A COMPOSITION COMPRISING GRAPHITE OXIDE AND AN INFRARED ABSORBING COMPOUND

[DESCRIPTION]

FIELD OF THE INVENTION

[0001] The present invention relates to a composition

comprising graphite oxide capable of switching form a hydrophilic state into a hydrophobic state upon exposure to heat and/or light.

BACKGROUND OF THE INVENTION

[0002] Graphite is a crystalline carbon-allotrope consisting of stacked layers of sp ² -hybridised carbon aromatic rings. Graphene corresponds to one or some of these pure monolayers. Graphene is chemically inert, strong, electrical conductive and hydrophobic and has been the subject of many research projects over the past years.

[0003] A preferred method in the art for preparing graphene involves oxidation of graphite to graphite oxide followed by a reduction reaction of the graphite oxide to graphene. During the oxidation of graphite to graphite oxide, the interaction between the different layers in the graphite is disturbed and the

introduction of oxygen- containing polar groups renders the obtained graphite oxide hydrophilic and dispersible in water in the form of macroscopic flakes. Chemical reduction of these graphite oxide flakes yields a suspension of graphene flakes. For example, the reduction can be achieved by treating suspended graphite oxide with hydrazine hydrate at 100 °C for 24 hours, by exposing graphite oxide to hydrogen plasma for a few seconds, or by exposure to a strong pulse of light, for example a Xenon flash. However, manifold defects already present in graphite oxide may hamper the

effectiveness of this reduction. Thus, the graphene quality obtained after reduction is limited by both the precursor quality

(graphite oxide) and the efficiency of the reducing reaction.

Alternatively, graphene may also be produced through thermal methods. For example, by rapid heating (>2000 °C/min) to 1050 °C carbon dioxide releases and the oxygen functionalities are removed. Exposing a film of graphite oxide to a laser emitting at 355 nm or 532 nm has also revealed to produce quality graphene at a low cost.

[0004] WO 2011/072213 discloses a method for producing graphene by exposing graphite oxide with ultraviolet, visible or infrared radiant energy. The method is used for locally generating heat for example in phototherapy, domestic purposes and/or desalination of water. It is shown that, for aqueous graphite oxide solutions, the strong absorption of the IR radiation by water and the very weak absorption of the IR photons by graphite oxide prevents the conversion of graphite oxide to graphene. With laser radiation of 532 nm ( 7 W, 30 Hz) , graphite oxide is converted to graphene, while upon laser irradiation at a wavelength of 1064 nm no reduction of graphite oxide is observed. Also the publications of Zhang et al . in Adv. Optical Mater. 2014,2, 10-28 and Feng et al . in Appl. Phys . Lettt . , 2010 , 96 report that no reduction of graphite oxide to graphene is observed under infrared irradiation of graphite oxide solutions .

SUMMARY OF THE INVENTION

[0005] It is an object of the present invention to provide a graphite oxide composition that can efficiently be reduced to graphene or graphene-like structures upon absorption of heat and/or light produced by low-cost lasers; more specifically upon infrared irradiation. Also a method of making graphene or graphene-like structures by exposing a graphite oxide composition with heat and/or light is an aspect of the present invention.

[0006] It was found that a composition including graphite oxide and an infrared absorbing compound results in an efficient

formation of chemically inert, strong, electrical conductive and hydrophobic graphene or graphene-like structures upon exposure to heat and/or light.

[0007] According to the present invention there is further provided a method of producing graphene or graphene-like structures comprising the step of exposing a composition including graphite oxide and an infrared absorbing compound to heat and/or infrared light. In contrast to prior art methods, the method of the present invention does not require the use of reducing agents to convert graphite oxide to graphene or graphene-like structures and

contamination of the graphene or graphene-like structures by such agents and/or the generation of noxious by-products is eliminated. Moreover, the technology provided herein is convenient, cost- efficient and is favorable from an environmental point of view.

[0008] Preferred embodiments of the present invention are described in the dependent claims.

