JPH03229713A - Production of ethylene copolymer - Google Patents

Abstract

PURPOSE:To enable the stable long-term production of an ethylene copolymer by conducting the radical copolymn. of ethylene with a radical-polymerizable acid anhydride in the form of a specific emulsion in the presence of a polymn. initiator under a high pressure. CONSTITUTION:10-50wt.% disperse phase comprising a radical-polymerizable acid anhydride which contains at least one radical-polymerizable unsatd. bond and at least one acid anhydride group, pref. cyclic, in the molecule and which, when polymerized, is capable of introducing an acid anhydride group into the polymer is dispersed in a dispersion medium comprising a poor solvent for the acid anhydride to give an emulsion. Then, ethylene is copolymerized with the acid anhydride in the emulsion in the presence of a polymn. initiator under 700-300atm at 100-300 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing an ethylene copolymer. More specifically, the present invention relates to a production method for copolymerizing ethylene and a radically polymerizable acid anhydride under high pressure to stably obtain a copolymer with excellent adhesiveness and paintability over a long period of time.

[Prior Art] Copolymers of ethylene and various polymers have been produced in order to improve adhesiveness, paintability, etc., which are disadvantages of polyethylene. Copolymers of ethylene and radically polymerizable acid anhydrides such as maleic anhydride have also been produced from this perspective.
For example, in the case of maleic anhydride, it is solid at room temperature, so if it is injected alone into the system, it may cause problems with clogging of piping, or the reaction may not be stable due to insufficient mixing with ethylene.

In order to solve this problem, it is possible to dissolve maleic anhydride in a solvent and inject it into the system as a solution, as disclosed in JP-A-61-60708 and JP-A-61-60709.

However, in the technology disclosed in the above patent, the radically polymerizable acid anhydride is basically injected into the reaction system using a solvent that is not compatible with ethylene, so ethylene and the acid anhydride solution are mixed. The reaction is very unstable,
In particular, when trying to increase the amount of acid anhydride in the product, stable operation for a long period of time was impossible.

[Problem to be Solved by the Invention J] The present invention provides a method for producing a copolymer of ethylene and a radically polymerizable acid anhydride in a stable manner over a long period of time.

[Means for Solving the Problems] In order to solve the problems mentioned above, as a result of intensive research, we found that when ethylene and a radically polymerizable acid anhydride are radically copolymerized under high pressure using a polymerization initiator, a radically polymerizable acid By injecting the anhydride into the reaction system as an emulsion in which the radically polymerizable acid anhydride itself or the radically polymerizable acid anhydride solution is the dispersed phase using a poor solvent as a dispersion medium, a copolymer of excellent quality can be produced. was found to be stably obtained.

The present invention will be explained in detail below.

The radically polymerizable acid anhydride referred to in the present invention refers to one or more radically polymerizable unsaturated bonds and one or more acid anhydride groups in the molecule, so that the acid anhydride group can be introduced into the polymer through polymerization. means a chemical compound.

The acid anhydride is preferably a cyclic one, and specific examples of the compound include maleic anhydride, itaconic anhydride, citraconic anhydride, endic anhydride, dodecenyl succinic anhydride, etc. Maleic anhydride and itaconic anhydride are particularly preferred. In some cases, two or more of these may be used in combination.

In the present invention, the radically polymerizable acid anhydride is injected into the reaction system in the form of an emulsion. In preparing the emulsion, the radically polymerizable acid anhydride may be heated above its melting point to form a dispersed phase in the melt state, or the radically polymerizable acid anhydride may be dissolved in a good solvent to form a solution. may be used as the dispersed phase. When heating the radically polymerizable acid anhydride, the inside of the adjustment tank must be completely purged with inert gas since there is a possibility of thermal polymerization in air.

First, the acid anhydride is made into a solution, and then mixed into a dispersion medium to obtain an emulsion using this solution as the dispersion medium.The optimal solvent will vary depending on the type of the radically polymerizable acid anhydride. , compounds that react with acid anhydrides cannot be used. Specific examples of good solvents include acetone, 2
- Ketones such as butanone and esters such as methyl acetate and ethyl acetate can be mentioned.

The dispersion medium of the emulsion must be a poor solvent for the radically polymerizable acid anhydride and a solvent that has good compatibility with ethylene. It's good.

More specific chemical compounds include hexane, octane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane (including both linear and branched types), benzene, toluene, xylene, etc. A mixture may also be used. When adjusting the emulsion,
A small amount of a surfactant component typified by higher fatty acids or derivatives thereof may be added.

