JP2005067096A - Offset printing method and rubber sheet to be used therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an offset printing method which can prevent a shock-streak pattern from occurring on a printed matter due to vibration and impact in a machine occurring during printing operation and can prevent paper from being curled and torn by further enhancing paper discharge performance, and to provide a rubber sheet used therefor. <P>SOLUTION: For the offset printing method, an ink image transferred onto a surface of a printing blanket 11 is printed on a surface of paper by inserting it between a blanket cylinder 1 and the rubber sheet 21 under a state wherein the blanket cylinder 1 having the printing blanket 11 installed onto an outer circumference of a blanket cylinder shaft 10 and an impression cylinder 20 having the rubber sheet 21 containing a surface rubber layer installed on an outer circumference of a cylinder shaft 20 are kept into pressure contact with each other. The rubber sheet 21 comprises the surface rubber layer 0.15-0.40 in loss tangent tanδ and 0.4-3.0 mm in thickness. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a novel offset printing method and a rubber sheet used therefor.

  A paper is inserted between a blanket cylinder having a printing blanket attached to the outer periphery of the blanket cylinder and a pressure cylinder pressed against the blanket cylinder, and the ink image transferred to the surface of the printing blanket is printed on the surface of the paper. In the offset printing method, there is a problem in that the printing pattern is disturbed by mechanical vibration or impact generated during printing, and strip-like density unevenness called shock eyes is generated in the printed matter, resulting in a decrease in printing quality.

Therefore, as a printing blanket, a compressible layer made of porous rubber is provided at an arbitrary position below the rubber surface printed layer that constitutes the surface, and by absorbing the shock to this compressible layer, shock eyes are generated. It has been done to prevent the occurrence.
However, the greater the thickness of the compressible layer, the better the ability to absorb the impact, but there is a problem that when the printing is repeated, the voids are crushed and the thickness gradually decreases.

Therefore, in order to prevent settling, Patent Document 1 proposes a combination of a compressible layer having a continuous pore structure and a compressible layer having an independent pore structure. Has proposed that vulcanized rubber particles be dispersed in a compressible layer having a continuous pore structure.
In addition, in the offset printing method, especially when printing at high speed or printing on smooth paper such as coated paper, the paper tends to curl or tear due to the adhesive force generated between the paper and the printing blanket. There is also.

This is because the paper is more likely to stick to the surface print layer, which is mainly made of rubber, located on the outermost surface of the printing blanket and in direct contact with the paper, rather than the surface of the impression cylinder made of metal. Therefore, the printing blanket is a phenomenon that occurs because paper discharge performance (paper separation performance) is deteriorated. When such a phenomenon occurs, printing productivity is greatly reduced.
Therefore, various studies have been made to improve the paper discharge performance of the printing blanket.

For example, in patent document 3, the surface shape of the surface printing layer of a printing blanket is made sticky to paper by making it a concavo-convex shape with a 10-point average roughness of 4-9 μm and an average peak spacing of 30-48 μm. It has been proposed to improve the paper discharge performance by reducing the above.
In Patent Document 4, it is proposed that the surface printed layer is formed of a mixture of oil-resistant rubber and polysulfide rubber, thereby reducing the adhesiveness to paper and improving the paper discharge performance. Yes.
JP-A-10-181235 (Claim 1, column 0011, column 0012 to column 0013, FIG. 1 (a), FIG. 2) Japanese Patent Application Laid-Open No. 11-208140 (Claim 1, Column 0009, Column 0011, FIG. 1 (a) (b)) Japanese Patent No. 2535693 (Claim 1, columns 0005 to 0006, Table 1, Table 2, FIG. 4, FIG. 5) Japanese Patent No. 2540674 (Claim 1, columns 0008 to 0009, Table 1, Table 2)

However, the configurations of Patent Documents 1 and 2 have a problem that in either case, the manufacturing process becomes complicated and the cost of the printing blanket increases.
In general, as the surface roughness of the surface print layer, that is, the height of the unevenness is increased, the paper discharge property can be improved, but the halftone dot shape of printing tends to deteriorate. Therefore, in Patent Document 3, as described above, not only the height of the unevenness (surface roughness) on the surface of the surface printed layer is specified, but also the interval of the unevenness is specified by the average peak interval, We are trying to prevent the shape from deteriorating.

