JPH0155282B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention uses a saponified ethylene-vinyl acetate copolymer (saponification degree of 85% or more) as a methanol solution or tertiary butyl alcohol (hereinafter referred to as t).
- butanol) - obtained by saponifying a methanol mixed solution in the presence of an alkali or alkali metal alcoholate, methanol or t-butanol is used as a polymerization solvent, a radical initiator is used, and the concentration of the solvent is 20 Continuous copolymerization is carried out by keeping the temperature at 35-80℃ and meeting specific conditions set between the average residence time, half-life of the initiator used, and the reaction rate of vinyl acetate. The present invention relates to a method for producing a molded product of a saponified ethylene-vinyl acetate copolymer having surface properties, particularly, less stickiness, using the ethylene-vinyl acetate copolymer obtained by using the ethylene-vinyl acetate copolymer. What is saponified ethylene-vinyl acetate copolymer?Ethylene-vinyl acetate copolymer or ethylene-vinyl acetate copolymer
Those manufactured by saponifying a terpolymer obtained by copolymerizing vinyl acetate and one type of other polymerizable third component and containing appropriate amounts of ethylene and vinyl alcohol components can be mechanically processed. It is well known that it is a useful thermoplastic polymer that provides film moldings with excellent oxygen gas barrier properties. Saponified ethylene-vinyl acetate copolymer is
It is usually obtained by saponifying an ethylene-vinyl acetate copolymer by adding a caustic alkali or an alkali metal alcoholate, but if the saponified product is directly melt-molded or melt-formed, it is easily thermally decomposed and the melt viscosity In addition to a decrease in the thermal stability, various measures have been taken to improve thermal stability due to significant coloration that makes it unusable. That is, in order to saponify an ethylene/vinyl acetate copolymer to obtain a saponified product of the copolymer, known techniques are used, for example, to saponify the copolymer with methanol or methanol-t.
- A method of saponification using an alcohol decomposition catalyst such as an alkali or an alkali metal alcoholate in a mixed solution of butanol is adopted.
If water is present in the reaction system during this saponification reaction, these catalysts will react with the acetate ester produced during the reaction and will be rapidly destroyed, so it is preferable that the water content of the reaction system is as low as possible. Also, Special Publication No. 14958 and Special Publication No. 14958
According to the method disclosed in Japanese Patent No. 40547, a methanol solution or a mixed solution of methanol and t-butanol of the copolymer to be saponified is fed from the upper part of the column-type reactor, and a saturated or superheated solution is fed from the lower part of the column. Methanol vapor is blown into the column to form a uniform solution layer in the column under normal pressure or under increased pressure to allow the reaction to proceed, and methyl acetate vapor is expelled from the system along with methanol vapor or methanol-t-butanol vapor. A method of saponification while removing is preferred;
This is particularly preferred when obtaining a saponified product of the copolymer with a high degree of saponification. Separation of the saponified copolymer from a methanol solution of the saponified copolymer after the saponification reaction or a solution containing a portion of t-butanol in methanol is disclosed in Japanese Patent Publication No. 38634/1983, etc. The method described can be used. The saponified copolymer obtained in this way has poor thermal stability and requires thermal stabilization treatment. It is added by immersion in an aqueous acid solution, or by adding certain metal salts.
It is disclosed in Japanese Patent Publication No. 48-25048, Japanese Patent Publication No. 51-88544, Japanese Patent Application Laid-Open No. 51-88545, Japanese Patent Publication No. 57-5834, etc. Furthermore, suitable methods for drying the resin are disclosed in, for example, Japanese Patent Publication No. 56-206, and the resin can be dried by these methods. The main purpose of these various thermal stabilization operations and drying methods is to prevent thermal decomposition, gelation, coloration, etc. of the resin that occurs when molding the resin into a film, etc., and especially to prevent these phenomena. It also aims to eliminate the occurrence of so-called fish eyes that occur in connection with this.
