GB1583481A - Suspension polymerization of vinyl chloride and monomer components predominantly thereof - Google Patents

Description

(54) SUSPENSION POLYMERIZATION OF VINYL CHLORIDE AND MONOMER COMPONENTS PREDOMINANTLY THEREOF (71) We, KUREHA KAGAKU KOGYO KABUSHIKI KAISHA, a company organized and existing under the Laws of Japan, of 8, Nihonbashi Horidome-Cho 1-Chome Chuo-Ku, Tokyo-To, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates generally to improvements in and relating to the process of suspension polymerization in an aqueous dispersion medium of vinyl chloride by itself or of a mixture of vinyl chloride as the predominant constituent and another vinyl monomer copolymerizable therewith.

More particularly, the invention relates to an improved process of the kind referred to above by which resins having good particulate characteristics, porosity, and good workability and, moreover, containing very little residual vinyl chloride monomer can be produced.

Because of their good physical properties and chemical characteristics, vinyl chloride resins including homopolymers of vinyl chloride are widely used as materials for various moulding operations in the fields of rigid and flexible products, and the advantageous features of these materials are well known.

The principal process used at present for the polymerization of these resins is the suspension polymerization process. In the present state of the art, however, the production of the resins by suspension polymerization is often accompanied by the problems of (1) the slow absorption of workability additives such as stabilizers and plasticizers in comparison with the processes of emulsion polymerization and bulk polymerization; (2) the existence of differences in this absorptive characteristic within particles and between particles, and (3) the influence of these factors on the workability of the resins at the time of working which has a great effect even on the quality of the shaped final products. The resulting suspension polymerization 'products therefore need improvement in these respects.

So-called "fish-eyes" are defects which greatly impair the commodity value of shaped products from the view-points of external appearance and quality generally. A major cause of fish eyes is considered to be the heterogeneity within the particles and between the particles of the suspension polymerization product. More specifically, in practical forming or moulding and working. the melting of these particles is heterogeneous. For this reason, it is very difficult to attain uniformity in the mixture of the unmelted parts and the molten parts, and unmelted material remains and even appears in the final product.

It is known that the lower the degree of polymerization of polymerizates whereby the polymerizates are more easily workable or processable. the more prominent is the heterogeneity of the polymerizates.

The reason for this is that. since the polymerization is ordinarily carried out at a high temperature in order to produce a polymer with a low degree of polymerization, the particles of the suspension polymerization product undergo, among other effects, mutual fusion during polymerization, and assume a nonporous character. In particular, in the case of a transparent, rigid shaped article which is compounded with a stabilizer as substantially the sole additive, e.g. a product such as a rigid vinyl chloride resin sheet, film, or blow-moulded article, the external appearance of the formed article is greatly impaired for this reason, whereby the commodity value of the article is lost in many cases. It is also known that, in a polymer with a high degree of polymerization, heterogeneity within and between the particles is a great defect in the quality of flexible and rigid formed articles.

Vinyl chloride resins including homopolymers of vinyl chloride and copolymers with a predominance of vinyl chloride are being used for a wide range of products such as materials for industrial use, sundry goods, and packaging materials for food products. The processes for producing these products also vary greatly in accordance with the characteristics of the various formed articles.

Rccently, minute quantities of vinyl chloride monomer have become a problem arising from considerations of food sanitation, and there is a great damand for a reduction of residual vinyl chloride monomer within vinyl chloride resins. It may be possible to reduce residual vinyl chloride monomer by subjecting the polymer, for example, to heat and/or vacuum conditions as in a drying step or in compounding processing. Fundamentally, however, it is necessary to render the interior of the particles porous and to attain homogeneity between particles.

A large number of proposals have been made with regard to improvements in vinyl chloride resins and copolymers having vinyl chloride as the predominant component in the suspension polymerization. However, it is considered in the art that it is very difficult to satisfy the requirement of reducing the residual vinyl chloride monomer and all of the conditions of a wide range of uses and of the working methods for producing formed articles.

For example, a resin which has been produced with an effort made towards imparting porosity to the particles and reducing the residual vinyl chloride monomer possesses desirable features as a polymer such as a tendency to have a low apparent specific gravity, a high gelation rate, and good absorption of plasticizers. On the other hand, however, it is frequently observed that such resins have disadvantageous features such as the ready occurrence of a reduction in extrusion quantity (rate) in extrusion forming and of an increase in the load at the time of gelation.

It is an object of this invention to provide an improved process for the suspension polymerization of a vinyl chloride monomer component of the character referred to above in which the above-described problems have been overcome.

