Plastic wrap

Abstract

To provide a wrap film which prevents rice from adhering to the wrap film, for example, when a rice ball is cooked using the wrap film.SOLUTION: A wrap film contains a vinylidene chloride-based resin, wherein the vinylidene chloride-based resin contains 72 mol%-93 mol% of vinylidene chloride, with the contact angle of water to the surface of the wrap film being 70° or more and 120° or less.SELECTED DRAWING: None

Description

Technical Field

[0003]

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

Background Art

[0002] Vinylidene chloride-based resins are excellent in properties such as transparency, water resistance, and gas barrier properties, and are thus used as food packaging materials such as wrap films. In recent years, food packaging materials are required not only to have the above properties but also to improve properties such as molding processability and thermal stability, and to be further highly functionalized. As a method for highly functionalizing food packaging materials, for example, a method of blending additives such as plasticizers and heat stabilizers can be mentioned. As such additives, for example, epoxidized vegetable oil is used to suppress color tone changes in wrap films (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, it is generally practiced to cook hand-rolled rice balls such as onigiri and sushi using a wrap film. Specifically, for example, the wrap film is spread out, salt is sprinkled thereon, the rice and ingredients are placed thereon, and it is wrapped with the wrap film from all sides, and the wrap is squeezed to cook the onigiri. At this time, by using the wrap film, there is an advantage that it is hygienic because it does not directly touch the onigiri. Further, when using a vinylidene chloride-based wrap film, since it has high heat resistance, polymers and the like do not elute from the wrap film, and it is hygienic.

[0005] However, for example, when cooked rice, the sticky components of the rice seep out to the outside, and as these sticky components dry, the rice becomes more prone to sticking. As the moisture at the interface between the surface of the rice and the plastic wrap decreases, the cooked rice may stick to the plastic wrap.

[0006] This invention has been made in view of the above circumstances, and aims to provide, for example, a plastic wrap film that prevents rice from sticking to it when rice balls are cooked using the film.

[0007] The inventors diligently studied to solve the above problems. As a result, they found that the above problems can be solved by setting the amount of vinylidene chloride in the vinylidene chloride resin to a specific range and the contact angle of water with the surface of the wrap film to a specific range in a wrap film containing a vinylidene chloride resin, and thus completed the present invention.

[0008] In other words, the present invention is as follows: [1] It contains vinylidene chloride resin, The aforementioned vinylidene chloride resin contains 72 mol% to 93 mol% vinylidene chloride, The contact angle of water with the surface of the wrap film is between 70° and 120°. Plastic wrap. [2] The tensile modulus in the MD direction is 250 MPa to 600 MPa. [1] The wrap film described above. [3] The tear strength in the TD direction is 2 cN to 6 cN. The wrap film described in [1] or [2]. [4] The thickness is 6 μm to 18 μm. The wrap film described in any of [1] to [3]. [Effects of the Invention]

[0009] According to the present invention, for example, when cooking rice balls using plastic wrap, it is possible to provide a plastic wrap that prevents rice from sticking to the wrap. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram of an example of the manufacturing process for the wrap film of the present invention. [Modes for carrying out the invention]

[0011] The following describes in detail an embodiment of the present invention (hereinafter referred to as "this embodiment"), but the present invention is not limited thereto, and various modifications are possible without departing from its essence.

[0012] In this embodiment, "TD direction" refers to the width direction of the resin in the film-forming line, which is perpendicular to the direction in which the wrap film is pulled out from the winding body when it is made into a wrap film. Also, "MD direction" refers to the flow direction of the resin in the film-forming line, which is the direction in which the wrap film is pulled out from the winding body when it is made into a wrap film.

[0013] [Wrap film] The wrap film of this embodiment contains a vinylidene chloride-based resin, the vinylidene chloride-based resin contains 72 mol% to 93 mol% vinylidene chloride, and the contact angle of water with respect to the surface of the wrap film is 70° to 120°.

[0014] The wrap film of this embodiment has a water contact angle with the surface of the wrap film of 70° to 120°, which has the effect of preventing rice from sticking to the wrap film when cooking rice balls using the wrap film. Although the mechanism by which this effect is achieved is not clear, the inventor of the present invention has made the following assumptions. The wrap film of the present embodiment has a water contact angle of 70° or more with respect to the surface of the wrap film. For example, when cooking hand-rolled rice balls using the wrap film, the water that seeps out from the surface of the rice can spread within a certain range but can be retained in a hemispherical shape with a certain thickness. Also, because the water contact angle is 120° or less, although the retained water approaches a spherical shape, it can stay in place. As a result, when cooking hand-rolled rice balls using the wrap film of the present embodiment, for example, it is considered that the rice balls will not stick to the wrap film. From a similar perspective, it is preferable that the water contact angle of the wrap film of the present embodiment with respect to the surface of the wrap film is 70° or more and 120° or less, and more preferably 70° or more and 100° or less. The method for setting the water contact angle of the wrap film with respect to the surface within the above range is not particularly limited, but examples include appropriately adjusting the type and amount of additives contained in the wrap film. In the present embodiment, the water contact angle of the wrap film with respect to the surface can be measured by the method described in the examples.