Despite the efforts of those skilled in the art,
It should be noted that the elimination of hard eyes during molding of the saponified copolymer into films, etc. is not completely satisfactory, and is still inferior to various commercially available films such as commercially available cellophane, and has poor appearance, printing, etc. There are many problems with this, and this is one of the important technical issues in improving the quality of the saponified copolymer. The present inventors conducted intensive research from a viewpoint completely different from the conventionally disclosed technical viewpoint, arrived at the method of the present invention, and succeeded in eliminating the manifestation of the fish eye. Conventionally, the expression of undesirable properties of the saponified copolymer itself has been suppressed by thermal stabilization treatment, or the initiator, alkaline substance remaining in the saponified copolymer, or their modification has been suppressed. In the past, the quality was improved only when removing objects, etc. However, the present application seeks to find out the latent factors for the appearance of fisheye in the copolymerization process and its related processes, and studies the saponified copolymer obtained by saponifying the copolymer obtained under specific copolymerization conditions. This was considered from the point of view of eliminating. the result,
The objective of eliminating fisheyes, which could not be removed using conventional techniques, has been achieved. In other words, as a result of using ethylene-vinyl acetate copolymers with different polymerization conditions and applying the conventional heat stabilization treatment and drying method under the same conditions, the gel obtained by continuous polymerization under specific conditions. It has been found that only when the copolymer is used, which has no or extremely few fish eyes, molded products such as films with substantially no fish eyes can be obtained. The new and important factor for the development of fisheye is the copolymerization process,
In particular, we focused on the fact that there is a correlation with gel-like substances generated during the copolymerization process when continuous copolymerization is carried out under specific conditions, and established copolymerization conditions that prevent the formation of gel-like substances. Based on this, we have arrived at a method for producing molded products of the saponified copolymer that can eliminate the fish eyes, which could not be eliminated using conventional techniques, and have excellent surface properties. That is, a saponified copolymer represented by the following general formula (1) (saponification degree of 85% or more) is added to a methanol solution of the copolymer, or When obtaining methanol or t-butanol by saponifying it in the presence of an alkali or alkali metal alcoholate in a mixed solution of t-butanol,
Butanol is used as a polymerization solvent, a radical initiator is used, the concentration of the solvent is 20% by weight or less, and the temperature is 35-80%.
The copolymer obtained by continuous copolymerization at ℃ and maintaining the following conditions (2) is used.
This is a method for producing a molded product of a saponified vinyl acetate copolymer. However, in formula (1), X/(Y+Z)=0.3 to 1.5, Z/Y=0 to 0.1, R is hydrogen or a methyl group, and R ¹ is a methyl group or a COOR group. In the formula (2), x0.85 x is the polymerization rate of vinyl acetate, is the average residence time in the polymerization tank, and θ is the half-life of the polymerization initiator. Conventionally, various methods have been known for polymerizing vinyl monomers, but the continuous polymerization method has been widely adopted because it is industrially advantageous in terms of uniformity of productivity and quality. The present inventors have investigated in detail the relationship between various factors of the polymerization conditions and the gel-like substance generated in the polymerization tank in the ethylene/vinyl acetate copolymerization reaction, and have found that these factors and the gel-like substance We have discovered that there is a certain relationship between the formations, and based on this we have developed a continuous copolymerization method that can prevent the formation of gel-like substances, which has been difficult in the past. That is, when producing the copolymer represented by the following general formula (1), methanol Alternatively, a continuous copolymerization reaction is carried out by using t-butanol as a polymerization solvent, using a radical initiator, setting the solvent concentration to 20% by weight or less, and setting the temperature to 35 to 80°C, and further maintaining the conditions of the following formula (2). It has been found that the formation of a gel-like substance can be prevented by /θ1.5x/1−x (2). The formation of gel-like substances is not yet clear, but in the copolymerization system, one of the polymerization components is vinyl acetate, and due to so-called polymer chain transfer, crosslinking phenomenon easily occurs, and the degree of crosslinking is As the amount increases, the cross-linked structured product produced as a by-product becomes insoluble in the reaction solution, and as the X/(X+Y) value (hereinafter referred to as ethylene content) increases, the formation and accumulation of the gel-like material is promoted. However, the site of the ethylene-vinyl acetate copolymerization reaction requires the dissolution of ethylene, which is one of the copolymerization components, and the dissolved ethylene concentration increases as the ethylene content increases;
