Kraft pulp and craft paper

Abstract

To provide kraft pulp efficiently from which kraft paper that has both excellent a specific tear strength and a specific tensile strength can be produced.SOLUTION: Kraft pulp includes as raw materials non-wood vein fibers, or a mixture of non-wood vein fibers and at least one species selected from hardwoods and softwoods. Kraft paper is made from the kraft pulp that includes as raw materials non-wood vein fibers, or a mixture of non-wood vein fibers and at least one species selected from hardwoods and softwoods. A method for producing kraft pulp by subjecting non-wood vein fibers, or a mixture of non-wood vein fibers and at least one species selected from hardwoods and softwoods, to the kraft pulping process.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to kraft pulp and kraft paper.

Background Art

[0002] Conventionally, wood used as a raw material for pulp has generally been digested by the kraft method (kraft digestion) to be pulped. On the other hand, non-wood vein fibers such as Manila hemp have generally been digested by the sulfite method (sulfite digestion) to be pulped.

[0003] Patent Document 1 discloses a kraft paper obtained by papermaking from a raw material pulp in which kraft pulp and vein fiber pulp are mixed, and the freeness of the vein fiber pulp is a specific value or more. The kraft paper has a single-layer structure but has high tensile strength and elongation, and has few fiber bundles and excellent formation, and thus can be suitably used as an electrical insulation paper for various electrical equipment, particularly as a kraft paper for wire winding paper.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The kraft paper described in Patent Document 1 uses a raw material pulp in which kraft pulp and vein fiber pulp, which are separately digested and pulped, are mixed, so the number of manufacturing steps is large. Further, since the kraft paper described in Patent Document 1 is particularly suitable for wire winding paper applications, the tear strength has not been focused on. Therefore, it has been desired to realize a kraft paper that achieves both specific tear strength and specific tensile strength, which are important strengths for kraft paper.

[0006] The present invention has been made in view of the existence of the above problems, and an object thereof is to efficiently provide kraft pulp capable of producing kraft paper that achieves both excellent specific tear strength and specific tensile strength.

Means for Solving the Problems

[0007] The inventors have found that kraft paper made from kraft pulp containing non-wood vein fibers or a combination of non-wood vein fibers and one or more selected from broad-leaved trees and coniferous trees can achieve both excellent specific tear strength and specific tensile strength. That is, the present invention has the following configuration. <1> Kraft pulp containing non-wood vein fibers or a combination of non-wood vein fibers and one or more selected from broad-leaved trees and coniferous trees as raw materials. <2> The kraft pulp according to <1>, wherein the length-weighted average fiber length is 0.9 mm or more and 4.2 mm or less. <3> The kraft pulp according to <1> or <2>, wherein the Canadian standard drainage degree is 600 mL or less. <4> The kraft pulp according to any one of <1> to <3>, wherein the raw materials contain 2% by mass or more of non-wood vein fibers. <5> Kraft paper formed by papermaking using the kraft pulp according to any one of <1> to <4>. <6> The kraft paper according to <5>, wherein the specific tensile strength is 54 N·m / g or more. <7> The specific tear strength is 14 mN·m 2 / g or more, and the kraft paper according to <5> or <6>. <8> The basis weight is 30 g / m 2 or more and 200 g / m 2 or less, and the kraft paper according to any one of <5> to <7>. <9> A method for producing kraft pulp by cooking non-wood vein fibers or a combination of non-wood vein fibers and one or more selected from broad-leaved trees and coniferous trees by the kraft method.

Effects of the Invention

[0008] According to the present invention, kraft pulp capable of efficiently producing kraft paper that achieves both excellent specific tear strength and specific tensile strength is provided.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be specifically described. The description of the constituent elements described below may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, a numerical range represented by "X to Y" means a numerical range including X as the lower limit value and Y as the upper limit value. When a numerical range is described stepwise, the upper and lower limits of each numerical range can be arbitrarily combined.

[0010] [Kraft Pulp] The kraft pulp of this embodiment (hereinafter also simply referred to as kraft pulp) contains non-wood leaf vein fibers or a combination of non-wood leaf vein fibers and one or more selected from hardwoods and softwoods as raw materials. The kraft pulp of this embodiment contains non-wood leaf vein fiber kraft pulp obtained by kraft cooking non-wood leaf vein fibers, thereby providing kraft paper that is excellent in specific tear strength and also excellent in specific tensile strength.

