Wrap film

Abstract

To efficiently provide a wrap film capable of suppressing longitudinal tearing trouble by improving drawability (for example, capable of suppressing puncture trouble during inflation).SOLUTION: A wrap film has a TD orientation index of 1.10 to 1.45.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a wrap film. [Background technology]

[0002] Traditionally, wrap films have been used in many ordinary households as wrap films for food, etc., due to their excellent properties, such as adhesion to other films and to substrates, gas barrier properties against gases such as water vapor and oxygen, and ease of cutting when used in decorative boxes. Household wrap films are primarily used to store food in refrigerators or freezers, or to overlap when heating food in containers in a microwave oven.

[0003] Among the household wrap films currently on the market, those that are rated as the most user-friendly are those made primarily of vinylidene chloride resins. Other commercially available films, such as those made primarily of polyethylene resins, polypropylene resins, polyvinyl chloride resins, or poly-4-methylpentene-1 resins, are also available, but none of these have the adhesive properties of vinylidene chloride wrap films and are therefore inferior in terms of wrapping suitability, making vinylidene chloride wrap films the more widely used.

[0004] For example, Patent Document 1 discloses a transparent wrap film that has an effect of suppressing unwinding when cut, has good oxygen and water barrier properties, and has good adhesion when in use.

[0005] Furthermore, for example, Patent Document 2 discloses a vinylidene chloride resin wrap film that is suppressed from vertical tearing and has excellent adhesion and transparency.

[0006] Furthermore, for example, Patent Document 3 discloses a food packaging material that can suppress surface stickiness even when stored at high temperatures for a long period of time, and that has, for example, better drawability in a rolled state and better stability.

[0007] Furthermore, for example, Patent Document 4 discloses a vinylidene chloride resin wrap film that has a high elastic modulus, excellent firmness and resilience, and excellent adhesion between wrap films. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 7326208 [Patent Document 2] Patent No. 5501791 [Patent Document 3] Patent No. 6339435 [Patent Document 4] Japanese Patent Application Publication No. 8-134306 Summary of the Invention [Problem to be solved by the invention]

[0009] In addition to the film's adhesiveness and transparency, household wrap films must also be easy to use when placed inside a gift box. In terms of film properties, the film must have low pulling force in the machine direction to prevent vertical tearing, and it must also be easy to cut in the width direction.

[0010] For example, vinylidene chloride-based wrap film rolls placed in a decorative box have excellent cuttability in the width direction. However, if tears occur on the cut edge of the film when opening the lid of the decorative box and cutting it, the film may tear in the machine direction (vertical tearing) when pulled out or when rewinding the film to restore it to a usable state, resulting in a problem known as vertical tearing, making it unusable. To prevent this vertical tearing problem, the film must have sufficient tear strength to prevent tearing in the machine direction.

[0011] Furthermore, when household wrap film is stored at high temperatures for a long period of time, for example, the unrollability of the film may decrease, increasing the risk of vertical tearing when the film is unrolled.

[0012] Patent Documents 1 to 4 do not consider efficiently providing a wrap film that reduces problems with vertical tearing by improving the pull-out properties (for example, that can reduce problems with punctures during inflation).

[0013] Therefore, an object of the present invention is to provide a wrap film that efficiently prevents problems with vertical tearing by improving the pull-out properties (for example, preventing problems with punctures during inflation). [Means for solving the problem]

[0014] As a result of extensive research, the present inventors have found that the above problems can be solved by using a specific configuration, and have completed the present invention.

[0015] That is, the present invention relates to, for example, the following: [1] A wrap film having a TD orientation index of 1.10 to 1.45. [2] The vinylidene chloride resin has a weight average molecular weight of 11.0×10 4 ~14.0×10 4 (Polystyrene equivalent value) The wrap film according to [1]. [3] The wrap film according to [1] or [2], which has a drawing force of 70 cN to 90 cN. [4] A roll in which the wrap film according to any one of [1] to [3] is wound around a core. [5] Stretching an unstretched sheet in both the machine direction (MD) and the transverse direction (TD), A method for producing a wrap film, in which the stretching ratio in the direction perpendicular to the machine direction (TD) is smaller than the stretching ratio in the machine direction (MD), and the TD orientation index of the resulting wrap film is 1.10 to 1.45. [6] The method for producing a wrap film according to [5], wherein the stretching ratio in the machine direction (MD) is 3.0 times or more and 6.0 times or less, and the stretching ratio in the direction perpendicular to the machine direction (TD) is 2.5 times or more and 5.5 times or less. [7] The weight average molecular weight of the raw material vinylidene chloride resin is 11.0 x 10 4 ~14.0×10 4 (Polystyrene equivalent value) [5] or [6]. The method for producing a wrap film according to [5] or [6]. [Effects of the Invention]

