JP2022136971A - Ethylene-vinyl acetate copolymer, and film comprising the same - Google Patents

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

The present invention relates to ethylene-vinyl acetate copolymers and films containing the same.

Ethylene-vinyl acetate copolymer is excellent in performance such as transparency, flexibility, mechanical strength, electrical insulation, weather resistance, and durability. , drainage hoses, etc. Furthermore, it is processed into a single layer or laminated film by inflation or T-die film production, etc., and is used in a wide range of industrial fields such as agricultural polyolefin films and automobile mudguard covers. .

As a film using an ethylene-vinyl acetate copolymer, for example, Patent Document 1 proposes an ethylene-vinyl acetate copolymer film having high tear strength and heat retention even with a high vinyl acetate content. ing.

JP-A-2004-161881

However, in the ethylene-vinyl acetate copolymer as described in Patent Document 1, as the vinyl acetate content increases, the entanglement of the molecular chains increases, and in addition to being easily broken when stretched during melting, the crystalline component is Therefore, when the film is formed, the stiffness tends to decrease.

The present invention has been made in view of the above problems, and provides an ethylene-vinyl acetate copolymer excellent in thin film processability, stiffness, transparency, and durometer hardness of the resulting film, and a film containing the same. intended to

The present inventors have diligently studied to solve the above problems. As a result, the ratio of vinyl acetate units tends to decrease as the molecular weight distribution increases from low molecular weight components to high molecular weight components, and the above problems can be solved by ethylene-vinyl acetate copolymers having a predetermined number of branches. We have found that it is possible, and have completed the present invention.

That is, the present invention is as follows.
[1]
11% by mass or more and 25% by mass or less of vinyl acetate units and ethylene units,
By GPC-FTIR, the molecular weight distribution, the absorbance I attributed to the methylene group for each molecular weight _(-CH2-) , the absorbance I attributed to the carbonyl group _(-C=O-) , and the absorbance I attributed to the methyl group When measuring I _(-CH3) and
The slope of the least-squares approximation 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 P is -1.0 ≤ P < 0.0,
The average value Q of the absorbance ratio (I _(-CH3) /I _(-CH2-) ) of each molecular weight M _i in the half-width region of the molecular weight distribution is 20.0 ≤ Q ≤ 26.0.
Ethylene-vinyl acetate copolymer.
[2]
long chain branching determined from ¹³ C-NMR is 0.30/100 C or more and less than 0.55/100 C;
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,
The ethylene-vinyl acetate copolymer according to any one of [1] to [3].
[5]
containing the ethylene-vinyl acetate copolymer according to any one of [1] to [4],
the film.
[6]
is for packaging,
The film according to [5].
[7]
having two or more layers,
The film according to [5] or [6].

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an ethylene-vinyl acetate copolymer excellent in thin film processability, stiffness, transparency, and durometer hardness of the resulting film, and a film containing the same.

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

Hereinafter, an embodiment of the present invention (hereinafter referred to as "this embodiment") will be described in detail, but the present invention is not limited to this, and various modifications are possible without departing from the gist thereof. is.

[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 absorbance I attributed _(-CH2-) , the absorbance I attributed to the carbonyl group _(-C=O-) , and the absorbance I attributed to the methyl group _(-CH3) were measured, the molecular weight distribution 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 −1.0≦P<0.0, and the average value Q of the absorbance ratio (I _(-CH3) /I _(-CH2-) ) of each molecular weight M _i in the half-width region of the molecular weight distribution is 20 .0≤Q≤26.0.

As a result of intensive studies by the present inventors, it has been found that the high-molecular-weight component of the ethylene-vinyl acetate copolymer has few vinyl acetate units and the number of branches of the ethylene-vinyl acetate copolymer is small. It has been found that the stiffness and durometer hardness of the resulting film are further improved. Although not particularly limited, the reason for this is considered as follows.

When there are few vinyl acetate units contained in the high molecular weight component side of the ethylene-vinyl acetate copolymer, the entanglement of molecular chains tends to be less. The less entanglement of molecular chains, the more difficult it is to break when the ethylene-vinyl acetate copolymer is melted and stretched.

In addition, the smaller the number of branches of the ethylene-vinyl acetate copolymer, the less the entanglement of the molecular chains, so the crystal component increases, the elastic modulus improves, and the stiffness and durometer hardness of the obtained film are further improved. It is considered that

In the present embodiment, it is defined 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 smaller number of branches. do.

GPC-FTIR is equipped with an FTIR device downstream of the column of the GPC device, and is a device that enables molecular weight measurement by GPC and composition analysis of each molecular weight sample eluted from the column by IR measurement at the same time. Thereby, it is possible to measure the change in the copolymerization ratio of the monomers from the high molecular weight side to the low molecular weight side of the GPC chart.

In this GPC-FTIR, quantitative analysis of sample composition is generally performed by the intensity ratio of absorbance. For example, in a fraction of a certain molecular weight, the absorbance ratio of the absorbance I attributed to the methylene group _(-CH2-) and the absorbance I attributed to the carbonyl group _(-C=O) is used as the basis for the fraction with the methylene group It is possible to evaluate whether many carbonyl groups are included or whether they are included in a small amount. In addition, by comparing the absorbance ratios of a plurality of fractions with different molecular weights, it is possible to evaluate whether a relatively large amount or a small amount of carbonyl groups is contained on the high molecular weight side or the low molecular weight side.

The ethylene-vinyl acetate copolymer of the present embodiment will be described in detail below.

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

The slope P is the least-squares approximation straight line of the absorbance ratio (Ii(-C _{= O)} / _Ii(-CH2-) ) to the logarithm log(Mi ₎ of each molecular weight Mi in the half-width region of the molecular weight distribution. Defined as the slope of the relational expression. The absorbance ratio (I _i(-C=O) /I _i(-CH2-) ) is the absorbance I _i(-CH2-) attributed to the methylene group and the absorbance I _{i(-C =O)} , and indicates the content of carbonyl groups at each molecular weight of the ethylene-vinyl acetate copolymer.

