Paper, and methods of manufacture thereof

Abstract

To provide high-quality paper made from kraft pulp and a method for producing them.SOLUTION: The present invention uses paper and kraft pulp as paper raw materials in which the paper raw materials contain kraft pulp and have a prescribed relationship between density and fracture length or between density and flexural stiffness. The kraft pulp is preferably obtained by digesting a wood raw material having a volumetric weight of 635 kg / m3 or more and a fiber length of 1.1 mm or less. Kraft pulp digestion is preferably carried out under conditions of an active alkali addition rate of 5-40%.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to papers and methods for their manufacture. [Background technology]

[0002] In order to prevent global warming and build a sustainable society, it is necessary to reduce greenhouse gas emissions and CO 2 It is important to promote the absorption and fixation of carbon dioxide, and to promote the use of biomass, which is a recyclable resource. In order to reduce greenhouse gas emissions, it is effective to switch to non-fossil fuels and promote energy conservation, and biomass fuels are expected to become more important in the future because of their carbon neutral nature. 2 Large-scale commercial afforestation is an effective method for absorbing and fixing carbon dioxide and increasing the production of biomass resources. When implementing commercial afforestation, it is essential to reduce costs, and in order to do so, it is necessary to increase the yield (weight) of biomass obtained per unit area. Wood chips obtained from commercial afforestation are transported by chip ships. Since the loading capacity of chip ships is limited, there is a demand for high-volume, heavy-duty chips that can carry larger amounts of chips in the same volume (reducing transportation costs).

[0003] In Patent Document 1, the volume weight is 450 kg / m 3 It is disclosed that when the mechanical pulp derived from the above-mentioned Eucalyptus genus is used in the production of coated printing paper, the bulky structure of the base paper can be maintained and a low-density coated printing paper can be produced. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-106421 A Summary of the Invention [Problem to be solved by the invention]

[0005] Mechanical pulp as described in Patent Document 1 makes it easier to obtain higher quality paper than kraft pulp, but because it is produced by mechanically defibrating wood or chips, it tends to consume a lot of electricity. As a result, there is a risk that this will lead to an increase in greenhouse gas (GHG) emissions, which have become a global issue in recent years.

[0006] An object of the present invention is to provide high quality paper made from kraft pulp and a method for producing the same. [Means for solving the problem]

[0007] The present invention provides the following [1] to [6]. [1] The paper raw material contains kraft pulp, Paper whose density and breaking length satisfy the relationship of the following formula 1. (Formula 1) B≧26.537×A-8.153 (In formula 1, A is density (g / cm 3 ) and 0.3≦A≦0.7. B represents the breaking length (km) and B>0. ) [2] The paper according to [1], wherein the density and bending stiffness are related by the following formula 2. (Formula 2) C≧-387.35×A+510.75 (In Equation 2, A is density (g / cm 3 ) and 0.3≦A≦0.7. C is the bending stiffness (μN m 2 / m) [3] A method for producing paper according to [1] or [2], in which kraft pulp is used as the paper raw material. [4] Volumetric weight 635kg / m 3 The method for producing paper according to [3], further comprising: kraft pulp cooking a wood raw material having a fiber length of 1.1 mm or less to obtain kraft pulp; and producing paper using the pulp containing the kraft pulp as a raw material. [5] The method for producing paper according to [3] or [4], wherein the kraft pulp cooking is carried out under conditions of an active alkali addition rate of 5 to 40%. [6] A method for producing paper according to [4] or [5], in which at least one treatment selected from a delignification treatment, a bleaching treatment, and a beating treatment is carried out after the kraft pulp cooking. Effect of the Invention