[0016] According to the present invention, it is possible to efficiently provide a wrap film that has reduced problems with vertical tearing (for example, it is possible to reduce problems with punctures during inflation) by improving the pull-out properties. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a conceptual diagram of an example of a method for producing a wrap film according to this embodiment. [Figure 2] FIG. 2 is a schematic diagram of the device used to evaluate the unwindability of the wrap film in this example. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, a detailed description will be given of an embodiment of the present invention (hereinafter abbreviated as "the present embodiment"). The following embodiment is an example for explaining the present invention, and the present invention is not limited to these. That is, the present invention can be implemented by modifying it as desired without departing from the gist of the present invention. In each drawing, components with the same reference numerals have the same or similar configurations. Furthermore, descriptions of configurations similar to conventional configurations will be omitted as appropriate.

[0019] The wrap film of this embodiment has a TD orientation index of 1.10 to 1.45. With a TD orientation index within this range, the wrap film of this embodiment can be produced efficiently (for example, by reducing puncture problems during inflation). From the same perspective, the wrap film of this embodiment preferably has a TD orientation index of 1.35 to 1.45.

[0020] The method for controlling the TD orientation index within the above range is not particularly limited. For example, in the production of wrap films, the weight average molecular weight of the vinylidene chloride resin raw material is controlled to fall within a specific range (preferably 11.0×10 4 ~14.0×10 4 (in terms of polystyrene) and appropriately adjusting the stretching ratio in the TD direction and the stretching ratio in the MD direction during inflation. This method tends to promote oriented crystallization in the TD direction during the TD stretching stage during inflation.

[0021] In this embodiment, the TD orientation index is an index representing the degree to which crystals are oriented in the direction (TD direction) perpendicular to the machine direction (MD direction) of the wound film, and can be calculated by the following method.

[0022] [Crystal orientation index analysis] The crystal orientation index of the wrap film is measured by transmission wide-angle X-ray scattering (WAXS) using a Rigaku NANOPIX. For this measurement, a wrap film roll wound around a core is used as the sample after 24 hours of storage at 23±2°C and 50±10% RH. The sample is irradiated with CuKα radiation, and scattering is detected using a semiconductor detector, HyPix-6000. The measurement is performed with a sample-to-detector distance of 86 mm and an output of 40 kV and 30 mA. A point focus optical system is used, with slit diameters of 1st slit: φ=0.55 mm, 2nd slit: open, and guard slit: φ=0.35 mm. The up-down direction of the sample is defined as the TD direction, and the X-rays are incident from the normal direction of the sample.

[0023] (crystal orientation index f) The WAXS profile I(2θ, φ) is obtained by circular averaging the X-ray scattering pattern obtained from the HyPix-6000 detector. The vertical direction of the sample is defined as φ=0°, and the azimuthal angle distribution I(φ) of the scattering intensity in the range of 24°<2θ<26° is calculated using Equation 1 below. In addition, to make the data easier to compare, I(φ) is normalized using Equation 2 below.

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[0024] In the calculated graph of the azimuth angle dependency, the maximum value of the mountain-shaped peak and the minimum value of the valley-shaped peak are used to calculate the crystal orientation index f to TD from the following formula 3, and this f is defined as the TD orientation index.

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[0025] [Components of wrap film] The wrap film of this embodiment is preferably formed from a constituent component that includes a polymer.

[0026] In this embodiment, the polymer is a polymer capable of forming a film, and this polymer means a polymer that accounts for 50% by weight or more of the entire film.

