Packaging paper

Abstract

To provide a packaging paper with reduced used amount of plastics as well as having good heat seal strength on heat sealing of a heat seal layer face with an original paper face at low temperature.SOLUTION: A packaging paper is characterized by including: on one face of a base paper, a heat seal layer including at least one or more kinds selected from a group consisting of an ionomer, an ethylene-based copolymer, a thermoplastic urethane, polyvinylidene chloride, polylactic acid, and polybutylene succinate; and on the other face of the base paper, an adhesion auxiliary layer obtained by coating polyethyleneimine. A coefficient of static friction measured by laminating the heat seal layer face and the adhesion auxiliary layer face is 0.20 or over.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to packaging paper that reduces the amount of plastic used and has good heat seal strength even when heat sealing the heat seal layer surface and the base paper surface at low temperatures. [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 large portion and contributing significantly to plastic waste. Plastic does not decompose semi-permanently, and its waste breaks down into microplastics in the natural environment, severely impacting ecosystems. Marine pollution, in particular, is severe, and the resulting plastic waste is considered impossible to recover. Reducing plastic use is essential for the global environment.

[0003] Among the plastics used in packaging containers, polyethylene terephthalate (PET), used in beverage bottles, and polyethylene (PE) and polypropylene (PP), used in shopping bags and container laminations, are particularly common. As a measure to reduce the amount of plastic used, it has been proposed to replace plastic with paper. However, even when replacing plastic with paper, a large amount of polyethylene or polypropylene is laminated as a heat sealant when processing bags and containers. The amount of these plastics laminated varies depending on the product concept, but is generally around 30-50 g / m². 2 It is approximately 300g / m² depending on the application. 2 It is sometimes used in large quantities.

[0004] Laminated paper is often designed to adhere to each other on the laminated surfaces, but depending on the design of the container during processing, adhesion between the laminated surface and the base paper surface (the back of the laminated surface, which does not have a laminate layer) may also be required. For example, when bonding single-sided laminated paper to a cylindrical shape, such as the body of a paper cup, good adhesion between the laminated surface and the base paper surface is essential. In addition, the specifications of the processing machine may not allow for high heat sealing temperatures. Generally, the adhesion between the laminated surface and the base paper surface is lower than the adhesion between the laminated surfaces themselves, and low-temperature heat sealing often leads to a decrease in adhesive strength. One known method to increase the adhesive strength of the laminated surface is to increase the amount of laminate applied. When conditions that reduce adhesive strength overlap, it may be necessary to further increase the amount of laminate applied to the laminated surface to be bonded to the base paper surface, or to apply a plastic laminate to the base paper surface as well.

[0005] Therefore, even with paper containers that replace plastic with paper, the amount of plastic used is still not sufficiently reduced, and there is an urgent need for means to reduce plastic use quickly and directly.

[0006] One proposed packaging paper for this purpose has a heat-sealable layer containing a styrene-acrylic ester copolymer resin on a paper substrate, thereby providing heat-sealability and ease of disintegration during recycling (see Patent Document 1). Another proposed packaging paper has at least one heat-sealable layer on at least one surface of the paper substrate, wherein the heat-sealable layer contains an ionomer, and the dry coating amount of the heat-sealable layer is 2 to 10 g / m² for the entire layer. 2 There are proposals to reduce the amount of plastic used and provide heat-sealability by doing so (see Patent Document 2).

[0007] However, in the packaging paper described in Patent Document 1, although there is heat-sealing property between the heat-sealing layers, the heat-sealing property between the heat-sealing layer and the base paper surface is insufficient. For this reason, in the heat-sealing between the heat-sealing layer and the base paper surface, when formed into a bag or a cup under the same conditions as conventional laminated paper, the heat-sealing part may not adhere, or the seal part may peel off before or during the use of the container. In addition, in the packaging paper described in Patent Document 2, although there is an effect of reducing the amount of plastic used and heat-sealing property between the heat-sealing layer and the base paper surface at high temperatures, the heat-sealing property between the heat-sealing layer and the base paper surface at low temperatures (about 100 to 130 °C) is insufficient. When the heat-sealing temperature cannot be sufficiently ensured due to the specifications of the processing machine, there is a risk that the heat-sealing part will not adhere. Here, the "heat-sealing property" means the adhesiveness of the heat-sealing surface.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

[0012] In the present invention, the heat-sealing layer preferably has a dry coating amount in the range of 1 to 20 g / m 2 . By adopting such a configuration, compared with the case where the amount of plastic used in conventional poly lam paper exceeds 30 g / m 2 , the amount of plastic contained in the heat-sealing layer can be reduced to about 40 to 67% of the conventional amount.

[0013] In the present invention, the adhesion assisting layer preferably has a dry coating amount in the range of 0.05 to 3 g / m 2 . By adopting such a configuration, a packaging paper having sufficient heat-sealability and being less likely to block between the packaging papers and having good processing suitability can be obtained.

[0014] In the present invention, an underlayer containing a binder may be further provided between the base paper and the heat-seal layer. Providing an underlayer results in better barrier properties, making the packaging paper superior in water resistance, oil resistance, and other properties.

[0015] In the present invention, it is preferable that the smoothness of the surface having the adhesive auxiliary layer is 5 seconds or more. With this configuration, the adhesion between the heat seal layer surface and the base paper surface is improved, and packaging paper with excellent heat seal strength can be obtained.

