JP2024138893A - Polyvinyl alcohol resin and its manufacturing method, and polyvinyl ester polymer and its manufacturing method - Google Patents

Abstract

To provide a polyvinyl alcohol-based resin which has a very small amount of a copolymerizable monomer remaining in a polymerization step, and is excellent in gas barrier property and moldability and a method for producing the same, and a polyvinyl ester-based resin as a raw material of the same and a method for producing the same.SOLUTION: A polyvinyl alcohol-based resin has a structural unit represented by the following general formula (1) or the following general formula (2). In the formula (2), R1 is a metal atom, a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.SELECTED DRAWING: None

Description

The present invention relates to a polyvinyl alcohol resin and a method for producing the same, and a polyvinyl ester polymer and a method for producing the same.

Polyvinyl ester polymers have been widely used as raw materials for polyvinyl alcohol resins, etc. Polyvinyl alcohol resins are crystalline water-soluble polymeric materials obtained by saponifying polyvinyl ester polymers such as polyvinyl acetate, and are used in emulsifiers, suspending agents, surfactants, fiber processing agents, various binders, paper processing agents, adhesives, films, etc., taking advantage of their excellent water solubility and film properties (strength, oil resistance, film-forming properties, oxygen gas barrier properties, etc.).

Furthermore, in order to prevent food, medicine, etc. from deteriorating or spoiling due to oxygen in the air, etc., the packaging materials used for these products are required to have gas barrier properties (particularly oxygen barrier properties). Polyvinyl alcohol resins, which have excellent gas barrier properties, transparency, aroma retention, etc., are used as such packaging materials.

On the other hand, it is known that polyvinyl alcohol resin has a high melting point and poor moldability, and that under high humidity, the crystallinity is reduced by water molecules, and the gas barrier property is also reduced. For this reason, a method of lowering the melting point and improving the moldability and the gas barrier property by modifying the polyvinyl alcohol resin has been proposed. For example, Patent Document 1 describes that the barrier property under high humidity is improved by increasing the glass transition point (Tg) by introducing an alicyclic skeleton into the polyvinyl alcohol resin.

JP 2008-202048 A

However, when a monomer such as 2-norbornene described in Patent Document 1 is introduced into a polyvinyl alcohol resin by radical copolymerization, a chain transfer reaction to 2-norbornene occurs very easily during polymerization, which makes it difficult to control the modification rate and polymerization degree. If the modification rate is low, the melting point is not lowered much, making it difficult to improve moldability.
However, olefins such as 2-norbornene have poor copolymerizability with vinyl ester monomers such as vinyl acetate, and 2-norbornene is likely to remain at the end of polymerization, which poses a problem in terms of productivity.

Under these circumstances, the present invention aims to provide a polyvinyl alcohol-based resin which has an extremely small amount of copolymerized monomer remaining in the polymerization step and is excellent in productivity, and which also has excellent gas barrier properties and moldability, and a production method thereof, as well as a polyvinyl ester-based resin which is a raw material thereof and a production method thereof.

However, the present inventors have found that the gas barrier properties and moldability under high humidity conditions can be improved by introducing a structural unit represented by general formula (1) and/or general formula (2) into a polyvinyl alcohol resin, that the polyvinyl alcohol resin can be modified with a structure represented by general formula (1) and/or general formula (2) by using a compound represented by general formula (3) as a copolymerization monomer, and further that the amount of copolymerization monomer remaining at the end of polymerization is small, and have completed the present invention.

That is, the gist of the present invention is the following [1] to [6].
[1] A polyvinyl alcohol-based resin having a structural unit represented by the following general formula (1) and/or the following general formula (2):

(In the above formula (2), R ₁ is a metal atom, a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms.)
[2] The resin contains structural units represented by the above general formula (1) and/or the above general formula (2) in an amount of 0.1 to 30 mol % based on the total amount of monomer structural units in the resin. [1]
The polyvinyl alcohol resin according to claim 1.
[3] [1] or [2], characterized in that the degree of saponification is 80 to 99.9 mol% or less.
The polyvinyl alcohol resin according to claim 1.
[4] The polyvinyl alcohol-based resin according to any one of [1] to [3], characterized in that the average polymerization degree is 200 to 5,000.
[5] A polyvinyl ester polymer having a structural unit represented by the above general formula (2).
[6] The polyvinyl ester polymer according to [5], characterized in that the structural unit represented by the above general formula (2) is contained in an amount of 0.1 to 30 mol % based on the total amount of monomer structural units in the polymer.
[7] A method for producing a polyvinyl alcohol-based resin according to claim 1, which has a structural unit represented by the general formula (1) and/or the general formula (2), comprising a step of saponifying a polyvinyl ester-based polymer having a structural unit represented by the general formula (2).
[8] A method for producing a polyvinyl ester polymer according to [5] or [6] having a structural unit represented by the above general formula (2), comprising reacting a vinyl ester monomer with a compound represented by the following general formula (3):
and a compound represented by the formula (I) above.

