JPH0529537B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a laminated biaxially stretched film having excellent gas barrier properties. Specifically, the present invention relates to a laminated biaxially stretched film suitable for use in food packaging, etc., 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 is rapidly growing, surpassing the cellophane film market. but
Since OPP film itself has poor gas barrier properties against oxygen and other gases, OPP coated with polyvinylidene chloride (PVDC) (commonly known as K-OPP) is mainly used in food packaging and other packaging fields. However, PVDC
Although it has good gas barrier properties (particularly low humidity dependence), it has problems such as odor, discoloration, damage to incineration channels when discarded, and air pollution. EVOH film is used in various fields because of its excellent gas barrier properties, odor, discoloration, and incineration properties, but it is not used alone because of its poor water resistance and heat sealability. It has generally been used by laminating layers by extrusion lamination, dry lamination, coextrusion lamination, or the like. However, these methods have limitations in reducing the thickness of the EVOH resin layer, which is economically disadvantageous. Particularly when attempting to use an EVOH resin layer with a thickness of several microns below 10 microns, it is difficult to produce a single EVOH film beautifully due to problems such as wrinkles and film breakage. Furthermore, when the EVOH resin layer was made several microns thick, there was a problem that the gas barrier properties were poor. The following documents are known regarding film technology using EVOH resin. JP-A-51-6276: After closely laminating an EVOH resin layer and another stretchable thermoplastic film,
There is a description that the EVOH resin layer to be stretched is uniformly stretched and thinned by a biaxial stretching method, but the thinned biaxially stretched EVOH resin layer can be wound into a long length without wrinkles and used as a single layer film. is difficult. JP-A-52-15570: Description of a final biaxial stretching method in which a water-impregnated EVOH resin layer is stretched in one direction, further stretched in a direction perpendicular to the stretching direction while changing the stretching temperature, and then heat treated. However, if the film is made as thin as a few microns, it is difficult to wind it up into a long length without wrinkles, and similarly to the above, it is difficult to use it as a single layer film. JP-A-52-54784: A film in which an adhesive resin layer and an EVOH resin layer are laminated on a uniaxially stretched polypropylene resin layer (hereinafter referred to as PP) is extrusion laminated, and then the EVOH layer is There is a description of a final biaxial stretching method in which the EVOH resin layer is subjected to hydrous treatment and then stretched using a tenter method.
However, since it is supported by the PP resin layer, there will be no wrinkles, and the problems caused by thinner walls are thought to be solved. JP-A-52-57274, JP-A-53-142882: Same technique as above JP-A-55-2075: PP resin layer and adhesive resin layer are coextruded, this is uniaxially stretched, and EVOH resin is applied on top of it. There is a description of a final biaxial stretching method in which layers are extrusion laminated and the film is stretched in the orthogonal direction. The above method is based on a 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 film. JP-A-52-129777, JP-A-57-25920: Method of impregnating an EVOH resin layer with water and subjecting it to tubular biaxial stretching. JP-A-57-41924: Polyamide resin and
