WO2024075655A1

WO2024075655A1 - Heat seal sheet and sterilized package

Info

Publication number: WO2024075655A1
Application number: PCT/JP2023/035722
Authority: WO
Inventors: 律雄萬道; 幸子小口; 真裕川北; 美紗名古屋; 健司柳沢
Original assignee: 王子ホールディングス株式会社
Priority date: 2022-10-05
Filing date: 2023-09-29
Publication date: 2024-04-11

Abstract

The purpose of the present invention is to provide: an excellent heat seal sheet that has sufficient heat adhesiveness and air permeability throughout the whole heat seal surface thereof, and that has a high strength and a reduced amount of lint generated therefrom; a production method for the heat seal sheet; and a sterilized package using the heat seal sheet.　The heat seal sheet according to the present invention comprises: one or more thermoplastic resin fiber nonwoven fabric layers A; and one or more thermoplastic resin fiber nonwoven fabric layers B. The thermoplastic resin fiber nonwoven fabric layers B each contain a low-melting-point polyester resin, polyester fibers, and a polyethylene resin. The mass ratio of the low-melting-point polyester resin, the polyester fibers, and the polyethylene resin (low-melting-point polyester resin : polyester fibers : polyethylene resin) is 13.75:11.25:75 to 41.25:33.75:25. The Oken-type air permeability of the heat seal sheet as measured in accordance with JIS P 8117:2009 is at most 700 seconds, and the tear strength of the heat seal sheet as measured in accordance with JIS P 8116:2000 is at least 700 mN.

Description

Heat-sealed sheets and sterile packaging

The present invention relates to a heat seal sheet and a sterile package.

Instruments used in surgery, treatment, etc. are sterilized by being placed in sterile packaging before use. Sterilization methods used by hospitals and medical equipment manufacturers include placing scalpels, forceps, and other items to be sterilized in sterile packaging and sealing it, and then sterilizing them using gas sterilization, high-pressure steam sterilization, radiation sterilization, etc. In gas sterilization, the package is placed in a pressure-resistant container, the pressure inside the container is reduced, the air inside the package is expelled, and then ethylene oxide gas (EOG) or the like is filled into the container to permeate the inside of the package and sterilize it. In high-pressure steam sterilization, the package is exposed to high-temperature steam using an autoclave or the like, and sterilized by repeatedly reducing and pressurizing the pressure. In radiation sterilization, sterilization is performed by exposing the package to radiation. Of these, gas sterilization and high-pressure steam sterilization are often used due to their cost and simplicity.

After sterilization, instruments are stored in this sterile packaging until they are to be used in surgery, etc., and are opened when they are to be used in surgery or treatment. When opening the packaging, the peel-open or tear-off method is generally used so that doctors and practitioners in hospitals can easily open the packaging even if they are wearing gloves. Sterilized packaging using the peel-open method is manufactured by bonding two rectangular sheets, one on the front and one on the back, so that they can be peeled off. Sterilized packaging using the tear-off method is manufactured using an easily tearable (easy to tear open) sheet.

The sterilization packaging used in the gas sterilization and high-pressure steam sterilization methods described above must be breathable due to the sterilization method used. Sterilization packaging used in radiation sterilization is also preferably breathable, as residual solvents and odors contained in the contents may evaporate during the sterilization process. For this reason, breathable sheets are used for the sterilization packaging.

For bag- or container-shaped sterilized packages, heat seal sheets that form a hermetic seal by thermocompression are used. For example, heat seal sheets that form lids for molded containers such as trays and cups are thermocompression-bonded to the flanges surrounding the openings to seal the containers.
Heat seal sheets are required to ensure breathability that allows sterilization while achieving complete closure (maintaining the sterile state) after sterilization.

Patent Document 1 proposes that the heat adhesive layer of the heat seal sheet is formed in a mesh-like shape to ensure breathability. However, the flange portion where the heat seal sheet is thermocompressed is usually narrow, and there are doubts about the integrity of the closure with a mesh-like heat adhesive layer.
On the other hand, Patent Document 2 proposes a heat seal sheet in which a granular thermoplastic resin is blended into the thermal adhesive layer, making it possible to make the thermal adhesive layer a so-called solid coating while ensuring breathability.
When using paper as the breathable base material, these heat seal sheets must limit their basis weight to ensure sufficient breathability, which limits their strength. In addition, there is a concern that lint may be generated due to the detachment of pulp fibers, and therefore, although they are applicable to the sterilization of small and lightweight medical instruments or general medical instruments, they are not currently applicable to heavy medical instruments, large medical instruments such as sheets and gowns, or advanced medical instruments such as catheters.

JP 2017-43866 A JP 2017-20130 A

The objective of the present invention is to provide an excellent heat seal sheet that has sufficient thermal adhesion and breathability over the entire heat seal surface, is strong, and minimizes the amount of lint (fiber fluff) generated, a method for producing the same, and a sterilized package using the same.

The present invention has the following aspects.
<1> A heat seal sheet having one or more thermoplastic resin fiber nonwoven fabric layers A and one or more thermoplastic resin fiber nonwoven fabric layers B,
the thermoplastic resin fiber nonwoven fabric layer B contains a low-melting point polyester resin, polyester fibers, and a polyethylene resin, and a mass ratio of the low-melting point polyester resin, polyester fibers, and polyethylene resin (low-melting point polyester resin:polyester fibers:polyethylene resin) is 13.75:11.25:75 to 41.25:33.75:25;
The heat seal sheet has an Oken air permeability of 700 seconds or less as measured in accordance with JIS P 8117:2009, and
The heat seal sheet has a tear strength of 700 mN or more as measured in accordance with JIS P 8116:2000.
<2> The heat seal sheet according to <1>, wherein the thermoplastic resin fiber nonwoven fabric layer A is a nonwoven fabric layer derived from at least one selected from the group consisting of a spunbonded nonwoven fabric, a thermally bonded nonwoven fabric, a chemically bonded nonwoven fabric, a needle-punched nonwoven fabric, a spunlace nonwoven fabric, a meltblown nonwoven fabric, and a wet-laid nonwoven fabric.
<3> The heat sealable sheet according to <1> or <2>, wherein the thermoplastic resin fiber nonwoven fabric layer A contains at least one fiber selected from the group consisting of polypropylene resin fibers, polyester fibers, and polyamide fibers.
<4> The heat sealable sheet according to any one of <1> to <3>, wherein the thermoplastic resin fiber nonwoven fabric layer A retains a fibrous shape.
<5> The heat seal sheet according to any one of <1> to <4>, wherein the peel strength when the heat seal sheet is peeled off at 180° from a sterilization packaging material such as paper, a film, or a molded container for sterilization at a peel speed of 300 mm/min in accordance with JIS P 8113:2006 is 1.0/15 mm or more and 15 N/15 mm or less.
<6> The heat seal sheet according to any one of <1> to <5>, having a basis weight of 30 g/ ^m2 or more and 150 g/ ^m2 or less.
<7> The heat seal sheet according to any one of <1> to <6>, wherein the thermoplastic resin fiber nonwoven fabric layer A and the thermoplastic resin fiber nonwoven fabric layer B are laminated together so that the thermoplastic resin fiber nonwoven fabric layer B serves as a surface layer.
<8> A sterilized package obtained by thermocompression bonding a sterilized packaging material to the heat seal sheet according to any one of <1> to <7>.
<9> A method for producing a heat seal sheet according to any one of <1> to <7>, comprising the following steps 1 to 3 in this order:
Step 1: preparing a thermoplastic resin fiber nonwoven fabric a and a thermoplastic resin fiber nonwoven fabric b; Step 2: laminating one or more layers of a thermoplastic resin fiber nonwoven fabric a and one or more layers of a thermoplastic resin fiber nonwoven fabric b to obtain a laminate; Step 3: heat-sealing the laminate obtained in step 2. <10> The method for producing a heat-sealable sheet according to <9>, wherein the thermoplastic resin fiber nonwoven fabric b contains 25 to 75% by mass of polyethylene hyperbranched fibers.
<11> The method for producing a heat sealable sheet according to <9> or <10>, wherein the thermoplastic resin fiber nonwoven fabric b contains a core-sheath polyester fiber.
<12> The method for producing a heat-sealable sheet according to any one of <9> to <11>, wherein the thermoplastic resin fiber nonwoven fabric b is a nonwoven fabric obtained by a wet papermaking method.

