IE43835B1 - Production of dispersions of polyvinyl acetate - Google Patents

Abstract

1517067 Production of polyvinyl acetategrafted-PVA dispersions ANIC SpA 23 June 1976 [24 June 1975] 26003/76 Heading C3P An aqueous dispersion of polyvinyl acetate in which the polyvinyl acetate is grafted on to a polyvinyl alcohol, is prepared by polymerizing vinyl acetate in aqueous dispersion in the presence of (a) at least one peroxide and/or persulphate, (b) a reducing agent comprising at least one mono- and/or dicarboxylic acid, (c) an acetate and/or sulphate of an element of Group VIII of the Periodic Table, (d) a bicarbonate and/or an acetate of an alkali and/or alkaline earth metal and (e) polyvinyl alcohol or a partially esterified polyvinyl alcohol; component (d) being added throughout the polymerization. An optional additional component is a modifier which is an aldehyde with a boiling point under 70‹ C. or an ester of a butyl alcohol with a boiling point above 150‹ C. Specific examples of component (b) are formic acid, tartaric acid, maleic acid and oxalic acid. Preferred Group VIII elements for the salt of component (c) are Fe and Co. Specific optional modifiers are propionaldehyde, acetaldehyde, crotonaldehyde, butyraldehyde, and butyl glycolate. The dispersions are used as adhesives.

Description

This invention relates to a process for producing polyvinyl acetate dispersions and the dispersions obtained thereby. For example, this invention relates to a process for producing polyvinyl acetate adhesives in the form of high-viscosity aqueous dispersions containing extremely fine polymer particles, using low amounts of protective colloid and without the need to use surfactants.

Polyvinyl acetate dispersiorsare widely used as adhesives for wood, paper and paper-boards, and for the preparation of composites of leather, sawdust, cork and textile fibres. Usually, the dispersions are produced by polymerization in the presence of a water-soluble protective colldid such as gum Arabic, methyl cellulose, gelatin, starch, polyvinylpyrrolidone and polyvinyl alcohol. Usually, in commercial practice, an emulsifying system is also used, which system is constituted by (a) polyvinyl alcohol, as the protective colloid, in an amount of from 5% to 10% by weight of the total dispersion, the polyvinyl alcohol being obtained by alkaline alcoholysis of polyvinyl acetate, and containing from 80 to 90 mol per cent of vinyl alcohol units and having a block distribution of its acetoxy groups, and (b) an anionic or non-ionic surfactant in an amount of from 0.5% to 1.5% by weight. Polyvinyl alcohol obtained by acidic alcoholysis of polyvinyl acetate, containing from 80 to 90 mol per cent of vinyl alcohol groups and having a random distribution of its acetoxy groups, is not used in general, because the dispersions obtained with this kind of polyvinyl alcohol have very poor rheological and adhesive properties.

As a rule, the polyvinyl acetate dispersions intended for adhesives are required to have a high viscosity for ease of practical application. High viscosities are obtained according to the known art by increasing the amount of protective colloid. However, such dispersions have a high cost and adhesive properties which are not always acceptable, such as a slow setting speed and a long open time. In addition, the protective colloid reduces the resistance of the film to water.

For these reasons, it is desirable to keep at the lowest possible level the concentration of the colloid to be used, but, by so doing, low-performance dispersions are obtained, the dispersions tending to agglomerate after a long storage time, exhibiting a low viscosity and a limited resistance to mechanical and heat stresses, and the size of the polymer particles being high.

The use of surfactants results in the formation of polymer particles which are small on average and have a narrow particle size distribution, but the dispersions have a low viscosity and poor adhesion properties.

It is apparent that the selection of the emulsifier-protective colloid system to be used is of fundamental importance, both from the point of view of rheological behaviour and of economy.

The initiators which are most commonly used in the production of polyvinyl acetate dispersions are water-soluble and free-radical producing substances such as ammonium and potassium persulphate and hydrogen peroxide. 43335 Oxidation-reduction systems are often used to give shorter reaction time5:. These systems usually comprise HgOg together with zinc formaldehyde sulphoxylate, or with iron chloride and ascorbic acid, or with ammonium persulphate and sodium bisulphate, or with tert.butyl hydroperoxide and zinc formaldehyde sulphoxylate.