  However, it is not easy to polish the surface of the surface printed layer into a surface shape that satisfies both a predetermined surface roughness and an average peak interval. In particular, if the composition of the rubber composition forming the surface print layer is different, the polishing conditions are also different accordingly, so printing provided with a surface print layer having a surface shape satisfying both a predetermined surface roughness and an average peak interval It is difficult to manufacture a blanket with a high yield.

Further, in the method of blending polysulfide rubber with oil-resistant rubber for forming the surface print layer described in Patent Document 4, the polysulfide rubber is expensive and the material cost is high, and the polysulfide rubber is liquid. In addition, the kneading operation with the solid rubber is not easy and the odor is strong, which may affect the working environment and the living environment around the factory.
In addition, the improvement of the printing blanket as described in Patent Documents 1 to 4 has a limit in the effect of preventing the occurrence of shocks in the offset printing method or the effect of improving the paper discharge performance. The current situation is that it is no longer possible to meet the demands of the company.

  The object of the present invention is to prevent the occurrence of shock eyes more reliably than before without increasing the thickness of the compressible layer of the printing blanket or making it a complicated structure. Especially when printing at high speed or printing on smooth paper such as coated paper, it is possible to improve paper discharge more than ever and more reliably prevent paper from curling or tearing. It is to provide a novel offset printing method that can be used and a rubber sheet that can be suitably used for the printing method.

  According to the first aspect of the present invention, the ink is transferred onto the surface of the printing blanket by inserting paper between the blanket cylinder having the printing blanket attached to the outer periphery of the blanket cylinder shaft and the impression cylinder pressed against the blanket cylinder. An offset printing method for printing an image on the surface of a paper, wherein the pressure cylinder is a cylinder in which a rubber sheet including a surface rubber layer is mounted on the outer periphery of the cylinder shaft. It is.

The invention according to claim 2 is a rubber sheet used in the offset printing method according to claim 1, wherein the loss tangent tan δ is 0.15 to 0.40 and the thickness is 0.4 to 3.0 mm. A rubber sheet comprising a surface rubber layer.
The invention according to claim 3 is the rubber sheet according to claim 2, wherein the Shore A hardness of the surface rubber layer is 30 to 80 °.

  Further, the invention according to claim 4 is the rubber sheet according to claim 2, which has a laminated structure in which a surface rubber layer is formed on one side of at least one base material.

In the structure of Claim 1, the surface rubber layer which has adhesiveness with respect to paper similarly to the surface printing layer of a printing blanket is arrange | positioned on the surface of an impression cylinder, and paper is printed by the adhesive force of the said surface rubber layer. It can be peeled off from the printed surface of the blanket and discharged.
In other words, paper can be peeled off from both layers without being unilaterally adhered to either one by the adhesive force from both the surface printing layer of the printing blanket and the surface rubber layer of the rubber sheet. it can.

The rubber layer on the surface of the rubber sheet, together with the printing blanket, also serves to absorb mechanical vibrations and shocks that occur during printing, and to prevent shocks from occurring on the printed matter.
For this reason, according to the first aspect of the present invention, it is possible to generate shock eyes more reliably than before without increasing the thickness of the compressible layer of the printing blanket or using a complicated structure. In addition to preventing paper curling and tearing, it is possible to improve paper ejection, especially when printing at high speeds or printing on smooth paper such as coated paper. It becomes.

In addition, when the rubber sheet of claim 2 is used in the offset printing method of claim 1, it is possible to more reliably prevent the occurrence of shock eyes, as is apparent from the results of Examples and Comparative Examples described later. Further, the paper discharge performance can be further improved, and the paper can be more reliably prevented from curling or tearing.
That is, the surface rubber layer of the rubber sheet according to claim 2 has a loss tangent tan δ of 0.15 or more, which is an index of adhesiveness with paper, and a surface printing layer of a normal printing blanket (loss tangent tan δ is 0.08 to 0). .14)), the adhesive strength between the surface printed layer and the paper, which acts in addition to the adhesive strength between the rubber and the paper, as well as the adhesive strength due to the ink interposed between the two, is overcome. Thus, the paper can be satisfactorily peeled off from the surface print layer. Further, it is possible to prevent the occurrence of shock eyes by imparting good vibration damping performance to the surface rubber layer.