More specifically. an object of this invention is to provide an improved process by which polymers and copolymers of vinyl chloride having porosity. excellent particulate characteristics and workability and. moreover. containing only a minor quantity of residual vinyl chloride monomer can be produced.

According to this invention. briefly summarized. there is provided an improved process of suspension polymerization. in which a monomer component comprising vinyl chloride by itself or a mixture containing vinyl chloride as the predominant constituent and another vinyl monomer copolymerizable therewith. is subjected to suspension polymerization in an aqueous medium in the presence of an oil-soluble catalyst. in the presence of a protective colloid as a suspension agent and in the presence of from 0.05 to 2.5 parts by weight; in particular from 0.1 to 2.0 parts by weight. relative to 100 parts by weight of the monomer component, of a higher alcohol ester of a dibasic acid represented by the formula: ROOC (X) COOR' where: X is a bivalent saturated or cyclic hydrocarbon group having from 2 to 8 carbon atoms; R is a monovalent saturated or unsaturated hydrocarbon group having from 10 to 32 carbon atoms; and R' is hydrogen. the same hydrocarbon group as R. or a different monovalent saturated or unsaturated hydrocarbon group having from 10 to 32 carbon atoms.

The invention is now further described in detail.

We have carried out various studies with the aim of obtaining by suspension polymerization of vinyl chloride a polymer in which the reduction of residual vinyl chloride monomer and ease of workability are well balanced. As noted hereinbefore. however, rendering the polymer porous gives rise to a lowering of the apparent specific gravity. and it has been difficult hitherto to obtain a vinyl chloride suspension polymerization product of practical quality capable of casily achieving compatibility between these characteristics.

A surprising feature of the suspension polymerization process according to this invention is that it produces polymers satisfying the characteristics of reduced residual vinyl chloride monomer and good workability and having practically well balanced characteristics.

We have found that almost no significant diffcrence is detectable between the properties such as tlic external appearance and apparent specific gravity of the polymers according to this invention and the corresponding properties of conventional suspension-polymerized vinyl. chloride resins. Furthermore, when the surface structure of the individual particles of the two kinds of resins were compared by observation through a microscope, no distinguishable differences were'found.

However, according to the conventional view, it is clear that differences in the surface structure of particles can be distinguished by microscopic examination between porous particles in which residual vinyl chloride monomer can be reduced, and non-porous particles, but a polymer with the addition of a dibasic acid higher alcohol ester according to this invention is exactly the same as that without the addition, and no difference is detectable.

In spite of this, in the suspension polymerization products of this invention, residual vinyl chloride monomer is very surprisingly found to have been reduced to 1/20th or even less than that in the case where the dibasic acid higher alcohol ester is not added.

This surprising discovery is an important basis of the present invention.

Various features of the invention are now discussed.

Ester A dibasic acid higher alcohol ester suitable for use in this invention is represented by the following general formula.

ROOC (X) COOR' where: X is a bivalent saturated, preferably linear, or cyclic, preferably aromatic, hydrocar bon group having from 2 to 8 carbon atoms; R is a monovalent saturated or unsaturated, preferably linear, hydrocarbon group having from 10 to 32 carbon atoms; and R' is hydrogen or the same group (ordinarily the same group) as R, or a different monovalent saturated or unsaturated, preferably linear, hydrocarbon group having from 10 to 32 carbon atoms.

Examples of the dibasic acid component of the ester used in the process of this invention are succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and phthalic acid (iso- or tere-). Monovalent higher alcohols which can react with this dibasic acid by undergoing esterification to produce the esters of the present invention are those having a hydrocarbon group with from 10 to 32 carbon atoms such as, for example, decyl alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, arachidyl alcohol (eicosanol), behenyl alcohol, carnaubyl alcohol, myricyl alcohol, lacceryl alcohol and oleyl alcohol. As a result of this esterification reaction. a monoester or diester is obtained. An alcohol having from 12 to 24 carbon atoms is advantageous also from the viewpoint of economy.

Compounds wherein the Groups R and R' indicated in the formula set forth above have a sturcture with from 1 to 8 carbon atoms are known as conventional plasticizers such as, for example. dioctyl adipate (DOA). diisobutyl adipate (DIBS) dibutyl sebacate (DBS) and diocyl phthalate (DOP). Esters having 10 or more carbon atoms, however, not only are ineffective as plasticizers but are compounds which are very rarely used in practice.

The practice of mixing these known plasticizer compounds with vinyl chloride monomer thereby to carry out suspension polymerization is also known. However, while these plasticizers can be absorbed in the resulting polymer more efficiently by this method, they have almost no effect in rendering the particles porous, but. rather, the reduction of the residual vinyl chloride monomer is obstructed. This may be attributed to the ease with which interfusion occurs among the polymer particles during polymerization.