The heat seal sheet of the present invention has sufficient thermal adhesion and breathability over the entire heat seal surface, is strong, and keeps lint generation to a minimum, making it an excellent sterilized medical packaging material.

FIG. 1 is a cross-sectional view of one embodiment of a sterile package. FIG. 2 is a cross-sectional view of one embodiment of a heat seal sheet. FIG. 2 is a cross-sectional view of another embodiment of a heat seal sheet. FIG. 2 is a cross-sectional view of another embodiment of a heat seal sheet.

In the present invention, the term "sheet" is a general term for thin sheets such as sheets, films, nonwoven fabrics, and laminates thereof.
"Oken air permeability" is a value measured in accordance with JIS P 8117:2009.
"Basis weight" is a value measured in accordance with JIS P 8124:2011.
"Melting point" is the melting peak temperature measured in accordance with JIS K 7121:1987.
The "tear strength" is the geometric mean value of the measured values in the longitudinal and transverse directions of the sheet measured in accordance with JIS P 8116:2000.

Hereinafter, an embodiment of the heat seal sheet and the sterilization package will be described with reference to Figs.
[Heat seal sheet and sterilized packaging]
The sterilization package (11) comprises a heat seal sheet (21) and an adherend (31) (Figure 1).
The heat seal sheet (21) comprises one or more thermoplastic resin fiber nonwoven fabric layers A (22) and one or more thermoplastic resin fiber nonwoven fabric layers B (23) (FIGS. 2 and 3). As long as the heat seal sheet (21) comprises one or more thermoplastic resin fiber nonwoven fabric layers A (22) and one or more thermoplastic resin fiber nonwoven fabric layers B (23), it may also comprise a thermoplastic resin fiber nonwoven fabric layer C (41) different from the thermoplastic resin fiber nonwoven fabric layer A (22) and the thermoplastic resin fiber nonwoven fabric layer B (23) (FIG. 4).
As described later, the heat seal sheet (21) is preferably obtained by laminating one or more layers of a thermoplastic resin fiber nonwoven fabric a and one or more layers of a thermoplastic resin fiber nonwoven fabric b, and heat fusing them together, the thermoplastic resin fiber nonwoven fabric layer A being a layer derived from the thermoplastic resin fiber nonwoven fabric a, and the thermoplastic resin fiber nonwoven fabric layer B being a layer derived from the thermoplastic resin fiber nonwoven fabric b.
The heat seal sheet (21) also has an Oken air permeability of 700 seconds or less as measured in accordance with JIS P 8117:2009, and a tear strength of 700 mN or more as measured in accordance with JIS P 8116:2000.
Furthermore, the thermoplastic resin fiber nonwoven fabric layer B contains a low melting point polyester resin, polyester fibers, and polyethylene resin, and the mass ratio of the low melting point polyester resin, polyester fibers, and polyethylene resin (low melting point polyester resin:polyester fibers:polyethylene resin) is 13.75:11.25:75 to 41.25:33.75:25.
The heat seal sheet of this embodiment has sufficient thermal adhesiveness and breathability over the entire heat seal surface, and also has high strength, particularly tear strength, and suppresses the amount of lint generation.
The detailed reasons why the above effects are obtained are unclear, but some of them are thought to be as follows. That is, by having an Oken air permeability of 700 seconds or less, moderate breathability is obtained, and by having a tear strength of 700 mN or more, a heat seal sheet with high strength is obtained. In addition, by having the thermoplastic resin fiber nonwoven fabric layer B have a specific resin composition, it is thought that the layer has excellent thermal adhesion and suppresses the generation of fiber fluff called lint and fiber debris that falls off when the sheet is opened.

(Oken air permeability)
The heat seal sheet (21) has an Oken air permeability of 700 seconds or less, measured according to JIS P 8117:2009. The Oken air permeability of 700 seconds or less is preferable because ethylene oxide gas sterilization can be applied. The Oken air permeability of the heat seal sheet (21) is more preferably 300 seconds or less, even more preferably 150 seconds or less, and even more preferably 100 seconds or less. There is no particular limit to the lower limit of the Oken air permeability.

(Tear strength)
The heat seal sheet (21) has a tear strength of 700 mN or more as measured according to JIS P 8116:2000. If the tear strength is 700 mN or more, it is preferable because it can be used as a sterilization packaging material for relatively large medical equipment or medical instruments with a large mass. The tear strength of the heat seal sheet (21) is more preferably 800 mN or more, even more preferably 1000 mN or more, even more preferably 1500 mN or more, and particularly preferably 2000 mN or more. The upper limit of the tear strength is not particularly limited, but from the viewpoint of ease of production, it is preferably 5000 mN or less, more preferably 4000 mN or less.

(grammage)
From the viewpoints of ease of production, appropriate heat seal strength, and tear strength, the basis weight of the heat seal sheet of this embodiment is preferably 30 g/ ^m2 or more, more preferably 50 g/ ^m2 or more, even more preferably 70 g/ ^m2 or more, and is preferably 300 g/ ^m2 or less, more preferably 200 g/ ^m2 or less, even more preferably 150 g/ ^m2 or less, and even more preferably 100 g/ ^m2 or less.
The basis weight of the heat seal sheet can be adjusted to a desired range by adjusting the basis weights of the thermoplastic resin fiber nonwoven fabric a and the thermoplastic resin fiber nonwoven fabric b to appropriate ranges.

<Thermoplastic resin fiber nonwoven fabric layer A>
The heat seal sheet (21) of this embodiment has one or more thermoplastic resin fiber nonwoven fabric layers A. The thermoplastic resin fiber nonwoven fabric layer A (22) is a layer derived from a thermoplastic resin fiber nonwoven fabric a obtained by forming one or more types of thermoplastic resin fibers a group into a sheet by various known methods.
Examples of the sheeting method include spunbonding, thermal bonding, chemical bonding, needle punching, spunlace, melt blowing, and wet sheeting, among which the spunbonding method is preferred because it is made of continuous fibers, so that it has high strength and is less susceptible to fiber detachment, and the wet sheeting method is preferred because it can produce a uniform nonwoven fabric.