In addition, the loss tangent tan δ of the surface rubber layer is set to 0.40 or less so that the adhesiveness to the paper does not become too high. Therefore, the paper can be discharged well without being caught on the side of the impression cylinder. Can be paper. In addition, it is possible to reduce the trouble of removing the paper dust by stopping the machine during printing by suppressing the paper dust from adhering to the surface rubber layer.
Moreover, since the thickness of the surface rubber layer is set to 0.4 mm or more and the rubber sheet is imparted with a good shock absorption, it is possible to prevent shocks from occurring on the printed matter.

Moreover, the thickness of the surface rubber layer is 3.0 mm or less, which gives the rubber sheet good flexibility and makes it easy to wrap around the cylinder of the impression cylinder. Can also be improved.
According to the third aspect of the present invention, the Shore A hardness of the surface rubber layer is set to 30 ° or more so that the adhesiveness to the paper does not become too high. Without any problem, it is possible to further improve the effect of discharging the sheet satisfactorily. Further, it is possible to further improve the effect of reducing the trouble of removing the paper dust by stopping the machine during printing by suppressing the paper dust from adhering to the surface rubber layer.

In addition, the Shore A hardness of the surface rubber layer is set to 80 ° or less so that the rubber sheet is given good flexibility and is easily wound around the cylinder shaft of the impression cylinder. Workability can be further improved. In addition, it is possible to give a good impact absorbability to the rubber sheet, and more reliably prevent the occurrence of shock eyes on the printed matter.
Furthermore, in the structure of claim 4, since the surface rubber layer is reinforced with at least one base material, when a stress is applied to the rubber sheet, such as when the impression cylinder is wound around the cylinder shaft or during printing. In addition, the rubber sheet can be prevented from breaking.

FIG. 1 is a front view showing a portion around a blanket cylinder, which is a main part of an example of an offset printing machine, for carrying out the offset printing method of the present invention.
As shown in the figure, the offset printing machine of this example has a blanket cylinder 1, a pressure cylinder 2 pressed against the blanket cylinder 1, and a plate cylinder 3 also pressed against the blanket cylinder 1. These cylinders 1 to 3 are arranged so that they can be rotated in directions indicated by arrows in the drawing by a power mechanism (not shown) of the offset printing press.

In the figure, the one-dot chain line arrows indicate the flow of paper that passes between the blanket cylinder 1 and the impression cylinder 2 that rotate while being pressed against each other.
Although not shown, the plate cylinder 3 is in contact with an inking device for supplying ink to the outer peripheral surface of the plate cylinder 3, a fountain solution device, and the like, as in the prior art. In the case of an offset sheet-fed printing press, an intermediate cylinder or the like for transporting the sheet is disposed in contact with or separated from the impression cylinder 2.

The blanket cylinder 1 has a blanket cylinder shaft 10 formed of metal or the like as in the prior art, and a printing blanket 11 attached to the outer periphery of the blanket cylinder shaft 10.
Among these, as the printing blanket 11, those having various conventionally known configurations can be employed. That is, a sheet-like shape having at least one base material, a surface printed layer, and a compressible layer made of porous rubber disposed at an arbitrary position below the surface printed layer as necessary. A printing blanket or a cylindrical printing blanket in which each of the above layers is formed in a seamless cylindrical shape around a cylindrical sleeve can be used.

Among these, as a base material, conventionally well-known various base materials can be used as a base material of the printing blanket 11, such as a plastic film, a woven fabric, and a nonwoven fabric, for example.
Further, since the surface printing layer is in direct contact with the ink, it is preferably formed of an oil resistant rubber such as nitrile-butadiene copolymer rubber (NBR), chloroprene rubber (CR), urethane rubber (U). . The compressible layer is also preferably formed of the same oil-resistant rubber as that of the surface print layer in consideration of securing the resistance to ink.

The loss tangent tan δ of the surface print layer is preferably about the same as that in the past, that is, 0.08 to 0.14 in consideration of improving the paper discharge performance by reducing the adhesion to paper.
When the loss tangent tan δ exceeds 0.14, the adhesiveness of the surface printing layer to the paper becomes too strong, and even when combined with the rubber sheet 21 on the impression cylinder 2 side, the printed paper is removed from the surface printing layer. It may be difficult to peel off and the paper may not be discharged well. Further, if the loss tangent tan δ is less than 0.08, the surface printing layer becomes too hard to give a good impact absorbability to the printing blanket. Therefore, even when combined with the rubber sheet 21 on the impression cylinder 2 side, the printed matter is shocked. May not be prevented.

