NO158746B - PROCEDURE FOR THE PREPARATION OF VINYL CHLORIDE POLYMERS. - Google Patents

Abstract

A process for the preparation of vinyl dispersion resins by the emulsion polymerization technique is described. The vinyl monomer or monomers are reacted in an aqueous medium using a water-insoluble free radical scavenging catalyst, an emulsifier or emulsifier system and a small amount of water-insoluble plasticizer thereby greatly reducing the required amount of emulsifier or agents. All the reaction components are thoroughly mixed and homogenized before polymerization at a temperature of from about 30 to approx. 70 ° C. The paste resins thus prepared have improved properties, such as foam properties, and polymer build-up in the reactor is reduced.

Description

The present invention relates to a method

for the production of vinyl chloride polymers.

In the usual emulsion polymerization process, it has

It has been difficult to obtain suitable latexes because the latexes usually contain particles of varying sizes and are either too fine or too large. In addition to particle size uniformity, there is a need to improve other properties of the resins produced by emulsion polymerization, such as plastisol viscosity, clarity, gel temperature,

as well as rash and bleeding properties in products made from it. So far, various proposals have been put forward with some success to improve these properties, but not with the final desired result. The use of different emulsifiers and catalysts has e.g. been proposed. It has also been suggested to vary the polymerization conditions.

In most of these cases, however, too extensive coagulation has occurred with the result that the resulting latex contains too much coagulum or partially agglomerated

pea particles that precipitate and thus reduce the yield.

Furthermore, the storage time for such latexes is very short.

It is desirable to obtain latexes which change very little during storage with regard to viscosity and have and maintain good heat stability.

One of the main difficulties with the production of vinyl dispersion resins or polymers using the emulsion polymerization technique is the large amounts of emulsifier or soap that must be used. These high dosage levels not only lead to high raw material costs, but more importantly, these dosages limit the desired resin properties that can be achieved with the emulsion polymerization method. A reduction in the amount of emulsifier or soap required in the polymerization composition would be highly desirable.

Another unfavorable problem in the commercial production of polymers from vinyl chloride is the formation of unwanted polymer build-up on the inner surfaces of the reactor. This build-up is particularly pronounced when large amounts of emulsifier are used. This deposition or build-up of polymer on said reactor surfaces not only interferes with heat transfer, but also reduces productivity and has an adverse effect on polymer quality, producing finer particles than desired with the resulting detrimental effect on viscosity. This polymer build-up must obviously be removed and its removal is difficult and time-consuming.. It would of course be very desirable to

arrive at a polymerization process in which polymer build-up does not occur or in which polymer build-up is reduced to a minimum and which build-up is of the "sandy" type or is of a type that is easily removed.

In emulsion polymerization of vinyl monomers during the production of vinyl dispersion polymers, it has unexpectedly been found that a substantial reduction in the amount of emulsifier or agents required can be achieved by adding a small amount of a water-insoluble plasticizer to the polymerization composition. It has further been found that by using water-insoluble initiators and homogenizing the entire reaction mixture, prior to polymerization, the foam properties of plastisols prepared from the polymers are greatly improved. The plasticizer increases the stability of the monomer droplets in the premixing and homogenization steps and thus allows a reduction in emulsifier without impairing the overall polymerization colloidal stability. The reduction in emulsifier concentration results in a significant reduction in polymer build-up during polymerization.

In the present invention, "vinyl dispersion ion resin" refers to polymers of vinyl chloride.

The most preferred vinyl dispersion resin is polyvinyl chloride (PVC), and the invention will, for the sake of simplicity and expediency, be described in connection with it.

It should be noted that it has heretofore been proposed to polymerize vinyl monomers in the presence of a plasticizer. See e.g.

US Patent No. 3,867,331. In this patent, an emulsion polymerization process is used in which the composition used contains a plasticizer. In the said patent, however, the purpose is

to get as much of the plasticizer as possible in the finished resin,

and this is not the purpose of the present invention.

In the patent, 5-100 parts by weight of plasticizer are used, and preferably 15-90 parts, which is far more than what is used in the present invention, as will be apparent from the discussion below. There is no mention in the said patent that the plasticizer is used to reduce the amount of emulsifier used. One can actually infer the opposite because the amount of emulsifier used in the patent is much higher than that used in the present invention.