[0016] Furthermore, the present invention can also be considered as an invention relating to a method for manufacturing packaging paper. The method for manufacturing packaging paper according to the present invention comprises the steps of preparing a base paper and coating one side of the base paper with polyethyleneimine using one of the methods selected from the group consisting of coating, sizing press, gate roll, impregnation, and spraying, with a dry coating amount of 0.05 to 3 g / m². 2 The process involves applying an adhesive auxiliary layer to the base paper surface within a certain range, and then applying a heat seal layer coating liquid containing one or more of the following to the other side of the base paper, in a dry coating amount of 1 to 20 g / m²: ionomer, ethylene copolymer, thermoplastic urethane, polyvinylidene chloride, polylactic acid, and polybutylene succinate. 2 The present invention is characterized by comprising the step of applying a heat seal layer to the other surface of the base paper by coating within a certain range. With the present invention's method for manufacturing packaging paper, it is possible to obtain packaging paper that reduces the amount of plastic used and has good heat seal strength even when heat sealing the heat seal layer surface and the base paper surface at low temperatures.

[0017] In the present invention, in the step of applying the heat seal layer, it is preferable that the coating liquid for the heat seal layer is an aqueous emulsion. By using an aqueous emulsion, it is possible to control the amount of coating to a relatively low level, and furthermore, the burden on the natural environment can be reduced by eliminating VOC (volatile organic compound) emissions.

[0018] In the present invention, it is preferable that the coating liquid for the heat seal layer contains only water and one or more selected from the group consisting of ionomers, ethylene copolymers, thermoplastic urethanes, polyvinylidene chloride, polylactic acid, and polybutylene succinate. With such a configuration, since it does not contain additives that may lead to a decrease in heat seal strength, it is possible to obtain packaging paper with more stable heat seal strength. [Effects of the Invention]

[0019] As described above, the present invention makes it possible to manufacture packaging paper that reduces the amount of plastic used and has good heat seal strength even when heat sealing the heat seal layer surface and the base paper surface at low temperatures. If a container product using the packaging paper of the present invention is released into nature as waste, it is possible to reduce the adverse impact on the natural environment as plastic waste, thus contributing to the solution of the plastic waste problem. The packaging paper of the present invention can be processed into, for example, primary and secondary bags in food packaging, food cups for ice cream, lids for cup containers, beverage cups for coffee, food containers for hot snacks, trays, boxes, cases, and all kinds of paper containers. [Brief explanation of the drawing]

[0020] [Figure 1] This figure shows an example of the structure of packaging paper according to the present invention. [Figure 2] This is a diagram showing the physical properties of the packaging paper obtained from the examples and comparative examples. [Modes for carrying out the invention]

[0021] Next, the present invention will be described in detail with reference to an example of an embodiment, but the present invention is not to be construed as being limited to this description. Various modifications of the embodiment are possible as long as the effects of the present invention are achieved.

[0022] An example of the structure of the packaging paper according to the present invention is shown in Figure 1. In the figure, 1 is the packaging paper, 11 is the heat-seal layer, 11a is the upper layer of the heat-seal layer, 11b is the bottom layer of the heat-seal layer, 12 is the underlayer, 13 is the base paper, 14 is the paper substrate, 15 is the printing layer, and 16 is the adhesive auxiliary layer. Also, in Figure 1, the thickness of each layer shown in the figure is not proportional to the actual thickness.

[0023] Figure 1(a) shows an example in which a single heat-seal layer 11 is provided on one side of the base paper 13, and a single adhesive auxiliary layer 16 is provided on the other side. Figure 1(b) shows a paper substrate 14 formed by providing an underlayer 12 on one side of the base paper 13 and a printing layer 15 on the other side, and a heat-seal layer 11 consisting of a total of two layers, the bottom heat-seal layer 11b and the top heat-seal layer 11a, is coated on the underlayer 12. This is an example in which a single adhesive auxiliary layer 16 is provided on the other side of the base paper 13. Note that in the example of Figure 1(b), multiple layers of the top heat-seal layer 11a may be provided.

[0024] In this embodiment, the heat seal layer is characterized by containing one or more of the following: ionomer, ethylene copolymer, thermoplastic urethane, polyvinylidene chloride, polylactic acid, and polybutylene succinate. Here, ionomer refers to a synthetic resin in which polymers are aggregated using the cohesive force of metal ions, and includes all materials in which resin and metal cations are intermolecularly bonded to form aggregates. Examples include metal salts of ethylene-methacrylic acid copolymer, metal salts of ethylene-acrylic acid copolymer, metal salts of ethylene-urethane copolymer, and metal salts of ethylene-fluorine polymer copolymer. In the present invention, metal salts of ethylene-acrylic acid or ethylene-methacrylic acid copolymers are preferred among ionsomers because they can provide heat seal strength at low temperatures even with a relatively small dry coating amount. Furthermore, as the ethylene copolymer, it is preferable that it be one of the following: ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-acrylic acid ester copolymer, ethylene-methacrylic acid ester copolymer, or ethylene vinyl acetate copolymer, because it exhibits particularly excellent heat seal strength. There are no particular restrictions on the thermoplastic urethane, but it is preferably an ester-based, ester-ether-based, carbonate-based, or aromatic isocyanate-based thermoplastic urethane. The polyvinylidene chloride may be vinylidene chloride alone or a copolymer with other polymers. There are no particular restrictions, but it is preferably a copolymer with latex, vinyl chloride, methacrylic acid ester, acrylic acid ester, or an unsaturated carboxylic acid. The polylactic acid may be polylactic acid alone or a copolymer with other polymers. L-lactic acid and D-lactic acid exist, and these are polymerized to form polylactic acid, but the ratio of L-lactic acid to D-lactic acid can be any ratio as long as it does not affect the heat seal performance. Furthermore, it is preferably a copolymer with hydroxycarboxylic acid, aliphatic cyclic ester, dicarboxylic acid, or polyhydric alcohols. The polybutylene succinate resin may be polybutylene succinate alone or a copolymer with other polymers. There are no particular restrictions, but it may be a copolymer with adipic acid or polyethylene glycol, for example.In the present invention, ionomers or ethylene copolymers are particularly preferred. They exhibit particularly excellent heat seal strength between the heat seal layer surface and the base paper surface. The packaging paper of the present invention may contain other resins as long as they do not affect the heat seal performance, and may also contain a mixture of multiple resins.

