Packaging base paper and its manufacturing method

Abstract

To provide a base paper for a packaging which can be correctly processed into a packaging even though being a paper-made packaging by using a packaging processor supposed to be essentially used in conventional plastic films and has excellent coating suitability and printability.SOLUTION: A base paper for a packaging containing a pulp as its main component is provided in which a relative tensile strength in its longitudinal direction is 0.09 kN / m or over, a relative tear strength in its transverse direction is 10.0 mN m2 / g or over, 50 mass% or over of the pulp comprises coniferous tree kraft pulp, and a disintegration freeness is 400-600 mlCSF.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a packaging base paper, and more specifically to a packaging base paper having excellent suitability for packaging processing, in particular, having excellent suitability for coating and printing, and excellent resistance to tearing in a packaging processing machine. [Background technology]

[0002] In recent years, the problem of plastic waste has become more serious. It is said that the world's plastic production exceeds 400 million tons per year, and among these, the amount of plastic produced in the packaging container sector is particularly large, which is the cause of plastic waste. The most commonly used plastics for packaging containers are polyethylene terephthalate (PET), which is used for beverage bottles, polyethylene (PE), which is used for laminating plastic bags and containers, and polypropylene (PP). Plastic does not decompose for a long time, and the waste turns into microplastics in the natural environment, causing serious adverse effects on the ecosystem. In particular, the pollution of the oceans is severe, and it is said that the plastic waste cannot be recovered. In the future, it will be necessary for the global environment to reduce the use of plastic.

[0003] When large-scale packaging is carried out industrially, packaging processing machines are generally used. Examples of packaging processing machines used for this purpose include so-called pillow packaging machines that process plastic film into bags and fill them with contents. Since pillow packaging machines are designed on the assumption that plastic film will be used, when the packaging material is replaced from plastic film to paper in order to reduce the use of plastic, there is a problem that the packaging paper will tear and the packaging process cannot be carried out normally. Packaging machines other than pillow packaging machines are also designed on the assumption that plastic film will be used, and have the same problem.

[0004] Kraft paper is currently in circulation for heavy-duty packaging, but because heavy-duty kraft paper has a low tensile strength ratio and high stiffness due to its low density, there is a risk of problems occurring when used with pillow packaging machines and other packaging machines that are designed to use flexible plastic films. In pillow packaging machines, bag making and packaging of the contents are carried out almost simultaneously, so if the stiffness of the package is too high, wrinkles and tears may occur during the process of forming the package into a tube.

[0005] As a conventional technique, there is a technique described in Patent Document 1, which uses bleached hardwood kraft pulp, bleached softwood kraft pulp, and unbleached softwood kraft pulp as raw material pulps, and the freeness of the bleached hardwood kraft pulp is 500mlCSF or less, the freeness of the bleached softwood kraft pulp is 660mlCSF or more, and the freeness of the unbleached softwood kraft pulp is 660mlCSF or more, but since the specific tensile strength in the longitudinal direction is weak, the paper may be cut by the packaging machine and may not be packaged properly. There is a technique described in Patent Document 2, which uses unbleached softwood kraft pulp and is manufactured by a gap former type papermaking machine, but the density is low and the suitability for coating and printing is poor. In addition, the density is low for heavy packaging applications, and the stiffness is high due to the low density, which may cause problems with packaging machines such as pillow packaging, making it unsuitable as packaging base paper. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-131922 A [Patent Document 2] JP 2014-055372 A Summary of the Invention [Problem to be solved by the invention]

[0007] The object of the present invention is to provide a packaging base paper which, although being a paper package, can be normally packaged using a packaging machine designed for use with conventional plastic films, and which has excellent suitability for coating and printing.

[0008] Another object of the present invention is to provide a method for producing packaging base paper having excellent coatability and printability.

[0009] Further objects and advantages of the present invention will become readily apparent to those skilled in the art by reading the following description. [Means for solving the problem]

[0010] In order to solve the above problems, the packaging base paper of the present invention is a packaging base paper mainly composed of pulp, and has a longitudinal tensile index of 0.09 or less. kN·m / g The transverse tear strength is 10.0 mN m or more. 2 / g or more, 50 mass % or more of the pulp is softwood kraft pulp, and the disintegration freeness is 400 to 600 ml CSF.

