WO2018094715A1

WO2018094715A1 - Treatment methods for printing plates

Info

Publication number: WO2018094715A1
Application number: PCT/CN2016/107414
Authority: WO
Inventors: Peter Andrew Reath Bennett
Original assignee: Shenzhen Zhongchuang Green Plate Technology Ltd.
Priority date: 2016-11-28
Filing date: 2016-11-28
Publication date: 2018-05-31
Also published as: EP3544821A4; EP3544821A1; CN110121427A

Abstract

A method of treating an aluminium printing form precursor for use in lithographic printing. The treatment conditions comprise a relative humidity of at least 30 ％, a temperature in the range 60 to 120 ℃, a pressure of from 0.9 to 10 atmospheres and a treatment time in these conditions of at least 10 minutes. The method may be used for preparing an aluminium printing form precursor for imaging and subsequent printing. The method may provide a beneficial decrease in hydrophilicity and a beneficial increase in oleophilicity of the aluminium printing form precursor. An improved aluminium printing form precursor is also described.

Description

Treatment Methods for Printing Plates

Field

The present invention relates to improvements in printing, specifically to methods for treating printing plates for lithographic printing. The present invention also relates to methods of printing and to printing plates treated by the method.

Background

Fundamentally, all lithographic printing processes take a printing form precursor having a specially prepared surface which is uniform throughout and modifies selected regions of it, leaving reciprocal regions unmodified.

In many such processes the printing form precursor comprises a photosensitive coating, selected regions of which are modified and then subjected to a chemical developer. The chemical developer acts upon either the modified or unmodified regions to produce the differentiation needed for printing, for example a differentiation in the acceptance of an oleophilic ink component of a ink/water fountain solution. Optionally the developed surface is treated to harden the remaining areas of the coating, for example by baking, prior to printing.

It should be noted that in this specification we use the term ‘printing form precursor’ to denote the initial article having a surface undifferentiated in its acceptance or rejection of ink； and ‘printing form’ to denote the subsequently produced article having a differentiated surface which can be printed from. The term printing form herein may be substituted by the term ‘printing plate’ . The term printing form is preferred in describing and defining the invention because it is of broad connotation. The term printing plate or just plate may nevertheless be used herein for ease of reading. Furthermore the terms ‘printing form precursor’ or ‘printing form’ mean to refer to a surface or surfaces of the ‘printing form precursor’ or ‘printing form’ which are intended to be imaged and used for printing. Both surfaces of a sheet-like ‘printing form precursor’ or ‘printing form’ may not necessarily be suitable for and/or intended to be imaged and used for printing and therefore the methods (and all steps thereof) of the present invention are carried out on the surface or surfaces which are suitable for and/or intended to be imaged and used for printing.

The present inventors have previously shown that a printing form precursor can be prepared for printing by applying energy in the form of pulses of electromagnetic radiation having a pulse length of not greater than 1 x 10^-6 seconds, in an imagewise manner, to an imageable surface of the printing form precursor which may avoid the use of chemical coatings and developers. This is described in WO 2010/029341 which is incorporated herein by reference, Aluminium printing form precursors can be prepared for such imaging steps by anodising and/or roughening (also known as graining) using methods well known in the art.

The present invention relates to alternative and/or improved methods for preparing aluminium printing form precursors for subsequent imaging.

Summary of the Invention

The hydrophilicity and hydrophobicity of a printing form precursor are important parameters in determining the quality and performance of a printing form produced from said printing form precursor.

Contact angle measurement is the usual method of determining hydrophilicity and hydrophobicity, i.e., wetting behaviour, of a printing form precursor. Such measurements involve probing the target surface of the printing form precursor with small drops of water. The angle subtended by the tangent of the surface of the drop where it meets the target surface is the water contact angle (WCA) in air. Typically a hydrophobic material has a WCA of > 90° and a hydrophilic material has a WCA of < 90°.

However, there are no reliable and useful methods for measuring the oleophilicity of a surface by measuring an “oil contact angle” (OCA) .

Therefore one aim of the present invention may be to provide a useful measurement method for oil contact angle for use in improving aluminium printing form precursor preparation.

The inventors have found that the ink-accepting part of a lithographic plate would benefit from a high WCA and a low OCA whilst the water-accepting regions would benefit from a low WCA and a high OCA.

The inventors note that commercial printing form precursors having developable coatings surprisingly have coatings that have both WCA and OCA between 80 and 100°. Therefore these commercial printing form precursors would be considered amphiphilic materials, rather than only hydrophilic or oleophilic.

This compromise of WCA and OCA values may be related to the difficulty in finding developable coatings (for example polymers) which give high WCA and low OCA and which are compatible with other functional materials in the formulation (dyes, photosensitive materials) and with suitable solvents for use in developing the coating.

The process described in WO 2010/029341 provides a printing form precursor surface that requires no processing, no coating and no solvent. The inventors have found that this can be exploited by the present invention to break the previously accepted constraints on printing form precursor surface WCA and OCA and therefore to maximize WCA and minimize OCA for the ink-accepting regions of printing forms/printing form precursors.

It is one aim of the present invention, amongst others, to provide a method of treating an aluminium printing form precursor that addresses at least one disadvantage of the prior art, whether identified here or elsewhere, or to provide an alternative to existing methods. For instance it may be an aim of the present invention to provide a method of treating an aluminium printing form precursor which increases the water contact angle and/or decreases the oil contact angle of the aluminium printing form precursor. Such a method may then lead to an improved printing form precursor and/or printing form and to an improved subsequent imaging and printing process.

According to aspects of the present invention, there is provided methods and products as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

According to a first aspect of the present invention, there is provided a method of treating an aluminium printing form precursor, the method comprising the step of:

subjecting the aluminium printing form precursor to an environment of at least 30 ％relative humidity at a temperature in the range 60 to 120 ℃.

Suitably the step of subjecting the aluminium printing form precursor to said conditions is carried out at a pressure of from 0.9 to 10 atmospheres.

Suitably the step of subjecting the aluminium printing form precursor to said conditions is carried out for at least 10 minutes.

Suitably the method of this first aspect comprises the step of:

subjecting the aluminium printing form precursor to an environment of at least 30 ％relative humidity at a temperature in the range 60 to 120 ℃, a pressure of from 0.9 to 10 atmospheres and for at least 10 minutes.

The inventor’s have found that treating an aluminium printing form precursor according to the method of this first aspect may provide a beneficial decrease in hydrophilicity and a beneficial increase in oleophilicity. For example the method of this first aspect may increase the water contact angle and decrease the oil contact angle of the aluminium printing form precursor.

The inventors have found that heat alone has little effect on such aluminium printing form precursors, for example anodised aluminium printing form precursors. We are, therefore, surprised to find that, by applying heat in conjunction with a water-wet environment, aluminium printing form precursors can be provided with relatively high WCAs and relatively low OCAs.

