JP2983477B2 - Method for producing a lithographic printing plate including on-press development - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a lithographic printing plate. More particularly, the present invention relates to a method by which a lithographic printing plate can be developed with ordinary water or aqueous liquid.

[0002]

BACKGROUND OF THE INVENTION A lithographic process is a method of printing from a specially prepared surface such that some portions of the surface are capable of receiving lithographic ink while others are not receptive to ink when wetted with water. . The ink-receiving portions form the printed image portions and the ink-reject portions form the background portions.

In the photolithographic technique, photographic materials are image-wise against oily or greasy inks in exposed (negative-working) and unexposed (positive-working) areas on a hydrophilic background. Made receptive to

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

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

[0006] Commercially available diazo-based printing plates most commonly use anodized and roughened aluminum as a support with a hydrophilic surface. However, commercial versions are also available that use a flexible support, such as a paper provided with a hydrophilic layer. For example, Lithocraft 10008 FOTOPLATE ^™ is a diazo-based printing plate comprising a paper support having a hydrophilic layer provided with a diazo-based photosensitive layer on top. According to the supplier's instructions for the plate, the lithographic printing plate precursor or image-forming element is image-wise exposed, the exposed image-forming element is placed on a printing press and its surface is exposed to Lithocraft 10008.
A plate can be produced by wiping with a development desensitizer. The plate instructions also contemplate methods that do not use development desensitizers. In practice, however, development desensitizers are almost always required, since such methods very often lead to poor lithographic performance.

A particular disadvantage of the above-described photosensitive imaging elements for producing printing plates is that they must be shielded from light. This is due to the on-press development, since the installation of the image-wise exposed imaging element is generally performed in normal sunlight, which limits the handling time required for the installation of the imaging element. This is particularly a drawback when intentional. Furthermore, diazo-based aluminum type printing plates are completely unsuitable for on-press development.

[0008] On the other hand, methods involving the use of imaging elements that are heat-sensitive rather than light-sensitive are known for making printing plates. For example, Research Diet in January 1992
Sclosure no. 33303 discloses a heat-sensitive imaging element comprising a support and a cross-linked hydrophilic layer containing thermoplastic polymer particles and an infrared-absorbing pigment such as, for example, 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 portions ink-receiving without further development. A disadvantage of this method is that when a certain amount of pressure is applied to the non-printing parts, the resulting printing plate is easily damaged since the parts can become ink-receptive. Furthermore, under critical conditions, the lithographic performance of such printing plates is poor and consequently such printing plates have little lithographic tolerance.

[0009]

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

Other objects of the present invention will become clear from the description hereinafter.

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

The present invention further provides (1) (i) hydrophobic thermoplastic polymer particles having a glass transition temperature Tg of at least 80 ° C., dispersed in a hydrophilic binder, on a lithographic base hydrophilic surface. an image forming layer comprising comprise, and image-wise exposed imaging element comprising a compound capable of conversion to (ii) Ru contained in said image forming layer or a layer adjacent thereto, a light into heat, ( 2) placing the image-wise exposed imaging element thus obtained without development on a printing cylinder of a printing machine; (3) supplying an aqueous dampening solution to the imaging layer of the imaging element; while supplying / or ink by rotating the printing cylinder, and (4) providing a work Seisuru method multiple copies of the original image ink comprising the step of transferring the receiving element from said imaging element.

The present invention further provides: (1) (i) hydrophobic thermoplastic polymer particles 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, (ii) Ru contained in said image forming layer or a layer adjacent thereto, a light onto printing cylinder of an imaging element comprising a compound capable of converting into heat press (2) exposing the imaging element image-wise with a laser or LED, (3) and supplying an aqueous dampening solution and / or ink to the imaging layer while rotating the printing cylinder. Developing a lithographic printing plate comprising developing the image-wise exposed imaging element thus obtained.