DETAILED DESCRIPTION OF THE INVENTION

[0009] According to the present invention, it was found that a composition including both graphite oxide and an infrared absorbing compound can be reduced to graphene or graphene-like structures by means of irradiation with visible and/or infrared light. Graphene- like structures means graphene which may include some defects. The reduction reaction of hydrophilic graphite oxide causes the formation of hydrophobic graphene or graphene-like structures. It was found that by including an infrared absorbing compound to graphite oxide, an efficient reduction of the graphite oxide can be achieved which is characterized by a low power consumption. Visible light refers to electromagnetic radiation from about 390 nm to about 750 nm and infrared light refers to electromagnetic radiation from about 750 nm to about 1400 nm.

[0010] By including an infrared absorbing compound which converts the absorbed light into heat in the composition of the current invention, it was surprisingly found that an efficient reduction of graphite oxide into high quality graphene or graphene- like structures is obtained. The composition is mainly sensitized for infrared lasers such as lasers emitting at 830 nm or 1064 nm and/or for visible light, for example for exposure by an Ar laser (488 nm) or a FD-YAG laser (532 nm) .

[0011] Graphite oxide is preferably in the form of flakes. The flakes preferably have a diameter of 200 to 2000 nanometer; more preferably a diameter of 400 to 1500 nanometer; and most

prerferably a diameter of 600 to 800 nanometer. The average thickness of the flakes may be between 1 and 50 nm. The amount of graphite oxide in the composition of the current invention is preferably from 0.05 mg/m ² to 10 mg/m ² ; more preferably from 0.1 mg/m ² to 5 mg/m ² ; most preferably from 50 mg/m ² to 2 g/m ² .

[0012] The graphite oxide may be dispersed in a liquid medium such as for example an aqueous solution or a solution including one or more organic solvents. Liquid media suitably used to disperse graphite oxide include but are not limited to aqueous-based media such as water; aqueous solutions including water and alcohols such as ethanol (e.g. the ethanol may be present in an amount from 10 to 90%, preferably from 20 to 80%, more preferably from 30 to 70% or from 40 to 60%, and most preferably in an amount of about 50% ethanol); solutions of polyethylene glycol (PEG) in water (e.g. from about 1% to about 10%, e.g. about 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10% PEG in water) ; other alcohols such as methanol, isopropanol, etc., or other polar liquids such as acetonitrile ,

dimethylsulfoxide etc.. The concentration of graphite oxide in the solution is preferably in the range from about 0.1 mg/ml (or even less) to about 10 mg/ml (or greater) , more preferably in the range from about 1 mg/ml to about 8 mg/ml, and most preferably in the range between 2 and 6 mg/ml.

[0013] The composition of the current invention includes one or more infrared absorbing compound (s) which absorb visible and/or infrared (IR) radiation light and converts the absorbed energy into heat. The infrared absorbing compound, also referred to herein as IR-absorbing compound, is preferably an infrared dye (IR-dye) or infrared pigment (IR-pigment) , most preferably an IR-dye. More preferably, the IR-dye is an organic infrared absorbing dye and is preferably water dispersible, more preferably self dispersing (no addition of surfactant) or encapsulated, and is preferably added to the composition as an aqueous dispersion. The IR-dye preferably includes a conjugated system also referred to as "chromophoric moiety". The chromophoric moiety has its main absorption in the infrared region, i.e. radiation having a wavelength in the range from 750 to 1500 nm, preferably in the range from 750 nm to 1250 nm, more preferably in the range from 750 nm to 1100 nm, and most preferably in the range from 780 nm to 900 nm. Preferably the chromophoric group has its absorption maximum in the infrared region. The IR-dye preferably absorbs laser light of 830 nm. In a particular embodiment, the IR-dye may be bonded by for example one or more covalent bond(s) to the graphene oxide.

