Heat-sealable sheets and sterile packaging

Abstract

To provide a heat seal sheet and a sterilization package which can improve easy peelability and humidity stability.SOLUTION: A heat seal sheet includes a base material, and a heat adhesive layer positioned on one surface of the base material, wherein the heat adhesive layer contains a thermoplastic resin and an antistatic agent. Preferably, 0.5 to 20 pts.mass of the antistatic agent is contained with respect to 100 pts.mass of the thermoplastic resin. Preferably, the antistatic agent contains one or more kinds of anionic antistatic agents.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to heat-sealable sheets and sterile packaging. [Background technology]

[0002] Instruments used in surgery and treatment are sterilized before use while stored in sterile packaging. Sterilization methods used in hospitals and other facilities include, for example, sealing the items to be sterilized, such as scalpels and forceps, inside sterile packaging, and then using gas sterilization, autoclaving, or radiation sterilization. In gas sterilization, the pressure in a pressure-resistant container containing the sterile packaging is reduced, and then ethylene oxide gas (EOG) is filled into the container, allowing the gas to permeate the sterile packaging and sterilize it. In autoclaving, the sterile packaging is exposed to high-temperature steam using an autoclave, and sterilization is performed by repeatedly reducing and increasing the pressure. In radiation sterilization, the sterile packaging is irradiated with radiation to sterilize it. Of these sterilization methods, autoclaving and gas sterilization are widely used because they are inexpensive and the procedures are simple.

[0003] On the other hand, sterile packaging containing items to be sterilized is stored until it is used in surgery or other procedures, and is opened when it is used. Therefore, to make it easy for doctors and practitioners wearing gloves to open, sterile packaging is made by bonding two rectangular sheets or films together so that they can be peeled apart, or by using thin sheets that are easy to tear open. When opening, a peel-open method is generally used, in which one thin sheet is separated from the other, or a tear-open method is used, in which the two thin sheets are torn apart.

[0004] In the peel-open type sterile packaging described above, when the adherend is peeled off the sterile paper, paper dust and other particles may scatter due to the breakage of the base material of the sterile paper. Paper dust and other particles (lint) resulting from the breakage of the base material can re-contaminate sterile items such as medical instruments after sterilization. Therefore, sterile paper needs to have improved easy-peel properties, which make it easy to peel off, and to suppress the scattering of lint during peeling. The demand for improved easy-peel properties is particularly pronounced in medical settings that require a high level of cleanliness, such as operating rooms and anterooms.

[0005] As an example of the sterile packaging described above, the configurations described in Patent Documents 1 to 8 are known. The sterile packaging described in Patent Document 1 has a thermoplastic resin layer on one side of the base paper. The sterile packaging described in Patent Document 2 is obtained by coating an acrylic acid copolymer onto a base paper containing aluminate. The sterile packaging described in Patent Document 3 has a thermoplastic resin layer containing a hollow polymer pigment on the surface of the base paper. The sterile packaging described in Patent Document 4 is obtained by impregnating a low air permeability base paper of 10 seconds or less with an impregnating agent mainly composed of polyvinyl alcohol. The sterile packaging described in Patent Document 5 has a coating layer on at least one side of the base paper, the coating layer is mainly crosslinked polyvinyl alcohol and has a dry weight of 0.1 g / m² after coating. 2 More than 6g / m 2 The following applies: The sterile packaging described in Patent Document 6 is obtained by impregnating a low-permeability base paper of 20 seconds or less with an impregnating agent mainly composed of an acrylic copolymer. The sterile packaging described in Patent Document 7 has a thermoplastic resin layer containing a polyolefin resin, an inorganic material, and a surfactant on one side of the base paper. Patent Document 8 describes sterile paper and sterile packaging having a heat-sealable layer containing a thermoplastic resin and calcium fatty acid. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2001-122348 [Patent Document 2] Japanese Patent Application Laid-Open No. 9-290808 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-196188 [Patent Document 4] Japanese Patent Application Laid-Open No. 2001-200493 [Patent Document 5] Japanese Patent Application Laid-Open No. 2004-84131 [Patent Document 6] Japanese Patent Application Laid-Open No. 2002-173900 [Patent Document 7] Japanese Patent Application Laid-Open No. 2008-105374 [Patent Document 8] Japanese Patent Application Laid-Open No. 2022-68392 [Summary of the Invention] [Problems to be Solved by the Invention]

[0007] The above-described easy-peelability may deteriorate depending on the storage conditions. In particular, storage under high humidity conditions may increase the peel strength and cause substrate breakage. The present invention provides a heat-seal sheet and a sterilized package that can maintain easy-peelability even after storage under high humidity. [Means for Solving the Problems]

