JP2023077422A - Modified ethylene-vinyl alcohol copolymer particles - Google Patents

Abstract

To provide a modified ethylene-vinyl alcohol-based resin composition which appropriately lowers a crystallization rate of an ethylene-vinyl alcohol-based resin, and thereby has gas barrier property and biodegradability, and can improve workability, especially, drawing workability, and is excellent in thermal stability.SOLUTION: Ethylene-vinyl alcohol copolymer particles are modified ethylene-vinyl alcohol copolymer particles having a primary hydroxyl group structural unit on a side chain and a content of an ethylene structural unit of 7.1-16.5 mol%. Therein, the following expression (3) is satisfied between degrees Cw(30°C) and Cw(70°C) of underwater crystallinity, and a content of the ethylene structural unit. Expression (3): 3.5×E-21≤(100-Cw(30°C))/100×(Cw(30°C)-Cw(70°C)) (where E is a content of the ethylene structural unit of the ethylene-vinyl alcohol copolymer particles).SELECTED DRAWING: None

Description

The present invention relates to modified ethylene-vinyl alcohol copolymer particles.

Conventionally, attempts have been made to form a gas barrier layer on a base material by applying a solution of polyvinyl alcohol to the base material, and to use the base material as a gas barrier material. However, although a gas barrier layer made of polyvinyl alcohol homopolymer exhibits high gas barrier properties in a dry atmosphere, it is known that the polyvinyl alcohol homopolymer exhibits significant moisture absorption under high relative humidity conditions, resulting in a decrease in gas barrier properties. ing.

As a method for reducing the hygroscopicity of a polyvinyl alcohol homopolymer, a method using an ethylene-vinyl alcohol copolymer obtained by copolymerizing 20 mol % or more of ethylene is known. However, such an ethylene-vinyl alcohol copolymer is insoluble in water, and when handled in solution, an organic solvent must be used in combination, which requires new equipment for solvent recovery. There was a problem.

In order to solve such problems, for example, Patent Document 1 discloses an ethylene-vinyl alcohol copolymer having an ethylene unit content of 1 mol% or more and less than 20 mol% and having a specific viscosity-average degree of polymerization and a degree of saponification. and the degree of crystallinity in water at 30° C. and 70° C. determined by pulse NMR satisfies specific conditions.

Patent Document 1 describes that particles having a very wide range of crystallinity in water have excellent solubility in water and are less likely to become lumpy. However, there is a demand for further improvement in the solubility in water, particularly at room temperature (25°C) to about 30°C.
Further, in Patent Document 1, in determining the degree of crystallinity in water, the magnetization attenuation curve obtained by pulse NMR measurement is approximated using equation (1) to determine the parameters, but the parameters are obtained only by the Solid Echo method. In the equation (1), the attenuation curve obtained does not converge by the method of least squares, and the crystallinity in water may not be obtained. Therefore, another evaluation method is required.

Furthermore, in recent years, gas barrier resins with excellent biodegradability have been in demand from the viewpoint of reducing environmental impact (for example, marine problems). unknown.

International publication WO19/078181

The present invention has been made in view of the above circumstances, and a modified ethylene-vinyl alcohol copolymer (hereinafter referred to as "ethylene-vinyl The purpose of the present invention is to provide particles for which "alcohol copolymers" are sometimes referred to as "EVOH-based resins."

As a result of intensive research, the inventors of the present invention have found that modified EVOH-based resin particles having a primary hydroxyl group structural unit in the side chain and an ethylene structural unit content of 7.1 to 16.5 mol% were analyzed using pulse NMR. Measured in heavy water using the Solid Echo method and the CPMG method, the component ratio is obtained from the magnetization attenuation curve y(t) obtained by combining, and the crystallinity in water at 30 ° C. and 70 ° C. are obtained from the component ratio. When the relationship between the degree of crystallinity in water and the content of ethylene structural units is within a specific range, it has excellent solubility in water and excellent biodegradability, and the film made from an aqueous solution has excellent gas barrier properties. We found that and completed the present invention.

（ただし、式（１）の第１項は結晶性で緩和時間が短い成分を示し、Ａ₁はその成分比、Ｔ_2Sはその緩和時間を示す。第２項は結晶性よりも長い緩和時間の成分を示し、Ａ₂はその成分比、Ｔ_2Mはその緩和時間を示す。第３項は定数を示す。Ｗはワイブル係数であり、Ａ₁＋Ａ₂＋ｙ₀＝１である。）
前記３０℃および７０℃のＡ₁およびＡ₂から下記式（２）により水中結晶化度（単位％）Ｃ_w（３０℃）、Ｃｗ（７０℃）を求めたとき、
Ｃ_w（Ｘ℃）＝Ａ₁／（Ａ₁＋Ａ₂）×１００ ・・・（２）
（ただし、Ｘは３０または７０である。）
前記水中結晶化度Ｃ_w（３０℃）、Ｃ_w（７０℃）と変性ＥＶＯＨ系樹脂粒子のエチレン構造単位の含有量（Ｅ）との間で、下記式（３）を満たす変性ＥＶＯＨ系樹脂粒子。
３．５×Ｅ－２１≦（１００－Ｃｗ（３０℃））／１００×（Ｃｗ（３０℃）－Ｃｗ（７０℃））・・・（３）
［２］ さらに式（４）を満足する、［１］に記載の変性ＥＶＯＨ系樹脂粒子
５≦Ｃｗ（７０℃）≦１１・・・（４）
［３］ ＪＩＳ Ｚ８８０１目開き２．３６ｍｍの篩を通過する粒子の割合が８０質量％以上であり、目開き１５０μｍの篩を通過する粒子の割合が１０質量％以上２０質量％以下である、［１］または［２］記載の変性ＥＶＯＨ系樹脂粒子。
［４］ ケン化度が９５ｍｏｌ％以上である、［１］～［３］のいずれかに記載の変性ＥＶＯＨ系樹脂粒子。
［５］ 側鎖一級水酸基構造の導入量が２．５ｍｏｌ％以上である、［１］～［４］のいずれかに記載の変性ＥＶＯＨ系樹脂粒子。
［６］再アセチル化後のエチレン－ビニルエステル系共重合体のテトラヒドロフラン溶液の粘度平均分子量が、５．５×１０⁴～１．１×１０⁵である［１］～［５］のいずれかの変性ＥＶＯＨ系樹脂粒子。 That is, the present invention has the following aspects.
[1] Modified EVOH resin particles having a primary hydroxyl group structural unit in a side chain and an ethylene structural unit content of 7.1 to 16.5 mol%, the modified EVOH resin particles being measured by pulse NMR. , measured using the Solid Echo method and the CPMG method at measurement temperatures of 30 ° C. and 70 ° C., and the magnetization decay curve y(t) obtained by combining is a function of the time t when the magnetization is observed. The following formula (1 ) to obtain the component ratios A ₁ and A ₂ at 30° C. and the component ratios A ₁ and A ₂ at 70° C.,

(However, the first term in formula (1) indicates a crystalline component with a short relaxation time, A ₁ indicates the component ratio, and T _2S indicates the relaxation time. The second term indicates a longer relaxation time than the crystalline A ₂ is its component ratio, T _2M is its relaxation time, the third term is a constant, W is the Weibull coefficient, and A ₁ +A ₂ +y ₀ =1.)
When the degree of crystallinity in water (unit %) _Cw (30°C) and Cw (70°C) is obtained from the above A ₁ and A ₂ at 30°C and 70°C by the following formula (2),
C _w (X° C.)=A ₁ /(A ₁ +A ₂ )×100 (2)
(However, X is 30 or 70.)
Modified EVOH resin that satisfies the following formula (3) between the degree of crystallinity in water C _w (30° C.) and C _w (70° C.) and the content (E) of the ethylene structural unit of the modified EVOH resin particles particle.
3.5×E−21≦(100−Cw (30° C.))/100×(Cw (30° C.)−Cw (70° C.)) (3)
[2] Modified EVOH resin particles according to [1], further satisfying formula (4) 5≤Cw(70°C)≤11 (4)
[3] The proportion of particles passing through a JIS Z8801 sieve with an opening of 2.36 mm is 80% by mass or more, and the proportion of particles passing through a sieve with an opening of 150 μm is 10% by mass or more and 20% by mass or less. Modified EVOH resin particles according to 1] or [2].
[4] The modified EVOH resin particles according to any one of [1] to [3], which have a degree of saponification of 95 mol % or more.
[5] The modified EVOH resin particles according to any one of [1] to [4], wherein the introduced amount of the side chain primary hydroxyl group structure is 2.5 mol % or more.
[6] Any one of [1] to [5], wherein the tetrahydrofuran solution of the ethylene-vinyl ester copolymer after reacetylation has a viscosity-average molecular weight of 5.5×10 ⁴ to 1.1×10 ⁵ . modified EVOH resin particles.

