Packaging paper

Abstract

To provide a packaging paper having hot water resistance and moisture resistance and a method for producing the same.SOLUTION: There is provided a packaging paper, comprising a wet paper strength agent, a sizing agent and a polymer material in paper in which a main component is pulp, wherein the polymer material is one kind or two or more kinds selected from styrene-butadiene-based latex, an urethane-based resin, and an acrylic-based resin.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a packaging paper having excellent hot water resistance and moisture resistance, and a method for producing the same. [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, of which a large amount is produced in the packaging container sector, which is the cause of plastic waste. Plastic does not decompose for a long time, and the waste turns into microplastics in the natural environment, causing serious damage to the ecosystem. The most commonly used plastics for packaging containers are polyethylene terephthalate (PET), which is used for drinking cups and bottles, and polyethylene (PE) and polypropylene (PP), which are used for plastic bags and container lamination. Ocean pollution is particularly severe, and it is said that the plastic waste is impossible to recover. In the future, it will be necessary for the global environment to reduce the use of plastics.

[0003] In response to these problems, the replacement of plastic with paper has progressed in many fields, and many paper products exist in the field of packaging containers. Furthermore, in the field of packaging containers, packaging containers using paper packaging paper have been developed instead of plastic containers that are both heat-resistant and water-resistant, and among these packaging papers are packaging papers for food. "Soft packaging" used for packaging food is generally made of soft plastic materials such as polyethylene and polypropylene. In place of such plastic packaging films for soft packaging applications, food packaging papers that are water-resistant and oil-resistant, and food packaging papers that are water-absorbent and oil-absorbent have been developed.

[0004] Furthermore, since it is a food packaging paper, ingredients and foods may be cooked together with the food packaging paper. For example, ingredients and foods may be cooked together with the food packaging paper by baking in an oven, boiling in hot water, steaming, heating in a microwave oven, etc. Furthermore, there is also retort packaging for retort used for retort foods. Retort foods refer to foods that are retort sterilized in retort packaging such as retort pouches used for retort sterilization. Retort sterilization is a method of sterilizing foods packaged in retort packaging using steam or pressurized hot water at 100°C or higher. Retort packaging includes retort pouches such as aluminum foil pouches and retort containers such as tray-shaped containers, and is selected depending on the purpose. Retort foods packaged in such retort packaging have the advantages of being safe and hygienic without the use of preservatives, allowing for long-term distribution and storage, and reducing the loss of nutrients by treating the food under vacuum as necessary. For consumers, there are also advantages in that cooking can be done in a short time by placing it in a hot water bath, and that it is lightweight and easy to open.

[0005] Thus, in recent years, attempts have been made to use paper instead of plastic packaging in order to reduce the amount of plastic used and to curb carbon dioxide emissions, both for packaging paper used in retort packaging and for packaging paper for foods that are processed by baking in an oven, boiling in hot water, steaming, heating in a microwave oven, etc. To achieve this, in addition to the strength required for packaging paper, the paper must be resistant to the hot water used in retort sterilization and cooking (hot water resistance), and it must also have strength when immersed in water and absorbs water, i.e., when wet (wet resistance).

[0006] When paper is used for packaging that requires water resistance, such as retort packaging, it is common to coat or laminate one or both sides of the paper with a water-resistant agent. However, these methods cannot suppress water absorption from the edge of the paper. Laminated water-resistant paper is one technology for imparting water resistance to the edge of paper (see Patent Document 1), but there is no description of hot water resistance against hot water, which penetrates more easily than water at room temperature. In addition, paper has problems such as a decrease in strength and delamination when in a wet state. Paper containers that have strong hot water resistance even in a wet state are exemplified (see Patent Document 2), but no measures are shown for the puncture strength required for soft packaging applications. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2004-308094 A [Patent Document 2] JP 2001-270516 A Summary of the Invention [Problem to be solved by the invention]

[0008] In view of the above problems, the present invention aims to provide a wrapping paper having hot water resistance and wet resistance, and a manufacturing method thereof. In particular, the present invention aims to provide a wrapping paper that can suppress water absorption from the paper edge when exposed to hot water, suppress a decrease in puncture strength when wet, and maintain internal bond strength, and a manufacturing method thereof. [Means for solving the problem]

[0009] The present invention relates to a packaging paper that contains a wet strength agent, a sizing agent, and a polymeric material in a paper that is mainly composed of pulp, and the polymeric material is one or more selected from styrene-butadiene latex, urethane resin, and acrylic resin. By using a combination of a wet strength agent and a sizing agent in addition to a specific polymeric material, it is possible to obtain a packaging paper of the present invention that can suppress water absorption from the paper edge surface in hot water, suppress a decrease in puncture strength when wet, and maintain internal bond strength.

