CN112552623B

CN112552623B - Fresh-keeping film

Info

Publication number: CN112552623B
Application number: CN202011015033.5A
Authority: CN
Inventors: 田中达夫; 田中利采
Original assignee: Asahi Kasei Corp
Current assignee: Asahi Kasei Corp
Priority date: 2019-09-26
Filing date: 2020-09-24
Publication date: 2023-03-10
Anticipated expiration: 2040-09-24
Also published as: CN112552623A; JP2021055086A

Abstract

The purpose of the present invention is to provide a wrap film which is less frequently damaged, is suppressed in cracking failure, and is excellent in cuttability. A wrap film comprising a vinylidene chloride resin and at least one compound selected from the group consisting of citric acid esters, dibasic acid esters and acetylated fatty acid glycerides, wherein the vinylidene chloride resin contains 72 to 93mol% of a vinylidene chloride repeating unit, the content of the compound is more than 8% by weight and 19% by weight or less with respect to the total amount of the wrap film, and the tear strength of the wrap film in the TD direction is 2.0 to 4.2cN.

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.

As the vinylidene chloride resin forming the wrap film, a vinylidene chloride copolymer obtained by copolymerizing vinylidene chloride and another monomer copolymerizable with vinylidene chloride such as vinyl chloride is generally used from the viewpoint of extrusion processability, crystallinity, transparency, softening temperature and the like of the film.

A wrap film made of a vinylidene chloride resin is generally produced by melt-extruding a vinylidene chloride resin and then stretching, and is wound around a paper core and stored in a packaging box (carton).

The wound body wound around the paper core is automatically inserted into the package from the end of the package, for example, but in this case, the wound body may be damaged by friction between the wound body and paper on, for example, the bottom surface of the package, and there is a problem that the wound body is damaged from the damage as a starting point during use.

In addition, when the shearing force of the extruder is large during melt extrusion, the vinylidene chloride resin may be decomposed or carbonized, and the carbide may become an inclusion. When the film is subsequently stretched, for example, blown film formation, the blow may cause perforation starting from the inclusions, resulting in a decrease in productivity (see, for example, patent document 1).

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2014-125561

Disclosure of Invention

Problems to be solved by the invention

Patent document 1 discloses that when supplying a resin to an extruder, the use of a vacuum hopper improves the extrusion processability. However, in melt extrusion, the vinylidene chloride resin stays in the extruder for a certain period of time, and the vinylidene chloride resin is decomposed, and the like, and patent document 1 does not disclose a solution to this.

Even when inclusions are generated in melt extrusion, depending on the degree of the inclusions, it is possible to produce a wrap film normally without causing perforation when the wrap film is blown. However, in such a case, it is known that the frequency of occurrence of breakage due to inclusions increases, a crack failure occurs starting from the inclusions, and the cuttability of the resulting wrap film decreases.

The present invention has been made to solve the above problems, and an object thereof is to provide a wrap film which is less frequently damaged, is suppressed in cracking failure, and is excellent in cuttability.

Means for solving the problems

The present inventors have conducted intensive studies to solve the above problems. As a result, they 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 wrap film, wherein,

comprising a vinylidene chloride resin containing 72 to 93mol% of a vinylidene chloride repeating unit 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 more than 8 weight percent and less than 19 weight percent relative to the total weight of the preservative film,

the tearing strength of the preservative film in the TD direction is 2.0-4.2 cN.

[2]

The wrap film according to [1], wherein the tensile modulus of elasticity in the MD direction is 250 to 600MPa.

[3]

The wrap film according to [1], wherein the tensile modulus of elasticity in the MD direction is 350 to 500MPa.

[4]

The wrap film according to any one of [1] to [3], wherein a low-temperature crystallization initiation temperature measured by a temperature-modulated differential scanning calorimeter is 40 to 60 ℃.

[5]

The wrap film according to any one of [1] to [4], wherein the wrap film has a thickness of 6 to 18 μm.

