JPH02206548A - Wrap film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a wrap film.

For more details, see simple packaging for various foods such as vegetables, fruits, fish and shellfish, and livestock meat, as well as prepared foods for households, supermarkets, food processing companies, department stores, grocery stores, frozen/refrigerated companies, and restaurants such as sushi restaurants and soba restaurants. This invention relates to a polyolefin wrap film used as a material.

[Prior Art] Conventional wrap films made of materials such as polyvinylidene chloride, polyvinyl chloride, high-pressure polyethylene, ethylene-vinyl acetate copolymer, polypropylene, linear low-density polyethylene, and polybutadiene have been proposed. Polyvinylidene chloride, polyvinyl chloride, high-pressure polyethylene, polybutadiene, etc. have been put into practical use.

Wrap films are used to easily package, protect, store, distribute, and display fresh foods, so they are 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 appropriate 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.

The wrap film product has a width of 20 cm to 45 cm, a thickness of 7 to 20 μm, and a length of 2 C) to 50 m wrapped around a paper tube shaft, which is then wrapped around a tin plate with a thickness of about 0.2 mm. It comes in a cardboard storage box with a saw-shaped blade made of , so when you use it, pull out the cling film from the storage box, use the saw-shaped blade,
Cut and use. Therefore, the wrap film must be easily cut with a relatively weak force...Also, in the case of commercial wrap films, when making cuts with a knife, it is necessary to cut the wrap film cleanly and quickly in the horizontal direction. If it is not cut, workability will be poor, but it may change direction in the vertical direction and tear during cutting, which is undesirable.

Since the content is often food, the material must not contain ingredients that pose a food hygiene problem, and must be moisture-proof, water-proof, moisture-proof, air-proof, acid-proof, oil-proof, moderate strength, Stretchability and shrinkability are required.

Furthermore, since it is displayed as a product, transparency, drip-proofing, anti-fogging properties, glossiness, etc. are required so that the contents can be clearly seen.

In storage, in order to maintain freshness for a long period of time, ultra-low temperature refrigerators of -50 degrees Celsius have recently come into use, so the low-temperature embrittlement resistance of cling 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 the 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, and the like.

However, when cutting polyvinylidene chloride with a saw blade, the bag tends to run in arbitrary directions regardless of the user's opinion, and may be cut diagonally, and when used in a microwave oven, it may be cut diagonally There is a problem that the film shrinks and breaks very much, and in high temperature conditions, there is a risk of generating hydrochloric acid gas, chlorine gas, and vinylidene chloride, which is undesirable from a food hygiene perspective, and there is also concern 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 cuttability with a saw blade is also very poor.

Ethylene-vinyl acetate copolymer systems have improved adhesiveness, but have problems with mechanical strength, stiffness, etc. Although polypropylene has excellent heat resistance, it has 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 low-density polyethylene, but when it is formed using the normal blown film processing method, the balance between vertical and horizontal orientation is poor. It is difficult to cut with a saw blade because it is not smooth and the vertical orientation is large.
Cannot be used 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 problems in that it has low mechanical strength such as tear strength and is extremely expensive.

[Problems to be Solved by the Invention] Conventional wrap films have various problems as described above.

The present invention has no food hygiene problems and is excellent in mechanical strength, transparency, adhesiveness, food protection, cuttability with a saw blade, puncture resistance, impact resistance, heat resistance, heat sealability, etc. The purpose is to provide wrap films.

