JP2001138661A - Block copy sheet for lithographic printing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a block copy sheet for a lithographic printing plate which prevents the lithographic printing plate on a plate cylinder of a printing press from being deviated. SOLUTION: In the block copy sheet for a lithographic printing plate which is interposed between a plate cylinder and a lithographic printing plate and has irregularities of a desired shape formed on the surface and protrusions, making up the irregularities, which are formed of a plurality of particle groups, the average particle diameter of the particle group whose particle diameter is larger than the intermediate value between a maximum particle dia. and a min. particle diameter is more than twice as large as the average particle diameter of the particle group whose particle diameter is smaller than the intermediate value. In addition, the durometer hardness of the particle group whose particle diameter is larger than the intermediate value, is 65 or less and the height of the protrusion formed of particles of an average particle diameter of the particle group whose particle dia. is larger than the intermediate value, is within the range of 50-200 μm. Further, the sum of the maximum sectional areas per unit are of the faces, in parallel with the sheet face, of the protrusions made up of the particles of the average particle diameter of the particle group whose particle diameter is larger than the intermediate value, is set to be 0.1% or more of the unit area.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithographic printing plate undersheet for preventing a lithographic printing plate from being displaced on a plate cylinder of a printing press.

[0002]

2. Description of the Related Art Generally, in a lithographic printing press,
The lithographic printing plate is wound around the plate cylinder and mechanically fixed, and printing is performed.

Hitherto, as a support for a lithographic printing plate, a support made of a material such as metal, plastic film, and paper has been used. A lithographic printing plate using a material other than a metal as a support is excellent in handleability, but lacks dimensional stability, as compared with a lithographic printing plate using a metal as a support.

[0004]

In a lithographic printing press, when a lithographic printing plate having at least a back surface made of a material other than metal as a support is used, the support is soft and the front end of the plate cylinder is bitten. The position tends to be poor, in which case the vertical position accuracy (the accuracy along the circumferential direction of the plate cylinder) is deteriorated, and in some cases, the plate may be fixed at an angle. Further, for example, there is a problem in that distortion is partially generated due to friction with the plate cylinder during printing, and the positional accuracy with respect to paper is reduced.

Therefore, a lithographic printing plate having at least a back surface made of a material other than metal as a support is used only for printing a small number of sheets which do not cause a problem even if the registration accuracy of the printed matter is low. When printing a large number of sheets using a large printing machine, color shift may occur.

On the other hand, CTP (Computer
The plate making and printing method using plate to plate is compared with the conventional conventional plate making and printing method (the exposure process of the plate material is based on contact exposure using a lith film). And the advantage is that registration in multicolor printing is easy.

However, in the case of a lithographic printing plate using a material other than metal such as a plastic film or paper as a support as described above, the lithographic printing plate has the above-mentioned problems,
The advantage of easy registration in multicolor printing of P is not utilized.

Recently, it has been proposed that a sheet material having an initial elastic modulus of 300 kg / mm ² or less be interposed between the printing plate and the printing cylinder in order to solve the above-mentioned problems (see, for example, Japanese Patent Application Laid-Open No. H11-157556). JP-A-11-20130). This sheet
Fine glass beads and the like are bonded and fixed so that the center line average roughness Ra is 2 or more.

[0009] However, as described in the publication, this sheet material can be formed by densely and uniformly fixing fine glass beads or the like to the surface of the sheet material, and the sheet material has irregularities. To do so, a liquid in which fine particles are dispersed at a high concentration is required.

Since fine particles of this kind are generally expensive, a large amount of fine particles are required to fix them densely and uniformly as described above, which leads to an increase in sheet cost and a high concentration of fine particles. Not only is it difficult to disperse in the liquid, but also in the case of high-concentration dispersion, aggregation tends to occur in the liquid to form coarse particles, which causes a problem that the coarse particles deteriorate the print quality.

An object of the present invention is to provide a plate under sheet for a lithographic printing plate which can surely prevent displacement of the lithographic printing plate on a plate cylinder of a printing press, and which is excellent in cost reduction and production suitability. It is in.

