Zipper bag

Abstract

To provide a zipper bag that is highly biodegradable and has excellent abrasion resistance (hereinafter also referred to as wet-rub resistance) when wet. [Solution] The bag body is made of a paper substrate having a coating layer containing PHBH and EVA on its inner surface, and the bag has a zipper part fused to the coating layer. The aforementioned chuck portion is mainly composed of PBS, The coating layer contains 1 to 250 parts by mass of EVA per 100 parts by mass of PHBH, A zipper bag in which the aforementioned EVA has a glass transition temperature (Tg) of -50°C or higher and 30°C or lower.

Description

[Technical Field]

[0001] This invention relates to a zipper bag. [Background technology]

[0002] Zipper bags, which have a zipper fixed to the inside of the bag as the opening and can be opened and closed repeatedly, are used for packaging food, pharmaceuticals, daily necessities, and other items. In recent years, efforts have begun to prevent environmental damage caused by plastic waste, and there is a demand to replace single-use plastic products with materials that have a smaller environmental impact. For example, resealable bags have been proposed that use paper for the bag itself to reduce plastic usage (see Patent Documents 1 and 2, etc.). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-155200 [Patent Document 2] Japanese Patent Publication No. 2024-110165 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] While zipper bags with a paper body have been proposed, they all utilize non-biodegradable resins in the heat-sealing layer, sealant layer, and zipper section, resulting in insufficient biodegradability. Furthermore, resealable bags are often used to package items containing moisture, and condensation may occur inside them due to refrigeration or freezing, so they are frequently required to be usable in humid environments. This invention was developed based on the above background, and aims to provide a zipper bag that is highly biodegradable and has excellent abrasion resistance (hereinafter also referred to as wet-rub resistance) when water is present. [Means for solving the problem]

[0005] The means for solving the problems of the present invention are as follows. 1. The bag body is made of a paper substrate having a coating layer containing PHBH and EVA on its inner surface, and the bag has a zipper portion fused to the coating layer. The aforementioned chuck portion is mainly composed of PBS, The coating layer contains 1 to 250 parts by mass of EVA per 100 parts by mass of PHBH, A zipper bag characterized in that the EVA has a glass transition temperature (Tg) of -50°C or higher and 30°C or lower. 2. The zipper bag according to claim 1, characterized in that the coating layer contains an inorganic pigment. 3. The zipper bag according to 1. or 2., characterized in that the height of the zipper portion when fitted is 2.5 mm or less. [Effects of the Invention]

[0006] The zipper bag of the present invention is highly biodegradable and decomposes quickly even if it is released into the environment as waste. The zipper bag of the present invention is suitable for packaging foods and other items that contain a lot of moisture because the coating layer is resistant to peeling even when rubbed while wet. The paper substrate used in the present invention has excellent wet-rub properties even if the coating layer contains inorganic pigments, so it is possible to impart functionalities such as barrier properties derived from inorganic pigments. The zipper portion of the zipper bag of the present invention is firmly fused to the paper substrate, making it difficult for the zipper portion to peel off from the paper substrate. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic diagram of a zipper bag, which is one embodiment of the design. [Figure 2] A diagram showing how to open a resealable bag, which is one embodiment of the process. [Figure 3] A diagram showing how to open a resealable bag, which is one embodiment of the process. [Modes for carrying out the invention]

[0008] The chuck bag of the present invention has a bag body made of a paper base material provided with a coating layer containing PHBH and EVA on the inner surface, and a chuck portion fused to the coating layer. The chuck portion is mainly composed of PBS. The coating layer contains 1 to 250 parts by mass of EVA with respect to 100 parts by mass of PHBH. EVA has a glass transition temperature (Tg) of -50°C or higher and 30°C or lower. In addition, in this specification, the description of "A to B" (A and B are numerical values or ratios) means a numerical range including A and B.

[0009] (Paper base material) The paper base material includes a base paper and a coating layer on the outermost surface that becomes the inner surface of the bag. The paper base material only needs to have a coating layer on the outermost surface that becomes the inner surface of the bag, and it can also have the same coating layer on the outermost surface that becomes the outer surface. However, when high printing suitability is required, it is preferable to have a pigment coating layer on the outermost surface that becomes the outer surface. In addition, the paper base material can also have other layers such as an anchor layer, a water vapor barrier layer, a gas barrier layer, and an ink receiving layer.

