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

Abstract

To provide an ethylene-vinyl acetate copolymer having excellent impact strength, environmental stress cracking resistance, releasability, and transparency, and a molding, a sheet, and a foam comprising the same.SOLUTION: An ethylene-vinyl acetate copolymer contains a vinyl acetate unit of 11 mass% or more and 25 mass% or less and an ethylene unit. By GPC-FTIR, a molecular weight distribution, as well as a methylene group-attributable absorbance I(-CH2-), a carbonyl group-attributable absorbance I(-C=O), and a methyl group-attributable I(-CH3) for each molecular weight are measured, so that a gradient P of the least-squares method approximate linear relational expression of an absorbance ratio (Ii(-C=O) / Ii(-CH2-)) to a logarithm log(Mi) of each molecular weight Mi in a half-width region of the molecular weight distribution is 0.00≤P≤1.40, and an average value Q of an absorbance ratio (Ii(-CH3) / Ii(-CH2-)) of each molecular weight Mi in the half-width region of the molecular weight distribution is 23.0≤Q≤30.0.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 transparency, flexibility, mechanical strength, electrical insulation, weather resistance, and durability, and are used in applications such as artificial turf mats, automobile mat guards, and drainage hoses through injection molding or extrusion molding.They are also processed into single-layer or laminated films using inflation or T-die film forming, and are used in a wide range of industrial fields, such as agricultural polyolefin films and automobile mudguard covers.

[0003] As a film using an ethylene-vinyl acetate copolymer, for example, Patent Document 1 proposes an ethylene-vinyl acetate copolymer film that has high tear strength and heat retention even though it has a high vinyl acetate content. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-161881 Summary of the Invention [Problem to be solved by the invention]

[0005] However, while the transparency, flexibility, and adhesiveness of ethylene-vinyl acetate copolymers improve with an increase in the vinyl acetate content, the crystallization temperature decreases and the releasability tends to decrease.

[0006] In recent years, as the fields in which ethylene-vinyl acetate copolymers are used have expanded, the market has come to demand even more advanced performance. Specific examples of the required performance include high transparency to enhance design, and in applications such as drainage pipes, artificial turf, and automobile mudguard covers, where the copolymers are exposed to stresses such as internal pressure while in contact with various liquids for extended periods of time, the copolymers must be free from environmental stress cracking when left in chemicals under a certain level of stress, i.e., have high environmental stress cracking resistance (hereinafter also referred to as "ESCR"), and high falling weight impact strength.

[0007] Generally, methods for increasing the ESCR include increasing the molecular weight of the ethylene-vinyl acetate copolymer or increasing the vinyl acetate content, but increasing the molecular weight tends to decrease processability, and increasing the vinyl acetate content tends to decrease mold releasability as described above. Therefore, there is a demand for ethylene-vinyl acetate copolymers that are excellent in mold releasability and ESCR.

[0008] The ethylene-vinyl acetate copolymer film described in Patent Document 1 has room for improvement in terms of transparency and ESCR, since the vinyl acetate content at each molecular weight of the ethylene-vinyl acetate copolymer decreases as the molecular weight increases.

[0009] 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 impact strength, environmental stress crack resistance, mold releasability, and transparency, and a molded article, sheet, and foam containing the same. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have found that the above-mentioned problems can be solved by an ethylene-vinyl acetate copolymer in which the proportion of vinyl acetate units tends to remain constant or increase as the molecular weight distribution shifts from low to high molecular weight components and the copolymer has a predetermined number of branches, thereby completing the present invention.

[0011] That is, the present invention is as follows. [1] Contains 11% by mass or more and 25% by mass or less of vinyl acetate units and ethylene units, GPC-FTIR was used to measure the molecular weight distribution and the absorbance I attributed to the methylene group for each molecular weight. (-CH2-) and the absorbance I attributed to the carbonyl group (-C=O) and the absorbance I attributed to the methyl group (-CH3) When measuring and Each molecular weight M in the half width region of the molecular weight distribution i log(M i ) to absorbance ratio (I i(-C=O) / I i(-CH2-) ) the slope P of the least squares approximation linear relationship equation is 0.00≦P≦1.40, Each molecular weight M in the half width region of the molecular weight distribution i The absorbance ratio (I i(-CH3) / I i(-CH2-) ) the average value Q is 23.0≦Q≦30.0, Ethylene-vinyl acetate copolymer. [2] 13 The methyl branch (20.07 ppm) determined by C-NMR is less than 0.16 / 100C. The ethylene-vinyl acetate copolymer according to [1]. [3] The heat of fusion (ΔH) determined by differential scanning calorimetry is 43 J / g or more and 90 J / g or less. The ethylene-vinyl acetate copolymer according to [1] or [2]. [4] The melt flow rate is 0.1 g / 10 min or more and less than 30 g / 10 min. 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]. Sheet. [7] [1] to [4], comprising the ethylene-vinyl acetate copolymer according to any one of [1] to [4]. Foam. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an ethylene-vinyl acetate copolymer that is excellent in falling weight impact strength, environmental stress cracking resistance, mold releasability, and transparency, as well as a molded article, sheet, and foam containing the same. [Brief explanation of the drawings]

[0013] [Figure 1] Schematic diagram for explaining the slope P measured by GPC-FTIR. [Figure 2] Schematic diagram for explaining the average value Q measured by GPC-FTIR. [Figure 3] Schematic diagram for explaining the temperature from the reactor inlet to the outlet. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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.

[0015] [Ethylene-vinyl acetate copolymer] The ethylene-vinyl acetate copolymer of the present embodiment contains 11% by mass or more and 25% by mass or less of vinyl acetate units and ethylene units, and the molecular weight distribution and the absorbance I attributable to methylene groups for each molecular weight are measured by GPC-FTIR. (-CH2-) and the absorbance I attributed to the carbonyl group (-C=O) and the absorbance I attributed to the methyl group (-CH3) and when the molecular weights M i log(M i ) to absorbance ratio (I i(-C=O) / Ii(-CH2-) ) the slope P of the least squares approximation linear relational expression is 0.00≦P≦1.40, and each molecular weight M i The absorbance ratio (I i(-CH3) / I i(-CH2-) ) the average value Q is 23.0≦Q≦30.0.

[0016] As a result of extensive investigations, the present inventors have found that the high molecular weight component of an ethylene-vinyl acetate copolymer contains many vinyl acetate units and the ethylene-vinyl acetate copolymer has a large number of branches, which leads to further improvements in falling weight impact strength, environmental stress cracking resistance, mold releasability, and transparency. The reasons for this are not particularly limited, but are thought to be as follows.

[0017] When the high molecular weight component of an ethylene-vinyl acetate copolymer contains a large amount of vinyl acetate units, the crystallinity tends to decrease due to steric hindrance of the molecular chain, and the proportion of amorphous components in the ethylene-vinyl acetate copolymer increases. It is believed that a higher proportion of amorphous components improves the flexibility of the ethylene-vinyl acetate copolymer, further improving the environmental stress crack resistance of the resulting molded article and further improving transparency.

