Packaging base paper

Abstract

To provide a packaging base paper which is resistant to tearing even when folded and is resistant to tearing even when it comes into contact with a sharp object or a protruding object.SOLUTION: A problem of the present invention is solved by a packaging base paper made of a base paper mainly composed of pulp, in which 70 mass% or more of the pulp is softwood pulp, the macerated freeness is 440 to 690 ml (CSF), the formation index measured by the total β-ray ground is 1 or less, and a metal salt of carboxymethylcellulose is applied to at least one surface of the base paper.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to packaging base paper, and more particularly to packaging base paper that is resistant to tearing even when folded, and resistant to tearing even when in contact with sharp objects or protrusions. [Background technology]

[0002] In recent years, the plastic waste problem has become increasingly serious. Global plastic production is said to exceed 400 million tons per year, with the packaging sector accounting for a particularly large portion and being the main cause of plastic waste. The most commonly used plastics for packaging are polyethylene terephthalate (PET), used in beverage bottles, and polyethylene (PE) and polypropylene (PP), used in shopping bags and container laminations. Plastics do not decompose semi-permanently, and their waste breaks down into microplastics in the natural environment, causing serious damage to ecosystems. In particular, marine pollution by microplastics is severe, and it is said that this plastic waste is impossible to recover. Reducing plastic use in the future is necessary for the global environment.

[0003] In response to this problem, there is a growing movement to replace plastic packaging with paper packaging. For example, for airtight packaging, various products are available that use a paper base with a laminate or heat-seal layer. However, paper is more prone to bending than plastic, so if its bending strength is insufficient, it can easily tear at the folds. Furthermore, it is susceptible to punctures and tears from contact with sharp objects or protrusions during distribution. When such problems occur, the contents can leak, making it unsuitable as an airtight container.

[0004] To avoid these problems, it is necessary to increase the strength of the paper, particularly its folding strength and resistance to contact with sharp objects and protrusions. However, no technology to enhance the aforementioned resistance has been reported to date.

[0005] As a technique for imparting strength to a paper substrate, Patent Document 1 proposes a packaging paper characterized by the addition of 0.01 to 3.0% by mass of carboxymethylcellulose with a substitution degree of 0.3 to 0.6 in order to obtain excellent sizing properties and paper strength in both wet and dry conditions. Furthermore, Patent Document 2 proposes an impregnated paper in which an impregnation resin is made up of an acrylic acid ester copolymer, characterized by containing 75 to 98% by mass of constituent units derived from 10 to 100% by mass of methyl acrylate and 0 to 90% by mass of methyl methacrylate and / or ethyl acrylate, and 2 to 15% by mass of constituent units derived from one or more monomers selected from (meth)acrylamide, N-alkyl substituted derivatives of (meth)acrylamide and (meth)acrylic acid, and having a glass transition temperature (Tg) of -30 to +30°C, in order to obtain excellent internal bonding strength and folding strength. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2003-027399 [Patent Document 2] Japanese Patent Publication No. 2005-281431 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, the packaging paper described in Patent Document 1 had problems such as low resistance to contact with sharp objects and protrusions (puncture strength), making it prone to holes and tears during distribution. Furthermore, the invention described in Patent Document 2 required a large amount of resin impregnation to obtain excellent strength, resulting in the problem of excessive plastic usage.

[0008] This invention was made in view of these problems, and aims to provide a packaging base paper that has high strength against bending, excellent resistance to contact with sharp objects and protrusions, and maintains strength that prevents tearing even during distribution after the contents have been packaged. [Means for solving the problem]

[0009] The packaging base paper of the present invention is characterized by comprising a base paper mainly composed of pulp, wherein 70% or more by mass of the pulp is softwood pulp (hereinafter also referred to as "N pulp"), and the disintegration-freeness of the packaging base paper is 440 to 690 ml (CSF). Furthermore, the present invention is characterized by having at least more of the following four features: A metal salt of carboxymethylcellulose, preferably a sodium salt of carboxymethylcellulose (sodium carboxymethylcellulose), is coated on at least one surface of the base paper (item A). Furthermore, the present invention has a form index of 1 or less as measured by β-ray base total (item B), contains polyacrylamide resin (item C), and has a density of 0.55 to 0.90 g / cm³. 3 The present invention is characterized by having (item D). If the packaging paper of the present invention has two or more of the items A to D, it is possible to obtain a sealed container that has high resistance to contact with sharp objects and protrusions (puncture strength) and is difficult to tear even after the contents have been packaged. In this invention, the term "sealed container" includes not only relatively airtight containers such as retort pouches for food, but also containers that allow gas to permeate but prevent solid or liquid foreign matter from entering under normal handling, transport, or storage conditions, thereby preventing loss, efflorescence, deliquescence, or evaporation of the contents.

[0010] The packaging base paper of the present invention preferably contains a paper strength enhancer and / or a sizing agent. The packaging base paper of the present invention may further contain a sizing agent. With such a configuration, carboxymethylcellulose is more easily distributed on the surface of the base paper, and a packaging base paper with higher puncture strength can be obtained. The packaging base paper of the present invention may also contain a paper strength enhancer. This allows for the production of a packaging base paper with high puncture strength. The paper strength enhancer may be a polyacrylamide resin or a material other than a polyacrylamide resin.

[0011] Furthermore, the packaging base paper of the present invention has a coating amount of the carboxymethylcellulose metal salt equivalent to 0.1 to 1.2 g / m² of solid content per side of the base paper. 2 This may also be the case. A packaging base paper with higher puncture resistance can be obtained. Furthermore, the packaging base paper of the present invention may also contain a sizing agent. With such a configuration, carboxymethylcellulose is more easily distributed on the surface of the base paper, and a packaging base paper with higher puncture resistance can be obtained.

[0012] Furthermore, the packaging base paper of the present invention may be made of two or more layers of laminated paper. With such a configuration, it is easier to produce a base paper with good formability, and a packaging base paper with higher puncture resistance can be obtained. Furthermore, the packaging base paper of the present invention may also contain a sizing agent. With such a configuration, a packaging base paper with even higher puncture resistance can be obtained. In addition, the basis weight of the packaging base paper of the present invention is 50 to 150 g / m². 2 It is desirable that this be the case. This makes it possible to obtain packaging paper with high puncture resistance. The packaging paper of the present invention has a puncture resistance of 0.087 N / g / m². 2 Preferably 0.095 N / g / m³ 2 More precisely, 0.100 N / g / m³ 2 It is desirable that the packaging paper has the above puncture strength per unit basis weight. Sealed containers made from such packaging paper are less likely to tear even when subjected to impacts during distribution after the contents have been packaged, making them suitable containers for storage and transportation, and are particularly suitable as containers for liquids and powders. Here, the puncture strength according to the present invention is the strength specified in "7.5 Puncture Strength Test" of "JIS Z 1707:2019 General Rules for Plastic Films for Food Packaging", and the puncture strength per unit basis weight is obtained by dividing the said puncture strength by the basis weight in grams.

[0013] Furthermore, the packaging base paper of the present invention may contain a polyacrylamide resin content of 0.1 to 0.9% by mass relative to the pulp in the base paper. With such a configuration, a packaging base paper with higher puncture resistance can be obtained. Furthermore, the packaging base paper of the present invention may have a mass-average molecular weight of 350,000 to 3,700,000 of the polyacrylamide resin. With such a configuration, a packaging base paper with higher puncture resistance can be obtained.

[0014] Furthermore, in the method for producing the packaging base paper of the present invention, a pulp slurry is prepared in which 70% by mass or more of the pulp is softwood pulp. Then, the concentration of the raw material at the paper machine inlet (raw material concentration) is set to 0.1 to 0.9% by mass, and paper is made using a paper machine. After that, the obtained base paper is impregnated with an aqueous carboxymethylcellulose solution and dried to produce the packaging base paper of the present invention having a disintegration freeness of 440 to 690 ml (CSF).

[0015] Furthermore, in the method for producing the packaging base paper of the present invention, a pulp slurry is prepared in which 70% by mass or more of the pulp is softwood pulp. Then, a raw material slurry containing 0.1 to 0.9 parts by mass of polyacrylamide resin per 100 parts by mass of the pulp slurry is prepared. Paper is then made using the obtained raw material slurry in a paper machine. After that, the obtained base paper is impregnated with an aqueous carboxymethylcellulose solution and dried to produce the packaging base paper of the present invention having a disintegration-freeness of 440 to 690 ml (CSF).

[0016] Furthermore, in the method for producing the packaging base paper of the present invention, a pulp slurry is prepared in which 70% by mass or more of the pulp is softwood pulp. Then, a raw material slurry containing 0.1 to 0.9 parts by mass of polyacrylamide resin per 100 parts by mass of the pulp slurry is prepared. Using the obtained raw material slurry, the concentration of the raw material at the paper machine inlet (raw material concentration) is set to 0.1 to 0.9% by mass, and paper is made using a paper machine to produce the packaging base paper of the present invention having a disintegration freeness of 440 to 690 ml (CSF).

