EP0983150A1

EP0983150A1 - Planographic printing

Info

Publication number: EP0983150A1
Application number: EP98922955A
Authority: EP
Inventors: Harjit Singh Bhambra; Robert Michael Organ
Original assignee: Kodak Graphics Holding Inc
Current assignee: Kodak Graphics Holding Inc
Priority date: 1997-05-23
Filing date: 1998-05-22
Publication date: 2000-03-08
Also published as: AU7541598A; JP2001525746A; WO1998052769A1; GB9710553D0

Abstract

A substrate for a planographic printing member comprising a support and a hydrophilic layer which includes particulate material, especially alumina and titania, and a binder material having Si-O bonds, especially one derived from a silicate. A method of preparing a substrate and a lithographic printing plate comprising such a substrate are also described.

Description

PLANOGRAPHIC PRINTING

This invention relates to planographic printing and provides a substrate for a planographic printing member, a printing member per se and a method of preparing a substrate for a planographic printing member. Particularly, although not exclusively, the invention relates to lithographic printing.

Lithographic processes involve establishing image (printing) and non-image (non-printing) areas on a substrate, substantially on a common plane. When such processes are used in printing industries, non-image areas are generally hydrophilic and image areas are generally oleophillic. Consequently, oil based inks are repelled from the non-image areas after water has been applied to the substrate.

Image and non-image areas can be created by processes which include a step of exposing a layer of image material on the surface of the substrate to radiation. The exposure to radiation creates solubility differences in the image material corresponding to image and non-image areas. During development, the more soluble areas are removed, leaving a pattern on the substrate corresponding to the image .

Preparation of a substrate for receiving a layer of the image material must ensure that the image material bonds to the substrate. However, it must allow release of the soluble image material during development.

One of the most common substrates used in lithographic printing comprises an aluminium base layer which is treated to make it suitable for use. In general, the aluminium layer comprises high quality aluminium, for example 1050 alloy which is at least 99.5% pure. For preparation of a substrate, the aluminium is roughened, for example by electrograining, anodised and then conditioned by chemical means, for example by treatment with water, a solution of phosphate or silicate salt, or a polycarboxylic acid.

Aluminium is a preferred substrate material in circumstances where it is desired to produce a printing plate which can be used to produce many prints, for example greater than 100,000.

Other known substrates include plastics supports which carry a subbing layer over which an image layer is applied. For example, US 5,462,833 ( Agfa-Gevaert ) describes the preparation of a lithographic printing plate which comprises a polyethylene terephthalate support coated with a subbing layer containing a latex of copoly ( vinylidenechloride/methyl methacrylate/itaconic acid) and silica. A hydrophilic layer comprising titania, polyvinyl alcohol and tetramethyl orthosilicate is applied over the subbing layer and hardened by subjecting it to a temperature of 60°C for 1 week.

There are numerous requirements that must be considered when preparing hydrophilic surfaces of substrates for printing plates, for example, as follows:

- the surface must be capable of providing a suitable ink-water balance;

the surface should not pick up ink; the surface should be durable in order to give a high potential number of prints and to resist scratching;

the surface should preferably be able to be used with a range of different types of image layers;

the surface should have appropriate aesthetics and allow good contrast between image and non-image areas;

- the surface should preferably not readily become stained with dyes used in image layers ;

the surface should not affect the ability of an image layer to change colour on exposure;

the surface should not affect the ability of an image layer to be deleted using deletion fluids;

the surface should be cheap to prepare.

It is an object of the present invention to address problems associated with planographic printing members.

According to a first aspect of the present invention, there is provided a substrate for a planographic printing member, the substrate comprising a support and a hydrophilic layer which includes particulate material and a binder material having Si-O bonds.

