Craft paper

Abstract

To provide a craft paper that has both excellent specific tear strength and specific tensile strength, as well as excellent formation.SOLUTION: The craft paper is made by paper-making from raw pulp containing hardwood pulp and leaf vein fiber pulp, and the weighted average fiber length of the raw pulp is 0.80 mm or more and 2.20 mm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to kraft paper. [Background technology]

[0002] In the past, raw pulp containing softwood pulp as the main component was often used for applications requiring high tear strength and tensile strength, and raw pulp containing leaf vein fiber pulp was sometimes used to improve tensile strength and elongation.

[0003] Patent Document 1 discloses kraft paper obtained by papermaking a raw pulp that is a mixture of kraft pulp and leaf vein fiber pulp, in which the freeness of the leaf vein fiber pulp is equal to or greater than a specific value. It describes that this kraft paper has a single-layer structure but has high tensile strength and elongation, and has little fiber bundling and excellent formation, making it suitable for use as electrical insulating paper for various electrical devices, and in particular as kraft paper for wrapping electrical wires. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-185260 Summary of the Invention [Problem to be solved by the invention]

[0005] The kraft paper described in Patent Document 1 is particularly suitable for use as wrapping paper for electric wires, and therefore does not focus on tear strength. Therefore, there has been a demand for kraft paper that has both tear index and tensile index, which are important strengths for kraft paper, and also has excellent texture.

[0006] The present invention has been made in view of the existence of the above problems, and has an object to provide kraft paper that has both excellent tear index and tensile index and also has excellent texture. [Means for solving the problem]

[0007] The inventors have discovered that kraft paper made from raw pulp containing hardwood pulp and vein fiber pulp and having a length-weighted average fiber length within a specific range has both excellent tear index and tensile index, and also has excellent texture. That is, the present invention has the following configuration. <1> A kraft paper made by papermaking from a raw material pulp containing hardwood pulp and leaf vein fiber pulp, wherein the length-weighted average fiber length of the raw material pulp is 0.80 mm or more and 2.20 mm or less. <2> The Canadian standard freeness of the disintegrated pulp obtained by re-disintegration is 600 mL or less. <1> Kraft paper according to claim 1. <3> The raw pulp has a fiber coarseness of 0.14 mg / m or less. <1> or <2> Kraft paper according to claim 1. <4> Basis weight: 45g / m 2 More than 200g / m 2 Below is the <1> ~ <3> 1. Kraft paper according to any one of the preceding items. <5> Specific tear strength is 10mN·m 2 / g or more, <1> ~ <4> 1. Kraft paper according to any one of the preceding items. <6> The tensile strength is 60N·m / g or more. <1> ~ <5> 1. Kraft paper according to any one of the preceding items. <7> The content of the hardwood pulp in the raw material pulp is 20% by mass or more and 98% by mass or less, and the content of the leaf vein fiber pulp in the raw material pulp is 2% by mass or more and 80% by mass or less. <1> ~ <6> 1. Kraft paper according to any one of the preceding items. <8> The Canadian Standard Freeness of the hardwood pulp in the raw pulp is 300 mL or more and 500 mL or less, and the Canadian Standard Freeness of the leaf vein fiber pulp in the raw pulp is less than 600 mL. <1> ~ <7> 1. Kraft paper according to any one of the preceding items. [Effects of the Invention]

[0008] According to the present invention, kraft paper is provided which has both excellent tear index and tensile index and is excellent in texture. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail. The following description of the constituent elements 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 expressed using "X to Y" means a numerical range including X as the lower limit and Y as the upper limit. When a numerical range is described in stages, the upper and lower limits of each numerical range can be combined in any way.

[0010] [Kraft paper] The kraft paper of this embodiment (hereinafter simply referred to as kraft paper) is made by papermaking raw material pulp containing hardwood pulp and vein fiber pulp, and the length-weighted average fiber length of the raw material pulp is 0.80 mm or more and 2.20 mm or less. The kraft paper of this embodiment is made by papermaking raw material pulp containing hardwood pulp and vein fiber pulp and having a length-weighted average fiber length within a specific range, so that it has both excellent tear index and tensile index and excellent texture.