[0017] Furthermore, in the method for producing the packaging base paper of the present invention, a pulp slurry is prepared in which 70% by mass or more of the pulp is softwood pulp. Then, a raw material slurry containing 0.1 to 0.9 parts by mass of polyacrylamide resin per 100 parts by mass of the pulp slurry is prepared. Using the obtained raw material slurry, paper is made using a paper machine with a raw material concentration at the paper machine inlet (raw material concentration) of 0.1 to 0.9% by mass. After that, the obtained base paper is impregnated with an aqueous carboxymethylcellulose solution and dried to produce the packaging base paper of the present invention having a disintegration freeness of 440 to 690 ml (CSF).

[0018] Furthermore, the method for manufacturing packaging base paper of the present invention preferably includes a step of calendering the dried packaging base paper at a linear pressure of 10 to 100 kg / cm and / or with a nip count of 1 to 3 nip. [Effects of the Invention]

[0019] The packaging paper of the present invention not only has excellent tensile strength and is tear-resistant, but also has high strength against bending and high puncture strength, for example, a puncture strength of 0.087 N / g / m² per unit basis weight. 2 Because of its high properties, it offers excellent resistance to impacts during distribution after packaging the contents, making it suitable for use as a sealed container such as a packaging bag. It can also be suitably used as a base paper to replace some or all of conventional plastic packaging with paper packaging. [Modes for carrying out the invention]

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

[0021] The packaging base paper used in the present invention is mainly composed of pulp. Examples of pulp used here include unbleached wood chemical pulps such as unbleached hardwood kraft pulp (LUKP), unbleached softwood kraft pulp (NUKP), unbleached hardwood sulfite pulp (LUSP), and unbleached softwood sulfite pulp (NUSP); bleached wood chemical pulps such as bleached hardwood kraft pulp (LBKP), bleached softwood kraft pulp (NBKP), bleached hardwood sulfite pulp (LBSP), and bleached softwood sulfite pulp (NBSP); and mechanical pulps such as thermomechanical pulp (TMP), refiner ground pulp (RGP), and crushed wood pulp (GP). The proportion of pulp in the packaging base paper of the present invention is not particularly limited, but it is preferably 90% by mass or more, for example, 90 to 99% by mass of the packaging base paper. While it is possible to reduce the proportion of pulp by adding fillers and other materials, this is undesirable because it also leads to a decrease in the paper's various strengths.

[0022] In the present invention, 70% by mass or more of the pulp is softwood pulp. Preferably, it is 75% by mass or more, 80% by mass or more, and more preferably 85% by mass or more. For example, it is preferable that softwood pulp make up 70-100% by mass of the total pulp, more preferably 75-100% by mass, 80-100% by mass, 85-100% by mass, 90-100% by mass, for example, 95-100% by mass. If pulp other than softwood pulp is used, hardwood pulp is preferred from the viewpoint of cost, etc., and for example, bleached hardwood kraft pulp (LBKP) is preferred. For example, it is sufficient to use pulp containing 70-100% by mass of softwood pulp and 30-0% by mass of hardwood pulp in total pulp, or even pulp containing 75-100% by mass of softwood pulp and 25-0% by mass of hardwood pulp in total pulp, pulp containing 80-100% by mass of softwood pulp and 20-0% by mass of hardwood pulp in total pulp, pulp containing 85-100% by mass of softwood pulp and 15-0% by mass of hardwood pulp in total pulp, pulp containing 90-100% by mass of softwood pulp and 10-0% by mass of hardwood pulp in total pulp, or pulp containing 95-100% by mass of softwood pulp and 5-0% by mass of hardwood pulp in total pulp. While there are no particular limitations on the type of softwood pulp used, NUKP, NUSP, NBKP, or NBSP can be used. Among these, NUKP is more preferable because it allows for better improvement in strength properties such as bending strength. If the proportion of softwood pulp in the total pulp is less than 70% by mass, it becomes difficult to satisfy the required strength against bending, and the proportion of long-fiber pulp in the paper decreases, making it impossible to obtain sufficient puncture strength.

[0023] In this invention, the disintegration freeness of the packaging base paper is set to 440-690 ml (CSF). Preferably, it is 500-670 ml (CSF), and more preferably, 530-650 ml (CSF). By setting the disintegration freeness of the packaging base paper within this range, with 70% or more by mass of the total pulp in the base paper being softwood pulp, the puncture strength can be further improved. Before coating with the metal salt of carboxymethylcellulose, the puncture strength of the base paper tends to decrease as the disintegration freeness value decreases, for example, below 500 ml (CSF). This is a different trend from various strengths such as tensile strength, which improve as fibrillation progresses to a certain extent. Therefore, it is difficult to adjust the balance between these strengths and puncture strength solely by the pulp freeness, but this can be solved by coating with the metal salt of carboxymethylcellulose. In other words, even with base paper having a relatively low disintegration-freeness of 440-530 ml (CSF), puncture strength can be improved by coating it with a metal salt of carboxymethylcellulose, making it easy to balance with other strengths such as tensile strength and tear strength. The effect of coating with a metal salt of carboxymethylcellulose on improving puncture strength tends to be greater as the disintegration-freeness decreases (the lower the puncture strength of the base paper before coating with carboxymethylcellulose), but it can also be observed in the range of 531-690 ml, where the disintegration-freeness is relatively high. If the disintegration-freeness of the packaging paper is less than 440 ml (CSF), the pulp fibrillation may have progressed too much, resulting in little improvement in puncture strength. Conversely, if the disintegration-freeness exceeds 690 ml (CSF), the pulp fibrillation is insufficient, resulting in little improvement in puncture strength. Here, disintegration freeness refers to the Canadian Standard Freeness (Canadian Standard Pulp Dilution Rate) value measured according to the method of JIS P 8121-2:2012 using a pulp slurry obtained by disintegration according to the method of JIS P 8220-1:2012. In addition, examples of metal salts of carboxymethylcellulose used in this invention include sodium salt, lithium salt, potassium salt, magnesium salt, and calcium salt, but sodium salt is preferred.Although metal salts of carboxymethylcellulose are generally referred to as carboxymethylcellulose, in this specification, metal salts of carboxymethylcellulose will also be referred to as "carboxymethylcellulose" or "CMC," and when it is necessary to specify the metal species of the metal salt, it will be indicated as sodium carboxymethylcellulose, etc.

[0024] The method of beating the raw pulp is not particularly limited, 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 uses the pulp described above and is further characterized by having at least several of the following four items. Specifically, at least one surface of the base paper is coated with a metal salt of carboxymethylcellulose, preferably a sodium salt of carboxymethylcellulose (sodium carboxymethylcellulose) (item A). Furthermore, the present invention has a form index of 1 or less as measured by β-ray base total (item B), contains a polyacrylamide resin (item C), and has a density of 0.55 to 0.90 g / cm³. 3 The present invention is characterized by (item D). If the packaging paper of the present invention has two or more of the features of items A to D, it is possible to obtain a sealed container that has high resistance to contact with sharp objects and protrusions (puncture strength) and is less likely to tear even after the contents have been packaged. Any combination of items A to D is sufficient as long as there are two or more items, and each of these items has the effect of improving resistance to contact with sharp objects and protrusions (puncture strength). The puncture strength improvement effects of each of these items do not hinder each other, and the puncture strength can be improved additively by combining more than two of items A, B, C, and D. In other words, even if the packaging paper of the present invention has two or more of items A, B, C, and D, it will have sufficient puncture strength, but if the packaging paper has three or more, or even four or more, of items A, B, C, and D, a packaging paper with even better puncture strength can be obtained.

[0026] That is, the embodiments of the packaging paper of the present invention include at least the following forms. As one embodiment of the present invention, there is provided a packaging base paper obtained by combining items A and B, which is composed of a base paper containing pulp as a main component, wherein 70% by mass or more of the pulp is softwood pulp, the defibration freeness is 440 to 690 ml (CSF), the formation index measured by a β-ray formation tester is 1 or less, and at least one surface of the base paper is coated with a metal salt of carboxymethyl cellulose.

[0027] As one embodiment of the present invention, there is provided a packaging base paper obtained by combining items A and C, which is composed of a base paper containing pulp as a main component, wherein 70% by mass or more of the pulp is softwood pulp, the defibration freeness is 440 to 690 ml (CSF), the base paper contains a polyacrylamide-based resin, and at least one surface of the base paper is coated with a metal salt of carboxymethyl cellulose.

[0028] As one embodiment of the present invention, there is provided a packaging base paper obtained by combining items A and D, which is composed of a base paper containing pulp as a main component, wherein 70% by mass or more of the pulp is softwood pulp, the defibration freeness is 440 to 690 ml (CSF), and the density is 0.55 to 0.90 g / cm 3 , and at least one surface of the base paper is coated with a metal salt of carboxymethyl cellulose.

