JP2002234243A - Method for ink jet recording - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink composition used for an on-demand ink jet recording system for the purpose of printing plain paper (acidic paper) at a high speed, and to provide a method for recording. SOLUTION: A method for on-demand ink jet recording comprises the steps of injecting an ink liquid droplet on a non-coated paper recording medium having a Beck smoothness of 80 s or less and a pH of 6.2 or less at a recording speed of 10 ips or more of a relative speed between a nozzle and a sheet to form recording dots. In this case, a roundness of the dot on the medium = (perimeter)2/(4π*dot area) is 2.5 or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an on-demand type ink jet recording apparatus, and more particularly, to a recording method of an ink jet recording apparatus for performing high-speed recording on uncoated paper.

[0002]

2. Description of the Related Art Conventionally, in ink jet recording,
In order to prevent excessive penetration and bleeding of ink droplets to achieve high density and saturation printing, and to further improve water resistance and storage characteristics, special substrates (inkjet paper) may be used. It was customary. There have been many reports on this, for example, USP 5,854,649, USP
5,853,899, JP-A-11-192778, JP-A-11-129610
No., JP-A-11-078223, JP-A-11-078221, JP-A-11
-034485, JP-A-11-028861, JP-A-11-020300,
Japanese Patent No. 2845832, Japanese Patent Application Laid-Open No. 11-506991, and the like describe that improving the ink adsorbability by applying a specific water-soluble resin, for example, USP 5,516,364, JP-A No. 192775, JP-A-11-157207, JP-A-11-12960
No. 6, JP-A-11-048604, JP-A-11-034481, Patent 2,
No. 938, 917, Patent No. 2887098, Patent No. 2883299, Patent No. 2877740, etc. include specific clays, inorganic materials such as alumina, etc. It is described what to do. Regarding the pH of the paper, JP-A-2000-119572 and JP-A-2000-154344
There is a report in the official gazette.

At the same time, many reports have been made on ink-jet ink compositions for realizing high-quality printing. Because it is enormous, one example is described in JP-A-6-3
06320, Patent No. 2136873, Patent No. 2116198, Patent No. 2
No. 037450, Patent No. 2037453, Patent No. 2894568, Patent No.
No. 2710138, Japanese Patent No. 2792135, Japanese Patent No. 2841678, Japanese Patent No. 1927399, and the like describe inks with less bleeding or water resistance.

There have been many reports on the relevance of the physical properties of paper and ink, see JP-A-10-330666 and JP-A-10-330666.
316915, JP-A-10-272828, Patent No. 2618361, Patent No. 2801295, Patent No. 2529154, Patent No.2516218, Patent No.2825224, etc. The report describes the degree, the Bristow wetting time of paper and ink, the absorption coefficient, the evaporation rate of ink, and the like.

[0005] As a general commentary on the above-mentioned ink and paper (substrate), for example, "Development of high image quality and high speed technology of ink jet recording and related materials", Technical Information Association, 1999, "Printing and Information" Paper characteristics and printability in records and analysis and evaluation ”, Technical Information Association, 19
Published in 1999.

On the other hand, in recent years, there has been an increasing demand for high-quality printing on general paper (plain paper) instead of special paper specially manufactured for inkjet. This is true not only for paper price reduction, but also for fields that were conventionally processed by other printing methods (such as offset, flexographic printing, ink printing, laser printers, non-impact printers such as thermal recording, and impact printers). This is a problem that is inevitably encountered when applying the ink jet recording method. In particular, in the office field where high-speed printing of many office documents such as fixed-form documents, slips, and forms, the use of plain paper and high-speed printing are indispensable requirements. And it was extremely difficult to realize by the recording method.

[0007]

In the case of ink using water and a water-soluble solvent as a solvent, bleeding and set-off (bleed-through) caused by permeation and adsorption of paper into cellulose fibers are achieved.
Phenomena that lower the print quality cannot be prevented in principle. For this reason, as described above, a method of maintaining print quality by treating paper (substrate) has been adopted as a basic measure. However, plain paper (uncoated paper), particularly acidic paper, intended by the present invention is used. Not suitable for printing on.

[0008]

The gist of the present invention to solve the above problems is that the relative speed between the nozzle and the paper is 10 ips on an uncoated paper recording medium having a Beck smoothness of 80 s or less and a pH of 6.2 or less. In the ink jet recording method for forming recording dots by ejecting ink droplets at the recording speeds described above, the roundness of the recording dots on the recording medium = (perimeter) ² / (4π * dot area) is 2. 5 or less.

