JP4030975B2 - Inkjet recording sheet and method for producing the same - Google Patents

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 suction 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. Ink droplets are made to fly and adhere to a recording sheet such as paper to record images and characters. High-speed printing is possible, and noise is not generated during printing. As a recording method capable of color printing, it is rapidly spreading in various applications.

  As a recording sheet used for such ink jet recording, the ink adhering to the recording sheet can be absorbed quickly so that the ink does not bleed or flow and impair the print quality. In order to form dots, a recording sheet is proposed 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 the paper itself. ing.

  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, the present invention relates to a recording sheet in which at least one ink receiving layer is provided on at least one side of a base sheet, and the ink receiving layer has a high molecular weight hydrophilicity to which organic polyisocyanate and fine particle alumina are added. A polyol and / or a polyamine (hereinafter referred to as “hydrophilic component”), a compound having at least one active hydrogen-containing group and at least one tertiary amino group in the same molecule, and at least one reactivity. A high molecular weight hydrophilic polyol or polyamine comprising a hydrophilic polyurethane resin obtained by reacting a group and a compound having at least one hydrolyzable silyl group in the same molecule, the particle containing alumina. Is obtained by removing the dispersion medium of the alumina sol from the mixture of the polyol or polyamine and the alumina sol. A is the content of the fine particles alumina, the composition is an amount which accounts for 5 to 95 mass% in the composition comprising the finally obtained the hydrophilic polyurethane resin and the fine particles of alumina (hereinafter "composition of the present invention The recording sheet is characterized in that the recording sheet is formed.

  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 comprises an organic polyisocyanate, a hydrophilic component, a compound having at least one active hydrogen-containing group and at least one tertiary amino group in the same molecule, and at least 1 It is a hydrophilic polyurethane resin obtained by reacting a compound having one reactive group and at least one hydrolyzable silyl group in the same molecule, if necessary, 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, the mixture of the hydrophilic component and the fine particle alumina is not the one in which the fine particle alumina is mechanically mixed and dispersed in the hydrophilic component, but a dispersion medium of the alumina sol from the mixture of the hydrophilic component and the alumina sol. Use the one obtained by removing. When the hydrophilic component is used as a solution of the soluble organic solvent, the soluble organic solvent is also removed from the mixture together with the alumina sol dispersion 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, in the case of forming an ink receiving layer of a recording sheet, a method using a resin solution or a dispersion liquid 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, but this method is because water and alcohol which are dispersion media of the alumina sol react with polyisocyanate which is a raw material of the polyurethane resin. However, a polyurethane resin solution having excellent dispersion stability of fine particle alumina cannot be obtained even if other solvent-based alumina sol is used.

  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 is obtained, and the dispersion amount of the particulate alumina in the hydrophilic component is increased. However, the increase in the viscosity of the hydrophilic component is small, and the fine particle alumina uses a dispersant in the hydrophilic polyurethane resin solution by reacting the fine particle alumina dispersed hydrophilic component with another polyurethane raw material in a solvent. Even if not, a stably dispersed dispersion 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, the fine particle alumina may be agglomerated, and the dispersion stability of the fine particle alumina may be lowered, and a finely divided fine particle alumina dispersed hydrophilic component may be generated. . When the hydrophilic component is used as an organic solvent solution, the organic solvent is removed together with the alumina sol dispersion medium. 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 of the present invention consisting of the finally obtained hydrophilic polyurethane resin and fine particle alumina, and more preferably. The amount occupying 10 to 90% by mass.

  In the present invention, the hydrophilic polyurethane resin constituting the composition of the present invention comprises a hydrophilic segment having a hydrophilic component in the resin molecule as a structural unit and a component having at least one tertiary amino group as the structural unit. It has a tertiary amino group-containing segment and a hydrolyzable silyl group-containing segment whose constituent unit is a component having at least one hydrolyzable silyl group. 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, in addition to the above bonds.