[0015] (Vinylidene chloride resin) The vinylidene chloride resin used in the present embodiment is not particularly limited as long as it contains 72 mol% to 93 mol% of vinylidene chloride, and examples include vinylidene chloride copolymers containing monomers copolymerizable with vinylidene chloride.

[0016] The monomers copolymerizable with vinylidene chloride are not particularly limited. 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, etc. These monomers may be used alone or in combination of two or more. Among these, vinyl chloride is more preferable.

[0017] The content of vinylidene chloride is 72 mol% to 93 mol%, preferably 75 mol% to 87 mol%, more preferably 79 mol% to 85 mol% with respect to the total amount of the vinylidene chloride-based resin. When the content of vinylidene chloride is 72 mol% or more, the glass transition temperature of the vinylidene chloride-based resin is low, and the wrap film tends to become soft. Thereby, for example, tearing of the wrap film can be reduced even when used in a low-temperature environment such as in winter. On the other hand, when the content of vinylidene chloride is 93 mol% or less, a significant increase in crystallinity is suppressed, and deterioration of the molding processability during film stretching tends to be suppressed.

[0018] The method for measuring the content of vinylidene chloride is not particularly limited. For example, it can be measured using a high-resolution proton nuclear magnetic resonance measuring device (400 MHz or higher). More specifically, 0.5 g of the wrap film is dissolved in 10 mL of THF (tetrahydrofuran), about 30 mL of methanol is added to precipitate the resin component, and then the precipitate is separated by centrifugation and vacuum dried to obtain a sample for measuring the vinylidene chloride-based resin. Then, the obtained sample for measurement is dissolved in deuterated tetrahydrofuran to a concentration of 5% by mass, and this solution is subjected to H-NMR measurement at a measurement ambient temperature of about 27°C. The content of vinylidene chloride is calculated using the specific chemical shift based on tetramethylsilane in the obtained spectrum. For example, in the copolymer of vinylidene chloride and vinyl chloride, it is calculated using the peaks at 3.50 to 4.20 ppm, 2.80 to 3.50 ppm, and 2.00 to 2.80 ppm.

[0019] Also, in the vinylidene chloride-based resin, the content of the monomer copolymerizable with vinylidene chloride is preferably 7 to 28 mol%, more preferably 13 to 25 mol%, and even more preferably 15 to 21 mol%. When the content of the monomer copolymerizable with vinylidene chloride is within the above range, tearing of the wrap film is reduced even when used in a low-temperature environment, and deterioration of the molding processability during film stretching tends to be more suppressed.

[0020] The weight-average molecular weight (Mw) of the vinylidene chloride resin is preferably 50,000 to 250,000, more preferably 60,000 to 230,000, and even more preferably 80,000 to 200,000. When the weight-average molecular weight (Mw) of the vinylidene chloride resin is within the above range, the mechanical strength of the wrap film tends to improve. A vinylidene chloride resin with a weight-average molecular weight within the above range can be obtained, for example, by controlling the charging ratio of vinylidene chloride monomer to vinyl chloride monomer, the amount of polymerization initiator, or the polymerization temperature. In this embodiment, the weight-average molecular weight (Mw) can be determined using a standard polystyrene calibration curve by gel permeation chromatography (GPC).

[0021] The content of vinylidene chloride resin is preferably 79% to 96% by mass relative to the total amount of the wrap film. When the vinylidene chloride resin content is within this range, the plasticizing effect of additives reduces the share of melt extrusion, thus further suppressing the generation of foreign matter. Furthermore, when the vinylidene chloride resin content is within this range, the film tends to stretch more easily, further improving the film's cutability. Note that the method for measuring the content of each component from the wrap film varies depending on the analyte. For example, the vinylidene chloride resin content can be obtained by dissolving 0.5g of the sample in 10mL of THF (tetrahydrofuran), adding approximately 30mL of methanol to precipitate the resin, separating the precipitate by centrifugation, drying it, and weighing it.

[0022] (Additives) The wrap film of this embodiment may contain various additives in addition to the vinylidene chloride resin described above. As described above, for example, by appropriately adjusting the various additives, the water contact angle with the surface of the wrap film can be set to 70° or more and 120° or less, the vinylidene chloride resin can be plasticized, improving moldability and tactile feel. The following is a detailed explanation of the various additives.

[0023] (Long-chain alkyl stearate) The wrap film of this embodiment may contain long-chain alkyl stearate as an additive. The wrap film of this embodiment tends to have a water contact angle of 70° to 120° on the surface of the wrap film when it contains long-chain alkyl stearate as an additive. The reason for this is not clear, but it is thought that the carbonyl group of the long-chain alkyl stearate exhibits a moderate affinity for water, and the long-chain alkyl portion has a water-repellent effect.

[0024] The long-chain alkyl ester of stearate is not particularly limited, but it is preferably a saturated alkyl or unsaturated alkyl group with 4 or more alkyl groups. Specifically, although not particularly limited, examples include butyl stearate, pentyl stearate, hexyl stearate, and octyl stearate.

[0025] The content of long-chain alkyl stearate is preferably more than 1% by mass and 10% by mass or less, relative to the total amount of the wrap film. When the content of long-chain alkyl stearate is within this range, it bleeds onto the surface of the wrap film and stretches, resulting in a desired water contact angle. Furthermore, the vinylidene chloride resin is plasticized, leading to improved moldability and a tendency for improved tactile feel.