Here, for example, the fact that the slope P is negative means that the proportion of vinyl acetate units tends to decrease as the copolymer of the present embodiment changes from a low molecular weight component to a high molecular weight component in the molecular weight distribution. means In other words, the slope P can also be said to be a parameter indicating the distribution of vinyl acetate units (carbonyl groups) in the molecular weight distribution.

As described above, the fact that the slope P is negative means that less vinyl acetate is introduced into the high-molecular-weight component that is important for the development of mechanical properties in the ethylene-vinyl acetate copolymer. Due to the small content of vinyl acetate units in the high-molecular-weight component, the degree of crystallinity tends to increase due to steric hindrance of the molecular chains. From this, the ethylene-vinyl acetate copolymer having a negative slope P has less entanglement of the molecular chains in the high molecular weight component, even if the content of the vinyl acetate unit is about the same as a whole. Therefore, the processability of a thin film is further improved when forming a film or the like. In addition, since the slope P is negative, the degree of crystallinity of the ethylene-vinyl acetate copolymer increases, so that the stiffness of the obtained film is further improved.

Here, the half width means the width of a peak having an intensity half the height A of the peak top (1/2A) in the peak of the molecular weight distribution. 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 the detection error in the tail region of the peak of the molecular weight distribution. This also applies to the average value Q, which will be described later.

In addition, the slope P is expressed as the slope of the following linear least _squares approximate _linear relational expression. By showing the relationship between _i(-C=O) /I _i(-CH2-) ) with an approximate straight line, it is possible to express the increasing/decreasing tendency of vinyl acetate units in the molecular weight distribution. In addition, in the following formula, "a" is a constant.
Absorbance ratio (I _{i (-C=O)} /I _{i (-CH2-)} ) = slope P x log (M _i ) + a

In the present embodiment, the slope P is -1.0 ≤ P < 0.0, preferably -0.80 ≤ P ≤ -0.10, more preferably -0.60 ≤ P ≤ - 0.20. When the slope P is within the above range, the number of vinyl acetate units contained in the high molecular weight component of the ethylene-vinyl acetate copolymer is reduced, so that thin film processability, stiffness, transparency, and durometer hardness of the obtained film are improved. is better.

The method for adjusting the slope P to the above range is not particularly limited, but for example, an ethylene-vinyl acetate copolymer is polymerized in a tube reactor, and the polymerization peak temperature is gradually increased from upstream to downstream of the tube reactor. can be considered. When the initiator is added after ethylene and vinyl acetate are added to the reactor, the temperature inside the reactor rises due to the heat of polymerization, and the temperature rise decreases when the reactor is cooled. When the highest polymerization temperature at this time is defined as the polymerization peak temperature, it is preferable that the polymerization peak temperature on the rear stage side is lower than the polymerization peak temperature on the front stage side. This is because when the polymerization temperature is high, 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 raising the polymerization peak temperature from upstream to downstream of the tube reactor, vinyl acetate polymerization proceeds preferentially in the upstream, and ethylene polymerization proceeds preferentially in the downstream where the molecular weight increases. can be done.

In addition, as one means for achieving the above temperature conditions, the reactor has a double-tube structure, and ethylene, vinyl acetate, and ethylene-vinyl acetate copolymer, etc., are circulated in the inner tube by steam circulating in the outer tube. Temperature can be adjusted.

In addition, other methods for adjusting the slope P to the above range are not particularly limited. to reduce the temperature difference between Specifically, ethylene and vinyl acetate introduced from the front and middle stages of the reactor are pre-cooled. When raw materials such as ethylene and vinyl acetate are introduced from the middle of the tube reactor, the temperature drops once, but the temperature rises again due to the heat of polymerization. In the reactor, the temperature changes depending on the position where the raw material is introduced. In this embodiment, in order to increase the temperature difference between the front stage and the middle stage of the reactor and promote the reaction, the temperature is raised by pressurization for charging the raw material into the reactor. By pre-cooling ethylene and vinyl acetate before charging, the polymerization proceeds at low temperatures in the first and middle stages, so that the state in which the polymerization of vinyl acetate progresses preferentially can be maintained. Moreover, it is preferable to make the temperature difference between the bottom temperature and the peak temperature in the latter stage smaller than the temperature difference in the middle stage.

In GPC-FTIR, the absorbance I attributed to the methylene group _(-CH2-) was measured as an absorption at 2928 cm ^-1 , and the absorbance I attributed to the carbonyl group _(-C=O) was measured as an absorption at 1741 cm ^-1 . measured as Specific measurement by GPC-FTIR can be performed by the method described in Examples.

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

The average value Q is defined as the average value of the absorbance ratios ( _Ii(-CH3) /Ii _(-CH2-) ) of 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 absorbance I _i(-CH2-) attributed to the methylene group and the absorbance I i( _-CH3 ) attributed to the methyl group. , and indicates the content ratio of methyl groups at each molecular weight of the ethylene-vinyl acetate copolymer. Since the terminal of the ethylene-vinyl acetate copolymer has a high ratio of termination with a methyl group, a low methyl group content means a small number of branches. Therefore, a low average absorbance ratio (I _i(-CH3) /I _i(-CH2-) ) means that the copolymer of the present embodiment has a small number of branches.

The absorbance ratio ( _Ii(-CH3) /Ii _(-CH2-) ) obtained as described above is the number of carbon atoms in " _-CH3 " per 1000 carbon atoms in " _-CH2- ". It indicates quantity. Further, the average value Q means the average value of carbon atoms in "--CH ₃ " per 1000 carbon atoms in "--CH ₂ --" in the half-width region of the molecular weight distribution.

In the present embodiment, the average value Q is 20.0≤Q≤26.0, preferably 21.0≤Q≤25.0, more preferably 21.5≤Q≤24.0. be. When the average value Q is within the above range, the entanglement of molecular chains in the ethylene-vinyl acetate copolymer is reduced, so that the stiffness and transparency of the film are improved. Regarding the entanglement of molecular chains in the ethylene-vinyl acetate copolymer, entanglement derived from vinyl acetate units and entanglement derived from branching can be considered, but from the viewpoint of improving the stiffness of the film, the contribution of the average value Q is considered to be larger than

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

When 0.50 mol% or more of propylene is added, hydrogen abstraction from the molecular chains in the ethylene-vinyl acetate resin increases and free radicals are generated. It is in.

