JP7601686B2 - Laminated film and its manufacturing method - Google Patents

Description

The present invention relates to a laminated film with excellent paper dust reduction and printability, and a method for manufacturing the same.

Conventionally, various printing papers, various poster papers, various label papers, inkjet recording papers, thermal recording papers, thermal transfer receiving papers, pressure-sensitive transfer recording papers, electrophotographic recording papers, and other recording papers for applications requiring water resistance, weather resistance, and durability, as well as adhesive papers using the above recording papers, have been proposed, including synthetic paper using a film method in which a filler is mixed with thermoplastic resins such as polyolefin resins and polyester resins and stretched, and stretched films whose main raw material is the above thermoplastic resins, with a coating layer suitable for the above recording methods applied to at least one side of the support.

By including filler in the stretched film, costs can be reduced by reducing the amount of resin used, the synthetic paper can be made whiter, and the film can be made lighter because holes are created around the filler as a core during stretching. However, there is a problem in that the filler easily falls out of the holes in the stretched film, resulting in paper powder that contaminates the blanket cylinder of the recording device.

As an example of a stretched film that can prevent the filler from falling off, Patent Document 1 describes a multilayer stretched polypropylene film having a base layer formed from a polypropylene-based resin material and a skin layer formed from a polypropylene-based resin composition containing a propylene-α-olefin random copolymer and calcium carbonate particles with specific properties.

On the other hand, Patent Documents 2 to 4 describe coating layers that use resin particle emulsions as coating layers with good print quality.

JP 2001-071432 A International Publication No. 2017/110599 International Publication No. 2014/087670 JP 2017-159651 A

However, in recent years, there has been a demand for further reduction in paper dust and improvement in printability, and there is still room for further study.
An object of the present invention is to provide a laminated film which allows for a high degree of reduction in paper dust and also has excellent printability.

As a result of intensive research conducted by the inventors to solve the above-mentioned problems, they found that the above-mentioned problems can be solved by forming a resin layer on a base material layer, the resin layer containing a filler and a thermoplastic resin with a lower melting point than the thermoplastic resin contained in the base material layer, and having a porosity of 15% or less, and further laminating a specific ink receiving layer on top of the resin layer.
That is, the present invention is as follows.

(1) A laminate film having an ink-receiving layer, a first resin layer, and a base layer in this order,
The base layer contains a thermoplastic resin A and a filler,
the first resin layer is a layer containing a thermoplastic resin B having a lower melting point than the thermoplastic resin A and a filler, and having a porosity of 15% or less;
the ink receiving layer contains a resin component derived from an emulsion, and the minimum film-forming temperature of the resin component is 100° C. or lower;
Laminated film.
(2) The laminate film according to (1), wherein the content of the filler in the first resin layer is 10% by mass or more.
(3) The laminated film according to (1) or (2), wherein the thermoplastic resin A is a propylene homopolymer.
(4) The laminated film according to any one of (1) to (3), wherein the thermoplastic resin B is a random copolymer of propylene and a monomer copolymerizable with propylene.
(5) The laminate film according to any one of (1) to (4), wherein the resin component has a volume average particle size of 0.01 to 3.0 μm.
(6) A second resin layer is further provided on the surface of the base layer opposite to the first resin layer,
The laminate film according to any one of (1) to (5), wherein the second resin layer has a porosity of 15% or less.
(7) The laminate film according to any one of (1) to (6), wherein the base material layer and the first resin layer are stretched films stretched in at least one axial direction.
(8) The method for producing a laminated film according to any one of (1) to (7), further comprising laminating an ink-receiving layer, a first resin layer, and a base layer in this order,
The method includes a step of laminating the first resin layer on the base layer and then simultaneously stretching the laminate in at least one axial direction.

The present invention can provide a laminated film that reduces paper dust and has excellent printability.

FIG. 2 is a cross-sectional view showing an example of a laminated film. FIG. 4 is a cross-sectional view showing another example of a laminated film.

The laminated film of the present invention will be described in detail below. The following is one example (representative example) of the present invention, and the present invention is not limited thereto.

In the following description, the term "(meth)acrylic" refers to both acrylic and methacrylic.

[Laminated film]
The laminate film of the present invention is a laminate film having an ink-receiving layer, a first resin layer, and a base layer in this order,
The base layer contains a thermoplastic resin A and a filler,
the first resin layer is a layer containing a thermoplastic resin B having a lower melting point than the thermoplastic resin A and a filler, and having a porosity of 15% or less;
The ink receiving layer contains a component derived from an emulsion, and the minimum film-forming temperature of the resin component is 100° C. or lower.

The present inventors speculate as follows about the mechanism by which the laminate film of the present invention has a high paper dust reducing effect and excellent printability.
The laminated film of the present invention has a first resin layer on a base layer, the first resin layer having a porosity of 15% or less. Normally, a resin film containing a filler generates voids due to the filler during stretching, but the first resin layer in the laminated film of the present invention has a characteristic of having a low porosity despite being a stretched film containing a filler, and as a result, it is believed that detachment of the filler contained in the base layer and the first resin layer can be suppressed, and paper dust can be reduced.
The reason why the above-mentioned first resin layer can be formed is as follows. As described later, the laminated film of the present invention is preferably obtained by laminating the base material layer and the first resin layer and stretching them simultaneously in the production thereof. Here, the resin (thermoplastic resin B) used in the first resin layer of the laminated film of the present invention has a lower melting point than the resin (thermoplastic resin A) used in the base material layer. Therefore, when the base material layer and the first resin layer are laminated and stretched simultaneously, it is necessary to set the stretching temperature at which the thermoplastic resin A with a higher melting point can be stretched, and the first resin layer containing the thermoplastic resin B is stretched in a molten state. As a result, although pores due to the filler are generated in the base material layer, pores are unlikely to be generated in the first resin layer, and it is possible to make the porosity of the first resin layer 15% or less.

In addition, it was found that providing a specific ink-receiving layer on the first resin layer not only improves printability but also reduces paper dust. Although the reason for this is unclear, it is speculated that this is because the resin that can be used for the ink-receiving layer in the present invention has high viscosity, is unlikely to peel off from the laminated film and cause paper dust, and has good film-forming properties.
Each layer will be described below.

(Base layer)
The substrate layer is a resin film having excellent mechanical strength, and is provided as a support for the laminated film. The substrate layer can be formed by forming a resin composition containing a thermoplastic resin A and a filler into a film.
The substrate layer is a stretched film that is stretched at least uniaxially.

<Thermoplastic resin A>
The thermoplastic resin A is preferably a polyolefin resin. Specific examples of the polyolefin resin include polypropylene resin, polyethylene resin, and polymethyl-1-pentene.

The polypropylene resin is not particularly limited as long as propylene is used as the main monomer. For example, an isotactic polymer or a syndiotactic polymer obtained by homopolymerizing propylene can be used. In addition, a propylene-α-olefin copolymer, which is a copolymer of propylene as the main component and an α-olefin such as ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, or 1-octene, can also be used. The copolymer may be a binary or ternary or higher multi-component system of monomer components, and may be a random copolymer or a block copolymer. A propylene homopolymer and a propylene copolymer may also be used in combination.

