Ethylene-vinyl acetate copolymer, and molded article, sheet, and foam containing the same

Abstract

To provide: an ethylene-vinyl acetate copolymer having excellent flexural moduli, thermostability, weatherability, and foaming uniformity; and a molding, sheet, and foam comprising the same.SOLUTION: An ethylene-vinyl acetate copolymer comprises 3.0 mass% or more and less than 11.0 mass% of a vinyl acetate unit, and an ethylene unit. When a free movement decay (M(t)) at 80°C measured by Solid Echo method of pulsed NMR is fitted by using the following formula 1 for three-components approximation, a compositional ratio of a component (α) with the lowest mobility is 28.0% or more and 36.0% or less and a relaxation time (Tγ) of a component (γ) with the highest mobility is 375 μs or more and less than 600 μs. Formula 1: (M(t))=α exp{(-1 / 1.5)(t / Tα)1.5}+β exp(-t / Tβ)+γ exp(-t / Tγ) [α: a compositional ratio (%) of a component (α) with the lowest mobility, Tα: a relaxation time (msec) of the component (α), β: a compositional ratio (%) of an intermediate mobile component (β), Tβ: a relaxation time (msec) of the component (β), γ: a compositional ratio (γ) of a component with the highest mobility, Tγ: a relaxation time (msec) of the component (γ), t: observation time (msec)].SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an ethylene-vinyl acetate copolymer, and a molded article, a sheet, and a foamed article containing the same. [Background technology]

[0002] Ethylene-vinyl acetate copolymers have excellent properties such as flexibility, mechanical strength, electrical insulation, weather resistance, and durability, and are therefore used in a wide range of industrial fields as heat insulating materials and cushioning materials, including as cushioning materials for electronic devices and in-vehicle parts, and in traffic cones (registered trademark).

[0003] 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 when it is a thin foam sheet. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2018 / 181498 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, as the fields of use of ethylene-vinyl acetate copolymers have expanded, the market has come to demand even more advanced performance. Specific examples of the required performance include high rigidity even in foamed products for applications such as automotive parts. Meanwhile, for such applications, high rigidity is also required, along with high heat resistance and weather resistance even in high-temperature summer environments, and excellent foam uniformity during foam formation.

[0006] However, the ethylene-vinyl acetate copolymer described in Patent Document 1 has a relatively high vinyl acetate content, and although it has excellent flexibility, there is 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, yet also has high heat resistance and weather resistance even in high-temperature summer environments, and exhibits excellent foam uniformity when forming a foam.

[0007] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an ethylene-vinyl acetate copolymer that is excellent in flexural modulus, heat resistance, weather resistance, and foaming uniformity, and a molded article, sheet, and foam containing the same. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above problems, and as a result have found that the above problems can be solved by using an ethylene-vinyl acetate copolymer having a relatively large amount of crystalline portions and low molecular chain mobility in amorphous portions, which has led to the completion of the present invention.

[0009] That is, the present invention is as follows. [1] Contains 3.0% by mass or more and less than 11.0% by mass of vinyl acetate units and ethylene units, When the free motion decay (M(t)) at 80°C measured by the solid echo method of pulsed NMR is fitted using the following equation 1, a three-component approximation is obtained: The composition rate of the least mobile component (α) is 28.0% or more and 36.0% or less, The relaxation time (Tγ) of the most mobile component (γ) is 375 μs or more and less than 600 μs. Ethylene-vinyl acetate copolymer. (M(t))=α·exp{(-1 / 1.5)(t / Tα) 1.5}+β·exp(-t / Tβ)+γ·exp(-t / Tγ)···Formula 1 [α: composition ratio (%) of the least mobile component (α), Tα: relaxation time of component (α) (msec), β: composition ratio (%) of intermediate mobile component (β), Tβ: relaxation time of component (β) (msec), γ: composition ratio (%) of the most mobile component (γ), Tγ: relaxation time of component (γ) (msec), t: observation time (msec)] [2] The molecular weight distribution (Mw / Mn) is 3.7 or more and 7.0 or less. The ethylene-vinyl acetate copolymer according to [1]. [3] The melt flow rate is 0.3 g / 10 min or more and 5.0 g / 10 min or less. The ethylene-vinyl acetate copolymer according to [1] or [2]. [4] The melt elongation is 5.0 m / min or more and 30.0 m / min or less. The ethylene-vinyl acetate copolymer according to any one of [1] to [3]. [5] [1] to [4], comprising the ethylene-vinyl acetate copolymer according to any one of [1] to [4]. Molded body. [6] [1] to [4], comprising the ethylene-vinyl acetate copolymer according to any one of [1] to [4]. Foam. [7] [1] to [4], comprising the ethylene-vinyl acetate copolymer according to any one of [1] to [4]. Sheet. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an ethylene-vinyl acetate copolymer having excellent flexural modulus, heat resistance, weather resistance, and foam uniformity, as well as a molded article, sheet, and foam containing the same. DETAILED DESCRIPTION OF THE INVENTION

[0011] Below, we will explain in detail the embodiment of the present invention (hereinafter referred to as the ``present embodiment''), but the present invention is not limited to this and various modifications are possible within the scope of the gist of the present invention.

[0012] [Ethylene-vinyl acetate copolymer] The ethylene-vinyl acetate copolymer of this embodiment contains 3.0 mass % or more and less than 11.0 mass % vinyl acetate units and ethylene units, and when the free motion decay (M(t)) at 80°C measured by the Solid Echo method of pulsed NMR is fitted using the following equation 1 to obtain a three-component approximation, the composition ratio (α) of the component with the lowest mobility is 28.0% or more and 36.0% or less, and the relaxation time (Tγ) of the component with the highest mobility 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) ···Equation 1 [α: composition ratio (%) of the least mobile component (α), Tα: relaxation time of component (α) (msec), β: composition ratio (%) of intermediate mobile component (β), Tβ: relaxation time of component (β) (msec), γ: composition ratio (%) of the most mobile component (γ), Tγ: relaxation time of component (γ) (msec), t: observation time (msec)]

[0013] As a result of extensive research, the present inventors have found that an ethylene-vinyl acetate copolymer contains a relatively large amount of crystalline portions and has low molecular chain mobility in the amorphous portions, which leads to further improvements in flexural modulus, heat resistance, weather resistance, and foam uniformity. The reason for this is not particularly limited, but it is believed that the flexural modulus and heat resistance are improved by the large amount of crystalline portions.

[0014] Regarding foamability, too much branching tends to increase the melt tension and prevent uniform foaming. On the other hand, too little branching tends to cause cells to break during foaming, resulting in open cells. Therefore, it is believed that by reducing the mobility of the molecular chains in the amorphous portion, i.e., by controlling the branching to a certain amount, a good foam with uniform foaming and few open cells can be obtained.

