FI62845C - FOERFARANDE FOER FRAMSTAELLNING AV VINYLPOLYMERLATEX - Google Patents

Description

|. · * · · · * Ϊ | FBI «(.KUUj-UUSUS PUBLICATION <5 2 8 4 5 LJ {'utlAccninosskrift / 511 Kvik.3 / iot.a.3 C08 F 2/24, 14/06, (51, Kv.ik. /iM.o. 12 / 08i 220/13 $ UOM I --FI N LAN D (21) Pfnttiiwknwit — ptumuMmim 770522 (22) HtkmniipUvt - Aneöknlnpdtg 17.02.77 ^ (23) AUmpllv · —GlMghtcadtf 17 · 02.77 (41) Tullut (foreign) offancllg 20.08.77 (44) NlhUv * k * lp «noo ji kuLjulktliun pvm. - Qo *** ·" * · ech reglsterstyrelsen AmMcmi utlagd och utl-ikriften publleend 30.11.82 (32) (33) (31) pyylmy «Uotkvn-togtri prlorlut 19 02.76 Norway-Norway (NO) 76055 ^ (71) Sintef, Gl ^ shaugen, N-7000 Trondheim, Norway-Norway (NO) (72) John Ugelstad, Trondheim, Norway-NO (NO) ( The present invention relates to a process for the production of latex by emulsion polymerization.

In a conventional process for the preparation of latex by emulsion polymerization, water, monomer, emulsifier and water-soluble initiator are mixed with conventional mixing equipment. The monomer droplets occur as droplets with a size of about 10 .mu.m. The emulsifier is present as monomer-thickened micelles. Only a very small portion of the emulsifier is adsorbed on the surface of the monomer droplets because the total surface area of the droplets is very small due to their relatively large size. The polymerization begins with the radicals formed by the water-soluble initiator diffusing into micelles with a much larger total surface area than the monomer droplets. As the radicals react with the monomer, a polymer is formed in the micelles, and the micelles are converted to polymer particles to thicken the monomer. In individual cases where the monomer is slightly water-soluble, the radicals formed in the aqueous phase react with the monomer, in which case polymer particles are also formed directly in the aqueous phase as the polymer molecules precipitate when they have reached a sufficient chain length. The formation of the particles themselves is usually over 2,62845 even after a couple of percent reaction. In this case, monomer-thickened polymer particles + monomer droplets are present in the system. The polymerization continues in the polymer particles so that the radicals from the aqueous phase are absorbed therein and react here with the monomer. The monomer droplets only act as a reservoir for the monomer, which monomer diffuses from these through the aqueous phase, initially to the micelles, later to the polymer particles and keeps the concentration of the monomer constant, which is gradually used as the monomer in the polymerization.

Thus, the most important point in conventional emulsion polymerization is that the formation of particles takes place in the aqueous phase, either by absorbing the radicals in the micelles or by precipitating the polymer formed by the monomer and the initiator radicals dissolved in the aqueous phase. No particle formation or polymerization occurs in the monomer droplets.

In order to maintain the high stability of the latex formed in the polymerization, a relatively high emulsifier content must be used. As a result, a very large number of micelles and then a large number of small particles are formed in conventional processes, and the particle size cannot be controlled except in special processes in which the emulsifier is gradually added or in graft polymerization.

Another method of making latex is the so-called dispersion polymerization. In this method, the monomer, water, emulsifier, and oil-soluble initiator are effectively dispersed in the homogenizer so that the monomer is present as fine droplets. The size of the droplets is determined by the efficiency of the homogenization. Because an oil-soluble initiator is used, the polymerization occurs largely in the monomer droplets formed in the homogenization, and the Keko of the finished latex particles corresponds to the original droplet size. This method, which is known from the literature, e.g. from Norwegian patent 112,092, represents a very time-consuming and expensive homogenization process.

Although the process can be somewhat simplified by not homogenizing the entire polymerization mixture, e.g. as described in German application 2,501,630, this too does not give a completely satisfactory result.

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Another difficulty is that growth and agglomeration easily occur during polymerization, which can be attributed to the presence or formation of larger droplets in the polymerization, and in addition to the fact that the latex coagulates to some extent.