Since the modified EVOH-based resin particles of the present invention have excellent solubility in water, they can be easily prepared into an aqueous solution and have excellent biodegradability. Also, a film made of a coating agent obtained by dissolving the modified EVOH-based resin particles of the present invention in water has excellent gas barrier properties.

Hereinafter, the present invention will be described in more detail based on embodiments of the present invention, but the present invention is not limited to these embodiments.
In the present invention, when expressing "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, "X or more and Y or less" and "preferably larger than X" or "preferably It also includes the meaning of "smaller than Y".
In addition, when expressed as "X or more" (X is any number) or "Y or less" (Y is any number), the statement "preferably larger than X" or "preferably less than Y" It also includes intent.
Furthermore, in the present invention, "x and/or y (x and y are arbitrary constituents or components)" means three combinations of x only, y only, and x and y.

（ただし、式（１）の第１項は結晶性で緩和時間が短い成分を示し、Ａ₁はその成分比、Ｔ_2Sはその緩和時間を示す。第２項は結晶性よりも長い緩和時間の成分を示し、Ａ₂はその成分比、Ｔ_2Mはその緩和時間を示す。第３項は定数を示す。Ｗはワイブル係数であり、Ａ₁＋Ａ₂＋ｙ₀＝１である。）
前記３０℃および７０℃のＡ₁およびＡ₂から下記式（２）により水中結晶化度（単位％）Ｃ_w（３０℃）、Ｃｗ（７０℃）を求めたとき、
Ｃ_w（Ｘ℃）＝Ａ₁／（Ａ₁＋Ａ₂）×１００ ・・・（２）
（ただし、Ｘは３０または７０である。）
前記水中結晶化度Ｃ_w（３０℃）とＣ_w（７０℃）との差が、下記式（３）を満たす変性ＥＶＯＨ系樹脂粒子である。
３．５×Ｅ－２１≦（１００－Ｃｗ（３０℃））／１００×（Ｃｗ（３０℃）－Ｃｗ（７０℃））・・・（３）
（ただし、Ｅは、変性ＥＶＯＨ系樹脂粒子のエチレン構造単位の含有量である。） The modified EVOH-based resin-based resin particles of the present invention (hereinafter referred to as "this modified EVOH-based resin particles") has primary hydroxyl group structural units in side chains and has an ethylene structural unit content of 7.1 to 16.5. The magnetization decay curve y(t ) is a function of the magnetization observation time t, the component ratios A ₁ and A ₂ at 30° C. and the component ratios A ₁ and A ₂ at 70° C. are obtained from the following equation (1),

(However, the first term in formula (1) indicates a crystalline component with a short relaxation time, A ₁ indicates the component ratio, and T _2S indicates the relaxation time. The second term indicates a longer relaxation time than the crystalline A ₂ is its component ratio, T _2M is its relaxation time, the third term is a constant, W is the Weibull coefficient, and A ₁ +A ₂ +y ₀ =1.)
When the degree of crystallinity in water (unit %) _Cw (30°C) and Cw (70°C) is obtained from the above A ₁ and A ₂ at 30°C and 70°C by the following formula (2),
C _w (X° C.)=A ₁ /(A ₁ +A ₂ )×100 (2)
(However, X is 30 or 70.)
The difference between the degree of crystallinity in water C _w (30° C.) and C _w (70° C.) is the modified EVOH resin particles satisfying the following formula (3).
3.5×E−21≦(100−Cw (30° C.))/100×(Cw (30° C.)−Cw (70° C.)) (3)
(However, E is the content of ethylene structural units in the modified EVOH resin particles.)

Conventionally, the difference in molecular mobility in a polymer sample is evaluated by T2 relaxation in the Solid-echo method of pulse NMR, and this is separated into different components with different relaxation time components for analysis. It is known to be a degree of quenching. The NMR relaxation can generally be approximated as a mixture of Gaussian and Lorentzian waveforms.
However, the Solid Echo method is generally low in molecular mobility and is a measurement method suitable for samples with a short spin relaxation time of approximately 100 μs or less. A polymer dissolved in water is affected by the magnetization of the polymer dissolved in water. Therefore, the magnetization attenuation curve measured by the Solid Echo method may not be able to be approximated by the least squares method.
This problem can be solved by measuring the magnetization attenuation curve obtained by the measurement by the Solid Echo method and the CPMG method and using them in combination. The CPMG method is a measurement method suitable for samples with high molecular mobility and longer spin-spin relaxation times than the above.
The present modified EVOH-based resin particles are measured using the Solid Echo method and CPMG method of pulse NMR.

In the pulse NMR measurement, a sample of the modified EVOH-based resin particles was mixed in heavy water to a concentration of 4% by mass, allowed to stand at 30°C or 70°C for 40 minutes, and then heated to the same standing temperature. Measurements are taken under temperature. The range of 0 to 70 ms of the relaxation curve obtained is fitted using the error least squares method in the above equation (1) to obtain A ₁ , A ₂ , T _2S , T _2M , W, y ₀ at 30 ° C. and A ₁ , A ₂ , T _2S , T _2M , W and y ₀ at 70°C.
Specifically, the magnetization decay curve for the part with a short relaxation time of t = 0 to 0.05 ms uses the data obtained by the Solid Echo method, and the magnetization decay curve for t greater than 0.05 ms is obtained from CPMG y(t) in equation (1) can be approximated by a least-squares method using the data obtained by the modulus.

In the above formula (1), it is known that the component with low molecular mobility is Gaussian and the component with high molecular mobility is Lorentzian, and the Gaussian/Lorentzian ratio of each component can be known from the Weibull coefficient (W). . For example, if the Weibull coefficient is 1, it is Lorentzian 100%, and if it is 2, it is Gaussian 100%. At this time, the crystalline component with a short relaxation time has low mobility and has a Gaussian shape. Further, the other components can be considered as the component with W=1 to 2 like the second term and the constant of the third term, and the relaxation can be expressed as the sum of them. At this time, A ₁ and A ₂ represent a crystalline component with a short relaxation time and a component with a longer relaxation time than the crystalline component, respectively. ℃) can be used as the degree of crystallinity in water.

EVOH-based resins are usually copolymerized with ethylene, so they are difficult to dissolve in water. Therefore, in order to obtain an aqueous solution from an EVOH-based resin, a procedure of dispersing EVOH-based resin particles in water at about room temperature (25° C.) and then heating as necessary is commonly used. At this time, as described later, in water near room temperature, while increasing the contact area with water, while maintaining an appropriate degree of crystallinity, only the surface of the particles is easily soluble. In addition, it is preferable that the degree of crystallinity is rapidly lowered after heating and dissolved in a short period of time.

As an index for obtaining such EVOH-based resin particles, it was found that the relationship between the degree of crystallinity in water C _w (30° C.), C _w (70° C.) and the content of ethylene structural units is important.

That is, the present modified EVOH-based resin particles are composed of ethylene structural units (mol%), the _degree of crystallinity in water at 30°C (30°C) determined by pulse NMR in heavy water _, (70° C.), the following formula (3) is satisfied.
3.5×E−21≦(100−Cw (30° C.))/100×(Cw (30° C.)−Cw (70° C.)) (3)
In the above formula (3), E is the content of ethylene structural units in the modified EVOH resin particles.
Since the modified EVOH-based resin particles satisfy the above formula (3), they can be rapidly dissolved when heated to 70°C while maintaining a state in which the particles are easily dispersed in water at 30°C.

The value of (100−Cw(30° C.))/100×(Cw(30° C.)−Cw(70° C.)) is preferably 5 to 21, more preferably 6.6 to 13.
In order to make the value of (100−Cw (30° C.))/100×(Cw (30° C.)−Cw (70° C.)) less than 5, Cw (30° C.) = about 5.3 to 35 It must be controlled within the range of Cw (30° C.)−Cw (70° C.)=5.3 to 7.3. Such modified EVOH-based resin particles have almost no change in crystallinity in water between 30° C. and 70° C., making it difficult to control dissolution by heating, and tend to be unsuitable for practical use.
Also, in order to make the value of (100−Cw (30° C.))/100×(Cw (30° C.)−Cw (70° C.)) greater than 21, Cw (30° C.)=30 to 70 , Cw (70° C.)=0 to 8.4. Such modified EVOH-based resin particles tend to undergo abrupt changes in crystallinity in water due to temperature changes, making it difficult to raise the temperature during dissolution.

The C _w (30° C.) is preferably 52% or less, more preferably 15 to 52%, even more preferably 16 to 45%, particularly preferably 20 to 25%. If C _w (30° C.) exceeds 52%, dispersibility in water at 30° C. is preferable, but dissolution tends to take a long time even with heating. Also, if C _w (30° C.) is less than 15%, the particles tend to fuse together in water at 30° C., and the fused particles tend to turn into lumps and take a long time to dissolve.

