JPH06256539A - Film for stretch packing - Google Patents

Abstract

PURPOSE:To obtain a film used for stretch packaging excellent in self- adhesiveness and deformation recovery factor together with transparency, flexibility and extensibility. CONSTITUTION:This film for stretch packaging consists of a polypropylene based resin having 80000-500000 weight average molecular weight and 20-80wt.% resin eluted amount measured at 10 deg.C by the cross-fractionation, 5-45wt.% at 10 deg.C-65 deg.C, 1-18wt.% at 65 deg.C-90 deg.C and 10-35wt.% at 90 deg.C-125 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stretch packaging film which is transparent and has uniform elongation.

[0002]

2. Description of the Related Art Stretch wrapping films are used for wrapping various things, and are preferably used for wrapping foods such as fruits and vegetables and fresh foods (fish, meat, prepared foods). When packaging food etc. using this stretch wrapping film, usually, the article to be packaged is placed in a plastic container made of Styrofoam, etc., the stretch wrapping film is put on the container to pull the film end, and the film itself is Try to wrap the container while stretching. Therefore, the stretch packaging film is required to have excellent self-adhesiveness and deformation recovery rate in addition to transparency, flexibility and extensibility.

Conventionally, as a stretch film used for the above-mentioned packaging and the like, one having a plasticized polyvinyl chloride (hereinafter referred to as plasticized PVC) as a main component has been widely used from the viewpoint of cost and ease of use. . However, considering that it is used for packaging foods, and in the case of packaging fresh foods, it comes into direct contact with foods, etc., it is not desirable to use a stretch packaging film containing plasticized PVC as a main component. . In particular, in recent years, the problem of environmental pollution has been emphasized, and the use of plasticized PVC containing chlorine is
It is regarded as a problem in all fields.

Therefore, recently, as a substitute material for the plasticized PVC, a stretch packaging film using a polyolefin resin has been actively developed. Examples of such stretch film include those made of polyethylene, ethylene-vinyl acetate copolymer, and polybutadiene.

[0005]

However, the stretch film using the above-mentioned polyolefin resin cannot obtain the properties necessary for a stretch packaging film, such as self-adhesiveness and deformation recovery during packaging. For this reason, the packaged film may be easily removed from the container or the film may be wrinkled, which is not suitable for actual use.

In order to solve this problem, Japanese Patent Laid-Open No. 61-
Japanese Patent Laid-Open No. 62-5144 proposes a laminated stretch packaging film in which a random copolymer of various α-olefins and propylene is used as a central layer.
Japanese Patent Laid-Open Publication No. 0 (1994) proposes a laminated stretch packaging film having a central layer of a block copolymer of an aromatic hydrocarbon polymer such as styrene and a conjugated diene elastomer. However, none of the above copolymers can be used as a stretch packaging film in a single layer, and it is necessary to laminate another resin. Further, there is a problem that the cost becomes high when the above elastomer is used. Therefore, at present, as a substitute for a stretch film containing plasticized PVC as a main component, a stretch packaging film that sufficiently satisfies the market demand has not been realized.

The present invention has been made to solve the above problems, and its purpose is to use no plasticized PVC,
It is an object of the present invention to provide a single-layer or multi-layer stretch packaging film having excellent self-adhesiveness and deformation recovery rate, and having transparency, flexibility and extensibility.

[0008]

The present inventors have found that plasticized P
Excellent self-adhesiveness and deformation recovery rate without using VC,
And as a result of earnest research to obtain a film for stretch packaging having both transparency, flexibility and extensibility,
The present invention has been completed by finding a resin that meets the purpose of the present invention.

The stretch packaging film of the first invention is
The weight average molecular weight is 80,000 or more and 500,000 or less, and the resin elution amount measured by the cross fractionation method is 20% by weight at 10 ° C.
80 wt% or less and 5 wt% at 10 ° C to 65 ° C
45% by weight or less and 1% by weight at 65 ° C to 90 ° C
The above-mentioned object is achieved by the polypropylene resin which is 18% by weight or less and 10% by weight or more and 35% by weight or less at 90 ° C to 125 ° C.