[0018] Furthermore, when the high molecular weight component of an ethylene-vinyl acetate copolymer contains a large number of vinyl acetate units, the molecular chains tend to become more entangled, improving the melt tension of the ethylene-vinyl acetate copolymer. Improved melt tension is thought to facilitate orientation of the molecular chains during injection molding and the like, further improving the falling weight impact strength of the resulting molded article.

[0019] Furthermore, when the number of branches of the ethylene-vinyl acetate copolymer is large, the molecular chains become more entangled, which is thought to reduce the crystallinity and further improve the mold releasability and transparency of the resulting molded article, etc.

[0020] In this embodiment, it is determined by GPC-FTIR that the high molecular weight component of the ethylene-vinyl acetate copolymer contains a larger amount of vinyl acetate units and that the ethylene-vinyl acetate copolymer has a larger number of branches.

[0021] GPC-FTIR is an instrument equipped with an FTIR device downstream of the column of a GPC instrument, which enables molecular weight measurement by GPC while simultaneously analyzing the composition of each molecular weight sample eluted from the column by IR measurement. This makes it possible to measure changes in the copolymerization ratio of monomers from the high molecular weight side to the low molecular weight side of the GPC chart.

[0022] In GPC-FTIR, the sample composition is generally quantitatively analyzed based on the absorbance intensity ratio. For example, the absorbance I attributed to the methylene group in a certain molecular weight fraction is (-CH2-) and the absorbance I attributed to the carbonyl group (-C=O) Based on the absorbance ratio, it is possible to evaluate whether the fraction contains a large amount of carbonyl groups relative to the methylene group. Furthermore, by comparing the absorbance ratios of multiple fractions with different molecular weights, it is possible to evaluate whether the high-molecular-weight or low-molecular-weight fraction contains a relatively large amount of carbonyl groups or a relatively small amount of carbonyl groups.

[0023] The ethylene-vinyl acetate copolymer of this embodiment will be described in detail below.

[0024] (tilt P) FIG. 1 shows a schematic diagram for explaining the slope P measured by GPC-FTIR. In FIG. 1, the left vertical axis represents the detected intensity of the copolymer in GPC, and the right vertical axis represents the absorbance ratio (I (-C=O) / I (-CH2-) ) and the horizontal axis represents the molecular weight of the copolymer in logarithm.

[0025] The slope P is the slope of each molecular weight M i log(M i ) to absorbance ratio (I i(-C=O) / I i(-CH2-) ) is defined as the slope of the least squares linear fit equation. i(-C=O) / I i(-CH2-) ) is the absorbance I attributed to the methylene group i(-CH2-)and the absorbance I attributed to the carbonyl group i(-C=O) and indicates the carbonyl group content in each molecular weight of ethylene-vinyl acetate copolymer.

[0026] Here, for example, when the slope P is 0 or positive, it means that the proportion of vinyl acetate units in the copolymer of this embodiment tends to be constant or to increase as the molecular weight distribution shifts from low molecular weight components to high molecular weight components. In other words, the slope P can be said to be a parameter that indicates the distribution of vinyl acetate units (carbonyl groups) in the molecular weight distribution.

[0027] As described above, a slope P of 0 or positive means that vinyl acetate is selectively incorporated into the high-molecular-weight component, which is important for the development of mechanical properties in an ethylene-vinyl acetate copolymer. Because the molecular weight of vinyl acetate is higher than that of ethylene, a high content of vinyl acetate units in the high-molecular-weight component tends to reduce crystallinity due to steric hindrance of the molecular chain. Thus, even if the overall content of vinyl acetate units is the same, an ethylene-vinyl acetate copolymer with a slope P of 0 or positive has a higher amorphous component ratio. This results in improved environmental stress crack resistance and transparency of the resulting molded article. Furthermore, an ethylene-vinyl acetate copolymer with a slope P of 0 or positive exhibits stronger molecular chain entanglement, which improves melt tension and molecular chain orientation during injection molding, etc., resulting in improved drop weight impact strength of the resulting molded article.

[0028] Here, the half-width refers to the width of the peak in the molecular weight distribution, which has an intensity half (1 / 2A) of the peak top height A. By defining the slope P in the half-width region, it is possible to express the increasing tendency of vinyl acetate units without being affected by detection errors in the region at the base of the molecular weight distribution peak. This also applies to the average value Q described below.

[0029] The slope P is expressed as the slope of the following least squares approximate linear relational expression. i log(Mi ) and the absorbance ratio (I i(-C=O) / I i(-CH2-) ) with an approximate straight line, it is possible to show the tendency of the vinyl acetate units to increase or decrease in the molecular weight distribution. In the following formula, "a" is a constant. Absorbance ratio (I i(-C=O) / I i(-CH2-) ) = slope P × log(M i )+a

[0030] In this embodiment, the slope P is 0.00≦P≦1.40, preferably 0.05≦P≦1.30, and more preferably 0.10≦P≦1.20. When the slope P is 0.00 or more, the high molecular weight component of the ethylene-vinyl acetate copolymer contains a large amount of vinyl acetate units, which further improves the falling weight impact strength, environmental stress cracking resistance, and transparency of the resulting molded article. Furthermore, when the slope P is 1.40 or less, the mold releasability of the resulting molded article is further improved.

[0031] The method for adjusting the slope P within the above range is not particularly limited. For example, one possible method is to polymerize ethylene-vinyl acetate copolymer in a tube reactor and gradually lower the polymerization peak temperature from upstream to downstream of the tube reactor. Figure 3 shows a schematic diagram illustrating the temperature from the reactor inlet to the outlet. When ethylene and vinyl acetate are introduced into the reactor and then an initiator is introduced, the temperature inside the reactor rises due to the heat of polymerization. This temperature rise is reduced by cooling the reactor. If the highest polymerization temperature at this time is defined as the polymerization peak temperature, the downstream polymerization peak temperature is lower than the upstream polymerization peak temperature. This is thought to be because, at high polymerization temperatures, ethylene polymerization proceeds preferentially over vinyl acetate, and as the polymerization temperature decreases, vinyl acetate polymerization proceeds more easily. Therefore, by gradually lowering the polymerization peak temperature from upstream to downstream of the tube reactor, ethylene polymerization can proceed preferentially upstream, while vinyl acetate polymerization can proceed preferentially downstream, where the molecular weight increases.

[0032] Furthermore, one of the means for achieving the above temperature conditions is to use a reactor with a double-tube structure, and adjust the temperature of ethylene, vinyl acetate, ethylene-vinyl acetate copolymer, etc. flowing through the inner tube by using steam flowing through the outer tube.

[0033] Other methods for adjusting the slope P within the above range include, but are not limited to, reducing the temperature difference caused by introducing raw materials into the front and middle sections of the reactor, and / or making the temperature difference in the rear section greater than the temperature difference in the middle section. Specifically, it is preferable to introduce raw materials such as ethylene and vinyl acetate into the front and middle sections of the reactor. Another method is to preheat the ethylene and vinyl acetate introduced into the front and middle sections of the reactor. The temperature temporarily drops when raw materials such as ethylene and vinyl acetate are introduced midway through the tube reactor, but then rises again due to the heat of polymerization. While the temperature within the reactor varies depending on the location of raw material introduction, in this embodiment, in order to reduce the temperature difference between the front and middle sections of the reactor, preheating the ethylene and vinyl acetate before introduction allows the polymerization of ethylene to proceed preferentially in the front and middle sections. It is also preferable to make the temperature difference in the rear section greater than the temperature difference in the middle section.

