JP2699001B2 - Manufacturing method of laminated biaxially stretched film - Google Patents

Description

The present invention relates to a method for producing a laminated biaxially stretched film having excellent gas barrier properties by an inflation method, in particular, a saponified ethylene-vinyl acetate copolymer (hereinafter, referred to as "the saponified product"). EVOH
Abbreviated as "), and a method for producing a laminated biaxially stretched film suitable for use in food packaging and the like.

(Prior Art) Some of the present inventors consisted of an EVOH layer and a layer of a polypropylene-based resin (hereinafter abbreviated as a PP-based resin). The EVOH layer was sufficiently thin and had a gas barrier. There is no peculiar smell, no discoloration, no problems such as damaging the incinerator when discarded, and gas barrier properties, as in the case of using polyvinylidene chloride, which is well known to impart properties. With the purpose of obtaining a laminated film with excellent
A method for producing a laminated biaxially stretched film having a PP-based resin layer has been invented (see JP-A-1-108028). That is, the present invention provides a non-stretched film by extruding a downward tubular laminate in the order of lamination of an EVOH layer, an adhesive layer, and a PP-based resin layer from the outside by coextrusion molding, and quenching with cooling water from the outside. The tubular unstretched film is obtained, the EVOH layer is subjected to tubular biaxial stretching with a water content of 5 to 15% by weight, and then heat-fixed. It has the following features.

(B) The tubular biaxial stretching method was selected and the stable stretching ratio of the EVOH layer and the PP resin layer was matched.

(B) The tubular biaxial stretching method was selected because it is difficult to stretch the EVOH layer by the sequential biaxial stretching method and the simultaneous biaxial stretching method is suitable.

(C) The external direct water-cooling method was used in the process of making a non-stretched film by using the EVOH layer as the outer layer, and quenching was performed at the same time that the EVOH layer was made to contain water to facilitate the stretching of the EVOH layer.

(D) When the EVOH layer and the PP-based resin layer were co-extruded with an adhesive resin, the adhesive strength was determined by an external water-cooling method using an inflation method rather than using a T-die molding method to form a laminated unstretched film. Is much larger, and the adhesive strength after stretching remains the same.

(E) Since the EVOH layer is thin (several μ), it is necessary to increase the oxygen gas barrier property. The barrier property is improved by combining the biaxial stretching effect and the heat treatment effect.

(Problem to be Solved by the Invention) The method for producing a laminated biaxially stretched film disclosed in the above-mentioned publication has the useful features as described above, but is uniformly stretched without thickness unevenness. There is a problem that a film cannot be obtained, and it is necessary to solve such a problem.

(Means for Solving the Problems) In the case of using the method described in the above-mentioned publication, the results of various studies were repeated in order to investigate the cause of a failure to obtain a uniformly stretched film without thickness unevenness. The following turned out. That is, when the laminated film is manufactured by co-extrusion molding by an inflation method such that the EVOH layer is on the outside and the PP resin layer is laminated thereon, the resin tube is extruded downward, and the EVOH layer of the outer layer of the tube is formed. It is preferable that the cooling water is brought into direct contact with the cooling water for rapid cooling. Since the EVOH layer is hydrophilic, this layer is hydrated, but the water content of the EVOH layer is adjusted to 5 to 15% by weight in biaxial stretching. The reason that the water content is kept in this range is that if the water content is less than 5% by weight, the plasticizer effect by water is not exhibited, and it is difficult to obtain a uniform stretched film. %, The adhesive force between the adhesive resin layer and the adhesive resin layer interposed for laminating the PP-based resin is reduced, or bubbles may be generated in some cases.

As described above, when performing tubular biaxial stretching, the water content of the EVOH layer needs to be within the range of 5 to 15% by weight. On the other hand, as described above, the tube extruded by the co-extrusion molding is cooled by direct contact with the cooling water, and as a result, the water content of the EVOH layer may be 5 to 15% by weight. Is less than 5% by weight. Therefore, in order to increase the water content of the EVOH layer, the EVOH layer is passed through a hot water bath or brought into contact with heated steam so that the EVOH layer has a required water content. However, as a result of these treatments, water remains on the surface of the outer EVOH layer of the extruded tube in the form of droplets, and the remaining water droplets are then successively absorbed by the EVOH layer, The water content at this point locally increases.

That is, when the water content of the EVOH layer is adjusted to a desired range, there is no significant change even if there is a slight fluctuation locally. However, due to the sequential absorption of residual water droplets, uneven water content occurs, and this is uneven thickness during tubular biaxial stretching.
This has been considered to be a cause of uneven stretching. Thus
After adjusting the water content of the EVOH layer, the inventor found that it is sufficient to remove the remaining water droplets promptly and completed the present invention.