[0008] The present invention for solving the above problems has the following configuration. (1) A heat-seal sheet having a heat-adhesive layer on at least one surface of a substrate, wherein the heat-adhesive layer contains a thermoplastic resin and an antistatic agent. (2) The heat-seal sheet according to claim 1, wherein the antistatic agent is contained in an amount of 0.5 to 20 parts by mass based on 100 parts by mass of the thermoplastic resin. (3) The heat-seal sheet according to any one of claims 1 to 2, wherein the antistatic agent contains one or more anionic antistatic agents. (4) The heat-seal sheet according to any one of claims 1 to 3, wherein the Gurley air permeability measured according to JIS P 8121:2012 is 700 seconds or less. (5) The heat seal sheet according to any one of claims 1 to 4, wherein the paper substrate comprises a polyacrylamide resin. (6) A packaging body having at least one heat-seal sheet as described in any one of claims 1 to 5. (7) A packaging body having a heat-bonded portion obtained by overlapping and heat-pressing at least a portion of the heat-bonding layer of the heat-seal sheet according to any one of claims 1 to 5 with at least a portion of another substrate. (8) The packaging according to claim 7, wherein the 180° peel strength when the heat-bonded portion is peeled off at a peeling speed of 300 mm / min in accordance with JIS P 8113:2006 is 0.5 to 15 N / 15 mm. [Brief explanation of the drawing]

[0009] [Figure 1] A cross-sectional view showing the cross-sectional structure of one embodiment of the packaging. [Explanation of Symbols]

[0010] S...space, 11...packaging, 11E...heat-sealed portion, 21...heat-seal sheet, 22...base material, 23...heat-sealed layer, 31...adhered object, 31E...one end. [Modes for carrying out the invention]

[0011] Hereinafter, an embodiment of the heat-seal sheet and packaging will be described with reference to Figure 1. [Packaging 11] The packaging 11 comprises a heat-seal sheet 21 and an adherend 31. The heat-seal sheet 21 comprises a base material 22 and a heat-adhesive layer 23 located on one side of the base material 22.

[0012] The adherend 31 is, for example, wrapping paper, laminated paper, film, or a molded container for sterilization. The material constituting the adherend 31 is, for example, at least one resin selected from the group consisting of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate, polyvinyl chloride, polyvinylidene chloride, polystyrene, ethylene-vinyl acetate copolymer resin, and ethylene-acrylic copolymer resin. Alternatively, the adherend 31 may be composed of a composite material in which these resins and other materials are laminated. The material constituting the adherend 31 may be a mixture of two or more different types of resin. The adherend 31 can also be realized as a laminate in which two or more different types of resins form separate layers.

[0013] A sterile packaging material, which is one embodiment of the application of the heat-seal sheet of the present invention, will be described. The packaging body 11 includes a heat-sealable portion 11E. The heat-sealable portion 11E has an annular shape in which the heat-sealable sheet 21 and the adherend 31 are heat-sealed to each other.

[0014] The packaging 11 includes a space S surrounded by a heat-sealed portion 11E between the heat-seal sheet 21 and the object to be adhered to 31. The space S in the sterile packaging 11 is a space for containing the object to be sterilized, such as a medical instrument. The sterile packaging 11 is, for example, used to contain the object to be sterilized within the space S, and then subjected to sterilization treatment such as autoclaving, ethylene oxide gas (EOG) sterilization, electron beam sterilization, or gamma ray sterilization. When gas sterilization is performed, the base material 22 is made of a breathable base material. When the sterilized object to be used is used, one end 31E of the adherend 31, which is separated from the heat seal sheet 21, is pulled up relative to the base material 22, and the adherend 31 is peeled off from the heat seal sheet 21. Then, the space S is released, and the object to be sterilized is exposed to the space where the sterilized package 11 is located. The heat-bonding layer 23 can be formed on one side of the base material 22 where the adherend 31 is located, and on the opposite side.

[0015] [Thermal adhesive layer 23] The heat-bonding layer 23 comprises at least a thermoplastic resin and an antistatic agent. The thermoplastic resin is preferably one containing a polyolefin structure. Examples of polyolefin structures include polyethylene and polypropylene. Commercially available thermoplastic resins that can be used in this invention include the DIC Seal E series from DIC Graphics and the Chemipearl series from Mitsui Chemicals.

[0016] Examples of the antistatic agents include cationic antistatic agents having cationic functional groups such as quaternary ammonium salts, pyridinium salts, and primary, secondary, and tertiary amino groups; anionic antistatic agents having anionic functional groups such as sulfonates, sulfate esters, phosphonates, and phosphate esters; amphoteric antistatic agents such as alkyl betaines and their derivatives, imidazolines and their derivatives, and alanine and its derivatives; nonionic antistatic agents such as amino alcohols and their derivatives, glycerin and its derivatives, and polyethylene glycol and its derivatives; and ion-conductive polymers obtained by polymerizing or copolymerizing monomers having the cationic, anionic, or amphoteric ion-conductive groups mentioned above. The antistatic agents can be used individually or in combination of two or more types. Among these, it is preferable to include an anionic antistatic agent, and it is even more preferable to include a phosphate ester salt.

[0017] The amount of the antistatic agent is preferably 0.5 to 20 parts by mass, more preferably 1 to 15 parts by mass, and even more preferably 1 to 10 parts by mass, per 100 parts by mass of the thermoplastic resin. If the amount is 20 parts by mass or more, the peel strength decreases and the adhesiveness is affected. If the amount is 0.5 parts by mass or less, the effect is difficult to obtain.

