GB2357060A - Planographic printing - Google Patents

Abstract

The problems of piling, ink spots and dye stain associated with planographic printing plates are addressed. The problems can be solved by varying the composition of a hydrophilic layer of the printing plate as set forth in the examples in the specification. A preferred hydrophilic layer described comprises an alkali metal silicate which acts as a binder for particulate material or materials.

Description

2357060 f. I 1 PLANOGRAPHIC PRINTING This invention relates to

planographic printing and provides methods of preparing substrates for planographic printing members, uses of specified components in the preparation of such substrates, substrates for planographic printing members and printing members per 'se.

PCT Publication No. W097/19819 (Horsell) describes a method of preparing a substrate for a planographic printing plate which comprises contacting a support with a liquid comprising a sodium silicate solution in which alumina and titania are dispersed thereby to produce a hydrophilic layer over the support. In each of the examples, the ratio of the wt% of alumina to titania is 1:1. However, investigations have shown that there are significant problems with blanket piling, undesirable ink sensitive spots and dyestaining of the hydrophilic layer in non-image areas, after development, associated with the use of the formulations described. Furthermore, disadvantageously, the formulations described tend to settle too quickly before application.

Paper used on a sheet fed offset printing press is normally smaller than the plate used to print. "Blanket piling" is the build-up of ink on the blanket within the area contacted by the plate but not by the paper. It can lead to problems over longer press runs by transferring ink to the edge of the paper being printed. In addition, the press needs to be stopped more frequently for blanket cleaning where piling is a problem. On conventional substrates, the cause of piling is usually due to poor 2 ink/water balance, non-waterproof ink or the surface chemistry and morphology of the substrate.

Ink-sensitive spots have been observed on printing plates prepared as described in W097/19819 after the plates have been cleaned either during or after a print run and then, subsequently, re-run on press - the slots appear once the press is restarted. Although the spots are removable by cleaning the plates for a second time, the effect is undesirable since, if the plates are not properly cleaned (as could easily happen in a commercial printing environment), the spots would result in ink being transferred to printing sheets which would, therefore, be rendered useless.

The dyestaining of the hydrophilic layer is caused by transfer of dye from the photocoat to the hydrophilic layer, with the staining being revealed in non-image areas defined after photocoat has been removed. The dyestaining is generally cosmetically unacceptable.

It is one object of the present invention to address the piling problem described above. It is another object to address the ink spot problem described above. It is a further object to address other problems associated with the formulations described in W097/19819.

The invention as described according to a first aspect hereinafter is based on the discovery that piling on a planographic printing member can be reduced by decreasing the ratio of the wt% of particulate material to binder material used in a hydrophilic layer of the member.

Accordingly, in a first aspect, the invention provides the 3 use of a fluid wherein the ratio of the wt% of particulate material to the wt% of binder material is less than 3 in the preparation of a hydrophilic layer of a planographic printing member for reducing the susceptibility of the printing member to piling.

The invention extends to a method of preparing a substrate for a planographic printing member having a reduced susceptibility to piling, the method including the step of forming a hydrophilic layer on a support by contacting the support with a fluid comprising a particulate material and a binder material for binding the particulate material in position on the support, wherein the ratio of the wt% of particulate material to the wt% of binder material is less than 3.

The planographic printing member suitably has a reduced susceptibility to piling compared to a planographic printing member which is identical except that said ratio is 3 or greater.

The invention extends to a method of printing using a printing member having image and non-image areas defined in association with a substrate according to said first aspect, wherein said printing member has a reduced susceptibility to piling compared to a printing member which is identical except that said ratio is 3 or greater.

Said ratio may be 2.7 or less, suitably 2.4 or less, preferably 2.0 or less, more preferably 1.5 or less especially 1.3 or less. Said ratio may be at least 0. 5, preferably at least 0.8, especially at least 1.1.

4 The piling susceptibility may be reduced in the manner described, irrespective of the nature of the binder material. For example, a major amount of the binder material may be an organic material, for example comprising a hydrophilic polymer or copolymer such as polyvinyl alcohol, optionally in combination with a cross linking agent such as a tetralkyl orthosilicAte.

Preferably, however, a major amount of said binder material is an inorganic binder material. An especially preferred binder material is a silicate which is suitably provided in solution in said fluid.

In the context of this specification, a "major amount" means that the referenced component suitably represents at least 70wt%, preferably at least 8Owt%, more preferably at least 90wt%, especially at least 95wt% of the total. In some situations, the total amount of a material referred to may consist essentially of the referenced component.

Said fluid may include a silicate solution which 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 nonmetal silicate. A meLal 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, 1 1 5 for example Si02., to the number of moles of cationic, for example, metal, species is at least 0.25, preferably at least 0 - 5. The ratio may be less than 10, preferably less than 6, especially less than 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 M20 in said silicate, where M represents an alkali metal, may be at least 0.25, suitably at least 1, preferably at least 2, more preferably at least 2.5, especially at least 3. Said ratio may be less than 6, preferably less than 5, more preferably less than 4. In some cases, the ratio may be less than 3. 5.

Preferred alkali metal silicates include lithium, sodium and potassium silicates, with lithium and/or sodium silicate being especially preferred. Said alkali metal silicate preferably includes a major amount of sodium silicate. In some cases, silicate solution comprising only sodium silicate may be preferred.

Said fluid may include at least Swt%, preferably at least 9wt%, more preferably at least 12wt%, especially at least 14wt% of binder material. The amount of binder material may be less than 25wt%, preferably less than 20wt%, more preferably less than 18wt%.

Said fluid may include at least 5wt%, suitably at least lOwt%, preferably at least 14wt%, more preferably at least 18wt% of particulate material, suitably in total.

The amount of said particulate material may be less than 30wt%, preferably less than 28wt%, more preferably less than 25wt%, especially less than 22wt%.

6 Said particulate material may be an organic or an inorganic material. 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, aluminosilica-tes, talcs, clays, (e.g kaolin), lithopone, calcium carbonate and titanium oxide.

Said fluid may include more than 20 wt%, suitably more than 30 wt%, preferably more than 40 wt%, more preferably more than 50 wt%, water. Said fluid may include less than wt%, preferably less than 75 wt%, more preferably less than 70 wt%.

Said particulate material may comprise a first material having 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 first material may comprise flattened particles or platelets. Said first material may have a mean particle size of at least 0.1 pm, preferably at least 0.5 pm and, more preferably, at least 1 pm. Said first material may have a mean particle size of less than 200 pm, suitably less than 100 pm, preferably less than 45 pm, more preferably less than 20 pm, especially less than 10 pm and, most preferably, less than 5 pm. The particle size distribution for 95% of particles of the first material may be in the range 0.01 to 150pm, preferably in the range of 0.05 to 75pm, more preferably in the range 0.05 to 30pm. Said first material is preferably alumina.

7 The reference to alumina includes a reference to A1203 per se and hydrates thereof, for example A1203 -3H20 Preferably however, said material is 111203 per se.

References to particle sizes herein are to the volume mean particle size, unless otherwise stated.

