WO2018007355A1 - Coating containing metal particles - Google Patents

Coating containing metal particles Download PDF

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Publication number
WO2018007355A1
WO2018007355A1 PCT/EP2017/066575 EP2017066575W WO2018007355A1 WO 2018007355 A1 WO2018007355 A1 WO 2018007355A1 EP 2017066575 W EP2017066575 W EP 2017066575W WO 2018007355 A1 WO2018007355 A1 WO 2018007355A1
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WO
WIPO (PCT)
Prior art keywords
coating
substrate
range
layer
μιη
Prior art date
Application number
PCT/EP2017/066575
Other languages
French (fr)
Inventor
Herve Dietsch
Jens Carsten RÖDER
Frank Bartels
Original Assignee
Basf Se
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Basf Se filed Critical Basf Se
Publication of WO2018007355A1 publication Critical patent/WO2018007355A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B17/00—Layered products essentially comprising sheet glass, or glass, slag, or like fibres
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B17/00—Layered products essentially comprising sheet glass, or glass, slag, or like fibres
    • B32B17/06—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material
    • B32B17/10—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material of synthetic resin
    • B32B17/10005—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material of synthetic resin laminated safety glass or glazing
    • B32B17/1055—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material of synthetic resin laminated safety glass or glazing characterized by the resin layer, i.e. interlayer
    • B32B17/10614—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material of synthetic resin laminated safety glass or glazing characterized by the resin layer, i.e. interlayer comprising particles for purposes other than dyeing
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B32B17/00—Layered products essentially comprising sheet glass, or glass, slag, or like fibres
    • B32B17/06—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material
    • B32B17/10—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material of synthetic resin
    • B32B17/10005—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material of synthetic resin laminated safety glass or glazing
    • B32B17/1055—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material of synthetic resin laminated safety glass or glazing characterized by the resin layer, i.e. interlayer
    • B32B17/10761—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material of synthetic resin laminated safety glass or glazing characterized by the resin layer, i.e. interlayer containing vinyl acetal
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    • B32B23/08—Layered products comprising a layer of cellulosic plastic substances, i.e. substances obtained by chemical modification of cellulose, e.g. cellulose ethers, cellulose esters, viscose comprising such cellulosic plastic substance as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
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    • B32B27/302—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers comprising aromatic vinyl (co)polymers, e.g. styrenic (co)polymers
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    • B32B27/306—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers comprising vinyl acetate or vinyl alcohol (co)polymers
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    • B32B27/34—Layered products comprising a layer of synthetic resin comprising polyamides
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    • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B32B2255/00—Coating on the layer surface
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B32B2255/00—Coating on the layer surface
    • B32B2255/10—Coating on the layer surface on synthetic resin layer or on natural or synthetic rubber layer
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    • B32B2255/00—Coating on the layer surface
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    • B32B2255/205—Metallic coating
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Definitions

  • the present invention relates to an article comprising a layer assembly consisting of a substrate comprising polyvinyl butyral and a coating arranged on a surface of said substrate, said coating comprising a matrix formed of one or more organic polymers and metal nanoobjects dispersed within said matrix, and to a process for preparing said article.
  • WO 2015/109198 discloses a coated polyvinyl butyral (PVB) film or sheet comprising a PVB layer that includes no plasticizer or less than about 5 wt.-% of a volatile plasticizer; and a conductive or reflective coating; wherein the conductive or reflective coating directly coats the PVB layer, wherein said coating e.g. comprises silver or a silver alloy, and a method for coating a PVB film or sheet, said method comprising providing a PVB film or sheet that includes little or no volatile material and directly applying in a vacuum a conductive or reflective coating to the PVB film or sheet. Said coating is deposited on the PVB film or sheet e.g. by physical vapor deposition or by magnetron sputtering.
  • PVB polyvinyl butyral
  • WO 2015/109198 involves certain disadvantages and constraints.
  • Commercially available films, sheets or foils made of PVB typically contain plasticizers in order to render said films, sheets or foils flexible (e.g. to allow bending without wrinkling, e.g. bending around the complex curves typical of glass in vehicle applications), soft and elastically.
  • plasticizers e.g. to allow bending without wrinkling, e.g. bending around the complex curves typical of glass in vehicle applications
  • polymer substrates comprising plasticizers are virtually impossible to be used as substrates for physical vapor deposition in high vacuum due to softness, extensibility and pliability.
  • vacuum deposition is problematic because of the outgas- sing of volatile impurities and/or the plasticizer itself, unless the plasticizer has very low volatility.
  • limitation of the amount of volatile plasticizers in the PVB layer to 5 wt.-% or less, and preferably complete omitting of volatile plasticizers in the PVB layer, is required according to WO 2015
  • polyvinyl butyral is obtained by acidic hydrolysis (e.g. using hydrochloric acid) of polyvinyl acetate and subsequent (at least partial) acetalization of the obtained polyvinyl alcohol with butanal (butyraldehyde).
  • acidic hydrolysis e.g. using hydrochloric acid
  • butanal (butyraldehyde) e.g. using butanal (butyraldehyde).
  • the obtained product often contains residues of hydrochloric acid and/or acetic acid.
  • PET polyethylene terephthalate
  • a PET foil coated with a conductive coating to a curved structure, e.g. a curved glass structure, without formation of wrinkles, which may introduce optical heterogeneities and disrupt conduction paths.
  • An important application wherein polyvinylbutyral is virtually indispensible is safety glass.
  • Safety glass as typically used e.g.
  • a sandwich structure consisting a first and a second pane of floatglass and a foil comprising polyvinylbutyral between said first and said second pane of floatglass, wherein said foil is fused to said fist pane and to said second pane of floatglass by heating the sandwich structure in an autoclave.
  • float glass and polyvinylbutyral After fusing, float glass and polyvinylbutyral have the same refractive index, thus avoiding optical heterogeneity.
  • Said article comprises a layer assembly consisting of
  • said coating comprising a matrix formed of one or more organic polymers
  • matrix metal nanoobjects having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 ⁇ to 100 ⁇ , in each case determined by transmission electron microscopy.
  • an article according to the present invention consists of a layer assembly consisting of
  • said coating comprising a matrix formed of one or more organic polymers
  • the coating is a composite comprising (i) an optically transparent contiguous solid phase (herein referred to as a matrix) and (ii) a conductive network of metal nanoobjects which extends throughout said matrix.
  • the matrix is formed of one or more optically transparent polymers (polymers having a light transmission of 80 % or more as measured according to ASTM D1003 (procedure A)).
  • Said matrix binds and accommodates the metal nanoobjects within the coating, fills the voids between said metal nanoobjects, provides mechanical integrity and stability to the coating and binds the coating to the surface of the substrate.
  • the metal nanoobjects dispersed within said matrix form a conductive network enabling the flow of electrons between adjacent and overlapping electroconductive nanoobjects within the coating. Due to the small dimensions of the metal nanoobjects, their influence on the optical behavior of the coating is minor, thus allowing for the formation of a coating which is optically transparent and electroconductive. Accordingly, said coating is also referred to as an "optically transparent conductive layer". In certain cases, said coating consists of
  • matrix metal nanoobjects having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 ⁇ to 100 ⁇ , in each case determined by transmission electron microscopy.
  • the coating comprises a matrix formed of one or more organic polymers (hereinbelow also referred to as "organic polymer matrix").
  • organic polymer matrix a matrix formed of one or more organic polymers (hereinbelow also referred to as "organic polymer matrix”).
  • polymer as used herein includes co-polymers (polymers obtained by co-polymerization of two or more kinds of co- polymerizable monomers).
  • said polymer matrix comprises one or more polymers selected from the group consisting of cellulose, cellulose alkyl ethers, cellulose hydroxyalkyi ethers, cellulose esters, dextranes, polyacrylamides, polyvinylalcohol, polyvinylpyrrolidone, polystyrenesulfonic acid, polystyrene, styrene/(meth)acrylic copolymers, styrene- butadiene copolymers, polyacrylates, polymethacrylates, copolymers of acrylates and methacrylates.
  • polymers selected from the group consisting of cellulose, cellulose alkyl ethers, cellulose hydroxyalkyi ethers, cellulose esters, dextranes, polyacrylamides, polyvinylalcohol, polyvinylpyrrolidone, polystyrenesulfonic acid, polystyrene, styrene/(meth)acrylic copolymers, s
  • said coating comprises polyvinylbutyral in an amount of less than 3 wt.-%, further preferably less than 1 wt.-%, particularly less than 0.5 wt.-%, based on the total weight of said coating.
  • the polymer matrix does not comprise polyvinylbutyrals.
  • the polymer matrix does not comprise any polyvinylacetals.
  • One kind of preferred matrix-forming polymers are styrene/(meth)acrylic copolymers having a number average molecular weight in the range of from 500 g/mol to 22000 g/mol
  • the term "(meth)acrylic” includes “methacrylic” and "acrylic”.
  • each molecule comprises or consists of units derived from monoalkenyl aromatic monomers and units derived from (meth)acrylic monomers, in copolymerized form.
  • Such styrene/(meth)acrylic copolymers are obtainable by copolymerisation of one or more kinds of monoalkenyl aromatic monomers with one or more kinds of (meth)acrylic monomers.
  • each molecule comprises or consists of units C1 derived from monoalkenyl aromatic monomers MC1
  • R-i independently from the R-i of each other unit C1 , is selected from the group consisting of hydrogen and alkyl (including unbranched alkyl, preferably methyl, and branched alkyl, preferably tert-butyl)
  • R 2 independently from the R 2 of each other unit C1 , is selected from the group consisting of halogen (preferably chlorine) and alkyl (preferably methyl), and R 2 is situated in a position selected from the group consisting of ortho, meta and para;
  • R 3 independently from the R 3 of each other unit C2, is selected from the group consisting of hydrogen, methyl, halogen (preferably chlorine) and cyano,
  • R 4 independently from the R 4 of each other unit C2, is selected from the group consisting of -COOH,
  • X is a cation selected from alkali metal cations, ammonium cations and substituted ammonium cations,
  • R 5 is selected from the group consisting of branched and unbranched alkyl groups, branched and unbranched alkenyl groups, branched and unbranched alkinyl groups, cycloalkyl groups, aralkyl groups, aralkenyl groups, furfuryl, tetrahydrofurfuryl, isopropylidene glyceryl, glycidyl and tetrahydropyranyl, wherein said branched and unbranched alkyl groups, alkenyl groups and alkinyl groups include branched and un- branched alkyl groups, alkenyl groups and alkinyl groups substituted with one or more groups selected from the group consisting of hydroxy, alkoxy, phenoxy, halogen, sulfo, nitro, oxazolidinyl, monoalkylamino and dialkylamino groups
  • R 6 and R 7 are independently selected from the group consisting of hy- drogen, alkyl and phenyl.
  • Such styrene/(meth)acrylic copolymers are obtainable by copolymerisation of one or more kinds of monoalkenyl aromatic monomers MC1 having the formula
  • R-i independently from the R-i of each other monomer MC1 , is selected from the group consisting of hydrogen and alkyl (including unbranched alkyl, preferably methyl, and branched alkyl, preferably tert-butyl) and wherein R 2 , independently from the R 2 of each other monomer MC1 , is selected from the group consisting of halogen (preferably chlorine) and alkyl (preferably methyl) and R 2 is situated in a position selected from the group consisting of ortho, meta and para, with one or more kinds of (meth)acrylic monomers MC2 having the formula
  • R 3 independently from the R 3 of each other monomer MC2 is selected from the group consisting of hydrogen, methyl, halogen (preferably chlorine) and cyano
  • R 4 independently from the R 4 of each other unit MC2 is selected from the group consisting of
  • X is a cation selected from alkali metal cations, ammonium cations and substituted ammonium cations,
  • R 5 is selected from the group consisting of branched and unbranched alkyl groups, branched and unbranched alkenyl groups, branched and unbranched alkinyl groups, cycloalkyl groups, aralkyl groups, aralkenyl groups, furfuryl, tetrahydrofurfuryl, isopropylidene glyceryl, glycidyl and tetrahydropyranyl, wherein said branched and unbranched alkyl groups, alkenyl groups and alkinyl groups include branched and un- branched alkyl groups, alkenyl groups and alkinyl groups substituted with one or more groups selected from the group consisting of hydroxy, alkoxy, phenoxy, halogen, sulfo, nitro, oxazolidinyl, monoalkylamino and dialkylamino groups
  • R 6 and R 7 are independently selected from the group consisting of hy- drogen, alkyl and phenyl.
  • (meth)acrylic monomer MC2 as employed herein includes acrylic acid and salts, esters and amides of acrylic acid, acrylonitrile and acrolein, as well as methacrylic acid and salts, esters and amides of methacrylic acid, methacrylonitrile, and methacrolein.
  • (Meth)acrylic monomers wherein R 3 is hydrogen or methyl, resp., and R 4 is -COOR 5 as defined above are esters of acrylic acid or esters of methacrylic acid, resp.
  • (Meth)acrylic monomers wherein R 3 is hydrogen or methyl, resp., and R 4 is -COOX as defined above, are salts of acrylic acid or salts of methacrylic acid, resp.
  • Styrene/(meth)acrylic copolymers obtainable by copolymerization of one or more kinds of monoalkenyl aromatic monomers MC1 and one or more (meth)acrylic monomers from the group consisting of acrylonitrile and methacrylonitrile and no other (meth)acrylic monomers MC2 are not preferred.
  • (meth)acrylic monomers selected from the group consisting of acrylonitrile and methacrylonitrile are used in combination with other (meth)acrylic monomers MC2 as defined herein.
  • (Meth)acrylic monomers wherein R 3 is hydrogen or methyl, resp., and ⁇ 3 ⁇ 4 is -NR 6 R 7 as defined above, are amides of acrylic acid or amides of methacrylic acid, resp.
  • Preferable monoalkenyl aromatic monomers MC1 are selected from the group consisting of alpha-methyl styrene, styrene, vinyl toluene, tertiary butyl styrene and ortho- chlorostyrene.
  • suitable (meth)acrylic monomers include the following methacrylate esters (methacrylic acid esters): methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, n-hexyl methacrylate, isoamyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxy propyl methacrylate, ⁇ , ⁇ -dimethylaminoethyl methacrylate,
  • methacrylate esters methacrylic acid esters
  • Typical acrylate esters employed include: methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate and n-decyl acrylate, methyl alpha-chloroacrylate, methyl 2-cyanoacrylate.
  • Suitable (meth)acrylic monomers include methacrylonitrile, methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, N,N-diethylmethacryl- amide, ⁇ , ⁇ -dimethylmethacrylamide, N-phenylmethacrylamide and methacrolein, acrylo- nitrile, acrylamide, N-ethylacrylamide, ⁇ , ⁇ -diethylacrylamide and acrolein.
  • esters of methacrylic acid or acrylic acid containing a suitable condensable cross linkable functional group may be used as the monomer.
  • esters include t-butylaminoethyl methacrylate, isopropylidene glyceryl methacrylate and oxazolidinylethyl methacrylate.
  • Typical preferred cross-linkable acrylates and methacrylates include hydroxy alkyl acry- lates, hydroxyl alkyl methacrylates and hydroxyesters of glycidyl acrylates or methacrylates.
  • preferred hydroxy functional monomers include 2-hydroxyethyl acrylate, 3-chloro-2-hydroxypropyl acrylate, 2-hydroxy-butyl acrylate, 6-hydroxyhexyl acrylate, 2-hydroxy methyl methacrylate, 2-hydroxy propyl methacrylate, 6-hydroxyhexyl methacrylate, 5,6-dihydroxyhexyl methacrylate and the like.
  • styrene/(meth)acrylic copolymer as employed herein includes copolymers obtainable from mixtures consisting of two or more (meth)acrylic monomers and one or more monoalkenyl aromatic monomers, as well as copolymers obtainable from mixtures of at least one (meth)acrylic monomer and at least one non-acrylic ethylenic monomer and one or more monoalkenyl aromatic monomers.
  • Suitable ethylenic monomers include: vinyl pyridine, vinyl pyrrolidone, sodium crotonate, methyl crotonate, crotonic acid and maleic anhydride.
  • the number average molecular weight of said styrene/(meth)acrylic copolymers is in the range of from 500 g/mol to 22000 g/mol, preferably of from 1700 g/mol to 15500 g/mol, further preferably of from 5000 g/mol to 10000 g/mol.
  • said styrene/(meth)acrylic copolymers are amphiphilic, because their molecules contain non-polar hydrophobic regions derived from the monoalkenyl aromatic monomers and polar hydrophilic regions derived from the (meth)acrylic monomers.
  • the desired amphiphilic behavior is obtainable by appropriate selection of the hydrophobic monoalkenyl aromatic monomers and the hydrophilic (meth)acrylic monomers and appropriate adjustment of the ratio between monoalkenyl aromatic monomers and (meth)acrylic monomers so that a styrene/(meth)acrylic copolymer is obtained which has an appropriate ratio between hydrophobic units derived from monoalkenyl aromatic monomers and hydrophilic units derived from (meth)acrylic monomers to allow for amphiphilic behavior of the copolymer.
  • said water-soluble styrene/(meth)acrylic copolymers behave like surfactants (tensides), i.e. they are capable of forming micelles.
  • a micelle is an aggregate formed by association of dissolved amphiphilic molecules.
  • Preferably said micelles have a diameter of up to 5 nm.
  • Typical water-soluble styrene/(meth)acrylic copolymers are known in the art and commercially available. Typically such copolymers are commercially available in the form of aqueous solutions.
  • a second kind of preferred matrix-forming polymers is crystalline cellulose.
  • said crystalline cellulose is in the form of fibers having a length in the range of from 80 nm to 300 nm and a diameter in the range of from 5 nm to 30 nm.
  • said fibers of crystalline cellulose have a length in the range of from 80 nm to 150 nm and a diameter in the range of from 5 nm to 10 nm.
