Stencil printing emulsion ink

Abstract: A stencil printing emulsion ink of a water-in-oil type is disclosed which contains in an oil phase 1 to 50 % by weight, based on the weight of a water phase, of a volatile solvent having a distillation starting temperature of 275°C or higher and having a viscosity of 10 mm²/s·40°C or less, and has a weight ratio of the oil phase/water phase of 20 to 50/80 to 50.

Description: The present invention relates to a stencil printing emulsion ink. More particularly, the present invention relates to a stencil printing emulsion ink of a water-in-oil type which has only a small viscosity change when left in air for a long period of time, and is low in offensive smell and toxic character. Stencil printing is a method of printing wherein a stencil printing master sheet is perforated and ink is forced to pass through the perforations formed in the stencil printing master sheet to print on a body such as paper. Heretofore, a water-in-oil type emulsion ink has been used as a stencil printing ink, and a volatile solvent, non-volatile solvent, resin, colorant and surfactant are contained in an oil phase of the emulsion ink, and an electrolyte, anti-freezing agent and preservative are contained in a water phase of the emulsion ink. When such an ink is left in air for a long period of time, volatile components evaporate from the oil phase and water evaporates from the water phase. Whereas the amount of the volatile components which evaporate from the oil phase is determined by the temperature of the emulsion ink, the amount of water which evaporates from the water phase is determined by the absolute humidity of the surroundings. Accordingly, the amount of volatile solvent and water which evaporates from the oil phase and water phase is different depending on the temperature and the absolute humidity. Thus, it has been very difficult to obtain an emulsion ink having excellent stability when left in air for a long period of time. In order to solve this problem, several methods have been proposed wherein the range of the boiling point or initial boiling point (at distillation) of a volatile solvent used for a water-in-oil type emulsion ink is restricted. For instance, in Unexamined Japanese Patent Publication No. 61-255967, the boiling point of the volatile solvent used is restricted to the range of from 180 to 270°C. In Unexamined Japanese Patent Publication No. 5-125320, the initial boiling point (at distillation) is restricted to the range of from 150 to 210°C. A significant amount of the volatile solvents used in these methods evaporates into the air at a temperature of from 0 to 40°C, at which stencil printing is carried out, and the amount of water which evaporates increases with the increase in the evaporation of the volatile solvents. Thus, the emulsion ink, after evaporation of the volatile solvents and water, exhibits, due to the change in the composition of the ink resulting from the evaporation, a behaviour similar to ink comprising an oil phase only, and the ink after evaporation is liable to cause offset. Also, the content of a pigment in the oil phase in the ink increases, and thus the trend of the print concentration to increase to a level higher than the print concentration in the case where the emulsion ink has not been left for a long period of time before its use is noticed. Particularly, when the initial boiling point (at distillation) is selected to be in the range of from 150 to 210°C, the amount of volatile solvent which evaporates increases and a large amount of water evaporates along with the evaporating solvent, leading to a remarkable change in the appearance of the print. Further, when a stencil printing emulsion ink is prepared using a non-volatile solvent without any volatile solvent in order not to clog perforations in a perforated stencil printing sheet when the ink is left in the printing sheet, only water in the emulsion ink evaporates thereby decreasing the viscosity of the ink, and thus bleeding (or blotting) of printed picture images and offset of the ink due to the increase in the amount of ink transferred occurs more easily. Since stencil printing is easy to perform, such printing has been used in a wide range of applications including in offices, and thus it is necessary to suppress an offensive smell of the stencil printing ink. An aim of the present invention is to solve the problem in the prior art mentioned above and to provide a stencil printing emulsion ink in which the evaporation of a volatile solvent in the ink component when left in air is suppressed; the increase in the print concentration, offset and bleeding of the ink are reduced; and an offensive smell, toxicity and skin stimulation with the solvent are removed. The present invention is concerned with a stencil printing emulsion ink of a water-in-oil type containing in an oil phase a non-volatile solvent and from 1 to 50% by weight, based on the weight of a water phase, of a volatile solvent having an initial boiling point (at