TWI811924B - Ethylene-vinyl acetate copolymer, moldings, sheets and foams containing it - Google Patents

Abstract

An object of the present invention is to provide an ethylene-vinyl acetate copolymer excellent in flexural modulus, heat resistance, weather resistance and foaming uniformity, and a molded article, sheet and foam containing the same.

The ethylene-vinyl acetate copolymer of the present invention contains 3.0 mass % or more and less than 11.0 mass % of vinyl acetate units and ethylene units, and is formed by using the following formula 1 using the pulse NMR solid echo method When the measured free motion attenuation (M(t)) at 80°C is fitted to perform a three-component approximation, the component with the lowest mobility (α) has a composition rate of 28.0% or more and 36.0% or less, and the highest mobility is The relaxation time (Tγ) of the component (γ) is 375 μs or more and less than 600 μs.

(M(t))=α‧exp{(-1/1.5)(t/Tα) ^1.5 }+β‧exp(-t/Tβ)+γ‧exp(-t/Tγ) Formula 1

[α: The composition rate (%) of the component with the lowest mobility (α); Tα: The relaxation time (msec) of the component (α); β: The composition rate (%) of the intermediate motion component (β); Tβ: relaxation time of component (β) (msec); γ: component rate (%) of the most mobile component (γ); Tγ: relaxation time of component (γ) (msec); t: observation time (msec)]

Description

Ethylene-vinyl acetate copolymer, molded articles, sheets and foams containing the same

The present invention relates to an ethylene-vinyl acetate copolymer, molded bodies, sheets and foams containing the same.

Ethylene-vinyl acetate copolymer has excellent properties such as flexibility, mechanical strength, electrical insulation, weather resistance, and durability. Therefore, it is used in a wide range of industrial fields as thermal insulation materials or buffer materials, and is also used in electronic equipment, for example. Or cushioning materials for vehicle parts, color cones, etc.

As a foam using an ethylene-vinyl acetate copolymer, for example, Patent Document 1 proposes a foam sheet that has good flexibility and mechanical strength even if it is a thin foam sheet.

[Prior technical literature] [Patent Document]

[Patent Document 1] International Publication No. 2018/181498

In recent years, with the expansion of the application fields of ethylene-vinyl acetate copolymer, the market requires it to have higher performance. As for the specific content of required performance, in applications such as automotive parts, foams are required to have high rigidity. On the other hand, in such applications, it is also required to have high rigidity, high heat resistance or weather resistance even in high temperature environments in summer, and excellent foaming uniformity when forming a foam.

However, the ethylene-vinyl acetate copolymer described in Patent Document 1 has a relatively high vinyl acetate content. Although it has excellent flexibility, there is still room for improvement in rigidity such as flexural modulus. Furthermore, there is no particular disclosure of an ethylene-vinyl acetate copolymer that has high rigidity, high heat resistance or weather resistance even in a high-temperature environment in summer, and has excellent foaming uniformity when forming a foam. .

The present invention was made in view of the above-mentioned problems, and its object is to provide an ethylene-vinyl acetate copolymer excellent in flexural modulus, heat resistance, weather resistance and foaming uniformity, as well as a molded article, sheet and material containing the same. Foam.

The present inventors conducted intensive research in order to solve the above-mentioned problems. As a result, it was discovered that the above-mentioned problems can be solved by an ethylene-vinyl acetate copolymer having a relatively large number of crystalline parts and low mobility of the molecular chain of the amorphous part, leading to the completion of the present invention.

That is, the present invention is as follows.

[1]

An ethylene-vinyl acetate copolymer, which contains 3.0 mass % or more and less than 11.0 mass % of vinyl acetate units, and contains ethylene units, and is produced by using the following formula 1 to analyze pulse NMR (Nuclear Magnetic Resonance) When three-component approximation is performed by fitting the free motion attenuation (M(t)) at 80°C measured by the resonance) solid-state echo method, the composition rate of the component with the lowest mobility (α) is 28.0% or more 36.0 % or less, and the relaxation time (Tγ) of the most mobile component (γ) is 375 μs or more and less than 600 μs.

(M(t))=α‧exp{(-1/1.5)(t/Tα) ^1.5 }+β‧exp(-t/Tβ)+γ‧exp(-t/Tγ) Formula 1

[α: The composition rate (%) of the component with the lowest mobility (α); Tα: The relaxation time (msec) of the component (α); β: The composition rate (%) of the intermediate motion component (β); Tβ: relaxation time of component (β) (msec); γ: component rate (%) of the most mobile component (γ); Tγ: relaxation time of component (γ) (msec); t: observation time (msec)]

[2]

The ethylene-vinyl acetate copolymer described in [1] has a molecular weight distribution (Mw/Mn) of 3.7 to 7.0.

[3]

The ethylene-vinyl acetate copolymer described in [1] or [2] has a melt flow rate of 0.3 g/10 min or more and 5.0 g/10 min or less.

[4]

The ethylene-vinyl acetate copolymer as described in any one of [1] to [3], the melt elongation of which The rate is above 5.0m/min and below 30.0m/min.

[5]

A molded article containing the ethylene-vinyl acetate copolymer described in any one of [1] to [4].

[6]

A foam containing the ethylene-vinyl acetate copolymer described in any one of [1] to [4].

[7]

A sheet containing the ethylene-vinyl acetate copolymer described in any one of [1] to [4].

According to the present invention, it is possible to provide an ethylene-vinyl acetate copolymer excellent in flexural modulus, heat resistance, weather resistance, and foaming uniformity, as well as molded articles, sheets, and foams containing the same.

Hereinafter, embodiments of the present invention (hereinafter referred to as "this embodiment") will be described in detail. However, the present invention is not limited thereto, and various changes can be made without departing from the gist of the invention.

[Ethylene-vinyl acetate copolymer]

The ethylene-vinyl acetate copolymer of this embodiment contains 3.0 mass % or more and less than 11.0 mass % of vinyl acetate units and contains ethylene units, and is utilized by using the following formula 1 When three-component approximation is performed by fitting the free motion attenuation (M(t)) at 80°C measured by the pulse NMR solid-state echo method, the composition ratio (α) of the component with the lowest mobility is 28.0% or more 36.0 % or less, and the relaxation time (Tγ) of the most mobile component is more than 375 μs and less than 600 μs.

(M(t))=α‧exp{(-1/1.5)(t/Tα) ^1.5 }+β‧exp(-t/Tβ)+γ‧exp(-t/Tγ) Formula 1

[α: The composition rate (%) of the component with the lowest mobility (α); Tα: The relaxation time (msec) of the component (α); β: The composition rate (%) of the intermediate motion component (β); Tβ: relaxation time of component (β) (msec); γ: component rate (%) of the most mobile component (γ); Tγ: relaxation time of component (γ) (msec); t: observation time (msec)]

The inventors of the present invention conducted intensive research and learned that by making the ethylene-vinyl acetate copolymer contain a relatively large number of crystalline parts and the mobility of the molecular chains of the amorphous part is low, the flexural modulus, heat resistance, and weather resistance are improved. The properties and foaming uniformity are further improved. The reason for this is not particularly limited, but it is considered that the flexural modulus and heat resistance are improved because there are more crystal parts.

