CA1195038A

CA1195038A - Carboxylated latex

Info

Publication number: CA1195038A
Application number: CA000426470A
Authority: CA
Inventors: Prakash Mallya
Original assignee: Polysar Ltd
Current assignee: Polysar Ltd
Priority date: 1983-04-25
Filing date: 1983-04-25
Publication date: 1985-10-08
Also published as: IT8467416A0; FR2544721B1; JPH0233042B2; US4780503A; NL8401294A; FR2544721A1; NO162912B; NL190072B; DE3415453C2; SE460970B; GB2138830A; FI841567A; NL190072C; US4657966A; CH660597A5; ES8507586A1; FI80053B; SE8402182D0; SE8402182L; NO162912C

Abstract

CARBOXYLATED LATEX
Abstract of the Disclosure A high solids latex of a functional monomer may be prepared by emulsion polymerization of the monomer charge to a specified overall conversion and then introducing an additional micelle forming surfactant or a unimodal seed latex and continuing the polymerization.

Description

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Polymeric material in aqueous dispersions are finding a wide range of applications ln a number of diverse fields. Latices of polymers containing functional groups are becoming increasingly popular as the polymer may be tailored to specific end use applications. Such latices tend to be stable and are less subject to particle agglomeration than non-Eunctional polymers which do not contain stabilizing functional groups. It is uneconomical to subject latices of polymers containing functional groups to conventional techniques which make it possible to increase the polymeric solids content of the latex above about 55 per cent. This presents a number of drawbacks inc]uding the cost of shipping and costs of removal of water from the latex compound in the manuEacture of products.
Additionally, at a polymeric solids content of about 55 per cent, latices of polymers containlng Eunctional groups tend to have a relatively high viscosity. This presents a drawback in the application of ~0 such latices in coating compositions as the viscosity of the composition should usually be low.
United States Patent 3,637,563 issued January 25, 1972, to Christena, assigned to the Celanese Corporation discloses a process for the manufacture of high solids acrylate latices. In the process, a pre-emulsion is made. The pre-emulsion is a water in hydrocarbon emulsion. The present invention does not require the use oE such pre-emulsion.
British Patent 1,l91,G49 published May 13~ 1970, in the name of the Celanese Corporation discloses a process wherein a high solicls vinyl acetate latex is produced by polymerizing a monomer emulsion in water in the presence of a minimum amount of surfactant and catalyst to form a relatively large par~icle size latex.

- 2 -At about 50 to gO per cent conversion, additiona]
surfactant is added to further sta~ilize the latex originally formed. The present process contempla-tes the addition of the surfactant to create a new population of particles.
United States Patent 4,130,523 issued December 19, 1978, to Hoy et al, ass;gned to Union Carbide teaches a process for producing a high solids latex which requires the continuous withdrawal of a portion of the partially polymerized emulsion and adding fresh monomer dispersion.
In tlle final step the withdrawn emulsion is returned to the reaction vessel. The present patent application does not require the withdrawl or cycling of partially polymerized monomer dispersion.
In theory, the method for increasing the solids content of a latex is to improve the degree of packing oE
the polymer particles. If the latex contains only particles of a relatively large uniform size, there are significant voids between the polymer particles which can now be filled with smaller particles.
Tbe object of the prior art patents, and the present patent is to produce a high solids latex having a low viscosityr To do this, one must create a bimodal or polydisperse particle size distribution ;n the latex cluring polymerization. In the prior art, when ]atices of different particle sizes were blended and concentrated, solicls :Levels could be increased when the diameters of the large particles was about 1600 A and the diameters of the small p&rtîcles was about 900 A. The weight ratio of large to small particles was in the range of ahout 70:30 to 75:25.
The applicant has found it possible to directly produce a latex having a bimodal particle distribution by the introduction of additional micelle forming surfactant

