JP7352414B2 - wrap film - Google Patents

Description

The present invention relates to a wrap film.

Vinylidene chloride resins have excellent properties such as transparency, water resistance, and gas barrier properties, and are therefore used as food packaging materials such as wrap films. In recent years, there has been a demand for food packaging materials to have not only the above-mentioned properties but also properties such as moldability and thermal stability, and to be highly functional. Examples of methods for making food packaging materials highly functional include adding additives such as plasticizers and heat stabilizers. As such an additive, for example, epoxidized vegetable oil is used to suppress a change in color tone of the wrap film.

However, when food packaging materials containing epoxidized vegetable oils are stored for a long period of time, problems such as odor caused by the epoxidized vegetable oils may occur. In order to improve these problems, various food packaging materials have been proposed.

For example, Patent Document 1 proposes a food packaging material with reduced odor by limiting the peroxide value of epoxidized soybean oil to a specific value or less. Furthermore, Patent Document 2 proposes a wrap film that achieves both adhesion and pullability by blending epoxidized vegetable oil with specific amounts of glycerin fatty acid ester and aliphatic dibasic acid ester. . Further, Patent Document 3 proposes a polywrap film that achieves both odor reduction and thermal decomposition suppression by controlling the peroxide value, compounding amount, and epoxy ring opening rate of epoxidized soybean oil.

Japanese Patent Application Publication No. 8-27341 Japanese Unexamined Patent Publication No. 11-199736 Japanese Patent Application Publication No. 2008-74955

However, even if conventional food packaging materials are blended with epoxidized vegetable oil, they cannot sufficiently capture hydrogen chloride gas generated from vinylidene chloride resin, and the odor caused by the hydrogen chloride gas may become a problem. be. On the other hand, in food packaging materials that contain a large amount of epoxidized vegetable oil in order to sufficiently capture the hydrogen chloride gas, the epoxidized vegetable oil bleeds out and the texture deteriorates. Tearing problems and reduced drawability are likely to occur.

Therefore, conventional food packaging materials containing epoxidized vegetable oil have room for improvement in odor, coloring, texture, tearing problems, and pullability due to bleed-out of epoxidized vegetable oil.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a wrap film that has an excellent feel to the touch, suppresses tearing troubles and deterioration in drawability, and has excellent color resistance.

The present inventors have made extensive studies to solve the above problems. As a result, the inventors discovered that the above problems could be solved by using a predetermined epoxidized fatty acid alkyl ester, and completed the present invention.

That is, the present invention is as follows.
[1]
Contains a vinylidene chloride resin and an epoxidized fatty acid alkyl ester having a viscosity of 100 mPa·s or less at 30°C,
The low-temperature crystallization initiation temperature measured by a temperature modulation differential scanning calorimeter is 40 to 60°C,
The thickness is 6 to 18 μm.
wrap film.
[2]
The content of the epoxidized fatty acid alkyl ester is 0.1 to 3% by mass based on the total amount of the wrap film.
The wrap film according to [1].
[3]
The wrap film according to [1] or [2], which has a tear strength in the TD direction of 2 to 6 cN.
[4]
The wrap film according to any one of [1] to [3], which has a tensile modulus in the MD direction of 250 to 600 MPa.
[5]
The vinylidene chloride-based resin contains 72 to 93% by mass of vinylidene chloride repeating units,
The wrap film according to any one of [1] to [4].
[6]
Contains at least one compound selected from the group consisting of citric acid esters and dibasic acid esters,
The content of the compound is 3 to 8% by weight based on the total amount of the wrap film.
The wrap film according to any one of [1] to [5].

According to the present invention, it is possible to provide a wrap film that has an excellent feel to the touch, suppresses tearing troubles and deterioration in drawability, and has excellent color resistance.

1 is a schematic diagram of an apparatus used in the film forming process of the present invention. It is an example of the utilization form of the film of this invention.

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

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

[Wrap film]
The wrap film of this embodiment contains a vinylidene chloride resin and an epoxidized fatty acid alkyl ester with a viscosity of 100 mPa·s or less at 30°C, and contains low-temperature crystals measured with a temperature modulated differential scanning calorimeter. The starting temperature is 40 to 60°C, and the thickness is 6 to 18 μm. This embodiment will be described in detail below.

(vinylidene chloride resin)
Vinylidene chloride-based resins are not particularly limited as long as they contain vinylidene chloride repeating units, and include vinylidene chloride homopolymers as well as vinylidene chloride copolymers containing monomer repeating units that can be polymerized with vinylidene chloride repeating units. can be mentioned. Among these, vinylidene chloride copolymer is preferred.

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

The content of vinylidene chloride repeating units is preferably 72 to 93% by mass, more preferably 81 to 90% by mass, based on the total amount of vinylidene chloride resin. When the content of vinylidene chloride repeating units is within the above range, crystal formation tends to be suppressed. Therefore, even when stored at high temperatures for a long period of time, bleed-out of the epoxidized vegetable oil is suppressed, which further improves the feel of the wrap film and prevents tearing problems and decreases in pullability. can.

