JPH0472841B2 - - Google Patents

Description

Detailed Description of the Invention A: Technical Field of the Invention The present invention relates to a method for producing a saponified ethylene-vinyl acetate copolymer (hereinafter referred to as EVOH) which has outstanding melt formability and stretch formability. Specifically, the ethylene-vinyl acetate copolymer obtained by copolymerizing ethylene and vinyl acetate under two or more specific different conditions that are changed in stages (hereinafter referred to as
characterized by saponifying EVAc),
The present invention relates to a method for producing EVOH, which exhibits excellent melt moldability, stretch moldability, and excellent stretch moldability when used as a laminated molding material.

B. Prior Art Conventionally, EVOH is widely known as a thermoformable thermoplastic resin with excellent gas barrier properties, oil resistance, solvent resistance, etc., and is used as packaging films in various packaging fields, especially food packaging films, In addition to being suitably used for sheets, containers, etc., it is useful for a wide variety of applications, including electrical and electronic equipment parts and mechanical appliance parts.

However, EVOH is difficult to melt mold compared to thermoplastic resins such as polyolefin.
When subjected to melt molding, the layer thickness stability is not necessarily sufficient when extrusion molding films, sheets, etc. It has the disadvantage that it has poor moldability and is prone to holes, breakage, etc. during plastic processing such as drawing, pressure forming, plug assist forming, and stretch blow molding. In recent years, as the performance requirements for various packaging containers have become more sophisticated, they are increasingly being used in combination with other resins; It is used as an intermediate phase in multilayer sheets laminated with a thermoplastic resin.
32nd Annual sponsored by Plastic Engineers
Presented at the Technical Conference (held in 1974)
For example, by deep drawing into cup containers with a drawing ratio of 0.5 to 3, it has become mainstream to use some form of stretch forming to improve physical properties. There is. However, EVOH with an ethylene content of 25 to 45 mol%, especially 25 to 40 mol%, which has better gas barrier properties, has significantly poorer melt moldability and stretchability, and these properties are required. The reality is that in this field, EVOH with an ethylene content of more than 40 mol%, especially more than 45 mol%, must be used at the expense of gas barrier properties.

The actual situation is the same when the EVOH film is subjected to stretching processing either alone or in the form of a laminate of other thermoplastic resins. In other words, when biaxially stretching an EVOH single film in the ethylene content range, for example, a satisfactory biaxially stretched film cannot be obtained unless moisture is added through some kind of humidity control or hydration operation. The reality is that
15570, JP-A-53-30670, etc.). In addition, a laminated film with the EVOH as an intermediate layer,
When a film in which an EVOH layer is laminated on one side of a thermoplastic resin film is stretched, especially biaxially stretched, in a state where the EVOH layer does not contain water, the film is stretched in the same way as in the above-mentioned drawing process and stretch blow molding.
The drawback is that the EVOH layer is prone to holes, cracks, and breaks.

On the other hand, as a method to improve the melt moldability of EVOH, a resin composition obtained by melting and kneading two different types of EVOH in a specific ethylene content range and having specific characteristics is used for extrusion molding of films, sheets, and containers. Special Publication No. 58-20976), and
Blends of EVOH and nylon have been tried and proposed as a method for significantly improving the stretchability of EVOH (for example, Japanese Patent Application Laid-open Nos. 58-129035 and 58-154755). However, the effect of improving melt moldability in the former method is limited by the fact that it is a melt-kneaded composition, i.e., it has a different ethylene content.
It is clear that there is a limit to the improvement of the effect that depends only on the mere physical mixing of EVOH, and it cannot be satisfactory, so it has not been put into practical use. In the case of the latter blend,
In addition to impairing the high gas barrier properties of EVOH, it also has poor thermal stability, and is difficult to use in practical applications due to the generation of gel-like substances, which are thought to be caused by the reaction between the two, especially during thermal operations during melt molding. It has not yet been used satisfactorily.

It has excellent melt formability, sufficient layer thickness stability, suppresses the occurrence of hard eyes, etc., and also has good stretch formability during the plastic working, especially drawing with a drawing ratio of 0.5 or more, pressure forming, In the case of vacuum forming, plug-assist molding, or biaxial stretch blow molding, and especially in the case of biaxial stretching of the laminated film with an area magnification of 5 times or more, it is necessary to use stretch moldability suitable for these forming processes and excellent EVOH with barrier properties, i.e. ethylene content
It is in the range of 25 to 45 mol%, especially 25 to 40 mol%,
At least 35℃, relative humidity (hereinafter referred to as RH) 0%
The oxygen permeability coefficient of 1×10 ^-13 cc. cm/ ^cm2 , sec, cm
Hg or less, especially 5×10 ^-14 cc. cm/ ^cm2 , sec, cmHg
There is a strong desire for the emergence of EVOH which has the following properties and has excellent stretch formability.