[0011] <Non-wood leaf vein fibers> Non-wood leaf vein fibers are fibers that utilize the leaf veins of plants. Examples include Manila hemp, sisal hemp, esparto, New Zealand hemp, African fan palm, aloe, ficus, henequen, masai, new zealand flax, tampico, curava, pineapple, banana, and the like. The non-wood leaf vein fibers as raw materials for the kraft pulp of this embodiment are preferably Manila hemp from the viewpoint of strength.

[0012] The content of non-wood leaf vein fibers is preferably 2% by mass or more, more preferably 5% by mass or more, still more preferably 8% by mass or more, and 100% by mass or less, preferably 80% by mass or less, more preferably 60% by mass or less, from the viewpoint of further improving the specific tear strength in the raw material of kraft pulp and as a result, obtaining kraft paper that balances the specific tensile strength and the specific tear strength.

[0013] <Hardwood and softwood> When hardwood or softwood is included as the raw material of kraft pulp, the types of hardwood and softwood are not particularly limited, and those conventionally used as known wood pulp can be used. Examples of hardwood include Eucalyptus, Fagus, Quercus, Betula, Acacia, etc. Specific examples include Eucalyptus globulus, Eucalyptus grandis, Eucalyptus urophylla x grandis, Eucalyptus maculata, Eucalyptus punctata, Eucalyptus saligna, Eucalyptus tereticornis, Eucalyptus perriniana, Eucalyptus camaldulensis, Eucalyptus deglupta, Eucalyptus brassiana, Eucalyptus nitens, Eucalyptus urophylla, Acacia mangium, Acacia auriculiformis, Acacia catechu, Acacia decurrens, Acacia holosericea, Acacia leptocarpa, Acacia mearnsii, Acacia melanoxylon, Acacia nilotica, Acacia nilotica subsp. indica, Acacia nilotica subsp. adstringens, Acacia nilotica subsp. cupressiformis, Acacia nilotica subsp. indica, Acacia nilotica subsp. adstringens, Acacia nilotica subsp. cupressiformis, etc. Hybrid varieties of these may also be used. Examples of softwood include Picea, Tsuga, Abies, Pinus, Cryptomeria, etc. Specific examples include white spruce, black spruce, hemlock, white fir, Douglas fir, balsam fir, southern pine, radiata pine, lodgepole pine, Elliott pine, Caribbean pine, slash pine, redwood, aspen, larch, red cedar, etc. Hardwood and / or softwood may be used alone or in combination of two or more. Coniferous trees tend to have a longer length-weighted average fiber length and are more likely to have improved tear strength compared to broadleaf trees. On the other hand, broadleaf trees tend to have less variation in texture compared to coniferous trees.

[0014] The content of broadleaf trees and coniferous trees is 0% by mass or more, preferably 20% by mass or more, more preferably 40% by mass or more, and preferably 98% by mass or less, more preferably 95% by mass or less, and even more preferably 92% by mass or less, from the viewpoint of further improving the specific tear strength and obtaining kraft paper that balances specific tensile strength and specific tear strength in the raw material of kraft pulp. When using a combination of broadleaf trees and coniferous trees, the content ratio (mass ratio: broadleaf tree / coniferous tree) of broadleaf trees and coniferous trees can be appropriately selected within the range of 0 / 100 to 100 / 0. From the viewpoint of improving the specific tear strength and reducing texture unevenness, this content ratio is preferably in the range of 10 / 90 to 55 / 45, and more preferably in the range of 30 / 70 to 50 / 50.

[0015] The raw material of kraft pulp may contain non-wood vein fibers, natural fibers other than broadleaf trees and coniferous trees, waste paper, organic synthetic fibers, inorganic fibers, etc., as long as the effects of the present invention are not inhibited. When containing fibers other than non-wood vein fibers, broadleaf trees, and coniferous trees, the content is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 0% by mass in the raw material of kraft pulp.

