DK147160B - PROCEDURE FOR PREPARING VINYL CHLORIDE POLYMERS - Google Patents

Description

147160

The present invention relates to a process for preparing vinyl chloride polymers by polymerizing vinyl chloride in an aqueous dispersion of a pre-made vinyl chloride polymer.

Polymerization of vinyl chloride in aqueous dispersion is a well-known operation. When the dispersion of the monomer and the polymeric material formed is in the form of large droplets or particles coated with a protective agent, the polymerization reaction is usually initiated by a polymerisation soluble in oil and the dispersion of these droplets or particles in the water is induced by mechanical stirring, the polymerization process is called a suspension polymerization, and polymer particles having a mean diameter of usually 10-500 µm, preferably 50-300 µm, are obtained.

When the dispersion of monomer and the polymeric material formed is in the form of fine droplets or particles, which are usually used in such an amount that the aqueous dispersion is stable for a certain time after the stirring is stopped and the polymerization reaction is initiated by a water-soluble polymerization initiator, the polymerization process is referred to as an emulsion polymerization and it results in very small polymer particles whose diameter is generally 0.02-2 microns.

The process of the invention consists in depositing, during an emulsion polymerization of vinyl chloride, the particles formed with a particle size of approx. 0.02 to 2 µm on particles of vinyl chloride polymers prepared in advance by mass or suspension polymerization. The method consists of two steps which can be schematized as follows: 1) Vinyl chloride polymers are prepared by mass or suspension polymerization in aqueous dispersion to obtain particles A.

2) In the preceding dispersion, a polymerization is carried out in the presence of the necessary additives for the emulsion polymerization, namely an emulsifier and a water-soluble polymerization initiator. Hereby it is found that the fine particles formed cover the particles A.

During the first step, it is essential that polymer A is prepared by mass or suspension polymerization and that it is in dispersion in the medium prior to the second polymerization step in the presence of additives for emulsion polymerization. The process of the invention comprises the following three cases: a) Polymer A may be a previously prepared final product which has been redispersed; b) Polymer A may be prepared in an immediately preceding suspension polymerization in excess of monomer prior to the addition of additives to the emulsion polymerization and addition of additional monomer, or c) Polymer A may be prepared immediately by suspension polymerization in excess of monomer before the addition of additives to the emulsion polymer. , where this addition marks the start of the second step. This latter method is the most interesting variant of the process according to the invention, since this variant enables the greatest porosity of the finished particles to be obtained. Namely, it is found that excess monomer more or less enclosed in particles A formed during the first step in the second emulsion polymerization step will migrate and polymerize as fine particles on the surface of particles A.

The object of the present invention is, based on particles having a particle size of 10-500 µm, to change the structure of these particles, thereby increasing the porosity and, for example, modifying the density and melting time. By contrast, the purpose is not to increase the particle size, and there is no significant change in the original particles in terms of their dimensions.

3 147160

From Swedish Patent Specification No. 330,057 a classic method for polymerizing vinyl chloride in aqueous emulsion is known in the presence of a graft latex (germ latex) which is grown to a greater or lesser extent.

According to the above Swedish presentation specification, the emulsion polymerization is started with a graft latex whose particle size according to the examples is 0.3-0.4 µm. Such a latex, having regard to the particle size mentioned, can only be made by emulsion polymerization. Thus, it is an emulsion polymerization followed by another emulsion polymerization and not a suspension or mass polymerization followed by an emulsion polymerization as in the process of the invention.

French Patent Specification No. 1,485,547 discloses a process for continuous suspension polymerization whereby the monomer, together with a pre-prepared grafted product enclosing a catalyst, is placed in an aqueous reaction zone.

Thus, it is not a suspension or mass polymerization followed by an emulsion polymerization as in the process of the invention, but a suspension polymerization, which is emphasized that the catalyst is a water-insoluble compound but soluble in the monomer.

German Publication No. 2,023,970 relates to a method of increasing the size of finely divided particles in such a way that larger compact grains are obtained by grafting. Such an inoculation technique assumes a small particle whose size is then increased while maintaining a homogeneous morphology. A latex whose particle size is a maximum of 4 µm (preferably 0.1-2 µm) and which contains an excess of a polymerization initiator is assumed. This initiator is selected from compounds which are not soluble in water but only in the monomer. In the polymerization, a powder is obtained and not, as in the process according to the invention, an aqueous dispersion.

