JP2003277411A - Method for producing ethylene-vinyl acetate-based resin emulsion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an ethylene-vinyl acetate copolymer-based resin emulsion presenting a film having little discoloration, excellent in control of emulsion polymerization, containing little vinyl acetate monomer and almost or absolutely no aldehyde compounds such as formaldehyde, acetaldehyde and the like, having almost no odor and giving little load to the environment. <P>SOLUTION: The method for producing the ethylene-vinyl acetate-based resin emulsion is to copolymerize ethylene with vinyl acetate in emulsion by using a vinyl alcohol-based polymer having ≥70 mole% degree of saponification as a dispersant and a redox initiator comprising hydrogen peroxide, tartaric acid and/or its metal salt and adding an iron compound. In the polymerization the polymerization system is adjusted to have pH 3-7, an inorganic reducing agent and/or a compound having -NH- bond is or are added and, when the content of unreacted vinyl acetate monomer in the polymerization system becomes ≤5 wt.%, a hydroperoxide is added. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to ethylene having no odor, little coloring when formed into a film, little vinyl acetate monomer remaining, an emulsion containing almost no aldehyde compound, and excellent emulsion polymerization controllability. -A method for producing a vinyl acetate resin emulsion.

Conventionally, polyvinyl alcohol (hereinafter, PV
Polyvinyl acetate-based resin emulsion containing (A may be abbreviated as A) a protective colloid is used for various adhesives for paper, woodworking and plastics, various binders for impregnated paper and non-woven products, and admixtures. , Splicing material, paint,
Widely used in the fields of paper processing, textile processing, wallpaper, etc. Hydrogen peroxide is widely used in the production of ethylene-vinyl acetate copolymer-based resin emulsion, which is a type of polyvinyl acetate-based resin emulsion containing PVA as a protective colloid, from the viewpoint of polymerization stability, water resistance of the emulsion, and the like. Because of its sensitive redox reaction with hydrogen peroxide, sodium formaldehyde sulfoxylate (commonly referred to as Rongalit, hereinafter referred to as Rongalit) has been frequently used. However, since Rongalit generates formaldehyde upon decomposition, it has a serious problem that formaldehyde is contained in the obtained emulsion. Due to recent environmental problems, the use of Rongalit is avoided. In addition, acetaldehyde derived from hydrolysis of vinyl acetate monomer is also repelled similarly to formaldehyde, and there is an urgent need to achieve complete non-aldehyde conversion. On the other hand, it has recently been pointed out that vinyl acetate monomers may have mutagenicity, and it is strongly desired to reduce the amount of unreacted vinyl acetate monomers remaining in the emulsion in consideration of the environment. . However, since the ethylene-vinyl acetate resin emulsion is obtained by copolymerization with ethylene, it is difficult to reduce the unreacted vinyl acetate monomer, and conventionally contains about 0.5% by weight of unreacted vinyl acetate monomer. It was the current situation. Under such circumstances, in order to realize reduction of non-aldehyde, unreacted vinyl acetate monomers, it is essential to reconstruct the polymerization initiator and the polymerization conditions. In JP 2001-163910 A, it is reported that non-formaldehyde can be formed by using erythorbic acid or ascorbic acid as a reducing agent, but reduction of unreacted vinyl acetate monomer is not realized, and vinyl acetate monomer is not realized. The present situation is that acetaldehyde derived from the hydrolysis of is still contained in the system and is far from the required physical properties. It was also clarified that such a method newly causes problems such as coloring of the emulsion and generation of odor.

[0003]

Under the circumstances, the present invention provides an emulsion which has no odor, little coloring when formed into a film, little residual vinyl acetate monomer, and almost no aldehyde compound. It is an object of the present invention to provide a method for producing an ethylene-vinyl acetate resin emulsion, which is excellent in controllability of emulsion polymerization.

