JP6337987B2 - Ink composition, ink jet recording method, recorded matter, and ink jet recording apparatus - Google Patents

Description

  The present invention relates to a pigment dispersion, an ink composition, an ink set, a recording apparatus, an inkjet recording method, and a recorded matter, and in particular, a pigment dispersion capable of forming an image having a metallic luster, an ink composition, an ink set, The present invention relates to a recording apparatus, an inkjet recording method, and a recorded matter.

  Conventionally, in order to form a coating film having a metallic luster on printed matter, gold powder made from brass, aluminum fine particles, etc., printing ink using silver powder as a pigment, foil press printing using metal foil, metal foil is used. The thermal transfer method that has been used is used.

  However, a coating film made of printing ink using gold powder or silver powder has a large average particle diameter of 10 to 30 μm, and a matte metallic luster is obtained, but it is difficult to obtain a mirror gloss. there were. Also, in foil stamping or thermal transfer using metal foil, an adhesive is applied to the print medium, a smooth metal foil is pressed onto the print medium, the recording medium and the metal foil are in close contact and heated, and the metal foil and the recording medium are thermally melted. Take the method of wearing. For this reason, relatively good gloss can be obtained, but since the number of manufacturing processes increases and pressure and heat are applied during the manufacturing processes, there is a limitation that the recording medium is limited to recording media that are resistant to heat and deformation.

  In recent years, many applications of inkjet in printing have been seen, and one of the applications is metallic printing. For example, Japanese Patent Laid-Open No. 2002-179960 discloses a technique in which a metal film is formed on the surface of plastic spherical particles, and an ink composition containing the pigment is subjected to a printing process by ink jet printing (Patent Document 1). ). However, in order to obtain a high metallic luster, it is necessary to deform and flatten the sphere and smooth the surface. In this technique, it is said that it is necessary to simultaneously perform the press treatment with a roller and the heat treatment. Therefore, it is inevitable that the apparatus and the manufacturing process are complicated in this respect, and the recording medium is also limited.

  Japanese Patent Laid-Open No. 2003-292836 also discloses a technique using an ink composition in which a precious metal colloid such as gold or silver is dispersed (Patent Documents 2 and 3). However, when the noble metal colloid is prioritized in dispersion stability and the particle diameter is reduced to several nanometers to several tens of nanometers, color development derived from plasmon absorption appears, and a metallic luster cannot be obtained as an ink composition. In this case, after the coating film is dried, a metallic luster is obtained by fusing the colloidal particles by heat treatment at a temperature of 150 ° C. or higher. In addition, even if metallic gloss is obtained with these technologies, high metallic specular gloss with a specular gloss of 20 degrees, 60 degrees, and 85 degrees exceeding 200, 200, and 100 is obtained on a uniform and uniform surface. It was difficult. When the particle size is increased in favor of metallic luster, the dispersion stability is lowered, the problem of aggregation and sedimentation cannot be avoided, and the shelf life of the ink composition is remarkably reduced. Further, it is obvious that using a noble metal as a material greatly increases the cost of the ink composition, and therefore can only be used for high value-added applications, which is disadvantageous in terms of cost.

JP 2002-179960 A Japanese Patent Laid-Open No. 2003-292836 JP 2003-306625 A

The present invention focuses on aluminum as a relatively inexpensive metal material, and provides a pigment dispersion having a high metal specular gloss, an ink composition, a recording apparatus, an ink jet recording method using the ink composition, and a recorded material. With the goal.
Another object of the present invention is to provide an ink set capable of forming a coating film having different metallic luster on a printed matter by constituting an ink set containing ink compositions having different metal pigment concentrations. To do.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive studies. As a result, due to metal pigment dispersions, ink compositions, ink jet recording methods and recorded materials using specific metal pigments, it has been impossible in the past. It was found that a printed matter having a high specular gloss was obtained. The present invention has been made on the basis of such knowledge, and provides the following inventions.

  (1) A pigment dispersion containing a metal pigment, wherein the metal pigment is a tabular particle, the major axis on the plane of the tabular grain is X, the minor axis is Y, and the thickness is Z. A pigment dispersion in which a 50% average particle diameter R50 of an equivalent circle diameter determined from the area of an XY plane of tabular grains is 0.5 to 3 μm and satisfies the condition of R50 / Z> 5.

