JP2000247053A - Dry method for preparing thermal lithographic printing plate precursor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make adapted to preparation of a printing master for normally lithographic printing by using a direct press plate process, a direct printing method or an on-press coating method and capable of needing no treatment or treating with fresh water and exposing by using an inner drum and an external drum image setter. SOLUTION: The thermal lithographic printing plate precursor comprises the step of applying dry powder containing at least one compound for converting a light into a heat and an organic compound to a surface of a non-charging metal support in such a manner that an amount of the organic compound in the powder is in a range of 51 to 91 wt.%. Thus, a negatively operable non- ablative image forming material adapted to manufacture of a lithographic printing plate can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a direct printing plate (compute).
er-to-plate) and direct printing (com
The present invention relates to a method for producing a heat mode lithographic printing plate precursor and a lithographic printing master by a putter-to-press method.

[0002]

BACKGROUND OF THE INVENTION Rotary printing presses use a so-called master, such as a printing plate, mounted on the cylinder of the printing press. The master has an image bounded by the ink-receiving area of the printing surface, and the print is obtained by applying ink to the surface and then transferring the ink from the master onto a substrate, typically a paper substrate. Can be In normal lithographic printing, ink and an aqueous dampening solution are supplied to the printing surface of the master, which is referred to herein as the lithographic printing surface (lit).
It is called a holographic surface and is composed of a lipophilic (or hydrophobic, ie, ink receptive, water repellent) region and a hydrophilic (or oleophobic, ie, water receptive, ink repellent) region.

[0003] Print masters are generally referred to as computer-to-film methods.
-Film method, in which the typeface selection is performed.
n), scanning, color separation, screening, trapping,
Various prepress steps such as layout and imposition are performed digitally, and each color selection is transferred to a graphic arts film using an imagesetter. After processing, the film can be used as a mask for exposure of an imaging material, called a plate precursor, to give a printing plate that can be used as a master after processing the plate.

In recent years, the so-called direct printing method (com)
The puter-to-plate method has gained much interest. Direct printing method (direct-
This method, also referred to as to-plate method, bypasses the production of the film because the digital document is transferred directly to the plate precursor using a so-called platesetter. The following improvements are currently being studied in the field of such direct printing: (i) on-press im.
aging). A special type of direct printing method involves exposing the plate precursor using an image setter built into the press while mounted on the plate cylinder of the press. This method can be called "direct printing",
Printing presses with an integrated image setter are sometimes referred to as digital printing presses. For an overview of digital printing presses, see Proceedings of the Image.
ing Science & Technology '
s 1997 International Conf
erence on Digital Printin
g Technologies (Non-Impact
Printing 13). The direct printing method is described in, for example, EP-A 770 495, EP
-A 770 496, WO 94001280, EP
-A 580 394 and EP-A 774 364. The most known imaging methods are based on ablation. A problem associated with ablative plates is the generation of debris that is difficult to remove and can disrupt the printing process or contaminate the exposed optics of the incorporated imagesetter. Other methods require treatment with chemicals, which can damage printing press electronics and other equipment. (Ii) On-press coating
coating). Plate precursors usually consist of a sheet-like support and one or more functional coatings, but are coated with a composition capable of forming a lithographic printing surface when exposed imagewise and optionally processed to form a lithographic printing surface. A direct printing method, which is applied directly on the surface of a sheet, is described.
EP-A 101 266 describes the direct coating of a hydrophobic layer on the hydrophilic surface of a plate cylinder. The master is obtained after removing the non-printed areas by ablation. However, as discussed above, direct printing requires that ablation be avoided. US-P 5,
No. 713,287 describes a direct printing method in which a so-called switchable polymer such as tetrahydro-pyranylmethyl methacrylate is applied directly on the surface of the plate cylinder. The switchable polymer is converted from an initial water-sensitivity to an opposite water-sensitivity by image-wise exposure.
The latter method requires a curing step and the polymer is very expensive because it is thermally unstable and therefore difficult to synthesize. EP-A 802 457 describes a hybrid method in which a functional coating is provided on a plate support mounted on the cylinder of a printing press. This method also requires processing. A major problem associated with the known on-press coating method is the need for a wet coating device, which must be incorporated into the printing press. (Iii) elimination of chemical treatment. The development of functional coatings that do not require treatment or can be treated with fresh water is another major trend in plate making. WO 90002
044, WO 91008108 and EP-A 580
Although 394 discloses such a plate, it is all an ablative plate. Furthermore, these methods typically require multilayer materials, which makes the method less suitable for on-press coating. Non-ablationable plates that can be treated with fresh water are, for example, EP-A 770 497 and EP-A
773112. Such plates also allow for on-press processing by wiping the exposed plate with water while mounted on a printing press or by a dampening solution during the first step of the printing operation. ing. (Iv) Thermal imaging
g). Most of the direct printing methods mentioned above use so-called thermal materials, i.e. plate precursors or on-press coatable compositions containing compounds that convert absorbed light into heat. The heat generated upon image-wise exposure initiates (physical-) chemical processes such as ablation, polymerization, insolubilization by polymer crosslinking, decomposition or coagulation of particles of the thermoplastic polymer latex. This heat mode process then produces a lithographic printing surface consisting of ink receptive and ink repellent areas.

