NO119252B - - Google Patents

Description

Process for the production of stable water dispersions

of a polymer of at least one vinyl monomer.

Addendum to patent no. 106,657

The invention relates to the polymerization of vinyl compounds i

aqueous dispersion, in such a way that stable polymer dispersions are formed, whereby in a single polymerization reaction at least two separate groups of polymer particles of different particle sizes are ensured, of which at least one has a uniform particle size.

The invention constitutes an improvement in relation to the

method described in patent no. IO6,657. Certain vinyl and/or vinylidene polymer dispersions are described herein, in which polymer

the particles are spherical and of equal shape, regulated size and which are produced by polymerization of vinyl monomer in an aqueous medium using an "insoluble soap" as the only emulsifying agent

medium. However, the dispersions produced in this way are unstable and are exposed to shear forces (shear unstable), i.e. the polymer particles are separated from the dispersion if extreme caution is not observed with regard to the degree and type of stirring that is carried out during the polymerization reaction. This is definitely a disadvantage, especially when working on a factory scale.

The present invention relates to the production of a stable aqueous dispersion of a polymer of at least one vinyl monomer by polymerization of the monomer in an aqueous medium, which from the beginning contains a water-insoluble soap as the only emulsifying agent, according to patent no. 106,657, and the method is characterized in that a water-soluble emulsifier is added to the water-containing medium after at least 1% and at most 50% transfer of the monomer to polymer particles, preferably in the form of

Na or K salt of a monocarboxylic fatty acid or a hydrocarbon sulfate with 8-22 carbon atoms in an amount that constitutes a regulated excess over and above what is needed to stabilize the polymer particles during the polymerization for the formation or initiation of a group of new polymer particles as the polymerization progresses , whereby in a single polymerization reaction at least two separate groups of polymer particles of different particle size are ensured, of which at least one has a uniform particle size.

The addition of the water-soluble emulsifier in controlled excess beyond that required for stabilization of the polymer particles during the polymerization to form or initiate a group of new polymer particles as the polymerization progresses provides a method of ensuring in a single polymerization reaction at least two distinct groups of polymer particles of different sizes, of which one and the largest has a uniform particle size. Such mixtures with polymer particles of different sizes are valuable as plastisol resins, since the resulting plastisol, when the resin is suspended in a plasticizer, has highly desirable flow properties.

The invention shall be described in more detail with regard to 1) the properties of the vinyl monomers used, 2) the properties of the insoluble soap used, 3) the properties of the added water-soluble emulsifier.

The vinyl monomers are those with a single polymerizable

or CH2=grouping, it being clear that the term "vinyl"

is meant to include both vinyl and vinylidene. Typical examples of such monomers are vinyl chloride, vinylidene chloride, vinyl acetate, methyl methacrylate, ethyl methacrylate, ethyl acrylate, n-butyl acrylate, tert-butyl acrylate, styrene and the like as well as their equivalents. Most suitable as vinyl monomers in the method are vinyl chloride, vinylidene chloride, vinyl acetate, methyl methacrylate and styrene and mixtures thereof. The most suitable monomers according to the invention are those which consist of at least 70% by weight of at least one of the specified monomers and from 0 to 10% of at least one other copolymerizable monomer.

The most suitable monomers to be used in the present process are those which are made up of 70-100% by weight of vinyl chloride, vinylidene chloride, vinyl acetate, methyl methacrylate and styrene and from 0 to 30% by weight of at least one other copolymerizable monomer.

