Ethylene-vinyl acetate copolymer and film containing same

Abstract

To provide an ethylene-vinyl acetate copolymer that can be easily processed into a thin film and can give a film having excellent resilience, transparency, and durometer hardness, and a film 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 (I(-C=O-) / I(-CH2-)) to a logarithm log(Mi) of each molecular weight Mi in a half-width region of the molecular weight distribution is -1.0≤P<0.0, and an average value Q of an absorbance ratio (I(-CH3) / I(-CH2-)) of each molecular weight Mi in the half-width region of the molecular weight distribution is 20.0≤Q≤26.0.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an ethylene-vinyl acetate copolymer and a film comprising 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, in the ethylene-vinyl acetate copolymer described in Patent Document 1, as the vinyl acetate content increases, the molecular chains become more entangled, making the copolymer more susceptible to breaking when stretched in a melt. In addition, the crystalline components decrease, which tends to reduce stiffness when molded into a film.

[0006] The present invention has been made in consideration of the above-mentioned problems, and aims to provide an ethylene-vinyl acetate copolymer that is excellent in thin film processability, stiffness, transparency, and durometer hardness of the obtained film, and a film containing the same. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have found that the proportion of vinyl acetate units tends to decrease as the molecular weight distribution shifts from low to high molecular weight components, and that the above-mentioned problems can be solved by an ethylene-vinyl acetate copolymer having a predetermined number of branches, which has led to the completion of the present invention.

[0008] 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 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 (-C=O-) / I (-CH2-) ) the slope P of the least squares approximation linear relationship equation is -1.0≦P<0.0, Each molecular weight M in the half width region of the molecular weight distribution i The absorbance ratio (I (-CH3) / I (-CH2-) ) the average value Q is 20.0≦Q≦26.0, Ethylene-vinyl acetate copolymer. [2] 13 The long chain branching determined by C-NMR is 0.30 / 100C or more and less than 0.55 / 100C, The ethylene-vinyl acetate copolymer according to [1]. [3] The heat of fusion (△H) determined by differential scanning calorimetry is 53 J / g or more and 89 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 10 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]. film. [6] It is for packaging, The film according to [5]. [7] having two or more layers, The film according to [5] or [6]. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an ethylene-vinyl acetate copolymer which is excellent in thin film processability, stiffness, transparency, and durometer hardness of the obtained film, and a film containing the same. [Brief explanation of the drawings]

[0010] [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. 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 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 I attributed to the methyl group (-CH3) and when the molecular weights M i log(M i ) to absorbance ratio (I (-C=O-) / I (-CH2-) ) the slope P of the least squares approximation linear relational expression is -1.0≦P<0.0, and each molecular weight M i The absorbance ratio (I (-CH3) / I (-CH2-) ) the average value Q is 20.0≦Q≦26.0.

[0013] As a result of extensive research, the present inventors have found that the thin film processability, stiffness, and durometer hardness of the resulting film are improved by having a low content of vinyl acetate units in the high molecular weight component of the ethylene-vinyl acetate copolymer and by having a low number of branches in the ethylene-vinyl acetate copolymer. The reason for this is thought to be, but is not limited to, as follows.

[0014] When the high molecular weight component of ethylene-vinyl acetate copolymer contains fewer vinyl acetate units, the molecular chains tend to become less entangled. The less entangled the molecular chains, the less likely the ethylene-vinyl acetate copolymer is to break when melted and stretched, which is thought to improve thin film processability.

[0015] Furthermore, it is believed that the fewer the number of branches in the ethylene-vinyl acetate copolymer, the less entanglement of molecular chains there is, resulting in a greater amount of crystalline components, an improved elastic modulus, and improved stiffness and durometer hardness of the resulting film.

[0016] In this embodiment, it is specified by GPC-FTIR that the ethylene-vinyl acetate copolymer contains fewer vinyl acetate units on the high molecular weight component side and that the ethylene-vinyl acetate copolymer has a small number of branches.

[0017] 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.