[0018] The heat-bonding layer may contain wax. Including wax in the heat-bonding layer is effective in maintaining easy-peel properties not only after storage in a high-humidity environment, but also after storage in a high-temperature environment.

[0019] Examples of the aforementioned waxes include natural oil-based waxes derived from animals and plants, such as paraffin wax and carnauba wax, and synthetic waxes such as polyethylene wax. One type of wax or a mixture of two or more types can be used. Among these, it is preferable that carnauba wax is included.

[0020] The heat-bonding layer may contain other materials as long as they do not impair the effects of the present invention. Specifically, these include auxiliary agents such as dispersants, water-retaining agents, and defoaming agents, as well as various inorganic pigments and organic pigments.

[0021] The heat-bonding layer 23 is obtained, for example, by applying a heat-bonding layer coating to one surface (the top surface in the figure) of the substrate 22 and drying the applied heat-bonding layer coating. The heat-bonding layer coating includes a thermoplastic resin, an antistatic agent, other materials, and a liquid medium. In addition to the heat-bonding layer on one surface of the substrate 22, it is also possible to have another heat-bonding layer 23 on the opposite surface. The heat-bonding layer coating may be a water-based coating or a solvent-based coating.

[0022] Various known wet coating methods can be used for applying the heat-adhesive layer. For example, on-machine size presses on paper machines, transfer roll coaters (such as shimsizers and gate roll coaters), and spray devices can be used. Off-machine equipment can utilize general coating devices such as blade coaters, air knife coaters, roll coaters, reverse roll coaters, shimsizers, gate roll coaters, bar coaters, curtain coaters, slot die coaters, gravure coaters, champlex coaters, brush coaters, two-roll coaters, bill blade coaters, and short dwell coaters. For drying the heat-adhesive layer coating, it is preferable to use an air dryer or infrared heater that does not come into contact with the coated surface, from the viewpoint of reliably suppressing contamination of the equipment. It is also possible to use a cylinder dryer that directly contacts the coated surface for drying the heat-adhesive layer coating.

[0023] The amount of heat-bonding coating to be applied is, for example, 0.1 g / m². 2 More than 20g / m2 Hereinafter, preferably, 0.5 g / m 2 or more and 12 g / m 2 or less, more preferably, 1.0 g / m 2 or more and 7.0 g / m 2 or less. When the coating amount of the heat - adhesive layer paint is 0.1 g / m 2 or more, it becomes possible to ensure the adhesive strength required for the heat - adhesive layer 23. Also, when the coating amount of the heat - adhesive layer paint is 20 g / m 2 or less, the air permeability required in the sterilization process of the sterilized package is ensured.

[0024] This will be described using FIG. 1. By containing a thermoplastic resin and an antistatic agent in the heat - adhesive layer 23, sufficient adhesive force with the adherend and easy peeling of one from the other between the base material 22 and the heat - adhesive layer 23 improve the easy - peel property when opening the sterilized package 11. After peeling, the heat - adhesive layer 23 transfers to the adherend 31, thereby easily visualizing that the heat - adhesive layer 23 is located on the adherend 31, and thus, that the adherend 31 is peeled from the heat - seal sheet 21.

[0025] [Base material 22] The base material 22 includes, for example, a paper base material and an undercoat layer provided as necessary. The paper base material is obtained by papermaking of a papermaking raw material containing pulp slurry. The pulp used in the pulp slurry is, for example, wood pulp or non - wood pulp. The wood pulp is, for example, at least one selected from the group consisting of softwood pulp and hardwood pulp. The steaming method and bleaching method of the wood pulp are not particularly limited. The non - wood pulp is, for example, at least one selected from the group consisting of hemp pulp, kenaf pulp, and bamboo pulp. The pulp slurry can contain materials other than pulp fibers, such as rayon fibers, nylon fibers, and other heat - fusible fibers, as auxiliary materials.

[0026] Pulp slurry is obtained by beating pulp in the presence of water. For the pulp beating method and the beating equipment used, a double disc refiner (DDR), which has high beating efficiency, is preferably used. Pulp beating is carried out so that the pulp freeness (hereinafter also referred to as "standard freeness"), measured according to JIS P 8121-2:2012, is between 250 mL and 700 mL, more preferably between 250 mL and 600 mL, and even more preferably between 300 mL and 500 mL. When the standard freeness of the pulp is 250 mL or more, it is possible to ensure the air permeability of the paper. Furthermore, when the standard freeness of the pulp is 250 mL or less, it is possible to improve the strength of the paper and enhance its easy-peel properties.

[0027] Generally, the relationship between pulp beating and paper strength is such that if the beating process is not advanced enough, it is difficult to obtain sufficient paper strength. This is thought to be because the entanglement between pulp fibers is weak and there are few points of interfiber bonding (hydrogen bonding). Paper strength improves as the beating process progresses to a certain extent. On the other hand, as the beating process progresses, the entanglement between pulp fibers increases and the number of interfiber bonding points increases, resulting in increased paper strength, but the voids between fibers decrease, and the air permeability of the paper substrate decreases. In this regard, if the standard freeness of the pulp is in the range of 250 mL to 700 mL, it is possible to achieve sufficiently high paper strength while maintaining the air permeability of the paper substrate and, consequently, the substrate 22. As a result, the easy-peel suitability of the heat-seal sheet 21 can be further improved.

