GB2079760A - Aqueous terpolymer emulsion - Google Patents

Abstract

An emulsion of a terpolymer of ethylene, vinyl chloride and vinyl acetate is produced by using monomers at ratios of (a) 5 to 30 wt.% of ethylene (b) 10 to 50 wt.% of vinyl chloride and (c) 30 to 80 wt.% of vinyl acetate and polymerizing monomers in the presence of a water soluble copolymer of methacrylic acid or a salt thereof and an ethylenically unsaturated sulfonic acid or a salt thereof in an amount of 0.5 to 6 wt.% based on the total monomers. The terpolymer emulsion has excellent storage stability and antifoamability and can form a film having excellent water resistance and alkali resistance without any external plasticization

Description

SPECIFICATION Process for producing emulsion of terpolymer BACKGROUND OF THE INVENTION: FIELD OF THE INVENTION: The present invention relates to a process for producing an emulsion of a terpolymer. More particularly, it relates to a process for producing an emulsion of a terpolymer of ethylene-vinyl chloride-vinyl acetate having excellent storage stability and antifoamability which can form a film having excellent water resistance and alkali resistance without any external plasticization.

DESCRIPTION OF THE PRIOR ARTS: Vinyl acetate type emulsions have been well known. The polymers for the vinyl acetate type emulsion have usually high secondary transition point and have not a membrane formability at room temperature. In order to impart the membrane formability at room temperature, it is indispensable to incorporate a plasticizer such as dioctyl phthalate.

When the polymer is externally plasticized with a plasticizer, the plasticizer is a lower molecular compound having certain volatility whereby the plasticized polymer has inferior water resistance and alkali resistance and a film made of the plasticized polymer is easily deteriorated because of a migration of the plasticizer.

In a production of a known vinyl acetate type emulsion, vinyl acetate-ethylene emulsion or vinyl acetate-vinyl chloride type copolymer emulsion, an anionic, cationic or nonionic surfactant is usually used. The surfactant is incorporated in the emulsion to further deteriorate characteristics of water resistance and alkali resistance of the film formed by it. In order to improve the disadvantages, it has been proposed to provide a process for producing an emulsion of a copolymer of vinyl acetate and vinyl chloride in the presence of a water soluble copolymer of methacrylic acid or a salt thereof and an ethylenically unsaturated sulfonic acid or a salt thereof instead of the surfactant (B.P. 1,488,561). The adverse effect of the external plasticization can not be eliminated by such improvement.

It has been also known to use a protective colloid such as polyvinyl alcohol or cellulose ether in an emulsion polymerization of a vinyl acetate type emulsion such as an emulsion of vinyl acetate or vinyl acetate and ethylene. When such protective colloid is used, coarse particles are formed for the emulsion and the resulted product is not suitable for a paint. When a large amount of the protective colloid is used, an emulsion of fine particles can be obtained, however as the same as the result of the use of the surfactant, the film made of the emulsion incorporates a protective colloid to have inferior characteristics of water resistance and alkali resistance.

It has been known to produce an emulsion of a terpolymer of ethylene, vinyl chloride and vinyl acetate in the presence of a nonionic surfactant such as polyoxyethylenephenyl ethers and polyoxyethylenesorbitan esters; or an anionic surfactant such as sodium laurylsulfate and sodium dodecylbenzenesulfonate so as to overcome said disadvantages caused by an external plasticization. (U.S.P. 3,632,542).

In accordance with this process, the copolymer having a low secondary transit point can be obtained and accordingly, an emulsion of the polymer which does not require any external plasticization is obtained. However, when an amount of the surfactant is small, coarse particles are formed as the emulsion and the emulsion is unstable in the storage stability to be undesirable for forming a film. In order to form fine particles and to increase the stability of the emulsion, the amount of the surfactant should be increased. When the amount of the surfactant is increased, the foam is formed in the resulting emulsion. As a result, pinholes are formed in the film made of the emulsion to lose a surface gloss and to lose the water resistance and alkali resistance. When the formation of the foam is severe, the use of an antifoaming agent is sometimes required.The use of the antifoaming agent together with the surfactant causes deterioration of the characteristics of the resulting film. The improvement of the problem is required.

SUMMARY OF THE INVENTION: It is an object of the present invention to provide a process for producing, an emulsion of a terpolymer having fine particles which need not externally plasticized, even though a surfactant is not used.

