JP2006124476A - Emulsion ink for mimeographing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an emulsion ink for mimeographing that has increased stability more than conventional product without deterioration of the storage stability under elevated temperature condition and no occurrence of bleeding and offset. <P>SOLUTION: The first carbon black having DBP oil absorption of more than 90 cm<SP>3</SP>/100 g and the second carbon black having DBP oil absorption of less than 50 cm<SP>3</SP>/100 g are used together as a coloring pigment and charged in the oil phase constituting the emulsion ink for W/O type mimeographing. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an emulsion ink for stencil printing.

  Stencil printing is simpler and easier to operate than offset printing and other full-fledged printing methods. Before electrostatic copiers became popular, simple printing for office use, etc. Widely used. However, in recent years, it has become possible to digitize by combining a heat-sensitive stencil sheet and a thermal head, and accordingly, the perforation size of the stencil sheet has been standardized, making it easier to control the amount of ink transferred, Since it has become possible to improve the image quality of printed images, stencil printing has become a spotlight as a new printing method that is easy to operate and has a high printing speed, similar to electrostatic copying machines. is there.

In a digital stencil printing apparatus, a heat-sensitive stencil sheet, which is usually formed into a long strip and rolled up in a roll, is fed into a document image read by an image scanner while being fed out a predetermined amount from the roll. By operating the thermal head in accordance with the corresponding digital signal, a minute through hole corresponding to the original image is punched in the stencil sheet that has been fed out.
Next, in a state where the stencil sheet with the through-holes is wound around the outer periphery of the plate cylinder formed in the porous structure, together with the printing medium such as paper stacked on the outer side, the entire plate cylinder, A squeegee roll disposed in the plate cylinder and supplied with ink on the surface thereof, and a pressure roll pressed against the squeegee roll from the outside of the plate cylinder with the plate cylinder, the stencil sheet, and the printing medium in between. Pass between. As a result, the ink passes selectively from the squeegee roll side to the printing body side only on the portion of the stencil sheet where the through-holes are perforated, and a printed image corresponding to the original image is printed on the surface of the printing body. The

In recent years, each of the above parts has been placed in a casing of the same size as an electrostatic copying machine, etc., and each process has been automated so that it can be performed with the same simple operation as copying with an electrostatic copying machine. Things are in practical use.
As the ink for the stencil printing apparatus, generally used is an emulsion ink having a W / O (water-in-oil) type composed of an oil phase and an aqueous phase and containing a color pigment in the oil phase. In this emulsion ink, the ratio of the aqueous phase is generally set higher than that of the oil phase. This is because the aqueous phase reduces the viscosity change of the emulsion ink with respect to the temperature change, increases the penetration speed into the printing medium such as paper, increases the structural viscosity, prevents dripping in the stencil printing apparatus, This is because it has an effect of preventing the yarn from being unwound when the substrate is peeled off from the stencil sheet. Further, in the oil phase, it is common to add a volatile solvent to the base solvent in order to prevent dripping while lowering the viscosity of the emulsion ink.

  However, W / O type emulsion inks in which the ratio of the aqueous phase is increased and the volatile solvent is contained in the oil phase, the volatile solvent is removed when the stencil printing apparatus is stopped for a long time. Vaporization changes the composition or the emulsions coalesce, making the emulsions easily disintegrated. When the emulsions disintegrate, only the colored pigment with a small oil absorption can retain the oil retained by the whole emulsion. Therefore, there is a problem that excessive oil is discharged and so-called dripping of ink tends to occur inside the stencil printing apparatus. Specifically, ink whose viscosity has fallen significantly due to the collapse of the emulsion and the excess oil being discharged flows down from the surface of the squeegee roll, collects on the inner periphery of the plate cylinder, and oozes out from the gap with the stencil sheet. Or flows out of the gap between the plate cylinder and the flange that supports the plate cylinder.

Therefore, in order to prevent the emulsion from collapsing even if the stencil printing machine is stopped and left for a long time, an emulsion ink is used in combination with a color pigment and an extender pigment having a larger DBP oil absorption than the color pigment. It has been proposed to improve the stability (see Patent Document 1).
JP 2001-311027 A (claim 1, column 0006, column 0009 to column 0015)

  However, according to the inventor's study, especially when an extender pigment having a DBP oil absorption larger than that of carbon black is added to a black emulsion ink containing carbon black as a color pigment, which is widely used for monochrome printing, When the emulsion ink is stored in a high temperature environment, there arises a new problem that the emulsion collapses or the viscosity greatly fluctuates. This is because the extender pigment is not well dispersed in the oil phase suitable for the dispersion of carbon black, and is particularly easily separated from the oil phase during storage at a high temperature.

  Therefore, the inventor studied to improve the stability of the emulsion ink by using carbon black as a coloring pigment, which has a higher DBP oil absorption than before, and hardly releases oil. However, in that case, the fluidity of the emulsion ink is greatly reduced, and the permeability to the printing medium such as paper is deteriorated. It has been found that when a new printed material to be printed next is superimposed on the body, the printing is blurred or the back surface of the stacked printed material is stained, so-called set-off.

  The object of the present invention is to reduce the storage stability at high temperature of black emulsion ink for stencil printing containing carbon black as a coloring pigment, without causing bleeding or setback of printing during continuous printing. It is to improve its stability more than ever.

