NO800138L - PROCEDURE FOR THE PREPARATION OF ELASTOMER VINYL ACETATETHYLEN COPOLYMERS - Google Patents

Description

Vinyl acetate-ethylene copolymers (VAE copolymers) constitute a well-known class of synthetic plastics that exhibit a wide range of properties depending on the relative amounts of copolymerized ethylene and vinyl acetate (and other ethylenic monomers that may be present) in the copolymer chain. Elastomeric, amorphous, VAE rubber materials containing from 40 to 70% by weight of vinyl acetate randomly distributed in the copolymer chain have, when crosslinked, e.g. with a peroxide cross-linking agent, properties that make them particularly useful as elastomers for the production of rubber materials, as base copolymers for the production of adhesives and as impact modifiers for polyvinyl chloride (PVC). Among the physical and chemical properties that make the rubbery VAE copolymers suitable for such applications are the following: resistance to heat aging, resistance to oil and solvents, low permanent compression deformation, good low-temperature properties, excellent weather resistance and resistance to ozone, resistance to natural light,

ability to give transparent vulcanizates and vulcanizates on the black-and-white scale, ability to absorb large amounts of fillers, ability to be affected by dielectric heating and good wetting properties. The elastomeric VAE copolymers are thus excellent for use in car production, e.g. such as gaskets, seals and O-rings, cable insulation, radiator hoses, bumper strips and bezels in dashboards,

and they are also ideal for other demanding applications, e.g. as foundations for machines, weather-resistant sealing strips, washing machine hoses, seals for freezers and the like.

According to the present invention, VAE elastomers are produced in the form of latexes using an improved emulsion copolymerization process, and the elastomers are recovered using conventional methods, such as by coagulation. Usually, a VAE latex is produced by first adding an aqueous phase containing water, over-. surfactant, a buffer, a catalyst or a free-radical type catalyst system and usually a protective colloid, such as polyvinyl alcohol (PVA) for a reactor, e.g. as described in US patent 3,708,388. In some methods, the reactor is also supplied with a first filling of vinyl acetate monomer and in other methods the entire quantity of vinyl acetate monomer. The reactor is flushed with nitrogen and sealed, after which stirring begins. Ethy-

len is then pumped to the reactor, until the desired pressure is reached. The reactor can be pressurized again one or more times, if the batch production is carried out under variable ethylene pressure, or a constant pressure can be automatically maintained using well-known methods. After the reactor pressure has stabilized, the reactor contents are heated to the polymerization temperature, usually by circulating hot water or steam in a jacket that surrounds the reactor. When the desired polymerization temperature is reached (usually a temperature from 48.9° to 73.9°C), the temperature is maintained at this level by automatic regulation. Then a co-catalyst, such as sodium hydrogen sulphite (NaHSO^) can be added to the reactor (if a catalyst system is used in which a reducing agent is used to form free radicals in a redox reaction)/where any remaining vinyl acetate monomer is added . When the polymerization has been completed, this will make itself felt by the need for a new supply of ethylene ending and by the cooling temperature stabilizing at a temperature approx. 3 -

4°C above the reactor temperature. After completion of polymerization, the reactor contents are cooled and withdrawn through a pressure relief valve to a receiver reservoir at atmospheric pressure, from which unreacted ethylene is discharged. The manufacturing process is completed by passing the obtained VAE latex through a sieve of the desired mesh size.

Many manipulations of both the amount and nature of the components in the VAE copolymerization medium and of the process variables have previously been attempted to optimize one or more properties of the manufactured latex. In US patent 3,644,262, a copolymerization process is described in which one knows

to regulate the addition of vinyl acetate to an aqueous, emulsifying mixture containing a free-radical activator so that the concentration of unpolymerized vinyl acetate does not exceed approx. 3.5% by weight of the emulsifying mixture, even

tually by delaying the addition of surfactant, makes it possible to introduce significantly more ethylene into the copolymer at a given pressure and a given temperature than would otherwise be possible. The obtained VAE copolymer latexes with high ethylene content are said to be better suited for their intended application than latexes with relative ethylene content. Another way of obtaining improved VAE copolymer latexes is described in US patent document 3,423,352, where VAE copolymer latexes with a high solids content and with reduced viscosity and improved freeze-thaw stability are obtained through regulation of the addition of monomer, catalyst and surfactant medium. According to this patent, relatively large amounts of surfactant, i.e. amounts from 3 to 10% by weight, and catalyst are added to a conventionally produced polyvinyl acetate latex with a solids content of up to approx.