Examples of polyethylene resins include high-density polyethylene having a density of 0.940 to 0.965 g/ ^cm3 , medium-density polyethylene having a density of 0.920 to 0.935 g/ ^cm3 , linear low-density polyethylene having a density of 0.900 g/cm3 or ^more and less than 0.920 g/ ^cm3 , copolymers mainly composed of ethylene and copolymerized with α-olefins such as propylene, butene, hexene, heptene, octene, and 4-methylpentene-1, maleic acid-modified ethylene-vinyl acetate copolymers, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-acrylic acid alkyl ester copolymers, ethylene-methacrylic acid alkyl ester copolymers, metal salts of ethylene-methacrylic acid copolymers (metals include zinc, aluminum, lithium, sodium, potassium, etc.), ethylene-cyclic olefin copolymers, and maleic acid-modified polyethylene.

As the polyolefin resin, a graft-modified product thereof may also be used as necessary from the viewpoint of improving the adhesiveness or moldability of the resin film.
A known method can be used for the graft modification. Specifically, a graft modification using an unsaturated carboxylic acid or a derivative thereof as a graft monomer can be mentioned. Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, and citraconic acid. Examples of the derivatives of the unsaturated carboxylic acid include anhydrides, esters, amides, imides, and metal salts of the unsaturated carboxylic acids.

Specific examples of graft monomers include maleic anhydride, itaconic anhydride, citraconic anhydride, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, glycidyl (meth)acrylate, maleic acid monoethyl ester, maleic acid diethyl ester, fumaric acid monomethyl ester, fumaric acid dimethyl ester, itaconic acid monomethyl ester, itaconic acid diethyl ester, (meth)acrylamide, maleic acid monoamide, maleic acid diamide, maleic acid - Examples include N-monoethylamide, maleic acid-N,N-diethylamide, maleic acid-N-monobutylamide, maleic acid-N,N-dibutylamide, fumaric acid monoamide, fumaric acid diamide, fumaric acid-N-monoethylamide, fumaric acid-N,N-diethylamide, fumaric acid-N-monobutylamide, fumaric acid-N,N-dibutylamide, maleimide, N-butylmaleimide, N-phenylmaleimide, sodium (meth)acrylate, and potassium (meth)acrylate.

The graft monomer can be used in an amount of usually 0.005 to 10% by mass, preferably 0.01 to 5% by mass, relative to the polyolefin resin.

As the thermoplastic resin A used in the base layer, one of the above polyolefin-based resins may be used alone, or two or more of them may be used in combination. From the viewpoints of moldability, mechanical strength, cost, etc., the base layer is preferably a resin film of a polypropylene-based resin or a polyethylene-based resin, and a polypropylene-based resin is more preferable. Among them, a propylene homopolymer is preferable because it is easy to handle as the main raw material of the base layer.

From the viewpoint of film formability, it is possible to use a resin having a melting point equal to or lower than that of propylene homopolymer in a polypropylene-based resin film. Such a resin can be a polyethylene-based resin, specifically a high-density or low-density polyethylene. The amount of polyethylene-based resin to be mixed can be, for example, 0.1 to 25% by mass relative to the propylene homopolymer.

The substrate layer may be a resin film using only a polyolefin-based resin as the thermoplastic resin A, or may contain a thermoplastic resin other than a polyolefin-based resin as long as the effect of the present invention is not impaired. Examples of thermoplastic resins that can be used in combination include polyamide-based resins such as nylon-6 and nylon-6,6; thermoplastic polyester-based resins such as polyethylene terephthalate or its copolymers, polybutylene terephthalate, polybutylene succinate, and aliphatic polyesters such as polylactic acid; polycarbonate; and styrene-based resins such as atactic polystyrene or syndiotactic polystyrene.

The melting point of the thermoplastic resin A used in the base layer is not particularly limited, but is preferably, for example, 150 to 300°C.

The weight average molecular weight (Mw) of thermoplastic resin A is not particularly limited, but from the viewpoint of moldability, it is preferable that it be, for example, 50,000 to 500,000.

The content of thermoplastic resin A in the substrate layer (the total amount when two or more types are used) is preferably 20% by mass or more, and more preferably 50% by mass or more. By keeping it in the above range, it is possible to impart suitable rigidity, moldability, etc. as a substrate.

<Filler>
The substrate layer contains a filler. Examples of fillers that can be used include inorganic fillers and organic fillers. The filler makes it easy to adjust the whiteness or opacity of the film, and is less expensive than resins, which also leads to cost reduction. In addition, voids are easily formed inside the film by stretching, which makes it possible to reduce the weight of the substrate layer and, in turn, the laminated film. If the substrate layer is porous, the heat insulation of the laminated film is also easily improved.

<<Inorganic filler>>
Examples of inorganic fillers that can be used include inorganic particles such as calcium carbonate, calcined clay, silica, diatomaceous earth, white clay, talc, titanium oxide, barium sulfate, barium titanate, alumina, zeolite, mica, sericite, bentonite, sepiolite, vermiculite, dolomite, wollastonite, and glass fiber. The average particle size of the inorganic filler measured with a particle size distribution meter using laser diffraction is usually 0.01 to 15 μm, and preferably 0.1 to 5 μm.

<<Organic filler>>
As the organic filler, it is preferable to select a resin of a type different from the polyolefin resin that is the main component of the base layer. As such an organic filler, for example, a polymer such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, nylon-6, nylon-6,6, cyclic polyolefin, polystyrene, or polymethacrylate, which has a melting point (e.g., 170 to 300°C) or a high glass transition temperature (e.g., 170 to 280°C) higher than the melting point of the polyolefin resin and is incompatible with the polyolefin resin, can be used.

As the filler, the above-mentioned inorganic fillers and organic fillers can be used alone or in combination.
The content of the filler in the base layer (when an inorganic filler and an organic filler are used in combination, the total amount of the fillers) is preferably 5% by mass or more, more preferably 10% by mass or more, from the viewpoint of making the base layer porous, and is preferably 60% by mass or less, more preferably 40% by mass or less, and even more preferably 20% by mass or less, from the viewpoint of maintaining strength.

<Other ingredients>
The substrate layer may further contain a heat stabilizer (antioxidant), a light stabilizer, a dispersant, a lubricant, a nucleating agent, or the like, as necessary.
As the heat stabilizer, for example, a sterically hindered phenol-based antioxidant, a phosphorus-based antioxidant, or an amine-based antioxidant can be used usually in the range of 0.001 to 1% by mass based on the total amount of the base layer.
As the light stabilizer, for example, a sterically hindered amine light stabilizer, a benzotriazole light stabilizer, or a benzophenone light stabilizer can be used usually in the range of 0.001 to 1% by mass based on the total amount of the base layer.
Examples of the dispersant or lubricant include a silane coupling agent, a higher fatty acid such as oleic acid or stearic acid, a metal soap, polyacrylic acid, polymethacrylic acid, or a salt thereof, etc. These can be used in an amount of usually 0.01 to 4 mass % based on the total amount of the base layer for the purpose of dispersing the filler, for example.

<Structure of Base Layer>
The substrate layer may have a single layer structure or a multi-layer structure of two or more layers. By forming a multi-layer structure, it is possible to impart various functions such as mechanical properties, writability, abrasion resistance, and secondary processing suitability to the substrate layer.

