JP7740908B2 - Antibacterial Film - Google Patents

Description

The present invention relates to an antibacterial film.

Patent Document 1 discloses an antibacterial film used in packaging for contents such as cut vegetables. This antibacterial film comprises a base layer and a sealing layer laminated on the base layer. The sealing layer is made of a material containing an antibacterial agent. This makes it possible to inhibit the proliferation of bacteria adhering to the contents within the packaging.

Japanese Patent Application Laid-Open No. 2021-49657

The objective of the present invention is to provide a highly effective antibacterial film that can inhibit the growth of bacteria attached to the contents.

The antibacterial film according to a first aspect of the present invention comprises a base layer and a sealing layer laminated on the base layer, wherein the base layer is made of a material containing a propylene-based resin, and the sealing layer is made of a material containing a propylene-based random copolymer and an antibacterial agent, the antibacterial agent containing particles, and the mode particle size of the antibacterial agent particles is larger than the thickness of the sealing layer.

The antibacterial film is produced by, for example, using a vertical pillow packaging machine to heat-seal the sealing layers on the back and bottom of the cylindrical antibacterial film. Next, the contents, such as cut vegetables, are placed inside the top opening, and while the contents are being degassed, the sealing layers are heat-sealed to close the top opening, producing a package containing the contents.

With the above antibacterial film, the mode particle size of the antibacterial agent particles is larger than the thickness of the sealing layer, so the antibacterial agent particles are exposed from the sealing layer. This means that the contents contained in the package come into contact with the particles contained in the antibacterial agent, or the particles contained in the antibacterial agent are close to the contents. This makes it more effective at inhibiting the growth of bacteria adhering to the contents than when the particles contained in the antibacterial agent are present within the sealing layer.

In the antibacterial film according to the second aspect of the present invention, the ratio of the mode particle size of the antibacterial agent to the thickness of the sealing layer is 20/3 or less.

The above-mentioned antibacterial film enhances the effectiveness of inhibiting bacterial growth while maintaining good sealing properties of the sealing layer.

In the antibacterial film according to the third aspect of the present invention, the ratio of the mode particle size of the antibacterial agent particles to the thickness of the sealing layer is 4 or less.

The above-mentioned antibacterial film further enhances the effectiveness of inhibiting bacterial growth while maintaining good sealing properties of the sealing layer.

In the antibacterial film according to the fourth aspect of the present invention, the ratio of the most frequent particle size of the antibacterial agent particles to the thickness of the sealing layer is 4/3 or less.

The above-mentioned antibacterial film further enhances the effectiveness of inhibiting bacterial growth while maintaining good sealing properties of the sealing layer.

In the antibacterial film according to the fifth aspect of the present invention, the proportion of the antibacterial agent in the material constituting the sealing layer is in the range of 0.02% by weight to 2.00% by weight.

The above-mentioned antibacterial film further enhances the effect of inhibiting bacterial growth.

In the antibacterial film according to the sixth aspect of the present invention, the mode particle size of the antibacterial agent particles is in the range of 0.5 μm to 6.0 μm.

When the material constituting the sealing layer contains an antibacterial agent, the antibacterial film described above provides good sealing properties while maintaining the thickness generally required for the sealing layer of antibacterial films used in packaging.

The antibacterial film of the present invention is highly effective in inhibiting the growth of bacteria attached to the contents.

1 is a cross-sectional view of an antibacterial film according to an embodiment. 1 is a table showing the specifications of the antibacterial films of Examples 1 to 4. 1 is a table showing the specifications of the antibacterial films of Examples 5 to 9. 1 is a table showing the specifications of the antibacterial films of Comparative Examples 1 and 2 and the film of Reference Example. 1 is a table showing the results of the first to third tests of the antibacterial films of Examples 1 to 4. 1 is a table showing the results of the first to third tests of the antibacterial films of Examples 5 to 9. 1 is a table showing the results of the first to third tests of the antibacterial films of Comparative Examples 1 and 2 and the film of the Reference Example. 1 is a table showing the results of additional testing of the second test of the antimicrobial films of Examples 1-4. 1 is a table showing the results of additional testing of the second test of the antimicrobial films of Examples 5-9. 1 is a table showing the results of a second additional test of the antibacterial films of Comparative Examples 1 and 2 and the film of the Reference Example. Table showing the results of the fifth test.

An antibacterial film according to one embodiment of the present invention will now be described with reference to the drawings.

