JP3796010B2 - Ethylene vinyl acetate copolymer saponified resin sheet and method for producing stretched film thereof - Google Patents

Description

【００４１】
【発明の効果】
以上説明した本発明によれば、高ガスバリヤー性で且つ優れた強靭性を兼ね備えたエチレン酢酸ビニル共重合体けん化樹脂のシート及びその延伸フイルムを安定的に製造することが出来る。すなわち、本発明によれば、特に、食品包装、医療・医薬包装、衣料包装、その他の包装材料として有用な上記のシート及びフイルムを安価に提供することが出来る。従って、本発明の工業的価値は大きい。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ethylene vinyl acetate copolymer saponified resin sheet and a method for producing the stretched film, and more specifically, an ethylene vinyl acetate copolymer saponified resin sheet having high gas barrier properties and excellent toughness. And a method for stably producing the stretched film.
[0002]
[Prior art]
An ethylene vinyl acetate copolymer saponified resin (hereinafter abbreviated as saponified resin) has an extremely excellent barrier property against oxygen gas, and also has excellent transparency and oil resistance. However, the saponified resin has poor thermal stability, and the resin is colored or gel is generated during melt extrusion. And the roughness generate | occur | produces on the surface of the extruded molten resin sheet. In addition, when the resin sheet obtained by cooling is stretched or heat-treated, the gel part breaks, the torque of the extruder increases due to the increase in viscosity, and extrusion may be impossible. It is difficult to perform continuous operation.
[0003]
In order to prevent the adhesion of the resin, the above-mentioned problems include measures such as applying chrome plating to the resin contact portion of the melt extrusion device, and simplifying the shape of the melt line as much as possible to reduce resin retention. However, it is not solved sufficiently.
[0004]
As a method for preventing the generation of the gel as described above, JP-A-53-88067 and JP-B-47-29578 disclose a saponified resin containing 15 to 60 parts by weight of water per 100 parts by weight of resin. A method for producing an unstretched film by melting at 80 to 120 ° C. after melting is described.
[0005]
However, the unstretched film manufactured by the above method is inferior in physical properties such as tensile strength. In order to improve such physical properties, when moisture is removed after extrusion and stretching is performed later, saponification resin is crystallized while moisture is removed, and the subsequent stretching process becomes unstable.
[0006]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and an object thereof is to stably produce an ethylene vinyl acetate copolymer saponified resin sheet having high gas barrier properties and excellent toughness, and a stretched film thereof. It is to provide a manufacturing method.
[0007]
[Means for Solving the Problems]
As a result of various investigations for achieving the above-mentioned problems, the present inventors use a resin whose water content is adjusted to 10 to 50% by weight, and the molten resin sheet is rapidly cooled, whereby the tensile strength after stretching is increased. The present invention has been completed with the idea of improvement. That is, the first gist of the present invention is an ethylene vinyl acetate copolymer having an ethylene content of 10 to 60 mol%, a saponification degree of 90 mol% or more, and a water content of 10 to 50 wt%. A saponified resin is melt-kneaded with a melt-extrusion apparatus, extruded from a die at 90 to 110 ° C., and the extruded molten resin sheet is brought into close contact with a cooling roll of 40 ° C. or less and rapidly cooled. It exists in the manufacturing method of a coalescence saponification resin sheet. And the 2nd summary of this invention exists in the manufacturing method of the ethylene vinyl acetate copolymer saponification resin stretched film characterized by extending | stretching said ethylene vinyl acetate copolymer saponification resin sheet | seat to at least 1 direction.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail. The invention according to the first aspect of the present invention (first invention) comprises melt-extrusion of a saponified resin, and the resulting molten resin sheet is brought into close contact with a cooling roll and rapidly cooled to obtain a resin sheet.
[0009]
The saponified resin is usually produced by saponifying an ethylene vinyl acetate copolymer. The ethylene content in the saponified resin is 10 to 60 mol%, preferably 20 to 50 mol%, and the saponification degree of the vinyl acetate component is 90 mol% or more, preferably 95 mol% or more. When the ethylene content exceeds 60 mol%, properties such as oxygen barrier properties and printability are inferior. On the other hand, when the degree of saponification is less than 90 mol%, oxygen barrier properties and moisture resistance are lowered.
[0010]
In addition, the saponified resin may contain (1) an α-olefin such as propylene, isobutene, α-octene, α-dedecene, α-octadecene, (2) an unsaturated carboxylic acid, a salt thereof, a partial alkyl ester, It may contain a complete alkyl ester, (3) a nitrile such as acrylonitrile, (4) an amide such as a capramide, (5) an anhydride such as maleic anhydride, and (6) an unsaturated sulfonic acid or a salt thereof as a comonomer. .
