GB1588641A - Manufacture of dust-free and non-caking granules - Google Patents

Abstract

Dust-free and non-caking granular materials, especially broken granules from fertilisers and salts are prepared by applying coatings consisting of polymer mixtures. The granular materials have applied to them aqueous suspensions or solutions of a) urea-aldehyde condensation products and/or alkylol ureas and b) polyenes, the amount of solid applied being from 0.3 to 4.0% by weight, based on the amount of granular material.

Description

(54) MANUFACTURE OF DUST-FREE AND NON-CAKING GRANULES (71) We, BASF AKTIENGESELLSCHAFT, a German Joint Stock Company of 6700 Ludwigshafen, Federal Republic of Germany, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following Statement: The present invention relates to the manufacture of dust-free and non-caking granules, especially irregularly shaped granules, particularly those of fertilizers and salts.

Whilst the conventional granules of solids, formed in the presence of moisture or from a melt, in granulating equipment, for example drums and prilling towers, are round and mostly smooth, irregularly shaped granules are obtained if salts and other substances, individually or in the form of mixtures, are compacted dry between two smooth rollers and are then comminuted, or moist materials are extruded to strands which are dried and comminuted, or materials which have been consolidated in other types of apparatus are comminuted. These irregularly shaped granules, which possess points, edges, raised portions and recesses, suffer greater abrasion on handling than do the conventional round granules. Depending on their composition they may also carry very fine dust, originating from the comminution process, in their recesses; this dust is not released even if the granules are carefully screened, and instead is only liberated when they are stored in silos with drop heights of up to 20 meters or when the fertilizer is applied by means of a spreader. Because the dust is very fine, it then constitutes a long-lasting nuisance. This nuisance arises even if the amount of very fine dust is low, for example less than 0.8 per cent by weight, based on the total material, of particles of less than 0.1 mm diameter. With round granules, on the other hand, problems mostly arise when the granules consist of materials which are light or soft and tend to produce fines on abrasion.

Several proposals for avoiding the dusting and caking of salts or fertilizers have been disclosed.

German Patents 1,062,713 and 1,072,256 propose the manufacture of non-hardening and non-dusting calcium ammonium nitrate granules by spraying them at an elevated temperature with aqueous solutions of condensation products of formaldehyde and urea which have been sulfite-modified, and dusting them immediately afterwards with limestone powder. This process thus requires two steps, namely spraying and subsequent dusting of the granules. The subsequent application of a layer of powder, the adhesion of which to the surface declines, especially after prolonged storage, is, however, once again a reason why dusting of the fertilizer cannot be reliably prevented.

U.S. Patent 2,502,996 discloses granules, containing ammonium nitrate, which are also coated with a urea-formaldehyde condensation product. The granules are coated with these condensates in a solid, finely divided form in amounts of from 5 to 25 per cent by weight.

British Patent 815,829 discloses the coating of fertilizer granules first with a shell of an inorganic substance and then with a water-insoluble polymeric material. This method is again expensive, since it entails at least two steps.

French Patent 1,394,629 discloses a process for the manufacture of slow-acting fertilizers wherein the latter are coated with mixtures of a paraffin wax of low melting point and a polyalkylene of molecular weight not exceeding 10,000. It is true that this treatment results in fertilizers which release the active ingredient slowly, but the fertilizers still have a great tendency to cake, and consequently they require additional coating with a powder which, as stated above, has an adverse effect (i.e. dusting not prevented) during handling.

A number of processes have also been disclosed in which fertilizers and salts are rendered non-dusting and non-caking by treating them with mixtures which contain polyethylene or polypropylene waxes or oxyalkylates, together with surfactants (German Patents 1,905,834, 2,018,623 and 2,109,199). It is true that these processes give good results with normal round granules, but are unsuitable for coating irregularly shaped granules since the process results in the main in coating the points and ridges whilst the recesses, in which the very fine dust lodges, are not affected by the treatment. Furthermore, it is essential to carry out the treatment at an elevated temperature whilst this is not necessary in the process of the present invention.