[6]

The wrap film according to any one of [1] to [5],

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 wt% relative to the total amount of the preservative film.

[7]

The wrap film according to any one of [1] to [6], wherein the vinylidene chloride resin contains a vinylidene chloride repeating unit in an amount of 86 to 93mol%.

[8]

The wrap film according to any one of [1] to [7], wherein a ratio of the high motility component measured by pulse NMR is 11.5% or less.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a wrap film that is less likely to cause breakage, is suppressed in cracking failure, and is excellent in cuttability can be provided.

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.

Fig. 3 is a schematic diagram showing an evaluation method for evaluating the frequency of occurrence of breakage.

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 pulled out from the roll when the wrap is formed. 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 comprises a vinylidene chloride resin containing 72 to 93mol% of vinylidene chloride repeating units and at least one compound selected from the group consisting of citric acid esters, dibasic acid esters and acetylated fatty acid glycerides, and has a TD tear strength of 2.0 to 4.2cN in a range of more than 8% by weight and not more than 19% by weight based on the total amount of the wrap film.

In the present embodiment, in the wrap film having the above-described predetermined configuration, the content of at least one compound selected from the group consisting of citric acid esters, dibasic acid esters, and acetylated fatty acid glycerides is more than 8% by weight and 19% by weight or less, whereby the effect of reducing the frequency of occurrence of breakage and suppressing cracking failure is exerted. In addition, the wrap film of the present embodiment also exhibits an effect of excellent cuttability.

The reason why the frequency of occurrence of breakage and the suppression of cracking failure when inserting the wrap film into the package box can be reduced by adjusting the content of the above-mentioned compound is not clear, and is considered as follows. That is, the resin stays in the extruder for a certain time at the time of melt extrusion, and the shear force of melt extrusion can be reduced by adjusting the content of the above-mentioned compound. It is known that if the shear force of melt extrusion can be reduced, the vinylidene chloride resin can smoothly pass through the extruder, thermal decomposition of the vinylidene chloride resin is further suppressed, and the amount of inclusions derived from the vinylidene chloride resin is reduced. Therefore, it is considered that the obtained wrap film is less likely to be broken when inserted into a packaging box, and the cracking failure is suppressed. In addition, in the case where the content of the compound is within the above range, the plastic property of the wrap film is increased and the coefficient of dynamic friction with paper is decreased, and thus the wrap film is not easily damaged. The reason is assumed to be, but not limited to, this. 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 a vinylidene chloride repeating unit, and examples thereof include vinylidene chloride copolymers containing a monomer repeating unit polymerizable with a vinylidene chloride repeating unit.

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 content of the vinylidene chloride repeating unit is preferably 72 to 93mol%, more preferably 81 to 93mol%, and further preferably 86 to 93mol% with respect to the total amount of the vinylidene chloride-based resin. When the content of the vinylidene chloride repeating unit is 72mol% or more, the glass transition temperature of the vinylidene chloride resin is low and the wrap film tends to be soft. Thus, even when used in a low-temperature environment such as winter, for example, cracking of the wrap film can be reduced. On the other hand, when the content of the vinylidene chloride repeating unit is 93mol% or less, a large increase in crystallinity and deterioration in moldability at the time of film stretching tend to be suppressed. When the content of the vinylidene chloride repeating unit is 72 to 93mol%, the vinylidene chloride resin is easily carbonized, and the productivity is easily lowered. Therefore, the present invention in which the content of the above-mentioned compound is adjusted as described above is useful.

The content of the vinylidene chloride repeating unit can be measured, for example, using a high-resolution proton nuclear magnetic resonance measuring apparatus (400 MHz or more), but is not particularly limited. More specifically, 0.5g of the wrap film was dissolved in 10ml of THF (tetrahydrofuran), 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. Then, the obtained sample for measurement was dissolved in deuterated tetrahydrofuran at 5 mass%, and then the solution was subjected to H-NMR measurement under the condition that the temperature of the measurement atmosphere was about 27 ℃. The vinylidene chloride repeating unit 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 values are calculated from 3.50 to 4.20ppm, 2.80 to 3.50ppm and 2.00 to 2.80 ppm.

