JP2024007578A - wrap film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wrap film which prevents bitterness from being transited to a rice ball when the rice ball is cooked by using the wrap film, and is also excellent in handleability at low temperature.

SOLUTION: A wrap film contains vinylidene chloride resin, and has a content of 40 ppm or more and 200 ppm or less in the wrap film of a specified compound.

SELECTED DRAWING: None

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a wrap film.

Vinylidene chloride resins have excellent properties such as transparency, water resistance, and gas barrier properties, and are therefore used as food packaging materials such as wrap films. In recent years, wrap films have been proposed as food packaging materials that not only have the above properties but also have improved properties such as adhesion. As such a wrap film, for example, Patent Document 1 describes a vinylidene chloride-based resin film containing a vinylidene chloride-vinyl chloride copolymer, in which the copolymer contains one structural unit derived from vinylidene chloride and Proposed is a wrap film made of a resin film in which the molar fraction of two consecutive moieties with one constitutional unit derived from vinyl chloride is 25.3 mol% or more and 26.5 mol% or less, based on all the constitutional units. has been done.

International Publication No. 2018/030040

In recent years, there has been a demand for food packaging materials to have even higher functionality by improving properties such as moldability and thermal stability. Examples of methods for making food packaging materials highly functional include adding additives such as plasticizers and heat stabilizers. As such an additive, acetylated tributyl citrate and the like are used.

By the way, it is common practice to use cling film to cook rice balls, sushi, and other rice balls. Specifically, for example, spread cling film, sprinkle salt on top, place cooked rice and ingredients on top of it, wrap it with cling film from all sides, and squeeze the plastic wrap to cook the rice ball. By using a cling film at this time, there is an advantage that it is hygienic because the rice balls are not touched directly.

However, with wrap films that contain additives to make them highly functional, for example, trace amounts of odor and bitter components contained in the wrap film ooze out from the wrap film and transfer to the cooked rice, causing the rice to deteriorate. It may affect the aroma and taste of the product.

The present invention has been made in view of the above-mentioned circumstances. For example, when a rice ball is cooked using a cling film, the bitterness does not transfer to the rice ball, and the present invention provides a cling film that has excellent handling properties at low temperatures. The purpose is to provide.

The present inventor conducted extensive studies to solve the above problems. As a result, the inventors have found that the above problems can be solved by controlling the amount of a specific compound within a specific range in a wrap film containing a vinylidene chloride resin, and have completed the present invention.

That is, the present invention is as follows.
[1]
A wrap film containing vinylidene chloride resin,
A wrap film in which the content of a compound represented by the following formula (1) in the wrap film is 40 ppm or more and 200 ppm or less.
(In formula (1), each R ₁ independently represents an alkyl group.)
[2]
The wrap film according to [1], wherein the content of the compound represented by the following formula (2) is 2% by mass or more and less than 8% by mass based on the total amount of the wrap film.
(In formula (2), each R ₂ independently represents an alkyl group.)
[3]
The wrap film according to [1] or [2], which has a thickness of 6 μm to 18 μm.

According to the present invention, for example, it is possible to provide a wrap film that does not transfer bitterness to the rice balls when the rice balls are cooked using the wrap film, and is also excellent in handleability at low temperatures.

It is a schematic diagram of an example of the manufacturing process of the wrap film of this invention.

Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail, but the present invention is not limited thereto, and various modifications can be made without departing from the gist thereof. It is.

In this embodiment, the "TD direction" refers to the width direction of the resin on the film forming line, and refers to the direction perpendicular to the direction in which the wrap film is pulled out from the roll when it is made into a wrap film. Moreover, "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 rolled body when it is made into a wrap film.

[Wrap film]
The wrap film of this embodiment contains a vinylidene chloride resin, and the content of the compound represented by the following formula (1) in the wrap film is 40 ppm or more and 200 ppm or less.
(In formula (1), each R ₁ independently represents an alkyl group.)
The wrap film of this embodiment has a content of the compound represented by the above formula (1) in the wrap film of 40 ppm or more and 200 ppm or less, so that, for example, when a rice ball is cooked using the wrap film, It does not transfer bitterness to the rice balls, and is also easy to handle at low temperatures.

(vinylidene chloride resin)
The vinylidene chloride resin used in this embodiment is not particularly limited, and examples include vinylidene chloride copolymers containing vinylidene chloride and a polymerizable monomer.