[0011] Here, "disintegrated freeness" refers to the value obtained by measuring the freeness (Canadian standard freeness) according to JIS P 8121-2 after disintegrating the packaging base paper according to JIS P 8220-1. Furthermore, the longitudinal direction refers to the machine direction on the papermaking machine, and the transverse direction refers to the cross direction on the papermaking machine.

[0012] By adopting such a constitution, it is possible to obtain a packaging base paper that has excellent suitability for coating and printing, and has excellent resistance to tearing in packaging processing machines.

[0013] In a preferred embodiment of the present invention, 90% by mass or more of the pulp may be softwood kraft pulp, which improves the tensile strength index in the longitudinal direction and the tear strength index in the transverse direction, thereby providing a packaging base paper with excellent resistance to tearing in packaging machines.

[0014] In a preferred embodiment of the present invention, the softwood kraft pulp may be unbleached softwood kraft pulp, which can provide a packaging base paper with excellent longitudinal tensile index and transverse tear index, and excellent resistance to tearing in a packaging machine.

[0015] In a preferred embodiment of the present invention, the density of the packaging base paper is 0.7 to 1.3 g / cm 3 It is possible to obtain a packaging base paper having better coating suitability and printability, and having better resistance to tearing in a packaging processing machine.

[0016] In a preferred embodiment of the present invention, the basis weight of the packaging base paper is 50 to 200 g / m 2 It is possible to obtain a packaging base paper having better longitudinal tensile strength index and transverse tear strength index, and thus better resistance to tearing in a packaging machine.

[0017] The present invention also provides a method for producing packaging base paper, comprising the steps of: making a pulp slurry containing 50% by mass or more of softwood kraft pulp in a cylinder paper machine; and making the pulp slurry have a freeness of 400 to 600 ml CSF and a tensile specific strength in the machine direction of 0.09 or less. kN·m / g The transverse tear strength must be 10.0 mN m or more. 2 / g or more, and the density is 0.7 to 1.3 g / cm 3 It is possible to obtain a packaging base paper having excellent tensile strength index in the longitudinal direction and tear strength index in the transverse direction, and excellent resistance to tearing in a packaging machine. Effect of the Invention

[0018] The packaging base paper of the present invention has excellent suitability for coating and printing, and has excellent resistance to tearing in packaging processing machines, so it can be suitably processed into packaging bags and can be suitably used as a base paper to replace conventional plastic packaging bags with paper packaging. [Brief description of the drawings]

[0019] [Figure 1] 1 is a table showing the composition and physical properties of packaging base paper according to examples and comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Next, the present invention will be described in detail with reference to the embodiments, but the present invention is not limited to these descriptions. Various modifications of the embodiments may be made as long as the effects of the present invention are achieved.

[0021] The packaging base paper of the present invention is mainly composed of pulp. Examples of the pulp used here include unbleached wood chemical pulp, such as softwood unbleached kraft pulp (NUKP), softwood unbleached sulfite pulp (NUSP), hardwood unbleached kraft pulp (LUKP), and hardwood unbleached sulfite pulp (LUSP), bleached wood chemical pulp, such as softwood bleached kraft pulp (NBKP), softwood bleached sulfite pulp (NBSP), hardwood bleached kraft pulp (LBKP), and hardwood bleached sulfite pulp (LBSP), and mechanical pulp, such as thermomechanical pulp (TMP), refiner ground pulp (RGP), and groundwood pulp (GP). Among these, it is preferable to use softwood kraft pulp, which is easier to improve the longitudinal tensile strength index and transverse tear strength index, and unbleached softwood kraft pulp is even more preferable because it has a relatively long fiber length and is not damaged during the bleaching process.

[0022] In the present invention, 50% by mass or more of the pulp is softwood kraft pulp, and it is more preferable that the ratio of softwood kraft pulp is 90% by mass or more. By using 50% by mass or more of softwood kraft pulp, it is possible to obtain a packaging base paper having excellent longitudinal tensile strength index and transverse tear strength index. If the ratio of softwood kraft pulp is less than 50%, the longitudinal tensile strength index and transverse tear strength index are inferior.