[0014] Suitable examples of infrared dyes include, but are not limited to, polymethyl indoliums, metal complex IR dyes, indocyanine green, polymethine dyes, croconium dyes, cyanine dyes, merocyanine dyes, squarylium dyes, chalcogenopyryloarylidene dyes, metal thiolate complex dyes, bis (chalcogenopyrylo) polymethine dyes, oxyindolizine dyes, bis (aminoaryl) polymethine dyes, indolizine dyes, pyrylium dyes, quinoid dyes, dyes including a barbituric group, quinone dyes, phthalocyanine dyes, naphthalocyanine dyes, azo dyes,

(metalized) azomethine dyes and combinations thereof. The cyanine dyes including five, seven or nine methine-groups disclosed in US 6 515 811 in column 3 to column 40 having an absorption maximum in the wavelength region of 700 to 1200 nm; the infrared dyes having a chemical structure A-B-C disclosed in EP 2 722 367 [044] to [0081] and the dyes disclosed in EP 1 093 015 and in EP 719 304 are preferred dyes.

[0015] Cyanine dyes are particularly preferred. The dyes described in EP 1 614 541 and PCT 2006/063327 which become

intensively colored after exposure by infrared irradiation or heating and thereby form a visible image are of special interest. Examples of such cyanine dyes are disclosed in EP-A 1 142 707, paragraph [143] , EP-A 1 614 541 (page 20 line 25 to page 44 line 29), EP 1 736 312 (paragraphs [0014] to [0021]), EP 1 910 082 and WO 2010/031758 page 6 to page 35. The latter application discloses infrared dyes which result in a higher sensitivity and contain a substituent selected from bromo and iodo.

[0016] Other preferred IR-dyes are those disclosed in the EP 2

072 570. These infrared dyes have a structural element according to the following Formula:

SH EET I NCORPORATED BY REFERENCE (RU LE 20.6)

wherein

B represents hydrogen, halogen or a monovalent organic group; Y and Y' independently represent -CH- or -N- ;

R ^x and R ^x' independently represent hydrogen, an optionally substituted alkyl or aryl group or represent the necessary atoms to form a ring; and

* represent the linking positions to the rest of the infrared dye .

[0017] The monovalent organic group preferably represents an

a b optionally substitued alkyl, aralkyl or aryl group, -OR , -SR , -S0 ₂ R ^b , -NR ^b R ^C , -NR ^b (S0 ₂ R ^d ) or -NR ^b (C0 ₂ R ^e ) wherein R ^a and R ^C represent an optionally substituted aryl group; R ^b represents an optionally substituted alkyl, aralkyl, aryl or heteroaryl group, R ^d represents an optionally substituted alkyl or aryl group or -NR ¹¹ R ^l2 wherein R ¹¹ and R ^l2 independently represent hydrogen, an optionally substituted alkyl or aryl group and R ^e represents an optionally substituted alkyl group. Specific examples of suitable dyes are given in [0025] of EP 2 072 570.

[0018] IR-dyes disclosed in EP 1 736 312 in [0017] to [0025] wherein at least one group transformes by a chemical reaction induced by exposure to IR radiation or heat into a group which is a stronger electron-donor, are also preferred. Other preferred IR-dyes are N-meso substituted cyanine, merocyanine or oxonole dyes

including electron withdrawing groups and have a structural element according to one of the following Formula's, as disclosed in WO 2009/080689:

SHEET I NCORPORATED BY REFERENCE (RU LE 20.6)

Wherein

A represents hydrogen, halogen, -NR^-CO-R ² or -NR^-SC^R ³ ;

R ¹ represents hydrogen or an optionally substituted alkyl or (hetero)aryl group, S0 ₃ ^~ , COOR ⁴ or forms together with R ² or R ³ a ring structure ;

R ² and R ³ independently represent an optionally substituted alkyl or (hetero)aryl group, OR ⁵ , NR ⁶ R ⁷ or CF ₃ ;

R ⁵ represents an optionally substituted alkyl or (hetero)aryl group ;

R ⁶ and R ⁷ independently represent hydrogen, an optionally substituted alkyl or (hetero)aryl group, or form a ring structure together ;

R ^Y and R ^y independently represent hydrogen, an optionally substituted alkyl group or represent the necessary atoms to form an optionally substituted ring structure, preferably an optionally substituted 5- or 6-membered ring; most preferably an optionally substituted 5-membered ring;

and * represent the linking positions to the rest of the IR dye .