The method according to this first aspect therefore may provide an aluminium printing form precursor which, after a subsequent imaging step, has improved printing properties compared to a similar aluminium printing form precursor which has not been treated according to the method of this first aspect. This improvement is due to the increase in water-repellency (decrease in hydrophilicity) and the increase in ink-acceptance (increase in oleophilicity) of the areas of the aluminium printing form precursor which have not been subsequently imaged (for example in an imaging process which decreases the water-repellency (increases the hydrophilicity) and decreases the ink-acceptance (decreases the oleophilicity) of the imaged regions) .

Suitably the method of this first aspect provides the aluminium printing form precursor with a hydrophobic surface.

Suitably the method of this first aspect provides the aluminium printing form precursor with an oleophilic surface.

Suitably the method of this first aspect provides the aluminium printing form precursor with a hydrophobic and oleophilic surface.

It is believed that heating the aluminium printing form precursor in an atmosphere having a minimum relative humidity and for sufficient time provides these advantageous properties to the aluminium printing form precursor.

Temperature

The method of this first aspect involves a step of subjecting the aluminium printing form precursor to an environment of at least 30 ％relative humidity at a temperature in the range 60 to 120 ℃.

Suitably the step is carried out at a temperature in the range 70 to 120 ℃, suitably 60 to 110 ℃, suitably 70 to 110 ℃, suitably 80 to 110 ℃, suitably 70 to 100 ℃, suitably 80 to 100 ℃.

Time

The method of this first aspect involves a step of subjecting the aluminium printing form precursor to an environment of at least 30 ％relative humidity at a temperature in the range 60 to 120 ℃, suitably for at least 10 minutes.

Suitably the step is carried out for at least 30 minutes, suitably at least 1 hour, suitably at least 2 hours.

Suitably the step is carried out for up to 72 hours, suitably up to 48 hours, suitably up to 24 hours, suitably up to 12 hours.

The time required to produce a suitable increase in the water contact angle and a decrease in the oil contact angle of the aluminium printing form precursor may vary according to the temperature, relative humidity and pressure of the step and also according to the nature of the surface of the aluminium printing form precursor. With knowledge of the present invention and the experimental details provided herein, the skilled person would be able to determine the time required to provide a beneficial increase in the water contact angle and a decrease in the oil contact angle of the aluminium printing form precursor.

In some embodiments, the method of this first aspect comprises the step of subjecting the aluminium printing form precursor to an environment of at least 30 ％relative humidity at a temperature in the range 60 to 120 ℃ for less than 10 minutes, suitably less than 5 minutes, suitably less than 2 minutes. In such embodiments the step of subjecting the aluminium printing form precursor to an environment of at least 30 ％relative humidity at a temperature in the range 60 to 120 ℃ may be carried out for at least 30 seconds, suitably at least 1 minute. In such embodiments the method of this first aspect may be carried out “in-line” as part of a production line process for preparing printing forms and/or printing form precursor.

Relative humidity

Suitably the step involves subjecting the aluminium printing form precursor to an environment of at least 40 ％relative humidity, suitably at least 50 ％, suitably at least 60 ％, suitably at least 70 ％, suitably at least 80 ％, suitably at least 90 ％relative humidity.

The relative humidity required to produce a beneficial increase in the water contact angle and a decrease in the oil contact angle of the aluminium printing form precursor may vary according to the temperature, time and pressure of the step and also according to the nature of the surface of the aluminium printing form precursor. With knowledge of the present invention and the experimental details provided herein, the skilled person would be able to determine the relative humidity required to provide a beneficial increase in the water contact angle and a decrease in the oil contact angle of the aluminium printing form precursor. For example, using a higher relative humidity may decrease the required time for the step.

Pressure

Suitably the step of subjecting the aluminium printing form precursor to said conditions is carried out at a pressure of from 0.9 to 10 atmospheres. The step may be carried out at ambient pressure. The step may be carried out at high pressure. Suitably the step is carried out at a pressure of from 0.9 to 5 atmospheres.

High pressure method

In some embodiments, the step of the method of this first aspect is carried out at a pressure of at least 1.5 atmospheres.

Suitably the step of the method of this first aspect involves subjecting the aluminium printing form precursor to an environment of at least 30 ％relative humidity at a temperature in the range 60 to 120 ℃, a pressure of at least 1.5 atmospheres and suitably for at least 10 minutes.

Suitably the step is carried out temperature is in the range 70 to 120 ℃, suitably 80 to 120 ℃, suitably 90 to 120 ℃, suitably 100 to 120 ℃, suitably 90 to 110 ℃, suitably 100 to 110 ℃.

Suitably the step is carried out for up to 24 hours, suitably up to 12 hours, suitably up to 6 hours, suitably up to 3 hours, suitably up to 2 hours, suitably up to 1 hour, suitably up to 30 minutes.

Suitably the step is carried out a pressure of up to 10 atmospheres, suitably up to 8 atmospheres, suitably up to 6 atmospheres, suitably up to 5 atmospheres, suitably up to 4 atmospheres, suitably up to 3 atmospheres.

The inventors have found that carrying out the step of the method of this first aspect at a pressure of at least 1.5 atmospheres decreases the time required to produce a beneficial increase in the water contact angle and a decrease in the oil contact angle of the aluminium printing form precursor, compared to a method carried out a pressure below 1.5 atmospheres.

Ambient pressure method

In some embodiments, the step of the method of this first aspect is carried out at a temperature in the range 60 to 100 ℃, at a pressure of below 1.5 atmospheres and for at least 2 hours.

Suitably the step of the method of this first aspect involves subjecting the aluminium printing form precursor to an environment of at least 30 ％relative humidity at a temperature in the range 60 to 100 ℃, at a pressure of below 1.5 atmospheres and for at least 2 hours.

Suitably the step is carried out at a temperature in the range 70 to 100 ℃, suitably 60 to 90 ℃, suitably 70 to 90 ℃.

Suitably the step is carried out at a pressure of up to 1.2 atmospheres, suitably up to 1.1 atmospheres. Suitably the step is carried out at ambient pressure.

pH

Suitably the step of the method of this first aspect is carried out at a pH in the range 6 to 8.

Suitably the step of the method of this first aspect involves subjecting the aluminium printing form precursor to an environment of at least 30 ％relative humidity, having a pH in the range 6 to 8, at a temperature in the range 60 to 120 ℃, suitably for at least 10 minutes.

Suitably the pH is approximately neutral, for example about 7.

In some embodiments the step of the method of this first aspect is carried out at a pH of less than 6, suitably less than 5, suitably less than 4, suitably less than 3. The inventors have found that using such an acidic pH may decrease the time required to produce the beneficial increase in the water contact angle and a decrease in the oil contact angle of the aluminium printing form precursor.

Oil and water contact angles

Suitably the method of this first aspect provides a beneficial decrease in hydrophilicity and a beneficial increase in oleophilicity of the aluminium printing form precursor. Such a decrease in hydrophilicity may be measured by an increase the in the water contact angle of the aluminium printing form precursor. Such an increase in oleophilicity may be measured by a decrease in the oil contact angle of the aluminium printing form precursor.