[0011] <Raw pulp> The kraft paper of this embodiment contains hardwood pulp and vein fiber pulp as raw material pulp. The raw material pulp is preferably beaten to more effectively increase the tensile index and tear index of the kraft paper. The beating method 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 the pulp. The beating method is not particularly limited, but can be performed using a refiner such as a double-disc refiner, a single-disc refiner, or a conical refiner.

[0012] (Hardwood pulp) The type of hardwood pulp is not particularly limited, and any known wood pulp that has been conventionally used can be used. Examples of hardwood trees that can be used as raw materials for hardwood pulp include Eucalyptus, Beech, Oak, Birch, and Acacia. Specific examples include Eucalyptus globulus, Eucalyptus grandis, Eucalyptus eurograndis, Eucalyptus maculata, Eucalyptus punctata, Eucalyptus saligna, Eucalyptus telenicornis, Eucalyptus pelita, Eucalyptus camaldulensis, Eucalyptus deglupta, Eucalyptus brassiana, Eucalyptus nitens, Eucalyptus europhylla, Acacia mangium, Acacia auriculformis, Acacia catechu, Acacia decarens, Acacia holosericia, Acacia leptocarpa, Acacia maydenii, Acacia melanthy, Acacia melanoxylon, Acacia neriphora, Acacia silivestris, Acacia peregrinalis, Acacia aulacocarpa, Acacia crassicarpa, etc. Hybrids of these species may also be used. From the viewpoint of production efficiency, it is preferable to use Eucalyptus such as Eucalyptus camaldulensis. One type of broad-leaved tree may be used alone, or two or more types may be used in combination.

[0013] The hardwood pulp content in the raw material pulp is preferably 20% by mass or more, more preferably 25% by mass or more, even more preferably 30% by mass or more, from the viewpoint of achieving both better tensile strength index and tear strength index and obtaining kraft paper with better texture, and is preferably 98% by mass or less, more preferably 96% by mass or less, even more preferably 95% by mass or less.

[0014] (Leaf vein fiber pulp) In the present invention, the vein fibers used as the raw material for the vein fiber pulp are fibers utilizing the veins of non-wood plants, such as Manila hemp, sisal hemp, esparto, New Zealand hemp, African grass, aloe, ficu, henequen, mazaie, New Zealand lantern plant, tampico, kula, pineapple, and banana. From the viewpoint of strength, the vein fibers are preferably Manila hemp. One type of vein fiber may be used alone, or two or more types may be used in combination.

[0015] The content of vein fiber pulp in the raw material pulp is preferably 2% by mass or more, more preferably 4% by mass or more, and preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 72% by mass or less, from the viewpoint of obtaining kraft paper with better texture while achieving both better tensile strength index and tear strength index.

[0016] The raw material pulp may contain natural fibers other than hardwood and vein fibers, waste paper, organic synthetic fibers, inorganic fibers, etc., as long as the effects of the present invention are not impaired. When fibers other than hardwood and vein fibers are contained, the content of such fibers in the raw material pulp is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 0% by mass. In other words, the content of hardwood pulp and vein fiber pulp in the raw material pulp is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 100% by mass.

[0017] <Physical properties of raw pulp> (length-weighted average fiber length) The length-weighted average fiber length of the raw pulp is 0.80 mm or more, preferably 0.82 mm or more, more preferably 0.84 mm or more, and 2.20 mm or less, preferably 2.10 mm or less, more preferably 2.05 mm or less, and even more preferably 2.00 mm or less, from the viewpoint of obtaining kraft paper with both better tensile strength index and tear strength index and with better texture. The length-weighted average fiber length of the raw pulp can be adjusted by adjusting the blending ratio of the pulps constituting the raw pulp. Specifically, the length-weighted average fiber length tends to be longer when the content of leaf vein fiber pulp is high. The length-weighted average fiber length of fibers in a raw pulp means the length-weighted average fiber length of the beaten raw pulp when the raw pulp is beaten, and is measured in accordance with ISO 16065-2:2007.