[0012]

The above object of the present invention is achieved by the following constitution. The unevenness of the required shape is provided on the surface between the plate cylinder and the lithographic printing plate, and the projections constituting the unevenness have a maximum particle size and a minimum particle size in the lithographic printing plate underlay sheet comprising a plurality of particle groups. The average particle diameter of the particle group having a particle diameter larger than the intermediate value is twice or more the average particle diameter of the particle group having a particle diameter smaller than the intermediate value, and the durometer of the particle group having a particle diameter larger than the intermediate value. Is 65 or less, and the height of the projections composed of particles having an average particle diameter lower than the durometer of the particle group having a particle diameter smaller than the intermediate value and larger than the intermediate value is 5 μm to 200 μm. And the sum of the maximum cross-sectional area per unit area of the surface parallel to the sheet surface of the projections composed of particles having an average particle diameter of the particle group having a particle diameter larger than the above-mentioned intermediate value is equal to 0.1 in the unit area. 1% or more of lithographic printing plate To

[0013] The sum of the maximum cross-sectional area per unit area of the surface parallel to the sheet surface of the protrusions composed of particles having an average particle diameter of the particle group having a particle diameter smaller than the intermediate value is 0.1 to 0.1 in the unit area. The underlay sheet for a lithographic printing plate as described above, which is in a range of 99.9%.

In the following description, particles having a particle size larger than the intermediate value are referred to as large particles, and particles having a particle size smaller than the intermediate value are referred to as small particles. The intermediate value is a value that is の of the sum of the maximum particle size and the minimum particle size. The preferred particle size of the small particles is 1.0 to 100 μm, more preferably 1.0 to 100 μm.
It is in the range of 25 μm.

Since the large particles have a low durometer of 65 or less, the viscoelasticity of the large particles causes a large frictional force with the underside of the plate to prevent plate misalignment. The durometer referred to in the present invention is a value (durometer hardness) measured using a type A spring-type hardness tester (durometer) manufactured by Shore, USA.

Since the small particles are harder than the large particles, they adhere firmly to the support under the plate, and adhere to the periphery of the large particles to prevent the deformation of the large particles. It also prevents

Therefore, according to the present invention, by providing two types of projections having different hardnesses on the surface of the underlay sheet,
It is possible to provide an underlay sheet that is excellent in prevention of misregistration, printing unevenness appearing as spot-like ink stains, cost, and manufacturing suitability.

In the present invention, the sum of the maximum cross-sectional area per unit area of the surface parallel to the sheet surface of the projections composed of particles having an average particle diameter of the particle group having a particle diameter larger than the intermediate value is defined as It is in the range of 0.1-4.0%.

In the present invention, the ratio of the sum of the maximum cross-sectional area of the projection parallel to the sheet surface per unit area to the unit area is referred to as the area occupancy, and is calculated as follows. A photograph of the surface of the sample is taken from directly above with an optical microscope, and the number n of particles present in S in a certain area is read. The area occupancy is obtained from the average diameter R of the particles as follows. Area occupancy = ^{[n × (πR 2/4)} / S ] × 100 (%)

When the area occupation ratio of the large particles is 0.1% or more, displacement on the plate cylinder can be reliably prevented. The area occupancy of the large particles is preferably 0.1 to 90%.
Range.

Although the distribution of the large particles is not particularly limited, as described above, when the diameter of the large particles exceeds 200 μm, printing unevenness is likely to occur. Therefore, it is particularly preferable that the large particles are uniformly dispersed. It is preferable to provide them on the surface of the underlaying sheet so that the particles do not agglomerate during the formation of the projections. Also, by setting the area occupation ratio of the large particles to 4% or less, the overlapping of the particles can be effectively prevented, and the occurrence of printing unevenness can be suppressed.

In the present invention, it is preferable that the area occupancy of the projections composed of particles having an average particle diameter of a particle group having a particle diameter smaller than the intermediate value is in the range of 0.1 to 99.9%.

The amount of the small particles added to the large particles is preferably in the range of 1/2 to 1000 times, more preferably 1 to 1000 times.
The range is 2 times to 200 times, particularly preferably 1 time to 25 times.

In the present invention, the projections constituting the unevenness of the underlay sheet are composed of a plurality of particle groups, and as the large particles, polymer particles having relatively low hardness such as low density polyethylene are used. As the small particles, inorganic fine particles such as glass beads, polymer fine particles having relatively high hardness such as polystyrene, and the like are used.

