JP2021017579A - Ethylene-vinyl acetate copolymer resin and film - Google Patents

Abstract

To provide an ethylene-vinyl acetate copolymer resin excellent in film-forming workability and excellent in exterior appearance when used as a film, and to provide the film using the same.SOLUTION: An ethylene-vinyl acetate copolymer resin comprises 3 mass% or more and 30 mass% or less of a vinyl acetate unit, wherein a ratio (AIR/BIR) between a ratio AIR of absorbance and a ratio BIR of absorbance is 0.80 or more and 1.40 or less. The ethylene-vinyl acetate copolymer resin can be obtained by a test method having the following steps (1) to (4): a step (1) of producing a test film under a predetermined production condition by using the ethylene-vinyl acetate copolymer resin; a step (2) of detecting a part A to be detected and a part B not to be detected, in the test film by using a film-testing apparatus under such conditions that a measurement interval is 0.1 mm and the longest diameter of an irregularity size to be detected is 0.2 mm or more and 1.0 mm or less; a step (3) of obtaining a ratio AIR between absorbance at 965 cm-1 and absorbance at 720 cm-1 through a microscopic infrared absorption measurement (a transmission method) to a core part in the part A; and a step (4) of obtaining a ratio BIR between absorbance at 965 cm-1 and absorbance at 720 cm-1 through the microscopic infrared absorption measurement (the transmission method) to the part B.SELECTED DRAWING: None

Description

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

Ethylene-vinyl acetate copolymer resin is used in a wide range of industrial fields because it has excellent performance such as transparency, flexibility, mechanical strength, electrical insulation, and durability, and is processed into a single layer or laminated film. It is widely used in agricultural polyolefin films, food packaging wraps, sealants, etc.

The required characteristics for the quality of various films are becoming stricter year by year, and in particular, reduction of fish eyes that impair the appearance is required. For example, in food packaging wraps and the like, it is used to quickly and tightly wrap a plurality of products at the same time, but the presence of fish eyes impairs the appearance of the obtained package and reduces the value of the product. Problems such as occur. Here, fisheye is one of the drawbacks of resin film, which is derived from the fact that if there is a gel-like substance in the film, the peripheral part becomes an uneven part and looks like a fisheye when viewed with the naked eye, a polarizing plate, or a microscope. Is.

As a method of inspecting whether the ethylene-vinyl acetate copolymer resin produces such a fish eye, there is a method of forming a film in a test form and inspecting it. When fish eyes are confirmed on the formed test film, various examinations such as resin kneading conditions are made to try to reduce the fish eyes, but there are fish eyes that disappear and fish eyes that do not disappear.

As a method for reducing fish eyes, it has been proposed that a radical polymerization inhibitor coexists in the reaction system when ethylene is polymerized under specific polymerization conditions in the presence of a radical polymerization inhibitor (for example, a patent). See Document 1).

JP-A-2003-342307

As shown in Patent Document 1, even if the fish eye is reduced, when a film of ethylene-vinyl acetate copolymer resin is formed and these are wound up, air pools are observed and there is a problem in appearance. Was. Further, even if the appearance is improved, there may be a problem that the processability at the time of film forming deteriorates (for example, stepping up of an extruder), and an ethylene-vinyl acetate copolymer resin having film forming processability is required. ..

Therefore, an object of the present invention is to provide an ethylene-vinyl acetate copolymer resin having excellent film-forming processability and an excellent appearance when made into a film, and a film using the same.

As a result of diligent studies to solve the above problems, the present inventors have found that the content of vinyl acetate unit is in a specific range, and the ratio of the absorbance ratio A _IR to the absorbance ratio B _{IR according} to a predetermined measurement method ( We have found that an ethylene-vinyl acetate copolymer resin having an A _IR / B _IR ) in a predetermined range can solve the above-mentioned problems, and have completed the present invention.

That is, the present invention is as follows.
[1]
An ethylene-vinyl acetate copolymer resin containing 3% by mass or more and 30% by mass or less of vinyl acetate units.
The ethylene-vinyl acetate copolymer resin has a ratio (A _IR / B _IR ) of the absorbance ratio A _IR to the absorbance ratio B _IR obtained by the test method having the following steps (1) to (4). An ethylene-vinyl acetate copolymer resin having a ratio of 0.80 or more and 1.40 or less.
Step (1): A step of preparing a test film using the ethylene-vinyl acetate copolymer resin under the following production conditions. Step (2): The test film is measured at intervals of 0 using a film inspection device. Step of detecting the detected portion A and the undetected portion B under the condition of 1 mm and the maximum unevenness detection size of 0.2 mm or more and 1.0 mm or less Step (3): Microinfrared of the core portion of the portion A absorption measurement and the absorbance of the (transmission method) by 965 cm ^-1, step step (4) determining the ratio a _IR absorbance of 720 cm ^-1: absorbance of the partial microscopic infrared absorption measurement of B (transmission method) by 965 cm ^-1 and a step of determining the ratio B _IR absorbance of 720 cm ^-1 <Preparation conditions>
A test film having a cylinder temperature of 140 ° C. and a die temperature of 140 ° C. is kneaded using a single-screw vertical extruder, and a test film having a thickness of 50 μm and a width of 100 mm is obtained by a T-die method at a take-up speed of 4 m / min. A filter is not used at the screw outlet of the single-screw vertical extruder, and a test film is prepared by sandwiching only the breaker plate.
[2]
The ethylene-vinyl acetate copolymer resin according to the above [1], wherein the portion A is 1 piece / 5 m ² or more and 100 pieces / 5 m ² or less in the test film.
[3]
Among the parts A, the portion A _b having irregularities having a maximum major axis of 0.4 mm or more and 1.0 mm or less is 1 piece / 5 m ² or more and 40 pieces / 5 m ² or less in the test film. Alternatively, the ethylene-vinyl acetate copolymer resin according to [2].
[4]
The ethylene-vinyl acetate copolymer resin according to any one of [1] to [3] above, wherein the ethylene-vinyl acetate copolymer resin has a melt flow rate of 0.5 g / 10 min or more and 4.0 g / 10 min or less. Copolymer resin.
[5]
The ethylene-vinyl acetate copolymer resin according to any one of [1] to [4] above, wherein the ethylene-vinyl acetate copolymer resin has a molecular weight distribution (Mw / Mn) of 8.0 or less.
[6]
A film containing the ethylene-vinyl acetate copolymer according to any one of the above [1] to [5].
[7]
A packaging film containing the ethylene-vinyl acetate copolymer according to any one of [1] to [5].
[8]
A laminated film containing the ethylene-vinyl acetate copolymer according to any one of [1] to [5].
[9]
A film containing an ethylene-vinyl acetate copolymer resin containing 3% by mass or more and 30% by mass or less of vinyl acetate units.
The film is obtained by the test method having the following steps (2 ') - (4'), the ratio of _IR 'ratio B of _IR and absorbance' ratio A absorbance (A _'IR / B' _IR) is 0 A film that is .80 or more and 1.40 or less.
Step (2'): A portion A and detection of the film using a film inspection device under the conditions that the measurement interval is 0.1 mm and the unevenness detection size is 0.2 mm or more and 1.0 mm or less in the longest diameter. step step (3 ') for detecting a portion B which are not: the absorbance of the 965 cm ^-1 by microscopic infrared absorption measurement of the nuclear portion (transmission method) of the portion a, the ratio a of the absorbance at 720 cm ^-1' obtaining a _IR step (4 '): and the absorbance of 965 cm ^-1 by microscopic infrared absorption measurement (transmission method) of the portion B, the ratio B of the absorbance at 720 cm ^-1' obtaining a _IR

According to the present invention, it is possible to provide an ethylene-vinyl acetate copolymer resin having excellent film-forming processability and excellent appearance when made into a film, and a film using the same.