Moreover, it is preferable to charge raw materials such as ethylene and vinyl acetate into the reactor from the front stage and the middle stage. Polymerization proceeds by charging raw materials such as ethylene and vinyl acetate from the reactor inlet, and a polymer layer and a gas layer coexist in the reactor. By adding new raw materials such as ethylene and vinyl acetate, the polymer layer and the gas layer are agitated and the polymerization is accelerated, so that the number of branches can be appropriately adjusted.

In addition, when raw materials such as ethylene and vinyl acetate are charged only from the inlet of the reactor, the amount of polymer obtained is small, which is not preferable from the viewpoint of productivity.

In GPC-FTIR, the absorbance I _(-CH2-) 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 . be done. Specific measurement by GPC-FTIR can be performed by the method described in Examples.

(Long chain branch)
The long-chain branching of the ethylene-vinyl acetate copolymer of the present embodiment determined by ¹³ C-NMR is preferably 0.30/100C or more and less than 0.55/100C, more preferably 0.31/100C. 0.50/100C or less, more preferably 0.32/100C or more and 0.45/100C or less. When the long-chain branching is within the above range, there is a tendency that thin film processability, stiffness, transparency, and durometer hardness of the resulting film are further improved.

Long chain branching can be adjusted by the type and amount of the chain transfer agent. In addition, the method for measuring long chain branching can follow the method described in Examples.

(heat of fusion)
The heat of fusion (ΔH) of the ethylene-vinyl acetate copolymer of the present embodiment determined by differential scanning calorimetry is preferably 53 J/g or more and 89 J/g or less, more preferably 64 J/g or more and 87 J/g. or less, more preferably 67 J/g or more and 85 J/g or less. When the heat of fusion is within the above range, there tends to be an excellent balance among thin film processability, stiffness, transparency, and durometer hardness of the resulting film.

The heat of fusion can be adjusted by VA concentration, molecular weight distribution, and the like. Moreover, the method for measuring the heat of fusion can follow the method described in the Examples.

(Melt flow rate)
The melt flow rate of the ethylene-vinyl acetate copolymer of the present 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, More preferably, it is 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, there is a tendency that the thin film workability, the stiffness of the resulting film, and the durometer hardness are further improved.

The method for adjusting the melt flow rate of the ethylene-vinyl acetate copolymer is not particularly limited, but examples thereof include a method of adjusting the reaction temperature and/or reaction pressure when polymerizing the ethylene-vinyl acetate copolymer. be done. More specifically, when polymerizing an ethylene-vinyl acetate copolymer, the melt flow rate of the ethylene-vinyl acetate copolymer tends to increase as the reaction temperature increases, and the ethylene-vinyl acetate copolymer tends to increase as the reaction pressure increases. The melt flow rate of copolymers tends to be small.

The melt flow rate can be measured according to 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, more preferably 13% by mass, based on the total amount of the ethylene-vinyl acetate copolymer. % or more and 19 mass % or less. When the content of the vinyl acetate unit is within the above range, there tends to be an excellent balance among thin film processability, stiffness of the resulting film, and durometer hardness.

The method for adjusting the content of vinyl acetate units is not particularly limited, but for example, the amount of vinyl acetate monomer added in the step of polymerizing the ethylene-vinyl acetate copolymer, the polymerization temperature, and the polymerization pressure may be adjusted as appropriate. etc.

The content of vinyl acetate units conforms to JIS K7192: 1999, and as a reference test method, prepare a calibration curve by saponification and potentiometric titration, and as a control test method, convert to vinyl acetate by infrared spectroscopy. can be measured in Specifically, it can be measured by the method described in Examples described later.

(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 still more preferably It is 81 mass % or more and 87 mass % or less. When the ethylene unit content is within the above range, thin film processability, stiffness of the resulting film, and durometer hardness tend to be further improved.

The ethylene-vinyl acetate copolymer of the present embodiment may contain monomer units other than ethylene units and vinyl acetate units. Other monomer units are not particularly limited, but include, for example, units derived from propylene or the like. Monomer units other than ethylene units and vinyl acetate units are 10.0 mol % or less, more preferably 5.0 mol, relative to ethylene, from the viewpoint of thin film processability, stiffness of the resulting film, and durometer hardness. % or less.

As the ethylene-vinyl acetate copolymer of the present embodiment, two or more ethylene-vinyl acetate copolymers may be dry-blended or melt-blended at any ratio. When two or more types of ethylene-vinyl acetate copolymers are used, the content of vinyl acetate units in the entirety of these resins is preferably within the above 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 in the presence of a polymerization initiator under heating under pressure. A chain transfer agent may be added to the polymerization system, if necessary.

The polymerization method of the ethylene-vinyl acetate copolymer is not particularly limited, but examples thereof include an autoclave method and a tubular method. Among these, it is preferable to use a tube reactor having a long annular 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 more and 350 MPa or less, more preferably 120 MPa or more and 280 MPa or less, and still more preferably 180 MPa or more and 270 MPa or less.

In addition, the reactor may have a plurality of points for feeding ethylene, vinyl acetate, and a polymerization initiator. In this embodiment, the temperature in the vicinity of each feed portion is once lowered by the introduction of raw materials and the like, and then the temperature inside the reactor rises again due to the heat of polymerization. After that, it is preferable to raise the temperature in the reactor again by the heat of polymerization. In the present embodiment, the raw material to be supplied is pressurized and introduced into the tube reactor, so that the temperature rises to some extent. However, it is preferable to pre-cool the raw material to be supplied. As a result, from the viewpoint of controlling the slope P, it is possible to preferentially proceed the polymerization of vinyl acetate in the upstream and preferentially proceed the polymerization of ethylene in the downstream where the molecular weight is high. The temperature of the raw material supplied to the reactor is preferably 60-80°C.