[0004]

Means for Solving the Problems As a result of intensive studies to develop a method for producing an ethylene-vinyl acetate resin emulsion having the above-mentioned preferable properties, the present inventors have found that
Ethylene and vinyl acetate are prepared by using a redox polymerization initiator composed of hydrogen peroxide and tartaric acid and / or a metal salt thereof as a dispersant using a vinyl alcohol polymer having a saponification degree of 70 mol% or more. During emulsion polymerization, the pH of the polymerization system is adjusted to 3 to 7, an inorganic reducing agent and / or a compound having a -NH- bond is added during emulsion polymerization, and the unreacted vinyl acetate monomer in the polymerization system is further added. The present invention found that a method for producing an ethylene-vinyl acetate resin emulsion characterized by adding hydroperoxides at a time when the amount becomes 5% by weight or less satisfies the above object. Has been completed.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION A vinyl alcohol polymer having a saponification degree of 70 mol% or more, which is used as a dispersant in the present invention (hereinafter sometimes abbreviated as PVA polymer).
Can be obtained by saponifying a vinyl ester polymer by a conventional method.

The dispersant may be a copolymer of ethylenically unsaturated monomers copolymerizable within the range not impairing the object of the present invention. Examples of such ethylenically unsaturated monomers include ethylene, propylene, acrylic acid, methacrylic acid, fumaric acid, (anhydrous) maleic acid, itaconic acid, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, and trimethyl- (3-
Acrylamide-3-dimethylpropyl) -ammonium chloride, acrylamido-2-methylpropanesulfonic acid and its sodium salt, ethyl vinyl ether, butyl vinyl ether, N-vinylpyrrolidone, vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, fluorine Examples thereof include vinylidene chloride, tetrafluoroethylene, sodium vinyl sulfonate, sodium allyl sulfonate, and the like. Further, a terminal modified product obtained by polymerizing vinyl acetate in the presence of a thiol compound such as thiolacetic acid or mercaptopropionic acid and saponifying the obtained copolymer can also be used. Of these ethylenically unsaturated monomers, ethylene is preferred,
The content of the ethylenically unsaturated monomer, especially ethylene, is preferably 0.5 to 20 mol%, more preferably 1 to 15 mol%.

The degree of saponification of the PVA polymer used in the present invention is required to be 70 mol% or more, more preferably 80 mol% or more, and further preferably 85 mol% or more. If the degree of saponification is less than 70 mol%, the water solubility, which is the original property of the PVA-based polymer, may decrease, and the emulsion polymerization stability may decrease. The viscosity average degree of polymerization of the PVA polymer is 100 to 8
The range of 000 is preferable, and the range of 300 to 3000 is more preferable. When the degree of polymerization is less than 100, the function as a PVA protective colloid is not exhibited, and when it exceeds 8000, there is a problem in industrial production of the PVA-based polymer.

The amount of the PVA polymer used as the dispersant is not particularly limited, but the dispersoid (ethylene-
2 parts by weight per 100 parts by weight of vinyl acetate resin)
˜15 parts by weight, more preferably 3 to 10 parts by weight. If the amount used is less than 2 parts by weight or more than 15 parts by weight, the polymerization stability may be lowered or the emulsion may be colored.

The monomers used in the emulsion polymerization in the present invention are mainly ethylene and vinyl acetate, but within a range not impairing the object of the present invention, an ethylenically unsaturated monomer and / or a diene monomer. May be used as a copolymerization component. Such monomers include propylene,
Olefin such as isobutylene, vinyl chloride, vinyl fluoride, halogenated olefin such as vinylidene chloride, vinylidene fluoride, acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, acrylic Acrylic acid and its ester such as 2-hydroxyethyl acid, methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, 2-methacrylic acid
Methacrylic acid and its esters such as hydroxyethyl, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate and quaternary products thereof, and further acrylamide, methacrylamide, N-methylolacrylamide, N, N-dimethylacrylamide,
Acrylamide-based monomers such as acrylamido-2-methylpropanesulfonic acid and its sodium salt, styrene-based monomers such as styrene, α-methylstyrene, p-styrenesulfonic acid and sodium and potassium salts,
Others such as N-vinylpyrrolidone, butadiene,
Examples thereof include diene-based monomers such as isoprene and chloroprene, and polyfunctional monomers such as triallyl cyanurate, triallyl isocyanurate and diallyl phthalate. The ethylene content of the dispersoid thus obtained by emulsion polymerization is preferably 5 to 50% by weight, more preferably 1
It is 0 to 40% by weight.

