JPH08283313A - Dispersion stabilizer for suspension polymerization of vinyl compound - Google Patents

Abstract

PURPOSE: To obtain a dispersion stabilizer which exhibits low foaming properties in the suspension polymn. of a vinyl compd. and is excellent in capability of producing uniform and porous vinyl polymer particles. CONSTITUTION: This stabilizer comprises a polyvinyl alcohol of which the absorbance at 280nm (A) in an ultraviolet absorption spectrum of a 0.1wt.% aq. soln. is 0.1 or higher, the absorbance at 320nm (B) is 0.03 or higher, and the ratio of absorbance A to absorbance B is lower than 0.3 and in which the block character of residual acetic acid groups is 0.4 or higher.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a dispersion stabilizer for suspension polymerization of vinyl compounds. More specifically, it relates to a dispersion stabilizer for suspension polymerization of vinyl compounds such as vinyl chloride, which has an excellent antifoaming effect.

[0002]

2. Description of the Related Art When a vinyl polymer such as a vinyl chloride resin is industrially produced, a vinyl compound such as vinyl chloride is dispersed in an aqueous medium in the presence of a dispersion stabilizer to obtain an oil-soluble catalyst. Suspension polymerization in which polymerization is carried out using is widely used. In general, factors that control the quality of vinyl polymers include polymerization rate, water-monomer ratio, polymerization temperature, type and amount of catalyst, type of polymerization tank, stirring speed or type of dispersion stabilizer. Among them, the influence of the type of dispersion stabilizer is extremely large.

The performance required of a dispersion stabilizer for suspension polymerization of vinyl compounds is that it has the function of making the particle size distribution of the resulting vinyl polymer particles as sharp as possible, and increases the absorption rate of the plasticizer. Each polymer particle is made porous to facilitate processability, facilitate removal of monomers such as vinyl chloride remaining in the polymer particle, and prevent formation of fish eyes in the molded product. And the function of forming polymer particles having a high filling specific gravity. Conventionally, as a dispersion stabilizer for suspension polymerization of vinyl compounds, cellulose derivatives such as methyl cellulose and carboxymethyl cellulose, partially saponified polyvinyl alcohol and the like have been used alone or in combination. However,
The conventional dispersion stabilizers have a problem that they do not satisfy the above required performances.

Suspension polymerization of vinyl compounds such as vinyl chloride is usually carried out in a batch system, and an aqueous medium, a dispersion stabilizer, a polymerization initiator, a vinyl compound and the like are charged in a polymerization vessel and further required. After adding the additive, it is common to raise the temperature to carry out the polymerization reaction. Recently, in order to improve productivity, it is required to shorten the time required for one batch of polymerization, and in the suspension polymerization of vinyl compounds, a reflux condenser or the like may be installed to improve the heat removal efficiency of the polymerization heat. A method of shortening the temperature rising time by a method of charging a preheated aqueous medium (hot charging method) is used. However, when a conventional dispersion stabilizer for suspension polymerization of vinyl-based compounds is used, the foaming during the polymerization is severe, so the effective volume in the polymerization vessel decreases and the productivity decreases, and the reflux condenser is used. There was a fatal defect that the temperature could not be controlled by using the attached polymerization vessel, and the porosity of the vinyl polymer particles was lowered by using the hot charge method. On the other hand, when an antifoaming agent or the like is added to prevent foaming, there is a problem that the thermal stability of the vinyl polymer particles produced is lowered.

Poval (Publisher: Kobunshi Kobunkai, 198
4) [Publication (a)] describes, as a dispersion stabilizer for suspension polymerization of vinyl chloride, polyvinyl alcohol having a degree of polymerization of 2000 and a degree of saponification of 80 mol% and a degree of polymerization of 700 to 80.
0, polyvinyl alcohol having a saponification degree of 70 mol% is described. However, the dispersion stabilizer described in the known document (a) has a drawback that satisfactory performance cannot be obtained in response to the above-mentioned requirements (1) to (4) and the foamability during polymerization is severe. Japanese Patent Publication No. 5-88251 [Publication (b)]
Includes an average degree of polymerization of 500 or more, a ratio of the weight average degree of polymerization to the number average degree of polymerization of 3.0 or less, having a carbonyl group in the molecule, and having a vinylene group adjacent thereto.
280 nm by UV absorption spectrum of 0.1% aqueous solution
And the absorbance at 320 nm is 0.3 or more and 0.1, respectively.
Dispersion stabilizers for suspension polymerization of vinyl compounds composed of polyvinyl alcohol having a ratio of absorbance at 320 nm to 280 nm of 0.30 or more at 5 or more are described.
However, the dispersion stabilizer described in the known document (b) has a problem that the foamability in the polymerization vessel is severe.