[0026] (Long-chain alkyl oleate) The wrap film of this embodiment may contain a long-chain alkyl oleate as an additive. The wrap film of this embodiment tends to have a water contact angle of 70° to 120° on the surface of the wrap film when it contains a long-chain alkyl oleate as an additive. The reason for this is not clear, but it is thought that the carbonyl group of the long-chain alkyl oleate exhibits a moderate affinity for water, and the long-chain alkyl portion has a water-repellent effect.

[0027] While there are no particular limitations on the long-chain alkyl ester of oleic acid, those with four or more saturated or unsaturated alkyl groups are preferred. Specifically, although not particularly limited, examples include butyl oleate, pentyl oleate, hexyl oleate, and octyl oleate.

[0028] The content of long-chain alkyl oleate is preferably more than 1% by mass and 10% by mass or less, relative to the total amount of the wrap film. When the content of long-chain alkyl oleate is within the above range, it bleeds onto the surface of the wrap film and stretches, resulting in a desired water contact angle. Furthermore, the vinylidene chloride resin is plasticized, leading to improved moldability and a tendency for improved tactile feel.

[0029] (Monoacetylated fatty acid ester) The wrap film of this embodiment may contain a monoacetylated fatty acid ester as an additive. The wrap film of this embodiment tends to have a water contact angle of 70° to 120° on the surface of the wrap film when it contains a monoacetylated fatty acid ester as an additive. The reason for this is not clear, but it is thought that the two carbonyl groups of the monoacetylated fatty acid ester exhibit a moderate affinity for water, and the long-chain alkyl portion of the fatty acid has a water-repellent effect.

[0030] While monoacetylated fatty acid esters are not particularly limited, O-acetylhydroxy fatty acid esters are preferred. Examples of O-acetylhydroxy fatty acid esters are not particularly limited, but include ethyl acetyllactate, butyl acetyllactate, ethyl acetylhydroxybutyrate, methyl acetylricinoleate, and butyl acetylricinoleate.

[0031] The content of monoacetylated fatty acid ester is preferably more than 1% by mass and 10% by mass or less, relative to the total amount of the wrap film. When the monoacetylated fatty acid ester content is within this range, it bleeds onto the surface of the wrap film and stretches, resulting in a desired water contact angle. Furthermore, the vinylidene chloride resin is plasticized, leading to improved moldability and a tendency for a better tactile feel.

[0032] (Hydrogenated rosin derivative) The wrap film of this embodiment may contain a monoacetylated fatty acid ester as an additive. The wrap film of this embodiment tends to have a water contact angle of 70° to 120° on the surface of the wrap film when it contains a hydrogenated rosin derivative as an additive. The reason for this is not clear, but it is thought that the carbonyl group of the hydrogenated rosin derivative exhibits a moderate affinity for water, and the 6-membered ring structure of the rosin has a water-repellent effect.

[0033] Hydrogenated rosin derivatives are not particularly limited, but examples include hydrogenated rosin, hydrogenated glyceryl rosinate, hydrogenated pentaerythrityl rosinate, hydrogenated methyl rosinate, (hydrogenated rosin / diisostearate) glyceryl, trihydrogenated rosinate glyceryl, (hydroxystearate / stearate / rosinate) pentaerythrityl, and partially hydrogenated methyl rosinate. Among these, hydrogenated methyl rosinate is preferred.

[0034] The hydrogenated rosin derivative content is preferably more than 1% by mass and 10% by mass or less relative to the total amount of the wrap film. When the hydrogenated rosin derivative content is within this range, it bleeds onto the surface of the wrap film and spreads, resulting in a desired water contact angle. Furthermore, the vinylidene chloride resin is plasticized, leading to improved moldability and a tendency for improved tactile feel.

[0035] (Triethylene glycol fatty acid diester) The wrap film of this embodiment may contain a monoacetylated fatty acid ester as an additive. The wrap film of this embodiment tends to have a water contact angle of 70° to 120° on the surface of the wrap film when it contains a triethylene glycol fatty acid diester as an additive. The reason for this is not clear, but it is thought that the triethylene glycol portion of the triethylene glycol fatty acid diester exhibits compatibility with water, while the long-chain alkyl portion of the fatty acid ester has a water-repellent effect.

[0036] The fatty acid diester of triethylene glycol is not particularly limited, but examples include triethylene glycol dicaprylate, triethylene dicaprate, and triethylene glycol distearate. Among these, triethylene glycol dicaprylate and triethylene dicaprate are preferred.

[0037] The content of triethylene glycol fatty acid diester is preferably more than 1% by mass and 10% by mass or less, relative to the total amount of the wrap film. When the content of triethylene glycol fatty acid diester is within the above range, it bleeds onto the surface of the wrap film and stretches, resulting in a desired water contact angle. Furthermore, the vinylidene chloride resin is plasticized, leading to improved moldability and a tendency for improved tactile feel.

[0038] (Other additives) The wrap film of this embodiment may contain at least one compound selected from the group consisting of citrate esters, dibasic acid esters, and acetylated fatty acid glycerides. Citrate esters are preferred from the viewpoint of ease of handling, and tributyl acetylcitrate is particularly preferred.