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or unimodal seed particles into the emulsion being polymerized~ This avoids subsequent steps of blending and concentrating the latex.
The present invention provides a process for the synthesis of a latex having a viscosity of less than about 3000 cps and a bimodal particle size distribution so that from about 65 to 85 per cent by weight of the polymer particles have a diameter of from about 1700 A to about 3000 A and from about 35 to 15 per cent by weight of the polymeric particles have a diameter of from about 300 A to about 1000 A by the polymerization of an emulsion containing from about 50 to about 75 parts by weight of water per 100 parts by weight of nonvolatiles comprising nonmonomeric additives and a mixture of ethylenically unsaturated monomers containing from about 0.5 to 10 parts by weight per 100 parts by weight of monomers of a monomer frorn the group comprising C3_6 ethylenically unsaturated acids, aldehydes, ketones and amides which may be unsubstituted or substituted by a Cl_4 alkyl group or a Cl_4 alkanol group; or a mixture thereof and from 0 to 25 parts by weight per 100 parts by weight of a Cl 8 alkyl or alkanol ester of a C3_6 ethylenically unsaturated acid; which comprises nucleating polymer particles in the emulsion and polymerizing the monomer therein to an overall conversion of from about 40 to 60 weight per cent and then introducing either (a) from about 0.75 to 2~0 additional parts by weight of a micelle ~orming surEactant per 100 parts by weight of tota]
monomer, or (b) from about 2.5 to 4.5 parts by weight per 100 parts of monomer of a unirnodal seed latex having a particle size of from about 275 A to about 400 A, and continuing the polymerization substantially to completion.
The present invention also provides a latex containing from about 58 to 65 per cent by weight of

4 _ polymeric solids of ethylenically unsaturated monomers containing from about 0.05 to 10 per cent by weight of the polymeric solids of the residue of a C3-6 ethylenically unsaturated acid, aldehyde ketone or amide which may be unsubstituted or substituted by a C1-4 alkyl or alkanol group, and from 0 to 25 per cent by weight of a C1-8 alkyl or alkanol ester of a C3-6 ethylenically unsaturated acid, or a mixture thereof which at a polymeric solids content of about 61 per cent by weight has a viscosity of less than about 3000 cps. and has a bimodal particle size distribution so that from about 65 to 85 per cent by weight of the polymer particles have a diameter of from about 1700 A to about 3000 A and from about 35 to 15 per cent by weight of the particles have a diameter of from about 300 A to about 1000 A.
The large diameter particles will have a particle size of from 1700 A to 3000 A and the small particles will have a particle size of from about 400 A to about 1000 A.
Preferably from about 65 to 80 per cent by weight of the latex particles have a diameter of from about 1800 A to about 2100 A and from about 35 to 20 per cent by weight of the particles have a diameter of from about 450 A to about 650 A.
The methods of emulsion polymerization are well known in the art. There are many texts, papers and publications dealing with conventional methods of emulsion polymerization. Useful reference texts discussing emulsion polymerization techniques include:
"High Polymer Latices" by D. C. Blackley, 1966 MacLaren & Sons Limited, London (Chapter 5);
"Synthetic Rubber" by G. S. Whitby, John Wiley &
Sons Inc., 1954, New York;
"Emulsion Polymerization", Piirma & Gardon, American Chemical Society, 1976, Washington, D.C.; and