Preferably, the ink composition forming the recording dots has a surface tension at 25 ° C. of at least 33 mN / m and a viscosity in the range of 5 to 20 mPa · s.

The ink composition for forming the recording dots preferably contains water, glycerin and a pigment as essential components.

It is to be noted that by adding a step of drying the recording dots after forming the recording dots on the recording medium, the roundness of the recording dots can be easily controlled.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As a classification of paper, a classification method used in production statistics of the Ministry of International Trade and Industry is often used.
According to this, printing information paper, packaging paper, sanitary paper, and miscellaneous paper are roughly classified, and the printing information paper is divided into uncoated paper, lightly coated paper, coated paper, special printing paper, and information paper. is there. Paper for the purpose of the present invention belongs to a part of uncoated paper, special printing paper and information paper. The composition of paper varies widely, depending on the pulp material, the type and amount of paint, and the production method, and there are many methods for evaluating and classifying paper. For example, paper density, thickness, front / back difference,
There are side grain (making direction), porosity of pores, air permeability, water absorption / oil absorption, size, surface roughness, gloss, pH, surface strength, peel strength, stiffness, folding strength, chargeability, etc. Affects print quality.

The inventor paid attention to surface smoothness as a method for generally defining paper in the field intended by the present invention. These include Beck smoothness, smoother smoothness, Chapman smoothness and the like, which are specified in TAPPI-T479, JIS P8119 and the like. The Beck smoothness, the smoother smoothness, and the smoothness by the Oken-type smoothness tester all measure air flow velocity or pressure change, and can be mutually converted. The papers intended by the present invention are all uncoated papers and have a Beck smoothness of 80 s or less. Further, among them, uncoated paper having a high acidity having a pH of 6.2 or less often has poor image quality. An object of the present invention is to obtain good image quality on acidic paper.

The pH of the paper can be easily measured by a known method. For example, JAPAN TAPPI paper pulp test method No. It can be measured by the method specified as 6. An indicator solution for pH measurement is dropped on the measurement surface of the test piece, and spread thinly with absorbent cotton. After the color becomes uniform, the pH is measured by comparing with the hue in the pH standard color change table.

The uncoated paper refers to a paper having a substantial amount of paint (filler) of 12 g / m ² or less on both sides (fine coated paper or less in the definition of the production statistics described above). Ink-jet printing on paper and the like that does not fall under these is outside the scope of the object of the present invention. Examples of the paper of the present invention include high-grade printing paper, intermediate-grade printing paper, lower-grade printing paper, thin printing paper, finely coated printing paper, special printing paper such as high-quality paper, foam paper, PPC paper, and other information paper. There are, specifically, the following papers and various modified / processed papers using them, but the present invention is not particularly limited thereto.

