JP2004217724A - Method for manufacturing aqueous emulsion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an aqueous emulsion which has excellent water resistance and freeze/thaw stability, is excellent in polymerization stability even at low viscosity, and is excellent in storage stability. <P>SOLUTION: The method for manufacturing an aqueous emulsion is characterized in that a vinyl ester monomer is subjected to emulsion polymerization wherein (1) a vinyl alcohol polymer having a degree of saponification of 75 mol% or higher is used as a dispersant, (2) at least one polymerization initiator selected from hydrogen peroxide, ammonium persulfate and potassium persulfate is used, (3) the vinyl ester monomer in an amount less than 15 wt.% based on the whole amount of the monomer is charged in the initial period of polymerization, (4) the vinyl ester monomer in an amount of 85 wt.% or more based on the whole amount of the monomer is continuously or discontinuously added in the latter period of polymerization, and (5) the average amount of residual vinyl ester monomer in the latter period of polymerization is kept to 7 wt.% or less. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００４１】
表１中、
Ｅｔ…エチレン単位
ＤＨ…けん化度
分散剤ＰＶＡの量（ｐｈｍ）…全酢酸ビニル１００重量部に対する重量部
をそれぞれ示す。
【００４２】
【発明の効果】
本発明によれば、優れた耐水性および凍結融解安定性を有し、低粘度においても重合安定性に優れ、貯蔵安定性に優れる水性エマルジョンを得ることができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing an aqueous emulsion having excellent water resistance and freeze-thaw stability, excellent polymerization stability even at a low viscosity, and excellent storage stability.
[0002]
[Prior art]
Conventionally, polyvinyl alcohol (hereinafter sometimes abbreviated as PVA) has been widely used as a protective colloid for emulsion polymerization of ethylenically unsaturated monomers, particularly vinyl ester monomers represented by vinyl acetate, The vinyl ester aqueous emulsion obtained by emulsion polymerization using this as a protective colloid is used for various adhesives for paper, woodworking and plastics, various binders for impregnated paper and nonwoven products, admixtures, Widely used in fields such as splicing materials, paints, paper processing and fiber processing.
By adjusting the degree of saponification of the PVA-based polymer, such an aqueous emulsion generally has a low viscosity, has a viscosity close to a Newtonian flow, and has a relatively good water resistance. Since it has high viscosity and relatively low temperature dependence of emulsion viscosity, it has been awarded for various uses.
[0003]
PVA-based polymers as dispersants for emulsion polymerization generally include so-called "fully saponified PVA" having a saponification degree of about 98 mol% and "partially saponified PVA" having a saponification degree of about 88 mol%, and the former is used. In this case, although the water resistance is relatively good, there is a disadvantage that the stability at extremely low temperatures such as below freezing, that is, the freeze-thaw stability is insufficient.On the other hand, when the latter PVA polymer is used, the freeze-thaw stability is poor. Has excellent properties but has poor water resistance. In order to improve such disadvantages, both PVA-based polymers are used in combination, and a PVA-based polymer having an intermediate saponification degree is used, but water resistance and freeze-thaw stability are simultaneously improved. I was not satisfied. Therefore, vinyl alcohol-based polymers containing ethylene units have been proposed (Patent Documents 1 to 3, etc.), and the water resistance and the low-temperature storage stability have been greatly improved. Further, a vinyl alcohol-based polymer containing a large amount of 1,2-glycol bonds has been proposed (Patent Document 4), and the low-temperature stability, polymerization stability, and the like have been significantly improved. However, even with these emulsions, water resistance and freeze-thaw stability were not completely satisfied at the same time.
In addition, the emulsion of the conventional PVA-based protective colloid has a poor polymerization stability, especially when preparing a low-viscosity emulsion such as 1000 MPa · s or less, because the particle size of the emulsion is larger than that of the emulsifier-based emulsion. At present, there are problems such as settling during standing, and there is a difficulty in adjusting the emulsion viscosity.
[0004]
Prior art documents related to the invention of this application include the following.
