Heat-sealing paper and packaging material

Abstract

To provide heat seal paper which does not contain laminate paper and a plastic film having high environmental loads, and is excellent in a crack suppression effect by a fold in a region laminated with the heat seal paper while securing heat seal strength.SOLUTION: Heat seal paper has a paper base material containing conifer unbleached kraft pulp as a main component, and a heat seal layer laminated on one surface of the paper base material, in which folding strength in a flow direction of the paper base material is 500 times or more and 1,000 times or less, folding strength in a width direction thereof is 80 times or more and 200 times or less, Bekk smoothness on the surface of a laminate surface of the heat seal layer is 3 sec or longer and 230 sec or shorter, the main component of the heat seal layer is an ionomer resin, and a coating amount of the heat seal layer is 1.5 g / m2 or more and 10.0 g / m2 or less. A content of the conifer unbleached kraft pulp in the total pulp of the paper base material is preferably 95 mass% or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to heat-sealing paper and packaging materials.

Background Art

[0002] Generally, for pillow packaging widely used in the packaging of confectionery, pharmaceuticals, sanitary products, etc., laminated paper or plastic film obtained by extruding polyethylene resin or polypropylene resin on a base paper is used. When such laminated paper or plastic film is used, it is excellent in strength, water resistance, and moisture resistance, but since a non-decomposable plastic film remains, it cannot be used as waste paper, and there is a risk that it may cause marine pollution as microplastics without being subjected to waste treatment after use, leading to an environmental burden.

[0003] For this reason, in the prior art, packaging paper has been proposed that improves heat-sealing strength by providing a heat-sealing layer containing an ionomer on a paper substrate and reduces the amount of plastic used (see Patent Document 1). In addition, a heat-sealing sheet capable of being recycled has been proposed by providing a thermally adhesive layer containing a styrene-butadiene copolymer latex and setting the smoothness of the thermally adhesive surface within a specific range (see Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] When such heat-sealing paper is bagged using a jig to open the mouth in order to facilitate enclosing the contents with a bag-making machine, creases may form in the area where the heat-sealing layer is laminated. When creases form in the heat-sealing paper, there is a risk of cracks occurring from the creases. However, in the above-mentioned conventional packaging paper and heat-sealing sheet, the folding strength of the area where the heat-sealing layer is laminated is not sufficient, and there is room for improvement.

[0006] The present invention has been made based on the above circumstances, and an object thereof is to provide heat-sealing paper that does not include laminate paper or plastic film with a high environmental load, ensures heat-sealing strength, and has an excellent effect of suppressing cracks due to creases in the area where the heat-sealing layer is laminated.

Means for Solving the Problems

[0007] The heat-sealing paper according to one aspect of the present invention includes a paper base material mainly composed of unbleached softwood kraft pulp and a heat-sealing layer laminated on one side of the paper base material. The folding strength of the paper base material in the flow direction is 500 or more and 1,000 or less times, the folding strength in the width direction is 80 or more and 200 or less times, the Bekk smoothness of the surface of the heat-sealing layer lamination surface is 3 seconds or more and 230 seconds or less, the main component of the heat-sealing layer is an ionomer resin, and the coating amount of the heat-sealing layer is 1.5 g / m 2 or more and 10.0 g / m 2 or less.

Effects of the Invention

[0008] According to the present invention, it is possible to provide heat-sealing paper that does not include laminate paper or plastic film with a high environmental load, ensures heat-sealing strength, and has an excellent effect of suppressing cracks due to creases in the area where the heat-sealing layer is laminated.

Embodiments for Carrying Out the Invention

[0009] [Description of Embodiments of the Present Invention] The heat-sealing paper according to one aspect of the present invention includes a paper base material mainly composed of unbleached softwood kraft pulp, and a heat-sealing layer laminated on one side of the paper base material. The folding strength in the flow direction of the paper base material is 500 or more and 1,000 or less times, the folding strength in the width direction is 80 or more and 200 or less times, the Bekk smoothness of the surface of the heat-sealing layer laminated surface is 3 seconds or more and 230 seconds or less, the main component of the heat-sealing layer is an ionomer resin, and the coating amount of the heat-sealing layer is 1.5 g / m 2 or more and 10.0 g / m 2 or less.