The content of vinylidene chloride repeating units is not particularly limited, but can be measured using, for example, a high-resolution proton nuclear magnetic resonance measuring device (400 MHz or higher). More specifically, the reprecipitated filtrate of the wrap film is vacuum-dried, and a solution in which 5% by weight is dissolved in deuterated tetrahydrofuran is subjected to H-NMR measurement at a measurement atmosphere temperature of about 27°C. The vinylidene chloride repeating unit is calculated using the characteristic chemical shift based on tetramethylsilane in the obtained spectrum. For example, for a copolymer of vinylidene chloride and vinyl chloride, calculation is performed using peaks of 3.50 to 4.20 ppm, 2.80 to 3.50 ppm, and 2.00 to 2.80 ppm.

To obtain the reprecipitated filtrate of the wrap film, dissolve 0.5 g of the sample in 10 ml of THF (tetrahydrofuran), add about 30 ml of methanol to precipitate the resin content, and then separate the precipitate by centrifugation. One method is to dry it.

Further, the comonomer (vinyl chloride) content of 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 feel of the wrap film is further improved, and tearing troubles and deterioration in drawability tend to be suppressed.

The weight average molecular weight of the vinylidene chloride copolymer is preferably 80,000 to 200,000, more preferably 90,000 to 180,000, and even more preferably 100,000 to 170,000. When the weight average molecular weight (Mw) is within the above range, deterioration of the wrap film due to shear heat generation during melt extrusion tends to be suppressed. This tends to suppress the ring opening of the epoxy group of the epoxy compound in the wrap film, and further suppress the multimerization of the epoxy compound. As a result, even when the wrap film is stored at high temperatures for a long period of time, bleed-out of the epoxy compound is suppressed, resulting in an even better texture of the wrap film and suppressing tearing problems and deterioration in pullability. I can do it. Moreover, the mechanical strength of the wrap film tends to be further improved. A vinylidene chloride resin having a weight average molecular weight within the above range can be obtained by, for example, controlling the charging ratio of vinylidene chloride monomer and vinyl chloride monomer, the amount of polymerization initiator, or the polymerization temperature. In this embodiment, the weight average molecular weight (Mw) can be determined by gel permeation chromatography (GPC) using a standard polystyrene calibration curve.

The content of the vinylidene chloride resin is more preferably 90.0 to 97.0% by weight, more preferably 92.0 to 95.5% by weight, and even more preferably It is 92.5 to 94.0% by weight. When the content of vinylidene chloride resin is within the above range, processability during melt extrusion molding tends to be further improved. Note that the method for measuring the content of each component from the wrap film differs depending on the substance to be analyzed. For example, the content of vinylidene chloride resin can be obtained by vacuum drying a reprecipitated filtrate of a wrap film and measuring its weight.

(Epoxidized fatty acid alkyl ester)
The viscosity of the epoxidized fatty acid alkyl ester at 30° C. is 100 mPa·s or less, preferably 5 to 70 mPa·s, and more preferably 10 to 40 mPa·s. When the viscosity is within the above range, compatibility with the vinylidene chloride resin is improved, so bleed-out is suppressed and the feel to the touch is further improved.
In addition, epoxidized fatty acid alkyl esters have a significantly lower viscosity at 30°C than epoxidized vegetable oils such as epoxidized soybean oil and epoxidized linseed oil, which suppresses bleed-out and improves the texture. This will further improve the feeling.

The number of carbon atoms in the alkyl group in the epoxidized fatty acid alkyl ester is preferably 1 to 30, more preferably 3 to 18. The alkyl group may be linear or branched. Such epoxidized fatty acid alkyl esters include, but are not particularly limited to, epoxidized fatty acid 2-ethylhexyl, epoxidized fatty acid butyl, and the like. By using an epoxidized fatty acid alkyl ester, bleeding is suppressed, and even if it bleeds out, the sticky feeling is suppressed, so the feel to the touch tends to be further improved.

Further, the concentration of oxirane oxygen in the epoxidized fatty acid ester is preferably 3% by mass or more and 15% by mass or less, more preferably 5% by mass or more and 13% by mass or less.

The content of the epoxidized fatty acid alkyl ester is preferably 0.1 to 3% by mass, more preferably 0.5 to 2.5% by mass, even more preferably 1.5% by mass, based on the total amount of the wrap film. It is 0 to 2.3% by mass. When the content of the epoxidized fatty acid alkyl ester is within the above range, the bleed-out of the epoxidized fatty acid alkyl ester is further suppressed, the feel is good to the touch, and tearing problems and deterioration in drawability tend to be suppressed. . Note that the method for measuring the content of each component from the wrap film differs depending on the substance to be analyzed. For example, the content of epoxidized fatty acid alkyl ester can be obtained by extracting the additive from the wrap film using an organic solvent such as acetone and analyzing it by gas chromatography.

(citric acid ester)
The wrap film of this embodiment may also contain citric acid ester. Examples of the citric acid ester include, but are not limited to, triethyl citrate, tributyl citrate, acetyl triethyl citrate, acetyl tributyl citrate (ATBC), and tri-n-(2-ethylhexyl acetyl citrate). Among these, tributyl acetyl citrate is preferred. By using such a citric acid ester, the vinylidene chloride resin is plasticized and moldability tends to be further improved.

