NO761330L - - Google Patents

Description

The present invention relates to a new method for the production of vesicular polyester resin granules.

It has been proposed to use granules of vesicular polymer with diameters in the order of 0.5 to 500 microns as feeding and texturing agents in paints and plastics and as fillers. substances in paper. Granules of this general type are discussed, e.g. in Australian patent 439 432, where it is further stated that the ratio between granule diameter and bladder diameter should be at least 5/1.

From Australian patent 455 277 it is known that usable vesicular, cross-linked polyester resin granules can be produced from selected carboxylated, unsaturated polyester resins by a method which comprises the emulsification of an unsaturated monomer, e.g. styrene, in water in the presence of a strong base; followed by the curing of the resin. The pigment particles can be mixed into the granules by first pigmenting the polyester resin solution and by a double emulsion technique, whereby a pigment dispersion in water is first suspended in droplet form in the unsaturated polyester resin solution. The suspension is then dispersed in globular form in water.

The spheres are stabilized in the presence of a water-soluble polymer, e.g. a partially hydrolyzed polyvinyl acetate, in the outer water phase. The curing of the unsaturated polyester resin is initiated in a conventional manner, e.g. by using free radical initiators. The resulting product is an aqueous suspension of vesicular, crosslinked polyester resin granules.

While vesicular granules in the form of aqueous suspensions can be well suited for direct mixing into aqueous products, e.g. aqueous latex paints, without first extracting and drying the granules, this step cannot be avoided when producing non-aqueous end products. The presence of water-soluble polymeric stabilizer or protective colloid in the suspension may cause undesirable economic and technical difficulties in the extraction and drying process. so that when one wishes to obtain water-free granules it will be desirable to eliminate or drastically reduce the use of such a water-soluble polymer component.

The present invention thus relates to a method for the production of vesicular polyester resin granules, whereby certain limitations of known methods can be avoided. The granules produced in this way have certain important surprising properties compared to hitherto known vesicular polyester resin granules.

The method involves the use of an unsaturated polyester resin containing chains of polyethylene oxide. This resin co-reacts in known manner with ethylenically unsaturated monomer.

A solution of the resin in ethylenically unsaturated monomer further forms, on stirring with water, a self-stabilizing, spherical dispersion of the resin solution in water and the individual small spheres spontaneously acquire a vesicular structure.

There is thus provided a method for producing an aqueous suspension of vesicular polyester resin granules by stirring in water a solution of an unsaturated polyester resin in ethylenically unsaturated monomer to form a dispersion in water of small spheres of unsaturated polyester resin solution and then adding to the dispersion a free radical initiator to initiate the co-reaction of the unsaturated monomer, the method being further characterized in that (1) the polyester resin contains 2-50% by weight of polyethylene oxide chains with an average molecular weight of 1000 - 10,000 which are water-soluble at the granule processing temperature , and (2) the ethylenically unsaturated monomer has a solubility of less than 5% by weight in water.

The polyester resin granules can be separated from the water

in the suspension and dried.

Unsaturated polyester resins which co-react with ethylenically unsaturated monomer to produce a cross-linked polymeric structure are, as a class, well known to those skilled in the art, as is the initiation of the polymerization reaction. The best-known type of unsaturated polyester resin is the condensation product of polyols and polybasic acids, at least part of the acid being ethylenically unsaturated, e.g. ethylene glycol reacted with maleic acid or acid anhydride. A resin of this type will usually contain unreacted carboxyl groups, and the concentration of these is indicated as the acid number of the resin, and is expressed as mgKOH and is equivalent to 1 g of resin.

There are no special requirements for the type or acid value of the polyester resin to be used, apart from the requirement with regard to polyethylene oxide content. In order to achieve the most stable conditions possible, however, it has proved preferable to work with resins that have acid values of 10-50 mg KOH per g.

The selection of suitable components is illustrated, but not limited, by the following examples;

Unsaturated aliphatic acids, e.g. maleic acid, fumaric acid,

itaconic acid, citraconic acid and mesaconic acid,

saturated aliphatic acids, e.g. malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, azaleic acid, hexahydrophthalic acid and sebacic acid, and

aromatic acids, e.g. phthalic acid, isophthalic acid, terephthalic acid, tetrachlorophthalic acid, trimellitic acid and trimesic acid.

