Kraft paper and method for manufacturing kraft paper

Abstract

The invention discloses kraft paper and a manufacturing method of the kraft paper. [Problem] To provide kraft paper that can be manufactured inexpensively and has excellent strength such as tear strength. [Solution] A kraft paper containing broad-leaved kraft pulp as a starting material pulp, the content of the broad-leaved kraft pulp in the starting material pulp being 90 mass% or more, the Kara value of the pulp after re-dissociation being 9.5 or more, and the pulp viscosity of the kraft paper measured in accordance with TAPPI T 230 being 15 mPa * s or more.

Description

Technical Field

[0001] The present invention relates to kraft paper and a method for making kraft paper. Background Art

[0002] Kraft paper is a paper made of kraft pulp and has excellent strength. Kraft paper is used, for example, for light packaging of small items, or for heavy packaging of heavy industrial objects such as cement, fertilizer, and pesticides. Kraft paper used in the above applications is required to have strength that can withstand the impact of the contents caused by vibration during transportation of the contents.

[0003] Patent document 1 discloses a kraft paper that contains substantially no filler, has excellent whiteness, and has good paper strength and printing suitability, with the aim of providing kraft paper that is substantially free of fillers and has excellent whiteness. The kraft paper contains bleached kraft pulp, a sizing agent, a paper strength agent, aluminum sulfate, and a (meth)acrylamide resin, and substantially contains no filler. In the composition of the bleached kraft pulp, the content of bleached kraft pulp made from coniferous trees having a CSF filterability of a specific value or more is within a specific range, and the content of bleached kraft pulp made from broadleaf trees having a CSF filterability of a specific range is within a specific range.

[0004] Patent document 2 aims to provide kraft paper having sufficient paper strength despite the use of pulp with thick fiber walls and small internal voids, and a method for producing the same, and discloses the following kraft paper, characterized in that it is kraft paper with kraft pulp as the main component, the overall average fiber length of the decomposed pulp obtained by decomposing the kraft paper by the pulp decomposition method described in JIS P 8220:2012 is within a specific range, and the kraft paper contains fibers having a fiber length of a specific value or more, namely, a fraction (A), and fibers having a fiber length of a specific value or less, namely, a fraction (B), the Runkel ratio of the fraction (A) is above a specific value, and the total content of the fraction (A) and the fraction (B) in the decomposed pulp is above a specific value.

[0005] Patent document 3 discloses the following kraft paper for the purpose of providing kraft paper with a small difference between the front and back and sufficiently improved strength. The kraft paper is characterized in that the kraft paper is made using a sandwich forming papermaking machine, the tensile strength in the MD direction relative to the CD direction is within a specific range, and the tensile strength in the CD direction is within a specific range.

[0006] Patent document 4 discloses bleached kraft paper that satisfies the following conditions (1) to (8) in order to provide kraft packaging paper that has a sufficiently high sizing effect even when a large amount of old paper pulp is mixed, solves the problem of paper powder during printing or roughness during processing, and has processing adaptability as packaging paper. (1) In the raw material pulp, the content of coniferous tree bleached kraft pulp is within a specific range, and the content of broadleaf tree bleached kraft pulp is within a specific range. (2) The freeness of coniferous tree bleached kraft pulp is within a specific range, and the freeness of broadleaf tree bleached kraft pulp is within a specific range. (3) Calcium carbonate is added in a specific amount or more as a filler, and the ash content is set to a specific range. (4) A surface treatment agent containing an adhesive as the main component is applied to each single side in an amount within a specific range. (5) An internally added sizing agent and a surface sizing agent are used to The sizing degree is set to a specific value or more. (6) The whiteness is set to a specific value or more. (7) The oil absorption is set to a specific range. (8) The smoothness is set to a specific range.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2022-90158

[0010] Patent Document 2: Japanese Patent Application Publication No. 2021-38487

[0011] Patent Document 3: Japanese Patent Application Publication No. 2015-21209

[0012] Patent Document 4: Japanese Patent Application Publication No. 2013-100624 Summary of the invention

[0013] Problem that the invention aims to solve

[0014] From the viewpoint of tear strength, tensile strength and other strengths required of kraft paper, the kraft paper described in Patent Documents 1 to 4 uses coniferous kraft pulp as raw material pulp. However, coniferous kraft pulp is more expensive than broadleaf kraft pulp, and therefore, it is desired to develop a kraft paper that is cheaper and satisfies the strength required of kraft paper by using a raw material pulp containing broadleaf kraft pulp as a main component.

[0015] An object of the present invention is to provide kraft paper which can be produced at low cost and has excellent strength such as tear strength.

[0016] Solutions for solving problems

[0017] The present inventors have found that the above-mentioned problems can be solved by setting the content of hardwood kraft pulp in the raw material pulp to a specific value or more, setting the kappa value of the pulp after re-dissociation to a specific value or more, and setting the pulp viscosity of the kraft paper measured according to TAPPI T 230 to a specific value or more in kraft paper containing hardwood kraft pulp as raw material pulp. That is, the present invention relates to the following technical solutions.

[0018] <1> A kraft paper comprising broadleaf kraft pulp as raw material pulp, wherein the content of broadleaf kraft pulp in the raw material pulp is 90% by mass or more, the kappa number of the pulp after dissociation is 9.5 or more, and the pulp viscosity of the kraft paper measured according to TAPPI T 230 is 15 mPa·s or more.