Suitably the method provides an increase the in water contact angle of the aluminium printing form precursor of at least 50°, suitably at least 60°, suitably at least 70°.

Suitably the method provides an aluminium printing form precursor comprising a substantially uniform surface having a water contact angle of between 70 and 175°, suitably between 80 and 175°, suitably between 90 and 175°, suitably between 100 and 175°.

Suitably the method provides a decrease in the oil contact angle of the aluminium printing form precursor of at least 10°, suitably at least 15°, suitably at least 20°, suitably at least 25°, suitably at least 30°.

Suitably the method provides an aluminium printing form precursor comprising a substantially uniform surface having an oil contact angle of between 0 and 120°, suitably between 0 and 110°, suitably between 0 and 100°, suitably between 0 and 90°.

For example, the method may provide an aluminium printing form precursor comprising a substantially uniform surface having a water contact angle of between 70 and 175° and an oil contact angle of between 0 and 120°.

The above oil and water contact angles may be measured by techniques known in the art. However, although measuring water contact angles is well known, the measurement of oil contact angles is more difficult due to oils having little cohesive force and a tendency to flow under the force of gravity whether they “wet” the target surface or not (i.e. whether the target surface is oleophilic or oleophobic) . Known hysteresis methods often refer to the time taken for an oil droplet to be perfectly wetting after application but this says nothing about the stability of the surface over time.

The inventors have developed a method to determine the oil contact angle (OCA) as a measure of oleophilicity (OCA < 90°) or oleophobicity (OCA > 90°) . The method involves using di-iodomethane as the oil probe whilst the target surface is itself submerged in distilled water. The advantage of using di-iodomethane is that it has similar Hansen Solubility Parameters to linseed oil, a common constituent of printing inks, whilst having a density > 1. The method has two advantages； it reduces the gravitational effect and hence flow and since the surface is wet with water first, it indicates how easily the water is displaced by the “oil” (in other words, how spontaneous the wet surface wets with the “oil” ) . This is clearly relevant to lithographic printing as, in application, a printing form surface is first wetted with water and then ink is applied to the water wet printing form.

Suitably the oil contact angles referred to herein are measured according to the di-iodomethane method described above and as described in more detail in the experimental section.

Aluminium printing form precursors

By aluminium printing form precursor we mean an aluminium substrate suitable for use in a lithographic printing method, for example after a subsequent imaging step.

Suitably the aluminium printing form precursor treated in the method of this first aspect is uncoated by a developable image layer. Suitably the aluminium printing form precursor is uncoated by a developable image layer and comprises a substantially uniform hydrophilic surface, before the method is carried out. Suitably such a surface is intended for use in subsequent imaging and printing steps.

By “uncoated by a developable image layer” we mean that it does not carry a layer which is developable imagewise, in a developer liquid. Such a layer typically comprises an organic material, such as a film-forming polymer. It may be said that the aluminium printing form precursor has no potential for providing energy-induced solubility differential in a developer liquid.

Suitably the anodised aluminium surface, before the method of this first aspect is carried out, has a water contact angle of up to 100°, suitably up to 75°, suitably up to 50°.

Suitably the anodised aluminium surface, before the method of this first aspect is carried out, has an oil contact angle of at least 80°, suitably at least 100℃, suitably at least 120°.

Anodised aluminium printing form precursors

The aluminium printing form precursor on which the method of this first aspect is carried out may have an anodised aluminium surface suitable for use in printing.

Suitably the aluminium printing form precursor is an anodised aluminium printing form precursor. Suitable anodised aluminium printing form precursors are known in the art.

Suitably the anodised aluminium surface has a thickness in the range 0.20 μm to 10 μm.

Suitably the anodised aluminium surface has a thickness in the range 0.20 μm to 5 μm, suitably in the range 0.20 μm to 3 μm, suitably in the range 0.50 μm to 2 μm.

Suitably the anodised aluminium surface is uncoated by a developable image layer. Suitably the anodised aluminium surface comprises a substantially uniform hydrophilic surface, before the method is carried out. Suitably the anodised aluminium surface is uncoated by a developable image layer and comprises a substantially uniform hydrophilic surface, before the method is carried out. Suitably such a surface is intended for use in subsequent imaging and printing steps.

In embodiments wherein the step of the method of this first aspect is carried out at a pressure of at least 1.5 atmospheres and wherein the aluminium printing form precursor is an anodised aluminium printing form precursor, suitably the step is carried out for less than 5 minutes per μm thickness of anodised aluminium surface, suitably for less than 2 minutes per μm thickness, suitably for less than 1 minutes per μm thickness.

In embodiments wherein, the step of the method of this first aspect is carried out at a temperature in the range 60 to 100 ℃, at a pressure of below 1.5 atmospheres and for at least 2 hours, and wherein the aluminium printing form precursor is an anodised aluminium printing form precursor, suitably the step is carried out for at least 5 minutes per μm thickness of anodised aluminium surface, suitably at least 10 minutes per μm thickness, suitably at least 15 minutes per μm thickness.

In such embodiments, suitably the suitably the step is carried out for less than 1 hour per μm thickness of anodised aluminium surface, suitably for less than 30 minutes per μm thickness, suitably for less than 20 minutes per μm thickness.

In some embodiments, the anodised aluminium surface is non-roughened.

In some embodiments, the anodised aluminium surface is roughened.

Roughened aluminium printing form precursors

The surface of the printing form precursor used in the above methods may advantageously be roughened ( “roughened” may be alternatively referred to as “grained” ) prior to carrying out the imaging method, to develop the topography of the printing surface and to render the surface more suitable for imaging and/or printing.

Known methods of roughening the surface of a printing form precursor include chemical treatment with a solution, such as mineral acid； electrochemical roughening using a hydrochloric acid electrolyte； and mechanical roughening using a slurry brush, for example.

Laser roughened aluminium printing form precursors

Suitably the aluminium printing form precursor on which the method of this first aspect is carried out has been roughened by a laser.

The aluminium printing form precursor on which the method of this first aspect is carried out may have a laser roughened surface suitable for use in printing.

Suitably the aluminium printing form precursor is a laser roughened aluminium printing form precursor. Suitable laser roughened aluminium printing form precursors are disclosed in PCT/GB2016/051530 which is incorporated herein by reference.

By roughened we mean provided with a plurality of surface details on the printing form precursor which alters the water contact angle of the surface. Roughness can be characterised by average roughness or fineness (Ra, typically measured in μm) , mean maximum roughness depth (Rz, typically measured in μm) and surface area (typically measured in mm²) .

Suitably the laser roughened surface has been produced by exposing the printing form precursor to energy in the form of pulses of electromagnetic radiation having a pulse length of from 1 x 10^-15 s to 1 x 10^-6 s to produce a uniformly hydrophilic roughened surface.

The pulses of electromagnetic radiation used for roughening

Suitable laser roughening methods are described in PCT/GB2016/051530 which is incorporated herein by reference.