Said hydrophilic layer may have an average thickness of less than lOOμ , suitably less than 50 μm, preferably less than 20 μm, more preferably less than 10 μm, especially less than 5 μm. In some cases, the layer may have an average thickness of less than 3 μm. Said hydrophilic layer may have an average thickness of greater than 0.1 μm, suitably greater than 0.3 μm, preferably greater than 0.5 μm, more preferably greater than 1 μm.

The Ra of the hydrophilic layer may be measured using a Talysurf Plus unit fitted with a 112/2564-430 head, supplied by Rank Taylor Hobson Inc. of Leicester, U.K. The Ra may be at least 0.2 μm, suitably at least 0.25 μm, preferably at least 0.3 μm, more preferably at least 0.35 μm, especially at least 0.4 μm. The Ra may be less than 1.5 μm, suitably less than 1 μm, preferably less than 0.8 μm, more preferably less than 0.7 μm, especially less than 0.6 μm, most preferably less than 0.5 μm.

Said hydrophilic layer may include 1 to 20 g of material per metre squared of substrate. Preferably said layer includes 3 to 20 g, more preferably 5 to 18 g, of material per metre squared of substrate. Most preferably, said layer includes 8 to 16 g of material per metre squared.

Said binder material may be a component of a polymeric material which includes Si-O bonds. Said polymeric material may include -Si-O-Si-, especially -Si- O-Si-O-, moieties.

At least 50 wt%, suitably at least 60 wt%, preferably at least 70 wt%, more preferably at least 80 wt%, especially at least 90 wt% of said binder material is made up of a polymeric material having Si-O bonds as described. Preferably, said binder material consists essentially of a polymeric material having Si-O bonds as described.

Said binder material may make up at least 5 wt%, preferably at least 10 wt%, more preferably at least 15 wt%, especially at least 20 wt% of said hydrophilic layer. Said binder material may make up less than 50 wt%, preferably less than 40 wt%, more preferably less than 30 wt%, especially less than 25 wt%, of said hydrophilic layer.

Said binder material may be derived or derivable from a silicate material for example water glasses, metasilicates , orthosilicates , sesquisilicates and modified silicates such as borosilicate and phosphosilicate. Said binder material is preferably derived or derivable from a silicate solution.

Said binder material preferably includes less than 10 wt%, preferably less than 5 wt%, more preferably less than 1 wt%, especially substantially no, organic material, for example polymeric organic material.

Said particulate material is preferably dispersed in said binder material. Suitably, 30 to 85 wt%, preferably 40 to 80 wt%, more preferably 50 to 80 wt%, especially 60 to 80 wt% of said hydrophilic layer is composed of said particulate material.

Said particulate material may be organic or inorganic. Organic particulate materials may be provided by latexes or organosols or polymeric balls, such as of nylon. Inorganic particulate materials may be selected from alumina, silica, silicon carbide, zinc sulphide, zirconia, barium sulphate, talcs, clays (e.g. kaolin), lithopone and titanium oxide.

Said particulate material may comprise a first particulate material. Said first material may have a hardness of greater than 8 Modified Mohs (on a scale of 0 to 15), preferably greater than 9 and, more preferably, greater than 10 Modified Mohs. Said first material may comprise generally spherical particles. Alternatively, said material may comprise flattened particles or platelets . Said first material may have a mean particle size of at least 0.1 μm, preferably at least 0.5 μm and, more preferably at least lμm. Said first material may have a mean particle size of less than 200 μm, suitably less than 100 μm, preferably less than 45 μm, more preferably less than 20 μm, especially less than 10 μm and, most preferably, less than 5 μm. The particle size distribution for 95% of particles of the first material may be in the range 0.01 to 150 μm, preferably in the range 0.05 to 75 μm, more preferably in the range 0.05 to 30 μm. Said first material preferably comprises an inorganic material. Said first material preferably comprises alumina which term includes Al₂0₃ and hydrates thereof, for example Al₂0₃.3H₂0. Preferably, said material is A1₂0₃.