[0025] In embodiments of the present invention, a heat seal layer can be provided by coating one side of a base paper with a coating liquid for a heat seal layer containing an aqueous emulsion comprising one or more of ionomers, ethylene copolymers, thermoplastic urethanes, polyvinylidene chlorides, polylactic acid, and polybutylene succinate, and then drying it. It is preferable that the resin used in the heat seal layer, comprising one or more of ionomers, ethylene copolymers, thermoplastic urethanes, polyvinylidene chlorides, polylactic acid, and polybutylene succinate, is an aqueous emulsion. By using an aqueous emulsion, the amount of coating can be controlled to be relatively low, and furthermore, the burden on the natural environment can be reduced by eliminating VOC emissions.

[0026] In embodiments of the present invention, the coating liquid for the heat seal layer may contain, in addition to an aqueous emulsion containing one or more of ionomers, ethylene copolymers, thermoplastic urethanes, polyvinylidene chloride, polylactic acid, and polybutylene succinate, various auxiliary agents may be added to the extent that they do not impair the effects of the present invention. Examples include viscosity modifiers, defoamers, leveling agents such as surfactants and alcohols, coloring pigments, coloring dyes, lubricants such as waxes, and pigments such as clay and calcium carbonate. However, since the addition of these auxiliary agents tends to reduce the heat seal strength, it is preferable to add them in small amounts, and it is more preferable that the coating liquid for the heat seal layer consists only of an aqueous emulsion containing one or more of ionomers, ethylene copolymers, thermoplastic urethanes, polyvinylidene chloride, polylactic acid, and polybutylene succinate.

[0027] In this invention, the amount of heat-seal layer applied is 1 to 20 g / m² in terms of solid content per side of the base paper.2 is preferably 3 to 15 g / m 2 and more preferably so. If the coating amount is less than 1 g / m 2 , there is a risk that sufficient heat seal strength cannot be obtained. Conversely, if it exceeds 20 g / m 2 , sufficient heat seal strength can be obtained, but since the amount of plastic used also increases, there is a risk that the plastic reduction effect will be poor. In the packaging paper of the present invention, the heat seal layer is usually provided not only on a part of the surface of the base paper but on the entire surface. That is, the heat seal layer is preferably provided so as to cover the entire surface of the base paper, rather than being provided only on the parts necessary for adhesion by heat seal, such as in a net shape, island shape, or linear shape.

[0028] In an embodiment of the present invention, the heat seal layer may be formed of two or more layers. By making the heat seal layer two or more layers, the air permeability of the packaging paper can be increased, and further water resistance, oil resistance, and moisture resistance can be imparted to obtain a barrier property at the same level as poly-laminated paper. When the heat seal layer is two or more layers, it is preferable that the coating amount of the lowermost heat seal layer closest to the base paper is larger than the total coating amount of the upper heat seal layers. By configuring in this way, the air permeability of the packaging paper can be further improved, and the water resistance, oil resistance, and moisture resistance are further enhanced. Even when the heat seal layer is two or more layers, the total coating amount of the heat seal layer is preferably 1 to 20 g / m in terms of solid content 2 and more preferably 3 to 15 g / m 2 .

[0029] The method for applying the coating liquid for the heat seal layer in the present invention is not particularly limited, and commonly used coating equipment can be used. For example, various known coating equipment such as air knife coaters, blade coaters, gravure coaters, flexo coaters, rod blade coaters, roll coaters, reverse roll coaters, bar coaters, curtain coaters, die slot coaters, champlex coaters, metering blade type size press coaters, short dwell coaters, spray coaters, gate roll coaters, and lip coaters can be used.

[0030] In embodiments of the present invention, an underlayer may be provided between the base paper and the heat-seal layer. When the heat-seal layer is directly applied to the surface of the base paper, the coating liquid for the heat-seal layer is easily absorbed by the base paper, which may cause defects in the resin film of the heat-seal layer. Therefore, especially in applications where barrier properties such as water resistance and oil resistance are required, measures such as increasing the amount of coating liquid for the heat-seal layer are necessary. However, increasing the amount of coating liquid for the heat-seal layer also increases the amount of plastic used proportionally, which has the problem of reducing the plastic reduction effect. In the present invention, an underlayer is provided between the base paper and the heat-seal layer as a means of improving barrier properties without increasing the amount of plastic used. By providing an underlayer, the coating liquid for the heat-seal layer is less likely to be absorbed by the base paper, and barrier properties such as water resistance and oil resistance can be improved without changing the composition or amount of the coating liquid for the heat-seal layer. The underlayer has a sealing effect that prevents the coating liquid for the heat-seal layer from penetrating into the base paper, so it is easier to form a resin film with fewer defects even with a small amount of heat-seal layer coating, and packaging paper with better barrier properties can be obtained. Furthermore, the underlayer itself has an effect of preventing the penetration of water and oil, and through a synergistic effect with the heat-seal layer, excellent barrier properties can be obtained.