<Stretched film>
The base layer includes a stretched film stretched at least uniaxially, more specifically, a stretched film simultaneously stretched at least uniaxially together with a first resin layer described below. From the viewpoint of mechanical strength, it is preferable that the base layer includes a biaxially stretched film.
The base layer containing the stretched film has high mechanical strength and excellent thickness uniformity, so that a laminated film with excellent post-processability can be obtained. In addition, since voids caused by the filler are generated by the stretching, the film can be made lighter.
When the base material layer has a multilayer structure, the number of stretching axes of each layer may be uniaxial/uniaxial, uniaxial/biaxial, biaxial/uniaxial, uniaxial/uniaxial/biaxial, uniaxial/biaxial/uniaxial, biaxial/uniaxial/uniaxial, uniaxial/biaxial/biaxial, biaxial/biaxial/uniaxial, or biaxial/biaxial/biaxial.

<Porosity>
From the viewpoint of weight reduction or improvement of whiteness, the porosity of the base layer is preferably more than 0%, more preferably 20% or more. On the other hand, it is preferably 50% or less, more preferably 40% or less. If the porosity is 50% or less, adjacent pores are unlikely to be connected to each other, and it is easy to maintain strength. In addition, when other layers are laminated after the stretching of the base layer, it is easy to suppress the filler in the base layer from being detached from the base layer before the other layers are laminated.
The porosity can be determined from the ratio of the area occupied by pores to a certain region of the cross section of the film observed under an electron microscope.

(First Resin Layer)
The laminated film of the present invention has a first resin layer on a substrate layer. The first resin layer can be formed by film-molding a resin composition containing a filler and a thermoplastic resin B having a lower melting point than a thermoplastic resin A contained in the substrate layer.
The first resin layer is a stretched film that is stretched at least uniaxially.

<Thermoplastic resin B>
Thermoplastic resin B is a resin having a lower melting point than the above-mentioned thermoplastic resin A. Therefore, in the production of the laminated film, when the base material layer and the first resin layer are laminated and simultaneously stretched at a stretching temperature at which the thermoplastic resin A can be stretched, the thermoplastic resin B melts, and voids are less likely to occur in the first resin layer. As a result, it is possible to suppress the dropout of the filler contained in the base material layer and the first resin layer, and to reduce the generation of paper powder.

There are no limitations on the melting point of thermoplastic resin B as long as it is lower than that of thermoplastic resin A, but from the viewpoint of suppressing the generation of voids, it is preferable that the difference between the melting points of thermoplastic resin A and thermoplastic resin B is 10° C. or more. In addition, it is preferable that the melting point of thermoplastic resin B is, for example, 50 to 200° C.
In addition, when the above-mentioned base layer contains two or more types of thermoplastic resin A, the thermoplastic resin B has a lower melting point than at least the main component thermoplastic resin A. Here, the "main component thermoplastic resin A" refers to a component contained in an amount of 50 mass% or more based on the total amount of the thermoplastic resin A.

Thermoplastic resin B is preferably a polyolefin resin having a lower melting point than thermoplastic resin A. Specific examples of polyolefin resins as thermoplastic resin B include polypropylene resins, polyethylene resins, and polymethyl-1-pentene, which are given as specific examples of thermoplastic resin A, and which have a lower melting point than thermoplastic resin A contained in the base layer.

The thermoplastic resin B used in the first resin layer may be one of the above polyolefin resins or a combination of two or more of them. From the viewpoints of moldability, mechanical strength, cost, etc., the first resin layer is preferably a resin film of a polypropylene resin or a polyethylene resin, and more preferably a polypropylene resin.
Among these, a random copolymer of propylene and a monomer copolymerizable with propylene is preferred, specifically, a propylene-α-olefin random copolymer, which is a copolymer of propylene and an α-olefin such as ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, or 1-octene, is preferred, and a propylene-ethylene random copolymer is particularly preferred.

The weight average molecular weight (Mw) of thermoplastic resin B is not particularly limited, but from the viewpoint of moldability, it is preferable that it be, for example, 50,000 to 500,000.

The content of thermoplastic resin B in the first resin layer (the total amount when two or more types are used in combination) is preferably 20% by mass or more, and more preferably 50% by mass or more, from the viewpoint of suppressing the generation of voids.

The first resin layer may be a resin film using only thermoplastic resin B as the thermoplastic resin, or may contain a thermoplastic resin other than thermoplastic resin B within a range that does not impair the effects of the present invention. Examples of thermoplastic resins that can be used in combination include, for example, polyolefin-based resins listed as specific examples of thermoplastic resin A, resins having the same melting point as thermoplastic resin A contained in the base layer, and thermoplastic resins that can be used in combination with the polyolefin-based resins listed as specific examples of thermoplastic resin A.

<Filler>
The first resin layer contains a filler. Specific examples of the filler that can be used in the first resin layer include the inorganic fillers and organic fillers exemplified as the specific examples of the filler contained in the above-mentioned base layer.

As the filler, the above-mentioned inorganic fillers and organic fillers can be used alone or in combination.
The content of the filler in the first resin layer (when an inorganic filler and an organic filler are used in combination, the total amount of the fillers) is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, and is preferably 80% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.
By setting the content at or above the lower limit, it is easy to obtain whitening due to the addition of the filler, cost reduction effects, etc. By setting the content at or below the upper limit, it is easy to obtain the paper dust reduction effect of the present invention, and the film formability and strength of the resin film are improved.

<Other ingredients>
The first resin layer may contain other components that the above-mentioned base layer may contain, if necessary, and specific examples and preferred amounts of these components are also the same.

<Stretched film>
The first resin layer is a stretched film stretched at least uniaxially, more specifically, a stretched film stretched at least uniaxially together with the above-mentioned base layer. The first resin layer is a stretched film containing a filler, but has a low porosity, which provides the whitening effect and cost reduction effect of the addition of the filler, and suppresses the generation of paper powder. In addition, the thickness uniformity is excellent due to the stretching, so that a laminated film with excellent post-processability can be obtained.

<Porosity>
In the laminated film of the present invention, the porosity of the first resin layer is 15% or less. By setting the porosity to 15% or less, it is possible to suppress the detachment of the filler contained in the first resin layer and the filler contained in the base layer, and reduce paper dust. From the viewpoint of the paper dust reduction effect, the porosity is preferably 10% or less, more preferably 5% or less.
The lower limit of the porosity is not particularly limited and may be 0% or more than 0%. However, since the first resin layer is a stretched film as described above, the lower limit is generally more than 0% in consideration of the influence of stretching.
The porosity can be determined in the same manner as the porosity in the substrate layer.

(Ink Receiving Layer)
The ink-receiving layer is provided on the first resin layer and is located on the outermost surface of the laminate film of the present invention. Ink is transferred onto the ink-receiving layer by printing.

The ink receiving layer contains a component derived from an emulsion (hereinafter, sometimes simply referred to as an emulsion). The ink receiving layer can be formed by applying a coating liquid containing the emulsion to the surface of the first resin layer and drying it.

Here, the components derived from the emulsion are the remaining components after the dispersion medium of the emulsion in the coating liquid for the ink receiving layer evaporates. For example, the remaining components are the resin components in the emulsion and other components added as necessary. These components may contain modified substances that have been modified during the process of forming the ink receiving layer. The resin components in the remaining components exist in the form of particles in the ink receiving layer, but may melt and deform due to overheating during printing.