Conventional EVOHs are all controlled to have a single copolymerization condition when copolymerizing ethylene and vinyl acetate, from the viewpoint that it is more preferable to have a narrower composition distribution. This is the obtained EVOH and two different ethylene contents.
Even when using a blend of EVOH species, it is a blend of EVOHs obtained by controlling the copolymerization conditions to be the same,
Moreover, at most the differential scanning calorimetry (hereinafter referred to as
Strong care has been taken to prevent the composition distribution from becoming too wide, such as by limiting the melting curve to an extent that does not exceed the range in which the melting curve (hereinafter referred to as DSC) shows essentially a single peak (for example, Japanese Patent Publication No. 58-20976). .
As shown in Comparative Example 5 of Japanese Patent Publication No. 58-20976, two conventional methods with different ethylene contents were simply used.
Blends of EVOH whose melting curves show two peaks according to DSC have drawbacks such as the formation of fissure eyes in the resulting molded products, and are said to be problematic.

C Structure, Objectives, and Effects of the Present Invention After extensive research, the present inventors found that, contrary to conventional technical ideas, the present inventors actively changed the copolymerization conditions in a specific stepwise manner during the copolymerization process. I gave and got
There is a new phenomenon in which the behavior of EVOH regarding melt formability and stretch formability is different from that of conventional EVOH, which has the same measured value of ethylene content obtained by controlling the conventional copolymerization conditions to be uniform. After discovering this fact, we have completed the present invention.

That is, the present invention copolymerizes ethylene and vinyl acetate, and further saponifies the obtained copolymer to produce a copolymer having an ethylene content of 25 to 45 mol% and a saponification degree of the vinyl acetate component of 95% or more. In obtaining the saponified product, the copolymerization reaction of ethylene and vinyl acetate is carried out under two or more different conditions within the temperature and ethylene pressure ranges of the following formulas (1) and (2), and at least one adjacent While maintaining the difference in ethylene pressure between different copolymerization reaction conditions at 5 kg/cm ² or more and/or the difference in temperature at 10°C or more, and further changing the different copolymerization reaction conditions in a substantially stepwise manner, The method is characterized in that the amount of ethylene-vinyl acetate copolymer produced under each copolymerization reaction condition is at least 10% by weight of the total amount produced, and then the obtained copolymer is saponified. A method for producing a saponified ethylene-vinyl acetate copolymer.

0.5T−7.5< P <0.9T+18 (1) 35≦T≦80 (2) However, P is ethylene pressure (Kg/cm ²・G), T
is the temperature (°C).

The method of the present invention is carried out under two or more different conditions within the temperature and pressure range that satisfy the above formulas (1) and (2), and the difference in ethylene pressure between at least one adjacent different condition is 5 kg. /cm ² or more and/or the temperature difference is kept at 10°C or more, and the different copolymerization reaction conditions are changed substantially stepwise, and the amount of the copolymer produced under each polymerization condition is The main point is to saponify EVA _C obtained by copolymerization so that it is at least 10% by weight of the total production amount, and conventional EVOH or blends thereof obtained based on such operations. Applicable for the first time with a new EVOH different from the
Although the characteristics of EVOH can be improved, the effects of the present invention cannot be enjoyed unless all of the constituent requirements of the present invention are satisfied.

Even if the copolymerization reaction is carried out in a temperature and pressure range not included in the temperature and pressure ranges expressed by formulas (1) and (2), and other requirements are met, the present invention maintains good melt formability and stretch formability. It cannot be an EVOH. Although the details are not clear, under these conditions, those with too low ethylene content, those with too high ethylene content,
Alternatively, EVOH may contain too high a degree of polymerization or too low a degree of polymerization, or the difference in ethylene content of EVOH produced under different copolymerization conditions may become too large. It is presumed that favorable interaction between EVOH produced under these conditions becomes difficult to occur. If the polymerization temperature is in a lower range, the polymerization rate will be lower, which is not only economically disadvantageous, but also, in a flow system operation using a stirred mixing type polymerization tank, an insoluble gel-like substance will be generated in the polymerization tank. The production of substances increases and accumulates in the tank as a huge gel-like substance,
It is more preferable to carry out the polymerization in a relatively high temperature range since this increases the tendency for it to become difficult to carry out satisfactory continuous polymerization over a long period of time. However, when the temperature reaches a temperature range higher than 80°C, it is not clear whether this is based on the above-mentioned inferred factors or because a slight difference occurs in the polymer structure, but it is difficult to enjoy the effects of the present invention as mentioned above. That's right. Preferably, the temperature is 40 to 80°C, more preferably 45 to 75°C.