In addition, regarding the foamability, if there are too many branches, the melt tension tends to be high and uniform foaming may not occur. On the other hand, if there are too few branches, the microcells will tend to rupture during foaming to form continuous bubbles. Therefore, it is considered that by lowering the mobility of the molecular chains in the amorphous portion, that is, by controlling branching to a fixed amount, a good foam with uniform foaming and fewer continuous cells can be obtained.

Regarding the weather resistance, generally the lower the content of the vinyl acetate unit of the ethylene-vinyl acetate copolymer, the lower the weather resistance tends to be. However, when the content of the vinyl acetate unit is low, it is easy to be removed from the branch part. Hydrogen causes deterioration to develop, so the more branches there are, the better the weather resistance. tendency to decline. Therefore, it is considered that the weather resistance of an ethylene-vinyl acetate copolymer with a low vinyl acetate content can be improved by lowering the mobility of the molecular chain in the amorphous portion, that is, having fewer branches.

In this embodiment, the amount of crystalline parts and the mobility in the amorphous part contained in the ethylene-vinyl acetate copolymer are specified by pulse NMR. Pulse NMR orients the spins of hydrogen atoms in the polymer chain in a magnetic field to measure the spin-spin relaxation time. Qualitative and quantitative analysis of objects can be performed based on the relaxation time. When the molecular mobility is high, the relaxation time tends to become longer. This can be used to evaluate the fluidity of the molecular chain of the ethylene-vinyl acetate copolymer.

Regarding pulse NMR, when a plurality of components with different mobilities are mixed in the sample, the ratio or relaxation time of each component can be obtained by performing waveform processing. For example, by fitting the free induction attenuation obtained by pulse NMR to three components: the lowest mobility component (α), the intermediate motion component (β), and the highest mobility component (γ), each motion can be understood The content ratio of the kinetic components, or the fluidity (relaxation time) of each movable component.

Here, it is considered that the component with the lowest mobility (α) corresponds to the crystalline part, the component with the highest mobility (γ) corresponds to the amorphous part, and the intermediate component (β) with motion corresponds to the amorphous part subjected to high speed. Therefore, the amount of the crystalline part can be expressed by the amount of the component (α), and the mobility in the amorphous part can be expressed by the relaxation time of the component (γ).

Hereinafter, the ethylene-vinyl acetate copolymer of this embodiment will be described in detail.

[Pulse NMR]

In this embodiment, the following formula 1 is used to perform a three-component approximate fitting of the free induction attenuation (M(t)) at 80°C measured by the pulsed NMR solid-state echo method. By this, the amounts of the lowest mobility component (α), the middle mobility component (β) and the highest mobility component (γ) in the ethylene-vinyl acetate copolymer, as well as the relaxation time (mobility ) to evaluate.

M(t)=α‧exp{(-1/1.5)(t/Tα) ^1.5 }+β‧exp(-t/Tβ)+γ‧exp(-t/Tγ) Formula 1

α: Composition rate (%) of the component with the lowest mobility (α)

Tα: Relaxation time of component (α) (msec)

β: Composition rate (%) of the middle motion component (β)

Tβ: Relaxation time of component (β) (msec)

γ: Composition rate (%) of the most active ingredient (γ)

Tγ: Relaxation time of component (γ) (msec)

t: observation time (msec)

The composition ratio of the component (α) with the lowest mobility is not less than 28.0% and not more than 36.0%, preferably not less than 29.0% and not more than 35.0%, more preferably not less than 30.0% and not more than 34.0%. By setting the composition ratio of the component (α) to 28.0% or more, the flexural modulus and heat resistance become excellent. Furthermore, by setting the composition ratio of component (α) to 36.0% or less, the balance between weather resistance and foaming uniformity tends to be excellent.

The relaxation time (Tα) of component (α) is not particularly limited, but is preferably 5 μsec or more and 30 μsec It is preferable that it is less than or equal to 7 μsec and not more than 7 μsec and not more than 20 μsec, and even more preferably that it is not less than 10 μsec and not more than 15 μsec.

The composition rate of the intermediate motion component (β) is not particularly limited, but it is preferably in the range of 30.0% or more and 50.0% or less, preferably 35.0% or more and 48.0% or less, and more preferably 40.0% or more and 47.0% or less.

The relaxation time (Tβ) of the component (β) is not particularly limited, but is preferably in the range of 50 μsec to 130 μsec, more preferably 60 μsec to 120 μsec, and further preferably 70 μsec to 110 μsec.

The composition rate of the highest mobility component (γ) is preferably 23.0% or more and 29.0% or less, more preferably 24.0% or more and 27.5% or less, and further preferably 25.0% or more and 26.0% or less. By setting the composition ratio of the component (γ) within the above range, the amorphous portion is relatively reduced, and the bending modulus and heat resistance tend to become excellent.

The relaxation time (Tγ) of the component (γ) is 375 μs or more and less than 600 μs, preferably 400 μs or more and 575 μs or less, preferably 425 μs or more and 550 μs or less. By setting the relaxation time (Tγ) within the above range, the balance between weather resistance and foaming uniformity tends to be excellent.

There are no particular restrictions on the method of adjusting the composition ratios and relaxation times (Tα) to (Tγ) of the components (α) to (γ) within the above ranges. Examples include adjusting the type and addition of the chain transfer agent. Method of measurement. Generally speaking, by using chain transfer agents, there is introduction into ethylene-vinyl acetate copolymer The long chain branches tend to decrease.

On the other hand, since α-olefins with double bonds also function as comonomers together with chain transfer agents, if α-olefins with double bonds are used, alkyl short-chain branches will be introduced into the molecular chain. Introducing a short alkyl chain branch inhibits crystallization, and as a result, the crystallization portion tends to decrease. Therefore, by using a chain transfer agent other than the α-olefin having a double bond in a specific amount, the composition ratio of the components (α) to (γ) and the relaxation time (Tα) to (Tγ) can be adjusted to the above within the range.

In addition, there are no particular limitations on other methods for adjusting the composition ratios and relaxation times (Tα) to (Tγ) of the components (α) to (γ) within the above ranges. For example, unreacted In a reaction method in which raw materials are recycled, the composition of the chain transfer agent of the recycled unreacted raw materials is adjusted. Since unreacted raw materials are recycled and reused, unreacted chain transfer agents with lower chain transfer constants are aggregated in the raw materials, resulting in an increase in the number of long chain branches introduced into the ethylene-vinyl acetate copolymer. For example, when a chain transfer agent containing n-butane and isobutane is used, although the difference in chain transfer constants between n-butane and isobutane is small, it is considered that the chain transfer constants accumulate due to recycling. Lower n-butane increases the number of branch chains introduced into the ethylene-vinyl acetate copolymer.

Therefore, the method for achieving the composition conditions of the chain transfer agent is not particularly limited. A part of the gas recovered from the high-pressure separator can be leaked out of the system to reduce the chain transfer constant accumulated due to recycling. The lower amount of unreacted raw materials suppresses the increase of branch chains, thereby adjusting the composition ratio and relaxation time of each component to the above range.

In addition, there are no particular limitations on other methods for achieving the composition conditions of the chain transfer agent. An example of the method is to change the temperature of a drain pot that is usually used for high-pressure separators to a high temperature. Remove low molecular weight components from the recovered gas. Normally, lowering the temperature is performed in order to efficiently remove low molecular weight components. However, it is considered to selectively and efficiently remove the high boiling point components of the chain transfer agent by weakening the cooling of the drain tank and raising the temperature of the drain tank to a high temperature. Methods for adjusting the ratio of chain transfer agents. For example, when a chain transfer agent containing n-butane and isobutane is used, by changing the temperature of the drain tank to a high temperature, n-butane with a boiling point higher than isobutane can be selectively and efficiently removed. alkyl.