The corresponding acid anhydrides, if these exist,

are also common components of such polyesters.

Suitable dihydric alcohols are e.g. ethylene glycol, di-ethylene glycol, hexane-1, 6-diol, propylene glycol, dicyclohexanol and neopentyl glycol. Alternatively, the alcohol can be one that originally contains three or more hydroxyl groups, the groups beyond two can optionally be at least partially etherified with e.g. an equal. alcohol, e.g. methanol, ethanol, and n-butanol, or esterified with a monovalent acid, e.g. benzoic acid, p-tert-butyl-benzoic acid and chain-like aliphatic acids with a chain length

of up to 18 carbon atoms, e.g. coconut fatty acid.

The methods for formulating unsaturated polyesters of this

type is well known to the person skilled in the art.

In the formulation, the essential requirement is that the unsaturated polyester resin must contain 2-50% by weight of polyethylene oxide side chains. For some applications, the preferred range is 2-20% by weight. There are a number of ways in which a group of this type can be incorporated into a polyester resin. End groups of polyethylene oxide chains in common preparation are hydroxyl, though

(depending on the polymerization method used) a group can be alkoxy, e.g. methoxy group. With regard to the hydroxyl group concentration, polyethylene oxide can thus be mono- or di-

functional, difunctional types are usually referred to as polyethylene glycols. The properties of the polyethylene oxides are well known and are discussed e.g. in "Organic Polymer chemistry", Saunders, K.J., Chapman and Hall, London 1973. The most direct way to link a polyethylene oxide group to an unsaturated polyester is thus to utilize the hydroxyl group or groups in an esterification reaction. A polyethylene oxide with a terminal mono-hydroxy group can e.g. is reacted via its hydroxyl group and a carboxyl group in the polyester resin to unite both components via an ester bond. on the other hand, if the polyethylene oxide chain is terminated at both ends with hydroxyl groups, it can be used as a dihydric alcohol in the production of the unsaturated polyester itself.

Polyethylene oxide for use in this way can be easily produced by known methods from ethylene oxide and is also known commercially, e.g. certain products sold under the trade name "Carbowax", (Union Carbide Corp., U.S.A.). For our purposes, polyethylene oxide must be water-soluble at the granulation temperature and have an average molecular weight of 1000-10,000. Although the polymers must mainly be polymers of ethylene oxide, we do not exclude the use of a smaller amount of another alkylene oxide, e.g. propylene oxide, provided that the polyalkylene oxide as a whole remains water-soluble at the granulate processing temperature.

An alternative indirect way of introducing polyethylene oxide into the polyester is to first react a polyethylene oxide with a terminal monohydroxyl group with a trivalent acid, e.g. trimellitic anhydride, in equimolar amounts, and then using the thus produced divalent acid ester in the production of unsaturated polyester resin as a dibasic reactant-

The first step in the production of vesicular granules according to the present invention is to dissolve the selected unsaturated polyester resin in ethylenically unsaturated monomer, with which it will co-react when the polymerization is initiated by a free-radical mechanism. The unsaturated monomer should be mainly water-insoluble and for our purposes we have found that monomers with a solubility of less than 5% by weight in water are useful.

A single monomer or a mixture of monomers can be used and usually the monomer only contains a single polymerizable double bond. However, it is known that polyfunctional monomers, i.e. monomers containing more than one polymerizable double bond, can also be used to crosslink unsaturated polyester resins. However, such polyfunctional monomers are usually only present as a minor component of a mixture of monomers, the main amount being monofunctional monomers. Mixtures containing e.g. divinylbenzene can therefore be used according to the present invention.

The basis for selecting an ethylenically unsaturated monomer which will react with an unsaturated polymer is well known in the field and can easily be used directly in the method according to the present invention. In practice, we have found that the generally most applicable monomer is styrene, since it can be easily polymerized with a variety of unsaturated polyester resins. However, excellent results are obtained with mixtures of styrene and other monomers, e.g. "vinyltoluene" and methyl methacrylate. In order to achieve the best results, it is preferred that the monomer constitutes the least. 50% by weight styrene.