In the present embodiment, the front stage of the reactor refers to a position (entrance) 0% to 10% of the entire length of the reactor, and the middle stage of the reactor refers to a distance of 10% to 40% of the entire length of the reactor from the entrance. The rear stage of the reactor refers to a position 40% to 70% of the length of the entire reactor from the inlet.

Ethylene and vinyl acetate fed to the reactor may be gaseous or liquid, preferably gaseous.

The polymerization initiator is not particularly limited, and examples thereof 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-butylperoxyacetate, t-butylperoxypivalate, di-t-butylperoxide. etc.

Chain transfer agents include, but are not limited to, alcohols such as methanol, ethanol, normal propyl alcohol, isopropyl alcohol, normal butyl alcohol, isobutyl alcohol; ethane, propane, propylene, butane, 1-butene, 2-butene. alkanes or alkenes such as; Ketones such as isovaleraldehyde or aldehydes can be mentioned.

The ethylene-vinyl acetate copolymer polymerized as described above is preferably separated from the raw material and granulated into pellets by an extruder. For example, in the case of using a tubular system, the ethylene-vinyl acetate copolymer is separated from the raw materials while lowering the pressure with a high-pressure separator and a low-pressure separator, and the ethylene-vinyl acetate copolymer in a molten state is separated. Pelletization in an extruder is preferred.

In the high-pressure separator and the low-pressure separator, the molten ethylene-vinyl acetate copolymer and unreacted gas such as raw material ethylene gas and vinyl acetate gas exist as a gas-liquid mixed fluid. Unreacted gas may be recovered from the top of each separator vessel and reused in the polymerization.

After pelletizing the ethylene-vinyl acetate copolymer in the extruder, it is preferred to blow dry air into the silo in which the pellets are stored.

The ethylene-vinyl acetate copolymer of the present embodiment contains, if necessary, known additives such as antioxidants, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, and coloring pigments. It's okay.

Examples of antioxidants include, but are not limited to, 2,6-di-t-butyl-4-methylphenol, pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate], phenolic antioxidants such as octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate; tris(2,4-di-t-butylphenyl) phosphite, tetrakis ( Phosphorus antioxidants such as 2,4-di-t-butylphenyl)-4,4-biphenylene-diphosphonite; 6-tert-butyl-4-[3-(2,4,8,10- Phosphorus/phenolic antioxidants such as tetra-t-butyldibenzo[d,f][1,3,2]dioxaphosphepin-6-yloxy)propyl]-o-cresol; dilauryl-thio-dipropionate, etc. of sulfur-based antioxidants.

[Molded body]
The molded article of this embodiment contains the ethylene-vinyl acetate copolymer described above. The molded article of the present embodiment is not particularly limited, but can be obtained by, for example, injection molding, extrusion molding, or stretch molding, and can be suitably used for various purposes. Specific examples include, but are not limited to, artificial turf mats, automobile mat guards, mudguard covers, and drainage hoses. It can also be used as a fiber or the like.

[the film]
The film of this embodiment contains the ethylene-vinyl acetate copolymer described above. Examples of film manufacturing methods include T-die molding, inflation molding, calender molding, scaife molding, and the like. In particular, inflation molding or T-die extrusion molding is preferred.

The film of the present embodiment can be suitably used as an agricultural polyolefin film, a packaging film, and a flexible container exterior film, and among these, it can be suitably used as a packaging film. Specific examples include, but are not particularly limited to, food packaging films, food wrap films, overlap films, shrinkable overlap films, and sealant films.

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, more preferably 10 to 200 μm.

In addition, the film of the present embodiment may have two or more layers, and may have a laminated structure having other layers in addition to the layer composed of the ethylene-vinyl acetate copolymer described above. good. The method for producing such a laminated film is not particularly limited, but examples thereof include a method of laminating films together by a lamination process, and a method of producing by a lamination extrusion process.

[Foam]
The foam of this embodiment contains the ethylene-vinyl acetate copolymer described above. The foam of the present embodiment is not particularly limited, but can be obtained, for example, by using foamed microparticles, and can be suitably used for various purposes.

Hereinafter, the present invention will be described more specifically using examples and comparative examples. The present invention is by no means limited by the following examples.

[GPC-IR measurement (gradient P of carbonyl group)]
GPC-IR measurement (gradient P of carbonyl group) was performed under the following conditions. As sample pretreatment, the sample was weighed, a solvent (0.05%-BHT-added TCE) was added, and the sample was shaken and dissolved at 110° C. for 1 hour. The molecular weight was calibrated by a cubic approximation curve using Tosoh standard polystyrene. 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 from 2850 to 2940 cm ^-1 using SEC-FTIR software (manufactured by Thermo Nicolet). Also, the vinyl acetate content was calculated by preparing a calibration curve from the absorbance ratio of C═O stretching vibration at 1741 cm ⁻¹ and CH ₂ stretching vibration at 2928 cm ⁻¹ using EVA of known composition.

The slope P of the carbonyl group was measured by GPC (apparatus: HLC-8121GPC/HT manufactured by Tosoh Corporation) and obtained using (Avatar 370 manufactured by Thermo Nicolet) as a detector, and the vinyl acetate ratio (VAc ratio) in each molecular weight range was determined. Plots were obtained from square-law approximation straight lines. In addition, the elution curve of GPC-IR is a component amount (d (W) / d ( The value of logM)) was determined to be 1/2A and the VAc ratio for the molecular weight range of 1/2A.
(Measurement condition)
GPC device: HLC-8121GPC/HT (manufactured by Tosoh)
FT-IR device: Avatar 370 (manufactured by Thermo Nicolet)
Column: TSKgel GMHHR-H (20) HT (7.9 mm ID × 30 cm) × 2 (manufactured by Tosoh)
Eluent: Tetrachlorethylene (Special grade manufactured by Fujifilm Wako Pure Chemical Industries)
Flow rate: 0.7mL/min
Sample concentration: 2.0 mg/mL
Injection volume: 0.3 mL
Column temperature: 110°C
Detector temperature: 110°C
Measurement wavenumber: 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-) ) at each molecular weight was calculated, and in the half-width region, the logarithm of each molecular weight M _i (M _i ) and the absorbance ratio (I _i(-C=O) /I _i(-CH2-) ) was represented by an approximate linear relational expression by the least squares method (see FIG. 1). A slope P was obtained from the approximate linear relational expression thus obtained.

