JP2005231291A - Inkjet recording sheet and method for manufacturing it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording sheet which has an ink receiving layer with excellent absorbing properties of an aqueous ink, with a sharp ink dot shape, with excellent color developing properties of the ink, giving a stable and high quality printed image, with excellent water resistance, moisture resistance and transparency, and furthermore, with excellent carrying properties and blocking resistance. <P>SOLUTION: The inkjet recording sheet is provided with at least one ink receiving layer on at least one face of a substrate sheet. The ink receiving layer is formed by using a composition comprising a hydrophilic polyurethane resin obtained by reacting an organic polyisocyanate, a high molecular weight hydrophilic polyol and/or a polyamine, and a compound having at least one active hydrogen-containing group and at least one tertiary amino group in the same molecule, and a fine particle alumina. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ink jet recording sheet (hereinafter simply referred to as “recording sheet”) and a method for producing the same, and more specifically, imparts excellent water resistance and moisture resistance to a printed image, and absorbs ink and develops ink. The present invention relates to a recording sheet that has an ink receiving layer that is excellent in transparency, can stably record high-quality printed images, has excellent transparency and blocking resistance, and has excellent transportability, and a method for producing the same.

  The ink jet recording method is based on various operating principles, for example, an electrostatic attraction method, a method of applying mechanical vibration or displacement to the ink using a piezoelectric element, a method of heating and foaming the ink, and utilizing the pressure. Is used to record images, characters, etc. by flying them on a recording sheet such as paper, enabling high-speed printing, generating less noise during printing, high-quality printing, and multicolor printing. As a recording method capable of printing, it is rapidly spreading in various applications.

  As a recording sheet used for such an ink jet recording, the ink adhering to the recording sheet is allowed to absorb ink quickly so that the ink does not bleed or flow, and the print quality is not impaired. Recording sheets in which an ink-receiving layer mainly composed of various pigments and resins is provided on a support such as paper, or a porous pigment is embedded in paper itself have been proposed. Yes.

  For example, Patent Document 1 describes that an inorganic pigment and an organic pigment are used in combination as a pigment and an ink receiving layer made of a water-soluble polymer is provided, and Patent Document 2 discloses fine powder alumina and silanol group. It is described that an ink receiving layer made of a polyvinyl alcohol copolymer having a water content is provided.

However, as the performance of inkjet recording devices such as high-speed recording, high-definition or full-color is improved and applications are expanded, it is required that recording sheets have the following advanced characteristics. It was.
(1) fast ink absorption and large ink absorption capacity;
(2) High color developability of the ink,
(3) the surface strength of the ink receiving layer is high;
(4) The support has water resistance, and the ink does not cause irregularities or curls on the support,
(5) The image printed on the ink receiving layer has good image storability such as water resistance and ozone resistance,
(6) The ink receiving layer does not change with time.

  Conventionally, porous pigments and water-soluble polymers having excellent ink absorbency are used as components of the ink receiving layer provided on the recording sheet to satisfy these requirements, and latex is used to improve the water resistance of the ink receiving layer. In addition, it has been proposed and studied to use synthetic paper or plastic film having water resistance as the support itself.

  However, a recording sheet having an ink receiving layer formed using paper as a support or using only a water-soluble polymer has poor water resistance of the image formed thereon, and the printed portion is blurred, resulting in a clear image. Inferior to sex. Also, a recording sheet in which a porous pigment is dispersed in an ink receiving layer generally reduces the transparency of the ink receiving layer so that the porous pigment is usually used as a matting agent (matting agent). Even if the dispersion amount is as small as 5% by mass or less, the transparency is remarkably lowered. On the other hand, for those using synthetic paper or plastic film for the support or using latex for the resin of the ink receiving layer, the adhesion between the ink receiving layer and the support, the ink absorption in the ink receiving layer and the ink absorption There is a problem with drying.

JP 57-82085 A Japanese Patent Laid-Open No. 62-268682

  The present invention is particularly excellent in water-based ink absorbability, the ink dot shape is sharp, the ink coloring property is excellent, and a stable and high-quality printed image is provided. Further, transparency, blocking resistance, water resistance and An object of the present invention is to provide a recording sheet having an ink receiving layer having excellent moisture resistance and excellent transportability.

  The above object is achieved by the present invention described below. That is, according to the present invention, in a recording sheet in which at least one ink receiving layer is provided on at least one side of a base sheet, the ink receiving layer is composed of an organic polyisocyanate, a high molecular weight hydrophilic polyol and / or a polyamine (hereinafter referred to as “polyamine”). A hydrophilic polyurethane resin obtained by reacting a "hydrophilic component" with a compound having at least one active hydrogen-containing group and at least one tertiary amino group in the same molecule, and particulate alumina And a recording sheet (hereinafter referred to as “the composition of the present invention”).

  Further, the present invention provides a method for producing a recording sheet by providing at least one ink receiving layer on at least one side of a base sheet, and the ink receiving layer is coated with a paint containing the composition of the present invention. Provided is a method for producing an inkjet recording sheet, which is formed by applying and drying on at least one side.