The foregoing and other objects of the present invention have been attained by providing a process for producing an emulsion of a terpolymer of ethylene, vinyl chloride and vinyl acetate by using monomers at ratios of (a) 5 to 30 wt.% of ethylene, (b) 10 to 50 wt.% of vinyl chloride and (c) 30 to 80 wt.% of vinyl acetate and polymerizing the monomers in the presence of a water soluble copolymer obtained by a copolymerization of methacrylic acid or a salt thereof and an ethylenically unsaturated sulfonic acid or a salt thereof at a ratio of 0.5 to 6 wt.% based on the total monomers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS: The ratios of the monomer components for the terpolymers in the present invention are (a) 5 to 30 wt.% preferably 10 to 25 wt.% of ethylene; (b) 10 to 50 wt.% preferably 1 5 to 40 wt.% of vinyl chloride and (c) 30 to 80 wt.% preferably 35 to 75 wt.% of vinyl acetate. When the ratios are out of said ranges, the secondary transition point of the terpolymer for the emulsion is changed to lose the membrane formability at room temperature or to deteriorate the mechanical strength of the film.

The water soluble copolymer used in the process of the present invention can be obtained by copolymerizing methacrylic acid or a salt thereof and an ethylenically unsaturated sulfonic acid or a salt thereof.

The ethylenically unsaturated sulfonic acid or a salt thereof which is copolymerized with methacrylic acid or a salt thereof to form the water soluble copolymer can be a sulfonated unsaturated hydrocarbon such as sulfonated ethylene, allylsulfonic acid, methacrylsulfonic acid and a salt thereof. In view of easy availability, it is preferable to use p-styrenesulfonic acid, sodium salt thereof, 2-acrylamide-2-methylpropanesulfonic acid or sodium salt thereof. The ratio of methacrylic acid or a salt thereof to the ethylenically unsaturated sulfonic acid or a salt thereof is preferably in a range of 60:40 to 90:10 by weight. The polymerization degree of the water soluble polymer need not to be strictly limited.It is usual to use the water soluble polymer having an intrinsic viscosity [77 = 0.3 to 0.7 at 30"C in 1 N-NaCI aqueous solution. It is selected depending upon a desired practical viscosity in the field of the application of the emulsion.

An amount of the water soluble polymer is in a range of 0.5 to 6 wt.% preferably 1 to 4 wt.% based on the total monomer components of the terpolymer for the emulsion. When it is too small, a stable emulsion is not obtained whereas when it is too much, the water resistance of the film made of the emulsion is deteriorated.

A conventional emulsion polymerization is employed for the polymerization in the present invention. That is, a water soluble peroxide such as hydrogen peroxide, potassium peroxide and ammonium peroxide is used as a polymerization initiator. It is also to use the water soluble peroxide with a small amount of a reducing agent such as sodium thiosulfate, sodium sulfite, sodium hydrogen sulfite, ascorbic acid, Rongalit, Mohr's acid.

The polymerization initiator is usually added at a ratio of 0.05 to 8 wt.% based on total monomer components.

A temperature and a pressure in the polymerization are selected as desired depending upon a formulation of the terpolymer especially an ethylene content. In the process of the present invention, the temperature is usually in a range of 10 to 1 00 C preferably 40 to 80"C and the pressure is usually in a range of 5 to 500 kg/cm2 preferably 10 to 100 kg/cm2.

As it is clearly found in the following examples, in accordance with the process of the present invention, it is unnecessary to give any external plasticization and the particles of the terpolymer are fine and the emulsion of the terpolymer having excellent stability without a foaming is obtained. Such emulsion of the fine particles has an improved pigment bonding force and accordingly, a content of a pigment can be increased by using the emulsion as the binder.

When a film is formed by using the emulsion obtained by the process of the present invention, the film substantially has not a pinhole and has excellent surface gloss and excellent characteristics such as water resistance, alkali resistance and weatherbility.

The present invention will be further illustrated by certain examples and references which are provided for purposes of illustration only and are not intended to be limiting the present invention.

In the examples and references, the terms "%" and "part" respectively designate "% by weight" and "part by weight" and water purified by a treatment with cationic and anionic ion exchange resins was used.

EXAMPLE 1: Five kinds of water soluble copolymers of sodium p-styrenesulfonate (NASS) and methacrylic acid (MAA) having the following formulations were respectively prepared.

Copolymer I II Ill IV V MAA/NASS 50/50 70/30 80/20 90/10 100/0 In a 1 liter three necked glass flask equipped with a stirrer, 100 wt. parts of water was charged and the flask was purged with nitrogen gas and heated at 80"C and then, an aqueous solution of 1 wt.part of ammonium peroxide in 100 wt.parts of water and an aqueous solution of 100 wt.parts of each monomer mixture (NASS/MAA) in 200 wt.parts of water were respectively fed dropwise during 3 hours from each different dropping funnel to polymerize the monomers and the polymerization was continued for 1 hour and the reaction mixture was cooled to obtain the copolymer (I). The other copolymers (Il)-(V) were respectively produced under the same condition except changing a formulation of a monomer mixture.The resulting solution of the polymer was diluted with water to use it for the following emulsion polymerization.

