JP2007152873A - Ink jet recording method and ink jet recording ink used therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink jet recording method excellent in character quality, strikethrough property, curling property, and continuous ejection property in printing on an ordinary paper sheet. <P>SOLUTION: The ink jet recording method is provided in which an ink jet recording apparatus satisfies a specific requirement and an ink jet recording ink contains at least water, water-soluble organic solvents and a pigment, wherein a total amount of the water-soluble organic solvents is not less than 50% by mass and less than 90% by mass based on a total amount of an ink, and a water-soluble organic solvent having a solubility parameter (SP value) of not less than 16.5 and less than 24.6 among the water-soluble organic solvents is contained in an amount of 30% by mass or more based on the total amount of ink. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink jet recording method, and more particularly to an ink jet recording method capable of obtaining high image quality in ejection stability of an ink jet recording head and printing on plain paper. The present invention also relates to an ink for ink jet recording suitable for the method.

  In recent years, the ink jet recording system can create images easily and inexpensively, and thus has been applied to various printing fields such as photographs, various printing, marking, and special printing such as color filters. In particular, ink jet recording devices that emit and control fine dots, ink with improved color reproduction gamut, durability, and emission suitability, ink absorbency, coloring material color development, surface gloss, etc. are dramatically improved. It is also possible to obtain image quality comparable to silver halide photography using special paper.

  However, in an inkjet image recording system that requires dedicated paper, there are problems in that the recording media that can be used are limited and the cost of the recording media is increased.

  On the other hand, in the office, there is an increasing need for a system that can perform full-color printing at high speed without being restricted by a recording medium (for example, plain paper, coated paper, art paper).

  In particular, it is desired to perform high-quality printing at high speed on plain paper (for example, PPC paper, non-coated paper for printing, etc.) that is inexpensive and easily available. When aqueous ink is used, there are problems such as character image quality, image bleeding, low reflection density, curling after printing, cockling, and the like. When oil-based ink is used, there is no problem with curling and cockling, but there are problems such as character image quality inferior to aqueous ink, intense bleeding, and low reflection density. In addition, when performing double-sided printing, back-through (print-through) is also a major problem. In order to solve the problem of printing on plain paper, various studies have been conducted including the composition of ink.

  As one of the improvement methods for water-based inks, a technique for improving image bleeding and ink back-through during printing on plain paper by using an ink containing a vinylpyrrolidone and an acrylic acid copolymer having a molecular weight of 80,000 to 250,000 is disclosed. (For example, refer to Patent Document 1). However, in this method, when the ink attached to the nozzle plate is wiped off by the wiping operation, the wiping residue is likely to occur (because the added ultra-high molecular weight polymer is likely to stick to the nozzle plate), and the liquid caused by this There has been a problem that image deterioration is likely to occur due to a deviation in the landing positions of the droplets.

  As another method, a technique for reducing feathering, bleeding, and back-through during printing on plain paper using an ink containing alginic acid or alginate is disclosed (for example, see Patent Document 2). In this method, the alginic acid or alginate contained in the ink reacts with a polyvalent metal cation such as calcium or aluminum contained in the plain paper to cause gelation and thickening, thereby improving feathering, bleeding and strike-through. However, polyvalent metal ions such as calcium and aluminum in plain paper are not essential components, but are contained as impurities. The content varies depending on the brand of the paper, and some of the plain paper has extremely low content. Exists. Therefore, the magnitude of these effects depends on the brand of paper to be printed, and there is a problem that a sufficient effect cannot be obtained depending on the brand of paper.

On the other hand, in such a printing field suitable for plain paper, high-speed printability is required, but a method for improving the emission stability (crosstalk) of a multi-nozzle type recording head is known. The water-soluble organic solvent and the ink with a specific content are not described at all (see Patent Document 3).
Japanese Patent Laid-Open No. 10-1629 JP 2003-176432 A Japanese Patent Laid-Open No. 2002-19103

  The present invention has been made in view of the above problems, and its purpose is to be suitable for an ink jet recording method excellent in character quality when printed on plain paper, through-through properties, curl characteristics, and continuous emission properties, and the method. Ink jet recording ink is provided.

  The above object of the present invention is achieved by the following configurations.

1. The inkjet recording apparatus satisfies the following requirements (1) to (3), and the inkjet recording ink contains at least water, a water-soluble organic solvent and a pigment, and the total amount of the water-soluble organic solvent is 50% by mass of the total ink. The water-soluble organic solvent having a solubility parameter (SP value) of 16.5 or more and less than 24.6 among the water-soluble organic solvent is 30% by mass or more of the total ink. Inkjet recording method.
(1) A plurality of ink chambers provided with ink nozzles for ejecting ink droplets that form partition walls by an actuator that deforms in response to an applied voltage of an adjacent ink chamber are arranged, and ink is communicated with each of the ink chambers to receive ink. An ink jet recording head provided with a common ink chamber to be supplied is provided.
(2) Between an expansion pulse that expands the volume of the ink chamber by deforming the actuator constituting the ink chamber partition wall and a contraction pulse that contracts the volume of the ink chamber by deforming the actuator. Drive signal generating means for continuously generating a drive signal to be applied to the actuator a plurality of times with a predetermined pause time.
(3) The volume of the ink chamber is repeatedly expanded and contracted by generating the drive signal from the drive signal generating means a plurality of times, so that a plurality of ink droplets are continuously ejected from the ink nozzles, and the pause time is adjacent. The ink for ink jet recording is ejected onto the recording material by an ink jet recording head set to a time for reducing the crosstalk between the ink chambers.