[0010] When the heat-sealing paper is made into a bag using a bag-making machine and the mouth is opened with a jig to facilitate enclosing the contents, folds are formed, and there is a risk of cracks occurring from these folds. By providing a paper base material mainly composed of unbleached softwood kraft pulp, the heat-sealing agent is appropriately impregnated into the interior of the paper base material, improving the strength of the paper base material itself. This is because unbleached softwood kraft pulp has long fiber length and width and is thick, so there are many voids on the surface layer of the paper base material, and it is difficult for the heat-sealing agent to stay on the surface of the paper base material. Therefore, it is considered that cracks generated from the surface layer of the paper base material are suppressed. In addition, since the folding strength in the flow direction of the paper base material is 500 or more and 1,000 or less times, and the folding strength in the width direction is 80 or more and 200 or less times, the effect of suppressing cracks due to folds in the area where the heat-sealing layer is laminated is improved, and the effect of suppressing tearing and wrinkles in the bag-making process is excellent. By having the Bekk smoothness of the surface of the heat-sealing layer laminated surface of the paper base material be 3 seconds or more and 230 seconds or less, it is possible to achieve both the heat-sealing strength and the suppression of blocking of the heat-fused surface of the heat-sealing layer. Furthermore, in the heat-sealing paper, the main component of the heat-sealing layer is an ionomer resin, and the coating amount (in terms of solid content) of the heat-sealing layer is 1.5 g / m 2 or more and 10.0 g / m 2The following is the case. Since the main component of the heat-sealing layer is an ionomer resin, the heat-sealing strength is good not only at normal temperature but also at low temperature. Further, by the coating amount of the heat-sealing layer being within the above range, the heat-sealing strength and the suppression of blocking of the heat-fused surface of the heat-sealing layer can be further improved. Therefore, the heat-sealing paper is excellent in the effect of suppressing cracks due to folds in the region where the heat-sealing layer is laminated while ensuring the heat-sealing strength. In addition, since the heat-sealing paper does not contain laminated paper or plastic film that cannot be recycled and has a high environmental load, it is environmentally friendly. In the present invention, the "heat-sealing layer" refers to a coating layer in which a heat-fusion process is performed. The "main component" refers to the substance having the highest content rate among the constituent substances, preferably having a content rate of 50% by mass or more. The "flow direction" means the papermaking direction (MD: Machine Direction), and the "width direction" means the direction perpendicular to the above flow direction (CD: Cross Direction).

[0011] It is preferable that the content of the softwood unbleached kraft pulp in all the pulp of the paper base material is 95% by mass or more. By the content of the softwood unbleached kraft pulp being 95% by mass or more, the effect of suppressing cracks due to folds in the region where the heat-sealing layer is laminated can be further enhanced.

[0012] It is preferable that the Bekk smoothness of the surface of the heat-sealing layer is 20 seconds or more and 250 seconds or less. By the Bekk smoothness of the surface of the heat-sealing layer being within the above range, the heat-sealing paper can further improve the heat-sealing strength and the suppression of blocking of the heat-fused surface. The Bekk smoothness evaluates the smoothness from the air flow rate (air leak). The Bekk smoothness defined in JIS-P8119 (1998) sandwiches a sheet, which is the object to be measured, between an optically flat glass sample table and a rubber pressing plate at a pressure of 100 kPa, and 10 ml of air is relatively widely distributed over 10 cm 2It is represented by the time required to flow into the container maintained at a reduced pressure of about 370 mm of mercury column through the space between the glass standard surface, and indicates the smoothness of the so-called surface of the object to be measured. Bekk smoothness evaluates the macroscopic smoothness on a relatively wide surface. In the heat-sealing paper, the undulation of the surface can be evaluated by Bekk smoothness. Therefore, the surface of the heat-sealing layer of the heat-sealing paper can be more appropriately evaluated by Bekk smoothness.

[0013] The moisture permeability of the paper base material of the heat-sealing paper is 300 g / m 2 ·24 hours or more and 1,200 g / m 2 ·24 hours or less is preferable. When the moisture permeability of the paper base material of the heat-sealing paper is within the above range, the moisture in the contents to be packaged is less likely to become water droplets, and the humidity is appropriately maintained, so that the quality of the contents can be kept good. Here, the "moisture permeability of the paper base material" is a value measured in accordance with JIS-Z0208 (1976).

[0014] The packaging material according to another embodiment of the present invention has the heat-sealing paper. Since the packaging material has the heat-sealing paper, while ensuring the heat-sealing strength, it is excellent in the effect of suppressing cracks due to folds in the region where the heat-sealing layer is laminated. In addition, since the packaging material does not contain laminated paper or plastic film with a high environmental load, environmental conservation can be achieved.