(2) The pigment dispersion according to (1), wherein the maximum particle diameter Rmax of the equivalent circle diameter determined from the area of the XY plane of the tabular grains is 10 μm or less;
(3) The pigment dispersion according to (1) or (2), wherein the metal pigment is aluminum or an aluminum alloy;
(4) The pigment dispersion according to any one of (1) to (3), wherein the metal pigment is prepared by crushing a metal vapor-deposited film;
(5) The pigment dispersion liquid according to any one of (1) to (4), wherein a particle size distribution CV value of the metal pigment obtained by the following formula is 60 or less.
[Formula 1] CV value = standard deviation of particle size distribution / average value of particle diameter × 100;
(6) An ink composition comprising the pigment dispersion according to any one of (1) to (5), an organic solvent, and a resin;
(7) The ink composition according to (6), wherein the concentration of the metal pigment in the ink composition is 0.1 to 3.0% by weight;
(8) The ink composition according to (6) or (7), wherein the organic solvent contains one or more alkylene glycol ethers that are liquid at normal temperature and pressure.
(9) The ink composition according to any one of (6) and (7), wherein the organic solvent is a mixture of alkylene glycol diether, alkylene glycol monoether and lactone;
(10) The ink composition according to any one of (6) to (9), wherein the resin is at least one selected from the group consisting of polyvinyl butyral, cellulose acetate butyrate, and polyacryl polyol. ;
(11) The ink composition according to any one of (6) to (10), comprising at least one acetylene glycol-based and / or silicone-based surfactant;
(12) When applied to an ink jet recording apparatus in which the nozzle diameter L μm of the ink jet head and the opening W μm of the mesh filter provided in the ink flow path satisfy the condition L ≧ 5 W, the X− The number of tabular grains satisfying the condition that R> (L / 5) is the average grain diameter R μm of equivalent circle diameters determined from the area of the Y plane is 5% or less of the total number of tabular grains. (6) To the ink composition according to any one of (11);
(13) An ink set comprising a plurality of ink compositions according to any one of (1) to (12), wherein each ink composition has a different metal pigment concentration;
(14) Among the ink compositions, the concentration of the metal pigment of at least one ink composition is 0.1 wt% or more and less than 1.5 wt%, and the metal pigment of at least one other ink composition The ink set according to (13), wherein the concentration of is 1.5% by weight or more and 3.0% by weight or less;
(15) A recording apparatus comprising the ink set according to (13) or (14);
(16) An ink jet recording method for performing recording by discharging droplets of the ink composition according to any one of (1) to (12) and attaching the droplets to a recording medium;
(17) On the recording medium, an image having a metallic luster in which measured values of 20 °, 60 °, and 85 ° specular gloss specified in JIS Z8741 are respectively 200, 200, and 100 or more is formed. The inkjet recording method according to (16),
(18) On the recording medium, an image having a metallic luster in which the measured values of the 20 °, 60 °, and 85 ° specular glossiness specified in JIS Z8741 are simultaneously 400, 400, and 100 or more is formed. The inkjet recording method according to (16),
(19) On the recording medium, an image having a metallic luster in which measured values of 20 °, 60 °, and 85 ° specular gloss specified in JIS Z8741 are values of 600, 600, and 100 or more simultaneously is formed. The inkjet recording method according to (16),
(20) The inkjet recording method according to any one of (16) to (19), wherein an ejection amount of the ink composition ejected on the recording medium is 0.1 to 100 mg / cm ² .
(21) The inkjet recording according to any one of (16) to (20), wherein a dry weight of the metal pigment that forms an image on the recording medium is 0.0001 to 3.0 mg / cm ^2. Method;
(22) The inkjet recording method according to any one of (16) to (21), wherein a method of discharging the ink composition is a non-heating method;
(23) The inkjet recording method according to any one of (16) to (22), wherein the recording medium is heated and printed;
(24) The inkjet recording method according to (23), wherein the heating temperature is from 30 ° C to 80 ° C;
(25) The inkjet recording method according to (24), wherein the heating is performed before printing and / or simultaneously with printing and / or after printing;
(26) A recorded matter recorded by the inkjet recording method according to any one of (16) to (25).

  According to the present invention, by using a metal pigment having a specific shape and a controlled particle size, an image having a high metallic gloss (so-called metallic gloss) that has been impossible in the past can be formed on a recording medium. It becomes possible.

FIG. 2 is an exploded perspective view illustrating a configuration of a recording head. It is sectional drawing explaining the structure of an ink introduction needle | hook.

[Pigment dispersion]
The pigment dispersion of the present embodiment is a pigment dispersion containing a metal pigment (hereinafter referred to as “metallic pigment”), and the metallic pigment is tabular particles created by crushing a metal vapor-deposited film, When the major axis on the plane of the tabular grain is X, the minor axis is Y, and the thickness is Z, the 50% average grain diameter R50 of the equivalent circle diameter determined from the area of the XY plane of the tabular grain is 0. 0.5 to 3 μm and satisfy the condition of R50 / Z> 5.

  A “tabular grain” refers to a grain having a substantially flat surface (XY plane) and a substantially uniform thickness (Z). Since the plate-like particles are prepared by crushing a metal vapor-deposited film, metal particles having a substantially flat surface and a substantially uniform thickness can be obtained. Therefore, the major axis on the plane of the tabular grains can be defined as X, the minor axis as Y, and the thickness as Z.

  “Equivalent circle diameter” is the diameter of the circle when assuming that the substantially flat surface (XY plane) of the tabular particles of the metallic pigment is a circle having the same projected area as the projected area of the particles of the metallic pigment. It is. For example, when the substantially flat surface (XY plane) of the tabular grain of the metallic pigment is a polygon, the diameter of the circle obtained by converting the projected surface of the polygon into a circle is calculated by using the diameter of the metallic pigment. It is called the equivalent circle diameter of tabular grains.

  The 50% average particle diameter R50 of the equivalent circle diameter determined from the area of the XY plane of the tabular grains is more preferably 0.5 to 3 μm from the viewpoints of metallic luster and printing stability, and is 0.75. More preferably, it is ˜2 μm. When the 50% average particle diameter R50 is less than 0.5 μm, the gloss is insufficient. On the other hand, when the 50% average particle diameter R50 exceeds 3 μm, the printing stability is lowered.

  Further, in the relationship between the 50% average particle diameter R50 of the equivalent circle diameter and the thickness Z, R50 / Z> 5 from the viewpoint of securing a high metallic luster. When R50 / Z is 5 or less, there is a problem that the metallic luster is insufficient.

  The maximum equivalent particle diameter Rmax obtained from the area of the XY plane of the tabular grains is preferably 10 μm or less from the viewpoint of preventing clogging of the ink composition in the ink jet recording apparatus. By setting Rmax to 10 μm or less, it is possible to prevent clogging of the nozzles of the ink jet recording apparatus and the mesh filter provided in the ink flow path.

  The metallic pigment is preferably aluminum or an aluminum alloy from the viewpoint of cost and ensuring a metallic luster. When an aluminum alloy is used, another metal element or non-metal element that can be added to aluminum is not particularly limited as long as it has a function such as having a metallic luster, but silver, gold, platinum, Examples thereof include nickel, chromium, tin, zinc, indium, titanium, copper, and the like, and at least one of these simple substances or alloys thereof and mixtures thereof is preferably used.

  The method for producing the metallic pigment includes, for example, the metal or alloy layer of the composite pigment base material and the release resin having a structure in which a release resin layer and a metal or alloy layer are sequentially laminated on a sheet-like substrate surface. Tabular grains are obtained by peeling off from the sheet-like substrate, crushing and refining at the boundary of the layers. And when the major axis on the plane of the obtained tabular grains is X, the minor axis is Y, and the thickness is Z, 50% average grains of the equivalent circle diameter determined from the area of the XY plane of the tabular grains A material having a diameter R50 of 0.5 to 3 μm and a condition satisfying R50 / Z> 5 is collected.

  The major axis X, minor axis Y, and equivalent circle diameter on the plane of the metallic pigment (tabular particles) can be measured using a particle image analyzer. As the particle image analyzer, for example, flow type particle image analyzers FPIA-2100, FPIA-3000, and FPIA-3000S manufactured by Sysmex Corporation can be used.

