JPH09131850A - Preparation of lithographic printing plate including development on press - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply produce a printing plate having excellent printing characteristics by an environmentally gentle method. SOLUTION: An image forming element obtained by an image forming layer wherein hydrophobic thermoplastic polymer particles are dispersed in a hydrophilic binder on the hydrophilic surface of a planograpahic base and containing a compd. capable of converting light to heat in the image forming layer or the layer adjacent thereto is imagewise exposed. The imagewise exposed image forming element thus obtained is rinsed with ordinary water or an aq. liquid to be developed to produce a planographic printing plate.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method of making a lithographic printing plate. More particularly, the present invention relates to methods by which lithographic printing plates can be developed with ordinary water or aqueous liquids.

[0002]

BACKGROUND OF THE INVENTION A lithographic process is a method of printing from a specially manufactured surface such that some areas of the surface are receptive to lithographic ink and other areas are impermeable to ink when wetted with water. . The ink-receptive areas form the printed image areas and the ink-rejection areas form the background areas.

In the photographic lithographic technique, the photographic material is image-wise for oily or greasy inks in exposed (negative-working) and unexposed (positive-working) areas on a hydrophilic background. To be receptive to.

In the manufacture of conventional lithographic printing plates, also referred to as surface lithographic or planographic printing plates, a support having or having an affinity for water, or having such an affinity by chemical treatment, can be used in a thin photosensitive composition. Coating in layers. Coatings for this purpose include photopolymer layers containing diazo compounds, dichromate sensitized hydrophilic colloids and various synthetic photopolymers. In particular, diazo-sensitized systems are widely used.

Image-wise exposure of the photosensitive layer renders the exposed image areas insoluble and the unexposed areas soluble. The plate is then developed with a suitable liquid to remove the diazonium salt or diazo resin in the unexposed areas.

Commercially available diazo-based printing plates most commonly use anodized and roughened aluminum as a support having a hydrophilic surface. However, commercial plates are also available which use a flexible support such as paper provided with a hydrophilic layer. For example, Lithocraft 10008 FOTOPLATE ^™ is a diazo-based printing plate comprising a hydrophilic layer on top of which a diazo-based photosensitive layer is applied on a paper support. According to the supplier's plate instructions, the lithographic printing plate precursor or imaging element is image-wise exposed, the exposed imaging element is placed on a printing machine and its surface is Lithocraft 10008.
A plate can be produced by wiping with a development desensitizer. The plate instructions also contemplate methods without the use of development desensitizers. However, in practice development desensitizers are almost always needed, since such methods very often result in poor lithographic performance.

A particular drawback of the above described photosensitive imaging elements for making printing plates is that they must be shielded from light. This is an on-press development because the installation of image-wise exposed imaging elements is generally done in normal sunlight, which limits the handling time required to install the imaging element. Is especially disadvantageous when intended. Moreover, diazo-based aluminum type printing plates are completely unsuitable for on-press development.

On the other hand, methods are known for making printing plates which involve the use of imaging elements which are heat-sensitive rather than light-sensitive. For example, Research Di in January 1992
Sclosure no. 33303 discloses a heat-sensitive imaging element comprising a thermoplastic polymer particle on a support and a cross-linked hydrophilic layer containing an infrared absorbing pigment such as carbon black. Upon image-wise exposure to an infrared laser, the thermoplastic polymer particles solidify image-wise, thereby rendering the surface of the imaging element and these parts ink-receptive without further development. A disadvantage of this method is that when some pressure is applied to the non-printing areas they may become ink receptive and the resulting printing plates are easily damaged. Furthermore, under critical conditions the lithographic performance of such printing plates is poor and as a result such printing plates have little lithographic printing latitude.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a printing plate having excellent printing characteristics by a simple and environmentally friendly method.

Other objects of the invention will be apparent from the following description.

According to the invention: (1) (i) hydrophobic thermoplastic polymer particles having a glass transition temperature Tg of at least 80 ° C. dispersed in a hydrophilic binder on the hydrophilic surface of the lithographic base. And (ii) image-wise exposing an imaging element comprising (ii) a compound capable of converting light into heat and comprising a compound contained in said imaging layer or its adjacent layers, (2) and placing the image-wise exposed imaging element thus obtained on a printing cylinder of a printing machine and supplying an aqueous fountain solution and / or ink to said imaging layer while rotating the printing cylinder. Thereby provide a method of making a lithographic printing plate comprising the step of developing the element.