[0018] In this 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.

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

[0020] (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.

[0021] 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.

[0022] Here, for example, a negative slope P means that the proportion of vinyl acetate units in the copolymer of the present embodiment tends to decrease as the molecular weight distribution shifts from low to high molecular weight components. In other words, the slope P can be considered a parameter that indicates the distribution of vinyl acetate units (carbonyl groups) in the molecular weight distribution.

[0023] As described above, a negative slope P means that less vinyl acetate is incorporated into the high-molecular-weight component, which is important for the development of mechanical properties in ethylene-vinyl acetate copolymers. A low content of vinyl acetate units in the high-molecular-weight component tends to result in a higher degree of crystallinity due to steric hindrance of the molecular chain. Therefore, even if the overall content of vinyl acetate units is the same, an ethylene-vinyl acetate copolymer with a negative slope P exhibits less entanglement of molecular chains in the high-molecular-weight component. This improves thin-film processability during film formation. Furthermore, a negative slope P increases the crystallinity of the ethylene-vinyl acetate copolymer, thereby improving the stiffness of the resulting film.

[0024] 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.

[0025] The slope P is expressed as the slope of the following least squares approximate linear relational expression. i log(M i ) 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

[0026] In this embodiment, the slope P satisfies -1.0≦P<0.0, preferably -0.80≦P≦-0.10, and more preferably -0.60≦P≦-0.20. When the slope P is within the above range, the amount of vinyl acetate units contained in the high molecular weight component of the ethylene-vinyl acetate copolymer is reduced, thereby further improving the thin film processability and the stiffness, transparency, and durometer hardness of the obtained film.

[0027] The method for adjusting the slope P within the above range is not particularly limited. For example, one possible method is to polymerize an ethylene-vinyl acetate copolymer in a tube reactor and gradually increase the polymerization peak temperature from upstream to downstream of the tube reactor. When ethylene and vinyl acetate are added to the reactor and then an initiator is added, the temperature inside the reactor rises due to the heat of polymerization, and this temperature increase can be reduced by cooling the reactor. If the highest polymerization temperature at this time is defined as the polymerization peak temperature, it is preferable to lower the polymerization peak temperature in the later stage than in the earlier stage. This is because, at high polymerization temperatures, the polymerization of ethylene proceeds preferentially over vinyl acetate, and as the polymerization temperature decreases, the polymerization of vinyl acetate proceeds more easily. Therefore, by gradually increasing the polymerization peak temperature from upstream to downstream of the tube reactor, the polymerization of vinyl acetate can proceed preferentially upstream, while the polymerization of ethylene can proceed preferentially downstream, where the molecular weight increases.

[0028] 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.

[0029] Other methods for adjusting the slope P within the above range include, but are not limited to, increasing the temperature difference between the upstream and middle stages of the reactor, or reducing the temperature difference between the downstream stages compared to the temperature difference between the downstream stages. Specifically, pre-cooling the ethylene and vinyl acetate introduced into the upstream and middle stages of the reactor is one example. The temperature initially drops when ethylene, vinyl acetate, and other raw materials 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 increase the temperature difference between the upstream and middle stages of the reactor and promote the reaction, the ethylene and vinyl acetate, whose temperature has been increased by pressurization before being introduced into the reactor, are pre-cooled beforehand. This allows polymerization to proceed at low temperatures in the upstream and middle stages, thereby maintaining a state in which vinyl acetate polymerization proceeds preferentially. It is also preferable to reduce the temperature difference between the bottom temperature and peak temperature in the downstream stages compared to the temperature difference in the middle stage.

[0030] 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.

[0031] (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.

[0032] 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 low methyl group content means a low number of branches. Therefore, the absorbance ratio (I i(-CH3) / I i(-CH2-) ) means that the copolymer of this embodiment has a small number of branches.

[0033] 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.