[0011]
The saponification resin is adjusted to a moisture content of 10 to 50% by weight, preferably 25 to 35% by weight, and is supplied to the melt extrusion apparatus. When the moisture content is less than 10% by weight, the stability effect during extrusion by moisture is small, and conversely, when the moisture content exceeds 50% by weight, the resin and a part of moisture are easily separated during melt extrusion. As a result, extrusion becomes unstable.
[0012]
As a method for adjusting the water content, for example, (1) a method of adjusting drying conditions in the production process of the saponified resin, (2) a method of treating the saponified resin in hot water (retort treatment), (3) A method of kneading a saponified resin and water with a twin screw extruder or the like is mentioned.
[0013]
As the screw of the melt extruder, a general full flight screw can be used. However, in order to improve the kneading effect, a screw with a mixing zone is preferable, and a biaxial melt extruder is more preferable.
[0014]
The melting temperature of the saponification resin until it reaches the die exit described later can be set regardless of the temperature of the saponification resin controlled at the die exit, but melt kneading is sufficient from the viewpoint of thermal degradation of the resin and energy consumption. And lower within the range that can be extruded, for example, 150 ° C. or less.
[0015]
Further, a metering discharge pump such as a gear pump and a filtration device such as a filter can be incorporated in the melt line of the saponified resin as necessary. Further, a T die is usually used as a die that is an extrusion port of the molten resin. At that time, it is preferable to select a die that takes into consideration that the molten resin stays in the lip portion of the die as much as possible.
[0016]
The temperature of the saponification resin when extruding from the die is controlled in the range of 90 to 110 ° C. When the melt kneading temperature exceeds 110 ° C., it is cooled to the above temperature range using a heat exchanger or the like in the melt line before reaching the die outlet. When extrusion temperature exceeds 110 degreeC, when resin is extruded from die | dye, the water | moisture content in resin foams and it is easy to make a hole in a film. Moreover, when extrusion temperature is less than 90 degreeC, since the viscosity of molten resin is high, the load to an extruder becomes large.
[0017]
The molten resin sheet extruded as described above is brought into close contact with a cooling roll of 40 ° C. or less, preferably 35 ° C. or less, and rapidly cooled. When the temperature exceeds 40 ° C., there are the following problems. That is, crystallization does not proceed due to the moisture content of the saponified resin, and as a result, a resin sheet with good transparency can be obtained, and further, the subsequent stretching process can be performed without any problem, but the obtained stretching can be performed. The tensile strength of the film is lowered. The lower limit of the cooling roll temperature is usually about 10 ° C.
[0018]
The invention according to the second aspect of the present invention (second invention) comprises subjecting the sheet obtained by the rapid cooling to stretching treatment. By such stretching, a film having excellent transparency and gas barrier properties and high strength can be obtained.
[0019]
In the case where the stretching process is performed only in the uniaxial direction, the roll stretching method is usually preferably employed. In this case, the stretching temperature is usually 45 to 100 ° C., and the stretching ratio is usually 2.5 to 8 times, preferably 3 to 8 times. When the draw ratio is less than 2.5, the effect of stretching is small and the strength of the stretched film is poor. When the draw ratio exceeds 8 times, the film breaks during stretching, and it is difficult to carry out continuous operation stably for a long time.
[0020]
In addition, when stretching in the biaxial direction, a sequential biaxial stretching method or a simultaneous biaxial stretching method is usually employed.
[0021]
In the case of the sequential biaxial stretching method, a roll type longitudinal stretching machine is usually used as the stretching device for the first stage stretching. In this case, the stretching temperature is usually 40 ° C. to 80 ° C., and the stretching ratio is usually 2.5 to 8 times, preferably 3 to 8 times. For the second stage stretching, a tenter-type transverse stretching machine is usually used as a stretching apparatus. In this case, the stretching temperature is usually 60 ° C. to 100 ° C., and the stretching ratio is usually 2.5 to 8 times, preferably 3 to 8 times.
[0022]
In the case of the simultaneous biaxial stretching method, a tenter type simultaneous biaxial stretching machine is usually used as the stretching device. In this case, the stretching temperature is usually 60 ° C. to 100 ° C., and the stretching ratio is usually 2.5 to 8 times, preferably 3 to 8 times, both vertically and horizontally.
[0023]
In each of the above biaxial stretching processes, when the stretching ratio in each axial direction is less than 2.5 times, the stretching effect is small, the film strength is inferior, and when the stretching ratio exceeds 8 times, the stretching is performed. Film breakage increases, and continuous operation for a long time is difficult in practice.