(Thermoplastic resin fiber nonwoven fabric a)
As the thermoplastic resin fibers a group constituting the thermoplastic resin fiber nonwoven fabric a, various known materials can be used, but those having a melting point higher than the melting point (not particularly limited, for example, 150° C. or lower) of the fibers constituting the thermoplastic resin fibers b group used in the thermoplastic resin fiber nonwoven fabric layer B (23) are preferred because they tend to maintain their fiber shape even after thermal lamination and to obtain high tear strength (tear strength measured by the Elmendorf method, which measures the tear strength of a portion that has been previously torn).
Examples of the fibers constituting the group a of thermoplastic resin fibers include, but are not limited to, polypropylene fibers, polyester fibers, and polyamide fibers.
That is, the thermoplastic resin fiber nonwoven fabric a and the thermoplastic resin fiber nonwoven fabric layer A preferably contain at least one fiber selected from the group consisting of polypropylene resin fibers, polyester fibers, and polyamide fibers, and more preferably contain polypropylene resin fibers or polyester fibers.
From the viewpoint of improving the interlayer adhesion between the thermoplastic resin fiber nonwoven fabric layer A and the thermoplastic resin fiber nonwoven fabric layer B, polypropylene fibers are preferred.
Furthermore, by including polyester fibers, as described below, when thermoplastic resin fiber nonwoven fabric a and thermoplastic resin fiber nonwoven fabric b are laminated, the difference in melting point between the resin constituting thermoplastic resin fiber nonwoven fabric a and the resin constituting thermoplastic resin fiber nonwoven fabric b can be increased, and melting of the resin constituting thermoplastic resin fiber nonwoven fabric a can be suppressed during thermal lamination. As a result, the resin shape is better maintained in the thermoplastic resin fiber nonwoven fabric layer A, which is preferable because it improves the strength as a heat seal sheet.
In addition, it is preferable that the thermoplastic resin fibers constituting the thermoplastic resin fiber nonwoven fabric a do not melt in the heat fusion step described below, and it is preferable that the fiber shape remains in the thermoplastic resin fiber nonwoven fabric layer A even in the heat seal sheet (21).

In particular, when the thermoplastic resin fiber nonwoven fabric layer A (22) is constructed as the surface layer of the heat seal sheet (21), it is preferable to use polypropylene resin fibers as the thermoplastic resin group a, which are easy to suppress surface raising during thermal lamination.
Furthermore, it is possible to use natural pulp fibers, regenerated fibers, and other chemical fibers in combination, provided that the object of the present invention is not impaired.

The average fiber diameter of group a of thermoplastic resin fibers is not particularly limited, but is, for example, 0.5 μm or more and 50 μm or less, and preferably 5 μm or more and 30 μm or less.

The thermoplastic resin fiber nonwoven fabric a is preferably any nonwoven fabric selected from the group consisting of a spunbond nonwoven fabric, a thermal bond nonwoven fabric, a chemical bond nonwoven fabric, a needle punched nonwoven fabric, a spunlace nonwoven fabric, a meltblown nonwoven fabric, and a wet nonwoven fabric, more preferably any nonwoven fabric selected from the group consisting of a meltblown nonwoven fabric, a spunbond nonwoven fabric, and a wet nonwoven fabric, and even more preferably a spunbond nonwoven fabric or a wet nonwoven fabric.
Spunbond nonwoven fabrics are preferred because they are produced by melting a thermoplastic resin and extruding it into continuous long fibers, which allows the production of a heat sealable sheet having excellent strength.
Wet-laid nonwoven fabrics are preferred because they are highly uniform.

The basis weight of the thermoplastic resin fiber nonwoven fabric a and the thermoplastic resin fiber nonwoven fabric layer A (22) is not particularly limited, but is adjusted, for example, in the range of about 5 g/ ^m2 or more and 100 g/ ^m2 or less. From the viewpoint of obtaining sufficient thermal adhesiveness, breathability, and tear strength, it is preferably 10 g/ ^m2 or more and 80 g/ ^m2 or less, more preferably 20 g/ ^m2 or more and 50 g/ ^m2 or less.
When the heat seal sheet has two or more thermoplastic resin fiber nonwoven fabric layers A (22), the above-mentioned preferable range of basis weight is the preferable range of basis weight of each layer.

The thermoplastic resin fiber nonwoven fabric layer A (22) may be a single layer or a multi-layer structure of two or more layers. In addition, the thermoplastic resin fiber nonwoven fabric layer B (23) and the thermoplastic resin fiber nonwoven fabric layer C (41) may be laminated in any order.

<Thermoplastic resin fiber nonwoven fabric layer B>
The thermoplastic resin fiber nonwoven fabric layer B (23) is a layer derived from a thermoplastic resin fiber nonwoven fabric b obtained by forming one or more kinds of thermoplastic resin fibers b into a sheet by any of various known methods.
The thermoplastic resin fiber nonwoven fabric layer B contains a low melting point polyester resin, polyester fibers, and polyethylene resin, and the mass ratio of the low melting point polyester resin, polyester fibers, and polyethylene resin (low melting point polyester resin:polyester fibers:polyethylene resin) is 13.75:11.25:75 to 41.25:33.75:25.

(Thermoplastic resin fiber nonwoven fabric b)
One or more types of thermoplastic resin fibers can be used as the thermoplastic resin fiber group b constituting the thermoplastic resin fiber nonwoven fabric b. In order to bond with the thermoplastic resin fiber nonwoven fabric layer A (22) after thermal lamination and to exhibit the heat sealability of the heat seal sheet, it is preferable that the fibers constituting the thermoplastic resin fiber group b contain fibers having a melting point of less than 150°C.
The fibers constituting the thermoplastic resin fiber group b may have a single structure or a core-sheath structure of two or more layers. In the case of a core-sheath structure, the melting point of the sheath resin is preferably less than 150°C, and the melting point of the core resin may be 150°C or higher.

Examples of thermoplastic resin fibers group b include various polyethylene resin fibers, polyethylene-vinyl acetate ester resin fibers, low melting point polyester resin fibers, composite fibers with a core-sheath structure in which the core is a normal polyester resin and the sheath is the various polyethylene resin fibers mentioned above, polyethylene-vinyl acetate ester resin, and composite resins with a core-sheath structure in which the core is a normal polyester resin and the sheath is a low melting point polyester resin. These resin fibers can also be used in a multi-branched structure.

