JP2007118530A - Inkjet recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an inkjet recording medium has superior cutting strength and peel strength while maintaining high gloss, printing density and ink absorbency. <P>SOLUTION: This inkjet recording medium is manufactured in such a manner that a water-absorbing inorganic pigment, a lower-layer coating composition and an upper-layer coating composition are sequentially applied onto an air-permeable substrate and subjected to casting treatment. The lower-layer coating composition contains a dispersion of a polyurethane resin, in which tensile strength specified by JIS K7311 is in the range of 30-70 MPa, in which elongation specified by JIS K7311 is in the range of 300-800%, and in which a particle diameter measured by a dynamic light scattering method is in the range of 10-100 nm. The upper-layer coating composition contains a submicronic pigment and polyvinyl alcohol. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink jet recording medium having excellent cutting strength and peeling strength while maintaining good gloss, print density, and ink absorbency.

  In recent years, the technology of inkjet printers has advanced rapidly, and it has become possible to obtain recorded matter having an image quality equivalent to or higher than that obtained by a general silver salt photography method. Along with this, there is a demand for ink jet recording media having the same texture as photographic paper used in silver salt photography.

  Conventionally, cast coated paper as proposed in Patent Document 1 has been used as a glossy inkjet recording medium. However, although the recording medium produced by the present technology has a certain degree of gloss, it cannot be said that the surface strength is low and the surface strength is equivalent to that of photographic paper used for silver salt photography.

  In the present invention, the surface strength refers to the difficulty of scratching the surface of the coating layer of the ink jet recording medium, and the cutting strength refers to the removal of dust when the ink jet recording medium is cut with a sharp object such as a cutter. Peel strength refers to the difficulty of peeling off the coated film when a sticky tape such as cellophane tape is attached to an ink jet recording medium, and these are independent of each other. Even in an ink jet recording medium having extremely excellent strength, the peel strength is often extremely low.

  In patent document 2, in order to solve this subject, it is proposed to harden a coating layer with an electron beam. However, a curing apparatus using an electron beam is generally large and has a problem that its maintenance and adjustment are extremely complicated. Further, when the ink jet recording medium is put into practical use, the weak cutting strength has been a problem.

  As a new means, Patent Document 3 proposes to use an ethylene / vinyl acetate copolymer as a binder for the lower layer. Although this improves the cutting strength, there is a disadvantage that smoothening by thermocompression between the coating layer and the mirror surface at the time of casting becomes difficult to achieve with the increase in strength, and sufficient gloss cannot be obtained.

  Therefore, in Patent Document 4 and Patent Document 5, the balance between glossiness and cutting strength is achieved by a combination of two types of resins characterized by the elongation percentage of the binder of the ink receiving layer and the tensile strength. However, there is a drawback that the cutting strength is not sufficient.

Further, in Patent Document 6, it is proposed that the surface strength of the coating layer is improved by using a polyurethane resin as a binder for the ink receiving layer. There was a problem that the strength was weak.
Japanese Patent Publication No. 7-55579 JP 2004-330725 A JP 2004-114475 A JP 2005-1332 A JP 2005-1334 A JP 2004-306450 A

  An object of the present invention is to provide an ink jet recording medium that is excellent in cutting strength and peel strength while maintaining high glossiness, printing density, and ink absorbency.

  As a result of examining the above problems, a water-absorbing inorganic pigment, a tensile strength specified in JIS K7311 of 30 to 70 MPa, and an elongation specified in JIS K7311 of 300 to 800% are formed on a gas-permeable support. The lower layer coating composition containing a polyurethane resin dispersion having a particle diameter measured by a dynamic light scattering method of 10 to 100 nm, and the upper layer coating composition containing a submicron pigment and polyvinyl alcohol are sequentially applied. The ink jet recording medium that has been processed and casted can provide an ink jet recording medium that is excellent in cutting strength and peel strength while maintaining high gloss, print density, and ink absorbency.

  Furthermore, when the particle diameter measured by the dynamic light scattering method of the polyurethane resin dispersion is 10 to 60 nm, it is possible to provide an ink jet recording medium having particularly excellent peel strength.

  Furthermore, since the polyurethane resin is a self-emulsifying type dispersion, it has become possible to provide an ink jet recording medium having particularly excellent peel strength.

  Further, since the polyurethane resin is an aliphatic polyurethane resin, it is possible to provide an ink jet recording medium having particularly excellent cutting strength.

  Furthermore, it has become possible to provide an ink jet recording medium having particularly high ink absorptivity when the polyurethane resin is a polyether-based or polycarbonate-based polyurethane resin.

  Furthermore, since the polyurethane resin is anionic, it is possible to provide an ink jet recording medium capable of obtaining a particularly high printing density.

  According to the present invention, it is possible to provide an ink jet recording medium excellent in cutting strength and peeling strength while maintaining high glossiness, printing density, and ink absorbability.