In the production method of the present invention, a redox type polymerization initiator comprising hydrogen peroxide and tartaric acid and / or its metal salt is used as a polymerization initiator. Examples of tartaric acid include dextrorotatory L (+) tartaric acid, levorotatory D (-) tartaric acid, and DL tartaric acid which is a racemic compound of these enantiomers, and are not particularly limited, but among these, L (+) tartaric acid When (1) is used, the emulsion polymerization controllability is remarkably good and it is preferably used. It is also possible to use a metal salt of tartaric acid, and the kind of metal is not particularly limited, but sodium tartarate is usually used. Of these, sodium L (+) tartrate is preferably used. L
When (+) sodium tartrate is used, not only the polymerization controllability is excellent, but also the pH adjustment with an alkali such as ammonia or caustic soda that is usually performed after emulsion polymerization is not necessary. The amount of hydrogen peroxide used is preferably 0.01 to 0.2 parts by weight, more preferably 0.02 to 0.
15 parts by weight.

Hydrogen peroxide and tartaric acid as a reducing agent and /
Further, the use ratio of the metal salt is not particularly limited, but usually 50 to 500 parts by weight, preferably 70 parts by weight of tartaric acid and / or the metal salt thereof is added to 100 parts by weight of hydrogen peroxide.
To 400 parts by weight, more preferably 80 to 350 parts by weight. By using tartaric acid and / or its metal salt in this range, the emulsion polymerization controllability becomes better and the pH adjustment of the emulsion polymerization system becomes easier. The ratio of the redox-based polymerization initiator used is
The amount used until the unreacted vinyl acetate monomer reaches 5% by weight is shown.

In the production method of the present invention, it is necessary to adjust the pH of the emulsion polymerization system to 3 to 7, and to adjust the pH to 4
It is preferable to adjust to -6, and further to 4.5-5.5. When the pH of the emulsion polymerization system is lower than 3, the redox reaction rate between hydrogen peroxide and tartaric acid and / or its metal salt is remarkably reduced, and it is unsuitable because it is difficult to control the emulsion polymerization. When the pH of the emulsion polymerization system is higher than 7, vinyl acetate is hydrolyzed during the emulsion polymerization and a large amount of acetaldehyde may be generated, which is inappropriate. The method for adjusting the pH of the emulsion polymerization system is not particularly limited,
Although any buffering agent can be used, usually, sodium acetate, acetic acid / sodium acetate system, sodium hydroxide, sodium carbonate and the like are preferably used. In the present invention, the pH of the emulsion polymerization system refers to the pH from the beginning of the polymerization to the end of the polymerization, and in the present invention, it is important that the pH is 3 to 7 at any point of the polymerization.

In the production method of the present invention, it is essential to add an iron compound to the emulsion polymerization system. The iron compound is not particularly limited, but at least one selected from ferrous chloride, ferrous sulfate, ferric chloride, ferric nitrate, and ferric sulfate.
Iron compounds are preferably used, among them ferrous chloride,
Ferrous sulfate is particularly preferably used.

The amount of iron compound used is not particularly limited,
The amount used is 1 ppm to 100 ppm, more preferably 5 ppm to 50 ppm, based on all monomers. If the amount of the iron compound used is less than 1 ppm, the redox reaction rate between hydrogen peroxide and tartaric acid and / or its metal salt may be significantly reduced, and it may be difficult to control the polymerization. If the amount of iron compound used is more than 100 ppm, coloring may occur when the obtained emulsion is formed into a film.

