CN112745605A

CN112745605A - Fresh-keeping film

Info

Publication number: CN112745605A
Application number: CN202011178912.XA
Authority: CN
Inventors: 河村笃志; 田中达夫
Original assignee: Asahi Kasei Corp
Current assignee: Asahi Kasei Corp; Asahi Chemical Industry Co Ltd
Priority date: 2019-10-31
Filing date: 2020-10-29
Publication date: 2021-05-04
Also published as: JP2021075338A

Abstract

The invention relates to a preservative film, and aims to provide a preservative film which is prevented from cracking, excellent in oxygen barrier property and excellent in hand touch. A cling film, comprising: a vinylidene chloride resin containing 72 to 93 mass% of vinylidene chloride; and at least one compound selected from the group consisting of citric acid esters, dibasic acid esters and acetylated fatty acid glycerides, wherein the content of the compound is 0.5% by mass or more and less than 3% by mass relative to the total amount of the wrap film, the tensile elastic modulus in the MD direction is 250 to 570MPa, and the low-temperature crystallization initiation temperature measured by a temperature-modulated differential scanning calorimeter is 40 to 60 ℃.

Description

Fresh-keeping film

Technical Field

The invention relates to a preservative film.

Background

A wrap film made of a vinylidene chloride resin is excellent in oxygen barrier property, water vapor barrier property (moisture barrier property) and transparency, and can be heated in a microwave oven, and therefore, is widely used for packaging of fresh fish, raw meat, processed meat, fresh vegetables, non-staple food, and the like for the purpose of oxygen barrier property, moisture barrier property, and the like.

In particular, in recent years, from the viewpoints of antioxidation of fat and oil components, preservation of active ingredients such as vitamins, and prevention of putrefaction due to propagation of mold, fungus, or yeast, etc., it has been strongly required that a wrap film has oxygen barrier properties (for example, see patent document 1).

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2019-43677

Disclosure of Invention

Problems to be solved by the invention

In addition, when the vinylidene chloride resin is retained in the extruder for a certain period of time during melt extrusion, the vinylidene chloride resin is decomposed and carbonized, and carbide becomes an impurity. Even when impurities are generated in melt extrusion, depending on the degree of the impurities, a wrap film can be normally produced without causing perforation in film formation by inflation. However, in such a case, it is considered that a crack failure is generated starting from the impurities.

Therefore, the vinylidene chloride resin is added with various additives in view of extrusion processability of the film, crystallinity, transparency, softening temperature and the like, and is usually added with a plasticizer in view of extrusion processability of the film in particular. However, it has been found that the oxygen barrier property and the hand feeling are rather lowered depending on the kind and amount of the plasticizer used.

The present invention has been made to solve the above problems, and an object thereof is to provide a wrap film which is suppressed in cracking failure, excellent in oxygen barrier properties, and also excellent in hand touch.

Means for solving the problems

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

Namely, the present invention is as follows.

[1]

A cling film, comprising:

a vinylidene chloride resin containing 72 to 93 mass% of vinylidene chloride; and

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 mass% or more and less than 3 mass% relative to the total amount of the wrap film,

a tensile elastic modulus in the MD direction of 250 to 570MPa,

the low-temperature crystallization starting temperature measured by a temperature modulation type differential scanning calorimeter is 40-60 ℃.

[2]

The wrap film according to [1], wherein the tear strength in the TD direction is 2.0 to 6.0 cN.

[3]

The wrap film as recited in the item [1] or [2], wherein the thickness is 6 to 18 μm.

[4]

The wrap film according to any one of [1] to [3],

comprises an epoxidized vegetable oil and a process for producing the epoxidized vegetable oil,

the content of the epoxidized vegetable oil is 0.5 to 3 mass% relative to the total amount of the preservative film.

[5]

Such as [1]]～[4]The wrap film according to any one of the above items, wherein an oxygen transmission rate at 23 ℃ is 110cm³/m²Day atm or less.

[6]

The wrap film according to any one of [1] to [5], wherein a ratio of the high motility component measured by pulse NMR is 4.5% or less.

[7]

The wrap film according to any one of [1] to [6], wherein a ratio of the low motility component measured by pulse NMR is 65.0% or less.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a wrap film can be provided which has suppressed cracking failure, excellent oxygen barrier properties, and excellent hand feel.

Drawings

Fig. 1 is a schematic view of an apparatus used in the film-forming process of the present invention.

FIG. 2 shows an example of an application form of the film of the present invention.

Description of the symbols

1 … extruder, 2 … die, 3 … die, 4 … soaking part (tubular composition), 5 … soaking liquid (stripping agent for inflation molding), 6 … cold water tank, 7 … first pinch roll 1, 8 … parison, 9 … second pinch roll 2, 10 … bubble, 11 …

third pinch roll

3, 12 … double-layer film, 13 … take-up roll, 14 … packaging box, 15 … film cutting blade, 16 … winding body, 17 … preservative film

Detailed Description

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.

In the present embodiment, the "TD direction" refers to the width direction of the resin in the film-forming line, and refers to a direction perpendicular to the direction in which the wrap is taken out from the roll after the wrap is produced. The "MD direction" refers to the flow direction of the resin in the film-forming line, and refers to the direction in which the wrap is drawn from the roll when the wrap is formed.

[ preservative film ]

The wrap film of the present embodiment contains a vinylidene chloride resin (containing 72 to 93 mass% of vinylidene chloride) and at least one compound selected from the group consisting of citric acid esters, dibasic acid esters and acetylated fatty acid glycerides, wherein the content of the compound is 0.5 mass% or more and less than 3 mass% with respect to the total amount of the wrap film, the tensile elastic modulus in the MD direction is 250 to 570MPa, and the low-temperature crystallization initiation temperature measured by a temperature modulation differential scanning calorimeter is 40 to 60 ℃.

In the present embodiment, 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-described predetermined structure is 0.5 mass% or more and less than 3 mass%, whereby an effect of exhibiting a sufficient oxygen barrier property can be exhibited. In addition, the wrap film of the present embodiment exhibits the effect of suppressing cracking failure and also exhibiting excellent hand touch feeling.

The reason why the cracking failure is suppressed and the oxygen barrier property is further improved by adjusting the content of the above-mentioned compound is not clear, and the following is considered. That is, in melt extrusion, the resin is retained in the extruder for a certain period of time, and by adjusting the content of the above compound, the low-mobility component of the vinylidene chloride resin is increased, thereby further improving the oxygen barrier property. Further, by adjusting the content of the above compound, the hand feeling is also excellent. The reason is not limited to this, but is an estimation reason. 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 thereof include vinylidene chloride copolymers containing monomers polymerizable with vinylidene chloride.