[0023] In the packaging base paper according to the present invention, the disintegrated freeness of the raw material pulp is adjusted to be in the range of 400 to 600 mlCSF. By setting the disintegrated freeness in this range, a packaging base paper excellent in longitudinal tensile strength index and transverse tear strength index can be obtained. It is preferable to set the disintegrated freeness in the range of 400 to 550 mlCSF, since a packaging base paper excellent in longitudinal tensile strength index can be obtained. If the disintegrated freeness of the packaging base paper is less than 400 mlCSF, the transverse tear strength index may decrease. If it exceeds 600 mlCSF, the density and air permeability may decrease, which may impair the coating suitability and printability.

[0024] The disintegrated freeness can be controlled by beating the raw pulp. There are no particular limitations on the beating method, and any beating machine such as a beater, Jordan, deluxe finer, or double disc refiner may be used alone or in combination.

[0025] The packaging base paper of the present invention has a longitudinal tensile index of 0.09 kN·m / g More than 10.0mN m of specific tear strength in the transverse direction 2 By configuring the specific tensile strength and specific tear strength to be in these ranges, a packaging base paper with excellent suitability for packaging processing, and particularly with excellent resistance to tearing in a packaging processing machine, can be obtained. In the packaging process using a packaging processing machine, there is a process in which a roll of packaging base paper is continuously processed into bags, and when the specific tensile strength is 0.09 kN·m / g If the tear strength is less than 10.0 mN m, a partial cut in the paper will occur, causing stress to concentrate in that area, resulting in a chain reaction of tears and the roll breaking, which may reduce processing efficiency. 2 If the tensile strength is less than 0.1 / g, the paper may be cut and torn in the packaging machine, resulting in reduced processing efficiency. kN·m / g More preferably, the tear strength should be 11.0 mN m or more. 2 / g or more is preferable, and 12.0 mN m 2 / g or more is more preferable.

[0026] By having both the tensile strength index and tear strength index within the range of the present invention, it is possible to obtain a packaging base paper with excellent tear resistance. In general, there is a trade-off between the tensile strength index and the tear strength index; for example, lowering the freeness of the raw pulp improves the tensile strength index but decreases the tear strength index. Also, lowering the density of the packaging base paper improves the tear strength index but decreases the tensile strength index. Examples of means for maintaining both the tensile strength index and tear strength index at a high level include appropriate control of the density, the raw pulp type and blending ratio, fiber orientation, and disintegration freeness, and these means can be appropriately combined. As an example, fiber orientation can be relatively easily controlled by using a cylinder papermaking machine.

[0027] The tear strength index can be measured according to JIS P 8116, and is the value obtained by dividing the tear strength by the basis weight. The tensile strength index can be measured according to JIS P 8113, and is the value obtained by dividing the tensile strength by the basis weight.

[0028] In the present invention, the packaging base paper has a density of 0.7 to 1.3 g / cm 3 and preferably 0.75 to 1.0 g / cm 3 It is more preferable that the density is within this range. By setting the density within this range, it becomes easier to obtain a packaging base paper having excellent tensile strength index in the longitudinal direction and tear strength index in the transverse direction. 3 If the density is less than 1.3 g / cm, the tear strength will be improved, but the stiffness will be high, which may reduce the processing efficiency in packaging machines. Also, the voids inside the packaging base paper will be very large, which may reduce the suitability for coating and printing. 3 If the density exceeds this value, the tensile strength index will improve, but the tear strength index will decrease, which may result in a decrease in processing efficiency in packaging machines. The density can be adjusted by the disintegration freeness, the type of raw pulp, the machine calendar, and the wet press.

[0029] In the present invention, the packaging base paper preferably has an air permeability in the range of 50 seconds or more. By setting it in this range, it is possible to obtain a packaging base paper with better coating suitability and printability. If the air permeability is below 50 seconds, the coating suitability and printability may deteriorate. It is necessary to impart various suitabilities to the packaging base paper depending on the contents to be packaged, and such suitabilities include, for example, water resistance, oil resistance, oxygen barrier property, water vapor barrier property, etc. As a method for imparting these suitabilities, for example, there is a method of applying a coating liquid to one or both sides of the packaging base paper, and in this case, if the air permeability or density is too low, the voids inside the packaging base paper become very large, so that the coating liquid is excessively absorbed into the voids, and the desired suitability may not be obtained.