[0008] According to the present invention, there is provided paper having good quality and exhibiting paper quality equivalent to that of mechanical pulp, and a method for producing the same. Normally, mechanical pulp mechanically defibrates wood or chips, which tends to consume a lot of electricity and may lead to an increase in greenhouse gas (GHG) emissions, which have been regarded as a global problem in recent years. According to the present invention, it is possible to obtain paper having a quality equivalent to that of mechanical pulp, and therefore it is possible to provide an alternative material to mechanical pulp, which is expected to contribute to reducing power consumption, achieving carbon neutrality, and achieving the SDGs. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a graph showing the relationship between breaking length and density in the examples. [Diagram 2] FIG. 2 is a graph showing the relationship between bending stiffness and density in the examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] 1. Physical properties of paper -Density and breaking length- It is preferable that the density and breaking length of the paper satisfy the relationship given by Equation 1. (Formula 1) B≧26.537×A-8.153 In formula 1, A is the density (g / cm 3 ) and 0.3≦A≦0.7, preferably 0.4≦A≦0.65. B represents the breaking length (km), and B>0. The breaking length can be measured in accordance with JIS P 8113:2006.

[0011] -Density and bending strength- It is preferable that the density and bending stiffness of the paper satisfy the relationship given by Equation 2. (Formula 2) C≧-387.35×A+510.75 In Equation 2, A is the density (g / cm 3 ) and 0.3≦A≦0.7. C is the bending stiffness (μN m 2 / m). Bending stiffness can be measured in accordance with ISO2493-2:2020.

[0012] -density- Density is calculated by dividing the paper weight by the paper thickness, and is usually between 0.3 and 0.7 g / cm 3 and preferably 0.4 to 0.65 g / cm 3 , more preferably 0.45 to 0.6 g / cm 3 It is.

[0013] Paper that satisfies (Equation 1) or (Equation 2) can exhibit good bulkiness, strength, or stiffness. In addition, because the paper has good bulkiness, strength, and stiffness at the same density, it can be used as base paper for coated paper, etc., and can therefore reduce weight, leading to cost reduction and resource conservation. For this reason, the paper can be used for a variety of purposes, including printing paper and packaging material.

[0014] [2.Paper raw materials] The paper of the present invention is obtained by using kraft pulp as a paper raw material. In this specification, kraft pulp is a fiber extracted from a wood raw material by a kraft cooking method using an active alkali. Kraft pulp has a volume density of 635 kg / m 3 It is preferable that the fiber length of the sintered material is 1.1 mm or less and that the fiber length of the sintered material is 1.1 mm or less.

[0015] -Volume Weight- The volume density of wood, the raw material for kraft pulp, is 635 kg / m 3 More than 650kg / m 3That's all. Wood whose bulk density satisfies the above values ​​tends to have a thick fiber wall (film thickness) and a structure with few voids (lumen diameter). Most of the water in wood exists in the voids, so a structure with few voids can make it difficult for water to be absorbed. Also, wood whose bulk density satisfies the above values ​​can transport a larger amount of wood at one time for the same volume compared to wood that does not satisfy the above values, improving transport efficiency. Furthermore, since wood can be produced from wood with a larger amount of carbon dioxide fixation, the amount of carbon dioxide fixation can be increased as a result of mass production of such wood chips, which can contribute to the realization of a sustainable society as a measure to mitigate global environmental change and curb global warming. The upper limit is usually 800 kg / m 3 Less than or equal to 750 kg / m 3 Less than or equal to 730 kg / m 3 More preferably, 720 kg / m 3 The following are just examples and are not particularly limited.

[0016] Volume weight is the ratio of weight to volume. Volume weight can be measured by putting a sample into a measuring cylinder containing water, reading the increased scale, confirming the increase in volume, drying the chips, measuring the bone dry weight, and calculating the volume weight (JAPAN TAPPI No. 3: 2000). The measurement method in the following examples is similar.

[0017] - Fiber length - The fiber length of the kraft pulp is usually 1.1 mm or less, preferably 1.05 mm or less, and more preferably 1 mm or less. The lower limit is usually 0.5 mm or more, preferably 0.55 mm or more, more preferably 0.60 mm or more, and even more preferably 0.65 mm or more. These are just examples and are not particularly limited.

[0018] The fiber length can be measured as a length-weighted average fiber length using a fiber tester (manufactured by Lorentzen & Wettre) in accordance with JIS P 8226:2011 "Pulp - Fiber length measurement method by optical automatic analysis method", and the measurement method in the following examples is the same.