[0006]

DISCLOSURE OF THE INVENTION An object of the present invention is to use a conventional general suspension polymerization method for vinyl compounds, that is, a method for charging an aqueous medium at room temperature into a polymerization vessel (cold charge method) and the inside of the polymerization vessel. The defoaming effect in the polymerization vessel is remarkable not only in the method of controlling the polymerization temperature by using the jacket or coil, but also in the method of using a polymerization vessel with a condenser, the hot charging method and the hot charging method using a polymerization vessel with a condenser. An object of the present invention is to provide a dispersion stabilizer which is excellent and simultaneously satisfies the above required properties.

[0007]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that the absorbance (a) at 280 nm of an aqueous solution of 0.1 wt% in concentration at 280 nm is 0.1. It is larger, the absorbance (b) at 320 nm according to the ultraviolet absorption spectrum of the aqueous solution is 0.03 or more, the absorbance (b) / the absorbance (a) is less than 0.3, and the residual acetic acid group block character Is 0.4
The present invention has completed the present invention by finding a dispersion stabilizer for suspension polymerization of a vinyl compound composed of the above polyvinyl alcohol polymer.

The present invention will be described in more detail. The preferred range of the saponification degree of the polyvinyl alcohol polymer of the present invention is 60 to 88 mol%, more preferably 65 to 75 mol%, and even more preferably 68 to 74 mol%. The preferred range of the viscosity average degree of polymerization (hereinafter abbreviated as average degree of polymerization) of the polyvinyl alcohol-based polymer is 5
It is 00 to 1500, 600 to 1200 is more preferable, and 680 to 900 is further preferable.

The polyvinyl alcohol-based polymer of the present invention has an absorbance (a) at 280 nm of an aqueous solution of 0.1 wt.
It is preferably 0.2 or more, and more preferably 0.25 or more. According to the UV absorption spectrum of the same solution 32
Absorbance (b) at 0 nm is 0.03 or more, 0.05
It is preferable that it is ˜0.2. Absorbance (b) / absorbance (a) is less than 0.3, preferably 0.25 or less,
0.2 or less is more preferable.

The residual acetic acid group block character of the polyvinyl alcohol polymer of the present invention is 0.4 or more, preferably 0.43 or more, and more preferably 0.5 or more. Regarding the block character of the residual acetic acid group, Poval (publishing office: Kobunshi Kaikai, 1984) and Macromolecules, 10, 532 (19)
77), its measuring method and the like are described in detail.

The method for producing the polyvinyl alcohol polymer of the present invention is not particularly limited, but in the case where a vinyl ester monomer is radically polymerized, a compound having a carbonyl group in the molecule, such as acetaldehyde or butyraldehyde, is present. The method of saponifying the vinyl ester polymer by polymerizing the resulting polymer and treating the resulting polymer with an alkali such as sodium hydroxide or ammonia or an acid such as hydrochloric acid or paratoluenesulfonic acid is simple and efficient. The method for adjusting the block character of the residual acetic acid group of the polyvinyl alcohol-based polymer of the present invention to 0.4 or more can be obtained by acid-saponifying a polyvinyl ester as a raw material. Even when the raw material polyvinyl ester is saponified with an alkali, it can be obtained by heat-treating the obtained polyvinyl alcohol polymer. In this case, before heat-treating the obtained polyvinyl alcohol-based polymer, the polyvinyl alcohol-based polymer is washed with an organic solvent such as acetone, methanol, or methyl acetate to adjust the content of salts such as sodium acetate to the polyvinyl alcohol-based polymer. A method in which the heat treatment is performed after the content is 0.7% by weight or less, preferably 0.5% by weight or less with respect to the coalescence is suitable. Examples of the vinyl ester when radically polymerizing a vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caproate, and vinyl caprylate. Examples thereof include vinyl caprylate, vinyl laurate, vinyl palmitate, vinyl stearate and vinyl oleate. The polyvinyl alcohol-based polymer used in the present invention may incorporate 10 mol% or less of an ionic group such as an ammonium group, a carboxyl group, a sulfone group, a nonionic group or a (long chain) alkyl group. The degree of saponification in this case is calculated from the vinyl ester group and the vinyl alcohol group, and does not include the introduced ionic group or the like.