[0019] <2> according to <1> The kraft paper, wherein the kappa number of the pulp after re-dissociation is less than 30, and the viscosity of the pulp of the kraft paper is less than 120 mPa·s.

[0020] <3> according to <1> or <2> The longitudinal tear index of the kraft paper is 8.0 mN·m 2 / g or more, and the transverse tear index is 8.8mN·m 2 / g or above.

[0021] <4> according to <1> ~ <3> The kraft paper described in any one of the above has a basis weight of 70 g / m 2 Above and 150g / m 2 the following.

[0022] <5> according to <1> ~ <4> The kraft paper described in any one of the above has a density of 0.65 g / cm 3 Above and 0.85g / cm 3 the following.

[0023] <6> according to <1> ~ <5> The kraft paper described in any one of the above is used for light packaging.

[0024] <7> A method for producing kraft paper, comprising: making kraft paper from a raw material pulp containing broadleaf kraft pulp, wherein the content of broadleaf kraft pulp in the raw material pulp is 90% by mass or more, the kappa number of the raw material pulp is 9.5 or more, and the pulp viscosity of the raw material pulp measured according to TAPPI T 230 is 15 mPa·s or more, and the method for producing the raw material pulp comprises a cooking step of cooking wood, and the concentration of active alkali in the cooking step is 10% by mass or more and 30% by mass or less.

[0025] Effects of the Invention

[0026] According to the present invention, there can be provided kraft paper which can be produced at low cost and has excellent strength such as tear strength and tensile strength. DETAILED DESCRIPTION

[0027] The preferred embodiment of the present invention is described below. It should be noted that, in this specification, "X to Y" indicating a range means "above X and below Y". In addition, in this specification, unless otherwise specified, operations and measurements of physical properties are carried out under the conditions of room temperature (20 to 25°C) / relative humidity of 40 to 55%. In this specification, the "longitudinal direction" of kraft paper refers to the direction corresponding to the papermaking direction (MD direction) of kraft paper. In addition, the "transverse direction" of kraft paper refers to the direction orthogonal to the "longitudinal direction" of kraft paper, which is the direction corresponding to the width direction (CD direction).

[0028] [Kraft paper]

[0029] The kraft paper of the present embodiment (hereinafter also referred to as kraft paper) is kraft paper containing broadleaf kraft pulp as raw material pulp, the content of broadleaf kraft pulp in the aforementioned raw material pulp is 90% by mass or more, the kappa number of the pulp after dissociation is 9.5 or more, and the pulp viscosity of the kraft paper measured according to TAPPI T 230 is 15 mPa·s or more.

[0030] The kraft paper of the present embodiment is composed of raw material pulp containing 90% or more of broadleaf kraft pulp by mass, and therefore, it can be manufactured cheaply compared to the kraft paper composed of raw material pulp with coniferous kraft pulp as the main component used in the past from the viewpoint of the strength required by the kraft paper. If it is composed of raw material pulp containing broadleaf kraft pulp, there is a tendency for the strength of the kraft paper to decrease. However, even in the case where the kraft paper is composed of raw material pulp containing 90% or more of broadleaf kraft pulp by mass, by setting the carba value of the pulp after re-dissociation to a specific value or more, and setting the pulp viscosity of the kraft paper to a specific value or more, it is also possible to make the strength such as tear strength required by the kraft paper excellent. The mechanism for exerting this effect is still uncertain, but it can be speculated as follows. It can be considered that by moderately and not excessively cooking the small pieces of wood (wood small pieces) used as the material of the raw material pulp, the collapse of the pulp (cellulose) is suppressed, and as a result, the strength such as tear strength required by the kraft paper is excellent. It should be noted that the effects of the present invention are not limited to the above-mentioned mechanism.

[0031] <Raw material pulp>

[0032] The kraft paper of the present embodiment is made of raw material pulp containing hardwood kraft pulp. Specifically, the content of hardwood kraft pulp in the raw material pulp is 90 mass % or more, preferably 92 mass % or more, more preferably 94 mass % or more, and is 100 mass % or less.

[0033] As the raw material of hardwood kraft pulp, from the viewpoint of easily adjusting the kappa number of the pulp after re-dissociation and the pulp viscosity of kraft paper to the desired range, at least one selected from the group consisting of Eucalyptus and Acacia is preferred, and Eucalyptus is more preferred.

[0034] As long as the kappa number and pulp viscosity of the pulp after re-dissociation can be adjusted to the desired range, the hardwood kraft pulp may be any one of hardwood unbleached kraft pulp, hardwood semi-bleached kraft pulp and hardwood bleached kraft pulp. Among these, from the viewpoint of easily adjusting the kappa number and kraft pulp viscosity of the pulp after re-dissociation to the desired range, preferably at least one selected from the group consisting of hardwood semi-bleached kraft pulp and hardwood unbleached kraft pulp is used, and more preferably hardwood unbleached kraft pulp is used.

[0035] In addition to hardwood kraft pulp, the raw material pulp may also be hardwood kraft pulp, mechanical pulp, waste paper pulp, hemp and other herb pulps. When the raw material pulp contains pulp other than hardwood kraft pulp (preferably hardwood semi-bleached kraft pulp or hardwood unbleached kraft pulp), among these, hardwood kraft pulp is preferred, and hardwood unbleached kraft pulp is more preferred.