[0015] [Details of Embodiments of the Present Invention] Hereinafter, the heat-sealing paper according to an embodiment of the present invention will be described in detail. In addition, the blending amount (dry internal addition amount) of each material blended in the paper base material described below refers to the mass ratio with respect to the dry mass of the pulp of the paper base material unless otherwise specified. In addition, the content rate of each material blended in the composition for forming the heat-sealing layer refers to the dry mass ratio of each material with respect to the total mass of the heat-sealing layer unless otherwise specified.

[0016] <Heat-sealing paper> The heat-sealing paper includes a heat-sealing layer on one surface of the paper base material. The heat-sealing layer may be either a single-layer or multi-layer structure.

[0017] [Paper base material] The paper base material is obtained by papermaking a slurry containing raw material pulp. The paper base material may be either single-layer or multi-layer.

[0018] (Raw material pulp) The paper base material is mainly composed of unbleached softwood kraft pulp (NUKP). By providing a paper base material mainly composed of unbleached softwood kraft pulp, the heat-sealing agent is moderately impregnated into the interior of the paper base material, improving the strength of the paper base material itself. This is because unbleached softwood kraft pulp has long fiber length and fiber width and is thick, so there are many voids on the surface layer of the paper base material, and it is difficult for the heat-sealing agent to stay on the surface of the paper base material. Therefore, it is considered that the folding strength of the heat-sealing paper is improved compared to the folding strength of the paper base material, suppressing cracks generated from the surface layer.

[0019] It is preferable that the content of the unbleached softwood kraft pulp in all the pulp of the paper base material is 95% by mass or more. By having the content of the unbleached softwood kraft pulp be 95% by mass or more, the effect of suppressing cracks due to folds in the region where the heat-sealing layer is laminated can be enhanced more.

[0020] As the raw material pulp constituting the paper base material, other raw material pulps other than unbleached softwood kraft pulp can also be used. Examples of other raw material pulps include virgin pulp other than unbleached softwood kraft pulp, waste paper pulp, and combinations of these pulps.

[0021] As virgin pulp other than softwood unbleached kraft pulp, for example, chemical pulps such as softwood bleached kraft pulp (NBKP), hardwood bleached kraft pulp (LBKP), hardwood semi-bleached kraft pulp (LSBKP), softwood semi-bleached kraft pulp (NSBKP), hardwood sulfite pulp, softwood sulfite pulp, etc.; mechanical pulps (MP) such as stone ground pulp (SGP), pressure stone ground pulp (TGP), chemiground pulp (CGP), groundwood pulp (GP), thermomechanical pulp (TMP), etc., pulps produced chemically or mechanically, etc. can be used alone or in combination of a plurality thereof.

[0022] As waste paper pulp, for example, repulped waste paper pulp, repulped and deinked waste paper pulp (DIP), repulped, deinked and bleached waste paper pulp, etc. produced from tea waste paper, kraft envelope waste paper, magazine waste paper, newspaper waste paper, flyer waste paper, office waste paper, cardboard waste paper, high-quality waste paper, Kent waste paper, imitation waste paper, deed waste paper, etc. can be used alone or in combination of a plurality thereof.

[0023] (Other additives) Other additives can be added to the paper base material as necessary. As additives, for example, fillers, pigments, sizing agents, coagulants, oil-resistant agents, fluorescent brighteners, sulfate bands, yield improvers, drainage improvers, dry paper strength enhancers, wet paper strength enhancers, coloring dyes, coloring pigments, water resistance agents, etc. can be used alone or in combination of a plurality thereof.

[0024] (Basis weight of the paper base material) The basis weight of the heat-sealable paper is preferably 40.0 g / m 2 or more and 100.0 g / m 2 or less. If the basis weight of the paper base material is less than 40.0 g / m 2 , there may be insufficient strength as a bag. If the basis weight of the paper base material exceeds 100.0 g / m 2 , the rigidity is high and folding defects may occur in the bag-making process. By having the basis weight of the paper base material within the above range, the low basis weight and weight reduction of the heat-sealable paper can be achieved while ensuring rigidity.