4 147160

The present invention relates, as mentioned, to a process for preparing vinyl chloride polymers by polymerizing vinyl chloride in an aqueous dispersion of a pre-prepared vinyl chloride polymer, characterized in that the aqueous dispersion of a vinyl chloride pulp polymer or vinyl chloride suspension polymer has a -500 µm, optionally containing vinyl chloride monomer, sets a water-soluble free radical-forming initiator and the other necessary additives to the emulsion polymerization, after which the polymerization of the vinyl chloride monomer optionally present in the reactor prior to introduction of the emulsion polymerization is carried out. , and / or the vinyl chloride monomer added after the introduction of the additives, as an emulsion polymerization.

An embodiment of the process of the invention consists in first preparing a vinyl chloride pulp polymer or suspension polymer under a prior pulp or suspension polymerization in a known manner, whereby the vinyl chloride polymer is introduced into an aqueous dispersion; add emulsifier, emulsion polymerization initiator system and monomer, and conduct the polymerization.

When the polymerization is carried out in the presence of a vinyl chloride suspension polymer prepared during a prior polymerization process, this polymer can either be filtered and dried or simply filtered off before being transferred into an aqueous dispersion. From an economic point of view, it is advantageous to conduct the polymerization in the presence of a vinyl chloride suspension polymer dispersed in the aqueous phase in which it is made.

It is an advantage to proceed with the first embodiment in cases where it is useful to know the weight ratio of the monomer participating in the polymerization after the introduction of emulsion polymerization additives and the amount of mass or suspension polymer present at the time the additives are added. , very carefully.

5 147160

In another particularly advantageous embodiment, the total amount of polymer obtained at the end of the present polymerization process can be obtained in a single polymerization operation, the suspension polymerization constituting the first phase of the process and the polymerization of the monomer after the addition of emulsion polymerization additives. second phase.

The vinyl chloride monomer consumed during the polymerization can be introduced into the reactor at once. The process of the invention therefore consists in polymerizing a portion of the vinyl chloride monomer under suspension polymerization conditions, and then adding the conventional additives to emulsion polymerization systems, after which the polymerization is continued to the desired degree of conversion.

In a variant of the second embodiment of the process of the invention, the vinyl chloride monomer is added to the reactor in several steps, two-step ice, it being advantageous to introduce the second fraction of the monomer after the emulsion polymerization additives have been added.

The use of vinyl chloride pulp or suspension polymer and / or mixtures of vinyl chloride with other copolymerizable monomers for practicing the process of the invention makes it possible to obtain interesting mixed products.

For example, vinyl esters such as vinyl acetate, esters of acrylic and methacrylic acid, maleic and fumaric acid esters, as well as vinylidene chloride can act as suitable comonomers to obtain copolymers in the process of the invention.

When a vinyl chloride suspension polymer is used in the process of the invention, the usual suspending agents, initiators and additives can be used.

Among the suspending agents useful are carboxymethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, methylcellulose, partial hydrolysis, vinyl] olyetate, gelatin and similar substances, and mixtures thereof 0.00% by weight - 2% by weight, calculated on the monomer used in the suspension polymerization phase.

The oil-soluble polymerization initiator may be selected from organic peresters and peroxides or azo-isobutyronitrile-type compounds. Thus, for example, one can use lauroyl peroxide, benzoyl peroxide, tert.-butyl perpivalate, acetylcyclohexane sulfonyl peroxide, diisopropyl peroxypercarbonate, azo-isobutyro nitrile and also combinations of at least two of these initiators. The initiators are used in amounts of 0.0002 - 1% by weight, preferably 0.001 - 0.1% by weight, calculated on the monomer used in the suspension polymerization phase.

The products commonly used in suspension polymerizations, e.g. buffers such as sodium bicarbonate and chain transfer agents such as trichlorethylene may also be used.

The usual emulsion polymerization components used in the process of the invention are emulsifiers and emulsion polymerization initiators.