[0019] More preferably, A represents -NR ⁸ -CO-OC (CH ₃ ) ₃ ; -NR ⁸ -S0 ₂ - CF ₃ or -NR ⁸ -S0 ₂ -C ₆ H ₄ -R ⁹ , wherein R ⁸ and R ⁹ independently represent hydrogen or an alkyl group. For example -NCH ₃ -CO-OC (CH ₃ ) ₃ -, -NCH ₃ - S0 ₂ -CF ₃ or -NCH ₃ -S0 ₂ -C ₆ H ₄ -CH ₃ are particularly preferred groups.

Specific dyes are disclosed on page 18 line 1 to page 21 line 5 and on page 26 line 5 to page 33 line 10 of WO2009/080689. For example, the dyes according to the following formula are particularly preferred:

Wherein

A and R ^y and R ^Y are as defined above;

T and Ί" independently represent one or more substituents or an annulated ring such as one or more optionally substituted 5- or 6-membered rings;

Z and Z' independently represent -0-, -S-, -CR ¹⁰ R ^1:L C- or -CH=CH-

10 11

wherein R and R independently represent an alkyl or aryl group; preferably R ¹⁰ and R ¹¹ independently represent an alkyl group; most preferably R ¹⁰ and R ¹¹ independently represent a methyl or ethyl gorup;

z z '

R and R independently represent an optionally substituted alkyl group; preferably a methyl, ethyl, or a SO3 substitued alkyl group such as -C ₂ H4-S0 ₃ ^~ , -C ₃ H ₆ -S0 _3/ -C ₄ H ₈ -S0 ₃ ^~ or -C ₅ H ₁₀ - S0 ₃ ^" ;

X renders the dye neutral; preferably X represents a halide anion such as Cl ^~ , Br or I , a sulfonate anion such as CH ₃ S0 ₃ ,

CF3SO3 , p-toluene sulfonate, tetrafluoroborate or

hexafluorophosphate anion. ] Specific structures of suitable dyes include: - 9 -

[0021] The alkyl group referred to herein is preferably a Ci to

C ₆ -alkyl group such as for example methyl; ethyl; propyl; n-propyl; isopropyl; n-butyl; isobutyl; tertiary-butyl; n-pentyl; 1,1- dimethyl -propyl ; 2 , 2 -dimethylpropyl or 2 -methyl -butyl . The aryl group is preferably a phenyl, naphthyl , benzyl, tolyl, ortho- meta- or para-xylyl, anthracenyl or phenanthrenyl . A phenyl group or naphthyl group are most preferred. The heteroaryl group referred to herein is preferably a five- or six-membered ring substituted by one, two or three oxygen atoms, nitrogen atoms, sulphur atoms, selenium atoms or combinations thereof. Examples include pyridyl, pyrimidyl, pyrazoyl , triazinyl, imidazolyl, (1,2,3,)- and (1,2,4)- triazolyl, tetrazolyl, furyl, thienyl, isoxazolyl, thiazolyl and carbazoyl .

[0022] The optionally substituted 5- or 6-membered ring preferably represent an aryl or heteroaryl group.

[0023] The aralalkyl group referred to herein is preferably a phenyl or naphthyl group including one, two, three or more Ci to C ₆ - alkyl groups . Suitable aralkyl groups include for example phenyl groups or naphthyl groups including one, two, three or more Ci to C ₆ -alkyl groups.

