WO2018033241A1

WO2018033241A1 - Process for the preparation of flat films with controlled surface energy

Info

Publication number: WO2018033241A1
Application number: PCT/EP2017/000978
Authority: WO
Inventors: Anthony MORFA; Gerardo Hernandez-Sosa; Tobias ROEDLEMEIER
Original assignee: Innovationlab Gmbh
Priority date: 2016-08-15
Filing date: 2017-08-15
Publication date: 2018-02-22

Abstract

The present invention relates to a method for the preparation of flat films, preferably for the preparation of flat films with a controlled surface energy. The films prepared with the present process are particularly suited for printing applications requiring a high degree of accuracy, such as for example for electronic devices.

Description

Process for the Preparation of Flat Films with Controlled Surface Energy

Technical Field

The present invention relates to a process for the preparation of flat films, preferably for the preparation of flat films with a controlled surface energy. The films prepared with the present process are particularly suited for printing applications requiring a high degree of accuracy, such as for example for electronic devices.

Background and description of the prior art Printing processes, such as offset printing, gravure printing, flexographic printing, inkjet printing, roller printing, reverse roller printing or web coating, have made significant progress in the manufacturing of technical parts such as, for example, electronic devices, optical devices or electro-optical devices. It has recently even been shown that current technology allows manufacturing electronic devices, such as organic photovoltaic cells or thin film transistors, on flexible substrates by printing processes alone. Because printing processes are generally performed under ambient conditions and thereby avoid the difficulties and cost of vacuum deposition processes, industry is very interested in furthering printing technology.

It has, however, been found that the properties of the ink and the properties of the substrate need to be very well matched so as to obtain good printing results, particularly for printed elements that become smaller and smaller in size.

Up to now this matching of properties of ink and substrate has primarily been achieved by adapting the properties of the ink, for example, by changing the viscosity and/or the wetting properties, by various means, such as the addition of surfactants etc.. This unfortunately leads to frequent changeovers of the ink in the printing equipment, resulting in a significant amount of ink wasted for purging the equipment and for transitioning from one ink to another. Such changeovers are not only time-consuming but may also come at significant costs, particularly if the ink comprises rather valuable materials such as, for example, organic semiconducting compounds, organic photoactive compounds or noble metal compounds.

There is therefore a need in industry for an easier and less costly way of transitioning, for example, between different types of substrates.

It is therefore an objective of the present application to provide for such a method.

It is also an objective of the present application to provide for a method that allows for easy modification of the surface properties of a substrate, particularly for easy modification of the surface roughness or the surface energy of the substrate or both.

Furthermore, it is an objective of the present application to provide for a substrate that can be used in a more versatile way, for example a substrate that can be used with a wider range of inks.

Other objectives of the present application are immediately evident to the expert from the following detailed description and examples.

Summary of the invention

The present inventors have now surprisingly found that the above objects may be attained either individually or in any combination by the process and the film of the present application.

The present application therefore provides for a process for the preparation of films, said process comprising the steps of

(a) providing a polymeric film having a first surface roughness;

(b) heating said polymeric film to a temperature of at least TG - 10°C to TG + 50°C to obtain a heated polymeric film; and

(c) pressing said heated polymeric film against the surface of a cleaved and polished single crystal, thereby obtaining a polymeric film having a second surface roughness, wherein the second surface roughness is lower than the first surface roughness.

The present application therefore also provides for a composite film as defined in claim 12.

Detailed description of the invention

For the purposes of the present application, the terms "ink" and "formulation" are used synonymously and denote a composition comprising at least one solvent and the at least one compound that is to be deposited.

As used herein, the term "organyl group" is used to denote any organic substituent group, regardless of functional type, having one or more, preferably one, free valence at a carbon atom (see also International Union of Pure and Applied Chemistry, Compendium of Chemical Technology, Gold Book, Version 2.3.2, 2012- 08-09, page 1040).

As used herein, the term "organoheteryl group" is used to denote any univalent or polyvalent group, preferably any univalent group, comprising carbon, said group being thus organic, but which has its free valence at an atom otherthan carbon (see also International Union of Pure and Applied Chemistry, Compendium of Chemical Technology, Gold Book, Version 2.3.2, 2012-08-09, page 1038). For the purposes of the present application the term "carbyl group" includes both, organyl groups and organoheteryl groups.

For the purposes of the present application the term "hydrocarbyl group" is used to denote any univalent or polyvalent group, preferably univalent group, formed by removing one or more, preferably one, hydrogen from a hydrocarbon, i.e. compounds consisting of carbon and hydrogen only (see also International Union of Pure and Applied Chemistry, Compendium of Chemical Technology, Gold Book, Version 2.3.2, 2012-08-09, page 694). The present application relates to a process for the preparation of flat films, preferably for the preparation of flat films with a controlled surface energy. Such films are believed to be particularly useful for printing processes,

In general terms the present application relates to a process comprising the steps of planarization of the surface of a polymeric film to obtain a flat polymeric film, optionally subsequently oxidizing the surface of said flat polymeric film to obtain a hydroxylated film, and optionally then treating said hydroxylated film with a silane to obtain a silanized film.