A method of coextruding EVOH resin and tubular biaxial stretching. [Problems with the prior art] When attempting to achieve the object of the present invention using the prior art method described above, there is a temporary biaxial stretching method mainly based on the T-die method, but this method has the following problems. There is a point. In other words, because the stable stretching ratio of EVOH resin film (the ratio that eliminates netting and eliminates thickness unevenness) and the stable stretching ratio of PP resin film are different, (The product of these is 10 to 20, preferably 12 to 16, whereas the product of the stable stretching ratios of the PP resin film is 30 to 55.) The two stretching ratios do not match, resulting in poor moldability. For this reason, it is necessary to improve one or both of the resins by adding an elastomer that eliminates netting at low stretching ratios, or to use PP resin (graft-modified products are also possible) and EVOH resin as in ``JP-A-52-146487''. Stretching a film co-extruded with
As disclosed in ``JP-A-52-103481,'' a method is used in which a PP resin (graft-modified product) is placed on both sides and an EVOH resin is used as an intermediate layer, and the EVOH resin is melted during stretching to match the stretching ratio. Furthermore, for example, ``Japanese Patent Application Laid-Open No. 58-89325'' states that when a film made by coextrusion or extrusion lamination of PP resin (graft-modified product) and EVOH resin is biaxially stretched, there is a strong tendency for whitening and cracking of the EVOH resin to occur. There is also a statement that the effect only occurs when PP resin (graft modified product) is laminated on both sides of the resin layer. [Object of the invention] The present invention consists of an EVOH resin and a PP resin,
The object of the present invention is to obtain a laminated film having a sufficiently thin EVOH layer, excellent gas barrier properties, no odor or discoloration, and easily incinerated, and suitable for use as a base material for dry lamination and extrusion lamination. The gist of the present invention is to produce a laminated biaxially stretched film having a saponified ethylene-vinyl acetate copolymer (EVOH) layer as a surface layer, by extruding the EVOH layer in a tube shape as an inner surface layer by coextrusion molding, By bringing cooling water into direct contact with the EVOH layer and rapidly cooling it, an unstretched laminated film with an EVOH layer water content of 5 to 15% by weight is obtained.The obtained tubular unstretched laminated film is subjected to tubular biaxial stretching, and then The present invention relates to a method for producing a laminated biaxially stretched film, which is characterized by heat treatment at a temperature of 140 to 160°C. In the present invention, the EVOH resin is not particularly limited as long as it is manufactured by a known method, and it may have an ethylene content of 25 to 50 mol%, a degree of saponification of 90% or more, and a high oxygen barrier property. There is no particular 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 graft modification include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid, and among these, maleic anhydride is preferred. The amount of graft modification is in the range of 0.05 to 5 parts by weight per 100 parts by weight of the polymer. PP resin can be PP resin alone or a mixture, and also
Any mixture of PP resin and other polyolefin resin with a polypropylene resin component of 70 wt% or more is acceptable, but PP resin is preferred, and propylene homopolymers, propylene and ethylene, butene, Examples include copolymers with α-olefins other than propylene such as hexene. Various additives may be mixed into the above polymer depending on the purpose. The feature of the manufacturing method of the present invention is that the Γ tubular biaxial stretching method is selected to suppress the evaporation of water due to preheating etc. during stretching from the EVOH layer, and to match the stable stretching ratio with the PP layer. The tubular biaxial stretching method was selected because the ΓEVOH layer is difficult to be drawn using the simultaneous biaxial stretching method and the simultaneous biaxial stretching method is suitable. In the process of making an unstretched film, the ΓEVOH layer is used as an inner layer, and an internal water cooling method is selected to rapidly cool the film.