In the underlay sheet for lithographic printing plate according to the present invention, as described above, even if the large particles forming the large projections constituting the irregularities of the required shape provided on the surface are at least small, it is necessary to prevent the displacement. Sufficiently, the large projections formed by the large particles are pressed against the back surface of the lithographic printing plate, so that the large particles come into close contact with the lithographic printing plate with high frictional force due to the viscoelasticity of the large particles. Therefore, during printing by the printing press, it is possible to reliably prevent the lithographic printing plate from being displaced on the plate cylinder due to, for example, pressure applied during printing.

In the present invention, the underprint sheet is pressed against the back surface of the lithographic printing plate because the lithographic printing plate and the underprint sheet are wound around the plate cylinder while the underprint sheet is placed between the lithographic printing plate and the plate cylinder. It may be in the process of sandwiching the sheet, and in the process of sandwiching the underlay sheet between the lithographic printing plate and the plate cylinder, it does not press against the back of the lithographic printing plate for the first time when applying printing pressure after sandwiching May be.

The type of the lithographic printing plate used in the present invention is not particularly limited.
Plates, those having a silver diffusible photosensitive layer, those made by electrophotographic plate making, those made by direct drawing plate making, and the like.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the illustrated embodiments. FIG. 1 is a schematic side view showing a multicolor lithographic printing press to which a lithographic printing plate underlay sheet according to one embodiment of the present invention is applied, and FIG. 2 is a multicolor lithographic printing press shown in FIG. FIG. 2 is a schematic perspective view showing a plate cylinder of the machine and an under sheet for planographic printing plate. FIG. 3 is a schematic perspective view showing a state in which the release layer of the lithographic printing plate underlay sheet is partially removed.

Referring to FIG. 1, in a printing press 10 for multicolor lithographic printing, sheets 13 stacked on a pallet 12 of a sheet feeding unit 11 are supplied to a printing unit 14 one by one.
The printing unit 14 performs multicolor lithographic printing. The printed paper 13 is transported to the paper discharge unit 15.

The printing unit 14 is provided with a printing unit 16 for each color of black, cyan, yellow and magenta. Each printing unit 16 sequentially prints each color on a sheet 13 conveyed to each printing unit 16 sequentially by a plurality of paper transfer cylinders 17 using a lithographic printing plate 30 mounted on a plate cylinder 18.

That is, in each printing unit 16, a large number of ink rollers 20 are supplied from the ink supply unit 19 to each of the planographic printing plates 30 mounted on the plate cylinder 18.
Is supplied through the lithographic printing plate 30.
Is attached on the object. Water is supplied to each lithographic printing plate 30 from a dampening solution unit 21 via a dampening solution roller 22, and is applied to a non-image area of each lithographic printing plate 30.

In this state, each of the lithographic printing plates 30 transfers the ink attached on the object to the blanket cylinder 23,
In the sheet 13 supplied between the blanket cylinder 23 and the impression cylinder 24,
Printing of a predetermined color is performed via the blanket cylinder 23.

Referring to FIG. 1 and FIG. 2, each lithographic printing plate 30 has its leading end and trailing end locked by claws 25 provided on the plate cylinder 18, so that each printing unit 16
On the plate cylinder 18 of the lithographic printing plate,
(Referred to as an underlay sheet 31). That is, an underprint sheet 31 for adjusting the printing pressure is interposed between the rear surface of each lithographic printing plate 30 and the outer peripheral surface of the plate cylinder 18.

Referring to FIG. 1 to FIG.
Each of the substrates 1 is provided with an irregularity 32 of a required shape on the surface of a support 31a, and provided on the back surface of the support 31a with an adhesive layer 33 for releasably adhering to the plate cylinder 18. The release layer 3 is provided on the bonding surface with the body 18.
6 (hereinafter, referred to as a release sheet 36).

Each under sheet 31 is pressed into contact with the back surface of the lithographic printing plate 30 so that the irregularities 32 on the surface are cut into the back surface of the lithographic printing plate 30 to be dented. At a predetermined position, the adhesive layer 33 on the back surface is peeled off from the release sheet 36 and adhered. Thereby, each under sheet 31 adjusts the printing pressure by the blanket cylinder 23 and the impression cylinder 24, respectively, and also prevents the lithographic printing plate 30 from being displaced on the plate cylinder 18 due to the pressurization.