Said particulate material may include less than 90wt%, suitably less than 80wt%, preferably less than 70wt%, more preferably less than 60wt%, especially 50wt% or less of said first material. Said particulate material may include at least lOwt%, suitably at least 20wt%, preferably at least 30wt%, more preferably at least 40wt%, especially at least 45wt% of said first material.

Said particulate material may comprise a second material. Said second material may have a mean particle size by mass of at least 0.05 pm, preferably at least 0.10 jim, more preferably at least 0.15 pm, especially at least 0.19 PM. The mean particle size may be less than 2 Lm, suitably less than 1.5 pm, preferably less than 1 Lm, more preferably less than 0.5 n, especially less than 0.35 tm.

Said second material is preferably titania. Said titania may include an anatase titania. Said titania may include a coated titania, for example a titania provided with a coating comprising a material which is harder than the titania it coats. The coating may make up less than S wt%, preferably 4.5 wt% or less of the titania. Said coating may comprise alumina.

8 Said titania may include more than one type of titania. For example, one type may be an anatase titania, the other may be a rutile titania; and/or one type of titania may be coated and the other may be substantially non-coated.

The ratio of the wt% of said first material to tha-t of said second material is preferably in the range 0 to 1.

The sum of the wt% of the first and second materials preferably represents a major component of said particulate material.

The invention as described according to a second aspect hereinafter is based on the discovery that piling on a planographic printing member increases as the amount of alumina in a hydrophilic layer of the member increases.

Accordingly, in a second aspect, the invention provides the use of particulate material comprising less than SOwt% of particulate alumina in the preparation of a hydrophilic layer of a planographic printing member for reducing the susceptibility of the printing member to piling, wherein said hydrophilic layer comprises particulate material and a binder material for binding the particulate material in position.

The invention extends to the use of particulate material comprising less that SOwt% of particulate alumina in a hydrophilic layer of a planographic printing member for reducing the susceptibility of said printing member to piling, wherein said hydrophilic layer comprises particulate material and a binder material binding the particulate material in position.

9 The invention extends to a method of preparing a substrate for a planographic printing member having a reduced susceptibility to piling, the method including the step of forming a hydrophilic layer on a support by contacting the support with a fluid comprising a particulate material and a binder material for bindingthe particulate material in position on the support, wherein said particulate material comprises less than 50wt% of particulate alumina.

The invention further extends to a substrate for a planographic printing member having a reduced susceptibility to piling, the substrate comprising a support and a hydrophilic layer which includes a binder material and particulate material, wherein said particulate material includes less than 50wt% of particulate alumina.

Preferably, in use on a printing press, said planographic printing member has a reduced susceptibility to piling compared to a planographic printing member which is identical except that it comprises 50wt% or more of particulate alumina.

The invention extends to a method of printing using a printing member having image and non-image areas defined in association with a substrate according to said second aspect, wherein said printing member has a reduced susceptibility to piling compared to a printing member which is identical except that said particulate material includes 50wt% or more of particulate alumina.

Preferably, said substrate of the second aspect includes some particulate alumina.

The invention as described according to said third aspect hereinafter is based on the discovery that piling on a planographic printing member reduces when smaller particulate material is used. Accordingly, in a tl"fird aspect, the invention provides the use of particulate material which includes greater than SOwt% of material of a particle size of less than 3pm in the preparation of a hydrophilic layer of a planographic printing member for reducing the susceptibility of the printing member to piling, wherein said hydrophilic layer comprises a binder material for binding the material in position and said particulate material.

The invention extends to a method of preparing a substrate for a planographic printing member having a reduced susceptibility to piling, the method including the step of forming a hydrophilic layer on a support by contacting the support with a fluid comprising a particulate material and a binder material for binding the particulate material in position on the support, wherein said particulate material includes greater than 50 wt% of material of a particle size of less than 3pm.

The invention extends to the use of particulate material which includes greater than SOwt% of material of a particle size of less than 3pm in a hydrophilic layer of a planographic printing member for reducing the susceptibility of the printing member to piling, wherein said hydrophilic layer comprises a binder material for binding the material in position and said particulate material.

The invention further extends to a substrate for a planographic printing member having a reduced susceptibility to piling, the substrate comprising a support and a hydrophilic: layer which includes a birder material and particulate material, wherein said particulate material comprises greater than 50 wt% of material of a particle size of less than 3pm.

Preferably, in use on a printing press, said planographic printing member has a reduced susceptibility to piling compared to a planographic printing member which is identical except that it includes 50wt% or more of a material of a particle size of greater than 31im.

The invention extends to a method of printing using a printing member having image and non-image areas defined in association with a substrate according to said third aspect, wherein said printing member has a reduced susceptibility to piling compared to a printing member which is identical except that it comprises SOwt% or more of a material of a particle size of greater than 3pm.

Suitably, greater than 50 wt% of material may have a particle size of less than 2.5pm, preferably of less than 2pm, more preferably less than 1.5pm, especially 1.4pm or less.

Preferably, said particulate material includes alumina (suitably greater than SOwt% thereof) of a particle size of less than 3pm. Suitably, the alumina has a particle 12 size of less than 2.5pm, preferably less than 2pm, more preferably less than 1.5pm.

According to a fourth aspect of the invention, there is provided a method of preparing an improved printing member of a type comprising a substrate which includes a hydrophilic layer comprising a binder and particuate material, wherein said improved printing member has a reduced susceptibility to piling compared to a comparison printing member which is identical to said improved printing member except that said improved printing member includes at least one of the following differences:

a) a reduction in the ratio of the wt% of the particulate material to the wt% of binder material; b) a reduction in the amount of alumina in said hydrophilic layer; c) a reduction in the mean particle size of the particulate material in said hydrophilic layer; the method comprising preparing said improved printing member with at least one of the aforementioned differences compared to said comparison printing member.

The method preferably includes the step of selecting a known printing member which is susceptible to piling and preparing an improved member with one of the differences described.

The invention according to the fourth aspect extends to the use of a said improved printing member for printing 13 using a printing press and a method of printing using said improved printing member.

The invention as described according to a fifth aspect hereinafter is based on the discovery that ink spots on a printing member which includes a hydrophilic layer of a type which includes a binder derived from a metal silic-ate can be reduced by increasing the ratio of the number of moles Of Si02 to the number of moles M20, where M represents an alkali metal, in the metal silicate.

Accordingly, in a fifth aspect, the invention provides the use of a fluid comprising a dissolved alkali metal silicate, wherein the ratio of the number of moles Of Si02 to the number of moles Of M20 in the fluid (preferably in the alkali metal silicate used in the preparation of said fluid) is greater than 3. 5, in the preparation of a planographic printing member for reducing t h e susceptibility of the printing member to ink spots.

The invention extends to a method of preparing a substrate for a planographic printing member having a reduced susceptibility to ink spots, the method including the step of forming a hydrophilic layer on a support by contacting the support with a fluid comprising a particulate material and a binder material for binding the particulate material in position on the support, wherein the binder material comprises dissolved alkali metal silicate, wherein the ratio of the number of moles Of Si02 to the number of moles Of M20 in the f luid, where M represents an alkali metal, is greater than 3.5.