The present invention further comprises (1) (i) hydrophobic thermoplastic polymer particles having a glass transition temperature Tg of at least 80 ° C. dispersed in a hydrophilic binder on the hydrophilic surface of the lithographic base. An image-wise exposing an image-forming layer comprising, and (ii) an image-forming element capable of converting light into heat and comprising a compound contained in the image-forming layer or an adjacent layer thereof, 2) placing the image-wise exposed imaging element thus obtained on the printing cylinder of the printing machine without development, (3) supplying an aqueous fountain solution to the imaging layer of the imaging element and And / or rotating the printing cylinder while supplying ink, and (4) transferring ink from the imaging element to a receiving element to provide a method of making multiple copies of the original image.

The invention further comprises (1) (i) hydrophobic thermoplastic polymer particles having a glass transition temperature Tg of at least 80 ° C. dispersed in a hydrophilic binder on the hydrophilic surface of the lithographic base. An imaging layer comprising, and (ii) an imaging element capable of converting light to heat and comprising a compound contained in said imaging layer or its adjacent layers onto a printing cylinder of a printing press. By (2) exposing the imaging element image-wise by means of a laser or an LED, (3) and feeding the imaging layer with an aqueous dampening solution and / or ink while rotating the printing cylinder. It relates to a method of making a lithographic printing plate comprising the step of developing the image-wise exposed imaging element thus obtained.

The present invention further comprises (1) (i) hydrophobic thermoplastic polymer particles having a glass transition temperature Tg of at least 80 ° C. dispersed in a hydrophilic binder on the hydrophilic surface of the lithographic base. An imaging layer comprising, and (ii) an imaging element capable of converting light to heat and comprising a compound contained in said imaging layer or its adjacent layers onto a printing cylinder of a printing press. By (2) exposing the imaging element image-wise by means of a laser or an LED, (3) and feeding the imaging layer with an aqueous dampening solution and / or ink while rotating the printing cylinder. Disclosed is a method of making a plurality of copies from an original comprising the step of developing the image-wise exposed imaging element thus obtained and (4) transferring ink from the imaging element to the receiving element.

The invention also comprises (i) a printing cylinder, means for mounting an imaging element on the printing cylinder, at least one laser or LED device, said laser or LE Means for guiding the output of the D. device to focus on the surface of the imaging element; -moving the guiding means and the supporting means relative to each other for imaging by the output of the laser or the L.E. At least one printing station including means for performing scanning of the surface of the element; (ii) means for supplying dampening liquid to the printing cylinder; (iii) means for supplying ink to the printing cylinder; iv) A printing device comprising means for transferring a receiving element to the printing station, (v) means for transferring ink from the printing cylinder to the receiving element.

In yet another aspect, the invention provides (1) (i) a hydrophobic thermoplastic having a glass transition temperature Tg of at least 80 ° C. dispersed in a hydrophilic binder on a hydrophilic surface of a lithographic base. An image-forming layer comprising polymer particles, and (ii) an image-forming element which is capable of converting light to heat and which comprises a compound contained in the image-forming layer or its adjacent layers. It also relates to a method for making a lithographic printing plate comprising the steps of exposing, (2) and developing the image-wise exposed imaging element thus obtained by rinsing with ordinary water or an aqueous liquid.

The present invention will be described with respect to the drawings, but the invention is not limited thereto.

[0018]

DETAILED DESCRIPTION OF THE INVENTION An imaging element for use in accordance with the present invention comprises a hydrophobic heat transfer material having a glass transition temperature Tg of at least 80 ° C. dispersed in a hydrophilic binder on a hydrophilic surface of a lithographic base. It comprises an imaging layer comprising plastic polymer particles. The hydrophilic binders used according to the invention are preferably not crosslinked or only slightly crosslinked. The imaging element further comprises a compound capable of converting light into heat. This compound is preferably contained in the imaging layer, but can also be provided in a layer adjacent to the imaging layer.

According to one aspect of the invention, the lithographic base may be anodized aluminum. A particularly preferred lithographic base is an electrochemically grained and anodized aluminum support. According to the present invention, an anodized aluminum support may be treated to improve the hydrophilic properties of its surface. For example, the support may be silicate treated by treating the surface of the aluminum support with a sodium silicate solution at an elevated temperature such as 95 ° C. Alternatively, a phosphate treatment may be applied which involves treating the aluminum oxide surface with a phosphate solution which may further contain inorganic fluoride. Further, the aluminum oxide surface may be rinsed with a citric acid or citrate solution. This treatment may be performed at room temperature or about 30-5.
It can also be carried out at a slightly elevated temperature of 0 ° C. A further interesting treatment involves rinsing the aluminum oxide surface with a bicarbonate solution. It has also been demonstrated that one or more of these post-treatments can be used alone or in combination.

According to another aspect of the invention, the lithographic base comprises a flexible support provided with a cross-linked hydrophilic layer, such as paper or plastic film. Particularly suitable cross-linked hydrophilic layers are obtained from hydrophilic binders cross-linked with a cross-linking agent such as, for example, formaldehyde, glyoxal, polyisocyanate or hydrolyzed tetra-alkyl orthosilicate. The latter is particularly preferred.