  According to the present invention described above, by forming an ink receiving layer using the composition of the present invention, it is possible to record a high-quality printed image with excellent ink absorptivity, drying property, and color developability. Furthermore, a recording sheet having an ink receiving layer excellent in transparency, blocking resistance and water resistance of a printed image is provided.

Next, the present invention will be described in more detail with reference to the best mode for carrying out the invention.
In the recording sheet of the present invention, the ink receiving layer is composed of a hydrophilic polyurethane resin as a resin component and fine particle alumina. The hydrophilic polyurethane resin used in the present invention requires an organic polyisocyanate, a hydrophilic component, and a compound having at least one active hydrogen-containing group and at least one tertiary amino group in the same molecule. And a hydrophilic polyurethane resin obtained by reacting in the presence of a chain extender.

  In the present invention, the fine particle alumina is contained in the hydrophilic polyurethane resin produced by synthesizing the hydrophilic polyurethane resin by adding the fine particle alumina in advance to the hydrophilic component when the hydrophilic polyurethane resin is synthesized. The (dispersed) fine alumina particles are stably dispersed in the hydrophilic polyurethane resin solution despite the fact that no dispersant is used. The ink receiving layer of the recording sheet of the present invention is formed using the composition of the present invention. In the present invention, the polyurethane resin is a generic term for a polyurethane resin, a polyurea resin, and a polyurethane-polyurea resin.

  In the present invention, as the mixture of the hydrophilic component and the fine particle alumina, a mixture obtained by mechanically mixing and dispersing the fine particle alumina in the hydrophilic component can be used. It is preferable to use one obtained by removing the medium. The alumina sol in the present invention is a dispersion in which fine particle alumina is usually stably dispersed in water and / or alcohol as a dispersion medium. As the dispersion medium, ketones, esters, and other organic solvents are also used. The average particle diameter of the fine particle alumina in the alumina sol is usually 1 μm or less, particularly preferably 1 to 300 mμm (nm).

  Conventionally, when an ink receiving layer of a recording sheet is formed, a method using a resin solution or a resin dispersion is generally used. As a method for dispersing fine particle alumina in a polyurethane resin solution, the following method may be mentioned. For example, a method (1) in which fine particle alumina is mixed and dispersed in a polyurethane resin using an ordinary dispersion mixer, and this is dissolved in a solvent, and a method in which fine particle alumina or alumina sol is added and dispersed in a polyurethane resin solution (2) ) Is considered.

  However, the above method (1) is economically disadvantageous because a stable dispersion of fine particulate alumina cannot be obtained even if a dispersant is used. Further, although the method (2) is a general method, the fine particle alumina cannot be stably dispersed even with this method or using a dispersant. Further, even when alumina sol is used as the fine particle alumina in the method (2), the dispersion stability of the fine particle alumina is low, and both the polyurethane resin solution and the fine particle alumina easily separate with time. This is because the compatibility (affinity) between the polyurethane resin and the alumina sol, the stability of the both to changes in pH, or the surface properties of the polyurethane resin and the fine particle alumina are different.

  As another method, a method of adding alumina sol to the synthesis system during the synthesis reaction of the polyurethane resin is also conceivable. However, it is not possible to use alumina sol, and even if other solvent-based alumina sol is used, a polyurethane resin solution having excellent dispersion stability of fine particle alumina cannot be obtained.

  However, the hydrophilic component described later used in the present invention has extremely high compatibility (affinity) with the alumina sol due to its hydrophilicity, and can be stably mixed with the alumina sol at an arbitrary ratio. Then, by removing the dispersion medium of the alumina sol from this mixture by an arbitrary method, a hydrophilic component in which the particulate alumina is dispersed extremely stably (hereinafter referred to as “particulate alumina dispersed hydrophilic component”) is obtained. Even if the dispersion amount of the fine particle alumina in the hydrophilic component is increased, the increase in the viscosity of the hydrophilic component is small, and the hydrophilic polyurethane is obtained by reacting the fine particle alumina dispersed hydrophilic component with another polyurethane raw material in a solvent. A dispersion in which fine-particle alumina is stably dispersed in the resin solution without using a dispersant can be obtained. When the polyurethane resin is synthesized without a solvent, the same stable dispersion as described above can be obtained by dissolving the obtained polyurethane resin in the soluble organic solvent. These dispersions are all very transparent, and the film (coating film) formed from them is also transparent.

  The removal of the dispersion medium of the alumina sol from the mixture of the hydrophilic component and the alumina sol can generally be easily performed under reduced pressure. In this case, the dispersion medium is preferably distilled off under reduced pressure and at a low temperature, and it is particularly preferred that the dispersion medium is distilled off at a temperature of 70 ° C. or lower. When the dispersion medium is distilled off at a higher temperature than this, aggregation of fine particle alumina in the alumina sol may occur, and the dispersion stability of the fine particle alumina is lowered and a finely divided fine particle alumina dispersed hydrophilic component is generated. Sometimes. When the hydrophilic component is used as a solution of the organic solvent, the organic solvent is removed together with the dispersion medium of the alumina sol. The mixing ratio of the hydrophilic component and the alumina sol is preferably such that the fine particle alumina accounts for 5 to 95% by mass in the composition comprising the finally obtained hydrophilic polyurethane resin and fine particle alumina, more preferably 10 to 90%. It is the amount occupying mass%.

