JP2023135996A - Laminated paper and paper products obtained by processing the laminated paper - Google Patents

Abstract

To provide laminated paper that excellently achieves both strength and formability.SOLUTION: Laminated paper contains at least two layers of base paper and an adhesive layer between the at least two layers of base paper, where the length-weighted average fiber length of pulp contained in each of two or more layers of the base paper is 0.60 mm to 1.50 mm, and the average fiber width of the pulp contained in each of two or more layers of the base paper is 14.0 μm to 35.0 μm. The thickness of the laminated paper is 0.68 mm to 1.40 mm.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an interleaving paper made by pasting a plurality of papers together, and a processed paper product obtained by processing the interleaving paper.

Conventionally, molded bodies of plastics such as synthetic resins have been widely used for disposable tableware, stationery, medical instruments, and the like. However, from the viewpoint of environmental protection such as greenhouse gas generation and marine pollution, substitution of plastic products with paper products is being promoted.
For example, in Patent Document 1, in order to increase the toughness and durability of coated paper for tableware, the amount of bleached softwood kraft pulp and bleached hardwood kraft pulp used in each layer of multilayer paper is controlled, and completely saponified polyvinyl alcohol is added to the surface layer. A technique for containing is disclosed.
Furthermore, Patent Document 2 discloses a technique for controlling the amount of bleached softwood kraft pulp and bleached hardwood kraft pulp used in each layer of multilayer paper, and further controlling the basis weight of each layer, from the viewpoint of sufficient thickness and strength. There is.

Japanese Patent Application Publication No. 2020-196990 Japanese Patent Application Publication No. 2021-080590

However, according to the studies of the present inventors, although high strength can certainly be obtained with the technique of the above-mentioned document, it is not sufficient from the viewpoint of moldability when processing into various products as a substitute for plastic products is envisaged.
The present disclosure provides interleaf paper that is highly compatible with strength and formability.

As a result of extensive studies, the present inventors used base papers having a specific length-weighted average fiber length and average fiber width, and controlled the thickness of interleaf paper made by laminating these base papers together via an adhesive layer. We have found that the above problems can be solved by doing so.
That is, the present disclosure relates to <1> to <7> below.
<1> An interleaf paper comprising at least two layers of base paper and an adhesive layer between the at least two layers of base paper,
The length-weighted average fiber length of the pulp contained in each of the two or more layers of the base paper is 0.60 mm to 1.50 mm,
Of the base paper, the average fiber width of the pulp contained in each of the two or more layers of the base paper is 14.0 μm to 35.0 μm,
The interleaf paper has a thickness of 0.68 mm to 1.40 mm.
<2> The interleaf paper according to <1>, wherein the pulp contained in each of two or more layers of the base paper has a length-weighted average fiber length of 0.80 mm to 1.30 mm.
<3> The interleaf paper according to <1> or <2>, wherein the at least two layers of base paper are three layers of base paper.
<4> The interleaf paper according to any one of <1> to <3>, wherein the interleaf paper has a thermoplastic resin layer on at least one surface.
<5> The length-weighted average fiber length of the pulp contained in the interleaf paper is 0.60 mm to 1.50 mm,
The interleaving paper according to any one of <1> to <4>, wherein the average fiber width of the pulp contained in the interleaving paper is 14.0 μm to 35.0 μm.
<6> The interleaf paper according to any one of <1> to <5>, wherein the base paper has a basis weight of 200 g/m ² to 550 g/m ² .
<7> A processed paper product obtained by processing the interleaf paper according to any one of <1> to <6>.

According to the present disclosure, it is possible to provide interleaf paper that has both high strength and moldability.

This is an example of an embodiment of interleaf paper when it includes two layers of base paper (paper base layer). FIG. 3 is a diagram illustrating how to arrange samples in strength evaluation.

In this specification, the expressions "X or more and Y or less" or "X to Y" expressing a numerical range mean a numerical range that includes the lower limit and upper limit, which are the endpoints, unless otherwise specified. When numerical ranges are described in stages, the upper and lower limits of each numerical range can be arbitrarily combined.

<Interleaf paper>
The interleaf paper according to this embodiment includes at least two layers of base paper and an adhesive layer between the at least two layers of base paper. For example, it may be an interleaf paper consisting only of base paper A, an adhesive layer, and base paper B, or it may be an interleaf paper in which other base papers are laminated with an adhesive layer interposed therebetween. The at least two layer base paper is preferably a three layer base paper. In this case, the interleaf paper includes, for example, base paper A, adhesive layer, base paper B, adhesive layer, and base paper C in this order.
Further, the interleaving paper may have a thermoplastic resin layer on at least one surface, or may have a thermoplastic resin layer on both surfaces. FIG. 1 shows an embodiment in which the interleaving paper 10 has thermoplastic resin layers 4 on both sides. In FIG. 1, base paper 1 and base paper 2 are laminated with an adhesive layer 3 in between, and base paper 1 and base paper 2 have a thermoplastic resin layer 4 on their outer surfaces.

<Base paper>
The base paper is not particularly limited as long as it is a commonly used paper, but it is preferably a paper containing plant-derived pulp as a main component, and more preferably a paper containing wood pulp as a main component.
Specific examples include kraft paper, high-quality paper, (white) paperboard, base paper for folding cartons, base paper for milk cartons, base paper for cups, liner paper, coated paper, glossy paper, glassine paper, graphene paper, and the like. Among these, kraft paper, high-quality paper, (white) paperboard, base paper for folding cartons, base paper for cups, and single-glazed paper are preferred.From the viewpoint of rigidity, among (white) paperboards, high-grade paperboard, special paperboard, base paper for cups, and kraft paper are preferred. Paper is more preferred. Examples of the kraft paper include bleached kraft paper, unbleached kraft paper, and single-gloss bleached kraft paper, with bleached kraft paper and single-gloss bleached kraft paper being preferred from the viewpoint of printability and hygiene.