As hydrophilic binders, hydrophilic (co) polymers such as vinyl alcohol, acrylamide, methylol acrylamide, methylol methacrylamide,
Homopolymers and copolymers of acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate or maleic anhydride / vinyl methyl ether copolymers can be used. Preferably the hydrophilicity of the (co) polymer or (co) polymer mixture used is at least 60.
It is equal to or higher than the hydrophilicity of polyvinyl acetate hydrolyzed to the extent of weight percent, preferably 80 weight percent.

The amount of cross-linking binder, especially tetraalkyl orthosilicate, is at least 0.2 parts by weight per part by weight of hydrophilic binder, preferably between 0.5 and 5 parts by weight, more preferably 1 part by weight. It is between 0.0 and 3 parts by weight.

The crosslinked hydrophilic layer in the lithographic base used according to the invention preferably also contains substances which enhance the mechanical strength and porosity of the layer. Colloidal silica can be used for this purpose. The colloidal silica used is for example up to 40 nm, eg 20 nm
May be in the form of commercially available water-dispersion of colloidal silica having an average particle size. In addition, inert particles larger than colloidal silica, such as J.
Colloid and Interface Sci., Vol. 26, 1968, pages 6
Particles having a mean diameter of at least 100 nm, which are particles of silica or titanium dioxide or other heavy metal oxides manufactured by Stoeber as described in 2-69, can also be added. By adding these particles,
The surface of the cross-linked hydrophilic layer is provided with a uniform, rough texture of microscopic irregularities, which serve as storage places for water in the background.

The thickness of the crosslinked hydrophilic layer in the lithographic base according to this embodiment can vary from 0.2 to 25 μm and is preferably from 1 to 10 μm.

Specific examples of cross-linked hydrophilic layers suitable for use in accordance with the present invention are EP-A601240, GB-
P-1419512, FR-P-2300354, US
-P-3971660, US-P-4284705 and EP-A 514490.

It is particularly preferable to use a plastic film such as a polyethylene terephthalate film, a cellulose acetate film, a polystyrene film or a polycarbonate film, which is used as a substrate, as the lithographic base flexible support in this embodiment. The plastic film support may be opaque or transparent.

It is particularly preferred to use a polyester film support provided with an adhesion improving layer. Particularly suitable adhesion improving layers for use according to the invention are EP-A 619.
524, EP-A 620502 and EP-A 619
525, hydrophilic binders and colloidal silica. The amount of silica in the adhesion improving layer to not 200mg per 1 m ² 1 m ² per 750mg
Between. Further, the ratio of silica to hydrophilic binder is preferably greater than 1 and the surface area of the colloidal silica is preferably at least 300 m ² per gram, more preferably 500 m ² per gram.

According to the invention, an imaging layer is provided on top of the hydrophilic surface. Optionally, one or more intermediate layers may be provided between the lithographic base and the imaging layer. The imaging layer according to the present invention comprises thermoplastic polymer particles dispersed in a hydrophilic binder.

Hydrophilic binders suitable for use in the imaging layer according to the invention are, for example, synthetic homo or copolymers, such as polyvinyl alcohol, poly (meth) acrylic acid, poly (meth) acrylamide, poly (meth) acrylic. Hydroxyethyl acid, polyvinyl methyl ether or natural binders such as gelatin, polysaccharides such as dextran,
They are pullulan, cellulose, gum arabic and alginic acid.

The hydrophobic thermoplastic polymer particles used in connection with the present invention preferably have a glass transition temperature of at least 90 ° C, more preferably at least 100 ° C.

The hydrophobic thermoplastic polymer particles used in connection with the present invention preferably have a coagulation temperature above 50 ° C, or more preferably above 70 ° C. Solidification may result from softening or melting of thermoplastic polymer particles under the influence of heat. There is no particular upper limit to the coagulation temperature of the thermoplastic hydrophobic polymer particles, but this temperature must be well below the decomposition point of the polymer particles. Suitably the coagulation temperature is at least 10 ° C below the temperature at which the decomposition of the polymer particles takes place. When the polymer particles are exposed to temperatures above the coagulation temperature, they coagulate to form hydrophobic agglomerates in the hydrophilic layer, so that in these parts the hydrophilic layer is in ordinary water or aqueous liquid. Becomes insoluble in.

Specific examples of hydrophobic polymer particles for use in connection with the present invention are, for example, polystyrene, polyvinyl chloride, polymethylmethacrylate, polyvinylidene chloride,
Polyacrylonitrile, polyvinylcarbazole, etc. or their copolymers and / or mixtures.
Polymethylmethacrylate is most preferably used.