In addition, there are no particular limitations on other methods for adjusting the composition ratio of the components (α) to (γ) and the relaxation time (Tα) to (Tγ) within the above ranges. For example, after The method of cooling the piping just after the pressure drops. By cooling the piping immediately after the pressure drops after the tubular reactor, the sudden rise in temperature caused by the inverse Joule-Thomson effect can be suppressed, and the reaction caused by the backbiting reaction can be suppressed. Short chain branches that hinder crystallization.

More specifically, pulse NMR can be measured by the method described in the Examples.

(molecular weight distribution)

The molecular weight distribution (Mw/Mn) of the ethylene-vinyl acetate copolymer of this embodiment is preferably 3.7 or more and 7.0 or less, more preferably 4.0 or more and 6.5 or less, still more preferably 4.3 or more and 6.0 or less. By setting the molecular weight distribution (Mw/Mn) within the above range, foaming uniformity tends to become more excellent.

The molecular weight distribution (Mw/Mn) can be adjusted using polymerization temperature, polymerization pressure, etc. In addition, the molecular weight distribution (Mw/Mn) can be measured by gel permeation chromatography (hereinafter also referred to as "GPC") based on a calibration using commercially available monodisperse polystyrene. Find the curve. More specifically, the method described in the Examples can be used for measurement.

(melt flow rate)

The melt flow rate of the ethylene-vinyl acetate copolymer of this embodiment is preferably 0.3g/10min or more and 5.0g/10min or less, more preferably 0.3g/10min or more and 3.0g/10min or less, and still more preferably 0.3g /10min or more 1.0g/10min or less. By setting the melt flow rate within the above range, the balance between the flexural modulus and foaming uniformity of the obtained molded article or the like tends to become more excellent.

The method of adjusting the melt flow rate of the ethylene-vinyl acetate copolymer is not particularly limited. For example, when polymerizing the ethylene-vinyl acetate copolymer, adjusting the reaction temperature and/or reaction pressure, or chain Type or amount of transfer agent, etc. More specifically, when polymerizing an ethylene-vinyl acetate copolymer, if the reaction temperature is raised, the melt flow rate of the ethylene-vinyl acetate copolymer tends to increase, and if the reaction pressure is raised, the melt flow rate of the ethylene-vinyl acetate copolymer tends to increase. The melt flow rate of vinyl acetate copolymer tends to become smaller. If the amount of chain transfer agent is increased, the melt flow rate of ethylene-vinyl acetate copolymer tends to increase.

The melt flow rate can be measured based on JIS K7210: 1999 standard D (temperature = 190°C, load = 2.16kg).

(Melt elongation)

The melt elongation of the ethylene-vinyl acetate copolymer of this embodiment is preferably 5.0 m/min or more and 30.0 m/min or less, more preferably 6.0 m/min or more and 22.5 m/min or less, and still more preferably 7.0 m/min. min above 15.0m/min below. By setting the melt elongation within the above range, foaming uniformity tends to become more excellent.

As a method of adjusting the melt elongation of the ethylene-vinyl acetate copolymer, for example, when polymerizing the ethylene-vinyl acetate copolymer, the reaction temperature and/or the reaction pressure and/or the type or amount of the chain transfer agent are used. to make adjustments. In addition, the melt elongation can be measured by the method described in the Examples.

(vinyl acetate unit)

The content of the vinyl acetate unit is 3.0 mass% or more and less than 11.0 mass%, preferably 3.5 mass% or more and 9.0 mass% or less, more preferably 4.0 mass%, relative to the total amount of the ethylene-vinyl acetate copolymer. % or more and 6.0 mass% or less. By setting the content of the vinyl acetate unit within the above range, the obtained molded article or the like has an excellent balance of flexural modulus, heat resistance and weather resistance.

The method for adjusting the content of the vinyl acetate unit is not particularly limited, for example Examples include the following methods: appropriately adjusting the amount of vinyl acetate monomer added, the polymerization temperature, and the polymerization pressure in the step of polymerizing the ethylene-vinyl acetate copolymer.

Furthermore, regarding the content of vinyl acetate units, a calibration curve can be prepared by saponification and potentiometric titration in accordance with JIS K7192:1999 as a benchmark test method, and as a control test method, vinyl acetate conversion can be performed by infrared spectroscopy. To measure. Specifically, it can be measured using the method described in the Examples mentioned later.

(ethylene unit)

The content of ethylene units relative to the total amount of the ethylene-vinyl acetate copolymer is preferably more than 89.0 mass % and 97.0 mass % or less, more preferably 91.0 mass % or more and 96.5 mass % or less, and still more preferably 94.0 More than 96.0% by mass and less than 96.0% by mass. By setting the content of the ethylene unit within the above range, the obtained molded article or the like tends to have an excellent balance of flexural modulus, heat resistance and weather resistance.

The ethylene-vinyl acetate copolymer of this embodiment may also contain monomer units other than ethylene units and vinyl acetate units. The other monomer units are not particularly limited, and examples thereof include units derived from propylene, butane, and the like.

The ethylene-vinyl acetate copolymer of this embodiment may be obtained by dry-blending or melt-blending two or more kinds of ethylene-vinyl acetate copolymers at any ratio. When two or more types of ethylene-vinyl acetate copolymers are used, it is preferable that the content of vinyl acetate units in the entire resin is within the above range.

[Production method of ethylene-vinyl acetate copolymer]

The ethylene-vinyl acetate copolymer of this embodiment is not particularly limited. For example, ethylene and vinyl acetate can be polymerized under pressure and heating in the presence of a polymerization initiator to obtain an ethylene-vinyl acetate copolymer. . Chain transfer agents can also be added to the polymerization system if necessary.

The polymerization method of the ethylene-vinyl acetate copolymer is not particularly limited, and examples include: autoclave method and tubular method. Among them, it is preferable to use a tubular reactor with a longer ring structure. By using a tubular reactor, the polymerization temperature, etc. can be appropriately adjusted in each zone from upstream to downstream.

The average polymerization temperature is preferably from 150°C to 280°C, more preferably from 180°C to 260°C. Moreover, the average polymerization pressure is preferably from 100 MPa to 350 MPa, more preferably from 120 MPa to 270 MPa, further preferably from 180 MPa to 260 MPa.

Furthermore, the reactor may also have a plurality of positions for feeding ethylene, vinyl acetate and polymerization initiator.

The ethylene and vinyl acetate supplied to the reactor may be in gaseous or liquid form.

The polymerization initiator is not particularly limited, and examples thereof include radical generators such as peroxides. The free radical generator such as peroxide is not particularly limited, and examples thereof include: tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxyacetate, and tert-butyl peroxypivalate. Butyl ester, di-tertiary butyl peroxide, etc.

The chain transfer agent is not particularly limited, and examples thereof include alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol; ethane, propane, propylene, butane, 1- Butene, 2-butene and other alkanes or alkenes; acetone, methyl ethyl ketone, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, diisobutyl ketone, methyl Isopropyl ketone, formaldehyde, acetaldehyde, n-butyraldehyde, isobutyraldehyde, n-valeraldehyde, isovaleraldehyde and other ketones or aldehydes.

