JP3347953B2 - Suspension polymerization of vinyl chloride resin - Google Patents

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 Conventionally, vinyl chloride resins (hereinafter referred to as P
VC) has excellent mechanical strength, weather resistance, and chemical resistance, and is widely used in piping materials, building materials, and the like. However, moldability is not always excellent.
Further improvements are required. Representative methods for evaluating the moldability of PVC include a method of measuring the amount of plasticizer absorbed and a method of measuring torque and gel time using a plastmill. In the former, the plasticizer penetrates into the PVC in a short time, and in the latter, the maximum torque is low, and
The gelation time is short.

[0003] One of the factors that is considered to be the greatest factor inhibiting moldability is the presence of a skin on the PVC surface.
The term “skin” means a skin layer present on the surface of PVC particles, and its components are mainly grafted onto a dispersant (eg, partially saponified polyvinyl acetate, a cellulose derivative, etc.) or PVC used for polymerization and PVC. It is thought that it was a layer. Originally, the skin protects the surface of the oil droplets of the monomers in the polymerization system and regulates the splitting and coalescence of the oil droplets, thereby stabilizing the polymerization system. However, PVC
At the stage of forming, it is necessary to grind the PVC suspended particles to submicron units (primary particles or less), and it is considered that the presence of a strong skin layer is rather a major obstacle.

[0004] Therefore, in order to obtain PVC particles having excellent processing characteristics, it is desirable that the surface of the PVC particles has little or no skin, and that the liquid stabilizer and plasticizer incorporated into the PVC particles easily diffuse. It is considered important that many micropores exist between the primary particles inside the PVC particles so that they can be absorbed. As a method for producing PVC having excellent moldability as described above, for example,
JP-A-6-22445 discloses a suspension polymerization method in which a higher fatty acid ester of sorbitan and a higher fatty acid ester of polyoxyethylene sorbitan are used in combination, but the resulting PVC has poor porosity and resin There was a defect that many scales adhered.

[0005] In order to solve the above-mentioned problems, a number of methods have been proposed. For example, Japanese Patent Publication No. 53-13395 discloses a method in which a lipophilic sorbitan higher fatty acid ester and a hydrophilic poly-ester are used in the presence of a basic compound. Using a dispersant in combination with oxyethylene sorbitan higher fatty acid ester,
When the VC polymerization conversion reaches 5 to 40%, a method of adding a water-soluble cellulose derivative is disclosed. Japanese Patent Publication No. 5-86408 discloses that a sorbitan higher fatty acid ester is used as a dispersant, A method is disclosed in which polymerization is started under stirring by a Faudler blade, and a water-soluble dispersant is added when the polymerization conversion reaches 5 to 40%.

In these polymerization methods, however, a resin scale does not adhere to the inner wall of the polymerization vessel during the polymerization, and a highly porous PVC can be obtained. However, the bulk specific gravity becomes low, and the dispersant is added later. In addition, the operation becomes complicated in the polymerization step, a large amount of the dispersant remains on the surface of PVC, and there remains a problem of deteriorating the physical properties of the obtained PVC.

[0007] Japanese Patent Application Laid-Open No. 5-295008 discloses that
Known suspension dispersants, low saponification partially saponified polyvinyl acetate, a nonionic surfactant such as sorbitan monolaurate, by adding at a specific ratio, a method of performing polymerization has been proposed, In the PVC produced by this method, although the skin portion on the surface is reduced, it is necessary to control the power required for stirring in the initial stage of polymerization, and the gelling properties, plasticizer absorbency, etc. of the obtained PVC are still insufficient. there were.

Further, Japanese Patent Application Laid-Open No. Hei 8-59713 discloses that
A method of polymerizing a suspension dispersant having a specific cloud point or a sorbitan-based higher fatty acid ester having a specific HLB value with a cellulose derivative is introduced.
JP 120007 discloses that a sorbitan-based higher fatty acid ester having a specific HLB value as a dispersant and a specific thickener,
There are disclosed methods of polymerizing using a higher fatty acid having 8 to 25 carbon atoms in combination. However, in these methods, additives can be added all at once, there is no need for complicated production, and a surface for removing a skin portion of PVC is removed. However, the molding processability of PVC is not improved.