The weight average molecular weight of the polymer is 5,000 to 1,
It may be in the range of, 000,000 g / mol.

The hydrophobic particles are from 0.01 μm to 50 μm,
More preferably it may have a particle size between 0.05 μm and 10 μm and most preferably between 0.05 μm and 2 μm.

The polymer particles are present as a dispersion in the aqueous coating liquid of the imaging layer and are described in US-P-3.
It can be manufactured by the method disclosed in 476.937. Another method, which is particularly suitable for producing an aqueous dispersion of thermoplastic polymer particles, is: dissolving the hydrophobic thermoplastic polymer in an organic water-immiscible solvent, the solution thus obtained in water or in water. Dispersing in a medium, and-removing the organic solvent by evaporation.

The amount of hydrophobic thermoplastic polymer particles contained in the imaging layer is preferably between 20% and 65% by weight and more preferably between 25% and 55% by weight and most preferably. Between 30% and 45% by weight.

Suitable compounds capable of converting light to heat are preferably infrared absorbing components, but as long as the absorption of the compound used is within the wavelength range of the light source used for image-wise exposure Is not important. Particularly useful compounds are, for example, dyes and in particular infrared dyes, carbon blacks, metal carbides, borides, nitrides, carbonitrides, bronze-structured oxides and structurally related components of the bronze family, but the component , For example WO _2.9- free oxides. It is also possible to use conductive polymer dispersions, for example conductive polymer dispersions based on polypyrrole or polyaniline. The lithographic performance obtained, and especially the print resistance, depends on the heat sensitivity of the imaging element. In this regard, carbon black gives very good and favorable results.

The light to heat converting compound of the present invention is most preferably added to the imaging layer, although at least some of the light to heat converting compound may be included in a nearby layer. . Such a layer may be, for example, a crosslinked hydrophilic layer of a lithographic base according to the second aspect of the lithographic base described above.

According to the method of the invention for obtaining a printing plate, the imaging element is image-wise exposed and then placed on the printing cylinder of a printing press. According to a preferred embodiment, the printing machine is then started and the dampening agent roller supplying the dampening fluid is dropped onto the imaging element while rotating the printing cylinder with the imaging element mounted on top and then Then drop the ink roller on it. Generally, after about 10 rotations of the print cylinder, a first clean, useful print is obtained.

According to another method, the ink roller and the dampening agent roller may be dropped simultaneously or the ink roller may be dropped first.

Suitable dampening fluids which can be used in connection with the present invention are generally aqueous fluids which have an acidic pH and which comprise an alcohol, for example isopropanol. There are no particular restrictions on the fountain solution useful in the present invention and commercially available fountain solutions, also known as fountain solutions, can be used.

The image-forming layer of the image-wise exposed imaging element is wiped with a water-soaked pad, for example a cotton pad or sponge, before installation on the printing press or at least before starting up the printing press. This will remove some non-image portions, but will not actually develop the imaging element. However, it has the advantage that considerable damaging of the dampening system of the printing press and the ink used can be avoided.

According to another method, the imaging element is first placed on the printing cylinder of the printing press and then image-wise exposed directly on the printing press. After exposure, the imaging element can be developed as described above.

According to yet another method of the invention, the imaging element can be developed by image-wise exposing it and then rinsing it with plain water.

Preferably during or after the development of the image-wise exposed imaging element the element is treated with a rubber such as gum arabic, dextranes, dextrins, water soluble cellulose derivatives, pullulan and the like.

Image-wise exposure in the context of the present invention is preferably an image-wise scanning exposure involving the use of a laser or LED. For the purposes of the present invention emitting in the infrared (IR) and / or near infrared region, ie 700-1500 nm
It is highly preferred to use a laser which emits in the wavelength range of Laser diodes that emit in the near infrared region are particularly preferred for use with the present invention.

Suitable imaging devices suitable for image-wise scanning exposure according to the present invention are preferably applied directly to the imaging element surface via lenses or other ray-guiding elements or at remote locations using fiber optic cables. Includes laser power that can be delivered from a laser to the surface of the blank imaging element. An adjuster and associated positioning hardware keeps the light output in the correct orientation with respect to the imaging element surface,
The output is scanned onto the surface and the laser is activated at adjacent selected points or portions of the imaging element. The controller responds on the imaging element to an input image signal depending on the original document and / or picture to be copied to form the exact negative or positive image of that original. These image signals are stored in the computer as bitmap data files. Such files may be created by a laser image processor (RIP) or other suitable means. For example, a RIP can accept input data in a page-written language or as a combination of a page-written language and one or more image data files that define all the features required to be transferred onto the imaging element. Bitmaps are created to define screen frequencies and angles in the case of tone and amplification adjustment screening. However, the invention is for example EP-A.
571010, EP-A 620677 and EP-A
It is particularly suitable for use in combination with the frequency adjusted screening disclosed in 620674.