By carring out according to this invention the polymerization of vinyl chloride or of a monomer mixture containing vinyl chloride as the predominant monomer and another monomer copolymerizable therewith. with the addition of 0.05 to 2.5 parts by weight of any of these dibasic acid higher alcohol esters. relative to 100 parts of the monomer or mixture, a suspension polymerization product with a remarkably reduced quantity of residual vinyl chloride monomer can be produced. The quantity of the dibasic acid higher alcohol ester is preferably from 0. 1 to 2.0 parts by weight.

A dibasic acid higher alcohol ester as used in this invention is deficient in its plasticizing action with respect to the vinyl chloride polymer as mentioned hereinbefore, but when it is used in a small quantity. it dissolves in the polymer in a molten stage at the time of the working of the polymer and is uniformly dispersed. When the polymer is cooled and the ester loses its solubility also. the particles become extremely small. For this reason. there is no possibility of a lowering of the transparency of the formed products of the polymer. and. by promoting the melting of the polymer at the time of forming, the physical properties such as impact strength. in general. are increased. However. in the case where the added quantity is more than 2.5 parts by weight. in general. there is no complete solution of the ester in the resin at the time of forming. and phase separation occurs partly. whereby the transparency of the formed product is impaired. Furthermore. the separated part has a strong effect as a lubricant at the time of forming and has a deleterious effect on the kneading within the extruder. whereby the physical properties, on the contrary, deteriorate.

Oil-soluble catalyst For the oil-soluble catalyst of this invention, various oil-soluble radical catalysts such as diacyl peroxides, e.g. lauroyl peroxide or benzoyl peroxide, diisopropylperoxy di-carbonate, di-(2-ethylhexyl)-peroxy dicarbonates, or azo compounds represented by azobisisobutylinitrile may be used.

Monomer Examples of monomers copolymerizable with vinyl chloride monomer are: vinyl esters, c.g., vinyl acetate and vinyl propionate; vinyl ethers, e.g., vinyl methylester and vinyl octylether; vinylidene halides, e.g., vinylidene chloride and vinylidene fluoride; vinyl halides, other than chloride, e.g. vinyl fluoride and vinyl bromide; acrylic esters, particularly those whose alcohol part has from I to 8 carbon atoms; methacrylic esters, particularly those whose alcohol part has from I to 8 carbon atoms; and monoolefins, e.g., ethylene and its homologucs e.g. propylenc; and mixtures thereof.

The quantity of each of these comonomers is less than 50% by weight within the mixture with vinyl chloride, being ordinarily and preferably up to 20 percent by weight.

Suspending agent Examples of the suspension used in the suspension polymerization are known protective colloids, for example, water-soluble polymers such as polyvinyl alcohols, polyethylene oxide, water-soluble cellulose derivatives such as methyl cellulose, polyvinyl pyrrolidone, gelatin and vinyl acctatc-maleic anhydride copolymers, these suspensions being used alone or as mixtures in a quantity, ordinarily, in a range of 0.01 to 0.5 part by weight, preferably 0.04 to 0.2 part by weight. relative to 100 parts by weight of the monomer component.

The process of this invention is essentially related to an aqueous suspension polymerization of vinyl chloride. Therefore, the operation of the process of this invention, basically, is the same as that adopted in a process for the suspension polymerization of vinyl chloride.

Accordingly. the prefcrred operation comprises, for example, dissolving a protective colloid in an aqueous medium or a monomer component. dispersing an oil-soluble polymerization initiator in the aqueous medium or dissolving it in the monomer component, dissolving or dispersing the dibasic acid higher alcohol ester in the aqueous medium or dissolving it in the monomer component. dispersing the monomer component in this aqueous medium, and agitating the reaction system at a temperature of from 20 to 800C. During this reaction, the pressure and temperature of the reaction system need not be maintained at constant values.

Upon completion of the polymerization, the resulting polymer is separated from the aqueous medium. This polymer is. generally. a particulate product with a particle size of from 60 to 200 mesh (Tyler. A.S.T.M.). The particulate vinyl chloride polymer produced by the process according to this invention. after drying for 20 hours in a stream of air at 600C, has a vinyl chloride monomer content of less than 30 ppm. In conventionally produced vinyl chloride polymers. this vinyl chloride monomer content is in the range of from 100 to 500 ppm.

In order to indicate more fully various features of this invention, the following specific examples of practice constituting preferred embodiments of the invention are set forth, it being understood that these examples are presented as illustrative only. and that they are not intended to limit the scope of the invention.

Exaszlple /.