Suitably the pulses of electromagnetic radiation used to provide the laser roughened surface have a pulse length of at least 1 x 10^-15 s, suitably at least 1 x 10^-14 s, for example at least 1 x 10^-13 s, suitably at least 1 x 10^-12 s, at least 1 x 10^-11 s, at least 1 x 10^-10 s or at least 1 x 10^- ⁹ s, suitably at least 1 x 10^-8 s.

Suitably the pulses of electromagnetic radiation have a pulse length of up to 1 x 10^-6 s, suitably up to 5 x 10^-7 s, for example up to 2.5 x 10^-7 s.

Suitably the pulses of electromagnetic radiation have a pulse length of from 1 x 10^-15 s to 1 x 10^-6 s, suitably from 1 x 10^-12 s to 1 x 10^-6 s, for example from 1 x 10^-10 s to 1 x 10^-6 s, suitably from 1 x 10^-9 s to 1 x 10^-6 s or from 1 x 10^-8 s to 5 x 10^-7 s.

Thus, suitably the method employs, to provide the energy in the form of pulse of electromagnetic energy, nanosecond, picosecond or femtosecond lasers. Such lasers provide pulses of high intensity； they are not adapted or gated CW lasers. Suitably the method employs, as the imaging device, a nanosecond and/or a picosecond laser fitted with a device, such as a Q-switch, to release intense pulses of laser energy “stored” during dwell times (in which the laser was still pumped but not releasing the photon energy produced) .

One type of laser suitable for use in the laser roughening is a femtosecond laser, for example a laser capable of emitting pulses of pulse length in the range 30-1,000 femtoseconds (fs) , suitably 50-400 fs, for example 100-250 fs.

Another type of laser preferred for use in the laser roughening is a picosecond laser, for example a laser capable of emitting pulses of pulse length in the range 1-200 picoseconds (ps) , for example 5-100 ps. Suitably the picosecond laser is capable of emitting pulses having a pulse length of 80 ps.

Another type of laser preferred for use in the laser roughening is a nanosecond laser, for example a laser capable of emitting pulses of pulse length in the range 0.1-500 nanoseconds (ns) , for example 1-200 ns. Suitably the nanosecond laser is capable of emitting pulses having a pulse length of 100 ns.

Suitably the pulses of electromagnetic radiation have a pulse energy of at least 0.001 mJ, suitably at least 0.005 mJ, for example at least 0.0075 mJ, suitably at least 0.010 mJ.

Suitably the pulses of electromagnetic radiation have a pulse energy of up to 500 mJ, suitably up to 100 mJ, for example up to 50 mJ, suitably up to 10 mJ.

Suitably the pulses of electromagnetic radiation have a pulse energy of up to 2.0 mJ, suitably up to 1.5 mJ, for example up to 1.0 mJ, suitably up to 0.75 mJ.

Suitably the pulses of electromagnetic radiation have a pulse energy of from 0.001 mJ to 500 mJ, for example from 0.001 mJ to 100 mJ.

Suitably the pulses of electromagnetic radiation have a pulse energy of from 0.001 mJ to 2.0 mJ, suitably from 0.005 mJ to 1.5 mJ, for example from 0.0075 mJ to 1.0 mJ, suitably from 0.0075 mJ to 0.75 mJ.

Suitably the pulses of electromagnetic radiation have a pulse length in the range of 1 x 10^-11 s to 1 x 10^-6 s and a pulse energy in the range of 0.05 mJ to 2.0 mJ, suitably a pulse length in the range of 1 x 10^-9 s to 1 x 10^-6 s and a pulse energy in the range of 0.05 mJ to 1.0 mJ.

Suitably the pulses of electromagnetic radiation have a pulse length in the range of 1 x 10^-11 s to 1 x 10^-8 s and a pulse energy in the range of 0.001 mJ to 0.5 mJ, suitably a pulse length in the range of 1 x 10^-10 s to 5 x 10^-9 s and a pulse energy in the range of 0.005 mJ to 0.2 mJ.

Suitably the pulses of electromagnetic radiation have a pulse length in the range of 1 x 10^-15 s to 1 x 10^-12 s and a pulse energy in the range of 0.001 mJ to 0.1 mJ, suitably a pulse length in the range of 1 x 10^-14 s to 5 x 10^-13 s and a pulse energy in the range of 0.001 mJ to 0.01 mJ.

This invention uses pulsed radiation. Regarding energy density, the simplest analysis is when each pulse of electromagnetic radiation exposes a unique and previously unexposed spot on the surface. Furthermore if the beam is stationary at the arrival and throughout the duration of the pulse, then the energy density can be simply calculated. The beam power during the pulse can be estimated as the pulse energy, E (J) , divided by the pulse length (s) . The Power density is defined as this power divided by the spot area. However the exposure time is now solely the length of the pulse (s) and so the energy density becomes simply the pulse energy divided by the spot area, E/D². This energy density is commonly referred to as “fluence” in the literature.

Normally it is not desirable to stop the beam movement to deliver pulses as this introduces delays and does not optimise the throughput of the process. Thus the beam traverses the surface during the extent of the pulse, as discussed below in relation to overlap. This can be regarded as elongating the spot in the direction of beam travel by an extent given by multiplying the traverse speed v by the pulse length τ, with the spot area now being defined as D(D+ τv) . The formula for fluence, F, becomes:

F ＝ E/ (D (D+ τv) ＝ E/D² (1+ τv/D)

If τv/D<<1 then the effect of traverse speed can be ignored. For a spot size of 20 μm travelling at 1 ms^-1 and a pulse length of 10 pS then τv/D ＝ 5 x 10^-7 so the effect of travel speed on the fluence can be safely ignored.

Another factor is related to pulse overlap. In embodiments wherein the laser roughening is carried out by scanning across the surface of a printing form precursor a single laser beam set to produce the energy in the form of pulses of electromagnetic radiation, the pulses may overlap. If the speed (v) is sufficiently high for a given frequency then the individual pulses do not overlap on the surface of the material. In such a case, it is simple to show that fD/v<1, where f is the repetition frequency of the pulsed electromagnetic source. When the traverse speed is such that the pulses are not spatially separated then the effect of overlapping pulses on the material surface may have to be considered. It is common in the literature of short pulsed laser processing to refer to the effect of overlapping pulses as “incubation” and to measure the degree of incubation by estimating the number of overlapping pulses, N, as N ＝ fD/v. N is sometimes referred to as the incubation number or incubation factor and does not need to be an integer. If N < 1 there is no overlap of pulses. When N ＝ 1 the exposure spots of successive pulses are touching, and as N increases there is increasing overlap of spots. For low values of N, say N < 5, there may be little influence on incubation. However at high values of N a process may be regarded as a “quasi CW” process, and the energy density may be better expressed in terms of “Specific Energy” .

Suitably the pulses of electromagnetic radiation have a fluence of up to 200 J/cm², suitably up to 100 J/cm², for example up to 75 J/cm².