The content of the comonomer (vinyl chloride) in the vinylidene chloride-vinyl chloride copolymer is preferably 7 to 28% by mass, more preferably 10 to 19% by 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 tends to be reduced, and the deterioration of the moldability at the time of film stretching tends to be further 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 resin having a weight average molecular weight within the above range can be obtained by controlling the charging ratio of vinylidene chloride monomer to vinyl chloride monomer, the amount of polymerization initiator, or the polymerization temperature, for example. In the present 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 81 to 92% by weight based on the total amount of the wrap film. When the content of the vinylidene chloride resin is in the above range, the shearing force of melt extrusion tends to be reduced by the plasticizing effect of the additive or the like, and the generation of inclusions tends to be further suppressed. When the content of the vinylidene chloride resin is within the above range, the film tends to be prevented from being easily stretched and the cuttability of the film tends to be further improved. The method of measuring the content of each component by the wrap film differs depending on the analyte. For example, the content of the vinylidene chloride resin can be obtained as follows: 0.5g of the sample was dissolved in 10ml of THF (tetrahydrofuran), about 30ml of methanol was added to precipitate a resin component, and then the precipitate was separated by centrifugation, dried and subjected to gravimetric determination, thereby obtaining 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 tends to be plasticized and the moldability tends to be further improved. In addition, the frequency of occurrence of breakage is reduced, cracking failure is suppressed, and the cuttability is likely to be further improved.

The content of the citrate is more than 8 wt% and 19 wt% or less, preferably 8.1 to 15 wt%, more preferably 8.1 to 11 wt% with respect to the total amount of the wrap. When the content of the citric acid ester is within the above range, the moldability tends to be further improved. In addition, the frequency of occurrence of breakage is reduced, cracking failure is suppressed, and the cuttability is likely to be further improved. The method for measuring the content of each component in the preservative film differs depending on the analyte. The additive can be extracted from the preservative film by using organic solvents such as acetone and the like, and the content of the citrate can be obtained by gas chromatography analysis.

(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 a dibasic acid ester, the vinylidene chloride resin tends to be plasticized and the moldability tends to be further improved. In addition, the frequency of occurrence of breakage is reduced, cracking failure is suppressed, and the cuttability is likely to be further improved.

The content of the dibasic acid ester is more than 8% by weight and 19% by weight or less, preferably 8.1 to 15% by weight, and more preferably 8.1 to 11% by weight based on the total amount of the wrap film. When the content of the dibasic acid ester is within the above range, the moldability tends to be further improved. In addition, the frequency of occurrence of breakage is reduced, cracking failure is suppressed, and the cuttability is likely to be further improved. The method of measuring the content of each component by the wrap film differs depending on the analyte. The additive can be extracted from the preservative film by using organic solvents such as acetone and the like, and the content of the citrate and the dibasic acid ester can be obtained by gas chromatography analysis.

(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 tetradecanoate, 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 acetylated fatty acid glycerides, the frequency of occurrence of breakage is reduced, cracking failure is suppressed, and the cuttability is further improved.

The content of acetylated fatty acid glycerides is preferably more than 8% by weight and 19% by weight or less, preferably 8.1 to 15% by weight, more preferably 8.1 to 11% by weight, based on the total amount of the wrap film. When the content of the acetylated fatty acid glyceride is in the above range, the moldability tends to be further improved. In addition, the frequency of occurrence of breakage is reduced, cracking failure is suppressed, and the cuttability is likely to be further improved. The method of measuring the content of each component by the wrap film differs depending on the analyte. The additive can be extracted from the preservative film by using organic solvents such as acetone and the like, and the content of acetylated fatty glyceride can be obtained by 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 greater than 8% by weight and 19% by weight or less, preferably 8.1 to 15% by weight, more preferably 8.1 to 11% by weight, relative to the total amount of the wrap film. When the total content of the above-mentioned compounds is more than 8% by weight, the shear force of melt extrusion can be reduced, and the composition can smoothly pass through the extruder, thereby suppressing the thermal decomposition of the vinylidene chloride resin. Therefore, the frequency of occurrence of breakage is reduced, and cracking failure is suppressed. When the total content of the above compounds is 19 wt% or less, the elastic modulus of the film is increased appropriately. Therefore, the cuttability is further improved.