Useful emulsifiers include ammonium or alkali metal salts of fatty acids, such as sodium laurate or myristate, alkyl sulfonates, alkylarylsulfonates and alkyl sulfates, in amounts of 0.005 - 10% by weight, preferably 0.05-5% by weight, based on the monomer taking part in the polymer. after the addition of the emulsifier. Among the useful polymerization initiators are potassium and ammonium persulfate and redox pairs, in amounts of 0.0001 - 5% by weight, preferably 0.001 - 2% by weight, calculated on the monomer participating in the polymerization reaction after the addition of the initiator.

The initiators, suspending agents, emulsifiers, buffers, chain transfer agents and other agents used in the emulsion polymerization are well known and the invention is not limited to the above mentioned agents.

147160

In the present vinyl chloride polymerization process, the weight of the polymer present in the reaction medium at the time of addition of the emulsion polymerization components is between 5 and 99%, preferably 10 - 95%, of the total weight of this polymer and the monomers and thus the weight of the total amount of polymer obtained at the end of the polymerization. The obtained vinyl chloride polymers consist of particles of vinyl chloride suspension polymer or pulp polymer on whose surface there are agglutinated vinyl chloride polymer granules having the same dimensions as the vinyl chloride polymer particles usually obtained by emulsion polymerization. They can be isolated from the aqueous phase and dried by the methods usually used to dry vinyl chloride suspension polymers. These products have a viscosity index of 50 - 200 measured according to French standard NF T 51 013.

Vinyl chloride polymers prepared by the process of the invention have improved properties over vinyl chloride suspension polymers prepared in known manner.

After drying, a vinyl chloride suspension polymer is capable of absorbing a certain amount of plasticizer and / or various additives by simple mixing in a Henschel or Papenmeier type blender to form a dry powder, also called "drying agent". blend "which can be used directly to feed processing machines. This mixing operation is accompanied by an increase in the apparent density of the product, and it is known that it is advantageous to feed the processing machines with mixtures having a high apparent density and good gel. formation properties.

The vinyl chloride polymers prepared by the process of the invention are particularly advantageous because in the preparation of dry mixtures in the quick mixer at a given mixing temperature they yield mixtures with a higher apparent density than the mixtures obtained from a conventional vinyl chloride suspension polymer.

Furthermore, it has been found that the polymers produced are characterized by very short melting times, ie. that when exposed to heat treatment under load, e.g. in a processing machine, melts after a shorter time than usual suspension polymers. This improvement in the melting time is also observed in dry mixtures prepared from these polymers.

The use of the second embodiment of the process of the invention results in vinyl chloride polymers having higher plasticizer absorbency than suspension polymers obtained with the same protective colloid system.

The process according to the invention is further illustrated by the following examples, examples 4, 10 and 12 being comparative examples.

The characteristics obtained for the products listed in the various tables are determined as follows:

The apparent density of resins and dry mixtures is determined according to the standard A.F.N.O.R. I 51 042.

The melting times are determined by a Brabender apparatus on dry mixtures prepared in a Papenmeier mixer at 120 ° C from the following constituents (parts by weight):.

Polyvinyl chloride resin 100

Calcium stearate 1.2

Wax 0.6 Measurements were made under the following conditions:

Mixing chamber 170 ° C

Rotary speed of rotors 30 rpm.

Load 60.5 g.

The ability of the plastics to absorb plasticizer is assessed by determining the uptake time of plasticizer in an oven.

9 147160 100 grams of polyvinyl chloride resin "are mixed with 70 g of dioctyl phthalate (D.O.P.) and this mixture is placed on a glass plate in an oven at 80 ° C.

The recording time of the plasticizer is defined as the time from which a sample taken from the furnace does not wet a sheet of filter paper under the following conditions: A sheet of filter paper, powder, a sheet of filter paper, a glass plate and a load of 5 kg in that order on top of a glass plate.

Examples 1 to 3 below illustrate the first embodiment of the invention by conducting the polymerization in the presence of a polyvinyl chloride resin prepared by a prior polymerization operation. Examples 4-13 illustrate the second embodiment of the invention wherein the entire amount of polymer is obtained in a single polymerization operation.