[0034] In this embodiment, the average value Q is 20.0≦Q≦26.0, preferably 21.0≦Q≦25.0, and more preferably 21.5≦Q≦24.0. When the average value Q is within the above range, entanglement of molecular chains in the ethylene-vinyl acetate copolymer is reduced, thereby improving the stiffness and transparency of the film. Note that, although entanglement of molecular chains in the ethylene-vinyl acetate copolymer can be mediated by entanglement derived from vinyl acetate units and entanglement derived from branches, the average value Q is considered to contribute more to improving the stiffness of the film.

[0035] The method for adjusting the average Q value to the above range is not particularly limited, but can be controlled, for example, by the amounts of chain transfer agent, vinyl acetate, initiator, etc. The amount of propylene used as a chain transfer agent is less than 0.50 mol%, preferably less than 0.48 mol%, and more preferably less than 0.45 mol%.

[0036] When propylene is added in an amount of 0.50 mol% or more, hydrogen abstraction in the molecular chains of 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] (long chain branching) The ethylene-vinyl acetate copolymer of this embodiment, 13The long chain branching determined by C-NMR is preferably 0.30 / 100C or more and less than 0.55 / 100C, more preferably 0.31 / 100C or more and 0.50 / 100C or less, and even more preferably 0.32 / 100C or more and 0.45 / 100C or less. When the long chain branching is within the above range, thin film processability, stiffness, transparency, and durometer hardness of the obtained film tend to be further improved.

[0041] The long chain branching can be adjusted by the type and amount of a chain transfer agent. The long chain branching can be measured according to the method described in the Examples.

[0042] (heat of fusion) The ethylene-vinyl acetate copolymer of this embodiment has a heat of fusion (ΔH) determined by differential scanning calorimetry of preferably 53 to 89 J / g, more preferably 64 to 87 J / g, and even more preferably 67 to 85 J / g. When the heat of fusion is within the above range, the film tends to have an excellent balance of thin film processability, stiffness, transparency, and durometer hardness.

[0043] The heat of fusion can be adjusted by the VA concentration, molecular weight distribution, etc. The heat of fusion can be measured according to the method described in the Examples.

[0044] (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 10 g / 10 min, more preferably 0.6 g / 10 min or more and 8.0 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, thin film processability, stiffness, and durometer hardness of the obtained film tend to be further improved.

[0045] 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.

[0046] The melt flow rate can be measured in accordance with JIS K7210:1999 Code D (temperature = 190°C, load = 2.16 kg).

[0047] (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 22% by mass or less, and more preferably 13% by mass or more and 19% 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 balance between thin film processability, stiffness, and durometer hardness of the obtained film tends to be excellent.

[0048] 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.

[0049] 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.

[0050] (ethylene units) The content of ethylene units is preferably 75% by mass or more and 89% by mass or less, more preferably 78% by mass or more and 88% by mass or less, and even more preferably 81% 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, thin film processability, stiffness, and durometer hardness of the obtained film tend to be further improved.

[0051] 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 may be, for example, a unit derived from propylene. From the viewpoints of thin film processability, stiffness, and durometer hardness of the resulting film, the content of the monomer unit other than the ethylene unit or the vinyl acetate unit is 10.0 mol % or less, more preferably 5.0 mol % or less, relative to the ethylene content.

[0052] 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.

[0053] [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.

[0054] 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.

[0055] 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 350 MPa or lower, more preferably 120 MPa or higher and 280 MPa or lower, and even more preferably 180 MPa or higher and 270 MPa or lower.

[0056] The reactor may have multiple points for feeding ethylene, vinyl acetate, and a polymerization initiator. In this embodiment, the temperature drops temporarily near each feed point due to the introduction of raw materials, and then the temperature inside the reactor rises again due to the heat of polymerization. It is preferable that the temperature inside the reactor then rises again due to the heat of polymerization. In this embodiment, the raw materials to be fed are pressurized before being introduced into the tube reactor, so their temperature rises to a certain extent. However, it is also preferable to pre-cool the raw materials to be fed. This allows the polymerization of vinyl acetate to proceed preferentially upstream and the polymerization of ethylene to proceed preferentially downstream, where the molecular weight increases, from the viewpoint of controlling the gradient P. The temperature of the raw materials to be fed to the reactor is preferably 60 to 80°C.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] After the ethylene-vinyl acetate copolymer is pelletized in an extruder, it is preferable to blow dry air into the silo in which the pellets are stored.

