EP0991678A1

EP0991678A1 - Polyvinyl chloride, processes for its production, and compositions containing it

Info

Publication number: EP0991678A1
Application number: EP99918171A
Authority: EP
Inventors: Stefano Forcolin; Raymond Evans
Original assignee: EVC Technology AG
Current assignee: EVC Technology AG
Priority date: 1998-04-27
Filing date: 1999-04-23
Publication date: 2000-04-12
Also published as: AU3620299A; KR20010020484A; GB9808934D0; NO996444L; WO1999055745A1; JP2002506482A; NO996444D0

Abstract

Polyvinyl chloride pastes and plastisols having good foam forming properties and low viscosity are made from resins produced by (co)polymerising vinyl chloride in the presence of an alkyl sulphate or alkyl sulphate mixture having at least 30 %, preferably at least 50 %, branching. Alternatively the branched alkyl sulphate or mixture can be compounded with the polymer after polymerisation.

Description

Polyvinyl Chloride, Processes for its Production, and Compositions containing it.

This invention relates to polyvinyl chloride (hereinafter "PVC"), its production and compositions containing it. The invention is especially concerned with the production of PVC-containing pastes or plastisols having improved properties.

Pastes or plastisols are used for the production of a wide range of products, including floor and wall coverings, artificial leather or leathercloth, soft moulded products, and dipped items such as protective gloves. The pastes or plastisols are normally made from PVC homopolymer latices which are spray-dried and milled to form powders which are then compounded with plasticizers to form pastes. The PVC latices themselves are usually the products of emulsion, microsuspension or mini emulsion polymerisation processes. Pastes and plastisols may also be made from PVC copolymers, which are produced by polymerising vinyl chloride with a copolymerisable monomer. Examples of the latter include vinyl esters, acrylic esters, vinylidene chloride and acrylonitrile. The comonomer may be present in amounts up to 40% by weight based on the total of vinyl chloride and comonomer, suitably in amounts of 10 to 30%, on the same basis. A particularly useful copolymer contains up to 20% by weight vinyl acetate.

Emulsion polymerization is carried out in the presence of, inter alia, a suitable emulsifier. This emulsifier has a twofold role, since it is (i) essential for the stabilization of the polymer particles and therefore necessary for an industrially acceptable process, but also (ii) if the polymer is isolated by drying, as in the case of PVC, it remains into the final product and therefore influences its properties in the plastisols subsequently formed.

The literature describes many classes of emulsifiers, both nonionic and anionic. As anionic emulsifiers there are alkyl carboxylates, alkyl sulphates, alkyl sulphonates, alkylaryl sulphonates, and salts of sulphosuccinic acid. All these molecules, to be effective as emulsifiers, should have a particular structure: they must have a hydrophilic 2 head (which generally is the carboxylic or the sulphate group) and a hydrophobic tail (which is the organic portion of the molecule). Such molecules have a limited solubility in water, but when their concentration exceeds a certain critical value (critical micellar concentration) they tend to aggregate in agglomerates called micelles, with the hydrophilic head on the external part of the micelle, and the hydrophobic tail at the internal end (see for example P.F. Flory, Principles of Polymer Chemistry, Cornell University Press, Ithaca, New York 1953, p.204; see also F. Bovey, I.M. Kolthoff, A.I. Medalia, E.J. Meehan, Emulsion Polymerization, Interscience Publishers, New York 1955, page. 141 et seq).

Alkyl sulphates have been known and used as emulsifiers for a long time, but their usage has been restricted to the class of emulsifiers obtained from straight chain alcohols.

Alkyl sulphates can be produced by sulphatation of a fatty alcohol, generally using SO₃ (A.S. Davidsohn, B. Milwidsky, Synthetic Detergents, 7th edition, Longman Scientific & Technical, Harlow 1987, page. 157 et seq.). In principle there is no restriction to the type of alcohol that can be used as substrate. The reaction is the following

R-CH₂-OH + SO₃ > R-CH₂-O-SO₃H

The alkylsulphuric acid so obtained is not stable and is hydrolysed quite quickly, so industrial practice requires an immediate neutralization (done usually with caustic) to give the final product, sodium alkylsulphate (chemical structure R-CH₂-O-SO₃ ^"Na⁺) which can be used as an emulsifier for example in the emulsion polymerization. It is important to note that in this reaction the alkyl group R does not undergo any modification in its structure, i.e. it remains substantially unchanged. This means that the chemical structure of the alcohol determines the chemical structure of the derived emulsifier.