Further, Japanese Patent Application Laid-Open No. H8-3206,
JP-109207 discloses a method using partially saponified vinyl acetate and high-viscosity hydroxypropylmethylcellulose, or a cross-linked copolymer containing a carboxyl group, and the like. Is excellent, but has a low bulk specific gravity and is not satisfactory.

Japanese Unexamined Patent Publications Nos. 6-107712 and 7-53607 propose a method of combining low-saponified polyvinyl acetate and high-saponified polyvinyl acetate. Partial coverage, low bulk specific gravity, and essentially no high gelling properties. Furthermore, Japanese Patent Application Laid-Open No. 4-304210 proposes a method for improving gelation characteristics by using low, medium and high saponified polyvinyl acetates, but the degree of improvement in the gelation rate is low.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and has no resin scale attached to the inner wall of a polymerization vessel, and the obtained PVC has a sharp particle size distribution. It is an object of the present invention to provide a suspension polymerization method for PVC, which has a high bulk specific gravity, has almost no skin portion in particles, and has extremely good moldability.

[0011]

The suspension polymerization method for PVC of the present invention comprises a reaction system for suspension polymerization of a vinyl chloride monomer in an aqueous medium in the presence of an oil-soluble polymerization initiator. A partially saponified polyvinyl acetate (a) having a saponification degree of 60 to 90 mol%, a partially saponified polyvinyl acetate (b) having a saponification degree of 20 to 55 mol%, and an emulsifier of a sorbitan higher fatty acid ester having an HLB value of 3 to 10 ( c) a higher fatty acid having 8 to 25 carbon atoms (d) and 10 to 20 carbon atoms at normal temperature and normal pressure.
A thickener (e) having a Brookfields viscosity of 0 cps is added.

In the present invention, PVC means a homopolymer of vinyl chloride and a copolymer of vinyl chloride in an amount of 50% by weight or more and a monomer copolymerizable therewith. Monomers copolymerizable with vinyl chloride include, for example, alkyl vinyl esters such as vinyl acetate; α-monoolefins such as ethylene and propylene; methyl (meth) acrylate, ethyl (meth) acrylate, octyl acrylate, and the like. Alkyl (meth) acrylates; alkyl vinyl ethers; maleimides, vinylidene chloride, styrene and the like, and at least one of these is used.

The partially saponified polyvinyl acetate (a) is used as a dispersant, and preferably has a saponification degree of 60 to 90 mol%, more preferably 65 to 80 mol%. When the degree of saponification is less than 60 mol%, oil solubility becomes strong, and the ability to disperse a monomer such as vinyl chloride (hereinafter simply referred to as a monomer) is insufficient. Increase. On the other hand, if the content exceeds 90 mol%, the protective colloid property becomes strong, so that a strong skin is formed on the particle surface, and the gelling properties are deteriorated.

Average polymerization of partially saponified polyvinyl acetate (a)
The degree is preferably from 500 to 3,000, more preferably from 700 to 1,500. If the average degree of polymerization is less than 500, the monomer is insufficient in dispersing ability, and the PVC tends to become coarse particles or blocks. If it exceeds 3,000, the skin layer becomes thicker and the porosity is insufficient, so that molding is performed. Workability decreases.

The partially saponified polyvinyl acetate (b) has a saponification degree of preferably 20 to 55 mol%, more preferably 35 to 50 mol%. When the saponification degree is less than 20 mol%, the solubility in the monomer is lowered, so that the polymerization system becomes unstable and the obtained PVC has many coarse particles. On the other hand, if it exceeds 55 mol%, the compatibility with the partially saponified polyvinyl acetate (a) becomes poor, and the gelation properties of PVC deteriorate.

Average polymerization of partially saponified polyvinyl acetate (b)
The degree is preferably from 200 to 1,000, and more preferably from 250 to 800. If the average degree of polymerization is less than 200, the monomer is insufficient in dispersing ability and the PVC tends to be coarse particles or blocks, and if it exceeds 1,000, the skin layer becomes thicker and lacks porosity to form. Workability decreases.