Invention according to claim 1, a W / O type emulsion ink for stencil printing consisting of an oil phase and an aqueous phase, an oil phase, DBP oil absorption amount first is 90cm ^3/100 g or more carbon black and a stencil printing emulsion ink DBP oil absorption is characterized by containing a second carbon black is less than 50 cm ^3/100 g.
The invention described in claim 2 is a B-type viscometer and a No. The viscosity of the oil phase η ₁ when the rotational speed of the rotor is 6 rpm and the viscosity η ₂ of the oil phase when the rotational speed is 60 rpm, measured at a measurement temperature of 23 ± 1 ° C. using a 4-rotor. The emulsion ink for stencil printing according to claim ₁ , wherein the ratio η ₁ / η ₂ is 2.0 to 4.5 and the viscosity η ₂ is 1000 to 3000 cP.

The invention according to claim 3 is the emulsion ink for stencil printing according to claim 1, wherein the first carbon black has a nitrogen adsorption specific surface area of 100 m ² / g or less.

In the emulsion ink of the invention described in claim 1, as a coloring pigment, DBP oil absorption amount are used in combination with different first and second carbon black is the one, DBP oil absorption of 90cm ^3/100 g or more first Since the carbon black of 1 functions to keep the oil in the oil phase well, the stability of the emulsion ink can be improved. Therefore, even if the stencil printing apparatus is stopped and left for a long time, it is possible to prevent the emulsion from collapsing and prevent ink dripping or the like from occurring.

Moreover, in the said emulsion ink, since the 2nd carbon black whose DBP oil absorption is 50 cm < ³ > / 100g or less is used together, it can suppress that the fluidity | liquidity of emulsion ink falls significantly. For this reason, the emulsion ink maintains good penetrability to the printed material such as paper, prevents the drying of the printing from slowing down, and prevents the printing from bleeding or set off during continuous printing. Can be prevented.

Moreover, since the emulsion ink does not contain solid components that do not dissolve in the oil phase, such as extender pigments, in addition to the first and second carbon blacks as the color pigment, the emulsion ink was stored particularly in a high-temperature environment. At this time, the emulsion does not collapse or the viscosity does not fluctuate greatly.
Therefore, according to the first aspect of the invention, the black emulsion ink for stencil printing containing carbon black as a color pigment is deteriorated in storage stability at high temperature, or bleeding or setback of printing is observed during continuous printing. Without it occurring, the stability can be improved more than before.

Incidentally, in the invention according to the first aspect, the DBP oil absorption of the first carbon black is limited to 90cm ^3/100 or more, the DBP oil absorption is less than 90cm ^3/100 g, the first carbon black This is because, by blending, the oil in the oil phase is favorably retained and the effect of improving the stability of the emulsion ink cannot be obtained. Further, the DBP oil absorption of the second carbon black is limited to 50 cm ^3/100 g, when the DBP oil absorption amount exceeds 50 cm ^3/100 g is by using them in combination with the second carbon black, This is because the effect of maintaining good penetrability of the emulsion ink into the printing medium by suppressing the fluidity of the emulsion ink from being greatly reduced cannot be obtained.

The oil phase comprising the two types of carbon black and constituting the emulsion ink together with the aqueous phase is, as described in claim 2, a B-type viscometer and no. The viscosity of the oil phase η ₁ when the rotational speed of the rotor is 6 rpm and the viscosity η ₂ of the oil phase when the rotational speed is 60 rpm, measured at a measurement temperature of 23 ± 1 ° C. using a 4-rotor. And the ratio η ₁ / η ₂ is 2.0 to 4.5, and the viscosity η ₂ is preferably 1000 to 3000 cP.

When the viscosity η _{2 of the} oil phase is less than 1000 cP, the aqueous phases that are the internal phases of the W / O type emulsion are likely to aggregate, and the stability of the emulsion ink may be reduced. In addition, the W / O emulsion ink generally has an oil phase that is an outer phase that is more easily penetrated into a printing medium such as paper than a water phase that is an inner phase, and has a lower surface tension. At the time of printing, the oil phase first penetrates into the printing medium, and then the water phase penetrates and / or volatilizes. Therefore, when the viscosity η _{2 of the} oil phase exceeds 3000 cP, the permeability of the oil phase to the printing medium decreases, so that the emulsion ink does not penetrate into the printing medium and remains on the surface. The time becomes longer, the drying of the printing becomes slower, and there is a possibility that the printing may be blurred or set off when continuously printed. On the other hand, if the viscosity η _{2 of the} oil phase is 1000 to 3000 cP, the drying of the printing is prevented from slowing down, and the bleeding and set-off of the printing is prevented during continuous printing. The effect of improving the stability can be further improved.

Further, when the ratio η ₁ / η ₂ of the viscosity of the oil phase is less than 2.0, the amount of transfer of the emulsion ink to one printed material is too large, the drying of the printing becomes slow, and during continuous printing, There is a tendency to cause print bleeding and set-off. Further, since the amount of ink consumed increases, the number of printed sheets per ink container that supplies ink to the squeegee roll decreases, and the ink container must be frequently replaced. On the other hand, when the ratio η ₁ / η ₂ exceeds 4.5, the transfer amount of the emulsion ink to one printing medium becomes too small, and the image density of the printed image may be lowered. On the other hand, when the ratio η ₁ / η ₂ of the oil phase viscosity is 2.0 to 4.5, the drying of the printing is prevented from slowing down, and the bleeding and setback of printing occurs during continuous printing. In addition, it is possible to form a printed image having a sufficient image density while preventing ink consumption.