  By introducing a tertiary amino group and a hydrolyzable silyl group into the hydrophilic polyurethane resin, the composition of the present invention is provided with excellent adhesion to various materials, and the above composition is used. The ink-receiving layer formed in this way is imparted with excellent water absorption, antifogging properties, transparency, flexibility, water-based ink writing properties, water resistance, blocking resistance, and lubricity.

The ink receiving layer of the recording sheet of the present invention is formed of the composition of the present invention, and is introduced into the hydrophilic polyurethane resin when printing on the recording sheet having the ink receiving layer using an inkjet ink. The action of the tertiary amino group and hydrolyzable silyl group will be described.
The dye in the inkjet ink generally has an anionic carboxyl group or sulfonic acid group in the molecule, and when the hydrophilic polyurethane resin forming the ink receiving layer comes into contact with the ink, An ionic bond is formed between the anionic group in the dye and the tertiary amino group in the resin. As a result, the dye fixing property in the ink receiving layer and the water resistance of the recorded image are considered to be 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, but actually the receiving layer of the recording sheet of the present invention. And the water resistance of 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.

  Further, by introducing a hydrolyzable silyl group, the hydrophilic polyurethane resin in the present invention can be crosslinked by moisture, and the composition of the present invention is given excellent adhesion to various materials by crosslinking. In addition, the ink-receiving layer formed using the above composition is provided with excellent water absorption, anti-fogging property, transparency, flexibility, water-based ink writing property, water resistance, blocking resistance and slipperiness. The The site for introducing the hydrolyzable silyl group in the hydrophilic polyurethane resin is not particularly limited, but is usually a molecular chain terminal and / or a side chain of the resin.

  The hydrolyzable silyl group introduced into the molecular chain terminal and / or side chain of the hydrophilic polyurethane resin crosslinks the resin with moisture by, for example, the reaction shown in the following formula (I) and / or (II). be able to. By crosslinking, the resin has improved water resistance, and also improved the surface strength of the resin film and improved blocking resistance.

  The crosslinking of the hydrophilic polyurethane resin used in the present invention is caused by moisture. However, since the resin is hydrophilic, it can be crosslinked using moisture in the air. Crosslinking is performed by converting a hydrolyzable silyl group into a silanol group by moisture as described above, and condensing this silanol group. Therefore, a catalyst is added to the composition of the present invention to promote silanol condensation. It is preferable to keep it. Such a catalyst is generally preferably a tin carboxylate, an acidic catalyst or a basic catalyst, and the amount used is preferably in the range of 0.0001 to 10% by mass relative to the hydrophilic polyurethane resin.

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 is at least one active hydrogen-containing group (reactive group) in the molecule, such as an amino group, an epoxy group, or a hydroxyl group. , A mercapto group, a carboxyl group, or a compound having an alkoxy group, an acid halide group, a carboxy ester group, an acid anhydride group, etc. that can be converted into a hydroxyl group or a carboxyl group, and a tertiary amino group in the molecular chain. .

（式中の、Ｒ₁は炭素数２０以下のアルキル基、脂環族基、又は芳香族基（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—. , —CO—, —COO—, —NHCO—, —S—, —SO—, —SO ₂ — and the like, and X and Y are —OH, —COOH, — Reactive groups such as NH ₂ , —NHR ₁ , —SH, etc. X and Y may be the same or different, and X and Y are epoxy groups, alkoxy groups, acid halides that can be derived from the above reactive groups. It may be a group, an acid anhydride group, or a carboxy 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 compounds represented by the above general formulas (1), (2) and (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の整数を表わす。） 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.)

  In the present invention, the compound used for introducing the hydrolyzable silyl group into the hydrophilic polyurethane resin includes at least one reactive group such as an amino group, an epoxy group, a hydroxyl group, a mercapto group, a carboxyl group, and an isocyanate. Examples thereof include a silane coupling agent having a reactive group such as a group and a hydrolyzable silyl group, or a reaction product of the silane coupling agent and an organic polyisocyanate. Typical examples of the hydrolyzable silyl group in the silane coupling agent are alkoxylated silyl groups such as a methoxylated silyl group, an ethoxylated silyl group, and a methoxyethoxylated silyl group. Of course, it can be used.