[0034] In GPC-FTIR, absorbance I attributed to methylene groups (-CH2-) is 2928cm -1 The absorbance I is measured as the absorption of (-C=O) is 1741cm -1 The specific measurement by GPC-FTIR can be carried out by the method described in the Examples.

[0035] (Average Q) Figure 2 shows a schematic diagram for explaining the average value Q measured by GPC-FTIR. In Figure 2, the left vertical axis shows the detected intensity of the copolymer in GPC, and the right vertical axis shows the absorbance ratio (I (-CH3) / I (-CH2-)) and the horizontal axis represents the molecular weight of the copolymer in logarithm.

[0036] The average value Q is the value of each molecular weight M in the half-width region of the molecular weight distribution. i The absorbance ratio (I i(-CH3) / I i(-CH2-) The absorbance ratio (I i(-CH3) / I i(-CH2-) ) is the absorbance I attributed to the methylene group i(-CH2-) and the absorbance I attributed to the methyl group i(-CH3) It is the ratio of the absorbance ratio (I) to the methyl group content of each molecular weight of ethylene-vinyl acetate copolymer. Since the terminals of ethylene-vinyl acetate copolymers are highly terminated with methyl groups, a high methyl group content means a large number of branches. Therefore, the absorbance ratio (I i(-CH3) / I i(-CH2-) ) is high means that the copolymer of this embodiment has a large number of branches.

[0037] The absorbance ratio (I i(-CH3) / I i(-CH2-) ) indicates the amount of carbon atoms in "-CH3" per 1000 carbon atoms in "-CH2-". Also, the average value Q means the average value of carbon atoms in "-CH3" per 1000 carbon atoms in "-CH2-" in the half width region of the molecular weight distribution.

[0038] In this embodiment, the average value Q is 23.0≦Q≦30.0, preferably 23.5≦Q≦28.0, and more preferably 24.0≦Q≦26.0. When the average value Q is 23.0 or more, the ethylene-vinyl acetate copolymer exhibits increased entanglement of molecular chains, resulting in a decrease in crystallinity and improved transparency. Furthermore, when the average value Q is 30.0 or less, the releasability is further improved.

[0039] The method for adjusting the average Q value to the above range is not particularly limited, and can be controlled by the amounts of chain transfer agent, vinyl acetate, initiator, etc. For example, the amount of propylene used as a chain transfer agent can be set to 0.30 mol % or less, preferably 0.28 mol % or less, and more preferably 0.25 mol % or less.

[0040] If more than 0.3 mol% of propylene is added, hydrogen abstraction from the molecular chains in the ethylene vinyl acetate resin increases, generating free radicals, which then bond with each other and cause a termination reaction, which tends to reduce the number of branches.

[0041] It is also preferable to feed raw materials such as ethylene and vinyl acetate into the reactor from the front and middle stages. By feeding raw materials such as ethylene and vinyl acetate from the reactor inlet, polymerization progresses, and a polymer layer and a gas layer are mixed inside the reactor. By newly feeding raw materials such as ethylene and vinyl acetate into this stage, the polymer layer and the gas layer are agitated, which promotes polymerization and makes it possible to appropriately adjust the number of branches.

[0042] When raw materials such as ethylene and vinyl acetate are introduced only from the reactor inlet, the amount of polymer obtained is small, which is not preferable from the viewpoint of productivity.

[0043] In GPC-FTIR, absorbance I attributed to methylene groups (-CH2-) is 2928cm -1 The absorbance I is measured as the absorption of (-CH3) is 2960cm -1 The specific measurement by GPC-FTIR can be carried out by the method described in the Examples.

[0044] (Methyl branched) The ethylene-vinyl acetate copolymer of this embodiment, 13The methyl branching determined by C-NMR is preferably 0.00 / 100C or more and less than 0.16 / 100C, more preferably 0.00 / 100C or more and 0.13 / 100C or less, and even more preferably 0.00 / 100C or more and 0.10 / 100C or less. When the methyl branching is less than 0.16 / 100C, the resulting molded article or the like tends to have further improved falling weight impact strength, environmental stress cracking resistance, mold releasability, and transparency.

[0045] The methyl branching can be adjusted by the type and amount of the chain transfer agent. The methyl branching can be measured according to the method described in the Examples.

[0046] (heat of fusion) The ethylene-vinyl acetate copolymer of this embodiment has a heat of fusion (ΔH) determined by differential scanning calorimetry of preferably 43 to 90 J / g, more preferably 50 to 88 J / g, and even more preferably 61 to 83 J / g. When the heat of fusion is within the above range, the resulting molded article or the like has an excellent balance of falling weight impact strength, environmental stress cracking resistance, mold releasability, and transparency.

[0047] The heat of fusion can be adjusted by the vinyl acetate concentration, molecular weight distribution, etc. The heat of fusion can be measured according to the method described in the Examples.

[0048] (Melt Flow Rate) The melt flow rate of the ethylene-vinyl acetate copolymer of this embodiment is preferably 0.1 g / 10 min or more and less than 30 g / 10 min, more preferably 0.6 g / 10 min or more and 10 g / 10 min or less, and even more preferably 0.8 g / 10 min or more and 4.0 g / 10 min or less. When the melt flow rate is within the above range, the resulting molded article and the like tend to have improved falling weight impact strength and environmental stress crack resistance.

[0049] The method for adjusting the melt flow rate of the ethylene-vinyl acetate copolymer is not particularly limited, and examples thereof include a method of adjusting the reaction temperature and / or reaction pressure 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, and increasing the reaction pressure tends to decrease the melt flow rate of the ethylene-vinyl acetate copolymer.

[0050] The melt flow rate can be measured in accordance with JIS K7210:1999 Code D (temperature = 190°C, load = 2.16 kg).

[0051] (vinyl acetate units) The content of vinyl acetate units is 11% by mass or more and 25% by mass or less, preferably 12% by mass or more and 23% by mass or less, and more preferably 13% by mass or more and 20% 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 falling weight impact strength, environmental stress cracking resistance, mold releasability, and transparency.

[0052] 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.

[0053] 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.

[0054] (ethylene units) The content of ethylene units is preferably 75% by mass or more and 89% by mass or less, more preferably 77% by mass or more and 88% by mass or less, and even more preferably 80% by mass or more and 87% 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 has an excellent balance of falling weight impact strength, environmental stress cracking resistance, mold releasability, and transparency.

[0055] The ethylene-vinyl acetate copolymer of this embodiment may contain a monomer unit other than an ethylene unit or a vinyl acetate unit. The other monomer unit is not particularly limited, but examples thereof include units derived from propylene, etc. From the viewpoints of drop weight impact strength, environmental stress crack resistance, and transparency, the amount of the monomer unit other than the ethylene unit or the vinyl acetate unit is preferably 0.3 mol % or less relative to the ethylene.

[0056] 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.

[0057] [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.