  In the present invention, the hydrophilic polyurethane resin used as the resin constituting the ink receiving layer has a hydrophilic segment having a hydrophilic component as a structural unit and a component having at least one tertiary amino group as a structural unit. And a tertiary amino group-containing segment. When a chain extender is not used during the synthesis of the hydrophilic polyurethane resin, these segments are bonded at random by urethane bonds, urea bonds, or urethane-urea bonds, respectively. When a chain extender is used during the synthesis of the hydrophilic polyurethane resin, a short chain that is a residue of the chain extender exists between these bonds together with these bonds.

  When the tertiary amino group is introduced into the hydrophilic polyurethane resin, the composition of the present invention is given excellent adhesion to various materials, and when the ink receiving layer is formed from the composition. Is provided with excellent water absorption, anti-fogging property, transparency, flexibility, water-based ink writing property, water resistance, and further excellent blocking resistance and lubricity. .

  The reason why excellent water resistance is imparted to the ink receiving layer and image to be formed is not clear, but is considered as follows. Dyes that are colorants for ink-jet inks generally have an anionic carboxyl group or sulfonic acid group in the molecule, and are hydrophilic to form the ink receiving layer of the recording sheet of the present invention. When the polyurethane resin comes into contact with the above ink, an ionic bond is formed between the anionic group of the dye in the ink and the tertiary amino group in the resin, thereby fixing the dye and the recorded image. It is thought that water resistance is improved.

  However, in the presence of moisture, the ionic bonds as described above are easily dissociated, and it should not be expected to improve the water resistance of the ink receiving layer and the image formed thereon. The water resistance of the receiving layer and the image formed thereon is significantly improved. The reason for this improvement in water resistance is not clear, but the polyurethane resin used in the present invention is hydrophilic, but also has a hydrophobic portion in the molecule, and the tertiary amino group and dye in the resin are present. After the ionic bond is formed between the polyurethane resin, the hydrophobic part of the polyurethane resin surrounds the hydrophilic part (hydrophilic segment) and the ionic bond part. It is.

Next, the raw material of the hydrophilic polyurethane resin used in the present invention will be described.
In the present invention, the compound used for introducing a tertiary amino group into the hydrophilic polyurethane resin described above includes, for example, an amino group, an epoxy group, a hydroxyl group, a mercapto group, a carboxyl group as at least one active hydrogen-containing group. A reactive group that can be converted to a hydroxyl group or a carboxyl group such as an alkoxy group, an acid halide group, a carboxy ester group, and an acid anhydride group, and at least one tertiary amino group in the molecular chain A compound.

（式中の、Ｒ₁は炭素数２０以下のアルキル基、脂環族基、芳香族基（ハロゲン、アルキル基で置換されていてもよい）であり、Ｒ₂及びＲ₃は−Ｏ−、−ＣＯ−、−ＣＯＯ−、−ＮＨＣＯ−、−Ｓ−、−ＳＯ−、−ＳＯ₂−等で連結されていてもよい低級アルキレン基であり、Ｘ及びＹは−ＯＨ、−ＣＯＯＨ、−ＮＨ₂、−ＮＨＲ₁、−ＳＨ等の反応性基であり、Ｘ及びＹは同一でも異なってもよい。又、Ｘ及びＹは、上記の反応性基に誘導できるエポキシ基、アルコキシ基、酸ハライド基、酸無水物基、又はカルボキシルエステル基でもよい。） Preferable examples of the tertiary amino group-containing compound having a reactive group as described above include compounds represented by the following general formulas (1) to (3).

(In the formula, R ₁ is an alkyl group having 20 or less carbon atoms, an alicyclic group, or an aromatic group (which may be substituted with a halogen or an alkyl group), and R ₂ and R ₃ are —O—, A lower alkylene group which may be linked by —CO—, —COO—, —NHCO—, —S—, —SO—, —SO ₂ —, etc., and X and Y are —OH, —COOH, —NH ₂ , a reactive group such as —NHR ₁ , —SH, etc. X and Y may be the same or different, and X and Y are an epoxy group, an alkoxy group, an acid halide that can be derived from the reactive group described above. It may be a group, an acid anhydride group, or a carboxyl ester group.)

（式中の、Ｒ₁、Ｒ₂、Ｒ₃、Ｘ及びＹは前記と同じ定義であるが、但し二つのＲ₁同士は環状構造を形成するものであってもよい。Ｒ₄は−(ＣＨ₂)_n−（ｎは０〜２０の整数）である。）

(In the formula, R ₁ , R ₂ , R ₃ , X and Y have the same definitions as above, but two R _{1 s} may form a cyclic structure. R ₄ is-( CH _{2) n} - (n is an integer of 0 to 20)).