That is, the gist of the present invention is that the film in which the saponified layer of the ethylene-vinyl acetate copolymer is used as the outer layer by the inflation method and co-extrusion molding and the polypropylene-based resin layer is laminated thereon is extruded downward in a tubular shape. Then, cooling water was brought into direct contact with the outer layer of the extruded tube to obtain a non-stretched film by cooling, and the moisture content of the saponified ethylene-vinyl acetate copolymer layer of the outer layer of the obtained tubular unstretched film. In a method for producing a laminated biaxially stretched film in which tubular biaxial stretching is performed with 5 to 15% by weight, before performing the tubular biaxial stretching,
The method is characterized in that an outer layer of a tubular unstretched film is brought into contact with a water-absorbing device, water droplets adhering on the outer layer are absorbed, and the remaining water droplets have a diameter of 0.5 mm or less.

The resin for forming the EVOH layer in the present invention may be a resin produced by a conventionally known method, having an ethylene content of 25 to 50 mol%, a saponification degree of 90% or more, and a high oxygen barrier property. Is useful.

As the resin forming the PP-based resin layer in the present invention,
In addition to homopolymers of propylene, a mixture containing polypropylene as a predominant amount (for example, 70% by weight or more), such as a mixture of polypropylene and another polyolefin resin, or other monomers containing propylene as a predominant amount, such as ethylene, butene, Copolymers with hexene and the like can be mentioned. A commonly used additive may be appropriately added to these polymers.

As an adhesive for forming an adhesive layer for laminating the EVOH layer and the PP-based resin layer, one that strongly adheres the EVOH layer and the PP-based resin layer is used, and specifically, a polyolefin resin (particularly preferable) Preferably, polypropylene is graft-modified with an unsaturated carboxylic acid (or anhydride thereof) such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, or the like. Particularly preferred are those obtained by modifying polypropylene with maleic anhydride. The graft modification amount is preferably in the range of 0.05 to 5 parts by weight based on 100 parts by weight of the polymer.

In the method of the present invention, it is conventionally known that a film in which an EVOH layer is formed as an outer layer, and a PP-based resin layer is laminated on the outer layer through an adhesive layer made of the above-mentioned adhesive by a co-extrusion molding, is downwardly formed in a tubular shape. What is necessary is just to carry out according to the inflation-type coextrusion molding method used.

The extruded tubular film is cooled by bringing cooling water into direct contact with the outer layer. The water content of the EVOH layer is affected by the cooling water temperature during cooling, the amount of cooling water, and the contact time with the cooling water. The water content of the rapidly cooled product is high, and that of the slowly cooled product is low. In the case of the present invention, rapid cooling is preferred. Then, at the time of inflation molding, it is preferable that the film is cooled from the inside by using an inside mandrel, in addition to directly cooling the outer layer of the formed tube with an outside mandrel.

When performing tubular biaxial stretching, the water content of the EVOH layer is
As mentioned earlier, it must be 5 to 15% by weight, preferably 8 to 12% by weight. Therefore, the moisture content of the outer EVOH layer in the laminated unstretched film before the tubular biaxial stretching treatment must be within the above range. Thus, if the water content of the EVOH layer of the laminated unstretched film extruded by the inflation method and quenched by water is within the above range, it is not necessary to further adjust the water content, but generally, the quenching is performed. Even if added, the water content is often less than 5% by weight. In such a case, the water content is increased by immersing in warm water or by contact with warm steam.

For example, EV of unstretched film quenched by cooling water
Measure the water content of the OH layer, and measure the water content of 3.5% by weight at 50 ° C.
The solution was passed through hot water for 40 seconds and taken out to remove water adhering to the surface, whereby a water content of 8.0% by weight was obtained.

The unstretched film obtained in this manner has water droplets adhered to its surface.
Entrapped in the layer, causing uneven moisture content in the EVOH layer. Therefore, in order to remove the attached water droplets, water is removed with a water absorbing tool. This water absorbing device will be described with reference to FIG.