[0018] (Fiber coarseness) The coarseness (fiber coarseness) of the raw pulp is preferably 0.14 mg / m or less, more preferably 0.12 mg / m or less, and preferably 0.05 mg / m or more, more preferably 0.06 mg / m or more, from the viewpoint of achieving both better tensile strength index and tear strength index and obtaining kraft paper with better texture. The fiber coarseness of the raw pulp can be adjusted by adjusting the blending ratio of the pulps constituting the raw pulp. Specifically, a high content of leaf vein fiber pulp tends to increase the fiber coarseness, while a high content of hardwood pulp tends to decrease the fiber coarseness. The coarseness of the fibers in the raw pulp means the coarseness of the fibers in the beaten raw pulp when the raw pulp is beaten, and is measured in accordance with ISO 16065-2:2007.

[0019] (fiber width) From the viewpoint of obtaining kraft paper with excellent texture and achieving both excellent tensile strength index and tear strength index, the fiber width of the raw material pulp is preferably 15.0 μm or more, more preferably 17.0 μm or more, and preferably 45.0 μm or less, more preferably 40.0 μm or less, even more preferably 35.0 μm or less, even more preferably 30.0 μm or less, and even more preferably 25.0 μm or less. The fiber width of the raw material pulp can be adjusted by adjusting the blending ratio of the pulps that make up the raw material pulp. Specifically, the fiber width tends to be smaller when the content of hardwood pulp is high. The fiber width of the fibers in the raw pulp means the fiber width of the fibers in the beaten raw pulp when the raw pulp is beaten, and is measured in accordance with ISO 16065-2:2007.

[0020] (Canadian Standard Freeness (CSF)) The Canadian Standard Freeness (CSF) of the hardwood pulp in the beaten raw material pulp is preferably 300 mL or more, more preferably 330 mL or more, even more preferably 350 mL or more, and even more preferably 370 mL or more, from the viewpoint of obtaining kraft paper with excellent formation while achieving both better tensile strength index and tear strength index, and is preferably 500 mL or less, more preferably 450 mL or less, even more preferably 420 mL or less, and even more preferably 400 mL or less, from the viewpoint of obtaining kraft paper with excellent formation. The CSF of hardwood pulp in the beaten raw pulp is measured in accordance with JIS P 8121-2:2012.

[0021] The Canadian Standard Freeness (CSF) of the vein fiber pulp in the beaten raw pulp is preferably less than 600 mL, more preferably 580 mL or less, and even more preferably 560 mL or less, from the viewpoint of achieving both better tensile strength index and tear strength index and obtaining kraft paper with better texture.The lower limit is not particularly limited, but is preferably 300 mL or more, more preferably 350 mL or more, and even more preferably 400 mL or more. The CSF of the vein fiber pulp in the beaten raw pulp is measured in accordance with JIS P 8121-2:2012.

[0022] From the viewpoint of achieving both better tensile strength index and tear strength index and obtaining kraft paper with better texture, the CSF of the beaten raw pulp (mixed pulp) is preferably 590 mL or less, more preferably 580 mL or less, even more preferably 570 mL or less, and even more preferably 560 mL or less, and although there is no particular lower limit, it is preferably 400 mL or more, more preferably 450 mL or more, and even more preferably 470 mL or more. The CSF of the raw pulp can be adjusted appropriately by the degree of beating. The CSF of beaten raw pulp is measured in accordance with JIS P 8121-2:2012.