Finally, U.S. Patent 3,223,518 discloses a process wherein fertilizer granules are coated with several layers of which at least one consists of a copolymer of dicyclopentadiene with glycerol esters of unsaturated fatty acids. For the first and middle layers of coating it is possible to employ, inter alia, urea-formaldehyde resins, phenol-formaldehyde resins, alkyd resins, polyvinyl acetate, polyvinyl chloride and polyacrylates.

However, hitherto no coating agent has been disclosed which effectively prevents the dusting and caking, especially of irregularly shaped granules.

The present invention seeks to provide a process by means of which dusting and caking can be effectively prevented, especially in the case of irregularly shaped granules.

According to the present invention there is provided a process for the manufacture of dust-free and non-caking granules, which process comprises applying to the granules a surface coating of (a) a urea-aldehyde condensation product, employed as an aqueous solution or suspension, and/or an alkylolurea, employed as a 40 to 75% by weight strength aqueous solution which is weakly alkaline, and (b) a polyene, employed as an aqueous suspension or dispersion, the surface coating being applied in an amount of from 0.3 to 4 per cent by weight of condensation product and/or alkylolurea plus polyene, based on the amount of granules.

Surprisingly, the granular fertilizers etc. which have been treated in accordance with the invention are effectively and uniformly coated even in the case of irregularly shaped granules, so that the very fine dust located in the recesses remains bonded, whilst in the case of soft round granules abrasion is significantly reduced. Electron micrographs clearly show the surprisingly good coating.

Fertilizers and salts which are coated with a combination of a urea-aldehyde condensation product and a polyene bind the dust more completely, and exhibit better storage characteristics, than if a urea-aldehyde condensate alone or a polyene alone is used. In fact, if the granules are sprayed only with an aqueous solution of an alkylolurea or an aqueous solution or suspension of a urea- aldehyde condensate, the dust swirling in the coating drum is admittedly precipitated very rapidly and there is no dust nuisance, but after the water has disappeared, mainly by evaporation but partially by absorption into the granules, the dust nuisance recurs on handling - for example storing or application by means of spreaders. The dust is encountered especially in the case of irregularly shaped granules, because the ureaaldehyde resin contracts on the surface of the particles and the recesses in which the very fine dust lodges become exposed. Furthermore, the urea-aldehyde resins, which are mostly brittle, tend to crack and flake off, which in turn leads to dust. If a polymer (homo polymer or copolymer of an ethylenically unsaturated compound) is used alone, the dust swirling in the coating drum is not precipitated; it is true that the coating on round particles from a polyene is more uniform than that from a urea-aldehyde condensates, but a polyene coating on irregularly shaped granules is once again not continuous and is therefore only able to bind the dust completely if large amounts of the polyene are used. Furthermore, the polyene coatings are tackier than the coatings obtained by a process according to the invention.

Specific examples of suitable urea-aldehyde condensation products are full condensates and precondensates of urea and aliphatic saturated or unsaturated aldehydes of 1 to 7 carbon atoms or mixtures of such aldehydes, with molar ratios of urea to aldehyde of from 1:1:.1 to 1:2.2, preferably from 1:1.3 to 1:1.8. Formaldehyde is the preferred aldehyde. The ureaaldehyde condensates can be modified in conventional manner with an alkali metal sulfite, alkanolamine or alkylenediamine. For example, from 1 to 10 per cent by weight (based on urea-aldehyde condensation product) of alkali metal sulfite or up to 1 part by weight of alkanolamine, eg. diethanolamine, or alkylenediamine, eg. ethylenediamine, may be added to the solution or suspension. To obtain more readily water-soluble condensates, alcohols, especially polyhydric alcohols. eg. ethylene glycol, glycerol and the like, and also sugars, may at times be added in conventional manner.

The urea-aldehyde condensation products are employed in the form of an aqueous solution or suspension containing preferably from 30 to 60 per cent by weight of condensation product. Suitable solvents are especially water, but also mixtures of water with alcohols, eg. ethylene glycol.