For example, OK fine paper, new OK fine paper,
Sunflower, Phoenix, OK Royal White,
Export high quality paper (NPP, NCP, NWP, Royal White), OK foam, OKH, NIP-N, OK Everlight, OK Everlight W, OK Starlight, OK
Snow Light, Shiratoma Paper, OK New Light, OK Magazine Paper, OK Cream Everlight, OK High Parky, OK High Magazine Paper, OK Skylight, OK Fine Paper L, Everlight R, OK Bright, O
K Royal Light S, Royal Light H, New Light R, New Light RS, Royal Light N, Clean Hit M, Cree Hit D, Clean Hit S, JJ, O
KF, OKH, NIP, KS form, 3800 paper,
KIP-N (from New Oji Paper), continuous slip paper, high-quality NIP paper, gold king, Toko, export fine paper, special demand fine paper, Pyrene, Highland, Andes, Rocky, lightweight off-wheel, Alps, Himalaya, Seine , High Caster, Easter DX, Pyrenees DX, Super Pyrenees DX,
Andean DX, Super Andean DX, Seine DX, Super Seine DX, Golden Foam, Silver Foam, Excellent Foam, Silver Recycle NI
P, KRF supermarket, SKF, GOLF-NIP, PP
C paper, NPI form DX (Nippon Paper), pearl, Kinbishi, diamond form, ruby light O, ruby light,
Ruby Light L, Mitsubishi NIP, Inkjet Foam (Mitsubishi Paper), Kanari V, Kanari SW, White Elephant, High-grade Publishing Paper, HNF Semi Fine Wood, Shiromari, Tokuginmari,
Kinmari L, Alpha Super, Semi-top KL, High Beta, Beta Super, Shiromari L, High Gamma,
Gamma Super, HNK, HNF (Hokuetsu Paper)
Shiraoi, DSK, HAKURO, Sharon, Tokushi Lion, White Lion, Libyan, Super Commercial Paper, AA Henry, BB Henry, CC Henry, DD Henry, EE
Henry, EE Henry S, DSK, DSK38, DS
KN (above Daishowa Paper), silver ring, gold ring, gold yang (W), bridge, capital, excellent form, silver form, KRF, FPLB, KCR (above Nippon Paper), Sendai MP fine paper, Kinko, Thunderbird fine,
Hanging paper, colored paper base paper, continuous slip paper, chaton, Emine, R
CP, Sendai Form, Thunderbird Form (Made by Chuetsu Pulp), OP Kinzakura (Made by Chuetsutsu), Gold Sand, Reference Paper, Exchange Certificate Paper (White), Form Printing Paper, KRF, White Form, Color Form, (K) NIP, Fine PP
C, Kishu inkjet paper (made by Kishu Paper), Taiou, Bright form, Kant, Kant white, Dante, CM paper, Dante comic, Heine, Paperback book paper, Heine S, New AD paper, Utrilo Excel, Excel Super A, Kant Excel, Excel Super B, Dante Excel, Heine Excel, Excel Super C, Excel Super D, AD Excel, Excel Super E, New Bright Form, New Bright N
IP (above Daio Paper), sun ring, moon ring, cloud ridge, galaxy, baiyun, weiss, moon ring ace, baiyun ace, Uncen ace (above made by Nippon Paper Industries), Taiou, bright foam, bright nip (more Nagoya pulp), Peony A, Golden pigeon, Toku peony, White peony A, White peony C, Silver pigeon, Super white peony A, Light cream white peony, Special medium paper, White pigeon, Super medium paper, Blue pigeon, Red Pigeon, Golden Pigeon M Snow Vision, Snow Vision, Golden Pigeon Snow Vision, White Pigeon M, Super DX, Hamanasu O, Red Pigeon M, HK Super Printing Paper (Honshu Paper)
Star Linden (A.AW), Star Elm, Star Maple, Star Laurel, Star Poplar, MOP, Star Cherry I, Cherry I Super, Cherry II Super, Star Cherry III, Star Cherry IV, Cherry III Super, Cherry IV Super ( As mentioned above, Maruzumi Paper), SHF (Toyo Pulp) and TRP (Tokai Pulp).

As the recording medium, paper having a size of 2 or more according to JIS P8122 "Testing method for paper Skillet size" can be used without any particular limitation. For example, 40kg paper,
Examples include high-quality paper and color high-quality paper such as 55 kg paper, 70 kg paper, 90 kg paper, and 135 kg paper, Xerox 4024, inkjet plain paper and special paper, recycled paper, and slip paper.

The recording medium of the present invention can also be defined by a surface roughness coefficient. Although not strict, for example, paper having an average surface roughness Rz of 10 μm or more substantially corresponds to this.

Although the thickness of the recording medium of the present invention is not particularly limited, for example, paper having a thickness of 80 to 200 μm substantially corresponds. Film thickness 95 to 11 widely used as ordinary paper
5 μm paper is particularly preferred for the purposes of the present invention.

The recording medium to which the present invention is applied is desirably uncoated paper. For example, in terms of the ratio of the elemental components of the paper, the number of aluminum and silicon elements is 150, 200 or less for 100 carbon elements, respectively. It is desirable that

The printing speed of the printer in the field of the object of the present invention is characterized in that it is significantly higher than the conventional ink jet recording. On-demand ink jet recording heads or recording methods include line recording,
There are various modes such as a serial type recording and a transfer type (shuttle type) recording, but the present invention is used without any particular limitation. In any case, the relative movement speed between the nozzle and the paper (recording medium) is 10 ips (inch).
/ S) or more. For example, in the case where the head portion is fixed and only the paper moves as in the case of line-type recording, the paper moving speed (paper feed speed) corresponds to the relative speed, and the serial-type recording, that is, the head Is moved perpendicularly to the paper feed direction and sequentially recorded, and the paper is intermittently fed, the head moving speed (carriage speed) corresponds to the relative speed.
The paper is installed on a rotating drum or the like and records on it.
Alternatively, in the case of a transfer type in which the image is temporarily recorded on a drum and then transferred to a sheet, it is understood that the speed at which the relative position between the moving sheet or the drum surface and the nozzle changes. In any case, the printing speed is directly related to the nozzle ejection frequency and the printing resolution. For example, the paper feed speed of line type recording or the head moving speed of serial type (ie, recording speed)
V is represented by the ejection frequency f of the ink droplet and the recording resolution R,
V = f × R. 5 ips or less (usually 1
In the recording of (ips or less), a large number of ink compositions reported conventionally can be applied as they are.