[Means for Solving the Problems] The present inventors focused on a recently developed linear low-density ethylene-olefin copolymer with a density of 0.910 g/ml or less, and took advantage of its excellent properties. The present invention was completed by compensating for this drawback 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/mβ 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 having a density of 0.910 g/ml or less refers to
occupies 0% to 75%, α-olefin accounts for 80% to 25%
preferably 40% to 60%,
α-olefin accounts for 60% to 40%,
α-olefin refers to one having 3 to 12 carbon atoms, where the α-olefin may be linear or branched, such as propylene, 1-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-1
etc. 0 The density used in the present invention is 0.910g
/mβ or less linear ethylene-α-olefin copolymer is heated in a fluidized bed reaction zone at a temperature of 10 to 80°C and 7.0°C.
(a) 0.35: l at a pressure of 00 Pa or less
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; and (b) at least 25 mol % of at least one higher α-olefin. a gas mixture containing a diluent gas with the formula % [[wherein R is an aliphatic or aromatic hydrocarbon group having 1 to 14 carbon atoms or COR', where R
o is an aliphatic or aromatic hydrocarbon group having 1 to 14 carbon atoms, X is selected from the group consisting of CLBr, I and mixtures thereof, ED is an alkyl ester of an aliphatic or aromatic acid , aliphatic ether, cyclic ether, and aliphatic ketone, m is 0.5-56, n is 0.1 or 2, and p is 2-56. 116 and q is 2 to 85], said precursor composition is diluted with an inert carrier material and the formula % is [Here 6, X'' is C1 or OR'', and R'' and R
'' is a saturated hydrocarbon group having 1 to 14 carbon atoms, e is Om1.5, f is 0 or 1, and d+e+f=3] fully activated with an organoaluminum compound having let me,
A process for the continuous production of ethylene copolymers, characterized in that the activation compound is used in an amount such that the molar ratio of total aluminum to titanium in the reaction zone is from 10:1 to 400:1. It is particularly desirable that the material be of the same type, and is described in detail in Japanese Patent Application Laid-Open No. 59-230011.

The ethylene-vinyl acetate copolymer used in the present invention is M
It is desirable that l is in the range of 0.3 to 3.0 g/l Omin. If Ml is less than 0.3, there is a drawback that during film forming, an excessive 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 property will not be expressed, and the extensibility, flexibility, and transparency will be insufficient, which is undesirable. If it exceeds 25% by weight, it will have poor heat resistance, tensile strength, tear resistance due to sharp corners, etc. The ethylene-vinyl acetate copolymer used in the present invention has a melting point (MP) and a vinyl acetate content (V
The relationship with A) is expressed as MP = 114-1.44VA (MP unit is °C, VA unit is wt%),
Particularly preferred are those having a molecular weight distribution (Uw/in) of less than 4 (where Hw is the weight average molecular weight and in is the number average molecular weight, measured by gel permeation chromatography (GPC)). The reason for this is that when compared at the same VA%, the melting point is 2-5° C. higher than that of a general ethylene-vinyl acetate copolymer, so the heat resistance is improved.

In addition, when 'FJr w / 'FX n is less than 4, a particularly tough film can be obtained and there is little odor.An antifogging agent is added to the ethylene-vinyl acetate copolymer of the present invention. It is desirable to use glycerin fatty acid ester, nrubitan fatty acid ester, polyglycerin fatty acid ester, propylene glycol fatty acid ester, ethylene oxide adduct alone or in a mixture thereof, but other antifogging agents can also be used.
Linear ethylene-α with a density of 0.910 g/m42 or less
-By using an olefin copolymer as an intermediate layer, 13
It has heat resistance that can withstand temperatures down to around 0°C, and the properties of the wrap film include transparency, flexibility, low temperature resistance, puncture resistance, impact resistance, and cutability with a saw blade.
By using the ethylene-vinyl acetate copolymer as the outer layer, the wrap film has properties such as clinging properties to the object to be wrapped, self-adhesive properties between the wrap films, heat fusion properties, extensibility, etc. A wrap film with excellent properties is provided, which compensates for the drawbacks of the above configurations.

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 , polypropylene, polybutadiene, density 0.91g
/ml or more of a linear ethylene-α-olefin copolymer (so-called L-LDPE), etc. is used as an intermediate layer,
Effects like those 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 o, 9tg/mβ or less
When a wrap film is composed only of an olefin copolymer, it has better transparency, clinging properties, self-adhesiveness, extensibility, antifogging properties, antistatic properties, etc. than when the outer layer is supplemented with an ethylene-vinyl acetate copolymer. is inferior to ethylene, and the cost is lower than that of ethylene.
Since it is more expensive than vinyl acetate copolymer, it is preferable to use it in combination with ethylene-vinyl acetate copolymer, which is cheaper, than to use it alone because the cost of the entire wrap film can be lowered.

The wrap 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 wrap film of the present invention is 10 to 50μ, preferably 12 to 2C1. If it is thinner than 10μ,
This is not desirable because it is inconvenient to handle and has insufficient strength.