[0015] Generally, the weather resistance tends to decrease as the vinyl acetate unit content of an ethylene-vinyl acetate copolymer decreases, but when the vinyl acetate unit content is low, deterioration due to hydrogen abstraction from the branched portions tends to progress, so the weather resistance tends to decrease as the number of branches increases. Therefore, it is thought that the low mobility of molecular chains in the amorphous portion, i.e., the low number of branches, improves the weather resistance even in ethylene-vinyl acetate copolymers with a low vinyl acetate content.

[0016] In this embodiment, the amount of crystalline portions contained in ethylene-vinyl acetate copolymer and the mobility of the amorphous portions are determined by pulsed NMR. Pulsed NMR orients the spins of hydrogen atoms in polymer chains in a magnetic field and measures the spin-spin relaxation time, enabling qualitative and quantitative analysis of the target depending on the relaxation time. High molecular mobility tends to result in long relaxation times, which allows the evaluation of the mobility of the molecular chains of ethylene-vinyl acetate copolymer.

[0017] In pulsed NMR, when multiple components with different mobilities are present in a sample, waveform processing can be used to determine the ratio and relaxation time of each component. For example, by fitting the free induction decay obtained by pulsed NMR to three components: the least mobile component (α), the intermediate mobile component (β), and the most mobile component (γ), the proportion of each mobile component and the mobility (relaxation time) of each mobile component can be determined.

[0018] Here, the component with the lowest mobility (α) corresponds to the crystalline portion, the component with the highest mobility (γ) corresponds to the amorphous portion, and the intermediate component with intermediate mobility (β) corresponds to the amorphous portion subjected to high speed. Therefore, the amount of component (α) can be expressed as the amount of crystalline portion, and the relaxation time of component (γ) can be expressed as the mobility in the amorphous portion.

[0019] The ethylene-vinyl acetate copolymer of this embodiment will be described in detail below.

[0020] [Pulsed NMR] In this embodiment, the free induction decay (M(t)) at 80°C measured by the solid echo method of pulsed NMR is fitted to three components using the following equation 1. This makes it possible to evaluate the amounts and relaxation times (mobility) of the least mobile component (α), the intermediate mobile component (β), and the most mobile component (γ) in ethylene-vinyl acetate copolymer. M(t)=α·exp{(-1 / 1.5)(t / Tα) 1.5}+β·exp(-t / Tβ)+γ·exp(-t / Tγ) ···Equation 1 α: The composition ratio (%) of the least mobile component (α) Tα: Relaxation time of component (α) (msec) β: Composition rate (%) of intermediate motion component (β) Tβ: Relaxation time of component (β) (msec) γ: The percentage of the most mobile component (γ) (%) Tγ: Relaxation time of component (γ) (msec) t: Observation time (msec)

[0021] The composition ratio of the component (α) with the lowest mobility is 28.0% or more and 36.0% or less, preferably 29.0% or more and 35.0% or less, and more preferably 30.0% or more and 34.0% or less. When the composition ratio of component (α) is 28.0% or more, the flexural modulus and heat resistance are excellent. When the composition ratio is 36.0% or less, the balance between weather resistance and foam uniformity tends to be excellent.

[0022] The relaxation time (Tα) of component (α) is not particularly limited, but is preferably in the range of 5 μsec to 30 μsec, more preferably 7 μsec to 20 μsec, and even more preferably 10 μsec to 15 μsec.

[0023] The composition ratio of the intermediate motion component (β) is not particularly limited, but is preferably in the range of 30.0% to 50.0%, more preferably 35.0% to 48.0%, and even more preferably 40.0% to 47.0%.

[0024] The relaxation time (Tβ) of the component (β) is not particularly limited, but is preferably in the range of 50 μsec or more and 130 μsec or less, more preferably 60 μsec or more and 120 μsec or less, and even more preferably 70 μsec or more and 110 μsec or less.

[0025] The composition ratio of the component (γ) with the highest mobility is preferably 23.0% or more and 29.0% or less, more preferably 24.0% or more and 27.5% or less, and even more preferably 25.0% or more and 26.0% or less. When the composition ratio of the component (γ) is within the above range, the amorphous portion becomes relatively small, and the flexural modulus and heat resistance tend to be excellent.

[0026] The relaxation time (Tγ) of component (γ) is 375 μs or more and less than 600 μs, preferably 400 μs or more and 575 μs or less, and preferably 425 μs or more and 550 μs or less. When the relaxation time (Tγ) is within the above range, the balance between weather resistance and foam uniformity tends to be excellent.

[0027] The method for adjusting the composition ratios of components (α) to (γ) and the relaxation times (Tα) to (Tγ) within the above ranges is not particularly limited, but includes, for example, a method of adjusting the type and amount of a chain transfer agent. By using a chain transfer agent, the amount of long-chain branches introduced into the ethylene-vinyl acetate copolymer generally tends to be reduced.

[0028] On the other hand, because α-olefins with double bonds function as comonomers with chain transfer agents, the use of α-olefins with double bonds introduces short alkyl chain branches into the molecular chain. The introduction of short alkyl chain branches inhibits crystallization, resulting in a tendency for the crystalline portion to decrease. Therefore, by using a predetermined amount of a chain transfer agent other than an α-olefin with double bonds, the composition ratios of components (α) to (γ) and the relaxation times (Tα) to (Tγ) can be adjusted within the above ranges.

[0029] Other methods for adjusting the composition ratios of components (α) to (γ) and the relaxation times (Tα) to (Tγ) within the above ranges include, but are not limited to, a method of adjusting the composition of the chain transfer agent in the unreacted raw materials in a reaction system in which the unreacted raw materials are recycled and reused. By recycling and reusing the unreacted raw materials, unreacted chain transfer agents with low chain transfer constants accumulate in the raw materials, increasing the amount of long-chain branched chains introduced into the ethylene-vinyl acetate copolymer. For example, when using a chain transfer agent containing n-butane and iso-butane, although the difference in the chain transfer constants between n-butane and iso-butane is small, recycling and reusing the agent may accumulate n-butane with a low chain transfer constant, thereby increasing the amount of branched chains introduced into the ethylene-vinyl acetate copolymer.

[0030] Therefore, the means for achieving the composition conditions of the chain transfer agent is not particularly limited, but by bleeding out a part of the gas recovered in the high-pressure separator to the outside of the system and circulating and reusing it, the amount of accumulated unreacted raw material with a low chain transfer constant can be reduced, thereby suppressing an increase in branched chains and adjusting the composition ratio and relaxation time of each component within the above-mentioned ranges.

[0031] Another method for achieving the compositional requirements for the chain transfer agent is, but is not limited to, raising the temperature of a drain pot, which is typically used to remove low-molecular-weight components from the gas recovered in the high-pressure separator. While lowering the temperature is common to efficiently remove low-molecular-weight components, another method is to reduce the cooling of the drain pot and raise its temperature, thereby selectively and efficiently removing the high-boiling components of the chain transfer agent and adjusting the ratio of the chain transfer agent. For example, when using a chain transfer agent containing n-butane and iso-butane, raising the temperature of the drain pot can selectively and efficiently remove n-butane, which has a higher boiling point than iso-butane.