[0036] When conifer kraft pulp is used, the raw material of conifer kraft pulp is preferably at least one selected from the group consisting of Pseudotsuga and Pinus, and Pseudotsuga is more preferred, from the viewpoint of easily adjusting the kappa value of the pulp after re-dissociation and the pulp viscosity of kraft paper to the desired range.

[0037] <Kappa Value>

[0038] From the viewpoint of improving the strength such as tear strength required for kraft paper, the carba value of the pulp constituting kraft paper after re-disintegration (re-disintegrated pulp) is 9.5 or more, preferably 9.7 or more, and more preferably 10 or more, and from the viewpoint of pulp yield, reduction of uncooked matter, and improvement of handleability, it is preferably 50 or less, more preferably 40 or less, further preferably 30 or less, further preferably 25 or less, further preferably 22 or less, and further preferably 20 or less. The carba value of the re-disintegrated pulp is measured in accordance with JIS P 8211:2011 using as a sample pulp of kraft paper disintegrated in accordance with JIS P 8220-1:2012.

[0039] The kappa number of the pulp after re-dissociation (re-dissociated pulp) constituting kraft paper can be adjusted by adjusting the material type of the raw material pulp, the concentration of active alkali during the later cooking treatment, adjusting the time of the later cooking treatment, and adjusting the temperature of the later cooking treatment.

[0040] <Pulp Viscosity>

[0041] From the viewpoint of improving the tear strength and other strengths required for kraft paper, the pulp viscosity of kraft paper is 15 mPa·s or more, preferably 16 mPa·s or more, and more preferably 17 mPa·s or more, and from the viewpoint of workability when manufacturing kraft paper, it is preferably 120 mPa·s or less, more preferably 100 mPa·s or less, further preferably 80 mPa·s or less, further preferably 70 mPa·s or less, further preferably 60 mPa·s or less, further preferably 50 mPa·s or less, and further preferably 40 mPa·s or less. The pulp viscosity of kraft paper is measured according to TAPPI T 230.

[0042] The viscosity of kraft paper pulp can be adjusted by adjusting the material type of the raw material pulp, the concentration of active alkali during the cooking treatment described later, the time of the cooking treatment described later, and the temperature of the cooking treatment described later.

[0043] <Tear Index: Longitudinal>

[0044] From the viewpoint of effectively suppressing bag breakage when kraft paper is used for, for example, light packaging, the longitudinal tear index of kraft paper is preferably 8.0 mN·m 2 / g or more, more preferably 8.3mN·m 2 / g or more, more preferably 8.5mN·m 2 / g or more, and the upper limit is not particularly limited, but is preferably 30 mN·m 2 / g or less, more preferably 20mN·m 2 The tear index in the longitudinal direction of kraft paper is measured in accordance with JIS P 8116:2000.

[0045] <Tear Index: Horizontal>

[0046] From the viewpoint of effectively suppressing bag breakage when kraft paper is used for, for example, light packaging, the transverse tear index of kraft paper is preferably 8.8 mN·m 2 / g or more, more preferably 9.0 mN·m 2 / g or more, and the upper limit is not particularly limited, but is preferably 30 mN·m 2 / g or less, more preferably 20mN·m 2 The tear index in the transverse direction of kraft paper is measured in accordance with JIS P8116:2000.

[0047] <Basis Weight>

[0048] The basis weight of the kraft paper is not particularly limited, but is preferably 70 g / m2 from the viewpoint of strength when the kraft paper is used, for example, for light packaging. 2 More preferably 90 g / m 2 More preferably, 100 g / m 2 More preferably, 110 g / m 2 From the viewpoint of the ease of manufacturing kraft paper and the processability of kraft paper, 150 g / m 2 Below, more preferably 140g / m 2 Below, more preferably 130g / m 2 The basis weight of kraft paper was measured in accordance with JIS P 8124:2011.

[0049] <Thickness>

[0050] The thickness of kraft paper is not particularly limited, but is preferably 100 μm or more, more preferably 120 μm or more, and further preferably 140 μm or more from the viewpoint of strength when kraft paper is used for, for example, light packaging, and is preferably 200 μm or less, more preferably 180 μm or less, and further preferably 170 μm or less from the viewpoint of ease of manufacture and processability of kraft paper. The thickness of kraft paper is measured in accordance with JIS P 8118:2014.

[0051] <density>

[0052] The density of kraft paper is not particularly limited, but is preferably 0.60 g / cm2 from the viewpoint of strength when kraft paper is used, for example, for light packaging. 3 More preferably, 0.63 g / cm 3 More preferably, 0.65 g / cm 3 More preferably, 0.67 g / cm 3 More preferably, 0.70 g / cm 3 In addition, from the viewpoint of the ease of manufacturing kraft paper and the processability of kraft paper, 0.90 g / cm 3 Below, more preferably 0.85g / cm 3 The density of the kraft paper is calculated based on the basis weight and thickness of the kraft paper obtained by the above-mentioned measurement method.