Making EVOH hydrated makes it easier to stretch the EVOH layer. By the way, when EVOH is rapidly cooled, it easily absorbs water, and when it is slowly cooled, the water content decreases. When the ΓEVOH layer and PP resin are coextruded with adhesive resin, the adhesive strength is
The adhesive strength is much greater when using the water-cooling method than when making an unstretched film, and the same tendency remains in the adhesive strength after stretching. , the adhesive force is higher when slowly cooled than when rapidly cooled, and the same trend is observed in air-cooled inflation molding. Adhesive strength increases only when cooled (quenched) by contact with water. Although there are various theories, the reason for this is currently unknown. ] Since ΓEVOH resin is used in a thin wall (several microns),
It was necessary to improve oxygen gas barrier properties, and the barrier properties were improved by combining the effects of biaxial stretching treatment and heat treatment. By discovering the above, we were able to complete the first K-OPP-like film. The tubular biaxial stretching method is not particularly limited as long as it is a conventionally known method, but it is preferable to control the temperature (preheating, stretching, cooling, heat treatment) more precisely. The water content of the EVOH resin layer when creating an unstretched film is affected by the cooling water temperature, amount of cooling water, and contact time with the cooling water during cooling. Few. In the case of the present invention, it is desirable to perform rapid cooling as much as possible in the process of producing an unstretched film. When performing tubular biaxial stretching, the water content of the EVOH layer is important. The moisture content can be controlled under the cooling conditions mentioned above, and EVOH
By controlling the water content of the layer, smooth stretching is possible. When impregnating an unstretched film with water, it is very important to do so evenly. When a three-layer unstretched film is subjected to tubular biaxial stretching, the water content of the EVOH resin layer is 5 to 15% by weight (wt), preferably 8 to 12% by weight. 5wt%
If it is less than 15wt%, the water will not have a plasticizing effect and a uniform stretched film will not be produced, and if it is more than 15wt%, the adhesive strength between the EVOH resin layer and the adhesive resin layer may decrease, and in some cases, bubbles may occur. There is. In this way, to adjust the water content of the EVOH layer,
The EVOH layer must be located inside the tube. The stretching temperature for tubular biaxial stretching is
The degree of cooling of the unstretched film (quick cooling or slow cooling),
100℃ depending on the moisture content of the EVOH resin layer
~140°C, preferably 110°C to 130°C. If the stretching temperature is less than 100°C, it becomes difficult to stretch the PP resin layer, and if the stretching temperature is 140°C or higher, the stretching of the EVOH resin layer becomes unstable. Regarding the stretching ratio, a longitudinal stretching ratio of 2.5 to 5 times and a horizontal stretching ratio of 2.5 to 5 times are possible, but preferably the product of the longitudinal stretching ratio and the horizontal stretching ratio is 9 to 25, and the ratio of the longitudinal stretching ratio and the horizontal stretching ratio is It is desirable that the ratio is 1:1 to 1.2:1. Heat treatment can be carried out by any method such as a tenter method, a roll method, or a tubular method, and the temperature condition is preferably 140° C. or higher and 160° C. or lower. If it is below 140°C, the oxygen barrier property will not be improved much, and if it is above 160°C, the melting point of the PP resin will be close to each other, which is not preferable. As for the method of producing unstretched film, we have described the use of a downward internal water cooling method, but the internal water cooling method involves circulating cooling water using an inside mandrel so that the cooling water directly contacts the EVOH layer (inner layer). It is desirable to use both methods.
It is also preferable to rapidly cool the film from the outside using a water cooling method. The thickness of each layer of the film after biaxial stretching depends on the application, but the thickness of the EVOH layer on the inner surface layer is 1 to 1.
10μ, preferably about 2 to 5μ, with a total thickness of 10μ to