As a method of forming irregularities on the surface of the support of the underlay sheet, low-density polyethylene, high-density polyethylene, rubber, polystyrene, acrylic polymer, phenol polymer, alumina, silicon carbide, corundum, diamond abrasive, glass (The average particle diameter of a particle group having a particle diameter larger than the intermediate value between the maximum particle diameter and the minimum particle diameter is 2% of the average particle diameter of the particle group having a particle diameter smaller than the intermediate value).
And the like is fixed to the surface of the support under the plate to form irregularities.

Specific examples of the method of forming irregularities by fixing particles on the support surface of the underlay sheet include a method of coating and drying a liquid in which particles are dispersed in a binder, and a method of applying a mechanical pressure after forming a binder film. And a method of electrodepositing particles after forming the binder film.

In particular, in order to suppress aggregation and obtain unevenness with high uniformity, a method of applying and dispersing in the form of an aqueous dispersion in the presence of a trace amount of latex or a dispersion stabilizer (for example, phthalic anhydride, etc.) It is preferable to use a method in which a large amount of binder is coexistent and a method of dispersing and applying, a method of dispersing using ultrasonic waves, or the like, alone or in an appropriate combination.

Further, a thin layer (overcoat layer) may be provided on the underlaying sheet having projections obtained as described above for the purpose of further preventing falling off. The overcoat layer can be provided by a method such as spray coating or bar coating.

The support of the underlaying sheet may be any as long as it has a good fit with the plate cylinder. That is, for example,
Examples include plastics such as polyethylene terephthalate, polypropylene, and polyethylene, metals such as aluminum and SUS, and paper, synthetic paper, and cloth.

As a method for fixing the underlay sheet to the plate cylinder, an adhesive layer is provided on the back surface of the support of the underlay sheet, and an adhesive or pressure-sensitive adhesive such as a spray paste or a double-sided tape is used for the adhesive layer. Method.

The elastomer which is a main component of the pressure-sensitive adhesive is
A polymer material that has rubber-like elasticity at room temperature and provides cohesiveness. Specifically, polyisobrene (natural and synthetic),
Polymers such as styrene butadiene rubber (SBR), thermoplastic rubber (SBS, SIS), butyl rubber, polyisobutylene, chlorobrene rubber, silicone rubber, recycled rubber, various polyacrylates, and polyvinyl ether are preferably used. The release sheet 36 of the underlay sheet 31 is formed by applying a release agent of 0.04 to 0.1 g / m ² and a thickness of about several μm on a sheet-like support.

Examples of the release agent include a copolymer having a long-chain alkyl group, a long-chain alkylation of a natural or synthetic polymer, a compound containing a perfluoroalkyl group, a silicon or other metal-containing substance, and a low-alkyl compound containing no long-chain alkyl group. Adhesive polymers and the like can be mentioned. These, alone or mixed,
Alternatively, they are mixed in a polymer as a binder and coated on a support.

Further, there is a method in which the underlay sheet is not provided with an adhesive layer, and the leading end and the rear end of the underlay sheet are locked by claws provided on the plate cylinder. Alternatively, a method in which they are combined can be used.

The operation of the present embodiment will be described. At the time of printing by a lithographic printing press, each lithographic printing plate is mounted on a plate cylinder of each printing unit via an underlay sheet.
At this time, each of the underlay sheets is pressed against the back surface of the lithographic printing plate, whereby the underlay sheet adheres to the underside of the underlay plate due to the viscoelasticity of the large particles. Thus, each under-sheet adjusts the printing pressure of the blanket cylinder and the impression cylinder, respectively, and also prevents the lithographic printing plate from being displaced on the plate cylinder due to the pressurization.

Next, a method for preventing the lithographic printing plate from shifting will be described. An underlay sheet provided with irregularities of a required shape on the surface of the support is interposed between the lithographic printing plate and the plate cylinder of each printing unit. At this time, plate misregistration is prevented by the frictional force of the projections on the surface of each under sheet.

Since the large particles on the surface of the underlay sheet have viscoelasticity, when a large number of underlay sheets are laminated, the underlay sheets may adhere to each other. Therefore, in order to prevent adhesion of the underlay sheets, a release sheet, for example, a silicon-treated sheet may be stacked as a cover sheet on the surface of the underlay sheet.