[0025] (Thickness of the paper substrate) The thickness of the paper substrate of the heat-sealing paper is measured in accordance with the "Test Methods for Thickness and Density of Paper and Paperboard" described in JIS-P8118 (2014). As the lower limit of the thickness of the paper substrate, 50 μm is preferable, and 60 μm is more preferable. As the upper limit of the thickness of the paper substrate, 150 μm is preferable, and 120 μm is more preferable. When the thickness of the paper substrate of the heat-sealing paper is within the above range, the workability and processability when manufacturing a packaging material using the heat-sealing paper can be improved.

[0026] (Density of the paper substrate) The density of the paper substrate of the heat-sealing paper is preferably 0.65 g / cm 3 or more and 0.80 g / cm 3 or less. When the density of the paper substrate is within the above range, low basis weight and weight reduction can be achieved while maintaining the folding strength, so the heat-sealing paper is excellent in processability.

[0027] (Folding strength in the machine direction) The folding strength in the machine direction is the folding strength in the papermaking direction and is measured in accordance with the "Test Method for Folding Strength of Paper and Paperboard - MIT Tester Method" described in JIS-P8115 (2001). As the lower limit of the folding strength in the papermaking direction, it is 500 times, and 600 times is preferable. As the upper limit of the folding strength in the papermaking direction, it is 1,000 times, and 900 times is more preferable. If the folding strength in the papermaking direction is less than the above lower limit, there is a risk of breaking without being able to withstand the tension in the advancing direction in the bag-making process. On the other hand, if the folding strength in the papermaking direction exceeds the above upper limit, the rigidity becomes high and there is a risk of wrinkling without being bent in the bag-making process.

[0028] (Folding strength in the cross direction) The folding strength in the width direction is the folding strength in the width direction (the direction perpendicular to the above flow direction). The lower limit of the folding strength in the width direction is 80 times, preferably 90 times. The upper limit of the folding strength in the width direction is 200 times, preferably 140 times. If the folding strength in the width direction is less than the above lower limit, there is a risk of breakage at the location where the jig contacts during the bag-making process. On the other hand, if the folding strength in the width direction exceeds the above upper limit, the rigidity increases and there is a risk of wrinkles without being bent during the bag-making process.

[0029] [Heat-sealing layer] The heat-sealing layer is laminated on one side of the above paper substrate. The above heat-sealing layer is formed by coating a composition for forming a heat-sealing layer on one side of the paper substrate.

[0030] As the main component of the above heat-sealing layer, an ionomer resin is preferably used. Since the main component of the above heat-sealing layer is an ionomer resin, the heat-sealing strength is good not only at normal temperature but also at low temperatures. The above "ionomer resin" refers to a synthetic resin in which polymers are aggregated using the cohesive force of metal ions. The above ionomer resin can be produced, for example, by adding metal cations such as sodium and zinc to an acrylic polymer and ethylene and bonding them intermolecularly.

[0031] As the above ionomer resin, for example, ethylene-based ionomers are preferred, and specifically, ionomers of ethylene·(meth)acrylic acid copolymers and ionomers of ethylene·(meth)acrylate copolymers can be mentioned.

[0032] The lower limit of the content rate of the ionomer resin with respect to the total solid content of the heat-sealing layer is 50.0% by mass, preferably 90.0% by mass. If the content rate of the above ionomer resin is less than 50.0% by mass, there is a risk that sufficient heat-sealability cannot be obtained. On the other hand, the upper limit of the content rate of the above ionomer resin is 100.0% by mass, preferably 95.0% by mass.

[0033] The heat-sealing layer may contain a resin other than the above-mentioned ionomer resin. Examples of the resin other than the ionomer resin include polyethylene-based resins and polypropylene-based resins. Examples of the polyethylene-based resin include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), ethylene-acrylic acid copolymer (EAA), ethylene-methacrylic acid copolymer (EMAA), ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl acrylate copolymer (EMA), ethylene-vinyl acetate copolymer (EVA), carboxylic acid-modified polyethylene, and derivatives thereof, and mixtures thereof. Examples of the polypropylene-based resin include polypropylene (PP) homopolymer, random polypropylene (random PP), block polypropylene (block PP), chlorinated polypropylene, carboxylic acid-modified polypropylene, styrene acrylic acid, styrene butadiene latex, and derivatives thereof, and mixtures thereof. Among these, an ethylene-acrylic acid copolymer is more preferable from the viewpoint of heat-sealing properties in a low-temperature range of around 100 to 130°C.

