WO1998000762A1

WO1998000762A1 - Optical coatings containing a binder and one or more of polyhydroxyflavones, hydroxylated benzoic acid derivatives and hydroxylated naphthoic acid derivatives

Info

Publication number: WO1998000762A1
Application number: PCT/GB1997/001433
Authority: WO
Inventors: Michael Ellwood
Original assignee: Zeneca Limited
Priority date: 1996-07-02
Filing date: 1997-05-27
Publication date: 1998-01-08
Also published as: GB9613811D0; AU2967697A

Abstract

A durable polymeric optical coating for a metal substrate comprising a polymeric binder and an additive selected from a polyhydroxyflavone, a polyhydroxy benzoic acid derivative or a hydroxy or polyhydroxy naphthoic acid or a mixture thereof. The coatings of the present invention are particularly useful for the preparation of polymeric photoreceptors for use in printing and imaging technologies; and for polymeric optical coatings for metallised optical data storage discs and metallised diffraction gratings.

Description

OPTICAL COAΗNGS CONTAINING A BINDER AND ONE OR MORE OF POLYHYDROXYFLAVONES, HYDROXYLATED BENZOIC ACID DERIVATIVES AND HYDROXYLATED NAPHTHOIC ACID DERIVATIVES

This invention relates to polymeric coatings for metal substrates, particularly to polymeric optical coatings and more particularly to a polymeric photoreceptor on a metal substrate for use in printing and imaging technologies, to polymeric optical coatings for metallised optical data storage discs and metallised diffraction gratings and to a process for the formation of such coatings.

There are many optical devices which require a polymeric coating to be applied to a metal surface. Such coatings are often used as a barrier layer to protect the underlying metal surface, for example optical data storage discs such as a compact discs are coated with a protective polymeric layer. Similarly, diffraction gratings are often produced by forming the grating profile on a suitable substrate, for example a thermoplastic, which is subsequently coated with a metal to enhance the reflectivity and optical efficiency of the grating. Such gratings are often coated with a polymer passivating layer which acts to both protect the grating profile from damage and to prevent the formation of surface oxides and contamination on the metal grating surface. Diffraction gratings are used widely in optical apparatus, for example, in spectroscopy, optical telecommunications and for the production of optical diffraction pigments.

In other optical applications, the polymeric coating on the metal substrate forms an active part of the optical device. For example, in electrophotographic applications a photoreceptor is formed on a metal substrate. Conventionally the photoreceptor comprises a charge generation material (hereinafter referred to as CGM) and a charge transport material (hereinafter referred to as CTM). The CGM and CTM are dispersed in suitable binder polymer(s) and are coated onto the metal substrate. In operation the CGM absorbs incident photons to generate a charge carrier which is transported to the surface of the photoreceptor, via the CTM, under the influence of an electric field applied between the surface of the photoreceptor and the metal substrate.

In all of the aforementioned applications it is important that a durable bond is formed between the polymeric optical coating and the metal substrate so as to maximise the performance and operating life of the apparatus or device into which the polymeric coatings are incorporated. The polymeric optical coatings are often exposed to severe environmental conditions of high temperature and high humidity in combination with repeated mechanical contact within the apparatus in which they are utilised. For example, a photoreceptor formed on a metal drum in an electrophotographic device will typically undergo 20,000 rotations in contact with particulate toner materials during the lifetime of the photoreceptor. In such operating conditions a durable metal - polymeric bond is highly desirable. It is particularly important that the photoreceptor used in electrophotographic applications remains intact during operation. Delamination of the photoreceptor from the metal substrate can result in flakes, or particles, of the coating contaminating the imaging surface of the photoconductor. This has the effect of distorting the image formed on the photoreceptor which results in a deterioration in the print quality produced by the electrophotographic device.

An object of the present invention is to provide polymeric optical coatings which are high durable.

According to a first aspect of the present invention there is provided a polymeric optical coating for a metal substrate comprising a polymeric binder and an additive selected from a polyhydroxyflavone, a hydroxy or polyhydroxy benzoic acid derivative and a hydroxy or polyhydroxy naphthoic acid or a mixture thereof. The metal substrate comprises any metal surface and includes the surfaces of a metallic body and the metal surfaces of metal coated objects such as metallised polymers. The metal which comprises the metal substrate may be aluminium; zinc; nickel; copper; silver; indium; palladium; chromium; iron; platinum; gold, tin; alloys which include one or more of the hereinbefore mentioned metals, especially steel, stainless steel, brass and alloys of aluminium; or composite metals for example, galvanised steel.