Instead of a urea-aldehyde condensation product it is possible, particularly in the case of granules of urea or of fertilizers containing urea, to employ from 40 to 75 per cent strength by weight aqueous solutions of alkylolureas which are weakly alkaline, the solutions having a pH of, for example, up to 9. Suitable aldehydes to provide the alkylol moiety are especially those of 1 to 4 carbon atoms, in particular formaldehyde. The molar ratio of urea to aldehyde, especially to formaldehyde, is usually from 1:1 to 1:4.5, preferably from 1:3 to 1:4. The alkylol-urea can condense with the urea on or in the granules and thereby result in efficient binding of the coating layer.

If a minor amount (as a rule from 0.5 to 4 per cent by weight suffice) of an ammonium salt, e.g. ammonium sulfate or ammonium chloride, is added to the purely aqueous or aqueousalcoholic solution or suspension of urea-formaldehyde condensation product or a alkylolurea, the further condensation of the urea-formaldehyde compounds takes place more rapidly and hence the coatings are formed more rapidly.

The polyenes which are employed in the process, in aqueous dispersion or suspension, are polymers of ethylenically unsaturated compounds, such as homo polymers and copolymers of vinyl chloride, vinylidene chloride, vinyl acetate, vinyl propionate, acrylic acid, acrylates, acrylamides, butadiene and styrene. Examples are copolymers of from 80 to 95 parts by weight of vinylidene chloride, from 20 to 5 parts by weight of methyl acrylate and up to 1 part by weight of acrylamide; or copolymers of from 40 to 60 parts by weight of n-butyl acrylate, from 60 to 40 parts by weight of vinyl acetate and/or vinyl proprionate and up to 2 parts by weight of acrylic acid; but preferably copolymers of from 30 to 70 parts by weight of styrene and from 65 to 25 parts by weight of butadiene with or without u to 15 parts by weight of acrylic acid, acrylamide, methacrylamide or N-methylolmethacrylamide. The aqueous dispersions and suspensions of the polyenes employed usually contain from 10 to 70 per cent by weight, especially from 30 to 55 per cent by weight, of polymer.

The aqueous media containing the urea-aldehyde condensation product and/or alkylolurea and the polyene can be added separately to the granules, e.g. of salt or fertilizer, but it is advantageous to mix them with one another and hence apply the components to the granules in a single step. In that event the medium preferably contains a total of from 30 to 65 per cent by weight of solids. The proportion of urea-aldehyde condensation product and/or alkylolurea is preferably from 30 to 90 per cent by weight, based on the total content of this material and the polyene.

In order to lower the surface tension and hence achieve better distribution of the coating on the granules a surfactant can be added to the aqueous material(s). Cationic, anionic or non-ionic surfactants may be used for this purpose, either separately or as mixtures. These surfactants may be added to the suspensions in amounts of up to 1 per cent by weight.

Examples of cationic substances are primary, secondary and tertiary amines, their salts, and quaternary ammonium compounds. The positive charge is borne by the nitrogen. In addition to one or more amino groups or quaternary ammonium ions as the hydrophilic parts of the compound, these substances contain hydrophobic, aliphatic or cycloaliphatic hydrocarbon radicals of 4 to about 25 carbon atoms. Amongst the great number of conventional substances, specific examples are decylamine, dodecylamine, stearylamine and dicyclohexylamine. Pyridinium salts, alkylpyridinium salts, morpholine derivatives, condensates of fatty acids with diamines and polyamines, and sulfonium and phosphonium compounds may also be employed as cationic compounds.

Examples of anionic compounds are those which contain the sulfonate group ( - S03 ), the sulfato group (-0 - SO3, , ie. the group of a sulfuric acid half-ester) and the carboxyl group (-COO - ) as the hydrophilic part of the molecule, with fairly long-chain aliphatic hydrocarbon radicals, aryl radicals and alkyl-substituted aryl radicals as the hydrophobic part of the molecule. The hydrophobic radical may also contain linking members, eg. ether oxygen, aminoalkyl, oxyalkyl, ester, carboxamide and sulfonamide groups. As a rule, the hydrophobic radical is of 6 to 30 carbon atoms.

