JP2905098B2 - Heat shrinkable multilayer film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-shrinkable multilayer film excellent in flexibility, transparency, heat-sealing property and heat-shrinkability and suitable for overlap packaging.

[0002]

2. Description of the Related Art Conventionally, general products and the like have been packaged by a so-called overlap packaging method, in which loose packaging is performed, followed by heat shrinkage and tightly sealed packaging. As the heat-shrinkable film used for such overlap packaging, for example, a film made of a polypropylene-based resin, a polyethylene-based resin, or the like is used after being stretched by biaxial stretching (for example, a tubular stretching method) or the like. However, the above-mentioned film has poor flexibility, and the shrink-wrapped film has a hard feel, and in particular, the corners are hard and wrinkles are liable to occur, and the packaging finish tends to be poor, which is not preferable. Was. Also,
For example, in the case of a heat-shrinkable polypropylene film in which a flat film made of a polypropylene-based resin (single or composite film or the like) is successively stretched by a biaxial stretching method, an extreme difference occurs in shrinkage between the longitudinal direction and the transverse direction. Easy and has a problem with shrink finish.

Further, in order to form a heat-shrinkable polypropylene-based film having excellent flexibility, a heat-shrinkable film for an overlap packaging is prepared from a composition obtained by blending an ethylene-vinyl acetate copolymer (EVA) with a polypropylene-based resin. A film has been deposited. Such a flexible film tends to have reduced transparency after stretching, and it has been pointed out that it cannot be used particularly in the packaging field where transparency is required. Further, in the case of successive biaxial stretching, for example, if stretching is performed in the longitudinal direction and subsequently in the transverse direction, thickness unevenness, breakage, and the like are likely to occur, and an excellent heat-shrinkable film tends not to be obtained. Was.

[0004]

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, the present invention provides a heat-shrinkable multilayer film which is excellent in flexibility, transparency, heat-sealing property and heat-shrinkability and is suitable for overlap packaging. With the goal.

[0005]

Means for Solving the Problems As a result of intensive studies for the above-mentioned object, the present inventors have found that both surface layers composed of a propylene-ethylene random copolymer having a specific composition have a polybutene component and a propylene-ethylene copolymer. Laminated via an intermediate layer made of a propylene-ethylene random copolymer containing a block copolymer consisting of an ethylene random copolymer component or a propylene component and a propylene-ethylene random copolymer component, and biaxially stretched, The inventors have found that a heat-shrinkable multilayer film in which the ratio of the total thickness of the surface layer to the thickness of the intermediate layer is specified achieves the above object, and has reached the present invention.

The present invention is characterized in that (A) 98 to 70% by weight of a propylene-ethylene random copolymer having an ethylene content of 2 to 5% by weight and 2 to 30% of a petroleum resin.
(B) 10 to 90% by weight of a block copolymer comprising a polybutene component and a propylene-ethylene random copolymer component or a propylene component and a propylene-ethylene random copolymer component. Propylene having an ethylene content of 2 to 5 wt.
An intermediate layer comprising a composition of 90 to 10% by weight of an ethylene random copolymer is laminated in at least three layers, formed into a flat film, and biaxially stretched in the vertical and horizontal directions. An object of the present invention is to provide a heat-shrinkable multilayer film which is provided with shrinkability and has a ratio of the total thickness of the layer (A) to the total thickness of the layer (B) of 1:10 to 5: 1.

The propylene-ethylene random copolymer according to the both surface layers (A) of the present invention has an ethylene content of 2 to 2.
Any propylene-ethylene random copolymer of 5% by weight may be used. If the ethylene content exceeds 5% by weight, it tends to be too flexible and the tensile modulus tends to be significantly reduced. The slipperiness of the film and the automatic feeding of the packaging film to the automatic packaging machine are deteriorated, and the package tends to have wrinkles, scratches, scratches, etc., and 2% by weight.
If it is less than 10, the flexibility is poor, the stretchability is reduced, the thickness unevenness is likely to occur, and the transparency tends to deteriorate, which is not preferable.