  In the present invention, paper is usually used as the air-permeable support, but a support other than paper such as a nonwoven fabric can be used as necessary.

  In the present invention, the lower layer refers to a coating layer formed on the side closer to the support of the recording medium, and the lower layer coating composition refers to a liquid composition for drying to form a lower layer. In the present invention, the upper layer refers to a coating layer formed on the side closer to the surface of the recording medium, and the upper layer coating composition refers to a liquid composition for drying to form an upper layer. These coating compositions are usually used in the form of an aqueous liquid in which each material is dissolved or dispersed in water. In the present invention, the lower layer and the upper layer are usually adjacent to each other, but one or two or more intermediate layers may be provided between the lower layer and the upper layer, as long as the interaction between the lower layer and the upper layer is not strongly inhibited. One or two or more coating layers may be provided between the lower layer and the support and on the upper surface side.

  In the present invention, the cast treatment refers to pressing a coated layer in a wet state onto a heated mirror surface, transferring the mirror surface shape to the surface of the coating layer, and removing moisture from the coated layer to dry the recording medium. Refers to the process to be granted. The apparatus used for the casting process (casting apparatus) is usually an apparatus having a structure in which the coated paper is continuously crimped to the surface of the cylinder whose surface is chrome-plated using an elastic roll. A device having another structure having the same action may be used. The so-called rewetting method, in which the coating method used in producing the ink jet recording medium of the present invention is a so-called rewetting method in which the coating composition is once dried after being applied and then re-applied with moisture, and then pressure-bonded to the mirror surface of the casting apparatus. Examples of methods such as a so-called direct method in which a coating composition or both upper and lower coating compositions are coated and then directly applied to the mirror surface of a casting apparatus without being dried can be exemplified, but are not limited thereto. is not.

  In the present invention, the water-absorbing inorganic pigment means that water is used in place of linseed oil, and when a test according to the test method for oil absorption defined in JIS K 5101 is performed, 100 ml or more of water per 100 g is reached by the end point. Examples of inorganic pigments used include heavy calcium carbonate, light calcium carbonate, wet synthetic silica, diatomaceous earth, calcium silicate, talc, magnesium hydroxide, halloysite, activated clay, acid clay, hydrotalc. Site, alumina hydrate, aluminum hydroxide, bentonite clay, zeolite, kaolin, calcined kaolin, gypsum, titanium oxide, barium sulfate and the like. One of these pigments may be used alone, or two or more thereof may be used in combination.

  Among such water-absorbing inorganic pigments, wet synthetic silica is particularly preferably used because an inkjet recording medium having good ink absorbability can be obtained even with a small coating amount. In the present invention, wet synthetic silica refers to porous silicon dioxide obtained by mixing a silicate such as sodium silicate and an acid such as sulfuric acid, followed by steps such as washing, aging and pulverization. As the production method, a precipitation method and a gel method are known, and any of them can be preferably used for the lower layer coating composition of the present invention.

  The oil absorption amount of the wet synthetic silica used in the lower layer coating composition of the present invention is preferably higher from the viewpoint of ink absorbency. On the other hand, if the oil absorption amount is too high, the strength of the coating layer may decrease. Absent. Specifically, the oil absorption of the wet synthetic silica used for the lower layer coating composition of the present invention is preferably 1 to 5 ml / g, more preferably 2 to 4 ml / g. Moreover, since the particle size of the wet synthetic silica used for the lower layer coating composition of the present invention is too small, the viscosity of the coating composition becomes high and the coating operation may be difficult. The gloss of the recording medium after the casting process is not preferable because it may be difficult to express. Specifically, the particle size of the wet synthetic silica used in the lower layer coating composition of the present invention measured by the Marvin method is preferably 2 to 20 μm, more preferably 3 to 15 μm.

  In the present invention, the polyurethane resin refers to a polymer obtained by reacting a compound having two or more isocyanate groups with a compound having two or more active hydrogen groups, and is obtained by reacting an isocyanate with a polyvalent active hydrogen compound. A case where the obtained bond is other than a urethane bond such as a urea bond is also included.

  As the polyurethane resin used in the present invention, a urethane polymer is mixed with water in the presence of a surfactant and dispersed in water by applying a strong shearing force, or an acetone solution of a polyurethane resin is mixed and emulsified with water. A dispersion in which a polyurethane resin is dispersed in the form of fine particles in an aqueous medium can be used by a so-called acetone method in which acetone is volatilized and removed under reduced pressure.