The method for adding the redox polymerization initiator is not particularly limited. Examples of the method of performing hydrogen peroxide by ordinary emulsion polymerization, that is, a method of adding in a shot at the initial stage of polymerization initiation, a method of sequentially adding during hydrogenation, and the like can be mentioned. The tartaric acid and / or its metal salt may be used by adding the entire amount at the initial stage of the emulsion polymerization, or may be added sequentially during the emulsion polymerization, but the total amount is usually added at the initial stage of the emulsion polymerization and used. . The addition method of the iron compound is not particularly limited, but it is usually used by adding the entire amount at the initial stage of emulsion polymerization.

In the production method of the present invention, when the amount of unreacted vinyl acetate monomer in the polymerization system becomes 5% by weight or less,
It is essential to add hydroperoxides.
Preferably, the hydroperoxides are added at the time when the amount becomes 4% by weight or less. The amount of unreacted vinyl acetate monomer is 5
If it is added at a time of more than wt%, the polymerization reaction may be too fast and the polymerization may not be controlled, which is inappropriate. As hydroperoxides,
t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, p-menthane hydroperoxide, 1,1,
3,3-tetramethylbutyl hydroperoxide can be mentioned, and among them, t-butyl hydroperoxide and cumene hydroperoxide are preferably used.

The amount of the hydroperoxides added is not particularly limited, but usually, it is 0.
005 to 5 molar equivalents, preferably 0.01 to 3 molar equivalents are added. When the added amount is less than 0.005 molar equivalent,
The residual amount of unreacted vinyl acetate monomer may exceed 0.2% by weight. If the amount added exceeds 5 molar equivalents, the water resistance of the resulting emulsion may decrease.

In the production method of the present invention, it is essential to add an inorganic reducing agent and / or a compound having a --NH-- bond during emulsion polymerization. The timing of addition is not particularly limited as long as it is from the beginning of the polymerization to the end of the polymerization, but it is particularly preferable to add it at the latter stage of the polymerization when the residual vinyl acetate monomer is less than 5% by weight. Furthermore, it is also a preferable embodiment to add these inorganic reducing agents and / or compounds having a —NH— bond additionally after emulsion polymerization.

The inorganic reducing agent is not particularly limited, but sulfites are preferably used. As sulfites, sodium sulfite, potassium sulfite, aluminum sulfite, ammonium sulfite, zinc sulfite, calcium sulfite, magnesium sulfite, chromium sulfite, sodium hydrogen sulfite, ammonium hydrogen sulfite, calcium hydrogen sulfite, potassium hydrogen sulfite, ammonium pyrosulfite, pyro Examples include sodium sulfite and potassium pyrosulfite. Among these, sodium bisulfite,
Sodium pyrosulfite and ammonium hydrogen sulfite are preferably used.

The amount of the inorganic reducing agent added during emulsion polymerization is not particularly limited, but usually 0.01 to 10 parts by weight, based on 100 parts by weight of emulsion solids after polymerization,
Preferably 0.02 to 5 parts by weight, more preferably 0.0
3 to 3 parts by weight. By using the inorganic reducing agent in this range, the residual amount of the aldehyde compound and the residual vinyl acetate monomer in the emulsion can be reduced, and the odor of the obtained emulsion can be reduced. When the inorganic reducing agent is additionally added after the emulsion polymerization, the additional amount is preferably selected from the same range as described above.

The compound having a —NH— bond is not particularly limited, but an amino bond, a urea bond, an amide bond,
A compound having an imide bond or a hydrazino bond is preferably used. Further, a low molecular weight compound is suitable as the compound.

As the compound having an amino bond, hydroxylamine, chloramine, ammonia, methanolamine, ethanolamine, dimethylamine, diethylamine, isopropylamine, butylamine, proline, hydroxyproline, dicyanodiamide, ethyleneimine, ethylenediamine, propylenediamine, Diethylenetriamine, 2-diethylaminoethanol, 2
-Dimethylaminoethanol, 1,2-diaminopropane, 1,3-diaminopropane, triethylenetetramine, tetraethylenepentamine, iminobispropylamine, tetramethylenediamine, guanidine carbonate, glycine, alanine, sarcosine, glutamic acid, hexamethylene Diamine, melamine, morpholine, 2-amino-
4,5-Dicyanoimidazole, 3-azahexane-
1,6-diamine, 2-acrylamido-2-methylpropanesulfonic acid, α-amino-ε-caprolactam,
Acetoguanamine, guanine, acetaldehyde ammonia, 4,7-diazadecane-1,10-diamine, pyrrolidine, piperidine, piperazine, polyethyleneimine, polyallylamine, polyvinylamine, aminobenzoate and the like.