[0023] [Kraft paper manufacturing method] The method for producing kraft paper of this embodiment includes a step of beating a stock pulp containing hardwood pulp and leaf vein fiber pulp and having a length-weighted average fiber size of 0.80 mm to 2.20 mm, and then making paper. The stock pulp may be any of the above-mentioned stock pulps. If necessary, known internal additives may be added to the pulp slurry of the raw pulp, such as fillers, sizing agents, dry strength agents, wet strength agents, retention aids (e.g., aluminum sulfate), pH adjusters, drainage aids, waterproofing agents, softeners, antistatic agents, antifoaming agents, slime control agents, dyes, and pigments. Examples of fillers 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 hollow fine particles thereof. Examples of sizing agents include rosin-based, alkyl ketene dimer-based, alkenyl succinic anhydride-based, styrene-acrylic, higher fatty acid-based, and petroleum resin-based sizing agents. Examples of dry paper strength agents (paper strength agents) include cationized starch, unmodified, cationic or amphoteric polyacrylamide polymers, carboxymethyl cellulose, and the like. Examples of wet strength agents include polyamide polyamine epichlorohydrin resin (PAE), melamine-formaldehyde resin, and urea-formaldehyde resin.

[0024] The method of beating is not particularly limited, but it is preferable to disperse the cooked raw pulp in water to prepare a pulp dispersion, and then beat the pulp. The beating method is not particularly limited, but can be carried out using a refiner such as a double disc refiner, a single disc refiner, or a conical refiner. The papermaking method is not particularly limited, and examples include the acidic papermaking method in which papermaking is carried out at a pH of around 4.5, and the neutral papermaking method in which papermaking is carried out at a pH of about 6 to about 9. During the papermaking process, chemicals for the papermaking process such as pH adjusters, antifoaming agents, pitch control agents, slime control agents, etc. can be added as needed. The papermaking machine is also not particularly limited, and examples include continuous papermaking machines such as Fourdrinier, cylinder, and tilting types, or multi-layer papermaking machines that combine these.

[0025] The kraft paper obtained as described above may be subjected to a surface treatment using a calendar to make the thickness and profile uniform. A known calendaring machine may be appropriately selected and used for the calendering treatment. A surface sizing agent may also be applied to the surface of the kraft paper.

[0026] [Physical properties of kraft paper] <Basic weight> The basis weight of the kraft paper is not particularly limited, but from the viewpoint of strength, it is preferably 45 g / m 2 More preferably, 50 g / m 2More preferably, 55 g / m 2 and preferably 200 g / m 2 or less, more preferably 150 g / m 2 More preferably, 100 g / m or less 2 or less, even more preferably 80 g / m 2 The following is the result. The basis weight of kraft paper is measured in accordance with JIS P 8124:2011.

[0027] <Thickness> The thickness of the kraft paper is not particularly limited, but from the viewpoint of strength, it is preferably 65 μm or more, more preferably 80 μm or more, even more preferably 90 μm or more, and preferably 200 μm or less, more preferably 150 μm or less, even more preferably 130 μm or less. The thickness of kraft paper is measured in accordance with JIS P 8118:2014.

[0028] <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 More preferably, 0.40 g / cm 3 More preferably, 0.50 g / cm 3 More preferably, 0.55 g / cm 3 and preferably 1.00 g / cm 3 or less, more preferably 0.80 g / cm 3 or less, more preferably 0.70 g / cm 3 or less, even more preferably 0.66 g / cm 3 or less, even more preferably 0.65 g / cm 3 is less than. The density of the kraft paper is calculated from the basis weight and thickness of the kraft paper obtained by the above-mentioned measurement method.

[0029] <Tear strength index> The tear strength of the kraft paper is preferably 10 mN·m from the viewpoint of effectively suppressing bag breakage when the kraft paper is used for light packaging, for example.2 / g or more, preferably 10.5 mN m 2 / g or more, and although there is no particular upper limit, from the viewpoint of ease of production of kraft paper, it is preferably 100 mN m 2 / g or less, preferably 70 mN m 2 / g or less, more preferably 50 mN m 2 / g or less. The tear strength index of kraft paper can be adjusted by adjusting the blending ratio of the pulps that make up the raw pulp and the beating conditions. Specifically, the tear strength index tends to be higher when the leaf vein fiber content is high. Also, if the blending ratio of the pulps that make up the raw pulp is the same, the tear strength index tends to be higher when the beating degree is increased and the CSF is lowered. The tear strength index of kraft paper is measured in accordance with JIS P 8116:2000. In addition, if the kraft paper is oriented, the specific tear strength (mN m 2 / g) is the value obtained by measuring the tear strength in the machine direction and the tear strength in the cross direction in accordance with JIS P 8116:2000, calculating the geometric mean of the tear strength in the machine direction and the tear strength in the cross direction, and dividing this by the basis weight. In this specification, the term "longitudinal direction" refers to a direction parallel to the paper-making direction, and the term "transverse direction" refers to a direction perpendicular to the paper-making direction.