[Patent Document 1]
JP-A-8-81666
[Patent Document 2]
JP-A-6-80709
[Patent Document 3]
JP-A-10-226774
[Patent Document 4]
JP 2001-220484 A
[0005]
[Problems to be solved by the invention]
The present invention has solved these disadvantages of the prior art, has excellent water resistance and freeze-thaw stability, has excellent polymerization stability even at low viscosity, and has excellent storage stability. The purpose is to provide.
[0006]
[Means for Solving the Problems]
The above object is to carry out emulsion polymerization of a vinyl ester monomer, (1) using a vinyl alcohol polymer having a saponification degree of 75 mol% or more as a dispersant, and (2) hydrogen peroxide, ammonium persulfate and potassium persulfate. (3) less than 15% by weight of a vinyl ester monomer based on the total amount of the monomer in the initial stage of polymerization, and (4) a vinyl ester monomer in the latter stage of the polymerization. Is continuously or intermittently added in an amount of 85% by weight or more based on the total amount of the monomers, and (5) maintaining the average residual amount of the vinyl ester monomer in the late stage of the polymerization at 7% by weight or less. This is achieved by providing a method of making an emulsion.
Further, in the present invention, by using a vinyl alcohol polymer having 1 to 15 mol% of ethylene units in the molecule or a 1.9 mol% or more of 1,2-glycol bond in the molecule, water resistance is improved. Properties and freeze-thaw stability can be more suitably achieved.
Further, by the above production method, a low-viscosity aqueous emulsion having a viscosity of not more than 1000 MPa · s at 20 ° C. and 20 rpm by a B-type viscometer can be stably obtained.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, the vinyl alcohol-based polymer having a degree of saponification of 75 mol% or more used as a dispersant for the aqueous emulsion of the above (1) is obtained by, for example, saponifying a vinyl ester-based polymer obtained by polymerizing a vinyl ester. Manufactured. The saponification degree of the vinyl alcohol-based polymer needs to be 75 mol% or more, preferably 80 mol% or more, more preferably 85 mol% or more. When the degree of saponification is less than 75 mol%, there is a concern that the water solubility, which is an intrinsic property of the vinyl alcohol polymer, is reduced. The viscosity average degree of polymerization (hereinafter abbreviated as degree of polymerization) of the vinyl alcohol polymer is not particularly limited, but is preferably in the range of 100 to 8000, and more preferably 300 to 3000.
[0008]
Here, examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate and the like, and vinyl acetate is economically preferable.
[0009]
In the present invention, by using a vinyl alcohol-based polymer containing 1 to 15 mol% of ethylene units in the molecule as the vinyl alcohol-based polymer used as the dispersant of the above (1), excellent water resistance is obtained. Further, it is possible to obtain an aqueous emulsion having excellent polymerization stability. The vinyl alcohol-based polymer can be obtained by saponifying a copolymer of a vinyl ester and ethylene. The ethylene unit content of the vinyl alcohol-based polymer is preferably 3 to 13 mol%, more preferably 4 to 12 mol%.
[0010]
In the present invention, freeze-thaw stability is achieved by using a vinyl alcohol-based polymer having 1,2-glycol bonds of 1.9 mol% or more as the vinyl alcohol-based polymer used as the dispersant of the above (1). It is possible to obtain an aqueous emulsion having excellent properties. The method for producing a vinyl alcohol-based polymer having 1.9 mol% or more of 1,2-glycol bonds is not particularly limited, and a known method can be used. As an example, a method in which vinylene carbonate is copolymerized with a vinyl ester so as to have the above-mentioned 1,2-glycol bond amount, the polymerization temperature of the vinyl ester is higher than usual, for example, 75 to 200 ° C., and the polymerization is performed under pressure And the like. In the latter method, the polymerization temperature is preferably from 95 to 190 ° C, particularly preferably from 100 to 180 ° C. It is important to select the pressure condition so that the polymerization system has a boiling point or less, preferably 0.2 MPa or more, more preferably 0.3 MPa or more. The upper limit is preferably 5 MPa or less, and more preferably 3 MPa or less. Polymerization can be performed by any method such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization in the presence of a radical polymerization initiator.Solution polymerization, especially solution polymerization using methanol as a solvent, can be used. It is suitable. By saponifying the thus obtained vinyl ester polymer by a usual method, a vinyl alcohol polymer having 1.9 mol% or more of 1,2-glycol bond can be obtained. The content of 1,2-glycol bonds in the vinyl alcohol polymer is more preferably 1.95 mol% or more, further preferably 2.0 mol% or more, and most preferably 2.1 mol% or more. Further, the content of the 1,2-glycol bond is preferably 4 mol% or less, more preferably 3.5 mol% or less, and most preferably 3.2 mol% or less. Here, the content of the 1,2-glycol bond is determined from the analysis of the NMR spectrum.