  • Said fibers are also referred to as nanocrystalline cellulose or cellulose nanofibers or cellulose II (see WO 2010/127451 ). They are obtaina- ble by disrupting the amorphous domains of natural cellulose fibers and disintegration of the micrometer-sized cellulose fibers into rod-like rigid crystallites. The obtained crystallites typically have the above-mentioned dimensions.
  • crystalline cellulose fibers having the above-mentioned dimensions are obtainable by chemical treatment or by enzymatic treatment or by mechanical treatment of natural cellulose fibers or by combinations of different types of treatment, e.g. chemical treatment (e.g. with sulfuric acid or sodium chlorite) or enzymatic treatment followed by high-pressure homogenization, or by milling of natural cellulose fibers and subsequent hydrolysis to remove amorphous regions.
  • chemical treatment e.g. with sulfuric acid or sodium chlorite
  • enzymatic treatment followed by high-pressure homogenization, or by milling of natural cellulose fibers and subsequent hydrolysis to remove amorphous regions.
  • said cellulose fibers When a dispersion of fibers of crystalline cellulose in a liquid is dried (i.e. the liquid is removed from the dispersion), the cellulose fibers become packed together by capillary action during the evaporation of the water. Accordingly, said cellulose fibers are capable of forming a matrix and binding metal nanoobjects so as to form a coating as defined above. Furthermore, due to their outstanding mechanical stability, said fibers impart mechanical reinforcement to the obtained coating. Due to their external dimensions, said fibers of crystalline cellulose are nanoobjects in the sense of to ISO/TS 27687:2008 (as published in 2008), see below, and do not scatter visible light. However, said fibers of crystalline cellulose do not comprise any materials capable of allowing the flow of electrons.
  • said fibers of crystalline cellulose are fibers of sulfated crystalline cellulose. They are obtainable by treatment of cellulose with sulfuric acid. Fibers of this kind of crystalline cellulose contain sulfur in the form of sulfate groups. Especially preferred are fibers of sulfated crystalline cellulose II obtainable by be the process described in WO 2010/127451 . Said sulfated crystalline cellulose II has a degree of polymerization of 60 or below. For further details, reference is made to WO 2010/127451 .
  • the composition according to the present invention does not comprise fibers of crystalline cellulose obtained by means of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation of cellulose.
  • TEMPO 2,2,6,6-tetramethylpiperidine-1-oxyl
  • This kind of crystalline cellulose fibers exhibits a high density of carboxylate groups on their surfaces.
  • Said carboxylate groups are formed by oxidation of primary hydroxyl groups of cellulose.
  • Suitable fibers of crystalline cellulose are commercially available, e.g. from Celluforce.
  • a third kind of preferred matrix-forming polymers are polymers having a number average molecular weight of 25000 g/mol or higher in the form of dispersed particles. Preferably, the number average molecular weight of said polymer is not higher than 200000 g/mol.
  • Said polymer is either a homopolymer or a copolymer.
  • Said particles are either particles of one kind of polymer or a mixture of particles of different polymers.
  • Such particles are also referred to as polymer beads.
  • a polymer bead consists of several entangled polymer chains.
  • Said polymer beads have an average particle diameter in the range from 10 nm to 1000 nm, in particular in the range from 50 nm to 600 nm determined by dynamic light scattering on an aqueous polymer dispersion (from 0.005 to 0.01 percent by weight) at 23 °C by means of an Autosizer IIC from of Malvern Instruments, England.
  • Preferred polymers beads comprise, in copolymerized form, from 50 to 99.9% by weight of
  • (meth)acrylate includes “methacrylate” and "acrylate”.”
  • the polyacrylates are either homo- or copolymers.
  • each molecule consists of units each derived from one kind of acrylate monomer.
  • each molecule comprises or consists of units derived from different kinds of acrylate monomers in copolymerized form.
  • the polymethacrylates are either homo- or copolymers.
  • each molecule consists of units each derived from one kind of methacrylate monomer.
  • each molecule comprises or consists of units derived from differ- ent kinds of methacrylate monomers in copolymerized form.
  • each molecule comprises or consists of units derived from acrylate monomers and units derived from methacrylate monomers in copolymerized form
  • each molecule comprises or consists of units derived from monoalkenyl aromatic monomers and units derived from (meth)acrylic monomers in copolymerized form.
  • Such polymer beads are known in the art and commercially available in the form of aqueous dispersions of said polymer beads (aqueous polymer dispersions).
  • aqueous polymer dispersions typically, the dispersed polymers are present in colloidal dispersion.
  • aqueous polymer disper- sions are obtainable by polymerization of suitable monomers in an aqueous liquid phase, e.g. by means of suspension polymerization or emulsion polymerization.
  • Preferred aqueous polymer dispersions are obtainable by free-radically initiated aqueous emulsion polymerization of ethylenically unsaturated monomers.
  • the free-radically initiated aqueous emulsion polymerization is effected typically in such a way that at least one ethylenically unsaturated monomer, frequently in the presence of dispersing assistants, is distributed in a disperse manner in an aqueous medium and polymerized by means of at least one free-radical polymerization initiator.
  • dispersing assistants for further details, reference is made to US 7,999,045 B2 and the prior art cited therein.
  • An aqueous colloidal dispersion of polymer particles is also referred to as a latex.
  • Colloi- dal stability of a latex is achieved by a balancing of electrostatic repulsion, van der Waals attraction and steric attraction or repulsion.
  • the above-defined polymer dispersions typically comprise dispersing assistants which serve to ensure the stability of the aqueous polymer dispersions.
  • Suitable dispersing agents are selected from the group consisting of protective colloids and surfactants.
  • Preferred surfactants are sodium dodecylsulfate (SDS), and water soluble amphiphilic styrene/(meth)acrylic copolymers having a number average molecular weight in the range of from 500 g/mol to 22000 g/mol as defined above.
  • Said water soluble amphiphilic styrene/(meth)acrylic copolymers are preferred surfactants because they are capable of co-acting with the polymer beads in forming a matrix and binding the above-defined metal nanoobjects.
  • Further preferred matrix-forming polymers are selected from the group consisting of cellulose alkyl ethers, cellulose hydroxyalkyl ethers (e.g.
  • hydroxypropyl methyl cellulose cellulose esters (e.g. carboxymethyl cellulose), polyacrylamides, polyvinylalcohol, polyvinylpyrrolidone, polystyrenesulfonic acid, and dextranes.
  • suitable matrix-forming polymers are polyolefin copolymer resins comprising an olefin monomer and acrylic acid comonomer or (meth)acrylic acid comonomer as described in EP 2 960 310 A1.
  • the polymer matrix is formed of one or more of the above-mentioned polymers.
  • the matrix comprises polyvinylpyrrolidone (see below) and one or more further polymers, preferably one or more of the above-defined preferred polymers.
  • the polymer matrix comprises
  • Said metal nanoobjects which are dispersed within said polymer matrix have two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 ⁇ to 100 ⁇ .
  • the term "nanoobject” refers to an object having one, two or three external dimensions in the nanoscale, i.e. in the size range from approximately 1 nm to 100 nm.
  • the electroconductive nanoobjects to be used for the present invention are electroconductive nanoobjects having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 ⁇ to 100 ⁇ .
  • said two external dimensions which are in the range of from 1 nm to 100 nm are similar i.e. they differ in size by less than three times.
  • the third dimension of said electroconductive nanoobjects is significantly larger, i.e. it differs from the other two external dimensions by more than three times.
  • nanoobjects having two similar external dimensions in the nanoscale, while the third external dimension is significantly larger are generally referred to as nanofibers.
  • Electrically conductive nanofibers are also referred to as nan- owires.
  • Hollow nanofibers (irrespective of their electrical conductivity) are also referred to as nanotubes.
  • Metal nanoobjects as defined above which are to be used for the present invention typically have a cross section close to circular shape. Said cross section extends perpendicu- larly to said external dimension which is in the range of from 1 ⁇ to 100 ⁇ . Thus, said two external dimensions which are in the nanoscale are defined by the diameter of said circular cross section. Said third external dimension extending perpendicularly to said diameter is referred to as the length.
  • the coating comprises metal nanoobjects having a length in the range of from 1 ⁇ to 100 ⁇ , preferably of from 3 ⁇ to 50 ⁇ , more preferably of from 10 ⁇ to 50 ⁇ , and a diameter in the range of from 1 nm to 100 nm, preferably of from 2 nm to 50 nm, more preferably of from 15 nm to 30 nm, length and diameter in each case being determined by transmission electron microscopy.
  • metal nanoobject means that the nanoobject comprises or consists of one or more materials selected from the group consisting of metals and alloys of metals.
  • a plurality of such metal nanoobjects may form a conductive network of adjacent and overlapping nanoobjects capable of carrying an electric current throughout said matrix, provided that there is sufficient inter- connection (mutual contact) between individual metal nanoobjects so as to enable the transport of electrons along the interconnected metal nanoobjects within the network.
  • said metal nanoobjects consist of materials selected from the group consisting of silver, copper, gold, platinum, tungsten, aluminum, iron, cobalt and nickel and alloys of two or more metals selected from the group consisting of silver, copper, gold, platinum, tungsten, aluminum, iron, cobalt and nickel.
  • said metal nanoobjects are selected from the group consisting of nanowires and nanotubes.
  • Preferred nanowires comprise or consist of one or more metals selected from the group consisting of silver, copper and gold.
  • nanowires are preferred.
  • said metal nanoobjects are nanowires consisting of a metal selected from the group consisting of silver, copper, gold, platinum, tungsten, aluminum, iron, cobalt and nickel, or of an alloy of two or more metals selected from silver, copper, gold, platinum, tungsten, aluminum, iron, cobalt and nickel, wherein said nanowires preferably have a length in the range of from 1 ⁇ to 100 ⁇ , preferably of from 3 ⁇ to 50 ⁇ , more preferably of from 10 ⁇ to 50 ⁇ , and a diameter in the range of from 1 nm to 100 nm, preferably 10 nm to 50 nm, most preferably 15 nm to 30 nm, length and diameter in each case being determined by transmission electron microscopy.
  • Most preferred metal nanoobjects are silver nanowires having the above-mentioned dimensions.
  • Suitable metal nanoobjects as defined above are known in the art (see e.g. US7922787) and are commercially available.
  • Silver nanowires (as well as nanowires of other metals) are typically commercially available in the form of an aqueous dispersion wherein polyvinylpyrrolidone is adsorbed onto the surface of the silver nanowires in order to render the dispersion stable. Any matter adsorbed on the surface of the nanowires is not included in the above-defined dimensions and composition of the metal nanoobjects.
  • the silver nanowires are obtained by the procedure described by Yugang Sun and Younan Xia in Adv. Mater. 2002 14 No. 1 1 , June 5, pages 833-837.
  • the ratio between the total weight of said metal nanoobjects and the total weight of said organic polymers is in the range of from 1 : 20 to 20 : 1 , preferably in the range of from 1 : 5 to 5 : 1 .
  • the substrate comprises polyvinylbutyral (PVB) and optionally plasticizers.
  • the substrate consists of polyvinylbutyral and optionally plasticizers.
  • Polyvinylbutyrals are a class of polyvinylacetates obtainable by (at least partial) acetalisation of polyvinyl alcohol with butyraldehyde as explained above.
  • Said substrate comprising polyvinylbutyral is in the form of a sheet, a foil or a film.
  • Suitable substrates are commercially available e.g. as Mowital LPBFTM or Trosifol OGTM.
  • Such commercially available films, sheets or foils typically contain plasticizers. It is important to note that the present invention does not impose any limitation regarding the amount of plasticizers in the substrate. Thus, the amount of plasticizers can be adjusted according to the desired flexibility of the substrate.
  • said substrate comprises plasticizers in an amount of 5 % or less, based on the weight of polyvinylbutyral in said substrate.
  • said substrate has a light transmission of 80 % or more, preferably 90 % or more, further preferably 95 % or more, in each case measured according to ASTM D1003 (Procedure A) as published in November 2013, and a haze of 3 % or less, more preferably 2 % or less, further preferably 1 % or less, especially preferably of 0.5 % or less, in each case measured according to ASTM D1003 (Procedure A) as published in November 2013.
  • the above-defined coating (optically transparent conductive layer) is arranged on a surface of said substrate in such manner that the coating partially or completely covers a surface of said substrate.
  • the coating forms a pattern on said surface of said substrate.
  • the pattern may be selected from any random and non-random structures, like grids, stripes, waves, dots and circles.
  • said substrate has at least one surface which is not covered by the above-defined coating.
  • the substrate has a first surface on which said coating is arranged and a second surface opposite to said first surface, wherein on said second surface none such coating is arranged.
  • This second surface of the substrate is also referred to as the surface of the substrate facing away from said coating.
  • said substrate has a thickness in the range of from 4 ⁇ to 250 ⁇ , and/or said coating has a thickness in the range of from 50 nm to 500 nm.
  • the lower limit of the thickness of the coating is determined by the smallest dimension of the metal nanoobjects.
  • said substrate has a thickness in the range of from 4 ⁇ to 250 ⁇ , and said coating has a thickness in the range of from 50 nm to 500 nm.
  • said coating (as defined above) has
  • Light transmission refers to the percentage of an incident light which is transmitted through a medium.
  • the light transmission of the coating is 85 % or more, more preferably 90 % or more, further preferably 95 % or more, in each case measured according to ASTM D1003 (Procedure A) as published in November 2013.
  • a preferred coating exhibits a haze of 2 % or less as measured according to ASTM D1003 (Procedure A) as published in November 2013, and/or a sheet resistance of 100 Ohms/square or less as measured by the four point probe at a temperature of 23 °C and a pressure of 101.3 kPa.
  • the haze of the coating 1.8 % or less, more preferably 1.5 % or less, further preferably 1 % or less, in each case measured according to ASTM D1003 (Procedure A) as published in November 2013.
  • the sheet resistance of the coating is 100 Ohms/square or less, more preferably 80 Ohms/square or less, further preferably 40 Ohms/square or less, in each case measured by the four point probe at a temperature of 23 °C and a pressure of 101.3 kPa.
  • haze and light transmission in ASTM D1003 as published in November 2013 referred to as luminous transmittance which is the ratio of the luminous flux transmitted by a body to the flux incident upon it) by means of a hazemeter is defined in ASTM-D1003 as published in November 2013 as "Procedure A -Hazemeter”.
  • the values of haze and light transmission (corresponding to the luminous transmittance as defined in ASTM D1003 as published in November 2013) given in the context of the present invention refer to this procedure.
  • haze is an index of the light diffusion. It refers to the percentage of the quantity of light which is separated from the incident light and scattered during transmission.
  • haze is often a production concern and is typically caused by surface roughness, and by embedded particles or compositional heterogeneities in the medium.
  • haze is the scattering of light by a specimen responsible for the reduction in contrast of objects viewed through said specimen, i.e. the percent of transmitted light that is scattered so that its direction deviates more than a specified angle (2.5 °) from the direction of the incident beam.
  • the sheet resistance is a measure of resistance of a thin body (sheet) namely uniform in thickness.
  • sheet resistance implies that the current flow is along the plane of the sheet, not perpendicular to it.
  • R sh is the sheet resistance. Accordingly the sheet resistance R sh is the sheet resistance. Accordingly the sheet resistance R sh is the sheet resistance.
  • the bulk resistance R is multiplied with a dimensionless quantity (W/L) to obtain the sheet resistance R sh , thus the unit of sheet resistance is Ohms.
  • the sheet resistance is measured by means of a four point-probe at a temperature of 23 °C and a pressure of 101.3 kPa.
  • said coating exhibits one or more of the following features:
  • said coating exhibits the following features:
  • Preferred coatings according to the present invention are those wherein two or more of the above-defined preferred features are combined.
  • Preferred layer assemblies according to the present invention are those wherein two or more of the above-defined preferred features are combined.
  • a preferred article according to the present invention comprises
  • first support layer comprising a material selected from the group consisting of metals, glass and organic polymers
  • second support layer comprising a material selected from the group consisting of metal, glass and or- ganic polymers
  • said layer assembly is arranged between said first support layer and said second support layer.
  • Said first and second support layer are both in a form selected from the group consisting of foils, films, webs, panes and plates.
  • said first and said second support layer are both of the same material, the same form and have equal dimensions.
  • the materials of the support layers are selected such that at least one of said support layers has a light transmission of 80 % or more, preferably 90 % or more, measured according to ASTM D1003 (Procedure A) as published in November 2013.
  • both of said support layers has a light transmission of 80 % or more, preferably 90 % or more, measured according to ASTM D1003 (Procedure A) as published in November 2013.
  • Said support layers comprise one or more materials selected from the group consisting of metals, glasses and organic polymers.
  • Preferred types of glass are e.g. float glass, low iron float glass, heat strengthened glass and chemically strengthened glass.
  • the glass has a low-emissivity (low-e) coating, sun-protection coating or any other coating on the surface facing away from the above-described layer assembly.
  • antireflection (AR) coating can be used to enhance the transmittance through optical devices, and a variety of low refractive index, nanoporous, and/or nanostructured coatings can be applied to glass and plastic substrates (see for example: C. G. Granqvist, Transparent conductors as solar energy materials: a panoramic review, Solar Energy Mater. Solar Cells 91 , 1529-1598 (2007)). It has been demonstrated that coating both sides of a glass pane with self-assembled silica nanoparticle films made it possible to obtain a transmittance as large as 99.5% in the middle of the luminous spectrum (cf. P. Nostel, A. Roos, and B.
  • Preferred organic polymers are selected from the group consisting of polymethylmethacrylate (PMMA, commercially available e.g. as PlexiglasTM), polycarbonate (PC), polyethylene (PE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), polypropylene (PP), low density polypropylene (LDPP), polyeth- ylene therephthalate (PET), glycol modified polyethylene therephthalate, polyethylene napthalate (PEN), cellulose acetate butyrate, polylactide (PL), polystyrene (PS), polyvinyl chloride (PVC), polyimides (PI), polypropyleneoxide (PPO) and mixtures thereof.