The present invention can be effectively used in high-speed recording of at least 5 ips or more, particularly preferably 10 ips or more. Although it is possible to realize sufficiently practical printing characteristics without particularly using a drying and heating step, it is also possible to add a heating and drying step and the like in order to more effectively implement the high speed of the present invention. . The ink or the recording medium may be heated by contacting the recording medium, or may be heated without contacting the recording medium, such as by irradiating infrared rays or blowing hot air. The temperature suitable for drying should be 1 to avoid fumes and discoloration of the recording paper.
The temperature is desirably 80 ° C. or lower.

The roundness characteristic of the present invention will be described below. For the measurement, an image captured by a CCD camera from a microscope with a magnification of 20 times was analyzed using automatic image quality evaluation software (Image Pro Plus manufactured by Media Cybemetrics). Roundness is defined by the following equation.

[0024]

(Equation 1)

As can be seen from the above equation, in the case of a perfect circle, the roundness is 1. On the other hand, in the jagged dots as shown in FIG. 1, the perimeter becomes longer with respect to the dot area,
Roundness increases.

The dot shape has been reported in the above-mentioned JP-A-6-306320, and is given by the following equation.

[0027]

(Equation 2)

Although the dot shape coefficient Y is 1 in the case of a perfect circle, it is closer to the visual image quality judgment to define the dot shape coefficient Y using the circumference than the maximum dot diameter. Specifically, in the case of uncoated paper, the landed ink has a complicated shape along the cellulose fibers. Therefore, using the perimeter instead of the maximum diameter of the dot gives a better dot shape.
(Including not only the element of the maximum diameter, but also information of the minimum diameter) can be reproduced more faithfully.

For example, in the case of the dot as shown in FIG. 2, the unevenness is large and has a considerably jagged shape, and the unevenness substantially corresponds to the center line of the dot (on the solid line in the figure). In this case, since the diameter and the maximum diameter when the dot is assumed to be a perfect circle (the dotted line portion in the figure) are substantially equal, the dot shape coefficient Y is a value close to 1. On the other hand, the roundness of the present inventors is a value considerably larger than 1, because the circumference is used instead of the maximum diameter. Therefore, the actual dot shape can be reproduced more faithfully by using the roundness of the present inventors.

Although the details will be described later, the roundness is 3 or less, preferably 2.5 or less, and it can be judged that the image is beautiful. Naturally, the special paper specially manufactured for the ink jet has a substantially circular shape, that is, the circularity. Becomes a value close to 1. In addition, the pH of the uncoated paper exceeds 6.2 (especially 6.4 or more).
Neutral paper (particularly what is called inkjet plain paper)
Found that a relatively well-formed dot shape having a roundness of 2 to 2.5 was formed. Therefore, the present inventors
It is intended to obtain good image quality on non-coated paper having a high acidity of H of 6.2 or less, so-called acidic paper.

The surface tension of the ink composition of the present invention does not need to be particularly limited. Inks having a surface tension of 33 mN / m or more at 25 ° C. can provide good image quality on non-coated paper having a high acidity of pH 6.2 or less. Can be obtained.

The viscosity of the ink composition of the present invention is not particularly limited, but the viscosity at 25 ° C. is preferably in the range of 5 to 20 mPa · s in order to maintain stable ejection characteristics. 5mP
When the viscosity is less than a · s, the shape and frequency characteristics of the ink droplet tend to be poor, and when the viscosity is more than 20 mPa · s, the ejection is difficult and the stability is difficult. Although the ink composition of the present invention desirably exhibits Newtonian fluid behavior under the temperature conditions used, the shear rate (about 100 rpm) usually used for measurement is preferably used.
m), if the above conditions are met, there is no problem even if the apparent viscosity has some shear rate dependence.