[0010] ·Base paper The base paper is a sheet mainly made of pulp, and is obtained by papermaking a paper stock containing fillers, various auxiliaries, etc. Examples of the pulp include chemical pulps such as hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), softwood unbleached pulp (NUKP), and sulfite pulp, mechanical pulps such as stone ground pulp and thermomechanical pulp, deinked pulp, wood fibers such as wastepaper pulp, and non-wood fibers obtained from kenaf, bamboo, hemp, etc. One or more of these can be appropriately blended and used. Among these, chemical pulps of wood fibers and mechanical pulps of wood fibers are preferably used because it is difficult for foreign matter to mix into the base paper and they are suitable for packaging oral intake products such as foods and pharmaceuticals. It is more preferable to use chemical pulps of wood fibers. Also, when whiteness is required, it is preferable to use bleached pulp as the chemical pulp, and when a natural feeling is required, it is preferable to use unbleached pulp. The blending amount of chemical pulps of wood fibers such as LBKP and NBKP in the total pulp is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and most preferably 100% by mass.

[0011] As the filler, known fillers such as inorganic fillers such as talc, kaolin, calcined kaolin, clay, heavy calcium carbonate, light calcium carbonate, white carbon, zeolite, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, barium sulfate, and calcium sulfate, and organic fillers such as urea-formalin resin, polystyrene resin, phenolic resin, and micro hollow particles can be used. Note that the filler is not an essential material and may not be used.

[0012] Examples of various additives include sizing agents such as rosin, alkyl ketene dimer (AKD), and alkenyl succinic anhydride (ASA); dry strength enhancers such as polyacrylamide polymers, polyvinyl alcohol polymers, cationized starch, various modified starches, urea-formaldehyde resins, and melamine-formaldehyde resins; wet strength enhancers; yield enhancers; water drainage enhancers; coagulants; aluminum sulfate; bulk enhancers; dyes; fluorescent whitening agents; pH adjusters; defoamers; UV inhibitors; fade inhibitors; pitch control agents; and slime control agents. These can be selected and used as needed.

[0013] The base paper may have its surface treated with various chemicals. Examples of chemicals include oxidized starch, hydroxyethyl etherified starch, enzyme-modified starch, polyacrylamide, polyvinyl alcohol, surface sizing agents, water-resistant agents, water-retaining agents, thickeners, and lubricants, which can be used individually or in combination of two or more. Furthermore, these various chemicals may be used in combination with pigments. Examples of pigments include inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white, as well as organic pigments such as dense, hollow, or core-shell types, which can be used individually or in combination of two or more.

[0014] The basis weight of the base paper is 20 g / m², considering factors such as strength, flexibility, and lightness. 2 More than 200g / m 2 The following is preferable: The basis weight of the base paper is 150 g / m². 2 The following is more preferable: 120 g / m 2 The following is even more preferable: 100 g / m 2 The following is even more preferable: 80 g / m 2 The following are even more preferable. The density of the base paper is 0.5 g / cm³. 3 More than 1.0g / cm 3 The following are preferred. In the present invention, the base paper may be either a paper consisting of only a single layer or a multilayer paper having two or more layers. If the base paper is a multilayer paper, the pulp, basis weight, etc. of each layer may be the same or different.

[0015] The papermaking method for the base paper is not particularly limited, and known papermaking methods and papermaking machines such as long-wire papermaking machines, cylinder papermaking machines, short-wire papermaking machines, gap formers, hybrid formers (on-top formers), and twin-wire papermaking machines can be selected. Furthermore, the pH during papermaking can be in the acidic range (acidic papermaking), pseudo-neutral range (pseudo-neutral papermaking), neutral range (neutral papermaking), or alkaline range (alkaline papermaking), and an alkaline agent may be applied to the surface of the paper layer after papermaking in the acidic range. Furthermore, when treating the surface of the base paper with chemicals, the surface treatment method is not particularly limited, and known coating equipment such as rod metering size presses, pound-type size presses, gate roll coaters, spray coaters, blade coaters, and curtain coaters can be used.

[0016] • Coating layer The coating layer is located on at least one of the outermost surfaces of the paper substrate and contains at least PHBH and EVA, with EVA being 1 part by mass or more and 250 parts by mass per 100 parts by mass of PHBH.