  2. The pause time between the expansion pulse and the contraction pulse is set such that the time difference between the center of the expansion pulse and the center of the contraction pulse is equal to the natural vibration period of the ink in the ink chamber. 2. The ink jet recording method according to 1.

  3. 3. An ink for ink jet recording, which is used in the ink jet recording method described in 1 or 2 above.

  According to the configuration of the present invention, it is possible to provide an ink jet recording method that is excellent in character quality when printed on plain paper, show-through properties, curl characteristics, and continuous emission properties, and an ink for ink jet recording suitable for the method.

  The ink used in the recording method of the present invention is a water-based ink. However, when such an ink is used, the emission stability from the head is often unstable. In the recording head driving method described below, crosstalk has been improved, but the problem of droplet ejection properties after ejection has not been sufficient. In order to reduce such problems, the present invention can solve this problem by using the drive method of the present invention for the drive method of the recording head at the same time as devising the ink composition. The droplet emission property here means not only ink ejection stability (does not eject) but also that the ink droplets after ejection are formed as chitin and no ink splattering occurs. The effect of improving quality and the like was obtained. This is because the wettability of the ink around the head nozzle is improved by the ink containing the specific water-soluble organic solvent of the present invention and the specific amount of the water-soluble organic solvent in the ink. This was achieved by making the head drive conditions suitable for the physical properties.

  As a result of intensive studies in view of the above problems, the present inventor has determined that a plurality of ink chambers provided with ink nozzles that eject ink droplets that form partition walls by an actuator that deforms in response to an applied voltage between adjacent ink chambers. An inkjet recording head provided with a common ink chamber that is arranged and communicates with each of the ink chambers to supply ink; and an expansion pulse that expands the volume of the ink chamber by deforming the actuator that constitutes the ink chamber partition wall. Drive signal generating means for continuously generating a drive signal to be applied to the actuator with a predetermined pause time between the contraction pulse for contracting the actuator and contracting the volume of the ink chamber; And repeatedly expanding and contracting the volume of the ink chamber by generating the drive signal from the drive signal generating means a plurality of times. In the inkjet recording head in which a plurality of ink droplets are continuously ejected and the rest time is set to a time for reducing crosstalk between adjacent ink chambers, the total amount of water-soluble organic solvent in the water-based ink The water-soluble organic solvent having a solubility parameter (SP value) of 16.5 or more and less than 24.6 among the water-soluble organic solvent is 30% by mass or more of the total ink. As a result of finding the ejection stability and high image quality in plain paper printing by the characteristic ink jet recording method, the present invention has been achieved.

Here, the solubility parameter (SP value) is an index defined by the formula (molar evaporation energy / molar volume) ^1/2 , that is, a value expressed by the square root of the molecular cohesive energy. There is a description in Handbook (Second Edition), Chapter IV, Solubility Parameter Values, and the value is used. The unit is (J / cm ³ ) ^1/2 and refers to the value at 25 ° C. In addition, about what does not have description of data, it can calculate by calculating | requiring evaporation heat from a boiling point.

  Hereinafter, the present invention and components will be described in detail.

<Inkjet recording device>
Details of the driving method for preventing crosstalk with the ink jet recording head according to the present invention will be described.

  As an ink jet recording head, an on-demand ink jet recording head in which a partition between adjacent ink chambers is configured by an actuator such as a piezoelectric member is known. This head has an advantage that a large number of ink chambers partitioned by partition walls can be easily arranged at high density.

  For example, as shown in FIGS. 1 and 2, an ink jet recording head using a piezoelectric member as an actuator has two rectangular piezoelectric members 1 and 2 whose polarization directions are opposite to each other in the plate thickness direction. The piezoelectric members 1 and 2 are fixed to the substrate 3 having a dielectric constant lower than that of the piezoelectric member, and the piezoelectric members 1 and 2 are parallel with the same width at regular intervals using, for example, a diamond cutter. A plurality of long grooves having the same depth and the same length are cut to form the ink chamber 4.

  Electrodes 5 are formed by electroless nickel plating on the side and bottom surfaces of the ink chamber 4, and electrodes 6 are also formed by electroless nickel plating on the rear upper surface of the substrate 3 from the rear end of the ink chamber 4. A circuit board 7 having a drive circuit formed on the upper end face is bonded and fixed.

  A frame-like member 9 constituting a common ink chamber 8 is bonded and fixed on the ink chamber 4 of the piezoelectric members 1 and 2, and an ink supply port 10 that communicates with the common ink chamber 8 on the frame-like member 9. It is closed by the top plate 11 provided with. Further, an orifice plate 13 provided with a plurality of ink discharge ports 12 at the tip of each of the piezoelectric members 1 and 2 is bonded and fixed with an adhesive.

  Next, the operating principle of this ink jet recording head will be described.

