JPH03182348A - Co-extrusion laminated water cooled inflation film - Google Patents

Abstract

PURPOSE:To obtain a transparent packing film excellent in low temp. strength, tear resistance, transparency, opening resistance and blocking resistance and having good processability and workability by using a mixture of specific straight chain low density polyethylene and high density polyethylene, a specific crystalline propylene polymer and straight chain low density polyethylene to subject all of them to co-extrusion. CONSTITUTION:In a composite film wherein a B-layer and a C-layer are laminated to both surfaces of an A-layer, the A-layer is composed of a straight chain low density polyethylene being a copolymer containing 3-20wt.% of 4 or more C alpha-olefin and having density of 0.910-0.940g/cc. The C-layer is formed from a mixture of 100 pts.wt. of straight chain low density polyethylene and 20-230 pts.wt. of high density polyethylene having an MFR of 5.0g/10min or more. The B-layer is composed of a crystalline propylene copolymer consisting of propylene and ethylene or 4 or more C alpha-olefin. The thickness of each of the A- and B-layers is pref. set to 30-60% of the total thickness and that of the C-layer is pref. set to 10-30% and the total thickness of the film is desirably 10-100mu.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a coextruded laminated film produced by a water-cooled inflation method. More specifically, the present invention relates to a coextruded laminated film produced by a water-cooled inflation method that has excellent low-temperature impact resistance, tear resistance, transparency, opening properties, and bag-making properties.

[Conventional technology]

Polypropylene films have high rigidity, good transparency, and heat sealability, so they are widely used mainly for food packaging. However, on the other hand, the film has the disadvantage that it has extremely poor low-temperature strength and weak tear strength, so it is susceptible to seasonal changes in physical properties, and there are many problems such as bag breakage in winter.

We also offer melt-cut seal bags, which are often used in textile packaging, etc.
In other words, in the case of a method of making bags by heat-sealing and cutting at the same time as using a hot wire such as a nichrome wire, there is also the disadvantage that there are many troubles of bag breakage because the sealed portion of the bag made of the polypropylene film is very brittle and easily torn. Ta. Particularly at low temperatures, bag breakage from this seal was noticeable.

Although attempts have been made to improve low-temperature properties by copolymerizing ethylene with crystalline propylene polymers, no significant improvement effect has been observed at present.

On the other hand, polyethylene films have excellent low-temperature strength but poor transparency, so they are not suitable for high-grade packaging applications that require clear identification of contents, decorative properties, etc.

Furthermore, in addition to conventional high-density polyethylene and low-density polyethylene, a new type of linear low-density polyethylene has been developed in recent years, which has excellent impact resistance and improved transparency compared to conventional polyethylene. Its uses are expanding as its characteristics are taken advantage of. However, its rigidity and transparency, depending on the molding method, are still inferior to polypropylene films. Moreover, if transparency is improved by modifying the polymer such as changing the copolymerization ratio or by molding method, the blocking resistance and slipping property will be significantly reduced, and the processability and workability of printing, bag making, etc. will only be reduced. However, the opening of the bag is poor, and filling the bag with contents is also difficult. In particular, in the water-cooled inflation processing method, which aims to improve transparency, the above-mentioned drawbacks are noticeable, and the current situation is that a good balance between transparency and openness cannot be achieved.

Since there are limits to improving the conventional single-layer polypropylene or single-layer polyethylene film itself, methods have been proposed to improve the shortcomings of the single-layer film by making the single-layer multilayer. For example, JP-A-58-1402
No. 8 contains polypropylene/linear low density polyethylene/
A laminated film made of high-pressure low-density polyethylene or ethylene-vinyl acetate copolymer has been disclosed, but the purpose of this is to impart heat sealability to polypropylene, and other problems have not been solved.

In this way, all conventional films have advantages and disadvantages,
This was a major constraint in terms of application development.

[Problem to be solved by the invention]

The purpose of the present invention is to solve the drawbacks of the conventional film,
An object of the present invention is to provide a transparent packaging film that has excellent low-temperature strength, tear resistance, transparency, opening property, and blocking resistance, and has good processability and workability.

[Means to solve the problem]

As a result of intensive research to solve the above problems, the present inventors found that a mixture of a specific linear low-density polyethylene and a high-density polyethylene, a specific crystalline propylene polymer or copolymer, and a linear The present invention was achieved by discovering that a film with excellent properties can be obtained by coextruding the film with chain low-density polyethylene in a certain range of configurations.

The present invention is a composite film in which a (B) layer and a (C) layer are laminated on both sides of an (A) layer by a coextrusion method, and the (A) layer is a layer made of linear low-density polyethylene. The (B) layer is a layer made of a crystalline propylene polymer or copolymer, and the (C) layer is a layer consisting of 100 parts by weight of linear low-density polyethylene with a density of 0.910 to 0.940 g/cc. , relates to a coextruded laminated film having a layer made of a mixture with 20 to 230 parts by weight of high-density polyethylene having a melt flow rate (hereinafter referred to as MFR) of 5.0 g/10 inches or more.