[0031] In embodiments of the present invention, the underlayer is preferably composed of a combination of pigment and binder, or a binder alone. As the pigment in the underlayer, known pigments used in the coating layer of general printing coated paper can be used. Examples of such pigments include inorganic pigments such as kaolin clay, calcium carbonate (heavy calcium carbonate, light calcium carbonate, etc.), calcined clay, talc, magnesium carbonate, barium sulfate, calcium sulfate, titanium dioxide, zinc oxide, zinc sulfate, zinc carbonate, calcium silicate, aluminum silicate, magnesium silicate, diatomaceous earth, aluminum hydroxide, and magnesium hydroxide, or organic pigments such as acrylic, styrene, vinyl chloride, nylon itself, or obtained by copolymerizing these (so-called plastic pigments (hereinafter sometimes abbreviated as "PP particles")).

[0032] In embodiments of the present invention, known binders used in the coating layers of general printing coated paper can also be used for the binder in the underlayer. Examples of such binders include starches such as butadiene copolymer latex, crosslinking agent modified starch, oxidized starch, enzyme modified starch, esterified starch, etherified starch, cationic starch, and amphoteric starch; water-soluble polymers such as gelatin, casein, soy protein, and polyvinyl alcohol; synthetic resins such as vinyl acetate, ethylene vinyl acetate, polyurethane resins, acrylic resins, polyester resins, polyamide resins, ionomers, thermoplastic urethanes, polyvinylidene chloride, polylactic acid, polybutylene succinate, and other ethylene copolymers.

[0033] In embodiments of the present invention, the underlayer may contain various auxiliary agents to the extent that they do not impair the effects intended for the present invention. For example, it may contain viscosity modifiers, softeners, gloss enhancers, water-resistant agents, dispersants, flow modifiers, UV absorbers, stabilizers, antistatic agents, crosslinking agents, sizing agents, fluorescent whitening agents, colorants, pH adjusters, defoamers, plasticizers, and preservatives.

[0034] The method for applying the undercoat coating liquid is not particularly limited, and various known coating devices that are commonly used can be used. For example, various known coating devices such as air knife coaters, blade coaters, gravure coaters, flexo coaters, rod blade coaters, roll coaters, reverse roll coaters, bar coaters, curtain coaters, die slot coaters, champlex coaters, metering blade type size press coaters, short dwell coaters, spray coaters, gate roll coaters, and lip coaters can be used.

[0035] Embodiments of the present invention may include a step of smoothing the base paper or paper substrate. The method for smoothing the base paper and paper substrate is not particularly limited, and commonly used calendering devices can be used. For example, various known smoothing devices such as machine calenders, soft calenders, supercalenders, gloss calenders, and shoe-nip calenders can be used. Furthermore, a step of transferring the mirror surface of a Yankee dryer, as used for single-sided gloss kraft paper, and smoothing it may also be included. By applying a heat seal layer to the smoothed surface, the coating liquid for the heat seal layer is more easily applied uniformly to the paper substrate and the underlayer surface, resulting in a high sealing effect and a packaging paper with good water resistance.

[0036] In embodiments of the present invention, the base paper surface has an adhesive auxiliary layer coated with polyethyleneimine. Polyethyleneimine is a polymer of ethyleneimine and is a resin with excellent adhesive properties. Therefore, even at low heat-seal temperatures, it acts as an adhesive auxiliary agent on the base paper surface for thermoplastic resins, particularly ionomers, ethylene copolymers, thermoplastic urethanes, polyvinylidene chloride, polylactic acid, and polybutylene succinate, providing good heat sealability and heat seal strength. Specific trade names for polyethyleneimine include, for example, the Epomin® series (manufactured by Nippon Shokubai Co., Ltd.) and Seikadine 4100 (manufactured by Dainichi Seika Co., Ltd.). In the packaging paper of the present invention, other types of polyethyleneimine may be used as long as they do not affect the heat sealability.

[0037] In embodiments of the present invention, an adhesive auxiliary layer can be provided on the base paper surface by applying an aqueous emulsion containing polyethyleneimine to the base paper surface using one of the methods selected from coating, sizing press, gate roll, impregnation, and spraying. In this embodiment, it is preferable that polyethyleneimine is abundantly distributed on the surface of the base paper surface. The presence of polyethyleneimine on the surface of the base paper surface allows the heat seal layer and polyethyleneimine to adhere closely together, even during low-temperature heat sealing between the heat seal layer surface and the base paper surface, providing good heat seal strength. For example, a coating solution containing an aqueous emulsion containing polyethyleneimine can be applied to the surface of the base paper surface and dried. Alternatively, a coating solution containing an aqueous emulsion containing polyethyleneimine can be applied to the base paper surface using a gate roll coater, rod metering coater, two-roll coater, etc., during the sizing press process when the base paper is made. The method for providing the adhesive auxiliary layer is not limited to the above, and various known coating, sizing press, gate roll, impregnation, and spraying methods can be used.

[0038] In embodiments of the present invention, it is preferable that the coating liquid or application liquid used for the heat seal layer, underlayer, and adhesive auxiliary layer is an aqueous emulsion. By using an aqueous emulsion, it is possible to control the coating amount to a relatively low level, and furthermore, VOC emissions are eliminated, reducing the burden on the natural environment. The polyethyleneimine content is 0.05 to 3 g / m² in terms of solid content per side of the base paper. 2 The concentration is preferably 0.1 to 1 g / m 2 It is 0.05 g / m 2 If the value is less than 3g / m, sufficient quality cannot be obtained in terms of heat seal strength at low temperatures. Conversely, if it is less than 3g / m, sufficient quality cannot be obtained. 2 If the temperature exceeds a certain level, sufficient heat seal strength can be obtained even at low temperatures, but this may lead to blocking and deterioration of slipperiness, potentially impairing the processability. In the packaging paper of the present invention, the polyethyleneimine adhesive auxiliary layer may be applied to the entire surface, or it may be provided only in the parts necessary for heat sealing adhesion between the heat seal layer surface of the base paper and the base paper surface.