[0016] [Method for manufacturing kraft pulp] Kraft pulp containing non-wood vein fibers or a combination of non-wood vein fibers and one or more selected from broadleaf trees and coniferous trees as raw materials is obtained by cooking the raw materials by the kraft method. That is, kraft pulp is manufactured by cooking non-wood vein fibers or a combination of non-wood vein fibers and one or more selected from broadleaf trees and coniferous trees by the kraft method. As the cooking method, a conventional kraft method can be adopted. For example, a batch cooking method using a batch digester can be adopted. As the kraft white liquor containing sodium hydroxide and sodium sulfide, known ones can be used, and known treatments using kraft white liquor can also be adopted. The liquor ratio (mass of kraft white liquor including the moisture of the raw material / absolute dry mass of the raw material) is usually 3 to 5. The sulfidity of the kraft white liquor is preferably 5 to 50%, more preferably 10 to 40%, and still more preferably 20 to 35%. The active alkali concentration of the kraft white liquor, in terms of Na2O, is preferably 5 to 30% by mass, more preferably 10 to 20% by mass. The treatment temperature (cooking temperature) in cooking is preferably 100 to 250 °C, more preferably 130 to 200 °C, and still more preferably 150 to 180 °C. The treatment time (cooking time) in cooking is preferably 0.5 to 4 hours, more preferably 1 to 3 hours.

[0017] The kraft pulp cooked by the kraft process is preferably beaten from the viewpoint of more effectively increasing the specific tensile strength of kraft paper. The method of the beating treatment is not particularly limited, but it is preferable to disperse the cooked raw material pulp in water to prepare a pulp dispersion and then beat it. The beating treatment method is not particularly limited, but for example, it can be carried out using refiners such as double disk refiners, single disk refiners, and conical refiners.

[0018] [Physical properties of kraft pulp] <Length-weighted average fiber length> The length-weighted average fiber length of the kraft pulp is preferably 0.8 mm or more, more preferably 0.9 mm or more, and preferably 4.2 mm or less, more preferably 4.0 mm or less, still more preferably 3.8 mm or less, and even more preferably 3.5 mm or less, from the viewpoint of obtaining kraft paper that achieves both better tensile strength and tear strength. The length-weighted average fiber length of the kraft pulp can be adjusted by adjusting the blending ratio of the raw materials of the kraft pulp and the beating conditions. Specifically, when the content of non-wood vein fibers is high, the length-weighted average fiber length tends to be long. Also, when using non-wood vein fibers and hardwoods and / or softwoods, the length-weighted average fiber length tends to be longer when the content of softwoods is higher. Further, when the blending ratio of the raw materials of the kraft pulp is the same, increasing the beating degree and lowering the Canadian Standard Freeness (CSF) described later tend to shorten the length-weighted average fiber length. The length-weighted average fiber length of the fibers in the kraft pulp is measured in accordance with ISO 16065-2:2007.

[0019] <Canadian Standard Freeness> The Canadian Standard Freeness (CSF) of the beaten kraft pulp is preferably 600 mL or less, more preferably 580 mL or less, still more preferably 570 mL or less, and even more preferably 560 mL or less, from the viewpoint of obtaining kraft paper that achieves both better tensile strength and tear strength. The lower limit is not particularly limited, but is preferably 400 mL or more, more preferably 450 mL or more, and still more preferably 470 mL or more. The CSF of the kraft pulp can be appropriately adjusted according to the degree of beating. The CSF of the kraft pulp is measured in accordance with JIS P 8121-2:2012.

[0020] <Copper number> The copper number of the kraft pulp is preferably 5.0 or more, more preferably 6.0 or more, from the viewpoint of obtaining kraft paper that achieves both better tensile strength per unit weight and tear strength per unit weight, and is preferably 40 or less, more preferably 30 or less, still more preferably 28 or less, from the viewpoint of the yield of the kraft pulp. The copper number indicates the residual lignin content and is used as an index representing the degree of cooking. The copper number can be adjusted by adjusting the blending ratio of the raw materials of the kraft pulp and the active alkali concentration, cooking time, and cooking temperature of the cooking white liquor in the cooking process. Regarding the blending ratio of the raw materials, the copper number tends to increase in the order of non-wood vein fibers, hardwoods, and softwoods. That is, the copper number tends to increase when the content of softwoods is high, and tends to decrease when the content of non-wood vein fibers is high. The copper number of the kraft pulp is measured in accordance with JIS P 8211:2011.

[0021] As described above, conventionally, non-wood vein fibers have generally been cooked by the sulfite method with milder cooking conditions than kraft cooking. However, the inventors have found that kraft paper formed by papermaking from kraft pulp obtained by kraft cooking a raw material containing non-wood vein fibers or a raw material containing non-wood vein fibers and one or more selected from hardwoods and softwoods can achieve both excellent tear strength per unit weight and tensile strength per unit weight. Further, the kraft pulp of the present embodiment can be easily manufactured because, even when a raw material containing hardwoods or softwoods is used in addition to non-wood vein fibers, there is no need for separate cooking.