Among these, polyester fibers and polyethylene fibers having a core-sheath structure in which a low melting point polyester is used for the sheath and a normal polyester is used for the core are preferably used because they have excellent thermal lamination properties and heat sealability with the thermoplastic resin fiber nonwoven fabric a.
Here, the low melting point polyester used in the sheath has a melting point less than 150° C., preferably 140° C. or less, more preferably 130° C. or less, and even more preferably 120° C. or less. On the other hand, the polyester used in the core has a melting point of 150° C. or more, preferably 180° C. or more, more preferably 200° C. or more, and even more preferably 240° C. or more. An example of the polyester used in the core is polyethylene terephthalate.
In addition, it is preferable that the polyethylene fibers are polyethylene hyperbranched fibers obtained by quasi-pulping polyethylene, because this allows the thermoplastic resin fiber nonwoven fabric b to be produced by wet papermaking. By producing the thermoplastic resin fiber nonwoven fabric b by wet papermaking, it is preferable that a nonwoven fabric having better texture, better uniformity, and more dense can be obtained.
In addition, when the thermoplastic resin fiber nonwoven fabric b is a nonwoven fabric obtained by using a core-sheath structure polyester fiber in which a low melting point polyester is used as the sheath and a normal polyester is used as the core, and a polyethylene fiber, the low melting point polyester resin in the sheath of the core-sheath structure polyester fiber and the polyethylene fiber are partially melted in the thermoplastic resin fiber nonwoven fabric layer B after heat fusion, and therefore the fiber shape is not necessarily maintained. In addition, it is not limited to the case where all of the low melting point polyester resin and the polyethylene fiber are melted, and it is sufficient that at least a portion is melted.

The thermoplastic resin fiber nonwoven fabric b is preferably a nonwoven fabric obtained by a wet papermaking method, and is preferably obtained by wet papermaking of a core-sheath polyester fiber in which the low melting point polyester is used for the sheath and a normal polyester is used for the core, and a polyethylene hyperbranched fiber.
The thermoplastic resin fiber nonwoven fabric b contains a core-sheath structure polyester fiber using a low melting point polyester for the sheath and a normal polyester for the core, in an amount of preferably 25% by mass or more and 75% by mass or less, more preferably 30% by mass or more and 70% by mass or less, and even more preferably 40% by mass or more and 60% by mass or less.
The mass ratio of the sheath to the core (sheath/core) is preferably 20/80 or more and 80/20 or less, more preferably 30/70 or more and 70/30 or less, and even more preferably 40/60 or more and 60/40 or less.
Examples of polyester fibers having a core-sheath structure in which a low melting point polyester is used for the sheath and a normal polyester is used for the core include the Tepyrus series manufactured by Teijin Frontier Co., Ltd. and PET-based binder fibers manufactured by Kuraray Co., Ltd.

The thermoplastic resin fiber nonwoven fabric b contains polyethylene hyperbranched fibers in an amount of preferably 25% by mass or more and 75% by mass or less, more preferably 30% by mass or more and 70% by mass or less, and even more preferably 35% by mass or more and 60% by mass or less.
Examples of polyethylene hyperbranched fibers obtained by quasi-pulping polyethylene include the SWP (registered trademark) series manufactured by Mitsui Chemicals, Inc.

In the thermoplastic resin fiber nonwoven fabric layer B derived from the thermoplastic resin fiber nonwoven fabric b obtained using these thermoplastic resin fibers b group, as described above, the mass ratio of the low melting point polyester resin, polyester fiber, and polyethylene resin (low melting point polyester resin: polyester fiber: polyethylene resin) is 13.75: 11.25: 75 to 41.25: 33.75: 25. Since the polyester fiber is preferably in a fibrous form, it is referred to as "polyester fiber", while the low melting point polyester and polyethylene constituting the thermoplastic resin fiber are at least partially melted, and therefore are referred to as "low melting point polyester resin" and "polyethylene resin", respectively.
When the total amount of the low melting point polyester resin, the polyester fiber, and the polyethylene resin is 100 parts by mass, the content of the low melting point polyester resin is 13.75 parts by mass or more and 41.25 parts by mass or less, preferably 16.5 parts by mass or more and 38.5 parts by mass or less, and more preferably 22 parts by mass or more and 33 parts by mass or less. Note that, as described above, the low melting point polyester resin is a polyester resin having a melting point of less than 150° C.
When the total amount of the low melting point polyester resin, polyester fiber, and polyethylene resin is 100 parts by mass, the content of the polyester resin is 11.25 parts by mass or more and 33.75 parts by mass or less, preferably 13.5 parts by mass or more and 31.5 parts by mass or less, and more preferably 18 parts by mass or more and 27 parts by mass or less. In this embodiment, the "polyester fiber" has a melting point of 150° C. or more, preferably 180° C. or more, more preferably 200° C. or more, and even more preferably 240° C. or more, and an example of such a fiber is polyethylene terephthalate.
Furthermore, when the total amount of the low-melting point polyester resin, the polyester fiber, and the polyethylene resin is 100 parts by mass, the content of the polyethylene resin is 25 parts by mass or more and 75 parts by mass or less, preferably 30 parts by mass or more and 70 parts by mass or less, and more preferably 35 parts by mass or more and 60 parts by mass or less.

The total content of low melting point polyester resin, polyester fiber and polyethylene resin in the thermoplastic resin fiber nonwoven fabric layer B is 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 85% by mass or more, with the upper limit being 100% by mass or less.

Furthermore, as long as the object of the present invention is not impaired, it is possible to use natural pulp fibers, regenerated fibers, and other chemical fibers in combination as the thermoplastic resin fiber group b. From the viewpoint of reducing the environmental load and improving strength, natural pulp may also be used in combination. Examples of natural pulp include wood pulp (softwood pulp, hardwood pulp, etc.) and non-wood pulp (hemp pulp, cotton pulp, straw pulp, etc.).

The fiber diameter of the fibers used in the thermoplastic resin fiber nonwoven fabric b is not particularly limited, but is, for example, 1 μm or more and 60 μm or less, and preferably 1 μm or more and 40 μm or less.

The basis weight of the thermoplastic resin fiber nonwoven fabric b and the thermoplastic resin fiber nonwoven fabric layer B (23) is not particularly limited, but is adjusted, for example, in the range of about 5 g/ ^m2 or more and 100 g/ ^m2 or less. From the viewpoint of obtaining sufficient thermal adhesiveness, breathability, and tear strength, it is preferably 10 g/ ^m2 or more and 80 g/ ^m2 or less, more preferably 15 g/ ^m2 or more and 60 g/ ^m2 or less.
When the heat seal sheet has two or more thermoplastic resin fiber nonwoven fabric layers B (23), the above-mentioned preferable range of basis weight is the preferable range of basis weight of each layer.

The thermoplastic resin fiber nonwoven fabric layer B (23) may be a single layer or a multi-layer consisting of two or more layers. As mentioned above, the lamination method with the thermoplastic resin fiber nonwoven fabric layer A (22) can also be carried out in any order.

Various known methods can be used to manufacture the thermoplastic resin fiber nonwoven fabric b, but among them, the wet papermaking method is preferred because it is easy to obtain good texture even at low basis weights and is less likely to produce pinholes that impair the antibacterial properties of the heat seal sheet.

Wet papermaking methods include those using a Fourdrinier papermaking machine, a short wire papermaking machine, a cylinder papermaking machine, an inclined papermaking machine, etc. Among these, a cylinder papermaking machine and an inclined papermaking machine are preferred because they can be used with materials with relatively long fiber lengths, and an inclined papermaking machine is more preferred.

Various dispersants, surfactants, thickeners and other internal additives can also be added to the raw material slurry to improve the texture.

