JPS5921317B2 - Carrier sheet for offset printing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a carrier sheet for use in simple offset printing machines.

Simple offset printing is a method used for printing relatively small numbers of copies. In normal offset printing, a zinc plate is used as a printing carrier, but if the number of copies to be printed is not that large, it is not desirable to use an expensive zinc plate from the viewpoint of cost. In terms of materials, any material may be used as long as it has sufficient performance to print the desired number of copies, and even a rubber sheet can achieve the intended purpose. By adopting a printing carrier using this rubber sheet, it has become possible to significantly reduce costs. However, this method has problems such as toxicity and fire danger due to the solvent used to clean the print carrier after printing, and it also takes time to clean the print carrier, so it is not necessarily preferable. .

In order to overcome these drawbacks, a method has been proposed in which a removable, disposable carrier sheet is used instead of a print carrier using a rubber sheet.

In this method, the carrier sheet after printing is discarded as it is and does not require cleaning with a solvent, so it has excellent features in terms of health, disaster prevention, and workability. In this way, the practicality of simple offset printing machines has increased with the development of disposable carrier sheets.

In particular, the development of a method of using rubber latex foam as a carrier sheet has solved many problems required for carrier sheets, such as water wettability, ink absorption, ink receptivity, and ink transferability.

JP-A-50-26609 discloses a method in which filler-free rubber latex is coated onto a carrier substrate, suitably reticulated and used as an intermediate carrier sheet. The carrier sheet produced by this method has excellent printability and has the necessary physical properties as a carrier sheet, such as resilience, which allows it to maintain sufficient contact with the substrate for a long period of time; It has the strength to withstand mechanical tension, tearing force, etc.

Furthermore, since inexpensive paper can be used as the carrier base material and latex can be continuously coated, the cost of the carrier sheet can be significantly reduced. However, the carrier sheet produced by this method has the following drawbacks when used for offset printing.

1. The elasticity of foamed rubber latex decreases over time, limiting the number of copies that can be printed.

2. Ink absorbency decreases due to swelling and deterioration of rubber due to printing ink.

3. It is difficult to maintain surface uniformity at the stage of foaming, gelling, and reticulating rubber latex to produce a carrier sheet, and as a result, the gloss and clarity of the printed surface are impaired.

4. Since the surface strength of the carrier sheet is low, the carrier sheet will be damaged if a highly tack ink is used.

The inventors of the present invention have made intensive studies to improve these drawbacks, and have discovered that by specifying the rubber latex to be used, an excellent carrier sheet that has improved these drawbacks can be obtained, and has thus arrived at the present invention.

That is, in the present invention, bound styrene is 15 to 40% by weight,
For offset printing made by foaming, applying and molding a styrene-butadiene copolymer latex with an average polymer particle diameter of 2,500 to 7,000 particles, a rubber solid content of 60 to 75% by weight, and a gel content of 20 to 70% by weight. It is a carrier seat.

The styrene-butadiene copolymer latex (hereinafter referred to as SBR latex) used in the carrier sheet of the present invention is obtained by adding styrene monomer and butadiene monomer in a predetermined ratio in a pressure vessel and carrying out conventional emulsion polymerization.

In addition, the particle size of latex can be determined using known chemical methods.
It can be controlled by a physical particle size enlargement method. The proportion of styrene in the copolymer in SBR latex is 15 to 40% by weight, more preferably 2% by weight.
It is 0 to 30% by weight. Outside this range, the ink receptivity of the carrier sheet used and the transferability to the printing material will deteriorate rapidly. In other words, if the styrene content is less than 15% by weight, compatibility with the ink is good, but the picking resistance of the carrier sheet surface decreases due to swelling or softening caused by the ink over time, and an ink with a high tack value is used. If the content of styrene exceeds 40% by weight, it becomes difficult to make the latex reticulate, making it difficult to obtain optimal printability, and at the same time, elasticity is lost and printing durability (number of printable copies) is reduced. Note that the SBR latex used in the present invention may be a polar group-containing latex.

Examples of polar groups include carboxyl groups, ester groups, and nitrile groups.