The sheet-shaped printing blanket 11 is attached to the outer periphery of the blanket cylinder shaft 10 by winding it around the outer periphery of the blanket cylinder shaft 10 while applying tension in the circumferential direction and fixing the blanket cylinder 11 using a clamping jig (not shown). To do.
In addition, the cylindrical printing blanket 11 is externally attached to the blanket cylinder shaft 10 in a state where the sleeve is slightly enlarged in the radial direction by applying pressure, and then the pressure is stopped and the sleeve is reduced in the radial direction. The blanket cylinder shaft 10 is attached to the outer periphery by being fixed.

Normally, the impression cylinder 2 is integrally formed of metal or the like as described above. In the present invention, the impression cylinder 2 is constituted by a cylinder shaft 20 formed of metal or the like and a rubber sheet 21 attached to the outer periphery of the cylinder shaft 20. To do.
As the rubber sheet 21, those having various layer configurations including a surface rubber layer having adhesiveness to paper similar to the surface printing layer of the printing blanket 11 can be used. It is preferable to use one having a laminated structure in which a surface rubber layer is formed on one surface of at least one substrate.

  The rubber sheet 21 having such a laminated structure is prepared by, for example, applying an unvulcanized liquid rubber paste containing each component that is a base of the surface rubber layer to one side of a base material, drying and vulcanizing the rubber. Form a surface rubber layer, or laminate a sheet of unvulcanized rubber containing each component that becomes the basis of the surface rubber layer on one side of the substrate via a vulcanized adhesive or directly, Manufactured by vulcanizing rubber to form a surface rubber layer.

Among these, as a base material, various base materials similar to the base material of the printing blanket 11, such as a plastic film, a woven fabric, and a nonwoven fabric, can be used, for example.
Two or more base materials may be laminated. However, as long as it is possible to prevent the rubber sheet 21 from being broken as described above, only one sheet is considered in consideration of simplifying the structure of the rubber sheet 21. It is preferable to do this.

  In addition, the surface rubber layer does not come into direct contact with ink during printing, so it can be formed of various rubbers, soft resins, or thermoplastic elastomers. Since it is in direct contact with the surface printing layer of the printing blanket in the gaps between them, it is preferable to form the oil-resistant rubber such as NBR, CR, U or the like.

The loss tangent tan δ of the surface rubber layer in the rubber sheet 21 of the present invention needs to be 0.15 to 0.40 as described above.
That is, when the loss tangent tan δ is less than 0.15, the adhesiveness of the surface rubber layer to the paper is not sufficient, so that it is difficult to peel off the printed paper from the surface printed layer, and the paper cannot be discharged well. Arise. In addition, since a good vibration damping performance cannot be imparted to the surface rubber layer, there is a problem that it is impossible to prevent the occurrence of shock eyes.

Further, when the loss tangent tan δ exceeds 0.40, the adhesiveness to the paper becomes too high, so that the paper is entangled on the side of the impression cylinder, and the paper cannot be discharged well. . Further, since paper dust easily adheres to the surface rubber layer, there also arises a problem that the machine must be stopped frequently during printing to remove the paper dust.
In addition, the adhesiveness of the surface rubber layer to paper is further improved, paper discharge performance is further improved, and a good vibration damping performance is imparted to the surface rubber layer, which causes shock eyes. In view of more reliably preventing the loss tangent tan δ of the surface rubber layer, it is particularly preferable that the loss tangent tan δ is 0.20 or more even within the above range.

In addition, it is possible to prevent the surface rubber layer from becoming too sticky to the paper, to further improve the paper discharge performance and to more reliably prevent the paper dust from adhering to the surface rubber layer. The loss tangent tan δ of the rubber layer is particularly preferably 0.35 or less even within the above range.
In order to adjust the loss tangent tan δ of the surface rubber layer or the surface printing layer of the printing blanket, the type of vulcanizing agent or vulcanization accelerator added to the rubber composition forming the surface rubber layer or the like is selected. A method of adjusting the amount or adjusting the degree of rubber vulcanization, or selecting the type of rubber forming the surface rubber layer or the like may be combined. For example, when NBR is used as the rubber, medium / high nitrile NBR, high nitrile NBR, and extremely high nitrile NBR classified by nitrile amount may be selected and used.