52% and containing relatively large amounts of vinyl acetate, at specified times as soon as the polymerization has progressed to a certain point. This is said to result in a marked reduction in the viscosity of the emulsion. Often these and other known methods for producing VAE copolymer latexes will provide an improvement in one or two properties, but at the expense of one or more other vital properties.

According to an emulsion copolymerization process

which is described in US patent literature (US patent application

) VAE copolymer latexes are produced by copolymerizing from 40% to 70% by weight of vinyl acetate with from 60 to

30% by weight of ethylene in an emulsion reaction medium containing a surfactant in an amount of from 1.0 to 2.0

% by weight of the total amount of monomer, a catalyst and a protective colloid, the entire amount of surfactant and vinyl acetate being added to the reaction medium in portions and during a certain time before and after the start of the copolymerization. The obtained VAE copolymer latexes, which are used as such as base materials for paints and other surface, coating preparations, such as adhesives, textile treatment agents and the like, have a high intrinsic viscosity, namely an intrinsic viscosity of at least 1.90, and give good results on curing^ the time test and the vinyl moisture test.

Such properties are particularly desirable in a VAE polymer latex. However, in the case of VAE elastomers for use in gummy teeth, as is the case here, it is other physical properties, particularly Mooney viscosity and gel content, which are most important when assessing the resin's usability.

The present emulsion copolymerization process

is a relatively simple method for the production of VAE elastomers with high Mooney viscosity and low gel content and which are ideally suited materials for the production of rubber-like objects that satisfy rather strict specifications. The terms "high Mooney viscosity" and "low gel content" refer to VAE elastomers having a Mooney viscosity at 100°C of from 30 ML (1+4) to 80 ML (1+4), preferably from 30 ML (1 +4) to 70 ML (1+4) and a gel content determined by measuring insoluble material in xylene at 80°C

of no more than 2% by weight, preferably no more than 1% by weight.

The method according to the invention is distinguished by the fact that

a) from 40 to 70% by weight vinyl acetate monomer is copolymerized with from 60-30% by weight ethylene monomer in a water

dig emulsion reaction medium for the production of a latex, which reaction medium for VAE elastomers contains:

(i) at least one surfactant in an amount of at least 2% by weight of the total amount of monomer, (ii) a polymerization catalyst, and (iii) at least one protective colloid in an amount of less than 1 part by weight per part by weight of the total amount of surfactant, the entire amount of the surfactant and vinyl acetate being present in the reaction medium at the beginning of the copolymerization, and

b) The VAE elastomer is recovered from the latex.

The recovery of the VAE elastomer from the latex can be carried out

by known methods, such as by coagulation of the elastomer,

by freezing the latex or by adding a coagulant amount of a salt, such as sodium chloride, to the latex and subsequent filtration of the coagulate. The VAE elastomer can then be subjected to further processing, e.g. cross-linking

or mixing with antioxidants, stabilizers, fillers, other modifying polymers, etc.

The amount of vinyl acetate monomer that is copolymerized with the ethylene monomer will vary from 40 to 70% by weight of the total monomer supply, the rest of the supply being made up of ethylene and, if desired, small amounts, i.e. up to 15%, of one or more other ethylenically unsaturated comonomers which does not exceed the amount of ethylene. Among such additional comonomers can be mentioned monoethylenically unsaturated aliphatic hydrocarbons, such as propylene and isobutylene, monoethylenically unsaturated substituted aliphatic hydrocarbons, such as vinyl fluoride, vinyl chloride, vinyl bromide, vinylidene fluoride, 1-chloro-1-fluoroethylene, chlorotrifluoroethylene and tetrafluoroethylene, unsaturated acids, such as acrylic acid, methacrylic acid, crotonic acid and itaconic acid, and polymerizable derivatives thereof, e.g. alkyl acrylates and methacrylates, such as methyl acrylates, ethyl acrylates, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, 1,6-hexanediol diacrylate and isobutyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, N-methylolaacrylamide, alkylated N-methylolacrylamides, such as N-methoxymethylacrylamide and N-butoxymethylacrylamide, and acrolein; aliphatic vinyl esters such as vinyl formate, vinyl propionate and vinyl butyrate; aliphatic vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and n-butyl vinyl ether; vinyl ketones, such as methyl vinyl ketone, ethyl vinyl ketone and isobutyl vinyl ketone; allyl esters of saturated mono-carboxylic acids, e.g. allyl acetate, allyl propionate and allyl lactate; and alkyl esters of monoethylenically unsaturated dicarboxylic acids, e.g. diethyl maleate, dibutyl maleate, dioct<y>lmaleate, dipropyl fumarate, dibutyl fumarate, dipctyl fumarate, dodecyl fumarate, dibutyl itaconate and dioctyl itaconate.