Said ratio may be greater than 3. 6, preferably greater than 3.7, more preferably greater than 3.8, especially 14 greater than 3.9. Said ratio may be less than 5, preferably less than 4.5, more preferably less than 4.1.

The invention extends to a substrate prepared as described and a method of printing using such a substrate.

The invention as described according to a sixth asl:ect hereinafter is based on the discovery that ink spots on a printing member which includes a hydrophilic layer of a type which includes a binder material and particulate material can be reduced by using particulate material which is more spherical. Accordingly, in a sixth aspect, the invention provides the use of a fluid comprising a binder material and particulate material in the preparation of a hydrophilic layer of a planographic printing member for reducing the susceptibility of the printing member to ink spots, wherein the particulate material includes a material, preferably a major amount thereof, which is more spherical compared to a particulate material which comprises hexagonal platelets.

The invention extends to the use of a particulate material which is more spherical than hexagonal platelets in a hydrophilic layer of a planographic printing member for reducing the susceptibility of the printing member to ink spots, wherein said hydrophilic layer comprises particulate material and a binder material for binding the particulate material in position.

The invention extends to a method of preparing a substrate for a planographic printing member having a reduced susceptibility to ink spots, said method including the step of forming a hydrophilic layer on a support by contacting the support with a fluid comprising a particulate material and a binder material for binding the particulate material in position on the support, wherein the particulate material comprises a material which is more spherical compared to a particulate material comprising hexagonal platelets.

The invention further extends to a substrate for a planographic: printing member having a reduced susceptibility to ink spots, the substrate comprising a support and a hydrophilic layer which includes a binder material and particulate material, wherein said particulate material includes a material, preferably a major amount thereof, which is more spherical compared to a particulate material comprising hexagonal platelets.

Typically, said material which is more spherical is an alumina.

Preferably, in use on a printing press, said planographic printing member has a reduced susceptibility to ink spots compared to a planographic printing member which is identical except that it includes particulate material which is less spherical. The invention therefore extends to a method of printing using a planographic printing member as described.

The invention as described according to a seventh aspect hereinafter is based on the discovery that ink spots on a planographic printing member can be reduced by providing an additional coating below or above a hydrophilic: layer of a type which comprises a binder and particulate material. Accordingly, in a seventh aspect, 16 the invention provides the use of an ink spot reduction layer above or below a hydrophilic layer of a planographic printing member, wherein the hydrophilic layer comprises particulate material and a binder material for binding the particulate material in position.

The invention extends to a method of preparinq a substrate for a planographic printing member having a reduced susceptibility to ink spots, the method including the step of forming a hydrophilic layer over a support using a fluid comprising a particulate material and a binder material for binding the particulate material in position, wherein an ink spot reduction layer is provided below or above the hydrophilic layer.

Preferably, the ink spot reduction layer is formed using a fluid which includes the same material as that used as said binder in said hydrophilic layer.

Preferably, said ink spot reduction layer is formed using a fluid comprising a silicate solution. Said silicate solution may be as described in any statement herein. Preferably, said fluid does not include particulate material. Preferably, it consists essentially of alkali metal silicate. Said fluid may include less than Swt%, suitably less than 4wt%, preferably less than 3wt%, more preferably less than 2wt%, especially less than lwt% of dissolved alkali metal silicate. Said f luid may include at least O.lwt%, preferably at least 0.2wt%, more preferably at least 0.25wt% of dissolved alkali metal silicate solids.

17 The invention extends to a substrate prepared as described and a method of printing using such a substrate.

The invention as described according to an eighth aspect hereinafter is based on the discovery that ink spots on a planographic printing member can be reduced by increasing the amount of a lower atomic number al]Zali metal used in a binder material of a hydrophilic layer of the member. Accordingly, in an eighth aspect, the invention provides the use of a fluid comprising a particulate material and a binder material in the preparation of a hydrophilic layer of a planographic printing member for reducing the susceptibility of the printing member to ink spots, wherein the binder material includes at least some dissolved lithium silicate.

The invention extends to a method of preparing a substrate for a planographic printing member having reduced susceptibility to ink spots, the method including the step of forming a hydrophilic layer on a support by contacting the support with a fluid comprising a particulate material and a binder material for binding the particulate material in position on the support, wherein the binder material includes at least some dissolved lithium silicate.

The invention extends to a substrate prepared as described and a method of printing using such a substrate.

According to a ninth aspect of the invention, there is provided a method of preparing an improved printing member of a type comprising a substrate which includes a hydrophilic layer comprising a binder and particulate material, wherein said improved printing member has a reduced susceptibility to ink spots compared to a comparison printing member which is identical to said improved printing member except that said improved printing member includes at least one of the following differences:

a) the binder material is derived from an alkali metal silicate wherein the ratio of the number of moles of Si02 to the number of moles Of M20 is greater; b) the particulate material is more spherical; C) an ink spot reduction layer below or above the hydrophilic layer; d) said binder material includes more lithium silicate; the method comprising preparing said improved printing member with a least one of the aforementioned differences compared to said comparison printing member.

The method preferably includes the step of selecting a known printing member which is susceptible to ink-spots and preparing an improved printing member with one of the differences described.

The invention as described according to a tenth aspect hereinafter is based on the discovery that dyestain of the hydrophilic background of a planographic printing member can be reduced by decreasing the ratio of the wt% of particulate material to binder material used in a hydrophilic layer of the member. Accordingly, in a tenth 19 aspect, the invention provides the use of a fluid wherein the ratio of the wt% of particulate material to the wt% of binder material is less than 3 in the preparation of a hydrophilic layer of a planographic printing member for reducing the susceptibility of the printing member to dyestain.

The invention extends to a method of preparing a substrate for a planographic printing member having a reduced susceptibility to dyestain, the method including the step of forming a hydrophilic layer on a support by contacting the support with a fluid comprising a particulate material and a binder material for binding the particulate material in position on the support, wherein the ratio of the wt% of particulate material to the wt% of binder material is less than 3.

Said ratio may be 2.7 or less, preferably 2.3 or less, more preferably 2 or less. Said ratio may be at least 0.5, preferably at least 0.8, especially at least 1.1.

The susceptibility to dyestain may be reduced in the manner described, irrespective of the nature of the binder material. The binder material may be as described according to said first aspect and said particulate material may be as described according to said first aspect.

The invention extends to a substrate prepared as described and a method of printing using such a substrate.

The invention according to an eleventh aspect hereinafter is based on thediscovery that the susceptibility of a hydrophilic layer of a type derived from a silicate, for example an alkali metal silicate, to dyestain is affected by the nature of the silicate used and more particularly that the susceptibility to dyestain is reduced by reducing the ratio of the number of moles of Si02 to the number of moles Of M20 in the metal silicate.

Accordingly, in an eleventh aspect, the invention provfdes the use of a fluid comprising an alkali metal silicate wherein the ratio of the number of moles Of Si02 to the number of moles Of M20 is less that 3 in the preparation of a hydrophilic layer of a printing member for reducing the susceptibility of the hydrophilic layer to dyestain.