Monomers copolymerizable with vinylidene chloride are not particularly limited, but include, for example, vinyl chloride; acrylic esters such as methyl acrylate and butyl acrylate; methacrylic esters such as methyl methacrylate and butyl methacrylate; acrylic acid , methacrylic acid; acrylonitrile; vinyl acetate and the like. These monomers may be used alone or in combination of two or more. Among these, vinyl chloride is more preferred.

The content of vinylidene chloride is preferably 72 mol% to 93 mol%, more preferably 75 mol% to 87 mol%, and even more preferably 79 mol% to 85 mol%, based on the total amount of vinylidene chloride resin. When the content of vinylidene chloride is 72 mol % or more, the glass transition temperature of the vinylidene chloride resin is low, and the wrap film tends to be soft. As a result, tearing of the wrap film can be reduced even when the wrap film is used in a low-temperature environment such as in winter. On the other hand, when the content of vinylidene chloride is 93 mol% or less, a significant increase in crystallinity is suppressed, and deterioration of moldability during film stretching tends to be suppressed.

The method for measuring the content of vinylidene chloride is not particularly limited, but it can be measured using, for example, a high-resolution proton nuclear magnetic resonance measuring device (400 MHz or higher). More specifically, it can be measured by the method described in Examples below.

Further, in the vinylidene chloride resin, the content of monomers that can be polymerized with vinylidene chloride is preferably 7 to 28 mol%, more preferably 13 to 25 mol%, and even more preferably 15 to 21 mol%. . By having the content of vinylidene chloride and polymerizable monomers within the above range, tearing of the wrap film is reduced even when used in low-temperature environments, and deterioration of moldability during film stretching is further suppressed. There is a tendency to

The weight average molecular weight (Mw) of the vinylidene chloride resin is preferably 50,000 to 250,000, more preferably 60,000 to 230,000, and even more preferably 80,000 to 200,000. . When the weight average molecular weight (Mw) of the vinylidene chloride resin is 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 by, for example, 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 the vinylidene chloride resin is preferably 79% by mass to 96% by mass based on the total amount of the wrap film. When the content of the vinylidene chloride resin is within the above range, the plasticizing effect of additives and the like reduces the share of melt extrusion, so that the generation of foreign matter tends to be further suppressed. Furthermore, when the content of the vinylidene chloride resin is within the above range, it is possible to suppress the film from becoming easily stretched, and the cuttability of the film tends to be further improved. Note that the method for measuring the content of each component from the wrap film differs depending on the substance to be analyzed. For example, the content of vinylidene chloride resin can be determined by dissolving 0.5 g of a sample in 10 mL of THF (tetrahydrofuran), adding about 30 mL of methanol to precipitate the resin, and then separating the precipitate by centrifugation and drying it. It can be obtained by measuring weight.

(Additive)
The wrap film of this embodiment may contain various additives in addition to the above-mentioned vinylidene chloride resin. As described above, for example, by appropriately adjusting various additives, the vinylidene chloride resin is plasticized, thereby further improving moldability and texture.
Various additives will be explained in detail below.

The wrap film of this embodiment may contain a compound represented by the following formula (2).
(In formula (2), each R ₂ independently represents an alkyl group.)
The wrap film of this embodiment has a content of the compound represented by the above formula (2) in order to provide better molding processability and prevent excessive adhesion of the wrap film when containing a high amount of additives. is preferably 2% by mass or more and less than 8% by mass, more preferably 3.5% by mass to 7% by mass, based on the total amount of the wrap film.

In the above formula (2), R ₂ each independently represents an alkyl group, and the number of carbon atoms in the alkyl group is preferably 1 or more and 12 or less, more preferably 1 or more and 8 or less. Specific examples of the compound represented by the above formula (2) include, but are not limited to, triethyl acetyl citrate, tributyl acetyl citrate (ATBC), tri-n-(2-ethylhexyl) acetyl citrate, etc. Can be mentioned.

Among these, tributyl acetyl citrate is preferred. By using such a compound represented by the above formula (2), vinylidene chloride resin is plasticized, moldability is further improved, and adhesion is improved by imparting flexibility to the wrap film. In addition, the feel to the touch tends to be improved.

(Other additives)
The wrap film of the present embodiment may contain other additives, including, but not limited to, at least one compound selected from the group consisting of dibasic acid esters and acetylated fatty acid glycerides.

(Dibasic acid ester)
Dibasic acid esters include, but are not particularly limited to, adipate esters such as dibutyl adipate, di-n-hexyl adipate, di-2-ethylhexyl adipate, and dioctyl adipate; di-2-ethylhexyl azelaate. , azelaic acid esters such as octyl azelate; sebacic acid 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 a dibasic acid ester, the vinylidene chloride resin is plasticized, which improves its moldability, and by adding flexibility to the wrap film, it improves adhesion and improves the feel to the touch. It tends to improve further.