<Length weighted average fiber length, average fiber width, thickness of interleaf paper>
In order to achieve both strength and formability of the interleaving paper, the length-weighted average fiber length and average fiber width of the pulp contained in each of two or more layers of base paper used for the interleaving paper are controlled within a specific range. In addition, it is necessary to control the thickness of the interleaving paper.
As the thickness of the interleaving paper increases and more papers are pasted together, the strength improves, but the formability decreases. The present inventors conducted studies to achieve a high level of both strength and formability of interleaf paper, and found that in order to further improve strength without affecting formability, the length-weighted average of the pulp It has been found that controlling fiber length and average fiber width is important.

When the length-weighted average fiber length and average fiber width of the pulp are small, it indicates that a large amount of short fibers with a small width is contained. Although this reduces the strength of the paper itself, it is assumed that the movement of the fibers is less likely to be inhibited and the formability is likely to be improved. On the other hand, when the values of the length-weighted average fiber length and average fiber width of the pulp are large, it indicates that a large amount of long fibers with a larger width is contained. This increases the number of starting points for paper entanglement and fiber-to-fiber contact, which increases fiber-to-fiber bonding and tends to improve strength. However, if the values of the length-weighted average fiber length and average fiber width are too large, it is assumed that the paper becomes difficult to stretch and the formability tends to decrease.
Furthermore, the inventors' studies have shown that strength and formability can be improved by controlling the length-weighted average fiber length and average fiber width of the pulp within a specific range, and then controlling the thickness of the entire interleaving paper. We have found that both methods are highly compatible.

Among the base papers in the interleaf paper, the length-weighted average fiber length of the pulp contained in each of two or more layers of base paper is 0.60 mm to 1.50 mm. By setting the length-weighted average fiber length of the pulp contained in the base paper within the above range, both strength and moldability can be achieved.
When the length weighted average fiber length is less than the above lower limit, the strength of the interleaf paper tends to decrease. On the other hand, when the length-weighted average fiber length exceeds the above upper limit, moldability tends to decrease.

The length-weighted average fiber length of the pulp is preferably 0.80 mm to 1.30 mm, more preferably 0.85 mm to 1.25 mm, and even more preferably 0.85 mm to 1.00 mm. preferable. It is preferable that the length-weighted average fiber length of the pulp satisfies the above range for all the base papers included in the interleaving paper. That is, it is preferable that the length-weighted average fiber length of the pulp contained in each of the base papers in the interleaving paper satisfies the above range.
The length-weighted average fiber length of the pulp can be controlled by the type of pulp used.

Among the base papers in the interleaf paper, the average fiber width of the pulp contained in each of two or more layers of base paper is 14.0 μm to 35.0 μm. By setting the average fiber width of the pulp within the above range, both strength and moldability can be achieved.
When the average fiber width of the pulp is less than the above lower limit, the strength of the interleaf paper tends to decrease. On the other hand, when the average fiber width of the pulp exceeds the above upper limit, moldability tends to decrease.

The average fiber width of the pulp is preferably 15.0 μm to 32.0 μm, more preferably 15.5 μm to 31.0 μm, and even more preferably 18.0 μm to 22.0 μm. It is preferable that the average fiber width of the pulp of all the base papers included in the interleaf paper satisfies the above range. That is, it is preferable that the average fiber width of the pulp contained in each of the base papers in the interleaf paper satisfies the above range.
The average fiber width of the pulp can be controlled by, for example, cooking wood chips. By increasing the cooking temperature or increasing the cooking time, the average fiber width can be reduced. On the other hand, by lowering the cooking temperature or shortening the cooking time, the average fiber width can be increased. When cooking is insufficient, the average fiber width tends to exceed the above upper limit.

Of the at least two layers of base paper, the length-weighted average fiber length and average fiber width of the pulp contained in each of the two or more layers of base paper satisfy the above specific range. This means that among the plurality of layers of base paper in the interleaf paper, each of at least two layers of base paper satisfies the above specific range. For example, when there are two layers of base paper in the interleaving paper, it means that both of the two layers of base paper satisfy the above specific range. When there are three or more layers of base paper in the interleaving paper, it is sufficient that two or more of the base papers satisfy the length-weighted average fiber length and average fiber width ranges of the above-mentioned specific pulp.
For example, it is sufficient that the interleaving paper has three layers of base paper, and each of the two layers of base paper satisfies the length-weighted average fiber length and average fiber width ranges of the above-mentioned specific pulp. Preferably, in the interleaf paper, at least two layers of base paper are three layers of base paper. It is preferable that all three layers of base paper satisfy the length-weighted average fiber length and average fiber width ranges of the above-mentioned specific pulp. That is, it is preferable that each of the at least two layers of base paper included in the interleaf paper satisfy the length-weighted average fiber length and average fiber width ranges of the above-described specific pulp. By using three layers of base paper, it becomes easier to achieve both strength and formability.