[0019] -Trees- The wood raw material of kraft pulp is usually derived from plants, and the plants are usually woody plants. Woody plants are usually forest trees, such as broad-leaved trees such as eucalyptus, acacia, birch, and beech, and coniferous trees such as red pine, cedar, and cypress, and are preferably broad-leaved trees, more preferably Acacia plants and Eucalyptus plants, and even more preferably Eucalyptus plants. Eucalyptus plants grow quickly, so the yield of wood chips is large, and they are also suitable for fuel chips. In addition, after felling, reforestation by sprouting from stumps is possible, making sustainable afforestation possible.

[0020] Examples of plants of the genus Eucalyptus include Eucalyptus pellita, Eucalyptus brassiana, Eucalyptus urophylla×Eucalyptus grandis, Eucalyptus pellita×Eucalyptus brassiana, Eucalyptus urophylla, Eucalyptus grandis, Eucalyptus maculata, Eucalyptus tereticornis, Eucalyptus camaldulensis, Eucalyptus rudis, Eucalyptus resinifera, Eucalyptus propinqua, Eucalyptus sideroxylon, Eucalyptus botryoides, Eucalyptus viminalis, Eucalyptus saligna, Eucalyptus ovata, Eucalyptus globulus, Eucalyptus nitens, Eucalyptus saligna, Eucalyptus Examples of suitable species include E. cladocalyx, Eucalyptus urograndis, and hybrids of two or more tree species selected from these. Of these, species suitable for the environment of the plantation site can be selected (for example, when planting in the tropics, species that can be adapted to the tropics) and preferred are E. pellita, E. brassiana, E. urophylla, E. urograndis, hybrids of E. brassiana and E. pellita, hybrids of E. urophylla and E. pellita, and hybrids of two or more tree species selected from these, with hybrids of E. brassiana and E. pellita and E. urograndis being more preferred. Species with high bulk density (for example, 500 kg / m 3 It is believed that by crossbreeding the above individuals and selecting the resulting F1 individuals, individuals with superior traits can be obtained.

[0021] The plants from which the timber is derived are usually plantation trees grown from clones and seedlings. There are no particular limitations on the age of the trees, and they may be of any age at which timber can be obtained (usually 2 years or more), preferably 5 years or more. There is no particular upper limit in terms of quality, but from an economical point of view, the shorter the better. In the case of Eucalyptus plants, although it depends on the plantation area, they are usually 15 years or less, preferably 10 years or less.

[0022] The wood raw material for kraft pulp may be wood derived from a single plant, or may be a combination of two or more woods derived from plants of different species and ages. The method for producing kraft pulp from wood raw materials is not particularly limited, but is preferably the method described below.

[0023] - Pulp other than kraft pulp - The paper raw material may contain pulp other than kraft pulp. For example, pulp obtained by a chemical method other than the kraft method, such as cooking with a sulfite method, a soda method, or a polysulfide method (chemical pulp), pulp obtained by a mechanical method using equipment such as a refiner or grinder (mechanical pulp), and a method of pulping by mechanical force after pretreatment with chemicals (semi-chemical pulp) can be mentioned. The proportion of kraft pulp in the paper raw material is preferably 90% by weight or more, more preferably 95% by weight or more, even more preferably 98% by weight or more, even more preferably 99% by weight or more (substantially does not contain any raw material other than kraft pulp), and particularly preferably 100% by weight (consisting only of kraft pulp).

[0024] 3. Paper manufacturing method Paper can be produced using kraft pulp as the paper raw material. -Kraft pulp manufacturing method- Kraft pulp has a volume weight of 635kg / m 3 Kraft pulp made from wood raw material having fiber length of 1.1 mm or less is preferable. The volume density and fiber length are as described above.

[0025] -Wood raw materials- The wood raw material may be prepared from the above-mentioned plants (e.g., Eucalyptus plants) according to a conventional method, and may be, for example, wood chips. For example, a method for producing wood chips may include a method in which after felling a plant, the bark is removed from the wood part (trunk and branches), and the plant is cut or crushed. The size of the wood chips is not particularly limited and may be determined according to the intended use.

