JP2023071094A - Recording paper - Google Patents

Abstract

To provide a recording paper with which it is possible to achieve printing with various inks, such as ultraviolet-curable ink, solvent ink, thermofusible transfer recording ink and aqueous ink, according to a printing method.SOLUTION: A recording paper includes a base material including a thermoplastic resin, and a print receptive layer disposed on at least one surface of the base material. The surface of the print receptive layer has Oken type smoothness of 200 seconds or more which is measured according to JIS P8155(2010). The recording paper has a Cobb water absorption degree of 1-5 g/m2 in a test method for water absorption degree defined in JIS P8140:1998.SELECTED DRAWING: Figure 1

Description

The present invention relates to recording paper applicable to various printing methods.

Conventionally, offset printing has been commonly used as a printing method in commercial printing, but in addition to gravure printing and flexo printing, digital printing such as electrophotography (toner method) and inkjet method is increasing in recent years. there is In the field of label printing, fusion heat transfer printing and the like are also widely used.

For such a wide variety of printing methods, dedicated recording papers suitable for the inks used for each method have been proposed. For example, recording paper suitable for offset printing with a smooth printing surface and good transferability of oil-based ink and UV curable ink, and water-based inkjet printing with high water absorption and good ink drying properties. Recording paper (for example, Patent Document 1) and the like.

On the other hand, as the required properties of recording paper vary depending on the printing method and the ink used, there is an increasing need for recording paper that can be applied to a wide variety of printing methods.

JP-A-2005-7675

However, conventional recording paper suitable for offset printing often has insufficient water absorbency and tends to be unsuitable for water-based ink jet printing. Further, conventional recording paper suitable for water-based ink jet printing often has a high surface roughness and is not suitable for offset printing. Thus, no recording paper has been obtained which is sufficiently applicable to various printing methods.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a recording paper that can be applied to a wide variety of printing methods, such as offset printing using oil-based ink or UV-curable ink, fusion heat transfer printing, water-based inkjet printing, and the like.

The inventors of the present invention have made intensive studies to solve the above problems, and found that a recording paper comprising a substrate containing a thermoplastic resin and a print-receiving layer provided on at least one surface of the substrate , it was found that by setting the smoothness of the print-receiving layer side surface to a specific range and the water absorbency to a specific range, a recording paper that can be applied to a wide variety of printing methods can be obtained. Completed.

That is, the present invention is as follows.
[1] A substrate containing a thermoplastic resin and a print-receiving layer provided on at least one surface of the substrate,
Oken type smoothness measured in accordance with JIS P8155 (2010) of the surface of the print-receiving layer side is 200 seconds or more,
Recording paper having a bump water absorbency of 1 to 5 g/m ² in the water absorbency test method specified in JIS P 8140:1998.
[2] The recording paper according to [1] above, wherein the print-receiving layer contains an inorganic filler, a carboxy group-containing resin, and a cross-linking agent.
[3] The recording paper according to [2] above, wherein the inorganic filler contains calcium carbonate and amorphous silicon dioxide fine powder.
[4] The recording paper according to [2] or [3] above, wherein the content of the carboxy group-containing resin in the print-receiving layer is 10 to 50 parts by mass with respect to 100 parts by mass of the inorganic filler.
[5] The recording paper according to any one of [1] to [4] above, wherein the print-receiving layer has a basis weight of 5 to 20 g/m ² .
[6] The carboxy group-containing resin contains at least one selected from the group consisting of carboxy-modified styrene-butadiene copolymers, styrene-acrylic copolymers, and carboxy-modified ethylene-vinyl acetate copolymers. The recording paper according to any one of [2] to [5].
[7] Any one of [2] to [6] above, wherein the cross-linking agent contains one or more selected from the group consisting of an aziridine cross-linking agent, an oxazoline cross-linking agent, a carbodiimide cross-linking agent, and a metal cross-linking agent. Recording paper as described.
[8] The substrate according to any one of [1] to [7] above, wherein the substrate is a porous film containing a thermoplastic resin and at least one selected from the group consisting of inorganic fillers and organic fillers. Recording sheet.

According to the present invention, it is possible to provide recording paper that can be printed with various inks, such as ultraviolet curable ink, oil-based ink, fusion thermal transfer recording ink, and water-based ink, according to the printing method.

2 is a cross-sectional view showing an example of recording paper; FIG.

The recording paper of the present invention will be described in detail below. The following description is an example (representative example) of the present invention, and the present invention is not limited to these contents. In the following description, the description of "(meth)acryl" indicates both acryl and methacryl. The description of "(co)polymer" indicates both homopolymers and copolymers.

[Recording sheet]
The recording paper of the present invention comprises a substrate containing a thermoplastic resin, and a print receiving layer provided on at least one surface of the substrate,
Oken type smoothness measured in accordance with JIS P8155 (2010) of the surface of the print-receiving layer side is 200 seconds or more,
Cobb water absorbency is 1 to 5 g/m ² in the water absorbency test method specified in JIS P 8140:1998.

The recording paper of the present invention has a substrate and a print-receiving layer.
FIG. 1 shows a recording sheet 1 as a specific example.
A recording paper 1 illustrated in FIG. 1 has a substrate 11 and a print receiving layer 12 . The print-receiving layer 12 is laminated on one surface of the substrate 11 .