The present invention further provides (1) (i) hydrophobic thermoplastic polymer particles having a glass transition temperature Tg of at least 80 ° C., dispersed in a hydrophilic binder, on a lithographic base hydrophilic surface. an image forming layer comprising, (ii) Ru contained in said image forming layer or a layer adjacent thereto, a light onto printing cylinder of an imaging element comprising a compound capable of converting into heat press (2) exposing the imaging element image-wise with a laser or LED, (3) and supplying an aqueous dampening solution and / or ink to the imaging layer while rotating the printing cylinder. the imaging element thus imagewise resulting exposed and developed, discloses (4) create a plurality of copies of the ink from the original comprising the step of transferring the receiving element from said imaging element Seisuru method.

The invention also provides (i) a printing cylinder; means for mounting an imaging element on the printing cylinder; at least one laser or LED device; Means for guiding the output of the D.D. device to focus on the imaging element surface;-moving the guiding means and the support means relative to one another to form the image by the output of the laser or the L.D.D. At least one printing station including means for performing a scan of the element surface; (ii) means for supplying a fountain solution 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, and (v) means for transferring ink from the printing cylinder to the receiving element.

In yet another aspect, the invention relates to (1) (i) a hydrophobic thermoplastic having a glass transition temperature Tg of at least 80 ° C., dispersed in a hydrophilic binder, on a lithographic base hydrophilic surface. an image forming layer comprising polymer particles, (ii) Ru contained in said image forming layer or a layer adjacent thereto, the optical imaging element comprising a compound capable of converting into heat image-wise Exposing and (2) developing the lithographic printing plate comprising developing the image-wise exposed imaging element thus obtained by rinsing with an ordinary water or aqueous liquid.

The present invention will be described with reference 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, on a hydrophilic surface of a lithographic base, a hydrophobic thermostat having a glass transition temperature Tg of at least 80 ° C. dispersed in a hydrophilic binder. An imaging layer comprising the plastic polymer particles. The hydrophilic binder used in connection with the present invention is preferably uncrosslinked or only slightly crosslinked. The imaging element also includes a compound that can convert light to heat. The compound is preferably included 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 granulated and anodized aluminum support. According to the present invention, the anodized aluminum support may be treated to improve the hydrophilic properties of its surface. For example, the aluminum 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 performed alone or in combination.

According to another aspect of the present 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 the hydrophilic binder, hydrophilic (co) polymers such as vinyl alcohol, acrylamide, methylolacrylamide, methylolmethacrylamide,
Homopolymers and copolymers of acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate or maleic anhydride / vinyl methyl ether copolymer can be used. The (co) polymer or (co) polymer mixture used preferably has a hydrophilicity of at least 60.
By weight, preferably equal to or higher than the hydrophilicity of the hydrolyzed polyvinyl acetate to the extent of 80% by weight.

The amount of crosslinking agent, in particular tetraalkyl orthosilicate, is at least 0.2 part by weight, preferably between 0.5 and 5 parts by weight, more preferably 1 part by weight, per part by weight of hydrophilic binder. 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 increase the mechanical strength and the porosity of the layer. Colloidal silica can be used for this purpose. The colloidal silica used is for example up to 40 nm, for example 20 nm
May be in the form of a commercially available water-dispersion of colloidal silica having an average particle size. In addition, inert particles larger in size than colloidal silica, such as J.
Colloid and Interface Sci., Vol. 26, 1968, pages 6
It is also possible to add particles having an average 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. By adding these particles,
The surface of the cross-linked hydrophilic layer is provided with a uniform, rough texture of microscopic asperities, which serve as storage 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.

Particular examples of cross-linked hydrophilic layers suitable for use according to the invention are EP-A 601 240, GB-
P-1419512, FR-P-2300354, US
-P-397660, US-P-4284705 and EP-A 514490.

As a lithographic base flexible support for this embodiment, it is particularly preferred to use plastic films, for example polyethylene terephthalate films, cellulose acetate films, polystyrene films, polycarbonate films, etc. as substrates. 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, a hydrophilic binder 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 present 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 image forming layer. The imaging layer according to the present invention comprises thermoplastic polymer particles dispersed in a hydrophilic binder.

Suitable hydrophilic binders for use in the imaging layer according to the present 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,
Pullulan, cellulose, gum arabic, alginic acid.

[0030] 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.