<Emulsion>
An emulsion is a liquid in which a fine particle resin component (resin particles) is emulsified or dispersed in a dispersion medium. In the present invention, the resin component (resin particles) refers to a fine particle resin that is dispersed in a dispersion medium to form an emulsion. From the viewpoint of ease of handling, an O/W emulsion in which resin particles are emulsified or dispersed in an aqueous dispersion medium is preferred.

When the ink receiving layer contains a component derived from the emulsion, good printability can be obtained in various printing methods such as offset printing, thermal melt transfer printing, and electrophotographic printing.
This is presumably because the emulsion imparts hydrophobicity to the ink-receiving layer and prevents it from becoming excessively hydrophilic. This action prevents ink bleeding caused by contact between the moisture around the ink-receiving layer and the ink transferred onto the ink-receiving layer, improving printability.

It was also found that the ink receiving layer can further reduce paper dust by including a resin component derived from the emulsion. In addition to the emulsion-based coating liquid used in the present invention, the coating liquid used to form the ink receiving layer can also be a solvent-based coating liquid in which a resin is dissolved in a solvent. However, the resin suitable for emulsion-based coating liquid has a higher viscosity than the resin used in solvent-based coating liquid. Therefore, it is presumed that the resin itself is less likely to peel off from the laminated film after film formation, and is less likely to cause paper dust.

<<Volume average particle size of resin component (resin particles)>>
The volume average particle size of the resin component (resin particles) contained in the emulsion is preferably 0.01 to 3.0 μm. The volume average particle size of the resin component (resin particles) is measured using a laser diffraction type particle size distribution measuring device (SALD-2200, manufactured by Shimadzu Corporation).

If the volume average particle size is 3.0 μm or less, a dense film can be formed depending on the heating and drying conditions when forming the ink receiving layer, and the paper dust reduction effect is further improved. Also, if the volume average particle size is 0.01 μm or more, it is easy to prepare an emulsion with a suitable viscosity, and handling is likely to be improved.

The volume average particle size of the resin component (resin particles) is preferably 0.05 μm or more. On the other hand, it is preferably 2.0 μm or less, and more preferably 1.6 μm or less.

<<Minimum film-forming temperature of resin components>>
The minimum film forming temperature (MFT) of the resin component is 100° C. or less. By setting the MFT to 100° C. or less, the film-forming property of the ink receiving layer, particularly the film-forming property at room temperature, becomes good, and the paper dust reduction effect is further improved. The MFT is preferably 80° C. or less, more preferably 40° C. or less, and even more preferably 10° C. or less. There is no particular lower limit, but it is usually −20° C. or more.

<<Type of resin>>
Examples of the resin that can be used as the resin component in the emulsion include urethane-based resins, olefin-based copolymers, styrene-based resins, etc. Among these, urethane-based resins and olefin-based copolymers are preferred, and urethane-based resins are more preferred from the viewpoint of the minimum film-forming temperature.

<<<Urethane resin>>>
As the urethane resin, a cationic urethane resin can be preferably used. The cationic urethane resin is a copolymer in which a cationic group is introduced into a polyurethane resin skeleton. This copolymer can be produced by reacting a tertiary amino group-containing polyol obtained by reacting a compound having two epoxy groups in one molecule with a secondary amine with a polyisocyanate to produce a polyurethane resin, and then quaternizing the polyurethane resin with a quaternizing agent. Alternatively, the copolymer can also be produced by adding one or more selected from the group consisting of N,N-dialkylalkanolamines; N-alkyl-N,N-dialkanolamines such as N-methyl-N,N-diethanolamine and N-butyl-N,N-diethanolamine; and trialkanolamines to a part of the polyol, reacting the polyurethane resin with a polyisocyanate to produce a polyurethane resin, and then quaternizing the polyurethane resin with a quaternizing agent.

Examples of cationic polyurethane resin emulsions that can be used include Superflex 600, 610, 620, and 650 (product names) manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Hydran CP-7030, 7050, and 7060 (product names) manufactured by DIC Corporation, and Neo Sticker manufactured by Nicca Chemical Co., Ltd.

<<<Olefin copolymer>>>
As the olefin copolymer, it is preferable to use an olefin copolymer having good emulsifiability, which contains a carboxyl group or its salt as a copolymerization component, or contains an ester bond in the repeating unit. Representative examples of the olefin copolymer containing a carboxyl group or its salt as a copolymerization component include copolymers of an olefin monomer and an unsaturated carboxylic acid or its anhydride, and salts thereof. These olefin copolymers may be used alone or in combination of two or more.

Among the olefin copolymers containing a carboxy group or its salt as a copolymerization component, it is preferable to use an olefin copolymer in which the above-mentioned unsaturated carboxylic acid or its anhydride is copolymerized.

Specific examples of such copolymers include ethylene-(meth)acrylic acid copolymers, ethylene-methyl acrylate copolymers (EMA), ethylene-methyl methacrylate copolymers (EMMA), and other ethylene-(meth)acrylic acid alkyl ester copolymers, alkali (earth) metal salts of ethylene-(meth)acrylic acid copolymers, ethylene-(meth)acrylic acid ester-(anhydride) maleic acid copolymers, (meth)acrylic acid grafted polyethylene, (anhydride) maleic acid grafted polyethylene, (anhydride) maleic acid grafted ethylene-vinyl acetate copolymer, (anhydride) maleic acid grafted (meth)acrylic acid ester-ethylene copolymer, (anhydride) maleic acid grafted polypropylene, (anhydride) maleic acid grafted ethylene-propylene copolymer, (anhydride) maleic acid grafted ethylene-butene copolymer, (anhydride) maleic acid grafted ethylene-butene copolymer, and (anhydride) maleic acid grafted propylene-butene copolymer.

Among olefin copolymers, from the viewpoint of printability, ethylene-(meth)acrylic acid copolymers such as ethylene-(meth)acrylic acid copolymer, ethylene-(meth)acrylic acid alkyl ester copolymer, ethylene-(meth)acrylic acid ester-(anhydride) maleic acid copolymer, (anhydride) maleic acid grafted ethylene-vinyl acetate copolymer, (anhydride) maleic acid grafted (meth)acrylic acid ester-ethylene copolymer, (anhydride) maleic acid grafted ethylene-propylene-butene copolymer, (anhydride) maleic acid grafted ethylene-butene copolymer, or (anhydride) maleic acid grafted propylene-butene copolymer are more preferred, ethylene-(meth)acrylic acid alkyl ester copolymer is even more preferred, and ethylene-methyl acrylate copolymer (EMA) is particularly preferred.

<<Resin component content in emulsion>>
The content of the resin component in the emulsion is preferably 5% by mass or more, more preferably 10% by mass or more. The content is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less. If the content is equal to or more than the above lower limit or equal to or less than the above upper limit, it becomes easy to prepare an emulsion in which the volume average particle size of the resin component (resin particles) is 0.01 to 3.0 μm.

<<Content of emulsion-derived components in ink-receiving layer>>
The content of the solids of the emulsion-derived components in the ink receiving layer is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, based on the total solids content of the ink receiving layer. The content is preferably 99% by mass or less, more preferably 98% by mass or less, and even more preferably 95% by mass or less. If the content is equal to or more than the lower limit, the paper dust reduction effect and printability of the laminated film are likely to be improved, and if the content is equal to or less than the upper limit, the preparation of the emulsion is easy.