[0027] From the viewpoint of adhesion, in this embodiment, it is preferable not to use an amorphous polymer as the main polymer of the film. However, even amorphous polymers can be blended and used in an amount that allows the crystalline polymer to partially crystallize. Furthermore, crystalline polymers can also be hydrogen-bonded polymers such as cellulose and aromatic polyamides that do not have a clear crystalline melting point. However, if the crystalline melting point is above the decomposition temperature, wet film formation will be attempted, which requires steps such as solvent recovery, which is disadvantageous from an operational standpoint. Therefore, from the viewpoint of operability, polymers with a crystalline melting point of 350°C or less that can be melt-molded during the manufacturing process are preferably used.

[0028] The polymers used to form the wrap film of this embodiment are preferably vinylidene chloride resins, olefin resins, ester resins, and amide resins. Examples of olefin resins include, but are not limited to, polyethylene, polypropylene, polybutene-1, poly-4-methylpentene-1, and copolymers based on these. Examples of ester resins include, but are not limited to, polyethylene terephthalate, polypropylene terephthalate, poly-1,4-cyclohexanedimethylene terephthalate, polyethylene-2,6-naphthalate, polylactic acid, and polyhydroxyglycolic acid. Examples of amide resins include, but are not limited to, nylon 6, nylon 7, nylon 66, nylon 610, nylon 612, nylon 46, and nylon 6T.

[0029] The polymer forming the wrap film of this embodiment more preferably contains a vinylidene chloride resin composition. The vinylidene chloride resin composition may be a homopolymer of a vinylidene chloride monomer, or a copolymer of a vinylidene chloride monomer and a monomer copolymerizable therewith. In this specification, a vinylidene chloride resin wrap film refers to a wrap film containing a vinylidene chloride resin composition. The vinylidene chloride resin composition may contain one type of vinylidene chloride resin, or may contain two or more types of vinylidene chloride resins.

[0030] The monomer copolymerizable with vinylidene chloride monomer is not particularly limited, and examples thereof include vinyl chloride, acrylic acid esters such as methyl acrylate and butyl acrylate, methacrylic acid esters such as methyl methacrylate and butyl methacrylate, acrylonitrile, vinyl acetate, etc. Among these, vinyl chloride is preferred from the viewpoints of easily achieving a balance between oxygen / water barrier properties and extrusion processability and also having excellent film adhesion. These may be used alone or in combination of two or more.

[0031] When a copolymer of vinylidene chloride monomer and the above-mentioned monomers is used, it is preferable that the copolymer is composed of 85 to 97 mass% vinylidene chloride monomer and 15 to 3 mass% of a monomer copolymerizable therewith, from the viewpoints of crystallinity, processability, film properties, etc. By making the vinylidene chloride monomer ratio 85 mass% or more, it is possible to further improve the oxygen / water barrier properties and film cuttability, and by making the vinylidene chloride monomer ratio 97 mass% or less, it is possible to further improve the processability. The monomer ratio was measured using an FX-270 (manufactured by JEOL Ltd.) using d-THF as a solvent. 1 The value was calculated from the integral ratio of the peaks derived from each monomer component in the H-NMR spectrum.

[0032] The vinylidene chloride resin composition can be blended with known additives such as plasticizers and stabilizers. The plasticizer is not particularly limited, and known ones can be used. Examples include acetyl tributyl citrate, acetylated monoglyceride, and dibutyl sebacate. The stabilizer is not particularly limited, and known ones can be used. Examples include epoxidized vegetable oils such as epoxidized soybean oil and epoxidized linseed oil.

[0033] In addition, known weather resistance improvers, antifogging agents, antibacterial agents, oligomers such as polyester, polymers such as MBS (methyl methacrylate-butadiene-styrene), and the like used in food packaging materials may be added as long as the effects of this embodiment are not impaired. The weather resistance improvers are not particularly limited, and known ones can be used. Examples include ultraviolet absorbers such as 2-(2'-hydroxy-3'5'-di-tert-butylphenyl)-5-chlorobenzotriazole. The antifogging agents are not particularly limited, and known ones can be used. Examples include surfactants such as glycerin fatty acid esters, diglycerin fatty acid esters, and sorbitan fatty acid esters. The antibacterial agents are not particularly limited, and known ones can be used. Examples include natural antibacterial agents such as grapefruit seed extract and moso bamboo extract.

[0034] The wrap film of this embodiment does not necessarily have to be a single-layer composition; in the case of a multi-layer structure, as long as the layer that comes into contact with the container is primarily made of a crystalline polymer and contains a liquid component, the practical adhesion will not change, and the wrap film may be made up of a multi-layer structure of two or more layers.