The invention extends to a method of preparing a substrate for a planographic printing member comprising a hydrophilic layer having a reduced susceptibility to dyestain, the method including the step of forming a hydrophilic layer on a support by contacting the support with a fluid comprising particulate material and an alkali metal silicate for binding the particulate material in position on the support, wherein the ratio of the number of moles of Si02 to the number of moles Of M20 in the silicate is less than 3.

Said ratio may be less than 2. 9, preferably less than 2.8, more preferably less than 2.7, especially less than 2.6. Said ratio may be at least 2, preferably at least 2.1, more preferably at least 2.3, especially at least 2.5.

Said silicate is preferably a sodium silicate, with sodium polysilicate being preferred.

21 The invention extends to a substrate prepared as described and a method of printing using such a substrate.

The invention according to a twelfth aspect is based on the discovery that the susceptibility of a hydrophilic layer of a type comprising a particulate material and a binder material to dyestain is reduced as the size of the particulate material increases. Accordingly, in a twelfth aspect, there is provided a method of preparing an improved printing member of a type comprising a substrate which includes a hydrophilic layer comprising a binder and particulate material, wherein said improved printing member has a reduced susceptibility to dyestain compared to a comparison printing member which is identical to said improved printing member except that it includes particulate material of a smaller size than that of said improved printing member, the method comprising preparing said improved printing member by contacting a support with a fluid comprising a particulate material and a binder material for binding the particulate material in position on the support, wherein the particulate material has a greater size than that used for said comparison printing member.

The dyestain susceptibility may be reduced in the manner described, irrespective of the nature of the binder material. However, the binder material is preferably as described according to said first aspect.

The invention according to the thirteenth aspect is based on the discovery that the susceptibility of a hydrophilic layer of a type comprising a particulate material which includes alumina and a binder material to 22 dyestain is reduced as the level of alumina increases.

Accordingly, in a thirteenth aspect, there is provided a method of preparing an improved printing member of a type comprising a substrate which includes a hydrophilic layer comprising a binder material and particulate material which includes alumina, wherein said improved printing member has a reduced susceptibility to dyestain compared to a comparison printing member which is identical to said improved printing member except that said comparison printing member includes a reduced level of alumina, the method comprising preparing said improved printing member by contacting a support with a fluid comprising a particulate material and a binder material for binding the particulate material in position on the support, wherein the particulate material includes alumina at an increased level compared to that used in the preparation of said comparison printing member.

The dyestain susceptibility may be reduced in the manner described, irrespective of the nature of the binder material. However, preferably, the binder material is as described according to said first aspect. The susceptibility to dyestain may be reduced in the manner described particularly where the alumina comprises alumina in the form of platelets. In this case, preferably, the amount of platelet alumina is reduced.

The invention according to a fourteenth aspect is based on the discovery that the susceptibility of a hydrophilic layer of a type comprising a particulate material and a binder material to dyestain can be reduced according to the type of particulate material used.

Accordingly, in a fourteenth aspect, there is provided a 23 method of preparing an improved printing member of a type comprising a substrate which includes a hydrophilic layer comprising a binder and particulate material, wherein said improved printing member has a reduced susceptibility to dyestain compared to a comparison printing member which is identical to said improved printing member except that said improved member includes particulate matel!ial selected so that, when incorporated in said hydrophilic layer, said layer has a reduced susceptibility to dyestain, the method comprising preparing said improved printing member by contacting a support with a fluid comprising a particulate material and a binder material for binding the particulate material in position on support, wherein the particulate material includes said selected particulate material.

The invention according to the fifteenth aspect is based on the discovery that the susceptibility of a hydrophilic layer of a type comprising a particulate material and a binder material to dyestain can be reduced by incorporating a selected surfactant in a fluid which is used in the preparation of said hydrophilic layer.

Accordingly, in a fifteenth aspect, the invention provides a method of preparing an improved printing member of a type comprising a substrate which includes a hydrophilic layer comprising a binder and particulate material, wherein said improved printing member has a reduced susceptibility to dyestain compared to a comparison printing member which is identical to said improved printing member except that said impro ved member includes a surfactant selected to reduce the susceptibility of the hydrophilic layer to dyestain, the method comprising the step of contacting a support with a fluid comprising a 24 particulate material and a binder material for binding the particulate material in position on the support, wherein the fluid also includes a surfactant selected to reduce the susceptibility of the hydrophilic layer to dyestain compared to that of said comparison printing member.

The invention according to a sixteenth aspect is b;sed on the discovery that the susceptibility of particulate material in a fluid for use in the preparation of a hydrophilic layer of a planographic printing member to settle out is reduced by: increasing the ratio of the wt% of particulate material to the wt% of silicate; reducing the amount of alumina in said particulate material; adding a viscosity modifier; reducing the particle sizes of the particulate material; or increasing the concentration of solid material dissolved or dispersed in the fluid.

Accordingly, in a sixteenth aspect, the invention provides a method of preparing a printing member of a type comprising a substrate which includes a hydrophilic layer comprising a binder material and particulate material, the method using an improved fluid which has a reduced susceptibility to settling compared to a comparison fluid which is identical to said improved fluid except that said improved fluid includes at least one of the following 2S differences: a) an increase in the ratio of the wt% of particulate material to the wt% of silicate; b) a reduction in the amount of alumina in said particulate material; c) the addition of a viscosity modifier to said fluid; d) a reduction in the particle sizes of said particulate material; and e) an increase in the concentration of solids in said fluid, the method comprising preparing said printing member using a fluid with at least one of the aforementioned differences compared to sald comparison fluid.

An invention described according to any aspect herein may include any feature described according to any other aspect of embodiment described herein, unless such a feature is inconsistent. 1 The following statements may apply to any aspect described above, unless a particular statement is inconsistent with a specific statement made according to a particular aspect.

A binder material of a hydrophilic layer of a printing member prepared in a method described herein may be a component of a polymeric material which includes Si-0 bonds. Said polymeric material may include -Si-O-Si-, especially -Si-O-Si-0-, 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%, most preferably at least 95 wt% of said binder material is made up of a polymeric material having Si-0 bonds as described. Preferably, said binder material consists essentially of a polymeric material having Si-0 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 26 wt%, especially less than 25 wt%, of said hydrophilic layer.

Said binder material preferably includes less than 10 wt%, preferably less than 5 wt%, more preferably less than 1 wt%, organic material, for example polymeric organic material. Preferably, said binder material incli-rdes substantially no polymeric organic material.

Said particulate material is preferably dispersed in said binder material. Said particulate material is preferably substantially water insoluble. Suitably at least 30 wt%, preferably at least 40 wt%, more preferably at least 50 wt%, especially at least 60 wt% of said hydrophilic layer is composed of said particulate material. Suitably less than 90 wt%, preferably less than wt%, more preferably less than 80 wt%, especially less than 75 wt% of particulate material is dispersed in said binder material.