[0011]
Further, as the vinyl alcohol polymer used as the dispersant of the above (1), a vinyl alcohol containing 1 to 15 mol% of ethylene units in the molecule and having 1.9 mol% or more of 1,2-glycol bond is used. By using the system polymer, it is possible to obtain an aqueous emulsion which is more excellent in water resistance, freeze-thaw stability and polymerization stability.
[0012]
The vinyl alcohol polymer may be a copolymer of an ethylenically unsaturated monomer copolymerizable within a range not to impair the object of the present invention. Such ethylenically unsaturated monomers include, for example, acrylic acid, methacrylic acid, fumaric acid, (anhydride) maleic acid, itaconic acid, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, trimethyl- (3-acrylamide -3-dimethylpropyl) -ammonium chloride, acrylamide-2-methylpropanesulfonic acid and its sodium salt, ethyl vinyl ether, butyl vinyl ether, N-vinylpyrrolidone, vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, fluoride Vinylidene, tetrafluoroethylene, sodium vinyl sulfonate, sodium allyl sulfonate and the like can be mentioned.
Further, in the presence of a thiol compound such as thiolacetic acid and mercaptopropionic acid, a vinyl ester monomer such as vinyl acetate is polymerized, or a vinyl ester monomer and the above ethylenically unsaturated monomer are polymerized. A modified product having a mercapto group or a carboxyl group at a terminal obtained by copolymerizing and saponifying the obtained (co) polymer can also be used.
[0013]
Examples of the vinyl ester monomer used for emulsion polymerization in the present invention include vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate, and the like. Vinyl acetate is economically preferable.
[0014]
In the present invention, a vinyl ester monomer is mainly used as a monomer used for emulsion polymerization, but it is also a preferable embodiment to use a vinyl ester monomer and ethylene in combination. By subjecting these monomers to emulsion polymerization, an aqueous emulsion containing a vinyl ester-based polymer or a vinyl ester-ethylene-based copolymer as a dispersoid can be obtained.
[0015]
In the emulsion polymerization, an ethylenically unsaturated monomer and a diene-based monomer may be copolymerized as long as the object of the present invention is not impaired. Such monomers include propylene, olefins such as isobutylene, vinyl chloride, vinyl fluoride, vinylidene chloride, halogenated olefins such as vinylidene fluoride, acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, Acrylic acid and its esters such as 2-ethylhexyl acrylate, dodecyl acrylate and 2-hydroxyethyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, methacryl Methacrylic acid such as 2-hydroxyethyl acid and its esters, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate and quaternary products thereof, furthermore, acrylamide, methacrylic acid Amide, N-methylolacrylamide, N, N-dimethylacrylamide, acrylamide monomers such as acrylamide-2-methylpropanesulfonic acid and its sodium salt, styrene, α-methylstyrene, p-styrenesulfonic acid and sodium and potassium Examples include styrene-based monomers such as salts, N-vinylpyrrolidone, and the like, and diene-based monomers such as butadiene, isoprene, and chloroprene.