[0039] (Citrate ester) The citrate esters are not particularly limited, but examples include triethyl citrate, tributyl citrate, triethyl acetyl citrate, tributyl acetyl citrate (ATBC), and tri-n-(2-ethylhexyl) acetyl citrate.

[0040] Among these, tributyl acetyl citrate is preferred. By using such a citrate ester, the vinylidene chloride resin is plasticized, improving moldability, and by imparting flexibility to the wrap film, adhesion is improved, as well as the tactile feel tends to be enhanced.

[0041] (Dibasic acid ester) Examples of dibasic acid esters include, but are not particularly limited, adipic acid esters such as dibutyl adipate, di-n-hexyl adipate, di-2-ethylhexyl adipate, and dioctyl adipate; azelaic acid esters such as di-2-ethylhexyl azelaic acid and octyl azelaic acid; sebacate acid esters such as dibutyl sebacate (DBS) and di-2-ethylhexyl sebacate; and phthalate esters such as dimethyl phthalate, diethyl phthalate, and dioctyl phthalate.

[0042] Among these, aliphatic dibasic acid esters are preferred, and dibutyl sebacate is more preferred. By using such dibasic acid esters, the vinylidene chloride resin is plasticized, improving moldability, and by imparting flexibility to the wrap film, adhesion is improved, as well as the tactile feel tends to be improved.

[0043] (Acetylated fatty acid glycerides) There are no particular limitations on the acetylated fatty acid glycerides, but examples include acetylated caprylic acid glyceride, acetylated capric acid glyceride, acetylated laurate glyceride, acetylated myristic acid glyceride, acetylated palm kernel oil glyceride, acetylated coconut oil glyceride, acetylated castor oil glyceride, and acetylated hydrogenated castor oil glyceride.

[0044] The above-mentioned acetylated fatty acid glycerides may be acetylated monoglycerides, acetylated diglycerides, or acetylated triglycerides of fatty acids. For example, the above-mentioned acetylated laurate glycerides include acetylated monoglycerides of lauric acid, acetylated diglycerides of lauric acid (DALG: diacetyllauroylglycerol), and acetylated triglycerides of lauric acid. Among these, acetylated laurate glycerides are preferred, and acetylated diglycerides of lauric acid are more preferred. By using such acetylated fatty acid glycerides, flexibility is imparted to the wrap film, improving adhesion and tending to enhance the tactile feel.

[0045] The content of citrate esters, dibasic acid esters, and acetylated fatty acid glycerides can be determined by extracting the additives from the wrap film using an organic solvent such as acetone at a temperature 5-10°C lower than the boiling point of the extraction solvent, and then performing gas chromatography analysis.

[0046] The total content of at least one compound selected from the group consisting of citrate esters, dibasic acid esters, and acetylated fatty acid glycerides is preferably 3% to 8% by mass, and more preferably 3.5% to 7% by mass, relative to the total amount of the wrap film, in order to provide better moldability and prevent excessive adhesion of the wrap film when the additive content is high. In particular, when the vinylidene chloride resin wrap film contains 3% by mass or more of citrate esters or dibasic acid esters, the mobility of the molecular chains of the vinylidene chloride resin increases, making it easier for rearrangement such as the formation and growth of microcrystals to occur, making it more susceptible to physical degradation when exposed to high temperatures, and also making the film more stretchable, which makes it difficult for the cutting blade to bite into the film and tends to reduce the cutting performance. Therefore, the effects of the configuration of the present invention are remarkable.

[0047] (Epoxy vegetable oil) The wrap film of this embodiment may contain epoxidized vegetable oil. The epoxidized vegetable oil can act as a stabilizer for vinylidene chloride resin extrusion processing. The epoxidized vegetable oil is not particularly limited, but generally, those produced by epoxidizing edible oils and fats are examples. Specifically, examples of epoxidized vegetable oils include epoxidized soybean oil (ESO) and epoxidized linseed oil. Among these, epoxidized soybean oil is preferred. By using such an epoxidized vegetable oil, the tactile feel of the wrap film tends to be improved, and the ease of pulling the film out of the cosmetic box also tends to be improved.

[0048] In this embodiment, the content of epoxidized vegetable oil is preferably 0.5% to 3% by mass, more preferably 1% to 2.5% by mass, and even more preferably 1% to 2% by mass, relative to the total amount of wrap film. When the content of epoxidized vegetable oil is 0.5% by mass or more, the quality changes of the wrap film tend to be further suppressed. Furthermore, when the content of epoxidized vegetable oil is 3% by mass or less, the color changes of the wrap film tend to be further suppressed, and stickiness due to bleeding tends to be suppressed. Note that the method for measuring the content of each component from the wrap film varies depending on the analyte. For example, the content of epoxidized vegetable oil can be obtained by analyzing the re-precipitation filtrate of the wrap film by NMR.

[0049] Specifically, the sample is weighed to 50 mg, dissolved in a deuterated solvent (solvent: deuterated tetrahydrofuran, internal standard: dimethyl terephthalate, volume: 0.7 mL), measured using 400 MHz proton NMR (number of integrations: 512 times), the integral ratio is taken as the ratio of the integral value of 2.23 to 2.33 ppm to the integral value of 8.05 to 8.11 ppm, and the quantitative value is calculated using the absolute calibration curve method to obtain the result. Integral ratio = Integral value (2.23~2.33 ppm) / Integral value (8.05~8.11 ppm)

[0050] The wrap film of this embodiment may contain additives other than those mentioned above. Such additives are not particularly limited, but examples include plasticizers other than those mentioned above, stabilizers other than those mentioned above, weather resistance improvers, colorants such as dyes or pigments, antifogging agents, antibacterial agents, lubricants, nucleating agents, oligomers such as polyester, polymers such as methyl methacrylate-butadiene-styrene copolymer (MBS), and the like.

