WO2023176552A1 - Sheet, and paper for printing - Google Patents

Abstract

The problem addressed by the present invention is to provide a resin sheet having excellent transportability and tear resistance during printing while also reducing environmental impact.　The resin sheet of the present invention is equipped with a biaxially oriented layer containing a thermoplastic resin. The thermoplastic resin contains a chemically recycled polyolefin. The degree of crystallization of the thermoplastic resin in the biaxially oriented layer is 40-52%. The biaxially oriented layer is a biaxially oriented porous layer containing particles.

Description

Sheets and printing paper

The present invention relates to sheets and printing paper.

Conventionally, resin sheets have been widely used as printing paper for labels, wrapping paper, posters, calendars, catalogs, public notices, etc. In order to clearly display printed contents like pulp paper, the resin sheet must have an appropriate degree of whiteness. Therefore, resin sheets used for printing paper often have a porous layer (see, for example, Patent Document 1).

Japanese Patent Application Publication No. 8-142286

Recently, interest in recycling has increased due to growing awareness of environmental issues. Recycling of plastic waste includes thermal recycling, material recycling, chemical recycling, etc. Among these, chemical recycling produces new materials from raw materials obtained by chemically decomposing waste, so it is possible to produce materials with fewer foreign substances.

The resin sheet having the porous layer described above is manufactured by molding a resin composition into a sheet shape using a molding device. However, when resin sheets are manufactured in the same way using resin manufactured through chemical recycling, the rigidity of the sheets is low, leading to transportation problems during printing (paper feeding/ejection, etc.) and reduced tear resistance. there were.

An object of the present invention is to provide a sheet that has excellent transportability during printing and tear resistance while reducing environmental load.

As a result of intensive studies to solve the above problems, the present inventors completed the present invention as follows.

[1] A sheet comprising a biaxially stretched layer containing a thermoplastic resin,
The thermoplastic resin includes a chemically recycled polyolefin,
The crystallinity of the thermoplastic resin in the biaxially stretched layer is 40 to 52%,
A sheet in which the biaxially stretched layer is a biaxially stretched porous layer containing particles.

[2] The sheet according to [1] above, wherein the content of the chemically recycled polyolefin in the thermoplastic resin is 3% by mass or more.

[3] The sheet according to [1] or [2] above, wherein the chemically recycled polyolefin includes chemically recycled polypropylene.

[4] The sheet according to any one of [1] to [3] above, comprising a surface layer on the biaxially stretched layer.

[5] The surface layer is a uniaxially stretched porous layer containing a thermoplastic resin and particles,
The sheet according to [4] above, wherein the content of the particles in the surface layer is 30 to 80% by mass.

[6] The thermoplastic resin in the surface layer contains a chemically recycled polyolefin,
The sheet according to [5] above, wherein the thermoplastic resin in the surface layer has a crystallinity of 45 to 50%.

[7] The sheet according to [5] or [6] above, wherein the thermoplastic resin in the surface layer contains an acid-modified polyolefin.

[8] Printing paper comprising the sheet according to any one of [1] to [7] above.

According to the present invention, it is possible to provide a sheet that has excellent transportability during printing and tear resistance while reducing environmental load.

It is a sectional view showing an example of a sheet.

Hereinafter, the sheet and printing paper of the present invention will be explained in detail. The following explanation is an 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.

(sheet)
The sheet of the present invention includes a biaxially stretched layer containing a thermoplastic resin. The thermoplastic resin in the biaxially stretched layer has a crystallinity of 40 to 52% and contains chemically recycled polyolefin. In the present invention, chemically recycled polyolefin refers to a polyolefin resin produced by a chemical recycling method, for example, by collecting a used polyolefin resin and depolymerizing it to repolymerize the decomposed monomer. refers to a polyolefin resin obtained by

By using recycled polyolefin resins in this way, it is possible to reduce the amount of newly manufactured unused (hereinafter referred to as virgin) resin, thereby reducing the environmental impact. be. In addition, polyolefin resins produced by chemical recycling methods are less likely to contain foreign substances such as particles than material recycling methods, in which used polyolefin resins are melted and pelletized and reused as raw materials for new products. There tends to be less. Since tearing of the sheet caused by foreign matter can be reduced, the tear resistance of the sheet can be increased while reducing the environmental load.

Furthermore, the biaxially stretched layer in the present invention has less anisotropy in the direction of the stretching axis than the uniaxially stretched layer, so it is possible to improve the tear resistance of the sheet. In addition, by using a thermoplastic resin with a crystallinity of 52% or less, deterioration in tear resistance due to orientation of the thermoplastic resin is suppressed.

Further, the biaxially stretched layer has higher rigidity and superior mechanical strength than the non-stretched layer or the uniaxially stretched layer. The stiffness of this biaxially stretched layer is further increased by using a thermoplastic resin with a crystallinity of 40% or more. It is possible to provide a sheet that is less likely to stick to rollers, wrinkle or twist during paper feeding or ejection in a printing device, and has excellent conveyance properties. Therefore, it is possible to provide a sheet that has excellent conveyance properties and tear resistance while reducing environmental load.

<Biaxially stretched layer>
The biaxially stretched layer is a layer in which a resin composition is stretched in one direction (the longitudinal direction (MD) of the sheet) and in a direction substantially perpendicular to the one direction (the transverse direction (TD) of the sheet). The biaxially stretched layer contains a thermoplastic resin having a specific degree of crystallinity as described above, and contains chemically recycled polyolefin as all or part of the thermoplastic resin.

<<Crystallinity>>
The crystallinity of the thermoplastic resin is 40% or more, preferably 42% or more, more preferably 44% or more, from the viewpoint of sheet conveyance, pore formation, gloss, etc. From the viewpoint of resistance, it is 52% or less, preferably 51% or less, and more preferably 50% or less.
The crystallinity is measured by differential scanning calorimetry.