(Acetylated fatty acid glyceride)
Examples of acetylated fatty acid glycerides include, but are not limited to, acetylated caprylic acid glyceride, acetylated capric acid glyceride, acetylated lauric acid glyceride, acetylated myristic acid glyceride, acetylated palm kernel oil glyceride, and 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 glyceride includes acetylated monoglyceride of lauric acid, acetylated diglyceride of lauric acid (DALG: diacetyl lauroylglycerol), and acetylated triglyceride of lauric acid. Among these, acetylated lauric acid glyceride is preferred, and acetylated lauric acid diglyceride is more preferred. By using such acetylated fatty acid glycerides, flexibility is imparted to the wrap film, which not only improves adhesion but also tends to improve the feel to the touch.

The content of the compound represented by the above formula (2), dibasic acid ester, and acetylated fatty acid glyceride is determined by using a wrap film using an organic solvent such as acetone at a temperature 5 to 10 degrees Celsius lower than the boiling point of the extraction solvent. It can be obtained by extracting the additive from and analyzing it by gas chromatography. Examples of the extraction solvent include, but are not limited to, acetone, dichloromethane, methanol, ethanol, hexane, and the like. Among these, a solvent that dissolves each component well and does not cause a reaction is preferred. Among them, acetone is more suitable.

The total content of at least one compound selected from the group consisting of the compound represented by the above formula (2), dibasic acid ester, and acetylated fatty acid glyceride is such that the total content of at least one compound selected from the group consisting of the compound represented by formula (2) above, From the viewpoint of imparting properties and preventing excessive adhesion of the wrap film when containing a high additive content, the amount is preferably 2% by mass to 8% by mass, and more preferably 3.5% by mass to 7% by mass. In particular, when the vinylidene chloride resin wrap film contains 2% by mass or more of the compound represented by the above formula (2) or dibasic acid ester, the mobility of the molecular chains of the vinylidene chloride resin increases, so Rearrangements such as crystal formation and growth are likely to occur, and physical deterioration is likely to occur when exposed to high temperatures.Furthermore, the film stretches easily, making it difficult for the cutting blade to dig into the film, reducing cutting performance. Therefore, the effect of the configuration of the present invention is remarkable.

(Epoxidized vegetable oil)
The wrap film of this embodiment may contain epoxidized vegetable oil. Epoxidized vegetable oils can act as stabilizers for vinylidene chloride-based resin extrusion processing. Epoxidized vegetable oils are not particularly limited, but generally include those produced by epoxidizing edible fats and oils. Specifically, examples of epoxidized vegetable oils include, but are not limited to, 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 ease with which the film can be pulled out from the cosmetic case also tends to be improved.

The content of the epoxidized vegetable oil used in this embodiment is preferably 0.5% by mass to 3% by mass, more preferably 1% by mass to 2.5% by mass, based on the total amount of the wrap film. More preferably, it is 1% by mass to 2% by mass. When the content of the epoxidized vegetable oil is 0.5% by mass or more, changes in the quality of the wrap film tend to be further suppressed. Furthermore, when the content of the epoxidized vegetable oil is 3% by mass or less, the change in color tone of the wrap film is further suppressed, and stickiness due to bleeding tends to be suppressed. Note that the method for measuring the content of each component from the wrap film differs depending on the substance to be analyzed. For example, the content of epoxidized vegetable oil can be obtained by analyzing the reprecipitation filtrate of the wrap film by NMR.

Specifically, 50 mg of the sample was weighed, 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). It can be obtained by using the ratio of the integral value of 2.23 to 2.33 ppm to the integral value of 8.05 to 8.11 ppm as the integral ratio, and calculating the quantitative value using the absolute calibration curve method.
Integral ratio = integral value (2.23 to 2.33 ppm)/integral value (8.05 to 8.11 ppm)

The wrap film of this embodiment may contain additives other than those mentioned above. Such additives are not particularly limited, but include, for example, plasticizers other than those listed above, stabilizers other than those listed above, weather resistance improvers, colorants such as dyes or pigments, antifogging agents, antibacterial agents, lubricants, and cores. Examples include polymers such as methyl methacrylate-butadiene-styrene copolymer (MBS), oligomers such as polyester, and polymers such as methyl methacrylate-butadiene-styrene copolymer (MBS).