[0010] In the embodiment of the packaging paper of the present invention, the wet strength agent is preferably one or more selected from urea formaldehyde resin, melamine formaldehyde resin, polyamide epichlorohydrin resin, and epoxidized polyamide resin. By using these wet strength agents, it is possible to further suppress the decrease in strength of the paper when wet, and to obtain a packaging paper that has strength even when wet.

[0011] In the embodiment of the packaging paper of the present invention, the sizing agent is preferably one or more selected from alkyl ketene dimer sizing agents, rosin sizing agents, alkenyl succinic anhydride sizing agents, and styrene acrylic sizing agents, which can appropriately suppress water penetration and further suppress water absorption from the paper edge surface when exposed to hot water.

[0012] In an embodiment of the wrapping paper of the present invention, the pulp is preferably softwood pulp, which can provide wrapping paper with more suppressed decrease in puncture strength when wet and more improved internal bond strength.

[0013] In the method for producing packaging paper of the present invention, it is preferable to add the polymeric material by impregnating a paper base material mainly composed of pulp. With such a production method, a larger amount of polymeric material can be contained in the paper, the polymeric material can easily penetrate, and a water-resistant coating can be formed in the gaps between the fibers, resulting in a packaging paper with improved hot water resistance against hot water.

[0014] In an embodiment of the packaging paper of the present invention, the basis weight of the packaging paper is 40 to 150 g / m 2 If the paper has such a basis weight, it can be suitably used for flexible packaging applications, specifically, as a packaging paper having hot water resistance and moisture resistance for retort packaging and food.

[0015] In the embodiment of the packaging paper of the present invention, it is preferable that the puncture strength of the packaging paper when wet (after immersion in water at 23°C for 15 minutes) declines by 15% or less and the wet internal bond strength is 100 mJ or more. Packaging paper with such moisture resistance can be appropriately used as packaging paper for food without losing much strength even when immersed in water for retort sterilization, cooking, etc.

[0016] In an embodiment of the packaging paper of the present invention, the hot water absorption rate of the packaging paper is 2.0 g / 1000 mm 2 Packaging paper having such hot water resistance can suppress water absorption from the paper edge and can be used appropriately in hot water.

[0017] The packaging paper of the present invention, which has excellent moisture resistance and hot water resistance as described above, can be boiled in hot water, for example, and can be used as packaging paper for food. Furthermore, in the embodiment of the packaging paper of the present invention, the packaging paper of the present invention can preferably be used as packaging paper for retort packaging. Effect of the Invention

[0018] The present invention can provide a wrapping paper that is resistant to hot water and moisture while reducing the amount of plastic used. Specifically, it can provide a wrapping paper that can suppress the absorption of hot water from the paper edge, suppress the decrease in puncture strength when wet, and maintain the internal bond strength. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The wrapping paper of the present invention is characterized in that it contains a wet strength agent, a sizing agent, and a polymeric material in paper whose main component is pulp, and the polymeric material is one or more selected from styrene-butadiene latex, urethane resin, and acrylic resin. By containing a combination of a wet strength agent, a sizing agent, and a specific polymeric material, the wrapping paper of the present invention has hot water resistance and moisture resistance.

[0020] In the present invention, the paper contains a wet strength agent. In the packaging paper of the present invention, by containing a polymeric material in combination with the wet strength agent, the gaps between the pulp fibers can be filled, the fiber bonds can be reinforced, and the strength of the paper itself can be increased, and the decrease in strength of the packaging paper when wet can be suppressed (wet resistance). In other words, the combination of the wet strength agent and the polymeric material can impart wet resistance to the packaging paper. In a preferred embodiment of the present invention, the wet strength agent is preferably one or more selected from urea formaldehyde resin, melamine formaldehyde resin, polyamide epichlorohydrin resin, and epoxidized polyamide resin. It is particularly preferable to use polyamide epichlorohydrin resin. By using these wet strength agents, the decrease in strength of the paper when wet can be further suppressed, and packaging paper that has strength even when wet can be obtained.