The present invention will be explained in detail below.

The linear low-density polyethylene used for the layer (A) of the coextruded laminated film of the present invention is produced by processing the main components ethylene and carbon under relatively low pressure using a catalyst that usually combines a transition metal compound and an organometallic compound. It is a substantially linear polyethylene obtained by copolymerizing α-olefin with 4 or more atoms, and ethylene is polymerized by a radical reaction under high pressure using the commonly known oxygen radical as an initiator. It is known that the molecular structure, melting characteristics, crystallization characteristics, solid state physical properties, etc. of the two are completely different from the long-branched low-density polyethylene obtained by the process.

This linear low-density polyethylene generally has 9% ethylene.
It is a copolymer consisting of 7 to 80% by weight and 3 to 20% by weight of α-olefin having 4 or more carbon atoms, and among these, the layer (A) of the present invention has a density of 0.910 to 0.9.
Within the range of 40 g/cc, preferably 0.93
The amount within the range of 0 to 0.940 g/cc is used.

In addition, in layer (C), 20 to 230 parts by weight of high-density polyethylene with an MFR of 5.0 g/10 + ain or more is mixed with 100 parts by weight of this linear low-density polyethylene, but this high-density polyethylene is usually It is produced by a low-pressure method using a Chiveday type catalyst and a medium-pressure method using a metal oxide as a catalyst, but is not particularly limited by the production method. However, in the present invention, the MFR is 5. Must be 0g/10min or more. If the MFR is less than 5.0 g/10 min, the transparency of the obtained laminated film, which is one of the objects of the present invention, will be reduced, and the smoothness of the film will also be reduced, which is not preferable.

Linear low-density polyethylene (hereinafter referred to as L
-LDPE) and high-density polyethylene (hereinafter referred to as
It is preferable to use a limited range of HDPE.

That is, L-LDPE contains 5 to 15% by weight of α-olefin having 4 to 8 carbon atoms and has a density of 0.910 to 0.
．． 940 g/cc, preferably 0.930-0.94
In the range of 0 g/cc, VFRo, 5-10 g/lo
@in, preferably 0.8-2.0 g/10a
is an ethylene/a-olefin copolymer in the range of iin, HDPE has a density of 0.950 g/cc or more, preferably 0.950 to 0.970 g/cc, MF R5,
0~l 5.0 g/10min, and L-LD
It is desirable that the density of the mixture of PE and HDPE is 0.940 g/CC or more, and the L-
The amount of LLDPE mixed into LDPE is as described above.
HDPE should be in the range of 20 to 230 parts by weight to 0.00 parts by weight. If the amount is less than 20 parts by weight, the opening properties during film processing will be poor, causing problems in blocking properties over time, and if it exceeds 230 parts by weight, the tear strength and transparency of the film will be significantly reduced, which is not preferred. It is particularly preferable to mix in the range of 50 to 100 parts by weight within the above range, as this will provide well-balanced and improved properties in the laminated film and will maximize the characteristics of the present invention.

In the present invention, the use of a resin having the above-mentioned specific composition for the (C) layer improves the openness and blocking resistance of the laminated film, and also takes full advantage of the characteristics of the resins of the (B) and (A) layers. This is the most important element in solving the problem.

In the present invention, the crystalline propylene polymer or copolymer used for layer (B) is propylene alone or a copolymer of propylene as a main component and ethylene or an α-olefin having 4 or more carbon atoms, For example, crystalline polypropylene, crystalline ethylene/propylene random copolymer, crystalline propylene/butene-1 copolymer, crystalline propylene/ethylene/butene-1 terpolymer, etc. are generally well known.

These can be produced by homopolymerization or copolymerization using known stereoregular α-olefin catalysts such as the Ziegler-Natsuta system, by known methods such as slurry method, solution method, gas phase method, or a combination thereof. Obtainable.

These propylene-based polymers or copolymers are known, but in the present invention, low-temperature strength improvement is achieved by (A)
L-LDPE in the layer and HDP in the (C) layer
Since this is possible due to L-LDPH used as a mixture with E, it is particularly desirable to use a crystalline propylene polymer having good transparency even in the polypropylene content in the layer (B).

A composition obtained by mixing a specific L-LDPE and a specific HD PE used in the (C) layer of the present invention, L-LDPE used in the (A) layer, and a crystalline propylene copolymer used in the (B) layer. For coalescence, heat stabilizers such as phenol and phosphorus, which have been commonly used as additives for polyolefin films, antioxidants, slip agents mainly composed of fatty acid amides, anti-blocking agents such as silica and zeolite, etc.
Antistatic agents mainly composed of surfactants such as glyceride amine derivatives, antifogging agents, ultraviolet absorbers, coloring agents, etc. can be optionally added as long as they do not impair the object of the present invention.