In this invention, loss tangent tan-delta means the value measured by the following method.
・ Measurement of loss tangent tan δ A test piece having a width of 4 mm, a length of 30 mm and a thickness of 0.2 mm is prepared by slicing and taking out the surface rubber layer or the surface print layer, and a viscoelastic spectrometer is used for the test piece. The loss tangent tan δ is measured under the conditions of a temperature of 23 ° C., a chuck distance of 20 mm, an amplitude of 50 μm, a vibration frequency of 10 Hz, and an initial strain of 2 mm.

Moreover, the thickness of the surface rubber layer in the rubber sheet 21 of this invention needs to be 0.4-3.0 mm.
If the thickness is less than 0.4 mm, good impact absorbability cannot be imparted to the rubber sheet 21, so that the effect of preventing the occurrence of shock eyes on the printed matter cannot be obtained. For this reason, the problem that print quality falls arises.

If the thickness exceeds 3.0 mm, the rubber sheet 21 cannot be provided with good flexibility, so that it is difficult to wind the rubber sheet 21 around the cylinder shaft of the impression cylinder, and the workability when mounting on the cylinder axis of the impression cylinder is reduced. This causes a problem.
In consideration of further improving the effect of imparting good shock absorption to the rubber sheet 21 and preventing the occurrence of shock eyes, the thickness of the surface rubber layer is particularly 0.8 mm or more even in the above range. It is preferable that it is 2 mm or more.

Furthermore, it is preferable that the hardness of the surface rubber layer in the rubber sheet 21 of the present invention is 30 to 80 ° in Shore A hardness.
If the Shore A hardness is less than 30 °, the adhesiveness to the paper becomes too high, and the paper may be entangled on the side of the impression cylinder and not discharged properly. Also, paper dust tends to adhere to the surface rubber layer, and there is a possibility that the machine must be stopped frequently during printing to remove the paper dust.

If the Shore A hardness exceeds 80 °, the rubber sheet 21 cannot be given good flexibility, and it is difficult to wind the rubber sheet 21 around the cylinder shaft of the impression cylinder. May decrease. In addition, since the rubber sheet 21 cannot be given good shock absorption, there is a possibility that it is impossible to reliably prevent the occurrence of shock eyes on the printed matter.
In consideration of suppressing the adhesiveness to paper from becoming too high, the Shore A hardness of the surface rubber layer is preferably 50 ° or more even in the above range.

In consideration of further improving the effect of imparting good shock absorption to the rubber sheet 21 and preventing the occurrence of shock eyes, the Shore A hardness of the surface rubber layer is particularly 70 even within the above range. It is preferable that it is below.
To adjust the Shore A hardness of the surface rubber layer, select the type of vulcanizing agent, vulcanization accelerator, etc. to be added to the rubber composition forming the surface rubber layer, etc. as described above, or adjust the amount. For example, a method of adjusting the degree of rubber vulcanization or selecting a type of rubber for forming a surface rubber layer may be combined. Carbon black that functions as a rubber reinforcing agent may be blended or the amount thereof may be adjusted.

  In order to mount the rubber sheet 21 on the outer periphery of the cylinder shaft 20 of the impression cylinder 2, the same method as that for mounting the printing blanket 11 on the outer periphery of the blanket cylinder shaft 10 can be employed. That is, the rubber sheet 21 formed in a sheet shape is wound around the outer periphery of the barrel shaft 20 while applying tension in the circumferential direction, and fixed using a clamping jig (not shown), or each of the above layers is formed in a cylindrical shape. The cylindrical rubber sheet 21 formed in a seamless cylindrical shape around the sleeve is extrapolated to the barrel shaft 20 in a state where the sleeve is pressurized and slightly expanded in the radial direction, and then the pressure is applied. It can be stopped and reduced in the radial direction and fixed.

  However, unlike the printing blanket 11 that directly affects the printing quality, the rubber sheet 21 only needs to be fixed to the outer periphery of the barrel shaft 20, so that, more simply, for example, via an adhesive layer or an adhesive layer, It may be simply pasted and fixed directly to the outer periphery of the barrel shaft 20. Specifically, for example, an adhesive layer or an adhesive layer is formed by applying an adhesive or an adhesive to the back surface of the base material of the rubber sheet 21, that is, the surface opposite to the surface on which the surface rubber layer is formed. Alternatively, the rubber sheet 21 may be attached and fixed directly to the outer periphery of the barrel shaft 20 via an adhesive layer.