  In FIG. 3A, paying attention to the five ink chambers 4a, 4b, 4c, 4d, and 4e, the electrodes 5a to 5e of the respective ink chambers 4a to 4e are set to the ground potential, and the electrodes of the central ink chamber 4c. When a positive voltage is applied to 5c, the piezoelectric members 1 and 2 have their polarization directions facing outward as indicated by arrows in the figure, so that both sides of the ink chamber 4c contract the volume of the ink chamber 4c due to shear strain. Deform inward as you do.

  Further, a positive voltage is applied to the electrodes 5a, 5b, 5d, and 5e of the ink chambers 4a, 4b, 4d, and 4e adjacent to the central ink chamber 4c with the electrodes 5a to 5e of the ink chambers 4a to 4e at the ground potential. When applied, as shown in FIG. 3B, both side surfaces of the electrode 5c of the ink chamber 4c are deformed outward so as to enlarge the volume of the ink chamber 4c. By utilizing such deformation of the ink chamber, ink droplets are ejected from the ink chamber. Specifically, the volume of the ink chamber is enlarged and the ink chamber 8 is filled with ink from the common ink chamber 8, and then the volume of the ink chamber is contracted to increase the pressure in the ink chamber from the ink discharge port 12. Ink droplets are ejected.

  Next, a method for driving the ink jet recording head according to the present invention will be described.

  FIG. 4 is a block diagram showing the configuration of the drive device for the ink jet recording head of the present embodiment. In FIG. 4, 21 is a printer controller for controlling each part, 22 is an image memory for storing print data from the printer controller 21, 23 is controlled by the printer controller 21, and print data stored in the image memory 22 is converted into a head drive circuit. 24 is a print data transfer block to be transferred to 24.

  The head drive circuit 24 drives the inkjet recording head 25 based on the print data transferred from the print data transfer block 23. A drive waveform when the head drive circuit 24 drives the ink jet recording head 25 is controlled by a drive waveform control circuit 26, and this drive waveform control circuit 26 is controlled by the printer controller 21.

  The ink jet recording head 25 used in the present invention is a share mode type ink jet recording head, and has the same configuration as the ink jet recording head shown in FIGS.

  5 to 7 are diagrams showing driving waveforms when the head driving circuit 24 drives the ink chambers of the ink jet recording head 25. In the drawing, i-3, i-2, i-1, i, i + 1, i + 2, and i + 3 indicate ink chambers that are continuously connected.

  FIG. 5 shows a driving waveform when a positive voltage is applied to each of the ink chambers i-3 to i + 3 at a predetermined timing to perform 7-drop driving, and FIG. 6 shows the voltage applied to the ink chamber that does not operate as the ground potential. The drive waveforms when the ink chambers i-3 to i + 3 are each driven with 7 drops are shown.

  The ink chamber performs the same operation regardless of whether the driving waveform of FIG. 5 or the driving waveform of FIG. 6 is used. Here, the case where the ink chamber is driven using the driving waveform of FIG. State.

  In this share mode type recording head, the i-3th, ith, and i + 3th ink chambers are driven simultaneously, but the i ± 2nd and i ± 1st ink chambers in between are not driven simultaneously, The i-2th and i + 1th ink chambers are driven simultaneously, but the ith and i-1th ink chambers in between are not driven simultaneously, and the i-1th and i + 2th ink chambers are driven simultaneously. The i-th and i + 1-th ink chambers in between are driven in three divisions so that they are not driven simultaneously. The ink chamber adjacent to the ink chamber driven by the three-division driving is directly affected, for example, so that erroneous ink ejection or the like does not occur.

  Each drive waveform W3 shown in FIG. 6 is a series of seven drive pulses W4 having the configuration shown in FIG. 7. Each drive pulse W4 is applied with an expansion pulse W4a that is a negative voltage pulse for expanding the ink chamber and pulse application. Is formed by a rest time W4b for stopping the ink and a contraction pulse W4c which is a positive voltage pulse for contracting the ink chamber.

  The ink jet recording head is driven by 1 drop for discharging one small ink droplet when one drive pulse W4 is applied, and is driven by 1 to 7 drops by connecting the drive pulses W4 in a range of 1 to 7 Thus, 7 gradation printing is possible except white.

  The time difference between the center of the expansion pulse W4a and the center of the contraction pulse W4c is 2AL, which is set to a time equal to the natural vibration period of the ink in the ink chamber. The pulse time width of the expansion pulse W4a is set to 1AL, and the pulse time width of the contraction pulse W4c is set in the range of 0.6AL to 1AL, here 1AL. Note that AL is a unit of time, and is the time for the pressure in the ink chamber to reverse from positive pressure to negative pressure or from negative pressure to positive pressure due to natural vibration, which is half of the natural vibration period of ink in the ink chamber. It's time.

  Next, a change in pressure in the ink chamber when the drive pulse shown in FIG. 7 is applied to the ink chamber of the inkjet recording head 25 will be described with reference to FIG. First, the expansion pulse W4a expands the volume of the ink chamber at the falling edge of the waveform, and the internal ink pressure becomes the negative pressure P1. When the time of 1AL has elapsed from the fall of the waveform, the ink pressure in the ink chamber becomes positive pressure P2 due to natural vibration. Further, when the expansion pulse W4a ends, the ink chamber contracts, the ink pressure further increases from P2 to P3, and ink discharge is started from the ink discharge port of the ink chamber.