The stretch packaging film of the second invention is
On both sides of the central layer made of polypropylene resin, propylene-ethylene random copolymer resin, propylene-α
A weight average molecular weight of the polypropylene resin, which is a stretch film in which surface layers each comprising at least one selected from the group consisting of an olefin copolymer resin and an ethylene-vinyl acetate copolymer resin are laminated. Is 80,000 or more and 500,000 or less, and the resin elution amount of the polypropylene resin measured by the cross fractionation method is 1
20% by weight to 80% by weight at 0 ° C, 10 ° C to
5% by weight or more and 45% by weight or less at 65 ° C.
1% by weight or more and 18% by weight or less at 90 ° C,
It is 10% by weight or more and 35 ° C or less by weight at 125 ° C., whereby the above object is achieved.

In the first and second inventions, the resin elution amount by the cross fractionation method was measured as follows. First, the resin is dissolved in o-dichlorobenzene at 140 ° C. or a temperature at which the resin is completely dissolved. next,
The solution is cooled at a constant temperature to form a thin polymer layer on the surface of an inert simple substance prepared in advance. At this time,
The resin components are formed as a polymer layer in the order of high crystallinity and in the order of large molecular weight. Thereafter, the temperature is raised continuously or stepwise, the concentration of the resin component which is eluted in sequence is detected, and the composition distribution (crystallinity distribution) is measured (temperature rising elution fractionation). At the same time, high temperature GPC (gas phase
Chromatograph) measures the molecular weight and molecular weight distribution of the eluted components. Temperature rising elution fractionation (TREF
= Temperature Rising Elution Fractionation part and the high temperature GPC (for example, SEC = Size Exclusion)
Chromatograph part was used as a system to measure the resin elution amount using a cross fractionation chromatograph device (CFC-T150A type: manufactured by Mitsubishi Petrochemical Co., Ltd.).

The stretch packaging film of the first invention is
Made of polypropylene resin. When other olefin resins are used, sufficient properties cannot be obtained in terms of heat resistance and strength.

The polypropylene resin has a weight average molecular weight of 80,000 or more and 500,000 or less. It is preferably 80,000 or more and 450,000 or less, and more preferably 100,000 or more and 400,000 or less. When the weight average molecular weight is less than 80,000, the extensibility and strength of the resulting stretch packaging film are not sufficient, and when it exceeds 500,000, the flexibility of the obtained stretch packaging film is insufficient. .

The polypropylene resin has a resin elution amount of 20% by weight or more and 80% by weight or less at 10 ° C., preferably 25% by weight or more and 75% by weight, based on the total polypropylene resin, measured by a cross fractionation method. % Or less. When the resin elution amount is less than 20% by weight, the resulting stretch packaging film has no flexibility and is 80% by weight.
If it exceeds, the strength of the resulting stretch wrapping film is insufficient.

The polypropylene resin has a resin elution amount measured by a cross fractionation method of 5% by weight or more and 45% by weight or more at 10 ° C. to 65 ° C. with respect to the total polypropylene resin.
It is below, preferably 6% by weight or more and 40% by weight or less. If the resin elution amount is less than 5% by weight, the resulting stretch packaging film has no flexibility and is 45% by weight.
If it exceeds, deformation recovery of the resulting stretch wrapping film is insufficient.

The polypropylene-based resin has a resin elution amount of 1% by weight or more and 18% by weight at 65 ° C. to 90 ° C. with respect to the total polypropylene-based resin measured by the cross fractionation method.
It is below, preferably 1% by weight or more and 16% by weight or less. If the resin elution amount is less than 1%, the deformation recovery of the resulting stretch packaging film is insufficient, and 1
If it exceeds 8%, the strength of the resulting stretch packaging film is insufficient.

