JPH10316706A - Suspenssion polymerization method of vinyl chloride resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing a vinyl chloride resin which has a sharp particle size distribution, a high bulk specific gravity, almost skin-free particle surfaces and very good moldability can be obtained without resin scale deposition on the inside wall of the polymerizer by suspension polymerization. SOLUTION: There is provided a process for producing a vinyl chloride resin by suspension-polymerizing a vinyl chloride monomer in the presence of an oil-soluble polymerization initiator in an aqueous medium, which process comprises adding a partially saponified polyvinyl acetate (a) having a degree of saponification of 60-90 mol%, a partially saponified polyvinyl acetate (b) having a degree of saponification of 20-45 mol%, an average degree of polymerization of 150-450 and a viscosity of 2-8 cP (as measured in a 4 wt. % solution in a solvent (water/methanol 1/1 (wt.) mixture) at 20 deg.C with a B-type viscometer according to JIS K 6726), an 8-25 C higher fatty acid (c), a water-soluble thickener (d) having a Brookfield viscosity of 10-200 cP (as measured in a 0.1 wt.% aqueous solution at ordinary temperature and atmospheric pressure) to the reaction system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for suspension polymerization of a vinyl chloride resin.

[0002]

2. Description of the Related Art Vinyl chloride resins are widely used in the fields of piping materials, building materials, etc. because of their excellent mechanical strength, weather resistance, chemical resistance and the like. However, moldability is not always excellent, and further improvement is required.

[0003] Typical methods for evaluating the moldability of a vinyl chloride resin include a method for measuring the absorbency of a plasticizer and a method for measuring torque and gel time using a plastmill. Excellent molding processability means that in the former, the plasticizer permeates into the vinyl chloride resin in a short time, and in the latter, the maximum torque is low and the gelation time is short. is there.

[0004] The greatest factor that inhibits moldability is the presence of a skin layer on the surface of vinyl chloride resin particles. The skin layer is a skin layer present on the surface of the vinyl chloride resin particles, and the partially saponified polyvinyl acetate, a cellulose derivative, etc. used as a dispersant in the polymerization is firmly grafted on the vinyl chloride resin. This is considered to be a layer formed by performing the above.

[0005] Originally, the skin layer functions to protect the surface of the monomer oil droplets in the polymerization system and to stabilize the polymerization system by adjusting the splitting and coalescence of the oil droplets. However, at the stage of molding and processing the vinyl chloride resin, it is necessary to grind the vinyl chloride resin particles into submicron units (primary particles or less), and the presence of a strong skin layer is rather a major obstacle. It is thought that it is.

Therefore, in order to obtain a vinyl chloride resin having excellent moldability, it is desirable that the skin layer on the surface of the vinyl chloride resin particles is small or almost nonexistent. In addition, many fine pores exist between the primary particles inside the vinyl chloride resin particles so that the liquid stabilizer, plasticizer, etc. taken in the vinyl chloride resin particles can be easily diffused and absorbed. It is considered important to be excellent.

As a method for producing a vinyl chloride resin having excellent moldability, for example, Japanese Patent Publication No. 36-22445 discloses a suspension polymerization using a higher fatty acid ester of sorbitan and a higher fatty acid ester of polyoxyethylene sorbitan in combination. A method is disclosed. However, the vinyl chloride resin obtained by this method has poor porosity and has a defect that a large amount of resin scale adheres to the inner wall of the polymerization vessel.

In Japanese Patent Publication No. 53-13395, a dispersant obtained by combining a lipophilic sorbitan higher fatty acid and a hydrophilic polyoxyethylene sorbitan higher fatty acid ester in the presence of a basic compound is used. Is 5
A method of adding a water-soluble cellulose derivative when it reaches 40% is disclosed. In addition, Japanese Patent Publication 5-86408
Japanese Patent Application Publication No. JP-A-2005-17764 discloses a method in which a higher fatty acid ester of sorbitan is used as a dispersant, polymerization is started under stirring by a Faudler blade, and a water-soluble dispersant is added when the polymerization addition rate reaches 5 to 40%. Have been.