Below, this invention is demonstrated based on an Example and a comparative example.
Examples 1 to 5, Comparative Examples 1 and 2
(Production of rubber sheet)
Each component shown in Table 1 is dissolved in toluene twice as much as the total amount of each component to prepare a rubber paste, and this rubber paste is placed on one side of a 0.3 mm-thick cotton cloth as a base material with a doctor blade. Used to paste.

Next, the laminate was passed through a continuous vulcanizer and continuously vulcanized under conditions of a vulcanization temperature of 160 ° C., a vulcanization pressure of 2 kg / cm ² , and a vulcanization time of 20 minutes, and the surface was polished to a thickness of 0. An 8 mm surface rubber layer was formed.
Then, on the back side of the base material after vulcanization, using a coater, an acrylic resin adhesive was applied to a thickness of 0.1 mm to form an adhesive layer to prepare a rubber sheet.

(Measurement of loss tangent tan δ)
The surface rubber layer was sliced and taken out to prepare a test piece having a width of 4 mm, a length of 30 mm, and a thickness of 0.2 mm. For this test piece, the loss tangent tan δ was measured using a viscoelastic spectrometer (manufactured by Rheology Co., Ltd.) at a temperature of 23 ° C., a chuck distance of 20 mm, an amplitude of 50 μm, a vibration frequency of 10 Hz, and an initial strain of 2 mm. It was measured.

(Measurement of Shore A hardness)
About the test piece used above, Shore A hardness (type A durometer hardness) was measured based on Japanese Industrial Standard JIS K6253 _-1997 “Hardness test method of vulcanized rubber and thermoplastic rubber”.
(Real machine test)
The produced rubber sheet was directly attached and fixed to the outer periphery of the impression cylinder of an offset printing machine [560 type manufactured by Ryobi Co., Ltd.] via an adhesive layer.

As the printing blanket, a printing blanket having a loss tangent tan δ of 0.11 was used.
The following evaluations were performed while continuously printing on coated paper under the following conditions.
Printing speed: 10,000 sheets / hour Ink: Brand name New Champion Naturalis Red Co., Ltd., manufactured by Dainippon Ink Co., Ltd. Coated paper: Product name Utrilo Coat 110 kg, manufactured by Daio Paper Co., Ltd.
Printing pattern: Total solid Ink density during printing: 1.8
(1) Impact absorption evaluation Impact generated when feeding the gears of the printing press appears as band-like density unevenness in the width direction of the print, that is, shock eyes. Measure the density difference of solid printing using a densitometer. Then, the density difference between the density of the highest density part and the density of the lowest density part was obtained. If the density difference is 0.04 or less, there is no shock and the shock absorption is good, and if the density difference exceeds 0.04, there is a shock and the shock absorption is poor.

(2) Evaluation of paper discharge properties As shown in FIGS. 2 (a) and 2 (b), 100 sheets of coated paper P printed with a total solid, and the paper when stacked on the surface plate S with the printing surface up The amount of warpage was measured. The amount of warpage is described as (−) in the case shown in FIG. 2 (a) and (+) in the case shown in FIG. 2 (b). The closer the warp amount is to 0, the better the paper discharge property. When the absolute value of the warp amount exceeds 10, the paper discharge property is poor.

(3) Evaluation of paper dust residue After continuous printing of 100,000 sheets, the amount of paper dust adhered to the surface of the rubber sheet was visually evaluated. The evaluation criteria were as follows.
○: No paper dust adhered.
(Triangle | delta): Paper dust had adhered to the part through which the edge of paper passed.

X: Paper dust adhered to the entire surface.
(4) Wearability evaluation The ease of work when a rubber sheet was affixed to the impression cylinder was evaluated. The evaluation criteria were as follows.
○: Can be easily pasted.

Δ: peeled off just by pasting, but no longer peeled off after pressure bonding.
X: Partial lifting was observed even when pasted, and this lifting was not eliminated even after pressure bonding.
The results are shown in Table 1.

From the results of Comparative Example 1 in the table, when the loss tangent tan δ of the surface rubber layer of the rubber sheet is less than 0.15, a shock is generated and the paper cannot be peeled well from the printing blanket, so the paper discharge performance cannot be improved. I understood it.
Further, from the result of Comparative Example 2, it is found that when the loss tangent tan δ exceeds 0.40, the paper sticks to the rubber sheet side and the paper discharge performance is deteriorated, and paper dust residue is likely to be generated. It was.