[0064] 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.

[0065] 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.

[0066] [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.

[0067] [film] The film of this embodiment contains the above-mentioned ethylene-vinyl acetate copolymer. Examples of methods for producing the film include T-die molding, inflation molding, calendar molding, and skiff molding. Inflation molding and T-die extrusion molding are particularly preferred.

[0068] The film of the present embodiment can be suitably used as an agricultural polyolefin film, a packaging film, or a film for exterior packaging of a flexible container, and is particularly suitable for use as a packaging film. Specific examples of the film include, but are not limited to, food packaging films, food wrap films, overwrap films, shrinkable overwrap films, and sealant films.

[0069] The term "film" refers to a plastic film having a thickness of less than 250 μm. The thickness of the film of this embodiment is preferably 10 to 240 μm, and more preferably 10 to 200 μm.

[0070] The film of the present embodiment may have two or more layers, and may have a laminate structure having other layers in addition to the layer made of the ethylene-vinyl acetate copolymer. The method for producing such a laminated film is not particularly limited, but examples thereof include a method of producing the film by laminating layers together using a lamination process, or a method of producing the film by a lamination extrusion process.

[0071] [Foam] The foam of the present embodiment contains the above-mentioned ethylene-vinyl acetate copolymer. The foam of the present embodiment is not particularly limited, but can be obtained using, for example, foamed microparticles, and is suitable for various applications. [Example]

[0072] 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.

[0073] [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.

[0074] 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 of 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.

[0075] 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 GMHHR-H(20)HT (7.9 mm ID x 30 cm) x 2 (Tosoh) Eluent: Tetrachloroethylene (Fujifilm Wako Pure Chemical Industries, 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

[0076] 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.

[0077] 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

[0078] [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.

[0079] The amount of terminal methyl groups was measured using a Polymer Char 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 GPC-IR) using an FT-IR (Polymer Char IR5) as the detector.

[0080] The amount of terminal methyl groups was determined by calculating 1 / 2A, where A is the peak top value of the component amount (d(W) / d(logM)) measured by GPC, and the average amount of CH3 per 1000c, Q, was calculated for 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

[0081] Based on the obtained IR data, the absorbance ratio (I i(-CH3) / I i(-CH2-) ) was calculated using GPC-ONE (Polymer Char) software, and the absorbance ratio (I i(-CH3) / I i(-CH2-) ) was averaged to obtain the mean value Q.

[0082] 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

[0083] [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.

[0084] [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).

[0085] [ 13 C-NMR measurement (long chain branching) 13 C-NMR measurements (long chain 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. Long chain branching was measured using a Bruker AVANCE500HD nuclear magnetic resonance spectrometer, with the methylene carbon signal at 29.9 ppm as the reference.

[0086] The long chain branching ratio was measured as described above. 13 It was calculated from the ratio of the area intensity of the methylene carbon signal and the long-chain branch signal observed in the C-NMR spectrum. The ratio of long-chain branches was defined as the ratio of branches with pentyl or longer branches. 13 The intensity of the methylene carbon signal was calculated as a ratio of the signal around 22.65 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) to 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℃

[0087] [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).

[0088] [Thin film processability] Using a Hokushin Sangyo Co., Ltd. T-die film-making machine, HM40N (screw diameter 40 mm, die width 300 mm, die gap 0.6 mm), molding was carried out at a cylinder temperature of 230°C, a die temperature of 230°C, an extrusion rate of 5 kg / hour, and a take-up speed of 10 m / min, and a 35 micrometer-thick T-die-formed film was produced in 30 minutes.