The process of the present application comprises the steps of

(a) providing a polymeric film having a first roughness;

(b) heating said polymeric film; and

(c) pressing said heated polymeric film to a surface, thereby obtaining a polymeric film having a second roughness.

In a first step a polymeric film is provided. Said polymeric film is characterized by a first surface roughness.

The type of polymeric film is not particularly limited. It may, for example, be a monolayer film or a multilayer film, i.e. a film comprising at least two layers that differ in composition and may also have different thicknesses. Such a multilayer film may also be referred to as "composite film".

The film may also be produced "in line" with the present process, i.e. it may be fed directly, or at most with only a very limited storing time, into the present process. Alternatively, the film may also be provided as such to the present process, i.e. having been produced, rolled up, optionally then stored for some time, and finally be fed from a roll into the present process.

Examples of materials suitable as polymer for such polymeric film may be selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyimide, polyethylene naphthalate, polymeric hydrocarbon, cellulosic polymer, polycarbonate, polyamide, polyimide, polyether, polyether ketone, poly(lactic acid), polyethylene, polypropylene, polystyrene, polyaniline, poly(acryl amide), polycaprolactone, poly(vinylidene fluoride), polysulfone (PSU), polyethersulfone (PES), all of which may be homopolymers or copolymers, and blends thereof.

The thickness of the polymeric films is not particularly limited. It is, nevertheless, preferred that the thickness of the present polymeric films is at least 10 nm and at most 1 mm.

In step (b) the polymeric film is heated up to a temperature that is at least 10°C below and at most 50°C above the glass transition temperature TG of the polymer, i e- heating the polymeric film to a temperature of at least TG - 10°C to TG + 50°C. More preferably, said temperature is at least 5°C below the glass transition temperature TG of the polymer. More preferably, said temperature is at most 45°C or 40°C or 35°C or 30 °C above the glass-transition temperature T₆ of the polymer. Subsequently to heating, the heated polymeric film is then pressed against a surface. While the nature of such surface is not particularly limited, it has been found that in order to reduce the roughness of the polymeric film such surface needs to very flat and preferably also smooth. It has been found that the surfaces of cleaved and polished single crystals are particularly suitable for the present method.

Examples of suitable single crystals may be selected from the group consisting of single crystals of metals, metal alloys, metal oxides, metal nitrides, metal halides, and metal oxynitrides. Examples of suitable metals are silicon and germanium. An example of suitable metal oxides is aluminum oxide. An example of suitable metal nitrides is titanium nitride. Examples of suitable metal halides are magnesium fluoride and calcium fluoride. An example of suitable metal oxynitrides is aluminum oxynitride. The time, for which the heated polymeric film is pressed against the surface of the single crystal in step (c), is not particularly limited and may with simple experimentation be adapted such that it fits the specific requirements of the intended application. It is, however, preferred that said time is at least 1 s, more preferably at least 5 s or 10 s or 20 s or 30 s or 45 s, even more preferably at least 1 min, still even more preferably at least 2 min and most preferably at least 3 min. It is preferred that said time is at most 1 h, more preferably at most 50 min or 40 min or 30 min, even more preferably at most 25 min or 20 min, and most preferably at most 15 min. It is also evident to the expert that the time may have to be adapted in view of the temperature of the film in step (c).

The pressure, with which the heated polymeric film is pressed against the surface of the single crystal in step (c), is not particularly limited. It is, however, preferred that said pressure is at least 0.5 bar, more preferably at least 1.0 bar or 1.5 bar, even more preferably at least 2 bar or 2.5 bar, still even more preferably at least 3.0 bar or 3.5 bar, and most preferably at least 4.0 bar. It is preferred that said pressure is at most 20 bar, more preferably at most 15 bar or 10 bar, even more preferably at most 9 bar or 8 bar, and most preferably at most 7 bar.

Starting with a polymeric film having a first surface roughness, the present process allows obtaining a polymeric film having a second surface roughness, wherein the second roughness is lower than the first surface roughness. The difference of first and second surface roughness will depend upon the degree of the first roughness as well as the desired second surface roughness. The second surface roughness is preferably at most 90 % or 80 %, more preferably at most 70 % or 60 %, even more preferably at most 50 % or 40 %, still even more preferably at most 30 % or 20 %, and most preferably at most 10 % of the first surface roughness. Surface roughness may be determined as indicated in the test methods.

The so-obtained flat film, i.e. the polymeric film having the second surface roughness, is characterized by good to excellent surface flatness and as such well suited for printing applications, particularly for high-precision printing applications. However, it seems that such flat film still lacks for some printing processes. Without wishing to be bound by theory it is believed that this may be caused by a non- homogeneous distribution of surface energy.

Thus, preferably the present process further comprises a step (d) of oxidizing the surface of the polymeric film obtained in step (c), thereby obtaining a hydroxylated polymeric film.

The means for oxidizing the surface of said flat polymeric film are not particularly limited. The surface of the flat polymeric film may, for example, be oxidized by plasma treatment, for example, by treatment with argon plasma or oxygen plasma, with oxygen plasma being preferred. Alternatively, the surface of the flat polymeric film may be oxidized by chemical treatment or physical treatment. An example of chemical treatment is treatment with peroxides, preferably organic peroxides. An example of physical treatment is Corona discharge.