[0029] As one embodiment of the present invention, there is provided a packaging base paper obtained by combining items B and C, which is composed of a base paper containing pulp as a main component, wherein 70% by mass or more of the pulp is softwood pulp, the defibration freeness is 440 to 690 ml (CSF), the formation index measured by a β-ray formation tester is 1 or less, and the base paper contains a polyacrylamide-based resin.

[0030] One embodiment of the present invention combines items B and D to form a base paper mainly composed of pulp, wherein 70% or more of the pulp is softwood pulp, the disintegration-freeness is 440-690 ml (CSF), the form index measured by β-ray total is 1 or less, and the density is 0.55-0.90 g / cm³. 3 This packaging paper is characterized by the following features.

[0031] One embodiment of the present invention combines items C and D to provide a base paper mainly composed of pulp, wherein 70% or more of the pulp is softwood pulp, the disintegration-freeness is 440-690 ml (CSF), it contains polyacrylamide resin, and the density is 0.55-0.90 g / cm³. 3 This packaging paper is characterized by the following features.

[0032] Furthermore, it is even more preferable to have a packaging base paper of the present invention that has three or more features from items A to D. That is, it is possible to obtain a sealed container that is even more resistant to contact with sharp objects and protrusions (puncture strength) and is less likely to tear even after the contents have been packaged. One embodiment of the present invention is a packaging base paper that combines items A, B, and C, and is made of a base paper mainly composed of pulp, in which 70% or more by mass of the pulp is softwood pulp, the disintegration freeness is 440 to 690 ml (CSF), the form index measured by β-ray base total is 1 or less, contains a polyacrylamide resin, and is characterized in that a metal salt of carboxymethylcellulose is applied to at least one side of the base paper.

[0033] One embodiment of the present invention combines items A, B, and D to form a base paper mainly composed of pulp, wherein 70% or more of the pulp is softwood pulp, the disintegration freeness is 440-690 ml (CSF), the form index measured by β-ray total is 1 or less, and the density is 0.55-0.90 g / cm³. 3 The packaging base paper is characterized in that a metal salt of carboxymethylcellulose is coated on at least one side of the base paper.

[0034] One embodiment of the present invention combines items A, C, and D to form a base paper mainly composed of pulp, wherein 70% or more of the pulp is softwood pulp, the disintegration-freeness is 440-690 ml (CSF), it contains polyacrylamide resin, and the density is 0.55-0.90 g / cm³. 3 The packaging base paper is characterized in that a metal salt of carboxymethylcellulose is coated on at least one side of the base paper.

[0035] One embodiment of the present invention combines items B, C, and D to form a base paper mainly composed of pulp, wherein 70% or more of the pulp is softwood pulp, the disintegration-freeness is 440-690 ml (CSF), the form index measured by β-ray total is 1 or less, it contains polyacrylamide resin, and the density is 0.55-0.90 g / cm³. 3 This packaging paper is characterized by the following features.

[0036] In one of the most preferred embodiments of the present invention, items A, B, C, and D are combined to form a base paper mainly composed of pulp, wherein 70% or more of the pulp is softwood pulp, the disintegration-freeness is 440-690 ml (CSF), the form index measured by β-ray total is 1 or less, it contains polyacrylamide resin, and the density is 0.55-0.90 g / cm³. 3 The packaging base paper is characterized in that a metal salt of carboxymethylcellulose is coated on at least one side of the base paper. In this embodiment, the puncture strength per unit basis weight is 0.095 N / g / m². 2 This allows us to obtain packaging paper with exceptionally high puncture resistance.

[0037] In the packaging paper of the present invention, it is preferable that carboxymethylcellulose is coated on at least one surface of the paper (item A). By coating the surface of the paper with carboxymethylcellulose, effects such as reinforcing interfiber bonds, filling voids between fibers, and providing strength through the coating are obtained, improving folding strength and elongation at break, as well as improving puncture strength. Furthermore, the higher the moisture content in the paper, the higher the puncture strength. Since carboxymethylcellulose has high water retention, it is also expected to have the effect of maintaining a high moisture content in the paper, and is therefore expected to improve puncture strength.

[0038] The packaging base paper of the present invention preferably has a moisture content (hereinafter sometimes referred to as "equilibrium moisture content") of 6.5 to 8.5% by mass after 24 hours of humidity control in a 23°C × 50% RH environment. More preferably, it is 7.0 to 8.0% by mass. This has the effect of improving puncture strength. If the equilibrium moisture content is less than 6.5% by mass, the effect of improving puncture strength may be poor. Conversely, even if the equilibrium moisture content exceeds 8.5% by mass, the effect of improving puncture strength plateaus, but in order to make the equilibrium moisture content 8.5% by mass or higher, it is necessary to impart excessive water retention to the paper, which may reduce its suitability for processing into packaging bags, etc. It should be noted that when the packaging base paper of the present invention is humidified for 24 hours in, for example, a 40°C × 90% RH environment, the moisture content may become about 12% by mass, but even in this case, it has been found that the puncture strength is good. Therefore, a container using the packaging base paper of the present invention can be made into a container that has sufficient puncture strength even in a high humidity environment.

[0039] The carboxymethylcellulose used in this invention can, for example, have a degree of substitution of 0.6 to 0.7, a degree of polymerization of 220 to 250, and a molecular weight of 47,000 to 135,000. A molecular weight of 47,000 to 54,000 is particularly preferred. Within this range, it dissolves easily in water, has low viscosity, resulting in good operability, easily penetrates and impregnates the base paper uniformly, and easily improves puncture strength.

[0040] The method of applying carboxymethylcellulose is not particularly limited, and various known coating or impregnation devices can be used. For example, coating methods such as size press, dipping, coater, and spray methods can be used. By adhering carboxymethylcellulose to the surface of the base paper, the surface strength of the paper is improved, and its resistance to abrasion and puncture is enhanced, making it suitable for use as packaging paper. The amount of carboxymethylcellulose adhering to the base paper is 0.1 to 1.2 g / m² in terms of solid content per side of the base paper. 2 For example, 0.2~1.0 g / m 2 This is preferable. More preferably 0.3 to 0.8 g / m 2 It is 0.1g / m 2 Below 1.2g / m², the effect of the coating in providing strength and maintaining a high equilibrium moisture content may be difficult to obtain, potentially resulting in inferior improvement in puncture resistance. 2 If the moisture content exceeds a certain level, the equilibrium moisture content of the paper can be increased, but the rigidity of the packaging base paper may become too high, making it prone to cracking and tearing, and its suitability for processing into packaging bags, etc., may also decrease. In this invention, a packaging base paper with higher puncture resistance can be made by coating both sides of the base paper with carboxymethylcellulose. For example, both sides of the base paper can be coated with 0.2 to 2.2 g / m² in terms of solid content using an impregnation device. 2 Preferably 0.4 to 2.0 g / m 2 , more preferably 0.5~1.5 g / m 2 By impregnating the paper with carboxymethylcellulose, a packaging base paper with higher puncture resistance can be obtained.

[0041] The drying method after coating the base paper with carboxymethylcellulose is not particularly limited, and various methods can be used, such as air drying methods represented by hot air drying methods such as multi-cylinder dryers, Yankee dryers, and air dryers, and radiant drying methods represented by infrared devices.

[0042] The packaging base paper of the present invention preferably has a form index of 1 or less, as measured by the total beta radiation exposure (item B). By setting the form index to 1 or less, the number of areas with locally low puncture strength can be reduced, resulting in packaging base paper that is less prone to tearing. The form index is preferably 0.8 or less, and more preferably 0.6 or less. If the form index exceeds 1, the unevenness of the form, i.e., the unevenness of the basis weight, increases, resulting in areas of the base paper with locally high and low basis weight. As a result, localized variations in puncture strength occur, and areas with poor puncture strength may tear easily when in contact with sharp objects or protrusions. The lower limit of the form index is not particularly limited, but it is preferably 0.3 or higher, and more preferably 0.5 or higher. While reducing the form index reduces the unevenness of the basis weight and suppresses variations in puncture strength, if the form index is reduced too much, the effect of improving puncture strength plateaus, and manufacturing problems may arise, such as the need to drastically reduce the raw material concentration, as described later. Furthermore, a decrease in the elongation rate of the base paper may impair its suitability for processing when the paper needs to stretch, such as when processing it into a bag shape.