(In the above formula (3), _R2 is a metal atom, a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms.)
[1] The method for producing a polyvinyl ester polymer according to [8], characterized in that in the step of radically polymerizing a vinyl ester monomer and a compound represented by the general formula (3), a solution containing the compound represented by the general formula (3) is continuously added dropwise.

The polyvinyl alcohol-based resin of the present invention has high gas barrier properties under high humidity conditions and can be suitably used as a gas barrier layer for packaging materials for foods, medicines, etc. In addition, the polyvinyl alcohol-based resin of the present invention has a low melting point and excellent moldability.
In addition, by using a compound having a structure of general formula (3) as a monomer, it is possible to modify a polyvinyl alcohol resin with a structure of general formula (1) and/or general formula (2),
Furthermore, the amount of copolymerization monomer remaining at the end of polymerization is small, resulting in excellent productivity.

The present invention will be described in more detail below. The polyvinyl alcohol-based resin (hereinafter, sometimes referred to as "PVA-based resin") of the present invention is characterized in that it contains a vinyl alcohol structural unit and a structural unit represented by the following general formula (1) and/or general formula (2) in the polyvinyl alcohol-based resin. Each of the components of the present invention will be described below.

[Vinyl alcohol structural unit]
The PVA resin of the present invention has at least a vinyl alcohol structural unit. The vinyl alcohol structural unit can be obtained by saponifying a structural unit derived from a vinyl ester monomer. Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, and vinyl versatate. Among them, vinyl acetate is preferably used from an economical viewpoint.

The content of vinyl alcohol units in the polyvinyl alcohol resin is not particularly limited, but is preferably 40 mol% or more and less than 99.9 mol%, more preferably 50 mol% or more and 99 mol% or less, and even more preferably 60 mol% or more and 98 mol% or less, based on 100 mol% of all structural units. If the content is less than 40 mol%, the gas barrier property may be insufficient.

[Structural unit represented by formula (1)]
The structural unit represented by the following general formula (1) is a structural unit derived from 2-(allyloxymethyl)acrylic acid or a salt thereof, or a 2-(allyloxymethyl)acrylic acid ester,
It is a structural unit obtained by lactonization of a structural unit derived from vinyl alcohol or a vinyl ester monomer. Examples of salts of 2-(allyloxymethyl)acrylic acid include sodium salts, lithium salts, potassium salts, calcium salts, and magnesium salts.
Examples of 2-(allyloxymethyl)acrylic acid esters include methyl 2-(allyloxymethyl)acrylate, ethyl 2-(allyloxymethyl)acrylate, n-propyl 2-(allyloxymethyl)acrylate, i-propyl 2-(allyloxymethyl)acrylate, and 2-
n-Butyl (allyloxymethyl)acrylate, i-butyl 2-(allyloxymethyl)acrylate, t-butyl 2-(allyloxymethyl)acrylate, n-pentyl 2-(allyloxymethyl)acrylate, n-hexyl 2-(allyloxymethyl)acrylate,
Among them, 2-(allyloxymethyl) acrylate is preferably used from the economical viewpoint.

[Structural unit represented by formula (2)]
In the structural unit represented by the following general formula (2), R ₁ is a metal atom, a hydrogen atom, or a compound having 1 carbon atom.
The alkyl group is an alkyl group having a substituent of 1 to 6, preferably a hydrogen atom, a methyl group, or an ethyl group, and particularly preferably a methyl group.
The structural unit represented by the general formula (2) is a structural unit derived from 2-(allyloxymethyl)acrylic acid or a salt thereof, or a 2-(allyloxymethyl)acrylic acid ester.
Examples of the salt of 2-(allyloxymethyl)acrylic acid include sodium salt, lithium salt, potassium salt, calcium salt, magnesium salt, etc. Examples of the 2-(allyloxymethyl)acrylic acid ester include methyl 2-(allyloxymethyl)acrylate, ethyl 2-(allyloxymethyl)acrylate, n-propyl 2-(allyloxymethyl)acrylate, i-propyl 2-(allyloxymethyl)acrylate, n-butyl 2-(allyloxymethyl)acrylate, i-butyl 2-(allyloxymethyl)acrylate, t-butyl 2-(allyloxymethyl)acrylate, n-pentyl 2-(allyloxymethyl)acrylate, n-hexyl 2-(allyloxymethyl)acrylate, and cyclohexyl 2-(allyloxymethyl)acrylate, with methyl 2-(allyloxymethyl)acrylate being preferred from an economical standpoint.