[0024]
The uniaxial and biaxial stretching temperatures are preferably controlled within the above-described range of the stretching temperature and within a range in which moisture contained in the stretching treatment step can be removed by evaporation as much as possible.
[0025]
The stretched film obtained by stretching as described above becomes a stretched film having excellent dimensional stability by heat treatment thereafter. Such heat treatment is usually performed for 2 to 10 seconds in a range of 110 ° C. or higher and 5 ° C. or lower than the melting point of the saponified resin in the absolutely dry state. By appropriately adjusting the temperature and the treatment time within such a condition range, stretched films having various hot water shrinkage rates can be obtained.
[0026]
The stretched film of the saponified resin obtained as described above has not only inferior oxygen permeability as compared with the conventional stretched saponified resin film, for example, 20 kg in each of the machine direction (MD) and the transverse direction (TD). High tensile breaking strength of / mm ² or more can be realized, and the boil resistance is also improved. That is, according to the present invention, it is possible to obtain a stretched film of a saponified resin that does not impair excellent gas barrier properties and that has improved tensile break strength and boil resistance. It can be used as a packaging material that is very advantageous for product packaging and many other packaging fields.
[0027]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to a following example, unless the summary is exceeded.
[0028]
Example 1
After retorting a saponification resin (“Soarnol DC3203” manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) having an ethylene content of 32 mol% and a saponification degree of 99.5 mol% in hot water at 120 ° C. in a high-pressure vessel for 5 hours, The molten resin was extruded in the form of a strand having an outer diameter of 5 mm from the bottom of the tube, cooled in cold water, and then cut into a length of 5 mm to obtain pellets. The pellets were sprayed with dry air at 30 ° C. for 1 hour to dry the moisture on the surface. The moisture content of this pellet was measured with a moisture meter (FD-620, manufactured by Kett Science Laboratory), and was found to be 30.5% by weight.
[0029]
The pellets described above were supplied to a 65 mm diameter melt extruder equipped with a coat hanger T die, melted and kneaded at 130 ° C, extruded with a 98 ° C molten resin cooled by a heat exchange method, and then cooled to 25 ° C. The molten resin sheet was brought into close contact with the cooling roll having a diameter of 800 mm and quenched to obtain a resin sheet having a thickness of about 300 μm. The obtained resin sheet was heated to 50 ° C., and then stretched 4 times in the length direction (longitudinal direction) with a roll-type stretching machine to obtain a uniaxially stretched film, and then the film temperature was set to 90 ° C. with a tenter device. And stretched 4.5 times in the transverse direction. The obtained stretched film was heat-treated for 4 seconds in hot air at a temperature of 160 ° C. to obtain a biaxially stretched film having a thickness of about 12 μm.
[0030]
The melt extrusion process, stretching process, and heat treatment process as described above were continued for 3 weeks. Meanwhile, as a result of observing roughness of the film surface, generation of gel, torque-up of the stretching apparatus, etc., gel was hardly generated in the melt extrusion process, and the operation could be performed smoothly. The above period is shown in Table 1 as continuous processability.
[0031]
The oxygen transmission rate and tensile breaking strength of the above biaxially stretched film were measured. The oxygen permeability was measured under the condition of 25 ° C. × 50% RH using an oxygen permeability measuring device (“OXTRAN100” manufactured by Modern Control). In addition, the tensile strength at break of the biaxially stretched film was measured using an autograph (manufactured by Shimadzu Corporation) under the conditions of 23 ° C. × 50% RH under conditions of 50 mm between chucks, 10 mm sample width, and 50 mm / min tensile speed. did. The measured value was converted into the load per unit cross-sectional area to obtain the tensile breaking strength, and the results are shown in Table 1.
[0032]
Example 2
In Example 1, melt extrusion, stretching, and heat treatment were performed in the same manner as in Example 1 except that the temperature of the cooling roll used for cooling the molten resin sheet was set to 35 ° C. As a result, melt extrusion, stretching and heat treatment had no problems at all, and almost no gel was generated for 3 weeks after the start of operation, and the operation could be performed smoothly and continuously. The obtained biaxially stretched film was evaluated for oxygen permeability, tensile breaking strength, and continuous processing period, and the results are shown in Table 1.
[0033]
Example 3
70 parts by weight of methanol and 4 parts by weight of sodium hydroxide were added to 40 parts by weight of ethylene vinyl acetate copolymer of 32 mol% of ethylene, and the mixture was heated at 60 ° C. for 3 hours to carry out a saponification reaction. The obtained methanol solution was concentrated so that the saponification resin concentration was 40% by weight, and 26 parts by weight of water was added per 100 parts by weight of the obtained solution to obtain a methanol-water mixed solvent saponification resin solution. The obtained saponified resin had a saponification degree of 98.5 mol% and an ethylene content of 32 mol%.