Said hydrophilic layer may have an average thickness of less than 100 pm, suitably less than 50 pm, preferably less than 20 pm, more preferably less than 10 pm, especially less than 5 pm. In some cases, the layer may have an average thickness of less than 3 pm. Said hydrophilic layer may have an average thickness of greater than 0.1 pm, suitably greater than 0.3 pm, preferably greater than 0.5 jim, more preferably greater than 1 pm.

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 pm, suitably at least 0.25pm, 27 preferably at least 0.3 pm. The Ra may be less than 1. 5 pm, suitably less than 1 pm, preferably less than 0. 8 pm, more preferably less than 0.7 pm, especially less than 0.6 pm, most preferably less than 0.5 pm.

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 6 to 14 g of material per metre squared.

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.

28 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 be pre-treated 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, elect roc leaning, 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, 5 th 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.

29 A printing member described herein preferably comprises a substrate of a type described and an image layer.

The term "image layer" includes a layer that can subsequently be partially removed in order to define ar'eas 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 depolymerisation 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 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.

A fluid used in the preparation of a printing member described herein may include a surfactant. Said formulation may include 0 to 1 wt%, suitably 0 to 0.8 wt%, preferably 0 to 0.6 wt%, more preferably 0 to 0.4 wt%, especially 0 to 0.3 wt% of surfactant.

Said fluid may have a viscosity of less than 100 centipoise when measured at 200C 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 to form a hydrophilic layer having an average thickness after drying, of less than 20 pm, preferably less than 10 pm and, more preferably, less than 5 pm. Especially preferred is the case wherein the average thickness is less than 3 pm.

The method preferably includes the step 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 31 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 2300C, preferably does not exceed 2000C and, more preferably, does not exceed 1750C.

Especially preferred is the case wherein the support temperature does not exceed 1500c.

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 planographic printing member comprising applying an image layer over a substrate prepared as described herein.

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

Specific embodiments of the invention will now be described, by way of example.

2S The following materials are referred to hereinafter.

Microgrit C3 - a 3 micron hexagonal platelet alumina supplied by Peter Wolters, London, U.K.

Hombitan LW - a 0.2 micron anatase titania supplied by Hubron Sales Ltd., Manchester, U.K.

32 Ti-Pure R900 - a 0.23 micron rutile titania coated with alumina (95% titania 5% alumina) supplied by Marlow Chemical Company Ltd., Westerham, Kent, U.K.

Attagel 50 - 0. 1 micron atapulgite thixotropic thickener supplied by Lawrence Industries, Tamworth, U.K..

Blanc Fixe N - 3 micron barium sulphate supplied by Hubron Sales Ltd., Manchester, U.K.

CR1 - 1.2 micron spherical alumina supplied by Peter Wolters, London, U.K.

CR6 - 0. 6 micron spherical alumina supplied by Peter Wolters, London, U.K.

CR15 - 0.5 micron spherical alumina supplied by Peter Wolters, London, U. K.

RA203LS - 1. 4 micron oblate calcined alumina supplied by Alcan Chemicals Europe, Burntisland, Fife, U.K.

RA207LS - 0.4 micron oblate calcined alumina supplied by Alcan Chemicals Europe, Burntisland, Fife, U.K.

RA7 - 1.1 micron calcined alumina supplied by Alcan Chemicals Europe, Burntisland, Fife, U.K.

RA10 - 2.1 micron calcined alumina supplied by Alcan Chemicals Europe, Burntisland, Fife, U.K.

RA12 - 4.0 micron calcined alumina supplied by Alcan Chemicals Europe, Burntisland, Fife, U.K.

33 RA15 - 2.7 micron calcined alumina supplied by Alcan Chemicals Europe, Burntisland, Fife, U.K.

Baco MA2LS - 8.0 micron calcined alumina supplied by Alcan Chemicals Europe, Burntisland, Fife, U.K.

Alumina C - High temperature flame hydolysed hydrophilic alumina; average primary particle size 13nm supplied by Degussa, England, U.K.

Aerosil 200 - High temperature flame hydolysed hydrophilic silica; average primary particle size 12nm supplied by Degussa, England, U.K.

Crystal 75 - sodium polysilicate with mean molar ratio Si02:Na2O of 3.30:1 and mean solids of 36.2% supplied by Crosfields, Warrington, U.K.

Crystal 0503 - sodium polysilicate with mean molar ratio Si02:Na2O of 2.58:1 and mean solids of 43.6% supplied by Crosfields, Warrington, U.K.

Crystal K78 - potassium polysilicate with mean molar ratio Si02:K20 of 3.27:1 and mean solids of 40.1% supplied by Crosfields, Warrington, U.K.

Crystal SID623 - lithium polysilicate with mean molar ratio Si02:Li2O of 3.30:1 and mean solids of 20.0% supplied by Crosfields, Warrington, U.K.

34 Crystal 52 - sodium polysilicate with mean molar ratio Si02:Na2O of 3.97:1 and mean solids of 28.0% supplied by Crosfields, Warrington, U.K.

Dowfax 2A1 - a mixture of mono- and di-dodecyl disulphonated diphenyl oxide, sodium salt supplied by Dow Chemical Company Ltd., Uxbridge, U.K. I Lubrophos HR-719 - Complex organic phosphate ester supplied by Rhone-Poulenc, England.

Surfaron A6008 - 2-Ethyl Hexyl Sulphate supplied by Protex, England.

Aluminium Sulphate dodecahydrate supplied by Hy-Per-Graph Ltd., Morley, U.K.

Developer A: Goldstar - 14% sodium metasilicate pentahydrate in water supplied by Kodak Polychrome Graphics, Morley, U.K.

Substrate A: 0.3mm sheet lithographic 1050 grade aluminium supplied by Alcan UK.

Capricorn DH Positive printing plate supplied by Kodak Polychrome Graphics, Morley, U.K.

Capricorn DH coating supplied by Kodak Polychrome Graphics, Morley, U.K.

Hydrokleen press cleaning chemical supplied by Kodak Polychrome Graphics, Morley, U.K.

Emerald Fount solution supplied by Kodak Polychrome Graphics, Morley, U.K.

Rapid Ink supplied by Kodak PolYchrome Graphics, Morley, U.K.

Multigum supplied by Kodak Polychrome Graphics, Morley, U.K.

Geneva alcolor black printing ink supplied by Gibbon Inks, Leeds, UK.

Duo Laser Brilliance paper GSM 80, long grain paper supplied by Federal Tait Paper Products, UK.

Montakop 95M supplied by Siegfried Theimer GmbH, Obersotzbach, Germany.

Aura 650 Plate Processor supplied by Kodak Polychrome Graphics, Morley, U.K.

Heidelberg SpeedMaster 52 Printing Press supplied by Heidelberg, Leeds, UK.

Marr Convection Oven supplied by Marr Engineering, Leeds, UK.

Example 1 - Preparation of coating formulations Coating formulations used in the examples described hereinafter were prepared by mixing, in the order given, the components of the formulations in a high shear mixer.