(In the above formula (2), R ₁ is a metal atom, a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms.)

The PVA-based resin of the present invention preferably contains the structural units represented by the above general formula (1) and/or the above general formula (2) in an amount of 0.1 to 30 mol %, particularly preferably 0.5 to 20 mol %, and further preferably 1 to 10 mol %, based on the total amount of monomer structural units in the resin.
When the content is within the above specific range, the gas barrier property and productivity tend to be good, which is preferable. In addition, the abundance ratio of the structural unit represented by the general formula (1) to the structural unit represented by the general formula (2) is preferably such that the structural unit represented by the general formula (1) is more.

[Ethylene structural unit]
The PVA-based resin of the present invention is preferably copolymerized with ethylene, since the crystallinity of the copolymer is reduced and the melting point is lowered, which facilitates melt molding. The ratio of the ethylene structural unit to the total amount of the monomer structural units in the resin is usually 1 to 70 mol %, preferably 1.
It is preferably from 0 to 60 mol %, more preferably from 25 to 50 mol %.

[Other structural units]
Furthermore, the PVA-based resin of the present invention may be copolymerized with a copolymerizable ethylenically unsaturated monomer other than ethylene, usually in an amount of up to 10 mol %, within the scope of the invention.
Examples of such monomers include olefins such as propylene, 1-butene, and isobutene; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, (anhydrous) phthalic acid, (anhydrous) maleic acid, and (anhydrous) itaconic acid, their salts, and mono- or dialkyl esters having 1 to 18 carbon atoms; acrylamide, N-alkylacrylamide having 1 to 18 carbon atoms, N,N-dimethylacrylamide, 2-acrylamidopropanesulfonic acid or its salt, acrylamidopropyldimethylamine, its salt, and its quaternary salt; methacrylamide, N-alkylmethacrylamide having 1 to 18 carbon atoms, N,N-dimethylmethacrylamide, 2-methacrylamidopropanesulfonic acid or its salt, acrylamidopropyldimethylamine, its salt, and its quaternary salt; Sulfonic acid or its salt, methacrylamide propyl dimethylamine, its salt or its quaternary salt, and other methacrylamides; N-vinyl amides such as N-vinylpyrrolidone, N-vinylformamide, and N-vinylacetamide; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl ethers such as alkyl vinyl ethers, hydroxyalkyl vinyl ethers, and alkoxyalkyl vinyl ethers having 1 to 18 carbon atoms; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, and vinyl bromide; vinyl silanes such as vinyl trimethoxysilane, vinyl methyl dimethoxysilane, and vinyl dimethoxysilane; allyl acetate; 2-
Methylallyl; 3,4-diacetoxy-1-butene; vinyl ethylene carbonate; allyl chloride; allyl alcohol; 2-methylallyl alcohol; dimethylallyl alcohol;
Examples of the acrylamido-2-methylpropanesulfonic acid include 3,4-dihydroxy-1-butene; trimethyl-(3-acrylamido-3-dimethylpropyl)-ammonium chloride; and acrylamido-2-methylpropanesulfonic acid.

The degree of saponification of the polyvinyl alcohol resin of the present invention is usually 80 mol % or more, preferably 90 mol % or more, and particularly preferably 98 mol % or more.

The average degree of polymerization of the polyvinyl alcohol resin of the present invention (measured in accordance with JIS K 6726) is preferably usually 200 to 5,000, more preferably 300 to 3,000, and even more preferably 500 to 2,200.

The polyvinyl alcohol resin of the present invention usually has a glass transition point (Tg) of 75 to 180° C.
The glass transition temperature (Tg) of the PVA-based resin according to the present invention in the case where ethylene is copolymerized therewith is usually 60 to 150° C., preferably 78 to 140° C., and particularly preferably 82 to 120° C.
The glass transition temperature (Tg) is preferably 60° C., more preferably 65 to 130° C., and particularly preferably 70 to 110° C. The higher the glass transition temperature (Tg), the better the gas barrier property tends to be. The glass transition temperature (Tg) is the temperature measured during the second heating run (second run) using a differential scanning calorimeter.