By adding a surfactant component, the emulsion can be easily adjusted and the dispersed particle size becomes smaller, resulting in a stable emulsion. Therefore, more uniform mixing of ethylene and acid anhydride is promoted, which may contribute to improving the stability of one reaction. Examples of compounds that can be used as surfactants include stearic acid, barmitic acid, sodium stearate, calcium stearate, polyoxyethylene alkyl ethers, and the amount of these compounds added is usually 0.01. It is about 2%.

The ratio of the dispersion medium to the dispersed phase of the emulsion is such that the dispersed phase is 1
It must be 0 to 50% by weight; if the proportion is less than 10%, the amount of solvent injection to introduce a predetermined amount of acid anhydride into the product increases, making it difficult to increase the molecular weight of the polymer by chain transfer reaction. If the ratio exceeds 50%, agglomeration of the dispersed phase tends to occur in the emulsion, and the reaction stability, which is a feature of the present invention, cannot be exhibited.

The reason why the reaction stability is improved by injecting the emulsion as an emulsion is not clear, but because the dispersion medium has good compatibility with ethylene, the miscibility is good, and compared to when the emulsion is injected as a solution, the comonomer radical This is presumed to be because uniform dispersion of the polymerizable acid anhydride is promoted and local reactions do not occur.

For copolymerization of ethylene and radically polymerizable acid anhydride, high-pressure low-density polyethylene manufacturing equipment and technology can be used.

As the reactor type, an autoclave or tubular type reactor equipped with a stirrer can be used, and if necessary, a plurality of reactors can be connected in series or in parallel to perform multistage polymerization. Furthermore, in the case of an autoclave-type reactor, by partitioning the inside of the reactor into multiple zones,
It is also possible to create a −degree distribution and perform more precise temperature control.

The most common method is the bulk copolymerization method, which has a polymerization rate of 700 to 300
It is produced by radical polymerization in a temperature range of 100 to 300°C under a pressure of 0 atmospheres.

The preferred pressure and temperature range is 1500 to 2500
The atmospheric pressure and the average temperature in the reactor can be 150 to 250°C.

If the pressure is below 700 atm, the molecular weight of the polymer cannot be made sufficiently large, resulting in poor moldability and physical properties. Pressures above 3000 atmospheres are practically meaningless (and only increase production costs).

If the temperature is below 100° C., the reaction is not stable and the conversion rate to the polymer decreases, which is an economical problem. 300℃
If this is exceeded, the molecular weight of the polymer cannot be increased and there is a risk of runaway reaction.

More specifically, an emulsion of ethylene and a radically polymerizable acid anhydride according to the present invention is compressed and injected into a reactor.
Polymerization is performed using a radical initiator that is separately injected.

The effects of the present invention can be enjoyed if the emulsion is used during preparation and injection into the reaction system.

For example, in a certain part of the reaction system, the temperature may be below the melting point of the dispersed phase of the emulsion, and an emulsion may not be formed in the strict sense, but for convenience, this is also included within the scope of the emulsion of the present invention. shall be included.

It is preferable that ethylene and the acid anhydride emulsion be thoroughly mixed beforehand during injection, but it is not preferable that the radical initiator and ethylene and the acid anhydride emulsion come into contact with each other until they enter the reactor. If the radical initiator and chlorine come into contact before the reactor, polymerization may occur within the pipes, which may cause problems such as pipe blockages. Ethylene is usually compressed in two stages using two compressors: a primary compressor and a secondary compressor. It is preferable to use a high pressure pump. This promotes the mixing of the 1,000-mer particles within the secondary compressor, and allows smooth copolymerization within the reactor.

It is possible to directly inject the acid anhydride emulsion into the piping inside the secondary compressor or into the reactor, but in this case, the monomers may not mix sufficiently and the reaction may not be stable, or the acid anhydride emulsion may not be compressed directly to ultra-high pressure. Therefore, troubles such as crystallization or polymerization of the acid anhydride emulsion may occur in the pump or piping.6 Also, a method of injecting the acid anhydride emulsion before the primary compressor is considered. However, in this case, a large amount of the acid anhydride falls as drain in the middle or discharge part of the compressor, so it is not a preferable method from an economical point of view and problems such as disposal of drain waste.

Providing a mixing device such as a static mixer immediately before the inlet of the reactor in order to improve the mixing of ethylene and the emulsion is highly effective in practice and is preferred in promoting the mixing of ethylene and the acid anhydride emulsion.

It is preferable to thoroughly mix the acid anhydride emulsion before the suction tank of the injection pump.

When mixing with ethylene, the emulsion can be heated as necessary, or a strong stirring device such as a homogenizer can be used. At this time, a compound for stabilizing the reaction within the reactor, such as an antioxidant, may be mixed at the same time, depending on the case.