  When a time of about 0.5 AL has elapsed since the start of ink ejection, the pressure of the ink in the ink chamber changes to a negative pressure P4 due to natural vibration. Then, when 1AL has elapsed from the rise of the expansion pulse W4a, the ink ejection ends. At that time, the pause time W4b ends, the ink chamber contracts by the rise of the contraction pulse W4c, and the negative pressure state of the ink chamber is relaxed from P5 to P6.

  At the time when 1 AL has elapsed from the rise of the contraction pulse W4c, the ink pressure is positive pressure P7. At that time, the contraction pulse W4c falls, the contracted ink chamber returns to the original state, and the pressure in the ink chamber becomes almost zero. As described above, by applying the drive pulse shown in FIG. 7 to the ink chamber of the ink jet recording head, the residual pressure vibration having the natural vibration frequency of the ink that easily generates crosstalk can be made substantially zero.

  Further, a drive pulse W6 as shown in FIG. 9 may be used as the drive pulse. This drive pulse W6 is obtained by reducing the pulse time width of the contraction pulse W6c while keeping the time difference between the center of the expansion pulse W6a and the center of the contraction pulse W6c at 2AL, and the rest time W6b is longer than 1AL accordingly. Become.

  Such a drive pulse W6 is effective in the case of a head in which, for example, the pressure vibration generated by the expansion pulse W6a is attenuated at the time of applying the contraction pulse W6c. There is an effect that the residual pressure vibration can be further attenuated.

(ink)
Next, the ink according to the present invention will be described.

  When an ink having a high water content ratio in ink such as a general water-based ink is recorded on plain paper, the permeation into the paper is not so great, and a reasonable character image quality and a not-so-high penetration are obtained. On the other hand, the curl is very large.

  This is because the water in the ink is coordinated with the cellulose constituting the plain paper, so that the penetration is small, and for curls, a force in the shrinking direction works by evaporating and drying the water. It is considered that curling occurs as a result of insufficient force for suppressing drying shrinkage due to separation of bonds between celluloses by coordinating to cellulose.

  On the other hand, when water-free, for example, oil-based ink is recorded on plain paper, the penetration of the ink into the plain paper is large, and the surface image density is lowered and the ink see-through is increased.

  This is thought to be because the interaction between the oily solvent and cellulose is small, and the oily solvent easily diffuses through the gaps between the cellulose, so that the penetration increases, the image density decreases, and the showthrough increases. On the other hand, since the coordination to cellulose is small and the bond between celluloses is not broken, the paper structure before recording is maintained, and it is considered that curling is difficult.

  In the aqueous ink of the present invention, the total amount of the water-soluble organic solvent is 50% by mass or more and less than 90% by mass of the total ink, and the solubility parameter (SP value) of the water-soluble organic solvent is 16.5 or more and less than 24.6. The first feature is that a water-soluble organic solvent is contained in an amount of 30% by mass or more based on the total ink. With this solvent composition, it is possible to obtain a print that is excellent in character image quality even when recorded on plain paper, has little show-through, and has almost no curl. Furthermore, the effect of achieving both character image quality, back-through and curl suppression is completely deviated from the trend of water-based ink and oil-based ink.

  As a mechanism of manifestation of the above effect, the total amount of the water-soluble organic solvent is 50% by mass or more and less than 90% by mass of the total ink, and the water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6. By containing 30% by mass or more of an organic solvent and further containing at least water, the interaction between the ink and cellulose is reduced, and the amount of inter-cellulose bonds necessary to resist drying shrinkage after recording is reduced. It is considered that curling is suppressed by making it remain, and that there is a portion that interacts with cellulose by containing water, though it is small, so that character image quality and show-through are good. More preferably, the water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 is contained by 50% by mass or more of the total ink.

  Furthermore, the ink of the present invention preferably has a total amount of alkali metals (lithium, sodium, potassium) in the ink of less than 500 ppm. By making the total amount of alkali metals in the ink less than 500 ppm, the total amount of the water-soluble organic solvent is 50% by mass or more of the total ink, and the SP value of the water-soluble organic solvent is 16.5 or more and less than 24.6. Even in a solvent composition containing 30% by mass or more of the water-soluble organic solvent and further containing at least water, the pigment dispersion can be more stably present.

  In order to obtain such an ink, it is preferable to use a combination of a surfactant for dispersing a pigment, a method of adding a dispersant as a salt of an organic base, and the like.

  Hereinafter, the ink according to the present invention will be described in more detail.

  The solvent composition according to the present invention includes at least water and the total amount of the water-soluble organic solvent is 50% by mass or more and less than 90% by mass of the total ink, and the solubility parameter (SP value) of the water-soluble organic solvent is 16.5 or more and less than 24.6 water-soluble organic solvent is contained in an amount of 30% by mass or more of the total ink. Furthermore, the total amount of the water-soluble organic solvent having an SP value of 16.5 or more and less than 22.5 is preferably 30% by mass or more of the ink. In this range of ink composition, not only the curl and see-through properties, but also the liquid physical properties in head driving and the wettability around the head are improved and the crosstalk characteristics are improved. It is thought that the quality of characters is greatly improved by the fact that the ejected ink droplets are very stable and the scattering is reduced.