As said 1st carbon black, as described in Claim 3, it is preferable to use what has a nitrogen adsorption specific surface area of 100 m < ² > / g or less. Carbon black with a nitrogen adsorption specific surface area of more than 100 m ² / g has many extremely fine pores even if the DBP adsorption amount is the same, so that the capillary force is too strong and the retained oil is quickly released during printing. It tends to be difficult. For this reason, the drying of the printing becomes slow, and there is a possibility that the printing may be blurred or set off during continuous printing. In contrast, carbon black having a nitrogen adsorption specific surface area of 100 m ² / g or less has an appropriate capillary force and can quickly release the retained oil during printing. Accordingly, it is possible to further improve the effect of preventing the drying of the printing from being slowed and preventing the occurrence of printing bleeding and setback during continuous printing.

Stencil printing emulsion ink of the present invention is a W / O type emulsion consisting of an oil phase and an aqueous phase, in the oil phase, the first carbon black DBP oil absorption amount is 90cm ^3/100 g or more When, is characterized in that it contains a second carbon black DBP oil absorption amount is less than 50 cm ^3/100 g.
Of these, the DBP oil absorption of the first carbon black is limited to the above 90cm ^3/100 g, in the DBP oil absorption is less than 90cm ^3/100 g, by blending the first carbon black, oil phase This is because the effect of improving the stability of the emulsion ink cannot be obtained by maintaining the oil inside. Incidentally, DBP oil absorption of the first carbon black, even within the above range, particularly ^preferably not more than 130 cm 3/100 g. DBP oil absorption of 130cm 3 ^/ more than 100g of carbon black, at the time of printing, immediately there is a release tends to be difficult to hold the oil, drying of printing is too slow, at the time of continuous printing, resulting in the printing of bleeding and setoff There is a fear.

As the first carbon black DBP oil absorption satisfying the above conditions, for example, Cabot (CABOT) manufactured by Elf Tex (R) 8 [DBP oil absorption ^amount: 100 cm 3/100 g, the nitrogen adsorption specific surface area 81m ² / g], Elftex® 12 [DBP oil ^absorption: 95cm 3/100 g, the nitrogen adsorption specific surface area ^43m 2 / g], Mitsubishi Chemical Co., Ltd. MA-100 [DBP oil absorption ^amount: 100 cm 3/100 g, the nitrogen adsorption specific surface area 110m ² / g], MA-230 [DBP oil ^absorption: 113cm 3/100 g, the nitrogen adsorption specific surface area ^74m 2 / g], Degussa (Degussa) Co. Printex (TM) 40 [DBP oil absorption amount: 114 cm ^3/100 g, the nitrogen adsorption specific surface area ^90m 2 / g], Printex 60 [DBP oil absorption amount: 114 cm ^3/100 g, the nitrogen adsorption specific surface area 115m ² / g], Printex 30 [DBP oil absorption ^amount: 105 cm 3/100 g, the nitrogen adsorption specific surface area ^{80m 2} / g], Printex 3 [DBP oil absorption ^amount: 123 cm 3/100 g, 1 type or 2 or more types, such as nitrogen adsorption specific surface area 80m < ² > / g].

The first carbon black preferably has a nitrogen adsorption specific surface area of 100 m ² / g or less. Carbon black with a nitrogen adsorption specific surface area of more than 100 m ² / g has many extremely fine pores even if the DBP adsorption amount is the same, so that the capillary force is too strong and the retained oil is quickly released during printing. The printing tends to be difficult, and the drying of the printing becomes slow, and there is a possibility of causing bleeding and set-off of printing during continuous printing. The nitrogen adsorption specific surface area of the first carbon black is particularly preferably 40 m ² / g or more, even within the above range. Carbon black having a nitrogen adsorption specific surface area of less than 40 m ² / g has the same DBP adsorption amount, but the capillary force is too weak to keep the oil in the oil phase well and improve the stability of the emulsion ink. The effect may not be obtained sufficiently.

As the first carbon black having a nitrogen adsorption specific surface area satisfying the above conditions, among the various carbon blacks exemplified above, Elftex 8 and Elftex 12 manufactured by Cabot Corporation, MA-230 manufactured by Mitsubishi Chemical Corporation. , Degussa's Printex 40, Printex 30, Printex 3 or the like.
In combination with the first carbon black, the DBP oil absorption of the second carbon black is limited to 50 cm ^3/100 g, when the DBP oil absorption amount exceeds 50 cm ^3/100 g is the second This is because the use of the carbon black together prevents the fluidity of the emulsion ink from greatly decreasing, and the effect of maintaining good permeability of the emulsion ink to the printing medium cannot be obtained. The second carbon black preferably functions to assist the retention of oil by the first carbon black. For this purpose, the DBP oil absorption amount of the second carbon black is within the above range. , in ^particular, it is preferably at 30 cm 3/100 g or more.