However, the choice of monomer is not limited to the above-mentioned monomers alone. Bearing in mind the requirement that the total monomer must be mainly insoluble in water and also be a solvent for the unsaturated polyester resin, a smaller amount of other polymerizable unsaturated monomers may be present, e.g. to modify the physical properties of the co-reacted resins. Typical comonomers are e.g. ethyl acrylate, n-butyl methacrylate, acrylonitrile, and triallyl cyanurate. Generally, it has been found that the upper limit for the use of such monomers is 10% by weight based on the total monomer used. Higher concentrations give granules which can either be too brittle or too rubbery for use e.g. in paint mixtures.

Optionally, a few % by weight of a non-polymerizing, organic liquid can be added, e.g. n-butanol or toluene, to the monomer to increase the solubility of the polyester resin in it or can be added as a random part, e.g. in the manufacture of the polyester. •

When a solution of unsaturated polyester in polymerizable monomer of this type is added to water under vigorous stirring, a self-stabilizing suspension of small globules of polyester solution in water is formed. The vigorous stirring is continued until the desired ball size is obtained, which roughly corresponds to the final granule size. The reduction of the spheres to the correct size can be accelerated by the addition of water in a limited amount, not more than 5% by weight of the polyester, of an anionic surfactant, such as e.g. "Aerosol" M.A. (Aerosol is the trade term of AmericalCyanamid Co.), or a water-soluble colloid, e.g. hydroxyethyl cellulose. At the same time, small separate fluid-filled blisters form inside the balls of polyester resin solution. Each ball contains a number of blisters and the diameters of these are relatively smaller than the ball diameter. Bladder volumes are in the range 20-60% of the ball volume.

When the small spheres have been reduced by stirring to the desired granule diameter, a free radical initiator is added to the suspension to polymerize and thus cross-link the polyester resin granules. The initiator can e.g. be an 'organic peroxide', e.g. benzoyl peroxide, di-tert-butyl peroxide and methyl ethyl ketone peroxide, together with an accelerator, such as e.g. diethylaniline.

_It has been suggested e.g. in the Australian patent' indicated above, that the applicability of vesicular polymer granules is increased by the addition of pigments,' particularly opaque, white pigments, such as e.g. titanium dioxide. The pigments can be mixed into the granules according to the present invention by predispersing the particles of the selected pigment in the unsaturated polyester resin solution. When the granules contain a certain amount of pigment, it has generally been found to be preferred to add up to 5% by weight of the polyester of an anionic surfactant or a water-soluble colloid, e.g. hydroxyethyl cellulose, to the water where the small balls of unsaturated polyester resin are produced.

The granules according to the present invention can be produced without adding polymeric stabilizers, and this seems to contribute to the fact that they can be easily separated from water and dried.

The suspension of granules prepared as indicated above can be concentrated by sedimentation and then decantation, the granules can then be centrifuged or filtered from most of the remaining water. The wet granules can then be dried by e.g. tray drying in a hot air atmosphere or by using fluid bed techniques.

The granules of the above-mentioned type, i.e. granula-

t are of cross-linked polyester resins containing 2-50% by weight of groups of polyethylene oxide with an average molecular weight of 1000-10,000, are particularly useful as components in paint films.

A surprising and valuable feature of these granules is that when they are used at high volume concentrations in dry paint films, i.e. when they make up 60-90% by volume of the paint, the paint usually has an improved stain resistance compared to formulations made from known granules.

The invention is illustrated by the following examples where all parts are indicated by weight:

EXAMPLE 1

Preparation of a polyethylene oxide modified unsaturated polyester resin.

A mixture of 29 parts propylene glycol, 27 parts fumaric acid, 12 parts phthalic anhydride and 7 parts of a polyethylene oxide with a. molecular weight of 6000, known as "carbowax" 6000 (trade name) was heated, in a reaction vessel equipped with a stirrer, thermometer and cooler and kept under reflux conditions for two hours. 3.5 parts of xylene were then added to the flask and a Dean-Stark trap was connected to collect distilled water from the reaction. The reaction mixture was refluxed at a temperature up to 210°C and the water was removed until the acid value of the polyester dropped to 30 mg KOH/g resin. The heating was then stopped and the reaction mixture cooled. 0.015 part hydroquinone was added to the resin when the temperature had dropped to 140°C, and 21 parts styrene was added when the temperature had dropped to 110°C. The product was a viscous, yellow colored liquid.