Examples of the above substances are, inter alia, salts of fatty acids, fatty acid/ aminocarboxylic acid condensates (fatty acid sarcosides), alkylsulfonates, ligninsulfonates, mineral oil sulfonates, alkylbenzenesulfonates, alkylnaphtalenesulfonates, polymeric alkylnaphthalenesulfonates, fatty acid/aminoalkylsulfonic acid condensates, sulfodicarboxylic acid esters. sulfated oxyethylated compounds, fatty alcohol sulfates and sulfated fatty acid glycerides. Preferably, the various sulfonates and fatty alcohol sulfates, especially the alkali metal salts of fatty alcohol sulfates of 8 to 18 carbon atoms, are used for the combined suspensions according to the invention.

The non-ionic surfactants which may be added, by themselves or in mixtures, to the suspensions, include fatty acid alkylolamides, polyalcohols, fatty acid esters of polyalcohols, sugar alcohols and sugars, as well as oxyethylation products, for example the adducts formed from ethylene oxide or propylene oxide and alcohols, fatty acids, alkylphenols, alkylnaphthols, amines and fatty acid amides in the presence of catalysts. Depending on the amount of the alkylene oxide, polyether chains of varying length are built onto the starting compound, and terminate in a hydroxyl group.

In addition to the surfactant(s), an inorganic filler, organic filler and/ or thickener may also be added to the suspensions. Inorganic fillers which may be used include limestone powder or precipitated calcite, chalk, barite, talc, kaolin, quartz powder and kieselguhr, but also kieserite. Organic fillers include polymethylene-urea powders. Examples of thickeners are carboxymethylcellulose, cellulose ethers, acrylic acid polymers and copolymers based on vinylpyrrolidone, and silicas.

The suspensions may be sprayed onto either hot or, more particularly, cold pellets, e.g. irregularly shaped granules. If the stated amount of from 0.3 to 4 per cent by weight, especially of from 0.7 to 2 per cent by weight, of total polymeric coating substance (ureaaldehyde and/or alkylol-urea plus polyene) is employed and a suspension which contains from 30 to 65 per cent by weight of total polymeric coating substance, with or without a filler and/or a thickener is used, the residual water content is not objectionable. The granules remain free-flowing and the greater part of the water is released in the coating drum and in downstream transporting or conveying equipment. A lesser proportion of the water is absorbed by the granules. If the granules are warmed only slightly (to from 30 to 500C), as takes place, for example, in the compacting equipment, the evaporation of water is so great that the absolute increase in the water content of the granules is only about 0.5 per cent by weight.

In practice, the procedure followed is, as a rule, to produce a sheet of cascading granules in a rotary drum equipped with baffles, or in some other apparatus. These cascades are sprayed with the appropriate nozzles, which ensure good distribution of the polymer suspensions according to the invention. It is possible either to spray the cascades, which are formed parallel to the axis of the drum by the baffles which raise and throw off the granules, at an acute angle to the direction of the cascade, or to spray the cascade at an angle in a downward direction so that the suspension particles which do not adhere to the granules strike the mass of tumbling granules in the bottom quarter of the drum. Using these methods, virtually no aqueous suspension particles strike the wall of the drum, and caking and encrusting is prevented.

The method according to the invention is applicable to granular or crystalline bulk solids which dust or are hygroscopic, but in particular to irregular granules of such materials.

Examples which may be mentioned are ammonium sulfate, potassium chloride, potassium sulfate, sodium chloride, urea, calcium ammonium nitrate and multi-component fertilizers which contain urea-formaldehyde condensates, isobutylidene-urea or crotonylidene-diurea and/or urea, ammonium sulfate, ammonium nitrate, potassium nitrate, ammonium phosphates, calcium phosphates, potassium chloride, potassium sulfate, magnesium sulfate, calcium carbonate and trace element compounds.

The process according to the invention is particularly advantageous because the suspensions required can readily be made up by mixing, the spraying can be carried out in equipment which in any case forms part of a granulating or compacting unit, the material to be sprayed can be cold or hot without residual water being detrimental, and the combination of ureaaldehyde compounds and polyenes, employed in accordance with the invention, is more effective, in relatively small amounts, than are the indivudual polymer systems alone. The fertilizers and salts which are coated with the polymer combinations according to the invention cause little or no dust nuisance on handling and remain free-flowing even on prolonged storage.

EXAMPLES In the Examples, the percentages and parts are by weight.