EXAMPLE 1 20 kg of deionized water, 4.70 kg of suspension polyvinyl chloride marketed by the applicants under the trade name "Ekavyl SK.64," and 22 g of sodium laurate are successively introduced into a 30 liter autoclave which is glazed internally and fitted with a stirrer. a vacuum is established in the autoclave while the stirrer is rotating at 160 rpm and 2 kg of vinyl chloride is introduced.

The temperature of the reactant is raised to 60 ° C and a solution of 4.5 g of potassium persulfate is introduced into 100 g of water, keeping the autoclave under nitrogen pressure.

After 1 hour and 45 minutes of polymerization at this temperature, while the stirring speed is 160 rpm, the pressure gauge in the autoclave has decreased by 3 bar. The reaction medium is then cooled and the residual monomer is degassed.

The product, which is easily filtered, gives a clear filtrate. After drying, 5.90 kg of resin is obtained.

10 147160

The essential characteristics of the obtained plastic material are summarized in Table I below as compared to "Ekavyl SK.64".

EXAMPLE 2

Proceed as in Example 1, however, raising the sodium laurate to 66 grams. After polymerization for 2 hours, the pressure gauge in the autoclave has decreased by 3 bar. 6.10 g of dry resin are collected.

The essential characteristics are given in Table I.

EXAMPLE 3 In the above autoclave, 20 kg of deionized water, 4.70 kg of suspension polyvinyl chloride negotiated by the applicant under the trade name "Ekavyl SK.66®" and 22 g of sodium laurate are successively introduced. A vacuum is established in the autoclave while the stirrer is rotating at 160 ° C. The temperature of the reaction mixture is raised to 58.5 ° 0 and a solution of 4.5 g of potassium persulfate in 100 g of water is maintained, maintaining a nitrogen pressure. this temperature, keeping the stirring speed at 160 rpm, the pressure gauge in the autoclave has dropped by 3 bar, the reaction medium is cooled and the residual monomer is degassed.

After filtration and drying, 5.70 kg of resin is collected.

The essential characteristics of the obtained plastic material for comparison with "Ekavyl SK.66" are listed in Table I below.

TABLE I

Medium Vision - Apparent mass granular mass - Melting density of dry mix lometry filling time produced by

pm (g / cm 3) (min) 50 ° C 80 ° C 120 ° C

Ekavyl SK.64 155 0.58 6 0.63 0.63 0.66 1 152 0.58 4 0.68 0.71 0.73 2 149 0.57 1.5 0.67 0.68 0.75

Equilibrium SK.66 135 0.57 0.63 0.64 0.66 3 148 0.58 0.66 0.66 0.70 Example 4 11.

147160 (Comparative Example for Examples 5-9)

A conventional vinyl chloride suspension polymer is prepared as set forth below from the following ingredients:

Deionized water 20 kg

Vinyl chloride 6.75 kg

Polyvinyl acetate with a degree of hydrolysis expressed in mole percent of 72 f> and with a viscosity of a 4 $> aqueous solution at 20 ° C of 5 cp. 13.5 g

Methyl cellulose 3 »4 g

Acetylcyelohexanesulfonyl peroxide 1 g

Tert.-butyl perpivalate 1.7 g

The colloids are first dissolved in 10 kg of water and then the solution of colloids, 10 kg of water and the oil-soluble polymerization initiators is introduced into the autoclave described in Example 1. Vacuum is then established in the autoclave while the stirrer is rotating at 160 rpm and the 6.75 kg of vinyl chloride is introduced. The temperature of the reaction medium is raised to 59.5 ° 0. After polymerization for 8 hours and 45 minutes at this temperature and the above stirring rate, the pressure gauge in the autoclave is decreased by 1 bar. The reaction medium is cooled and residual monomer is degassed.

The obtained product is filtered and 5.4 kg of substance is collected after drying.

The essential characteristics of the product are given in Table III below, where they can be compared with the resins obtained below in Examples 5-8.

