Multi-layer paper

Abstract

To provide multilayered paper with sufficient thickness and sufficient strength.SOLUTION: The multilayered paper comprises a plurality of middle layers and a pair of surface layers each formed on the top and the bottom of the middle layers respectively, with the pulp of the surface layers and the middle layers including conifer kraft pulp and broad leaf kraft pulp in an amount of at least 80%. For the surface layer pulp material, the surface layer has a pulp freeness of 375 to 465 ml. The middle layer has a pulp freeness of 460 to 550 ml. The middle layers consist of 3 to 7 layers. The total basis weight of the middle layers is 600 to 950 g / m2. The basis weight of each surface layer is 75 to 260 g / m2. The total basis weight of the multilayered paper is 750 to 1470 g / m2.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to multi-layer paper.

Background Art

[0002] Conventionally, disposable tableware, medical instruments, and furniture are widely made of molded plastic resins. Although there are also bamboo and wooden products as alternatives to these conventional plastic resins, they have problems such as high manufacturing costs and complicated manufacturing due to the need for molding. In addition, since plastic products affect marine pollution and the ecosystem of marine organisms, in recent years, from the perspective of environmental protection, the establishment of alternative technologies for plastic tableware, medical instruments, and furniture has been demanded.

[0003] On the other hand, in the prior art, paper stirring sticks and spoons with improved water resistance and hot water resistance have been proposed as alternative materials (see, for example, Patent Document 1). In addition, medical instruments obtained by folding a single cardboard multiple times and paper furniture obtained by laminating a plurality of cardboards have also been proposed (see, for example, Patent Document 2 and Patent Document 3).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the above prior art, the strength required for applications such as tableware, medical instruments, and furniture is still not sufficient. Therefore, in a form where a single piece of cardboard is laminated to satisfy strength and the like, a lamination process is required, which not only increases costs but also requires a synthetic material for adhesive lamination and is not suitable for applications that come into direct contact with the human body.

[0006] Therefore, the main object of the present invention is to provide a multi-layer paper that exhibits sufficient strength.

Means for Solving the Problems

[0007] The multi-layer paper of the present invention that solves the above problems has a plurality of middle layers and a pair of surface layers formed on the front and back of these middle layers, the pulp of the surface layer and the middle layer does not contain waste paper pulp and contains 80% by mass or more of softwood kraft pulp and hardwood kraft pulp, does not contain a wet paper strength enhancer, the basis weight of the surface layer is 75 g / m per layer 2 ~260 g / m 2 and the basis weight of the entire middle layer is 600 g / m 2 ~950 g / m 2 and the overall basis weight is 860~1470 g / m 2 , the tensile strength in the longitudinal direction is 55.00 kN / m or more, and the tensile strength in the transverse direction is 44.00 kN / m or more, the bending strength is 10.0 N or more, the bending strength in the longitudinal direction is 5.00 N or more, and the bending strength in the transverse direction is 3.00 N or more, the middle layer is composed of 3 to 7 layers, and together with the pair of surface layers, it is 5 to 9 layers, the density is 0.65~1.00 g / cm 3 and is characterized by this.

[0008] This multi-layer paper has excellent strength characteristics. Also, in terms of application, an object can be obtained from a single piece of thick paper instead of a laminated structure, which is advantageous in terms of cost and productivity.

[0009]

[0010]

Advantages of the Invention

[0011] According to the present invention, it is possible to provide a multi-layer paper that exhibits sufficient strength.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, a multi-layer paper according to an embodiment of the present invention will be described in detail. <Multi-layer paper> The multi-layer paper has a plurality of middle layers and a pair of surface layers formed on the front and back of the middle layer. The middle layer is 3 to 7 layers.