The surface of the print-receiving layer side of the recording paper of the present invention has an Oken smoothness measured in accordance with JIS P8155 (2010) of 200 seconds or more. By setting the smoothness to 200 seconds or more, the ink transferability of oil-based inks and ultraviolet curable inks (hereinafter also referred to as UV inks) is improved, making it possible to use these inks for offset printing, for example. . The smoothness is preferably 250 seconds or more, more preferably 300 seconds or more, from the viewpoint of ink transferability.
The upper limit of the smoothness is preferably 10000 seconds or less. By having surface irregularities with a smoothness of 10,000 seconds or less, the anchor effect is exhibited, and the ink transferability of oil-based inks and UV inks is improved. For example, these inks can be preferably used in offset printing. The smoothness is more preferably 8000 seconds or less, even more preferably 6000 seconds or less.

The smoothness of the print-receiving layer side surface can be obtained by, for example, setting the type, addition amount, and average primary particle size of the inorganic filler contained in the print-receiving layer, and the basis weight of the print-receiving layer within the ranges described below. It can be adjusted as appropriate.

The above smoothness can be measured, for example, with an Oken smoothness tester ("EYO-55-1M" manufactured by Asahi Seiko Co., Ltd.).

The recording paper of the present invention has a Cobb water absorbency of 1 to 5 g/m ² in the water absorbency test method specified in JIS P 8140:1998. By setting the Cobb water absorbency to 1 g/m ² or more, the drying property of the water-based ink is improved, and it becomes possible to preferably use it for water-based inkjet printing, for example. From the same viewpoint, the Cobb water absorbency is preferably 1.2 g/m ² or more, more preferably 1.5 g/m ² or more.
Further, by setting the Cobb water absorbency to 5 g/m ² or less, the abrasion resistance when the ink is subjected to fusion heat transfer printing is improved, and the ink can be preferably used for fusion heat transfer printing. From the same viewpoint, the Cobb water absorbency is preferably 4.8 g/m ² or less, more preferably 4.5 g/m ² or less.

Cobb water absorbency can be adjusted as appropriate by, for example, setting the type and amount of inorganic filler contained in the print-receiving layer, the average primary particle size, and the basis weight of the print-receiving layer within the ranges described below. can.

The Cobb water absorbency can be measured by, for example, a Gurley Cobb size tester.

The details of each layer of the recording paper will be described below.

(Print receiving layer)
The print-receiving layer preferably contains an inorganic filler, a carboxy group-containing resin and a cross-linking agent. The inorganic filler that can be contained in the print-receiving layer is distinguished from the orientation filler that can be contained in the base material described later, but the same type of filler may be used, or a different type of filler may be used. may

<Carboxy group-containing resin>
The carboxy group-containing resin has the function of enhancing the adhesion between the print-receiving layer and the ink, and also of dispersing the inorganic filler uniformly in the print-receiving layer. In addition, the carboxyl group-containing resin can improve the water resistance of the print-receiving layer by reacting with a cross-linking agent which will be described later. Since the carboxy group-containing resin also improves the adhesion between the inorganic filler and the base material, it can also improve the water abrasion resistance of the recording paper.

The carboxy group-containing resin that can be used in the print-receiving layer is not particularly limited, but is preferably a (meth)acrylic acid-based (co)polymer, a styrene-based (co)polymer, or a combination of styrene and (meth)acrylic acid ester. styrene-(meth)acrylic copolymers such as copolymers, styrene-butadiene copolymers, ethylene-vinyl acetate copolymers, carboxy-modified resins such as urethane copolymers, and mixtures thereof. be done.

Among them, carboxy-modified styrene-butadiene copolymers, styrene-acrylic copolymers, and carboxy-modified ethylene-vinyl acetate copolymers are used for the print-receiving layer because they have appropriate polarity and can form flexible layers. It is preferable to contain one or more selected from the group consisting of.

From the viewpoint of improving the adhesion between the base material and the ink and the robustness of the layer itself, the content of the carboxy group-containing resin in the print receiving layer is 10 parts by mass with respect to 100 parts by mass of the inorganic filler in the print receiving layer. parts by mass or more, and more preferably 20 parts by mass or more. From the viewpoint of drying properties of water-based ink, the content is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, relative to 100 parts by mass of the inorganic filler.
That is, the content of the carboxy group-containing resin in the print-receiving layer is preferably 10 to 50 parts by mass with respect to 100 parts by mass of the inorganic filler.

The print-receiving layer may contain a resin other than the carboxy group-containing resin as long as the effects of the present invention are not impaired.

<Inorganic filler>
The inorganic filler that can be contained in the print-receiving layer enhances the drying properties of the ink in the print-receiving layer. In the print-receiving layer, the particles of the inorganic filler randomly agglomerate, and fine pores between the particles spread over the entire print-receiving layer. Since the solvent in the ink is quickly absorbed into the pores, excellent drying properties of the ink can be obtained. If the ink in the print-receiving layer dries quickly, gloss ghosts are less likely to occur. In addition, when recording sheets after printing are piled up, backing is less likely to occur, and the drying property of the overlaid areas is high. Furthermore, the inclusion of the inorganic filler increases the surface roughness of the print-receiving layer and enhances the ink receptivity due to the anchor effect.

Examples of inorganic fillers that can be used in the print-receiving layer include calcium carbonate, magnesium carbonate, layered silicate, titanium oxide, silicon dioxide, boric acid, zinc borate, lead borate, sodium borate (borax), expandable Inorganic particles such as graphite, glass (glass balloon), shirasu (shirasu balloon), zinc oxide, zirconium oxide, alumina, silica-alumina, magnesia, zeolite, aluminum hydroxide, and magnesium hydroxide can be used. One of these may be used, or two or more may be used.

Among the inorganic fillers, calcium carbonate is preferable because it easily improves whiteness and easily forms irregularities on the layer surface suitable for improving ink transferability.
Silicon dioxide is preferable from the viewpoint of water-based ink drying properties, and amorphous silicon dioxide fine powder is more preferable. Aggregates of fine amorphous silicon dioxide powder formed in the print-receiving layer can further enhance the drying property of water-based inks due to the capillary action of the fine pores of the aggregates themselves.
More preferably, the print-receiving layer contains calcium carbonate and amorphous silicon dioxide fine powder as inorganic fillers.