<1. Structure of antibacterial film>
1 is a cross-sectional view showing an example of the layer structure of an antibacterial film 10. The antibacterial film 10 is used in a package that contains contents. The contents are, for example, fruits and vegetables. The fruits and vegetables include, for example, cut vegetables such as cabbage, lettuce, or carrots, as well as vegetables such as green onions, bean sprouts, spinach, broccoli, or bell peppers.

The antibacterial film 10 includes a base layer 20 and a sealing layer 30. The materials constituting the base layer 20 and sealing layer 30, as well as the material content and other specifications, are described in the prior art document (JP 2021-49657 A), and therefore detailed explanations are omitted here.

The thickness of the antibacterial film 10 can be selected as desired. Given that the antibacterial film 10 will be used in the manufacture of packaging, it is preferable that the thickness of the antibacterial film 10 be in the range of 10 μm to 50 μm.

When a package is manufactured using the antibacterial film 10, the substrate layer 20 is the outermost layer, in other words, the layer that faces the external space. The thickness of the substrate layer 20 can be selected as desired. Since the antibacterial film 10 is used to manufacture packages, the thickness of the substrate layer 20 is preferably in the range of 2 μm to 49 μm. In this embodiment, the thickness of the substrate layer 20 is 26 μm.

The material constituting the base layer 20 is a material containing a propylene-based resin. Examples of propylene-based resins include homopropylene polymer (HPP) and propylene-based random polymers. Propylene-based random copolymers are copolymers of propylene and other α-olefins. Examples of α-olefins other than propylene include α-olefins other than propylene having 2 to 10 carbon atoms, specifically α-olefins such as ethylene, 1-butene, 1-pentene, and 1-hexene. In addition to propylene-based resins, the material constituting the base layer 20 may also contain at least one of a hydrogenated styrene-based thermoplastic elastomer (SEBS) and a styrene-based thermoplastic elastomer (SBC).

When a package is manufactured using the antibacterial film 10, the sealing layer 30 is the innermost layer, in other words, the layer facing the internal space that contains the contents. The sealing layer 30 is laminated onto the base layer 20. In this embodiment, the sealing layer 30 is laminated directly onto the base layer 20. The sealing layer 30 may also be laminated onto the base layer 20 via an optional intermediate layer. The thickness of the sealing layer 30 can be selected as desired. From the perspective that the antibacterial film 10 will be used in the manufacture of packages, the thickness of the sealing layer 30 is preferably in the range of 1 μm to 8 μm. In this embodiment, the thickness of the sealing layer 30 is 1.5 μm.

The material constituting the sealing layer 30 is a material containing a propylene-based random copolymer and an antibacterial agent. The propylene-based random copolymer contained in the material constituting the sealing layer 30 is a binary copolymer or a ternary copolymer. In this embodiment, the propylene-based random copolymer contained in the material constituting the sealing layer 30 is a ternary copolymer. The antibacterial agent is, for example, an inorganic antibacterial agent or an organic antibacterial substance. Examples of inorganic antibacterial agents include metal compounds containing metal ions, and specific examples include metal compounds containing silver ions, copper ions, or zinc ions.

In this embodiment, the mode particle diameter of particles such as metal compounds contained in the antibacterial agent is larger than the thickness of the sealing layer 30 so that the particles contained in the antibacterial agent are exposed to the internal space from the sealing layer 30. From the perspective of enhancing antibacterial performance alone, the larger the mode particle diameter of the particles contained in the antibacterial agent, the higher the antibacterial performance. However, if the mode particle diameter of the particles contained in the antibacterial agent is too large relative to the thickness of the sealing layer 30, the sealing performance of the sealing layer 30 may be reduced, and good sealing performance may not be achieved under normal heat-sealing temperature conditions. From this perspective, the ratio of the mode particle diameter of the antibacterial agent particles to the thickness of the sealing layer 30 (hereinafter referred to as the "ratio RA") is preferably 20/3 or less. The ratio RA is more preferably 4 or less. The ratio RA is even more preferably 4/3 or less. The mode particle diameter is the particle diameter at the maximum value of the particle distribution and can be measured using, for example, a flow particle image analyzer or a laser diffraction particle size analyzer.

Furthermore, when the material constituting the sealing layer 30 contains an antibacterial agent, it is preferable that the sealing layer 30 achieves good sealing properties while maintaining the thickness generally required for the sealing layer 30 of the antibacterial film 10 used in packaging. From this perspective, it is preferable that the mode particle size of the antibacterial agent particles be in the range of 0.5 μm to 6.0 μm.