The content of citric acid ester is preferably 3 to 8% by weight, more preferably 3.5 to 7% by weight, and still more preferably 4 to 6% by weight, based on the total amount of the wrap film. When the content of citric acid ester is within the above range, moldability tends to be further improved. Note that the method for measuring the content of each component from the wrap film differs depending on the substance to be analyzed. The content of citric acid ester can be obtained by extracting the additive from the wrap film using an organic solvent such as acetone and analyzing it by gas chromatography.

(Dibasic acid ester)
The wrap film of this embodiment may contain a dibasic acid ester. Examples of dibasic acid esters include, but are not particularly limited to, adipate esters such as dibutyl adipate, di-n-hexyl adipate, di-2-ethylhexyl adipate, and dioctyl adipate; di-2-ethylhexyl azelaate; Azelaic acid esters such as octyl azelate; sebacic acid esters such as dibutyl sebacate (DBS) and di-2-ethylhexyl sebacate; and phthalic acid esters such as dimethyl phthalate, diethyl phthalate, and dioctyl phthalate. Among these, aliphatic dibasic acid esters are preferred, and dibutyl sebacate is more preferred. By using such a dibasic acid ester, the vinylidene chloride resin is plasticized and moldability tends to be further improved.

The content of the dibasic acid ester is preferably 3 to 8% by weight, more preferably 3.5 to 7% by weight, and even more preferably 4 to 6% by weight based on the total amount of the wrap film. . When the content of the dibasic acid ester is within the above range, moldability tends to be further improved. Note that the method for measuring the content of each component from the wrap film differs depending on the substance to be analyzed. The content of citric acid ester and dibasic acid ester can be obtained by extracting the additive from the wrap film using an organic solvent such as acetone and analyzing it by gas chromatography.

The wrap film of this embodiment may contain at least one compound selected from the group consisting of citric acid esters and dibasic acid esters. In this case, the total content of citric acid ester and dibasic acid ester is preferably 3 to 8% by weight, more preferably 3.5 to 7% by weight, and even more preferably is 4 to 6% by weight. By having the total content of citric acid ester and dibasic acid ester within the above range, molding processability is further improved and excessive stickiness due to bleeding of the wrap film when containing a high content of epoxidized vegetable oil is suppressed. There is a tendency.

(Other additives)
The wrap film of this embodiment may contain other additives as necessary. Such additives are not particularly limited, but include, for example, stabilizers other than epoxidized fatty acid alkyl esters, plasticizers other than citric acid esters and dibasic acid esters, weather resistance improvers, and colorants such as dyes or pigments. , antifogging agents, antibacterial agents, lubricants, nucleating agents, oligomers such as polyester, and polymers such as MBS (methyl methacrylate-butadiene-styrene copolymer).

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

The content of the plasticizer is preferably 1.0 to 6.0% by mass, more preferably 1.5 to 5.5% by mass, and even more preferably 2.0% by mass, based on the total amount of the wrap film. ~5.0% by mass. When the content of the plasticizer is 1.0% by mass or more, the adhesion of the wrap film tends to be further improved. Moreover, when the content of the plasticizer is 6.0% by mass or less, bleed-out is suppressed and the feel to the touch tends to be further improved.

Stabilizers other than epoxidized fatty acid alkyl esters are not particularly limited, but specifically include 2,5-t-butylhydroquinone, 2,6-di-t-butyl-p-cresol, 4,4'- Thiobis-(6-t-butylphenol), 2,2'-methylene-bis-(4-methyl-6-t-butylphenol), octadecyl-3-(3',5'-di-t-butyl-4' -hydroxyphenyl) propionate, and antioxidants such as 4,4'-thiobis-(6-tert-butylphenol); laurate, myristate, palmitate, stearate, isostearate, oleate. , ricinoleate, 2-ethyl-hexylate, isodecanoate, neodecanoate, and calcium benzoate. The stabilizers may be used alone or in combination of two or more.

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

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

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

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

The lubricant is not particularly limited, but specifically includes fatty acid hydrocarbon lubricants such as ethylene bissteramide, butyl stearate, polyethylene wax, paraffin wax, carnauba wax, myristyl myristate, stearyl stearate, and higher fatty acid lubricants. , fatty acid amide lubricants, and fatty acid ester lubricants. The lubricants may be used alone or in combination of two or more.

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

The content of other additives is preferably 5% by weight or less, more preferably 3% by weight or less, even more preferably 1% by weight or less, particularly preferably 0.1% by weight, based on the total amount of the wrap film. It is as follows. Further, the lower limit of the content of other additives is not particularly limited, but is 0% by weight or more based on the total amount of the wrap film.

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

More specifically, when the thickness is 6 μm or more, the tensile strength of the wrap film in the TD direction and the MD direction is further improved, and film breakage during use is further suppressed. Further, since the thickness is 6 μm or more, there is little significant decrease in tear strength. Therefore, when pulling out the wrap film from the rolled body or picking out the end of the film that has been rewound into the gift box, the problem of the wrap film tearing from the edge cut by the cutting blade attached to the gift box is more likely. suppressed.

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

(tear strength)
The wrap film of this embodiment has a tear strength in the TD direction of 2 to 6 cN, preferably 2.5 to 4 cN. When the tear strength in the TD direction is 2 cN or more, it is possible to reduce tearing particularly when the wrap film is pulled out from the wound body, and it is also possible to suppress unintended tearing troubles when the wrap film is used. On the other hand, when the tear strength in the TD direction is 6 cN or less, the film is easily torn when cut in the TD direction with a saw blade attached to the cosmetic box, and the cutting performance is improved.