[0017] <phbh> PHBH is a copolymer of 3-hydroxybutyrate (hereinafter also referred to as 3HB) and 3-hydroxyhexanoate (hereinafter also referred to as 3HH), and is a biodegradable resin known to be produced by microorganisms. In the present invention, PHBH may be derived from microorganisms or from petroleum resources, but it is preferable to use PHBH derived from microorganisms from the viewpoint of reducing environmental impact.

[0018] The composition ratio (mol%) of PHBH is preferably 3HB:3HH = 97:3 to 75:25, and more preferably 95:5 to 85:15. The composition ratio of PHBH can be measured by NMR analysis of the powder obtained by centrifuging an aqueous dispersion and then drying it. Microbially produced PHBH is a random copolymer. Methods to adjust the molar ratio of the copolymer include selecting the microbial cells, selecting the carbon source as the raw material, blending with PHBH of different molar ratios, and blending with 3HB homopolymer.

[0019] The weight-average molecular weight of PHBH is preferably between 50,000 and 1,500,000. When the weight-average molecular weight of PHBH is within this range, film formation at low temperatures is possible when coating with PHBH, and heat sealing at low temperatures is also possible. A weight-average molecular weight of 100,000 to 500,000 is more preferable, and 150,000 to 450,000 is even more preferable. The weight-average molecular weight of PHBH can be determined by gel permeation chromatography (GPC, such as Showa Denko's "Shodex GPC-101") using a polystyrene gel column (such as Showa Denko's "Shodex K-804") with chloroform as the mobile phase, and the molecular weight converted to polystyrene equivalent. For measurement, a powder obtained by centrifuging and drying an aqueous dispersion containing PHBH is used.

[0020] The average particle size of PHBH is preferably 0.1 to 50 μm. PHBH with an average particle size of less than 0.1 μm is difficult to produce by microorganisms, and even when obtained by chemical synthesis, a process of micronization is required. If the average particle size exceeds 50 μm, uneven coating may occur on the surface when a coating solution containing PHBH is applied. The average particle size of PHBH is more preferably 0.5 to 10 μm. The average particle size of PHBH refers to the particle size corresponding to the 50% accumulation of all particles measured by adjusting an aqueous suspension of PHBH to a predetermined concentration using a general-purpose particle size analyzer such as a Microtrac particle size analyzer (Nikkiso, FRA).

[0021] <eva> EVA (ethylene vinyl acetate copolymer) is a copolymer in which ethylene and vinyl acetate are monomers, and other monomers may also be used as monomers. However, the EVA of the present invention is not saponified and does not have vinyl alcohol units produced by the saponification of vinyl acetate units. When the EVA has other monomers as monomers, the content of constituent units derived from other monomers relative to the total EVA is preferably 30% by mass or less. This content is not particularly limited as long as it does not impair the effects of the present invention, and can be, for example, 20% by mass or less, 10% by mass or less, 5% by mass or less, 3% by mass or less, 1% by mass or less, etc.

[0022] The glass transition temperature of EVA is -50 to 30°C from the viewpoint of heat seal strength. This glass transition temperature is more preferably -40°C or higher, even more preferably -35°C or higher, even more preferably 20°C or lower, and even more preferably 10°C or lower. In this specification, the glass transition temperature refers to the intermediate glass transition temperature measured in accordance with JIS K 7121-1987. In EVA, the molar ratio of ethylene to vinyl acetate (component units derived from ethylene:component units derived from vinyl acetate, also expressed as ethylene:vinyl acetate, with a total of 100) is preferably 1:99 to 60:40 from the viewpoint of heat seal strength. This molar ratio is more preferably 3:97 to 50:50, and even more preferably 5:95 to 45:55.

[0023] The coating layer contains 1 to 250 parts by mass of EVA per 100 parts by mass of PHBH. The coating layer exhibits excellent wet-rub properties due to the inclusion of PHBH and EVA in this ratio. The ratio of EVA to 100 parts by mass of PHBH is preferably 6 parts by mass or more, more preferably 11 parts by mass or more, and even more preferably 16 parts by mass or more. There is no particular upper limit to this ratio of EVA, but for example, it can be 230 parts by mass or less, 210 parts by mass or less, 190 parts by mass or less, etc.