[0058] The polymerization method for the ethylene-vinyl acetate copolymer is not particularly limited, and 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, the polymerization temperature and polymerization pressure can be appropriately adjusted in each region from upstream to downstream.

[0059] The average polymerization temperature is preferably 150° C. or higher and 280° C. or lower, more preferably 180° C. or higher and 240° C. or lower. The average polymerization pressure is preferably 100 MPa or higher and 275 MPa or lower, more preferably 120 MPa or higher and 270 MPa or lower, and even more preferably 180 MPa or higher and 265 MPa or lower.

[0060] The reactor may have multiple points for feeding ethylene, vinyl acetate, and a polymerization initiator. The temperature drops temporarily near each feed point when raw materials are introduced, but then the temperature inside the reactor rises again due to the heat of polymerization. In this embodiment, the raw materials introduced from the front and middle stages are pressurized before being introduced into the tube reactor. Therefore, although the temperature rises to some extent due to the pressurization, it is preferable to preheat the raw materials to be introduced. This prevents the temperature at the upstream side from dropping due to the introduction of relatively high-temperature raw materials. Therefore, from the viewpoint of controlling the gradient P, the polymerization temperature can be gradually lowered from the upstream to the downstream side of the polymerization.

[0061] In this embodiment, the front stage of the reactor refers to a position (inlet) that is 0% to 10% of the total length of the reactor, the middle stage of the reactor refers to a position from the inlet that is 10% to 40% of the total length of the reactor, and the rear stage of the reactor refers to a position from the inlet that is 40% to 70% of the total length of the reactor.

[0062] The ethylene and vinyl acetate supplied to the reactor may be in the form of gas or liquid, and are preferably in the form of gas.

[0063] 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.

[0064] 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.

[0065] The ethylene-vinyl acetate copolymer polymerized as described above is preferably separated from the raw materials and granulated into pellets in an extruder. For example, when a tubular system is used, it is preferable to separate the ethylene-vinyl acetate copolymer from the raw materials and the like while reducing the pressure in a high-pressure separator and a low-pressure separator, and then granulate the molten ethylene-vinyl acetate copolymer into pellets in an extruder.

[0066] In the high-pressure separator and the low-pressure separator, the molten ethylene-vinyl acetate copolymer and unreacted gases such as raw material ethylene gas and vinyl acetate gas exist as a gas-liquid mixture. The unreacted gases may be recovered from the top of the vessels of each separator and reused for polymerization.

[0067] After the ethylene-vinyl acetate copolymer is pelletized in an extruder, it is preferable to dry the pellets in a silo.

[0068] 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.

[0069] 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.

[0070] [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, artificial turf mats, automobile mat guards, mudguard covers, drainage hoses, and the like. It can also be used as fibers, etc.

[0071] 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. T-die molding and inflation molding are particularly preferred.

[0072] 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 more preferably 0.5 to 10 mm.

[0073] The sheet of this embodiment may have a laminated structure having other layers in addition to the layer made of the ethylene-vinyl acetate copolymer. The method for producing such a laminated sheet is not particularly limited, but examples thereof include a method of producing the laminated sheet by laminating layers together using a lamination process or a method of producing the laminated sheet by a lamination extrusion process.

[0074] [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, foamed microparticles, and is suitable for various applications such as impact-absorbing flooring materials. [Example]

[0075] 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.

[0076] [GPC-IR measurement (carbonyl group gradient P)] GPC-IR measurements (carbonyl group gradient P) were performed under the following conditions. For sample pretreatment, the sample was weighed, a solvent (TCE with 0.05% BHT added) was added, and the sample was dissolved by shaking at 110°C for 1 hour. Molecular weight calibration was performed using a cubic approximation curve using standard polystyrene from Tosoh. The molecular weight was converted to polyethylene molecular weight using a factor.

[0077] 2850-2940 cm using SEC-FTIR software (Thermo Nicolet). -1 The average molecular weight was calculated from the elution curve based on the absorbance peak area of ​​1741 cm using EVA with a known composition. -1 C=O stretching vibration at 2928cm -1 A calibration curve was created from the absorbance ratio of the CH2 stretching vibration and the value was calculated.

[0078] The carbonyl group slope P was measured by GPC (apparatus: Tosoh HLC-8121GPC / HT) using a Thermo Nicolet Avatar 370 detector, and the vinyl acetate ratio (VAc ratio) in each molecular weight region was plotted and calculated using a square law approximation line. For the GPC-IR elution curve, the component amount (d(W) / d(logM)) at the peak top of the GPC measurement was set to A, and the value of 1 / 2 of the component amount (d(W) / d(logM)) was calculated as 1 / 2A, which was the VAc ratio in the molecular weight range of 1 / 2A. (Measurement conditions) GPC equipment: HLC-8121GPC / HT (Tosoh) FT-IR device: Avatar370 (manufactured by Thermo Nicolet) Column: TSKgel GMH HR -H(20)HT(7.8mmID×30cm)×2 (Tosoh) Eluent: Tetrachloroethylene (Fujifilm Wako Pure Chemical Industries, Ltd., special grade) Flow rate: 0.7mL / min Sample concentration: 2.0 mg / mL Injection volume: 0.3mL Column temperature: 110℃ Detector temperature: 110℃ Measurement wave number: 4000~650cm -1 Resolution: 4cm -1 Number of scans: 8 times / 1 point

[0079] Based on the obtained IR data, the absorbance ratio (I i(-C=O) / I i(-CH2-) ) is calculated, and each molecular weight M i log(M i ) and the absorbance ratio (I i(-C=O) / I i(-CH2-) ) was expressed by an approximate linear equation using the least squares method (see Figure 1). The slope P was obtained from the approximate linear equation thus obtained.

[0080] The absorbance I attributed to the methylene group(-CH2-) is 2928cm -1 The absorbance I attributed to the carbonyl group is measured as the absorption of (-C=O) is 1741cm -1 The absorbance was measured as

[0081] [GPC-IR measurement (average value of terminal methyl groups Q)] GPC-IR measurements (average Q of terminal methyl groups) were performed under the following conditions. Sample pretreatment consisted of weighing the sample, adding the solvent orthodichlorobenzene, and dissolving it by shaking at 140°C for 90 minutes. Molecular weight calibration was performed using 12 standard polystyrene MWs (Molecular Weights) from Tosoh Corporation 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.

[0082] The amount of terminal methyl groups was measured using Polymer Char's Composition Calibration Kit (Octene) CH3 / 1000C at six points in the range of 2.6 to 45.9 to create a calibration curve, and then measured by GPC (apparatus: Polymer Char's GPC-IR) using FT-IR (Polymer Char's IR5) as the detector.

[0083] The amount of terminal methyl groups was determined by determining 1 / 2A as the value of the component amount (d(W) / d(logM)) at half the peak top value of the component amount (d(W) / d(logM)) measured by GPC, where A is the value of the component amount at half the peak top value, and calculating Q as the average amount of CH3 per 1000C within the molecular weight range of 1 / 2A. (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

[0084] Based on the obtained IR data, the absorbance ratio (I i(-CH3) / I i(-CH2-) ) is calculated, and the absorbance ratio (I i(-CH3) / I i(-CH2-) ) was averaged to obtain the mean value Q.

