GB2230786A - Emulsion polymerisation of vinyl alkanoates - Google Patents

Abstract

Vinyl C1 to C3 alkanoate is polymerised in an emulsion containing polyvinyl alcohol with seed latex added in at least two stages during polymerisation. The resultant emulsion polymers are of value in adhesives where fast setting times are obtained. Ethylenic hydrocarbons, eg ethylene, may form up to 30% by weight of monomers.

Description

TITLE: EMULSION POLYMERISATION FIELD OF THE INVENTION: The invention relates to aqueous polymer emulsions suitable for use in packaging adhesive applications and having vinyl C1 to C3 alkanoates, especially vinyl acetate, as the major component.

BACKGROUND TO THE INVENTION: Adhesive compositions, especially those intended for use in preparing packaging materials, are required to have specific properties which are exemplified by fast setting times and low shear thinning to allow these compositions to be used on machinery adapted for coating and hence joining large areas of paper or similar cellulosic material on a high speed mechanised basis. The present invention is specifically directed to the preparation of polymer compositions in which vinyl C1 to C3 alkanoates form the sole or a major component and the emulsion polymerisation is stabilised by an effective amount of polyvinyl alcohol. Other vinyl alkanoates which are usable are vinyl propionate.Optionally the vinyl alkanoate copolymer may include other monomer feedstocks for example dibutyl maleate, acrylic acid and longer chain length vinyl alkanoates, eg. Versatates.

For copolymers of vinyl C1 to C3 alkanoate, preferably vinyl acetate, and ethylene the level of the alkanoate will usually be at least about 70% by weight.

The invention extends to copolymers including a third or additional monomers; in these formulations the level of alkanoate may be below 70% of the total but it would still form at least about 70% by weight of the alkanoate and ethylenic hydrocarbon total.

GENERAL DESCRIPTION OF THE INVENTION: The invention provides a process of preparing an aqueous emulsion of vinyl C1 to C3 alkanoate polymer optionally copolymerised with up to about 30% by weight C2 to C4 ethylenic hydrocarbons in which vinyl alkanoate is polymerised in the presence of polyvinyl alcohol with seed latex being added in at least two stages during polymerisation. Ethylene is the preferred ethylenic comonomer but propylene, butylene and isobutene are also usable. Preferably the seed latex is added in an amount up to about 38 by weight (dry) on the dry weight of total copolymerisable monomers.

An effective amount of the seed latex will be added at each stage, but preferably at least about 0.58 by weight (dry) of seed latex based on dry weight of total copolymerisable monomers is added at each stage. The process is particularly advantageous in providing usable products having a solids content of at least about 65% weight.

Preferably the additions of seed latex are made after at least about 10% of the copolymerisable monomers have been added and up to about 50% , more preferably below about 40%. In the example described additions were made at 20% and 30%.

Methods for the preparing the copolymer emulsions of the invention are well characterised in the literature.

Polymer Synthesis (vols I and II) by Sandler & Karo (Academic Press 1974) and Preparative Methods of Polymer Chemistry (2nd Ed) by Sorenson & Campbell (Interscience 1968) provide preparative information. Methoden der Organischen Chemie (Houben-Weyl) Band XIV published by Georg Thieme Verlag Stuttgart (1961) also provides preparative descriptions.

TEST METHODS: i) The solids content of the resultant latex emulsion was measured by heating a ca 1g sample at 1200C in an oven for 1 hour.

ii) Particle size distribution was measured by a Joyce Loebel disc centrifuge.

iii) Viscosity was measured using a Brookfield viscometer at 250C.

iv) The speed of setting of the emulsion is tested by measuring the bonding speed between two paper sheets. A layer of emulsion 0.1 mm deep is placed on a paper sheet held on a large glass plate and a sample of high standard paper, for example Mellowtex smooth hi-white paper placed over the adhesive and pressed on to it by the aid of a roller. The top sheet was then peeled back at the rate of 10 mm per second with an angle of peel as close as possible to 1800. The fibre tear time (FTT) in seconds was measured at the point when a crease occurred in the top layer of the paper in the direction of peel. This time indicates the point when the adhesive has set sufficiently to provide a bond between the two paper surfaces. The test is sufficiently reproducible to demonstrate differences in adhesives which would effect the commercial processes.

This test is an accepted method of comparing adhesive properties but the absolute values are dependent on the operator.

v) The time required for the adhesive emulsion to provide a satisfactory packaging flap joint is measured as the flap joint time (FJT) in seconds. A sheet of Invercote D paper is attached to a flat metal area with its smooth side exposed. A layer of emulsion 0.004" deep is spread on the paper over an area 10 cm by 2.5 cm and a second sheet of paper placed with its smooth side in contact with the emulsion. A metal sheet is then placed over the area with a weight of 1 Kg applied.