As the ink composition of the present invention, various materials are used without limitation. Generally, a binder, a physical property adjuster such as viscosity, surface tension, pH, etc., a fungicide, and the like are added to a main material of a colorant and a solvent. The colorant is a dye or a pigment, and the solvent is mainly water or a water-soluble organic solvent, but a non-aqueous solvent is also possible. These solvents may not only function as a solvent but also act as an anti-drying agent (wetting agent), a penetrant (surface tension reducing agent), a viscosity, an evaporation rate controlling agent, etc. Materials showing properties, boiling points, evaporation rates, flash points and the like are used. For example, diethylene glycol, polyethylene glycol, acetylene glycol, glycerin, N
MP, sodium lactate, DMSO, polyoxyethylene alkylphenol, polyoxyethylene fatty acid ester, ethylene glycol alkyl ether, diethylene glycol alkyl ether, alcohols such as ethanol and propanol.

Examples of the physical property modifier include metal hydroxides such as KOH, various surfactants, alcohol amines such as diethanolamine and triethanolamine, phosphoric acid, alcohol amine salts of strong acids, ammonium salts, lower carboxylic acids and glycols. Various additives such as hydroxycarboxylic acids such as acid and lactic acid, fungicides such as sodium benzoate, potassium sorbate, thiabendazole and benzimidazole, chelating agents, deoxidizers, defoamers, and conductivity-imparting agents are used. Can be used according to

In the present invention, an ink composition containing water, glycerin and a pigment as essential components can be suitably used. Polyhydric alcohols such as (poly) alkylene glycols such as polyethylene glycol and glycerin have conventionally been used as wetting agents because of their slow evaporation rates. In the present invention, it has been found that glycerin is particularly desirable as a viscosity modifier and further as a viscosity increasing agent for aqueous inks containing water as a main component.

In general, glycol ethers are added for the purpose of preventing the tip of a ball-point pen or the nozzle of an ink jet from drying without increasing the viscosity of the recording liquid due to its low viscosity. Specific glycol ethers include:
Ethylene glycol ethers and methyl such as methyl glycol, methyl diglycol, methyl triglycol, methyl polyglycol, isopropyl glycol, butyl glycol, butyl diglycol, butyl triglycol, isobutyl glycol, isobutyl diglycol (all manufactured by Nippon Emulsifier) Selected from propylene glycol ethers such as propylene glycol, methyl propylene diglycol, methyl propylene triglycol, propyl propylene glycol, propyl propylene diglycol, butyl propylene glycol, butyl propylene diglycol, and phenyl propylene glycol (all manufactured by Nippon Emulsifier) It is desirable to contain 0 to 30% by weight of ether. If it exceeds 30% by weight, the surface tension is reduced and the print quality is reduced.

A water-soluble solvent may be added for improving the characteristics. For example, acetone, methyl ethyl ketone, methyl isobutyl ketone, methanol, ethanol, ketones such as isopropanol and lower alcohols and ethylene glycol, propylene glycol, glycols such as diethylene glycol and dipropylene glycol,
Acetates, thiodiglycol, N-methyl-2-
Nitrogen-containing compounds such as pyrrolidone, 1,3-dimethylimidazolidinone and amino alcohol may be used alone or as a mixed solvent.

The pigment which is an essential component for achieving the object of the present invention is preferably a pigment which is well dispersed in the above-mentioned vehicle and has excellent weather resistance. The color development (color density per added concentration) of the pigments used particularly in the present invention is not always high, and in addition, it is difficult to produce a uniform fine particle dispersion. Therefore, it has not been practically used as an inkjet ink.
Although not particularly limited, organic or inorganic pigments having the following numbers described in, for example, a color index can be used in the present invention.

As a red or magenta pigment, Pigmen
t Red 3, 5, 19, 22, 31, 38, 43, 48: 1, 48: 2, 48:
3, 48: 4, 48: 5, 49: 1, 53: 1, 57: 1, 57: 2, 58:
4, 63: 1, 81, 81: 1, 81: 2, 81: 3, 81: 4, 88, 10
4, 108, 112, 122, 123, 144, 146, 149, 166, 168, 16
9, 170, 177, 178, 179, 184, 185, 208, 216, 226, 25
7, Pigment Violet 3, 19, 23, 29, 30, 37, 50, 88, P
pigment Orange 13, 16, 20, 36, and blue or cyan pigments include pigment blue 1, 15, 15: 1, 15: 2, 15: 3, 1
5: 4, 15: 6, 16, 17-1, 22, 27, 28, 29, 36, 60, as a green pigment, Pigment Green 7, 26, 36, 50, as a yellow pigment, Pigment Yellow 1, 3, 12, 13, 14, 17, 3
4, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 10
9, 110, 137, 138, 139, 153, 154, 155, 157, 166, 16
7, 168, 180, 185, 193, as the black pigment, Pigment Bla
ck 7, 28, 26, etc. can be used according to the purpose.

