JPH0585348B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to wrapped film. For more details, please refer to various food products such as vegetables, fruits, fish and shellfish, and livestock meat, as well as prepared products at home, supermarkets, food processing companies, department stores, grocery stores, refrigeration companies, sushi restaurants, soba restaurants, and other restaurants. This invention relates to a polyolefin wrap film used as a packaging material. [Prior art] Conventional wrap films include polyvinylidene chloride, polyvinyl chloride, high-pressure polyethylene, ethylene-vinyl acetate copolymer, polypropylene,
Materials made of linear low-density polyethylene, polybutadiene, etc. have been proposed, and polyvinylidene chloride, polyvinyl chloride, high-pressure polyethylene, polybutadiene, etc. have been put into practical use. Wrap film is used to easily package, protect, store, distribute, and display fresh foods, so it is required to have the following performance characteristics. Since the wrap film covers the article to be packaged and temporarily adheres the wrap films to each other by pressure bonding, it must have an appropriate degree of adhesiveness, and must be easily peeled off when the article is to be removed. In the case of simple packaging for business use, it may be packaged by heat sealing, so it must have good heat sealability. Wrap film is wrapped around a paper tube shaft with a width of 20cm to 45cm, a thickness of 7 to 20μ, and a length of 20 to 50m, which is shaped like a saw made from a tin plate about 0.2mm thick. It comes in a cardboard storage box with a knife attached, so when you want to use it, pull the wrap film out of the box and cut it with a knife. Therefore, the wrap film must be easily cut with relatively low force. In addition, in the case of business-use wrap film, when making cuts with a knife and cutting it, the work efficiency will be poor if the wrap film is not cut cleanly and quickly in the horizontal direction, but it will change direction in the vertical direction midway through the cut and tear. However, this kind of thing is not desirable. Since the content is often food, the material must not contain ingredients that pose a food hygiene problem, and must be heat-proof, waterproof, moisture-proof, air-proof, acid-proof, oil-proof, and have appropriate strength. , stretchability, and shrinkability are required. Furthermore, since it is displayed as a product, transparency, drip-proofing, anti-fogging properties, photoselectivity, etc. are required so that the contents can be clearly seen. During storage, in order to maintain freshness for a long time,
Recently, as ultra-low temperature refrigerators as low as -50°C have come into use, the low-temperature embrittlement resistance of wrap film materials has become an issue. When cooking using a microwave oven, heat resistance is required, and a material that does not cause the film to shrink or tear due to heat is required. Since wrap film is a consumable item, it is desired that the price be as low as possible. Conventionally, wrap films commercially available are mainly made from polyvinylidene chloride, polyvinyl chloride, low density polyethylene, ethylene-vinyl acetate copolymer, polybutadiene, etc. However, when cutting polyvinylidene chloride with a saw blade, the cracks tend to run in arbitrary directions regardless of the user's opinion, resulting in diagonal cuts, and when used in a microwave oven, they may be cut diagonally. There is a problem that the film shrinks greatly and breaks, and in high temperature conditions, it is exposed to hydrochloric acid gas,
There is a risk of generating chlorine gas and vinylidene chloride, which is undesirable from a food hygiene perspective, and there are concerns that it may be carcinogenic. Polyvinyl chloride-based materials are inexpensive and are used commercially, but they tend to whiten when exposed to boiling water and contain large amounts of plasticizers, and have the same problems as polyvinylidene chloride-based materials. In addition, polyvinylidene chloride and polyvinyl chloride contain chlorine, making them flame-retardant and difficult to dispose of.Furthermore, they emit gas harmful to the human body when burned or film-formed, which poses a problem. Low-temperature embrittlement is also poor. To overcome the drawbacks of chlorinated resins, non-chlorinated high-pressure low-density polyethylene has been commercialized, but it lacks tackiness, so a large amount of tackifier must be added to provide the necessary adhesive strength. As a result, the mechanical strength and stiffness of the film are reduced, and the cutting performance with a saw blade is also very poor. Ethylene-vinyl acetate copolymer systems have improved adhesiveness, but have problems with mechanical strength, stiffness, etc. Polypropylene-based materials have excellent heat resistance, but have problems with low-temperature embrittlement resistance, adhesion, and cutability with a saw blade. Linear low-density polyethylene has superior mechanical strength compared to high-pressure processed low-density polyethylene, but when it is formed using a normal blown film processing method, it has poor orientation in the vertical and horizontal directions. It is unbalanced and highly oriented in the vertical direction, making it difficult to cut with a saw blade, making it unusable as a wrap film. Furthermore, the film has poor peelability when used after being peeled off from the roll. Although polybutadiene has many excellent properties such as adhesiveness, low-temperature embrittlement, transparency, and cuttability with a saw blade, it has low mechanical strength such as tear strength. Another problem is that it is extremely expensive. [Problems to be Solved by the Invention] Conventional wrapped films have various problems as described above. The present invention has no food hygiene problems, mechanical strength, transparency, adhesiveness, food protection, cuttability with a saw blade, puncture resistance, impact resistance, heat resistance,
The purpose is to provide a wrap film with excellent heat sealability. [Means for solving the problem] The present inventor has recently developed a solution with a density of 0.910 g/ml.