distillation) of 275°C or higher and a viscosity of 10mm 2 /s·40°C or less, and having a weight ratio of the oil phase/water phase of 20 to 50/80 to 50. The content of an aromatic component in the volatile solvent is preferably 1% by weight or less. The stencil printing emulsion ink of the present invention has preferably a viscosity of from 27 to 38mm in terms of spread-o-meter value (diameter after 1 minute) at 25°C. The water-in-oil type emulsion ink of the present invention can be prepared by gradually adding from 80 to 50% by weight of a water phase to from 20 to 50% by weight of an oil phase to form an emulsion. In the oil phase, a volatile solvent, non-volatile solvent and emulsifier are contained. A resin is also contained in the oil phase when necessary. In the water phase, water-soluble additives such as a wetting agent, water-soluble resin, electrolyte, mildew-proofing agent, anti-oxidant and anti-freezing agent can be added when necessary. A colorant can be added to the oil phase and/or water phase. In the present invention, a volatile solvent having an initial boiling point (at distillation) of 275°C or higher, preferably in the range of from 275 to 310°C, and having a viscosity of 10mm 2 /s·40°C or less, preferably in the range of from 0.1 to 6mm 2 /s·40°C, is contained in a ratio of from 1 to 50% by weight, preferably in a ratio of from 3 to 20% by weight, based on the weight of the water phase. When the initial boiling point (at distillation) is lower than 275°C, the amount of evaporation of volatile solvent at a temperature of lower than 40°C is increased and the evaporation of water from the water phase which accompanies the evaporation of the volatile solvent is increased. Thus, the ink, after evaporation of the volatile solvent and water, tends to have a character similar to that of the ink comprising only an oil phase containing a non-volatile solvent, and offset readily occurs. In the present invention, since the evaporation of the volatile solvent is decreased and the evaporation of water which accompanies the evaporation of the volatile solvent is suppressed to the utmost by selecting a volatile solvent having an initial boiling point (at distillation) of 275°C or higher, as the solvent, the change in the composition of the emulsion ink when left in air for a long period of time is decreased. The reason why control of the evaporation of a volatile solvent at a temperature lower than 40°C is necessary is that stencil printing is actually conducted in an environment at a temperature of lower than 40°C. When the viscosity of the volatile solvent exceeds 10mm 2 /s·40°C, the viscosity of the emulsion ink prepared with the solvent becomes high, the fluidity of the ink worsens, and thus the emulsion ink becomes unsuitable for stencil printing. When the amount of the volatile solvent to be blended is less than 1% by weight based on the weight of the water phase, the viscosity of the emulsion ink obtained is high, the fluidity of the ink worsens, the decrease in the viscosity of the ink when left in air is remarkable and bleeding of printed picture images and offset of the ink, due to the increase in the amount of ink transferred, occur readily. On the other hand, when the amount of volatile solvent to be blended exceeds 50% by weight, the viscosity of the emulsion ink obtained is too low and the amount of ink transferred is increased. As a result, it becomes a cause of a high print concentration, and leads to the development of offset and bleeding. The volatile solvent which is used in the present invention, and has an initial boiling point (at distillation) of 275°C or higher and a viscosity of 10mm 2 /s·40°C or less, includes, for example, the following: Product of Exxon Chemical Japan Ltd.: Trade name: EXXSOL-D130: Initial boiling point (at distillation) : 277°C; viscosity: 3.8mm 2 /s·40°C Products of NIPPON OIL COMPANY LTD.: Trade name: Teclean N-28: Initial boiling point (at distillation) : 277°C; viscosity: 4.2mm 2 /s·40°C Trade name: Teclean N-30: Initial boiling point (at distillation) : 296°C; viscosity: 5.5mm 2 /s·40°C Trade name: Teclean N-32: Initial boiling point (at distillation) : 317°C; viscosity: 7.5mm 2 /s·40°C Trade name: Teclean N-33: Initial boiling point (at distillation) : 325°C; viscosity: 10.0mm 2 /s·40°C Trade name: AF-5: Initial boiling point (at distillation) : 279°C; viscosity: 4.2mm 2 /s·40°C Trade name: AF-6: Initial boiling point (at distillation) : 301°C; viscosity: 5.6mm 2 /s·40°C In the present invention, the content of an aromatic component in the volatile solvent is preferably adjusted to 1% by weight or less. When the content of the aromatic component in the volatile solvent exceeds 1 by weight, the solvent may emit an offensive smell peculiar to the aromatic component, and thus its content is preferably maintained as small as possible. The viscosity of the emulsion ink in the present invention is preferably adjusted in the range of from 27 to 38mm, more desirably from 29 to 35mm, in terms of the spread-o-meter