[0032] Other methods for adjusting the composition ratios of components (α) to (γ) and the relaxation times (Tα) to (Tγ) within the above ranges include, but are not limited to, cooling the piping immediately after the pressure drop after the tubular reactor. Cooling the piping immediately after the pressure drop after the tubular reactor suppresses a sudden rise in temperature due to the inverse Joule-Thomson effect and suppresses short-chain branches that are generated by the backbiting reaction and inhibit crystallization.

[0033] More specifically, pulsed NMR can be measured by the method described in the Examples.

[0034] (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, and even more preferably 4.3 or more and 6.0 or less. When the molecular weight distribution (Mw / Mn) is within the above range, foam uniformity tends to be more excellent.

[0035] The molecular weight distribution (Mw / Mn) can be adjusted by the polymerization temperature, polymerization pressure, etc. The molecular weight distribution (Mw / Mn) can be measured by gel permeation chromatography (hereinafter also referred to as "GPC") and determined based on a calibration curve prepared using commercially available monodisperse polystyrene. More specifically, it can be measured by the method described in the Examples.

[0036] (Melt Flow Rate) The melt flow rate of the ethylene-vinyl acetate copolymer of this embodiment is preferably 0.3 g / 10 min to 5.0 g / 10 min, more preferably 0.3 g / 10 min to 3.0 g / 10 min, and even more preferably 0.3 g / 10 min to 1.0 g / 10 min. When the melt flow rate is within the above range, the resulting molded article or the like tends to have a better balance between the flexural modulus and foaming uniformity.

[0037] The method for adjusting the melt flow rate of an ethylene-vinyl acetate copolymer is not particularly limited, and examples thereof include a method of adjusting the reaction temperature and / or reaction pressure, the type or amount of a chain transfer agent, etc., when polymerizing the ethylene-vinyl acetate copolymer. More specifically, when polymerizing the ethylene-vinyl acetate copolymer, increasing the reaction temperature tends to increase the melt flow rate of the ethylene-vinyl acetate copolymer, increasing the reaction pressure tends to decrease the melt flow rate of the ethylene-vinyl acetate copolymer, and increasing the amount of the chain transfer agent tends to increase the melt flow rate.

[0038] The melt flow rate can be measured in accordance with JIS K7210:1999 Code D (temperature = 190°C, load = 2.16 kg).

[0039] (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 even more preferably 7.0 m / min or more and 15.0 m / min or less. When the melt elongation is within the above range, foaming uniformity tends to be more excellent.

[0040] The melt elongation of the ethylene-vinyl acetate copolymer can be adjusted by adjusting the reaction temperature and / or reaction pressure and / or the type or amount of a chain transfer agent during polymerization of the ethylene-vinyl acetate copolymer. The melt elongation can be measured by the method described in the Examples.

[0041] (vinyl acetate units) The content of vinyl acetate units is 3.0% by mass or more and less than 11.0% by mass, preferably 3.5% by mass or more and 9.0% by mass or less, and more preferably 4.0% by mass or more and 6.0% by mass or less, based on the total amount of the ethylene-vinyl acetate copolymer. When the content of vinyl acetate units is within the above range, the resulting molded article or the like has an excellent balance of flexural modulus, heat resistance, and weather resistance.

[0042] The method for adjusting the content of vinyl acetate units is not particularly limited, and examples thereof include appropriately adjusting the amount of vinyl acetate monomer added in the step of polymerizing an ethylene-vinyl acetate copolymer, or the polymerization temperature or polymerization pressure.

[0043] The content of vinyl acetate units can be measured in accordance with JIS K7192:1999 by preparing a calibration curve by saponification and potentiometric titration as a standard test method, and converting the content into vinyl acetate by infrared spectroscopy as a control test method. Specifically, it can be measured by the method described in the examples below.

[0044] (ethylene units) The content of ethylene units is preferably more than 89.0% by mass and not more than 97.0% by mass, more preferably 91.0% by mass or more and 96.5% by mass or less, and even more preferably 94.0% by mass or more and 96.0% by mass or less, based on the total amount of the ethylene-vinyl acetate copolymer. When the content of ethylene units is within the above range, the resulting molded article or the like tends to have an excellent balance of flexural modulus, heat resistance, and weather resistance.

[0045] The ethylene-vinyl acetate copolymer of the present embodiment may contain a monomer unit other than an ethylene unit and a vinyl acetate unit. The other monomer unit is not particularly limited, but examples thereof include units derived from propylene, butane, etc.

[0046] The ethylene-vinyl acetate copolymer of the present embodiment may be a dry blend or melt blend of two or more ethylene-vinyl acetate copolymers in any ratio. When two or more ethylene-vinyl acetate copolymers are used, the content of vinyl acetate units in the entire resin is preferably within the above-mentioned range.

[0047] [Method for producing ethylene-vinyl acetate copolymer] The ethylene-vinyl acetate copolymer of the present embodiment is not particularly limited, but can be obtained, for example, by polymerizing ethylene and vinyl acetate under pressure and heat in the presence of a polymerization initiator. A chain transfer agent may be added to the polymerization system as needed.

[0048] The polymerization method for the ethylene-vinyl acetate copolymer is not particularly limited, but examples thereof include an autoclave method and a tubular method. Among these, it is preferable to use a tube reactor having a long ring structure. By using a tube reactor, it is possible to appropriately adjust the polymerization temperature and the like in each region from upstream to downstream.

[0049] The average polymerization temperature is preferably 150° C. or higher and 280° C. or lower, more preferably 180° C. or higher and 260° C. or lower. The average polymerization pressure is preferably 100 MPa or higher and 350 MPa or lower, more preferably 120 MPa or higher and 270 MPa or lower, and even more preferably 180 MPa or higher and 260 MPa or lower.

[0050] The reactor may have a plurality of feeding points for ethylene, vinyl acetate and the polymerization initiator.

[0051] The ethylene and vinyl acetate fed to the reactor may be in gaseous or liquid form.

[0052] The polymerization initiator is not particularly limited, but examples thereof include free radical generators such as peroxides, etc. Examples of free radical generators such as peroxides are not particularly limited, but examples thereof include t-butyl-peroxy-2-ethylhexanoate, t-butyl peroxyacetate, t-butyl peroxypivalate, di-t-butyl peroxide, etc.

[0053] The chain transfer agent is not particularly limited, and examples thereof include alcohols such as methanol, ethanol, normal propyl alcohol, isopropyl alcohol, normal butyl alcohol, and isobutyl alcohol; alkanes or alkenes such as ethane, propane, propylene, butane, 1-butene, and 2-butene; and ketones or aldehydes such as acetone, methyl ethyl ketone, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, diisobutyl ketone, methyl isopropyl ketone, formaldehyde, acetaldehyde, normal butyraldehyde, isobutyraldehyde, normal valeraldehyde, and isovaleraldehyde.