This seems to be related to the decrease in solubility of the crosslinked structure of the copolymer. Usually, in order to obtain the polymer with a relatively high degree of polymerization, it is necessary to keep the solvent concentration in the polymerization tank low.On the other hand, when carrying out continuous polymerization while keeping the solvent concentration low, the gel-like There is a trade-off that the production and accumulation of things becomes significant. For example, when an ethylene vinyl alcohol polymer is used as a raw material resin for a molded product, it is required to maintain the solvent concentration at 20% by weight or less in order to ensure the necessary degree of polymerization of the polymer. The formation and accumulation of the gel-like substance is particularly remarkable in the low solvent concentration region. The copolymerization method provides extremely significant effects at such low solvent concentrations of 20% by weight or less and eliminates the above-mentioned obstacles. When the concentration of the solvent exceeds 20% by weight, the formation and accumulation of the gel-like substance is moderated, and the effect of the copolymerization method is diminished. The degree of polymerization of the copolymer and the like decreases as the polymerization temperature rises, so it is often selected to be 80° C. or lower, and gel-like substances are likely to form in this temperature range. The copolymerization method exhibits remarkable effects in such a temperature range and eliminates the above-mentioned problems. On the other hand, in a temperature range higher than 80° C., the degree of polymerization of the copolymer decreases, and the effect of the copolymerization method becomes insignificant. The lower the polymerization temperature is, the more preferable it is from the viewpoint of the degree of polymerization, but it is not preferable from an economic point of view because the polymerization rate decreases as the temperature decreases. In order to compensate for this disadvantage, it is possible to take measures such as increasing the polymerization rate by increasing the initiator concentration, but in this case, in the region where the polymerization temperature is lower than 35°C, it is thought to be related to an increase in the degree of polymerization. Although it is not clear yet, even if this copolymerization method is applied, the formation of the gel-like material cannot be effectively prevented. If the polymerization solvent is different, the solubility of the gel-like substance, which is considered to be a crosslinked structure of the copolymer, will differ, and the degree of generation and accumulation of the gel-like substance will also differ. Each solvent requires different copolymerization conditions, but as a polymerization solvent,
When methanol or t-butanol is used, the effects of the copolymerization method can be enjoyed.
Methanol is the most advantageous because it is inexpensive from an industrial standpoint, and t-butanol is preferred when a copolymer with a high degree of polymerization is desired. In order to obtain an ethylene/vinyl acetate copolymer through a copolymerization reaction of ethylene and vinyl acetate, etc., it is essential that ethylene is dissolved in the vinyl acetate, etc. and solvent in the polymerization tank at the time of the copolymerization reaction. The required dissolved ethylene concentration increases with increasing ethylene content of the copolymer. The solubility of the resulting gel-like material, which is considered to be a crosslinked structure of the ethylene/vinyl acetate copolymer, in the copolymerization reaction solution decreases as the dissolved ethylene concentration and the ethylene content of the copolymer increase. Although it seems that
As the ethylene content increases, the degree of formation and accumulation of the gel-like substance becomes remarkable, and in the region where the ethylene content exceeds 60 mol%, even if the copolymerization method is applied, the effect is not so significant. It is not. On the other hand, in the region where the ethylene content is low, from the above point of view, the formation and accumulation of the gel-like substance is thought to be alleviated, but on the other hand, in the region, under conditions such as the same solvent concentration and the same polymerization concentration, Although it is not clear yet, a considerable amount of gel-like material was observed to be formed, perhaps because the degree of polymerization of the resulting copolymer increased as the ethylene content decreased. Although this problem is particularly severe in the region where the solvent concentration is 20% by weight or less, the effects of the copolymerization method can be enjoyed even in such a region with low ethylene content and low solvent concentration. The copolymerization method can exhibit its effects even in a copolymerization reaction system containing a relatively small amount of a third component other than ethylene and vinyl acetate. As the amount of the third component increases, the properties of the resulting copolymer change, and the type of third component also influences the