Said hydrophilic layer may include at least 10 wt%, suitably at least 20 wt%, preferably at least 25 wt%, more preferably at least 30 wt%, especially at least 35 wt% of said first particulate material. Said hydrophilic layer may include less than 80 wt%, suitably less than 70 wt%, preferably less than 60 wt%, more preferably less than 50 wt%, especially less than 40 wt% of said first particulate material.

The ratio of the wt% of said first particulate material to binder material may be in the range 0.5 to 2, preferably in the range 1 to 2 , more preferably in the range 1.4 to 1.8.

Said particulate material may comprise a second particulate material. Said second particulate material may have a mean particle size of at least 0.001 μm, suitably at least 0.005 μm, preferably at least 0.01 μm, more preferably at least 0.05 μm, especially at least 0.1 μm. Said mean particle size may be less than 200 μm, suitably less than 100 μm, preferably less than 50 μm, more preferably less than 10 μm, especially less than lμm, most preferably less than 0.5 μm.

Said hydrophilic layer may include at least 10 wt%, suitably at least 20 wt%, preferably at least 25 wt%, more preferably at least 30 wt%, especially at least 35 wt% of said second particulate material. Said hydrophilic layer may include less than 80 wt%, suitably less than 70 wt%, preferably less than 60 wt%, more preferably less than 50 wt%, especially less than 40 wt% of said second particulate material.

Said second material is preferably a pigment. Said second material is preferably inorganic. Said second material is preferably titanium dioxide.

The ratio of the wt% of said second particulate material to binder material may be in the range 0.5 to 2, preferably in the range 1 to 2 , more preferably in the range 1.4 to 1.8.

Said first and second materials preferably define a multimodal, for example a bimodal particle size distribution.

The ratio of the wt% of said first particulate material to said second particulate material may be in the range 0.3 to 3, preferably 0.5 to 2, more preferably 0.75 to 1.33, especially about 1 : 1. Said hydrophilic layer may include one or more additional materials for improving its adhesion to a support, especially a plastics support. A preferred additional material is organic and is preferably polymeric. Resins are preferred.

Said support may comprise a metal layer. Preferred metals include aluminium, zinc and titanium, with aluminium being especially preferred. Said support may comprise an alloy of the aforesaid metals. Other alloys that may be used include brass and steel, for example stainless steel.

Said support may comprise a non-metal layer. Preferred non-metal layers include layers of plastics, paper or the like. Preferred plastics include polyester, especially polyethylene terephthlate.

Said support may include one or a plurality of layers. Where the support comprises a plurality of layers, it may comprise a plastics, paper or textile layer and another layer. Said other layer may be a metal layer, suitably of a type described above. In this case, said support may comprise a metal to plastics or paper laminate; or metal may be applied by other means to plastics or paper, for example by sputtering or the like.

Said support may be any type of support used in printing. For example, it may comprise a cylinder or, preferably, a plate. Said support may have a width of at least 10 cm, suitably at least 20 cm, preferably at least 30 cm, more preferably at least 40 cm, especially at least 50 cm. Said support may have a width of less than 300 cm, suitably less than 200 cm, preferably less than 160 cm, more preferably less than 100 cm, especially less than 80 cm. The support suitably does not have a width of about 23 cm.

Said support may comprise a web of material which may have a width as described above. Preferably the web has a width in the range 0.7 m to 1.5 m.

Said support may have a length of at least 20 cm, suitably at least 40 cm, preferably at least 60 cm. Said support may have a length of less than 300 cm, suitably less than 250 cm, preferably less than 200 cm, more preferably less than 150 cm, especially less than 105 cm. The support suitably does not have a length of about 35 cm.

Said support may have a thickness of at least 0.1 mm. Said support may have a thickness of less than 0.6 mm.