The monomer copolymerizable with the vinylidene chloride monomer is not particularly limited, and examples thereof include vinyl chloride; acrylic 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, and the like. These monomers may be used alone or in combination of two or more. Among them, vinyl chloride is more preferable.

The vinylidene chloride content is 72 to 93 mass%, preferably 80 to 93 mass%, more preferably 82 to 93 mass% with respect to the total amount of the vinylidene chloride resin. When the vinylidene chloride content is 72% by mass or more, the glass transition temperature of the vinylidene chloride resin tends to be low and the wrap film tends to be soft. This can reduce the cracking of the wrap film even when used in a low-temperature environment, for example. On the other hand, when the vinylidene chloride content is 93% by mass or less, a large increase in crystallinity and deterioration in moldability at the time of film stretching tend to be suppressed.

The vinylidene chloride content can be measured, for example, using a high-resolution proton nuclear magnetic resonance measuring apparatus (400MHz or more), but is not particularly limited. More specifically, 0.5g of the wrap film was dissolved in 10ml of Tetrahydrofuran (THF), about 30ml of methanol was added to precipitate a resin component, and then the precipitate was separated by centrifugation and dried under vacuum to obtain a sample for measurement of a vinylidene chloride resin. The obtained sample for measurement was then dissolved in deuterated tetrahydrofuran at 5 mass%, and then H-NMR measurement was performed on the solution under the condition that the measurement atmosphere temperature was about 27 ℃. Vinylidene chloride was calculated from the specific chemical shift in the obtained spectrum based on tetramethylsilane. For example, in the copolymer of vinylidene chloride and vinyl chloride, the peak of 3.50 to 4.20ppm, 2.80 to 3.50ppm, 2.00 to 2.80ppm is used for calculation.

The vinylidene chloride-vinyl chloride copolymer preferably has a comonomer (vinyl chloride) content of 7 to 28 mass%, more preferably 10 to 19 mass%, based on the total amount of the copolymer. When the comonomer content of the vinylidene chloride copolymer is within the above range, the cracking of the wrap film can be reduced, and the deterioration of the moldability during film stretching tends to be suppressed.

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

The content of the vinylidene chloride resin is preferably 88 to 98 mass%, more preferably 90 to 99 mass%, based on the total amount of the wrap film. When the content of the vinylidene chloride resin is within the above range, the low-mobility component of the vinylidene chloride resin tends to be increased by the plasticizing effect of the additive or the like, and the oxygen barrier property tends to be further improved. When the content of the vinylidene chloride resin is within the above range, the film tends to be prevented from being easily stretched and from further cracking. The method of measuring the content of each component by the wrap film differs depending on the analyte. For example, 0.5g of the sample is dissolved in 10ml of tetrahydrofuran, about 30ml of methanol is added to precipitate a resin component, and then the precipitate is separated by centrifugation, dried, and subjected to weight measurement to obtain the content of the vinylidene chloride resin.

(additives)

The preservative film of the present embodiment contains at least one compound selected from the group consisting of citric acid esters, dibasic acid esters, and acetylated fatty acid glycerides. In view of handling properties, citric acid esters are preferred, and acetyl tributyl citrate is particularly preferred.

(citric acid ester)

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

Among these, acetyl tributyl citrate is preferred. By using such a citric acid ester, the vinylidene chloride resin is plasticized, the molding processability is further improved, and the low-mobility component of the vinylidene chloride resin is increased, whereby the oxygen barrier property tends to be further improved and the hand feeling tends to be further improved.

(dibasic acid ester)

The dibasic acid ester is not particularly limited, and 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 azelate and octyl azelate; sebacates such as dibutyl sebacate (DBS) and di-2-ethylhexyl sebacate; phthalic acid esters such as dimethyl phthalate, diethyl phthalate, and dioctyl phthalate.

Among these, aliphatic dibasic acid esters are preferable, and dibutyl sebacate is more preferable. By using such dibasic acid esters, the vinylidene chloride resin is plasticized, the moldability is further improved, and the low-mobility components of the vinylidene chloride resin are increased, so that the oxygen barrier property is further improved and the hand feeling tends to be further improved.

(acetylated fatty acid glycerides)

The acetylated fatty acid glyceride is not particularly limited, and examples thereof include acetylated glyceryl caprylate, acetylated glyceryl caprate, acetylated glyceryl laurate, acetylated glyceryl myristate, 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 an acetylated monoglyceride of a fatty acid, an acetylated diglyceride of a fatty acid, and an acetylated triglyceride of a fatty acid. For example, the acetylated glyceryl laurate may include acetylated monoglyceride of lauric acid, acetylated diglyceride of lauric acid (DALG: diacetyl lauroyl glycerol), and acetylated triglyceride of lauric acid. Among them, acetylated glyceryl laurate is preferable, and acetylated diglyceride of lauric acid is more preferable. By using such an acetylated fatty acid glyceride, the low-mobility component of the vinylidene chloride resin increases, and the oxygen barrier property and the hand feeling tend to be further improved.

The content of citric acid ester, dibasic acid ester and acetylated fatty acid glyceride can be obtained by extracting the additive from the preservative film by using an organic solvent such as acetone and performing gas chromatography analysis.

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, relative to the total amount of the wrap film. When the total content of the above compounds is 0.5% by mass or more, the shear force of melt extrusion is moderate, and the composition smoothly passes through the extruder, thereby suppressing thermal decomposition of the vinylidene chloride resin. When the total content of the above compounds is less than 3 mass%, the low-motility component of the vinylidene chloride resin is increased, whereby the oxygen barrier property is further improved and the hand feeling is further improved.

(epoxidized vegetable oil)

The wrap of the present embodiment may contain epoxidized vegetable oil. The epoxidized vegetable oil can function as a stabilizer for extrusion processing of vinylidene chloride resins. The epoxidized vegetable oil is not particularly limited, and generally, epoxidized vegetable oil produced by epoxidizing an edible oil or fat can be used. Specifically, examples of the epoxidized vegetable oil include Epoxidized Soybean Oil (ESO) and epoxidized linseed oil. Among these, epoxidized soybean oil is preferred. By using such an epoxidized vegetable oil, the hand feeling of the wrap film tends to be further improved, and the film drawability from the package box tends to be further improved.