（式中のＲ₁は低級アルキル基、Ｒ₂は低級アルキル基、低級アルコキシ基又はイソシアネート基を、Ｘは、何もないか、又は２価の有機基、好ましいものはＣ₀〜Ｃ₅₀のアルキレン鎖、芳香族環又は脂肪族環であり、これらの基はその中に連結基として、−Ｎ−、−Ｏ−、−ＣＯ−、−ＣＯＯ−、−ＮＨＣＯ−、−Ｓ−、−ＳＯ−、−ＳＯ₂−等を含んでいてもよい。又、ｍ＝０〜３の整数、ｎ＝３−ｍである。） Examples of the silane coupling agent having a reactive group used in the present invention include the following compounds.
[1] A silane coupling agent represented by the general formula (1) having at least one free isocyanate group.

Wherein R ₁ is a lower alkyl group, R ₂ is a lower alkyl group, a lower alkoxy group or an isocyanate group, X is nothing or a divalent organic group, preferably a C _{0 to} C ₅₀ An alkylene chain, an aromatic ring or an aliphatic ring, and these groups include —N—, —O—, —CO—, —COO—, —NHCO—, —S—, —SO as a linking group therein. -, - SO ₂ - and the like may also contain the addition, m = 0 to 3 integers and n = 3-m)..

Preferred specific examples of the compound represented by the general formula (1) are as follows.

（式中のＹは、−ＮＨ−、−ＮＲ₃−、−Ｏ−、−Ｓ−であり、Ｒ₁、Ｒ₂、Ｘ、ｍ及びｎは前記定義の通りである。Ｒ₃は低級アルキル基である。） [2] A reaction product of a silane coupling agent having an active hydrogen-containing group and an organic polyisocyanate, wherein the product has at least one free isocyanate group in the molecule.
As said silane coupling agent, what is represented by following General formula (2) is mentioned, for example.

(In the formula, Y is —NH—, —NR ₃ —, —O—, —S—, and R ₁ , R ₂ , X, m and n are as defined above. R ₃ is lower alkyl. Group.)

Preferred specific examples of the silane coupling agent represented by the general formula (2) are as follows. In addition, the epoxy group in the following compound is used by opening the ring.

以上のシランカップリング剤は、本発明において使用する好ましいシランカップリング剤の例示であって、本発明はこれらに限定されるものではない。従って、上記の例示の化合物のみならず、その他公知の現在市販されており、市場から容易に入手し得る化合物は、いずれも本発明において使用することができる。

The above silane coupling agents are examples of preferred silane coupling agents used in the present invention, and the present invention is not limited thereto. Therefore, not only the above-exemplified compounds, but also other known compounds that are currently commercially available and can be easily obtained from the market can be used in the present invention.

Hydrophilic polyurethane resins can be introduced with hydrolyzable silyl groups at the time of synthesis, but after synthesizing hydrophilic polyurethane resins into which hydrolyzable silyl groups have not been introduced, the molecular chain ends and / or sides are synthesized. It is preferable to introduce a hydrolyzable silyl group at these sites by reacting the reactive group in the chain with the silane coupling agent as described below.
[1] Introduction to molecular chain end

（上記式中のＲ₁、Ｒ₂、Ｘ及びＹは前記と同じであり、Ｚは−Ｏ−、−Ｓ−、−ＮＲ₃−、−ＮＨ−であり、〔Ｐ〕は重合体１分子当たり少なくとも２つのウレタン結合及び／又はウレア結合を含有する親水性ポリウレタン樹脂の分子鎖を表す。又、Ｒ₃は低級アルキル基であり、ｍ及びｎは前記定義の通りである。） [2] Introduction to molecular chain side chain

(R ₁ , R ₂ , X and Y in the above formula are the same as above, Z is —O—, —S—, —NR ₃ —, —NH—, and [P] is one molecule of polymer. This represents a molecular chain of a hydrophilic polyurethane resin containing at least two urethane bonds and / or urea bonds per unit, R ₃ is a lower alkyl group, and m and n are as defined above.