Said support may be pretreated prior to the application of said hydrophilic layer by one or more conventional methods used in the surface treatment of aluminium or other supports, for example caustic etch cleaning, solvent etching, acid cleaning, brush graining, mechanical graining, slurry graining, sand blasting, abrasive cleaning, electrocleaning, solvent degreasing, ultrasonic cleaning, alkali non-etch cleaning, primer coating, flame treatment, grit/shot blasting and electrograining. Details of such methods are provided in: "The surface treatment and finishing of aluminium and its alloys" S. Wernick, R. Pinner and P. G. Sheasby published by Finishing Publication Ltd., ASM International, 5th edition 1987. Said support may be provided with a roughened surface over which the hydrophilic layer may be provided.

Alternatively, a subbing layer or layers may be provided over the support. In another example, said support may be subjected to a Corona treatment.

A subbing layer may include a polymeric or polymerisable material which may be organic or inorganic. Said layer may comprise a proteinaceous material, for example gelatin or a resin which may include or be prepared using monomers selected from vinyl moieties, such as styrene; alkenyl moieties such as butadiene; and acid moieties such as acrylic. Said resin may include ester or carboxylic acid functional groups.

Particulate material may be provided in the subbing layer. Said particulate material may comprise any particulate material described in any statement herein.

According to a second aspect of the present invention, there is provided a printing member comprising a substrate according to said first aspect and an image layer.

The term "image layer" includes a layer that can subsequently be partially removed in order to define areas to be printed and includes a layer which already defines areas to be printed. Said image layer may include one or a plurality of layers.

Said image layer is preferably arranged to be removed during or after exposure to radiation, in order to define areas to be printed. Said hydrophilic layer is preferably arranged between said support and said image layer. Said image layer preferably contacts said hydrophilic layer.

The image layer may be provided over the entire surface of said hydrophilic layer. It may comprise any known photosensitive material whether arranged to form a positive or negative plate. Examples of photosensitive materials include diazonium/diazide materials, polymers which undergo depo lymer i s at i o n or addition photopolymerisation and silver halide gelatin assemblies. Examples of suitable materials are disclosed in GB 1 592 281, GB 2 031 442, GB 2 069 164, GB 2 080 964, GB 2 109 573, EP 0 377 589, US 4 268 609 and US 4 567 131. Preferably, the light sensitive material is a quinone diazide material.

Alternatively, said image layer in the form of a desired image for use in planographic printing may be deposited over said hydrophilic layer by a deposition process such as ink jet or laser ablation transfer. An example of the latter is described in US 5 171 650.

The invention extends to a package with which a printing member as described is associated.

The package may include means for restricting the passage of radiation, especially light, from impinging the printing member. The package may be made of a material which is opaque to light. Said package preferably fully encloses said printing member.

The invention extends to a plurality of printing members which are associated with one another. For example, one printing member may overlie another printing member. Said plurality of printing members may be provided in a package of the type described. Spacing means may be provided between adjacent printing members of said plurality of printing members.

According to a third aspect of the present invention, there is provided a printing member according to said second aspect which carries printable information.

According to a fourth aspect of the present invention, there is provided a method of preparing a substrate for a planographic printing member including the step of forming a hydrophilic layer on a support by contacting the support with a fluid comprising a silicate solution in which particulate material as described in any statement herein is dispersed.

Said silicate solution may comprise a solution of any soluble silicate including compounds often referred to as water glasses, metasilicates , orthosilicates and sesquisilicates. Said silicate solution may comprise a solution of a modified silicate for example a borosilicate or phosphosilicate.

Said silicate solution may comprise one or more, preferably only one, metal or non-metal silicate. A metal silicate may be an alkali metal silicate. A non-metal silicate may be quaternary ammonium silicate.

Said silicate solution may be formed from silicate wherein the ratio of the number of moles of Si species, for example Si0₂, to the number of moles of cationic, for example metal species is in the range 0.25 to 10, preferably in the range 0.25 to about 6, more preferably in the range 0.5 to 4. Said silicate is preferably alkali metal silicate. In this case, the ratio of the number of moles of Si0₂ to the number of moles of M₂0 in said silicate, where M represents an alkali metal may be at least 0.25, suitably at least 0.5, preferably at least 1, more preferably at least 1.5. Especially preferred is the case wherein said ratio is at least 2.5. Said ratio may be less than 6, preferably less than 5 and more preferably less than 4.