[0053] <Stretching index: longitudinal direction>

[0054] From the viewpoint of effectively suppressing bag breakage when kraft paper is used for light packaging, for example, the longitudinal tensile index of kraft paper is preferably 55 N·m / g or more, more preferably 60 N·m / g or more, and further preferably 65 N·m / g or more, and the upper limit thereof is not particularly limited, but from the viewpoint of ease of manufacturing kraft paper, it is preferably 150 N·m / g or less, and more preferably 120 N·m / g or less. The longitudinal tensile index of kraft paper is measured in accordance with JIS P 8113:2006.

[0055] <Stretching index: horizontal>

[0056] From the viewpoint of effectively suppressing bag breakage when kraft paper is used for light packaging, for example, the transverse tensile index of kraft paper is preferably 25 N·m / g or more, more preferably 30 N·m / g or more, and further preferably 32 N·m / g or more, and the upper limit thereof is not particularly limited, but from the viewpoint of ease of manufacturing kraft paper, it is preferably 100 N·m / g or less, more preferably 80 N·m / g or less, and further preferably 70 N·m / g or less. The transverse tensile index of kraft paper is measured in accordance with JIS P 8113:2006.

[0057] <Rupture Index>

[0058] From the viewpoint of effectively suppressing bag breakage when kraft paper is used for, for example, light packaging, the rupture index of kraft paper is preferably 3.0 kPa·m 2 / g or more, more preferably 3.5 kPa·m 2 / g or more, and the upper limit is not particularly limited, but is preferably 10.0 kPa·m from the viewpoint of ease of production of kraft paper. 2 / g or less, more preferably 8.0 kPa·m 2 / g or less, more preferably 7.0 kPa·m 2 The bursting index of kraft paper is measured in accordance with JIS P 8112:2008.

[0059] [Manufacturing method of kraft paper]

[0060] The method for producing kraft paper of the present embodiment is a method for producing kraft paper by papermaking from raw material pulp containing broadleaf kraft pulp, wherein the content of broadleaf kraft pulp in the raw material pulp is 90% by mass or more, the kappa number of the raw material pulp is 9.5 or more, and the pulp viscosity of the raw material pulp measured according to TAPPI T 230 is 15 mPa·s or more, and the method for producing the raw material pulp comprises a cooking step of cooking wood, and the concentration of active alkali in the cooking step is 10% by mass or more and 30% by mass or less.

[0061] <Cooking process>

[0062] The steaming step is a step of steaming wood to obtain raw pulp having a kappa number of 9.5 or more and a pulp viscosity of 15 mPa·s or more by treating wood chips used as raw pulp material at an active alkali concentration of 10% by mass or more and 30% by mass or less.

[0063] The apparatus used in the cooking treatment is not particularly limited, and a general-purpose continuous cooking kettle, batch cooking kettle, etc. can be used. As the cooking method, known cooking methods such as sulfate cooking, polysulfide cooking, sodium carbonate cooking, and alkali sulfide cooking can be used. From the viewpoint of pulp quality, energy efficiency, etc., sulfate cooking is preferred.

[0064] (Raw pulp)

[0065] In the present embodiment, the wood chips used as the raw material pulp are chips containing broadleaf trees as the main component. The broadleaf trees used in the wood chips are preferably at least one selected from the group consisting of Eucalyptus and Acacia, and more preferably Eucalyptus, from the viewpoint of easily adjusting the kappa value of the raw material pulp and the pulp viscosity of the raw material pulp to the desired range.

[0066] The content of hardwood kraft pulp in the raw material pulp obtained from the wood chips is 90% by mass or more, preferably 92% by mass or more, more preferably 94% by mass or more, and 100% by mass or less. In the raw material pulp, in addition to hardwood kraft pulp (preferably hardwood semi-bleached kraft pulp or hardwood unbleached kraft pulp), kraft pulp such as conifer kraft pulp, mechanical pulp, waste paper pulp, and herb pulp such as hemp can also be used. When the raw material pulp contains pulp other than hardwood kraft pulp, among these, conifer kraft pulp is preferred, and conifer unbleached kraft pulp is more preferred.

[0067] When the raw material pulp contains conifer kraft pulp, the conifer used in the wood chips is preferably at least one selected from the group consisting of Pseudotsuga and Pinus, and more preferably Pseudotsuga, from the viewpoint of easily adjusting the kappa value of the raw material pulp and the pulp viscosity of the raw material pulp to the desired range.

[0068] <<Kappa Value>>

[0069] From the viewpoint of improving the tear strength and other strengths required for kraft paper, the carba number of the raw pulp is 9.5 or more, preferably 9.7 or more, and more preferably 10 or more. From the viewpoint of pulp yield, reduction of uncooked matter, and improvement of handleability, it is preferably 50 or less, more preferably 40 or less, further preferably 30 or less, further preferably 25 or less, further preferably 22 or less, and further preferably 20 or less. The carba number of the raw pulp is measured in accordance with JIS P 8211:2011.

[0070] Pulp viscosity

[0071] From the viewpoint of improving the tear strength and other strengths required for kraft paper, the pulp viscosity of the raw material pulp is 15 mPa·s or more, preferably 16 mPa·s or more, and more preferably 17 mPa·s or more, and from the viewpoint of workability when manufacturing kraft paper, it is preferably 120 mPa·s or less, more preferably 100 mPa·s or less, further preferably 80 mPa·s or less, further preferably 70 mPa·s or less, further preferably 60 mPa·s or less, further preferably 50 mPa·s or less, and further preferably 40 mPa·s or less. The pulp viscosity of the raw material pulp is measured in accordance with TAPPI T 230.