The propylene-ethylene random copolymer of both surface layers (A) may have a boiling n-heptane extraction insoluble content of 90% by weight or more, and a melt flow rate (MFR) of 0.5 to 0.5%. 20 g / 10 min, preferably 1 to 10 g / 10 min, more preferably 1 to 5 g / 10 min. The content of the propylene-ethylene random copolymer in both surface layers (A) is 98 to 70.
If it exceeds 98% by weight, the heat sealability tends to decrease, and low-temperature and high-speed heat sealing with an automatic packaging machine tends to be difficult. If it is less than 70% by weight, the tensile elasticity decreases and the material becomes too soft. Not preferred.

As the petroleum resin constituting the layer (A) of the present invention, an aliphatic petroleum resin (C) obtained by polymerizing a fraction containing an unsaturated hydrocarbon purified by pyrolysis of petroleum naphtha or the like can be used. ₅ fraction system), aromatic petroleum resin (C ₉ fraction system), cyclopentadiene petroleum resin, and hydrogenated hydrogenated petroleum resin thereof. Specifically, isoprene, 1-pentene, 1.3 pentadiene,
Examples thereof include petroleum resins obtained by polymerizing and copolymerizing unsaturated hydrocarbons such as vinyltoluene, indene, methylstyrene, styrene, methylindene, butadiene, piperylene, pentylene, and dicyclopentadiene, and hydrogenated petroleum resins thereof.

The content of the above petroleum resin is 2-3
0% by weight is preferred. When the content of the petroleum resin is less than 2% by weight, the stretchability is reduced, and the thickness unevenness and the unstretched portion are easily generated, which is not preferable. If the content of the petroleum resin exceeds 30% by weight, the frictional resistance tends to be high, and when packaging with an automatic packaging machine, the automatic supply of the packaging material to the automatic packaging machine is poor, and the packaging body is damaged. It is not preferable because wrinkles and scratches are easily generated and a tight package after shrinkage is difficult to obtain. Furthermore,
In the case of successive biaxial stretching, there is a tendency of fusing and sticking to a heating roll for stretching, which is not preferable.

Next, the propylene-ethylene random copolymer forming the intermediate layer (B) according to the present invention includes:
The same type as the propylene-ethylene random copolymer used for the surface layer (A) may be used, but the melt flow rate of the propylene-ethylene random copolymer (230
° C, 2.16 kg) is 0.1 to 30 g / 10 min,
More preferably, 0.5 to 10 g / 10 min. Can be exemplified. Melt flow rate is 0.1g / 10mi
n. If it is less than, for example, during co-extrusion molding (especially T-die co-extrusion molding), the mutual melt fluidity with the surface layer (A) is poor, flow unevenness easily occurs, and the adhesion with the surface layer (A) , And tends to decrease, and 30 g / 10 min. If it exceeds, the thickness stability tends to decrease, which is not preferred.

The block copolymer according to the intermediate layer (B) of the present invention is a block copolymer of a polybutene component and a propylene-ethylene random copolymer component or a polypropylene component and a propylene-ethylene random copolymer component. Are preferred. Such a block copolymer is a block copolymer comprising a polybutene component of 0.1 to 10% by weight, a total amount of a propylene-ethylene random copolymer component and a polypropylene component of 99.9 to 90% by weight, and 0 to 30% by weight of polypropylene component
Block copolymers containing are preferred. Here, the propylene-ethylene random copolymer component is composed of a random copolymer containing 15 to 80 mol% of a monomer unit based on ethylene and 85 to 20 mol% of a monomer unit based on propylene. Can be exemplified. Furthermore, flexibility, stretchability, heat shrinkage properties (low temperature heat shrinkage, shrink finish)
In consideration of the above, the block copolymer has a Vicat softening point of 40 to 100 ° C. and a melt flow rate of 0.5 to 1
0 g / 10 min. Are preferred.

At this time, if the polybutene component exceeds 10% by weight, it tends to be difficult to uniformly melt the block copolymer, and it is difficult to form a film, which is not preferable. If the polybutene component is less than 0.1% by weight, the transparency of the film composed of the block copolymer tends to decrease, which is not preferred. On the other hand, a block copolymer comprising a polybutene component, 0 to 30% by weight of a polypropylene component and a propylene-ethylene random copolymer component has a flowability of the block copolymer when the content of the polypropylene component is 30% by weight or less. This tends to improve the mechanical strength (eg, tensile modulus), heat resistance, and the like of the film. When the content of the polypropylene component exceeds 30% by weight, the flexibility, transparency and the like of the film decrease, and the object of the present invention cannot be achieved.