The content of the epoxidized vegetable oil in the present embodiment is preferably 0.5 to 3 mass%, more preferably 1 to 2.5 mass%, and still more preferably 1 to 2 mass% with respect to the total amount of the wrap. By setting the content of the epoxidized vegetable oil to 0.5 mass% or more, the quality of the wrap tends to be further suppressed from changing. Further, when the content of the epoxidized vegetable oil is 3% by mass or less, the color change of the wrap film is further suppressed, and the stickiness due to bleeding out is likely to be suppressed. The method of measuring the content of each component by the wrap film differs depending on the analyte. For example, the reprecipitation filtrate of the plastic wrap can be analyzed by NMR to obtain the content of the epoxidized vegetable oil.

Specifically, 50mg of a sample was weighed, dissolved in a deuterated solvent (solvent: deuterated tetrahydrofuran, internal standard: dimethyl terephthalate, volume: 0.7ml), and subjected to 400MHz proton NMR (cumulative count: 512 times), and the ratio of the integrated value of 2.23 to 2.33ppm to the integrated value of 8.05 to 8.11ppm was defined as an integrated ratio, and the quantitative value was calculated by an absolute calibration curve method, whereby the content of epoxidized vegetable oil could be obtained.

Integral value (2.23 to 2.33 ppm)/integral value (8.05 to 8.11ppm)

(other additives)

The wrap film of the present embodiment may contain additives other than those described above. Such additives are not particularly limited, and examples thereof include plasticizers other than the above, stabilizers other than the above, weather resistance improvers, colorants such as dyes and pigments, antifogging agents, antibacterial agents, lubricants, nucleating agents, oligomers such as polyesters, and polymers such as methyl methacrylate-butadiene-styrene copolymer (MBS).

The plasticizer other than the citric acid ester, dibasic acid ester and acetylated fatty acid glyceride is not particularly limited, and specific examples thereof include glycerin, glycerin ester, wax, liquid paraffin, and phosphoric acid ester. One kind of the plasticizer may be used alone, or two or more kinds may be used in combination.

The stabilizer other than the epoxidized vegetable oil is not particularly limited, and specific examples thereof include antioxidants such as 2, 5-t-butylhydroquinone, 2, 6-di-t-butyl-p-cresol, 4 '-thiobis (6-t-butylphenol), 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); thermal stabilizers such as laurate, myristate, palmitate, stearate, isostearate, oleate, ricinoleate, 2-ethyl-hexanoate, isodecanoate, neodecanoate, and calcium benzoate. One kind of stabilizer may be used alone, or two or more kinds may be used in combination.

The weather resistance improver is not particularly limited, and specific examples thereof include ethylene-2-cyano-3, 3 ' -diphenylacrylate, 2- (2 ' -hydroxy-5 ' -methylphenyl) benzotriazole, 2- (2 ' -hydroxy-3 ' -tert-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.

The colorant such as a dye or a pigment is not particularly limited, and specific examples thereof include carbon black, phthalocyanine, quinacridone, indoline, azo pigments, and red iron oxide. One kind of the colorant may be used alone, or two or more kinds may be used in combination.

The antifogging agent is not particularly limited, and specific examples thereof 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. The antifogging agent may be used alone or in combination of two or more.

The antibacterial agent is not particularly limited, and specific examples thereof include silver-based inorganic antibacterial agents. One or more of the antibacterial agents may be used alone or in combination.

The lubricant is not particularly limited, and specific examples thereof include fatty acid hydrocarbon-based lubricants such as ethylene bis stearamide, butyl stearate, polyethylene wax, paraffin wax, carnauba wax, myristyl myristate, and stearyl stearate, higher fatty acid lubricants, fatty amide-based lubricants, and fatty acid ester lubricants. One kind of the lubricant may be used alone, or two or more kinds may be used in combination.

The nucleating agent is not particularly limited, and specific examples thereof include phosphate metal salts. One kind of nucleating agent may be used alone, or two or more kinds may be used in combination.

The content of the other additives is preferably 5% by mass or less, more preferably 3% by mass or less, further preferably 1% by mass or less, and particularly preferably 0.1% by mass or less, based on the total amount of the wrap film. The lower limit of the content of the other additives is not particularly limited, and is 0 mass% or more with respect to the total amount of the wrap film.

(thickness of wrap film)

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

More specifically, when the thickness is 6 μm or more, the tensile strength of the wrap film in the TD direction and the MD direction tends to be further improved, and the film breakage during use tends to be further suppressed. Further, when the thickness is 6 μm or more, the tear strength tends to be remarkably reduced. Therefore, it is possible to further suppress the trouble that the wrap film is cracked from the end portion cut by the cutting blade attached to the package box when the wrap film is drawn out from the roll body and when the film end portion wound back into the package box is unwound.

On the other hand, by setting the thickness to 18 μm or less, the force required to cut the wrap film by the cutting edge attached to the package box can be reduced, and the cutting property tends to be further improved. Further, by setting the thickness to 18 μm or less, the wrap film is easily attached to the shape of the container, and the adhesion to the container tends to be further improved.

(tear Strength)

The tear strength of the wrap film in the TD direction of the present embodiment is preferably 2.0 to 6.0cN, more preferably 2.0 to 4.0cN, and still more preferably 2.2 to 3.0 cN. By setting the tear strength in the TD direction to 2.0cN or more, cracking when the wrap is taken out from the roll body can be reduced, and unexpected cracking failure when the wrap is used can be suppressed. On the other hand, when the tear strength in the TD direction is 6.0cN or less, the film is easily cracked when cut in the TD direction by a cutting blade attached to the package box, and the cuttability is improved.

The tear strength in the TD direction of the wrap film of the present embodiment can be adjusted by the composition of the vinylidene chloride resin, the composition of the additive, the stretch ratio and the stretch speed of the film, the thickness of the film, and the like. There are no particular limitations on the amount of the thermoplastic resin, and for example, the tear strength in the TD direction tends to be improved by reducing the stretch ratio in the TD direction or by increasing the thickness of the wrap film; by increasing the TD-direction stretch ratio or thinning the wrap film, the TD-direction tear strength tends to decrease. The tear strength was measured by the method described in examples.

(tensile modulus of elasticity)

The plastic wrap of the present embodiment has a tensile modulus of elasticity in the MD of 250 to 570MPa, preferably 300 to 500MPa, and more preferably 350 to 500 MPa. When the tensile elastic modulus in the MD direction is 250MPa or more, elongation of the film in the MD direction can be suppressed when a force is applied to cut the film with the cutting blade, the cutting blade can easily bite into the film, and the cuttability is improved. On the other hand, when the tensile elastic modulus in the MD direction is 570MPa or less, the film is soft, and can be cut neatly along the shape of the cutting blade, and the occurrence of a large number of cracks at the cut end face tends to be suppressed. As a result, there is a tendency that the film can be prevented from being cracked from the cut end face when the film is taken out from the roll and when the film is unwound and wound back to the film end in the package box.