  The compound having two or more isocyanate groups is not particularly limited, and examples thereof include chain aliphatic isocyanates such as tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate, 1,3-cyclohexylene diisocyanate, 1,4-cyclohexylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 3,3'-dimethyl-4,4'-dicyclohexylmethane diisocyanate, etc. Aliphatic isocyanate having a cyclic structure of 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-phenylene dii Cyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 3,3 ' -Dimethoxy-4,4'-biphenylene diisocyanate, 3,3'-dichloro-4,4'-biphenylene diisocyanate, 1,5-naphthalene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate Aromatic isocyanates such as One of these may be used alone, or two or more thereof may be used in combination. Among these isocyanates, since a flexible coating film can be formed, an aliphatic isocyanate is particularly preferable in terms of cutting strength. In the present invention, an aliphatic polyurethane resin using an aliphatic isocyanate is preferably used.

  A compound having two or more active hydrogen groups includes polyhydric alcohols and polyamines. Examples of the polyhydric alcohol include polyester polyols, polyether polyols, polycarbonate polyols, polyacetal polyols, polyacrylate polyols, polyester amide polyols, polythioether polyols, polyolefin polyols such as polybutadienes, and the like. Polycarbonate polyol is particularly preferable, and in the present invention, it is preferable to use a polyether-based polyurethane resin using a polyether polyol or a polycarbonate-based polyurethane resin using a polycarbonate polyol.

  As the polyester polyol, polyester obtained by dehydration condensation reaction of polyvalent carboxylic acid and polyhydric alcohol, polyester obtained by ring-opening polymerization reaction of cyclic ester, polyester obtained by condensation polymerization of hydroxycarboxylic acid, or , And these copolyesters.

  Examples of the polyvalent carboxylic acid include succinic acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dimer acid, maleic acid, fumaric acid and other aliphatic dicarboxylic acids, and 1,4-cyclohexanedicarboxylic acid. Aliphatic dicarboxylic acids such as polymellitic acids, polyfunctional carboxylic acids such as trimellitic acid, pyromellitic acid and cyclohexanetricarboxylic acid and their anhydrides or ester-forming derivatives, terephthalic acid, isophthalic acid, phthalic acid, 1 Fragrance such as 1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, naphthalic acid, biphenyldicarboxylic acid, 1,2-bis (phenoxy) ethane-p, p'-dicarboxylic acid Group dicarboxylic acids and their anhydrides or ester-forming derivatives It can be. These polyvalent carboxylic acids may be used alone or in combination of two or more. Examples of cyclic esters that can be used include ε-caprolactone and γ-valerolactone. Moreover, as hydroxycarboxylic acid, p-hydroxybenzoic acid, lactic acid, etc. can be used.

  On the other hand, as the polyhydric alcohol, ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, Neopentyl glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, 3-methyl-1,5-pentanediol, 2-butyl-2-ethyl 1,3-propanediol, With aliphatic diols such as 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, hydrogenated bisphenol A, bisphenol A, hydroquinone, bishydroxyethoxybenzene and their alkylene oxides Body polyols, also glycerol as a multifunctional component, trimethylolpropane, polyols such as pentaerythritol, and the like. These may be used alone or in combination of two or more.

  The polyether polyol may be used alone or in combination with a cyclic ether compound such as ethylene oxide, propylene oxide, butylene oxide, styrene oxide, tetrahydrofuran, or epichlorohydrin, using a compound having an active hydrogen atom as a catalyst. A polymer obtained by, for example, mixing ring-opening polymerization by mixing more than one species. Specific examples include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. These may be used alone or in combination of two or more.

  Examples of the polycarbonate polyol include diols such as 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, polyethylene glycol, polypropylene glycol, or polytetramethylene glycol, and phosgene. And a reaction product with a dialkyl carbonate such as dimethyl carbonate or a cyclic carbonate such as ethylene carbonate. These may be used alone or in combination of two or more.

  Examples of the polyvalent amines described above as the constituent components of the polyurethane resin include 1,2-diaminoethane, 1,2- or 1,3-diaminopropane, 1,2- or 1,3- or 1,4- Diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, piperazine, N, N′-bis- (2-aminoethyl) piperazine, 1-amino-3-aminomethyl-3,5,5-trimethyl Cyclohexane (isophoronediamine), bis- (4-aminocyclohexyl) methane, bis- (4-amino-3-butylcyclohexyl) methane, 1,2-, 1,3- or 1,4-diaminocyclohexane or 1, Diamines such as 3-diaminopropane, polyamines such as diethylenetriamine and triethylenetetramine, hydrazine, or azide Hydrazine derivatives such as phosphate dihydrazide, N-(2-sulfoethyl) ethylenediamine metal salt and 2-(beta-amino alkyl - amino propionamide) - can be used diaminosulphonate such as alkane sulfonic acid salts. These may be used alone or in combination of two or more.