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

(Tensile modulus)
The wrap film of this embodiment has a tensile modulus in the MD direction of 250 to 600 MPa, preferably 350 to 550 MPa. By having a tensile modulus of elasticity in the MD direction of 250 MPa or more, when applying force to cut the film with a saw blade, the extension of the film in the MD direction can be suppressed, the saw blade can easily bite into the film, and the cutting properties can be improved. will improve. On the other hand, since the tensile modulus in the MD direction is 600 MPa or less, the film is soft and can be cut neatly along the shape of the saw blade, and the generation of many tears on the cut end surface can be suppressed. As a result, when the film is pulled out from the roll and when the end of the film rewound into the presentation box is picked out, it is possible to suppress the occurrence of troubles in which the film is torn from the cut end surface.

The tensile modulus of the wrap film of this embodiment in the MD direction can be adjusted by adjusting the composition of the vinylidene chloride resin, the additive composition, the stretching ratio of the film, the stretching speed, and the like. Although not particularly limited, for example, the tensile modulus in the MD direction tends to be improved by increasing the draw ratio or reducing the amount of additives. As a result, it tends to decline. Note that the tensile modulus is measured by the method described in Examples.

(Low temperature crystallization start temperature)
In the wrap film of this embodiment, the wrap film undergoes physical deterioration due to heat history during distribution and storage, and tearing troubles caused by this are suppressed by the low crystallization start temperature. The low-temperature crystallization onset temperature is an index that indicates the thermal stability of microcrystals that are formed and grown by exposure to high temperatures during distribution and warehouse storage after manufacturing the wrap film. The degree of alignment, that is, the ease with which tearing problems occur due to physical deterioration of the wrap film can be evaluated.

From the above point of view, the low-temperature crystallization initiation temperature of the wrap film of the present embodiment measured by a temperature-modulated differential scanning calorimeter (hereinafter also referred to as "temperature-modulated DSC") is preferably 40 to 60°C. is 40 to 55°C, more preferably 40 to 50°C. When the low-temperature crystallization initiation temperature is within the above range, tearing troubles can be suppressed while maintaining the cuttability of the wrap film. The details will be explained below.

The low-temperature crystallization initiation temperature of conventional wrap films exceeds 60°C. On the other hand, the low-temperature crystallization start temperature of the wrap film of this embodiment is 60° C. or lower, and is set at a lower temperature. When the low-temperature crystallization initiation temperature is within the above range, the rearrangement of molecular chains is suppressed, and the trouble of tearing the wrap film is further suppressed.

More specifically, due to the difference in low-temperature crystallization initiation temperature, the wrap film of this embodiment and the conventional wrap film behave differently when heated. For example, it is thought that when conventional wrap films are exposed to an atmosphere of 20°C or higher for a long time during distribution or storage in a warehouse, the molecular chains of the vinylidene chloride resin rearrange, causing the formation and growth of microcrystals. It will be done. It is presumed that such molecular chain rearrangement occurs because the molecular chain orientation of the produced wrap film or the stress of the film is not sufficiently relaxed. It is thought that the more a wrap film is exposed to high temperatures, the more rearrangement of molecular chains occurs, which leads to physical deterioration of the film and the more likely it is to cause tearing problems.

On the other hand, in the wrap film of this embodiment, the low-temperature crystallization initiation temperature is set to 60° C. or lower by sufficiently relaxing the orientation of the molecular chains of the vinylidene chloride resin and the stress of the film during production. As a result, in the wrap film of this embodiment, even if it is exposed to temperatures of 20° C. or higher for a long period of time during distribution and storage in a warehouse, rearrangement of molecular chains is unlikely to occur, and deterioration of the film and further tearing problems are suppressed. As a result, it is possible to simultaneously achieve the contradictory tasks of suppressing tearing troubles while maintaining cuttability.

On the other hand, the present inventors investigated and found that the low-temperature crystallization initiation temperature was 40°C when the wrap film was stored at -30°C, which is below the glass transition temperature, after production. That is, the low-temperature crystallization initiation temperature was 40° C. when it can be considered that the wrap film was not exposed to any heat after production. It is thought that the closer the low-temperature crystallization initiation temperature is to this temperature, the more the molecular chain rearrangement and furthermore the tearing trouble can be suppressed, so the lower limit of the temperature range of the low-temperature crystallization initiation temperature is set at 40°C.

Note that the method for adjusting the low-temperature crystallization initiation temperature within the above range is not particularly limited, but includes, for example, a method of sufficiently relaxing the orientation of the molecular chains of the vinylidene chloride resin and the stress of the film. More specifically, a method of storing the wrap film at a low temperature for a predetermined period of time can be mentioned.

Here, "low-temperature crystallization initiation temperature" refers to the exothermic peak due to low-temperature crystallization (the method described in JIS K7121 Similarly, in temperature rise measurement, it is the temperature at the intersection of the line extending the baseline on the low temperature side to the high temperature side and the point of contact drawn at the point where the gradient is maximum on the curve on the low temperature side of the crystallization peak.