Test series I 2 kg samples of granules and irregularly shaped granules of various fertilizers and salts are sprayed on a small whirler-coater with combinations, according to the invention of aqueous or aqueous-alcoholic solutions or suspensions of urea-aldehyde condensates and/or ureaalkylol compounds and aqueous dispersions of polyenes, the combinations being applied by means of a spray gun. For comparison, the salts and fertilizers are also sprayed with the individual components. The amounts of coating substances applied by spraying are from 0.5% to 2 per cent by weight, the time required for spraying being about 10 minutes. The samples are then left in the whirler-coater for from 2 to 5 minutes longer, after which they are filled into polyethylene bags. After from 2 to 4 days, the proportion of very fine dust (particle size < 0.1 mm) which remains in the recesses of the irregularly shaped granules even during screening, and which is responsible for the prolonged dust nuisance during handling, is determined. In addition, the samples are subjected to a modified Fisons caking test. In addition to the sprayed samples, an unsprayed sample of each fertilizer or salt is sprayed on the coater for the same period of time.

To prepare comparable starting samples, 30 kg of each fertilizer or salt are screened into fractions of > 4mm, from 4 to 3 mm, from 3 to 1.5 mm and < 1.5 mm, and test samples of equal proportions of oversized material, material of the correct size and fines are then made up from these sieved fractions.

Test series II Using a rotating drum of 10 m length and 1.8 m diameter, provided with baffles for producing a sheet of cascading granules, the fertilizer or salt granules are passed through at a rate of 4 t/h or 5 t/h and are sprayed, through slit nozzles, with the comparative coating mixture and the coating mixtures according to the invention in such amounts that from 0.5% to 1 per cent by weight of the substance is present on the various fertilizer or salt granules. The determination of fine dust is carried out with representative average samples. Instead of the caking test used in the Examples of Test series I, a bag storage test and a silo test with a 16 m drop height are carried out.

The comparative solutions or suspensions, and combinations according to the invention, used in the Examples were as follows: 1. Urea-aldehyde condensation products and condensable urea-alkylol compounds: Mixture A/1: aqueous suspension containing about 66% of resin; molar ratio urea: formaldehyde = 1:1.4; modified with 0.1 %ofdiethanolamine.

Mixture A/2: aqueous suspension containing about 60% of resin; molar ratio urea:formaldehyde = 1:1.6.

Mixture A/3: aqueous suspension containing about 40% of resin; molar ratio urea:formaldehyde = 1:1.6; modified with 6% of sulfite waste liquor in the form of calcium ligninsulfonate with the addition of 10% of ethylene glycol.

Mixture A/4: aqueous suspension containing 50% of resin; molar ratio urea:formaldehyde = 1:1.8; formaldehyde modified with higher aldehydes (n-butyraldehyde).

Mixture A/5: aqueous suspension containing 55% of resin; molar ratio urea:formaldehyde = 1:1.3; modified with 3% of butanediol, 6% of sodium sulfite and 1.5% of p-toluenesulfonic acid.

Mixture A/6: alkaline 60% strength aqueous solution (pH 8) of 20 parts of urea and 40 parts of formaldehyde (molar ratio urea:formaldehyde = 1:4).

2. Aqueous dispersions ofpolyenes Mixture B/ 1: aqueous dispersion with 50% polymer content and 1.8% of sodium laurylsulfate as surfactant. The polymer is a copolymer of 48.5% of styrene, 48.5% of butadiene, 2% of acrylic acid and 1 % of acrylamide.

Mixture B/2: aqueous dispersion with 48% polymer content and 1.2% of sodium laurylsulfate as surfactant. The polymer is a copolymer of 52.5% of butadiene, 38.4% of styrene, 5.1 % of acrylic acid and 4%of N-methylol-methacrylamide.

Mixture B/3: aqueous dispersion with 50% polymer content and 1.5 % of sodium laurylsulfate as surfactant. The polymer is a copolymer of 64% of styrene, 33% of butadiene, 2% of acrylic acid and 1 % of methacrylamide.

Mixture B/4: aqueous dispersion with 40% polymer content and 1.8% of sodium laurylsulfate as surfactant. The polymer is a copolymer of 62.3% of butadiene, 32.6% of styrene and 5.1 % of N-methylol-methacrylamide.