The particle size distribution (CV value) of the metallic pigment (tabular particles) can be obtained by the following formula.
[Formula 1] CV value = standard deviation of particle size distribution / average value of particle diameter × 100

  Here, the CV value obtained is preferably 60 or less, more preferably 50 or less, and still more preferably 40 or less. By selecting a metallic pigment having a CV value of 60 or less, the effect of excellent printing stability can be obtained.

  The metal or alloy layer is preferably formed by vacuum deposition, ion plating or sputtering.

  The metal or alloy layer has a thickness of 20 nm to 100 nm. Thereby, a pigment having an average thickness of 20 nm to 100 nm is obtained. By setting it to 20 nm or more, it is excellent in reflectivity and glitter, and the performance as a metallic pigment is enhanced. By setting it to 100 nm or less, increase in apparent specific gravity can be suppressed and dispersion stability of the metallic pigment can be secured. .

  The release resin layer in the composite pigment raw material is an undercoat layer of the metal or alloy layer, but is a peelable layer for improving the peelability from the sheet-like substrate surface. As the resin used for the release resin layer, for example, polyvinyl alcohol, polyvinyl butyral, polyethylene glycol, polyacrylic acid, polyacrylamide, cellulose derivative, acrylic acid polymer, or modified nylon resin is preferable.

  A layer is formed by applying a solution of one or a mixture of the above to a recording medium and drying. After coating, additives such as a viscosity modifier can be contained.

  The release resin layer is applied by generally used gravure coating, roll coating, blade coating, extrusion coating, dip coating, spin coating, or the like. After coating and drying, the surface is smoothed by calendaring if necessary.

  Although the thickness of the resin layer for peeling is not specifically limited, 0.5-50 micrometers is preferable, More preferably, it is 1-10 micrometers. If it is less than 0.5 μm, the amount as a dispersion resin is insufficient, and if it exceeds 50 μm, when it is rolled, it tends to peel off at the interface with the pigment layer.

  The sheet-like substrate is not particularly limited, but may be a polyester film such as polytetrafluoroethylene, polyethylene, polypropylene, or polyethylene terephthalate, a polyamide film such as 66 nylon or 6 nylon, a polycarbonate film, a triacetate film, a polyimide film, or the like. An example is a moldable film. A preferable sheet-like substrate is polyethylene terephthalate or a copolymer thereof.

  Although the thickness of these sheet-like base materials is not specifically limited, 10-150 micrometers is preferable. If it is 10 μm or more, there is no problem in handleability in the process or the like, and if it is 150 μm or less, it is rich in flexibility and there is no problem in roll formation, peeling and the like.

  The metal or alloy layer may be sandwiched between protective layers as exemplified in JP-A-2005-68250. Examples of the protective layer include a silicon oxide layer and a protective resin layer.

  The silicon oxide layer is not particularly limited as long as it is a layer containing silicon oxide, but is preferably formed from a silicon alkoxide such as tetraalkoxysilane or a polymer thereof by a sol-gel method.

  An alcohol solution in which the silicon alkoxide or a polymer thereof is dissolved is applied and heated and fired to form a silicon oxide layer coating film.

  The protective resin layer is not particularly limited as long as it is a resin that does not dissolve in the dispersion medium, and examples thereof include polyvinyl alcohol, polyethylene glycol, polyacrylic acid, polyacrylamide, and cellulose derivatives. Or it is preferable to form from a cellulose derivative.

  A layer obtained by applying an aqueous solution of one or a mixture of two or more of the above resins and performing drying or the like is formed. The coating solution can contain additives such as a viscosity modifier.

  The silicon oxide and the resin are applied by the same method as the application of the release resin layer.

  Although the thickness of the said protective layer is not specifically limited, The range of 50-150 nm is preferable. If it is less than 50 nm, the mechanical strength is insufficient, and if it exceeds 150 nm, the strength becomes too high, so that pulverization / dispersion becomes difficult, and peeling may occur at the interface with the metal or alloy layer.

  Further, as exemplified in JP-A-2005-68251, a color material layer may be provided between the “protective layer” and the “metal or alloy layer”.

  The color material layer is introduced to obtain an arbitrary colored composite pigment, and can contain a color material capable of imparting an arbitrary color tone and hue in addition to the metallic luster and glitter of the metallic pigment used in the present invention. If it is, it will not specifically limit. The color material used for the color material layer may be either a dye or a pigment. Moreover, as a dye and a pigment, a well-known thing can be used suitably.

  In this case, the “pigment” used in the color material layer means a natural pigment, a synthetic organic pigment, a synthetic inorganic pigment, or the like defined in the field of general pigment chemistry. Etc., which are different from those processed into a laminated structure.

  A method for forming the color material layer is not particularly limited, but it is preferable to form the color material layer by coating.

  Further, when the color material used in the color material layer is a pigment, it is preferable to further include a color material dispersion resin. Examples of the color material dispersion resin include a pigment, a color material dispersion resin, and other materials as necessary. It is preferable to form a resin thin film by dispersing or dissolving these additives in a solvent and forming a uniform liquid film by spin coating as a solution, followed by drying.

  In the production of the composite pigment base material, it is preferable in terms of work efficiency that both the colorant layer and the protective layer are formed by coating.

  As the composite pigment base material, a layer structure having a plurality of sequential laminated structures of the peeling resin layer, a metal or alloy layer, and a protective layer is also possible. In that case, the total thickness of the laminated structure consisting of a plurality of metal or alloy layers, that is, excluding the sheet-like substrate and the release resin layer immediately above it, metal or alloy-release resin layer-metal or alloy layer, Alternatively, the thickness of the release resin layer-metal or alloy layer is preferably 5000 nm or less. When it is 5000 nm or less, even when the composite pigment base material is rolled up, it is difficult to cause cracking and peeling and is excellent in storage stability. In addition, when pigmented, it is excellent in glitter and preferable.

  Moreover, although the structure where the resin layer for peeling and the metal or alloy layer were laminated | stacked in order on both surfaces of the sheet-like base material surface is mentioned, it is not limited to these.