An example of a method for measuring the low-temperature crystallization initiation temperature will be described. First, a differential scanning calorimeter (DSC) (input compensation type double furnace DSC 8500) manufactured by PerkinElmer is used to obtain a temperature-heat flow curve of the irreversible component in step scan measurement mode. The conditions for the step scan measurement at this time are that the measurement temperature is 0 to 180°C, the temperature increase rate is 10°C/min, the temperature increase step width is 4°C, and the isothermal time is 1 min. In the obtained temperature-heat flow curve, the extrapolation start temperature of the exothermic peak due to low-temperature crystallization is defined as the low-temperature crystallization start temperature.

In temperature-rise measurements using differential scanning calorimetry, crystallization and crystal melting occur in competition. Therefore, in the conventional DSC measurement method, the heat flow originating from the formation/growth and melting of microcrystals cancels each other out, making it difficult to study the thermal behavior of microcrystals. It was difficult to distinguish. On the other hand, when temperature-modulated DSC is used, it is possible to separate the heat flow into irreversible components such as crystallization and reversible components such as crystal melting and glass transition, making it possible to evaluate the thermal behavior of microcrystals. . Therefore, in the measurement of the low-temperature crystallization start temperature in this embodiment, a temperature modulation type DSC is used.

[Method for manufacturing wrap film]
The method for producing the wrap film of the present embodiment is not particularly limited, but for example, a composition containing a vinylidene chloride resin and an epoxidized fatty acid alkyl ester having a viscosity of 100 mPa·s or less at 30°C is melt-extruded to form a film. The method includes a step of forming the film into a shape, and a step of stretching the obtained film in the MD direction and the TD direction. The details will be explained below.

(Mixing process)
FIG. 1 shows a schematic diagram of an example of a process for manufacturing a wrap film. First, a composition is obtained by mixing a vinylidene chloride resin and an epoxidized fatty acid alkyl ester using a mixer. At this time, various additives may be mixed as necessary. The mixer is not particularly limited, and for example, a ribbon blender, Henschel mixer, or the like can be used. The obtained composition is preferably aged for about 1 to 30 hours before being used in the next step.

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

(cooling process)
A sock liquid 5 is injected into the inside of the sock 4, and the outside of the sock 4 is brought into contact with cold water in a cold water tank 6. As a result, the sock 4 is cooled from both the inside and the outside, and the film forming the sock 4 is solidified. The solidified sock 4 is folded by a first pinch roll 7 to form a parison 8.

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

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

The process from the first pinch roll 7 to the third pinch roll 11 is called a stretching process. Since the stretchability of parison 8 improves when the stretching speed is lowered, in the conventional wrap film production method, 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. It was adjusted to 0x/s or less. On the other hand, in the method for producing a wrap film of the present embodiment in which the crystallization start temperature is controlled at 40 to 60°C, the stretching ratio in the MD and TD directions and the stretching speed in the MD and TD directions are adjusted to predetermined values. It is preferable to adjust it within a range.

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

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

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

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

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

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

The relaxation ratio in the relaxation process using the third pinch roll 11 and the take-up roll 13 is preferably 7 to 15%, more preferably 10 to 14%. When the relaxation ratio is 15% or less, the occurrence of wrinkles due to the occurrence of slack in the film between the third pinch roll 11 and the take-up roll 13 tends to be more suppressed. In addition, by having a relaxation ratio of 7% or more, the wrap film can be sufficiently relaxed, suppressing the rearrangement of molecular chains even when exposed to high temperatures, and suppressing low-temperature crystallization. The starting temperature can be set to 60°C or lower. This also tends to reduce tearing problems. Here, the "relaxation ratio" refers to the ratio at which the double-ply film 12 is contracted between the third pinch roll 11 and the take-up roll 13. For example, in the case of FIG. It can be calculated using the ratio of the take-up roll 13.

Further, the ambient temperature in the relaxation step using the third pinch roll 11 and the take-up roll 13 is preferably 25 to 32°C, more preferably 28 to 30°C. When the ambient temperature is within the above range, the formation and growth of microcrystals tends to be suppressed.

(slitting process)
The wrap film wound up as described above is slit and wound up while being peeled off into a single wrap film, and is temporarily stored in the original form for 1 to 3 days. Finally, the raw material is rewound onto a paper tube and packed into a gift box, thereby obtaining a wrap film roll housed in a gift box.

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

By adjusting the ambient temperature during storage, it is possible to suppress the formation and growth of microcrystals that can cause increased film tearing problems. Generally, raw fabric storage locations are often located at relatively high temperatures because they are adjacent to the wrap film manufacturing process or are not temperature-controlled.

In contrast, in the wrap film manufacturing method of the present embodiment, by keeping the ambient temperature at 19°C or lower during storage of the slit original fabric, physical deterioration of the film due to molecular chain rearrangement tends to be suppressed. . This prevents the wrap film from being easily torn from the edge cut with the cutting blade attached to the gift box when pulling out the wrap film from the roll or picking out the end of the film that has been rewound into the gift box. tends to be suppressed.

