JP7786958B2 - Ethylene-vinyl acetate copolymer and film containing same - Google Patents

Description

The present invention relates to an ethylene-vinyl acetate copolymer and a film containing the same.

Ethylene-vinyl acetate copolymers offer 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 and extrusion molding. They are also processed into single-layer or laminated films through inflation and T-die film forming, and are used in a wide range of industrial applications, including agricultural polyolefin films and automobile mudguard covers.

As an example of a film using ethylene-vinyl acetate copolymer, Patent Document 1 proposes an ethylene-vinyl acetate copolymer film that has high tear strength and heat retention properties despite having a high vinyl acetate content.

Japanese Patent Application Laid-Open No. 2004-161881

However, with an increase in the vinyl acetate content of the ethylene-vinyl acetate copolymer described in Patent Document 1, the molecular chains become more entangled, making the copolymer more susceptible to breaking when stretched during melting. Furthermore, the crystalline content decreases, which tends to result in a decrease in stiffness when molded into a film.

The present invention was made in consideration of the above-mentioned problems, and aims to provide an ethylene-vinyl acetate copolymer that exhibits excellent thin-film processability, stiffness, transparency, and durometer hardness in the resulting film, as well as a film containing the copolymer.

The inventors conducted extensive research to solve the above-mentioned problems. As a result, they discovered 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 using an ethylene-vinyl acetate copolymer with a specified number of branches, which led to the completion of the present invention.

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,
When the molecular weight distribution and the absorbance I _(-CH-) attributed to the methylene group, the absorbance I _(-C=O-) attributed to the carbonyl group, and the absorbance I _(-CH) attributed to the methyl group were measured by GPC-FTIR,
a slope P of a least squares approximate linear relationship of the absorbance ratio (I _(-C=O-) /I _(-CH2-) ) to the logarithm log(M _i ) of each molecular weight M _i in the half width region of the molecular weight distribution is −1.0≦P<0.0;
an average value Q of the 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;
Ethylene-vinyl acetate copolymer.
[2]
the long chain branching determined by ^13C -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 (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 [1] or [2].
[4]
The melt flow rate is 0.1 g/10 min or more and less than 10 g/10 min.
[1] 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]
For packaging,
The film according to [5].
[7]
having two or more layers,
The film according to [5] or [6].

The present invention provides an ethylene-vinyl acetate copolymer and a film containing the copolymer, which exhibits excellent thin-film processability, stiffness, transparency, and durometer hardness.

Schematic diagram for explaining the slope P measured by GPC-FTIR. Schematic diagram for explaining the average value Q measured by GPC-FTIR.

The following describes in detail an embodiment of the present invention (hereinafter referred to as the "present embodiment"); however, the present invention is not limited to this embodiment, and various modifications are possible without departing from the spirit of the present invention.

[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. When the molecular weight distribution and the absorbance I _(-CH2-) attributable to methylene groups, the absorbance I _(-C=O-) attributable to carbonyl groups, and the absorbance I _(-CH3) attributable to methyl groups for each molecular weight are measured by GPC-FTIR, the slope P of the least squares approximate linear relational expression of the absorbance ratio (I(-C=O-)/I _(-CH2-) ) to the logarithm log(M _i ) of each molecular weight M _i in the half width region of the molecular weight distribution is −1.0≦P<0.0, and the average value Q of the absorbance ratio (I _{(-CH3) /} I _(-CH2-) ) for each molecular weight M _i in the half width region of the molecular weight distribution is 20.0≦Q≦26.0.

After extensive research, the inventors have discovered that the thin film processability, stiffness, and durometer hardness of the resulting film are improved when the high molecular weight component of the ethylene-vinyl acetate copolymer contains fewer vinyl acetate units and the ethylene-vinyl acetate copolymer has a smaller number of branches. The reasons for this are not particularly limited, but are thought to be as follows:

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.

Furthermore, the fewer the number of branches in the ethylene-vinyl acetate copolymer, the less entanglement of the molecular chains there is, which increases the crystalline component, improves the elastic modulus, and is thought to further improve the stiffness and durometer hardness of the resulting film.

In this embodiment, GPC-FTIR is used to determine whether the ethylene-vinyl acetate copolymer contains fewer vinyl acetate units in the high-molecular-weight component side and whether the ethylene-vinyl acetate copolymer has a small number of branches.