FIG. 1 is an example of a spectrum obtained by microinfrared absorption measurement.

Hereinafter, embodiments for carrying out the present invention (hereinafter, referred to as “the present embodiment”) will be described in detail. The present invention is not limited to the following description, and can be implemented with various modifications within the scope of the gist thereof.

[Ethylene-vinyl acetate copolymer resin]
The ethylene-vinyl acetate copolymer resin of the present embodiment contains 3% by mass or more and 30% by mass or less of vinyl acetate units.
The ethylene-vinyl acetate copolymer resin of the present embodiment is obtained by the test method having the following steps (1) to (4), and is the ratio of the absorbance ratio A _IR to the absorbance ratio B _IR (A _IR / B). _IR ) (hereinafter, also simply referred to as “ratio (A _IR / B _IR )”) is 0.80 or more and 1.40 or less.
Step (1): A step of preparing a test film using the ethylene-vinyl acetate copolymer resin under the following production conditions. Step (2): The test film is measured at intervals of 0 using a film inspection device. Step of detecting the detected portion A and the undetected portion B under the condition of 1 mm and the maximum unevenness detection size of 0.2 mm or more and 1.0 mm or less Step (3): Microinfrared of the core portion of the portion A absorption measurement and the absorbance of the (transmission method) by 965 cm ^-1, step step (4) determining the ratio a _IR absorbance of 720 cm ^-1: absorbance of the partial microscopic infrared absorption measurement of B (transmission method) by 965 cm ^-1 and a step of determining the ratio B _IR absorbance of 720 cm ^-1 <Preparation conditions>
A test film having a cylinder temperature of 140 ° C. and a die temperature of 140 ° C. is kneaded using a single-screw vertical extruder, and a test film having a thickness of 50 μm and a width of 100 mm is obtained by a T-die method at a take-up speed of 4 m / min. A filter is not used at the screw outlet of the single-screw vertical extruder, and a test film is prepared by sandwiching only the breaker plate.

The above ethylene-vinyl acetate copolymer resin is excellent in film forming processability and excellent in appearance when made into a film. Regarding the film-forming processability, more specifically, it is excellent in melt elongation, suppresses an increase in resin pressure due to an extruder, and further suppresses a decrease in film width and film breakage due to unevenness such as fish eyes. Can be done.

The ethylene-vinyl acetate copolymer resin of the present embodiment is a copolymer containing an ethylene unit and a vinyl acetate unit.

(VA content)
The ethylene-vinyl acetate copolymer resin of the present embodiment has a vinyl acetate unit content (hereinafter, also referred to as “VA content”) from the viewpoint of film-forming processability and appearance when formed into a film. 3.0% by mass or more and 30.0% by mass or less, preferably 4.0% by mass or more and 25.0% by mass or less, more preferably 4 with respect to the total amount of the ethylene-vinyl acetate copolymer resin. It is 8.8% by mass or more and 20.0% by mass or less.

As a method of adjusting the VA content to 3.0% by mass or more and 30.0% by mass or less, the amount of vinyl acetate monomer added in the step of polymerizing the ethylene-vinyl acetate copolymer resin, the polymerization temperature, and the polymerization pressure are adjusted. It is possible to make appropriate adjustments.

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

In the ethylene-vinyl acetate copolymer resin of the present embodiment, the content of the ethylene unit is based on the total amount of the ethylene-vinyl acetate copolymer resin from the viewpoint of film-forming processability and appearance when formed into a film. It is preferably 70.0% by mass or more and 97.0% by mass or less, more preferably 75.0% by mass or more and 96.0% by mass or less, and further preferably 80.0% by mass or more and 95.2% by mass or less. It is as follows.

The ethylene-vinyl acetate copolymer resin of the present embodiment may contain a monomer unit other than ethylene and vinyl acetate. The other monomer is not particularly limited, and examples thereof include propylene and the like. The content of the other monomer unit is preferably 30% by mass or less, more preferably 15% by mass or less, and further preferably 5% by mass or less.

As the ethylene-vinyl acetate copolymer resin of the present embodiment, two or more kinds of ethylene-vinyl acetate copolymer resins can be dry-blended or melt-blended at an arbitrary ratio. When two or more kinds of ethylene-vinyl acetate copolymer resins are used, it is preferable that the VA content and the like in the whole of these resins are in the above range.

<Ratio (A _IR / B _IR )>
The ethylene-vinyl acetate copolymer resin of the present embodiment has a ratio (A _IR / B _IR ) of 0.80 or more and 1.40 or less. By including the ratio (A _IR / B _IR ) in the above range, the ethylene-vinyl acetate copolymer resin is excellent in film-forming processability and excellent in appearance when made into a film. The ratio (A _IR / B _IR ) is preferably 0.82 or more and 1.30 or less, more preferably 0.84 or more, from the viewpoint of further improving the film-forming processability and the appearance of the film. It is 20 or less.

In general, the fish eye generated when the ethylene-vinyl acetate copolymer resin is actually formed can be eliminated by optimizing the kneading conditions of the resin, and can be eliminated by the optimization. There are two types of things that cannot be done. As a result of diligent studies for the purpose of suppressing the formation of fish eyes of a type that cannot be eliminated by optimizing the kneading conditions of the resin, the present inventor of the ethylene-vinyl acetate copolymer resin of the portion A. Absorbance ratio A _IR (965 cm ^-1 / 720 cm ^-1 ) and partial B absorbance ratio B _IR (965 cm ^-1 / 720 cm ^-1 ) both tend to increase as the VA content increases, but their ratios It was found that (A _IR / B _IR ) mainly depends on factors other than the VA content, which will be described later. Further, the present inventor controls the ratio (A _IR / B _IR ) to eliminate the resin even if the kneading conditions of the resin are optimized while maintaining a sufficiently good appearance as a film. We have found that it is possible to suppress the production of types of fish eyes that cannot be achieved. That is, by controlling the absorbance ratio ratio (A _IR / B _IR ) within a predetermined range, the present inventor optimizes the kneading conditions of the resin while maintaining a sufficiently good appearance as a film. It was found that the formation of fish eyes of a type that cannot be eliminated even if they are converted can be suppressed. The present inventor has conventional ethylene - In vinyl acetate copolymer resin, part A absorbance ratio A _IR of (965cm ^-1 / 720cm ^-1) is part B of the absorbance ratio ^{_{B IR (965cm -1 / 720cm -1}} ) That is, the absorbance ratio ratio (A _IR / B _IR ) tends to be larger than that of the above, so that many fish eyes that do not disappear even by optimizing the kneading conditions of the resin are generated, and the film forming processability is easy. And it is presumed that the appearance when made into a film tends to be inferior.

When the absorbance ratio ratio (A _IR / B _IR ) is 1.40 or less, the formation of the fish eye is reduced, the pressure of the extruder during kneading and the puncture during inflation molding are less likely to occur, and ethylene is further produced. -The melt elongation (ME) of the vinyl acetate copolymer resin is also improved, and it becomes easier to process into a thin film, so that the film forming processability is excellent. Further, when the ratio (A _IR / B _IR ) is 0.80 or more, the molten resin is appropriately heated or sheared to be homogeneous during kneading, so that the appearance of the film is excellent.