The dispersions obtained in the commercial practice, however, contain particles having a size o£ the order of magnitude of 5,000 to 50,000 ft units (that is a wide particle size distribution and a very high particle size.) Also, the dispersions have 1θ a limited resistance to mechanical and thermal stresses, poor resistance to storage, and adhesive power which does not exceed 130 kg/cm , and a comparatively high cost due to their high content of protective colloids.

According to the present invention, there is provided a process for producing a dispersion of polyvinyl acetate, which process comprises polymerizing vinyl acetate in an aqueous dispersion in the presence of (a) an oxidizing agent comprising at least one peroxide and/or. persulphate, (b) a reducing agent comprising at least one mono- and/or dicarboxylic acid, (c) an acetate and/or a sulphate of an element of Group VIII of the Periodic Table, (d) a bicarbonate and/or an acetate of an alkali metal and/or alkaline earth metal, and (e) polyvinyl alcohol or partially esterified polyvinyl alcohol, component (d) being added throughout the polymerization. *3335 The dispersions obtained by the process of the invention usually have a polymer particle diameter not exceeding 12,000 Angstrom units, a ratio of the minimum to the maximum particle size of not less than 1:6, a content of dry solids of from 35% to 60% by weight, a viscosity of up to 50,000 centipoises, and an 2 adhesive power greater than 180 kg/cm .

In a preferred embodiment of the invention, a modifier selected from aldehydes having a boiling point under 70°C and esters of butyl alcohols having a boiling point above 150°C is additionally present during the polymerization.

The oxidizing agent preferably comprises HgOg or a persulphate, especially ammonium persulphate, an alkali metal persulphate or an alkaline earth metal persulphate. The reducing agent preferably comprises formic acid, tartaric acid, maleic acid or oxalic acid.

The acetate and/or sulphate of an element of Group VIII is preferably an acetate and/or sulphate of iron or cobalt, and the bicarbonate and/or acetate of an alkali metal and/or alkaline earth metal is preferably a bicarbonate and/or acetate of sodium or potassium. The modifier, when used, is preferably propionaldehyde, acetaldehyde, crotonaldehyde, butyraldehyde or butyl glycolate.

The polyvinyl alcohol or the partially esterified polyvinyl alcohol, for example partially esterified polyvinyl alcohol obtained by acidic or alkaline alcoholysis of a polyvinyl ester, is preferably used in an amount of from 1 to 5% by weight based on the total weight of the dispersion.

The bicarbonate and/or acetate of an alkali metal or an alkaline-earth metal is preferably added intermittently or continuously during polymerization. This is a surprising aspect of the process according to the invention, in which, conversely, all the other components may be added to the reactor all at once. The amount of bicarbonate and/or acetate used is preferably from 0.05 to 0.5% by weight based on the weight of monomer.

The acetate and/or sulphate of the element of GrouD VIII of the Periodic Table is preferably used in an amount of from 0.001 to 0.005% by weight based on the weight of monomer.

The polyvinyl alcohol or partially esterified polyvinyl alcohol used according to the present invention bonds to the polyvinyl acetate by a grafting reaction with the vinyl acetate.

The procedures to be followed for characterizing the dispersions are reported below. Such procedures were followed when testing the products of the following Examples which illustrate the present invention, apart from Example 1 which is included for comparative purposes.

CHARACTERIZATION PROCEDURES 1 - Particle Size The particle size of the polyvinyl acetate dispersion and the distribution of the particle size are examined with the aid of a microscope having a graduated eyepiece, the dispersion having previously been diluted with water.

- Adhesive power The resistance to unsticking is determined on glued maple samples The test is performed on a tensile testing machine.

- Resistance to freezing and thawing The sample is introduced in a programmed-cycle thermostatic cell.

Usually there are five cycles, which range from - 12°C to + 20°C. Every cycle lasts 12 hours. On completion of each cycle, the viscosity of the dispersions is measured.