<<Dispersant>>
A dispersant may be added to the emulsion as necessary, which allows the resin component to be uniformly dispersed in the dispersion medium, making it easier to obtain a uniform coating film.
As the dispersant, it is preferable to use at least one selected from the group consisting of nonionic surfactants, nonionic water-soluble polymers, cationic surfactants and cationic water-soluble polymers.

Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkyl aryl ethers, polyoxyethylene-polyoxypropylene block polymers, polyethylene glycol fatty acid esters, and polyoxyethylene sorbitan fatty acid esters.
Examples of non-ionic water-soluble polymers include fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol and modified products thereof, and hydroxyethyl cellulose.
Examples of the cationic surfactant include stearylamine hydrochloride, lauryltrimethylammonium chloride, and trimethyloctadecylammonium chloride.
Examples of the cationic water-soluble polymer include a polymer having a quaternary ammonium salt structure or a phosphonium salt structure, a nitrogen-containing (meth)acrylic polymer, or a (meth)acrylic polymer having nitrogen in a quaternary ammonium salt structure.
Among these, from the viewpoint of adhesion to the first resin layer, it is particularly preferable to use a cationic water-soluble polymer such as a nitrogen-containing (meth)acrylic polymer or a (meth)acrylic polymer having nitrogen in a quaternary ammonium salt structure.

The amount of dispersant added to the emulsion is, in terms of solid content, preferably 1 part by mass or more per 100 parts by mass of the resin component, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more. The amount added is preferably 40 parts by mass or less, more preferably 35 parts by mass or less, and even more preferably 30 parts by mass or less.

If the amount of dispersant added is within the above range, it is easy to uniformly disperse the resin component (resin particles) so that the volume average particle size is 0.01 to 3.0 μm.

<<Aqueous Dispersion Medium>>
The aqueous dispersion medium for the emulsion may be an aqueous dispersion medium that does not dissolve or hardly dissolves the resin component used. Specific examples of such an aqueous dispersion medium include water, as well as a mixture of water and a solvent such as ethanol, isopropanol, or acetone.

<Ethyleneimine Resin>
The ink receiving layer may contain other resins in addition to the resin components derived from the emulsion. As the other resins, ethyleneimine-based resins that have high affinity with various inks are preferable.
The content of the ethyleneimine-based resin in the coating liquid is, in terms of solid content, preferably 1 part by mass or more, more preferably 2 parts by mass or more, per 100 parts by mass of the solid content of the emulsion. On the other hand, it is preferably 30 parts by mass or less, more preferably 25 parts by mass or less. If the content is equal to or more than the lower limit, the print quality is likely to be improved, and if the content is equal to or less than the upper limit, the effect of reducing paper dust by using the resin component derived from the emulsion is not likely to be hindered.

<Other ingredients>
The ink receiving layer may contain other additives such as an antistatic agent, if necessary, to the extent that the printing properties are not impaired.

<<Antistatic Agent>>
The antistatic agent can reduce problems such as adhesion of dust due to charging of the film surface or problems due to static electricity during printing.
The antistatic agent is not particularly limited, and may be a cationic, anionic, amphoteric, or nonionic antistatic agent, etc. In addition, it may be a low molecular weight antistatic agent or a high molecular weight (polymer) antistatic agent.

As the antistatic agent, a nitrogen-containing polymer type antistatic agent is preferably used, and more preferably a tertiary nitrogen- or quaternary nitrogen-containing acrylic resin is used.
These antistatic agents may be used alone or in combination of two or more.

The amount of antistatic agent added to the coating liquid is preferably 2 parts by mass or more per 100 parts by mass of the solid content of the emulsion, and is preferably 30 parts by mass or less, and more preferably 20 parts by mass or less. If the amount of antistatic agent added is within the above range, sufficient ink transferability is likely to be obtained during printing.

<<Fixing agent>>
If necessary, a fixing agent may be added to the emulsion. By including the fixing agent, the resin component is less likely to peel off from the laminated film after film formation. Therefore, paper dust originating from the resin component in the ink receiving layer can be reduced.
The fixing agent may be a silane coupling agent.
The amount of the fixing agent added to the emulsion is preferably 0.01 to 10 parts by mass, calculated as solid content, per 100 parts by mass of the resin component.

(Second Resin Layer)
The laminated film of the present invention preferably further comprises a second resin layer having a porosity of 15% or less on the surface of the base layer opposite to the first resin layer. By providing the second resin layer having a low porosity, it is possible to suppress the detachment of the filler contained in the base layer from the surface of the base layer opposite to the first resin layer, and further reduce paper dust.
The second resin layer is preferably a stretched film.

The second resin layer is not particularly limited in its configuration as long as it has a porosity of 15% or less, but a first preferred embodiment is to use a resin film containing the same resin as the base layer. That is, the second resin layer is a resin film containing thermoplastic resin A, and may contain a filler as necessary. The thermoplastic resin and filler that can be used in the second resin layer are the same as those listed in the base layer section, and the preferred materials are also the same as those in the base layer.

In the first preferred embodiment, the filler content in the second resin layer is preferably 15% by mass or less, and more preferably 10% by mass or less. There is no particular lower limit, but an appropriate amount is added when it is desired to obtain a cost reduction effect by adding filler. If the filler content is equal to or less than the above upper limit, it is easy to make the porosity when stretched 15% or less.

A second preferred embodiment is a resin film similar to the first resin layer described above. That is, the second resin layer is a resin film containing thermoplastic resin B and a filler. In this case, the thermoplastic resin and filler that can be used for the second resin layer are the same as the materials listed in the section for the first resin layer, and the preferred materials are also the same as those for the first resin layer.

<Stretched film>
The second resin layer may or may not be stretched, but from the viewpoint of mechanical strength, it is preferably a stretched film stretched at least uniaxially. However, when the second resin layer is the second preferred embodiment, that is, a resin film similar to the first resin layer, it is a stretched film stretched at least uniaxially. More specifically, it is a stretched film simultaneously stretched at least uniaxially together with the base layer, or together with the base layer and the first resin layer.

<Porosity>
From the viewpoint of the paper dust reducing effect, the porosity of the second resin layer is preferably 15% or less, more preferably 10% or less, and even more preferably 5% or less.
The porosity can be determined in the same manner as the porosity in the substrate layer.

(Other resin layers)
The laminated film of the present invention may have layers other than the ink receiving layer, the first resin layer, the base layer, and the second resin layer described above. For example, when each layer is formed separately and then laminated from the viewpoint of production efficiency, another resin layer may be provided that also serves as a support for the first resin layer or the second resin layer and has the effect of favorably laminating the layer to the base layer. The other resin layer is formed together with the first resin layer or the second resin layer by coextrusion or the like.
The other resin layer after lamination adheres well to the substrate layer and can function as a support that enhances the mechanical strength of the laminated film. In other words, the other resin layer/substrate layer/other resin layer can be said to be a substrate layer having a three-layer structure.

As the other resin layer, it is preferable to use a resin film similar to that of the base layer. That is, the resin layer is a resin film containing thermoplastic resin A, and may contain a filler as necessary. The thermoplastic resins and fillers that can be used in the resin layer are the same as those listed in the base layer section, and the preferred materials are also the same as those for the base layer.