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

[GPC-IR measurement (average value Q of terminal methyl group)]
GPC-IR measurement (average value Q of terminal methyl groups) was performed under the following conditions. As sample pretreatment, the sample was weighed, the solvent ortho-dichlorobenzene was added, and the sample was shaken and dissolved at 140° C. for 90 minutes. Molecular weight calibration is performed at 12 points in the range of 1,050 to 20,600,000 in the MW (Molecular weight) of standard polystyrene manufactured by Tosoh Corporation, and the MW of each standard polystyrene is multiplied by a coefficient of 0.43. The weight average molecular weight (Mw) and the number average molecular weight (Mn) were determined by plotting the elution time and polyethylene equivalent molecular weight, and creating a primary calibration straight line from the polyethylene equivalent molecular weight.

The amount of terminal methyl groups was measured by Polymer Char's Composition Calibration Kit (Octene) CH ₃ /1000c: 6 points in the range of 2.6 to 45.9 to create a calibration curve, and GPC (apparatus: Polymer Char's GPC -IR), and FT-IR (IR5 manufactured by Polymer Char) was used as a detector.

In addition, the amount of terminal methyl groups is 1/2 the amount of the component (d (W) / d (log M )) was determined to be 1/2A, and the average value Q of the amount of CH ₃ per 1000c was calculated for the molecular weight range of 1/2A.
(Measurement condition)
Apparatus: GPC-IR manufactured by Polymer Char
Detector: IR5 manufactured by Polymer Char
Column: UT-807 (1 piece) manufactured by Showa Denko K.K. and GMHHR-H(S)HT (2 pieces) manufactured by Tosoh Corporation are connected in series and used Mobile phase: ortho-dichlorobenzene 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 (manufactured by Polymer Char) software. An average value Q was obtained by calculating the average of the absorbance ratios (I _i(-CH3) /I _i(-CH2-) ) in the range of values.

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

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

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

[ ¹³ C-NMR measurement (long chain branching)]
¹³ C-NMR measurement (long chain branching) was performed under the following conditions. As sample pretreatment, the sample was weighed, the solvent ortho-dichlorobenzene was added, and the sample was shaken and dissolved at 140° C. for 180 minutes. Long-chain branching was measured using a Bruker AVANCE 500HD nuclear magnetic resonance spectrometer with a methylene carbon signal of 29.9 ppm as a reference.

The long-chain branching ratio was calculated from the area intensity ratio of the methylene carbon signal and the long-chain branching signal observed in the ¹³ C-NMR spectrum measured above. The ratio of long-chain branching is the ratio of pentyl branching or more branching, and is around 22.65 ppm in the ¹³ C-NMR spectrum (Attribution of branched species of low-density polyethylene by C-13 NMR, Analytic Kagaku, Atsuo Nishimura et al., P774 (29) 1980) was obtained from the ratio when the intensity of the methylene carbon signal was taken as 100.
(Measurement condition)
Measuring device: AVANCE-500HD manufactured by Bruker
Observation nucleus: ^13C
Observation frequency: 125.77MHz
Pulse width: 5.0 μsec
PD: 5 seconds
Measurement temperature: 120°C
Accumulated times: 8,000 times Standard: PE (-eee-) signal at 29.9 ppm
Solvent: ortho-dichlorobenzene _- d4
Sample concentration: 5 wt/vol%
Melting temperature: 140°C

[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 Examples and Comparative Examples was weighed as a sample and placed in an aluminum sample pan. The aluminum sample pan was fitted with an aluminum cover and placed in a differential scanning calorimeter. While purging nitrogen at a flow rate of 20 mL/min, the measurement sample and the reference sample were held at 0° C. for 1 minute, then heated to 150° C. at a rate of 200° C./min, and held at 150° C. for 5 minutes, After the temperature was lowered at a rate of 10 ° C./min and held at 0 ° C. for 5 minutes, the heat of fusion (ΔH ).

[Thin film workability]
Hokushin Sangyo Co., Ltd. T-die film forming machine, HM40N (screw diameter 40 mm, die width 300 mm, die gap 0.6 mm), cylinder temperature 230 ° C., die temperature 230 ° C., extrusion amount 5 kg / hour, take-up speed 10 m / A T-die molded film having a thickness of 35 μm was formed for 30 minutes.

The sum of the neck-in distances for both ears of the obtained film was defined as the neck-in (mm) width, and the ratio to the die width and the presence or absence of film breakage were evaluated according to the following criteria.
○ (excellent): neck-in less than 25% △ (good): neck-in 25% or more and less than 30% × (improper): neck-in 30% or more or film breakage

[Transparency measurement (Haze)]
An aluminum plate with a thickness of 0.1 mm was placed on a smooth iron plate with a thickness of 5 mm, and a polyethylene terephthalate film (Lumirror manufactured by Toray Industries, Inc.) with a thickness of 50 μm was placed on the aluminum plate. A mold having a length of 200 mm, a width of 200 mm, and a thickness of 50 μm was placed on this, and the ethylene-vinyl acetate copolymers obtained in Examples and Comparative Examples were put into the mold. Then, a polyethylene terephthalate film similar to that described above, an aluminum plate similar to that described above, and an iron plate similar to that described above were further placed thereon.

This is placed in a compression molding machine (SFA-37 manufactured by Shindo Kinzoku Kogyo Co., Ltd.) whose temperature is adjusted to 180 ° C., preheated at 180 ° C. and 0.1 MPa for 180 seconds, and then air is removed for 5 seconds (10 MPa). Pressurization was performed at 180° C. and 15 MPa for 120 seconds.