Among them, it is preferable to use a chain transfer agent whose chain transfer constant, represented by the ratio of the rate constant of the chain transfer reaction and the rate constant of the propagation reaction, is within a specific range. The chain transfer constant of the chain transfer agent is preferably from 0.0020 to 0.010, more preferably from 0.0030 to 0.008, further preferably from 0.0035 to 0.006. By using a chain transfer agent with such a chain transfer constant, it is easy to change the composition ratio of the components (α) ~ (γ) and the relaxation time (Tα) ~ (Tγ), especially the component ratio of the component (α) And the relaxation time (Tγ) is adjusted to the above range. In addition, the above-mentioned chain transfer constant is a value at 1350 atm and 130°C.

Examples of the chain transfer agent having the above chain transfer constant include n-butane, isobutane, and the like.

The usage amount of the chain transfer agent is preferably 0.1 mol% or more and 4.0 mol% or less, more preferably 0.5 mol% or more and 4.0 mol% or less, and further preferably 1.5 mol% or more relative to the ethylene introduced into the reactor. 3.0mol%. By setting the usage amount of the chain transfer agent within the above range, it is easy to adjust the composition ratio and relaxation time (Tα) ~ (Tγ) of the components (α) ~ (γ), especially the component (α) The composition ratio and relaxation time (Tγ) are adjusted to fall within the above ranges.

Regarding the composition of the chain transfer agent during polymerization, it is preferable that the composition of isobutane is at least 40%, preferably at least 50%, and more preferably at least 60%. By adjusting the composition of the chain transfer agent in this way, it is easy to adjust the composition ratio and relaxation time (Tα) ~ (Tγ) of the components (α) ~ (γ), especially the composition ratio and relaxation time of the component (α). (Tγ) is adjusted to the above range.

The piping immediately after the pressure drops after the tubular reactor is preferably cooled to 30°C or more and 200°C or less, more preferably 60°C or more and 180°C or less, and further preferably 120°C or more and 160°C or less. It is easy to adjust the composition ratio and relaxation time (Tα) to (Tγ) of the components (α) to (γ), especially the composition ratio and the relaxation time (Tγ) of the component (α) to the above ranges.

The ethylene-vinyl acetate copolymer polymerized as described above is preferably separated into polymer and gas using a high-pressure separator. The extracted gas is removed from low molecular weight components in the discharge tank midway. The residual gas such as ethylene, vinyl acetate and chain transfer agent can also be transported to the inlet of the multi-stage compressor for polymerization reuse. The residual gas is preferably seeped out of the system and discarded.

The drain tank is preferably cooled to 30°C or more and 200°C or less, more preferably 60°C or more and 180°C or less, and further preferably 130°C or more and 160°C or less, so that the ingredients (α) ~ (γ ), the composition ratio and relaxation time (Tα) ~ (Tγ), especially the composition ratio and relaxation time (Tγ) of component (α), are adjusted to the above ranges.

High pressure separator leakage (HPR leakage) is preferably above 200kg/hr and below 600kg/hr, more Preferably, it is 300kg/hr or more and 600kg/hr or less, and more preferably, it is 300kg/hr or more and 600kg/hr or less. By setting the HPR exudation within the above range, it is easy to adjust the composition ratio and relaxation time (Tα) to (Tγ) of the components (α) to (γ), especially the composition ratio and relaxation time of the component (α). (Tγ) is adjusted to the above range.

Next, the polymer separated by the high-pressure separator is preferably introduced into a low-pressure separator and further separated into ethylene-vinyl acetate copolymer and gas.

The ethylene-vinyl acetate copolymer obtained by polymerizing and separating from the raw materials in the above manner is preferably granulated into granules using an extruder.

After using an extruder to make the ethylene-vinyl acetate copolymer into pellets, the pellets can also be stored in a storage bin.

The ethylene-vinyl acetate copolymer of this embodiment may optionally contain known additives such as antioxidants, ultraviolet absorbers, light stabilizers, antistatic agents, anti-fogging agents, and color pigments.

The antioxidant is not particularly limited, and examples thereof include: 2,6-di-tert-butyl-4-methylphenol, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) phenolic antioxidants such as octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; tris(2,4-di-tert-butyl) propionate phosphorus antioxidants such as tetrakis(2,4-di-tert-butylphenyl)-4,4-biphenyl-diphosphite; 6-tert-butyl-4 -[3-(2,4,8,10-tetra-tert-butyldiphenyl[d,f][1,3,2]dioxa Phosphorus/phenolic antioxidants such as phosphohepten-6-yl-oxy)propyl]-o-cresol; sulfur-based antioxidants such as dilauryl thiodipropionate.

[molded body]

The molded article of this embodiment contains the above-mentioned ethylene-vinyl acetate copolymer. The molded article of this embodiment is not particularly limited, and can be obtained by, for example, injection molding, extrusion molding, or stretch molding, and can be preferably used in various applications. Specifically, it is not particularly limited, and examples thereof include: cushioning materials for electronic equipment or vehicle parts, colored cones, artificial grass mats, automobile mudguards, mud guards, drainage pipes, etc. In addition, it can also be used as fiber.

[Sheet]

The sheet of this embodiment contains the above-mentioned ethylene-vinyl acetate copolymer. Examples of sheet manufacturing methods include T-die molding, inflation molding, calendering, skive molding, and the like. In particular, T-die molding, extrusion molding, and inflation molding are preferred.

The sheet of this embodiment can be preferably used for automobile fenders and mud covers. Furthermore, "sheet" refers to a plastic sheet with a thickness of 250 μm or more. The thickness of the sheet in this embodiment is preferably 250 μm or more, more preferably 300 μm ~ 10 mm, and further preferably 0.5 ~ 10 mm.

[Foam]

The foam of this embodiment contains the above-mentioned ethylene-vinyl acetate copolymer. The foam of the present embodiment is not particularly limited. For example, it can be obtained by using cushioning materials for electronic equipment or vehicle parts, foamed fine particles, etc., and can be preferably used for various purposes.

[Example]

Hereinafter, the present invention will be described in more detail using Examples and Comparative Examples. The present invention is not limited by the following examples.

[Determination of content of vinyl acetate units]

According to JIS K7192: 1999, as a reference test method, a calibration curve is prepared by using a VAC reference sample of an ethylene-vinyl acetate copolymer with a known content of vinyl acetate units through saponification and potentiometric titration. As a control test method, use Infrared spectroscopy was used to measure the content of vinyl acetate units (VA content) in the ethylene-vinyl acetate copolymers obtained in the Examples and Comparative Examples.

[Pulse NMR]

First, a sample tube filled with ethylene-vinyl acetate copolymer to a height of 1 cm from the bottom was put into a TD-NMR device (model: minispec mq20) manufactured by Bruker that was set so that the internal temperature of the sample tube was 40°C. ), heat the sample tube according to the <heating conditions> shown below. The temperatures shown in the following heating conditions are values obtained by measuring the internal temperature of the sample using a thermocouple.

<Heating conditions>

Step 1: Raise the temperature from 40°C at a rate of 10°C/min and let stand at 70°C for 13 minutes.

Step 2: Raise the temperature from 70°C at a rate of 10°C/min and let stand at 80°C for 5 minutes.

