JP2004359944A - Ink for inkjet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink for inkjet recording which even when it is printed on a non-coated paper, causes hardly permeation to the thickness direction of a recording medium of a vehicle, and oozing to the horizontal direction thereof, and even when it is left for a long period of time, causes hardly clogging of a nozzle. <P>SOLUTION: In the ink for the inkjet recording comprising a vehicle and a coloring agent dispersed in the vehicle, and on demand, a dispersant for the coloring agent, the vehicle comprises at least a first solvent component and a second solvent component, the first solvent component having the lowest boiling point among constituent components of the ink, and higher viscosity than that of the ink, and the second solvent component having higher boiling point than that of the first solvent component. The boiling point of the first solvent component is preferably ≤280°C, and a content thereof is preferably 10-80 wt.% to the whole amount of the ink. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to an ink jet recording ink obtained by dispersing a colorant in a non-aqueous vehicle.

  The ink jet recording method is a printing method in which a liquid ink having a high fluidity is ejected from fine nozzles of a recording head and adheres to a recording medium such as paper to perform printing. This method has a feature that high-resolution and high-quality images can be printed at high speed and with low noise using a relatively inexpensive apparatus, and has recently been rapidly spreading.

  As the ink used in such an inkjet recording system, a water-soluble dye or pigment such as an acid dye, a direct dye, or a basic dye is dissolved or dissolved in a water-based vehicle composed of water and a glycol-based solvent or a water-soluble organic solvent. Dispersed aqueous inks are commonly used. However, if the recording head filled with the water-based ink is left in the atmosphere, water in the ink evaporates, the viscosity of the ink increases, and the ejection from the nozzle becomes unstable or impossible. As a countermeasure, a number of methods have been proposed in which the ink whose viscosity has increased is removed in advance by so-called preliminary ejection, in which the ink is ejected to a place other than the recording medium, thereby stabilizing the ejection during printing. However, both methods have a disadvantage that ink must be consumed for purposes other than recording.

  In contrast to the water-based ink, the non-aqueous ink containing no water is roughly classified into a solvent-based ink whose vehicle is mainly composed of a volatile solvent and an oil-based ink whose vehicle is mainly composed of a nonvolatile solvent. In particular, oil-based inks are difficult to evaporate the solvent, so that when the recording head is left in the atmosphere, the viscosity of the ink in the nozzles hardly increases, and the number of times of cleaning and preliminary ejection during printing can be reduced. It has features and is suitable as ink for high-speed inkjet printers.

  However, conventional oil-based inks have a low surface tension and a low viscosity of a vehicle mainly composed of a dispersant and a solvent, so that the ink has a high penetration rate, and the vehicle is mainly composed of a nonvolatile solvent. Therefore, when a recording medium having ink permeability, such as paper, is used, the vehicle penetrates in the thickness direction of the recording medium or oozes out in the horizontal direction, so that a certain printing quality cannot be maintained. was there. Further, since the vehicle is likely to remain on the recording medium, the paper may penetrate through the remaining portion to cause strikethrough.

  In order to solve such a problem, it is conceivable to use so-called coated paper or finely coated paper in which a pigment or the like is coated on the surface of paper or the like as a recording medium. Papermaking is more expensive and less economical than uncoated paper.

  In order to prevent exudation or strike-through of the vehicle by improving the formulation of the ink, it is conceivable to prevent the vehicle from remaining on the recording medium, specifically, to use a solvent having a low boiling point as a solvent. . However, when the boiling point of the solvent is low, the solvent evaporates from the ink in the nozzles when the recording head is left in the air, and the viscosity of the ink increases, which causes a problem that ejection failure occurs.