The second carbon black DBP oil absorption satisfying the above conditions, for example, Degussa Printex 25 [DBP oil ^absorption: 45cm 3/100 g, the nitrogen adsorption specific surface area ^{45 m} 2 / g], Printex 35 [DBP oil ^absorption: 42cm 3/100 g, the nitrogen adsorption specific surface area ^{65 m} 2 / g], Printex 55 [DBP oil ^absorption: 46cm 3/100 g, the nitrogen adsorption specific surface area 110m ² / g], Special black 350 of Degussa [DBP oil ^absorption: 45cm 3/100 g, the nitrogen adsorption specific surface area ^{65 m} 2 / g], Special black 250 [DBP oil ^absorption: 46cm 3/100 g, the nitrogen adsorption specific surface area ^{40 m} 2 / g], Special black 550 [DBP oil absorption amount : 47cm ³ / 100g, nitrogen adsorption specific surface area 110m ² / g], such as It includes more species or in combination.

In addition, the second carbon black assists the retention of the oil by the first carbon black, keeps the oil well, and considers that the retained oil is quickly released during printing. As in the case of carbon black, the nitrogen adsorption specific surface area is preferably 40 to 100 m ² / g. The second carbon black specific surface area by nitrogen adsorption satisfying this condition, among the above-exemplified various carbon blacks, Degussa Printex 25 [DBP oil ^absorption: 45cm 3/100 g, the nitrogen adsorption specific surface area 45 m ² / g], Printex 35 [DBP oil ^absorption: 42cm 3/100 g, the nitrogen adsorption specific surface area ^{65 m} 2 / g], Special black 350 [DBP oil ^absorption: 45cm 3/100 g, the nitrogen adsorption specific surface area ^{65 m} 2 / g], Special black 250 [DBP oil ^absorption: 46cm 3 / 100g, nitrogen adsorption specific surface area ^{40 m} 2 / g] of one or more can be mentioned, such as.

  Although 1st carbon black and 2nd carbon black can be used together in arbitrary ratios, it represents by weight ratio and it is preferable to use together in the range of 10 / 90-90 / 10. When the amount of the first carbon black is less than this range, the effect of improving the stability of the emulsion ink can be obtained by blending the first carbon black, maintaining good oil in the oil phase. There is a risk of not. In addition, when the second carbon black is less than the above range, the fluidity of the emulsion ink due to the combined use of the second carbon black is prevented from greatly decreasing, and the emulsion ink is coated. There is a possibility that the effect of maintaining good permeability to the printed body cannot be obtained.

It should be noted that the stability of the emulsion ink is prevented while preventing the printing from slowing down due to the combined use of the first and second carbon blacks, and preventing the occurrence of bleeding and set-off during continuous printing. Further improving the effect of improving the ratio of the oil phase viscosity η ₁ and η ₂ η ₁ / η ₂ to be in the range of 2.0 to 4.5, In consideration of adjusting the viscosity η ₂ to 1000 to 3000 cP, the blending ratio (weight ratio) of both carbon blacks is more preferably 20/80 to 80/20, particularly within the above range. . Further, the total amount of the first and second carbon blacks added is preferably 1 to 15% by weight, particularly 2 to 10% by weight, based on the total amount of the emulsion ink.

The oil phase can be configured in the same manner as in the prior art except that the first and second carbon blacks are used in combination. That is, the oil phase is constituted by appropriately adding a resin, a surfactant and other additives to the solvent in addition to the first and second carbon blacks as the color pigment.
Among these solvents, for example, petroleum solvents (paraffinic (methane train) hydrocarbons, naphthenic (cycloparaffinic hydrocarbons), olefinic (ethylene train) hydrocarbons, aromatic hydrocarbons, etc.], spindle oils, etc. Mineral oils such as oil oil, kerosene, machine oil, gear oil, lubricating oil, motor oil; vegetable oils such as sesame oil, tall oil, corn oil, olive oil, rapeseed oil, castor oil, soybean oil, dehydrated castor oil; Vegetable oils such as coconut oil and palm oil; polyisobutylenes, hydrogenated polydecenes, trimethylolpropane esters, neopentyl esters, pentaerythritol esters, siloxanes, silicones, fluorocarbons, alkyl-substituted diphenyl ethers, 1 or 2 types of synthetic oils such as phthalates and phosphates Above, and the like.

As described above, as described above, it is preferable to combine a base solvent and a volatile solvent in order to prevent dripping while lowering the viscosity of the emulsion ink. Examples of such a combination include a combination of a paraffinic hydrocarbon as a base solvent and a naphthenic hydrocarbon as a volatile solvent.
The resin improves the wettability of the colored pigment to the solvent, improves the dispersibility in the oil phase, and improves the stability of the emulsion ink. It is added to fix it on the surface. Examples of the resin include rosin resins such as rosin, polymerized rosin, hydrogenated rosin, rosin ester, and hydrogenated rosin ester; rosin modified resins such as rosin modified phenolic resin; alkyd resin; phenol resin; 1 type, or 2 or more types, such as petroleum resin; rubber derivative; polymerized castor oil. In particular, an alkyd resin excellent in the effect of improving the wettability of the color pigment to the solvent is preferable. The addition amount of the resin is preferably 20% by weight or less, particularly 1 to 7% by weight of the total amount of the emulsion ink.