Methods for controlling the crystallinity of the thermoplastic resin within a desired range include, for example, a method of controlling the stereoregularity of the thermoplastic resin, a method of mixing thermoplastic resins with different degrees of crystallinity, and the like. In particular, when a copolymerizable monomer other than the monomer constituting the target resin is mixed during the synthesis of a thermoplastic resin, the degree of crystallinity of the synthesized thermoplastic resin may change significantly. For example, if a trace amount of ethylene is mixed during the synthesis of polypropylene, polypropylene may be obtained that has a lower degree of crystallinity than polypropylene containing only propylene monomer. In such cases, resins with different crystallinities may be obtained for each unit, such as a synthetic lot.

<<Thermoplastic resin>>
The melting point of the thermoplastic resin is preferably 120°C or higher, more preferably 140°C or higher, and 160°C or higher, from the viewpoint of ensuring shape stability when placed under high temperatures in various printing methods. It is more preferable that it is above. From the viewpoint of facilitating molding, the melting point is preferably 250°C or lower, more preferably 220°C or lower, even more preferably 200°C or lower, and particularly preferably 180°C or lower. . Here, the melting point refers to the endothermic peak top temperature accompanying melting in differential scanning calorimetry.

The melt flow rate (MFR) (230° C., 2.16 kg load) of the thermoplastic resin is preferably 1.0 g/10 minutes or more, more preferably 2.0 g/10 minutes or more, and 4. More preferably, it is 0 g/10 minutes or more. The melt flow rate is preferably 20 g/10 minutes or less, more preferably 12 g/10 minutes or less, even more preferably 10 g/10 minutes or less. The above melt flow rate is obtained in accordance with JIS K7210-1:2014. Moreover, when the thermoplastic resin contains two or more types of resins, it is preferable from the viewpoint of moldability that resins having different melt flow rates are included. More specifically, the thermoplastic resin includes a first resin having a melt flow rate of 1.0 g/10 minutes or more and 5.0 g/10 minutes or less, and a first resin having a melt flow rate of more than 5.0 g/10 minutes and 30 g/10 minutes. /10 minutes or less.

Examples of thermoplastic resins that can be used in the biaxially stretched layer include polyolefin resins; polyester resins; polyamide resins; polycarbonate resins; polystyrene resins; polyphenylene sulfide resins. From the viewpoint of controlling the crystallinity of the thermoplastic resin within a desired range, one or more of these can be used.

From the viewpoint of mechanical strength, the thermoplastic resin preferably contains a polyolefin resin or a polyester resin, more preferably a polyolefin resin, and even more preferably a polypropylene resin. From the same viewpoint, the thermoplastic resin preferably consists of a polyolefin resin or a polyester resin, more preferably a polyolefin resin, and even more preferably a polypropylene resin.

In this specification, the polyolefin resin refers to a resin having 50% by mass or more of olefin as a constituent unit. The polyolefin resin may have only olefin as its constituent unit. Examples of the polyolefin resin include polyethylene resin, polypropylene resin, polymethylpentene resin, cyclic olefin resin, and copolymers thereof.
Examples of the polyester resin include polyethylene terephthalate, polyethylene naphthalate, and aliphatic polyester.

The content of the thermoplastic resin in the biaxially stretched layer is preferably 20% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and 60% by mass or more, from the viewpoint of improving sheet formability or mechanical strength. Particularly preferably % by mass or more. From the viewpoint of imparting various functions, the content of the thermoplastic resin is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less.

<<Chemical recycled polyolefin>>
As long as the chemically recycled polyolefin that can be used in the biaxially stretched layer is produced by the chemical recycling method as described above, the method of depolymerization and subsequent repolymerization of the recovered used resin is not particularly limited. From the viewpoint of mechanical strength, it is preferable that the chemically recycled polyolefin contains chemically recycled polypropylene.

The degree of crystallinity of the chemically recycled polyolefin is preferably 30% or more, more preferably 35% or more, even more preferably 40% or more, and 45% from the viewpoint of sheet conveyance properties and pore formation properties of the biaxially stretched layer. The above is particularly preferable. From the viewpoint of tear resistance, the degree of crystallinity of the chemically recycled polyolefin is preferably 60% or less, more preferably 55% or less, and even more preferably 50% or less.

The content of chemically recycled polyolefin in the thermoplastic resin in the biaxially stretched layer is preferably 3% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and 30% by mass from the viewpoint of reducing environmental load. % or more is particularly preferred, 40% by mass or more is even more particularly preferred, and even more particularly preferably 50% by mass or more. The content of the chemically recycled polyolefin may be 100% by mass, but from the viewpoint of crystallinity control, it is preferably less than 100% by mass, more preferably 90% by mass or less, and even more preferably 80% by mass or less. , 70% by mass or less is particularly preferred.
Note that the preferred content of chemically recycled polyolefin in all thermoplastic resins used in the entire sheet is also the same as above.

<<Unused polyolefin resin>>
In addition to the above-mentioned chemically recycled polyolefin, the thermoplastic resin may contain an unused (virgin) polyolefin resin that is a new raw material.

The content of unused polyolefin resin in the thermoplastic resin in the biaxially stretched layer is, for example, 10% by mass or more, preferably 20% by mass or more, and 30% by mass or more, from the viewpoint of controlling the crystallinity within a desired range. It is more preferably at least 40% by mass, even more preferably at least 40% by mass. From the viewpoint of reducing environmental load, the content of the unused polyolefin resin is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, and particularly preferably 60% by mass or less. .

<<Polyolefin resin derived from biomass>>
The unused polyolefin resin may include a biomass-derived polyolefin resin. By including biomass-derived polyolefin resin, compared to petroleum-derived polyolefin resin, it is possible to reduce the amount of carbon dioxide gas emitted per sheet volume during the manufacturing stage, contributing to a reduction in environmental impact.