[0054] Among these, it is preferable to use a chain transfer agent whose chain transfer constant, which is the ratio of the rate constant of the chain transfer reaction to the rate constant of the propagation reaction, is within a predetermined range. The chain transfer constant of the chain transfer agent is preferably 0.0020 or more and 0.010 or less, more preferably 0.0030 or more and 0.008 or less, and even more preferably 0.0035 or more and 0.006 or less. By using a chain transfer agent having such a chain transfer constant, it becomes easier to adjust the composition ratios and relaxation times (Tα) to (Tγ) of components (α) to (γ), particularly the composition ratio and relaxation time (Tγ) of component (α), within the above ranges. The above chain transfer constants are values ​​measured at 1350 atm and 130°C.

[0055] Examples of chain transfer agents having the above chain transfer constant include n-butane and iso-butane.

[0056] The amount of the chain transfer agent used is preferably 0.1 mol% to 4.0 mol%, more preferably 0.5 mol% to 4.0 mol%, and even more preferably 1.5 mol% to 3.0 mol%, based on the ethylene introduced into the reactor. By setting the amount of the chain transfer agent used within the above range, it becomes easier to adjust the composition ratios and relaxation times (Tα) to (Tγ) of components (α) to (γ), particularly the composition ratio and relaxation time (Tγ) of component (α), within the above range.

[0057] The composition of the chain transfer agent during polymerization preferably contains 40% or more, preferably 50% or more, more preferably 60% or more of isobutane. By adjusting the composition of the chain transfer agent in this manner, the composition ratios and relaxation times (Tα) to (Tγ) of components (α) to (γ), particularly the composition ratio and relaxation time (Tγ) of component (α), can be easily adjusted within the above ranges.

[0058] The piping immediately after the pressure drop after the tube reactor is cooled to preferably 30°C or higher and 200°C or lower, more preferably 60°C or higher and 180°C or lower, and even more preferably 120°C or higher and 160°C or lower, which makes it easier to adjust the composition ratios and relaxation times (Tα) to (Tγ) of components (α) to (γ), particularly the composition ratio and relaxation time (Tγ) of component (α), within the above ranges.

[0059] The ethylene-vinyl acetate copolymer polymerized as described above is preferably separated into polymer and gas in a high-pressure separator. Low molecular weight components are removed from the extracted gas in a drain pot along the way, and the remaining gas, including ethylene, vinyl acetate, and chain transfer agent, may be sent to the inlet of the multistage compressor and reused for polymerization. The remaining gas is preferably bled out of the system and discarded.

[0060] The drain pot is cooled to preferably 30°C or higher and 200°C or lower, more preferably 60°C or higher and 180°C or lower, and even more preferably 130°C or higher and 160°C or lower, which makes it easier to adjust the composition ratios and relaxation times (Tα) to (Tγ) of components (α) to (γ), particularly the composition ratio and relaxation time (Tγ) of component (α), within the above ranges.

[0061] The high-pressure separator bleedout (HPR bleed) is preferably 200 kg / hr or more and 600 kg / hr or less, more preferably 300 kg / hr or more and 600 kg / hr or less, and more preferably 300 kg / hr or more and 600 kg / hr or less. By setting the HPR bleed within the above range, it becomes easier to adjust the composition ratios and relaxation times (Tα) to (Tγ) of the components (α) to (γ), particularly the composition ratio and relaxation time (Tγ) of the component (α), within the above range.

[0062] Subsequently, the polymer separated in the high-pressure separator is preferably introduced into a low-pressure separator, where it is further separated into the ethylene-vinyl acetate copolymer and gas.

[0063] The ethylene-vinyl acetate copolymer obtained by the polymerization as described above and separation from the raw materials is preferably granulated into pellets using an extruder.

[0064] After the ethylene-vinyl acetate copolymer is pelletized in the extruder, the pellets may be stored in a silo.

[0065] The ethylene-vinyl acetate copolymer of the present embodiment may contain known additives, such as antioxidants, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, and coloring pigments, as needed.

[0066] The antioxidant is not particularly limited, but examples thereof include phenolic antioxidants such as 2,6-di-t-butyl-4-methylphenol, pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], and octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate; phosphorus-based antioxidants such as tris(2,4-di-t-butylphenyl)phosphite and tetrakis(2,4-di-t-butylphenyl)-4,4-biphenylene-diphosphonite; phosphorus / phenolic antioxidants such as 6-tert-butyl-4-[3-(2,4,8,10-tetra-t-butyldibenzo[d,f][1,3,2]dioxaphosphepin-6-yloxy)propyl]-o-cresol; and sulfur-based antioxidants such as dilauryl-thio-dipropionate.

[0067] [Molded body] The molded article of this embodiment contains the above-mentioned ethylene-vinyl acetate copolymer. The molded article of this embodiment can be obtained by, but is not limited to, injection molding, extrusion molding, or stretch molding, and can be suitably used in a variety of applications. Specific examples include, but are not limited to, cushioning materials for electronic devices and in-vehicle parts, traffic cones, artificial turf mats, automobile mat guards, mudguard covers, drainage hoses, and the like. It can also be used as fibers, etc.

[0068] Sheet The sheet of this embodiment contains the above-mentioned ethylene-vinyl acetate copolymer. Examples of methods for producing the sheet include T-die molding, inflation molding, calendar molding, and skiff molding. In particular, T-die molding or extrusion inflation molding is preferred.

[0069] The sheet of this embodiment can be suitably used for automobile mudguards and mudguard covers. The term "sheet" refers to a thin plastic plate having a thickness of 250 μm or more. The thickness of the sheet of this embodiment is preferably 250 μm or more, more preferably 300 μm to 10 mm, and even more preferably 0.5 to 10 mm.

[0070] [Foam] The foam of this embodiment contains the above-mentioned ethylene-vinyl acetate copolymer. The foam of this embodiment is not particularly limited, but can be obtained using, for example, a cushioning material for electronic devices or vehicle-mounted parts, foamed microparticles, etc., and can be suitably used for a variety of applications. [Example]

[0071] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0072] [Measurement of vinyl acetate unit content] In accordance with JIS K7192:1999, a calibration curve was prepared as a reference test method using VAC standard samples of ethylene-vinyl acetate copolymers with known contents of vinyl acetate units by saponification and potentiometric titration, and as a control test method, the vinyl acetate unit contents (VA contents) of the ethylene-vinyl acetate copolymers obtained in the examples and comparative examples were measured by infrared spectroscopy.

[0073] [Pulsed NMR] First, a sample tube filled with ethylene-vinyl acetate copolymer to a height of 1 cm from the bottom was placed in a Bruker TD-NMR apparatus (model: minispec mq20) set to keep the internal temperature of the sample tube at 40°C, and the sample tube was heated according to the <heating conditions> shown below. The temperatures shown in the heating conditions below are values ​​obtained by measuring the internal temperature of the sample with a thermocouple. <Temperature increase conditions> Step 1: Raise the temperature from 40°C at a rate of 10°C / min and leave at 70°C for 13 minutes. Step 2: Raise the temperature from 70°C at a rate of 10°C / min and leave at 80°C for 5 minutes.