Examples of compounds having a urea bond include urea, thiourea, methylurea, ethylurea, dimethylurea, diethylurea, ethyleneurea, acetylurea, guanylurea, guanylthiourea, azodicarboxylic acid amide, glycolylurea and acetyl. There are urea etc.

Examples of the compound having an amide bond include formamide, acetamide, benzamide, oxamide, pyrrolidone, pyrrolidonecarboxylic acid, oxamic acid, succinic acid amide, oxazolidone and malonamide. Examples of compounds having an imide bond include succinimide, phthalimide, maleimide, succinimide, hydantoin, barbituric acid, 1-methylol-5,5-
Examples include dimethylhydantoin and isocyanuric acid.

As the compound having a hydrazino bond,
Hydrazine, hydrazinobenzoic acid, α-hydrazinoisobutyric acid, hydrazinoacetic acid, hydrazinoformic acid, α-hydrazinopropionic acid, 2-hydrazinoethanol, oxalic acid dihydrazide, succinic acid dihydrazide, malonic acid dihydrazide, glutaric acid dihydrazide, adipic acid, adipic acid. Acid dihydrazide, maleic acid dihydrazide, fumaric acid dihydrazide, itaconic acid dihydrazide,
Ethylene-1,2-dihydrazine, propylene-1,3
-Dihydrazine, a reaction product of polyacrylamide and hydrazine hydrate, a reaction product of a water-soluble or water-dispersible polymer having an amide group and / or an ester group, and hydrazine hydrate. These are used alone or in combination of two or more.

The amount of the compound having a --NH-- bond added during emulsion polymerization is not particularly limited, but usually 0.01 to 10 per 100 parts by weight of the solid content of the emulsion.
Parts by weight, preferably 0.02 to 5 parts by weight, more preferably 0.03 to 3 parts by weight are used. Addition amount is 0.01
If the amount is less than 10 parts by weight, the effect of reducing aldehyde may not be exhibited, and if the addition amount exceeds 10 parts by weight,
The water resistance of the resulting emulsion may be adversely affected. When a compound having a —NH— bond is additionally added after the emulsion polymerization, the additional amount is preferably selected from the same range as above.

In the present invention, the emulsion polymerization is carried out under pressure, preferably under a pressure of 20 to 70 kg / cm ² , and during the emulsion polymerization, for example, when the residual vinyl acetate concentration reaches 10% by weight, 5 to 35 kg / from the initial polymerization pressure
cm ² Under low pressure, preferably 10 to 30 kg / cm ²
It is preferable to release a part of ethylene under a low pressure and to add hydroperoxides to complete the polymerization when the residual vinyl acetate concentration becomes 5% by weight or less.

In the present invention, in the latter stage of polymerization, 3
Under reduced pressure of 0 to 200 mmHg, preferably 50 to 180 mmHg, 10 to 70 ° C., preferably 15 to 60 ° C.
Then, by performing ethylene removal for 0.5 to 5 hours, preferably 1 to 4 hours, it is possible to more reliably reduce the amount of unreacted vinyl acetate monomer.

The ethylene-vinyl acetate resin emulsion obtained by the production method of the present invention has an unreacted vinyl acetate monomer content of 0.2% by weight or less, particularly 0.15% by weight or less, and a formaldehyde concentration of It is 1 ppm or less and the acetaldehyde concentration is 5 ppm or less. Here, the measurement of the amount of unreacted vinyl acetate monomer in the emulsion refers to the value measured by the titration method described in JIS K6828. When the amount of unreacted vinyl acetate monomer exceeds 0.2% by weight, particularly 0.15% by weight, it cannot be said that the amount of unreacted vinyl acetate monomer is reduced. Further, the measurement of the formaldehyde concentration and acetaldehyde concentration in the emulsion refers to the values measured using a gas detector tube. When the formaldehyde concentration contained in the emulsion is 1 ppm or more or when the acetaldehyde concentration is 5 ppm or more, the so-called non-aldehyde emulsion cannot be said.