The peak of 965 cm ^{-1 in} the infrared absorption spectrum is due to the absorption of transalkenes, but as a process of producing transalkenes, long-term retention in a low-pressure separator or the like in the production process of ethylene-vinyl acetate copolymer resin It is presumed that this is due to thermal deterioration (deacetic acid reaction) caused by such factors. It is considered that the produced transalkene undergoes a cross-linking reaction when exposed to a higher temperature, and becomes a gel that causes fish eyes that does not disappear even when the kneading conditions are optimized. Therefore, the ratio (A _IR / B _IR ) is adjusted, that is, the amount of transalkene of the portion A in the ethylene-vinyl acetate copolymer resin is relatively reduced, and the absorbance ratio A _IR of the portion A is changed to the absorbance of the portion B. By setting the ratio to the same level as B _IR , the formation of the above gel can be suppressed. As a result, it is considered that the formation of fish eyes that do not disappear even by optimizing the kneading conditions and the like can be suppressed. However, the factors are not limited to this.

As a method of controlling the absorbance ratio ratio (A _IR / B _IR ), it is important to keep the state of the molten resin constant in the low pressure separator in the step of polymerizing the ethylene-vinyl acetate copolymer resin. .. Keeping the state of the molten resin constant means keeping the viscosity, liquid level, liquid level, etc. of the molten resin constant without changing. Specific methods include, but are not limited to, applying a Teflon (registered trademark) coating to the wall surface of the low-pressure separator, providing an umbrella-shaped nozzle in the inlet pipe of the low-pressure separator, and providing an outlet of the low-pressure separator. The pipe size should be gradually increased, and a stirrer should be installed in the low-pressure separator.

The ratio (A _IR / B _IR ) is calculated from the absorbance ratio A _IR and the absorbance ratio B _IR obtained by the test method having the following steps (1) to (4).

(Step (1): Preparation of test film)
In the step (1), a test film is prepared using an ethylene-vinyl acetate copolymer resin under predetermined production conditions.
<Production conditions>
A test film having a cylinder temperature of 140 ° C. and a die temperature of 140 ° C. is kneaded using a single-screw vertical extruder, and a test film having a thickness of 50 μm and a width of 100 mm is obtained by a T-die method at a take-up speed of 4 m / min. A filter is not used at the screw outlet of the single-screw vertical extruder, and a test film is prepared by sandwiching only the breaker plate.

Specific examples of the single-screw vertical extruder include a single-screw vertical extruder (full flight screw, screw diameter 20 mm, die 100 mm width) manufactured by Landcastle.
The surface of the die is coated with hard chrome to prevent sticking of shavings and kogation. Further, in order not to remove the gel generated in the ethylene-vinyl acetate copolymer resin with a filter, a filter is not used at the screw outlet, and only the breaker plate is sandwiched between the screws.

(Step (2): Detection of part A and part B)
In the step (2), the test film obtained in the step (1) is subjected to the conditions that the measurement interval is 0.1 mm and the unevenness detection size is 0.2 mm or more and 1.0 mm or less by using a film inspection device. , The detected part A and the undetected part B are detected.
In the present embodiment, "part A" refers to fish eyes generated from polyethylene or ethylene-vinyl acetate copolymer resin, and excludes foreign substances and scratches.
“Part B” refers to a portion that is not detected by the film inspection device and does not contain foreign matter or scratches.

The test film is measured at intervals of 0.1 mm using a film inspection device, and the one having the longest diameter of 0.2 mm or more and 1.0 mm or less is detected as the detected portion A from those in which unevenness is detected. More specifically, 25 mm (50 mm in total) width and 100 m in length from the center of the test film were measured by the film inspection device at 0.1 mm intervals, and the longest diameter was 0.2 mm or more from the detected irregularities. Those having a thickness of 1.0 mm or less are detected as part A.
Specific examples of the film inspection device include a plain surface quality inspection device (MUJIKEN) manufactured by Nireco Corporation.

(Step (3): Absorbance ratio A _IR )
In step (3), for each part A detected in step (2), the ratio of the absorbance of 965 cm ^{-1 to} the absorbance of 720 cm ^-1 by microinfrared absorption measurement (transmission method) of the core part of part A. _Ask for A _IR .
The core portion of the portion A refers to the portion forming the core of the fish eye. A part A of the test film is cut out in the thickness direction and further cut to a thickness of 10 μm in the cutout direction to prepare a test piece A', and a transmission observation (bright field observation) in a bright field or a phase contrast filter is performed with an optical microscope. By inserting observation (phase contrast observation), observing with a differential interference filter inserted (differential interference contrast observation), observing fluorescence emission by UV fluorescence illumination (fluorescence observation), etc., the core part can be seen from a shape different from the surrounding part. Can be identified.

Microscopic infrared absorption measurements, nuclear portion of the above test piece A ', to measure the absorbance at 965 cm ^-1 and 720 cm ^-1 by a transmission method. The aperture size is set so that the measurement range is covered with the core portion of the test piece A'.

The absorption peak in the infrared absorption spectrum is 965 cm ^-1 : CH out-of-plane change, as described in "New Edition, Polymer Analysis Handbook", edited by the Japan Society for Analytical Chemistry, Polymer Analysis Research Council, pages 590 and 591. Angular vibration (trans C = C), 720 cm ^-1 : Absorption attributed to methylene lateral vibration. The values of the peaks of 965 cm ^-1 and 720 cm ^-1 may change slightly depending on the VA content. In that case, the peaks attributed to the above vibrations near 965 cm ^-1 or 720 cm ^-1. Calculated from the peak top value of.

The microinfrared absorption measurement of the part A measures up to 20 points. However, if the number of parts A detected by the film inspection device in the test film is less than 20, measurement is performed on all the detected parts. Calculating the absorbance ratio from the height of the peak top of the absorbance at 965 cm ^-1 and 720 cm ^-1 measured at each point of the portion ^{A (965cm -1 / 720cm -1)} , the absorbance ratio at the point of maximum value _Let be A _IR . FIG. 1 is an example of a spectrum obtained by microinfrared absorption measurement. The height of the peak top is calculated from the difference between the baseline and the peak top set according to the method described in JIS K7192: 1999 4.1.3.2.5.

(Step (4): Absorbance ratio B _IR )
In step (4), and the absorbance of 965 cm ^-1 by microscopic infrared absorption measurement (transmission method) part B, determining the ratio B _IR absorbance of 720 cm ^-1.
Similar to the part A, the part B of the test film is also cut out in the thickness direction of the test film, sliced parallel to the cross section to a thickness of 10 μm to prepare a test piece, and microinfrared absorption measurement (transmission method) is performed. Measure the absorbance at 965 cm ^-1 and 720 cm ^-1 . The measurement range is set to the same aperture size as when the detected portion A is measured.

Infrared absorption measurement of part B measures up to 20 points. Calculating the absorbance ratio (965cm ^-1 / ^{720cm -1)} from the absorbance at 965 cm ^-1 and 720 cm ^-1 measured at each point of the portion B, and the absorbance ratio at the point where the maximum value and B _IR.

(Number of parts A)
The number of portions A detected in the test film prepared under the conditions of the above step (1) of the ethylene-vinyl acetate copolymer resin of the present embodiment is preferably 1 or more and 100 or less, and more. The number is preferably 1 or more and 90 or less, and more preferably 2 or more and 80 or less. When the number of the portions A is 1 or more and 100 or less, the film appearance tends to be good and the film forming processability tends to be excellent. Examples of the method for controlling the number of portions A include appropriately adjusting the polymerization temperature, the polymerization pressure and the separator temperature, and the separator pressure.