[0034] The lower limit of the coating amount (in terms of solid content) of the heat-sealing layer is preferably 1.5 g / m 2 and more preferably 2.0 g / m 2 On the other hand, the upper limit of this coating amount is preferably 10.0 g / m 2 and more preferably 8.0 g / m 2 If the coating amount is less than the above lower limit, it may not have sufficient heat-sealing strength, and there is a risk that sufficient sealing cannot be achieved when made into a bag. If the coating amount exceeds the above upper limit, the blocking resistance of the heat-sealing surface may decrease, and it may become difficult to slide in the bag-making process, increasing the risk of breakage. Since the main component of the heat-sealing paper is an ionomer resin, it is possible to achieve both sufficient heat-sealing strength and suppression of blocking of the heat-sealing surface of the heat-sealing layer within the above range of coating amounts.

[0035] (Other additives) Other additives other than those described above can be incorporated into the heat-sealing layer of the present invention. Examples of other additives include water-soluble polymers, adhesives, inorganic pigments, organic pigments, sizing agents, viscosity modifiers, coloring dyes, coloring pigments, water resistance agents, lubricants, etc., which can be used alone or in combination of two or more.

[0036] [Physical properties of heat-sealing paper] (Bekk smoothness) The lower limit of the Bekk smoothness of the surface of the heat-sealing layer laminated surface in the paper base material is 3 seconds, and preferably 5 seconds. The upper limit of the Bekk smoothness of the surface of the heat-sealing layer laminated surface in the paper base material is 230 seconds, and preferably 180 seconds. When the Bekk smoothness is below the lower limit, the surface of the heat-sealing paper becomes rough, resulting in a smaller contact area and a possible decrease in heat-sealing strength. When the Bekk smoothness exceeds the upper limit, the blocking suppression effect of the heat-fused surface of the heat-sealing layer may decrease.

[0037] The lower limit of the Bekk smoothness of the surface of the heat-sealing layer is preferably 20 seconds, and more preferably 23 seconds. The upper limit of the Bekk smoothness of the surface of the heat-sealing layer is preferably 250 seconds, and more preferably 200 seconds. When the Bekk smoothness of the surface of the heat-sealing layer is below the lower limit, the surface of the heat-sealing paper becomes rough (resulting in a smaller contact area), and the heat-sealing strength may decrease. When the Bekk smoothness of the surface of the heat-sealing layer exceeds the upper limit, the blocking suppression effect of the heat-fused surface of the heat-sealing layer may decrease.

[0038] (Folding endurance in the width direction of heat-sealing paper) The folding endurance in the width direction of the heat-sealing paper is the folding endurance in the width direction (the direction perpendicular to the above flow direction), and is measured in accordance with the "Paper and Paperboard - Test Method for Folding Endurance - MIT Tester Method" described in JIS-P8115 (2001). The ratio of the folding endurance in the width direction of the paper base material to the folding endurance in the width direction of the heat-sealing paper (hereinafter, also referred to as the improvement rate of the folding endurance in the width direction before and after the formation of the heat-sealing layer) is preferably 300% or more, and more preferably 550% or more. When the improvement rate of the folding endurance in the width direction before and after the formation of the above heat-sealing layer is less than 300%, cracks due to folds in the area where the heat-sealing layer is laminated occur, which is unsuitable for packaging applications.

[0039] (Moisture permeability of the paper base material) The moisture permeability of the paper base material of the heat-sealing paper is measured based on Condition B in accordance with JIS-Z0208

[1976] Test Method for Moisture Permeability of Moisture-proof Packaging Materials [Cup Method]. As the lower limit of the moisture permeability of the above paper base material, 300 g / m 2 ·24hr is preferable, and 500 g / m 2 ·24h is more preferable. Also, as the upper limit of the moisture permeability of the above paper base material, 1,200 g / m 2 ·24h is preferable, and (1,000 g / m 2 ·24h is more preferable. When the moisture permeability of the above paper base material is within the above range, the moisture of the packaged contents is less likely to become water droplets, and the quality of the contents can be kept good to maintain an appropriate humidity.

[0040] According to the heat-sealing paper, while ensuring the heat-sealing strength, it has an excellent effect of suppressing cracks due to folds in the area where the heat-sealing layer is laminated. In addition, since the heat-sealing paper does not contain laminated paper or plastic film with a high environmental load, environmental protection can be achieved.

[0041] [Manufacturing method of heat-sealing paper] The manufacturing method of the heat-sealing paper is not particularly limited. For example, it has a step of papermaking a pulp slurry as a raw material of the paper base material, a step of generating a composition for forming a heat-sealing layer, and a step of coating the composition for forming a heat-sealing layer on at least one surface of the paper base material.