It has now surprisingly been found that a water-soluble initiator can be used in a method comprising homogenization. This method avoids the disadvantages of the known methods, but retains the advantages. It was expected that when a water-soluble initiator was used, particle formation would occur in the aqueous phase, as is common in emulsion polymerization with water-soluble initiators, and therefore the advantages associated with monomer droplet initiation in an oil-soluble initiator could not be obtained.

The characteristic features of the invention are set out in the appended claims.

According to the invention, there is provided a process for preparing a latex by homogenizing a water + emulsifier + a water-insoluble monomer solubilizer (hereinafter also referred to as "substance I" for practical reasons) to form a very stable pre-emulsion.

The remaining water + monomer or monomer mixture + water-soluble initiator is usually added to the emulsion formed in the homogenization with stirring. The polymerization is carried out in the usual manner at a higher temperature of 50-70 ° C. Studies of the system at various stages have shown that the emulsion formed has very small droplets after homogenization, but when the amount of substance I is very small, most of the emulsifier is still in the aqueous phase. When the monomer is added to the homogenized mixture, the monomer diffuses into the droplets formed during homogenization and the monomer forms a stable emulsion. As the monomer diffuses into the droplets formed during homogenization and causes these to swell, the total surface area of the droplets increases and the bulk of the emulsifier is adsorbed to the droplets. It is essential to the invention that in this way an emulsion of the monomer is obtained so fine and stable that most of the emulsifier is adsorbed on the droplets swollen by the monomer. The large surface area of the monomer-expanded droplets, together with the fact that in this way only a small part of the emulsifier remains in the aqueous phase, ensures that radicals, although formed in the water-soluble initiator in the aqueous phase, adhere so efficiently to little or no particle formation occurs.

During the homogenization, only a part of the required water may be used and the remaining water is added with the monomer and the water-soluble initiator after the homogenization.

The substance to be homogenized I is required to have a water solubility of <10 .mu.g / l H2O at 25 ° C. Such substances include, for example, alkanes, straight-chain and branched, which may optionally be partially halogenated and contain at least 10 carbon atoms.

Of particular interest is the fact that substances which have the desired function in the finished polymer can be used as substance I. As substance I, e.g. phosphates, adipates and phthalates containing organic groups having the desired water insolubility can be advantageously used. These three types of compounds act as plasticizers when the main monomer is vinyl chloride. Furthermore, epoxidized soybean oil can be used as substance I, which, when the monomer is vinyl chloride, acts as a stabilizer. In addition, water-insoluble monomers can generally be used as substance I, which subsequently copolymerize with the main monomer in the subsequent dust polymerization. Such monomers include, for example, acrylates, CH 2 = CHCl 3, methacrylates, j 3,

CH2 = C-COOR

vinyl ethers CH2 = CHOR, vinyl esters CH2 = CH00CR and substituted vinylbenzenes CH = CH2, in each case R is organic

Cu which gives the desired water insolubility.

It is a condition that substance I is a solvent for the monomer and is capable of dissolving the monomer (s) in a ratio of> 100: 1 under given conditions, i.e. in emulsion, i.e. at least 100 parts by weight of monomer must be dissolved in 1 part by weight of substance. This presupposes that the molecular weight of substance I is not too high, in which case, for example, it is not possible to use a polymer. Preferably, the ratio of the molecular weight of substance I to the molar weight of the monomer should not exceed 20.

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The present method provides a number of advantages over previously known methods in which the initiation takes place in droplets and which are all dispersion methods using an oil-soluble initiator.

Since the initiator is not present in the homogenization, this can be performed at any temperature, even in the presence of monomers or comonomers, which facilitates homogenization. The resulting homogenized emulsion containing a water-insoluble component remains stable for several weeks at room temperature. Since no initiator is present, there is no risk of decomposition of the initiator, and if monomer is present, there is no risk of polymerization in the pre-emulsion.