GPC-FTIR is an instrument equipped with an FTIR device downstream of the column of a GPC device, which enables molecular weight measurement by GPC while simultaneously analyzing the composition of each molecular weight sample eluted from the column using 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.

In GPC-FTIR, quantitative analysis of sample composition is generally performed based on the absorbance intensity ratio. For example, the absorbance ratio of the absorbance I _(-CH2-) attributed to methylene groups to the absorbance I _(-C=O) attributed to carbonyl groups in a certain molecular weight fraction can be used 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.

The ethylene-vinyl acetate copolymer of this embodiment is described in detail below.

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

The slope P is defined as the slope of the least-squares linear approximation of the absorbance ratio ( _Ii(-C=O) /Ii _(-CH2-) ) to the logarithm log( _Mi ) of each molecular weight _M in the half-width region of the molecular weight distribution. The absorbance ratio ( _Ii(-C=O) /Ii _(-CH2-) ) is the ratio of the absorbance Ii _(-CH2-) attributable to methylene groups to the absorbance _Ii(-C=O) attributable to carbonyl groups, and indicates the proportion of carbonyl groups in each molecular weight of the ethylene-vinyl acetate copolymer.

Here, for example, a negative slope P means that the proportion of vinyl acetate units in the copolymer of this 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.

As mentioned above, a negative slope P means that less vinyl acetate is introduced 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 chains. Therefore, even if the overall content of vinyl acetate units is the same, an ethylene-vinyl acetate copolymer with a negative slope P will have 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, further improving the stiffness of the resulting film.

Here, the half-width refers to the width of the peak in the molecular weight distribution that has an intensity equal to 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 trend of vinyl acetate units without being affected by detection errors in the region at the base of the molecular weight distribution peak. The same applies to the average value Q, which will be described later.

The slope P is expressed as the slope of the following least squares linear approximation equation, and by expressing the relationship between the logarithm log(M _i ) of each molecular weight M _i and the absorbance ratio (I _i(-C=O) /I _i(-CH2-) ) with an approximation line in this way, it becomes possible to express the tendency of increase or decrease in vinyl acetate units in the molecular weight distribution. In the following equation, "a" is a constant.
Absorbance ratio ( _Ii(-C=O) /Ii _(-CH2-) ) = slope P × log( _Mi ) + a

In this embodiment, the slope P is -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 thin film processability and the stiffness, transparency, and durometer hardness of the resulting film.

Methods for adjusting the slope P within the above range are not particularly limited. For example, one possible method is to polymerize 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 stages than in the earlier stages. This is 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 increasing the polymerization peak temperature from upstream to downstream of the tube reactor, vinyl acetate polymerization can proceed preferentially upstream, while ethylene polymerization can proceed preferentially downstream, where the molecular weight increases.

In addition, one way to achieve the above temperature conditions is to use a double-tube reactor, and the temperature of the ethylene, vinyl acetate, ethylene-vinyl acetate copolymer, etc. flowing through the inner tube can be adjusted by using steam flowing through the outer tube.

Other methods for adjusting the slope P within the above range include, but are not limited to, increasing the temperature difference between the front and middle sections of the reactor and reducing the temperature difference between the rear sections compared to the temperature difference between the rear sections. Specifically, pre-cooling the ethylene and vinyl acetate introduced into the front and middle sections 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, the ethylene and vinyl acetate, whose temperature has risen due to pressurization before being introduced into the reactor, are pre-cooled beforehand to increase the temperature difference between the front and middle sections of the reactor and promote the reaction. This allows polymerization to proceed at low temperatures in the front and middle sections, thereby maintaining a state in which vinyl acetate polymerization takes precedence. It is also preferable to reduce the temperature difference between the bottom temperature and peak temperature in the rear sections compared to the temperature difference in the middle section.

In GPC-FTIR, the absorbance I _(-CH-) attributed to the methylene group is measured as an absorption at 2928 cm ^-1 , and the absorbance I _(-C=O) attributed to the carbonyl group is measured as an absorption at 1741 cm ^-1 . Specific measurements by GPC-FTIR can be performed by the method described in the Examples.