(epoxidized vegetable oil)

The wrap of the present embodiment may contain epoxidized vegetable oil. The epoxidized vegetable oil can be used 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 change in color tone of the wrap film is further suppressed, 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 wt%, more preferably 1 to 2.5 wt%, and still more preferably 1 to 2 wt% with respect to the total amount of the wrap. By setting the content of the epoxidized vegetable oil to 0.5 wt% 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 wt% or less, the color tone change of the wrap film is further suppressed, and the stickiness due to bleeding is also suppressed. The method of measuring the content of each component by the wrap film differs depending on the analyte. For example, the content of epoxidized vegetable oil can be obtained by analyzing reprecipitation filtrate of a plastic wrap by NMR.

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

Integral = integral (2.23-2.33 ppm)/integral (8.05-8.11 ppm)

(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 MBS (methyl methacrylate-butadiene-styrene copolymer).

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-tert-butylhydroquinone, 2,6-di-tert-butyl-p-cresol, 4,4 '-thiobis (6-tert-butylphenol), 2,2' -methylenebis (4-methyl-6-tert-butylphenol), octadecyl-3- (3 ',5' -di-tert-butyl-4 '-hydroxyphenyl) propionate, and 4,4' -thiobis (6-tert-butylphenol); thermal stabilizers such as laurate, myristate, palmitate, stearate, isostearate, oleate, ricinoleate, 2-ethylhexanoate, isodecanoate, neodecanoate, and calcium benzoate. The stabilizer may be used alone or in combination of two or more.

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, 2,2' -dihydroxy-4-methoxybenzophenone, and the like. 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 iron oxide red. 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 weight or less, more preferably 3% by weight or less, further preferably 1% by weight or less, and particularly preferably 0.1% by weight 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 wt% 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 failure of film breakage is suppressed, the cuttability is further improved, and the adhesion is further improved.

More specifically, by setting the thickness to 6 μm or more, the tear 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. In addition, by making the thickness 6 μm or more, a significant decrease in tear strength tends to be reduced. Therefore, it is possible to further suppress the trouble of the end portion of the wrap film cut by the cutting blade attached to the package box from being cracked when the wrap film is pulled out from the roll body and when the end portion of the wrap film wound back into the package box is pinched out.

On the other hand, by setting the thickness to 18 μm or less, the force required for cutting 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 of the present embodiment in the TD direction is 2.0 to 4.2cN, preferably 2.0 to 4.0cN, and more preferably 2.0 to 3.0cN. By setting the tear strength in the TD direction to 2.0cN or more, cracking particularly when the wrap is pulled out from the roll 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 4.2cN 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, and for example, tear strength in the TD direction tends to be improved by reducing the stretch ratio in the TD direction or by thickening 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 tensile modulus of elasticity in the MD direction of the wrap film of the present embodiment is preferably 250 to 600MPa, more preferably 350 to 500MPa, and still more preferably 350 to 470MPa. 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 tends to be improved. On the other hand, when the tensile elastic modulus in the MD direction is 600MPa or less, the film is soft, and can be cut regularly 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 drawn from the roll body and when the film end portion wound back into the package box is pinched out.

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. Without particular limitation, 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, the wrap film is physically deteriorated by a thermal history experienced during distribution or storage, and a crack failure is generated 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 susceptibility to cracking failure of the wrap due to physical deterioration can be evaluated by the low-temperature crystallization initiation temperature.