As the ethylene-vinyl acetate resin emulsion obtained by the production method of the present invention, the emulsion obtained by the above method can be used as it is, but an alkaline substance such as ammonia or caustic soda is added to the emulsion after emulsion polymerization. Therefore, it is preferable to adjust the pH to 4 to 7, and further to 4.5 to 7 for use because it is possible to prevent a change in the performance of the emulsion due to hydrolysis. If desired, various conventionally known emulsions can be added and used within a range that does not impair the effects of the present invention. As the dispersant used in the present invention, a PVA polymer having a saponification degree of 70 mol% or more is used. If necessary, a conventionally known anionic, nonionic or cationic surfactant or ,
Other PVA-based polymers, hydroxyethyl cellulose and the like can also be used in combination.

The ethylene-vinyl acetate resin emulsion obtained by the production method of the present invention has little coloration, little odor, a small amount of unreacted vinyl acetate monomer in the emulsion, and further contains almost no aldehyde compound in the emulsion. It has the advantage that it is not used, and it is preferably used as a base emulsion for wallpaper, an adhesive for building materials, especially an adhesive for interiors, a paint, etc., and an adhesive for paper processing such as paper tubes, bags, interleaving paper, corrugated board, and pulp. Adhesives, adhesives for woodworking such as general woodworking, adhesives for various plastics, binders for impregnated paper, nonwoven products, admixtures, splicing materials,
It is also preferably used in fields such as paper processing and textile processing.

[0032]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples and Comparative Examples. In the following Examples and Comparative Examples, "parts" and "%" mean weight basis unless otherwise specified. In addition, analysis and evaluation of the obtained emulsion,
The controllability of emulsion polymerization and the like were evaluated in the following manner.

(Evaluation method) (1) 0.1 g of the emulsion was collected in a glass vial containing 10 ml of formaldehyde, heated at 40 ° C. for 1 hour, and then a gas detector tube (No. 17).
1SB: measured by Komei Rikagaku Kogyo, 100 ml suction). (2) Acetaldehyde content 0.1 ml of the emulsion was collected in a glass vial and heated at 40 ° C for 1 hour, and then a gas detector tube (No. 13).
3SB: measured by Komei Rikagaku Kogyo, 100 ml suction). (3) Vinyl acetate monomer content The vinyl acetate monomer content in the emulsion was determined according to JIS K6828. (4) Emulsion Polymerization Control Whether the heat generation due to polymerization is stopped immediately when the addition of hydrogen peroxide is stopped, or whether the polymerization proceeds rapidly and heat is generated when the addition of hydrogen peroxide is started. Whether or not it was observed was evaluated according to the following criteria. That is, the polymerization temperature is adjusted by adding or stopping the addition of hydrogen peroxide,
It was evaluated based on the extent of the temperature fluctuation around 0 ° C. ⊚: Very good controllability (temperature fluctuation range ± 1 ° C
○: Good controllability (temperature fluctuation within ± 3 ° C) △: Slightly poor controllability (temperature fluctuation within ± 5 ° C) ×: Uncontrollable (temperature fluctuation within ± 5 ° C) (5) Odor The odor level of the aqueous emulsion was examined by a sensory test and evaluated according to the following criteria. ◯: Almost no odor is felt Δ: Slight odor is felt X: Smells odor strongly (6) Coloring of the film At 20 ° C., the emulsion was formed into a film having a thickness of 500 μm. The obtained film is placed in a dryer at 120 ° C for 2 minutes.
It was left for 0 minutes. Then, the coloring of the film was visually observed and evaluated according to the following criteria. ◯: Almost no coloration, Δ: slightly yellow coloration, ×: yellow coloration