EXAMPLE 2

Production of pigmented, vesicular polyester granules according to the invention1.

14.16 parts of the polyester from Example 1 was mixed with 5.80 parts of styrene, and 16.00 parts of rutile titanium dioxide pigment was dispersed into the mixture at high speed. ■ 0.50 part of a paste consisting of 55% benzoyl peroxide in n-butyl benzyl phthalate was added to the dispersion and mixed well.

The above mixture was added with stirring to a mixture of 62.40 parts water and 0.29 parts hydroxyethyl cellulose. The grade used was "Natrosol" 250 HR ("Natrosol" is the trade name of Hercules Co., U.S.A.). After 1 minute of stirring, 0.46 part of an 80% aqueous solution of sodium dihexyl sulfosuccinate was added and stirring was continued. A stable oil-in-water emulsion was formed of small globules of polyester resin solution in water and stirring was continued until the maximum emulsion particle size under microscope was 30 microns. Then 0.16 parts of diethylaniline were added and the stirring stopped. Within 1 hour the temperature rose from 20°C to 40°C indicating that an exothermic polymerization is taking place. The product was a suspension of spherical, pigmented, vesicular polymer granules, and the bladder volume was estimated by microscope to be 50% of the total granule volume.

EXAMPLE 3

Comparative example of a paint showing improved properties over a similar paint containing vesicular polymer granules of the type disclosed in Australian patent 445 277.

Maling A

To 43.86 parts of the polymer granulate suspension from Example 2 were added 19.92 parts of an aqueous acrylic latex ("AC 61" from Rohm and Haas was used) and 16.58 parts of a 71% aqueous dispersion of rutile titanium dioxide pigment. 1.4 parts of tributyl phosphate, 16.5 parts of water and 0.18 parts of hydroxyethyl cellulose were slowly added and the mixture was stirred until constant viscosity.

Paint B

A similar paint to paint A was produced, except that the polymeric granules used in paint A were replaced on a solids basis with vesicular polyester resin granules of the same size, but produced according to the teachings of Australian patent 445 277.

Paint A and Paint B were drawn side by side on a "Most hiding power chart" to films of the same thickness and allowed to air dry overnight, then aged for a further 24 hours. Stains, comprising a dispersion of carbon black in mineral oil, black pencil, red chalk and household dust, were then evenly applied to both paint films.

The paints were scrubbed with a rag dampened with water and household detergent. It was observed that the stains were removed more easily from paint A than from paint B. In the case of mineral oil stains, the removal was almost complete from film A, but very little from film B.

EXAMPLE 4

Production of pigment-free, vesicular polyester resin granules by the method according to the invention.

To 90 parts of polyester resin prepared as in example 1, 30 parts of styrene and 3 parts of a 55% by weight paste of benzoyl peroxide in n-butyl benzyl phthalate were added, and a clear solution was obtained. This solution was then added with stirring to 200 parts of water and a stable dispersion of the water-in-oil type was obtained.

0.8 part of diethylaniline was added to the prepared dispersion, which initiated an exothermic polymerization that lasted for approx. 2 hours. The product thus produced was an aqueous suspension of polyester resin granules with a maximum diameter of

about. 50 micrometers, which corresponds to the maximum diameter of the unpolymerized initial dispersion of the water-in-oil type. The granules turned out to contain approx. 50 volume-% fine blisters, which had formed spontaneously during the production of the granules.

Spread on trays and exposed to a stream of hot air, the suspension dried to a soft, white powder.

The preparation was repeated by adding 0.7 part of hydroxyethyl cellulose to the water in which the initial emulsion of the oil-in-water type was prepared. About the same degree of agitation was used in the preparation of the dispersion, but in this case the resulting maximum granule diameter was of the order of 20 micrometres, thus showing how useful a water-soluble colloid is in facilitating the size reduction of the granules. The size and degree of blister formation and how easily these granules can be dried are similar to those for the granules of the order of 50 micrometres.

EXAMPLE 5

This example illustrates the preparation of 30 micrometer, pigmented, vesicular, polymeric polyester resin granules according to the invention.