（式中の、Ｘ及びＹは前記の定義と同じであり、Ｗは窒素含有複素環、窒素と酸素含有複素環、又は窒素と硫黄含有複素環を表す。）

(In the formula, X and Y are as defined above, and W represents a nitrogen-containing heterocycle, nitrogen and oxygen-containing heterocycle, or nitrogen and sulfur-containing heterocycle.)

  Specific examples of the compound represented by the general formula (1), (2) or (3) include the following. N, N-dihydroxyethyl-methylamine, N, N-dihydroxyethyl-ethylamine, N, N-dihydroxyethyl-isopropylamine, N, N-dihydroxyethyl-n-butylamine, N, N-dihydroxyethyl-t-butylamine Methyliminobispropylamine, N, N-dihydroxyethylaniline, N, N-dihydroxyethyl-m-toluidine, N, N-dihydroxyethyl-p-toluidine, N, N-dihydroxyethyl-m-chloroaniline, N , N-dihydroxyethylbenzylamine, N, N-dimethyl-N ′, N′-dihydroxyethyl-1,3-diaminopropane, N, N-diethyl-N ′, N′-dihydroxyethyl-1,3-diamino Propane, N-hydroxyethyl-piperazine, N, N-di Droxyethyl-piperazine, N-hydroxyethoxyethyl-piperazine, 1,4-bisaminopropyl-piperazine, N-aminopropyl-piperazine, dipicolinic acid, 2,3-diaminopyridine, 2,5-diaminopyridine, 2,6- Diaminopyridine, 2,6-diamino-4-methylpyridine, 2,6-dihydroxypyridine, 2,6-pyridine-dimethanol, 2- (4-pyridyl) -4,6-dihydroxypyrimidine, 2,6-diamino Triazine, 2,5-diaminotriazole, 2,5-diaminooxazole and the like.

（上記式中のｎは１〜６０の整数を、ｍは１〜６の整数を表す。） Also, ethylene oxide adducts and propylene oxide adducts of these tertiary amino compounds can be used in the present invention. Examples of the adduct include compounds represented by the following structural formula.

(In the above formula, n represents an integer of 1 to 60, and m represents an integer of 1 to 6.)

  As the organic polyisocyanate used in the present invention, any of those conventionally used in the synthesis of polyurethane resins can be used, and is not particularly limited. Preferred examples include 4,4′-diphenylmethane diisocyanate (MDI), hydrogenated MDI, isophorone diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, 2,4-tolylene diisocyanate, 2, 6-tolylene diisocyanate, 1,5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, etc., or polyurethane obtained by reacting these organic polyisocyanates with low molecular weight polyols or polyamines to form terminal isocyanates A prepolymer or the like can also be used.

As the hydrophilic component used in the present invention, those having a hydroxyl group, amino group, carboxyl group or the like in the molecule and having a weight average molecular weight in the range of 400 to 8,000 are preferable.
Examples of the polyol having a terminal hydroxyl group and hydrophilicity include polyethylene glycol, polyethylene glycol / polytetramethylene glycol copolymer polyol, polyethylene glycol / polypropylene glycol copolymer polyol, polyethylene glycol adipate polyol, polyethylene glycol succinate polyol, polyethylene Examples include glycol / poly-ε-caprolactone copolymer polyol and polyethylene glycol / polyvalerolactone copolymer polyol. Particularly preferred is polyethylene glycol.

  Examples of the polyamine having a terminal amino group and hydrophilicity include polyethylene oxide diamine, polyethylene oxide propylene oxide diamine, polyethylene oxide triamine, and polyethylene oxide propylene oxide triamine. Other examples include ethylene oxide adducts having a carboxyl group or a vinyl group.

  In the present invention, in order to impart water resistance to the hydrophilic polyurethane resin, it is also possible to use other polyols, polyamines, polycarboxylic acids and the like not having a hydrophilic chain together with the above hydrophilic component.

  As the chain extender used as necessary in the present invention, for example, any conventionally known chain extender such as a low molecular weight diol or diamine can be used, and it is not particularly limited. For example, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, ethylenediamine, hexamethylenediamine and the like can be mentioned.

  The composition used in the present invention is obtained by removing the dispersion medium of the alumina sol from the mixture of the hydrophilic component and alumina sol described above, that is, the particulate alumina-dispersed hydrophilic component, the organic polyisocyanate, and at least A compound having one active hydrogen-containing group and at least one tertiary amino group in the same molecule is reacted in the presence of a chain extender, if necessary, according to a conventionally known method for producing a polyurethane resin. Can be obtained. The reaction may be performed in an organic solvent or without a solvent. When performed in an organic solvent, the resulting composition of the present invention is in a state in which fine particle alumina is stably dispersed in a hydrophilic polyurethane resin solution. When the reaction is performed in the absence of a solvent, the resulting composition of the present invention is solid, and the solid composition is dissolved in the soluble organic solvent of the hydrophilic polyurethane resin constituting the composition. And use it. The soluble organic solvent is not particularly limited, and preferred examples include dimethylformamide and methyl ethyl ketone. As the soluble organic solvent, a solvent used for the synthesis of a hydrophilic polyurethane resin can also be used. The solutions of the composition of the present invention are all dispersions in which fine particle alumina is stably dispersed in a hydrophilic polyurethane resin solution.

