JP7574041B2 - Plastic wrap - Google Patents

Description

The present invention relates to a wrap film.

Wrapping films made from vinylidene chloride resins have excellent oxygen gas barrier properties, water vapor barrier properties (moisture resistance), and transparency, and can also be heated in a microwave oven, so they are widely used for packaging fresh fish, raw meat, processed meat, fresh vegetables, prepared foods, etc., for the purposes of blocking oxygen and preventing moisture.

In particular, in recent years, there has been a strong demand for wrap films to have oxygen gas barrier properties in order to prevent oxidation of fats and oils, preserve active ingredients such as vitamins, and prevent spoilage due to the proliferation of mold, fungi, and yeast (see, for example, Reference 1).

JP 2019-43677 A

During melt extrusion, if vinylidene chloride resin remains in the extruder for a certain period of time, the vinylidene chloride resin may decompose and carbonize, and the carbonized matter may become foreign matter. Even if foreign matter is generated during melt extrusion, depending on the level of the matter, punctures may not occur during inflation film formation, and wrap film may be produced normally. However, in such cases, it is possible that tearing problems may occur due to the foreign matter.

For this reason, various additives are added to vinylidene chloride resins from the viewpoints of the film's extrusion processability, crystallinity, transparency, softening temperature, etc., and plasticizers are generally added in particular from the viewpoint of the film's extrusion processability. However, it has been found that depending on the type and amount of plasticizer used, the oxygen gas barrier properties and the feel to the touch can actually be reduced.

The present invention has been made to solve the above problems, and aims to provide a wrap film that reduces tearing problems, has excellent oxygen gas barrier properties, and is also excellent in feel.

The present inventors have conducted extensive research to solve the above problems. As a result, they have discovered that the above problems can be solved by adjusting the content of at least one compound selected from the group consisting of citrate esters, dibasic acid esters, and acetylated fatty acid glycerides, and have completed the present invention.

That is, the present invention is as follows.
[1]
a vinylidene chloride resin containing 72 to 93 mol % of vinylidene chloride repeating units;
Contains at least one compound selected from the group consisting of citric acid esters, dibasic acid esters, and acetylated fatty acid glycerides;
The content of the compound is 0.5% by mass or more and less than 3% by mass based on the total amount of the wrap film,
The tensile modulus in the MD direction is 250 to 570 MPa,
The low-temperature crystallization onset temperature measured by a temperature modulated differential scanning calorimeter is 40 to 60°C.
Plastic wrap.
[2]
The tear strength in the TD direction is 2.0 to 6.0 cN.
The wrap film according to [1].
[3]
The thickness is 6 to 18 μm.
The wrap film according to [1] or [2].
[4]
Contains epoxidized vegetable oil,
The content of the epoxidized vegetable oil is 0.5 to 3 mass% based on the total amount of the wrap film.
The wrap film according to any one of [1] to [3].
[5]
The oxygen permeability at 23°C is 110 ^cm3 / ^m2 ·day·atm or less.
The wrap film according to any one of [1] to [4].
[6]
The ratio of highly mobile components measured by pulsed NMR is 4.5% or less;
The wrap film according to any one of [1] to [5].
[7]
The ratio of low mobility components measured by pulse NMR is 65.0% or less;
The wrap film according to any one of [1] to [6].

The present invention provides a wrap film that is less prone to tearing, has excellent oxygen gas barrier properties, and is pleasant to the touch.

FIG. 1 is a schematic diagram of an apparatus used in the film-forming process of the present invention. 1 is an example of a use form of the film of the present invention.

The following describes in detail an embodiment of the present invention (hereinafter referred to as the "present embodiment"); however, the present invention is not limited to this embodiment, and various modifications are possible without departing from the gist of the present invention.

In this embodiment, the "TD direction" refers to the width direction of the resin in the film production line, and refers to the direction perpendicular to the direction in which the wrap film is pulled out from the roll when the wrap film is made. The "MD direction" refers to the flow direction of the resin in the film production line, and refers to the direction in which the wrap film is pulled out from the roll when the wrap film is made.

[Wrapping film]
The wrap film of this embodiment contains a vinylidene chloride resin containing 72 to 93 mol% of vinylidene chloride repeating units and at least one compound selected from the group consisting of citrate esters, dibasic acid esters, and acetylated fatty acid glycerides, the content of the compound being 0.5 mass% or more and less than 3 mass% relative to the total amount of the wrap film, the tensile modulus in the MD direction being 250 to 570 MPa, and the low-temperature crystallization onset temperature measured with a temperature-modulated differential scanning calorimeter being 40 to 60°C.

In this embodiment, by setting the content of at least one compound selected from the group consisting of citric acid esters, dibasic acid esters, and acetylated fatty acid glycerides in the wrap film having the above-mentioned specified configuration to 0.5% by mass or more and less than 3% by mass, the wrap film has the effect of exhibiting sufficient oxygen gas barrier properties. In addition, the wrap film of this embodiment also has the effect of suppressing tearing problems and providing an excellent feel to the touch.

The reason why adjusting the content of the above compounds suppresses cracking problems and improves oxygen gas barrier properties is unclear, but it is thought to be as follows. That is, during melt extrusion, the resin remains in the extruder for a certain period of time, and by adjusting the content of the above compounds, the amount of low-mobility components in the vinylidene chloride resin increases, which is thought to improve the oxygen gas barrier properties. In addition, by adjusting the content of the above compounds, the feel of the material is also excellent. Note that the above reasons are only speculations and are not limited to these. The present embodiment will be described in detail below.

(Vinylidene chloride resin)
The vinylidene chloride resin is not particularly limited as long as it contains vinylidene chloride, and examples of the vinylidene chloride resin include vinylidene chloride copolymers containing a monomer polymerizable with vinylidene chloride.

Monomers that can be copolymerized with vinylidene chloride monomers are not particularly limited, but examples include vinyl chloride; acrylic acid esters such as methyl acrylate and butyl acrylate; methacrylic acid esters such as methyl methacrylate and butyl methacrylate; acrylic acid, methacrylic acid; acrylonitrile; vinyl acetate, etc. These monomers may be used alone or in combination of two or more. Among these, vinyl chloride is more preferable.

The content of vinylidene chloride repeat units is 72 to 93 mol%, preferably 80 to 93 mol%, and more preferably 82 to 93 mol%, based on the total amount of vinylidene chloride resin. When the content of vinylidene chloride repeat units is 72 mol% or more, the glass transition temperature of the vinylidene chloride resin is low, and the wrap film tends to become softer. This makes it possible to reduce tearing of the wrap film, for example, even when used in a low-temperature environment. On the other hand, when the content of vinylidene chloride repeat units is 93 mol% or less, a significant increase in crystallinity is suppressed, and deterioration of molding processability during film stretching tends to be suppressed.