The tensile elastic modulus in the MD direction of the wrap film of the present embodiment can be adjusted by the composition of the vinylidene chloride resin, the composition of the additive, the stretch ratio and the stretching speed of the film, and the like. There are no particular limitations thereon, and for example, the tensile elastic modulus in the MD direction tends to be increased by increasing the stretch ratio or decreasing the amount of the additive; the tensile elastic modulus in the MD direction tends to decrease by decreasing the stretch ratio or increasing the amount of the additive. The tensile modulus was measured by the method described in examples.

(Low temperature crystallization initiation temperature)

In the wrap film of the present embodiment, physical deterioration of the wrap film occurs due to thermal history experienced during distribution or storage, and a crack failure occurs due to the physical deterioration, and the crack failure can be estimated from the low-temperature crystallization start temperature. The low-temperature crystallization initiation temperature is an index indicating the thermal stability of microcrystals formed and grown by exposure to high temperature during distribution/storage of the wrap after production, and the degree of rearrangement of molecular chains, that is, the ease of occurrence of cracking failure of the wrap due to physical deterioration can be evaluated by the low-temperature crystallization initiation temperature.

From the above-mentioned points, the low-temperature crystallization initiation temperature of the wrap film according to the present embodiment measured by a temperature modulation type differential scanning calorimeter (hereinafter also referred to as "temperature modulation type DSC") is preferably 40 to 60 ℃, more preferably 40 to 55 ℃, and still more preferably 40 to 50 ℃. When the low-temperature crystallization initiation temperature is within the above range, the cutting property of the wrap film is maintained, and cracking failure and hand feeling tend to be further improved. The details will be described below.

The low-temperature crystallization starting temperature of the existing preservative film exceeds 60 ℃. In contrast, the low-temperature crystallization initiation temperature of the wrap film of the present embodiment is 60 ℃ or lower and set to a lower temperature. By setting the low-temperature crystallization initiation temperature within the above range, rearrangement of the molecular chains is suppressed, and the cracking failure of the wrap film is further suppressed.

More specifically, the behavior of the wrap of the present embodiment when heated differs from that of the conventional wrap along with the difference in the low-temperature crystallization initiation temperature. For example, in a conventional wrap film, when exposed to an atmosphere of 20 ℃ or higher for a long period of time during distribution and storage in a warehouse, molecular chains of a vinylidene chloride resin are rearranged, and formation and growth of microcrystals are considered to occur. Such rearrangement of the molecular chains is presumed to occur because the orientation of the molecular chains of the produced wrap film or the stress of the film is not sufficiently relaxed. It is believed that the more the wrap film is exposed to high temperatures, the more easily the molecular chains are rearranged, and therefore the physical deterioration of the film occurs, and cracking failure is easily induced.

In contrast, in the wrap film of the present embodiment, the orientation of the molecular chains of the vinylidene chloride resin and the film stress are sufficiently relaxed during production, so that the low-temperature crystallization initiation temperature is 60 ℃ or lower. Thus, in the wrap film of the present embodiment, even if the wrap film is exposed to 20 ℃ or more for a long period of time during distribution and storage in a warehouse, rearrangement of molecular chains is not easily caused, deterioration of the film is suppressed, and further, cracking failure is suppressed. As a result, the problem of the reverse of the problem of suppressing the cracking failure while maintaining the cuttability can be achieved.

On the other hand, according to the study of the present inventors, when the preservative film was stored at-30 ℃ (glass transition temperature or lower) after the production thereof, the low-temperature crystallization initiation temperature was 40 ℃. That is, when the wrap is considered to be completely unheated after production, the low-temperature crystallization initiation temperature is 40 ℃. Since it is considered that rearrangement of the molecular chains and hence cracking failure can be suppressed as the low-temperature crystallization initiation temperature approaches this temperature, the lower limit of the temperature range of the low-temperature crystallization initiation temperature is set to 40 ℃.

The method for adjusting the low-temperature crystallization initiation temperature to the above range is not particularly limited, and for example, a method for sufficiently relaxing the molecular chain orientation of the vinylidene chloride resin or the film stress can be given. More specifically, the wrap film is stored at a low temperature for a predetermined time.

Here, the "low-temperature crystallization onset temperature" refers to an extrapolated onset temperature of an exothermic peak due to low-temperature crystallization in a temperature-heat flow curve of a non-reversible component obtained by temperature rise measurement by temperature-modulated DSC (temperature at an intersection of a line extending a base line on a low-temperature side toward a high-temperature side in temperature rise measurement and a tangent line drawn at a point on a curve on the low-temperature side of a crystallization peak where the slope is maximum).

An example of a method for measuring the low-temperature crystallization initiation temperature will be described. First, a temperature-heat flow curve of an irreversible component was obtained in a step-and-scan measurement mode using a Differential Scanning Calorimeter (DSC) manufactured by Perkin Elmer (power compensation type dual-furnace DSC 8500). In the step-and-scan measurement conditions, the measurement temperature is set to 0 to 180 ℃, the temperature rise rate is set to 10 ℃/min, the temperature rise step width is set to 4 ℃, and the isothermal time is set to 1 minute. The extrapolated onset temperature of the exothermic peak due to low-temperature crystallization in the obtained temperature-heat flow curve was taken as the low-temperature crystallization onset temperature.

In the temperature rise measurement by the differential scanning calorimeter, crystallization and crystal melting occur competitively. Therefore, in the conventional DSC measurement method, heat flows resulting from the formation and growth of microcrystals are balanced with heat flows resulting from melting, and it is difficult to study the thermal behavior of microcrystals, and it is difficult to distinguish the conventional wrap from the wrap of the present embodiment. On the other hand, in the case of using the temperature-modulated DSC, a heat flow of an irreversible component such as crystallization and a reversible component such as crystal melting and glass transition can be separated, and the thermal behavior of the microcrystal can be evaluated. Therefore, in the measurement of the low-temperature crystallization initiation temperature according to the present embodiment, a temperature modulation type DSC is used.