[0031] The hydrophobic thermoplastic polymer particles used in connection with the present invention preferably have a solidification temperature above 50 ° C, or more preferably above 70 ° C. Solidification may result from the softening or melting of the thermoplastic polymer particles under the influence of heat. There is no particular upper limit on the solidification 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 a hydrophobic agglomerate in the hydrophilic layer, so that in these parts the hydrophilic layer is Insoluble in

Specific examples of hydrophobic polymer particles for use in connection with the present invention include, for example, polystyrene, polyvinyl chloride, polymethyl methacrylate, polyvinylidene chloride,
Polyacrylonitrile, polyvinyl carbazole and the like, or copolymers and / or mixtures thereof.
Polymethyl methacrylate is most preferably used.

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

The hydrophobic particles are 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 solution of the imaging layer and are disclosed in US Pat.
It can be produced by the method disclosed in 476.937. Other methods particularly suitable for preparing aqueous dispersions of thermoplastic polymer particles include: dissolving a hydrophobic thermoplastic polymer in an organic, water-immiscible solvent; and dissolving the resulting solution in water or aqueous. 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 the absorption wavelength is limited 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 structurally related to, for example, dyes and especially infrared dyes, carbon blacks, metal carbides, borides, nitrides, carbonitrides, bronze-structured oxides and the bronze family, but the A component. For example, an oxide containing no WO _2.9 . Conductive polymer dispersions, such as those based on polypyrrole or polyaniline, can also be used. 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 conversion compound according to the invention is most preferably added to the imaging layer, but at least a portion of the light-to-heat conversion compound may be contained in a nearby layer. . Such a layer may be, for example, a lithographic base cross-linked hydrophilic layer 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 press is then started and the dampener roller supplying the dampening solution is dropped onto the imaging element while rotating the printing cylinder on which the imaging element is mounted, and then Drop the ink roller on it. Generally, after about 10 rotations of the printing cylinder, the first clean and useful prints are obtained.

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

Suitable fountain solutions that can be used in connection with the present invention are generally aqueous solutions having an acidic pH and comprising an alcohol such as, for example, isopropanol. There is no particular restriction 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 soak, for example with a cotton pad or sponge, before placing it 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 contamination which may occur of the dampening system of the printing press and of the ink used is avoided.

According to another method, the imaging element is first placed on the printing cylinder of a 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 present invention, the imaging element can be developed by exposing it image-wise and then rinsing it with ordinary water.

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

The image-wise exposure according to the present invention is preferably an image-wise scanning exposure involving the use of a laser or LED. For the present invention it emits in the infrared (IR) and / or near infrared region, ie 700-1500 nm
It is highly preferred to use a laser that emits in the wavelength range of Laser diodes emitting in the near infrared range are particularly preferred for use in connection 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 light-guiding components or at a remote location using fiber optic cables. Includes laser power that can be transmitted from one laser to the surface of the blank imaging element. An adjuster and associated positioning hardware keep the beam output in the correct orientation with respect to the imaging element surface,
The output is scanned over 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 corresponding to the original document and / or picture to be copied to form an accurate negative or positive image of the original. These image signals are stored in a computer as a bitmap data file. Such a file may be created by a laser image processor (RIP) or other suitable means. For example, a RIP can accept input data in a page-description language or as a combination of a page-description language and one or more image data files that define all the features required to be transferred onto an imaging element. A bitmap is created to define the tone and screen frequency and angle in the case of amplification adjustment screening. However, the present invention provides, for example, EP-A
571010, EP-A 620677 and EP-A
Particularly suitable for use in combination with the frequency-adjusted screening disclosed in US Pat.

The imaging device can operate itself to function only as a plate making machine, or can be added directly into a lithographic printing press having means for supplying a dampening solution. In the latter case, printing may start immediately after image-wise exposure and development, thereby significantly reducing press set-up time. The image forming device can be configured as a flatbed recorder or as a drum recorder having a lithographic blank located on the inner and outer cylindrical surfaces of the drum. Obviously, an external drum design is more suitable for use on a lithographic printing press in situ, in which case the printing cylinder itself constitutes the drum part of the recorder or plotter.