Partially saponified polyvinyl acetate (a) and (b)
Is added in an amount of 20 to 3,000 ppm based on the monomer.
Is preferred. If the amount is less than 20 ppm, the oil droplets of the monomer become unstable, and the PVC tends to be in a block shape.
If it exceeds 00 ppm, the skin layer on the surface of the PVC particles becomes thick and the moldability deteriorates. Further, the addition ratio (a) / (b) of the above partial polyvinyl acetate is 98/2 to 2
0/80 is preferable, and more preferably, 95/5 to 40
/ 60.

The HLB value (hydrophilic-lipophilic equilibrium value) is defined by
C. Griffin [J. Soc. Cosmetic
Chem. 1, 1st page, 311 (1949)] means the balance between the hydrophilic group and the hydrophobic group of the nonionic surfactant. The larger the value, the more hydrophilic, and the smaller the value, the more hydrophobic. growing.

H of sorbitan higher fatty acid ester (c)
The LB value needs to be 3 to 10, preferably 4 to 9.
It is. HLB value of sorbitan higher fatty acid ester is 3
If it is less than 3, the lipophilicity is strong, so that the emulsifying and dispersing ability of the monomer in water is low, and the particle size distribution of the obtained PVC is wide including coarse particles. When the HLB value exceeds 10, the hydrophilicity is large, so that the oil droplets of the monomer during polymerization become unstable, and the aggregation of the monomer particles easily occurs.
PVC becomes an aggregate of block-like and coarse particles.

Examples of the sorbitan higher fatty acid ester (c) having an HLB value of 3 to 10 include sorbitan monolaurate, sorbitan monomyristate, sorbitan monopalmitate, sorbitan monostearate, sorbitan distearate, and sorbitan tristearate. And sorbitan saturated higher fatty acid esters such as acrylates and unsaturated higher fatty acid esters, and at least one of them is used.

The amount of the higher sorbitan fatty acid ester added is preferably 50 to 3,500 ppm, more preferably 100 to 2,500 ppm, based on the monomer.
If it is less than 50 ppm, the skin is formed thick, lacks porosity, and molding processability is poor. Also, 3,500
If it exceeds ppm, the particle size distribution is wide and resin scale adheres to the inner wall of the polymerization vessel.

The effect of the higher fatty acid (d) is not reduced by the degree of unsaturation or branching of the main chain.
Straight-chain saturated fatty acids are preferred, and those having 8 to 25 carbon atoms are preferred, and those having 11 to 22 carbon atoms are more preferred. When the number of carbon atoms is less than 8, the higher fatty acid is not distributed to an oily layer of a monomer such as vinyl chloride during polymerization because the polymer is hydrophilic.
Does not exhibit gelation promoting effect. On the other hand, when the number of carbon atoms exceeds 25, the melting point of the higher fatty acid increases, so that it is difficult to exhibit the gelation promoting effect even at the temperature of the molding process of PVC.

Specific examples of higher fatty acids having 8 to 25 carbon atoms include isostearic acid, stearic acid, n-heptadecanoic acid, palmitic acid, n-pentadecanoic acid, myristic acid, aragic acid, nonadecanoic acid and n-tridecane. Acid, lauric acid, undecylic acid and the like are used, and at least one of them is used. These carbon numbers are 8
The addition amount of the higher fatty acid of 25 to 25 is 50 to
15,000 ppm is preferred.

In the present invention, at normal temperature and normal pressure,
0.1 wt% aqueous solution is 10 to 200 cps (mPa
Examples of the water-soluble thickener (e) having a Brookfield viscosity of s) include polyethylene oxide, polyvinylpyrrolidone, polyacrylamide, polyacrylamide copolymer, crosslinked (meth) acrylic resin,
Examples include methylcellulose calcium, sodium starch glycolate, sodium starch phosphate, sodium alginate, propylene glycol alginate, sodium carboxymethylcellulose, calcium carboxymethylcellulose, and at least one of these is used.

Of the above-mentioned substances, more specifically, polyethylene oxide has an average molecular weight of from 170 to 170.
5.5 million is preferable, and when 430-4.8 million is converted into a 0.1% by weight aqueous solution, the Brookfield viscosity becomes 12 cps. Further, polyacrylamide having an average molecular weight of preferably 8 to 14,000,000 is preferable. In particular, when a polyacrylamide having an average molecular weight of 1200 to 14,000,000 is converted into a 0.1% by weight aqueous solution, the Brookfield viscosity becomes 51c.
ps.