[0005] EP-A-786 337 discloses a method for imaging a printing plate in which the printing plate is charged over the entire surface and the entire surface is covered with oppositely charged toner particles. On top of that there is a layer formed by particles which are fixed image-wise or image-ablated by infrared exposure on the surface of the printing plate. The unfixed portions are then removed, and the non-ablated areas are optionally fixed by heating over the surface of the plate. This method requires cumbersome development.

A problem associated with most thermal materials disclosed in the prior art is that these materials may have an internal drum imagesetter (ie, typically high power short exposure) or an external drum imagesetter (ie, relatively low power). Long exposure). Providing a universal material that can be exposed with satisfactory results in both of these types of laser devices known in the art is a difficult requirement to meet.

[0007]

OBJECTS OF THE INVENTION It is an object of the present invention to prepare a printing master for normal lithographic printing by using a direct printing method, a direct printing method or an on-press coating method, which requires processing. It is to provide a cost-effective method for producing a material that can be processed with or without fresh water. Another object of the invention is to provide a method for the production of universal materials that can be exposed using internal as well as external drum imagesetters.

[0008] Further advantages of the present invention will become clear from the description hereinafter.

[0009]

SUMMARY OF THE INVENTION According to the present invention, the method comprises applying a dry powder containing at least one compound capable of converting light to heat and an organic compound to the surface of a non-charged metal support. A method for producing a negative-working non-ablationable imaging material suitable for preparing a lithographic printing plate, characterized in that the amount of the organic compound therein is in the range of 51 to 95% by weight.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The organic compound is present in the powder in an amount of at least 51%. The organic compound is preferably thermoplastic polymer particles, more preferably 0.02
μm to 10 μm, most preferably 0.050 μm to 2 μm
m. Preferred thermoplastic polymers are novolaks, polystyrenes or polyacrylates, used alone or in admixture with one or two of the other components. Preferably, the thermoplastic polymer particles contain a reactive compound inside or outside of these particles. Particles containing the reactive compound inside the particles are produced according to well-known methods for the production of microcapsules or by adding the reactive compound in a water-immiscible solvent to the particles dispersed in water. Particles containing the reactive compound outside of the particles are prepared according to well known methods of loading latex as described in EP-A-483 416. Reactive compounds are compounds that can cause crosslinking. Preferred reactive compounds are melamine resins, urethanes, phenol-formaldehyde resins and epoxy compounds.

The compound capable of converting light into heat is preferably an organic dye or pigment, carbon black, graphite, metal carbide, boride, nitride, carbonitride or oxide.

The materials produced by the method of the present invention are preferably sensitive to near infrared light. Thus, the compound capable of converting light to heat is preferably a near-infrared absorbing compound, such as carbon or an infrared dye. For example, it is also possible to use dry finely divided polymer particles comprising a polymer based on polypyrrole or polyaniline. The infrared dyes listed in Table 1 are very preferred.

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

[Table 3]

[0016]

[Table 4]

The amount of the compound capable of converting light into heat is 5 to 49% by weight, more preferably 10 to 49% by weight of the dry powder.
Within the range.

The compound capable of converting light to heat can also be introduced into or adsorbed on or admixed with the polymeric particles, or be mixed heterogeneously with the organic compound.

The materials produced by the method of the present invention require no treatment or can be treated with fresh water. Since the method of the present invention is a dry coating method, it is very suitable for use in direct printing and an on-press coating method.