The biomass-derived polyolefin resin that can be used is not particularly limited as long as it contains structural units derived from monomers produced using biomass as a raw material. For example, some or all of the propylene used as a monomer for polypropylene resins may be derived from biomass, and some or all of the ethylene or α-olefin used as a comonomer may be derived from biomass. .

From the perspective of reducing carbon dioxide gas emissions, the content of biomass-derived polyolefin resin in unused polyolefin resin is, for example, 5% by mass or more, preferably 10% by mass or more, and 20% by mass or more. is more preferable, and even more preferably 30% by mass or more. From the viewpoint of stretching stability, the content of the biomass-derived polyolefin is preferably less than 100% by mass, more preferably 90% by mass or less, and even more preferably 80% by mass or less.

<<Acid-modified polyolefin resin>>
The thermoplastic resin in the biaxially oriented layer can include acid-modified polyolefin. When the sheet of the present invention does not have the surface layer described below and the biaxially oriented layer constitutes the outermost surface of the sheet, the acid-modified polyolefin reduces paper dust generated during printing when the biaxially oriented layer contains particles. Easier to reduce.

Examples of acid-modified polyolefins that can be used include acid anhydride group-containing polyolefins obtained by random copolymerization or graft copolymerization of maleic anhydride; carboxylic acid group-containing polyolefins obtained by random copolymerization or graft copolymerization of unsaturated carboxylic acids such as (meth)acrylic acid; Containing polyolefin; epoxy group-containing polyolefin obtained by random copolymerization or graft copolymerization of glycidyl (meth)acrylate, and the like.

More specifically, examples include maleic anhydride-modified polypropylene, maleic anhydride-modified polyethylene, acrylic acid-modified polypropylene, ethylene/methacrylic acid random copolymer, ethylene/glycidyl methacrylate random copolymer, or glycidyl methacrylate-modified polypropylene. . Among these, maleic anhydride-modified polypropylene or maleic anhydride-modified polyethylene is preferred.

The acid modification rate of the acid-modified polyolefin is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, preferably 20% by mass or less, and more preferably 15% by mass or less.
If the acid modification rate is 0.01% by mass or more, the effect of suppressing paper dust can be easily obtained. If the acid modification rate is 20% by mass or less, the softening point of the acid-modified polyolefin will not become too low, and kneading with the thermoplastic resin will be relatively easy.

The content of acid-modified polyolefin in the biaxially stretched layer when containing acid-modified polyolefin is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and 30 parts by mass or more, based on 100 parts by mass of particles. It is preferably at most 20 parts by mass, more preferably at most 20 parts by mass.
When the content of the acid-modified polyolefin is 0.5 parts by mass or more, the adhesive force between the thermoplastic resin and the particles increases, so that the effect of suppressing paper dust can be easily obtained. When the content of the acid-modified polyolefin is 30 parts by mass or less, stretchability is good and it becomes easy to suppress stretching breakage during molding.

<<particles>>
In the present invention, the biaxially stretched layer can further contain particles. From the viewpoint of reducing environmental load, the biaxially stretched layer is preferably a biaxially stretched porous layer containing particles. When a resin film containing particles in addition to a thermoplastic resin with a desired degree of crystallinity is stretched, a large number of flat fine pores are formed inside the film, starting from the particles and extending in the stretching direction, resulting in a porous state. It can be a layer.

In the biaxially stretched porous layer, long flat pores may be formed in the stretching axis direction (plane direction) around the particles. According to such a stretched porous layer, it is easy to whiten the sheet, make it opaque, and reduce the weight while imparting strength to the sheet. Since the resin component in the biaxially stretched layer is replaced with particles or holes, the amount of resin in the biaxially stretched layer can be further reduced. Since the carbon dioxide gas emission coefficient of the pores is 0, the amount of carbon dioxide gas emitted during the manufacturing stage can also be reduced, which can greatly contribute to reducing the environmental load. By setting the crystallinity of the thermoplastic resin contained together with the particles in the biaxially stretched layer to 40% or more, sufficient pores are easily formed to make the biaxially stretched layer white, opaque, and lightweight. Become.

Particles that can be used include, for example, inorganic particles or organic particles. Among these, inorganic particles are preferable from the viewpoint of reducing environmental load because they have a smaller carbon dioxide gas emission coefficient than resins.

Inorganic particles that can be used include, for example, calcium carbonate, calcined clay, talc, diatomaceous earth, clay, barium sulfate, magnesium oxide, zinc oxide, titanium oxide, barium titanate, silica, alumina, zeolite, mica, sericite, bentonite, sepiolite. , vermiculite, dolomite, wollastonite, or glass fiber. From the viewpoint of stability of pore formation during stretching, calcium carbonate, calcined clay, or talc are preferred, and calcium carbonate is more preferred. The surface of the inorganic particles may be treated with a fatty acid, a polymeric surfactant, an antistatic agent, or the like.

Examples of the organic particles include polyester, polystyrene, polyamide, polycarbonate, polycyclic olefin, poly(meth)acrylate, polyethylene sulfide, polyphenylene sulfide, polyimide, polyether ketone, and polyether ether ketone.

One type of inorganic particles and organic particles may be selected from the above and used alone, or two or more types may be used in combination. When two or more types are combined, it may be a combination of inorganic particles and organic particles.

The average particle diameter of the particles is preferably 0.01 μm or more, more preferably 0.1 μm or more, and even more preferably 0.5 μm or more, from the viewpoint of ease of mixing with the thermoplastic resin or pore-forming property. From the viewpoint of suppressing minute tears on the sheet surface originating from the particles, the average particle diameter of the particles is preferably 30 μm or less, more preferably 15 μm or less, and even more preferably 5 μm or less.

