JPH09175003A - Ink-jet recording sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a recording sheet that is excellent in water and moisture resistances, by a method wherein resin components that form an ink receptive layer include polyvinyl alcohol based copolymer resin into which fatty polyester is grafted. SOLUTION: If polyvinyl alcohol based copolymer resin into which fatty polyester is grafted is a resin produced by grafting fatty polyester into polyvinyl alcohol, any sort of it can be used. However, a graft copolymer resin that can be obtained by ring-opening polymerization of lactone compound, that forms fatty polyester, in the presence of polyvinyl alcohol is desirable. It is desirable that polyvinyl alcohol has a saponification value of at least 60mol% in vinyl acetate unit and a weight-average degree of polymerization of 20-20,000. As graft copolymer resin is used as a resin component that forms an ink receptive layer, the water-absorption property of the ink receptive layer can be controlled to an optimum capacity. Thereby, a stable, high-quality printed image that is excellent in color developing property can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording sheet for ink jet, and more particularly, to an ink receiving layer excellent in water-based ink absorptivity, giving a stable and high-quality printed image, and excellent in water resistance and moisture resistance. The present invention relates to a recording sheet for inkjet.

[0002]

2. Description of the Related Art Ink jet recording has various operating principles, for example, an electrostatic suction method, a method of applying mechanical vibration or displacement to ink using a piezoelectric element, a method of heating ink for foaming and utilizing its pressure. , Etc. to eject fine droplets of ink to adhere to a recording sheet such as paper,
It is used for recording characters and the like, and it is rapidly spreading to various uses as a recording system that produces little noise and can perform high-speed printing, high-quality printing, and multicolor printing.

In a recording medium used for such ink jet recording, ink is adhered to a support such as paper so that the ink adhered on the recording medium does not cause bleeding or flow and impair the printing quality. A sheet provided with an ink receiving layer containing various pigments and resins as main components so as to accelerate absorption and form clear ink dots, or a recording sheet in which porous pigment is incorporated into the paper itself. Is proposed.

For example, JP-A-57-82085 discloses an ink receiving layer comprising a water-soluble polymer in which an inorganic pigment and an organic pigment are used in combination as a pigment, and JP-A-62-268.
Japanese Patent No. 682 each discloses providing an ink receiving layer made of finely powdered silica and a polyvinyl alcohol copolymer having a silanol group.

However, with the improvement of the performance of the ink jet recording apparatus such as speeding up, high definition or full color of the apparatus and the expansion of applications, it is required that the ink jet recording sheet also has the following high-level characteristics. It has started to be done. (1) The ink absorption is fast and the absorption capacity is large. (2) The color development of the ink is high. (3) The surface strength of the ink receiving layer is high. (4) The support has water resistance and the ink does not cause unevenness or curl on the support. (5) The ink receiving layer has good image storability such as water resistance and ozone resistance after image printing. (6) The ink receiving layer should not change with time.

[0006] Conventionally, in order to meet these requirements, a porous pigment or a water-soluble polymer having excellent ink absorbability is used as a component of an ink receiving layer provided in an ink jet recording sheet, or the water resistance of the ink receiving layer is used. For the purpose of improvement, it has been carried out and studied to use a water-resistant polymer latex and further to use synthetic paper or plastic having water resistance for the support itself.

However, when a paper is used for the support or an aqueous polymer alone is used as an ink receiving layer, the water resistance is poor, the printed portion is bleeding, and the sharpness is poor. On the other hand, when a synthetic paper or a plastic film is used for the support or a water-resistant polymer latex is used for the resin of the ink receiving layer, the adhesiveness between the ink receiving layer and the support, the ink absorbency and the drying property, etc. I have a problem.

[0008]

SUMMARY OF THE INVENTION Therefore, the object of the present invention is to provide a stable and high-quality printed image, in particular, having excellent absorptivity of water-based ink, sharp shape, and excellent color developability of ink. It is intended to provide an inkjet recording sheet having an ink receiving layer having excellent water resistance and moisture resistance.