  The molecular weight of the hydrophilic polyurethane resin constituting the composition used in the present invention is not particularly limited, and the weight average molecular weight in terms of standard polystyrene is preferably in the range of 3,000 to 800,000 as measured by GPC. Preferably it is the range of 5,000-500,000.

  In the composition used in the present invention, the content of the particulate alumina is preferably an amount occupying 5 to 95% by mass, more preferably 10 to 90% by mass in the composition. If the content of fine particle alumina is less than 5% by mass, the surface characteristics of the ink receiving layer, such as blocking resistance and lubricity, which are the objects of the present invention, will be insufficiently developed. This is not preferable because the strength of the layer and the adhesion of the ink receiving layer to the base material sheet become poor. Surprisingly, when the content of the particulate alumina is 75 to 95% by mass, a microporous material having a size of several m μm (nm) is obtained by coating a base material sheet with a paint using the composition of the present invention. In addition, a film (ink receiving layer) excellent in transparency is formed.

  The content of the tertiary amino group in the hydrophilic polyurethane resin in the present invention is preferably in the range of 0.1 to 50 meq (milli equivalent) / g, more preferably 0.5 to 20 meq / g. When the content of the tertiary amino group is less than 0.1 meq / g, that is, less than 1 per 10,000 molecular weight, the proportion of the high molecular weight hydrophilic segment is relatively large, which is an intended object of the present invention. Insufficient surface properties of the ink-receiving layer such as water resistance and blocking resistance are insufficient, while when the content of tertiary amino groups exceeds 50 meq / g, that is, 500 molecules per 10,000 molecular weight. On the other hand, the high molecular weight hydrophilic segment in the resin is relatively reduced, and as a result, the water repellency becomes strong, and the water absorbing performance and antifogging property of the ink receiving layer become inferior.

  Moreover, 30-80 mass% is preferable, and, as for content of the hydrophilic segment in the hydrophilic polyurethane resin in this invention, More preferably, it is 50-75 mass%. If the content of the hydrophilic segment is less than 30% by mass, the water-absorbing and anti-fogging properties of the ink receiving layer to be formed become inferior. And it becomes inferior to blocking resistance, which is not preferable.

  As the base sheet of the recording sheet of the present invention, for example, paper, plastic film, glass, cloth, wood, metal and the like are used, but are not particularly limited. Examples of the paper include high quality paper, medium quality paper, coated paper, cast coated paper, and the like. Examples of the plastic film include sheets having a thickness of 50 to 250 μm, such as polyester, cellulose triacetate, polycarbonate, polyvinyl chloride, polypropylene, polyamide, polystyrene, polyethylene, polymethyl methacrylate, and the like. In addition, the base sheet is provided with a primer layer for providing adhesion to the ink receiving layer as required, a recording sheet curl prevention layer on the back surface of the base sheet on the non-receptive layer side, and a slipping layer for improving the coefficient of friction. Can also be provided.

  In the present invention, the above-described composition of the present invention is used to form an ink receiving layer. The resin component constituting the ink receiving layer may be the hydrophilic polyurethane resin alone in the above composition, but the ink receiving layer may further have hydrophilicity and / or water absorption depending on the composition of the ink jet ink used for printing. In order to impart or adjust, a known water-soluble polymer may be used in combination with the composition. Examples of these water-soluble polymers include polyvinyl alcohol, modified polyvinyl alcohol, hydroxyethyl cellulose, CMC, cellulose derivatives, polyvinyl pyrrolidone, polyacrylic acid, polyacrylic acid copolymer, starch, cationic starch, gelatin, and casein. Is mentioned.

  Further, in order to further impart water resistance and durability to the ink receiving layer and the printed image, a hydrophobic polymer may be used in combination with the composition of the present invention. Examples of these hydrophobic polymers include polyester resin, polyvinyl chloride resin, polystyrene resin, polymethyl methacrylate resin, polycarbonate resin, polyurethane resin, vinyl chloride-vinyl acetate copolymer resin, acrylonitrile-styrene copolymer resin, polyvinyl chloride. Examples thereof include synthetic resins generally used for forming the ink receiving layer, such as butyral resin, polyamide resin, epoxy resin, urea resin, and melamine resin.

  In addition, the fat composition of the present invention contains inorganic and organic pigments, resin particles, and the like for the purpose of improving ink absorbability, fixing properties, color developability, and blocking resistance and water resistance of the ink receiving layer. Can be made. Examples of pigments and resin particles used include kaolin, delaminated kaolin, aluminum hydroxide, silica, diatomaceous earth, calcium carbonate, talc, titanium oxide, calcium sulfate, barium sulfate, zinc oxide, alumina, calcium silicate, magnesium silicate, Mineral pigments such as colloidal silica, zeolite, bennite, sericite, lithopone, porous pigments, polystyrene resin, urea resin, acrylic resin, melamine resin, benzoguanamine resin, polyurethane resin, other fine particles such as organic pigment, porous fine particles and Among known pigments such as hollow particles and resin particles, one or more kinds are appropriately used according to the quality design of the ink receiving layer. In this case, the amount of these pigments and resin particles used is in the range of 0 to 95% by mass, preferably 10 to 90% by mass, based on the total solid content of the composition of the present invention used for forming the ink receiving layer.