The present invention was completed by paying attention to the following linear low-density ethylene-α-olefin copolymer, taking advantage of its excellent properties, and compensating for its drawbacks with an ethylene-vinyl acetate copolymer. That is, the present invention is a wrap film in which an intermediate layer made of a linear ethylene-α-olefin copolymer having a density of 0.910 g/ml or less and an outer layer made of an ethylene-vinyl acetate copolymer are laminated. In the present invention, a linear ethylene-α-olefin copolymer with a density of 0.910 g/ml or less means that ethylene accounts for 20% to 75% and α-olefin accounts for 80%.
~25%, preferably 40% to 60% ethylene
α-olefin accounts for 60% to 40%, and α-olefin has 3 to 12 carbon atoms. Here, the α-olefin may be linear or branched, for example propylene, butene-
1, hexene-1, heptene-1, octene-
1, nonene-1, decene-1, undecene-1,
Dodecene-1,4-methylpentene-1,4-methylhexene-1,4,4-dimethylpentene-
It means 1st class. The density used in this invention is
A linear ethylene-α-olefin copolymer of 0.910 g/ml or less was prepared in a fluidized bed reaction zone at a temperature of 10 to 80°C and a pressure of 7000 KPa or less to (a) 0.35:1 to
ethylene and at least one higher α-olefin having from 3 to 12 carbon atoms in a higher α-olefin to ethylene molar ratio of 8.0:1; (b) at least 25 mol % of at least one diluent gas; A gas mixture containing the formula Mg _n Ti (OR) _o X _p [ED] _q [where R is an aliphatic or aromatic hydrocarbon group having 1 to 14 carbon atoms or COR'
where R' is an aliphatic or aromatic hydrocarbon group having 1 to 14 carbon atoms, X is selected from the group consisting of Cl, Br, I and mixtures thereof, and ED is an aliphatic or aromatic hydrocarbon group an organic electron-donating compound selected from the group consisting of alkyl esters of acids, aliphatic ethers, cyclic ethers, and aliphatic ketones, m is 0.5 to 56, n is 0.1 or 2, and p is 2 to 116 and q is from 2 to 85], the precursor composition is diluted with an inert carrier material and the formula Al(R' ) _d X′ _e H _f [where X′ is Cl or OR″, R′ and
R'' is a saturated hydrocarbon group having 1 to 14 carbon atoms, e is 0 to 1.5, f is 0 or 1, and d+e+f=3]. the activation compound in a total aluminum to titanium molar ratio in the reaction zone of 10:1 to 10:1.
It is particularly desirable that the ethylene copolymer be produced by a continuous production method characterized in that it is used in an amount of 400:1;
It is explained in detail in No. 230011. The ethylene-vinyl acetate copolymer used in the present invention preferably has an Ml in the range of 0.3 to 3.0 g/10 min. If Ml is less than 0.3, there is a drawback that during film molding, too much load is placed on the extruder and productivity cannot be improved. On the other hand, if Ml is greater than 3.0, problems may arise in the tensile strength of the film, resistance to tearing due to sharp corners, etc., which is undesirable. Further, the content of vinyl acetate is 5 to 25% by weight, preferably 10 to 20% by weight. If it is less than 5% by weight, the clinging properties will not be exhibited, and the extensibility, flexibility, and transparency will be insufficient, which is not desirable. If it exceeds 25% by weight, heat resistance, tensile strength, resistance to tearing due to sharp corners, etc. will be insufficient, which is not desirable. The relationship between the melting point (MP) and the vinyl acetate content (VA) of the ethylene-vinyl acetate copolymer used in the present invention is as follows: MP = 114-1.44VA (MP is in °C, VA is in wt%). Particularly preferred are those having a molecular weight distribution (w/n) of less than 4 (where w is the weight average molecular weight and n is the number average molecular weight, measured by gel permeation chromatography (GPC)). It is. The reason for this is that when compared at the same VA%, the melting point is 2-5°C higher than that of general ethylene-vinyl acetate copolymers, so heat resistance is improved. Further, when w/n is less than 4, a particularly tough film can be obtained, and there is little odor. It is desirable to add an antifogging agent to the ethylene-vinyl acetate copolymer of the present invention, such as glycerin fatty acid ester, sorbitan fatty acid ester,
Particularly preferred are polyglycerol fatty acid ester, propylene glycol fatty acid ester, and ethylene oxide adducts, or mixtures thereof, but other antifogging agents can also be used. The present invention has a density of 0.910
By using a linear ethylene-α-olefin copolymer of less than g/ml as the intermediate layer, it has heat resistance up to about 130℃, and has transparency, flexibility, low temperature resistance, and puncture resistance. By imparting properties such as strength, impact resistance, and cutability with a saw blade to the wrap film, and by using an ethylene-vinyl acetate copolymer as the outer layer, the wrap film has excellent clingability to the object to be wrapped, self-adhesiveness of the wrap film itself, and thermal melting properties. A wrapped film with excellent properties is provided by imparting adhesion, extensibility, etc. to the wrapped film, thereby compensating for the drawbacks of the wrapped film formed by each individually. Plastics conventionally used as materials for wrap films other than the linear ethylene-α-olefin copolymer with a density of 0.91 g/ml or less of the present invention, such as polyvinylidene chloride, polyvinyl chloride, high-pressure polyethylene, and polypropylene. , polybutadiene, linear ethylene-α-olefin copolymer with a density of 0.91 g/ml or more (so-called L-
