JPH0761680B2 - Method for producing laminated biaxially stretched film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laminated biaxially stretched film having excellent gas barrier properties. More specifically, the present invention relates to a laminated biaxially stretched film suitable for use in food packaging having a saponified ethylene-vinyl acetate copolymer resin (hereinafter referred to as EVOH) layer.

[Conventional technology]

Biaxially oriented polypropylene film (hereinafter referred to as OPP)
Has excellent properties such as transparency, mechanical properties, water resistance, and packaging suitability, and has achieved rapid growth while surpassing the market of cellophane film. However, since the OPP film itself has a poor gas barrier property against oxygen and the like, OPP coated with polyvinylidene chloride (PVDC) (commonly known as K-OPP) is mainly used in the food packaging and other packaging fields. However, PVDC has a good gas barrier property (especially less humidity dependency), but has a problem of odor, discoloration, and damages the incinerator when discarded.
There are problems such as air pollution.

EVOH film is used in various fields because it has excellent gas barrier properties, odor, discoloration, incineration, etc.
Since it is inferior in water resistance and heat sealability, it is not used alone, but it is generally used by being laminated by an extrusion laminating method, a dry laminating method, a co-extrusion laminating method or the like.

However, these methods have a limitation in reducing the thickness of the EVOH resin layer, which is economically disadvantageous.

Especially when it is attempted to use the EVOH resin layer with a thickness of 10 μ or less and a few μ, it is difficult to produce a beautiful single EVOH film because of problems such as wrinkles and film breakage. Furthermore, when the EVOH resin layer is made to have a thickness of several μ, there is a problem that the gas barrier property is deteriorated.

The following documents are known as documents relating to the technology of a film using an EVOH resin.

JP-A-51-6276: After the EVOH resin layer and other stretchable thermoplastic film are adhered and laminated, there is a description that the EVOH resin layer is stretched uniformly by a biaxial stretching method to reduce the thickness. It is difficult to wind a thin biaxially stretched EVOH resin layer independently without wrinkles and use it as a single layer film.

JP-A-52-15570: Description of a biaxial stretching method in which a water-containing EVOH resin layer is stretched in one direction, further stretched in a direction perpendicular to the stretching direction by changing the stretching temperature, and then heat treated. However, if it is as thin as a few μ, it is difficult to wind it into a long length alone without wrinkles, and it is difficult to use it as a single layer film as described above.

JP-A-52-54784: Polypropylene resin layer (hereinafter P
EVOH with a resin layer for adhesion on the uniaxially stretched
Extrusion lamination of a film laminated with a resin layer, after that, the EVOH layer is subjected to a water-containing treatment, and there is a description of a biaxial stretching method at a time in which the EVOH layer is stretched by a tenter method.
Even so, since it is supported by the PP resin layer, wrinkles will not occur and the damage due to thinning will be resolved.

JP-A-52-57274, JP-A-53-142882: Same as above JP-A-55-2075: Co-extrusion of a PP resin layer and an adhesive resin layer, uniaxially stretching this, and then EVOH resin There is a description of a temporary biaxial stretching method in which layers are extrusion laminated and the film is stretched in a perpendicular direction.

The above is based on the biaxial stretching method mainly based on the T-die method.

In addition to the T-die method, there is a tubular method as a biaxial stretching method for a film.

JP-A-52-129777, JP-A-57-25920: EVOH
A method of biaxially stretching a resin layer containing water.

JP-A-57-41924: A method in which a polyamide resin and an EVOH resin are coextruded and biaxially stretched in a tubular manner.

[Problems of conventional technology]

In order to achieve the object of the present invention by the above-mentioned conventional method, there is a temporary biaxial stretching method mainly composed of the T-die method, but this method has the following problems.

That is, because the stable stretch ratio of EVOH resin film (the ratio that eliminates necking and eliminates thickness unevenness) and the stable stretch ratio of PP resin film are different (the stable stretch ratio of EVOH resin film is the longitudinal stretch ratio and the transverse stretch ratio). With the product of
10 to 20, preferably 12 to 16, whereas the product of the stable stretching ratio of the PP resin film is 30 to 55.) The stretching ratios of the two do not match and the moldability is poor.