A method of mixing LLDPE and HDPE used in the (C) layer of the laminated film of the present invention, and L-LDPE or the crystalline propylene polymer or copolymer used in the (A) layer or (B) layer and the various additions described above. The method of combining with the agent is
Any method may be used as long as these can be uniformly dispersed and mixed, and specifically, for example, a method can be used to thoroughly mix and disperse them uniformly using a ribbon blender, Henshil mixer, Banbury mixer, etc., and the mixture can be further mixed using an extruder or kneading It is also possible to follow a method in which the composition is melt-kneaded using a roll or the like, cooled and cut, and then used as a pellet-like composition.

The laminated film of the present invention has the (A) layer as a core layer, and the (B) layer and (C) layer are laminated on both sides of the core layer, respectively.
Using one extruder for each of the (A), (B), and (C) layers, the materials for each layer are melt-extruded from these, and laminated in a molten state by a known method such as a coextrusion multilayer circular die.
After blowing, it can be obtained by a coextrusion lamination water-cooled inflation method in which it is slowly cooled in an air ring and then water-cooled in a sizing ring.

In addition, as a modification of the present invention, a film in which two or more layers of any one of (A), (B), and (C) are laminated, for example, (B) / (8) / (B) / (8) / ( C), (
The present invention naturally includes those having four or more layers such as B)/(A)/(A)/(C).

By this coextrusion lamination method, the thickness of each layer (A), (B), and (C) can be arbitrarily selected, and the film has an ultra-thin layer with a total thickness of 30μ or less and one layer of 2 to 3μ. It is also easy to obtain.

In addition, layer (C) is molded as the inner surface of the tube, and the total thickness is 1
Even when the thickness is 5μ or less, it exhibits extremely excellent performance in terms of opening property and blocking resistance.

The present invention uses a coextrusion lamination method with (A), (B) the thickness of each layer is 30-60% of the total thickness, and (C) the thickness of the layer is 10%.
It is preferable to set it within a range of 30%.

Further, the total thickness of the film is usually preferably 10 to 100 microns, particularly preferably 15 to 50 microns.

This coextrusion lamination method usually uses three extruders to melt and extrude the materials for each layer, and then laminates them in the molten state using a three-layer circular die.The extruded laminate is then blown with air. It can be slowly cooled in a ring and then rapidly cooled in a direct water cooling type sizing ring to form a tubular film, but the water temperature in this sizing is preferably 20 to 30°C. If this temperature is too low (less than 20° C.), problems such as curling and wrinkles of the film will occur, while if it is too high (more than 30° C.), problems with poor transparency will occur.

The cooled and solidified film is wound up and subjected to the next process, for example, secondary processing such as printing and bag making, and then used for the intended purpose.

Measurement and evaluation of characteristics in the present invention were performed using the following methods and criteria.

(1) Density: 23℃ according to JIS K 7112
It was measured with (Unit: g/cc) (2) Melt flow rate (MFR): J I
According to SK 7210, crystalline polypropylene polymers and copolymers are tested under test conditions 14 (230°C, 2.16
kg), polyethylene under test conditions 4 (190℃, 2
．． 16 kg).

(3) Haze: ASTM D 10O
3. The smaller this value is, the better the transparency is.

(4) Opening property: represents the degree of opening when the cut end of a tubular film is lightly rubbed between the thumb and eight fingers during film processing.

(5) Blocking resistance: 4kg for tubular film
It is expressed as the load (g) required to peel two films in a flat state after aging at 50° C. for 24 hours under a load of /100Ci.

(6) Tear strength: Based on Elmendorf tear strength of ASTM D 1922.

(Unit: kg/cm) (7) Impact strength: Based on ASTM D 1709-A. (Unit: F, □) (8) Tear load: Measured under conditions of room temperature (23°C), -5°C, and -1.5°C in accordance with JIS K 6781. (Unit: 2 g) (9) Drop bag strength: Width 15 cm with heat sealer.

A bag made to a size of 15 aa in length was filled with 100 g of polyethylene pellets and top-sealed. After leaving this bag in a constant temperature room at -10℃ for 24 hours,
．． It is expressed as the number of broken bags when 10 bags are dropped from 0 m.

a[l Stiffness: ASTM D 882+=compliant. (Unit: ICg/Ci) [Example] The present invention will be explained in more detail by showing Examples and Comparative Examples of the present invention below, but these are not intended to limit the present invention in any way.