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

The average value Q is defined as the average value of the absorbance ratio (I _i(-CH3) /I _i(-CH2-) ) for each molecular weight M _i in the half-width region of the molecular weight distribution. The absorbance ratio (I _i(-CH3) /I _i(-CH2-) ) is the ratio of the absorbance I _i(-CH2-) attributable to methylene groups to the absorbance I _i(-CH3) attributable to methyl groups, and indicates the methyl group content at each molecular weight of the ethylene-vinyl acetate copolymer. Because a high proportion of ethylene-vinyl acetate copolymers are terminated with methyl groups, a low methyl group content means a low number of branches. Therefore, a low average value of the absorbance ratio (I _i(-CH3) /I _i(-CH2-) ) means that the copolymer of this embodiment has a low number of branches.

The absorbance ratio ( _Ii(-CH3) /Ii _(-CH2-) ) determined as described above indicates the number of carbon atoms in " _-CH3 " per 1000 carbon atoms in " _-CH2- ". The average value Q means the average number of carbon atoms in " _-CH3 " per 1000 carbon atoms in " _-CH2- " in the half width region of the molecular weight distribution.

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. Having the average value Q within this range reduces entanglement of molecular chains in the ethylene-vinyl acetate copolymer, thereby improving the stiffness and transparency of the film. While entanglement of molecular chains in ethylene-vinyl acetate copolymers can be attributed to entanglement derived from vinyl acetate units and entanglement derived from branches, the average value Q is considered to have a greater contribution from the perspective of improving the stiffness of the film.

The method for adjusting the average Q value to fall within the above range is not particularly limited, but can be controlled, for example, by adjusting 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%.

When propylene is added in an amount of 0.50 mol% or more, hydrogen abstraction from the molecular chains of the ethylene vinyl acetate resin increases, generating free radicals. These free radicals combine with each other and undergo a termination reaction, which tends to reduce the number of branches.

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 into the reactor inlet, polymerization progresses, and a polymer layer and a gas layer coexist 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, promoting polymerization and making it possible to appropriately adjust the number of branches.

However, if raw materials such as ethylene and vinyl acetate are added only through the reactor inlet, the amount of polymer obtained will be small, which is undesirable from the standpoint of productivity.

In GPC-FTIR, the absorbance I _(-CH-) attributed to the methylene group is measured as an absorption at 2928 cm ^-1 , and the absorbance I _(-CH3) attributed to the methyl group is measured as an absorption at 2960 cm ^-1 . Specific measurements by GPC-FTIR can be performed by the method described in the Examples.

(long chain branching)
The long chain branching of the ethylene-vinyl acetate copolymer of this embodiment, as determined by ^13C -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.

Long chain branching can be adjusted by changing the type and amount of chain transfer agent. Long chain branching can be measured according to the method described in the Examples.

(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 J/g to 89 J/g, more preferably 64 J/g to 87 J/g, and even more preferably 67 J/g to 85 J/g. When the heat of fusion is within the above range, the thin film processability and the balance of stiffness, transparency, and durometer hardness of the resulting film tend to be excellent.

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

(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.

The method for adjusting the melt flow rate of the ethylene-vinyl acetate copolymer is not particularly limited, but examples include 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.

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

(vinyl acetate unit)
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.

The method for adjusting the vinyl acetate unit content is not particularly limited, but examples include appropriately adjusting the amount of vinyl acetate monomer added in the process of polymerizing the ethylene-vinyl acetate copolymer, as well as the polymerization temperature and polymerization pressure.

The vinyl acetate unit content can be measured in accordance with JIS K7192:1999, using a calibration curve prepared by saponification and potentiometric titration as the reference test method, and converting the content into vinyl acetate using infrared spectroscopy as the control test method. Specifically, it can be measured using the method described in the examples below.

(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.

The ethylene-vinyl acetate copolymer of this embodiment may contain monomer units other than ethylene units and vinyl acetate units. The other monomer units are not particularly limited, but examples include units derived from propylene, etc. From the viewpoints of thin film processability, stiffness, and durometer hardness of the resulting film, the content of monomer units other than ethylene units and vinyl acetate units is 10.0 mol % or less, more preferably 5.0 mol % or less, relative to ethylene.

The ethylene-vinyl acetate copolymer of this embodiment can also 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, it is preferable that the content of vinyl acetate units in the entire resin be within the above-mentioned range.