Suitably the pulses of electromagnetic radiation have a fluence of at least 0.1 J/cm², suitably at least 0.2 J/cm², for example at least 0.5 J/cm².

Suitably the pulses of electromagnetic radiation have a fluence in the range of from 0.1 J/cm² to 200 J/cm², suitably in the range of from 0.1 J/cm² to 100 J/cm², for example in the range of from 0.2 J/cm² to 75 J/cm².

By fluence we mean the fluence of each individual pulses of electromagnetic radiation, considered separately, not the fluence produced by a plurality of such pulses.

Suitably the pulses of electromagnetic radiation have a frequency of up to 20,000 kHz, suitably up to 2,000 kHz, for example up to 1,000 kHz.

Suitably the pulses of electromagnetic radiation have a frequency of at least 1 kHz, suitably at least 10 kHz, for example at least 50 kHz.

Suitably the pulses of electromagnetic radiation have a frequency in the range of from 1 kHz to 20,000 kHz, suitably in the range of from 10 kHz to 1,000 kHz, for example in the range of from 50 kHz to 1,000 kHz.

The pulses of electromagnetic radiation used to provide the laser roughened surface may generate a spot or pixel of any shape, for example circular, oval and rectangular, including square. Rectangular is preferred, as being able to provide full imaging of desired regions, without overlapping and/or missed regions.

Suitably the pulses of electromagnetic radiation are applied to an area of less than 0.2 cm² (e.g. a 5 mm diameter circle) , suitably less than 7.8 x 10^-3 cm² (e.g. an 1 mm diameter circle) , for example less than 7.8 x 10^-5 cm² (e.g. a 0.1 mm diameter circle) .

Suitably the pulses of electromagnetic radiation are applied to an area greater than 1x10^-7 cm² (e.g. a 3.5 μm diameter circle) , suitably greater than 5x10^-7 cm² (e.g. a 8 μm diameter circle) , for example greater than 1x10^-6 cm² (e.g. a 11 μm diameter circle) .

The natural profile of a laser beam, by which is suitably meant the energy or intensity, is Gaussian. However other beam profiles are equally suitable to carry out the laser roughening, especially laser beams with a square or rectangular profile (i.e. energy or intensity across the laser beam) . The cross-sectional profile of the laser beam may be circular, elliptical, square or rectangular and suitably the intensity of the laser beam energy (or "profile" of the laser beam) is substantially uniform across the whole area of the cross-section.

Suitably the pulses of electromagnetic radiation have a peak power of at least 50 MW/cm², suitably at least 100 MW/cm², for example at least 150 MW/cm².

Suitably the wavelength of the pulses of electromagnetic radiation is in the range of 150 to 1400 nm, suitably in the range of 300 to 1200 nm, for example in the range of 400 to 1100 nm. For example, the pulses of electromagnetic radiation may be delivered by a nanosecond or picosecond laser and have a wavelength of 1064 nm. The pulses of electromagnetic radiation may be delivered by a femtosecond laser and have a wavelength of 800 nm.

Suitably the characteristics of the energy, for example the pulse length, pulse energy and fluence of the energy, are selected to produce a uniformly hydrophilic roughened surface on the printing form precursor, with a desired roughness, for example a particular fineness (Ra) . The inventors have found that the characteristics of the energy which produce the desired uniformly hydrophilic roughened surface on the printing form precursor, varies according to the substrate used. In the Examples of PCT/GB2016/051530, a “matrix” of energies is shown, for example in Table 2, which have each been tested to determine the nature of the surface produced by said energies in the method. Such a matrix and the accompanying experimental procedure shows how the energy required to produce a uniformly hydrophilic roughened surface on the printing form precursor can be determined and therefore implemented for any suitable surface/printing form precursor.

In addition to focussed, single spot laser exposure for producing the requisite roughening as discussed above, the laser roughening may involve Direct Laser Interference Patterning (DLIP) using, for example, high power pulsed nanosecond diode pumped solid state (DPSS) lasers, to provide the energy for roughening the surface. To produce such a DLIP roughening, an array of a small number of nanosecond lasers may be used to set up the interference exposure pattern. Alternatively, a beam-splitting optical pathway for a single laser could be used to deliver a similar effect. A particular advantage of the DLIP roughening may be that it provides a more effective and faster exposure coverage than can a focussed single spot exposure, potentially improving the throughput of a printing form/printing form precursor production process whilst using relatively low cost nanosecond lasers.

Roughness of a surface may be quantified by the value Ra. Ra can be measured using different techniques which give different values. For example, Ra can be measured by profilometry using a stylus traversing over a given distance on an apparatus such as a Mitutoyo SJ-210. An alternative technique involves using light interference microscopy which provides much higher levels of Z-axis resolution. The Ra value obtained by light interference microscopy is approximately twice that obtained by profilometry.

It has been suggested that having a fine roughness (Ra less than 0.45 as measured by profilometry) leads to a longer press life (see EP 1,356,926 and US 2003, 200, 886)

Suitably the laser roughened surface has a roughness Ra value, measured using light interference microscopy, of from 0.15 to 12 μm and/or a roughness Rz value, measured using light interference microscopy, of from 2.0 to 120 μm.

Suitably the laser roughening provides the surface of the printing form precursor with a uniform roughness having an Ra value, measured using light interference microscopy, of up to 11 μm, suitably up to 10 μm, for example up to 8 μm.

Suitably the laser roughening provides the surface of the printing form precursor with a uniform roughness having an Ra value, measured using light interference microscopy, of at least 0.2 μm, suitably at least 0.4 μm, for example at least 0.6 μm.

Suitably the laser roughening provides the surface of the printing form precursor with a uniform roughness having an Ra value, measured using light interference microscopy, of from 0.15 to 7 μm, for example from 0.2 to 7 μm.

Suitably the laser roughening provides the surface of the printing form precursor with a uniform roughness having an Rz value, measured using light interference microscopy, of from 2.0 to 100 μm, for example from 2.0 to 80 μm.

Suitably the laser roughened surface is uncoated by a developable image layer. Suitably the laser roughened surface comprises a substantially uniform hydrophilic surface, before the method is carried out. Suitably the laser roughened surface is uncoated by a developable image layer and comprises a substantially uniform hydrophilic surface, before the method is carried out. Suitably such a surface is intended for use in subsequent imaging and printing steps.

Suitably the laser roughened surface, before the method of this first aspect is carried out, has a water contact angle of up to 100°, suitably up to 75°, suitably up to 50°.

Suitably the laser roughened surface, before the method of this first aspect is carried out, has an oil contact angle of at least 80°, suitably at least 100℃, suitably at least 120°.

The inventors have found that carrying out the method of this first aspect on a laser roughened surface may provide a particularly advantageous combination of water contact angle and oil contact angle which provides an improved subsequent imaging and printing process.

Imaging

Suitably the method of this first aspect is carried out before an imaging step.

Suitably the method of this first aspect prepares the aluminium printing form precursor for imaging.