[0085] The absorbance I attributed to the methylene group (-CH2-) is 2928cm -1 The absorbance I attributed to the methyl group is measured as the absorption of (-CH3) is 2960cm -1 The absorbance was measured as

[0086] [Measurement of vinyl acetate unit content] In accordance with JIS K7192:1999, a calibration curve was prepared using a VAc standard sample of an ethylene-vinyl acetate copolymer with a known content of vinyl acetate units by saponification and potentiometric titration as the standard test method, and the vinyl acetate unit content (VA content) of the ethylene-vinyl acetate copolymer obtained in the examples and comparative examples was measured by infrared spectroscopy as the control test method.

[0087] [Melt flow rate (MFR) measurement] The melt flow rates of the ethylene-vinyl acetate copolymers obtained in the examples and comparative examples were measured in accordance with JIS K7210:1999 Code D (temperature = 190°C, load = 2.16 kg).

[0088] [ 13 C-NMR measurement (methyl branch) 13C-NMR measurements (methyl branching) were carried out under the following conditions: As sample pretreatment, the sample was weighed, and the solvent orthodichlorobenzene was added and the sample was dissolved by shaking at 140°C for 180 minutes. Methyl branching was measured using a Bruker AVANCE500HD nuclear magnetic resonance spectrometer, with the methylene carbon signal at 29.9 ppm as the reference.

[0089] The ratio of methyl branches was measured as above. 13 The ratio was calculated from the ratio of the area intensity of the methylene carbon signal (29.9 ppm) and the methyl branch (20.07 ppm) observed in the C-NMR spectrum. 13 The intensity of the signal around 20.07 ppm in the C-NMR spectrum (Assignment of branched species in low-density polyethylene by C-13 NMR, Analytical Chemistry, Nishimura Atsuo et al., p. 774(29)1980) was calculated as a ratio with the intensity of the methylene signal taken as 100. (Measurement conditions) Measurement device: Bruker AVANCE-500HD Observation kernel: 13 C Observation frequency: 125.77MHz Pulse width: 5.0 μsec PD: 5 seconds Measurement temperature: 120℃ Accumulation count: 8,000 times Reference: PE (-eee-) signal is 29.9 ppm Solvent: orthodichlorobenzene-d4 Sample concentration: 5 wt / vol% Melting temperature: 140℃

[0090] [Differential scanning calorimetry (heat of fusion)] The heat of fusion ΔH was measured using a DSC (manufactured by PerkinElmer, product name: DSC8000). Specifically, 8 mg of the ethylene-vinyl acetate copolymer obtained in the examples and comparative examples was weighed out as a sample and placed in an aluminum sample pan. An aluminum cover was attached to this aluminum sample pan and placed in a differential scanning calorimeter. While purging with nitrogen at a flow rate of 20 mL / min, the measurement sample and reference sample were held at 0°C for 1 minute, then heated to 150°C at a rate of 200°C / min, held at 150°C for 5 minutes, cooled at a rate of 10°C / min, held at 0°C for 5 minutes, and then heated from 0°C to 150°C. The total heat calculated from the melting peak area was divided by the mass of the sample to determine the heat of fusion (ΔH).

[0091] [Falling weight impact strength] Using the ethylene-vinyl acetate copolymers obtained in the Examples and Comparative Examples, 100 × 100 × 2.0 mm flat test pieces were produced using a Sumitomo all-electric injection molding machine 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. The obtained flat test pieces were subjected to a drop weight impact test using a graphic impact tester (manufactured by Toyo Seiki Co., Ltd.) under the following conditions, and the total absorbed energy was measured. (conditions) Holder diameter: 76mm Striker diameter: 12.7mm Striker weight: 6.5kg Height: 100cm Temperature: 23℃

[0092] [Environmental Stress Crack Resistance (ESCR)] To evaluate environmental stress cracking resistance, the ethylene-vinyl acetate copolymers obtained in the examples and comparative examples were subjected to b-ESCR (constant strain environmental stress cracking test) measurement in accordance with ASTM D 1693. A 10% by mass aqueous solution of IGEPAL (registered trademark) CO-630 manufactured by Rhodia Nikka Co., Ltd. was used as the test solution, and the time required for the probability of cracking due to environmental stress to reach 50% (hereinafter referred to as F50 value) was measured and used as the environmental stress cracking resistance (ESCR) value of the ethylene-vinyl acetate copolymer. The unit is hr (hours). The higher this value, the better the environmental stress cracking resistance.

[0093] [Transparency measurement (Haze)] 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.) was placed on top of the aluminum plate. A mold measuring 200 mm in length, 200 mm in width, and 3.1 mm in thickness was placed on top of this, and 130 g of the ethylene-vinyl acetate copolymer obtained in the Examples and Comparative Examples was placed into this mold. Then, the same polyethylene terephthalate film as above, the same aluminum plate as above, and the same iron plate as above were further placed on top of that.

[0094] This was placed in a compression molding machine (SFA-37 manufactured by Shinto Metal Industry Co., Ltd.) whose temperature was adjusted to 180°C, and after preheating at 180°C and 0.1 MPa for 180 seconds, air was removed for 5 seconds (10 MPa), and compression was performed at 180°C and 15 MPa for 120 seconds.

[0095] 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.) 5 seconds after removal, which was then placed at 25°C and 10 MPa for 300 seconds while being cooled 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 23°C and 50% humidity.

[0096] The thickness of the press sheet obtained as described above was measured using a constant pressure thickness gauge (manufactured by TECLOCK CORPORATION, model PG-02, minimum display 0.001 mm), and a portion of the press sheet with a thickness of 3.1 mm was selected. The haze value of the 3.1 mm thick portion was then measured in accordance with ASTM D1003 using a haze meter HM-150 manufactured by Murakami Color Research Laboratory Co., Ltd. The smaller the haze value, the better the transparency.

[0097] [Mold releasability] Using the ethylene-vinyl acetate copolymers obtained in the examples and comparative examples, pin-gate flat test pieces measuring 200 × 200 × 4.0 mm were prepared using a Sumitomo all-electric injection molding machine SE130DUZ-C360 (cylinder temperature set to 200°C, mold temperature set to 40°C) with an injection time of 20 seconds and a cooling time of 30 seconds. The mold releasability was evaluated according to the following criteria when the ejector was set to four (electric), ejector ejection force was 10 KN, ejector speed was 10 mm / s, and the number of ejections was 1. Good: 10 plates molded and 0 plates did not peel off from the mold △: Out of 10 molded plates, the number of plates that do not peel off from the mold is 1 to 5 ×: 5 or more plates do not peel off from the mold out of 10 molded plates ◯ and △ were considered to be passing.

[0098] Example 1 Polymerization was carried out using a tubular reactor with multiple feed ports. Specifically, ethylene and vinyl acetate were preheated to 160°C through the feed port on the front side of the tubular reactor and then introduced into the reactor. Subsequently, t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator to initiate polymerization. Subsequently, ethylene and vinyl acetate preheated to 160°C were additionally introduced through the feed port on the middle side of the tubular reactor, and subsequently, t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator from the middle and rear sides. The overall amount of vinyl acetate was 7 mol% relative to ethylene.