FIG. 1 is an explanatory diagram of an example of a water absorbing tool. In the figure, 2 is a guide roll (for example, a rubber roll), and 3 and 4 are water absorbing rolls. The flatly folded unstretched film 1 continuously fed through an inflation molding device or further a device for adjusting the water content of the EVOH layer is guided by a guide roll 2 as shown in FIG. Water droplets adhering to one surface of the unstretched film 1 are removed, and then, water-absorbing rolls 4 remove water droplets adhering to the other surface of the unstretched film 1 and are sent to a tubular biaxial stretching device. . The water absorbing rolls 3 and 4 have the same structure,
These water-absorbing rolls 3 and 4 are each formed by surrounding a tubular rotating shaft 5 with a plastic sponge 6 made of open cells in a cylindrical shape, and further covering the above with a microfine polyester fiber nonwoven fabric 7 having a high capillary effect. A number of suction holes 8 are provided in the tube wall of the rotating shaft 5, and the rotating shaft 5 is connected to a conduit 9.
When suction is performed in the direction of arrow P by this suction pump, water droplets adhering to the film surface via the suction hole 8, the sponge 6, and the nonwoven fabric 7 are sucked and removed. The water-absorbing roll may be formed by winding the sponge 6 with a non-highly dense nonwoven fabric instead of the sponge. In other words, the sponge 6 may be any as long as the reduced pressure in the rotating shaft 5 passes through the outer peripheral surface of the roll.

Even by the above-described water absorption treatment, the moisture adhering to the surface of the EVOH layer is not necessarily completely removed immediately. However, if the diameter of the attached water droplet (diameter when the water droplet is viewed from above) is as small as 0.5 mm or less, the water content of the EVOH layer will fluctuate greatly even if it is subsequently absorbed into the EVOH layer. Therefore, no unfavorable thickness unevenness or stretching unevenness occurs as a result of the biaxial stretching treatment.

The water-absorbed unstretched film is then subjected to tubular biaxial stretching and heat treatment, and these methods may be performed according to conventionally known methods,
It is preferable to perform the temperature control (preheating, stretching, cooling, heat treatment) more precisely. Stretching ratio is 2.5 to 5 in longitudinal stretching ratio.
Times, the transverse stretching ratio can be 2.5 to 5 times, preferably the product of the longitudinal stretching ratio and the transverse stretching ratio is 9 to 25, and the ratio between the longitudinal stretching ratio and the transverse stretching ratio is 1: 1 to 1.2: 1. Desirably. The stretching temperature is 100 to 140 ° C, preferably 110 to 130 ° C.

After the stretching treatment, heat treatment is performed, and the temperature condition at this time is preferably 140 to 160 ° C.

The thickness of each layer after biaxial stretching depends on the application.
Layer: adhesive layer: PP resin layer thickness ratio is 1 to 1.5: 0.2 to 3: 8.8
It is preferably a laminate having a thickness of about 5.5 and a total thickness of 10 to 40 μm.

(Example) Next, an example of the present invention will be described, but the present invention is not limited by this example unless it exceeds the gist.

Example 1 Production of tubular laminated unstretched film: An outside mandrel (water temperature of about 10 ° C.) equipped with an extruder shown below, coextruding a laminated tube downward, and directly cooling with cooling water, and water and a refrigerant Using a blown film manufacturing apparatus having an inside mandrel (water temperature of about 10 ° C.), a laminated unstretched film was manufactured under the following conditions.

(Extruder) Outer extruder (EVOH layer): 35mmφ, L / D = 22, compression ratio = 3.0 Intermediate layer extruder (adhesive resin layer): 40mmφ, L / D = 26, compression ratio = 3.5, interior extrusion Machine (PP layer): 40mmφ, L / D = 26, compression ratio = 3.5 (die) Three-layer die: 75mmφ, clearance = 1.2mm, manufactured by Tommy Machine Industry Co., Ltd. Die temperature: 230 ° C (extrusion amount) kg / Hour, outer layer: middle layer: interior = 1 kg: 1 kg: 8 kg (folded diameter and thickness of the obtained unstretched film) 110 mm, 250 μ (raw resin) Outer layer (EVOH resin): Nippon Gosei Co., Ltd., trade name “ Soarnol ET ”ethylene content 38 mol%, saponification degree 98% or more, MP173 ° C, MFI (210
℃) 4.0, Intermediate layer (adhesive resin): Adhesive polymer made by Mitsubishi Kasei Corporation, trade name “Novatech AP196P” polypropylene modified with maleic anhydride, density 0.89, MP140 ° C, MFI (230 ° C) 2.6 , Inner layer (PP resin): manufactured by Mitsubishi Kasei Co., Ltd., product name “Novatech-P1220F”,
Density 0.90, MP 165 ° C, MFI (230 ° C) 2.0, Removal of water droplets adhering to the exterior surface: The moisture content in the EVOH layer of the laminated unstretched film obtained by the inflation device as described above was 3.5% by weight. Was. Put this in a bath filled with 50 ° C warm water,
Immerse in the guide roll for about 40 seconds. by this
The water content of the EVOH layer was adjusted to 8.0% by weight. The film whose water content was adjusted as described above was suction-removed using the water-absorbing device shown in FIG. 1, and then sent to a tubular biaxial stretching device, where biaxial stretching was performed under the following conditions. went. In addition, although fine water droplets remained on the outer layer of the film treated with the water absorbing device, each had a diameter of 0.5 mm or less.

