CA2011552A1 - Method for producing a vinyl chloride resin - Google Patents

Abstract

ABSTRACT
A method for producing a vinyl chloride resin, which comprises suspension-polymerizing vinyl chloride, or a mixture of vinyl chloride with a co-monomer copolymerizable therewith, in an aqueous medium in the presence of an oil-soluble polymerization catalyst, a dispersant and an emulsifier by means of a homogenizer under an emulsifying pressure within a range of from 5 to 50 kg/cm2 in such a state that the organic phase is dispersed in the aqueous phase.

Description

2 ~ 2 Our Ref.: MB-ll METHOD FOR PRODUCING A VIN~ CHLORIDE ~ESIN
The present invention relates to a method f~r producing a vinyl chloride resin. More particularly, it relates to a method ~or producing a vinyl chloride.resin for paste technique having a low vîscosity and excellent coating properties.
: Paste techni~ues employing paste sol~ such a~
plastisols or organosols, including casting t dip orming - and rotational moldin~, are used in a ~ield oF
application of vinyl chloride resins. Among tham, in a .`:`i~ : :
case where high speed processing is required7 it is strongly desired to lowe~ the viscosity oE the paste sol as Ear as possible.
: As compared with a vinyl chloride resin for general purpose, the vinyl chloride resin ~or paste technique (i.e. the paste resin) has an average particle size as small as about 0.8 ~m and a particle size distribution as narrow as ~rom 0.2 to 2 ~m. Hereto~ore, as a method ~or reducing the viscosity o~ the paste ~ol, it has been 29 ~ prbposed to substitute a part of the paste resin in the ~ ," 1 .

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sol by a resin having a larye particle size at a level of from 10 to 70 ~m. The resin having a large particle size to be used, is required to have little voids in the particles and have a particle shape which is substantially spherical. If voids in the particles are s~lbstantial, or the particle shape is not substantially spherical, the reduction of the viscosity tends to be poorl and it becomes disadvantages to prepare a thin ~ilm by a coating method, since the resin contains a substantial amount of particles of e.g. S0 ~m or larger.
It is an ob~ect of the present invention to produce a paste resin capable of providing a paste sol having a low viscosity and excellent coating properties industrially advan~ageously.
The present inventors have conducted extensive studies to overcome the above drawbacks o the conventional techniques and to obtain a paste sol having a low viscosity and excellent coating properties. As a ::;
~ ~ result, it has been ~ound possible to obtain a vinyl ;~ 20 chloride resin having a particle size distribution of !
~xom 0.1 to 20 ~um by conducting suspension-polymerization under a certain speci~ic condition and thereby obtain a paste sol having a low viscosity, whereby the above object can be attained~ ~he present invention has been accomplished on the basis o~ this discovery.
The present invention provides a method ~or producing a vinyl chloride resin, which comprises suspension-~, ~,,~ , .
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polymerizing vinyl chloride, or a mixture oE vinyl chloride with a co-monomer copolymerizable therewith, in an aqueous medium in the presence of an oil-soluble polymerization catalyst, a dispersant and an emulsi~ier by means of a homogenizer under an emulsifying pressure within a range of ~rom 5 to S0 kg/cm~ in such a ~tate that the organic phase is di~persed in the aqueous phase.
Now, the present invention will be described in detail with reference to the preferred embodiments.
lU The monomer to be used for the method of the present invention includes, in addition to vinyl chloride, a mixture comprising vinyl chloride as the main component and a Yinyl co-monomer copolymerizable therewith. Such a vinyl monomer includes, for example, an oil-soluble 15 monomer such as vinyl acetate, styrene, acrylonitrile, an acrylic acid ester, a methacrylic acid ester or ethylene;
a water-soluble monomer such as acrylic acid, methacrylic acid, maleic acid or crotonic acid; and an inorganic salt o~ a vinyl monomer such as sodium acrylate, sodium fumarate or calcium acrylate. Further r it may be a vinyl monomer having a polyfunctional group copolymerizable with vinyl chloride, such as divinylbenzene, diallyl phthalate or diallyl maleate. When such as vinyl monomer having a polyfunctional group is used, a vinyl chloride resin having a cross-linked structure, is obtainable.
As the polymerization catalyst in the method of the present invention, a well known oil-soluble ,~. i ; ~1 ~: - . , , 2 ~ 2 polymerization initiator capable of generating free radicals, such as ben~oyl peroxide, lauroyl peroxide or di-tert-butyl peroxide, is used usually in an amount of from 0.01 to 0.1 part by weight per 100 parts by weight of the vinyl chloride monomer (from 0.01 to 0.1 PHM).
As the dispersant, various polyvinyl alcohols obtainable by partially saponifying polyvinyl acetate, various water soluble cellulose derivatives or suspension stabilizers such as gelatin, which are commonly employed, may be used in an amount within a range of from 0.02 to 2 PHM.
As the emulsifier, a well known alkyl sulfate salt and an alkylaryl sulfonate salt such as sodium lauryl . sulfate and ~odium dodecylbenzene sulEonate, may be used in an amount within a range of from 0.02 to 2 PHM.