After a period has elapsed following spread of the adhesive the weight is removed and the adhesive joint tested by applying a low separating force perpendicular to the bond area. The time in seconds to develop a satisfactory joint is noted.

EXAMPLE: This example describes the preparation and use of a vinyl acetate homopolymer latex.

Water (25g) and polyvinyl alcohol powder (4g) were charged to a reaction vessel (0.75 litres). The polyvinyl alcohol was hydrolysed to 88% and had a low molecular weight, it is obtainable from Nippon Gohsei of Japan under the trade name Gohsenol GL05. This solution was then heated to 700C to 750C with stirring and held there for 1 hour. The solution was then cooled to 600C and solution A and ferric chloride (5ppm Fe3+) added in turn, stirring continued for a further 5 minutes.

A. sodium bicarbonate ..................... 0.284g nonylphenol 50.E0 ...................... 0.5g water .................................. 2.752g Then vinyl acetate (100Kg) was added continuously over 5 hours together with solutions B and C which were each added over 5 hours.

B. hydrogen peroxide (35%) ............... 0.813g water .................................. 6.497g C. sodium formaldehyde sulphoxylate ...... 0.244g water ................................. 7.062g The reaction mass was allowed to exothern to 700C to 720C as rapidly as possible and maintained at this temperature during polymerisation.

A seed latex comprising a vinyl acetate copolymer (502 non volatiles) had been prepared previously. This polymer was surfactant stabilised and employed a thermal initiation. Particle size analysis on a Joyce Loebel disc centrifuge gave a uniform and narrow distribution with a peak diameter of 0.15 micron. 60 minutes after the continuous additions had commenced 3.050g of the seed latex (1% on vinyl acetate) was added rapidly, i.e. over a period considerably below 5 minutes. After 90 minutes from commencement of continuous additions a further 2.030g of seed latex (18 on vinyl acetate) was added rapidly.

When all additions had been completed the temperature was allowed to rise to 750C and held there for 60 minutes.

The mass was then cooled to 600C, solutions D and E added and held for 30 to 45 minutes before cooling.

D. t-butyl hydroperoxide ................... 0.305g water ................................... 0.423g E. sodium formaldehyde sulphoxylate ........ 0.203g water ................................... 0.423g Example III repeated Ex I replacing 25% of the low MW polyvinyl alcohol with a medium MW polyvinyl alcohol obtainable from Nippon Gohsei under the trade name Gohsenol GM14. The process characteristics followed those of Example I except where shown.

Comparative Example II followed the conditions of Example I but without addition of seed latex and comparative Example IV added 2.5% by weight seed latex in a single addition after 60 minutes.

The results are given in Table I.

The addition of seed latex at two points during polymerisation, which is performed in the presence of polyvinyl alcohol, provides an emulsion with relatively high solids content and usable low viscosity.

Additionally the emulsion has particular favourable adhesive properties for use in packaging.

TABLE I PROCESS FEATURE/ EXAMPLE I II* III IV* Seed latex added 60 mins 1.5% nil 1.5% 2.5% 90 mins 1.0% nil 1.0% nil Stabiliser low MW 4% 4% 3% 4% high MW nil nil 1% nil Properties: Solids content 69.8 NM 65.1 69.9 (% non volatile) Viscosity in Poise 86 NM 25 520 Peak particle sizes 0.58 NM 0.7 1.0 in micron 1.1 1.8 3.0 1.7 FTT (secs) 11 NM 11 NM FJT (secs) 6 NM 12 NM * Comparison examples.

NM Not measured because product not suitable for test.

Example II solidified after 3 hours reaction.

Example IV was dilatant.

Claims (7)

CLAIMS:

1. A process of preparing an aqueous emulsion of vinyl C1 to C3 alkanoate polymer, optionally copolymerised with up to about 30% by weight of C2 to C4 ethylenic hydrocarbon, in which the vinyl alkanoate is polymerised in the presence of polyvinyl alcohol with seed latex being added in at least two stages during polymerisation.

2. A process according to claim 1 wherein the seed latex is added in an amount up to about 3% by weight (dry) based on the total copolymerisable monomers.

3. A process according to claim 1 or 2 wherein the vinyl alkanoate is vinyl acetate.

4. A process according to claim 1 or 2 or 3 wherein the ethylenic hydrocarbon is ethylene.

5. A process according to any preceding claim wherein the seed latex is added in an amount of at least about 0.58 by wt. based on the dry weight of total copolymerisable monomers at each stage.

6. A process according to any preceding claim wherein the process provides a product emulsion having a solids content of at least about 65% by weight.

7. The aqueous emulsion obtained by the process claimed in any preceding claim.