expression of the effect. In order to enjoy the effects of the present invention, the third component must be CH ₂ CRR ¹ [wherein R is hydrogen or a methyl group, and R ¹ is a methyl group or COOR], and the resulting copolymer The amount of the third component contained in the copolymer must have a molar ratio (Z/Y) of the copolymer to the acetic acid component of 0 to 0.1. The effect is often diminished. The effect of the copolymerization method is related to the polymerization rate of vinyl acetate in ethylene/vinyl acetate copolymerization, and in the high polymerization rate region exceeding 85%, the effect of the copolymerization method is reduced and the effect of the copolymerization method is substantially reduced. cannot be applied effectively. It is more preferable that the polymerization rate is 80% or less. In this copolymerization method, the average residence time in a stirring-mixing polymerization tank is determined by the following formula /θ1.5x/1−x where x0.85 [wherein, the average residence time is the average residence time, θ is the half-life of the initiator, and x is acetic acid It represents the polymerization rate of vinyl. ] must be selected so as to satisfy the above average residence time, and the effects of the copolymerization method cannot be enjoyed unless the above average residence time is maintained. The half-life of the initiator in the copolymerization method means the half-life in the concentration and solvent used, and the average residence time refers to the amount of reaction liquid in the polymerization tank in a steady state during continuous polymerization. It is given as the quotient divided by the flow rate of the reaction liquid discharged from the polymerization tank. Regarding the relationship between the average residence time and the gel-like material, there is a possibility that it may be related to the chronological order of the polymerization reaction and the decomposition reaction of the initiator in the production of the gel-like material. It's still not clear. However, selecting and maintaining the average residence time is one of the extremely important requirements of the copolymerization method, along with other requirements. The average residence time is desired to be short from an economical point of view, and is usually selected to be within about 15 hours. In the present invention, almost any radical initiator can be used within the range that satisfies the conditions of the copolymerization method. Examples of suitably used radical initiators include 2,2'-azobis-(4-methoxy-2,
4-dimethylvaleronitrile), 2,2'-azobis-(2,4-dimethylvaleronitrile), 2,
Azo compounds such as 2'-azobis-(2,4,4-trimethylvaleronitrile), 2,2'-azobis-isobutyronitrile, alkyl peresters such as t-butylperpivalate, bis-( 4
-t-butyl cyclohexyl) peroxy
dicarbonate, di-cyclohexyl peroxy dicarbonate, bis-(2-ethylhexyl) di-sec-butyl peroxy dicarbonate, di-isopropyl peroxy dicarbonate
Examples include peroxy dicarbonates such as carbonate, peroxides such as dilauroyl peroxide, didecanoyl peroxide, dioctanoyl peroxide, and dipropyl peroxide. As mentioned above, from an economic point of view, it is preferable to reduce the average residence time in order to increase the efficiency of the polymerization tank, and from this point of view, the initiator used in the copolymerization method has a relatively short half-life. Short initiators are preferred. Particularly preferred are initiators whose half-life is, for example, 5 hours or less,
To give examples 2 and 3, when the polymerization reaction temperature is 60°C, 2,2'-azobis-(4-methoxy-2,4
-dimethylvaleronitrile), 2,2'-azobis-(2,4-dimethylvaleronitrile), t-butyl peroxy neodecanoate, bis-
(4・t-butylcyclohexyl)peroxy・
dicarbonate, etc., and the polymerization temperature is
In addition to these initiators, 2,2'-azobisisobutyronitrile may be used in the temperature range of 75 to 80°C. The saponified copolymer has excellent oxygen barrier properties and is suitably used for food packaging, but in this case, strict requirements are presented regarding the color, odor, etc. of the saponified copolymer. In particular, the saponified product usually has an odor that is thought to be caused by the initiator and/or its modified product, and the requirements in this regard are the most stringent. Among the initiators, the copolymer saponified product obtained using 2,2'-azobis-(4-methoxy-2,4-dimethylvaleronitrile) has virtually no odor, and the copolymer saponified product has no odor. It is the most suitable initiator for the production of compounds. In this copolymerization method, the reaction rate of vinyl acetate is at most 85%, so when producing this copolymer industrially, it is recommended to separate and recover the unreacted portions of vinyl acetate and ethylene and recycle them. It's normal. The unreacted portion of ethylene dissolved in the copolymerization reaction solution can be easily separated and recovered by bringing the reaction solution to normal pressure. A method suitable for recycling and reusing the separated and recovered ethylene is disclosed in Japanese Patent Application Laid-Open No. 119801/1983. The unreacted portion of vinyl acetate is removed from the polymerization reaction solution by a known method, for example, by a stripping operation in which the copolymerization reaction solution after separating unreacted ethylene is led to a plate column and solvent vapor is blown into the lower part of the column. As a mixture with the solvent,