Preferred alkali metal silicates include lithium, sodium and potassium silicates, with lithium and/or sodium silicate being especially preferred. A silicate solution comprising only sodium silicate is most preferred.

Said fluid may comprise 2 to 30 wt% of silicate (e.g. dissolved sodium silicate solid), preferably 5 to 20 wt%, more preferably 8 to 16 wt%. The fluid may be prepared using 10 to 60 wt%, preferably 30 to 50 wt%, more preferably 35 to 45 wt% of a silicate solution which comprises 30 to 40 wt% silicate.

Said fluid may include 5 to 60 wt% of particulate material. Preferably, the fluid includes 10 to 50 wt%, more preferably 15 to 45 wt%, especially 20 to 40 wt% of particulate material.

The ratio of the weight of silicate to the weight of particulate material in the fluid is preferably in the range 0.1 to 2 and, more preferably, in the range 0.1 to 1. Especially preferred is the case wherein the ratio is in the range 0.2 to 0.6.

Said fluid may include more than 20 wt%, preferably more than 30 wt%, more preferably more than 40 wt%, especially more than 45 wt% water (including water included in said silicate solution) . Said fluid may include less than 80 wt%, preferably less than 70 wt%, more preferably less than 65 wt%, especially less than about 60 wt% water.

Where the fluid comprises a silicate and said particulate material comprises a first material and a second material as described, the ratio of the wt% of silicate (e.g. dissolved sodium silicate solid) to the wt% of said first material may be in the range 0.25 to 4, preferably in the range 0.5 to 1.5 and more preferably about 1. Similarly, the ratio of the wt% of silicate to the wt% of said second material may be in the range 0.25 to 4, preferably in the range 0.5 to 1.5 and more preferably about 1. The ratio of the wt% of first material to the wt% of second material may be in the range 0.5 to 2, preferably in the range 0.75 to 1.5, more preferably about 1 to 1.

Said particulate material may include a third material which is preferably adapted to lower the pH of the fluid. Said third material may be a colloid, suitably colloidal silica or an inorganic salt, suitably a phosphate, with aluminium phosphate being preferred. Where a third material is provided, preferably less than 30wt% more preferably less than 20wt%, especially less than 10wt% of said particulate material is comprised by said third material.

The pH of said fluid may be greater than 9.0, is preferably greater than 9.5 and, more preferably, greater than 10.0. Especially preferred is the case wherein the pH is greater than 10.5. The pH is suitably controlled so that the silicate remains in solution and does not form a gel. A gel is generally formed when the pH of a silicate solution falls below pH9. The pH of said fluid is preferably less than 14, more preferably less than 13.

The fluid may include other compounds for adjusting its properties. For example, the fluid may include one or more surfactants. Said fluid may include 0 to 1 wt% of surfactant ( s ) . A suitable class of surfactants comprises anionic sulphates or sulphonates. The fluid may include viscosity builders for adjusting the viscosity of the fluid. Said fluid may include 0 to 10 wt%, preferably 0 to 5 wt% of viscosity builder (s). Also, the fluid may include dispersants for dispersing the inorganic particulate material throughout the fluid. Said fluid may include 0 to 2 wt% of dispersant ( s ) . A suitable dispersant may be sodium hexametaphosphate.

Said fluid may have a viscosity of less than 100 centipoise when measured at 20°C and a shear rate of 200s^"1 using a Mettler Rheomat 180 Viscometer incorporating a double gap measuring geometry. Preferably, said viscosity is less than 50 centipoise, more preferably less than 30 centipoise when measured as aforesaid. Especially preferred is the case wherein the viscosity is less than 20 centipoise.

Said fluid may be applied to said support by any suitable means which is preferably non-electrochemical.