[0021] The content of the wet strength agent is 0.01 to 5.0 parts by mass, for example, 0.02 to 3.0 parts by mass, preferably 0.05 to 1.0 parts by mass, more preferably 0.1 to 0.5 parts by mass, for example, 0.1 to 0.3 parts by mass, relative to 100 parts by mass of pulp. The wet strength agent is preferably added by adding an appropriate amount of the wet strength agent to the pulp slurry. With such an amount added, the decrease in strength of the paper when wet can be appropriately suppressed.

[0022] In the present invention, the paper further contains a sizing agent. In the packaging paper of the present invention, by containing a polymeric material in combination with the sizing agent, it is possible to obtain a packaging paper that can suppress water absorption from the paper edge surface in hot water (hot water resistance). In other words, hot water resistance can be imparted to the packaging paper by combining the sizing agent with the polymeric material. In a preferred embodiment of the present invention, it is preferable that the sizing agent is one or more selected from alkyl ketene dimer sizing agents, rosin sizing agents, alkenyl succinic anhydride sizing agents, and styrene acrylic sizing agents. With these sizing agents, it is possible to obtain a packaging paper that can appropriately suppress water penetration and further suppress water absorption from the paper edge surface in hot water.

[0023] The content of the sizing agent is 0.01 to 4.0 parts by mass, for example, 0.01 to 2.0 parts by mass, preferably 0.03 to 0.8 parts by mass, more preferably 0.05 to 0.4 parts by mass, for example, 0.05 to 0.15 parts by mass, relative to 100 parts by mass of pulp. With such an added amount, the strength of the paper can be appropriately suppressed from decreasing even when the packaging paper is wet. The sizing agent can be added by adding an appropriate amount of the sizing agent to the pulp slurry. It is also preferable to add the sizing agent by impregnating the paper base material with an impregnation liquid containing the sizing agent and the polymer material using a size press or the like.

[0024] In the present invention, the paper contains one or more polymeric materials selected from styrene-butadiene latex, urethane resin, and acrylic resin. By using these polymeric materials in the packaging paper of the present invention, a coating with high film-forming properties and water resistance can be formed, and packaging paper with hot water resistance against hot water can be obtained. Furthermore, by using a combination of a wet strength agent and a sizing agent in addition to these polymeric materials, it is possible to obtain a packaging paper that can suppress the absorption of hot water from the paper edge surface, and further suppress the decrease in puncture strength when wet and maintain internal bond strength, that is, a packaging paper that combines wet resistance and hot water resistance.

[0025] The content of the polymeric material is 3 to 40 parts by mass, preferably 5 to 30 parts by mass, more preferably 6 to 20 parts by mass, for example, 8 to 18 parts by mass, 10 to 16 parts by mass, relative to 100 parts by mass of pulp. Such an addition amount can further suppress the absorption of hot water from the paper edge, and can more appropriately suppress the decrease in strength of the paper even when the packaging paper is wet. Furthermore, the total content of the wet paper strength agent, sizing agent, and polymeric material is 5 to 40 parts by mass, preferably 8 to 35 parts by mass, and more preferably 10 to 30 parts by mass, relative to 100 parts by mass of pulp. If the total content of these three is less than 5 parts by mass, the voids in the paper cannot be filled, and packaging paper having appropriate hot water resistance and wet resistance may not be obtained. In addition, if the total content of these three exceeds 40 parts by mass, the effects on hot water resistance and wet resistance will reach a plateau and the cost will increase, which is not preferable. Furthermore, if the content of the polymeric material is particularly high, the effect of reducing plastic will be lost. The polymeric material can be added by incorporating an appropriate amount of the polymeric material in the pulp slurry (internal addition). Furthermore, it is preferable to add the polymeric material by impregnating the paper substrate with an impregnation liquid containing the polymeric material using a size press or the like. By impregnating the polymeric material rather than by internal addition, a larger amount of the polymeric material can be incorporated into the paper, the polymeric material can easily penetrate, and a water-resistant coating can be formed in the gaps between the fibers, resulting in a packaging paper with improved hot water resistance against hot water. Furthermore, the particle size of the polymeric material (measured by dynamic light scattering using ELS Z-1000 (manufactured by Otsuka Electronics Co., Ltd.)) may be 400 nm or less, preferably 200 nm or less, and these particle sizes allow the polymeric material to penetrate more easily into the paper.