Mixture B/5: aqueous dispersion with 55%polymer content and 1.2% of sodium methylnaphthalenesulfonate as surfactant. The polymer is a copolymer of 90.7% of vinylidene chloride, 9% of methyl acrylate and 0.3%of acrylamide.

Mixture B/6: aqueous dispersion with 38% polymer content and 1% of sodium n-dodecylbenzenesulfonate as surfactant. The polymer is a copolymer of 48% of n-butyl acrylate, 48% of styrene, 2% of acrylic acid and 2% of acrylamide.

Mixture B /7: aqueous dispersion with 50% polymer content. The polymer is a copolymer of 55.3 %of butyl acrylate, 42.7%of vinyl acetate and 2%of acrylic acid.

Mixture B/ 8: aqueous dispersion with 48%polymer content. The polymer is a copolymer of 99 %butyl acrylate and 1 % of acrylic acid.

3. Combinations according to the invention: Mixture C/ 1: a combined suspension of 80 parts of A/ 1 and 20 parts of B / 1 = a spraying mixture containing about 63 parts of coating polymer mixture.

Mixture C/ 2: a combined suspension of 80 parts of A/1 and 20 parts of B/ 2 = a spraying mixture containing about 62 parts of coating polymer mixture.

Mixture C/3: a combined suspension of 70 parts of A/3 and 30 partsofB/3 = a spraying mixture containing about 43 parts of coating polymer mixture.

Mixture C/4: a combined suspension of 73 parts of A/1, 18 parts B/1 and 9 parts of kieselguhr as the filler = a spraying mixture containing about 57 parts of coating polymer mixture, modified with 9 parts of kieselguhr, as a water-binding substance, in the plastic coating.

Mixture C/ 5: a combined suspension of 50 parts of A/6 and 50 partsofB/4 = a spraying mixture containing about 60 parts of coating polymer mixture.

Mixture C/6: a combined suspension of 60 parts of A/4, 25 parts of B/S, 5,13 parts of water and 2 parts of finely divided silica to act as a thickener = a spraying mixture containing about 44 parts of coating polymer mixture and 2 parts of finely divided silica.

Mixture C/7: a combined suspension of 75 parts of A/1 and 25 parts of B/6 = a spraying mixture containing about 59 parts of coating polymer mixture.

Mixture C/ 8: a combined suspension of 80 parts of A/1 and 20 parts of B/ 7 = a spraying mixture containing about 63 parts of coating polymer mixture.

Mixture C/ 9: a combined suspension of 80 parts of A/1 and 20 parts of B/ 8 = a spraying mixture containing about 62 parts of coating polymer mixture.

Mixture C/ 10: a combined suspension of 75 partsof A/5 and 25 parts of B/4 = a spraying mixture containing about 51 parts of coating polymer mixture.

Test for fine dust: 50 g of an average sample of the granules to be examined are placed on an air-jet sieve. The stainless steel gauze fitted in the sieve has a mesh size of 0.1 mm. The fine dust is separated from the remaining granules by fluidization, with simultaneous suction extraction. The amount of fine dust is deduced by weighing the residue.

Caking test: As a second criterion, the tendency of the unsprayed and sprayed granule samples to cake is measured using a test developed by Levington Research Station, Fisons Ltd. (J. Sci. Food Agric. 10, 557-591 (1957); Fisons Fertilisers Limited, Levington Research Station, R. J.

Nunn; Paper repres. at ISMA Technical Conference, Wiesbaden, September 1961).

The more or less caked cylindrical mass of granules is tested in a pressure-testing apparatus (Frank Company, type 581-293). The crushing pressure is measured in kg.

Storage test: 25 kg or 50 kg of the fertilizer or salt granules to be tested are packed in airtight and moisture-tight sacks and subjected to 20 times their own weight for 5 weeks. The sack is then opened, the material is carefully emptied out and its free-flowing character is assessed.

Silo test: The material to be assessed is filled from the test production run into trucks, emptied into an underground bunker in the wardhouse, transported from there by means of a conveyor belt, elevator or the like into the silo and dropped from 16 m height onto the warehouse floor.