[0043] To reduce the formability index measured by the β-ray formability total to 1 or less, it is preferable to lower the concentration of the raw material at the paper machine inlet, i.e., the concentration of the raw material slurry (mass of raw material slurry / mass of water + mass of raw material slurry, hereafter sometimes referred to as raw material concentration), thereby improving the formability of the base paper and consequently reducing the formability index. The raw material concentration is preferably 0.9 mass% or less, more preferably 0.5 mass% or less, and even better 0.3 mass% or less. In the case of a cylinder paper machine, the raw material concentration in the vat at the paper machine inlet corresponds to the raw material concentration, and in the case of a wire screen paper machine, the concentration at the inlet of the headbox corresponds to the raw material concentration. If the raw material concentration is too high, it becomes difficult to adjust the formability, and as a result, the formability index tends to exceed 1. Thus, it is preferable to adjust the formability index by adjusting the raw material concentration, but if the raw material concentration is less than 0.1 mass%, it becomes difficult to peel the sheet from the wire and the yield on the wire also decreases, so 0.1 mass% is the practical lower limit. The lower limit of the raw material concentration is more preferably 0.15 mass%. In particular, in the case of multilayer papermaking, it is preferable that the raw material concentrations in the surface and back layers fall within this range. Furthermore, when papermaking is performed using a wire screen machine, the formation can be improved by using a shaking device, thereby reducing the formation index. In addition, depending on the usage conditions, the formation index can be reduced by using yield improvers or coagulants such as aluminum sulfate. Therefore, in the method for manufacturing packaging base paper of the present invention, packaging base paper with an appropriate formation index can be obtained by adjusting the pulp slurry, then setting the raw material concentration at the paper machine inlet (raw material concentration) to 0.1 to 0.9% by mass, and manufacturing the paper using a paper machine.

[0044] As mentioned above, the packaging base paper of the present invention contains a relatively large amount of softwood pulp and has a relatively high disintegration-freeness. To simply improve the form, it would be better to use more hardwood pulp than softwood pulp, promote pulp beating, and keep the disintegration-freeness in a relatively low range. However, these actions lead to a decrease in puncture strength that outweighs the benefits of improving the form. The packaging base paper of the present invention contains 70% by mass or more of softwood pulp and improves puncture strength by creating a base paper with good form while maintaining a disintegration-freeness of 440-690 ml (CSF).

[0045] The basis weight used in measuring the basis weight index in this invention is the beta-ray basis weight, i.e., the basis weight measured using a beta-ray radiation source, and represents the distribution of basis weight (sometimes called grammage). While widely used basis weights are measured by light transmission, factors such as pulp composition, type and amount of filler, hue, whiteness, and degree of pulp beating also fluctuate, making them unsuitable for evaluating basis weight. The basis weight index measured using the beta-ray basis weight is an index of the difference in basis weight (referred to as unit basis weight) measured at a diameter of 1 mm of the packaging paper. If the basis weight index measured using the beta-ray basis weight is 1 or less, the local difference in basis weight is small. On the other hand, if the basis weight index measured using the beta-ray basis weight exceeds 1, the local difference in basis weight becomes large, and the puncture strength decreases in areas with small unit basis weight. Therefore, good basis weight is important for the packaging paper of this invention.

[0046] The packaging base paper of the present invention preferably contains a dry paper strength enhancer as a paper strength enhancer, and the dry paper strength enhancer may include polyacrylamide (item C). As the polyacrylamide (polyacrylamide resin), amphoteric polyacrylamide resins that have excellent fixation properties are particularly preferred. With such a configuration, high folding strength can be obtained, and the strength against bending is increased. In addition, a sealed container can be obtained that has high resistance to contact with sharp objects and protrusions (puncture strength) and is less likely to tear even after the contents have been packaged.

[0047] Furthermore, the packaging base paper of the present invention may contain a polyacrylamide resin content of 0.1 to 0.9% by mass relative to the pulp in the base paper. With such a configuration, a packaging base paper with higher puncture resistance can be obtained. Furthermore, the packaging base paper of the present invention may have a mass-average molecular weight of 350,000 to 3,700,000 of the polyacrylamide resin. With such a configuration, a packaging base paper with higher puncture resistance can be obtained.

[0048] The packaging paper of the present invention may further contain dry strength enhancers other than polyacrylamide resins. Examples of such dry strength enhancers include starches such as oxidized starch, cationized starch, or modified starch, plant gum, polyvinyl alcohol, modified polyvinyl alcohol, rubber latex, polyethylene oxide, and polyamide resins, and one or more of these can be used. Among these, polyacrylamide resins, and especially amphoteric polyacrylamide resins with excellent fixation properties, are preferred. The method of application to the paper is not particularly limited, and internal or external addition methods can be used, but adding it to the pulp slurry (internal addition) makes it easier to obtain paper with excellent puncture strength.

[0049] The dry strength enhancer content in the packaging base paper is preferably 0.10 to 2.2 parts by mass, and more preferably 0.12 to 1.0 parts by mass, per 100 parts by mass of pulp. More preferably, it is 0.15 to 0.8 parts by mass. Below 0.1 parts by mass, the effect of improving puncture strength may be insufficient. Conversely, above 2.2 parts by mass, aggregates derived from the strength enhancer may be generated in the paper machine, potentially causing contamination of the paper.

[0050] In the present invention, the packaging base paper may further contain a sizing agent. One or more sizing agents can be used from among paraffin wax-based sizing agents, microcrystalline wax-based sizing agents, carnauba (carnauba wax)-based sizing agents, alkyl ketene dimer-based sizing agents, rosin-based sizing agents, alkenyl succinic anhydride-based sizing agents, styrene acrylic-based sizing agents, etc. In the packaging base paper of the present invention, carboxymethylcellulose may be applied to the surface of the base paper. In this case, by incorporating a sizing agent into the base paper, the penetration of carboxymethylcellulose into the base paper is suppressed, and it is more likely to remain on the surface of the base paper. As a result, a packaging base paper with higher puncture resistance can be obtained. The method of applying the sizing agent to the base paper is not particularly limited; internal or external application methods can be used, but it is preferable to add it to the pulp slurry (internal application). When external application is used, it is preferable to apply the sizing agent to the base paper first, and then apply the carboxymethylcellulose. The sizing agent content is preferably 0.1 to 0.5 parts by mass, and more preferably 0.15 to 0.35 parts by mass, per 100 parts by mass of pulp. In the present invention, for example, it is preferable to add 0.1 to 0.5 parts by mass of a rosin-based sizing agent, preferably a modified rosin emulsion, per 100 parts by mass of pulp.

[0051] The packaging base paper of the present invention may contain various papermaking materials such as wet strength enhancers, aluminum sulfate, fillers, yield enhancers, coloring dyes, coloring pigments, and bulking agents, to the extent that they do not impair the effects intended for the present invention. As fillers, one or more known fillers such as hydrated silicic acid, white carbon, talc, kaolin, clay, calcium carbonate, titanium dioxide, aluminosilicate, calcined clay, barium sulfate, and synthetic resin fillers can be used. For example, 0.1 to 2.0 parts by mass of aluminum sulfate can be included per 100 parts by mass of pulp.

[0052] In this embodiment, the density of the base paper is 0.55 to 0.90 g / cm³. 3It is preferable that this be the case (item D). By setting it within this range, sharp objects such as needles will not easily penetrate it, and the base material will not easily crack, thus achieving high puncture strength. The density should be 0.60 to 0.85 g / cm³. 3 It is more preferable that the concentration be 0.65-0.80 g / cm³. 3 It is even more preferable that the density is lower. Generally, various strengths of paper, such as tensile strength and folding strength, tend to decrease as the density decreases when comparing base paper of the same basis weight. However, there is an optimal density range for puncture strength, and puncture strength decreases if the density is too high or too low. Therefore, in this embodiment, in order to obtain a packaging base paper that has high puncture strength while maintaining a balance with other strengths, the density is set to the above range. The density of the base paper is 0.55 g / cm³. 3 If the density is less than 0.90 g / cm³, the paper's various strengths, such as tensile strength, decrease, impairing its workability, and its puncture resistance also tends to be low. 3 Beyond a certain point, the cushioning effect decreases, which also reduces the puncture resistance.

[0053] While not particularly limited, one method for adjusting the density of the base paper is calendering. The calendering method is also not particularly limited and can be selected from known methods such as supercalendering, gloss calendering, shoenip calendering, and soft calendering. The calendering temperature, linear pressure, and nip count can be appropriately set within the range required to obtain the desired density. Increasing the density through calendering improves the smoothness of the base paper, resulting in packaging paper with superior printability. On the other hand, increasing the linear pressure and nip count during calendering increases the density; therefore, the density can be adjusted by appropriately controlling these factors. In this invention, to obtain an appropriate density, the linear pressure is preferably 10 to 100 kg / cm², and the nip count is preferably 1 to 3 nip.

[0054] Another method for adjusting density is multi-layer papermaking. In this invention, it is preferable that the packaging base paper be made of two or more layers. When multi-layer papermaking is used, the density tends to be higher than that of single-layer papermaking. Furthermore, this configuration suppresses unevenness in the base paper, resulting in packaging base paper with superior puncture resistance. If unevenness in the base paper exists, the paper may tear easily in areas where the base paper is thin, potentially resulting in areas with poor puncture resistance in those areas. Therefore, it is preferable to minimize unevenness in the base paper. To minimize unevenness in the base paper, it is preferable to use base paper with a relatively high basis weight, for example, a basis weight of 60 g / m². 2 If the amount exceeds this, it is preferable to make a multi-layered paper by reducing the basis weight per layer rather than making a single layer. When multi-layered papermaking is performed, three or more layers are preferable, and four or more layers are preferable. There is no particular upper limit to the number of layers, but the basis weight of the packaging paper of the present invention is 50 to 150 g / m². 2 It is also within the range of 7 layers or less, and more preferably 6 layers or less.