[0028] The pulp slurry obtained by beating can also be used as a papermaking raw material prepared by adding various internal additives for papermaking. These internal additives include, for example, sizing agents, paper strength enhancers, wet paper strength enhancers, aluminum sulfate, and various fixatives such as cationized starch. In addition to these, yield enhancers, defoamers, fillers, colorants, and other internal additives can also be optionally blended with the papermaking raw material.

[0029] The paper strength enhancer includes, for example, at least one selected from polyacrylamide resin, cationized starch, and polyvinyl alcohol. Among these paper strength enhancers, adding a polyacrylamide resin-based paper strength enhancer internally makes it possible to more effectively improve the strength of the substrate and further enhance its easy-peel properties. Furthermore, in order to exhibit a paper strength enhancing effect after the addition of the paper strength enhancer, it is preferable that the mass average molecular weight is 2 million (Mw) or more. Furthermore, in order to obtain an appropriate viscosity during the operation of adding the paper strength enhancer and to facilitate addition, it is preferable that the mass average molecular weight is 10 million (Mw) or less. The mass average molecular weight of the polyacrylamide resin is the polyethylene oxide equivalent value measured by gel permeation chromatography (GPC). Furthermore, as the polyacrylamide resin used as the paper strength enhancer, for example, anionic, cationic, amphoteric, or nonionic polyacrylic resins can be used, but among these, it is particularly preferable to use an amphoteric polyacrylamide resin. The sizing agent includes, for example, at least one selected from the group consisting of alkenyl succinic acid, alkyl ketene dimer, and rosin. The wet paper strength enhancer includes, for example, at least one selected from the group consisting of epichloro resin and melamine resin.

[0030] It is also possible to apply a primer, which is a coating liquid containing polyacrylamide resin, to at least one surface of the substrate. Applying the primer further enhances the ease-peel properties. When the primer is applied to only one surface of the substrate, the primer is applied to the surface on which the heat-bonding layer 23 of the substrate is provided. The primer may also be applied to both one surface of the substrate and the opposite surface.

[0031] The paper substrate 22 is obtained, for example, by papermaking using a standard method with prepared papermaking raw materials. The basis weight of the substrate 22 can be appropriately set according to the basis weight of the paper substrate and the amount of primer applied.

[0032] The primer contains a polyacrylamide resin. Polyacrylamide resin is a polymer consisting of repeating (meth)acrylamide units. (Meth)acrylamide is a general term for acrylamide and methacrylamide. The polyacrylamide resin may have either acrylamide units or methacrylamide units, or both. The polyacrylamide resin may also have other units besides (meth)acrylamide units.

[0033] The polyacrylamide resins contained in the primer include, for example, anionic polyacrylamide resins, cationic polyacrylamide resins, amphoteric polyacrylamide resins, and nonionic polyacrylamide resins. These primers are used as paper strength agents in the papermaking field, etc. One type of polyacrylamide resin may be used alone, or two or more types may be used in combination. In terms of availability, anionic polyacrylamide resin is preferred.

[0034] Anionic polyacrylamide resins contain anionic functional groups such as carboxyl groups, sulfonic acid groups, phosphate groups, or salts thereof. Anionic polyacrylamide resins are, for example, copolymers of (meth)acrylamide and anionic functional group-containing monomers such as acrylic acid, or partial hydrolysates of poly(meth)acrylamide.

[0035] The mass-average molecular weight (Mw) of the polyacrylamide resin contained in the primer is preferably between 50,000 and 2,000,000, more preferably between 50,000 and 500,000, and even more preferably between 50,000 and 300,000. If the mass-average molecular weight of the polyacrylamide resin contained in the primer layer is between 50,000 and 2,000,000, the effect of suppressing fuzzing on the surface of the substrate 22 due to peeling of the adherend 31 is better. If the mass-average molecular weight is 50,000 or more, the effect of suppressing fuzzing on the surface of the substrate 22 when the heat-bonded layer 23 peels off is easily obtained. If the mass-average molecular weight is 2,000,000 or less, the low viscosity required for application of the primer can be sufficiently obtained, making the preparation and application of the primer easy. In addition, the concentration of polyacrylamide resin contained in the primer can be increased within the desired viscosity range, making it easier to obtain the desired application amount. The mass-average molecular weight of the polyacrylamide resin is the polyethylene oxide equivalent value measured by gel permeation chromatography (GPC).

[0036] The liquid medium contained in the primer is preferably one that dissolves the polyacrylamide resin, such as water. The primer may also contain other components besides the polyacrylamide resin, as long as it does not impair the easy-peel properties. Other components include, for example, water-soluble polymer compounds, aqueous polymer compounds, release agents, defoamers, dispersants, wetting agents, colored dyes, colored pigments, and white pigments. These may be used individually or in combination of two or more. Examples of water-soluble polymer compounds include starch, modified starch, polyvinyl alcohol, modified polyvinyl alcohol, hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, gelatin, casein, gum arabic, diisobutylene-maleic anhydride copolymer salt, and styrene-maleic anhydride copolymer salt. Examples of aqueous polymer compounds include styrene-butadiene copolymer emulsion, acrylic acid ester copolymer emulsion, urethane resin, urea resin, styrene-acrylic resin emulsion, and ethylene-acrylic resin emulsion.