Here, the propylene-ethylene random copolymer component used in the layer (B) has a monomer unit based on ethylene of less than 15 mol% and a monomer unit based on propylene exceeding 85 mol%. However, the flexibility of the intermediate layer (B) of the multilayer film of the present invention is not sufficient, which is not preferable. When the monomer unit based on ethylene exceeds 80 mol% and the monomer unit based on propylene is less than 20 mol%, the tensile strength and heat resistance of the intermediate layer (B) of the multilayer film of the present invention Tends to decrease, which is not preferred.

Further, the layer (B) according to the present invention comprises 90 to 10% by weight of a propylene-ethylene random copolymer having an ethylene component content of 2 to 5% by weight and 10 to 90% by weight of the block copolymer described above. % Of the composition. In this case, if the amount of the block copolymer is less than 10% by weight, the flexibility tends to decrease, and if the amount exceeds 90% by weight, the transparency deteriorates, which is not preferable.

According to the present invention, a resin composition containing a petroleum resin in the propylene-ethylene random copolymer of the layer (A) and a block copolymer in the propylene-ethylene random copolymer of the layer (B) are used. The method for preparing the composition to be contained is not particularly limited, but may be any of the methods commonly used in the conventional methods for producing various resin compositions, for example, kneaders, Banbury mixers, kneaders such as rolls, ribbon blenders, Henschel. Examples thereof include a method in which the mixture is heated and melt-kneaded using a mixer such as a mixer or a single-screw or twin-screw extruder.

The heat-shrinkable multilayer film according to the present invention comprises at least three layers consisting of the above-mentioned outer layer (A) and intermediate layer (B). For example, (A) / (B) /
It is preferable to form a multilayer structure such as (A), (A) / (B) / (A) / (B) / (A).

The thickness of each layer constituting the heat-shrinkable multilayer film according to the present invention is such that the ratio of the total thickness of both outer layers (A) to the total thickness of the intermediate layer (B) is from 1:10 to 5: It is preferably set to 1. At this time, if the total thickness of both outer layers (A) exceeds 5 times the total thickness of the layers (B), it is difficult to impart flexibility to the heat-shrinkable multilayer film of the present invention. When the total thickness of the layers (A) and (A) is less than 0.1 times the total thickness of the intermediate layer (B), the heat-shrinkable multilayer film of the present invention has mechanical strength, for example, However, the tensile modulus is lowered, and the transparency is deteriorated.

The method for producing the heat-shrinkable multilayer film of the present invention is as follows:
Although there is no particular limitation, examples thereof include a coextrusion method, a lamination method, and a dry lamination method. Of these, it is preferable to form a multilayer by a co-extrusion method in which melt bonding is performed inside or outside a die. Specifically, to a number of extruders corresponding to the number of layers to be multilayered, for example, a T-die is connected, melt-extruded, and after being multilayered in a molten state, using a cooling roll, a method of cooling with water or air cooling. A method of forming a multilayer film can be exemplified. Alternatively, a tubular film may be formed by using an annular die, and then cut into a flat shape.

In order to impart heat shrinkage to the multilayer film according to the present invention, it is preferable to stretch. As the stretching method, the stretching may be performed by a sequential biaxial stretching method, a simultaneous biaxial stretching method, a tube stretching method, or the like. Among them, the sequential biaxial stretching method is convenient.