The polyvinyl alcohol-based polymer (A) of the present invention exhibits excellent performance even when used alone as a dispersion stabilizer, but the polyvinyl alcohol-based polymer (B) has a saponification degree of less than 60 mol%. In the combination system of, the weight ratio (A) / (B) of the component (A) and the component (B) is 40/6.
When it is 0 to 95/5, excellent performance is exhibited.

The degree of saponification of the polyvinyl ester polymer (B) is less than 60 mol%, preferably 20 to 55 mol%, more preferably 25 to 45 mol%. The weight ratio (A) / (B) of component (A) and component (B) is 40/6.
It is 0-95 / 5, 50 / 50-90 / 10 is more preferable, and 60 / 40-80 / 20 is still more preferable. When the weight ratio (A) / (B) of the component (A) and the component (B) is larger than 95/5, the porosity improving effect may not be observed, and when it is less than 40/60, the polymerization Stability may be lost. The degree of polymerization of the polyvinyl ester polymer (B) is not particularly limited, but 10
00 or less is preferable, 100 to 550 is more preferable,
200 to 400 is even more preferable.

The polyvinyl ester polymer (B) may be water-insoluble or water-dispersible, and may have self-emulsifying property by introducing an ionic group or the like. In the present invention, a form in which the polyvinyl ester polymer (B) is also used as a dispersion aid in the polyvinyl alcohol polymer dispersion stabilizer of the present invention is also referred to as a dispersant stabilizer.

The method for producing the polyvinyl ester polymer (B) is not particularly limited, and conventionally known ones are preferably used. For example, a polyvinyl ester-based polymer having an ionic group in the side chain described in JP-A-1-95103,
A polyvinyl ester polymer having an ionic group at the terminal and a known polyvinyl ester polymer having 10 mol% or less of a nonionic group or a (long chain) alkyl group described in WO91 / 15518 are preferably used.

Next, a method for producing a vinyl polymer by suspension polymerization of a vinyl compound using the dispersion stabilizer of the present invention will be described. The temperature of the aqueous medium used in the method for producing the vinyl polymer is not particularly limited, and not only cold water at about 20 ° C but also warm water at 90 ° C or higher is preferably used. The medium that constitutes this heated aqueous medium is pure water,
An aqueous solution containing various additive components or an aqueous medium containing other organic solvent may be mentioned. Further, the amount of the heating aqueous medium supplied when charging the polymerization reaction system may be an amount capable of sufficiently heating the polymerization reaction system. Further, a polymerization vessel with a reflux condenser is also preferably used in order to enhance the heat removal efficiency. In the method for producing a vinyl polymer, the amount of the dispersion stabilizer used is not particularly limited, but is usually 5 parts by weight or less with respect to 100 parts by weight of the vinyl compound, and 0.01 to
1 part by weight is preferred, and 0.02-0.2 parts by weight is even more preferred. The dispersion stabilizer of the present invention may be used alone, but a saponification degree of 65 to 98 which is usually used when suspension-polymerizing a vinyl compound such as vinyl chloride in an aqueous medium.
Mol% of polyvinyl alcohol, water-soluble cellulose ether such as methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, water-soluble polymer such as gelatin, sorbitan monolaurate, sorbitan trioleate, glycerin tristearate, ethylene oxide propylene oxide block You may use together oil-soluble emulsifiers, such as a copolymer, water-soluble emulsifiers, such as polyoxyethylene sorbitan monolaurate, polyoxyethylene glycerin oleate, and sodium laurate. The amount of addition is not particularly limited, but is preferably 0.01 to 1.0 part by weight per 100 parts by weight of a vinyl compound such as vinyl chloride.