[0072] (Active alkali concentration)

[0073] From the viewpoint of easily adjusting the carba number of the raw pulp and the pulp viscosity of the raw pulp to the desired range, the active alkali concentration in the cooking process is 10% by mass or more, preferably 13% by mass or more, and is 30% by mass or less, preferably 27% by mass or less, and more preferably 24% by mass or less. By setting the active alkali concentration in the cooking process to 10% by mass or more, it is possible to reduce uncooked materials and improve operability. On the other hand, by setting the active alkali concentration in the cooking process to 30% by mass or less, it is possible to suppress the collapse of the pulp and improve the strength. The active alkali concentration in the cooking white liquor is the active alkali concentration relative to the wood chips (absolute dry mass) used as the material of the raw pulp, and is converted in the form of the addition rate of Na2O. Specifically, it is calculated by the following formula.

[0074] Active alkali concentration = NaOH addition rate × 0.775 + Na2S addition rate × 0.795

[0075] (Degree of Vulcanization)

[0076] The sulfidation degree of the cooking white liquor is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less. In the case of the kraft cooking method, the sulfidation degree of the cooking white liquor is determined by the percentage of Na2S relative to the active alkali expressed as Na2O, and is specifically calculated by the following formula (JIS P 0001: 1998).

[0077] Sulfidation degree (mass %) = Na2S / (NaOH+Na2S)×100

[0078] (Liquid ratio)

[0079] From the viewpoint of uniformity of pulp quality, the ratio of the mass of the cooking white liquor to the aforementioned wood chips (absolute dry mass) (liquid ratio) is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more, and from the viewpoint of production efficiency of kraft paper, it is preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less.

[0080] (Cooking temperature)

[0081] From the viewpoint of more easily adjusting the kaba value of the raw material pulp and the pulp viscosity of the raw material pulp to the desired range, the treatment temperature (cooking temperature) in the cooking process is preferably 100°C or more, more preferably 130°C or more, further preferably 150°C or more, and is preferably 250°C or less, more preferably 200°C or less, further preferably 180°C or less.

[0082] (Steaming time)

[0083] From the viewpoint of making it easier to adjust the kappa number of the raw material pulp and the pulp viscosity of the raw material pulp to the desired range, the treatment time (cooking time) in the cooking step is preferably 30 minutes or more, more preferably 1 hour or more, further preferably 1.5 hours or more, and is preferably 4 hours or less, more preferably 3 hours or less.

[0084] <Beating process>

[0085] From the viewpoint of more effectively improving the tear index of kraft paper, the raw pulp subjected to the cooking treatment is preferably subjected to a beating treatment. The beating treatment method is not particularly limited, and it is preferred that the raw pulp subjected to the cooking treatment is dispersed in water to prepare a pulp dispersion and then beated. The beating treatment method is not particularly limited, and can be carried out using a refiner such as a double-disc refiner, a single-disc refiner, or a conical refiner.

[0086] The Canadian Standard Freeness (CSF) of the raw pulp after the beating treatment is not particularly limited, but is preferably 300 mL or more, more preferably 330 mL or more, and preferably 700 mL or less, more preferably 600 mL or less, and further preferably 550 mL or less from the viewpoint of more effectively improving the tear index of kraft paper. The CSF of the raw pulp is measured in accordance with JIS P 8121-2:2012.

[0087] <Papermaking process>

[0088] The papermaking step is preferably a step of making paper from raw material pulp (pulp slurry) that has been subjected to a pulping treatment. There is no particular limitation on the papermaking method, and examples thereof include an acidic papermaking method in which papermaking is performed at a pH of about 4.5, and a neutral papermaking method in which papermaking is performed at a pH of about 6 to about 9. There is no particular limitation on the papermaking machine, and a known wet papermaking machine, such as a fourdrinier papermaking machine, a gap forming papermaking machine, a cylinder papermaking machine, a short-wire papermaking machine, etc., can be appropriately selected and used.

[0089] The method for manufacturing kraft paper of the present embodiment preferably allows known internally added chemicals to be appropriately added during the papermaking process. Examples of the internally added chemicals include sizing agents, dry paper strength enhancers, wet paper strength enhancers, yield improvers, pH adjusters, filterability improvers, water resistance agents, softeners, antistatic agents, defoamers, slime control agents, dyes, pigments, and the like.

[0090] (Sizing agent)

[0091] From the viewpoint of obtaining kraft paper with better water resistance, it is preferred to add a sizing agent to the pulp slurry. Examples of the sizing agent include various well-known sizing agents for paper such as rosin-based, alkyl ketene dimer-based, alkenyl succinic anhydride-based, maleic anhydride-based, styrene-acrylic acid-based, and styrene-acrylic acid-based sizing agents.

[0092] When a sizing agent is added to the aforementioned pulp slurry, the content of the sizing agent (calculated as solid content) is preferably 0.001 parts by mass or more, more preferably 0.01 parts by mass or more, and further preferably 0.05 parts by mass or more, and is preferably 4.0 parts by mass or less, more preferably 2.0 parts by mass or less, further preferably 1.0 parts by mass or less, and further preferably 0.5 parts by mass or less, relative to 100 parts by mass (calculated as solid content) of pulp fibers constituting the pulp slurry (raw material pulp).