[0022] [Kraft Paper] The kraft paper of the present embodiment (hereinafter also simply referred to as kraft paper) is preferably formed by papermaking the above kraft pulp. Known internal additives may be added to the pulp slurry of the above kraft pulp as needed. Examples of the internal additives include fillers, sizing agents, dry paper strength enhancers, wet paper strength enhancers, yield improvers (e.g., sulfuric acid bands), pH adjusters, drainage improvers, water resistance agents, softeners, antistatic agents, defoamers, slime control agents, dyes, pigments, and the like. Examples of the filler include mineral pigments such as kaolin, calcined kaolin, calcium carbonate, calcium sulfate, barium sulfate, titanium dioxide, talc, zinc oxide, alumina, magnesium carbonate, magnesium oxide, silica, white carbon, bentonite, zeolite, sericite, and smectite, and organic pigments such as polystyrene resin, urea resin, melamine resin, acrylic resin, vinylidene chloride resin, and their fine hollow particles. Examples of the sizing agent include rosin-based, alkyl ketene dimer-based, alkenyl succinic anhydride-based, styrene-acrylic-based, higher fatty acid-based, and petroleum resin-based sizing agents. Examples of the dry paper strength enhancer (paper strength enhancer) include cationized starch, unmodified or cationic or amphoteric polyacrylamide-based polymers, and carboxymethyl cellulose. Examples of the wet paper strength enhancer include polyamide polyamine epichlorohydrin resin (PAE), melamine-formaldehyde resin, and urea-formaldehyde resin.

[0023] The papermaking method is not particularly limited, and examples thereof include an acidic papermaking method in which papermaking is performed at a pH of around 4.5, and a neutral papermaking method in which papermaking is performed at a pH of about 6 to about 9. In the papermaking process, papermaking process chemicals such as a pH adjuster, an antifoaming agent, a pitch control agent, and a slime control agent can be appropriately added as necessary. The paper machine is also not particularly limited, and examples thereof include a continuous paper machine such as a fourdrinier type, a cylinder type, and an inclined type, or a multi-layer combined papermaking machine combining these.

[0024] Further, the kraft paper obtained as described above may be subjected to surface treatment with a calendar to make the thickness and profile uniform. As the calendar treatment, a known calendar treatment machine can be appropriately selected and used. Also, a surface sizing agent may be applied to the surface of the kraft paper.

[0025] [Physical properties of kraft paper] [Specific tensile strength] The specific tensile strength of the kraft paper is preferably 54 N·m / g or more, more preferably 55 N·m / g or more, from the viewpoint of effectively suppressing bag breakage when the kraft paper is used, for example, for heavy packaging. The upper limit is not particularly limited, but from the viewpoint of ease of manufacturing the kraft paper, it is preferably 150 N·m / g or less, more preferably 100 N·m / g or less. The specific tensile strength of the kraft paper can be adjusted by adjusting the blending ratio of the raw materials of the kraft pulp and the beating conditions. If the blending ratio of the raw materials of the kraft pulp is the same, increasing the beating degree and lowering the CSF tend to increase the specific tensile strength. The specific tensile strength of the kraft paper is measured in accordance with JIS P 8113:2006. Further, in the case of a kraft paper having orientation, the specific tensile strength (N·m / g) is obtained by measuring the tensile strength in the longitudinal direction and the tensile strength in the transverse direction in accordance with JIS P 8113:2006, respectively, calculating the geometric mean of the tensile strength in the longitudinal direction and the tensile strength in the transverse direction, and dividing this value by the basis weight. In this specification, the "longitudinal direction" means a direction parallel to the papermaking direction, and the "transverse direction" means a direction perpendicular to the papermaking direction.

[0026] <Specific tear strength> The specific tear strength of the kraft paper is preferably 14 mN·m 2 / g or more, more preferably 15 mN·m 2 / g or more, and the upper limit is not particularly limited, but preferably 100 mN·m 2 / g or less, more preferably 80 mN·m 2 / g or less, still more preferably 60 mN·m 2It is below / g. The specific tearing strength of kraft paper can be adjusted by adjusting the blending ratio of the raw materials of kraft pulp and the beating conditions. Specifically, when the content of non-wood vein fibers is high, the specific tearing strength tends to be high. Also, when using non-wood vein fibers and hardwoods and / or softwoods, the specific tearing strength tends to be higher when the content of softwoods is higher than that of hardwoods. Further, when the blending ratio of the raw materials of kraft pulp is the same, reducing the beating degree and increasing the CSF tend to result in a higher specific tearing strength. The specific tearing strength of kraft paper is measured in accordance with JIS P 8116:2000. Also, in the case of kraft paper with orientation, the specific tearing strength (mN / g / m 2 ) is the value obtained by measuring the longitudinal tearing strength and the transverse tearing strength in accordance with JIS P 8116:2000 respectively, calculating the geometric mean of the longitudinal tearing strength and the transverse tearing strength, and dividing this by the basis weight.