Examples of surfactants include anionic surfactants such as metal soaps, higher alcohol sulfated salts, sulfated salts of polyoxyethylene adducts; primary to tertiary amine salts, and quaternary ammonium salts. 1 type or 2 or more types, such as a cationic surfactant; and a nonionic surfactant, are mentioned, A nonionic surfactant is especially preferable.
Nonionic surfactants include sorbitan fatty acid esters such as sorbitan monooleate, sorbitan monolaurate, sorbitan monopalmitate, sorbitan sesquioleate, polyoxyethylene sorbitan fatty acid ester; glycerin fatty acid ester, polyglycerin. Fatty acid esters of polyhydric alcohols such as fatty acid esters, propylene glycol fatty acid esters, pentaerythritol fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyoxyethylene glycerin fatty acid esters, polyethylene glycol fatty acid esters; polyoxyethylene alkyl ethers, poly Oxyethylene ether, polyoxyethylene ether of higher alcohol, polyoxyethylene of polyglycerin fatty acid ester Polyoxyethylene ethers such as lenether, polyoxyethylene phytosterol ether, polyoxyethylene polyoxypropylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, polyoxyethylene lanolin derivatives; 1 type, or 2 or more types, such as oxyethylene alkylamine; polyoxyethylene fatty acid amide; polyoxyethylene alkylphenyl formaldehyde condensate, is mentioned.

In particular, sorbitan fatty acid ester is preferable. The addition amount of the surfactant takes into consideration the molar concentration of each surfactant and the area of the interface between the water phase and the oil phase in the emulsion (some areas of the interface between the oil phase and the color pigment). However, it is preferably 1 to 20% by weight, particularly 1 to 5% by weight, based on the total amount of the emulsion ink.
Examples of other additives include pigment dispersants, gelling agents, antioxidants, and the like. Further, as an auxiliary agent for adjusting fluidity, a compound mainly composed of wax or the like can be added. Examples of the pigment dispersant include the surfactants described above, alkylamine polymer compounds, aluminum chelate compounds, styrene / maleic anhydride copolymers, partial alkyl esters of polyacrylic acid, polyalkylene polyamines. Aliphatic polycarboxylic acid, polyether, ester type anionic surfactant, long chain amine salt of high molecular weight polycarboxylic acid, polyamide, phosphate ester surfactant, alkyl sulfocarboxylate, α-olefin sulfonate, 1 type (s) or 2 or more types, such as dioctyl sulfosuccinate, can also be used. The addition amount of the pigment dispersant is preferably 40% by weight or less, particularly 2 to 35% by weight, based on the total amount of the first and second carbon blacks as the color pigment.

  The gelling agent is for gelling a resin contained in the oil phase to improve the storage stability and fixing property of the emulsion ink. Examples of gelling agents include organic acid salts containing metals such as Li, Na, K, Al, Ca, Co, Fe, Mn, Mg, Pb, Zn, and Zr; organic chelate compounds; metal soap oligomers, A compound that coordinates with the resin in the oil phase is preferred. Specific examples of the gelling agent include, for example, octylic acid metal salts such as aluminum octylate; naphthenic acid metal salts such as manganese naphthenate; stearates such as zinc stearate; aluminum diisopropoxide monoethyl acetoacetate and the like. 1 type or 2 types or more, such as these organic chelate compounds. The addition amount of the gelling agent is preferably 15% by weight or less, particularly 5 to 10% by weight, based on the total amount of the resin contained in the oil phase.

  Examples of the antioxidant include one or more of dibutylhydroxytoluene, propyl gallate, butylhydroxyanisole, and the like. By adding an antioxidant, oxidation of the resin or the like in the oil phase is prevented, and an increase in the viscosity of the emulsion ink is prevented. The addition amount of the antioxidant is preferably 2% by weight or less, particularly 0.1 to 1.0% by weight, based on the total amount of the oil phase. In addition, a wax may be added to the oil phase in order to improve the releasability between the printing medium and the stencil paper and prevent the printing medium from rolling up during printing.

The oil phase containing each of the above components is a B-type viscometer and The viscosity of the oil phase η ₁ when the rotational speed of the rotor is 6 rpm and the viscosity η ₂ of the oil phase when the rotational speed is 60 rpm, measured at a measurement temperature of 23 ± 1 ° C. using a 4-rotor. And the ratio η ₁ / η ₂ is 2.0 to 4.5, and the viscosity η ₂ is preferably 1000 to 3000 cP.
If the ratio η ₁ / η _{2 of the} oil phase viscosity is 2.0 to 4.5, it prevents the drying of printing from slowing down and prevents the occurrence of bleeding and set-off during continuous printing. At the same time, it is possible to form a printed image having a sufficient image density while suppressing ink consumption. In order to further improve these effects, the oil phase viscosity ratio η ₁ / η ₂ is more preferably 2.5 to 4.0, even within the above range.

Also, if the oil phase viscosity η ₂ is 1000 to 3000 cP, it prevents the drying of printing from slowing down, prevents the occurrence of bleeding and set-off during continuous printing, and the stability of the emulsion ink. The effect of improving can be further improved. In order to further improve these effects, the viscosity η _{2 of the} oil phase is preferably 1200 to 2700 cP, even within the above range.