In general, the resolution of a printed image on an ink jet recording sheet depends on the amount of ink absorbed, and if the ink absorbency is too high, the density of the printed image decreases and the sharpness and color developability also decrease. However, the resolution will be inferior. On the other hand, if the ink absorbency is too low, the print image density increases, but there are drawbacks such as deterioration of the print image quality due to uneven density and bleeding, and longer ink drying time.

The inventors of the present invention have conducted various studies to solve the problems of the conventional ink jet recording sheet as described above, and as a result, formed an ink receiving layer of a specific polymer to obtain an aqueous ink. It is possible to obtain an inkjet recording sheet having an ink-receiving layer that has excellent water absorption and moisture resistance, has a sharp shape, is excellent in ink color development, gives a stable and high-quality printed image, and is also excellent in water resistance and moisture resistance. Found.

[0011]

The above object is achieved by the present invention described below. That is, the present invention is an inkjet recording sheet in which at least one or more ink receiving layers are provided on one surface of a base sheet used for inkjet recording, and the resin component constituting the ink receiving layer is
An inkjet recording sheet comprising a polyvinyl alcohol-based copolymer resin grafted with an aliphatic polyester.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention will be described in detail with reference to embodiments of the present invention. The inkjet recording sheet of the present invention is provided with at least one or more ink receiving layers on one surface of the base sheet, and the ink receiving layer is formed by using a polyvinyl alcohol-based copolymer resin grafted with an aliphatic polyester as a constituent resin component. Is a feature.

The polyvinyl alcohol-based copolymer resin represented by the aliphatic polyester used in the present invention may be any resin as long as the aliphatic polyester is grafted onto polyvinyl alcohol, regardless of the production method. However, a particularly preferable resin is a graft copolymer resin obtained by ring-opening polymerization of a lactone compound forming an aliphatic polyester in the presence of polyvinyl alcohol.

The polyvinyl alcohol used in the present invention has a degree of saponification of vinyl acetate units of 60 mol% or more and a weight average degree of polymerization of 20 to 20,000, preferably 200 to 3.
000 is preferable. If the degree of saponification is less than 60 mol%, it is difficult to control the grafting reaction, which is not preferable. It is more preferably 70 to 99.5 mol%.

As the lactone compound which is subjected to ring-opening polymerization in the presence of polyvinyl alcohol in the present invention, any lactone compound which can form an aliphatic polyester by conventionally known lactone ring-opening polymerization can be used. Particularly preferred lactone compounds are ε-caprolactone compounds and / or δ-valerolactone compounds.

Examples of the ε-caprolactone compound include 1 to 1 carbon atoms such as ε-caprolactone, monomethyl-ε-caprolactone, monoethyl-ε-caprolactone, monopropyl-ε-caprolactone, and monododecyl-ε-caprolactone. Dialkyl-ε having about 15 various monoalkyl-ε-caprolactones or two same alkyl groups respectively substituted and bonded with hydrogen of different carbon atoms other than the carbon atom at the ε-position. -Caprolactones or lactone ring ε-
The hydrogen of the carbon atom at the position is not substituted at all or is mono-substituted, and one hydrogen of the other 2 or 3 carbon atoms is substituted by 2 or 3 alkyl groups respectively. Alkoxy-ε-caprolactones such as trialkyl-ε-caprolactone and ethoxy-ε-caprolactone, or cycloalkyl-ε-caprolactone such as cyclohexyl, phenyl- and benzyl-ε-caprolactone, aryl-
Examples include ε-caprolactone and aralkyl-ε-caprolactone.

Examples of the δ-valerolactone compound include 5-valerolactone, 3-methyl-5-valerolactone, 3,3, -dimethyl-5-valerolactone, 2-methyl-5-valerolactone, 3-ethyl-5
-Valerolactone and the like. The above lactone compounds are used alone or in combination of two or more.

The ring-opening polymerization of the lactone compound in the presence of polyvinyl alcohol is preferably carried out by mixing solid polyvinyl alcohol and a liquid lactone compound, preferably using a ring-opening polymerization catalyst under a nitrogen stream. ~ 220
The reaction is carried out at a temperature of ° C for several hours to several tens of hours to obtain a thermoplastic polyvinyl alcohol-based copolymer resin in which polyvinyl alcohol is grafted with an aliphatic polyester. In the conventional reaction using polyvinyl alcohol, polyvinyl alcohol is generally used in an emulsified and dispersed state or in a state of being dissolved in a solvent such as water or alcohol. This is because, in addition to the extremely high softening temperature of polyvinyl alcohol, polyvinyl alcohol gradually undergoes thermal decomposition when heated at a temperature of 100 ° C. or higher for a long time.