The average particle diameter of the particles in the biaxially stretched layer can be determined by observing the cross section of the biaxially stretched layer with a scanning electron microscope (SEM). From the image captured by SEM, the diameter of the circumscribed circle of the particles contained in the biaxially stretched layer can be measured at 10 points for arbitrarily selected particles, and the diameter that corresponds to 50% of the cumulative number of particles can be determined as the average particle diameter. can.

The content of particles in the biaxially stretched layer when containing particles is preferably 5% by mass or more, more preferably 15% by mass or more from the viewpoint of pore formation, and 80% by mass or less from the viewpoint of formability. It is preferably 70% by mass or less, more preferably 60% by mass or less, particularly preferably 50% by mass or less, even more preferably 40% by mass or less, even more particularly preferably 30% by mass or less.

<<Additives>>
The biaxially stretched layer can further include additives. Examples of additives that can be used include heat stabilizers (antioxidants), neutralizers, nucleating agents, light stabilizers, dispersants, lubricants, colorants, plasticizers, mold release agents, flame retardants, antistatic agents, Alternatively, examples include ultraviolet absorbers.

A heat stabilizer may be added for the purpose of suppressing deterioration of the thermoplastic resin and allowing the sheet to be used stably over a long period of time. As the heat stabilizer, one or more types can be appropriately used from among the commonly known hindered phenol type, phosphorus type, or amine type heat stabilizers.
When the biaxially stretched layer contains a heat stabilizer, the content of the heat stabilizer in the biaxially stretched layer is preferably 0.01% by mass or more, for example, from the viewpoint of expressing the function of the heat stabilizer. is 0.05% by mass or more, more preferably 0.1% by mass or more, and from the viewpoint of improving molding stability or appearance, is preferably 1.5% by mass or less, and more preferably 1% by mass or less.

As the light stabilizer, one or more kinds of commonly known light stabilizers such as hindered amine type, benzotriazole type, or benzophenone type can be used as appropriate. It is also preferable to use a light stabilizer and the above heat stabilizer in combination.
When the biaxially stretched layer contains a light stabilizer, from the viewpoint of expressing the function of the light stabilizer, the content of the light stabilizer in the biaxially stretched layer is preferably 0.01% by mass or more, and the molding stability Alternatively, from the viewpoint of improving the appearance, the content is preferably 1.5% by mass or less, more preferably 1% by mass or less.

Dispersants and lubricants include, for example, silane coupling agents; fatty acids having 8 to 24 carbon atoms such as oleic acid and stearic acid, metal salts thereof, amides thereof, or esters with alcohols having 1 to 6 carbon atoms; Examples include poly(meth)acrylic acid or metal salts thereof, and one type or two or more types thereof can be used.

<Surface layer>
The sheet of the present invention can include a surface layer on the biaxially stretched layer. By coating the surface of the biaxially stretched layer with the surface layer, it is possible to suppress the particles from falling off from the biaxially stretched layer and reduce the generation of paper dust. From the viewpoint of reducing paper dust, it is preferable that the surface layer is provided not only on one side but also on both sides of the biaxially stretched layer.

FIG. 1 shows an example of a sheet 10 that includes a surface layer. The sheet 10 illustrated in FIG. 1 includes a biaxially stretched layer 1 and a surface layer 2 on both sides thereof.

In the present invention, the surface layer is preferably a uniaxially stretched porous layer containing a thermoplastic resin and particles. If the surface layer is a uniaxially stretched porous layer, it will be easier to give the sheet a paper texture and reduce the generation of paper dust, but compared to the case where the surface layer is a biaxially stretched layer, the stiffness and uniformity of the sheet will be lower. The tear resistance in this direction tends to decrease.
Therefore, in order to suppress the decrease in stiffness and tear resistance of the sheet while obtaining the effects of the surface layer being a uniaxially stretched porous layer, the crystallinity and particle content of the thermoplastic resin are designed to It is preferable to change it from a biaxially stretched layer. In addition, when a surface layer is provided on both surfaces of a biaxially stretched layer, the design of the material of two surface layers, its content, etc. may be the same or different.

<<Thermoplastic resin>>
Examples of the thermoplastic resin that can be used for the surface layer include the same materials as those described in the section of <Biaxially Stretched Layer>.

The crystallinity of the thermoplastic resin in the surface layer is preferably 45% or more, more preferably 46% or more, and still more preferably 47% or more, from the viewpoint of sheet conveyance properties and pore-forming properties. , from the viewpoint of tear resistance, preferably 50% or less.

From the viewpoint of moldability or mechanical strength, the content of the thermoplastic resin in the surface layer is preferably 20% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and 60% by mass or more. Particularly preferred. From the viewpoint of imparting various functions, the content of the thermoplastic resin is preferably 80% by mass or less, more preferably 70% by mass or less, further preferably 60% by mass or less, and particularly preferably 50% by mass or less.

<<Chemical recycled polyolefin>>
Preferably, the thermoplastic resin in the surface layer includes chemically recycled polyolefin. Examples of the chemically recycled polyolefin that can be used include the same materials as those described in the section of <Biaxially Stretched Layer>.

The degree of crystallinity of the chemically recycled polyolefin in the surface layer is preferably 40% or more, more preferably 42% or more, even more preferably 44% or more, from the viewpoint of sheet conveyance properties and pore formation properties in the surface layer. It is particularly preferably at least 46%, and from the viewpoint of tear resistance, it is preferably at most 52%, more preferably at most 51%, even more preferably at most 50%.

The content of chemically recycled polyolefin in the thermoplastic resin in the surface layer is preferably 3% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and 30% by mass or more from the viewpoint of reducing environmental load. is particularly preferred, 40% by mass or more is particularly preferred, and 50% by mass or more is even more particularly preferred. The content of the chemically recycled polyolefin may be 100% by mass, but from the viewpoint of crystallinity control, it is preferably less than 100% by mass, more preferably 90% by mass or less, even more preferably 80% by mass or less, Particularly preferred is 70% by mass or less.