One of the most important requirements of the present invention is that two different
When conducting under the above conditions, the difference in ethylene pressure between at least one adjacent different condition must be set to 5.
Kg/cm ² or more and/or the temperature difference is kept at 10° C. or more, and the different copolymerization reaction conditions are changed substantially stepwise. The copolymerization conditions are
Substantially stepwise change can also be achieved by once stopping the copolymerization reaction and then polymerizing under different conditions; however, if the reaction is stopped during the copolymerization reaction, More preferably, it is carried out without any In the latter case, the most suitable method is to use a stirring-mixing polymerization tank and operate the flow system in at least two stages. It can be done by changing the In batch operations, it is more preferable to adopt a method in which the pressure is changed stepwise during the course of the polymerization reaction, which has a faster response, than a method in which the temperature is changed, which has a slower response. The pressure to be changed stepwise is
Must be 5Kg/cm2 or ^more . More preferably, it is 10 Kg/cm ² or more. Additionally, the temperature is required to change by 10°C or more.

Furthermore, in the method of the present invention, the amount of the copolymer produced under each condition is at least the total amount produced.
Unless it is copolymerized at a concentration of 10% by weight, improvements in melt moldability and the like cannot be expected. In one of the more preferred embodiments, the copolymerization reaction is carried out using a stirring-mixing polymerization tank under different pressures of 10 kg/cm ² or more and at substantially the same temperature, or
2 under different temperatures that increased and decreased in the opposite direction to the change in pressure.
When the copolymer is produced using a stage flow system operation, and the amount of the copolymer produced under higher pressure conditions is A, and the amount produced under lower pressure conditions is B, the ratio (weight) of A/A + B is 0.65. ~0.3 is more preferable for improving melt formability and stretch formability, particularly 0.55~
A value of 0.45 is suitable for improving stretch formability.

EVOH obtained by the method of the present invention includes:
whose melting curve measured by differential scanning calorimeter (hereinafter referred to as DSC) shows substantially a single peak;
There are peaks that contain two or more independent peaks, and the former is when the change in conditions is relatively small, and the latter is related to the production rate of the copolymer under each condition, such as A/A+B. However, it is obtained when the change in conditions is relatively large.
The _DSC melting curve referred to in the present invention is obtained using DSC-2C manufactured by Perkin Elmer.
This is a melting curve measured at a heating rate of 10°C/min.
Among the EVOH obtained by the method of the present invention, the above-mentioned
EVOH obtained by performing at least two stages of flow system operation under conditions different by 10 kg/cm ² or more often has at least two peaks. EVOH having the plurality of peaks not only has excellent melt moldability but also excellent stretch moldability. In particular, among the plurality of independent peaks, the largest temperature difference between two adjacent peaks is 5°C.
As mentioned above, if the temperature is preferably 10° C. or higher, the stretch formability will be even more excellent. Such EVOH is
For example, the above-mentioned copolymerization reaction is carried out in two stages using a stirring-mixing polymerization tank, under pressures different by 10 kg/cm ² or more, and at substantially the same temperature, or at a temperature that increases or decreases in the opposite direction to the change in pressure. It is obtained by carrying out flow system operation such that the ratio of A/A+B is between 0.65 and 0.3. Among these, it is more preferable that the ratio of A/A+B is 0.60 to 0.40. The reason why these exhibit superior stretch formability is still not clear in detail. Compared to conventional EVOH with the same ethylene content, the EVOH obtained by the method of the present invention, which has particularly excellent stretchability, exhibits a lower Bitskart softening point by at least 3°C. It is presumed that it makes an important contribution to improving the stretch formability at the forming temperature during a forming process that involves some form of stretching, such as by solid phase pressure forming. What is more distinctive is that compared to an EVOH blend of the same ethylene content obtained by blending two types of conventional EVOH so that A/A+B is the same, the EVOH produced by the method of the present invention has This point shows more remarkable stretch formability. This suggests the existence of not only the above-mentioned Bitskart softening point but also other new factors, although the details are not clear yet, and shows that the EVOH produced by the method of the present invention is unique. be. The Bitzkart softening point as used in the present invention is defined as when a constant load (1000 g) is applied to a needle with a flat tip with a cross-sectional area of 1 mm ² , and
This is the temperature when the penetration depth reaches 1 mm when the temperature is increased in a constant temperature oil bath at a rate of 50 °C, and is determined by ASTM,
This refers to the value measured according to D-1525-58T. The softening point can be lowered by drawing from a preform such as a film, sheet, parison, etc. in which the EVOH is laminated with another thermoplastic resin, especially a laminated preform in which the EVOH is arranged as an intermediate layer. It is particularly closely related to stretch formability during plastic working such as biaxial stretch blow molding, and when the softening point difference is less than 3°C, the effect of improving stretch formability is reduced.