value (diameter after 1 minute) at 25°C. When the spread-o-meter value is less than 27 mm, the fluidity of the ink is inferior, the amount of ink to be transferred when stencil printing is conducted becomes small, and the print concentration of printed materials is decreased in some cases. Conversely, when the value exceeds 38 mm, the viscosity of the ink is excessively low, the amount of ink transferred is increased and the print concentration of printed materials is excessively high, causing offset and bleeding. As the non-volatile solvent in the oil phase, an oil can be used such as olive oil, castor oil, spindle oil, motor oil and salad oil. As an emulsifier, a non-ionic surfactant is preferably used which includes a sorbitan higher fatty acid ester (for example, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate and sorbitan sesquioleate), fatty acid monoglyceride (for example, oleic acid monoglyceride and oleic acid diglyceride) and ethylene oxide adduct with a polyhydric alcohol, alkyl phenol or fatty acid. When a colorant is contained in the oil phase, a resin is preferably contained also in the oil phase in order to secure the fixing of the ink to paper. The resin includes a phenolic resin, maleic resin, petroleum resin and alkyd resin. On the other hand, when a colorant is contained in the water phase, a resin is also contained in the water phase for the same reason as in the case where a colorant is contained in the oil phase. As the resin, a water-dispersible resin and water-soluble resin can be mentioned. The water-dispersible resin includes a polyvinyl acetate, ethylene-vinyl acetate copolymer, vinyl acetate-acrylic ester copolymer, polymethacrylic ester, polystyrene, styrene-acrylic ester copolymer, styrene-butadiene copolymer, vinylidene chloride-acrylic acid ester copolymer, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer and polyurethane. The water-soluble resin includes a polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, polyvinyl pyrrolidone, ethylene-vinyl alcohol copolymer, polyethylene oxide, gum arabic, starch and water-soluble polyurethane. In the present invention, a colorant can be contained in the oil phase and/or water phase. The colorant includes carbon blacks such as furnace carbon black, lamp black and brilliant first scarlet, metals such as copper, iron, titanium oxide and calcium carbonate, metal oxides, organic pigments such as an azo, cyanine, dioxane and quinacridone pigment. A wetting agent, for changing the evaporation rate of water from the water phase, can be added in the water phase as required. The amount of the wetting agent to be added is preferably determined by the evaporation rate of the volatile solvent used in the present invention. The wetting agent includes polyhydric alcohols, for example, ethylene glycol, propylene glycol, diethylene glycol and glycerine. The stencil printing emulsion ink of the present invention can suppress the evaporation of water which accompanies the evaporation of the volatile solvent since the evaporation of the volatile solvent when the emulsion ink is left in air is small. Thus, according to the present invention, a stencil printing emulsion ink can be provided which exhibits only a small change in ink performance when the emulsion ink is left for a long period of time and thus exhibits excellent ink stability. Further, according to the present invention, a stencil printing water-in-oil type emulsion ink can be provided in which the change in print concentration, offset, bleeding and paper loss can be decreased when the ink has been left for a long period of time. This improvement is achieved because the evaporation of the volatile solvent is small and the change in the composition of the emulsion ink is small even when the emulsion ink is left in a stencil printing machine for a long period of time. Still further, a stencil printing emulsion ink having a low offensive smell and low toxicity can be provided by the present invention. Still further, the present invention can provide an ink having an excellent printability for stencil printing. Now, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, it should be understood that the present invention is by no means restricted by such specific Examples. In the Examples, "parts" means "parts by weight" unless specified otherwise. Trade names, initial boiling points (at distillation), viscosities and contents of aromatic components of the volatile solvents used in Examples 1 to 5 and Comparative Examples 1 to 3, 5 and 6 are given in Table 1. Trade name of volatile solvent Initial boiling point (at distillation) (°C) Viscosity (mm 2 / s/40 °C) Content of aromatic component (% by weight) Example 1 EXXSOL-D130 277 3.8 0.8 Example 2 AF-5 279 4.2 less than 1.0 Example 3 Teclean N-30 296 5.5 less than 1.0 Example 4 AF-6 301 5.6 less than 1.0 Example 5 EXXSOL-D130 277 3.8 0.8 Comparative Example 1 EXXSOL-D80 204 1.7 0.01 Comparative Example 2 Solvent No. 4 235 2.7 18.0 Comparative Example 3 Ink oil No. 11 276 18.0 16.0 