The average primary particle diameter (D50) of the inorganic filler is preferably 0.03 µm or more, more preferably 0.05 µm or more, and even more preferably 0.1 µm or more, from the viewpoint of improving ink drying properties by forming fine pores. . The average primary particle diameter is preferably 4.5 μm or less, more preferably 3.5 μm or less, from the viewpoint of increasing the smoothness of the print-receiving layer surface and suppressing the inorganic filler from falling off from the layer.
If the inorganic filler used has a large average primary particle size, it may be subjected to a sand grinder treatment to adjust the particle shape and particle size so that the print-receiving layer has a desired smoothness.

The average primary particle size (D50) is measured by a laser light diffraction/scattering method. For the measurement, for example, Microtrac MT3300EXII (manufactured by Microtrac Bell) can be used.

The content of the inorganic filler in the print-receiving layer is preferably 50% by mass or more, more preferably 70% by mass or more, from the viewpoint of pore-forming properties and unevenness-forming properties on the layer surface. From the viewpoint of the robustness of the print-receiving layer itself and the prevention of falling off of the inorganic filler, the content thereof is preferably 95% by mass or less, more preferably 85% by mass or less. When two or more inorganic fillers are used in combination, the total content of these is preferably within the above range.

<Crosslinking agent>
Preferably, the print-receiving layer further contains a cross-linking agent, and the carboxy group-containing resin in the print-receiving layer is cross-linked by the cross-linking agent. Crosslinking of the carboxyl group-containing resin can improve the water resistance of the print-receiving layer, and further improve the water-scratching resistance of the printed portion of the surface of the print-receiving layer.

A conventionally known cross-linking agent can be used as the cross-linking agent. Examples of cross-linking agents that can be used include metal cross-linking agents such as ammonium zirconium carbonate, aziridine cross-linking agents such as ethyleneimine derivatives such as aldehyde and acrolein, oxazoline cross-linking agents such as oxazoline group-containing polymers, carbodiimide cross-linking agents, polyglycerol poly Examples thereof include epoxy-based cross-linking agents such as glycidyl ether, polyamide epichlorohydrin resins, polyamine epichlorohydrin resins, and epichlorohydrin-based cross-linking agents such as epichlorohydrin adducts of polyamine polyamides.

From the viewpoint of improving the water scratch resistance of the surface of the print-receiving layer, the print-receiving layer contains at least one selected from the group consisting of the above-mentioned aziridine cross-linking agent, oxazoline-based cross-linking agent, carbodiimide cross-linking agent, and metal-based cross-linking agent. However, the carboxy group-containing resin is preferably crosslinked by these crosslinking agents, and the crosslinking agent is preferably one or more selected from the group consisting of the above-described metal-based crosslinking agents and aziridine crosslinking agents. Among metal-based cross-linking agents, ammonium zirconium carbonate is more preferable.

The content of the cross-linking agent in the print-receiving layer is preferably 0.1% by mass or more. Within this range, sufficient cross-linking tends to increase water abrasion resistance. From the viewpoint of water scratch resistance of the print-receiving layer, it is more preferably 0.2% by mass or more. From the viewpoint of preventing the print-receiving layer from becoming brittle due to excessive progress of the cross-linking reaction, the content is more preferably 5.0% by mass or less, further preferably 4.0% by mass or less.

<Binder migration inhibitor>
The print-receiving layer may contain isocyanate-modified polyethylene glycol in order to suppress binder migration in which a carboxy group-containing resin, which is a binder component, moves to the layer surface. By uniformly dispersing the isocyanate-modified polyethylene glycol in the print-receiving layer, it is possible to sufficiently disperse the carboxy group-containing resin and suppress binder migration even with a small amount. It suppresses the increase in the viscosity of the coating solution for forming the print-receiving layer due to an increase in the compounding amount, and facilitates process control.

<Surfactant>
The print-receiving layer may further contain a surfactant. Even if the surface of the print-receiving layer becomes charged due to friction, the surfactant can quickly attenuate the charge. Therefore, it is possible to reduce transport troubles such as double feeding of recording paper, sticking to printing members, paper jams, and misalignment during printing.

As the surfactant, cationic, anionic, nonionic or amphoteric surfactants can be used, but anionic surfactants are preferred. As an anionic surfactant, for example, dioctyl sodium sulfosuccinate is preferred.

By incorporating a surfactant into the print-receiving layer, the frictional electrification voltage of the layer surface can be reduced, but on the other hand, the water-resistant adhesion of the layer itself tends to decrease. In order to achieve both the frictional electrification attenuation property of the print-receiving layer surface and the water-resistant adhesion of the print-receiving layer itself, it is necessary to minimize the blending amount of the surfactant. Specifically, the content of the surfactant in the print-receiving layer is preferably 0.6% by mass or more, more preferably 0.7% by mass or more, from the viewpoint of frictional static voltage attenuation. In addition, the content is preferably 4.5% by mass or less, more preferably 2.3% by mass or less, from the viewpoint of water-resistant adhesion.

<Other additives>
The print-receiving layer may contain other additives, if necessary, as long as the effects of the present invention are not impaired. Additives that can be used include, for example, antifoaming agents, dispersants, thickeners, water retention agents, water resistance agents, coloring agents, preservatives, and the like. For example, as a dispersing agent, for example, polycarboxylic acid or the like can be usually added in an amount of 0.05 to 5% by mass.