[Characteristics of laminated film]
(Thickness of each layer)
The thickness of the substrate layer is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more. The thickness of the substrate layer is preferably 500 μm or less, more preferably 200 μm or less, and even more preferably 100 μm or less. If the thickness of the substrate layer is within the above range, it is easy to obtain appropriate rigidity and stiffness as a substrate.

The thickness of the first resin layer is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. If the thickness of the first resin layer is equal to or more than the above lower limit, the paper dust reduction effect is easily obtained, and there is a tendency for a laminate film with the desired performance to be easily obtained. The thickness of the first resin layer is preferably 200 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. If the thickness of the first resin layer is equal to or less than the above upper limit, the rigidity of the layer can be reduced, so that the flexibility of the laminate film is easily increased, and it is easy to use it as a packaging material. In addition, the effect of reducing costs can be obtained.

The thickness of the ink receiving layer is preferably 0.01 μm or more, more preferably 0.05 μm or more, and even more preferably 0.1 μm or more. On the other hand, it is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 1 μm or less. If the thickness is within this range, a laminated film with a texture similar to that of general printing paper can be obtained. In addition, by making the thickness 0.01 μm or more, it is easier to achieve a paper dust reduction effect.

The thickness of the second resin layer is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. If the thickness of the second resin layer is equal to or greater than the above lower limit, the effect of reducing paper dust is easily obtained. The thickness of the second resin layer is preferably 200 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. If the thickness of the second resin layer is equal to or less than the above upper limit, the rigidity of the layer can be reduced, so that the flexibility of the laminated film is easily increased, and it is easy to use it as a packaging material. In addition, the effect of reducing costs can be obtained.

[Method of manufacturing laminated film]
The laminated film of the present invention can be produced by laminating an ink-receiving layer, a first resin layer, and a base layer in this order, and is suitably produced by including a step of simultaneously stretching the first resin layer on the base layer in at least one axial direction.
For example, the laminated film of the present invention can be produced by forming a film of a first resin layer and a base material layer, laminating them and stretching them simultaneously, and then applying a coating liquid for forming an ink-receiving layer onto the first resin layer to form an ink-receiving layer.

(Film forming and lamination)
Examples of methods for forming a film include cast molding in which a molten resin is extruded into a sheet shape using a single-layer or multi-layer T-die, I-die, or the like connected to a screw-type extruder, calendar molding, rolling molding, inflation molding, etc. A film may be formed by casting or calendar molding a mixture of a thermoplastic resin and an organic solvent or oil, and then removing the solvent or oil.

Methods for laminating films include co-extrusion, extrusion lamination, and coating, and these can also be combined. In the co-extrusion method, the resin compositions for each layer, which have been melt-kneaded in separate extruders, are layered and extruded in a feed block or multi-manifold, and film formation and lamination are carried out in parallel. In the extrusion lamination method, a resin composition is extruded onto a preformed film to laminate the film. In the coating method, a resin solution, emulsion, or dispersion is applied onto a film and then dried to form and laminate the film.

From the viewpoint of manufacturing efficiency, when a first resin layer, a base layer, and a second resin layer are included, it is preferable to form the second resin layer separately and then laminate each layer.

FIG. 1 shows an example of the laminated film of the present invention.
1, an ink-receiving layer 3, a first resin layer 2, and a base layer 1 are laminated in this order. A print layer 5 can be formed on the ink-receiving layer 3 by printing.
FIG. 2 shows a laminated film 10B in which a second resin layer 4 is further provided.

In the case of the laminated film 10A illustrated in FIG. 1, for example, the film can be laminated by extrusion laminating the resin composition for forming the first resin layer onto a substrate layer that has been extruded in advance. Also, for example, the resin compositions of the first resin layer and the substrate layer may be co-extruded.

In the case of the laminated film 10B illustrated in FIG. 2, for example, the resin composition for forming the first resin layer is extrusion laminated onto a substrate layer that has been extruded in advance, and then the resin composition for forming the second resin layer is extrusion laminated onto the other surface of the substrate layer, thereby laminating the films of the respective layers. Also, for example, the first resin layer, substrate layer, and second resin layer may be laminated in this order and co-extruded.

(Extension)
<Stretching of Base Material Layer>
The base layer may be stretched or may not be stretched before the lamination of the first resin layer, but is simultaneously stretched in at least one axial direction after the lamination of the first resin layer.
From the viewpoint of mechanical strength, the base layer is preferably biaxially stretched. Although the base layer may be biaxially stretched simultaneously after lamination of the first resin layer, it is more preferable to stretch the base layer in a uniaxial direction before lamination of the first resin layer, and then further stretch the base layer in a direction perpendicular to the stretching direction before lamination after lamination of the first resin layer, thereby achieving biaxial stretching.

<Stretching of First Resin Layer>
The first resin layer is unstretched before lamination, and is stretched simultaneously in at least one axial direction after lamination to the base layer. The first resin layer may be stretched uniaxially or biaxially, but is preferably stretched uniaxially.

<Stretching of Second Resin Layer>
When the second resin layer is the first preferred embodiment described above, i.e., a resin film containing the same resin as the base layer, the second resin layer may be stretched or unstretched, but from the viewpoint of mechanical strength, it is preferable to stretch the second resin layer in at least one axial direction before or after lamination to the base layer, or both.
When the second resin layer is the above-mentioned second preferred embodiment, i.e., a resin film similar to the first resin layer, it is laminated on the base layer and then simultaneously stretched in at least one axial direction together with the base layer, or together with the base layer and the first resin layer.

When stretching a film, the stretching method can be, for example, a longitudinal stretching method that uses the difference in peripheral speed between a group of rolls, a transverse stretching method that uses a tenter oven, a sequential biaxial stretching method that combines these, a rolling method, a simultaneous biaxial stretching method that uses a combination of a tenter oven and a pantograph, and a simultaneous biaxial stretching method that uses a combination of a tenter oven and a linear motor. In addition, a simultaneous biaxial stretching (inflation molding) method can also be used in which molten resin is extruded into a tube shape using a circular die connected to a screw-type extruder, and then air is blown into the extruded resin.

The stretching temperature during stretching is preferably in the range of not less than the glass transition temperature of the thermoplastic resin when the thermoplastic resin used for the film is a non-crystalline resin, and is preferably in the range of not less than the glass transition temperature of the non-crystalline part of the thermoplastic resin and not more than the melting point of the crystalline part of the thermoplastic resin when the thermoplastic resin is a crystalline resin, specifically, it is preferably in the range of not less than the glass transition temperature of the non-crystalline part of the thermoplastic resin and not more than the melting point of the crystalline part of the thermoplastic resin, and more specifically, it is preferably a temperature 5 to 60° C. lower than the melting point of the thermoplastic resin.
The stretching temperature when the base layer and the first resin layer are simultaneously stretched after lamination is within the above-mentioned preferred temperature range for the thermoplastic resin A contained in the base layer, and is higher than the temperature for the thermoplastic resin B contained in the first resin layer.