In order to adjust the viscosity ratio η ₁ / η ₂ and the viscosity η ₂ of the oil phase, as described above, the blending ratio (weight ratio) of the first and second carbon blacks may be adjusted. Also, combining the first and second carbon blacks with different DBP oil absorption amounts, adjusting the total amount of both carbon blacks added to the oil phase, and changing the type and composition of the solvent combined with both carbon blacks In other words, the viscosity ratio η ₁ / η ₂ and the viscosity η ₂ of the oil phase can be adjusted.

The water phase constituting the emulsion ink together with the oil phase is, as before, water, O / W resin emulsion, water-soluble resin, wetting agent, antifreezing agent, electrolyte, antiseptic / antifungal agent, pH adjuster, etc. It is comprised by adding an additive suitably.
Of these, it is sufficient that the water is clean, and any of tap water, pure water (ion exchange water), distilled water, and the like can be used. O / W type resin emulsions and water-soluble resins are added for moisturizing and thickening. Among these, examples of O / W type resin emulsions include polyvinyl acetate and ethylene-vinyl acetate copolymers. , Vinyl acetate-acrylic acid ester copolymer, polymethacrylic acid ester, polystyrene, styrene-acrylic acid ester copolymer, styrene-butadiene copolymer, vinylidene chloride-acrylic acid ester copolymer, vinyl chloride, vinyl chloride One type or two or more types of emulsions of resins such as vinyl acetate copolymer and urethane may be used.

  Examples of water-soluble resins include starch, mannan, sodium alginate, galactan, tragacanth gum, gum arabic, pullulan, dextran, xanthan gum, glue, gelatin, collagen, casein, and other natural polymers; carboxymethylcellulose, methylcellulose, hydroxyethylcellulose , Semi-synthetic polymers such as hydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxymethyl starch, carboxymethyl starch, dialdehyde starch; acrylic resin derivatives (polyacrylic acid, sodium polyacrylate, polyethanolamine polyacrylate, etc.), polyvinyl Alcohol, polyvinylpyrrolidone, polyacrylamide, polyethylene oxide, polyethylene-polyvinyl alcohol copolymer Body, polyvinyl methyl ether, one or more of such synthetic polymers such as water-soluble urethane. The addition amount of the O / W type resin emulsion and / or the water-soluble resin is preferably 25% by weight or less, particularly 0.5 to 15% by weight of the amount of water contained in the aqueous phase.

  Wetting agents and antifreeze agents can be used together. Examples include glycols such as ethylene glycol, diethylene glycol, polyethylene glycol and propylene glycol; lower saturated monohydric alcohols such as methanol, ethanol, isopropanol, butanol and isobutanol. 1 type, or 2 or more types, such as polyhydric alcohols, such as glycerol and sorbitol. The amount added is preferably 15% by weight or less, particularly 4 to 12% by weight of the amount of water contained in the aqueous phase.

  The electrolyte is for improving the stability of the emulsion. As an example, a salt containing an anion or a cation having a high liquid separation sequence and effective for improving the stability of the emulsion is preferable. Examples of the anion having high separation permutation include citrate ion, tartrate ion, sulfate ion, and acetate ion. Examples of the cation having high separation permutation include alkali metal ions and alkaline earth metal ions. Is mentioned. The electrolyte only needs to contain at least one of the above anions and cations. Specific examples of such an electrolyte include magnesium sulfate, sodium sulfate, sodium citrate, sodium hydrogen phosphate, sodium borate, 1 type, or 2 or more types, such as sodium acetate, are mentioned. The amount of electrolyte added is preferably 0.1 to 2% by weight, particularly 0.5 to 1.5% by weight, based on the total amount of the aqueous phase.

Examples of the moisture and fungicide include aromatic hydroxy compounds such as salicylic acid, phenols, methyl p-oxybenzoate and ethyl p-oxybenzoate and chlorinated products thereof; sorbic acid; one or two of dehydroacetic acid More than species. The addition amount of the moisture / antifungal agent is preferably 3% by weight or less, particularly preferably 0.1 to 1.2% by weight of the amount of water contained in the aqueous phase.
Examples of the pH adjuster include triethanolamine, sodium acetate, triallylamine and the like. In a system containing a water-soluble resin, if necessary, a pH adjuster is added to adjust the pH of the aqueous phase to 6 to 8, and the water-soluble resin can effectively exhibit the moisturizing and thickening effects. Can be made. Moreover, a rust preventive agent or an antifoaming agent can be added to the aqueous phase to prevent the metal portion of the stencil printing apparatus from rusting or ink from bubbling during printing.

  The emulsion ink for stencil printing of the present invention has a W / O type emulsion structure composed of an oil phase and an aqueous phase composed of the above components. Such an emulsion ink is produced by gradually dropping and emulsifying the aqueous phase while stirring the oil phase as in the prior art. The blending ratio of the oil phase and the water phase is not particularly limited, but it is preferably blended in the range of oil phase / water phase (weight ratio) in the range of oil phase / water phase = 10/90 to 50/50, In particular, as described above, it is more preferable to set the ratio of the aqueous phase higher than that of the oil phase.