The proportion of the antibacterial agent in the material that constitutes the sealing layer 30 can be selected as desired. In a preferred example, the proportion of the antibacterial agent in the material that constitutes the sealing layer 30 is preferably in the range of 0.02% to 2.00% by weight.

<2. Action and effect of antibacterial film>
The antibacterial film 10 is heat-sealed, for example, by a vertical pillow packaging machine, at the sealing layers 30 on the back and bottom of the cylindrical antibacterial film 10. Next, contents such as cut vegetables are placed in the upper opening, and while degassing, the sealing layer 30 is heat-sealed to close the upper opening, thereby producing a package containing the contents.

In the antibacterial film 10, the mode particle diameter of the antibacterial agent particles is larger than the thickness of the sealing layer 30, so the antibacterial agent particles are exposed from the sealing layer 30. As a result, the contents contained in the package come into contact with the particles contained in the antibacterial agent, or the particles contained in the antibacterial agent are close to the contents. This makes it more effective at inhibiting the growth of bacteria adhering to the contents than if the particles contained in the antibacterial agent were present within the sealing layer 30.

3. Examples
The inventor(s) of the present application manufactured antibacterial films of Examples, Comparative Examples, and Reference Examples, and conducted tests to evaluate the properties of the antibacterial films. The tests included Test 1, Test 2, Test 3, Test 4, and Test 5. For ease of explanation, the following description will be given with the same reference numerals as in the embodiment for elements constituting the antibacterial films of Examples and Comparative Examples. In the antibacterial films of Examples and Comparative Examples, an Ag—Zn-based antibacterial agent was used as the antibacterial agent.

Figures 2A to 2C are tables showing the specifications of the antibacterial films 10 of Examples 1 to 9, the antibacterial films 10 of Comparative Examples 1 and 2, and the film of the Reference Example. As shown in Figure 2C, the antibacterial films 10 of Comparative Examples 1 and 2 have a ratio RA of 1 or less. The film of the Reference Example does not contain an antibacterial agent in the material that makes up the sealing layer 30. Figures 3A to 3C are tables showing the results of Tests 1 to 3. Tests 1 to 3 were conducted to evaluate the properties of the antibacterial films 10 of Examples 1 to 9, the antibacterial films 10 of Comparative Examples 1 and 2, and the film of the Reference Example before packaging was produced, i.e., when the film was in its standalone state.

<3-1. First Exam>
The first test was a test to evaluate the antibacterial properties of the film. In the first test, the antibacterial properties of the antibacterial films 10 of Examples 1 to 9, the antibacterial films 10 of Comparative Examples 1 and 2, and the film of the Reference Example were evaluated based on JIS Z2801. In the antibacterial property section of Figures 2A to 2C, "◯" indicates an antibacterial activity value of 2.0 or more, and "×" indicates an antibacterial activity value of less than 2.0. In the antibacterial films 10 of Examples 1 to 9 and Comparative Examples 1 and 2, the material constituting the sealing layer 30 contains an antibacterial agent, and therefore, it can be seen that the antibacterial properties were evaluated to be high.

<3-2. Second Exam>
The second test was a test to confirm the seal strength when two films were heat-sealed. For each of the antibacterial films 10 of Examples 1 to 9, Comparative Examples 1 and 2, and the Reference Example film, two films were cut to 70 mm in the machine direction (MD) and 200 mm in the transverse direction (TD). The two films were then stacked with the seal layers facing each other, and heat-sealed under specified conditions using a heat-sealing machine (HG-100-2, manufactured by Toyo Seiki Seisakusho, Ltd.) to produce measurement samples. The specified conditions were a sealing temperature of 150°C, a gauge pressure of 0.26 MPa, and a sealing time of 0.5 seconds.

Next, measurement samples were cut to dimensions of 10 mm in the MD x 50 mm in the TD, with the heat-sealed portion of the resulting measurement sample at the very edge and with an area of 10 mm in the MD x 10 mm in the TD. The cut measurement samples were pulled in the TD using a digital force gauge (Imada ZTS-100N) attached to a measurement stand (Imada MX-500N), and the heat-sealed portion was peeled off. The heat-seal strength was measured five times for each measurement sample. The seal strength values shown in Figures 3A to 3C are the average of the five measurements, each multiplied by 1.5.

As shown in Figure 3B, under the heat sealing conditions of the second test, the seal strength of the antibacterial film 10 of Example 9 was found to be somewhat low. This is thought to be due to the relatively large ratio RA.