Example 1 PVA-1 {polymerization degree 1700, saponification degree 88 mol%, PVA-217 manufactured by Kuraray Co., Ltd.) 1061 g, ion in a pressure-resistant 50 liter autoclave equipped with a nitrogen blowing port, a thermometer and a stirrer Exchanged water 19440 g, L (+) sodium tartrate 12.7 g, sodium acetate 10.6 g,
0.4g of ferrous chloride was charged and completely dissolved at 95 ° C,
Then, it cooled at 60 degreeC and performed nitrogen substitution. Next, after charging 22360 g of vinyl acetate, 45 kg of ethylene /
The mixture was pressurized to cm ² and introduced, 1000 g of 0.4% hydrogen peroxide aqueous solution was introduced under pressure for 5 hours, and emulsion polymerization was performed at 60 ° C. When the pH at the beginning of the polymerization was confirmed, pH = 5.
It was 2. When the amount of residual vinyl acetate reached 10%, ethylene was released and the ethylene pressure was 20 kg / cm ^2.
Then, 50 g of a 3% hydrogen peroxide aqueous solution was press-fitted to continue the polymerization. When the amount of residual vinyl acetate monomer in the emulsion reached 1.5%, ethylene was released and cooled. After cooling, pH was confirmed to be pH = 4.8. Then, 20 g of sodium hydrogen sulfite was added, and the temperature was 30 ° C.
The ethylene was removed under a reduced pressure of 00 mmHg for 1 hour. The system was returned to atmospheric pressure with nitrogen, 10 g of t-butyl hydroperoxide was added, and the mixture was stirred for 2 hours. PH at the end of polymerization
Was confirmed, it was pH = 4.7. This emulsion was filtered using a 60-mesh stainless steel wire net to obtain a solid content concentration of 54.4% and an ethylene content of 18% by weight.
To obtain an ethylene-vinyl acetate copolymer resin emulsion. The conditions at the time of polymerization are shown in Table 1, and the evaluation results of the obtained emulsion are shown in Table 2.

Example 2 To the emulsion obtained in Example 1, 20 g of sodium bisulfite was added, and the solid content concentration was 54.4%.
An ethylene-vinyl acetate copolymer-based resin emulsion having an ethylene content of 18% by weight was obtained. The conditions at the time of polymerization and the evaluation results of the obtained emulsion are shown in Table 1 and Table 2, respectively.

Example 3 Emulsion polymerization was carried out in the same manner as in Example 1 except that 30 g of adipic acid dihydrazide was used in place of 20 g of sodium bisulfite, and the solid content concentration was 54.
An ethylene-vinyl acetate copolymer type resin emulsion having 4% and an ethylene content of 18% by weight was obtained. The conditions at the time of polymerization and the evaluation results of the obtained emulsion are shown in Table 1 and Table 2, respectively.

Comparative Example 1 Emulsion polymerization was carried out in the same manner as in Example 1 except that Rongalite was used in place of L (+) sodium tartrate in Example 1, solid content concentration 54.4%, ethylene content 1
An 8% by weight ethylene-vinyl acetate copolymer resin emulsion was obtained. The conditions at the time of polymerization and the evaluation results of the obtained emulsion are shown in Table 1 and Table 2, respectively.

Example 4 Sodium bisulfite 2 additionally added in Example 2
Solid content concentration 54.4% in the same manner as in Example 2 except that 30 g of adipic dihydrazide was used instead of 0 g.
An ethylene-vinyl acetate copolymer-based resin emulsion having an ethylene content of 18% by weight was obtained. The conditions at the time of polymerization and the evaluation results of the obtained emulsion are shown in Table 1 and Table 2, respectively.

Comparative Example 2 Emulsion polymerization was attempted in the same manner as in Example 1 except that ferrous chloride was not used, but the controllability of the polymerization was poor and it was dangerous, so it was stopped. .

Comparative Example 3 The solid content concentration was 54.4 in the same manner as in Example 1 except that sodium hydrogen sulfite was not used.
%, An ethylene-vinyl acetate copolymer resin emulsion having an ethylene content of 18% by weight was obtained. The conditions at the time of polymerization and the evaluation results of the obtained emulsion are shown in Table 1 and Table 2, respectively.