[0074] After the temperature increase was completed by the above procedure, the spin-spin relaxation time (T2, sometimes simply referred to as "relaxation time" in this specification) of the sample was measured under the measurement conditions shown below. <Measurement conditions> Observation kernel: 1 H Measurement: T2 Measurement method: Solid echo method Accumulation count: 256 times Measurement temperature: 80℃ Repeat time: 3 seconds Capture time: 1 ms

[0075] The obtained free motion decay (M(t)) was fitted using the following equation 1 by an analysis program software (TDNMR-A) manufactured by Bruker, to approximate it to three components. M(t)=α·exp{(-1 / 1.5)(t / Tα) 1.5}+β·exp(-t / Tβ)+γ·exp(-t / Tγ) ···Equation 1 α: The composition ratio (%) of the least mobile component (α) Tα: Relaxation time of component (α) (msec) β: Composition rate (%) of intermediate motion component (β) Tβ: Relaxation time of component (β) (msec) γ: The percentage of the most mobile component (γ) (%) Tγ: Relaxation time of component (γ) (msec) t: Observation time (msec)

[0076] [Measurement of molecular weight and molecular weight distribution] The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the ethylene-vinyl acetate copolymer were determined by gel permeation chromatography (GPC). The ratio (Mw / Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) determined by GPC was defined as the molecular weight distribution. GPC measurements were performed under the following measurement conditions. Molecular weight calibration was performed using 12 standard polystyrenes manufactured by Tosoh Corporation with molecular weights ranging from 1,050 to 20,600,000. The MW of each standard polystyrene was multiplied by a coefficient of 0.43 to obtain the polyethylene-equivalent molecular weight. A primary calibration line was created by plotting the elution time against the polyethylene-equivalent molecular weight, and the weight-average molecular weight (Mw) and number-average molecular weight (Mn) were determined. (Measurement conditions) Equipment: Polymer Char GPC-IR Detector: Polymer Char IR5 Column: Showa Denko UT-807 (1 column) and Tosoh GMHHR-H(S)HT (2 columns) connected in series Mobile phase: orthodichlorobenzene Column temperature: 140℃ Flow rate: 1.0mL / min Sample concentration: 16mg / 8mL Sample dissolution temperature: 140℃ Sample dissolution time: 60 minutes

[0077] [Melt flow rate (MFR) measurement] The MFR of the ethylene-vinyl acetate copolymer was measured in accordance with JIS K7210:1999 Code D (temperature = 190°C, load = 2.16 kg).

[0078] [Melt elongation (ME) measurement] Using a Toyo Seiki Co., Ltd. Capillograph 1D equipped with a capillary of 2.095 mm diameter and 7.98 mm length, the sample was fully melted at 190°C for 5 minutes, and then the piston was operated at a constant piston speed of 6 mm / min. Ethylene-vinyl acetate copolymer was extruded at 190°C, and the take-up speed was started at 3 m / min. After 1 minute, the take-up speed was increased to 10 m / min, and the elongation at which the strand broke was measured as the melt elongation (ME).

[0079] [Preparation of molded body 1] A 0.1 mm thick aluminum plate was placed on a 5 mm thick smooth iron plate, and a 50 μm thick polyethylene terephthalate film (Lumirror, manufactured by Toray Industries, Inc.) that was not coated with cellophane was placed on top of the aluminum plate. A mold measuring 200 mm in length, 200 mm in width, and 4.0 mm in thickness was placed on top of this, and 160 g of ethylene-vinyl acetate copolymer was placed inside. The polyethylene terephthalate film was then placed on top of this, and the aluminum plate and then the iron plate were placed on top of this.

[0080] This was placed in a compression molding machine (SFA-37) manufactured by Shinto Metal Industries Co., Ltd., which was temperature-controlled at 180°C, and after preheating at 180°C and 0.1 MPa for 180 seconds, air was removed for 5 seconds (10 MPa), and pressure was applied at 180°C and 15 MPa for 120 seconds.

[0081] After the pressing was completed, the sample was removed and placed in a compression molding machine (SFA-37) manufactured by Shinto Metal Industries Co., Ltd., whose temperature had been adjusted to 25°C, 5 seconds after removal. The sample was then cooled while being pressed at 25°C and 10 MPa for 300 seconds to produce a pressed sheet. After cooling, the pressed sheet was removed from the mold and left to stand for at least 24 hours in an environment at a temperature of 23°C and a humidity of 50%.

[0082] [Measurement of flexural modulus] The molded body 1 was punched out to a thickness of 4.0 mm, length of 80.0 mm, and width of 10.0 mm to prepare a test piece. According to JIS K7171:2008, the flexural modulus of the ethylene-vinyl acetate copolymer was measured using an Autograph AG-X Refresh manufactured by Shimadzu Corporation at a test speed of 2 mm / min and a support distance of 64 mm, and the flexural modulus was evaluated according to the following criteria: ⊚ and ◯ were deemed acceptable. (Evaluation criteria) ◎ (Excellent): Flexural modulus of elasticity 150 MPa or more ○ (Good): Flexural modulus of elasticity 120 MPa or more and less than 150 MPa × (Not acceptable): Flexural modulus less than 120 MPa

[0083] [Preparation of molded body 2] A 0.1 mm thick aluminum plate was placed on a 5 mm thick smooth iron plate, and a 50 μm thick polyethylene terephthalate film (Lumirror, manufactured by Toray Industries, Inc.) that was not coated with cellophane was placed on top of the aluminum plate. A mold measuring 200 mm in length, 200 mm in width, and 0.6 mm in thickness was placed on top of this, and 24 g of ethylene-vinyl acetate copolymer was placed inside. The polyethylene terephthalate film was then placed on top of this, and the aluminum plate was then placed on top of this, and the iron plate was then placed on top of this.

[0084] This was placed in a compression molding machine (SFA-37) manufactured by Shinto Metal Industries Co., Ltd., which was temperature-controlled at 180°C, and after preheating at 180°C and 0.1 MPa for 180 seconds, air was removed for 5 seconds (10 MPa), and pressure was applied at 180°C and 15 MPa for 120 seconds.

[0085] After the pressing was completed, the sample was removed and placed in a compression molding machine (SFA-37) manufactured by Shinto Metal Industries Co., Ltd., whose temperature had been adjusted to 25°C, 5 seconds after removal. The sample was then cooled while being pressed at 25°C and 10 MPa for 300 seconds to produce a pressed sheet. After cooling, the pressed sheet was removed from the mold and left to stand for at least 24 hours in an environment at a temperature of 23°C and a humidity of 50%.