When using a water-soluble initiator which is added only during the polymerization, the fine distribution of the whole substance before the polymerization is not very dependent. When a water-soluble initiator is used, the droplets formed in the homogenization, which are then swollen with the monomer, preferably absorb the radicals formed from the initiator in the water phase. Even if some of the monomer appears as large droplets, no polymerization occurs in these droplets because most of the small droplets adsorb all free radicals from the aqueous phase.

However, when using an oil-soluble initiator, the presence of large droplets is very detrimental to the performance of the process and leads to growth and agglomeration. In addition, the use of such oil-soluble initiators requires the use of relatively large amounts of relatively polar solvent to dissolve the initiator. This is not necessary in the present process, where only the presence of substance I, which is the solvent of the monomer (s), is required.

A certain variation of the method is possible in individual cases where it is desired to use substance I as little as possible. This is especially the case when substance I has no function or is undesirable in the finished polymer, as is usually the case for alkanes. Also when using substances such as said plasticizers and comonomers, it is often desired to use these in relatively small amounts for economic reasons.

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Although it is absolutely essential for the process that some substance I is present in the homogenisation, it has been found that a significant part of this substance can be replaced by another substance (hereinafter also referred to as "substance II") which does not have the same water insolubility requirements but has the same water solubility as the polymerizable monomer.

For example, when vinyl chloride is used, this ingredient may be a common plasticizer, such as dioctyl phthalate or tricresyl phosphate. It may furthermore be part of the main monomer or one of the main monomers or another monomer which, in a subsequent polymerization after the addition of the main monomer, copolymerizes with it. By way of example, when vinyl chloride is the main monomer, acrylates such as methyl acrylate or butyl acrylate can be added as substance II in addition to substance I in the homogenization. With styrene as the main monomer, in addition to substance I, butyl acrylate can be added as substance II in the homogenization.

In the preparation of the styrene-butadiene copolymer, in addition to substance I, part of the styrene can be added.

It is essential for the invention that no volatile solvent is present during the drying process, which is ensured by a sufficiently high boiling point of the added substances or by copolymerization with the main monomer.

In homogenization, the homogenization pressure determines the droplet size of the homogenized emulsion, while by varying the amount of substances to be homogenized (substance I + possibly substance II), the number of emulsion droplets can be changed at a given homogenization pressure. When the monomer is added to the homogenized emulsion, the monomer is approximately evenly distributed among the droplets (if these are the same size), and the size of the monomer expanded droplets and thus finished latex particles will be proportional to the amount of monomer and inversely proportional to homogenized pressure. The increased homogenization pressure produces smaller but more droplets in the homogenized emulsion (and finished latex).

If only a very small amount of substance I is used, this can lead to * too few droplets being formed during homogenization.

This again results in the droplets becoming too large after mixing the monomer 7 62845 because large amounts of monomer have diffused into each droplet, which can lead to an undesirably large size of latex particles. Similarly, the fact that there is a small number of large droplets after diffusion of the monomer can cause almost all of the emulsifier to be sufficiently adsorbed on the droplets, forming particles in the aqueous phase and obtaining an undesirably large number of very small particles.

When more substance II is added in the homogenization, in addition to said small amount of substance I, the number of droplets is increased at a given homogenization pressure. Therefore, after the addition of the monomer, there is a larger number of droplets in this case, thus ensuring a more efficient adsorption of the emulsifier on the droplets and preventing the formation of particles in the aqueous phase. It is also clear that by using a certain homogenization pressure and a certain amount of substance I, the particle size of the finished latex can be varied by varying the amount of more water-soluble substance II in the homogenization.

Substance I, together with substance II, forms droplets of the same size in homogenization on the substance I alone, but in a larger number. The monomer then obtains more droplets into which it can diffuse, and the particle size of the finished latex is reduced compared to the use of a certain amount of substance I alone in the homogenization.

The process according to the present invention can be carried out with very small amounts of water-insoluble substance I, e.g. 5-10 g of substance per 1/1000 g of water. This also allows the homogenization to be carried out with a much smaller amount of water, e.g. 25 ml / 5 g of substance I.

If it is desired to use the smallest possible amount of substance I, as mentioned, some of this can be replaced by partially water-soluble substance II. For example, if it is desired to homogenize 10 g in the first step to obtain the desired particle size, 1 g of substance I and 9 g of substance II can be used.