[0042] In the papermaking process, a raw material slurry containing the above-described raw material pulp, oil-resistant agent, and other additives is carried out using a known paper machine. Further, the Bekk smoothness of the surface of the heat-sealing layer laminated surface of the paper substrate can be easily adjusted by using a machine calender or a soft calender.

[0043] In the heat-sealing layer forming composition production step, a heat-sealing layer forming composition containing an ionomer resin as a main component is produced.

[0044] As the coating method of the heat-sealing layer forming composition, a known coating method can be adopted. For example, known coating machines such as a two-roll size press coater, a gate roll coater, a blade metering coater, a rod metering coater, a blade coater, an air knife coater, a roll coater, a brush coater, a kiss coater, a squeeze coater, a curtain coater, a die coater, a bar coater, a gravure coater, etc. can be used.

[0045] For drying the coated heat-sealing layer forming composition, a known drying device can be adopted. For example, an infrared drying device, a hot air drying device, a contact type dryer drying device, etc. can be used.

[0046] The heat-sealing paper thus obtained can utilize various known finishing devices, such as a super calender, a gloss calender, a soft calender, a mat calender, etc., and can also perform appropriate product finishing.

[0047] <Packaging material> The packaging material according to another embodiment of the present invention has the heat-sealing paper. Since the packaging material has the heat-sealing paper, it is excellent in the effect of suppressing cracks due to folds in the region where the heat-sealing layer is laminated while ensuring the heat-sealing strength. Further, since the packaging material does not include laminated paper or plastic film with a high environmental load, environmental conservation can be achieved.

[0048] <Other embodiments> The present invention is not limited to the above-described embodiments, and can be implemented in various modified and improved forms in addition to the above aspects.

Example

[0049] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples.

[0050] [Examples 1 to 7 and Comparative Examples 1 to 2] (Manufacture of paper substrate) First, 100% by mass of softwood unbleached kraft pulp was prepared to obtain a pulp slurry. To this pulp slurry, barium sulfate, a retention aid, and a sizing agent were added as additives, respectively. The obtained pulp slurry was formed into paper using an on-top type fourdrinier paper machine. Next, treatment was performed at a pressure of 50 kg / cm and a temperature of 100 °C using one soft calender to adjust the Bekk smoothness of the surface of the heat-seal layer laminated surface. Then, paper substrates of Examples 1 to 7 and Comparative Examples 1 to 2 having the basis weights, thicknesses, and densities shown in Table 1 were obtained. The Bekk smoothness of the surface on which the heat-seal layer was laminated was measured by the method described later.

[0051] (Lamination of heat-seal layer) Next, a heat-seal layer was formed on one side of the paper substrate to obtain a heat-seal paper. The composition and coating amount of the composition for forming the heat-seal layer were as shown in Table 1. Further, as the ionomer resin of the composition for forming the heat-seal layer, an ionomer of an ethylene-acrylic acid copolymer was used. The content of the ionomer resin with respect to the total solid content was 100.0% by mass.

[0052] [Comparative Example 3] A single-layer laminated paper containing a polypropylene film was produced. The base paper was composed of commercially available kraft paper (basis weight 65.0 g / m 2 ). The polypropylene film was obtained by extruding and laminating a commercially available polypropylene resin using a pelletizer and laminating it on only one side of the base paper with a thickness of 20 μm.

[0053] Various evaluations were performed on the heat-sealing paper obtained as described above.

[0054] (Beck smoothness of the heat-sealing layer) Based on JIS-P8119 (1998), the Beck smoothness of the heat-sealing layer laminated surface, the non-laminated surface of the heat-sealing layer, and the surface of the heat-sealing layer on the paper substrate was measured.

[0055] (Moisture vapor transmission rate of the paper substrate) Regarding the moisture vapor transmission rate of the paper substrate of the heat-sealing paper of the examples and comparative examples, it was measured based on condition B in accordance with JIS-Z0208 (1976) Moisture Vapor Transmission Test Method for Moisture-proof Packaging Materials [Cup Method].

[0056] (Folding strength in the flow direction) The "folding strength (number of folds) in the flow direction (longitudinal direction)" was measured for the folding strength in the flow direction, which is the papermaking direction, in accordance with the "Paper and Paperboard - Test Method for Folding Strength - MIT Tester Method" described in JIS-P8115 (2001).