In a preferred drum configuration, the drum (and the imaging element mounted thereon) is rotated about its axis and a light beam parallel to the axis of rotation is moved, thereby moving the imaging element circumferentially. To "grow" the image in the axial direction to provide the necessary relative motion between the laser beam and the imaging element. Alternatively, the beam may be moved parallel to the drum axis and the image may be "grown" circumferentially on the imaging element at increasing angles after each pass over the imaging element. In both cases, after complete scanning and development by the light beam, an image corresponding to the original will have been applied to the surface of the imaging element. In 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 necessary relative movement between the light beam and the imaging element may be caused by the movement of the imaging element rather than (or in addition to) the movement of the light beam.

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

The preferred embodiments of the image forming apparatus suitable for use in connection with the present invention are described in further detail below.

A. 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 comprises 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 common pinching means (not shown). The size of the blank portion can vary greatly depending on the environment in which the cylinder 50 is used.

Desirably, the cylinder 50 is added directly into the general lithographic printing press design having means for supplying a fountain solution to the imaging element and functions as a printing cylinder for the printing press. In a typical printing press configuration, the imaging element 55 receives ink and dampening fluid from an ink train and a series of dampening cylinders, respectively.
The terminal 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, typically a sheet of paper. The printing press can have more than one such printing assembly arranged in a linear array. Alternatively, a plurality of assemblies may be rotationally meshed with all the blanket cylinders around a large central impression cylinder.

The cylinder 50 is supported in a frame and rotates by a standard electric motor or other common means (shown schematically in FIG. 2). Cylinder 5
The angular position of 0 is monitored by the axis encoder (FIG. 4).
checking). A writing arrangement 65 mounted for movement on a lead screw 67 and guide rod 69 traverses the imaging element 55 as it rotates. The axial movement of the writing array 65 results from the rotation of the stepper motor, which
7 and thereby move the axial position of the writing arrangement 65. The stepper motor 72 will operate during the time that the writing array 65 is located above the blank 60 after the writing array 65 has passed over the entire surface of the imaging element 55. The rotation of the stepper motor 72 moves the writing array 65 to the appropriate axial position and begins 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 it, and by the desired resolution. As shown in FIG. 2, a series of laser sources L1, L2, L that are excited by a suitable laser exciter, indicated generally by reference numeral 75.
3,... Ln provide their respective outputs to the 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 bundles 77 and separately added to writing array 65. In order to maintain 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 maintain total internal reflection).

As also shown in FIG. 2, the regulator 80 activates the laser exciter 75 when the relevant laser reaches a suitable point opposite the imaging element, and furthermore the stopper motor 72 and the cylinder The drive motor 82 is operated.

Controller 80 receives data from two sources. The angular position of the cylinder 50 with respect to the writing arrangement 65 is constantly monitored by a detector 85, which provides a signal to the regulator 80 indicative of that position. Further, an image data source (eg, a computer) also provides a data signal to the controller 80. The image data defines the point on the imaging element 55 where the image point is to be written. Accordingly, controller 80 includes writing arrangement 65 and imaging element 55 (detector 85).
The appropriate laser exciter is activated at the appropriate time during the scanning of the imaging element 55, in correlation with the instantaneous relative position of the image forming element 55 and the image data. The necessary adjustment circuits to supplement this scheme are known in the scanner and plotter art.

The laser output cable provides a writing arrangement 6 for focusing the light beam exactly on the surface of the imaging element 55.
5 terminates in a lens assembly 96 suitably located within. Suitable lens-assembly designs are described below, and for the purposes of the present discussion, these assemblies are generally indicated by reference numeral 96. A suitable configuration is shown in FIG. 3, in which the lens assemblies 96 are staggered beyond the plane of the body 65.