The thickness of the interleaf paper is 0.68 mm to 1.40 mm. By setting the thickness of the interleaving paper within the above range, both strength and moldability can be achieved.
When the thickness of the interleaving paper is less than the above lower limit, the strength of the interleaving paper tends to decrease. On the other hand, if the thickness of the interleaving paper exceeds the above upper limit, moldability tends to decrease.
The thickness of the interleaving paper is preferably 0.80 mm to 1.35 mm, more preferably 0.85 mm to 1.32 mm. Note that the thickness of the interleaving paper is the total thickness of the interleaving paper including the thickness of the adhesive layer between at least two layers of base paper. When the interleaving paper includes a resin layer such as a thermoplastic resin on the front surface or the back surface, the thickness includes the thickness of the thermoplastic resin layer.

The length-weighted average fiber length of the pulp contained in the interleaving paper (the entire interleaving paper) is preferably 0.60 mm to 1.50 mm, more preferably 0.80 mm to 1.30 mm, and 0.85 mm. It is more preferably from 1.25 mm to 1.25 mm, and even more preferably from 0.85 mm to 1.00 mm. By being within the above range, it becomes easier to achieve both strength and moldability.
Further, the average fiber width of the pulp contained in the interleaving paper (the entire interleaving paper) is preferably 14.0 μm to 35.0 μm, more preferably 15.0 μm to 32.0 μm, and 15.5 μm to It is more preferably 31.0 μm, and even more preferably 18.0 μm to 22.0 μm. By being within the above range, it becomes easier to achieve both strength and moldability.

The basis weight of each base paper is preferably 160 g/m ² to 650 g/m ² , more preferably 200 g/m ² to 550 g/m ² , and 260 g/m ² to 480 g/m ² It is more preferably 310 g/m ² to 400 g/m ² . By being within the above range, it becomes easier to achieve both strength and moldability.
In addition, the density of each base paper is usually 0.50 g/cm ³ to 1.20 g/cm 3 , preferably 0.70 g/cm ³ to 1.00 g/cm ³ from the viewpoint of moldability ^. .
Further, the thickness of each base paper is usually 0.10 mm to 1.00 mm, more preferably 0.20 mm to 0.70 mm, and even more preferably 0.30 mm to 0.60 mm. By being within the above range, it becomes easier to achieve both strength and moldability.

The base paper may have a single-layer structure or a multi-layer structure, but it is preferably a single-layer structure (that is, single-layer papermaking). When the base paper has a multilayer structure, the number of layers constituting the base paper is usually 2 to 10, preferably 2 to 5, and more preferably 2 to 4.

The basis weight of the entire base paper in the interleaving paper is preferably 400 g/m ² to 1800 g/m ² , more preferably 500 g/m ² to 1100 g/m ² , and 550 g/m ² to 900 g/m ² It is more preferably 600 g/m ² to 850 g/m ² .
The density of the interleaf paper is usually 0.50 g/cm ³ to 1.20 g/cm ³ , preferably 0.70 g/cm ³ to 1.00 g/cm ³ .

As mentioned above, the raw material pulp contained in the base paper is preferably wood pulp, and preferably kraft pulp. Kraft pulp includes hardwood kraft pulp (LKP) and softwood kraft pulp (NKP), depending on the raw material. In addition, bleached kraft pulp (BKP), unbleached kraft pulp (UKP), and oxygen-bleached kraft pulp (OKP) can be cited based on the difference in processing conditions, and bleached kraft pulp (BKP) is preferable from the viewpoint of suitability for printing.
Among these, as the raw material pulp, hardwood kraft pulp (LKP) and softwood kraft pulp (NKP) are preferable, and it is more preferable to use hardwood kraft pulp (LKP) and softwood kraft pulp (NKP) in combination. The mass ratio (LKP/NKP) when hardwood kraft pulp (LKP) and softwood kraft pulp (NKP) are used together is not particularly limited as long as it is a ratio used for general paper, and is 1/99 to 99/1. is preferable, 30/70 to 98/2 is more preferable, 50/50 to 97/3 is even more preferable, 70/30 to 95/5 is even more preferable, and 80/20 to 92/8 is even more preferable.
In addition, as the hardwood kraft pulp (LKP), hardwood bleached kraft pulp (LBKP) is preferable, and as the softwood kraft pulp (NKP), softwood bleached kraft pulp (NBKP) is preferable.

As the hardwood kraft pulp (LKP), for example, wood chips of known hardwoods such as eucalyptus, tan oak, and acacia can be used. Further, as the softwood kraft pulp (NKP), for example, wood chips of known softwood such as larch, spruce, cedar, and slash pine can be used.

Internal additives may be added during the preparation of the raw material pulp. Internal additives include sizing agents, fillers, paper strength enhancers, retention improvers, pH adjusters, drainage improvers, water resistance agents, softeners, antistatic agents, antifoaming agents, slime control agents, dyes, etc. Examples include pigments.

In the production of base paper, it is preferable to subject wood chips to kraft cooking. The average fiber width can be easily controlled within the above range by adjusting the temperature and time of kraft cooking. The white cooking liquor used in kraft cooking is not particularly limited, and any known one may be used. The time for kraft cooking may be changed as appropriate depending on the desired fiber width, and is preferably 0.5 to 6 hours, more preferably 1 to 4 hours. The temperature for kraft cooking may also be changed as appropriate depending on the desired fiber width, and is preferably 140 to 190°C, more preferably 150 to 180°C. For example, the kappa number is preferably 20.0 to 30.0, more preferably 23.0 to 28.0 for hardwoods, and preferably 25.0 to 35.0, more preferably 28.0 for softwoods. Cooking should be carried out so that the temperature is ~32.0.