  • PMMA polymethylmethacrylate
  • PC polycarbonate
  • PE polyethylene
  • LDPE low density polyethylene
  • LLDPE linear low density polyethylene
  • PP polypropylene
  • LDPP low density polypropylene
  • PET polyeth- ylene therephthalate
  • PEN polyethylene napthalate
  • said first support layer is attached to the above-defined coating (optically transparent conductive layer) which in turn is ar- ranged on a first surface of said substrate comprising PVB, and said second support layer is attached to said second surface of said substrate comprising PVB facing away from said coating.
  • said article comprises an adhesive layer between said coating and said first support layer and/or an adhesive layer between said substrate comprising polyvinylbutyral and said second support layer.
  • said article comprises a first adhesive layer between said coating and said first support layer and a second adhesive layer between said substrate comprising polyvinylbutyral and said second support layer.
  • the adhesives are selected such that the adhesive layer has a light transmission which does not exceed the light transmission of the support layer which is attached to the layer assembly by said adhesive.
  • Suitable adhesives are thermoplastics, e.g. polyvinylbutyral commercially available e.g. under the trade names Butvar, Mowital, Pioloform, BUTACITE, SAFLEX, S-Lec, TROSIFOL, polyvinylalcohol, polyvinylacetate, ethylene-vinylacetate-copolymers, silicones, polyurethanes, ionomer resins (commercially available e.g. under the trade name SentryGlas®) and polymethylmethacrylate (PMMA).
  • the adhesives of said first adhesive layer and said second adhesive layer have identical or different chemical composition.
  • Preferred are two identical adhesives, especially preferred are two identical adhesives from the group consisting of polyvinylbutyrals.
  • further layers are arranged between said first support layer and said coating (optically transparent conductive layer), and/or between said second support layer and said substrate comprising PVB.
  • Said further layers are herein also referred to as functional layers.
  • such further layers comprise one or more items from the group consisting of liquid crystals (LC), polymer dispersed liquid crystals (PDLC), nano polymer dispersed liquid crystals (nPDLC), LC guest-host systems comprising dyes, PDLC guest-host systems comprising dyes, nPDLC guest-host systems comprising dyes, photochromic materials, electrochromic materials, photo-electrochromic materials and thermochromic materials.
  • Particularly preferred are functional layers comprising one or more electrochromic materials.
  • dyes as used herein includes dichroic dyes.
  • a preferred article according to the invention comprises a first layer assembly and a second layer assembly as defined above, and a functional layer as defined above or a sequence of two or more functional layers (as defined above) arranged between said first layer assembly and said second layer assembly such that the functional layer or the sequence of functional layers is in contact with the coating of the first layer assembly and with the coating of the second layer assembly.
  • the coating of the first layer assembly and the coating of the second layer assembly each face towards the functional layer or towards the sequence of functional layers, thus sandwiching the functional layer or the sequence of functional layers, and the substrate of the first layer assembly and the substrate of the second layer assembly face away from said functional layer or said sequence of functional layers.
  • the coat- ing of the first layer assembly and the coating of the second layer assembly interact as electrodes with the functional layer, i.e. enable applying an electrical field across said functional layer.
  • the functional layer comprises an electrochro- mic material or the sequence of functional layers comprises at least one functional layer comprising an electrochromic material.
  • said sequence of functional layers comprises or consists of a first functional layer comprising a first electrochromic material in contact with the coating of the first layer assembly, a second functional layer comprising an ion-conducting material which virtually blocks electron flow, and a third functional layer comprising a second electrochromic material in contact with the coating of the second layer assembly.
  • said support layers each have a thickness in the range of from 0.1 mm to 10 mm, preferably 0.5 mm to 6 mm, particularly preferably 2 mm to 6 mm.
  • said adhesive layers each have a thickness in the range of from 0.1 mm to 2 mm, preferably 0.3 mm to 2 mm, particularly preferably 0.38 to 1.52 mm.
  • said support layers each have a thickness in the range of from 0.1 mm to 10 mm, preferably 0.5 mm to 6 mm, particularly preferably 2 mm to 6 mm, and said adhesive layers each have a thickness in the range of from 0.1 mm to 2 mm, preferably 0.3 mm to 2 mm, particularly preferably 0.38 to 1 .52 mm.
  • a preferred article according to the present invention comprises
  • a layer assembly as described above a first support layer and a second support layer as described above, wherein said layer assembly is arranged between said first support layer and said second support layer
  • one or more further support layers attached to one or both of the first and second support layer.
  • an adhesive layer is arranged between said first support layer and said further support layer.
  • an adhesive layer is arranged between said second support layer and said further support layer.
  • Preferred articles according to the present invention are those wherein two or more of the above-defined preferred features are combined.
  • the layer assembly can be combined with the support layers without introducing optical heterogeneities, because the substrate comprising polyvinylbutyral readily adapts itself to the surface of the support layer, even in the case that the support layer has a curved shape.
  • FIGS. 1 and 2 are schematic side elevation of said article not drawn to scale.
  • the article 1 according to figure 1 consists of
  • a layer assembly 15 consisting of
  • a matrix 26 formed of one or more organic polymers and dispersed within said matrix 26, metal nanoobjects 27 having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 ⁇ to 100 ⁇ , in each case determined by transmission electron microscopy a substrate 35 comprising polyvinylbutyral, said substrate having a first surface 36 and a second surface 37
  • said layer assembly 15 is arranged between said first support layer 1 1 and said second support layer 12.
  • Said layer assembly 15 consists of a substrate 35 and a coating 25 arranged on a first surface 36 of said substrate.
  • Said coating 25 comprises a matrix 26 formed of one or more organic polymers and, dispersed within said matrix 26, metal nanoobjects 27 having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 ⁇ to 100 ⁇ , in each case determined by transmission electron microscopy.
  • Substrate 35 has a second surface 37 facing away from said coating 25.
  • Article 1 further comprises a first adhesive layer 13 between said coating 25 and said first support layer 1 1 and a second adhesive layer 14 between said substrate 35 and said second support layer 12.
  • said first support layer 1 1 is attached by means of first adhesive layer 13 to the above-defined coating 25 arranged on a first surface 36 of said substrate 35
  • said second support layer 12 is attached by means of second adhesive layer 14 to said second surface 37 of said substrate 35 facing away from said coating 25.
  • Article 1 further comprises a third adhesive layer 18 between said first support layer 1 1 and said third support layer 16, and a fourth adhesive layer 19 between said second support layer 12 and said fourth support layer 17.
  • said first support layer 1 1 is attached by means of third adhesive layer 18 to the third support layer 16, and said second support layer 12 is attached by means of fourth adhesive layer 19 to said fourth support layer 17.
  • the article 2 according to figure 2 consists of
  • a first layer assembly 1 15 consisting of
  • a substrate 135 comprising polyvinylbutyral, said substrate having a first surface 136 and a second surface 137
  • a matrix 126 formed of one or more organic polymers and dispersed within said matrix 126, metal nanoobjects 127 having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 ⁇ to 100 ⁇ , in each case determined by transmission electron microscopy a functional layer 100
  • a second layer assembly 215 consisting of
  • a coating 225 comprising
  • a matrix 226 formed of one or more organic polymers and dispersed within said matrix 226, metal nanoobjects 227 having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 ⁇ to 100 ⁇ , in each case determined by transmission electron microscopy.
  • a substrate 235 comprising polyvinylbutyral, said substrate having a first surface 236 and a second surface 237
  • Said first layer assembly 1 15 consists of substrate 135 and coating 125 arranged on first surface 136 of said substrate.
  • Said coating 125 comprises a matrix 126 formed of one or more organic polymers and, dispersed within said matrix 126, metal nanoobjects 127 having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 ⁇ to 100 ⁇ , in each case determined by transmission electron microscopy.
  • Substrate 135 has a second surface 137 facing away from said coating 125.
  • Said second layer assembly 215 consists of substrate 235 and coating 225 arranged on first surface 236 of said substrate.
  • Said coating 225 comprises a matrix 226 formed of one or more organic polymers and, dispersed within said matrix 226, metal nanoobjects 227 having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 ⁇ to 100 ⁇ , in each case determined by transmission electron microscopy.
  • Substrate 235 has a second surface 237 facing away from said coating 225.
  • said functional layer 100 is arranged between and in contact with coating 125 of said first layer assembly 1 15 and coating 225 of said second layer assembly 215,
  • coatings 125 and 225 sandwich the functional layer 100
  • the substrate 135 of the first layer assembly 1 15 and the substrate 235 of the second layer assembly 215 face away from said functional layer 100.
  • a sequence of functional layer may be arranged between coating 125 of said first layer assembly 1 15 and coating 225 of said second layer assembly 215.
  • Said functional layer 100 comprises one or more items from the group consisting of liquid crystals (LC), polymer dispersed liquid crystals (PDLC), nano polymer dispersed liquid crystals (nPDLC), LC guest-host systems comprising dyes, PDLC guest-host systems comprising dyes, nPDLC guest-host systems comprising dyes, photochromic materials, electrochromic materials, photo-electrochromic materials and thermochromic materials.
  • functional layer 100 comprises an electrochromic material.
  • Article 2 further comprises a first adhesive layer 13 between said substrate 135 and said first support layer 1 1 and a second adhesive layer 14 between said substrate 235 and said second support layer 12.
  • said first support layer 1 1 is attached by means of first adhesive layer 13 to said surface 137 of said substrate 135 facing away from said coating 125
  • said second support layer 12 is attached by means of second adhesive layer 14 to said surface 237 of said substrate 235 facing away from said coating 225.
  • Article 2 further comprises a third adhesive layer 18 between said first support layer 1 1 and said third support layer 16, and a fourth adhesive layer 19 between said second support layer 12 and said fourth support layer 17.
  • said first support layer 1 1 is attached by means of third adhesive layer 18 to the third support layer 16
  • said second support layer 12 is attached by means of fourth adhesive layer 19 to said fourth support layer 17.
  • Typical articles according to the invention are selected from the group consisting of transparent electrodes, touch panels, wire polarizers, capacitive and resistive touch sensors, NIR reflection, EMI shielding, transparent and non transparent heaters (e.g. for mirror and / or glass and / or window defogging, automotive, ships, space crafts, aircrafts, transportation devices and / or vehicles, indoor and outdoor spaces and / or living space and other applications), flexible displays, plasma displays, electrophoretic displays, liquid crystal displays, transparent antennas, electrochromic devises (e.g.
  • smart windows photovoltaic devices (especially thin-film photovoltaic cells), electroluminescent devices, light emitting devices (LED) and organic light emitting devices (OLED), flexible devices that can be worn (so-called wearables) such as flexible watches or foldable screens, as well as functional coatings imparting anti-fogging, anti-icing or antistatic properties, and dielectric and ferroelectric haptic films.
  • wearables such as flexible watches or foldable screens
  • transparent heaters specially preferred transparent heaters for automotive applications, e.g. for windshields, particularly preferred transparent heaters for electro automotive applications (e-cars).
  • a further aspect of the present invention relates to a process for preparing an article according to the present invention as defined above, said process comprising
  • said coating comprising a matrix formed of one or more organic polymers
  • matrix metal nanoobjects having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 ⁇ to 100 ⁇ , in each case determined by transmission electron microscopy
  • forming said layer assembly comprises the steps of
  • A-2 one or more alcohols selected from the group consisting of methanol, etha- nol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol,
  • said metal nanoobjects (B) having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 ⁇ to 100 ⁇ , in each case determined by transmission electron microscopy,
  • the total weight fraction of said metal nanoobjects (B) is in the range of from 0.01 wt.-% to 2 wt.-% based on the total weight of the composition, (C) one or more organic polymers dispersed or dissolved in said mixture (A), wherein the total weight fraction of said organic polymers (C) is in the range of from 0.02 wt.-% to 5 wt.-%, based on the total weight of the composition providing a substrate comprising polyvinylbutyral,
  • a composition used in the process according to the invention (as defined above) is also referred to as an ink.
  • the main constituent which at 25 °C and 101.325 kPa is liquid is a mixture (A) comprising
  • (A-2) one or more alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol;
  • the main constituents which at 25 °C and 101.325 kPa are solid are the above- defined metal nanoobjects (B) and the above-defined one or more organic polymers (C).
  • the total concentration of constituents which at 25 °C and 101.325 kPa are solid (solid constituents) is 10 wt.-% or less, preferably 8 wt.-% or less, further preferably 5 wt.-% or less, in each case based on the total weight of said ink.
  • Constituent (A) of the ink used in the process according to the present invention is a mixture comprising
  • (A-2) one or more alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol.
  • Said mixture (A) is monophase (i.e. forms a single phase in said ink).
  • the presence of one or more alcohols (A-2) as defined above does not only promote wetting of the surface of a substrate to which the ink is applied but also promotes the dispersibility of the nanoobjects (B) (especially in the case of nanoobjects (B) in the form of silver nanowires) in the ink, resulting in improved connectivity of the conductive network formed in the coating obtainable from said ink.
  • the mixture (A) consists of
  • (A-2) one or more alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol.
  • mixture (A) consists of
  • (A-2) from > 0 to 30 % of one or more alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol, in each case based on the total volume of the mixture (A).
  • mixture (A) consists of
  • (A-2) 2 % to 30 % of one or more alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol, in each case based on the total volume of the mixture (A).
  • the drying speed of the ink is quite fast, which may result in clogging of fluid passages in the coating equipment which the ink must pass in the process of coating. If the proportion of said alcohols (A-2) is less than 2 % based on the total volume of the mixture (A), the drying speed of the ink is quite low, which makes the coating process inefficient.
  • the rather low thermal stability of PVB precludes application of temperatures above 80 °C. Thus, speeding up of the removal the constituents which at 25 °C and 101.325 kPa are liquid by increase of the temperature is limited to temperatures of at most 80 °C. Therefore, it is important to apply an ink which exhibits an appropriate drying speed at a temperature of 80 °C or below.
  • the mixture (A) consists of
  • (A-2) 15 % to 25 % of one or more alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol, in each case based on the total volume of the mixture (A).
  • i-butanol is less preferred due to its low solubility in water. Furthermore, in some cases methanol and ethanol are not preferred because of restrictive legal regulations.
  • the one or more alcohols (A-2) are selected from the group consisting of i-propanol, n-butanol and t-butanol, because they are miscible with water in the desired range, and use of inks comprising one or more of these alcohols results in coatings with best optical properties and electronic conductivity among all of the alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol.
  • Constituent (B) of the ink used in the process according to the present invention consists of metal nanoobjects as defined above.
  • the total weight fraction of said electroconductive nanoobjects (B) as defined above is 2.0 wt.-% or less, based on the total weight of the ink.
  • the total weight fraction of said electroconductive nanoobjects (B) is not less than 0.01 wt.-%, based on the total weight of the ink, because a total weight fraction of less than 0.01 wt.-% of electroconductive nanoobjects (B) may be not sufficient for forming a conductive network.
  • the total weight fraction of said metal nanoobjects (B) is not less than 0.02 wt.-%, preferably not less than 0.05 wt.-%.
  • Constituent (C) of the ink according to the present invention (as defined above) consists of one or more organic polymers as described above.
  • Said organic polymers are selected from the group consisting of polymers dissolved in mixture (A) and polymers suspended in mixture (A).
  • the mixture (A) as defined above and the one or more dissolved polymers (C) as defined above are monophase (i.e. form a single phase).
  • Polymers suspended in mixture (A) substantially do not dissolve in mixture (A) and are present in the ink in the form of dispersed discrete solid particles e.g. fibers or polymer beads.
  • Water-soluble polymers are known in the art and commercially available. Typically such copolymers are commercially available in the form of aqueous solutions.
  • Preferred water- soluble polymers are selected from the group consisting of cellulose alkyl ethers, cellulose hydroxyalkyl ethers, cellulose esters, dextranes, polyacrylamides, polyvinylalcohol, polyvinylpyrrolidone, polystyrenesulfonic acid, and the above-described sty- rene/(meth)acrylic copolymers having a number average molecular weight in the range of from 500 g/mol to 22000 g/mol.
  • Polymer beads are known in the art and commercially available in the form of aqueous dispersions of said polymer beads (aqueous polymer dispersions). Typically, the dispersed polymers are present in colloidal dispersion. An aqueous colloidal dispersion of polymer particles is also referred to as a latex.
  • a latex typically comprises dispersing assistants which serve to ensure the stability of the aqueous polymer dispersions. Suitable dispersing agents are selected from the group consisting of protective colloids and surfactants.
  • a latex film arises from the 'coalescence' i.e. compaction, deformation, cohesion and polymer chain interdiffusion of the individual latex particles (polymer beads) which in the aqueous dispersion are held apart by stabilizing forces (electrostatic and/or steric) resulting e g. from charged polymer chain endgroups or adsorbed surfactants.
  • stabilizing forces electrostatic and/or steric
  • the total weight fraction of said polymers (C) is less than 2 wt.-%, more preferably 1.8 wt.- % or less, further preferably 1.5 wt.-% or less, especially preferably 1 wt.-% or less, based on the total weight of the ink.
  • the total weight fraction of said polymers (C) is not less than 0.02 wt.-%, based on the total weight of the ink, because a total weight fraction of less than 0.02 wt.-% of said polymers (C) may be not sufficient for binding the metal nanoobjects (B).
  • the total weight fraction of said polymers (C) is not less than 0.05 wt.-%, preferably not less than 0.1 wt.-%.
  • the ratio between the total weight of said metal nanoobjects (B) and the total weight of said polymers (C) is in the range of from 1 :20 to 20:1 , preferably from 1 : 10 to 5: 1 , further preferably from 1 :5 to 5: 1.
  • the ink for the process according to the present invention optionally comprises further constituents beside the above-defined constituents (A) to (C), e.g. defoaming agents, rheological controlling agents, corrosion inhibitors, wetting agents resp. surfactants and other auxiliary agents. Suitable wetting agents, surfactants, defoaming agents, rheologi- cal controlling agents and corrosion inhibitors are known in the art and commercially available.