  The polyurethane resin used in the present invention has a tensile strength specified in JIS K7311 of 30 to 70 MPa, an elongation specified in JIS K7311 of 300 to 800%, and a particle diameter measured by a dynamic light scattering method of dispersion. Is required to be 10 to 100 nm, and strong cutting strength and peel strength are exhibited for the first time within the range. And even if any one of these three physical properties is missing, the cutting strength and peel strength are greatly reduced. Furthermore, when a dispersion of polyurethane resin having a particle size of 10 to 60 nm is used, further improvement in peel strength is observed, which is more preferable.

  The test piece used for the test was a 150 μm-thick film obtained by drying the resin for 1 day under the conditions of 23 ° C. and 65% RH and then drying at 150 ° C. for 5 minutes. The tensile strength and elongation were measured using an autograph AG-IS manufactured by Shimadzu Corporation according to the method defined in JIS K7311 under the condition of a tensile speed of 300 mm / min.

  The polyurethane resin is forced emulsified by applying a high mechanical shear force in the presence of a surfactant, and hydrophilicity is imparted by introducing a polar group into the molecular chain, helping the surfactant. And self-emulsifying type stably dispersed in water. Among them, the self-emulsification type is preferable because the peel strength is further increased. Although this mechanism is not clear, the self-emulsifying type is considered to contain more polar groups in the molecular chain than the forced emulsifying type, and that it improves the adhesion to other adjacent layers.

  Self-emulsifying polyurethane resins can be either cation type (amino group etc. introduced), anion type (carboxyl group or sulfone group etc. introduced), nonion type (polyethylene glycol group etc. introduced) depending on the type of polar group to be introduced. being classified. Among these, it is preferable to use an anionic polyurethane resin because a particularly high printing density can be obtained. Although this principle has not been clarified, in general, water-based inks are anionic. By making the upper layer cationic and the lower layer anionic, the dye component of the ink can be prevented from penetrating into the lower layer, and the dye component can be efficiently used. It is thought that it will be possible to remain in the upper layer.

  In the present invention, if the amount of the polyurethane resin added to the lower layer coating composition is too small, the cutting strength and the peel strength may not be sufficiently obtained. If the amount is too large, the absorbability of the ink solvent may be insufficient. Since the gloss after casting may not be sufficiently obtained, the mass ratio of polyurethane resin / water-absorbing inorganic pigment is preferably 20/100 to 60/100, and preferably 25/100 to 40/100. It is more preferable.

  In the present invention, the submicron pigment means that when the dispersion is dispersed on a substrate and observed with a scanning electron microscope, 80% or more of the area occupied by the particles in the observation field is composed of particles having a long side of 1 μm or less. It refers to the occupied inorganic pigment. The type of submicron pigment used in the upper layer coating composition of the present invention is not particularly limited, but examples include gel method silica, precipitation method silica, colloidal silica, gas phase method silica, gas phase method alumina, and pseudoboehmite. it can. In particular, it is preferable to use an inorganic pigment in which particles having a long side of 400 nm or less occupy 80% or more of the area occupied by the particles in the observation field because particularly high surface gloss can be obtained. Further, when an inorganic pigment occupying 80% or more of the area occupied by the particles in the observation field and particles having a long side of 100 nm or more is used, the coating layer is torn even if the upper coating composition is dried at high speed after coating. This is preferable because defects such as

As the submicron pigment used in the upper layer coating composition of the present invention, a pigment having a specific surface area of a certain level or more is preferable because a high printing density can be obtained. On the other hand, if the specific surface area is too large, the ink absorptivity may decrease, which is not preferable. Specifically, it is preferable to use one having a specific surface area of 60 to 600 m ² / g by the BET method, and more preferably 150 to 400 m ² / g. In addition, the pigment having such a specific surface area is usually a pigment formed by forming a higher order structure in which primary particles having a diameter of several tens of nm or less are combined and voids are formed inside the primary particles.

  In the present invention, when the rewetting method is used as a casting method, pseudoboehmite is preferably used as the submicron pigment of the upper coating composition because an ink jet recording medium having particularly high gloss can be obtained.

  As the polyvinyl alcohol used in the upper layer coating composition of the present invention, polyvinyl alcohol having various saponification degrees from 70 mol% to 100 mol% can be used, but when the rewetting method is used as the method of the casting process used in the present invention. It is preferable to use one having a saponification degree of 95 mol% or less because gloss is easily developed. Also, modified polyvinyl alcohol in which various functional groups such as silyl group, carboxyl group, amino group, and acetoacetyl group are introduced, and other monomers such as ethylene are introduced randomly, grafted, or in blocks are also used. Can do. If the amount of polyvinyl alcohol added in the present invention is too small, cracks may occur during drying, or the surface strength of the ink jet recording medium to be formed may be insufficient. On the other hand, if the amount of polyvinyl alcohol added is too large. This is not preferable because the ink absorbability may be lowered. Specifically, the addition amount of polyvinyl alcohol is preferably 2 to 40% by mass of the submicron pigment, and more preferably 5 to 25% by mass.