[0026] In addition to the above-mentioned essential polymeric materials of the present invention, polymeric materials for imparting strength to the packaging paper can be added. For example, water-soluble or water-dispersible resins are preferred, but in addition to the above, polyvinyl alcohol, starch, carboxymethyl cellulose, etc. can also be added. However, since these are hydrophilic, the water resistance of the paper cross section is reduced, so even if they are used, the amount is small compared to the essential polymeric materials (for example, less than 3 parts by mass per 100 parts by mass of pulp). Furthermore, it is preferable not to use these polymeric materials. On the other hand, various waxes can also be used as polymeric materials for imparting water resistance to the paper. However, if a large amount of wax is contained, the strength of the paper is reduced, and since wax has a low melting point, it may be eluted in hot water, and the hot water resistance is rather reduced. Therefore, even if waxes are used, the amount is small compared to the essential polymeric materials (for example, less than 3 parts by mass per 100 parts by mass of pulp). Furthermore, it is preferable not to use these polymeric materials.

[0027] The paper base material used in this embodiment is not particularly limited, and any known paper base material containing pulp as the main component can be used. As the pulp that is the main component of the paper base material, chemical pulp such as LBKP (hardwood bleached kraft pulp) and NBKP (softwood bleached kraft pulp), mechanical pulp such as GP (groundwood pulp), PGW (pressurized groundwood pulp), RMP (refiner mechanical pulp), TMP (thermo-mechanical pulp), CTMP (chemi-thermo-mechanical pulp), CMP (chemi-mechanical pulp), and CGP (chemi-ground pulp), wood pulp such as DIP (deinked pulp), and non-wood pulp such as kenaf, bagasse, bamboo, and cotton can be used. In addition, unbleached pulp such as LUKP (hardwood unbleached kraft pulp) and NUKP (softwood unbleached kraft pulp) can also be used. These can be used alone or mixed in any ratio. The pulp of the present invention is preferably softwood pulp (e.g., NBKP, NUKP) and unbleached pulp such as NUKP (softwood unbleached kraft pulp) and LUKP (hardwood unbleached kraft pulp). For example, 90 to 100 parts by mass of softwood pulp such as NBKP (softwood bleached kraft pulp) or NUKP (softwood unbleached kraft pulp) can be used as the pulp. Alternatively, 90 to 100 parts by mass of unbleached pulp can be used as the pulp. It is also preferable to use only softwood pulp or unbleached pulp as the pulp. By using softwood pulp or unbleached pulp, it is possible to obtain a packaging paper in which the decrease in puncture strength when wet is more suppressed and the internal bond strength is more improved. The beating degree of the pulp may be in any range, but is preferably, for example, 450 to 750 mlCSF, for example, 400 to 650 mlCSF, 500 to 700 mlCSF, or even 550 to 650 mlCSF in Canadian standard freeness (JIS P 8121:1995 "Testing method for freeness of pulp") within these Canadian standard freeness (freeness) ranges, which allows the polymer material to penetrate more easily, and the strength of the paper can be further increased.

[0028] The packaging paper of the present invention has a basis weight of 40 to 150 g / m 2 and more preferably, the basis weight is 50 to 120 g / m 2 Such a basis weight is more suitable for use in flexible packaging applications, i.e., as a packaging paper having hot water resistance and moisture resistance for retort packaging and food. 2 If the basis weight of the packaging paper is less than 150 g / m, it may not be possible to ensure the thickness, strength, and stiffness required for packaging paper with hot water resistance and moisture resistance, and for retort packaging paper. 2 If it exceeds this value, the stiffness of the wrapping paper may be too high, making it difficult to use and process it as a flexible wrapping paper.

[0029] The packaging paper of the present invention can be a packaging paper in which the rate of decrease in puncture strength from dry to wet (after immersion in water at 23°C for 15 minutes) is 15% or less, and the wet internal bond strength after immersion in water at 23°C for 15 minutes is 100 mJ or more, preferably 150 mJ or more. Such packaging paper can be appropriately used as packaging paper for food, with almost no decrease in strength (wet resistance) even when immersed in water for retort cooking and the paper absorbs water, i.e., when wet. Furthermore, the packaging paper of the present invention can be preferably used as a packaging paper that can also be used for retort packaging.