Various other additives can be added as required. Examples of the various additives include polymerization degree regulators such as acetaldehyde, butyraldehyde, trichloroethylene, perchloroethylene or mercaptans, and polymerization inhibitors such as phenol compounds, sulfur compounds and N-oxide compounds. Further, it is optional to add a pH adjuster, a scale inhibitor, a cross-linking agent and the like, and a plurality of the above-mentioned additives may be used in combination.
On the other hand, the polymerization initiator may also be one conventionally used for the polymerization of vinyl compounds such as vinyl chloride, and examples thereof include diisopropyl peroxydicarbonate and di-2-
Percarbonate compounds such as ethylhexyl peroxydicarbonate and diethoxyethyl peroxydicarbonate, t-butyl peroxyneodecanate, α-
Perester compounds such as cumyl peroxyneodecanate and t-butyl peroxyneodecanate, acetylcyclohexylsulfonyl peroxide, 2,4,4-
Peroxides such as trimethylpentyl-2-peroxyphenoxyacetate, 2,2'-azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile,
Examples thereof include azo compounds such as azobis (4-methoxy-2,4-dimethylvaleronitrile), and these can also be used in combination with potassium persulfate, ammonium persulfate, hydrogen peroxide and the like.

The vinyl compound which can be suspension-polymerized by using the dispersion stabilizer of the present invention is specifically vinyl chloride alone or a monomer mixture containing vinyl chloride as a main component (vinyl chloride 50% by weight). % Or more) and as a comonomer to be copolymerized with this vinyl chloride, vinyl acetate, vinyl ester such as vinyl propionate, and (meth) acrylic acid such as methyl (meth) acrylate and ethyl (meth) acrylate can be used. Examples thereof include esters, olefins such as ethylene and propylene, maleic anhydride, acrylonitrile, itaconic acid, styrene, vinylidene chloride, vinyl ether, and other monomers copolymerizable with vinyl chloride. Furthermore, the dispersion stabilizer of the present invention can be used even in homopolymerization or copolymerization of the above vinyl compound containing no vinyl chloride. In carrying out suspension polymerization using the dispersion stabilizer of the present invention, the charging ratio of each component, the polymerization temperature, etc. may be determined according to the conditions conventionally used in suspension polymerization of vinyl compounds such as vinyl chloride. Good.
Further, the order and ratio of the vinyl compound, the polymerization initiator, the dispersion stabilizer, the heated aqueous medium and the other additives are not limited at all. Further, a method in which hot water is used and at the same time the vinyl compound is heated before charging the vinyl compound into the polymerization vessel is also suitably used.

[0019]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In the following examples, "%" and "part" are "% by weight" unless otherwise specified.
And "parts by weight".

Production Example [Polyvinyl alcohol polymer] Vinyl acetate (hereinafter referred to as V
(Abbreviated as Ac) 5235 parts, methanol 380 parts, and acetaldehyde 115 parts were placed in a reaction vessel and the inside was sufficiently replaced with nitrogen, and then the external temperature was raised to 65 ° C and the internal temperature was 60 ° C.
2,2'- which had been replaced with nitrogen in advance
20 parts of a methanol solution containing 1 part of azobisisobutyronitrile was added. The polymerization rate after 5 hours was 60.7%. After 5 hours, cool the container and leave VAc remaining under reduced pressure.
And the like are expelled from the system with methanol while adding methanol, and the polyvinyl ester (hereinafter PV
A methanol solution of Ac) was obtained (concentration 55).
%). A part of this methanol solution was taken, the PVAc concentration was 30%, the water content was 2%, and [NaOH] / [VAc] = 0.
Saponification was carried out at a molar ratio of 05, and the obtained polyvinyl alcohol (PVA) was purified by Soxhlet washing with methanol, and the saponification degree was measured to be 99.2 mol%. Also, measure the intrinsic viscosity at 30 ℃ in water,
The average degree of polymerization was calculated to be 780. Next, a part of the above methanol solution is taken, water, methanol and methyl acetate are added, and a methanol solution of NaOH is added so that [NaOH] / [VAc] = 0.02 (molar ratio), and a PVAc concentration of 20 is added. %, Water content 1%, methyl acetate 30
Saponification was carried out at 40 ° C. under the conditions of%. 5 minutes after the addition of alkali, the system gelled, so it was crushed with a mixer and the same amount of a mixed solution of methyl acetate / water = 8/2 was added as in the saponification system, and the temperature was 60 ° C.
The mixture was heated to 1, and the reaction was continued for another hour. After that, the saponified product (PVA) is filtered and dried at 60 ° C in a hot air drier.
VA was obtained. The obtained PVA was purified by performing Soxhlet washing with methanol for 10 hours. The sodium acetate content measured by isotachophoresis (isotachophoresis) was 0.48%. After that, 150 ℃
In a hot air drier of 4 hours under an air atmosphere. The saponification degree was measured and found to be 72 mol%. 0.1%
280 nm and 32 by ultraviolet absorption spectrum of aqueous solution
The absorbance at 0 nm was 0.45 and 0.08, respectively. The residual acetic acid group block character measured by C ¹³ -NMR was 0.46. By appropriately changing the amounts of VAc, methanol, acetaldehyde, etc., and using an alkali or an acid as a saponification catalyst, and appropriately changing the temperature and time of heat treatment in a hot air dryer, a polyvinyl alcohol polymer as shown in Table 1 is obtained. Was prepared.