[0013] Examples of the uses of this multi-layer paper include "tableware", "medical instruments", "furniture", "stationery", etc. "Tableware" is a broad concept that includes not only tableware such as plates, bowls, chopsticks, cups, coasters, trays, ladles, spoons, forks, and paper tableware, but also cooking utensils such as knives and kitchen knives. "Medical instruments" can include tongue depressors, ear picks, combs, washbasins, and other alternatives to current plastic medical instruments. "Furniture" can include hangers and other alternatives to current plastic furniture. "Stationery" can include alternatives to current plastic stationery such as clear boards, clips, pens, etc.

[0014] The pulp of the surface layer and the middle layer contains 80% or more of softwood kraft pulp and hardwood kraft pulp. Preferably, it does not contain waste paper pulp. Excessive inclusion of waste paper pulp results in a decrease in strength, but if the upper limit is set to 20% by mass, the impact on strength is small.

[0015] It is desirable to mix and blend softwood kraft pulp and hardwood kraft pulp. As a result, the paper thickness increases and sufficient strength can be ensured. In addition, by setting the mass ratio (%) of the softwood kraft pulp and the hardwood kraft pulp in the surface layer to be 5 / 95 or more and 40 / 60 or less, since it contains a large amount of hardwood kraft pulp which is relatively rigid and easy to densify, the pair of surface layers can obtain high-density and rigid characteristics and are excellent in strength. Furthermore, the surface layer can enhance the effect of suppressing the penetration of moisture or oil components derived from an object such as food into the interior. On the other hand, by setting the mass ratio (%) of the softwood kraft pulp and the hardwood kraft pulp in the middle layer to be 20 / 80 or more and 40 / 60 or less, since it contains a large amount of softwood kraft pulp which is rich in flexibility, the middle layer has good flexibility.

[0016] (Softwood kraft pulp, Hardwood kraft pulp) Here, the softwood kraft pulp is, for example, unbleached softwood kraft pulp (NUKP), semi-bleached softwood kraft pulp (NSBKP), or bleached softwood kraft pulp (NBKP). Also, the hardwood kraft pulp is, for example, unbleached hardwood kraft pulp (LUKP), semi-bleached hardwood kraft pulp (LSBKP), or bleached hardwood kraft pulp (LBKP). Among these, from the viewpoint of achieving both the appearance and strength of the processed product, it is preferable to use bleached softwood kraft pulp and bleached hardwood kraft pulp.

[0017] Each layer of the multi-layer paper can be appropriately combined and used with chemical pulps such as hardwood sulfite pulp and softwood sulfite pulp as needed. When the multi-layer paper of the embodiment is used for, for example, paper tableware, it comes into direct contact with an object to be treated such as food. Therefore, as the other pulp used for the multi-layer paper, chemical pulp is preferably used, and among them, ECF pulp, TCF pulp, and unbleached kraft pulp (UKP) are more preferable. ECF pulp is a chlorine-free bleached chemical pulp produced by bleaching with chlorine dioxide (ClO2) without using chlorine (Cl2). TCF pulp is a completely chlorine-free bleached chemical pulp produced by bleaching with oxygen (O), hydrogen peroxide (P), or ozone (Z) without using chlorine (Cl2). That is, since the ECF pulp and the TCF pulp have a very small or zero chlorine ion content, there is an advantage that there is little risk of generating organochlorine compounds such as dioxins even by low-temperature incineration, and as a result, the environmental load can be reduced. In addition, unbleached kraft pulp can be made to resemble the color of wood by using it, and by omitting the bleaching process, it is possible to reduce the environmental load such as energy reduction and CO2 reduction.

[0018] The multi-layer paper of the embodiment has a multi-layer forming structure that combines a pair of surface layers having the property of being hard to bend and a middle layer having flexibility, so that while ensuring elasticity with a high density, the surface layer can suppress distortion and breakage.