After the completion of pressurization, the sample was taken out, and 5 seconds after taking it out, it was placed in a compression molding machine (SFA-37 manufactured by Shindo Kinzoku Kogyo Co., Ltd.) whose temperature was adjusted to 25 ° C., and pressurized at 25 ° C. and 10 MPa for 300 seconds. A press sheet was produced by cooling while cooling. After cooling, the press sheet taken out from the mold was allowed to stand in an environment with a temperature of 23° C. and a humidity of 50% for 24 hours or more.

The thickness of the press sheet obtained as described above is measured using a constant pressure thickness gauge (manufactured by TECLOCK CORPORATION, model PG-02, minimum display amount 0.001 mm), and the thickness of the 50 μm portion of the press sheet was selected. Then, in a portion having a thickness of 50 μm, a Haze value was measured according to ASTM D1003 using a HAZE METER HM-150 manufactured by Murakami Color Research Laboratory. The smaller the haze value, the better the transparency.

[Film stiffness (2% modulus)]
Blown 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), 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. of ethylene-vinyl acetate copolymer resin film is formed, and the modulus when the strain of the film reaches 2% in accordance with JIS K 7127 in the direction (MD) and the direction (TD) perpendicular to the resin flow. It was obtained by measuring the value.

[Durometer hardness]
An aluminum plate with a thickness of 0.1 mm was placed on a smooth iron plate with a thickness of 5 mm, and a polyethylene terephthalate film (Lumirror manufactured by Toray Industries, Inc.) with a thickness of 50 μm not coated with cellophane was placed on the aluminum plate. . A mold having a length of 200 mm, a width of 200 mm, and a thickness of 3.1 mm is placed on this, and 130 g of ethylene-vinyl acetate copolymer resin is placed in the mold. An aluminum plate similar to the above was placed, and an iron plate similar to the above was placed.

This was placed in a compression molding machine (SFA-37 manufactured by Shindo Kinzoku Kogyo Co., Ltd.) whose temperature was adjusted to 180 ° C., preheated at 180 ° C. and 0.1 MPa for 180 seconds, and then air was removed (10 MPa) for 5 seconds. C. and 15 MPa for 120 seconds.

After the completion of pressurization, the sample was taken out, and 5 seconds after taking it out, it was placed in a compression molding machine (SFA-37 manufactured by Shindo Kinzoku Kogyo Co., Ltd.) whose temperature was adjusted to 25 ° C., and pressurized at 25 ° C. and 10 MPa for 300 seconds. A press sheet was produced by cooling while cooling. After cooling, the press sheet taken out from the mold was allowed to stand in an environment with 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 according to JIS-K7215 using a HARDNESS TESTER manufactured by Toyo Seiki.

[Example 1]
Polymerization was carried out using a tubular reactor with multiple feed ports. Specifically, ethylene and vinyl acetate were cooled to 70° C. and then introduced into the reactor from the feed port on the front stage side of the tubular reactor, followed by heating in the reactor and then t-butyl as a polymerization initiator. -Peroxy-2-ethylhexanoate was introduced to initiate polymerization. Subsequently, ethylene and vinyl acetate precooled to 70° C. were additionally introduced at the feed port on the middle stage side of the tubular reactor, and then t-butyl-peroxy-2- Ethylhexanoate and di-t-butyl peroxide were introduced. Incidentally, as a whole, the amount of vinyl acetate was set to 7 mol % with respect to ethylene.

The average polymerization temperature in the tubular reactor was 224° C., and the polymerization pressure was 264 MPa. The polymerization temperature of the tubular reactor was adjusted so that the peak top temperature of the front stage was 223°C, the peak top temperature of the middle stage was 255°C, and the peak top temperature of the rear stage was 275°C. In addition, 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 side was 93°C. The difference between the temperature and the peak top temperature was 44°C.

The unpurified ethylene-vinyl acetate copolymer discharged from the tubular reactor was introduced into a high-pressure separator to separate unreacted gas and the like. Subsequently, the ethylene-vinyl acetate copolymer discharged from the high-pressure separator was introduced into the low-pressure separator, and the remaining unreacted gas and the like were separated to obtain a molten ethylene-vinyl acetate copolymer.

The resulting molten ethylene-vinyl acetate copolymer was fed to an extruder and pelletized to obtain pellets of the ethylene-vinyl acetate copolymer. The physical properties and properties of the obtained ethylene-vinyl acetate copolymer were measured by the methods described above. Table 1 shows the measurement results.

[Example 2]
Ethylene and vinyl acetate were cooled at 70° C. and then introduced into the reactor from the feed port on the front stage side of the tubular reactor. Subsequently, after heating in the reactor, t-butyl-peroxy-2- Ethylhexanoate was introduced to initiate polymerization. Subsequently, ethylene and vinyl acetate precooled to 70° C. were additionally introduced at the feed port on the middle stage side of the tubular reactor, and then t-butyl-peroxy-2- Ethylhexanoate and di-t-butyl peroxide were introduced. Incidentally, as a whole, the amount of vinyl acetate was set to 7 mol % with respect to ethylene.

The average polymerization temperature in the tubular reactor was 229° C., and the polymerization pressure was 264 MPa. The polymerization temperature of the tubular reactor was adjusted so that the peak top temperature of the front stage was 240°C, the peak top temperature of the middle stage was 254°C, and the peak top temperature of the rear stage was 277°C. In addition, 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 side was 79°C. An ethylene-vinyl acetate copolymer of Example 2 was obtained in the same manner as in Example 1 except that the difference between the temperature and the peak top temperature was 47°C. Table 1 shows the measurement results.

[Example 3]
Ethylene and vinyl acetate were cooled at 70° C. and then introduced into the reactor from the feed port on the front stage side of the tubular reactor. Subsequently, after heating in the reactor, t-butyl-peroxy-2- Ethylhexanoate was introduced to initiate polymerization. Subsequently, ethylene and vinyl acetate precooled to 70° C. were additionally introduced at the feed port on the middle stage side of the tubular reactor, and then t-butyl-peroxy-2-ethylhexanoate was used as a polymerization initiator from the middle stage side. Art was introduced, and t-butyl-peroxy-2-ethylhexanoate and di-t-butyl peroxide were introduced from the latter stage. Incidentally, as a whole, the amount of vinyl acetate was set to 6 mol % with respect to ethylene.