US patent no. 4,113,687 describes an emulsion polymerization process in which the composition used contains a solvent for the monomer. The patent also uses a water-insoluble initiator, while in the present invention, on the other hand, a water-insoluble initiator is used. Furthermore, in the patent some water plus emulsifier plus the monomer dissolving substance (solvent) is homogenized to form an emulsion. Then the rest of the water plus the monomer or monomer mixture plus the water-soluble initiator is added to the emulsion with the usual stirring. In the present invention, the entire reaction mixture is homogenized together and fed to the reactor.

According to the present invention, a method for the production of polymers of vinyl chloride is provided, and this method is characterized by forming a monomer premix containing the monomer to be polymerized, the aqueous reaction medium, 0.01-0.5% by weight of a water-insoluble, free radical-generating catalyst based on the weight of monomer being polymerized, an emulsifier system comprising 0.4-4.0% by weight based on the weight of monomer of compounds selected from alkali metal or ammonium salts of long-chain saturated fatty acids containing 8-20 carbon atoms and alkali metal or ammonium salts of. the sulfates of alcohols containing 8-18 carbon atoms, and 0.05-4.5% by weight based on the weight of monomer of a water-insoluble plasticizer, homogenize the entire premix at a temperature below the reactivity of the catalyst or catalysts used, polymerize the homogenized premix in a reaction zone at a temperature in the range of 30-70°C while maintaining its pH value in the range of 2.0-10.5 until the reaction is complete, and then recovers the polymer.

The important feature of the present invention is the use in the polymerization composition of a small amount of water-insoluble plasticizer which allows a reduction of up to 50% or more in the amount of emulsifier or soap required in the polymerization composition. Examples of water-insoluble plasticizers include dioctyl adipate, epoxidized soybean oil, dioctyl phthalate, dioctyl azelate, dicapryl adipate, diisodecyl phthalate, isopropyl myristate, isopropyl palmitate, n-heptyl-n-nonyl adipate o„1. The amount of plasticizer used is small and is in the range of 0.05-4.5% by weight, based on the weight of monomer being polymerized. The amount of plasticizer is preferably in the range of 0.1-1.0% by weight. The plasticizer is added to the premix before homogenization together with the other components in the usual way, as no special or extraordinary technique is necessary.

In the production of vinyl dispersion resins, whereby the aqueous emulsion polymerization technique is used,

will the aqueous reaction medium contain one or more emulsifiers or an emulsifier system, such as a salt of a long-chain fatty acid and a long-chain saturated alcohol. In order to achieve the correct and improved properties in films produced from the vinyl dispersion resins, such as e.g. improved water resistance, heat resistance and the like, an alkali metal or ammonium salt of a long-chain fatty acid is used as emulsifier or as part of the emulsifier system. The aforementioned saturated fatty acids can be either natural or synthetic, and should contain 8-20 carbon atoms. Examples of such acids include lauric acid, mystiric acid, palmitic acid, margarine acid, stearic acid, etc., beef tallow, coconut oil, etc. Excellent results have also been achieved by using anionic emulsifiers such as the alkali metal or ammonium salts of the sulphates or alcohols with 8.18 carbon

atoms. Examples of such emulsifiers include sodium lauryl sulfate, ethanolamine lauryl sulfate, ethylamine lauryl sulfate, etc., alkali metal and ammonium salts of sulfonated petroleum and paraffin oil; sodium salts of hydrocarbon sulfonic acids, such as dodecane-1-sulfonic acid and octadiene-1-sulfonic acid; sodium salts of alpha-olefin sulfonates; aralkyl sulfonates, such as sodium isopropylbenzene sulfonate, sodium dodecylbenzene sulfonate, sodium isobutyl naphthalene sulfonate, and the like; alkali metal and ammonium salts of sulfonate and the like; alkali metal and ammonium salts of sulfonate dicarboxylic acid esters, such as sodium dioctyl sulfosuccinate, disodium n-octadecyl sulfosuccinate, etc.; alkali metal and ammonium salts of free acid of complex organic mono- and diphosphate esters, etc. Non-ionic emulsifiers such as octyl or nonylphenyl polyethoxyethanol can also be used. Vinyl polymer latexes with excellent stability are obtained by using the alkali metal and ammonium salts of aromatic sulfonic acid, aralkyl sulfonates and long chain sulfonates. Emulsifiers are used as mentioned in the range 0.4-4.0

% by weight based on the weight of the monomer being polymerized. The emulsifier is preferably used in an amount in the range of 0.6-1.2% by weight. If more than one emulsifier is used in the system, the combined weight will be in the same range.