Among other monomers which can be used in smaller amounts in the copolymerization of the essentially indicated monomers indicated above, monoolefinically unsaturated monomers are noted, especially those with a CH2=C grouping or a -CH=CH grouping. Typical monoolefinically unsaturated monomers include other vinyl halides, such as vinyl bromide, vinyl fluoride, vinylidene bromide, vinylidene fluoride, chlorotrifluoroethene, 1,2-dichloroethene and the like; other vinyl esters, such as vinyl propionate, vinyl butyrate, vinyl benzoate, vinyl laurate, isopropylencaproate and the like; acrylate and other methacrylate esters, such as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, amyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, dodecyl acrylate, phenyl acrylate, cyclohexyl acrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, amyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, decyl methacrylate, nonyl methacrylate , dodecyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate and the like, maleate and fumar esters, such as diethyl maleate, dipropyl maleate, dibutyl maleate, diamyl maleate, dihexyl maleate, dioctyl maleate, dilauryl maleate, dimethyl fumarate, diethyl fumarate, di-propyl fumarate, dibutyl fumarate, diheptyl fumarate, dioctyl fumarate, di-decyl fumarate, dicyclohexyl fumarate , diphenyl fumarate and the like; other vinyl aromatic monomers, such as α-methylstyrene, vinyltoluene, vinylxylene, vinylnaphthalene and the like; monoolefins, such as ethylene, propene, butene, pentene, hexene, cyclohexene and the like; vinyl ethers, such as vinyl methyl ether, vinyl ethyl ether, vinyl propyl ether, vinyl butyl ether, vinyl amyl ether, vinyl hexyl ether, vinyl octyl ether, vinyl cyclohexyl ether, vinyl phenyl ether, vinyl benzyl ether and the like; allyl esters and ethers, such as allyl acetate, allyl laurate, allyl benzoate, allyl methyl ether, allyl ethyl ether and the like; vinyl cyanide such as acrylonitrile, methacrylonitrile, inylidene cyanide and the like; a,p-olefinically unsaturated carboxylic acids and anhydrides thereof, such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, citraconic acid, aconitic acid and the like; α,β-olefinically unsaturated acid amides, such as acrylamide, methacrylamide, N-methylacrylamide, N,N-diethylacrylamide, N,N-dipropylmethacrylamide, N-phenylacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, N-vinylpyrrolidone and the like; vinylamine, such as vinylpyridines and the like as well as others.

Particularly suitable is a copolymer of 70-100 weight percent vinyl chloride and 0-30 weight percent of one or more monomers with the formula

wherein R denotes hydrogen or an alkyl group with 1-4 carbon atoms and R-^ denotes a hydrocarbon group with 1-12 carbon atoms. Most suitable are monomers in which R in the stated formulas is an alkyl group with 1-8 carbon atoms.

"Insoluble soaps", to be used.

"Insoluble soaps" which are useful as the sole initial emulsifier in the present process are insoluble metal soaps, such as lithium salts and polyvalent metal salts of saturated, unsaturated and substituted fatty acids. The fatty acid part, which is most appropriate in the present insoluble soaps, is octanoic acid, stearic acid, oleic acid, linolenic acid, ricinoleic acid, palmitic acid, abietic acid and the like. Most suitable are monobasic saturated acids with 8-22 carbon atoms.

Included in the present invention are the insoluble soaps having the formula (X-COO)nM, where X denotes an alkyl group with 7-21 carbon atoms and M denotes lithium, barium, calcium, magnesium, cadmium, zinc, lead, tin or aluminum and n is an integer, which corresponds to the valence of M. The soluble soaps can be introduced as such into the reaction mixture before the initiation of the polymerization or they can be prepared in the prepolymerized mixture by reaction of one of the specified fatty acids with a soluble salt or a base of an appropriate metal , e.g. its hydroxy, sulfate, phosphate, etc. Available insoluble soap emulsifiers are most applicable in the interval from approx. 0.075 to 3 parts by weight, for-

gradually from 0.1 to 1.0 parts by weight per 100 parts by weight monomer.

It is by variation of the chain length of the organic part i

the "insoluble soap" emulsifier used in the present process, it is possible to vary the final particle size of a given vinyl polymer product. An insoluble soap emulsifier with a longer chain length of the fatty acid usually produces resins with a larger particle size than soap emulsifiers with shorter fatty acids. For fatty acids with less than 12 carbon atoms, however, the particle size increases again.

Added water-soluble emulsifier.

The water-soluble emulsifier added according to the invention can be one of the well-known, cationic, anionic or non-ionic types of the emulsifier and surfactant.

The soluble emulsifiers are sometimes divided into wetting agents, stabilizers, detergents, suspending agents etc.

An emulsifier is used in an emulsion preparation to increase the ease of formation of the emulsion and promote the emulsion's stability. These effects are usually followed by a reduction in the voltage in the boundary layer between the two phases, resp. of acting as a protective colloid.

Depending on their behavior, the emulsifiers can be divided into ionic and non-ionic. The ionic type of emulsifier consists of an organic, lyophilic group and a hydrophilic group. The ionic types can be further divided into anionic and cationic, depending on the properties of the ionic group. The lyophilic part of the molecule is usually considered to be the surfactant part. In soap, the surface-active fatty acid part of the molecule thus constitutes the anion in the molecule,

and soaps are therefore classified as anionic emulsifiers. As might be expected, anionic and cationic surfactants are not mutually combinable. Because of the opposite ionic charges, they tend to neutralize each other and their surface-active effect is canceled out.