[0016]
In the method for producing an aqueous emulsion of the present invention, it is important to use at least one polymerization initiator selected from hydrogen peroxide, ammonium persulfate, and potassium persulfate, and among them, hydrogen peroxide is particularly preferred. The amount of the polymerization initiator to be used is not particularly limited, but usually, the emulsion polymerization is carried out using a molar ratio of 0.001 to 0.01 with respect to all monomers, preferably 0.002 to 0.007. And more preferably 0.0025 to 0.005. By using the polymerization initiator in the above range, an aqueous emulsion with further improved water resistance can be obtained.
[0017]
Further, the polymerization initiator may be used in combination with a reducing agent and used in a redox system. In that case, hydrogen peroxide is usually used together with tartaric acid, L-ascorbic acid, Rongalit and the like. Ammonium persulfate and potassium persulfate are used together with sodium hydrogen sulfite, sodium hydrogen carbonate and the like. The amount of the reducing agent to be used is not particularly limited either, but usually 0.05 to 3 equivalents, preferably 0.1 to 2 equivalents, more preferably 0.3 to 1.5 equivalents, relative to the polymerization initiator.
[0018]
The method of adding the polymerization initiator in the early stage or late stage of the polymerization is not particularly limited, and a method of batch addition, a method of continuous addition, and the like can be used. In the early stage of the polymerization, preferably, a method of adding the polymerization initiator all at once is used. In the latter stage of the polymerization, a method of continuously adding a polymerization initiator is preferably used.
[0019]
In the present invention, it is necessary to charge less than 15% by weight of the total amount of the vinyl ester-based monomer in the initial stage of polymerization. The charge amount of the vinyl ester monomer in the initial stage of the polymerization may be 0% by weight, but is preferably 5% by weight or more, and most preferably 7% by weight. When the amount of the initially charged monomer is 15% by weight or more, it is difficult to keep the average residual amount of the vinyl ester monomer at less than 7% by weight in the latter stage of the polymerization, and the freeze-thaw stability of the emulsion may be reduced. There is. The amount of the polymerization initiator added in the early stage of the polymerization is not particularly limited, but is usually 0.005 to 0.025, preferably 0.008 to 0.020, more preferably 0.005 to 0.025 in terms of a molar ratio with respect to all monomers charged in the initial stage of the polymerization. Is 0.01 to 0.018.
As described above, by adding a predetermined amount of the polymerization initiator in the early stage of the polymerization, the water resistance is further improved.
In the initial polymerization, a monomer and a polymerization initiator are added to an aqueous solution of a dispersant, and the polymerization temperature is 50 to 70 ° C., preferably 55 to 65 ° C., and the polymerization time is 15 to 60 minutes, preferably 20 to 50 minutes. Done below. It is preferable that the monomers used in the initial stage of polymerization are added all at once.
[0020]
The amount of the vinyl alcohol-based polymer used as a dispersant is not particularly limited, but is preferably 1 to 20 parts by weight, more preferably 1.5 to 15 parts by weight, based on 100 parts by weight of all monomers. Range. When the amount is less than 1 part by weight or more than 20 parts by weight, the polymerization stability may be lowered or the storage stability may be lowered.
[0021]
The initial polymerization is terminated when the residual concentration of vinyl ester (% by weight based on the whole system) becomes 7% or less, preferably 3% or less, more preferably 1% or less. After the initial polymerization, it enters into the late stage of the polymerization. In the latter stage polymerization, it is important to add the monomer continuously or intermittently, and among them, continuous addition is particularly optimal. By the continuous or intermittent addition, an aqueous emulsion intended for the present invention is obtained. In the latter stage polymerization, the polymerization initiator is preferably added continuously, but may be added all at once or intermittently. In the latter stage polymerization, the polymerization temperature is preferably 5 to 30 ° C. higher than the initial polymerization temperature, and is in the range of 55 to 100 ° C., preferably 60 to 95 ° C., more preferably 70 to 90 ° C. Done.