  Further, if necessary, the composition of the present invention may be used in addition to the above thickeners, mold release agents, penetrants, wetting agents, thermal gelling agents, sizing agents, antifoaming agents, foam suppressors, foaming agents, and coloring agents. Agent, fluorescent brightening agent, ultraviolet absorber, antioxidant, quencher agent, preservative, antistatic agent, crosslinking agent, dispersant, lubricant, plasticizer, pH adjuster, fluidity improver, solidification accelerator, Various auxiliaries such as water-resistant agents can be appropriately blended.

  As the composition of the present invention used for forming the ink receiving layer in the present invention, it is preferable to use the solution of the composition of the present invention synthesized in a solvent as it is, and the composition of the present invention without solvent is used. When manufactured, the composition can be used by dissolving in an appropriate solvent. If necessary, a solvent-soluble or insoluble additive may be added to these solutions. The solution is usually prepared as a paint having a solid content of about 5 to 15% by mass.

  The ink-receiving layer is formed by applying and drying the paint on at least one side of the substrate sheet by gravure coating, direct or reverse roll coating, wire bar coating, air knife coating, curtain coating, blade coating, rod coating, die coating, etc. . Furthermore, the ink receiving layer after drying is subjected to surface finishing using a calendar such as a machine calendar, a super calendar, or a soft calendar, whereby the recording sheet of the present invention is obtained.

The thickness of the ink receiving layer formed, the thickness to be 5 to 100 g / m ² approximately on a dry coated amount of the coating material is preferred, more preferably 10 to 50 g / m ² approximately. When the thickness of the ink receiving layer is less than 5 g / m ² , the ink absorption by the ink receiving layer becomes insufficient, and when the thickness exceeds 100 g / m ² , the obtained effect becomes saturated and uneconomical. Generation of cracks or curling of the recording sheet is likely to occur.

  Next, the present invention will be described in more detail with reference examples, examples and comparative examples. In the text, “part” or “%” is based on mass unless otherwise specified.

Reference example 1
700 parts of polyethylene glycol (molecular weight: 1,000) and 750 parts of alumina water sol (average particle diameter of alumina: 150 to 160 nm, solid content: 40%) are mixed thoroughly, and the resulting mixture is decompressed at 70 ° C. while stirring. Dehydration was performed. After the theoretical amount of water was distilled off, the temperature was raised to 120 ° C. and water was further removed under reduced pressure of 133.3 Pa or less to obtain a white solid polyol (A) having an alumina content of 30%. This polyol (A) had a hydroxyl value of 76 mgKOH / g, a moisture content of 0.15%, was transparent at 80 ° C., and had a viscosity of 380 dPa · s.

Reference example 2
100 parts of polyethylene glycol (molecular weight 590) and 500 parts of alumina water sol (average particle size of alumina 10-20 nm, solid content 20%) are thoroughly mixed, and the resulting mixture is stirred under reduced pressure at 70 ° C. under reduced pressure. went. After the theoretical amount of water was distilled off, the temperature was raised to 120 ° C. and water was further removed under reduced pressure of 133.3 Pa or less to obtain a white solid polyol (B) having an alumina content of 50%. This polyol (B) was softened at 90 ° C. with a hydroxyl value of 95 mgKOH / g, a moisture content of 0.12%.

Reference example 3
100 parts of polyethylene oxide diamine (Jefamine ED manufactured by Texaco Chemical Co., Ltd .; molecular weight 600) and 2,250 parts of alumina water sol (alumina average particle size 150 to 160 nm, solid content 40%) were sufficiently mixed, and the resulting mixture was obtained. The mixture was stirred under reduced pressure at 70 ° C. with stirring. After the theoretical amount of water was distilled off, the temperature was raised to 120 ° C. and water was further removed under reduced pressure of 133.3 Pa or less to obtain a white solid polyamine (C) having an alumina content of 90%. This polyamine (C) was softened at an amine equivalent of 30 g / mol, a water content of 0.20%, and 110 ° C.

Reference example 4
(Production of the composition of the present invention)
50 parts of polyethylene glycol (molecular weight 2,040), 100 parts of polyol (A) of Reference Example 1, 20 parts of N-methyldiethanolamine, 5 parts of diethylene glycol, 200 parts of methyl ethyl ketone and 200 parts of dimethylformamide A solution obtained by dissolving 80 parts of hydrogenated MDI in 200 parts of methyl ethyl ketone was gradually added dropwise while dissolving in a mixed solvent and stirring well at 60 ° C. After completion of the dropwise addition, the mixture was reacted at 80 ° C. for 8 hours, and then 420 parts of dimethylformamide was added to obtain a solution (paint) of the composition of the present invention.