  The ink according to the present invention contains 30% by mass or more of a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6. It is more preferable to contain 50% by mass or more. When this addition amount is less than 30% by mass, curling and cockling during recording on plain paper become extremely large.

  If the SP value of the organic solvent is also less than 16.5, the compatibility with water is deteriorated and separation occurs. Conversely, an organic solvent having an SP value of 24.6 or more has an insufficient curl suppressing effect.

  The range of the SP value of the organic solvent is more preferably 20.0 or more and less than 22.5.

  Hereinafter, examples of water-soluble organic solvents having an SP value of 16.5 or more and less than 24.6 are shown together with the SP value. Needless to say, the present invention is not limited to this.

Ethylene glycol monomethyl ether (SP value: 24.5)
Ethylene glycol monoethyl ether (23.5)
Ethylene glycol monobutyl ether (22.1)
Ethylene glycol monoisopropyl ether (22.3)
Diethylene glycol monomethyl ether (23.0)
Diethylene glycol monoethyl ether (22.4)
Diethylene glycol monobutyl ether (21.5)
Diethylene glycol diethyl ether (16.8)
Triethylene glycol monomethyl ether (22.1)
Triethylene glycol monoethyl ether (21.7)
Triethylene glycol monobutyl ether (21.1)
Propylene glycol monomethyl ether (23.0)
Propylene glycol monophenyl ether (24.2)
Dipropylene glycol monomethyl ether (21.3)
Tripropylene glycol monomethyl ether (20.4)
1,3-dimethyl-2-imidazolidinone (21.8)
In the present invention, in addition to the water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6, various water-soluble organic solvents are used in combination, and the total amount of the water-soluble organic solvent is 50% by mass or more and less than 90% by mass of the total amount of the ink. can do. Examples of water-soluble organic solvents are shown below.

  Examples of water-soluble organic solvents preferably used include alcohols (eg, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, pentanol, hexanol, cyclohexanol, benzyl alcohol, etc.), Polyhydric alcohols (for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol, 1,3 -Propanediol, 1,4-butanediol, 1,5-pentanediol, 1,2-pentanediol 1,2-hexanediol, 1,2,6-hexanetriol, etc.), amines (eg, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine) , Diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amides (eg, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, etc.), Heterocycles (eg, 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexyl pyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone), sulfo Kishido compound (such as dimethyl sulfoxide, etc.), sulfones (e.g., sulfolane), urea, acetonitrile, and acetone.

  Moreover, it is preferable that water is 10-45 mass% in all the inks. The presence of 10% by mass or more of water is preferable for the penetration property, and the presence of 45% by mass or less of water is preferable from the viewpoint of curling suppression.

  The total amount of alkali metals (lithium, sodium, potassium) in the ink of the present invention is preferably less than 500 ppm. If it is 500 ppm or more, ink storage stability deteriorates such as aggregation of pigments or metal oxide colloids or increase in ink viscosity during storage.

  Alkali metals in ink are often brought in as salts of surfactants and pigment dispersants. Therefore, in order to control the alkali metal, ion exchange water is naturally used at the time of ink production. When a surfactant is used in addition to this, a nonionic surfactant is used. As the dispersant used for dispersing the pigment, a dispersant neutralized with an organic base is used. The content of the pigment is 0.1% by mass or more and less than 12% by mass with respect to the total mass of the ink.

(Pigment)
As the pigment that can be used in the present invention, conventionally known pigments can be used without particular limitation, and any of water-dispersible pigments, solvent-dispersible pigments, and the like can be used, for example, organic pigments such as insoluble pigments and lake pigments, An inorganic pigment such as carbon black can be preferably used. This pigment is present in a dispersed state in the ink. The dispersion method may be any of self-dispersion, activator dispersion, polymer dispersion, and microcapsule dispersion, but polymer dispersion and microcapsule dispersion are fixable. This is particularly preferable.

  The insoluble pigment is not particularly limited. Dioxazine, thiazole, phthalocyanine, diketopyrrolopyrrole and the like are preferable.

  Specific pigments that can be preferably used include the following pigments.

  Examples of the magenta or red pigment include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. And CI Pigment Red 222.

  Examples of the pigment for orange or yellow include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 15: 3, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 128, C.I. I. Pigment yellow 94, C.I. I. And CI Pigment Yellow 138.

  Examples of the pigment for green or cyan include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. And CI Pigment Green 7.

In addition to the above, when red, green, blue and intermediate colors are required, the following pigments are preferably used alone or in combination. I. Pigment Red; 209, 224, 177, 194,
C. I. Pigment Orange; 43,
C. I. Vat Violet; 3,
C. I. Pigment Violet; 19, 23, 37,
C. I. Pigment Green; 36, 7,
C. I. Pigment Blue; 15: 6,
Etc. are used.

  Examples of black pigments include C.I. I. Pigment black 1, C.I. I. Pigment black 6, C.I. I. Pigment black 7 and the like.