[0039] In embodiments of the present invention, the coating solution or application liquid containing polyethyleneimine emulsion applied to the base paper surface may contain various additives in addition to the polyethyleneimine aqueous emulsion. Examples include viscosity modifiers, defoamers, leveling agents such as surfactants and alcohols, coloring pigments, coloring dyes, water-resistant agents, lubricants such as waxes, pigments such as clay and calcium carbonate, and various binders, which are known papermaking chemicals. In the packaging paper of the present invention, other additives may be included as long as they do not affect the heat-seal performance, and furthermore, multiple additives may be mixed.

[0040] The methods for coating, sizing, gate rolling, impregnation, and spraying polyethyleneimine in the present invention are not particularly limited, and commonly used coating equipment can be used. For example, various known coating equipment such as air knife coaters, blade coaters, gravure coaters, flexo coaters, rod blade coaters, roll coaters, reverse roll coaters, bar coaters, curtain coaters, die slot coaters, champlex coaters, gate roll coaters, rod metering coaters, two-roll coaters, short dwell coaters, spray coaters, gate roll coaters, and lip coaters can be used.

[0041] In embodiments of the present invention, it is preferable that the smoothness of the surface having the adhesive auxiliary layer is 5 seconds or more. The heat seal layer of this embodiment has a dry coating amount of 1 to 20 g / m². 2 Packaging paper in this range contains less plastic that acts as an adhesive during heat sealing compared to conventional poly-laminated paper, which is particularly disadvantageous when heat sealing the heat-seal layer and the base paper surface at low temperatures. Therefore, it is necessary to improve the heat-sealability of the base paper surface. By having a smoothness of 5 seconds or more on the surface with the adhesive auxiliary layer, the adhesion between the heat-seal layer surface and the base paper surface is increased during heat sealing, and packaging paper with excellent heat-seal strength can be obtained. In this embodiment, it is preferable that the smoothness of the surface with the adhesive auxiliary layer be 5 seconds or more. More preferably, it is 10 seconds or more. In this embodiment, the smoothness was measured using a Beck smoothness tester (NKE-A1272) in accordance with JIS P 8119:1998.

[0042] In embodiments of the present invention, the method for smoothing the surface having the adhesive auxiliary layer may involve smoothing the base paper or paper substrate in a step before applying the adhesive auxiliary layer, or performing the smoothing treatment after applying the adhesive auxiliary layer. The method for performing the smoothing treatment is not particularly limited, and commonly used calendering devices can be used. For example, various known smoothing devices such as machine calenders, soft calenders, supercalenders, gloss calenders, and shoe-nip calenders can be used. Furthermore, the method may include a step of transferring the mirror surface of a Yankee dryer, as used for single-sided gloss kraft paper, and then performing the smoothing treatment.

[0043] In embodiments of the present invention, a printing layer may be provided on the base paper surface, and the printing layer preferably contains a combination of pigment, binder, and various auxiliary agents, for example, as in the coating layer of known printed coated paper. The composition of the printing layer is not particularly limited, but the same pigment, binder, and various auxiliary agents as in the underlayer can be used. When the base paper surface is processed into bags, cups, or containers and becomes the outside of the container, printing may be done to indicate the contents or to advertise them. Therefore, packaging paper with a printing layer on the base paper surface can be obtained with good printability. In addition, the printing layer makes the base paper surface smooth, which increases adhesion with the heat seal layer surface during heat sealing, resulting in packaging paper with superior heat seal strength. When providing a printing layer on the base paper surface, providing an adhesive auxiliary layer on top of the printing layer, or including polyethyleneimine in the printing layer, allows the polyethyleneimine to act as an adhesive auxiliary agent with the heat seal layer surface on the outermost surface of the base paper surface, thereby obtaining good heat seal strength.

[0044] In this embodiment of the present invention, the static friction coefficient measured by overlapping the heat seal layer surface and the adhesive auxiliary layer surface is configured to be 0.20 or higher, more preferably 0.30 or higher. By setting the static friction coefficient measured by overlapping the heat seal layer surface and the adhesive auxiliary layer surface to 0.20 or higher, slippage between the heat seal layer surface and the base paper surface (adhesive auxiliary layer surface) during the heat seal process can be suppressed, and good heat seal strength can be obtained even at relatively low heat seal temperatures. Packaging paper with a static friction coefficient of less than 0.20 may experience slippage during the heat seal process, causing the seal position to shift from its original position, reducing the heat seal area, and potentially lowering the heat seal strength. Furthermore, if the adhesive auxiliary layer is provided only in the heat seal portion, the shift in the seal position may cause the adhesive auxiliary layer to no longer overlap the seal position, potentially resulting in poor heat seal strength at low temperatures. In this embodiment, the static friction coefficient was measured using a universal tester, Strograph (VG10E), in accordance with the horizontal method of JIS P 8147:2010.

[0045] In embodiments of the present invention, the method for achieving a static friction coefficient of 0.20 or higher between the heat seal layer surface and the adhesive auxiliary layer surface is not particularly limited. For example, the papermaking chemicals such as AKD (alkyl ketene dimer) used to improve slipperiness may not be added to the base paper, or the smoothness of the heat seal layer surface and the surface having the adhesive auxiliary layer may be reduced. A high static friction coefficient is advantageous for heat seal strength as it reduces slippage. However, if the surface texture is made too rough solely to increase the static friction coefficient, the adhesion between the heat seal layer surface and the base paper surface may decrease, resulting in inferior heat seal strength. Furthermore, increasing the amount of coating on the heat seal layer surface, changing the resin used in the heat seal layer, adding various auxiliary agents to the heat seal layer, or providing an underlayer between the heat seal layer and the base paper may increase the smoothness of the heat seal layer surface, resulting in a decrease in the static friction coefficient. While there are no particular restrictions on performing these actions, care must be taken to ensure that the static friction coefficient between the heat seal layer surface and the adhesive auxiliary layer surface does not fall below 0.20.