From the above-described points, the low-temperature crystallization initiation temperature of the plastic wrap of the present embodiment, as measured by a temperature-modulated differential scanning calorimeter (hereinafter also referred to as "temperature-modulated 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 the cracking failure tends to be suppressed. 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 is set to a lower temperature. By setting the low-temperature crystallization starting temperature within the above range, rearrangement of molecular chains is suppressed, and 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 existing wrap along with the difference in the low-temperature crystallization initiation temperature. For example, it is known that, 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 caused. 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 known that, as the preservative film is exposed to high temperatures, rearrangement of molecular chains is more likely to occur, and thus the film is physically deteriorated and a crack failure is likely to be 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 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, in the case where the wrap is regarded as not heated at all after the production, the low-temperature crystallization start temperature is 40 ℃. Since it is considered that the lower the low-temperature crystallization initiation temperature, the closer to this temperature, the more the rearrangement of the molecular chains and the cracking failure can be suppressed, the lower limit of the temperature range of the low-temperature crystallization initiation temperature is set to 40 ℃.

The method of adjusting the low-temperature crystallization initiation temperature to the above range is not particularly limited, and for example, a method of 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 start temperature" refers to an extrapolated crystallization start 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 modulation DSC (which is a temperature of an intersection of an extension line of a base line on a low-temperature side to a high-temperature side in temperature rise measurement and a tangent line drawn at a point where an inclination becomes maximum on a curve on the low-temperature side of a crystallization peak, as described in JIS K7121).

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 was set to 0 to 180 ℃, the temperature rise rate was set to 10 ℃/min, the temperature rise step width was set to 4 ℃, and the isothermal time was 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 a differential scanning calorimeter, crystallization and crystal melting occur competitively. Therefore, in the conventional DSC measurement method, the heat flow resulting from the formation/growth of the microcrystals is balanced with the heat flow of melting, and it is difficult to study the thermal behavior of the 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 step-and-scan measurement by 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, step-and-scan measurement by temperature modulation DSC is used for measuring the low-temperature crystallization initiation temperature in the present embodiment.

(pulse NMR)

In the wrap film of the present embodiment, the ratio of the high motility component measured by pulse NMR is preferably 11.5% or less, more preferably 11% or less, further preferably 10% or less, and particularly preferably 9.7% or less. The lower limit of the proportion of the high motility component is preferably 4% or more, more preferably 6% or more, and preferably 8% or more. When the ratio of the high motility component is within the above range, the frequency of occurrence of breakage tends to be further reduced.

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 is 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.

[ number 1]

Here, the number of the first and second electrodes,

ts: relaxation time of Low-mobility Components

Tm: relaxation time of intermediate component

Tl: relaxation time of highly mobile components

Wa: weber (Weibull) coefficient (fixed at 1.0).

As specific conditions for the pulse NMR measurement, the following conditions in examples can be employed.

[ 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 93mol% of vinylidene chloride repeating units) 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 compounded as necessary. The mixer is not particularly limited, and for example, a ribbon mixer, a henschel mixer, or the like can be used. The obtained composition is preferably used in the next step after aging for about 1 to 30 hours.

(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 1 st pinch roll 7 and 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. Then, the parison 8 is reheated with warm water in an opened state to a temperature suitable for stretching. The 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 an appropriate temperature as described above, and the bubble 10 is formed. The air expands the parison from the inside, thereby stretching the film to obtain a stretched film. The stretching of the film in the TD direction is mainly performed by the amount of air, and the 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 4 to 6 times, and more preferably 4.5 to 5.5 times. 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, for example, 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. 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 bubbles 10.

The stretching speed in the MD in the stretching step of the present embodiment is preferably 0.09 to 0.13 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.

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 and the stretching ratio 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. 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, but 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 roll 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 wrap films 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 relaxation ratio in the relaxation step 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, rearrangement of molecular chains can be suppressed, 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 step)

The wrap film thus wound is slit, and is wound while being peeled off so as to be a single wrap film, and is stored in a large roll for 1 to 3 days. Finally, the rolled wrap is returned from the large roll to the 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 lower, 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 the slit roll, it is possible to suppress the physical deterioration of the film due to the rearrangement of the molecular chains. This tends to prevent the end of the wrap film, which is easily cut by the cutting blade attached to the package box, from being cracked when the wrap film is pulled out from the roll body or when the end of the wrap film is pinched out into the package box.