[0024] The coating layer may contain PHBH and EVA, and may also contain other thermoplastic resins or inorganic pigments. <Other thermoplastic resins> Other thermoplastic resins that have heat-seal properties at the temperature at which PHBH is fused can be used without particular limitation, but biodegradable resins such as aliphatic polyester resins such as polycaprolactone, polybutylene succinate adipate, polybutylene succinate, and polylactic acid, and aliphatic aromatic polyester resins such as polybutylene adipate terephthalate and polybutylene azelate terephthalate are preferred.

[0025] When the coating layer contains other thermoplastic resins, the total ratio of PHBH and EVA to the total thermoplastic resins contained in the coating layer is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and most preferably 100% by mass.

[0026] <Inorganic pigments> As inorganic pigments, those used in coating paper can be used without particular limitations. Examples include kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, bentonite, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white. One or more of these can be used. Among these, one or more of kaolin, heavy calcium carbonate, light calcium carbonate, mica, talc, and bentonite are preferred.

[0027] From the viewpoint of adhesion to the coating layer, it is preferable that the inorganic pigment has a 50% volume average particle diameter (D50, hereinafter also referred to as "average particle diameter") of 6.0 μm or less, as measured by laser diffraction / scattering. Examples of laser diffraction / scattering measurement devices include Horiba's particle size distribution analyzer "Partica" and Malvern's particle size distribution analyzer "MASTER SIZER S". From the viewpoint of adhesion to the coating layer, the average particle diameter of the inorganic pigment is more preferably 5.0 μm or less, even more preferably 4.0 μm or less, even more preferably 3.0 μm or less, and even more preferably 2.0 μm or less. There is no particular lower limit to the average particle diameter of the inorganic pigment, but from the viewpoint of dispersibility, for example, it is preferably 0.1 μm or more, and more preferably 0.2 μm or more. When two or more inorganic pigments are included, it is preferable that the average particle size of at least one of them is within the numerical range described above, and it is preferable that the proportion of inorganic pigments satisfying this average particle size to the total inorganic pigments is 50% by mass or more, and more preferably 70% by mass or more.

[0028] When the coating layer contains an inorganic pigment, the solid content mass ratio of PHBH to the inorganic pigment (PHBH:inorganic pigment, total 100) is preferably 90:10 to 0.01:99.99. By further incorporating an inorganic pigment into a coating solution containing PHBH and EVA, the adhesion of the resulting coating layer is improved. Although the mechanism is unknown, the inventors speculate that because inorganic pigments have superior thermal conductivity compared to organic substances such as PHBH and EVA, the inorganic pigment heats up quickly when heated, and this heat is transferred from the inorganic pigment to the PHBH, causing the PHBH to heat up and soften sufficiently, making it easier to adhere to the substrate paper. The solid content mass ratio of PHBH to inorganic pigment (PHBH:inorganic pigment, total 100) is more preferably 70:30 to 1:99, even more preferably 60:40 to 2:98, and even more preferably 50:50 to 3:97, from the viewpoint of adhesion of the coating layer.

[0029] In addition to PHBH, EVA, other thermoplastic resins, and inorganic pigments, the coating layer can contain other water-soluble resins and water-dispersible resins. Furthermore, if necessary, it can contain various auxiliaries formulated in coating liquids in the paper-making field, such as dispersants, viscosity improvers, defoamers, water resistance agents, pH adjusters, cationic resins, anionic resins, ultraviolet absorbers, metal salts, lubricants, coloring dyes, pigments, etc.

[0030] The paper substrate has a heat seal strength of 4.0 N / 15 mm or more, more preferably 5.0 N / 15 mm or more, still more preferably 6.0 N / 15 mm or more, and even more preferably 6.5 N / 15 mm or more when T-peeling is performed on a heat-sealed product that is heat-sealed at a pressure temperature of 160 °C, a pressure of 0.2 MPa (20.0 N / cm 2 ) and a pressure time of 1.0 second, measured in accordance with JIS Z1707:2019 7.4 "Heat Seal Strength Test". In addition, for the coated paper of the present invention, the heat seal strength measured in the same manner except that the pressure temperature is 180 °C is preferably 4.0 N / 15 mm or more, more preferably 5.0 N / 15 mm or more, still more preferably 6.0 N / 15 mm or more, and even more preferably 6.5 N / 15 mm or more.