The polypropylene resin has an amount of resin elution measured by a cross fractionation method of 10% by weight or more and 35% by weight or less, preferably 12% by weight or more, at 90 ° C. to 125 ° C. 32% by weight
It is the following. If the resin elution amount is less than 10% by weight,
The strength of the obtained stretch wrapping film is insufficient, and when it exceeds 35% by weight, the flexibility of the stretch wrapping film obtained is insufficient.

The polypropylene resin can be manufactured, for example, as follows.

First, in the first stage polymerization, a titanium-containing polyolefin is produced in the presence of a titanium compound and an aluminum compound. The titanium-containing polyolefin obtained here is a propylene homopolymer, propylene-
It is an ethylene copolymer or a propylene-α-olefin copolymer. As the α-olefin, 1-
Butene is preferably used.

Next, in the second and subsequent polymerizations, propylene and ethylene are copolymerized with the titanium-containing polyolefin, or propylene and α-olefin are copolymerized with the titanium-containing polyolefin in the presence of the titanium compound and the aluminum compound. Polymerize. As a result, a propylene-ethylene copolymer or a propylene-α-olefin copolymer is obtained. These copolymers can be used as the polypropylene resin.

As the above manufacturing method, several methods have been conventionally proposed. For example, JP-A-4-22480
In Japanese Patent Laid-Open No. 9-90, titanium trichloride and magnesium chloride are co-ground as the titanium compound, and n-orthotitanate is used.
Spherical and average particle size of 15 μm obtained by treatment with butyl, 2-ethyl-1-hexanol, ethyl p-toluate, silicon tetrachloride, diisobutyl phthalate and the like.
Polymerization is carried out using the solid Ti catalyst described in 1. above and alkyl aluminum such as triethyl aluminum as the aluminum compound. At this time, a silicon compound, especially diphenyldimethoxysilane, was added as an electron donor, and ethyl iodide was added as an iodine compound to improve the properties of the obtained polymer. The most important feature of this production method is that the polymerization does not end in one step but is composed of two or more steps. By making the polymerization in multiple stages, it becomes possible to continuously prepare a plurality of kinds of polymers at the time of polymerization, and it is possible to perform blending at the molecular level. Therefore, it is possible to obtain a copolymer of a blend type which is completely different from a usual polymer blend. Further, by utilizing such multi-step polymerization, it becomes possible to prepare a blend compound which is impossible in terms of resin viscosity by blending with a usual extruder or the like.

As the above-mentioned manufacturing method, for example, JP-A-4-96912, 4-96907 and 3
-174410, 2-170803, 2-
170802, JP-A 61-42553, and JP-A-3-205439 disclose the same.

Further, in Japanese Patent Laid-Open No. 3-97747,
As the titanium compound, an adduct of magnesium chloride and alcohol treated with titanium tetrachloride and an electron donor is used.

The polyolefin resin used for the stretch packaging film of the first invention can be obtained by any of the above-mentioned methods. Examples of the resin obtained by the above production method include "PER" which is being studied by Tokuyama Soda Co., Ltd. and "Cataloy" which is commercially available from Highmont Co., Ltd.

The thickness of the stretch packaging film of the first invention is preferably 6 μm or more and 50 μm or less, more preferably 8 μm or more and 40 μm or less. When the thickness is out of the above range, the deformation recovery rate of the obtained stretch wrapping film may be insufficient.

The stretch packaging film of the second invention is
On both sides of the central layer made of polypropylene resin, propylene-ethylene random copolymer resin, propylene-α
A surface layer made of at least one of an olefin copolymer resin and an ethylene-vinyl acetate copolymer resin is laminated.

The first polypropylene resin is
The stretch wrapping film of the invention may be used.

As the propylene-ethylene random copolymer resin, propylene-α-olefin copolymer resin and ethylene-vinyl acetate copolymer resin, those conventionally used for stretch packaging films can be used. it can.

