PHOTOSENSITIVE RESIN PRINTING MATERIAL FOR LETTERSET PRINTING

Abstract

 A photosensitive resin printing material for letterset ' printing using, as a member for supporting a photosensitive resin layer, a steel plate which has a tensile strength of 57 kg/mm² or more, an elongation factor of 8% or less, and a thickness machine or easily removed therefrom, and which exhibits excellent smoothness on the printing surface, excellent picture reproducibility and excellent printing durability.

Description

Field of Art

[0001] This invention relates to a photosensitive resin printing material for letterset printing.
In particular, this invention relates to a photosensitive resin printing material for letterset printing which can provide a printing plate which can be easily handled including in the plate making step, especially can be easily mounted on the cylinder of rotary press machine and easily removed therefrom, and is difficult to be deformed on the plate surface, accordingly, is superior in keeping a smoothness of the plate surface, and can provide the prints with high image-reproducibility.

Background Art

[0002] A lithography has become a main technology for printing in place of a relief printing, but there are remained some problems in the lithography to be solved which are caused by dampening water used in the printing step. For instance, an emulsification of oily ink can not be avoided and the resulting state of emulsion changes after a start of printing and it takes a relatively long time till the state of emulsion can be stabilized, which results in forming a lot of overplus printing papers. In particular, in case of multi-colour process it takes the time for stabilizing the state of emulsion necessary for each printing of each colour and, accordingly, the overplus printing papers are formed in the amount proportional to the numbers of colour.

[0003] Another problem of lithography is that lithography can not be used for obtaining the prints which have a high level of dimension accuracy because the printing papers are deformed by dampening water used in the printing step.

[0004] Recently an ink with stronger oiliness has been developed and put into practice. Such an ink can reduce the above-mentioned defects caused by dampening water used in the printing step to some degree, but it has such a disadvantage that it needs a special type of printing paper.

[0005] On the other hand, there has been known the letterset printing which may be called relief offset printing, which comprises transferring an image on the blanket and printing by using the imaged blanket. This letterset printing technology has the advantages of both being superior in printing durability and image reproducibility compared with the lithography, and causing less overplus printing papers than the lithography does, and, therefore, has been put into practice.

[0006] The conventional photosensitive resin printing plate used for letterset printing, however, has the following defect owing to the plate structure, and therefore has not been widely used compared with the lithography.

[0007] Namely, in the conventional photosensitive resin relief printing plate, the usual type of rolled iron plate or aluminum plate are used as a support for a photosensitive resin layer and this support is necessary to have a thickness more than 0.15 mm in order to support the photocured photosensitive resin which constitutes the image-transferred portions, that is, printing area strongly and with a high stability and to keep smoothness of the plate surface by preventing the plate from bending or breaking, and this photosensitive resin layer is necessary to have a thickness more than 0.2 mm in order to prevent the portions on which image is not transferred, that is, non-printing area, from being stained with ink.

[0008] Accordingly, the total thickness of the plate becomes more than 0.35 mm (0.15 mm + 0.20 mm) and such a plate can be said to be too thick compared with the lithography plate most of which has a thickness less than 0.35 mm. That is why the photosensitive resin relief printing plate is difficult to be mounted on the conventional offset printing machine and needs a special type of cylinder if such a mounting dare be expected to be done, which constitutes a great obstacle when attempting to apply a photosensitive resin relief printing plate for letterset printing. Accordingly, a photosensitive resin relief printing plate is mainly used for direct printing.

Disclosure of the Invention

[0009] First object of the present invention is to provide a photosensitive resin printing plate for letterset printing which can be applied to the conventional lithography offset printing machine without a substantial remodeling thereto except taking off water-supplying means.

[0010] Second object of the present invention is to provide a photosensitive resin printing material for letterset printing which can provide a printing plate which is difficult to suffer from deformation on the surface thereof and can produce the prints having a high image producibility.

[0011] These objects have been now attained by a photosensitive resin printing material for letterset printing which comprises using as a support for a photosensitive resin layer the iron plate which has a tensile strength of 57 kg/mm 2 or more, preferably more than 60 kg/mm 2 and has an elongation of 8 % or less, preferably, less than 5 %, and has a thickness falling within the range of 0.03 mm to 0.12 mm, preferably, 0.05 mm to 0.10 mm.

[0012] The object of the present invention has been more preferably attained by the above-mentioned photosensitive resin printing material for letterset printing wherein the thickness of the photosensitive resin layer falls whithin the range of 0.10 mm to 0.50 mm, preferably, 0.15 mm to 0.45 mm.

[0013] The thickness of the photosensitive resin printing material according to the present invention is preferably 0.35 mm or less.

[0014] Namely, according to the present invention, a photosensitive resin printing material for letterset printing having the desirous properties aimed at by the present invention has been provided by using the iron plate having both a specified property and a specified thickness as a support for photosensitive resin layer.

[0015] In the conventional type of printing plate for letterset printing, there has been used a iron plate support for photosensitive resin layer having a tensile strength of 30 to 55 kg/mm 2 and an elongation more than 10 % and a thickness more than 0.15 mm, which are entirely different from those of the iron plate support of the present invention.