The dust generated is assessed qualitatively.

The results obtained in Test series I and II are summ arized in Tables 1 and 2. It may be seen from these that the fertilizers sprayed with the mixtures according to the invention and identified by C produce a substantially lower proportion of dust haze.

TABLE 1: Examples from test series I Fertilizer used Spraying Caking test: Proportion of fine dust Notes mixture used crushing ( < 0.1 mm) in % at x % coating pressure in kg x = 0.00 x = 0.50 x = 0.75 x = 1.00 x = 1.50 x = 2.00

NPK fertilizer none 32.0 1.36 - - - - 15 + 9 + 15 + 2 A/1 12.5 - 9.0 1.00 0.90 1.10 1.20 1.25 coationg flakes off asirregularly # shaped granules B/1 11.4-14.8 1.25 0.68 0.65 0.63 0.65 coating flakes off " " " B/6 10 - 8.5 - 0.39 - 0.52 coating flakes off " " " B/7 13.5-22 0.55 - 1.12 - 1.41 coating flakes off " " " B/8 10.5 lumps form; higher amounts of coating cannot be screened substance show tackiness " " " C/1 16.7-12.4 0.45 0.25 0.22 0.20 0.19 very good binding of fine dust " " " C/7 10.75-10.25 0.28 - 0.17 - 0.34 " " " C/8 10.25- 9.75 0.44 - 0.37 - 0.19 very good binding of fine dust " " " C/9 8.5- 9.5 0.73 - 0.32 - 0.27 " " " none 28.5 1.20 " " " A/3 1.25 - 1.00 0.80 0.87 coating brittle " " " B/3 0.80 - 0.88 - 0.64 " " " C/3 0.34 - 0.21 - - very goo CONTINUATION 1 TABLE 1: Examples from test series I Fertilizer used Spraying Caking test: Proportion of fine dust Notes mixture used crushing ( < 0.1 mm) in % at x % coating pressure

in kg x = 0.00 x = 0.50 x = 0.75 x = 1.00 x = 1.50 x = 2.00 15 + 9 + 15 + 2 asirregularly # A/4 0.50 0.76 0.80 1.43 1.45 coating detaches, and shaped granules dust forms " " " B/5 - 0.83 0.65 - " " " C/6 - 0.30 0.31 - - acceptable binding of dust " " " A/6 - 0.90 0.85 - 1.00 " " " B/4 - 0.80 0.60 - " " " C/5 - 0.28 0.23 - - good binding of dust NPK fertilizer none, without 35.0 0.54 - - - -

kieselguhr 15 + 9 + 15 none, with 15 -20 1.12 - - - # round granules 0.4% kieselguhr " " " A/1 9.5-10.5 0.30 0.30 0.34 0.40 0.59 " " " B/1 18.5-25 0.56 0.35 0.35 0.50 0.61 " " " C/1 26.5-13.7 0.30 0.27 0.25 0.22 0.20 good binding of dust

NPK fertilizer none 25.5 1.16 - - - - 20 + 5 + 8 + 2 asirregularly # A/1 14.7- 8.3 0.87 - 0.78 0.85 - coating is brittle shaped granules CONTINUATION2 TABLE 1: Examples from test series I Fertilizer used Spraying Caking test: Proportion of fine dust Notes mixture used crushing (0.1mm) in % at x % coating pressure in kg x = 0.00 x = 0.50 x = 0.75 x = 1.00 x = 1.50 x = 2.00 20 + 5 + 8 + 2 B/1 12.0-16.0 0.62 - 0.58 0.50 irregularly shaped granules " " " B/6 9.0-16.5 0.70 - 0.69 0.55 " " " B/7 13.3-33 0.85 0.82 0.79 " " " C/1 23.3-16.5 0.35 0.29 0.18 0.17 - very good binding of dust " " " C/7 26.0-32.0 0.36 - 0.29 0.30 - good binding of dust " " " C/8 39.7-42.3 0.44 - 0.20 0.19 - very good binding of dust