In addition, as an additional test to the second test, the inventor(s) also measured the seal strength using the same method as in the second test under the specified heat sealing conditions of sealing temperatures of 135°C, 140°C, and 145°C. Figures 4A to 4C show the results of the additional test to the second test.

As shown in Figures 4A and 4B, it was confirmed that the antibacterial films 10 of Examples 1, 4, 5, and 8, which have an RA ratio of 4/3, exhibit good sealing properties even when the heat-sealing temperature is relatively low.

<3-3. Third Exam>
The third test was a test to evaluate the permeability of the film. In the third test, the antibacterial films 10 of Examples 1 to 9, the antibacterial films 10 of Comparative Examples 1 and 2, and the film of the Reference Example were each cut into strips measuring 10 cm in the MD direction and 10 cm in the TD direction to produce measurement samples. For each measurement sample, the seal layer was set facing the light source, and the haze value (%) was measured using a haze meter (NDH5000 manufactured by Nippon Denshoku Industries Co., Ltd.). The measurement was performed four times. The haze value items shown in Figures 3A to 3C are the average values of the four measurements.

As shown in Figures 3A to 3C, it was confirmed that the antibacterial films 10 of Examples 1 to 9, the antibacterial films 10 of Comparative Examples 1 and 2, and the film of the Reference Example had a transmittance level generally required for packaging.

<3-4. Fourth Exam>
The fourth test is a test to confirm the Young's modulus, oxygen permeability, and carbon dioxide permeability of the film. In the fourth test, the Young's modulus, oxygen permeability, and carbon dioxide permeability of the antibacterial films 10 of Examples 1 and 4 were measured.

The Young's modulus of the antibacterial film 10 of Example 1 was MD/TD = 0.9/2.2 (GPa). The Young's modulus of the antibacterial film 10 of Example 4 was MD/TD = 2.1/5.0 (GPa). Because the base layer 20 of the antibacterial film 10 of Example 1 contains SEBS, it was confirmed to have softer properties than the antibacterial film 10 of Example 4, whose base layer 20 is composed solely of HPP. For this reason, it is believed that the antibacterial film 10 of Example 1 can be degassed more effectively after the package is manufactured than the antibacterial film 10 of Example 4.

The antibacterial film 10 of Example 1 had an oxygen permeability of 3110 ( ^cm3 / ^m2 ·24h·atm) and an oxygen dioxide permeability of 11100 ( ^cm3 / ^m2 ·24h·atm). The antibacterial film 10 of Example 4 had an oxygen permeability of 1920 ( ^cm3 / ^m2 ·24h·atm) and an oxygen dioxide permeability of 5400 ( ^cm3 / ^m2 ·24h·atm). It was confirmed that the antibacterial film 10 of Example 1 had higher breathability than the antibacterial film 10 of Example 4.

<3-5. Fifth Exam>
The fifth test was conducted to confirm the effect of inhibiting bacterial growth when a package was manufactured using the film. In the fifth test, 130 g of cut cabbage was placed in the packages of the antibacterial films 10 of Examples 1 to 9, the antibacterial films 10 of Comparative Examples 1 and 2, and the film of the Reference Example. The packages were placed in a vertical pillow packaging machine (Daisei Machinery Co., Ltd.) and degassed to produce packages with the contents sealed inside. The resulting packages were 240 mm long and 195 mm wide, and five were produced for each degassing level described below. The seal widths of the top, bottom, and back panel of the resulting packages were all 10 mm. These packages were stored in an environment of 10°C for 120 hours (5 days). After 5 days, the contents were removed from the packages, and 10 g of the contents were homogenized in 90 cc of phosphate buffer solution. 1 mL of the resulting 10-fold diluted solution was taken and diluted with 9 mL of phosphate buffer to obtain a sample solution further diluted 10-fold. Next, the diluted solution diluted to an appropriate dilution ratio was cultured in Petrifilm medium (3M) at 35°C for 48 hours, and the general viable bacterial count was counted.

In the fifth test, the relationship between the degassing index of the package containing the contents and the total viable bacterial count was confirmed. The degassing index of the package is an index uniquely defined by the inventor(s) of the present application, which is defined by the following formula (1) as the volume of the internal space of the package per gram of the contents enclosed in the package.
Degassing index = Degree of degassing / Weight of contents to be sealed (130 g in this test) (1)

The degree of degassing in formula (1) is the ratio of the volume V (ml) of the package to the inner surface area S ( ^mm2 ) of the package. The volume of the package can be determined, for example, by submerging the package in a bucket of water and measuring the volume of water that overflows from the bucket.