[0020] The imaging mechanism of the material produced according to the present invention is unknown, but may rely on the thermal interaction between the light absorbing compound and the metal support.

The features of the invention as defined in the claims should be understood as set forth below. As used herein, the term "image" is used within lithographic printing, i.e., "a pattern consisting of lipophilic and hydrophilic regions". The material produced according to the invention is negative-working, which means that the areas exposed to light are made lipophilic and thus ink-receptive due to said exposure. Within the scope of the present invention, the feature "negative acting" refers to "non-ablation" (non-ablatable).
iv), which can be considered as equivalent to the feature that, in an ablative material, the functional layer is completely removed from the underlying (hydrophilic) metal support when exposed image-wise to a positive image (exposed area). Is hydrophilicity and ink repellency). Analysis of the exposed areas of the material produced according to the method of the present invention shows that, in fact, when exposed imagewise, the layer or stack of layers is not removed and is converted to a hydrophobic surface on the metal support. Was. The unexposed areas are hydrophilic or become hydrophilic after treatment with fresh water.

The dry powder used in the present invention further comprises:
Non-reactive compounds can be included, ie, inert ingredients such as matting agents or fillers. The term "inert" is not to be understood in the sense of "non-functional", because it means that the surface roughness and the coefficient of friction of the applied layer or certain physical properties such as the rheological properties of the powder This is because these inert compounds can be added to the powder in order to adjust the viscosity. Although the term "inert" is to be understood rather as meaning "not essential to the imaging process", some inert compounds can have a (small) effect on the sensitivity and image quality of the material.

While a stack of layers can be applied on a metal support using the method of the present invention, a single layer is preferred. The compound capable of converting light to heat can be present in all layers of the stack or can be one of the stacks.
It can be localized only in one layer. In the case of the method according to the latter embodiment, the layer comprising the compound capable of converting light to heat is preferably applied directly on the metal support. The layer containing the compound capable of converting light to heat is preferably very thin, ie has a dry layer thickness of less than 2 μm, preferably 1 μm or less.

The support used in the present invention is a non-charged metal support. Preferred examples of such metal supports are steel, especially polished stainless steel and aluminum. Phosphor bronze (an alloy containing> 90% by weight of copper, <10% by weight of tin and a small amount of phosphorus) can also be used. The aluminum support is preferably an electrochemically polished and anodized aluminum support. Most preferably, the aluminum support is polished in nitric acid to provide an imaging element with higher sensitivity. The anodized aluminum support can be treated to increase its surface hydrophilicity. For example, an aluminum support, for example, 95
Silicification can be achieved by treating the surface with a sodium silicate solution at an elevated temperature such as ° C. In another case, a phosphating can be applied, which comprises treating the aluminum oxide surface with a phosphating solution, which can further contain inorganic fluoride. Additionally, the aluminum oxide surface can be rinsed with a citric acid or citrate solution. This treatment can be performed at room temperature or at slightly elevated temperatures of about 30-50 ° C. Yet another treatment may include rinsing the aluminum oxide surface with a bicarbonate solution. Further, the surface of the aluminum oxide is treated with poly (vinyl phosphonic acid), poly (vinyl methyl phosphonic acid), phosphoric acid ester of poly (pinyl alcohol), poly (vinyl sulfonic acid), poly (vinyl benzene sulfonic acid), poly (vinyl alcohol) And the acetal of poly (vinyl alcohol) produced by the reaction with a sulfonate and a sulfonated aliphatic aldehyde. Obviously, one or more of these post-treatments can be performed alone or in combination.

A highly preferred material made according to the present invention comprises a non-charged anodized aluminum support, on which a single recording layer is provided directly, which can essentially convert light to heat. Consists of a compound and thermoplastic polymer particles. An uppermost layer for protecting the recording layer against moisture, chemicals, oxygen, mechanical shock and the like can be provided on the recording layer.

According to the present invention, the dry powder can be applied to a non-charged metal support by rubbing the dry powder on the surface of the support. Alternatively, a dry coating method can be used, for example, sputter-coating of the powder on a metal support.

The method of the present invention may be applied to a direct printing (off-press exposure) method or a direct printing (on-press exposure).
Method. The method can also include on-press coating, i.e., applying the dry powder of the invention directly onto the non-charged metal surface of a rotary printing press cylinder. The on-press coating can also be performed indirectly by applying the dry powder on a metal support mounted on a rotary printing press cylinder. In yet another method according to the present invention, the composition can be applied on a metal sleeve, which is then transferred to a rotary printing press cylinder after image-wise exposure and optional processing.