In addition, by keeping the ambient temperature at 5°C or higher during storage of the slit material, the wrap film is sufficiently relaxed, and if it is exposed to 20°C or higher during subsequent distribution and storage, molecular chain rearrangement is unlikely to occur. There is a tendency to

Therefore, it is preferable to store the slit original fabric under the above-mentioned storage conditions, thereby obtaining a film in which the molecular chains in the amorphous portion are relaxed in orientation while suppressing the formation and growth of microcrystals. In this way, by relaxing the orientation of the molecular chains during storage of the original film, it becomes difficult for microcrystals to form and grow even if the film is exposed to high temperatures during distribution and storage, and tearing problems can be suppressed.

After storage, the slit original fabric is rewound onto a paper tube or the like, for example, although it is not particularly limited, and stored as a rolled body 16 in a decorative box 1 equipped with a film cutting blade 15 as shown in FIG. As illustrated in FIG. 2, the wrap film 17 is pulled out and used.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples, but the present invention is not limited by these in any way. The evaluation methods used in Examples and Comparative Examples are as follows.

[Content of vinylidene chloride repeating unit]
The ratio of vinylidene chloride repeating units in the wrap film was measured using a high-resolution proton nuclear magnetic resonance spectrometer (H-NMR: JEOL α-400). The reprecipitated filtrate of the wrap film was vacuum-dried, and a solution of 5% by weight dissolved in deuterated tetrahydrofuran was subjected to H-NMR measurement at a measurement atmosphere temperature of about 27°C. Regarding the copolymer of vinylidene chloride and vinyl chloride, use the peaks of 3.50 to 4.20 ppm, 2.80 to 3.50 ppm, and 2.00 to 2.80 ppm of the copolymer based on tetramethylsilane. The content of vinylidene chloride repeating units was calculated.

[Film thickness]
Assuming that the wrap film would be distributed after shipping and stored at home, the produced wrap film was stored in a constant temperature bath set at 28° C. for one month, and then the thickness of the wrap film was measured. The thickness was measured using a dial gauge (manufactured by Techlock) in an atmosphere of 23° C. and 50% RH.

[Tear strength]
Assuming that the wrap film will be distributed after shipment and stored at home, the produced wrap film will be stored in a thermostatic oven set at 28°C for one month, and then stored in accordance with the method described in JIS-P-8116. The tear strength was measured. A light load tear tester (manufactured by Toyo Seiki Co., Ltd.) was used for the measurement, and the tear strength was measured in an atmosphere of 23° C. and 50% RH.

[Tensile modulus]
Assuming that the wrap film will be distributed after shipment and stored at home, the produced wrap film will be stored in a thermostatic oven set at 28°C for one month, and then stored in accordance with the method described in ASTM-D-882. The tensile modulus was measured. Autograph AG-IS (manufactured by Shimadzu Corporation) was used for the measurement, and the tensile modulus was measured in an atmosphere of 23° C. and 50% RH. More specifically, the tensile modulus was measured from the load at 2% elongation under the conditions of a tensile speed of 5 mm/min and a distance between chucks of 100 mm.

[Low temperature crystallization start temperature]
Assuming that the wrap film would be distributed after shipping and stored at home, the measurement sample used was a wrap film that had been produced and had been stored in a constant temperature bath set at 28° C. for one month. For measurement, a PerkinElmer differential scanning calorimeter (DSC) (input compensated double furnace DSC 8500) was used in step scan measurement mode (sample weight: 6 mg, sample pan material: aluminum, measurement temperature: 0). ~180°C, temperature increase rate: 10°C/min, temperature increase step width: 4°C, isothermal time: 1 min). An empty aluminum sample pan was also measured under the same conditions, and the temperature-heat flow curve of the wrap film was corrected. In the irreversible component of the corrected temperature-heat flow curve, the temperature at which heat generation due to low-temperature crystallization starts was defined as the low-temperature crystallization start temperature.

[Feeling (smooth feel)]
Assuming that the wrap film would be distributed after shipment and stored at home, the wrap film roll immediately after production was stored in a constant temperature oven set at 28° C. for one month. Thereafter, the feel (smooth feel) of the wrap film was evaluated. As evaluators, 100 people who use food packaging wrap films on a daily basis were selected, and evaluations were made based on their sensory evaluations. Each evaluator was given 10 points, 0 points were given to those that felt sticky, and 10 points were given to those that felt smooth, and the average score of the 100 evaluators was calculated. This average score was used for evaluation. Note that the evaluation environment was an atmosphere of 23° C. and relative humidity of 50% RH.
[Evaluation criteria for feel (smooth feel)]
◎: 8 points or more: Very good level with no stickiness and smooth texture.
○: 3 points or more and less than 8 points: Good level with almost no stickiness.
△: Less than 3 points: Slightly sticky and slightly uncomfortable level.

[Tearing trouble occurrence rate]
Assuming that the wrap film would be distributed after shipment and stored at home, the wrap film roll immediately after production was stored in a constant temperature oven set at 28° C. for one month. Then, in order to reproduce the vibrations during distribution, a vibration testing machine (manufactured by Idex Co., Ltd., product number BF-50UC) was used to vibrate the wrap film roll housed in the container (presentation box). I let it happen. The vibration test was conducted as follows.