The optical coatings of the present invention are especially suitable for aluminium and aluminium alloy substrates. Suitable forms of aluminium include bare aluminium

(aluminium which has not been subjected to a surface treatment), aluminium alloys, especially alloys with one or more of Cu, Si, Mn, Mg, Cr, Zn and Fe, clad aluminium or aluminium which has been etched or anodised. Especially preferred forms of aluminium are bare aluminium, aluminium alloys and clad aluminium.

The binder polymer may be an addition polymer, a poly addition polymer, a poly condensation polymer or a copolymer of the above mentioned types of polymers. Examples of suitable binder polymers include polyethylenes; polyurethanes; polyesters, especially polycarbonates; polyimides; polyamides; polyvinylacetates; polyvinylacetals alkyd resins; melamine resins; silicone resins; polymers derived from acrylates, acrylamides, vinyl chloride, vinyl acetate, methacrylamides and isocyanates; condensates of carboxylic acids and orthoformaldehyde; melamine formaldehyde resin condensates and their derivatives and copolymers thereof. It is preferred that the binder polymer is selected from polyamides; polyimides; polyethylenes; acrylamides; melamine formaldehyde resin condensates; polyesters, especially polycarbonates; alkyd resins; polyvinyl butyrate polyvinylbutyrals; or vinyl- chloride - vinyl acetate copolymers.

Especially preferred binder polymers are polyvinylbutyrals; polycarbonate-A, which is characterised by units of the structured formula:

and polycarbonate-Z, which is characterised by units of the structural formula:

When the additive in the optical coating is a polyhydroxyflavone, it contains from 2 to 10 hydroxy groups, preferably from 2 to 8 hydroxy groups and especially from 3 to 7 hydroxy groups. Examples of polyhydroxyflavones suitable for use as an additive include 5,7-dihydroxyflavone, 4',5,7-trihydroxyflavone, 3,3',4',7-tetrahydroxyflavone, 2', 3,4', 5,7- pentahydroxyflavone, 3,3',4',5,7-pentahydroxyflavone and 3,3',4',5,5',7- hexahydroxyflavone.

Where the additive is a hydroxy or polyhydroxy naphthoic acid, it contains from 1 to 8 hydroxy groups, preferably from 1 to 6 hydroxy groups and especially from 1 to 5 hydroxy groups. Examples of suitable hydroxy or polyhydroxy naphthoic acids include 2- hydroxynaphthoic acid, 2,4-dihydroxynaphthoic acid and 2,6,8-trihydroxynaphthoic acid.

Where the additive is a hydroxy or polyhydroxy benzoic acid derivative, it is preferably a compound of the formula (1):

(1) wherein;

R¹ is H or alkyl; and

R², R³, R⁴, R⁵ and R⁶ each independently is H or hydroxy.

Where R¹ is alkyl, suitable groups include, for example C_{1 6} alkyl, preferably C..→ alkyl and especially methyl and ethyl groups. It is preferred that R¹ is H.

It is preferred that the compound of formula (1) contains from 1 to 5, more preferably from 2 to 4 hydroxy groups. Examples of suitable polyhydroxybenzoic acid derivatives include, dihydroxy and tnhydroxy benzoic acids, preferably 3,4-dιhydroxy benzoic acid, 3,5-dιhydroxybenzoιc acid and 3,4,5-tπhydroxybenzoιc acid and especially 3,4,5-trιhydroxybenzoιc acid

It is preferred that the additive is a polyhydroxyflavone, more preferably a polyhydroxyflavone with 3 to 6 hydroxy groups and especially 2', 3, 4', 5, 7- pentahydroxyflavone

The additive may be present in the polymeric binder or it may be present on the surface of the metal substrate such that the additive forms an inter layer between the metal substrate and the polymeric binder When the additive is present in the polymeric binder, it is preferred that the additive is uniformly distributed throughout the polymeric binder It is preferred that the additive is present in the polymeric binder at a concentration in the range of from 0 01 % to 10%, more preferably in the range of from 0 01% to 5% based upon the weight of the polymeric binder According to a further feature of the present invention there is provided a composition comprising one or more addιtιve(s) and one or more polymeric binders The addιtιve(s) and binder polymer(s) are as hereinbefore defined