6.000 grams (g.) of ion-exchanged water in which 1.2 g. of polyvinyl alcohol (product of Nippon Gosci Corp.. Japan and 0.6 g. of methyl cellulose (product of Shin etsu Kagaku Corp.. Japan) had been dissolved and 1.5 g. of lauroyl peroxide were charged into a 10-liter stainless-steel autoclave. The reaction system was then sealed, thoroughly purged with nitrogell and thereafter cvacuated. 3.000 g. of vinyl chloride monomer in which a specific quantity of a dibasic acid higher alcohol ester had been dissolved were introduced under its own pressure into this system. which was then dispersed under agitation for 30 minutes.

Thereafter. the temperature of the system was raised to 57.5 "C under agitation. and polymerization was carried out.

Thcn. when the pressure within the autoclave had fallen below the equilibrium pressure and had reached 4.5 kg./icm.?. gaugc. the polymerization reaction was stopped, and the contents of the autoclave were taken out. washed with water and dehydrated. The polymer thus obtained was dried for '() hours in an air-stream dryer at 6() C. The quantity of the residual vinyl chloride monomer in this polymer was measured in the following manner.

A specific quantity of the polymer powder immcdiately after the drying process was taken and dissolved in a specific quantity of tetrahydrofuran. and a specific quantity of the resulting solution was subjected to gas chromatography so as to determine the vinyl chloride monomer content.

The rcsults are shown in Table I together with those of comparison examples.

Table 1 Run Additive Additive Apparent Residual No. quantity, density vinyl (parts by (g/cc) chloride wt. per 100 monomer parts of (ppm) monomer) Refer- 1- 1 (none) - 0.53 350 ence Example 1- 2 dilauryl adipate 0.1 0.54 23 3 3 (ditto) 1.5 0.53 7 1- 4 monostearyl adipate 0.5 0.54 18 This inven- 1- 5 distearyl adipate 0.2 0.53 20 tion 1- 6 (ditto) 1.0 0.54 4 1- 7 dicetyl sebacate 1.0 0.52 6 1- 8 distearyl phthalate 0.5 0.54 18 1- 9 dibehenyl adipate 1.0 0.52 5 Refer- 1-10 dioctyl adipate 0.5 0.52 360 ence (DOA) example 1-11 dioctyl phthalate 0.5 0.53 340 (DOP) Almost no differences were observable between the states of resin adhesion within the polymerization vessel, the polymer particle size distributions, and the polymer external appearances of Run Nos. 1-2 to 1-9 in Table 1. The particles produced by Run Nos. 1-10 and 1-11 had surfaces which were somewhat glossy and smooth, which seemed to indicate that the action of rendering these polymers porous was hindered.

The formabilities by extrusion of the polymers produced in the aforedescribed manner and set forth in Table 1 were examined and found to be as set forth in Table 2 below.

Parts Compounding Recipe: by weight Resin (each of Run Nos. 1-1 to 1-11 in Table 1) 100 Tribasic lead sulphate 0.5 Dibasic lead stearate 0.3 Lead stearate 1.0 Calcium stearate 1.0 Stearic acid 0.3 Titanium white (rutile) 0.5 The ingredients set forth above were mixed by agitation in a 10-liter Henschel mixer until they reached a maximum temperature of 120cm to prepare a compound.

Extruding Conditions: i) Extruder and die 35-mm. borc, single-shaft extruder screw Icngth: 630 mm. compression ratio : 2.4 die outlet dimensions : 20 x 5 mm. rectangular die ii) Extruding conditions: Cylinder No. 1 150 to 155 C Cylinder No. 2 165 to 1700C Cylinder No. 3 175 to 1800C Adapter 175 to 1800C Die 190 to 192"C Screw rotational speed: 20 rpm Table 2 Run Additive Extruding Screw shaft Extrusion Charpy No. (parts added per rate torque resin temp. impact 100 parts monomer) strength (g/min.) (m.kg) ( C) (kg.cm/cm2) Reference 1- 1 (none) 96 27.6 196.5 4.5 Example 1- 2 dilauryl adipate 104 25.0 195.0 5.8 (0.1) This 1- 3 (ditto) 117 20.0 193.0 8.3 inven- (1.5) tion 1- 4 monosteary adipate 110 21.0 193.5 7.5 (0.5) 1- 5 distearyl adipate 108 20.5 194.0 6.5 (0.2) 1- 6 (ditto) 112 20.3 193.0 8.5 (1.0) 1- 7 dicetyl sebacate 110 20.5 193.5 9.7 (1.0) 1- 8 distearyl phthalate 108 21.8 195.0 6.7 (0.5) 1- 9 dibehenyl adipate 112 20.0 193.5 8.7 (1.0) Refer- 1-10 dioctyl adipate 101 25.8 195.5 3.2 ence (DOA) (0.5) example 1-11 dioctyl phthalate 100 24.7 195.0 3.5 (DOP) (0.5) Charpy impact strengths were measured in accordance with the testing method specified in Japanese Industrial Standards designation JIS-7111, at 20"C. As indicated in the above Table 2, the samples of Run Nos. 1-2 to 1-9 exhibited improved extrusion characteristics in comparison with the sample of Run No. 1-1 as indicated by increased extrusion gravimetric rate, decreased load and lowered extrusion resin temperature. Furthermore, improvements in physical properties such as increased impact strength were also attained.