[0019] (Surface layer fineness) For the Canadian Standard Freeness (CSF) of the pulp used for the surface layer of the multi-layer paper in the embodiments, the lower limit is preferably 375 ml, particularly 410 ml. When the CSF of the pulp used for the surface layer is a low value, the drainage property deteriorates during the papermaking of the multi-layer paper surface layer, and there is a risk of difficulty in drying property. As a result, there is a risk of leading to delamination between the surface layers. On the other hand, as the upper limit of the CSF of the pulp used for the surface layer, 465 ml, particularly 450 ml is preferable. When the CSF is high, it becomes difficult to adjust the pulp fiber orientation in the paper machine, resulting in poor formation of the multi-layer paper, and there is a risk that the paper strength and rigidity will decrease when used as a paper container. The multi-layer paper can be made thicker and the stiffness can be improved by mixing and blending softwood bleached kraft pulp and hardwood bleached kraft pulp with high freeness. Here, the Canadian Standard Freeness (CSF) is the value measured by dissociating the pulp in accordance with the pulp dissociation method of JIS-P8220-1(2012) to obtain the dissociated pulp, and this dissociated pulp is measured in accordance with the Canadian standard drainage degree test method of JIS-P8121-2(2012).

[0020] (Middle layer) It includes a plurality of middle layers disposed between the pair of surface layers. The middle layer is composed of softwood kraft pulp and hardwood kraft pulp. Also, the mass ratio (%) of the softwood bleached kraft pulp to the hardwood bleached kraft pulp in the middle layer is 30 / 70 or more and 40 / 60 or less. By setting the mass ratio of the softwood kraft pulp to the hardwood kraft pulp in the middle layer within the above range, since it contains a large amount of softwood kraft pulp rich in flexibility, the middle layer has good flexibility. Therefore, as described above, since a flexible middle layer is combined with a pair of surface layers having stiffness and being hard but prone to breakage, the multi-layer paper is excellent in toughness and durability.

[0021] (Middle layer freeness) The lower limit of the Canadian Standard Freeness (CSF) of the pulp used in the middle layer of the multi-layer paper of the embodiment is preferably 460 ml, particularly preferably 470 ml. When the CSF has a low value, the water drainage property in the paper machine deteriorates. Furthermore, there is a risk of reduced rigidity. On the other hand, the upper limit of the CSF of the pulp used in the middle layer is preferably 550 ml, particularly preferably 520 ml. When the CSF is excessively high, there is a risk of less fibrillation and a decrease in strength and interlayer strength. Furthermore, it is preferable that the Canadian Standard Freeness of the pulp used in the middle layer is higher than the Canadian Standard Freeness of the pulp used in the pair of surface layers from the viewpoint of ensuring elastic force while maintaining the interlayer strength of the middle layer.

[0022] The total number of the middle layers is preferably 3 layers or more, particularly preferably 5 layers. By having 3 or more middle layers, the toughness and durability of the multi-layer paper can be further improved. From the viewpoint of maintaining the interlayer strength, the upper limit of the total number of the middle layers is preferably 7 layers or less. When operating while maintaining the interlayer strength in the case of using a cylinder multi-cylinder papermaking machine, 3 to 7 layers are suitable.

[0023] [Additives] It is preferable to add a sizing agent and a paper strength enhancer as papermaking additives to the surface layer and the middle layer of the multi-layer paper.

[0024] (Sizing agent) In order to further suppress the penetration of moisture or oil components derived from an object such as food into the multi-layer paper, a sizing agent can be added to each layer. Examples of the sizing agent include styrene-based sizing agents, alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), neutral rosin sizing agents, rosin sizing agents, and modified rosin emulsion sizing agents. Among these, rosin sizing agents and modified rosin emulsion sizing agents are preferable.

[0025] The rosin sizing agent is a conventionally well-known one in the paper-making field and is not particularly limited. Rosin-based substances include, for example, reinforced rosins obtained by modifying rosins such as gum rosin, wood rosin, and tall oil rosin with α,β-unsaturated carboxylic acids such as fumaric acid, maleic acid, and acrylic acid or their anhydrides, and rosin esters obtained by reacting the above-mentioned rosins with polyhydric alcohols such as glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, and diglycerin. In addition, in the present invention, the rosin-based sizing agent includes those obtained by emulsifying these alone or as a mixture, those obtained by emulsifying them alone and then mixing them, and those obtained by adding various polymers to the emulsified product to further improve the sizing performance.