  Since the polyvinyl alcohol of the upper layer coating composition of the present invention has a higher viscosity of its aqueous solution, cracks are less likely to occur when the coated coating composition is dried even if the amount added is relatively small. The amount added can be reduced, and as a result, the ink absorbability can be improved, which is preferable. However, if the viscosity of the aqueous solution is too high, the viscosity of the coating composition obtained by the present invention becomes too high, which may make the coating operation difficult, which is not preferable. Specifically, the viscosity of an aqueous solution having a solid content concentration of 4% by mass measured at 25 ° C. using an Ubbelohde viscometer based on JIS Z8803 is preferably 15 to 400 mPa · sec, and 30 to 200 mPa · sec. More preferably. One of these polyvinyl alcohols may be used alone, or two or more thereof having different degrees of saponification, viscosity, modification and the like may be used in combination.

  The upper layer coating composition of the present invention may contain a cationic water-soluble polymer for the purpose of improving the printing density or water resistance. Examples of the cationic water-soluble polymer include polyethyleneimine quaternary ammonium salt derivatives, polyamide epichlorohydrin resin, cationic polyvinyl alcohol, and cationic starch. These may be used alone or in combination of two or more.

Further, when boric acid or a salt thereof is added to the lower layer coating composition, the coating amount of the upper layer can be reduced without lowering the gloss, and as a result, the cutting strength is improved, which is favorable. The addition amount of boric acid or a salt thereof is preferably 0.2 to 10% by mass, converted to H ₃ BO _{3 based} on the boron atom, based on the water-absorbing inorganic pigment, and is 0.4 to 5% % Is more preferable.

  For each coating layer of the present invention, various additives such as a surfactant, an antifoaming agent, a thickener, a color adjuster, a fluorescent whitening agent, an antioxidant, and an ultraviolet absorber are added as necessary. It can also be added.

In the present invention, the method for coating the coating composition of each coating layer is not particularly limited, and is an air knife coater, blade coater, rod blade coater, bar coater, reverse roll coater, comma coater, gate roll coater, film transfer. Various coating methods such as a coater, a lip coater, a die coater, and a curtain coater can be used. Among these, the curtain coater has a high uniformity of the obtained coating layer, and furthermore, when the upper layer is applied, the coating composition hardly penetrates into the lower layer and gives a very good surface quality. It is preferably used for coating a work layer, particularly an upper layer coating composition. The amount of the coating composition of the present invention applied on the support is not particularly limited, but in order to achieve both ink absorbency and economy, each layer is usually 5 to 20 g / m ² as a solid content. It is preferable to apply 10 to 40 g / m ² in the total of both layers. However, particularly when it is required to absorb a large amount of ink, it may be preferable to apply a maximum of about 50 g / m ^{2 in} total for both layers.

  It is also possible to carry out the cast treatment after increasing the smoothness with a calender device such as a soft calender or a super calender after or after the lower layer coating composition or the upper layer coating composition is applied and dried. is there.

  In addition, a release agent such as an oily substance or an aqueous dispersion of an oily substance is added to the coating composition of the present invention for the purpose of improving the peelability from the mirror surface in the casting apparatus, or is applied prior to the casting treatment. When using the rewetting method as a casting method, it is preferable to add to the water used for the rewetting because stable production can be achieved over a long period of time. Examples of substances that can be used as a release agent in the present invention include higher alkylamines such as dimethyloctylamine and dimethyloctadecylamine or salts thereof, higher alkyl quaternary ammoniums such as trimethyloctylammonium chloride and trimethyloctadecylammonium chloride. Examples thereof include salts, higher carboxylic acids such as oleic acid, stearic acid and caprylic acid or salts thereof, higher alcohols such as octyl alcohol and octadecyl alcohol, liquid paraffin, polyethylene wax and silicone oil.

  Examples of the present invention will be described below. In the examples, unless otherwise specified, parts are parts by mass, and% is mass%.

[Example 1]
[Preparation of lower layer coating composition 1]
2 parts of sodium hydroxide was dissolved in 350 parts of water, 100 parts of wet synthetic silica (Fukuseal X-37B manufactured by Tokuyama Co., Ltd.) was added thereto, and then sufficiently dispersed using a disperser having a saw blade. Subsequently, 30 parts of a polyester aliphatic polyurethane resin having a tensile strength of 46 MPa, an elongation of 610%, a particle size of 10 nm, an anionic and a self-emulsifying type as a solid content was added and mixed to obtain a lower coating composition 1. In addition, about the wet synthetic silica used here, water was used instead of linseed oil, and when a test according to the oil absorption test defined in JIS K 5101 was performed, 300 ml of water per 100 g was obtained by the end point. Used.