[0030] The wrapping paper of the present invention has a hot water absorption rate of 2.0 g / 1000 mm 2 Less than 1.0g / 1000mm, preferably 1.0g / 1000mm 2 The packaging paper of the present invention can be made to have the following properties. Such packaging paper can suppress water absorption from the paper edge surface and can be used appropriately in hot water. The packaging paper of the present invention, which has such excellent water absorption suppression properties even when exposed to hot water, can be used, for example, as packaging paper for food that can be boiled in hot water. Furthermore, the packaging paper of the present invention can provide a packaging paper that can preferably be used as retort packaging.

[0031] In this embodiment, the density of the packaging paper is 0.6 to 1.1 g / cm 3 It is preferable that the temperature is within this range. By setting the temperature within this range, it is possible to suppress the absorption of water from the paper edge surface in hot water, and further suppress the decrease in puncture strength when wet, resulting in a packaging paper that can maintain its internal bond strength. The method for adjusting the density of the packaging paper is not particularly limited, but may include calendaring the base paper. The calendaring method is not particularly limited, and may be selected from known methods such as super calendaring, gross calendaring, shoe nip calendaring, and soft calendaring. The temperature, line pressure, and number of nips in the calendaring process may be appropriately set within a range that allows the desired density to be obtained.

[0032] The wrapping paper of the present invention may contain various papermaking materials such as aluminum sulfate, fillers, retention aids, coloring dyes, coloring pigments, and bulking agents, within the scope of the intended effects of the present invention. As the filler, one or more known fillers such as hydrated silicic acid, white carbon, talc, kaolin, clay, calcium carbonate, titanium oxide, aluminosilicate, calcined clay, barium sulfate, and synthetic resin fillers may be used. For example, 0.05 to 1.0 parts by mass, for example 0.1 to 0.5 parts by mass of aluminum sulfate may be contained per 100 parts by mass of pulp. Although the present invention can provide wrapping paper with excellent hot water resistance and wet resistance without lamination, the wrapping paper of the present invention may also be multi-layered. Furthermore, other layers such as laminates and coating layers may be added as necessary, and wrapping paper with even better hot water resistance and wet resistance may be obtained.

[0033] In the manufacturing method of the present invention, a pulp slurry with an appropriately adjusted freeness is dispersed in water, and a wet strength agent and, optionally, a sizing agent are added thereto and stirred to obtain a raw material slurry, which is then used to manufacture a base paper. Furthermore, it is preferable to impregnate the base paper with an impregnation liquid containing one or more polymeric materials selected from styrene-butadiene latex, urethane resin, and acrylic resin, and, optionally, a sizing agent, thereby obtaining the packaging paper of the present invention. In the manufacturing method of the present invention, it is preferable to add the polymeric material by impregnating the paper base material containing pulp as the main component. By impregnating the polymeric material rather than adding it internally, more of the polymeric material can be contained in the paper, which makes it easier for the polymeric material to penetrate, and a water-resistant coating can be formed in the gaps between the fibers, thereby obtaining a packaging paper with improved hot water resistance against hot water. EXAMPLES

[0034] <Example 1> 100 parts of NBKP, the freeness of which was adjusted to 600 ml CSF, was dispersed in water to prepare a pulp slurry. 0.2 parts of aluminum sulfate and 0.14 parts of a polyamide epichlorohydrin-based wet strength agent (product name: WS4020, manufactured by Seiko PMC) were added as a wet strength agent and stirred to obtain a raw slurry. This raw slurry was used to produce a pulp slurry of 61 g / m 2 Next, an impregnation solution with a solid content of 25% was applied to the base paper in a size press, which was a mixture of 100 parts of styrene acrylic latex (product name: Repellet A-9, manufactured by Nisshin Chemical Laboratory) as a polymer material and 0.6 parts of an alkyl ketene dimer sizing agent (product name: SE2360, manufactured by Seiko PMC Corporation) as a sizing agent, so that the impregnation amount of the base paper was 9 g / m. 2 The material is impregnated so that the basis weight is 70g / m 2 I got the packaging paper.

[0035] <Example 2> In Example 1, 100 parts of NUKP was used as the pulp, the wet strength agent was a polyamide epoxy resin-based wet strength agent (product name: Sumirez Resin 675A, manufactured by Taoka Chemical Co., Ltd.), and 0.09 parts of a rosin-based sizing agent (product name: AL1300, manufactured by Seiko PMC Co., Ltd.) were used as the sizing agent. The same procedures as in Example 1 were repeated except that these were added to the pulp slurry, and the impregnation liquid was made solely of a polymer material, a styrene-butadiene-based latex (product name: Smartex PA3802, manufactured by Nippon A&L Co., Ltd.).