[0093] When a sizing agent is added to the pulp slurry, it is preferred to further add a yield improver such as aluminum sulfate to the pulp slurry from the viewpoint of fixing the added sizing agent. When a yield improver is added to the pulp slurry, the content of the yield improver (in terms of solid content) is preferably 0.001 parts by mass or more, more preferably 0.01 parts by mass or more, further preferably 0.1 parts by mass or more, and further preferably 0.3 parts by mass or more, and is preferably 4.0 parts by mass or less, more preferably 2.0 parts by mass or less, and further preferably 1.0 parts by mass or less, relative to 100 parts by mass (in terms of solid content) of pulp fibers constituting the pulp slurry (raw pulp).

[0094] (Dry paper strength enhancer)

[0095] From the viewpoint of more effectively improving the strength of kraft paper, it is preferred to add a dry paper strength enhancer to the pulp slurry. Examples of the dry paper strength enhancer include polyacrylamide polymers, starches such as cationic starch, urea resins, polyamide-polyamine resins, polyethyleneimine, polyamines, polyvinyl alcohol, polyethylene oxide, and the like.

[0096] When a dry paper strengthening agent is added to the above-mentioned pulp slurry, the content of the dry paper strengthening agent (calculated as solid content) is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, further preferably 0.1 parts by mass or more, and further preferably 0.5 parts by mass or more, and is preferably 8.0 parts by mass or less, more preferably 7.0 parts by mass or less, further preferably 5.0 parts by mass or less, and further preferably 3.0 parts by mass or less, relative to 100 parts by mass (calculated as solid content) of pulp fibers constituting the pulp slurry (raw material pulp).

[0097] (Wet paper strength enhancer)

[0098] From the viewpoint of more effectively improving the strength of kraft paper, it is preferred to add a wet paper strength enhancer to the pulp slurry. Examples of the wet paper strength enhancer include melamine resins, urea resins, and polyamide-polyamine-epichlorohydrin resins.

[0099] When a wet paper strengthening agent is added to the aforementioned pulp slurry, the content of the wet paper strengthening agent (calculated as solid content) is preferably 0.001 parts by mass or more, more preferably 0.01 parts by mass or more, and even more preferably 0.1 parts by mass or more, and is preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, even more preferably 1.0 parts by mass or less, and even more preferably 0.5 parts by mass or less, relative to 100 parts by mass (calculated as solid content) of pulp fibers constituting the pulp slurry (raw material pulp).

[0100] <Surface treatment process>

[0101] The method for producing kraft paper of the present embodiment may include a surface treatment step of applying a chemical to the surface of the kraft paper for treatment. Chemicals used in the surface treatment step include surface sizing agents, surface paper strength agents, and the like.

[0102] Examples of the surface sizing agent include alkyl ketene dimer compounds and the like.

[0103] Examples of the surface strength agent include modified starches such as oxidized starch, enzyme-treated starch, and acid-treated starch; aqueous resins such as polyvinyl alcohol (PVA); styrene-acrylic acid copolymers, and styrene-methacrylic acid copolymers.

[0104] These may be used alone or in combination of two or more.

[0105] From the viewpoint of improving the surface strength of kraft paper, the amount of the surface sizing agent and the surface paper strength agent applied is preferably 0.01 g / m 2 More preferably 0.1 g / m 2 More preferably, 0.3 g / m 2 More preferably, 0.4 g / m 2 From the viewpoint of making the surface strength of kraft paper moderate, it is preferably 5.0 g / m 2 Below, more preferably 3.0g / m 2 Below, more preferably 1.0 g / m 2 When a surface sizing agent and a surface paper strength agent are used in combination, it is preferred that the amount of each applied is within the above range.

[0106] The method for producing kraft paper of the present embodiment includes the above-mentioned steaming step and papermaking step, preferably includes the above-mentioned steaming step, pulping step and papermaking step, and more preferably includes the above-mentioned steaming step, pulping step, papermaking step and surface treatment step.

[0107] The kraft paper of the present embodiment is excellent in strength such as tear strength required for kraft paper and can be suitably used for light packaging.

[0108] Example

[0109] Hereinafter, the effects of the present invention will be described in detail by way of examples. The materials, dosages, proportions, processing contents, processing steps, etc. shown in the following examples can be appropriately changed within the scope of the gist of the present invention. Therefore, the scope of the present invention should not be construed restrictively by the specific examples shown below. In addition, the "parts" and "%" in the examples and comparative examples represent "parts by mass" and "% by mass" respectively unless otherwise specified. In addition, the operations of the examples and comparative examples are carried out under the conditions of room temperature (20-25°C) and normal humidity (40-55%RH) unless otherwise specified.

[0110] [Measurement]

[0111] <Raw material pulp>

[0112] (Canadian Standard Freeness)

[0113] The Canadian standard freeness of raw pulp was measured in accordance with JIS P 8121-2:2012.

[0114] (Kappa value)

[0115] The kappa number of the raw material pulp is measured in accordance with JIS P 8211:2011.

[0116] (Pulp viscosity)

[0117] The pulp viscosity of the raw pulp was measured according to TAPPI T230.