The surface-active agents that can be used in the method according to the invention are all the known and conventional surface-active agents and emulsifiers, mainly the non-ionic and anionic materials and mixtures of such that have hitherto been used in the emulsion copolymerisation of vinyl acetate and ethylene. A group of non-ionic surfactants that can be used have a water-insoluble polyoxyalkylene glycol core (where the glycol is not ethylene glycol) with a molecular weight higher than 900, which has been extended with water-soluble polyoxyethylene groups at each end. The water-soluble part of the molecule should make up at least 50% by weight of the molecule. The polyoxyalkylene glycol may be aliphatic, aromatic or alicyclic, it may be saturated or unsaturated, and it may be represented by the formula:

where x, y, m and n are whole numbers. When (CmHnO)x is saturated and aliphatic, n equals 2m.

Compounds in this class are described in US Patents 2,674,619 and 2,677,700.

The polyoxyalkylene compounds according to US patent document 2,674,619 which can be used in the method according to the invention, are defined by the formula:

where Y is the radical of an organic compound containing x active hydrogen atoms, n is an integer, and x is an integer greater than 1. The values of n and x are such that the molecular weight of the compound, disregarding E, is at least 900, determined by . the hydroxyl number. E is a polyoxyalkylene chain where the oxygen:carbon atomic ratio is at least 0.5. E constitutes at least 50% by weight of the compound. The polyoxyalkylene compounds according to US patent 2,677,700 which are applicable in the method are defined by the formula

where Y is the radical of an organic compound containing a single hydrogen atom with ability. to react with a 1,3-alkylene oxide, , R2, R^ and R^ are selected from hydrogen,

aliphatic radicals and aromatic radicals, at least one such substituent being a radical other than hydrogen; n is a number greater than 6.4 determined by the hydroxyl number, and X is a water-solubilizing group that is nonionic and constitutes at least 50% by weight of the total compound.

The compounds according to US Patent 2,674,619 are sold under the trade name Pluronic (BASF Wyandotte Corp.). The following are examples of compounds corresponding to the above formula:

Another group of surfactants that can be used have a water-insoluble core with a molecular weight of at least 900, which contains an organic compound with several reactive hydrogen atoms, which is condensed with an alkylene oxide other than ethylene oxide and has water-soluble groups at each end . The amount in % by weight of the hydrophilic part of the molecule should be at least 50. These ethylene oxide derivatives of an aliphatic diamine, such as ethylenediamine extended with propylene oxide, have the following formula:

Compounds in this class are described in US Patents 2,674,619 and 3,250,719 and are sold under the trademark "Tetronic" (BASF Wyandotte Corp.). The following are examples of compounds corresponding to the above formula:

Another useful group of nonionic materials are those sold under the trademark "Igepal" (GAF Corp. Chemical Products). These form a homologous series of alkylphenoxypoly-(ethyleneoxy)-ethanols which can be represented by the general formula:

where R denotes an alkyl radical and n denotes the number of moles of ethylene oxide used. Among these can be mentioned alkyl-phenoxypoly-(ethyleneoxy)-ethanols with alkyl groups containing from 7 to 18 carbon atoms and with 4 - 100 ethyleneoxy units, such as the heptylphenoxypoly-(ethyleneoxy)-ethanols, the nonylphenoxy-poly-(ethyleneoxy)-ethanols and the dodecylphenoxypoly-(ethyleneoxy)ethanols, the sodium or ammonium salts of the sulfate esters of these alkylphenoxypoly-(ethyleneoxy)ethanols; alkyl poly-(ethyleneoxy) ethanols; alkyl-poly-(propyleneoxy)-ethanols; octylphenoxyethoxyethyl-dimethylbenzylammonium chloride and polyethylene glycol tert.-dodecylthioether.

Other compounds in this class are ethylene oxide adducts of polyhydric alcohols extended with alkylene oxide, e.g. the materials sold under the Tween trademark

(ICI United States Inc.), ethylene oxide adducts of polyoxyalkylene esters of polyhydric acids, ethylene oxide adducts of polyoxyalkylene-extended amides of polyhydric acids, ethylene oxide adducts of polyoxyalkylene-extended alkyl, alkenyl-

and alkyny1-aminoalkanols, where the hydrophobic core should have a molecular weight of at least 900 and the hydrophilic part of the molecule should make up at least 50% by weight of the molecule's total weight. It will be understood that the above-mentioned organic compounds with several active

hydrogen atoms and the polyoxyalkylene glycols may be aliphatic, aromatic or alicyclic and may contain unsaturated bonds.