[0055] In this invention, the papermaking method for the base paper is not particularly limited, and it can be made using conventionally known papermaking machines such as cylinder papermaking machines, short-screen papermaking machines, long-screen papermaking machines, and combination papermaking machines of these machines. The drying method in the papermaking machine is not particularly limited, and multi-cylinder dryer systems, Yankee dryer systems, air drying systems such as hot air drying, and radiant drying systems such as infrared devices can be used. Among these, the multi-cylinder dryer system or the Yankee dryer system is preferred, and the Yankee dryer system is particularly preferred. By drying with the Yankee dryer system, the mirror surface of the Yankee dryer is transferred to one side of the base paper, resulting in a paper with one-sided gloss, and a packaging base paper with superior puncture resistance can be obtained.

[0056] In this embodiment, the basis weight of the packaging paper is 50-150 g / m². 2 It would be preferable if it were 70g / m². More preferably 70g / m². 2 ~130g / m 2 For example, 75g / m 2 ~85g / m 2or 80g / m 2 ~110g / m 2 This is more preferable. Within this range, the material will have excellent folding strength and puncture strength while maintaining suitability for processing into packaging bags, etc. Basis weight of 50 g / m² 2 If the weight is less than 150g / m², it may have inferior bending and puncture strength. 2 If the value exceeds a certain point, the puncture strength increases, but the rigidity also becomes too high, which may reduce its suitability for processing into packaging bags and other materials.

[0057] Furthermore, the present invention relates to a method for manufacturing packaging paper, and the embodiments of this manufacturing method include at least the following forms. One embodiment of the present invention relates to a method for producing packaging base paper, characterized by preparing a pulp slurry in which 70% by mass or more of the pulp is softwood pulp, then producing paper using a paper machine with a raw material concentration (raw material concentration) of 0.1 to 0.9% by mass at the paper machine inlet, and then impregnating the obtained base paper with an aqueous solution of carboxymethylcellulose and drying it. This makes it possible to obtain packaging base paper of the present invention that has a form index of 1 or less as measured by β-ray base total, has a metal salt of carboxymethylcellulose coated on at least one side of the base paper, and has a disintegration freeness of 440 to 690 ml (CSF), and contains items A and B.

[0058] One embodiment of the present invention relates to a method for producing packaging base paper, characterized by preparing a pulp slurry in which 70% by mass or more of the pulp is softwood pulp, then preparing a raw material slurry containing 0.1 to 0.9 parts by mass of polyacrylamide resin per 100 parts by mass of the pulp slurry, making paper using the obtained raw material slurry with a paper machine, and then impregnating the obtained base paper with an aqueous solution of carboxymethylcellulose and drying it. By doing so, it is possible to obtain the packaging base paper of the present invention that contains polyacrylamide resin, has a metal salt of carboxymethylcellulose coated on at least one side of the base paper, has a disintegration-freeness of 440 to 690 ml (CSF), and includes items A and C.

[0059] One embodiment of the present invention relates to a method for producing packaging base paper, characterized by preparing a pulp slurry in which 70% by mass or more of the pulp is softwood pulp, then, after preparing the pulp slurry, preparing a raw material slurry containing 0.1 to 0.9 parts by mass of polyacrylamide resin per 100 parts by mass of the pulp slurry, and then using the obtained raw material slurry to produce paper using a paper machine with a raw material concentration (raw material concentration) of 0.1 to 0.9% by mass. This makes it possible to obtain the packaging base paper of the present invention that has a formability index of 1 or less as measured by β-ray base total, contains polyacrylamide resin, and has a disintegration freeness of 440 to 690 ml (CSF), and includes items B and C.

[0060] One embodiment of the present invention relates to a method for producing packaging base paper, characterized by preparing a pulp slurry in which 70% by mass or more of the pulp is softwood pulp, then, after preparing the pulp slurry, preparing a raw material slurry containing 0.1 to 0.9 parts by mass of polyacrylamide resin and preferably 0.1 to 0.5 parts by mass of sizing agent per 100 parts by mass of the pulp slurry, using the obtained raw material slurry to produce paper using a paper machine with a raw material concentration at the paper machine inlet (raw material concentration) of 0.1 to 0.9% by mass, and then impregnating the obtained base paper with an aqueous solution of carboxymethylcellulose and drying it. This makes it possible to obtain the packaging base paper of the present invention that has a form index of 1 or less as measured by β-ray base total, contains polyacrylamide resin, has a metal salt of carboxymethylcellulose coated on at least one side of the base paper, and has a disintegration freeness of 440 to 690 ml (CSF), and includes items A, B, and C.

[0061] In the method for manufacturing packaging base paper, it is preferable to calender the dried packaging base paper at a linear pressure of 10 to 100 kg / cm² and / or with a nip count of 1 to 3 nip. This results in a density of 0.55 to 0.90 g / cm². 3 A packaging base paper can be obtained. Furthermore, in the manufacturing method of the present invention, the packaging base paper is beaten within an appropriate range so that its pulp freeness is 440 to 690 ml (CSF) to prepare a pulp slurry.

[0062] The packaging base paper of the present invention has a puncture strength of 0.087 N / g / m² per unit basis weight. 2 Preferably, it is 0.095 N / g / m³ 2 It is even more preferable that the value be greater than or equal to 0.100 N / g / m 2 The above is most preferable. In addition, it is preferable that the tensile strength is 6.0 kN / m or more. For example, it is preferable that the tensile strength of the packaging base paper of the present invention is 6.0 kN / m to 10.0 kN / m. Furthermore, it is preferable that the puncture strength of the packaging base paper of the present invention is 7.00 N or more, and more preferably 7.50 N or more. With this level of strength, it is possible to create a packaging base paper that has excellent physical strength, is resistant to tearing, has high resistance to bending, and has excellent resistance to impacts during distribution after packaging the contents, and can be suitably used as a base paper to replace some or all of conventional plastic packaging with paper packaging. Furthermore, the packaging base paper of the present invention can be used as a bag-shaped sealed container by applying an adhesive or a heat-sealable resin, for example, and then processing it into a bag. It is also possible to laminate one side with polyethylene or the like and then process it into a bag to create a sealed container. Applying such lamination involves the use of plastic materials, but since part of the sealed container is made of paper, it leads to a reduction in the amount of plastic used. The form of bag manufacturing is not particularly limited, and depending on the application, for example, pillow packaging, caramel packaging, or a combination thereof can be used. Thus, the packaging base paper of the present invention is suitable as packaging base paper for sealed containers, and is particularly suitable as packaging base paper for bag-shaped sealed containers.

[0063] Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" refers to "solid parts" unless otherwise specified. Note that the number of added parts is a value based on solid content.

[0064] (Example 1) <Manufacturing of base paper> A pulp slurry was prepared by dispersing 100 parts of beaten softwood bleached kraft pulp in water. To this pulp slurry, 0.2 parts of a polyacrylamide resin with a mass-average molecular weight (Mw) of 3 million as a dry paper strength enhancer, 0.25 parts of a sizing agent (product name: AL1300 / manufactured by Seikoh PMC, modified rosin emulsion), and 0.5 parts of aluminum sulfate were added to obtain a raw material slurry. Using the obtained raw material slurry, paper was made using a wire screen paper machine to obtain a single-layer base paper. The inlet concentration (raw material concentration) in the headbox was 0.2% by mass.

[0065] <apply> An aqueous solution of carboxymethylcellulose (indicated as "CMC" in the table) (product name: SG Cellogen PR, sodium carboxymethylcellulose, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., degree of substitution 0.6-0.7, degree of polymerization 220-250, molecular weight 47000-54000) was applied to the obtained base paper using a two-roll press, and dried at 130°C in a rotary dryer to obtain the desired packaging base paper. The amount of carboxymethylcellulose adhering to the base paper was 1.12 g / m² in terms of solid content per side of the base paper. 2 (0.56 g / m² per side) 2 The result was [result]. After drying, no calendering treatment was performed. The basis weight of the obtained packaging paper was 80.8 g / m². 2 The disintegration-freeness of the packaging paper is 600 ml CSF, and its density is 0.62 g / cm³. 3 That was the case.

[0066] (Example 2) In preparing the pulp slurry of Example 1, 75 parts of beaten softwood bleached kraft pulp and 25 parts of beaten hardwood bleached kraft pulp were used, and the amount of carboxymethylcellulose attached was 1.00 g / m² on both sides of the base paper in terms of solid content. 2 (0.50 g / m² per side) 2 Packaging base paper was obtained in the same manner as in Example 1, except that the following was done. The basis weight of the obtained packaging base paper was 80.0 g / m². 2 The packaging paper has a disintegration-freeness of 580 mlCSF and a density of 0.60 g / cm³. 3 That was the case.