  The solution of the above composition has a solid content of 20%, a viscosity of 22 dPa · s (25 ° C.), and is measured by GPC of the hydrophilic polyurethane resin constituting the above composition. The average molecular weight (same in the following examples) is 52,000, the tertiary amino group content in the resin is 0.52 meq / g, the hydrophilic segment content is 33.8%, The content of alumina in the composition (solid content) was 11.7%. The film formed from the solution of the above composition was transparent, the breaking strength was 23.7 Mpa, the breaking elongation was 55%, and the softening point was 155 ° C.

Reference Example 5
(Production of the composition of the present invention)
30 parts of polyethylene oxide diamine (Jefamine ED; molecular weight 2,000), 120 parts of polyol (B) of Reference Example 2, N, N-dimethyl-N ′, N′-dihydroxyethyl-1,3-diaminopropane 25 parts are dissolved in a mixed solvent of 100 parts of methyl ethyl ketone and 200 parts of dimethylformamide, and a solution of 65 parts of hydrogenated MDI dissolved in 100 parts of methyl ethyl ketone is gradually added dropwise with good stirring at 60 ° C. . After completion of the dropwise addition, the mixture was reacted at 80 ° C. for 8 hours, and then 560 parts of dimethylformamide was added to obtain a solution (paint) of the composition of the present invention.

  The solution of the above composition had a solid content of 20% and a viscosity of 40 dPa · s (25 ° C.). The hydrophilic polyurethane-polyurea resin constituting the composition has a weight average molecular weight of 51,000, the tertiary amino group content in the resin is 1.08 meq / g, and the hydrophilic segment content. Was 48.5%, and the content of alumina in the composition (solid content) was 24.0%. The film formed from the solution of the composition was transparent, the breaking strength was 18.5 Mpa, the breaking elongation was 20%, and the softening point was 165 ° C.

Reference Example 6
(Production of the composition of the present invention)
5 parts of polyethylene oxide diamine (Jefamine ED; molecular weight 2,000), 145 parts of polyamine (C) of Reference Example 3 and 3 parts of methyliminobispropylamine are dissolved in 250 parts of dimethylformamide, and the liquid temperature is adjusted. A solution prepared by dissolving 7 parts of hydrogenated MDI in 100 parts of dimethylformamide was gradually dropped and reacted while maintaining at 0 to -5 ° C. and sufficiently stirring. After completion of the dropwise addition, the liquid temperature was gradually raised, and when the temperature reached 50 ° C., the mixture was further reacted for 5 hours, and then 310 parts of dimethylformamide was added to obtain a solution (paint) of the composition of the present invention.

  The solution of the composition has a solid content of 20%, a viscosity of 80 dPa · s (25 ° C.), and the hydrophilic polyurea resin constituting the composition has a weight average molecular weight of 38,000, The tertiary amino group content in the resin was 0.45 meq / g, the hydrophilic segment content was 65.0%, and the alumina content in the composition (solid content) was 79%. It was. The film formed from the solution of the above composition was slightly translucent and porous, had a breaking strength of 4.2 Mpa, a breaking elongation of 3%, and a softening point of 210 ° C.

Reference Example 7
A polyurethane resin solution (paint) was obtained by the same material and formulation as in Reference Example 4 except that N-methyldiethanolamine was not used and the polyol (A) of Reference Example 1 except for the alumina was used. This resin solution had a solid content of 20%, a viscosity of 50 dPa · s (25 ° C.), and the weight-average molecular weight of the polyurethane resin was 68,000. The film formed from the resin solution had a breaking strength of 35.0 Mpa, a breaking elongation of 450%, and a softening point of 103 ° C.

Reference Example 8
Reference Example 5 except that N, N-dimethyl-N ′, N′-dihydroxyethyl-1,3-diaminopropane is not used and the polyol (B) of Reference Example 2 except for alumina is used. A polyurethane-polyurea resin solution (paint) was obtained using the same material and formulation. This resin solution had a solid content of 20%, a viscosity of 40 dPa · s (25 ° C.), and the polyurethane-polyurea resin had a weight average molecular weight of 55,000. The film formed from the resin solution had a breaking strength of 25.3 MPa, a breaking elongation of 400%, and a softening point of 95 ° C.

Reference Example 9
A solution (paint) of a polyurea resin was obtained by the same material and formulation as in Reference Example 6 except that methyliminobispropylamine was not used and the polyamine (C) in Reference Example 3 except for the alumina was used. . This resin solution had a solid content of 20%, a viscosity of 25 dPa · s (25 ° C.), and the polyurea resin had a weight average molecular weight of 32,000. The film formed from the resin solution had a breaking strength of 22.7 MPa, a breaking elongation of 350%, and a softening point of 115 ° C.

Reference Examples 10-12
The alumina water sols of Reference Examples 1 to 3 were added to the resin solutions of Reference Examples 7 to 9 with stirring, but fine particle alumina was precipitated, and the solution (paint) became opaque.

