JP3053167B2 - Blanket for offset printing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a blanket for offset printing used in an offset printing machine.

[0002]

2. Description of the Related Art In offset printing, an image from a printing plate is once transferred to a blanket, and the image transferred to the blanket is printed on paper. A printing unit in an offset printing press will be described. A general printing unit is, as shown in FIG. 2, a plate cylinder 3 on which a printing plate 1 is mounted.
An ink device 5 for supplying ink to the printer and a water supply device 7 for supplying dampening water are arranged. Further, a printing paper 11 is provided together with a blanket cylinder 10 mounted with a blanket 9 which rotates in conjunction with the plate cylinder 3. Is basically constituted by an impression cylinder 13 which presses and clamps a blanket cylinder 10. When using this, first, the printing plate 1 is supplied with dampening water from the water supply device 7, then the ink is supplied from the inking device 5, and the ink image on the plate is transferred to the blanket 9, and this image is transferred to the blanket 9. Is printed on the printing paper 11 that passes between the impression cylinder 13.

[0003] Such fountain solution is used to prevent ink from adhering to non-image areas. The main components of the fountain solution conventionally used are acids such as phosphoric acid, citric acid and tannic acid, salts such as phosphate, nitrate and dichromate, and water-soluble solutions such as gum arabic, carboxymethyl cellulose and sodium alginate. It is composed of a functional polymer, alcohol such as isopropyl alcohol, ethyl alcohol and glycols.

[0004]

However, offset printing using such dampening solution has the following problems. That is, when one printing is completed, the blanket surface is cleaned and the printing plate is replaced with a new printing plate. By this plate change, when the non-image area was changed to the image area at the time of the previous printing on the blanket, the ink transfer was reduced at the non-image area at the time of the previous printing, and the ink ride became thinner. is there. This phenomenon is generally called a non-image portion ghost.

[0005] A non-image portion ghost will be described with reference to FIG. FIG. 3A shows the image portion 15 at the time of printing before the plate change.
3 and (B) are the image portion 19 and the non-image portion 20 at the time of printing after the plate change, and FIG.
When the image portion 19 is printed as shown in (c), the portion of the image portion 19 excluding the portion overlapping with the image portion 15, that is, the portion shown by oblique lines is printed thinner than the portion overlapping with the image portion 15.

Various studies have been conducted on why such non-image area ghosts occur, and based on the expectation that they may be related to the dampening solution and the surface rubber layer of the blanket. Then, the blanket in which the non-image area ghost occurred was collected, and the shaded area (the area with low image density) in the image area 19 except for the area overlapping with the image area 15 was analyzed with an x-ray microanalyzer. Turned out to exist. Calcium phosphate is insoluble in water, but is very hydrophilic. Then, it is considered that the ink affinity from the plate to the blanket is hindered because the ink affinity at the portion where the calcium phosphate adheres is reduced, and as a result, the image density on the paper at the portion is reduced. The mechanism of deposition of calcium phosphate on the blanket is thought to be that calcium in the ink or paper reacts with the phosphoric acid in the dampening solution on the blanket to form.

In particular, since a large amount of calcium carbonate is contained in the coating agent on the surface of the printing paper, the calcium carbonate separates from the paper and deposits on the blanket and reacts with the phosphoric acid component in the dampening solution. Probably generated. The calcium phosphate deposited on this blanket is insoluble and the crystals are fine. Further, fine irregularities are formed on the surface of the blanket in order to maintain the reproducibility of halftone dots forming the print image and the removability of the blanket. There is a problem that it is difficult to remove calcium carbonate once deposited due to the fine unevenness. Therefore, even if the blanket is washed at the time of plate change, it cannot be removed,
The ghost in the non-image area could not be eliminated.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the invention is to modify at least the uppermost layer of the surface rubber layer to thereby provide offset printing with excellent print quality without a non-image area ghost. It is intended to provide a blanket.

[0009]

The present invention has the following configuration to achieve the above object. That is, the offset printing blanket according to claim 1 of the present invention is an offset printing blanket comprising a support composed of one or more sheets and a surface rubber layer laminated on the support. At least the uppermost layer is formed of a rubber containing an anion scavenger for trapping an acid component contained in dampening water. The offset printing blanket according to claim 2 is characterized in that the anion scavenger is an inorganic acid salt . In addition, the Mu
Wherein the Kisanshio compound is hydrotalcite. Further, the inorganic acid salts are tribasic lead sulfate. The blanket for offset printing according to claim 5 is characterized in that the anion scavenger is blended in a proportion of 2 parts by weight or more.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A blanket according to the present invention
If it is a compressible blanket, it does not matter whether it is an incompressible blanket. For example, as shown in FIG. 1, rubber paste is applied to a cotton cloth and laminated in two layers to form a support body 15, After the compressible layer 17 is formed thereon, an oil-resistant surface rubber layer 20 is further laminated on the compressible layer 17 via a support 19 made of cotton cloth. 21 has a structure formed of a rubber in which an anion scavenger for scavenging an acid component contained in water is added. The support 15 and the support 19 may be made of a known woven cloth such as rayon cloth or polyester cloth in addition to cotton cloth. The surface rubber layer 20 may be made of, for example, chloroprene rubber, nitrile rubber, acrylic rubber, or the like. One or more of a vulcanizing agent such as sulfur, a vulcanization accelerator, an antioxidant and the like are added to the oil-resistant rubber.