  As a proposal using a solvent having a predetermined boiling point, there is, for example, JP-A-2002-201387. Here, by containing a solvent component having a boiling point of 180 ° C. to 260 ° C. and a vapor pressure at room temperature of 0.5 mmHg or less at 90% or more of the total amount of the solvent, a sharp increase in the viscosity of the ink and clogging of nozzles are prevented. It is described that the possibility that the solvent remains in the coating film is reduced. In addition, JP-A-2001-164157 discloses an inkjet ink using a high boiling point solvent having a boiling point of 180 ° C. or higher. Further, an ink jet ink using a polar solvent having a boiling point of at least 100 ° C., more preferably 200 ° C. or more, and a non-polar solvent in combination is disclosed in WO 96/12772. However, even with these proposals, although a rapid increase in the viscosity of the ink can be suppressed, if the recording head is left for several hours or longer, the viscosity of the ink increases, and a discharge failure still occurs. It was necessary to frequently perform a nozzle recovery operation such as an operation.

JP 2002-201387 A JP 2001-164157 A WO 96/12772 pamphlet

  In view of such a situation, the present invention has low penetration of the vehicle into the recording medium in the thickness direction and horizontal bleeding even when printing on uncoated paper, and clogging of the nozzles even when left for a long time. An object of the present invention is to provide an ink jet recording ink that hardly occurs.

  According to the present invention, there is provided an inkjet recording ink comprising a vehicle and a colorant dispersed in the vehicle, wherein the vehicle includes at least a first solvent component and a second solvent component, One solvent component has the lowest boiling point among the components of the ink, and has a viscosity higher than the viscosity of the ink, and the second solvent component has a higher boiling point than the first solvent component. An ink for inkjet recording characterized by comprising:

  In the present invention, a solvent comprising at least two kinds of components, a first solvent component and a second solvent component, is contained in the vehicle of the ink, and the first solvent component has a low boiling point and a high viscosity, The most characteristic feature is that the solvent component has a high boiling point and a low viscosity. Thus, even if the recording head is left open and the vehicle is volatilized, the first solvent component having a low boiling point and high viscosity volatilizes preferentially over the second solvent component having a high boiling point and low viscosity. That is, since the high-viscosity solvent component is volatilized preferentially, the increase in the ink viscosity in the nozzles of the print head is suppressed, and the occurrence of ejection failure is suppressed. Since the solvent volatilizes well, no solvent remains in the recording medium, and the exudation and strike-through of the vehicle are prevented.

  As described in detail above, the present invention includes a solvent comprising at least two types of components, a first solvent component and a second solvent component, in a vehicle of an ink, wherein the first solvent component has a low boiling point and a high viscosity. Since the second solvent component has a high boiling point and a low viscosity, even if the recording head is left open and the vehicle volatilizes, the first solvent component having a low boiling point and a high viscosity is used. Is volatilized preferentially over the high-boiling point and low-viscosity second solvent component, the increase in ink viscosity in the nozzles of the print head is suppressed, and the occurrence of ejection failure is suppressed, and when the ink is ejected to the recording medium, Since the solvent volatilizes well, the solvent does not remain in the recording medium, and the exudation and strike-through of the vehicle are prevented.

  The ink of the present invention basically comprises a vehicle and a colorant dispersed in the vehicle. The vehicle basically consists of a non-aqueous solvent, and may optionally contain other additives such as a dispersant.

  The non-aqueous solvent constituting the vehicle is, as described above, a mixture of at least two types of solvent components, and specifically has the lowest boiling point among the components of the ink, and is higher than the viscosity of the ink. It comprises at least a first solvent component having a viscosity and a second solvent component having a higher boiling point than the first solvent component. Since the viscosity of the first solvent component is higher than the viscosity of the ink, the viscosity of the second solvent component is usually lower than that of the first solvent component.

  Each of the first solvent component and the second solvent component can be appropriately selected and used from various non-aqueous solvents as long as the relative conditions of the boiling point and the viscosity are satisfied. Such a solvent may be either a polar solvent or a non-polar solvent, and may be used in combination as long as a single phase is formed.

