JP4231828B2 - Inkjet recording method and inkjet ink - Google Patents

Description

  The present invention relates to an inkjet recording method, an inkjet recording apparatus, and an inkjet ink.

  An ink jet recording apparatus, which is one of the print recording methods, uses, for example, electrostatic attraction, pressurization by vibration or distortion using a piezoelectric element, pressurization by heating and foaming of ink, and the like to drop ink droplets. In this recording method, the ink is generated from an ink head and is made to fly, and is attached to a recording medium such as paper or a synthetic resin film.

  As an ink composition used for such ink jet recording, a solvent-type ink in which a dye or pigment or a mixture thereof is used as a coloring material and dispersed or dissolved in an aqueous or oil-based solvent is known, and many Is used in combination with a dedicated recording medium according to the ink composition, and the ink is absorbed by an ink receiving layer provided on the recording medium, so that a very good printed matter can be obtained.

  On the other hand, a UV inkjet method is known as a method for printing on various types of recording media. The ink used for the UV inkjet method is produced by dispersing a photocuring initiator and a pigment using a photocurable resin as a base material. The characteristic feature is that the recording medium does not require a receiving layer because the droplets adhering in a hemispherical shape on the recording medium after printing are cured by ultraviolet irradiation.

  Similarly, as a method for printing on various types of recording media, there is a solid ink jet method using a solid ink at room temperature in which a heat-meltable resin or wax and a color material are mixed. In this case, the ink is an ink jet head. The ink is held at a temperature exceeding the melting point of the ink, ejected from the head and landed on the recording medium. At the same time, the droplets are cooled to the ambient temperature and solidified, so that “bleeding” does not occur. However, since hemispherical ink dots are formed, the printed surface is irregularly reflected and loses gloss.

  To solve this problem, as shown in FIG. 3, the recording medium 13 such as ink-jet recorded paper that is heated and cured while passing over the heater plate 12 passes between the pair of pressure rollers 14 and 15. Thus, there is a known apparatus that smoothes the ink surface by heating and smoothing the ink dots on the recording medium 13 and also increases the diameter of the recording dots and strengthens the adhesion between the paper and the ink (Patent Document). 1).

  Further, a method is disclosed that has both the characteristics of the UV ink and the solid ink and can fix the ink without a mechanism such as a heat roller for fixing the ink (Patent Document 2).

  Similarly, as a method that combines the characteristics of both UV ink and solid ink, in order to improve the fixability and control the ink dot shape without using a pressure roller, By adjusting the temperature of the ink head, etc., or using radiation curable ink, etc., the ink is spread as it is by irradiating it with radiation for a time of 1 second or less after adhering to the ink recording material. An image quality control method for setting the average thickness to an appropriate numerical value range is disclosed (Patent Document 3).

  In addition, in the conventional inkjet method combined with radiation curing, in order to completely cure the curable plastic material in the ink, the content of the coloring material in the ink is reduced, the transparency is increased and the energy of the crosslinking radiation is increased. Needed to reach every corner of the ink.

JP-A-8-11299 (see paragraphs [0002] and [0004], FIG. 4) Japanese Unexamined Patent Publication No. 2000-44857 (see paragraph [0070]) Japanese Patent Laying-Open No. 2003-145914 (see paragraphs [0015] and [0033])

  However, the above-described conventional inkjet recording method and inkjet recording apparatus require a dedicated recording medium in order to obtain high image quality in a method using water-based ink. In the UV inkjet method, when ink droplets adhering to a recording medium are combined with ink droplets adhering to each other in the same manner, the two droplets are attracted to one side, and different color materials are mixed together. It may cause “bleeding”. In the solid ink jet system, there is a problem that the printed image strength is low because the melting point of the wax component which is the main component of ink is low.

  In the system that combines the characteristics of both UV ink and solid ink, strong print image strength can be obtained, but monomers that are not involved in the polymerization reaction may remain due to the use of radiation curable ink. The final printed product user may ingest residual monomers, which may lead to health problems for the final printed product user. In addition, when there is a large amount of residual monomer, sufficient ink hardness cannot be exhibited, so that there is a problem that the scratch resistance of the printed surface is weak.