Example 2: Similarly, as in Example I, an aqueous solution of a suspension agent, vinyl chloride monomer, and each of the diesters set forth in Table 3 were charged into a 10-liter stainlesssteel autoclave and dispersed under agitation for 30 minutes at room temperature. The reaction system was caused to rise in temperature to 670C under agitation, thereby to carry out polymerization. The polymerization reaction was completed at the instant when the pressure within the autoclave dropped 6.0 kg./cm2. from the equilibrium pressure. The contents of the autoclave were taken out, washed and dehydrated. The polymer thus obtained was dried for 20 hours in an air stream at 60"C in a dryer, and the quantity of the residual vinyl chloride monomer in this polymer was then measured in the same manner as in Example 1. The results are set forth in Table 3 as follows: Table 3 Run Additive Apparent Residual No. (parts by weight per 100 density vinyl parts of monomer) chloride monomer (g/cc) (ppm) Reference 2-1 (none) (0) 0.53 680 Example '-' distcaryl sebacate (0.5) - 0.54 10 This 2-3 (ditto) (1.0) 0.53 6 invention 2-4 distearyl adipate (0.5) 0.54 12 2-5 (ditto) (1.0) 0.54 5 2-6 dilauryl adipate (1.0) 0.53 5 Each of the polymers listed in Table 3 was packaged in a paper bag and left standing at room temperature for two days. after which the contents of residual vinyl chloride monomer were again measured. As a rcsult. it was found that the residual vinyl chloride monomer content in the sample of Run No. 2- l was 450 to 430 ppm. but was not detected in any of the samples of this invention to which a dibasic acid higher alcohol ester had been added.

Claims (8)

1. WHAT WE CLAIM IS: 1. A process of suspension polymerization in which a monomer component comprising vinyl chloride or a mixture containing vinyl chloride as the predominant constituent and another vinyl monomer copolymerizable therewith is subjected to suspension polymerization in the presence of an oil-soluble catalyst and a protective colloid as a suspension agent in an aqueous medium. and in the presence of from 0.05 to 2.5 parts by weight. relative to 100 parts by weight oi the monomer component. of a dibasic acid higher alcohol ester represented by the general formula: ROOC (X) COOR' where: X consists of a bivalent saturated or cyclic hydrocarbon group having from 2 to 8 carbon atoms; R consists of a monovalent saturated or unsaturated hydrocarbon group having from l() to 32 carbon atoms; and R' consists of hydrogen. the same hydrocarbon group as R. or a monovalent saturated or unsaturated hydrocarbon group other than R. having from 10 to 32 carbon atoms.
2. 2. A process as claimed in claim I in which the monomer component consists only of vinyl chloride.
3. 3. A process as claimed in claim l or 2 in which the dibasic acid higher alcohol ester consists of dilauryl adipate. monostcaivl adipate. distearyl adipate. dibehenyl adipate. dicetyl sebacate or distearyl phthalate.
4. A. A process as claimed in any of claims I to 3 in which the quantity of the dibasic acid higher alcohol ester is from (). 1 to '.() parts by weight relative to l 100 parts by weight of the monomer component.
5. 5. A process as claimed in any of claims 1 to 4 in which the quantity of the protective colloid is from 0.01 to 0.5 part by weight relative to 100 parts by weight of the monomer component.
6. 6. A process as claimed in any of claims 1 to 5, in which the monomer component containing the dibasic acid higher alcohol ester dissolved therein is dispersed in the aqueous medium in which the protective colloid has been dissolved, and the resulting dispersion is heated in contact with the oil-soluble catalyst so as to polymerize the monomer component.
7. 7. A process according to claim I for suspension polymerization of vinyl chloride by itself or of a mixture containing vinyl chloride as the predominant constituent and another vinyl monomer copolymerizable therewith, substantially as hereinbefore described with reference to any of the specific Examples.
8. 8. A polymer whenever produced by the process of any of the preceding claims.