- Mechanical stability The test aims to detect viscosity decreases attributable to rapid stirring, shear stresses, twists, laminations and compression. The products are subjected to vigorous stirring by means of a turbodisperser, at 1,500 rpm. After a 24-hour stay, the viscosity is determined.

- Measurement of the sediment The dispersion is diluted with water and then filtered through a sieve having meshes of 0.15-mm opening. The value is expressed in milligrams per kilogram (mg/kg).

- Resistance to accelerated storage The dispersion is kept in an oven at 50°C for 30 days . and the initial and the final viscosities are compared.

- Viscosity The viscosity is measured at 20° C with a HAT Brookfield Viscometer at a speed of 20 rpm. The readings are expressed in centipoises.

- SoTids The percentage of dry matter is determined after having dried 5 the dispersion in an oven at 200°C for 15 to 20 minutes, - pH The readings are taken at 20°C on a pH-meter.

EXAMPLE 1 (for comparison).

Water 1,200 grams Partially esterified polyvinyl alcohol obtained by alkaline alcoholysis of a polyvinyl ester 115 grams Sodium dodecylbenzensulphonate 6. 5 grams Vinyl acetate 1,250 grams Hydrogen peroxide (35%) 25 grams A stainless steel reactor equipped with an anchor-shaped stirrer rotated at 100 rpm and a reflux condenser, was charged with water, the polyvinyl alcohol, the sodium dodecylbenzenesulphonate which had been previously dissolved in the water, the hydrogen peroxide and 450 grams of the vinyl acetate. The mixture was heated to 68°C and polymerisation was carried out whilst feeding in the remaining vinyl acetate over a period of 4 hours. During polymerization the reaction temperature was maintained in the range of from 68°C to 70°C. -££835 Characerization Solids Viscosity PH Sediment Adhesive power Freeze-thaw cycles Particle size Mechanical stability Storage resistance EXAMPLE 2 Water Partially esterified polyvinyl alcohol obtained by alkaline alcoholysis of a polyvinyl ester Vinyl acetate Sodium peroxide Formic acid Manganese acetate Ammonium persulphate Sodium bicarbonate Acetaldehyde (as modifier) 50.3% 3,400 cps 4.35 150 ppm (parts per million) 135 kg/cm2 thickened at second cycle % at about 50,000 8 70% “ 30,000 % 10,000 A . a few clumps, bad bad 1,200 grams grams 1,250 grams grams grams 0.1 grams 2 grams grams grams 900 Grams of the water were mixed with the polyvinyl alcohol which had been previously dissolved, the sodium peroxide, the formic acid, the manganese acetate, the ammonium persulphate, the acetaldehyde, and 250 grams of the vinyl acetate. The mixture was heated to 68°C and polymerization was carried out whilst feeding in the balance of the vinyl acetate, the balance of the water and the sodium bicarbonate, over a period of 3 hours.

During polymerization, the temperature was maintained in the range 75 - 80°C.

Characterization Solids Viscosity pH Sediment Adhesive power Freeze-thaw cycles 49.9% 27,000 cps 4.75 ppm 198 kg/cm2 Particle size unaltered % at about 10,000 8 90% “ 5,000 I Mechanical stability Storage resistance no clumping Extremely good Extremely good Water EXAMPLE 3 1,400 grams Partially esterified polyvinyl alcohol obtained by alkaline alcoholysis of a polyvinyl ester grams Vinyl acetate % Hydrogen peroxide 900 grams 28 grams 43S3S Tartaric acid 8 grams Cobalt acetate 0.16 grams Potassium persulphate 2 grams Sodium bicarbonate 21 grams Butyl acetate 63 grams The procedure was the same as in Example 2, with 500 grams of the water, 600 grams of the vinyl acetate and the sodium bicarbonate being fed in during polymerization. The reaction temperature was 75 - 80°C.