[0036] <Example 3> Packaging paper was obtained in the same manner as in Example 1, except that the polymer material was a urethane-based latex (product name: Hydran HW-350, manufactured by DIC Corporation) and the sizing agent was a styrene-acrylic sizing agent (product name: Keicoat S-930K2, manufactured by Toho Chemical Industry Co., Ltd.).

[0037] <Comparative Example 1> In Example 1, a melamine resin-based wet strength agent (product name: Sumirez Resin 8% AC, manufactured by Taoka Chemical Industry Co., Ltd.) was used as the wet strength agent, no polymer material or sizing agent was added, and no impregnation treatment was performed. Except for this, packaging paper was obtained in the same manner as in Example 1.

[0038] <Comparative Example 2> In Example 1, no wet strength agent or sizing agent was added to the pulp slurry, and only a styrene-acrylic sizing agent (product name: Keicoat S-930K2, manufactured by Toho Chemical Industry Co., Ltd.) was added to the impregnation liquid at an impregnation amount of 0.18 g / m. 2 A wrapping paper was obtained in the same manner as in Example 1, except that the paper was impregnated so as to obtain a wrapping paper.

[0039] <Comparative Example 3> A packaging paper was obtained in the same manner as in Example 1, except that no wet strength agent was added and no sizing agent was included in the impregnation liquid.

[0040] <Comparative Example 4> In Example 2, the amount of wet strength agent added was 0.2 parts, the amount of sizing agent added was 0.5 parts, no polymer material was added, and no impregnation treatment was performed. In the same manner as in Example 2, except that, packaging paper was obtained.

[0041] <Comparative Example 5> A packaging paper was obtained in the same manner as in Example 2, except that no wet strength agent was added and the amount of sizing agent added was 0.6 parts.

[0042] <Comparative Example 6> In Example 3, the impregnation solution did not contain a sizing agent, and the impregnation amount was 15 g / m 2 The basis weight of the packaging paper is 76 g / m 2 A packaging paper was obtained in the same manner as in Example 3, except that the above-mentioned was used.

[0043] <Comparative Example 7> A packaging paper was obtained in the same manner as in Example 1, except that the impregnation liquid did not contain a sizing agent and the polymer material was wax (product name: Petrox P300, manufactured by Meisei Chemical Industry Co., Ltd.).

[0044] <Comparative Example 8> In Example 2, no wet strength agent was added, the amount of sizing agent added was 0.5 parts, the polymer material was sodium salt of carboxymethylcellulose (product name: Cellogen PR, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and the impregnation amount was 3.5 g / m 2 The basis weight of the packaging paper is 64.5 g / m 2 A packaging paper was obtained in the same manner as in Example 3, except that the above-mentioned was used.

[0045] <Comparative Example 9> In Example 2, the amount of the wet strength agent was 0.2 parts, the amount of the sizing agent was 0.25 parts, the polymer material of the impregnation solution was sodium carboxymethylcellulose (product name: Cellogen PR, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and the impregnation amount was 3.5 g / m 2 The basis weight of the packaging paper is 64.5 g / m 2 A packaging paper was obtained in the same manner as in Example 2, except that:

[0046] <Comparative Example 10> A packaging paper was obtained in the same manner as in Example 1, except that the polymer material in the impregnation liquid was changed to wax (product name: Petrox P300, manufactured by Meisei Chemical Industry Co., Ltd.).

[0047] The puncture strength of the packaging paper obtained above was measured under the conditions below before wetting (i.e., when dry) and after wetting (after immersion for 15 minutes in water adjusted to a temperature of 23°C x 50% rh), and the reduction rate (%) of puncture strength when wet compared to when dry was calculated, and the results are shown in Table 1.

[0048] Physical property measurement conditions ·Puncture strength···(A) Using an Autograph Precision Universal Tester (AGS-10kNX: manufactured by Shimadzu Corporation), measurements were taken according to the following method in accordance with "7.5 Puncture Strength Test" in "JIS Z 1707:2019 General Rules for Food Packaging Plastic Films". The test pieces of packaging base paper were conditioned for 24 hours at 23°C x 50% rh. (A) 1. The test piece 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 pierced at a test speed of 50 mm / min, and the maximum force (N) until the needle penetrated was measured. 2. Each test piece was pierced at 15 points, and the average value was taken as the piercing strength (N). Wet puncture strength (B) The test piece was immersed in water adjusted to 23℃ x 50% rh for 15 minutes, the moisture on the surface was wiped off, and then the measurement was performed according to the above method. -Puncture strength reduction rate (%) = (AB) x 100 / A

[0049] The wet internal bond strength of the packaging paper obtained above was measured under the conditions below, and the results are shown in Table 1. The wet internal bond strength is the strength at which the internal paper layers of the paper are peeled off, and the strength within the paper layers was measured after wetting (after immersion in temperature-controlled water in an environment of 23°C x 50% rh for 15 minutes).