In the present invention, it is important to keep the average residual amount (% by weight based on the entire system) of the vinyl ester monomer in the late stage of the polymerization at 7% or less, preferably 6% or less, more preferably 5% or less. is there. Here, the average residual amount is a value measured by a method described later. If the average residual amount is 7% or more, freeze-thaw stability and water resistance may be reduced.
If the average residual amount of the vinyl ester monomer is 7% or less in the latter stage of the polymerization, the dropping time of the vinyl ester monomer is not particularly limited, but is usually 3 hours or more, preferably 4 hours or more, and more preferably 4.5 hours or more.
[0022]
The polymerization pressure may be normal pressure in both the initial polymerization and the late polymerization, but it is necessary to increase the pressure if necessary. In particular, when producing a copolymer emulsion of a vinyl ester and another monomer, for example, ethylene, it is necessary to carry out under pressure.
[0023]
In the present invention, an emulsion excellent in freeze-thaw stability, water resistance and the like can be obtained, but at the same time, an emulsion having a low viscosity of 1000 MPa · s or less can be obtained stably. Here, the emulsion viscosity was measured under the conditions of 20 rpm and 20 ° C. using a B-type viscometer. Those having a viscosity of preferably less than 900 MPa · s, more preferably less than 800 MPa · s, are suitably used in applications requiring a low-viscosity emulsion.
[0024]
As the aqueous emulsion obtained by the present invention, the aqueous emulsion obtained by the above method can be used as it is, but if necessary, conventionally known various emulsions are added and used as long as the effects of the present invention are not impaired. be able to.
As the dispersant in the aqueous emulsion of the present invention, the above-mentioned vinyl alcohol-based polymer is used, and if necessary, a conventionally known anionic, nonionic or cationic surfactant, or hydroxyethyl cellulose, etc. Can also be used in combination.
[0025]
According to the present invention, an aqueous emulsion having excellent polymerization stability even at a low viscosity can be obtained. Further, since the obtained aqueous emulsion has excellent water resistance and freeze-thaw stability, it can be used for paper tubes, bag making, Adhesives for processing paper such as paper and corrugated cardboard, paper for pulp, etc., flash panels, glued glue, wood veneer, plywood processing, secondary processing of plywood (kneading), woodworking adhesives for general woodworking and various plastics Adhesives, impregnated papers, binders for non-woven products, admixtures, joints, paints, paper processing and textile processing.
[0026]
【Example】
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 on a weight basis unless otherwise specified. Further, the water resistance and standing stability of the obtained emulsion were evaluated in the following manner.
[0027]
(Evaluation of emulsion)
The viscosity was measured using a B-type viscometer (20 rpm).
(1) Water resistance of the film
The obtained aqueous emulsion was cast on polyethylene terephthalate (PET) under the conditions of 20 ° C. and 65% RH, and dried for 7 days to obtain a dry film having a thickness of 500 μm. The film was punched out to a diameter of 2.5 cm, and the sample was immersed in water at 20 ° C. for 24 hours to determine the elution rate of the film.
Dissolution rate (%): {1− (weight of dried film after immersion / weight of dried film before immersion)} × 100
Absolute dry weight of the coating before immersion; weight of the coating before immersion (water content)-{weight of the coating before immersion (water content) x moisture content of the coating (%) / 100}
Film moisture content: The film (a sample different from the sample immersed in water at 20 ° C.) is absolutely dried at 105 ° C. for 4 hours, and the moisture content of the film is determined in advance.
Absolute dry weight of film after immersion; weight of absolutely dried film after immersion at 105 ° C for 4 hours.
(2) Freeze-thaw stability
50 g of the sample was placed in a polyethylene bottle, the sample was kept at −15 ° C. for 16 hours, then left in a constant temperature water bath at 30 ° C. for 1 hour, and the state was observed and evaluated according to the following criteria.
◎ Good fluidity, ○ Thickening but fluidity, △ Recovering fluidity when mixed, × Gellation
(3) Polymerization stability
Filtration residue
After the polymerization, the mixture was filtered through a 60-mesh wire gauze, and the remaining amount (%) of filtration (solid content of the emulsion) was measured. The smaller the filtration residue, the better the polymerization stability.