The method for drying the thermoplastic resin fiber nonwoven fabric b after wet papermaking is not particularly limited, and a multi-cylinder dryer, Yankee dryer, hot air dryer, infrared dryer, etc. can be used. When using a multi-cylinder dryer or Yankee dryer, it is preferable to set the drying temperature below the melting point of the thermoplastic resin fiber, or to coat the surface of the multi-cylinder dryer or Yankee dryer with a fluororesin to prevent surface contamination due to adhesion of the thermoplastic resin.

<Thermoplastic resin fiber nonwoven fabric layer C>
The thermoplastic resin fiber nonwoven fabric layer C (41) is a layer derived from a thermoplastic resin fiber nonwoven fabric c obtained by forming one or more types of thermoplastic resin fibers c into a sheet by any of various known methods.
The thermoplastic resin fiber nonwoven fabric layer C is a layer provided on the side of the heat seal sheet of this embodiment that is not to be heat sealed.

(Thermoplastic resin fiber nonwoven fabric c)
One or more types of fibers may be used as the thermoplastic resin fiber group c constituting the thermoplastic resin fiber nonwoven fabric c. For adhesion to the thermoplastic resin fiber nonwoven fabric layer A (22) after thermal lamination, it is preferable that the fibers constituting the thermoplastic resin fiber group c contain thermoplastic resin fibers having a melting point of less than 150°C.

Thermoplastic resin fibers group C include, for example, various polyethylene resin fibers, polyethylene-vinyl acetate ester resin fibers, low-melting point polyester resin fibers, composite fibers with a core-sheath structure in which the core is a normal polyester resin and the sheath is the various polyethylene resin fibers mentioned above, polyethylene-vinyl acetate ester resin, and composite resins with a core-sheath structure in which the core is a normal polyester resin and the sheath is a low-melting point polyester resin. These resin fibers may also have a multi-branched structure. Natural pulp fibers, recycled fibers, and other chemical fibers may also be used in combination. Examples of natural pulp include wood pulp (softwood pulp, hardwood pulp, etc.) and non-wood pulp (hemp pulp, cotton pulp, straw pulp, etc.).

Among these, it is preferable that the thermoplastic resin fiber nonwoven fabric c contains natural pulp as a fiber group constituting the thermoplastic resin fiber nonwoven fabric c. When tension is applied in a heated state during thermal fusion (thermal lamination) in step 3 described below, the thermoplastic resin fiber nonwoven fabric layer A and the thermoplastic resin fiber nonwoven fabric layer B may open up and the air permeability may decrease. It is preferable that the thermoplastic resin fiber nonwoven fabric c contains natural pulp, since this suppresses the above-mentioned opening up and suppresses the decrease in air permeability.
Furthermore, the thermoplastic resin fiber nonwoven fabric b may shrink during heat fusion, causing the heat seal sheet to curl, but by using the thermoplastic resin fiber nonwoven fabric c containing pulp, curling can be suppressed, which is preferable.
The content of natural pulp in the thermoplastic resin fiber nonwoven fabric c is preferably 5% by mass or more, and more preferably 10% by mass or more.

The basis weight of the thermoplastic resin fiber nonwoven fabric c and the thermoplastic resin fiber nonwoven fabric layer C (41) is not particularly limited, but is adjusted, for example, in the range of about 10 g/ ^m2 or more and 100 g/ ^m2 or less. From the viewpoint of obtaining sufficient thermal adhesiveness, breathability, and tear strength, it is preferably 15 g/ ^m2 or more and 80 g/ ^m2 or less, more preferably 20 g/ ^m2 or more and 60 g/ ^m2 or less.
As described below, in the case of a b/a/c laminated structure, the basis weight of the thermoplastic resin fiber nonwoven fabric c and the thermoplastic resin fiber nonwoven fabric layer C (41) is preferably larger than the basis weight of the thermoplastic resin fiber nonwoven fabric b and the thermoplastic resin fiber nonwoven fabric layer B (23), and more preferably is 5 g/ ^m2 or more larger. This configuration is preferable because it suppresses curling of the heat seal paper due to curling of the thermoplastic resin fiber nonwoven fabric b and the thermoplastic resin fiber nonwoven fabric layer B (23).

[Method of manufacturing heat seal sheet]
The method for producing a heat seal sheet of the present embodiment preferably includes the following steps 1 to 3 in this order.
Step 1: preparing a thermoplastic resin fiber nonwoven fabric a and a thermoplastic resin fiber nonwoven fabric b; Step 2: laminating one or more layers of a thermoplastic resin fiber nonwoven fabric a and one or more layers of a thermoplastic resin fiber nonwoven fabric b to obtain a laminate; Step 3: heat-sealing the laminate obtained in step 2

<Step 1>
Step 1 is a step of preparing a thermoplastic resin fiber nonwoven fabric a and a thermoplastic resin fiber nonwoven fabric b.
The thermoplastic resin fiber nonwoven fabric a and the thermoplastic resin fiber nonwoven fabric b may be prepared by the method described above.

<Step 2>
Step 2 is a step of laminating one or more layers of a thermoplastic resin fiber nonwoven fabric a and one or more layers of a thermoplastic resin fiber nonwoven fabric b to obtain a laminate.
The method of laminating the thermoplastic resin fiber nonwoven fabric a and the thermoplastic resin fiber nonwoven fabric b is not limited to a specific order, except that, from the viewpoint of heat sealability, the outermost surface of either the front or back surface is the thermoplastic resin fiber nonwoven fabric b. Furthermore, each layer may be a single layer or may be a multilayer of two or more layers.
Among these, in order to reduce curling after thermal lamination, it is preferable that the front and back layers are symmetrical or in a similar order from the center layer.
Therefore, it is preferable to have a laminate structure of b/(a/b)n/a/b (n is an _integer of 0 or more), such as a three-layer structure in which thermoplastic resin fiber nonwoven fabric b/thermoplastic resin fiber nonwoven fabric a/thermoplastic resin fiber nonwoven fabric b are laminated in this order, or a five-layer structure in which b/a/b/a/b are laminated. Among these, it is preferable to have a three-layer structure of b/a/b or a five-layer structure of b/a/b/a/b, and from the viewpoint of ease of production, it is more preferable to have a three-layer structure of b/a/b.
In addition, a three-layer structure of b/a/c may be used. When the three-layer structure is used, it is preferable to reduce the basis weight of the nonwoven fabric layer B, which has a higher thermal shrinkage rate among the thermoplastic resin fiber nonwoven fabrics b and c, because curling after thermal lamination can be reduced.

<Step 3>
Step 3 is a step of thermally fusing the laminate obtained in step 2. In step 3, the thermoplastic resin fiber nonwoven fabrics a and b constituting the laminate are thermally fusing (thermally laminating).
The heat fusion step is carried out by passing the laminate obtained in step 2 between two heated rolls.