The Canadian Standard Freeness (CSF) of the pulp is not particularly limited, but is preferably 350 to 700 ml, more preferably 500 to 600 ml.
Note that CSF is the freeness value measured using a Canadian standard freeness tester according to JIS-P8121 after disintegrating a sample using a standard disintegrator according to JIS-P8220.

In making the base paper, a known wet paper machine can be appropriately selected and used. Examples of the paper machine include a Fourdrinier paper machine, a gap former paper machine, a cylinder paper machine, a short wire paper machine, and the like.
It is preferable that the paper layer formed by the paper machine is conveyed using felt and dried using a dryer, for example. A multi-stage cylinder dryer may be used as a pre-dryer before drying.

Furthermore, the base paper obtained as described above may be subjected to surface treatment using a calendar to make the thickness and profile uniform. For the calendering process, a known calendering machine can be appropriately selected and used.

The Oken type smoothness (JIS P 8155:2010) of the base paper is not particularly limited, but it is preferably 5 seconds or more, more preferably 10 to 1000 seconds. The 75° glossiness of the base paper is also not particularly limited, but it is preferably 5% or more, more preferably 10 to 70%.

<Adhesive layer>
The interleaf paper includes an adhesive layer between at least two layers of base paper. That is, the base paper and the base paper are laminated with an adhesive layer interposed therebetween. The adhesive layer may be any layer as long as it is made of a material that has adhesive properties. The adhesive layer is preferably a resin adhesive suitable for dry lamination and wet lamination. Adhesives suitable for wet lamination are more preferred.
The base paper may be laminated using an adhesive as the adhesive layer. The adhesive is not particularly limited, but water-based, solvent-based, UV-based, and other types can be used, and among these, water-based adhesives are preferred. That is, the adhesive layer is preferably a water-based adhesive layer formed of a water-based adhesive. Among water-based adhesives, at least one selected from the group consisting of acrylic adhesives, polyurethane adhesives, and isocyanate adhesives is preferable, from the viewpoint of easy control of adhesive strength and heat resistance. Acrylic adhesives are more preferred.

When using an adhesive, the amount per unit area of the adhesive layer (for example, the amount of coating after drying) is preferably 1 to 50 g/m ² , more preferably 5 to 20 g/m ² . be. It is preferable to coat the base paper so that the solid content is in this amount.
For coating, it is preferable to use a coating liquid containing an adhesive, and it is more preferable to use a mixed coating liquid in which a curing agent is mixed with a coating liquid containing an adhesive. For example, the adhesive layer is preferably a cured product of a water-based adhesive.

The adhesive layer may be a layer containing a thermoplastic resin. By using a thermoplastic resin, a laminate of interleaf paper can be easily obtained by coating a base paper with a heated and molten resin and laminating the other base paper.
The thermoplastic resin used in the thermoplastic resin layer is not particularly limited, and may be appropriately selected from known thermoplastic resins.
Specifically, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, polybutylene succinate, polyvinyl chloride, polyvinylidene chloride, polybutene, polybutadiene, ethylene-vinyl acetate copolymer, Examples include polyolefin resins such as polyethylene, polypropylene, ethylene-propylene copolymer, and polymethylpentene; polycarbonate; polyurethane; polyamide; polyacrylonitrile; and poly(meth)acrylate.

Among these, polyolefins such as polyethylene, polypropylene, and ethylene-propylene copolymers, polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, and polybutylene succinate are preferred; polyethylene, polypropylene, polyethylene terephthalate, Polylactic acid and polybutylene succinate are more preferred, polyethylene and polypropylene are even more preferred, and polyethylene is even more preferred.
Furthermore, in addition to the above-mentioned materials, biomass resin or biodegradable resin may be used as the resin. These resins may be used alone or in combination of two or more.

A thermoplastic resin that can be laminated onto a sheet base material may be used as the laminate layer. Among thermoplastic resins, polyethylene is preferred because it has excellent extrusion lamination properties and barrier properties.
Polyethylene (PE) is broadly classified into linear low density polyethylene (LLDPE), low density polyethylene (LDPE), medium density polyethylene (MDPE), and high density polyethylene (HDPE). Among these, low density polyethylene (LDPE) is preferred because it has excellent extrusion lamination properties and foamability.

The thermoplastic resin layer may be manufactured by appropriately selecting from known manufacturing methods, such as melt extrusion, melt casting, calendering, and the like.

The adhesive layer may be formed of a single layer of a single resin, a single layer of a mixture of multiple resins, or multiple layers of the same or different types of resin. Good too.
The thickness of the adhesive layer is not particularly limited, but from the viewpoint of suitability for molding, it is preferably 5 to 100 μm, more preferably 10 to 50 μm.

<Thermoplastic resin layer>
From the viewpoint of improving waterproofness and stain resistance, the interleaving paper may have a thermoplastic resin layer on at least one surface. In addition, other resin layers may be provided on the interleaving paper to the extent that the above effects are not impaired. The interleaf paper may have a thermoplastic resin layer on one side, or may have a thermoplastic resin layer on both sides.

The thermoplastic resin used for the thermoplastic resin layer is not particularly limited, and may be appropriately selected from the known thermoplastic resins mentioned above as the thermoplastic resin for the adhesive layer.
The thickness of the thermoplastic resin layer is preferably 1 to 200 μm, more preferably 5 to 100 μm, and still more preferably 10 to 50 μm.