- 5 -~5~3~1 "Emulsion Polymerization" by Irja Piirma, Academic Press Inc., 1982, New York.
Useful monomers contain an eLhylenically unsaturated carbon-carbon bond such as vinyl chloride, vinylidene chloride, acrylates or methacrylates, or vinyl monoaromatic monomers such as styrene. The vinyl monomers may be unsubstituted or substituted by a Cl 4 alkyl group or chlorine or bromine atoms such as ~-methyl styrene, p-methyl styrene, vinyl toluene, or their brominated or chlorinated derivatives. Useful monomers also include aliphatic C4 8 conjugated dienes such as 1,3-butadiene and isoprene.
The present invention requires the incorporation of one or more monomers with a functional group in an amount Erom 0.5 to about 10, preferably about 5 parts by weight per 100 parts by weight of total monomer.
As used herein, the term functional group is intended to mean a polar group such as an acid, aldehyde, ketone or amide group. Such monomers will contain, in ~0 addition to the functional group, at least one ethylenic unsaturation. The functional monomers will preferably be relatively ~hort, containing straight chain alkenyl radicals of up to about 8 carbon atoms. ~lost preferred are alkenyl radicals of Up to about 6 carbon atoms.
In the manufacture of latices of rubbery polymers of a vinyl monomer and a conjugated diene the ratio of the charge of vinyl monomer to diene will vary over a broad range. In latices of polymers of vinyl monoaromatic-conjugated diene containing a functional group the vinyl monoaromatic monomer may be present in an amount of from about 20 to 70 weight per cent of ~he monomer charge and the conjugated diene may be present in an amount from about 20 to 70 weight per cent of the monomer charge.
Preferably the vinyl monoaromatic monomer is present in an 3~
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amount from about 30 to 60 weight per cent of the monomer charge and the conjugated diene is present in an amount of from about 30 to 60 weight per cent of the monomer charged.
The monomer containing the functional group may be present in an amount from about 0.5 to about 10 weight per cent of the monomer charge. The amount used usually depends upon the intended use of the polymer. In many instances a preferred range oE functional monomer is from about 0.5 to 5 weight per cent of the total monomer c~arge. A most preferred range of functional monomer is from about 0.75 to about 3 weight per cent of the monomer charge.
Preferred monomers containing functional groups are acids or amides which may be unsubstituted or substituted by a Cl_4 alkyl or a Cl_4 alkanol group.
Typical acids include mono- or di- acids such as acrylic, methacrylic, maleic, fumaric and itaconic acid. Typical amides include C3 6 amides which may be unsubstituted or substituted by a Cl ~ a]kyl group or a Cl_4 alkanol group such as acrylamide, methacrylamide, and N-methylol acrylamide. Useful 31de~ydes include C3_6 aldehydes including c;nnamaldehyde.
Tl7e monomer mixture may optionally include up to 25 parts by weight per 100 parts by weight of monomers oE
a Cl_8 alkyl or alkanol ester of a C3 6 ethylenically unsaturated acid. If present the ester is usually used in amounts up to about 10 per cent by weight, most preEerably in amounts not greater than 5 weight per cent. Typical esters include methyl, ethyl, propyl, butyl, pentyl, hexyl, 2-ethyl hexyl, ~-hydroxy ethyl esters of acrylic, methacrylic, 3-butenoic acid, crotonic acid, 4-pentenoic and 5-hexenoic acid.
The additional micelle forming surfact3nt or unimodal seed particles are introduced into the emulsion -- 7 ~

31~1 being polyme~ized w~en the overalL conversion has reached about 40 to 60 weight per cent based on t~e weight of the total monomers being polymerized. Most preferably the surfactant or tbe seed particles are introduced w~en t~e overall conversion is abou~ 50 weight per cent.
T~ere are a great many surfactants available for emulsion polymerization. Commercially available surfactants are widely promoted in trade literature suc~
as "McCutc~on's Emulsifiers and Detergents" published annually. The initial polymerization may be conducted using a mixed nonionic and anionic emulsifier or an anionic emulsifier.
Preferably t~e additional micelle surfactant is anionicO Conventional anionic surfactants include alkali salts, alkaline eart~ metal salts, or quaternary amine derivatives of alkyl ether sulfates, alkyl sulfates, aryl sulfates, alkyl aryl sulfates, alkyl phosphates, aryl phosp~ates, alkyl aryl phospha-tes, alkyl sulfonates, aryl sulfonates or alkyl aryl sulfonates. T~e alkyl radical in suc~ surfactants are usually medium to long chain groups hav;ng from 8 to about 25 carbon atoms, suc~ as stearic or lauryl radicals. Aryl substituents are aromatic compounds o~ from about ~ to 10 carbon atoms suc~ as benzene, napt~alene, toluene, or xylene. Typical anionic surfactants include sodium lauryl sulfate, sodium lauryl sulfonate, sodium dodecyl ben%ene sulfona~e, sodium dodecyl benzene sulfate, sodium xylene sulfonate, and potassium oleate.
The unimodal seed particle has a particle size between 250 A alld 400 A, preferably about 300 A. The seed latex must be sufficiently stable so that it wil:L not coagulate when added to the emulsion. Additionally the seed latex must be compatible with t~e polymer being ~ormed in the emulsion. Preferably the seed latex is a ~3s~