  Also, in order to set the ink dot bleeding, circularity, and average thickness to appropriate numerical ranges using radiation curable ink, a relatively large amount of ink is required, and there is room for improvement in terms of printing efficiency. was there.

  In addition, when using a radiation curable ink with a predetermined viscosity and printing on the paper even if the circularity and average thickness of the ink dots are adjusted at a predetermined temperature, a smooth surface without sufficient irregularities cannot be formed, and the glossiness Further improvements are required in this respect.

  Also, if the content of the coloring material in the ink is reduced and the transparency is increased so that the energy of the crosslinkable radiation reaches every corner of the ink, then it becomes difficult to sufficiently improve the colorability of the ink. Become.

  Therefore, the object of the present invention is to solve the above-described problems, and in an inkjet recording method and an inkjet recording apparatus using a radiation curable ink, a glossy smooth printing surface can be obtained even on various recording media, which is harmful. Efficient ink jet recording method in which there is no residual monomer, sufficient scratch resistance of the printing surface of the recording medium is obtained, the ink coloring property is sufficiently enhanced, and a high density printing surface can be obtained with a small amount of ink And an inkjet recording apparatus.

  In order to solve the above-mentioned problems, in the present invention, a heat-melting / radiation-crosslinking ink containing a radiation-crosslinking resin and a heat-meltable color developing agent and a coloring material is provided, and its droplets After spraying onto the recording medium from an inkjet head, the printing surface of the recording medium is pressurized so that the surface of the droplet after landing becomes flat ink dots, and then radiation is applied to the flattened ink dots. This is an ink jet recording method comprising curing by irradiation.

  In the ink jet recording method of the present invention configured as described above, by pressurizing the printing surface of the recording medium, the droplets of the heat-melting / radiation crosslinkable ink are flattened, and the thickness through which the radiation passes is reduced. Since the ink dots were cured by irradiating with crosslinkable radiation, the radiation reached the inside of the ink dots reliably, and the polymerization reaction occurred sufficiently, thus generating residual monomers that did not contribute to the reaction. Will definitely decrease.

  For this reason, the ink dots having a flattened shape and increased in diameter are surely fixed and cured on the recording medium, and sufficient scratch resistance is obtained. Even when the recording medium is paper, a glossy smooth surface can be obtained. .

  In addition, since the printing surface of the recording medium is pressurized so as to be flat ink dots, the ink dots are flattened as compared with the conventional method in which the ink dots are flattened only by adjusting the ink viscosity and the temperature of the ink head. The amount used is small and a high-density printed surface can be obtained, resulting in improved efficiency.

  Further, in the present invention, after the heat-melting / radiation crosslinkable ink is adhered onto the recording medium, it is flattened by pressurization, so that the content of the coloring material is set to 1 to 30% by weight, for example, in the conventional radiation curable ink. Even when the content of the coloring material is increased (1 to 10% by weight), the curable plastic material can be completely cured.

  In order to ensure such an action, in the above-described inkjet recording method, it is preferable that the flat ink dot is a flat ink dot that is reduced by 30% or more from the height of the droplet immediately after landing, The height of the flat ink dot after pressurization is preferably 10 μm at the maximum, preferably 5 μm or less, and the heat-melting / radiation-crosslinking ink used in this case is preferably a solid ink at room temperature.

  In order to obtain an ink jet recording apparatus that exhibits the same action as described above, in an ink jet recording apparatus that ejects droplets of a heat-meltable and radiation-crosslinkable ink containing a heat-crosslinkable colorant and a colorant containing a radiation-crosslinkable resin, An ink jet recording apparatus comprising a roller that presses the recording medium on which the ejected ink droplets are placed, and a radiation irradiating apparatus that irradiates radiation to the pressed and flattened ink dots is employed. can do.

  An ink jet recording method, an ink jet recording apparatus, and an ink jet ink according to the present invention include: a droplet of a heat-melting / radiation crosslinkable ink is ejected from an ink jet head onto a recording medium, and after landing, the surface of the droplet after landing is flat. Pressurize the printing surface of the recording medium so that it becomes ink dots, then irradiate and cure the flattened ink dots with crosslinkable radiation, so that a glossy smooth printing surface can be obtained on various recording media. There is no harmful residual monomer, the scratch resistance of the printing surface of the recording medium is sufficiently obtained, and the coloring property of the ink is sufficiently enhanced, and a high density printing surface can be obtained with a small amount of ink. There exists an advantage used as an inkjet recording method, an inkjet recording device, and an inkjet ink.

