JPH1149997A - Emulsion ink for stencil printing - Google Patents

Abstract

(57) [Summary] [Problem] Clogging of a print drum screen does not occur.
Provided is a fluorescent emulsion ink for stencil printing which has good fixability, little image bleeding or strike-through, high fluorescent coloring, and good storage stability. SOLUTION: 20-80% by weight of oil phase and 80-20% of aqueous phase
In a water-in-oil (W / O) emulsion ink constituted by weight%, a pigment contained as a colorant in the ink is a fluorescent pigment obtained by a synthetic resin solid solution type bulk resin pulverization method, An emulsion ink for stencil printing, characterized in that the pigment has an average particle size of 0.2 to 1.3 μm, preferably 0.4 to 1.3 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an emulsion ink for stencil printing, and more particularly to water-in-oil (W / O).
The present invention relates to a stencil printing ink, which is a fluorescent ink of a type emulsion type, which has high fluorescent coloring property and good fixability.

[0002]

2. Description of the Related Art In stencil printing, stencil printing is performed using a stencil sheet, and ink is passed through a perforated portion of the stencil sheet to perform printing on a printing material such as paper. This stencil printing is used in a wide range of fields because of easy production of the stencil.

Conventionally, a water-in-oil (W / O) emulsion ink is generally used as a stencil printing ink, and a pigment or dye is used as a colorant. By using a mixture of a plurality of pigments or dyes of different colors, inks of almost any color can be produced without impairing printability.

For ordinary pigments such as furnace carbon black and cyanine blue, pigments having an average particle size of 0.4 μm or less, particularly 0.15 to 0.4 μm, are added as a colorant to the oil phase, It has already been reported that by setting the diameter to 10 μm or less, an emulsion ink having excellent fixability and storage stability can be obtained (JP-A-7-17-1).
No. 79799). Also, as for carbon black, by adding a carbon black having an average particle size of 20 to 45 nm and having a constant BET surface area as a colorant into an oil phase, an emulsion ink having excellent fixability and little set-off can be obtained. It has been reported (JP-A-8-737).
No. 95).

[0005]

However, in the case of a fluorescent color ink, the use of a fluorescent pigment cannot be obtained by mixing ordinary organic and inorganic pigments, so that the use of a fluorescent pigment is required. Fluorescent pigments used in general inks and paints are of the synthetic resin solid solution type, which is used for dissolving or dyeing the fluorescent dye during or after bulk polymerization of the synthetic resin, and obtaining the resulting colored bulk resin. Is pulverized into fine particles. However, the primary particle size of this fluorescent pigment is several times to several tens times larger than ordinary organic and inorganic pigments,
The pigment itself has a property that it is not easily crushed by mechanical force. Therefore, in the dispersion by three rolls used in the normal printing ink production process, the particle size distribution of the pigment hardly changes, and when a stencil emulsion ink of fluorescent color is produced by such a method, the printing drum screen and the plate This may cause clogging and the like, preventing proper printing.

The fixing of the stencil printing ink is performed through a process in which the ink permeates into the printing paper. Therefore, even if the pigment particles are successfully passed through the printing drum screen and the plate by taking measures such as increasing the opening diameter of the printing drum screen and the plate, the fluorescent pigment has a large particle diameter because of the pigment particle size. There are inconveniences such as that the pigment itself hardly penetrates into the paper, remains on the surface of the printing paper, and the fixability is likely to be deteriorated, and the fluorescent pigment is dropped off by applying only a slight friction to the printing surface.

Some of the synthetic resin solid solution type fluorescent pigments are obtained by an emulsion polymerization method. This type of fluorescent pigment is an ultrafine particle having an average particle size of 1 μm or less, and is generally used for paper coating, water-based ink, and marker, and has good printability. However, when this is used in a stencil printing emulsion ink, although the fixing property is improved, the ionic surfactant remains in the pigment in the pigment production process, so that the storage stability of the emulsion ink is significantly impaired. It is not practical.

In the case of the fluorescent pigment, since the affinity for the oil phase of the emulsion ink is considered to be different from that of ordinary organic and inorganic pigments since it is based on a synthetic resin, the fixing property of the fluorescent color emulsion ink and the backing property of the fluorescent ink are different. In order to solve the transfer, Japanese Patent Application Laid-Open Nos. 7-179799 and 8-7
The suggestion in 3795 is not helpful.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art, to prevent clogging of a printing drum screen, to have good fixability, to reduce image bleeding or strike-through, and to have high fluorescence coloring. It is an object of the present invention to provide a fluorescent emulsion ink for stencil printing having good storage stability.

[0010]

According to the present invention, an object of the present invention is to provide a water-in-oil (W / O) emulsion ink comprising 20 to 80% by weight of an oil phase and 80 to 20% by weight of an aqueous phase. A pigment contained as a colorant in the ink is a fluorescent pigment obtained by a synthetic resin solid solution type bulk resin pulverization method, and the average particle size of the fluorescent pigment is 0.2 to
1.3 μm, preferably greater than 0.4 μm and 1.3
It is achieved by an emulsion ink for stencil printing, which is not more than μm.