[Preparation of Alumina Hydrate Sol]
Mix 299 parts of water with 1 part of acetic acid, add 100 parts of alumina hydrate having a pseudo-boehmite structure (Dispersal HP14 manufactured by Sasol Co., Ltd.), stir for 2 hours as it is, and peptize to obtain an alumina with a solid content concentration of 25%. A hydrated sol was obtained. When this dispersion was diluted 100 times with water, dispersed on a glass substrate and observed with a scanning electron microscope, 80% or more of the area occupied by particles in the observation field was occupied by particles having a long side of 100 to 400 nm. It was.

[Preparation of upper layer coating composition 1]
2 parts by weight of a 10% aqueous solution of polyvinyl alcohol (PVA235 manufactured by Kuraray Co., Ltd.) having a viscosity of 95 mPa · s at a saponification degree of 88 mol% and a 4% aqueous solution at 25 ° C. is added to the above-mentioned alumina hydrate sol equivalent to 25 parts as a solid content It added and the upper-layer coating composition 1 was prepared.

[Preparation of inkjet recording medium]
The base coating composition 1 is coated on a base paper having a basis weight of 157 g / m ² (Diafoam manufactured by Mitsubishi Paper Industries Co., Ltd.) using an air knife coater so that the coating amount after drying is 20 g / m ^2. Then, it was dried using a hot air dryer. Next, after the obtained coated paper was treated using a soft calender, the upper coating composition 1 was coated using an air knife coater so that the coating amount after drying was 20 g / m ^2, and hot air was applied. It was dried using a mold dryer. Furthermore, the obtained coated paper was processed using a soft calendar. The coated surface of the coated paper is wetted by contact with water for 5 seconds, and then pressure-bonded to a mirror surface chrome plating cylinder of a casting apparatus heated to a temperature of 95 ° C. at a linear pressure of 20 kN / m and a speed of 15 m / min, and then dried. The ink jet recording medium of Example 1 was produced by peeling from the cylinder later.

[Examples 2 to 6]
Instead of polyester aliphatic polyurethane resin with tensile strength of 46 MPa, elongation of 610%, particle size of 10 nm, anionic and self-emulsifying type, the resin is changed to the polyurethane resin shown in Table 1 so that the solid content is the same. In the same manner as in Example 1, ink jet recording media of Examples 2 to 6 were produced.

[Example 7]
[Preparation of vapor phase silica dispersion]
While stirring 392 parts of water, 8 parts of a 50% aqueous solution of a dimethyldiallylammonium chloride polymer having a viscosity of 400 mPa · s (solid content 4 parts), gas phase method silica (specific surface area 90 m ² / g by BET method) 100 Part was added and predispersed using a blade type disperser. The obtained preliminary dispersion was treated with a colloid mill to obtain a vapor phase silica dispersion having a solid concentration of 20.8%. When this dispersion was diluted 100 times with water, dispersed on a glass substrate and observed with a scanning electron microscope, 80% or more of the area occupied by the particles in the observation field was occupied by particles having a long side of 100 to 400 nm. It was.

[Preparation of upper layer coating composition 2]
A 10% aqueous solution of polyvinyl alcohol (PVA235 manufactured by Kuraray Co., Ltd.) having a viscosity of 95 mPa · s at a saponification degree of 88 mol% and a 4% aqueous solution at 25 ° C. was added to the above-mentioned gas phase method silica dispersion equivalent to 20.8 parts as a solid content. 3 parts were added to prepare an upper layer coating composition.

[Preparation of inkjet recording medium]
On the base paper, the lower layer coating composition used in Example 5 was applied so that the coating amount after drying was 20 g / m ^2, and dried using a hot air dryer. Subsequently, after processing the obtained coated paper using a soft calender, the upper layer coating composition 2 is applied so that the coating amount after drying is 20 g / m ^2, and before the water volatilizes. Then, the ink jet recording medium of Example 7 was produced by pressure-bonding to a mirror chrome plating cylinder heated to 90 ° C. of a casting apparatus at a linear pressure of 20 kN / m and a speed of 5 m / min, and peeling from the cylinder after drying.

[Example 8]
[Preparation of lower layer coating composition 2]
6 parts of sodium tetraborate decahydrate (0.97 parts in terms of H ₃ BO ₃ ) was dissolved in 350 parts of water, and 100 parts of wet synthetic silica (Fine Seal X-37B manufactured by Tokuyama Corporation) was added thereto. It was fully dispersed using a disperser having a post-saw blade. Subsequently, 30 parts of polyether aliphatic polyurethane resin having a tensile strength of 40 MPa, an elongation of 750%, a particle diameter of 50 nm, an anionic and a self-emulsifying type as a solid content was added and mixed to obtain a lower coating composition 2.