  The peeling treatment method from the sheet-like substrate is not particularly limited, but is a method that is performed by immersing the composite pigment raw material in a liquid, or ultrasonic treatment is performed at the same time as the immersion in the liquid. A method of pulverizing the composite pigment separated from the treatment is preferred.

  In the pigment obtained as described above, the release resin layer has a role of a protective colloid, and a stable dispersion can be obtained only by performing a dispersion treatment in a solvent. In the ink composition using the pigment, the resin derived from the release resin layer also has a function of imparting adhesiveness to a recording medium such as paper.

[Ink composition]
The ink composition of this embodiment contains the metallic pigment described above, an organic solvent, and a resin.

The concentration of the metallic pigment in the ink composition is preferably 0.1 to 3.0% by weight when only one type of the ink set is a metallic ink in the ink set, preferably 0.25 to 2. It is more preferably 5% by weight, and further preferably 0.5-2% by weight.
The concentration of the metallic pigment in the ink composition is such that when there are a plurality of metallic ink compositions in the ink set, the concentration of the metallic pigment in at least one of the ink compositions is 0. It is preferable that the concentration of the metal pigment in the other at least one ink composition is 1.5 wt% or more and 3.0 wt% or less.

  When the concentration of the metallic pigment in the ink composition is 0.1% by weight or more and less than 1.5% by weight, a glossy surface like a half mirror is obtained by ejecting an amount of ink that cannot sufficiently cover the printing surface, Although a feeling of gloss can be felt, it is possible to print a texture that allows the background to show through, and a high gloss metallic glossy surface can be formed by discharging a sufficient amount of ink to cover the printing surface. Therefore, for example, it is suitable for forming a half mirror image on a transparent recording medium or for expressing a highly glossy metallic glossy surface. Further, when the concentration of the metallic pigment in the ink composition is 1.5% by weight or more and 3.0% by weight or less, the metallic pigment is randomly arranged on the printing surface, so that high gloss cannot be obtained and the matte tone is obtained. A metallic gloss surface can be formed. Therefore, for example, it is suitable for forming a shielding layer on a transparent recording medium.

  The organic solvent is preferably a polar organic solvent such as alcohols (for example, methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, isopropyl alcohol, or fluorinated alcohol), ketones (for example, acetone, methyl ethyl ketone, Or cyclohexanone), carboxylic acid esters (eg, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, or ethyl propionate), or ethers (eg, diethyl ether, dipropyl ether, tetrahydrofuran, Alternatively, dioxane or the like can be used.

  In particular, the organic solvent preferably contains one or more alkylene glycol ethers that are liquid at normal temperature and pressure.

  Alkylene glycol ethers are ethylene glycols based on methyl, n-propyl, i-propyl, n-butyl, i-butyl, hexyl and 2-ethylhexyl aliphatic, allyl with double bonds and phenyl groups. Ether and propylene glycol ether, colorless and odorless, with ether and hydroxyl groups in the molecule, so it is liquid at room temperature with both alcohol and ether properties . Moreover, there are a monoether type in which only one hydroxyl group is substituted and a diether type in which both hydroxyl groups are substituted, and these can be used in combination.

  In particular, the organic solvent is preferably a mixture of alkylene glycol diether, alkylene glycol monoether, and lactone.

  As alkylene glycol monoether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, Diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol Over monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether and the like.

  Examples of the alkylene glycol diether include ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol dibutyl ether, tetra Ethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol dibutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, etc. It is below.

  Examples of the lactone include γ-butyrolactone, δ-valerolactone, and ε-caprolactone.

  By setting it as such a suitable structure, the objective of this invention can be achieved further.

  Examples of the resin used in the ink composition include acrylic resin, styrene-acrylic resin, rosin-modified resin, terpene resin, polyester resin, polyamide resin, epoxy resin, vinyl chloride resin, vinyl chloride-vinyl acetate copolymer. And cellulose resin (for example, cellulose acetate butyrate, hydroxypropyl cellulose), polyvinyl butyral, polyacryl polyol, polyvinyl alcohol, polyurethane and the like.

Non-aqueous emulsion type polymer fine particles (NAD = Non Aqueous Dispersion) can also be used as the resin. This is a dispersion in which fine particles such as a polyurethane resin, an acrylic resin, and an acrylic polyol resin are stably dispersed in an organic solvent.
Examples of the polyurethane resin include Sanprene IB-501 and Sanprene IB-F370 manufactured by Sanyo Chemical Industries, and examples of the acrylic polyol resin include N-2043-60MEX and N-2043-AF-1 manufactured by Harima Chemical. .

  The resin emulsion is preferably added in an amount of 0.1% by weight to 10% by weight in the ink composition in order to further improve the fixability of the pigment to the recording medium. If the addition amount is excessive, the printing stability cannot be obtained, and if it is too small, the fixing property is insufficient.

  The ink composition preferably contains at least one glycerin, polyalkylene glycol, or saccharide. The total amount of the one or more kinds of glycerin, polyalkylene glycol, or saccharide is preferably added in the ink composition in the range of 0.1 wt% to 10 wt%.

  With such a preferable configuration, it is possible to stabilize ink discharge and improve the image quality of the recorded matter while suppressing drying of the ink and preventing clogging.

  The polyalkylene glycol is a linear polymer compound having a repeating structure of an ether bond in the main chain, and is produced, for example, by ring-opening polymerization of a cyclic ether.

  Specific examples of the polyalkylene glycol include polymers such as polyethylene glycol and polypropylene glycol, ethylene oxide-propylene oxide copolymers and derivatives thereof. As the copolymer, any copolymer such as a random copolymer, a block copolymer, a graft copolymer, and an alternating copolymer can be used.

  Preferable specific examples of the polyalkylene glycol include those represented by the following formula.

_{HO- (C n H 2n O)} m -H ( in the above formula, n represents an integer of 1 to 5, m is an integer of 1 to 100)

In the above formula, (C _n H _2n O) _m may be one constant or a combination of two or more numbers within the range of the integer value n. For example, when n is 3, it is (C ₃ H ₆ O) _m , and when n is a combination of 1 and 4, it is (CH ₂ O—C ₄ H ₈ O) _m . Further, the integer value m may be one constant or a combination of two or more numbers within the range. For example, in the above example, when m is a combination of 20 and 40, it is (CH ₂ O) _20- (C ₂ H ₄ O) ₄₀ , and when m is a combination of 10 and 30, (CH ₂ O ) ₁₀ - (a C ₄ H ₈ O) _30. Further, the integer values n and m may be arbitrarily combined within the above range.