The image-forming device can be operated by itself so that it functions only as a plate-making machine, or it can be added directly into a lithographic printing machine having means for supplying a dampening liquid. In the latter case, printing may be started immediately after the image-wise exposure and development, which considerably reduces the set-up time of the printing press. The image forming device can be configured as a flatbed recorder or as a drum recorder with lithographic blanks mounted on the inner and outer cylindrical surfaces of the drum. Obviously, the external drum design is more suitable for use on-the-fly on a lithographic press, in which case the printing cylinder itself constitutes the drum part of the recorder or plotter.

In the preferred drum construction, the drum (and the imaging element mounted thereon) is rotated about its axis and a ray parallel to the axis of rotation is moved, thereby circumferentially moving the imaging element. By axially "growing" the image by scanning, the necessary relative movement between the laser beam and the imaging element is obtained. Alternatively, the light beam can be moved parallel to the drum axis and increased in angle after each pass over the imaging element to "grow" the image circumferentially on the imaging element. In both cases, after complete scanning with light and development, the image according to the original will have been applied to the surface of the imaging element. With the flatbed structure,
Rays are drawn along either axis of the imaging element, and are designated along the other axis after each pass.
Of course, the required relative movement between the ray and the imaging element may be caused by movement of the imaging element rather than (or in addition to) movement of the ray.

Regardless of how the beam is scanned, it is generally preferred (for speed reasons) to use multiple lasers and direct their output into a single writing array.
After the completion of each pass over or along the imaging element, the writing array is then specified, the distance being the number of rays emanating from the array and the desired resolution (ie image point per unit length). Number).

In the following, preferred embodiments of imaging devices suitable for use with the present invention will be described in more detail.

External-Drum Recording Reference is first made to FIG. 1 of the drawings which illustrates an external drum embodiment of an imaging system suitable for use with the present invention. This assembly includes a cylinder 50 surrounded by an imaging element 55.
including. Cylinder 50 includes a blank portion 60 in which the outer margin of imaging element 55 is secured by conventional pinching means (not shown). The size of the blank portion can be greatly changed depending on the environment in which the cylinder 50 is used.

Cylinder 50 is preferably added directly into the design of a typical lithographic printing machine having means for supplying dampening fluid to the imaging element, and functions as the printing cylinder of the printing machine. In a typical press construction, the imaging element 55 receives ink and dampening fluid from an ink train and a series of dampening cylinders, respectively.
The end cylinder is in rotational engagement with the cylinder 50. The latter cylinder also rotates in contact with a blanket cylinder that transfers the ink to a receiving element, which is typically a paper sheet. The printing press can have more than one such printing assembly arranged in a linear array. Alternatively, multiple assemblies may be rotationally interlocked with all blanket cylinders around a large central impression cylinder.

Cylinder 50 is supported within the frame and is rotated by a standard electric motor or other conventional means (shown schematically in FIG. 2). Cylinder 5
The angular position of 0 is monitored by the axis encoder (Fig. 4
checking). A writing array 65 movably mounted on a lead screw 67 and a guide rod 69 traverses the imaging element 55 as it rotates. The axial movement of the writing arrangement 65 results from the rotation of the stepper motor, which leads to the lead screw 6
7. Rotate 7 and thereby move the axial position of writing array 65. The stepper motor 72 will be activated during the time that the writing array 65 is over the blank 60 after the writing array 65 has passed over the entire surface of the imaging element 55. Rotation of the stepper motor 72 moves the writing array 65 to the proper axial position to begin the next imaging pass.

The specified axial distance between successive imaging passes is determined by the number of imaging objects in writing array 65 and their configuration within them, as well as the desired resolution. As shown in FIG. 2, a series of laser sources L1, L2, L excited by a suitable laser exciter, generally designated by the reference numeral 75.
3, ... Ln provides each output to a fiber optic cable. The laser is preferably a gallium arsenide model, but other lasers can be used.

The cables carrying the laser output are collected in a bundle 77 and added separately to the writing arrangement 65. In order to retain the force, it has proven desirable to keep the bundle in a structure that does not require bending above the critical refraction angle of the fiber (and thereby keep total internal reflection).

As also shown in FIG. 2, the regulator 80 actuates the laser exciter 75 when the associated laser reaches the appropriate point opposite the imaging element, and also the stopper motor 72 and cylinder. The drive motor 82 is operated.