[0086] [Heat resistance (shrinkage rate)] Two molded bodies 2 were prepared: an unirradiated test specimen and an irradiated test specimen. The unirradiated test specimen was left standing for at least 24 hours in an environment at 23°C and 50% humidity. The irradiated test specimens were cut into a width of 70 mm and a length of 150 mm and irradiated for 720 hours with ultraviolet light at a wavelength of 300-400 nm and an irradiance of 60 W / m² using a Suga Test Instruments X75 xenon weather meter equipped with a 7.5 kW xenon lamp. The BPT temperature was 83°C ± 2°C. After irradiation, the irradiated test specimens were removed and left standing for at least 24 hours in an environment at 23°C and 50% humidity, after which the dimensions of the irradiated test specimens were measured. The shrinkage rate Hw was calculated using the following formula 2 using the initial test specimen length H0 and the post-irradiation test specimen length H1, and evaluated according to the following criteria. ◎ and ◯ were considered acceptable. Hw[%]=(H0-H1) / H0×100...Equation 2 ◎ (Excellent): Shrinkage rate Hw is less than 1% Good: Shrinkage rate Hw is 1% or more and less than 2% × (Not acceptable): Shrinkage rate Hw is 2% or more

[0087] [Weather resistance (retained elongation)] Unirradiated and irradiated test specimens were randomly cut to the dimensions of the weather resistance test specimens specified in JIS K 6783:1994. Using an Orientec tensile testing machine (TENSIRON (RTC-1310A)), the specimens were pulled at a temperature of 25°C and a pulling rate of 500 mm / min. The elongation between the gauge lines at the time the specimen broke was determined. Test specimens cut outside the gauge lines were excluded, and spare test specimens were added, with N = 3 measurements. The elongation retention rate (Lw) was calculated using the initial gauge length (L0), the average gauge length elongation (L1) of the unirradiated test specimens, and the average gauge length elongation (L2) of the irradiated test specimens, according to the following formula (3). Based on the elongation retention rate (Lw) obtained, weather resistance was evaluated according to the following criteria. Excellent and excellent were deemed acceptable. Lw[%]={[(L2-L0) / L0] / [(L1-L0) / L0]}×100...Equation 3 (Evaluation criteria) ◎ (Excellent): Elongation retention rate Lw 70% or more Good: Elongation retention rate Lw 50% or more but less than 70% × (Not acceptable): Elongation remaining rate Lw less than 50%

[0088] [Preparation of foam] To 100 parts by mass of ethylene-vinyl acetate copolymer, 2 parts by mass of an inorganic foaming agent (Polythrene EE275F) manufactured by Eiwa Chemical Industry Co., Ltd. was added, and the mixture was dry-blended in a pellet blender. A 100 x 100 x 2.0 mm flat test piece (film gate) was produced using a fully electric injection molding machine manufactured by Sumitomo, SE130DUZ-C360 (cylinder temperature set at 200°C, mold temperature set at 40°C) with an injection time of 20 seconds and a cooling time of 30 seconds. ◎ and ◯ were rated as pass.

[0089] [Measurement of foam uniformity] Cross sections of the flat test pieces of the ethylene-vinyl acetate copolymer resin foam were cut out at 5 mm from the gate end and 5 mm from the flow end, and visually observed using an optical microscope (10x magnification). (Evaluation criteria) ◎: The size of the bubbles on the cross section 5 mm from the gate end and 5 mm from the flow end is uniform and the bubbles are not connected together. ○: There is some variation in the size of the bubbles on the cross section 5 mm from the gate end and 5 mm from the flow end, and the bubbles are not connected together. ×: There is variation in the size of the bubbles in the cross section at 5 mm from the end of the gate side and 5 mm from the end of the flow side, and the bubbles are connected together.

[0090] 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 temperature was 240°C, the average polymerization pressure was 250 MPa, and polymerization was carried out using t-butyl peroxy-2-ethylhexanoate and di-t-butyl peroxide as polymerization initiators. The piping immediately after the pressure drop from the tubular reactor was cooled to 150°C. After polymerization, the mixture was introduced into a high-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. The gas recovered from the high-pressure separator was passed through a drain pot cooled to 160°C to remove low-molecular-weight components. Unreacted gases, such as residual ethylene, vinyl acetate, and butane, were bled out of the system at 600 kg / h, and the remainder was sent to the inlet of a multi-stage compressor for reuse in the polymerization. The mixture was then introduced into a low-pressure separator, where the ethylene-vinyl acetate copolymer and gas were separated. The composition of the raw material chain transfer agent added to adjust the amount of chain transfer agent was 35% isobutane and 65% n-butane, but the composition of the chain transfer agent during polymerization in the reactor was 60% isobutane and 40% n-butane. The resulting ethylene-vinyl acetate copolymer molten resin was fed into an extruder and pelletized to obtain an ethylene-vinyl acetate copolymer. The physical properties and characteristics of the resulting ethylene-vinyl acetate copolymer were measured using the methods described above. The measurement results are shown in Table 1.

[0091] 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 temperature was 230°C, the average polymerization pressure was 220 MPa, and polymerization was carried out using t-butyl peroxy-2-ethylhexanoate and di-t-butyl peroxide as polymerization initiators. The piping immediately after the pressure drop from the tubular reactor was cooled to 180°C. After polymerization, the mixture was introduced into a high-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. The gas recovered from the high-pressure separator was passed through a drain pot cooled to 160°C to remove low-molecular-weight components. Unreacted gases, such as residual ethylene, vinyl acetate, and butane, were bled out of the system at 600 kg / h, and the remainder was sent to the inlet of a multi-stage compressor for reuse in the polymerization. The mixture was then introduced into a low-pressure separator, where the ethylene-vinyl acetate copolymer and gas were separated. The composition of the raw material chain transfer agent added to adjust the amount of chain transfer agent was 35% isobutane and 65% n-butane, but the composition of the chain transfer agent during polymerization in the reactor was 60% isobutane and 40% n-butane. The resulting ethylene-vinyl acetate copolymer molten resin was fed into an extruder and pelletized to obtain an ethylene-vinyl acetate copolymer. The physical properties and characteristics of the resulting ethylene-vinyl acetate copolymer were measured using the methods described above. The measurement results are shown in Table 1.

[0092] 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 temperature was 250°C, the average polymerization pressure was 210 MPa, and polymerization was carried out using t-butyl peroxy-2-ethylhexanoate and di-t-butyl peroxide as polymerization initiators. The piping immediately after the pressure drop from the tubular reactor was cooled to 150°C. After polymerization, the mixture was introduced into a high-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. The gas recovered from the high-pressure separator was passed through a drain pot cooled to 160°C to remove low-molecular-weight components. Unreacted gases, such as residual ethylene, vinyl acetate, and butane, were bled out of the system at 600 kg / h, and the remainder was sent to the inlet of a multi-stage compressor for reuse in the polymerization. The mixture was then introduced into a low-pressure separator, where the ethylene-vinyl acetate copolymer and gas were separated. The composition of the raw material chain transfer agent added to adjust the amount of chain transfer agent was 35% isobutane and 65% n-butane, but the composition of the chain transfer agent during polymerization in the reactor was 60% isobutane and 40% n-butane. The resulting ethylene-vinyl acetate copolymer molten resin was fed into an extruder and pelletized to obtain an ethylene-vinyl acetate copolymer. The physical properties and characteristics of the resulting ethylene-vinyl acetate copolymer were measured using the methods described above. The measurement results are shown in Table 1.