  • inks which do not contain any further constituents beyond the above-defined constituents (A-1 ), (A-2), (B) and (C) are suitable for the preparation of coatings having superior optical properties as well as satisfying electronic conductivity. Accordingly, the addition of any auxiliary agents can be omitted, thus rendering the formulation of the ink less complex and facilitating preparation of such ink.
  • wetting agents resp. surfactants usually are substances which are either solid at 25 °C and 101.325 kPa or have such a high boiling point at 101 .325 kPa that they are not readily removed after the ink is applied to the substrate. Thus, the wetting agents resp.
  • surfactants remain as foreign matter in the coating which is formed on said surface of said substrate, thereby introducing compositional heterogeneity in said coating and affecting the characteristics of said coating. More specifically, such wetting agents resp. surfactants do not contribute to the electronic conductivity of the coating, and typically do not contribute to matrix formation, but often may have a detrimental effect on the optical properties of the coating, even if said wetting agents resp. surfactants are present in the ink in a quite low concentration. In addition, the presence of a surfactant in the ink may induce foam formation which may result in inhomogeneity and discontinuity of a coating prepared using said ink.
  • the ink consists of above-defined constituents (A-1 ), (A-2), (B) and (C). Nevertheless, in certain cases the ink used in the process according to the present invention (as defined above) comprises one or more auxiliary agents, especially those as defined above.
  • the ink used in the process according to the present invention does not contain any surfactants which are neither polymers (C) as defined above nor alcohols (A-2) as defined above.
  • any further constituents (beside the above-defined constituents (A) to (C)) of the ink used in the process according to the present invention (as defined above) as well as the amounts of such further constituents have to be selected in such manner that the electrical conductivity and the optical properties of a coating obtainable from said ink are not compromised.
  • compositions for the process according to the present invention are those wherein two or more of the above-defined preferred features are combined.
  • composition comprising or consisting of
  • (A-2) 2 % to 30 % of one or more alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol in each case based on the total volume of the mixture (A);
  • the total weight fraction of said silver nanowires (B) is 2 wt.-% or less, based on the total weight of the composition
  • the total weight fraction of constituents (C1 ) and (C2) is less than 2 wt.-%, preferably 1.5 wt.-% or less, based on the total weight of the composition wherein the ratio between
  • a composition for use in the process according to the present invention is preparable e.g. by suspending an appropriate amount of the above-defined metal nanoobjects (B) in water (A-1 ) and dissolving and/or suspending an appropriate amount of the above- defined polymers (C) in water (A-1 ) and adding an appropriate amount of one or more alcohols (A-2) as defined above, or by combining appropriate amounts of a pre- manufactured aqueous suspension of said metal nanoobjects (B) and of a pre- manufactured aqueous solution or suspension of said one or more polymers (C) and adding an appropriate amount of one or more alcohols (A-2) as defined above, or by suspending an appropriate amount of said metal nanoobjects (B) in a pre-manufactured aqueous solution or suspension of said one or more polymers (C) and adding an appropriate amount of one or more alcohols (A-2) as defined above, or by dissolving or suspending an appropriate amount of said one or more polymers (C) in a pre-manufact
  • the composition is subjected to ball- milling in order to improve homogenization of the composition.
  • a prolonged homogenization treatment is preferably in order to ensure that the obtained coatings have a low haze.
  • said ink is applied to said surface of said solid substrate by coating or printing, preferably by a continuous coating or printing technique.
  • coating or printing preferably by a continuous coating or printing technique.
  • Such techniques are generally considered advantageous for large scale production, when compared to vacuum-based techniques.
  • Applying said composition to said surface of said substrate is carried out by means of a technique selected from the group consisting of spin coating, draw down coating, roll-to-roll coating, gravure printing, microgravure printing, screen-printing, flexoprinting and slot-die coating.
  • said composition is applied to said surface of said substrate in a thickness in a range of from 1 ⁇ to 200 ⁇ , preferably of from 2 ⁇ to 60 ⁇ .
  • Said thickness is also referred to as "wet thickness” and relates to the thickness of the wet film before removing the liquid constituents of the ink.
  • the thickness and accordingly the opacity of the obtainable coating increases with increasing concentration of solid constituents in the applied ink.
  • the wet thickness of the applied ink may be the higher the lower the concentration of solid constituents is in the ink.
  • the process of applying the ink is facilitated when there is no constraint to apply the ink in particular low wet thickness. This is achieved by means of the above-described ink, because in said ink the concentration of solid constituents is sufficiently low.
  • the constituents which at 25 °C and 101.325 kPa are liquid are removed from said wet film on said surface of said substrate by exposing said wet film to a temperature in the range of from 40 °C to 80 °C, preferably 40 °C to 60 °C, most preferably 40 °C to 50 °C, thereby forming said coating on said surface of said substrate, said coating comprising
  • matrix metal nanoobjects having two external dimen- sions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 ⁇ to 100 ⁇ , in each case determined by transmission electron microscopy.
  • the process step of removing the constituents which at 25 °C and 101.325 kPa are liquid from said wet film applied to said surface of said substrate to such extent that a coating is formed on said surface of said substrate is also referred to as drying.
  • the liquid constituents are removed by evaporation.
  • the process step of removing the constituents which at 25 °C and 101 .325 kPa are liquid from said wet film applied to said surface of said substrate is carried out by exposing said wet film to a temperature in the range of from 40 °C to 60 °C, preferably 40 °C to 50 °C, in order to avoid that the substrate comprising PVB suffers from thermal stress.
  • Limitation of the temperature to which the PVB substrate is exposed to at most 60 °C, preferably at most 50 °C is an important advantage of this preferred process according to the present invention, compared to the vacuum deposition methods according to WO 2015/109198, which may require that during physical vapor deposition or during sputtering the substrate experiences temperatures up to 75 °C or even up to 100 °C.
  • forming said coating on said surface of said substrate further comprises cross-linking said polymers.
  • Suitable means for initiating cross-linking are known in the art.
  • Preferred processes according to the present invention are those wherein two or more of the above-defined preferred features are combined.
  • preparing said article further comprises the step of arranging said layer assembly between a first support layer comprising a material selected from the group consisting of metals, glass and organic poly- mers, and a second support layer comprising a material selected from the group consisting of metals, glass and organic polymers.
  • a first support layer comprising a material selected from the group consisting of metals, glass and organic poly- mers
  • second support layer comprising a material selected from the group consisting of metals, glass and organic polymers.
  • said first support layer is attached to said coating arranged on a surface of said substrate.
  • said second support layer is attached to said substrate comprising polyvinylbutyral.
  • a preferred process according to the present invention further comprises the step of arranging said layer assembly between a first support layer comprising a material selected from the group consisting of metals, glass and organic polymers, and a second support layer comprising a material selected from the group consisting of metals, glass and organic polymers, by
  • first support layer and second support layer merely denote the position of said support layers relative to the coating and the substrate (as defined above) in the article to be formed, and not the sequence of carrying out the steps of attaching said support layers to said coating or substrate resp. More specifically, attaching said second support layer to said substrate comprising polyvinylbutyral may be completed before attaching said first support layer to said coating arranged on a surface of said substrate, and vice versa.
  • attaching said first support layer to said coating comprises applying an adhesive layer between said coating and said first support layer and/or attaching said second support layer to said substrate comprises applying an adhesive layer between said substrate and said second support layer.
  • attaching said first support layer to said coating comprises applying a first adhesive layer between said coating and said first support layer and attaching said second support layer to said substrate comprises applying a second adhesive layer between said substrate and said second support layer.
  • attaching said support layers to said layer assembly comprises placing said layer assembly on the (optionally adhesive- coated) surface of one of the support layers and then placing the other support layer on the layer assembly, thus obtaining a prelaminate assembly wherein the layer assembly is arranged between a first support layer and a second support layer.
  • the prelaminate assembly is treated with heated rolls, followed by heating the prelaminate assembly at elevated pressure in some kind of chamber like an autoclave.
  • the prelaminate assembly is placed in a flexible vacuum bag followed by evacuating and heating said vacuum bag so that atmospheric forces press on the bag and hence the prelaminate. This is followed by further heating the vacuum-bagged prelaminate assembly either at atmospheric pressure or at elevated pressure in some kind of chamber like an autoclave.
  • further layers are arranged between said first support layer and said optically transparent conductive layer, and/or between said second support layer and said substrate comprising PVB.
  • compositions comprising
  • A-2 one or more alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol,
  • said metal nanoobjects (B) having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 ⁇ to 100 ⁇ , in each case determined by transmission electron microscopy wherein the total weight fraction of said metal nanoobjects (B) is in the range of from 0.01 wt.-% to 2 wt.-% based on the total weight of the composition,
  • compositions selected from the above-defined preferred compositions.
  • a further aspect of the present invention relates to the use of an article according to the present invention as defined above in automotive applications, especially in car windshields.
  • An aqueous dispersion of silver nanowires (nanoobjects (B) as defined above) and an aqueous mixture comprising a first polymer (C-1 ) in the dissolved state and suspended fibers of a second polymer (C-2) is mixed with (A-2) isopropanol for a dispersing time of 30 minutes so as to obtain an ink having a concentration of silver nanowires (B) of 7 mg/ml and a total polymer concentration (C) of 21 mg/ml.
  • the constituents which at 25 °C and 101 .325 kPa are liquid are removed from said wet film by exposing said wet film to a temperature in the range of from 40 °C to 50 °C for a duration of five minutes, thereby obtaining coating on said surface of said substrate.
  • Said polymer (C-1 ) is selected from the group consisting of cellulose alkyl ethers, cellu- lose hydroxyalkyi ethers and cellulose esters.
  • Said fibers of polymer (C-2) are fibers of crystalline cellulose.
  • the sheet resistance Rsh given in Ohms/square (OPS) of the obtained coating is measured by a four-point probe station (Lucas lab pro-4) at a temperature of 23 °C and a pressure of 101.3 kPa, and the optical properties (as defined above) are measured according to ASTM D1003 procedure A-Hazemeter (as published in November 2013) by a haze-gard plus hazemeter (BYK Gardner). Transmission including the substrate is found to be 90.10 % total haze including the substrate 1.67 % (accordingly the haze of the coating is not more than 1.67 %) and the sheet resistance is found to be 23 Ohms per square.

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Abstract

Described are an article comprising a layer assembly consisting of a substrate comprising polyvinylbutyral and a coating arranged on a surface of said substrate, said coating comprising a matrix formed of one or more organic polymers and metal nanoobjects dispersed within said matrix, and to a process for preparing said article.

Description

Coating containing metal particles
The present invention relates to an article comprising a layer assembly consisting of a substrate comprising polyvinyl butyral and a coating arranged on a surface of said substrate, said coating comprising a matrix formed of one or more organic polymers and metal nanoobjects dispersed within said matrix, and to a process for preparing said article.
WO 2015/109198 discloses a coated polyvinyl butyral (PVB) film or sheet comprising a PVB layer that includes no plasticizer or less than about 5 wt.-% of a volatile plasticizer; and a conductive or reflective coating; wherein the conductive or reflective coating directly coats the PVB layer, wherein said coating e.g. comprises silver or a silver alloy, and a method for coating a PVB film or sheet, said method comprising providing a PVB film or sheet that includes little or no volatile material and directly applying in a vacuum a conductive or reflective coating to the PVB film or sheet. Said coating is deposited on the PVB film or sheet e.g. by physical vapor deposition or by magnetron sputtering.
The method according to WO 2015/109198 involves certain disadvantages and constraints. Commercially available films, sheets or foils made of PVB typically contain plasticizers in order to render said films, sheets or foils flexible (e.g. to allow bending without wrinkling, e.g. bending around the complex curves typical of glass in vehicle applications), soft and elastically. Unfortunately, polymer substrates comprising plasticizers are virtually impossible to be used as substrates for physical vapor deposition in high vacuum due to softness, extensibility and pliability. In addition, vacuum deposition is problematic because of the outgas- sing of volatile impurities and/or the plasticizer itself, unless the plasticizer has very low volatility. In order to avoid such problems, limitation of the amount of volatile plasticizers in the PVB layer to 5 wt.-% or less, and preferably complete omitting of volatile plasticizers in the PVB layer, is required according to WO 2015/109198.
Related art is also
US 2015/202846 A1 (family member of WO 2015/109198)
US 3 576 662 A
RU 2 581 359 C1
JP H07 24957 A
CN 203 543 235 U.
Furthermore, residual acid present in the polyvinyl butyral may react with metal coated on said a substrate comprising PVB, resulting in impairment of electronic conductivity and reduced light transmission due to the formation of colored reaction products. Polyvinyl butyral is obtained by acidic hydrolysis (e.g. using hydrochloric acid) of polyvinyl acetate and subsequent (at least partial) acetalization of the obtained polyvinyl alcohol with butanal (butyraldehyde). The obtained product often contains residues of hydrochloric acid and/or acetic acid.
Finally it was found that there is a certain risk that a coating applied by vacuum deposition to a polyvinyl butyral film or sheet suffers from crack formation when the coated polyvinyl butyral film or sheet is bent.
On the other hand, for certain applications substrates comprising commonly used poly- mers like polyethylene terephthalate (PET) are not suitable because of their rather low flexibility, or resp. their rather high stiffness, which commonly does not allow bending without wrinkling. Thus, it is hardly possible to attach a PET foil coated with a conductive coating to a curved structure, e.g. a curved glass structure, without formation of wrinkles, which may introduce optical heterogeneities and disrupt conduction paths. An important application wherein polyvinylbutyral is virtually indispensible is safety glass. Safety glass as typically used e.g. in car windshields comprises a sandwich structure consisting a first and a second pane of floatglass and a foil comprising polyvinylbutyral between said first and said second pane of floatglass, wherein said foil is fused to said fist pane and to said second pane of floatglass by heating the sandwich structure in an autoclave. After fusing, float glass and polyvinylbutyral have the same refractive index, thus avoiding optical heterogeneity.
Accordingly, there is a need for an article comprising a layer assembly consisting of a substrate comprising polyvinylbutyral and a conductive coating arranged on a surface of said substrate and for a process for preparing said article, which overcome the disadvantages and constraints of the prior art.
These and other objects are achieved by an article according to the present invention. Said article comprises a layer assembly consisting of
a substrate comprising polyvinylbutyral
and a coating arranged on a surface of said substrate, said coating comprising a matrix formed of one or more organic polymers
and dispersed within said matrix metal nanoobjects having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 μιη to 100 μιη, in each case determined by transmission electron microscopy.
In certain specific cases, an article according to the present invention consists of a layer assembly consisting of
a substrate comprising polyvinylbutyral
and a coating arranged on a surface of said substrate, said coating comprising a matrix formed of one or more organic polymers
and dispersed within said matrix metal nanoobjects having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 μιη to 100 μιη, in each case determined by transmission electron microscopy. In said layer assembly according to the present invention, the coating is a composite comprising (i) an optically transparent contiguous solid phase (herein referred to as a matrix) and (ii) a conductive network of metal nanoobjects which extends throughout said matrix. The matrix is formed of one or more optically transparent polymers (polymers having a light transmission of 80 % or more as measured according to ASTM D1003 (procedure A)). Said matrix binds and accommodates the metal nanoobjects within the coating, fills the voids between said metal nanoobjects, provides mechanical integrity and stability to the coating and binds the coating to the surface of the substrate. The metal nanoobjects dispersed within said matrix form a conductive network enabling the flow of electrons between adjacent and overlapping electroconductive nanoobjects within the coating. Due to the small dimensions of the metal nanoobjects, their influence on the optical behavior of the coating is minor, thus allowing for the formation of a coating which is optically transparent and electroconductive. Accordingly, said coating is also referred to as an "optically transparent conductive layer". In certain cases, said coating consists of
a matrix formed of one or more organic polymers
and dispersed within said matrix metal nanoobjects having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 μιη to 100 μιη, in each case determined by transmission electron microscopy.
Without wishing to be bound by theory, it is assumed that embedding the metal nanoobjects in a polymer matrix protects the metal nanoobjects from undesirable reactions with constituents of the substrate comprising PVB, and that the presence of the polymer matrix renders the coating smooth and pliant so that it can adapt itself to any bending of the substrate without the risk of crack formation.
The constituents of said coating and their functions within said coating are described in further detail below.
The coating comprises a matrix formed of one or more organic polymers (hereinbelow also referred to as "organic polymer matrix"). The term "polymer" as used herein includes co-polymers (polymers obtained by co-polymerization of two or more kinds of co- polymerizable monomers). Preferably, said polymer matrix comprises one or more polymers selected from the group consisting of cellulose, cellulose alkyl ethers, cellulose hydroxyalkyi ethers, cellulose esters, dextranes, polyacrylamides, polyvinylalcohol, polyvinylpyrrolidone, polystyrenesulfonic acid, polystyrene, styrene/(meth)acrylic copolymers, styrene- butadiene copolymers, polyacrylates, polymethacrylates, copolymers of acrylates and methacrylates.
Preferably, said coating comprises polyvinylbutyral in an amount of less than 3 wt.-%, further preferably less than 1 wt.-%, particularly less than 0.5 wt.-%, based on the total weight of said coating. Most preferably, the polymer matrix does not comprise polyvinylbutyrals. Preferably the polymer matrix does not comprise any polyvinylacetals.
One kind of preferred matrix-forming polymers are styrene/(meth)acrylic copolymers having a number average molecular weight in the range of from 500 g/mol to 22000 g/mol Herein, the term "(meth)acrylic" includes "methacrylic" and "acrylic". In said copolymers each molecule comprises or consists of units derived from monoalkenyl aromatic monomers and units derived from (meth)acrylic monomers, in copolymerized form. Such styrene/(meth)acrylic copolymers are obtainable by copolymerisation of one or more kinds of monoalkenyl aromatic monomers with one or more kinds of (meth)acrylic monomers.