The regulator 80 receives data from two sources. The angular position of the cylinder 50 with respect to the writing array 65 is constantly monitored by the detector 85, which provides a signal to the regulator 80 which is an indication of that position. In addition, the image data source (eg, computer) also provides a data signal to the adjuster 80. The image data defines the point on the imaging element 55 at which the image point is to be written. Accordingly, the adjuster 80 includes the writing array 65 and the imaging element 55 (the detector 85
Report) and the instantaneous relative position of the image data with a suitable laser exciter at a suitable time during the scanning of the imaging element 55. The conditioning circuitry required to supplement this scheme is known in the scanner and plotter art.

The laser output cable has a writing arrangement 6 for accurately focusing the light rays onto the surface of the imaging element 55.
It terminates in a lens assembly 96, which is preferably installed in 5. Suitable lens-assembly designs are described below, and for the purposes of the present discussion, these assemblies are generally designated by the reference numeral 96. A suitable configuration is shown in FIG. 3, in which the lens assemblies 96 are staggered across the face of the body 65.

The staggered lens design allows more lens assemblies to be used in a head than is possible with a linear arrangement. And since the image formation time depends directly on the number of lens elements, the staggered design also gives an overall image formation potential. The adjuster 80 advances column-wise the contents of a storage buffer containing a complete bitmapped representation of the image to be received or transferred in vertical columns, each corresponding to a different lens assembly. Alternatively, a sample can be collected. In either case, the adjuster 80 recognizes the different relative positions of the lens assembly with respect to the imaging element 55 and only when the associated lens assembly is over the point to be imaged is the appropriate laser. Operate.

Another sequence design is shown in FIG.
This also shows the detector 85 installed on the cylinder 50. In this case, the writing arrangement, indicated by reference numeral 150, comprises an elongated tubular body provided by a fiber optic cable drawn from bundle 77. Writing sequence 1
The interior of 50, or a portion thereof, contains threads that mate with lead screw 67, the rotation of which advances writing array 150 along imaging element 55 as discussed above. The individual lens assemblies 96 are uniformly separated from each other by a distance B. Distance B corresponds to the difference between the axial lengths of plate 55 as well as the distance between the first and last lens assemblies, which represents the total axial distance traveled by writing arrangement 150 during the entire scanning process. . Each time the writing array 150 encounters the blank portion 60, the stepper motor 72 rotates and the writing array 1
Advance 50 by an axial distance equal to the desired distance (ie print density) between imaging passes. This distance is smaller than the distance (writing array 65) indicated by the previous embodiment by a factor of n, where n is the number of lens assemblies included in the writing array 65.

B. Output (Guide and Lens Assembly) Suitable means for guiding the laser output to the surface of the imaging element is shown in FIGS. 5-7. Reference is first made to FIG. 5, which shows a remote laser assembly that uses a fiber-optic cable to deliver laser pulses to the imaging element. In this arrangement, the laser source 250 is installed at the rear of the housing 255. 2 on the front of the housing
One or more focusing lenses 260a, 26
0b are installed and they preferably (but not necessarily) remove the radiation emitted by the laser 250 by means of a detachable retaining cap 267 on the housing 255.
Focus on the end face of the fiber optic cable 265 secured within. Cable 265 is laser 250
To the output assembly 270, which is shown in more detail in FIG.

Referring to that figure, a fiber optic cable 265 enters the assembly 270 via a retaining cap 274 (preferably removable). Owned cap 2
74 fits on a generally tubular body 276 containing a series of threads 278. Two or more focusing lenses 280a, 280b are installed at the front of the body 276 and the cable 265 is carried part way through the body 276 by the sleeve 280. The body 276 defines a hollow groove between the inner lens 280b and the end of the sleeve 280 so that the end surface of the cable 265 extends a selected distance A from the inner lens 280b. Distance A
And the focal lengths of lenses 280a, 280b are selected so that the light rays emanating from cable 265 at the normal working distance from imaging element 55 are accurately focused on the imaging element surface. This distance can be varied to vary the dimensions of the image features.

The body 276 can be secured to the writing arrangement 65 in any suitable manner. In the embodiment shown, the nut 28
2 engages threads 278 and secures outer edge 284 of body 276 against the outer surface of writing array 65. The rim may optionally contain a transparent window 290 to protect the lens from possible damage.

Alternatively, the lens assembly is placed in a writing lens on a pivot that allows rotation in the axial direction (ie, in the direction of FIG. 6, the direction through the plane of the paper) for fine adjustment of the axial position. You may make it easier. If the rotation angle is kept at 4 ° or less, the circumferential error caused by rotation can be electronically corrected by moving the image data before it is transmitted to the adjuster 80.