It is preferable that the present modified EVOH-based resin particles further satisfy the formula (4) in water crystallinity C _w (70° C.) at 70° C.
5≦Cw (70° C.)≦11 (4)
If Cw (70° C.) is less than 5, the particles tend to fuse together during melting at elevated temperature, which tends to lengthen the time required for melting, which is not preferable.
When Cw (70°C) exceeds 11, it means that a high degree of crystallinity is maintained in water even at 70°C, and there is a tendency that it is difficult to dissolve in water and difficult to form into a gas barrier material by coating an aqueous solution. be.

Methods for controlling the degree of crystallinity in water _Cw at 30°C and 70°C include, for example,
(I) a method of mixing a resin having a resin structure different from that of the modified EVOH resin;
(II) a method for controlling the resin structure of a modified EVOH resin;
(III) A method of controlling the molecular weight of the modified EVOH-based resin (IV) A method of mixing modified EVOH-based resins with different degrees of saponification,
(V) A method of adding an additive that acts on the hydrogen bonding of the modified EVOH resin, such as nanosilica,
(VI) A method of adding a plasticizer that acts on the amorphous portion of the modified EVOH-based resin (VII) A method of controlling the particle size of the modified EVOH-based resin particles,
etc.
In the present invention, the degree of crystallinity in water can be controlled by using these alone or in combination of two or more. Among them, (II) a method of controlling the resin structure of the modified EVOH resin and (VII) a method of controlling the particle size of the modified EVOH resin particles are preferably used in combination.

Methods for controlling the resin structure of the (II) modified EVOH resin include, for example, a method of controlling the content of ethylene structural units in the modified EVOH resin, a method of controlling the degree of saponification, and a primary hydroxyl group structure in the side chain. The method of introducing units is preferable because it is easy to control and the degree of crystallinity of particles can be uniformly controlled. These methods are described below.

First, a method for controlling the content (E) of ethylene structural units will be described.
The ethylene structural unit makes it difficult for the vinyl alcohol structural unit having a secondary hydroxyl group to exist adjacently in the modified EVOH resin, and thus has the effect of adjusting the compatibility with water due to the interaction between the secondary hydroxyl groups. be.

The ethylene structural unit content (E) of the modified EVOH resin particles is 7.1 to 16.5 mol%, preferably 7.2 to 11 mol%, more preferably 7.5 to 10 mol%. .
When the ethylene structural unit content exceeds 16.5 mol %, it becomes difficult to dissolve in water. Further, when the content of the ethylene structural unit is less than 7.1 mol %, the gas barrier properties under high humidity conditions are lowered when the aqueous solution is applied to the base material to prepare the gas barrier material, and the compatibility with water described above is reduced. There is little effect of adjusting ease.

When the content (E) of the ethylene structural unit is less than 7.1 mol% and the degree of saponification is high, )) tends to be a value of 17 or more and does not satisfy the above formula (3). This is because the value of _Cw (30°C) becomes too large, so _Cw (70°C) also tends to increase, but the effect of increasing Cw (30°C) - Cw (70°C) overcomes it. it is conceivable that. In such a case, it becomes difficult to dissolve in water at 70°C.
In this case, by reducing the degree of saponification or introducing a primary hydroxyl group structure to the side chain, the value can be reduced, it is difficult to satisfy the equation (3).

When the content (E) of the ethylene structural unit is 7.1 mol% or more, in order to satisfy the formula (3), for example, a modified EVOH resin with a high degree of saponification and a low molecular weight may be used, or the side chain It is preferable to increase the introduction amount of the primary hydroxyl group structural unit.

Next, a method for controlling the degree of saponification will be described.
The degree of saponification of the modified EVOH resin used in the present invention is usually 95 mol % or more, preferably 98.5 mol % or more, and particularly preferably 99 mol % or more.
In the present invention, the use of a modified EVOH resin with a high degree of saponification tends to make it easier to satisfy the formula (3). Further, when the gas barrier material is prepared by applying an aqueous solution to a base material, if the degree of saponification is too low, the gas barrier properties, aroma retention properties, solvent resistance, and oil resistance tend to deteriorate, especially at high humidity.

Furthermore, a method for controlling the introduction amount (D) of the side chain primary hydroxyl group structural unit will be described.
In the present modified EVOH-based resin particles, the introduction amount (D) of the side chain primary hydroxyl group structural unit is preferably 2.5 mol% or more, more preferably 2.5 mol% or more and less than 10 mol%, and 3 to 6 mol%. More preferably, 3 to 4.5 mol % is particularly preferable. When the introduction amount (D) of the side chain primary hydroxyl group structural unit is 2.5 mol % or more, the formula (3) tends to be easily satisfied. This is because the introduction amount (D) of the side chain primary hydroxyl group structural unit is 2.5 mol % or more, so that the Cw (30 ° C.) is lowered, but the surface of the modified EVOH resin particles does not dissolve at once. presumably to preserve sexuality. Then, the larger the introduction amount (D) of the side chain primary hydroxyl group structural unit, the smaller the value of 100−Cw (30° C.))/100×(Cw (30° C.)−Cw (70° C.)). .
If the introduction amount (D) of the side chain primary hydroxyl group structural unit is too large, a large amount of a monomer having a primary hydroxyl group in the side chain or a monomer having the primary hydroxyl group in the side chain protected with an ester or the like, which will be described later, is used during the copolymerization reaction. It is necessary and tends to be economically disadvantageous.

Next, the method (VII) for controlling the particle size of the modified EVOH resin particles will be described.
The particle size of the modified EVOH-based resin particles can be controlled to some extent by the saponification and subsequent treatment methods described below.
In the present modified EVOH-based resin particles, the proportion of particles passing through a sieve with a mesh size of 150 μm is usually 10 to 20% by mass, preferably 15 to 19% by mass. Such particles tend to easily satisfy the formula (3), prevent aggregation in water at 30°C, and shorten the dissolution time at 70°C.
If the proportion of particles passing through a sieve with an opening of 150 μm exceeds 20% by mass, it tends to be difficult to satisfy the above (3), and tends to aggregate even in water at 30 ° C. be.
If the proportion of particles passing through a sieve with an opening of 150 μm is less than 10% by mass, even if the content of ethylene structural units is increased, it tends to be difficult to satisfy the above formula (3). For example, the range of 3.5×E−21>(100−Cw (30° C.))/100×(Cw (30° C.)−Cw (70° C.)) is likely to occur, and such particles are Cw (70 ° C) is large and the solubility in water at 70 ° C is low, and although the individual values of Cw (30 ° C) and Cw (70 ° C) are well controlled, the balance It tends to take a long time to dissolve to the core of the particles.

A method for producing the modified EVOH-based resin particles will be described below.

EVOH resins are thermoplastic resins usually obtained by saponifying ethylene-vinyl ester copolymers, which are copolymers of ethylene and vinyl ester monomers, and are composed of ethylene structural units and vinyl alcohol structures. units, and usually contains a small amount of vinyl ester structural units remaining unsaponified.

Vinyl ester monomers used in the present modified EVOH resin particles include, for example, vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl versatate, vinyl trifluoroacetate and the like. These may be used alone or in combination of two or more. Among these, vinyl acetate is preferable from an economical point of view.

In addition to the vinyl ester-based monomers, other copolymers such as monomers having a primary hydroxyl group in the side chain, monomers in which the primary hydroxyl group in the side chain is protected with an ester or the like, ethylenically unsaturated monomers, etc. Polymerized monomers may also be used. These may be used alone or in combination of two or more.
Among others, as a method for obtaining a modified EVOH resin having a primary hydroxyl group structure in the side chain used in the present invention, it is possible to use a monomer having a primary hydroxyl group in the side chain or a monomer having the primary hydroxyl group in the side chain protected with an ester or the like. preferable.

Examples of the monomer having a primary hydroxyl group in the side chain include allyl alcohol, 3-buten-1-ol, 4-penten-1-ol, 5-hexene-1-ol, 6-hepten-1-ol, meta Monohydroxyalkyl group-containing monomers such as lyl alcohol; 2-methylene-1,3-propanediol, 3,4-diol-1-butene, 4,5-diol-1-pentene, 4,5-diol-3- Dihydroxyalkyl group-containing monomers such as methyl-1-pentene, 5,6-diol-1-hexene and glycerin monoallyl ether can be used.