[0009] However, these polymerization methods can provide a highly porous vinyl chloride resin without resin scale adhering to the inner wall of the polymerization vessel during polymerization, but have a low bulk specific gravity and a dispersing agent. Because of the post-addition, the operation is complicated in the polymerization step, and a large amount of the dispersant remains on the surface of the vinyl chloride-based resin particles, thus deteriorating the physical properties of the obtained vinyl chloride-based resin.

JP-A-5-295008 discloses a method in which a known suspending dispersant, a non-ionic surfactant such as partially saponified polyvinyl acetate having a low saponification degree and sorbitan monolaurate are added at a specific ratio to carry out polymerization. Is disclosed. However, in the vinyl chloride resin obtained by this method, although the skin layer portion on the particle surface is reduced, it is necessary to control the power required for stirring in the initial stage of polymerization, and the gelation properties of the obtained vinyl chloride resin, The plasticizer absorption and the like were still insufficient.

JP-A-8-59731 discloses a suspending / dispersing agent having a specific cloud point, or a cellulose derivative and a sorbitan-based higher fatty acid ester having a specific HLB value, a specific thickening agent, and a carbon number of 8 There is disclosed a method of polymerizing together with higher fatty acids of 25 to 25. However, this method has been greatly improved in that the additives can be added in a lump, there is no complexity in the manufacturing process, and the skin layer portion of the vinyl chloride resin particles is removed. The moldability of the obtained vinyl chloride resin was not improved.

JP-A-8-3206, JP-A-8-1
No. 09207 discloses a method using a partially saponified polyvinyl alcohol and a high-viscosity hydroxypropylmethylcellulose or a crosslinked copolymer having a carboxyl group. However, the vinyl chloride resin obtained by this method is excellent in plasticizer absorption,
The bulk specific gravity was low and was not satisfactory.

JP-A-6-107712, JP-A-7-107712
No. 53607 discloses a method of combining low-saponified polyvinyl acetate and high-saponified polyvinyl acetate. However, the vinyl chloride-based resin particles obtained by this method are covered with a skin layer, have a low bulk specific gravity, and have not essentially obtained high gelling properties. Further, Japanese Patent Application Laid-Open No. 4-304210 discloses a method for improving gelation characteristics by using low-saponified polyvinyl acetate, medium-saponified polyvinyl acetate and high-saponified polyvinyl acetate. The degree of speed improvement was low.

[0014]

DISCLOSURE OF THE INVENTION In view of the above, it is an object of the present invention to provide a vinyl chloride resin having a sharp particle size distribution and a high bulk specific gravity without resin scale adhering to the inner wall of a polymerization vessel. It is an object of the present invention to provide a method for suspension polymerization of a vinyl chloride resin, which has almost no skin layer portion and has extremely good moldability.

[0015]

SUMMARY OF THE INVENTION The present invention is a suspension polymerization method for a vinyl chloride resin in which a vinyl chloride monomer is subjected to suspension polymerization in an aqueous medium in the presence of an oil-soluble polymerization initiator. ,
In the reaction system, partially saponified polyvinyl acetate (a) having a saponification degree of 60 to 90 mol%, a saponification degree of 20 to 45 mol%, an average polymerization degree of 150 to 450, and a viscosity (water / methanol = Viscosity of a 4% by weight solution with respect to a solvent of 1/1 (weight ratio), and B according to JIS K 6726
Partially saponified polyvinyl acetate (b) having a value of 2 to 8 cP (measured at 20 ° C. by a viscometer), higher fatty acid (c) having a carbon number of 8 to 25, and 0.1 wt. % Aqueous solution has a Brookfield viscosity of 10 to 200 c
This is a suspension polymerization method for a vinyl chloride resin to which a water-soluble thickener (d) as P is added. Hereinafter, the present invention will be described in detail.