[0099] The average polymerization temperature in the tubular reactor was 221°C, and the polymerization pressure was 236 MPa. The polymerization temperature in the tubular reactor was adjusted so that the first peak top temperature was 250°C, the middle peak top temperature was 246°C, the latter peak top temperature was 230°C, and the reactor outlet temperature was 171°C. The difference between the bottom temperature and the peak top temperature before and after the introduction of ethylene, vinyl acetate, and the polymerization initiator at the feed port on the middle stage was 10°C, and the difference between the bottom temperature and the peak top temperature before and after the introduction of the polymerization initiator at the feed port on the latter stage was 66°C.

[0100] The ethylene-vinyl acetate copolymer discharged from the tubular reactor was introduced into a high-pressure separator to separate unreacted gases, etc. Subsequently, the ethylene-vinyl acetate copolymer discharged from the high-pressure separator was introduced into a low-pressure separator to separate remaining unreacted gases, etc., to obtain a molten ethylene-vinyl acetate copolymer.

[0101] The resulting molten ethylene-vinyl acetate copolymer was fed into an extruder and pelletized to obtain ethylene-vinyl acetate copolymer pellets. The physical properties and characteristics of the resulting ethylene-vinyl acetate copolymer were measured by the methods described above. The measurement results are shown in Table 1.

[0102] Example 2 Ethylene, vinyl acetate, and propylene were preheated to 160°C through the feed ports on the front and middle stages of the tubular reactor and then introduced into the reactor, and the overall amount of propylene was 0.11 mol% relative to the ethylene. An ethylene-vinyl acetate copolymer of Example 2 was obtained in the same manner as in Example 1, except that the amount of propylene was 0.11 mol% relative to the ethylene.

[0103] Example 3 Ethylene, vinyl acetate, and propylene were preheated to 160°C through the feed ports on the front and middle stages of the tubular reactor and then introduced into the reactor, and the overall amount of propylene was 0.17 mol% relative to ethylene. An ethylene-vinyl acetate copolymer of Example 3 was obtained in the same manner as in Example 1, except that the amount of propylene was 0.17 mol% relative to ethylene.

[0104] Example 4 Ethylene and vinyl acetate were preheated to 160°C through a feed port on the front side of the tubular reactor and then introduced into the reactor. Subsequently, t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator to initiate polymerization. Subsequently, ethylene and vinyl acetate preheated to 160°C were additionally introduced through a feed port on the middle side of the tubular reactor, followed by the introduction of t-butyl-peroxy-2-ethylhexanoate as a polymerization initiator from the middle and rear sides. The overall amount of vinyl acetate relative to ethylene was 7 mol%.

[0105] The average polymerization temperature in the tubular reactor was 222°C, and the polymerization pressure was 264 MPa. The polymerization temperature in the tubular reactor was adjusted so that the first peak top temperature was 255°C, the middle peak top temperature was 237°C, the latter peak top temperature was 230°C, and the reactor outlet temperature was 175°C. The ethylene-vinyl acetate copolymer of Example 4 was obtained in the same manner as in Example 1, except that the difference between the bottom temperature and the peak top temperature before and after introducing ethylene, vinyl acetate, and the polymerization initiator at the middle feed port was 20°C, and the difference between the bottom temperature and the peak top temperature before and after introducing the polymerization initiator at the latter feed port was 69°C.

[0106] Example 5 Ethylene and vinyl acetate were preheated to 160°C through a feed port on the front side of the tubular reactor and then introduced into the reactor. Subsequently, t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator to initiate polymerization. Subsequently, ethylene and vinyl acetate preheated to 160°C were additionally introduced through a feed port on the middle side of the tubular reactor. Subsequently, t-butyl-peroxy-2-ethylhexanoate and di-t-butyl peroxide were introduced as polymerization initiators from the middle side. The overall amount of vinyl acetate was 7 mol% relative to ethylene.

[0107] The average polymerization temperature in the tubular reactor was 240°C, and the polymerization pressure was 264 MPa. The polymerization temperature in the tubular reactor was adjusted so that the first peak top temperature was 275°C, the middle peak top temperature was 268°C, the latter peak top temperature was 255°C, and the reactor outlet temperature was 189°C. The ethylene-vinyl acetate copolymer of Example 5 was obtained in the same manner as in Example 1, except that the difference between the bottom temperature and the peak top temperature before and after introducing ethylene, vinyl acetate, and the polymerization initiator at the middle feed port was 27°C, and the difference between the bottom temperature and the peak top temperature before and after introducing the polymerization initiator at the latter feed port was 64°C.

[0108] Example 6 Ethylene and vinyl acetate were preheated to 160°C through a feed port on the front side of the tubular reactor and then introduced into the reactor. Subsequently, t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator to initiate polymerization. Subsequently, ethylene and vinyl acetate preheated to 160°C were additionally introduced through a feed port on the middle side of the tubular reactor, and then t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator from the middle side. The overall amount of vinyl acetate relative to ethylene was 8.1 mol%.

[0109] The average polymerization temperature in the tubular reactor was 195°C, and the polymerization pressure was 264 MPa. The polymerization temperature in the tubular reactor was adjusted so that the first peak top temperature was 238°C, the middle peak top temperature was 220°C, and the reactor outlet temperature was 150°C. The ethylene-vinyl acetate copolymer of Example 6 was obtained in the same manner as in Example 1, except that the difference between the bottom temperature and the peak top temperature before and after introducing ethylene, vinyl acetate, and a polymerization initiator into the feed port on the middle stage was 7°C.

[0110] Example 7 Ethylene and vinyl acetate were preheated to 160°C through a feed port on the front side of the tubular reactor and then introduced into the reactor. Subsequently, t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator to initiate polymerization. Subsequently, ethylene and vinyl acetate preheated to 160°C were additionally introduced through a feed port on the middle side of the tubular reactor, and then t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator from the middle side. The overall amount of vinyl acetate relative to ethylene was 8.7 mol%.

[0111] The average polymerization temperature in the tubular reactor was 196°C, and the polymerization pressure was 264 MPa. The reactor was adjusted so that the first peak top temperature was 238°C, the middle peak top temperature was 220°C, and the reactor outlet temperature was 155°C. The ethylene-vinyl acetate copolymer of Example 7 was obtained in the same manner as in Example 1, except that the difference between the bottom temperature and the peak top temperature before and after the introduction of ethylene, vinyl acetate, and a polymerization initiator into the feed port on the middle stage was 7°C.

[0112] Example 8 Ethylene and vinyl acetate were preheated to 160°C through a feed port on the front side of the tubular reactor and then introduced into the reactor. Subsequently, t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator to initiate polymerization. Subsequently, ethylene and vinyl acetate preheated to 160°C were additionally introduced through a feed port on the middle side of the tubular reactor. Subsequently, t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator from the middle and rear sides. The overall amount of vinyl acetate relative to ethylene was 5.8 mol%.