Reference is now made to FIG. 7 which shows another design without transmission by a fiber optic cable in which a laser source illuminates the imaging element surface directly. As shown in the drawing, the laser source 250 is installed in the rear part of the release housing 300. Two or more focusing lenses 302a in the front of the housing 300,
302b are provided, which focus the radiation emitted by the laser 250 onto the surface of the imaging element 55. The housing may include a transparent window 305 and a heat sink 307, optionally with a flush at the open end.

C. Exciter Circuit A suitable circuit for exciting a diode-type (eg, gallium arsenide) laser is shown schematically in FIG. The operation of the circuit is a high speed, high current MOSFET exciter 325
Is controlled by a regulator 80 which produces a fixed pulse width signal (preferably a period of 5 to 20 μsec). The output terminal of the exciter 325 is connected to the gate of the MOSFET 327. The exciter 325 can supply a high output current to rapidly charge the MOSFET gate capacitance, so that the turn-on and turn-off times of the MOSFET 327 are very short (preferably within 0.5 μs) despite the capacitive load. ). MOSFE
The source terminal of T327 is connected to the ground potential.

When MOSFET 327 is placed in the conducting state, current flows through it and thereby activates the laser diode. Various current limiting resistors 332 are M
It is sandwiched between OSFET 327 and laser diode 330 to allow adjustment of the diode output. Such adjustments are useful, for example, to compensate for different diode efficiencies and produce the same output in all lasers in the system, or to vary the laser output as an image size adjustment means.

A capacitor 334 is placed across the terminals of the laser diode 330 to prevent damage to the current overshoot as a result of, for example, wire inductance combined with low laser-diode electrode capacitance.

The present invention is further illustrated by the following examples, but the invention is not limited thereto. All parts are by weight unless otherwise indicated.

[0071]

【Example】

Example 1 Preparation of a lithographic base An aluminum foil 0.2 mm thick was degreased by immersing the foil in an aqueous solution containing 5 g / l sodium hydroxide at 50 ° C. and rinsed with demineralized water. The foil was then subjected to an alternating current in an aqueous solution containing 4 g / l hydrochloric acid, 4 g / l hydroboric acid and 0.5 g / l aluminum ions at a temperature of 35 ° C. and 1200 A / m ² . electrochemically grained in current density to form a surface shape having a center line average roughness R _a of 0.5 [mu] m.

After rinsing with demineralised water, the aluminum foil was then etched with an aqueous solution containing 300 g / l sulfuric acid for 180 seconds at 60 ° C. and rinsed with demineralised water for 30 seconds at 25 ° C.

The foil is subsequently immersed in an aqueous solution containing 200 g / l sulfuric acid at a temperature of 45 ° C., a voltage of about 10 V and 1
Anodic oxidation at a current density of 50 A / m ² for about 300 seconds to form an anodized film of ₃ g / m ² Al ₂ O ₃ , then washed with demineralized water and containing 20 g / l sodium hydrogen carbonate The solution was worked up at 40 ° C. for 30 seconds and then 120 ° C. with demineralized water.
Rinsed and dried for seconds.

The lithographic base obtained was immersed in an aqueous solution containing 5% by weight of citric acid for 60 seconds, rinsed with demineralized water and dried at 40.degree.

Preparation of Imaging Element I (Material) The following Coating Composition 1 was prepared and coated on the lithographic base described above in an amount of 30 g / m ² (wet coating amount) and it was 35 ° C. Imaging element I according to the present invention was prepared by drying in.

Preparation of Coating Composition 1 Hostapal B (1% to polymer) stabilized 20% dispersion of demethylated polymethylmethacrylate (Tg 105 ° C.) (average particle diameter 90 nm) in deionized water 6. 75 g
To 7 g of 15% carbon black dispersion and 1 ml
Aqueous solution of wetting agent, 73 g of water are added successively, and finally 5% of 98% hydrolyzed polyvinyl acetate having a weight average molecular weight of 200.000 g / mol with stirring.
12% solution is added.

Preparation of Imaging Element II (Material) Imaging except that polymethylmethacrylate was replaced by a 16/84% copolymer of butyl acrylate-methylmethacrylate (Tg 84.2 ° C) in the coating solution. Imaging Element II according to the present invention was prepared in the same manner as Element I.

Preparation of Imaging Element III (Material) Imaging except that polymethylmethacrylate was replaced by a 28/72% copolymer of butyl acrylate-methylmethacrylate (Tg 61.5 ° C.) in the coating solution. Imaging Element III (Comparative Material) according to the present invention was prepared in the same manner as Element I.

Production of printing plates and printed copies Scanning Nd emitting these imaging elements at 1050 nm.
Targeted to a YLF infrared laser (scanning speed 4 m / sec on the surface of the imaging element, spot size 15 μm and 170 m
W horsepower).