[0051] Other stabilizers besides epoxidized vegetable oils are not particularly limited, but specifically include antioxidants such as 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 4,4'-thiobis-(6-t-butylphenol); and heat stabilizers such as laurate, myristicate, palmitate, stearate, isostearate, oleate, ricinoleate, 2-ethylhexylate, isodecanate, neodecanoate, and calcium benzoate. Stabilizers may be used individually or in combination of two or more.

[0052] The weather resistance improver is not particularly limited, but specific examples include ethylene-2-cyano-3,3'-diphenyl acrylate, 2-(2'-hydroxy-5'-methylphenyl)benzolytriazole, 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)5-chlorobenzotriazole, 2-hydroxy-4-methoxybenzophenone, and 2,2'-dihydroxy-4-methoxybenzophenone. The weather resistance improver may be used alone or in combination of two or more.

[0053] The colorants, such as dyes or pigments, are not particularly limited, but specific examples include carbon black, phthalocyanine, quinacridone, indoline, azo pigments, and red iron oxide. The colorants may be used individually or in combination of two or more.

[0054] The anti-fogging agent is not particularly limited, but specific examples include glycerin fatty acid esters, sorbitan fatty acid esters, polyoxyethylene fatty acid alcohol ethers, polyoxyethylene glycerin fatty acid esters, and polyoxyethylene sorbitan fatty acid esters. The anti-fogging agent may be used alone or in combination of two or more types.

[0055] The antibacterial agent is not particularly limited, but specific examples include silver-based inorganic antibacterial agents. The antibacterial agent may be used alone or in combination of two or more types.

[0056] The lubricant is not particularly limited, but specific examples include fatty acid hydrocarbon lubricants such as ethylene bissteramide, butyl stearate, polyethylene wax, paraffin wax, carnauba wax, myristyl myristate, and stearyl stearate, as well as higher fatty acid lubricants, fatty acid amide lubricants, and fatty acid ester lubricants. The lubricant may be used alone or in combination of two or more types.

[0057] The nucleating agent is not particularly limited, but specific examples include phosphate ester metal salts. The nucleating agent may be used alone or in combination of two or more.

[0058] (Thickness of the plastic wrap) The thickness of the wrap film in this embodiment is preferably 6 μm to 18 μm, and more preferably 9 μm to 12 μm. By having the wrap film thickness within the above range, problems with film tearing are suppressed, cutability is further improved, and adhesion is further improved.

[0059] More specifically, a wrap film thickness of 6 μm or more improves the tear strength of the wrap film in the TD and MD directions, and tends to reduce film tearing during use. Furthermore, a wrap film thickness of 6 μm or more tends to result in less significant reduction in tear strength. Therefore, when pulling the wrap film from the winding and when picking up the end of the film wound back into the packaging box, problems such as the wrap film tearing at the end cut by the cutting blade attached to the packaging box are further reduced.

[0060] On the other hand, a wrap film thickness of 18 μm or less reduces the force required to cut the wrap film with the cutting blade attached to the packaging box, which tends to improve cutting performance. Also, a wrap film thickness of 18 μm or less makes it easier for the wrap film to conform to the shape of the container, which tends to improve adhesion to the container.

[0061] (tear strength) The tear strength in the TD direction of the wrap film in this embodiment is preferably 2.0 cN to 6.0 cN, more preferably 2.0 cN to 4.0 cN, and even more preferably 2.2 cN to 3.0 cN. A tear strength of 2.0 cN or higher in the TD direction reduces tearing, especially when pulling the wrap film from the winding, and suppresses unintended tearing problems when using the wrap film. On the other hand, a tear strength of 6.0 cN or lower in the TD direction makes it easier to tear the film in the TD direction when cutting it with a cutting blade attached to the cosmetic box, improving cutability.

[0062] 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, and the thickness of the film. While not particularly limited, for example, the tear strength in the TD direction tends to improve by lowering the stretching ratio in the TD direction or increasing the thickness of the wrap film, and tends to decrease by increasing the stretching ratio in the TD direction or thinning the wrap film. The tear strength is measured by the method described in the examples.

[0063] (Tensile modulus of elasticity) The tensile modulus of elasticity in the MD direction of the wrap film in this embodiment is preferably 250 MPa to 600 MPa, more preferably 300 MPa to 500 MPa, and even more preferably 350 MPa to 500 MPa. When the tensile modulus of elasticity in the MD direction is 250 MPa or higher, when force is applied to cut the film with a cutting blade, the elongation of the film in the MD direction can be suppressed, the cutting blade can bite into the film more easily, and the cutting performance is improved. On the other hand, when the tensile modulus of elasticity in the MD direction is 600 MPa or lower, the film is softer, the film can be cut cleanly along the shape of the cutting blade, and the occurrence of numerous tears on the cut end surface tends to be suppressed. As a result, when pulling the film out from the winding body and when picking up the end of the film that has been wound back into the cosmetic box, the problem of the film tearing from the cut end surface tends to be suppressed.