Alternatively, after being separated from the solvent, it is led to a polymerization tank and recycled for reuse. The solvent solution of the copolymer discharged from the stripping tower is saponified by a known method as described above, and the saponified copolymer is separated, washed, thermally stabilized, and dried. . The cause of the appearance of fisheye is not yet clear, but the gel-like substance is mixed into the saponified product.The gel-like substance in a swollen state that occurs when copolymerization is continuously carried out by conventional technology is extremely viscous. Disadvantages caused by being dispersed in the reaction solution in dissolved form, such as the fact that during the stripping operation, it is extremely difficult for the polymerization inhibitor that is usually present to diffuse and permeate into the gel-like material. It seems that there is a connection. After the copolymerization reaction, in the step of separating and recovering unreacted ethylene and vinyl acetate, the copolymerization reaction is carried out in order to prevent the unreacted monomers from further polymerizing and producing polymers with different properties. Usually, a polymerization inhibitor is added at a later stage. Examples of the inhibitor include copper acetate, thiourea, etc., but in order to be suitably used in the production of the saponified product, it must not impart color or odor to the saponified product during the subsequent saponification process, etc. The types of inhibitors that can be used are severely restricted. Furthermore, even if an inhibitor has become usable, it is preferable to reduce its added amount as much as possible, and for this purpose, it is required to have an extremely high ability to inhibit polymerization. It is also preferable to further improve the inhibition ability of copper acetate, thiourea, etc., and this point was also one of the technical problems to be solved. In connection with the copolymerization method, the present inventors have conducted various studies on means for relatively improving the polymerization inhibiting ability of the inhibitor, and have arrived at an extremely effective method. In other words, when performing the copolymerization reaction using an initiator with an extremely short half-life, after the copolymerization reaction, the reaction time is at least 0.5 hours or more under the same conditions as the copolymerization reaction without further addition of an initiator. This is a method in which unreacted ethylene is diffused from the copolymerization reaction solution after the residence time is maintained, and unreacted vinyl acetate is separated and recovered. 2,2'-azobis-(4-
methoxy-2,4-dimethylvaleronitrile). Even if the initiator is used, if the residence time after the reaction is less than 0.5 hours, the effect of performing this operation after the copolymerization reaction is small. Also, after the copolymerization reaction, 0.5
When maintaining a residence time of 2 hours or more, if the temperature is lower than 50°C, the residence time is 2 hours or more, making it difficult to carry out the operation efficiently. By holding the temperature above 50℃,
For the first time, significant effects can be obtained from the efficiency of the operation. Various conventional methods such as extrusion molding, blow molding, and vacuum molding can be used to mold the saponified copolymer. In addition, the product shape is film,
Any plastic material is possible. These molded products can be used for various purposes such as containers and packaging films. The present invention will be explained in detail below with reference to Examples.
In the examples, for the convenience of evaluating the surface condition, only product shapes related to films were mentioned, but the present invention is not limited to films. Example 1 Continuous polymerization was carried out under the conditions shown below to produce an ethylene/vinyl acetate copolymer in a polymerization tank having a capacity of 1 m ³ and equipped with a stirrer and having a cooling coil inside. Vinyl acetate supply amount 48Kg/hr Methanol 4 〃 2,2'-azobisisobutyronitrile supply amount
3.3g/hr Polymerization temperature 77℃ Polymerization tank ethylene pressure 60Kg/cm ² G Average residence time 6hrs Under the above conditions, the half-life of azobisisobutyronitrile is approximately 2 hours, and the polymerization rate of vinyl acetate is approximately 50%. It was hot. The polymerization reaction solution was discharged from the polymerization tank at 70 kg/hr and had the following composition. Ethylene/vinyl acetate copolymer (ethylene content: 40 mol%) 42% by weight Vinyl acetate 34 〃 Ethylene 18 〃 Methanol 6 〃 During continuous operation for 45 days, polymerization temperature control by cooling from the coil was performed stably, and No gel-like substance was observed in the polymerization reaction solution. Immediately after the polymerization reaction liquid is discharged from the polymerization tank, 10 g of thiourea/methanol solution is added and mixed at a rate of 2/hr, and then led to a tray column, where methanol vapor is blown in from the bottom of the column at a rate of 40 kg/hr to remove any unreacted materials. Vinyl acetate and ethylene are separated from the column, and a methanol solution containing 45% by weight of ethylene/vinyl acetate copolymer is extracted from the bottom of the column.