  Examples of the saccharide include monosaccharides such as pentose, hexose, heptose, and octose; polysaccharides such as disaccharide, trisaccharide, and tetrasaccharide; or sugar alcohols that are derivatives thereof, reduced derivatives such as deoxyacid, aldonic acid, uronic acid, and the like. Examples include oxidized derivatives, dehydrated derivatives such as glycosene, amino acids, thiosugars, and the like. Polysaccharides refer to sugars in a broad sense and include substances that exist widely in nature, such as alginic acid, dextrin, and cellulose.

  The ink composition preferably contains at least one acetylene glycol surfactant and / or silicone surfactant. The surfactant is preferably added in an amount of 0.01% by weight to 10% by weight with respect to the pigment content in the ink composition.

  By adopting such a suitable configuration, the wettability of the ink composition to the recording medium is improved, and quick fixability can be obtained.

  Examples of acetylene glycol surfactants include Surfinol (registered trademark) 465 (trademark), Surfynol 104 (trademark) (trade name, manufactured by Air Products and Chemicals, Inc.), Olphine STG (trademark), Olfine ( Preferred examples include registered trademark E1010 (trademark) (trade name, manufactured by Nissin Chemical Co., Ltd.) and the like.

  As the silicone surfactant, polyester-modified silicone or polyether-modified silicone is preferably used. Specific examples include BYK-347, BYK-348, BYK-UV3500, BYK-UV3570, BYK-UV3510, BYK-UV3530 (Bic Chemie Japan Co., Ltd.).

  The ink composition can be prepared by a known conventional method. For example, first, after mixing the metallic pigment, the dispersant, and the liquid medium described above, a pigment dispersion is prepared by a ball mill, a bead mill, an ultrasonic wave, a jet mill, or the like, and adjusted to have desired ink characteristics. To do. Subsequently, a binder resin, the liquid medium, and other additives (for example, a dispersion aid or a viscosity modifier) can be added with stirring to obtain a pigment ink composition.

  In addition, the composite pigment base may be sonicated in a liquid medium once to obtain a composite pigment dispersion, and then mixed with the necessary ink liquid medium. The ink composition may be directly subjected to ultrasonic treatment in an ink medium.

  The physical properties of the ink composition are not particularly limited. For example, the surface tension is preferably 20 to 50 mN / m. If the surface tension is less than 20 mN / m, the ink composition may spread or ooze out on the surface of the ink jet recording printer head, making it difficult to eject ink droplets. The surface tension is 50 mN / m. If it exceeds 1, the surface of the recording medium will not spread and good printing may not be possible.

[Ink set]
The ink set of the present embodiment includes a plurality of the ink compositions, and each ink composition has a different metal pigment concentration. Among the ink compositions, the concentration of the metal pigment in at least one ink composition is 0.1 wt% or more and less than 1.5 wt%, and the concentration of the metal pigment in at least one other ink composition is It is preferable that it is 1.5 to 3.0 weight%.

[Recording device]
The recording apparatus of this embodiment is an ink jet recording apparatus provided with the ink set.
Next, the configuration of the recording head 3 of the ink jet recording apparatus will be described. Here, FIG. 1 is a schematic perspective view of the recording head 3 accommodated in a carriage (not shown). FIG. 2 is a cross-sectional view of the ink introduction needle 19 inserted into the ink cartridge.

  The illustrated recording head 3 has a cartridge base 15 (hereinafter referred to as “base”). A head case 16 is attached to the base 15. A flow path unit 17 is attached (arranged) to the tip of the head case 16. The base 15 is formed of, for example, synthetic resin, and a plurality of compartments 15 ′ (liquid storage member mounting portions) are provided on the upper surface thereof.

An ink introduction needle 19 is attached to each section 15 ′ with a mesh filter 18 interposed therebetween. An ink cartridge (not shown) is mounted in these compartments 15 '. That is, the ink cartridge is disposed on the base 15. Details of the ink introduction needle 19 inserted into the ink cartridge will be described later.
A circuit board 20 is attached to the other surface of the base 15 on the side opposite to the section 15 '. And this circuit board 20 is attached to the base 15 via the sheet | seat member 21 which functions as packing.

  The head case 16 is fixed to the base 15 and is a casing for housing the vibrator unit 22 having a piezoelectric vibrator. And the flow path unit 17 is being fixed to the front end surface on the opposite side to the attachment surface of the base 15 of the head case 16 with the adhesive agent. The flow path unit 17 is manufactured by sequentially laminating the elastic plate 23, the flow path forming substrate 24, and the nozzle plate 25, and fixing and integrating them with an adhesive or the like.

  Here, the nozzle plate 25 is a plate-like member made of, for example, a stainless steel thin plate, and fine nozzle openings 26 are formed in a row at a pitch corresponding to the dot formation density of the printer. Moreover, the head cover 27 is comprised by the metal thin plate member, for example.

  As shown in FIG. 2, the ink introduction needle 19 to be inserted into the ink cartridge is a hollow needle having an upstream tip formed conically and having an ink introduction path 41 formed therein. Is formed in a tapered shape that expands from the upstream side toward the downstream side. In addition, an ink introduction hole 42 that connects the external space and the ink introduction path 41 is formed at the distal end side of the ink introduction needle 19.

  The ink introduction needle 19 is attached to the base 15 by ultrasonic welding, for example, with the mesh filter 18 interposed. As a result, the ink introduction path 41 of the ink introduction needle 19 and the ink communication path 37 of the head case 16 communicate with each other.

  When an ink cartridge (not shown) is attached to the section 15 ′ of the base 15, the ink introduction needle 19 is inserted into the needle insertion opening of the ink cartridge, and the ink introduction into the ink cartridge inner space and the ink introduction needle 19 is introduced. The passage 41 communicates with the ink introduction hole 42. Thereafter, the ink stored in the ink cartridge is introduced into the ink introduction path 41 through the ink introduction hole 42 and ejected from the nozzle opening 26 through the ink communication path 37.