Next, the method for producing the polyvinyl alcohol resin of the present invention will be described.
The method for producing the polyvinyl alcohol resin having the structural units represented by the general formula (1) and/or the general formula (2) of the present invention is not particularly limited, but may be a method for producing a polyvinyl alcohol resin having the structural units represented by the general formula (2
It is preferable that the polyvinyl ester polymer having a structural unit represented by the general formula (2) is produced by radical polymerization of a vinyl ester monomer and a compound represented by the general formula (3).
The above manufacturing method will now be described in detail.

[Method for producing polyvinyl ester polymer having a structural unit represented by formula (2) (polymerization step)]
First, the compound represented by the following general formula (3) will be described.
In the compound represented by the following general formula (3), R ₂ is a metal atom, a hydrogen atom, or a C1-C1
6, preferably a hydrogen atom, a methyl group, or an ethyl group, and particularly preferably a methyl group.
Specific examples of the compound represented by the following general formula (3) include 2-(allyloxymethyl)acrylic acid, sodium 2-(allyloxymethyl)acrylate, lithium 2-(allyloxymethyl)acrylate, potassium 2-(allyloxymethyl)acrylate, 2-
Calcium 2-(allyloxymethyl)acrylate, magnesium 2-(allyloxymethyl)acrylate, methyl 2-(allyloxymethyl)acrylate, ethyl 2-(allyloxymethyl)acrylate, n-propyl 2-(allyloxymethyl)acrylate, i-propyl 2-(allyloxymethyl)acrylate, n-propyl 2-(allyloxymethyl)acrylate
-butyl, 2-(allyloxymethyl)acrylate i-butyl, 2-(allyloxymethyl)acrylate t-butyl, 2-(allyloxymethyl)acrylate n-pentyl, 2-
Examples of such acrylates include n-hexyl 2-(allyloxymethyl)acrylate and cyclohexyl 2-(allyloxymethyl)acrylate, with methyl 2-(allyloxymethyl)acrylate being preferred.

(In the above formula (3), _R2 is a metal atom, a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms.)

[Polymerization process]
The method of radical polymerization of a vinyl ester monomer and a compound represented by the above general formula (3) is not particularly limited, and any known method such as bulk polymerization, solution polymerization, suspension polymerization, dispersion polymerization, or emulsion polymerization can be adopted, but solution polymerization is usually carried out.
The method of feeding the monomer components during radical polymerization is not particularly limited, and any method such as bulk feeding, divided feeding, continuous feeding, etc. can be used. However, it is preferable to continuously dropwise add a solution containing the compound represented by general formula (3) so that the compound represented by general formula (3) is uniformly incorporated into the polymer produced during polymerization.
In the case of copolymerizing ethylene, for example, pressurized polymerization of ethylene can be adopted. By adjusting the pressure of ethylene, it is possible to control the amount of ethylene introduced.
Although it depends on the desired ethylene content, the pressure is usually 1 to 80 kg/ ^cm2.
is selected from.

Solvents used in such radical polymerization usually include lower alcohols such as methanol, ethanol, propanol, butanol, ketones such as acetone, methyl ethyl ketone, and esters such as methyl acetate, ethyl acetate, and butyl acetate, and methanol is preferably used industrially. The amount of the solvent used may be appropriately selected in consideration of the chain transfer constant of the solvent according to the desired degree of polymerization. For example, when the solvent is methanol, the solvent/monomer ratio is selected from the range of about 0.01 to 10 (mass ratio), preferably about 0.05 to 3 (mass ratio).
Examples of polymerization initiators used in such radical polymerization include known radical polymerization initiators such as 2,2'-azobisisobutyronitrile, acetyl peroxide, benzoyl peroxide, and lauryl peroxide, and radical polymerization initiators for low-temperature polymerization such as 2,2'-azobis(2,4-dimethylvaleronitrile) and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). The amount of polymerization initiator used varies depending on the type of initiator and is not generally determined, but is selected arbitrarily depending on the polymerization rate. For example, when azoisobutyronitrile or acetyl peroxide is used, it is 0.001 to 0.2 mol% based on the vinyl ester monomer.
is preferable, and 0.01 to 0.1 mol % is particularly preferable.