The charges used for each emulsion polymerization were as follows.

Charge Charged parts Water soluble polymer 3.5 (I, II, Ill, IV or V) Potassium hydrogen carbonate 0.6 Water 165 Vinyl acetate 100 Vinyl chloride 48 Ammonium persulfate 1 Sodium persulfite 1 Ethylene 50 kg/cm2 Into 131 wt.parts of water, 3.5 wt.parts of water soluble polymer was dissolved and the solution was charged in a reactor and 11 wt.parts of vinyl acetate was added. The reactor was purged with ethylene and heated to maintain 60"C and an aqueous solution of ammonium persulfate dissolved in 5 wt.parts of water was added and ethylene was fed to maintain the ethylene pressure of 50 kg/cm2. Vinyl acetate and vinyl chloride were fed during 4 hours and an aqueous solution of sodium persulfite in 29 wt.parts of water was fed during 6 hours into the reactor by each pump.The ethylene pressure was maintained to 50 kg/cm2 during the reaction and the reaction mixture was continuously stirred for 6 hours.

Diameters of particles of each terpolymer in each emulsion were measured as an average diameter by light-scattering photometer method. The results are as follows.

Viscosities of the emulsions (Brookfield viscometer: 12 r.p.m. 25"C) are also shown.

Water soluble polymer I II Ill IV V Viscosity S-L Sep. 2800 2350 3600 S-L Sep.

(c.p.) X X Average diameter of particle (mix) X 180 1 50 1 70 X Note: X: it can not be measured S-L Sep.: solid-liquid separation As the results, when the water soluble polymer (I) or (V) was used, the particles of the terpolymer were agglomerated into a mass in the way of the emulsion polymerization or a final stage thereof. On the other hand, when the water soluble polymer (if), (III) or (IV) was used, each emulsion having a low viscosity which contains fine particles of the terpolymer was obtained. Each film of the terpolymer obtained from each emulsion were analyzed to find the formulation of ethylene:vinyl acetate:vinyl chloride of 16:2:56.3:27.4.

EXAMPLE 2: A surface tension, a foamability, a storage stability, a freezing-melting stability and a chemical stability of the emulsion obtained by using the water soluble polymer Ill of Example 1 and a water resistance of a film made of the emulsion by a flow spreading method.

The conditions for measurements are as follows. Surface tension: The emulsion was diluted with water to give 10% of solid content and the surface tension was measured by an electrosurface tension meter manufactured by Kyowa Kagaku K.K. Foamability: The foamability was evaluated from heights of foams (mm) just after dropping the emulsion and after 5 minutes in standstill by Ross-miles Test.

Storage stability: The emulsion was treated by a centrifugal separator manufactured by Hitachi Seisaku Sho K.K. under the condition of 1000 G for 3 hours and the supernatant and the precipitate were weighed to evaluate it.

Freezing-melting stability: The emulsion was freezed and melted by a cycle of - 5"C: 4 hours/room temperature: 20 hours for 3 times and a formation of agglomerate was observed to evaluate it.

Chemical stability: The emulsion was diluted to 100 times and 50 ml. of 10% aqueous solution of aluminum sulfate was added dropwise to 25 ml of the diluted emulsion and an aggregate was observed to evaluate it.

Water resistance of film made by flow-spreading method: A film having a thickness of 0.5 mm and a size of 2 x 2 cm made of the emulsion was dipped in water at 25"C for 24 hours and a weight increase of the film was measured to evaluate it.

REFERENCE 1: In accordance with the process of Example 1 except using 0.7 wt.part of sodium dodecylbenzenesulfonate (Nansa SS60) and 2.8 wt.parts of polyoxyethylenenonylphenol ether (Akropal N 300) instead of the water soluble polymer of NASS and MAA, an emulsion polymerization was carried out.

A viscosity of the resulting emulsion and a particle diameter and a formulation of the terpolymer were measured by the methods in Example 1. The results are as follows.

Formulation of terpolymer: ethylene:vinyl acetate:vinyl chloride = 16.5:56.1:27.4 Viscosity of emulsion: 2870 c.p.