Therefore, one or both of the resins is improved by adding an elastomer that eliminates necking at a low draw ratio, and PP resin (also graft modified product) and EVOH resin can be used as described in "Japanese Patent Laid-Open No. 52-146487". The film co-extruded is stretched in a specific temperature range to prevent uneven stretching, and as in "JP-A-52-103481", PP resin (grafted modified product) is stretched on both sides with EVOH resin as an intermediate layer. At the same time, the EVOH resin is melted and the draw ratio is matched.

Further, for example, in "JP-A-58-89325", when the PP resin (graft modified product) and the EVOH resin are coextruded or extrusion-laminated, the EVOH resin layer tends to be whitened and cracked when biaxially stretched. It is also stated that the effect will not be produced until the PP resin (graft modified product) is laminated on both sides of the EVOH resin layer.

[Object of the Invention]

An object of the present invention is to obtain a laminated film comprising an EVOH resin and a PP resin, having an EVOH layer that is sufficiently thin, has excellent gas barrier properties, has no odor and discoloration, and is easily incinerated.

The gist of the present invention is to manufacture a laminated biaxially stretched film having a saponified ethylene-vinyl acetate copolymer (resin A) layer and a polypropylene-based resin (resin B) layer from the outside by coextrusion molding. A, the adhesive layer, and the resin B are laminated in this order and extruded downward in a tubular shape to obtain an unstretched film by quenching with cooling water from the outside, and the water content of the resin A layer of the obtained tubular unstretched film. 5 to 15
After performing biaxial tubular stretching to make the weight% 140-1
A method for producing a laminated biaxially stretched film is characterized in that heat treatment is performed at a temperature of 60 ° C.

In the present invention, EVOH resin is not particularly limited as long as it is produced by a known method, ethylene content 25 to 50 mol%, saponification degree is 90% or more, high oxygen barrier property. If there is no problem.

The adhesive resin forming the adhesive layer is not particularly limited as long as it is a polyolefin resin graft-modified with an unsaturated carboxylic acid, but a resin mainly composed of PP is preferably used.

Examples of the unsaturated carboxylic acid used for the graft modification include acrylic acid, methacrylic acid, maleic acid, fumaric acid and itaconic acid, and of these, maleic anhydride is preferred. The amount of graft modification is in the range of 0.05 to 5 parts by weight with respect to 100 parts by weight of the polymer.

The PP resin may be a PP resin alone or a mixture, and further, a polypropylene resin component of 70% by weight or more in a mixture of the PP resin and another polyolefin resin may be used, but the PP resin is preferable. , A homopolymer of propylene, and a copolymer of propylene and an α-olefin other than propylene such as ethylene, butene, and hexene.

Various additives may be mixed with the above polymer depending on the purpose.

A feature of the manufacturing method of the present invention is that a tubular biaxial stretching method is selected to achieve stable stretching ratio matching between the EVOH layer and the PP layer.

Since the EVOH layer is difficult to use with the biaxial stretching method at a time, and the simultaneous biaxial stretching method is suitable, the tubular biaxial stretching method was selected.

The EVOH layer is the outer layer, and in the process of making a non-stretched film, the external water cooling method is selected and rapidly cooled, and at the same time, the EVOH layer is made water-containing to facilitate stretching.

When the EVOH layer and PP resin are co-extruded with an adhesive resin, the adhesive strength is much larger when the external water cooling method is used than when the unstretched film is made by the T die molding method. Adhesive strength of the same tendency remains [in the case of T-die molding,
Slow cooling has higher adhesive strength than rapid cooling, and the same tendency is observed in air-cooled inflation molding. Cool by contact with water (quenching)
Only when it does, the adhesive strength becomes high. There are various theories: The reason for this is currently unclear. Since EVOH resin is used in a thin wall (several μ), it is necessary to improve the oxygen gas barrier property, and the barrier property was improved by combining the effect of biaxial stretching treatment and the heat treatment effect.

By discovering the above, the K-OPP-like film was completed for the first time.

The tubular biaxial stretching method is not particularly limited as long as it is conventionally known, but it is preferable to make temperature control (preheating, stretching, cooling, heat treatment) more precise.