The staggered lens design allows more lens assemblies to be used in one head than is possible with a linear arrangement. And since the imaging time is directly dependent on the number of lens elements, the staggered design also offers the possibility of enhancing the overall imaging. Conditioner 80 receives the image data already located in the vertical columns, each corresponding to a different lens assembly, or progressively advances the contents of a storage buffer containing a complete bitmap representation of the image to be transferred in a columnar manner. It is also possible to collect samples. In each case, the adjuster 80 recognizes the different relative positions of the lens assembly with respect to the imaging element 55 and will only provide the appropriate laser when the associated lens assembly is located above the point to be imaged. Activate

Another sequence design is shown in FIG.
This also shows the detector 85 installed on the cylinder 50. In this case, the writing arrangement designated by reference numeral 150 comprises a long tubular body supplied by a fiber optic cable drawn from bundle 77. Writing arrangement 1
The interior of 50 or a portion thereof contains threads that mesh with a lead screw 67, the rotation of which advances writing arrangement 150 along imaging element 55 as discussed above. The individual lens assemblies 96 are evenly 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 arrangement 150 encounters a blank 60, the stepper motor 72 rotates and the writing arrangement 1
Advance 50 by an axial distance equal to the desired distance between imaging passes (ie, print density). This distance is smaller than the distance shown by the previous embodiment (writing array 65) by a factor of n, where n is the number of lens assemblies included in writing array 65.

B. Output (Guiding and Lens Assembly) Suitable means for guiding the laser output to the surface of the imaging element are shown in FIGS. 5-7. First, reference is made to FIG. 5, which illustrates a remote laser assembly that uses fiber-optic cables to deliver laser pulses to an imaging element. In this arrangement, the laser source 250 is located at the rear of the housing 255. 2 at the front of the housing
One or more focusing lenses 260a, 26
0b are installed, which preferably (but not necessarily) remove the radiation emitted from the laser 250 by means of a removable holding cap 267 to the housing 255.
Focus on the end face of 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 the figure, fiber optic cable 265 enters assembly 270 via retaining cap 274 (preferably removable). Holding 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 halfway through the body 276 by the sleeve 280. Body 276 defines a hollow groove between inner lens 280b and the end of sleeve 280, so that the end surface of cable 265 extends a selected distance A from inner lens 280b. Distance A
And the focal lengths of the lenses 280a, 280b are selected so that light rays generated from the cable 265 at a normal working distance from the imaging element 55 are accurately focused on the imaging element surface. By varying this distance, the dimensions of the image features can be varied.

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 damage that may occur.

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

Reference is now made to FIG. 7, which shows another design without transmission by a fiber optic cable in which the laser source illuminates the imaging element surface directly. As shown, the laser source 250 is located in the rear of the release housing 300. Within the front of the housing 300 are two or more focusing lenses 302a,
302 b are provided, which focus the radiation generated by the laser 250 on the surface of the imaging element 55. The housing may optionally include a transparent window 305 and a heat sink 307 with a flash installed 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 governed by a regulator 80 which generates a signal of fixed pulse width (preferably for a period of 5-20 .mu.sec). 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 despite the capacitive load (preferably within 0.5 microseconds). ). MOSFE
The source terminal of T327 is connected to ground potential.

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

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

The present invention will be further described by the following examples, which should not be construed as limiting the invention thereto. All parts are by weight unless otherwise indicated.

[0071]

【Example】

Example 1 Preparation of a lithographic base Aluminum foil 0.2 mm thick was degreased by immersion at 50 ° C. in an aqueous solution containing 5 g / l of sodium hydroxide and rinsed with demineralized water. The foil is then heated using 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 demineralized water, the aluminum foil was then etched with an aqueous solution containing 300 g / l sulfuric acid at 60 ° C. for 180 seconds and rinsed with demineralized water at 25 ° C. for 30 seconds.

The foil is subsequently immersed in an aqueous solution containing 200 g / l of sulfuric acid at a temperature of 45 ° C., a voltage of about 10 V and
Anodizing 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 washing with demineralized water and containing 20 g / l sodium bicarbonate The solution was worked up at 40 ° C. for 30 seconds, followed by 120 ° C.
Rinsed for seconds and dried.

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 ° C.

Preparation of Imaging Element I (Material) The following coating composition 1 was prepared and it was coated on the above lithographic base in an amount of 30 g / m ² (wet coating amount) and it was coated at 35 ° C. To produce an imaging element I according to the invention.