[0030] <Tensile index> The tensile index of kraft paper is preferably 55 N·m / g or more, more preferably 60 N·m / g or more, from the viewpoint of effectively preventing bag breakage when the kraft paper is used for light packaging, for example. While there is no particular upper limit, from the viewpoint of ease of kraft paper production, it is preferably 150 N·m / g or less, more preferably 100 N·m / g or less. The tensile index of kraft paper can be adjusted by adjusting the blending ratio of the pulp constituting the raw pulp and the beating conditions. Specifically, the tensile index tends to be higher when the leaf vein fiber content is higher. For the same blending ratio of the pulp constituting the raw pulp, increasing the degree of beating and decreasing the CSF tends to increase the tensile index. The tensile index of kraft paper is measured in accordance with JIS P 8113:2006. For oriented kraft paper, the tensile index (N·m / g) is calculated by measuring the tensile strength in the machine direction and the tensile strength in the cross direction in accordance with JIS P 8113:2006, calculating the geometric mean of the tensile strength in the machine direction and the tensile strength in the cross direction, and dividing this by the basis weight.

[0031] <CSF of disintegrated pulp> The Canadian Standard Freeness (CSF) of the disintegrated pulp obtained by re-disintegrating kraft paper is preferably 600 mL or less, more preferably 580 mL or less, and even more preferably 560 mL or less, from the viewpoint of achieving both better tensile strength index and tear strength index and obtaining kraft paper with better texture.The lower limit is not particularly limited, but is preferably 300 mL or more, more preferably 350 mL or more, even more preferably 400 mL or more, and even more preferably 450 mL or more. The CSF of disintegrated pulp obtained by disintegrating kraft paper is measured in accordance with JIS P 8220-1:2012, and the CSF of disintegrated pulp obtained by disintegrating kraft paper is measured in accordance with JIS P 8121-2:2012.

[0032] The kraft paper of this embodiment has both excellent tensile strength index and tear strength index, and also has excellent texture, so it can be suitably used for light packaging, for example. [Example]

[0033] The effects of the present invention will be explained in detail below using examples. The materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below. Furthermore, "parts" and "%" in the examples and comparative examples represent "parts by mass" and "% by mass," respectively, unless otherwise specified.

[0034] [measurement] <Raw pulp> (length-weighted average fiber length) The length-weighted average fiber length of the raw pulp was measured for the fibers in the beaten raw pulp in accordance with ISO 16065-2:2007.

[0035] (Fiber coarseness) The coarseness (fiber coarseness) of the raw pulp was measured in accordance with ISO 16065-2:2007 for the fibers in the beaten raw pulp.

[0036] (fiber width) The fiber width of the fibers in the raw pulp was measured in accordance with ISO 16065-2:2007 for the fibers in the beaten raw pulp.

[0037] (Canadian Standard Freeness (CSF)) The CSF of the beaten raw pulp, hardwood pulp, vein fiber pulp, and softwood pulp in the raw pulp was measured in accordance with JIS P 8121-2:2012.

[0038] <Kraft paper> (Basic weight) The basis weight of the kraft paper was measured in accordance with JIS P 8124:2011.

[0039] (Thickness) The thickness of the kraft paper was measured in accordance with JIS P 8118:2014.

[0040] (density) The density of the kraft paper was calculated from the basis weight and thickness of the kraft paper obtained by the above-mentioned measurement method.

[0041] (tear strength index) The tear strength index of the kraft paper was measured in accordance with JIS P 8116:2000.

[0042] (tensile index) The tensile index of the kraft paper was measured in accordance with JIS P 8113:2006.