In the propylene-ethylene random copolymer resin, the ethylene content is 0.5% by weight or more and 1
It is preferably 0% by weight or less. When the ethylene content is out of the above range, the stretch packaging film obtained may have insufficient extensibility and flexibility.
The melt flow rate is preferably 0.1 to 5 g / 10 minutes, more preferably 0.5 to 4 g / 10.
Minutes. When the melt flow rate is less than 0.1 g / 10 minutes, the elongation of the obtained stretch packaging film may be low, and the melt flow rate is 5 g.
When it exceeds / 10 minutes, the breaking strength of the resulting stretch packaging film may be low in elongation,
In either case, the extensibility becomes insufficient.

In the propylene-α-olefin copolymer resin, the α-olefin is, for example, 1-
Butene and the like are preferably used. The α-olefin content in this copolymer is preferably 0.5% by weight or more and 35% by weight or less. If the α-olefin content is out of the above range, the stretch packaging film obtained may have insufficient stretchability and flexibility. The melt flow rate is preferably 0.1 to 5 g / 10 minutes, more preferably 0.5 to 4 g / 10 minutes.
When the melt flow rate is less than 0.1 g / 10 minutes, the elongation of the resulting stretch packaging film may be low, and when the melt flow rate exceeds 5 g / 10 minutes, the stretch packaging obtained. The breaking strength of the film for use may be low, and in any case, the extensibility is insufficient.

In the above ethylene-vinyl acetate copolymer resin, the vinyl acetate content is preferably 3% by weight or more and 30% by weight or less, more preferably 5% by weight or more and 25% by weight or less. When the vinyl acetate content is out of the above range, flexibility and self-adhesiveness of the obtained stretch film may be insufficient. The melt flow rate is preferably 0.1 to 5 g / 10 minutes, more preferably 0.5 to 4 g / 10 minutes.
When the melt flow rate is less than 0.1 g / 10 minutes, the elongation of the resulting stretch packaging film may be low, and when the melt flow rate exceeds 5 g / 10 minutes, the stretch packaging obtained. The breaking strength of the film for use may be low, and in any case, the extensibility is insufficient.

Self-adhesive to stretch packaging film,
An aliphatic alcohol or an aliphatic alcohol-based fatty acid ester may be added to the ethylene-vinyl acetate copolymer resin in order to impart antifogging properties, antistatic properties, and the like.
Examples of the aliphatic alcohol fatty acid ester, for example, monoglycerin oleate, polyglycerin oleate, glycerin triricinoleate, glycerin acetyl ricinoleate, methyl acetyl ricinoleate, ethyl acetyl ricinoleate, butyl acetyl ricinoleate,
Propylene glycol oleate, propylene glycol laurate, pentaerythritol oleate, polyethylene glycol oleate, polypropylene glycol oleate, polyoxyethylene glycerin, polyoxypropylene glycerin, polyoxypropylene glycerin, sorbitan oleate, sorbitan laurate, Examples thereof include polyethylene glycol sorbitan oleate, polyethylene glycol sorbitan laurate, and the like; and polyalkylene ether polyols such as polyethylene glycol and polypropylene glycol.

The thickness of the stretch packaging film of the second invention is preferably 6 μm or more and 50 μm or less, more preferably 8 μm or more and 40 μm or less. The thickness of the central layer made of the polypropylene resin is 2 μm or more 3
It is preferably 0 μm or less, more preferably 2 μm.
It is not less than m and not more than 20 μm. The thickness of the surface layer made of the copolymer resin is preferably 2 μm or more and 10 μm or less, and more preferably 3 μm or more and 10 μm or less. When the thickness is out of this range, the deformation recovery rate of the obtained stretch wrapping film may be insufficient.

The stretch packaging film and stretch film of the present invention can be produced by a conventionally known technique. For example, it can be produced by a single extrusion or a plurality of extruders, a single extrusion by inflation molding or T-die molding, a coextrusion or an extrusion lamination. When manufactured by inflation molding, the blow ratio is preferably about 2 to 6.