latex of a carboxylated styrene butadiene polymer. rt is advan~ageous if the seed is fairly highly carboxylated having at least about 1.0% carboxylation. The amount of seed latex added depends on the particle size of this seed latex and the final particle size after polymerization that is desired.
The following examples are intended to illustrate the scope of the invention and are not intended to limit the invention. In the examples unless otherwise s-Lated the parts in the ormulation are parts by weight per 100 parts of monomer.
La~ex was prepared using conventional free radical emulsion polymerization methods from a feed stock comprising about 60 parts styrene, 38 parts butadiene and the specified parts of functional monomer and ester. The reaction time was about 10 hours to greater than 95 per cent conversion and a theoretical solids level of about 60 per cent.
In Table :L, sodium lauryl ether sulfate was introduced into the emulsion polymerization at the specified weight per cent of solids in the reactor in the specified amount. The actual solids, t'ne theoretical solids and the viscosity of tte resulting latex was determined. In the last example, N, a seed latex having a number average diameter of 368 A was added instead of the surfactant. The amo-Jnt of seed latex added was 3.12 pphm.

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In t~e table the abbreviations have the following meanings-IA = itaconic acid MA = me-~hacrylic acid AA = acrylic acid AM = acrylamide n~BA = n butyl acrylate MM~ = met~yl methacrylate DL = diameter of large particles, ~
DS = diameter of small particles, A
WL & W~ = weight percentages of large and small particles Tl~e viscosity was measured using a ~.rookfield LV~. (trade name) viscometer using a ~3 spindle at 3Q rpm~
As used in this specification A = A = Angstroms.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the synthesis of a latex having a viscosity of less than about 3000 cps and a bimodal particle size distribution so that from about 65 to 85 per cent by weight of the polymer particles have a diameter of from about 1700 A to about 3000 A and from about 35 to 15 per cent by weight of the polymeric particles have a diameter of from about 300 A to about 1000 A by the polymerization of an emulsion containing from about 50 to about 75 parts by weight of water per 100 parts by weight of nonvolatiles comprising nonmonomeric additives and a mixture of ethylenically unsaturated monomers containing from about 0.5 to 10 parts by weight per 100 parts by weight of monomers of a monomer from the group comprising C3-6 ethylenically unsaturated acids, aldehydes, ketones and amides which may be unsubstituted or substituted by a C1-4 alkyl group or a C1-4 alkanol group; or a mixture thereof and from 0 to 25 parts by weight per 100 parts by weight of a C1-8 alkyl or alkanol ester of a C3-6 ethylenically unsaturated acid; which comprises nucleating polymer particles in the emulsion and polymerizing the monomer therein to an overall conversion of from about 40 to 60 weight per cent and then introducing either (a) from about 0.75 to 2.0 additional parts by weight of a micelle forming surfactant per 100 parts by weight of total monomer, or (b) from about 2.5 to 4.5 parts by weight per 100 parts of monomer of a unimodal seed latex having a particle size of from about 275 A to about 400 A and continuing the polymerization substantially to completion.

2. A process according to Claim 1 wherein the latex has a particle size distribution so that from about 65 to about 80 per cent by weight of the polymer particles have an average diameter of from about 1800 A to about 2100 A
and about 35 to about 20 weight per cent by weight of the particles have an average diameter of from about 450 A to about 650 A.

3. A process according to Claim 2 wherein there is added to the emulsion additional micelle forming surfactant which is an anionic surfactant.

4. A process according to Claim 3 wherein the anionic surfactant is selected from an alkali salt, an alkaline earth salt, an ammonium salt or an amine derivative of a C8-25 alkyl ether sulfate, a C8-25 alkyl sulfate, a C8-25 alkyl sulfonate, C8-25 alkyl aryl sulfonate, and a C8-25 alkyl succinate.