[0024] The optional substituents mentioned above are preferably selected from an alkyl group such as a methyl, ethyl, n-propyl, isopropyl, n-butyl, 1-isobutyl, 2-isobutyl and tertiary-butyl group; an ester, amide, ether, thioether, ketone, aldehyde, sulfoxide, sulfone, sulfonate ester or sulphonamide group, a halogen such as fluorine, chlorine, bromine or iodine, -OH, -SH, - CN and -N0 ₂ , and/or combinations thereof. [0025] Suitable examples of IR-pigments include, organic pigments, inorganic pigments, carbon black, metallic powder pigments and fluorescent pigments. Specific examples of organic pigments include quinacridone pigments, quinacridonequinone pigments, dioxazine pigments, phthalocyanine pigments,

anthrapyrimidine pigments, anthanthrone pigments, indanthrone pigments, flavanthrone pigments, perylene pigments,

diketopyrrolopyrrole pigments, perinone pigments, quinophthalone pigments, anthraquinone pigments, thioindigo pigments,

benzimidazolone pigments, isoindolinone pigments, azomethine pigments, and azo pigments.

[0026] In a preferred embodiment of the present invention, the pigments have a hydrophilic surface. The hydrophilicity of the surface may be formed by the presence of hydrophilic groups, such as anionic or non- ionic groups, on the surface of the pigment particle. A hydrophilic surface may be formed by surface treatment, coating or adsorption of compounds such as hydrophilic polymers, reactive materials (e.g. silane coupling agent, an epoxy compound, polyisocyanate , or the like), surfactants (e.g. anionic or non- ionic surfactants) or water soluble salts (e.g. salts of phosphoric acid) . Typical hydrophilic polymers are polymers or copolymers having anionic groups such as carboxylic acid, sulphonic acid, phosphonic acid, phosphoric acid, or salts thereof, or having a polyalkylene oxide group such as polyethyleneoxide . Carbon

dispersions in water such as CAB O JET 200 and phthalocyanine pigment dispersions in water such as CAB O JET 250, both

commercially available from CABOT, are most preferred. Suitable examples of pigments with surface treatment are the modified pigments described in WO 02/04210 and EP 1 524 112.

[0027] The pigments preferably have a particle size which is preferably less than 10 μπι, more preferably less than 5 μτη and especially preferably less than 3 μπι. Preferably, the pigment is dispersed in a liquid, preferably an aqueous liquid. Such aqueous liquids include water and mixtures of water with water- miscible organic solvents such as alcohols e.g. methanol, ethanol, 2- propanol, butanol , iso-amyl alcohol, octanol, cetyl alcohol etc; glycols e.g. ethylene glycol; glycerine; N-methyl pyrrolidone ; methoxypropanol ; and ketones e.g. 2-propanone and 2-butanone etc. The dispersion preferably includes one or more compounds which stabilise the dispersion and prevents coalescing of the particles. Suitable dispersing agents are surfactants and/or polymers which are soluble in the dispersion liquid.

[0028] The amount of IR-absorbing compound in the composition is preferably at least 4 % by weight, more preferred at least 6 % by weight, and most preferably at least 10 % by weight. In a preferred embodiment, the amount of IR-absorbing compound in the composition is preferably between 5 and 50 % by weight, more preferably between 8 and 40 % by weight and most preferably between 10 and 20 % by weight. These amounts are relative to the

composition as a whole.

[0029] The composition may also contain one or more additional ingredients. For example, one or more binders, polymer particles such as matting agents and spacers, surfactants such as perfluoro surfactants, silicon or titanium dioxide particles, or colorants are well-known components.

[0030] According to the present invention there is also provided a method for making graphene or graphene-like structures comprising the steps of exposing the composition as disclosed above including graphite oxide and an infrared absorbing compound directly with heat or indirectly by visible and/or infrared light, preferably near infrared light. Preferably, before the exposure step, the composition as disclosed above including graphite oxide and an infrared absorbing is applied onto a support and dried. The composition may be applied on to the support by wet coating or by other known methods such as for example vapor deposition, jetting or spray coating. While applying the coating solution, a roller for rubbing and/or brushing the coating may be used. Preferable, the coating layer, i.e. the applied composition, has a thickness upto 10 μτη, more preferably upto 5 μπι. Alternatively, the coating layer preferably has a thickness between 0.01 μπι to 1 μπι, more preferably bewteen 0.02 μπι to 0.5 μτη and most preferably between 0.03 μπι to 0.1 μχα.