[0016] In the present invention, the support, iron plate, is necessary to have a tensile strength of 57 kg/mm2 or more. If this tensile strength is less than 57 kg/mm², the iron plate cannot be avoided to undergo an unfabourable change in dimensions when the printing plate is mounted on printing machine and while the printing is carried out. In the present invention, said support is necessary to have an elongation of 8 % or less. If the elongation is more than 8 %, the printing material is apt to undergo a deformation and to become uneven on the surface.

[0017] Even if the iron plate has a tensile strength of 57 kg/mm² or more and an elongation of 8 % or less, the iron plate becomes too rigid to mount the printing plate on the cylinder if it has a thickness more than 0.12 mm. and the iron plate does not function as a sufficient support, namely becomes brittle if it has a thickness less than 0.03 mm. The object of the present inveniton cannot be attained by these both cases.

[0018] According to the present invention, there has been provided the letterset printing material having both the same thickness that an usual lithography printing material has, that is, 0.24 mm or 0.30 mm and superior properties.

The Best Forms to Practice the Invention

[0019] The printing material of the present invention can be applied to the printing according to the conventional sheet-fed offset press and offset rotary press.

[0020] The mounting of the plate on the printing machine is carried out using a gripper bar system or an inserting and fitting system in the same manner as the case of using the lithography plate. A magnet fitting system using magnet cylinder is particularly fabourable for the mounting of the plate of the present invention on the printing machine.

[0021] As a photosensitive resin layer in the present invention, the conventional one can be used, and the composition obtained by adding photopolymerizable component, optical sensitizer, heat stabilizer, plasticizer and so on to the base polymer is usually used.

[0022] As a base polymer there are used, for example, saponified polyvinylacetate, partially saponified polyvinylacetate, ethyleneoxide-modified resin of partially saponified polyvinylacetate, partially saponified vinylacetate/ethylene copolymer, solvent soluble polyamide, water soluble polyamide, polyetheresteramide, cellulose derivatives such as methylcellulose, ehtyl- cellulose, hydroxyethylcellulose, and solvent soluble polyester.

[0023] The photopolymerizable component used in the present invention is not restricted to a special one. There can be used in the present invention any photopolymerizable component which has an ehtylenic unsaturated bond and has an affinity to the base polymer or can be uniformly mixed with it.

[0024] As an optical sensitizer these can be used any conventional one such as benzophenone type, benzyl type, benzylalkylketal type, acetophenone type, benzoinalkylether type, and anthraquinone type.

[0025] There may be included in the photosensitive resin layer of the present invention the conventional additives such as heat stabilizer, plasticizer, surfactant, ultraviolet rays absorber, dyestaff, and pigment.

[0026] Thickness of the photosensitive resin layer is preferably 0.10 mm or more. If the thickness is less than 0.10 mm, so-called scomming is caused by the adherence of ink to the concave of the plate because the height difference between convex and concave of the plate becomes too small, and therefore good printing cannot be expected. And if the thickness of the plate is more than 0.50 mm, an exposure shrinkage of the photosensitive resin layer becomes too large to be disregarded, which has the plate curled to the direction of the plate surface and renders the plate difficult to be mounted on the plate-fitting device or cylinder. Accordingly, the thickness of the photosensitive resin layer of the present invention is preferably within the range of 0.10 mm to 0.50 mm, more preferably 0.15 mm to 0.45 mm, most preferably 0.20 mm to 0.40 mm.

[0027] As an iron plate support for the photosensitive resin layer in the present invention there is used, for example, the non-annealing ultra-thin rolled steel plate which is generally called by zinc first steel plate or tin first steel plate which can be obtained by rolling zinc-plated or tin-plated steel sheet to the aimed thickness.

[0028] The favourable iron plate used in the present invention has a tens ile strength of 60 kg /mm² or more, an eicnsation of 5% or I _CsS. and a thickness within the range cf 0.05 mm 10 0.10mm.

[0029] It is preferable that the surface of the support is treated for preventing it from getting rusty, for example, by means of Dialing treatment or the other chemicai treaiment. but is not limited thereto.

[0030] In the present invention, the fixing between the pnotosensitive polymer layer and the support is usually carried out using an aghesive.

[0031] The strong fixing between tnem can be attained using the aghesive selected from enoxy compound. cpoxy resin, pnenol resin, isocyanate resin, polyurethane. polyester. polyvinylacetate, or chloroprene rubber singly or the mixture thereof in the adequate ratio.

[0032] A suitable film layer can De put on the surface of the photosensitive resin layer in order to prevent it t from being damagea. As such am film there can be used. for example. polyester film. polypropyrene film. polyerhylene film. and polyvinylidenechloride. Polyester film. especiaily polyethylene terephthalate film is preferably used thanks to high dimension stabiiity and superior oxygen permeability. If the matted film is used, it becomes easy to adhere the printing piate to a negative film in vacuum because the shape of the matted film is transferred on the surface of the printing plate. Of course. the printing plate can be subjecled to a practical use without being covered with such a film.

[0033] The photosensitive resin printing material of the present invention can be easily used as a ietterset printing plale by being subjected to conventional exposure step and processing step.