A thickness of 50 μm or more does not cause any performance problems as a wrap film, but is undesirable because it is disadvantageous in terms of cost.

The thickness of the intermediate layer made of an ethylene-〇-olefin copolymer having a density of 0.91 g/m or less is 3 to 30 μm, preferably 5 to 15 μm.

If it is thinner than 3μ, the heat resistance, mechanical strength, etc. of the wrap film will be insufficient, which is not desirable. Moreover, if it is thicker than 30 μm, it is not desirable because it is inferior in transparency and disadvantageous in terms of cost. ~15μ. If it is thinner than 2μ, self-adhesiveness, clinging properties, and transparency cannot be imparted to the wrap film, which is 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.

[Example] A wrap film was produced by the inflation method using the following raw materials for the intermediate layer and both outer layers.

■ Middle layer: Density is 0.890 g/mf2, M1=1.0
An ethylene-butene-1 copolymer (DEFD-1210 manufactured by Nippon Unicar) prepared by a gas phase low pressure method was used.

Both outer layers: An ethylene-vinyl acetate copolymer (DQDJ-1868 manufactured by Nippon Unicar) prepared by a high-pressure method with a density of 0.94 g/ml and M1 = 2.5 was used.

Antifogging agents and sorbitan monooleate (manufactured by Nikko Chemicals) at 2% by weight. It was added to the filter.

Inflation film ゛1 A blown film was manufactured in an air cooling section using the following equipment and processing conditions.

(1) Extrusion equipment: Braco blown film processing equipment diameter 40mm x 3 units (2) Annular cobblestone die: 0150mm gap + 1.0mm (3) Cooling device with single lip straight and conical collar (4) Discharge volume : 45 kg/hr (5) Die temperature: 180°C (6) Blow ratio: 4.5 Film bow 1 tear strength: longitudinal tear strength is 35 kg/cm
The tear strength in the transverse direction is 110 kg/cm, which is sufficient for practical use.

- Haze: Measured according to JIS K-6714, and the value is 2.5, which is sufficient for practical use.

・Cutability: When the film was continuously cut in the horizontal direction with a saw blade, it was cut cleanly.

・Heat resistance: Curry rice at 120°C was placed in a polypropylene tray and wrapped, but the film did not tear due to heat.

・Self-adhesiveness: Although the films were pressed together and left to stand, they remained intact and did not peel off.

- Puncture resistance Two crab legs were tied together, placed in a tray, and wrapped in cling film, but the crab legs did not tear the film.

- Low-temperature embrittlement: Parsley was placed in a tray, wrapped in cling film, placed in a refrigerator at -50°C, taken out after 30 minutes, and dropped from a height of 1 m, but did not break.

- Stretchability: An apple with a diameter of 10 cm was 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.

2-6 and 1-6 Experiments similar to those in Example 1 were conducted by changing the raw materials and layer thicknesses of the intermediate layer and both outer layers as shown in Table 1, and the resultant film was We conducted an evaluation.

*1 Density: 0.890 g/m Q, Ml: 1.0 manufactured by Nippon Unicar *2 Density: 0.906 g/mf2, Ml: 0.8 manufactured by Nippon Unicar *3 Density: 0.921 g/nu, Ml:1. O manufactured by Nippon Unicar 0.923 g/nu, Ml: 2.4 manufactured by Nippon Unicar 0.9.4 g/nu, M1: 2.5 manufactured by Nippon Unicar Vinyl acetate content 18 wt% *6 Density: 0. 93 g/mI2, Ml: 1.3 Made by Nippon Unicar Vinyl acetate content 10 wt% *7 Density: 0.94 g7mf2, Ml: 1.5 Made by Nippon Unicar Vinyl acetate content 15 wt% Melting point 93°C, molecular weight distribution 3. 0 *8 Density: 0.931 g/mI2, Ml: 2.3
Manufactured by Nippon Yugocar *4 Density *5 Density: Vinyl acetate content 7.5 wt% Melting point 96°C, molecular weight distribution 3.5 *9 Density: 0.923 g/ml, Ml: 2.4 Manufactured by Nippon Yugocar *1O Outer layer (1) *11 Intermediate layer *12 Outer 1N (2) *130 = longitudinal tear strength of 30 kg/cm or more,
The tear strength in the transverse direction is 120 kg/cm or less, making it practical.