The reaction temperature of such radical polymerization is preferably about 20° C. to the boiling point depending on the solvent and pressure used. It is not necessary to carry out the polymerization at a constant temperature until the end of the polymerization, and the temperature may be changed, for example, by adding monomers and a polymerization initiator.
In the case of a batch polymerization, the polymerization time is preferably 1 to 20 hours, more preferably 2 to 12 hours. In the case of a continuous polymerization, the average residence time in the polymerization tank is preferably 2 to 10 hours, more preferably 2 to 8 hours. If the polymerization time (residence time) is too short, it becomes difficult to control the polymerization to achieve high productivity (high polymerization rate), whereas if it is too long, it is not preferable because there is a problem in terms of productivity.
If necessary, a polymerization inhibitor may be added to terminate the polymerization. Examples of the polymerization inhibitor include:
Examples of the amine include, but are not limited to, hydroquinone, aniline, anthracene, nitrobenzene,
Examples of the solvent include dinitrobenzene, trinitrobenzene, benzonitrile, benzophenone, N,N-dimethylformamide, cinnamic alcohol, cinnamic acid, sorbic acid, etc. After the polymerization is terminated, unreacted monomers and the like are removed by distillation.

The polyvinyl ester polymer of the present invention preferably contains the structural unit represented by the above general formula (2) in an amount of 0.1 to 30 mol %, particularly preferably 0.5 to 20 mol %, and further preferably 1 to 10 mol %, based on the total amount of monomer structural units in the resin. If the content is within a specific range, the polyvinyl alcohol resin obtained by saponifying the polyvinyl ester polymer tends to have good gas barrier properties and excellent productivity, which is preferable.

[Method for producing polyvinyl alcohol resin having structural units represented by general formula (1) and/or general formula (2) (saponification step)]
The polyvinyl alcohol-based resin having the structural unit represented by general formula (1) and/or general formula (2) of the present invention is preferably produced by saponifying the polyvinyl ester-based polymer having the structural unit represented by general formula (2) obtained above in a saponification step described below.
The polyvinyl ester polymer having a structural unit represented by general formula (2) obtained above is saponified by a batch method using a stirrer or kneader, or a continuous method on a belt or in a column.
The saponification is carried out by dissolving the polyvinyl ester polymer having the structural unit represented by the general formula (2) obtained above in alcohol or water-containing alcohol, and using an alkali catalyst or an acid catalyst. Examples of the alcohol include methanol, ethanol, propanol, and tert-butanol, and methanol is particularly preferred. The concentration of the copolymer in the alcohol is appropriately selected depending on the viscosity of the system, and is usually selected from the range of 4 to 60 mass %.

The catalyst used for saponification is not particularly limited, and examples thereof include alkali catalysts such as hydroxides or alcoholates of alkali metals, such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate, potassium methylate, and lithium methylate; and acid catalysts such as sulfuric acid, hydrochloric acid, nitric acid, methanesulfonic acid, zeolite, and cation exchange resins.
The amount of the saponification catalyst used is appropriately selected depending on the saponification method, the desired degree of saponification, etc., but when an alkali catalyst is used, the amount is usually 0.01 to 5 mol %, preferably 0.2 to 1.7 mol %, based on the total amount of monomer structural units of the polyvinyl ester polymer having a structural unit represented by general formula (2).

The reaction temperature of the saponification reaction is not particularly limited, but is preferably 10 to 80° C., and more preferably 20 to 70° C. The saponification reaction is usually carried out for 0.5 to 5 hours. These conditions are appropriately adjusted so as to obtain the desired degree of saponification.

After completion of saponification, the obtained slurry is subjected to solid-liquid separation by a known method, washed with methyl acetate, methanol, or the like, and, if necessary, stranded and then pelletized, and dried to obtain a polyvinyl alcohol-based resin having structural units represented by general formula (1) and/or general formula (2) of the present invention.
When an alkali catalyst is used, it is preferable to neutralize the alkali catalyst with an acid such as acetic acid after completion of saponification. By neutralizing the alkali, lactonization proceeds and the structural unit represented by general formula (1) in the polyvinyl alcohol resin increases.

In order to provide the polyvinyl alcohol-based resin having the structural units represented by the general formula (1) and/or the general formula (2) of the present invention for various applications, the resin may be mixed with a different PVA-based resin for the purpose of imparting suitable physical properties to the resin.
Such other PVA-based resins include those having different degrees of saponification, different degrees of polymerization, different modifying groups, different degrees of modification, etc. For the purpose of adjusting the degree of modification, etc., an unmodified PVA-based resin or an ethylene-vinyl alcohol copolymer may be mixed.