Figure 5 is a table showing the results of the fifth test. Figure 5 shows the ratio of the general viable bacterial count in the packages produced using the antibacterial films 10 of Examples 1 to 9 and the antibacterial films 10 of Comparative Examples 1 and 2, when the general viable bacterial count in the package produced using the film of the Reference Example is set to 1.

As shown in Figure 5, it was confirmed that the packages manufactured using the antibacterial films 10 of Examples 1 to 9 had a lower viable bacterial count than the packages manufactured using the antibacterial films 10 of Comparative Examples 1 and 2; in other words, they were more effective at inhibiting bacterial growth. This is thought to be because the antibacterial films 10 of Examples 1 to 9 had a ratio RA greater than 1. It was also confirmed that the smaller the degassing index, the lower the viable bacterial count. This is thought to be because the smaller the degassing index, in other words, the smaller the volume of the internal space of the package per gram of contents enclosed in the package, the closer the distance between the antibacterial agent particles exposed from the sealing layer 30 of the package and the contents, or the closer the contact between the antibacterial agent particles exposed from the sealing layer 30 of the package and the contents.

4. Modified Examples
The above-described embodiments are merely examples of possible forms of the antibacterial film of the present invention, and are not intended to limit the forms. The antibacterial film of the present invention may take forms different from those exemplified in the embodiments. Examples include forms in which part of the configuration of the embodiments is replaced, modified, or omitted, or forms in which a new configuration is added to the embodiments. Some examples of modifications of the embodiments are shown below.

<4-1>
The material constituting the sealing layer 30 can be changed as desired. For example, the material constituting the sealing layer 30 may contain a deodorizer. Examples of the deodorizer include inorganic deodorizers. Examples of the inorganic deodorizer include zirconium phosphate; aluminosilicate (zeolite); zinc aluminosilicate; carbonates such as sodium carbonate, sodium bicarbonate, and calcium carbonate; and metal oxides such as calcium oxide, magnesium oxide, aluminum oxide, zinc oxide, copper oxide, iron oxide, titanium oxide, and alum.

<4-2>
In the above embodiment, a package is produced from one antibacterial film 10 using a vertical pillow packaging machine, but a package may also be produced by heat-sealing two or more antibacterial films 10, for example.

<4-3>
In the above embodiment, the sealing layers 30 of the antibacterial film 10 are joined together by heat sealing, but the means for sealing the sealing layers 30 of the antibacterial film 10 together can be changed as desired. For example, the sealing layers 30 of the antibacterial film 10 may be sealed together by impulse sealing, high frequency sealing, or ultrasonic sealing.

10: Antibacterial film 20: Base layer 30: Sealing layer

Claims (6)

A method for manufacturing a package, comprising:
The packaging body is configured to include an antibacterial film,
The antibacterial film comprises:
a substrate layer;
a seal layer laminated on the base material layer,
the base layer is made of a material containing a propylene-based resin,
the sealing layer is made of a material containing a propylene-based random copolymer and an antibacterial agent,
the antimicrobial agent comprises particles;
the mode particle size of the antibacterial agent particles is greater than the thickness of the sealing layer;
The method for manufacturing the packaging body includes:
Enclosing contents inside the package;
and a degassing step so that the degassing index calculated by the following formula (1) is 4.56 × 10 ⁻⁵ or less.
Degassing index = Degree of degassing / Weight of contents to be sealed (g) (1)
Here, the degree of degassing is the ratio of the volume V (ml) of the package to the inner surface area S (mm ² ) of the package.
A method for manufacturing a package . The method for manufacturing a package according to claim 1 , wherein a ratio of a mode particle diameter of the antibacterial agent particles to a thickness of the sealing layer is 20/3 or less. The method for manufacturing a package according to claim 2 , wherein a ratio of a mode particle diameter of the antibacterial agent particles to a thickness of the sealing layer is 4 or less. The method for manufacturing a package according to claim 3, wherein a ratio of a mode particle diameter of the antibacterial agent particles to a thickness of the sealing layer is 4/3 or less. The method for manufacturing a package according to any one of claims 1 to 4, wherein the content of the antibacterial agent in the material constituting the sealing layer is in the range of 0.02% by weight to 2.00% by weight. The method for manufacturing a package according to any one of claims 1 to 5, wherein the mode particle size of the antibacterial agent particles is in the range of 0.5 µm to 6.0 µm.