[0089] The sum of the neck-in distances at both edges of the obtained film was taken as the neck-in width (mm), and the ratio to the die width and the presence or absence of film breakage were evaluated according to the following criteria. 〇 (Excellent): Neck-in less than 25% △ (Good): Neck-in 25% or more but less than 30% × (Fail): Neck-in is 30% or more or film is broken

[0090] [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 50 μm in thickness was placed on top of this, and 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.

[0091] 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.

[0092] 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.

[0093] 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 50 μm was selected. The haze value of the 50 μm 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.

[0094] [Film stiffness (2% modulus)] Using an inflation film manufacturing apparatus (D-50, manufactured by Sumitomo Heavy Industries Modern Co., Ltd.) (screw diameter 50 mm, screw: L (extrusion screw length) / D (extrusion screw diameter) = 28, die: 100 mm, lip gap: 1.0 mm), the film was cooled and the film formation was stabilized at a cylinder temperature of 160°C, die temperature of 160°C, extrusion rate of 20.0 kg / hour, blow ratio of 2.0, and frost height of 300 mm to produce a 50 μm thick ethylene-vinyl acetate copolymer resin film. The modulus was determined by measuring the film strain at 2% in both the direction parallel to the resin flow (MD) and the direction perpendicular to the resin flow (TD) according to JIS K 7127.

[0095] [Durometer hardness] 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 3.1 mm in thickness was placed on top of this, and 130 g of ethylene-vinyl acetate copolymer resin was placed inside. The same polyethylene terephthalate film as above was then placed on top of this, and the same aluminum plate as above was then placed on top of this, and the same iron plate as above was then placed on top of this.

[0096] 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.

[0097] After the pressure application 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 cooled while being pressurized at 25 ° C. and 10 MPa for 300 seconds to produce a press sheet. After cooling, the press sheet removed from the mold was left standing in an environment at a temperature of 23 ° C. and a humidity of 50% for 24 hours or more. The durometer hardness (HDD) value of the press sheet thus obtained was measured in accordance with JIS-K7215 using a Toyo Seiki Hardness Tester.

[0098] Example 1 Polymerization was carried out using a tubular reactor with multiple feed ports. Specifically, ethylene and vinyl acetate were cooled to 70°C through the feed port on the front side of the tubular reactor and then introduced into the reactor. Subsequently, after heating within the reactor, t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator to initiate polymerization. Subsequently, ethylene and vinyl acetate pre-cooled to 70°C were additionally introduced through the 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 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 224°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 223°C, the peak top temperature in the middle stage was 255°C, and the peak top temperature in the rear stage was 275°C. 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 93°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.

[0100] The ethylene-vinyl acetate copolymer before purification 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 and vinyl acetate were cooled to 70°C through a feed port on the front side of the tubular reactor and then introduced into the reactor. Subsequently, after heating within the reactor, t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator to initiate polymerization. Subsequently, ethylene and vinyl acetate pre-cooled to 70°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 and rear sides. The overall amount of vinyl acetate relative to ethylene was 7 mol%.

[0103] 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 240°C, the peak top temperature in the middle stage was 254°C, and the peak top temperature in the rear stage was 277°C. The ethylene-vinyl acetate copolymer of Example 2 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 the polymerization initiator at the feed port on the middle stage was 79°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 rear stage was 47°C. The measurement results are shown in Table 1.

[0104] Example 3 Ethylene and vinyl acetate were cooled to 70°C through a feed port on the front side of the tubular reactor and then introduced into the reactor. Subsequently, after heating within the reactor, t-butyl peroxy-2-ethylhexanoate was introduced as a polymerization initiator to initiate polymerization. Subsequently, ethylene and vinyl acetate pre-cooled to 70°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 side, and t-butyl peroxy-2-ethylhexanoate and di-t-butyl peroxide were introduced from the rear side. The overall amount of vinyl acetate relative to ethylene was 6 mol%.