  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 hydroxyl group at the end 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; at least one reactive group and at least one hydrolyzable silyl group in the same molecule; It can obtain by making it react according to the manufacturing method of a conventionally well-known polyurethane resin with presence of a chain extender if needed. 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 obtained composition of the present invention is in the form of a solid, and the solid composition is used as a soluble organic solvent for the hydrophilic polyurethane resin constituting the composition. Dissolve and use. The soluble organic solvent is not particularly limited, and preferred examples include dimethylformamide and methyl ethyl ketone. Moreover, the solvent used for the synthesis | combination of a hydrophilic polyurethane resin can be used similarly as a soluble organic solvent. 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 are deteriorated. Surprisingly, when the content of fine particle alumina is 75 to 95% by mass, a microporous having a size of several m μm (nm) is obtained by coating the base sheet with a coating liquid using the composition of the present invention. An ink-receiving layer (film) that is high in quality and 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 hydrophilic segments in the resin is relatively large, The ink receiving layer formed using the target resin is insufficient in the development of properties such as water resistance and blocking resistance, while the content of the tertiary amino group exceeds 50 meq / g, that is, When the molecular weight exceeds 500 per 10,000, the ratio of the hydrophilic segment in the resin is relatively decreased, and as a result, the water-repellent property of the ink receiving layer becomes strong, and the water absorption performance and antifogging property are inferior. This is not preferable.

  The content of the hydrolyzable silyl group in the hydrophilic polyurethane resin in the present invention is preferably in the range of 0.001 to 1 meq (milli equivalent) / g, more preferably 0.1 to 1.0 meq / g. If the content of the hydrolyzable silyl group is less than 0.001 meq / g, that is, less than 0.01 per 10,000 molecular weight, the proportion of the hydrophilic segment is relatively large, which is the intended object of the present invention. Insufficient surface properties of the ink-receiving layer such as water resistance and blocking resistance are insufficient. On the other hand, when the content of hydrolyzable silyl groups exceeds 10 meq / g, that is, when the molecular weight is 10,000 per 10,000. On the other hand, the hydrophilic segment in the resin is relatively reduced, and as a result, the water repellency (water resistance) 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. On the other hand, if it exceeds 80% by mass, the water resistance of the ink receiving layer to be formed is 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 of the recording sheet of the present invention, a hydrophobic polymer may be used in combination with the above composition. 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 organic pigment fine particles, 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 of 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 is used without a solvent. 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 solution is preferably, 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 and curling of the recording sheet are 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) was a transparent liquid at a hydroxyl value of 76 mgKOH / g, a water content of 0.15% and at 80 ° C., and the viscosity of the liquid at that time was 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
Obtained by sufficiently mixing 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 (average particle size of alumina 20-30 nm, solid content 40%). The mixture was dehydrated 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)
30 parts of polyethylene glycol (molecular weight 2,040), 120 parts of polyol (A) of Reference Example 1, 7 parts of 1,3-butylene glycol, 9 parts of N-methyldiethanolamine, 200 parts of methyl ethyl ketone and 200 parts In a mixed solvent of dimethylformamide, 65 parts of hydrogenated MDI dissolved in 100 parts of methyl ethyl ketone was gradually added dropwise with stirring at 60 ° C. After completion of the addition, the mixture was stirred at 80 ° C for 8 hours. Reacted. When the obtained resin was analyzed with an infrared spectrophotometer, no absorption of hydroxyl groups was observed in the infrared absorption spectrum, and hydroxyl groups were also confirmed by quantification by the pyridine method (JISK-0070 2.5). There wasn't.

Next, 8 parts of a silane coupling agent having an isocyanate group [(C ₂ H ₅ O) ₃ Si (CH ₂ ) ₃ NCO] is added to the above resin solution and reacted at 80 ° C. for 8 hours. After confirming that the isocyanate group had disappeared from the resulting resin, dimethylformamide was added to adjust the solid content to 20% to obtain a solution (paint) of the composition of the present invention.
The solution of this composition had a viscosity of 25 dPa · s (25 ° C.). Measured by GPC of the hydrophilic polyurethane resin constituting the composition, the weight average molecular weight in terms of standard polystyrene (same in the following examples) is 63,000, and the alumina in the composition (solid content) The content is 15.0%, the tertiary amino group content in the polyurethane resin is 0.36 meq / g, the hydrolyzable silyl group content is 0.08 meq / g, and the hydrophilic segment content is It was 56.1%.