The Brookfield's viscosity of the water-soluble thickener (e) is from 10 to 200 cps in a 0.1% by weight aqueous solution.
Is required, and more preferably 11 to 140 cps. If the viscosity of the aqueous solution is less than 10 cps and becomes too low, or if it exceeds 200 cps and becomes too high, the obtained PVC has a poor particle size distribution.

The amount of the water-soluble thickener (e) to be added is preferably from 5 to 2,000 ppm, more preferably from 10 to 500 ppm, based on the monomer. If it is less than 5 ppm, the viscosity is low, so that the effect of improving the particle size distribution of PVC is low. If it exceeds 2000 ppm, a strong skin layer is formed on the surface of the PVC, and the gelation rate is reduced.

The oil-soluble polymerization initiator means a known radical initiator generally used for the polymerization of PVC, for example, t-butyl peroxy neodecanoate, t-hexyl peroxy neodecanoate. , T-hexyl peroxypivalate, α-cumylperoxy neodecanoate, t-hexyl neohexanoate, 2,4,4-
Perester compounds such as trimethylpentyl-2-peroxy-2-neodecanoate; diisopropylperoxydicarbonate, di-2-ethylhexylperoxydicarbonate, di-2-ethoxyethylperoxydicarbonate, dimethoxyisopropylperoxydicarbonate, etc. Percarbonate compounds; decanoyl peroxide, lauroyl peroxide, benzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, 2,4-dichlorobenzoyl peroxide, p-menthane hydroperoxide,
Peroxide compounds such as 3,5,5-trimethylhexanoyl peroxide and isobutyl peroxide; α,
Azo compounds such as α'-azobisisobutyronitrile, α, α'-azobis (2,4-dimethylvaleronitrile), α, α'-azobis (4-methoxy-2,4-dimethylvaleronitrile) and the like And at least one of these is used.

In the polymerization method of the present invention, the shape and structure of the polymerization vessel (pressure-resistant autoclave) used are as follows:
There is no particular limitation, and a conventionally known polymerization vessel is used.
In addition, examples of the stirring blade include a Faudler blade, a paddle blade, a turbine blade, a fan turbine blade, and a blue margin blade, and among these, the Faudler blade is preferable. The combination of the wing and the baffle is not particularly limited.

In the suspension polymerization method of the present invention, a method of adding deionized water, a suspension dispersant, an emulsifier, a water-soluble thickener, a monomer containing vinyl chloride, and the like is a conventionally known method. Depending on the polymerization conditions, a polymerization regulator, a chain transfer agent, an antistatic agent, a crosslinking agent, a stabilizer, a filler, and a scale inhibitor may be appropriately added at all.

[0031]

In the suspension polymerization method of the present invention, a predetermined amount of various suspension polymerization agents such as dispersants, emulsifiers, fatty acids and thickeners having different saponification degrees are added to a reaction system, and a vinyl chloride system is added. By stabilizing the monomer oil droplets and promoting the polymerization, it is possible to obtain a resin having good moldability without a skin layer on the surface of the PVC particles without resin scale adhering to the reactor.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to explain the present invention in more detail, examples and comparative examples will be described. (I) Example of the first invention, Comparative Example Example 1 A polymerization vessel having an internal volume of 100 liter (pressure-resistant autoclave)
, 50 kg of deionized water was added thereto, and further, as shown in Table 1, partially saponified polyvinyl acetate (saponification degree: 72 mol%, average polymerization degree: 700) was added to the vinyl chloride monomer.
m, partially saponified polyvinyl acetate (degree of saponification 45 mol%, average degree of polymerization 350) 150 ppm, sorbitan monolaurate (HLB = 8.6) 600 ppm, lauric acid 600
ppm, polyethylene oxide (average molecular weight 430-
4.80 million, 12 cps / 0.1% aqueous solution) 90 ppm,
500 ppm of t-butyl peroxy neodecanoate was charged. Next, after degassing the inside of the polymerization vessel to 40 mmHg, 33 kg of a vinyl chloride monomer was charged and stirring was started.

The polymerization temperature was 57.degree. C., and this temperature was maintained until the completion of the polymerization. When the polymerization conversion rate reaches 90%, the reaction is terminated, and after the unreacted monomer in the reactor is recovered, the polymer is taken out of the system in the form of a slurry, dehydrated and dried. The plasticizer absorbency, particle size distribution, bulk specific gravity, maximum torque, gel time, and skin-free rate were evaluated according to the test methods described below. The results are shown in Table 2.