Said fluid may be applied to both sides of said support in order to form a hydrophilic layer on both sides. A support with such a layer on both sides may be used to prepare a double-sided lithographic plate. Alternatively, if such a support is used for a single- sided plate, the side of the plate which does not carry an image layer may be protected by the hydrophilic layer. Said fluid is preferably applied to only one surface of said support.

Said fluid may be applied to said support to form a hydrophilic layer having an average thickness after drying, of less than 20 μm, preferably less than 10 μm and, more preferably, less than 5 μm. Especially preferred is the case wherein the average thickness is less than 3 μm.

The method preferably includes the steps of providing suitable conditions for the removal of water from the fluid after it has been applied to the support. Suitable conditions may involve passive or active removal of water and may comprise causing an air flow over the support and/or adjusting the humidity of air surrounding the support. Preferably, the method includes the step of arranging the support in a heated environment. The support may be placed in an environment so that its temperature does not exceed 230°C, preferably does not exceed 200°C and, more preferably, does not exceed 175°C. Especially preferred is the case wherein the support temperature does not exceed 150°C.

The support may be arranged in the heated environment for less than 180 seconds, preferably less than 120 seconds and, more preferably, less than 100 seconds.

The invention extends to a method of preparing a printing member comprising applying an image layer over a substrate prepared according to said fourth aspect.

Any feature of any aspect of any invention or embodiment described herein may be combined with any feature of any other aspect of any invention or embodiment described herein.

The invention will now be described, by way of example .

The following products are referred to hereinafter:

Stainless Steel A1S1 304 foil - a foil comprising Cr (18 wt%), Ni (10 wt%) and Fe (balance) obtained from Goodfellow Cambridge Limited of Cambridge, England.

Titanium & zinc metals - obtained from Goodfellow Cambridge Limited of Cambridge, England.

Melinex 539 - Biaxial polyethylene terephthlate (PET) with an anti-static coating supplied by ICI Melinex of Wilton, England.

Melinex 0 - As for Melinex 539 but no anti-static coating.

PP2500 PET - refers to laser overhead acetates from 3M.

Tektronic PET - refers to an electrophotographic PET.

Tyvek 55 - refers to a non-cellulose based paper obtained from Samuel Grant Limited of England.

Simcote 400 - refers to a cellulose paper with a polyethylene surface coating and a clear matt finish obtained from Samuel Grant Limited of England. Simcote 479 - refers to a cellulose paper with a polyethylene surface coating and a high density matt finish obtained from Samuel Grant Limited of England.

Kaowool - a paper manufactured from ceramic fibres obtained from Thermal Ceramics Ltd of Merseyside, England.

Simcote 450A1 - a paper with a vapour deposited aluminium layer obtained from Samuel Grant Limited of England.

Simcote 450Ag - a paper with a vapour deposited silver layer obtained from Samuel Grant Limited of England.

Mylar - refers to Cronar 486 PET obtained from Dupont .

Glasocol LS26 - a styrene acrylic polymer microemulsion obtained from Allied Colloids of Bradford, England.

Epikote 1004 - a solid bisphenol A-epichlorohydrin epoxide resin obtained from Shell Resins of England.

PES 613D - a saturate polyester copolymer dispersion (20wt% in water) obtained from Siber Hegner Limited of Kent, England.

WAC-10 and WAC-20 - modified copolyester resin dispersions (20wt% in water) obtained from Siber Hegner Limited of Kent, England. Tesafix tape - refers to tesa 4965 double-sided self- adhesive tape comprising a polyester backing and an acrylic adhesive, obtained from Beiersdorf UK Ltd of Milton Keynes, England.

A. Preparation of lithographic printing plate.

Example 1

Step 1

Preparation of Aluminium

A 0.2 mm gauge aluminium alloy sheet of designation AA1050 was cut to a size of 459 mm by 525 mm. The sheet was then immersed face up in a solution of sodium hydroxide dissolved in distilled water (lOOg/1) at ambient temperature for 60 seconds and thoroughly rinsed with water.