<<Acid-modified polyolefin>>
The thermoplastic resin in the surface layer preferably contains acid-modified polyolefin. The acid-modified polyolefin makes it easier for the thermoplastic resin in the surface layer to adhere to the particles, suppressing the particles from falling off from the surface layer, which is the outermost surface of the sheet, and suppressing the generation of paper dust. Examples of the acid-modified polyolefin that can be used for the surface layer include the same materials as those described in the section <Biaxially oriented layer>.

When the surface layer contains an acid-modified polyolefin, the content of the acid-modified polyolefin in the surface layer is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and 1 part by mass or more, based on 100 parts by mass of particles. More preferably .5 parts by mass or more, preferably 30 parts by mass or less, more preferably 20 parts by mass or less, even more preferably 10 parts by mass or less, even more preferably 5 parts by mass or less, particularly preferably 3 parts by mass or less. .
When the content of the acid-modified polyolefin is 0.5 parts by mass or more, the adhesive force between the thermoplastic resin and the particles increases, so that the effect of suppressing paper dust can be easily obtained. When the content of the acid-modified polyolefin is 30 parts by mass or less, stretchability is good and it becomes easy to suppress stretching breakage during molding.

<<particles>>
Particles that can be used in the surface layer include the same materials as those described in the <Biaxially oriented layer> section, and preferred materials, average particle diameters, etc. are also as described in the <Biaxially oriented layer> section. be.

In the case of containing particles, the content of particles in the surface layer is preferably 30% by mass or more, more preferably 35% by mass or more, and 40% by mass or more, from the viewpoint of increasing whiteness etc. and imparting a paper texture to the sheet appearance. It is more preferably 65% by mass or less, more preferably 60% by mass or less, and even more preferably 55% by mass or less, from the viewpoint of suppressing a decrease in the stiffness and tear resistance of the sheet.

<Sheet properties>
＜＜Thickness＞＞
The thickness of the biaxially stretched layer is preferably 50 μm or more, more preferably 60 μm or more, even more preferably 70 μm or more, from the viewpoint of imparting mechanical strength, and preferably 500 μm or less, from the viewpoint of imparting lightness, and 400 μm or more. The thickness is more preferably below, further preferably 300 μm or less, particularly preferably 200 μm or less.

The thickness of the surface layer is preferably 1 μm or more, 1.5 μm or more, or 2 μm or more from the viewpoint of imparting mechanical strength to the sheet and suppressing bleed-out of specific components from the biaxially stretched layer to the sheet surface. preferable. From the viewpoint of suppressing a decrease in stiffness and tear resistance and from the viewpoint of imparting lightness, the thickness of the surface layer is preferably 100 μm or less, more preferably 50 μm or less, further preferably 30 μm or less, and particularly preferably 20 μm or less.
When surface layers are provided on both sides of the biaxially stretched layer, the thickness of each surface layer may be the same or different.

<<Porosity>>
When the biaxially stretched layer has pores inside, the porosity is preferably 10% or more, and 15% or more from the viewpoint of whiteness, opacity, weight reduction, or reduction of environmental load. It is more preferable that the amount is at least 20%, and even more preferably 20% or more. From the viewpoint of maintaining mechanical strength, the porosity is preferably 45% or less, more preferably 40% or less, and even more preferably 35% or less.

When the surface layer has pores inside, the porosity is preferably 7% or more, and preferably 10% or more from the viewpoint of whiteness, opacity, weight reduction, or reduction of environmental load. is more preferable, and even more preferably 15% or more. From the viewpoint of maintaining mechanical strength, the porosity is preferably 40% or less, more preferably 35% or less, and even more preferably 30% or less.
The above-mentioned porosity is measured by the method described in Examples described later.

<<Clark stiffness>>
The Clark stiffness (S value) of the sheet of the present invention, whichever is smaller in the longitudinal direction or the transverse direction, is preferably 15 or more, more preferably 20 or more, and even more preferably 25 or more. The Clark stiffness is preferably 50 or less, more preferably 45 or less, and even more preferably 40 or less. When the above-mentioned Clark stiffness is 15 or more, the sheet is less likely to bend during conveyance, and wrinkles and the like of the sheet tend to be suppressed. When the Clark stiffness is 50 or less, the sheet tends to easily follow the shape of the conveyance roller, making it easier to convey the sheet at high speed. The above Clark stiffness is measured in accordance with JIS-P-8143.

(Manufacturing method of sheet)
The method for manufacturing the sheet of the present invention is not particularly limited. For example, a sheet with a single layer structure consisting of biaxially stretched layers can be obtained by forming a resin composition containing the above-mentioned thermoplastic resin and other components into a sheet shape, and then biaxially stretching the resin composition. Further, a sheet having a multilayer structure including a surface layer can be obtained by forming a sheet of the surface layer and laminating it on a biaxially stretched layer.

Examples of the sheet forming method include cast molding, calendar molding, rolling molding, inflation molding, etc. in which molten resin is extruded into a sheet shape using a single-layer or multi-layer T-die, I-die, etc. connected to a screw extruder. A method can also be used in which a mixture of a thermoplastic resin and an organic solvent or oil is cast or calendered and then the solvent or oil is removed.

Examples of the method for forming a sheet with a multilayer structure include a multilayer die method using a feed block or multi-manifold, an extrusion lamination method using multiple dies, etc., and each method can be combined.

Stretching methods include, for example, a longitudinal stretching method using a difference in the peripheral speed of a group of rolls, a lateral stretching method using a tenter oven, a sequential biaxial stretching method that combines these, a rolling method, and a simultaneous biaxial stretching method that uses a combination of a tenter oven and a pantograph. Examples include an axial stretching method and a simultaneous biaxial stretching method using a combination of a tenter oven and a linear motor. Alternatively, a simultaneous biaxial stretching (inflation molding) method in which a molten resin is extruded into a tube shape using a circular die connected to a screw extruder and air is blown into the tube can also be used.