According to the above method of the present invention, however, the white powder of polyvinyl alcohol and the liquid lactone compound are in a non-uniform state in the initial mixed state, but the white powder of polyvinyl alcohol disappears as the reaction progresses. Then, a uniform state was obtained, and no thermal decomposition of polyvinyl alcohol in an unreacted state was observed even under high temperature. In addition, the reaction is a single and twin screw extruder, Banbury mixer,
It is also possible to perform the heating and melting with a kneader such as a kneader or Brabender.

In the present invention, by changing the molecular weight of the aliphatic polyester grafted onto polyvinyl alcohol, that is, the weight ratio of polyvinyl alcohol and the aliphatic polyester, a polyvinyl alcohol-based polymer having the respective properties of polyvinyl alcohol and aliphatic polyester is obtained. A copolymer resin is obtained. The preferred polyvinyl alcohol-based copolymer resin of the present invention is polyvinyl alcohol 95-
30% by weight, preferably 80-40% by weight, aliphatic polyester 5-70% by weight, preferably 20-60% by weight
It is a resin composed of.

Therefore, by using a resin obtained by graft-copolymerizing a hydrophobic aliphatic polyester with polyvinyl alcohol, which is the most hydrophilic water-soluble polymer, as a resin component constituting the ink receiving layer of an ink jet recording sheet, The water absorption of the ink receiving layer can be controlled to the optimum performance. That is, it is possible to improve the adhesiveness and flexibility of the aliphatic polyester with the base sheet, water resistance, and moisture resistance without impairing the surface strength and water absorption of polyvinyl alcohol, and to obtain an extremely excellent ink receiving layer. be able to.

As the base material of the ink jet recording sheet of the present invention, paper, plastic film, glass or the like is used. Examples of the paper include high quality paper, medium quality paper, coated paper, cast coated paper and the like. As the plastic film, the thickness of polyester, polyamide, cellulose triacetate, polycarbonate, polyvinyl chloride, polyethylene, polypropylene, polystyrene, polymethylmethacrylate, etc. is 50 to 2
A 50 μm sheet or the like can be mentioned. In addition, if necessary, a primer layer that imparts adhesiveness to the substrate and a back surface that is the non-receptive layer side can be provided with a curl prevention layer or a slipping layer that improves the friction coefficient.

The polyvinyl alcohol-based copolymer resin of the present invention may be used alone as the resin component constituting the ink receiving layer, but depending on the ink composition of the ink jet, it further imparts hydrophilicity and / or water absorption. Alternatively, it may be used in combination with a water-soluble polymer for the purpose of adjusting. Examples of the water-soluble polymer include polyvinyl alcohol, modified polyvinyl alcohol, hydroxyethyl cellulose, CMC, cellulose derivative, polyvinylpyrrolidone, starch, cationic starch, gelatin, casein, acrylic acid polymer and the like.

A hydrophobic polymer may be used in combination for the purpose of further imparting water resistance and durability to the ink receiving layer and the printed image. Examples of the hydrophobic polymer include polyester resin, polyvinyl chloride resin, polystyrene resin, polymethylmethacrylate resin, polycarbonate resin, polyurethane resin, vinyl chloride-vinyl acetate copolymer resin, acrylonitrile-styrene copolymer resin, polyvinyl butyral resin. Commonly used synthetic resins such as polyamide resin, epoxy resin, urea resin and melamine resin can be used.