36 Example 2 - Preparation of print-ing plate precursors A 0.3 mm gauge aluminium alloy sheet of designation AA 1050 was cut to a size of 230 mm by 350 mm, with the grain running lengthways. The sheet was then inunersed face up in a solution of sodium hydroxide dissolved in distilled water (100 g/1) at ambient temperature for 60 seconds and thoroughly rinsed with water. The coating formulations prepared as described in Example 1 were coated onto the aluminium sheet using a rotating meyer bar coater (designation K303) to give a 8 im wet film thickness. The coated sheet was then placed in a Marr convection oven at 130'C for 60 seconds. The sheet was then removed from the oven and allowed to cool to ambient temperature. The dried sheet was immersed in aluminium sulphate (0.1M) for thirty seconds. The sheet was then spray rinsed for about thirty seconds using tap water and fan dried. A printing plate was produced from the sheet by coating, using a meyer bar, a light sensitive material of the quinone diazide/novolak resin type (Capricorn DH positive coating) at a dry coating weight of 2 gm-2. The light sensitive material was dried at 130'C for 80 seconds in a Marr convection oven.

Example 3 - Exposure and development Printing plate precursors made as described in Example 2 were imaged in a commercially available light frame, the Montakop 95M with a THS-3020 bulb. The plates were then developed using developer A for 1 minute and dried under ambient conditions.

37 Example _4 - Assessment of piling tendency of printing plate A press test was carried out on the SpeedMaster 52 printing press using a Capricorn DH positive plate as a standard. All the plates assessed were subjected to al3out 2000 impressions. Once a test had been completed, the region outside of the paper area was inspected. A plate showing a smaller amount of ink build up in these areas is described as having a lower piling, which would allow the printer to spend less time cleaning the press during normal printing. Also, a value is given to the relative level of piling for each plate, to allow the plates to be compared. The value is determined visually.

The plates of Examples 8 to 17 were assessed in the manner described.

Example 5 - Assessment of susceptibility to ink-sensitive spots A 5% aqueous solution of sodium chloride was applied to the surface of the hydrophilic layer of selected plates prepared as described in Example 1, after treatment with aluminium sulphate and prior to application of the light sensitive material, using a cotton wool swab and left for minutes. During this period the substrates were re wetted to prevent them drying out. After the salt solution had been applied to the hydrophilic layers for the full period, the substrates were rinsed thoroughly with water and any excess water removed using a squeegee.

An inking solution was then applied to the substrate 38 surfaces and left for a period of 5 minutes. The solution contained 50g of Rapid Ink., 100g of Hydrokleen and 2 drops of Emerald Fount solution. After the time was complete, the solution was re-applied for a further 5 minutes and the procedure repeated until a total dwell time of 15 minutes had been achieved. The inking solution was then rinsed with water and the substrates inspe(ted for ink sensitive spots. A value is given to the relative level of ink-spots for each plate, to allow the plates to be compared. The value is determined visually.

The plates of Examples 18 to 31 were assessed in the manner described.

Example 6 - Assessment of susceptibility to dyestain This was measured after development of a plate as described in Example 3, using a Minolta CR-331 chromometer.

The plates of Examples 32 to 55 were assessed in the manner described.

Example 7 - Assessment of susceptibility of coating formulations to settling 50cm 3 of each selected coating formulation prepared as described in Example 1 was placed in a 50CM3 measuring cylinder and the top was sealed so that no evaporation could occur. The degree of settling was noted after a period of 24 hours determining by the amount of clear liquor above the remaining "milky" formulation.

39 A. Assessment of Factors Affecting Piling (a) Decreasing the ratio of particulates to silicate Materlals/g Example 8 Example 9 Hombitan LW 9.6 14.3 Microgrit C3 9.6 14.3 Crystal 75 57.3 31.7 Deionised water 23.4 39.8 Wt% Particulates: 1.2:1 3.2:1 Wt% Silicate (solids) Piling Slight-2 Severe-8 It will be noted that, as the ratio of the wt% of silicate reduces, the piling tendency reduces.

(b) Increasing alumina content Materlals/g Example 10 Example 11 Hombitan LW 14.2 23.7 Microgrit C3 14.2 0 Crystal 75 31.6 26.3 Deionised water 40 50 Piling Severe-8 V.Slight-l It will be noted that, as the level of alumina increases, the piling tendency increases.

(c) Using smaller particulates Materials/ Example Example Example Example Example Example 9 12 13 14 15 16 17 Hombitan 14.2 28.4 LW Microgrit 28.4 14.2 C3 RA207LS 28.4 RA203LS 28.4 RA7 28.4 Crystal 75 31.6 31.6 31.6 31.6 31.6 31.6 Deionised 40 40 40 40 40 40 water Piling Severe-9 Severe-7 Slight-2 V.Slight Moderate Slight-3 It will be noted that, as the size of the particulates reduces, the piling tendency reduces.

B. Assessment of Factors Affecting Ink Spots (a) Altering the ratio of Si02 to M20 in the silicate io Materials/g Example 18 Example 19 Example 20 Hombitan LW 14.22 14.22 14.22 Microgrit C3 14.22 14.22 14.22 Crystal 75 31.5 Crystal 0503 26.15 Crystal C52 40.73 Deionised 40.05 45.4 30.82 Water Molar Ratio 3.3:1 2.58:1 3.97:1 (Si02/M20) Ink Spots Moderate-5 Severe-8 Slight-3 It will be noted that, as the molar ratio Of Si02 to M20 increases, susceptibility to ink spots decreases.

41 (b) Use of more spherical particulates Materials/ Example Example Example Example Example 9 21 22 23 24 25 Ti-Pure 28.4 R900 Hombitan 28.4 LW Microgrit 28.4 C3 RA207LS 28.4 Blanc Fixe 28.4 N Crystal 75 31.6 31.631.6 31.6 31.6 Deionised 40 40 40 40 40 water Ink Spots None-1 Moderate Severe-8 None-O Slight-2 -5 1 It will be noted that, as more spherical extenders are used, the susceptibility to ink spots decreases.

(c) Inclusion of additional top/bottom coating Coating formulations as described in Example 13 were further assessed for ink spots wherein Example 26 is the coating of Example 13 with no additional treatment; Example 27 included a treatment with a 1% solution of Crystal 75 before application of the hydrophilic layer; and Example 28 included a treatment with a 1% solution of Crystal 75 after application of the hydrophilic layer.

Results are provided below.

Example No. Ink Spots 26 Severe-8 27 None-O 28 None-O 42 It will be noted that a top or bottom silicate coating significantly reduces susceptibility to ink spots.

(d) Altering the silicate cation Materials/g Example 29 Example 30 Example 31 Hombitan LW 14.22 14.22 14.22 Microgrit C3 14.22 14.22 14.22 Crystal 75 31.5 SID 623 57.02 Crystal K78 28.44 Deionised 40.05 14.4 43.11 Water Cation of Na+ Li+ K + Silicate Ink Spots Moderate-6 Slight-1 Severe-9 It will be noted that the nature of the silicate cation affects the susceptibility to ink spots with use of lower atomic number cations reducing susceptibility.