[0031] An example of a spray nozzle which can be used in the spraying technique, is an air assisted spray nozzle of the type SUJ1, commercially available at Spraying Systems Belgium, Brussels. The spray nozzle may be mounted on a distance of 50 mm to 200 mm between nozzle and receiving substrate. The flow rate of the spray solution may be set to 7 ml/min. During the spray process an air pressure in the range of 4.80x10^ Pa may be used on the spray head. This layer may be dried during the spraying process and/or after the spraying process. Typical examples of jet nozzles which can be used in the jetting technique, are ink-jet nozzles and valve-jet nozzles.

[0032] The composition of the present invention can be exposed directly with heat, e.g. by means of a thermal head, or indirectly by infrared light, preferably near infrared light. Preferably, the composition is image-wise exposed producing hydrophobic graphene at the exposed areas. The infrared light is converted into heat by an IR light absorbing compound as discussed above. Any source that provides a suitable wavelength of light may be used in the practice of the invention. The composition of the present invention can be exposed to infrared light by means of e.g. LEDs or an infrared laser. Preferably, the light used for the exposure is a laser emitting near infrared light having a wavelength in the range from about 700 to about 1500 nm, e.g. a semiconductor laser diode, a Nd:YAG or a Nd:YLF laser. The laser power is determined by the pixel dwell time of the laser beam, which is determined by the spot diameter (typical value of modern plate-setters at l/e ² of maximum intensity : 10-25 μπι) , the scan speed and the resolution of the exposure apparatus (i.e. the number of addressable pixels per unit of linear distance, often expressed in dots per inch or dpi; typical value : 1000-4000 dpi) . The power of the laser radiation is

preferably in the range from about 1 Watt (W) to about 10 W, preferably in the range from about 2W to about 9 W, more preferably in the range from about 3W to about 8 W, i.e. about 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 W. The frequency (i.e. the number of cycles per second, "hertz" or "Hz") is preferably in the range from about 10 to about 50 Hz, more preferably from about 20 to about 40 Hz, and most preferably about 30 Hz. It is up to the person skilled in the art to adapt the above described variables, i.e. wavelength, power and frequency, which are interdependent.

[0033] The support may be a transparent polymeric support such as a transparent axially stretched polyester support. Suitable transparent polymeric supports include cellulose acetate propionate or cellulose acetate butyrate, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyamides,

polycarbonates, polyimides, polyolefins, polyvinylchlorides , polyvinylacetals , polyethers and polysulphonamides . The transparent polymeric support may be provided with a hydrophylic layer such as a cross- linked hydrophilic layer obtained from a hydrophilic binder cross -linked with a hardening agent such as formaldehyde, glyoxal, polyisocyanate or a hydrolyzed tetra-alkylorthosilicate . The hydrophilic binder may for example be a hydrophilic (co) polymer such as homopolymers and copolymers of vinyl alcohol, acrylamide, methylol acrylamide, methylol methacrylamide , acrylate acid, methacrylate acid, hydroxyethyl acrylate, hydroxyethyl methacrylate or maleic anhydride/vinylmethylether copolymers.

[0034] Preferably, the support is a metal support such as aluminium or stainless steel. The support can also be a laminate comprising an aluminium foil and a plastic layer, e.g. polyester film. Preferably, the support is aluminium, more preferred grained and anodized aluminium. The aluminium is preferably grained by electrochemical graining, and preferably anodized by means of anodizing techniques employing phosphoric acid or a sulphuric acid/phosphoric acid mixture. Methods of both graining and

anodization of aluminium are very well known in the art. The grained and anodized aluminium support may be post-treated to improve the hydrophilic properties of its surface.