After the temperature rise is completed according to the above sequence, the spin-self test of the sample is carried out according to the measurement conditions shown below. The spin relaxation time (T2, sometimes referred to as "relaxation time" in this specification) is measured.

<Measurement conditions>

Observation core: ¹ H

Determination: T2

Measuring method: solid echo method

Cumulative times: 256 times

Measuring temperature: 80℃

Repeat time: 3s

Scan time: 1ms

The obtained free motion attenuation (M(t)) was fitted using the following equation 1 using analytical program analysis software (TDNMR-A) manufactured by Bruker Corporation, thereby performing a three-component approximation.

M(t)=α‧exp{(-1/1.5)(t/Tα) ^1.5 }+β‧exp(-t/Tβ)+γ‧exp(-t/Tγ) Formula 1

α: Composition rate (%) of the component with the lowest mobility (α)

Tα: Relaxation time of component (α) (msec)

β: Composition rate (%) of the middle motion component (β)

Tβ: Relaxation time of component (β) (msec)

γ: Composition rate (%) of the most active ingredient (γ)

Tγ: Relaxation time of component (γ) (msec)

t: observation time (msec)

[Determination of molecular weight and molecular weight distribution]

The weight average molecular weight (Mw) and the number average molecular weight (Mn) of the ethylene-vinyl acetate copolymer were measured by gel permeation chromatography (GPC). The ratio (Mw/Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) determined by GPC measurement was defined as the molecular weight distribution. GPC measurement was performed according to the measurement conditions shown below. Molecular weight calibration is performed at 12 locations in the range of MW (Molecular weight, molecular weight) of standard polystyrene manufactured by Tosoh Corporation, ranging from 1,050 to 20,600,000. The MW of each standard polystyrene is multiplied by a coefficient of 0.43 to obtain polyethylene. To convert molecular weight, a primary correction straight line is made from the curve of dissolution time and polyethylene converted molecular weight to determine the weight average molecular weight (Mw) and number average molecular weight (Mn).

(Measurement conditions)

Device: GPC-IR manufactured by Polymer Char Corporation

Detector: IR5 manufactured by Polymer Char Company

Pipe string: UT-807 (1 piece) manufactured by Showa Denko Co., Ltd. and GMHHR-H(S)HT (2 pieces) manufactured by Tosoh Co., Ltd. are connected in series and used.

Mobile phase: o-dichlorobenzene

Column temperature: 140℃

Flow: 1.0mL/min

Sample concentration: 16mg/8mL

Sample dissolution temperature: 140℃

Sample dissolution time: 60 minutes

[Melt Flow Rate (MFR) Measurement]

According to JIS K7210: 1999 standard D (temperature = 190°C, load = 2.16kg), the MFR of ethylene-vinyl acetate copolymer was measured.

[Melt elongation (ME) measurement]

A Capillograph 1D manufactured by Toyo Seiki Co., Ltd. with a capillary tube of 2.095 mm in diameter and 7.98 mm in length was used. After the sample was fully melted at 190°C for 5 minutes, the piston was operated at a fixed piston speed of 6 mm/min. Extrude the ethylene-vinyl acetate copolymer at 190°C, and start pulling at 3m/min. After 1 minute, increase the pulling speed to 10m/min, and measure the elongation when the strand is broken as the melt elongation. (ME).

[Production of molded body 1]

An aluminum plate with a thickness of 0.1 mm was placed on a smooth iron plate with a thickness of 5 mm, and a polyethylene terephthalate film (Lumirror manufactured by Toray) with a thickness of 50 μm that was not coated with cellulan was placed on the aluminum plate. . Place a mold with a length of 200mm, a width of 200mm, and a thickness of 4.0mm on it, add 160g of ethylene-vinyl acetate copolymer, place the above-mentioned polyethylene terephthalate film on it, and then place the above-mentioned aluminum plate, and then Place the above iron plate.

The above-mentioned laminated body was put into a compression molding machine (SFA-37) manufactured by Shinto Metal Industry Co., Ltd. whose temperature was adjusted to 180°C, preheated at 180°C and 0.1MPa for 180 seconds, and then degassed for 5 seconds. (10MPa), pressurize at 180°C and 15MPa for 120 seconds.

After the completion of the pressurization, the sample was taken out, and after 5 seconds had elapsed since the removal, it was placed in a compression molding machine (SFA-37) manufactured by Shinto Metal Industry Co., Ltd. with a temperature adjusted to 25°C. Pressure was applied for 300 seconds while cooling, thereby producing a pressurized sheet. After cooling, the pressurized sheet taken out from the mold is left to stand for 24 hours at a temperature of 23°C and a humidity of 50%. superior.

[Bending modulus measurement]

The above-mentioned molded body 1 was punched into a thickness of 4.0 mm, a length of 80.0 mm, and a width of 10.0 mm to prepare a test piece. According to JIS K7171:2008, the flexural modulus of ethylene-vinyl acetate copolymer was measured using Autograph AG-X Refresh manufactured by Shimadzu Corporation at a test speed of 2mm/min and a distance between fulcrums of 64mm, and the flexural modulus was measured according to the following standards Evaluation. ◎, ○ are considered qualified.

(evaluation criteria)

◎(Excellent): Bending modulus is above 150MPa

○(Good): Bending modulus is 120MPa or more and less than 150MPa

× (Defect): Bending modulus does not reach 120MPa

[Production of molded body 2]

An aluminum plate with a thickness of 0.1 mm was placed on a smooth iron plate with a thickness of 5 mm, and a polyethylene terephthalate film (Lumirror manufactured by Toray) with a thickness of 50 μm that was not coated with cellulan was placed on the aluminum plate. . Place a mold with a length of 200mm, a width of 200mm, and a thickness of 0.6mm on it, add 24g of ethylene-vinyl acetate copolymer, place the above-mentioned polyethylene terephthalate film on it, and then place the above-mentioned aluminum plate, and then Place the above iron plate.

The above-mentioned laminated body was put into a compression molding machine (SFA-37) manufactured by Shinto Metal Industry Co., Ltd. whose temperature was adjusted to 180°C, preheated at 180°C and 0.1MPa for 180 seconds, and then degassed for 5 seconds. (10MPa), and pressurized at 180°C and 15MPa for 120 seconds.

After the completion of the pressurization, the sample was taken out, and after 5 seconds had elapsed since the removal, it was placed in a compression molding machine (SFA-37) manufactured by Shinto Metal Industry Co., Ltd. with a temperature adjusted to 25°C. Pressure was applied for 300 seconds while cooling, thereby producing a pressurized sheet. After cooling, let the pressurized sheet taken out from the mold stand for more than 24 hours in an environment with a temperature of 23°C and a humidity of 50%.

[Heat resistance (shrinkage)]

Regarding the above-mentioned molded body 2, two types of unirradiated test pieces and irradiated test pieces were prepared. Let the unirradiated test piece stand for more than 24 hours in an environment with a temperature of 23°C and a humidity of 50%. Furthermore, the irradiation test piece was cut into a width of 70 mm and a length of 150 mm, and the xenon lamp weathering tester X75 manufactured by Suga Test Instruments equipped with a 7.5kW xenon lamp was used to irradiate the measurement wavelength at 300 to 400 nm and the irradiation illumination intensity of 60 W/m ² 720 hours of UV light. At this time, the BPT (Black Panel Thermometer) temperature is 83°C±2. After the irradiation is completed, take out the irradiated test piece and let it stand for more than 24 hours in an environment with a temperature of 23°C and a humidity of 50%, and then measure the size of the irradiated test piece. The heat resistance was evaluated based on the following criteria by calculating the shrinkage rate Hw by the following equation 2 using the length H ₀ of the initial test piece and the length H ₁ of the test piece after irradiation. ◎, ○ are considered qualified.