[0113] The average polymerization temperature in the tubular reactor was 212°C, and the polymerization pressure was 236 MPa. The polymerization temperature in the tubular reactor was adjusted so that the first peak top temperature was 245°C, the middle peak top temperature was 227°C, the latter peak top temperature was 218°C, and the reactor outlet temperature was 155°C. The ethylene-vinyl acetate copolymer of Example 8 was obtained in the same manner as in Example 1, except that the difference between the bottom temperature and the peak top temperature before and after introducing ethylene, vinyl acetate, and the polymerization initiator at the middle feed port was 19°C, and the difference between the bottom temperature and the peak top temperature before and after introducing the polymerization initiator at the latter feed port was 50°C.

[0114] Example 9 Ethylene, vinyl acetate, and propylene were preheated to 160°C through a feed port on the front side of the tubular reactor and then introduced into the reactor. Subsequently, t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator to initiate polymerization. Subsequently, ethylene and vinyl acetate preheated to 160°C were additionally introduced through a feed port on the middle side of the tubular reactor, followed by the introduction of t-butyl-peroxy-2-ethylhexanoate as a polymerization initiator from the middle and rear sides. The overall amount of vinyl acetate relative to ethylene was 7 mol%, and the amount of propylene relative to ethylene was 0.27 mol%.

[0115] The average polymerization temperature in the tubular reactor was 221°C, and the polymerization pressure was 236 MPa. The polymerization temperature in the tubular reactor was adjusted so that the first peak top temperature was 252°C, the middle peak top temperature was 247°C, the latter peak top temperature was 229°C, and the reactor outlet temperature was 170°C. The ethylene-vinyl acetate copolymer of Example 9 was obtained in the same manner as in Example 1, except that the difference between the bottom temperature and the peak top temperature before and after introducing ethylene, vinyl acetate, and the polymerization initiator at the middle feed port was 26°C, and the difference between the bottom temperature and the peak top temperature before and after introducing the polymerization initiator at the latter feed port was 65°C.

[0116] Example 10 Ethylene and vinyl acetate were preheated to 160°C through a feed port on the front side of the tubular reactor and then introduced into the reactor. Subsequently, t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator to initiate polymerization. Subsequently, ethylene and vinyl acetate preheated to 160°C were additionally introduced through a feed port on the middle side of the tubular reactor, and then t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator from the middle side. The overall amount of vinyl acetate relative to ethylene was 7.0 mol%.

[0117] The average polymerization temperature in the tubular reactor was 224°C, and the polymerization pressure was 236 MPa. The polymerization temperature in the tubular reactor was adjusted so that the first peak top temperature was 252°C, the middle peak top temperature was 221°C, and the reactor outlet temperature was 173°C. The ethylene-vinyl acetate copolymer of Example 10 was obtained in the same manner as in Example 1, except that the difference between the bottom temperature and the peak top temperature before and after introducing ethylene, vinyl acetate, and the polymerization initiator into the feed port on the middle stage was 25°C.

[0118] Comparative Example 1 Ethylene and vinyl acetate were introduced into the feed port on the front side of the tubular reactor, followed by the introduction of t-butyl-peroxy-2-ethylhexanoate as a polymerization initiator to initiate polymerization. Subsequently, additional ethylene and vinyl acetate were introduced into the feed port on the middle side of the tubular reactor, followed by the introduction of t-butyl-peroxy-2-ethylhexanoate and di-t-butyl peroxide as polymerization initiators from the middle and rear sides. The overall amount of vinyl acetate relative to ethylene was 7 mol%.

[0119] The average polymerization temperature in the tubular reactor was 235°C, and the polymerization pressure was 264 MPa. The polymerization temperatures in the tubular reactor were adjusted so that the peak top temperature in the front stage was 243°C, the peak top temperature in the middle stage was 255°C, and the peak top temperature in the rear stage was 275°C, and the reactor outlet temperature was 191°C. The ethylene-vinyl acetate copolymer of Comparative Example 1 was obtained in the same manner as in Example 1, except that the difference between the bottom temperature and the peak top temperature before and after introducing ethylene, vinyl acetate, and the polymerization initiator at the feed port on the middle stage was 64°C, and the difference between the bottom temperature and the peak top temperature before and after introducing the polymerization initiator at the feed port on the rear stage was 44°C.

[0120] Comparative Example 2 An ethylene-vinyl acetate copolymer of Comparative Example 2 was obtained in the same manner as in Example 1, except that ethylene, vinyl acetate, and propylene were preheated to 160°C and then introduced into the reactor through a feed port on the upstream side of the tubular reactor, and the overall amount of propylene was 0.34 mol% relative to ethylene.

[0121] Comparative Example 3 Ethylene, vinyl acetate, and propylene were introduced into the feed port on the front side of the tubular reactor, followed by the introduction of t-butyl peroxy-2-ethylhexanoate as a polymerization initiator to initiate polymerization. Subsequently, additional ethylene and vinyl acetate were introduced into the feed port on the middle side of the tubular reactor, followed by the introduction of t-butyl peroxy-2-ethylhexanoate and di-t-butyl peroxide as polymerization initiators from the middle and rear sides. The overall amount of vinyl acetate relative to ethylene was 2 mol %, and the amount of propylene relative to ethylene was 0.5 mol %.

[0122] The average polymerization temperature in the tubular reactor was 237°C, and the polymerization pressure was 264 MPa. The polymerization temperatures in the tubular reactor were adjusted so that the peak top temperature in the front stage was 260°C, the peak top temperature in the middle stage was 265°C, and the peak top temperature in the rear stage was 275°C, with the reactor outlet temperature being 198°C. The ethylene-vinyl acetate copolymer of Comparative Example 3 was obtained in the same manner as in Example 1, except that the difference between the bottom temperature and the peak top temperature before and after introducing ethylene, vinyl acetate, and the polymerization initiator into the feed port on the middle stage was 67°C, and the difference between the bottom temperature and the peak top temperature before and after introducing the polymerization initiator into the feed port on the rear stage was 44°C.

[0123] Comparative Example 4 Ethylene, vinyl acetate, and propylene were introduced into the feed port on the front side of the tubular reactor, followed by the introduction of t-butyl peroxy-2-ethylhexanoate as a polymerization initiator to initiate polymerization. Subsequently, additional ethylene and vinyl acetate were introduced into the feed port on the middle side of the tubular reactor, followed by the introduction of t-butyl peroxy-2-ethylhexanoate and di-t-butyl peroxide as polymerization initiators from the middle and rear sides. The overall amount of vinyl acetate relative to ethylene was 4 mol%, and the amount of propylene relative to ethylene was 0.5 mol%.

[0124] The average polymerization temperature in the tubular reactor was 229°C, and the polymerization pressure was 264 MPa. The polymerization temperatures in the tubular reactor were adjusted so that the peak top temperature in the front stage was 250°C, the peak top temperature in the middle stage was 260°C, and the peak top temperature in the rear stage was 275°C, and the reactor outlet temperature was 197°C. The ethylene-vinyl acetate copolymer of Comparative Example 4 was obtained in the same manner as in Example 1, except that the difference between the bottom temperature and the peak top temperature before and after introducing ethylene, vinyl acetate, and the polymerization initiator into the feed port on the middle stage was 63°C, and the difference between the bottom temperature and the peak top temperature before and after introducing the polymerization initiator into the feed port on the rear stage was 40°C.