Step 2

Preparation of coating formulation

The following reagents are used in the preparation;

- Sodium silicate solution having a ratio Si0₂ : Na₂0 in the range 3.17 to 3.45 (average about 3.3); a composition of 27.1 - 28.1 wt% Si0₂, 8.4 - 8.8 wt% Na,0, with the balance being water; and a density of about 75 Twaddel (°Tw) , equivalent to 39.5 Baume (°Be) and a specific gravity of 1.375.

- Deionised water having a resistivity of 5 Mohm.cm

- A1₂0₃ powder comprising alumina (99.6%) in the shape of hexagonal platelets. The mean particle size is 3 μm. The powder has a hardness of 9 Moh (on a 0 - 10 hardness scale). - Anatase titanium dioxide having a mean primary particle size of 0.2 μm.

Deionised water _(150g; 40 wt%) was added to a 250ml beaker and sheared using a Silverson high shear mixer. Titanium dioxide powder (53.29g; 14.21 wt% ) was then added in portions over a period of four minutes with the shearing continuing. Then, alumina powder (53.29g; 14.21wt%) was added in portions over a period of four minutes with the shearing continuing. On completion of the addition, sodium silicate solution (118.43g; 31.58 wt%) was added with shearing for a further three minutes . The viscosity of the liquid was found to be about 10 centipoise when measured at 20°C and a shear rate of 200s^"1 using a Mettler Rheomat 180 Viscometer incorporating a double gap measuring geometry.

Step 3

Application of coating formulation

The coating formulation prepared in Step 2 was coated onto the aluminium sheet prepared in Step 1 using a rotating Meyer bar coater (designation K303) to give a 12 μm wet film thickness.

Step 4

Drying the formulation

The coated sheet prepared in Step 3 was placed in an oven at 130°C for 80 seconds. The plate was then removed from the oven and allowed to cool to ambient temperature.

The Ra of the sheet was 0.45 μm measured using a Hommelmeter T2000 having an LV-50 measuring head. Step 5

Post-drying treatment

The dried sheet prepared in Step 4 was immersed in aluminium sulphate (0.1M) for thirty seconds. The sheet was then spray rinsed for about twenty seconds using tap water and fan dried.

Step 6 Application of light sensitive coating

A printing plate was produced from the sheet prepared in Step 5 by coating, using a Meyer bar, a light sensitive material of the quinone diazide/novolak resin type at a dry coating weight of 2 g/m². The light sensitive material was dried at 130°C for 80 seconds.

B. Preparation of other substrates for lithographic printing plates.

The coating formulation of Example 1, Step 2 was applied as described in Steps 3 and 4 (unless otherwise stated) to supports described in Table 1 below which had, in some cases, been pre-treated as described in the table. In the examples, the pre-treatments (if any) were applied using a Meyer bar to give a wet film thickness of 12 μm followed by oven drying at 130°C for 80 seconds. Example 43

The coating formulation of Example 1, Step 2 was applied as described in Example 1, Steps 3 and 4, to an aluminized surface of a laminate obtained from Alcan which comprises PET (125μm thick) and aluminium (25μm thick). After drying, the material was immersed in 0. IM aluminium sulphate at 20°C for 60 seconds, followed by fan drying and application of a light sensitive coating as described in Example 1, Step 6.

Examples 44 to 46

The coating formulation of Example 1, Step 2 was modified by the inclusion of additives at certain wt%, as specified in Table 2, and applied to a Melinex 539 support using a Meyer bar as described with reference to Example

2 et seq.

Example 47

Instead of applying a single layer as described in Example 1, step 3, three layers having a 6μm wet film thickness were applied. C. Assessments and Observations

Assessment 1: Scratch resistance - the hydrophilic layers of the substrates prepared as described were assessed for scratch resistance by placing each substrate on a hard flat surface and pressing hard down onto the hydrophilic layer with a fingernail, followed by dragging the nail across the surface. If no coating was removed, then the layer was regarded as scratch resistant.