[0067] (Example 3) In Example 1, a three-ply papermaking process was carried out, and after drying, calendering was performed at a linear pressure of 80 kg / cm and 1 nip. The only other difference was that a packaging base paper was obtained in the same manner as in Example 1. The basis weight of the obtained packaging base paper was 80.8 g / m². 2 The packaging paper has a disintegration-freeness of 600 ml CSF and a density of 0.79 g / cm³. 3 That was the case.

[0068] (Example 4) In Example 3, a packaging base paper was obtained in the same manner as in Example 3, except that a polyacrylamide resin was not added as a dry strength enhancer and carboxymethylcellulose was not applied. The basis weight of the obtained packaging base paper was 77.7 g / m². 2 The packaging paper has a disintegration-freeness of 580 mlCSF and a density of 0.79 g / cm³. 3 That was the case.

[0069] (Example 5) In Example 1, packaging base paper was obtained in the same manner as in Example 1, except that carboxymethylcellulose was not applied. The basis weight of the obtained packaging base paper was 80.5 g / m². 2 The disintegration-freeness of the packaging paper is 580 mlCSF, and its density is 0.59 g / cm³. 3 That was the case.

[0070] (Example 6) In Example 1, the amount of carboxymethylcellulose attached to the base paper was 1.15 g / m² in terms of solid content per side of the base paper. 2 (0.575g / m² per side) 2 Packaging base paper was obtained in the same manner as in Example 1, except that a polyacrylamide resin was not added as a drying strength enhancer. The basis weight of the obtained packaging base paper was 81.1 g / m². 2 The disintegration-freeness of the packaging paper is 580 mlCSF, and its density is 0.62 g / cm³. 3 That was the case.

[0071] (Example 7) In Example 3, packaging base paper was obtained in the same manner as in Example 3, except that calendering was performed after drying at a linear pressure of 150 kg / cm and 3 nips. The basis weight of the obtained packaging base paper was 80.8 g / m². 2 The disintegration-freeness of the packaging paper is 600 ml CSF, and its density is 0.96 g / cm³. 3 That was the case.

[0072] ( refer to Example 8) A pulp slurry was prepared by dispersing 100 parts of beaten softwood bleached kraft pulp in water. To this pulp slurry, 0.2 parts of a dry paper strength enhancer (product name: DA4104 / Seiko PMC, polyacrylamide resin) with a mass-average molecular weight (Mw) of approximately 1 million, 0.5 parts of a sizing agent (product name: AL1300 / Seiko PMC, modified rosin emulsion), and 1.2 parts of aluminum sulfate were added to obtain a raw material slurry. Using the obtained raw material slurry, paper was made using a wire screen paper machine to obtain a single-layer base paper. The inlet concentration (raw material concentration) in the headbox was 1.0% by mass. Subsequently, a 1% starch aqueous solution was added to both sides of the base paper at a solid content of 2.0 g / m² using a two-roll size press. 2 (1.0g / m² per side) 2 The paper was coated and dried, and then calendered at a linear pressure of 80 kg / cm and 1 nip to obtain the desired packaging base paper. The basis weight of the obtained packaging base paper was 81.3 g / m². 2 The packaging paper has a disintegration-freeness of 580 mlCSF and a density of 0.75 g / cm³. 3 That was the case.

[0073] (Example 9) <Manufacturing of base paper> A pulp slurry was prepared by dispersing 100 parts of beaten unbleached coniferous kraft pulp in water. To this pulp slurry, 0.2 parts of a dry paper strength enhancer (product name: DA4104 / Seiko PMC, polyacrylamide resin) with a mass-average molecular weight (Mw) of approximately 1 million, 0.25 parts of a sizing agent (product name: AL1300 / Seiko PMC, modified rosin emulsion), and 0.5 parts of aluminum sulfate were added to obtain a raw material slurry. Using the obtained raw material slurry, papermaking was performed using a standard square sheet machine, followed by drying at 120°C in a hot air dryer. Calendering was then performed at a linear pressure of 80 kg / cm and 1 nip, resulting in a basis weight of 81.0 g / m². 2 We obtained the base paper.

[0074] <apply> The obtained base paper was impregnated with an aqueous solution of carboxymethylcellulose (product name: SG Cellogen PR, sodium carboxymethylcellulose, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., degree of substitution 0.6-0.7, degree of polymerization 220-250, molecular weight 47000-54000), dried in a rotary dryer at 130°C, and the desired packaging base paper was obtained. The amount of carboxymethylcellulose adhering to the base paper was 1.0 g / m² in terms of solid content per side of the base paper. 2 (0.5g / m² per side) 2 The basis weight of the obtained packaging paper was 82.0 g / m². 2 The disintegration-freeness of the packaging paper is 580 mlCSF, and its density is 0.70 g / cm³. 3 That was the case.

[0075] (Example 10) In Example 9, the carboxymethylcellulose aqueous solution was not applied, and a polyvinyl alcohol aqueous solution (indicated as "pva" in the table) was applied at a solid content of 4.0 g / m² per side of the base paper. 2 (2.0g / m² per side) 2 Packaging base paper was obtained in the same manner as in Example 9, except that it was impregnated. The basis weight of the obtained packaging base paper was 85.0 g / m². 2 The disintegration-freeness of the packaging paper is 580 mlCSF, and its density is 0.70 g / cm³. 3 That was the case.

[0076] (Example 11) A pulp slurry was prepared by dispersing 100 parts of beaten softwood bleached kraft pulp in water. To this pulp slurry, 0.2 parts of a dry paper strength enhancer (product name: DA4104 / Seiko PMC, polyacrylamide resin) with a mass-average molecular weight (Mw) of approximately 1 million, 0.5 parts of a sizing agent (product name: AL1300 / Seiko PMC, modified rosin emulsion), and 1.2 parts of aluminum sulfate were added to obtain a raw material slurry. Using the obtained raw material slurry, paper was made using a wire screen paper machine to obtain a single-layer base paper. The inlet concentration (raw material concentration) in the headbox was 0.2% by mass. After drying, calendering was performed at a linear pressure of 80 kg / cm and 1 nip to obtain the desired packaging base paper. The basis weight of the obtained packaging base paper was 81.3 g / m². 2 The packaging paper has a disintegration-freeness of 580 mlCSF and a density of 0.75 g / cm³. 3 That was the case.

[0077] (Example 12) Packaging base paper was obtained in the same manner as in Example 11, except that a cylinder screen paper machine was used instead of a long screen paper machine to obtain two layers of base paper. The same raw material slurry was used to make the base paper, and two layers were formed by combining them so that the basis weight of each layer was the same. The raw material concentration in the vat at the entrance of the cylinder screen paper machine was 0.2% by mass for both layers. The basis weight of the obtained packaging base paper was 79.4 g / m². 2 The packaging paper has a disintegration-freeness of 580 mlCSF and a density of 0.75 g / cm³. 3 That was the case.

[0078] (Example 13) Packaging base paper was obtained in the same manner as in Example 11, except that a cylinder screen paper machine was used instead of a long screen paper machine to obtain a three-layer base paper. The base paper was made using the same raw material slurry, and the three layers were assembled so that the basis weight of each layer was the same. The raw material concentration in the vat at the entrance of the cylinder screen paper machine was 0.2% by mass for all three layers. The basis weight of the obtained packaging base paper was 79.0 g / m². 2 The disintegration-freeness of the packaging paper is 580 mlCSF, and its density is 0.77 g / cm³. 3 That was the case.

[0079] (Example 14) <Manufacturing of base paper> 100 parts of beaten softwood bleached kraft pulp were dispersed in water to prepare a pulp slurry, 0.25 parts of a sizing agent (trade name: AL1300, manufactured by Seiko PMC Co., Ltd., modified rosin emulsion) and 0.5 parts of aluminum sulfate were added to the pulp slurry to obtain a raw material slurry. Using the obtained raw material slurry, paper was made with a standard square sheet machine, followed by drying at 120°C in a hot air dryer to give a basis weight of 80 g / m 2 A single-layer base paper was obtained. <Coating> An aqueous starch solution was applied to the obtained base paper, followed by drying at 130°C in a rotary dryer to obtain the target packaging base paper. The adhesion amount of starch to the base paper was 1 g / m per both sides of the base paper 2 . The basis weight of the obtained packaging base paper was 81.0 g / m 2 , the disintegration freeness of the packaging base paper was 580 ml, and the density was 0.62 g / cm 3 .

[0080] (Example 15) A packaging base paper was obtained in the same manner as in Example 3, except that the application of the aqueous carboxymethyl cellulose solution in Example 3 was not performed. The basis weight of the obtained packaging base paper was 80.5 g / m 2 , the disintegration freeness of the packaging base paper was 580 ml CSF, and the density was 0.79 g / cm 3 .