  Specific examples of the polar solvent include fatty acids, esters, alcohols, ethers and the like. Fatty acids include isopalmitic acid, oleic acid and isostearic acid. Esters include methyl laurate, isopropyl laurate, isopropyl myristate, isopropyl palmitate, isostearyl palmitate, methyl oleate, ethyl oleate, isopropyl oleate, butyl oleate, methyl linoleate, isobutyl linoleate, Ethyl linoleate, isopropyl isostearate, soybean oil methyl, soybean oil isobutyl, tall oil methyl, tall oil isobutyl, diisopropyl adipate, diisopropyl sebacate, diethyl sebacate, propylene glycol monocaprate, trimethylolpropane tri-2-ethylhexanoate And glyceryl tri-2-ethylhexanoate. Examples of alcohols include isopalmityl alcohol, isostearyl alcohol, oleyl alcohol, and the like. Examples of the ethers include glycol ether solvents such as diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, propylene glycol monobutyl ether, and propylene glycol dibutyl ether.

  Examples of the non-polar solvent include naphthene-based, paraffin-based, and isoparaffin-based solvents. Specific examples of the non-polar solvent include Isopar and Exol manufactured by Exxon, AF Solvent manufactured by Nippon Oil Co., Ltd., and Sansen and Sampar manufactured by Sun Oil. These are the trade names or registered trademarks of each company.

  The boiling point of the first solvent component is preferably 280 ° C or lower, more preferably 150 to 280 ° C, and particularly preferably 200 to 280 ° C. If the boiling point is too high, the solvent will not evaporate during printing, and the solvent will remain in the recording medium, causing seepage or strike-through of the vehicle. If the boiling point is too low, the volatilization rate is high, and the pigment concentration of the ink in the nozzle is improved in a relatively short time, and the ejection becomes unstable. The viscosity of the first solvent component at 23 ° C. is usually at least 10 mPa · s, preferably at least 20 mPa · s, more preferably at least 30 mPa · s, most preferably at least 50 mPa · s. If the viscosity is too low, the followability of ejection in a high-frequency head is reduced.

  As the first solvent component, a polar solvent is preferable, and particularly, an alcohol solvent having 6 or more carbon atoms is preferable from the viewpoint of the corrosion resistance of the material used for the ink jet recording head. Preferable examples of such alcohol solvents include linear aliphatic alcohol solvents such as hexanol, heptanol, octanol, nonanol, decanol and undecanol, branched higher alcohols such as isomiristyl alcohol, and monomers such as α-terpineol. Terpene alcohols and the like.

  The first solvent component is preferably used in an amount of 10 to 80% by weight, more preferably 15 to 45% by weight, and particularly preferably 20 to 40% by weight based on the total amount of the ink. If the content is less than 10% by weight, the leaching and strike-through of the vehicle cannot be prevented due to the low volatile content. If it exceeds 80% by weight, the pigment concentration increases after long-term storage, the viscosity increases, and nozzle clogging occurs.

  As the second solvent component, a solvent having a higher boiling point and a lower viscosity than the selected first solvent component may be appropriately selected from the various solvents listed above. The boiling point of the second solvent component is preferably 235 ° C. or higher, more preferably 250 to 360 ° C. If the boiling point is too high, the solvent will not evaporate during printing, and the solvent will remain in the recording medium, causing seepage or strike-through of the vehicle. If the boiling point is too low, the volatilization rate is high, and the pigment concentration of the ink in the nozzle is improved in a relatively short time, and the ejection becomes unstable. The viscosity of the second solvent component at 23 ° C. is preferably less than 10 mPa · s, preferably 7 mPa · s or less, more preferably 6 mPa · s or less. If the viscosity is too high, discharge becomes impossible when the environmental temperature at the time of discharge is low. Preferred specific examples of the second solvent component include fatty acid esters such as methyl soybean oil, and solvents such as naphthenic, paraffinic and isoparaffinic solvents.

  In the present invention, it goes without saying that, in addition to the first and second solvent components, the vehicle may contain other solvent components in order to achieve the purpose of adjusting the viscosity of the ink or diluting the pigment. .

  The dispersant used in the vehicle is not particularly limited as long as the colorant to be used is stably dispersed in a solvent, and among them, a polymer dispersant is preferably used.