 Tubular biaxial stretching: Biaxial stretching was performed under the following conditions.

Delivery speed (low speed side) 3m / min drawing speed (high speed side) 10.5 m / min preheat cylinder: 200 mm, height 1m heating system: hot air Eyaringu system air volume 6 m ³ / min, a hot air temperature of 140 ° C., the film temperature in the stretching point 131 ° C., stretch ratio: 3.5 times longitudinal, 3.5 times transverse Heat treatment: After stretching the biaxially stretched film obtained as described above, oven heat treatment was immediately performed in a batch system.

Heat treatment temperature 160 ° C, heat treatment time 10 seconds, The film obtained as above has good transparency,
The stretchability was also stable, the thickness unevenness was small, and the oxygen barrier property was excellent. Table 1 shows the physical property evaluation of the obtained film.

 These physical properties were evaluated according to the following methods.

Optical properties Haze: According to JIS K6714. (23 ℃, 65% R
H) Tensile strength and elongation: According to JIS K6782. (23 ° C., 65% RH) Oxygen permeability: conformed to JIS Z1707. (23 ° C., 0% RH) The parameter V (%) indicating the thickness unevenness was defined as follows.

The average thickness of the film was measured every 1 cm in the circumferential direction, and the average value of the thicknesses was obtained.

Comparative Example 1 In Example 1, the laminated unstretched film obtained by the inflation device was subjected to warm water treatment to adjust the water content of the EVOH layer to 8% by weight, and thereafter, the attached water droplets on the outer layer surface were absorbed by a water absorbing device. Was suction-removed, but the suction-removal treatment of the attached water droplets was not performed, and the other steps were the same as in Example 1 to obtain a laminated biaxially stretched film. Table 1 shows the physical property evaluation results of the obtained films. As is clear from this table,
The thickness unevenness was large, and stretching unevenness was present, and thus it was unsuitable as a packaging film.

(Effects of the Invention) According to the method of the present invention, a stretched biaxially stretched film having excellent gas barrier properties can be obtained by stretching uniformly without stretching unevenness and laminating an EVOH layer as a gas barrier layer.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an example of a water-absorbing device used for continuously absorbing and removing water droplets adhering to the surface of an unstretched film in the method of the present invention. In the figure, 1 is a film to be treated, 3 and 4 are water absorbing rolls,
5 is a tubular rotating shaft, 6 is a plastic sponge, 7 is a nonwoven fabric surrounding the plastic sponge 6, 8 is a rotating shaft 5
Is a suction hole provided in the wall of the tube.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication B29L 9:00 (72) Inventor Tsuyoshi Shimofuji 1000 Kamoshidacho, Midori-ku, Yokohama-shi, Kanagawa Prefecture Mitsubishi Chemical (56) References JP-A-1-108028 (JP, A) JP-A-2-251418 (JP, A)

Claims (2)

(57) [Claims] 1. A film in which a saponified layer of an ethylene-vinyl acetate copolymer is used as an outer layer and a polypropylene-based resin layer is laminated on the outer layer by inflation and co-extrusion molding, and the film is extruded downward in a tube shape and extruded. Cooling water was brought into direct contact with the outer layer of the above-mentioned tube and cooled to obtain an unstretched film, and the water content of the ethylene-vinyl acetate copolymer saponified layer of the outer layer of the obtained tubular unstretched film was 5 to 15%. In the method for producing a laminated biaxially stretched film in which tubular biaxial stretching is performed by weight percent, the outer layer of the tube-shaped unstretched film is brought into contact with a water-absorbing device and adhered to the outer layer before performing the tubular biaxial stretching. Water droplets to be absorbed and the remaining water droplets have a diameter of 0.5 mm or less. 2. A water-absorbing device comprising a tubular rotating shaft connected to a suction device and having a large number of suction holes in a tube wall, and a water-absorbing material formed of a sponge body or an aggregate of fibers wound around the rotating shaft. The roll-shaped water-absorbing device is rotated and brought into contact with an outer layer surface of a continuously fed unstretched film, and water droplets adhering to the outer layer surface are suctioned and removed. How to describe