<Basis weight>
In the present invention, the basis weight of the print-receiving layer is preferably 5-20 g/m ² . From the viewpoint of drying properties of water-based ink, the basis weight is preferably 5 g/m ² or more, more preferably 6 g/m ² or more. It is preferably 20 g/m ² or less, more preferably 18 g/m ² or less, so as not to impair the flexibility of the printing paper.
The thickness of the print-receiving layer is more preferably 3 μm or more, and more preferably 18 μm or less.
The basis weight is measured according to JIS P8124 (2011).

(Base material)
The base material contains a thermoplastic resin and imparts mechanical strength to the recording paper.

<Thermoplastic resin>
The thermoplastic resin used for the substrate is not particularly limited, and examples thereof include olefin resins, polyester resins, polyamide resins, polystyrene resins, polyvinyl chloride resins, and polycarbonate resins. These can be used alone or in combination of two or more.

Among them, olefin resins are preferable from the viewpoint of productivity, ease of processing, water resistance, chemical resistance, recyclability and cost. Olefin-based resins that can be used for the substrate layer include propylene-based resins and ethylene-based resins. Among olefin resins, propylene resins are preferable from the viewpoint of moldability and mechanical strength.

Propylene-based resins include, for example, propylene homopolymers exhibiting isotactic, syndiotactic or various stereoregularity, propylene as a main component, propylene and ethylene, butene-1, hexene-1, heptene-1, Examples include propylene copolymers with α-olefins such as 4-methylpentene-1. Here, the “main component” monomer means a monomer that accounts for 50 mass % or more of the repeating units constituting the copolymer. The copolymer may be a binary system, a ternary system, or a quaternary system, and may be a random copolymer or a block copolymer. Among them, propylene homopolymer is preferable from the viewpoint of rigidity suitable for offset printing. From the viewpoint of improving the adhesion between the print-receiving layer and the substrate, random copolymers of propylene and α-olefin are preferred, and ethylene-propylene random copolymers are particularly preferred. Combined use is particularly preferred.

When a propylene-based resin is used, a thermoplastic resin having a melting point lower than that of the propylene-based resin, such as polyethylene, polystyrene, ethylene-vinyl acetate copolymer, etc., is added to 100% by mass of the propylene-based resin from the viewpoint of enhancing stretchability. 3 to 25% by mass can be used together.

<Filler>
The substrate preferably contains a filler together with the thermoplastic resin. The filler facilitates the formation of pores in the substrate, making it possible to make the substrate opaque. In addition, it becomes easy to adjust the whiteness of the recording paper. Furthermore, the surface roughness of the substrate can be adjusted by the filler.

Examples of fillers that can be used in the substrate include inorganic fillers and organic fillers.
That is, the substrate is preferably a porous film containing a thermoplastic resin and at least one selected from the group consisting of inorganic fillers and organic fillers.

Examples of inorganic fillers include inorganic particles such as calcium carbonate, calcined clay, silica, diatomaceous earth, talc, barium sulfate, aluminum sulfate, magnesium oxide, alumina, or ultraviolet absorbing fillers. Examples of ultraviolet absorbing fillers include titanium dioxide and zinc oxide. Among them, calcium carbonate is preferable from the viewpoint of cost and pore-forming properties.

Examples of organic fillers include polyethylene terephthalate, polybutylene terephthalate, polycarbonate, nylon-6, nylon-6,6, cyclic olefin polymers, or cyclic olefin and ethylene and having a melting point higher than the melting point of the olefin resin used, for example, in the range of 120 to 300°C, or a resin particle having a glass transition temperature in the range of, for example, 120 to 280°C.

You may use 1 type individually or in combination of 2 or more types from the said inorganic filler or organic filler. When two or more types are combined, an inorganic filler and an organic filler may be mixed and used.

The average particle size of the filler is preferably 0.01-15 μm, more preferably 0.05-10 μm. When the average particle diameter is 15 μm or less, the uniformity of the pores tends to increase. Moreover, when the average particle size is 0.01 μm or more, there is a tendency that pores of a predetermined size are easily obtained.
The average particle size of the filler is the average value of the measured particle sizes of 100 particles randomly extracted from the observation area of the cut surface in the thickness direction of the base material observed with an electron microscope. The particle diameter is determined from the maximum distance (maximum diameter) between two points on the contour of the particle.

The filler content in the substrate is preferably 8% by mass or more, more preferably 14% by mass or more, and is preferably 65% by mass or less, more preferably 50% by mass or less.
When the content of the filler is at least the above lower limit, a sufficient number of pores tends to be obtained, and a desired whiteness or opacity tends to be imparted to the recording paper. Further, when the content is equal to or less than the above upper limit, sufficient strength is likely to be obtained, and there is a tendency that breakage during stretch molding is difficult to occur.

When adjusting the arithmetic mean roughness Ra of the base material surface by blending the filler, it is effective to increase the average particle size of the filler in the base material. Therefore, from the viewpoint of adjusting the surface roughness, the average particle size of the filler is preferably 0.5 μm or more, more preferably 1.5 μm or more, preferably 15 μm or less, and more preferably 10 μm or less.

<Additive>
The substrate can also contain optional additives as needed. Optional additives include, for example, heat stabilizers, UV stabilizers (light stabilizers), dispersants, antistatic agents, antioxidants, fluorescent brighteners, UV absorbers, dyes, pigments, lubricants, and anti-adhesives. , antiblocking agents, or flame retardants. As the heat stabilizer, for example, a sterically hindered phenol-based, phosphorus-based, or amine-based, etc., can be usually added in an amount of 0.001 to 1 mass %. As the light stabilizer, for example, a sterically hindered amine type, benzotriazole type, benzophenone type or the like can be blended usually in an amount of 0.001 to 1% by weight. As the dispersant, for example, silane coupling agents, higher fatty acids such as oleic acid and stearic acid, metal soaps, polyacrylic acid, polymethacrylic acid, salts thereof, and the like can be usually blended in an amount of 0.01 to 4% by weight. As an antistatic agent, for example, a low-molecular-weight surfactant such as stearic acid monoglyceride or stearyldiethanolamine can be usually blended in an amount of 0.01 to 4% by mass.