<Method for manufacturing interleaf paper>
The method for manufacturing interleaf paper is not particularly limited, and any known method can be employed. An example of the manufacturing method is shown below.
First, base paper A and base paper B are prepared, one side of base paper A is coated with an adhesive that will become the adhesive layer, and base paper B is wet laminated and bonded to this coated surface to obtain interleaving paper. can. The thermoplastic resin layer may be melt-extruded coated on one or both sides of the resulting interleaf paper.

As described above, the interleaving paper includes at least two layers of base paper (for example, base paper A and base paper B), but may include three or more layers of base paper. When the interleaving paper includes three or more layers of base paper, the adhesive layers that adhere the base papers to each other may be different or the same.

Furthermore, the obtained interleaf paper may be cut into appropriate dimensions, taking into consideration the size and shape of the stored articles, suitability for transportation, and display. The cutting is preferably performed by punching from the viewpoint of efficiently obtaining interleaving sheets of the same shape.
The punching process is preferably performed using a high-speed automatic punching machine, a flat plate punching machine, or a rotary punching machine, and more preferably a high-speed automatic punching machine. Using a high-speed automatic punching machine or a flat plate punching machine, it is possible to easily and efficiently obtain interleaf sheets having shapes such as squares, rounded squares, and ellipses.

<Paper processed products>
The use of the interleaf paper is not particularly limited, and it may be used as a processed paper product by processing it appropriately. It is preferable that the interleaf paper is for use in paper products. Examples of paper products include paper containers such as cups and trays, paper cutlery such as paper spoons, paper forks, paper knives, paper stirrers, paper straws, and paper hangers. It can also be used in medical devices such as tongue depressors. The processing method is not particularly limited, and any known method may be employed. For example, it can be processed into a desired shape by press molding or vacuum-pressure molding.

Below, methods for measuring each physical property will be described.
<Length weighted average fiber length and average fiber width of pulp>
The length-weighted average fiber length of the pulp contained in the base paper is measured in accordance with ISO 16065-2:2007. Specifically, the details are as follows.
(Separation of base paper)
Separation of base paper from interleaf paper is performed as follows. First, one side of an interleaf paper cut to a predetermined size (40 cm square) is soaked in an enzyme such as cellulase, and it is confirmed that the base paper on one side of the interleaf paper is completely dissolved. When the interleaving paper is formed from three layers of base paper, two layers may be dissolved to obtain one layer of interleaving paper to be measured. Thereafter, the length-weighted average fiber length of the pulp is measured using the obtained base paper. Note that the base paper may be provided with a resin layer, and there will be no difference in the length-weighted average fiber length of the pulp contained in the base paper. Alternatively, the pulp is impregnated with hot water at 100° C., a portion of the base paper is collected with a spatula, etc., and the length-weighted average fiber length of the pulp is measured using the collected material.

(Measuring method)
The base paper is cut into 40 cm square pieces, immersed in ion-exchanged water, adjusted to a solid content concentration of 2% by mass, and then immersed for 24 hours. After soaking for 24 hours, a standard disintegrator (manufactured by Kumagai Riki Kogyo Co., Ltd.) is used to perform disintegration treatment for 20 minutes to disintegrate the pulp into fibers. If undisintegrated pulp is found, disintegration treatment is performed again for 20 minutes to disintegrate the pulp into fibers. When the base paper has a resin layer, the above-mentioned disaggregation treatment is performed in the form having the resin layer, and the slurry (pulp fiber dispersion) is separated. Moreover, if the resin layer can be removed, it is preferable to perform the disaggregation treatment with the resin layer removed. Note that disaggregation is performed in accordance with JISP8220-2:2012.

Using the obtained fiber sample, the "length-weighted average fiber length" is measured using a fiber length measuring machine (Model FS-5 with UHD base unit, manufactured by Valmet). Note that the measurement is performed in accordance with ISO 16065-2:2007.
The device is also capable of detecting and measuring each fiber using an attached camera, and photographs are taken within a measurement cell with a depth of field of 0.5 mm in accordance with the ISO16505-2:2007 standard. The same device photographs fiber lengths of 0.01 mm or more and 10.00 mm or less. For the measurement of "fiber length" and "fiber width", fibers with a length of 0.2 mm or more and 7.6 mm or less shall be selected.

By the above method, the fiber width can also be measured at the same time. The arithmetic average value of the fiber widths of all the obtained fibers is defined as the average fiber width.

The length-weighted average fiber length and average fiber width of the pulp in the entire interleaf paper shall be calculated based on all fiber lengths and fiber widths measured from the separated base paper.

<Basic weight>
The basis weight of the base paper or interleaf paper is measured in accordance with JIS P 8124:2011.
In addition, when the interleaf paper has a resin layer in addition to the base paper, the basis weight of the base paper can be calculated after specifying the material, thickness, density, etc. of the resin layer using a known method and the following procedure.
Specifically, the weight of the base paper with the resin layer cut to a predetermined size is measured (total weight), and then the base paper with the resin layer is soaked in an enzyme such as cellulase to completely dissolve the base paper. Check that the Thereafter, the weight of only the resin layer (resin layer weight) is measured, and the weight of only the base paper is calculated by subtracting the weight of the resin layer from the total weight, and the basis weight of the base paper is measured.

<Thickness>
The thickness of the interleaving paper (paper thickness) is measured in accordance with JIS P 8118:2014. As the measuring device, a paper thickness meter (company name: Toyo Seiki Seisakusho Co., Ltd., model number: No. 132 digital thickness meter) can be used.

<Density>
The density of the base paper is calculated from the thickness and basis weight obtained by the above-mentioned measuring method.