[0026] -Kraft pulp cooking- Kraft pulp can be obtained by subjecting wood raw materials to Kraft pulp cooking. Kraft pulp cooking may be performed by the Kraft process. The Kraft pulp cooking may be modified Kraft cooking such as MCC, EMCC, ITC, or Lo-solid. The cooking type of the Kraft pulp cooking may be, for example, a one-vessel liquid phase type, a one-vessel gas phase / liquid phase type, a two-vessel liquid phase / gas phase type, or a two-vessel liquid phase type, and any of these may be used.

[0027] (Active alkali addition rate) In kraft pulp cooking, the active alkali addition rate is preferably 5% or more, more preferably 8% or more, and even more preferably 10% or more. This allows lignin and hemicellulose to be sufficiently removed. The upper limit is preferably 40% or less, more preferably 30% or less, and even more preferably 20% or less. This allows the quality and / or yield to be prevented from decreasing, and kraft pulp cooking to proceed efficiently. Therefore, the active alkali addition rate is preferably 5 to 40%, more preferably 8 to 30%, and even more preferably 10 to 20%. In this specification, the active alkali addition rate refers to the amount of Na per absolute dry wood chip weight. 2 O addition rate, and the total addition rate of NaOH and Na2S is Na 2 This is the conversion value of the addition rate of NaOH. 2 By multiplying the amount of S added by 0.795, Na 2 This can be converted into the O addition rate.

[0028] (sulfidity) The sulfidity is preferably 20% or more. This makes it possible to suppress a decrease in delignification property and / or pulp viscosity and an increase in the lees ratio. The upper limit is usually 35% or less.

[0029] (Temperature conditions) The temperature in the kraft cooking is adjusted, for example, so that the maximum temperature is preferably 180°C or less, more preferably 160°C or less. This can suppress a decrease in the degree of polymerization (viscosity) of cellulose. The minimum temperature is preferably 120°C or more, more preferably 140°C or more. This allows delignification to be sufficiently carried out. In addition, the retention time (the time from when the cooking temperature reaches the maximum temperature until the temperature starts to drop) is preferably 60 minutes or more, more preferably 120 minutes or more. This allows pulping to proceed sufficiently. The upper limit is preferably 600 minutes or less, more preferably 360 minutes or less. If the cooking time is less than 60 minutes, pulping does not proceed, and if it exceeds 600 minutes, pulp production efficiency is deteriorated, which is not preferable.

[0030] (H factor) The H factor (Hf) in kraft cooking is preferably 300 to 2000, more preferably 350 to 1500, and further preferably 400 to 1000. In this specification, Hf is an index representing the total amount of heat given to the reaction system in the cooking process, and is represented by the following formula. Hf = ∫exp(43.20-16113 / T)dt [where T represents the absolute temperature at a given point in time] Hf can be used as a measure of the total amount of heat given to the reaction system during the cooking process, and the conditions of kraft cooking (e.g., processing temperature and processing time) can be set using Hf as an index.

[0031] -Delignification treatment- The pulp after the kraft pulp cooking is preferably subjected to a delignification treatment. The delignification treatment may be performed by a conventional method, but is preferably performed by oxygen delignification treatment. An example of the oxygen delignification treatment is as follows. An alkaline agent (e.g., NaOH) is added to the kraft pulp after the cooking treatment to make it alkaline, and then a chemical is added as necessary to perform an oxidation treatment under oxygen pressure. The pulp concentration in the system may be either 8 to 15 mass% (medium concentration method) or 20 to 35 mass% (high concentration method). The oxygen pressure (start pressure) is, for example, 3 to 9 Bar, preferably 4 to 7 Bar. The amount of the alkaline agent added (relative to the absolute dry pulp weight) is, for example, 0.5 to 5%, preferably 1 to 3%. The temperature is, for example, 80 to 120°C, preferably 85 to 105°C. The amount of oxygen added (relative to the absolute dry pulp weight) is, for example, 0.5 to 5%, preferably 1 to 3%. The reaction time is, for example, 30 to 180 minutes, preferably 60 to 90 minutes.