Characterization Solids 36.3% Viscosity 30,500 cps PH 4.75 Sediment 28 ppm Adhesive power 191 kg/cm2 Freeze'thaw cycles unaltered 20% at about 10,000 X Particle size -1 80% “ 5,000 8 no clumping Mechanical stability Extremely good Storage resistance Extremely good EXAMPLE 4 Water 900 grams Partially esterified polyvinyl alcohol obtained by acidic alcoholysis of a polyvinyl ester 25 grams 35% Hydrogen peroxide 14 grams Potassium persulphonate Ferrous sulphate 2.2 grams 0.15 grams Butyl butyrate 29 grams Vinyl acetate 1,500 grams Maleic acid 13 grams Sodium acetate 23 grams procedure was as in Example 2. 75 - 85°C. The reaction temperature Characterization Solids 60.7% Viscosity 33,000 cps PH 4.65 Sediment 37 ppm Adhesive power 206 kg/cmZ Freeze-thaw cycles unaltered Particle size f 100% at about 5,1 | no clumps Mechanical stability Extremely good Storage resistance Extremely good EXAMPLE 5 Water 1,000 grams Partially esterified polyvinyl obtained by acidic alcoholysis polyvinyl ester alcohol of a 71 grams Vinyl acetate 1,350 grams Sodium peroxide 19 grams Tartaric acid 12 grams Cobalt acetate 0.11 grams Ammonium persulphate 7 grams Crotonaldehyde 18 grams Sodium bicarbonate 18 grams The procedure was the same as for Example 3. The reaction temperature was 75 - 85°C. o u Characterization Solids 53.3% Viscosity 41,500 cps PH 4.7 Sediment 52 ppm Adhesive power 200 kg/cm2 Freeze-thaw cycles unaltered Particle size £ 100% at about 3,000 no clumping Mehanical stability Extremely good Storage resistance Extremely good EXAMPLE 6 Water 1,200 grams Partially esterified polyvinyl alcohol obtained by alkaline alcoholysis of a polyvinyl ester 75 grams Vinyl acetate 1,250 grams 35% Hydrogen peroxide 22 grams Formic acid 12 grams Cobalt acetate 0.33 grams Potassium persulphate 1.5 grams NaHCOj 30 grams 900 Grams of the water were charged into the reactor, together with the previously dissolved polyvinyl alcohol, the hydrogen peroxide, the formic acid, the cobalt acetate, the potassium persulphate and 250 grams of the vinyl acetate. The mixture was heated to 68°C and polymerization was carried out whilst feeding in the balance of the vinyl acetate, the balance of the water and the NaHCOg over a period of 3 hours. During polymerization the temperature was maintained at about 75 - 80°C.

Characterization Solids Viscn-ity pH Sediment Adhesive power Freeze-thaw cycles Particle size Resistance to mechanical stresses Storage resistance 50.1% 37,000 cps 4.75 ppm 198 kg/cm2 unaltered o % at about 10,000 A 90% » 5,000 X a few clumps Fair - viscosity decreased by 25% Extremely good EXAMPLE 7 Water 1,400 grams partially esterified polyvinyl alcohol obtained by alkaline alcoholysis of a polyvinyl ester 100 grams Vinyl acetate 900 grams 35% Hydrogen peroxide 28 grams Formic acid 12 grams Cobalt acetate 0.33 grams Potassium persulphate 1.3 grams NaHC03 22 grams The procedure was the same as for Example 2, with 500 grams of water, 600 grams of the vinyl acetate and the NaHCOg being continuously fed in during polymerization. The reaction temperature was 75 - 85°C.