Kg/hr. A methanol solution prepared by adding 1 part by weight of caustic soda to 100 parts by weight of the ethylene/vinyl acetate copolymer solution thus obtained was saponified at 110°C under 3.5 kg/cm ² G for 30 minutes while blowing methanol vapor. The reaction was carried out, and methyl acetate produced during the reaction was distilled out together with a portion of methanol and removed from the system. Water-methanol vapor is further blown into the obtained saponified solution to distill out the methanol-water mixed vapor, resulting in saponification of the copolymer with a degree of saponification of 99.3 mol% and a methanol-water mixed system with a saponified product concentration of 35% by weight. A solution (methanol/water = 7/3 weight ratio) was obtained. This solution was discharged into a water/methanol mixture (methanol 10% by weight) at 5° C. through a die with a hole of 2 mm in diameter, and coagulated into a strand. After cutting this strand-like material with a cutter to make pellet-like material with a length of 2.5 to 3.5 mm, 15 parts by weight of the pellet-like material is
Washing was performed using parts by weight of process water. After washing, the pellets were further immersed in an acetic acid aqueous solution with an acetic acid concentration of 2 g/min, and then dried at 105°C for 24 hours.
When this was extruded at 220° C. to obtain a film with a thickness of 17 μm, the film surface appearance was extremely good and the number of fish eyes was 0.02/m ² . Control Example 1 Polymerization was carried out in Example 1, except that only the polymerization initiator was changed, and the other conditions were exactly the same. T- as an initiator
Using butyl peroxyisobutyrate, 7.8
Continuous polymerization was carried out by feeding at a rate of g/hr. The ethylene content of the obtained ethylene/vinyl acetate copolymer was 40 mol%, and the polymerization rate of vinyl acetate was about 50%. Further, the half-life of t-butyl peroxyisobutyrate under the above conditions was about 12 hours. From the fourth day of continuous operation, gel-like substances were observed in the reaction solution discharged from the polymerization tank, and the operation was stopped. The polymerization reaction solution was then treated in the same manner as in Example 1 to obtain a 17μ thick film of saponified ethylene/vinyl acetate copolymer. It turned out like this:

[Table] Example 2 Using the same polymerization tank as in Example 1, continuous polymerization was carried out under the conditions shown below. Vinyl acetate supply amount 44Kg/hr t-butanol supply amount 6 〃 Isobutylene supply amount 1.5 〃 2,2'-azobis-(4-methoxy-2,4-
Dimethylvaleronitrile) supply rate 17g/hr Polymerization temperature 60℃ Polymerization tank ethylene pressure 47Kg/cm ² G Average residence time 8hrs As a result, ethylene/vinyl acetate/isobutylene copolymer was obtained at 29Kg/hr, and the copolymer The ethylene content is 36 mol% and the vinyl acetate polymerization rate is approximately
It was 55%. Also, azobis under the above conditions
The half-life of (4-methoxy-2,4-dimethylvaleronitrile) was approximately 15 minutes. During continuous operation for three months, the polymerization temperature was stably controlled by cooling from the coil, and no gel-like substances were observed in the polymerization reaction solution. After the polymerization solution was discharged from the polymerization tank, it was treated in the same manner as in Example 1 to obtain saponified ethylene-vinyl acetate-isobutylene copolymer pellets.