The fluorescent pigment used in the present invention is obtained by dissolving or dyeing a fluorescent dye which develops various hues during or after bulk polymerization of a synthetic resin and pulverizing the obtained colored bulk resin to obtain fine particles. It is a so-called synthetic resin solid solution type. As the synthetic resin for supporting the dye, melamine resin, urea resin, sulfonamide resin, alkyd resin, polyvinyl chloride, and the like can be used. Generally, synthetic resin solid solution type fluorescent pigments on the market are powders having an average particle size of about 2 to 6 μm, and are not easily pulverized by ordinary premixing or dispersion with three rolls. It cannot be used in the emulsion ink of the present invention. However, these commercially available fluorescent pigments can be controlled to an average particle size of 0.2 to 1.3 μm by making them into fine particles with a known disperser or pulverizer. As the disperser or pulverizer, for example, commercially available ones such as a general vertical or horizontal sand mill, a coball mill, and a pearl mill PM-DCP type can be used. In this case, it is convenient to mix the fluorescent pigment with another oil phase component such as a solvent and wet-pulverize the mixture. The fluorescent pigment is desirably contained in an amount of 6 to 25% by weight, preferably 10 to 20% by weight based on the total amount of the ink of the present invention.

It is generally assumed that the W / O emulsion ink for stencil printing has been fixed on a printing medium through the following process. That is, the oil phase, which is the external phase of the emulsion, is mainly composed of a so-called varnish composed of a solvent and a resin, and has a very high affinity for paper fibers. Wet quickly and separate from aqueous phase components. The paper fiber wetted with the oil phase component becomes a flow path for transporting the emulsion that flows one after another due to the printing pressure in the thickness direction of the printing paper, and reaches this emulsion to a portion that is not wet with the oil phase component. When the emulsion reaches this portion, the paper fibers are wetted by the oil phase component and separate from the aqueous phase component, as described above. The above-described phenomenon is repeated in the thickness direction of the printing paper sequentially until the ink pushed out to the printing paper by the printing pressure runs out. During this process, or for a while after the termination, the volatile solvent in the water and oil phase evaporates, and finally the fixing of the emulsion ink is terminated.

Since the pigment is dispersed in the oil phase, it usually penetrates the printing paper together with the oil phase. However, when the wettability between the pigment and the varnish is low, the pigment separates from the oil phase while the oil phase penetrates the printing paper, and the other oil phase components penetrate deep into the paper, while the pigment is printed on the printing paper. It may be left on the surface layer and cause deterioration of fixability and set-off. But,
Since the fluorescent pigment used in the present invention is based on a synthetic resin, it has a good affinity for varnish, and there is almost no problem of such separation from the oil phase.

If the particle size of the pigment is larger than the gap between the paper fibers, the pigment may separate from the oil phase on the surface of the printing paper and cause poor fixability and set-off, as described above. is there. Conversely, if the pigment particle size is too small, the pigment may penetrate too much in the plane direction and thickness direction of the printing paper, resulting in low print density, fine print bleeding, strikethrough, and the like. However, in the present invention, the average particle size is 0.2 to 1.3 μm.
m Preferably, the fluorescent pigment controlled to 0.4 to 1.3 μm is used, so that the fluorescent pigment contained in the oil phase is fixed at an appropriate position in the printing paper, and the fluorescent coloring property is good. Image bleeding, strikethrough, and fixability are improved.

[0015] Further, the emulsion ink of the present invention comprises:
Since the synthetic resin-based fluorescent pigment having a high affinity for varnish is contained by controlling to the above average particle diameter, the dispersion stability in the emulsion is high, the storage stability over time is also good, and It is practical without causing clogging of the pigment in the printing drum screen and plate.

The water-in-oil (W / O) emulsion ink of the present invention can be used, for example, in an oil phase of 20 to 80% by weight,
It can be produced by gradually adding and emulsifying a 20% by weight aqueous phase. The oil phase is basically composed of the fluorescent pigment, resin, solvent, emulsifier, and the like. The aqueous phase can be composed of water, if necessary, containing an electrolyte, a fungicide, an antioxidant, a water evaporation inhibitor, a water-soluble polymer, and the like.

The solvent can be composed of a nonvolatile solvent and a volatile solvent. As the non-volatile solvent, mineral oils such as motor oil, spindle oil, machine oil and liquid paraffin, olive oil, castor oil, vegetable oils such as salad oil are used, and as the volatile solvent, known mineral oil solvents and vegetable oils A solvent is used. The proportions of these (nonvolatile solvent / volatile solvent) vary depending on the blending ratio of the oil phase and the aqueous phase, but are 50 to 95/50 to 5 by weight.
A range of weight percent is desirable.