[0026] The addition amount of the sizing agent in the surface layer is preferably 0.5 kg / t or more and 5.0 kg / t or less in terms of solid content. Also, the addition amount of the sizing agent in the middle layer is preferably 2.0 kg / t or more and 5.0 kg / t or less in terms of solid content. Note that "kg / t" indicates the mass (kg) per 1 t of pulp. By setting the addition amount of the sizing agent within the above range, the water resistance can be improved.

[0027] (Paper strength enhancer) For the multi-layer paper, a paper strength enhancer sizing agent can be added to each layer. By adding a paper strength enhancer, appropriate strengths for using as a paper tableware can be imparted to each layer.

[0028] As the paper strength enhancer, various known ones such as polyacrylamide resins, polyamide resins, polyamine resins, acrylic resin systems, melamine resins, urea resins, polyamide epichlorohydrin resins, etc. can be used. Among these, it is preferable to use an amphoteric paper strength enhancer. Examples of amphoteric polyacrylamide include copolymers of acrylamide and the above-mentioned anionic monomer and cationic monomer, Mannich-modified products of copolymers of acrylamide and the above-mentioned anionic monomer, Hofmann degradation products, etc. In the findings of the present inventors, amphoteric polyacrylamide is particularly preferable. Since amphoteric polyacrylamide has a self-fixing function, even if it is added to improve the inter-paper strength, it will not become cation-excessive, and the modified rosin emulsion sizing agent can be stably fixed.

[0029] As the addition amount of the paper strength enhancer for each layer, it is preferably 12 kg / t or more and 30 kg / t or less in terms of solid content. By setting the addition amount of the paper strength enhancer within the above range, various paper strengths such as the inter-layer strength of multi-layer paper can be imparted. If the addition amount of the paper strength enhancer is below the above range, there is a risk that the inter-layer strength may not be sufficient. On the other hand, if the addition amount of the paper strength enhancer exceeds the above range, the improvement of the inter-layer strength will be almost flat, and furthermore, the yield of the added paper strength enhancer will decrease, resulting in dirt, foaming, etc. in the papermaking machine system, and there is a risk that the operability (deterioration of dewatering property) will decrease. As a result, there is a possibility of inter-layer peeling due to poor drying in the drying process.

[0030] (Other Additives) Moreover, the multi-layer paper may contain various other papermaking additives within a range that does not impair the effects of the present invention. Examples of other additives that can be added to the multi-layer paper include known papermaking chemicals, etc.

[0031] [Physical Properties of Multi-Layer Paper] (Grammage) The basis weight is measured in accordance with JIS-P8124 (2011). The basis weight of each layer of the multi-layer paper does not necessarily have to be uniform. The basis weight of the surface layer and the middle layer is not particularly limited, but as the basis weight of the surface layer, it is preferably 75.0 g / m2 or more and 260.0 g / m2 or less per layer. Also, as the basis weight of the entire middle layer, it is preferably 600 g / m2 or more and 950 g / m2 or less.

[0032] As the lower limit of the basis weight of the entire multi-layer paper, from the viewpoint of obtaining sufficient stiffness, 750 g / m2 is preferable, and 860 g / m2 is more preferable. As the upper limit of the basis weight of the entire multi-layer paper, 1470 g / m2 is preferable, and 1240 g / m2 is more preferable. When the basis weight is high, it is easier to obtain sufficient stiffness, but there is a risk that the thickness will increase and folding and wrinkles will easily occur on the calendar roll during papermaking.

[0033] The ratio of the total basis weight of the pair of surface layers to the basis weight of the entire multi-layer paper is preferably 25.0% or more and 35.0% or less. In the multi-layer paper provided with a pair of surface layers having rigidity and a middle layer having flexibility, by setting the ratio of the total basis weight of the pair of surface layers within the above range, it is possible to impart the property of being difficult to bend.