[Additives]
In order to use the polyvinyl alcohol resin having the structural units represented by the general formula (1) and/or the general formula (2) of the present invention for various applications, it is necessary to add lubricants, inorganic salts (e.g., hydrotalcite, etc.), plasticizers (e.g., ethylene glycol,
Aliphatic polyhydric alcohols such as glycerol and hexanediol), oxygen absorbers, heat stabilizers, light stabilizers, antioxidants, UV absorbers, colorants, antistatic agents, surfactants, antibacterial agents,
It may contain anti-blocking agents, slip agents, fillers (eg, inorganic fillers), other resins (eg, polyolefins, polyamides), and the like.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following examples and comparative examples, "parts" and "%" are based on mass unless otherwise specified.

Example 1
[Polymerization process]
A reactor equipped with a stirrer, a thermometer, a reflux condenser, and a sample inlet was charged with 120 parts by mass of vinyl acetate,
60 parts by mass of methanol and 0.109 parts by mass of distilled AOMA (manufactured by Nippon Shokubai Co., Ltd., 2-(allyloxymethyl)methyl acrylate) were charged. The reactor was immersed in a water bath, and the water bath was heated until the liquid inside boiled. 0.12 parts by mass of 2,2'-azobisisobutyronitrile was added as a radical initiator to initiate polymerization. At the same time as the start of polymerization, the distilled AOM was
The dropwise addition of a monomer mixture of AOMA and vinyl acetate was started. The dropwise addition rate was 10.5 parts by mass/hr, and the monomer mixture was prepared in advance so that the weight ratio of AOMA to vinyl acetate was 6:94. After polymerization for 1.5 hours, heating was stopped, and m-
The polymerization was terminated by adding 0.03 parts by mass of dinitrobenzene and 200 parts by mass of methanol. At this time, the polymerization rate was 28%. In order to remove the vinyl acetate monomer from the obtained solution, methanol and vinyl acetate were distilled off under reduced pressure. When the viscosity increased appropriately, methanol was added to expel the remaining vinyl acetate, thereby obtaining a methanol solution of modified polyvinyl acetate. A part of this methanol solution was sampled and dried to obtain modified polyvinyl acetate (polyvinyl ester polymer). The modification rate of the obtained modified polyvinyl acetate was calculated by measuring ¹ H-NMR, and the AOMA modification rate was 1.6 mol%. This value was
This coincides with the modification rate (1.6 mol%) calculated on the assumption that the total amount of AOMA charged before the start of polymerization and the amount of AOMA dropped during polymerization was entirely incorporated into the polymer, and it can be said that almost all of the AOMA present in the polymerization system was consumed.
[Saponification step]
Next, the methanol solution of the modified polyvinyl acetate was diluted with methanol to a concentration of 8% by mass, and 400 parts by mass of this modified polyvinyl acetate methanol solution (32 parts by mass as modified polyvinyl acetate) was charged into the same reactor as above. The reactor was immersed in a water bath until the internal temperature reached 65° C.
The mixture was heated to a temperature of 8.5° C. A 3.5% by mass solution of sodium hydroxide in methanol was added thereto.
The saponification reaction was started by adding 5 parts by mass of ethyl alcohol. As the saponification reaction proceeded, a saponified product precipitated.
Stirring was continued as it was. The saponified product precipitated 1.5 hours after the addition of the methanol solution of sodium hydroxide was filtered off and charged again into the reactor, where 240 parts by mass of methanol was added and heated to 65 ° C. 8.5 parts by mass of a 3.5% by mass methanol solution of sodium hydroxide was added thereto and reacted for 2.5 hours to drive the saponification reaction. Thereafter, 0.36 parts by mass of acetic acid was added to neutralize, and the saponified product was removed by suction filtration while washing with methanol. 1000 mass of methanol was added to the saponified product and stirred at 65 ° C for 30 minutes to wash the saponified product. The washed saponified product was removed by suction filtration, and then dried in a vacuum dryer at 50 ° C for 12 hours to obtain a polyvinyl alcohol resin modified with AOMA.