In order to achieve certain desired properties, in many cases, in addition to the compounds mentioned above, a long-chain saturated alcohol containing 8-24 carbon atoms is used in the emulsifier system. The addition of the alcohol to the system increases the colloidal stability of the polymerization system. Furthermore, the presence of alcohol reduces the amount of polymer build-up and coagulum.

Examples of such alcohols include octanol, mono-nol, decanol, undecanol, dodecanol, tridecandl, tetradecanol, pentadecanol, hexadecanol, heptadecanol, octadecanol, nona-decanol, eicosanol, heneicosanol, docosanol, tricosanol, tetracosanol, etc. Mixtures of the alcohols can also be used. It can e.g. an alcohol containing 12 Alcohols with a lower carbon content can also be used in a mixture with the alcohols with a longer chain. An example here is a mixture of dodecanol and octadecanol. Furthermore, ethoxylated alcohols can be used, such as a mixture of ethoxylated linear primary alcohols containing 12-15 carbon atoms, etc. US patent no. 4,076,920 shows the use of said alcohols together with the emulsifier compounds in the emulsifier system. In said patent, however, the emulsifier is limited to the ammonium salt of the fatty acid and the ratio between alcohol and fatty acid salt can be 1.0, while the ratio is preferably greater than 1.0. When an alcohol is used in the present invention, on the other hand, said ratio between alcohol and emulsifier is less than 1.0 and preferably in the range 0.15-0.75.

The present emulsion polymerization process is carried out at a high pH value. The process is carried out at a pH value in the range 2.0-10.5. If the pH value is too high, too much alkali is used, and if the pH value is too low, e.g. below 5.0, the coagulum increases. The amount of alkaline agent necessary for a correct setting and maintenance of the correct pH value will depend in part on the particular emulsifier system used in the reaction mixture.

As in all vinyl polymerization processes, the present method is carried out in the presence of a compound which can initiate the polymerization reaction. Free radical-yielding initiators which are normally used for the polymerization of olefinically unsaturated monomers are satisfactory for use in the present process. However, it is very important that the initiator is water-insoluble. The useful initiators or catalysts include, e.g. the various peroxygen compounds, such as lauryl peroxy, isopropyl peroxydicarbonate, bis(4-tert-butylcyclohexyl)peroxydicarbonate, di(2-ethylhexyl)peroxydicarbonate, diisononanoyl peroxide, benzoyl peroxide, t-butyl hydroperoxide, t-butyl hydroperoxide, t-butylperoxypivalate, cumene hydroperoxide, t- butyl diperphthalate, pelargonyl peroxide, 1-hydroxycyclohexyl hydroperoxide, tert.butyl peroxyneodecanoate, etc.; azo compounds such as azodiisobutyronitrile, dimethylazodiisobutyrate etc. The amount of initiator used will usually be in the range 0.01-0.05% by weight, based on the weight of monomer being polymerised, and preferably between 0.015 and 0.15% by weight %.

The initiator is added completely at the beginning of the polymerization. When the initiator is added at the beginning, it is added to the monomer premix together with the other components of the reaction mixture. This is particularly the case when the premix is homogenised before introduction into the reactor. When the initiator is added to the premix and then homogenization is carried out, it is however necessary that the temperature during the premixing and homogenization steps is kept below the minimum temperature for the reactivity of the particular initiator or initiators used. When preparing a premix of vinyl chloride, water, plasticizer and suitable emulsifiers and then adding isopropyl peroxydicarbonate thereto, e.g. the temperature at 20°C during the mixing step and then during the homogenization step. When introducing the homogenized mixture into the polymeriza ion reactor, the temperature is then raised to that at which the reaction is to take place.

It is important that the monomer!-premix is thoroughly mixed before introduction into the reactor. Mixing is usually done in a separate container or premix tank. When the catalyst is added at the beginning of the reaction, it is the last component added to the premix. Since the catalyst used is not water-soluble, it should also be added to the premix in a suitable solvent for this, which will ensure emulsification in the premix and uniform distribution therein. It should be unnecessary to mention that any such solvent should be inert to the reaction components and the reaction conditions. When you e.g. uses isopropyl peroxydicarbonate as a catalyst or initiator, it is dissolved in witch hazel and then added to the premix.

After the monomer premix or reaction premix is thoroughly mixed, it is then subjected to homogenization before entering the polymerization step or the reactor. It is very important in the present invention that all the components of the polymerization composition are homogenized together at the same time. Any suitable device for homogenization can be used. It has been found that either a one-stage or a two-stage Manton-Gaulin homogenizer can be used as a suitable device for homogenizing the premixes relevant in the present invention. The premix leaves the homogenizer and goes directly into the reaction vessel which preferably contains an inert atmosphere, such as nitrogen.