Example 1:
(Preparation of oil phase)
4 parts by weight of alkyd resin, 2.5 parts by weight of sorbitan monooleate, 0.1 parts by weight of antioxidant, 4.5 parts by weight of paraffinic hydrocarbon, 13.5 parts by weight of naphthenic hydrocarbon, A resin varnish was prepared by dissolving in a mixed solvent. Next, 24.6 parts by weight of this resin varnish, DBP oil absorption of 100 cm ^3/100 g, the first carbon black [manufactured by Cabot Corporation of Elftex® 8] a nitrogen adsorption specific surface area of ^81m 2 / g 1.25 and parts by weight, DBP oil absorption of 45cm ^3/100 g, after nitrogen adsorption specific surface area was premixed and second carbon black [Degussa Printex 25] 3.75 parts by weight of ^{45 m} 2 / g, An oil phase was prepared by passing through a three-roll mill five times and pulverizing until the secondary particle diameter of the carbon black became 10 μm.

(Preparation of aqueous phase)
An aqueous phase was prepared by mixing 1 part by weight of magnesium sulfate, 4 parts by weight of ethylene glycol, and 65.4 parts by weight of pure water using a disper.
(Manufacture of emulsion ink for stencil printing)
While stirring 29.6 parts by weight of an oil phase using a disper, 70.4 parts by weight of an aqueous phase is gradually dropped and emulsified to obtain an emulsion ink for stencil printing having a W / O type emulsion structure. Manufactured.

Examples 2 to 5, Comparative Examples 1 and 2:
An emulsion ink for stencil printing was produced in the same manner as in Example 1 except that the addition amounts of the first and second carbon blacks were the values shown in Table 1, respectively.

Example 6:
As a first carbon black, instead of the Elftex® 8 manufactured by Cabot Corporation, DBP oil absorption of 100 cm ^3/100 g, the nitrogen adsorption specific surface area of 110m ² / g of carbon black [manufactured by Mitsubishi Chemical Co., Ltd. MA- 100] An emulsion ink for stencil printing was produced in the same manner as in Example 2 except that 2.5 parts by weight were added.

Comparative Example 3:
As a first carbon black, instead of the Elftex® 8 manufactured by Cabot Corporation, DBP oil absorption of 85cm ^3/100 g, carbon black [manufactured by Cabot Corporation of Regal 300R] nitrogen adsorption specific surface area of ^89m 2 / g 2. An emulsion ink for stencil printing was produced in the same manner as in Example 2 except that 5 parts by weight were added.

Comparative Example 4:
As a second carbon black, instead of Degussa Printex 25, DBP oil absorption of 66cm ^3/100 g, carbon black [Degussa Printex 300] Nitrogen adsorption specific surface area of ^{80 m} 2 / g 2 An emulsion ink for stencil printing was produced in the same manner as in Example 2 except for adding 5 parts by weight.

Comparative Example 5:
Instead of the first carbon black, talc is extender pigment (DBP oil absorption: except for the addition of 60cm ³ /100g)2.5 parts to produce stencil printing emulsion ink in the same manner as in Example 2 .
Oil phase viscosity measurement:
For the oil phase prepared in Examples 1 to 6 and Comparative Examples 1 to 5 before emulsification by adding an aqueous phase, B-type viscometer BM [manufactured by Tokimec Co., Ltd.] and No. 4 Using a rotor, the viscosity η ₁ was measured under the conditions of a measurement temperature of 23 ± 1 ° C. and a rotor rotation speed of 6 rpm, and the measurement temperature of 23 ± 1 ° C. and the rotation speed of the rotor of 60 rpm. ₂ was measured. And viscosity ratio (eta) ₁ / (eta) ₂ was calculated | required from both the measurement results. The measurement is carried out by placing a predetermined amount of the oil phase in a measurement container of a B-type viscometer, leaving the whole viscometer in an environment of a temperature of 23 ± 1 ° C. and a relative humidity of 60% for 1 hour, and then in that environment I went there.

Actual machine test:
The emulsion ink for stencil printing produced in Examples 1 to 6 and Comparative Examples 1 to 5 was filled into a commercially available ink container for a stencil printing apparatus in which a heat-sensitive stencil sheet and a thermal head were combined. Attached to a stencil printing apparatus, the following items were evaluated.
(Ink dripping)
After moving the stencil printing device, supplying the emulsion ink from the ink container to the surface of the squeegee roll, the device was stopped and left at room temperature of 23 ± 1 ° C. for 1 month, then the inside Was observed. The presence or absence of ink dripping was evaluated according to the following criteria.

○: No change from 1 month ago. No ink dripping.
X: Ink dripped from the squeegee roll. There is ink dripping.
(Set down)
The stencil printing apparatus was moved to perform continuous printing of 20 sheets on plain paper. Then, after printing, the back side of 20 sheets of plain paper superimposed on the paper discharge unit of the apparatus was observed, and the presence or absence of set-off was evaluated according to the following criteria.

○: There is no stain at all, or the portion that has been in contact with the solid print portion is slightly dirty. No setback.
(Triangle | delta): Although there was dirt, it was a level which is satisfactory practically. There is almost no setback.
X: Remarkably dirty. There is an inside-out.
(Ink consumption)
The stencil printing apparatus was moved to perform 1000 continuous printings on plain paper, and then the amount of ink remaining in the ink container was measured. The ink consumption was evaluated according to the following criteria.

A: The ink consumption was less than or equal to the appropriate value predicted from the printed image. Low ink consumption.
X: The ink consumption exceeded an appropriate value. Excessive ink consumption.
(Image density)
The stencil printing machine was moved to print on plain paper. And the image density of the solid printing part of a printed image was measured using the reflection densitometer RD-914 by Gretag Macbeth, and the image density was evaluated on the following reference | standard.