Specifications Nos. EP-A-90142, EP-A-108884 and EP-A-144614 disclose the use of alkali or ammonium salts of alkylsulphonates or alkylarylsulphonates or sulphosuccinates with 10 to 20 carbon atoms in the molecule, and give as examples Na- decylsulphonate, Na-dodecylsulphonate, Na-myristylsulphonate and blends thereof which are prepared by sulphonation of technical grade alkane mixtures. The technology described refers to the use of a long chain alcohol in a process similar to the above mentioned "miniemulsion". Specification GB-A-1277289 discloses the use of potassium and lithium alkylsulphonates to improve the transparency of PVC resins.

Specification GB-A-1168920 describes the use as emulsifiers of water soluble salts of aliphatic or araliphatic saturated monocarboxylic acids which are branched in the alpha- position to the carboxyl group and which have at least 8 carbon atoms per molecule, claiming that they allow the production of polymers which, whilst avoiding undesired coagulation of the PVC emulsion, are thermally very stable or can easily be thermally stabilized.

Russian Specification No. 181286 proposes the sulphonation of mixtures of naphthene hydrocarbons with paraffin branch-chain, improving the thermal stability of the polymer.

One of the biggest problems in emulsion PVC technology is to obtain resins which, after mixing with suitable plasticizers, give pastes with low viscosity. Several factors influence the viscosity of the paste obtainable, inter alia the molecular weight of the polymer, the size distribution of the polymer particles, the conditions of drying, and the type and quantity of emulsifιer(s) and other additives present.

PVC pastes are often used to produce chemically foamed products, the paste, containing, amongst others, a suitable foaming agent which decomposes at high temperature. Amongst the factors which influence the structure of the pastes so obtained, there are, again, the molecular weight of the polymer, the size distribution of the polymer particles, and the type and quantity of emulsifιer(s) and other additives present.

As a general rule, it is difficult, if not impossible, to match low paste viscosity and good foaming properties; polymers which give pastes with very low viscosities generally give bad/coarse foam structures, while resins which give very good and fine foam structures 4 normally give pastes with medium/high viscosities. As far as the chemical nature of the emulsifiers is concerned, emulsifiers such as alkylaryl sulphonates and sulphosuccinates give, in general, low viscosity but coarse bad foam structure, while alkylsulphates are used to produce resins with good foam properties, but not particularly low viscosity. JP-A-49-111990 for example describes the use of salts of alkyl sulphates and ethoxylated alkyl sulphates in the emulsion (co)polymerisation of vinyl chloride, and specifically mentions methyl-branched compounds. However, whilst the properties of foams made from such (co)polymers are generally very good, the viscosities of the resin pastes are unacceptably high.

It is an object of the present invention to provide a PVC which can be compounded into a paste or plastisol which, whilst having low viscosity, can be used to produce products having a good and fine foam structure.

According to the present invention there is provided a process for the polymerisation of vinyl chloride by emulsion, microsuspension or miniemulsion polymerisation which comprises polymerising vinyl chloride monomer, with or without a copolymerisable monomer, in the presence of an emulsifier, wherein a branched alkyl sulphate is used as the or an emulsifier, or is added to the polymer after formation.

Thus, according to a first aspect of the invention a process for the polymerisation of vinyl chloride which comprises polymerising vinyl chloride monomer, with or without a copolymerisable monomer, in the presence of an emulsifier, is characterised in (i) that the emulsifier contains a mixture of alkyl sulphates at least 30% (molar) of which is branched, or (ii) that a mixture of said alkyl sulphates is added to the formed polymer, the branched alkyl sulphates being of the general formula [I]

R - CH₂ CH— R¹

[I]

CH₂O-SO₃ ^" M ⁺ 5 wherein each of R and R¹ is a linear or branched alkyl group containing 1 to 15 carbon atoms and M is a salt-forming element or group, the branched alkyl sulphates containing from 7 to 20 carbon atoms.