In the present invention, a vinyl chloride monomer is subjected to suspension polymerization in an aqueous medium in the presence of an oil-soluble polymerization initiator. As the vinyl chloride-based monomer, a monomer copolymerizable with vinyl chloride can be used in addition to vinyl chloride. The monomer copolymerizable with the vinyl chloride is not particularly limited, and includes, for example, alkyl vinyl esters such as vinyl acetate; α-monoolefins such as ethylene and propylene; methyl (meth) acrylate, ethyl (meth) Alkyl (meth) acrylates such as acrylate and octyl acrylate; alkyl vinyl ether; maleimides; vinylidene chloride; These may be used alone or in combination of two or more. When vinyl chloride is copolymerized with a monomer copolymerizable with the above-mentioned vinyl chloride, the vinyl chloride is added at 50.
It is preferable that the content be not less than% by weight.

As the oil-soluble polymerization initiator, known radical polymerization initiators generally used for polymerization of vinyl chloride resins can be used. The radical polymerization initiator is not particularly limited, and may be, for example, t-butyl peroxy neodecanoate, t-hexyl peroxy neodecanoate, t-hexyl peroxy pivalate, α-
Cumyl peroxy neodecanoate, t-hexyl neohexanoate, 2,4,4-trimethylpentyl-2
A perester compound such as peroxy-2-neodecanoate; diisopropylperoxydicarbonate, di-2-ethylhexylperoxydicarbonate, di-
Percarbonate compounds such as 2-ethoxyethylperoxydicarbonate and dimethoxyisopropylperoxydicarbonate; decanoyl peroxide, lauroyl peroxide, benzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide,
Peroxide compounds such as 2,4-dichlorobenzoyl peroxide, p-menthane hydroperoxide, 3,5,5-trimethylhexanoyl peroxide and isobutyl peroxide; α, α'-azobisisobutyronitrile, α, α Examples include azo compounds such as α′-azobis (dimethylvaleronitrile) and α, α′-azobis (4-methoxy-2,4-dimethylvaleronitrile). These may be used alone or in combination of two or more.

The water-soluble medium is not particularly limited.
For example, deionized water or the like can be used.

In the present invention, a partially saponified polyvinyl acetate (a), a partially saponified polyvinyl acetate (b), a higher fatty acid (c) and a water-soluble thickener (d) are added to the reaction system. Perform turbid polymerization.

The partially saponified polyvinyl acetate (a) is used as a dispersant and has a saponification degree of 60 to 9
0 mol%. If it is less than 60 mol%, the oil solubility becomes strong, and the ability to disperse the vinyl chloride monomer is reduced, so that the obtained vinyl chloride resin has many coarse particles, and if it exceeds 90 mol%, In addition, since the protective colloid property becomes strong, a strong skin layer is formed on the surface of the obtained vinyl chloride resin particles, and the gelling property is deteriorated. Preferably, it is 65 to 80 mol%.

The average degree of polymerization of the partially saponified polyvinyl acetate (a) is preferably from 500 to 3,000. If it is less than 500, the dispersing ability of the vinyl chloride-based monomer is lacking, and the obtained vinyl chloride-based resin tends to become coarse particles or blocks, and if it exceeds 3,000, the skin layer becomes thick and the porosity is increased. Insufficient molding processability will result. More preferably, it is 700-1500.

The partially saponified polyvinyl acetate (b) is used as a dispersant and has a saponification degree of 20 to 4
5 mol%. If the amount is less than 20 mol%, the solubility in the vinyl chloride monomer is reduced, so that the polymerization system becomes unstable, and the obtained vinyl chloride resin has many coarse particles. , The compatibility with the partially saponified polyvinyl acetate (a) is deteriorated, and the gelation properties of the obtained vinyl chloride resin are deteriorated.
It is limited within the above range. Preferably, 30 to 40 mol%
It is.

The average degree of polymerization of the partially saponified polyvinyl acetate (b) is from 150 to 450. If it is less than 150, the dispersing ability of the vinyl chloride-based monomer is lacking, and the obtained vinyl chloride-based resin tends to be coarse particles or blocks.If it exceeds 450, the skin layer becomes thicker,
Since the porosity is insufficient and the moldability decreases, the content is limited to the above range. Preferably, it is 200 to 350.