[Preparation of inkjet recording medium]
On the base paper, the lower layer coating composition 2 was applied using an air knife coater so that the coating amount after drying was 20 g / m ^2, and dried using a hot air dryer. Next, after the obtained coated paper was treated using a soft calender, the upper coating composition 1 was coated using an air knife coater so that the coating amount after drying was 20 g / m ^2, and hot air was applied. It was dried using a mold dryer. Furthermore, the obtained coated paper was processed using a soft calendar. The coated surface of the coated paper is wetted by contact with water for 5 seconds, and then pressure-bonded to a mirror surface chrome plating cylinder of a casting apparatus heated to a temperature of 95 ° C. at a linear pressure of 20 kN / m and a speed of 5 m / min, and then dried. The ink jet recording medium of Example 8 was produced by peeling from the cylinder later.

[Example 9]
An inkjet recording medium of Example 9 was produced in the same manner as Example 8 except that the coating amount after drying the upper layer was changed to 10 g / m ² .

[Example 10]
An ink jet recording medium of Example 10 was produced in the same manner as in Example 5 except that the addition amount of the polyurethane resin was changed from 30 parts to 14 parts as a solid content.

[Example 11]
An inkjet recording medium of Example 11 was produced in the same manner as Example 5 except that the amount of polyurethane resin added was changed from 30 parts to 21 parts as a solid content.

[Example 12]
An inkjet recording medium of Example 12 was produced in the same manner as Example 5 except that the amount of polyurethane resin added was changed from 30 parts to 56 parts as a solid content.

[Example 13]
An ink jet recording medium of Example 13 was produced in the same manner as in Example 5 except that the addition amount of the polyurethane resin was changed from 30 parts to 84 parts as a solid content.

[Comparative Examples 1-6]
Instead of polyester aliphatic polyurethane resin with tensile strength of 46 MPa, elongation of 610%, particle size of 10 nm, anionic and self-emulsifying type, the resin is changed to the polyurethane resin shown in Table 2 so that the solid content is the same. In the same manner as in Example 1, inkjet recording media of Comparative Examples 1 to 6 were produced.

[Comparative Example 7]
As a resin, instead of a polyether aliphatic polyurethane resin having a tensile strength of 68 MPa, an elongation of 6%, a particle diameter of 20 nm, an anionic and a self-emulsifying type, polyvinyl alcohol (PVA235 manufactured by Kuraray Co., Ltd.) is used so that the solid content is the same. The inkjet recording medium of Comparative Example 7 was produced in the same manner as Comparative Example 1 except that the aqueous solution was changed to a 10% aqueous solution.

[Comparative Examples 8-12]
As a resin, instead of a polyether aliphatic polyurethane resin having a tensile strength of 68 MPa, an elongation of 6%, a particle diameter of 20 nm, an anionic and a self-emulsifying type, the resin is changed to the resin shown in Table 2 so as to have the same solid content. Except that, inkjet recording media of Comparative Examples 8 to 12 were produced in the same manner as Comparative Example 1.

[Comparative Example 13]
Comparative Example 4 except that the addition amount of the polycarbonate aliphatic polyurethane resin of tensile strength 25 MPa, elongation 750%, particle size 30 nm, anionic and self-emulsifying type was changed from 30 parts to 70 parts as a solid content. Similarly, an inkjet recording medium of Comparative Example 13 was produced.

[Comparative Example 14]
An inkjet recording medium of Comparative Example 14 was produced in the same manner as Comparative Example 9, except that the addition amount of styrene-butadiene latex was changed from 30 parts to 70 parts as a solid content.

[Comparative Examples 15 to 16]
As the resin, instead of a polyether aliphatic polyurethane resin having a tensile strength of 40 MPa, an elongation of 750%, a particle diameter of 50 nm, an anionic and a self-emulsifying type, a tensile strength of 25 MPa and an elongation of 750 so that the solid content becomes the same amount. %, Particle size 30 nm, anionic, self-emulsifying type polycarbonate-based aliphatic polyurethane resin was used, and ink jet recording media of Comparative Examples 15 and 16 were prepared in the same manner as in Examples 8 and 9.

[Evaluation of image clarity]
The image clarity was excellent in correlation with visual gloss. In addition, the measurement was performed using a Suga Test Instruments Co., Ltd. image clarity measuring device at a measurement angle of 45 ° and an optical comb width of 2.0 mm. In the measurement by this method, in general, a recording medium giving 60 or more image clarity has a high gloss feeling, and a recording medium giving 65 or more image clarity has a very high gloss feeling.

[Evaluation of print density]
A solid black image was printed using a Seiko Epson PM-900C type ink jet printer, and the optical reflection density was measured with a Macbeth RD-918 model.

[Evaluation of ink absorbency]
A predetermined evaluation image is printed on a recording medium cut to A4 size using a PM-900C type ink jet printer manufactured by Seiko Epson Corporation. The ink absorbability of each recording medium is determined based on the readability of the details of the image, and the following 5 Classified into stages. A (very good), B (good), C (normal), D (acceptable), E (unacceptable).