When injecting ethylene and the acid anhydride emulsion into the reactor, the injection position, temperature, flow rate, etc. can be appropriately selected depending on the purpose. That is, the acid anhydride emulsion may be injected into multiple locations within the reactor, or when using a reactor with multiple reactors or multiple zones, the acid anhydride emulsion may be injected only into a specific reactor or specific zone. By changing the flow rate balance to each reactor or zone, it is possible to obtain a polymer having a preferable molecular weight and molecular weight distribution depending on the purpose. Furthermore, by appropriately adjusting the temperature at the inlet of the reactor, it is possible to change the polymerization stability within the reactor and the molecular weight distribution of the produced polymer.

Compounds that generate free radicals, mainly organic peroxides, are used as polymerization initiators. For example, dialkyl peroxides such as di-1-butyl peroxide, dicumyl peroxide, and t-butylcumyl peroxide; diacyl peroxides such as acetyl peroxide, l-butyl peroxide, and octanoyl peroxide; peroxycarbonates such as vilpa oxydicarbonate and di-2-ethylhexyl peroxydicarbonate;
Peroxy esters such as t-butyl peroxyvivalate and t-butyl peroxylaurate, ketone peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide, 1.1-bis-t-butyl peroxycyclohexane, 2.2- Examples include peroxyketals such as bis-t-butyl peroxyoctane, hydroperoxides such as t-butyl hydroperoxide and cumene hydroperoxide, azo compounds such as 2,2-azobisisobutyronitrile, and oxygen. It will be done.

It is also possible to use various chain transfer agents as molecular weight regulators during polymerization. Examples of chain transfer agents include olefins such as propylene, butene and hexene, paraffins such as ethane, propane and butane, toluene,
Aromatic hydrocarbons such as xylene and ethylbenzene can be mentioned.

The copolymer obtained by polymerization by the method described above is discharged from the reactor together with unreacted monomers and solvent, and passes through a high-pressure separator, optionally a medium-pressure separator, and a low-pressure separator to separate the polymer and monomer or After separating the low molecular weight polymer, it is pelletized through an extruder, and unreacted ethylene is recycled after removing the low molecular weight polymer with a filter. When pelletizing, various additives as described later can be added.

The amount of acid anhydride groups contained in the copolymer obtained by this production method can vary depending on the use, but numerically, the number of repeating units is in the range of 0.03 to 3 moβ%. . If the amount of acid anhydride is less than 0.03 moβ%, functions such as adhesiveness will not be fully exhibited, and copolymers with more than 12% 3mo are extremely difficult to produce and are not practical.

MFR as a guideline for molecular weight (JIS-7210
190°C) cannot be unconditionally defined depending on the application, but as a normal molded product, it is generally o, i ~ 5000°C.
g/10 minutes. If the MFR is smaller than 0.1/10 minutes, there will be problems in molding. The MFR is 5000g/10
If it exceeds 100%, it will be difficult to mold it into a normal molded product and it will not be able to exhibit sufficient strength. However, for hot melt, adhesive coating, or resin improver applications, it may be possible to use the MFR above 5000 g/10 minutes.

According to the production method shown above, a copolymer of ethylene and a radically polymerizable acid anhydride can be stably produced, and the obtained copolymer can be used to make adhesive resins and resin modifications by taking advantage of its properties. Can be used for materials, etc. The present invention will be described in detail below with reference to Examples.

[Example 1] In the following Examples and Comparative Examples, a polymerization reaction was carried out continuously using a low-density polyethylene manufacturing facility equipped with an autoclave-type reactor equipped with a stirrer and divided into two zones with an internal volume of 42. .

Tert-butyl peroxybivalate was used as a polymerization initiator.

After thoroughly mixing the radically polymerizable acid anhydride emulsion in the tank, it is pressurized into the suction pipe of the secondary compressor using a high-pressure pump, compressed together with ethylene, and the ethylene monomer is injected into the first zone of the reactor. The temperature of is about 4
It was 0°C.

The polymer obtained after polymerization was passed through a high-pressure separator and a low-pressure separator to separate it into polymer and unreacted polymer, and the residual polymer was recycled through a cooler and a filter. The polymer was pelletized into a product using an extruder and granulation device installed at the bottom of the low-pressure separator.

The amount of acid anhydride in the copolymer was determined using infrared absorption spectroscopy.

As a measure of polymerization reaction stability, the width of temperature hunting at the temperature control point in the lower part of the first zone of the reactor is described.

The numbers listed here are for automatic driving under certain control conditions.
This is the difference between the highest and lowest temperature over a period of time.

(Example 1) 50 kg of maleic anhydride and 200 kg of dodecane were charged into a tank with an internal volume of 400 e and equipped with a high-speed stirrer, and heated at 60°C.
The emulsion was prepared by stirring at high speed at 250 rpm. The emulsion was injected into the reaction system using a high-pressure pump without lowering the temperature. The flow rate of ethylene at the reaction filling port was 100 Kg/hr, and the flow rate of the comonomer emulsion was 2 liter/hr.