[0035] The wrap film of this embodiment may contain a liquid component.

[0036] The liquid component that is preferably used varies depending on the type of polymer, and from the viewpoint of imparting flexibility to the film, for example, in the case of an aliphatic hydrocarbon polymer, a liquid component having an alkyl group or a methylene chain moiety is preferably used, and in the case of an ester-based polymer or an amide-based polymer, a liquid component having a functional group capable of hydrogen bonding, such as a carbonyl group, an ether group, or a hydroxyl group, is preferably used.

[0037] For example, those having an alkyl group include mineral oil, liquid paraffin, saturated hydrocarbon compounds, etc. Those containing a functional group capable of forming a hydrogen bond, such as a carbonyl group, an ether group, or a hydroxyl group, include aliphatic alcohols, alicyclic alcohols, polyhydric alcohols thereof, esters of the above-mentioned alcohol components with aliphatic or aromatic (polyvalent) carboxylic acids, esters of aliphatic hydroxycarboxylic acids with alcohols and / or fatty acids, modified products of these esters, and polyoxyethylene alkyl ethers and / or esters thereof. More specifically, examples of suitable materials include polyglycerols such as glycerin, diglycerin, triglycerin, and tetraglycerin, and the like, which are used as the starting material for the alcohol component and, as the acid component, mono-, di-, and triesters, polyesters, etc., of fatty acids such as lauric acid, palmitic acid, stearic acid, oleic acid, and linoleic acid, or esters of sorbitan and the above fatty acids, or esters of ethylene glycol, propylene glycol, tetramethylene glycol, and condensates thereof with the above fatty acids, or esters of aliphatic hydroxycarboxylic acids such as citric acid, malic acid, and tartaric acid with lower alcohols having 10 or less carbon atoms, or esters of polycarboxylic acids such as malonic acid, succinic acid, glutaric acid, and adipic acid with aliphatic alcohols, or modified products of these esters such as epoxidized soybean oil and epoxidized linseed oil. In particular, when used as a food packaging wrap, liquid components that are food additives as defined by the Food Sanitation Act are preferably used. Furthermore, from the standpoint of heat resistance, liquid components with a boiling point of 200°C or higher are preferably used.

[0038] The wrap film of this embodiment contains a vinylidene chloride resin, and the weight average molecular weight of the vinylidene chloride resin is 11.0 × 10 4 ~14.0×10 4(Polystyrene equivalent value). In the wrap film of this embodiment, when the weight average molecular weight of the vinylidene chloride resin is within the above range, even if the stretch ratio in the MD direction is reduced, the bubbles do not loosen and a wrap film with a high TD orientation index tends to be formed. Furthermore, it becomes possible to make the stretch ratio in the TD direction smaller than the stretch ratio in the MD direction, and a wrap film with a high TD orientation index can be formed with small bubbles, which tends to suppress puncture problems and enable more efficient production. From the same perspective, in the wrap film of this embodiment, the weight average molecular weight of the vinylidene chloride resin is 13.0 × 10 4 ~13.5×10 4 It is more preferable that:

[0039] Conventionally, in the production of wrap films, the stretch ratio in the TD direction is usually set higher than the stretch ratio in the MD direction to maintain the bubble during inflation. On the other hand, in the wrap film of this embodiment, when the weight-average molecular weight of the vinylidene chloride resin contained therein is within the above-mentioned range, the bubble during inflation can be maintained even if the stretch ratio in the TD direction is set lower than the stretch ratio in the MD direction during production of the wrap film, which tends to more efficiently promote oriented crystallization in the TD direction during the TD stretching stage during inflation.

[0040] In this embodiment, the weight-average molecular weight is a value measured by gel permeation chromatography (GPC) using tetrahydrofuran as a mobile phase, calibrated with polystyrene of known molecular weight, and converted. Specifically, it can be measured by the method described in the Examples below.

[0041] The wrap film of this embodiment preferably has a drawing force of 70 cN to 90 cN. When the drawing force is within this range, the wrap film of this embodiment tends to have even better drawing properties. From the same perspective, the drawing force of the wrap film of this embodiment is more preferably 70 cN to 80 cN.