The content of vinylidene chloride repeat units is not particularly limited, but can be measured, for example, using a high-resolution proton nuclear magnetic resonance measurement device (400 MHz or higher). More specifically, 0.5 g of wrap film is dissolved in 10 ml of tetrahydrofuran (THF), and about 30 ml of methanol is added to precipitate the resin content, and the precipitate is separated by centrifugation and vacuum dried to obtain a measurement sample of vinylidene chloride resin. The measurement sample obtained is then dissolved in deuterated tetrahydrofuran to a concentration of 5 mass%, and this solution is subjected to H-NMR measurement at a measurement atmosphere temperature of about 27°C. The content of vinylidene chloride repeat units is calculated using a specific chemical shift based on tetramethylsilane in the obtained spectrum. For example, in the case of a copolymer of vinylidene chloride and vinyl chloride, the calculation is performed using peaks at 3.50 to 4.20 ppm, 2.80 to 3.50 ppm, and 2.00 to 2.80 ppm.

The content of repeating comonomer (vinyl chloride) units in the vinylidene chloride-vinyl chloride copolymer is preferably 7 to 28 mol %, and more preferably 10 to 19 mol %, relative to the total amount of the copolymer. By having the comonomer content of the vinylidene chloride copolymer within the above range, tearing of the wrap film is reduced, and deterioration of the molding processability during film stretching tends to be further suppressed.

The weight average molecular weight (Mw) of the vinylidene chloride copolymer is preferably 50,000 to 250,000, more preferably 60,000 to 230,000, and even more preferably 80,000 to 200,000. By having the weight average molecular weight (Mw) within the above range, the mechanical strength of the wrap film tends to be further improved. A vinylidene chloride resin having a weight average molecular weight within the above range can be obtained, for example, by controlling the charging ratio of vinylidene chloride monomer and vinyl chloride monomer, the amount of polymerization initiator, or the polymerization temperature. In this embodiment, the weight average molecular weight (Mw) can be determined by gel permeation chromatography (GPC) using a standard polystyrene calibration curve.

The content of vinylidene chloride resin is preferably 88 to 98% by mass, more preferably 90 to 99% by mass, based on the total amount of the wrap film. When the content of vinylidene chloride resin is within the above range, the low-mobility components of the vinylidene chloride resin increase due to the plasticizing effect of additives, etc., which tends to further improve the oxygen gas barrier properties. In addition, when the content of vinylidene chloride resin is within the above range, the film can be prevented from easily stretching, and tearing problems tend to be further suppressed. The method for measuring the content of each component from the wrap film varies depending on the object to be analyzed. For example, the content of vinylidene chloride resin can be obtained by dissolving 0.5 g of a sample in 10 ml of tetrahydrofuran, adding about 30 ml of methanol to precipitate the resin, separating the precipitate by centrifugation, drying, and measuring the weight.

(Additives)
The wrap film of this embodiment contains at least one compound selected from the group consisting of citrate esters, dibasic acid esters, and acetylated fatty acid glycerides. From the viewpoint of ease of handling, citrate esters are preferred, and acetyl tributyl citrate is particularly preferred.

(Citrate ester)
The citrate ester is not particularly limited, but examples thereof include triethyl citrate, tributyl citrate, triethyl acetyl citrate, tributyl acetyl citrate (ATBC), and tri-n-(2-ethylhexyl) acetyl citrate.

Among these, acetyl tributyl citrate is preferred. By using such a citrate ester, the vinylidene chloride resin is plasticized, improving moldability and increasing the amount of low-mobility components in the vinylidene chloride resin, which in turn improves the oxygen gas barrier properties and tends to improve the feel to the touch.

(Dibasic acid ester)
The dibasic acid ester is not particularly limited, but examples thereof include adipic acid esters such as dibutyl adipate, di-n-hexyl adipate, di-2-ethylhexyl adipate, and dioctyl adipate; azelaic acid esters such as di-2-ethylhexyl azelaate and octyl azelaate; sebacate esters such as dibutyl sebacate (DBS) and di-2-ethylhexyl sebacate; and phthalic acid esters such as dimethyl phthalate, diethyl phthalate, and dioctyl phthalate.

Among these, aliphatic dibasic acid esters are preferred, and dibutyl sebacate is more preferred. By using such dibasic acid esters, the vinylidene chloride resin is plasticized, improving moldability and increasing the amount of low-mobility components in the vinylidene chloride resin, which in turn improves the oxygen gas barrier properties and tends to improve the feel to the touch.

(Acetylated fatty acid glycerides)
The acetylated fatty acid glyceride is not particularly limited, but examples thereof include acetylated caprylic acid glyceride, acetylated capric acid glyceride, acetylated lauric acid glyceride, acetylated myristic acid glyceride, acetylated palm kernel oil glyceride, acetylated coconut oil glyceride, acetylated castor oil glyceride, and acetylated hydrogenated castor oil glyceride.

The acetylated fatty acid glyceride may be any of acetylated monoglycerides of fatty acids, acetylated diglycerides of fatty acids, and acetylated triglycerides of fatty acids. For example, the acetylated lauric acid glycerides include acetylated monoglycerides of lauric acid, acetylated diglycerides of lauric acid (DALG: diacetyl lauroyl glycerol), and acetylated triglycerides of lauric acid. Among these, acetylated lauric acid glycerides are preferred, and acetylated diglycerides of lauric acid are more preferred. By using such acetylated fatty acid glycerides, the amount of low-mobility components in the vinylidene chloride resin increases, which improves the oxygen gas barrier properties and tends to improve the feel to the touch.

The content of citrate esters, dibasic acid esters, and acetylated fatty acid glycerides can be obtained by extracting the additives from the wrap film using an organic solvent such as acetone at a temperature 5 to 10°C lower than the boiling point of the extraction solvent, and then analyzing the extract by gas chromatography.

The total content of at least one compound selected from the group consisting of citric acid esters, dibasic acid esters, and acetylated fatty acid glycerides is 0.5% by mass or more and less than 3% by mass, preferably 0.5 to 2.5% by mass, and more preferably 0.7 to 2.5% by mass, based on the total amount of the wrap film. When the total content of the above compounds is 0.5% by mass or more, the share of the melt extrusion becomes appropriate, and the composition passes smoothly through the extruder, suppressing thermal decomposition of the vinylidene chloride resin. In addition, when the total content of the above compounds is less than 3% by mass, the vinylidene chloride resin contains more low-mobility components, which further improves the oxygen gas barrier properties and the feel to the touch.