Reference Example 13
A 5% aqueous solution (paint) of polyvinyl alcohol (polymerization degree 550) having a saponification degree of 98.5% was prepared.

Examples 1-3
Each of the solutions (paints) of the composition of the present invention obtained in Reference Examples 4 to 6 was applied to high-quality paper having a basis weight of 35 g / m ² with an air knife coater so that the thickness after drying was 25 μm. The ink receiving layer was formed by drying to obtain a recording sheet of the present invention.

Comparative Examples 1-7
Each of the resin solutions (paints) obtained in Reference Examples 7 to 13 was applied and dried on a high-quality paper having a basis weight of 35 g / m ² with an air knife coater so that the thickness after drying was 25 μm. A receiving layer was formed to obtain a recording sheet of a comparative example.

[Evaluation of recording sheet]
The 10 types of recording sheets obtained as described above are printed using four colors of yellow, magenta, cyan, and black with an ink jet printer (PM-800C manufactured by Seiko Epson Corporation) that records and records with water-soluble dye ink. Records were made and the following items were evaluated.

(1) Blocking resistance An untreated PET film was stacked on the surface of the ink receiving layer, and the blocking resistance after standing for one day at a load of 0.29 MPa and a temperature of 40 ° C. was evaluated. The results are displayed as follows:
○: No blocking property Δ: Some blocking property ×: Blocking property

(2) Transparency The haze on the surface of the ink receiving layer was visually determined. The results are displayed as follows:
○: Completely transparent △: Slightly cloudy ×: Completely opaque

(3) Color clarity The color clarity of the obtained color image was visually observed after color printing on the ink receiving layer with an inkjet printer. The results are displayed as follows:
○: Clear with no blurring △: Slightly blurring and slightly blurry

(4) Dryability of ink After color printing on the ink receiving layer with an ink jet printer, the filter paper was pressed against the print surface for 5 seconds under a load of 50 g / m ² , and the time until the ink was not transferred to the filter paper was measured.

(5) Water resistance of the printed image After color printing on the ink receiving layer with an ink jet printer, the recording sheet is immersed in water (20 ° C, 1 hour), and then dried at room temperature. Was observed visually. The results are displayed as follows:
◯: No blurring or color development of the image Δ: Change is observed in the image and the ink receiving layer ×: The image can be considerably taken or taken together with the ink receiving layer The above evaluation results are shown in Table 1.

According to the present invention described above, by forming an ink receiving layer using the composition of the present invention, it is possible to record a high-quality printed image with excellent ink absorbability, drying property, and color developability. Furthermore, a recording sheet having an ink receiving layer excellent in transparency, blocking resistance and water resistance of a printed image is provided.

Claims (10)

  In an inkjet recording sheet in which at least one ink receiving layer is provided on at least one side of a substrate sheet, the ink receiving layer comprises an organic polyisocyanate, a high molecular weight hydrophilic polyol and / or a polyamine, and at least one It is formed using a composition comprising a hydrophilic polyurethane resin obtained by reacting a compound having an active hydrogen-containing group and at least one tertiary amino group in the same molecule and fine particle alumina. An ink jet recording sheet.   2. The inkjet recording sheet according to claim 1, wherein the content of the fine particle alumina is an amount occupying 5 to 95% by mass in the composition.   The inkjet recording sheet according to claim 1, wherein the fine particle alumina is added to the high molecular weight hydrophilic polyol and / or polyamine when the hydrophilic polyurethane resin is synthesized.   The inkjet recording sheet according to claim 1, wherein the particulate alumina is particulate alumina having an average particle diameter of 1 to 300 nm.   The inkjet recording sheet according to claim 1, wherein the content of the hydrophilic segment and the tertiary amino group in the hydrophilic polyurethane resin is 30 to 80% by mass and 0.1 to 50 meq / g, respectively.   In a method for producing an inkjet recording sheet by providing at least one ink receiving layer on at least one side of a substrate sheet, the ink receiving layer comprises an organic polyisocyanate, a high molecular weight hydrophilic polyol and / or a polyamine, and at least A paint comprising a composition comprising a hydrophilic polyurethane resin obtained by reacting a compound having one active hydrogen-containing group and at least one tertiary amino group in the same molecule, and fine particle alumina. A method for producing an inkjet recording sheet, wherein the recording sheet is formed by applying and drying on at least one side of a material sheet.   The method for producing an ink jet recording sheet according to claim 6, wherein the fine particle alumina is added to the high molecular weight hydrophilic polyol and / or polyamine when the hydrophilic polyurethane resin is synthesized.   The method for producing an ink jet recording sheet according to claim 6, wherein the content of the particulate alumina is an amount occupying 5 to 95% by mass in the composition.   The method for producing an ink jet recording sheet according to claim 6, wherein the fine particle alumina is fine particle alumina having an average particle diameter of 1 to 300 nm. The method for producing an inkjet recording sheet according to claim 6, wherein the hydrophilic segment and the tertiary amino group in the hydrophilic polyurethane resin have a content of 30 to 80% by mass and 0.1 to 50 meq / g, respectively.