[Evaluation of peel strength]
A recording medium cut to A4 size was conditioned for 24 hours in an environment of 23 ° C. and 50% RH, and then 50 mm of 100 mm cellophane tape manufactured by Nichiban Co., Ltd. was adhered to the coated surface of the sample. After rubbing and attaching the cellophane tape, hold the one of the cellophane tape 1-2 minutes later and peel it 120 ° at a peel rate of 20 mm / sec. Classified. A (the peeling of the coating layer is not visually recognized), B (the peeling of the coating layer is not observed at first glance, but a very small amount of peeling is observed when observed closely), C (50% of the coating layer) ), D (the coating layer is slightly peeled although there is some resistance), E (the coating layer is almost peeled without any resistance).

[Evaluation of cutting strength]
The recording medium cut to A4 size was conditioned for 24 hours in an environment of 23 ° C. and 50% RH, and then the sample was cut with a cutter along the ruler with the coated surface as the surface. The broken state of the cut surface was classified into the following five stages. A (no tobacco loss, no damage to the cut surface), B (slight tobacco loss was observed, but the cut surface was hardly damaged), C (combustion was observed) , One side of the cut surface was damaged, but no damage was seen on the other side) D (combing was seen, one side of the cut surface was severely damaged, the other side was slightly damaged ), E (a lot of tobacco drops were seen, and the cut surface was severely damaged on both sides).

  Tables 3 and 4 show the image clarity, print density, ink absorbability, peel strength, and cutting strength of the recording media obtained in each Example and each Comparative Example.

  By comparing Examples 1 to 6 with Comparative Example 4, even if the elongation of the polyurethane resin is 300 to 800% and the particle size of the dispersion is 10 to 100 nm, the tensile strength deviates from 30 to 70 MPa. It can be seen that the cutting strength and peel strength deteriorate rapidly.

  By comparing Examples 1 to 6 and Comparative Examples 1, 3, and 5, even if the tensile strength of the polyurethane resin is 30 to 70 MPa and the particle size of the dispersion is 10 to 100 nm, the elongation is 300 to 800%. When it deviates from, it turns out that cutting strength and peel strength deteriorate rapidly.

  By comparing Examples 1 to 6 with Comparative Examples 2 and 6, even when the elongation of the polyurethane resin is 300 to 800% and the tensile strength is 30 to 70 MPa, the particle size of the dispersion deviates from 10 to 100 nm. It can be seen that the cutting strength and peel strength deteriorate rapidly.

  From the above, when the polyurethane resin contained in the lower layer has three conditions of a tensile strength of 30 to 70 MPa, an elongation of 300 to 800%, and a particle size of the dispersion of 10 to 100 nm, high glossiness and print density, It can be seen that an ink jet recording medium excellent in cutting strength and peel strength can be obtained while maintaining ink absorbability. In addition, it was possible to obtain an inkjet recording medium having high cutting strength and peeling strength even with conventional techniques, for example, Comparative Example 13 and Comparative Example 14, but the image clarity is significantly reduced due to the increase in the amount of resin. I understand that.

  By comparing Example 2 with Examples 1 and 3 to 6, it can be seen that when the particle size of the dispersion is 10 to 60 nm, the peel strength is particularly excellent.

  By comparing Example 4 with Examples 1-3, 5, and 6, it can be seen that the cutting strength is particularly good in the case of an aliphatic polyurethane resin.

  By comparing Examples 3, 5, and 6 with Examples 1, 2, and 4, it can be seen that an inkjet recording medium having particularly good ink absorbability can be obtained by using a polyether-based or polycarbonate-based polyurethane resin. .

Claims (6)

  In an inkjet recording medium produced by casting at least a lower layer and an upper layer on a gas-permeable support, the lower layer is formed from a coating composition containing a dispersion of a water-absorbing inorganic pigment and a polyurethane resin. And an upper layer formed from a coating composition containing a submicron pigment and polyvinyl alcohol, wherein the polyurethane resin has a tensile strength defined by JIS K7311 of 30 to 70 MPa, JIS An ink jet recording medium having an elongation specified by K7311 of 300 to 800% and a particle diameter measured by a dispersion dynamic light scattering method of 10 to 100 nm.   2. The ink jet recording medium according to claim 1, wherein the particle diameter of the polyurethane resin dispersion measured by a dynamic light scattering method is 10 to 60 nm.   3. The ink jet recording medium according to claim 1, wherein the polyurethane resin is a self-emulsifying dispersion.   The inkjet recording medium according to claim 1, wherein the polyurethane resin is an aliphatic polyurethane resin.   The inkjet recording medium according to claim 1, wherein the polyurethane resin is a polyether-based or polycarbonate-based polyurethane resin.   The inkjet recording medium according to claim 1, wherein the polyurethane resin is anionic.