First, 60 rolled body containers each containing one rolled body were placed inside a rectangular parallelepiped-shaped container (inner dimensions: 42 mm x 42 mm x approximately 233 mm) in a cardboard box (inner dimensions: 28 cm x 46 cm x 24 cm), and was fixed to the vibration table with a belt so that the longitudinal direction of the wound body was perpendicular to the vibration table. A vibration test was conducted by operating a vibration tester in an atmosphere of 23° C. and 50% RH. The vibration test was conducted for 20 minutes using the auto mode in a cycle in which the frequency was changed in the order of 5 Hz, 30 Hz, and 5 Hz for 30 seconds.

Thereafter, tearing trouble evaluation was performed in an atmosphere of 23° C. and relative humidity of 50% RH. As evaluators, 100 people who use cling film for food packaging on a daily basis were selected. The evaluator pulled out 50 cm of the film from a roll of approximately 23 cm wide housed in the container, and then cut the film using a tin film cutting blade attached to the presentation case, performing a series of operations 10 times each. That is, out of a total of 1,000 times in which 100 people pulled out the film 10 times each, the incidence of film tearing trouble was derived from the number of times that tearing occurred and the film could not be pulled out smoothly when pulling out the film from the roll.

[Tearing trouble occurrence rate evaluation criteria]
◎: Less than 5%: Almost no tearing trouble and very easy to use.
○: 5% or more and less than 10%: Less tearing trouble and excellent usability.
●: 10% or more and less than 15%: Easy to use with little tearing trouble.
△: 15% or more and less than 20%: Slightly more tearing troubles and poor usability.
×: 20% or more: There are many tearing problems and the usability is very poor.

[Drawing power]
Assuming distribution after shipment of the wrap film in the summer and storage at home, the wrap film roll immediately after production was stored in a constant temperature oven set at 40° C. for one month. Thereafter, the drawability of the film was evaluated.

The evaluation was performed in an atmosphere of 23°C and relative humidity of 50% RH. We selected 100 people who use cling film for food packaging on a daily basis as evaluators.The evaluators pulled out 50 cm of the film from a 22 cm wide roll housed in a container, then examined the tin plate attached to the cosmetic case. The series of operations of cutting the film using a manufactured film cutting blade was repeated 10 times. Each evaluator was given 10 points, 0 points were given to those who felt a great deal of resistance when pulling out the film, and 10 points were given to those that could be pulled out smoothly.Evaluation was made based on the average score of 100 people.

[Drawing force evaluation criteria]
◎: 8 points or more: Can be pulled out easily and smoothly.
○: 5 points or more and less than 8 points: Easily pulled out.
△: Less than 5 points: Resistance was felt when withdrawing, and the withdrawability was poor.

[Coloring]
Assuming that the wrap film would be distributed after shipment and stored at home, the wrap film roll immediately after production was stored in a constant temperature oven set at 28° C. for one month. Thereafter, the coloring of the film was evaluated.

As evaluators, 100 people who use food packaging wrap films on a daily basis were selected and evaluated in an atmosphere of 23° C. and 50% RH according to the following criteria. The evaluation was determined by the average of 100 evaluators.

[Coloring evaluation criteria]
◎: Even people who are sensitive to film coloring do not notice the coloring at all.
○: People who are sensitive to film coloring may be slightly concerned about coloring.
△: The level of coloring is a little worrisome even for people who are not sensitive to film coloring.

[Example 1]
93.4% by mass of vinylidene chloride resin with a weight average molecular weight of 115,000 (85% by weight of vinylidene chloride repeating units, 15% by weight of vinyl chloride repeating units), tributyl acetyl citrate (Taoka Chemical Industry Co., Ltd.)5. 5% by mass and 1.1% by mass of epoxidized fatty acid 2-ethylhexyl (Sansocizer E-6000, Shin Nippon Rika Co., Ltd.) were mixed for 5 minutes in a Henschel mixer. After mixing, the mixture was aged for 24 hours or more to obtain a composition.

The resulting composition was fed into a melt extruder, melted, and melt extruded through an annular die attached to the tip of the extruder to form a sock. At this time, the heating conditions of the extruder were adjusted so that the molten resin temperature at the slit exit of the annular die was 170° C., and the resin was extruded annularly at an extrusion rate of 10 kg/hr.

After cooling this in a sock solution and a cold water bath, the parison was opened to form a bubble and inflation stretching was performed. At this time, the cylindrical film ( bubble) was formed.

After the obtained cylindrical film was nipped and folded flat, the film was relaxed by 10% in the MD direction by controlling the speed ratio of the pinch roll and the winding roll, and a two-layer film with a fold width of 280 mm was wound. It was wound up at a take-up speed of 18 m/min. This film was slit into a width of 220 mm, and while being peeled off into a single film, it was re-wound onto a paper tube with an outer diameter of 92 mm. Thereafter, it was stored at 15° C. for 30 hours and wound up for 20 m around a paper tube having an outer diameter of 36 mm and a length of 230 mm to obtain a wrap film roll.

When the physical properties of the obtained wrap film were measured by the above measurement method, the low-temperature crystallization initiation temperature was 49 ° C., the thickness was 11 μm, the tear strength in the TD direction was 2.9 cN, and the tensile modulus in the MD direction was 530 MPa. .

