JPH0152404B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention uses an alcohol having 1 to 4 carbon atoms as a polymerization solvent and a radical polymerization initiator to prevent the formation of a gel-like substance when performing a continuous polymerization reaction to obtain an ethylene/vinyl acetate copolymer. This relates to a continuous ethylene/vinyl acetate copolymerization method. Conventionally, various methods are known for polymerizing vinyl monomers, but the continuous polymerization method has low productivity and
It is widely used as a vinyl acetate polymerization method due to its industrial advantages such as uniformity of quality. The present inventors have investigated in detail the relationship between various factors of the polymerization conditions and the gel-like substance produced in the polymerization tank in the ethylene/vinyl acetate copolymerization reaction. It has been discovered that there is a certain relationship between the two, and based on this, the present invention has been developed which can prevent the formation of gel-like substances, which has been difficult in the past. That is, the present invention provides for continuous copolymerization of ethylene and vinyl acetate to produce an ethylene/vinyl acetate copolymer having an ethylene content of 20 to 60 mol%. continuous copolymerization of ethylene and vinyl acetate, characterized in that the concentration of the polymerization solvent is 20% by weight or less, the temperature is 35 to 80°C, and the continuous copolymerization is carried out under conditions that satisfy the following formula (1). It's legal. ○/H/θ≧1.5x/1−x (0.85≧x≧0.2)……(1) {x is the polymerization rate of vinyl acetate, (H) is the average residence time in the polymerization tank, θ is the polymerization initiator Indicates half-life (hours). } Although the formation of gel-like substances is not yet clear, in the copolymerization system, one of the polymerization components is vinyl acetate, and crosslinking tends to occur due to so-called polymer chain transfer, and the degree of crosslinking increases. However, as the ethylene content increases, the formation and accumulation of the gel-like material is facilitated, but the ethylene/vinyl acetate copolymerization reaction The dissolution of ethylene, which is one of the copolymerization components, is an essential requirement in the field, and the concentration of dissolved ethylene increases as the ethylene content increases, and the solubility of the crosslinked structure of the copolymer decreases. It seems that there is a connection. Normally, 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, and on the other hand, when carrying out continuous polymerization while keeping the solvent concentration low, it is necessary to maintain the gel-like substance. There is a trade-off between generation and accumulation. 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 present invention provides extremely significant effects at such low solvent concentrations of 20% by weight or less and eliminates the above-mentioned problems. When the concentration of the solvent exceeds 20% by weight, the formation and accumulation of the gel-like substance is moderated, and the effects of the present invention are 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 present invention 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 effects of the present invention become less noticeable. Although a lower polymerization temperature is preferable from the viewpoint of the degree of polymerization, it is not preferable from an economic point of view because the polymerization rate decreases as the temperature decreases. 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, it seems to be related to an increase in the degree of polymerization in the region where the polymerization temperature is lower than 35°C. Although it is not clear yet, even if the method of the present invention is applied, the formation of the gel-like substance 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 product of the copolymer, will differ, and the degree of generation and accumulation of the gel-like substance will also differ, so in order to prevent the generation and accumulation, different methods are required. Although different copolymerization conditions are required for each solvent, the effects of the present invention can be enjoyed when an alcohol having 1 to 4 carbon atoms is used as the polymerization solvent. From an industrial standpoint, cheap methanol is the most advantageous, and if a high degree of polymerization is desired, tertiary methanol is the most advantageous.
Butyl alcohol (hereinafter referred to as t-butanol) is preferred. 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 during the copolymerization reaction. and
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 structured product of the ethylene/vinyl acetate copolymer, in the copolymerization reaction solution is as follows:
This seems to be because it decreases as the dissolved ethylene concentration and the ethylene content of the copolymer increases, but as the ethylene content increases, the degree of formation and accumulation of the gel-like substance becomes remarkable, and the ethylene content increases.
In a region exceeding 60 mol%, even if the present invention is applied, the effect will no longer be significant. 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 temperature, Although it is not clear yet, a considerable amount of gel-like material was observed to be produced, probably because the degree of polymerization of the produced 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 present invention can be enjoyed even in such a region where the ethylene content is low and the solvent concentration is low. Therefore, the lower limit of the ethylene content is not particularly limited, but is preferably 20 mol% or less. The present invention provides a third method other than ethylene and vinyl acetate.
This effect is also exhibited in copolymerization reaction systems containing relatively small amounts of components. The third component is CH ₂ .
CRR' [wherein R is hydrogen or a methyl group, R' is a methyl group or COOR], and the amount of the third component contained in the produced copolymer is the molar amount relative to the vinyl acetate component of the copolymer. It is necessary that the ratio is 0.1 or less, and if the amount of the third component is exceeded, the effect of the present invention is often diminished. The effects of the present invention are related to the polymerization rate of vinyl acetate in ethylene/vinyl acetate copolymerization, and in the high polymerization rate region exceeding 85%, the effects of the present invention are reduced and the present invention is effectively reduced. cannot be applied. It is more preferable that the polymerization rate is 80% or less. Further, the polymerization rate is preferably 20% or more. In the present invention, the average residence time in a stirring and mixing polymerization tank is determined by the following formula: ○/H/θ1.5x/1−x where x0.85 [wherein, the average residence time is the half-life of the initiator, and x is acetic acid] (representing the polymerization rate of vinyl)], and unless the average residence time is maintained, the effects