[0037] The polyacrylamide resin content (concentration) in the primer is preferably 50% to 100% by mass, and more preferably 80% to 100% by mass, relative to the total solids content (100% by mass) in the primer. If the polyacrylamide resin content is 50% by mass or more, the easy-peel suitability of the heat seal sheet 21 can be further improved. The total solids content is the total amount of the primer excluding the liquid medium, and if other components other than polyacrylamide resin are included, it is the sum of the polyacrylamide resin and the other components.

[0038] The amount of primer applied to the substrate is set appropriately according to the polyacrylamide resin content in the primer. The amount of primer applied to the side of the substrate where the heat-bonding layer 23 is located is converted to 0.05 g / m² in terms of polyacrylamide resin content. 2 More than 20g / m 2 Preferably, it is 0.1 g / m 2 More than 15g / m 2 It is more preferable that the following is the case: 0.2 g / m 2 More than 10g / m 2 It is even more preferable that the amount of polyacrylamide resin applied is 0.05 g / m². 2 With the above conditions, when peeling the adherend 31 from the heat seal sheet 21, the substrate 22 and the heat adhesive layer 23 will separate smoothly, and this separation will not cause fuzzing on the surface of the substrate 22 or damage to the substrate 22. In addition, the amount of polyacrylamide resin applied is 20 g / m². 2 If the following conditions are met, uneven adhesion can be suppressed when heat-sealing the heat-seal sheet 21, and for example, the adhesive can be applied substantially uniformly to the entire surface of the substrate on which the heat-adhesive layer 23 is located. On the other hand, the primer may be applied to the surface of the substrate on which the heat-adhesive layer 23 is provided in a predetermined pattern.

[0039] The components of the undercoat layer may also include components other than polyacrylamide resin. These other components are, for example, at least one selected from the group consisting of starch, resins such as polyvinyl alcohol and styrene-butadiene resin, and pigments such as kaolin, talc, calcium carbonate, and white carbon. The polyacrylamide resin contained in the undercoat applied to one side may be the same as, for example, the polyacrylamide resin contained in the undercoat applied to the other side, or they may be different from each other. When applying the undercoat to the other side of the paper substrate, the amount of undercoat applied should, for example, be 0.01 g / m² in terms of solid content. 2 More than 20g / m 2 The following is true: 0.01 g / m 2 More than 5g / m 2 Preferably, it is 0.01 g / m 2 More than 3g / m 2 It is more preferable that the following is the case: 0.1 g / m 2 More than 2g / m 2 It is even more preferable that the amount of primer applied is 20 g / m². 2 The following conditions ensure good air permeability of the heat-seal sheet 21. Furthermore, by adjusting the amount of primer applied to the other side of the paper substrate in this manner, it becomes easy to appropriately adjust the concentration of polyacrylamide resin on one side of the paper substrate, the other side, and the intermediate level between the two sides. When applying primer to both sides of the paper substrate, for example, it is preferable to set the ratio of the amount applied to one side to the amount applied to the other side to 3:7 to 7:3. This ratio of application amounts makes it even easier to increase the concentration of polyacrylamide resin in the substrate to a level greater than the intermediate level on both sides of the substrate. From the viewpoint of reducing the manufacturing cost of the heat-seal sheet 21, one preferred embodiment is to not apply primer to the other side of the paper substrate.

[0040] Various known wet coating methods can be used for applying the primer. For example, the primer can be applied using an on-machine size press on the paper machine, a transfer roll coater (such as a shim sizer or gate roll coater), or a spray device. Off-machine equipment can also be used, such as a blade coater, air knife coater, roll coater, reverse roll coater, shim sizer, gate roll coater, bar coater, curtain coater, slot die coater, gravure coater, champlex coater, brush coater, two-roll coater, bill blade coater, or short dwell coater. From the viewpoint of improving operability and productivity, it is preferable to use on-machine equipment for the application and drying of the primer. The type of paper machine used to make the paper substrate is preferably one equipped with an on-machine coating machine, such as a wire screen paper machine, short screen paper machine, or cylinder screen paper machine. The polyacrylamide resin content in the base material 22 is, for example, 1.0% by mass or more and 30% by mass or less.

[0041] The basis weight of the base material 22 is, for example, 30 g / m². 2 Preferably, it is 40 g / m 2 It is more preferable that the amount be greater than or equal to 45 g / m 2 It is even more preferable that the basis weight of the base material 22 be 30 g / m². 2 With the above conditions met, the substrate 22 is more likely to have sufficient strength to withstand the peeling of the adherend 31 from the substrate 22, and the substrate 22 is less likely to break during peeling. In addition, the occurrence of pinholes is suppressed, which is also preferable from the viewpoint of bacterial barrier properties.