  Here, when the diameter of the nozzle opening 26 of the recording head 3 of the ink jet recording apparatus is L μm and the opening of the mesh filter 18 provided in the ink introduction path 41 is W μm, the nozzle diameter Lμm and the opening of the mesh filter are set. It is preferable that the eye W μm satisfies the relationship of L ≧ 5W. When the ink composition containing the pigment dispersion liquid of the present embodiment is used in an ink jet recording apparatus that satisfies such a relationship, clogging of the metallic pigment at the nozzle opening 26 is prevented, and the ejection stability of the ink composition is ensured. From this viewpoint, when the average particle diameter of the equivalent circle diameter obtained from the area of the XY plane of the tabular grains is R μm, the number of tabular grains satisfying the condition of R> (L / 5) is the tabular grains. It is preferable that it is 5% or less of the whole number.

[Inkjet recording method]
In the ink jet recording method of the present embodiment, recording is performed by discharging droplets of the ink composition and attaching the droplets to a recording medium.
From the viewpoint of angle dependency, the measured values of 20 °, 60 °, and 85 ° specular gloss on the recording medium according to JIS Z8741 have a metallic luster that indicates values of 200, 200, 100 or more at the same time, respectively. It is preferable to form an image, and the measured values of 20 °, 60 °, and 85 ° specular gloss specified in JIS Z8741 are preferably 400, 400, and 100 or more at the same time, respectively, and specified in JIS Z8741. More preferably, the measured values of 20 °, 60 °, and 85 ° specular gloss are 600, 600, and 100 or more at the same time, respectively.

  Images with measured values of 20 °, 60 °, and 85 ° specular gloss specified in JIS Z8741 that are simultaneously 200 or more and less than 400, 200 or more and less than 400, and 100 or more are matte. Has a metallic luster.

  Images with measured values of 20 °, 60 °, and 85 ° specular gloss specified in JIS Z8741 of 400 or more and less than 600, 400 or more and less than 600, and 100 or more are reflected in the formed image. It has a glossy metallic luster so that the object can be distinguished slightly.

  An image having a metallic luster in which measured values of specular gloss of 20 degrees, 60 degrees, and 85 degrees specular gloss specified in JIS Z8741 are values of 600 or more, 600 or more, and 100 or more are sharp and formed. The object has a gloss that allows the object reflected in the image to be clearly distinguished, that is, a metallic luster having a so-called “mirror gloss”.

  Therefore, according to the ink jet recording method of the present embodiment, the measured values of 20 °, 60 °, and 85 ° specular gloss on the recording medium are 200, 200, and 100 or more simultaneously, respectively. By appropriately combining images having a metallic luster indicating the above, an image having a desired metallic luster can be formed from a matte tone image to a glossy image.

  On the other hand, when the measured values of 20 °, 60 °, and 85 ° specular gloss do not show values of 200, 200, and 100 or more, such images do not feel metallic gloss when visually observed, and are gray. As observed. In addition, the effect of the present invention cannot be obtained even when any of the measured values of 20 °, 60 °, and 85 ° specular gloss does not show a value greater than or equal to the above value.

The discharge amount of the ink composition discharged onto the recording medium is preferably 0.1 to 100 mg / cm ² from the viewpoint of securing metallic luster, the viewpoint of the printing process, and the cost. More preferably, it is -50 mg / cm < ² >.

The dry weight of the metallic pigment that forms an image on the recording medium is preferably 0.0001 to 3.0 mg / cm ² from the viewpoint of metallic luster, printing process, and cost. The lower the dry weight of the metallic pigment, the more glossy metallic surface can be formed. Therefore, for example, it is suitable for forming a half mirror image on a transparent recording medium. Further, the higher the dry weight of the metallic pigment, the more matte metallic glossy surface can be formed. Therefore, for example, it is suitable for forming a shielding layer on a transparent recording medium.

  Examples of the method for discharging the ink composition include the methods described below.

  As a first method, there is an electrostatic suction method, in which a strong electric field is applied between the nozzle and the acceleration electrode placed in front of the nozzle, and ink is continuously ejected from the nozzle in the form of droplets. This is a method in which a print information signal is applied to the deflection electrode while the ink droplet is flying between the deflection electrodes and recorded, or a method in which the ink droplet is ejected in response to the print information signal without being deflected.

  The second method is a method in which ink droplets are forcibly ejected by applying pressure to the ink liquid with a small pump and mechanically vibrating the nozzle with a crystal resonator or the like. The ejected ink droplet is charged simultaneously with the ejection, and a printing information signal is given to the deflection electrode and recorded while the ink droplet flies between the deflection electrodes.

  The third method is a method using a piezoelectric element (piezo element), in which pressure and a print information signal are simultaneously applied to an ink liquid by a piezoelectric element to eject and record ink droplets.

  The fourth method is a method in which the ink liquid is rapidly expanded in volume by the action of heat energy, and the ink liquid is heated and bubbled by a microelectrode in accordance with a print information signal to eject and record ink droplets.

  Any of the above methods can be used in the ink jet recording method of the present embodiment, but from the viewpoint of high-speed printing, the method of discharging the ink composition is preferably a non-heating method. That is, it is preferable to employ the first method, the second method, or the third method.

  There are no particular restrictions on the recording medium. For example, plain paper, inkjet paper (matte paper, glossy paper), plastic films such as glass and PVC, films with a plastic or receiving layer coated on a substrate, metal, printed wiring Various recording media such as a substrate can be used.

  When the recording medium has an ink receiving layer, it is preferable to print the recording medium without heating from the viewpoint of not causing thermal damage.

  On the other hand, when the recording medium does not have an ink receiving layer, it is preferable to print by heating the recording medium from the viewpoint of increasing the drying speed and obtaining high gloss.

  Heating is performed without bringing the recording medium into contact with the recording medium, such as heating by bringing a heat source into contact with the recording medium, irradiating infrared rays or microwaves (electromagnetic waves having a maximum wavelength of about 2,450 MHz), or blowing hot air. The method etc. are mentioned.