Further, the ink absorbency of the ink receiving layer,
Inorganic or organic pigments or resin particles may be added and used for the purpose of improving fixability, color development property, blocking property, and water resistance. Examples of pigments and resin particles used include kaolin, deramikaolin, aluminum hydroxide, silica, diatomaceous earth, calcium carbonate, talc, titanium oxide, calcium sulfate, barium sulfate, zinc oxide,
Alumina, calcium silicate, magnesium silicate, colloidal silica, zeolite, bentonite, sericite,
Known pigments and resins such as mineral pigments such as lithopone, porous pigments, polystyrene resins, urea resins, acrylic resins, melamine resins, benzoguanamine resins, polyurethane resins, other fine particles such as organic pigments, porous fine particles, and hollow particles From the particles, one kind or two or more kinds are appropriately used depending on the quality design of the inkjet recording sheet. In this case, the amount of these pigments and resin particles used is 0 to 95% by weight, preferably 10 to 90% by weight, based on the total solid content of the resin composition for forming the ink receiving layer.

In addition to the resin and the pigment, a thickener, a release agent, a penetrant, a wetting agent, and
Thermal gelling agent, sizing agent, defoaming agent, defoaming agent, foaming agent, coloring agent, fluorescent whitening agent, ultraviolet absorber, antioxidant, quencher, preservative, antistatic agent, cross-linking agent, dispersion Agent, lubricant,
It is also possible to appropriately mix various auxiliaries such as a plasticizer, a pH adjuster, a fluidity improver, a solidification accelerator, and a waterproofing agent.

In order to form the ink receiving layer on the substrate, the polyvinyl alcohol copolymer resin of the present invention is used alone.
Or dissolved in various organic solvents and water with other resins, further coating liquid prepared by the pigment or resin particles and various auxiliaries, for example, gravure coating, direct or reverse roll coating, wire bar coating, air knife coating, It is applied by a method such as curtain coating, blade coating, rod coating or die coating. Further, after coating, finishing is performed using a calendar such as a machine calendar, a super calendar, and a soft calendar. The amount of the polyvinyl alcohol-based copolymer resin used is preferably 0.5 to 50 g / m ² in terms of dry weight, more preferably 3 to ²
It is about 0 g / m ² . If it is less than 0.5 g / m ² , the ink absorption is insufficient, and if it exceeds 50 g / m ² , the effect is saturated even if it is used more than this, and it is uneconomical, as well as bending, cracking and curling. It is not preferable because the occurrence of such as is likely to occur.

[0028]

Next, the present invention will be described more specifically with reference to examples and comparative examples. In the text and tables, parts and% are based on weight unless otherwise specified.

Reference Examples 1 to 4 Polyvinyl alcohol powder having a saponification degree of 98.5% (polymerization degree of 550) and ε-caprolactone in the amounts shown in Table 1 and ε-caprolactone were charged, and further tetrabutyl titanate was charged in a nitrogen stream. The temperature was raised at 1 ° C / 2 to 3 min with stirring. When it reaches 150 to 160 ° C, the heterogeneous system until then gradually becomes uniform, and at 180 to 200 ° C, it becomes a completely homogeneous system. When the reaction is continued at 200 to 220 ° C for 6 hours, the resin of the present invention is obtained. Table 1 shows polyvinyl alcohol and ε
The properties of each of the obtained polyvinyl alcohol-based copolymer resins are shown together with the proportion of caprolactone used.

Comparative Reference Example Using only polyvinyl alcohol having a saponification degree of 98.5% (polymerization degree of 550) of the reference example, physical properties were evaluated using a film cast from an aqueous solution. Table 1 shows the above results.

[0031]

[Table 1]

[Test Method] Each physical property was tested by the following methods. (1) Number average molecular weight GPC in N, N-dimethylformamide solution (5%)
measured value. (2) Hardness Sheets obtained by press-molding the resins obtained in Reference Examples 1 to 4 at a temperature of 160 ° C. were measured with an A-type hardness meter based on JIS K-6301. The polyvinyl alcohol of Comparative Example could not be press-molded. (3) 100% modulus (MPa), tensile strength (MP
a), Elongation (%) The press-formed sheets obtained in Examples 1 to 4 are JIS K
It was punched out with a No. 3731 dumbbell and the physical properties were measured according to the same JIS. Incidentally, the polyvinyl alcohol of the comparative example was punched out from a sheet obtained by casting an aqueous solution with a No. 3 dumbbell and the physical properties were measured. (4) Vicat Softening Point (° C.) The softening point of each resin was measured according to JIS K-7206. Incidentally, the polyvinyl alcohol of Comparative Example could not be measured because dehydration decomposition occurred as the temperature was raised.