D More detailed description of the present invention The ethylene content of the copolymer obtained by the method of the present invention is preferably in the range of 25 to 45 mol%, and if it is less than 25 mol%, the general moldability is poor. However, the expression of the above-mentioned excellent properties is also diminished, which is not preferable. Moreover, if it exceeds 45 mol%, not only will high gas barrier properties not be obtained, but the stretch formability will gradually become better even with conventional EVOH, even if it does not depend on the EVOH obtained by the method of the present invention. Therefore, the significance of the present invention is diminished. Also, EVOH according to the present invention
The degree of saponification of the vinyl acetate component is 95% or more. If it is less than 95%, the barrier properties will decrease and it will not be possible to obtain the high barrier EVOH that is the object of the present invention.

As mentioned above, since the EVOH according to the present invention adopts at least two stepwise changed copolymerization conditions, it is natural that the DSC melting curve has a plurality of independent peaks, or it has one independent peak. However, since the composition distribution of EVOH is considered to be different from that of conventional EVOH, the measured ethylene content does not necessarily indicate the same oxygen permeability coefficient as that of conventional EVOH. , the EVOH obtained by the method of the present invention has an oxygen permeability coefficient of 1×10 ^-13 cc. at 35°C and 0% RH. cm/ ^cm2 . sec.cmHg or less,
Especially 5×10 ^-14 cc. cm/ ^cm2 . sec.cmHg or less, which meets the requirements for high barrier properties and can be used suitably.

The method of the present invention relates to a method for producing a resin that is essentially EVOH, and α-olefins other than ethylene,
The copolymerization reaction can be carried out in the presence of a third component such as a silicon-containing olefinic unsaturated monomer.

In carrying out the method of the present invention, bulk polymerization, solution polymerization, and suspension polymerization can be employed. In the flow system operation using a stirring and mixing type polymerization tank, which is most suitable for the method of the present invention, a solution polymerization method is more suitable. The bulk polymerization method is inferior to the solution polymerization method in terms of removal of polymerization heat and polymerization stability, and the suspension polymerization method is inferior to the solution polymerization method in that it involves more technical difficulties in terms of suspension stability in the flow system operation. As the polymerization solvent in the solution polymerization method, alcohols such as methanol are preferably used, and methanol, which is inexpensive, or tertiary butanol, which has a small chain transfer constant, is particularly preferably used for industrial purposes. Solvent concentration is 25
It is preferable to use less than 25% by weight, and if the amount is more than 25% by weight, the resulting EVOH will often contain EVOH with a too low degree of polymerization, which is not suitable for the present invention. More preferably, the concentration is between 5 and 20% by weight.

In the copolymerization reaction of the present invention, various initiators known per se are used, such as 2,2'-
Nitriles such as azobis-(4-methoxy-2,4-dimethylvaleronitrile), 2,4,4-trimethylvaleronitrile, 2,2'-azobis-isobutyronitrile, di-n-propylperoxy carbonate, bis-4-t-butylcyclohexyl peroxydicarbonate, bis-2-
Examples include carbonates such as ethylhexyl peroxydicarbonate, acetylcyclohexane sulfonyl peroxide, peroxides such as benzoyl peroxide, and lauroyl peroxide. In particular, an initiator with a shorter half-life can almost completely or significantly suppress the formation of a gel-like substance insoluble in the polymerization system that is observed over time during the copolymerization process in the flow system operation. During long-term continuous polymerization operations,
More suitably used. In this case, it is preferable to also supply the initiator to the second and subsequent polymerization tanks in the flow system operation.

The copolymer obtained by polymerization is then subjected to a saponification reaction. The saponification reaction is advantageously carried out in a known manner, ie usually by alcoholysis, using the copolymer as an alcoholic solution, using an alkaline catalyst, for example. Among these, the method disclosed in Japanese Patent No. 575889 and Japanese Patent No. 611557 that uses a column reactor and removes methyl acetate, which is produced as a by-product during the saponification reaction, from the top of the column by blowing alcohol vapor into the bottom of the column is the most effective. It can be suitably used. As the alkaline catalyst used in the saponification reaction, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alcoholates such as sodium methylate and potassium methylate, and the like are used. Among these, sodium hydroxide is industrially and economically advantageous. Saponification temperature is 60~
Suitably selected from the range of 175°C. In particular, when using the tower type reactor, a temperature of 100° C. or higher is preferred from the viewpoint of shortening the reaction time, solubility of the EVOH in alcohol, etc., although this is also related to the composition of the copolymer.

After the saponification reaction, to isolate the EVOH, known methods can be applied, but the method disclosed in Japanese Patent No. 725520 in which the EVOH is precipitated in the form of strands and the polymer is separated is particularly preferred. used. The precipitated and isolated EVOH is washed with water and then dried by a known method.

When the EVOH obtained by the method of the present invention is used as a molding material, ASTM D-1238-
Melt index measured according to T (190
C, load 2160 g) is preferably 0.1 g/10 minutes or more, and particularly preferably 0.5 to 10 g/10 minutes.