Examples of the monomer in which the primary hydroxyl group in the side chain is protected with an ester or the like include acetic acid ester of the monomer having the primary hydroxyl group in the side chain. Specifically, for example, monoacetoxyalkyl group-containing monomers such as allyl acetate, 3-butenyl acetate, 4-pentenyl acetate, 5-hexenyl acetate, 6-heptenyl acetate, and methallyl acetate; 2-methylene-1,3-propane Diol diacetate, 3,4-diacetoxy-1-butene, 4,5-diacetoxy-1-pentene, 4,5-diacetoxy-3-methyl-1-pentene, 5,6-diacetoxy-1-hexene, 3- diacetoxyalkyl group-containing monomers such as allyloxy-1,2-propanediol diacetate;

Examples of the ethylenically unsaturated monomer include olefins such as propylene, 1-butene and isobutene; acrylic acid, methacrylic acid, crotonic acid, (anhydrous) phthalic acid, (anhydrous) maleic acid, (anhydrous) itacon Unsaturated acids such as acids or salts thereof or mono- or dialkyl esters having 1 to 18 carbon atoms; propanesulfonic acid or its salts; acrylamides such as acrylamidopropyldimethylamine or its acid salts or its quaternary salts; Methacrylamides such as amides, 2-methacrylamide propanesulfonic acid or salts thereof; N-vinylamides such as N-vinylpyrrolidone, N-vinylformamide and N-vinylacetamide; Vinyl cyanides such as acrylonitrile and methacrylonitrile vinyl ethers such as alkyl vinyl ether, hydroxyalkyl vinyl ether, and alkoxyalkyl vinyl ether having 1 to 18 carbon atoms in the alkyl group; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, and vinyl bromide; vinyl silanes and the like.

Among the other copolymerizable monomers, from the viewpoint of controlling the degree of crystallinity, a monomer having a primary hydroxyl group in the side chain, a monomer having the primary hydroxyl group in the side chain protected with an ester or the like is preferable, and the primary hydroxyl group in the side chain is an ester. From the viewpoint of productivity, a monomer protected by etc. is more preferable, 3,4-diacetoxy-1-butene and 2-methylene-1,3-propanediol diacetate are more preferable, and 3,4-diacetoxy-1-butene is Especially preferred.
When a monomer having a primary hydroxyl group in the side chain or a monomer having the primary hydroxyl group in the side chain protected with an ester or the like is used as a copolymerization component, a structural unit having a primary hydroxyl group in the side chain as shown in the following general formula (1) A modified EVOH resin having

R ¹ to R ³ are not particularly limited as long as they are hydrogen atoms or organic groups. Examples of the organic group include hydrocarbon groups such as alkyl groups, alkenyl groups, alkynyl groups, phenyl groups, and naphthyl groups (these hydrocarbon groups have hydroxyl groups, fluorine, chlorine, bromine, etc. as substituents). may also be used).
The linking chain (X) linking the polymer main chain and the primary hydroxyl group structure is not particularly limited. , and may have bromine or the like as a substituent), oxyalkylene, oxyalkenylene, oxyalkynylene, oxyphenylene, hydrocarbons such as oxynaphthylene that are bonded to the polymer main chain by ether bonds (these hydrocarbons are hydroxyl groups, may have fluorine, chlorine, bromine, etc. as substituents), —CO—, —CO(CH ₂ )mCO—, —CO(CH ₂ )mCOR ⁴ —, —NR ⁵ —, —CONR ^5- , etc. (R ⁴ and R ⁵ are independently optional substituents, preferably a hydrogen atom or an alkyl group, and m is a natural number). Note that Cw (30° C.) and Cw (70° C.) are not affected regardless of the structure of R ¹ , R ² , R ³ and X as long as the structure is represented by the general formula (1).

The modified EVOH-based resin particles are composed of the above ethylene and vinyl ester-based monomers, optionally monomers having primary hydroxyl groups in side chains and/or monomers in which primary hydroxyl groups in side chains are protected with esters or the like, and other copolymerized monomers. is copolymerized to obtain a modified ethylene-vinyl ester copolymer, which is then saponified.

In the copolymerization reaction, known methods such as bulk polymerization, solution polymerization, suspension polymerization, dispersion polymerization, or emulsion polymerization can be employed. Among them, solution polymerization is preferably used because copolymerization control is easy.

Solvents used when such copolymerization is carried out by solution polymerization include lower alcohols having 1 to 5 carbon atoms such as methanol, ethanol, 1-propanol, 2-propanol and 1-butanol, acetone, 2-butanone and the like. ketones are mentioned. These may be used alone or in combination of two or more. Among them, methanol is preferably used because of ease of control of the polymerization reaction. Also, 2-propanol is preferably used when synthesizing a copolymer with a low degree of polymerization.

The amount of the solvent used can be appropriately selected in consideration of the degree of polymerization of the desired modified EVOH-based resin and the chain transfer constant of the solvent. When the solvent is methanol or 2-propanol, S (solvent)/M (monomer) is preferably 0.01 to 10 (mass ratio), more preferably 0.05 to 7 (mass ratio).

As a method for charging the copolymerization components in the solution polymerization, any method such as initial batch charging, divided charging, continuous charging such as the Hanna method in consideration of the reactivity ratio of the monomers, and the like can be adopted.

A polymerization initiator is used for the copolymerization. Examples of such polymerization initiators include 2,2′-azobisisobutyronitrile, 2,2′-azobis(2,4-dimethylvaleronitrile), 2,2′-azobis(4-methoxy-2, 4-dimethylvaleronitrile), acetyl peroxide, benzoyl peroxide, lauryl peroxide, t-butyl peroxyneodecanoate, 1,1,3,3-tetramethylbutyl peroxyneodeca Noate, diisopropylperoxydicarbonate, di-2-ethylhexylperoxydicarbonate, and other peroxide initiators. These may be used alone or in combination of two or more.

The amount of the polymerization initiator to be used varies depending on the type of the polymerization catalyst and cannot be determined unconditionally, but is arbitrarily selected according to the polymerization rate and the target molecular weight. For example, when 2,2'-azobisisobutyronitrile or t-butyl peroxyneodecanoate is used, it is usually 10 to 2000 ppm, preferably 50 to 1000 ppm, relative to the vinyl ester monomer.

The polymerization temperature for copolymerization is preferably selected from the range of 40° C. to the boiling point depending on the solvent and ethylene pressure used.

Moreover, during the copolymerization, the copolymerization may be carried out in the presence of a chain transfer agent as long as the effects of the present invention are not impaired. Chain transfer agents include, for example, aldehydes such as acetaldehyde, propionaldehyde and crotonaldehyde; and mercaptans such as 2-hydroxyethanethiol. These may be used alone or in combination of two or more. Among them, aldehydes are preferably used. The amount of the chain transfer agent to be added during copolymerization is determined according to the chain transfer constant of the chain transfer agent and the degree of polymerization of the target EVOH-based resin. 0.1 to 10 parts by mass is preferable.

After the copolymerization components are copolymerized, it is also preferable to add a conjugated polyene such as sorbic acid as a polymerization inhibitor in order to reliably terminate the reaction.
Thus, a modified ethylene-vinyl ester copolymer having a structural unit in which the side chain primary hydroxyl group and/or the side chain primary hydroxyl group is protected with an ester is obtained.

A preferable molecular weight range of the ethylene-vinyl ester copolymer can be determined for the reacetylated ethylene-vinyl ester copolymer described later. A preferred molecular weight range will be described later.

The modified EVOH resin particles of the present invention can be obtained by saponifying the modified ethylene-vinyl ester copolymer. In addition, it is preferable to reduce the content of unreacted vinyl ester monomers remaining in the solution before saponification from the viewpoint of suppressing coloring of the resulting modified EVOH resin particles.

Saponification is carried out using a saponification catalyst while the modified ethylene-vinyl ester copolymer obtained above is dissolved in alcohol or hydrous alcohol.
Moreover, as described above, the preferred particle size control of the modified EVOH-based resin particles can be achieved by the saponification method and post-treatment.

Examples of the alcohol include lower alcohols having 1 to 5 carbon atoms such as methanol, ethanol and propanol. These may be used alone or in combination of two or more. Among them, methanol is preferred.

The concentration of the modified ethylene-vinyl ester copolymer in alcohol is appropriately selected depending on the viscosity, and is usually 5 to 60% by mass.

Examples of the saponification catalyst include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate, potassium methylate, and potassium ethylate; alkali catalysts such as alcoholates; , nitric acid, methasulfonic acid, zeolite, and cation exchange resins.
Among them, alkali catalysts such as alkali metal hydroxides and alcoholates are preferable.

Although the temperature for saponification is not limited, it is preferably in the range of 20 to 140°C.
At the beginning of the saponification reaction, a solution dissolved in a solvent such as alcohol or hydrous alcohol forms particulate matter as the saponification progresses, and the viscosity of the system increases significantly when the particulate matter is produced. .