The water content of the EVOH resin layer when making an unstretched film is affected by the cooling water temperature during cooling, the cooling water temperature, and the contact time with the cooling water. Little. In the case of the present invention, it is desirable to quench the film as much as possible in the process of producing the unstretched film. When conducting tubular biaxial stretching, the water content of the EVOH layer is important. The water content can be controlled under the cooling conditions described above, but if the production of the unstretched film and the tubular stretching are performed separately, or if it is necessary to adjust the water content in addition, a treatment device with hot water or heated steam is provided. You may make it hydrate. Needless to say, when the unstretched film is made to contain water, it is necessary to make it even.

When biaxially stretching a three-layer unstretched film
Water content of EVOH resin layer is 5 ~ 15wt%, preferably 8 ~ 12wt
%. If it is less than 5% by weight, the effect of water as a plasticizer does not appear and a uniform stretched film cannot be obtained. If it is more than 15% by weight, the adhesive force between the EVOH resin layer and the adhesive resin layer is reduced, and in some cases bubbles are generated. There is harm.

Thus, the EVOH layer needs to be located outside the tube in order to control the water content of the EVOH layer. When the EVOH layer is inside the tube, it is difficult to make the EVOH layer contain water, and stretching unevenness occurs (the EVOH layer becomes a mesh pattern), and in severe cases it bursts.

It is possible to make a tubular biaxial stretching by making an EVOH resin layer inside and making a non-stretched film by an internal water cooling method to make the EVOH resin layer contain water. At this time, the moisture contained inside is accumulated in the bubble, and the bubble diameter gradually expands, which causes the inconvenience that the folding diameter cannot be controlled.

The stretching temperature in the case of tubular biaxial stretching depends on the cooling degree of the non-stretched film (whether the rapid cooling is slow cooling), the water content of the EVOH resin layer, but it is 100 ° C to 140 ° C, preferably 110 ° C.
~ 130 ° C.

If the stretching temperature is less than 100 ° C, it is difficult to stretch the PP resin layer, and if it is 140 ° C or higher, the stretching of the EVOH resin layer becomes unstable.

About the draw ratio, the longitudinal draw ratio is 2.5-5 times, and the horizontal draw ratio
2.5 to 5 times is possible, but preferably the product of the longitudinal stretching ratio and the lateral stretching ratio is 9 to 25, and the ratio of the longitudinal stretching ratio to the lateral stretching ratio is
It is desirable to be 1: 1 to 1.2: 1. The heat treatment can be performed by any method such as a tenter type, a roll type, and a tubular type, and the temperature condition is preferably 140 ° C. or higher and 160 ° C. or lower. When the temperature is 140 ° C or lower, the oxygen barrier property is not improved so much, and when the temperature is 160 ° C or higher, the melting point of the PP resin is close, which is not preferable.

As a method for producing an unstretched film, it has been described that the downward external water cooling method is adopted, but an inside mandrel for cooling the inside of the tube may be used in combination with the external water cooling method.

The thickness of each layer of the film after biaxial stretching depends on the application, but the thickness ratio of each is (A) :( B) :( C) = 1 to 1.5:
A laminated biaxially stretched film having a thickness of 0.2 to 3: 8.8 to 5.5 and a total thickness of 10 μm to 40 μm.
A laminated biaxially stretched film characterized in that a non-stretched film is produced by a downward external water-cooled inflation method, and the EVOH resin layer is hydrated and then applied to a tubular biaxial stretching machine and then heat-treated. Is.

Next, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to these Examples as long as the gist thereof is not exceeded. Example 1 Conditions for producing unstretched film (coextrusion multilayer) Water-cooled inflation film) [Extruder] Outer layer extruder (EVOH layer): 35 mmφ, L / D = 22, compression ratio = 3.0 Intermediate layer extruder (adhesive resin layer): 40 mmφ, L / D = 26, compression ratio = 3.5 Inner layer extruder (PP layer): 40mmφ, L / D = 26, compression ratio = 3.5 [Dies] 3-layer die: 75mmφ, CL = 1.2mm, Tommy Machine Industry KK
Manufacturing, Die temperature: 230 ℃ [Extruder] kg / hr Outer layer: Middle layer: Inner layer = 1kg: 1kg: 8kg [Film folding diameter, thickness] 110mm, 250μ [Water temperature, water content] Cooling water temperature of external water cooling flu: 10 ° C EVOH resin layer water content adjusted to 8 wt% [Raw material resin] Outer layer: EVOH resin: Nippon Gohsei Co., Ltd., trade name "Soarnol ET" Ethylene content 38 mol% MP 173 ° C MFI (210 ° C) 4.0 Middle layer: Adhesive resin: Mitsubishi Kasei Co., Ltd., trade name "NOVATEC AP196P" Adhesive polymer based on polypropylene Density 0.89 MP 140 ℃ MFI (230 ℃) 2.6 Inner layer: PP resin: Mitsubishi Kasei ( Co., Ltd., product name "NOVATEC
-P1220F "Density 0.90 MP 165 ° C MFI (230 ° C) An unstretched film was prepared under the conditions of 2.0 or higher.