In the case of manufacturing by the successive biaxial stretching method, the stretching conditions are such that the stretching ratio is 2 to 5 times, preferably 3 times in the machine direction.
４4 times, 2-7 times, preferably 3-5 times in the horizontal direction. As the stretching temperature, in the case of the successive biaxial stretching method, the first stage is stretched in the longitudinal direction by a hot roll at 60 to 110 ° C, preferably 70 to 100 ° C, and the second stage is 70 to 110 ° C.
The method of extending | stretching in a horizontal direction with a tenter at 80 degreeC, Preferably 80-100 degreeC can be illustrated. At this time, if the stretching temperature in the longitudinal direction is less than 60 ° C., the stretching load is large, and the transparency tends to decrease. If the temperature exceeds 110 ° C., the film adheres to the roll and winds around the roll, or a stretching step pattern occurs. There is a tendency and it is not preferable. If the stretching ratio is less than 2 times, stretching unevenness or the like is likely to occur, and if the stretching ratio exceeds 6 times, breakage or the like tends to occur during the second stage stretching, which is not preferable. When performing transverse stretching with a tenter, if the ambient temperature in the tenter is lower than 70 ° C., the transparency decreases, stretching unevenness occurs,
If the temperature exceeds 110 ° C., shrinkage characteristics (for example, low-temperature heat shrinkability) tend to be poor, which is not preferable. Stretch ratio of 2 in tenter
If the ratio is less than 2 times, unstretching occurs, and if the stretching ratio exceeds 7 times, breakage or the like tends to occur, which is not preferable.

The surface layer (A) and the intermediate layer (B) according to the present invention may include various additives and fillers such as a heat stabilizer, if necessary, as long as the properties of each layer are not impaired. Antioxidants, light stabilizers, antistatic agents, lubricants, nucleating agents, flame retardants,
Pigments or dyes, calcium carbonate, calcium sulfate, barium sulfate, magnesium hydroxide, mica, talc, clay and the like can be added. Further, other α-olefin resins, thermoplastic elastomers, rubbers, hydrocarbon resins, and the like may be blended as long as the characteristics of the present invention are not impaired.

The surface layer (A) according to the present invention can be subjected to a surface treatment in order to improve printability, laminability and the like. Examples of the surface treatment method include, but are not particularly limited to, corona discharge treatment, plasma treatment, flame treatment, and acid treatment. A corona discharge treatment, a plasma treatment, and a flame treatment, which can be continuously processed and can be easily performed before the winding step in the production process of the film, are preferable, and the corona discharge treatment is particularly preferable in terms of operability, ease of installation, and the like. .

[0024]

According to the present invention, (A) the ethylene component content is from 2 to 5
98% by weight of a propylene-ethylene random copolymer
Both surface layers comprising a composition of 70% by weight and 2 to 30% by weight of petroleum resin, (B) 0.1 to 10% by weight of polybutene component and 2 to 5% by weight of ethylene component A block copolymer comprising 99.9 to 90% by weight of a polymer component and 0.1% of a polybutene component;
Block copolymers such as block copolymers comprising a total of 99.9 to 90% by weight of a polypropylene component containing 10 to 10% by weight and a polypropylene component of 0 to 30% by weight and an ethylene-propylene random copolymer component. 90% by weight, and an intermediate layer containing 90 to 10% by weight of a propylene-ethylene random copolymer having an ethylene component content of 2 to 5% by weight, laminated at least three layers, and biaxially stretched. A flat multilayer film comprising: a film having excellent flexibility, transparency, heat-sealing properties and a ratio of the total thickness of the surface layer (A) to the total thickness of the intermediate layer (B). A heat-shrinkable multilayer film suitable for heat-shrinkable overlap packaging can be provided.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. In the following Examples of the present invention, flexibility (evaluated by tensile modulus), transparency (evaluated by haze), heat sealability (evaluated by fusing seal strength), and heat shrinkage were evaluated by the following methods. [Tensile modulus (kg / cm ² )] ASTM D882
It measured according to. [Haze (%)] Measured according to ASTM D1003. [Heat seal strength (kg / cm)] Fusing seal 1
The 80 degree peel strength was measured. [Thermal Shrinkage (%)] The shrinkage when immersed in a glycerin bath at 80 to 120 ° C. for 30 seconds was measured.