As described above, the modified EVOH-based resin particles preferably have a specific particle size, and may be sieved as necessary to obtain the desired particle ratio. It is preferable to carry out the conversion reaction and the subsequent production of particles by any one of the following methods (1) to (3).
(1) After a solution of a modified ethylene-vinyl ester copolymer having a concentration of 30 to 60% by mass is charged into a reactor, the saponification catalyst is added so that the equivalent of the vinyl ester in the copolymer is 5 to 20 mmol. After adding the saponification catalyst, the time until the start of particulate matter generation is controlled to be 5 to 30 minutes, and the thickened system is stirred using a powerful stirrer such as a kneader. Method of obtaining particles by advancing the reaction (2) After charging a solution of modified ethylene-vinyl ester copolymer with a concentration of 5 to 20% by mass into a reactor, a saponification catalyst is added to the vinyl ester in the copolymer. After addition of the saponification catalyst, it was stirred under moderate conditions using a conventional stirrer so that the time until the start of particulate matter generation was 15 to 120 minutes. How to drive a reaction and get particles.
(3) A saponification catalyst is added to a modified ethylene-vinyl ester copolymer solution having a concentration of 20 to 50% by mass so that the equivalent amount of the saponification catalyst is 20 to 500 mmol relative to the vinyl ester in the copolymer. , After adding the saponification catalyst, mix quickly so that it takes 1 to 5 minutes to generate particulate matter and thicken, then allow the reaction to proceed by standing still, and crush immediately after thickening or at the end of the reaction. How to get particles.
In the method (1) or the method (2), the particle size of the particles after the saponification reaction is completed can be controlled by stirring from the start of generation of the particulate matter until the system becomes most viscous. By increasing the number of particles with a fine particle size, the number of particles can be increased.
On the other hand, in the method (3), the particle size can be controlled by the pulverization method, but the pulverization must be intensified in order to make the particle size smaller.

Among them, the methods (1) and (2) above for the saponification reaction and the subsequent method for producing particles are such that the amount of particles that easily pass through a 150 μm sieve is in the range of 10% by mass or more and 20% by mass or less. It is preferable because it can

After that, the particles are washed and dried to obtain the present modified EVOH resin particles.
Moreover, in order to increase the degree of saponification, it is also preferable to wash the particles once generated as secondary saponification, disperse them again in alcohol or the like, add a saponification catalyst, and further react them.

By the saponification, vinyl ester units in the modified ethylene-vinyl ester copolymer are converted to vinyl alcohol units to obtain modified EVOH resin particles.

In addition, when a monomer whose hydroxyl group is protected with an ester or the like is copolymerized as a copolymerization component, the ester of the monomer protected by saponification is also deprotected at the same time, converted to a primary hydroxyl group structure on the side chain, and a primary hydroxyl group on the side chain. Modified EVOH resin particles having a structural unit having a hydroxyl group are obtained.

For example, when 3,4-diacetoxy-1-butene is used as a copolymerization component, the modified EVOH-based resin particles obtained by deprotection by saponification or the like have primary hydroxyl groups represented by the following general formula (2). in the side chain.

Further, when, for example, 2-methylene-1,3-propanediol diacetate is used as a copolymerization component, the resulting modified EVOH-based resin particles have primary hydroxyl groups represented by the following general formula (3) as side chains. have in

In addition, in the present modified EVOH-based resin particles, a small amount of ester groups may remain without being completely saponified.

The modified EVOH-based resin particles can be obtained by such a method. The modified EVOH-based resin may have other hydroxyl group structures (secondary hydroxyl groups and tertiary hydroxyl groups) in the side chains in addition to the primary hydroxyl group structural units described above.

The content of ethylene structural units in the present modified EVOH-based resin particles is as described above, and can be controlled by adjusting the ethylene pressure during copolymerization.

The content (D) of the side chain primary hydroxyl group structural unit of the modified EVOH-based resin particles is as described above. It can be controlled by the amount of protected monomer charged.

The molecular weight of the modified EVOH resin particles is 5.5×10 ⁴ to 1.1×10 as the viscosity average molecular weight of a tetrahydrofuran solution of the ethylene-vinyl ester copolymer obtained by reacetylating the modified EVOH resin particles. ⁵ , and more preferably 6.0×10 ⁴ to 8.5×10 ⁴ . If the viscosity-average molecular weight is less than 5.5×10 ⁴ , when the modified EVOH-based resin particles are applied to a base material, the entanglement between resin molecules tends to be reduced, and the gas barrier material tends to become brittle. If it exceeds 1×10 ⁵ , the viscosity of the modified EVOH-based resin particles in an aqueous solution tends to increase, making it difficult to apply to a substrate.
Further, when the viscosity-average molecular weight is high, the EVOH resin after saponification tends to have a high degree of crystallinity in water C _w (30°C) at 30°C, which tends to make it difficult to satisfy the formula (3). .

Reacetylation of the modified EVOH-based particles can be carried out by the method described in Examples.
By using the viscosity average molecular weight of such an ethylene-vinyl ester copolymer as an index, when it is necessary to compare with the viscosity average degree of polymerization measured for an aqueous solution of an EVOH resin as shown in JIS K6726. , which has the advantage of matching criteria and facilitating comparisons. In particular, when the EVOH-based resin is not uniformly dissolved in water at 30° C., the molecular weight cannot be evaluated as the viscosity of the aqueous solution, but the method of the present invention has the advantage of being able to evaluate.

The viscosity-average molecular weight of the tetrahydrofuran solution of the reacetylated ethylene-vinyl ester copolymer is determined by size exclusion chromatography in tetrahydrofuran in accordance with JIS K7252-2. , as K and α in the Mark-Houwink-Sakurada formula, are given in Annex B of the same standard as the values of polyvinyl acetate in tetrahydrofuran, K=3.5×10 ² cm ³ /g, α=0 It is a value calculated using 0.63.

The biodegradability of the modified EVOH resin is preferably 20% or more, more preferably 25% or more, and particularly preferably 30% or more. The biodegradability is obtained from the biochemical oxygen consumption and the theoretical oxygen demand when tested under the following conditions with reference to the method described in JIS K6950.
・Equipment: BOD TESTER 200F (manufactured by Taitec Co., Ltd.)
・Inoculum source: Return sludge from a sewage treatment plant that treats domestic sewage ・Standard test culture solution: 100 mL
・ Seed concentration: 90 mg / L
・Temperature: 25±1℃
・Period: 28 days

Regarding the particle size of the modified EVOH-based resin particles, the content of particles passing through a JIS Z8801 sieve with a mesh size of 2.36 mm is preferably 80% by mass or more, particularly preferably 85% by mass or more. In addition, the content of particles passing through a sieve with a mesh size of 150 μm is preferably 10% by mass or more and 20% by mass or less from the viewpoint of ease of subsequent handling, and particularly 15% by mass or more and 19% by mass or less. This is good.
If the content of particles passing through a sieve with a mesh size of 2.36 mm is less than 80% by mass, it tends to take too long to dry the particles, and the particles cannot be dissolved even at a high temperature of 70 ° C. or higher when preparing an aqueous solution. It tends to be time consuming. The content of particles passing through a sieve with a mesh size of 150 μm, the effects on the crystallinity in water Cw (30° C.) and Cw (70° C.) of particles, and the reasons for the preferred range have already been described.

The modified EVOH-based resin particles can be mixed with other components to form a resin composition. Examples of the other components include other thermoplastic resins, plasticizers, lubricants, stabilizers, surfactants, colorants, ultraviolet absorbers, antistatic agents, desiccants, cross-linking agents, metal salts, fillers, Various fibers etc. are mentioned. These may be used alone or in combination of two or more.

The content of the modified EVOH-based resin particles in the resin composition is usually 80% by mass or more, preferably 90% by mass or more, and more preferably 95% by mass or more. In addition, an upper limit is 100 mass % normally.

The modified EVOH-based resin particles can be suitably used as a gas barrier material such as a food packaging material by making it into a film.
The method for obtaining the gas barrier material from the present modified EVOH resin particles is not particularly limited. (ii) a method of melt-molding the present modified EVOH resin particles to form a layer of the present EVOH resin particles to form a gas barrier material, and the like. .

In the method (i) above, the solvent used for the solution of the modified EVOH-based resin particles includes, for example, water, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and the like. -5 lower alcohols. These may be used alone or in combination of two or more. Among them, water and a mixed solvent of water and 2-propanol are preferred, and water is particularly preferred.

The solid content concentration in the solution of the modified EVOH resin particles is usually 0.5 to 30% by mass, preferably 5 to 20% by mass.

Examples of methods for applying the solution of the present modified EVOH resin particles include known methods such as bar coater, roll coating, die coating, gravure coating, comma coating and screen printing. Among them, a bar coater is preferable.

After coating, the gas barrier material made of the modified EVOH-based resin can be obtained by drying, for example, by heat treatment at 60 to 105° C. for 0.5 to 10 minutes.

Examples of the melt molding method in the above method (ii) include extrusion molding, injection molding, inflation molding, press molding, and blow molding.