  The average particle diameter of the pigment dispersion used in the recording method of the present invention is preferably 50 nm or more and less than 200 nm. When the average particle size of the pigment dispersion is less than 50 nm or 200 nm or more, the stability of the pigment dispersion tends to deteriorate, and the storage stability of the ink tends to deteriorate.

  The particle size of the pigment dispersion can be determined by a commercially available particle size measuring instrument using a dynamic light scattering method, an electrophoresis method, or the like. Accurate and often used.

  The pigment used in the present invention is preferably used after being dispersed by a disperser together with a dispersant and other necessary additives according to desired purposes. As the disperser, a conventionally known ball mill, sand mill, line mill, high-pressure homogenizer, or the like can be used. Among them, the dispersion by sand mill is preferable because the particle size distribution is sharp when the dispersion is aimed at an average particle diameter of around 100 nm. The material of the beads used for sand mill dispersion is preferably zirconia or zircon from the viewpoint of contamination of bead fragments and ionic components. Further, the bead diameter is preferably 0.1 mm or more and 0.5 mm.

  Examples of the polymer dispersant for dispersing the pigment of the present invention include higher fatty acid salts, alkyl sulfates, alkyl ester sulfates, alkyl sulfonates, sulfosuccinates, naphthalene sulfonates, alkyl phosphates, and polyoxyalkylene alkyls. Activators such as ether phosphate, polyoxyalkylene alkylphenyl ether, polyoxyethylene polyoxypropylene glycol, glycerin ester, sorbitan ester, polyoxyethylene fatty acid amide, amine oxide, or styrene, styrene derivatives, vinyl naphthalene derivatives, Block copolymer consisting of two or more monomers selected from acrylic acid, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acid derivatives, random copolymers Coalescence and the like, and salts thereof.

  The neutralizing base of the dispersant is preferably an organic base such as ammonia, monoethanolamine, diethanolamine, triethanolamine, or morpholine rather than a non-periodic base such as lithium hydroxide, sodium hydroxide, or potassium hydroxide. .

  Moreover, in this invention, it is preferable that the addition amount of a pigment dispersant is 10-100 mass% with respect to a pigment.

  Furthermore, a surfactant can be used as an additive at the time of dispersion. As the surfactant used in the present invention, any of cationic, anionic, amphoteric and nonionic surfactants can be used, but it is particularly preferable to use a nonionic surfactant from the viewpoint of dispersion stability.

  Nonionic activators include polyoxyethylene secondary alcohol ether, polyoxyethylene alkylphenyl ether, polyoxyethylene sterol ether, polyoxyethylene lanolin derivative polyoxyethylene polyoxypropylene alkyl ether, polyoxyethylene glycerin fatty acid ester, Oxyethylene castor oil, hydrogenated castor oil, polyoxyethylene sorbitol fatty acid ester, polyethylene glycol fatty acid ester, fatty acid monoglyceride, polyglycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, sucrose fatty acid ester, fatty acid alkanolamide, polyoxyethylene Fatty acid amide, polyoxyethylene alkylamine, alkylamine oxide, acetate Glycol, acetylene alcohol, and the like.

(Various additives)
In the ink of the present invention, in addition to the above description, if necessary, the output stability, print head and ink cartridge compatibility, storage stability, image storage stability, and other various performance improvement objectives are known. Various additives such as polysaccharides, viscosity modifiers, specific resistance regulators, film forming agents, ultraviolet absorbers, antioxidants, anti-fading agents, antifungal agents, rust preventives, etc. may be appropriately selected and used. For example, oil droplet fine particles such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, silicon oil, ultraviolet absorbers described in JP-A-57-74193, 57-87988, and 62-261476, As described in Kaisho 57-74192, 57-87989, 60-72785, 61-146591, JP-A-1-95091 and 3-13376, etc. Anti-fading agents, fluorescent whitening agents described in JP-A Nos. 59-42993, 59-52689, 62-280069, 61-242871, and JP-A-4-219266 Can be mentioned.

(Ink surface tension, etc.)
In the ink of the present invention having the above-described structure, the surface tension of the ink is preferably 25 to 40 mN / m at 25 ° C., more preferably 25 to 35 mN / m, still more preferably 30 to 35 mN / m. It is. The ink viscosity is preferably 1 to 40 mPa · s at 25 ° C., more preferably 5 to 40 mPa · s, and still more preferably 5 to 20 mPa · s.

  In addition, the dissolved oxygen concentration in the ink of the present invention is preferably 2 ppm or less at 25 ° C. By setting this dissolved oxygen concentration condition, the formation of bubbles can be suppressed, and the emission stability even in high-speed printing. An ink jet recording method having excellent properties can be realized. As a method for measuring the dissolved oxygen dissolved in the ink, for example, it can be measured using a dissolved oxygen measuring device DO-14P (manufactured by Toa Radio).

(recoding media)
The plain paper used in the ink jet recording method of the present invention is not particularly limited, and its constitution is mainly composed of chemical pulp represented by LBKP and NBKP, sizing agent and filler, and other paper making aids as necessary. Used and made by ordinary methods. As the pulp material used for the plain paper according to the present invention, mechanical pulp and recycled paper recycled pulp may be used in combination, and there is no problem even if these are used as the main material.