The single-layer and multi-layer stretch packaging films obtained as described above are excellent in deformation recovery and self-adhesiveness, and have transparency, flexibility and extensibility, and are plasticized PVC. It has sufficient characteristics as a substitute for a stretch film containing as a main component. Since the single-layer stretch packaging film has excellent heat resistance, it can be laminated with other resins.

The reason why such an effect is brought about is not clear, but it is estimated as follows. It is considered that the polypropylene-based resin used in the present invention is alloyed with a large amount of an amorphous polymer typified by an ethylene-propylene copolymer being introduced into polypropylene during the polymerization. The use of titanium-based catalysts, which are very active and have a long life during the polymerization, makes it possible to produce resins of this type. There are some copolymers having different molecular structures in the polymers obtained by such polymerization. Therefore, it is considered that a characteristic morphology is exhibited in the alloy of the ordinary resin portion such as polypropylene and the copolymer portion. As a result, it is considered that the resin exhibits physical properties very close to those of plasticized PVC even though the resin does not contain crosslinks.

[0037]

EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited thereto.

(Example 1) The molecular weight was 200,000, and the resin elution amount measured by the cross fractionation method was 35.1% by weight at 10 ° C.
36.6% by weight at 10 ° C to 65 ° C, 1 at 65 ° C to 90 ° C
2.4 wt%, polypropylene resin (manufactured by Tokuyama Soda Co., Ltd.), which is 15.9 wt% at 90 ° C to 125 ° C, has a caliber of 50
It was melt-kneaded at 180 ° C. with an extruder of mm, fed to an annular die, and inflation-molded at a die temperature of 190 ° C. and a blow ratio of 2.8 to produce a stretch-wrapping film having a thickness of 22 μm.

(Example 2) The same polypropylene resin as in Example 1 was used at 180 ° C with an extruder having a diameter of 50 mm.
It was melt-kneaded. On the other hand, an ethylene-vinyl acetate copolymer resin having a vinyl acetate content of 18% by weight and a melt flow rate of 2.5 g / min (vinyl acetate content of 15% by weight) was melted at 160 ° C. with an extruder having a diameter of 40 mm. Kneaded Supply both to one circular 3-layer die,
A 19 μm-thick central layer made of polypropylene resin and 3 μm-thick both surface layers made of an ethylene-vinyl acetate copolymer resin were laminated to prepare a stretch film.

(Example 3) The molecular weight was 190,000, and the resin elution amount measured by the cross fractionation method was 67.1% by weight at 10 ° C, 8.3% by weight at 10 ° C to 65 ° C, and 65 ° C to 90 ° C. A stretch packaging film was produced in the same manner as in Example 1 except that a polypropylene resin (manufactured by Tokuyama Soda Co., Ltd.) that was 2.9 wt% and 21.7 wt% at 90 ° C to 125 ° C was used.

(Example 4) The molecular weight was 350,000, and the resin elution amount measured by the cross fractionation method was 53.6% by weight at 10 ° C, 13.9% by weight at 10 ° C to 65 ° C, and 65 ° C to 90 ° C.
Was used, and a polypropylene resin (trade name, manufactured by Himond Co.) of 9.9% by weight and 22.6% by weight at 90 ° C. to 125 ° C. was kneaded at 180 ° C. with an extruder having a diameter of 50 mm.
On the other hand, a propylene-ethylene random copolymer resin having an ethylene content of 6% by weight and a melt flow rate of 2.0 g / 10 min was prepared at 185 ° C. with an extruder having a diameter of 40 mm.
Kneaded in. Both of them are supplied to one annular three-layer die, and a center layer of polypropylene resin having a thickness of 19 μm and both surface layers of propylene-ethylene random copolymer resin having a thickness of 3 μm are laminated to form a stretch film. Was produced.

