Recording liquid, method for its production and ink-jet recording method making use of it

Abstract: A recording liquid comprises a recording agent which is a component that forms a recorded image and a liquid medium in which said recording agent is dissolved or dispersed, wherein said recording agent comprises a dye (A) C.I. Reactive Red 23 and a dye (B) represented by R₁C₆H₃(SO₃M) n -N=N-C₁₀H₃(OH)(NHR₂)(SO₃M)₂, wherein R₁ represents H, halogen atom, carboxyl or alkyl; R₂ represents -COCH₃, -SO₂C₆H₄CH₃ or -COC₆H₄R₃, where R₃ represents H or Cl; M represents a base; and n represents either 0 or 1. An ink-jet recording method comprises applying a droplet of the recording liquid to a recording medium to carry out recording.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a recording liquid, a method for producing said liquid and an ink-jet recording method making use of said liquid. More particularly, it relates to such a recording liquid which is capable of giving a recorded image with a superior tone sharpness, light-resistance and gas resistance (see below). Related Background Art Hitherto having been used as inks in writing utensils such as fountain pens and felt pens are recording liquid comprising various types of dye dissolved in water or other organic solvent. Inks comprising various types of dye dissolved in water or other organic solvent are also used in ink-jet systems in which recording is performed by ejecting ink from an ejection orifice provided in a recording head, by the action of the oscillation attributable to a piezoelectric oscillator or the electrostatic force attributable to the application of a high voltage. The inks for ink-jet systems, however, are required to satisfy more severe conditions with respect to many performances than those required in the writing utensils such as fountain pens and felt pens commonly used. The ink-jet systems make a less noise and can afford to perform high-speed recording or color recording on a plain paper without taking any particular fixing step, and researches have been energetically made on various types. Various methods are available for the systems of this type, but all of them are required to have the performances such that the physical properties such as viscosity and surface tension are within the range of suitability, the recording agent has a dissolution capability high enough not to cause clogging of the minute ejection orifice, a recorded image can be obtained in a sufficiently high density, and changes in the values of physical properties, precipitation of solid contents, or the like may not occur during storage. In addition to the above performances, they are also required to have the properties that the recording can be performed without limitation on the type of recording members, they can achieve a high fixing speed, and they can give a recorded image with excellent water resistance, solvent resistance (resistance to alcohol, in particular), light-resistance, wear resistance, and resolution. Among these, particularly in relation to magenta color recording, recorded images tend to undergo color fading by light irradiation, in other words, have a poor light-resistance, causing a great problem. Thus, inks improved to eliminate these disadvantages have been strongly sought. From such viewpoints, many proposals relating to inks have been made. For example, Japanese JP-A-57-30773, JP-A- 63-46259 and JP-A-63-46260 propose to use monoazo metal complex dyes. Such metal-containing dyes, however, involve the disadvantages that they lack tone sharpness, and have a poor color reproducibility when a color image is fromed. Moreover, records obtained using the metal-containing dyes (in particular, records made on a coated paper containing silica on its surface) commonly undergo color fading due to gas in the air in addition to the color fading due to light, when they are stuck on a wall in the room. This phenomenon is particularly remarkable when they are stuck near a copying machine and may be ascribed to an ozone generation by the copier's corona discharges. This is a generally known effect inherent to any corona discharge. Because of the disadvantages involved as mentioned above, it is difficult to use the metal-containing dyes alone. JP-A- 62-190275 proposes to use by mixture a monoazo metal-free dye achievable of a sharp tone and a monoazo metal-containing dye. This method can obtain a record which is good and well-balanced in both the tone and light-resistance. However, the gas resistance as mentioned in the above has not been satisfactorily improved. The use of a monoazo-dye in an ink is also known from JP-A- 131 657. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a novel recording liquid that has overcome the above disadvantages in the prior art and satisfies the tone sharpness, light-resistance and gas resistance at the same time. Another object of the present invention is to provide a recording liquid that tends not to cause clogging of orifices and changes of properties or generation of precipitates during storage, and also has a superior recording performance, ejection stability and ejection response. Still another object of the present invention is to provide an ink-jet recording method that can give an image having a superior tone sharpness, light-resistance and gas resistance even when the coated paper containing silica on its surface is used. The above objects can be attained by the invention for a recording liquid as defined in claim 1 The present invention also provides an ink-jet recording method in which a droplet of the recording liquid as claimed is applied to a recording medium to carry out recording, The production of the recording liquid as claimed is the subject matter of claim 11. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS To achieve the objects of the present invention, the present inventors made detailed studies on dyes serving as recording agent components of inks, in particular, on magenta dyes. As a result, they found that a specific combination of dyes is preferred as the recording agent of inks, particularly as the recording agent of inks used in the ink-jet systems, and employment of such a specific combination of dyes as the recording agent of inks can bring about an ink capable of giving a recorded image that satisfies tone sharpness, light-resistance and gas resistance at the same time and also satisfies water resistance, resolution, alcohol resistance, and other required performance, when used in the ink-jet systems. The present invention will now be described below in greater detail by giving preferred embodiments. The dye (A) C.I. Reactive Red 23 (16202) used in the present invention is a dye having the following chemical structure, which is a dye with excellent light-resistance. The dye (B) used in the present invention, represented by the general formula, is a dye with excellent tone sharpness. The dye (B) includes any dyes so long as it is included in the general formula, but particularly preferred examples thereof include the following. These are exemplified mainly as sodium salts, but may also be formed into salts with any bases, such as lithium salts, potassium salts, ammonium salts and so forth. Exemplary Compound B-1 Exemplary Compound B-2 Exemplary Compound B-3 Exemplary Compound B-4 Exemplary Compound B-5 Exemplary Compound B-6 Exemplary Compound B-7 Exemplary Compound B-8 Exemplary Compound B-9 Exemplary Compound B-10 Exemplary Compound B-11 Exemplary Compound B-12 On the above-exemplified compounds, the compound B-6 is particularly preferred for the present invention, as later and concretely described in EXAMPLES . The present invention is mainly characterized by the use in combination of the dyes (A) and (B) as described above. An ink resulting from such a specific combination can give a recorded image concurrently having very superior tone sharpness, light-resistance and gas resistance, compared with conventional inks of the same kinds of colors in prior arts. The total content of the above dyes is determined depending on the type of the liquid medium component and the performances required in inks, but, in general, may be in the range of from 0.1 to 20 % by weight, preferably from 0.5 to 15 % by weight, and more preferably from 1 to 10 % by weight, based on the total weight of an ink. As to the amount of these dyes used, the effect of the present invention can be most remarkably achieved when the dyes (A) and (B) are used in a proportion of from 10:1 to 1:10, and preferably from 7:3 to 3:7, in weight ratio in the total weight of the dyes. The liquid medium preferably used in the ink of the present invention is water or a mixed solvent comprising water and a water soluble organic solvent. Particularly preferred is the mixed solvent comprising water and a water soluble organic solvent, and containing a polyhydric alcohol as the water-soluble organic solvent, which ahs the effect of preventing evaporation of ink. As the water, it is preferred to use not the common water, containing various ions, but deionized water. The water-soluble organic solvent used by mixture with water includes, for example, alkyl alcohols having 1 to 4 carbon atoms, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol and isobutyl alcohol; amides such as dimethylformamide and dimethylacetamide; ketones or ketoalcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; polyalkylene glycol such as polyethylene glycol and polypropylene glycol; alkylene glycols comprising an alkylene group having 2 to 6 carbon