[0032] -Bleaching treatment- Examples of the bleaching treatment include chlorine treatment (C), chlorine dioxide bleaching (D), alkaline extraction (E), hypochlorite bleaching (H), hydrogen peroxide bleaching (P), alkaline hydrogen peroxide treatment stage (Ep), alkaline hydrogen peroxide-oxygen treatment stage (Eop), ozone treatment (Z), chelate treatment (Q), and a method of performing a combination of two or more of these treatments. Examples of the combination (sequence) of two or more treatments include DE / PD, C / DEHD, ZED-PZ / D-Ep-D, Z / D-Ep-DP, D-Ep-D, D-Ep-DP, D-Ep-PD, Z-Eop-DD, Z / D-Eop-D, Z / D-Eop-DED (" / " in the sequence means that the treatments before and after " / " are performed consecutively without washing), and other commonly used methods, with DE / PD being preferred. The temperature during each treatment is, for example, 40 to 90°C, preferably 50 to 80°C. The reaction time for each treatment is, for example, 30 to 180 minutes, preferably 50 to 90 minutes. The brightness (ISO 2470-1:2016) of the pulp after the bleaching treatment is preferably 80% or more.

[0033] - Beating process - The beating treatment is preferably carried out using an apparatus of a high-speed rotation type, a colloid mill type, a high-pressure type, a roll mill type, an ultrasonic type, etc. Examples of the apparatus include a high-pressure or ultra-high-pressure homogenizer, a refiner, a beater, a PFI mill, a kneader, a disperser, a high-speed disintegrator, a top finer, etc., which act on the pulp fibers with a metal or blade around a rotating shaft, or which use friction between the pulp fibers.

[0034] -Papermaking process- The above-mentioned paper can be produced by papermaking the above-mentioned kraft pulp. The papermaking may be, for example, by a process of forming a sheet from kraft pulp. The sheet may be formed, for example, according to Japanese Industrial Standards (JIS) P 8122 "Pulp - Preparation method for test hand-made paper" (1989 edition), for example, by forming the pulp into a sheet using a papermaking machine. When forming the pulp into a sheet, additives generally used in papermaking applications may be added to the pulp. Examples of such additives include paper strength enhancers, bulking agents, pigments, retention aids, drainage improvers, internal sizing agents (rosin-based sizing agents, aluminum sulfate, etc.), pH adjusters, defoamers, pitch control agents, and slime control agents. The amount of the additives used is not particularly limited, and may be within a range that does not impair the effects of the present invention.

[0035] When forming the sheet, paper raw materials other than kraft pulp may be used, for example, other materials such as rayon fiber, film, etc. The paper raw material may be pulp obtained from the above-mentioned Eucalyptus plant and other materials previously formed into a shape such as a sheet, film, roll, etc. The paper raw material may contain pulp made from other plants, but preferably does not contain it.

[0036] Examples of the papermaking machine include a fourdrinier papermaking machine, a cylinder papermaking machine, a gap former, a hybrid former, a multi-layer papermaking machine, and a known papermaking machine combining papermaking methods in two or more papermaking machines selected from these. The press line pressure in the papermaking machine and the calender line pressure in the case of performing calendering in a subsequent stage may both be set within a range that does not impair operability and the performance of the obtained plasticized cellulose.

[0037] [4. Uses of Paper] The paper of the present invention easily gains bulk by satisfying formula 1 or formula 2, so that it can exhibit bulkiness even with a small amount of added bulk-increasing agent. In addition, since it easily gains strength at the same density, it is possible to obtain paper with high strength even with a small amount of added paper strength agent.

[0038] Applications of the paper of the present invention include, for example, printing paper, newspaper, inkjet paper, PPC paper, form paper, kraft paper, fine paper, coated paper, lightly coated paper, wrapping paper, tissue paper, colored fine paper, cast coated paper, non-carbon paper, label paper, thermal paper, various fancy papers, water-soluble paper, release paper, process paper, wallpaper base paper, flame retardant paper (non-combustible paper), laminated board base paper, printed electronics paper, battery separators, cushion paper, tracing paper, impregnated paper, ODP paper, building material paper, decorative paper, envelope paper, tape paper, heat exchange paper, synthetic fiber paper, sterilized paper, waterproof paper, oil-resistant paper, heat-resistant paper, photocatalytic paper, decorative paper (grease removal paper, etc.), various sanitary papers (toilet paper, tissue paper, wipers, diapers, sanitary products, etc.), tobacco paper, paperboard (liner, core base paper, white paperboard, etc.), paper plate base paper, cup base paper, baking paper, abrasive paper, synthetic paper, etc. Of these, printing paper, inkjet paper, PPC paper, form paper, craft paper, fine paper, coated paper, lightly coated paper, and wrapping paper are preferred because they have good strength and stiffness at the same density. EXAMPLES