[0030] Packaging base paper may be printed on one or both sides to give it various properties and to add design to the product. If the air permeability or density is too low, the ink may be absorbed too much into the voids inside the packaging base paper, causing the printed image to become unclear. Air permeability can be measured using an Oken air permeability and smoothness tester in accordance with JIS P 8117:2009.

[0031] The amount of coating liquid applied to packaging base paper is 3 to 20 g / m2 in terms of solid content per side of the base paper. 2It is preferable that the coating liquid is applied by any of various known coating methods such as a coater method and a spray method. For example, the coating liquid can be applied by an off-machine coater or an on-machine coater using a coating method such as a blade coater, a roll coater, a reverse roll coater, an air knife coater, a die coater, a bar coater, a gravure coater, a curtain coater, a champ flex coater, a lip coater, a rod coater, a gate roll coater, a spray coater, a size press coater, or a film transfer coater. The drying method after coating is also not particularly limited, and air drying methods such as hot air drying using a multi-cylinder cylinder dryer method, a Yankee dryer method, or an air dryer, or a radiation drying method such as an infrared device can be used. Among these, the hot air drying method is preferable because the coated paper coated with the coating liquid can be floated and dried with hot air, and therefore equipment such as rolls can be dried without being soiled with binder.

[0032] In the present invention, the packaging base paper has a basis weight of 50 to 200 g / cm 3 The range is preferably 60 to 120 g / m 2 It is more preferable if the weight is 50g / m 2 If the weight is less than this, it may break in the packaging machine. 2 If it exceeds this value, the stiffness will be too high and there is a risk that it will not be possible to process it properly in the packaging machine.

[0033] The packaging base paper used in the present invention can be obtained by papermaking using a pulp slurry. The pulp slurry can contain various papermaking materials such as aluminum sulfate, fillers, sizing agents, paper strength agents, retention aids, coloring dyes, coloring pigments, bulking agents, etc., within the scope of not impairing the intended effects of the present invention. As the filler, one or more of known fillers such as hydrated silicic acid, white carbon, talc, kaolin, clay, calcium carbonate, titanium oxide, aluminosilicate, calcined clay, barium sulfate, synthetic resin fillers, etc. can be used.

[0034] When using a sizing agent in the packaging base paper, one or more of paraffin wax-based sizing agents, microcrystalline wax-based sizing agents, carnauba (carnauba wax)-based sizing agents, alkyl ketene dimer wax-based sizing agents, rosin-based sizing agents, alkenyl succinic anhydride sizing agents, styrene acrylic-based sizing agents, etc. can be used.

[0035] Furthermore, when a paper strength agent is used in the packaging base paper, one or more of the following can be used: starch, cationized starch, other modified starches, polyacrylamide resins, urea-formaldehyde resins, melamine-formaldehyde resins, vegetable gums, polyvinyl alcohol, modified polyvinyl alcohol, rubber-based latex, polyethylene oxide, polyamide resins, etc. that promote improvement of dry paper strength; and urea-formaldehyde resins, melamine-formaldehyde resins, polyamide-epichlorohydrin-based epoxy resins, etc. that promote improvement of wet paper strength.

[0036] In the present invention, the method of making the packaging base paper is not particularly limited, and the paper can be made in a single layer or in combination using a conventionally known papermaking machine such as a cylinder papermaking machine, a short wire papermaking machine, a fourdrinier papermaking machine, or a combination of these papermaking machines. The drying method of the papermaking machine is not particularly limited, and a multi-cylinder dryer system, a Yankee dryer system, an air drying system represented by hot air drying, a radiation drying system represented by an infrared device, etc. can be used. Among them, the multi-cylinder dryer system or the Yankee dryer system is preferred, and the Yankee dryer system is particularly preferred. By drying using the Yankee dryer system, the mirror surface of the Yankee dryer is transferred to one side of the base paper, resulting in a one-sided gloss paper, and a packaging base paper with better coating suitability and printability can be obtained. By attaching a wet paper to the Yankee dryer and drying it, so-called tension drying, it is possible to prevent a decrease in tear strength, and by achieving both tear strength and tensile strength, a packaging base paper with better packaging processing suitability in a packaging processing machine can be obtained. A cylinder papermaking machine creates a fiber sheet by spinning the paper raw material in a tank with a cylindrical wire. Compared to a Fourdrinier papermaking machine, in which the paper raw material is loaded onto the wire at high speed, this machine produces a higher level of formation (uniformity) and makes it easier to control the fiber orientation. This makes it possible to achieve both tear strength and tensile strength, resulting in packaging base paper that is more suitable for packaging processing on packaging machines. EXAMPLES