Without wishing to be bound by theory it is believed that such oxidizing of the surface of the polymeric film obtained in step (c) will result in a hydroxylated polymeric film. Preferably, either following step (c) or step (d), the present process further comprises a silanization step, wherein the previously obtained film is treated with a silanizing agent as defined in the following so as to obtain a silanized film. Thus, the present process preferably further comprises a step (e) of silanizing the polymeric film obtained in step (c) or the hydroxylated polymeric film obtained in step (d) with a silanizing agent to obtain a silanized polymeric film.

Preferably said silanizing agent is a silane of the following formula (I)

wherein a, R¹, R² and R³ are as defined herein. a is at each occurrence independently 0, 1 or 2. Preferably a is at each occurrence independently 0 or 1. Most preferably a is 0.

R¹, R² and R³ are at each occurrence independently of each other selected from the group consisting of H and R^s.

R^s is at each occurrence independently a carbyl group as defined herein and preferably selected from the group consisting of any group R^T as defined herein, hydrocarbyl having from 1 to 40 carbon atoms wherein the hydrocarbyl may be further substituted with one or more groups R^T, and hydrocarbyl having from 1 to 40 carbon atoms comprising one or more heteroatoms selected from the group consisting of N, O, S, P, Si, Se, As, Te or Ge, with N, 0 and S being preferred heteroatoms, wherein the hydrocarbyl may be further substituted with one or more groups R^T. Preferred examples of hydrocarbyl suitable as R^s may at each occurrence be independently selected from phenyl, phenyl substituted with one or more groups R^T, alkyl and alkyl substituted with one or more groups R^T, wherein the alkyl has at least 1, preferably at least 5 and has at most 40, more preferably at most 30 or 25 or 20, even more preferably at most 15 and most preferably at most 12 carbon atoms. It is noted that for example alkyl suitable as R^s also includes fluorinated alkyl, i.e. alkyl wherein one or more hydrogen is replaced by fluorine, and perfluorinated alkyl, i.e. alkyl wherein all of the hydrogen are replaced by fluorine.

R^T is at each occurrence independently selected from the group consisting of F, CI, -NO2, -CN, -NC, -NCO, -NCS, -OCN, -SCN, R°, OR⁰, SR°, -C(=0)X°, -C(=0)R°, -C(=0)- OR°, -0-C(=0)-R°, -NR°R⁰⁰, -C(=0)NR°R°°, -SO3R⁰, -SO2R⁰, -OH, -NO2, -CF₃, -SF₅, or optionally substituted silyl, or carbyl or hydrocarbyl with 1 to 30, preferably 1 to 20 C atoms that is optionally substituted and optionally comprises one or more hetero atoms, with R° and R⁰⁰ as defined herein. Preferably R^T is at each occurrence independently selected from the group consisting of F, -CN, R°, -OR⁰, -SR°, -C(=0)- R°, -C(=0)-OR°, -0-C(=0)-R°, -0-C(=0)-OR°, and -C(=0)-NR°R°°, with R° and R⁰⁰ as defined herein

R°, R⁰⁰ and R⁰⁰⁰ are at each occurrence independently of each other selected from the group consisting of H, F and hydrocarbyl having from 1 to 40 carbon atoms. Said hydrocarbyl preferably has at most 30, more preferably at most 25 or 20, even more preferably at most 20, and most preferably at most 12 carbon atoms. Preferably, R°, R⁰⁰ and R⁰⁰⁰ are at each occurrence independently of each other selected from the group consisting of H, F, alkyl, fluorinated alkyl, alkenyl, alkynyl, phenyl and fluorinated phenyl. More preferably, R°, R⁰⁰ and R⁰⁰⁰ are at each occurrence independently of each other selected from the group consisting of H, F, alkyl, fluorinated, preferably perfluorinated, alkyl, phenyl and fluorinated, preferably perfluorinated, phenyl. Most preferably, R°, R⁰⁰ and R⁰⁰⁰ are at each occurrence independently of each other selected from the group consisting of H or straight- chain or branched alkyl with 1 to 20, preferably 1 to 12 C atoms that is optionally fluorinated.

It is noted that for example alkyl suitable as R°, R⁰⁰ and R⁰⁰⁰ also includes perfluorinated alkyl, i.e. alkyl wherein all of the hydrogen are replaced by fluorine. Examples of suitable alkyls may be selected from the group consisting of methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, tert-butyl (or "t-butyl"), pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl and eicosyl (-C20H41).

X° is halogen. Preferably X° is selected from the group consisting of F, CI and Br.

A hydrocarbyl group comprising a chain of 3 or more carbon atoms and heteroatoms combined may be straight chain, branched and/or cyclic, including spiro and/or fused rings.

Hydrocarbyl suitable as R^s, R°, R⁰⁰ and/or R⁰⁰⁰ may be saturated or unsaturated. Examples of saturated hydrocarbyl include alkyl. Examples of unsaturated hydrocarbyl may be selected from the group consisting of alkenyl (including acyclic and cyclic alkenyl), alkynyl, allyl, alkyldienyl, polyenyl, aryl and heteroaryl.