(Number of parts A _b )
Further, among the portions A, the number of portions A _b having irregularities having a maximum diameter of 0.4 mm or more and 1.0 mm or less is preferably 1 or more and 30 or less, more preferably 1 or more and 25 or less, and further preferably. Is 1 or more and 20 or less. When the number of portions A _b is 1 or more and 30 or less, the film breakage during film formation is small, and the thin film processability tends to be excellent. The portion A _b means that the longest diameter of the unevenness detected as the portion A is 0.4 mm or more and 1.0 mm or less. _Examples of the method for controlling the number of portions _Ab include adjusting the polymerization temperature, the polymerization pressure and the separator temperature, and the separator pressure as appropriate.

The absorbance ratio A _IR (965 cm ^-1 / 720 cm ^-1 ) measured by the method described above is preferably 0.19 or less, more preferably 0.14 or less, still more preferably 0.11. It is as follows. When the absorbance ratio A _IR (965 cm ^-1 / 720 cm ^-1 ) is 0.19 or less, the concentration of transalkenes tends to be low, and the formation of fish eyes tends to be further suppressed. The lower limit of the absorbance ratio A _IR (965 cm ^-1 / 720 cm ^-1 ) is not particularly limited, but is preferably 0.004 or more, more preferably 0.008 or more, and further preferably 0.010. That is all.

The absorbance ratio B _IR (965 cm ^-1 / 720 cm ^-1 ) measured by the method described above is preferably 0.13 or less, more preferably 0.10 or less, still more preferably 0.080. It is as follows. When the absorbance ratio B _IR (965 cm ^-1 / 720 cm ^-1 ) is 0.13 or less, the concentration of transalkenes tends to be low, and the formation of fish eyes tends to be further suppressed. The lower limit of the absorbance ratio B _IR (965 cm ^-1 / 720 cm ^-1 ) is not particularly limited, but is preferably 0.005 or more, more preferably 0.010 or more, and further preferably 0.013. That is all.

However, the preferable ranges of the absorbance ratio A _IR and the absorbance ratio B _IR are merely examples. For example, as the VA content in the resin increases, the absorbance ratio A _IR and the absorbance ratio B _IR tend to increase. However, by controlling the absorbance ratio ratio (A _IR / B _IR ) within the above range, it is possible to suppress the formation of fish eyes even when the absorbance ratio A _IR and the absorbance ratio B _IR are large.

(Molecular weight distribution (Mw / Mn))
The ethylene-vinyl acetate copolymer resin of the present embodiment has a molecular weight distribution Mw / Mn represented by the ratio of the weight average molecular weight to the number average molecular weight obtained by gel permeation chromatography (hereinafter, also referred to as “GPC”). From the viewpoint of the strength and appearance of the formed film, it is preferably 8.0 or less, more preferably 7.0 or less, and further preferably 6.0 or less.

The weight average molecular weight of the ethylene-vinyl acetate copolymer resin of the present embodiment is preferably 20,000 or more and 200,000 or less, more preferably 30,000 or more and 100,000 or less, and further preferably 40, It is 000 or more and 80,000 or less.

The number average molecular weight of the ethylene-vinyl acetate copolymer resin of the present embodiment is preferably 8,000 or more and 50,000 or less, more preferably 10,000 or more and 40,000 or less, and further preferably 12. It is 000 or more and 30,000 or less.

Examples of the method for controlling the molecular weight distribution, the number average molecular weight and the weight average molecular weight include appropriately adjusting the polymerization temperature and the polymerization pressure. The molecular weight distribution, the number average molecular weight, and the weight average molecular weight can be measured by the methods described in Examples.

(MFR)
The ethylene-vinyl acetate copolymer resin of the present embodiment has a melt flow rate (JIS K7210: 1999 code D, temperature 190 ° C., load 2.16 kg; hereinafter referred to as MFR), which has film strength and film-forming processability. From the viewpoint, it is preferably 0.5 g / 10 min or more and 4.0 g / 10 min or less, more preferably 0.8 g / 10 min or more and 3.5 g / 10 min or less, and further preferably 1.0 g / 10 min or more and 3.0 g. It is / 10 min or less. Examples of the method for controlling the MFR include appropriately adjusting the polymerization temperature and the polymerization pressure, and appropriately adding a chain transfer agent. The MFR can be measured by the method described in Examples.

[Manufacturing method of ethylene-vinyl acetate copolymer resin]
The ethylene-vinyl acetate copolymer resin of the present embodiment is obtained by polymerizing in the presence of a polymerization initiator at an ultrahigh pressure of 100 to 350 MPa using a multi-stage compressor. The polymerization method of the ethylene-vinyl acetate copolymer resin of the present embodiment is not limited to the following, and examples thereof include an autoclave method and a tubular method, and the polymerization method is preferably a tubular method.

When polymerizing by the tubular method, it is preferable to polymerize at an average polymerization reaction temperature of 150 ° C. or higher and 280 ° C. or lower and a polymerization pressure of 120 MPa or higher and 270 MPa or lower to produce an ethylene-vinyl acetate copolymer resin. More preferably, the average polymerization reaction temperature is 180 ° C. or higher and 240 ° C. or lower, and the polymerization pressure is 180 MPa or higher and 260 MPa or lower. Further, in order to narrow the molecular weight distribution of the ethylene-vinyl acetate copolymer resin, it is preferable that the polymerization temperature distribution in the polymerization vessel is made uniform.

In the tubular method, there are usually a plurality of places where ethylene, vinyl acetate and the polymerization initiator are fed to the reactor, and the temperature drops once by adding raw materials or the like in the vicinity of each feed part, but then rises due to the heat of polymerization. .. In the next feed portion, the temperature is similarly lowered by adding raw materials and the like, but the temperature is also raised by the heat of polymerization. In the reactor, the temperature can be non-uniform depending on the raw material input location, but in this embodiment, the difference between the high temperature peaks after feeding is 15 ° C or less, and the difference between the peak temperature and the bottom temperature is 60 ° C or less. Is preferable.

Examples of the polymerization initiator used for the polymerization of the ethylene-vinyl acetate copolymer resin of the present embodiment include air, a free radical generator such as peroxide, and the like. The free radical generator such as peroxide is not particularly limited, and for example, t-butyl-peroxy-2-ethylhexanoate, t-butyl peroxyacetate, t-butyl peroxypivalate, di-t-butyl peroxide. And so on. In order to narrow the molecular weight distribution, it is preferable not to use air as the polymerization initiator.

When polymerizing the ethylene-vinyl acetate copolymer resin of the present embodiment, if necessary, a chain transfer agent such as alcohols, alkanes, alkenes, ketones, aldehydes, etc. is used in order to reduce the molecular weight. You may use it.

The alcohols are not particularly limited, and examples thereof include methanol, ethanol, normal propyl alcohol, isopropyl alcohol, normal butyl alcohol, isobutyl alcohol and the like.

The alkanes or alkenes are not particularly limited, and examples thereof include ethane, propane, propylene, butane, 1-butene, and 2-butene.

The ketones or aldehydes are not particularly limited, but for example, acetone, methyl ethyl ketone, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, diisobutyl ketone, methyl isopropyl ketone, formaldehyde, acetaldehyde, normal butyl aldehyde, etc. Examples thereof include isobutyl aldehyde, normal barrel aldehyde, and isovaleraldehyde.

It is preferable that the polymerized ethylene-vinyl acetate copolymer resin is separated from the raw material ethylene gas and granulated into pellets by an extruder.