Hw[%]=(H ₀ -H ₁ )/H ₀ ×100 Equation 2

◎(Excellent): Shrinkage Hw does not reach 1%

○ (Good): Shrinkage Hw is 1% or more and less than 2%

× (Defect): Shrinkage Hw is 2% or more

[Weather resistance (residual elongation)]

For the unirradiated test piece and the irradiated test piece, the weather resistance test piece was punched according to the size of JIS K6783:1994, and the tensile testing machine (TENSIRON (RTC-1310A) manufactured by Orientec) was used to measure the temperature of 25°C. , stretch at a stretching speed of 500mm/min, and calculate the elongation between the marking lines when the test piece breaks. At this time, remove the broken test pieces outside the marking line, supplement the prepared test pieces, and conduct the measurement with N=3. The residual elongation rate Lw is calculated by using the initial distance between the marking lines L ₀ , the average elongation rate between the marking lines L ₁ of the unirradiated test piece, and the average elongation rate between the marking lines L ₂ of the irradiated test piece, by the following formula 3 Figure it out. Based on the obtained elongation residual rate Lw, the weather resistance was evaluated according to the following criteria. ◎, ○ are considered qualified.

Lw[%]={[(L ₂ -L ₀ )/L ₀ ]/[(L ₁ -L ₀ )/L ₀ ]}×100 Formula 3

(evaluation criteria)

◎(Excellent): Elongation residual Lw is more than 70%

○ (Good): The residual elongation rate Lw is 50% or more and less than 70%

× (Defect): Elongation residual rate Lw does not reach 50%

[Production of foam]

With respect to 100 parts by mass of ethylene-vinyl acetate copolymer, 2 parts by mass of an inorganic foaming agent (Polythlene EE275F) manufactured by Eiwa Chemical Industry Co., Ltd. was added, and dry blending was performed with a pellet blender. The all-electric injection molding machine SE130DUZ-C360 manufactured by the company (the cylinder temperature is set to 200°C, the mold temperature is set to 40°C), can produce a 100×100×2.0mm flat plate with an injection time of 20 seconds and a cooling time of 30 seconds. Test piece (film gate). ◎, ○ are considered qualified.

[Measurement of Foaming Uniformity]

For the flat test piece of the above-mentioned ethylene-vinyl acetate copolymer-based resin foam, a cross section was cut out at a position 5 mm from the end of the gate side and 5 mm from the flow end side, and using an optical microscope (magnification: 10 times), Make visual observations with the naked eye.

(evaluation criteria)

◎: The size of the bubbles in the cross section located 5mm from the end of the gate side and 5mm from the end of the flow is relatively uniform, and the bubbles are not connected.

○: Slight unevenness in bubble size is observed in the cross section 5 mm from the gate end and 5 mm from the flow end, and the bubbles are not connected.

×: Uneven bubble size is observed in the cross section 5 mm from the gate end and 5 mm from the flow end side, and the bubbles are connected.

[Example 1]

In a tubular reactor, 2.0 mol% vinyl acetate and 1.6 mol% chain transfer agent were introduced relative to ethylene, the average polymerization reaction temperature was set to 240°C, the average polymerization reaction pressure was set to 250 MPa, and peroxide-2- was used. Tert-butyl ethylhexanoate and di-tert-butyl peroxide are used as polymerization initiators for polymerization. In addition, the piping immediately after the pressure dropped after the tubular reactor was cooled to 150°C. After polymerization, it is introduced into a high-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the gas recovered from the high-pressure separator is removed from low molecular weight components through a drain tank cooled to 160°C. The remaining unreacted gases such as ethylene, vinyl acetate and butane leak out of the system at 600kg/h. , and the rest is transported to the inlet of the multi-stage compressor for polymerization and reuse. Then, it is introduced into a low-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the raw material composition of the additional chain transfer agent added in order to adjust the amount of the chain transfer agent is 35% isobutane and 65% n-butane, but the composition of the chain transfer agent during polymerization in the reactor is isobutane. 60%, positive Alkane 40%. The obtained molten resin of the ethylene-vinyl acetate copolymer is fed to an extruder, and the ethylene-vinyl acetate copolymer is obtained by granulation. The physical properties and characteristics of the obtained ethylene-vinyl acetate copolymer were measured using the method shown above. The measurement results are shown in Table 1.

[Example 2]

In the tubular reactor, 2.0 mol% vinyl acetate and 0.5 mol% chain transfer agent were introduced relative to ethylene, the average polymerization reaction temperature was set to 230°C, the average polymerization reaction pressure was set to 220 MPa, and peroxide-2- was used. Tert-butyl ethylhexanoate and di-tert-butyl peroxide are used as polymerization initiators for polymerization. In addition, the piping immediately after the pressure dropped after the tubular reactor was cooled to 180°C. After polymerization, it is introduced into a high-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the gas recovered from the high-pressure separator is removed from low molecular weight components through a drain tank cooled to 160°C. The remaining unreacted gases such as ethylene, vinyl acetate and butane leak out of the system at 600kg/h. , and the rest is transported to the inlet of the multi-stage compressor for polymerization and reuse. Then, it is introduced into a low-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the raw material composition of the additional chain transfer agent added in order to adjust the amount of the chain transfer agent is 35% isobutane and 65% n-butane, but the composition of the chain transfer agent during polymerization in the reactor is isobutane. 60%, n-butane 40%. The obtained molten resin of the ethylene-vinyl acetate copolymer is fed to an extruder, and the ethylene-vinyl acetate copolymer is obtained by granulation. The physical properties and characteristics of the obtained ethylene-vinyl acetate copolymer were measured using the method shown above. The measurement results are shown in Table 1.

[Example 3]

In a tubular reactor, 1.2 mol% vinyl acetate and 3.0 mol% chain transfer agent were introduced relative to ethylene, the average polymerization reaction temperature was set to 250°C, the average polymerization reaction pressure was set to 210 MPa, and 2-ethyl peroxide was used. Tert-butyl hexanoate and di-tert-butyl peroxide as poly polymerization using initiators. In addition, the piping immediately after the pressure dropped after the tubular reactor was cooled to 150°C. After polymerization, it is introduced into a high-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the gas recovered from the high-pressure separator is removed from low molecular weight components through a drain tank cooled to 160°C. The remaining unreacted gases such as ethylene, vinyl acetate and butane leak out of the system at 600kg/h. , and the rest is transported to the inlet of the multi-stage compressor for polymerization and reuse. Then, it is introduced into a low-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the raw material composition of the additional chain transfer agent added in order to adjust the amount of the chain transfer agent is 35% isobutane and 65% n-butane, but the composition of the chain transfer agent during polymerization in the reactor is isobutane. 60%, n-butane 40%. The obtained molten resin of the ethylene-vinyl acetate copolymer is fed to an extruder, and the ethylene-vinyl acetate copolymer is obtained by granulation. The physical properties and characteristics of the obtained ethylene-vinyl acetate copolymer were measured using the method shown above. The measurement results are shown in Table 1.