Specific examples of trade names are, for example, Chromofine Yellow 2080, 5900, 5930, AF-1300, 2700
L, Chromo Fine Orange 3700L, 6730, Chromo Fine Scarlet 6750, Chromo Fine Magenta 6880, 68
86, 6891N, 6790, 6887, Chromofine Violet
RE, Chromo Fine Red 6820, 6830, Chromo Fine Blue HS-3, 5187, 5108, 5197, 5085N, SR-5020, 50
26, 5050, 4920, 4927, 4937, 4824, 4933GN-EP, 494
0, 4973, 5205, 5208, 5214, 5221, 5000P, Chromofine Green 2GN, 2GO, 2G-550D, 5310, 5370, 6830,
Chromo Fine Black A-1103, Seika Fast Yellow 10GH, A-3, 2035, 2054, 2200, 2270, 2300, 2400
(B), 2500, 2600, ZAY-260, 2700 (B), 2770, Seika Fast Red 8040, C405 (F), CA120, LR-116, 1
531B, 8060R, 1547, ZAW-262, 1537B, GY, 4R-4016,
3820, 3891, ZA-215, Seika Fast Carmin 6B1476T
-7, 1483LT, 3840, 3870, Seika Fast Bordeaux 10B
−430, Seika Light Rose R40, Seika Light Violet B800, 7805, Seika Fast Maroon 460N, Seika Fast Orange 900, 2900, Seika Light Blue C71
8, A612, cyanine blue 4933M, 4933GN-EP, 4940, 49
73 (Daiichi Seika Kogyo), KET Yellow 401, 402, 40
3, 404, 405, 406, 416, 424, KET Orange 501, KET Re
d 301, 302, 303, 304, 305, 306, 307, 308, 309, 31
0, 336, 337, 338, 346, KET Blue 101, 102, 103, 10
4, 105, 106, 111, 118, 124, KET Green 201 (all manufactured by Dainippon Ink and Chemicals), Colortex Yellow 301, 314, 31
5, 316, P-624, 314, U10GN, U3GN, UNN, UA-414, U2
63, Finecol Yellow T-13, T-05, Pigment Yellow170
5, Colortex Orange 202, Colortex Red 101, 103, 11
5, 116, D3B, P-625, 102, H-1024, 105C, UFN, UC
N, UBN, U3BN, URN, UGN, UG276, U456, U457, 105C, U
SN, Colortex Maroon601, Colortex BrownB610N, Color
tex Violet600, PigmentRed 122, Colortex Blue516, 5
17, 518, 519, A818, P-908, 510, Colortex Green40
2, 403, Colortex Black 702, U905 (all manufactured by Sanyo Dye), Lionol Yellow1405G, Lionol Blue FG7330, FG73
50, FG7400G, FG7405G, ES, ESP-S (manufactured by Toyo Ink), Toner Magenta E02, Permanent RubinF6B, Toner
Yellow HG, Permanent Yellow GG-02, Hostapeam Blu
eB2G (from Hoechst Industries), carbon black # 2600, # 2400, # 2350, # 2200, # 1000, # 990,
# 980, # 970, # 960, # 950, # 850, MCF88, # 750,
# 650, MA600, MA7, MA8, MA11, MA100, MA100R, MA7
7, # 52, # 50, # 47, # 45, # 45L, # 40, # 33, # 3
2, # 30, # 25, # 20, # 10, # 5, # 44, CF9 (all manufactured by Mitsubishi Chemical) and the like. Further, a dispersion in which a pigment is dispersed in water or a solvent at a high concentration in advance can be used.
For example, MICROPIGMO WMBK-5, WMBE-5, WMRD-5, WMYW-
5, AMBK-2, AMYW-2, AMBE-4 (from Orient Chemical), JA Black 25W, GA Black 2821, GA Yellow 1, GA
Magenta1, GA Cyan 2 (Made by Okuni Pigment) CAB-O-JET20
0, CAB-O-JET300 (above, Cabot Specialty Chemicals) and the like.