For example, when the tubular method is used, the raw material ethylene gas and the ethylene-vinyl acetate copolymer resin are separated while reducing the pressure with a high-pressure separator and a low-pressure separator, and the molten ethylene-vinyl acetate copolymer is separated. It is preferable to granulate the resin into pellets with an extruder. In the high-pressure separator and the low-pressure separator, the molten ethylene-vinyl acetate copolymer resin and the raw material ethylene gas exist as a gas-liquid mixed fluid, but the unreacted gas is recovered from the upper part of the container of the separator, and the multi-stage It is sent to the compressor entrance and reused for polymerization.

The ethylene-vinyl acetate copolymer resin that has left the reactor is in a molten state and is guided to a high-pressure separator at a temperature of 150 ° C. or higher and 260 ° C. or lower as a gas-liquid mixed fluid together with unreacted gas, and the pressure is 15 MPa or higher and 30 MPa or lower. It is preferable that the pressure is lowered to. Further, the gas-liquid mixture fluid in the high-pressure separator is guided to the low-pressure separator and is stepped down to atmospheric pressure or more and 0.1 MPa or less at a temperature of 110 ° C. or higher and 250 ° C. or lower, preferably 120 ° C. or higher and 230 ° C. or lower. It is preferable that the mixture is introduced into a pellet and granulated into pellets.

In the present embodiment, it is preferable to apply a Teflon coating to the metal container wall surface of the low pressure separator. Further, it is preferable to provide an umbrella-shaped nozzle in the inlet pipe of the low-pressure separator or gradually increase the pipe size toward the discharge port. It is preferable to provide a stirrer in the low pressure separator, and the container temperature of the low pressure separator is preferably 110 ° C. or higher and 250 ° C. or lower. For example, the resin viscosity can be controlled by setting the container temperature of the low-pressure separator to 110 ° C. or higher and 250 ° C. or lower, and the state of the molten resin in the low-pressure separator, that is, the viscosity or liquid level of the molten resin. , The state of the liquid level can be kept constant.

After pelletizing the ethylene-vinyl acetate copolymer resin with an extruder, it is preferable to blow dry air at 30 ° C. or higher and lower than 50 ° C. for 5 hours or more in a silo in which the pellets are stored. The temperature of the dry air is preferably 30 ° C. or higher and lower than 50 ° C., more preferably 33 ° C. or higher and 47 ° C. or lower, and further preferably 35 ° C. or higher and 45 ° C. or lower from the viewpoint of removing low molecular weight components. preferable.

(Additive)
The ethylene-vinyl acetate copolymer resin of the present embodiment may contain known additives such as an antioxidant, an ultraviolet absorber, a light stabilizer, an antistatic agent, an antifogging agent, and a coloring pigment, if necessary. Good.

As the antioxidant, a phenolic antioxidant which is a primary antioxidant is preferable, and is not particularly limited, but for example, 2,6-di-t-butyl-4-methylphenol, pentaerythrityl-tetrakis- [. 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate and the like can be mentioned. A secondary antioxidant can also be used in combination with tris (2,4-di-t-butylphenyl) phosphite and tetrakis (2,4-di-t-butylphenyl) -4,4-. Phosphorus-based antioxidants such as biphenylene-diphosphonite can be mentioned. In addition, as a phosphorus / phenol-based antioxidant, 6-tert-butyl-4- [3- (2,4,8,10-tetra-t-butyldibenzo [d, f] [1,3,2] dibenzo] Oxaphosfepine-6-yloxy) propyl] -o-cresol and the like can be mentioned. Further, examples of the sulfur-based antioxidant include dilauryl-thio-dipropionate and the like.

[the film]
The ethylene-vinyl acetate copolymer resin of the present embodiment is not limited to the following, but can be suitably used for film applications. That is, the film of the present embodiment contains the ethylene-vinyl acetate copolymer resin of the present embodiment. The film of the present embodiment is made of the ethylene-vinyl acetate copolymer resin of the present embodiment. Examples of the use of the film according to the present embodiment include an agricultural polyolefin film, a packaging film described later, a flexible container exterior film, and the like. Examples of the film manufacturing method include T-die molding, inflation molding, calender molding, and skyf molding. Inflation molding or T-die extrusion molding is particularly preferable.

(VA content of film)
From the viewpoint of appearance, the film of the present embodiment has a VA content of 3.0% by mass or more and 30.0% by mass or less, preferably 4.0, based on the total amount of the ethylene-vinyl acetate copolymer resin. It is mass% or more and 25.0 mass% or less, and more preferably 5.0 mass% or more and 20.0. The VA content of the film of this embodiment is measured in accordance with JIS K7192: 1999 by preparing a calibration curve by saponification and potentiometric titration as a reference test method and converting it into vinyl acetate by infrared spectroscopy as a control test method. can do. Specifically, it can be measured by the method described in Examples.

(Ratio in film ( _A'IR / _B'IR )
The film of the present embodiment contains an ethylene-vinyl acetate copolymer resin containing 3% by mass or more and 30% by mass or less of vinyl acetate units. The film of this embodiment is obtained by the test method having the following steps (2 ') - (4'), the ratio of _IR 'ratio B of _IR and absorbance' ratio A absorbance (A _'IR / B ' _IR ) is 0.80 or more and 1.40 or less. When the ratio ( _A'IR / _B'IR ) is 0.80 or more and 1.40 or less, the film has an excellent appearance.
Step (2'): A portion of the film of the present embodiment that is detected by using a film inspection device under the conditions that the measurement interval is 0.1 mm and the unevenness detection size is 0.2 mm or more and 1.0 mm or less in the maximum diameter. step process to detect the a and not detected part B (3 '): and the absorbance of 965 cm ^-1 by microscopic infrared absorption measurement of the nuclear portion of the portion a (transmission method), the ratio a of the absorbance at 720 cm ^-1' _IR the obtaining process step (4 '): and the absorbance of 965 cm ^-1 by microscopic infrared absorption measurement (transmission method) of the portion B, the ratio B of the absorbance at 720 cm ^-1' obtaining a _IR

In the step (2'), the steps (2') to (4') and the above-mentioned steps (2) to (4) are the same method except that the film of the present embodiment is measured.

[Packaging film]
The film containing the ethylene-vinyl acetate copolymer resin of the present embodiment can be suitably used as a packaging film. Specific examples thereof include, but are not limited to, a food packaging film, a food wrap film, an overwrap film, a shrinkable overwrap film, and a sealant film.

[Laminated film]
The film containing the ethylene-vinyl acetate copolymer resin of the present embodiment may be a monolayer or a laminate. The laminated film may have one or more layers made of the ethylene-vinyl acetate copolymer resin of the present embodiment, or may have the ethylene-vinyl acetate copolymer resin of the present embodiment in all layers. it can. The method for producing the laminated film is not particularly limited, and for example, it can be produced by laminating by a lamination process or by a laminated extrusion step. In addition, the laminated film can consist of layers of the same material or layers of different materials.

The present invention will be specifically described below with reference to Examples. The present invention is not limited to these examples. The physical property measurement method and evaluation method in Examples and Comparative Examples are as follows.

(1) Melt flow rate (MFR) measurement The measurement was performed in accordance with JIS K7210: 1999 Code D (temperature = 190 ° C., load = 2.16 kg).

(2) Measurement of VA content Based on JIS K7192: 1999, a calibration curve was prepared using an EVAC reference sample with a known vinyl acetate content by saponification and potential differential titration as a reference test method, and red as a control test method. The content (VA content) of the ethylene-vinyl acetate copolymer resin in vinyl acetate units was measured by external spectroscopy.