In preferred styrene/(meth)acrylic copolymers, each molecule comprises or consists of units C1 derived from monoalkenyl aromatic monomers MC1
and
units C2 derived from (meth)acrylic monomers MC2
in copolymerized form, wherein
said units C1 (units derived from monoalkenyl aromatic monomers) have the chemical structure
Figure imgf000008_0001
(C1 )
wherein R-i , independently from the R-i of each other unit C1 , is selected from the group consisting of hydrogen and alkyl (including unbranched alkyl, preferably methyl, and branched alkyl, preferably tert-butyl)
and wherein R2, independently from the R2 of each other unit C1 , is selected from the group consisting of halogen (preferably chlorine) and alkyl (preferably methyl), and R2 is situated in a position selected from the group consisting of ortho, meta and para;
and said units C2 (units derived from (meth)acrylic monomers) have the chemical structure
Figure imgf000008_0002
(C2)
wherein R3, independently from the R3 of each other unit C2, is selected from the group consisting of hydrogen, methyl, halogen (preferably chlorine) and cyano,
and wherein R4, independently from the R4 of each other unit C2, is selected from the group consisting of -COOH,
-COOX wherein X is a cation selected from alkali metal cations, ammonium cations and substituted ammonium cations,
-CN,
-COOR5 wherein R5 is selected from the group consisting of branched and unbranched alkyl groups, branched and unbranched alkenyl groups, branched and unbranched alkinyl groups, cycloalkyl groups, aralkyl groups, aralkenyl groups, furfuryl, tetrahydrofurfuryl, isopropylidene glyceryl, glycidyl and tetrahydropyranyl, wherein said branched and unbranched alkyl groups, alkenyl groups and alkinyl groups include branched and un- branched alkyl groups, alkenyl groups and alkinyl groups substituted with one or more groups selected from the group consisting of hydroxy, alkoxy, phenoxy, halogen, sulfo, nitro, oxazolidinyl, monoalkylamino and dialkylamino groups
-CHO,
-NR6R7 wherein R6 and R7 are independently selected from the group consisting of hy- drogen, alkyl and phenyl.
Such styrene/(meth)acrylic copolymers are obtainable by copolymerisation of one or more kinds of monoalkenyl aromatic monomers MC1 having the formula
Figure imgf000009_0001
(MC1 )
wherein R-i , independently from the R-i of each other monomer MC1 , is selected from the group consisting of hydrogen and alkyl (including unbranched alkyl, preferably methyl, and branched alkyl, preferably tert-butyl) and wherein R2, independently from the R2 of each other monomer MC1 , is selected from the group consisting of halogen (preferably chlorine) and alkyl (preferably methyl) and R2 is situated in a position selected from the group consisting of ortho, meta and para, with one or more kinds of (meth)acrylic monomers MC2 having the formula
Figure imgf000010_0001
(MC2)
wherein R3, independently from the R3 of each other monomer MC2, is selected from the group consisting of hydrogen, methyl, halogen (preferably chlorine) and cyano, and wherein R4, independently from the R4 of each other unit MC2 is selected from the group consisting of
-COOH,
-COOX wherein X is a cation selected from alkali metal cations, ammonium cations and substituted ammonium cations,
-CN,
-COOR5 wherein R5 is selected from the group consisting of branched and unbranched alkyl groups, branched and unbranched alkenyl groups, branched and unbranched alkinyl groups, cycloalkyl groups, aralkyl groups, aralkenyl groups, furfuryl, tetrahydrofurfuryl, isopropylidene glyceryl, glycidyl and tetrahydropyranyl, wherein said branched and unbranched alkyl groups, alkenyl groups and alkinyl groups include branched and un- branched alkyl groups, alkenyl groups and alkinyl groups substituted with one or more groups selected from the group consisting of hydroxy, alkoxy, phenoxy, halogen, sulfo, nitro, oxazolidinyl, monoalkylamino and dialkylamino groups
-CHO,
-NR6R7 wherein R6 and R7 are independently selected from the group consisting of hy- drogen, alkyl and phenyl.
The term "(meth)acrylic monomer" MC2 as employed herein includes acrylic acid and salts, esters and amides of acrylic acid, acrylonitrile and acrolein, as well as methacrylic acid and salts, esters and amides of methacrylic acid, methacrylonitrile, and methacrolein. (Meth)acrylic monomers, wherein R3 is hydrogen or methyl, resp., and R4 is -COOH, are acrylic acid or methacrylic acid, resp.
(Meth)acrylic monomers wherein R3 is hydrogen or methyl, resp., and R4 is -COOR5 as defined above, are esters of acrylic acid or esters of methacrylic acid, resp. (Meth)acrylic monomers wherein R3 is hydrogen or methyl, resp., and R4 is -COOX as defined above, are salts of acrylic acid or salts of methacrylic acid, resp.
(Meth)acrylic monomers wherein R3 is hydrogen or methyl, resp., and R4 is -CN, are acrylonitrile or methacrylonitrile, resp.
Styrene/(meth)acrylic copolymers obtainable by copolymerization of one or more kinds of monoalkenyl aromatic monomers MC1 and one or more (meth)acrylic monomers from the group consisting of acrylonitrile and methacrylonitrile and no other (meth)acrylic monomers MC2 are not preferred. In this regard it is preferred that for the preparation of said copolymer (meth)acrylic monomers selected from the group consisting of acrylonitrile and methacrylonitrile are used in combination with other (meth)acrylic monomers MC2 as defined herein.
(Meth)acrylic monomers wherein R3 is hydrogen or methyl, resp., and Γ¾ is -NR6R7 as defined above, are amides of acrylic acid or amides of methacrylic acid, resp.
(Meth)acrylic monomers wherein R3 is hydrogen or methyl, resp., and R4 is -CHO are acrolein or methacrolein, resp. Preferable monoalkenyl aromatic monomers MC1 are selected from the group consisting of alpha-methyl styrene, styrene, vinyl toluene, tertiary butyl styrene and ortho- chlorostyrene.
Examples of suitable (meth)acrylic monomers include the following methacrylate esters (methacrylic acid esters): methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, n-hexyl methacrylate, isoamyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxy propyl methacrylate, Ν,Ν-dimethylaminoethyl methacrylate,
Ν,Ν-diethylaminoethyl methacrylate, t-butylaminoethyl methacrylate, 2-sulfoethyl methac- rylate, trifluoroethyl methacrylate, glycidyl methacrylate, benzyl methacrylate, allyl meth- acrylate, 2-n-butoxyethylmethacrylate, 2-chloroethyl methacrylate, secbutyl-methacrylate, tert-butyl methacrylate, 2-ethylbutyl methacrylate, cinnamyl methacrylate, crotyl methacrylate, cyclohexyl methacrylate, cyclopentyl methacrylate, 2-ethoxyethyl methacrylate, furfuryl methacrylate, hexafluoroisopropyl methacrylate, methallyl methacrylate, 3-methoxybutyl methacrylate, 2-methoxybutyl methacrylate, 2-nitro-2-methylpropyl methacrylate, n-octylmethacrylate, 2-ethylhexyl methacrylate, 2-phenoxyethyl methacrylate, 2-phenylethyl methacrylate, phenyl methacrylate, prop-2-inyl methacrylate, tetrahydrofurfurylmethacrylate and tetrahydropyranylmethacrylate. Typical acrylate esters employed include: methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate and n-decyl acrylate, methyl alpha-chloroacrylate, methyl 2-cyanoacrylate. Other suitable (meth)acrylic monomers include methacrylonitrile, methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, N,N-diethylmethacryl- amide, Ν,Ν-dimethylmethacrylamide, N-phenylmethacrylamide and methacrolein, acrylo- nitrile, acrylamide, N-ethylacrylamide, Ν,Ν-diethylacrylamide and acrolein.
Esters of methacrylic acid or acrylic acid containing a suitable condensable cross linkable functional group may be used as the monomer. Among such esters are t-butylaminoethyl methacrylate, isopropylidene glyceryl methacrylate and oxazolidinylethyl methacrylate.
Typical preferred cross-linkable acrylates and methacrylates include hydroxy alkyl acry- lates, hydroxyl alkyl methacrylates and hydroxyesters of glycidyl acrylates or methacrylates. Examples of preferred hydroxy functional monomers include 2-hydroxyethyl acrylate, 3-chloro-2-hydroxypropyl acrylate, 2-hydroxy-butyl acrylate, 6-hydroxyhexyl acrylate, 2-hydroxy methyl methacrylate, 2-hydroxy propyl methacrylate, 6-hydroxyhexyl methacrylate, 5,6-dihydroxyhexyl methacrylate and the like.
The term "styrene/(meth)acrylic copolymer" as employed herein includes copolymers obtainable from mixtures consisting of two or more (meth)acrylic monomers and one or more monoalkenyl aromatic monomers, as well as copolymers obtainable from mixtures of at least one (meth)acrylic monomer and at least one non-acrylic ethylenic monomer and one or more monoalkenyl aromatic monomers. Suitable ethylenic monomers include: vinyl pyridine, vinyl pyrrolidone, sodium crotonate, methyl crotonate, crotonic acid and maleic anhydride. For further details regarding the above-defined styrene/(meth)acrylic copolymers, reference is made to US 2008/0182090, US 4,414,370, US 4,529,787, US 4,546, 160, US 5,508,366 and the prior art cited therein.
The number average molecular weight of said styrene/(meth)acrylic copolymers is in the range of from 500 g/mol to 22000 g/mol, preferably of from 1700 g/mol to 15500 g/mol, further preferably of from 5000 g/mol to 10000 g/mol.
Typically, said styrene/(meth)acrylic copolymers are amphiphilic, because their molecules contain non-polar hydrophobic regions derived from the monoalkenyl aromatic monomers and polar hydrophilic regions derived from the (meth)acrylic monomers. Thus, the desired amphiphilic behavior is obtainable by appropriate selection of the hydrophobic monoalkenyl aromatic monomers and the hydrophilic (meth)acrylic monomers and appropriate adjustment of the ratio between monoalkenyl aromatic monomers and (meth)acrylic monomers so that a styrene/(meth)acrylic copolymer is obtained which has an appropriate ratio between hydrophobic units derived from monoalkenyl aromatic monomers and hydrophilic units derived from (meth)acrylic monomers to allow for amphiphilic behavior of the copolymer.
In aqueous solution said water-soluble styrene/(meth)acrylic copolymers behave like surfactants (tensides), i.e. they are capable of forming micelles. A micelle is an aggregate formed by association of dissolved amphiphilic molecules. Preferably said micelles have a diameter of up to 5 nm.
Typical water-soluble styrene/(meth)acrylic copolymers are known in the art and commercially available. Typically such copolymers are commercially available in the form of aqueous solutions.
A second kind of preferred matrix-forming polymers is crystalline cellulose. Preferably said crystalline cellulose is in the form of fibers having a length in the range of from 80 nm to 300 nm and a diameter in the range of from 5 nm to 30 nm. Preferably, said fibers of crystalline cellulose have a length in the range of from 80 nm to 150 nm and a diameter in the range of from 5 nm to 10 nm. Said fibers are also referred to as nanocrystalline cellulose or cellulose nanofibers or cellulose II (see WO 2010/127451 ). They are obtaina- ble by disrupting the amorphous domains of natural cellulose fibers and disintegration of the micrometer-sized cellulose fibers into rod-like rigid crystallites. The obtained crystallites typically have the above-mentioned dimensions.
More specifically, crystalline cellulose fibers having the above-mentioned dimensions are obtainable by chemical treatment or by enzymatic treatment or by mechanical treatment of natural cellulose fibers or by combinations of different types of treatment, e.g. chemical treatment (e.g. with sulfuric acid or sodium chlorite) or enzymatic treatment followed by high-pressure homogenization, or by milling of natural cellulose fibers and subsequent hydrolysis to remove amorphous regions.
When a dispersion of fibers of crystalline cellulose in a liquid is dried (i.e. the liquid is removed from the dispersion), the cellulose fibers become packed together by capillary action during the evaporation of the water. Accordingly, said cellulose fibers are capable of forming a matrix and binding metal nanoobjects so as to form a coating as defined above. Furthermore, due to their outstanding mechanical stability, said fibers impart mechanical reinforcement to the obtained coating. Due to their external dimensions, said fibers of crystalline cellulose are nanoobjects in the sense of to ISO/TS 27687:2008 (as published in 2008), see below, and do not scatter visible light. However, said fibers of crystalline cellulose do not comprise any materials capable of allowing the flow of electrons.
Preferably, said fibers of crystalline cellulose are fibers of sulfated crystalline cellulose. They are obtainable by treatment of cellulose with sulfuric acid. Fibers of this kind of crystalline cellulose contain sulfur in the form of sulfate groups. Especially preferred are fibers of sulfated crystalline cellulose II obtainable by be the process described in WO 2010/127451 . Said sulfated crystalline cellulose II has a degree of polymerization of 60 or below. For further details, reference is made to WO 2010/127451 . Preferably, the composition according to the present invention does not comprise fibers of crystalline cellulose obtained by means of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation of cellulose. This kind of crystalline cellulose fibers exhibits a high density of carboxylate groups on their surfaces. Said carboxylate groups are formed by oxidation of primary hydroxyl groups of cellulose. Suitable fibers of crystalline cellulose are commercially available, e.g. from Celluforce. A third kind of preferred matrix-forming polymers are polymers having a number average molecular weight of 25000 g/mol or higher in the form of dispersed particles. Preferably, the number average molecular weight of said polymer is not higher than 200000 g/mol. Said polymer is either a homopolymer or a copolymer. Said particles are either particles of one kind of polymer or a mixture of particles of different polymers.
Such particles are also referred to as polymer beads. Typically, a polymer bead consists of several entangled polymer chains. Said polymer beads have an average particle diameter in the range from 10 nm to 1000 nm, in particular in the range from 50 nm to 600 nm determined by dynamic light scattering on an aqueous polymer dispersion (from 0.005 to 0.01 percent by weight) at 23 °C by means of an Autosizer IIC from of Malvern Instruments, England.
Preferred polymers beads comprise, in copolymerized form, from 50 to 99.9% by weight of
esters of acrylic acid and/or methacrylic acid with alkanole having from 1 to 12 carbon atoms, or
styrene, or
styrene and butadiene, or
vinyl chloride and/or vinylidene chloride,
or from 40 to 99.9% by weight of vinyl acetate, vinyl propionate and/or ethylene. Particularly preferred are polyacrylates, polymethacrylates, copolymers of acrylates and methacrylates, and copolymers of styrene and (meth)acrylates. Herein, the term "(meth)acrylate" includes "methacrylate" and "acrylate"."
The polyacrylates are either homo- or copolymers. In the case of homopolymers each molecule consists of units each derived from one kind of acrylate monomer. In the case of copolymers each molecule comprises or consists of units derived from different kinds of acrylate monomers in copolymerized form.
The polymethacrylates are either homo- or copolymers. In the case of homopolymers each molecule consists of units each derived from one kind of methacrylate monomer. In the case of copolymers each molecule comprises or consists of units derived from differ- ent kinds of methacrylate monomers in copolymerized form. In said copolymers of acrylates and methacrylates each molecule comprises or consists of units derived from acrylate monomers and units derived from methacrylate monomers in copolymerized form
In said copolymers of styrene and (meth)acrylates, each molecule comprises or consists of units derived from monoalkenyl aromatic monomers and units derived from (meth)acrylic monomers in copolymerized form.
Such polymer beads are known in the art and commercially available in the form of aqueous dispersions of said polymer beads (aqueous polymer dispersions). Typically, the dispersed polymers are present in colloidal dispersion. Such aqueous polymer disper- sions are obtainable by polymerization of suitable monomers in an aqueous liquid phase, e.g. by means of suspension polymerization or emulsion polymerization. Preferred aqueous polymer dispersions are obtainable by free-radically initiated aqueous emulsion polymerization of ethylenically unsaturated monomers. The free-radically initiated aqueous emulsion polymerization is effected typically in such a way that at least one ethylenically unsaturated monomer, frequently in the presence of dispersing assistants, is distributed in a disperse manner in an aqueous medium and polymerized by means of at least one free-radical polymerization initiator. For further details, reference is made to US 7,999,045 B2 and the prior art cited therein.
An aqueous colloidal dispersion of polymer particles is also referred to as a latex. Colloi- dal stability of a latex is achieved by a balancing of electrostatic repulsion, van der Waals attraction and steric attraction or repulsion. The above-defined polymer dispersions typically comprise dispersing assistants which serve to ensure the stability of the aqueous polymer dispersions. Suitable dispersing agents are selected from the group consisting of protective colloids and surfactants. Preferred surfactants are sodium dodecylsulfate (SDS), and water soluble amphiphilic styrene/(meth)acrylic copolymers having a number average molecular weight in the range of from 500 g/mol to 22000 g/mol as defined above. Said water soluble amphiphilic styrene/(meth)acrylic copolymers are preferred surfactants because they are capable of co-acting with the polymer beads in forming a matrix and binding the above-defined metal nanoobjects. Further preferred matrix-forming polymers are selected from the group consisting of cellulose alkyl ethers, cellulose hydroxyalkyl ethers (e.g. hydroxypropyl methyl cellulose), cellulose esters (e.g. carboxymethyl cellulose), polyacrylamides, polyvinylalcohol, polyvinylpyrrolidone, polystyrenesulfonic acid, and dextranes.
Other suitable matrix-forming polymers are polyolefin copolymer resins comprising an olefin monomer and acrylic acid comonomer or (meth)acrylic acid comonomer as described in EP 2 960 310 A1.
The polymer matrix is formed of one or more of the above-mentioned polymers. In certain cases the matrix comprises polyvinylpyrrolidone (see below) and one or more further polymers, preferably one or more of the above-defined preferred polymers.
Preferably, the polymer matrix comprises
- one or organic polymers selected from the group consisting of cellulose alkyl ethers, cellulose hydroxyalkyl ethers and cellulose esters,
and fibers of crystalline cellulose as described above
and optionally polyvinylpyrrolidone.
Said metal nanoobjects which are dispersed within said polymer matrix have two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 μιη to 100 μιη.