Drying by contacting the surface of the non-charged metal support with another material containing a dry layer containing an organic compound and a compound capable of converting light to heat, and then transferring it to the metal support. The powder can also be applied on a non-charged metal support. The method of this aspect may include, for example, such a transfer material (t
transfer material).
Similar to the arrangement described in EP-A 698 488, it can be easily automated by introducing it into the printing station of a digital printing press. The transfer material is unwound from the supply roll and the layer containing the dry powder can then be brought into direct contact with the surface of the plate cylinder by one or more contact rollers. After the transfer step, which can be carried out by applying pressure and / or heat on the transfer material while in contact with the metal support, the used transfer material can be wound up again on a take-up roll. In the latter embodiment, the transfer of the dry powder can be performed so as to obtain a uniform layer, which can then be image-wise exposed. In other cases, the pressure and / or heat can be applied image-wise to cause the dry powder to be transferred image-wise to the metal support. This step can then be followed by strong global heating, for example by infrared laser exposure. However, if sufficient heat is applied during the image-wise transfer, a suitable print master can be obtained directly without strong overall heating.

In an even more preferred embodiment of the above-described automated method, the above-mentioned dry coating apparatus comprising a supply roll, one or more contact rollers and a take-up roll is mounted on the same carriage as the laser exposure apparatus of the external drum imagesetter. To be mounted on. For example, US-P
FIG. 1 of -5 713 287 is shown, which shows a similar apparatus in which the spray coating apparatus is mounted on the same carriage as the laser exposure apparatus with an external drum arrangement. In this way, the dry coating apparatus is equipped with a so-called slow scan axis before the laser exposure apparatus.
along the axis of the plate cylinder. When the plate cylinder rotates during image-wise exposure (fast scan movement), the entire surface of the cylinder passes through a dry coating device and the layers are coated along a spiral path around the cylinder. . Since the laser exposure system moves with the dry coating system, the coated area during one revolution of the cylinder is exposed by the laser exposure system after multiple revolutions, i.e. the coating and image-wise exposure are performed during the same scanning procedure. Can be done almost simultaneously.

The materials produced according to the present invention can be exposed to light by a light emitting diode or a laser such as a He / Ne or Ar laser. Preferably, a laser emitting near-infrared light having a wavelength in the range of about 700 to about 1500 nm, such as a semiconductor laser diode, Nd: YAG or Nd: YLF laser is used. The required laser power depends on the pixel dwell time of the laser beam, which is the spot diameter (1 / e of the maximum intensity)
Typical value of a modern platesetter at ² : 10
２５25 μm), scan speed and resolution (ie, the number of distinct pixels per unit of linear distance, often expressed in dots per inch or dpi); typical value: 100
0 to 4000 dpi). A major advantage of the materials produced according to the invention is that the internal drum (IT
D) as well as the exposure light by an external drum (XTD) imagesetter, which allows it to be used as a universal imaging material. ITD imagesetters are typically characterized by very fast scan speeds of up to 500 m / s and may require laser powers of a few watts. Satisfactory results have been obtained with the use of an XTD imagesetter having a typical laser power of 100 mW to 500 mW at slower scan speeds of, for example, 0.1 to 10 m / sec.

The unexposed areas of the material produced according to the present invention can be easily removed after exposure by wiping the material with fresh water. This step can be performed on-press, ie after the exposed plate has been mounted on the plate cylinder of the printing press. The material can even be used as a print master without additional processing immediately after image-wise exposure, which easily removes unexposed areas with a dampening solution or ink applied during the first step of the printing operation Because you can.

The printing plate of the present invention can be used in a printing process as a seamless sleeve printing plate. With this option, the printing plate is soldered in a cylindrical form using a laser. Instead of having a regular printing plate,
Print cylinder as diameter
er) is slid on a printing cylinder with this cylindrical printing plate. For more details on sleeves, see "Gra
fish Nieuws ", 15, 1995, pag
e4-6.

Most printing plates described in the prior art employ a so-called post-bake, ie, an overall heat treatment to improve the run length of the plate after image-wise exposure and optional processing. I need. The material produced according to the invention makes it possible to achieve a satisfactory run length without post-baking.