The EVOH obtained by the method of the present invention can be used alone or in a laminate with other thermoplastic resins, but is particularly preferably used in the form of a multilayer or a laminate. and can be thermoformed into preforms such as films, sheets or parisons. For thermoforming, a molding method known per se such as extrusion molding, injection molding, pre-blow molding, etc. can be employed. A method is employed in which an extruder for EVOH and an extruder for other resins are used to coextrude both resin layers in adjacent positions through multiple, multilayer dies. When used as a laminate, other thermoplastic resins, especially thermoplastic resins for the outer and outer layers of the intermediate layer formed from the EVOH, are preferably resins with excellent stretch formability, such as polypropylene, crystalline ethylene-propylene, etc. Thermoplastic polyester resins such as copolymers, ethylene-vinyl acetate copolymers, and polyethylene terephthalate, 6-
Polyamide resins such as nylon, 6,6-nylon, polystyrene, etc. can be used. Among these, preferred are polypropylene, crystalline ethylene-propylene copolymer, thermoplastic polyester resin, and polystyrene resin. The thermoplastic resins provided in the inner and outer layers may be of the same type or may be of different types. In addition, the structure in which the EVOH layer is laminated includes EVOH/thermoplastic resin, thermoplastic resin/EVOH/thermoplastic resin, thermoplastic resin/EVOH/thermoplastic resin/EVOH/thermoplastic resin, etc. The resin layer may be a single layer, or in some cases may be multilayer.

The EVOH obtained by the method of the present invention can be used alone in films, sheets, etc. to obtain improved layer thickness stability and to reduce fish eyes. In addition, by laminating other thermoplastic resins, especially by arranging the EVOH in the intermediate layer and laminating thermoplastic resins in the inner and outer layers, stretch formability is improved, and the resulting laminated film When stretching a laminated sheet, parison, etc., or deep drawing or stretch blow molding a laminated sheet, parison, etc., a product with excellent gas barrier properties that does not cause cracks in the layer made of EVOH can be obtained.

A laminate (film, sheet, parison) formed by arranging EVOH obtained by the method of the present invention in an intermediate layer may be at least a uniaxially stretched laminated film, a deep-drawn container, a stretched blow bottle, etc. Can be used as a material. It is particularly effective as a material for deep-drawn containers, particularly deep-drawn containers with a drawing ratio of 0.5 or more, and furthermore, a drawing ratio of 0.8 to 3. A deep-drawn container, for example, a cup-shaped container, is obtained by drawing, air pressure forming, vacuum forming, plug-assist forming, etc., using a laminated sheet containing the EVOH as an intermediate layer at a stretching temperature. In addition, the stretched blow bottle is
For example, EVOH obtained by the method of the present invention
It is obtained by mechanically stretching a preform, such as a parison, with a middle layer in the axial direction at a stretching temperature and blow-stretching it in the circumferential direction by blowing fluid.

In the case of a laminate using EVOH obtained by the method of the present invention, the thickness of the EVOH layer is:
For example, depending on the required performance of the resulting deep-drawn container, stretched blow bottle, etc.
It is preferable to keep the thickness at ~30μ.

Further, when obtaining a laminate using EVOH obtained by the method of the present invention, each layer is preferably arranged through an adhesive resin, and the adhesive resin is not particularly limited, but polyethylene , carboxyl group-containing modified products such as polypropylene, ethylene-vinyl acetate copolymer and ethylene-acrylic acid copolymer, especially maleic anhydride modified products, as they are or blended with the unmodified polymer, More suitably used.

Next, the present invention will be explained by giving Examples, but the scope of the present invention is not limited.

Example 1 In a flow system operation using two stirrer-equipped polymerization tanks having a capacity of 50 (first polymerization tank) and a capacity of 70 (second polymerization tank) each having a cooling coil inside, arranged in series, ethylene- In order to produce a vinyl acetate copolymer, continuous polymerization was carried out under the conditions shown below.