Nonionic emulsifiers are completely covalent and show no appreciable tendency to ionize. They can therefore be combined with other non-ionic surfactants and with either anionic or cationic agents. The non-ionic emulsifiers are likewise more insensitive to the influence of electrolytes than anionic surfactants.

Typical cationic emulsifiers include long chain quaternary salts such as cetyl triethyl ammonium chloride, alkyl dimethyl benzyl ammonium chlorides and the like. Anionic emulsifiers include sodium stearate, potassium laurate, morpholino oleate, sodium lauryl sulfate, sodium 2-ethylhexyl sulfate, sodium xylene sulfonate, sodium naphthalene sulfonate, sodium alkyl naphthalene sulfonate, sodium sulfosuccinate, sodium oleic acid sulfonate, sodium castor oil sulfonate, glycerol monostearate containing a sodium fatty alcohol sulfate, glycerol monostearate containing a soap, and the like. Nonionic emulsifiers include polyoxyethylene fatty alcohols, polyglycol fatty acid esters, polyoxyethylene modified fatty acid esters, polyoxyethylene polyol fatty acid esters, polyoxypropylene fatty alcohol esters, polypropylene glycol fatty acid esters, polyoxypropylene modified fatty acid esters, polyoxypropylene polyol fatty acid esters, polyol fatty acid monoesters, polyhydric alcohol fatty acid, di-, tri-, etc, esters, cholesterol, and fatty acid esters oxidized fatty oils and the like. Known emulsifiers and surfactants can also be used.

However, the most suitable soluble soaps are ammonium, sodium or potassium salts of monocarboxylic fatty acids with 8-22 carbon atoms, such as ammonium stearate, ammonium laurate, sodium laurate, potassium laurate, potassium myristate and the like.

The method is carried out by adding the water-soluble emulsifier in an amount that constitutes a regulated excess over and above what is needed to stabilize the polymer particles and can be added in portions or continuously during the polymerization reaction, the polymerization preferably continuing until more than 4-0$ of the monomer has been transferred to polymer particles.

The emulsifier can advantageously be added in excess of

3 to 25$ in addition to what is needed to stabilize the polymer particles.

The method comprises the following steps, namely that 1) the polymerization of one or more vinyl monomers, e.g. vinyl chloride, is carried out in an aqueous medium in the substantial absence of oxygen at a temperature from approx. 0 to 100°C or higher in the presence of an insoluble soap as the sole emulsifier until the transfer of monomer to polymer has reached a value of 1 to 5®f0> and then 2) a sample is taken from the polymerization mixture, the mixture is carefully degassed, the sample is cooled to room temperature and the sample latex is titrated with a standard solution of a common emulsifier, whereby the surface tension is set against the concentration of common emulsifier, and that 3) common emulsifier is added to the polymerization in excess of the concentration calculated from the breaking point in the curve over the surface tension in relation to the concentration of common emulsifier, and that the polymerization is allowed to progress to the desired transfer. The stated steps 2) and 3) can be repeated more than once during the polymerization. When higher polymerization temperatures are used, i.e. above approx. 50°C, the titration in step 2) should be carried out at polymerization temperatures to correct for the surface tension variation.

It is clear that the specified method can also be carried out in a routine manner after sufficient experimental values of the specified type have been obtained for a given composition, simply by 1) the polymerization of vinyl chloride in an aqueous medium in the presence of an insoluble soap as the sole emulsifier is initiated as well as that the polymerization is allowed to progress to a certain limited degree of transfer, that 2) the degree of transfer is determined by means such as pressure drop, saturation of dry matter content, etc. and that then ordinary emulsifier is added in an amount that is calculated in advance to be necessary surplus for a given transfer.

Example 1.

A 1 liter stainless steel lined reaction vessel equipped with a screen stirrer with a 7" 5 cm anchor and a pressure gauge was filled with the following ingredients:

Before adding the vinyl chloride monomer, the reaction vessel was purged of air using a stream of nitrogen gas and the polymerization reaction was carried out at approx. ^ >Q°C under stirring at 300-350 rpm. At certain limited transfer (in other words, at some time after the initiation of the polymerization reaction), a 20 g sample of the reaction mixture was withdrawn from the reaction vessel by means of a veterinary syringe (pressure type) and the exact value of the sample was determined. The sample was then carefully degassed (the vinyl chloride was carefully vented from the syringe) and then brought to room temperature. The surface tension of the sample was then measured using a Cenco Du Nuoy Interfacial Tensiometer. Small additions of an aqueous solution of standard emulsifier were then added to the sample, the sample was accurately stirred after each addition, and the sample's surface tension was remeasured. In this way, a deposition of surface tension was carried out in relation to the volume of the solution of standard emulsifier, and it was found that a straight line appeared with a sharp breaking point and leveling off as soon as an excess of emulsifier was present in the sample. The volume of the standard emulsifier at the break in the straight line in the diagram was then determined, the optimum volume of standard emulsifier to be added for accurate stabilization of the particles present was determined, and an otherwise determined excess beyond this optimum volume of standard emulsifier was added to the polymerization mixture. The optimum amount of standard emulsifier required to be added to the polymerization reaction mixture for stabilization without initiation of any new particles was determined as follows:

Weight of the reaction vessel's contents (latex) X

The weight of the sample

Volume of standard emulsifier =

(found through titration)

Optimum volume standard emulsifier, which

must be added to the reaction vessel.

"The weight of the reaction vessel's contents" in the given equation

is determined as follows:

The weight of the reaction vessel's contents = original weight of all filled components - combined weight of all samples taken from the reaction vessel.

Another way to determine the optimal amount of standard emulsifier to add to the reaction vessel is as follows:

Weight of just latex in the reaction vessel

weight of degassed sample

Volume of standard emulsifier

(found through titration)

in which "weight of latex alone in reaction vessel" is determined from measurement of total solids content or less accurately by pressure drop values.

Results of several polymerizations carried out in the indicated manner are listed in table 1. The solution of standard emulsifier used was a 5% aqueous solution of potassium laurate.

The particle size and shape were determined by taking a small latex sample, diluting this with dist. water, depositing a small amount of the diluted latex on a copper grid, accurate drying and electron microphotography of the deposited particles using a Phillips Model E.M. electron microscope. 100B.

Example 2.

The procedure in example 1 was repeated, except that a 2% water solution of sodium lauryl sulfate was used as a solution of standard emulsifier. The results of several trials are shown in table 2.

Example 3.

The procedure of Example 1 was repeated using the following composition:

The standard emulsifier used was a 0>~±g water solution of potassium laurate. Several trials were carried out and in each one two additions of standard emulsifier were made. The first addition was an excess of standard emulsifier, and the second addition at higher transmission was the theoretical amount of emulsifier exactly required to protect all particles present in the polymerization medium. The results of these tests are shown in table 3*

Example 4.

The procedure of Example 1 was repeated using the following composition:

The polymerization was carried out at 75°C. The water, barium laurate and KgSgOg were introduced into the reaction vessel, the temperature was brought to 75°C and nitrogen gas was bubbled through the reaction mixture in a continuous manner throughout the polymerization. Stirring was started and the styrene dosed into the reaction mixture at a rate of approx. 10 drops/min. during the course of polymerization. The standard emulsifier used in the titrations and additions was a 2% water solution of potassium laurate. The first addition of standard emulsifier was at 2.12% transfer, and a 10 weight percent excess soap was used (0.80 parts by weight). The particle size at the time of the first feed was 2200Å and the particles were uniform. The second addition of standard emulsifier occurred at 5 > 77% transfer, and a 10% excess emulsifier (based on the titration) was used. The latex particles were at the time Jbr the second supply in two even groups, the larger particles being even spheres with diameter J^ OoK, and the small particles being even with diameter 2200Å. The polymerization was carried out to 100% transfer and the final latex consisted of three distinct groups of uniform particles, the larger particles being 8100Å in diameter, the intermediate particles 56OOÅ in diameter and the small particles being 3000Å in diameter.

Claims (2)

1. Process for producing a stable aqueous dispersion of a polymer of at least one vinyl monomer by polymerizing the monomer in an aqueous medium, which from the beginning contains a water-insoluble soap as the only emulsifier, according to patent no. 106,657, characterized by that a water-soluble emulsifier is added to the water-containing medium after at least 1% and at most 50% transfer of the monomer to polymer particles, preferably in the form of an NH^-, Na- or K-salt of a monocarboxylic fatty acid or a hydrocarbon sulfate with 8- 22 carbon atoms in an amount that constitutes a regulated excess over and above what is needed for stability separation of the polymer particles during the polymerization to form or initiate a group of new polymer particles as the polymerization progresses, thereby ensuring in a single polymerization reaction at least two separate groups of polymer particles of different particle size, at least one of which has a uniform particle size. 2. Method according to claim 1, characterized in that the water-soluble emulsifier is added in amounts of 3 to 25% in excess.