Preferred hydrocarbyl suitable as R^s, R^T, R°, R⁰⁰ and/or R⁰⁰⁰ include hydrocarbyl comprising one or more heteroatoms and may for example be selected from the group consisting of alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy and alkoxycarbonyloxy, alkylaryloxy, arylcarbonyl, aryloxycarbonyl, arylcarbonyloxy and aryloxycarbonyloxy.

Preferred examples of aryl and heteroaryl comprise mono-, bi- or tricyclic aromatic or heteroaromatic groups that may also comprise condensed rings.

Especially preferred aryl and heteroaryl groups may be selected from the group consisting of phenyl, phenyl wherein one or more CH groups are replaced by N, naphthalene, fluorene, thiophene, pyrrole, preferably N-pyrrole, furan, pyridine, preferably 2- or 3-pyridine, pyrimidine, pyridazine, pyrazine, triazole, tetrazole, pyrazole, imidazole, isothiazole, thiazole, thiadiazole, isoxazole, oxazole, oxadiazole, thiophene, preferably 2-thiophene, selenophene, preferably 2- selenophene, thieno[3,2-b]thiophene, thieno[2,3-b]thiophene, dithienothiophene, furo[3,2-b]furan, furo[2,3-b]furan, seleno[3,2-b]selenophene, seleno[2,3- bjselenophene, thieno[3,2-b]selenophene, thieno[3,2-b]furan, indole, isoindole, benzo[b]furan, benzo[b]thiophene, benzo[l,2-b;4,5-b']dithiophene, benzo[2,l- b;3,4-b']dithiophene, quinole, 2- methylquinole, isoquinole, quinoxaline, quinazoline, benzotriazole, benzimidazole, benzothiazole, benzisothiazole, benzisoxazole, benzoxadiazole, benzoxazole and benzothiadiazole.

Preferred examples of an alkoxy group, i.e. a corresponding alkyl group wherein the terminal CH2 group is replaced by -0-, can be straight-chain or branched, preferably straight-chain (or linear). Suitable examples of such alkoxy group may be selected from the group consisting of methoxy, ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxy, octoxy, nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy, tetradecoxy, pentadecoxy, hexadecoxy, heptadecoxy and octadecoxy.

Preferred examples of alkenyl, i.e. a corresponding alkyl wherein two adjacent CH2 groups are replaced by -CH=CH- can be straight-chain or branched. It is preferably straight-chain. Said alkenyl preferably has 2 to 10 carbon atoms. Preferred examples of alkenyl may be selected from the group consisting of vinyl, prop-l-enyl, or prop-2-enyl, but-l-enyl, but-2-enyl or but-3-enyl, pent-l-enyl, pent-2-enyl, pent- 3-enyl or pent-4-enyl, hex-l-enyl, hex-2-enyl, hex-3-enyl, hex-4-enyl or hex-5-enyl, hept-l-enyl, hept-2-enyl, hept-3-enyl, hept-4-enyl, hept-5-enyl or hept-6-enyl, oct-l-enyl, oct-2-enyl, oct-3-enyl, oct-4-enyl, oct-5-enyl, oct-6-enyl or oct-7-enyl, non-l-enyl, non-2-enyl, non-3-enyl, non-4-enyl, non-5-enyl, non-6-enyl, non-7- enyl, non-8-enyl, dec-l-enyl, dec-2-enyl, dec-3-enyl, dec-4-enyl, dec-5-enyl, dec-6- enyl, dec-7-enyl, dec-8-enyl and dec-9-enyl.

Especially preferred alkenyl groups are C2-C7-lE-alkenyl, C4-C7-3E-alkenyl, C5-C7-4- alkenyl, C6-C7-5-alkenyl and C7-6-alkenyl, in particular C2-C7-lE-alkenyl, C4-C7-3E- alkenyl and Cs-C7-4-alkenyl. Examples of particularly preferred alkenyl groups are vinyl, lE-propenyl, lE-butenyl, lE-pentenyl, lE-hexenyl, lE-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Alkenyl groups having up to 5 C atoms are generally preferred.

Preferred examples of oxaalkyl, i.e. a corresponding alkyl wherein one non-terminal CH2 group is replaced by -0-, can be straight-chain or branched, preferably straight chain. Specific examples of oxaalkyl may be selected from the group consisting of 2-oxapropyl (=methoxymethyl), 2- (=ethoxymethyl) or 3-oxabutyl (=2- methoxyethyl), 2-, 3-, or 4-oxapentyl, 2-, 3-, 4-, or 5-oxahexyl, 2-, 3-, 4-, 5-, or 6- oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl and 2-, 3- , 4-, 5-, 6-,7-, 8- or 9-oxadecyl.

Preferred examples of carbonyloxy and oxycarbonyl, i.e. a corresponding alkyl wherein one CH2 group is replaced by -0- and one of the thereto adjacent CH2 groups is replaced by -C(O)-. may be selected from the group consisting of acetyloxy, propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetyloxypropyl, 3-propionyloxypropyl, 4-acetyloxybutyl, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxy- carbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl,

2- (methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(propoxycarbonyl)ethyl,

3- (methoxycarbonyl)propyl, 3-(ethoxycarbonyl)propyl, and 4-(methoxycarbonyl)- butyl.