Stabilizers other than epoxidized vegetable oils are not particularly limited, but specific examples include 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 antioxidants such as 4,4'-thiobis-(6-tert-butylphenol); laurate, myristate, palmitate, stearate, isostearate, oleate. , ricinoleate, 2-ethyl-hexylate, isodecanoate, neodecanoate, and calcium benzoate. The stabilizers may be used alone or in combination of two or more.

The weather resistance improver is not particularly limited, but specifically, for example, ethylene-2-cyano-3,3'-diphenylacrylate, 2-(2'-hydroxy-5'-methylphenyl)benzolitriazole , 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)5-chlorobenzotriazole, 2-hydroxy-4-methoxybenzophenone, and 2,2'-dihydroxy-4-methoxybenzophenone, etc. can be mentioned. The weather resistance improvers may be used alone or in combination of two or more.

Coloring agents such as dyes or pigments are not particularly limited, but specific examples include carbon black, phthalocyanine, quinacridone, indoline, azo pigments, and red iron. The coloring agents may be used alone or in combination of two or more.

The antifogging agent is not particularly limited, but specific examples include glycerin fatty acid ester, sorbitan fatty acid ester, polyoxyethylene fatty acid alcohol ether, polyoxyethylene glycerin fatty acid ester, and polyoxyethylene sorbitan fatty acid ester. It will be done. The antifogging agents may be used alone or in combination of two or more.

The antibacterial agent is 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.

The lubricant is not particularly limited, but specific examples include fatty acid hydrocarbon lubricants such as ethylene bissteramide, butyl stearate, polyethylene wax, paraffin wax, carnauba wax, myristyl myristate, and stearyl stearate, and high-grade lubricants. Examples include 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.

Although the nucleating agent is not particularly limited, specific examples thereof include phosphate metal salts and the like. Nucleating agents may be used alone or in combination of two or more.

(thickness of wrap film)
The thickness of the wrap film of this embodiment is preferably 6 μm to 18 μm, more preferably 9 μm to 12 μm. When the thickness of the wrap film is within the above range, the trouble of film breakage is suppressed, the cuttability is further improved, and the adhesion is further improved.

More specifically, when the thickness of the wrap film is 6 μm or more, the tear strength of the wrap film in the TD direction and the MD direction is further improved, and film breakage during use tends to be further suppressed. Further, when the thickness of the wrap film is 6 μm or more, there is a tendency that the tear strength does not significantly decrease. Therefore, when pulling out the wrap film from the rolled body or picking out the end of the film that has been rewound into the gift box, the problem of the wrap film tearing from the edge cut by the cutting blade attached to the gift box is more likely. suppressed.

On the other hand, when the thickness of the wrap film is 18 μm or less, the force required to cut the wrap film with the cutting blade attached to the gift box can be reduced, and the cutting performance tends to be further improved. Furthermore, when the thickness of the wrap film is 18 μm or less, the wrap film tends to fit the shape of the container more easily, and its adhesion to the container tends to be further improved.

(tear strength)
The tear strength in the TD direction of the wrap film of this embodiment is preferably 2.0 cN to 6.0 cN, more preferably 2.0 cN to 4.0 cN, and still more preferably 2.2 cN to 3.0 cN. be. When the tear strength in the TD direction is 2.0 cN or more, it is possible to reduce tearing particularly when the wrap film is pulled out from the wound body, and it is also possible to suppress unintended tearing troubles when the wrap film is used. On the other hand, when the tear strength in the TD direction is 6.0 cN or less, the film is easily torn when cut in the TD direction with a cutting blade attached to the presentation box, and the cutting performance is improved.

The tear strength in the TD direction of the wrap film of this embodiment can be adjusted by the composition of the vinylidene chloride resin, the additive composition, the stretching ratio of the film, the stretching speed, the thickness of the film, etc. Although not particularly limited, for example, the tear strength in the TD direction tends to be improved by lowering the stretching ratio in the TD direction or increasing the thickness of the wrap film; It tends to decrease by making it thinner.

In the wrap film of this embodiment, the content of the compound represented by the following formula (1) in the wrap film is 40 ppm or more and 200 ppm or less.
(In formula (1), each R ₁ independently represents an alkyl group.)
The wrap film of this embodiment has a content of the compound represented by the above formula (1) in the wrap film of 40 ppm or more and 200 ppm or less. This has the effect of not transferring odor or bitterness to the rice balls.

In the above formula (1), each R ₁ independently represents an alkyl group, and the number of carbon atoms in the alkyl group is preferably 1 or more and 12 or less, more preferably 1 or more and 8 or less. Specific examples of the compound represented by the above formula (1) include, but are not limited to, trimethyl citrate, triethyl citrate, tripropyl citrate, and tributyl citrate.