< pulse NMR >

In the wrap film of the present embodiment, the ratio of the high motility component measured by pulse NMR is preferably 4.5% or less, more preferably 4.0% or less, and further preferably 3.5% or less. The low motility component ratio is preferably 65.0% or less, more preferably 63.0% or less, and preferably 61.0% or more. When the ratio of the high motility component is in the above range, the frequency of occurrence of breakage tends to be further reduced. In addition, by setting the low motility component in the above range, the cracking failure is further suppressed.

Unlike high-resolution NMR which is generally used for the structural determination of organic compounds and the like, pulse NMR is an analytical method which can measure each relaxation time of 1H nuclei associated with molecular mobility in a system and can determine the presence ratio of each kinetic component in the system with high quantitative performance.

In the present embodiment, in obtaining Cs in the plastic wrap: mole fraction of low motility component, Cm: molar fraction of intermediate components and Cl: for the mole fraction of the high mobility component, the spin-spin relaxation time T2 of 1H was used. Specifically, the application (fitting) is preferably performed by using a linear least squares method so that the following equation is approximately applied to the Free Induction Decay (FID) signal obtained in the measurement of the spin-spin relaxation time T2 of 1H. As specific conditions for the pulse NMR measurement, the conditions described below in examples can be adopted.

[ formula 1]

Here, the number of the first and second electrodes,

C_s: mole fraction of low motility component

C_m: mole fraction of intermediate component

C_l: mole fraction of highly motile ingredient

T_s: relaxation time of Low-mobility Components

T_m: relaxation time of intermediate component

T_l: relaxation time of the high mobility component.

[ oxygen gas Barrier Property ]

Generally, in order to maintain freshness, oxygen barrier properties are required for a wrap film. The oxygen permeability of the preservative film of the embodiment at 23 ℃ is preferably 1 to 110cm³/m²Day atm, more preferably 1 to 77cm³/m²Day atm, more preferably 1 to 50cm³/m²Day atm. When the oxygen permeability is within the above range, the oxygen barrier property tends to be further improved, and the freshness of the food tends to be sufficiently maintained.

The oxygen permeability of the wrap film at 23 ℃ can be measured by the method described in examples. The method for controlling the oxygen permeability of the wrap film at 23 ℃ to the above range is not particularly limited, and examples thereof include a method in which the stretching ratio in the MD direction is 4.0 or less, preferably 3.8 or less, or the stretching ratio in the TD direction is 5.8 or more; a method of using a polymer having a low glass transition temperature or adding a nucleating agent as appropriate.

[ method for producing cling film ]

The method for producing the wrap film of the present embodiment is not particularly limited, and examples thereof include a method including the steps of: a step of melt-extruding a composition containing a vinylidene chloride resin (containing 72 to 93 mass% of vinylidene chloride) and at least one compound selected from the group consisting of citric acid esters, dibasic acid esters and acetylated fatty acid glycerides to form a film; and stretching the obtained film in the MD direction and the TD direction. The details will be described below.

(mixing Process)

Fig. 1 is a schematic diagram showing an example of a process for producing a wrap film. First, a vinylidene chloride resin, at least one compound selected from the group consisting of citric acid esters, dibasic acid esters, and acetylated fatty acid glycerides, and, if necessary, epoxidized vegetable oil are mixed by a mixer to obtain a composition. In this case, various additives may be mixed as necessary. The mixer is not particularly limited, and a ribbon mixer, a henschel mixer, or the like can be used, for example. The obtained composition is preferably cured for about 1 to 30 hours and then used in the next step.

(melt extrusion Process)

Next, the obtained composition is melted by the extruder 1, and a tubular film is extruded from the die orifice 3 of the die 2 to form the soaking section 4 (also referred to as a bank section).

(Cooling Process)

The immersion liquid 5 is poured into the inside of the immersion part 4, and the outside of the immersion part 4 is brought into contact with the cold water in the cold water tank 6. Thereby, the soak portion 4 is cooled from both the inside and the outside, and the film constituting the soak portion 4 is solidified. The solidified dipping portion 4 is folded by the first pinch roll 7 to be molded into a parison 8.

(stretching Process)

Next, air is injected into the parison 8, thereby opening the parison 8 to form an annular film. At this time, the soak solution 5 applied to the portion corresponding to the inner surface of the soak section 4 exerts an effect as an opening agent for the parison 8. Subsequently, the parison 8 is reheated with warm water to a temperature suitable for stretching in an opened state. Warm water adhering to the outside of the parison 8 is squeezed off by the 2 nd pinch roll 9.

Air is injected into the inside of the parison 8 heated to the appropriate temperature as above, and the bubble 10 is formed. The air expands the parison from the inside, thereby stretching the film to obtain a stretched film. Stretching of the film in the TD direction is mainly performed by the amount of air, and stretching of the film in the MD direction is mainly performed by applying tension in the flow direction of the film using the 2 nd pinch roller 9, the 3 rd pinch roller 11, and the like.

The process from the 1 st pinch roll 7 to the 3 rd pinch roll 11 is referred to as a drawing process. Since the stretching speed of the parison 8 is improved when the stretching speed is slow, 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 the conventional method for producing a wrap film. In contrast, in the method for producing a wrap film according to the present embodiment in which the crystallization initiation temperature is controlled to 40 to 60 ℃, the stretching ratios in the MD direction and the TD direction and the stretching speeds in the MD direction and the TD direction are preferably adjusted to predetermined ranges.

Specifically, the stretching ratios in the MD direction and the TD direction in the stretching step of the present embodiment are each independently preferably 1.5 to 3.5 times, and more preferably 1.7 to 3.0. The area magnification in the drawing step of the present embodiment is preferably 4.0 to 7.0 times, and more preferably 5.0 to 6.0 times. Here, the stretching ratio in the MD direction is a stretching ratio at which the parison 8 is stretched in the MD direction, and can be calculated from a ratio of the rotation speed of the 3 rd pinch roll 11 to the rotation speed of the 1 st pinch roll 7 in fig. 1, for example. The TD stretching ratio is a stretching ratio at which the parison 8 is stretched in the TD, and can be calculated from a ratio of the width of the bilayer film 12 to the width of the parison 8, for example, in fig. 1. The stretching ratio in the MD direction can be adjusted by, for example, the rotation speed ratio of the 1 st pinch roll 7 and the 3 rd pinch roll 11, and the stretching ratio in the TD direction can be adjusted by, for example, the stretching temperature of the parison 8 and the size of the bubble 10.