(3) Measurement of Molecular Weight and Molecular Weight Distribution The ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) obtained from GPC was defined as the molecular weight distribution. For GPC measurement, GPCV2000 manufactured by Waters Co., Ltd. was used, and the column used was UT-807 (1 piece) manufactured by Showa Denko Co., Ltd. and GMHHR-H (S) HT (2 pieces) manufactured by Tosoh Co., Ltd. connected in series. The procedure was carried out under the conditions of mobile phase ortho-dichlorobenzene (ODCB), column temperature 140 ° C., flow rate 1.0 ml / min, sample concentration 20 mg / 15 ml (ODCB), sample dissolution temperature 140 ° C., and sample dissolution time 2 hours. The molecular weight is calibrated at 12 points of standard polystyrene manufactured by Tosoh Corporation in the range of Mw of 105 to 2.06 million, and the Mw of each standard polystyrene is multiplied by a coefficient of 0.43 to obtain the polyethylene equivalent molecular weight, and the elution time and polyethylene conversion are obtained. A primary calibration line was created from the molecular weight plot to determine the molecular weight.

(4) Ratio (A _IR / B _IR )
(4-1) Preparation of test film (step (1))
Using a single-screw vertical extruder (full flight screw, screw diameter 20 mm, die 100 mm width) manufactured by Landcastle, knead at a cylinder temperature of 140 ° C and a die temperature of 140 ° C, and a take-up speed of 4 m / min by the T-die method. A test film having a thickness of 50 μm and a width of 100 mm was obtained. The surface of the die was coated with hard chrome to prevent adhesion of shavings and kogation. In addition, no filter was used at the screw outlet, and only the breaker plate was sandwiched to form a film.

(4-2) Detection of part A (step (2))
As a film inspection device, a plain surface quality inspection device (MUJIKEN) manufactured by Nireco Corporation is used, and each 25 mm (50 mm in total) width and 100 m from the center of the test film has a maximum diameter of 0.2 mm or more and 1.0 mm. The following irregularities were measured at 0.1 mm intervals to determine the number. The portion where the unevenness is formed is designated as portion A.
The camera specifications used were a monochrome line; a sensor camera unit of 8000 pixels or more, 160 MHz, a lens of 35 mm, and a lighting device; an LED of 400 mm in length.

(4-3) Infrared absorption spectrum measurement Next, using a rotary microtome manufactured by Japan Microtome Research Institute and an electronic sample freezer, parts A and B are cut out in the thickness direction of the film, and further parallel to the cross section. A test piece was prepared by slicing to a thickness of 10 μm. Subsequently, with the microscope device BX51TRF-6 (D) manufactured by Olympus Corporation and the epi-illumination system device HGLGPS-SET-D, part A is performed by various observation methods such as bright field observation, phase difference observation, fluorescence observation, and differential interference contrast observation. The test piece of the above was observed, and the core portion of the portion A was identified.
The infrared absorption spectrum (IR) of the test piece was measured using an FT / IR-6600 device manufactured by Nippon Spectroscopy Co., Ltd. and an IRT-5200 infrared microscope device with a resolution of 4 cm ^-1 and an integration frequency of 250 times. : a 4000～600Cm ^-1, by microscopic infrared absorption measurement (transmission method), the absorbance was measured at 965 cm ^-1 and 720 cm ^-1. Here, the absorbance was set to the value of the height of the peak top of 965 cm ^-1 and 720 cm ^-1 . The height of the peak top was calculated from the difference between the baseline and the peak top set according to the method described in JIS K7192: 1999 4.1.3.2.5 (see FIG. 1).
The core portion of the portion A and the infrared absorption measurement of the portion B were measured at 20 points each. However, when the number of the parts A was less than 20, all the core parts of the part A were measured. The calculated absorbance ratios from the absorbance at 965 cm ^-1 and 720 cm ^-1 measured at each point of the core portion of the portion A of (965cm ^-1 / ^{720cm -1),} the absorbance ratio at the point where the maximum value A _{It was IR} . The same operation was performed for the part B, and the maximum value was set to B _IR .
The ratio (A _IR / B _IR ) was calculated from the absorbance ratio A _IR and the absorbance ratio B _IR obtained by the above method.

(5) Measurement of melt elongation (ME) Using a Capillary Graph 1D manufactured by Toyo Seiki Co., Ltd. equipped with a capillary having a diameter of 2.095 mm and a length of 8.0 mm, an ethylene-vinyl acetate copolymer resin was prepared at 190 ° C. at 6 mm / min. And extruded at 230 ° C., pick-up was started at 2 m / min, and after 1 minute, the pick-up speed was increased at 10 m / min, and the elongation when the strand was cut was measured as the melt elongation (ME).

(6) Increase in resin pressure of extruder E-50 (screw diameter 50 mm, screw: L (extruded screw length) / D (extruded screw diameter) = 28), die (lip), inflation film manufacturing equipment manufactured by Sumitomo Heavy Industries Modern Co., Ltd. Using diameter, 100 mm, lip gap, 1.0 mm,), cylinder temperature 230 ° C, die temperature 230 ° C, extrusion rate 10 kg / hour, blow ratio 2.0, screw tip made of Ishikawa wire mesh, special twill tatami mat When a woven metal filter BMT50 and an average opening of 50 microns are attached, the resin pressure at the tip of the screw is measured, and an ethylene-vinyl acetate copolymer resin is formed by 8 hr extrusion molding with a film thickness of 15 microns. The boosting of the extruder was evaluated according to the following criteria. Here, the pressure of the extruder was measured by measuring the pressure at the tip of the screw.
◎ (Excellent): Extruder resin pressure increase less than 1% ○ (Good): Extruder resin pressure increase 1% or more and less than 2% × (No): Extruder resin pressure increase 2% or more

(7) Evaluation of film width reduction and film breakage The film width reduction or film breakage due to puncture at the fish eye base point when the film was formed by the inflation molding described in (6) above was evaluated according to the following criteria.
◎ (Excellent): Film width reduction or film cutting at the fish eye base point when 8 hours continuous film formation: 0 times ○ (Good): Film width reduction or film width reduction at the fish eye base point when 8 hours continuous film formation Cutting: 1 time or less × (impossible): Film width reduction at the fish eye base point or film cutting when 8 hours continuous film formation: 2 times or more

(8) Appearance evaluation of the film The film is formed by the inflation molding described in (6) above, the film is wound 100 m around the paper tube, and the entire circumference direction is visually inspected to check the unevenness of the paper tube wound film due to air accumulation or the like. It was evaluated according to the following criteria.
◎ (Excellent): 1 or less air pool in the entire circumference direction ○ (Good): 2 or more and 4 or less air pools in the entire circumference direction × (No): 5 or more air pools in the entire circumference direction

[Example 1]
In a tubular reactor, ethylene and 7 mol% vinyl acetate were introduced with respect to ethylene, the average polymerization reaction temperature was 220 ° C., the polymerization pressure was 235 MPa, and t-butyl-peroxy-2-ethylhexano as a polymerization initiator. Polymerized using art. After the polymerization, the gas was introduced into a high-pressure separator having a temperature of 220 ° C. and a pressure of 20 MPa to separate unreacted gas. Subsequently, the gas was introduced into a low-pressure separator having a temperature of 180 ° C. and a pressure of 0.04 MPa, and the remaining unreacted gas was separated. An umbrella-shaped nozzle was installed in the inlet pipe of the low-pressure separator, and a stirrer was installed in the low-pressure separator to perform stirring. The obtained molten resin was fed to an extruder and pelletized to obtain an ethylene-vinyl acetate copolymer resin. The physical characteristics and characteristics of the obtained ethylene-vinyl acetate copolymer resin were measured by the method shown above. The measurement results are shown in Table 1.