According to a second aspect of the present invention, there is provided a method of preparing an aluminium printing form for printing, the method comprising the steps of:

a) treating an aluminium printing form precursor according to the method of the first aspect； and

b) exposing the aluminium printing form precursor imagewise to electromagnetic radiation having a pulse duration of not greater than 1 x 10^-6 seconds.

Suitably the steps of the method of this second aspect are carried out in the order step a) followed by step b) .

Step b) may be carried out by an imaging method described in WO 2010/029341 and WO 2011/114169 which are incorporated herein by reference.

Suitably step b) involves exposing at least a part of the, suitably uniformly hydrophobic, aluminium printing form precursor to electromagnetic radiation having a pulse duration of not greater than 1 x 10^-6 seconds to provide hydrophilic “non-image” areas, leaving the hydrophobic “image” areas unaffected.

Exposing the surface imagewise to the electromagnetic radiation causes a change in the properties of the surface from hydrophobic (ink-accepting) to hydrophilic (ink-repelling) , in the part or parts subjected to the electromagnetic radiation. The part or parts which are not exposed to the electromagnetic radiation remain hydrophobic after step b) . The part or parts subjected to the electromagnetic radiation provide the non-image or negative (ink-repelling) part of the image in a subsequent printing process. The part or parts not subjected to the electromagnetic radiation provide the image or positive (ink-accepting) part of the image in a subsequent printing process. This method is therefore a form of positive working.

In such positive working embodiments, step b) involves reducing the water contact angle of the surface in the part or parts subjected to the electromagnetic radiation. Suitably the water contact angle of the surface in the part or parts subjected to the second energy is reduced from between 60 and 180° to less than 60°.

The pulses of electromagnetic radiation, used in the method of this second aspect to produce the image on the surface, may have a pulse length of from 1 x 10^-15 s to 1 x 10^-6 s, suitably from 1 x 10^-14 s to 1 x 10^-7 s, for example from 1 x 10^-13 s to 1 x 10^-8 s.

Suitably the pulses of electromagnetic radiation have a pulse energy of at least 0.0001 mJ, suitably at least 0.0005 mJ, for example at least 0.00075 mJ, suitably at least 0.0010 mJ.

Suitably the pulses of electromagnetic radiation have a pulse energy of from 0.0001 mJ to 2.0 mJ, suitably from 0.0005 mJ to 1.5 mJ, for example from 0.00075 mJ to 1.0 mJ, suitably from 0.00075 mJ to 0.75 mJ.

Suitably the pulses of electromagnetic radiation have a fluence of up to 10,000 J/cm², suitably up to 7,500 J/cm², for example up to 6,000 J/cm².

Suitably the pulses of electromagnetic radiation have a fluence of at least 0.001 J/cm², suitably at least 0.002 J/cm², for example at least 0.005 J/cm².

Suitably the pulses of electromagnetic radiation have a fluence in the range of from 0.001 J/cm² to 10,000 J/cm², suitably in the range of from 0.005 J/cm² to 10,000 J/cm², for example in the range of from 0.005 J/cm² to 7,500 J/cm².

Suitably the pulses of electromagnetic radiation have a frequency of up to 100,000 kHz, suitably up to 75,000 kHz, for example up to 50,000 kHz.

Suitably the pulses of electromagnetic radiation have a frequency of up to 1000 kHz, suitably up to 750 kHz, for example up to 500 kHz.

Suitably the pulses of electromagnetic radiation have a frequency in the range of from 1 kHz to 1000 kHz, suitably in the range of from 10 kHz to 1000 kHz, for example in the range of from 50 kHz to 750 kHz.

The pulses of electromagnetic radiation may generate a spot or pixel of any shape, for example circular, oval and rectangular, including square. Rectangular is preferred, as being able to provide full imaging of desired regions, without overlapping and/or missed regions.

Suitably the pulses of electromagnetic radiation are applied to an area of less than 1x10^-4 cm² (e.g. a 113 μm diameter circle) , suitably less than 5x10^-5 cm² (e.g. a 80 μm diameter circle) , for example less than 1x10^-5 cm² (e.g. a 35 μm diameter circle) .

In some embodiments, the pulsed radiation may be applied to an area of less than 0.2 cm² (e.g. a 5 mm diameter circle) , suitably less than 7.8 x 10^-3 cm² (e.g. an 1 mm diameter circle) , for example less than 7.8 x 10^-5 cm² (e.g. a 0.1 mm diameter circle) .

Suitably the pulses of electromagnetic radiation are applied to a circular spot with a diameter of between 1 and 100 μm.

The pulse shape of the pulses of electromagnetic radiation used in the method of this second aspect to produce the image on the surface are as described in relation to the pulses of electromagnetic radiation used in the method of the first aspect to produce the roughened surface.

Alternatively, step b) may involve exposing the aluminium printing form precursor to energy in the form of a quasi continuous wave of electromagnetic radiation. By quasi continuous wave of electromagnetic radiation we mean pulses of electromagnetic radiation having high values of N and therefore a high overlap in the fast scan direction. The quasi continuous wave of electromagnetic radiation may have a dwell time on a specific pixel of from 1 x 10^-15 s to 1 x 10^-6 s, suitably from 1 x 10^-14 s to 1 x 10^-7 s, for example from 1 x 10^-13 s to 1 x 10^-8 s.

The inventors have found that the method of this second aspect may provide a particularly advantageous printing form precursor which has an excellent contrast between hydrophilic (non-image) and oleophilic (image) areas and therefore produces high quality printing in a lithographic printing process.

Suitably steps a) and b) of the method of this second aspect are preceded by a step of exposing the printing form precursor to energy in the form of pulses of electromagnetic radiation having a pulse length of from 1 x 10^-15 s to 1 x 10^-6 s to produce a uniformly hydrophilic roughened surface.

The step of exposing the printing form precursor to energy in the form of pulses of electromagnetic radiation to produce a uniformly hydrophilic roughened surface may have any of the features of the laser roughening described in relation to the first aspect.

According to a third aspect of the present invention, there is provided a method of increasing the water contact angle and decreasing the oil contact angle of an aluminium printing form precursor, the method comprising treating the aluminium printing form precursor according to the method of the first aspect.

According to a fourth aspect of the present invention, there is provided an aluminium printing form precursor treated according to the method of first aspect.

According to a fifth aspect of the present invention, there is provided an aluminium printing form precursor comprising a substantially uniform surface having a water contact angle of between 70 and 175° and an oil contact angle of between 0 and 120°.

The printing form precursors of the fourth and/or fifth aspects may have any of the features and advantages described in relation to the first and second aspects.

Suitably the aluminium printing form precursor comprises a substantially uniform surface having a water contact angle of between 80 and 175°, suitably between 90 and 175°, suitably between 100 and 175°.

Suitably the aluminium printing form precursor comprises a substantially uniform surface having an oil contact angle of between 0 and 110°, suitably between 0 and 100°, suitably between 0 and 90°.