[0048]

EXAMPLES Next, as a comparative example, an underlay sheet of the present embodiment and an underlay sheet having irregularities on its surface outside the scope of the present invention were used as comparative examples.
Printing was actually performed by a lithographic printing press, and the positional deviation of the lithographic printing plate on the plate cylinder was measured. Specific conditions and results are shown below.

Examples 1-4 A 100 μm thick polyethylene terephthalate (PE
A solution in which the following formulation was dispersed by a homogenizer was applied to the surface of the support composed of T) by roller coating. Low-density polyethylene particles having a durometer of 58, 60, 65 (flow beads LE-1080, manufactured by Sumitomo Seika Co., Ltd.)
Flow Bead CL-2507, Flow Bead CL-20
80 three types) by a powder centrifuge.
m to obtain large-sized particles. In addition, glass beads having a durometer of 100 or more (Grade manufactured by Toshiba Glass Co., Ltd.)
B731) with a powder centrifuge for 1.5 to 100
The particles were classified to a size of μm to obtain small-sized particles.

At the time of mixing, a formulation was prepared in which the area occupancy was 1.5% with only the large particles of each average particle diameter, and the small particles were added thereto, followed by ultrasonic dispersion to obtain a coating solution. Also,
Acrylic resin was used as the binder. The formulation was made such that the area occupancy of the small particles was 3.0%.

Low-density polyethylene: large particles (diameter 3 to 290 μm) Xg average particle diameter 3 μm 0.10 g average particle diameter 5 μm 0.11 g average particle diameter 45 μm 0.17 g average particle diameter 105 μm 0.20 g average particle diameter 190 μm 22g Average particle size 290μm 0.31g

Glass beads: small particles (1.5 to 100 μm in diameter) mixed in the same amount as X Average particle diameter 1.5 μm 0.21 g Average particle diameter 20 μm 0.50 g Average particle diameter 30 μm 0.62 g Average particle diameter 42 μm 73 g Average particle size 100 μm 0.82 g Acrylic resin (40% toluene solution) 20 g Toluene 80 g

As a lithographic printing plate, a silver-diffusible photosensitive material having a thickness of 100 μm, made of polyethylene terephthalate (PET) as a support, made by Agfagewald Supermaster Plus (total thickness: 130 μm) was prepared by a dedicated plate maker SPM415 What was done was used. The lithographic printing plate can be obtained by a direct drawing printing plate in which an image receiving layer is provided on a support other than a metal or an electrophotographic plate making using an electrophotographic method.

Next, the obtained underlay sheet and planographic printing plate were each cut into a width of 560 mm and a length of 400 mm, and the planographic printing plate was cut such that the uneven surface of the underlay sheet was in contact with the back surface of the planographic printing plate. The printing plate and the underlay sheet were stacked. The stacked lithographic printing plate and underlay sheet were mounted on a plate cylinder of a single-sided printing press of Oliver 52 manufactured by Sakurai Co., Ltd.
Printed.

Before printing, the surface of the lithographic printing plate was squeezed with a sponge impregnated with the treatment liquid G671c. As the fountain solution on the printing press, the treatment solution G671c was mixed with water at 1:
The diluted one was used, and as the ink, New Champion F gloss 85 manufactured by Dainippon Ink and Chemicals, Inc. was used.

After printing, the position of the ruled line printed on the printed matter immediately after the start of printing is compared with the position of the ruled line printed on the printed matter after printing 2,000 sheets. The misalignment of the lithographic printing plate above was measured.

Comparative Examples 1 to 6 High density polyethylene particles having an average particle diameter of 45 μm and 190 μm as large particles in Example 1 described above (flow beads HE-5023 manufactured by Sumitomo Seika Co., Ltd .:
Protrusions were formed using each of the durometers of 75) (Comparative Examples 1 and 2).
Protrusions were formed using 100 μm glass beads (Duro hardness 100 or more), respectively (Comparative Examples 3 and 4).
Protrusions were formed using low-density polyethylene (Duro hardness 58) having an average particle size of 3 μm as large particles (Comparative Example 5), and low-density polyethylene (Duro hardness 65) having an average particle size of 290 μm as large particles. Using the same lithographic printing plate and printing press as in the above example, 2,000 sheets were printed in the same manner as in the above example. Table 1 shows the evaluation results of Example 1 and Comparative Examples 1 to 6.