Preferred examples of thioalkyi, i.e where one CH2 group is replaced by -S-, may be straight-chain or branched, preferably straight-chain. Suitable examples may be selected from the group consisting of thiomethyl (-SCH3), 1-thioethyl (-SCH2CH3), 1- thiopropyl (-SCH₂CH₂CH₃), l-(thiobutyl), l-(thiopentyl), l-(thiohexyl), 1- (thioheptyl), l-(thiooctyl), l-(thiononyl), l-(thiodecyl), l-(thioundecyl) and 1- (thiododecyl).

A fluoroalkyl group is preferably perfluoroalkyl CjF2i₊i, wherein i is an integer from 1 to 15, in particular CF3, C2F5, C3F7, C₄F₉, C5F11, C6F13, C7F15 or CsFi?, very preferably C6Fi3, or partially fluorinated alkyl, in particular 1,1-difluoroalkyl, all of which are straight-chain or branched.

Alkyl, alkoxy, alkenyl, oxaalkyl, thioalkyi, carbonyl and carbonyloxy groups can be achiral or chiral groups. Particularly preferred chiral groups are 2-butyl (=1- methylpropyl), 2-methylbutyl, 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2- propylpentyl, 2-butyloctyl, 2-hexyldecyl, 2-octyldodecyl, 7-decylnonadecyl, in particular 2-methylbutyl, 2-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2- ethyl-hexoxy, 1-methylhexoxy, 2-octyloxy, 2-oxa-3-methylbutyl, 3-oxa-4-methyl- pentyl, 4-methylhexyl, 2-butyloctyl, 2-hexyldecyl, 2-octyldodecyl, 7- decylnonadecyl, 3,8-dimethyloctyl, 2-hexyl, 2-octyl, 2-nonyl, 2-decyl, 2-dodecyl, 6- meth-oxyoctoxy, 6-methyloctoxy, 6-methyloctanoyloxy, 5-methylheptyloxy- carbonyl, 2-methylbutyryloxy, 3-methylvaleroyloxy, 4-methylhexanoyloxy, 2- chloropropionyloxy, 2-chloro-3-methylbutyryloxy, 2-chloro-4-methyl-valeryl-oxy, 2-chloro-3-methylvaleryloxy, 2-methyl-3-oxapentyl, 2-methyl-3-oxa-hexyl, 1- methoxypropyl-2-oxy, l-ethoxypropyl-2-oxy, l-propoxypropyl-2-oxy, 1- butoxypropyl-2-oxy, 2-fluorooctyloxy, 2-fluorodecyloxy, l,l,l-trifluoro-2-octyloxy, l,l,l-trifluoro-2-octyl, 2-fluoromethyloctyloxy for example. Most preferred is 2- ethylhexyl. Preferably R¹ is a hydrocarbyl group, preferably an alkyl or aryl group, having from 1 to 20 carbon atoms, more preferably from 1 to 15, even more preferably from 1 to 10, wherein one or more non-adjacent carbon atoms may be replaced with the respective number of heteroatom groups, with said heteroatom being preferably selected from the group consisting of O, S, N and P. Most preferably R¹ is an alkyl group having from 1 to 5 carbon atoms.

Exemplary hydrocarbyl group suitable for R¹ may be selected from respective alkyl groups and respective aryl groups. Examples of alkyl groups suitable for R¹ may be selected from the group consisting of methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, tert-butyl (or "t-butyl"), cyclobutyl, pentyl, cyclopentyl, hexyl, cyclohexyl, heptyl, cycloheptyl, octyl, cyclooctyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl and eicosyl (-C20H41); preferably from the group consisting of methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, tert- butyl (or "t-butyl"), and pentyl; even more preferably from the group consisting of methyl, ethyl, n-propyl, iso-propyl, and n-butyl; and most preferably are methyl or ethyl. Examples of aryl groups suitable for R¹ may be selected from phenyl or naphthyl, wherein in or more carbon atoms may be substituted with N.

Preferably R² is defined

Preferably, R³ is at each occurrence independently of the following formula (II) -(R⁴)b-X (ID with b, R⁴ and X¹ as defined herein, b is 0 or 1. For b being 0, R³ is -X¹.

Preferably, R⁴ is an alkylidene group or arylene group having from 1 to 20 carbon atoms, more preferably from 1 to 15 carbon atoms, and most preferably from 1 to 10 carbon atoms, wherein one or more carbon atoms may be replaced by one or more heteroatoms selected from the group consisting of N, O and S.

Examples of alkylidene groups suited as R⁴ may be -(CHh),- wherein c is an integer from 1 to 10 (i.e. 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10) and wherein one or more non-adjacent CH2-groups may be replaced by N-R_s, O or S, preferably by O, or wherein, for c being an integer from 2 to 10, two adjacent CH₂-groups may be replaced by -C=C- or - (R^S)C=C(R^S)-, preferably -C≡C- Such alkylidene groups may, for example, be represented by the following formula (III)

- (CH₂)d-X²-(CH₂)_e- (Ml) with d + e being an integer of from 1 to 9 (i.e. 1, 2, 3, 4, 5, 6, 7, 8 or 9) and X² being selected from O, S and N-R^s, preferably with X² being O, or with d + e being an integer of from 1 to 8 and X² being -C≡C- or -(R^S)C=C(R^S)-, preferably -C≡C-

Examples of arylene groups suited as R⁴ may be derived from phenyl or naphtalene, preferably from phenyl, wherein one or more carbon atom may optionally be replaced by N. For R⁴ being a phenylene it is preferred that it is of the following formula (IV)

i.e. is preferably para-substituted, wherein the asterisks ("*") denote the bonds to the neighboring atoms or groups.