According to ISO/TS 27687:2008 (as published in 2008), the term "nanoobject" refers to an object having one, two or three external dimensions in the nanoscale, i.e. in the size range from approximately 1 nm to 100 nm. The electroconductive nanoobjects to be used for the present invention are electroconductive nanoobjects having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 μιη to 100 μιη. Typically, said two external dimensions which are in the range of from 1 nm to 100 nm are similar i.e. they differ in size by less than three times. The third dimension of said electroconductive nanoobjects is significantly larger, i.e. it differs from the other two external dimensions by more than three times.
According to ISO/TS 27687:2008, nanoobjects having two similar external dimensions in the nanoscale, while the third external dimension is significantly larger, are generally referred to as nanofibers. Electrically conductive nanofibers are also referred to as nan- owires. Hollow nanofibers (irrespective of their electrical conductivity) are also referred to as nanotubes.
Metal nanoobjects as defined above which are to be used for the present invention typically have a cross section close to circular shape. Said cross section extends perpendicu- larly to said external dimension which is in the range of from 1 μιη to 100 μιη. Thus, said two external dimensions which are in the nanoscale are defined by the diameter of said circular cross section. Said third external dimension extending perpendicularly to said diameter is referred to as the length.
Preferably, in a layer assembly according to the present invention the coating comprises metal nanoobjects having a length in the range of from 1 μιη to 100 μιη, preferably of from 3 μιη to 50 μιη, more preferably of from 10 μιη to 50 μιη, and a diameter in the range of from 1 nm to 100 nm, preferably of from 2 nm to 50 nm, more preferably of from 15 nm to 30 nm, length and diameter in each case being determined by transmission electron microscopy. The term "metal nanoobject" means that the nanoobject comprises or consists of one or more materials selected from the group consisting of metals and alloys of metals. As metals are capable of allowing the flow of electrons, a plurality of such metal nanoobjects may form a conductive network of adjacent and overlapping nanoobjects capable of carrying an electric current throughout said matrix, provided that there is sufficient inter- connection (mutual contact) between individual metal nanoobjects so as to enable the transport of electrons along the interconnected metal nanoobjects within the network.
Preferably, said metal nanoobjects consist of materials selected from the group consisting of silver, copper, gold, platinum, tungsten, aluminum, iron, cobalt and nickel and alloys of two or more metals selected from the group consisting of silver, copper, gold, platinum, tungsten, aluminum, iron, cobalt and nickel.
Preferably, said metal nanoobjects are selected from the group consisting of nanowires and nanotubes. Preferred nanowires comprise or consist of one or more metals selected from the group consisting of silver, copper and gold.
Among nanowires and nanotubes, nanowires are preferred. Preferably, said metal nanoobjects are nanowires consisting of a metal selected from the group consisting of silver, copper, gold, platinum, tungsten, aluminum, iron, cobalt and nickel, or of an alloy of two or more metals selected from silver, copper, gold, platinum, tungsten, aluminum, iron, cobalt and nickel, wherein said nanowires preferably have a length in the range of from 1 μιη to 100 μιη, preferably of from 3 μιη to 50 μιη, more preferably of from 10 μιη to 50 μιη, and a diameter in the range of from 1 nm to 100 nm, preferably 10 nm to 50 nm, most preferably 15 nm to 30 nm, length and diameter in each case being determined by transmission electron microscopy.
Most preferred metal nanoobjects are silver nanowires having the above-mentioned dimensions.
Suitable metal nanoobjects as defined above are known in the art (see e.g. US7922787) and are commercially available.
Silver nanowires (as well as nanowires of other metals) are typically commercially available in the form of an aqueous dispersion wherein polyvinylpyrrolidone is adsorbed onto the surface of the silver nanowires in order to render the dispersion stable. Any matter adsorbed on the surface of the nanowires is not included in the above-defined dimensions and composition of the metal nanoobjects.
Preferably, the silver nanowires are obtained by the procedure described by Yugang Sun and Younan Xia in Adv. Mater. 2002 14 No. 1 1 , June 5, pages 833-837. Preferably, in said coating the ratio between the total weight of said metal nanoobjects and the total weight of said organic polymers is in the range of from 1 : 20 to 20 : 1 , preferably in the range of from 1 : 5 to 5 : 1 .
Without wishing to be bound to any theory, it is presently assumed that in the coating the network of metal nanoobjects exerts a reinforcing effect on the matrix, thus imparting stability against environmental influences as well as mechanical integrity to said coating.
In said layer assembly according to the present invention, the substrate comprises polyvinylbutyral (PVB) and optionally plasticizers. In certain cases the substrate consists of polyvinylbutyral and optionally plasticizers. Polyvinylbutyrals are a class of polyvinylacetates obtainable by (at least partial) acetalisation of polyvinyl alcohol with butyraldehyde as explained above.
Said substrate comprising polyvinylbutyral is in the form of a sheet, a foil or a film. Suitable substrates are commercially available e.g. as Mowital LPBF™ or Trosifol OG™. Such commercially available films, sheets or foils typically contain plasticizers. It is important to note that the present invention does not impose any limitation regarding the amount of plasticizers in the substrate. Thus, the amount of plasticizers can be adjusted according to the desired flexibility of the substrate.
In certain cases said substrate comprises plasticizers in an amount of 5 % or less, based on the weight of polyvinylbutyral in said substrate.
Preferably, said substrate has a light transmission of 80 % or more, preferably 90 % or more, further preferably 95 % or more, in each case measured according to ASTM D1003 (Procedure A) as published in November 2013, and a haze of 3 % or less, more preferably 2 % or less, further preferably 1 % or less, especially preferably of 0.5 % or less, in each case measured according to ASTM D1003 (Procedure A) as published in November 2013.
In the layer assembly, the above-defined coating (optically transparent conductive layer) is arranged on a surface of said substrate in such manner that the coating partially or completely covers a surface of said substrate. In specific cases the coating forms a pattern on said surface of said substrate. The pattern may be selected from any random and non-random structures, like grids, stripes, waves, dots and circles.
In said layer assembly, said substrate has at least one surface which is not covered by the above-defined coating. Typically, the substrate has a first surface on which said coating is arranged and a second surface opposite to said first surface, wherein on said second surface none such coating is arranged. This second surface of the substrate is also referred to as the surface of the substrate facing away from said coating.
In said layer assembly, preferably said substrate has a thickness in the range of from 4 μιη to 250 μιη, and/or said coating has a thickness in the range of from 50 nm to 500 nm. Generally the lower limit of the thickness of the coating is determined by the smallest dimension of the metal nanoobjects. Further preferably, said substrate has a thickness in the range of from 4 μΐη to 250 μΐη, and said coating has a thickness in the range of from 50 nm to 500 nm.
Preferably, in said layer assembly, said coating (as defined above) has
a haze of 3 % or less as measured according to ASTM D1003 (procedure A), - and a sheet resistance of 100 Ohms/square or less as measured by the four point probe at a temperature of 23 °C and a pressure of 101.3 kPa,
and a light transmission of 80 % or more as measured according to ASTM D1003 (procedure A).
"Light transmission" refers to the percentage of an incident light which is transmitted through a medium. Preferably the light transmission of the coating is 85 % or more, more preferably 90 % or more, further preferably 95 % or more, in each case measured according to ASTM D1003 (Procedure A) as published in November 2013.
A preferred coating exhibits a haze of 2 % or less as measured according to ASTM D1003 (Procedure A) as published in November 2013, and/or a sheet resistance of 100 Ohms/square or less as measured by the four point probe at a temperature of 23 °C and a pressure of 101.3 kPa.
Preferably the haze of the coating 1.8 % or less, more preferably 1.5 % or less, further preferably 1 % or less, in each case measured according to ASTM D1003 (Procedure A) as published in November 2013. Preferably the sheet resistance of the coating is 100 Ohms/square or less, more preferably 80 Ohms/square or less, further preferably 40 Ohms/square or less, in each case measured by the four point probe at a temperature of 23 °C and a pressure of 101.3 kPa.
The measurement of haze and light transmission (in ASTM D1003 as published in November 2013 referred to as luminous transmittance which is the ratio of the luminous flux transmitted by a body to the flux incident upon it) by means of a hazemeter is defined in ASTM-D1003 as published in November 2013 as "Procedure A -Hazemeter". The values of haze and light transmission (corresponding to the luminous transmittance as defined in ASTM D1003 as published in November 2013) given in the context of the present invention refer to this procedure. Generally, haze is an index of the light diffusion. It refers to the percentage of the quantity of light which is separated from the incident light and scattered during transmission. Unlike light transmission, which is largely a property of the medium, haze is often a production concern and is typically caused by surface roughness, and by embedded particles or compositional heterogeneities in the medium.
According to ASTM D1003 as published in November 2013, in transmission, haze is the scattering of light by a specimen responsible for the reduction in contrast of objects viewed through said specimen, i.e. the percent of transmitted light that is scattered so that its direction deviates more than a specified angle (2.5 °) from the direction of the incident beam.
The sheet resistance is a measure of resistance of a thin body (sheet) namely uniform in thickness. The term "sheet resistance" implies that the current flow is along the plane of the sheet, not perpendicular to it. For a sheet having a thickness t, a length L and a width W, the resistance R is R = p *— = ^ *— = Rsh *—
Wt t w w
wherein Rsh is the sheet resistance. Accordingly the sheet resistance Rsh is
W
Rsh = R *—
L
In the formula given above the bulk resistance R is multiplied with a dimensionless quantity (W/L) to obtain the sheet resistance Rsh, thus the unit of sheet resistance is Ohms. For the sake of avoiding confusion with the bulk resistance R, the value of the sheet resistance is commonly indicated as "Ohms per Square" (Ohms/square) because in the specific case of a square sheet W = L and R = Rsh. The sheet resistance is measured by means of a four point-probe at a temperature of 23 °C and a pressure of 101.3 kPa.
Further preferably, in said layer assembly said coating (as defined above) exhibits one or more of the following features:
a haze of 1 % or less as measured according to ASTM D1003 (procedure A) as published in November 2013,
a sheet resistance of 40 Ohms/square or less as measured by the four point probe at a temperature of 23 °C and a pressure of 101.3 kPa, a light transmission of 90 % or more as measured according to ASTM D1003 (procedure A) as published in November 2013.
Particularly preferably, in said layer assembly said coating (as defined above) exhibits the following features:
- a haze of 1 % or less as measured according to ASTM D1003 (Procedure A) as published in November 2013, and
a sheet resistance of 40 Ohms/square or less as measured by the four point probe at a temperature of 23 °C and a pressure of 101.3 kPa, and
a light transmission of 90 % or more as measured according to ASTM D1003 (Procedure A) as published in November 2013.
Preferred coatings according to the present invention are those wherein two or more of the above-defined preferred features are combined.
Preferred layer assemblies according to the present invention are those wherein two or more of the above-defined preferred features are combined. A preferred article according to the present invention comprises
a layer assembly as described above
and further comprises a first support layer comprising a material selected from the group consisting of metals, glass and organic polymers, and a second support layer comprising a material selected from the group consisting of metal, glass and or- ganic polymers,
wherein said layer assembly is arranged between said first support layer and said second support layer.
Said first and second support layer are both in a form selected from the group consisting of foils, films, webs, panes and plates. Preferably, said first and said second support layer are both of the same material, the same form and have equal dimensions.
The materials of the support layers are selected such that at least one of said support layers has a light transmission of 80 % or more, preferably 90 % or more, measured according to ASTM D1003 (Procedure A) as published in November 2013. Preferably, both of said support layers has a light transmission of 80 % or more, preferably 90 % or more, measured according to ASTM D1003 (Procedure A) as published in November 2013.
Said support layers comprise one or more materials selected from the group consisting of metals, glasses and organic polymers. Preferred types of glass are e.g. float glass, low iron float glass, heat strengthened glass and chemically strengthened glass. Optionally, the glass has a low-emissivity (low-e) coating, sun-protection coating or any other coating on the surface facing away from the above-described layer assembly.
Optionally, antireflection (AR) coating can be used to enhance the transmittance through optical devices, and a variety of low refractive index, nanoporous, and/or nanostructured coatings can be applied to glass and plastic substrates (see for example: C. G. Granqvist, Transparent conductors as solar energy materials: a panoramic review, Solar Energy Mater. Solar Cells 91 , 1529-1598 (2007)). It has been demonstrated that coating both sides of a glass pane with self-assembled silica nanoparticle films made it possible to obtain a transmittance as large as 99.5% in the middle of the luminous spectrum (cf. P. Nostel, A. Roos, and B. Karlsson, Optical and mechanical properties of sol-gel antireflec- tive films for solar energy applications, Thin Solid Films 351 , 170-175 (1999); S. E. Yancey, W. Zhong, J. R. Heflin, and A.L. Ritter, The influence of void space on antireflection coatings of silica nanoparticle self-assembled films, J. Appl. Phys. 99, 034313 vol. 1-10 (2006)).
Preferred organic polymers are selected from the group consisting of polymethylmethacrylate (PMMA, commercially available e.g. as Plexiglas™), polycarbonate (PC), polyethylene (PE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), polypropylene (PP), low density polypropylene (LDPP), polyeth- ylene therephthalate (PET), glycol modified polyethylene therephthalate, polyethylene napthalate (PEN), cellulose acetate butyrate, polylactide (PL), polystyrene (PS), polyvinyl chloride (PVC), polyimides (PI), polypropyleneoxide (PPO) and mixtures thereof.
In certain articles according to the present invention, said first support layer is attached to the above-defined coating (optically transparent conductive layer) which in turn is ar- ranged on a first surface of said substrate comprising PVB, and said second support layer is attached to said second surface of said substrate comprising PVB facing away from said coating. Preferably, said article comprises an adhesive layer between said coating and said first support layer and/or an adhesive layer between said substrate comprising polyvinylbutyral and said second support layer.
Further preferably, said article comprises a first adhesive layer between said coating and said first support layer and a second adhesive layer between said substrate comprising polyvinylbutyral and said second support layer.
The adhesives are selected such that the adhesive layer has a light transmission which does not exceed the light transmission of the support layer which is attached to the layer assembly by said adhesive. Suitable adhesives are thermoplastics, e.g. polyvinylbutyral commercially available e.g. under the trade names Butvar, Mowital, Pioloform, BUTACITE, SAFLEX, S-Lec, TROSIFOL, polyvinylalcohol, polyvinylacetate, ethylene-vinylacetate-copolymers, silicones, polyurethanes, ionomer resins (commercially available e.g. under the trade name SentryGlas®) and polymethylmethacrylate (PMMA). The adhesives of said first adhesive layer and said second adhesive layer have identical or different chemical composition. Preferred are two identical adhesives, especially preferred are two identical adhesives from the group consisting of polyvinylbutyrals.
In other articles according to the present invention, further layers are arranged between said first support layer and said coating (optically transparent conductive layer), and/or between said second support layer and said substrate comprising PVB. Said further layers are herein also referred to as functional layers. In preferred examples, such further layers comprise one or more items from the group consisting of liquid crystals (LC), polymer dispersed liquid crystals (PDLC), nano polymer dispersed liquid crystals (nPDLC), LC guest-host systems comprising dyes, PDLC guest-host systems comprising dyes, nPDLC guest-host systems comprising dyes, photochromic materials, electrochromic materials, photo-electrochromic materials and thermochromic materials. Particularly preferred are functional layers comprising one or more electrochromic materials. The term dyes as used herein includes dichroic dyes.
A preferred article according to the invention comprises a first layer assembly and a second layer assembly as defined above, and a functional layer as defined above or a sequence of two or more functional layers (as defined above) arranged between said first layer assembly and said second layer assembly such that the functional layer or the sequence of functional layers is in contact with the coating of the first layer assembly and with the coating of the second layer assembly. In other words, in said article the coating of the first layer assembly and the coating of the second layer assembly each face towards the functional layer or towards the sequence of functional layers, thus sandwiching the functional layer or the sequence of functional layers, and the substrate of the first layer assembly and the substrate of the second layer assembly face away from said functional layer or said sequence of functional layers. In some of such articles, the coat- ing of the first layer assembly and the coating of the second layer assembly interact as electrodes with the functional layer, i.e. enable applying an electrical field across said functional layer. Preferably, in such article the functional layer comprises an electrochro- mic material or the sequence of functional layers comprises at least one functional layer comprising an electrochromic material. Preferably, said sequence of functional layers comprises or consists of a first functional layer comprising a first electrochromic material in contact with the coating of the first layer assembly, a second functional layer comprising an ion-conducting material which virtually blocks electron flow, and a third functional layer comprising a second electrochromic material in contact with the coating of the second layer assembly. Preferably, in an article according to the present invention said support layers each have a thickness in the range of from 0.1 mm to 10 mm, preferably 0.5 mm to 6 mm, particularly preferably 2 mm to 6 mm.
Preferably, in an article according to the present invention said adhesive layers each have a thickness in the range of from 0.1 mm to 2 mm, preferably 0.3 mm to 2 mm, particularly preferably 0.38 to 1.52 mm.
Particularly preferably said support layers each have a thickness in the range of from 0.1 mm to 10 mm, preferably 0.5 mm to 6 mm, particularly preferably 2 mm to 6 mm, and said adhesive layers each have a thickness in the range of from 0.1 mm to 2 mm, preferably 0.3 mm to 2 mm, particularly preferably 0.38 to 1 .52 mm. A preferred article according to the present invention comprises
a layer assembly as described above a first support layer and a second support layer as described above, wherein said layer assembly is arranged between said first support layer and said second support layer
one or more further support layers attached to one or both of the first and second support layer.
In articles having a further support layer attached to said first support layer, preferably an adhesive layer is arranged between said first support layer and said further support layer.
In articles having a further support layer attached to said second support layer, preferably an adhesive layer is arranged between said second support layer and said further support layer.
Statements made above regarding preferred specific and preferred features and types of support layers and adhesives apply also to this preferred article of the present invention.
Preferred articles according to the present invention are those wherein two or more of the above-defined preferred features are combined.