  Examples of the sizing agent internally added to the plain paper according to the present invention include rosin size, AKD, Alnicel succinic anhydride, petroleum resin-based size, epichlorohydrin, cationic starch, and acrylamide.

  Examples of the filler internally added to the plain paper according to the present invention include finely divided silicic acid, aluminum silicate, diatomaceous earth, kaolin, kaolinite, halloysite, nacrite, dickite, pyrophyllite, sericite, titanium dioxide, bentonite and the like. Is mentioned.

(Inkjet recording method: image forming method)
In the recording method (image forming method) using the ink-jet ink of the present invention, for example, the ink is ejected as droplets from the ink-jet head based on a digital signal and attached to plain paper by a printer loaded with the ink-jet ink. An ink jet print is obtained.

  When an image is formed by ejecting the ink of the present invention, the inkjet head to be used may be an on-demand system or a continuous system. Also, as a discharge method, an electro-mechanical conversion method (for example, a single cavity type, a double cavity type, a bender type, a piston type, a shear mode type, a shared wall type, etc.), an electro-thermal conversion method (for example, thermal ink jet) Any ejection method such as a mold, a bubble jet (registered trademark) mold, or the like may be used.

  Among them, in the ink jet recording method of the present invention, the ink of the present invention is ejected from a piezo ink jet recording head having a nozzle diameter of 25 μm or less, recording is performed on plain paper, and the nozzle diameter is 25 μm or less. Recording is performed on plain paper by discharging from a piezo-type ink jet recording head of a line head type.

  In particular, the ink jet recording system of the present invention is characterized in that image printing is performed on both sides of plain paper.

  In double-sided printing, after printing on one side, plain paper is turned over and transported with the printing side down, but the ink of the present invention has the above-mentioned characteristics. Since there is no bleeding of characters, high density and excellent character quality on any surface, no conveyance failure occurs, and the conveyance belt is not contaminated with ink.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

[Preparation of Pigment Dispersion A to Pigment Dispersion E]
After mixing the colorant, water-soluble organic solvent, resin for dispersion and water with the combinations shown in Table 1, place them in a polypropylene plastic bottle with 200 g of zirconia beads having a diameter of 0.5 mm, and seal them with a paint shaker. Dispersion was performed for 5 hours to obtain pigment dispersion A to pigment dispersion E having a black pigment concentration of 15%.

  In addition, the kind and content of the water-soluble organic solvent described in Table 1 and Table 2 below are as follows.

DPGME: Dipropylene glycol monomethyl ether TPGME: Tripropylene glycol monomethyl ether TEGME: Triethylene glycol monomethyl ether EG: Ethylene glycol [Preparation of ink]
The following pigment dispersion, water-soluble organic solvent and water were added and stirred well. Subsequently, the liquid was filtered through a # 3500 mesh metal filter, and deaerated with a hollow fiber membrane to prepare an ink.

Pigment dispersion (types listed in Table 2) 26.7% (colorant 4.0%)
Water-soluble organic solvent (types shown in Table 2) Addition amounts shown in Table 2 After the above additives were mixed, water was added to finish the solution to 100%.

<< Inkjet image forming method >>
[Inkjet image recording device]
With respect to the recording head, an expansion pulse that expands the volume of the ink chamber by deforming the actuator that constitutes the ink chamber partition having the configuration described in detail with reference to FIGS. Drive signal generating means for continuously generating a drive signal to be applied to the actuator with a predetermined pause time between the contraction pulse for contracting the volume of the ink chamber, and from the drive signal generating means When the drive signal is generated multiple times, the ink chamber volume is repeatedly expanded and contracted to continuously eject a plurality of ink droplets from the ink nozzle, and the pause time is reduced to reduce crosstalk between adjacent ink chambers. Using the inkjet recording head set to the time, the pause time between the expansion pulse and the contraction pulse is set to the center of the expansion pulse and the contraction The time difference from the center of the pulse is set to be equal to the natural vibration period of the ink in the ink chamber, and ink temperature detecting means for detecting the ink temperature in the ink chamber is provided, and the ink temperature is detected by the ink temperature detecting means. By doing so, the pause time between the expansion pulse and the contraction pulse was controlled in accordance with the change in the natural vibration period of the ink depending on the ink temperature. This is called drive control method 1. Further, in place of the drive signal control method described above, image formation was also performed by a method having the drive waveforms shown in FIGS. 10 and 11 (hereinafter referred to as drive control method 2). The recording head was filled with the same ink, and the following evaluation was performed.

(Evaluation of character quality)
4 point MS Mincho characters are printed with black ink on Shirahoi paper (64 g / m ² ) manufactured by Daishowa Paper Co., Ltd., and the printed image is observed with a magnifier. Character quality was evaluated according to the following evaluation criteria.
A: There is no roughness and the dot shape is a perfect circle. O: A slight roughness is observed, but the dot shape is a perfect circle. Δ: A roughness is observed and the dot shape is slightly disturbed. X: A level in which roughness is recognized and the dot shape is bad, causing a practical problem.
XX: Both rough and dot shape are extremely bad.