[0042] The method for controlling the drawing force within the above range is not particularly limited, but for example, it may be possible to control the amount of oligomer that bleeds out onto the surface of the wrap film. In this embodiment, the pull-out force is the pull-out force of a wrap film roll in which the wrap film is wound around a core after storage at 40±2°C for two weeks, and can be measured by the method described in the examples below.

[0043] The thickness of the wrap film of this embodiment is not particularly limited, but from the viewpoint of usability, it is preferably 5 to 30 μm, more preferably 5 to 15 μm.

[0044] [Wound body] The roll of this embodiment is a roll in which the wrap film described above is wound around a core. Specifically, for example, the wrap film may be a roll that includes a cylindrical core and the wrap film wound around the core. The wrap film is wound around a core or the like to form a roll.

[0045] The material and size of the core are not particularly limited, and a known core such as a paper tube can be used. The roll of the present embodiment can be used, for example, by being stored in a decorative box having a cutting blade for cutting the wrap film.

[0046] [Wrap film manufacturing method] The wrap film manufacturing method of this embodiment includes a step of stretching an unstretched sheet in the machine direction (MD) and a direction perpendicular to the machine direction (TD), and it is preferable that the stretch ratio in the direction perpendicular to the machine direction (TD) is smaller than the stretch ratio in the machine direction (MD), and the resulting wrap film has a TD orientation index of 1.10 to 1.45. The wrap film manufacturing method of this embodiment has these characteristics, which improves drawability and allows for the efficient production of wrap film with reduced longitudinal tearing problems. In the wrap film manufacturing method of this embodiment, it is more preferable that the resulting wrap film has a TD orientation index of 1.35 to 1.45.

[0047] In the wrap film manufacturing method of this embodiment, the stretching ratio in the machine direction (MD) is preferably 3.0 to 6.0 times, and the stretching ratio in the direction perpendicular to the machine direction (TD) is preferably 2.5 to 5.5 times. By keeping the stretching ratios within these ranges, the wrap film manufacturing method of this embodiment tends to improve TD orientation.

[0048] In the wrap film manufacturing method of this embodiment, the stretching ratio in the machine direction (MD) is more preferably 4.0 or more and 5.0 or less.

[0049] Furthermore, in the wrap film manufacturing method of this embodiment, the stretching ratio in the direction perpendicular to the machine direction (TD) is more preferably 4.0 or more and 5.0 or less.

[0050] In the method for producing the wrap film of this embodiment, the weight average molecular weight of the vinylidene chloride resin raw material is 11.0 × 10 4 ~14.0×10 4 (polystyrene equivalent value). In the method for producing a wrap film of this embodiment, if the weight-average molecular weight of the vinylidene chloride resin raw material is within the above range, the drawability is improved, so that a wrap film with reduced longitudinal tearing problems tends to be obtained, and puncture problems during inflation tend to be reduced, making it possible to produce the wrap film more efficiently. From a similar perspective, in the method for producing a wrap film of this embodiment, it is preferable that the weight-average molecular weight of the vinylidene chloride resin raw material is 13 × 10 4 ~13.5×10 4 It is more preferable that:

[0051] In conventional wrap film production, the stretch ratio in the TD direction is usually set higher than the stretch ratio in the MD direction to maintain the bubble during inflation. However, in the wrap film production method of this embodiment, if the weight-average molecular weight of the raw material vinylidene chloride resin is within the above-mentioned range, the bubble during inflation can be maintained even if the stretch ratio in the TD direction is set lower than the stretch ratio in the MD direction during wrap film production, which tends to more efficiently promote oriented crystallization in the TD direction during the TD stretching stage during inflation.

[0052] Next, an example of a method for producing a wrap film according to this embodiment will be described. For example, various methods can be used to produce wrap films containing a vinylidene chloride resin composition, but typically, an inflation film-forming method is used. That is, according to this embodiment, a wrap film can be obtained by inflation molding. More preferably, the wrap film according to this embodiment can be produced by, for example, stretching the vinylidene chloride resin composition described above in both the MD and TD directions and then inflation molding it. In the inflation film-forming method, for example, a vinylidene chloride resin composition is melt-extruded into a tubular shape through a circular die, and the outside of the tubular resin is then contacted with a refrigerant such as cold water filled in a storage tank called a cold water tank. During this process, a refrigerant is injected into the interior of the tubular (cylindrical) resin sandwiched between the die opening and pinch rolls, and the refrigerant is then solidified by contacting the interior with a refrigerant such as mineral oil, thereby forming it into a film. In this specification, the tubular resin portion (extrudate) sandwiched between the die opening and pinch rolls is referred to as a "sock." The refrigerant (liquid) injected into the sock is called the "sock liquid." The sock is then folded by the pinch rolls or the like to form a tubular double-ply film, which is called a "parison."