C. Assessment of Factors Affecting Dyestain (a) Increasing the level of alumina Materials/ Example 32 Example 33 Example 34 Example 35 9 Hombitan 14.26 17.07 21.44 28.51 LW Microgrit 14.26 11.44 7.07 0 C3 Crystal 75 31.71 31.71 31.71 31.71 Deionised 39.78 39.78 39.78 39.78 Water Dyestain 0.57 0.89 1.59 1.71 43 It will be noted that the level of dyestain reduces as the amount of alumina increases.

(b) Altering the nature of the particulate material Materials/ Example Example Example Example 9 36 37 38 39 Hombitan 28.44 LW Ti-Pure 28.44 R900 Microgrit 28.44 C3 Blanc Fixe 28.44 N Crystal 75 31.5 31.5 31.5 31.5 Deionised 40.06 40.06 40.06 40.06 1 water Dyestain 6.23 1 1.36 0.81 0.66 It will be noted that the level of dyestain is affected by the nature of the particulate material with the smallest dyestain being observed for Blanc Fixe N (c) Altering the silicate cation and the ratio Of Si02 to M20 in the silicate Materials/g Example Example Example Example Example 41 42 43 44 Hombitan LW 14.22 14.22 14.22 14.22 14.22 Microgrit C3 14.22 14.22 14.22 14.22 14.22 Crystal 75 31.5 Crystal 0503 26.15 Crystal 52 40.73 SID 623 57.02 Crystal K78 28.44 Deionised 40.05 45.4 30.82 14.4 43.11 water 44 Molar Ratio 3. 3: 1 2. 58: 1 3. 97: 1 3. 3: 1 3. 277f- (Si02: M20) Cation of Na Na Na Li - K Silicate Dyestain 1 0.23 2.02 4.8 15.67 It will be noted that the level of dyestain reduces, as the ratio Of Si02 to M20 reduces.

(d) Decreasing the ratio of particulates to silicate Mater als/g Example 45 Example 46 Example 47 Hombitan LW 28.51 26.47 23.65 Crystal 75 31.71 37.37 45.18 Deionised 39.78 36.16 31.17 water Particulates: 3.2:1 2.53:1 1.87:1 Silicate Dyestain 1.71 1.3 0.56 It will be noted that, as the amount of particulates is reduced, the dyestain reduces.

(e) Altering the nature of surfactant Materials/g Example 48 Example 49 Example 50 Example 51 Ti-Pure R-900 24.5 24.5 24.5 24.5 Microgrit C3 4 4 4 4 Crystal 75 31.5 31.8 31.8 31.8 Deionised 39.7 39.7 39.7 39.7 water Surfaron 0.2 A6008 Gafen HR-719 0.2 Dowfax 2A1 45 5.06 0.2 Dyestain 3.24 0.37 0.24 It will be noted that the nature of the surfactant affects the level of dyestain.

(f) Increasing the particle size of the particul'ate material Haterials/g Example 52 Example 53 Example 54 Example 55 RA7 28.4 RAIO 28.4 RA12 28.4 RA15 28.4 Crystal 75 31.6 31.6 31.6 31.6 Deionised 40 40 40 40 water Size (pm) 1.1 2.1 4 2.7 Dyestain 0.57 0.39 0.33 0.37 It will be noted that, as the size of the particulates increases, the level of dyestain reduces.

I D. Assessment of Factors Affecting Settling of Formulations when Prepared as Described in Example 1 (a) Increasing the ratio of particulates to silicate Materials/g Example 56 Example 57 Example 58 CR1 0.29 0.26 0.23 CR6 0.86 0.79 0.69 CR15 1.71 1.58 1.38 Microgrit C3 14.25 13.14 11.5 Hombitan LW 11.39 10.51 9.21 46 SID623 31.8 37.91 46.95 Deionised 39.7 35.98 30.04 water Particulates: 3.2:1 2.475:1 1.75:1 Silicate Settling 14.5 21.6 3 5 It will be noted that, as the ratio of the weight of particulates to the weight of silicate reduces, the tendency of the formulation to settle reduces.

(b) Reducing the alumina content Materials/g Example 59 Example 60 Ti-Pure R900 19.69 22.67 Hombitan LW 6.68 6.68 Microgrit C3 5.64 2.67 Crystal 75 35.85 35.85 Deionised water 31.93 31.93 Surfaron A6008 0.2 0.2 Settling 27 18 It will be noted that, as the weight of alumina in the formulation decreases, the tendency to settle decreases.

(c) Addition of viscosity modifiers Materials/g Example 61 Example 62 Example 63 Example 64 Ti-Pure 24.5 24.5 24.5 24.5 R900 Microgrit 4 4 4 4 C3 Crystal 75 31.8 31.8 31.8 31.8 Ateagel 50 1 Alumina C 1 Aerosil 200 0.5 47 Deionised 39.7 38.7 38.7 39.2 water Surfaron 0.2 0.2 0.2 0.2 A6008 Settling 24 4 6 8 It will be noted that addition of viscosity modifiers can be used to reduce the tendency of the formulations to settle.

(d) Reducing the particle size of the particulate material Materials/g Example 65 Example 66 Example 67 Ti-Pure R900 13.75 13.75 13.75 Hombitan LW 13.75 13.75 13.75 Microgrit C3 4.51 Baco MA2LS 4.51 Baikalox CR6 4.51 Crystal 75 35.85 35.85 35.85 Deionised 31.93 31-93 31.93 water Surfaron A6008 0.2 0.2 0.2 Particle 3 8 0.6 Size/pm Settling 18 22 14 It will be noted that, as the particle size is reduced, the tendency of the formulations to settle reduces.

48 (e) Increasing the total solids concentration of the formulation Materials/g Example 68 Example 69 Example 70 Ti-Pure R900 24.4 27.5 30.57 Microgrit C3 4 4.51 5.01 Crystal 75 31.8 35.85 39.83 - Deionised 39.6 31.93 24.38 water Surfaron A6008 0.2 0.2 0.2 Total wt% of 40 45 50 solids Settling 34 26 1 It will be noted that, as the total solids concentration increases, the tendency of the formulation to settle reduces.

While the invention has been described in terms of the foregoing specific embodiments, it will be apparent to those skilled in the art that various alterations and modifications may be made to the described embodiments without departing from the scope of the invention, which is limited only by the appended claims. The disclosed embodiments are provided merely by way of example.

49

Claims (17)

1. Use of one of the following for preparing a printing member having a reduced susceptibility to piling:

a) a fluid wherein the ratio of the wt% of particulate material to the wt% of binder material is ess than 3 in the preparation of a hydrophilic layer of the printing member; b) a fluid comprising particulate material which includes less than 50wt% of particulate alumina in the preparation of a hydrophilic layer of the printing member, wherein said hydrophilic layer comprises particulate material and a binder material for binding the particulate material in position; C) a fluid comprising particulate material which includes greater than 50wt% of material of a particle size of less than 3pm in the preparation of a hydrophilic layer of the printing member, wherein said hydrophilic layer comprises particulate material and a binder material for binding the particulate material in position.

2. A use according to claim 1, wherein said ratio is 1. 3 or less.

3. A use according to claim 1 or claim 2, wherein said particulate material includes at least lOwt% alumina.

4. A use according to any preceding claim, wherein a silicate is provided in solution in said fluid for providing said binder material.