In the wrap film of the present embodiment, the content of the compound represented by the above formula (1) in the wrap film is 40 ppm or more, preferably 45 ppm or more, more preferably 50 ppm or more, and 60 ppm or more. It is more preferable that it is above. The compound represented by the above formula (1) is preferable because it has a high plasticizing effect on vinylidene chloride resin at low temperatures and is easy to use at low temperatures when added to a wrap film.

In the wrap film of this embodiment, the content of the compound represented by the above formula (1) in the wrap film is 200 ppm or less, preferably 160 ppm or less, more preferably 150 ppm or less, and 120 ppm or less. It is more preferable that it is the following. As a result, when the rice balls are cooked using the cling film, odor and bitterness are not transferred to the rice balls, which is preferable.
Although the mechanism by which this effect is produced is not clear, the inventor estimates it as follows. When bitterness components were studied, it was found that the compound represented by the above formula (1) in particular produces a strong bitterness even in small amounts. Therefore, after careful consideration, we found that by reducing the compound represented by the above formula (1) contained in the cling film to a certain extent, bitterness would not transfer to the rice balls when the rice balls were cooked using the cling film. There was found.

The method for adjusting the content of the compound represented by the above formula (1) in the wrap film is not particularly limited, but for example, the compound represented by the above formula (1) contained in the wrap film is Considering that the compound represented by the above formula (2) used as an agent is generated by decomposition, there are ways to adjust the amount of the compound represented by the above formula (2), and methods for adjusting the amount of the compound represented by the above formula (2). Examples include a method of producing a wrap film under conditions that do not decompose the compound.
Examples include a method in which the compound represented by the above formula (2) is used after being purified, and a method in which metal impurities contained in the additive are removed.
Other examples include a method of reducing the temperature in the melt extrusion step, which will be described later.

The content of the compound represented by the above formula (1) can be determined by extracting the additive from the wrap film using an organic solvent such as acetone at a temperature 5 to 10 degrees Celsius lower than the boiling point of the extraction solvent, and then performing gas chromatography analysis. You can get it. Specifically, it can be measured by the method described in Examples below. Examples of the extraction solvent include, but are not limited to, acetone, dichloromethane, methanol, ethanol, hexane, and the like. Among these, preferred are solvents that dissolve each component well and do not cause any reaction. Among them, acetone is more suitable.

[Method for manufacturing wrap film]
The method for producing the wrap film of the present embodiment is not particularly limited, but for example, a composition containing a vinylidene chloride resin containing 72 mol% to 93 mol% of vinylidene chloride and various additives is melt-extruded to form a film. The method includes a step of stretching the obtained film in the MD direction and the TD direction. The details will be explained below.

(Mixing process)
FIG. 1 shows a schematic diagram of an example of a process for manufacturing a wrap film. First, a composition is obtained by mixing vinylidene chloride resin and various additives using a mixer. At this time, various additives may be mixed as necessary. The mixer is not particularly limited, and for example, a ribbon blender, Henschel mixer, or the like 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 a tubular film is extruded from a die opening 3 of a die 2 to form a sock 4 (also called pile).
Here, the melt extrusion temperature is preferably 165°C to 175°C. By setting the melt extrusion temperature to a low temperature within the above range, the content of the compound represented by the above formula (1) in the wrap film tends to be reduced. In order to adjust the content of the compound represented by the above formula (1) in the wrap film to the above-mentioned predetermined range, the amount of the compound represented by the above formula (2) to be added is adjusted as described above. It is effective to perform a method of adjusting the melt extrusion temperature to the above range in addition to a method of purifying the compound represented by the above formula (2) and a method of removing metal impurities contained in the additive. It is.

(cooling process)
A sock liquid 5 is injected 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. As a result, the sock 4 is cooled from both the inside and the outside, and the film forming the sock 4 is solidified. The solidified sock 4 is folded by a first pinch roll 7 to form a parison 8.

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

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

The process from the first pinch roll 7 to the third pinch roll 11 is called a stretching process. Since the stretchability of parison 8 improves when the stretching speed is lowered, in the conventional wrap film manufacturing method, the stretching speed in the MD direction is adjusted to 0.08 times/second or less, and the stretching speed in the TD direction is adjusted to 3. It was adjusted to 0 times/second or less. On the other hand, in the wrap film manufacturing method of the present embodiment, it is preferable to adjust the stretching ratio in the MD direction and the TD direction and the stretching speed in the MD direction and the TD direction to be within a predetermined range.