Example 1 As a composition constituting both surface layers (A), an ethylene-propylene random copolymer (ethylene content: 3.2
Weight%, melt flow rate 2g / 10min) 95% by weight
And petroleum resin (aliphatic hydrocarbon resin, Vicat softening point 1
(15 ° C.) A composition containing 5% by weight and appropriate amounts of a lubricant and an antiblocking agent was used. Further, as a composition constituting the intermediate layer (B), an ethylene-propylene random copolymer (an ethylene component content of 3.2% by weight,
A block copolymer (Vicat softening point of 60) comprising 50% by weight of a melt flow rate (2 g / 10 minutes) and a polybutene component and a propylene-ethylene random copolymer component.
° C, melt flow rate 1.5g / 10min) 50% by weight
A composition prepared by blending an appropriate amount of a lubricant and an antiblocking agent was used.

Using the composition obtained above, (A) /
The thickness ratio of (B) / (A) is set to 2: 10: 2, and three extruders each having three independent layers and a three-layer T-die connected thereto are used to form a barrel of the extruder and Die temperature 2
After co-extrusion at 30 ° C, quenched with cast roll
A layer laminated sheet was obtained. Next, the obtained three-layer laminated sheet is stretched 3.5 times in the longitudinal direction using a heating roll at 90 ° C., and subsequently stretched 4.0 times in the transverse direction using a tenter at an ambient temperature of 100 ° C. Thus, a 15-μm-thick three-layer laminated film for overlap packaging having excellent flexibility, transparency, heat sealability, and heat shrinkage was formed stably.
Table 1 shows the tensile modulus, haze, fusing seal strength, and heat shrinkage of the three-layer laminated film.

Example 2 The block copolymer constituting the intermediate layer (B) is a block copolymer comprising a polybutene component, a propylene-ethylene copolymer component and propylene (Vicat softening point 8
A heat-shrinkable multilayer film having excellent flexibility, transparency, heat-sealing properties, and heat-shrinkability was obtained in the same manner as in Example 1 except for the temperature and the melt flow rate, which were 0.0 ° C. and a melt flow rate of 1.5 g / 10 minutes. Table 1 shows the tensile modulus, haze, fusing seal strength, and heat shrinkage of the three-layer laminated film.

Comparative Example 1 Ethylene-propylene random copolymer (content of ethylene component: 3.2% by weight, melt flow rate: 2 g / 10
Min) the barrel of an extruder equipped with a T die and the die temperature 23.
After melt-extrusion at 0 ° C., the mixture was quenched with a cast roll to obtain a single-layer sheet. Then, the film was stretched 3.5 times in the machine direction using a heating roll at 90 ° C., and subsequently, stretched 4.0 times in the transverse direction using a tenter at an ambient temperature of 100 ° C. to obtain a heat-shrinkable single-layer film. . Table 1 shows the tensile modulus, haze, fusing seal strength, and heat shrinkage of the film.

[0030]

[Table 1]

As is clear from Table 1, the heat-shrinkable multilayer film according to the present invention is more flexible (has a lower tensile modulus) than a single-layer heat-shrinkable film made of a conventional ethylene-propylene random copolymer. ), Transparency, heat seal strength, and heat shrinkability.

[0032]

The heat shrinkable multilayer film of the present invention has good flexibility, transparency, heat sealability and heat shrinkability,
It is a soft film suitable for overlap packaging. According to the present invention, the flexibility of the conventional polyolefin film,
Heat-shrinkable multilayer film for packaging with improved transparency, heat-sealing properties, heat-shrinkability, no problems with hygiene and environmental pollution such as soft vinyl chloride film, suitable for automatic wrapping machines, good shrink wrapping finish Can be obtained. Furthermore,
The present invention can be used for various uses other than the packaging field.

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Claims (1)

(57) [Claims] 1. A propylene-ethylene random copolymer having an ethylene component content of 2 to 5% by weight.
(B) a polybutene component and a propylene-ethylene random copolymer component or a propylene component and a propylene-ethylene random copolymer component. And a propylene-ethylene random copolymer having an ethylene component content of 2 to 5% by weight, and an intermediate layer of a composition of 10 to 90% by weight and an ethylene layer content of 2 to 5% by weight. And a multilayer film that is formed into a flat shape, and is biaxially stretched in the longitudinal and lateral directions and imparted with heat shrinkage. The total thickness of the A layer and the B layer A heat-shrinkable multilayer film having a ratio of 1:10 to 5: 1.