Among the many anionic surfactants that can be used in the process are Triton ^ X-200 (Rohm & Haas Co.), a sodium salt of an alkylaryl polyether sulfonate; Triton ® X-301 (Rohm&Haas Co.), a sodium salt of alkylaryl polyether sulfate; Triton ® QS-9 (Rohm&Haas Co.), a phosphate ester; "Alipal CO 433" (GAF), a sodium salt of sulfated nonylphenol-(ethyleneoxy)-ethanol; "Dupanol ME Dry" (DuPont),

a sodium lauryl sulfonate; Ultrawet (<R>) (Atlantic Refining Co.), an alkylaryl sulfonate; Sipon ESY (<S>) (Alcolac, Inc.), a sodium lauryl ethoxylate sulfate; and such. Sipon ESY (<R>), used as a 25.5% aqueous solution, has been shown to give particularly good results.

According to the invention, a protective colloid is incorporated into the aqueous emulsions. Such known and conventional protective colloids as the partially or fully hydrolyzed polyvinyl alcohols; cellulose ethers, e.g. hydroxymethylcellulose, hydroxyethylcellulose, ethyl-hydroxylethylcellulose and ethoxylated starch derivatives;

the natural and synthetic rubbers, e.g. gum tragacanth and gum arabic; polyacrylic acid and poly-(methylvinyl ether/maleic anhydride) are suitable for the purpose. The partially hydrolyzed polyvinyl alcohols, such as Gelvatol (^<r>) 20-30 (Monsanto), are particularly advantageous for use in the method according to the invention.

The catalysts used in the copolymerization reaction can be any of the known and con-

in conventional free-radical polymerization catalysts which have hitherto been used in the preparation of VAE copolymer latexes and comprise inorganic peroxides, such as hydrogen peroxide, sodium perchlorate and sodium perborate, inorganic

persulfates, such as sodium persulfate, potassium persulfate and

in ammonium persulfate, and reducing agents, such as sodium bisulfite. The catalyst (including reducing agent as co-catalyst, if such is used) is usually used in an amount of from 0.1 to 1% by weight of the total amount of co-monomers.

An alkaline buffering agent, such as sodium bicarbonate, ammonium bicarbonate, sodium acetate and the like, can be added to the aqueous system to maintain the pH value at the desired value. The amount of buffer is usually from 0.01 to 0.5% by weight, calculated on the amount of the monomer.

In order to obtain the VAE elastomers discussed here with high Mooney viscosity and low gel content, it has been found necessary to use an amount of surfactant that is at least 2.0% by weight of the total amount of monomer, and which can be

as large as 5.0% by weight of the total amount of monomer, although amounts in excess of this can also be used. Similarly, in order to achieve high Mooney viscosity and low gel content, it is necessary that the weight ratio between the protective colloid and the total amount of surfactant is lower than 1.1:1, preferably lower than 1:1. All of the surface-active agent and the entire amount of vinyl acetate monomer can be present in the polymerization medium from the start, in contrast to what is the case in other methods, where one or both of these components are added portionwise to the reaction medium during polymerization.

The temperature and pressure used in the present copolymerization reaction can be chosen within the ranges that have hitherto been used in VAE emulsion ion copolymerization. Consequently, temperatures from 21.1° to 71.1°C and pressures from 70.3 to 351.5 kg/cm2 can be used with good results. The person skilled in the art will understand that at the lower end of the temperature range it may be necessary to use a reducing agent to form the free radical required to initiate the copolymerization ring.

The VAE elastomer which is recovered from the latex obtained by the method according to the invention, preferably after being treated to remove residues of surfactant, protective colloid and other foreign substances, can then be cured with a cross-linking agent (vulcanizing agent), at the same time that it is optionally mixed with ingredients, such as fillers, antioxidants, modifying resins

(in an amount of from 10 to 40% by weight of the VAE copolymer), such as polyvinyl chloride, ethylene propylene rubber (EPR), polychloroprene,

polyacrylate rubber, polyurethane chlorinated polyethylene, polyester, ethylene propylene diene monomer (EPDM) terpolymer, ethylene methyl acrylate elastomers, ethylene butyl acrylate elastomers and acrylonitrile elastomers and other known additives for elastomers. The above-mentioned materials can be mixed with the VAE elastomer in conventional mixing equipment, e.g. in a two-roll rubber mill, in a mixing extruder or preferably in a mixer that produces high shear forces, such as a Banbury mixer, until a homogeneous mixture is obtained. When the mixing step is completed, the resin mixture is worked up into one of the many forms suitable for the subsequent manufacturing steps, e.g. for pellets in an underwater pelletizing machine, strings, etc.