  The heat-melting / radiation-crosslinking ink used in the present invention contains a color-crosslinking agent containing a radiation-crosslinking resin and a heat-melting property, and a coloring material. It contains various known additives. The heat melting property of the heat-melting / radiation-crosslinking ink is preferably solid at room temperature and the melting point is preferably in the range of 35 to 200 ° C, more preferably in the range of 50 to 90 ° C. For example, it is possible to mix a water-based solvent, the energy required for ink melting can be reduced, or the usable range of the ink jet head constituent member can be expanded.

  The heat-meltability of the color developing agent is made of a heat-meltable resin or wax and a radiation crosslinkable resin. Or you may comprise the color-melting agent with heat melting property only with radiation crosslinkable resin.

  As the heat-meltable resin or wax, a known substance having a thermoplastic property can be selected. For example, waxes, thermoplastic resins, copolymers and the like can be mentioned. Moreover, these can be used in mixture of 2 or more types individually or in arbitrary combinations, without specifically limiting a conventionally well-known thing.

  As waxes, natural waxes and synthetic waxes can be selectively employed. Specifically, natural wax candelilla wax, carnauba wax, rice wax (rice bran wax), wood wax, jojoba solid wax, hardened palm oil, rapeseed hardened oil, hardened soybean oil, coconut oil, auricule wax, Plant waxes such as sugarcane wax, esparto wax, bark wax, beeswax, lanolin wax and derivatives thereof, animal waxes such as whale wax, shellac wax, waterfowl wax, mineral waxes such as montan wax, ozokerite, ceresin wax And petroleum-based waxes such as paraffin wax, microcrystalline wax, and petrolatum can be selected.

  Synthetic waxes include synthetic hydrocarbons such as polyethylene wax and Fischer-Tropsch wax, montan wax derivatives such as Hoechst wax, modified waxes such as paraffin wax derivatives, microcrystalline wax derivatives and polyethylene wax derivatives, hydrogen such as hardened castor oil and hardened castor oil derivatives. Fatty acid amides such as modified wax, hydroxystearic acid such as 12-hydroxystearic acid, 12-hydroxystearic acid derivative, lauric acid amide, stearic acid amide, oleic acid amide, erucic acid amide, ricinoleic acid amide, N-substituted fatty acid amide , Ketones such as diheptadecyl ketone, diundecyl ketone, distearyl ketone, dodecylamine, tetradecylamine, octadecylamine, oleylamine, dioctylamine Amines such as decylamine, esters such as methyl stearate, stearyl stearate, octadecyl stearate, myristyl myristate, glycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, ethylene glycol fatty acid ester, polyoxyethylene fatty acid ester, Select higher waxes such as higher fatty acids such as behenic acid, stearic acid, palmitic acid, myristic acid, lauric acid, 12-hydroacid, higher alcohols such as stearyl alcohol, behenyl alcohol, myristyl alcohol, palmityl alcohol, cetyl alcohol I can do things.

  On the other hand, in thermoplastic resins, addition polymerization systems such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, fluororesin, polymethyl methacrylate, polycondensation systems such as polyamide, polyester, polycarbonate, polyphenylene oxide, thermoplasticity, etc. A polyaddition system such as urethane and a thermoplastic resin such as polyacetal can be selectively employed.

  As the copolymer, vinyl chloride-polyvinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-vinyl acetate copolymer, styrene-butadiene-acrylonitrile copolymer, ethylene -Α-Olefin copolymer elastomer, saponified ethylene-vinyl acetate copolymer and the like can be employed.

  The radiation crosslinkable resin used in the present invention is a high molecular polymer in which a monomer is polymerized by a chemical action of radiation (including an electron beam and is also referred to as radiation) and is cured with a crosslinking reaction. If necessary, additives such as a polymerization initiator and a crosslinking accelerator described later are also used in combination.