[0039] Examples 1 to 3 and Comparative Examples 1 to 9 Approximately 200,000 seedlings (seedlings) of Eucalyptus species, including hybrid species and species that can adapt to tropical and subtropical regions, were created and planted in plantations in Brazil. The seedlings (age of seedlings at planting: 100 days after cutting) were rooted in a greenhouse with a watering system for approximately 100 days after sowing (approximately 3 weeks, high humidity (approximately 100%), shading), acclimatized in a room (gradually decreasing shading and humidity), and then in an outdoor field, and planted in plantations during the rainy season (late December to June) (planting density: 1666 plants / ha). After cultivating for approximately 4 years, the trees were selected based on volume and tree shape, narrowing down the number to approximately 200. The selected individuals were then felled, and clonal seedlings were propagated by cuttings from the sprouting branches. The clone seedlings were transplanted to a sand culture rack, and the branches were allowed to grow as mother trees, and the clone seedlings were propagated by taking cuttings from the branches. After that, the second planting test was conducted using the clone seedlings (30 trees per line). After four years of cultivation, the volume, tree shape, and uniformity of the clones were confirmed, and the selection was narrowed down to 40 clones. After that, large-scale cutting propagation was conducted using the mother trees in the sand culture rack, and a third large-scale planting test was conducted using the clone seedlings (500 trees per line). After four years of cultivation, the volume, tree shape, uniformity, and disease suitability of the clones in a large area were evaluated, and the selection was narrowed down to 10 clones. Then, a pulping suitability test was conducted in accordance with TAPPI JAPAN, and several clones were selected. This process was repeated for five years, and selection was conducted from a total of one million individuals, and clones A to C (Examples 1 to 3) were selected.

[0040] Clones A and B were E. pellita × E. brassiana, and clone C was E. brassiana × E. pellita.

[0041] [Preparation of wood chips and physical property testing] (1) Preparation of chips The bark was removed from the wood of clones A to C, and the wood was cut to obtain wood chips. The wood chips were sieved using a gyrosifter, and the fraction with a diameter of 25.4 mmφpass to 9.5 mmφon was used for the cooking test. The bulk density of chips obtained from clones A to C was 655 kg / m 3 , 640kg / m 3 , 660kg / m3 The fiber lengths were 0.88 mm, 0.85 mm, and 0.90 mm, and the tree ages were 6.5 years, 6.0 years, and 6.8 years.

[0042] (2) Cooking test (KP cooking) Unbleached pulp was obtained from each material by kraft pulp cooking in a 2.5 L rotary autoclave (multi-digester). The cooking conditions were as shown in Table 1.

[0043] [Table 1]

[0044] The volume density of the clones was measured, and clone A was 655 kg / cm 3 , Clone B is 640kg / cm 3 , Clone C is 660 kg / cm 3 The fiber length was measured as 0.88 mm for Clone A, 0.85 mm for Clone B, and 0.90 mm for Clone C. The fiber length was measured as the length-weighted average fiber length using a fiber tester (Lorentzen & Wettre) in accordance with JIS P 8226:2011 "Pulp - Fiber length measurement method by optical automatic analysis method". The bulk density was measured in accordance with J TAPPI NO.3:2000 "Wood chips - Volume density test method".

[0045] (3) Oxygen delignification The unbleached pulp obtained in (2) was subjected to oxygen delignification in an oxygen deligninizing apparatus (CRS: Multipurpose Reactor, manufactured by CRS Reactor Engineering AB). The conditions for oxygen delignification were as shown in Table 2.

[0046] [Table 2]

[0047] [Notes for Table 2] The amount of oxygen added and the amount of NaOH added are expressed as a percentage based on the weight of bone-dry pulp.