[0031] (Manufacturing method) The coating layer can be manufactured by a conventionally known coating method. For example, coating devices include blade coaters, bar coaters, roll coaters, air knife coaters, reverse roll coaters, curtain coaters, spray coaters, size press coaters, gate roll coaters, etc. Also, coating systems include water-based coating using a solvent such as water and solvent-based coating using a solvent such as an organic solvent, etc., but water-based is preferred.

[0032] The coating amount of the coating layer is preferably 1 g / m 2 or more and 50 g / m 2 or less in terms of dry mass. If the coating amount is less than 1 g / m 2 , it may be difficult to form a uniform coating film. On the other hand, if it is 50 g / m 2 A higher amount increases the drying load during coating. The coating amount for the coating layer is 3g / m². 2 The above is more preferable: 5 g / m 2 The above is even more preferable, 40 g / m 2 The following is more preferable: 30g / m 2 The following are even more preferable.

[0033] (Zipper part) The chuck portion consists of at least one pair of male and female parts, the male part having, for example, a linear projection, and the female part having a recess that can be fitted into this projection. The chuck portion is primarily composed of PBS (polybutylene succinate). In this specification, "primary component" means that it accounts for 50% or more by mass. The chuck portion, which is mainly composed of PBS, can be firmly fused to the coating layer of the paper substrate that satisfies the above-mentioned specific composition, and peeling of the chuck portion from the paper substrate can be prevented. The proportion of PBS in the chuck portion is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and most preferably 100% by mass.

[0034] <Zipper bag> A zipper bag, which is one embodiment of the present invention, will be described based on Figures 1 to 3. The zipper bag 1 is a four-sided sealed bag comprising a bag body 11 made of the paper material described above and a zipper part 12, and has a sealing part 13 (with hatching) on ​​all four sides. The zipper portion 12 forms the opening of the zipper bag 1, and both ends of the zipper portion 12 are embedded in the sealing portions 13 located on both sides to prevent gaps from forming when the zipper portion 12 is fitted. Here, in order to heat seal the zipper portion 12 so that its ends are embedded in the sealing portions 13 on both sides of the zipper bag 1, heating and pressurizing to a degree that deforms the zipper portion 12 embedded in the sealing portions 13 is required, but the paper substrate is more prone to tearing than plastic film. In order to prevent the paper substrate from tearing when forming the sealing portions 13, it is preferable that the height of the zipper portion 12 when fitted is 2.5 mm or less. The height of the zipper portion 12 when fitted is equal to the distance between the opposing paper substrates when the zipper portion 12 is fitted. By making the height of the zipper portion when fitted 2.5 mm or less, the step created during heat sealing is reduced, and the occurrence of tearing of the paper substrate can be suppressed. The height of the chuck portion when fitted is more preferably 2.3 mm or less, even more preferably 2.0 mm or less, and even more preferably 1.8 mm or less.

[0035] In the zipper bag 1, the paper base material is mainly made of pulp, and the zipper part 12 is mainly composed of PBS, so the zipper bag 1 has very high biodegradability. Preferably, the ratio of biodegradable material to the total non-ash content of the zipper bag 1 is 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 97% by mass or more, even more preferably 98% by mass or more, and even more preferably 99% by mass or more. Note that the total non-ash content of the bag refers to the non-ash content of the entire bag measured in accordance with JIS P8251:2003, for example, if the ash content is 1%, it means the remaining 99%. Furthermore, biodegradable materials are defined as materials that are broken down by microorganisms into at least water and carbon dioxide, and whose aerobic biodegradation rate, measured according to ISO-14855-2 (2018), is 50% or more in 6 months. In the case of Zipper Bag 1, at least pulp, PHBH, EVA, and PBS qualify as biodegradable materials.

[0036] The shape of the zipper bag of the present invention is not limited to a four-sided sealed bag, but can be, for example, a three-sided sealed bag, a two-sided sealed bag, a gusseted bag, a bottom gusseted bag, a stand-up pouch, etc. Furthermore, the method of manufacturing the zipper bag is not particularly limited, and can be formed by, for example, fixing the zipper part (male part and female part) to the coated surface of a paper substrate by heat sealing, aligning the male and female parts of the zipper part by fitting them together, and then heat sealing the peripheral edges of the opposing paper substrates to form the bag body. The zipper bag of the present invention has a coating layer exposed on the inner surface of the bag that has excellent wet-rub properties, so it can be used for foods that contain a lot of moisture, as well as for refrigeration and freezing applications where condensation is likely to occur. [Examples]

[0037] The present invention will be specifically described below with reference to examples, but the present invention is of course not limited to these examples. Unless otherwise specified, parts and % in the examples refer to parts by mass and mass%, respectively.