The stretching speed is not particularly limited, but from the viewpoint of stable stretch forming, it is preferably within the range of 20 to 350 m/min.
The stretching ratio can also be appropriately determined in consideration of the properties of the thermoplastic resin used. For example, when a resin film containing a propylene homopolymer or a copolymer thereof is stretched in one direction, the stretching ratio has a lower limit of usually 1.2 times or more, preferably 2 times or more, while the upper limit is usually 12 times or less, preferably 10 times or less. When the stretching ratio is biaxially stretched, the lower limit is usually 1.5 times or more, preferably 10 times or more, while the upper limit is usually 60 times or less, preferably 50 times or less, in terms of area stretching ratio.

(Surface Treatment)
From the viewpoint of enhancing adhesion to the ink receiving layer, it is preferable that the first resin layer is subjected to a surface treatment to activate the surface.
Examples of the surface treatment include corona discharge treatment, flame treatment, plasma treatment, glow discharge treatment, ozone treatment, etc., and these treatments can be combined. Among these, corona discharge treatment or flame treatment is preferred, and corona treatment is more preferred.

(Formation of ink-receiving layer)
The ink receiving layer can be formed by preparing a coating liquid for forming the ink receiving layer and coating the first resin layer with the coating liquid.

<Preparation of Coating Fluid>
The coating liquid for forming the ink receiving layer can be prepared by blending additives and the like, if necessary, with the resin component derived from the above-mentioned emulsion.

When using a cationic urethane resin as a resin component, an emulsion can be prepared by dispersing in water a copolymer in which cationic hydrophilic groups have been introduced into the polyurethane resin skeleton. Specific examples include a method in which the monomers that make up the target polymer are emulsified and dispersed in water and polymerized, and a method in which the target polymer is obtained by bulk polymerization or the like, and then the raw resin is melt-kneaded and emulsified successively using a twin-screw extruder.

When using an olefin copolymer resin component, the method for preparing the emulsion is not particularly limited, but for example, the following method (1) or (2) can be used.

(1) An olefin copolymer is added to an aromatic hydrocarbon solvent and dissolved by heating to prepare a resin solution. A dispersant is added to this resin solution and mixed and stirred, and water is subsequently added to cause phase inversion. The aromatic hydrocarbon solvent is then distilled off, and the resulting aqueous dispersion is used as an emulsion.

(2) The olefin copolymer is melted using a twin-screw extruder, and then an aqueous solution of a dispersant is added and kneaded to obtain an aqueous dispersion, which is then used as an emulsion (see JP-B-62-29447).

When preparing an emulsion by these methods, it is preferable to use a polymer emulsifier such as a cationic water-soluble polymer as a dispersant, and further to use the dispersion method using a twin-screw extruder described above in (2). This makes it easy to adjust the volume average particle size of the resin component (resin particles) of the olefin copolymer in the emulsion to 0.01 to 3.00 μm. In the method described above in (2), the volume average particle size of the resin component (resin particles) of the olefin copolymer in the emulsion can be adjusted by controlling, for example, the amount of water relative to the olefin copolymer, the cylinder temperature and its profile, the residence time of the resin in the extruder, the barrel rotation speed of the extruder, and other operating conditions of the twin-screw extruder.

The solids concentration of the coating liquid is preferably 0.1% by mass or more, more preferably 1.5% by mass or more, and is preferably 20% by mass or less, more preferably 15% by mass or less, based on the total amount of the coating liquid.

The coating liquid can be applied using a coating device such as a roll coater, blade coater, bar coater, air knife coater, size press coater, gravure coater, die coater, lip coater, or spray coater.

The amount of the coating liquid, in terms of the amount of solid content after drying, is preferably 0.05 g/ ^m2 or more, more preferably 0.10 g/m2 or ^more , and particularly preferably 0.15 g/ ^m2 or more, and is preferably 1.40 g/m2 or ^less , more preferably 0.50 g/m2 or ^less , more preferably 0.30 g/m2 or ^less , and particularly preferably 0.24 g/m2 or ^less .
By setting the coating weight to be equal to or greater than the lower limit, it is easy to obtain a further effect of reducing paper dust, whereas by setting the coating weight to be equal to or less than the upper limit, it is easy to suppress stickiness of the resulting ink receiving layer, which also leads to cost reduction.

The ink receiving layer is preferably formed continuously by a roll-to-roll method, which can improve the productivity of the laminated film. In addition, the thickness of the ink receiving layer can be adjusted relatively easily by the roll-to-roll method, so that a laminated film with a desired texture can be easily manufactured, for example, by reducing the thickness of the ink receiving layer while maintaining printability.
Furthermore, the ink receiving layer may be formed in the same line as the lines for forming the layers other than the ink receiving layer, or may be formed in a different line.

(printing)
A printed layer can be formed by printing on the surface of the ink receiving layer of the laminate film of the present invention.
Usable printing methods include offset printing, gravure printing, flexographic printing, letterpress printing, screen printing, inkjet recording, thermal recording, thermal transfer recording, and electrophotographic recording. Of these, offset printing, gravure printing, and flexographic printing are preferred, as they are more likely to produce printed matter with excellent weather resistance and water resistance. Furthermore, the printing ink may be an oil-based ink, a water-based ink, or an ultraviolet-curable ink.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples. In the examples, the terms "parts", "%", etc. are based on mass unless otherwise specified.

[Raw materials]
The raw materials used in the examples and comparative examples are as follows.
(Thermoplastic resin)
Propylene homopolymer (product name: Novatec PP FY-4, manufactured by Japan Polypropylene Corporation, MFR: 5.0 g/10 min (230° C., 2.16 kg load), melting point: 164° C., density: 0.9 g/cm ³ )
Propylene-ethylene random copolymer (product name: Wintec WFW4, manufactured by Japan Polypropylene Corporation, melting point: 135°C)
Polyethylene (product name: Novatec HD HJ360, manufactured by Japan Polyethylene Co., Ltd., melting point: 132°C)

(Filler)
Heavy calcium carbonate (product name: Softon 1800 (manufactured by Bihoku Powder Chemical Industry Co., Ltd.), average particle size: 1.2 μm)

Table 1 below shows a list of the above materials.

(Urethane Resin Emulsion (E))
A cationic polyurethane water dispersion (product name: Hydran CP-7050, manufactured by DIC Corporation: MFT < 5°C) was used as emulsion (E). The solid content of this emulsion (E) was 25 mass%, and the volume average particle size of the resin component (resin particles) in emulsion (E) was 0.07 µm.

<Volume average particle size>
The volume average particle size was measured using a laser diffraction type particle size distribution measuring device (SALD-2200, manufactured by Shimadzu Corporation).

(Ethyleneimine-based resin solution (F))
Into a four-neck flask equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas inlet, 100 parts by mass of a 25% by mass aqueous solution of polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd., product name: Epomin P-1000), 10 parts by mass of 1-chlorobutane (manufactured by Wako Pure Chemical Industries, Ltd., reagent), and 10 parts by mass of propylene glycol monomethyl ether (manufactured by Wako Pure Chemical Industries, Ltd., reagent) were introduced. The mixture was then stirred under a nitrogen stream and subjected to a modification reaction at a temperature of 80° C. for 20 hours. Water was added to this solution to adjust the solid content concentration to 20% by mass, and an ethyleneimine-based resin solution (F) was obtained.

(Coating Liquid (1))
The urethane-based resin emulsion (E) and the ethyleneimine-based resin solution (F) were mixed so that the solid content concentration ratio was 80 parts by mass:20 parts by mass, and used as a coating liquid (1).