To 14.16 parts of polyethylene oxide-modified polyester from Example 1 was added 5.80 parts of styrene, and then 16.00 parts of rutile titanium dioxide pigment was dispersed into the mixture at high speed. 0.50 part of a paste consisting of 55% by weight benzoyl peroxide in n-butylbenzoyl phthalate was added to the dispersion and mixed well.

The above mixture was added with stirring to a mixture of 62.40 parts of water, 0.29 part of hydroxyethyl cellulose (as in Example 2) and 0.52 part of a 30% aqueous solution of polyphosphate pigment dispersant. After stirring for 1 minute, 0.46 part of an 80% aqueous solution of sodium dihexyl sulfosuccinate was added and stirring was continued. A stable oil-in-water type dispersion was formed and stirring continued until the maximum dispersed particle size was found to be 30 micrometers under the microscope, then 0.16 part of diethylaniline was added and stirring was stopped. Over a period of 1 hour the temperature rose from 20°C to 40°C indicating that an exothermic polymerization is taking place. The product was a suspension of spherical, pigmented, vesicular polyester granules, and the bladder volume of these was approx. 50% of the total granule volume. The aqueous suspension of granules was dried after washing and a soft powder of pigmented, vesicular granules is obtained.

EXAMPLE 6

Production of 5 micrometer, pigmented, vesicular, polymeric polyester resin granules according to the invention.

To 27 parts of polyethylene oxide-modified polyester from example 1 were added 11 parts of styrene and 31 parts of rutile titanium dioxide pigment dispersed in the mixture. To this mixture was then added 1 part of a 55% by weight paste of benzoyl peroxide in n-butyl benzyl phthalate. The above dispersion was added with stirring to a mixture of 118 parts water, 1.8 parts hydroxyethyl cellulose and 1.6 parts sodium dihexyl sulfosuccinate. A dispersion of the oil-in-water type was obtained, and the particle size was reduced under vigorous stirring to an average value of approx. 5 micrometers. 16 parts of water and 0.3 part of diethylaniline were added and an exothermic reaction was obtained which took place within 2 hours. the product was a suspension of pigmented, vesicular polymer granules with an average size of approx. 5 micrometers. These were dried, after washing, and a dry powder of pigmented, vesicular polyester granules was obtained.

EXAMPLE 7

Production according to the invention of pigmented polyester resin granules with a low. bladder volume.

To 27 parts of polyethylene oxide-modified polyester from Example 1, 11 parts of styrene were added, and then 31 parts of rutile titanium dioxide pigment were dispersed in the mixture. Then

was added 1 part of a 55% by weight paste of benzoyl peroxide in n-butyl benzyl phthalate. This mixture was then added with stirring to an aqueous phase consisting of 120 parts water, 0.5 part hydroxyethyl cellulose, 3.5 parts sodium chloride and 0.5 part sodium dihexyl sulfosuccinate. A dispersion of the oil-in-water type was obtained and the dispersed particles were reduced by stirring to approx. 30 micrometers in maximum diameter. Then 0.3 part of diethylaniline was added to the dispersion and an exothermic hardening reaction took place during 2 hours. the product was a suspension of pigmented polyester granules up to 30 micrometers in diameter

and with a bladder volume of approx. 20% of the total granule volume.

The suspension was dried in a stream of hot air to a soft white pigment.

EXAMPLE 8

This example illustrates the preparation of vesicular

polyester resin granules according to the invention.

A polyethylene oxide-modified polyester suitable for the production of vesicular polyester resin granules according to the invention was prepared as follows: 33 parts of a methoxy polyethylene oxide (containing one terminal methoxy and one terminal hydroxyl group per molecule) with an average molecular weight of 2100 was added to a reaction vessel which was equipped with a stirrer, thermometer and cooler and added 5 parts xylene and 3.2 parts trimellitic anhydridec This mixture was kept under reflux at approx. 160°C until the anhydride group concentration by infrared analysis had fallen to a constant low value. The mixture was cooled to 130°C, and 4 parts of phthalic anhydride, 14 parts of fumaric acid and 13 parts of propylene glycol were added. The mixture was heated under reflux and kept under reflux for 1 hour. A Dean&Stark trap was connected to collect condensed water from the reaction.' The mixture was kept under reflux at temperatures up to 210°C and the water was removed until the acid value of the polyester dropped to 30 mg KOH/g resin. The heating was then stopped and the reaction mixture was cooled. 0.015 part hydroquinone was added when the temperature had fallen to 140°C, and 26 parts styrene was added when the temperature had fallen to 110°C. The product was a viscous, cloudy, yellow colored liquid.