Using a total of three extruders with a diameter of 50 mm for the (A) layer and the (B) layer, and a diameter of 40 mm for the (C) layer, and a three-layer circular die connected to these extruders, the (A) layer (B)/(
A coextruded film having a total thickness of 15 μm was obtained by melt extrusion and water-cooled inflation method (sizing ring water temperature: 23° C.) with a composition of A)/(C) = 1.7: 2.3: 1.0.

The extrusion temperature was 2°00 for all three extruders and Gui.
It was performed as ℃.

The properties of the obtained film are listed in Table 1.

In the description of the properties, the evaluation of the openness was as follows: 20 Very good, ○ Good, △ Poor, × Very poor. Also, (A) in the bottom column of this table.

(B) and (C) The contents of the resin used in each layer are also listed.

Comparative Examples 1 to 4 As is clear from Table 1, (A), (
The films constituting the layers B) and (C) are significantly inferior in low-temperature strength and tear strength as compared to the film in which the layer (A) is made of linear low-density polyethylene.

Comparative examples 5 to 9 On the other hand, linear low density polyethylene (A).

The film with the (C) layer had significantly improved low-temperature strength compared to the case with only the (A) layer, and also had excellent results in other film properties.

However, the opening property and blocking resistance were poor, which caused practical problems.

Comparative Examples 10 to 14 In order to improve the opening properties of the tubular film, various high-density polyethylenes with different densities and MFRs were tested for the (C) layer. Although the opening properties were excellent, the crystallinity Three-layer film made of propylene homopolymer (Comparative Example 1)
could not be obtained, and was inferior to films made of ethylene-propylene random copolymer.

In addition, tear strength was a problem in practice.

Examples 1 to 5 Considering the shortcomings of the various test results shown in the comparative examples, the (A) layer was made of linear low-density polyethylene, the (B) layer was made of crystalline propylene homopolymer, and the (C) layer was made of straight chain low-density polyethylene. 100 parts by weight of linear low density polyethylene, M F Rl 2. Og/10
The test was conducted using a mixture of 11 to 230 parts by weight of high-density polyethylene with a density of 0.953 g/cc.

As a result, the mixing amount of high-density polyethylene in layer (C) was 1
At 1 part by weight, there was a slight problem with the opening property, but when the mixing amount was higher than this, the opening property was good in all cases, and the transparency was also good for the three-layer film made of ethylene-propylene random copolymer (Comparative Example 2) It was possible to obtain a film of the same level as the three-layer film made of crystalline propylene homopolymer (Comparative Example 1). Furthermore, these Examples i~
Film No. 5 had excellent low-temperature strength, tear strength, and anti-blocking properties, and did not pose any practical problems.

〔Effect of the invention〕

The coextruded laminated film produced by the water-cooled inflation method of the present invention has various excellent properties such as excellent opening properties, transparency, and blocking resistance, as well as low-temperature strength and tear strength, and good bag-making suitability. By taking advantage of this property, it can be widely used in various packaging applications that require cold resistance, which has caused practical problems with conventional polypropylene films.

Claims (6)

[Claims] (1) By coextrusion method, (B) layer, (
C) A composite film in which layers are laminated, where the (A) layer is a layer made of linear low density polyethylene, and the (B) layer is a layer made of a crystalline propylene polymer or copolymer. The layer (C) is made of 100 parts by weight of linear low-density polyethylene with a density of 0.910 to 0.940 g/cc and 20 to 230 parts by weight of high-density polyethylene with a melt flow rate (MFR) of 5.0 g/10 min or more. A coextruded laminated film that is a layer consisting of a mixture of (2) Laminated in the order of (B) layer / (A) layer / (C) layer,
The thickness of each of the (A) layer and (B) layer is 30 to 60% of the total thickness of the composite film, and the thickness of the (C) layer is 10 to 60% of the total thickness of the composite film.
The coextruded laminated film according to claim 1, wherein the coextruded laminate film has a content of 30%. (3) The linear low density polyethylene used in layer (C) contains 5 to 15% by weight of α-olefin having 4 to 8 carbon atoms, has a density of 0.910 to 0.940 g/cc, and has an MFR of 0.
It is an ethylene/α-olefin copolymer with a yield of 5 to 10 g/10 min, and high density polyethylene has a density of 0.950 g.
/cc or more, MFR 5.0 to 15.0 g/10 min, and the density of the mixture of linear low density polyethylene and high density polyethylene is 0.940 g/cc or more. film. (4) The coextruded laminate film according to claim 1, wherein the ethylene/α-olefin copolymer according to claim 3 is used in the layer (A). (5) The coextruded laminate film according to claim 1, wherein the crystalline propylene polymer or copolymer used in layer (B) has an MFR of 1.0 to 15.0 g/10 min and contains 95% by weight or more of a propylene component. (6) The coextruded laminated film according to claim 1, which is produced by a water-cooled inflation method, and the layer (C) is an inner surface layer of the tube.