Thus, a gas barrier material having a layer made of the modified EVOH resin particles is obtained. The gas barrier material may be a gas barrier material having a single-layer structure or a gas barrier material having a multi-layer structure, but preferably has a multi-layer structure. The multilayer barrier material preferably has at least one layer comprising the modified EVOH-based resin particles. Moreover, the gas barrier material having a multi-layer structure may be formed by laminating a layer composed of the present modified EVOH-based resin particles, or may be laminated with another base resin.

Examples of the base resin include linear low-density polyethylene, low-density polyethylene, ultra-low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-propylene (block and random) copolymer, and ethylene-α-olefin. Polyethylene resins such as (α-olefin having 4 to 20 carbon atoms) copolymer, polypropylene resin such as polypropylene, propylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymer, polybutene, polypentene (unmodified) polyolefin resins such as polycyclic olefin resins (polymers having a cyclic olefin structure in at least one of the main chain and the side chain), and graft modification of these polyolefins with unsaturated carboxylic acids or esters thereof Polyolefin resins in a broad sense, including modified olefin resins such as unsaturated carboxylic acid-modified polyolefin resins, ionomers, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-acrylic acid ester copolymers, Polyester resin, polyamide resin (including copolyamide), polyvinyl chloride, polyvinylidene chloride, acrylic resin, polystyrene, vinyl ester resin, polyester elastomer, polyurethane elastomer, polystyrene elastomer, chlorinated polyethylene, Examples include halogenated polyolefins such as chlorinated polypropylene, aromatic or aliphatic polyketones, and the like. These may be used alone or in combination of two or more. A biodegradable resin may be used in order to obtain a gas barrier material that imparts biodegradability to the entire material. Moreover, these base resins may be subjected to surface treatment such as corona treatment.

The thickness of the layer composed of the modified EVOH-based resin particles is generally 1 to 200 μm, preferably 1 to 100 μm, particularly preferably 1 to 50 μm. When the gas barrier material has a multi-layered structure, the thickness is the sum of the thicknesses of all the layers composed of the modified EVOH-based resin particles contained in the gas barrier material.

In addition, the oxygen permeability of the layer composed of the modified EVOH-based resin particles is preferably 5 cc·3 μm/m ² day·atm or less in an environment of 23° C. and 0% RH, and preferably 1 cc·3 μm/m ² . · It is more preferably 0.1 cc·3 μm/m ² ·day·atm or less, and particularly preferably 0.1 cc·3 µm/m 2 ·day·atm or less.
Furthermore, in an environment of 23° C. and 65% RH, it is preferably 30 cc·3 μm/m ² ·day·atm or less, more preferably 15 cc·3 μm/m ² ·day·atm or less, and 10 cc·3 μm. /m ² ·day·atm or less is particularly preferable.
The oxygen permeability can be determined by an oxygen permeability measuring device.

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. "Parts" and "%" in the examples are based on mass unless otherwise specified.

The methods of pulse NMR measurement and molecular weight measurement in Examples are shown below.

［水中結晶化度］
前記で求めた３０℃および７０℃におけるＡ₁及びＡ₂を用いて、下記の式（２）から３０℃における水中結晶化度Ｃ_w（３０℃）と、７０℃における水中結晶化度Ｃ_w（７０℃）を求めた。
水中結晶化度Ｃｗ（Ｘ℃）を求めた。
Ｃ_w（Ｘ℃）＝Ａ₁／（Ａ₁＋Ａ₂）×１００ ・・・（２） [Pulse NMR measurement]
29 mg of a sample of modified EVOH-based resin particles was weighed and placed in a glass sample tube for pulse NMR with a diameter of 10 mm. This sample was subjected to measurements by the SOlid Echo method and the CPMG method at 30° C. using a pulse NMR apparatus (Bruker, Mq20). Details of the measurement conditions other than the measurement temperature (30° C. or 70° C.) are as follows.
[Measurement condition]
^1H resonance frequency: 20MHz
Solid Echo method
¹ H 90° pulse width: 3.1 μs
FID observation time domain: 800 μs
Repeat time: 15s
Accumulation times: 128 times CPMG method
¹ H 90° pulse width: 3.1 μs
¹ H 180° pulse width: 6.2 μs
Pulse interval: 0.05ms
Number of measurement points: 800
Repeat time: 15s
Accumulated number: 64 times A ₂ , T _2M , and y ₀ of Equation (1) at 30°C and 70°C were obtained using magnetization attenuation curves obtained by the CPMG method. Note that A ₂ , T _2M , and y ₀ were calculated using software TDNMR-A attached to the apparatus. In addition to the above method, A ₂ , T _2M and y ₀ can also be obtained by converting the data into a text file, reading it with Microsoft's spreadsheet software Excel, and using the approximate calculation function.
After that, the magnetization decay curve obtained by the Solid Echo method was made into a text file and developed in spreadsheet software Excel to obtain (t, y(t)). Then, using this (t, y(t)) and A ₂ , T _2M , and y ₀ obtained above,
(t, y(t)-A ₂ ×exp[-t/T _2M ]-y ₀ ).
Using the approximate calculation function of the spreadsheet software Excel, A ₁ and T _2s of the following formula (1) at 30° C. and 70° C. were obtained.

[Degree of crystallinity in water]
Using A ₁ and A ₂ at 30 ° C. and 70 ° C. obtained above, from the following formula (2), the degree of crystallinity in water C _w at 30 ° C. (30 ° C.) and the degree of crystallinity in water C _w at 70 ° C. (70°C) was obtained.
Crystallinity in water Cw (X°C) was determined.
C _w (X° C.)=A ₁ /(A ₁ +A ₂ )×100 (2)

[Reacetylation of Modified EVOH Particles]
After dispersing 0.5 g of modified EVOH resin particles in a mixed solvent of 4.0 g of glacial acetic acid, 4.0 g of acetic anhydride, and 0.5 g of pyridine and dissolving the mixture at 130°C, the mixture was further stirred at 130°C with occasional stirring. The reaction was allowed to proceed for 3 hours. After completion of the reaction, the reaction mixture was cooled, poured onto a polytetrafluoroethylene sheet, and air-dried at room temperature for 2 days to form a film. This film was placed in a vacuum dryer at 60° C., and the volatile components were removed while occasionally turning it inside out to obtain a reacetylated product.

[Measurement of molecular weight]
A tetrahydrofuran solution was prepared from the re-acetylated product obtained as described above, and its viscosity average molecular weight was determined as follows according to JIS K7252-2. That is, a 0.5% solution of ethylene-vinyl ester copolymer in tetrahydrofuran (THF) was applied to a high-performance liquid chromatograph (ACQUITY APC system manufactured by Waters), and columns: one ACQUITY APC XT450 and one ACQUITY APC XT200. , ACQUITY APC XT45 were injected into a system using two ACQUITY APC XT45 in series, and the elution time and the signal intensity at that time were recorded using a differential refractive index detector. Molecular weights were calibrated with standard polystyrene. In addition, K and α in the Mark-Houwink-Sakurada formula for determining the viscosity-average molecular weight are shown in JIS K7252-2 Annex B as the value of polyvinyl acetate in tetrahydrofuran, K=3. .5×10 ² cm ³ /g, α=0.63 was used.

<Example 1>
[Synthesis of modified ethylene-vinyl ester copolymer]
A temperature-controllable autoclave was charged with 460 parts of vinyl acetate, 42 parts of 3,4-diacetoxy-1-butene as a monomer in which the primary hydroxyl group in the side chain was protected with an ester or the like, and 195 parts of methanol, and the system was filled with nitrogen gas. After the replacement was performed once, the content was replaced with ethylene, and the temperature was raised to 67° C. while stirring. After the temperature was raised, ethylene was pressurized so that its partial pressure was 1.0 MPa, and while stirring was continued, a solution of 0.102 parts of t-butyl peroxyneodecanoate dissolved in 5.1 parts of methanol was added. The polymerization reaction was carried out while adding over 4 hours. After the addition was completed, stirring was continued at 67° C. for 3 hours to continue the polymerization reaction.
After that, as a polymerization termination reaction, a solution of 0.096 parts of sorbic acid (0.021 parts with respect to 100 parts of charged vinyl acetate monomer) dissolved in 100 parts of methanol was added and cooled to room temperature (23° C.). Further, for the purpose of reducing unreacted monomers, removal of volatile matter by heating at 75° C. and addition of methanol were repeated to obtain a methanol solution of an ethylene-vinyl acetate-3,4-diacetoxybutene copolymer. At this time, the amount of residual vinyl acetate monomer in the solution was 10 ppm.