[0034] (Paper thickness) The paper thickness is measured in accordance with the "Test Method for Thickness and Density of Paper and Paperboard" described in JIS-P8118 (2014). As the paper thickness of the multi-layer paper, it is preferably 750 μm or more and 2,0200 μm or less. By the paper thickness of the multi-layer paper being within the above range, peeling of the paper layers of the multi-layer paper can be suppressed.

[0035] (Density) As for the density of the multi-layer paper, 0.65 to 1.00 g / cm3, particularly 0.73 to 0.85 g / cm3, is preferable. When the density of the multi-layer paper is within the above range, it exhibits contradictory properties of high basis weight, excellent rigidity, and being difficult to bend. When the density of the multi-layer paper is less than 0.65 g / cm3, although bending strength can be obtained, handling wrinkles and delamination between layers are likely to occur. On the other hand, when the density of the multi-layer paper exceeds 1.00 g / cm3, handling wrinkles and delamination between layers are less likely to occur, but the strength and rigidity may decrease. For example, the density of the multi-layer paper can be adjusted by the pulp freeness, ash content of the surface layer or middle layer, and the calendering process.

[0036] (Moisture) As for the moisture of the multi-layer paper measured in accordance with JIS-P8127 (2010), it is preferably 9.0% or more and 11.0% or less. When the moisture of the multi-layer paper is within the above range, the flexibility is improved, so when manufacturing tableware using the multi-layer paper, the workability in the folding machine and the effect of suppressing the breakage of the folded part can be improved.

[0037] (Ash content) The ash content is measured in accordance with JIS-P8251 (2003). As for the ash content of the multi-layer paper, 0.1% or more and 10.0% or less is preferable. When the ash content of the multi-layer paper is within the above range, the curl can be adjusted flat, and the decrease in the interlayer strength can be suppressed.

[0038] (Surface strength) The surface strength is measured in accordance with the "Surface Strength Test Method" according to JAPAN TAPPI Paper Pulp Test Method No. 1 m-72. As the lower limit of the surface strength of the multi-layer paper, 10 A is preferable. When the surface strength of the multi-layer paper is within the above range, the peeling of the surface layer, conveyance, and scratch resistance during the processing stage can be improved.

[0039] (Knot size degree) The cob size degree is measured using distilled water at 23°C in accordance with JIS-P8140 (1998). As the upper limit of the cob size degree of the multilayer paper, 50 g / m2 is preferable. When the cob size degree of the multilayer paper is equal to or higher than the upper limit, the multilayer paper may be prone to warping or wrinkling due to moisture absorption.

[0040] (Z-axis strength) The Z-axis strength is the Z-axis strength measured in accordance with JAPAN TAPPI Paper Pulp Test Method No. 18-1:2000, and preferably 380 kN / mm2 or more. By having the above Z-axis strength, delamination between layers and the occurrence of wrinkles during tableware forming can be suppressed.

[0041] (Bending strength) When the bending strength is 10.0 N or more, when processed into a tableware or the like with a sharp tip, no breakage occurs.

[0042] (Tensile strength) The tensile strength in the longitudinal direction is 55.00 kN / m equal to or more and the tensile strength in the transverse direction is 44.00 kN / m equal to or more, so that when processed into furniture or the like to which a load is applied for a long time, no breakage or torsion occurs.

[0043] (Flexural strength) When the flexural strength in the longitudinal direction is 5.00 N or more and the flexural strength in the transverse direction is 3.00 N or more, when processed into tableware or the like that requires deep-drawing processing, no cracks in the cross-section or the like occur.

[0044] According to the multilayer paper, it is excellent in toughness and durability and can be suitably used for paper tableware that replaces conventional plastic tableware.

[0045] [Manufacturing method of multilayer paper] The manufacturing method of the multilayer paper is not particularly limited. For example, it can be manufactured using a known multilayer papermaking machine through the following steps. (1) To the slurry obtained by dispersing pulp fibers in water, additives corresponding to each paper layer are added as necessary and mixed to prepare the paper stock for each paper layer.