Graft polymer
The aqueous emulsion was cast on a PET film at 20 ° C. and 65% RH and dried for 7 days to obtain a dried film having a thickness of 500 μm. A sample obtained by punching out this film to a diameter of 2.5 cm was subjected to Soxhlet extraction with acetone for 24 hours, followed by extraction in boiling water for 24 hours, and the insoluble content of the film after extraction (dispersed around the polymer of the dispersoid). (A graft polymer in which a vinyl alcohol polymer was chemically bonded). The larger the amount of the graft polymer, the more strongly the vinyl alcohol-based polymer as the dispersant protects the periphery of the polymer of the dispersoid. An aqueous emulsion having excellent polymerization stability in viscosity is obtained.
Graft polymer (%) = (absolute dry weight of membrane after extraction / absolute dry weight of membrane before extraction) × 100
Absolute dry weight of film before extraction = Weight of film before extraction (water content)-{Weight of film before extraction (water content) x moisture content of film (%) / 100}
* Coating water content: The coating (a sample different from the sample extracted with acetone and boiling water) is completely dried at 105 ° C. for 4 hours, and the water content of the coating is determined in advance.
* Absolute dry weight of the film after extraction: The weight of the film after extraction at 105 ° C. for 4 hours.
(4) Storage stability
After leaving the aqueous emulsion at 20 ° C. for 3 months, the state was observed and evaluated according to the following criteria.
○ No change, slight sedimentation is observed, × completely separated
[0028]
Example 1
In a 2-liter glass polymerization vessel equipped with a reflux condenser, a dropping funnel, a thermometer, and a nitrogen inlet, 750 g of ion-exchanged water, PVA-1 @ polymerization degree of 1700, saponification degree of 98 mol%: PVA- manufactured by Kuraray Co., Ltd. 117｝ 68.4 g was charged and completely dissolved at 95 ° C. Next, the PVA aqueous solution was cooled, replaced with nitrogen, and then adjusted to 60 ° C. while stirring at 200 rpm. Then, 12.8 g of a 10% aqueous solution of tartaric acid and 8.8 g of a 5% aqueous hydrogen peroxide solution (based on total vinyl acetate). , In a molar ratio of 0.015), and 76 g of vinyl acetate (10% of the total vinyl acetate) was charged to initiate polymerization. 30 minutes after the start of the polymerization, the end of the initial polymerization (the residual amount of vinyl acetate was 1% by weight) was confirmed. Next, 1.3 g of a 10% aqueous solution of tartaric acid was added all at once, and then 43.8 g of 1% hydrogen peroxide was continuously added over 5 hours. At the same time, 684 g of vinyl acetate was continuously added over 5 hours, and the polymerization temperature was maintained at 80 ° C. to complete the late polymerization. Thereafter, filtration was performed using a 60-mesh stainless steel wire mesh. The smaller the filtration residue, the better the polymerization stability, and the larger the filtration residue, the worse the polymerization stability.
As a result, a polyvinyl acetate emulsion having a solid content of 49.8% was obtained. This emulsion was evaluated according to the method described above.
The average amount of residual vinyl acetate in the late stage of polymerization was determined by measuring the amount of residual vinyl acetate (by the titration method described in JIS K-6828) every 30 minutes from the start to the end of late polymerization, and calculating the average. Table 1 shows the results.
[0029]
Comparative Example 1
A polyvinyl acetate emulsion having a solid content of 49.7% in the same manner as in Example 1 except that vinyl acetate and 1% aqueous hydrogen peroxide added over 5 hours were added in 2 hours. was gotten. Table 1 also shows the results.
[0030]
Example 2
In the same manner as in Example 1, except that PVA-2 (polymerization degree: 1700, saponification degree: 88 mol%: PVA-217 manufactured by Kuraray Co., Ltd.) was used instead of PVA-1, the solid content was changed. A polyvinyl acetate emulsion having a concentration of 49.7% was obtained. Table 1 also shows the results.