Characterization Solids Viscosity PH Sediment Adhesive power Freeze-thaw cycles Particle size 36.3% ,500 cps 4.74 28 ppm 191 kg/cm2 unaltered o % at about 5,000 A 80% 3,000 8 a few clumps Resistance to mechanical stresses Good Storage resistance Good EXAMPLE 8 Water 1,400 grams Partially esterified polyvinyl alcohol obtained by alkaline alcoholysis of a polyvinyl eiter 115 grams Vinyl acetate . 900 grams 35% Hydrogen peroxide 31 grams Formic acid 12 grams Cobalt acetate 0.33 grams Potassium persulphate 1.3 grams NaHC03 22 grams Butyl glycolate 50 grams The procedure was the same as that of Example 3. The reaction temperature was 75-85°C. 4S83S Characterization Solids Viscosity pH Sediment Adhesive power Freeze-thaw cycles Particle size Resistance to mechanical stresses Storage resistance EXAMPLE 9 Water Partially esterified polyvinyl aTcohol obtained by alkaline alcoholysis of a polyvinyl ester Vinyl acetate % Hydrogen peroxide Formic acid Cobalt acetate Potassium persulphate NaHC03 Propionaldehyde procedure was the same 'C - 85°C. as for Example 2. .9% 31,000 cps 4.65 37 ppm 206 kg/cm2 unaltered 100% at about 3,000 A no clumps Extremely good - no viscosity changes Very good - no viscosity changes 1,200 grams grams 1,250 grams grams 12 grams 0.33 grams 1.3 grams 30 grams 10 grams The reaction temperature ϊ 8 3 5 Characterization Solids Viscosity pH Sediment Adhesive power Freeze-thaw cycles Particle size 50.5% 24,000 cps 4.7 ppm 203 kq/cm2 unaltered o % at about 5,000 A 90% 3,000 8 no clumps Resistance to mechanical stresses Extremely good - viscosity unaltered Storage resistance EXAMPLE 10.

Extremely good - viscosity unaltered Water 1,250 grams Partially esterified polyvinyl alcohol obtained by alkaline alcoholysis of a polyvinyl ester 79 grams Vinyl acetate 35% Hydrogen peroxide Formic acid Cobalt acetate Potassium persulphate NaHCOg Butyl glycol ate 1,250 grams 27 grams 12 grams 0.33 qrams 1.3 grams grams 50 grams The procedure was the same as for Example 2. The reaction temperature was 75-85°C.

S δ 3 5 Characterization Solids Vise 'y pH Sediment Adhesive power Freeze-thaw cycles Particle size 49.9% 31,000 cps 4.7 ppm 195 kg/cm2 unaltered % at about 5,000 8 95% 3.000 8 Resistance to mechanical stresses Storage resistance no clumps Extremely good - viscosity unaltered Extremely good - viscosity unaltered EXAMPLE 11 Water 1,200 grams Partially esterified polyvinyl alcohol obtained by alkaline alcoholysis of a polyvinyl ester 84 grams Vinyl acetate 1,250 grams 35% Hydrogen peroxide 27 grams Formic acid 12 grams Cobalt acetate 0.33 grams Potassium persulphate 1.5 grams Sedium acetate 40 grams Propionaldeh.vde 10 grams The procedure was the same as for Example 2, the sodium acetate being continuously fed in during polymerization. The reaction temperature was 75 - 85°C. 4S835 Characterization Solids Viscosity pH Sediment.