First polymerization tank Vinyl acetate supply amount 5850g/hr Methanol supply amount 650g/hr Temperature 60℃ Ethylene pressure 40Kg/cm ² G 2,2'-azobisisobutyronitrile
2.1g/hr Average residence time 2.0hr Second polymerization tank temperature 60℃ Ethylene pressure 57Kg/cm ² G Average residence time 4.9hr Vinyl acetate and methanol are supplied to the first polymerization tank; The entire amount of the polymerization reaction liquid flowing out is supplied to the second polymerization tank. At this time, the polymerization rates of vinyl acetate measured in the first polymerization tank and the second polymerization tank were 18% and 38%, respectively.
Amount (weight) of the copolymer produced in the second polymerization tank
were almost the same. The ethylene content of the obtained copolymer was 37 mol%. After the ethylene dissolved in the copolymerization reaction liquid is diffused and removed by reducing the pressure to normal pressure, it is supplied to a purging tower, and by introducing methanol vapor from the bottom of the tower,
After removing unreacted vinyl acetate from the top of the column, a 45% methanol solution of the copolymer was obtained. Next, a methanol solution of the copolymer was introduced into a tower-type saponification tower, and sodium hydroxide was further supplied to the reactor at a molar ratio of 0.05 to the vinyl acetate component contained in the copolymer. Methanol vapor is blown into the bottom of the column, and a saponification reaction is carried out while removing by-product methyl acetate from the top of the column.
A methanol solution of EVOH was obtained. Mixed steam with a weight ratio of methanol/water = 7/3 was blown into the methanol solution to change the solvent composition in the solution to a water/methanol mixed system, and then discharged in the form of a strand into a 10% methanol aqueous solution at 5°C. The EVOH was isolated as a pellet by coagulation, precipitation, and cutting. After thoroughly washing with water, it was immersed in dilute aqueous acetic acid and dried at 65 to 110°C. The degree of saponification was 99.2 mol%. Perkin Elmer DSC−
Measurement was performed using 2C at a heating rate of 10°C/min. Applicable
The melting curve of EVOH shows two independent peaks, the low-temperature peak at 167℃, and the high-temperature peak at 167℃.
It was located at 186℃. The melt index is
It was 3.1g/10 minutes. Bitskart softening point is 158℃
Conventional ethylene content: 37 mol%, melt index: 3 g, obtained by continuous methanol solution polymerization under single conditions (pressure: 49 Kg/cm ² G, temperature: 60°C) using one stirred mixing type polymerization tank. /10 minutes, the DSC melting curve was 7.5°C lower than the softening point of EVOH (X) showing a single peak.

An extruder for inner and outer layers with a built-in full-flight screw with a diameter of 65 mm and an effective length of 1430 mm, and a melt channel that branches into two flow paths.
Intermediate extruder with full-flight screw of 50 mm and effective length of 1100 mm and the same diameter
A combination of an adhesive layer extruder with a built-in full-flight screw with an effective length of 1100 mm and a melt channel branched into two flow paths, and a multilayer 5-layer T-die is used to produce a product with a width of 200 mm and a wall thickness. A sheet with a diameter of 1.1 mm was extruded. The resin used for molding has a density (ASTM D-1505) of 0.910 g/cc for the inner and outer layers.
Melt index (ASTM.D-1238) is 1.6
g/10 minutes, isotactic polypropylene with a melting point of 160°C according to DSC thermal analysis, adhesive layer density 0.925 g/cc, melt index 3.0 g/cc.
Maleic anhydride-modified linear low-density polyethylene having a melting point of 120° C. according to the DSC thermal analysis was used for 10 minutes, and the intermediate layer was the obtained EVOH and the above EVOH (X) for comparison. After heating these multilayer sheets at 145°C for 20 seconds by solid phase pressure forming, the inner diameter (D) is 100 mm, the depth (L) is 200 mm (drawing ratio L/D = 2), and the wall thickness is An attempt was made to form a cylindrical cup with an internal volume of 0.5 mm and 1.57 mm. The thickness ratio of outer layer:adhesive layer:intermediate layer:adhesive layer:inner layer is 45:
It was 2.5:5:2.5:45. The obtained EVOH
When using the above, stretch moldability was good, and the molding was performed well without any problems. For comparison,
In a multilayer sheet using the above-described EVOH (X) in the intermediate layer, cracks were generated in the intermediate layer, the cup became partially cloudy, and molding could not be performed satisfactorily. Separately, in order to examine the gas barrier properties of the EVOH obtained above, 20μ
A film was obtained, and its oxygen permeability coefficient at 35°C and 0% RH was measured. The measured value of the unstretched film heat-treated at 140°C for 10 minutes was 1.8×10 ^-14 cc. cm/ ^cm2 ,
It was sec.cmHg. In addition, the obtained film has
Virtually no fisheyes were recognized. (4 pieces/100 cm x 100 cm) Example 2 Using the same polymerization tank as in Example 1, continuous polymerization was carried out in the same manner as in Example 1 under the following conditions.