Reference Example 5
(Production of the composition of the present invention)
(1) Production of isocyanate-terminated silane coupling agent 270 parts of an adduct of hexamethylene diisocyanate and water (Juranate 24A-100: manufactured by Asahi Kasei Co., Ltd., NCO% = 23.5) 111 parts of γ-aminopropyltriethoxysilane were gradually added dropwise and reacted to give a colorless and transparent liquid product (D). The obtained product (D) had 10.5% free isocyanate groups [theoretical value (the amount of the groups in the reaction product stoichiometrically generated when 100% reacted) was 11.2%. Theoretically, it seems to have the following structure.

(2) 8 parts of the above liquid product (D), 50 parts of toluene diisocyanate, 150 parts of polyol (B) of Reference Example 2, and N, N-dimethyl-N ′, N′-dihydroxyethyl-1,3 -An isocyanate-terminated polyurethane resin was obtained by reacting 9 parts of diaminopropane in a mixed solvent of 200 parts of dimethylformamide / methyl ethyl ketone (= 1/1 (mass ratio)) at 80 ° C for 5 hours. Next, the temperature of the resin solution was adjusted to 20 ° C., 9 parts of 1,4-diaminobutane dissolved in 50 parts of methyl ethyl ketone was gradually added dropwise, and the reaction was carried out at the same temperature for 1 hour after completion of the addition. Further, 14 parts of γ-aminopropyltrimethoxysilane dissolved in 50 parts of methyl ethyl ketone was gradually added dropwise and reacted at 30 ° C. for 1 hour. After confirming that the isocyanate group had disappeared from the resulting resin, dimethylformamide Was added to adjust the solid content to 20% to obtain a solution (paint) of the composition of the present invention.
The solution of this composition had a viscosity of 32 dPa · s (25 ° C.). The hydrophilic polyurethane-polyurea resin constituting the composition has a weight average molecular weight of 57,000, the alumina content in the composition (solid content) is 31.2%, and the third in the resin. The content of the secondary amino group was 0.60 meq / g, the content of the hydrolyzable silyl group was 0.30 meq / g, and the content of the hydrophilic segment was 45.4%.

Reference Example 6
(Production of the composition of the present invention)
19 parts of hydrogenated MDI, 5 parts of polyethylene oxide diamine (Jefamine ED; molecular weight 2,000), 145 parts of polyamine (C) of Reference Example 3, and 2 parts of methyliminobispropylamine The reaction was carried out in dimethylformamide at 30 ° C. for 4 hours to obtain an isocyanate-terminated polyurea resin. Next, the temperature of the resin solution was adjusted to 20 ° C., 1 part of 1,4-diaminobutane dissolved in 50 parts of methyl ethyl ketone was gradually added dropwise, and the reaction was allowed to proceed at the same temperature for 1 hour. Further, 3 parts of γ-aminopropyltrimethoxysilane dissolved in 50 parts of methyl ethyl ketone was gradually dropped and reacted at 30 ° C. for 1 hour, and it was confirmed that the isocyanate group had disappeared from the resulting resin in the same manner as described above. After that, dimethylformamide was added to adjust the solid content to 20% to obtain a solution (paint) of the composition of the present invention.
The solution of this composition had a viscosity of 17 dPa · s (25 ° C.). The hydrophilic polyurea resin constituting the composition has a weight average molecular weight of 38,000, the content of alumina in the composition (solid content) is 75%, and the tertiary amino group in the resin The content was 0.47 meq / g, the hydrolyzable silyl group content was 0.20 meq / g, and the hydrophilic segment content was 43.8%.