Preferred specific examples of silanes of formula (I) may be selected from the following formulae (1-1) to (1-8) OMe

I

MeO- Si-(CH₂)_f -CH₃

OMe (1-1) with f being an integer of from 1 to 9;

OEt

I

EtO-Si-(CH₂)_f -CH₃

OEt (1-2) with f being an integer of from 1 to 9;

OMe

I

-Si-(CH₂)_f -NH₂

OMe (1-5) with f being an integer of from 1 to 9; OEt

-Si-(CH₂)_f -NH₂

OEt (1-6) with f being an integer of from 1 to 9;

It is noted that silanization with compounds (1-7) and (1-8) may also be done in combination with UV-irradiation.

Following silanization the silanized polymeric film obtained in step (e) is preferably rinsed and dried. Thus, the present process preferably comprises the further step (f) rinsing and drying the silanized polymeric film obtained in step (e).

Rinsing may, for example, be done using water or a suitable organic solvent, such as for example an alcohol.

Drying may, for example, be done with heat or with a flow of gas, such as for example a flow of air or nitrogen or argon.

Additionally, the present application relates to a composite film comprising

(a) a polymeric film as obtained from step (d), and

(b) a self-assembled monolayer as obtained in step (e).

Said self-assembled monolayer is obtained in the silanization step (e), i.e. by reaction of the hydroxylated film with a silanizing agent as defined herein. It may, for example, be represented by the following formula (Ι')

(Z-0)₃-_a(R²)aSi-R³ (Ι') wherein a, R² and R³ are as defined herein and Z denotes the surface of the polymeric film.

The present inventors have been quite surprised to find that the present process allows to obtain films which are characterized by good to excellent flatness as well as by the fact that the surface properties of such films can be tuned to accommodate a broad range of different inks. The present process is therefore believed to greatly facilitate commercial production of printed articles, such as for example of printed electronic devices

The films produced with the present process are particularly suited for use in printing processes, i.e. for the production of printed articles. Thus, the present process preferable further comprises the following step of

(g) depositing a formulation by a printing process onto any one of the films selected from the group consisting of the polymeric film obtained in step (c) or the hydroxylated flat polymeric film obtained in step (d) or onto the film obtained in step (f).

Thus, the present process for the preparation of films may comprise the following steps

(a) providing a polymeric film having a first surface roughness;

(b) heating said polymeric film to a temperature of at least TG - 10°C to T_G + 50°C to obtain a heated polymeric film;

(c) pressing said heated polymeric film against the surface of a cleaved and polished single crystal, thereby obtaining a polymeric film having a second surface roughness, wherein the second surface roughness is lower than the first surface roughness;

(d) optionally oxidizing the polymeric film obtained in step (c), thus obtaining a hydroxylated polymeric film;

(e) optionally silanizing the polymeric film obtained in step (c) or the hydroxylated polymeric film obtained in step (d) with a silanizing agent to obtain a silanized polymeric film;

(f) rinsing and drying the silanized polymeric film obtained in step (e); and

Thus, the present application also provides for an electronic device comprising the composite as defined above. It is noted that the present process may in its entirety, i.e. preferably including the production of the polymeric film, be performed in a roll-to-roll process, i.e. in a continuous process. Exemplary printing processes may be selected from the group consisting of ink jet printing, nozzle printing, letter-press printing, screen printing, gravure printing, roller printing, reverse-roller printing, offset lithography printing, dry offset lithography printing, flexographic printing, web printing, and pad printing. Ink jet printing is particularly preferred when high resolution layers and devices need to be prepared. Selected formulations of the present invention may be applied to prefabricated device substrates by ink jet printing. Preferably industrial piezoelectric print heads such as but not limited to those supplied by Aprion, Hitachi-Koki, InkJet Technology, On Target Technology, Picojet, Spectra, Trident, Xaar may be used to apply the organic semiconductor layer to a substrate. Additionally semi-industrial heads such as those manufactured by Brother, Epson, Konica, Seiko Instruments Toshiba TEC or single nozzle microdispensers such as those produced by Microdrop and Microfab may be used. Electronic devices prepared in accordance with the present process may be selected from the group consisting of OFETs (organic field effect transistors), TFTs (thin-film transistors), ICs (integrated circuits), logic circuits, capacitors, RFID (radio frequency identification) tags, OLEDs (organic light emitting diodes), OLETs (organic light emitting transistors), OPEDs (organic photoemitting diodes), OPVs (organic photovoltaics), OPDs (organic photodetectors), solar cells, laser diodes, photoconductors, photodetectors, electrophotographic devices, electrophotographic recording devices, organic memory devices, sensor devices, charge injection layers, Schottky diodes, planarising layers, antistatic films, conducting substrates and conducting patterns.

The OPV device can for example be of any type known from the literature (see e.g. Waldauf et ai, Appl. Phys. Lett., 2006, 89, 233517).