[Example 2]
The ethylene-vinyl acetate copolymer resin of Example 2 was obtained by the same operation as in Example 1 except that the temperature of the low-pressure separator was set to 130 ° C. and the stirrer in the low-pressure separator was eliminated. The physical characteristics and characteristics of the obtained ethylene-vinyl acetate copolymer resin were measured by the method shown above. The measurement results are shown in Table 1.

[Example 3]
The ethylene-vinyl acetate copolymer resin of Example 3 was obtained by the same operation as in Example 1 except that the inlet shape in the low-pressure separator was a straight pipe. The physical characteristics and characteristics of the obtained ethylene-vinyl acetate copolymer resin were measured by the method shown above. The measurement results are shown in Table 1.

[Comparative Example 1]
The inlet pipe of the low-pressure separator was a straight pipe without an umbrella-shaped nozzle, and the same operation as in Example 1 was performed except that the stirrer in the low-pressure separator was eliminated, for both ethylene-vinyl acetate of Comparative Example 1. A polymer resin was obtained. The physical characteristics and characteristics of the obtained ethylene-vinyl acetate copolymer resin were measured by the method shown above. The measurement results are shown in Table 1.

[Example 4]
In a tubular reactor, ethylene and 7 mol% vinyl acetate were introduced with respect to ethylene, the average polymerization reaction temperature was 226 ° C., the polymerization pressure was 264 MPa, and t-butyl-peroxy-2-ethylhexano as a polymerization initiator. Polymerization was carried out using art and di-t-butyl peroxide. After the polymerization, the gas was introduced into a high-pressure separator having a temperature of 230 ° C. and a pressure of 20 MPa to separate unreacted gas. Subsequently, the gas was introduced into a low-pressure separator having a temperature of 190 ° C. and a pressure of 0.04 MPa to separate the remaining unreacted gas. An umbrella-shaped nozzle was installed in the inlet pipe of the low-pressure separator. The obtained molten resin was fed to an extruder and pelletized to obtain an ethylene-vinyl acetate copolymer resin. The physical characteristics and characteristics of the obtained ethylene-vinyl acetate copolymer resin were measured by the method shown above. The physical characteristics and characteristics of the obtained ethylene-vinyl acetate copolymer resin were measured by the method shown above. The measurement results are shown in Table 1.

[Example 5]
The ethylene-vinyl acetate copolymer of Example 5 was operated in the same manner as in Example 4 except that the inlet shape in the low-pressure separator was a straight pipe and a stirrer was installed in the low-pressure separator for stirring. A resin was obtained. The physical characteristics and characteristics of the obtained ethylene-vinyl acetate copolymer resin were measured by the method shown above. The measurement results are shown in Table 1.

[Comparative Example 2]
The temperature of the low-pressure separator was set to 260 ° C., the inlet pipe of the low-pressure separator was a straight pipe without an umbrella nozzle, and the stirrer in the low-pressure separator was eliminated. , The ethylene-vinyl acetate copolymer resin of Comparative Example 2 was obtained. The physical characteristics and characteristics of the obtained ethylene-vinyl acetate copolymer resin were measured by the method shown above. The measurement results are shown in Table 1.

[Example 6]
In a tubular reactor, ethylene and 7 mol% vinyl acetate were introduced with respect to ethylene, the average polymerization reaction temperature was 226 ° C., the polymerization pressure was 264 MPa, and t-butyl-peroxy-2-ethylhexano as a polymerization initiator. Polymerization was carried out using art and di-t-butyl peroxide. After the polymerization, the gas was introduced into a high-pressure separator having a temperature of 200 ° C. and a pressure of 22 MPa to separate unreacted gas. Subsequently, the gas was introduced into a low-pressure separator having a temperature of 180 ° C. and a pressure of 0.04 MPa, and the remaining unreacted gas was separated. An umbrella-shaped nozzle was installed in the inlet pipe of the low-pressure separator, and a stirrer was installed in the low-pressure separator to perform stirring. The obtained molten resin was fed to an extruder and pelletized to obtain an ethylene-vinyl acetate copolymer resin. The physical characteristics and characteristics of the obtained ethylene-vinyl acetate copolymer resin were measured by the method shown above. The measurement results are shown in Table 1.

[Example 7]
The ethylene-vinyl acetate copolymer resin of Example 7 was obtained by the same operation as in Example 6 except that the inlet pipe of the low-pressure separator was a straight pipe without installing an umbrella nozzle. The physical characteristics and characteristics of the obtained ethylene-vinyl acetate copolymer resin were measured by the method shown above. The measurement results are shown in Table 1.

[Example 8]
In a tubular reactor, ethylene and 8 mol% vinyl acetate with respect to ethylene were introduced, the average polymerization reaction temperature was 216 ° C., the polymerization pressure was 264 MPa, and t-butyl-peroxy-2-ethylhexano as a polymerization initiator. Polymerized using art. After the polymerization, the gas was introduced into a high-pressure separator having a temperature of 220 ° C. and a pressure of 20 MPa to separate unreacted gas. Subsequently, the gas was introduced into a low-pressure separator having a temperature of 180 ° C. and a pressure of 0.04 MPa, and the remaining unreacted gas was separated. An umbrella-shaped nozzle was installed in the inlet pipe of the low-pressure separator, and a stirrer was installed in the low-pressure separator to perform stirring. The obtained molten resin was fed to an extruder and pelletized to obtain an ethylene-vinyl acetate copolymer resin of Example 8. The physical characteristics and characteristics of the obtained ethylene-vinyl acetate copolymer resin were measured by the method shown above. The measurement results are shown in Table 1.

[Comparative Example 3]
The operation was the same as in Example 8 except that the temperature of the low-pressure separator was set to 100 ° C., the inlet pipe of the low-pressure separator was a straight pipe without an umbrella nozzle, and the stirrer in the low-pressure separator was eliminated. , The ethylene-vinyl acetate copolymer resin of Comparative Example 3 was obtained. The physical characteristics and characteristics of the obtained ethylene-vinyl acetate copolymer resin were measured by the method shown above. The measurement results are shown in Table 1.

[Comparative Example 4]
Except that the temperature of the high-pressure separator was set to 280 ° C, the temperature of the low-pressure separator was set to 280 ° C, the inlet pipe of the low-pressure separator was a straight pipe without an umbrella-shaped nozzle, and the stirrer in the low-pressure separator was eliminated. Obtained the ethylene-vinyl acetate copolymer resin of Comparative Example 4 by the same operation as in Example 8. The physical characteristics and characteristics of the obtained ethylene-vinyl acetate copolymer resin were measured by the method shown above. The measurement results are shown in Table 1.

[Example 9]
In a tubular reactor, 4 mol% vinyl acetate and 0.8 mol% propylene were introduced with respect to ethylene and ethylene, the average polymerization reaction temperature was 229 ° C., the polymerization pressure was 240 MPa, and t-butyl- was used as a polymerization initiator. Polymerization was carried out using peroxy-2-ethylhexanoate and di-t-butyl peroxide. After the polymerization, the gas was introduced into a high-pressure separator having a temperature of 230 ° C. and a pressure of 22 MPa to separate unreacted gas. Subsequently, the gas was introduced into a low-pressure separator having a temperature of 130 ° C. and a pressure of 0.04 MPa to separate the remaining unreacted gas. An umbrella-shaped nozzle was installed in the inlet pipe of the low-pressure separator, and a stirrer was installed in the low-pressure separator to perform stirring. The obtained molten resin was fed to an extruder and pelletized to obtain an ethylene-vinyl acetate copolymer resin of Example 9. The physical characteristics and characteristics of the obtained ethylene-vinyl acetate copolymer resin were measured by the method shown above. The measurement results are shown in Table 1.