[Example 2]
Vinylidene chloride resin with a weight average molecular weight of 115,000 (vinylidene chloride repeating unit: 85% by weight, vinyl chloride repeating unit: 15% by weight) 92.5% by mass, tributyl acetyl citrate 5.5% by mass, epoxidized fatty acid 2 A wrap film roll was obtained in the same manner as in Example 1 except that 2.0% by mass of ethylhexyl was mixed.

[Example 3]
Vinylidene chloride resin with a weight average molecular weight of 115,000 (vinylidene chloride repeating unit: 85% by weight, vinyl chloride repeating unit: 15% by weight) 91.5% by mass, tributyl acetyl citrate 5.5% by mass, epoxidized fatty acid 2 A wrap film roll was obtained in the same manner as in Example 1 except that 3.0% by mass of -ethylhexyl was mixed.

[Example 4]
Vinylidene chloride resin with a weight average molecular weight of 115,000 (vinylidene chloride repeating unit: 85% by weight, vinyl chloride repeating unit: 15% by weight) 92.5% by mass, dibutyl sebacate (Taoka Chemical Industry Co., Ltd.) 5.5% A wrap film roll was obtained in the same manner as in Example 1 except that 2.0% by mass of epoxidized fatty acid 2-ethylhexyl was mixed.

[Example 5]
Vinylidene chloride resin with a weight average molecular weight of 115,000 (85% by weight of vinylidene chloride repeating units, 15% by weight of vinyl chloride repeating units) 92.5% by mass, tributyl acetyl citrate 5.5% by mass, epoxidized butyl fatty acid (Sunsocizer E-4030, Shin Nippon Rika Co., Ltd.) A wrap film roll was obtained in the same manner as in Example 1 except that 2.0% by mass was mixed.

[Example 6]
93.4% by mass of vinylidene chloride resin (85% by weight of vinylidene chloride repeating units, 15% by weight of vinyl chloride repeating units) having a weight average molecular weight of 115,000, and 6.6% by mass of epoxidized fatty acid 2-ethylhexyl were mixed. A wrap film roll was obtained in the same manner as in Example 1 except for the above.

[Example 7]
Epoxidized fatty acid 2-ethylhexyl (Chemisizer E-5000, Sanwa Gosei Kagaku Co., Ltd.) in place of epoxidized fatty acid 2-ethylhexyl (Sansocizer E-6000, Shin Nippon Rika Co., Ltd. Oxirane oxygen concentration 5.4% by mass) A wrap film roll was obtained in the same manner as in Example 1, except that oxirane (oxyrane oxygen concentration: 5.8% by mass) was used.

[Example 8]
A wrap film roll was obtained in the same manner as in Example 1, except that epoxidized fatty acid octyl ester (ADEKASIZER D-32, ADEKA) was used instead of epoxidized fatty acid 2-ethylhexyl.

[Comparative example 1]
Vinylidene chloride resin with a weight average molecular weight of 115,000 (vinylidene chloride repeating unit: 85% by weight, vinyl chloride repeating unit: 15% by weight) 93.4% by mass, tributyl acetyl citrate 5.5% by mass, epoxidized soybean oil (Newsizer 510R, Nippon Oil & Fats Co., Ltd.) A wrap film roll was obtained in the same manner as in Example 1 except that 1.1% by mass was mixed.

[Comparative example 2]
Vinylidene chloride resin with a weight average molecular weight of 115,000 (vinylidene chloride repeating unit: 85% by weight, vinyl chloride repeating unit: 15% by weight) 92.5% by mass, tributyl acetyl citrate 5.5% by mass, epoxidized soybean oil A wrap film roll was obtained in the same manner as in Example 1 except that 3.0% by mass was mixed.

[Comparative example 3]
Vinylidene chloride resin with a weight average molecular weight of 115,000 (vinylidene chloride repeating unit: 85% by weight, vinyl chloride repeating unit: 15% by weight) 92.5% by mass, tributyl acetyl citrate 5.5% by mass, epoxidized linseed oil (Adekasizer O-180A, ADEKA Co., Ltd.) A wrap film roll was obtained in the same manner as in Example 1 except that 2.0% by mass was mixed.

ATBC: Acetyl tributyl citrate
DBS: dibutyl sebacate

In addition, all of the wrap films of Examples had low odor and were excellent in low odor properties.

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

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

Claims (6)

Contains a vinylidene chloride resin and an epoxidized fatty acid alkyl ester with a viscosity of 14 to 48 mPa·s at 30°C,
The low-temperature crystallization initiation temperature measured by a temperature modulation differential scanning calorimeter is 40 to 60°C,
The thickness is 6 to 18 μm.
wrap film. The content of the epoxidized fatty acid alkyl ester is based on the total amount of the wrap film,
0.1 to 3% by mass,
The wrap film according to claim 1. The wrap film according to claim 1 or 2, having a tear strength in the TD direction of 2 to 6 cN. The wrap film according to any one of claims 1 to 3, having a tensile modulus in the MD direction of 250 to 600 MPa. The vinylidene chloride-based resin contains 72 to 93% by mass of vinylidene chloride repeating units,
The wrap film according to any one of claims 1 to 4. Contains at least one compound selected from the group consisting of citric acid esters and dibasic acid esters,
The content of the compound is 3 to 8% by weight based on the total amount of the wrap film.
The wrap film according to any one of claims 1 to 5.