[0105] The average polymerization temperature in the tubular reactor was 211°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 223°C, the peak top temperature in the middle stage was 230°C, and the peak top temperature in the rear stage was 260°C. The ethylene-vinyl acetate copolymer of 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 the introduction of ethylene, vinyl acetate, and the polymerization initiator at the feed port on the middle stage was 68°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 rear stage was 50°C. The measurement results are shown in Table 1.

[0106] Example 4 Ethylene and vinyl acetate were cooled to 70°C through a feed port on the front side of the tubular reactor and then introduced into the reactor. Subsequently, after heating within the reactor, t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator to initiate polymerization. Subsequently, ethylene and vinyl acetate pre-cooled to 70°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 and rear sides. The overall amount of vinyl acetate was 5 mol% relative to ethylene.

[0107] The average polymerization temperature in the tubular reactor was 220°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 216°C, the peak top temperature in the middle stage was 247°C, and the peak top temperature in the rear stage was 275°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 the introduction of ethylene, vinyl acetate, and the polymerization initiator at the feed port on the middle stage was 89°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 rear stage was 45°C. The measurement results are shown in Table 1.

[0108] Example 5 Ethylene and vinyl acetate were cooled to 70°C through a feed port on the front side of the tubular reactor and then introduced into the reactor. Subsequently, after heating within the reactor, t-butyl peroxy-2-ethylhexanoate was introduced as a polymerization initiator to initiate polymerization. Subsequently, ethylene and vinyl acetate pre-cooled to 70°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 side, and t-butyl peroxy-2-ethylhexanoate and di-t-butyl peroxide were introduced as polymerization initiators from the rear side. The overall amount of vinyl acetate relative to ethylene was 8.7 mol%.

[0109] The average polymerization temperature in the tubular reactor was 214°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 205°C, the peak top temperature in the middle stage was 230°C, and the peak top temperature in the rear stage was 270°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 the introduction of ethylene, vinyl acetate, and the polymerization initiator at the feed port on the middle stage was 77°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 rear stage was 59°C. The measurement results are shown in Table 1.

[0110] Example 6 Ethylene and vinyl acetate were cooled to 70°C through a feed port on the front side of the tubular reactor and then introduced into the reactor. Subsequently, after heating within the reactor, t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator to initiate polymerization. Subsequently, ethylene and vinyl acetate pre-cooled to 70°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 and rear sides. The overall amount of vinyl acetate relative to ethylene was 7 mol%.

[0111] The average polymerization temperature in the tubular reactor was 234°C, and the polymerization pressure was 236 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 267°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 the introduction of ethylene, vinyl acetate, and the polymerization initiator at the feed port on the middle stage was 79°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 rear stage was 36°C. The measurement results are shown in Table 1.

[0112] Comparative Example 1 Ethylene, vinyl acetate, and propylene were introduced into the tubular reactor through a feed port on the front side. After heating, polymerization was initiated by introducing t-butyl peroxy-2-ethylhexanoate as a polymerization initiator. Subsequently, ethylene and vinyl acetate 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 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%.

[0113] The average polymerization temperature in the tubular reactor was 234°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 240°C, the peak top temperature in the middle stage was 260°C, and the peak top temperature in the rear stage was 270°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 the introduction of ethylene, vinyl acetate, and the polymerization initiator at the feed port on the middle stage was 65°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 rear stage was 35°C. The measurement results are shown in Table 1.

[0114] Comparative Example 2 Ethylene, vinyl acetate, and propylene were introduced into the tubular reactor through a feed port on the front side. After heating, polymerization was initiated by introducing t-butyl peroxy-2-ethylhexanoate as a polymerization initiator. Subsequently, ethylene and vinyl acetate 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 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%.

[0115] The average polymerization temperature in the tubular reactor was 238°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 235°C, the peak top temperature in the middle stage was 260°C, and the peak top temperature in the rear stage was 285°C. The ethylene-vinyl acetate copolymer of Comparative Example 2 was obtained in the same manner as in Comparative 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 the polymerization initiator at the feed port on the middle stage was 70°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 rear stage was 46°C. The measurement results are shown in Table 1.

