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

Abstract

The present invention relates to an opaque, white film with a thickness of from 10 to 500 μm whose principal constituent is a crystallizable thermoplastic. It also comprises at least barium sulfate and at least one optical brightener. The barium sulfate and/or the optical brightener here is either incorporated directly into the thermoplastic during preparation of the polymer or fed as a masterbatch during film production. The novel film is particularly suitable for interior decoration, for constructing exhibition stands, for exhibition requisites, for displays, for placards, for labels, for protective glazing of machines or of vehicles, in the lighting sector, in the fitting out of shops or of stores, as a promotional requisite or a laminating material, or in applications associated with food or drink.

What is claimed is:  
     
         1 . An opaque white film with a thickness of from 10 to 500 μm whose principal constituent is a crystallizable thermoplastic, wherein the film comprises at least barium sulfate and at least one optical brightener, and the barium sulfate or the optical brightener or the barium sulfate and the optical brightener is either incorporated directly into the thermoplastic during preparation of the polymer or fed as a masterbatch during film production.  
     
     
         2 . The opaque white film as claimed in  claim 1 , wherein the crystallizable thermoplastic has been selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate.  
     
     
         3 . The opaque white film as claimed in  claim 1 , wherein from 0.2 to 40% by weight of barium sulfate, based on the weight of the crystallizable thermoplastic, is present in the film and the barium sulfate is fed to the thermoplastic by way of masterbatch technology during film production.  
     
     
         4 . The opaque white film as claimed in  claim 1 , wherein from 10 to 50,000 ppm, of optical brightener, based on the weight of the crystallizable thermoplastic, is present in the film and the optical brightener is fed to the thermoplastic by way of masterbatch technology during film production.  
     
     
         5 . The opaque white film as claimed in  claim 4 , wherein the optical brightener has been selected from the group consisting of bisbenzoxazoles, phenylcoumarins and bisstearylbiphenyls.  
     
     
         6 . The opaque white film as claimed in  claim 1 , wherein a polyester-soluble blue dye selected from the group consisting of cobalt blue, ultramarine blue and anthraquinone dyes, is also present in the film, and the amount of blue dye is from 10 to 10,000 ppm, based on the weight of the crystallizable thermoplastic.  
     
     
         7 . The opaque white film as claimed in  claim 1 , wherein the barium sulphate is present as precipitated barium sulfate in the film and is in the form of fine-particle colorless powder with an average grain size of from 0.1 to 5 μm, measured by the Sedigraph method.  
     
     
         8 . The opaque white film as claimed in  claim 1 , wherein the surface gloss of the film measured to DIN 67530 (measurement angle 20°) is greater than or equal to 10, and the luminous transmittance (transparency) of the film, measured to ASTM-D 1003 is less than or equal to 30%.  
     
     
         9 . The opaque white film as claimed in  claim 1 , wherein the film has one or more layers, and the embodiment having more than one layer comprises at least one core layer and at least one outer layer.  
     
     
         10 . The opaque white film as claimed in  claim 9 , wherein, in the embodiment having more than one layer, the barium sulfate and the optical brightener are present in the core layer.  
     
     
         11 . The opaque white film as claimed in  claim 10 , wherein the outer layer(s), too, have been provided with barium sulfate and optical brightener.  
     
     
         12 . The opaque white film as claimed in  claim 1 , wherein a scratch-resistant coating, a copolyester or an adhesion promoter has been provided on at least one side of the film.  
     
     
         13 . A process for producing the opaque white film as claimed in  claim 1  by extrusion, in which the thermoplastic material barium sulfate and optical brightener melted in an extruder is compacted, extruded through a slot die and quenched on a chill roll, as a substantially amorphous prefilm, and then reheated and stretched longitudinally and transversely, or transversely and longitudinally, or longitudinally, transversely and again longitudinally and/or transversely, which comprises establishing the stretching temperatures at from T g +10 K to T g +60 K and establishing a longitudinal stretching ratio of from 2 to 5, and a transverse stretching ratio of from 2 to 5, and then heat-set the film.  
     
     
         14 . The process as claimed in  claim 13 , wherein the heat-setting of the film is carried out at oven temperatures of from 200 to 260° C.