It has been found that in an article according to the present invention the layer assembly can be combined with the support layers without introducing optical heterogeneities, because the substrate comprising polyvinylbutyral readily adapts itself to the surface of the support layer, even in the case that the support layer has a curved shape.
Exemplary preferred articles according to the present invention are illustrated in figures 1 and 2 which are schematic side elevation of said article not drawn to scale.
The article 1 according to figure 1 consists of
a first support layer 1 1
a first adhesive layer 13
a layer assembly 15 consisting of
a coating 25 comprising
a matrix 26 formed of one or more organic polymers and dispersed within said matrix 26, metal nanoobjects 27 having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 μιη to 100 μιη, in each case determined by transmission electron microscopy a substrate 35 comprising polyvinylbutyral, said substrate having a first surface 36 and a second surface 37
a second adhesive layer 14
a second support layer 12
a third support layer 16
a fourth support layer 17
a third adhesive layer 18
a fourth adhesive layer 19.
In said article 1 , said layer assembly 15 is arranged between said first support layer 1 1 and said second support layer 12. Said layer assembly 15 consists of a substrate 35 and a coating 25 arranged on a first surface 36 of said substrate. Said coating 25 comprises a matrix 26 formed of one or more organic polymers and, dispersed within said matrix 26, metal nanoobjects 27 having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 μιη to 100 μιη, in each case determined by transmission electron microscopy. Substrate 35 has a second surface 37 facing away from said coating 25.
Article 1 further comprises a first adhesive layer 13 between said coating 25 and said first support layer 1 1 and a second adhesive layer 14 between said substrate 35 and said second support layer 12. In said article, said first support layer 1 1 is attached by means of first adhesive layer 13 to the above-defined coating 25 arranged on a first surface 36 of said substrate 35, and said second support layer 12 is attached by means of second adhesive layer 14 to said second surface 37 of said substrate 35 facing away from said coating 25.
Article 1 further comprises a third adhesive layer 18 between said first support layer 1 1 and said third support layer 16, and a fourth adhesive layer 19 between said second support layer 12 and said fourth support layer 17. In said article, said first support layer 1 1 is attached by means of third adhesive layer 18 to the third support layer 16, and said second support layer 12 is attached by means of fourth adhesive layer 19 to said fourth support layer 17.
Based on article 1 as shown in figure 1 , one or more of the following modifications are possible, which correspond to other preferred articles according to the present invention: omitting one or both of adhesive layers 13 and 14
omitting one or both of adhesive layers 18 and 19
omitting support layer 16 and adhesive layer 18
omitting support layer 17 and adhesive layer 19
omitting support layers 16 and 17 and adhesive layers 18 and 19.
The article 2 according to figure 2 consists of
a first support layer 1 1
a first adhesive layer 13
a first layer assembly 1 15 consisting of
a substrate 135 comprising polyvinylbutyral, said substrate having a first surface 136 and a second surface 137
and a coating 125 comprising
a matrix 126 formed of one or more organic polymers and dispersed within said matrix 126, metal nanoobjects 127 having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 μιη to 100 μιη, in each case determined by transmission electron microscopy a functional layer 100
a second layer assembly 215 consisting of
a coating 225 comprising
a matrix 226 formed of one or more organic polymers and dispersed within said matrix 226, metal nanoobjects 227 having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 μιη to 100 μιη, in each case determined by transmission electron microscopy. and a substrate 235 comprising polyvinylbutyral, said substrate having a first surface 236 and a second surface 237
a second adhesive layer 14
a second support layer 12
a third support layer 16
a fourth support layer 17
a third adhesive layer 18
a fourth adhesive layer 19.
Said first layer assembly 1 15 consists of substrate 135 and coating 125 arranged on first surface 136 of said substrate. Said coating 125 comprises a matrix 126 formed of one or more organic polymers and, dispersed within said matrix 126, metal nanoobjects 127 having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 μιη to 100 μιη, in each case determined by transmission electron microscopy. Substrate 135 has a second surface 137 facing away from said coating 125.
Said second layer assembly 215 consists of substrate 235 and coating 225 arranged on first surface 236 of said substrate. Said coating 225 comprises a matrix 226 formed of one or more organic polymers and, dispersed within said matrix 226, metal nanoobjects 227 having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 μιη to 100 μιη, in each case determined by transmission electron microscopy. Substrate 235 has a second surface 237 facing away from said coating 225.
In said article 2, said functional layer 100 is arranged between and in contact with coating 125 of said first layer assembly 1 15 and coating 225 of said second layer assembly 215, Thus, coatings 125 and 225 sandwich the functional layer 100, and the substrate 135 of the first layer assembly 1 15 and the substrate 235 of the second layer assembly 215 face away from said functional layer 100. Instead of a single functional layer 100, a sequence of functional layer may be arranged between coating 125 of said first layer assembly 1 15 and coating 225 of said second layer assembly 215. Said functional layer 100 comprises one or more items from the group consisting of liquid crystals (LC), polymer dispersed liquid crystals (PDLC), nano polymer dispersed liquid crystals (nPDLC), LC guest-host systems comprising dyes, PDLC guest-host systems comprising dyes, nPDLC guest-host systems comprising dyes, photochromic materials, electrochromic materials, photo-electrochromic materials and thermochromic materials. Preferably, functional layer 100 comprises an electrochromic material.
Article 2 further comprises a first adhesive layer 13 between said substrate 135 and said first support layer 1 1 and a second adhesive layer 14 between said substrate 235 and said second support layer 12. In said article, said first support layer 1 1 is attached by means of first adhesive layer 13 to said surface 137 of said substrate 135 facing away from said coating 125, and said second support layer 12 is attached by means of second adhesive layer 14 to said surface 237 of said substrate 235 facing away from said coating 225.
Article 2 further comprises a third adhesive layer 18 between said first support layer 1 1 and said third support layer 16, and a fourth adhesive layer 19 between said second support layer 12 and said fourth support layer 17. In said article, said first support layer 1 1 is attached by means of third adhesive layer 18 to the third support layer 16, and said second support layer 12 is attached by means of fourth adhesive layer 19 to said fourth support layer 17. Based on article 2 as shown in figure 2, one or more of the following modifications are possible, which correspond to other preferred articles according to the present invention: omitting one or both of adhesive layers 13 and 14
omitting one or both of adhesive layers 18 and 19
omitting support layer 16 and adhesive layer 18
- omitting support layer 17 and adhesive layer 19
omitting support layers 16 and 17 and adhesive layers 18 and 19.
Typical articles according to the invention (as defined above) are selected from the group consisting of transparent electrodes, touch panels, wire polarizers, capacitive and resistive touch sensors, NIR reflection, EMI shielding, transparent and non transparent heaters (e.g. for mirror and / or glass and / or window defogging, automotive, ships, space crafts, aircrafts, transportation devices and / or vehicles, indoor and outdoor spaces and / or living space and other applications), flexible displays, plasma displays, electrophoretic displays, liquid crystal displays, transparent antennas, electrochromic devises (e.g. smart windows), photovoltaic devices (especially thin-film photovoltaic cells), electroluminescent devices, light emitting devices (LED) and organic light emitting devices (OLED), flexible devices that can be worn (so-called wearables) such as flexible watches or foldable screens, as well as functional coatings imparting anti-fogging, anti-icing or antistatic properties, and dielectric and ferroelectric haptic films. However the present invention is not limited by these applications and can be used in many other electro optical devices by those skilled in the art. Preferred are transparent heaters, specially preferred transparent heaters for automotive applications, e.g. for windshields, particularly preferred transparent heaters for electro automotive applications (e-cars).
A further aspect of the present invention relates to a process for preparing an article according to the present invention as defined above, said process comprising
forming a layer assembly consisting of
a substrate comprising polyvinylbutyral
and a coating arranged on a surface of said substrate, said coating comprising a matrix formed of one or more organic polymers
and dispersed within said matrix metal nanoobjects having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 μιη to 100 μιη, in each case determined by transmission electron microscopy
wherein forming said layer assembly comprises the steps of
preparing or providing a composition comprising
(A) a mixture comprising
(A-1 ) water,
(A-2) one or more alcohols selected from the group consisting of methanol, etha- nol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol,
(B) metal nanoobjects dispersed in said mixture (A),
said metal nanoobjects (B) having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 μιη to 100 μιη, in each case determined by transmission electron microscopy,
wherein the total weight fraction of said metal nanoobjects (B) is in the range of from 0.01 wt.-% to 2 wt.-% based on the total weight of the composition, (C) one or more organic polymers dispersed or dissolved in said mixture (A), wherein the total weight fraction of said organic polymers (C) is in the range of from 0.02 wt.-% to 5 wt.-%, based on the total weight of the composition providing a substrate comprising polyvinylbutyral,
forming on a surface of said substrate a wet film by applying said composition to said surface of said substrate,
removing the constituents which at 25 °C and 101.325 kPa are liquid from said wet film on said surface of said substrate by exposing said wet film to a temperature in the range of from 40 °C to 80 °C, preferably 40 °C to 60 °C, thereby forming said coating on said surface of said substrate. A composition used in the process according to the invention (as defined above) is also referred to as an ink.
In the ink used in the process according to the invention (as defined above), the main constituent which at 25 °C and 101.325 kPa is liquid is a mixture (A) comprising
(A-1 ) water and
(A-2) one or more alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol;
and the main constituents which at 25 °C and 101.325 kPa are solid are the above- defined metal nanoobjects (B) and the above-defined one or more organic polymers (C). In the ink used in the process according to the present invention (as defined above), the total concentration of constituents which at 25 °C and 101.325 kPa are solid (solid constituents) is 10 wt.-% or less, preferably 8 wt.-% or less, further preferably 5 wt.-% or less, in each case based on the total weight of said ink.
The above-defined mixture (A) does not remain in the coating to be formed but merely is a vehicle for wet processing. Constituent (A) of the ink used in the process according to the present invention (as defined above) is a mixture comprising
(A-1 ) water,
(A-2) one or more alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol.
Said mixture (A) is monophase (i.e. forms a single phase in said ink).
Surprisingly it has been found that the presence of one or more alcohols (A-2) as defined above does not only promote wetting of the surface of a substrate to which the ink is applied but also promotes the dispersibility of the nanoobjects (B) (especially in the case of nanoobjects (B) in the form of silver nanowires) in the ink, resulting in improved connectivity of the conductive network formed in the coating obtainable from said ink.
Preferably the mixture (A) consists of
(A-1 ) water and
(A-2) one or more alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol.
More preferably the mixture (A) consists of
(A-1 ) from 70 % to < 100 % of water,
(A-2) from > 0 to 30 % of one or more alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol, in each case based on the total volume of the mixture (A).
Further preferably the mixture (A) consists of
(A-1 ) 70 % to 98 % of water,
(A-2) 2 % to 30 % of one or more alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol, in each case based on the total volume of the mixture (A).
If the proportion of said alcohols (A-2) is more than 30 % based on the total volume of the mixture (A), the drying speed of the ink is quite fast, which may result in clogging of fluid passages in the coating equipment which the ink must pass in the process of coating. If the proportion of said alcohols (A-2) is less than 2 % based on the total volume of the mixture (A), the drying speed of the ink is quite low, which makes the coating process inefficient. The rather low thermal stability of PVB precludes application of temperatures above 80 °C. Thus, speeding up of the removal the constituents which at 25 °C and 101.325 kPa are liquid by increase of the temperature is limited to temperatures of at most 80 °C. Therefore, it is important to apply an ink which exhibits an appropriate drying speed at a temperature of 80 °C or below.
Particularly preferably the mixture (A) consists of
(A-1 ) 75 % to 85 % of water,
(A-2) 15 % to 25 % of one or more alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol, in each case based on the total volume of the mixture (A).
Among the alcohols (A-2) as defined above, i-butanol is less preferred due to its low solubility in water. Furthermore, in some cases methanol and ethanol are not preferred because of restrictive legal regulations.
Preferably the one or more alcohols (A-2) are selected from the group consisting of i-propanol, n-butanol and t-butanol, because they are miscible with water in the desired range, and use of inks comprising one or more of these alcohols results in coatings with best optical properties and electronic conductivity among all of the alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol.
Constituent (B) of the ink used in the process according to the present invention (as defined above) consists of metal nanoobjects as defined above. In the ink used in the process according to the invention (as defined above) the total weight fraction of said electroconductive nanoobjects (B) as defined above is 2.0 wt.-% or less, based on the total weight of the ink. The total weight fraction of said electroconductive nanoobjects (B) is not less than 0.01 wt.-%, based on the total weight of the ink, because a total weight fraction of less than 0.01 wt.-% of electroconductive nanoobjects (B) may be not sufficient for forming a conductive network. Further preferably the total weight fraction of said metal nanoobjects (B) is not less than 0.02 wt.-%, preferably not less than 0.05 wt.-%.
Constituent (C) of the ink according to the present invention (as defined above) consists of one or more organic polymers as described above. Said organic polymers are selected from the group consisting of polymers dissolved in mixture (A) and polymers suspended in mixture (A). The mixture (A) as defined above and the one or more dissolved polymers (C) as defined above are monophase (i.e. form a single phase). Polymers suspended in mixture (A) substantially do not dissolve in mixture (A) and are present in the ink in the form of dispersed discrete solid particles e.g. fibers or polymer beads. Water-soluble polymers are known in the art and commercially available. Typically such copolymers are commercially available in the form of aqueous solutions. Preferred water- soluble polymers are selected from the group consisting of cellulose alkyl ethers, cellulose hydroxyalkyl ethers, cellulose esters, dextranes, polyacrylamides, polyvinylalcohol, polyvinylpyrrolidone, polystyrenesulfonic acid, and the above-described sty- rene/(meth)acrylic copolymers having a number average molecular weight in the range of from 500 g/mol to 22000 g/mol.
Polymer beads are known in the art and commercially available in the form of aqueous dispersions of said polymer beads (aqueous polymer dispersions). Typically, the dispersed polymers are present in colloidal dispersion. An aqueous colloidal dispersion of polymer particles is also referred to as a latex.
Colloidal stability of latex is achieved by a balancing of electrostatic repulsion, van der Waals attraction and steric attraction or repulsion. A latex typically comprises dispersing assistants which serve to ensure the stability of the aqueous polymer dispersions. Suitable dispersing agents are selected from the group consisting of protective colloids and surfactants. When a latex is deposited on a substrate and evaporation of the liquid phase is allowed to proceed, a continuous, a homogeneous film (coating) is formed under appropriate conditions. This process is called film formation. The mechanism of film formation from latex is described e g. in Materials Science and Engineering, 21 101 -170 and in Advances in Colloid and Interface Science 86 (2000) 195-267. Generally, the formation of a latex film arises from the 'coalescence' i.e. compaction, deformation, cohesion and polymer chain interdiffusion of the individual latex particles (polymer beads) which in the aqueous dispersion are held apart by stabilizing forces (electrostatic and/or steric) resulting e g. from charged polymer chain endgroups or adsorbed surfactants. These and other forces resisting particle deformation are overcome upon evaporation of the continuous phase of the latex (water).
Preferably, in the ink used in the process according to the invention (as defined above), the total weight fraction of said polymers (C) is less than 2 wt.-%, more preferably 1.8 wt.- % or less, further preferably 1.5 wt.-% or less, especially preferably 1 wt.-% or less, based on the total weight of the ink. The total weight fraction of said polymers (C) is not less than 0.02 wt.-%, based on the total weight of the ink, because a total weight fraction of less than 0.02 wt.-% of said polymers (C) may be not sufficient for binding the metal nanoobjects (B). Further preferably the total weight fraction of said polymers (C) is not less than 0.05 wt.-%, preferably not less than 0.1 wt.-%.
Preferably, in the ink for the process according to the present invention (as defined above), the ratio between the total weight of said metal nanoobjects (B) and the total weight of said polymers (C) is in the range of from 1 :20 to 20:1 , preferably from 1 : 10 to 5: 1 , further preferably from 1 :5 to 5: 1.
The ink for the process according to the present invention optionally comprises further constituents beside the above-defined constituents (A) to (C), e.g. defoaming agents, rheological controlling agents, corrosion inhibitors, wetting agents resp. surfactants and other auxiliary agents. Suitable wetting agents, surfactants, defoaming agents, rheologi- cal controlling agents and corrosion inhibitors are known in the art and commercially available.
Surprisingly it has been found that inks which do not contain any further constituents beyond the above-defined constituents (A-1 ), (A-2), (B) and (C) are suitable for the preparation of coatings having superior optical properties as well as satisfying electronic conductivity. Accordingly, the addition of any auxiliary agents can be omitted, thus rendering the formulation of the ink less complex and facilitating preparation of such ink. Moreover wetting agents resp. surfactants usually are substances which are either solid at 25 °C and 101.325 kPa or have such a high boiling point at 101 .325 kPa that they are not readily removed after the ink is applied to the substrate. Thus, the wetting agents resp. surfactants remain as foreign matter in the coating which is formed on said surface of said substrate, thereby introducing compositional heterogeneity in said coating and affecting the characteristics of said coating. More specifically, such wetting agents resp. surfactants do not contribute to the electronic conductivity of the coating, and typically do not contribute to matrix formation, but often may have a detrimental effect on the optical properties of the coating, even if said wetting agents resp. surfactants are present in the ink in a quite low concentration. In addition, the presence of a surfactant in the ink may induce foam formation which may result in inhomogeneity and discontinuity of a coating prepared using said ink.
Accordingly, in preferred processes according to the present invention the ink consists of above-defined constituents (A-1 ), (A-2), (B) and (C). Nevertheless, in certain cases the ink used in the process according to the present invention (as defined above) comprises one or more auxiliary agents, especially those as defined above.
Particularly preferably the ink used in the process according to the present invention does not contain any surfactants which are neither polymers (C) as defined above nor alcohols (A-2) as defined above.
It is understood that any further constituents (beside the above-defined constituents (A) to (C)) of the ink used in the process according to the present invention (as defined above) as well as the amounts of such further constituents have to be selected in such manner that the electrical conductivity and the optical properties of a coating obtainable from said ink are not compromised.