[0043] (CSF of disintegrated pulp) The CSF of the disintegrated pulp obtained by disintegrating kraft paper was measured in accordance with JIS P 8220-1:2012, and the CSF of the disintegrated pulp obtained by disintegrating kraft paper was measured in accordance with JIS P 8121-2:2012.

[0044] [evaluation] <Market Conditions> The texture of the produced kraft paper was evaluated according to the following criteria: A or B is acceptable for practical use. A: When the paper surface is exposed to light, there are no irregularities in the texture of the paper surface. B: When the paper surface is exposed to light, slight irregularities in the texture are observed on the paper surface. C: When the paper surface is exposed to light, there is noticeable unevenness in the texture of the paper surface.

[0045] Example 1 Manila hemp pulp, which had a length-weighted average fiber length of 3.48 mm, a fiber coarseness of 0.170 mg / m, and a CSF of 440 mL after beating, was mixed with hardwood pulp (LBKP), which had a length-weighted average fiber length of 0.75 mm, a fiber coarseness of 0.049 mg / m, and a CSF of 380 mL after beating, in the proportions shown in Table 1 to prepare a raw pulp. Handmade sheets were made according to a method in accordance with JIS P 8222:2015, and kraft paper with the basis weights listed in Table 1 was obtained. The measurement and evaluation results are shown in Table 1.

[0046] Examples 2 to 5, Comparative Examples 1 to 4 Kraft paper was obtained in the same manner as in Example 1, except that the blending ratio of Manila hemp fiber pulp and LBKP in the raw material pulp was set to the ratio shown in Table 1. The measurement and evaluation results are shown in Table 1.

[0047] Example 6 Kraft paper was obtained in the same manner as in Example 2, except that the CSF after beating the Manila hemp fiber pulp was 550 mL. The measurement and evaluation results are shown in Table 1.

[0048] Comparative Example 5 Kraft paper was obtained in the same manner as in Example 1, except that 100% by mass of softwood pulp (NBKP) having a length-weighted average fiber length of 2.87 mm, a fiber coarseness of 0.270 mg / m, and a CSF of 460 mL after beating was used as the raw material pulp. The measurement and evaluation results are shown in Table 1.

[0049] [Table 1]

[0050] As can be seen from Table 1, kraft paper made from raw pulp containing leaf vein fiber pulp and hardwood pulp and having a length-weighted average fiber length within a specific range can achieve both excellent tensile strength index and tear strength index, and also has excellent texture. [Industrial Applicability]

[0051] The kraft paper of this embodiment has both excellent tensile strength index and tear strength index, and also has excellent texture, so it can be suitably used for light packaging, for example.

Claims

1. Kraft paper made by papermaking raw material pulp containing hardwood pulp and leaf vein fiber pulp, The length-weighted average fiber length of the raw material pulp is 0.80 mm or more and 2.20 mm or less.

2. 2. The kraft paper of claim 1, wherein the disintegrated pulp obtained by re-disintegration has a Canadian Standard Freeness of 600 ml or less.

3. 3. The kraft paper according to claim 1, wherein the raw pulp has a fiber coarseness of 0.14 mg / m or less.

4. Basis weight: 45 g / m ２ More than 200g / m ２ 3. The kraft paper of claim 1, wherein:

5. Specific tear strength is 10 mN m ２ 3. The kraft paper according to claim 1, wherein the kraft paper has a viscosity of 1 / g or more.

6. 3. The kraft paper according to claim 1, wherein the kraft paper has a tensile index of 60 N·m / g or more.

7. The content of the hardwood pulp in the raw material pulp is 20% by mass or more and 98% by mass or less, and 3. The kraft paper according to claim 1, wherein the content of the leaf vein fiber pulp in the raw material pulp is 2% by mass or more and 80% by mass or less.

8. The Canadian standard freeness of the hardwood pulp in the raw material pulp is 300 mL or more and 500 mL or less, 3. The kraft paper of claim 1 or 2, wherein the Canadian Standard Freeness of the vein fiber pulp in the raw pulp is less than 600 ml.

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