According to a further aspect of the present invention there is provided a photoreceptor for a metal substrate comprising a charge generating material (CGM), a charge transport material (CTM), a polymeric binder and an additive, wherein the polymeric binder and the additive are as hereinbefore defined

Suitable metal substrates for the photoreceptor are as hereinbefore defined

There are many CTM's and CGM's known in the art, any of which may be employed in the coatings of the present invention Examples of suitable CGM's which may be employed include azo and disazo pigments, perylenes, squaryliums, thiapyπliums, phthalocyanines, preferably metal free phthalocyanines and TiO- phthalocyanines and especially metal free phthalocyanines in the X- and τ- forms and type (I) and (IV) TiO-phthalocyanines, dithioketopyrrolopyroles, quinacridones, thiomdigoes and azulenium dyes Examples of suitable CTM's include tπarylamines, for example tπ-para-tolylamine, hydrazones for example N,N-dιethylamιnobenzaldehyde diphenylhydrazone, styπhcs, butadienes, stillbene derivatives, including N,N-dιphenyl-4-amιnostιllbene and derivatives thereof, phenyl benzidine derivatives, including N,N,N ,N-tetraphenylbenzιdιne and derivatives thereof tetracyanoethylene and tetracyanoquinodimethane Further specific examples of suitable CTM's and CGM's may be found in US 4,637,971 which are incorporated herein by reference thereto

The choice of specific combinations of CGM's and CTM's and binder polymer(s) will depend upon the required optical and electrical performances of the photoreceptor and will be readily made by one skilled in the electrophotography art As hereinbefore stated, the metal substrate may be comprised entirely of metal or may be a composite body comprising one or more different materials which has a metal surface onto which the photoreceptor is formed. For example, the metal substrate may comprise a polymer base with a metallised surface, the photoreceptor being formed on the metallised surface.

The metal substrate may be of any shape required to correspond with the electrophotographic device into which the photoreceptor is to be incorporated. Preferred substrate shapes are axially symmetric, for example cylindrical, the photoconductor being applied to the outer surface of the cylinder. This configuration enables the photoreceptor to be rotated about its axis which is advantageous for the electrostatic charging of the photoconductor and the exposure, development and transfer of the image to and from the surface of the photoreceptor. Other preferred metal substrate configurations are planar sheets, preferably flexible sheets which may be formed into strips or belts.

In one preferred embodiment the metal substrate is a metallised polymer, preferably a metallised polymer film, and especially a metallised polymer film which is flexible and thermally stable to the temperature to which the photoconductor will be exposed during operation of the electrophotographic device.

Examples of polymer substrates suitable for metallising include polyethylene terephthalate, polyimides, polyamides and kevlar. The polymer substrate may be metallised by any convenient method for example, vacuum deposition of the metal onto the polymer surface. Where the metallised polymer is in the form of a sheet or film, it may be cut to form a strip or a belt which is a preferred substrate configuration. The photoconductor may be applied before or after cutting the metallised polymer substrate into the shape required for incorporation into the electrophotographic device, it is preferred, however, to apply the photoconductor before cutting the metallised polymer substrate.

In one embodiment the photoreceptor is formed by mixing the polymeric binder, the CGM, the CTM and the additive together, preferably as a uniform dispersion and applying the mixture to the metal substrate. In other embodiments the photoreceptor is formed in a layered manner wherein the CTM and the CGM are contained in separate layers of binder polymer. For example, the CGM in a layer of binder polymer adjacent to the metal substrate with the CTM in a layer of binder polymer which overlays the layer containing the CGM.

In a further embodiment of the photoconductor, the metal substrate may be coated with the polymeric binder and the additive without the CGM or CTM, this layer forming a blocking layer on the metal substrate onto which the CTM and CGM in binder polymer(s) are applied. The CTM and CGM may be applied as separate layers in binder polymer(s) or as a single dispersion of CTM, CGM and binder polymer onto the blocking layer as hereinbefore described. In those embodiments where the photoreceptor is formed in a layered manner, the polymeric binder may be the same or different for each of the blocking layer (if present), the CGM layer and the CTM layer.