Example 2
In the polymerization step, the dropping rate was 10.7 parts by mass/hr, the weight ratio of AOMA and vinyl acetate in the mixed monomer used for dropping was 8:92, and the polymerization time was 2 hours. The polymerization rate at the time of stopping the polymerization was 29%. The modification rate was calculated by measuring ¹ H-NMR of the obtained modified polyvinyl acetate, and the AOMA modification rate was 2.7 mol%. This value coincides with the modification rate (2.7 mol%) calculated on the assumption that the total amount of AOMA charged before the start of polymerization and the amount of AOMA dropped during polymerization was all incorporated into the polymer, and almost all of the AOMA present in the polymerization system was consumed.

<Comparative Example 1>
As a general-purpose polyvinyl alcohol resin, Gohsenol NL-05 (manufactured by Mitsubishi Chemical Corporation, fully saponified polyvinyl alcohol, polymerization degree: 500) was used.

<Comparative Example 2>
[Polymerization process]
A reactor equipped with a stirrer, a thermometer, a reflux condenser, and a sample inlet was charged with 100 parts by mass of vinyl acetate,
3.38 parts by mass of norbornene (molar ratio of vinyl acetate to norbornene of 97:3) and 20.7 parts by mass of methanol were charged. The reactor was immersed in a water bath and the water bath was heated until the liquid inside boiled. 0.0 parts by mass of 2,2'-azobisisobutyronitrile was used as a radical initiator.
104 parts by mass of m-dinitrobenzene was added to initiate polymerization. After polymerization for 5 hours, heating was stopped, and 0.005 parts by mass of m-dinitrobenzene and 200 parts by mass of methanol were added as a polymerization terminator to terminate the polymerization. At this time, the polymerization rate was 33%. In order to remove vinyl acetate monomer and 2-norbornene from the obtained solution, methanol and vinyl acetate were distilled off under reduced pressure. When the viscosity increased appropriately, methanol was added to drive out the remaining vinyl acetate, and a methanol solution of modified polyvinyl acetate was obtained.
[Saponification step]
The saponification step was carried out in the same manner as in Example 1 to obtain a modified polyvinyl alcohol. The degree of modification was 2.1 mol%. The number of moles of units derived from 2-norbornene in the polymer was smaller than the number of moles of 2-norbornene charged during polymerization, and it was found that a larger amount of 2-norbornene remained at the end of polymerization compared to the cases where AOMA was used in Examples 1 and 2.

The polyvinyl ester polymers and polyvinyl alcohol resins obtained in Examples 1 and 2 and Comparative Example 2, and the polyvinyl alcohol resin used in Comparative Example 1 were subjected to the following measurements. The results are shown in Table 1.

[Measurement method]
<Measurement of polymerization rate>
About 1 to 2 g of a sample of the polymerization liquid in the reactor was weighed out and placed in an aluminum cup, and after drying for 30 minutes in a dryer at 140° C., the resin fraction at the end of polymerization was calculated from the amount of sample remaining in the aluminum cup. The weight of the reacted monomer was calculated from the measurement result of the resin fraction, and divided by the combined weight of the charged monomer and the dropped monomer to obtain the polymerization rate.

<Measurement of 2-(allyloxymethyl)methyl acrylate (AOMA) modification rate in polyvinyl acetate>
The content of AOMA in polyvinyl acetate (AOMA modification rate) was measured by ^1H -NMR. The measurement temperature was 23°C using an Ascend 400 manufactured by Bruker. _CDCl3 was used as the solvent and tetramethylsilane was used as the internal standard. 3.3 to 4.3 ppm
The peak is the methylene (CH ₂ ) adjacent to the oxygen atom of the THF ring in the structural unit of AOMA.
The peaks at 4.6 ppm to 5.3 ppm are the peaks of the methine ( _CH ) structural unit of vinyl acetate (H _b in the structural unit above, integral value b in FIG. 1), which is a total of seven hydrogen atoms, including the two hydrogen atoms in the vinyl acetate structural unit and the methyl (CH) of the ester group (H _a in the structural unit above, integral value a in FIG. 1).

<Measurement of Modification Ratio of 2-Norbornene Modified PVOH>
Calculated from ¹ H-NMR according to the method described in Patent Document JP-A-2008-202048.

<Measurement of average polymerization degree>
The average degree of polymerization was analyzed in accordance with JIS K 6726-1994.

<Measurement of Melting Point and Glass Transition Point (Tg)>
The polyvinyl alcohol resin was measured using a differential scanning calorimeter (TA Instruments "Q
2000"), under the conditions of _N2 flow rate 50 ml/min, modulation amplitude 5°C/min, modulation period 6 sec, the temperature was raised from -50°C to 260°C at 5°C/min, and then reduced to -5°C at 5°C/min.
The sample was cooled to 0° C. and held for 3 minutes, and then heated again from −50° C. to 260° C. at 5° C./min for measurement. The glass transition point was determined from the reversing heat flow during the second heating process, and the melting point was determined from the melting peak of the total heat flow.