LDPE) or the like as the intermediate layer, the effects of the present invention cannot be obtained. That is, polyvinylidene chloride, polyvinyl chloride, etc. contain chlorine, which causes problems when incinerated, high-pressure polyethylene, polypropylene, and L-LDPE have problems with transparency, flexibility, low-temperature properties, etc., and polybutadiene is expensive. It is very high, and its tear strength, heat resistance, oil resistance, etc. are also insufficient. Ethylene-α with an intermediate layer density of 0.91g/ml or less
- When the wrap film is composed of only an olefin copolymer, it has better transparency, clinging properties, self-adhesiveness, extensibility, antifogging properties, and antistatic properties than when the outer layer is supplemented with an ethylene-vinyl acetate copolymer. It is inferior to ethylene-vinyl acetate copolymer, and the cost is higher than that of ethylene-vinyl acetate copolymer. Therefore, rather than using it alone, it is preferable to use it in combination with ethylene-vinyl acetate copolymer, which is cheaper, because the overall cost of the wrap film can be lowered. The wrapped film of the present invention is molded using a coextrusion molding machine using a resin composition to form an intermediate layer and an outer layer. For example, they are laminated and molded by a known method such as an inflation method using a circular die or a T-die method using a flat die. The thickness of the wrapped film of the present invention is 10 to 50 microns, preferably 12 to 20 microns. If it is thinner than 10μ, it will be inconvenient to handle and the strength will be insufficient, which is not desirable. If it is 50μ or more, there will be no performance problem as a wrapped film, but it will be disadvantageous in terms of cost, so it is not desirable. The thickness of the intermediate layer made of an ethylene-α-olefin copolymer having a density of 0.91 g/ml or less is 3 to 30 μm, preferably 5 to 15 μm. If it is thinner than 3μ, the wrap film will have insufficient heat resistance, mechanical strength, etc., which is not desirable. Also,
If it is thicker than 30μ, it is not desirable because it has poor transparency and is disadvantageous in terms of cost. The thickness of each ethylene-vinyl acetate copolymer layered on both surfaces of the intermediate layer is 2 to 20 microns, preferably 5 to 15 microns.
If it is thinner than 2μ, self-adhesion, clinging properties, and transparency cannot be imparted to the wrap film.
Undesirable. Moreover, if it is thicker than 20μ, the heat resistance and mechanical strength of the wrap film will be impaired, which is not desirable. [Examples] Example 1 A wrap film was manufactured by the inflation method using the following raw materials for the intermediate layer and both outer layers. Raw Materials Intermediate layer: An ethylene-butene-1 copolymer (DEFD-1210 manufactured by Nippon Unicar) made by a gas phase low pressure method with a density of 0.890 g/ml and Ml = 1.0 was used. Both outer layers: An ethylene-vinyl acetate copolymer (DQDJ-1868 manufactured by Nippon Unicar) made by a high-pressure method with a density of 0.94 g/ml and Ml = 2.5 was used. An antifogging agent and sorbitan monooleate (manufactured by Nikko Chemicals) were added at a concentration of 2% by weight. Inflation film production method An inflation film was produced by air cooling using the following equipment and processing conditions. (1) Extrusion equipment: Inflation film processing equipment manufactured by Plako Co., Ltd. Diameter 40mm x 3 units L/D28 (2) Annular three-layer die: φ150mm Die gap: 1.0mm (3) Cooling equipment: Single lip straight and conical With collar (4) Discharge rate: 45Kg/hr (5) Die temperature: 180℃ (6) Blow ratio: 4.5 Manufactured wrap film Outer layer (1) Thickness 5μ Intermediate layer Thickness 5μ Outer layer (2) Thickness 5μ Wrap film evaluation Γ Film tear strength: longitudinal tear strength is 35
Kg/cm, and the tear strength in the transverse direction is 110 Kg/cm, which is sufficient for practical use. Γ Haze: Measured according to JIS K-6714, the value is 2.5, which is sufficient for practical use. ΓCutability When the film was continuously tightened in the horizontal direction with a saw blade, it was cut cleanly. Γ Heat resistance: Curry rice at 120°C was placed in a polypropylene tray and wrapped, but the film did not tear due to heat. Γ Self-adhesiveness: Although the films were pressed together and left to stand, they remained in that state and did not peel off. Γ Puncture resistance: Crab legs were bundled together, placed in a tray, and wrapped in wrap film, but the film was not torn by the crab legs. ΓLow temperature embrittlement: Put the parsley in a tray, wrap it with wrap film, and put it in the refrigerator at -50℃ for 30 minutes.