Preferred compositions for the process according to the present invention are those wherein two or more of the above-defined preferred features are combined.
Particularly preferred is a composition comprising or consisting of
(A) a mixture consisting of
(A-1 ) 70 % to 98 % of water,
(A-2) 2 % to 30 % of one or more alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol in each case based on the total volume of the mixture (A);
(B) silver nanowires dispersed in said mixture (A), said silver nanowires (B) having a length in the range of from 10 μιη to 50 μιη and a diameter in the range of from 3 nm to 30 nm, in each case determined by transmission electron microscopy,
wherein the total weight fraction of said silver nanowires (B) is 2 wt.-% or less, based on the total weight of the composition;
(C-1 ) dissolved in mixture (A), one or organic polymers selected from the group consisting of cellulose alkyl ethers, cellulose hydroxyalkyl ethers and cellulose esters
(C-2) suspended in mixture (A), fibers of crystalline cellulose
wherein the total weight fraction of constituents (C1 ) and (C2) is less than 2 wt.-%, preferably 1.5 wt.-% or less, based on the total weight of the composition wherein the ratio between
the total weight of said silver nanowires (B)
and
the total weight of constituents (C1 ) and (C2)
is in the range of from 1 :5 to 5: 1.
A composition for use in the process according to the present invention is preparable e.g. by suspending an appropriate amount of the above-defined metal nanoobjects (B) in water (A-1 ) and dissolving and/or suspending an appropriate amount of the above- defined polymers (C) in water (A-1 ) and adding an appropriate amount of one or more alcohols (A-2) as defined above, or by combining appropriate amounts of a pre- manufactured aqueous suspension of said metal nanoobjects (B) and of a pre- manufactured aqueous solution or suspension of said one or more polymers (C) and adding an appropriate amount of one or more alcohols (A-2) as defined above, or by suspending an appropriate amount of said metal nanoobjects (B) in a pre-manufactured aqueous solution or suspension of said one or more polymers (C) and adding an appropriate amount of one or more alcohols (A-2) as defined above, or by dissolving or suspending an appropriate amount of said one or more polymers (C) in a pre-manufactured aqueous suspension of said metal nanoobjects (B) and adding an appropriate amount of one or more alcohols (A-2) as defined above.
Preferably after combining the constituents (A-1 ), (A-2), (B) and (C) as defined above and optionally further constituents (as defined above), the composition is subjected to ball- milling in order to improve homogenization of the composition. In certain embodiments, a prolonged homogenization treatment is preferably in order to ensure that the obtained coatings have a low haze.
Preferably, said ink is applied to said surface of said solid substrate by coating or printing, preferably by a continuous coating or printing technique. Such techniques are generally considered advantageous for large scale production, when compared to vacuum-based techniques. Applying said composition to said surface of said substrate is carried out by means of a technique selected from the group consisting of spin coating, draw down coating, roll-to-roll coating, gravure printing, microgravure printing, screen-printing, flexoprinting and slot-die coating.
Preferably, said composition is applied to said surface of said substrate in a thickness in a range of from 1 μιη to 200 μιη, preferably of from 2 μιη to 60 μιη. Said thickness is also referred to as "wet thickness" and relates to the thickness of the wet film before removing the liquid constituents of the ink. At a given wet thickness of the ink applied to the surface of a substrate for the preparation of coating as defined above, the thickness and accordingly the opacity of the obtainable coating (after removing the constituents which at 25 °C and 101.325 kPa are liquid from said wet film) increases with increasing concentration of solid constituents in the applied ink. Unfortunately, decreasing the thickness and opacity of the obtainable coating by decreasing the wet thickness of the applied ink is limited, because for technical reasons there is a lower limit of the wet thickness. Thus, in order to obtain a useful coating at all, often the wet thickness must be as close to said lower limit as possible.
At a given target thickness (after removing the liquid constituents of the ink) and accordingly a given target sheet resistance and light transmission of the coating to be prepared, the wet thickness of the applied ink may be the higher the lower the concentration of solid constituents is in the ink. The process of applying the ink is facilitated when there is no constraint to apply the ink in particular low wet thickness. This is achieved by means of the above-described ink, because in said ink the concentration of solid constituents is sufficiently low. In the above-defined process according to the present invention, the constituents which at 25 °C and 101.325 kPa are liquid are removed from said wet film on said surface of said substrate by exposing said wet film to a temperature in the range of from 40 °C to 80 °C, preferably 40 °C to 60 °C, most preferably 40 °C to 50 °C, thereby forming said coating on said surface of said substrate, said coating comprising
a matrix formed of one or more organic polymers
and dispersed within said matrix metal nanoobjects having two external dimen- sions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 μιη to 100 μιη, in each case determined by transmission electron microscopy.
In the context of the present application, the process step of removing the constituents which at 25 °C and 101.325 kPa are liquid from said wet film applied to said surface of said substrate to such extent that a coating is formed on said surface of said substrate is also referred to as drying. Usually, the liquid constituents are removed by evaporation. Preferably, the process step of removing the constituents which at 25 °C and 101 .325 kPa are liquid from said wet film applied to said surface of said substrate is carried out by exposing said wet film to a temperature in the range of from 40 °C to 60 °C, preferably 40 °C to 50 °C, in order to avoid that the substrate comprising PVB suffers from thermal stress.
Limitation of the temperature to which the PVB substrate is exposed to at most 60 °C, preferably at most 50 °C is an important advantage of this preferred process according to the present invention, compared to the vacuum deposition methods according to WO 2015/109198, which may require that during physical vapor deposition or during sputtering the substrate experiences temperatures up to 75 °C or even up to 100 °C.
In cases where the one or more polymers comprise cross-linkable polymers, forming said coating on said surface of said substrate further comprises cross-linking said polymers. Suitable means for initiating cross-linking are known in the art. Preferred processes according to the present invention are those wherein two or more of the above-defined preferred features are combined.
In a preferred process according to the present invention, preparing said article further comprises the step of arranging said layer assembly between a first support layer comprising a material selected from the group consisting of metals, glass and organic poly- mers, and a second support layer comprising a material selected from the group consisting of metals, glass and organic polymers. In certain cases, in said process step
said first support layer is attached to said coating arranged on a surface of said substrate.
and
said second support layer is attached to said substrate comprising polyvinylbutyral.
Accordingly, a preferred process according to the present invention further comprises the step of arranging said layer assembly between a first support layer comprising a material selected from the group consisting of metals, glass and organic polymers, and a second support layer comprising a material selected from the group consisting of metals, glass and organic polymers, by
attaching said first support layer to said coating arranged on a surface of said substrate
attaching said second support layer to said substrate comprising polyvinylbutyral.
It is noted that in this context the terms first support layer and second support layer merely denote the position of said support layers relative to the coating and the substrate (as defined above) in the article to be formed, and not the sequence of carrying out the steps of attaching said support layers to said coating or substrate resp. More specifically, attaching said second support layer to said substrate comprising polyvinylbutyral may be completed before attaching said first support layer to said coating arranged on a surface of said substrate, and vice versa.
Preferably, attaching said first support layer to said coating comprises applying an adhesive layer between said coating and said first support layer and/or attaching said second support layer to said substrate comprises applying an adhesive layer between said substrate and said second support layer.
Further preferably, attaching said first support layer to said coating comprises applying a first adhesive layer between said coating and said first support layer and attaching said second support layer to said substrate comprises applying a second adhesive layer between said substrate and said second support layer.
Techniques for attaching said support layers to said layer assembly are known in the art and are described e.g. in WO 2015/109198. Typically, attaching said support layers to said layer assembly comprises placing said layer assembly on the (optionally adhesive- coated) surface of one of the support layers and then placing the other support layer on the layer assembly, thus obtaining a prelaminate assembly wherein the layer assembly is arranged between a first support layer and a second support layer. The prelaminate assembly is treated with heated rolls, followed by heating the prelaminate assembly at elevated pressure in some kind of chamber like an autoclave. According to a another technique, the prelaminate assembly is placed in a flexible vacuum bag followed by evacuating and heating said vacuum bag so that atmospheric forces press on the bag and hence the prelaminate. This is followed by further heating the vacuum-bagged prelaminate assembly either at atmospheric pressure or at elevated pressure in some kind of chamber like an autoclave.
Statements made above regarding preferred specific and preferred features and types of support layers and adhesives apply also to this aspect of the invention.
In other processes according to the present invention, in additional process steps further layers are arranged between said first support layer and said optically transparent conductive layer, and/or between said second support layer and said substrate comprising PVB.
Preferred processes according to the present invention are those wherein two or more of the above-defined preferred features are combined. A further aspect of the present invention relates to the use of a composition, said composition comprising
(A) a mixture comprising
(A-1 ) water,
(A-2) one or more alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol,
(B) metal nanoobjects dispersed in said mixture (A),
said metal nanoobjects (B) having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 μιη to 100 μιη, in each case determined by transmission electron microscopy wherein the total weight fraction of said metal nanoobjects (B) is in the range of from 0.01 wt.-% to 2 wt.-% based on the total weight of the composition,
(C) one or more organic polymers dispersed or dissolved in said mixture (A)
wherein the total weight fraction of said organic polymers (C) is in the range of from 0.02 wt.-% to 5 wt.-%, based on the total weight of the composition
for preparing a coating on a substrate comprising polyvinylbutyral.
Preferred is the use of a composition selected from the above-defined preferred compositions.
A further aspect of the present invention relates to the use of an article according to the present invention as defined above in automotive applications, especially in car windshields.
The invention is hereinafter further illustrated by means of an example.
An aqueous dispersion of silver nanowires (nanoobjects (B) as defined above) and an aqueous mixture comprising a first polymer (C-1 ) in the dissolved state and suspended fibers of a second polymer (C-2) is mixed with (A-2) isopropanol for a dispersing time of 30 minutes so as to obtain an ink having a concentration of silver nanowires (B) of 7 mg/ml and a total polymer concentration (C) of 21 mg/ml.
The ink is applied to a substrate comprising PVB (e. g. commercially available under the product specification Trosifol from Kuraray) using a draw-down bar (Erichsen K303) to obtain a wet film on said substrate (wet thickness t = 6 μιη, coating speed v = 2"/sec). The constituents which at 25 °C and 101 .325 kPa are liquid are removed from said wet film by exposing said wet film to a temperature in the range of from 40 °C to 50 °C for a duration of five minutes, thereby obtaining coating on said surface of said substrate.
Said polymer (C-1 ) is selected from the group consisting of cellulose alkyl ethers, cellu- lose hydroxyalkyi ethers and cellulose esters. Said fibers of polymer (C-2) are fibers of crystalline cellulose.
The sheet resistance Rsh given in Ohms/square (OPS) of the obtained coating is measured by a four-point probe station (Lucas lab pro-4) at a temperature of 23 °C and a pressure of 101.3 kPa, and the optical properties (as defined above) are measured according to ASTM D1003 procedure A-Hazemeter (as published in November 2013) by a haze-gard plus hazemeter (BYK Gardner). Transmission including the substrate is found to be 90.10 % total haze including the substrate 1.67 % (accordingly the haze of the coating is not more than 1.67 %) and the sheet resistance is found to be 23 Ohms per square.

Claims

Claims
1. An article comprising
a layer assembly consisting of
a substrate comprising polyvinylbutyral
and a coating arranged on a surface of said substrate, said coating comprising
a matrix formed of one or more organic polymers
and, dispersed within said matrix, metal nanoobjects having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 μιη to 100 μιη, in each case determined by transmission electron microscopy.
2. Article according to claim 1 , wherein
said substrate has a thickness in the range of from 4 μΐη to 250 μιη, preferably of from 50 to 250 μιη
and/or
said coating has a thickness in the range of from 50 nm to 500 nm, preferably of from 50 nm to 250 nm.
3. Article according to any preceding claim, wherein
said matrix comprises one or more polymers selected from the group consisting of cellulose, cellulose alkyl ethers, cellulose hydroxyalkly ethers, cellulose esters, dextranes, polyacrylamides, polyvinylalcohol, polyvinylpyrrolidone, polystyrenesulfonic acid, polystyrene, styrene/(meth)acrylic copolymers, styrene- butadiene copolymers, polyacrylates, polymethacrylates, copolymers of acrylates and methacrylates.
4. Article according to any preceding claim, wherein
said metal nanoobjects are nanowires consisting of a metal selected from the group consisting of silver, copper, gold, platinum, tungsten, aluminum, iron, cobalt and nickel, or of an alloy of two or more metals selected from silver, copper, gold, platinum, tungsten aluminum, iron, cobalt and nickel, wherein said nanowires preferably have a length in the range of from 1 μιη to 100 μιη, and a diameter in the range of from 1 nm to 100 nm, length and diameter in each case being determined by transmission electron microscopy.
5. Article according to any preceding claim, wherein in said coating the ratio between the total weight of said metal nanoobjects and
the total weight of said organic polymers
is in the range of from 1 : 20 to 20 : 1 .
6. Article according to any preceding claim, wherein said coating has
a haze of 3 % or less as measured according to ASTM D1003 (procedure A),
and a sheet resistance of 100 Ohms/square or less as measured by the four point probe at a temperature of 23 °C and a pressure of 101.3 kPa, and a light transmission of 80 % or more as measured according to ASTM D1003 (procedure A).
Article according to any preceding claim,
said article further comprising a first support layer comprising a material selected from the group consisting of metals, glass and organic polymers, and a second support layer comprising a material selected from the group consisting of metals, glass and organic polymers,
wherein said layer assembly is arranged between said first support layer and said second support layer.
Article according to claim 7, further comprising
an adhesive layer between said coating and said first support layer
and/or
an adhesive layer between said substrate comprising polyvinylbutyral and said second support layer. Article according to claim 7, said article comprising
a first layer assembly and a second layer assembly as defined in any of claims 1 to 6, and a functional layer arranged between said first layer assembly and said second layer assembly such that the functional layer is in contact with the coating of the first layer assembly and with the coating of the second layer assembly, wherein said functional layer comprises one or more items selected from the group consisting of liquid crystals (LC), polymer dispersed liquid crystals (PDLC), nanopolymer dispersed liquid crystals (nPDLC), LC guest-host systems comprising dyes, PDLC guest-host systems comprising dyes, nPDLC guest-host systems comprising dyes, photochromic materials, electrochromic materials, photo-electrochromic materials and thermochromic materials.
Process for preparing an article according to any of claims 1 to 9,
said process comprising forming a layer assembly consisting of
a substrate comprising polyvinylbutyral
and a coating arranged on a surface of said substrate, said coating comprising
a matrix formed of one or more organic polymers
and, dispersed within said matrix, metal nanoobjects having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 μιη to 100 μιη, in each case determined by transmission electron microscopy
wherein forming said layer assembly comprises the steps of
preparing or providing a composition comprising
(A) a mixture comprising
(A-1 ) water,
(A-2) one or more alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol,
(B) metal nanoobjects dispersed in said mixture (A),
said metal nanoobjects (B) having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 μιη to 100 μιη, in each case determined by transmission electron microscopy,
wherein the total weight fraction of said metal nanoobjects (B) is in the range of from 0.01 wt.-% to 2 wt.-% based on the total weight of the composition,
(C) one or more organic polymers dispersed or dissolved in said mixture (A),
wherein the total weight fraction of said organic polymers (C) is in the range of from 0.02 wt.-% to 5 wt.-%, based on the total weight of the composition
providing a substrate comprising polyvinylbutyral,
forming on a surface of said substrate a wet film by applying said composition to said surface of said substrate,
removing the constituents which at 25 °C and 101 .325 kPa are liquid from said wet film on said surface of said substrate by exposing said wet film to a temperature in the range of from 40 °C to 80 °C, preferably 40 °C to 60 °C, thereby forming said coating on said surface of said substrate.
1 1. Process according to claim 10, wherein
in said composition the mixture (A) consists of
(A-1 ) from 70 % to < 100 % of water,
(A-2) from > 0 % to 30 % of one or more alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t- butanol,
in each case based on the total volume of the mixture (A).
12. Process according to claim 10 or 1 1 wherein
in said composition the one or more alcohols (A-2) are selected from the group consisting of i-propanol, n-butanol and t-butanol. Process according to any of claims 10 to 12, wherein
applying said composition to said surface of said substrate is carried out by means of a technique selected from the group consisting of spin coating, draw down coating, roll-to-roll coating, gravure printing, microgravure printing, screen-printing, flexoprinting and slot-die coating.
Process according to any of claims 10 to 13, wherein preparing said article further comprises the step of
arranging said layer assembly between a first support layer comprising a material selected from the group consisting of metals, glass and organic polymers, and a second support layer comprising a material selected from the group consisting of metals, glass and organic polymers.
Process according to claim 14, wherein
said first support layer is attached to said coating of said layer assembly by applying an adhesive layer between said coating and said first support layer
and/or
said second support layer is attached to said substrate of said layer assembly by applying an adhesive layer between said substrate and said second support layer.
Use of a composition, said composition comprising
(A) a mixture comprising
(A-1 ) water,
(A-2) one or more alcohols selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and t-butanol,
(B) metal nanoobjects dispersed in said mixture (A),
said metal nanoobjects (B) having two external dimensions in the range of from 1 nm to 100 nm and their third external dimension in the range of from 1 μιη to 100 μιη, in each case determined by transmission electron microscopy
wherein the total weight fraction of said metal nanoobjects (B) is in the range of from 0.01 wt.-% to 2 wt.-% based on the total weight of the composition, (C) one or more organic polymers dispersed or dissolved in said mixture (A), wherein the total weight fraction of said organic polymers (C) is in the range of from 0.02 wt.-% to 5 wt.-%, based on the total weight of the composition for preparing a coating on a substrate comprising polyvinylbutyral.
Use of an article according to any of claims 1 to 9 in automotive applications, especially in windshields.
PCT/EP2017/066575 2016-07-06 2017-07-04 Coating containing metal particles WO2018007355A1 (en)

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