An appropriate amount of addition is a pigment concentration of 1 to 10% by weight. If the content is less than 1% by weight, the image quality deteriorates, and
If the amount is larger, the ink viscosity characteristics are adversely affected. In addition, two or more colorants can be mixed and used as needed for color adjustment and the like. In order to further develop functionality in the ink composition of the present invention, light stabilizers, surface treatment agents, surfactants, viscosity reducing agents, antioxidants, antioxidants, crosslinking accelerators, oxygen absorbers, plasticizers , A preservative, a rust preventive, an evaporation promoter, a pH adjuster, a defoamer, a humectant, a dispersant, a dye, and the like. A stirrer, a bead mill, and a homogenizer are optimal for mixing and dispersing the above-mentioned pigment and other components, but various known stirring, pulverizing or dispersing devices can be used without any particular limitation.

The ink composition of the present invention satisfies several well-known requirements for application to ink jet printers. That is, the ink has sufficient stability at room temperature, and has high reliability in storage before printing and image quality after printing.
After adhesion and curing on a recording medium, it has sufficient transparency and saturation and forms a uniform thin film to give a printed matter of good image quality.
It is necessary that the composition does not cause offset in a state where printed matter is stacked, and that the composition is highly safe in consideration of the environment and the human body.

Further, the ink composition can be used to eject ink droplets only when printing is required. Conventionally known ink jet printers, such as office printers, printers used for industrial marking, and wide format printers It can also be used for plate and plate making printers, label printers, and all types of high speed printers having this typical operation. Because high-speed drying is possible, as a recording medium, in addition to the above-mentioned paper, plastic film, capsule, gel, metal foil, glass,
Wood, cloth, etc. can be used. As long as non-contact printing is possible, a wide variety of media shapes can be used.

Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to the described examples. [Examples 1 to 3] A mixture of 35% by weight of purified water, 60% by weight of glycerin (manufactured by Wako Pure Chemical Industries, Ltd.) and 5% by weight of dipropylene glycol monomethyl ether was mixed with various black pigment aqueous dispersions (Examples). 1: MICROPIGMO W manufactured by Orient Chemical
MBK-5, pigment content 20% by weight, Example 2: Gokuku Pigment G
A BLACK 2821, pigment content 17.4% by weight, Example 3:
CAB-O-JET 20 manufactured by Cabot Specialty Chemicals
0, a pigment content of 19.5% by weight) so that the pigment concentration becomes constant, and a total of 300 g of the composition was rotated at 2,000 rpm using a homogenizer (HG30 manufactured by Hitachi Koki Co., Ltd.).
The mixture was dispersed at pm until a homogeneous mixture was obtained, followed by filtration to remove impurities and the like, to obtain three homogeneous ink compositions. The viscosity of these inks was measured using a rotational viscometer (E
DL model) and surface tension were measured by an automatic surface tensiometer (CVBP-Z model manufactured by Kyowa Interface Science Co., Ltd.). In each case, the measurement temperature was 25 ° C. The results are shown in Table 1.

[0045]

[Table 1]

The Beck smoothness was measured with an Oken type air permeability smoothness tester (KY-5 manufactured by Asahi Seiko). Paper pH is JAPAN TAPP
I Pulp and Paper Test Method No. Measured by the method specified as 6. Specifically, the indicator solution for pH measurement was dropped on the measurement surface of the test piece, spread thinly with absorbent cotton to make the color uniform, and then the pH was measured by comparing with the hue in the pH standard color change table. In each case, the measurement temperature was 25 ° C. Table 2 shows the results
It described in.

[0047]

[Table 2]

Each of the ink jet (IJ) exclusive papers 1 to 5 has a structure in which an ink receiving layer is laminated on the surface, and the plain papers 1 to 6 are uncoated papers. All the IJ-dedicated papers have a Beck smoothness exceeding 80 s, and all the plain papers have a value of 80 s or less. The pH of the paper for IJ is 5.8 to 7.6, slightly acidic to neutral. For plain paper, 2.
It is divided into those exhibiting an acidity of 6 to 5.6 and those exhibiting a neutrality of 6.4.

Using these inks and paper, the head portion of a direct plate making machine (SJ02A manufactured by Hitachi Koki) is extracted, fixed and used for printing, and the ink discharge speed is 3 kHz.
z, paper feed speed 10 ips, resolution 300
Printing was performed at (× 600) dpi at 10 ips.