After a minute, I took it out and dropped it from a height of 1m, but it did not break. Γ Stretchability: Apples with a diameter of 10 cm were placed in a tray and wrapped so that the wrap film was stretched by about 20% from the original shape, but the product was finished neatly without wrinkles or shrinkage. Examples 2 to 6 and Comparative Examples 1 to 6 The same experiments as in Example 1 were conducted by changing the raw materials and layer thicknesses of the intermediate layer and both outer layers of Example 1 as shown in the table, and the output We evaluated the rough film.

【table】

【table】

[Table] [Operations and Effects of the Present Invention] In the present invention, a specific ethylene-α-olefin copolymer is used as the intermediate layer, and both outer layers are made of ethylene-vinyl acetate copolymer. Each layer is combined to make the most of the material, making it an ideal product with unprecedented tear strength, haze, cuttability, heat resistance, self-adhesiveness, puncture resistance, low-temperature embrittlement, and extensibility. A lap film was obtained.

Claims (1)

[Claims] 1. Linear ethylene with a density of 0.910 g/ml or less
A wrap film formed by laminating an intermediate layer made of an α-olefin copolymer and an outer layer made of an ethylene-vinyl acetate copolymer. 2. The wrap film according to claim 1, wherein the linear ethylene-α-olefin copolymer is produced by a gas-phase, low-pressure method using an α-olefin having a carbon number in the range of 3 to 12. 3 A linear ethylene-α-olefin copolymer is combined with a transition metal compound of Groups 1 to 3 of the periodic table.
2. The wrap film according to claim 1, which is produced by a gas-phase, low-pressure method using a catalyst produced in combination with an organometallic compound of the above group, a so-called Ziegler catalyst. 4 A linear ethylene-α-olefin copolymer is heated in a fluidized bed reaction zone at a temperature of 10 to 80°C and
At pressures below 7000KPa, (a) 0.35:1 to 8.0:1
(b) at least 25 mole percent of at least one diluent gas; The gas mixture has the formula Mg _n Ti (OR) _o X _p [ED] _q [where R is an aliphatic or aromatic hydrocarbon group having 1 to 14 carbon atoms or COR'
where R' is an aliphatic or aromatic hydrocarbon group having 1 to 14 carbon atoms, X is selected from the group consisting of Cl, Br, I and mixtures thereof, and FD is an aliphatic or aromatic hydrocarbon group an organic electron-donating compound selected from the group consisting of alkyl esters of acids, aliphatic ethers, cyclic ethers, and aliphatic ketones, m is 0.5 to 56, n is 0.1 or 2, and p is 2 to 116 and q is from 2 to 85], the precursor composition is diluted with an inert carrier material and the formula Al(R' _{) d _} f is 0 or 1, and d+e+f=3], and the activation compound is added to a total aluminum to titanium molar ratio of 10:1 to 1 in the reaction zone.
2. The wrapped film according to claim 1, which is produced by a continuous method for producing an ethylene copolymer, characterized in that the ethylene copolymer is used in an amount of 400:1. 5 The ethylene-vinyl acetate resin in the outer layer has a melt index of 0.3 to 3 g/10 min and a vinyl acetate content of 5 to 20% by weight, and the relationship between melting point (MP) and vinyl acetate content (VA) is MP = 114- 1.44 VA (MP is in °C, VA is in wt%), and the molecular weight distribution (w/n) is less than 4 (where w is the weight average molecular weight and n is the number average molecular weight). 1. The wrap film described in 1. 6 The inner layer is linear ethylene-α- as shown in claim 4.
Claim 1, wherein the outer layer is an olefin copolymer, and the outer layer is an ethylene-vinyl acetate copolymer as shown in Claim 5.
Lap film as described.