A first preferred OPV device according to the invention comprises the following layers (in the sequence from bottom to top):

- optionally a substrate, - a high work function electrode, preferably comprising a metal oxide, like for example ITO, serving as anode,

- an optional conducting polymer layer or hole transport layer, preferably comprising an organic polymer or polymer blend, for example of PEDOT.PSS (poly(3,4-ethylenedioxythiophene): poly(styrene-sulfonate), or TBD (Ν,Ν'- dyphenyl-N-N'-bis(3-methylphenyl)-l, biphenyl-4,4'-diamine) or NBD (Ν,Ν'- dyphenyl-N-N'-bis(l-napthylphenyl)-l,l'biphenyl-4,4'-diamine),

- a layer, also referred to as "active layer", comprising a p-type and an n-type organic semiconductor, which can exist for example as a p-type/n-type bilayer or as distinct p-type and n-type layers, or as blend or p-type and n- type semiconductor, forming a BHJ,

- optionally a layer having electron transport properties, for example comprising LiF,

- a low work function electrode, preferably comprising a metal like for example aluminum, serving as cathode,

wherein at least one of the electrodes, preferably the anode, is transparent to visible light.

A second preferred OPV device according to the invention is an inverted OPV device and comprises the following layers (in the sequence from bottom to top):

- optionally a substrate,

- a high work function metal or metal oxide electrode, comprising for example ITO, serving as cathode,

- a layer having hole blocking properties, preferably comprising a metal oxide like TiOx or Zn_x,

- an active layer comprising a p-type and an n-type organic semiconductor, situated between the electrodes, which can exist for example as a p-type/n- type bilayer or as distinct p-type and n-type layers, or as blend or p-type and n-type semiconductor, forming a BHJ,

- an optional conducting polymer layer or hole transport layer, preferably comprising an organic polymer or polymer blend, for example of PEDOT: PSS or TBD or NBD,

- an electrode comprising a high work function metal like for example silver, serving as anode,

wherein at least one of the electrodes, preferably the cathode, is transparent to visible light. ln the OPV devices of the present invention the p-type and n-type semiconductor materials are preferably selected from the materials, like the polymer/fullerene systems, as described above

When the active layer is deposited on the substrate, it forms a BHJ that phase separates at nanoscale level. For discussion on nanoscale phase separation see Dennler et al, Proceedings of the IEEE, 2005, 93 (8), 1429 or Hoppe et al, Adv. Func. Mater, 2004, 14(10), 1005. An optional annealing step may be then necessary to optimize blend morpohology and consequently OPV device performance.

The films prepared by the present process may also be used in an OFET comprising a gate electrode, an insulating (or gate insulator) layer, a source electrode, a drain electrode and an organic semiconducting channel connecting the source and drain electrodes. Other features of the OFET are well known to those skilled in the art.

OFETs where an OSC material is arranged as a thin film between a gate dielectric and a drain and a source electrode, are generally known, and are described for example in US 5,892,244, US 5,998,804, US 6,723,394 and in the references cited in the background section. Due to the advantages, like low cost production using the solubility properties of the compounds according to the invention and thus the processibility of large surfaces, preferred applications of these FETs are such as integrated circuitry, TFT displays and security applications.

The gate, source and drain electrodes and the insulating and semiconducting layer in the OFET device may be arranged in any sequence, provided that the source and drain electrode are separated from the gate electrode by the insulating layer, the gate electrode and the semiconductor layer both contact the insulating layer, and the source electrode and the drain electrode both contact the semiconducting layer.

An OFET device according to the present invention preferably comprises:

- a source electrode,

- a drain electrode,

- a gate electrode,

- a semiconducting layer, - one or more gate insulator layers, and

- optionally a substrate. I

The OFET device can be a top gate device or a bottom gate device. Suitable structures and manufacturing methods of an OFET device are known to the skilled in the art and are described in the literature, for example in US 2007/0102696 Al.

In security applications, OFETs and other devices with semiconducting materials according to the present invention, like transistors or diodes, can be used for RFID tags or security markings to authenticate and prevent counterfeiting of documents of value like banknotes, credit cards or ID cards, national ID documents, licenses or any product with monetry value, like stamps, tickets, shares, cheques etc.

Alternatively, the films obtained by the present process may be used in OLEDs. Common OLEDs are realized using multilayer structures. An emission layer is generally sandwiched between one or more electron-transport and/or hole- transport layers. By applying an electric voltage electrons and holes as charge carriers move towards the emission layer where their recombination leads to the excitation and hence luminescence of the lumophor units contained in the emission layer, see, e.g., Muller ef a I, Synth. Metals, 2000, 111-112, 31-34, Alcala, J. Appl. Phys., 2000, 88, 7124-7128 and the literature cited therein.

The films prepared by the process according to the present invention may also be suitable for use in organic plasmon-emitting diodes (OPEDs), as described for example in Koller ef al., Nat. Photonics, 2008, 2, 684.