Usually, the finished emulsion contains 1000 g of water and 600-1000 g of monomer after the addition of additional water and monomer. In the homogenization, substance I is usually used before the addition of additional water and monomer

1-30 g. Optionally, 5-200 g of substance II are used. 25-500 ml of water is normally used during homogenization. The amount of emulsifier depends on the type of emulsifier used, and when Na-lauryl sulfate is used, 2-20 g is normally used.

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As indicated above, the remaining water, monomer and water-soluble initiator, e.g., K2 ^ 2 ° 8 # * loino9eno; '- are added to the emulsion, and the polymerization is carried out in the usual manner. The homogenized pre-emulsion can, of course, be prepared in larger amounts than those immediately used, and the final amount of pre-emulsion can be stored and used by the subsequent addition of monomer, water and initiator. Water and monomer can also be added to the homogenized pre-emulsion, usually with stirring, whereby the monomer diffuses into the droplets, so that a stable emulsion is obtained which remains unchanged for several days at up to 50 ° C. The water-soluble initiator can then be added to effect polymerization.

The following examples illustrate the invention.

Examples 1-6 show the use of different types of substance I, while Examples 7-10 show cases where part of substance I has been replaced by substance II. Comparative Examples A-C illustrate the preparation of latex by conventional emulsion polymerization.

Example 1a 10 g of hexadecane + 200 ml of H 2 O + 4 g of Na-lauryl sulfate were mixed in the usual manner and homogenized using a 2-stage Laboratory Homogenizer Model 15 M Gaulin Corporation, USA, for about 2 minutes. (Working pressure stage 1: 150 kg / cm, working pressure stage 2: 2 50 kg / cm). After homogenization, 800 ml of 00 + 800 g of vinyl chloride were added and stirred for 30 minutes at 50 ° C. 1.6 g of K 2 S 2 O 2 were then added and polymerized at 50 ° C. The latex formed contained particles with a size of 0.3-0.8 μm.

Example Ib

Homogenization using 10 g of hexadecane, 200 ml of H 2 O and 4 g of Na-lauryl sulfate was performed as in Example 1a. The resulting pre-emulsion was stored for one week at room temperature (about 25 ° C), after which it was subjected to the further treatment described in Example 1a with the same results.

Example le

The preparation of the pre-emulsion was performed as in Example 1a, and 800 ml of H 2 O + 800 g of vinyl chloride were added as in Example 1a. The resulting emulsion was stored for 24 hours at room temperature, after which 1.6 g of K 2 S 2 O 8 was added and the polymerization was carried out as in Example 1a with the same results.

Example 2

In order to show the possibility of varying the particle size of the final latex, experiments were performed with a smaller amount of hexadecane than used in Example 1.

5 g of hexadecane + 100 ml of 1 + 0 + 4 g of Na-lauryl sulfate were homogenized as described above. After homogenization, 900 ml of H2O + 800 g of vinyl chloride + 1.6 g of K2S20g were added. After polymerization, the latex contained particles with a size of 0.4-1. The lower amount of hexadecane results in a latex with larger particles because each drop formed in the homogenization was thickened by a larger amount of monomer. Growth and stability as in Example 1.

Example 3

The Comonomer of vinyl chloride can be used as the water-insoluble substance. Vinyl ether with a chain long enough was used to obtain sufficient water insolubility to meet the requirements for substance I.

20 g of a rhodium ether of the formula CH 2 = CHO (Cl 2) 21 x 3 was added to 300 ml of H 2 O + 4 g of Na-lauryl sulfate and homogenized as above. To this pre-emulsion was added 700 ml of K 2 O + 800 g of vinyl chloride + 1.6 g of K 2 S 2 O 8 and dusted at 50 ° C. The resulting latex contained particles ranging in size from 0.25 to 0.6.

In this example, the amount of water-insoluble matter is increased compared to the amount used in Example 1. The result is a latex with smaller particles because each drop formed in the homogenization is swollen with a smaller amount of monomer. Growth and stability as in Example 1.

