, white film with a thickness of from 10 to 500 μm whose principal constituent is a crystallizable thermoplastic. The film comprises barium sulfate and an optional optical brightener. Optionally, at least one surface of the film bears a functional coating with a thickness of from 5 to 100 nm, in order to confer on the film surface an additional function such as sealability, printability, metallizability, sterilizability, antistatic properties, aroma barrier properties or improved adhesion to materials which would not adhere to the film surface without the coating, for example photographic emulsions.

1 . An opaque, white film with a thickness of from 10 to 500 μm, said film comprising thermoplastic and a pigment, said thermoplastic consisting entirely of polyester and said pigment comprising barium sulfate, said film further exhibiting a modulus of elasticity in the transverse direction of greater than or equal to 4200 N/mm 2 .  
   
   
       2 . The film as claimed in  claim 1 , wherein the thermoplastic has been selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate.  
   
   
       3 . The film as claimed in  claim 1 , wherein from 0.2 to 40% by weight of barium sulfate is present as pigment in the film, based on the weight of the thermoplastic.  
   
   
       4 . The film as claimed in  claim 1 , said film further comprises optical brightener, said optical brightener present in an amount of from 10 to 50,000 ppm based on the weight of the thermoplastic.  
   
   
       5 . The film as claimed in  claim 4 , wherein the optical brightener has been selected from the group consisting of bisbenzoxazoles, phenylcoumarins and bisstearylbiphenyls.  
   
   
       6 . The film as claimed in  claim 4 , wherein, in addition to the optical brightener, a polyester-soluble blue dye selected from the group consisting of cobalt blue, ultramarine blue, anthraquinone dyes or combinations of these, is also present in the film, and wherein the amount of blue dye present in the film is from 10 to 10,000 ppm, based on the weight of the thermoplastic.  
   
   
       7 . The film as claimed in  claim 1 , wherein the barium sulfate is present as precipitated barium sulfate in the film in an amount of from 0.5 to 30% by weight, based on the weight of the thermoplastic, and wherein the average grain size of the barium sulfate is from 0.1 to 5 μm (Sedigraph method).  
   
   
       8 . The film as claimed in  claim 1 , wherein the surface gloss of the film, measured to DIN 67530 (measurement angle 20°) is ≧10, and wherein the luminous transmittance (transparency) of the film, measured to ASTM-D 1003 is ≦30%.  
   
   
       9 . The film as claimed in  claim 1 , wherein the film has one or more layers, and the film having more than one layer comprises at least one base layer and at least one outer layer.  
   
   
       10 . The film as claimed in  claim 1 , wherein at least one of the surfaces of the film bears a functional coating said coating comprising substances or compositions selected from the group consisting of acrylates, ethylvinyl alcohols, PVDC, waterglass (Na 2 SiO 4 ), hydrophilic polyesters, vinyl acetates, polyvinyl acetates, polyurethanes, silanes, the alkali metal or alkaline earth metal salts of C 10 -C 18  fatty acids, butadiene copolymers with acrylonitrile or methyl methacrylate, methacrylic acid, acrylic acid or esters thereof and mixtures of these.  
   
   
       11 . The film as claimed in  claim 10 , wherein the coating comprises from 0.05 to 5% by weight of additional additives.  
   
   
       12 . An opaque white film with a thickness of from 10 to 500 μm, comprising (i) a single thermoplastic consisting of polyester and (ii) barium sulfate, wherein the film exhibits tear strengths in the transverse direction of greater than or equal to 170 N/mn? 
   
   
       13 . The opaque white film as claimed in  claim 12 , wherein said opaque white film further comprises regrind formed from said film in amounts of up to 50 weight percent, said film having a thickness of up to 50 microns and exhibiting a yellowness of up to 20.  
   
   
       14 . The opaque white film as claimed in  claim 12 , wherein said opaque white film further comprises regrind formed from said film in amounts of up to 50 weight percent, said film having a thickness of from 50 to 250 microns and exhibiting a yellowness of up to 45.  
   
   
       15 . The opaque, white film as claimed in  claim 1 , wherein the luminous transmittance of said film is 15 to 20% lower than the luminous transmittance of a comparable film formed from said thermoplastic having the same thickness as said film and lower longitudinal orientation than said film.  
   
   
       16 . An opaque, white film with a thickness of from 10 to 500 μm, comprising a crystallizable thermoplastic and barium sulfate wherein said crystallizable thermoplastic consists entirely of polyester, said film exhibiting an elongation at break of greater than or equal to 120% in the machine direction.