The method of the present invention is conducted by suspension-polymerizing the above monomer, the oil-soluble polymerization catalystl the dispersant and the emulsifier, in an aqueous medium under an emulsiEying ~ : 20 pressure o~ from 5 to 50 kg/cm2 by means of a homogenizer ; in such a state that the organic phase is dispersed in the aqueous phasel The homogenizer is an apparatus for preparing a stabilized suspension by uniformly dispersing usually to a liquid other substances immissible therewith, which is so designed that the mixture to be treated, is forcibly passed under pressure through a narrow space formed .

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precisely by a rigid body, followed by releasing the pressure, whereby the mixture is formed into fine particles and uniformly dispersed by the li~uid ~riction, the abrupt reduction in the pressure, the shearing and the collision due to the vigorous turbulent flow thereby created.
In the method of the present invention, it i5 necessary to operate the homogenizer under a relatively low pressure at a level of from 5 to 50 k~/cm2G. It is particularly preferred to operate it under a pressure of from 10 to 20 kg/cm2G. For example, when the dispersion : is conducted under a pressure of 15 kg/cm2G, it is possible to obtain a paste resin having a ~inal particle size distribution of ~rom 0.1 to 20 ~m.
The dispersion thus obtained is reacted at a temperature of ~rom 1 ~o 90C, pr~ferably from 30 to 70C, in accordance with a usual suspension-: polymerization method, whereby it is possible to obtain a vinyl chloride resin having a particle size distribution of from 0.1 to 20 ~m, as shown by the Examples given hereinafter. As a result, it is possible to obtain a paste sol having a low viscosity and excellent coating l?rperties .
Now, the pxesent invention will be described in further detail with reference to Examples and Comparative Examples. However, it should be understood that the ~` present invention is by no means restricted to such ; i . , ~, : ~ , :;

~, 2 ~ 2 specific Examples. In the following Examples and Comparative Examples, the part.icle size and the viscosity oE the polyvinyl chloride resin were measured in : accordance with the following methods~
Particle size; Measured by a particle counter.
Viscosity: A sol was prepa~ed by mixing 100 parts by ; weight oE a resin and 60 parts by weight of dioctyl phthalate at a temperature of 23~C under-a humidity ~f 50~, and the viscosity was measured by means oE a Brookfield viscometer with No. 6 spindle rotated at 50 rpm.
: EXAMPLE 1 In~o an autoclave equipped with a s~irrer and having an internal capacity of 300 ~, 120 kg of water, 1.5 kg of a 4% polyvinyl alcohol aqueous solution (saponification value: 80), 9 kg of a 4% sodium lauryl sulfate aqueous solution and 600 g of lauroyl peroxide~ were charged.
. After flushing with nitrogen gas, 60 kg of vinyl chloride ;:~ was added under stirring at a rotational speed of 100 rpm.
~ The dispersion thus obtained wa~ supplied to a ; homogenizer (15M-8TA, manufactured by MANTON-GAULIN CO.) under an emulsi~ying pressure of 10 kg/cm2 for homogenizing treatm~nt. Then, the mixture was supplied to another autoclave equipped with a stirrer and having an internal capacity of 300 e, and the suspension-polymerization was conducted while stirrin~ the mlxture J
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at ~ rotational speed of lO0 rpm at 57C. The reaction was continued until the pressure started to drop. After completion of the polymerization re~ction, unreacted vinyl chloride monomer was removed, and the residue was dehydrated and dried to obtain a polyvinyl chloride resin.
'rhe particle size of the polyvinyl chloride resin thus obtained and the viscosity of ~he paste sol were measured. The results are shown in Table l.

Into the same autoclave as used in Example l, 120 kg of water, 3 kg of a 4% polyvinyl alcohol aqueous solution ; ~saponification value. 80), 3 kg of a 4~ sodium lauryl sulfate aqueous solution and 600 g of lauroyl peroxide were charged. After flushing with nitrogen gas, 60 kg of vinyl chloride was added under stirring at a rotational ~; speed o~ lO0 rpm.
; The dispersion thus obtained was supplied to the same homogenizer as used in Example l under an emulsifying pressure o~ 20 kg/cm2 ~or homogenizing treatment. Then, the suspension polymerization was conducted in the same manner as in Example l. ~he partic1e size of the polyvinyl chloride resin thus obtained and the viscosity of the paste sol were measured. The results are shown in Table l.
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~ Into the same autoclave as used in Example l r 120 kg ;`;;
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of water, 750 9 of a ~ polyvinyl alcohol a~ueous solution (saponification value; 80~, 6 kg of a 4% sodium dodecylbenzene sulEonate aqueous solution and 600 g of lauroyl peroxide were charged. After Elushing with nitrogen gas, 60 kg of vinyl chloride was added under s~irring at a rotational speed of 100 rpm.
The dispersion thus obtained was supplied to the same homogenizer as used in Example l under a pressure of lO
kg/cm2 for homogenizing treatment. Then, the suspension-polymeri~ation was oonducted in the same manner as inExample 1. The particle size of the polyvlnyl chloride resin thus obtained and the viscosity of the paste sol were measured. The results are shown in Table 1.