  The heating is preferably performed before printing and / or simultaneously with printing and / or after printing. In other words, the recording medium may be heated before printing, simultaneously, or after printing, and may be heated throughout printing. The heating temperature depends on the type of the recording medium, but is preferably 30 to 80 ° C, more preferably 40 to 60 ° C.

[Recordings]
The recorded matter of this embodiment is recorded by the inkjet recording method. Since this recorded matter was obtained by the above-described ink jet recording method using the above-described ink set, the 20 °, 60 °, and 85 ° specular gloss values were respectively 200, 200, and 100 or higher. A recorded matter having a metallic mirror gloss can be obtained. Further, since the metallic pigment concentration of the ink composition provided in the ink set differs depending on each ink composition, it is possible to simultaneously form an arbitrary metallic gloss from mirror gloss to matte.

[Example A]
1. Preparation of metallic pigment dispersion On a PET film having a film thickness of 100 μm, cellulose acetate butyrate (butylation rate: 35 to 39%, manufactured by Kanto Chemical Co., Ltd.) 3.0% by weight and diethylene glycol diethyl ether (manufactured by Nippon Emulsifier Co., Ltd.) 97% by weight % Resin layer coating solution was uniformly applied by the bar coating method and dried at 60 ° C. for 10 minutes to form a resin layer thin film on the PET film.

  Next, the aluminum vapor deposition layer with an average film thickness of 20 nm was formed on said resin layer using the vacuum vapor deposition apparatus (VE-1010 type vacuum vapor deposition apparatus by a vacuum device company).

  Next, the laminate formed by the above method is simultaneously peeled, refined, and dispersed in diethylene glycol diethyl ether using a VS-150 ultrasonic disperser (manufactured by ASONE), and integrated ultrasonic dispersion treatment. A metallic pigment dispersion having a time of 12 hours was prepared.

  The obtained metallic pigment dispersion was filtered with a SUS mesh filter having an opening of 5 μm to remove coarse particles. Subsequently, the filtrate was put into a round bottom flask, and diethylene glycol diethyl ether was distilled off using a rotary evaporator. Thereby, the metallic pigment dispersion was concentrated, and then the concentration of the metallic pigment dispersion was adjusted to obtain a metallic pigment dispersion 1 having a concentration of 5% by weight.

  Moreover, the metallic pigment dispersion liquids 2-11 which have a metallic pigment which changed vapor deposition conditions and / or ultrasonic dispersion time were obtained.

  Then, using a particle diameter / particle size distribution measuring apparatus (FPIA-3000S manufactured by Sysmex Corporation), 50% average particle diameter R50 of the equivalent diameter of the major axis (X direction) -minor axis (Y direction) plane of each metallic pigment, The average film thickness Z was measured, and R50 / Z was calculated based on the measured values of R50 and Z obtained. The particle size distribution value (CV value) was determined by the following formula: CV value = standard deviation of particle size distribution / average value of particle diameter × 100. The results are shown in Table 1.

2. Preparation of Metallic Pigment Ink Composition Metallic pigment ink compositions having the compositions shown in Tables 2 and 3 were prepared using the metallic pigment dispersion prepared by the above method. After mixing and dissolving the solvent and additives to make an ink solvent, the metallic pigment dispersion is added to the ink solvent, and further mixed and stirred with a magnetic stirrer at room temperature and normal pressure for 30 minutes to form a metallic pigment ink. It was set as the composition.

  In Tables 2 and 3, diethylene glycol diethyl ether (DEGDE), dipropylene glycol monobutyl ether (DPGMB), and tetraethylene glycol dimethyl ether (TEGDM) manufactured by Nippon Emulsifier Co., Ltd. were used. Further, γ-butyrolactone was manufactured by Kanto Chemical. Further, N-2043-60MEX and N-2043-AF-1 (resin emulsion) were manufactured by Harima Chemicals, and BYK-3500 (surfactant) was manufactured by Big Chemie Japan. The unit is% by weight.

3. Evaluation Test (1) Ejection Stability Using an inkjet printer EM-930C (manufactured by Seiko Epson Corporation), the ink composition is filled into a black row, and solid at room temperature on photographic paper <glossy> (model number: KA450PSK) manufactured by the same company. Printing was done.
At this time, the nozzle diameter (L) of the ink jet printer was 25 μm, and the opening (W) of the mesh filter provided in the ink flow path was 5 μm. Therefore, the ink jet printer used had a relationship of L = 5W. In addition, the average particle diameter (R) of the equivalent circle diameter obtained from the area of the XY plane of the tabular grains contained in the ink composition is related to the nozzle diameter (L) of the inkjet printer. The ratio (%) of the number of tabular grains satisfying the condition of R> (L / 5) was calculated.

About the obtained solid image, the presence or absence of the discharge defect (nozzle omission) was observed visually, and discharge stability was evaluated according to the following evaluation criteria. “Nozzle missing” means that the ink that should normally be ejected from the nozzles attached to the print head is not ejected due to nozzle clogging and affects the printing result. The evaluation results are shown in Table 3 together with the ratio (%) of the number of tabular grains satisfying the condition of R> (L / 5).
AA: Even if 30 sheets of A4 size solid images are continuously printed, no ejection defect (nozzle missing) occurs.
A: Even when 10 A4 size solid images are printed continuously, no ejection defect (nozzle missing) occurs.
B: When continuous images of A4 size are continuously printed, ejection defects (nozzle missing) occur in less than 10 sheets from the second sheet.
C: When continuously printing A4 size solid images, ejection defects (nozzle missing) occur on the first sheet.

(2) Glossiness measurement Using an inkjet printer EM-930C (manufactured by Seiko Epson Corporation), on a photographic paper <glossy> (model number: KA450PSK) manufactured by the company having an ink receiving layer filled with an ink composition in a black row. The solid printing was performed at room temperature. At this time, the discharge amount of the ink composition was 1.2 mg / cm ² , and the dry weight of the metal pigment was 12 μg / cm ² . The glossiness of the obtained image was measured using a gloss meter (MULTITI Gloss 268 manufactured by Konica Minolta). The results are shown in Tables 4 and 5.