Specifically, the stretching ratios in the MD direction and the TD direction in the stretching process used in this embodiment are each independently preferably 4 times to 6 times, more preferably 4.1 times to 5.6 times. It is. Here, the stretching ratio in the MD direction refers to the stretching ratio at which the parison 8 is stretched in the MD direction. For example, in FIG. It can be calculated. The stretching ratio in the TD direction refers to the stretching ratio when the parison 8 is stretched in the TD direction, and for example, in FIG. 1, it can be calculated by the ratio of the width of the double-ply film 12 to the width of the parison 8. Can be done. The stretching ratio in the MD direction can be adjusted, for example, by the rotational speed ratio of the first pinch roll 7 and the third pinch roll 11, and the stretching ratio in the TD direction can be adjusted, for example, by adjusting the stretching temperature of the parison 8 and the size of the bubbles 10. It can be adjusted with

Further, the stretching speed in the MD direction in the stretching step used in this embodiment is preferably 0.09 times/second to 0.12 times/second. The average stretching speed in the MD direction refers to the stretching ratio in the MD direction relative to the time the parison passes between the first pinch roll 7 and the third pinch roll 11. For example, in FIG. It can be calculated based on the rotation speed, the rotation speed of the third pinch roll 11, and the time required 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 by, for example, the rotational 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.

Further, the stretching speed in the TD direction in the stretching step used in this embodiment is preferably 3.1 times/second to 4.0 times/second. 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 to the bubble 10. For example, in FIG. 1, it was measured using a still image of the parison 8 and the bubble 10. It can be calculated from the time required for stretching in the TD direction calculated from the stretching length and the rotational 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 by, for example, the rotation speed of the third pinch roll 11.

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

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

(Relaxation process)
In the method for producing a wrap film of the present embodiment, it is preferable to include a relaxing step of relaxing the wrap film immediately after stretching. A relatively common relaxation method used in the production of wrap films is to relax the film using heat from an infrared heater or the like after stretching. However, in the present embodiment, instead of this relaxing step, it is preferable to use a method of relaxing the stretched film by lowering the rotational speed of the take-up roll 13 than the third pinch roll 11. This is because, in this embodiment, when a conventional relaxation method using heat is used, there is a risk that the heat may cause the formation and growth of microcrystals that cause film tearing.

The relaxation ratio in the relaxation process using the third pinch roll 11 and the take-up roll 13 is preferably 7% to 15%, more preferably 9% to 13%. When the relaxation ratio is 15% or less, 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 tends to be more suppressed. Further, by having a relaxation ratio of 7% or more, the wrap film can be sufficiently relaxed, and molecular chain rearrangement can occur even when exposed to high temperatures. This also tends to reduce tearing problems. Here, the "relaxation ratio" refers to the ratio at which the double-ply film 12 is contracted between the third pinch roll 11 and the take-up roll 13. For example, in the case of FIG. It can be calculated using the ratio of the take-up roll 13.

Further, the ambient temperature in the relaxation process using the third pinch roll 11 and the take-up roll 13 is preferably 25°C to 32°C. When the ambient temperature is 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 being peeled off into a single wrap film, and is temporarily stored in the original form for 1 to 3 days. Finally, the raw material is rewound onto a paper tube and packed into a gift box, thereby obtaining a wrap film roll housed in a gift box.

(Storage process)
In the method for manufacturing a wrap film according to the present embodiment, after the wrap film is slit, a storage step may be performed in which the wrap film is stored in its original form. The storage temperature is preferably 19°C or lower, more preferably 5°C to 19°C, even more preferably 5°C to 15°C. Further, the storage time is preferably 20 hours to 50 hours, more preferably 24 hours to 40 hours.

Hereinafter, the present invention will be explained in more detail using Examples and Comparative Examples. Note that the present invention is not limited in any way by the following examples.

[Content of vinylidene chloride]
The content of vinylidene chloride-derived structural units and vinyl chloride-derived structural units was measured as follows using a high-resolution proton nuclear magnetic resonance (hereinafter also referred to as "H-NMR") measuring device (integrated number of times: 512 times). The reprecipitated filtrate of the wrap film was vacuum-dried, and a solution dissolved in deuterated tetrahydrofuran to a concentration of 5% by mass was subjected to H-NMR measurement in a measurement atmosphere of 23±2° C. and 50±10% RH.
For example, the constitutional unit derived from vinylidene chloride (-CH ₂ --CCl ₂ --) is denoted as A, and the constitutional unit derived from vinyl chloride (-CH ₂ --CHCl-) is denoted as B, and the signals 1 and 2 obtained on the spectrum are , and 3 were assigned as follows.
- Signal 1 (approximately 5.2 to 4.5 ppm) was assigned to the CH signal of B (methine (CH) group, a constitutional unit derived from vinyl chloride).
- Signal 2 (approximately 4.2 to 3.8 ppm) was assigned to the CH ₂ signal (methylene (CH ₂ ) group of the structural unit derived from vinylidene chloride) of one A of AA.
- Signal 3 (approximately 3.5 to 2.8 ppm) was assigned to the CH ₂ signal (methylene (CH ₂ ) group of the constitutional unit derived from vinylidene chloride) of A of both AB and BA.