Comparative Example 4 Ethylene vinyl acetate having a solid content concentration of 54.4% and an ethylene content of 18% by weight was prepared in the same manner as in Example 1 except that t-butyl hydroperoxide was not used. A copolymer resin emulsion was obtained. The conditions at the time of polymerization and the evaluation results of the obtained emulsion are shown in Table 1 and Table 2, respectively.

Example 5 In Example 1, L (+) sodium tartrate 12.7
An emulsion was obtained under the same emulsion polymerization conditions as in Example 1 except that 8.3 g of L (+)-tartaric acid was used instead of g and the addition amount of sodium acetate was changed from 10.6 g to 50 g. Caustic soda was added to the emulsion after polymerization to adjust the pH to 5.5, and the mixture was filtered using a 60-mesh stainless steel wire net to give an ethylene-vinyl acetate copolymer having a solid content concentration of 54.4% and an ethylene content of 18% by weight. A system resin emulsion was obtained. The conditions at the time of polymerization and the evaluation results of the obtained emulsion are shown in Table 1 and Table 2, respectively.

Comparative Example 5 Polymerization was carried out in the same manner as in Example 5 except that sodium acetate was not added, but the temperature control of the polymerization became unstable, and the polymerization was stopped midway. After the polymerization was stopped, the pH of the system was measured and found to be 2.6.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

The method for producing an ethylene-vinyl acetate resin emulsion of the present invention is excellent in emulsion polymerization controllability, and the emulsion obtained by the production method of the present invention has little coloring when formed into a film and remains. Low vinyl acetate monomer, almost no aldehyde compound,
In addition, because it has almost no odor, it has a very low environmental impact.

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Claims (7)

[Claims] 1. A redox-based polymerization initiator comprising hydrogen peroxide and tartaric acid and / or its metal salt as a dispersant, a vinyl alcohol-based polymer having a saponification degree of 70 mol% or more, and an iron compound added thereto. When emulsion-polymerizing ethylene and vinyl acetate, the pH of the polymerization system is adjusted to 3 to 7,
An inorganic reducing agent and / or a compound having a -NH- bond is added during emulsion polymerization, and hydroperoxides are added when the amount of unreacted vinyl acetate monomer in the polymerization system becomes 5% by weight or less. A method for producing an ethylene-vinyl acetate-based resin emulsion, comprising: 2. The method for producing an ethylene-vinyl acetate resin emulsion according to claim 1, wherein the inorganic reducing agent is a sulfite. 3. Hydroperoxides are t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, p
-Menthane hydroperoxide, and 1,1,3,
The method for producing an ethylene-vinyl acetate resin emulsion according to claim 1 or 2, which is at least one hydroperoxide selected from 3-tetramethylbutylhydroperoxide. 4. The production of an ethylene-vinyl acetate resin emulsion according to claim 1, wherein the hydroperoxides are added in an amount of 0.005 to 5 molar equivalents based on all unreacted monomers. Method. 5. Tartaric acid and / or its metal salt is L
(+) Tartaric acid and / or L (+) sodium tartrate, The manufacturing method of the ethylene vinyl acetate resin emulsion in any one of Claims 1-4. 6. After the amount of unreacted vinyl acetate monomer in the polymerization system becomes 5% by weight or less, ethylene removal is carried out at 10 to 70 ° C. under reduced pressure of 30 to 200 mmHg for 0.5 to 5 hours. The method for producing an ethylene-vinyl acetate resin emulsion according to claim 1, wherein hydroperoxides are added thereafter. 7. An ethylene-vinyl acetate resin emulsion obtained by the method according to claim 1, wherein the amount of unreacted vinyl acetate monomer contained in the emulsion is 0.2% by weight or less. , An ethylene-vinyl acetate resin emulsion having a formaldehyde concentration of 1 ppm or less and an acetaldehyde concentration of 5 ppm or less.