The temperature of the heating roll is adjusted within a range of not less than the melting point of the thermoplastic resin fiber with the lowest melting point used in the thermoplastic resin fiber nonwoven fabric b and not more than the melting point of the thermoplastic resin fiber with the lowest melting point used in the thermoplastic resin fiber nonwoven fabric a + 20°C.
By setting the temperature of the heating roll not lower than the melting point of the thermoplastic resin fiber with the lowest melting point used in the thermoplastic resin fiber nonwoven fabric b, the effect of suppressing the raising of the surface of the thermoplastic resin fiber nonwoven fabric b can be sufficiently obtained, and the heat seal strength can also be obtained. In addition, the occurrence of raising and destruction of the heat-bonded surface when peeling off the adherend (31) is suppressed. In addition, by setting the temperature of the heating roll to the melting point of the thermoplastic resin fiber with the lowest melting point used in the thermoplastic resin fiber nonwoven fabric a + 20°C or less, the fiber shape is maintained in the thermoplastic resin fiber nonwoven fabric layer A (22) even after heat fusion, and sufficient tear strength can be obtained, which is preferable.

It is also preferable to coat the surface of the heating roll with a fluororesin to prevent surface contamination caused by the adhesion of thermoplastic resin.

The surface temperatures of the upper and lower heating rolls may be the same or different. Also, heat fusion may be performed with one nip or with two or more nips.
In the case of two or more nips, the process may be performed in one pass or in two or more passes.
When the laminate obtained in step 2 has three or more layers, the heat fusion may be carried out simultaneously for all layers, or a portion of the layers may be heat fused first, and then another layer may be added and heat fused.
During heat fusion, a step of providing residual heat, such as by heating using a preheater, to the thermoplastic resin fiber nonwoven fabric a and/or the thermoplastic resin fiber nonwoven fabric b before contacting them with a heating roll may be added before pressurization.
Other known techniques can also be applied.

[Action and Effect]
The heat seal sheet (21) of the present invention is obtained by heat fusing (thermal laminating) a thermoplastic resin fiber nonwoven fabric a and a thermoplastic resin fiber nonwoven fabric b, and has sufficient thermal adhesion and breathability over the entire heat seal surface, high strength, and keeps lint generation to a minimum, making it an excellent sterilized medical packaging material.

[Application]
The heat seal sheet (21) is used, for example, in a sterilization package (11). A part of the heat seal sheet (21) and a part of an adherend (31) such as wrapping paper, laminated paper, a film, or a molded container for sterilization are overlapped and heat-pressed together so that a space is formed inside, thereby forming a sterilization package in which the heat seal sheet (21) and the adherend (31) are heat-pressed together.
Examples of the film or molded container for sterilization include films or molded containers for sterilization made of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate, polyvinyl chloride, polyvinylidene chloride, polystyrene, ethylene-vinyl acetate copolymer resins, ethylene-acrylic copolymer resins, or laminates of these.
The molded container for sterilization typically has one or more recesses for accommodating contents. In this case, the heat seal sheet (21) is typically used as a lid material for sealing the opening of the one or more recesses.
The adherend to be thermocompressed with the heat seal sheet (21) is preferably a molded container for sterilization, since sufficient peel strength is required without destroying the substrate even with a relatively narrow seal width.

In the sterilized package (11), a space for accommodating contents such as medical instruments is formed by a heat seal sheet (21) and an adherend (31) that are heat-pressed together. The heat seal sheet (21) and the adherend (31) are heat-pressed together after the contents are accommodated.
The medical instruments to be contained are not particularly limited as long as they are medical instruments that need to be sterilized before use, and specific examples include injection needles, syringes, catheters, gloves, scalpels, forceps, scissors, gauze, and bandages.

The sterile package is subjected to a sterilization treatment while containing the contents therein. For example, the sterilization treatment is carried out by a sterilization method such as autoclave, ethylene oxide gas (EOG) sterilization, electron beam sterilization, gamma ray sterilization, etc. When the contents are to be used, the heat seal sheet (21) is peeled off from the adherend to remove the contents.
The use of the heat seal sheet (21) is not limited to sterilized packaging, but can also be used for packaging food, various freshness-preserving agents such as desiccants and oxygen absorbers, general industrial products, etc.
It is also possible to perform printing on either the front or back surface, or on the outermost surface of both surfaces.

In the sterilized package (11) of the heat seal sheet (21) and the adherend (31), the peel strength when the heat seal sheet (21) and the adherend (31) are peeled at 180° at a peel speed of 300 mm/min is preferably 1.0 N/15 mm to 15 N/15 mm, more preferably 1.5 N/15 mm to 12 N/15 mm, even more preferably 2.0 N/15 mm to 10.5 N/15 mm, still more preferably 4.0 N/15 mm to 10.5 N/15 mm, particularly preferably 4.5 N/15 mm to 10.5 N/15 mm, and most preferably 5.0 N/15 mm to 7.5 N/15 mm. When the peel strength is within the above range, the balance between easy peel property and heat seal property is excellent.
The heat seal peel strength is measured by the method described in the Examples.
The heat seal peel strength can be adjusted within a desired range by setting the basis weight of the thermoplastic resin fiber nonwoven fabric layer B (23) constituting the heat seal surface, the polyethylene resin content in the thermoplastic resin fiber nonwoven fabric layer B (23), the heat fusion conditions in the heat fusion step of the laminate when producing the heat seal sheet, and the heat fusion conditions with the adherend, all within appropriate ranges.

The present invention will be specifically explained below with reference to examples. Note that the present invention is in no way limited to these examples. Note that, unless otherwise specified, % means % by mass and parts means parts by mass.

[Examples 1 to 7, Comparative Examples 1 to 3]
<Production of Thermoplastic Resin Fiber Nonwoven Fabric b>
A raw material slurry was obtained by mixing and stirring the specified amounts shown in Table 1 of polyethylene hyperbranched fiber (trade name: SWP (registered trademark) E400, melting point 135°C, average fiber length 0.9 mm, fiber diameter about 1 to 30 μm, manufactured by Mitsui Chemicals, Inc.), core-sheath structure polyester fiber (trade name: Tepyrus (registered trademark) TJ04CN, fineness 1.1 dtex, fiber length 5 mm, fiber diameter about 10 μm, sheath melting point 110°C, core (polyethylene terephthalate) melting point 260°C, sheath/core mass ratio = 55/45, manufactured by Teijin Frontier Co., Ltd.), and hemp pulp (Canadian standard freeness (freeness) described in JIS P 8121-2:2012: 620 mL) and modified polyester resin dispersant (trade name: SR-1800R, manufactured by Takamatsu Oil Co., Ltd.) in an amount of 0.5 parts by mass per 100 parts by mass of the fibers in total.
The raw material slurry was made into a sheet using a wet inclined papermaking machine and dried with a Yankee dryer at a surface temperature of 105°C to obtain a thermoplastic resin fiber nonwoven fabric b having a basis weight of 25 g/ ^m2 in Examples 1 to 6 and Comparative Examples 1 to 3. In Example 7, a thermoplastic resin fiber nonwoven fabric b having a basis weight of 35 g/ ^m2 was obtained.