The cross-linking agents which can be used in connection

with the invention, include peroxides such as tert-butyl perbenzoate, dicumyl peroxide; 2,5-dimethyl-2,5-di-(tert-butyl-peroxy)-hexane; 2,5-dimethyl-2,5-di-(tert.butyl-peroxy)-hexyn-

3; 1,3,5-tris-[α,α-dimethyl-α-(tert-butyl-peroxy)]-methyl-benzene; α,α-bis-(tert-butyl-peroxy)-diisopropylbenzene and n-butyl-4,4-bis-(tert-butyl-peroxy)-valerate. These cross-linking agents can be used alone or together with any of several multifunctional auxiliary cross-linking agents, such as triallyl phosphate; trimethylolpropane triacrylate;

diallylf umarate; triallyl cyanurate; triallyl isocyanurate; penta-erythritol-tetra acrylate; trimethylolpropane trimethacrylate;

1,3-butylene glycol dimethacrylate; allyl methacrylate; ethylene glycol dimethacrylate and 1,3-butylene glycol diacrylate. A preferred curing agent for use in the method,

(s)

is Vul-Cup 40 KE (40% dicumyl peroxide on calcium carbonate) from Hercules Inc. The amount of peroxide cross-linking agent can vary from 1.0 to 10.0 parts, preferably from 2.0 to 5.0 parts, per 100 parts EVA copolymer. The multifunctional auxiliary cross-linking agents can be used in amounts ranging from

0.1 to 3.0 parts per 100 parts EVA rubber base.

Examples of fillers that can be advantageously used,

is "Hydral 710", an aluminum trihydrate manufactured by Alcoa; "Hi-Sil EP" and "Hi-Sil 233", amorphous precipitated hydrated silicic acids manufactured by PPG Industries, Inc.;

® Corporation;

Cab-O-Sil, a fumed silica manufactured by Cabot Corporation;

Mistron Monomix, a talc (magnesium silicate) from the Cyprus Industrial Minerals Company; Burgess^KE, a surface-treated (silane-treated) calcined kaolin clay (anhydrous aluminum silicate) manufactured by the Burgess Pigment Company, and antimony oxide. The person skilled in the art will understand that the amounts of filler that can be incorporated into a polymer mixture obtained according to the invention will depend on the nature of the filler and on the properties desired in the finished product. Non-reinforcing fillers, such as aluminum oxide trihydrate, can be used in amounts from 5.0 parts to 400.0 parts, preferably in amounts from 100.0 parts to 150.0 parts, per 100 parts polymer blend. Reinforcing fillers, such as hydrated silicic acid, carbon black and sintered colloidal silicic acid, are applicable in the range from 5 parts to 100 parts per 100 parts polymer mixture, but the upper, practical range is limited by the high viscosity that fillers of this type promote. The preferred amounts of these reinforcing fillers are from 20 parts to 80 parts per 100 parts polymer mixture as far as hydrated silicic acid and carbon black are concerned, and from 10 parts to 50 parts per 100 parts polymer mixture as far as sintered colloidal silicic acid is concerned.

Any one of many conventional and conventional antioxidants may be incorporated into the polymer compositions obtained according to the invention in amounts of from 0.1 part to 4.0 parts, preferably in an amount of about 1.0 part per 100 parts resin. "Algerite MA" (R.T. Vanderbilt Company, Inc.), an antioxidant consisting of a polymerized trimethyldihydroquinoline, has been used with good results.

Among the following examples, where all percentages are calculated on a weight basis, examples 1 and 2 are comparative examples, while the other examples, which illustrate the invention, show the critical importance of the presence of both the protective colloid and the surface-active agent in the polymerization medium.

Example 1. (Comparison example)

This example shows that using a protective colloid alone produces a polymer with a high Mooney viscosity (higher than

30) but high gel content. The following solution was prepared:

(Salvatol ® 20-30 is a polyvinyl alcohol from the Monsanto Company, which is 87 - 89% hydrolyzed and has a viscosity of 4.7 - 5.4 cp

in 4% solution). The polyvinyl alcohol and bicarbonate were slurried in the water, and the mixture was stirred until all was dissolved. The solution was purged with nitrogen for 30 minutes, after which 0.04 g (4 ml of a 1% solution) of ferrous sulfate heptahydrate was added. The resolution was joined by:

Vinyl acetate 800 g

Ammonium persulfate 3.3 g dissolved in 50 ml water added to a 3.8 liter pressure reactor of stainless steel, equipped with externally placed electric heating elements, an internal cooling coil and a stirrer. The reactor was then purged with nitrogen to remove all oxygen. The charge

was heated to 48.9°C. During the heating phase, the reactor was stirred at 670 rpm. minute, and ethylene was added until a pressure of 175.8 kg/cm 2 was reached. When the reaction conditions with regard to pressure and temperature were reached, . the polymerization was started by adding 2 g of sodium bisulphite dissolved in 65 ml of water. The temperature and pressure of the reactor were kept constant during the experiment. The polymerization was considered complete 7.5 hours after the addition of the bisulfite, at which time the consumption of ethylene ceased. The emulsion was cooled to room temperature, after which the polymer was coagulated from the emulsion by freezing the latex. The coagulated polymer was then dried in an air-circulated oven at 48.9°C.