According to a second aspect of the invention a process for the polymerisation of vinyl chloride which comprises polymerising vinyl chloride monomer, with or without a copolymerisable monomer, in the presence of an emulsifier, is characterised in (i) that the emulsifier contains one or more alkyl sulphate at least 30% (molar) of which is branched, or (ii) that said one or more alkyl sulphate is added to the formed polymer, the or each branched alkyl sulphate being of the general formula [I]

R - CH₂ CH — R¹

[I]

CH₂O-SO₃ ^■ M ⁺

wherein each of R and R , ι is a linear or branched alkyl group containing 2 to 15 carbon atoms and M is a salt-forming element or group, the or each branched alkyl sulphate containing from 7 to 20 carbon atoms.

The invention also provides a branched alkyl sulphate of general formula [I] above, when used for the polymerisation or copolymerisation of vinyl chloride monomer.

The invention further provides a PVC paste or plastisol, made from PVC produced using a branched alkyl sulphate as emulsifier or additive to the formed polymer, and containing a plasticiser.

The salt-forming element or group M is preferably ammonium or an alkali metal, suitably sodium, and suitably the or each branched alkyl sulphate contains from 7 to 18 carbon atoms, most suitably from 9 to 16 carbon atoms. Examples of alkyl groups R and R include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, and hexyl.

The branched alkyl sulphates used in the process of the invention may be produced by sulphatation of alcohols of formula [II];

R_CH₂ CH R¹

[II] CH₂OH

where R and R¹ are as specified above.

The alcohols of general formula [II] may be produced by the catalytic hydroformylation of an olefin to an aldehyde, followed by hydrogenation, according to the following reaction sequence:

R-CH=CH-R' + CO + H₂ → R-CH₂-CH(CHO) - R¹ → R-CH₂ - CH (CH₂OH) - R

where R and R¹ are as above.

In general, mixtures of different isomers are obtained in this way; these mixtures may contain also variable amounts of the corresponding linear isomer(s), which can be separated by means of physical methods known in the art.

Alcohols with a similar structure to [II] above can be obtained also via another mechanism, the so-called Guerbet process, which consists of a dimerization of a short chain alcohol (see for example W. Teilheimer, Synthetic Methods of Organic Chemistiy, 6, 736 (p. 270); Basel 1952); in this case, a pure product can be obtained; if for example the substrate is hexanol, the alcohol obtained corresponds to the structure [II] with R=pentyl and R¹⁼butyl. If the substrate comprises a mixture of short chain alcohols, a mixture of branched alcohols of formula [II] will be obtained. WO ,»₅,« _ rCT,_CB_W01*₇

The alcohols of formula [II] are then submitted to a sulphatation stage, to produce the alkylsulphates of formula [I].

In the preferred process the alkyl sulphate is a mixture of alkyl sulphates

The alkyl sulphates used in the invention may be wholly branched or may contain a mixture of straight chain and branched products. Ideally the alkyl sulphate is 100% branched; however, so long as the alkyl sulphate is at least 30% (molar) branched, preferably at least 50% (molar) branched, and most preferably at least 75 % (molar) branched, the objects of the invention are achieved. That is to say, it is possible to obtain resins which show a pronounced decrease of the paste viscosity in comparison with resins prepared using the same process, but with straight chain emulsifiers. Furthermore, the foam structure obtainable with the PVC paste containing this type of emulsifier is very good, and is not sensibly deteriorated when compared with those containing linear emulsifiers.

The branched alkylsulphates may be used in the production of PVC by the "classical emulsion" polymerization technique (in its two variants seeded and unseeded), the so called "Microsuspension" (where a predispersion of vinyl chloride in water is obtained by means of a high shear mechanical homogenizer), and the so called "miniemulsion" (where a dispersion of vinyl chloride in water is obtained by means of particular ingredients, namely fatty alcohols, which have the dual role of reducing the interfacial tension and of stabilizing the monomer droplets against diffusion). These three polymerisation techniques are briefly described below, and it will be appreciated that many variations of these techniques are known and possible for the skilled man.

EMULSION

The polymerization initiator is (optionally) a redox system comprising an oxidizing species (for example potassium peroxydisulphate), a transition metal (for example CuSO₄), and a reducing species (for example sodium bisulphite).

Some initial ingredients are firstly charged into the reactor. These include: an initial quantity of water; optionally a seed latex; the potassium persulphate the copper sulphate optionally some emulsifier other ingredients e.g. buffer etc.