[Example 4]

In the tubular reactor, 4.0 mol% vinyl acetate and 4.0 mol% chain transfer agent were introduced relative to ethylene, the average polymerization reaction temperature was set to 230°C, the average polymerization reaction pressure was set to 260 MPa, and 2-ethyl peroxide was used. Tert-butyl hexanoate and di-tert-butyl peroxide were used as polymerization initiators for polymerization. In addition, the piping immediately after the pressure dropped after the tubular reactor was cooled to 150°C. After polymerization, it is introduced into a high-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the gas recovered from the high-pressure separator is removed from low molecular weight components through a drain tank cooled to 160°C. The remaining unreacted gases such as ethylene, vinyl acetate and butane leak out of the system at 600kg/h. , and the rest is transported to the inlet of the multi-stage compressor for polymerization and reuse. Then, it is introduced into a low-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the raw material composition of the chain transfer agent added in order to adjust the amount of the chain transfer agent is 35% isobutane, 35% normal Butane is 65%, but the composition of the chain transfer agent during polymerization in the reactor is 60% isobutane and 40% n-butane. The obtained molten resin of the ethylene-vinyl acetate copolymer is fed to an extruder, and the ethylene-vinyl acetate copolymer is obtained by granulation. The physical properties and characteristics of the obtained ethylene-vinyl acetate copolymer were measured using the method shown above. The measurement results are shown in Table 1.

[Example 5]

In a tubular reactor, 1.5 mol% vinyl acetate and 3.0 mol% chain transfer agent were introduced relative to ethylene, the average polymerization reaction temperature was set to 250°C, the average polymerization reaction pressure was set to 250 MPa, and 2-ethyl peroxide was used. Tert-butyl hexanoate and di-tert-butyl peroxide were used as polymerization initiators for polymerization. In addition, the piping immediately after the pressure dropped after the tubular reactor was cooled to 180°C. After polymerization, it is introduced into a high-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the gas recovered from the high-pressure separator is removed from low molecular weight components through a drain tank cooled to 160°C. The remaining unreacted gases such as ethylene, vinyl acetate and butane leak out of the system at a rate of 300kg/h. , and the rest is transported to the inlet of the multi-stage compressor for polymerization and reuse. Then, it is introduced into a low-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the raw material composition of the additional chain transfer agent added in order to adjust the amount of the chain transfer agent is 28% isobutane, 52% n-butane, and 20% propylene. However, the composition of the chain transfer agent during polymerization in the reactor It is composed of 50% isobutane, 40% n-butane and 10% propylene. The obtained molten resin of the ethylene-vinyl acetate copolymer is fed to an extruder, and the ethylene-vinyl acetate copolymer is obtained by granulation. The physical properties and characteristics of the obtained ethylene-vinyl acetate copolymer were measured using the method shown above. The measurement results are shown in Table 1.

[Example 6]

In a tubular reactor, 1.2 mol% vinyl acetate and 3.0 mol% chain transfer agent were introduced relative to ethylene, the average polymerization reaction temperature was set to 250°C, the average polymerization reaction pressure was set to 210 MPa, and 2-ethyl peroxide was used. Tert-butyl hexanoate and di-tert-butyl peroxide were used as polymerization initiators for polymerization. In addition, the piping immediately after the pressure dropped after the tubular reactor was cooled to 180°C. After polymerization, it is introduced into a high-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the gas recovered from the high-pressure separator is removed from low molecular weight components through a drain tank cooled to 130°C, and the remaining unreacted gases such as ethylene, vinyl acetate, butane, etc. leak out of the system at a rate of 300kg/h. , and the rest is transported to the inlet of the multi-stage compressor for polymerization and reuse. Then, it is introduced into a low-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the raw material composition of the additional chain transfer agent added in order to adjust the amount of the chain transfer agent is 35% isobutane and 65% n-butane, but the composition of the chain transfer agent during polymerization in the reactor is isobutane. 50%, n-butane 50%. The obtained molten resin of the ethylene-vinyl acetate copolymer is fed to an extruder, and the ethylene-vinyl acetate copolymer is obtained by granulation. The physical properties and characteristics of the obtained ethylene-vinyl acetate copolymer were measured using the method shown above. The measurement results are shown in Table 1.

[Comparative example 1]

In a tubular reactor, 2.0 mol% vinyl acetate and 1.5 mol% chain transfer agent were introduced relative to ethylene, the average polymerization reaction temperature was set to 240°C, the average polymerization reaction pressure was set to 250 MPa, and 2-ethyl peroxide was used. Tert-butyl hexanoate and di-tert-butyl peroxide were used as polymerization initiators for polymerization. In addition, polymerization is performed without cooling the piping immediately after the pressure drops after the tubular reactor, and then introduced into a high-pressure separator to separate into ethylene-vinyl acetate copolymer and gas. Furthermore, the gas recovered from the high-pressure separator is passed through a drain tank cooled to 100°C to remove low molecular weight components, etc., and the remaining unreacted ethylene, vinyl acetate, butane, etc. The gas leaks out of the system at a rate of 600kg/h, and the rest is transported to the inlet of the multi-stage compressor for polymerization and reuse. Then, it is introduced into a low-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the raw material composition of the chain transfer agent added in order to adjust the amount of the chain transfer agent is 100% propylene, and the composition of the chain transfer agent during polymerization in the reactor is also 100% propylene. The obtained molten resin of the ethylene-vinyl acetate copolymer is fed to an extruder, and the ethylene-vinyl acetate copolymer is obtained by granulation. The physical properties and characteristics of the obtained ethylene-vinyl acetate copolymer were measured using the method shown above. The measurement results are shown in Table 1.

[Comparative example 2]

In a tubular reactor, 2.0 mol% vinyl acetate and 0.5 mol% chain transfer agent were introduced relative to ethylene, the average polymerization reaction temperature was set to 230°C, the average polymerization reaction pressure was set to 220 MPa, and 2-ethyl peroxide was used. Tert-butyl hexanoate and di-tert-butyl peroxide were used as polymerization initiators for polymerization. In addition, polymerization is performed without cooling the piping immediately after the pressure drops after the tubular reactor, and then introduced into a high-pressure separator to separate into ethylene-vinyl acetate copolymer and gas. Furthermore, the gas recovered from the high-pressure separator is cooled to 100°C in a drain tank to remove low molecular weight components, and the remaining unreacted gases such as ethylene, vinyl acetate, butane, etc. are transported to the inlet of the multi-stage compressor for supply Aggregation and reuse. Then, it is introduced into a low-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the raw material composition of the additional chain transfer agent added in order to adjust the amount of the chain transfer agent is 35% isobutane and 65% n-butane, but the composition of the chain transfer agent during polymerization in the reactor is isobutane. 20%, n-butane 80%. The obtained molten resin of the ethylene-vinyl acetate copolymer is fed to an extruder, and the ethylene-vinyl acetate copolymer is obtained by granulation. The physical properties and characteristics of the obtained ethylene-vinyl acetate copolymer were measured using the method shown above. The measurement results are shown in Table 1.