(Epoxidized vegetable oil)
The wrap film of this embodiment may contain epoxidized vegetable oil. The epoxidized vegetable oil may act as a stabilizer for vinylidene chloride resin extrusion processing. The epoxidized vegetable oil is not particularly limited, but generally includes those produced by epoxidizing edible oils and fats. Specifically, the epoxidized vegetable oil includes, for example, epoxidized soybean oil (ESO) and epoxidized linseed oil. Among these, epoxidized soybean oil is preferred. By using such an epoxidized vegetable oil, the touch of the wrap film is further improved, and the film tends to be more easily pulled out from the decorative box.

In this embodiment, the content of the epoxidized vegetable oil is preferably 0.5 to 3 mass%, more preferably 1 to 2.5 mass%, and even more preferably 1 to 2 mass% relative to the total amount of the wrap film. When the content of the epoxidized vegetable oil is 0.5 mass% or more, changes in the quality of the wrap film tend to be more suppressed. Furthermore, when the content of the epoxidized vegetable oil is 3 mass% or less, changes in the color tone of the wrap film tend to be more suppressed, and stickiness due to bleeding tends to be suppressed. The method for measuring the content of each component from the wrap film varies depending on the object to be analyzed. For example, the content of the epoxidized vegetable oil can be obtained by analyzing the re-precipitated filtrate of the wrap film by NMR.

Specifically, 50 mg of a sample is weighed out, dissolved in a heavy solvent (solvent: deuterated tetrahydrofuran, internal standard: dimethyl terephthalate, volume: 0.7 ml), and measured by 400 MHz proton NMR (accumulation number: 512 times). The ratio of the integral value from 2.23 to 2.33 ppm to the integral value from 8.05 to 8.11 ppm is taken as the integral ratio, and a quantitative value is calculated by the absolute calibration curve method, whereby the amount of the compound can be obtained.
Integral ratio = integral value (2.23-2.33 ppm) / integral value (8.05-8.11 ppm)

(Other additives)
The wrap film of this embodiment may contain additives other than those mentioned above. Examples of such additives include, but are not limited to, plasticizers other than those mentioned above, stabilizers other than those mentioned above, weather resistance improvers, colorants such as dyes or pigments, antifogging agents, antibacterial agents, lubricants, nucleating agents, oligomers such as polyesters, polymers such as methyl methacrylate-butadiene-styrene copolymers (MBS), and the like.

Plasticizers other than citric acid esters, dibasic acid esters, and acetylated fatty acid glycerides are not particularly limited, but specific examples include glycerin, glycerin esters, wax, liquid paraffin, and phosphate esters. The plasticizers may be used alone or in combination of two or more.

Stabilizers other than epoxidized vegetable oils are not particularly limited, but specific examples include antioxidants such as 2,5-t-butylhydroquinone, 2,6-di-t-butyl-p-cresol, 4,4'-thiobis-(6-t-butylphenol), 2,2'-methylene-bis-(4-methyl-6-t-butylphenol), octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate, and 4,4'-thiobis-(6-t-butylphenol); and heat stabilizers such as laurate, myristate, palmitate, stearate, isostearate, oleate, ricinoleate, 2-ethyl-hexylate, isodecanoate, neodecanoate, and calcium benzoate. Stabilizers may be used alone or in combination.

The weather resistance improver is not particularly limited, but specific examples include ethylene-2-cyano-3,3'-diphenylacrylate, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)5-chlorobenzotriazole, 2-hydroxy-4-methoxybenzophenone, and 2,2'-dihydroxy-4-methoxybenzophenone. The weather resistance improver may be used alone or in combination of two or more kinds.

The coloring agent such as a dye or pigment is not particularly limited, but specific examples include carbon black, phthalocyanine, quinacridone, indoline, azo pigments, and red iron oxide. The coloring agent may be used alone or in combination of two or more types.

Antifogging agents are not particularly limited, but specific examples include glycerin fatty acid esters, sorbitan fatty acid esters, polyoxyethylene fatty acid alcohol ethers, polyoxyethylene glycerin fatty acid esters, and polyoxyethylene sorbitan fatty acid esters. Antifogging agents may be used alone or in combination of two or more.

Antibacterial agents are not particularly limited, but specific examples include silver-based inorganic antibacterial agents. Antibacterial agents may be used alone or in combination of two or more types.

The lubricant is not particularly limited, but specific examples include fatty acid hydrocarbon lubricants such as ethylene bis(steramide), butyl stearate, polyethylene wax, paraffin wax, carnauba wax, myristyl myristate, and stearyl stearate, higher fatty acid lubricants, fatty acid amide lubricants, and fatty acid ester lubricants. The lubricants may be used alone or in combination of two or more.

The nucleating agent is not particularly limited, but specific examples include metal salts of phosphate esters. The nucleating agents may be used alone or in combination of two or more.

The content of other additives is preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 1% by mass or less, and particularly preferably 0.1% by mass or less, based on the total amount of the wrap film. There is no particular lower limit to the content of other additives, but it is 0% by mass or more based on the total amount of the wrap film.

(Thickness of wrap film)
The wrap film of this embodiment has a thickness of preferably 6 to 18 μm, more preferably 9 to 12 μm. By having the wrap film have a thickness within the above range, problems with the film tearing are suppressed, the cuttability is improved, and the adhesion is also improved.

More specifically, a thickness of 6 μm or more improves the tear strength of the wrap film in the TD and MD directions, and tends to prevent the film from breaking during use. Also, a thickness of 6 μm or more tends to prevent a significant decrease in tear strength. Therefore, when pulling out the wrap film from the roll and when picking out the end of the film that has been rewound into the presentation box, problems such as the wrap film tearing at the end cut by the cutting blade attached to the presentation box are further reduced.

On the other hand, by having a thickness of 18 μm or less, the force required to cut the wrap film with a cutting blade attached to the presentation box can be reduced, and cutting properties tend to be improved. In addition, by having a thickness of 18 μm or less, the wrap film tends to fit the shape of the container more easily, and adhesion to the container tends to be improved.

(Tear strength)
The tear strength in the TD direction of the wrap film of this embodiment is preferably 2.0 to 6.0 cN, more preferably 2.0 to 4.0 cN, and even more preferably 2.2 to 3.0 cN. A tear strength in the TD direction of 2.0 cN or more can reduce tearing, particularly when the wrap film is pulled out from the roll, and can also suppress unintended tearing problems when the wrap film is used. On the other hand, a tear strength in the TD direction of 6.0 cN or less makes the film easier to tear when cut in the TD direction with a cutting blade attached to the decorative box, improving cuttability.