~ dispersion obtained in the same manner as in Example 2 except that instead of 3 kg of the 4~ polyvinyl alcohol aqueous solution having a saponi~ication value of 80 used in Example 2, 3 kg of a 4~ po~yvinyl alcohol aqueous solution having a saponi~ication value of 70, was used, was subjected to homogenixing treatment in the same mannex as in Example 2, followed by suspension-polymerization. The particle size of the polyvinyl chloride resin thus obtained and the viscosity of the paste sol were measured. The results are as shown in 2S Table 1.

The treatment was conducted in the same manner as in ~ .

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2 ~ 2 Example 1 except that instead of the homogenizer manufactured by MANTON-GAULIN CO. used in Example 1, an Inline Homomixer (0/100 Model, manufactured by EUROTEC, LTD.) was used, and the treatment was conduc~ed under an emulsifying pressure of 10 kg/cm2G.
The particle size of the polyvinyl chloride resin thus ohtained and the ~iscosity of the paste sol were measured. The results are shown i~ Table 1.
EX~MPLE 6 The treatment was conducted in the same manner as in Example 3 except that instead of the homogenizer manu~actured by M~NTON-GAULIN CO. used in Example 3, the same Inline Homomixer as used in Example 5 was used/ and the treatment was conducted under an emulsifying pressure of 20 kg/cm2G.
., The particle size of the polyvinyl chloride resin ~, thus obtained and the viscosity of the paste sol were measured. The results are shown in Table 1.
COMPARATI~E EX~P~ES 1 to 5 The treatments were conducted in the same manner as in ~xamples 1 to 5, respectively, except that the pressure for homogenizing treatment in Examples 1 to 5 was changed to 150 kg/cm2G (Comparative Examples 1 to 4) or to 100 kg/cm2G (Comparative Example 5).
The particle sizes of the polyvinyl chloride resins thus obtained and the viscosities of the paste sol were measured. The results are shown in Table 1. In each : l `I

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case, the particle size was finer the particle size distribution was sharp, and the viscosity was very high.

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As shown in Table, according to the method of the present invention, it is possible to obtain a vinyl chloride resin having a certain specific particle size distribution (0.1-20 ~m) and a low viscosity~ ~s a result, it is possible to obtain a paste sol having excellent coating properties, which is useful in the ; field o~ casting, dip forming or rotational molding where a high speed processing is required.

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Claims (8)

1. A method for producing a vinyl chloride resin, which comprises suspension-polymerizing vinyl chloride, or a mixture of vinyl chloride with a co-monomer copolymerizable therewith, in an aqueous medium in the presence of an oil-soluble polymerization catalyst, a dispersant and an emulsifier by means of a homogenizer under an emulsifying pressure within a range of from 5 to 50 kg/cm2 in such a state that the organic phase is dispersed in the aqueous phase.

2. The method according to Claim 1, wherein the co--monomer copolymerizable with vinyl chloride is vinyl acetate, styrene, acrylonitrile, an acrylic acid ester, a methacrylic acid ester, ethylene, acrylic acid, methacrylic acid, maleic acid, crotonic acid, sodium acrylate, sodium fumarate, calcium acrylate, divinylbenzene, diallyl phthalate or diallyl maleate.

3. The method according to Claim 1, wherein the polymerization catalyst is benzoyl peroxide, lauroyl peroxide or di-text-butyl peroxide used in an amount of from 0.01 to 0.1 part by weight per 100 parts by weight of the vinyl chloride monomer.

4. The method according to Claim 1, wherein the dispersant is a polyvinyl alcohol obtained by partial saponification of polyvinyl acetate, a water-soluble cellulose derivative or a suspension stabilizer such as gelatin used within a range of from 0.02 to 2 PHM.

5. The method according to Claim 1, wherein the emulsifier is an alkyl sulfate salt or an alkylaryl sulfonate salt used in an amount of from 0.02 to 2 PHM.

6. The method according to Claim 1, wherein the emulsifying pressure is within a range of from 10 to 20 kg/cm2.

7. The method according to Claim 1, wherein the suspension-polymerization is conducted at a temperature of from 1 to 90°C.

8. The method according to Claim 1, wherein the vinyl chloride resin has a particle size distribution of from 0.1 to 20 µm.