[0116] Comparative Example 3 Ethylene and vinyl acetate were introduced into the tubular reactor through a feed port on the front side. After heating the reactor, t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator to initiate polymerization. Further, ethylene and vinyl acetate were 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 side. The overall amount of vinyl acetate relative to ethylene was 14 mol%.

[0117] 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 and the peak top temperature in the middle stage was 223°C. The ethylene-vinyl acetate copolymer of Comparative Example 3 was obtained in the same manner as in Comparative 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 in the middle stage was 48°C. The measurement results are shown in Table 1.

[0118] Comparative Example 4 Ethylene, vinyl acetate, and propylene were introduced into the tubular reactor through a feed port on the front side. After heating, polymerization was initiated by introducing t-butyl peroxy-2-ethylhexanoate as a polymerization initiator. Subsequently, ethylene and vinyl acetate 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%.

[0119] The average polymerization temperature in the tubular reactor was 225°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 233°C, the peak top temperature in the middle stage was 230°C, and the peak top temperature in the rear stage was 237°C. The ethylene-vinyl acetate copolymer of Comparative Example 4 was obtained in the same manner as in Comparative 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 the polymerization initiator at the feed port on the middle stage was 15°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 rear stage was 16°C. The measurement results are shown in Table 1.

[0120] Comparative Example 5 Ethylene and vinyl acetate were cooled to 70°C through a feed port on the front side of the tubular reactor and then introduced into the reactor. Subsequently, after heating within the reactor, t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator to initiate polymerization. Subsequently, ethylene and vinyl acetate pre-cooled to 70°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 side. The overall amount of vinyl acetate relative to ethylene was 7 mol%.

[0121] 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 peak top temperature in the front stage was 243°C and the peak top temperature in the middle stage was 255°C. The ethylene-vinyl acetate copolymer of Comparative Example 5 was obtained in the same manner as in Comparative 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 in the middle stage was 78°C. The measurement results are shown in Table 1.

[0122] Comparative Example 6 Ethylene, vinyl acetate, and propylene were introduced into the tubular reactor through a feed port on the front side. After heating the reactor, polymerization was initiated by introducing t-butyl-peroxy-2-ethylhexanoate as a polymerization initiator. Subsequently, ethylene and vinyl acetate pre-cooled to 70°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 7 mol%.

[0123] The average polymerization temperature in the tubular reactor was 223°C, and the polymerization pressure was 236 MPa. The polymerization temperatures in the tubular reactor were adjusted so that the peak top temperature in the front stage was 253°C, the peak top temperature in the middle stage was 246°C, and the peak top temperature in the rear stage was 235°C. The ethylene-vinyl acetate copolymer of Comparative Example 6 was obtained in the same manner as in Comparative 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 29°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 15°C. The measurement results are shown in Table 1.

[0124] [Table 1] [Industrial Applicability]

[0125] 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 19% 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 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 (-C=O-) / I (-CH2-) ) the slope P of the least squares approximation linear relational expression is -1.0≦P< 0.0, Each molecular weight M in the half width region of the molecular weight distribution i The absorbance ratio (I (-CH3) / I (-CH2-) ) the average value Q is 20.0≦Q≦26.0; Ethylene-vinyl acetate copolymer.

2. 13 the long chain branching determined by C-NMR is 0.30 / 100C or more and less than 0.55 / 100C; The ethylene-vinyl acetate copolymer according to claim 1.

3. The heat of fusion (ΔH) determined by differential scanning calorimetry is 53 J / g or more and 89 J / g or less. The ethylene-vinyl acetate copolymer according to claim 1 or 2.

4. The melt flow rate measured in accordance with JIS K7210:1999 Code D (temperature = 190°C, load = 2.16 kg) is 0.1 g / 10 min or more and less than 10 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, film.

6. It is for packaging, The film of claim 5.

7. having two or more layers, 7. The film according to claim 5 or 6.

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