<Production of heat seal sheet>
In Examples 1 to 5 and Comparative Examples 1 to 3, three layers of the thermoplastic resin fiber nonwoven fabric b obtained above, polypropylene spunbond nonwoven fabric a (fiber diameter about 15 μm, basis weight 30 g/ ^m2 ), and thermoplastic resin fiber nonwoven fabric b were stacked in this order and thermally laminated using a thermal laminator having heating rolls with fluorine-coated surfaces at a roll temperature of 150°C for the upper and lower rolls to obtain heat seal sheets of Examples 1 to 5 and Comparative Examples 1 to 3 having a basis weight of 80 g/ ^m2 .
In Example 6, a heat seal sheet having a basis weight of 75 g/ ^m2 was obtained in the same manner as in Example 1, except that a polyester spunbond nonwoven fabric (fiber diameter: approximately 12 μm, basis weight: 25 g/m2) was used as the thermoplastic resin fiber nonwoven fabric ^a .
In Example 7, a heat seal sheet having a basis weight of 90 g/ ^m2 was obtained in the same manner as in Example 1, except that a polyester wet-laid nonwoven fabric (fiber diameter: approximately 14 μm, fiber length: approximately 5 mm, basis weight: 20 g/ ^m2 ) was used as the thermoplastic resin fiber nonwoven fabric a.

[Example 8]
<Production of Thermoplastic Resin Fiber Nonwoven Fabric c>
The mixture was mixed with 60 parts by mass of polyethylene hyperbranched fiber (product name: SWP (registered trademark) E400, melting point 135°C, average fiber length 0.9 mm, fiber diameter approximately 1 to 30 μm, manufactured by Mitsui Chemicals, Inc.), 10 parts by mass of core-sheath structure polyester fiber (product name: Tepyrus (registered trademark) TJ04CN, fineness 1.1 dtex, fiber length 5 mm, fiber diameter approximately 10 μm, sheath melting point 110°C, core (polyethylene terephthalate) melting point 260°C, sheath/core mass ratio = 55/45, manufactured by Teijin Frontier Co., Ltd.), and 10 parts by mass of hardwood bleached kraft pulp (LBKP) (JIS P A raw material slurry was obtained by mixing and stirring 30 parts by mass of a fiber mixture containing 30 parts by mass of a modified polyester resin dispersant (product name: SR-1800R, manufactured by Takamatsu Oil Co., Ltd.) and 0.5 parts by mass of a modified polyester resin dispersant per 100 parts by mass of the fibers.
The raw material slurry was made into a paper sheet using a wet inclined papermaking machine, and dried with a Yankee dryer at a surface temperature of 105° C. to obtain a thermoplastic resin fiber nonwoven fabric c having a basis weight of 30 g/m ² .

<Production of heat seal sheet>
Three layers of the thermoplastic resin fiber nonwoven fabric b obtained in the same manner as in Example 1, the thermoplastic resin fiber nonwoven fabric a, and the thermoplastic resin fiber nonwoven fabric c obtained above were stacked in this order and subjected to a thermal lamination treatment at a roll temperature of 150°C for the upper and lower rolls using a thermal laminator having heating rolls with fluorine-coated surfaces, to obtain a heat seal sheet of Example 8 having a basis weight of 75 g/ ^m2 .
As the thermoplastic resin fiber nonwoven fabric a, a polyester wet nonwoven fabric (fiber diameter: about 14 μm, fiber length: about 5 mm, basis weight: 20 g/m ² ) was used.

[Comparative Example 4]
<Preparation of paper substrate>
Hardwood bleached kraft pulp (LBKP) was beaten with a DDR (double disc refiner) to a Canadian standard freeness (freeness) of 390 mL as described in JIS P 8121-2:2012 to obtain a pulp slurry. The pulp slurry was added with 0.5 parts by mass of aluminum sulfate in an absolute dry state, 0.05 parts by mass of an alkenyl succinic anhydride sizing agent dispersion previously dispersed in cationic starch as the solid content of the alkenyl succinic anhydride sizing agent, 0.7 parts by mass of an amphoteric polyacrylamide resin paper strength enhancer (PAM) (trade name: Polystron OFT-3, manufactured by Arakawa Chemical Industries Co., Ltd., weight average molecular weight 3 million), and 0.4 parts by mass of an epichloro resin wet paper strength enhancer (trade name: WS4024, manufactured by Seiko PMC Co., Ltd.) as an internal additive chemical relative to 100 parts by mass of pulp to obtain a papermaking raw material. The papermaking raw material was made into paper on a Fourdrinier papermaking machine to obtain a breathable base material. The resulting breathable substrate had a basis weight of 60 g/ ^m2 .
The "alkenyl succinic anhydride sizing agent dispersion previously dispersed in cationic starch" was prepared as follows: A 2% by mass aqueous solution of cationic starch (Pillar 3YK, manufactured by Pillar Starch Co., Ltd.) was prepared, and an alkenyl succinic anhydride sizing agent was added thereto so that the solid content concentration was cationic starch (Pillar 3YK, manufactured by Pillar Starch Co., Ltd.)/alkenyl succinic anhydride sizing agent (Fibran 81K, manufactured by Arakawa Chemical Industries Co., Ltd.) 4/1. The aqueous solution prepared as described above was added in an amount of 0.05 parts by mass as the solid content of alkenyl succinic anhydride.

<Preparation of paint for thermal adhesive layer>
A coating material for a thermal adhesive layer with a solid content of 25% was obtained by mixing and stirring 138 parts of an EVA dispersion (Chemipearl V200, manufactured by Mitsui Chemicals, Inc., EVA particle average particle size 7 μm, minimum film formation temperature 85° C., solid content 40%), 90 parts of a PE dispersion (Chemipearl W400, manufactured by Mitsui Chemicals, Inc., PE particle average particle size 4 μm, solid content 40%, PE density 920 kg/ ^m3 , softening point 110° C.), 18 parts of a reinforced rosin emulsion (Sizepine N775, manufactured by Arakawa Chemical Industries, Ltd., softening point less than 100° C., solid content 50%), and 154 parts of dilution water.

<Production of heat seal sheet>
The above-mentioned coating material for thermal adhesive layer was applied to one side of the above-obtained breathable substrate using a bar coater, and then dried in a blower dryer at 100°C for 1 minute to form a thermal adhesive layer. Here, the coating material for thermal adhesive layer was applied so that the coating amount after drying was 2.0 g/ ^m2 . This resulted in a heat seal sheet of Comparative Example 4.

[Measuring method]
The heat sealable sheets and nonwoven fabrics obtained in the Examples and Comparative Examples were evaluated as follows.
<Basance weight>
The basis weight was measured in accordance with JIS P 8124:2011.

<Oken air permeability measurement>
The Oken air permeability of the heat seal sheet was measured in accordance with JIS P 8117:2009.
When the air permeability is 700 seconds or less, it is preferable because ethylene oxide gas sterilization treatment can be applied, whereas when the air permeability is more than 700 seconds, it is not preferable because the penetration speed of ethylene oxide gas decreases and the sterilization efficiency decreases.

<Measurement of tear strength>
The tear strength of the heat seal sheet was measured in the longitudinal and transverse directions of the sheet in accordance with JIS P 8116:2000, and the geometric mean value of these values was calculated.
A tear strength of 700 mN or more is preferable because it can be used as a sterilized packaging material for relatively large medical devices or heavy medical instruments. If the tear strength is less than 700 mN, the sterilized medical packaging material may tear during transportation or if it is accidentally dropped when a relatively large medical device or heavy medical instrument is contained inside, and the sterilized state inside the package may not be maintained.