As described above, once the calcium carbonate contained in the printing paper reacts with the phosphoric acid component in the fountain solution and deposits on the blanket, fine irregularities are formed on the blanket surface. It is extremely difficult to remove them. Therefore, in order to prevent the deposition of calcium phosphate on the blanket, it is desirable to inhibit the reaction between the phosphoric acid component in the fountain solution and the calcium component coming from printing paper or ink. The present invention is characterized in that in order to inhibit the reaction between the phosphoric acid component and the calcium component, an anion scavenger for trapping the phosphoric acid component contained in the fountain solution is blended in the surface rubber layer.

The entire surface rubber layer 20 may be formed of a rubber containing an anion scavenger, but at least the uppermost layer 21 in contact with the printing paper is formed of a rubber containing an anion scavenger. The addition of an anion scavenger acts to immobilize phosphate ions on the blanket.
Inorganic acid salts such as hydrotalcite and tribasic lead sulfate can be used as the anion scavenger. A typical composition of the hydrotalcite is Mg ₆ Al ₂ (OH)
₁₆ CO ₃ .4H ₂ O. The anion scavenger,
It is preferable to mix at a ratio of 2 parts by weight or more.

[0013]

EXAMPLES Examples of the present invention will be described below together with comparative examples. The configuration of the blanket in the following Examples and Comparative Examples was a compressible blanket with normal surface polishing. The composition of the surface rubber layer is as shown in Tables 1 and 2.

[0014]

[Table 1]

[0015]

[Table 2]

The printing conditions are as follows. The printing machine used was Lithrone 226 (trade name) manufactured by Komori Corporation.
F Recommended fountain solution. The printing paper used was Shinto Oji Paper's Kinto Art 76.5 kg, and the printing plate used was a non-image part on the entire surface. Printing speed is 10,000 sheets /
At this time, the printing pressure was 0.10 mm and the printing pressure was 0.15 mm.

[0017]

[Table 3]

In the printing procedure, the ink roller of the inking unit was separated from the plate cylinder, and only the dampening solution was supplied to the printing plate to perform printing under the above conditions. After printing a predetermined number of sheets, the blanket was removed, the blanket surface was washed with distilled water, and after drying, the surface layer was analyzed with an X-ray microanalyzer to check for the formation of calcium phosphate. The results are as shown in Table 4.

[0019]

[Table 4]

As is clear from the above results, the formation of calcium phosphate on the blanket can be suppressed by adding an anion scavenger. The anion scavenger is
In order to obtain a sufficient effect, it is preferable to add 2 parts by weight or more.

[0021]

In the blanket for offset printing according to the present invention, at least the uppermost layer of the surface rubber layer is formed of a rubber containing an anion trapping agent for trapping an acid component contained in the dampening water. And the deposition of calcium phosphate on the blanket can be prevented. As a result, a blanket with improved ink transferability and stable print quality can be obtained.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view showing an example of a blanket according to the present invention.

FIG. 2 is an explanatory diagram of a printing unit in the offset printing press.

FIG. 3 is an explanatory diagram illustrating a non-image portion ghost phenomenon.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 printing plate 3 plate cylinder 5 inking device 7 water supply device 9 blanket 10 blanket cylinder 11 printing paper 13 impression cylinder 15 support 17 compressible layer 19 support 20 surface rubber layer 21 uppermost layer of surface rubber layer

Claims (5)

(57) [Claims] 1. An offset printing blanket comprising at least one support and a surface rubber layer laminated on the support, wherein at least the uppermost layer of the surface rubber layer is contained in dampening water. A blanket for offset printing, wherein the blanket is made of a rubber compounded with an anion scavenger for trapping an acid component. 2. The offset printing blanket according to claim 1, wherein the anion scavenger is an inorganic acid salt . 3. The blanket for offset printing according to claim 2, wherein said inorganic acid salt is hydrotalcite. 4. A blanket for offset printing according to claim 2, wherein said inorganic acid salt is tribasic lead sulfate. 5. The blanket for offset printing according to claim 2, wherein the anion scavenger is blended in a proportion of 2 parts by weight or more.