[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.

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

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.

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 when raw materials are introduced, and then the temperature inside the reactor rises again due to the heat of polymerization. It is preferable for the temperature inside the reactor to then rise again due to the heat of polymerization. In this embodiment, the raw materials 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 before introduction. This allows for 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 perspective of controlling the gradient P. The temperature of the raw materials supplied to the reactor is preferably 60 to 80°C.

In this embodiment, the front section of the reactor refers to a position (inlet) that is 0% to 10% of the total length of the reactor, the middle section 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 section of the reactor refers to a position from the inlet that is 40% to 70% of the total length of the reactor.

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

Polymerization initiators are not particularly limited, but examples include free radical generators such as peroxides. Free radical generators such as peroxides are not particularly limited, but examples include t-butyl-peroxy-2-ethylhexanoate, t-butyl peroxyacetate, t-butyl peroxypivalate, and di-t-butyl peroxide.

The chain transfer agent is not particularly limited, but examples 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.

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

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

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

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

Antioxidants are not particularly limited, but examples 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.

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

[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.

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

Note that "film" refers to a plastic membrane with a thickness of less than 250 μm. The thickness of the film in this embodiment is preferably 10 to 240 μm, and more preferably 10 to 200 μm.

The film of this embodiment may also 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 described above. There are no particular limitations on the method for producing such a laminate film, but examples include a method in which layers are bonded together using a lamination process, or a method in which layers are produced using a lamination extrusion process.

[Foam]
The foam of the present embodiment contains the above-described 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.

The present invention will be explained in more detail below using examples and comparative examples. The present invention is not limited in any way by the following examples.

[GPC-IR measurement (carbonyl group gradient P)]
GPC-IR measurement (carbonyl group gradient P) was performed under the following conditions. For sample pretreatment, the sample was weighed, a solvent (0.05% BHT-added TCE) 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 manufactured by Tosoh. The molecular weight was converted to polyethylene molecular weight using a factor.

The average molecular weight was calculated from the elution curve based on the absorbance peak area between 2850 and 2940 ^cm using SEC-FTIR software (Thermo Nicolet). The vinyl acetate content was calculated by creating a calibration curve using EVA of known composition from the absorbance ratio between the C=O stretching vibration at 1741 ^cm and the _CH stretching vibration at 2928 ^cm .

The carbonyl group slope P was measured by GPC (apparatus: HLC-8121GPC/HT manufactured by Tosoh Corporation) using an Avatar 370 detector manufactured by Thermo Nicolet, and the vinyl acetate ratio (VAc ratio) in each molecular weight region was plotted and calculated from a square law approximation line. For the GPC-IR elution curve, the value of the component amount (d(W)/d(logM)) at half the peak top value in the GPC measurement (d(W)/d(logM)) was calculated as 1/2A, and this was taken as the VAc ratio in the molecular weight range of 1/2A.
(Measurement conditions)
GPC device: HLC-8121GPC/HT (manufactured by 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°C
Detector temperature: 110°C
Measurement wave number: 4000 to 650 cm-1
Resolution: 4cm-1
Number of scans: 8 times/1 point

Based on the obtained IR data, the absorbance ratio ( _Ii(-C=O) /Ii _(-CH2-) ) for each molecular weight was calculated, and the relationship between the logarithm log( _Mi ) of each molecular weight _Mi and the absorbance ratio ( _Ii(-C=O) /Ii _(-CH2-) ) in the half-width region 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.

The absorbance I _(-CH2-) attributed to the methylene group was measured as the absorption at 2928 cm ^-1 , and the absorbance I _(-C=O) attributed to the carbonyl group was measured as the absorption at 1741 cm ^-1 .

[GPC-IR measurement (average value Q of terminal methyl groups)]
GPC-IR measurement (average value Q of terminal methyl groups) was performed 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 90 minutes. Molecular weight calibration was performed using 12 points in the range of MW (molecular weight) of standard polystyrene manufactured by Tosoh Corporation 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 from a plot of elution time and polyethylene-equivalent molecular weight, and the weight-average molecular weight (Mw) and number-average molecular weight (Mn) were determined.

The amount of terminal methyl groups was measured using a Polymer Char Composition Calibration Kit (Octene) CH ₃ /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.