The mole fraction of the constituent units was determined from the spectral area values of these signals (the area of the signals in the NMR spectrum). In addition, each mole fraction is expressed as follows.
・Mole fraction of A (mol%): P(A)
・Mole fraction of B (mol%): P(B)

From the area values (areas of peaks in the NMR spectrum) of signals 1, 2, and 3 assigned as described above, the integral values of the signals on the spectrum were assigned as follows.
・The integral value of signal 1 (approximately 5.2 to 4.5 ppm) is equal to one 1H of B ・The integral value of signal 2 (approximately 4.2 to 3.8 ppm) is equal to two 1H of A ・Signal 3 (approximately 3 .5 to 2.8 ppm) for 1H4 pieces of A

Each mole fraction was calculated using the formula below.
・P(A) + P(B) = 100

P(A) and P(B) were determined using the following equations.
・P(B):P(A) = Integral value of signal 1: (integral value of signal 2 + integral value of signal 3/2)/2
・P(A)=100-P(B)

The molecular weight of A, which is a vinylidene chloride-derived structural unit (-CH ₂ -CCl ₂ -), is 97.0, and the molecular weight of B, which is a vinyl chloride-derived structural unit (-CH ₂ -CHCl-), is 62.5. , each mass fraction was calculated using the following formula. In addition, each mass fraction is expressed as follows.
・Mass fraction of A (mass%): Q (A)
・Mass fraction of B (mass%): Q (B)
・Q(A) =
(P(A) × 97.0) /
(P(A) × 97.0 + P(B) × 62.5) × 100
・Q(B) = 100 - Q(A)

[Weight average molecular weight (Mw) of vinylidene chloride resin]
The weight average molecular weight (Mw) of the vinylidene chloride resin was determined by gel permeation chromatography (GPC method) using a standard polystyrene calibration curve.

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

[Bitterness measurement]
A taste recognition device TS-5000Z (manufactured by Intelligent Sensor Technology) was used to measure bitterness. Bitter taste was measured as follows at room temperature (23° C.) using taste sensors CA0, C00, AE1, AAE, CT0 (manufactured by Intelligent Sensor Technology).
Wrap films prepared in Examples and Comparative Examples described below were cut into 220 mm x 220 mm squares, and the measurement specimens were wrapped. Porridge (manufactured by GreenMind/for use over 12 months) was used as the measurement sample. A sample was prepared by wrapping 80 g of porridge in a plate shape of 8 cm x 7 cm with cling film. The obtained sample was frozen in a household freezer for 24 hours, and then thawed by heating in a microwave oven (Mitsubishi Electric Home Equipment Co., Ltd./R0-S5A) at 500 W for 1 minute and 50 seconds. For the blank, porridge that had been frozen and thawed in a heat-resistant container in the same manner as above was used. The sample after thawing was homogenized, 5 times the volume of 3 times diluted standard solution was added, and the mixture was stirred for 1 minute using a food mill. After stirring, the solution was filtered through a filter paper and used as a test solution. The reference solution used was a 0.3 mmol/L tartaric acid solution containing 30 mmol/L potassium chloride.
The potential measured by each taste sensor in the reference solution was set as zero, and the difference from the potential measured in the test solution was defined as the taste. Thereafter, each taste sensor was washed with a reference solution, and the potential when the reference solution was measured again was used as the aftertaste. Compare the measured values of each test solution and the blank, and if the difference in potential output value of the taste sensor exceeds 1, it is determined that there is a difference in taste, and if the difference is 1 or less, there is a difference in taste. It was determined that there was no bitterness (no bitterness transferred).