When stretching multiple layers, each layer may be stretched individually before being laminated, or may be stretched all at once after being laminated. Alternatively, the stretched layers may be stretched again after being laminated.

When the thermoplastic resin used is an amorphous resin, the stretching temperature during stretching is preferably in a range equal to or higher than the glass transition temperature of the thermoplastic resin. In addition, when the thermoplastic resin is a crystalline resin, the stretching temperature must be within a range that is above the glass transition point of the amorphous portion of the thermoplastic resin and below the melting point of the crystalline portion of the thermoplastic resin. The temperature is preferably 2 to 60°C lower than the melting point of the thermoplastic resin. By setting the stretching temperature within the above range, when the resin film contains particles, flat fine pores that are elongated in the stretching direction starting from the particles are likely to be formed.

The stretching speed is not particularly limited, but from the viewpoint of stable stretching and 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 characteristics of the thermoplastic resin used. For example, when stretching a thermoplastic resin film containing a propylene homopolymer or its copolymer in one direction, the lower limit of the stretching ratio is usually 1.2 times or more, preferably 2 times or more, and the upper limit is 1.2 times or more, preferably 2 times or more. is usually 12 times or less, preferably 10 times or less. On the other hand, in the case of biaxial stretching, the lower limit of the area stretching ratio is usually 1.5 times or more, preferably 10 times or more, and the upper limit is usually 60 times or less, preferably 50 times or less.

When stretching a thermoplastic resin film containing a polyester resin in one direction, the upper limit of the stretching ratio is usually 1.2 times or more, preferably 2 times or more, and the lower limit is usually 10 times or less, preferably It is 5 times or less. The stretching ratio in the case of biaxial stretching is an area stretching ratio, and the lower limit is usually 1.5 times or more, preferably 4 times or more, and the upper limit is usually 20 times or less, preferably 12 times or less.
If the stretching ratio is within the above range, the desired porosity can be obtained and the opacity can be easily improved. In addition, the sheet is less likely to break, and stable stretch molding tends to be possible.

(printing paper)
The printing paper of the present invention includes the sheet described above. Therefore, like the sheet described above, it is possible to provide printing paper that not only reduces environmental impact but also has excellent transportability during printing and tear resistance.

Printing is possible on the surface of either the biaxially stretched layer or the surface layer that constitutes the outermost surface of the sheet. Therefore, the printing paper may be made of the above-mentioned sheet, but it may also be provided with other layers, such as a coating layer or the like, on the sheet from the viewpoint of improving adhesion with ink. The printing method is not particularly limited, and not only general printing methods such as offset printing method using oil-based ink or UV ink, UV flexo printing method, etc., but also UV inkjet printing method, dry electrophotographic printing method, etc. can be used. I can do it.

Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples. In addition, descriptions such as "parts" and "%" in the examples mean descriptions based on mass unless otherwise specified.

Table 1 lists the materials used.

(Resin composition (a1))
Virgin PP (unused propylene homopolymer (manufactured by Nippon Polypro Co., Ltd., trade name: Novatec PP FY4, melting point: 162°C, MFR (230°C, 2.16 kg load): 5.0 g/10 min)) 39 parts by mass and 40 parts by mass of chemically recycled PP2 (polypropylene (crystallinity: 36%) obtained by extracting the propylene component from the monomer obtained by depolymerizing the recovered used polypropylene resin and polymerizing it) , 20 parts by mass of calcium carbonate (heavy calcium carbonate (manufactured by Bihoku Funka Kogyo Co., Ltd., trade name: Softon 1800, average particle size: 1.2 μm)), acid-modified PP (maleic acid-modified polypropylene (manufactured by Mitsubishi Chemical Corporation) , trade name: Modic P908, softening point: 140° C.)) 1 part by mass was prepared.

(Resin compositions (a2) to (a4))
Chemical recycled PP2 and chemical recycled PP3 (polypropylene obtained by extracting a propylene component from a monomer obtained by depolymerizing collected used polypropylene resin and polymerizing it (crystallinity: 42%) ), chemically recycled PP4 (polypropylene obtained by extracting the propylene component from the monomer obtained by depolymerizing the recovered used polypropylene resin and polymerizing it (crystallinity: 48%, melting point: 161°C) , MFR (230°C, 2.16 kg load): 8.6 g/10 minutes), chemical recycling PP5 (propylene component is extracted from the monomer obtained by depolymerizing the recovered used polypropylene resin, and Resin compositions (a2) to (a4) were prepared in the same manner as resin composition (a1), except that polypropylene obtained by polymerization (crystallinity: 54%) was used.

(Resin compositions (a5) to (a9), (a11))
Each resin composition (a5) to (a9) and (a11) was prepared in the same manner as resin composition (a3) except that the blending amount of each component of resin composition (a3) was changed as shown in Table 2. Prepared.

(Resin compositions (a10) and (a14))
59 parts by mass of virgin PP (unused propylene homopolymer (manufactured by Nippon Polypropylene Co., Ltd., product name: Novatec PP FY4)) and chemically recycled PP6 (from monomers obtained by depolymerizing recovered used polypropylene resins) 20 parts by mass of polypropylene (crystallinity: 60%) obtained by extracting the propylene component and polymerizing it; A resin composition consisting of 20 parts by mass (average particle diameter: 1.2 μm)) and 1 part by mass of acid-modified PP (maleic acid-modified polypropylene (manufactured by Mitsubishi Chemical Corporation, trade name: Modic P908, softening point: 140°C)) Product (a10) was prepared.
A resin composition (a14) was prepared in the same manner as the resin composition (a10) except that the blending amounts of each component of the resin composition (a10) were changed as shown in Table 2.

(Resin composition (a12))
A resin composition (a12) was prepared in the same manner as resin composition (a1) except that chemically recycled PP2 was not blended and the blended amount of virgin PP was changed to 79 parts by mass.