According to a sixth aspect of the present invention, there is provided the use of an aluminium printing form precursor according to the fourth and fifth aspects in a lithographic printing process.

According to a seventh aspect of the present invention, there is provided a method of treating an aluminium printing form precursor, the method comprising the step of:

subjecting the aluminium printing form precursor to an environment of at least 30 ％relative humidity to provide the aluminium printing form precursor with a water contact angle of between 70 and 175° and an oil contact angle of between 0 and 120°.

Suitably the step of subjecting the aluminium printing form precursor to an environment of at least 30 ％relative humidity is carried out at a sufficient temperature and for a sufficient time to provide the aluminium printing form precursor with a water contact angle of between 70 and 175° and an oil contact angle of between 0 and 120°.

The method of this seventh aspect may have any of the suitable features and advantages described in relation to the first and second aspects.

Examples

Measurement of water contact angle (WCA) and oil contact angle (OCA)

The instrument used for the studies described below was a Maist Vision DropMeter^TM Experience A-300. On this instrument, a backlight illuminates drops of water or oil which are visualised through a magnified CCD camera lens, with accurate focussing enabled through the software. The user ensures that the sample bed lies horizontally. Droplets of typically 3 μl are dispensed, with the user making fine adjustments to the height of the platform on which the sample is placed.

For water, the technique is well-established. Once a drop has been dispensed, an image is captured. The instrument’s software is then used to fit a curve and to calculate the contact angle. Three readings are obtained and –provided they are broadly consistent–the average is quoted as the WCA. In the case of samples that are extremely hydrophobic (with a WCA>160°) it may be necessary to dispense larger droplets from the syringe to enable a drop to leave the syringe and overcome the repulsive forces of the surface.

For oil, we have needed to develop a method in order to enable the research described in this invention. The technique is similar except that the sample is placed on a block that is submerged in distilled water. Di-iodomethane, typically as 2 μl droplets, is dispensed from the syringe following the principles already explained. As with the WCA, it may be necessary to dispense larger droplets in the case of highly oleophobic samples.

Use of contact angles to find recommended exposure in laser imaging

In all plates, be they conventional or digital, a key measurement parameter is the recommended exposure-the applied energy that provides optimum performance for most of the plate properties including resolution, printability and productivity. It is a value that often represents a compromise between important responses–for example, the correct exposure to cause suitable process-ability in developer may not be the best exposure for dot reproduction. This process is carried out by irradiating the plate with different quantities of light energy, processing and then reading the density of the exposed area with a densitometer. For a positive working plate the density at zero exposure is at its maximum and after suitable exposure to provide a clear substrate is at its minimum. The difference is the contrast.

The technology described in patent numbers WO 2010/029341 and WO 2011/114169 does not have a coating but still requires a method by which samples can be compared with each other in any test considered to be exposure sensitive. Since this technology has no coating and will be used directly on press after imaging, a suitable method for identifying “printability” is required and since lithography requires the differentiation of ink acceptance and repulsion of water in the ink accepting areas and water acceptance and ink repulsion on the non-printing areas, the measurement of water and oil contact angles relative to exposure energy seems appropriate.

Hence, the laboratory method to be developed relied on evaluating both the oil and water contact angles as a function of incremental exposure energy increases, looking for the point of maximum lithographic contrast and then hand inking to confirm ink acceptance and background cleanliness.

Two 0.5 x 0.5cm squares were written for each exposure energy and one used to determine WCA, the other being used for OCA. An example of a chart of contact angles for each energy is shown below

In Figure 1, the test material has become both super-hydrophilic (WCA ＝ zero) and highly super-oleophobic (OCA ＝ 165°) at a pulse energy of 2.5 μJ/cm².

One objective of this invention is to convert the hydrophilic, oleophobic surface of anodised or laser roughened aluminium into a surface that readily accepts ink. The imaged areas of this surface return to being hydrophilic, thereby providing the required contrast to enable lithographic printing. The inventors have discovered that the converted surface needs to have:

water contact angle (WCA) of > 90°, preferably > 110°

oil contact angle (OCA) of < 120°, preferably < 100°

The greater the WCA and the less the OCA, the sharper is the image after exposure.

Comparative Example Set 1 -high temperature processing of anodised aluminium

A sample of commercial electrochemically grained and anodised aluminium printing form precursor substrate with an anodic film thickness of 0.75 μm was immersed into boiling deionised water at pH 7 and kept between 90 and 100 ℃ for 15 minutes. The sample was removed and dried with a hot air gun.

Example 1 was repeated but adjusting the water to pH 6 with acetic acid.

Example 1 was repeated but after removal from the boiling water the sample was placed in an oven for 2 hours at 100 ℃.

Table 1 displays the results of experiments 1-3.

The results show that if a sealing process is occurring, that it renders the surface more hydrophilic than the untreated sample and with no beneficial change in the oleophilicity.

Example Set 2–high temperature and humidity processing of anodised aluminium

Samples of the same batch of anodised aluminium were processed by heating at 80 ℃ and a relative humidity of 90 ％for various times. Table 2 displays the effect on water and “oil” contact angles.

Table 2

This shows that the high temperature and humidity process increases the water contact angle to hydrophobic (>90°) within 1 hour but that the WCA and the OCA are optimised and seems stable from between 2 and 20 hours. A time of 12 hours was selected as standard as a process centre point to maximise robustness of the process.

Samples 2A to 2E were printed by mounting on the plate cylinder together and 100 copies were printed to establish any differences in printability relating to contact angles. Figure 2 shows images of the results.

The test demonstrates that as WCA increases from 2A to 2D the image density increases. 2D and 2E have similar WCA but 2E has a much lower OCA which can be seen as a better resolved image.

In two further sets of experiments under the same conditions, the effect of plate size was examined. Experiments 2T show that the conversion process occurred more slowly on larger plates, this being especially seen with the oil contact angle. Experiments 2U, 2V were carried out on a different batch of material showing that, even on a press-sized plate, efficient conversion had been achieved overnight.

Table 3–effect of plate size on contact angle after treatment

Example Set 3–high temperature and humidity processing of pulsed laser roughened aluminium

A sample of 1050A aluminium alloy was laser processed using a pulsed laser using the following conditions: Pulse length ＝ 2.3 ns, pulse energy ＝ 28.25 μJ, spot size ＝ 15 μm, horizontal overlap N ＝ 3 and vertical overlap H ＝ 3. The Ra resulting from the roughening process was 1.058 μm and Rz 17.2 μm as measured by Bruker interferometer, the water contact angle was 0° and oil contact angle 160°.

The sample was treated as in example set 2 at 80 ℃ and an RH of 90 ％for 12 hours.

The resulting WCA was 153° and OCA 68°.

Example Set 4–pressure cooker with humidity

The experiments covered by this example are depicted schematically in Figure 3 above. The test sample was placed in a beaker within the pressure cooker. In some tests the beaker contained deionised water (DI) to around 20％of its volume, in others, no water was used. In some tests the beaker was sealed with aluminium foil； in others, not.