(Comparative Example 1) The molecular weight was 260,000, and the resin elution amount measured by the cross fractionation method was 0% by weight at 10 ° C.
8.3 wt% at ℃ ~ 65 ℃, 50.7 at 65 ℃ ~ 90 ℃
A stretch packaging film was produced in the same manner as in Example 1 except that a polypropylene resin (manufactured by Chisso Corporation), which was 41.0% by weight at 90 ° C to 125% by weight, was used.

Comparative Example 2 The molecular weight was 450,000 and the resin elution amount measured by the cross fractionation method was 0% by weight at 10 ° C. and 10
3.7% by weight at ℃ to 65 ℃, 11.0 at 65 ℃ to 90 ℃
A stretch packaging film was produced in the same manner as in Example 1 except that a polypropylene resin (manufactured by Chisso Corporation), which was 8% by weight at 90 ° C. to 125 ° C., was used.

The following evaluation results are shown in Table 1 for the films obtained in Examples 1 to 3 and Comparative Examples 1 and 2.

(Tensile test) The strength and elongation of the film were measured at room temperature using Shimadzu Autograph, based on JIS K6758.

(Evaluation of Appearance during Packaging) The film was placed on a foam polystyrene container and packaged, and the film breakage due to the corner of the container and the wrinkle of the film were visually evaluated. ○ If there are no tears and wrinkles
The case of (good), tear or wrinkle is indicated by x (bad).

(Evaluation of Transparency) The transparency of the film was visually evaluated. Good transparency is indicated by ◯, and poor transparency is indicated by x.

(Deformation recovery rate) The film is 200% at room temperature.
After stretching and standing for 5 minutes, the dimensional recovery rate was measured and expressed in%.

(Self-adhesiveness) After the film was packaged in a plastic container, the degree of peeling of the film was visually evaluated for self-adhesiveness. The case where peeling did not occur and the packaging condition was good is shown by ◯, and the case where it was bad is shown by x.

[0050]

[Table 1]

From Table 1, it can be seen that the films of Examples 1 to 4 are excellent in self-adhesiveness and deformation recovery rate, and are also excellent in transparency, flexibility and extensibility.

[0052]

As is apparent from the above description, according to the present invention, by molding a polypropylene resin having a specific weight average molecular weight and a resin elution amount at a specific temperature within a specific range. Thus, a single-layer or multi-layer stretch packaging film having excellent self-adhesiveness and deformation recovery rate and also having transparency, flexibility and extensibility can be obtained. Since this stretch wrapping film does not use a plasticized PVC material, there is no problem in using it for food wrapping and no environmental problem in manufacturing.

Continuation of front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display area // C08L 23:10

Claims (2)

[Claims] 1. The weight average molecular weight is 80,000 or more and 500,000 or less, and the resin elution amount measured by the cross fractionation method is 10 or less.
20% by weight to 80% by weight inclusive at 10 ° C to 6 ° C
5% by weight or more and 45% by weight or less at 5 ° C, 65 ° C to 9%
1% by weight to 18% by weight at 0 ° C, 90 ° C to 1%
A stretch packaging film made of a polypropylene-based resin that is 10% by weight or more and 35% by weight or less at 25 ° C. 2. A propylene-ethylene random copolymer resin on both sides of a central layer made of polypropylene resin,
A stretch film formed by laminating surface layers each comprising at least one selected from the group consisting of a propylene-α-olefin copolymer resin and an ethylene-vinyl acetate copolymer resin, the stretch film comprising: Weight average molecular weight of 80,000 or more 5
The amount of resin elution of the polypropylene resin measured by the cross fractionation method is 20% by weight or more and 80% by weight or less at 10 ° C, and 5% by weight or more and 45% by weight or less at 10 ° C to 65 ° C. The film for stretch packaging is 1% by weight or more and 18% by weight or less at 65 ° C to 90 ° C and 10% by weight or more and 35 ° C or less by weight at 90 ° C to 125 ° C.