(Evaluation of strikethrough resistance)
A solid image was printed on Shirahoi paper (64 g / m ² ) manufactured by Daishowa Paper Co., Ltd. under the conditions of an ink adhesion amount of 10 ml / m ² and an image size of 200 × 280 mm. Was placed on the plate for 1 day and dried to create an image. The back side of the sample printed on the plain paper was visually observed and evaluated for through-through resistance according to the following criteria.

◎: No ink bleed or show-through on the back side is observed ○: Ink bleed or show-through on the back side is slightly recognized and acceptable quality △: Ink bleed or show-through is observed on the back side Slightly recognized, but not of concern when printing on the back side ×: Ink bleed and back-through on the back side are quite acceptable, and unacceptable quality for back side printing XX: Clear ink bleed on the back side, back Omission is observed and the quality is unsuitable for backside printing <Evaluation of curling characteristics after printing>
Under a condition of 23 ° C. and 30% RH, a solid image was obtained on a white paper (64 g / m ² ) manufactured by Daishowa Paper Co., Ltd. under the conditions of an ink adhesion amount of 10 ml / m ² and an image size of 200 × 280 mm. On a flat table, the printing surface was left for one week, and then the heights of the four corners were measured. For the negative curl sample with the central part floating upside down, the sample was allowed to stand for another day after being turned upside down. The raised heights of the four corners were measured as described above, and the curl characteristics were evaluated according to the following criteria.

A: Almost flat, even at the most floating part at the four corners, the lifting height is less than 5 mm. The height of the lifted portion is 10 mm or more and less than 20 mm. X: The height of the lifted portion at the four corners is 20 mm or more and less than 50 mm. XX: The height of the lifted portion of the four corners. Is 50mm or more or rounded into a cylindrical shape and cannot be measured (evaluation of continuous discharge)
Under the conditions of discharging in an environment of 23 ° C. and 30% RH, the state after discharging was continuously continued for 1 hour without cleaning was visually observed, and the discharge stability was evaluated according to the following criteria.

◎: Normal emission from all nozzles ○: Clogging is observed in 1 to 3 nozzles, but recovered by suction cleaning from the nozzle surface △: Clogging occurs in 4 or more nozzles and cannot be recovered by suction cleaning Clogging occurs in one nozzle, but is in a practically acceptable range. X: Clogging occurs in 7 or more nozzles, and clogging that cannot be recovered by suction cleaning occurs in 2 nozzles. Xx: Clogging in 10 or more nozzles. Table 3 shows the results of the various evaluations described above.

  As is apparent from Table 3, it can be seen that the recording method of the present invention is superior to the comparative example in character quality, show-through properties, curl characteristics, and continuous emission.

1 is a longitudinal sectional view showing an example of the configuration of an inkjet head used in the present invention. Cross-sectional view showing an example of a portion of an inkjet head used in the present invention Sectional drawing which shows an example of the operation principle of the inkjet head used for this invention The block diagram which shows an example of a structure of the inkjet head drive device used for this invention The figure which shows an example of the head drive waveform which concerns on this invention The figure which shows another example of the head drive waveform which concerns on this invention The figure which shows an example of a structure of one drive pulse of the drive waveform in FIG. Waveform diagram showing a change in pressure in the ink chamber when the drive pulse of FIG. 7 is applied to the ink chamber The figure which shows another example of the drive pulse which concerns on this invention The figure which shows the drive waveform at the time of the conventional 3 division drive The figure which shows the structure of one drive pulse of the drive waveform of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Piezoelectric member 4 Ink chamber 12 Ink discharge port 24 Ink drive circuit 25 Inkjet head 26 Drive waveform control circuit

Claims (3)

The inkjet recording apparatus satisfies the following requirements (1) to (3), and the inkjet recording ink contains at least water, a water-soluble organic solvent and a pigment, and the total amount of the water-soluble organic solvent is 50% by mass of the total ink. The water-soluble organic solvent having a solubility parameter (SP value) of 16.5 or more and less than 24.6 among the water-soluble organic solvent is 30% by mass or more of the total ink. Inkjet recording method.
(1) A plurality of ink chambers provided with ink nozzles for ejecting ink droplets that form partition walls by an actuator that deforms in response to an applied voltage of an adjacent ink chamber are arranged, and ink is communicated with each of the ink chambers to receive ink. An ink jet recording head provided with a common ink chamber to be supplied is provided.
(2) Between an expansion pulse that expands the volume of the ink chamber by deforming the actuator constituting the ink chamber partition wall and a contraction pulse that contracts the volume of the ink chamber by deforming the actuator. Drive signal generating means for continuously generating a drive signal to be applied to the actuator a plurality of times with a predetermined pause time.
(3) The volume of the ink chamber is repeatedly expanded and contracted by generating the drive signal from the drive signal generating means a plurality of times, so that a plurality of ink droplets are continuously ejected from the ink nozzles, and the pause time is adjacent. The ink for ink jet recording is ejected onto the recording material by an ink jet recording head set to a time for reducing the crosstalk between the ink chambers. The pause time between the expansion pulse and the contraction pulse is set so that the time difference between the center of the expansion pulse and the center of the contraction pulse is equal to the natural vibration period of the ink in the ink chamber. Item 10. The ink jet recording method according to Item 1. An ink for ink jet recording, which is used in the ink jet recording method according to claim 1.