  Incidentally, radiation is an electromagnetic wave emitted from an object, such as γ rays, X rays, ultraviolet rays, visible rays, infrared rays, etc., and any radiation having an active energy capable of polymerizing / crosslinking the radiation-crosslinkable resin may be used. However, it is not necessary to adopt a specific limitation.

  The radiation crosslinkable resin used in the present invention can be selected using a curable monomer, oligomer, or prepolymer as a raw material. For example, a radical polymerizable compound, a cationic polymerizable compound, an anion polymerizable compound and the like can be mentioned.

  The radically polymerizable compound is a compound having at least one ethylenically unsaturated double bond capable of radical polymerization in the molecule. Specifically, for example, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid and their salts, esters, urethanes, amides and anhydrides, acrylonitrile, styrene, and various Examples include radically polymerizable compounds such as unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes.

  Cationic polymerizable compounds include, for example, alicyclic polyepoxides, polyglycidyl esters of polybasic acids, polyglycidyl ethers of polyhydric alcohols, polyglycidyl ethers of polyoxyalkylene glycols, polyglycidyl ethers of aromatic polyols And hydrogenated compounds of polyglycidyl ethers of aromatic polyols, urethane polyepoxy compounds and epoxidized polybutadienes, styrene derivatives, vinyl naphthalene derivatives, vinyl ethers, N-vinyl compounds and the like.

  These radiation crosslinkable resins can be used without any particular limitation as long as they are conventionally known. In addition, some radiation crosslinkable resins have a room-temperature solid heat melting property, and the color developing agent used in the ink can be used without using a heat melting resin or wax. It is also possible to configure only with a functional resin.

  The ratio of the radiation crosslinkable resin and the heat-meltable resin or wax in the ink composition of the present invention is preferably included in the range of 10: 1 to 1:10 by weight. . When the weight ratio is out of the above range, various problems are likely to occur.

  For example, when the ratio of the radiation crosslinkable resin in the ink becomes too small, the resistance after the ink is fixed to the recording medium by irradiation with radiation is remarkably lowered. On the other hand, if the ratio of the radiation-crosslinkable resin in the ink becomes too large, the ink will not easily become a solid at room temperature, and the ink will bleed between adjacent ink droplets before landing on the recording medium and curing by radiation irradiation. The problem is likely to occur. However, when the color developing agent used in the ink is composed of only a radiation crosslinkable resin as described above, the above description regarding the weight ratio is not applicable.

  The ink used in the present invention contains a radiation crosslinkable resin that crosslinks and cures by a polymerization reaction due to radiation irradiation. However, in the radiation crosslinkable resin, in order to initiate the polymerization reaction, only radiation irradiation is performed. In addition, many require a polymerization initiator.

  Therefore, in the ink used in the present invention, conventionally known polymerization initiators can be contained alone or in a combination of two or more in any combination, without any particular limitation, if necessary.

  As the color material used in the ink of the present invention, a known pigment or dye used in paints, printing inks, and the like can be selectively employed.

  As the pigment, a commonly used pigment can be adopted regardless of whether it is an inorganic pigment or an organic pigment. Specific examples include carbon black, black iron oxide, bengara, vermilion, molybdenum red, cadmium red, iron oxide red, resurge, yellow iron oxide, titanium yellow, cadmium yellow, chrome yellow, ultramarine blue, Prussian blue. Inorganic pigments such as cobalt blue, titanium oxide, zinc white, lead white, chromium oxide, chromium green, viridian, titanium cobalt green, molybdenum orange, and manganese violet can be used.

  Organic pigments include soluble or insoluble azo pigments, phthalocyanine pigments, and anthraquinone, quinacridone, perylene, diketopyrrolopyrrole, perinone, isoindolinone, quinophthalone, slenine, dioxazine. And condensed polycyclic pigments such as indigo and the like.

  As dyes, azo dyes, disazo dyes, metal complex dyes, naphthol dyes, anthraquinone dyes, indigo dyes, carbonium dyes, quinoneimine dyes, cyanine dyes, quinoline dyes, nitro dyes, nitroso dyes, benzoquinone dyes, naphthoquinone dyes, xanthene dyes, Phthalocyanine dyes, metal phthalocyanine dyes, and the like can be used. These pigments and dyes are not particularly limited and may be used alone or in combination.