Monomers having carboxyl groups include unsaturated monomers such as acrylic acid, methacrylic acid, itaconic acid, and maleic acid;
or dicarboxylic acids, and examples of monomers having ester groups include unsaturated acid esters such as acrylic esters, methacrylic esters, itaconic esters, and maleic esters. Further, examples having a nitrile group include acrylonitrile and the like. Latexes obtained by copolymerizing monomers having these polar groups with styrene monomers and butadiene monomers can also be used in the present invention. For a carrier sheet to have excellent printability, the smoothness of the sheet surface and the uniformity of the foam structure are extremely important, and these are greatly influenced by the latex.

In other words, in order to prevent the occurrence of surface cracks or destruction of the foam structure caused by volumetric shrinkage due to drying of the latex foam used as a carrier sheet, and to maintain surface uniformity,
The solids content of the latex used should be between 60 and 75% by weight, more preferably between 65 and 75%. In addition, in order to form a uniform foam structure, the average particle diameter of the latex should be 2500 to 7000λ, more preferably 3
It must be between 000 and 6500λ. SB of the present invention
In manufacturing a carrier sheet using R latex, a compounded latex is first prepared by adding a desired chemical to the latex. These chemicals include stabilizers, anti-aging agents, vulcanization accelerators, vulcanizing agents, thickeners, etc. Furthermore, an anti-tack agent, an antistatic agent, etc. may be added as necessary. The chemically loaded latex is then mechanically foamed in batches or continuously and applied to the carrier substrate.

A gelling agent is added if necessary prior to foaming. As the gelling agent, common latex gelling agents such as sodium silicate and ammonium acetate can be used. The carrier base material coated with the foamed latex is gelled by a method such as preheating, and then subjected to a heating process to complete reticulation and obtain a carrier sheet. In the present invention, the gel content (ratio of toluene-insoluble matter in the copolymer) in the SBR latex is 20 to 70% by weight, preferably 40 to 65% by weight. This makes it possible to improve ink affinity, ink receptivity, and therefore printing durability without deteriorating the physical properties of the carrier sheet. Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

Examples and Comparative Examples Chemicals were placed in an autoclave according to the formulations shown in Table 1, and reacted at 5° C. with stirring.

When the conversion rate reached 60%, the reaction was stopped to obtain SBR latex. Further, the particle size of the latex was enlarged by mechanical stirring. Unreacted monomers were removed and concentrated to 69% solids by vacuum evaporation to form latexes A-D, J.
,K was obtained. Latexes E and I were obtained by adjusting the degree of enlargement of the particle size of latex C.

Dilute Latex C with water and adjust the solid content to 40%.
Latex F and latex C were further concentrated to 70% to obtain latex G. Latex H was obtained by polymerization in exactly the same manner as Latex C, except that 6.0 parts by weight of potassium oleate was used. The general properties of these latexes are shown in Table 2. Using latex A-K, table-
A formulation was prepared by mixing No. 3. These formulations in Table 3 were foamed to about 2.5 times the volume using a whisk, and 1.0 part by weight (solid content) of a 15% ammonium acetate aqueous solution was added.

The mixture was further stirred at low speed for 1 minute to stabilize the foam. This was applied to a thickness of about 0.1 mm on high-quality non-coated paper, the surface was heated with an infrared heater for 30 seconds, and further dried for 10 minutes with a hot air dryer at 130° C. to obtain a carrier sheet. M-
This carrier sheet was attached to a Type 3 offset printing machine (manufactured by Miyakoshi Kikai Seizo Co., Ltd.) and printing was performed, and the results are shown in Table 4.

According to the results in Table 4, if the bound styrene content is less than 15% (4
) If the printing inkability is poor, if it exceeds 40%, the printing durability will decrease, and if the solid content of the latex is low (F1 shows that the function as printability is generally poor 〇 Furthermore, the average particle If the diameter is less than the specified range (or the gel content is less than the specified range), the strength of the carrier sheet will decrease and it will be easily damaged during printing, and if the gel content exceeds the specified range ( J) It can be seen that when the ink receptivity deteriorates and the average particle diameter exceeds a predetermined range, (1) halftone dot reproducibility in printing durability is poor.

Claims (1)

[Claims] 1. A styrene-butadiene copolymer latex containing 15 to 40% by weight of bound styrene, an average polymer particle diameter of 2,500 to 7,000 Å, a rubber solid content of 60 to 75% by weight, and a gel content of 20 to 70% by weight is foamed. A carrier sheet for offset printing that is coated and formed.