We have found that the additives of the present invention enhance the durability of the bonding of the binder polymer to the metal substrate. The additives appear to have little effect upon the durability of the bonding formed between adjacent polymeric layers, for example the bond between a CGM layer and a CTM layer. Accordingly, in an especially preferred embodiment of the photoconductor, the additive is only present in that layer which is deposited onto the metal substrate, the subsequent polymeric over layers comprising the remainder of the photoconductor being substantially free from additive.

It is preferred that the metal substrate onto which the photoreceptor is formed is aluminium or an alloy which contains aluminium.

In all embodiments of the photoconductor, the additive may be applied directly to the surface of the metal substrate or may be present in the polymeric binder, preferably as a uniform dispersion.

When the additive is present in the polymeric binder used for the photoconductor it is preferably present at a concentration as hereinbefore defined for the polymeric optical coatings of the present invention. In view of the forgoing preferences, a particularly preferred photoconductor comprises a binder polymer; a CTM; a CGM; a metal substrate comprising aluminium or an aluminium alloy; and 2',3,4',5,7-pentahydroxyflavone; wherein the polymeric binder, the CGM and the CTM are as hereinbefore defined.

According to a further feature of the present invention there is provided a composition comprising one or more additive(s); one or more binder polymer(s); and one or more CTM's and/or CGM's. The additive(s), binder polymer(s), CTM's and CGM's are as hereinbefore defined.

According to a still further aspect of the present invention there is provided an optical data storage disc having a metal surface with a polymeric optical coating comprising a polymeric binder and an additive; wherein the polymeric binder and the additive are as hereinbefore defined; and the metal is as hereinbefore defined for the metal substrate. Examples of optical data storage discs suitable for the polymeric optical coating include compact discs and video discs.

According to another feature of the present invention there is provided a diffraction grating having a metal surface with a polymeric optical coating comprising a polymeric binder and an additive; wherein the polymeric binder and the additive are as hereinbefore defined; and the metal surface is as hereinbefore defined for the metal substrate.

Examples of diffraction gratings suitable for coating include metal diffraction gratings or diffraction gratings which have been coated with a metal for use as optical diffraction pigments, for example as a pigment in a paint for plastic.

A further aspect of the present invention provides a method for the preparation of a polymeric optical coating according to the present invention comprising applying to a metal substrate a binder polymer; an additive; optionally a CGM; and optionally a CTM.

In one embodiment of the method for preparing the coatings of the present invention a solution or dispersion of the binder polymer; the additive; optional CGM; and optional CTM in a liquid medium are applied to the metal substrate followed by drying of the coating. Suitable liquid media for use in this method include aromatic organic liquids, for example benzene, toluene and xylene; aliphatic alcohols for example, C..₆-alkanols including methanol, ethanol and isopropanol; aromatic alcohols for example, phenol, benzyl alcohol and cresol; aromatic and aliphatic esters for example, C^-alkylacetates including ethyl acetate and n-butyl acetate, ethyl butyrate and phenyl acetate; ethers for example, diethyl ether, n-butylethylether, alkyl ethers of polyhydric alcohols for example, 2-ethoxyethanol, 2-butoxyethanol and ethylene glycol dimethylether and cyclic ethers including tetrahydrofuran and dioxane; aromatic and aliphatic ketones for example, acetone, ethylmethylketone, diethylketone cyclohexanone, acetophenone N-methyl 2- pyrrolidinone and propiophenone; amines for example, C^-alky! substituted amines including n-butylamine, ethylamine, diethylamine, C,.₆-alkanol substituted amines including methanol amine; and diethanolamine and chlorinated organic liquids for example, ethylene chloride, tetrachloroethane and chloroform; and mixtures thereof.

Preferred liquid media include n-butyl acetate, methanol, ethanol, methylethyl ketone, tetrahydrofuran, dioxane, ethylene chloride and tetrachloroethane. It is preferred that the concentration of the binder polymer in the liquid medium is from 0.1% to 40% (w/v).

