A method for preparing a film that contains a thermoplastic polymer mixture by gelling or sintering a mixture of thermoplastic and plasticiser, having the following steps: a) providing a mixture of a thermoplastic and a mixture of a first plasticiser and at least one further plasticiser; b) applying the mixture that was provided in step a) to a mould surface, and distributing the mixture over the mould surface; c) heating the mixture that is on the mould surface to a predetermined sintering temperature for a predetermined period in order to gel the mixture; d) cooling the mixture that is on the mould surface; characterised - in that the first plasticiser is a phthalic acid ester or a terephthalic acid ester having two alcohol groups or a trimellitic acid ester having three alcohol groups, and contains or is formed with heptanol (C 7 H 16 O) and/or nonanol (C 9 H 20 O) and/or undecanol (C 11 H 24 O), and - in that the at least one further plasticiser comprises one of the substances of the two substance groups listed below or any desired mixtures of the substances of one or both of these substance groups, namely: - first substance group: phthalic acid ester or terephthalic acid ester having two alcohol groups or trimellitic acid ester having three alcohol groups, wherein the ester contains at least one alcohol in the list below or is formed with such an alcohol: • phenylmethanol (C 7 H 8 O) • 1-phenylethanol (C 8 H 10 O) • 2-phenylethanol (C 8 H 10 O) • 2-cyclohexylethanol (C 8 H 16 O) • 2-phenoxyethanol (C 8 H 10 O 2) • 2-methoxyphenol (C 7 H 8 O 2) [guaiacol] • 3-phenyl-1-propanol (C 9 H 12 O) • 3-phenyl allyl alcohol (C 9 H 10 O) • 4-methoxybenzyl alcohol (C 8 H 10 O 2) [anisyl alcohol] • borneol and isomers thereof (C 10 H 18 O) - second substance group: pentaerythryl monoacetals and pentaerythryl diacetals of the general formulae where R 1 represents a first aldehyde and R 2 represents a second aldehyde. a) providing a mixture of a thermoplastic and a mixture of a first plasticiser and at least one further plasticiser; b) applying the mixture that was provided in step a) to a mould surface, and distributing the mixture over the mould surface; c) heating the mixture that is on the mould surface to a predetermined sintering temperature for a predetermined period in order to gel the mixture; d) cooling the mixture that is on the mould surface; - in that the first plasticiser is a phthalic acid ester or a terephthalic acid ester having two alcohol groups or a trimellitic acid ester having three alcohol groups, and contains or is formed with heptanol (C 7 H 16 O) and/or nonanol (C 9 H 20 O) and/or undecanol (C 11 H 24 O), and - in that the at least one further plasticiser comprises one of the substances of the two substance groups listed below or any desired mixtures of the substances of one or both of these substance groups, namely: - first substance group: phthalic acid ester or terephthalic acid ester having two alcohol groups or trimellitic acid ester having three alcohol groups, wherein the ester contains at least one alcohol in the list below or is formed with such an alcohol: • phenylmethanol (C 7 H 8 O) • 1-phenylethanol (C 8 H 10 O) • 2-phenylethanol (C 8 H 10 O) • 2-cyclohexylethanol (C 8 H 16 O) • 2-phenoxyethanol (C 8 H 10 O 2) • 2-methoxyphenol (C 7 H 8 O 2) [guaiacol] • 3-phenyl-1-propanol (C 9 H 12 O) • 3-phenyl allyl alcohol (C 9 H 10 O) • 4-methoxybenzyl alcohol (C 8 H 10 O 2) [anisyl alcohol] • borneol and isomers thereof (C 10 H 18 O) - second substance group: pentaerythryl monoacetals and pentaerythryl diacetals of the general formulae where R 1 represents a first aldehyde and R 2 represents a second aldehyde. - first substance group: phthalic acid ester or terephthalic acid ester having two alcohol groups or trimellitic acid ester having three alcohol groups, wherein the ester contains at least one alcohol in the list below or is formed with such an alcohol: • phenylmethanol (C 7 H 8 O) • 1-phenylethanol (C 8 H 10 O) • 2-phenylethanol (C 8 H 10 O) • 2-cyclohexylethanol (C 8 H 16 O) • 2-phenoxyethanol (C 8 H 10 O 2) • 2-methoxyphenol (C 7 H 8 O 2) [guaiacol] • 3-phenyl-1-propanol (C 9 H 12 O) • 3-phenyl allyl alcohol (C 9 H 10 O) • 4-methoxybenzyl alcohol (C 8 H 10 O 2) [anisyl alcohol] • borneol and isomers thereof (C 10 H 18 O) phthalic acid ester or terephthalic acid ester having two alcohol groups or trimellitic acid ester having three alcohol groups, wherein the ester contains at least one alcohol in the list below or is formed with such an alcohol: • phenylmethanol (C 7 H 8 O) • 1-phenylethanol (C 8 H 10 O) • 2-phenylethanol (C 8 H 10 O) • 2-cyclohexylethanol (C 8 H 16 O) • 2-phenoxyethanol (C 8 H 10 O 2) • 2-methoxyphenol (C 7 H 8 O 2) [guaiacol] • 3-phenyl-1-propanol (C 9 H 12 O) • 3-phenyl allyl alcohol (C 9 H 10 O) • 4-methoxybenzyl alcohol (C 8 H 10 O 2) [anisyl alcohol] • borneol and isomers thereof (C 10 H 18 O) • phenylmethanol (C 7 H 8 O) • 1-phenylethanol (C 8 H 10 O) • 2-phenylethanol (C 8 H 10 O) • 2-cyclohexylethanol (C 8 H 16 O) • 2-phenoxyethanol (C 8 H 10 O 2) • 2-methoxyphenol (C 7 H 8 O 2) [guaiacol] • 3-phenyl-1-propanol (C 9 H 12 O) • 3-phenyl allyl alcohol (C 9 H 10 O) • 4-methoxybenzyl alcohol (C 8 H 10 O 2) [anisyl alcohol] • borneol and isomers thereof (C 10 H 18 O) - second substance group: pentaerythryl monoacetals and pentaerythryl diacetals of the general formulae where R 1 represents a first aldehyde and R 2 represents a second aldehyde. pentaerythryl monoacetals and pentaerythryl diacetals of the general formulae where R 1 represents a first aldehyde and R 2 represents a second aldehyde.