The viscosity of the partially saponified polyvinyl acetate (b) (water / methanol = 1/1 (weight ratio) with respect to a solvent
The viscosity of the solution at 20% by a B-type viscometer according to JIS K 6726 is 2 to 8%.
cP. If it is less than 2 cP, the skin layer cannot obtain the minimum necessary strength near the interface of the vinyl chloride monomer oil droplet, which is considered to be present with the partially saponified polyvinyl acetate (b), and the polymerization becomes unstable. The resulting vinyl chloride resin has a large number of coarse particles, and if it exceeds 8 cp, the strength of the skin layer is too strong near the interface of the vinyl chloride monomer oil droplets, and the resulting vinyl chloride resin gels. Since the properties are deteriorated and the moldability is reduced, the content is limited to the above range. Preferably, it is 3 to 6 cP.

It is presumed that the viscosity of the partially saponified polyvinyl acetate (b) has a great influence not on the thickness of the skin layer but on the strength of the skin layer. The reactivity of the vinyl monomer and the formation of a molecular structure including its branched structure are involved.

The partially saponified polyvinyl acetate (a) and the partially saponified polyvinyl acetate (b) are added in an amount of 15 to 2500 p
pm is preferred. When the amount is less than 15 ppm, the oil droplets of the vinyl chloride-based monomer become unstable, and the obtained vinyl chloride-based resin tends to be block-shaped, and when the amount exceeds 2500 ppm, a skin layer on the surface of the obtained vinyl chloride-based resin particles. And the molding processability deteriorates. More preferably, each is 300 to 2000 ppm.

The addition ratio of the partially saponified polyvinyl acetate (a) to the partially saponified polyvinyl acetate (b) (a) /
(B) is preferably 80/20 to 20/80. More preferably, it is 60/40 to 30/70.

The above partially saponified polyvinyl acetate (a) and the partially saponified polyvinyl acetate (b) exhibit high polymerization stability and excellent moldability due to a favorable synergistic effect relating to the formation of a skin layer at the oil droplet interface. I do. Therefore, in the present invention, it is possible to greatly reduce the amount of a nonionic surfactant such as a sorbitan fatty acid ester and an emulsifier such as an anionic surfactant. For example, the amount of the sorbitan higher fatty acid ester is 0 to 2000 pp.
m is preferred. More preferably, it is 5 to 1000 ppm.

The higher fatty acid (c) has 8 to 25 carbon atoms.
belongs to. When the number of carbon atoms is less than 8, the higher fatty acid (c) is not distributed to the oil layer of the vinyl chloride-based monomer during polymerization, and does not exhibit a gelation promoting effect. Is more than 25, the melting point of the higher fatty acid (c) is high, so that even if the obtained vinyl chloride resin is processed at a molding temperature, it is difficult to exhibit the gelation promoting effect, so that it is limited to the above range. Preferably, it has 11 to 22 carbon atoms. As the higher fatty acid (c), a linear saturated fatty acid is preferably used although the effect is not reduced by the degree of unsaturation or branching of the main chain.

The higher fatty acid (c) is not particularly restricted but includes, for example, isostearic acid, stearic acid, n-
Heptadecanoic acid, palmitic acid, n-pentadecanoic acid,
Myristic acid, araginic acid, nonadecanoic acid, n-tridecanoic acid, lauric acid, undecylic acid, and the like. These may be used alone or in combination of two or more. The added amount of the higher fatty acid (c) is preferably 300 to 20,000 ppm based on the vinyl chloride monomer.

The water-soluble thickener (d) has a Brookfield's viscosity of a 0.1% by weight aqueous solution at normal temperature and normal pressure,
10 to 200 cP. Even if it is less than 10 cP or more than 200 cP, the particle size distribution of the obtained vinyl chloride resin is deteriorated, so that it is limited to the above range. Preferably, it is 11 to 140 cP.

The water-soluble thickener (d) is not particularly restricted but includes, for example, polyethylene oxide, polyvinylpyrrolidone, polyacrylamide, polyacrylamide copolymer, crosslinked (meth) acrylic resin, methylcellulose calcium, starch Examples include sodium glycolate, sodium starch phosphate, sodium alginate, propylene glycol alginate, sodium carboxymethylcellulose, and calcium carboxymethylcellulose. These may be used alone or in combination of two or more.