The reactor is evacuated to remove oxygen, then vinyl chloride monomer VCM (together with any comonomer) is added. After that, the temperature is set to the reaction value, and the injection of the bisulphite takes place. The quantity of bisulphite added is determined by the reaction velocity. After a certain time from the start (from 0 to up to 1 hr), a solution of emulsifier composed of branched alkylsulphates is continuously added to the reactor, to stabilize the surface of the growing polymer particles. At approx 70% conversion, the reaction undergoes an acceleration, known as the Trommsdorff effect, and proceeds very quickly up to 90-92% conversion. At this point the residual monomer is vented off, an optional stabilizer is added, and the latex is discharged for subsequent stages.

Variants to this process include:

to reverse the order of addition of the initiator components i.e. to put the reducing agent such as the bisulphite in the reactor and to inject the oxidizing agent such as the persulphate;

to employ a monomer injection technique comprising charging only a fraction (typically 20-25% of total charge) of the monomer at the beginning, and then injecting the remaining quantity during the reaction either continuously or in discrete quantities;

to adopt mixtures of emulsifiers, i.e. to add the branched ones in admixture with other emulsifiers; to adopt a different emulsifier in the injection solution, then to add the branched alkylsulphates as "optional stabilizer" at the end of the polymerization or at any stage of the process before drying.

MICROSUSPENSION

Two reactors are used, a mixing vessel (MV) and a polymerisation reactor. The initiator system is composed of an oil-soluble oxidising agent (generally an organic peroxide, perester, peracid, etc.) and an optional water-soluble activating system comprising a reducing species especially ascorbic acid, but also e.g. bisulphite, accompanied by a transition metal complex (e.g. CuSO ).

A certain fraction of VCM (and any comonomer) is added to the MV, together with some water, a certain (small) quantity of branched alkylsulphate emulsifier and oil soluble initiator (LPO). The MV is stirred for a few minutes. In the meantime, the reactor is charged with the residual monomer(s), the residual water, and the CuSO catalyst. The contents of the mixing vessel are then transferred to the reactor through a high pressure pump (homogenizer) which causes a fragmentation of the emulsion contained into the MV into very small droplets. At the end of the transfer, the mixture is heated to the polymerisation temperature, then the injection of the activator (ascorbic acid) starts; the rate of injection is regulated in order to obtain an optimal profile for the velocity of the reaction itself. After a few minutes from the start, a solution of branched alkylsulphate emulsifier is continuously added to the polymerisation mixture in order to stabilize the surface of the growing polymer. At approx. 70% conversion the reaction undergoes an acceleration, known as the Trommsdorff effect, and proceeds very quickly up to 90-92%) conversion. At this point the residual monomer is vented off, an optional stabilizer is added, and the latex is discharged for subsequent stages.

Possible variants include: monomer injection technique as described above use of only oil soluble initiators, even in mixture, without any activator charge of all monomer into the MV e.g. total homogenization. use of different emulsifiers in the MV. to adopt a different emulsifier in the injection solution, then to add the branched alkylsulphates as "optional stabilizer" at the end of the polymerization or at any stage of the process before drying".

In another microsuspension process, a third compound, typically hexadecane, is homogenized in total absence of monomer and then the monomer is added. It swells the droplets by a diffusion mechanism. The initiators are a redox system, all the ingredients being water-soluble.

MINIEMULSION

In this process a mixture of long chain fatty alcohols is mixed with the branched emulsifiers to form a rather dilute (4-5%) aqueous solution in the presence, optionally of polymerization additives e.g. buffer agents. The mixture is then heated (e.g. 2 hrs at 70°) to create a liquid crystal structure. After that the "emulsion water" so formed is transferred into the polymerization vessel, copper sulphate and hydrogen peroxide are added, the reactor is evacuated, and then the VCM and any comonomer are added. The mixture is heated up to reaction temperature and the activator (ascorbic acid, but other water soluble reducing agents are possible) is injected; the rate of injection is regulated in order to obtain an optimal profile for the velocity of the reaction itself.