The homogenization step is important because it ensures the correct particle size of the polymer in the finished latex. A particle size in the range from 0.1-10.0 µm is desirable, with most of the particles having a size of 2 µm. When the polymer particles have the right size, this ensures good properties in the plastisol that is made on the basis of these particles.

The temperature at which the polymerization reaction is carried out is important because the intrinsic viscosity (IV) of the plastisols produced with the vinyl dispersion resins thus formed is a direct function of the reaction temperature. That is, the higher the temperature, the lower the IV value. Accordingly, the end use of the vinyl dispersion resin to be produced will normally dictate the temperature of the polymerization reaction. For example, when preparing vinyl dispersion resins for use in coatings or in casting flexible films, a lower reaction temperature will be used to achieve a higher IV value which is desirable for many coating applications. It has been found that for the end applications for which the vinyl dispersion resins are particularly adapted, polymerization temperatures in the range of 30-70°C are satisfactory. However, a temperature in the range from approx. 40-55°c. It should be noted that as reaction

temperature increases, the polymer build-up on the reactor's inner surfaces will generally increase. When carrying out the present invention, however, the polymer structure becomes

significantly reduced. This is due to the large reduction in the amount of emulsifier used, which in turn is due to the small amount of plasticizer present in the reaction mixture. The small amount of polymer build-up that forms is not of the hard, crusty type and can be easily removed by rinsing or flushing with water and without opening the reactor when appropriate spray nozzles are installed in the reactor. After the polymerization reaction is complete, the vinyl dispersion resin is isolated in powder form from the latex by spray drying. That is, a fine shower of polymer latex is injected into a heated air chamber to thereby remove the water and extract the dried resin in powder form.

Plastisols are produced with the vinyl dispersion resins obtained according to the invention by uniform mixing or intimate mixing, using conventional devices, with 100 parts by weight of the dispersion resin in powder form with 30-100 parts by weight of one or more plasticizers. The plasticizers usable for this purpose can be specified as alkyl and alkoxyalkyl esters of dicarboxylic acids or the esters of a polyhydric alcohol and a monobasic acid. Examples of such materials include dibutyl phthalate, dioctyl phthalate, dibutyl sebacate, dinonyl phthalate, di(2-ethylhexyl) phthalate, di(2-ethylhexyl) adipate, dilauryl phthalate, dimethyl tetrachlorophthalate, butyl phthalylbutylglycollate, glyceryl stearate and the like. The preferred plasticizers are the liquid diesters of aliphatic alcohols of 4-20 carbon atoms and dibasic carboxylic acids of 6-14 carbon atoms.

The plastisols prepared from the vinyl dispersion resins should have the desired yield. Yield is simply defined as the resistance to flow and is normally determined numerically by means of viscosity measurements using well-known standard techniques. Normally, such values are obtained by calculation from viscosity measurements using a Brookfield Model RVF viscometer according to AS TM method D1824-61T. Yield is determined from viscosity measurements of the plastisols at varying rpm. (revolutions per minute) after initial preparation and aging intervals. The viscosity is measured in centipoise (eps) at a temperature of 2 3°C. In the specific examples that follow below, viscosity measurements were made at 2 rpm. and 20 rpm. and are expressed as V 2 and V2q, respectively.

To further illustrate the present invention, the following specific examples are given. In the examples, all parts and percentages are calculated by weight unless otherwise stated.

Example I

In this example, several trials were conducted using different plasticizers, as shown in the table below. In the experiments, the following composition was used, the amount of plasticizer being shown in the table:

All the ingredients, including the plasticizer, were added to a premix tank whereby the vinyl chloride was added last after the tank had been placed under vacuum. The mixture was then stirred or agitated for 15 minutes at a temperature of 20°C. Then the premix was homogenized in a two-stage Manton-Gaulin model L-100 homogenizer at a temperature of 20°C in the polymerization reactor. The first stage in the homogenizer was carried out at 49 kg/cm<2> gauge pressure and the second stage at 42 kg/cm 9 gauge pressure. The reactor was evacuated before the addition of the homogenized premix. The reactor was heated to the reaction temperature of 45°C and the reaction carried out with stirring until completion. The polymer latex or slurry was removed from the reactor and spray dried to recover the dry PVC or resin.