It is a laminated biaxially stretched film with a thickness of about 50μ, preferably about 15μ to 40μ. The present invention relates to a laminated biaxially stretched film characterized in that it is subjected to a heat treatment after being placed in a stretching machine. Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples as long as the gist thereof is not exceeded. Example 1 Conditions for creating an unstretched film (coextruded multilayer water-cooled blown film) [Extruder configuration] Outer layer extruder (PP layer): 40 mmφ, L/D = 26, compression ratio = 3.5 Middle layer extruder (adhesive resin) Layer): 35mmφ, L/D
= 22, compression ratio = 3.0 Inner layer extruder (EVOH layer): 19mmφ, L/D = 22,
Compression ratio = 3.0 [Dice] 3-layer die: 75mmφ, die slit gap (CL)
= 1.2mm, Tomy Kikai Kogyo die temperature: 230℃ [Extrusion amount] Outer layer: Intermediate layer: Inner layer = 8Kg/hr: 1Kg/hr: 1
Kg/hr [Film folded diameter, thickness] Folded diameter: 110mm, thickness: 250μ [Cooling conditions] Internal and external water cooling mandrels and water tank (external cooling) used. Cooling water temperature of internal and external mandrels: 20℃ Contact time between EVOH layer and water: 24 seconds Cooling water temperature of water tank: 65℃ Cooling time in water tank: 60 seconds [Raw material resin] Outer layer: PP resin: Mitsubishi Chemical ( Ltd., product name: "Mitsubishi Polypro/1220F" Density: 0.90 g/cm ³ Melting point: 165°C MFI (230°C): 2.0 g/10 minutes Intermediate layer: Adhesive resin: Mitsubishi Kasei Ltd., product name "NOVATEC・AP196P" Adhesive polymer mainly composed of polypropylene Density: 0.89 g/cm ³ Melting point: 140°C MFI (230°C): 2.6 g/10 minutes Inner layer: EVOH resin: Made by Nippon Gosei Co., Ltd., product name: "Soarnol ET" Ethylene content: 38 mol% Melting point: 173°C MFI (210°C): 4.0g/10 min MFI (melt flow index) indicates that PP and adhesive polymer are
According to , EVOH is JIS K7210 (210℃, 2.16Kg)
Compliant with. Under the above conditions, an unstretched EVOH film with a moisture content of about 8% by weight was produced. [Tubular biaxial stretching conditions] Delivery speed (low speed side) 3 m/min Take-up speed (high speed side) 10.5 m/min Preheating tube: diameter 200φ, height 1 m Heating method Hot air air ring method Air volume 6 m ³ /min Hot air temperature 140 C. Film temperature at the stretching point: 129.degree. C. Stretching ratio: 3.5 times vertically, 3.5 times horizontally [Heat treatment conditions] Immediately after stretching, the tubular biaxially stretched film was subjected to oven heat treatment in batch mode. The film that was heat-treated at a temperature of 160° C. and for a heat treatment time of 10 seconds or more had good transparency and was beautiful with no uneven stretching. Table 1 shows the evaluation of the physical properties of the obtained film.
The evaluation was conducted using the following method. Optical properties Haze: According to JIS K6714 (23℃,
65%RH) Tensile strength According to JIS K6782 (23℃, 65%RH) Oxygen permeability
According to JIS K1707 (23°C, 0% RH) As shown in Table 1, the laminated biaxially stretched film had good transparency, stable stretchability, and excellent oxygen barrier properties. Example 2 The procedure was the same as in Example 1 except that the cooling water temperature of the water-cooled mandrel was 10° C. and the cooling time in the cooling layer was 80 seconds, and the water content of the EVOH resin layer of the unstretched film was 12 wt%. Stretching ratio: 3.7x vertically, horizontally
The stretching conditions were the same as in Example 1, except that the stretching was 3.7 times. The results are shown in Table 1, and a good film was obtained. Example 3 The conditions for producing a non-stretched film (coextruded multilayer water-cooled inflation film) were as follows. Outer layer extruder (EVOH layer): 40mmφ, L/D=26,
Compression ratio = 3.5 Intermediate layer extruder (adhesive resin layer): 35mmφ, L/D
= 22, compression ratio = 3.0 Inner layer extruder (EVOH layer): 19mmφ, L/D = 22,
Compression ratio = 3.0 [Dice] 3-layer die: 75mmφ, CL = 1.2mm, Tomy Machine Industry Co., Ltd. die temperature: 230℃ [Extrusion amount] Outer layer: Middle layer: Inner layer = 1Kg/hr: 8Kg/hr: 1
Kg/hr [Film folding diameter, thickness] Folding diameter: 110mm, thickness: 250μ [Cooling conditions] Internal and external water cooling mandrel and water tank used. Cooling water temperature of internal and external mandrels: 10°C Cooling water contact time with mandrel: 24 seconds Cooling water temperature of water tank: 65°C Cooling time in water tank: 60 seconds [Raw material resin] Same as Example 1. used. The resulting unstretched film has an outer layer EVOH of 8.