The evaluation criteria in the table are as follows. "Evaluation criteria" Misregistration less than 50 μm: ○ 50 μm or more and 100 μm
Less than m: １００ 100 μm or more: × Printing unevenness None: ○ Less: △ More: ×

In addition to the misregistration, print unevenness on the printed matter was evaluated. The printing unevenness is interpreted as follows. If there are coarse particles on the surface of the underlay sheet, the coarse particles deform the support of the soft printing plate such as PET and push up the surface of the printing plate in that part in a state where the printing plate is overlaid and printed. It is interpreted that spot-shaped printing stains are generated, and as a result, printing unevenness is confirmed on printed matter. In the case of this example, the large particles are soft with a durometer of 65 or less, but it is interpreted that when the particle size is large, the PET film is deformed to cause printing unevenness.

[0060]

[Table 1]

As is clear from the results shown in Table 1, the average particle size of the large particles is at least twice the average particle size of the small particles, the durometer of the large particles is 65 or less, and the durometer of the small particles is Larger, projection height by large particles is 5-200μ
With m, extremely good results were obtained with respect to all of the misregistration, printing unevenness, and misregistration difference. Therefore, the average particle size of the large particles is at least twice the average particle size of the small particles, the durometer of the large particles is 65 or less and larger than the durometer of the small particles, and the protrusion height of the large particles is 5 to 5. 200 μm
Indicates that good printing can be performed.

On the other hand, as apparent from Comparative Examples 1 and 2, even if the average particle size of the large particles is twice or more the average particle size of the small particles, the durometer of the large particles is larger than 65. It can be seen that there are plate misregistration and printing unevenness, and good printing cannot be performed.

As is clear from Comparative Examples 3 and 4, even if the durometer of the large particles is 65 or less and larger than the durometer of the small particles, the average particle diameter of the small particles is larger than that of the large particles. When it is 1/2 or more, the plate deviation is 50 μm or more, and it can be seen that good printing cannot be performed.

As is apparent from Comparative Examples 5 and 6,
Even if the average particle size of the small particles is 以下 or less of the average particle size of the large particles, and the durometer of the large particles is 65 or less and larger than the durometer of the small particles, the average particle size of the large particles is 5 μm.
If it is less than 100 μm, plate misregistration occurs at 100 μm or more, and if the average particle size of the large particles exceeds 200 μm, printing unevenness is large and good printing cannot be performed.

On the other hand, as the large particles in Table 1, a durometer of 58, a particle size of 5 μm, a durometer of 60, a particle size of 45 μm,
Duro hardness 65, particle size 105 μm, Duro hardness 6
5. The underlay sheet prepared using each of the four types having a particle size of 190 μm alone was compared with the underlay sheet in which soft large particles and hard small particles were mixed, before and during printing in the lithographic printing plate and underlay sheet. It was not easy to correct the twist and position during In particular, the underlay sheet using large particles having a durometer of 58 and a particle size of 5 μm has a problem in that it is difficult to peel off after the underlay sheet is stacked, in addition to correcting the position.

Next, Examples 1 (average particle diameter of small particles 1.5 μm, average particle diameter of large particles 5 μm, durometer 58 of large particles) and 4 (average particle diameter of small particles 42 μm,
Average particle size of large particles 200 μm, durometer 6 of large particles
In 5), an underlay sheet was prepared by changing the area occupancy of the large particles. Example 1 except that the area occupancy was changed.
And 4.

If the area occupancy of the large particles is less than 0.1%, the misregistration after printing 2000 sheets under the same conditions as in the example is 5%.
0 μm or less, but the area occupancy of large particles is 0.1 to
In the range of 4.0%, there was almost no misregistration of less than 50 μm. When the area occupancy of large particles exceeded 4.0%, printing unevenness was slight, but when the area occupancy of large particles was in the range of 0.1 to 4.0%, there was almost no printing unevenness. Further, when 10,000 sheets were printed under the same conditions, when the area occupation ratio of large particles was less than 0.1%, the plate misalignment exceeded 50 μm, and when it exceeded 4.0%, printing unevenness was clearly observed.
In the range of 1 to 4.0%, there was still almost no printing unevenness. This is presumably because when the area occupation ratio exceeded 4.0%, dispersion was insufficient and large particles were aggregated. Therefore, when the area occupation ratio of the large particles is in the range of 0.1% to 4.0%, it can be understood that extremely good printing is performed regardless of the dispersion state of the large particles.