(3) Evaluation of thermal printing Using an inkjet printer SJ-540 (manufactured by Roland DG), the ink composition of Example 1 is filled in a yellow row, and glossy PVC without an ink receiving layer (with gray glue) (model number) : SP-SG-1270G) was subjected to solid printing and heat drying. Subsequently, the glossiness of the obtained image was measured using a photometer (MULTI Gloss 268 manufactured by Konica Minolta). Table 6 shows the results and heating conditions. The heating conditions were the case where heating was performed at 40 ° C. during printing (Example 9), and the case where printing was performed at room temperature and then heated with a dryer at 60 ° C. (Example 10). As a control, the case where only normal temperature printing was performed and no heating was performed (reference example) was also examined.
Similarly, the same example (Example 15) as Example 9 was examined except that the ink composition of Example 13 was used.

[Example B]
1. Preparation of metallic pigment dispersion A metallic content dispersion was prepared in the same manner as in Example A.

2. Preparation of metallic pigment ink composition Using the metallic pigment dispersion prepared in Example A, metallic pigment ink compositions having the compositions shown in Tables 8 to 9 were prepared. After mixing and dissolving the solvent and additives to make an ink solvent, the metallic pigment dispersion is added to the ink solvent, and further mixed and stirred with a magnetic stirrer at room temperature and normal pressure for 30 minutes to form a metallic pigment ink. It was set as the composition.

  In Tables 8 to 9, diethylene glycol diethyl ether (DEGDE) and tetraethylene glycol dimethyl ether (TEGDM) manufactured by Nippon Emulsifier Co., Ltd. were used. Further, γ-butyrolactone was manufactured by Kanto Chemical. Further, N-2043-60MEX and N-2043-AF-1 (resin emulsion) were manufactured by Harima Chemicals, and BYK-3500 (surfactant) was manufactured by Big Chemie Japan. The unit is% by weight.

3. Evaluation test (1) Measurement of glossiness Photographic paper <gloss> made by the company having an ink receiving layer filled with an ink composition using an ink jet printer EM-930C (manufactured by Seiko Epson) (model number: KA450PSK) ) Solid printing was performed at room temperature. At this time, the discharge amount of the ink composition was 1.2 mg / cm ² , and the dry weight of the metal pigment was 12 μg / cm ² . The glossiness of the obtained image was measured using a gloss meter (MULTITI Gloss 268 manufactured by Konica Minolta). Furthermore, sensory evaluation of the printed matter was performed based on the following evaluation criteria. The results are shown in Tables 10 and 11.
AA: Specular Gloss (The reflected object can be distinguished well. With sharpness)
A: Gloss (metallic luster is felt but there is no sharpness)
B: Matte tone (matte metallic luster)
C: Gray tone (metal luster is not felt and is observed as gray)

  From the above results, it was found that the ink compositions (Examples 16 to 20) used in the ink set of the present invention can form images having different metallic luster depending on the concentration of the metallic pigment. Therefore, an ink set provided with ink compositions having different concentrations of metallic pigments has a high metal specular gloss indicating 20 °, 60 °, and 85 ° specular gloss values of 200, 200, and 100, respectively, and From the specular gloss, it became clear that a mat-like print could be printed at the same time.

  DESCRIPTION OF SYMBOLS 3 ... Recording head, 15 ... Base, 16 ... Head case, 17 ... Flow path unit, 18 ... Mesh filter, 19 ... Ink introduction needle, 20 ... Circuit board, 21 ... Sheet member, 22 ... Vibrator unit, 23 ... Elastic plate, 24 ... flow path forming substrate, 25 ... nozzle plate, 26 ... nozzle opening, 27 ... head cover, 37 ... ink communication port, 41 ... ink introduction path, 42 ... ink introduction hole.

Claims (9)

Used in an ink jet recording apparatus in which the nozzle diameter L μm of the ink jet head and the opening W μm of the mesh filter provided in the ink flow path satisfy the condition of L ≧ 5 W;
Containing a metal pigment and an organic solvent,
When the metal pigment is aluminum or an aluminum alloy and is a tabular grain, and the major axis on the plane of the tabular grain is X, the minor axis is Y, and the thickness is Z, the X- The 50% average particle diameter R50 of the equivalent circle diameter determined from the area of the Y plane is 0.5 to 3 μm, and satisfies the condition of R50 / Z> 5,
It said tabular grains, satisfies the number of tabular grains of R> (L / 5) in relation to the particle diameter Rμm of the equivalent circle diameter determined from the area of the X-Y plane of its said nozzle diameter Lμm is, An ink composition having 5% or less of the number of tabular grains.   The ink composition according to claim 1, wherein the maximum particle diameter Rmax of the equivalent circle diameter obtained from the area of the XY plane of the tabular grains is 10 μm or less. The ink composition according to claim 1 or 2 , wherein the concentration of the metal pigment in the ink composition is 0.1 to 3.0% by weight. The ink composition according to any one of claims 1 to 3 , comprising at least one acetylene glycol-based and / or silicone-based surfactant. Ejecting droplets of the ink composition according to any one of claims 1 to 4, an ink jet recording method for performing recording by depositing the droplets onto a recording medium. The inkjet recording method according to claim 5 , wherein the ejection amount of the ink composition ejected onto the recording medium is 0.1 to 100 mg / cm ² . The recording medium is heated for recording, ink jet recording method according to claim 5 or 6. A recorded matter recorded by the ink jet recording method according to any one of claims 5 to 7 . An ink jet recording apparatus comprising: an ink jet head having a nozzle for discharging an ink composition; and an ink flow path for supplying the ink composition to the ink jet head,
The ink flow path includes a mesh filter,
The nozzle diameter L μm of the nozzle and the opening W μm of the mesh filter satisfy the condition of L ≧ 5 W,
The ink composition contains a metal pigment and an organic solvent,
The metal pigment is aluminum or an aluminum alloy and is a tabular grain. When the major axis on the plane of the tabular grain is X, the minor axis is Y, and the thickness is Z, the X- The 50% average particle diameter R50 of the equivalent circle diameter determined from the area of the Y plane is 0.5 to 3 μm, and satisfies the condition of R50 / Z> 5,
It said tabular grains, satisfies the number of tabular grains of R> (L / 5) in relation to the particle diameter Rμm of the equivalent circle diameter determined from the area of the X-Y plane of its said nozzle diameter Lμm is, An ink jet recording apparatus that is 5% or less of the total number of tabular grains.

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