The average polymerization temperature in the tubular reactor was 211° C., and the polymerization pressure was 264 MPa. The polymerization temperature of the tubular reactor was adjusted so that the peak top temperature of the front stage was 223°C, the peak top temperature of the middle stage was 230°C, and the peak top temperature of the rear stage was 260°C. In addition, 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 side was 68°C. An ethylene-vinyl acetate copolymer of Example 3 was obtained in the same manner as in Example 1 except that the difference between the temperature and the peak top temperature was 50°C. Table 1 shows the measurement results.

[Example 4]
Ethylene and vinyl acetate were cooled at 70° C. and then introduced into the reactor from the feed port on the front stage side of the tubular reactor. Subsequently, after heating in the reactor, t-butyl-peroxy-2- Ethylhexanoate was introduced to initiate polymerization. Subsequently, ethylene and vinyl acetate precooled to 70° C. were additionally introduced at the feed port on the middle stage side of the tubular reactor, and then t-butyl-peroxy-2- Ethylhexanoate and di-t-butyl peroxide were introduced. Incidentally, as a whole, the amount of vinyl acetate was set to 5 mol % with respect to ethylene.

The average polymerization temperature in the tubular reactor was 220° C., and the polymerization pressure was 264 MPa. The polymerization temperature of the tubular reactor was adjusted so that the peak top temperature of the front stage was 216°C, the peak top temperature of the middle stage was 247°C, and the peak top temperature of the rear stage was 275°C. In addition, 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 side 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 side was 89°C. An ethylene-vinyl acetate copolymer of Example 4 was obtained in the same manner as in Example 1 except that the difference between the temperature and the peak top temperature was 45°C. Table 1 shows the measurement results.

[Example 5]
Ethylene and vinyl acetate were cooled at 70° C. and then introduced into the reactor from the feed port on the front stage side of the tubular reactor. Subsequently, after heating in the reactor, t-butyl-peroxy-2- Ethylhexanoate was introduced to initiate polymerization. Subsequently, ethylene and vinyl acetate precooled to 70° C. were additionally introduced at the feed port on the middle stage side of the tubular reactor, and then t-butyl-peroxy-2-ethylhexanoate was used as a polymerization initiator from the middle stage side. Art was introduced, and t-butyl-peroxy-2-ethylhexanoate and di-t-butyl peroxide were introduced as polymerization initiators from the latter stage. Incidentally, as a whole, the amount of vinyl acetate was set to 8.7 mol % with respect to ethylene.

The average polymerization temperature in the tubular reactor was 214° C., and the polymerization pressure was 264 MPa. The polymerization temperature of the tubular reactor was adjusted so that the peak top temperature of the front stage was 205°C, the peak top temperature of the middle stage was 230°C, and the peak top temperature of the rear stage was 270°C. In addition, 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 side was 77°C. An ethylene-vinyl acetate copolymer of Example 5 was obtained in the same manner as in Example 1 except that the difference between the temperature and the peak top temperature was 59°C. Table 1 shows the measurement results.

[Example 6]
Ethylene and vinyl acetate were cooled at 70° C. and then introduced into the reactor from the feed port on the front stage side of the tubular reactor. Subsequently, after heating in the reactor, t-butyl-peroxy-2- Ethylhexanoate was introduced to initiate polymerization. Subsequently, ethylene and vinyl acetate precooled to 70° C. were additionally introduced at the feed port on the middle stage side of the tubular reactor, and then t-butyl-peroxy-2- Ethylhexanoate and di-t-butyl peroxide were introduced. Incidentally, as a whole, the amount of vinyl acetate was set to 7 mol % with respect to ethylene.

The average polymerization temperature in the tubular reactor was 234° C., and the polymerization pressure was 236 MPa. The polymerization temperature of the tubular reactor was adjusted so that the peak top temperature of the front stage was 243°C, the peak top temperature of the middle stage was 255°C, and the peak top temperature of the rear stage was 267°C. In addition, 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 side was 79°C. An ethylene-vinyl acetate copolymer of Example 6 was obtained in the same manner as in Example 1 except that the difference between the temperature and the peak top temperature was 36°C. Table 1 shows the measurement results.

[Comparative Example 1]
Ethylene, vinyl acetate, and propylene were introduced into the reactor from the feed port on the front stage side of the tubular reactor, followed by introduction of t-butyl-peroxy-2-ethylhexanoate as a polymerization initiator after heating in the reactor. to initiate polymerization. Subsequently, ethylene and vinyl acetate were additionally introduced at the feed port on the middle stage side of the tubular reactor, followed by t-butyl-peroxy-2-ethylhexanoate as a polymerization initiator from the middle stage side and the latter stage side. Di-t-butyl peroxide was introduced. As a whole, the amount of vinyl acetate was 4 mol % relative to ethylene, and the amount of propylene was 0.5 mol % relative to ethylene.

The average polymerization temperature in the tubular reactor was 234° C., and the polymerization pressure was 264 MPa. The polymerization temperature of the tubular reactor was adjusted so that the peak top temperature of the front stage was 240°C, the peak top temperature of the middle stage was 260°C, and the peak top temperature of the rear stage was 270°C. In addition, the difference between the bottom temperature and the peak top temperature before and after introducing ethylene, vinyl acetate, and the polymerization initiator at the feed port on the middle side was 65°C. An ethylene-vinyl acetate copolymer of Comparative Example 1 was obtained in the same manner as in Example 1 except that the difference between the temperature and the peak top temperature was 35°C. Table 1 shows the measurement results.

[Comparative Example 2]
Ethylene, vinyl acetate, and propylene were introduced into the reactor from the feed port on the front stage side of the tubular reactor, followed by introduction of t-butyl-peroxy-2-ethylhexanoate as a polymerization initiator after heating in the reactor. to initiate polymerization. Subsequently, ethylene and vinyl acetate were additionally introduced at the feed port on the middle stage side of the tubular reactor, followed by t-butyl-peroxy-2-ethylhexanoate as a polymerization initiator from the middle stage side and the latter stage side. Di-t-butyl peroxide was introduced. As a whole, the amount of vinyl acetate was 4 mol % relative to ethylene, and the amount of propylene was 0.5 mol % relative to ethylene.