[0048] (4) Bleaching test (chlorine bleaching) The pulp obtained in (3) was hand-bleached in a D0-E / P-D1 flow. The bleaching conditions were as shown in Table 3. The final target brightness (ISO 2470-1:2016) was 86%.

[0049] [Table 3]

[0050] (5) Beating The pulp obtained in (4) was beaten using a PFI mill. The beating intensity was controlled by the mill rotation speed.

[0051] (6) Handmade paper production (5) The beaten pulp obtained in step (5) was used to prepare handsheets in accordance with JIS P 8222 "Pulp - Preparation method for test handsheets - Method using a standard handsheet machine". The target basis weight was 60 g / m 2 It was decided.

[0052] (7) Paper quality testing The breaking length (density 0.6 g / cm) of the hand-made paper obtained in (6) was 3 ) was measured in accordance with JIS P 8113:2006. In addition, bending stiffness (0.6g / cm 3 ) was measured in accordance with ISO2493-2:2020. In Comparative Examples 1 to 3, the breaking length and bending stiffness of the handmade paper obtained from the wood of the plant species and tree ages E. urophylla (tree age: 6.5 years), E. globulus (tree age: 10 years), and E. urograndis (tree age: 7 years) by (1) to (6) were measured in the same manner as in the Examples. The bulk density and fiber length of each wood pulp of Comparative Examples 1 to 3 were as follows: bulk density of Comparative Example 1: 530 kg / m 3 , fiber length: 0.86 mm; volume weight of Comparative Example 2: 516 kg / m 3, fiber length: 0.83 mm; volume weight of Comparative Example 3: 550 kg / m 3 , fiber length: 0.80 mm. Comparative Examples 4 to 9 were reprinted from the measured values ​​of breaking length of paper obtained from the following wood pulps, which were described in H. Nanko et al. "THE WORLD OF MARKET PULP" (2010) TAPPI Press: E. grandis hybrid wood pulp (fiber length: 0.76 mm: Comparative Example 4); E. grandis and E. globulus hybrid wood pulp (fiber length: 0.72 mm: Comparative Example 5); E. globulus (fiber length: 0.75 mm: Comparative Example 6); E. Caldumalesis wood pulp (fiber length: 0.65 mm: Comparative Example 7) (Table 4, Figures 1 and 2).

[0053] [Table 4]

[0054] The papers obtained in the examples have densities of 0.5 and 0.6 g / cm 3 In both cases, the breaking length satisfied formula 1. The bending stiffness also satisfied formula 2. On the other hand, the comparative paper had a density of 0.5 and 0.6 g / cm 3 In none of the cases did the breaking length satisfy formula 1, and the bending stiffness did not satisfy formula 2 (Table 4, Figures 1 and 2).

[0055] The above results show that in the present invention, paper having both bulkiness and high strength can be obtained from kraft pulp.

Claims

1. The paper raw material contains kraft pulp, The density and breaking length of the paper are related by the following formula 1. (Formula 1) B≧26.537×A−8.153 (In formula 1, A is density (g / cm 3 ) where A is 0.3≦A≦0.

7. B is the breaking length (km) where B>0.

2. 2. The paper according to claim 1, wherein the density and bending stiffness are related by the following formula 2: (Formula 2) C≧-387.35×A+510.75 (In formula 2, A is density (g / cm 3 ) and 0.3≦A≦0.

7. C is bending stiffness (μN·m 2 / m)

3. The method for producing paper according to claim 1 or 2, wherein kraft pulp is used as a paper raw material.

4. Volumetric weight 635kg / m 3 The method for producing paper according to claim 3, further comprising: kraft pulp cooking a wood raw material having a fiber length of 1.1 mm or less to obtain kraft pulp; and producing paper using the pulp containing the kraft pulp as a raw material.

5. The method for producing paper according to claim 3 or 4, wherein the kraft pulp cooking is carried out under conditions of an active alkali addition rate of 5 to 40%.

6. The method for producing paper according to claim 4 or 5, further comprising carrying out at least one treatment selected from a delignification treatment, a bleaching treatment and a beating treatment after the kraft pulp cooking.

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