× = Tear strength below the above and not practical.

*14 Q = Measured according to JIS K-6714, the value is 5 or less, and it is practical.

× = Value is 6 or more and is not practical.

*150 = The film can be cut cleanly when continuously cut in the horizontal direction with a saw blade.

× = Continuously use a saw blade in the lateral direction of the film * l 6 *17 *18 *19 When cutting, at the beginning of cutting It is difficult to cut, and the cut may be diagonal during cutting. It can be cut into pieces.

○ = Curry rice was placed in a polypropylene tray at 120°C and wrapped, but the film did not tear due to heat.

X = In the above, the film was torn by heat.

O = film comrades were crimped and left alone However, it remains intact and peels off. It never happened.

X=The film peeled off in the above.

○ = The crab legs were tied together, placed in a tray, and wrapped in cling film, but the film did not tear due to the crab legs.

X=Torn above.

○=Put the parsley in a tray, wrap it with cling film,
It was placed in a refrigerator at -50°C, taken out after 30 minutes, and dropped from a height of 1 m, but did not break.

×=The film was torn in the above.

*200 = An apple with a loam diameter was 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.

×=Wrinkles and shrinkage occurred in the above.

*21 △=Indicates that although the characteristics are inferior to O in each case, it is practical.

*22 0=Indicates that each characteristic is significantly superior to ○.

[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. Because each layer is combined, an ideal wrap film with unprecedented tear strength, haze, cuttability, heat resistance, self-adhesiveness, puncture resistance, low-temperature embrittlement resistance, and extensibility is created. Obtained.

Claims (6)

[Claims] (1) A wrap film comprising 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. (2) The wrap 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. film. (3) Using a catalyst in which a linear ethylene-α-olefin copolymer is produced by a combination of a transition metal compound from Groups IV to VIII of the Periodic Table and an organometallic compound from Groups I to III of the Periodic Table, the so-called Ziegler catalyst. The wrap film according to claim 1, which is produced by a gas phase/low pressure method. (4) The linear ethylene-α-olefin copolymer is heated to 7,000 KP at a temperature of 10 to 80°C in a fluidized bed reaction zone.
(a) ethylene and at least one higher α-olefin having from 3 to 12 carbon atoms in a molar ratio of higher α-olefins to ethylene of from 0.35:1 to 8.0:1;
- a gas mixture containing an olefin and (b) at least 25 mol % of at least one diluent gas with the formula Mg_mTi(OR)_nX_p[ED]_q [wherein
R is an aliphatic or aromatic hydrocarbon group having 1 to 14 carbon atoms or COR', where R' is 1 to
an aliphatic or aromatic hydrocarbon group having 14 carbon atoms, X is selected from the group consisting of Cl, Br, I and mixtures thereof; an organic electron-donating compound selected from the group consisting of ethers, cyclic ethers, and aliphatic ketones, m is 0.5 to 56, n is 0.1 or 2, and p is 2 to 116; , q is from 2 to 85], wherein said precursor composition is diluted with an inert carrier material and has the formula Al(R')_dX' _eH_f [where X' is Cl or OR'', R' and R'' are saturated hydrocarbon groups having 1 to 14 carbon atoms, e is 0 to 1.5, and f is 0 or 1, and d+e+f=3] completely activated with an organoaluminum compound having
A process for the continuous production of ethylene copolymers, characterized in that the activation compound is used in an amount such that the molar ratio of total aluminum to titanium in the reaction zone is from 10:1 to 400:1. The wrap film according to claim 1, which is a wrap film. (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.
~20% by weight, and the relationship between melting point (MP) and vinyl acetate content (VA) is expressed as MP = 114-1.44VA (MP unit is °C, VA unit is wt%), and the molecular weight is The wrap film according to claim 1, wherein the distribution (@M@w/@M@n) is less than 4 (where @M@w is the weight average molecular weight and @M@n is the number average molecular weight). (6) The wrap film according to claim 1, wherein the inner layer is the linear ethylene-α-olefin copolymer shown in claim 4, and the outer layer is the ethylene-vinyl acetate copolymer shown in claim 5.