In addition, the stretching speed in the MD direction in the stretching step of the present embodiment is preferably 0.09 to 0.12 times/s. The average stretching speed in the MD direction is a stretching ratio in the MD direction with respect to the time for the parison to pass between the 1 st pinch roll 7 and the 3 rd pinch roll 11, and can be calculated from, for example, the rotation speed of the 1 st pinch roll 7, the rotation speed of the 3 rd pinch roll 11, and the time required for the parison 8 to pass between the 1 st pinch roll 7 and the 3 rd pinch roll 11 in fig. 1. The stretching speed in the MD direction can be adjusted by, for example, the rotation speed of the 1 st pinch roller 7 or the 3 rd pinch roller 11, or the distance between the 1 st pinch roller 7 and the 3 rd pinch roller 11.

In addition, the stretching speed in the TD direction in the stretching step of the present embodiment is preferably 3.1 to 4.0 times/s. The average stretching speed in the TD direction is a stretching ratio in the TD direction with respect to the time required for the parison 8 to expand to the bubble 10, and for example, in fig. 1, it can be calculated from the time required for stretching in the TD direction calculated from the stretching length measured using the still images of the parison 8 and the bubble 10 and the rotation speed of the 3 rd pinch roll 11, and the stretching ratio in the TD direction. The TD stretching speed can be adjusted by, for example, the rotation speed of the 3 rd pinch roll 11.

The stretching temperature is not particularly limited, and is preferably 30 to 45 ℃.

After the stretching step, the stretched film is folded by the 3 rd pinch roll 11 to form a double-layer film 12. The double-layer film 12 is wound by a winding roller 13.

(relaxation step)

The method for producing a wrap film according to the present embodiment preferably includes a relaxation step of relaxing the wrap film immediately after stretching. A relatively common relaxation method in the production method of a wrap film is a method of relaxing a film by heat of an infrared heater or the like after stretching. However, in the present embodiment, it is preferable to use the following method instead of the relaxation step: the stretched film is relaxed by making the rotation speed of the take-up roller 13 slower than that of the 3 rd pinch roller 11. This is because, in the present embodiment, when the conventional relaxation method using heat is employed, formation and growth of crystallites which cause film cracking due to the action of heat may occur, and the crystallization initiation temperature may exceed 60 ℃.

The ratio of the slack in the slack process using the 3 rd pinch roll 11 and the take-up roll 13 is preferably 7 to 15%, more preferably 9 to 13%. By setting the sag ratio to 15% or less, the generation of wrinkles due to the sag of the film between the 3 rd pinch roller 11 and the winding roller 13 can be further suppressed. Further, by setting the relaxation ratio to 7% or more, the wrap film can be sufficiently relaxed, and even when exposed to high temperature, the molecular chains can be suppressed from being rearranged, and the low-temperature crystallization initiation temperature can be set to 60 ℃ or lower. In addition, this reduces the tendency for cracking failures. Here, the "slack ratio" refers to a ratio at which the double-layer film 12 contracts between the 3 rd pinch roller 11 and the winding roller 13, and can be calculated, for example, from a ratio of the rotation speed of the winding roller 13 with respect to the 3 rd pinch roller 11 in the case of fig. 1.

The atmosphere temperature in the relaxation step using the 3 rd pinch roll 11 and the take-up roll 13 is preferably 25 to 32 ℃. When the temperature of the atmosphere is in the above range, formation and growth of crystallites tend to be suppressed.

(cutting Process)

The wrap film wound as described above is cut, and is wound while being peeled off so as to be a single wrap film, and is temporarily stored in a large roll for 1 to 3 days. Finally, the rolled wrap is rewound from the large roll onto a paper core and is loaded into a package, thereby obtaining a wrap of wrap for wrap stored in the package.

(preservation Process)

In the method for producing a wrap film according to the present embodiment, a storage step of cutting the wrap film and storing the cut wrap film in a large roll state can be performed. The storage temperature is preferably 19 ℃ or less, more preferably 5 to 19 ℃, and still more preferably 5 to 15 ℃. The storage time is preferably 20 to 50 hours, more preferably 24 to 40 hours.

The formation and growth of crystallites that induce an increase in film cracking failure can be suppressed by the temperature of the atmosphere at the time of storage. In general, a large roll is often stored at a high temperature because the storage place is adjacent to a production process of a wrap film or because temperature control management is not performed.

In contrast, in the method for producing a wrap film according to the present embodiment, by setting the atmospheric temperature at 19 ℃ or lower when storing a cut large roll, the physical properties of the film tend to be inhibited from being deteriorated due to rearrangement of molecular chains. This makes it possible to suppress the film from easily cracking at the end cut by the cutting blade attached to the packaging box when the wrap is taken out from the roll or when the film is unwound and rewound into the packaging box.

Further, when the atmospheric temperature during storage of the cut large roll is set to 5 ℃ or higher, the wrap film is sufficiently loosened, and the molecular chains tend not to be easily rearranged when exposed to 20 ℃ or higher during subsequent distribution and storage.

Therefore, it is preferable to store the cut large roll under the above-mentioned storage condition, whereby a film in which the orientation of the molecular chains in the amorphous portion is relaxed while suppressing the formation and growth of crystallites can be obtained. By relaxing the orientation of the molecular chains during storage in a large roll in this manner, even if the film is exposed to high temperatures during distribution and storage, the formation and growth of crystallites are not easily caused, and cracking failure can be suppressed.

The cut large roll may be rewound, for example, onto a paper core or the like after storage, and stored in the package 1 provided with the film cutting blade 15 shown in fig. 2 in the form of a roll 16, but the invention is not limited thereto. As illustrated in fig. 2, the wrap 17 is drawn out for use at the time of use.

[ examples ]

The present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the examples.

[ vinylidene chloride content ]

The vinylidene chloride ratio of the preservative film was measured using a high resolution proton nuclear magnetic resonance measuring device. The reprecipitated filtrate of the preservative film was vacuum-dried, dissolved in deuterated tetrahydrofuran at 5 wt%, and the obtained solution was subjected to H-NMR measurement at a measurement atmosphere temperature of about 27 ℃. For example, the vinylidene chloride content of the copolymer of vinylidene chloride and vinyl chloride is calculated by using peaks at 3.50 to 4.20ppm, 2.80 to 3.50ppm and 2.00 to 2.80ppm of the copolymer based on tetramethylsilane. In addition, with respect to other copolymers, the content can also be calculated using the peak of each monomer.

[ thickness of film ]

Assuming distribution of the wrap after shipment and storage at home, the thickness of the wrap was measured after the wrap was stored for 1 month in a thermostatic bath set at 28 ℃. For the measurement, the thickness was measured by a dial thickness gauge (manufactured by TecLock) in an atmosphere of 23 ℃ and 50% RH.