EXAMPLE 5

A vinyl chloride polymer is prepared as described below from the following ingredients: 12 147160

Beionized water 20 kg

Vinyl chloride 6.75 kg

Polyvinyl acetate with a hydrolysis identical

with Example 4 13.5 S

Methyl cellulose 3.4 g

Acetylcyclohexanesulfonyl peroxide 1 g

Tert.-Hutyl Perpivalate 1.2 g

Sodium laurate 2 g

Potassium persulfate 5.4 g

The colloids are first dissolved in 10 kg of water and then sodium laurate and potassium persulfate are dissolved in 100 g of water, respectively.

The solution of colloids, 9.8 kg of water and oil-soluble polymerization initiators is introduced into the autoclave described in Example 1.

Ber is then established in a vacuum in the autoclave while the stirrer is rotating at 160 rpm and 6.75 kg of vinyl chloride is added. The temperature of the reaction medium is raised to 59.5 ° C. After polymerization for 7 hours at this temperature and at the above stirring rate, the sodium laurate solution and then the potassium sulfate solution are introduced while maintaining a nitrogen pressure and the polymerization is continued for an additional 2 hours and 15 minutes. The pressure gauge in the autoclave is then decreased by 2 bar. The reaction medium is cooled and the residual monomer is degassed.

The product, which is easily filtered, gives a clear filtrate. Berries collect 4.7 kg of plastic material after drying.

Essential characteristics of the resin are given in Table III.

EXAMPLES 6-9

Example 4 is presented, however, the amount of sodium laurate, the polymerization time t ^ before the introduction of the sodium laurate and potassium persulfate solutions into the autoclave, and the polymerization temperature tg after the solutions are varied. The test conditions are given in Table II below.

TABBI II

13 147160 Quantity Pressure drop at pre- Collected sodium + + end of search quantity

Ex, laurate U1 τ2 polymer 6 4 g 7b 2h 30min. 1 bar 4.8 kg 7 27 g 73a. 1h 45min. 1 bar 5.1 kg 8 27 g 7b 3b l5min. 2 bar 6.1 kg 9 30 g 8b 1h 45min. 1.5 bar 5.7 kg

The essential characteristics of the obtained materials are given in Table III.

TABLE III

Mean Absorption Time Apparent Density Granu- For Plastici Melt (g / cm2) for Dry Mixture Lometriation Time Prepared at

Ex. (μιη) (min) (min) 50 ° C 80 ° C 120 ° C

4 135 17 6 0.62 0.63 0.67 5 145 14 4.5 0.61 0.64 0.69 6 128 8 3 0.64 0.64 0.73 7 140 9 2.5 0.62 0.65 0.70 8 125 14 4 0.61 0.64 0.68 9 133 14 4.5 0.61 0.65 0.70 EXAMPLE · 10 (Comparative Example)

A conventional vinyl chloride suspension polymer is prepared as set forth below from the following ingredients:

Deionized water 20 kg

Vinyl chloride 6.75 kg

Hydroxypropylme thylc ellulo s e 17 g

Ethylcyclobexanesulfonyl peroxide 1.3 g

Tert.-Butyl Perpivalate 21, g

The hydroxypropylmethyl cellulose is dissolved in 10 kg of water.

14 147160

The solution of colloids, 10 kg of water and the oil-soluble polymerization initiators is introduced into the autoclave described in Example 1. Per, a vacuum is established while the stirrer is rotating at 160 rpm, and 6.75 kg of vinyl chloride is added. After polymerization for 5 hours and 45 minutes at this temperature and at the above mentioned speed of rotation, the pressure gauge in the autoclave has decreased by 1 bar. The reaction medium is cooled and the residual monomer is degassed.

The obtained product is filtered and 5.4 kg of plastic material is collected after drying.

The essential characteristics of the resin are given in Table IT below for comparison with the product of Example 2 prepared according to the invention.

EXAMPLE 11

A vinyl chloride polymer is prepared as indicated below from the following ingredients:

Deionized water 20 kg

Vinyl chloride 6.75 kg

Hydroxypropyl methyl cellulose 17 g

Acetylcyclohexanesulfonyl peroxide 1.3 g

Tert.-Butyl Perpivalate 21, g

Sodium laurate 27 g

Potassium persulfate ^ 4.5 g

The hydroxypropyl methyl cellulose is dissolved in 10 kg of water. The sodium laurate and potassium persulfate are dissolved separately in 100 g of water.