Test methods Surface energies were calculated from contact angles measured with solvents of known surface tension (water, diiodomethane, and glycerol) on a Kruss DSA-100 drop shape analyzer. Drops were measured once static (approximately 5 s after deposition) and were 2 μί in volume. Contact angles were taken as the average of at least 5 droplets and the standard deviation was typically no more than 2 degrees. Surface roughness and topography measurements were made on a Sensofar PLu Neox White Light 3D Interferometer. Samples were measured using a 10 times magnification objective, with white light, in the VSI measurement mode. Three locations were measured on each foil that was suspended in a foil holder and the root-mean-square roughness was averaged over these three results.

Examples

The following examples are given to illustrate the advantages of the present process in a non-limiting way.

Example 1

500 μηι thick cellulose acetate film obtained from Rachow Kunststoff-Folien GmbH were flattened by heating the film to 120°C and then pressing it against a cleaved silicon wafer under a pressure of 5.5 bar for 300 s. The so-obtained flat film was then first subjected to an oxygen plasma treatment, followed by 60 s of immersion in a solution of the respective silane. Water contact angles for the so-obtained silanized films are given in the following Table 1.

Table 1

Plasma treatment Silane Water contact angle

None None 78.4°

Oxygen None 16.6°

Argon None 26.3°

Oxygen (1-8) with UV-irradiation 49.8°

Oxygen (1-8) without UV-irradiation 58.2°

Oxygen (1-6) with f = 3 63.0°

Oxygen (1-4) 64.0°

Oxygen (1-2) with f = 7 65 - 71° The results clearly show that the present process allows the film surface to be adapted to a broad range of water contact angles, i.e. to a broad range of surface energy. Thus, the present method allows a film to be adapted by selecting a respective silane treatment to be adapted to a wide variety of potential printing formulations.

Example 2 500 μηη thick cellulose acetate film obtained from Rachow Kunststoff-Folien GmbH were flattened by heating the film to 120°C and then pressing it against a cleaved silicon wafer under a pressure of 5.5 bar for 300 s.

OLEDs were produced on cellulose acetate film from a combination of inkjet printing, spin-casting and thermal evaporation. The emitting material was PDY-132 aka Super Yellow (SY) (spin-cast), while the metal contact was LiF (1 nm)/aluminum (100 nm). Samples were tested in a nitrogen environment where the use of barrier foils was not necessary. Results are indicated in Table 2.

Table 2

The results clearly show the effect obtained by the use of a flattened film in the preparation of the OLEDs, in respect to the maximum average luminence as well as in respect to the average error for untreated film and treated film. Thus, the present process allows for the production of higher performing devices as well as for device with improved homogeneity.

Claims

1. Process for the preparation of films, said process comprising the steps of

(a) providing a polymeric film having a first surface roughness;

(c) pressing said heated polymeric film against the surface of a cleaved and polished single crystal, thereby obtaining a polymeric film having a second surface roughness,

wherein the second surface roughness is lower than the first surface roughness.

2. Process according to claim 1, wherein the single crystal is selected from the group consisting of single crystals of metals, metal alloys, metal oxides, metal nitrides, metal halides, and metal oxynitrides.

3. Process according to claim 1 or claim 2, wherein the single crystal is a silicon single crystal.

4. Process according to any one or more of the preceding claims, wherein in step (c) the surface of said heated polymeric film is pressed against the surface of a cleaved and polished single crystal under a pressure of at least 0.5 bar.

5. Process according to any one or more of the preceding claims, wherein in step

(c) the surface of said heated polymeric film is pressed against the surface of a cleaved and polished single crystal for a time of at least 1 s.

6. Process according to any one or more of the preceding claims, further comprising the step of

(d) oxidizing the polymeric film obtained in step (c), thus obtaining a hydroxylated polymeric film.

7. Process according to any one or more of the preceding claims, wherein in step (d) the surface of the polymeric film obtained in step (c) is oxidized by plasma treatment, preferably by treatment with oxygen plasma or argon plasma.

8. Process according to any one or more of the preceding claims, further comprising the step of

(e) silanizing the polymeric film obtained in step (c) or the hydroxylated polymeric film obtained in step (d) with a silanizing agent to obtain a silanized polymeric film.

9. Process according to any one or more of the preceding claims, wherein in step

(e) said silanizing agent is of general formula (I)

wherein a is at each occurrence independently 0, 1 or 2; and R¹, R² and R³ are at each occurrence independently of each other a carbyl group.

10. Process according to any one or more of the preceding claims, further comprising the step of

(f) rinsing and drying the silanized polymeric film obtained in step (e).

11. Process according to any one or more of the preceding claims, further comprising the step of

12. Composite film comprising

(a) a polymeric film as obtained from step (d), and

(b) a self-assembled monolayer as obtained in step (e).

13. Composite film according to claim 12, wherein the silanizing self-assembled monolayer is derived by reaction of the hydroxyl groups on the surface of the oxidized film obtained in step (d) and the silanizing agent of general formula (I)

(R¹0)3-a(R²)aSi-R³ (I) wherein a is at each occurrence independently 0, 1 or 2; and R¹, R² and R³ are at each occurrence independently of each other a carbyl group.

Composite film according to claim 12 or claim 13, wherein the self-assembled monolayer is of the following formula ( )

(2-0)₃-a(R²)aSi-R³ (Ι') wherein a, R² and R³ are as defined herein and Z denotes the surface of the polymeric film.