The polyester resin which was prepared in this way

was then used to prepare vesicular granules according to the method indicated in Examples 4-7. Granules with similar properties were obtained from the polyester in this example as from the polyester in example 1.

EXAMPLE 9

This example illustrates the production of vesicular polyester resin granules according to the invention using polyethylene oxide-modified polyester resins as indicated below: (a) A polyethylene oxide-modified polyester resin produced according to the method in example 1, but by replacing half of the propylene glycol with neopentyl glycol on an equimolar basis. (b) A polyethylene oxide-modified polyester resin was prepared following the procedure of Example 1, but substituting

the fumaric acid with maleic anhydride on an equimolar basis.

(c) A polyethylene oxide-modified polyester resin was prepared according to the method of Example 1, but by replacing 10% by weight of the styrene monomer with methyl methacrylate monomer. (d) A polyethylene oxide-modified polyester resin was prepared according to the procedure in Example 1, but by replacing 10% by weight of the styrene monomer with vinyl toluene monomer.

The above polyesters were then transferred to vesicular polymeric granules according to the procedure in example 2 and satisfactory vesicular polyester resin granules were obtained.

EXAMPLE 10

For comparison, this example illustrates a method for producing vesicular polyester resin granules which are not covered by the present invention.

An attempt was made to produce vesicular polyester granules where the polyester resins are as follows: (å) A polyester resin was produced according to the method in example 1, but by using 70 parts of a polyethylene oxide with a molecular weight of 6000 instead of 7 parts thereof.

The product was then cooled to a semi-solid dry substance and could not be transferred to vesicular polymer granules according to the method according to the invention.

(b) A polyester resin was prepared according to the method

in example 1, but by using 1 part of polyethylene oxide with a molecular weight of 6000 instead of 7 parts thereof. The product was a viscous, yellow-coloured liquid which did not give a stable dispersion in water following the method in example 2 and could not be hardened to produce a dispersion of vesicular polyester resin granules according to the invention.

(c) A polyester resin was prepared according to the method

in example 1, but using the equivalent amount by weight of a polyethylene oxide with an average molecular weight of 600 instead of the polyethylene oxide with an average molecular weight of 6000.

the product was a viscous, yellow-coloured liquid which did not form a stable dispersion in water by the method in example 2 and could not be hardened to produce a dispersion of vesicular polyester resin granules according to the invention.

Claims (5)

1.Process for the production of an aqueous suspension of vesicular polyester resin granules by stirring in water a solution of an unsaturated polyester resin in ethylenically unsaturated monomer to produce a dispersion in water of small spheres of unsaturated polyester resin solution, and then adding to the dispersion a free radical initiator to initiate the co-reaction of unsaturated polyester resin and ethylenically unsaturated monomer, the method being further characterized in that (1) the polyester resin contains 2-50% by weight of polyethylene oxide chains with an average molecular weight of 1000-10,000, which are water-soluble at the granulation processing temperature, and (2) the ethylenically unsaturated monomer has a solubility of less than 5% by weight in water. 2. Method as stated in claim 1, characterized in that the unsaturated polyester resin has an acid value of 10-50 mg KOH per g. 3. Method as stated in claim 1 or 2, characterized in that the ethylenically unsaturated monomer contains at least 50% by weight of styrene. 4. Method as stated in any one of claims 1-3, characterized in that the ethylenically unsaturated monomer contains up to 10% by weight of monomer selected from ethyl acrylate, n-butyl methacrylate, acrylonitrile and triallyl cyanurate. 5. Method as stated in any one of claims 1-4, characterized in that the dispersion in water of small spheres of unsaturated polyester resin solution prepared in the presence in the water of up to 5% by weight based on the polyester resin of an anionic surface-active agent or a water-soluble colloid .