Hereinafter, the invention will be specifically explained using examples, but the scope of the invention is not limited by the description of the examples. Also, unless otherwise specified, "parts" represent "parts by mass."

<Preparation of base paper A1>
Cooking white liquor was prepared using 45% by mass of eucalyptus, 15% by mass of tan oak, and 40% by mass of acacia as wood chips so that the liquid ratio was 4, the sulfidity was 30%, and the effective alkali was 17% by mass (as Na ₂ O). . Note that the liquid ratio is the ratio of the mass of white liquor (soda sulfide (Na ₂ S) + caustic soda (NaOH)) to the mass of pulp. The degree of sulfidation is calculated by sodium sulfide concentration/{(caustic soda concentration)+sodium sulfide concentration}×100.
A nonionic surfactant [trade name: Neugen LF-100X (polyoxyethylene alkyl ether), HLB: 14.5/manufactured by Daiichi Kogyo Seiyaku] was added to the obtained cooking white liquor based on the absolute dry weight of the wood chips. After adding the 2.1% dispersed material to wood chips in an autoclave, kraft cooking was performed at a cooking temperature of 165° C. for 2 hours.
After the cooking was completed, the black liquor was separated and the resulting pulp was defibrated using a high-density disintegrator, followed by centrifugal dehydration and water washing three times. Next, undigested materials were removed using a screen, and centrifugal dehydration was performed to obtain a digested, unbleached hardwood pulp having a kappa number of 25.8 and a content of ester compounds of sterols of 0.012% by mass based on the mass of bone-dry pulp. Obtained.

As wood chips, 50% by mass of larch, 20% by mass of Scots pine, 20% by mass of cedar, and 10% by mass of slash pine were used, and the liquid ratio was 4, the sulfidity was 27%, and the effective alkali was 13% by mass (as Na ₂ O). Cooking white liquor was prepared. Add a nonionic surfactant [trade name: Neugen LF-100X (polyoxyethylene alkyl ether), HLB: 14.5/Daiichi Kogyo Seiyaku Co., Ltd.] to the cooking white liquor at a rate of 1.9% based on the bone dry weight of the wood chips. After adding the dispersed material to wood chips in an autoclave, kraft cooking was performed at a cooking temperature of 155° C. for 2 hours.
After the cooking was completed, the black liquor was separated and the resulting pulp was defibrated using a high-density disintegrator, followed by centrifugal dehydration and water washing three times. Next, undigested materials were removed using a screen, and centrifugal dehydration was performed to obtain a digested, unbleached softwood pulp with a kappa number of 30.6 and a content of ester compounds of sterols of 0.010% by mass based on the mass of bone-dry pulp. Obtained.

Thereafter, bleached pulps LBKP and NBKP were obtained through a bleaching process, respectively. A pulp slurry was obtained by mixing and beating 85 parts of LBKP and 15 parts of NBKP to make 550 ml of CSF. To 100 parts of the obtained pulp slurry, 0.40 parts by mass as an internally added paper strength enhancer, 2.10 parts by mass as an internally added sizing agent, and 2.3 parts by mass of band sulfate were added to prepare a paper stock. . Using this stock, paper with a basis weight of 280 [g/m ² ] was made using a single-layer Fourdrinier paper machine.

<Preparation of base paper A2>
Base paper A2 was made under the same conditions as base paper A1, except that the basis weight was changed to paper with a basis weight of 340 [g/m ² ].

<Preparation of base paper A3>
Base paper A3 was made under the same conditions as A1, except that the basis weight was changed to paper with a basis weight of 530 [g/m ² ].

<Preparation of base paper A4>
Base paper A4 was made under the same conditions as A1, except that the beating was changed to a mixture of 90 parts of LBKP and 10 parts of NBKP, and the basis weight was changed to paper with a basis weight of 340 [g/m ² ].

<Preparation of base paper A5>
Base paper A5 was made under the same conditions as A1, except that the mixing of 60 parts of LBKP and 40 parts of NBKP was changed to a beaten paper, and the paper had a basis weight of 340 [g/m ² ].

<Preparation of base paper A6>
Base paper A6 was made under the same conditions as A1, except that 95 parts of LBKP and 5 parts of NBKP were mixed and beaten, and the basis weight was changed to paper with a basis weight of 340 [g/m ² ].

<Preparation of base paper A7>
Base paper A7 was made under the same conditions as A1, except that the beating was changed to a mixture of 40 parts of LBKP and 60 parts of NBKP, and the basis weight was changed to paper with a basis weight of 340 [g/m ² ].

<Preparation of base paper A8>
Base paper A8 was made under the same conditions as A1, except that the conditions for cooking the hardwood pulp and softwood pulp were changed to 3 hours of cooking at 175°C, and the basis weight was changed to paper with a basis weight of 340 [g/m ² ]. .

<Preparation of base paper A9>
Base paper A9 was made under the same conditions as A1, except that the conditions for cooking the hardwood pulp and softwood pulp were changed to 1 hour and 30 minutes, and the basis weight was changed to paper with a basis weight of 340 [g/m ² ].

<Preparation of base paper A10>
Base paper A10 was made under the same conditions as A1, except that the conditions for cooking the hardwood pulp and softwood pulp were changed to 1 hour cooking, and the basis weight was changed to paper with a basis weight of 340 [g/m ² ].

<Preparation of base paper A11>
Base paper A11 was made under the same conditions as A1 except that the basis weight was changed to paper with a basis weight of 230 [g/m ² ].