At approx 70% conversion the reaction undergoes the Trommsdorff effect, and proceeds very quickly up to 90-92% conversion. At this point the residual monomer is vented off, an optional stabilizer is added, and the latex is discharged for subsequent stages. Variants include:

monomer injection technique as described above

use of water-soluble organic peroxide or other water-soluble inorganic oxidizing species as initiators, to be activated by a suitable reducing agent

use of oil-soluble initiators, in general terms not activated, use of long chain alkanes instead of long chain fatty alcohols

As a variant of all the above-mentioned processes, there may be mentioned the continuous polymerization process, where the ingredients of polymerization (water, emulsifier, monomer(s), initiator(s), other additives) are continuously fed into the reaction vessel, which can be either a continuously stirred tank reactor (CSTR) or a tubular reactor. The continuous emulsion polymerization process of vinyl chloride in CSTR is known to be industrially exploited; the feasibility of this variant for the microsuspension and the miniemulsion process has been postulated by Aizpurua et. al., (Macromol. Symp., Ill, (1996), page 121).

The branched alkyl sulphate emulsifiers are suitably used in the polymerisation reaction in amounts up to 3% by weight, based on the weight of vinyl chloride monomer. Amounts up to 1% by weight on the VCM are particularly effective. When the branched alkyl sulphates are added to the polymer after formation, rather than during the polymerisation, they are suitably added in an amount up to 3%, especially up to 1%, by weight on the polymer.

EXAMPLES

The following Examples are given for the purpose of illustrating the invention.

Four branched alkyl sulphate emulsifiers, with different chain length distribution, as surnmarized in the table below as Emulsifiers A to C and I, have been investigated. 12

For the tests, we have used a different recipe for each of the two processes MSP and ME (microsuspension and miniemulsion), and two different recipes for the seeded emulsion process comparing one or more branched alkyl sulphates with one or more reference samples, an additional difference being that the latex obtained with the microsuspension route was blended with a different latex before drying. For reference purposes we have used three types of alkyl sulphate emulsifiers, one of them (Emulsifier D) being a commercial product containing from our evaluation approx. 20%) of branched molecules, and two linear products, one of them (Emulsifier E) consisting of chains with a length ranging from 10 to 16, the majority being C12-C14; and the other (Emulsifier F) being a very pure linear product, 99% of its chains being C12.

type of emulsifier degree of Total carbon atoms branching, molar % in molecule

Emulsifier A fully branched ca.95 C12-C13

Emulsifier B fully branched ca.95 C12-C15

Emulsifier C fully branched ca.95 C14-C15

Emulsifier D partially branched ca.20 C12-C13

Emulsifier E Linear 0 C10-C16 mainly C12-C14

Emulsifier F Linear 0 C12

Emulsifier I partially branched ca.50 Cι - C]

Emulsifiers A, B, C and I were produced by sulphatation of alcohols of general formula [II] above, the alcohols having been produced by the catalytic hydroformylation of the corresponding olefin, followed by hydrogenation of the mixture of aldehydes produced. 13

The results are as follows:

MICROSUSPENSION

Example Emulsifier Quantity Branching Particle Brookfield viscosity Used Used % size 20 RPM, 1 hr ageing (% on

(micron) VCM)

Complex' * Formulation

1 E App. 0.7 0 0.83 121

2 F App. 0.7 0 0.82 106

3 D Appr. 0.85 20 0.69 106

4 D Appr. 0.7 20 - 96

5 Appr. 0.85 94 0.75 72

A

6 Appr. 0.85 94 0.57 72

B

7 Appr. 0.85 94 0.75 73

C

8 Appr. 0.7 95 0.80 73

A

9 Appr. 0.7 95 0.59 72

B

10 Appr. 0.7 95 0.80 60

C

11. B Appr. 0.6 94 0.69 68

12 Appr. 0.6 20 0.69 134

D

I

13 Appr. 0.7 50 0.73 84 14

*The complex formulation comprises, in parts by weight:

PVC 80

PVC filler 20

TiO₂ 5

CaCO₃ 25

Plasticiser 55

Stabilizer 1.5 Foaming agent 3.5

SEEDED EMULSION

Example Emulsifier Quantity branching Brookf. Used used % viscosity, (% on 20 RPM, 1 hr ageing VCM) PVC/DOP

100/50

14 E 0.8 0 1,360

15 B 0.8 95 411

16 C 0.8 95 480

and, with a different recipe

17 E 0.8 0 313

18 B 0.8 95 91

19 C 0.8 95 174 15

MINIEMULSION

Example Emulsifier Quantity Branching Particle size, Brookf.