Comparative Example 5 AF-6 301 5.6 less than 1.0 Comparative Example 6 EXXSOL-D80 204 1.7 0.01 Examples 1 to 4 and Comparative Examples 1 to 5 Nine kinds of emulsion ink were prepared by the following procedures using the formulations as shown in Table 2: First, an alkyd resin, furnace carbon black, sorbitan monooleate, motor oil No. 40 and one of the volatile solvents as shown in Table 1 were added to each other. Then, they were sufficiently mixed, sufficiently kneaded with three rollers and stirred with a stirrer while gradually being supplemented with an aqueous solution comprising water and ethylene glycol to prepare the respective water-in-oil type emulsion inks. Example 5 and Comparative Example 6 Two kinds of emulsion ink were prepared by the following procedures using the formulations as shown in Table 2: First, deionized water, ethylene glycol, furnace carbon black and polyvinyl pyrrolidone (produced by BASF; Trade name: Luviskol K17) were added to each other, sufficiently mixed and dispersed with a ball mill to prepare a water phase. On the other hand, motor oil No. 40, sorbitan monooleate and one of the volatile solvents shown in Table 1 were added to each other and sufficiently stirred to prepare an oil phase. Then, the oil phase was stirred with a stirrer while being gradually supplemented with the water phase prepared by the procedures mentioned above to prepare the respective water-in-oil type emulsion inks. By using each of the water-in-oil type stencil printing emulsion inks obtained in Examples 1 to 5 and Comparative Examples 1 to 6, printing tests were carried out by means of a stencil printing machine, Risograph RC115D (Registered trademark; product of Riso Kagaku Corporation), before and after each of the emulsion inks was left in such a high temperature and high humidity atmosphere as 35°C and 70% RH for 120 hours. The results thus obtained are shown in Table 3. Printing tests were conducted to determine and evaluate the print concentration of the printed matter; offset property, bleeding property and offensive smell of the ink; and number of paper sheets printed until an ordinary print concentration was obtained (number of waste paper sheets) by the methods mentioned below. Determination of the viscosity of the emulsion ink with a spread-o-meter was conducted in an environment of 25°C. (1) Print concentration: The print concentration at the set-solid portions of the printed matter was determined by a Macbeth reflection densitometer (RD-920 produced by Macbeth Co.). (2) Offset property: Printing was continuously conducted for 30 paper sheets using a manuscript having many set-solid portions, and the emulsion ink which exhibited no offset was graded as o (circle), and the ink which exhibited offset was graded as x (crossing mark). (3) Bleeding property: Printing was conducted using a manuscript having many characters in slender writing. The bleeding condition was observed by using a microscope at a magnification of x100. In the case where bleeding of printed matter was only small, the evaluation of the ink was indicated by the sign o (circle), and the sign x (crossing mark) was given for the case where significant bleeding was observed. (4) Offensive smell: When printed matter was found not to emit any smell perceptible to the human nose, the ink was graded as o (circle), and when the printed matter was found to emit a smell the ink was graded as x (crossing mark). (5) Number of lost paper sheets: After each of the emulsion inks was left in an environment of such a high temperature and high humidity as 35°C and 70% RH for 120 hours, printing was conducted using a perforated stencil printing sheet. The number of waste paper sheets used by the time when the same print concentration as the case when the ink to be used had not been left was counted, and this number was regarded as the number of lost paper sheets. As will be understood from the results shown in Table 3 below, the water-in-oil type emulsion ink of the present invention exhibits excellent printing performance before and after being left for a long period of time in air.

Claims: A stencil printing emulsion ink of a water-in-oil type containing in an oil phase a non-volatile solvent and from 1 to 50% by weight, based on the weight of a water phase, of a volatile solvent having an initial boiling point (at distillation) of 275°C or higher and a viscosity of 10mm 2 /s·40°C or less, and having a weight ratio of the oil phase/water phase of 20 to 50/80 to 50. The stencil printing emulsion ink according to claim 1, wherein the content of an aromatic component in the volatile solvent is 1 by weight or less. The stencil printing emulsion ink according to claim 1 or 2, wherein the emulsion ink has a viscosity of 27 to 38mm in terms of the spread-o-meter value (diameter after 1 minute) at 25°C.

Inventors: OKUDA SADANAO, OKUDA, SADANAO, OKUDA, SADANAO, C/O RISO KAGAKU CORP.
Applicants: RISO KAGAKU CORP, RISO KAGAKU CORPORATION
Application year: 1995
Main classification: C09D11
IPC codes: C09D11