(Coating Liquid (2))
The ethyleneimine resin solution (F) was used as a coating liquid (2).

Table 2 below shows a list of the materials used for each coating solution.

[Production of laminated film]
Example 1
A resin composition consisting of 74 parts by mass of propylene homopolymer (Novatec PP FY-4), 10 parts by mass of polyethylene (Novatec HD HJ360), and 16 parts by mass of heavy calcium carbonate (Softon 1800) was melt-kneaded in an extruder set at 230 ° C. Thereafter, the resin composition was fed to an extrusion die set at 250 ° C. and extruded into a sheet, which was then cooled to 60 ° C. by a cooling device to obtain an unstretched sheet. This unstretched sheet was heated to 135 ° C. and stretched 5 times in the longitudinal direction using the difference in peripheral speed between the rolls to form a base layer.

Next, a resin composition consisting of 54 parts by mass of a propylene-based random copolymer (Wintec WFW4), 6 parts by mass of a propylene homopolymer (Novatec PP FY-4), and 40 parts by mass of heavy calcium carbonate (Softon 1800) was melt-kneaded in an extruder set at 230° C. Thereafter, the mixture was fed to an extrusion die set at 250° C. and extruded into a sheet shape onto the substrate layer.
As a result, the first resin layer was laminated on the base material layer.

The resulting laminated sheet was cooled to 60°C using a cooling device, and then heated to approximately 150°C using a tenter oven and stretched 8.5 times in the transverse direction. After heating to 160°C and heat treatment, it was cooled to 60°C and the edge portions were slit.

Next, the first resin layer of the laminate sheet was subjected to a corona discharge treatment using a continuous coating device. The corona discharge treatment was performed using a corona discharge treatment device (HF400F, manufactured by Kasuga Electric Co., Ltd.) with a gap of 5 mm between an aluminum discharge electrode having a length of 0.8 m and an insulating roll, a line processing speed of 15 m/min, and an applied energy density of 4200 J/ ^m2 . Next, the coating liquid (1) was applied onto the first resin layer, and the coating was dried in a hot air blowing drying device at 60°C to form an ink receiving layer. The solid content of the ink receiving layer after drying was 0.23 g/ ^m2 .

Then, the film was wound up using a roll winding device to obtain a three-layer laminate film (thickness: 90 μm, thickness of each layer: -/30 μm/60 μm, number of stretching axes for each layer: -/uniaxial/biaxial) in which the ink receiving layer/first resin layer/substrate layer were laminated in that order. Note that "-" means that the film was not measured.

(Example 2 and Comparative Examples 1 and 2)
A laminated film of Example 2 was obtained in the same manner as in Example 1, except that the compounding ratio of the thermoplastic resin used in forming the first resin layer was changed.

(Comparative Example 3)
A laminated film of Comparative Example 3 was obtained in the same manner as in Example 1, except that no ink-receiving layer was laminated.

(Reference Example 1)
A laminated film of Reference Example 1 was obtained in the same manner as in Example 1, except that the coating liquid (1) for forming the ink-receiving layer was changed to the coating liquid (2).

[evaluation]
The laminated films of the respective Examples and Comparative Examples were evaluated for their paper dust reducing effect and printability as follows.

(Paper dust reduction effect)
Each laminated resin film was cut into A3 size, and 2000 sheets of the cut laminated film were printed using an offset printing machine (device name: RYOBI3300CR, manufactured by Ryobi) and UV offset printing ink (product name: BC161, manufactured by T&K Toka). After printing, paper dust adhering to the blanket was visually confirmed and evaluated according to the following evaluation criteria. A score of 3 or more on the following criteria is a pass level.
4 (Good): No paper dust attached 3 (Fair): Paper dust attached in some places 2 (Poor): Paper dust attached in multiple places 1 (Poor): Paper dust attached over the entire surface

(Printability)
Print quality evaluation was carried out using an ultraviolet-curing inkjet printer (product name "OceArizona250GT", manufactured by Oce) and ultraviolet-curing inkjet printing ink (black).
Each laminated resin film was cut into A3 size to prepare printing paper. After storing the above printing paper for 3 days in an atmosphere of 23°C and 50% relative humidity, characters (ruled line thickness: 5 pt) were printed 100% solid on the surface of the ink receiving layer using the above printing machine. The printed characters were visually observed, and the printing quality was evaluated based on the bleeding of the ink according to the following criteria. A score of 2 or higher on the following criteria is a pass level.
3: Good (no ink bleeding observed)
2: Fair (slight ink bleeding observed)
1: Poor (ink bleeding observed)

The evaluation results are shown in Table 3. The P2 ratio in Table 3 indicates the mass ratio of the propylene-random copolymer (P2) to the total amount of thermoplastic resin contained in the first resin layer.

The laminated films of Examples 1 and 2, in which the porosity of the first resin layer was 15% or less, had no paper powder or only a portion of the paper powder. In addition, the printability was excellent with no ink bleeding.
In the examples, a laminated film was obtained that was capable of reducing paper dust and had excellent printability while maintaining the light weight, whiteness, and cost reduction effects achieved by including a filler.

On the other hand, the laminate films of Comparative Examples 1 and 2, in which the porosity of the first resin layer exceeds 15%, had excellent printability, but generated more paper dust than the laminate films of the Examples. This is thought to be because the porosity of the first resin layer was high, and the filler contained in the first resin layer was easily detached. In Comparative Example 3, in which no ink receiving layer was formed, the paper dust reduction effect was at an acceptable level, but the printability was poor.

In addition, a comparison between Example 1 and Reference Example 1 revealed that the paper dust reduction effect was further improved by using an emulsion-based coating agent to form the ink receiving layer.

10A, 10B...Laminated film 1...Base material layer 2...First resin layer 3...Ink receiving layer 4...Second resin layer 5...Printing layer

Claims (8)

A laminated film having an ink receiving layer, a first resin layer, and a base layer in this order,
The base layer contains a thermoplastic resin A and a filler,
the first resin layer is a layer containing a thermoplastic resin B having a lower melting point than the thermoplastic resin A and a filler, and having a porosity of 15% or less;
the ink receiving layer contains a resin component derived from an emulsion, and the minimum film-forming temperature of the resin component is 100° C. or lower;
Laminated film. The laminated film according to claim 1, wherein the content of the filler in the first resin layer is 10% by mass or more. The laminated film according to claim 1 or 2, wherein the thermoplastic resin A is a propylene homopolymer. The laminated film according to any one of claims 1 to 3, wherein the thermoplastic resin B is a random copolymer of propylene and a monomer copolymerizable with propylene. The laminated film according to any one of claims 1 to 4, wherein the volume average particle size of the resin component is 0.01 to 3.0 μm. A second resin layer is further provided on the surface of the base layer opposite to the first resin layer,
6. The laminated film according to claim 1, wherein the second resin layer has a porosity of 15% or less. The laminated film according to any one of claims 1 to 6, wherein the base layer and the first resin layer are stretched films stretched in at least one axial direction. The method for producing a laminated film according to any one of claims 1 to 7, comprising laminating an ink-receiving layer, a first resin layer, and a base layer in this order,
The method includes a step of laminating the first resin layer on the base layer and then simultaneously stretching the laminate in at least one axial direction.

Images