[ tear Strength ]

Assuming distribution of the wrap after shipment and storage at home, the tear strength was measured after the wrap after manufacture was stored in a thermostatic bath set at 28 ℃ for 1 month.

For the tear strength measurement of the wrap film, the tear strength was measured in an atmosphere of 23 ℃ and 50% RH using a light load tear tester model D (donyo seiki mechanism). The tear strength of the wrap was measured using only 1 wrap. Let the sample length in the tear direction be 63.5mm and the sample width be 50.0 mm. In the measurement, the pendulum was lifted and stopped, and then the test piece was carefully attached to the jig, and the chuck was firmly fastened so that the position of the notch was the center of the film width. A cut was then made in the film using a knife mounted in the apparatus. At this time, the position of the knife edge was adjusted so that the length of the cut of the film became 12.7 mm. + -. 0.5 mm. After the cut was made, the pendulum was carefully released and the amount of force required to tear the test piece was read. The test was conducted by excluding the test in which the tear line was not less than 10mm from the extension line of the cut mark and replacing the test with an additional test piece. However, in this case, the case where the tear occurs along the lines of the embossed pattern is not limited to this. In addition, as for the measurement result, the value of the second digit after the decimal point is rounded.

[ tensile elastic modulus ]

Assuming distribution of the wrap after shipment and storage at home, the tensile elastic modulus was measured after the wrap was stored for 1 month in a thermostatic bath set at 28 ℃.

The tensile modulus of the wrap film was evaluated by Autograph AG-IS (Shimadzu corporation) in an atmosphere of 23 ℃ and 50% RH. The load at 2% elongation was measured under the conditions of a stretching speed of 5 mm/min, a distance between chucks of 100mm, and a film width of 10mm, and the tensile modulus was measured at 50 times by dividing the load by the cross-sectional area of the measurement sample. During measurement, the test piece is attached to the jig so that the MD direction of the test piece coincides with the axis of the tester. In order to prevent the test piece from slipping and prevent the clamped portion from shifting during the test, the test piece is uniformly and firmly fastened by a jig. Further, the test piece was prevented from being cracked and rolled by the pressure between the jigs.

In addition, the measurement result was a 2-digit significant figure, and the 3 rd digit was rounded.

[ Low temperature crystallization initiation temperature ]

Assuming distribution of the wrap after shipment and storage at home, the wrap after production was stored in a thermostatic bath set at 28 ℃ for 1 month, and the stored wrap was used as a measurement sample. For the measurement, a Differential Scanning Calorimetry (DSC) apparatus (power-compensated dual-furnace DSC 8500) manufactured by Perkin Elmer was used, and a step-scan measurement mode (sample weight: 6mg, sample pan material: aluminum, measurement temperature: 0 to 180 ℃, temperature-raising rate: 10 ℃/min, temperature-raising step width: 4 ℃, isothermal time: 1 min) was used. The empty aluminum sample pan was also measured under the same temperature conditions and was used as a blank. The temperature at which heat release due to low-temperature crystallization starts out of the irreversible component of the temperature-heat flow curve is set as the low-temperature crystallization start temperature.

[ pulse NMR ]

Assuming distribution of the wrap after shipment and storage at home, the pulse NMR of the wrap was measured after the wrap was stored in a thermostatic bath set at 28 ℃ for 1 month. The cut and approximately square preservative film 1g was folded and gathered into a cylindrical shape, and the cylindrical shape was filled in an NMR tube having a diameter of 10mm, and the measurement was carried out by the following conditions using pulse NMR.

[ Condition ]

The device comprises the following steps: m inispec M Q20 manufactured by Bruker Bi o spin corporation

Nuclides: 1H

And (3) determination: t2

The determination method comprises the following steps: solid echo method

Measuring temperature: 40 deg.C (5 minutes after reaching the set temperature)

Cumulative number of times: 256 times

The repetition time is as follows: 1.0 second

Sample amount: about 1g

The obtained Free Induction Decay (FID) curve was separated into 3 components using the following formula, and the component ratio and relaxation time were determined for each component.

A component represented by a combined function of a Gaussian function and a sinc function of a first term of the following expression is set as a low-mobility component, a component represented by a Lorentz function of a second term of the following expression is set as an intermediate component, and a component represented by a Lorentz function of a third term of the following expression is set as a high-mobility component.

[ formula 2]

C_s: mole fraction of low motility component

C_m: mole fraction of intermediate component

C_l: mole fraction of highly motile ingredient

T_s: relaxation time of Low-mobility Components

T_m: relaxation time of intermediate component

T_l: relaxation time of highly mobile components

[ oxygen Transmission Rate ]

The oxygen transmission rate was measured according to ASTM D3985 in the measurement method using OX TRAN 2/21MH (trade name) manufactured by MOCON. The sample was placed in the apparatus and the value after 4 hours was used. The measurement was carried out at 23 ℃. The smaller the value of the oxygen transmission rate, the higher the oxygen barrier property.

[ cracking failure suppression Effect ]

Assuming distribution of wrap after shipment and storage at home, wrap of wrap immediately after manufacture was stored in a constant temperature bath set at 28 ℃ for 1 month. Thereafter, the wrap of wrap film contained in the container (packaging box) was vibrated using a vibration tester (model "BF-50 UC" manufactured by IDEX corporation) in order to reproduce vibration during distribution. The vibration test was performed as follows.

First, 1 wound body was housed in 1 rectangular parallelepiped container (package box inner size; 42mm × 42mm × about 233mm), 60 wound body housings were housed in a corrugated cardboard box (inner size 28cm × 46cm × 24cm) without a gap, and the wound body was fixed to a vibration table with a belt so that the longitudinal direction of the wound body was perpendicular to the vibration table. The vibration test was carried out by operating a vibration tester at 23 ℃ under an atmosphere having a relative humidity of 50% RH. The vibration test uses an automatic mode, and the frequency was changed in the order of 5Hz, 30Hz, and 5Hz during 30 seconds, and was performed for 20 minutes in this cycle.

Thereafter, cracking failure evaluation was performed in an atmosphere of 23 ℃ and a relative humidity of 50% RH. As evaluators, 100 persons who daily used the wrap film for food packaging were selected. The evaluator performed 10 times each of a series of operations of pulling out the film by 50cm from a roll having a width of about 23cm stored in the storage body and then cutting the film with a tin-plated iron sheet film cutting blade attached to the package box. That is, the occurrence rate of the film cracking failure was derived from the number of times that the film was cracked when the film was taken out from the roll and the film could not be smoothly taken out, in 10 times each of 100 persons, and 1000 times total.