A vinyl acetate/ethylene copolymer was obtained with

the following properties:

Example 2 (comparison example)

This example shows that the use of one or more surfactants as the only dispersant gives a . polymer with low Mooney viscosity (less than 30) and low gehnhold. After back-purging with nitrogen, the following solution was added to the reactor described in Example 1:

Together with this solution, the following materials were added to the reactor:

The polymerization was carried out in the manner described in example 1.

The polymer was coagulated from the emulsion by there

while stirring, a warm, saturated solution of sodium chloride was added. The coagulated polymer was washed four times with water and then dried in an air-circulated oven at 48.9°C. The obtained vinyl acetate/ethylene copolymer had the following properties:

Example 3

This example shows that using a combination of protective colloid and surfactants as dispersants gives a polymer with a high Mooney viscosity and low gel content. After blowing through with nitrogen, the following solution was added to the reactor described in example 1:

Together with this solution, the following was added to the reactor:

The polymerization was started with 1.08 g of sodium bisulphite dissolved in 35 ml of water. The remaining part of the experiment was carried out as indicated in Example 1. The polymer was recovered from the emulsion by coagulation of the latex with sodium chloride as described in Example 2.

The obtained vinyl acetate/ethylene copolymer had the following properties:

Although the combination of polyvinyl alcohol and surfactants used in this example, based on previous experience, would be expected to result in high or low values for both Mooney viscosity and gel content, or at best intermediate values of these in the copolymer product, showed surprisingly, the Mooney viscosity remained at a desirable level, while the gel content actually decreased. In subsequent examples (e.g. examples 4 and 5)

it is shown that the occurrences of gel can be practically eliminated, while achieving a desirable Mooney viscosity, by the correct selection of the quantity ratio between the protective colloid and the surface-active agent(s).

Example 4

This example shows that the ratio between the concentration of the protective colloid and the concentration of the surface-active agent or agents used as dispersant in example 3 can be varied within certain limits, without this affecting to any significant extent the desirable properties of the polymer with regard to high Mooney viscosity and low gel content. The following solution, after being blown through with nitrogen, was added to the reactor described in example 1:

Along with this solution, the reactor was fed:

The polymerization was started with 25 ml of a 3% sodium bisulphite solution. Every hour, a further 10 ml of this solution was then pumped into the reactor. Six such additions were made. The remaining part of the experiment was carried out as described in Example 1. The polymer was recovered from the latex as described in Example 2.

The obtained vinyl acetate/ethylene copolymer had the following properties:

Example 5

In this example, a different quantity ratio was used between the protective colloid and the surfactant(s). The following solution, after being blown through with nitrogen, was added to the reactor described in example 1:

Along with this solution, the reactor was added:

The experiment was carried out in the same way as in example 1, with 2 g of sodium bisulphite dissolved in 65 ml of water being used to start the polymerization. The polymer was recovered from the latex using the method described in Example 2.

The obtained vinyl acetate/ethylene copolymer had the following properties:

Example 6

This example shows that the incorporation of tert-butyl alcohol in the polymerization medium does not have any significant effect on the properties of the polymer. After blowing through with nitrogen, the following solution was added to the reactor described in example 1:

Along with this solution, the reactor was fed:

Since man. proceeded as described in example 1, the polymerization was started with 2 g of sodium bisulphite solution in 65 ml of water. Every two hours, a further 20 ml of this solution was then pumped into the reactor. Three such additions were made.

The polymer was recovered from the latex using the method described in example 2.

The following vinyl acetate/ethylene copolymer was obtained:

Example 7

This example shows the use of a higher total concentration of surfactant. The following solution was, after being blown through with nitrogen, added to the reactor described in example 1:

Along with this solution, the reactor was fed:

The polymerization was started with 25 ml of a 3% sodium bisulphite solution. Then every hour a further 10 ml of this solution was pumped into the reactor. Six such additions were made. The remaining part of the experiment was carried out as described in example 1. The polymer was recovered from the latex as described in example 2. The vinyl acetate/ethylene cppolymer obtained had the following properties:

Example 8

This example shows the further processing of the elastomers obtained according to the invention, and the products thereby obtained. The VAE copolymers prepared in Examples 3, 4, 6 and 7 were evaluated as elastomeric products. A VAE copolymer elastomer obtained by a commercial high-pressure process (Vynathene EY-907 from US

.Industrial Chemicals Co., with approx. 60% vinyl acetate content)

was used as standard. For the purposes of this evaluation, the elastomers were mixed according to the following recipe:

Mixing was done in a 152.4 mm x 304.8 mm (6"x2") two-roll rubber mill. The composite material was then cured into 152.4 mm x 152.4 mm x 1.9 mm (6"x6"x0.075") plates in an ASTM mold. The plates were pressed at a pressure of 140 kg/cm at a temperature of 202° C. for 5 minutes.The results of the investigation are given in Table I.