When a film with a thickness of 20 μm was obtained by extrusion at 220° C., the surface appearance of the film was extremely good, and the number of fiber eyes was 0.01/m ² . Example 3 In Example 2, the polymerization liquid discharged from the polymerization tank was led to a pipe with a diameter of 4 inches and a length of 6 m, and the temperature was
The temperature was maintained at 60° C. and the pressure was 47 Kg/cm ² G. The residence time of the polymerization liquid in the pipe was about 40 minutes. After the polymerization liquid was discharged from this pipe, it was led to a plate column without adding thiourea, and then treated in the same manner as in Example 2 to obtain saponified ethylene-vinyl acetate-isobutylene copolymer pellets. Well, this
When a film with a thickness of 20 μm was obtained by extrusion at 220° C., the film surface appearance was extremely good and the number of fish eyes was 0.02/m ² . On the other hand, in this example, the polymerization liquid discharged from the polymerization tank was immediately led to the tray column without passing through the pipe with a diameter of 4 inches and a length of 6 m, and thereafter treated in the same manner to obtain a 20μ film. The number of fisheyes increased to 1.5 pieces/ ^m2 . Examples 4 to 9 Using the same polymerization tank as in Example 1, continuous polymerization was carried out under the conditions shown in the table below, and stable operation was continued for 30 days, during which time the polymer solution discharged from the polymerization tank was No gel-like substance was observed at all. Immediately after the polymerization reaction liquid is discharged from the polymerization tank, 1 g of copper acetate/methanol solution is added and mixed (adding 5 ppm of copper acetate to the copolymer polymer), and then led to a tray column, where methanol vapor is released from the bottom of the column. By blowing, unreacted vinyl acetate and ethylene were separated from the top of the column, and a methanol solution of ethylene/vinyl acetate copolymer was obtained from the bottom of the column. 10% to the resulting solution
Add a caustic soda methanol solution (5% by weight of caustic soda added to the copolymer polymer) and heat at 60°C.
After carrying out the saponification reaction for 2 hours, the reaction solution was transferred to 5 times the volume of water, the polymer was fully extracted and deliquified, and the polymer was further washed twice with the same amount of water, and after deliquification, the same amount After being immersed and treated in an acetic acid aqueous solution (acetic acid concentration 1.5g/), it was dried at 105℃ for 24 hours, and the degree of saponification was 98-99.
A saponified ethylene/vinyl acetate copolymer of mol% was obtained. When this was extruded at 230° C. to obtain a film with a thickness of 20 μm, the surface appearance of the film was good and the number of fisheyes was extremely small at 0.02 to 0.05 as shown in the table below.

[Table] Control Examples 2 to 6 Using the same polymerization tank as in Example 1, continuous polymerization was carried out under the conditions shown in the table below, but in all cases, the polymerization tank was discharged after the second to fourth day of operation. There was no case where a gel-like substance was observed in the polymer solution and stable continuous polymerization operation was possible for more than 14 days. Example 4~
When a film with a thickness of 20 μm was obtained by processing in the same manner as in Example 9, the film surface was extremely rough and the number of fish eyes was as shown in the table below.

[Table] Examples 10 to 12, Control Example 7 In the same polymerization tank as in Example 1, vinyl acetate supply rate 45Kg/hr, methanol supply rate 5Kg/hr, polymerization temperature 40℃, polymerization tank ethylene pressure 35Kg/cm ² G , initiator 2,2'-azobis-(4-methoxy-2,4-dimethylvaleronitrile) (half-life under polymerization conditions is 2 to 3 hours), and continuous polymerization was carried out under conditions with an average residence time of 7 hours, An ethylene/vinyl acetate copolymer with an ethylene content of 34 to 37 mol% was obtained. In this case, the polymerization rate of vinyl acetate was varied by adjusting the amount of initiator supplied. The polymerization solution was treated in the same manner as in Example 1 to obtain a film of saponified ethylene/vinyl acetate copolymer having a thickness of 17 μm. The vinyl acetate polymerization rate, the number of days of continuous polymerization operation, and the number of fixation eyes of the film obtained from the corresponding polymer are as shown in the table below. As a control example, results with a polymerization rate of 70% are also shown.

[Table] Examples 13 to 15, Control Example 8 In the same polymerization tank as Example 1, the polymerization temperature was 50
℃, polymerization tank ethylene pressure 36Kg/cm ² G, 2,2'-azobis-(4-methoxy-2,4-
Continuous ethylene/vinyl acetate copolymerization was carried out using dimethylvaleronitrile (half-life 0.9 hours under polymerization conditions). In this case, the average residence time was adjusted by changing the amounts of vinyl acetate and methanol supplied as shown in the table below, and the rate of vinyl acetate polymerization was maintained at 65% by adjusting the amount of initiator supplied. The ethylene content of the obtained ethylene/vinyl acetate copolymer was 30 to 32 mol%. The polymerization solution was treated in the same manner as in Example 1 to obtain a film of saponified ethylene/vinyl acetate copolymer having a thickness of 17 μm. The average residence time in the polymerization tank, the number of days of continuous polymerization operation, and the corresponding number of fixation eyes of the film obtained from the polymer were as shown in the table below. Average residence time 2 as a control example
Results for time are also shown.

