Homeotropically aligned liquid crystal layer and process for the homeotropic alignment of liquid crystals on plastic substrates

A liquid crystal film with homeotropic alignment wherein said homeotropic alignment is achieved by an aligning layer on a substrate wherein said aligning layer is an Al2O3 layer with a surface sufficiently smooth such that liquid a crystal film formed thereon can be removed in one piece, wherein the liquid crystal film is prepared from a mixture comprising a reactive mesogenic compound of formula I

• P-(Sp-X)n-MG-R,
• wherein
• P is a polymerizable group
• Sp is a spacer group having 1 to 20 C atoms,
• X is a group selected from —O—, —S—, —CO—, —COO—, —OCO—, —OCO—O— or a single bond;
• n is 0 or 1,
• MG is a mesogenic or mesogenity supporting group, according to formula II
• -(A1-Z1)m-A2-Z2-A3- II
• wherein A1, A2 and A3 are independently from each other 1,4-phenylene in which, in addition, one or more CH groups may be replaced by N, 1,4-cyclohexylene in which, in addition, one or two non-adjacent CH2 groups may be replaced by O and/or S, 1,4-cyclohexenylene or napththalene-2,6-diyl, it being possible for all these groups to be unsubstituted, mono- or poly-substituted with halogen, cyano or nitro groups or alkyl, alkoxy or acyl groups having 1 to 7 C atoms wherein one or more H atoms may be substituted by F or Cl,
• Z1 and Z2 are each independently —COO—, —OCO—, CH2CH2—, —OCH2-, —CH2O—, —CH2═CH—, —C≡C—, —CH═CH—COO—, —CO—CH═CH— or a single bond,
• m is 0, 1 or 2, and
• R is an alkyl radical with up to 25 C atoms which may be unsubstituted, mono- or polysubstituted by halogen or CN, it being also possible for one or more non-adjacent CH2 groups to be replaced, in each case independently from one another, by —O—, —S—, —NH—, —N(CH3)—, —CO—, —COO— —OCO—, —OCO—O—, —S—CO—, —CO—S— or —C≡C— in such a manner that oxygen atoms are not linked directly to one another, or alternatively R is halogen, cyano or has independently one of the meanings given for P-(Sp-X)n-.