  The blending amount of such a coloring material is preferably contained in the range of 1 to 30% by weight in the heat-melt / radiation-crosslinkable ink composition. If the amount is less than 1% by weight, the original color development as a coloring material is not sufficient. In addition, in the present invention, after the heat-melting / radiation-crosslinking ink is adhered onto the recording medium, the radiation transmission is improved by flattening by pressurization, so the content of the coloring material in the conventional radiation-curable ink is included. It is possible to make it more than the amount (1 to 10% by weight) (that is, 11 to 30% by weight). This decreases the possibility that the amount of residual monomer in the ink after radiation curing will increase. In addition, if the color material concentration in the ink exceeds 30% by weight and becomes too high, the ink viscosity at the time of melting becomes excessively high and the ink is not stably ejected from the ink jet head, or the color material settles in the ink. Problems are likely to occur.

  Such a heat-melting / radiation-crosslinking ink is preferably adjusted to have a viscosity of 0.002 to 0.05 Pa · s under the condition of being heated to 50 to 200 ° C. by an ink jet head. This is because ink ejection from the inkjet head cannot be reliably performed outside the predetermined range.

  If necessary, the ink of the present invention further includes a dispersant, an antioxidant, an anti-gelling agent, a polymerization inhibitor, a sensitizer, a crosslinking accelerator, a stabilizer, a surface treatment agent, a surfactant, and a leveling agent. Various additives such as an agent, a viscosity reducing agent, a plasticizer, an antiseptic, a pH adjuster, an antifoaming agent, a moisturizing agent, and a flame retardant can be appropriately mixed.

  In this invention, in order to pressurize the printing surface of the recording medium so that the surface of the heat-melt / radiation-crosslinkable ink droplet becomes a flat ink dot, the pressure is applied by a roller on the drum or a pair of pressure-contact roller devices. For example, a well-known pressurizing means can be employed.

At this time, the height of the ink dot after pressurization is preferably 10 μm or less.
In addition, when the plastic deformation is flattened by the surface compression force of the ink dots on the recording medium, more preferable conditions are the film thickness (the height of the flattened dots on the recording medium at room temperature). The same is true.) The film thickness is in the range of 0.1 to 10 μm, more preferably 0.1 to 5 μm by applying a surface compression force of 0.01 to 0.5 kg / mm ² from the outside to the 10 to 50 μm dots. More preferably, the range is from 0.1 to 3 μm. By forming the ink dots with such a thin film thickness, the radiation penetrates into the ink dots, and the radiation crosslinking reaction is promoted and the residual monomer. Can be reduced.

Further, a dot having a film thickness of 10 to 30 μm on the recording medium is applied with a surface compression force of 0.01 to 0.5 kg / mm ² from the outside to reduce the film thickness to 70% or less, more preferably 50% or less. When the image is further reduced, more preferably reduced to 30% or less, and further preferably reduced to 10% or less, a smooth printed image surface can be obtained, and a printed matter having excellent gloss can be obtained.

  That is, in the invention according to each claim of the present application, by flattening the landing dots to an absolute film thickness of a predetermined value or less, the residual monomer is reduced, and the flattening is performed by plastic deformation to a predetermined height ratio or less. The effect of ensuring the gloss of the printed surface can be obtained.

The relationship between the printing resolution of the printing apparatus and the dot enlargement ratio due to the surface compression force will be described. d: ink dot diameter (mm) in a state of landing on the recording medium, A: enlargement ratio (%) of the ink dot diameter when the ink dots landed on the recording medium are expanded by applying a surface compression force, x : When the resolution (dpi) of the inkjet head is used, if d ≧ 25.4 × √2 / (xx × A / 100), a uniform solid image without a print gap can be obtained on the recording medium.
Therefore, while forming dots without gaps, the amount of ink required is reduced as the film thickness is reduced, and not only can the cost of consumables be suppressed, but there is also an effect that the discharge response can be increased secondaryly.

  In the step of irradiating and curing the flattened ink dots, for example, a radiation having crosslinkability such as ultraviolet rays may be irradiated using a mercury lamp or an ultraviolet light bulb.