[0037] Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. In the examples, "parts" and "%" respectively indicate parts by mass and % by mass calculated on a solid content basis unless otherwise specified. In addition, for aluminum sulfate, the solid content parts are expressed as aluminum sulfate 16-hydrate.

[0038] Example 1 As the raw pulp, 90% softwood unbleached kraft pulp (N-UKP) and 10% softwood bleached kraft pulp (N-BKP) were dispersed in water and beaten to obtain a pulp slurry. 2.5 parts of aluminum sulfate (manufactured by Techno Hokuetsu Co., Ltd.) and 0.35 parts of a rosin-based sizing material (product name: AL-1300, manufactured by Seiko PMC Co., Ltd.) were added to 100 parts of the pulp slurry to obtain a paper stock, which was then used to make paper on a cylinder paper machine and dried with a Yankee dryer to obtain a paper with a basis weight of 100 g / m. 2 , density 0.81g / cm 3 The resulting packaging base paper had a one-sided gloss and a freeness of 475 ml CSF.

[0039] Example 2 In Example 1, the ratio of raw pulp was 75% softwood unbleached kraft pulp (N-UKP) and 25% softwood bleached kraft pulp (N-BKP), and the disintegrated freeness was 410 ml CSF, and the same procedure was followed to obtain packaging base paper.

[0040] Example 3 In Example 1, the ratio of raw pulp was 55% unbleached softwood kraft pulp (N-UKP), 20% bleached softwood kraft pulp (N-BKP), and 25% bleached hardwood kraft pulp (L-BKP), and the disintegrated freeness was 410 ml CSF, but otherwise the same procedure was followed to obtain packaging base paper.

[0041] Example 4 In Example 1, density 0.72 g / cm 3 A packaging base paper was obtained in the same manner as in Example 1, except that the disintegrated freeness was set to 550 ml CSF.

[0042] Example 5 In Example 1, density 0.98 g / cm 3 A packaging base paper was obtained in the same manner as in Example 1, except that the disintegrated freeness was set to 410 ml CSF.

[0043] Example 6 A packaging base paper was obtained in the same manner as in Example 1, except that double-glazed packaging base paper was obtained by drying in a multi-cylinder dryer.

[0044] Example 7 In Example 1, the raw pulp was 100% softwood bleached kraft pulp (N-BKP) and had a density of 0.83 g / cm 3 A packaging base paper was obtained in the same manner as in Example 1, except that the disintegrated freeness was set to 420 ml CSF.

[0045] Example 8 In Example 1, the raw pulp was 55% softwood bleached kraft pulp (N-BKP) and 45% hardwood bleached kraft pulp (L-BKP), and had a density of 0.85 g / cm 3 A packaging base paper was obtained in the same manner as in Example 1, except that the above-mentioned procedure was followed.

[0046] Comparative Example 1 In Example 1, the raw pulp was 100% softwood unbleached kraft pulp (N-UKP), the papermaking was changed from a cylinder papermaking machine to a Fourdrinier papermaking machine, and the density was 0.78 g / cm 3 A packaging base paper was obtained in the same manner as in Example 1, except that the disintegrated freeness was set to 350 ml CSF.

[0047] Comparative Example 2 In Example 1, density 0.65 g / cm 3 A packaging base paper was obtained in the same manner as in Example 1, except that the disintegrated freeness was set to 410 ml CSF.

[0048] Comparative Example 3 In Example 1, the raw pulp was made up of 0% softwood unbleached kraft pulp (N-UKP), 10% softwood bleached kraft pulp (N-BKP), and 90% hardwood bleached kraft pulp (L-BKP), with a density of 0.74 g / cm 3 A packaging base paper was obtained in the same manner as in Example 1, except that the disintegrated freeness was set to 450 ml CSF and papermaking was changed from a cylinder papermaking machine to a Fourdrinier papermaking machine.