5. A process according to Claim 4 wherein the anionic surfactant is added to the emulsion when the overall conversion has reached about 50 weight per cent.

6. A process according to Claim 5 wherein the anionic surfactant is a sodium, potassium or ammonium salt of lauryl ether sulfate.

7. A process according to Claim 2 wherein there is added to the emulsion a unimodal seed latex having a particle size of from about 275 A to about 400 A.

8. A process according to Claim 6 wherein the seed latex has a particle size of about 300 A.

9. A process according to Claim 7 wherein the seed latex is a carboxylated styrene butadiene polymer.

10. A process according to Claim 5 or 9 wherein the ethylenically unsaturated monomers comprise:
- from about 20 to 70 weight per cent of an aliphatic C4-6 conjugated diolefin;
- from about 20 to 70 weight per cent of a vinyl monoaromatic monomer; and - from about 0.5 to about 10 weight per cent of at least one monomer selected from a C3-6 ethylenically unsaturated acids, aldehyde, ketone or amide which are unsubstituted or substituted by a C1-4 alkyl or C1-4 alkanol group, and from 0 to 25 weight per cent of a C2-8 alkyl or alkanol ester of a C3-6 ethylenically unsaturated acid.

11. A process according to Claim 5 or 9 wherein the ethylenically unsaturated monomers comprise:
from about 30 to 60 weight per cent of butadiene;
from about 30 to 60 weight per cent of styrene;
and from about 0.5 to 5 weight per cent of one or more monomers selected from acrylic acid, methacrylic acid, fumaric acid, itaconic acid, acrylamide, methacrylamide, and from 0.5 to 5 weight per cent of a selected monomer, butyl acrylate, ethyl hexyl acrylate, .beta.-hydroxyethyl acrylate and N-methylol acrylamide.

12. A latex containing from about 58 to 65 per cent by weight of polymeric solids of ethylenically unsaturated monomers containing from about 0.05 to 10 per cent by weight of the polymeric solids of the residue of a C3-6 ethylenically unsaturated acid, aldehyde ketone or amide which may be unsubstituted or substituted by a C1-4 alkyl or alkanol group, and from 0 to 25 per cent by weight of a C1-8 alkyl or alkanol ester of a C3-6 ethylenically unsaturated acid, or a mixture thereof which at a polymeric solids content of about 61 per cent by weight has a viscosity of less than about 3000 cps, and has a bimodal particle size distribution so that from about 65 to 85 per cent by weight of the polymer particles have a diameter of from about 1700 A to about 3000 A and from about 35 to 15 per cent by weight of the particles have a diameter of from about 300 A to about 1000 A.

13. A latex according to Claim 12 wherein the latex has a particle size distribution so that from about 65 to about 80 per cent by weight of the polymer particles have an average diameter of from about 1800 A to about 2100 A
and from about 35 to about 20 per cent by weight of the particles have an average diameter of from about 450 A to about 650 A.

14. A latex according to Claim 12 or 13 wherein the polymer comprises:
- from about 20 to 70 weight per cent of a C4-6 aliphatic conjugated diolefin;
- from about 20 to 70 weight per cent of a vinyl monoaromatic monomer; and - from about 0.5 to about 10 weight per cent of at least one monomer selected from a C3-6 ethylenically unsaturated acid, aldehyde, ketone or amide which are unsubstituted or substituted by a C1-4 alkyl group or a C1-4 alkanol group, and from 0 to about 25 per cent of a C1-8 alkyl or alkanol ester of a C3-6 ethylenically unsaturated acid.

15. A latex according to Claim 12 or 13 wherein the polymer comprises:
- from about 30 to 60 weight per cent of butadiene;
- from about 30 to 60 weight per cent of styrene;
and - from about 0.5 to 5 weight per cent of an monomer selected from acrylic acid, methacrylic acid, fumaric acid, itaconic acid, acrylamide, methacrylamide and N-methylol acrylamide, and from 0 to 5 weight per cent of an ester selected from butyl acrylate, ethyl bexyl acrylate, and .beta.-hydroxyethyl acrylate.