Examples 5 to 8 and Comparative Examples 7 to 12 In each of the material formulations used in Examples 1 to 4 and Comparative Examples 1 to 6, 0.1% by weight of phthalic anhydride was added to the large particles in the formulation. Except for the addition, the same materials were used in the same amounts.
All the dispersions were performed in the same manner as in Examples 1 to 4 and Comparative Examples 1 to 6, followed by a Bransonic 52 ultrasonic cleaner (YAMAT).
(Company O) for 20 minutes. This was applied by roller coating so that the area occupancy of the large particles became 55%. These were prepared in Examples 1 to 4 and Comparative Examples 1 to 6.
The same lithographic printing plate and printing press were used to print 2000 sheets in the same manner, and the same evaluation was performed. The results are shown in Table 2. In addition, Examples 5-8 are the formulations according to Examples 1-4, respectively, and Comparative Examples 7-12 are Comparative Examples 1-6, respectively.
It is a prescription according to.

[0069]

[Table 2]

It can be seen that even when the area occupation ratio of the large particles is 55%, the performance as a printing plate can be sufficiently exhibited. In addition, when the underlay sheet obtained by the above method was observed with a microscope, it was found that most of the large particles were present alone without being aggregated.

[0071]

According to the present invention, a lithographic printing plate is interposed between a plate cylinder and a lithographic printing plate, is provided with irregularities of a required shape on its surface, and the projections constituting the irregularities are composed of a plurality of particle groups. In the lower sheet, the average particle diameter of the particle group having a particle diameter larger than the intermediate value between the maximum particle diameter and the minimum particle diameter is twice or more the average particle diameter of the particle group having a particle diameter smaller than the intermediate value. The durometer of the particle group having a particle diameter larger than the value is 65 or less, and the height of the projections composed of the particle group having a particle diameter larger than the intermediate value, which is lower than the durometer of the particle group having a particle diameter smaller than the intermediate value, is larger than the intermediate value. When the average particle size is in the range of 5 μm to 200 μm and the area occupancy of large particles is 0.1% or more, misregistration and uneven printing can be prevented, and good printing can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing a multicolor lithographic printing press to which an underlay sheet for lithographic printing plate according to an embodiment of the invention is applied.

FIG. 2 is a schematic perspective view showing a plate cylinder and a lithographic printing plate undersheet of the multicolor lithographic printing press of FIG.

FIG. 3 is a schematic perspective view showing a state in which a release layer of a lithographic printing plate underlay sheet is partially peeled off.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Lithographic printing press 13 Paper 14 Printing part 16 Printing unit 18 Plate cylinder 19 Ink supply part 23 Rubber cylinder 24 Impression cylinder 30 Lithographic printing plate 31 Under plate 31a Supporting body 32 Irregularity 33 Adhesive layer 34 Glass particle 35 Binder 36 Separation Shape layer (release sheet)

Claims (2)

[Claims] 1. A lithographic printing plate undersheet comprising a plurality of particle groups, wherein projections constituting the projections and depressions are provided between the plate cylinder and the lithographic printing plate, and the projections constituting the projections and depressions are the largest particles. The average particle diameter of the particle group having a particle diameter larger than the intermediate value between the diameter and the minimum particle diameter is at least twice the average particle diameter of the particle group having a particle diameter smaller than the intermediate value, and the particle diameter is larger than the intermediate value. Duro hardness of particle group is 65
Or less, and the height of projections made of particles having an average particle diameter of a particle group having a particle diameter smaller than the intermediate value and lower than the durometer of the particle group having a particle diameter smaller than the intermediate value is 5 μm to 200 μm. The sum of the maximum cross-sectional area per unit area of the surface parallel to the sheet surface of the projections composed of particles having an average particle diameter of the particle group having a particle diameter larger than the intermediate value is 0.1% of the unit area. An underlay sheet for a lithographic printing plate, characterized in that: 2. The sum of the maximum cross-sectional area per unit area of a surface parallel to a sheet surface of projections made of particles having an average particle diameter of a particle group having a particle diameter smaller than the intermediate value is equal to 0.
2. The method according to claim 1, wherein the range is from 1 to 99.9%.
Underlay sheet for lithographic printing plate as described in.