5. A use according to any preceding claim, wherein said fluid includes an alkali metal silicate wherein the ratio of number of moles Of Si02 to the number of moles M20 in said silicate, wherein M represents an alkali metal, is at least 2.5 and less than 6.

6. A use according to any preceding claim, wherein said fluid includes at least 5wt% of binder material and at least 5wt% of particulate material.

7. A method of preparing a substrate for a planographic printing member having a reduced susceptibility to piling, the method including one of the following steps:

a) forming a hydrophilic layer on a support by contacting the support with a fluid comprising a particulate material and a binder material for binding the particulate material in position on the support, wherein the ratio of the wt% of particulate material to the wt% of binder material is less than 3; b) forming a hydrophilic layer on a support by contacting the support with a fluid comprising a particulate material and a binder material for binding the particulate material in position on the support, wherein said particulate material comprises less than SOwt% of particulate alumina; c) forming a hydrophilic layer on a support by contacting the support with a fluid comprising a particulate material and a binder material for binding the particulate material in position on the support, wherein said particulate material includes greater than 50wt% of material of a particle size of less than 3pm.

8. A method of preparing an improved printing member of a type comprising a substrate which includes a hydrophilic layer comprising a binder and particulate material, wherein said improved printing member has a reduced susceptibility to piling compared to a comparison printing member which is identical to said improved printing member except that said improved printing member includes at least one of the following differences:

a) a reduction in the ratio of the wt% of the particulate material to the wt% of binder material; b) a reduction in the amount of alumina in said hydrophilic layer; c) a reduction in the mean particle size of the particulate material in said hydrophilic layer; the method comprising preparing said improved printing member with at least one of the aforementioned differences compared to said comparison printing member.

9. Use of one of the following in the preparation of a planographic printing member for reducing the susceptibility of the printing member to ink spots:

a) a fluid comprising a dissolved alkali metal silicate, wherein the ratio of the number of moles of Si02 to the number of moles Of M20 in the fluid is greater than 3.5 in 52 the preparation of a hydrophilic layer of the printing member; b) a fluid comprising a binder material and particulate material in the preparation of a hydrophilic layer of a planographic printing member, wherein the particulate material includes a material which is more spheri"Cal compared to a particulate material which comprises hexagonal platelets; C) an ink spot reduction layer above or below a hydrophilic layer of a planographic printing member, wherein the hydrophilic layer comprises particulate material and a binder material for binding the particulate material in position; d) a fluid comprising a particulate material and a binder material in the preparation of a hydrophilic layer of a planographic printing member, wherein the binder material includes some dissolved lithium silicate.

10. A use according to claim 9, wherein said ink spot reduction layer is formed using a fluid which includes the same material as that used as said binder in said hydrophilic layer.

11. A method of preparing a substrate for a planographic printing member having a reduced susceptibility. to ink spots, the method including one of the following:

a) forming a hydrophilic layer on a support by contacting the support with a fluid comprising a particulate material and a binder material for binding the particulate material 53 in position on the support, wherein the binder material comprises dissolved alkali metal silicate, wherein the ratio of the number of moles Of Si02 to the number of moles M20 in the fluid, wherein M represents an alkali metal, is greater than 3.5; b) forming a hydrophilic layer on a support by contacting the support with a fluid comprising a particulate material and a binder material for binding the particulate material in position on the support, wherein the particulate material comprises a material which is more spherical compared to a particulate material comprising hexagonal platelets; C) forming a hydrophilic layer over a support using a fluid comprising a particulate material and a binder material for binding the particulate material in position, wherein an ink spot reduction layer is provided below or above the hydrophilic layer; d) forming a hydrophilic layer on a support by contacting the support with a fluid comprising a particulate material and a binder material for binding the particulate material in position on the support, wherein the binder material includes at least some dissolved lithium silicate.

12. A method of preparing an improved printing member of a type comprising a substrate which includes a hydrophilic layer comprising a binder and particulate material, wherein said improved printing member has a reduced susceptibility to ink spots compared to a comparison printing member which is identical to said improved 54 printing member except that said improved printing member includes at least one of the following differences:

a) the binder material is derived from an alkali metal silicate wherein the ratio of the number of moles of Si02 to the number of moles Of M20 is greater; b) the particulate material is more spherical; c) an ink spot reduction layer below or above the hydrophilic layer; d) said binder material includes more lithium silicate; the method comprising preparing said improved printing member with a least one of the aforementioned differences compared to said comparison printing member.

13. Use of one of the following in the preparation of a hydrophilic layer of a planographic printing member for reducing the susceptibility of the printing member to dyestain:

a) a fluid wherein the ratio of the wt% of particulate material to the wt% of binder material is less than 3; b) a fluid which includes an alkali metal silicate having a ratio of the number of moles Of Si02 to the number of moles Of M20, where M is an alkali metal, of less than 3.

14. A method of preparing an improved printing member of a type comprising a substrate which includes a hydrophilic layer comprising a binder and particulate material, wherein said improved printing member has a reduced susceptibility to dyestain compared to a comparison printing member which is identical to said improved printing member except that it includes particulate material of a smaller size than that of said improved printing member, the method comprising preparing said improved printing member by contacting a support witTi a fluid comprising a particulate material and a binder material for binding the particulate material in position on the support, wherein the particulate material has a greater size than that used for said comparison printing member.

15. A method of preparing an improved printing member of a type comprising a substrate which includes a hydrophilic layer comprising a binder material and particulate material which includes alumina, wherein said improved printing member has a reduced susceptibility to dyestain compared to a comparison printing member which is identical to said improved printing member except that said comparison printing member includes a reduced level of alumina, the method comprising preparing said improved printing member by contacting a support with a fluid comprising a particulate material and a binder material for binding the particulate material in position on the support, wherein the particulate material includes alumina at an increased level compared to that used in the preparation of said comparison printing member.

16. A method of preparing an improved printing member of a type comprising a substrate which includes a hydrophilic layer comprising a binder material and particulate 56 material, wherein said improved printing member has a reduced susceptibility to dyestain compared to a comparison printing member which is identical to said improved printing member except that said improved member includes particulate material selected so that, when incorporated in said hydrophilic layer, said layer has a reduced susceptibility to dyestain, the method comprising preparing said improved printing member by contacting a support with a fluid comprising a particulate material and a binder material for binding the particulate material in position on support, wherein the particulate material includes said selected particulate material.

17. A method of preparing an improved printing member of a type comprising a substrate which includes a hydrophilic layer comprising a binder and particulate material, wherein said improved printing member has a reduced susceptibility to dyestain compared to a comparison printing member which is identical to said improved printing member except that said improved member includes a surfactant selected to reduce the susceptibility of the hydrophilic layer to dyestain, the method comprising the step of contacting a support with a fluid comprising a particulate material and a binder material for binding the particulate material in position on the support, wherein the fluid also includes a surfactant selected to reduce the susceptibility of the hydrophilic layer to dyestain compared to that of said comparison printing member.