A: The image density was in the range of 0.84 to 1.20. Appropriate image density.
X: The image density was less than 0.84 or exceeded 1.20. Incorrect image density.
High temperature storage test:
The emulsion inks for stencil printing produced in Examples 1 to 6 and Comparative Examples 1 to 5 were stored in a thermostatic bath set at 60 ° C. for 2 weeks, and then the state was observed. Was evaluated for storage stability.

○: Oil-water separation due to the collapse of the emulsion was not observed, and there was no significant change in viscosity. Good storage stability at high temperatures.
X: Oil-water separation due to the disintegration of the emulsion was observed, or a significant change in viscosity was observed. Poor storage stability at high temperatures.
The results are shown in Table 2.

From Table, as a coloring pigment, DBP oil absorption amount 90cm ³ / emulsion ink of Comparative Example 1 in which only the added first carbon black is 100g or more, with ₂ the viscosity of the oil phase η exceeds 3000 cP, the flowability It has been found that since it greatly decreases, the permeability to the printing medium is deteriorated, and the set-off occurs during continuous printing. Further, since the emulsion ink of Comparative Example 1 has an oil phase viscosity ratio η ₁ / η ₂ of more than 4.5, the transfer amount with respect to one sheet of printing material becomes too small, and the image density of the printed image is too small. It was also found to decrease.

Further, the a first carbon black, emulsion ink of Comparative Example 4 DBP oil absorption is a combination of the second carbon black exceeds 50 cm ^3/100 g, the effect due to the combination of the second carbon black is obtained However, it was found that the viscosity η _{2 of the} oil phase still exceeds 3000 cP, the fluidity of the oil phase decreases, the permeability to the printing medium deteriorates, and the set-off occurs during continuous printing. In addition, the emulsion ink of Comparative Example 2 still has an oil phase viscosity ratio η ₁ / η ₂ of more than 4.5. It was found that the concentration decreased.

As colored pigments, emulsion ink of Comparative Example 2 with the addition of only the second carbon black DBP oil absorption amount is less than 50 cm ^3/100 g is ₂ the viscosity of the oil phase η is below 1000 cP, decrease the stability of the emulsion ink Therefore, it was found that the ink dripped when left for a long time. Further, since the emulsion ink of Comparative Example 2 has an oil phase viscosity ratio η ₁ / η ₂ of less than 2.0, the amount of transfer to a single substrate is too large, and the amount of consumption increases. At the same time, it was also found that the drying of the printing slows down and the set-off occurs during continuous printing.

Further, the second carbon black, the emulsion ink of Comparative Example 3 in which the DBP oil absorption is a combination of the first carbon black is less than 90cm ^3/100 g, the effect due to the compounding of the first carbon black It was not obtained and the viscosity η _{2 of the} oil phase was still less than 1000 cP, and the stability of the emulsion ink was lowered. Therefore, it was found that the ink drooped when left for a long time. In addition, the emulsion ink of Comparative Example 3 still has an oil phase viscosity ratio η ₁ / η ₂ of less than 2.0. It has also been found that as printing increases, drying of the printing slows down, causing set-off during continuous printing.

Furthermore, in the emulsion ink of Comparative Example 5 in which the second carbon black and the extender pigment talc were used in combination, oil-water separation and significant viscosity change due to the collapse of the emulsion were observed during storage at high temperature. Further, the emulsion ink of Comparative Example 5, since DBP oil absorption of the combination with talc is less than 90cm ^3/100 g, the effect of the combination can not be obtained, a long time, when allowed to stand, with resulting sagging of the ink It was also found that the consumption increased and the drying of the printing slowed down, causing a set-off during continuous printing.

On the other hand, all the emulsion inks of Examples 1 to 6 were evaluated as being ◯ to Δ in each test, and it was found that the emulsion inks had good characteristics. In addition, when Examples 1 to 3 were compared with Examples 4 and 5, Examples 1 to 3 had better evaluation of each item, and thus the viscosity ratio η ₁ / η _{2 of the} oil phase Was found to be preferably in the range of 2.0 to 4.5 and the viscosity η ₂ in the range of 1000 to 3000 cP. Furthermore, when Example 2 and Example 6 are compared, since the evaluation of each item was better in Example 2, as the first carbon black, the nitrogen adsorption specific surface area was 100 m ² / g. It has been found preferable to use the following:

Claims (3)

A oil phase and W / O type emulsion ink for stencil printing consisting of an aqueous phase, the oil phase, and the first carbon black DBP oil absorption amount is 90cm ^3/100 g or more, DBP absorption 50cm ^{3 /} stencil printing emulsion ink characterized by containing a second carbon black 100g or less. B-type viscometer and No. The viscosity of the oil phase η ₁ when the rotational speed of the rotor is 6 rpm and the viscosity η ₂ of the oil phase when the rotational speed is 60 rpm, measured at a measurement temperature of 23 ± 1 ° C. using a 4-rotor. The emulsion ink for stencil printing according to claim ₁ , wherein the ratio η ₁ / η ₂ is 2.0 to 4.5 and the viscosity η ₂ is 1000 to 3000 cP. The emulsion ink for stencil printing according to claim 1, wherein the first carbon black has a nitrogen adsorption specific surface area of 100 m ² / g or less.