(Resin composition (a13))
39 parts by mass of virgin PP (unused propylene homopolymer (manufactured by Nippon Polypropylene Co., Ltd., product name: Novatec PP FY4)) and chemically recycled PP1 (from monomers obtained by depolymerizing recovered used polypropylene resins) 40 parts by mass of polypropylene (crystallinity: 30%) obtained by extracting the propylene component and polymerizing it; A resin composition consisting of 20 parts by mass (average particle diameter: 1.2 μm)) and 1 part by mass of acid-modified PP (maleic acid-modified polypropylene (manufactured by Mitsubishi Chemical Corporation, trade name: Modic P908, softening point: 140°C)) Product (a13) was prepared.

(Resin composition (a15))
A resin composition (a15) was prepared in the same manner as the resin composition (a1) except that the blending amounts of each component of the resin composition (a1) were changed as shown in Table 2.

(Resin compositions (a16) and (a17))
The amount of virgin PP was changed to 20 parts by mass, and biomass PP (plant-derived propylene homopolymer (manufactured by Borealis, trade name: HC101BF, melting point: 163°C, MFR (230°C, 2.16 kg load): Each resin composition (a16) was prepared in the same manner as resin composition (a3) except that 19 parts by mass (5.0 g/10 min)) was added.
Further, the blending amounts of each component of the resin composition (a16) were changed as shown in Table 2, and a resin composition (a17) was prepared.

Table 2 is a list of the blending amounts of materials in each resin composition.

The following physical properties were determined for each resin composition and are shown in Table 2.
<Melting point>
When the resin composition contains one type of thermoplastic resin, the melting point of the resin composition is the melting point of the thermoplastic resin. When two or more types of thermoplastic resins were included, the weight average of the melting points of each thermoplastic resin was calculated as the melting point of the entire thermoplastic resin.

<Melt flow rate (MFR)>
The MFR of the resin composition was measured at a temperature of 230° C. and a load of 2.16 kg in accordance with JIS K7210:2014.

<Crystallinity>
5 mg of the thermoplastic resin used in the resin composition was collected, and heated at a rate of 10°C/min in nitrogen using a differential scanning calorimeter (manufactured by Hitachi High-Tech Science Co., Ltd., trade name: DSC7000X), and heated to 60°C. The heat of fusion was measured between ~180°C. Then, the crystallinity (%) of the thermoplastic resin was calculated using the following formula. The heat of complete crystal fusion of polypropylene and polyethylene was calculated as 207 J/g and 293 J/g.
Crystallinity (%) = Measured heat of fusion / Heat of fusion of perfectly crystalline body x 100

When the resin composition contained two or more types of thermoplastic resins, the weight average of the crystallinity of each thermoplastic resin was calculated as the crystallinity of the entire thermoplastic resin.

(Example 1)
The resin composition (a1) was kneaded in an extruder set at 230°C, then fed into a feed block die set at 250°C and extruded into a sheet. This was cooled with a cooling device, and the resulting unstretched sheet was heated to 135° C. and stretched 4 times in the longitudinal direction to obtain a 4 times stretched film. Next, the 4 times stretched film was cooled to 60° C., heated again to about 145° C. using a tenter oven, and stretched 8 times in the transverse direction. After performing an annealing treatment in an oven adjusted to 160°C, it was cooled to 60°C, and the edges were slit to obtain a sheet with a total thickness of 80 μm having a single layer structure (biaxially stretched layer).

(Examples 2 to 12 and Comparative Examples 1 to 4)
Sheets of Examples 2 to 12 and Comparative Examples 1 to 4 were obtained in the same manner as in Example 1, except that the resin composition was changed as shown in Table 3 to form a biaxially stretched layer.

(Example 13)
After kneading the resin composition (a3) in an extruder set at 230°C, it was supplied to an extrusion die set at 250°C and extruded into a sheet. This was cooled with a cooling device, and the obtained unstretched sheet was heated to 135° C. and stretched 4 times in the longitudinal direction using a large number of roll groups having different circumferential speeds to obtain a 4 times stretched film. Next, the resin composition (a11) was kneaded using two extruders set at 250°C. This was supplied to an extrusion die set at 250° C., extruded into a sheet, and laminated on both sides of the 4-fold stretched film to obtain a 3-layer laminated film.

The laminated film was cooled to 60°C, heated again to about 145°C using a tenter oven, and stretched 8 times in the transverse direction. Next, an annealing treatment was performed in an oven adjusted to 160°C, and after cooling to 60°C, the edges were slit to obtain the sheet of Example 13. The sheet of Example 13 had three layers in which a surface layer made of a resin composition (a11), a biaxially stretched layer made of a resin composition (a3), and a surface layer made of a resin composition (a11) were laminated in this order. It had a structure (composition: a11/a3/a11, thickness: 25 μm/60 μm/25 μm, number of stretching axes: uniaxial/biaxial/uniaxial), and the total thickness was 110 μm.

(measurement)
The following physical properties were measured for each sheet.

<Porosity>
Cut out any part of the sheet, embed it in epoxy resin and let it solidify, then cut it perpendicular to the plane of the sheet using a microtome, and attach it to the observation sample stand so that the cut surface becomes the observation surface. I attached it. Gold or gold-palladium or the like was deposited on the observation surface, and the pores were observed at an arbitrary magnification that was easy to observe (for example, a magnification of 500 times to 3000 times). The observation area was captured as image data, image processing was performed using an image analysis device, and the area ratio (%) occupied by the void portion was determined. In the case of a multilayer structure, the boundaries between each layer were determined based on the differences in their appearance, and the area ratio (%) of pores within each layer was determined. The measured values at ten or more arbitrary locations were averaged to determine the porosity (%).