[0034]

The present invention will now be described in connection with preferred embodiments thereof, but it will be understood that it is not intended to limit the invention to those embodiments. Example 1 An aluminum support was electrochemically polished with hydrochloric acid, anodized in sulfuric acid, and subsequently treated with polyvinylphosphonic acid. The resulting hydrophilic surface was further used for dry powder application.

A dry powder consisting of an organic compound and an infrared absorbing compound was used to rub with a cotton pad onto the hydrophilic surface of the electrochemically polished and anodized aluminum support described above.

Various types and ratios of organic compounds and IR-
A powder with the absorbing compound was prepared and applied by dry rubbing.

An aqueous carbon black dispersion was mixed with an aqueous latex or dispersion of an organic compound in a suitable ratio, and the aqueous mixture was freeze-dried to remove water from the mixture to prepare a carbon black-containing powder. The carbon black used in these experiments is Printex L6 ^™ , a trade name of Degussa, and various organic compounds are listed in Table 2.

In the case of composition 6, the IR-dye was contained in the latex particles, and in the case of composition 7, the IR-dye was absorbed on the latex particles.

[0039]

[Table 5]

After rubbing the powder onto the hydrophilic aluminum surface, the resulting imaging element was subjected to a 830 nm diode laser (Isomet-3600 dpi-spot size 11 μm-3.2 m / sec speed; ie 3.4 μm).
With a pixel dwell time of seconds-image plane output varied: 80 m
W-190 mW-292 mW) and printed on a conventional offset press equipped with conventional inks and dampening solution.

Printing was started without any processing between the image formation and the start of the printing press.

All of the compositions examined yielded excellent prints with excellent image quality. Example 2 An aluminum support was electrochemically polished with hydrochloric acid, anodized in sulfuric acid, and subsequently treated with polyvinylphosphonic acid.

The resulting hydrophilic surface was further used for the application of a dry powder consisting of 1 μm polymethyl methacrylate beads, and graphite (Ca) was used as infrared absorbing compound.
Graphite Natural ^™ , a trade name of rbone Lorraine, France-<20μ
having a particle size of m) is electrochemically polished as described above,
Used for dry rubbing with a cotton pad on the hydrophilic surface of an anodized aluminum support.

After rubbing the powder onto the hydrophilic aluminum surface, the resulting imaging element was treated with a 830 nm laser diode (Isomet-3600 dpi-spot size 11 μm-3.2 m / s speed; ie 3.4 μm).
With a pixel dwell time of seconds-image plane output varied: 200
mW and 300 mW) and a 1060 nm NdYLF laser (Isomet-3600 dpi-
Spot size 18 μm-at a speed of 3.2 m / sec-image plane output was varied: using 585 mW and 780 mW), using conventional offset printing with normal ink and fountain system. Printed on machine.

Printing was started without any processing between the image formation and the start of the printing press.

All of the powders tested produced excellent image quality, but differed in lithographic behavior, such as sensitivity and ink absorption.

The ink absorption as measured by Dmax on print 100 (see Table 3) indicates that at least 51% of the organic compound is present to print high densities (> 1.55 required). In the amount required; that amount of polymethyl methacrylate-
High density prints could not be guaranteed without beads.

When only organic compounds were used in the image forming material (no IR-absorbing compound), no image was formed.

[0049]

[Table 6]

Continued on the front page (72) Inventor Liyuk Laenders Belgium 2640 Maltcell Septes Trat 27 Agfa-Gevert na Mrose Fennoutjap (72) Inventor Augustin Meisters Belgium 2640 Maltcell・ Septes Trat 27 ・ Agfa-Gevuert Na Mrose / Fennault Shop

Claims (3)

[Claims] 1. A method comprising applying a dry powder containing at least one compound capable of converting light to heat and an organic compound to the surface of a non-charged metal support, the amount of the organic compound in the powder. Is in the range of 51 to 95% by weight, the method for producing a negative-working non-ablationable image forming material suitable for producing a lithographic printing plate. 2. The organic compound according to claim 1, wherein said organic compound comprises organic thermoplastic polymer particles having a diameter of 0.02 to 10 μm.
The method described in. 3. The method according to claim 1, wherein the organic compound comprises organic thermoplastic polymer particles having a diameter of 0.05 to 2 μm.