[Synthesis of modified EVOH-based resin-based resin particles]
A primary saponification was then carried out. The above solution was diluted with methanol to adjust the concentration to 30%, stirred with a kneader, and while maintaining the solution temperature at 45 ° C., an 8.7% methanol solution of sodium hydroxide was added to acetic acid, which is a copolymer of sodium hydroxide. An amount to give 9 mmol equivalents to vinyl units was added and stirring was continued. After about 15 minutes, the saponified product precipitated with an increase in viscosity, finally becoming a slurry containing particulate matter. After 1 hour, an 8.7% methanol solution of sodium hydroxide was added in such an amount that the sodium hydroxide was equivalent to 11 mmol with respect to the vinyl acetate units of the copolymer, and the primary saponification was continued for an additional hour.
For further saponification, secondary saponification was performed. After the resulting slurry was once filtered, the saponified product was again dispersed in 5 times the amount of methanol. was added in an amount of 50 mmol equivalent to the first vinyl acetate unit of , and reacted at 50°C for 3 hours. After the reaction, neutralize with acetic acid, filter the slurry again to obtain a wet cake, wash the wet cake 3 times with 5 times the mass of methanol, filter, and then place in a hot air dryer at 100°C for 8 hours. After drying, modified EVOH-based resin particles were obtained.
The resulting modified EVOH-based resin particles had a 1,2-butanediol structure as a primary hydroxyl group structural unit in the side chain.
Further, the degree of saponification of the obtained modified EVOH-based resin particles was 99.7 mol % when analyzed in terms of alkali consumption for hydrolysis of residual vinyl ester units.
The modified ethylene-vinyl ester copolymer obtained by reacetylating the modified EVOH resin particles had a viscosity average molecular weight of 6.03×10 ⁴ .
Further, the content of ethylene structural units and the content of 1,2-butanediol structural units by NMR measurement were 9.0 mol % and 4.0 mol %, respectively.
Further, 92% by mass of the obtained modified EVOH resin particles passed through a JIS Z8801 sieve with an opening of 2.36 mm, and 17% by mass of the particles passed through a sieve with an opening of 150 μm. .
The polymerization method, saponification method, presence or absence of secondary saponification, etc. of the modified EVOH-based resin particles of Example 1 are shown in Table 1 below, properties are shown in Table 2 below, and the results of pulse NMR measurement are shown in Table 3.

<Example 2>
[Synthesis of modified ethylene-vinyl ester copolymer]
A temperature-controllable autoclave was charged with 460 parts of vinyl acetate, 32 parts of 3,4-diacetoxy-1-butene as a monomer in which the primary hydroxyl group in the side chain was protected with an ester or the like, and 75 parts of methanol, and the system was filled with nitrogen gas. After the replacement was performed once, the content was replaced with ethylene, and the temperature was raised to 67° C. while stirring. After raising the temperature, ethylene was pressurized so that its partial pressure was 1.0 MPa, and a solution obtained by dissolving 0.082 parts of 2,2′-azobisisobutyronitrile in 10 parts of methanol was added and stirred. A polymerization reaction was carried out by keeping the internal temperature at 67° C. for 4 hours. After that, as a polymerization termination reaction, a solution of 0.096 parts of sorbic acid (0.021 parts with respect to 100 parts of charged vinyl acetate monomer) dissolved in 100 parts of methanol was added and cooled to room temperature (23° C.). Further, for the purpose of reducing unreacted monomers, volatile matter removal by heating at 40° C. under reduced pressure and addition of methanol were repeated to obtain a methanol solution of ethylene-vinyl acetate-3,4-diacetoxybutene copolymer. . At this time, the amount of residual vinyl acetate monomer in the solution was 10 ppm.

[Synthesis of modified EVOH-based resin-based resin particles]
A primary saponification was then carried out. The above solution is diluted with methanol to adjust the concentration to 10% and stirred, and while maintaining the solution temperature at 45 ° C., a 3.5% methanol solution of sodium hydroxide is added to the vinyl acetate unit of the sodium hydroxide copolymer. was added in an amount equivalent to 10 mmol with respect to the mixture, and the mixture was stirred. After about 20 minutes, the saponified product precipitated with an increase in viscosity, finally becoming a slurry containing particulate matter.
For further saponification, secondary saponification was performed. After the resulting slurry was once filtered, it was again dispersed in 20 times the amount of methanol as the saponified product, and a 3.5% methanol solution of sodium hydroxide was added to the copolymer so that sodium hydroxide was the first vinyl acetate unit in the copolymer. was added in an amount equivalent to 50 mmol with respect to , and reacted at 50°C for 3 hours. After the reaction, the mixture is neutralized with acetic acid, and the slurry is filtered again to obtain a wet cake. The wet cake is washed three times with twice the mass of methanol, filtered, and placed in a hot air dryer at 100°C for 8 hours. After drying, modified EVOH-based resin particles were obtained.
The resulting modified EVOH-based resin particles had a 1,2-butanediol structure as a primary hydroxyl group structural unit in the side chain.
The degree of saponification of the obtained EVOH-based resin particles was 99.8 mol % when analyzed by the amount of alkali consumed for hydrolysis of residual vinyl ester units.
Further, the content of the ethylene structural unit was 7.5 mol % and the content of the 1,2-butanediol structural unit was 3.3 mol % by NMR measurement.
Further, 92% by mass of the obtained modified EVOH resin particles passed through a JIS Z8801 sieve with an opening of 2.36 mm, and 18% by mass of the particles passed through a sieve with an opening of 150 μm.
The modified ethylene-vinyl ester copolymer obtained by reacetylating the modified EVOH resin particles had a viscosity average molecular weight of 8.29×10 ⁴ .
The polymerization method, saponification method, presence or absence of secondary saponification, etc. of the modified EVOH-based resin particles of Example 2 are shown in Table 1 below.

<Example 3, Comparative Examples 1 to 4>
Vinyl acetate in Example 2, types and amounts of monomers in which primary hydroxyl groups in side chains are protected with esters, etc., charged amounts of methanol and 2,2'-azobisisobutyronitrile, charged partial pressure of ethylene, termination of polymerization reaction Modified EVOH resin particles were obtained in the same manner as in Example 2, except that the amount of sorbic acid added and the presence or absence of secondary saponification were changed as shown in Table 1. Table 2 shows the properties of the modified EVOH-based copolymer, and Table 3 shows the results of pulse NMR measurement.

<Example 4>
Types and amounts of vinyl acetate, monomers whose side chain primary hydroxyl groups are protected with esters, etc., charged amounts of methanol and t-butyl peroxyneodecanoate, charged partial pressure of ethylene, amount of sorbic acid added at the time of stopping the polymerization reaction Modified EVOH resin particles were obtained in the same manner as in Example 1, except that the was changed as shown in Table 1. Table 2 shows the properties of the modified EVOH-based copolymer, and Table 3 shows the results of pulse NMR measurement.

<Comparative Example 5>
[Synthesis of modified ethylene-vinyl ester copolymer]
Vinyl acetate in Example 2, types and amounts of monomers in which primary hydroxyl groups in side chains are protected with esters, etc., charged amounts of methanol and 2,2'-azobisisobutyronitrile, charged partial pressure of ethylene, termination of polymerization reaction A methanol solution of an ethylene-vinyl acetate-3,4-diacetoxybutene copolymer was obtained in the same manner as in Example 2, except that the amount of sorbic acid added was changed as shown in Table 1.

[Synthesis of modified EVOH-based resin-based resin particles]
A primary saponification was then carried out. The above solution was diluted with methanol to adjust the concentration to 40%, and stirred while being kept at 35°C. An 8.7% methanol solution of sodium hydroxide was added thereto in such an amount that sodium hydroxide would be equivalent to 25 mmol with respect to the vinyl acetate units of the copolymer, and the mixture was thoroughly mixed for 1.5 minutes. This mixture was quickly transferred to a sealed container preheated to 50°C, and the container was left in a 50°C hot water bath. It was observed that the mixture turned white after 2 minutes and solidified into a wet cake after 4 minutes. After 30 minutes, the wet cake was removed and pulverized to obtain a slurry containing particulate matter. This was neutralized with acetic acid, washed three times with methanol twice the mass of the wet cake without performing secondary saponification, filtered, and dried in a hot air dryer at 100 ° C. for 8 hours. Modified EVOH resin particles were obtained.
The resulting modified EVOH-based resin particles had a 1,2-butanediol structure as a primary hydroxyl group structural unit in the side chain.
The degree of saponification of the obtained EVOH-based resin particles was 98.7 mol % when analyzed by the amount of alkali consumed for hydrolysis of residual vinyl ester units.
Further, the content of ethylene structural units and the content of 1,2-butanediol structural units by NMR measurement were 9.6 mol % and 3.8 mol %, respectively.
Further, 88% by mass of the obtained modified EVOH resin particles passed through a JIS Z8801 2.36 mm sieve, and 5% by mass passed a 150 μm sieve.
The modified ethylene-vinyl ester copolymer obtained by reacetylating the modified EVOH resin particles had a viscosity average molecular weight of 9.18×10 ⁴ .
The polymerization method, saponification method, presence or absence of secondary saponification, etc. of the modified EVOH resin particles of Comparative Example 5 are shown in Table 1 below, the properties are shown in Table 2 below, and the results of pulse NMR measurement are shown in Table 3.