[0064] The tensile modulus in the MD 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, and the stretching speed. While not particularly limited, for example, the tensile modulus in the MD direction tends to improve by increasing the stretching ratio or decreasing the amount of additive, and tends to decrease by decreasing the stretching ratio or increasing the amount of additive. The tensile modulus is measured by the method described in the examples.

[0065] [Method of manufacturing plastic wrap] The method for manufacturing the wrap film of this embodiment is not particularly limited, but examples include a method comprising the steps of melt-extruding a composition containing a vinylidene chloride-based resin containing 72 mol% to 93 mol% vinylidene chloride and various additives to form a film, and stretching the obtained film in the MD direction and TD direction. A detailed explanation follows below.

[0066] (Mixing process) Figure 1 shows a schematic diagram of an example of the manufacturing process for wrap film. First, a composition is obtained by mixing vinylidene chloride resin and various additives in a mixer. Various additives may be mixed in as needed. The mixer is not particularly limited, but for example, a ribbon blender or a Henschel mixer can be used. The obtained composition is preferably aged for about 1 to 30 hours before being used in the next step.

[0067] (Melting extrusion process) Next, the obtained composition is melted by the extruder 1, and a tubular film is extruded from the die opening 3 of the die 2 to form a sock 4 (also called a pile).

[0068] (cooling process) The sock liquid 5 is injected into the inside of the sock 4, and the outside of the sock 4 is brought into contact with the cold water in the cold water tank 6. As a result, the sock 4 is cooled from both the inside and the outside, and the film that makes up the sock 4 solidifies. The solidified sock 4 is folded by the first pinch roll 7 to form the parison 8.

[0069] (Stretching process) Next, air is injected into the inside of the parison 8 to open it and form an annular film. At this time, the sock liquid 5 applied to the part that is in contact with the inner surface of the sock 4 acts as an opening agent for the parison 8. Then, with the parison 8 open, it is reheated with hot water to a temperature suitable for stretching. The hot water adhering to the outside of the parison 8 is squeezed off by the second pinch roll 9.

[0070] As described above, air is injected into the parison 8, which has been heated to the appropriate temperature, to form a bubble 10. This air pushes the parison outward from the inside, stretching the film and obtaining a stretched film. Stretching of the film mainly in the TD direction is achieved by the amount of air, while stretching of the film in the MD direction is achieved by applying tension in the direction of film flow using the second pinch roll 9 and the third pinch roll 11, etc.

[0071] The process from the first pinch roll 7 to the third pinch roll 11 is called the stretching process. Since slowing down the stretching speed improves the stretchability of the parison 8, in conventional methods for manufacturing wrap film, the stretching speed in the MD direction was adjusted to 0.08 times / second or less, and the stretching speed in the TD direction was adjusted to 3.0 times / second or less. In contrast, in the method for manufacturing wrap film of this embodiment, it is preferable to adjust the stretching ratios in the MD and TD directions, and the stretching speeds in the MD and TD directions, to a predetermined range.

[0072] Specifically, the stretching ratios in the MD direction and TD direction in the stretching process used in this embodiment are preferably 4 to 6 times, and more preferably 4.1 to 5.6 times, independently of each other. Here, the stretching ratio in the MD direction refers to the stretching ratio when the parison 8 is stretched in the MD direction, and for example, in Figure 1, it can be calculated by the ratio of the rotation speed of the third pinch roll 11 to the rotation speed of the first pinch roll 7. 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 Figure 1, it can be calculated by the ratio of the width of the double ply film 12 to the width of the parison 8. The stretching ratio in the MD direction can be adjusted, for example, by the rotation 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 the stretching temperature of the parison 8 or the size of the bubble 10.

[0073] Furthermore, the stretching speed in the MD direction during the stretching process of this embodiment is preferably 0.09 times / second to 0.12 times / second. The average stretching speed in the MD direction refers to the stretching ratio in the MD direction relative to the time it takes for the parison to pass between the first pinch roll 7 and the third pinch roll 11. For example, in Figure 1, it can be calculated by the rotational speed of the first pinch roll 7, the rotational 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, for example, by the rotational speed of the first pinch roll 7 or the third pinch roll 11, or by the distance between the first pinch roll 7 and the third pinch roll 11.

[0074] Furthermore, the stretching speed in the TD direction during the stretching process of this embodiment is preferably 3.1 times / second to 4.0 times / second. The average stretching speed in the TD direction refers to the stretching ratio in the TD direction relative to the time required for the parison 8 to expand to the bubble 10. For example, in Figure 1, it can be calculated from the time required for stretching in the TD direction, which is calculated from the stretched length measured using still images of the parison 8 and bubble 10 and the rotation 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, for example, by the rotation speed of the third pinch roll 11.

[0075] The stretching temperature is not particularly limited, but is preferably 30°C to 45°C.

[0076] After the stretching process described above, the stretched film is folded by the third pinch roll 11 to form a double-ply film 12. The double-ply film 12 is then wound up by the winding roll 13.