Drying of the coating may be effected by any convenient means for example, by evaporation of the liquid medium. The coating may be dried at ambient temperature or by heating the coated surface, preferably in the temperature range of from 25 to 150°C. Where this method is used for the formation of a photoreceptor, it is preferred that the CTM and CGM are also dissolved or dispersed in the liquid medium with the polymeric binder and the additive prior to application to the metal substrate. Where the photoreceptor is formed in a layered manner, it is preferred that only that layer which is applied directly onto the metal substrate contains the additive and that subsequent polymeric layers are coated from solutions or dispersions which do not contain the additive.

The polymeric optical coatings may also be applied to the metal substrate without dissolving or dispersing the polymeric binder and additive in a liquid medium. This method of application to the metal substrate is especially suitable for those binder polymers which are in a liquid state before drying or curing.

In a further embodiment of the method for preparing the coatings of the present invention the additive is applied to at least part of the metal substrate followed by application of the polymeric binder, optional CTM and optional CGM to the treated metal substrate.

In those embodiments where the additive is applied to the metal substrate prior to the binder polymer, it is preferred that the additive is applied to the metal substrate as a solution or dispersion in a liquid. Suitable liquids for the solution or dispersion of the additive include aliphatic and aromatic alcohols, for example methanol, ethanol, phenol and aqueous solutions thereof; esters for example, ethyl acetate n-butylacetate and phenylacetate; ketones for example, acetone diethylketone and methylethyl ketone; and ethers especially alkyl ethers of polyhydric alcohols for example, ethylene glycol diethyl ether, C.^-alkoxyethanols, including 2-methoxyethanol, 2-ethoxyethanol and 2- butoxyethanol, HC^-alkoxy^-propanols including 1 -methoxy-2-propanol and 1-ethoxy- 2-propanol and 1,2-(C₁.₄-alkoxy) propanes including propylene glycol dimethyl ether and propylene glycol diethylether.

Where the additive is applied as a solution or dispersion in a liquid it is preferred that the concentration of the additive in the liquid is from 0.1 to 10%, more preferably from 0.5 to 5% and especially from 0.8% to 3% (w/v).

It is preferred that the additive is applied to the substrate at a temperature of from 0 to 100°C, preferably from 20 to 80°C and especially from 40 to 60°C.

The additive may be applied to the metal substrate using any convenient method for example by brushing, spraying, printing, dip coating, K-bar coating, slot coating, roller coating, curtain coating or by immersing the substrate into the additive or solution/dispersion containing the additive.

It is preferred that the additive is applied to the metal substrate by immersing that area of the substrate to be covered in the additive or dispersion/solution containing the additive. An immersion time of from 10 minutes to 6 hours, preferably of from 30 minutes to 3 hours is suitable for coating the metal substrate with the additive.

It is preferred that the metal substrate which has been treated with the additive, or additive solution, is rinsed with a liquid to remove excess additive which may be present on the metal surface. Suitable liquids include alcohols, esters, ketones or a glycol ethers as hereinbefore defined for the solution or dispersion of the additive. The metal substrate which has been coated with the additive is preferably substantially dry before applying the polymeric binder. The substrate may be dried using any convenient method for example, by allowing the substrate to dry at ambient temperature or by heating the substrate at a temperature in the range of from 25 to 150°C. The polymeric binder may be applied directly to the surface which has been coated with the additive or is preferably applied as a solution or dispersion in a liquid medium as hereinbefore described.

When this method is used for forming coatings on aluminium or substrates containing aluminium, it is preferred that the additive is a polyhydroxyflavone, more preferably a polyhydroxyflavone with 3 to 6 hydroxy groups and especially 2', 3,4', 5,7- pentahydroxyflavone.

Before applying the additive or a composition comprising the binder polymer, additive and/or liquid medium to the metal substrate, it is preferred that the metal substrate is subjected to a conventional de-greasing treatment, for example by treating the metal substrate with a halogenated hydrocarbon or the vapour thereof.

The polymeric optical coating of the present invention may be applied to the metal substrate by any convenient means for example, by spraying, dip coating, K-bar coating, slot coating, roller coating or curtain coating or any other known printing method. It is preferred that the polymeric optical coating is applied to the metal substrate by dip coating.

According to a further feature of the present invention there is provided a composition comprising one or more additive(s); one or more binder polymer(s); and one or more liquid media. The additive(s), binder polymer(s) and liquid media are as hereinbefore defined.