[0093] Example 4 In a tubular reactor, 4.0 mol% vinyl acetate and 4.0 mol% chain transfer agent were introduced relative to ethylene. The average polymerization temperature was 230°C, the average polymerization pressure was 260 MPa, and polymerization was carried out using t-butyl peroxy-2-ethylhexanoate and di-t-butyl peroxide as polymerization initiators. The piping immediately after the pressure drop from the tubular reactor was cooled to 150°C. After polymerization, the mixture was introduced into a high-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. The gas recovered from the high-pressure separator was passed through a drain pot cooled to 160°C to remove low-molecular-weight components. Unreacted gases, such as residual ethylene, vinyl acetate, and butane, were bled out of the system at 600 kg / h, and the remainder was sent to the inlet of a multi-stage compressor for reuse in the polymerization. The mixture was then introduced into a low-pressure separator, where the ethylene-vinyl acetate copolymer and gas were separated. The composition of the raw material chain transfer agent added to adjust the amount of chain transfer agent was 35% isobutane and 65% n-butane, but the composition of the chain transfer agent during polymerization in the reactor was 60% isobutane and 40% n-butane. The resulting ethylene-vinyl acetate copolymer molten resin was fed into an extruder and pelletized to obtain an ethylene-vinyl acetate copolymer. The physical properties and characteristics of the resulting ethylene-vinyl acetate copolymer were measured using the methods described above. The measurement results are shown in Table 1.

[0094] 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 temperature and pressure were set at 250°C and 250 MPa, respectively. Polymerization was carried out using t-butyl peroxy-2-ethylhexanoate and di-t-butyl peroxide as polymerization initiators. The piping immediately following the pressure drop after the tubular reactor was cooled to 180°C. After polymerization, the mixture was introduced into a high-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. The gas recovered from the high-pressure separator was passed through a drain pot cooled to 160°C to remove low-molecular-weight components. Unreacted gases, such as residual ethylene, vinyl acetate, and butane, were bled out of the system at 300 kg / h, and the remainder was sent to the inlet of a multi-stage compressor for reuse in the polymerization. The mixture was then introduced into a low-pressure separator, where the ethylene-vinyl acetate copolymer and gas were separated. The composition of the raw material chain transfer agent added to adjust the amount of chain transfer agent was 28% iso-butane, 52% n-butane, and 20% propylene, while the composition of the chain transfer agent during polymerization in the reactor was 50% iso-butane, 40% n-butane, and 10% propylene. The resulting ethylene-vinyl acetate copolymer molten resin was fed into an extruder and pelletized to obtain an ethylene-vinyl acetate copolymer. The physical properties and characteristics of the resulting ethylene-vinyl acetate copolymer were measured using the methods described above. The measurement results are shown in Table 1.

[0095] 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 temperature was 250°C, the average polymerization pressure was 210 MPa, and polymerization was carried out using t-butyl peroxy-2-ethylhexanoate and di-t-butyl peroxide as polymerization initiators. The piping immediately after the pressure drop from the tubular reactor was cooled to 180°C. After polymerization, the mixture was introduced into a high-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. The gas recovered from the high-pressure separator was passed through a drain pot cooled to 130°C to remove low-molecular-weight components. Unreacted gases, such as residual ethylene, vinyl acetate, and butane, were bled out of the system at 300 kg / h, and the remainder was sent to the inlet of a multi-stage compressor for reuse in the polymerization. The mixture was then introduced into a low-pressure separator, where the ethylene-vinyl acetate copolymer and gas were separated. The composition of the raw material chain transfer agent added to adjust the amount of chain transfer agent was 35% iso-butane and 65% n-butane, but the composition of the chain transfer agent during polymerization in the reactor was 50% iso-butane and 50% n-butane. The resulting ethylene-vinyl acetate copolymer molten resin was fed into an extruder and pelletized to obtain an ethylene-vinyl acetate copolymer. The physical properties and characteristics of the resulting ethylene-vinyl acetate copolymer were measured using the methods described above. The measurement results are shown in Table 1.

[0096] 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 temperature was 240°C, the average polymerization pressure was 250 MPa, and polymerization was carried out using t-butyl peroxy-2-ethylhexanoate and di-t-butyl peroxide as polymerization initiators. The piping immediately after the pressure drop from the tubular reactor was not cooled, and after polymerization, the mixture was introduced into a high-pressure separator to separate the ethylene-vinyl acetate copolymer and gas. The gas recovered in the high-pressure separator was passed through a drain pot cooled to 100°C to remove low-molecular-weight components. Unreacted gases such as residual ethylene, vinyl acetate, and butane were bled out of the system at 600 kg / h, and the remainder was sent to the inlet of a multi-stage compressor for reuse in the polymerization. The mixture was then introduced into a low-pressure separator to separate the ethylene-vinyl acetate copolymer and gas. The composition of the raw material for the chain transfer agent added to adjust the amount of chain transfer agent was 100% propylene, and the composition of the chain transfer agent during polymerization in the reactor was also 100% propylene. The resulting ethylene-vinyl acetate copolymer molten resin was fed into an extruder and pelletized to obtain an ethylene-vinyl acetate copolymer. The physical properties and characteristics of the resulting ethylene-vinyl acetate copolymer were measured using the methods described above. The measurement results are shown in Table 1.

[0097] 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 230°C, the average polymerization reaction pressure was 220 MPa, and polymerization was carried out using t-butyl peroxy-2-ethylhexanoate and di-t-butyl peroxide as polymerization initiators. The piping immediately after the pressure drop from the tubular reactor was not cooled, and after polymerization, the mixture was introduced into a high-pressure separator to separate the ethylene-vinyl acetate copolymer and gas. The gas recovered from the high-pressure separator was then passed through a drain pot cooled to 100°C to remove low-molecular-weight components. The remaining ethylene, vinyl acetate, and unreacted gases, such as butane, were sent to the inlet of a multi-stage compressor for reuse in the polymerization. The mixture was then introduced into a low-pressure separator to separate the ethylene-vinyl acetate copolymer and gas. The composition of the raw material chain transfer agent added to adjust the amount of chain transfer agent was 35% isobutane and 65% n-butane, but the composition of the chain transfer agent during polymerization in the reactor was 20% isobutane and 80% n-butane. The resulting ethylene-vinyl acetate copolymer molten resin was fed into an extruder and pelletized to obtain an ethylene-vinyl acetate copolymer. The physical properties and characteristics of the resulting ethylene-vinyl acetate copolymer were measured using the methods described above. The measurement results are shown in Table 1.