Example 4

Long-chain vinyl ester can also be used as the water-insoluble comonomer.

To 20 g of ester CH 2 = CH 2 CR, where R was CH 2 (Cl 2) n, where the mean n was 18, was added 300 ml of 1 O 0 + 4 g of Na-lauryl sulfate and homogenized as above. To this pre-emulsion was added 700 ml H 2 O + 800 g vinyl chloride + 1.6 g K 2 S 2 O 8 and polymerized at 50 ° C. The finished latex contained particles ranging in size from 0.25 to 0.6 .mu.m. The same amount of additive was used in the homogenization as in Example 3, and the particle sizes were approximately the same as in the two examples. Growth was somewhat non-existent, and the stability of the latex was very good compared to known latexes.

Example 5

The water-insoluble substance may be a plasticizer of PVC having sufficient water insolubility.

10 g of dimethyl phthalate + 4 g of Na-lauryl sulfate + 200 ml of H 2 O were homogenized as above. To this pre-emulsion was added 800 ml Η ,, Ο + 800 g vinyl chloride + 1.6 g K 2 S 2 ° 8 and polymerized at 50 ° C. The latex contained particles ranging in size from 0.3 to 0.8. Growth and stability as in Example 1.

Example 6

The procedure described in Example 1 was used, but with styrene as the monomer. 10 g of hexadecane + 5 g of Na lauryl sulfate + 200 ml of H 2 O were homogenized as described above. After homogenization, 800 ml of H 2 O + 600 g of styrene + 3 g of K 2 S 2 O 2 were added and polymerized at 60 ° C. The latex contained particles ranging in size from 0.20 to 0.7.

Example 7

Part of the water-insoluble substance I can be replaced by a more water-soluble substance II. In this example, a PVC plasticizer was used in combination with a small amount of hexadecane.

3 g of hexadecane + 6 g of dioctyl phthalate + 200 ml of H 2 O + 4 g of Na-lauryl sulfate were homogenized as mentioned above. To this premulsion was added 800 mL of H 2 O + 900 g of vinyl chloride + 1.6 g of K 2 S 2 O 2 and polymerized at 50 ° C. The latex contained particles ranging in size from 0.3 to 0.8 μm. The particle size is approximately the same as in Example 1. This 011 is expected because the total amount of substance I + substance II used in the homogenization was approximately the same as the amount of substance I in Example 1. Growth and stability as in Example 1.

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Example 8

In addition to a small amount of substance I, substance II, which is also a comonomer of vinyl chloride, can be used. Such comonomers are, for example, acrylates. 3 g of hexadecane + 10 g of butyl acrylate + 200 ml of ί ^ Ο + 4 g of Na-lauryl sulfate were homogenized as described above. To this pre-emulsion was added 800 ml of 1 + 0 + 800 g of vinyl chloride + 1.6 g of K 2 SO 4 and polymerized at 50 ° C. The latex contained particles with a size of 0.2-0.7 μm. The particle size is slightly smaller than in Example 1 because the substance was used slightly more in the homogenization. Xasvu and stability as in Example 1.

Example 9 This example corresponds to Example 6, but some substance I (hexadecane) was replaced with the same amount of substance II in the form of the main monomer (styrene).

3 g of hexadecane + 5 g of Na-lauryl sulfate + 7 g of styrene + 250 ml of H2O were homogenized as described above. To this pre-emulsion was added 750 ml H2O + 600 g styrene + 3 g K2S2 ° 8 and polymerized at 60 ° C. The latex contained particles ranging in size from 0.20 to 0.7.

The particle size is the same as in Example 6. This was to be expected because the amount of material used in the homogenization is approximately the same.

Example 10

As shown in Example 8 for vinyl chloride, a substance-like comonomer can also be used for styrene polymerization in addition to substance I in homogenization. 10 g of hexadecane + 5 g of Na-lauryl sulfate + 50 g of butyl acrylate + 250 ml of H2O were homogenized as described above.

To this pre-emulsion was added 750 ml H 2 O + 600 g styrene + 3 g K 2 S 2 ° 8 Polymerized at 60 ° C. The latex contained particles ranging in size from 0.08 to 0.25. In this example, more material was used in the homogenization than in the previous examples. As expected, a latex with very small particles was obtained.