[0027] <basis weight> The basis weight of kraft paper is not particularly limited, but from the perspective of strength, it is preferably 30 g / m 2 or more, more preferably 40 g / m 2 or more, still more preferably 50 g / m 2 or more, and preferably 200 g / m 2 or less, more preferably 150 g / m 2 or less, still more preferably 100 g / m 2 or less, even more preferably 80 g / m 2 or less. The basis weight of kraft paper is measured in accordance with JIS P 8124:2011.

[0028] <thickness> The thickness of kraft paper is not particularly limited, but from the perspective of strength, it is preferably 60 μm or more, more preferably 80 μm or more, still more preferably 95 μm or more, and preferably 200 μm or less, more preferably 180 μm or less, still more preferably 160 μm or less, even more preferably 140 μm or less. The thickness of the kraft paper is measured in accordance with JIS P 8118:2014.

[0029] <Density> The density of the kraft paper is not particularly limited, but from the viewpoint of strength, it is preferably 0.30 g / cm 3 or more, more preferably 0.40 g / cm 3 or more, and preferably 1.00 g / cm 3 or less, more preferably 0.80 g / cm 3 or less, still more preferably 0.70 g / cm 3 or less. The density of the kraft paper is calculated from the basis weight and thickness of the kraft paper obtained by the above-described measurement method.

[0030] Since the kraft paper of the present embodiment can achieve both excellent specific tensile strength and specific tear strength, for example, in addition to light packaging applications, it can be suitably used for heavy packaging applications.

Examples

[0031] Hereinafter, the effects of the present invention will be described in detail with reference to examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below. In addition, "parts" and "%" in the examples and comparative examples indicate "parts by mass" and "mass%", respectively, unless otherwise specified.

[0032] [Measurement] <Kraft pulp> (Copper number) In the pulp obtained after digestion, it was measured in accordance with JIS P 8211:2011.

[0033] (Canadian standard drainage) The Canadian standard drainage of the kraft pulp was measured in accordance with JIS P 8121-2:2012 before and after beating.

[0034] (Length-weighted average fiber length) The length-weighted average fiber length of the kraft pulp was measured in accordance with ISO 16065-2:2007.

[0035] <Kraft paper> (Grammage) The grammage of the kraft paper was measured in accordance with JIS P 8124:2011.

[0036] (Thickness) The thickness of the kraft paper was measured in accordance with JIS P 8118:2014.

[0037] (Density) The density of the kraft paper was calculated from the grammage and thickness of the kraft paper obtained by the above-described measurement method.

[0038] (Specific tensile strength) The specific tensile strength of the kraft paper was measured in accordance with JIS P 8113:2006.

[0039] (Specific tear strength) The specific tear strength of the kraft paper was measured in accordance with JIS P 8116:2000.

[0040] Example 1 <Production of kraft pulp> Using a raw material containing 10% by mass of Manila hemp as non-wood vein fibers and 90% by mass of Eucalyptus camaldulensis as hardwood, and cooking white liquor prepared to have a liquor ratio of 4, a sulfidity of 28%, and an effective alkali of 12% (in terms of Na2O), kraft cooking (batch cooking method) was performed at a cooking temperature of 160 °C for 2 hours. After kraft cooking, the black liquor was separated, and the obtained raw material was defibrated by a defibrator, followed by centrifugal dehydration and water washing with a filter cloth repeated three times. Then, the un-cooked material was removed by a screen, centrifugally dehydrated, and kraft pulp with the unbeaten CSF and kappa number shown in Table 1 was obtained. The obtained kraft pulp was beaten using a single refiner. Table 1 shows the results of the length-weighted average fiber length and CSF of the kraft pulp obtained after beating. <Production of kraft paper> Using the kraft pulp obtained after beating, a hand-sheet was made by a method conforming to JIS P 8222:2015, and kraft paper with a basis weight described in Table 1 was obtained. The measurement results are shown in Table 1.

[0041] Examples 2 and 3 Kraft pulp and kraft paper were obtained in the same manner as in Example 1, except that the content ratios of the raw materials Manila hemp and Eucalyptus camaldulensis were set to the ratios shown in Table 1. The measurement results are shown in Table 1.