Examples 1 to 4 40 parts of each of the resins obtained in Reference Examples 1 to 4 and fine particle synthetic amorphous silica (BET specific surface area 300 m ² / g,
100 parts of Mizusawa Chemical Co., Ltd. and 0.2 parts of a dispersant (sodium polypyrophosphate) were dispersed and mixed in a water-ethyl alcohol mixed solvent to adjust the solid content to 15% to obtain a coating liquid. Each coating liquid was applied to a high-quality paper having a basis weight of 35 g / m ² by using an air knife coater so that the coating amount was 10 g / m ² (dry basis) to form an ink receiving layer and dried. After that, a super calendar finish was performed at a linear pressure of 200 kg / cm.

Comparative Example 1 An ink receiving layer was formed in the same manner as in Examples 1 to 4 except that polyvinyl alcohol (polymerization degree 550) having a saponification degree of 98.5% in Reference Examples 1 to 4 was used.

Comparative Example 2 An ink receiving layer was formed in the same manner as in Examples 1 to 4 except that polyvinylpyrrolidone (molecular weight 360,000, manufactured by BASF) was used.

The six types of sheets having the ink receiving layer formed as described above are printed and recorded by using an ink jet printer for printing and recording with a water-soluble dye ink, using four colors of yellow, magenta, cyan and black. The following items were evaluated. Table 2 shows the results.

[Ink Absorption] The number of seconds until the printed ink dries was measured. ◯: 5 seconds or less Δ: 6 to 10 seconds ×: 11 seconds or more [Density unevenness] After printing a 50% halftone pattern with cyan ink, the obtained image was visually observed. ◯: No density unevenness occurs Δ: Some density unevenness occurs ×: Density unevenness occurs [Coloring sharpness] After printing a color image with the above printer,
The color development sharpness of the obtained color image was visually observed. ◯: Good Δ: Normal ×: Poor [Bleed] The degree of ink bleeding and runoff at the boundary between the overlapping printing of magenta and cyan was visually observed. ◯: Good Δ: Normal ×: Poor [Coating layer strength] The recording sheet was bent 10 times and the state such as peeling or cracking of the coating layer was observed. ◯: No change Δ: Slight change X: Peeling or cracking occurred [Water resistance of the receiving layer] Water was applied to the ink receiving layer, and the peeled state of the receiving layer when water was wiped off with a constant finger pressure was evaluated. ◯: No change Δ: Slight change X: Peeling [Water resistance of printed image] After printing on a printer, the recording sheet was immersed in water for 10 minutes and then dried at room temperature to cause bleeding of the recorded image and change in color development. Observe visually. ：: No change △: Slight discoloration ×: Discoloration

[0038]

[Table 2]

[0039]

According to the present invention as described above, by using a copolymer resin in which polyvinyl alcohol is grafted with an aliphatic polyester as a resin component constituting the ink receiving layer, ink absorption and coloring properties are excellent and stable. There is provided an inkjet recording sheet which gives a high-quality printed image and is excellent in water resistance and moisture resistance of the ink receiving layer and the stamp image.

Claims (5)

[Claims] 1. A recording sheet for ink-jet recording comprising at least one ink-receiving layer on at least one surface of a base sheet, wherein the resin component constituting the ink-receiving layer is a polyvinyl alcohol-based copolymer grafted with an aliphatic polyester. An ink jet recording sheet comprising a resin. 2. A polyvinyl alcohol-based copolymer resin,
The inkjet recording sheet according to claim 1, comprising 95 to 30% by weight of polyvinyl alcohol and 5 to 70% by weight of an aliphatic polyester. 3. The degree of saponification of polyvinyl alcohol is 60.
The ink jet recording sheet according to claim 1 or 2, wherein the content is mol% or more. 4. The inkjet recording sheet according to claim 1, wherein the aliphatic polyester is a ring-opening polymer of an ε-caprolactone compound and / or a δ-valerolactone compound. 5. A polyvinyl alcohol-based copolymer resin,
The resin obtained by ring-opening polymerization of a lactone compound in the presence of polyvinyl alcohol.
The inkjet recording sheet according to the item.