[0046] The base paper used in the embodiments of the present invention is not particularly limited, and known base papers mainly composed of pulp can be used. As the pulp that is the main component of the base paper, chemical pulps such as LBKP (bleached hardwood kraft pulp) and NBKP (bleached softwood kraft pulp), mechanical pulps such as GP (crushed wood pulp), PGW (pressure-processed crushed wood pulp), RMP (refiner mechanical pulp), TMP (thermomechanical pulp), CTMP (chemothermetic pulp), CMP (chemimechanical pulp), and CGP (chemigland pulp) can be used, as well as wood pulps such as DIP (deinking pulp) and non-wood pulps such as kenaf, bagasse, bamboo, and cotton. These can be used individually or mixed in any proportion. For example, 90 to 100 parts by mass of LBKP (bleached hardwood kraft pulp) can be used as the pulp. Furthermore, synthetic fibers can be further blended, as long as it does not impair the effects intended by the present invention. From an environmental perspective, ECF (Elemental Chlorine Free) pulp, TCF (Total Chlorine Free) pulp, recycled paper pulp, and pulp obtained from plantation trees are preferred. For example, an appropriate degree of pulp beating is 200-700 mlCSF, or for example, 450-620 mlCSF, in terms of Canadian standard freeness (JIS P 8121:1995 "Test Method for Freeness of Pulp").

[0047] The base paper may also contain fillers. Examples of fillers include kaolin clay, calcium carbonate (heavy calcium carbonate, light calcium carbonate, etc.), calcined clay, talc, titanium dioxide, and aluminum hydroxide. The filler content in the base paper is, for example, 1 to 30 parts by mass per 100 parts by mass of dry pulp. For example, it is preferable to include 1 to 10 parts by mass of light calcium carbonate per 100 parts by mass of dry pulp.

[0048] Furthermore, the base paper may contain various known papermaking additives in addition to pulp and fillers. Examples of papermaking additives include internal strength enhancers such as sizing agents, bulk enhancers, yield enhancers, water drainage enhancers, coloring dyes, coloring pigments, fluorescent whitening agents, fluorescent decolorizing agents, and pitch control agents. Water-soluble polymers such as starch, polyvinyl alcohol, and polyacrylamide may also be coated. If the base paper contains a wet strength enhancer, the recyclability of the packaging paper is poor, so it is preferable that the base paper does not contain a wet strength enhancer. As for the method of incorporating papermaking additives, they may be included in the pulp slurry, or they may be impregnated into the interior of the base paper after papermaking using a sizing press or gate roll.

[0049] The papermaking method for the base paper is not particularly limited and can be manufactured using various papermaking machines such as a long-wire papermaking machine, a long-wire multilayer papermaking machine, a cylinder papermaking machine, a cylinder multilayer papermaking machine, a long-wire cylinder combination multilayer papermaking machine, and a twin-wire papermaking machine. Furthermore, in this invention, the base paper may be single-layer or multilayer.

[0050] In embodiments of the present invention, the basis weight of the packaging paper is not particularly limited, but for example, 10 to 1000 g / m² 2 The basis weight of packaging paper that can also be used for flexible packaging is 30-500 g / m². 2 Preferably, 30-350 g / m² 2 That would be even better. [Examples]

[0051] 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" and "%" refer to "parts by mass" and "% by mass," respectively, unless otherwise specified. Note that the number of added parts is the value on a solid content basis.

[0052] (Example 1) (Preparation of the base paper) A pulp was prepared by adding water to 100 parts Canadian Standard Freeness 520ml csf hardwood bleached kraft pulp, 5 parts light calcium carbonate (product name: TP-121, manufactured by Okutama Kogyo Co., Ltd.), 0.2 parts cationized starch (product name: Neotack 30T, manufactured by Nippon Shokuhin Kako Co., Ltd.), and 0.2 parts neutral rosin sizing (product name: CC167, manufactured by Seikou PMC Co., Ltd.). The resulting paper was then processed using a multi-cylinder, long-wire paper machine to produce a basis weight of 228 g / m². 2 A sheet of paper was obtained. This sheet of paper was impregnated with oxidized starch (product name: MS3800, manufactured by Nippon Shokuhin Kako Co., Ltd.) as a paper strengthening agent using a pound-type sizing press, with a dry impregnation amount of 2 g / m². 2 The material is impregnated and dried, then smoothed with a calender, resulting in a basis weight of 230 g / m². 2 A base paper was obtained.

[0053] (Preparation of packaging paper) On one side of the base paper obtained above, apply a water-based ionomer emulsion (product name: Chemipearl S-300, manufactured by Mitsui Chemicals) with a dry coating weight of 5.0 g / m². 2 The surface is coated using an air knife coater to create a heat-seal layer, then dried to form a heat-seal layer. Next, polyethyleneimine emulsion (product name: Epomin P-1000, manufactured by Nippon Shokubai Co., Ltd.) is applied to the opposite side with a drying coating amount of 0.2 g / m². 2 A packaging paper was prepared by coating it using an air knife coater and drying it, resulting in a static friction coefficient of 0.61 between the heat-seal layer surface and the adhesive auxiliary layer surface.