The average polymerization temperature in the tubular reactor was 238° C., and the polymerization pressure was 264 MPa. The polymerization temperature of the tubular reactor was adjusted so that the peak top temperature of the front stage was 235°C, the peak top temperature of the middle stage was 260°C, and the peak top temperature of the rear stage was 285°C. In addition, the difference between the bottom temperature and the peak top temperature before and after introducing ethylene, vinyl acetate, and the polymerization initiator at the feed port on the middle side was 70° C., and the bottom temperature before and after introducing the polymerization initiator at the feed port on the rear side. An 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 temperature and the peak top temperature was 46°C. Table 1 shows the measurement results.

[Comparative Example 3]
Ethylene and vinyl acetate were introduced into the reactor from the feed port on the front stage side of the tubular reactor, and then t-butyl-peroxy-2-ethylhexanoate was introduced as a polymerization initiator after heating in the reactor. , initiated the polymerization. Subsequently, ethylene and vinyl acetate were additionally introduced at the feed port on the middle stage side of the tubular reactor, and then t-butyl-peroxy-2-ethylhexanoate was introduced from the middle stage side as a polymerization initiator. Incidentally, as a whole, the amount of vinyl acetate was set to 14 mol % with respect to ethylene.

The average polymerization temperature in the tubular reactor was 200° C., and the polymerization pressure was 265 MPa. The polymerization temperature of the tubular reactor was adjusted so that the peak top temperature on the front stage side was 210°C and the peak top temperature on the middle stage side was 223°C. In addition, the ethylene of Comparative Example 3 was prepared 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 at the feed port on the middle side was 48°C. - A vinyl acetate copolymer was obtained. Table 1 shows the measurement results.

[Comparative Example 4]
Ethylene, vinyl acetate, and propylene were introduced into the reactor from the feed port on the front stage side of the tubular reactor, followed by introduction of t-butyl-peroxy-2-ethylhexanoate as a polymerization initiator after heating in the reactor. to initiate polymerization. Subsequently, ethylene and vinyl acetate were additionally introduced at the feed port on the middle-stage side of the tubular reactor, and then t-butyl-peroxy-2-ethylhexanoate was added as a polymerization initiator from the middle-stage side and the latter-stage side. introduced. Incidentally, as a whole, the amount of vinyl acetate was set to 7 mol % with respect to ethylene.

The average polymerization temperature in the tubular reactor was 225° C., and the polymerization pressure was 264 MPa. The polymerization temperature of the tubular reactor was adjusted so that the peak top temperature of the front stage was 233°C, the peak top temperature of the middle stage was 230°C, and the peak top temperature of the rear stage was 237°C. In addition, 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 side 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 side was 15°C. An 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 temperature and the peak top temperature was 16°C. Table 1 shows the measurement results.

[Comparative Example 5]
Ethylene and vinyl acetate were cooled at 70° C. and then introduced into the reactor from the feed port on the front stage side of the tubular reactor. Subsequently, after heating in the reactor, t-butyl-peroxy-2- Ethylhexanoate was introduced to initiate polymerization. Subsequently, ethylene and vinyl acetate precooled to 70° C. were additionally introduced at the feed port on the middle stage side of the tubular reactor, and then t-butyl-peroxy-2-ethylhexanoate was used as a polymerization initiator from the middle stage side. introduced art. Incidentally, as a whole, the amount of vinyl acetate was set to 7 mol % with respect to ethylene.

The average polymerization temperature in the tubular reactor was 224° C., and the polymerization pressure was 236 MPa. The polymerization temperature of the tubular reactor was adjusted so that the peak top temperature on the front stage side was 243°C and the peak top temperature on the middle stage side was 255°C. In addition, the ethylene of Comparative Example 5 was prepared 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 78°C. - A vinyl acetate copolymer was obtained. Table 1 shows the measurement results.

[Comparative Example 6]
Ethylene, vinyl acetate, and propylene were introduced into the reactor from the feed port on the front stage side of the tubular reactor, followed by introduction of t-butyl-peroxy-2-ethylhexanoate as a polymerization initiator after heating in the reactor. to initiate polymerization. Subsequently, ethylene and vinyl acetate precooled to 70° C. were additionally introduced at the feed port on the middle stage side of the tubular reactor, and then t-butyl-peroxy-2 was used as a polymerization initiator from the middle stage side and the latter stage side. - Ethylhexanoate was introduced. Incidentally, as a whole, the amount of vinyl acetate was set to 7 mol % with respect to ethylene.

The average polymerization temperature in the tubular reactor was 223° C., and the polymerization pressure was 236 MPa. The polymerization temperature of the tubular reactor was adjusted so that the peak top temperature of the front stage was 253°C, the peak top temperature of the middle stage was 246°C, and the peak top temperature of the rear stage was 235°C. In addition, 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 side was 29°C. An 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 temperature and the peak top temperature was 15°C. Table 1 shows the measurement results.

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

Claims (7)

11% by mass or more and 25% by mass or less of vinyl acetate units and ethylene units,
By GPC-FTIR, the molecular weight distribution, the absorbance I attributed to the methylene group for each molecular weight _(-CH2-) , the absorbance I attributed to the carbonyl group _(-C=O-) , and the absorbance I attributed to the methyl group When measuring I _(-CH3) and
The slope of the least-squares approximation 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 P is -1.0 ≤ P < 0.0,
The average value Q of the absorbance ratio (I _(-CH3) /I _(-CH2-) ) of each molecular weight M _i in the half-width region of the molecular weight distribution is 20.0 ≤ Q ≤ 26.0.
Ethylene-vinyl acetate copolymer. long chain branching determined from ¹³ C-NMR is 0.30/100 C or more and less than 0.55/100 C;
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 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,
the film. is for packaging,
A film according to claim 5 . having two or more layers,
A film according to claim 5 or 6.

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