[Table] Example 16 In Example 13, similarly to Example 3, the polymerization liquid discharged from the polymerization tank was placed in a tube with a diameter of 4 inches and a length of 6 m.
was introduced into the pipe, and the temperature was maintained at 50°C and the pressure was maintained at 36 kg/cm ² G. The residence time of the polymerization liquid in the piping is approximately
It was hot in 40 minutes. After the polymerization liquid is discharged from this pipe, it is led to the plate tower without adding thiourea.
Thereafter, the film was processed in the same manner as in Example 13 to obtain a film with a thickness of 17 μm. The film surface appearance was extremely good and the number of fish eyes was 0.03 pieces/m ² . On the other hand, in this example, the polymerization liquid discharged from the polymerization tank was immediately led to the plate column without passing through the pipe with a diameter of 4 inches and a length of 6 m, and thereafter treated in the same manner.
When a 17μ film was obtained, the number of fish eyes increased to 1.2/m ² .

Claims (1)

[Claims] 1. A saponified product (saponification degree of 85% or more) of a copolymer represented by the following general formula (1) Methanol solution or methanol of the copolymer
In the process of saponifying a tertiary butyl alcohol mixed solution in the presence of an alkali or alkali metal alcoholate, methanol or tertiary butyl alcohol is used as a polymerization solvent, a radical initiator is used, and the solvent temperature is maintained at 20°C. It is characterized by using the copolymer obtained by carrying out continuous copolymerization at a temperature of 35-80℃ and the following conditions (2) below by weight /θ1.5x/1-x (2) A method for producing a molded article of a saponified ethylene-vinyl acetate copolymer having excellent surface properties. However, in formula (1), X/(Y+Z)=0.3 or
1.5 Z/Y=0 to 0.1 R is hydrogen or a methyl group, R ¹ is a methyl group or a COOR group. Also, in equation (2), x0.85
x is the polymerization rate of vinyl acetate, is the average residence time in the polymerization tank, and θ is the half-life of the polymerization initiator. 2. A method for producing a saponified ethylene-vinyl acetate copolymer molded product according to claim 1, which takes 15 hours. 3. The method for producing a saponified ethylene-vinyl acetate copolymer molded product according to claim 1 or 2, wherein the time is 3 θ5 hours. 4 The radical initiator is 2,2'-azobis-(4
-methoxy-2,4-dimethylvaleronitrile)
A method for producing a saponified ethylene-vinyl acetate copolymer molded product according to claim 1 or 2. 5 A saponified copolymer (saponification degree of 85% or more) represented by the following general formula (1), In obtaining the copolymer by saponification in the presence of an alkali or metal alcoholate in a methanol solution or a methanol-tertiary butyl alcohol mixed solution, using methanol or tertiary butyl alcohol as a polymerization solvent, 2. 2′−
Using azobis-(4-methoxy-2,4-dimethylvaleronitrile) as an initiator, the solvent concentration is 20% by weight or less, the temperature is 50 to 80°C, and the conditions of formula (2) below are maintained. After copolymerization, the copolymerization reaction solution was maintained at the polymerization temperature for at least 0.5 hours without further addition of an initiator. A method for producing a molded article of a saponified ethylene/vinyl acetate copolymer, the molded article having excellent surface properties, characterized by using the copolymer. However, in formula (1), X/(Y+Z)=0.3 or
1.5 Z/Y=0 to 0.1 R is a hydrogen atom or a methyl group, and R ¹ is a methyl group or a COOR group. Also, in equation (2), x
0.85 x is the polymerization rate of vinyl acetate, is the average residence time in the polymerization tank, and θ is the half-life of 2,2'-azobis-(4-methoxy-2,4-dimethylvaleronitrile).