[0125] Comparative Example 5 Ethylene, vinyl acetate, and propylene were introduced into the feed port on the front side of the tubular reactor, followed by the introduction of t-butyl peroxy-2-ethylhexanoate as a polymerization initiator to initiate polymerization. Subsequently, additional ethylene and vinyl acetate were introduced into the feed port on the middle side of the tubular reactor, followed by the introduction of t-butyl peroxy-2-ethylhexanoate and di-t-butyl peroxide as polymerization initiators from the middle and rear sides. The overall amount of vinyl acetate relative to ethylene was 4 mol%, and the amount of propylene relative to ethylene was 0.8 mol%.

[0126] The average polymerization temperature in the tubular reactor was 229°C, and the polymerization pressure was 264 MPa. The polymerization temperatures in the tubular reactor were adjusted so that the peak top temperature in the front stage was 250°C, the peak top temperature in the middle stage was 260°C, and the peak top temperature in the rear stage was 275°C, and the reactor outlet temperature was 205°C. The ethylene-vinyl acetate copolymer of Comparative Example 5 was obtained in the same manner as in Comparative Example 4, except that the difference between the bottom temperature and the peak top temperature before and after introducing ethylene, vinyl acetate, and the polymerization initiator at the feed port on the middle stage was 55°C, and the difference between the bottom temperature and the peak top temperature before and after introducing the polymerization initiator at the feed port on the rear stage was 49°C.

[0127] Comparative Example 6 Ethylene, vinyl acetate, and propylene were introduced into the feed port on the front side of the tubular reactor, followed by the introduction of t-butyl-peroxy-2-ethylhexanoate as a polymerization initiator to initiate polymerization. Subsequently, additional ethylene and vinyl acetate were introduced into the feed port on the middle side of the tubular reactor, followed by the introduction of t-butyl-peroxy-2-ethylhexanoate as a polymerization initiator from the middle side. The overall amount of vinyl acetate relative to ethylene was 14 mol%.

[0128] The average polymerization temperature in the tubular reactor was 200°C, and the polymerization pressure was 265 MPa. The polymerization temperature in the tubular reactor was adjusted so that the peak top temperature in the front stage was 210°C, the peak top temperature in the middle stage was 223°C, and the temperature at the reactor outlet was 171°C. The ethylene-vinyl acetate copolymer of Comparative Example 6 was obtained in the same manner as in Comparative Example 4, except that the difference between the bottom temperature and the peak top temperature before and after the introduction of ethylene, vinyl acetate, and a polymerization initiator into the feed port on the middle stage was 48°C.

[0129] Comparative Example 7 Ethylene, vinyl acetate, and propylene were introduced into the feed port on the front side of the tubular reactor, followed by the introduction of t-butyl-peroxy-2-ethylhexanoate as a polymerization initiator to initiate polymerization. Subsequently, additional ethylene and vinyl acetate were introduced into the feed port on the middle side of the tubular reactor, followed by the introduction of t-butyl-peroxy-2-ethylhexanoate as a polymerization initiator from the middle side. The overall amount of vinyl acetate relative to ethylene was 12.5 mol%.

[0130] The average polymerization temperature in the tubular reactor was 210°C, and the polymerization pressure was 265 MPa. The polymerization temperature in the tubular reactor was adjusted so that the peak top temperature in the front stage was 220°C, the peak top temperature in the middle stage was 230°C, and the temperature at the reactor outlet was 180°C. The ethylene-vinyl acetate copolymer of Comparative Example 7 was obtained in the same manner as in Comparative Example 4, except that the difference between the bottom temperature and the peak top temperature before and after the introduction of ethylene, vinyl acetate, and a polymerization initiator into the feed port on the middle stage was 59°C.

[0131] Comparative Example 8 Ethylene and vinyl acetate were introduced into the tubular reactor through a feed port at the upstream side, followed by the introduction of t-butyl-peroxy-2-ethylhexanoate as a polymerization initiator to initiate polymerization. The overall amount of vinyl acetate relative to ethylene was 7.0 mol%.

[0132] The average polymerization temperature in the tubular reactor was 228°C, and the polymerization pressure was 236 MPa. The polymerization temperature in the tubular reactor was adjusted so that the first peak top temperature was 255°C and the reactor outlet temperature was 175°C, but the same procedure as in Comparative Example 4 was repeated to obtain an ethylene-vinyl acetate copolymer of Comparative Example 8.

[0133] Comparative Example 9 Ethylene and vinyl acetate were preheated to 160°C through a feed port on the front side of the tubular reactor and then introduced into the reactor. Subsequently, t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator to initiate polymerization. Subsequently, ethylene and vinyl acetate preheated to 160°C were additionally introduced through a feed port on the middle side of the tubular reactor. Subsequently, t-butyl-peroxy-2-ethylhexanoate and di-t-butyl peroxide were introduced as polymerization initiators from the middle side. The overall amount of vinyl acetate was 7 mol% relative to ethylene.

[0134] The average polymerization temperature in the tubular reactor was 240°C, and the polymerization pressure was 276 MPa. The polymerization temperature in the tubular reactor was adjusted so that the first peak top temperature was 275°C, the middle peak top temperature was 268°C, the latter peak top temperature was 255°C, and the reactor outlet temperature was 191°C. The ethylene-vinyl acetate copolymer of Comparative Example 9 was obtained in the same manner as in Example 1, except that the difference between the bottom temperature and the peak top temperature before and after introducing ethylene, vinyl acetate, and the polymerization initiator at the middle feed port was 28°C, and the difference between the bottom temperature and the peak top temperature before and after introducing the polymerization initiator at the latter feed port was 64°C.

[0135] [Table 1]

[0136] [Table 2] [Industrial Applicability]

[0137] 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 11% by mass or more and 25% by mass or less of vinyl acetate units and ethylene units, By GPC-FTIR, the molecular weight distribution and the absorbance I attributed to the methylene group for each molecular weight were measured. (-CH2-) and the absorbance I attributed to the carbonyl group (-C=O) and the absorbance I attributed to the methyl group (-CH3) When measuring and Each molecular weight M in the half width region of the molecular weight distribution i The logarithm of log(M i ) to the absorbance ratio (I i(-C=O) / I i(-CH2-) ) the slope P of the least squares approximate linear relational expression is 0.014≦P≦1.40, Each molecular weight M in the half width region of the molecular weight distribution i The absorbance ratio (I i(-CH3) / I i(-CH2 -) ) the average value Q is 23.0≦Q≦30.0; Ethylene-vinyl acetate copolymer.

2. 13 The methyl branch (20.07 ppm) determined by C-NMR is less than 0.16 / 100C. The ethylene-vinyl acetate copolymer according to claim 1.

3. The heat of fusion (ΔH) determined by differential scanning calorimetry is 43 J / g or more and 90 J / g or less. The ethylene-vinyl acetate copolymer according to claim 1 or 2.

4. The melt flow rate at a temperature of 190°C and a load of 2.16 kg is 0.1 g / 10 min or more and less than 30 g / 10 min, 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, Sheet.

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

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