[0054] (Example 2) In Example 1, a second heat-seal layer was applied to the heat-seal surface of the packaging paper using an aqueous ionomer emulsion (product name: Chemipearl S-300, manufactured by Mitsui Chemicals, Inc.) with a dry coating amount of 5.0 g / m². 2 The coating was applied using an air knife coater and dried, resulting in a total dry coating weight of 10.0 g / m² for both layers. 2 Except for providing a second heat-seal layer to achieve the same result, packaging paper was prepared in the same manner as in Example 1, with a static friction coefficient of 0.22 between the heat-seal layer surface and the adhesive auxiliary layer surface.

[0055] (Example 3) In Example 1, the coating amount of the heat seal layer was 3.0 g / m². 2 Except for the change made, packaging paper was prepared in the same manner as in Example 1, with a static friction coefficient of 0.64 between the heat-seal layer surface and the adhesive auxiliary layer surface.

[0056] (Example 4) In Example 1, the amount of polyethyleneimine applied was 0.1 g / m². 2 Except for the change made, packaging paper was prepared in the same manner as in Example 1, with a static friction coefficient of 0.59 between the heat-seal layer surface and the adhesive auxiliary layer surface.

[0057] (Example 5) In Example 1, the amount of polyethyleneimine applied was 0.5 g / m². 2 Except for the change made, packaging paper was prepared in the same manner as in Example 1, with a static friction coefficient of 0.64 between the heat-seal layer surface and the adhesive auxiliary layer surface.

[0058] (Example 6) In Example 1, a packaging paper was prepared in the same manner as in Example 1, except that the resin used for the heat seal layer was changed to an aqueous ethylene-acrylic acid copolymer emulsion (product name: MICHEM FLEX P1883, manufactured by Michaelman). The static friction coefficient between the heat seal layer surface and the adhesive auxiliary layer surface was 0.86.

[0059] (Example 7) In Example 1, a packaging paper was prepared in the same manner as in Example 1, except that the resin used for the heat seal layer was changed to an aqueous ethylene vinyl acetate copolymer emulsion (product name: Aquatex AC-3100, manufactured by Japan Coating Resin Co., Ltd.), resulting in a static friction coefficient of 0.93 between the heat seal layer surface and the adhesive auxiliary layer surface.

[0060] (Example 8) In Example 1, the basis weight of the base paper was 50 g / m². 2 Except for the change made, packaging paper was prepared in the same manner as in Example 1, with a static friction coefficient of 0.27 between the heat-seal layer surface and the adhesive auxiliary layer surface.

[0061] (Example 9) In Example 1, a packaging paper was prepared in the same manner as in Example 1, except that the neutral rosin size of the base paper was changed to an AKD (alkyl ketene dimer) size (product name: SE2360, manufactured by Seikoh PMC). The static friction coefficient of the heat seal layer surface and the adhesive auxiliary layer surface was 0.23.

[0062] (Example 10) (Preparation of undercoat coating solution) 20 parts of kaolin clay (product name: Contour 1500, manufactured by Imerys) and 80 parts of heavy calcium carbonate (product name: Carvilax, manufactured by Imerys) were mixed with 0.2 parts of a dispersant (product name: Aron T-50, manufactured by Toagosei Co., Ltd.), water was added, and the mixture was dispersed in a Koles disperser to prepare a pigment slurry. To this pigment slurry, 2 parts of phosphated starch (product name: MS4600, manufactured by Nippon Shokuhin Kako Co., Ltd.) and 20 parts of styrene-butadiene copolymer latex (product name: L-1432X, manufactured by Asahi Kasei Chemicals, particle size 182 nm) were added as binders, and water was further added and dispersed to prepare an undercoat coating solution with a solid content of 50%.

[0063] (Preparation of paper substrate) On one side of the base paper obtained in Example 1, the undercoat coating liquid was applied with a dry coating amount of 20 g / m². 2 The surface was coated using a blade coater, dried, and then smoothed with a calender to achieve a basis weight of 250 g / m². 2 A paper substrate was fabricated.

[0064] (Preparation of packaging paper) On the surface of the underlayer of the paper substrate obtained above, apply a water-based ionomer emulsion (product name: Chemipearl S-300, manufactured by Mitsui Chemicals) with a dry coating amount of 5.0 g / m². 2 The surface is coated using an air knife coater to create a heat-seal layer, then dried to form a heat-seal layer. Next, polyethyleneimine emulsion (product name: Epomin P-1000, manufactured by Nippon Shokubai Co., Ltd.) is applied to the opposite side of the base paper with a drying coating amount of 0.2 g / m². 2 A packaging paper was prepared by coating it using an air knife coater and drying it so that the static friction coefficient between the heat seal layer surface and the adhesive auxiliary layer surface was 0.31.

[0065] (Comparative Example 1) In Example 1, the amount of polyethyleneimine applied was 0 g / m². 2 Except for the change made, packaging paper was prepared in the same manner as in Example 1, with a static friction coefficient of 0.53 between the heat-seal layer surface and the adhesive auxiliary layer surface (base paper surface).

[0066] (Comparative Example 2) In Example 1, the amount of heat seal layer applied was 0 g / m². 2 Except for the change made, packaging paper was prepared in the same manner as in Example 1, with a static friction coefficient of 0.70 between the heat-seal layer surface (base paper surface) and the adhesive auxiliary layer surface.

[0067] (Comparative Example 3) In Example 1, a packaging paper was prepared in the same manner as in Example 1, except that the resin used for the heat seal layer was changed to an aqueous styrene-acrylic copolymer emulsion (product name: Saibinol EK-754, manufactured by Saiden Chemical Co., Ltd.), resulting in a static friction coefficient of 0.32 between the heat seal layer surface and the adhesive auxiliary layer surface.