[0042] There is no particular upper limit to the basis weight of the base material 22, but from the viewpoint of obtaining breathability during sterilization, 300 g / m² is recommended. 2 Preferably, it is 250 g / m². 2 The following is more preferable: 200g / m 2 The following is even more preferable: The basis weight of the substrate 22 and the paper substrate is measured in accordance with, for example, JIS P 8124:2011.

[0043] The density of the base material 22 is, for example, 0.60 g / cm³. 3 More than 1.20g / cm 3 Preferably, it is 0.70 g / cm³. 3 More than 1.10g / cm 3 It is more preferable that the density of the base material 22 is 0.60 g / cm³. 3 If the above conditions are met, it is easier to obtain sufficient strength to withstand easy peeling, and the substrate 22 is less likely to break during peeling. 3 In that case, air permeability can be maintained. The density of the base material 22 can be calculated from the measured values ​​of thickness and basis weight, for example, by measuring the thickness in accordance with JIS P 8118:1998.

[0044] [Heat seal sheet 21] The heat-seal sheet 21 preferably has an Oguri-type air permeability measured in accordance with JIS P 8117:2009 of, for example, 700 seconds or less, more preferably 500 seconds or less, and particularly preferably 300 seconds or less. A heat-seal sheet 21 having an Oguri-type air permeability within this range can effectively improve the air permeability of the heat-seal sheet 21. On the other hand, the lower limit of the Oguri-type air permeability can be, for example, 5 seconds. The Oguri-type air permeability of the heat-seal sheet 21 can be adjusted by appropriately selecting, for example, the freeness of the pulp, the basis weight of the base material 22, and the amount of primer applied.

[0045] The heat-bonding surface of the heat-seal sheet 21, which is the surface of the heat-bonding layer 23, preferably has a Wang-Ran smoothness of, for example, 50 seconds or more, as measured in accordance with JIS P 8155:2010, because this reduces variations in seal strength and allows for short-time heating. The smoothness of the heat-bonding surface can be adjusted by applying a smoothing treatment to the base material 22 using various known methods, or by applying the smoothing treatment after the heat-bonding layer 23 has been formed.

[0046] The sterile packaging body 11 obtained by heat-bonding the heat-seal sheet 21 and the adherend 31 preferably has a peel strength of, for example, 0.5 N / 15 mm or more and 15 N / 15 mm or less when the adherend 31 is peeled 180° at a peeling speed of 300 mm / min in accordance with JIS P 8113:2006. If the heat-seal sheet 21 has a peel strength within this range, a sterile packaging body 11 with an excellent balance between easy peelability and heat adhesion strength can be obtained. Furthermore, from the viewpoint of more effectively improving the balance between easy peelability and heat adhesion strength, it is more preferable that the peel strength is 0.5 N / 15 mm or more and 7.0 N / 15 mm or less, and even more preferable that it is 1.0 N / 15 mm or more and 4.0 N / 15 mm or less. Note that the peel strength can be appropriately adjusted by selecting, for example, the type and amount of heat-bonding layer 23 applied.

[0047] [Effect] The sterile paper 21 has excellent easy-peel properties and temperature stability because it contains a thermoplastic resin and an antistatic agent in the heat-adhesive layer 23. For example, when peeling the sterile paper 21 from a film-like substrate 31 after heat-bonding it to the substrate 31, the heat-adhesive layer 23 remains attached to the substrate 31, making it easy to peel off from the interface with the substrate 22, and the substrate 22 is less likely to tear. Furthermore, since the heat-adhesive layer 23 is visible on the substrate 31, it is easy to confirm that it is uniformly bonded before peeling. In addition, the sterile paper 21 maintains its easy-peel properties even when stored in a high-humidity environment before heat bonding. And because the easy-peel properties are stabilized, fuzzing and peeling of paper fragments are stably suppressed, so it is possible to prevent lint and peeled paper fragments that fall off from fuzzed areas from adhering to the substrate 31 or its contents. As a result, it is possible to provide sterile paper 21 that suppresses fuzzing during peeling and can be used in a highly clean operating room.

[0048] Several sterilization methods exist for the sterile packaging 11, including autoclaving, ethylene oxide gas (EOG) sterilization, and gamma ray sterilization. However, EOG sterilization, in particular, requires gas replacement after sterilization. The heat-seal sheet 21 can be made to have excellent air permeability depending on the freeness of the pulp used in the manufacture of the base material 22 and the basis weight of the base material 22. By increasing the air permeability of the heat-seal sheet 21, the time required to replace the sterilization gas with air after sterilization can be shortened. This makes it possible to realize a heat-seal sheet 21 that is particularly suitable for EOG sterilization. Thus, the heat-seal sheet 21 is extremely useful in practice, with an excellent balance between easy peelability and air permeability.