Assessment 2: Tape test - each substrate was placed on a hard surface and a cm x 5 cm piece of TesaFix tape was applied and pressed downwards until no air bubbles were visible. The arrangement was left overnight and the tape was then pulled away from the surface in about 1 second and at an angle of about 45°. Good adhesion of the hydrophilic layer was indicated by no coating being attached to the tape when it was pulled from the surface.

Assessment 3: Ink receptivity - this was assessed by applying RAPIDINK (Trade Mark) to a coated surface using a damp sponge and visually assessing whether or not the surface was ink receptive.

Examples 1 to 47 - the substrate (more particularly, the coating formulation prepared as described in Example 1 Step 3) was assessed as described above in Assessments 1 to 3. In each case, the coating was found to be scratch and peel resistant and non-ink receptive.

Other Assessments

In other assessments made, the plate of Example 1 was found to provide good contrast between image and non-image areas (pre- and post development); to have non-image areas which were not stained by the dye in the image layer removed; to have excellent durability shown in a press test where after 500,000 impressions the plate was showing only slight wear; to show excellent ink-water balance on the press; to have excellent resistance to developer over a range of extreme conditions; to produce dots with high roundness; to be capable of high resolution; to be capable of wide exposure latitude; and to be capable of a broad dot range.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment ( s ) . The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A substrate for a planographic printing member, the substrate comprising a support and a hydrophilic layer which includes particulate material and a binder material having Si-O bonds.

2. A substrate according to Claim 1, wherein said hydrophilic layer has an average thickness of less than 100 ╬╝m.

3. A substrate according to Claim 1 or Claim 2, wherein said hydrophilic layer has an average thickness of less than 20 ╬╝m.

4. A substrate according to any preceding claim, wherein the hydrophilic layer has a surface roughness of at least 0.2 ╬╝m and less than 1.5 ╬╝m.

5. A substrate according to any preceding claim, wherein said binder material is derived or derivable from a silicate material.

6. A substrate according to any preceding claim, wherein 30 - 85 wt% of said hydrophilic layer is composed of said particulate material.

7. A substrate according to any preceding claim, wherein said particulate material comprises a first particulate material and a second particulate material, wherein the mean particle sizes of said first and second materials are different.

8. A substrate according to Claim 7, wherein said hydrophilic layer includes at least 10 wt% of said first particulate material.

9. A substrate according to Claim 7 or Claim 8, wherein the ratio of the wt% of said first particulate material to binder material is in the range 0.5 to 2.

10. A substrate according to any of Claims 7 to 9, wherein the mean particle size of said second particulate material is less than 50 ╬╝m.

11. A substrate according to any of Claims 7 to 10, wherein said hydrophilic layer includes at least 10 wt% of said second particulate material.

12. A substrate according to any of Claims 7 to 11, wherein the ratio of the wt% of said second particulate material to binder material is in the range 0.5 to 2.

13. A substrate according to any of Claims 7 to 12, wherein the ratio of the wt% of said first particulate material to said second particulate material is in the range 0.3 to 3.

14. A printing member comprising a substrate according to any of Claims 1 to 13 and an image layer.

15. A package with which a printing member according to Claim 14 is associated.

16. A printing member according to Claim 14 which carries printable information.

17. A method of preparing a substrate for a planographic printing member including the step of forming a hydrophilic layer on a support by contacting the support with a fluid comprising a silicate solution in which particulate material is dispersed.

18. A method according to Claim 17, wherein the pH of said fluid is greater than 9.0.

19. A method according to Claim 17 or Claim 18, wherein said fluid has a viscosity of less than 100 centipoise.

20. A method of preparing a printing member comprising applying an image layer over a substrate prepared according to any of Claims 17 to 19.