[0038] (Evaluation method) Wet Love The prepared paper substrate was placed on a horizontal surface and subjected to temperature and humidity control (conditions: 23°C, 50% humidity) for at least 24 hours. Then, a cross pattern was drawn on the coated surface using a new oil-based marker (ZEBRA Maki Extra Fine) that had been opened immediately before the test, and it was allowed to dry for 5 minutes. After that, the pattern was lightly traced back and forth 50 times with a wet finger, and the degree of pattern retention and peeling of the coating layer were evaluated according to the following criteria. A rating of 5 or 4 indicates that there are no practical problems. 5: No change 4: Less than 10% of white areas occurred. 3: White areas appearing in 10% to less than 50% of areas. 2: Whitening occurs in 20% to less than 50% of areas + leaching of the coating layer. 1: Whitening occurs in areas between 50% and 100% of the surface, and the coating layer is leached out. <Example of judgment> [Table 1]

[0039] Tape pick The prepared paper substrate was placed on a horizontal table and subjected to temperature and humidity control (conditions: 23°C, 50% humidity) for at least 24 hours. Then, a 12mm wide mending tape (3M Japan, Scotch® Mending Tape 810-1-12) was applied to the surface of the coating layer of the coated paper. A 130mm wide, 1.8kg rubber roller was then moved back and forth 20 times under its own weight over the mending tape to ensure close adhesion of the mending tape to the coating layer surface. Immediately afterward, the mending tape was quickly peeled off, and the ratio of the area where the coating layer adhered to the mending tape and peeled away from the substrate (interface failure area) to the area where the mending tape was applied, or the ratio of the area where part of the substrate adhered to the mending tape along with the coating layer and the substrate was damaged (internal substrate failure area), was calculated. The adhesion between the substrate and the coating layer was then evaluated according to the following criteria. An evaluation of 5 or 4 indicates no practical problems. 5: No peeling 4: Less than 0-10% peeling of the adhesive surface. 3: Less than 10-50% of the adhesive surface is peeled off. 2: Less than 50-90% of the adhesive surface is peeled off. 1: 90-100% of the adhesive surface has peeled off.

[0040] • Heat seal strength The test was conducted in accordance with JIS Z1707:2019 7.4 "Heat seal strength test". Two 100 mm square test pieces were cut from the obtained paper substrate, and the coated layers were brought into contact with each other. The test was performed at a pressurized temperature of 160°C or 180°C and a pressurized pressure of 0.2 MPa (20.0 N / cm²). 2 After heat-sealing with a pressurization time of 1.0 second, the specimen was left to stand for 24 hours in an environment of 23°C and 50% humidity. Then, a measurement sample was cut from the heat-sealed 100mm square test piece so that the long side was 100mm and the short side was 15mm. Subsequently, the peeled long edge was clamped in the upper and lower fixtures of a vertical tensile testing machine (Tensilon, manufactured by A&D Company, Ltd.), and the sample was peeled from the long edge side at a speed of 200 mm / min (T-type), while measuring the peel strength, i.e., the HS strength (N / 15 mm). Furthermore, the detached surface was visually inspected and evaluated according to the following criteria. Measurements are taken twice, and the average value of the peel strength is shown. If the evaluation results differ based on visual observation, both results are shown. ○: The entire surface of the heat-sealed area is damaged. △: Partial material damage on the heat-sealed surface ×: Delamination occurs between coating layers (no material breakage). -: Without heat sealing

[0041] (material) Base paper: Nippon Paper Industries, basis weight 64g / m² 2 Lamina of high quality (LM64PEDW) PHBH: Kaneka Corporation, mass-average molecular weight 600,000 Inorganic pigment: Shiraishi Industries Co., Ltd., kaolin, KCS, average particle size 3.6 μm, aspect ratio 10-15