The amount of terminal methyl groups was determined by determining 1/2A of the amount of the component (d(W)/d(logM)) when the peak top value of the amount of the component (d(W)/d(logM)) measured by GPC was defined as A, and the average amount Q of _CH3 per 1000c was calculated within the molecular weight range of 1/2A.
(Measurement conditions)
Apparatus: GPC-IR manufactured by Polymer Char
Detector: Polymer Char IR5
Column: UT-807 (1 column) manufactured by Showa Denko K.K. and GMHHR-H(S)HT (2 columns) manufactured by Tosoh Corporation connected in series Mobile phase: orthodichlorobenzene Column temperature: 140°C
Flow rate: 1.0 ml/min Sample concentration: 16 mg/8 mL

Based on the obtained IR data, the absorbance ratio (I _i(-CH3) /I _i(-CH2-) ) at each molecular weight was calculated using GPC-ONE (Polymer Char) software, and the average of the absorbance ratios (I _i(-CH3) /I _i(-CH2-) ) in the half-width region was calculated to obtain the average value Q.

The absorbance I _(-CH2-) attributed to the methylene group was measured as the absorption at 2928 cm ^-1 , and the absorbance I _(-CH3) attributed to the methyl group was measured as the absorption at 2960 cm ^-1 .

[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 a reference test method, and the content of vinyl acetate units (VA content) in the ethylene-vinyl acetate copolymers obtained in the examples and comparative examples was measured by infrared spectroscopy as a control test method.

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

[ ¹³ C-NMR Measurement (Long Chain Branching)]
^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 AVANCE 500HD nuclear magnetic resonance spectrometer, with the methylene carbon signal at 29.9 ppm as the reference.

The long chain branch ratio was calculated from the ratio of the area intensity of the methylene carbon signal to the area intensity of the long chain branch signal observed in ^the C-NMR spectrum measured above. The long chain branch ratio was defined as the ratio of branches with pentyl or longer branches, and was determined from the ratio of the intensity of the methylene carbon signal, which was taken as ¹⁰⁰ , to 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).
(Measurement conditions)
Measuring device: AVANCE-500HD manufactured by Bruker
Observed nucleus: ^13C
Observation frequency: 125.77MHz
Pulse width: 5.0 μsec
PD: 5 sec
Measurement temperature: 120℃
Number of integrations: 8,000 times Reference: PE (-eee-) signal, 29.9 ppm
Solvent: orthodichlorobenzene- _d4
Sample concentration: 5 wt/vol%
Melting temperature: 140℃

[Differential scanning calorimetry (heat of fusion)]
The heat of fusion ΔH was measured using a DSC (manufactured by PerkinElmer, trade 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).

[Thin film processability]
Using a T-die film-forming machine, HM40N (screw diameter 40 mm, die width 300 mm, die gap 0.6 mm) manufactured by Hokushin Sangyo Co., Ltd., 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 T-die-formed film with a thickness of 35 microns was produced for 30 minutes.

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% to less than 30% × (Unacceptable): Neck-in 30% or more or film break

[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.

This was placed in a compression molding machine (SFA-37, manufactured by Shinto Metal Industries Co., Ltd.) with a temperature setting of 180°C, preheated at 180°C and 0.1 MPa for 180 seconds, then air was removed for 5 seconds (10 MPa), and compression was performed at 180°C and 15 MPa for 120 seconds.

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

The thickness of the pressed 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 pressed 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.

[Film stiffness (2% modulus)]
An inflation film production 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) was used to produce a 50 μm thick ethylene-vinyl acetate copolymer resin film by cooling the film and stabilizing the film formation at a cylinder temperature of 160°C, a die temperature of 160°C, an extrusion rate of 20.0 kg/hour, a blow ratio of 2.0, and a frost height of 300 mm. The modulus was determined by measuring the film strain at 2% in accordance with JIS K 7127 in both the direction parallel to the resin flow (MD) and the direction perpendicular to the resin flow (TD).

[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.) not coated with cellophane was placed on 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 in this, and the same polyethylene terephthalate film as above was placed on top of this, and then the same aluminum plate as above was placed on top, and then the same iron plate as above was placed on top of this.