<Measurement of oxygen transmission rate (OTR)>
A 10% by weight aqueous solution of polyvinyl alcohol-based resin was prepared, and coated on a polyethylene terephthalate film (thickness 38 μm) whose surface had been corona-treated, using a bar coater so that the dry thickness was 3 μm. The coated film was dried (120° C. x 5 minutes) to form a film layer of polyvinyl alcohol-based resin on the PET film. The film layer of polyvinyl alcohol-based resin was taken out of this two-layer film, and the oxygen transmission rate (OTR) of the film layer taken out was evaluated.
Oxygen permeability (OTR, cc-3 μm/ ^m2 -day-atm) was measured at a temperature of 23°C and a humidity of 8
The measurement was carried out under the condition of 0% RH using an oxygen permeability measuring device ("OX-TRAN" manufactured by MOCON Co., Ltd.).

It is clear that the film using the polyvinyl alcohol-based resin of Example 1 has superior gas barrier properties compared to the films using the polyvinyl alcohol-based resins of Comparative Examples 1 and 2.
The film using the polyvinyl alcohol-based resin of Example 2 has a superior gas barrier property compared to the film using the polyvinyl alcohol-based resin of Comparative Example 1.
It can be seen that the polyvinyl alcohol-based resin of Example 1 has gas barrier properties similar to those of the polyvinyl alcohol-based resin of Comparative Examples 1 and 2, but the polyvinyl alcohol-based resin of Example 1 has a lower melting point and is excellent in moldability compared to the polyvinyl alcohol-based resins of Comparative Examples 1 and 2.

Moreover, it is understood that when the polyvinyl alcohol-based resins of Examples 1 and 2 are produced, the amount of remaining copolymerization monomer is smaller than that when the polyvinyl alcohol-based resin of Comparative Example 2 is produced, and thus the productivity is excellent.

The polyvinyl alcohol-based resin of the present invention has good gas barrier properties not only under dry conditions but also under high humidity conditions, so that a film using this resin, even if it is a single layer, is useful as various packaging materials such as food packaging materials, pharmaceutical packaging materials, industrial chemical packaging materials, agricultural chemical packaging materials, etc. Furthermore, when a single layer or two or more layers of other resin layers are further laminated to form a laminate having at least one layer containing the PVA-based resin of the present invention, the deterioration of gas barrier properties under high humidity conditions is further suppressed and the mechanical strength is increased, so that it is suitable as a packaging material for articles whose quality may deteriorate due to oxygen.

1 is a ¹ H-NMR chart of the polyvinyl ester polymer of Example 1.

Claims (9)

A polyvinyl alcohol-based resin having a structural unit represented by the following general formula (1) and/or the following general formula (2):

(In the above formula (2), R ₁ is a metal atom, a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms.) The polyvinyl alcohol-based resin according to claim 1, characterized in that the structural unit represented by the general formula (1) and/or the general formula (2) is contained in an amount of 0.1 to 30 mol % based on the total amount of monomer structural units in the resin. 2. The polyvinyl alcohol resin according to claim 1, wherein the degree of saponification is 80 to 99.9 mol %. 2. The polyvinyl alcohol resin according to claim 1, wherein the average degree of polymerization is 200 to 5,000. A polyvinyl ester polymer having a structural unit represented by the above general formula (2). The structural unit represented by the above general formula (2) is
6. The polyvinyl ester polymer according to claim 5, wherein the content is 0.1 to 30 mol %. A method for producing the polyvinyl alcohol-based resin according to claim 1, which has a structural unit represented by the general formula (1) and/or the general formula (2), comprising a step of saponifying a polyvinyl ester-based polymer having a structural unit represented by the general formula (2). 6. A method for producing a polyvinyl ester polymer according to claim 5, which has a structural unit represented by the general formula (2), comprising a step of radically polymerizing a vinyl ester monomer and a compound represented by the following general formula (3):

(In the above formula (3), _R2 is a metal atom, a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms.) The method for producing a polyvinyl ester polymer according to claim 8, characterized in that in the step of radically polymerizing a vinyl ester monomer and the compound represented by the general formula (3), a solution containing the compound represented by the general formula (3) is continuously added dropwise.

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