[Tubular biaxial stretching conditions]

Delivery speed (low speed side) 3m / min Pulling speed (high speed side) 10.5m / min Preheating cylinder: Diameter 200φ, height 1m Heating method Hot air air ring method Air volume 6m ³ / min Hot air temperature 140 ℃ Film temperature at stretching point 131 ℃ Stretching ratio Vertical 3.5 times Horizontal 3.5 times [Heat treatment conditions] The tubular biaxially stretched film was subjected to a batch type oven heat treatment immediately after stretching.

The film having a heat treatment temperature of 160 ° C. and a heat treatment time of 10 seconds or more had good transparency and was beautiful without stretching unevenness.

Table 1 shows the evaluation of physical properties of the obtained film.

The evaluation was performed by the following method.

Optical properties Haze: Comply with JIS K6714 (23 ℃, 65% R
H) Tensile strength and elongation According to JIS K6782 (23 ℃, 65% R
H) Oxygen permeability According to JIS K1707 (23 ℃, 0% R
H) As shown in Table 1, the laminated biaxially stretched film had good transparency, stable stretchability, and excellent oxygen barrier property.

Example-2 The procedure of Example-1 was repeated except that the water content of the EVOH resin layer of the unstretched film was changed to 12 wt% and the stretching ratio was changed to 3.7 times and 3.7 times. The results were as shown in Table 1 and good films were obtained.

Comparative Example-1 The procedure of Example-1 was repeated except that the water content of the EVOH resin layer of the unstretched film was changed to 3% by weight. The results are as shown in Table 1 and there was uneven stretching and the transparency was poor.

Comparative Example-2 The resin composition of the unstretched film was reversed from that of Example-1, and EV
Example 1 was repeated except that the water content of the OH resin layer was 0%. The results are as shown in Table 1, and the stretching unevenness was severe, sometimes the tearing occurred at the time of stretching, and the stretched film had a mesh-like unevenness, resulting in poor transparency.

Reference Example Table 1 shows the evaluation results of commercially available K-OPP. As can be seen from the above, the film of the present invention has almost the same transparency,
It had an excellent oxygen barrier property.

〔The invention's effect〕

The film obtained by the production method of the present invention has excellent gas barrier properties, has no odor and discoloration, and is very suitably used as various packaging films for food packaging and the like.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 54-41972 (JP, A) JP 57-131523 (JP, A) JP 62-268621 (JP, A) JP 53- 142482 (JP, A)

Claims (4)

[Claims] 1. When producing a laminated biaxially stretched film having a saponified ethylene-vinyl acetate copolymer (resin A) layer and a polypropylene-based resin (resin B) layer, the resin A is coextruded from the outside. , The adhesive layer, and the resin B are laminated in this order, extruded downward in the form of a tube, and rapidly cooled with cooling water from the outside to obtain a non-stretched film, and the water content of the resin A layer of the obtained tubular non-stretched film is After performing tubular biaxial stretching to 5 to 15% by weight, 140 to 160
A method for producing a laminated biaxially stretched film, which comprises heat treatment at a temperature of ° C. 2. The method according to claim 1, wherein the resin A is a saponified ethylene-vinyl acetate copolymer having an ethylene content of 25 to 50 mol% and a saponification degree of 90% or more. 3. The production method according to claim 1, wherein the resin B is made of polypropylene or a mixture of polypropylene and another polyolefin. 4. The method according to claim 1, wherein the adhesive layer is a polyolefin graft-modified with an unsaturated carboxylic acid.