[0081] (Example 16) A packaging base paper was obtained in the same manner as in Example 1, except that no polyacrylamide-based resin was added as a dry paper strength agent and the inlet concentration of the headbox was set to 1.0 mass% in Example 1. The basis weight of the obtained packaging base paper was 81.0 g / m 2 , the disintegration freeness of the packaging base paper was 580 ml CSF, and the density was 0.62 g / cm 3 .

[0082] (Example 17) A packaging base paper was obtained in the same manner as in Example 3, except that the application of the aqueous carboxymethyl cellulose solution was not performed, and calendering was performed after drying at a linear pressure of 150 kg / cm with 3 nips in Example 3. The basis weight of the obtained packaging base paper was 80.6 g / m2 , the freeness after disintegration of the packaging base paper was 580ml CSF, and the density was 0.96g / cm 3 .

[0083] (Example 18) In Example 1, a packaging base paper was obtained in the same manner as in Example 1, except that no polyacrylamide-based resin was added as a dry paper strength enhancer, and calendering treatment was performed after drying at a linear pressure of 150 kg / cm with 3 nips. The basis weight of the obtained packaging base paper was 81.0 g / m 2 , the freeness after disintegration of the packaging base paper was 580ml CSF, and the density was 0.96g / cm 3 .

[0084] (Example 19) In Example 1, the deposition amount of carboxymethyl cellulose on the base paper was 1.15 g / m in terms of solid content per both sides of the base paper 2 (0.575 g / m per one side 2 ), and the inlet consistency of the headbox was set to 1.0 mass%, and a packaging base paper was obtained in the same manner as in Example 1 except that calendering treatment was performed after drying at a linear pressure of 150 kg / cm with 3 nips. The basis weight of the obtained packaging base paper was 80.3 g / m 2 , the freeness after disintegration of the packaging base paper was 580ml CSF, and the density was 0.96g / cm 3 .

[0085] (Comparative Example 1) A packaging base paper was obtained in the same manner as in Example 1, except that the beating degree of bleached softwood kraft pulp was adjusted. The basis weight of the obtained packaging base paper was 81.3 g / m 2 , the freeness after disintegration was 420ml CSF, the density was 0.61g / cm 3 , and the deposition amount of carboxymethyl cellulose on the base paper was 1.0 g / m in terms of solid content per both sides of the base paper 2 (0.5 g / m per one side 2 ).

[0086] (Comparative Example 2) Packaging base paper was obtained in the same manner as in Example 1, except that 50 parts of beaten softwood bleached kraft pulp and 50 parts of beaten hardwood bleached kraft pulp were used in the preparation of the pulp slurry in Example 1. The basis weight of the obtained packaging base paper was 81.3 g / m². 2 The dissociation-freeness is 580 ml CSF, and the density is 0.62 g / cm³. 3 The amount of carboxymethylcellulose adhering to the base paper is 1.0 g / m² in terms of solid content per side of the base paper. 2 (0.5g / m² per side) 2 ) was.

[0087] (Comparative Example 3) A pulp slurry was prepared by dispersing 70 parts of beaten softwood bleached kraft pulp and 30 parts of beaten hardwood bleached kraft pulp in water. 0.25 parts of a sizing agent (product name: AL1300 / manufactured by Seikoh PMC, modified rosin emulsion) and 0.5 parts of aluminum sulfate were added to the pulp slurry to obtain a raw material slurry. Using the obtained raw material slurry, a single-layer base paper was obtained by papermaking using a wire screen paper machine. The inlet concentration (raw material concentration) in the headbox was 0.2% by mass. After drying, packaging base paper was obtained by calendering at a linear pressure of 150 kg / cm and 3 nips. The basis weight of the obtained packaging base paper was 80.0 g / m². 2 The packaging paper has a disintegration-freeness of 580 mlCSF and a density of 0.96 g / cm³. 3 That was the case.

[0088] (Comparative Example 4) <Manufacturing of base paper> A pulp slurry was prepared by dispersing 70 parts of beaten softwood bleached kraft pulp and 30 parts of beaten hardwood bleached kraft pulp in water. To this pulp slurry, 0.25 parts of a sizing agent (product name: AL1300 / manufactured by Seikoh PMC, modified rosin emulsion) and 0.5 parts of aluminum sulfate were added to obtain a raw material slurry. Using the obtained raw material slurry, paper was made using a wire screen paper machine to obtain a single-layer base paper. The inlet concentration (raw material concentration) in the headbox was 1.0% by mass. After drying, calendering was performed at a linear pressure of 150 kg / cm and 3 nips.

[0089] <apply> An aqueous solution of carboxymethylcellulose (product name: SG Cellogen PR, sodium carboxymethylcellulose, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., degree of substitution 0.6-0.7, degree of polymerization 220-250, molecular weight 47000-54000) was applied to the obtained base paper using a two-roll press, and dried at 130°C in a rotary dryer to obtain the desired packaging base paper. The amount of carboxymethylcellulose adhering to the base paper was 1.00 g / m² in terms of solid content per side of the base paper. 2 (0.50 g / m² per side) 2 The basis weight of the obtained packaging paper was 80.0 g / m². 2 The packaging paper has a disintegration-freeness of 580 mlCSF and a density of 0.96 g / cm³. 3 That was the case.

[0090] (Comparative Example 5) A pulp slurry was prepared by dispersing 70 parts of beaten softwood bleached kraft pulp and 30 parts of beaten hardwood bleached kraft pulp in water. To this pulp slurry, 0.2 parts of a polyacrylamide resin with a mass-average molecular weight (Mw) of 3 million as a dry paper strength enhancer, 0.25 parts of a sizing agent (product name: AL1300 / manufactured by Seikoh PMC, modified rosin emulsion), and 0.5 parts of aluminum sulfate were added to obtain a raw material slurry. Using the obtained raw material slurry, paper was made using a wire screen paper machine to obtain a single-layer base paper. The inlet concentration (raw material concentration) in the headbox was 1.0% by mass. After drying, packaging base paper was obtained by calendering at a linear pressure of 150 kg / cm and 3 nips. The basis weight of the obtained packaging base paper was 80.0 g / m². 2 The packaging paper has a disintegration-freeness of 580 mlCSF and a density of 0.96 g / cm³. 3 That was the case.

[0091] (Comparative Example 6) A pulp slurry was prepared by dispersing 70 parts of beaten softwood bleached kraft pulp and 30 parts of beaten hardwood bleached kraft pulp in water. 0.25 parts of a sizing agent (product name: AL1300 / manufactured by Seikoh PMC, modified rosin emulsion) and 0.5 parts of aluminum sulfate were added to the pulp slurry to obtain a raw material slurry. Using the obtained raw material slurry, paper was made using a wire screen paper machine to obtain a single-layer base paper. The inlet concentration (raw material concentration) in the headbox was 1.0% by mass. Calendering was not performed. The basis weight of the obtained packaging base paper was 80.0 g / m². 2 The disintegration-freeness of the packaging paper is 580 mlCSF, and its density is 0.62 g / cm³. 3 That was the case.

[0092] The obtained packaging base paper was evaluated using the method described below. The results are shown in Table 1. Although not shown here, tensile strength was also measured, and it was confirmed that Examples 1 to 19 had a longitudinal tensile strength of 6.0 kN / m or higher.

[0093] (formation index) The ground conditions index was calculated using a β-ray ground totalizer manufactured by Ambertec Co., Ltd., under the following measurement conditions. Measurement conditions: Measurement area 70mm x 70mm, measurement pitch 3.5mm x 3.5mm Calculation method: Formation index = STD ÷ (grammage weight) 1 / 2 In this case, STD represents the standard deviation of mass from basis weight. A smaller ground condition index indicates better ground conditions.

[0094] (Puncture strength) The puncture strength test was measured using an Autograph precision universal tester (AGS-10kNX: manufactured by Shimadzu Corporation) in accordance with "7.5 Puncture Strength Test" of "JIS Z 1707:2019 General Rules for Plastic Films for Food Packaging" using the following method. The test pieces of packaging paper were conditioned for 24 hours at 23°C × 50%rh. 1. The test specimen was fixed in a jig, and a semicircular needle with a diameter of 1.0 mm and a tip radius of 0.5 mm was inserted at a test speed of 50 mm / min. The maximum force (N) required for the needle to penetrate was measured. 2.1 test specimens were punctured at 15 points, and the average value was defined as the puncture strength (N).

[0095] (Penetration strength per unit basis weight) The puncture strength per unit basis weight was calculated using the following formula (1). Puncture strength tends to be proportional to the basis weight in rice, and in this embodiment, the comparison is made using the puncture strength per unit basis weight. Formula (1): Puncture strength (N) / Basis weight (g / m²) 2 ) = Puncture strength per unit basis weight (N / g / m 2 )

[0096] (Tensile strength) The tensile strength (kN / m) of the packaging paper was measured according to the method specified in JIS P 8113 "Paper and paperboard - Test methods for tensile properties - Part 2: Constant-rate elongation method".