The tear strength in the TD direction of the wrap film of this embodiment can be adjusted by the vinylidene chloride resin composition, additive composition, film stretch ratio, stretching speed, film thickness, etc. Although not particularly limited, for example, the tear strength in the TD direction tends to improve by lowering the stretch ratio in the TD direction or making the wrap film thicker, and tends to decrease by increasing the stretch ratio in the TD direction or making the wrap film thinner. The tear strength is measured by the method described in the examples.

(Tensile Modulus)
The tensile modulus in the MD direction of the wrap film of this embodiment is 250 to 570 MPa, preferably 300 to 500 MPa, and more preferably 350 to 500 MPa. By having a tensile modulus in the MD direction of 250 MPa or more, when a force is applied to cut the film with the cutting blade, the film can be prevented from stretching in the MD direction, making it easier for the cutting blade to bite into the film, and improving the cutting ability. On the other hand, by having a tensile modulus in the MD direction of 570 MPa or less, the film is soft and can be cut cleanly along the shape of the cutting blade, which tends to prevent the occurrence of numerous tears on the cut end surface. As a result, when the film is pulled out from the roll and when the end of the film that has been rewound into the presentation box is picked up, the occurrence of problems in which the film tears from the cut end surface tends to be prevented.

The tensile modulus in the MD direction of the wrap film of this embodiment can be adjusted by the composition of the vinylidene chloride resin, the composition of additives, the stretch ratio of the film, the stretching speed, etc. Although not particularly limited, for example, the tensile modulus in the MD direction tends to improve by increasing the stretch ratio or reducing the amount of additives, and tends to decrease by decreasing the stretch ratio or increasing the amount of additives. The tensile modulus is measured by the method described in the examples.

(Low temperature crystallization start temperature)
In the wrap film of this embodiment, the wrap film undergoes physical deterioration due to the heat history it receives during distribution and storage, and the tearing trouble caused by this can be estimated from the low-temperature crystallization onset temperature. The initiation temperature is an index showing the thermal stability of microcrystals formed and grown by exposure to high temperatures during distribution and storage in a warehouse after the wrap film is manufactured. The degree of rearrangement of molecular chains is determined by the low-temperature crystallization initiation temperature. In other words, it is possible to evaluate the likelihood of tearing problems occurring due to physical deterioration of the wrap film.

From the above viewpoints, the low-temperature crystallization onset temperature of the wrap film of this embodiment measured with a temperature-modulated differential scanning calorimeter (hereinafter also referred to as "temperature-modulated DSC") is preferably 40 to 60°C, more preferably 40 to 55°C, and even more preferably 40 to 50°C. By having the low-temperature crystallization onset temperature within the above range, tearing problems can be suppressed while maintaining the cuttability of the wrap film, and the feel of the wrap film tends to be further improved. Details are described below.

Conventional wrap films have a low-temperature crystallization onset temperature exceeding 60°C. In contrast, the wrap film of this embodiment has a low-temperature crystallization onset temperature of 60°C or less, which is set to a lower temperature. By having the low-temperature crystallization onset temperature within the above range, rearrangement of molecular chains is suppressed, and tearing problems in the wrap film are further suppressed.

More specifically, due to the difference in the low-temperature crystallization onset temperature, the wrap film of this embodiment and conventional wrap films behave differently when exposed to heat. For example, in the case of conventional wrap films, it is believed that when exposed to an atmosphere of 20°C or higher for a long period of time during distribution and warehouse storage, the molecular chains of the vinylidene chloride resin rearrange, causing the formation and growth of microcrystals. It is presumed that such molecular chain rearrangement occurs because the orientation of the molecular chains of the manufactured wrap film and the stress of the film are not sufficiently relaxed. The higher the temperature at which the wrap film is exposed, the more likely it is that molecular chain rearrangement will occur, which is thought to physically deteriorate the film and induce tearing problems.

In contrast, in the wrap film of this embodiment, the orientation of the molecular chains of the vinylidene chloride resin and the stress of the film are sufficiently relaxed during production, so that the low-temperature crystallization onset temperature is set to 60°C or lower. As a result, even if the wrap film of this embodiment is exposed to temperatures of 20°C or higher for long periods of time during distribution and warehouse storage, molecular chain rearrangement is unlikely to occur, and deterioration of the film and even tearing problems are suppressed. As a result, it is possible to simultaneously achieve the contradictory goals of maintaining cuttability while suppressing tearing problems.

Meanwhile, the inventors of the present invention have found that the low-temperature crystallization onset temperature is 40°C when the wrap film is stored at -30°C, which is below the glass transition temperature, after production. In other words, the low-temperature crystallization onset temperature is 40°C when the wrap film is considered to have not been exposed to heat at all after production. The closer the low-temperature crystallization onset temperature is to this temperature, the more likely it is that molecular chain rearrangement and even tearing problems can be suppressed, so the lower limit of the temperature range for the low-temperature crystallization onset temperature is set to 40°C.

The method for adjusting the low-temperature crystallization onset temperature to the above range is not particularly limited, but examples include a method of sufficiently aligning the molecular chains of the vinylidene chloride resin or relaxing the stress of the film. Specifically, examples include adjusting the product of the stretch ratio in the MD direction and the stretch ratio in the TD direction (MD stretch ratio x TD stretch ratio) or the temperature during stretching to adjust the stress applied during the stretching process and appropriately set the degree of oriented crystallization. Another example is a method of storing the wrap film at a low temperature for a specified period of time.

Here, "low-temperature crystallization onset temperature" refers to the extrapolated onset temperature of the heat generation peak due to low-temperature crystallization in the temperature-heat flow curve of the irreversible component obtained by heating measurement using temperature-modulated DSC (the temperature at the intersection of the line extending the baseline on the low-temperature side to the high-temperature side in the heating measurement and the tangent drawn at the point where the slope of the curve on the low-temperature side of the crystallization peak is maximum).

An example of a method for measuring the low-temperature crystallization onset temperature is described below. First, a PerkinElmer differential scanning calorimeter (DSC) (power compensation type double furnace DSC 8500) is used to obtain a temperature-heat flow curve of the irreversible components in step scan measurement mode. The conditions for the step scan measurement are a measurement temperature of 0 to 180°C, a heating rate of 10°C/min, a heating step width of 4°C, and an isothermal time of 1 min. In the obtained temperature-heat flow curve, the extrapolated onset temperature of the heat generation peak caused by low-temperature crystallization is taken as the low-temperature crystallization onset temperature.