% by weight, and the EVOH of the inner layer had a moisture content of 10% by weight. The stretching conditions and heat treatment conditions were also the same as in Example 1. Table 1 shows the results of evaluating the physical properties of the obtained stretched film. Example 4 The conditions for creating an unstretched film (coextruded multilayer water-cooled inflation film) were as follows: outer layer/resin adhesive layer/intermediate layer/
A resin adhesive layer/inner layer composition was used, and film molding was performed. Outer layer/inner layer extruder (EVOH layer): 40mmφ, L/D
= 26, compression ratio = 3.5 Middle layer extruder (PP layer): 35mmφ, L/D = 22, compression ratio = 3.0 Middle/inner/outer layer extruder (adhesive resin layer): 19mmφ,
L/D = 22, compression ratio = 3.0 [Dice] Three types of 5-layer die: 75 mmφ, CL = 1.2 mm, Tomy Machine Industry Co., Ltd. die temperature: 230°C [Extrusion amount] Outer layer: Resin Adhesive layer: Intermediate layer: Resin Adhesive layer: Inner layer 1Kg/hr: 0.5Kg/hr: 7Kg/hr: 0.5Kg/hr: 1
Kg/hr [Film folding diameter, thickness] Folding diameter: 110mm, thickness: 250μ [Cooling conditions] Internal and external water cooling mandrel and water tank used. Cooling water temperature of internal and external mandrels: 10°C Cooling water contact time with mandrel: 24 seconds Cooling water temperature of water tank: 65°C Cooling time in water tank: 60 seconds [Raw material resin] Same as Example 1. used. The resulting unstretched film has an outer layer EVOH of 8.
% by weight, and the EVOH of the inner layer had a moisture content of 10% by weight. The stretching conditions and heat treatment conditions were also the same as in Example 1. Table 1 shows the evaluation of the physical properties of the obtained stretched film. Comparative Example 1 In Example 1, after cooling with the cooling mandrel, the temperature of the cooling water in the water tank was set to 23°C, and cooling was performed for 60 seconds to obtain an unstretched film with an EVOH layer water content of 3% by weight. Stretching and heat treatment were carried out in the same manner. The results are shown in Table 1. Comparative Example 2 In Example 1, only cooling water was passed through the inner cooling mandrel, the cooling water was not allowed to flow down to the outer surface of the inner cooling mandrel, and the EVOH layer was cooled so as not to come into contact with the water. An unstretched EVOH film with a moisture content of 0% by weight was obtained, and stretched and heat treated in the same manner as in Example 1. The results are shown in Table 1. Reference Example Table 1 shows the evaluation results of commercially available K-OPP.
As can be seen from the above, the films of the present invention had substantially the same transparency and excellent oxygen barrier properties.

【table】

〔Effect of the invention〕

The film obtained by the production method of the present invention has excellent gas barrier properties, is free from odor and discoloration, and is very suitable for use as various packaging films such as food packaging.

Claims (1)

[Claims] 1. In producing a laminated biaxially stretched film having a saponified ethylene-vinyl acetate copolymer (EVOH) layer as a surface layer, the EVOH layer is extruded in a tube shape as an inner surface layer by coextrusion molding. ,
By bringing cooling water into direct contact with the EVOH layer and rapidly cooling it, an unstretched laminated film with an EVOH layer water content of 5 to 15% by weight is obtained.The obtained tubular unstretched laminated film is subjected to tubular biaxial stretching, and then A method for producing a laminated biaxially stretched film, characterized by heat treatment at a temperature of 140 to 160°C. 2 The EVOH layer has an ethylene content of 25 to 50 mol%,
The manufacturing method according to claim 1, wherein the layer is made of a saponified ethylene-vinyl acetate copolymer having a degree of saponification of 90% or more. 3. The manufacturing method according to claim 1, wherein the layer laminated with the EVOH layer is made of polypropylene or a mixture of polypropylene and other polyolefin. 4. The manufacturing method according to claim 1, wherein the adhesive layer that adheres the EVOH layer and other layers is a polyolefin graft-modified with an unsaturated carboxylic acid.