[0077] (relaxation process) In the method for manufacturing the wrap film of this embodiment, it is preferable to have a relaxation step to relax the wrap film immediately after stretching. A relatively common relaxation method in the manufacturing of wrap films is to relax the film after stretching by using heat such as an infrared heater. However, in this embodiment, it is preferable to use a method in which the stretched film is relaxed by slowing down the rotation speed of the winding roll 13 compared to the third pinch roll 11, instead of this relaxation step. This is because, in this embodiment, if the conventional relaxation method using heat is used, the heat will cause the formation and growth of microcrystals, which are the cause of tearing of the film.

[0078] The relaxation ratio in the relaxation process using the third pinch roll 11 and the winding roll 13 is preferably 7% to 15%, and more preferably 9% to 13%. A relaxation ratio of 15% or less tends to further suppress wrinkle formation due to the occurrence of film slack between the third pinch roll 11 and the winding roll 13. Furthermore, a relaxation ratio of 7% or more allows the wrap film to be sufficiently relaxed, enabling molecular chain rearrangement even when exposed to high temperatures. This also tends to reduce tearing problems. Here, "relaxation ratio" refers to the ratio of the shrinkage of the double-ply film 12 between the third pinch roll 11 and the winding roll 13. For example, in the case of Figure 1, it can be calculated using the ratio of the winding roll 13 to the rotation speed of the third pinch roll 11.

[0079] Furthermore, the ambient temperature during the relaxation process using the third pinch roll 11 and the winding roll 13 is preferably 25°C to 32°C. When the ambient temperature is within this range, the formation and growth of microcrystals tend to be suppressed.

[0080] (Slitting process) The wrap film, wound as described above, is slit and peeled off into individual sheets, which are then wound up and temporarily stored in its roll form for 1 to 3 days. Finally, it is wound back onto a cardboard tube and packed into a cosmetic box, resulting in a roll of wrap film stored in a cosmetic box.

[0081] (Storage process) In the method for manufacturing the wrap film of this embodiment, a storage step may be performed in which the wrap film is stored in its original roll state after slitting. The storage temperature is preferably 19°C or lower, more preferably 5°C to 19°C, and even more preferably 5°C to 15°C. The storage time is preferably 20 to 50 hours, and more preferably 24 to 40 hours. [Examples]

[0082] The present invention will be described more specifically below with reference to examples and comparative examples. The present invention is not limited in any way by the following examples.

[0083] [Vinylidene chloride content] The vinylidene chloride content (ratio) in polyvinylidene chloride resins in wrap films was determined from the content of vinylidene chloride repeating units measured using a high-resolution proton nuclear magnetic resonance (HNC) spectrometer. 0.5 g of wrap film was dissolved in 10 mL of THF (tetrahydrofuran), approximately 30 mL of methanol was added to precipitate the resin, and the precipitate was separated by centrifugation and vacuum-dried to obtain a sample of vinylidene chloride resin for measurement. The obtained sample was then dissolved in deuterated tetrahydrofuran to a concentration of 5% by mass, and the resulting solution was measured by H-NMR at a measurement ambient temperature of approximately 27°C. For example, in the case of copolymers of vinylidene chloride (VDC) and vinyl chloride (VC), the content of vinylidene chloride repeating units was calculated using the peaks of 3.50-4.20 ppm, 2.80-3.50 ppm, and 2.00-2.80 ppm of the copolymer based on tetramethylsilane, and this value was taken as the vinylidene chloride content. Furthermore, for other copolymers as well, the content of repeating units can be calculated using the peaks for each monomer.

[0084] [Film thickness] The thickness of the wrap film was measured using a dial gauge (manufactured by Teclock) in an atmosphere of 23°C and 50% RH.

[0085] [Tear strength] A light-load tear tester, Type D (manufactured by Toyo Seiki), was used to measure the tear strength of the wrap film. The tear strength was measured in an atmosphere of 23°C and 50% RH. Only one sheet of wrap film was used for the tear strength measurement. The sample length in the tear direction was 63.5 mm, and the sample width was 50.0 mm. During measurement, the pendulum was lifted and stopped, the test piece was carefully attached to the gripper, and the clamp was tightened firmly so that the slit was made in the center of the film width. Then, a slit was made in the film with a knife attached to the device. At this time, the blade position of the knife was adjusted so that the cut length of the film was 12.7 mm ± 0.5 mm. After making the slit, the pendulum was carefully released, and the force required to tear the test piece was read. This read value was taken as the tear strength in the TD direction. Tests in which the tear line deviated by more than 10 mm from the extension of the slit were excluded, and additional test pieces were tested instead. Furthermore, the measurement results were rounded to two decimal places. A total of five measurements were taken using different samples, and the average of these five measurements was used as the measured value.

[0086] [Tensile modulus of elasticity] The tensile modulus of the wrap film was measured using an Autograph AG-IS (Shimadzu Corporation) in an atmosphere of 23°C and 50% RH. The load at which the film was stretched by 2% was measured under conditions of a tensile speed of 5 mm / min, a chuck distance of 100 mm, and a film width of 10 mm. This load was then divided by the cross-sectional area of ​​the sample and multiplied by 50 to measure the tensile modulus in the MD direction. During measurement, the specimen was mounted in the grips so that its MD direction aligned with the axis of the testing machine. The specimen was tightly and evenly gripped to prevent slippage and to prevent the gripping portion from shifting during the test. Furthermore, cracking and rolling of the specimen should not occur due to the pressure between the grips. The measurement results were rounded to two significant figures, with the third digit rounded to the nearest tenth.