[0042] Examples 4 and 5 Kraft pulp and kraft paper were obtained in the same manner as in Example 1, except that the raw material Eucalyptus camaldulensis was changed to Caribbean pine, a coniferous tree, and the content ratio was set to the ratio shown in Table 1. The measurement results are shown in Table 1.

[0043] Example 6 Kraft pulp and kraft paper were obtained in the same manner as in Example 1, except that the content ratios of the raw materials Manila hemp, Eucalyptus camaldulensis and Caribbean pine were set to the ratios shown in Table 1. The measurement results are shown in Table 1.

[0044] Comparative Example 1 Kraft pulp and kraft paper were obtained in the same manner as in Example 1, except that the raw material was 100% by mass of Eucalyptus camaldulensis and kraft cooking (batch cooking method) was carried out at a cooking temperature of 160 °C for 2 hours using cooking white liquor prepared to have a liquor ratio of 4, a sulfidity of 28%, and an effective alkali of 16% (in terms of Na2O). The measurement results are shown in Table 1.

[0045] Comparative Example 2 Kraft pulp and kraft paper were obtained in the same manner as in Example 1, except that the raw material was 100% by mass of Caribbean pine and kraft cooking (batch cooking method) was carried out at a cooking temperature of 160 °C for 2 hours using cooking white liquor prepared to have a liquor ratio of 4, a sulfidity of 28%, and an effective alkali of 25% (in terms of Na2O). The measurement results are shown in Table 1.

[0046] Comparative Example 3 The raw materials were 50% by mass of Eucalyptus camaldulensis and 50% by mass of Caribbean pine, and kraft pulp and kraft paper were obtained in the same manner as in Example 1, except that kraft cooking (batch cooking method) was carried out at a cooking temperature of 160°C for 2 hours using cooking white liquor prepared to have a liquor ratio of 4, a sulfidity of 28%, and an effective alkali of 22% (in terms of Na2O). The measurement results are shown in Table 1.

[0047] Reference Example The raw material was changed to 100% by mass of Manila hemp, and a handsheet was prepared in the same manner as in Example 1, except that sulfite cooking (batch cooking method) was carried out at a cooking temperature of 160°C for 90 minutes using cooking chemicals adjusted to have a liquor ratio of 7.5, 6% NaOH, and 18% Na2SO3, and kraft paper with the basis weight described in Table 1 was obtained. The measurement results are shown in Table 1.

[0048]

Table 1

[0049] As can be seen from Table 1, kraft paper formed by papermaking kraft pulp containing leaf vein fibers, or leaf vein fibers and one or more selected from hardwoods and softwoods as raw materials, can achieve both excellent specific tensile strength and specific tear strength. When comparing Example 3 in which 100% by mass of Manila hemp was used as a raw material for kraft cooking and the reference example in which 100% by mass of Manila hemp was used as a raw material for sulfite cooking, the kraft paper of Example 3 subjected to kraft cooking has a higher specific tear strength, indicating that leaf vein fiber kraft pulp contributes to the specific tear strength.

Industrial Applicability

[0050] The kraft paper formed by papermaking the kraft pulp of the present embodiment can achieve both excellent specific tensile strength and specific tear strength, and thus can be suitably used, for example, not only for light packaging applications but also for heavy packaging applications.

Claims

1. A kraft pulp containing non-wood vein fibers or a combination of non-wood vein fibers and one or more selected from hardwoods and softwoods as raw materials.

2. The kraft pulp according to Claim 1, having a length-weighted average fiber length of 0.9 mm or more and 4.2 mm or less.

3. The kraft pulp according to Claim 1 or 2, having a Canadian standard drainage degree of 600 mL or less.

4. The kraft pulp according to Claim 1 or 2, wherein the raw materials contain 2% by mass or more of non-wood vein fibers.

5. A kraft paper formed by papermaking using the kraft pulp according to Claim 1 or 2.

6. The kraft paper according to Claim 5, having a specific tensile strength of 54 N·m / g or more.

7. The specific tearing strength is 14 mN·m ２ / g or more, and the kraft paper according to claim 5.

8. The basis weight is 30 g / m ２ or more and 200 g / m ２ or less, the kraft paper according to claim 5.

9. A method for producing kraft pulp, comprising digesting non-wood vein fibers or a combination of non-wood vein fibers and one or more selected from hardwoods and softwoods by the kraft process.