Reference Example 7
A polyurethane resin having the same material and formulation as in Reference Example 4 except that N-methyldiethanolamine and a silane coupling agent having an isocyanate group are not used, and the polyol (A) of Reference Example 1 except for the alumina is used. Solution (paint) was obtained.
This resin solution had a solid content concentration of 20%, a viscosity of 47 dPa · s (25 ° C.), and the polyurethane resin had a weight average molecular weight of 86,000.

Reference Example 8
N, N-dimethyl-N ′, N′-dihydroxyethyl-1,3-diaminopropane, an isocyanate-terminated silane coupling agent and γ-aminopropyltrimethoxysilane were not used, and the polyol (B A polyurethane-polyurea resin solution (paint) was obtained using the same materials and formulation as in Reference Example 5 except that the polyol of FIG.
This resin solution had a solid concentration of 20%, a viscosity of 55 dPa · s (25 ° C.), and the polyurethane-polyurea resin had a weight average molecular weight of 91,000.

Reference Example 9
Polyurea resin with the same materials and formulation as in Reference Example 6 except that methyliminobispropylamine and γ-aminopropyltrimethoxysilane are not used, and the polyamine (C) of Reference Example 3 except for polyamine is used. Solution (paint) was obtained.
This resin solution had a solid content concentration of 20%, a viscosity of 25 dPa · s (25 ° C.), and the polyurea resin had a weight average molecular weight of 68,000.

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
The paint obtained in Reference Examples 4 to 6 was applied to a high-quality paper having a basis weight of 35 g / m ² and dried with an air knife coater so that the thickness after drying was 25 μm, thereby forming an ink receiving layer. Recording sheet.

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 change in bleeding and 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 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.

Claims (6)

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 is a high molecular weight hydrophilic polyol to which organic polyisocyanate and fine particle alumina are added and / or A polyamine, a compound having at least one active hydrogen-containing group and at least one tertiary amino group in the same molecule, at least one reactive group and at least one hydrolyzable silyl group; A composition comprising a hydrophilic polyurethane resin obtained by reacting with a compound having the same molecule , wherein the high molecular weight hydrophilic polyol or polyamine containing fine particle alumina is converted into an alumina sol from the polyol or a mixture of polyamine and alumina sol. Obtained by removing the dispersion medium of Yes amount finally be formed from the composition is an amount which accounts for 5 to 95 mass% in the composition comprising the above-described hydrophilic polyurethane resin and the fine particles of alumina obtained inkjet recording, wherein Sheet.   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.   Content of the hydrophilic segment in a hydrophilic polyurethane resin, a tertiary amino group, and a hydrolysable silyl group is 30-80 mass%, 0.1-50 meq / g, and 0.001-10 meq / g, respectively. The inkjet recording sheet according to claim 1. In a method for producing an inkjet recording sheet by providing at least one ink receiving layer on at least one side of a base sheet, a high molecular weight hydrophilic polyol in which an organic polyisocyanate and particulate alumina are added to the ink receiving layer And / or a polyamine, a compound having at least one active hydrogen-containing group and at least one tertiary amino group in the same molecule, at least one reactive group and at least one hydrolyzable silyl. A composition comprising a hydrophilic polyurethane resin obtained by reacting a compound having a group in the same molecule , wherein the high molecular weight hydrophilic polyol or polyamine containing the fine particle alumina is a mixture of the polyol or polyamine and alumina sol. Fine particles obtained by removing the dispersion medium of alumina sol from the mixture The content of alumina is coated with a paint containing the composition is an amount which accounts for 5 to 95 mass% in the composition comprising the finally obtained the hydrophilic polyurethane resin and the fine particles of alumina on at least one surface of the substrate sheet and A method for producing an ink jet recording sheet, which is formed by drying. The method for producing an ink jet recording sheet according to claim 4 , wherein the fine particle alumina is fine particle alumina having an average particle diameter of 1 to 300 nm. Content of the hydrophilic segment in a hydrophilic polyurethane resin, a tertiary amino group, and a hydrolysable silyl group is 30-80 mass%, 0.1-50 meq / g, and 0.001-10 meq / g, respectively. The manufacturing method of the recording sheet for inkjets of Claim 4 .