Plastisols were prepared with the polymer from each trial for evaluation purposes. The plastisol composition used in each case was as follows:

Relevant data regarding the polymerization and plastisol properties are given in the following table:

(a) Used 0.9 parts of sodium lauryl sulfate and NaOA

instead of alpha-olefin sulfonate.

(b) Used 0.26 parts of each of 2 catalysts

(peroxide and peroxydicarbonate).

It appears from the above data that almost all the properties are comparable to previous dispersion resins, but with greatly reduced amounts of emulsifier. Furthermore, the thermal stability is increased by the use of the present invention.

Example II

In this example, three additional trials were conducted to demonstrate improved resin properties. The same method as shown in example I was used in these experiments. The compositions and properties are shown in the following table:

From the above results, the improvement in properties is evident, particularly in Brookfield viscosity and Sever's efflux. The improvement in clarity and gel temperature is particularly evident in trial no. 10.

Example III

In this example, two attempts were made, one using the present invention and the other using the prior art as shown in US Patent No. 4,113,687. The purpose of these tests was to show the improved foam properties achieved by the present invention. The compositions, polymerization conditions and properties are shown in the following table:

Plastisols were prepared with the resins to determine Brookfield viscosity, density, cell structure assessment and color assessment. The following plastisol composition was used and the ingredients were mixed in the usual way.

No. 11 No. 12 Parts Parts PVC (polyvinyl chloride) 100 100 Dioctyl phthalate 72 79.5 Butyl benzyl phthalate 25 27.5 50% dispersion of azo-bis-

formamide in dioctyl phthalate 6 6 zinc octoate 3 3

The plastisol properties are given in the following table:

The figures given above point out the improvement in shape properties of the present plastisols compared to those in the prior art. The cell structure of the foam is such that the pores therein are smaller and have a much more uniform distribution.

Example IV

In this example, an ethoxylated fatty alcohol was used and compared to a + alcohol to show the comparable properties and, as is evident from the data provided, improved properties in many respects. The polymerization was carried out as described in Example I and compositions and conditions together with properties are given in the following table. The plastisol composition was the same as indicated for trial 11 in Example III.

Again, the reported data show comparable and improved properties.

The many advantages of the present invention are apparent from the above description and the specific examples. The prepared vinyl dispersion resins, as defined herein, have improved Brookfield viscosity, Sever's efflux, better clarity, and improved gel temperature and air release. Furthermore, the runout and bleeding properties are improved with the lower emulsifier levels. A further important advantage of the present invention is improved plastisol foam properties. The lower emulsifier levels further provide a significant saving in manufacturing costs and thus form the basis for a more economical commercial process. Another, important factor in the present invention is the reduction in polymer build-up in the reactor, which not only reduces costs, but results in a better product quality as the product is produced in increased yields. Several other advantages of the invention will be apparent to the person skilled in the art.

Claims (6)

1. Process for the production of polymers of vinyl chloride, characterized by forming a monomer premix containing the monomer to be polymerized, the aqueous reaction medium, 0.01-0.5% by weight of a water-insoluble, free radical-generating catalyst based on the weight of monomer that is polymerized, an emulsifier system comprising 0.4-4.0% by weight based on the weight of monomer of compounds selected from alkali metal or ammonium salts of long-chain saturated fatty acids containing 8-20 carbon atoms and alkali metal or ammonium salts of the sulfates of alcohols containing 8~18 carbon atoms, and 0.05-4.5% by weight based on the weight of monomer of a water-insoluble plasticizer, homogenizes the entire premix at a temperature below the reactivity of the catalyst or catalysts used, polymerizes the homogenized premix in a reaction zone at a temperature in the range 30-70°C while maintaining its pH value in the range 2.0-10.5 until the reaction is complete ig, and then recovers the polymer. 2. Method according to claim 1, characterized in that an emulsifier system is used which contains at least one saturated alcohol with a long straight chain and containing 12-24 carbon atoms and a ratio between alcohol and emulsifier which is less than 1.0. 3. Method according to claim 1, characterized in that dioctyl phthalate is used as the plasticizer. 4. Process according to claim 1, characterized in that a mixture of di(2-ethylhexyl) peroxydicarbonate and diisononanoyl peroxide is used as catalyst. 5. Method according to claim 4, characterized in that an emulsifier system containing sodium lauryl sulfate, sodium alpha-olefin sulfonate, or a mixture thereof is used. 6. Method according to claims 1-5, characterized in that a pH value of 5.0-10.5 is used.