Preparation of Coating Composition 1 20% dispersion of depolymerized polymethyl methacrylate (Tg 105 ° C.) (Tg 105 ° C.) (average particle diameter of 90 nm) in deionized water stabilized with Hostapal B (1% based on polymer) 75g
Into, 7 g of a 15% dispersion of carbon black and 1 ml
Aqueous humectant, 73 g of water are added continuously and finally with stirring 5% of 98% hydrolyzed polyvinyl acetate having a weight average molecular weight of 200.000 g / mol.
12 g of a 1% solution are added.

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

Preparation of Imaging Element III (Material) Imaging except that polymethyl methacrylate was replaced in the coating solution by a 28/72% copolymer of butyl acrylate-methyl methacrylate (Tg 61.5 ° C.). An imaging element III according to the invention (comparative material) was prepared in the same manner as element I.

Production of Printing Plates and Print Copies Scanning Nd emitting these imaging elements at 1050 nm
Illuminated by a YLF infrared laser (scanning speed 4 m / s on the imaging element surface, spot size 15 μm and 170 m
W horsepower).

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

After installation of the imaging element, the printing press was started by rotating the printing cylinder on which the imaging element was mounted. The dampener roller of the printing press was dropped onto the imaging element to supply the dampening liquid to the imaging element and the ink roller was dropped after 10 rotations of the printing cylinder to supply ink. After a further 10 revolutions, imaging element I gave a clear print without ink absorption in the non-image areas. In the same step, imaging element II resulted in a very slight smeared print in the non-image areas. In the same step, a completely soiled print was obtained with imaging element III. Even by rotating the printing cylinder 50 times at each development stage, the lithographic printing plate was still completely soiled. Thus, imaging elements I and II having hydrophobic thermoplastic polymer particles having a Tg of at least 80 ° C. (imaging elements according to the invention) 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) On the hydrophilic surface of the lithographic base, at least 8 dispersed in a hydrophilic binder
An imaging layer comprising hydrophobic thermoplastic polymer particles having a glass transition temperature Tg of 0 ° C .; and (ii) capable of converting light to heat and contained in said imaging layer or an adjacent layer thereof. Exposing the image-forming element comprising the compound described above, and (2) and developing the image-wise exposed image-forming element thus obtained by rinsing with ordinary water or an aqueous liquid. Manufacturing method of 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 preceding clauses, wherein the image-wise exposure is performed with a laser, LED or a plurality of lasers.

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

5. A method according to any of the preceding clauses, wherein the lithographic base is anodized aluminum (anodised) or comprises a flexible support having a hydrophilic layer cross-linked thereon.

6. The thermoplastic polymer particles have at least 5
A method according to any of the preceding clauses having a solidification temperature of 0 ° C.

7. When 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, polymethyl methacrylate, polyvinylidene chloride, polyacrylonitrile, polyvinyl carbazole or copolymers and / or mixtures thereof. A method according to any of the preceding clauses.

[Brief description of the drawings]

FIG. 1 is a cylindrical-like isometric view of an imaging device suitable for use in accordance with the present invention, and 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 a more detailed view.

FIG. 3 is a front end view of an imaging writing arrangement according to the present invention, wherein the imaging elements are arranged in an oblique arrangement.

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

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

FIG. 6 is an enlarged partial cross-sectional view of a lens element for focusing a laser beam from an optical fiber onto a surface of an 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 in the present invention.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-8875 (JP, A) JP-A-9-90611 (JP, A) JP-A-8-108661 (JP, A) JP-A-7- 1850 (JP, A) JP-A-5-58071 (JP, A) JP-A-5-24374 (JP, A) JP-A-3-197191 (JP, A) JP-A-62-164049 (JP, A) JP-A-53-17408 (JP, A) JP-A-2-115462 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) B41N 1/14 B41C 1/10

Claims (1)

(57) [Claims] 1. (1) (i) on a hydrophilic surface of a lithographic base, at least 80 dispersed in a hydrophilic binder;
℃ and imaging layer comprising hydrophobic thermoplastic polymer particles having a glass transition temperature Tg of, (ii) said image forming layer or a Ru contained in a layer adjacent thereto, a compound capable of light converted into heat
Exposing an imaging element comprising a preparative imagewise lithographic comprising the step of developing by rinsing (2) and thus the image imaging element is exposed as obtained with plain water or an aqueous liquid Printing plate manufacturing method.