[0049] The heat seal sheet 21 is not limited to the embodiments described above. The configurations and combinations thereof in the embodiments are examples, and additions, omissions, substitutions, and other modifications are possible without departing from the spirit of the present invention. For example, the heat seal sheet 21 may have other layers between the base material 22 and the heat adhesive layer 23. Other layers may include, for example, a water vapor barrier layer, an oxygen barrier layer, a printing layer, a printability improving layer, an overprint layer, and a light-shielding layer. The other layer located between the base material 22 and the heat adhesive layer 23 may be one layer or two or more layers. Furthermore, without departing from the spirit of the present invention, the base material 22 may have printing layers on both sides. An overprint layer may also be provided on the printing layer. [Examples]

[0050] An example of the above embodiment is described below. <Example 1> [Production of base material] Hardwood bleached kraft pulp (LBKP) was beaten in a double disc refiner (DDR) to obtain a pulp slurry so that the Canadian standard freeness (filtration capacity) described in JIS P 8121-2:2012 was 400 mL. Then, internal additives were added to the pulp slurry to obtain papermaking raw material. The internal additives, added in oven-dry amounts relative to the pulp mass, are: 0.5% aluminum sulfate, 0.05% alkenyl succinate sizing agent (Fibran 81K, National Starch Co.) pre-dispersed with cationized starch (Pillar 3YK, Pillar Starch Co.), 0.7% amphoteric polyacrylamide resin paper strength enhancer (PAM) (product name: Polystron OFT-3, Arakawa Chemical Industries, mass-average molecular weight 3 million), and 0.4% polyamine-polyamide epichlorohydrin resin wet paper strength enhancer (WS4024, Seikoh PMC Co.). Next, the papermaking raw materials are made using a wirewheel papermaking machine to obtain base paper, and then the following coating A is applied to both sides at a rate of 29 mL / m² using a sizing press coating machine attached to the papermaking machine. 2 After coating and drying, the surface smoothness of the base paper, measured according to JIS P 8155:2010 using an on-machine calender attached to the paper machine, is adjusted to 100 seconds, resulting in a basis weight of 60 g / m². 2 Its density is 0.8 g / cm³. 3 The base material 22 of Example 1 was obtained. Paint A] Aqueous solution of anionic polyacrylamide resin (mass-average molecular weight 200,000) (prepared by diluting Polymerset® 512 manufactured by Arakawa Chemical Industries, Ltd. with water to adjust the anionic polyacrylamide resin concentration to 7% by mass).

[0051] [Manufacturing of Heat-Seal Sheet] 100 parts by mass of olefin-based aqueous emulsion (manufactured by Mitsui Chemicals, Inc.) as a thermoplastic resin, 3 parts by mass of electrostripper F (manufactured by Kao Corporation, polyoxyethylene alkyl ether phosphate potassium salt) and 10 parts by mass of ML160RPH (manufactured by Michaelman, carnauba wax) as antistatic agents were prepared to obtain a heat-sealable layer coating with a solid content concentration of 30%. Next, one side of the substrate 22 of Example 1 was coated using a bar coater, with a coating amount of 4.0 g / m² after drying. 2The heat-adhesive layer coating was applied and dried to form the heat-adhesive layer 23 of Example 1. This resulted in obtaining a heat-seal sheet 21 comprising the base material 22 of Example 1 and the heat-adhesive layer 23 of Example 1.

[0052] <Example 2> The heat seal sheet 21 of Example 2 was manufactured in the same manner as in Example 1, except that ML160RPH was not added during the manufacturing of the heat seal sheet 21 of Example 1.

[0053] <Example 3> The heat seal sheet 21 of Example 3 was manufactured in the same manner as in Example 2, except that the amount of antistatic agent was 5 parts by mass.

[0054] <Example 4> In the production of the heat seal sheet 21 of Example 2, the amount of antistatic agent was set to 20 parts by mass and the coating amount to 4.5 g / m2, except that the process was the same as in Example 2, to produce the heat seal sheet 21 of Example 4.

[0055] <Example 5> In the production of the heat seal sheet 21 of Example 2, the only difference was that the antistatic agent was changed to another antistatic agent, Electro Stripper AC (manufactured by Kao Corporation, imidazoline-based amphoteric surfactant, sodium linear alkylbenzene sulfonate). The heat seal sheet 21 of Example 5 was produced in the same manner as in Example 2.

[0056] <Comparative Example 1> The heat seal sheet 21 of Comparative Example 2 was manufactured in the same manner as in Example 1, except that no antistatic agent was added.

[0057] <Comparative Example 2> The heat seal sheet 21 of Comparative Example 2 was manufactured in the same manner as in Example 1, except that the antistatic agent was omitted during the manufacturing process of the heat seal sheet 21 of Example 1.

[0058] <Evaluation> The following measurements and evaluations were performed on each heat-seal sheet of Examples 1-4 and Comparative Examples 1-2. The formulation of the heat-bonding layer for each heat-seal sheet and the results of the measurement evaluation are shown in Table 1.

[0059] [Measurement of Oken-style air permeability] The Oken-style air permeability of each heat seal sheet was measured in accordance with JIS P 8117:2009. If the Oken-style air permeability is 300 seconds or less, it can be said to be suitable as a sterile packaging material. [Adhesion to the Adherent] Polyvinyl chloride film (manufactured by Mitsubishi Chemical Corporation, C-1436) was used as the adherend. The heat-seal sheets were placed so that the heat-bonding layer side was in contact with the film, and a heat press tester was used to apply heat pressure under heat bonding conditions of 150°C, 0.2 MPa, and 1.0 second, thereby obtaining heat-bonded samples with each heat-seal sheet. Furthermore, in order to ensure that the portion to be chucked by the tensile testing machine during the "measurement of peel strength" described later, a portion of the heat-bonded sample was left unbonded to the adherend and the heat-seal sheet.