An ink jet recording apparatus according to an embodiment of the present invention will be described below with reference to the accompanying drawings.
As shown in FIG. 1, the embodiment is an ink jet recording apparatus including a head 1 that ejects droplets of heat-melting / radiation-crosslinking ink, and records on paper or the like on which ejected ink droplets are placed. A pressing roller 4 that rotates while placing the medium 2 on the drum 3 and pressurizing the recording medium 2 from above is provided, and a radiation irradiating device 5 that irradiates radiation to the pressed and flattened ink dots is provided. Yes.

  More specifically, hot melt / radiation crosslinkable ink (hereinafter simply referred to as “ink”) is supplied to the tank 6 in a solid state and is negatively passed through the valve 8 by the pump 7 in a state of being heated to the melting point or higher. The head 1 is filled through the pressure generator 9 and the filter 10. The ink supply system is sealed with respect to the atmosphere except for the tank 6 and the ink jet nozzle section.

  The ink is stably held at the discharge temperature inside the head 1 at the time of printing standby. However, in the ink supply system other than the head 1, the ink is kept in a sufficiently fluid range from the melting point to the discharge temperature. When printing, the valve 8 is closed and a negative pressure is generated by the negative pressure generator 9 so that the ink in the inkjet nozzle can form a meniscus suitable for ejection.

  In addition, in the case of an inkjet ink using normal wax, a large volume shrinkage occurs when the ink is solidified in the head after the operation is stopped. As a result, there is a problem that air enters the generated void from the outside and bubbles are generated during re-dissolution, making inkjet discharge impossible. The head and the flow path may be held to avoid ink solidification and contraction and avoid the generation of bubbles. Also, by mixing multiple types of waxes with different melting points, the volume change near the melting point is broadened, and the temperature of the head is kept within the broad volume change range (below the melting point) to suppress the influence of shrinkage. be able to. In this case, there is an advantage that the ink is less likely to evaporate and deteriorate compared to the case where the ink is kept in the liquid state during the pause.

  A recording medium 2 such as paper is mounted on the drum 3 disposed so as to face the head nozzle surface, and the drum 3 is arranged on the outer periphery of the drum 3 further downstream from the printing position. There is provided a rotatable, fluorine-coated presser roller 4 which can be brought into contact with and separated from the peripheral surface of the recording medium and applies a compressive force to the recording medium.

  When a driving command corresponding to image data is sent to the head, ink is ejected from the head 1 onto the drum 3. When the ink dots ejected in the liquid state land on the recording medium 2 such as paper, they are cooled to the ambient temperature and solidified into a substantially hemispherical shape. At this time, even if another ink dot lands on the adjacent place, the ink dot after landing will immediately solidify, so the adjacent dots that are usually mentioned as obstacles of the ink jet method are merged and pulled to one side or colors are mixed The bleed phenomenon is not generated.

  The ink dots 11 solidified into a substantially hemispherical shape on the recording medium 2 (see FIG. 2) are compressed by the pressing roller 4 and plastically deformed and stretched into a film shape (the chain line shape in FIG. 2). It is possible to obtain a print quality excellent in gloss with a thin film thickness. At this time, the printed surface after landing may be heated by a heating means in order to increase the plastic deformability of the ink dots.

  About the hot-melt / radiation crosslinkable ink used in the embodiment, the composition, the production method thereof, and the results of evaluation by hardness and leveling test will be described below.

(1) 55% by weight of hardened palm oil (melting point: 57 ° C.) as a heat-meltable resin or wax,
(2) Radiation crosslinkable resins, such as tripropylene glycol diacrylate 10% by weight, neopentyl glycol diacrylate 8% by weight, isobornyl acrylate 10% by weight, polyester acrylate 5% by weight,
(3) As a polymerization initiator, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1 .. 3 wt%, 1-hydroxy-cyclohexyl-phenyl-ketone .. 1 wt. %
(4) As additives, pigment dispersants, antioxidants, anti-gelling agents ... 1% in total
(5) As a color material, quinacridone pigment (magenta) 7% by weight