[0034]
The methanol-water mixed solvent saponified resin solution is extruded from a nozzle having a diameter of 5 mm into a coagulating liquid consisting of a 30 wt% aqueous solution of methanol adjusted to 15 ° C. until the amount of the coagulating liquid becomes 0.1 wt times. Then, it was precipitated and solidified into a strand shape. By immersing this strand in water, the methanol content was sufficiently replaced with water and then cut into pellets. The pellets were sprayed with dry air at 30 ° C. for 4 hours to dry the surface moisture. The moisture content of the pellets was measured with a moisture meter (“FD-620” manufactured by Kett Science Laboratory) and found to be 31.5% by weight.
[0035]
In Example 1, melt extrusion, stretching treatment and heat treatment were performed in the same manner as in Example 1 except that the above pellets were used as the raw material resin. As a result, during the 3 weeks after the start of operation, there was almost no gel generation, and continuous operation could be performed smoothly. The obtained biaxially stretched film was evaluated for oxygen permeability, tensile break strength, film oxygen permeability, tensile break strength, and continuous processing period in the same manner as in Example 1, and the results are shown in Table 1. It was.
[0036]
Comparative Example 1
In Example 1, saponified resin pellets were produced in the same manner as in Example 1 except that the retort condition of the saponified resin was 100 ° C. × 4 hours. The moisture content of the dried saponified resin pellets was 8% by weight. Using the pellets, melt extrusion was carried out in the form of a sheet in a 65 mm diameter extruder in the same manner as in Example 1. However, unless the temperature was raised, the resin did not melt, and as a result, the resin temperature at the die exit became 125 ° C., and the film foamed and perforated frequently.
[0037]
Comparative Example 2
In Example 1, melt extrusion, stretching treatment and heat treatment were performed in the same manner as in Example 1 except that the cooling roll temperature was 70 ° C. Melt extrusion, stretching treatment and heat treatment could be carried out without any problem, and almost no gel was generated even after 3 weeks from the start of extrusion, and the operation could be performed smoothly. The obtained stretched film was evaluated for oxygen permeability, tensile strength at break, and continuous processing period, and the results are shown in Table 1. As a result, the tensile strength at break was extremely low.
[0038]
Comparative Example 3
An ethylene vinyl acetate copolymer saponification resin (“Soarnol DC3203” manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) (water content 0.5 wt%) having an ethylene content of 32 mol% and a saponification degree of 99.5 mol% is used as it is without retorting. It was supplied to an extruder with a diameter of 65 mm equipped with a coat hanger T die, melt extruded at a resin temperature of 230 ° C., and quenched with a cooling roll cooled to 25 ° C. to obtain a resin sheet having a thickness of about 135 μm.
[0039]
The obtained resin sheet was heated to 60 ° C., then stretched 3 times in the longitudinal direction by a roll type stretching machine, then heated to 90 ° C., then stretched 3 times in the transverse direction, and further 160 ° C. Was subjected to heat treatment for 4 seconds to obtain a biaxially stretched film of a saponified resin. However, when the operation was continued for one week after the start of extrusion, the generation of gel having a diameter of about 1 mm increased, and the film during stretching increased in number, so the operation was stopped there. The oxygen permeability and tensile strength at break of the obtained biaxially stretched film were evaluated, and the results are shown in Table 1 together with the continuous processing period.
[0040]
[Table 1]

[0041]
【The invention's effect】
According to the present invention described above, it is possible to stably produce an ethylene vinyl acetate copolymer saponified resin sheet having high gas barrier properties and excellent toughness, and a stretched film thereof. That is, according to the present invention, the above-described sheet and film useful as food packaging, medical / pharmaceutical packaging, clothing packaging, and other packaging materials can be provided at low cost. Therefore, the industrial value of the present invention is great.

Claims (2)

An ethylene vinyl acetate copolymer saponified resin having an ethylene content of 10 to 60 mol% and a saponification degree of 90 mol% or more and a water content adjusted to 10 to 50 wt% is melt-kneaded, and 90 to 110 from the die. A method for producing an ethylene vinyl acetate copolymer saponified resin sheet, characterized by extruding at a temperature of C and bringing the resulting molten resin sheet into close contact with a cooling roll of 40C or less and quenching. A method for producing an ethylene vinyl acetate copolymer saponified resin stretched film, wherein the ethylene vinyl acetate copolymer saponified resin sheet according to claim 1 is stretched in at least one direction.