[0049] The resulting packaging base paper was evaluated by the methods described below, and the results are shown in Table 1.

[0050] <Deflaking freeness of packaging base paper> The packaging base paper was disintegrated in accordance with JIS P 8220-1 "Pulp - Disintegration methods - Part 1: Disintegration of chemical pulp", and then the disintegrated freeness (mlCSF) of the packaging base paper was measured in accordance with JIS P 8121-2 "Pulp - Testing methods for freeness - Part 2: Canadian standard freeness method".

[0051] <Density of packaging base paper> The density of paper (g / cm3) was measured according to JIS P 8118 "Paper and paperboard - Test method for thickness, density and specific volume" 3 ) was measured.

[0052] <Tensile strength of packaging base paper> The tensile strength ratio ( kN·m / g ) was measured.

[0053] <Specific tear strength of packaging base paper> The specific tear strength (mN m) in the transverse direction (Y) of the paper was measured according to JIS P 8116 "Paper - Tear strength test method - Elmendorf type tear tester method". 2 / g) was measured.

[0054] <Coating suitability> A water-based acrylic resin (Henkel, AQUENCE BC-900F, diluted to 30% solids) was applied to one side of the packaging base paper at a dry coating weight of 5 g / m 2 The kit oil resistance was measured using paper prepared by coating with a Mayer bar so that the oil resistance was as follows: 120°C, 30 seconds in a hot air dryer. The kit oil resistance was measured according to TAPPI T-559cm-02 (oil-resistant paper kit method), and the coated surface of the water-based acrylic resin coating liquid was evaluated. The higher the value (kit value), the higher the oil resistance. A value of 5 or more is considered a practical level. ◯: The kit oil resistance is 5 to 12, the performance of the coating liquid is exhibited, and the coating suitability is satisfactory for practical use. ×: The kit oil resistance is 4 or less, and the performance of the coating liquid is not exhibited, so that the coating suitability is difficult to put into practical use.

[0055] The packaging base papers obtained in Examples 1 to 8 had a tensile strength ratio in the longitudinal direction of 0.09. kN·m / g The transverse tear strength is 10.0 mN m or more. 2 / g or more, it is expected to have the effect of being able to be packaged without tearing in a pillow packaging machine, for example, compared to the packaging base papers of Comparative Examples 1 to 3. The packaging base paper obtained in Comparative Example 1 was inferior in specific tear strength. This is thought to be due to the fact that the paper was made using a Fourdrinier papermaking machine. The packaging base paper obtained in Comparative Example 2 was inferior in specific tensile strength and coating suitability. This is thought to be due to the fact that the disintegration freeness was greater than 600 ml CSF. The packaging base paper obtained in Comparative Example 3 was inferior in specific tensile strength and specific tear strength. This is thought to be due to the fact that the blending ratio of softwood kraft pulp was low.

Claims

1. A packaging base paper mainly composed of pulp, having a longitudinal tensile strength index of 0.09 kN·m / g or more and a transverse tear strength index of 10.0 mN·m 2 / g or more, 50 mass % or more of the pulp is softwood kraft pulp, the disintegrated freeness is 400 to 600 ml CSF, and the density is 0.70 to 1.30 g / cm 3 .

2. 2. The packaging base paper according to claim 1, characterized in that 90% by mass or more of the pulp is softwood kraft pulp.

3. 3. The packaging base paper according to claim 1, wherein the softwood kraft pulp is unbleached softwood kraft pulp.

4. 4. The packaging base paper according to claim 1, wherein the packaging base paper has a one-sided gloss.

5. The packaging base paper has a basis weight of 50 to 200 g / m 2 The packaging base paper according to any one of claims 1 to 4, characterized in that

6. The present invention comprises a step of making paper from a pulp slurry containing 50% by mass or more of softwood kraft pulp using a cylinder paper machine, the pulp slurry having a disintegration freeness of 400 to 600 ml CSF, a longitudinal tensile strength index of 0.09 kN·m / g or more, and a transverse tear strength index of 10.0 mN·m. 2 / g or more, and the density is 0.70 to 1.30 g / cm 3 A method for producing packaging base paper, comprising the steps of:

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