In temperature rise measurements using a differential scanning calorimeter, crystallization and crystalline melting occur in competition with each other. Therefore, in conventional DSC measurement methods, the heat flow resulting from the formation and growth of microcrystals and melting cancel each other out, making it difficult to study the thermal behavior of the microcrystals and to distinguish between conventional wrap films and the wrap film of this embodiment. On the other hand, when using step-scan measurement with temperature-modulated DSC, the heat flow can be separated into irreversible components such as crystallization and reversible components such as crystalline melting and glass transition, making it possible to evaluate the thermal behavior of the microcrystals. Therefore, in the measurement of the low-temperature crystallization onset temperature in this embodiment, step-scan measurement with temperature-modulated DSC is used.

<Pulsed NMR>
In the wrap film of this embodiment, the high mobility component ratio measured by pulse NMR is preferably 4.5% or less, more preferably 4.0% or less, and even more preferably 3.5% or less. The low mobility component ratio is preferably 65.0% or less, more preferably 63.0% or less, and preferably 61.0% or more. When the high mobility component ratio is in the above range, the frequency of cuts tends to be lower. When the low mobility component is in the above range, tear trouble is further suppressed.

Pulsed NMR differs from high-resolution NMR, which is widely used in determining the structure of organic compounds, in that it can measure the relaxation times of 1H nuclei related to the molecular motion within a system, and by utilizing its high quantitativeness, it is an analytical method that can determine the proportion of each motion component within a system.

In this embodiment, the 1H spin-spin relaxation time T2 is used to determine the molar fraction of Cs (low mobility component), Cm (intermediate component), and Cl (high mobility component) in the wrap film.

Specifically, the fitting is preferably performed using the linear least squares method so that the free induction decay (FID) signal obtained in measuring the 1H spin-spin relaxation time T2 approximately fits the following equation:

Where:
C _s : molar fraction of low mobility component, C _m : molar fraction of intermediate component, C _l : molar fraction of high mobility component, T _s : relaxation time of low mobility component, T _m : relaxation time of intermediate component, T _l : relaxation time of high mobility component.

[Oxygen gas barrier properties]
Generally, wrap films are required to have oxygen gas barrier properties to maintain freshness. The wrap film of this embodiment has an oxygen permeability at 23° C. of preferably 1 to 110 cm ³ /m ² ·day ·atm, more preferably 1 to 77 cm ³ /m ² ·day ·atm, and even more preferably 1 to 50 cm ³ /m ² ·day ·atm. By having an oxygen permeability within the above range, the oxygen gas barrier properties are further improved, and the freshness of food tends to be sufficiently maintained.

The oxygen permeability of the wrap film at 23°C can be measured by the method described in the Examples. Methods for controlling the oxygen permeability of the wrap film at 23°C to within the above range are not particularly limited, but examples include a method of setting the stretch ratio in the MD direction to 4.0 or less, preferably 3.8 or less, a method of setting the stretch ratio in the TD direction to 5.8 or more, a method of using a polymer with a low glass transition temperature, and a method of adding a nucleating agent as appropriate.

[Method for producing wrap film]
The method for producing the wrap film of this embodiment is not particularly limited, but examples include a method having a step of melt-extruding a composition containing a vinylidene chloride resin containing 72 to 93 mol % of vinylidene chloride repeating units and at least one compound selected from the group consisting of citrate esters, dibasic acid esters, and acetylated fatty acid glycerides to form a film, and a step of stretching the obtained film in the MD and TD directions. This will be described in detail below.

(Mixing process)
FIG. 1 shows a schematic diagram of an example of a manufacturing process for a wrap film. First, a vinylidene chloride resin, at least one compound selected from the group consisting of citrate esters, dibasic acid esters, and acetylated fatty acid glycerides, and, if necessary, epoxidized vegetable oil are mixed in a mixer to obtain a composition. At this time, various additives may be mixed as necessary. The mixer is not particularly limited, but for example, a ribbon blender or a Henschel mixer can be used. The obtained composition is preferably aged for about 1 to 30 hours before being used in the next step.

(Melt extrusion process)
Next, the obtained composition is melted by an extruder 1 and extruded from a die opening 3 of a die 2 into a tubular film to form a sock 4 (also called a pile).

(Cooling process)
A sock liquid 5 is poured into the inside of the sock 4, and the outside of the sock 4 is brought into contact with cold water in a cold water tank 6. This allows the sock 4 to be cooled from both the inside and outside, and the film constituting the sock 4 is solidified. The solidified sock 4 is folded by a first pinch roll 7 to form a parison 8.

(Stretching process)
Next, air is injected into the inside of the parison 8 to open the parison 8 and form a ring-shaped film. At this time, the sock liquid 5 applied to the part that contacts the inner surface of the sock 4 acts as an opening agent for the parison 8. Next, the parison 8 is reheated with hot water in the open state to a temperature suitable for stretching. The hot water adhering to the outside of the parison 8 is squeezed out by the second pinch roll 9.

Air is injected into the parison 8 that has been heated to the appropriate temperature as described above to form a bubble 10. This air pushes the parison open from the inside, stretching the film and producing a stretched film. The film is stretched mainly in the TD direction by the amount of air, and the film is stretched in the MD direction by applying tension in the film flow direction using the second pinch roll 9, the third pinch roll 11, etc.

The process from the first pinch roll 7 to the third pinch roll 11 is called the stretching process. Since slowing down the stretching speed improves the stretchability of the parison 8, in conventional wrap film manufacturing methods, the stretching speed in the MD direction is adjusted to 0.08 times/s or less, and the stretching speed in the TD direction is adjusted to 3.0 times/s or less. In contrast, in the wrap film manufacturing method of this embodiment, in which the crystallization onset temperature is controlled to 40 to 60°C, it is preferable to adjust the stretch ratios in the MD and TD directions and the stretching speeds in the MD and TD directions to within a specified range.

Specifically, the stretch ratios in the MD and TD directions in the stretching process of this embodiment are each independently preferably 1.5 to 3.5 times, more preferably 1.7 to 3.0. The area ratio in the stretching process of this embodiment is preferably 4.0 to 7.0 times, more preferably 5.0 to 6.0. Here, the stretch ratio in the MD direction refers to the stretch ratio when the parison 8 is stretched in the MD direction, and can be calculated, for example, in FIG. 1, by the ratio of the rotation speed of the third pinch roll 11 to the rotation speed of the first pinch roll 7. The stretch ratio in the TD direction refers to the stretch ratio when the parison 8 is stretched in the TD direction, and can be calculated, for example, in FIG. 1, by the ratio of the width of the double-ply film 12 to the width of the parison 8. The stretch ratio in the MD direction can be adjusted, for example, by the rotation speed ratio of the first pinch roll 7 and the third pinch roll 11, and the stretch ratio in the TD direction can be adjusted, for example, by the stretching temperature of the parison 8 or the size of the bubble 10.