<Structure of base material>
The substrate may have either a single layer structure or a multilayer structure. In the case of a multi-layer structure, the types and amounts of materials in each layer may be the same or different. In the case of a multilayer structure, from the viewpoint of adhesion to the print-receiving layer, it is preferable that the layer in contact with the print-receiving layer is a layer containing the above-described thermoplastic resin and filler within the above-described preferred ranges. From the viewpoint of blocking resistance, the filler content in the surface layer in contact with the print-receiving layer may be higher than in other layers in order to adjust the surface roughness.

The substrate may be an unstretched film or a stretched film. From the viewpoint of increasing the rigidity of the substrate, the substrate is preferably a stretched film stretched in at least a uniaxial direction, and a stretched film stretched in a biaxial direction (hereinafter sometimes referred to as a biaxially stretched film. ) is more preferred. Since the biaxially stretched film is stretched in two directions, it is difficult to stretch when it is folded. When the base material has a multilayer structure, a layer of a non-stretched film and a layer of a stretched film can be combined, or stretched films having the same or different number of stretching axes in each layer can be combined. Preferably, one layer is a stretched film.

<Porosity>
When the substrate has pores inside, the porosity, which represents the ratio of pores in the substrate, is preferably 10% or more, more preferably 12% or more, from the viewpoint of obtaining opacity. It is preferably 15% or more, more preferably 20% or more. From the viewpoint of maintaining mechanical strength, the porosity is preferably 45% or less, more preferably 44% or less, further preferably 42% or less, and 40% or less. is particularly preferred.

The porosity can be determined from the area ratio occupied by pores in a certain region of the cross section of the substrate observed with an electron microscope. Specifically, an arbitrary part of the substrate is cut, embedded in epoxy resin and solidified, then cut perpendicular to the surface direction of the substrate using a microtome, and the cut surface becomes the observation surface. Attach it to the observation sample table as shown. Gold or gold-palladium is vapor-deposited on the observation surface, and the pores are observed at an arbitrary magnification that is easy to observe with an electron microscope (for example, magnification of 500 to 3000 times), and the observed area is captured as image data. . Image processing is performed on the obtained image data by an image analysis device, and the area ratio (%) of the void portion can be obtained and used as the porosity (%). In this case, the porosity can be obtained by averaging the measured values obtained by observation at arbitrary 10 or more points.

<Thickness>
The thickness of the substrate is not particularly limited, but is preferably 60 μm or more, more preferably 70 μm or more, and even more preferably 80 μm or more from the viewpoint of imparting stiffness suitable for transportation to the recording paper. From the viewpoint of ease of bending, the thickness is preferably 300 μm or less, more preferably 250 μm or less.

(Manufacturing method of recording paper)
The method for producing the recording paper of the present invention is not particularly limited, but it can usually be produced by laminating a print-receiving layer on a substrate.

<Formation of base material>
The substrate is usually obtained by film molding of a resin composition containing a thermoplastic resin.
The film forming method is not particularly limited, and various known forming methods can be used alone or in combination. Examples include cast molding, calender molding, roll molding, inflation molding, and the like in which a molten resin is extruded into a sheet using a single-layer or multilayer T-die, I-die, or the like connected to a screw-type extruder. A film can also be formed by casting or calendering a mixture of a thermoplastic resin and an organic solvent or oil and then removing the solvent or oil. Examples of film forming methods for a substrate having a multilayer structure include a film forming method such as a multi-layer die method using a feed block or a multi-manifold, or an extrusion lamination method using a plurality of dies, and these methods can also be combined. .

Film stretching methods include, for example, a longitudinal stretching method using a peripheral speed difference between rolls, a transverse stretching method using a tenter oven, a sequential biaxial stretching method combining these methods, a rolling method, and a combination of a tenter oven and a pantograph. A simultaneous biaxial stretching method or a simultaneous biaxial stretching method using a combination of a tenter oven and a linear motor can be used. A simultaneous biaxial stretching (inflation molding) method can also be used, in which a circular die connected to a screw extruder is used to extrude a molten resin into a tubular shape, and then air is blown into the tubular shape. When manufacturing a multi-layered base material containing a plurality of stretched films, each layer may be stretched individually before lamination, or may be stretched collectively after lamination. Further, the stretched layer may be stretched again after lamination.

When the thermoplastic resin used for the base material is a non-crystalline resin, the stretching temperature is preferably in the range of the glass transition temperature of the thermoplastic resin or higher. Also, when the thermoplastic resin is a crystalline resin, the stretching temperature should be above the glass transition point of the non-crystalline portion of the thermoplastic resin and below the melting point of the crystalline portion of the thermoplastic resin. is preferred, and specifically, a temperature lower than the melting point of the thermoplastic resin by 2 to 60°C is preferred.

Although the stretching speed of the film is not particularly limited, it is preferably in the range of 20 to 350 m/min from the viewpoint of stable stretching molding.
The draw ratio of the film can also be appropriately determined in consideration of the properties of the thermoplastic resin used. For example, when a film containing a propylene homopolymer or copolymer is uniaxially stretched, the draw ratio is usually about 1.2 times or more, preferably 2 times or more, and usually 12 times or less. and preferably 10 times or less. In the case of biaxial stretching, the draw ratio in area draw ratio is usually 1.5 times or more, preferably 10 times or more, while it is usually 60 times or less, preferably 50 times or less. .