1st polymerization tank Vinyl acetate supply amount 5000g/hr Methanol supply amount 1060g/hr Temperature 60℃ Ethylene pressure 28Kg/cm ² . G 2,2'-Azobis-(2,4-dimethylvaleronitrile) Supply amount 0.57g/hr Average residence time 1.5hr Second polymerization tank temperature 55℃ Ethylene pressure 45Kg/cm ² . G Average residence time 6.0hr The polymerization rates of vinyl acetate measured in the first polymerization tank and the second polymerization tank were 20% and 37%, respectively. The amount produced was the same. The ethylene content of the obtained copolymer was 33.1 mol%. Example 1
In the same manner as above, EVOH with a degree of saponification of 99.4% and a melt index of 2.9 g/10 minutes was obtained. The EVOH
The DSC melting curve of shows two independent peaks,
They were located at 169℃ and 190℃, respectively. In addition, the Bitskart softening point is 162°C, the conventional ethylene content is 33 mol%, the melt index is 2.8 g/10 minutes, and the DSC melting curve shows a single peak.
It showed a value 8°C lower than the softening point of EVOH (Y). A multilayer sheet was obtained in the same manner as in Example 1, and solid phase air pressure molding was performed. When the EVOH was used, the stretch moldability was good, and the molding was performed satisfactorily without any problems. For comparison, the above EVOH was added to the intermediate tank.
In the multilayer sheet using (Y), cracks and fractures occurred in the intermediate tank, and the cup obtained was unsatisfactory. Separately, in order to examine the gas barrier properties of the EVOH obtained above, a 20μ film was obtained and heated at 35°C.
The oxygen permeability coefficient at 0% RH was measured. 140℃, 10
The measured value of the unstretched film heat-treated for
7.5×10 ^-15 cc. cm/ ^cm2 . It was sec.cmHg. Further, the obtained film had virtually no stains. (3 pieces/100cm x 100cm) Example 3 Using the same polymerization tank as in Example 1, under the following conditions,
Continuous polymerization was carried out in the same manner as in Example 1.

First polymerization tank Vinyl acetate supply amount 2500g/hr Tertiary butanol 550g/hr Temperature 60℃ Ethylene pressure 43Kg/cm ² G 2,2'-Azobis isobutyronitrile supply amount
0.17g/hr Average residence time 7.0hr Second polymerization tank temperature 70℃ Ethylene pressure 36Kg/cm ² G Average residence time 2.3hr The polymerization rate of vinyl acetate measured in the first polymerization tank and the second polymerization tank is: They are 17% and 42%, respectively, and the ratio of the amount of the copolymer produced in the first polymerization tank and the second polymerization tank to the total production amount is 0.4, respectively.
and 0.6. The ethylene content of the obtained copolymer was 34.2 mol%. By operating according to Example 1, a methanol/tertiary butanol mixed system EVA _C solution was obtained from the bottom of the expelling tower, and this was introduced into a tower-type saponification tower and saponified in the same manner to remove the polymer. After separation, EVOH with a degree of saponification of 99.3 mol% and a melt index of 1.7 g/10 minutes was obtained. of the EVOH
The DSC curve showed two independent peaks, located at 165°C and 182°C, respectively. The EVOH is used as an intermediate tank, and melt index (ASTM D-
1238) is 0.5g/10min, density (ASTM D-1505)
The inner and outer layers are made of isotactic polypropylene homopolymer with a melting point of 0.91 g/cc and a melting point of 165°C.
Outer layer/adhesive layer/EVOH layer/adhesive layer made of a modified ethylene-vinyl acetate copolymer with a vinyl acetate content of 33% by weight and a degree of maleic anhydride modification of 1.5% by weight.
A bottomless laminated pipe consisting of 5 layers (adhesive layer/inner layer) with a diameter of 40 mm, effective length of 880 mm, one melt channel (for the adhesive layer) and a melt channel with a diameter of 65 mm and effective length of 1430 mm. The molding was performed using an extruder group having two flow paths (for inner and outer layers) for each dimension and a die for coextrusion with five layers. The resulting pipe has an overall wall thickness of approximately 10 mm, an inner diameter of 30 mm, and a length of
30mm, and the composition ratio of the layers of each pipe is: outer layer: adhesive layer: intermediate layer: adhesive layer: inner layer: 100:2:5:2:
It was 100. After heating the laminated pipe to 158°C, both ends of the pipe are held between clamps, first stretched in the vertical direction of the pipe, then held between blow molds, and then expanded in the horizontal direction with compressed air for blow molding. I went to The resulting biaxially stretched blow bottle was a cylindrical bottle with an inner diameter of 100 mm, a height of 150 mm, an average body wall thickness of 0.6 mm, and an internal volume of 1180 c.c. The biaxial stretching was performed 20 times, and no defects such as cracks in the intermediate layer were observed.

For comparison, ethylene content of 34 mol% and melt index of 1.8 g/
A melt blend of 4:6 (weight ratio) of EVOH for 10 minutes and two types of EVOH with peaks at 165°C and 182°C on the respective melting curves obtained under single conventional conditions. (Melt index: 1.7 g/10 minutes) was used as the intermediate layer.
In the former case, the stretch formability was poor, and all the intermediate layers had defects such as cracks and vertical streaks, so that no satisfactory result could be obtained. In the latter case, although it showed relatively good stretch formability, out of 20 times,
8 times had this defect.

Example 4 Copolymerization of ethylene and vinyl acetate was carried out in a batch operation under the following conditions using a polymerization tank with a capacity of 10 and equipped with a stirrer and a cooling coil inside.