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

Therefore, it is preferable that the slit large roll is stored under the above-mentioned storage condition, whereby a film in which the formation and growth of crystallites are suppressed and the orientation of the molecular chains in the amorphous portion is relaxed 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 slit large roll is not particularly limited after storage, and is wound back onto a paper core or the like, for example, and is stored in the package 1 having the film slitting blade 15 shown in fig. 2 in the form of a wound body 16. As illustrated in fig. 2, the wrap film 17 is pulled out for use.

[ examples ]

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

[ content of vinylidene chloride repeating units ]

The ratio of vinylidene chloride repeat units of the cling 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% by weight, and the resulting solution was subjected to H-NMR under the condition that the measurement atmosphere temperature was about 27 ℃. For example, the vinylidene chloride repeating unit content of the copolymer of vinylidene chloride and vinyl chloride is calculated from 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 the case of other copolymers, the content of the repeating unit can be calculated from 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 constant temperature bath set at 28 ℃. The thickness was measured in an atmosphere of 23 ℃ and 50% RH using an apparatus specified in JIS 7127.

[ 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 measurement of the tear strength of the wrap film, the tear strength was measured in an atmosphere of 23 ℃ and 50% RH using a light load tear tester type D (Toyo Seiki Seisaku-Sho Ltd.). The tear strength of the wrap was measured using only 1 wrap. The sample length in the tearing direction was set to 63.5mm, and the sample width was set to 50.0mm. 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. The film was then scored with a cut using a knife mounted in the apparatus, and the pendulum was carefully released to read the amount of force required to tear the test piece. 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 film after shipment and storage at home, the wrap film after production was stored in a constant temperature bath set at 28 ℃ for 1 month, and then the tensile modulus was measured. The tensile modulus of the wrap film was measured by using Autograph AG-IS (Shimadzu corporation) and evaluated in an atmosphere of 23 ℃ and 50% RH. The tensile modulus was measured at 50 times by dividing the load at 2% elongation by the cross-sectional area of the sample measured under the conditions of a stretching speed of 5 mm/min, a collet pitch of 100mm and a film width of 10 mm. 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. In addition, the test piece may not be cracked and rolled due to 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 film after shipment and storage at home, a measurement sample obtained by storing the wrap film after production in a constant temperature bath set at 28 ℃ for 1 month was used. 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 measurements were also performed under these conditions for an empty aluminum sample pan, and the temperature-heat flow curve of the cling film was corrected. The temperature at which heat release due to low-temperature crystallization starts out of the non-reversible components of the corrected temperature-heat flow curve is taken as the low-temperature crystallization start temperature.

[ pulse NMR ]

The cut roughly square wrap film (1 g) was rolled into a folded cylinder and filled into an NMR tube having a diameter of 10 mm. The spin-spin relaxation time T2 was measured using pulse NMR under the following conditions.

[ Condition ]

The device comprises the following steps: JEOL Mu25

Nuclides: 1H

And (3) determination: t2

The determination method comprises the following steps: solid echo method

Pulse width: 2.1-2.2 mu s

Pulse interval: 7.0 mus

Measuring temperature: 40 deg.C (15 minutes after reaching the set temperature)

Cumulative number of times: 256 times

Repetition time: 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 the following first term is taken as a low mobility component, a component represented by a weber function of the following second term is taken as an intermediate component, and a component represented by a Lorentz (Lorentz) function of the following third term is taken as a high mobility component.