Particle diameter: 400 mp The formulation and the viscosity were substantially the same as those of Example 1, however the particle diameter was about 3 times of that of Example 1. The other characteristics (surface tension, foamability, storage stability, freezing-melting stability, chemical stability and film water resistance) were also evaluated as Example 2. The result is shown in Table 1.

The foamability, the storage stability and the film water resistance of Reference were inferior to those of the present invention.

Table 1 Physical property Example 2 Reference 1 Surface tension (dyne/cm) 69.0 35.3 Foamability just after 67 110 5 5 min later 12 107 Storage stability (g/100 g emulsion) Supernatant 0 4 Precipitate 0 4 Freezing-melting stability good good Chemical stability none none Water resistance of film (%) 1 3 28 The emulsion of Example 2 had high surface tension, substantially non-foamahility, high storage stability and forms a film having high water resistance.

EXAMPLE 3: In accordance with the process of Example 1 except using a water soluble polymer (A/B = 70/30) obtained by polymerizing 2-acrylamide-2-methylpropanesulfonic acid, sulfopropyl methacrylate or sulfoethyl methacrylate instead of NASS as B component and methacrylic acid as B component, each emulsion polymerization was carried out. As a result, in all of the emulsion polymerizations, the emulsions of each terpolymer having similar formulation, viscosity and particle diameter to those of Example 1 were obtained.

The other characteristics of the emulsions were also excellent similar to those of Example 2.

EXAMPLE 4: In accordance with the process of Example 1 except using 107 wt.parts of vinyl acetate and 41 wt.parts of vinyl chloride, an emulsion polymerization was carried out under the same condition. As the result of Example 1, each fine emulsion having a low viscosity was obtained by using each water soluble polymer of MAA and NASS at each ratio of MAA/NASS of 70:30; 80:20; or 90:10.

According to an analysis of a film made of each emulsion, the product was a terpolymer having ratios of ethylene/vinyl acetate/vinyl chloride of 17.7:61.5:20.8 by weight. The other characteristics of the emulsions were also excellent similar to those of Example 2.

EXAMPLE 5: In accordance with the process of Example 1 except using 1 22 wt.parts of vinyl acetate and 30 wt.parts of vinyl chloride and feeding ethylene under an ethylene pressure of 39 kg/cm2, an emulsion polymerization was carried out under the same condition. As Example 1, each fine emulsion having a low viscosity was obtained by using each water soluble polymer of MAA and NASS at each ratio of MAA/NASS of 70:30; 80:20; or 90:10.

According to an analysis of a film made of each emulsion, the product was a terpolymer having ratios of ethylene/vinyl acetate/vinyl chloride of 14.0:70.5:15.3 by weight. The other characteristics of the emulsions were also excellent similar to those of Example 2.

Claims (9)

1. A process for producing an emulsion of a terpolymer of ethylene, vinyl chloride and vinyl acetate which comprises using monomers at ratios of (a) 5 to 30 wt.% of ethylene (b) 10 to 50 wt.% of vinyl chloride and (c) 30 to 80 wt.% of vinyl acetate and polymerizing monomers in the presence of a water soluble copolymer obtained by a copolymerization of methacrylic acid or a salt thereof and an ethylenically unsaturated sulfonic acid or a salt thereof at a ratio of 0.5 to 6 wt.% based on the total monomers.

2. The process according to Claim 1 wherein said ethylenically unsaturated sulfonic acid or salt thereof is a sulfonated unsaturated hydrocarbon or salt thereof.

3. The process according to Claim 1 wherein said ethylenically unsaturated sulfonic acid or salt thereof is p-styrene-sulfonic acid or sodium salt thereof.

4. The process according to Claim 1 wherein said water soluble polymer is incorporated at a ratio of 1 to 4 wt.% based on the total monomers.

5. The process according to Claim 1 wherein the ratios of the monomers are 10 to 25 wt.% of ethylene, 1 5 to 40 wt.% of vinyl chloride and 35 to 75 wt.% vinyl acetate.

6. The process according to Claim 1 wherein a ratio of methacrylic acid or a salt thereof to the ethylenically unsaturated sulfonic acid or a salt thereof is in a range of 60:40 to 90:10 by weight.

7. The process according to Claim 1 wherein an intrinsic viscosity [ of said water soluble polymer is in a range of 0.3 to 0.7 in 1 N-NaCI aqueous solution at 30"C.

8. The process according to Claim 1 wherein said polymerization is initiated with a polymerization initiator with or without a small amount of a reducing agent.

9. The process according to Claim 1 wherein said polymerization is performed at 10 to 100"C under a pressure of 5 to 500 kg/cm2.

1 0. A process according to Claim 1 substantially as herein described with reference to any one of the Examples.