The stretching speed in the MD direction in the stretching step of this embodiment is preferably 0.09 to 0.12 times/s. The average stretching speed in the MD direction refers to the stretching ratio in the MD direction relative to the time it takes for the parison to pass between the first pinch roll 7 and the third pinch roll 11. For example, in FIG. 1, it can be calculated from the rotation speed of the first pinch roll 7, the rotation speed of the third pinch roll 11, and the time it takes for the parison 8 to pass between the first pinch roll 7 and the third pinch roll 11. The stretching speed in the MD direction can be adjusted, for example, by the rotation speed of the first pinch roll 7 and the third pinch roll 11, or the distance between the first pinch roll 7 and the third pinch roll 11.

Furthermore, the stretching speed in the TD direction in the stretching process of this embodiment is preferably 3.1 to 4.0 times/s. The average stretching speed in the TD direction refers to the stretching ratio in the TD direction relative to the time required for the parison 8 to expand into the bubble 10, and in FIG. 1, for example, it can be calculated from the stretching length measured using still images of the parison 8 and the bubble 10, the time required for stretching in the TD direction calculated from the rotation speed of the third pinch roll 11, and the stretching ratio in the TD direction. The stretching speed in the TD direction can be adjusted, for example, by the rotation speed of the third pinch roll 11.

The stretching temperature is not particularly limited, but is preferably 30 to 45°C.

After the above stretching process, the stretched film is folded by the third pinch roll 11 to become the double-ply film 12. The double-ply film 12 is wound up by the winding roll 13.

(Relaxation process)
In the wrap film manufacturing method of this embodiment, it is preferable to have a relaxation step in which the wrap film is relaxed immediately after stretching. A relatively common relaxation method in wrap film manufacturing methods is to relax the film after stretching by using heat from an infrared heater or the like. However, in this embodiment, instead of this relaxation step, it is preferable to use a method in which the rotation speed of the take-up roll 13 is slower than that of the third pinch roll 11 to relax the stretched film. This is because, when a conventional relaxation method using heat is used in this embodiment, the heat causes the formation and growth of microcrystals that cause film tearing, and the crystallization onset temperature may exceed 60°C.

The relaxation ratio in the relaxation process using the third pinch roll 11 and the take-up roll 13 is preferably 7 to 15%, and more preferably 9 to 13%. A relaxation ratio of 15% or less tends to suppress the occurrence of wrinkles due to the occurrence of slack in the film between the third pinch roll 11 and the take-up roll 13. In addition, a relaxation ratio of 7% or more allows the wrap film to be sufficiently relaxed, suppressing the occurrence of rearrangement of molecular chains even when exposed to high temperatures, and allowing the low-temperature crystallization onset temperature to be 60°C or less. This also tends to reduce tearing problems. Here, the "relaxation ratio" refers to the ratio by which the double-ply film 12 is shrunk between the third pinch roll 11 and the take-up roll 13. For example, in the case of FIG. 1, it can be calculated using the ratio of the rotation speed of the take-up roll 13 to the rotation speed of the third pinch roll 11.

The atmospheric temperature during the relaxation process using the third pinch roll 11 and the take-up roll 13 is preferably 25 to 32°C. By keeping the atmospheric temperature within the above range, the formation and growth of microcrystals tends to be suppressed.

(Slitting process)
The wrap film wound up as described above is slit and wound up while peeling it off so as to become one sheet of wrap film, and is temporarily stored in the original roll state for 1 to 3 days. Finally, it is rewound from the original roll onto a paper tube and packed in a decorative box, thereby obtaining a wrap film roll stored in a decorative box.

(Storage process)
In the wrap film manufacturing method of this embodiment, after the wrap film is slit, a storage step may be carried out in which the wrap film is stored in its original roll state. The storage temperature is preferably 19° C. or lower, more preferably 5 to 19° C., and even more preferably 5 to 15° C. The storage time is preferably 20 to 50 hours, and more preferably 24 to 40 hours.

The atmospheric temperature during storage can suppress the formation and growth of microcrystals that lead to increased film tearing problems. In general, raw rolls are stored in locations that are relatively hot, such as adjacent to the wrap film manufacturing process or where the temperature is not controlled.

In contrast, in the wrap film manufacturing method of this embodiment, by keeping the ambient temperature during storage of the slit roll at 19°C or less, physical deterioration of the film due to molecular chain rearrangement tends to be suppressed. This tends to suppress the wrap film from easily tearing at the end cut by the cutting blade attached to the presentation box when pulling the wrap film out of the roll or when picking out the end of the film that has been rewound into the presentation box.

In addition, by keeping the ambient temperature at 5°C or higher during storage of the slit roll, the wrap film is sufficiently relaxed, and if it is exposed to temperatures of 20°C or higher during subsequent distribution and storage, rearrangement of the molecular chains tends to be less likely to occur.

Therefore, it is preferable to store the slit raw roll under the above-mentioned conditions, which results in a film in which the molecular chains in the amorphous portion are relaxed in orientation while suppressing the formation and growth of microcrystals. In this way, by relaxing the orientation of the molecular chains during storage of the raw roll, microcrystals are less likely to form and grow even when the film is exposed to high temperatures during distribution and storage, and tearing problems can be suppressed.

After storage, the slit roll is wound up, for example, on a paper tube, and stored as a roll 16 in a presentation box 1 equipped with a film cutting blade 15 as shown in FIG. 2. As shown in FIG. 2, the wrap film 17 is pulled out and used when it is to be used.

The present invention will be described in more detail below using examples and comparative examples. The present invention is not limited in any way by the following examples.

[Vinylidene chloride repeat unit content]
The vinylidene chloride repeating unit of the wrap film was measured using a high-resolution proton nuclear magnetic resonance measurement device. The reprecipitated filtrate of the wrap film was vacuum dried and dissolved in deuterated tetrahydrofuran to a concentration of 5% by mass, and the solution was subjected to H-NMR measurement at a measurement atmosphere temperature of about 27°C. For example, for a copolymer of vinylidene chloride and vinyl chloride, the content of the vinylidene chloride repeating unit was calculated using peaks of 3.50 to 4.20 ppm, 2.80 to 3.50 ppm, and 2.00 to 2.80 ppm of the copolymer based on tetramethylsilane. Note that for other copolymers, the content can also be calculated using the peaks of each monomer.