[0034] The most characteristic feature of the photosensitive resin printing malerial for leiterset printing is that said photosensitive resin printing material not only can be easily mounted on and removed from the printing macnine in the same manner as the lithography piate in suite of peionging to the reiiel printing plate. but also is superior in image reproducibility and durability for compared with the lithography plate printing. and. further. renuers it possible 10 lessen the overplus papers to a great degree compared with the lithography plate.

Examples 1. 2 and Comparative examples 1 to 3

[0035] The following steel plates (A) to (E) were coaten with polyester/isocyanate type of adhesives in the ammount sufficient to form a layer naving a thickness of 0.02mm in a dry state :

[0036] The adhesive-coated steel plates were kepl for five minulos in the over at 150 °C to remove the solvent. Thus, five supports (Λ) to (I) were preoared.

[0037] Next, the photosensitive poiymer sciution was prepared by soiving partiaiiy saponified potyvinylacetate having a saponifizatikon degree of 75 mol% and an approximate polymerization degree of 600 into a mixture of ethanol and water (50/50 by weight ), and then adding to the resulting solution propylene glycol diglycidilether diacrylate as a photopolymerizable monomer. benzyldinethyl ketal as an optical sensitizer. and diethylene glycol as a plasticizer.

[0038] The above aadhesive-treated steel plates (Λ) to (E) were coated with the resulting solution in the amount sufficient to form a layer of 0.20mm in dry state and then

in the oven of 50 'C for two hours to remove the solvent. Thus the pholosensitive resin printing materials (Λ) to (I) were obtained. On these photosensitive resin printing materials the negative film of ususal type of account slip was aadhered in vacuum and them rresuiting products were supjected to exposure for two hours by using an ultra-high pressure mercury lamp and then were subjected to processing by using a brush-type processor filled with neutral water until the non-cureu photosensitive resin layer was completely resoivea out. After that, the resulting plates were completely dryed in the oven of 50 U °C for ten minutes.

[0039] Five kinds of printing plate for letterset printing thus prepared were fitted on the conventional offset rotary press and the printing was carried out. The result is shown in lable 1.

[0040] O mark described in the item . Evaluation" means that the product was superior in the corresponding property, while x mark means that the product has a defect in the corresponding property.

[0041] From the result shown in Table 1 it has been substantiated that the printing plates obtained by using the supports (D) and (E) of the present invention were superior in the smoothness of the surface and could be easily mounted on and removed from the cylinder. and, further. from said printing plate there were obtained the exceilent prints.

Example 3 to 6 and Comparative exampies 4 and 5

[0042] As a base polymer there was employed water sweiling ccoloyamide, that is, nylon 6/6' 6/PGDA .6 (copoiymerization ratio : 20/20/60) which was derived from adipic acid, hexamethylene diamine. and diamine obtained by cyanoethylation and hydrogenation of polyethyleneglycol (this diamine is abbreviated to PGDA). This base polymer was solved into the mixture solvent of ethanol and water (70/30 by weight) and, then. into the resulting solution there were added and mixed propyleneglycoi digiycidylether acrylate and pentaerithritol triacrylate as photopolymerizable monomer and benzyl dimethylketal as photosensitizer.

[0043] The same supports (A), (B), (D) and (F) as employed in the examples 1.2 and comparative examples 1,2, which have been already treated with an adhesive, were coated with the resulting polymer solution in the amount sufficient to have a thickness of 0.23mm after being dryed and were dryed for three hours in the oven of 50 °C.

[0044] Further, the same support (E) of example 2. which has been already treated with an adhesive. was conated with the resulting polymer solution in the amount sufficient 10 nave a thickness of 0.31 mm after being dryed and was dryed for five hours in the oven of 50 'C.

[0045] from thus prepared photosensitive rresin printing materials the lettersel printing plates were obtained in the same manner as the examples 1_. 2 and comparative examples 1 to 3, and then. the printing test thereof was carried out. The result is shown in Table 2.

[0046] O x marks described in the item "Evaluation" mean that the product was superior and inferior respectively in the corresponding property.

[0047] From these results it is apparent that the printing plates obtained using the supports (D), (E) of the present invention are excellent for letterset printing.

Industrial Applicability of the Invention

[0048] THe photosensitive resin printing material for letterset printing of the present invention can be easily handled and is superior in property and can be applied effectively to letterset printing.

Claims

1. A photosensitive resin printing material for letterset printing which comprises using as a support for a photosensitive polymer layer the iron plate which has a tensi ie strength of 57 kg/ mm² or more, an elongation of 8% or less and a thickness failing with the range of 0.03 mm to 0.12mm.

2. A photosensitive resin printing material for letterset printing according to claim 1. wherein said iron plate has a tensiie strength of 60Kg/mm² or more and an elongation of 5% or less.

3. A photosensitive resin printing material for letterset printing according to claim 1. wherein said photosensitive resin layer has a thickness falling whithin the range of 0.10 mm to 0.50mm.

4. A photosensitive resin printing material for letterset printing according to ciaim 3. wherein said photosensitive resin layer has a thickness falling whithin the range of 0.20 mm to 0.40mm.