Used Used % (micron) Viscosity,

(% on 20 RPM, 1 hr ageing

VCM) PVC/DOP

100/50

20 E 1 0 0.49 310

21 B 1 95 0.56 155

22 C 1 95 0.51 139

It can readily be seen that the viscosity of the PVC paste depends on the degree of branching of the emulsifier used, and that highly branched molecules allow PVC to be obtained with lower viscosity than is obtainable using linear emulsifiers.

In a further set of experiments, done under slightly different conditions, a pure alkyl sulphate (G) of formula C H₉ [CH- CH₂ OSO₃ Na] C₆ Hι₃ was used as emulsifier in the microsuspension polymerisation of vinyl chloride, as was a mixture of alkyl sulphates (H) of formulae

R² [CH- CH₂ OSO₃ Na] R³ wherein

R² is CH₃ and R³ is C₉ H₁₉, R² is C₂ H₅ and R³ is C₈ H_π, R² is C₃ H₇ and R³ is C₇ H_!5, R² is C₄ H₉ and R³ is C₆ H_[3, and R² is C₅ Hn and R³ is C₅ Hn.

From the formed polymers, plastisols formulations were compounded, with the same complex formulation set out above, and the viscosity of the formulations was measured at 20 RPM. The results are given in the following Table. 16

Example Emulsifier Quantity used Branching Particle Brookf. used % on VCM) % size Viscosity (micron) 20 RPM, 1 hr ageing Complex formulation

23 G Approx. 0.7 Approx. 0.73 80.5 100%

24 H Approx. 0.7 Approx. 0.81 80 95%

These results also demonstrate the ability of the branched alkyl sulphates of the invention to produce PVC pastes of lower viscosity than are possible by using substantially linear alkyl sulphates.

Claims

1. A process for the polymerisation of vinyl chloride which comprises polymerising vinyl chloride monomer, with or without a copolymerisable monomer, in the presence of an emulsifier, characterised in that the emulsifier contains a mixture of alkyl sulphates at least 30% (molar) of which is branched, or that a mixture of said alkyl sulphates is added to the formed polymer, the branched alkyl sulphates being of the general formula [I]

R - CH₂- -CH- -R¹

[I]

CH₂ O-SO M ⁺

wherein each of R and R¹ is a linear or branched alkyl group containing 1 to 15 carbon atoms and M is a salt-forming element or group, the branched alkyl sulphates containing from 7 to 20 carbon atoms.

2. A process for the polymerisation of vinyl chloride which comprises polymerising vinyl chloride monomer, with or without a copolymerisable monomer, in the presence of an emulsifier, characterised in that the emulsifier contains one or more alkyl sulphate at least 30%) (molar) of which is branched, or that said one or more alkyl sulphate is added to the formed polymer, the or each branched alkyl sulphate being of the general formula [I]

R _ CH₂ CH R¹

[I] CH₂ O- SO₃ ^" M ⁺

wherein each of R and R¹ is a linear or branched alkyl group containing 2 to 15 carbon atoms and M is a salt-forming element or group, the or each branched alkyl sulphate containing from 7 to 20 carbon atoms. t o

3. A process as claimed in claim 1 or 2 wherein the alkyl sulphate(s) is at least 50%) (molar) branched.

4. A process as claimed in any of claims 1 to 3 wherein M is an alkali metal or ammonium.

5. A process as claimed in any of claims 1 to 4 wherein the branched alkyl sulphate contains from 9 to 16 carbon atoms.

6. A process as claimed in any of claims 1 to 5 wherein the branched alkyl sulphate(s) is present in an amount of up to 3%₀ by weight, based on the weight of vinyl chloride monomer.

7. A branched alkyl sulphate of formula [I] set forth in claim 1 or claim 2, when used as an emulsifier for the polymerisation or copolymerisation of vinyl chloride monomer.

8. A branched alkyl sulphate of formula [I] set forth in claim 1 or claim 2, when added to a vinyl chloride polymer or copolymer.

9. Vinyl chloride polymer or copolymer, whenever produced by the process of any of claims 1 to 6.

10. A polyvinyl chloride paste containing a vinyl chloride polymer or copolymer as claimed in claim 9 and at least one plasticiser.