[0097] Each example Reference Example Table 1 shows an overview of the composition and evaluation results of the packaging base paper obtained in the comparative examples. The packaging base paper obtained in each embodiment of the present invention that had two or more of the features of items A to D exhibited excellent puncture strength. Here, the packaging paper of Examples 1 to 3 and 9 that had all four items A to D had a puncture strength of 0.095 to 0.116 N / g / m² per unit basis weight. 2 This packaging paper has excellent puncture resistance and is the most preferred embodiment of the present invention. Furthermore, the packaging papers of Examples 5-7, 10-13, and 15, which have any three of the above four items, were packaging papers with excellent puncture resistance, with a puncture resistance of 0.089-0.099 per unit basis weight. Also, Example 4, which has any two of the above four items, 14. Refer to Example 8Furthermore, even with packaging papers of grades 16-19, the puncture strength per unit basis weight was 0.088-0.096, indicating excellent puncture resistance. Although not shown here, the tensile strength was also practically sufficient (longitudinal strength of 6.0 kN / m or more).

[0098] In contrast, the packaging papers of Comparative Examples 3-6, which possessed only one of the four items mentioned above, did not achieve sufficient puncture strength. Considering these examples and Comparative Examples 3-6, it was found that none of the four items A-D were particularly effective in improving puncture strength, and that all four items contributed to the improvement of puncture strength on average. In contrast, the packaging base paper obtained in Comparative Example 1 had low disintegration freeness and poor puncture strength. The packaging base paper obtained in Comparative Example 2 had too low a proportion of N pulp and poor puncture strength.

[0099] [Table 1]

Claims

1. A packaging base paper characterized by comprising a base paper mainly composed of pulp, wherein 70% or more of the pulp is softwood pulp, the disintegration freeness is 440 to 690 ml (CSF), the form index measured by β-ray total is 1 or less, and a metal salt of carboxymethylcellulose is coated on at least one side of the base paper.

2. A packaging base paper characterized by comprising a base paper mainly composed of pulp, wherein 70% or more by mass of the pulp is softwood pulp, the disintegration-freeness is 440 to 690 ml (CSF), it contains a polyacrylamide resin, and at least one side of the base paper is coated with a metal salt of carboxymethylcellulose.

3. It consists of a base paper mainly composed of pulp, with 70% or more by mass of the pulp being softwood pulp, a disintegration-freeness of 440 to 690 ml (CSF), and a density of over 0.60 to 0.90 g / cm³. ３ A packaging base paper characterized in that a metal salt of carboxymethylcellulose is coated on at least one side of the base paper.

4. A packaging base paper characterized by comprising a base paper mainly composed of pulp, wherein 70% or more of the pulp is softwood pulp, the disintegration freeness is 440 to 690 ml (CSF), the form index measured by total beta radiation is 0.6 or less, and it contains a polyacrylamide resin.

5. It consists of a base paper mainly composed of pulp, with 70% or more by mass of the pulp being coniferous pulp, a disintegration-freeness of 440-690 ml (CSF), a form index measured by total beta radiation of 1 or less, and a density of 0.55-0.90 g / cm³. ３ Packaging base paper characterized by the following:

6. The packaging base paper according to claim 3, characterized in that its density is 0.62 to 0.90 g / cm³.

7. A packaging base paper characterized by comprising a base paper mainly composed of pulp, wherein 70% or more of the pulp is softwood pulp, the disintegration-freeness is 440 to 690 ml (CSF), the form index measured by the total β-ray base is 1 or less, it contains a polyacrylamide resin, and at least one side of the base paper is coated with a metal salt of carboxymethylcellulose.

8. It consists of a base paper mainly composed of pulp, with 70% or more by mass of the pulp being coniferous pulp, a disintegration-freeness of 440-690 ml (CSF), a form index measured by total beta radiation of 1 or less, and a density of 0.55-0.90 g / cm³. ３ A packaging base paper characterized in that a metal salt of carboxymethylcellulose is coated on at least one side of the base paper.

9. It consists of a base paper mainly composed of pulp, with 70% or more by mass of the pulp being softwood pulp, having a disintegration-freeness of 440 to 690 ml (CSF), containing polyacrylamide resin, and having a density of 0.55 to 0.90 g / cm³. ３ A packaging base paper characterized in that a metal salt of carboxymethylcellulose is coated on at least one side of the base paper.

10. It consists of a base paper mainly composed of pulp, with 70% or more by mass of the pulp being coniferous pulp, having a disintegration-freeness of 440 to 690 ml (CSF), a form index measured by total beta radiation of 1 or less, containing polyacrylamide resin, and having a density of 0.55 to 0.90 g / cm³. ３ Packaging base paper characterized by the following:

11. It consists of a base paper mainly composed of pulp, with 70% or more by mass of the pulp being coniferous pulp, having a disintegration-freeness of 440 to 690 ml (CSF), a form index measured by total beta radiation of 1 or less, containing polyacrylamide resin, and having a density of 0.55 to 0.90 g / cm³. ３ A packaging base paper characterized in that a metal salt of carboxymethylcellulose is coated on at least one side of the base paper.

12. A packaging base paper according to any one of claims 1 to 11, characterized in that it contains a paper strength enhancer and / or a sizing agent.

13. The puncture strength per unit basis weight is 0.087 N / g / m ２ The packaging base paper according to any one of claims 1 to 11, characterized in that it is as described above.

14. Grain weight: 50-150 g / m² ２ A packaging base paper according to any one of claims 1 to 11, characterized in that it is the same as the one described above.

15. The coating amount of the metal salt of carboxymethyl cellulose is 0.1 to 1.2 g / m in terms of solid content per one side of the base paper ２ The packaging base paper according to any one of claims 1 to 3, 7 to 9, and 11, characterized in that

16. The packaging base paper according to any one of claims 1 to 3, 7 to 9, or 11, wherein the metal salt of carboxymethylcellulose is sodium carboxymethylcellulose.

17. The packaging base paper according to any one of claims 2, 4, 7, 9 to 11, characterized in that the content of the polyacrylamide resin is 0.1 to 0.9% by mass relative to the pulp in the base paper.

18. The packaging base paper according to any one of claims 2, 4, 7, 9 to 11, characterized in that the weight-average molecular weight (Mw) of the polyacrylamide resin is 350,000 to 3,700,000.

19. The packaging base paper according to any one of claims 1 to 11, characterized in that the base paper is made up of two or more layers.

20. The packaging base paper according to any one of claims 1 to 11, characterized in that the softwood pulp is unbleached softwood kraft pulp (NUKP).

21. A method for producing packaging base paper having a disintegration-freeness of 440 to 690 ml (CSF), characterized by preparing a pulp slurry in which 70% or more by mass of the pulp is softwood pulp, then making paper using a paper machine with a raw material concentration (raw material concentration) of 0.1 to 0.9% by mass at the paper machine inlet, and then impregnating the resulting base paper with an aqueous solution of a metal salt of carboxymethylcellulose and drying it.

22. A method for producing packaging base paper having a disintegration-freeness of 440 to 690 ml (CSF), characterized by preparing a pulp slurry in which 70% or more by mass of the pulp is softwood pulp, then preparing a raw material slurry containing 0.1 to 0.9 parts by mass of polyacrylamide resin per 100 parts by mass of the pulp slurry, making paper using the obtained raw material slurry with a paper machine, and then impregnating the obtained base paper with an aqueous solution of a metal salt of carboxymethylcellulose and drying it.

23. A method for producing packaging base paper having a disintegration-freeness of 440 to 690 ml (CSF), characterized by preparing a pulp slurry in which 70% or more by mass of the pulp is softwood pulp, then preparing a raw material slurry containing 0.1 to 0.9 parts by mass of polyacrylamide resin per 100 parts by mass of the pulp slurry, and using the obtained raw material slurry to make paper with a paper machine with a raw material concentration at the paper machine inlet (raw material concentration) of 0.1 to 0.9% by mass.

24. A method for producing packaging base paper having a disintegration-freeness of 440 to 690 ml (CSF), characterized by preparing a pulp slurry in which 70% or more by mass of the pulp is softwood pulp, then preparing a raw material slurry containing 0.1 to 0.9 parts by mass of polyacrylamide resin per 100 parts by mass of the pulp slurry, making paper using the obtained raw material slurry with a raw material concentration at the paper machine inlet (raw material concentration) of 0.1 to 0.9% by mass, and then impregnating the obtained base paper with an aqueous solution of a metal salt of carboxymethylcellulose and drying it.

25. A method for producing packaging base paper according to any one of claims 21 to 24, comprising calendering a dried packaging base paper at a linear pressure of 10 to 100 kg / cm and / or with a nip count of 1 to 3 nip.

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