Adhesive power Freeze-thaw cycles Particle size Resistance to mechanical stresses Storage resistance 50.7% 24,500 cps 4.55 78 ppm 188 kg/cmZ thickens at the fourth cycle % at about 10,000 8 % ” 7,000 A 60% 5,000 8 no clumps Extremely good - viscosity unaltered bad EXAMPLE 12 Water 1,200 grams Partially esterified polyvinyl alcohol obtained by alkaline alcoholysis nf a polyvinyl ester 43 grams Partially esterified polyvinyl alcohol obtained by acidic alcoholysis'of a polyvinyl ester 43 grams Vinyl acetate 1,250 grams % Hydrogen peroxide Formic acid Cobalt acetate Potassium persulphate Propionaldehyde NaHC03 The procedure was the same temperature was 75-85°C. 26.5 grams grams 0.33 grams 1.5 grams grams 27 grams as for Example 2. The reaction 2 8 3 5 Characterization Solids Viscosity PH Sediment '’•'hesivp —wer Freeze-thaw cycles Particle size Resistance to mechanical stresses Storage resistance 50.8% 26.500 cps 4.75 ppm 2C4 kg/cm2 unaltered % at about 5,000 8 90% 11 3,000 A no clumps Extremely good - viscosity unchanged » Extreme!·' good EXAMPLE 13 Water 800 grams Partially esterified polyvinyl alcohol obtained by acidic alcoholysis of a polyvinyl ester 69 grams Vinyl acetate % Hydrogen peroxide Formic acid Cobalt.acetate Potassium persulphate Propionaldehyde NaHCt^ The procedure was the same temnerature was 75 - 85°C1,250 grams grams 12 grams 0.33 grams 1.5 grams grams 22 grams as for Example 2. The reaction Characterization Solids Viscosity OH Sediment Adhesive power Frepze-thaw cvcles 60% ,500 cps 4.8 ppm 207 kg/cm2 unaltered 4383S Particle size Resistance to mechanical stresses Storage resistance EXAMPLE 14 Water Partially esterified polyvinyl alcohol obtained by acidic alcoholysis of a polyvinyl ester Vinyl acetate % Hydrogen peroxide Formic acid Cobalt acetate Potassium persulphate NaHCOg Butyl glycol ate o 100% at about 3,000 A, no clumps Extremely good - no viscosity changes good 800 grams grams 1,250 grams 26 grams 12 grams 0.33 grams 1.5 grams 22 grams 50 grams The procedure was the same as for Example 2. 15 was 75 - 85°C.

The reaction temperature Characterization Solids Viscosity PH Sediment Adhesive power, Freeze-thaw cycles Particle size Resistance to mechanical stresses Storage resistance 60.5% 29,500 cps 4.7 52 ppm 200 kg/cm2 unaltered f 100% at about 3,000 X L no clumps Extremely good - viscosity unchanged good.

Claims (14)

1. A process for producing a dispersion of polyvinyl acetate, which process comprises polymerizing vinyl acetate in an aqueous disp?. /on i; „..e presence of (a) an oxidizing agent comprising at least one peroxide and/or persulphate, (b) a reducing agent comprising at least one mono- and/or dicarboxylic acid, (c) an acetate and/or sulphate of Group VIII of the Periodic Table, (d) a bicarbonate and/or an acetate of an alkali metal and/or alkaline earth metal, and (e) polyvinyl alcohol or partially esterified polyvinyl alcohol, component (d) being added throuohout the polymerization.

2. A process according to claim 1, wherein a modifier selected from aldehydes having a boiling point under 70°C and esters of butyl alcohols having a boiling point above 150°C is additionally present during the polymerization.

3. A process according to claim 2, wherein the modifier is propionaldehyde, acetaldehyde, crotonaldehyde or butyraldehyde.

4. A process according to claim 2, wherein the modifier is butyl glycol ate.

5. A process according to any preceding claim, wherein component (e) is partially esterified polyvinyl alcohol obtained by acidic alcoholysis of a polyvinyl ester.

6. A process according to any preceding claim, wherein the peroxide is hydrogen peroxide.

7. A process according to any preceding claim, wherein the persulphate is selected from ammonium persulphate and the persulphates of the alkali metals and alkaline earth metals. 4Ξ835

8. A process according to any preceding claim, wherein the monoor dicarboxylic acid is selected from formic acid, tartaric acid, maleic acid and oxalic acid.

9. A process according to any preceding claim, wherein the element 5 of the Group VIII of the Periodic Table is selected from iron and cobalt.

10. A process according to any preceding claim, wherein the alkali metal is selected from Na and K.

11. A process according to any preceding claim, wherein the component (d) is fed continuously or intermittently throughout the polymerization. 10

12. A process according to claim 1, substantially as described in any one of the foregoing Examples 2 to 14.

13. A dispersion of polyvinyl acetate, whenever produced by a process according to any preceding claim.

14. A polyvinyl acetate dispersion having polymer particle diameter 15 not exceeding 12,000 Angstrom units, a ratio of the minimum to the maximum particle size of not less than 1:6, a content of dry solids of from 35% to 60% by weight, a viscosity of up to 50,000 centipoises, and an adhesive power greater than 180 kg/cm .