[0050] Wet internal bond strength The test piece was immersed in water adjusted to a temperature of 23°C x 50% rh for 15 minutes, and after wiping off the moisture on the surface, it was measured based on Japan TAPPI No. 18-2.

[0051] Packaging paper with a puncture strength reduction rate when wet of 15% or less and a wet internal bond strength of 100 mJ or more can be boiled in hot water and used as food packaging paper, and furthermore, has sufficient strength when wet to withstand use as retort packaging.

[0052] The hot water absorption rate of the end grain of the wrapping paper obtained above was measured under the following conditions, and the results are shown in Table 1. The hot water absorption rate of the end grain of the wrapping paper was measured under the following conditions. 2 It indicates the amount of hot water absorbed from the cut edge of the wood. 2 If the thickness is below this range, water absorption from the paper edge can be appropriately suppressed, the paper can be boiled in hot water, and the paper can be used as food packaging paper.Furthermore, the paper can be made to be suitable for use as retort packaging.

[0053] -Hot water wood end absorbency Tape (Carton Tape No. 660, Nichiban Co., Ltd.) was applied to both sides of the wrapping paper to prevent water absorption from the paper surface, and the paper was cut into 50 mm x 50 mm pieces to prepare test pieces. The test pieces were immersed in 90°C hot water for 20 minutes, and the hot water cut end water absorption was calculated using the following formula. Hot water wood end water absorption (g / 1000mm 2 ) = (weight after test (g) - weight before test (g)) x 1000 / (paper thickness (mm) x circumference of test piece (mm))

[0054] [Table 1]

[0055] In Table 1, the "%" for the total content of the wet strength agent, sizing agent, and polymeric material indicates the mass % relative to the pulp. The packaging paper of the present invention, which contains a specific polymeric material selected from styrene-butadiene latex, urethane resin, and acrylic resin, as well as the wet strength agent and sizing agent, has a puncture strength reduction rate of 15% or less when immersed in water at 23°C for 15 minutes, a wet internal bond strength of 100 mJ or more, and a hot water end grain water absorption of 2.0 g / 1000 mm. 2 That is, it has been shown that the present invention can provide a packaging paper that is excellent in hot water resistance and wet resistance, capable of suppressing absorption of hot water from the paper edge surface, suppressing a decrease in puncture strength when wet, and maintaining internal bond strength.

Claims

1. The packaging paper contains a wet strength agent, a sizing agent, and a polymeric material in paper containing pulp as a main component, and the polymeric material is one or more selected from the group consisting of styrene-butadiene latex, urethane resin, and acrylic resin.

2. 2. The packaging paper according to claim 1, wherein the wet strength agent is one or more selected from the group consisting of urea formaldehyde resin, melamine formaldehyde resin, polyamide epichlorohydrin resin, and epoxidized polyamide resin.

3. 3. The packaging paper according to claim 1, wherein the sizing agent is one or more selected from the group consisting of alkyl ketene dimer sizing agents, rosin sizing agents, alkenyl succinic anhydride sizing agents, and styrene acrylic sizing agents.

4. 3. The wrapping paper according to claim 1 or 2, characterized in that the pulp is softwood pulp.

5. 3. A method for producing a wrapping paper according to claim 1 or 2, characterized in that the polymeric material is added to a pulp-based paper base material by impregnation.

6. Basis weight: 40 to 150 g / m ２ The wrapping paper according to claim 1 or 2,

7. 3. The wrapping paper according to claim 1 or 2, characterized in that the decrease in puncture strength when wet after immersion in water at 23°C for 15 minutes from a dry state is 15% or less, and the wet internal bond strength is 100 mJ or more.

8. Hot water absorption at wood end is 2.0g / 1000mm ２ 3. The packaging paper according to claim 1 or 2, characterized in that:

9. 7. The wrapping paper according to claim 6, which is a wrapping paper for retort packaging.

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