<Measurement of heat seal peel strength (HS peel strength)>
Each heat seal sheet obtained in the Examples and Comparative Examples was overlapped with a laminate film of polyethylene terephthalate resin (PET) and PE (a laminate film obtained by dry-laminating a 50 μm-thick polyethylene film and a 12 μm-thick PET film) as an adherend, so that the surface of the heat seal sheet on the thermal adhesive layer side (thermal adhesive surface) was in contact with the PE side surface of the laminate film, and the heat seal sheet was thermally compressed using a heat press tester under thermal compression conditions of 150° C., 0.2 MPa, and 1.0 second to produce a thermal compression bonded product.
The thermocompression bonded product prepared by the above method was cut to a width of 15 mm to prepare a sample for measuring peel strength. The peel strength (N/15 mm) of the obtained sample for measuring peel strength was measured in accordance with JIS P 8113:2006 using a tensile tester (model: Tensilon RTC-1250A, manufactured by Orientec Co., Ltd.) by chucking the ends of the composite film and the heat seal sheet of the sample and peeling them at a peel speed of 300 mm/min by a 180° peel method.

<Evaluation of fluff after peeling>
A heat seal sheet cut to 25 mm x 100 mm and a laminated film of (PET) and PE (a laminated film obtained by dry laminating a 50 μm-thick polyethylene film and a 12 μm-thick PET film) were stacked so that the PE side of the laminated film was in contact with the heat seal sheet and the film was on top, and a heat press tester was used to heat-press the film under heat-pressing conditions of 150 ° C., 0.2 MPa, and 1.0 second to produce a heat-pressed product. The film of the heat-pressed product produced by the above method was peeled off by hand, and the state of the heat seal sheet surface after the film was peeled off was visually confirmed and evaluated according to the following criteria. Less fluffing after peeling means that lint generation is suppressed.
5: No fluff at all 4: A few fluffs 3: Little fluff 2: Much fluff 1: Considerable fluff or substrate destruction occurs

<Interlayer adhesion of heat seal sheet>
The state of the heat seal sheet after lamination by thermocompression was evaluated according to the following criteria.
5: Firmly attached and will not peel off 4: Firmly attached but parts can be peeled off 3: The entire sheet is adhered but easily peeled off 2: Parts of the sheet are not adhered and are floating 1: Almost not attached

The heat seal sheets of Examples 1 to 8 and Comparative Examples 1 to 4 were evaluated for their Oken air permeability, tear strength, peel test, post-peeling fuzz, and adhesion between thermoplastic resin fiber nonwoven fabric layer A and thermoplastic resin fiber nonwoven fabric layer B. The results are shown in Table 1.

The heat seal sheets of Examples 1 to 8 have low air permeability (seconds), and are therefore considered to be applicable to ethylene oxide gas sterilization. In addition, the tear strength is sufficiently high, and it is considered that they can be used for sterilization of large medical instruments or relatively heavy medical instruments. Furthermore, sufficient heat seal strength was obtained. Furthermore, the thermoplastic resin fiber nonwoven fabric layer A and the thermoplastic resin fiber nonwoven fabric layer B were well bonded, the interlayer adhesion was excellent, and the generation of lint was suppressed.
On the other hand, when the content of polyethylene resin in the thermoplastic resin fiber nonwoven fabric layer B exceeded the limit of the present invention as in Comparative Examples 1 and 2, the air permeability exceeded 700 seconds, making it impossible to apply sterilization with ethylene oxide. Also, when the content of low melting point polyester resin and polyester fiber in the thermoplastic resin fiber nonwoven fabric layer B exceeded the limit of the present invention as in Comparative Example 3, sufficient heat seal peel strength was not obtained, and the adhesion between layers was also poor. Furthermore, when a thermal adhesive layer was provided on the paper substrate as in Comparative Example 4, sufficient tear strength was not obtained.

11...sterilized package, 21...heat seal sheet, 22...thermoplastic resin fiber nonwoven fabric layer A, 23...thermoplastic resin fiber nonwoven fabric layer B, 31...adherend, 41...thermoplastic resin fiber nonwoven fabric layer C

Claims

A heat seal sheet having one or more thermoplastic resin fiber nonwoven fabric layers A and one or more thermoplastic resin fiber nonwoven fabric layers B,
the thermoplastic resin fiber nonwoven fabric layer B contains a low-melting point polyester resin, polyester fibers, and a polyethylene resin, and a mass ratio of the low-melting point polyester resin, polyester fibers, and polyethylene resin (low-melting point polyester resin:polyester fibers:polyethylene resin) is 13.75:11.25:75 to 41.25:33.75:25;
The heat seal sheet has an Oken air permeability of 700 seconds or less as measured in accordance with JIS P 8117:2009, and
The heat seal sheet has a tear strength of 700 mN or more as measured in accordance with JIS P 8116:2000.
The heat seal sheet according to claim 1, wherein the thermoplastic resin fiber nonwoven fabric layer A is a nonwoven fabric layer derived from at least one selected from the group consisting of spunbond nonwoven fabric, thermal bond nonwoven fabric, chemical bond nonwoven fabric, needle punch nonwoven fabric, spunlace nonwoven fabric, meltblown nonwoven fabric, and wet-laid nonwoven fabric.
The heat seal sheet according to claim 1, wherein the thermoplastic resin fiber nonwoven fabric layer A contains at least one fiber selected from the group consisting of polypropylene resin fibers, polyester fibers, and polyamide fibers.
The heat seal sheet according to claim 1, in which the thermoplastic resin fiber nonwoven fabric layer A retains a fibrous shape.
The heat seal sheet according to claim 1, wherein the peel strength when the heat seal sheet is peeled at 180° from a sterilization packaging material such as paper, film, or a sterilization molded container at a peel speed of 300 mm/min according to JIS P 8113:2006 is 1.0 N/15 mm or more and 15 N/15 mm or less.
2. The heat seal sheet according to claim 1, having a basis weight of 30 g/m2 or more and 150 g/ m2 or less .
The heat seal sheet according to claim 1, in which the thermoplastic resin fiber nonwoven fabric layer A and the thermoplastic resin fiber nonwoven fabric layer B are laminated together so that the thermoplastic resin fiber nonwoven fabric layer B is the surface layer.
A sterilized package in which the heat seal sheet of any one of claims 1 to 7 and a sterilized packaging material are heat-pressed together.
A method for producing the heat seal sheet according to any one of claims 1 to 7, comprising the following steps 1 to 3 in this order:
Step 1: preparing a thermoplastic resin fiber nonwoven fabric a and a thermoplastic resin fiber nonwoven fabric b; Step 2: laminating one or more layers of a thermoplastic resin fiber nonwoven fabric a and one or more layers of a thermoplastic resin fiber nonwoven fabric b to obtain a laminate; Step 3: heat-sealing the laminate obtained in step 2
The method for producing a heat seal sheet according to claim 9, wherein the thermoplastic resin fiber nonwoven fabric b contains 25 to 75 mass % of polyethylene hyperbranched fibers.
The method for producing a heat seal sheet according to claim 9, wherein the thermoplastic resin fiber nonwoven fabric b contains a core-sheath polyester fiber.
The method for producing a heat seal sheet according to claim 9, wherein the thermoplastic resin fiber nonwoven fabric b is a nonwoven fabric obtained by a wet papermaking method.