(1) Polyethylene glycol 1000 diacrylate (solid temperature, melting point 40 ° C.) 60% by weight, isobornyl acrylate 15% by weight, polyester as a heat-meltable color developing agent containing radiation crosslinkable resin Acrylate 10% by weight
(2) As a polymerization initiator, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1 .. 3 wt%, 1-hydroxy-cyclohexyl-phenyl-ketone .. 1 wt. %
(3) As additives, pigment dispersants, antioxidants, anti-gelling agents ... 1% in total
(4) As a color material, quinacridone pigment (magenta) 7% by weight

[Production method]
In the ink of Example 1, the radiation-crosslinkable resin, polymerization initiators, additives and coloring materials, and in the ink of Example 2, the radiation-crosslinkable resin excluding room temperature solid polyethylene glycol 1000 diacrylate, The polymerization initiators, additives and coloring materials were dispersed using a homogenizer until a homogeneous mixture was obtained. Next, the homogenous mixture was mixed with the above-mentioned hardened palm oil melted at 80 ° C. in the ink of Example 1, and with the above-mentioned polyethylene glycol 1000 diacrylate melted at 60 ° C. with the ink of Example 2. The mixture was stirred and filtered at the same temperature to remove impurities and the like, and radiation curable inks of Example 1 and Example 2 were obtained.
The ink of Example 1 was solid at room temperature, and had a melting point of about 55 ° C. and a viscosity at 75 ° C. of 0.015 Pa · s. The ink of Example 2 was solid at room temperature, the melting point was about 38 ° C., and the viscosity at 75 ° C. was 0.018 Pa · s.

[Experiment 1 (Ink / paper hardness comparison test)]
For the ink of Example 1 and Comparative Example 1 (commercial product manufactured by Fuji Xerox Co., Ltd .: Phaser850 ColorPrinter ink ColorStixInk, Magenta magenta ink) Spread in thickness and cool to room temperature. Similarly, the ink of Example 1 was heated to 80 ° C., spread on a glass preparation with a thickness of 0.5 mm, and cooled to room temperature. Three types of paper (Paper 1: A2 coated 127.9 g / m ² as general printing paper, Paper 2: Mirror coating 255.9 g / m ² as general cardboard printing paper, Paper 3: For comparison of paper 1 and 2 As a mirror coat 127.9g / m ² ), a total of 5 types of test samples are placed on a horizontal and smooth steel plate, and a steel ball with a diameter of 3.17mm is placed on each material in an environment kept at room temperature. Pressed with a load of 550 g. The state of the indentation after being pressed was observed with a laser microscope, the amount of plastic deformation was examined from the depth of the dent, and the results are shown in Table 1. The unit is μm,-in the table is unmeasured, and x indicates that it is below the measurement limit.

  As is clear from the results in Table 1, the amount of plastic deformation of the ink of Comparative Example 1 is 5.05 μm at a load of 350 g, and the paper 1 which is a general A2 coated paper has a plastic deformation of 5.86 μm at a load of 350 g. The amount of plastic deformation was 9.35 μm with respect to a load of 250 g even for the paper 2 which is a thick paper having a large deformation amount with respect to the load.

In contrast, the ink of Example 1 has a plastic deformation amount of 31.64 μm at a load of 150 g and 14.75 μm even at 70 g. I understand that
Therefore, the ink of Example 1 was soft and had good plastic deformation on general paper and had ductility, so that it could be leveled to form a thin film.

[Experiment 2 (Leveling test)]
Based on the results of Experiment 1, an experiment was conducted to determine what results would be obtained when ink was actually leveled on the recording medium. That is, the ink of Comparative Example 1 was heated to 180 ° C., and ink droplets having a diameter of about 0.4 mm were dropped on the paper 1 and a smooth stainless steel plate SUS304-CP having a thickness of 0.3 mm. Similarly, the ink of Example 1 was heated to 80 ° C., and ink droplets having a diameter of about 0.4 mm were dropped on the paper 1 and the stainless steel plate. Each surface load was crushed by applying a surface load of 25 g to 100 g, the state of the dots before and after crushing was observed with a laser microscope, the ratio of change in dot diameter and height was examined, and the results are shown in Table 2, FIG. 4 and FIG. .