[0053] The inflation film forming method will be described in more detail below. Figure 1 is a conceptual diagram of an example of the method for producing the wrap film of this embodiment.

[0054] First, in the extrusion step, a molten vinylidene chloride resin composition is extruded in a tubular shape from the die opening (3) of a circular die (2) by an extruder (1), to form a sock (tubular vinylidene chloride resin composition) (4).

[0055] Next, in the cooling and solidifying process, the outside of the sock (4), which is the extruded product, is brought into contact with cold water in a cold water bath (6), and sock liquid (5) is poured into the sock (4) by a conventional method and stored therein, thereby cooling and solidifying the sock (4) from the inside and outside. At this time, the sock (4) is in a state where the sock liquid (5) is applied to its inside. The solidified sock (4) is folded by a first pinch roll (7), and a parison (8), which is a double-ply sheet, is formed. The amount of sock liquid applied is controlled by the pinch pressure of the first pinch roll (7).

[0056] The sock liquid may be water, mineral oil, alcohols, polyhydric alcohols such as propylene glycol and glycerin, or aqueous solutions of cellulose or polyvinyl alcohol. These may be used alone or in combination of two or more. Furthermore, the sock liquid may contain the above-mentioned weather resistance improvers, anti-fogging agents, antibacterial agents, etc. used in food packaging materials, as long as the effects of this embodiment are not impaired.

[0057] The amount of sock liquid to be applied is not particularly limited, but from the viewpoint of the openability of the parison and the adhesion of the film, it is preferably 50 to 20,000 ppm, more preferably 100 to 15,000 ppm, and even more preferably 150 to 10,000 ppm. Here, the application amount (ppm) is the mass of the sock liquid applied to the sock relative to the total mass of the sock, expressed in ppm by mass.

[0058] Next, air is injected into the inside of the parison (8), opening it again and making it tubular. The parison (8) is reheated with hot water (not shown) to a temperature suitable for stretching. The hot water adhering to the outside of the parison (8) is squeezed out by a second pinch roll (9). Next, in the inflation process, air is injected into the tubular parison (8) heated to the appropriate temperature to form a bubble (10) by inflation stretching, and a stretched film is obtained.

[0059] The wrap film manufacturing method of this embodiment includes a step of stretching an unstretched sheet in the machine direction (MD) and a direction perpendicular to the machine direction (TD), with the stretch ratio in the direction perpendicular to the machine direction (TD) being smaller than the stretch ratio in the machine direction (MD). The stretch ratios in the TD and MD directions are as described above.

[0060] The method for controlling the stretch ratio is not particularly limited, and known methods can be used. For example, a method of controlling the stretch temperature by changing the temperature of hot water used for reheating can be used. To reduce the stretch ratio, a lower stretch temperature is preferable because the inflation bubble is stabilized at a low stretch ratio. From the viewpoint of inflation bubble stability, the stretching temperature is preferably higher than the room temperature for stretching. The stretching temperature is more preferably 34°C or lower, and even more preferably 25°C to 34°C. The stretching temperature is measured at a midpoint in the MD between the point where stretching in the MD and TD directions is completed and the point where winding begins.

[0061] The stretched film is then folded by a third pinch roll (11) to form a double-ply film (12). The double-ply film (12) is then taken up by a take-up roll (13). The film is then slit and peeled off to form a single film (single peeling). Finally, the film is wound up around a core such as a cardboard tube, and a paper-tube wrapped wrap film roll is obtained.

[0062] The above description is one example of the method for producing the wrap film of this embodiment, and the method may be carried out using various apparatus configurations and conditions other than those described above, and for example, other known methods may be used.