[0035] The support may be provided with one or more so-called primer or subbing layers which improves the adhesion of the other layers to the support, or an anti -halation layer containing dyes or pigments which absorb any light that has passed the light -absorbing layer (s) . Useful subbing layers for this purpose are well known in the photographic art and include, for example, polymers of

vinylidene chloride such as vinylidene

chloride/acrylonitrile/acrylic acid terpolymers or vinylidene chloride/methyl acrylate/itaconic acid terpolymers. Typpicaly, a subbing layer has a dry thickness of no more than 2 μτη or

preferably no more than 200 mg/m ² . [0036] To protect the surface of the coated composition, in particular from mechanical damage, a protective layer may also optionally be applied. The protective layer generally comprises at least one water-soluble polymeric binder, such as polyvinyl alcohol, polyvinylpyrrolidone, partially hydrolyzed polyvinyl acetates, gelatin, carbohydrates or hydroxyethylcellulose , and can be produced in any known manner such as from an aqueous solution or dispersion which may, if required, contain small amounts, i.e. less than 5% by weight, based on the total weight of the coating solvents for the protective layer, of organic solvents. The thickness of the

protective layer can suitably be any amount, advantageously up to 5.0 μιη, preferably from 0.05 to 3.0 μπι, particularly preferably from 0.10 to 1.0 μτη.

[0037] In a specific embodiment, the exposed composition may be developed by supplying to the coated composition an aqueous alkaline solution, and/or a suitable solvent, and/or a gum solution and/or by rinsing it with plain water or an aqueous liquid, whereby the non- exposed areas of the coated composition are removed. The gum solution which can be used in the development step, is typically an aqueous liquid which comprises one or more surface protective compounds that are capable of protecting the imaged areas of the composition against contamination or damaging. Suitable examples of such compounds are film-forming hydrophilic polymers or surfactants. The gum solution has preferably a pH from 4 to 10, more preferably from 5 to 8. Preferred gum solutions are described in EP 1,342,568.

[0038] The developing step may be combined with mechanical rubbing, e.g. by a rotating brush. During the development step, any water-soluble protective layer present is preferably also removed. The development step with an aqueous alkaline solution may be followed by a rinsing step and/or a gumming step.

[0039] The coated composition can, if required, be post-treated with a suitable correcting agent or preservative as known in the art .

[0040] The composition of the current invention can be used as a coating for a lithographic printing plate. Furthermore this switch is also a isolation - conductivity switch. Therefore this principle can be suitably used for the preparation of flexible electronics and other conductive materials.

EXAMPLES .

1. Preparation of the support

A 0.3 mm thick aluminium foil was degreased by spraying with an aqueous solution containing 34 g/1 NaOH at 70 °C for 6 seconds and rinsed with demineralised water for 3.6 seconds. The foil was then electrochemically grained during 8 seconds using an alternating current in an aqueous solution containing 15 g/1 HC1, 15 g/1 S0 ₄ ^2~ ions and 5 g/1 Al ³⁺ ions at a temperature of 37 °C and a current density of about 100 A/dm ² (charge density of about 800 C/dm ² ) .

Afterwards, the aluminium foil was desmutted by etching with an aqueous solution containing 6.5 g/1 of sodium hydroxide at 35°C for 5 seconds and rinsed with demineralised water for 4 seconds. The foil was subsequently subjected to anodic oxidation during 10 seconds in an aqueous solution containing 145 g/1 of sulfuric acid at a temperature of 57 °C and an anodic charge of 250 °C/dm ² , then washed with demineralised water for 7 seconds and dried at 120°C for 7 seconds .

The support thus obtained (support S-00) was characterised by a surface roughness R _a of 0.45-0.50 μτη (measured with interferometer NT3300 and had an anodic weight of about 3.0 g/m ² (gravimetric analysis) .

2. Test samples TS-00 to TS-03

The test samples TS-00 to TS-03 were produced by applying a coating solution respectively onto the above described support S-00 and on a PET substrate by means of a semi -automated coating device. The coating solutions were applied at a wet coating thickness of 34 μια and then dried at 60°C for 3 minutes. The dry coating weight in mg/m ² of each of the ingredients is indicated in Table 1.

The coating solutions contain the ingredients as defined in Table 1, dissolved in water. Table 1: dry coating weight of the coating compositions.