This was placed in a compression molding machine (SFA-37, manufactured by Shinto Metal Industries Co., Ltd.) with a temperature setting of 180°C, preheated at 180°C and 0.1 MPa for 180 seconds, then air was removed for 5 seconds (10 MPa), and compression was performed at 180°C and 15 MPa for 120 seconds.

After pressing, the sample was removed and, 5 seconds after removal, placed in a compression molding machine (SFA-37, manufactured by Shinto Metal Industries Co., Ltd.) temperature-controlled at 25°C. It was then cooled while being pressed at 25°C and 10 MPa for 300 seconds to produce a pressed sheet. After cooling, the pressed sheet was removed from the mold and allowed to stand in an environment at 23°C and 50% humidity for at least 24 hours. The durometer hardness (HDD) of the pressed sheet thus obtained was measured in accordance with JIS-K7215 using a HARDNESS TESTER manufactured by Toyo Seiki Seisakusho.

Example 1
Polymerization was carried out using a tubular reactor having multiple feed ports. Specifically, 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, and 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.

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 peak top temperature before and after the introduction of ethylene, vinyl acetate, and polymerization initiator at the feed port on the middle stage was 93°C, and the difference between the bottom temperature and peak top temperature before and after the introduction of polymerization initiator at the feed port on the rear stage was 44°C.

The unpurified ethylene-vinyl acetate copolymer discharged from the tubular reactor was introduced into a high-pressure separator, where unreacted gases and other components were separated. The ethylene-vinyl acetate copolymer discharged from the high-pressure separator was then introduced into a low-pressure separator, where remaining unreacted gases and other components were separated, yielding molten ethylene-vinyl acetate copolymer.

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 using the methods described above. The measurement results are shown in Table 1.

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, and 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.

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 peak top temperature before and after the introduction of ethylene, vinyl acetate, and polymerization initiator at the feed port on the middle stage was 79°C, and the difference between the bottom temperature and peak top temperature before and after the introduction of polymerization initiator at the feed port on the rear stage was 47°C. The measurement results are shown in Table 1.

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-butylperoxy-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-butylperoxy-2-ethylhexanoate was introduced as a polymerization initiator from the middle side, and t-butylperoxy-2-ethylhexanoate and di-t-butylperoxide were introduced from the rear side. The overall amount of vinyl acetate was 6 mol% relative to the ethylene.

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 peak top temperature before and after the introduction of ethylene, vinyl acetate, and polymerization initiator at the feed port on the middle stage was 68°C, and the difference between the bottom temperature and peak top temperature before and after the introduction of polymerization initiator at the feed port on the rear stage was 50°C. The measurement results are shown in Table 1.

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, and 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.

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 peak top temperature before and after the introduction of ethylene, vinyl acetate, and polymerization initiator at the feed port on the middle stage was 89°C, and the difference between the bottom temperature and peak top temperature before and after the introduction of polymerization initiator at the feed port on the rear stage was 45°C. The measurement results are shown in Table 1.

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-butylperoxy-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-butylperoxy-2-ethylhexanoate was introduced as a polymerization initiator from the middle side, and t-butylperoxy-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%.

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 peak top temperature before and after the introduction of ethylene, vinyl acetate, and polymerization initiator at the feed port on the middle stage was 77°C, and the difference between the bottom temperature and peak top temperature before and after the introduction of polymerization initiator at the feed port on the rear stage was 59°C. The measurement results are shown in Table 1.

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, and 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.

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 peak top temperature before and after the introduction of ethylene, vinyl acetate, and polymerization initiator at the feed port on the middle stage was 79°C, and the difference between the bottom temperature and peak top temperature before and after the introduction of polymerization initiator at the feed port on the rear stage was 36°C. The measurement results are shown in Table 1.

Comparative Example 1
Ethylene, vinyl acetate, and propylene were introduced into the tubular reactor through a feed port on the front stage, followed by heating within the reactor and introducing t-butylperoxy-2-ethylhexanoate as a polymerization initiator to initiate polymerization. Subsequently, ethylene and vinyl acetate were additionally introduced through a feed port on the middle stage of the tubular reactor, followed by introducing t-butylperoxy-2-ethylhexanoate and di-t-butyl peroxide as polymerization initiators from the middle and rear stages. The overall amount of vinyl acetate relative to ethylene was 4 mol %, and the amount of propylene relative to ethylene was 0.5 mol %.