[0063] The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The elements of the embodiments, as well as their arrangement, materials, conditions, shapes, sizes, etc., are not limited to those illustrated and can be modified as appropriate. Furthermore, configurations shown in different embodiments can be partially substituted or combined with each other. [Example]

[0064] The features of the present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited thereto. That is, the materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Furthermore, the values ​​of various production conditions and evaluation results in the following examples represent preferred upper or lower limits in the embodiments of the present invention, and preferred ranges may be defined by combining the above-mentioned upper or lower limits with the values ​​of the following examples or values ​​between the examples.

[0065] The measurement and evaluation methods used in the examples and comparative examples are as follows.

[0066] (1) TD orientation index The TD orientation index of the wrap film was calculated by the following method. [Crystal orientation index analysis] The crystal orientation index of the wrap film was measured by transmission wide-angle X-ray scattering (WAXS) using a Rigaku NANOPIX. For this measurement, a wrap film roll wound around a core was used as the sample after 24 hours of storage at 23±2°C and 50±10% RH. The sample was irradiated with CuKα radiation, and scattering was detected using a semiconductor detector, HyPix-6000. The sample-to-detector distance was 86 mm, and the output was 40 kV and 30 mA. A point-focus optical system was used, with slit diameters of 1st slit: φ=0.55 mm, 2nd slit: open, and guard slit: φ=0.35 mm. The vertical direction of the sample was defined as the TD direction, and the X-rays were incident from the normal direction of the sample. (crystal orientation index f) The WAXS profile I(2θ, φ) was obtained by circular averaging the X-ray scattering pattern obtained from the HyPix-6000 detector. The vertical direction of the sample was defined as φ=0°, and the azimuthal distribution I(φ) of the scattering intensity in the range of 24°<2θ<26° was calculated using the following equation 1. In addition, I(φ) was normalized using the following equation 2 to make the data easier to compare.

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[0067] (2) Vertical tearing problems (cutting problems) The longitudinal tearing trouble (cutting trouble) of the wrap film was evaluated as follows. A commercially available decorative wrap film box (Saran Wrap decorative box, 30 cm x 20 m, manufactured by Asahi Kasei Home Products Corporation) was used to conduct a cut test using the wrap film obtained in the Examples and Comparative Examples described below. The cut test was conducted in an atmosphere of 23°C ± 2°C and 50% ± 10% RH. Specifically, the film was cut with the opening angle of the decorative film fixed at 30°, and the probability (%) of vertical tearing of the film when pulling out the cut film was calculated. The number of measurements (number of times) was 500 (unit: %). The effect of suppressing vertical tearing (cutting trouble) was evaluated from the calculated cutting trouble rate according to the following criteria. (Evaluation criteria) ◎: Less than 20% 〇: 20% or more but less than 30% ×: 30% or more

[0068] (3) Pullability The drawability of the wrap film was evaluated as follows. Measurements of the wrap film's unwinding properties were performed in an atmosphere of 23°C ± 2°C and a relative humidity of 50% ± 10% RH. For measuring the unwinding force, the samples used were wrap film rolls in which the wrap film was wound around a core and stored at 40°C ± 2°C for two weeks. As shown in Figure 2, a plastic free roll consisting of a drive unit 14 with a length of approximately 310 mm and a diameter that matched the inner diameter of the paper tube 16 of the rolled wrap film 20, and a 330 mm long fulcrum shaft 15, was attached to the paper tube 16 of the rolled wrap film 20 so that the widthwise center of the rolled wrap film 20 was aligned with the lengthwise center of the free roll drive unit 14. The fulcrum shaft 15 of the free roll integrated with the rolled wrap film 20 was inserted and fixed in a bearing 19 installed at the bottom 18 of the tester so that the hanger 17 hanging from the load cell side at the top of the tensile / compression tester (Shimadzu Corporation; Autograph (AG-IS)) and the fulcrum shaft 15 were parallel, and the center of the width of the rolled wrap film 20 was positioned vertically to the center of the hanger 17. Furthermore, the rolled wrap film 20 integrated with the free roll was peeled off and fixed with double-sided tape to the hanger 17 hanging from the load cell side at the top of the tester without wrinkles. A tensile / compression test was performed in this state to measure the pull-out force (cN) of the wrap film. Based on the measurement results, the pull-out properties of the wrap film were evaluated according to the following criteria. (Evaluation criteria) ◎: 70cN or more and less than 80cN 〇: 80cN or more and 90cN or less ×: Over 90cN or under 70cN