[0060] [Measurement of Peel Strength] The heat-bonded samples obtained in the "Adhesion to the Adherent" step were cut to a width of 15 mm and a length of 100 mm to accommodate a measurement clearance, and samples for peel strength measurement were prepared. The peel strength (N / 15 mm) of each sample was measured in accordance with JIS P 8113:2006. In this process, a tensile testing machine (model: Tensilon RTC-1250A, manufactured by Orientec Co., Ltd.) was used to chuck one end 31E of the adherent and one end of the heat-seal sheet 21, and the peel strength was measured using the 180-degree peel method at a peel speed of 300 mm / min. Furthermore, in the measurement of peel strength, if the substrate broke instead of peeling at the interface between the heat-bonded layer or the heat-bonded layer and the adherent, "substrate breakage" was recorded instead of the measured value. A peel strength of 0.5 N / 15 mm or higher is acceptable for use as a sterile packaging material. Furthermore, a peel strength of 4.0 N / 15 mm or lower is suitable for easy peeling.

[0061] [Measurement of humidity stability] After supplementing the heat-seal sheets of Examples 1-5 and Comparative Examples 1-2 under the following two conditions, measurements were performed using the method described in "Measurement of peel strength" above. (Condition 1) Store in a constant temperature and humidity chamber at 40°C and 75% humidity for 30 days. (Condition 2) Store in a constant temperature and humidity chamber at 40°C and 95% humidity for one day. If the peel strength remains within the range of 0.5 to 4.0 N / 15 mm after storage under Condition 1, it can be said to have excellent durability in high-humidity environments. Furthermore, if both the peel strength after storage under Condition 1 and the peel strength after storage under Condition 2 remain within the range of 0.5 to 4.0 N / 15 mm, it can be said to have extremely excellent durability in high-humidity environments.

[0062] [Table 1]

[0063] As shown in Table 1, the heat-seal sheets of Examples 1 to 5 maintained a peel strength in the range of 0.5 to 4.0 N / 15 mm both before and after storage at 40°C and 75% humidity for 30 days, confirming their excellent easy-peel properties and humidity stability of the easy-peel properties. On the other hand, the heat-seal sheet of Comparative Example 1 lacked easy-peel properties immediately after manufacturing. Furthermore, while the heat-seal sheet of Comparative Example 2 exhibited easy-peel properties immediately after manufacturing, these properties were lost after storage in a high-humidity environment.

[0064] As described above, the embodiments provide the following advantages. By including a thermoplastic resin and an antistatic agent in the heat-sealing layer, sufficient adhesive strength for packaging contents is obtained when the heat-sealing sheet and the adherend are heat-sealed, and when peeling, the substrate and the heat-sealing layer can be easily separated from each other with moderate force (easy peel property). Furthermore, even if the heat-sealing sheet is stored in a high-humidity environment before heat-sealing, the easy peel property can be maintained when the heat-sealing sheet and adherend are heat-sealed. [Industrial applicability]

[0065] The present invention provides an excellent heat-seal sheet that has good heat-sealing properties and easy-peel properties, and that maintains its easy-peel properties even after the heat-seal sheet has been stored in a high-humidity environment before heat bonding and the heat-seal sheet and adherend are heat-sealed.

Claims

1. A heat seal sheet comprising a heat adhesive layer on at least one surface of a paper substrate, wherein the heat adhesive layer comprises a thermoplastic resin and an antistatic agent, The antistatic agent is an anionic antistatic agent containing a phosphate ester salt, or a sodium linear alkylbenzene sulfonate salt. A heat-sealable sheet with an air permeability of 700 seconds or less, measured according to JIS P 8121:2012 using the Ouken method.

2. The heat seal sheet according to claim 1, wherein the antistatic agent comprises 0.5 to 20 parts by mass per 100 parts by mass of the thermoplastic resin.

3. The heat seal sheet according to claim 1 or 2, wherein the anionic antistatic agent containing the phosphate ester salt is a polyoxyethylene alkyl ether phosphate potassium salt.

4. The heat seal sheet according to claim 1 or 2, wherein the heat adhesive layer further contains wax.

5. The heat seal sheet according to claim 1 or 2, wherein the paper substrate comprises a polyacrylamide resin.

6. A packaging body having at least as a part the heat-seal sheet described in Claim 1 or 2.

7. A packaging body having a heat-bonded portion formed by overlapping and heat-pressing at least a portion of the heat-bonding layer of the heat-seal sheet according to claim 1 or 2 with at least a portion of another substrate.

8. The packaging according to claim 7, wherein the 180° peel strength when the heat-bonded portion is peeled off at a peeling speed of 300 mm / min in accordance with JIS P 8113:2006 is 0.5 to 15 N / 15 mm.

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