[0046] (2) Next, using these raw material slurries, paper is made on a paper-making machine in the neutral range so that the pH of the multi-layer paper is 6 or more and 8 or less by laminating the surface layer, single or multi-layer middle layer, and surface layer. The papermaking method is not particularly limited, and known papermaking machines, that is, papermaking machines such as a fourdrinier, a cylinder machine, a hybrid former, and a gap former can be used. Particularly preferably, a cylinder multi-drum laminating papermaking machine is used, and paper is made in a multi-layer of 5 layers or more. In the papermaking process, a coating liquid can be applied to the surface of the surface layer using a coating device such as a size press, a rod metering size press, or a gate roll coater to form a surface coating layer.

[0047] (3) Next, it is pressed by a pressure roll to remove moisture.

[0048] (4) Next, it is dried by a dryer cylinder. After drying, a smoothing treatment may be performed using a calendar device such as a nip calendar, a super calendar, a machine calendar, or a soft calendar. By performing the smoothing treatment, a high gloss is imparted to the multi-layer paper, and it can be suitably used for high-quality paper tableware.

[0049] <Other Embodiments> The present invention is not limited to the above-described embodiments, and can be implemented in various modified and improved forms in addition to the above-described aspects.

Examples

[0050] Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to the following examples.

[0051] The measurement methods of the physical property values of the examples and comparative examples are as follows. [Freeness (mL)] The obtained multi-layer paper was disintegrated into disintegrated pulp by disintegrating it in accordance with the pulp disintegration method of JIS-P8220-1 (2012), and this disintegrated pulp was measured in accordance with the Canadian standard drainage degree test method of JIS-P8121-2 (2012).

[0052] [Grammage (g / m2)] It was measured in accordance with the "Paper and Paperboard - Grammage Measurement Method" described in JIS-P8124 (2011).

[0053] [Paper thickness (μm)] It was measured in accordance with the "Paper and Paperboard - Test Methods for Thickness and Density" described in JIS-P8118 (2014).

[0054] [Density (g / cm3)] It was measured in accordance with the "Paper and Paperboard - Test Methods for Thickness and Density" described in JIS-P8118 (2014).

[0055] [Folding strength] The folding strength was measured with a digital force gauge (manufactured by IMADA Co., Ltd.), and the test conditions were as follows. A test piece with a width of 15 mm and a length of 150 mm was fixed to a three-point bending jig, and the force gauge was lowered. The load at that time was taken as the folding strength (N). The test environment was carried out at a temperature of 26°C and a humidity of 70%.

[0056] [Tensile strength] The tensile strength is the value measured in accordance with JIS-P-8113 (2006).

[0057] [Bending strength] The bending strength was measured in accordance with JIS K7171:2016. The test piece was prepared with a width of 15 mm and a length of 150 mm.

[0058] [Handling wrinkle] The obtained multi-layer paper was wound around a paper tube (9-inch diameter), and the handling wrinkles on the surface of the multi-layer paper were evaluated as follows. The range of acceptable handling wrinkles was judged as an evaluation value of 3 or more. 5: There are no handling wrinkles and no abnormalities in appearance. 4: There are some small handling wrinkles, but no abnormalities in appearance. 3: There are handling wrinkles, but at a level where there are no problems in appearance. 2: There are handling wrinkles and there are problems in appearance. 1: Handling wrinkles are prominent throughout the surface and there are abnormalities in appearance.

[0059] [Interlayer delamination] The obtained multi-layer paper was wound around a paper tube (9-inch diameter), and the interlayer delamination on the surface of the multi-layer paper was evaluated as follows. The range of interlayer delamination that can be used was judged as an evaluation value of 3 or more. 5: There is no interlayer delamination and no abnormalities in appearance. 4: There is some slight interlayer delamination in part, but no abnormalities in appearance. 3: There is interlayer delamination, but at a level where there are no problems in appearance. 2: There is interlayer delamination and there are problems in appearance. 1: Large interlayer delamination is prominent and there are abnormalities in appearance.