The invention is illustrated but not limited by the following Example in which all parts and percentages are by weight unless indicated otherwise:

Example 1 Preparation of a Charge Generation Layer on an Aluminium Surface To 90%(v/v) aqueous ethanol (90% ethanol, 10% water) was dissolved 2',3,4',5,7- pentahydroxyflavone (PHF) to give a 1% (w/v) PHF solution. The solution was heated to 50°C and a sample of aluminised Melinex was immersed in the PHF solution for 1 hour. The treated film was then removed from the PHF solution, was rinsed with ethanol and was allowed to dry at ambient temperature. A charge generation material, X-form metal free phthalocyanine (0.2g) was dispersed into a solution of a polyvinylbutyral binder resin (0.1g) (available form Sekisui Chemical Co. Ltd, Japan) in n-butylacetate (10cm³). The dispersion was coated onto the treated aluminium surface of the Melinex film using a No. 2 K bar and was allowed to dry at ambient temperature. Scotch tape was then applied to the surface of the layer containing the charge generation material and was removed manually by peeling the tape from the coated surface whilst maintaining the angle between the tape and the Melinex film at approximately 90°. No removal of the layer containing the charge generation material was observed. Comparative Example A

The procedure in Example 1 was repeated except that the aluminised Melinex was not treated with 2',3,4',5,7-pentahydroxyflavone. Examination of the Scotch tape after peeling from the coated surface showed that some delamination of the layer containing the charge generation material from the aluminium surface had occurred.

MELINEX and SCOTCH are registered trade marks.

Claims

1 A polymeric optical coating for a metal substrate comprising a polymeric binder and an additive selected from a polyhydroxyflavone, a hydroxy or polyhydroxy benzoic acid derivative and a hydroxy or polyhydroxy naphthoic acid or a mixture thereof

2 A coating according to claim 1 in which the metal substrate is aluminium, zinc, nickel, copper, silver, indium, palladium, chromium, iron, platinum, gold, tin, alloys which include one or more of the hereinbefore mentioned metals

3 A coating according to claim 1 or claim 2 wherein the additive is a polyhydroxy flavone

4 A coating according to any one of the previous claims wherein the additive is 2',3,4',5,7-pentahydroxyflavone

5 A coating according to claim 1 or claim 2 wherein the polyhydroxy benzoic acid derivative is a compound of the formula (1)

(1) wherein,

R¹ is H or alkyl, and

R², R³, R\ R⁵ and R⁶ each independently is H or hydroxy

6 A coating according to any one of the previous claims wherein the metal substrate is aluminium or an aluminium alloy

7 A coating according to any one of the previous claims in which the additive is present in the polymeric binder at a concentration in the range of from 0 01% to 10% based upon the weight of the polymeric binder

8 A photoreceptor for a metal substrate comprising a polymeric optical coating according to any one of claims 1 to 7, a charge transport mateπal (CTM), and a charge generation material (CGM)

9 A photoreceptor according to claim 7 wherein the CTM and CGM are contained in separate layers of binder polymer

10 An optical data storage disc having a metal surface with a polymeric optical coating according to any one of claims 1 to 7

11 A diffraction grating having a metal surface with a polymeric optical coating according to any one of claims 1 to 7

12 A method for forming a coating according to any one of claims 1 to 9 comprising applying to a metal substrate a binder polymer, an additive, optionally a CGM, and optionally a CTM

13 A method according to claim 12 wherein a solution or dispersion of the binder polymer, the additive, optional CGM and optional CTM in a liquid medium are applied to the metal substrate followed by drying of the coating

14 A method according to claim 12 wherein the additive is applied to at least part of the metal substrate followed by application of the polymeric binder, optional CTM and optional CGM to the treated surface

15 A method according to claim 14 wherein the additive is applied to the metal substrate as a solution or dispersion in a liquid

16 A method according to claim 15 wherein the concentration of the additive in the liquid is from 0 1 to 10% (w/v)

17 A method according to any one of claims 12 to 16 wherein the coating is applied to the metal substrate by dip coating

18 A composition comprising one or more addιtιve(s) and one or more polymeric binders in which the addιtιve(s) are as defined in claim 1

19 A composition according to claim 16 further comprising one or more CTM and/or CGM

20. A composition according to claim 18 or claim 19 further comprising one or more liquid media.