[ number 2]

Cs: mole fraction of low motility component

Cm: mole fraction of intermediate component

Cl: mole fraction of highly motile ingredient

Ts: relaxation time of Low-mobility Components

Tm: relaxation time of intermediate component

Tl: relaxation time of highly mobile components

Wa: weber coefficient (fixed as 1.0)

[ evaluation of frequency of occurrence of breakage ]

In a process of loading a paper core wound with a cut and rewound film into a packaging box after film formation, when an end face of the film wound around the paper core comes into contact with paper on the inner surface of the packaging box, the end face of the film may be damaged by an impact at the time of contact to a length of 1mm or more. When a breakage having a length of 1mm or more occurs, the film may be continuously broken in the drawing direction from the broken portion as a starting point when the film is drawn.

From the above, the frequency of occurrence of breakage was evaluated as follows. Fig. 3 is a schematic diagram showing the evaluation of the frequency of occurrence of breakage. First, 15 wound bodies were prepared by winding 20m of the films prepared in examples and comparative examples, respectively, with a width of 29cm on a paper core having a length of 31cm, an inner diameter of 30mm, and a paper thickness of 2 mm. At this time, the distance between the end face of the paper core on one side and the film end was 5mm.

Next, assuming a slitting, rewinding and packaging step immediately after film formation, as shown in fig. 3, one end of the wound body immediately after film formation is fixed to a metal jig, and the other end edge is disposed in contact with paper used for a package attached to a conveyor. At this time, the roll body was inclined so that the inclination angle with respect to the paper of the package was 3.7 °. Then, the belt was moved at a speed of 0.27 m/min for 30cm while the film end of the roll was in contact therewith, whereby the film end was rubbed against the paper of the package.

The operation of rubbing the film end against the paper of the pack was performed 4 times while changing the position of the film end. Specifically, the film end portions at every 90 ° as viewed in the transverse direction of the paper core are rubbed against the paper of the package. Then, the occurrence of breakage was evaluated by confirming the presence or absence of breakage at 4 sites. The same operation was performed for all 15 wound bodies, and the mutual rubbing was performed for 60 sites in total of 15 × 4 sites. Thereafter, the 60-site mutual rubbing portions were confirmed, and the frequency of occurrence of breakage was evaluated as follows.

(evaluation criteria for frequency of occurrence of breakage)

Very good: the occurrence rate of breakage with a size of 1mm or more among 60 parts is less than 10%

Good component: the occurrence rate of breakage with a size of 1mm or more in 60 parts is 10% or more and less than 20%

And (delta): the occurrence rate of breakage with a size of 1mm or more in 60 parts is 20% or more and less than 30%

X: the occurrence rate of breakage of 1mm or more in size in 60 parts is 30% or more

[ incidence of cracking failure ]

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

First, 1 wound body was housed in 1 rectangular parallelepiped container (package box inner dimension: 42mm × 42mm × about 233 mm) to obtain a wound body housing, 60 wound body housings were housed in a corrugated box (inner dimension 28cm × 46cm × 24 cm) without a gap, and the wound body was fixed to a vibration table with a tape 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 in an atmosphere of 23 ℃ and relative humidity 50% RH. The vibration test was carried out in an automatic mode with the frequency changed in the order of 5Hz, 30Hz, 5Hz between 30 seconds for 20 minutes in this cycle.

Thereafter, cracking failure evaluation was performed in an atmosphere of 23 ℃ and relative humidity 50% RH. As an evaluator, 100 persons who daily used the wrap film for food packaging were selected. The evaluator performed 10 times a series of operations of pulling out a 50cm film from a roll having a width of about 23cm and 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 the film was pulled out from the roll body and could not be smoothly pulled out, which was the number of times 1000 times in total of 10 times for 100 persons each.

(evaluation criteria for cracking failure occurrence Rate)

Excellent: less than 5%: almost no cracking failure and excellent ease of use.

O: 5% or more and less than 10%: less cracking failure and excellent usability.

● :10% or more and less than 15%: has less cracking failure and good usability.

And (delta): 15% or more and less than 20%: cracking failure is slightly more, and usability is poor.

X: more than 20 percent: cracking failure is very numerous and ease of use is very poor.