When a film containing a polyester resin is uniaxially stretched, the draw ratio is usually 1.2 times or more, preferably 2 times or more, and usually 10 times or less, preferably 5 times or less. is. The draw ratio in biaxial stretching is usually 1.5 times or more, preferably 4 times or more, and usually 20 times or less, preferably 12 times or less, in terms of area draw ratio.
If the draw ratio is within the above range, there is a tendency that the film can be stretched stably. Also when a resin composition containing a thermoplastic resin and a filler is used, within the range of the draw ratio, the target porosity can be obtained, the opacity is easily improved, and the film is less likely to break.

<Surface treatment>
The base material is preferably surface-treated from the viewpoint of enhancing the adhesion to the adjacent layer of the base material, for example, the print-receiving layer.
Examples of surface treatment include corona discharge treatment, flame treatment, plasma treatment, glow discharge treatment, ozone treatment, and the like, and these treatments can be combined. Among them, corona discharge treatment or flame treatment is preferable, and corona treatment is more preferable.

The amount of discharge when performing corona discharge treatment is preferably 600 J/m ² (10 W·min/m ² ) or more, more preferably 1,200 J/m ² (20 W·min/m ² ) or more. . The discharge amount is preferably 12,000 J/m ² (200 W·min/m ² ) or less, more preferably 10,800 J/m ² (180 W·min/m ² ) or less. The amount of discharge when flame treatment is performed is preferably 8,000 J/m ² or more, more preferably 20,000 J/m ² or more. Also, the discharge amount is preferably 200,000 J/m ² or less, more preferably 100,000 J/m ² or less.

<Formation of print-receiving layer>
The method of forming the print-receiving layer is not particularly limited. For example, the print-receiving layer can be formed by preparing a coating liquid by dispersing or dissolving various components of the print-receiving layer in water, coating the coating liquid on a substrate, and drying. For coating, known coating equipment such as air knife coater, gravure coater, blade coater, roll coater, reverse roll coater, bar coater, curtain coater, die slot coater, champlex coater, size press coater, gate roll coater, Alternatively, a bill blade coater or the like can be used.

<Print>
The printing method for the print-receiving layer is not particularly limited, and in addition to various known plate printing methods such as gravure printing, offset printing, flexographic printing, seal printing, and screen printing, ink jet method, electrophotographic method, Alternatively, digital printing by various printers such as a liquid toner system, or fusion thermal transfer printing can also be performed.

Depending on the printing method, various inks such as ultraviolet curable ink, oil-based ink, oxidative polymerization curable ink, fusion thermal transfer recording ink, water-based ink, powder toner, or liquid toner (electro ink) are used for printing. can do.

In particular, the print-receiving layer of the present invention is excellent in receptivity for ultraviolet curable ink, oil-based ink, fusion heat transfer recording ink, and water-based ink. It has high printability for recording and water-based inkjet recording.

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. Descriptions of "parts", "%", etc. in the examples are based on mass unless otherwise specified.

(material)
The following materials were used for the print-receiving layer.
<Dispersant>
(PC): Polycarboxylic acid (trade name: Poise 520, manufactured by Kao Corporation)
<Inorganic filler>
(TP-123): light calcium carbonate (trade name: TP-123, manufactured by Okutama Kogyo Co., Ltd.), average primary particle size (D50): 0.2 μm
(#100S): Heavy calcium carbonate (trade name: Escalon #100S, manufactured by Sankyo Seifun Co., Ltd.), average primary particle size (D50): 5.4 μm
(#200): Heavy calcium carbonate (trade name: Escalon #200, manufactured by Sankyo Seifun Co., Ltd.), average primary particle size (D50): 4.1 µm
(P526): Synthetic amorphous silicon dioxide fine powder (trade name: Mizukasil P-526, manufactured by Mizusawa Chemical Co., Ltd.), average primary particle size (D50): 3.2 μm
<Carboxy group-containing resin>
(St-Ac copolymer): styrene-acrylic resin (trade name: Hylos-X ZE-1425, manufactured by Seiko PMC), solid content concentration: 47%
(AcOH polymer): acrylic resin (trade name: AE986B, manufactured by ETEC Co., Ltd.), solid content concentration: 35%
(St-Bg copolymer): carboxy-modified styrene-butadiene copolymer (trade name: LX407G51, manufactured by Nippon Zeon Co., Ltd.), solid content concentration: 49%
<Crosslinking agent>
(DZ-22E): aziridine compound (trade name: Chemitite DZ-22E, manufactured by Nippon Shokubai Co., Ltd.)
(5800MT): Ammonium zirconium carbonate (trade name: AZ Coat 5800MT, manufactured by San Nopco)

Table 1 below lists the materials mentioned above.

<Production of thermoplastic resin film (1)>
(I) Propylene homopolymer (trade name: Novatec PP MA3, manufactured by Nippon Polypropylene) 67 parts by mass, high-density polyethylene resin (trade name: Novatec HD HJ580N, manufactured by Japan Polyethylene) 10 parts by mass, heavy calcium carbonate particles (trade name: Softon 1800, manufactured by Bihoku Funka Kogyo Co., Ltd.) was mixed with 23 parts by mass to prepare a resin composition a.

(II) Next, the resin composition a was melt-kneaded by an extruder set at 260° C., extruded into a sheet from a die, and cooled by cooling rolls to obtain an unstretched sheet. Next, after heating the non-stretched sheet to 150° C. again, it was stretched 4.8 times in the sheet flow direction (MD) using the speed difference between rolls to obtain a longitudinally uniaxially stretched resin film.