Amount of vinyl acetate charged: 2500g Amount of methanol charged: 280g Amount of azobisisobutyronitrile charged: 3.8g Polymerization temperature: 60℃ Ethylene pressure during polymerization is the polymerization rate of vinyl acetate: 25
%, it was held at 40Kg/cm ² G, and thereafter it was held at 57Kg/cm2.
The copolymerization reaction was carried out while maintaining the pressure at cm ² G. The final polymerization rate of vinyl acetate was 48%. The ethylene content of the obtained copolymer was 37.2 mol%. Processed according to Example 1, with a saponification degree of 99.3% and independent peaks at 167°C and 186°C on the DSC melting curve.
An EVOH with a melt index of 3.0 g/10 minutes was obtained.
A multilayer sheet containing the EVOH as an intermediate layer was obtained in the same manner as in Example 1, and an attempt was made to form it into a cylindrical cup by solid phase pressure forming. Formability is good, 20
Although I carried out several cycles, I did not notice any defects such as cracks.

Example 5 In Example 4, after the vinyl acetate polymerization rate reached 25%, it was cooled once to stop the copolymerization reaction, and then the temperature was raised again and the polymerization reaction was carried out until the polymerization rate reached 48%. The rest was carried out in the same manner as in Example 4.
The ethylene content, melt index, and peaks on the DSC melting curve of the EVOH obtained were almost the same as those of the EVOH obtained in Example 4. A multilayer sheet containing the EVOH as an intermediate layer was obtained in the same manner as in Example 1, and an attempt was made to form it into a cylindrical cup by solid phase pressure forming. As a result of 20 attempts, a small crack was observed in the intermediate layer only once, but no other cracks were observed at all, and the stretch formability was generally good.

Example 6 Using the same polymerization tank as in Example 1, continuous polymerization was carried out in the same manner as in Example 1 under the following conditions.

First polymerization tank Vinyl acetate supply amount 4500g/hr Tertiary butanol supply amount 140g/hr Temperature 70℃ Ethylene pressure 44Kg/cm ² G 2,2'-azobis-(2,4-dimethylvaleronitrile) supply amount 0.013 g/hr Average residence time 4hr Second polymerization tank temperature 60℃ Ethylene pressure 44Kg/cm ² G 2,2'-azibis-(2,4-dimethylvaleronitrile) supply amount 0.17g/hr Tertiary butanol 630g /hr Average residence time 4hr The polymerization rates of vinyl acetate measured in the first polymerization tank and the second polymerization tank were 25% and 42%, respectively. The ratio of quantity to total production was 0.57 and 0.43, respectively. The ethylene content of the obtained copolymer was 34.4 mol%. The same procedure as in Example 3 was carried out to obtain EVOH with a degree of saponification of 99.4 mol% and a melt index of 1.76 g/10 minutes. of the EVOH
The DSC curve shows two independent peaks,
It was located at 181.5℃ and 165.5℃. Biaxially stretched blow molding was performed in the same manner as in Example 3 to obtain a similar biaxially stretched blow bottle. The biaxial stretching formability was good, and no cracks or the like were observed in the intermediate layer.

Claims (1)

[Claims] 1. Copolymerizing ethylene and vinyl acetate, and saponifying the resulting copolymer to obtain an ethylene content of 25 to 25%.
In order to obtain the saponified copolymer with a saponification degree of 45 mol% and vinyl acetate component of 95% or more, the copolymerization reaction of ethylene and vinyl acetate was carried out at the temperature and ethylene temperature according to the following formulas (1) and (2). The difference in ethylene pressure between two or more different conditions in the pressure region and at least one adjacent different copolymerization reaction condition is 5
Kg/cm ² or more and/or temperature difference of 10°C or more, and while changing the different copolymerization reaction conditions substantially stepwise, furthermore, ethylene-vinyl acetate under each copolymerization reaction condition. Production of a saponified ethylene-vinyl acetate copolymer, which is characterized in that the amount of copolymer produced is at least 10% by weight of the total amount produced, and then the obtained copolymer is saponified. Method. 0.5T−7.5< P <0.9T+18 (1) 35≦T≦80 (2) However, P is ethylene pressure (Kg/cm ²・G), T
is the temperature (°C). 2. The method for producing a saponified ethylene-vinyl acetate copolymer according to claim 1, wherein the copolymerization reaction under two or more different conditions is carried out continuously without being stopped. 3. The method for producing a saponified ethylene-vinyl acetate copolymer according to claim 1, wherein the copolymerization reaction is carried out in at least two stages of flow system operation using a stirring-mixing polymerization tank. 4 The copolymerization reaction used a stirring and mixing type polymerization tank, 2
The flow system is operated in stages, each with a pressure of 10
Kg/cm ² or more, the respective temperatures are substantially the same or the temperatures are changed in the opposite direction to the pressure change, and the amount of the copolymer produced under the higher pressure is greater than A. When the amount generated under low pressure is B, the ratio (weight) of A/A + B is 0.65
3. The method for producing a saponified ethylene-vinyl acetate copolymer according to claim 1, wherein the saponified ethylene-vinyl acetate copolymer has a molecular weight of 0.3.