The resin is contained in the oil phase as a fixing agent for the fluorescent pigment. Such resins include, for example, rosin-based resins, rosin-modified resins, phenolic resins, petroleum resins,
Examples thereof include alkyd resins, rubber derivatives, and polymerized castor oil, and one or more of these can be added. The addition amount of the resin is preferably 2 to 20% by weight based on the total amount of the ink.

The emulsifier is used to form a water-in-oil (W / O) emulsion, and a nonionic surfactant is preferably used. For example, a higher sorbitan fatty acid ester (eg, sorbitan monolaurate, Sorbitan monopalmitate, etc.), fatty acid glycerides (eg, oleic acid monoglyceride, oleic acid diglyceride, etc.), and higher alcohols, alkylphenols,
Examples include ethylene oxide adducts such as fatty acids.

[0020]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. In addition, the part in an example means a weight part.

Example 1 A W / O emulsion ink was prepared according to the formulation shown in Table 1 by the following method. First, fluorescent pigment, alkyd resin, #
Forty motor oil and Nisseki No. 5 solvent (manufactured by Nippon Oil Co., Ltd.) are sufficiently stirred, the fluorescent pigment is dispersed and pulverized by a sand mill, and sorbitan monooleate is added thereto and sufficiently stirred to obtain an oil phase component. While gradually adding ion-exchanged water in which ethylene glycol was sufficiently dissolved in the oil phase component, emulsification was performed with a stirrer to obtain a stencil printing emulsion ink. The average particle size of the fluorescent pigments shown in Table 1 is
It is a value measured by a laser diffraction particle size distribution analyzer (SALD2000A manufactured by Shimadzu Corporation) after dispersion and pulverization.

Examples 2 to 3 Emulsion inks for stencil printing were obtained in the same manner as in Example 1 except that the composition and average particle size were as shown in Table 1.

Comparative Examples 1 to 3 Emulsion inks for stencil printing were obtained in the same manner as in Example 1 except that the composition and the average particle size were as shown in Table 1.

[0024]

[Table 1]

Test Example A stencil printing machine (Risograph GR275, manufactured by Riso Kagaku Kogyo Co., Ltd.) using each of the fluorescent emulsion inks for stencil printing obtained in Examples 1 to 3 and Comparative Examples 1 to 3.
Stencil printing is performed, and the resulting printed matter has a fluorescent coloring property,
The strikethrough, bleeding, and fixability were evaluated. In addition, clogging of the drum screen and the plate was also evaluated. Each evaluation method is as follows. Also,
Table 2 shows the evaluation results.

(1) Fluorescent Chromogenicity: The solid portion of the printed matter was evaluated by visual observation. When the fluorescent chromaticity was particularly strong, it was evaluated as ◎, when it was strong, as ○, and when weak, it was evaluated as ×. (2) Run-through: The solid printed portion was visually evaluated on the back side of the solid portion. (3) Bleeding: The fine print portion of the printed matter was observed using a microscope (80x), and was evaluated as ○ when there was almost no bleeding, and as X when bleeding was conspicuous. (4) Fixing property: The solid portion of the printed matter 24 hours after printing was rubbed five times with a clock meter (manufactured by Toyo Seiki Co., Ltd.), and the degree of rubbing of the stamp surface after rubbing was observed. 、: The case where the rubbing was poor was evaluated by ×. (5) Clogging of the drum screen and plate: printing 1000 sheets, observing the 10th and 1000th images,
If the image portion of the 000th image did not change compared to the image of the 10th image, it was evaluated as ○.

[0027]

[Table 2]

From Table 2, it can be seen that Examples 1 to 3 are superior to Comparative Example 1 in terms of fluorescence coloring, strike-through, and bleeding, and are superior to Comparative Examples 2 and 3 in terms of fixing property, It was also shown that the plate was less clogged.

[0029]

The W / O emulsion ink of the present invention has, as a colorant, an average particle diameter obtained by a synthetic resin solid solution type bulk resin pulverization method of 0.2 to 1.3 μm,
Preferably, it contains a fluorescent pigment having a size of more than 0.4 and not more than 1.3 μm, so that clogging of the printing drum screen does not occur, fixability is good, image bleeding or strike-through is small, and fluorescent coloration is high. Thus, a fluorescent emulsion ink for stencil printing having excellent storage stability can be obtained.

Claims (2)

[Claims] 1. An oil phase of 20 to 80% by weight and an aqueous phase of 80 to 20%
In a water-in-oil (W / O) emulsion ink constituted by weight%, a pigment contained as a colorant in the ink is a fluorescent pigment obtained by a synthetic resin solid solution type bulk resin pulverization method, An emulsion ink for stencil printing, wherein the pigment has an average particle size of 0.2 to 1.3 [mu] m. 2. The emulsion ink for stencil printing according to claim 1, wherein the average particle size of the fluorescent pigment is larger than 0.4 μm.