[0057] (Folding strength in the width direction) The "folding strength (number of folds) in the width direction" was measured for the folding strength in the width direction (the direction perpendicular to the above-mentioned flow direction) in accordance with the "Paper and Paperboard - Test Method for Folding Strength - MIT Tester Method" described in JIS-P8115 (2001). Then, the folding strength before and after the formation of the heat-sealing layer in the width direction was measured, and the improvement rate [%] of the folding strength after the formation of the heat-sealing layer with respect to the folding strength in the width direction before the formation of the heat-sealing layer was calculated.

[0058] (Evaluation of the crease during bag making) For each example and comparative example, using a commercially available automatic bag-making machine, individual packaging bags were processed from the heat-sealing paper, and the crease during bag making was evaluated. The evaluation results were evaluated according to the following three criteria. When the evaluation is ○ and △, the inhibitory effect on the crease formation during bag making is good. ○: There are no wrinkles or tears in the creases at the bottom and ends of the individual packaging, and the appearance is good. △: There are wrinkles at the folds at the bottom and ends of the individual packaging, but it is at a level where there are no problems in use. ×: There are wrinkles and tears at the folds at the bottom and ends of the individual packaging, and it is at a level where there are problems in use.

[0059] (Heat seal strength) Using a heat gradient tester (manufactured by Toyo Seiki Seisakusho Co., Ltd.), after processing under the conditions of a sealer pressure of 2 kgf / cm 2 , a sealer time of 2 seconds, and a seal temperature of 140 °C, the peel strength of the heat seal part was measured using a load cell type tensile tester.

[0060] The evaluation results of each example and comparative example are shown in Table 1.

[0061]

Table 1

[0062] As shown in Table 1, Examples 1 to 7 having a paper base material mainly composed of unbleached kraft pulp from coniferous trees, with the folding strength in the machine direction of the paper base material being 500 or more and 1000 or less times, the folding strength in the cross direction being 80 or more and 200 or less times, the Bekk smoothness of the surface of the heat seal layer laminated surface being 3 seconds or more and 230 seconds or less, and the coating amount of the heat seal layer mainly composed of an ionomer resin being 1.5 g / m 2 or more and 10.0 g / m 2 or less had high folding strengths in the machine direction and cross direction and good heat seal strength. Also, it can be seen that the folding strength in the cross direction was significantly improved by the formation of the heat seal layer. As a result, the appearance of the folds during bag making was good. On the other hand, Comparative Examples 1 and 2 had inferior heat seal strength. Furthermore, the appearance defects of the folds during bag making were prominent. Comparative Example 3 is polypropylene (PP) laminated paper, which is not desirable from the perspective of environmental pollution. Also, since the moisture permeability of the paper base material is low, when used as a packaging material, it is considered that the freshness of the contents may decrease.

[0063] As a result of the above, it was shown that according to the heat-sealing paper, while ensuring the heat-sealing strength, it is excellent in the effect of suppressing cracks due to folds in the region where the heat-sealing layer is laminated. In addition, since the heat-sealing paper does not contain laminated paper or plastic film with a high environmental load, environmental conservation can be achieved.

Industrial Applicability

[0064] The heat-sealing paper of the present invention is environmentally friendly, excellent in the effect of suppressing cracks due to folds in the region where the heat-sealing layer is laminated while ensuring the heat-sealing strength, and is suitable as a packaging material.

Claims

1. A paper base material mainly composed of unbleached softwood kraft pulp; A heat seal layer laminated on one side of the paper base material; It is equipped with The folding endurance in the width direction is 453 times or more and 1208 times or less, The Beck smoothness of the heat seal layer surface is 9 seconds or more and 250 seconds or less, the main component of the heat seal layer is an ionomer of an ethylene / (meth)acrylic acid copolymer or an ionomer of an ethylene / (meth)acrylic acid ester copolymer, The coating amount of the heat seal layer is 1.5 g / m ２ 10.0g / m or more ２ Below is the heat seal paper.

2. 2. The heat seal paper according to claim 1, wherein the content of said unbleached softwood kraft pulp in the total pulp of said paper base material is 95% by mass or more.

3. 3. The heat seal paper according to claim 1, wherein the Beck smoothness of the surface of the heat seal layer is from 20 seconds to 250 seconds.

4. A packaging material comprising the heat seal paper according to any one of claims 1 to 3.

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