[0087] [Contact angle] The contact angle of water with the surface of the wrap film was determined by dropping a 2.0 μL droplet of pure water onto the surface of a test film attached to a slide, and then measuring the contact angle using the θ / 2 method, which calculates the contact angle from the angle of the line connecting the left and right endpoints and the apex of the dropped droplet relative to the surface of the test film, 1 second after the droplet has been placed on the surface. The water contact angle was measured using a DM 701 contact angle meter manufactured by Kyowa Interface Science Co., Ltd., in an atmosphere of 23°C and 50% RH. A total of five measurements were taken with different samples, and the average of the five measurements was used as the measured value.

[0088] [Texture (smoothness)] An evaluation of the tactile feel (smoothness) of plastic wrap was conducted. 100 people who regularly use food packaging plastic wrap were selected as evaluators, and their sensory evaluations were performed. Each evaluator was given a score of 10, with 0 points indicating stickiness and 10 points indicating a smooth, dry feel. The average score of the 100 evaluators was calculated and used for the evaluation. The evaluation environment was 23°C and 50% RH relative humidity. [Evaluation criteria for texture (smoothness)] ◎: 8 points or higher: Not sticky at all, very smooth and excellent quality. ○: 3 to less than 8 points: Very good level with almost no stickiness. ×: Less than 3 points: Slightly sticky and somewhat unpleasant.

[0089] [Amount of rice attached] The freshly cooked rice was placed on a tray, and once it had cooled slightly, 100g was measured out onto a piece of plastic wrap approximately 22cm wide and 30cm long. The rice was wrapped in the film from all four sides, and the rice ball was gently squeezed five times to shape it. The finished rice ball was left in a 23°C room for 3 hours, and then the plastic wrap was removed and the degree of rice grain adhesion was evaluated according to the following criteria. [Criteria for evaluating rice adhesion] ◎: No rice grains are stuck to it at all. ○: The number of attached rice grains is 10 or less. ×: The number of rice grains attached is more than 10.

[0090] [Example 1] A vinylidene chloride resin with a weight-average molecular weight of 90,000 (82 mol% vinylidene chloride repeating units, 18 mol% vinyl chloride repeating units) was mixed with 5.5% by mass of tributyl acetyl citrate (Taoka Chemical Industries, Ltd.), 1.1% by mass of epoxidized soybean oil (New Sizer 510R, Nippon Oil & Fats Co., Ltd.), and 1.0% by mass of n-butyl stearate (Excepearl BS, Kao Corporation) in a Henschel mixer for 5 minutes. After mixing, the mixture was aged for 24 hours or more to obtain the composition.

[0091] The obtained composition was supplied to a melt extruder and melted, and a sock was formed by melt extrusion through an annular die attached to the tip of the extruder. At this time, the heating conditions of the extruder were adjusted so that the molten resin temperature at the slit outlet of the annular die was 170°C, and the material was extruded in an annular shape at an extrusion rate of 10 kg / hour.

[0092] After cooling with sock solution and a chilled water bath, the parison was opened to form bubbles, and inflation stretching was performed under the stretching conditions shown in Table 1. During this process, the film was stretched 4.1 times in the MD direction and 5.6 times in the TD direction to form tubular films (bubbles). The stretching temperature was 35°C.

[0093] The obtained tubular film was nipped and folded flat. Then, by controlling the speed ratio of the pinch roll and the winding roll, the film was relaxed in the MD direction (relaxation ratio 10%), and a double-ply film with a width of 280 mm and two layers was wound up. This film was slit to a width of 220 mm, and while peeling it into a single film, it was rewound onto a paper tube with an outer diameter of 92 mm. Subsequently, 20 m was wound onto a paper tube with an outer diameter of 36 mm and a length of 230 mm to obtain a roll of wrap film (thickness: 11 μm). The obtained roll of wrap film was stored at 15°C for 30 hours, and each evaluation was performed using the method described above. The evaluation results are shown in Table 2.

[0094] [Examples 2-8 and Comparative Examples 1-3] Wrap film rolls were prepared in the same manner as in Example 1, except that the type and amount of additives were changed as shown in Table 1, and each evaluation was performed using the method described above. The evaluation results are shown in Table 2.

[0095] [Table 1]

[0096] [Table 2] [Industrial applicability]

[0097] The wrap film of the present invention can be effectively used for food packaging and other applications, for example, when cooking rice balls using the wrap film, as the rice does not stick to the wrap film. [Explanation of Symbols]

[0098] 1. Extruder 2 Dies 3 Die opening 4. Tubular vinylidene chloride copolymer 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. Rewinding Roll

Claims

1. Contains vinylidene chloride resin, The vinylidene chloride resin contains 72 mol % to 93 mol % of vinylidene chloride, The contact angle of water on the surface of the wrap film is 70° or more and 120° or less. Plastic wrap.

2. The tensile modulus in the MD direction is 250 MPa to 600 MPa. The wrap film according to claim 1.

3. The tear strength in the TD direction is 2 cN to 6 cN. The wrap film according to claim 1 or 2.

4. The thickness is 6 μm to 18 μm. The wrap film according to any one of claims 1 to 3.

Images