[0042] PVA1: Kuraray Co., Ltd., 28-98, fully saponified PVA PVA2: Kuraray Co., Ltd., HR3010, high water resistance Partially saponified EVA: Kuraray Co., Ltd., RS-1713 EVA1: Sumika Chemtex Co., Ltd., S-400HQ, Tg 0℃, Ethylene:Vinyl Acetate = 20:80 EVA2: Sumika Chemtex Co., Ltd., S-305HQ, Tg 7℃, Ethylene:Vinyl Acetate = 10:90 EVA3: Sumika Chemtex Co., Ltd., S-410HQ, Tg -18℃, Ethylene:Vinyl Acetate = 30:70 EVA4: Sumika Chemtex Co., Ltd., S-408HQE, Tg -30℃, Ethylene:Vinyl Acetate = 40:60

[0043] "Manufacturing of paper substrates" PHBH, EVA or PVA, and an inorganic pigment were mixed and stirred in the parts by mass shown in Table 2 to obtain a coating solution with a solid content concentration of 40% by mass. A coating solution was applied to one surface of the base paper using the bar-blade method to achieve the dry mass shown in Table 2. After drying at 105°C for 1 minute, a heat treatment was performed at 140°C for 1 minute to form a paper substrate with a coating layer on the outermost surface of one side of the base paper.

[0044] [Table 2]

[0045] Comparative Example 1, which had a coating layer of PHBH alone, received a wet-rub evaluation of "3". Comparative Examples 2 and 3, which added general-purpose PVA and highly water-resistant PVA, also received an evaluation of "2". Comparative Example 4, which further added pigment, also received an evaluation of "1", showing no improvement. Furthermore, Comparative Example 5, which added partially saponified EVA to PHBH, also received a wet-rub evaluation of "2", showing no improvement. In contrast, the wet-rub evaluation for Examples 1-3, which have a coating layer containing PHBH and EVA, was "5," confirming improvement. Examples 4-8 showed that the ratio of EVA to 100 parts by mass of PHBH was effective in the range of 20 to 235 parts by mass, and Examples 9-11 confirmed that the wet lab improvement effect was also observed with EVAs of different Tg values.

[0046] "Manufacturing of zipper bags" Two 16cm square pieces of paper were cut from the paper substrate obtained in Example 1. A 15cm long PBS chuck (MFS406, manufactured by Idemitsu Unitech Co., Ltd.) was prepared. The male and female parts were aligned parallel to each other at a distance of 25mm from one side of the paper, and the center of the chuck in the width direction was aligned with the paper, and it was fused at 150°C for 1.0 seconds at 0.3 MPa. Two pieces of paper were placed on top of each other with the male and female parts of the zipper engaged, and all four sides were fused together at 150°C for 1.0 seconds at 0.3 MPa, starting from the edge, with a width of 8 mm, to obtain a zipper bag with a four-sided seal. The height of this zipper bag with the zipper engaged was 1.8 mm. The resulting four-sided sealed bags were practical, with no tears in the seal area where the zipper was embedded.

[0047] The chuck portion was fused to a piece of paper in the same manner as described above, except that the portion above the fitting part of the chuck portion was not fused. A test specimen was then prepared by cutting the paper to a width of 15 mm so that the chuck portion extended in the width direction. In accordance with JIS Z1707:2019 7.4 "Heat seal strength test," the unfused portion of the paper and the upper part of the chuck were clamped between the upper and lower fixtures of a vertical tensile testing machine (Tensilon, manufactured by A&D Company, Limited), and peeled at a speed of 200 mm / min (T-type). The peel strength, i.e., the heat seal strength, was measured. Measurements were taken twice, once for the male and once for the female parts. The average heat seal strength was 3.3 N / 15 mm, confirming that the chuck was firmly fused to the paper substrate. [Explanation of symbols]

[0048] 1 Zipper bag 11 bags 12. Zipper part 13. Seal part< / eva> < / phbh>

Claims

1. The bag body is made of a paper substrate having a coating layer containing PHBH and EVA on its inner surface, and the zipper portion is fused to the coating layer. The chuck portion is mainly composed of PBS, The coating layer contains 1 to 250 parts by mass of EVA per 100 parts by mass of PHBH, A zipper bag characterized in that the EVA has a glass transition temperature (Tg) of -50°C or higher and 30°C or lower.

2. The zipper bag according to claim 1, characterized in that the coating layer contains an inorganic pigment.

3. The zipper bag according to claim 1 or 2, characterized in that the height of the zipper portion when fitted is 2.5 mm or less.

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