The solution of colloids, 9.8 kg of water and oil-soluble polymerization initiators is introduced into the autoclave described in Example 1.

A vacuum is established in the autoclave while the stirrer is rotating at 160 rpm and 6.75 kg of vinyl chloride is introduced. The temperature of the reaction medium is raised to 59.5 ° C. After polymerization for 4 hours and 15 minutes at this temperature and at the above rate of rotation, the solutions of sodium laurate and then potassium persulfate are added, maintaining a nitrogen pressure and the polymerization is continued for an additional 1 hour and 15 minutes. minutes.

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The pressure gauge in the autoclave has then decreased by 0.8 bar. The reaction medium is cooled and the residual monomer is degassed.

The product, which is easily filtered, gives a clear filtrate and, after drying, 5.4 kg of resin is collected, the characteristics of which are given in Table IV.

EXAMPLE · 12 (Comparative Example)

A conventional vinyl chloride suspension polymer is prepared as set forth below from the following ingredients:

Deionized water 20 kg

Vinyl chloride 6.75 kg

Polyvinyl acetate with a degree of hydrolysis expressed in mole percent of 85 ψ and with a viscosity of a 4 # aqueous solution at 20 ° C of 25 cp. 17 g

Acetylcyclohexanesulfonyl peroxide 1.3 g lert-butyl perpivalate 2.1 g

The solution of colloids, 10 kg of water and the oil-soluble polymerization initiators is then introduced into the autoclave described in Example 1. A vacuum is then established in the autoclave while the stirrer is rotating at 160 rpm and 6.75 kg of vinyl chloride is added. . After polymerization for 6 hours at this temperature and at the above speed of rotation, the pressure gauge in the autoclave has decreased by 1 bar. The reaction mixture is cooled and the residual monomer is gassed.

The product obtained is filtered and 5.3 kg of plastic material is collected after drying.

The essential properties are given in Table V, where they can be compared with the resin of Example 13 prepared according to the invention.

EXAMPLE 13

A vinyl chloride polymer is prepared as indicated below from the following ingredients: 16 147160

Deionized water 20 kg

Vinyl chloride 6.75 kg

Polyvinyl acetate identical to Example 12 17 g

Acetylcyclohexane sulfonyl peroxide 1.3 g

Tert.-butyl perpivalate 2.1 g

Sodium laurate 27 g

Potassium persulfate 4.5 g

The colloid is dissolved in 10 kg of water. Sodium laurate and potassium persulfate are dissolved in 100 g of water.

The solution of colloids, 9.8 kg of water and oil-soluble polymerization initiators is introduced into the autoclave "described in Example 1,

A vacuum is established in the autoclave while the stirrer is rotating at 160 rpm and 6.75 kg of vinyl chloride is introduced. The temperature of the reaction medium is raised to 59.5 ° C. After polymerization for 3.5 hours at this temperature and at the above rate of rotation, the solutions of sodium laurate and potassium persulphate are maintained, maintaining a nitrogen pressure and the polymerization is continued for an additional 2 hours. The pressure gauge in the autoclave is then decreased by 1 ha. The reaction medium is cooled and the residual monomer is degassed.

The product, which is easily filtered, gives a clear filtrate. After drying, 5.4 kg of resin, the properties of which are listed in Table V.

TABLE 17

Mean Recording Time Apparent Density Granu- For Plastici Melt (g / cm3) For Dry Mixture Lometriation Time Prepared By

Ex. (pm) (min) (min) 50 ° G 80 ° C 120 ° C

10 142 44 15 0.66 0.69 0.71 11 126 13 4f 0.69 0.72 0.74

TABLE V

147160 17

Mean Absorption Time Apparent Density Granu- For Plastici Melt (g / ccP) For Dry Mixture Lometriation Time Prepared By

Ex. (pm) (min) (min) 50 ° C 80 ° 0 120 ° C

12 117 58 15 0.68 0.70 0.72 13 142 19 7 0.72 0.75 0.76