The roundness of the dot printed under these conditions (=
(Perimeter) ² / (4π · dot area)). For the measurement of the dot shape, an image captured by a CCD camera from a microscope having a magnification of 20 times was analyzed using automatic image quality evaluation software (Image ProPlus manufactured by Media Cybemetrics). The number of measurement dots is 30 to 100. Table 2 shows the results
It described in. It has been found that the ink composition of the present invention has less disturbance of the ink dot shape having a roundness of 2.5 or less in both the IJ paper and the plain paper. [Examples 4 and 5] 50% by weight of purified water, average molecular weight 60
40% by weight of polyethylene glycol (manufactured by Wako Pure Chemical Industries, trade name: polyethylene glycol 600), and Table 1
10% by weight of each of the alkylene glycol alkyl ethers shown in Table 1, an aqueous dispersion of black pigment (Microp
igmo, pigment content 20% by weight) and 20% by weight were mixed to produce an ink composition in the same manner as in Example 1, and the same evaluation was performed. The results are shown in Tables 1 and 2. As in the ink compositions of Examples 1 to 3, the roundness of the IJ-dedicated paper and plain paper was also 2.
It was found that there was little disturbance of the ink dot shape of 5 or less. Comparative Examples 1 to 35 35% by weight of purified water, 60% by weight of glycerin and 5% by weight of ethylene glycol monoisobutyl ether having the composition shown in Table 1 were mixed.
Three kinds of ink compositions to which the same aqueous dispersions of black pigment as in Example 3 were added were manufactured, and the same measurements and evaluations as in Example 1 were performed.
The surface tension of each of these ink compositions was 33 mN /
m.

These inks form dots with less turbulence having a roundness of 1.7 or less on IJ paper. When looking at plain papers 1 to 5 having a Beck smoothness of 80 s or less and a pH of 6.2 or less, the roundness also shows remarkable turbulence (feathering or the like) of 2.8 or more, and the image quality is significantly poor. Plain paper 6 with pH 6.4
Showed a relatively good image having a roundness of 2.0 to 2.3. [Comparative Examples 4 and 5] Commercial inks A and B shown in Table 1 were used. The same measurement as in Example 1 was performed. As in Comparative Examples 1 to 3, the IJ-dedicated paper and the plain paper 6 having a pH of 6.4 exhibited good dot shapes. However, for plain papers 1 to 5 having a Beck smoothness of 80 s or less and a pH of 6.2 or less, the roundness is 2.
Significant disturbances (feathering etc.) of 8 or more are shown, and the image quality is significantly poor.

[0052]

The recording method of the ink jet printer according to the present invention provides a method capable of printing well on uncoated plain paper having a pH of 6.2 or less. The ink composition of the present invention enables high-quality printing with low dot smoothness and low dot bleeding on acidic paper.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating roundness.

FIG. 2 is a comparison diagram of a dot shape coefficient and roundness.

 ────────────────────────────────────────────────── ─── Continued on front page (72) Inventor Atsushi Tsunoda 2-2-2722 Suehiro, Chitose-shi, Hokkaido F-term (reference) 2C056 EA04 FC01 HA46 HA47 2H086 BA01 BA02 BA41 BA44 BA53 BA60 BA61 4J039 BA04 BE01 CA06 EA15 EA16 EA17 EA19 EA42 EA47 GA24

Claims (5)

[Claims] An ink droplet is formed on an uncoated paper recording medium having a Beck smoothness of 80 s or less and a pH of 6.2 or less at a recording speed at which the relative speed between the nozzle and the paper is 10 ips (inch / s) or more. In the ink jet recording method in which recording dots are formed by jetting, the roundness of the recording dots on the recording medium = (perimeter) ² / (4π)
(Dot area) is 2.5 or less. 2. The ink jet recording method according to claim 1, wherein the ink composition for forming the recording dots has a surface tension at 25 ° C. of 33 mN / m or more. 3. The ink jet recording method according to claim 1, wherein the ink composition forming the recording dots has a viscosity at 25 ° C. in the range of 5 to 20 mPa · s. . 4. The ink jet recording method according to claim 1, wherein the ink composition forming the recording dots contains water, glycerin and a pigment as essential components. 5. The ink jet recording method according to claim 1, further comprising a step of drying the recording dots after forming the recording dots on a recording medium.