(evaluation criteria for crack failure suppression Effect)

A: 0% or more and less than 10%: almost no cracking failure and excellent ease of use.

B: 10% or more and less than 15%: less cracking failure and excellent usability.

C: 15% or more: the cracking failure is more, and the usability is poor.

[ preservation of freshness of Contents ]

The handle part of 1 piece of banana produced by Ecuador is sealed by a preservative film in a mode of not contacting with the outside air, and then the whole banana is further coated by one layer of the preservative film to prevent the banana from contacting with the outside air. The packed bananas were placed in a constant temperature and humidity chamber at 5 ℃ and 50% humidity, and the number of days until discoloration was evaluated.

(evaluation criterion for freshness maintenance)

A: discoloration after more than 10 days

B: change color in 7 to 10 days

C: change color in less than 7 days

[ feeling of touch (dryness) ]

Evaluation of the hand touch (dry touch) of the wrap was carried out. As evaluators, 100 persons who routinely used the wrap film for food packaging were selected and evaluated by sensory evaluation by the evaluators. The evaluators were assigned 10 points, and the average of 100 evaluators was calculated by assigning 0 point for sticky feeling and 10 points for dry feeling. The average score was used for evaluation. The evaluation environment was 23 ℃ and an atmosphere having a relative humidity of 50% RH.

[ evaluation criteria for hand touch (dryness) ]

A: 8 min or more: dry and completely non-sticky, very good level.

B: 3 minutes or more and less than 8 minutes: almost no stickiness and good level.

C: less than 3 minutes: a slimy, slightly unpleasant level is slightly felt.

[ example 1]

96.0 parts by mass of a vinylidene chloride resin having a weight average molecular weight of 90,000 (82% by mass of vinylidene chloride and 18% by mass of vinyl chloride), 2.9 parts by mass of tributyl acetylcitrate (Taoka chemical Co., Ltd.), and 1.1 parts by mass of epoxidized soybean oil (Newcizer 510R, Japan fat and oil Co., Ltd.) were mixed in a Henschel mixer for 5 minutes. Mixing, and aging for more than 24 hr to obtain the composition.

The obtained composition was supplied to a melt extruder and melted, and melt-extruded from an annular die attached to the tip of the extruder to form a soaking part. At this time, heating conditions of the extruder were adjusted so that the temperature of the molten resin at the slit outlet of the annular die was 170 ℃, and the molten resin was extruded into an annular shape at an extrusion rate of 10 kg/hr.

After cooling in a bath and a cold water tank, the parison is opened to form a bubble, and inflation and stretching are performed. At this time, the film was stretched 2.7 times in the MD and 2.0 times in the TD to form a cylindrical film (bubble). The stretching temperature was 25 ℃.

The obtained tubular film was folded flat by nipping, and then the speed ratio of the pinch roll and the winding roll was controlled to relax the film in the MD direction, and 2 overlapped films having a fold width of 280mm were wound. The film was cut into a width of 220mm, and was rewound on a paper core having an outer diameter of 92mm while being peeled into 1 sheet. Then, 20m was wound on a paper core having an outer diameter of 36mm and a length of 230mm, thereby obtaining a wrap of wrap film. Each evaluation was performed using the wound body of the obtained wrap film.

Examples 2 to 4 and comparative examples 1 to 3

Rolls of wrap films of examples 2 to 4 and comparative examples 1 to 3 were obtained in the same manner as in example 1, except that the conditions shown in table 1 were changed. Each evaluation was performed using the wound body of the obtained wrap film.

[ Table 1]

	Example 1	Example 2	Example 3	Example 4	Comparative example 1	Comparative example 2	Comparative example 3
								Weight average molecular weight of vinylidene chloride resin	90000	90000	90000	90000	90000	90000	90000
Vinylidene chloride (% by mass)	88	88	88	88	91	91	91
								Vinyl chloride (% by mass)	12	12	12	12	9	9	9
Amount of ATBc added (% by mass)	2.9	2	0.7	0	5.5	2.8	1.5
								Addition amount (mass%) of ESO	1.1	1.1	1.1	1.1	1.1	1.5	1.5
Amount of DALG added (% by mass)	0	0	0	3	0	0	0
								MD stretch ratio (times)	2.7	2.7	2.7	2.7	4.1	4.1	4.1
TD stretch ratio (multiple)	2.0	2.0	2.0	2.0	5.6	5.6	5.6
								MD × TD stretch ratio (multiple times)	5.4	5.4	5.4	5.4	23.0	23.0	23.0
Stretching temperature (. degree.C.)	10	10	10	10	25	25	25
								Die head diameter (mm)	70	70	70	70	51	51	51
High motility component (%)	4.0	3.1	1.8	4.1	6.6	4.3	3.0
								Low motility component (%)	58.4	61.0	62.8	62.8	63.7	76.8	91.7
TD tear Strength (cN) value of 1 sheet	3	3	3	3	2	2	2
								Modulus of elasticity in MD tensile (MPa)	470	500	520	520	530	680	850
Low temperature crystallization onset temperature (. degree. C.)	45	48	49	49	53	48	47
								Film thickness (mum)	11	11	11	11	11	11	11
Oxygen transmission rate	80	70	60	90	110	100	90
								Cracking failure suppressing effect	A	A	A	A	B	C	C
Preservation of freshness of contents	A	A	A	A	B	A	A
								Hand touch	B	A	A	A	C	B	A

In addition, ATBC: acetyl tributyl citrate

DALG: diacetyl lauroyl glycerol

ESO: epoxidized soybean oil

Industrial applicability

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

Claims

1. A cling film, comprising:

a tensile elastic modulus in the MD direction of 250 to 570MPa,

2. The cling film of claim 1, wherein the TD tear strength is between 2.0cN and 6.0 cN.

3. The wrap film according to claim 1 or 2, wherein the thickness is 6 μm to 18 μm.

4. The wrap film of any one of claims 1 to 3,

5. The wrap film according to any one of claims 1 to 4, wherein an oxygen permeability at 23 ℃ is 110cm³/m²Day atm or less.

6. The wrap film according to any one of claims 1 to 5, wherein a ratio of the high-motility component measured by pulse NMR is 4.5% or less.

7. The wrap film according to any one of claims 1 to 6, wherein a ratio of a low-motility component measured by pulse NMR is 65.0% or less.