[ cuttability of film ]

Similarly to the cracking failure suppression effect, the film was evaluated for cuttability after storage of the roll immediately after manufacture in a thermostatic bath set at 28 ℃ for 1 month under assumption of distribution after shipment and storage at home.

The evaluation was carried out in an atmosphere of 23 ℃ and a relative humidity of 50% RH. 100 persons who daily used the wrap film for food packaging were selected as evaluators, and the evaluators each pulled out a 50cm film from a 22 cm-wide roll stored in a packaging box and then cut the film with a tin-plated iron sheet film cutting blade attached to the packaging box, evaluated the ease of cutting for 3 minutes per 1 person, and evaluated the total score of 100 persons. The score of each evaluator was very good in the case of 3 points, good in the case of 2 points, poor in the case of 1 point, and very poor in the case of 0 point. Based on the total score of 100 persons, the cuttability was evaluated in the following 4 grades.

Evaluation mark

Very good: the total content is more than 250: can cut very easily and smoothly

O: the total score is more than 200 and less than 250: can be easily and smoothly cut

And (delta): the total score is more than 150 and less than 200: can cut the film relatively easily

X: the total score is less than 150: the cutting force is required and the cutting property is poor

[ example 1]

91.3 parts by mass of a vinylidene chloride resin having a weight average molecular weight of 90,000 (having a vinylidene chloride repeating unit of 88mol% and a vinyl chloride repeating unit of 12 mol%), 8.1 parts by mass of tributyl acetylcitrate (Takaki Kagaku Co., ltd.), and 0.6 part by mass of epoxidized soybean oil (Newcizer 510R, nippon 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 branch 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 at an average stretching speed of 0.13 times/s to 4.1 times in the MD and 3.5 times/s to 5.8 times in the TD to form a cylindrical film (bubble).

After the obtained cylindrical film was folded flat by sandwiching it, the film was relaxed by 10% in the MD direction by controlling the speed ratio of the pinch roll to the take-up roll, and 2 overlapped films having a fold width of 280mm were taken up at a take-up speed of 18 m/min. 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, the film was stored at 17 ℃ and wound on a paper core having an outer diameter of 36mm and a length of 230mm for 20m to obtain a wound body of wrap film. Each evaluation was performed using the wound body of the obtained wrap film.

Examples 2 to 6 and comparative examples 1 to 7

Rolls of wrap films of examples 2 to 6 and comparative examples 1 to 7 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.

In addition, ATBC: acetyl tributyl citrate

DBS: sebacic acid dibutyl ester

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.

Description of the symbols

1 … extruder, 2 … die, 3 … die, 4 … soaking part (tubular composition), 5 … soaking liquid (peeling agent for inflation molding), 6 … cold water tank, 7 … first pinch roller, 8 … parison, 9 … second pinch roller, 10 … bubble, 11 … first 3 pinch roller, 12 … double-layer film, 13 … take-up roller, 14 … packing box, 15 … film cutting blade, 16 … winder, 17 … preservative film.

Claims

1. A plastic wrap, wherein,

the tearing strength of the preservative film in the TD direction is 2.0 cN-4.2 cN.

2. The wrap of claim 1, wherein the tensile modulus of elasticity in the MD direction is 250MPa to 600MPa.

3. The wrap of claim 1, wherein the tensile modulus of elasticity in the MD direction is 350MPa to 500MPa.

4. The wrap film according to any one of claims 1 to 3, wherein a low-temperature crystallization initiation temperature measured by a temperature-modulated differential scanning calorimeter is 40 to 60 ℃.

5. The cling film of claim 1, wherein the cling film has a thickness of 6-18 μm.

6. The cling film of claim 1,

7. The wrap film according to claim 1, wherein the vinylidene chloride resin contains a vinylidene chloride repeating unit in an amount of 86 to 93mol%.

8. The wrap film according to claim 1, wherein a ratio of the high motility component measured by pulse NMR is 11.5% or less.