<Preparation of base paper A12>
Base paper A12 was made under the same conditions as A1 except that the basis weight was changed to paper with a basis weight of 650 [g/m ² ].

<Preparation of base paper A13>
Base paper A13 was made under the same conditions as A1, except that the beating was changed to a mixture of 100 parts of LBKP and 0 parts of NBKP, and the basis weight was changed to paper with a basis weight of 340 [g/m ² ].

<Preparation of base paper A14>
Base paper A14 was made under the same conditions as A1, except that the mixed beating method was changed to 0 parts of LBKP and 100 parts of NBKP, and the basis weight was changed to paper with a basis weight of 340 [g/m ² ].

<Preparation of base paper A15>
Base paper A15 was made under the same conditions as A1, except that the conditions for cooking the hardwood pulp and softwood pulp were changed to 4 hours of cooking at 175°C, and the basis weight was changed to paper with a basis weight of 340 [g/m ² ]. .

<Preparation of base paper A16>
A1 except that the cooking conditions for softwood pulp were changed to cooking at 150°C for 1 hour, changed to mixed beating of 60 parts of LBKP and 40 parts of NBKP, and further changed to paper with a basis weight of 340 [g/m ² ]. Base paper A16 was made under the same conditions as above.

<Preparation of base paper A17>
Base paper A17 was made under the same conditions as A1 except that the basis weight was changed to paper with a basis weight of 680 [g/m ² ].

Table 1 shows the physical properties of the obtained base papers A1 to A17.

<Example 1>
A curing agent (CAT-EP8) was applied to the surface of base paper A1 to 100 parts of water-based acrylic adhesive (EA-G34, manufactured by Toyo Morton Co., Ltd.) so that the coating amount after heat drying was 15 g/ ^m2 . , manufactured by Toyo Morton Co., Ltd.) was coated using a reverse roll coater. Next, another base paper A1 was wet laminated on the adhesive-coated surface to obtain two layers of base paper.

<Examples 2, 3, 5-7, 12-17>
An interleaf paper was obtained in the same manner as in Example 1 except that the combination of base papers was changed as shown in Table 2.

<Examples 4, 8-11, 23-27>
The combinations of base papers were as shown in Table 2.
A hardening agent (CAT-EP8) was added to the surface of base paper 1 to ¹⁰⁰ parts of water-based acrylic adhesive (EA-G34, manufactured by Toyo Morton Co., Ltd.) so that the coating amount after heat drying was 15 g/m2. , manufactured by Toyo Morton Co., Ltd.) was coated using a reverse roll coater. Next, base paper 2 was wet-laminated on the adhesive-coated surface.
Further, on the surface of the base paper 2, a curing agent (CAT) was added to 100 parts of a water-based acrylic adhesive (EA-G34, manufactured by Toyo Morton Co., Ltd.) so that the coating amount after heat drying was 15 g/ ^m2 . A coating solution containing 3.5 parts of EP8 (manufactured by Toyo Morton Co., Ltd.) was coated using a reverse roll coater. Next, the base paper 3 was wet-laminated on the surface coated with the adhesive to obtain a three-layer interleaving paper.

<Example 18>
After producing two layers of interleaving paper in the same manner as in Example 1 except that the combination of base papers was changed as shown in Table 2, LDPE (company name: Japan Polyethylene Co., Ltd., model number: LC522) was applied to the surface of the base paper 1 side. Melt extrusion coating was carried out so that the dry film thickness was 20 μm to obtain interleaf paper.

<Example 19>
An interleaf paper was obtained in the same manner as in Example 19, except that the LDPE was melt-extruded coated so that the dry film thickness was 40 μm.

<Example 20>
After producing two layers of interleaf paper in the same manner as in Example 1 except that the combination of base papers was changed as shown in Table 2, PP (company name: Japan Polyethylene Co., Ltd., model number: PHA03A) was applied to the surface of the base paper 1 side. Melt extrusion coating was carried out so that the dry film thickness was 20 μm to obtain interleaf paper.

<Example 21>
After producing two layers of interleaving paper in the same manner as in Example 1 except that the combination of base papers was changed as shown in Table 2, LDPE (company name: Japan Polyethylene Co., Ltd., model number: LC522) was applied to the surface of the base paper 1 side. Melt extrusion coating was performed so that the dry film thickness was 20 μm. Thereafter, LDPE (company name: Japan Polyethylene Co., Ltd., model number: LC522) was melt-extruded coated on the surface of the base paper 2 so that the dry film thickness was 20 μm to obtain interleaf paper.

<Example 22>
After preparing three layers of interleaf paper in the same manner as in Example 4 with the combination of base papers as shown in Table 2, LDPE (company name: Japan Polyethylene Co., Ltd., model number: LC522) was applied to the surface of base paper 1 to a dry film thickness. Melt extrusion coating was performed so that the thickness was 20 μm. Thereafter, LDPE (company name: Japan Polyethylene Co., Ltd., model number: LC522) was melt-extruded coated on the surface of the base paper 3 side so that the dry film thickness was 20 μm to obtain interleaf paper.

<Comparative Examples 1 to 10>
An interleaf paper was obtained in the same manner as in Example 1 except that the combination of base papers was changed as shown in Table 2.

<Comparative example 11>
One sheet of base paper A17 was used as it was without being laminated.