The results, which were duplicated several times, show that on grained anodised aluminium:

- the samples in which the beaker contained water actually became more rather than less hydrophilic.

- the samples without water in the beaker performed better where no foil was present. Sample 4E has reached the standard normally expected for a plate suitable for laser imaging, and is similar in performance to examples 2E–2S above.

- the effect appears to have reversed on extending the cooking time.

On ungrained anodised aluminium, the desired conversion took place as on grained anodised aluminium. The results of these tests suggest that the effect of eliminating the graining step was to slightly reduce both the water and oil contact angles.

For the laser roughened aluminium, samples of 1050A alloy were processed using a pulsed laser using the following conditions: pulse length ＝ 17 ns, pulse energy ＝ 8-10 μJ, spot size ＝ 15 μm, horizontal overlap N ＝ 3.39 and vertical overlap H ＝ 3.39. The Ra resulting from the roughening process was around 0.9 μm and Rz 19-21 μm as measured by Bruker interferometer.

Table 4

On laser roughened aluminium the test samples –in which the beaker contained no water but was sealed with foil -became highly hydrophobic and moderately oleophilic.

Example Set 5-autoclave

Laser roughened aluminium was prepared as in Example Set 4, the samples being 5 cm x 8 cm in size. As in Set 4, steam was employed with the test sample placed inside a beaker sealed with foil.

Tests were carried out at 0.1 MPa (100℃) and at 0.2 MPa (120℃) . After 15 minutes’ treatment, the samples were withdrawn. Those autoclaved at 120 ℃ gave the following contact angles showing a high degree of conversion: -

Sample 1 WCA ＝ 168° OCA ＝ 88°

Sample 2 WCA ＝ 170° OCA ＝ 69°

As in Set 4, the samples after 30 minutes treatment were less superhydrophobic and were less oleophilic.

At 100 ℃, conversion was less complete.

The example embodiments described above may provide a method of preparing an aluminium printing form precursor which produces a beneficial decrease in hydrophilicity and a beneficial increase in oleophilicity. The method may provide a particularly advantageous combination of water contact angle and oil contact angle which provides an improved subsequent imaging and printing process. The method may be carried out in an efficient manner in terms of time, energy and chemical usage and particular may avoid the use of harsh chemicals. The method may provide an aluminium printing form precursor which has an excellent contrast between hydrophilic (non-image) and oleophilic (image) areas and therefore can produce high quality printing in a lithographic printing process. The method may provide such an aluminium printing form precursor without using developable coating chemicals common to the lithographic printing arts.

In summary the present invention provides a method of treating an aluminium printing form precursor for use in lithographic printing. The treatment conditions comprise a relative humidity of at least 30 ％, a temperature in the range 60 to 120 ℃, a pressure of from 0.9 to 10 atmospheres and a treatment time in these conditions of at least 10 minutes. The method may be used for preparing an aluminium printing form precursor for imaging and subsequent printing. The method may provide a beneficial decrease in hydrophilicity and a beneficial increase in oleophilicity of the aluminium printing form precursor. An improved aluminium printing form precursor is also provided.

Throughout this specification, the term “comprising” or “comprises” means including the component (s) specified but not to the exclusion of the presence of other components. The term “consisting essentially of” or “consists essentially of” means including the components specified but excluding other components except for materials present as impurities, unavoidable materials present as a result of processes used to provide the components, and components added for a purpose other than achieving the technical effect of the invention. Typically, when referring to compositions, a composition consisting essentially of a set of components will comprise less than 5％by weight, typically less than 3％by weight, more typically less than 1％by weight of non-specified components.

The term “consisting of” or “consists of” means including the components specified but excluding addition of other components.

Whenever appropriate, depending upon the context, the use of the term “comprises” or “comprising” may also be taken to encompass or include the meaning “consists essentially of” or “consisting essentially of” , and may also be taken to include the meaning “consists of” or “consisting of” .

The optional features set out herein may be used either individually or in combination with each other where appropriate and particularly in the combinations as set out in the accompanying claims. The optional features for each aspect or exemplary embodiment of the invention as set out herein are also to be read as applicable to any other aspect or exemplary embodiments of the invention, where appropriate. In other words, the skilled person reading this specification should consider the optional features for each exemplary embodiment of the invention as interchangeable and combinable between different exemplary embodiments.

Although a few preferred embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

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, 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, 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, and drawings) , or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

A method of treating an aluminium printing form precursor, the method comprising the step of:

subjecting the aluminium printing form precursor to an environment of at least 30 ％ relative humidity at a temperature in the range 60 to 120 ℃, a pressure of from 0.9 to 10 atmospheres and for at least 10 minutes.
The method according to claim 1, wherein the step is carried out at a pressure of at least 1.5 atmospheres.
The method according to claim 1, wherein the step is carried out at a temperature in the range 60 to 100 ℃, at a pressure of below 1.5 atmospheres and for at least 2 hours.
The method according to any preceding claim, wherein the step of subjecting the aluminium printing form precursor is carried out at a pH in the range 6 to 8.
The method according to any one of claims 1 to 3, wherein the aluminium printing form precursor has an anodised aluminium surface suitable for use in printing.
The method according to claim 5, wherein the anodised printing surface has a thickness in the range 0.20 μm to 10 μm.
The method according to any one of claims 1 to 3, wherein the aluminium printing form precursor has a laser roughened surface suitable for use in printing.
The method according to claim 7, wherein the laser roughened surface has been produced by exposing the printing form precursor to energy in the form of pulses of electromagnetic radiation having a pulse length of from 1 x 10^-15 s to 1 x 10^-6 s to produce a uniformly hydrophilic roughened surface.
The method according to claim 7 or 8, wherein the laser roughened surface has a roughness Ra value, measured using light interference microscopy, of from 0.15 to 12 μm and/or a roughness Rz value, measured using light interference microscopy, of from 2.0 to 120 μm.
The method according to any preceding claim, wherein the method is carried out before an imaging step.
The method according to any preceding claim, wherein the method prepares the aluminium printing form precursor for imaging.
An aluminium printing form precursor treated according to the method of any preceding claim.
An aluminium printing form precursor comprising a substantially uniform surface having a water contact angle of between 70 and 175° and an oil contact angle of between 0 and 120°.
A method of preparing an aluminium printing form for printing, the method comprising the steps of:

a) treating an aluminium printing form precursor according to the method of any one of claims 1 to 11； and

b) exposing the aluminium printing form precursor imagewise to electromagnetic radiation having a pulse duration of not greater than 1 x 10^-6 seconds.
The method according to claim 14, wherein steps a) and b) are preceded by a step of exposing the printing form precursor to energy in the form of pulses of electromagnetic radiation having a pulse length of from 1 x 10^-15 s to 1 x 10^-6 s to produce a uniformly hydrophilic roughened surface.
A method of increasing the water contact angle and decreasing the oil contact angle of an aluminium printing form precursor, the method comprising treating the aluminium printing form precursor according to any one of claims 1 to 11.