atoms, such as ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol and diethylene glycol; glycerol; lower alkyl ethers of polyhydric alcohols, such as ethylene glycol methol or ethyl ether, diethylene glycol methyl or ethyl ether, triethylene glycol methyl or ethyl ether; N-methyl-2-pyrrolidone, and 1,3-dimethyl-2-imidazolidinone. Of these many water-soluble organic solvents, preferred are polyhydric alcohols such as diethylene glycol, and lower alkyl ethers of polyhydric alcohols, such as triethylene glycol monomethyl or monoethyl ether. The above water-soluble organic solvent may be contained in the ink in an amount of generally from 5 to 90% by weight, preferably from 5 to 80 % by weight, and more preferably from 5 to 40 % by weight, based on the total weight of the ink. The content of the water used in the mixed solvent is determined in a vast range, depending on the type of the above solvent component, the composition thereof and the desired performances of inks, but should be within the range covering generally from 10 to 95 %, preferably 50 to 95 %, and more preferably from 60 to 95 %, based on the total weight of the ink. The ink of the present invention, made up with these components can be an excellent ink well balanced by itself in all the recording performances (such as signal response, droplet-forming stability, ejection stability, long-time continuous recording performance, and ejection stability after long-time stoppage of recording), shelf stability, and fixability to recording mediums, as well as the tone sharpness, light-resistance, gas resistance, water resistance and alcohol resistance of recorded images. For the purpose of further improving these performances, all sorts of conventionally known additives may also be further added and contained. They include, for example, viscosity modifiers such as polyvinyl alcohol, celluloses and water-soluble resins; surface tension modifiers such as all sorts of cationic, anionic or nonionic surface active agents, diethanolamine and triethanolamine; pH adjusters through buffer solution, and mildewproofing agents. A specific-resistance modifier comprised of inorganic salts and so forth such as lithium chloride, ammonium chloride or sodium chloride is also added in order to prepare inks used in ink-jet systems of the type the ink is electrostatically charged. Values of thermal properties as exemplified by specific heat, thermal expansion coefficient and thermal conductivity may often be modified in instances in which the ink is used in ink-jet systems of the type the ink is ejected by the action of heat energy. The ink of the present invention, as described above, is useful as inks for use in making records using various writing utensils, recording tools, etc., and particularly useful as inks for use in ink-jet systems. The ink-jet systems mentioned herein include any systems so long as they are systems in which an ink can be effectively released from a nozzle and applied to a recording medium serving as a target. As described above, the ink of the present invention comprises the dyes mixed in a specific combination. Thus, not only as ink used in general recording but also particularly as ink used in ink-jet systems, it particularly gives a recorded image having superior tone sharpness, light-resistance, gas resistance, water resistance, alcohol resistance, resolution and so forth. It also has superior recording performances such as long-term shelf stability, ejection stability and ejection response, and exhibits superior ink-fixing properties when it is applied on the recording medium. EXAMPLES The present invention will be described below in still greater detail by giving Examples, Comparative Examples, and Use Example. In the following, "part(s)" or "%" is by weight unless particularly mentioned. Example 1 C.I. Reactive Red 23 1.5 parts Exemplary Compound B-2 1.5 parts Diethylene glycol 20 parts Ethylene glycol 10 parts Ion-exchanged water 67 parts The above components were thoroughly mixed and dissolved in a vessel, and the solution was pressure-filtered using a Teflon filter having a pore diameter of 1 µm, followed by a deaeration treatment using a vacuum pump to obtain an ink of the present invention. Examples 2 to 6 Inks of the present invention, as shown in Table 1 below, were prepared in the same manner as Example 1. Comparative Example 1 C.I. Reactive Red 23 3 parts Diethylene glycol 20 parts Ethylene glycol 10 parts Ion-exchanged water 67 parts An ink of the comparative example was prepared in the same manner as Example 1, but using the above components. Comparative Example 2 Exemplary Compound B-2 3 parts Diethylene glycol 20 parts Ethylene glycol 10 parts Ion-exchanged water 67 parts An ink of the comparative example was prepared in the