<Comparative Examples 6 and 7>
Vinyl acetate in Comparative Example 7, types and amounts of monomers in which primary hydroxyl groups in side chains are protected with esters, etc., charged amounts of methanol and 2,2'-azobisisobutyronitrile, charged partial pressure of ethylene, termination of polymerization reaction A modified ethylene-vinyl ester copolymer was synthesized in the same manner as in Comparative Example 7, except that the amount of sorbic acid added was changed as shown in Table 1. Primary saponification was carried out in the same manner as in Comparative Example 7. Further, secondary saponification was carried out in the same manner as in Example 2 to obtain modified EVOH resin particles. Table 2 shows the properties of the modified EVOH-based copolymer, and Table 3 shows the results of pulse NMR measurement.

The dispersibility in water, solubility in water, oxygen permeability and biodegradability of the resin particles obtained in Examples and Comparative Examples were evaluated according to the following methods. The results are shown in Table 4 below.

[Dispersibility in water (30°C)]
150 mL of distilled water was placed in a 300 mL separable flask equipped with a stirrer, and 6 g of resin particles were added while stirring at an internal temperature of 30° C. and a rotation speed of 150 rpm.
The state of the resin particles immediately after injection was visually observed and evaluated according to the following criteria.
[Evaluation criteria]
A: It does not become mako B: It becomes mako, but the mako is removed by stirring for 5 minutes C: It becomes mamako, and even after stirring for 5 minutes, the mako is not removed.

[Solubility in water (70°C)]
While stirring at a rotation speed of 150 rpm, the liquid prepared with solubility in water (30 ° C.) was raised to an internal temperature of 70 ° C. within 30 minutes, maintained at 70 ° C. for 3 hours, and then allowed to cool to room temperature. . After that, the aqueous solution is no. 2, and part of the filtrate was dried at 140° C. for 30 minutes to obtain the mass A (g) of the resin particles dissolved in the aqueous solution. Further, by drying 6 g of the sample resin particles at 140° C. for 30 minutes, the non-volatile content B (g) in the resin particles was determined. Then, solubility (% by mass)=A÷B×100 was calculated, and the solubility was evaluated according to the following criteria.
[Evaluation criteria]
A: 60% by mass or more B: 50% by mass or more and less than 60% by mass C: less than 50% by mass

[Oxygen permeability]
Resin particles were dissolved in the solvent shown in Table 4 at a concentration of 10% by mass, and the solution was applied to a corona-treated PET film (thickness: 38 μm) using a bar coater, and then left for a while to confirm that the coated surface had lost its fluidity. bottom. After that, by drying at 80° C. for 5 minutes, a gas barrier material having a layer of resin particles having a thickness of about 3 μm was obtained. For this gas barrier material, the oxygen permeability at a temperature of 23° C. and a humidity of 0% RH and 65% RH was measured using an oxygen permeability measuring device ("OXTRAN 2/20" manufactured by MOCON). , was converted to a value for an EVOH-based resin having a thickness of 3 μm.

[Biodegradability]
Evaluation of biodegradability was performed under the following conditions with reference to the method described in JIS K6950. The results are shown in Table 5 below.
・Equipment: BOD TESTER 200F (manufactured by Taitec Co., Ltd.)
・Inoculum source: Return sludge from a sewage treatment plant that treats domestic sewage ・Standard test culture solution: 100 mL
・ Seed concentration: 90 mg / L
・Temperature: 25±1℃
- Duration: 28 days The degree of biodegradation was obtained from the biochemical oxygen consumption and the theoretical oxygen demand.

From the results in Table 4 above, the modified EVOH resin particles of Examples are excellent in water solubility and biodegradability, and the gas barrier material obtained from the aqueous solution of the modified EVOH resin particles has oxygen permeability It was low and biodegradable.
On the other hand, the EVOH-based resin particles or modified EVOH-based resin particles of Comparative Examples 1 to 4 were obtained by controlling the primary saponification method to control the particle size, resulting in (100-Cw (30°C))/ The relationship between the value of 100×(Cw (30° C.)−Cw (70° C.)) and the content of ethylene structural units (E) was within a preferable range.
However, in Comparative Examples 1 and 3, since the value of the content (E) of the ethylene structural unit was too low, the degree of crystallinity in water Cw (70°C) at 70°C was too large, resulting in the crystallinity in water at 70°C. The solubility was poor.
Further, in Comparative Example 2, while reducing the value of the content (E) of the ethylene structural unit, the side chain primary hydroxyl group structural unit (D) was introduced to the same extent as in each example, and the water at 70 ° C. However, the crystallinity in water Cw (70 ° C.) at 70 ° C. became too small, so the particles could be dispersed satisfactorily at 30 ° C. It took time to loosen it.
In Comparative Example 4, while reducing the value of the content (E) of the ethylene structural unit, the side chain primary hydroxyl group structural unit (D) was introduced in a smaller amount than in each example, aiming to improve Comparative Example 2. , the degree of crystallinity in water Cw (70°C) at 70°C was too large, and the solubility in water at 70°C was poor.
In the modified EVOH resin particles of Comparative Examples 5 to 7, the size of the particles could not be controlled within a predetermined range due to the change in the primary saponification method. °C)-Cw (70°C)) and the ethylene structural unit content (E) were out of the preferred range.
As a result, in Comparative Example 5, the balance between the ethylene structural unit content (E) and the side chain primary hydroxyl group structural unit (D) was poor, resulting in poor dispersibility at 30°C and poor solubility at 70°C. It was something.
Furthermore, in Comparative Examples 6 and 7, although the ethylene structural unit content (E) was about the same as in Example 4, the water solubility at 70°C was poor.

Since the modified EVOH-based resin particles are excellent in water solubility and biodegradability and have low oxygen permeability, they are useful as packaging materials, and are particularly suitable for use as packaging materials for foods, pharmaceuticals, and the like. can be done.

Claims (6)

Modified ethylene-vinyl alcohol copolymer particles having a primary hydroxyl group structural unit in a side chain and an ethylene structural unit content of 7.1 to 16.5 mol%, said modified ethylene-vinyl alcohol copolymer particles is measured by pulse NMR using the Solid Echo method and the CPMG method at measurement temperatures of 30 ° C. and 70 ° C., and the magnetization decay curve y (t) obtained by combining the magnetization is measured as a function of the time t when observing the magnetization Calculate the component ratios A 1 and A _{2 at 30 ° C. and the component ratios A 1 and A 2} at 70 ° C. from the following formula (1),

(However, the first term in formula (1) indicates a crystalline component with a short relaxation time, A ₁ indicates the component ratio, and T _2S indicates the relaxation time. The second term indicates a longer relaxation time than the crystalline A ₂ is its component ratio, T _2M is its relaxation time, the third term is a constant, W is the Weibull coefficient, and A ₁ +A ₂ +y ₀ =1.)
When the degree of crystallinity in water (unit %) _Cw (30°C) and Cw (70°C) is obtained from the above A ₁ and A ₂ at 30°C and 70°C by the following formula (2),
C _w (X° C.)=A ₁ /(A ₁ +A ₂ )×100 (2)
(However, X is 30 or 70.)
The following formula (3) is satisfied between the water crystallinity C _w (30° C.) and C _w (70° C.) and the content (E) of the ethylene structural unit of the modified ethylene-vinyl alcohol copolymer particles. Modified ethylene-vinyl alcohol copolymer particles.
3.5×E−21≦(100−Cw (30° C.))/100×(Cw (30° C.)−Cw (70° C.)) (3) 2. The modified ethylene-vinyl alcohol copolymer particles according to claim 1, further satisfying formula (4).
5≦Cw (70° C.)≦11 (4) Claim 1 or wherein the proportion of particles passing through a JIS Z8801 sieve with an opening of 2.36 mm is 80% by mass or more, and the proportion of particles passing through a sieve with an opening of 150 μm is 10% by mass or more and 20% by mass or less. 2. Modified ethylene-vinyl alcohol copolymer particles according to 2 above. 3. The modified ethylene-vinyl alcohol copolymer particles according to claim 1, wherein the degree of saponification is 95 mol % or more. 3. The modified ethylene-vinyl alcohol copolymer particles according to claim 1, wherein the introduced amount of the side chain primary hydroxyl group structure is 2.5 mol % or more. The modified ethylene-vinyl alcohol copolymer according to claim 1 or 2, wherein the tetrahydrofuran solution of the ethylene-vinyl ester copolymer after reacetylation has a viscosity-average molecular weight of 5.5 x 10 ⁴ to 1.1 x 10 ⁵ . polymer particles.