(III) Apart from the above, 51.5 parts by mass of propylene homopolymer (trade name: Novatec PP MA3, manufactured by Japan Polypropylene Corporation) and high-density polyethylene resin (trade name: Novatec HD HJ580N, manufactured by Japan Polyethylene Corporation)3. 5 parts by mass and 45 parts by mass of heavy calcium carbonate particles (trade name: Softon 1800, manufactured by Bihoku Funka Kogyo Co., Ltd.) were mixed to prepare a resin composition b.

(IV) The resin composition b is melt-kneaded with an extruder set at 250 ° C., extruded into a film form from a die on one side of the longitudinally uniaxially stretched film, laminated, and laminated to form a surface layer / core layer laminate (b / a) was obtained.
Furthermore, using another extruder, the resin composition b is melt-kneaded with an extruder set at 250 ° C., extruded into a film form from a die, and the core layer (a) side of the laminate (b / a) A laminate (b/a/b) having a three-layer structure of surface layer/core layer/back layer was obtained.

(V) This three-layer structure laminate is introduced into a tenter oven, heated to 155°C, stretched 8 times in the horizontal direction using a tenter, then heat-set (annealed) at 164°C, and further heated to 55°C. After cooling to , the edge was slit to obtain a thermoplastic resin film (1) having a thickness of 110 µm.

<Example 1>
<<Preparation of coating solution for print-receiving layer>>
50 parts by mass of styrene-acrylic resin (St-Ac copolymer) as a carboxy group-containing resin, 180 parts by mass of light calcium carbonate (TP-123) as an inorganic filler, synthetic amorphous silicon dioxide fine powder (P- 526) 15 parts by mass, 1.0 parts by mass of an aziridine compound (DZ-22E) as a cross-linking agent, and 1.4 parts by mass of polycarboxylic acid (PC) as a dispersant are mixed, and ion-exchanged water is added to a solid content concentration of 10% by mass. to obtain a coating solution for a print-receiving layer.

<<Manufacture of Recording Paper>>
On one side of the thermoplastic resin film (1) which is the base material, the coating solution for the print receiving layer was applied with a bar coater and then dried to form a print receiving layer having a basis weight of 10.0 g/m ² . , the recording paper of Example 1 was obtained. The smoothness and bump water absorbency of the print-receiving layer surface of the obtained recording paper were measured by the following methods.

<<Measurement of smoothness>>
The Oken type smoothness of the print receiving layer surface of the recording paper is measured according to JIS P 8155: 2010 "Paper and paperboard-Smoothness test method-Oken method", digital Oken type air permeability and smoothness tester (Asahi Seiko Co., Ltd. (manufactured by EYO-55-1M)).

<<Measurement of bump water absorption>>
The water absorbency of the surface of the print-receiving layer of the recording paper was measured according to JIS P 8140:1998 "Paper and paperboard-Water absorbency test method-Cobb method" with a contact time of 60 seconds.

<Examples 2 to 16>
A recording paper was prepared in the same manner as in Example 1, except that the raw material of the print-receiving layer coating liquid and the basis weight of the print-receiving layer were changed to those shown in Table 2.
In Examples 2 and 3, before using the heavy calcium carbonate (#100S or #200) as the inorganic filler, sand grinder treatment was performed to adjust the average primary particle size D50 to 2 μm.

<Comparative Example 1>
A recording paper was prepared in the same manner as in Example 1, except that light calcium carbonate (TP-123) was not used in the coating solution for the print-receiving layer.
<Comparative Example 2>
A recording paper was prepared in the same manner as in Example 1, except that silica (P-526) was not used in the coating solution for the print-receiving layer.
<Comparative Example 3>
A recording paper was prepared in the same manner as in Example 2, except that the heavy calcium carbonate (#100S) used in the coating solution for the print-receiving layer was not subjected to the sand grinder treatment.
<Comparative Example 4>
A recording paper was prepared in the same manner as in Example 2, except that the amount of silica (P-526) in the print-receiving layer coating liquid was changed to 45 parts by mass.
<Comparative Example 5>
A recording paper was prepared in the same manner as in Example 1, except that the basis weight of the print-receiving layer was changed to 2.0 g/m ² .

(evaluation)
The recording paper of each example and comparative example was subjected to offset printing, fusion heat transfer printing, and a writing test with a water-based pen, and the suitability was evaluated as follows. Good writability with a water-based pen indicates good printability with water-based ink.

<Suitability for offset printing>
<<Print>>
The recording paper of each example and comparative example was cut into an A2 size (420 mm×594 mm), and a design including a design was offset-printed on the surface of the print-receiving layer. For printing, an offset printing machine (trade name: SM102, manufactured by Heidelberg) and UV curable sheet-fed process ink (trade name: UV BC161 (black, indigo, red, yellow), manufactured by T&K TOKA) were used. The pattern was printed in four colors of black, indigo, red and yellow, and the density of each color was 100%. Specifically, under an environment of a temperature of 23° C. and a relative humidity of 50%, UV offset 4-color printing is performed at a speed of 6000 sheets/hour, and two metal halide lamps (manufactured by Eyegraphic Co., Ltd., 100 W/cm) are used. The ink on the printing surface was dried by passing under the printer, and 1000 sheets were continuously printed to obtain an offset printed matter.