[0060] [Example 1] (1) The formulations of the surface layer and the middle layer are shown below. (Surface layer) In 100 parts of pulp slurry with a freeness of 440 mL and an NBKP:LBKP of 10:90, the following raw materials were added. Rosin emulsion sizing agent: 0.8 kg / solid content per pulp t Acrylamide-based paper strength enhancer: 19.0 kg / solid content per pulp t (Middle layer) In 100 parts of pulp slurry with a freeness of 440 mL and an NBKP:LBKP of 35:65, the following raw materials were added. Modified rosin emulsion sizing agent: 6.0 kg / solid content per pulp t Acrylamide-based paper strength enhancer: 19.0 kg / solid content per pulp t (2) This pulp slurry was sheeted using a pair of surface layers and 5 middle layers with a total of 7 layers on a cylinder multi-cylinder sheet forming machine with a wire part. The basis weight of each layer is as shown in Tables 1 and 2. (3) A coating solution containing polyvinyl alcohol and paraffin wax was calendared onto the surface of the surface layer so as to have the following coating amounts to form a surface coating layer, thereby obtaining the multilayer paper of Example 1. Polyvinyl alcohol: 0.2 g / m2 Paraffin wax: 0.2 g / m2 Surface sizing agent: 0.6 g / m2

[0061] [Examples 2 to 7, Comparative Examples 1 to 5] Except that the types, contents, and physical property values of the raw materials were as shown in Tables 1 and 2, multilayer papers of Examples 2 to 7 and Comparative Examples 1 to 5 were obtained in the same manner as in Example 1. Comparative Example 4 is a multilayer paper formed only from the middle layer.

[0062]

Table 1

[0063]

Table 2

[0064]

Table 3

Industrial Applicability

[0065] The multilayer paper of the present invention can be suitably used for paper tableware, paper medical instruments, paper furniture, and paper stationery.

Claims

1. The device has a plurality of intermediate layers and a pair of surface layers formed on the front and rear sides of the intermediate layers, The pulp of the surface layer and the middle layer does not contain recycled paper pulp and contains 80 mass% or more of softwood kraft pulp and hardwood kraft pulp, Does not contain wet strength agents, The surface layer has a basis weight of 75 g / m per layer. ２ ~260g / m ２ The basis weight of the entire middle layer is 600 g / m2 to 950 g / m2. ２ The overall basis weight is 860 to 1470 g / m ２ , The tensile strength in the longitudinal direction is 55.00 kN / m or more, the tensile strength in the transverse direction is 44.00 kN / m or more, the bending strength is 10.0 N or more, the bending strength in the longitudinal direction is 5.00 N or more, and the bending strength in the transverse direction is 3.00 N or more, The intermediate layer is 3 to 7 layers, and the pair of surface layers is 5 to 9 layers in total, Density: 0.65 to 1.00 g / cm ３ That is, A multi-layer paper characterized by:

2. 2. The multi-layer paper according to claim 1, wherein the mass ratio (%) of the softwood kraft pulp to the hardwood kraft pulp in the surface layer is greater than the mass ratio in the middle layer.

3. 2. The multilayer paper according to claim 1, wherein the mass ratio (%) of the softwood kraft pulp to the hardwood kraft pulp in the surface layer is 5 / 95 or more and 40 / 60 or less, and the mass ratio (%) of the softwood kraft pulp to the hardwood kraft pulp in the middle layer is 20 / 80 or more and 40 / 60 or less.

4. 2. The multi-layer paper according to claim 1, wherein the amount of the paper strength agent added to each layer is 12 kg / t or more and 30 kg / t or less in terms of solid content.

5. Tableware, medical equipment, furniture, and stationery formed from the multi-layer paper of claim 1.

Images