[0068] (Comparative Example 4) In Example 1, the neutral rosin size of the base paper was changed to AKD (alkyl ketene dimer) size (product name: SE2360, manufactured by Seikoh PMC), and the polyethyleneimine coating amount was 0 g / m². 2 Except for the change made, packaging paper was prepared in the same manner as in Example 1, with a static friction coefficient of 0.16 between the heat-seal layer surface and the adhesive auxiliary layer surface (base paper surface).

[0069] The packaging paper obtained in each example and comparative example was evaluated using the method described below. The results are shown in Figure 2.

[0070] (1) Heat seal strength Two pieces of the obtained packaging paper were cut to a size of 15 mm in width and 15 cm in length. The heat-seal layer surface and the adhesive support layer surface (or the surface of the base paper if no heat-seal layer or adhesive support layer was provided) of the packaging paper were placed on top of each other, and the two pieces were heat-sealed using a hot tack tester (Labthink, model: HTT-L1) under specific conditions (adhesion width: 15 mm, temperature: 100°C and 180°C, pressure: 0.2 MPa, pressing time: 1.0 second). Next, the heat-sealed samples were peeled off using a peel strength tester (Shimadzu Corporation, model: Autograph AGS-X) under specific conditions (peeling speed: 300 mm / min) to evaluate the heat-seal strength. A higher value indicates stronger heat-seal strength. In this invention, a heat-seal strength of 3.00 N / 15 mm or higher is considered to be good heat-seal strength.

[0071] (2) Fracture of heat seal material The peeled surface of the packaging paper obtained in (1) was visually evaluated. ○: The entire seal portion is separated from the base paper and is usable. △: Part of the seal has torn from the base paper, but it is still usable. ×: The sealed area is peeling off or not adhering at the interface of the heat seal layer, making it unusable.

[0072] (3) Static friction coefficient In accordance with the horizontal method of JIS P 8147:2010, the heat-sealed layer side of the obtained packaging paper was cut for use as a weight, and the adhesive auxiliary layer side was cut for use as a horizontal plate. Each piece was fixed to the weight or horizontal plate, and the weight was moved at 10.0 mm / min using a universal testing machine, Stroggraph (VG10E), to measure the static friction coefficient when the heat-sealed layer side and the adhesive auxiliary layer side were superimposed.

[0073] As is clear from Figure 2, the packaging papers of Examples 1 to 9 showed significantly superior heat seal strength at low temperatures between the heat seal surface and the base paper surface, and superior heat seal material breakage compared to Comparative Examples 1 to 4. As the experimental results show, the present invention makes it possible to provide packaging paper that significantly reduces the amount of plastic used in the heat seal layer compared to conventional polyethylene laminates, contributing to the reduction of plastic waste, while also having good heat seal strength even at low temperatures between the heat seal layer surface and the base paper surface.

Claims

1. A heat-seal layer containing one or more selected from the group consisting of ionomer, ethylene copolymer, thermoplastic urethane, polyvinylidene chloride, polylactic acid, and polybutylene succinate is applied to one side of the base paper, with a dry coating amount of 1 to 20 g / m². 2 It has within the range, An adhesive auxiliary layer, which is made by coating the other side of the base paper with polyethyleneimine, is applied with a dry coating amount of 0.05 to 3 g / m². 2 It has within the range, The aforementioned base paper does not contain alkyl ketene dimers. The heat seal layer is provided directly on the base paper, The static friction coefficient measured by overlapping the heat seal layer surface with the heat seal layer and the adhesive auxiliary layer surface with the adhesive auxiliary layer is 0.20 or higher. A packaging paper characterized in that, when the heat-seal layer surface and the adhesive auxiliary layer surface are superimposed and heat-sealed under the conditions of temperature: 100°C, pressure: 0.2 MPa, and pressing time: 1.0 second, the heat-seal strength is 3.00 N / 15 mm or more.

2. The packaging paper according to claim 1, characterized in that the surface having the adhesive auxiliary layer has a smoothness of 5 seconds or more.

3. A process to prepare a base paper that does not contain alkyl ketene dimers, On one side of the aforementioned base paper, polyethyleneimine is applied by any method selected from the group consisting of coating, sizing press, gate roll, impregnation, and spraying, with a dry coating amount of 0.05 to 3 g / m². 2 The process involves applying an adhesive auxiliary layer to the base paper surface within a certain range, On the other side of the aforementioned base paper, a heat-seal coating liquid containing one or more selected from the group consisting of ionomer, ethylene copolymer, thermoplastic urethane, polyvinylidene chloride, polylactic acid, and polybutylene succinate is applied in a dry coating amount of 1 to 20 g / m². 2 Within this range, the process includes a step of directly coating the other surface of the base paper to apply a heat seal layer, The static friction coefficient measured by overlapping the heat seal layer surface with the heat seal layer and the adhesive auxiliary layer surface with the adhesive auxiliary layer is 0.20 or higher. A method for manufacturing packaging paper, characterized in that the heat seal strength is 3.00 N / 15 mm or more when the heat seal is performed by overlapping the heat seal layer surface and the adhesive auxiliary layer surface under the conditions of temperature: 100°C, pressure: 0.2 MPa, and pressing time: 1.0 second.

4. The method for manufacturing packaging paper according to claim 3, characterized in that, in the step of applying the heat seal layer, the coating liquid for the heat seal layer is an aqueous emulsion.

5. The method for producing packaging paper according to claim 3, characterized in that the coating liquid for the heat seal layer comprises only water and one or more selected from the group consisting of ionomers, ethylene copolymers, thermoplastic urethanes, polyvinylidene chloride, polylactic acid, and polybutylene succinate.

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