[0031]
Comparative Example 2
A polyvinyl acetate emulsion having a solid content of 49.7% in the same manner as in Example 2 except that vinyl acetate and 1% aqueous hydrogen peroxide added in 5 hours were added in 2 hours in Example 2. was gotten. Table 1 also shows the results.
[0032]
Example 3
In a 2 liter glass polymerization vessel equipped with a reflux condenser, a dropping funnel, a thermometer and a nitrogen inlet, 930 g of ion-exchanged water and 54 g of PVA-1 were charged and completely dissolved at 195 ° C. Next, the PVA aqueous solution was cooled, replaced with nitrogen, and then adjusted to 60 ° C. while stirring at 200 rpm. Then, 10.2 g of a 10% aqueous solution of tartaric acid and 6.9 g of a 5% hydrogen peroxide solution (based on total vinyl acetate) , In a molar ratio of 0.015), and then 60 g of vinyl acetate (10% based on the total vinyl acetate) was charged to initiate polymerization. 30 minutes after the start of the polymerization, the end of the initial polymerization (the residual amount of vinyl acetate was 1% by weight) was confirmed. Next, 1 g of a 10% aqueous solution of tartaric acid was added all at once, and 34.6 g of 1% hydrogen peroxide was continuously added over 5 hours. At the same time, 540 g of vinyl acetate was continuously added over 5 hours, and the polymerization temperature was maintained at 80 ° C. to complete the late polymerization. Thereafter, filtration was performed using a 60-mesh stainless steel wire mesh. As a result, a polyvinyl acetate emulsion having a solid content of 40.1% was obtained. This emulsion was evaluated according to the method described above. Table 1 also shows the results.
[0033]
Comparative Example 3
A polyvinyl acetate emulsion having a solid content of 38.8% in the same manner as in Example 3 except that vinyl acetate and 1% aqueous hydrogen peroxide added over 5 hours were added over 2 hours. was gotten. Table 1 also shows the results.
[0034]
Example 4
In the same manner as in Example 1, except that PVA-3 (polymerization degree 1700, saponification degree 98 mol%, ethylene unit content 5 mol%) was used in place of PVA-1, the solid content concentration was changed. A 49.8% polyvinyl acetate emulsion was obtained. Table 1 also shows the results.
[0035]
Example 5
In the same manner as in Example 1, except that PVA-4 (polymerization degree 1700, saponification degree 88 mol%, ethylene unit content 3 mol%) was used in place of PVA-1, the solid content concentration was changed. A 49.7% polyvinyl acetate emulsion was obtained. Table 1 also shows the results.
[0036]
Example 6
Example 1 is the same as Example 1 except that PVA-5 (polymerization degree 1700, saponification degree 98 mol%, 1,2-glycol bond content 2.2 mol%) was used in place of PVA-1. As a result, a polyvinyl acetate emulsion having a solid concentration of 49.9% was obtained. Table 1 also shows the results.
[0037]
Example 7
In a 2-liter glass polymerization vessel equipped with a reflux condenser, a dropping funnel, a thermometer, and a nitrogen inlet, 740 g of ion-exchanged water and 30 g of PVA-5 were charged and completely dissolved at 95 ° C. Next, the PVA aqueous solution was cooled, replaced with nitrogen, and then adjusted to 60 ° C. while stirring at 200 rpm. Then, 17 g of a 10% aqueous solution of tartaric acid and 11.5 g of a 5% aqueous hydrogen peroxide solution (mol After a batch addition of 0.015), 100 g of vinyl acetate (10% based on the total vinyl acetate) was charged to initiate polymerization. 30 minutes after the start of the polymerization, the end of the initial polymerization (the residual amount of vinyl acetate was 1% by weight) was confirmed. Next, 1.7 g of a 10% aqueous solution of tartaric acid was added all at once, and 57.6 g of 1% hydrogen peroxide was continuously added over 5 hours. At the same time, 900 g of vinyl acetate was continuously added over 5 hours, and the polymerization temperature was maintained at 80 ° C. to complete the late polymerization. Thereafter, filtration was performed using a 60-mesh stainless steel wire mesh. As a result, a polyvinyl acetate emulsion having a solid content of 54.8% was obtained. This emulsion was evaluated according to the method described above. Table 1 also shows the results.