of the present invention cannot be enjoyed. The half-life of an initiator as used in the present invention means the half-life at the operating temperature and in the 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 . Regarding the relationship between the average residence time and the gel-like material, it is speculated that it is related to the chronological order of the polymerization reaction and the decomposition reaction of the initiator in the production of the gel-like material, but it is still unclear. It's not clear. However, selecting and maintaining the average residence time is one of the extremely important requirements of the present invention, along with other requirements. In order to suppress the generation of gel-like substances and block-like substances, it is important to satisfy the equation (2) ○/H/θ1.5x/1-x, which has been discovered through various experiments. It is. If ○/H/θ is plotted on the vertical axis and the polymerization rate (x) is plotted on the horizontal axis, and ○/H/θ=1.5x/1-x is plotted in a graph, it will be as shown in Figure 1, which is within the scope of the present invention. is the upper part of the curve in FIG. In other words, the scope of the present invention shown in FIG.
This shows that as the polymerization rate (x) increases, it is important to use a polymerization initiator with a short half-life (θ) or to lengthen the residence time ((H)).
In addition, those that satisfy the formula (2) produce less gel-like substances and block-like substances, and those that do not satisfy the formula (2) produce many gel-like substances and block-like substances. 1 to 9 and Control Examples 1 to 6
It is clear from the description. 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 present invention.
Examples of suitably used radical initiators include:
2',2-azobis-(2,4-dimethylvaleronitrile), 2,2'-azobis-(2,4,4-trimethylvaleronitrile), 2,2'-azobisisobutyronitrile, 2, Azo compounds such as 2'-azobis-(4-methoxy-2,4-dimethylvaleronitrile), alkyl peresters such as t-butyl peroxy neo-decanoate and t-butyl perpivalate, bis-(4 -t-butylcyclohexyl) peroxy dicarbonate,
Peroxy dicarbonates such as dicyclohexyl peroxy dicarbonate, bis-(2-ethylhexyl) di-sec-butyl peroxy dicarbonate, diisopropyl peroxy dicarbonate, di lauroyl peroxide, di-decanoyl peroxide,
Peroxides include di-octanoyl peroxide and di-propyl 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 present invention is an initiator with a relatively short half-life. is suitable. Particularly preferred are initiators whose half-life is within 5 hours, for example, 2,2'-azobis-(2,2'-azobis-(2,
4-dimethylvaleronitrile), t-butylperoxy neo-decanoate, bis-(4-t-
butyl cyclohexyl) peroxy dicarbonate, etc., and the polymerization temperature is 75 to 80
In the temperature range of °C, examples include 2,2'-azobisisobutyronitrile. The present invention will be described in detail below with reference to Examples, but the present invention is not limited to these Examples. Example 1 Continuous polymerization was carried out under the conditions shown below to produce an ethylene/vinyl acetate copolymer in a polymerization tank with a capacity of 10 and equipped with a stirrer and a cooling coil inside. Vinyl acetate supply amount 480g/hr Methanol 〃 40 〃 2,2′-azobisisobutyronitrile supply amount
33mg/hr Polymerization temperature 77℃ Polymerization tank ethylene pressure 60Kg/cm ² G Average residence time 6hrs The ethylene content of the ethylene/vinyl acetate copolymer obtained at this time was 40 mol%, and the polymerization rate of vinyl acetate was approximately 50 It was %. Further, the half-life of azobisisobutyronitrile under the above conditions was about 2 hours. During continuous operation for 45 days, the polymerization temperature was controlled stably by cooling from the coil, and no gel-like substances were observed in the polymer solution discharged from the polymerization tank. After 45 days of continuous operation, the interior of the polymerization tank was inspected and no polymer scale or block-like material was found on the cooling coil, stirrer shaft, blades, tank inner wall, etc. Control Example 1 In Example 1, only the initiator was changed and the other conditions were the same. Using t-butylperoxyisobutyrate as initiator, 78mg/
Continuous polymerization was carried out by feeding at hr. The ethylene content of the ethylene/vinyl acetate copolymer obtained at this time was 40 mol%, and the polymerization rate of vinyl acetate was about 50%. Also, t under the above conditions
-The half-life of butyl peroxyisobutyrate is approximately
It was hot for 12 hours. From the 4th day of continuous operation, gel-like substances began to be observed in the polymer solution discharged from the polymerization tank, and on the 10th day, polymerization temperature control by cooling from the coil became unstable and operation was stopped. . When the inside of the polymerization tank was inspected, approximately 200g of polymer scale and block-like substances were found attached to the cooling coil, stirrer shaft, tank inner wall, etc. 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 440g/hr t-butanol supply amount 60 〃 Isobutylene 〃 15 〃 2,2'-azobis-(2,4-dimethylvaleronitrile) supply amount 110mg/hr Polymerization temperature 60℃ Polymerization tank ethylene pressure 47Kg/cm ² G Average residence time 8hrs As a result, ethylene/vinyl acetate/isobutene copolymer was obtained at 290g/hr, the ethylene content of the copolymer was 36 mol%, and the polymerization rate of vinyl acetate was approximately
It was 55%. Also, azobis under the above conditions
The half-life of (2,4-dimethylvaleronitrile) was approximately 3 hours. Operation continued stably for 60 days, during which time no gel-like substance was observed in the polymer solution discharged from the polymerization tank. After 60 days of continuous operation, the inside of the polymerization tank was inspected and found that there was only a small amount of polymer scale and block-like substances attached, weighing only about 7g. Control Example 2 In Example 2, 2,2'-azobis-(2,
4-dimethylvaleronitrile) supply amount to 260mg/
Continuous polymerization was carried out under the same conditions as above. The ethylene content of the obtained ethylene/vinyl acetate/isobutene copolymer was 38 mol%, and the vinyl acetate polymerization rate was about 65%. From the second day of continuous operation, gel-like substances began to be observed in the polymer solution discharged from the polymerization tank, and on the 12th day, polymerization temperature control by coil cooling became unstable, making polymerization operation impossible. It stopped. When I inspected the inside of the polymerization tank, I found that the cooling coil,
Approximately 250 g of polymer blocks were found attached to the stirrer shaft, blades, inner wall of the polymerization tank, etc. Examples 3 to 8 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 could be continued for 30 days in all cases. During this period, no gel-like substance was observed in the polymer solution discharged from the polymerization tank. After 30 days of continuous operation, the inside of the polymerization tank was inspected and the amount of polymer scale and block-like substances adhered was extremely small as shown in the table below.