The polyethylene oxide used as the water-soluble thickener (d) has an average molecular weight of 1.7 million to 55
A thing of 100,000 is preferable. In particular, it is preferable to use an aqueous solution of 4.3 million to 4.8 million as a 0.1% by weight aqueous solution because the Brookfield viscosity becomes 51 cP.

The amount of the water-soluble thickener (d) to be added is preferably 5 to 2,000 ppm based on the vinyl chloride monomer. If it is less than 5 ppm, the viscosity is low, and the effect of improving the particle size distribution of the obtained vinyl chloride resin is low,
If it exceeds 000 ppm, a strong skin layer is formed on the surface of the obtained vinyl chloride-based resin particles, so that the gelation rate is reduced. More preferably, it is 25 to 900 ppm.

In the present invention, suspension polymerization can be carried out by a conventionally known method or the like. For example, with respect to the aqueous medium placed in a polymerization vessel (pressure-resistant autoclave) or the like, the vinyl chloride-based monomer, the oil-soluble polymerization initiator,
The partially saponified polyvinyl acetate (a), the partially saponified polyvinyl acetate (b), the higher fatty acid (c), and the water-soluble thickener (d) are added, and the temperature is increased while stirring. Can be carried out. In this case, depending on the polymerization conditions, a polymerization regulator, a chain transfer agent,
An antistatic agent, a crosslinking agent, a stabilizer, a filler, a scale inhibitor, a pH adjuster, and the like may be appropriately added. The addition may be batch addition, intermittent or continuous addition. Further, in the present invention, it is not necessary to use an emulsifier usually used in suspension polymerization, and even if it is used, it is possible to reduce the amount of use.

The shape, structure and the like of the above polymerization vessel are not particularly limited, and conventionally known various polymerization vessels can be used. The stirring can be performed, for example, with a stirring blade and a baffle plate. The stirring blade is not particularly limited, and includes, for example, a Faudler blade, a paddle blade, a turbine blade, a fan turbine blade, a bull margin blade, and the like. Of these, Faudler blades are more preferably used. The combination of the stirring blade and the baffle is not particularly limited.

[0037]

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.

Example 1 A polymerization vessel having an internal volume of 100 liters (pressure-resistant autoclave)
And 45 kg of deionized water, and partially saponified polyvinyl acetate (a) (with a saponification degree of 72 mol% and an average degree of polymerization of 700) as shown in Table 1 with respect to the vinyl chloride monomer.
00 ppm, partially saponified polyvinyl acetate (b) (degree of saponification 3
5 mol%, average degree of polymerization 300, viscosity 4cP) 1300p
pm, 1200 ppm of lauric acid, polyacrylamide (average molecular weight: 12,000,000 to 14,000,000, 51 cP / 0.
100 ppm of a 1% aqueous solution) and 500 ppm of t-butyl peroxyneodecanoate. Next, after degassing the inside of the polymerization vessel to 40 mmHg, 45 kg of a vinyl chloride monomer was charged and stirring was started. The polymerization temperature is 57
° C and kept at this temperature until the end of the polymerization.

When the polymerization conversion reaches 90%, the reaction is terminated, the unreacted monomer in the polymerization vessel is recovered, the polymer is taken out of the system in the form of a slurry, and the polymer is obtained after dehydration and drying. For the vinyl chloride resin, according to the test method described below, plasticizer absorption, porosity, particle size distribution, bulk specific gravity, maximum torque,
The gelation time, skin-free ratio, and scale adhesion state were evaluated, and the results are shown in Table 1.

Examples 2 to 4 and Comparative Examples 1 to 5 Under the conditions shown in Table 1, a vinyl chloride resin was obtained in the same manner as in Example 1, and the performance was evaluated. The results are shown in Table 1.