  Specifically, "Solsperse 5000 (phthalocyanine ammonium salt-based), 13940 (polyesteramine-based), 17000, 18000 (aliphatic amine-based), 22,000, 24000, 28000" manufactured by Lubrizol Japan; "Efka" manufactured by Efka Chemicals 400, 401, 402, 403, 450, 451, 453 (modified polyacrylate), 46, 47, 48, 49, 4010, 4050, 4055 (modified polyurethane) "; Kao Corporation's" Demol P, EP "," Poise " 520, 521, 530 "," Homogenol L-18 (polycarboxylic acid type polymer surfactant) ";" Dispalon KS-860, KS-873N4 (amine salt of polymer polyester) "manufactured by Kusumoto Kasei; Industrial Pharmaceutical Co., Ltd. “Discall 202, 206 OA-202, OA-600 (multi-chain polymeric nonionic) ", and the like.

  Dyes such as oil-soluble dyes and pigments can be used as the colorant, and pigments are preferably used. As the pigment, conventionally known pigments generally used in the field of printing technology, such as organic pigments and inorganic pigments, can be used without any particular limitation. Specific examples of the pigment include carbon black, cadmium red, chrome yellow, cadmium yellow, titanium yellow, chromium oxide, pyridian, titanium cobalt green, ultramarine blue, Prussian blue, cobalt blue, an azo pigment, a phthalocyanine pigment, and quinacridone. Pigments, isoindolinone pigments, dioxazine pigments, sulene pigments, perylene pigments, thioindigo pigments, quinophthalone pigments, metal complex pigments and the like.

  The concentration of the colorant varies depending on the type of the colorant used, but is preferably 2 to 20% by weight of the total amount of the ink, and more preferably 4 to 15% by weight. The particle size of the pigment is preferably in the range of 0.01 to 1 μm.

  The ink of the present invention can be prepared by mixing components such as a solvent, a dispersant, and a colorant using a suitable disperser such as a bead mill.

  The viscosity of the ink of the present invention varies depending on the hole diameter of the nozzles of the recording head, driving conditions, the configuration of the recording head, and the like, but is preferably 5 to 30 mPa · s at 23 ° C. The viscosity is preferably adjusted by appropriately selecting the type and amount of each component such as a solvent, a dispersant, and a colorant, and can also be adjusted by appropriately adding a viscosity modifier and the like.

  Further, in the ink of the present invention, in order to prevent seepage or strike-through, the vehicle is unlikely to remain on the recording medium, in other words, it is preferable that the vehicle has higher volatility. Therefore, the weight loss of the ink when left open at 50 ° C. for 10 days is preferably 0.04 g / cm 2 or more. Here, the weight loss amount is calculated by dividing the weight change before and after leaving the ink in a certain container and leaving it open when it is left open, by the area of the gas-liquid interface.

  Further, the ink of the present invention is characterized in that the viscosity rise is small even when left open, and in practice, the viscosity change of the ink when the ink weight is reduced by 30% when left open at 50 ° C. It is desirable that the rate satisfies the following equation.

(Where η0 is the viscosity of the ink before being left open, η30 is the viscosity of the ink when the weight of the ink is reduced by 30% after being left open at 50 ° C., and 100 × (η30−η0) / η0 is the viscosity change rate of the ink. Is shown.)

  An ink that satisfies such weight loss and viscosity change rate can be prepared by appropriately selecting the types and amounts of components such as a solvent, a dispersant, and a colorant.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. In the following examples,% and parts are by weight unless otherwise specified.

(Example 1)
After mixing each solvent component according to the composition shown in Table 1, the dispersant was dissolved in the solvent to obtain a vehicle. After that, carbon black was added to a small amount of the vehicle and premixed, and then the carbon black and another vehicle were dispersed in a bead mill for a residence time of about 20 minutes to produce an ink. In addition, the viscosity of each solvent component and the obtained ink was measured by RE105L type viscometer manufactured by Toki Sangyo Co., Ltd.

(Examples 2 to 5 and Comparative Examples 1 to 3)
An ink was prepared in the same procedure as in Example 1, except that the composition was as shown in Table 1. The solvent components and the viscosity of the obtained ink were measured in the same manner as in Example 1.

(Test example)
Each of the inks obtained in the above examples was subjected to the following tests (1) to (3). Table 1 shows the results.