<<Ink Transferability>>
The degree of ink transfer in the design of the obtained offset printed matter was subjected to image processing using an image analyzer (manufactured by Nireco Co., Ltd.: model Luzex IID), and the area ratio of the ink transfer portion was calculated. .
In addition, the evaluation criteria are as follows.
◎ (excellent): 99% or more of the ink is transferred to the recording paper, good level ○ (good): 98% or more, less than 99% of the ink is transferred to the recording paper, generally good level △ (fair) ): 95% or more and less than 98% of the ink is transferred to the recording paper, practical level × (impossible): Less than 95% of the ink is transferred to the recording paper, practical level

<<water scratch resistance>>
The obtained offset printed material was punched out into a size of 70 mm×110 mm, which was immersed in deionized water at 23° C. for 24 hours, and then the printed material was taken out from the water. Set the removed printed matter in a Gakushin-type dyeing friction fastness tester (trade name “Friction Tester II”, manufactured by Suga Test Instruments Co., Ltd.) and conform to JIS L0849: 2004 (testing method for dyeing fastness to rubbing) Then, a friction test was conducted by rubbing the printed surface 100 times with a white cotton cloth (Kinfu No. 3) under a load of 215 g. The ink portion before and after the test was subjected to image processing with an image analyzer (manufactured by Nireco Co., Ltd.: model Luzex IID), and the residual rate of the area of the ink portion was calculated and judged according to the following criteria.
In addition, the evaluation criteria are as follows.
◎ (excellent): 95% or more of the ink remains on the recording paper, good level ○ (good): 90% or more, less than 95% of the ink remains on the recording paper, generally good level △ (fair) ): 70% or more and less than 90% of the ink remains on the recording paper, practical level × (impossible): Less than 70% of the ink remains on the recording paper, practically non-practical level

<Suitability for melting heat transfer>
<<Print>>
A barcode was printed using a printer on the surface of the print-receiving layer of the recording paper of each example and comparative example. A printer (trade name: B-30-S5, manufactured by Tech Co., Ltd.) and an ink ribbon (trade name: B110C, manufactured by Ricoh Co., Ltd.) were used for printing. Using JIS X 0503:2012 “Automatic recognition and data acquisition technology-Barcode symbology specification-Code 39” as a barcode, setting the print density to 25, and printing in an environment with a temperature of 23 ° C and a relative humidity of 50%, I got a print.

<<Scratch resistance>>
The resulting printed matter was punched into a size of 70 mm × 110 mm, set in a Gakushin-type dyeing friction fastness tester (trade name “Friction Tester II”, manufactured by Suga Test Instruments Co., Ltd.), and tested according to JIS L0849: 2004 ( Dyeing fastness test method against rubbing), the printed surface was rubbed 100 times with a white cotton cloth (Kinfu No. 3) under a load of 215 g. The resulting friction test piece was printed on recording paper and subjected to a friction test using a barcode verifier (trade name: LASERCHE II, manufactured by Fuji Electric Refrigeration Machinery Co., Ltd.). -Evaluated by ANSI GRADE (rank A to rank D) defined in 1990. The evaluation with the barcode verifier was performed three times at different locations.
In addition, the evaluation criteria are as follows.
◎ (Excellent): All three locations can be read in one scan ○ (Good): All three locations can be read in two scans or less △ (Acceptable): All three locations can be read in four scans or less × (Unacceptable) ): illegible after 4 scans in at least one location

<Water-based pen writing suitability>
<<Drying>>
A water-based pen (trade name: Ball Pentel B100, manufactured by Pentel) was used to write a straight line on the surface of the print-receiving layer of the recording paper of each example and comparative example, rubbed with a tissue every 5 seconds, and then written with a water-based pen and dried. Evaluate the time to
In addition, the evaluation criteria are as follows.
⊚ (Excellent): Dry within 30 seconds.
◯ (Good): Dries within 45 seconds over 30 seconds.
(triangle|delta) (good): It dries within 60 seconds over 45 seconds.
x (impossible): It does not dry even if it exceeds 60 seconds.

Table 2 below shows the evaluation results. In Table 2, the contents of liquid materials are shown in terms of solid content.

As can be seen from Table 2, the recording paper of the present invention has all of the evaluations of suitability for offset printing, suitability for fusion heat transfer, and suitability for writing with a water-based pen, all of which are at or above acceptable levels, and can be printed with various inks. rice field.

1... recording paper,
11 ... base material,
12... print receiving layer

Claims (8)

A substrate containing a thermoplastic resin, and a print-receiving layer provided on at least one surface of the substrate,
Oken type smoothness measured in accordance with JIS P8155 (2010) of the surface of the print-receiving layer side is 200 seconds or more,
Recording paper having a bump water absorbency of 1 to 5 g/m ² in the water absorbency test method specified in JIS P 8140:1998. 2. The recording paper according to claim 1, wherein the print-receiving layer contains an inorganic filler, a carboxy group-containing resin and a cross-linking agent. 3. The recording paper according to claim 2, wherein said inorganic filler contains calcium carbonate and amorphous silicon dioxide fine powder. 4. The recording paper according to claim 2, wherein the content of the carboxy group-containing resin in the print-receiving layer is 10 to 50 parts by mass with respect to 100 parts by mass of the inorganic filler. The recording paper according to any one of claims 1 to 4, wherein the print-receiving layer has a basis weight of 5 to 20 g/ ^m2 . 2-, wherein the carboxy group-containing resin contains at least one selected from the group consisting of carboxy-modified styrene-butadiene copolymers, styrene-acrylic copolymers, and carboxy-modified ethylene-vinyl acetate copolymers. 6. The recording paper according to any one of 5. The recording paper according to any one of claims 2 to 6, wherein the cross-linking agent contains one or more selected from the group consisting of an aziridine cross-linking agent, an oxazoline cross-linking agent, a carbodiimide cross-linking agent, and a metal cross-linking agent. . The recording paper according to any one of claims 1 to 7, wherein the base material is a porous film containing a thermoplastic resin and at least one selected from the group consisting of inorganic fillers and organic fillers.

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