[0038]
Example 8
In a 2-liter glass polymerization vessel equipped with a reflux condenser, a dropping funnel, a thermometer and a nitrogen inlet, 630 g of ion-exchanged water and 17.6 g of PVA-5 were charged and completely dissolved at 95 ° C. Next, the PVA aqueous solution was cooled, purged with nitrogen, and adjusted to 60 ° C. while stirring at 200 rpm. Then, 15 g of a 10% aqueous solution of tartaric acid and 10.1 g of a 5% aqueous hydrogen peroxide solution (mol After the batch addition of 0.015), 88 g of vinyl acetate (10% based on the total vinyl acetate) was charged to initiate polymerization. 30 minutes after the start of the polymerization, the end of the initial polymerization (the residual amount of vinyl acetate was 1% by weight) was confirmed. Next, 1.5 g of a 10% aqueous solution of tartaric acid was added all at once, and then 50.7 g of 1% hydrogen peroxide was continuously added over 5 hours. At the same time, 792 g of vinyl acetate was continuously added over 5 hours, and the polymerization temperature was maintained at 80 ° C. to complete the late polymerization. Thereafter, filtration was performed using a 60-mesh stainless steel wire mesh. As a result, a polyvinyl acetate emulsion having a solid content of 54.4% was obtained. This emulsion was evaluated according to the method described above. Table 1 also shows the results.
[0039]
Comparative Example 4
Example 8 A polyvinyl acetate emulsion having a solid content of 53.8% in the same manner as in Example 8, except that vinyl acetate and 1% aqueous hydrogen peroxide added over 5 hours were added over 2 hours. was gotten. Table 1 also shows the results.
[0040]
[Table 1]

[0041]
In Table 1,
Et: ethylene unit
DH: degree of saponification
Amount of dispersant PVA (phm): parts by weight based on 100 parts by weight of total vinyl acetate
Are respectively shown.
[0042]
【The invention's effect】
According to the present invention, an aqueous emulsion having excellent water resistance and freeze-thaw stability, excellent polymerization stability even at low viscosity, and excellent storage stability can be obtained.

Claims (5)

When emulsion-polymerizing a vinyl ester monomer, (1) a vinyl alcohol polymer having a saponification degree of 75 mol% or more is used as a dispersant, and (2) at least one selected from hydrogen peroxide, ammonium persulfate and potassium persulfate. Using a kind of polymerization initiator, (3) less than 15% by weight of vinyl ester monomer based on the total amount of monomer in the initial stage of polymerization, and (4) vinyl ester monomer in the latter stage of polymerization (5) A method for producing an aqueous emulsion, characterized in that 85% by weight or more of the total amount is continuously or intermittently added and (5) the average residual amount of the vinyl ester monomer in the late stage of polymerization is kept at 7% by weight or less. . The method for producing an aqueous emulsion according to claim 1, wherein the vinyl ester monomer is continuously or intermittently added over 3 hours or more in the latter stage of the polymerization of (4). The method for producing an aqueous emulsion according to claim 1 or 2, wherein the vinyl alcohol-based polymer (1) is a vinyl alcohol-based polymer containing 1 to 15 mol% of ethylene units in a molecule. 3. The method for producing an aqueous emulsion according to claim 1, wherein the vinyl alcohol-based polymer (1) is a vinyl alcohol-based polymer having 1.9 mol% or more of 1,2-glycol bonds. The method for producing an aqueous emulsion according to any one of claims 1 to 4, wherein a viscosity of the aqueous emulsion measured by a B-type viscometer at 20 ° C and 20 rpm is 1000 MPa · s or less.