12

Comparative Examples 6 2 8 4 5 A. As an example of a conventional vinyl chloride emulsion polymerization method, a mixture of 1000 ml of H 2 O + 800 g of vinyl chloride + 4 g of Na-lauryl sulfate was mixed in the usual manner, followed by the addition of 1.6 g of Κ2 ^ 2 ° 8 and polymerization. ° C. The latex contained particles ranging in size from 0.03 to 0.08 μm, and a large amount of about 10% of the precipitated polymer formed in the tubes and walls of the polymerization vessel (growth). In this case, the formation of particles took place only in the aqueous phase, which results in a very small particle size.

B. As an example of a conventional polystyrene preparation method by emulsion polymerization, 5 g of Na-lauryl sulfate + 1000 ml of H2O + 600 g of styrene were mixed in the usual manner, followed by the addition of 3 g of K2S2®8 P ° lymer at 60 ° C. The latex contained particles ranging in size from 0.06 to 0.1. Particle formation occurred here exclusively in the aqueous phase, resulting in a very small particle size.

C. An experiment was also performed in which 5 g of Na-lauryl sulfate + 100 ml of H2O + 600 g of styrene were homogenized for 1.5 minutes. Then 3 g of K2S2®8 P ° lymer ° it3 was added at 60 ° C. The latex contained particles with a size of 0.06-0.1 μm, and again in this case the formation of particles took place exclusively in the aqueous phase, resulting in a very small particle size. This is because the emulsion is very unstable after homogenization in the absence of a water-insoluble substance. The droplets coalesce very quickly, their surface area decreases, the emulsifier enters the aqueous phase. Both factors clearly lead to initiation in the aqueous phase.

Attempts have also been made to carry out the present process using cyclohexane, hexane, ethylene dichloride, chloroform or xylene, which are mentioned as initiator solvents in DE-A-2 501 630 instead of the water-insoluble solvent (substance I) mentioned here. Homogenization with water and emulsifier then resulted in unsustainable emulsions, and the addition of additional water, vinyl chloride, and water-soluble initiator resulted in the formation of particles in the aqueous phase alone, resulting in latexes with unfavorably small particles.

Claims (7)

13 62845 Instead of the potassium peroxide sulphate I ^ SjOg used in the examples, other water-soluble initiators can also be used, e.g. hydrogen peroxide (H 2 O 2) and ammonium peroxide sulphate f (NH 4) 2 S 2 O 9 -. A process for preparing a latex, in which an aqueous mixture containing an emulsifier is effectively homogenized, followed by adding a polymerizable vinyl monomer or a mixture of vin monomers to the homogenized mixture, characterized in that the aqueous mixture to be homogenized contains a water-insoluble solvent having a water solubility of H 2 O and capable of dissolving at least 100 times its own weight of the monomer (s) under the conditions given, part of the required water and possibly another partially water-soluble substance not subject to the same water-insolubility requirements as said water-insoluble substance, in which case the water-insoluble and the mixture of the partially water-soluble substance forms the solvent of the monomer and that a water-soluble polymerization initiator is added simultaneously with or after the addition of the monomer and the final water to the homogenized mixture. Process according to Claim 1, characterized in that a halogenated alkane having at least 10 carbon atoms is optionally used as the water-insoluble substance in the homogenization. Process according to Claim 1, characterized in that a substance which is the desired component of the finished latex is used as the water-insoluble solvent of the monomer (s). Process according to Claim 3, in which the monomer is vinyl chloride, characterized in that a plasticizer or stabilizer of polyvinyl chloride is used as the water-insoluble solvent. Process according to Claim 3, characterized in that a water-insoluble vinyl compound which copolymerizes with the main monomer in the polymerization is used as the water-insoluble solvent. Process according to Claim 5, characterized in that the vinyl compound used is vinyl ether, vinyl ester, vinyl acrylate or substituted styrene having a water solubility of <10 g / l. A method according to claim 1, characterized in that a substance which is a desired component of the finished polymer is used as the second substance. 15 62845