*: active ingredients in the coating

(1) Aqueous dispersion of graphite oxide; commercially available from Graphenea ;

(2) surfactant commercially available from Merck KGaA;

(3) polystyrene sulfonic acid;

(4) see Table 2;

Table 2: Test samples TS-00 to TS-

(1) IR-01: dispersion in water; may be prepared by well known synthesis methods such as for example disclosed in EP 2 072 570;

(2) IR-02: Dispersion in water, , synthesis as described in WO2009/080689, Example 15; Preparation of D-09, page 48:

(3) CAB-O-JET 300, 15%: carbon black; commercially available from CABOT

CORPORATION;

3. Visual appearance of the graphite oxide coatings

The visual evaluation of the coating was determined by

observing (i) the homogeneity of the coating, (ii) the level of overly concentrated dark regions of graphite oxide and (iii) the level of uncoated regions on the substrate . A scale ranging from 1 (= bad coating appearance) to 5 (= excellent coating appearance) was employed. The results of the evaluation are given in Table 3.

Table 3 : Visual evaluation of graphite oxide coatings on the Al support S-00 and on the PET support.

Visual appearance*

Test Sample

AL support PET support

TS-00 3.5 4.0

Reference

TS-01 3.5 4.0

inventive

TS-02 3.5 3.5

inventive

TS-03 4.5 4.5

inventive 1 = unhomogeneous coating including a high level of uncoated areas and a high level of overly concentrated regions;

2 = unhomogeneous coating including many uncoated areas and many overly concentrated regions;

3 = unhomogeneous to homogeneous coating including some uncoated areas and some overly concentrated regions;

4 = rather homogeneous coating including only a few overly concentrated regions;

5 = complete homogeneous coating evenly colored (no overly concentrated regions) .

The results indicate that the reference test sample and the test samples including a coating including graphite oxide and an infrared absorbing compound are well-coatable on both the Al and the PET support .

4. Image-wise exposure of the Test Samples TS-00 to TS-03

The test samples TS-00 to TS-03 were image-wise exposed at a range of energy densities (300 mJ/cm ² to 200 mJ/cm ² ) with ^' a Creo Trendsetter, a platesetter having a 40 infrared laser head (830 nm) commercially available from Eastman Kodak Corp.

Six different irradiation energies were tested to determine the the ability of the IR-absorbing compounds to show an improvement in the graphite oxide to graphene or graphene- like structures switch in comparison to the reference test TS-00 where no IR-absorbing compound is present. The evaluation of the switch was visual:

graphite oxide appears brownish whereas the graphene/graphene-like structures obtained after exposure are darker (black) . The results of the visual evaluation is given in Table 4.

Table 4: Evaluation of the graphite oxide to graphene switch

Exposure energy density

Test sample mJ/cm ² Result-S*

300 280 260 240 220 200

Reference + + +

TS-00

TS-01 ++ ++ +++ +++ +++ +++

TS-02 ++ ++ +++ +++ +++ +++

TS-03 ++ + + + + +

*: - : no clear graphite oxide to grapheme/graphene-like structures

switch;

+ : clear graphite oxide to garphene/graphene-like structures switch;

++: even more pronounced graphite oxide to graphene/graphene-like structures switch;

+++: excellent graphite oxide to grapheme/graphene-like structures switch.

The results show that at the lower exposure energies - i.e. 200 mJ/cm ² to 240 mJ/cm ² - there is no clear graphite oxide to graphene or graphene- like structures switch of the test sample TS-00 while at the higher exposure energies - i.e. 260 mJ/cm ² to 300 mJ/cm ² - a clear switch occurs. The IR-absorbing compounds IR-01 and IR-02 (test samples TS-01 and TS-02) improve the irradiation quality compared to the reference test sample TS- 00. The IR-pigment CABOJET-O-JET 300 (test sample TS-03) also improves the irradiation quality, especially at the lower exposure energies 220 mJ/cm ² to 240 mJ/cm ² .

Furthermore, the infrared absorbing compounds allow a large

operating window as the graphite oxide to graphene switch is

obtained at exposure energies ranging from 200 to 300 mJ/cm ² .