[Polymerization of vinyl chloride] In a glass-lined autoclave equipped with a reflux condenser,
1 part of deionized water in which the dispersion stabilizer shown in (Examples 1 to 11 and Comparative Examples 1 and 2) was dissolved and 0.04 part of a 70% toluene solution of diisopropyl peroxydicarbonate were charged, and the inside of the autoclave was adjusted to 50 mmHg. After degassing to remove oxygen until the temperature reached 39 parts, warm water at 80 ° C. (39 parts) and vinyl chloride monomer (30 parts) were simultaneously charged under stirring. The liquid level at the end of charging is 60% from the bottom of the polymerization vessel.
And the internal temperature was 50 ° C. Then the internal temperature is 5
Polymerization was continued at 0 ° C. At the start of polymerization, the pressure in the autoclave was 7.0 kg / cm ² G, polymerization initiator 6 hours after the polymerization was stopped at the time point when 4.0 kg / cm ² G, the vinyl chloride monomer unreacted After purging, the contents were taken out and dehydrated and dried. The performance of the obtained vinyl chloride resin was evaluated by the following method, and the results are shown in Table 2. The polymerization yield of the vinyl chloride polymer was 85%, and the average degree of polymerization was 1,300.

(1) Absorption of plasticizer In a planetary mixer connected to a plastograph,
Put 400 g of the obtained vinyl chloride polymer powder into 60 r
After preheating (4 minutes) while stirring at pm to 88 ° C., 200 g of dioctyl phthalate was added to this, and the time from the time of addition to the time point when the torque decreased was defined as the plasticizer absorbability (minute). (2) CPA (Cold Plasticizer A)
bsorption: cold plasticizer absorption amount) ASTM-D3
The absorption amount of dioctyl phthalate at 23 ° C. was measured by the method described in 367-75. (3) Evaluation of foaming property At the end of the polymerization, the foaming state in the polymerization vessel was visually observed,
It is indicated by the following symbols. ⊚: No foaming ◯: Bubbles were observed up to a height of 62 to 65% from the bottom of the polymerization vessel. B: Bubbles were observed up to a height of 66 to 70% from the bottom of the polymerization vessel. A: Bubbles were recognized up to a height of 90 to 100% from the bottom of the polymerization vessel. X: Bubbles were recognized up to a height of 100% from the bottom of the polymerization vessel, and the reflux condenser was also clogged with bubbles.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

EFFECTS OF THE INVENTION The dispersion stabilizer of the present invention has an extremely small foaming behavior during polymerization as compared with conventional dispersion stabilizers, so that the effective volume in the polymerization vessel is increased and the productivity is improved.
Suspension polymerization using a polymerizer with a reflux condenser,
In suspension polymerization by the hot charge method or suspension polymerization by the hot charge method using a polymerization vessel with a reflux condenser, the temperature control of the polymerization vessel becomes easy. When the dispersion stabilizer for suspension polymerization of the present invention is used, the obtained vinyl polymer particles have a large particle size, their distribution is sharp, and there is little scattering during handling,
Moreover, it has a good biteability into a molding machine, the porosity of the vinyl polymer particles is improved, the plasticizer absorption rate is high, and the filling specific gravity is high, so that it is highly evaluated industrially.

Claims (1)

[Claims] 1. An ultraviolet absorption spectrum of an aqueous solution having a concentration of 0.1% by weight has an absorbance (a) at 280 nm of more than 0.1, and an aqueous absorption spectrum of 320 n obtained by the ultraviolet absorption spectrum of the same solution.
The absorbance (b) of m is 0.03 or more, and the absorbance (b)
/ A dispersion stabilizer for suspension polymerization of a vinyl compound, which comprises a polyvinyl alcohol polymer having an absorbance (a) of less than 0.3 and a residual acetic acid group block character of 0.4 or more.