The resulting image-wise exposed imaging element
VARN KOMPAC ^TM II ABDIC 3 with dampening system
Installed on 60 ^TM offset printing machine. Ag as ink
Available VanSon available from fa-Geveart NV
RB2329 ^TM to and dampening liquid as G671c ^TM (3% in water)
It was used.

After installation of the imaging element, the printing machine was started by rotating the printing cylinder on which the imaging element was installed. The dampening agent roller of the printer was dropped onto the imaging element to supply the dampening fluid to the imaging element and after 10 revolutions of the printing cylinder the ink roller was dropped to supply the ink. After a further 10 rotations, imaging element I gave a clear print with no ink uptake in the non-image areas. In the same step, Imaging Element II produced a print with very little smear in the non-image areas. In the same step, a completely dirty print was obtained with Imaging Element III. Even with 50 revolutions of the printing cylinder at each development stage, the lithographic printing plate was still completely soiled. There, imaging elements I and II (imaging elements according to the invention) having a hydrophobic thermoplastic polymer particle with a Tg of at least 80 ° C. gave excellent or acceptable lithographic plates after exposure and development, but at 80 ° C. Imaging element III (Comparative Imaging element) with the lower Tg hydrophobic thermoplastic polymer particles gave a completely soiled lithographic plate after exposure and development.

The main features and aspects of the present invention are as follows.

1. (1) (i) At least 8 dispersed in a hydrophilic binder on the hydrophilic surface of the lithographic base.
An imaging layer comprising hydrophobic thermoplastic polymer particles having a glass transition temperature Tg of 0 ° C., and (ii) being capable of converting light into heat contained in said imaging layer or its adjacent layers. Comprising imagewise exposing an imaging element comprising the compound (2) and developing the thus obtained imagewise exposed imaging element by rinsing with ordinary water or an aqueous liquid. Method of manufacturing a lithographic printing plate.

2. The compound capable of converting light into heat is selected from the group consisting of infrared absorbing dyes, carbon black, metal borides, metal carbides, metal nitrides, metal carbonitrides and conductive polymer particles. A method according to 1 above.

3. A method according to any of the above paragraphs wherein the image-wise exposure is carried out by a laser, an LED or a plurality of lasers.

4. A method according to any of the preceding clauses wherein the compound capable of converting light into heat is contained in the imaging layer.

5. A method according to any of the preceding paragraphs wherein the lithographic base is anodized aluminum or comprises a flexible support having a hydrophilic layer crosslinked thereon.

6. The thermoplastic polymer particles are at least 5
A method according to any of the preceding paragraphs having a freezing temperature of 0 ° C.

7. The hydrophilic binder in the image forming layer is polyvinyl alcohol, poly (meth) acrylic acid, poly (meth)
The method according to any one of the above items selected from the group consisting of acrylamide, hydroxyethyl poly (meth) acrylate, polyvinyl methyl ether, and polysaccharide.

8. The hydrophobic thermoplastic polymer particles are selected from the group consisting of polystyrene, polyvinyl chloride, polymethylmethacrylate, polyvinylidene chloride, polyacrylonitrile, polyvinylcarbazole or copolymers and / or mixtures thereof. A method according to any of the above paragraphs.

[Brief description of the drawings]

1 is a cylindrical state-like isometric view of an imaging device suitable for use in accordance with the present invention, which operates in conjunction with a diagonal-array writing array.

FIG. 2 is a process diagram of the embodiment shown in FIG. 1 and its operating mechanism is shown in further detail.

FIG. 3 is a front end view of a writing array for imaging in accordance with the present invention, where the imaging elements are arranged in a diagonal array.

FIG. 4 is a cylindrical state-like isometric view of an imaging device suitable for use in accordance with the present invention, which operates in conjunction with a linear-array writing array.

FIG. 5 is a cross-sectional view of a remote laser and beam-guiding system.

FIG. 6 is a magnified partial cross-sectional view of a lens element for focusing laser light from an optical fiber onto the surface of the imaging element.

FIG. 7 is an enlarged partial cross-sectional view of a lens element having a constituent laser.

FIG. 8 is a schematic circuit diagram of a laser-exciter circuit suitable for use with the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location G03F 7/038 G03F 7/038 7/30 7/30

Claims (1)

[Claims] 1. (1) (i) At least 80 dispersed in a hydrophilic binder on the hydrophilic surface of the lithographic base.
An imaging layer comprising hydrophobic thermoplastic polymer particles having a glass transition temperature Tg of ° C, and (ii) being capable of converting light into heat contained in said imaging layer or adjacent layers thereof. A lithographic plate comprising the steps of image-wise exposing an image-forming element comprising a compound, and (2) developing the image-wise exposed image-forming element thus obtained by rinsing with ordinary water or an aqueous liquid. Printing plate manufacturing method.