(1) Measurement of Change in Viscosity of Ink 20 g of ink was added to a beaker having a capacity of 100 ml and an inner diameter of 50 mm, and was allowed to stand under a 50 ° C. environment.

(Where η0 is the viscosity of the ink before being left open, η30 is the viscosity of the ink when the weight of the ink is reduced by 30% when left open at 50 ° C. Each viscosity was measured by the same method as in Example 1.) .)

(2) Weight loss per unit surface area of the ink after standing at 50 ° C. for 10 days Add 20 g of the ink to a beaker having a capacity of 100 ml and an inner diameter of 50 mm, and leave it at 50 ° C. to measure the weight loss after 10 days. did. The weight loss per unit surface area was determined by dividing the obtained value of the weight loss by the surface area of the liquid surface.

(3) Exudation of vehicle Exudation of vehicle developed on the edge of the printed portion after one day after printing a 2 cm square solid on plain paper using a share wall mode type ink jet recording head manufactured by Xaar Company Was visually evaluated according to the following criteria.
○: None △: Slightly available ×: Available

(4) Clogging of nozzles After printing in the same manner as in (2) above, the ink jet recording head was left for 12 hours and then printing was performed, and it was confirmed whether or not ink was normally ejected from the head.
○: Ink is normally ejected from all nozzles ×: Some nozzles do not eject ink

The symbols in Table 1 mean the following.
MA8: Carbon black MA8 (trade name) manufactured by Mitsubishi Chemical Corporation
S13940: Pigment dispersant Solsperse S13940 (trade name) manufactured by Japan Lubrizol Corporation,
FOC140: Fine Oxocol 140 (trade name) manufactured by Nissan Chemical Industries, Ltd.
AF4: AF Solvent No. 4 (trade name) manufactured by Nippon Oil Corporation
AF5: AF Solvent No. 5 (trade name) manufactured by Nippon Oil Corporation
AF6: Nippon Oil Corporation AF Solvent No. 6 (trade name),
FOC180: Fine Oxocall 180 (trade name) manufactured by Nissan Chemical Industries, Ltd.

In Examples 1 to 5, since a low-boiling point and high-viscosity solvent component and a high-boiling point and low-viscosity solvent component were used in combination, good results were obtained in all of the test examples. On the other hand, in Comparative Examples 1 and 3, since the viscosity of the solvent component having the lowest boiling point was low, the rate of change in viscosity was high, and nozzle clogging occurred. In Comparative Example 2, the exudation of the vehicle occurred because the boiling points of all the solvent components were too high.

Claims (8)

An inkjet recording ink comprising a vehicle and a colorant dispersed in the vehicle, wherein the vehicle includes at least a first solvent component and a second solvent component, and the first solvent component is It has the lowest boiling point among the components of the ink, and has a higher viscosity than the viscosity of the ink, and the second solvent component has a higher boiling point than the first solvent component. Ink jet recording ink. The ink for inkjet recording according to claim 1, wherein the first solvent component has a boiling point of 280 ° C or lower. The ink for inkjet recording according to claim 2, wherein the first solvent component is a polar solvent. The ink for inkjet recording according to claim 3, wherein the polar solvent is an alcohol solvent having 6 or more carbon atoms. The ink for inkjet recording according to any one of claims 1 to 4, wherein the first solvent component is contained in an amount of 10 to 80% by weight based on the total amount of the ink. 2. The ink jet recording ink according to claim 1, wherein when the ink is left open at 50 [deg.] C. and the weight of the ink decreases by 30%, the viscosity change rate of the ink satisfies the following expression.

(Where, η0 is the viscosity of the ink before being left open, η30 is the viscosity of the ink when the weight of the ink is reduced by 30% when left open at 50 ° C., and 100 × (η30−η0) / η0 is the viscosity change rate of the ink. Is shown.) The ink for inkjet recording according to claim 1, wherein the viscosity of the ink at 23C is 5 to 30 mPas. 2. The ink jet recording ink according to claim 1, wherein the weight loss of the ink when left open at 50 ° C. for 10 days is 0.04 g / cm 2 or more.