<Strength evaluation>
The strength of the obtained interleaf papers of Examples 1 to 27 and Comparative Examples 1 to 11 was evaluated as follows.
The interleaving papers produced in Examples and Comparative Examples were cut into pieces of 100 mm lengthwise (paper-making direction MD) x 15 mm widthwise (direction CD perpendicular to the paper-making direction). The cut sample was left standing in an environment of 23° C. and 50% Rh for 24 hours, and the temperature and humidity were controlled.
The sample was set as shown in Figure 2 under the above environment. That is, the sample 22 was made to protrude 5 cm from the workbench 21, and was fixed to the workbench 21 with tape 23 so that the sample 22 would not move during the test. Disc weight 100g (company name: Shinko Denshi Co., Ltd., product number: M1DS-100G), disc weight 200g (company name: Shinko Denshi Co., Ltd., product number: M1DS-200G), or 300g weight 24 (300g weight is the above disc weight. A disc weight of 200 g was stacked on a 100 g weight) and was placed on the tip of each sample 22. The sample was placed so that the weight 24 was located at the center of the sample in the CD direction, and the tip of the sample 22 and the tip of the weight 24 were aligned. The sample and weight were fixed with double-sided tape (company name: 3M, product number: Scotch Super Strong Double-Sided Tape Premier Gold Super Versatile PPS-10). Evaluation was made based on the following criteria, and scores of 3 or higher were judged to be good. The results are shown in Table 2.
<Evaluation criteria>
4: No bending occurred in the sample with any of the weights.
3: No bending occurred in the sample with weights of 100g and 200g, but bending occurred with weight of 300g.
2: No bending occurred in the sample with a weight of 100 g, but bending occurred with weights of 200 g and 300 g.
1: With either weight, bending occurred in the sample.

<Evaluation of moldability>
The moldability of the obtained interleaf papers of Examples 1 to 23 and Comparative Examples 1 to 11 was evaluated as follows.
The interleaf paper produced in Examples and Comparative Examples was cut into 100 mm (MD) x 40 mm (CD). The cut sample was left standing in an environment of 23° C. and 50% Rh for 24 hours, and the temperature and humidity were controlled. Then, the sample was manually wrapped around a SUS tube with a diameter of 50 mm (company name: Nippon Steel Stainless Steel Tube Co., Ltd., product number: SUS304TPA 4 x 50 x 2M), and changes in the sample were visually observed when it was released from the wrapped state. Confirmed by. The condition of 50 mm in diameter is a severe condition in which wrinkles and folds are likely to occur due to the short diameter. Evaluation was made using the following criteria, and scores of 2 or higher were considered good. The results are shown in Table 2.
<Evaluation criteria>
3: After the test, there were only wrinkles on the inside of the sample.
2: After the test, wrinkles appeared on the inside of the sample, and creases occurred on the outside of the sample.
1: After the test, wrinkles appeared on the inside of the sample, creases appeared on the outside of the sample, and peeling was observed between the paper layers.

表中、原紙坪量は、合紙における原紙のみの坪量を示す。熱可塑性樹脂層の位置に関し、「１」は原紙１側の表面に熱可塑性樹脂層を設けたことを意味する。「１／２」は、原紙１側と原紙２側に、それぞれ、表に記載の種類・厚さの熱可塑性樹脂層を設けたことを意味する。

In the table, the base paper basis weight indicates the basis weight of only the base paper in the interleaf paper. Regarding the position of the thermoplastic resin layer, "1" means that the thermoplastic resin layer is provided on the surface of the base paper 1 side. "1/2" means that thermoplastic resin layers of the type and thickness described in the table were provided on the base paper 1 side and the base paper 2 side, respectively.

1, 2 Base paper 3 Adhesive layer 4 Thermoplastic resin layer 10 Interleaving paper 21 Workbench 22 Sample 23 Tape 24 Weight

<Paper processed products>
The use of the interleaf paper is not particularly limited, and it may be used as a processed paper product by processing it appropriately. It is preferable that the interleaf paper is for use in paper products. Examples of paper products include paper containers such as cups and trays, paper cutlery such as paper spoons, paper forks, paper knives, paper stirrers, and paper straws , and paper hangers . It can also be used in medical devices such as tongue depressors. The processing method is not particularly limited, and any known method may be employed. For example, it can be processed into a desired shape by press molding or vacuum-pressure molding.

Claims (7)

An interleaf paper comprising at least two layers of base paper and an adhesive layer between the at least two layers of base paper,
The length-weighted average fiber length of the pulp contained in each of the two or more layers of the base paper is 0.60 mm to 1.50 mm,
Of the base paper, the average fiber width of the pulp contained in each of the two or more layers of the base paper is 14.0 μm to 35.0 μm,
The interleaf paper has a thickness of 0.68 mm to 1.40 mm. The interleaf paper according to claim 1, wherein the length-weighted average fiber length of the pulp contained in each of the two or more layers of the base paper is 0.80 mm to 1.30 mm. The interleaf paper according to claim 1 or 2, wherein the at least two layers of base paper are three layers of base paper. The interleaf paper according to any one of claims 1 to 3, wherein the interleaf paper has a thermoplastic resin layer on at least one surface. The length-weighted average fiber length of the pulp contained in the interleaf paper is 0.60 mm to 1.50 mm,
The interleaving paper according to any one of claims 1 to 4, wherein the average fiber width of the pulp contained in the interleaving paper is 14.0 μm to 35.0 μm. The interleaf paper according to any one of claims 1 to 5, wherein each of the base papers has a basis weight of 200 g/m ² to 550 g/m ² . A processed paper product obtained by processing the interleaf paper according to any one of claims 1 to 6.

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