[Table] Control Examples 3 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. After the operation was stopped, the inside of the polymerization tank was inspected, and as shown in the table below, a large amount of polymer scale and block-like substances were found adhering to the cooling coil, stirrer shaft, inner wall of the polymerization tank, etc.

[Table] Example 9 In the same polymerization tank as in Example 1, vinyl acetate supply rate 450g/hr, methanol supply rate 50g/hr, polymerization temperature 60℃, polymerization tank ethylene pressure 45Kg/cm ² G initiator 2,2' -Azobis-(2,4-dimethylvaleronitrile) (half-life under polymerization conditions is 3 hours), continuous polymerization was carried out under conditions with an average residence time of 7 hours, and ethylene-vinyl acetate with an ethylene content of 34 to 37 mol% was co-polymerized. A polymer was obtained. In this case, when we changed the polymerization rate of vinyl acetate by adjusting the supply amount of 2,2'-azobis-(2,4-dimethylvaleronitrile), we found that the number of continuous operation days and the amount of polymer blocks attached inside the polymerization tank were The results shown in the table below were obtained. Polymerization rate of 70% as a control example
The results for the case are also shown at the same time.

[Table] Example 10 In the same polymerization tank as Example 1, the polymerization temperature was 65
Continuous ethylene/vinyl acetate copolymerization was carried out using t-butyl perpivalate (half-life under polymerization conditions of 3 hours) as an initiator at a temperature of 45 Kg/cm ² G in a polymerization tank. In this case, the amounts of vinyl acetate and methanol fed were changed as shown in the table below to adjust the average residence time, and the amount of t-butyl perpivalate fed was adjusted to maintain the vinyl acetate polymerization rate at about 55%. The ethylene content of the obtained ethylene/vinyl acetate copolymer was 29 to 31 mol%. By changing the average residence time, the number of days of continuous operation and the amount of polymer blocks deposited inside the polymerization tank were as shown in the table below. As a control example, the results with an average residence time of 5 hours are also shown.

【table】

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the curve /θ=1.5x/1−x, where the vertical axis shows /θ and the horizontal axis shows the polymerization rate (x).

Claims (1)

[Claims] 1. Continuous copolymerization of ethylene and vinyl acetate,
When producing an ethylene/vinyl acetate copolymer with an ethylene content of 20 to 60 mol%, an alcoholic polymerization solvent having 1 to 4 carbon atoms and a radical initiator are used, and the concentration of the polymerization solvent is maintained at a temperature of 20% by weight or less. 35
A continuous ethylene/vinyl acetate copolymerization method characterized by continuous copolymerization at ~80°C and under conditions that satisfy the following formula (1). ○/H/θ≧1.5x/1−x (0.85≧x≧0.2)……(1) {x is the polymerization rate of vinyl acetate, (H) is the average residence time in the polymerization tank, θ is the polymerization initiator Indicates half-life (hours). }