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 peak top temperature before and after the introduction of ethylene, vinyl acetate, and polymerization initiator at the feed port in the middle stage was 65°C, and the difference between the bottom temperature and peak top temperature before and after the introduction of polymerization initiator at the feed port in the rear stage was 35°C. The measurement results are shown in Table 1.

Comparative Example 2
Ethylene, vinyl acetate, and propylene were introduced into the tubular reactor through a feed port on the front stage, followed by heating within the reactor and introducing t-butylperoxy-2-ethylhexanoate as a polymerization initiator to initiate polymerization. Subsequently, ethylene and vinyl acetate were additionally introduced through a feed port on the middle stage of the tubular reactor, followed by introducing t-butylperoxy-2-ethylhexanoate and di-t-butyl peroxide as polymerization initiators from the middle and rear stages. The overall amount of vinyl acetate relative to ethylene was 4 mol %, and the amount of propylene relative to ethylene was 0.5 mol %.

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 peak top temperature before and after the introduction of ethylene, vinyl acetate, and polymerization initiator at the feed port in the middle stage was 70°C, and the difference between the bottom temperature and peak top temperature before and after the introduction of polymerization initiator at the feed port in the rear stage was 46°C. The measurement results are shown in Table 1.

Comparative Example 3
Ethylene and vinyl acetate were introduced into the tubular reactor through a feed port on the front side, and then, after heating inside the reactor, t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator to initiate polymerization. Subsequently, additional ethylene and vinyl acetate were 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 14 mol%.

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 peak top temperature before and after the introduction of ethylene, vinyl acetate, and polymerization initiator into the middle stage feed port was 48°C. The measurement results are shown in Table 1.

Comparative Example 4
Ethylene, vinyl acetate, and propylene were introduced into the tubular reactor through a feed port on the front stage side. Subsequently, after heating inside the reactor, t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator to initiate polymerization. Subsequently, ethylene and vinyl acetate were additionally introduced through a feed port on the middle stage side of the tubular reactor, and subsequently, t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator from the middle and rear stages. The overall amount of vinyl acetate was 7 mol% relative to ethylene.

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 peak top temperature before and after the introduction of ethylene, vinyl acetate, and polymerization initiator at the feed port on the middle stage was 15°C, and the difference between the bottom temperature and peak top temperature before and after the introduction of polymerization initiator at the feed port on the rear stage was 16°C. The measurement results are shown in Table 1.

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, and subsequently t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator from the middle side. The overall amount of vinyl acetate was 7 mol% relative to ethylene.

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 polymerization initiator into the feed port on the middle stage was 78°C. The measurement results are shown in Table 1.

Comparative Example 6
Ethylene, vinyl acetate, and propylene were introduced into the tubular reactor through a feed port on the front stage side. Subsequently, after heating inside 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 stage side of the tubular reactor, and subsequently t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator from the middle and rear stages. The overall amount of vinyl acetate was 7 mol% relative to ethylene.

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 peak top temperature before and after the introduction of ethylene, vinyl acetate, and polymerization initiator at the feed port on the middle stage was 29°C, and the difference between the bottom temperature and peak top temperature before and after the introduction of polymerization initiator at the feed port on the rear stage was 15°C. The measurement results are shown in Table 1.

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 (7)

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 _(-CH2-) attributed to the methylene group, the absorbance I _(-C=O-) attributed to the carbonyl group, and the absorbance I _(-
CH3) and when measured,
The slope P of the least squares approximate linear relational expression of the absorbance ratio (I _(-C=O-) /I _(-CH2-) ) to the logarithm log(M _i ) of each molecular weight M _i in the half width region of the molecular weight distribution is -1.0≦P<
0.0,
The absorbance ratio (I _(-CH3) / I _(-CH2-) of each molecular weight M _i in the half-width region of the molecular weight distribution
) the average value Q is 20.0≦Q≦26.0;
Ethylene-vinyl acetate copolymer. the long chain branching determined by ^13C -NMR is 0.30/100C or more and less than 0.55/100C;
The ethylene-vinyl acetate copolymer according to claim 1. 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. 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. The ethylene-vinyl acetate copolymer according to any one of claims 1 to 4,
film. It is for packaging,
The film of claim 5. having two or more layers,
The film according to claim 5 or 6.