The reaction temperature varies depending on the measurement point, but is 210-220℃
, when polymerization was carried out at a pressure of 1900 atm, the MFR (
A copolymer having a JIS-7'210-190°C) 95 and a maleic anhydride component content of 0.6 moQ% was obtained. The polymerization reaction was very stable, and the width of the temperature hunting in the first zone was 3°C.

(Example 2) Anhydrous Itacone! An emulsion was prepared in the same manner as in Example 1 using 140 kg of xylene and 200 kg of xylene at a temperature of 70°C.
When polymerized at atmospheric pressure, a copolymer with an MFR of 12 and an itaconic anhydride component of 0.45 moβ% was obtained. The polymerization reaction was stable, and the temperature hunting range was 4°C.

(Example 3) In the emulsion of Example 2, 1.5 kg of stearic acid was added as a surfactant. Polymerization was carried out under the same conditions as in Example 2 at 210-225°C and 1900 atm.
The reaction stability was very good and the temperature hunting was 2°C. The obtained copolymer had an MFR of 9 and an O1 itaconic anhydride component of 0.5 moβ%.

(Example 4) An emulsion was prepared in the same manner as in Example 1 using g of anhydrous maleic #30, 50 kg of acetone, and 150 kg of octadecane, and polymerization was carried out at 200 to 220°C and 1850 atm. The obtained copolymer had an MFRI of 2.3 and a maleic anhydride component of 0.41 moI of 2%. Reaction stability was particularly problematic (the width of the temperature hunting was 6°C).

(Comparative Example 1) Maleic anhydride was dissolved in ethyl acetate, a good solvent, in the same manner as in Example 1, and the solution was used to dissolve 195 to 23
Polymerization was carried out at 0°C and 1950 atm. Although a copolymer with an MFR of 28 and a maleic anhydride component content of 0.40 moβ% was obtained, the reaction was unstable and automatic operation was impossible, so manual control had to be used. The width of the temperature hunting was 18°C.

(Comparative Example 2) In the emulsion production of Example 1, 10 kg of maleic anhydride was used to prepare a low concentration emulsion. 1
Polymerization was carried out at 90 to 205°C and 1950 atm, but in order to make the maleic anhydride content in the copolymer 0.4 mo12% or more, if the ethylene flow rate was 100 g/hr, the ethylene flow rate was 10 R/hr or more. I had to inject emulsion.

For this reason, the MFR of the copolymer is as large as 60, which limits its use in boat fishing. Therefore, the same MF
In order to make the same R and the same degree of maleic anhydride in the copolymer, it became necessary to change everything from the polymerization conditions.

(Comparative Example 3) In the emulsion production of Example 1, anhydrous maleic a
lloOKg and dodecane 80Kg. Even with strong stirring, an emulsion state was not formed, and the reaction became extremely unstable as soon as the mixture was injected, making it impossible to continue the polymerization. Even if the temperature was controlled manually, the pressure was 1950 atm, the polymerization temperature was 190 to 230°C, and the temperature hunting width could not be lowered to 30°C or less.

[Effects of the Invention] Conventionally, polyethylene has been modified by copolymerization with radically polymerizable acid anhydrides, grafting, etc. for the purpose of improving the bendability and paintability of polyethylene. When a polymerizable acid anhydride is copolymerized, the polymerizable acid anhydride is injected into the reaction system in the form of an emulsion using a diaphragm as a dispersion medium.

As a result, since the dispersion medium has good compatibility with ethylene, the acid anhydride is uniformly dispersed in the reaction system, and there is no local reaction.
It is estimated that the reaction system will be able to operate stably for a long period of time.

Furthermore, the MFR of the produced copolymer can be easily adjusted, and a copolymer with excellent processability can be produced.

Claims (4)

[Claims] (1) When radically copolymerizing ethylene and a radically polymerizable acid anhydride under high pressure using a polymerization initiator, the poor solvent of the radically polymerizable acid anhydride solution is used as a dispersion medium, and the radically polymerizable acid anhydride is A method for producing an ethylene copolymer, which comprises injecting an emulsion as a dispersed phase into a reaction system. (2) The method for producing an ethylene copolymer according to claim 1, wherein the dispersed phase of the emulsion is a solution of a radically polymerizable acid anhydride dissolved in a good solvent thereof. (3) The method for producing an ethylene copolymer according to claims 1 and 2, wherein the dispersion medium of the emulsion is a paraffinic or aromatic hydrocarbon solvent. (4) The emulsion according to claims 1 and 2 is a method for producing an ethylene copolymer in which the dispersed phase is 10 to 50% by weight.