[Evaluation of ease of handling at low temperatures]
The handling properties of the wrap film at low temperatures were evaluated using the following procedure.
Wrap films prepared in Examples and Comparative Examples described below were cut into 220 mm x 220 mm squares, and the measurement specimens were wrapped.
White rice was used as the measurement sample. A sample was prepared by wrapping 150 g of white rice into a plate of 8 cm x 7 cm with cling film. Ten samples of this type were produced. The produced sample was frozen in a household freezer (-18°C) for 24 hours, then taken out from the freezer, the film was opened immediately, and the handleability of the wrap film at low temperatures was evaluated using the following criteria. In addition, "smooth opening" here means that the wrap film does not tear or crack when opened, that the wrap film maintains a suitable hardness even at low temperatures, and that no excessive force is applied. It is still possible to open the package.
(Evaluation criteria)
◎: 8 to 10 samples could be opened smoothly.
○: 4 to 7 samples could be opened smoothly.
Δ: The number of samples that could be opened smoothly was 3 or less.

[Measurement of content of compound represented by formula (1)]
The content (ppm) of the compound represented by the following formula (1) in the wrap film can be determined by extracting the additive from the wrap film using acetone at a temperature 5 to 10°C lower than the boiling point of the extraction solvent, and then extracting the additive from the wrap film using acetone. It was determined by chromatographic analysis.
(In formula (1), each R ₁ independently represents an alkyl group.)

[Example 1]
Tributyl acetyl citrate is added to 93.4% by mass of a vinylidene chloride resin having a weight average molecular weight of 120,000 (85 mol% vinylidene chloride repeating units, 15 mol% vinyl chloride repeating units) as a compound represented by formula (2). (Taoka Chemical Industry Co., Ltd.) 5.5% by mass and epoxidized soybean oil (Newsizer 510R, Nippon Oil & Fats Co., Ltd.) 1.1% by mass were mixed for 5 minutes in a Henschel mixer. At that time, tributyl acetyl citrate was purified by column chromatography and then mixed. After mixing, the mixture was aged for 24 hours or more to obtain a composition.

The resulting composition was fed into a melt extruder and melted, and melt extruded through an annular die attached to the tip of the extruder to form a sock (tubular film). At this time, the heating conditions of the extruder were adjusted so that the molten resin temperature (melt extrusion temperature) at the slit exit of the annular die was 168° C., and extrusion was performed annularly at an extrusion rate of 10 kg/hour.

After cooling the sock in a sock solution and a cold water bath, the parison was opened to form a bubble and inflation stretching was performed. At this time, the MD direction was stretched 4.1 times and the TD direction was stretched 5.6 times to form a cylindrical film (bubble). Note that the stretching temperature was 35°C.

After the obtained cylindrical film is nipped and folded flat, the film is relaxed in the MD direction (relaxation ratio 10%) by controlling the speed ratio of the pinch roll and take-up roll, and the width of the double-ply film is 280 mm. Two layers of film were wound up. This film was slit into a width of 220 mm, and while being peeled off into a single film, it was re-wound onto a paper tube with an outer diameter of 92 mm. Thereafter, it was wound up for 20 m around a paper tube having an outer diameter of 36 mm and a length of 230 mm to obtain a rolled body of wrap film (thickness: 10 μm). The obtained wrap film roll was stored at 15° C. for 30 hours, and was used for each evaluation according to the above method. The evaluation results are shown in Table 1.

[Example 2]
A roll of wrap film was prepared in the same manner as in Example 1, except that the tributyl acetyl citrate used was not purified, and each evaluation was performed by the above method. The evaluation results are shown in Table 1.
[Examples 3 and 4 and Comparative Examples 1 and 2]
A roll of wrap film was prepared in the same manner as in Example 1, except that the type and amount of the additive and the melt extrusion temperature of the film were changed as shown in Table 1, and each evaluation was performed by the above method. The evaluation results are shown in Table 1.

The cling film of the present invention has the advantage that, for example, when a rice ball is cooked using the cling film, bitterness does not transfer to the rice ball, and it is easy to handle at low temperatures. It can also be effectively used as an excellent wrapping film.

1 Extruder 2 Die 3 Die port 4 Sock (tubular film)
5 Sock liquid (release agent for inflation molding)
6 Cold water tank 7 First pinch roll 8 Parison 9 Second pinch roll 10 Bubble 11 Third pinch roll 12 Double ply film 13 Take-up roll

Claims (3)

A wrap film containing vinylidene chloride resin,
A wrap film in which the content of a compound represented by the following formula (1) in the wrap film is 40 ppm or more and 200 ppm or less.
(In formula (1), each R ₁ independently represents an alkyl group.) The wrap film according to claim 1, wherein the content of the compound represented by the following formula (2) is 2% by mass or more and less than 8% by mass based on the total amount of the wrap film.
(In formula (2), each R ₂ independently represents an alkyl group.) The wrap film according to claim 1 or 2, having a thickness of 6 μm to 18 μm.