[Example 10]
In a tubular reactor, 2 mol% vinyl acetate and 1.2 mol% propylene were introduced with respect to ethylene and ethylene, the average polymerization reaction temperature was 230 ° C., the polymerization pressure was 240 MPa, and t-butyl- was used as a polymerization initiator. Polymerization was carried out using peroxy-2-ethylhexanoate and di-t-butyl peroxide. After the polymerization, the gas was introduced into a high-pressure separator having a temperature of 190 ° C. and a pressure of 24 MPa to separate unreacted gas. Subsequently, the gas was introduced into a low-pressure separator having a temperature of 180 ° C. and a pressure of 0.04 MPa, and the remaining unreacted gas was separated. An umbrella-shaped nozzle was installed in the inlet pipe of the low-pressure separator, and a stirrer was installed in the low-pressure separator to perform stirring. The obtained molten resin was fed to an extruder and pelletized to obtain an ethylene-vinyl acetate copolymer resin of Example 10. The physical characteristics and characteristics of the obtained ethylene-vinyl acetate copolymer resin were measured by the method shown above. The measurement results are shown in Table 1.

[Comparative Example 5]
15 mol% vinyl acetate was introduced with respect to ethylene and ethylene, the average polymerization reaction temperature was 210 ° C., the polymerization pressure was 265 MPa, the temperature of the low pressure separator was 100 ° C, and the inlet piping of the low pressure separator was an umbrella nozzle. The ethylene-vinyl acetate copolymer resin of Comparative Example 5 was obtained by the same operation as in Example 8 except that the straight pipe was used without installation and the stirrer in the low-pressure separator was eliminated. The physical characteristics and characteristics of the obtained ethylene-vinyl acetate copolymer resin were measured by the method shown above. The measurement results are shown in Table 1. The melt elongation could not be measured because the melted resin hung down due to its own weight. Inflation molding was not possible because the bubbles hung down and came into contact with the air ring.

[Comparative Example 6]
1 mol% vinyl acetate and 0.5 mol% propylene were introduced with respect to ethylene and ethylene, the average polymerization reaction temperature was 240 ° C., the polymerization pressure was 210 MPa, the temperature of the low pressure separator was 260 ° C., and the low pressure separator The ethylene-vinyl acetate copolymer resin of Comparative Example 6 was used in the same operation as in Example 10 except that the inlet pipe was a straight pipe without installing an umbrella-shaped nozzle and the stirrer in the low-pressure separator was eliminated. Obtained. The physical characteristics and characteristics of the obtained ethylene-vinyl acetate copolymer resin were measured by the method shown above. The measurement results are shown in Table 1. Inflation molding was not possible because the bubbles were broken.

[Comparative Example 7]
1 mol% vinyl acetate and 1.4 mol% propylene were introduced with respect to ethylene and ethylene, the polymerization pressure was 210 MPa, the temperature of the low pressure separator was 260 ° C, and the inlet pipe of the low pressure separator was equipped with an umbrella type nozzle. The ethylene-vinyl acetate copolymer resin of Comparative Example 7 was obtained by the same operation as in Example 10 except that the straight pipe was used instead of the straight pipe and the stirrer in the low pressure separator was eliminated. The physical characteristics and characteristics of the obtained ethylene-vinyl acetate copolymer resin were measured by the method shown above. The measurement results are shown in Table 1. Inflation molding was not possible because the bubbles were broken.

The ethylene-vinyl acetate copolymer resin of the present invention has excellent film-forming processability and excellent appearance when made into a film, and is therefore suitably used for agricultural polyolefin films, packaging films, sealant applications and the like.

Claims (9)

An ethylene-vinyl acetate copolymer resin containing 3% by mass or more and 30% by mass or less of vinyl acetate units.
The ethylene-vinyl acetate copolymer resin has a ratio (A _IR / B _IR ) of the absorbance ratio A _IR to the absorbance ratio B _IR obtained by the test method having the following steps (1) to (4). An ethylene-vinyl acetate copolymer resin having a ratio of 0.80 or more and 1.40 or less.
Step (1): A step of preparing a test film using the ethylene-vinyl acetate copolymer resin under the following production conditions. Step (2): The test film is measured at intervals of 0 using a film inspection device. Step of detecting the detected portion A and the undetected portion B under the condition of 1 mm and the maximum unevenness detection size of 0.2 mm or more and 1.0 mm or less Step (3): Microinfrared of the core portion of the portion A absorption measurement and the absorbance of the (transmission method) by 965 cm ^-1, step step (4) determining the ratio a _IR absorbance of 720 cm ^-1: absorbance of the partial microscopic infrared absorption measurement of B (transmission method) by 965 cm ^-1 and a step of determining the ratio B _IR absorbance of 720 cm ^-1 <Preparation conditions>
A test film having a cylinder temperature of 140 ° C. and a die temperature of 140 ° C. is kneaded using a single-screw vertical extruder, and a test film having a thickness of 50 μm and a width of 100 mm is obtained by a T-die method at a take-up speed of 4 m / min. A filter is not used at the screw outlet of the single-screw vertical extruder, and a test film is prepared by sandwiching only the breaker plate. The ethylene-vinyl acetate copolymer resin according to claim 1, wherein the portion A is 1 piece / 5 m ² or more and 100 pieces / 5 m ² or less in the test film. Claim 1 or claim 1, wherein the portion A _b having irregularities having a maximum major axis of 0.4 mm or more and 1.0 mm or less is 1 piece / 5 m ² or more and 40 pieces / 5 m ² or less in the test film. The ethylene-vinyl acetate copolymer resin according to 2. The ethylene-vinyl acetate copolymer according to any one of claims 1 to 3, wherein the ethylene-vinyl acetate copolymer resin has a melt flow rate of 0.5 g / 10 min or more and 4.0 g / 10 min or less. resin. The ethylene-vinyl acetate copolymer resin according to any one of claims 1 to 4, wherein the ethylene-vinyl acetate copolymer resin has a molecular weight distribution (Mw / Mn) of 8.0 or less. A film containing the ethylene-vinyl acetate copolymer according to any one of claims 1 to 5. A packaging film containing the ethylene-vinyl acetate copolymer according to any one of claims 1 to 5. A laminated film containing the ethylene-vinyl acetate copolymer according to any one of claims 1 to 5. A film containing an ethylene-vinyl acetate copolymer resin containing 3% by mass or more and 30% by mass or less of vinyl acetate units.
The film is obtained by the test method having the following steps (2 ') - (4'), the ratio of _IR 'ratio B of _IR and absorbance' ratio A absorbance (A _'IR / B' _IR) is 0 A film that is .80 or more and 1.40 or less.
Step (2'): A portion A and detection of the film using a film inspection device under the conditions that the measurement interval is 0.1 mm and the unevenness detection size is 0.2 mm or more and 1.0 mm or less in the longest diameter. step step (3 ') for detecting a portion B which are not: the absorbance of the 965 cm ^-1 by microscopic infrared absorption measurement of the nuclear portion (transmission method) of the portion a, the ratio a of the absorbance at 720 cm ^-1' obtaining a _IR step (4 '): and the absorbance of 965 cm ^-1 by microscopic infrared absorption measurement (transmission method) of the portion B, the ratio B of the absorbance at 720 cm ^-1' obtaining a _IR