Example 9

This example shows that the VAE elastomers obtained according to the invention can cured resins with properties such as elongation and low temperature brittleness (material III),

which is better than for the resins available in the trade. Under

using the reaction medium and the polymerization conditions described in example 7, several portions of elastomer were produced. The obtained elastomers were mixed. and then cured using different amounts of curing agent and using an additive in the mix recipe. The mixture had the following characteristics: Content of vinyl acetate 62.5%

Mooney viscosity, ML() at 100°C 37.5

Vynathene ® EY-907 was used as a standard. The resin produced according to the invention and the commercial elastomer were mixed as indicated in Table II:

The quantity is stated in parts per 100 parts resin. The products were mixed and cured as previously indicated. The results of the survey are listed in Table III below.

Example 10

This example shows that the method according to the invention is not limited to the use of a single catalyst system. Thus, the Redox catalyst system ammonium persulfate/sodium formaldehyde sulfoxylate will reduce the polymerization time compared to ammonium persulfate/sodium bisulfite, while still achieving a fully satisfactory copolymer.

After being purged with nitrogen, the following solution was added to the reactor described in Example 1:

Together with this solution, the following was added to the reactor:

A 0.25% aqueous solution of sodium formaldehyde sulfoxylate was prepared and added to the catalyst feed vessel. Following the procedure described in example 1, the reactor was heated and pressurized with ethylene. When the reactor conditions with regard to temperature and pressure (48.9°C, 175.8 kg/cm 2 ) were reached, the polymerization was started by pumping the reducing agent solution to the reactor. The flow rate was set at approx. 40 ml per hour. The polymerization was considered complete when ethylene consumption ceased, which occurred 6 hours after the addition of the reducing agent began.

The polymer was recovered from the emulsion by coagulation of the latex with sodium chloride as described in Example 2.

The obtained VAE copolymer had the following properties:

. Example 11

This example shows the use of the ammonium persulfate/sodium hydrosulfite catalyst system.

The reactor described in example 1 was supplied with the same solution, persulphate and vinyl acetate, as that indicated in example 10. A 1.5% aqueous solution of sodium hydrosulfite was prepared and added to the catalyst feed vessel.

The reactor was heated and pressurized as described in Example 1. When the reactor conditions with regard to temperature and pressure (48.9°C, 175.8 kg/cm<2>) were reached, the polymerization was started by pumping the reducing agent solution to the reactor. The flow rate was set at approx. 60 ml per hour. The polymerization was considered to

be complete when ethylene consumption ceased, which occurred 5 hours after the addition of the reducing agent had begun.

The polymer was recovered from the emulsion by coagulation

of the latex with sodium chloride as described in example 2.

The obtained VAE copolymer had the following properties:

Example 12

This example shows the use of acrylic acid as a thermonomer and the associated production of a polymer which had a higher Mooney viscosity, without, however, having had its gel content increased.

The reactor described in example 1 was fed to the i

example 10 described resolution.

Together with this solution, the following was added to the reactor:

A 0.25% aqueous solution of sodium formaldehyde sulfoxylate was prepared and added to the catalyst feed vessel.

The reactor was heated and pressurized as described in example 1. When the reaction conditions with respect to temperature and pressure had been reached, the polymerization was started by pumping the reducing agent solution to the reactor. The flow rate was set at approx. 45 ml per hour. The polymerization was considered complete 6.5 hours after the addition of the reducing agent was started. The polymer was recovered from the emulsion by coagulation of the latex with sodium chloride as described in Example 2.