<Whiteness>
The whiteness was measured in accordance with JIS L-1015 using a measuring device (manufactured by Suga Test Instruments Co., Ltd.: SM-5), and the measured values are shown in Table 3. A whiteness of 90 or higher can be evaluated as having an appropriate whiteness.

<Clark stiffness (S value)>
The Clark stiffness (S value) in the longitudinal direction and the lateral direction of the sheet was measured in accordance with JIS-P8143:1996, and the smaller measured value is shown in Table 3.

(evaluation)
Each sheet was evaluated as follows.

<Environmental contribution>
The content of chemically recycled polyolefin in the thermoplastic resin of the entire sheet was evaluated according to the following criteria. A grade of C or above can be evaluated as having a high degree of contribution to the environment.
A: Content is 50% by mass or more B: Content is 20% by mass or more and less than 50% by mass C: Content is 3% by mass or more and less than 20% by mass D: Content is more than 0% by mass and less than 3% by mass E: Content is 0% by mass

<Transportability>
The sheets obtained in Examples and Comparative Examples were subjected to a printing machine to form a printed layer on the sheets. The transportability of the sheet to the printing machine during printing layer formation was evaluated according to the following criteria.
A: It is possible to print with normal drafting without changing the conditions from normal conditions. B: It is possible to print by making minor adjustments such as changing the position of the claws during printing and increasing the number of drafting. C: Printing can be done by changing the printing conditions and drafting. Printing is possible by increasing the number of times and lowering the printing speed. D: Even if you change the printing conditions, increase the number of drafts, and further reduce the printing speed, printing is not possible because wrinkles appear during printing.

<Tear resistance>
In accordance with JIS P-8116, the Elmendorf tear strength of the sheets obtained in Examples and Comparative Examples in the TD direction (transverse direction of the sheet) was measured. Tear resistance was evaluated by Elmendorf tear strength according to the following criteria.
A: Tear strength is 500 gf or more B: Tear strength is 200 gf or more and less than 500 gf C: Tear strength is less than 200 gf

<Stretching stability>
The stretching stability was visually evaluated based on the following criteria based on the presence or absence of stretching unevenness during sheet stretching.
A: A usable film was obtained with no stretching unevenness and a good appearance without any problems.B: There was stretching unevenness, but it was very slight, and a usable film was obtained without any problems that appeared in the appearance.C: A film with a practically usable appearance was obtained, although there was some stretching unevenness. D: A film with a poor appearance was obtained, with some stretching unevenness.

<Paper dust>
A printed layer was formed on the sheets obtained in the Examples and Comparative Examples using a 612CD type printing machine manufactured by Hamada Printing Machinery Co., Ltd. To form the printing layer, offset printing ink (trade name: Best SP Indigo) manufactured by T&KTOKA was used. The paper dust left on the printing press was evaluated by the whiteness of the blanket cylinder according to the following criteria.
A: When 2,000 sheets were passed through the printing press, the blanket was hardly stained and there was almost no paper dust. B: When 2,000 sheets were passed through the printing press, the whiteness of the stains removed with adhesive tape on the blanket was 1.3 or more, some paper dust is generated, but it is not a problem C: When 2,000 sheets are passed through the printing machine, the whiteness of the stain removed with adhesive tape on the blanket is 1.3 less than

Table 3 shows the evaluation results.

As shown in Table 3, the sheets of Examples 1 to 12 had porosity of the biaxially stretched layer in the range of 10 to 45%, and had appropriate whiteness. In all of the sheets of Examples 1 to 12, the biaxially stretched layer contains chemically recycled polyolefin, contributing to a reduction in environmental load. Further, the sheets of Examples 1 to 12, in which the crystallinity of the thermoplastic resin used for biaxial stretching is within the range of 40 to 52%, have excellent conveyance properties during printing and tear resistance.

On the other hand, in the sheet of Comparative Example 1, the porosity of the biaxially stretched layer was 0%, and the whiteness was as low as 88. The sheet of Comparative Example 2 does not use chemically recycled polyolefin and cannot contribute to reducing environmental load. The sheets of Comparative Examples 3 to 5 use chemically recycled polyolefin, but in Comparative Examples 3 and 5, the degree of crystallinity of the thermoplastic resin in the biaxially stretched layer is lower than 40%, and the prescribed stiffness cannot be obtained. transportability is low because it cannot be transported. Comparative Example 4 has low tear resistance because the crystallinity of the thermoplastic resin exceeds 52%.

This application claims priority based on Japanese Patent Application No. 2022-041926, which is a Japanese patent application filed on March 16, 2022, and incorporates all the contents of the Japanese patent application.

10 sheet 1 biaxially stretched layer 2 surface layer

Claims (8)

1. A sheet comprising a biaxially stretched layer containing a thermoplastic resin,
   The thermoplastic resin includes a chemically recycled polyolefin,
   The crystallinity of the thermoplastic resin in the biaxially stretched layer is 40 to 52%,
   A sheet in which the biaxially stretched layer is a biaxially stretched porous layer containing particles.
2. The sheet according to claim 1, wherein the content of the chemically recycled polyolefin in the thermoplastic resin is 3% by mass or more.
3. The sheet according to claim 1 or 2, wherein the chemically recycled polyolefin includes chemically recycled polypropylene.
4. The sheet according to any one of claims 1 to 3, comprising a surface layer on the biaxially stretched layer.
5. The surface layer is a uniaxially stretched porous layer containing a thermoplastic resin and particles,
   The sheet according to claim 4, wherein the content of the particles in the surface layer is 30 to 80% by mass.
6. The thermoplastic resin in the surface layer includes a chemically recycled polyolefin,
   The sheet according to claim 5, wherein the thermoplastic resin in the surface layer has a crystallinity of 45 to 50%.
7. The sheet according to claim 5 or 6, wherein the thermoplastic resin in the surface layer contains acid-modified polyolefin.
8. Printing paper comprising the sheet according to any one of claims 1 to 7.
   
   

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