[0098] 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 temperature was 250°C, the average polymerization pressure was 210 MPa, and polymerization was carried out using t-butyl peroxy-2-ethylhexanoate and di-t-butyl peroxide as polymerization initiators. The piping immediately after the pressure drop from the tubular reactor was cooled to 150°C. After polymerization, the mixture was introduced into a high-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. The gas recovered from the high-pressure separator was passed through a drain pot cooled to 160°C to remove low-molecular-weight components. Unreacted gases, such as residual ethylene, vinyl acetate, and butane, were bled out of the system at 600 kg / h, and the remainder was sent to the inlet of a multi-stage compressor for reuse in the polymerization. The mixture was then introduced into a low-pressure separator, where the ethylene-vinyl acetate copolymer and gas were separated. The composition of the raw material chain transfer agent added to adjust the amount of chain transfer agent was 35% isobutane and 65% n-butane, but the composition of the chain transfer agent during polymerization in the reactor was 60% isobutane and 40% n-butane. The resulting ethylene-vinyl acetate copolymer molten resin was fed into an extruder and pelletized to obtain an ethylene-vinyl acetate copolymer. The physical properties and characteristics of the resulting ethylene-vinyl acetate copolymer were measured using the methods described above. The measurement results are shown in Table 1.

[0099] Comparative Example 4 In a tubular reactor, 4.0 mol% vinyl acetate and 0.5 mol% chain transfer agent were introduced relative to ethylene. The average polymerization temperature was 230°C, the average polymerization pressure was 260 MPa, and polymerization was carried out using t-butyl peroxy-2-ethylhexanoate and di-t-butyl peroxide as polymerization initiators. The piping immediately after the pressure drop from the tubular reactor was not cooled, and after polymerization, the mixture was introduced into a high-pressure separator to separate the ethylene-vinyl acetate copolymer and gas. The gas recovered in the high-pressure separator was passed through a drain pot cooled to 100°C to remove low-molecular-weight components. Unreacted gases, such as residual ethylene, vinyl acetate, and butane, were bled out of the system at 300 kg / h, and the remainder was sent to the inlet of a multi-stage compressor for reuse in the polymerization. The mixture was then introduced into a low-pressure separator to separate the ethylene-vinyl acetate copolymer and gas. The composition of the raw material for the chain transfer agent added to adjust the amount of chain transfer agent was 100% propylene, and the composition of the chain transfer agent during polymerization in the reactor was also 100% propylene. The resulting ethylene-vinyl acetate copolymer molten resin was fed into an extruder and pelletized to obtain an ethylene-vinyl acetate copolymer. The physical properties and characteristics of the resulting ethylene-vinyl acetate copolymer were measured using the methods described above. The measurement results are shown in Table 1.

[0100] Comparative Example 5 In a tubular reactor, 5.0 mol% vinyl acetate and 4.0 mol% chain transfer agent were introduced relative to ethylene. The average polymerization temperature was 230°C, the average polymerization pressure was 270 MPa, and polymerization was carried out using t-butyl peroxy-2-ethylhexanoate and di-t-butyl peroxide as polymerization initiators. The piping immediately after the pressure drop from the tubular reactor was cooled to 150°C. After polymerization, the mixture was introduced into a high-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. The gas recovered from the high-pressure separator was passed through a drain pot cooled to 160°C to remove low-molecular-weight components. Unreacted gases, such as residual ethylene, vinyl acetate, and butane, were bled out of the system at 600 kg / h, and the remainder was sent to the inlet of a multi-stage compressor for reuse in the polymerization. The mixture was then introduced into a low-pressure separator, where the ethylene-vinyl acetate copolymer and gas were separated. The composition of the raw material chain transfer agent added to adjust the amount of chain transfer agent was 35% isobutane and 65% n-butane, but the composition of the chain transfer agent during polymerization in the reactor was 60% isobutane and 40% n-butane. The resulting ethylene-vinyl acetate copolymer molten resin was fed into an extruder and pelletized to obtain an ethylene-vinyl acetate copolymer. The physical properties and characteristics of the resulting ethylene-vinyl acetate copolymer were measured using the methods described above. The measurement results are shown in Table 1.

[0101] 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 250°C, the average polymerization reaction pressure was 210 MPa, and polymerization was carried out using t-butyl peroxy-2-ethylhexanoate and di-t-butyl peroxide as polymerization initiators. The piping immediately after the pressure drop from the tubular reactor was cooled to 180°C. After polymerization, the mixture was introduced into a high-pressure separator and separated into ethylene-vinyl acetate copolymer and gas. The gas recovered from the high-pressure separator was cooled to 130°C to remove low-molecular-weight components, and the remaining ethylene, vinyl acetate, and unreacted gases, such as butane, were sent to the inlet of a multi-stage compressor for reuse in the polymerization. The mixture was then introduced into a low-pressure separator, where the ethylene-vinyl acetate copolymer and gas were separated. The composition of the raw material chain transfer agent added to adjust the amount of chain transfer agent was 35% isobutane and 65% n-butane, but the composition of the chain transfer agent during polymerization in the reactor was 40% isobutane and 60% n-butane. The resulting ethylene-vinyl acetate copolymer molten resin was fed into an extruder and pelletized to obtain an ethylene-vinyl acetate copolymer. The physical properties and characteristics of the resulting ethylene-vinyl acetate copolymer were measured using the methods described above. The measurement results are shown in Table 1.

[0102] [Table 1]

[0103] [Table 2] [Industrial Applicability]

[0104] 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

1. Contains 3.0% by mass or more and less than 11.0% by mass of vinyl acetate units and ethylene units, When the free motion decay (M(t)) at 80°C measured by the solid echo method of pulsed NMR is fitted using the following equation 1 to obtain a three-component approximation, The composition ratio of the component (α) with the lowest mobility is 28.0% or more and 36.0% or less, The relaxation time (Tγ) of the most mobile component (γ) is 375 μs or more and less than 600 μs. Ethylene-vinyl acetate copolymer. M(t) = α · exp{(-1 / 1.5)(t / Tα)} 1.5} + β · exp(-t / Tβ) + γ · exp(-t / Tγ) ··· Equation 1 [α: composition ratio (%) of the least mobile component (α), Tα: relaxation time of component (α) (msec), β: composition ratio (%) of intermediate mobile component (β), Tβ: relaxation time of component (β) (msec), γ: composition ratio (%) of the most mobile component (γ), Tγ: relaxation time of component (γ) (msec), t: observation time (msec)]

2. The molecular weight distribution (Mw / Mn) is 3.7 or more and 7.0 or less. The ethylene-vinyl acetate copolymer according to claim 1.

3. A melt flow rate of 0.3 g / 10 min or more and 5.0 g / 10 min or less, measured in accordance with JIS K7210:1999 Code D (temperature = 190 °C, load = 2.16 kg). The ethylene-vinyl acetate copolymer according to claim 1 or 2.

4. The melt elongation is 5.0 m / min or more and 30.0 m / min or less, The ethylene-vinyl acetate copolymer according to any one of claims 1 to 3.

5. The ethylene-vinyl acetate copolymer according to any one of claims 1 to 4, Molded body.

6. The ethylene-vinyl acetate copolymer according to any one of claims 1 to 4, Foam.

7. The ethylene-vinyl acetate copolymer according to any one of claims 1 to 4, Sheet.

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