  As apparent from the results of Table 2 and FIGS. 4 and 5, at 25 g load, the ink of Example 1 expanded the dot diameter to about 130 to 150%, but no change was seen in the ink of Comparative Example 1. It was. Further, at a load of 50 g, the dot diameter of the ink of Example 1 expanded to about 140 to 170%, but no change was seen in the ink of Comparative Example 1. Furthermore, at 100 g load, the dot diameter of the ink of Example 1 expanded to about 160 to 190%, whereas the dot diameter of the ink of Comparative Example 1 expanded to about 132% only for the material dropped on the stainless steel plate. The thing dripped on the paper had almost no change. Regarding the dot height, at a load of 25 g, the dot height of the ink of Example 1 was reduced to about 50%, but the ink of Comparative Example 1 had a reduction rate of about 94%. At a load of 50 g, the ink of Example 1 had a dot reduction rate of 36 to 42%, whereas the ink of Comparative Example 1 had a reduction rate of 86% or more. Furthermore, at a load of 100 g, the ink of Example 1 had a dot reduction rate of 29 to 31%, whereas the ink of Comparative Example 1 had a reduction rate of about 57 to 90%.

  From these results, it was found that the dot height was reduced to about 30% from the state immediately after printing by leveling, and the film thickness could be made very thin. The ink of Example 1 has a reduction ratio about twice that of the same compression load as that of the ink of Comparative Example 1, and can be said to be soft and easy to be plastically deformed. From these results, it can be seen that the ink used in the present invention is very flexible and excellent in leveling suitability even at room temperature.

[Experiment 3 (Ink Suitability Test)]
A print comparison test was performed on the offset coated paper for the ink of Example 1 and the already known ink. The results are shown in Table 3. The ink used for the comparison was Comparative Example 2: a hot-melt photocurable ink having a melting point of 110 ° C. described in Examples Nos. 3 to 6 of JP-A No. 2000-0448857, and Comparative Example 3: implementation of JP-A No. 2003-145914. The heat-meltable ultraviolet curable ink described in Example 6 was used, and the ink ejection and fixing methods were performed according to the methods proposed for each ink.

  As is clear from the results in Table 3, this case shows balanced suitability with no weak points in terms of ease of use such as environmental compatibility such as odor, image quality such as bleeding and back-through, leveling characteristics at discharge temperature and room temperature, etc. I understand that.

Explanatory drawing which shows the apparatus and process of embodiment typically Side view showing enlarged ink dots Illustration of a conventional device Chart showing the results of the ink leveling test and the dot height for each example Chart showing the results of the ink leveling test and the dot diameter of each example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Head 2, 13 Recording medium 3 Drum 4 Press roller 5 Radiation irradiation device 6 Tank 7 Pump 8 Valve 9 Negative pressure generator 10 Filter 11 Ink dot 12 Heater plate 14, 15 Roller

Claims (4)

A color developing agent comprising a radiation-crosslinkable resin that is solid at room temperature and has a melting point of 35 to 200 ° C., or a radiation-crosslinkable resin and a heat-meltable resin or wax so as to exhibit the heat-meltability Is provided with a color developing agent blended in a weight ratio of 10: 1 to 1:10 and a solid heat-melting / radiation-crosslinking ink containing a coloring material at room temperature, and the droplets are applied from an inkjet head to a recording medium. The printing surface of the recording medium is pressurized so that the ink dots that are cooled immediately after landing and solidified without color mixing due to the coalescence of adjacent dots become flat, and then irradiate the flattened ink dots with radiation. And then curing the ink jet recording method. Flat ink dots, ink-jet recording method according to claim 1 which is an ink dots droplets height than 30% or more reduced flat immediately after landing. The inkjet recording method according to claim 1, wherein the flat ink dot height is 10 μm or less. A color developing agent comprising a radiation-crosslinkable resin that is solid at room temperature and has a melting point of 35 to 200 ° C., or a radiation-crosslinkable resin and a heat-meltable resin or wax so as to exhibit the heat-meltability A color developing agent blended in a weight ratio of 10: 1 to 1:10, and a heat-melting / radiation-crosslinking ink that contains a coloring material and is solid at room temperature. The ink dots that are cooled immediately after landing on the recording medium and solidified without color mixing due to the coalescence of adjacent dots are plastically deformed into flat ink dots according to the pressure applied from the pressurizing means. Ink-jet ink, wherein the ink is cured and fixed in the flat shape by being irradiated.

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