[0118] <Kraft Paper>

[0119] (Kappa value)

[0120] The kappa number of the pulp constituting the kraft paper was measured in accordance with JIS P 8211:2011 using as a sample the pulp of the kraft paper dissociated in accordance with JIS P 8220-1:2012.

[0121] (Pulp viscosity)

[0122] The pulp viscosity of the pulp constituting the kraft paper was measured according to TAPPI T230.

[0123] (Basis Weight)

[0124] The basis weight of kraft paper is measured in accordance with JIS P 8124:2011.

[0125] (thickness)

[0126] The thickness of kraft paper was measured in accordance with JIS P 8118:2014.

[0127] (density)

[0128] The density of kraft paper is calculated based on the basis weight and thickness of the kraft paper obtained by the above-mentioned measurement method.

[0129] (Tear Index)

[0130] The longitudinal and transverse tear indexes of kraft paper were measured in accordance with JIS P 8116:2000.

[0131] (Stretch Index)

[0132] The longitudinal and transverse tensile indices of kraft paper were measured in accordance with JIS P 8113:2006.

[0133] (Rupture Index)

[0134] The bursting index of kraft paper was measured in accordance with JIS P 8112:2008.

[0135] (Meal rate)

[0136] As described later, after the wood chips are cooked, when removing the uncooked materials, a 10-cut flat screen is used to separate the pulp from the uncooked materials, and the ratio of the uncooked materials (absolute dry mass) to the wood chips (absolute dry mass) used in the cooking is referred to as the meal rate. Regarding the evaluation criteria, a meal rate of 10% or more is referred to as C, 3% or more and less than 10% is referred to as B, and less than 3% is referred to as A. It should be noted that meal may become a cause of dirt and paper breakage in kraft paper products, and therefore, it is usually removed by a sieve after the cooking process. A high meal rate means that the cooking conditions are mild, and pulp and paper with a high degree of cellulose polymerization and strength can be produced. On the other hand, the lower the meal rate, the higher the yield of pulp with less inclusions, the lower the burden on the screen, and the higher the productivity.

[0137] Example 1

[0138] Using eucalyptus broadleaf wood as wood chips, using cooking white liquor adjusted to a liquid ratio of 4, a sulfidation degree of 28% by mass, and an active alkali concentration of 12.0% by mass (in terms of Na2O), kraft cooking (batch cooking) was performed at a cooking temperature of 160°C for 2 hours. After kraft cooking, the black liquor was separated, and the obtained chips were defibrated using a high-concentration disintegrator. Centrifugal dehydration and water washing were repeated 3 times using a filter cloth, and then the uncooked material was removed using a sieve, and centrifugal dehydration was performed to obtain a broadleaf unbleached kraft pulp having a kappa number of 28.7 and a viscosity of 45.5 mPa·s. The broadleaf unbleached kraft pulp was beaten using a refiner to a CSF of 350 mL.

[0139] To 100 parts (solid content conversion) of the above-mentioned pulp slurry (unbleached kraft pulp of broadleaf tree 100%) after beating, 0.6 parts (solid content conversion) of aluminum sulfate, 0.2 parts (solid content conversion) of polyamide-polyamine-epichlorohydrin-based wet paper strength enhancer (PAE), 0.1 parts (solid content conversion) of polyacrylamide-based dry paper strength enhancer (PAM), 0.1 parts (solid content conversion) of alkyl ketene dimer-based sizing agent (AKD) and 1.0 parts (solid content conversion) of cationic starch were added in sequence while stirring to prepare paper stock. The above-mentioned paper stock was used for papermaking by a two-wire papermaking machine, and 0.02 g / m2 of the surface sizing agent was applied. 2 (Based on pulp, solid content), surface paper strength agent 0.8g / m 2 (Calculated relative to pulp, solid content) Kraft paper having a basis weight shown in Table 1 was obtained. Table 1 shows the measurement results.

[0140] Example 2

[0141] Kraft paper was obtained in the same manner as in Example 1 except that the active alkali concentration was set to the value shown in Table 1 to obtain a hardwood unbleached kraft pulp having a kappa number of 19.8 and a viscosity of 65.9 mPa·s. The hardwood unbleached kraft pulp was used to obtain a kraft paper having a basis weight shown in Table 1.

[0142] Example 3

[0143] Kraft paper was obtained in the same manner as in Example 1 except that the active alkali concentration was set to the value shown in Table 1 to obtain a hardwood unbleached kraft pulp having a kappa number of 13.2 and a viscosity of 30.3 mPa·s. The hardwood unbleached kraft pulp was used to obtain a kraft paper having a basis weight shown in Table 1.

[0144] Example 4

[0145] Kraft paper was obtained in the same manner as in Example 1 except that the active alkali concentration was set to the value shown in Table 1 to obtain a hardwood unbleached kraft pulp having a kappa number of 10.9 and a viscosity of 24.3 mPa·s. The hardwood unbleached kraft pulp was used to obtain a kraft paper having a basis weight shown in Table 1.

[0146] Example 5

[0147] Kraft paper was obtained in the same manner as in Example 1 except that the active alkali concentration was set to the value shown in Table 1 to obtain a hardwood unbleached kraft pulp having a kappa number of 10.6 and a viscosity of 21.2 mPa·s. The hardwood unbleached kraft pulp was used to obtain a kraft paper having a basis weight shown in Table 1.