[Comparative example 3]

In a tubular reactor, 1.0 mol% vinyl acetate and 5.0 mol% chain transfer agent were introduced relative to ethylene, the average polymerization reaction temperature was set to 250°C, the average polymerization reaction pressure was set to 210 MPa, and 2-ethyl peroxide was used. Tert-butyl hexanoate and di-tert-butyl peroxide were used as polymerization initiators for polymerization. In addition, the piping immediately after the pressure dropped after the tubular reactor was cooled to 150°C. After polymerization, it is introduced into a high-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the gas recovered from the high-pressure separator is removed from low molecular weight components through a drain tank cooled to 160°C. The remaining unreacted gases such as ethylene, vinyl acetate and butane leak out of the system at 600kg/h. , and the rest is transported to the inlet of the multi-stage compressor for polymerization and reuse. Then, it is introduced into a low-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the raw material composition of the additional chain transfer agent added in order to adjust the amount of the chain transfer agent is 35% isobutane and 65% n-butane, but the composition of the chain transfer agent during polymerization in the reactor is isobutane. 60%, n-butane 40%. The obtained molten resin of the ethylene-vinyl acetate copolymer is fed to an extruder, and the ethylene-vinyl acetate copolymer is obtained by granulation. The physical properties and characteristics of the obtained ethylene-vinyl acetate copolymer were measured using the method shown above. The measurement results are shown in Table 1.

[Comparative example 4]

In the tubular reactor, 4.0 mol% vinyl acetate and 0.5 mol% chain transfer agent were introduced relative to ethylene, the average polymerization reaction temperature was set to 230°C, the average polymerization reaction pressure was set to 260 MPa, and 2-ethyl peroxide was used. Tert-butyl hexanoate and di-tert-butyl peroxide were used as polymerization initiators for polymerization. In addition, polymerization is carried out without cooling the piping immediately after the pressure drops after the tubular reactor, and then introduced into a high-pressure separator to separate into ethylene-vinyl acetate. Copolymers and gases. Furthermore, the gas recovered from the high-pressure separator is removed from low molecular weight components through a drain tank cooled to 100°C, and the remaining unreacted gases such as ethylene, vinyl acetate and butane leak out of the system at a rate of 300kg/h. , and the rest is transported to the inlet of the multi-stage compressor for polymerization and reuse. Then, it is introduced into a low-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the raw material composition of the chain transfer agent added in order to adjust the amount of the chain transfer agent is 100% propylene, and the composition of the chain transfer agent during polymerization in the reactor is also 100% propylene. The obtained molten resin of the ethylene-vinyl acetate copolymer is fed to an extruder, and the ethylene-vinyl acetate copolymer is obtained by granulation. The physical properties and characteristics of the obtained ethylene-vinyl acetate copolymer were measured using the method shown above. The measurement results are shown in Table 1.

[Comparative example 5]

In the tubular reactor, 5.0 mol% vinyl acetate and 4.0 mol% chain transfer agent were introduced relative to ethylene, the average polymerization reaction temperature was set to 230°C, the average polymerization reaction pressure was set to 270 MPa, and 2-ethyl peroxide was used. Tert-butyl hexanoate and di-tert-butyl peroxide were used as polymerization initiators for polymerization. In addition, the piping immediately after the pressure dropped after the tubular reactor was cooled to 150°C. After polymerization, it is introduced into a high-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the gas recovered from the high-pressure separator is removed from low molecular weight components through a drain tank cooled to 160°C. The remaining unreacted gases such as ethylene, vinyl acetate and butane leak out of the system at 600kg/h. , and the rest is transported to the inlet of the multi-stage compressor for polymerization and reuse. Then, it is introduced into a low-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the raw material composition of the additional chain transfer agent added in order to adjust the amount of the chain transfer agent is 35% isobutane and 65% n-butane, but the composition of the chain transfer agent during polymerization in the reactor is isobutane. 60%, n-butane 40%. The obtained molten resin of ethylene-vinyl acetate copolymer is fed to the extruder, Ethylene-vinyl acetate copolymer is obtained by granulation. The physical properties and characteristics of the obtained ethylene-vinyl acetate copolymer were measured using the method shown above. The measurement results are shown in Table 1.

[Comparative example 6]

In a tubular reactor, 1.2 mol% vinyl acetate and 3.0 mol% chain transfer agent were introduced relative to ethylene, the average polymerization reaction temperature was set to 250°C, the average polymerization reaction pressure was set to 210 MPa, and 2-ethyl peroxide was used. Tert-butyl hexanoate and di-tert-butyl peroxide were used as polymerization initiators for polymerization. In addition, the piping immediately after the pressure dropped after the tubular reactor was cooled to 180°C. After polymerization, it is introduced into a high-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the gas recovered from the high-pressure separator is cooled to 130°C in a drain tank to remove low molecular weight components, and the remaining unreacted gases such as ethylene, vinyl acetate, butane, etc. are transported to the inlet of the multi-stage compressor for supply Aggregation and reuse. Then, it is introduced into a low-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. Furthermore, the raw material composition of the additional chain transfer agent added in order to adjust the amount of the chain transfer agent is 35% isobutane and 65% n-butane, but the composition of the chain transfer agent during polymerization in the reactor is isobutane. 40%, n-butane 60%. The obtained molten resin of the ethylene-vinyl acetate copolymer is fed to an extruder, and the ethylene-vinyl acetate copolymer is obtained by granulation. The physical properties and characteristics of the obtained ethylene-vinyl acetate copolymer were measured using the method shown above. The measurement results are shown in Table 1.

[Industrial availability]

The ethylene-vinyl acetate copolymer of the present invention has industrial applicability as a resin raw material used in a wide range of industrial fields.

Claims (8)

An ethylene-vinyl acetate copolymer containing 3.0 mass % or more and less than 11.0 mass % of vinyl acetate units and containing ethylene units, and is measured by the pulse NMR solid echo method using the following formula 1 When the free motion attenuation (M(t)) obtained at 80°C is subjected to three-component approximate fitting, the composition rate of the component with the lowest mobility (α) is between 28.0% and below 36.0%, and the component with the highest mobility (γ )'s relaxation time (Tγ) is more than 375μs and less than 600μs; (M(t))=α‧exp{(-1/1.5)(t/Tα) ^1.5 }+β‧exp(-t/Tβ) +γ‧exp(-t/Tγ) Formula 1 [α: composition rate (%) of the component (α) with the lowest mobility; Tα: relaxation time (msec) of the component (α); β: motion in the middle Composition rate (%) of component (β); Tβ: relaxation time (msec) of component (β); γ: composition rate (%) of component (γ) with the highest mobility; Tγ: component (γ) Relaxation time (msec); t: observation time (msec)]. For example, the ethylene-vinyl acetate copolymer of claim 1 has a molecular weight distribution (Mw/Mn) of 3.7 or more and 7.0 or less. For example, the ethylene-vinyl acetate copolymer of claim 1 has a melt flow rate of 0.3g/10min or more and 5.0g/10min or less. Such as the ethylene-vinyl acetate copolymer of claim 2, which The melt flow rate is above 0.3g/10min and below 5.0g/10min. For example, the ethylene-vinyl acetate copolymer according to any one of claims 1 to 4 has a melt elongation of 5.0 m/min or more and 30.0 m/min or less. A shaped body comprising the ethylene-vinyl acetate copolymer according to any one of claims 1 to 5. A foam comprising the ethylene-vinyl acetate copolymer according to any one of claims 1 to 5. A sheet comprising the ethylene-vinyl acetate copolymer according to any one of claims 1 to 5.