The vinyl acetate/ethylene acrylic acid terpolymer obtained had the following properties:

Example 13

A vinyl acetate/ethylene-1,6-hexanediol diacrylate terpolymer with an unexpectedly low gel content and which provided improved cured elastomers was prepared. The following solution was prepared:

The polyvinyl alcohol, the Pluronic ® material and the sodium acetate were slurried in the water. The mixture was stirred for approx. 1.5 hours, until all components were completely dissolved. The solution was purged with nitrogen for 30 minutes, after which the Sipon ESY ® material and the ferrous sulfate heptahydrate (1% aqueous solution) were added. The resolution was.

together with

Vinyl acetate

1,6-hexanediol diacrylate

Ammonium persulphate 3.3 g dissolved in 50 ml of water added to a 3.8 liter stainless steel pressure reactor equipped with externally arranged electric heating elements,

an internal cooling coil and a stirrer. The reactor was then purged with nitrogen to remove all oxygen from the system. The reactor contents were heated to 48.9°C. During the heating, the reactor was stirred at 670 rpm. minute, and the ethylene was added until a pressure of 175.8 kg/cm 2 was reached. The polymerization was then started by adding 30 ml of

a 3% sodium bisulphite solution. Every hour it was like that

pumped another 10 ml of this solution into the reactor.

Six such additions were made. The reaction temperature

and the pressure was kept constant during the experiment. The polymerization was considered complete when ethylene consumption ceased, which occurred 7.5 hours after the first addition of sodium bisulfite.

The polymer was coagulated from the emulsion by the stirring addition of a warm, saturated sodium chloride solution.

The coagulated polymer was then washed four times with hot

water and dried in an air-circulated oven at 48.9°C.

This method was used during several runs, where increasing concentrations of 1,6-hexanediol-diacrylate were used.

The amounts of vinyl acetate and 1,6-hexanediol diacrylate

which was used during each experiment, is indicated in the table IV below.

Table V below provides a summary of the properties of the polymers produced in these experiments.

The produced polymers were subjected to evaluation as elastomeric products. A commercial VAE copolymer elastomer (ynathene® EY-907, Table III) was used as a standard. In order to carry out this evaluation, the resins were mixed and cured according to the method indicated in example 8. The results of the evaluation are given in table VI.

It will be seen that the terpolymer elastomers exhibit

great elongation, while the cured rubbers have improved resistance to loss of tensile strength during aging at 176.7°C. This combination of properties is surprising, as the diacrylate monomer, which is a cross-linking monomer, would be expected to reduce the elongation of the material.

Claims (12)

1. Procedure for the production of elastomers • vinyl acetate-ethylene copolymers with high Mooney viscosity and low gel content, in which vinyl acetate monomer is copolymerized with ethylene monomer in an aqueous emulsion reaction medium containing surfactant, polymerization catalyst and protective colloid, characterized by that a) from 40 to 70% by weight vinyl acetate monomer is copolymerized with from 60-30% by weight ethylene monomer. in an aqueous emulsion reaction medium for the production of a latex, which reaction medium for VAE elastomers contains: (i) at least one surfactant in an amount of at least 2% by weight of the total amount of monomer, (ii) a polymerization catalyst, and (iii) at least one protective colloid in an amount that is less than 1 part by weight per part by weight of the total amount of surfactant, the entire amount of the surfactant and vinyl acetate being present in the reaction medium at the beginning of the copolymerization, and b) The VAE elastomer is recovered from the latex. 2. Method according to claim 1, characterized in that the Mooney viscosity at 100 oC is from 30 ML(1+4) to 80 ML(l+4). 3. Method according to claim 2, characterized in that the Mooney viscosity at 100°C is from 30 MLU+4) to 70 ML (1 + 4). 4. Method according to claims 1-3, characterized in that the gel content measured by insolubility in xylene at 80°C is at most 2%. 5. Method according to claim 4, characterized in that the gel content, measured by insolubility in xylene at 80°C, is at most 1%. 6. Process according to claims 1-5, characterized in that during the copolymerization an additional ethylenically unsaturated monomer is used in an amount of up to 15% by weight of the total monomer supply, this amount not exceeding the amount of ethylene. 7. Method according to claim 6, characterized in that 1,6-hexanediol diacrylate is used as the further ethylenically unsaturated monomer. 8. Method according to claims 1-7, characterized in that a non-ionic polyalkyleneoxy material is used as surfactant. 9. Method according to claims 1 - 7, characterized in that an alkali metal sulfate of an aliphatic ether is used as surface-active agent. 10. Method according to claims 1-9, characterized in that a partially hydrolyzed polyvinyl alcohol is used as protective colloid. 11. Elastomer vinyl acetate/ethylene copolymer, characterized in that it has a Mooney viscosity at 100°C from 30 ML(1+4) to 80 ML(1+4), preferably from 30 ML(1+4) to 70 ML(1+4) and a gel content , measured by insolubility in xylene at 80°C, of no more than 2%, preferably no more than 1%, and that it can be produced by a method as stated in claims 1-10. 12. Elastomer vinyl acetate/ethylene copolymer according to claim 11, characterized in that it is also cross-linked.