[0148] Example 6

[0149] Kraft paper was obtained in the same manner as in Example 1 except that the active alkali concentration was set to the value shown in Table 1 to obtain a hardwood unbleached kraft pulp having a kappa number of 10.1 and a viscosity of 17.6 mPa·s. The hardwood unbleached kraft pulp was used to obtain a kraft paper having a basis weight shown in Table 1.

[0150] Example 7

[0151] Using eucalyptus broadleaf wood as wood chips, kraft cooking was performed at a cooking temperature of 160°C for 2 hours using cooking white liquor adjusted to a liquid ratio of 4, a sulfidation degree of 28% by mass, and an active alkali concentration of 19.0% (calculated as Na2O). Using Pseudo-fir coniferous wood as wood chips, kraft cooking (batch cooking method) was performed at a cooking temperature of 170°C for 2 hours using cooking white liquor adjusted to a liquid ratio of 4, a sulfidation degree of 28% by mass, and an active alkali concentration of 22.0% (calculated as Na2O). After kraft cooking, black liquor was separated, and the obtained chips were defibrated using a high-concentration disintegrator, and then centrifugal dehydration and water washing were repeated 3 times using filter cloth, and then uncooked materials were removed using a sieve, and centrifugal dehydration was performed to obtain unbleached kraft pulp. The unbleached kraft pulp was beaten using a refiner, and 950 parts (in terms of solid content) of unbleached broadleaf kraft pulp whose CSF was adjusted to 350 mL and 50 parts (in terms of solid content) of unbleached coniferous tree kraft pulp whose CSF was adjusted to 500 mL were mixed to obtain a pulp slurry having a kappa number of 14.2 and a viscosity of 30.7 mPa·s. To 100 parts (solid content conversion) of the pulp slurry (LUKP 95%, NUKP 5%), 0.6 parts (solid content conversion) of aluminum sulfate, 0.2 parts (solid content conversion) of a polyamide-polyamine-epichlorohydrin-based wet paper strength enhancer (PAE), 0.1 parts (solid content conversion) of a polyacrylamide-based dry paper strength enhancer (PAM), 0.1 parts (solid content conversion) of an alkyl ketene dimer-based sizing agent (AKD), and 1.0 parts (solid content conversion) of a cationic starch were added in order while stirring to prepare a paper stock. The paper stock was used to make paper using a two-wire papermaking machine, and 0.02 g / m2 of the surface sizing agent was applied. 2 (Based on pulp, solid content), surface paper strength agent 0.8g / m 2 (Calculated relative to pulp, solid content) Kraft paper having a basis weight shown in Table 1 was obtained. Table 1 shows the measurement results.

[0152] Comparative Example 1

[0153] Kraft paper was obtained in the same manner as in Example 1 except that the active alkali concentration was set to the value shown in Table 1 to obtain a hardwood unbleached kraft pulp having a kappa number of 8.9 and a viscosity of 11.9 mPa·s. The hardwood unbleached kraft pulp was used to obtain a kraft paper having a basis weight shown in Table 1.

[0154] Comparative Example 2

[0155] Kraft paper was obtained in the same manner as in Example 1 except that the active alkali concentration was set to the value shown in Table 1 to obtain a hardwood unbleached kraft pulp having a kappa number of 8.1 and a viscosity of 11.3 mPa·s. The hardwood unbleached kraft pulp was used to obtain a kraft paper having a basis weight shown in Table 1.

[0156] [Table 1]

[0157]

[0158] It can be seen from Table 1 that the tear index of the kraft papers of Examples 1 to 7 is particularly excellent. On the other hand, the tear index of the kraft papers of Comparative Examples 1 and 2 is particularly poor.

[0159] Industrial Applicability

[0160] The kraft paper of the present embodiment is excellent in strength such as tear strength required for kraft paper and can be suitably used for light packaging.

Claims

1. A kraft paper comprising kraft pulp of a broadleaf tree as raw material pulp, The content of hardwood kraft pulp in the raw material pulp is 90% by mass or more, The kappa number of the pulp after re-dissociation is 9.5 or more, and the viscosity of the kraft paper pulp measured according to TAPPI T 230 is 15 mPa·s or more.

2. The kraft paper according to claim 1, wherein: The kappa value of the re-dissociated pulp is less than 30, and the pulp viscosity of the kraft paper is less than 120 mPa·s.

3. The kraft paper according to claim 1 or 2, having a longitudinal tear index of 8.0 mN·m 2 / g or more, and the transverse tear index is 8.8mN·m 2 / g or above.

4. The kraft paper according to claim 1 or 2, having a basis weight of 70 g / m 2 Above and 150g / m 2 the following.

5. The kraft paper according to claim 1 or 2, having a density of 0.65 g / cm 3 Above and 0.85g / cm 3 the following.

6. The kraft paper according to claim 1 or 2, which is used for light packaging.

7. A method for producing kraft paper, comprising making paper from raw material pulp containing kraft pulp of a broadleaf tree, The content of hardwood kraft pulp in the raw material pulp is 90% by mass or more, The kappa value of the raw material pulp is 9.5 or more, and the pulp viscosity of the raw material pulp measured according to TAPPI T 230 is 15 mPa·s or more, The method for producing raw material pulp comprises a cooking step of cooking wood. The active alkali concentration in the steaming step is 10 mass % or more and 30 mass % or less.

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