[Film thickness]
The thickness of the wrap film was measured using a dial gauge (manufactured by Techlock Corporation) in an atmosphere of 23° C. and 50% RH.

[Tear strength]
Assuming distribution of the wrap film after shipment and storage at home, the wrap film after production was stored in a thermostatic chamber set at 28° C. for one month, and then the tear strength was measured.
A light load tear tester D type (manufactured by Toyo Seiki) was used to measure the tear strength of the wrap film, and the tear strength was measured in an atmosphere of 23°C and 50% RH. The tear strength measurement of the wrap film was performed using only one piece of wrap film. At this time, the measurement range was appropriately selected so that it was 20 to 80% of the full scale. The sample length in the tear direction was 63.5 mm, and the sample width was 50.0 mm. During the measurement, the pendulum was lifted and stopped, and then the test piece was carefully attached to the gripping tool, and the clamp was tightly tightened so that the position where the slit was to be made was the center of the film width. Then, a slit was made in the film with a knife attached to the device. At this time, the blade position of the knife was adjusted so that the length of the cut in the film was 12.7 mm ± 0.5 mm. After making the slit, the pendulum was carefully released, and the value of the force required to tear the test piece was read. Tests in which the tear line deviated from the extension of the slit by more than 10 mm were excluded and additional specimens were tested instead, except in cases where the tear was along the line of the embossed pattern. The results were rounded to the nearest tenth.

[Tensile modulus]
Assuming distribution of the wrap film after shipment and storage at home, the wrap film after production was stored in a thermostatic chamber set at 28° C. for one month, and then the tensile modulus was measured.
The tensile modulus of the wrap film was measured using an autograph AG-IS (manufactured by Shimadzu Corporation) in an atmosphere of 23°C and 50% RH. The load at 2% elongation was measured under the conditions of a pulling speed of 5 mm/min, a chuck distance of 100 mm, and a film width of 10 mm, and then divided by the cross-sectional area of the measured sample and multiplied by 50 to measure the tensile modulus. During the measurement, the test piece was attached to the grip so that the MD direction of the test piece coincided with the axis of the testing machine. The test piece was evenly and firmly clamped with the grip to prevent slippage and to prevent the grip part from shifting during the test. In addition, the pressure between the grips must not cause cracking or rolling of the test piece. In addition, the measurement results were rounded off to the nearest 2 significant digits.

[Low temperature crystallization start temperature]
The measurement samples were prepared by storing wrap films in a thermostatic chamber set at 28°C for one month, assuming distribution of wrap films after shipment and storage at home. A PerkinElmer differential scanning calorimeter (DSC) (input compensation type double furnace DSC 8500) was used, and the step scan measurement mode (sample weight: 6 mg, sample pan material: aluminum, measurement temperature: 0 to 180°C, The following temperature conditions were used: heating rate: 10° C./min, heating step width: 4° C., isothermal time: 1 min. An empty aluminum sample pan was also measured under the same temperature conditions and used as a blank. In the irreversible component of the heat flow curve, the temperature at which heat generation due to low-temperature crystallization begins was taken as the low-temperature crystallization onset temperature.

[Pulsed NMR]
Assuming distribution of the wrap film after shipment and storage at home, the wrap film after production was stored for one month in a thermostatic chamber set at 28° C., and then pulse NMR of the wrap film was measured. 1 g of wrap film cut into an approximately square shape was folded and rolled into a cylindrical shape, packed into an NMR tube with a diameter of 10 mm, and measured using pulse NMR under the following conditions.
[conditions]
Apparatus: Bruker Biospin Minispec MQ20
Nuclide: 1H
Measurement: T2
Measurement method: Solid echo method Measurement temperature: 40°C (measured 5 minutes after reaching the set temperature)
Number of times of accumulation: 256 times Repeat time: 1.0 sec
Sample size: Approximately 1 g

The obtained free induction decay (FID) curve was separated into three components using the following formula, and the component ratio and relaxation time of each were calculated.
The component represented by a function that combines a Gaussian function and a sinc function in the first term of the equation below was defined as the low mobility component, the component represented by the Lorentz function in the second term of the equation below was defined as the intermediate component, and the component represented by the Lorentz function in the third term of the equation below was defined as the high mobility component.

_Cs : Molar fraction of low mobility component _Cm : Molar fraction of intermediate component _Cl : Molar fraction of high mobility component _Ts : Relaxation time of low mobility component _Tm : Relaxation time of intermediate component _Tl : Relaxation time of high mobility component

[Oxygen permeability]
The measurement method used was OX TRAN 2/21MH manufactured by MOCON Corporation, and ASTM D3985 was used as a reference. The oxygen permeability was measured under conditions of a temperature of 23°C and a relative humidity of 50% RH. At this time, the sample was set in the device so that the measurement area was 50 ^cm2 , and the value after 4 hours was adopted. The smaller the oxygen permeability value, the higher the oxygen barrier property.

[Effective in preventing cracking problems]
Assuming distribution of the wrap film after shipment and storage at home, the wrap film roll immediately after production was stored for one month in a thermostatic chamber set at 28° C. After that, in order to reproduce the vibration during distribution, the wrap film roll contained in a container (gift box) was vibrated using a vibration tester (manufactured by IDEXX Corporation, product number "BF-50UT"). The vibration test was performed as follows.

First, 60 roll containers were prepared, each containing a roll of the film produced in the examples and comparative examples, wound 20 m wide and 220 mm long on a paper tube 230 mm long and 36 mm in outer diameter, in a rectangular container (inner dimensions of the gift box: 42 mm x 42 mm x approximately 233 mm). The roll was placed in a cardboard box (inner dimensions 28 cm x 46 cm x 24 cm) to prevent gaps, and fixed to a vibration table with a belt so that the longitudinal direction of the roll was perpendicular to the vibration table. A vibration test was performed in an atmosphere of 23°C and a relative humidity of 50% RH. The vibration test was performed for 20 minutes using the transport packaging mode, with the frequency changed in the order of 5 Hz, 30 Hz, and 5 Hz over a period of 30 seconds. The amplitude was set so that the acceleration at 30 Hz was 3 G.

After that, tearing trouble evaluation was carried out in an atmosphere of 23°C and a relative humidity of 50% RH. 100 people who use food packaging wrap film on a daily basis were selected as evaluators. The evaluators pulled out 50 cm of the film from the roll of approximately 23 cm width housed in the container, and then cut it with a tin film cutting blade attached to the presentation box, performing the series of tasks 10 times each. In other words, the occurrence rate of film tearing trouble was derived from the number of times that the film could not be pulled out smoothly when pulling it out from the roll, out of a total of 1,000 times (100 people each tried 10 times).