Examples 2 to 4 and Comparative Examples 1 to 4 In the same manner as in Example 1 under the conditions shown in Table 1, PV
C was prepared, the performance was evaluated, and the results were summarized in Table 2.

[0035]

[Table 1]

[0036]

[Table 2]

Performance Evaluation Method (Plasticizer Absorbency: Measurement of Porosity) 5 g of PVC was placed in a centrifuge tube equipped with a glass filter, excess plasticizer DOP (10 ml) was added to the PVC, mixed well, and mixed. Leave for a time. Then, centrifuge (made by domestic centrifuge company,
H-200N, rotation speed: 3000 rpm) for 30 minutes to separate excess DOP and determine the DOP absorption (g) per 100 g of PVC.

(Measurement of Particle Size Distribution) JIS Z-8801
In accordance with the above, the PVCs obtained in Examples and Comparative Examples were fractionated using sieves of 60, 100, and 150 mesh, respectively, and the weight% of the passing amount was determined.

(Measurement of Bulk Specific Gravity) According to JIS K-6721, the bulk specific gravity of the PVC obtained in Examples and Comparative Examples was measured.

(Measurement of processability (gelling performance)) Test sample: PVC 1 obtained by Examples and Comparative Examples
2 parts by weight of dibutyltin mercapto (organotin-based stabilizer; JF-10B, manufactured by Sankyoki Co., Ltd.) and montanic acid ester (lubricant; WAX OP, manufactured by Hoechst) were added to 00 parts by weight.
5 parts by weight were added, and the mixture was heated and mixed at 120 ° C. using a super mixer (manufactured by Mitsui Miike Co., Ltd.), and then cooled at 40 ° C. to obtain a test sample. Apparatus: Plastmill: manufactured by Toyo Seiki Co., Ltd., Model: Haake Rheocord 90 Test conditions: 60 g of the compounded resin is put into a test chamber at a temperature of 120 ° C., and the temperature is increased at a rate of 5 ° C./min. The mixture was kneaded in minutes until the temperature reached 200 ° C., and the gelation time and the maximum torque were measured.

(Evaluation of Surface Condition) The PVC particles obtained in Examples and Comparative Examples were scanned with a scanning electron microscope (manufactured by Hitachi, Ltd.).
According to FE-SEM S-4200), acceleration voltage: 2 k
V, 130x magnification, particle outline, skin part,
A portion where the skin does not exist (a portion where the primary particles are exposed, hereinafter referred to as a skin-free portion) is copied on a tracing paper (or an OHP sheet). Next, the tracing paper (or OHP sheet) is introduced into an image analysis device (PIAS-III, manufactured by Pierce), image analysis is performed, the particle area and the skin-free area are calculated, and the skin-free ratio (1 ) Was determined according to the following equation. Skin-free rate = (skin-free area / particle area) x 1
00

[0042]

The PVC suspension polymerization method of the present invention is constituted as described above, so that the polymerization agent can be charged at once, the resin does not adhere to the polymerization vessel, and the PVC particles obtained are:
Since the surface has a very small number of skin layers, a large bulk specific gravity, and a sharp particle size distribution, the resulting PVC has excellent moldability.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-9-263602 (JP, A) JP-A-8-120007 (JP, A) JP-A-8-295701 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C08F 2/00-2/60 C08F 14/06

Claims (1)

(57) [Claims] 1. A partially saponified polyvinyl acetate having a saponification degree of 60 to 90 mol% when a vinyl chloride monomer is subjected to suspension polymerization in an aqueous medium in the presence of an oil-soluble polymerization initiator. (A), partially saponified polyvinyl acetate having a saponification degree of 20 to 55 mol% (b), an emulsifier of a sorbitan higher fatty acid ester having an HLB value of 3 to 10 (c), a higher fatty acid having 8 to 25 carbon atoms (d) Suspension polymerization of a vinyl chloride resin, characterized by adding a thickener (e) having a Brookfields viscosity of 10 to 200 cps in an aqueous solution of 0.1% by weight at normal temperature and normal pressure. Method.