[0069] (4) Flat tire rate The puncture rate during the production of the wrap film was evaluated as follows. Wrap film is made by extruding heated and molten resin into a tubular shape from a circular die, then blowing air into the extruding material as it is extruded through an opening, expanding it to a certain size and forming it into a bag-like shape. The bag-like molded product formed during film production is called a bubble, and the failure phenomenon of the bubble bursting is called a puncture. The reduction in the number of punctures per ton of polymer during the production of the wrap film was evaluated using the number of punctures per ton of polymer when the wrap film was produced under conditions where the stretch ratio in the MD direction was 3.4 to 4.0 times and the stretch ratio in the TD direction was 5.8 to 8.5 times, and the stretch ratio in the TD direction was set higher than the stretch ratio in the MD direction. (Evaluation criteria) ◎: 30% or more 〇: 0 to less than 30% ×: Less than 0%

[0070] [Example 1] A polyvinylidene chloride resin composition with a weight-average molecular weight of 112,000 and a vinylidene chloride (VDC) / vinyl chloride (VC) ratio of 88 / 12 (mass ratio) was melted at 170°C and melt-extruded in a melt extruder. The resulting parison was stretched by inflation to form a tubular film. The weight-average molecular weight was measured by gel permeation chromatography (GPC) using tetrahydrofuran as the mobile phase and calibrated with polystyrene of known molecular weight. The stretching ratio in the MD direction was 5.0 times, and the stretching ratio in the TD direction was 4.5 times. The stretching temperature was 25°C. This tubular film was folded and wound up, then slit to a width of 300 mm, and while peeling off so as to become a single film, 20 m was wound around a paper tube with an outer diameter of 36.6 mm and a length of 305 mm, producing a paper tube-wrapped wrap film with a thickness of approximately 10 μm. The properties of the obtained film were measured by the above-mentioned methods, and the measurement results are shown in Table 1.

[0071] [Examples 2 to 6 and Comparative Examples 1 to 3] Wrap films were produced in the same manner as in Example 1, except that vinylidene chloride resins having the weight-average molecular weights shown in Table 1 were used as the raw vinylidene chloride resins, and the stretching ratios in the MD and TD directions were changed as shown in Table 1. The properties of the obtained film were measured by the above-mentioned methods, and the measurement results are shown in Table 1.

[0072] [Table 1] [Explanation of symbols]

[0073] 1. Extruder 2 circular dies 3 Die mouth 4. Tubular vinylidene chloride resin composition (sock) 5 Sock liquid 6 cold water tank 7. First Pinch Roll 8 parison 9. Second Pinch Roll 10. Bubbles 11 Third pinch roll 12 Double-ply film 13 Winding roll 14 Drive unit 15 Fulcrum Axis 16 Paper tube 17 Hanger 18 Lower part of the testing machine 19 Bearings 20 rolls of plastic wrap

Claims

1. A wrap film having a TD orientation index of 1.10 to 1.

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2. The vinylidene chloride resin has a weight average molecular weight of 11.0×10 ４ ~14.0 x 10 ４ The wrap film according to claim 1, wherein the polystyrene equivalent value is 0.015%.

3. The wrap film according to claim 1, wherein the pulling force is 70 cN to 90 cN.

4. A roll in which the wrap film according to any one of claims 1 to 3 is wound around a core.

5. The method includes a step of stretching an unstretched sheet in a machine direction (MD) and a direction perpendicular to the machine direction (TD), A method for producing a wrap film, in which the stretching ratio in the direction perpendicular to the machine direction (TD) is smaller than the stretching ratio in the machine direction (MD), and the TD orientation index of the resulting wrap film is 1.10 to 1.

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6. The method for producing a wrap film according to claim 5, wherein the stretching ratio in the machine direction (MD) is 3.0 times or more and 6.0 times or less, and the stretching ratio in the direction perpendicular to the machine direction (TD) is 2.5 times or more and 5.5 times or less.

7. The weight average molecular weight of the raw material vinylidene chloride resin is 11.0 × 10 ４ ~14.0 x 10 ４ The method for producing a wrap film according to claim 5 or 6, wherein the polystyrene equivalent value is 0.015 or 0.015.

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