(Evaluation criteria for crack trouble prevention effect)
A: 0% or more and less than 10%: Almost no tearing trouble, and very easy to use.
B: 10% or more but less than 15%: Little tearing trouble and excellent usability.
C: 15% or more: Many cracking problems, and poor usability.

[Maintaining freshness of contents]
The stem of one banana from Ecuador was sealed with plastic wrap to prevent it from coming into contact with the outside air, and then the whole banana was wrapped in a single layer of plastic wrap to prevent it from coming into contact with the outside air. The wrapped banana was placed in a constant temperature and humidity chamber at a temperature of 5°C and a humidity of 50%, and the number of days until it discolored was evaluated.
(Freshness retention evaluation criteria)
A: Discoloration in more than 10 days B: Discoloration in 7 to 10 days C: Discoloration in less than 7 days

[Texture (smooth feel)]
The feel of the wrap film (smoothness) was evaluated. 100 people who use food packaging wrap film on a daily basis were selected as evaluators, and the evaluation was performed by the evaluators' sensory evaluation. Each evaluator was given a score of 10, with 0 being a score for a sticky feel and 10 being a score for a smooth feel, and the average score of the 100 evaluators was calculated. This average score was used for the evaluation. The evaluation environment was an atmosphere of 23°C and a relative humidity of 50% RH.
[Evaluation criteria for texture (smoothness)]
A: 8 points or more: A very good level with no stickiness and a smooth feel.
B: 3 points or more and less than 8 points: Almost no stickiness, good level.
C: Less than 3 points: Slight stickiness is felt and it is somewhat uncomfortable.

[Example 1]
96.0 parts by mass of vinylidene chloride resin having a weight average molecular weight of 90,000 (vinylidene chloride repeating units: 82 mol%, vinyl chloride repeating units: 18 mol%), 2.9 parts by mass of acetyl tributyl citrate (Taoka Chemical Co., Ltd.), and 1.1 parts by mass of epoxidized soybean oil (Newsizer 510R, Nippon Oil & Fats Co., Ltd.) were mixed in a Henschel mixer for 5 minutes. After mixing, the mixture was aged for 24 hours or more to obtain a composition.

The resulting composition was fed to a melt extruder to melt it, and then melt extruded from an annular die attached to the tip of the extruder to form a sock. At this time, the heating conditions of the extruder were adjusted so that the molten resin temperature at the slit outlet of the annular die was 170°C, and the material was extruded in a circular shape at an extrusion rate of 10 kg/hr.

After cooling this with sock liquid and a cold water bath, the parison was opened to form a bubble, and inflation stretching was performed. At this time, the film was stretched 2.7 times in the MD direction and 2.0 times in the TD direction to form a tubular film (bubble). The stretching temperature was 25°C.

The obtained cylindrical film was nipped and folded flat, and then the film was relaxed in the MD direction by controlling the speed ratio of the pinch roll and the winding roll, and a two-ply film with a width of 280 mm was wound up. This film was slit to a width of 220 mm and rewound onto a paper tube with an outer diameter of 92 mm while peeling it into a single film. Then, 20 m of the film was wound onto a paper tube with an outer diameter of 36 mm and a length of 230 mm to obtain a roll of wrap film. Each evaluation was performed using the obtained roll of wrap film.

[Examples 2 to 4, Comparative Examples 1 to 3]
Wrap film rolls of Examples 2 to 4 and Comparative Examples 1 to 3 were obtained in the same manner as in Example 1, except for changing the conditions shown in Table 1. Each evaluation was carried out using the obtained wrap film rolls.

*ATBC: Acetyl tributyl citrate DALG: Diacetyl lauroyl glycerol ESO: Epoxidized soybean oil

The wrap film of the present invention has industrial applicability as a wrap film for food packaging, cooking, etc.

1...Extruder, 2...Die, 3...Die mouth, 4...Sock (tubular composition), 5...Sock liquid (release agent for inflation molding), 6...Cold water bath, 7...First pinch roll, 8...Parison, 9...Second pinch roll, 10...Bubble, 11...Third pinch roll, 12...Double-ply film, 13...Winding roll, 14...Decorative box, 15...Film cutting blade, 16...Wound body, 17...Wrapping film

Claims (6)

a vinylidene chloride resin containing 72 to 93 mol % of vinylidene chloride repeating units;
Contains citric acid esters ,
The content of the citric acid ester is 0.5% by mass or more and 2.0 % by mass or less based on the total amount of the wrap film,
The tensile modulus in the MD direction is 250 to 570 MPa,
The low-temperature crystallization onset temperature measured by a temperature modulated differential scanning calorimeter is 40 to 60°C,
The ratio of highly mobile components measured by pulsed NMR is 4.5% or less;
Plastic wrap.
(Here, the high mobility components and low mobility components measured by pulse NMR were measured by cutting 1 g of wrap film into an approximately square shape, folding it into a cylindrical shape, and packing it into an NMR tube with a diameter of 10 mm, and measuring it using pulse NMR under the following conditions:
[conditions]
Apparatus: Bruker Biospin Minispec MQ20
Nuclide: 1H
Measurement: T2
Measurement method: Solid echo method
Measurement temperature: 40°C (measured 5 minutes after reaching the set temperature)
Number of times accumulated: 256
Repeat time: 1.0 sec
Sample size: Approximately 1 g
The obtained free induction decay (FID) curve was separated into three components using the formula below, and the component ratio and relaxation time of each component were calculated. The component represented by a function that combines a Gaussian function and a sinc function in the first term of the formula below was defined as the low mobility component, the component represented by a Lorentz function in the second term of the formula below was defined as the intermediate component, and the component represented by a Lorentz function in the third term of the formula below was defined as the high mobility component.
C _s : Molar fraction of low mobility components
C _m : Molar fraction of intermediate component
C _l : Molar fraction of highly mobile components
T _s : Relaxation time of the low mobility component
T _m : Relaxation time of the intermediate component
T _l : relaxation time of the high mobility component
) The tear strength in the TD direction is 2.0 to 6.0 cN.
The wrap film according to claim 1. The thickness is 6 to 18 μm.
The wrap film according to claim 1 or 2. Contains epoxidized vegetable oil,
The content of the epoxidized vegetable oil is 0.5 to 3 mass% based on the total amount of the wrap film.
The wrap film according to any one of claims 1 to 3. The oxygen permeability at 23°C is 110 ^cm3 / ^m2 ·day·atm or less.
The wrap film according to any one of claims 1 to 4. The ratio of low mobility components measured by pulse NMR is 65.0% or less;
The wrap film according to any one of claims 1 to 5.