On the other hand, from the results of Examples 1 to 5, by setting the loss tangent tan δ within the range of 0.15 to 0.40, it is possible to more reliably prevent the occurrence of shock eyes and improve paper discharge performance. In addition, it was confirmed that paper dust residue could be prevented.
Moreover, when Examples 1-5 were compared, when the loss tangent tan-delta was in the range of 0.20-0.35, it turned out that these effects can be improved further.

Examples 6-11
(Production of rubber sheet)
Each component shown in Table 2 is dissolved in toluene twice as much as the total amount of each component to prepare a rubber paste. This rubber paste is placed on one side of a cotton cloth having a thickness of 0.3 mm as a base material, and a doctor blade is attached. Used to paste.

Next, the laminate was passed through a continuous vulcanizer and continuously vulcanized under conditions of a vulcanization temperature of 160 ° C., a vulcanization pressure of 2 kg / cm ² , and a vulcanization time of 20 minutes, and the surface was polished to a thickness of 0. An 8 mm surface rubber layer was formed.
Then, on the back side of the base material after vulcanization, using a coater, an acrylic resin adhesive was applied to a thickness of 0.1 mm to form an adhesive layer to prepare a rubber sheet.

  The rubber sheet of each of the above examples was subjected to each of the above tests to evaluate its characteristics. The results are shown in Table 2.

From the results of Example 6 in the table, it was found that when the Shore A hardness of the surface rubber layer of the rubber sheet is less than 30 °, the paper discharge performance is slightly lowered and the paper dust residue is slightly generated.
From the results of Example 11, it was found that when the Shore A hardness exceeds 80 °, the effect of preventing the occurrence of shock eyes is slightly lowered and the wearability is slightly lowered.

On the other hand, from the results of Examples 7 to 10, by making the Shore A hardness within a range of 30 to 80 °, it is possible to more reliably prevent paper dust residue and shocks from occurring, It was confirmed that the wearability could be further improved.
Moreover, when Examples 7-10 were compared, it turned out that these effects can further be improved by making Shore A hardness into the range of 50-70 degrees.

Examples 12 to 15 and Comparative Examples 3 and 4
A rubber sheet was produced in the same manner as in Example 3 except that the thickness of the surface rubber layer was adjusted to the value shown in Table 3.
Each of the above tests was performed on the rubber sheets of the above Examples and Comparative Examples, and the characteristics were evaluated. The results are shown in Table 3 together with the results of Example 3.

From the results of Comparative Example 3 in the table, it was found that shock eyes were generated when the thickness of the surface rubber layer of the rubber sheet was less than 0.4 mm.
Moreover, from the result of the comparative example 4, when thickness exceeded 3.0 mm, it turned out that mounting property falls.
On the other hand, from the results of Examples 3 and 12 to 15, it was confirmed that by making the thickness within the range of 0.4 to 3.0 mm, it is possible to improve the wearability while preventing the occurrence of shock eyes. .

  Moreover, when Example 3 and 12-15 were compared, it turned out that these effects can further be improved by making thickness into 0.8 mm or more, especially 2 mm or more.

It is a front view which shows the part of the circumference | surroundings of the blanket cylinder which is the principal part of an example of an offset printing machine for enforcing the offset printing method of this invention. FIGS. 4A and 4B are diagrams showing a method for measuring the amount of paper warpage in order to evaluate the paper discharge performance in the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Blanket cylinder 10 Blanket cylinder 11 Printing blanket 2 Pressure cylinder 20 Drum 21 Rubber sheet

Claims (4)

  A paper is inserted between a blanket cylinder with a printing blanket on the outer periphery of the blanket cylinder and an impression cylinder pressed against the blanket cylinder, and an ink image transferred to the surface of the printing blanket is printed on the surface of the paper. What is claimed is: 1. An offset printing method for carrying out the above-mentioned process, wherein the pressure cylinder has a rubber shaft including a surface rubber layer on the outer periphery of the cylinder shaft.   A rubber sheet for use in the offset printing method according to claim 1, comprising a surface rubber layer having a loss tangent tan δ of 0.15 to 0.40 and a thickness of 0.4 to 3.0 mm. Rubber sheet.   The rubber sheet according to claim 2, wherein the Shore A hardness of the surface rubber layer is 30 to 80 °.   The rubber sheet according to claim 2, which has a laminated structure in which a surface rubber layer is formed on one side of at least one base material.

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