Performance Evaluation Method (Measurement of Plasticizer Absorbency) 5 g of the obtained vinyl chloride resin was put into a centrifuge tube with a glass filter, and excess plasticizer DOP (10 mL) was added to the vinyl chloride resin.
Mix well for 1 hour. Thereafter, the mixture was treated with a centrifugal separator (H-200N, rotation speed: 3000 rpm, manufactured by Domestic Centrifuge Co., Ltd.) for 30 minutes to separate excess DOP, and the absorption amount of DOP per 100 g of the vinyl chloride resin was determined. I asked.

(Measurement of porosity) Using a mercury intrusion porosimeter (Porosimeter 2000, manufactured by ACOM Co.)
The porosity was determined by measuring the amount of mercury injected under pressure per 100 g of the vinyl chloride resin obtained at 96 MPa.

(Measurement of Particle Size Distribution) JIS Z8801
The obtained vinyl chloride-based resin is
The mixture was separated using a sieve of 0 or 200 mesh, and the weight% of the passing amount was determined.

(Measurement of Bulk Specific Gravity) The bulk specific gravity of the obtained vinyl chloride resin was measured according to JIS Z6721.

(Measurement of processability (maximum torque, gel time)) Test sample: 100 parts by weight of the obtained vinyl chloride resin was mixed with dibutyltin mercapto (organotin stabilizer: JF-1).
OB, 2 parts by weight of Sankyoki Co., Ltd.) and 0.5 parts by weight of montanic acid ester (lubricant: WAX OP, manufactured by Hoechst) were added to the mixture, and the mixture was prepared using a supermixer (Mitsui Miike).
After heating and mixing to 0 ° C., the mixture was cooled at 40 ° C. to obtain a test sample.

Apparatus: Plastmill: manufactured by Toyo Seiki Co., Ltd. Model: Haake Leo Code 90 Test conditions: 60 g of a test sample is placed in a test chamber at a temperature of 120 ° C., and the number of revolutions is increased while increasing the temperature at a rate of 5 ° C./min. The mixture was kneaded at 200 rpm at 50 rpm, and the maximum torque and the gelation time were measured.

(Evaluation of Surface Condition (Skin Free Rate)) The obtained vinyl chloride resin particles were subjected to a scanning electron microscope (FE).
-SEM S-4200, manufactured by Hitachi, Ltd.) was taken at an acceleration voltage of 2 kV and a magnification of 130 times, and the outline of the particles, the skin portion, and the portion where the skin did not exist (the portion where the primary particles were exposed; A tracing paper (or OHP sheet) was copied.
Next, tracing paper (or OHP sheet)
Was introduced into an image analyzer (PIAS-III, manufactured by Pierce), and image analysis was performed. The particle area and the skin-free area were calculated, and the skin-free ratio was determined according to the following equation. Skin-free rate = (skin-free area / particle area) x 1
00

[0048]

[Table 1]

[0049]

The method for suspension polymerization of vinyl chloride resin of the present invention is as described above, so that no resin scale adheres to the inner wall of the polymerization vessel, and a sharp particle size distribution and a high bulk specific gravity are obtained. However, it is possible to obtain a vinyl chloride resin having almost no skin layer portion on the particle surface and having extremely good moldability.

Claims (1)

[Claims] 1. A suspension polymerization method for a vinyl chloride resin in which a vinyl chloride monomer is suspension-polymerized in an aqueous medium in the presence of an oil-soluble polymerization initiator. Is 60
Partially saponified polyvinyl acetate (a) having a saponification degree of 20 to 45 mol% and an average degree of polymerization of 150 to 90 mol%
450, the viscosity of a 4% by weight solution in a solvent having a viscosity (water / methanol = 1/1 (weight ratio)),
Partially saponified polyvinyl acetate (b) having a value of 2 to 8 cP (measured at 20 ° C. by a B-type viscometer based on SK6726), higher fatty acid (c) having 8 to 25 carbon atoms, and normal temperature A suspension polymerization method for a vinyl chloride resin, which comprises adding a water-soluble thickener (d) having a Brookfield viscosity of 10 to 200 cP in a 0.1% by weight aqueous solution at normal pressure.