same manner as Example 1, but using the above components. Comparative Examples 3 to 9 Inks of the comparative examples, as shown in Table 1 below, were prepared in the same manner as Example 1. Use Example Using the inks of the present invention and the comparative examples, obtained in the above, recording was carried out using a recording apparatus having multiple heads of an on-demand type in which recording is performed by applying heat energy to the ink in the recording heads to generate droplets (ejection orifice diameter : 35 µm; resistivity of heating resistance element: 150 Ω; driving voltage: 30 V; frequency: 2 KHz), to obtain the results as shown in Table 1 below. Used as recording paper was a commercially available ink-jet recording paper IJ Mat Coat M (available from Mitsubishi Paper Mills, Ltd.), having a silica-coated layer on its surface. The valuation as shown in Table 1 was based on the following criterions. The light-resistance was based on changes in chromaticity (color difference ΔE) measured after irradiation for 100 hours using a xenon fademeter, and evaluated according to the following criterions. Ranks A and B were regarded as acceptable record. ΔE Rank 0 to 5 A 5 to 10 B 10 to 20 C 20 to 30 D Not less than 30 E The gas resistance was based on changes in chromaticity (color difference ΔE) measured on records stuck on the wall for 3 months with a distance of 1.5 m from the copying machine, and evaluated according to the following criterions. Ranks A and B were regarded as acceptable records. ΔE Rank 0 to 3 A 3 to 8 B 8 to 13 C 13 to 18 D Not less than 18 E The tone was based on visual observation. Dyes other than the dyes (A) and (B) used in Comparative Example are the following dyes. Dye C-1 Dye C-2 The inks shown in Table 1 have the following composition. Ink Composition 1 Dyes 3 parts (in total) N-methyl-2-pyrrolidone 15 parts Diethylene glycol 10 parts Ion-exchanged water 72 parts Ink Composition 2 Dyes 4 parts (in total) Glycerol 10 parts Ethylene glycol 20 parts Ion-exchanged water 76 parts Ink Composition 3 Dyes 2.5 parts (in total) Diethylene glycol 20 parts Glycerol 5 parts Ion-exchanged water 72.5 parts

Claims: A recording liquid comprising a dye composition as a component being capable of forming a recorded image and water or a mixture of water and a water-soluble organic solvent as a component for dissolving or dispersing the dye composition, wherein the dye composition comprises a dye (A) C.I. Reactive Red 23 and a dye (B) represented by the following general formula; said dyes being contained in the dye composition in a proportion ranging from 10:1 to 1:10 in weight ratio wherein R₁ represents a hydrogen atom, a halogen atom, a carboxyl group, or an alkyl group; R₂ represents a group COCH₃, or where R₃ represents a hydrogen atom or a chlorine atom; M represents a base selected from the group consisting of an alkali metal group, and an ammonium group; and n represents either 0 or 1. A recording liquid according to claim 1, wherein said dyes (A) and (B) are mixed in a proportion ranging from 7:3 to 3:7 in weight ratio. A recording liquid according to claim 1, wherein said dye (B) represented by said general formula is a dye represented by the following formula: A recording liquid according to anyone of claims 1 to 3, wherein, whenever comprising a mixture of water and a water-soluble organic solvent, said water is contained in an amount ranging from 10 to 95 % based on the total weight of the recording liquid. A recording liquid according to claim 4, in which said water is contained with 50 to 95 %, preferably with 60 to 95 %. A recording liquid according to claim 4 or 5, wherein said water-soluble organic solvent is contained in an amount ranging from 5 to 90 % based on the total weight of the recording liquid. A recording liquid according to claim 6, in which said water-soluble organic solvent is contained with 5 to 80 % preferably with 5 to 40 %. An ink-jet recording method comprising applying a droplet of a recording liquid as claimed in anyone of the preceding claims to a recording medium to carry out recording. An ink-jet recording method according to claim 8, by means of a system in which heat energy is applied to the recording liquid to cause droplets of the recording liquid to be ejected from an orifice. An ink-jet recording method according to claim 8 or 9, wherein said recording medium is a coated paper containing silica on its surface. Method for producing a recording liquid as claimed in anyone of claims 1 to 7 by mixing and filtering the indicated components in their specified range.

Inventors: IWATA KAZUO, SHIROTA KATSUHIRO, IWATA, KAZUO, SHIROTA, KATSUHIRO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1989
Main classification: C09D11
IPC codes: C09D11