fertilizer mixture ofiso- none 18.0 1.20 - - - - butylidenediurea # and urea, 32 + 0 + 0 A/1 11.0-14.3 0.91 1.00 12.0 1.10 1.08 brittle coating flakes irregularly off shaped granules A/6 12.7-10.5 1.04 0.80 1.03 1.00 1.40 " " " B/1 9.0-20.0 0.79 1.07 0.85 0.66 0.58 " " " B/2 10.0-13.0 0.83 0.85 0.88 0.78 0.64 " " " B/4 12.0-15.0 1.07 1.10 0.95 0.80 0.83 " " " C/1 14.0- 9.5 0.65 0.60 0.40 0.35 0.28 good binding of dust CONTINUATION3 TABLE 1: Examples from test series I Fertilizer used Spraying Caking test: Proportion of fine dust Notes mixture used crushing (0.1 mm) in % at x % coating pressure in kg x = 0.00 x = 0.50 x = 0.75 x = 1.00 x = 1.50 x = 2.00

fertilizer mixture of iso- C/2 10.0-13.5 0.78 0.63 0.60 0.50 0.33 acceptable binding of butylidenediurea dust and urea 32 + 0 + 0 # irregularly C/4 8.2- 9.6 0.69 0.61 0.55 0.53 0.34 acceptable binding of shaped granules dust C/5 0.63 0.51 0.48 0.35 0.23 very good binding of calcium ammonium none, dust nitrate not 52.8 0.10 - - - - 26 + 0 + 0 powdered round granules " " " none, 30.0 1.00 - - - - powdered with 2 % of kieselguhr

" " " A/2 55.0 - - 0.14 0.35 - # good binding of dust " " " B/5 62.0 - - 0.26 0.23 - " " " C/8 32.0 - - 0.08 0.10 - - very good binding of dust TABLE 2: Examples from test series II Fertilizer used Spraying Proportion of fine dust Bag storage test Notes on silo storage mixture used ( < 0.1 mm) in % at x % coating x = 0.00 x = 0.50 x = 0.75 x = 1.00 NPK fertilizer none 1.22 hard severe dust haze 15 + 9 + 15 + 2 A/1 0.90 0.88 0.68 slightly hardened dust haze irregularly A/5 0.72 0.65 0.50 slightly hardened dust haze shaped granules " " " B/1 0.53 0.50 0.48 very slightly caked dust haze " " " B/3 0.62 0.49 0.47 very slightly caked slight dust haze " " " C/1 0.34 0.22 0.18 free-flowing no dust haze " " " C/10 0.31 0.24 0.19 free-flowing no dust haze NPK fertilizer none 1.48 hardened very severe dust haze 12 + 5 + 19 + 3 A/1 0.85 0.88 0.79 slightly hardened dust haze irregularly shaped granules B/1 0.58 0.56 0.59 slightly caked slight dust haze " " " C/1 0.43 0.35 0.26 free-flowing no dust haze ammonium sulphate none 1.14 slightly hardened severe dust haze 21 + 0 + 0 A/1 0.98 0.84 slightly caked dust haze irregularly shaped granules B/1 0.71 0.68 slightly caked dust baze " " " C/1 0.57 0.29 free-flowing slight dust haze

Claims (18)

WHAT WE CLAIM IS:

1. A process for the manufacture of dust-free and non-caking granules, which process comprises applying to the granules a surface coating of (a) a urea-aldehyde condensation product, employed as an aqueous solution or suspension, and/or an alkylolurea, employed as a 40 to 75%by weight strength aqueous solution which is weakly alkaline, and (b) a polyene, employed as an aqueous suspension or dispersion, the surface coating being applied in an amount of from 0.3 to 4 per cent by weight of condensation product and/or alkylolurea plus polyene, based on the amount of granules.

2. A process as claimed in claim 1, in which an urea-aldehyde condensation product is used which consists of a condensate of urea with an aliphatic aldehyde of 1 to 7 carbon atoms in the molar ratio urea-aldehyde of from 1:1.1 to 1:2.2.

3. A process as claimed in claim 2, in which the aliphatic aldehyde is formaldehyde.

4. A process as claimed in any of claims 1 to 3, in which a urea-aldehyde condensation product is used which is modified with an alkali metal sulfite, alkanolamine or alkylenediamine.

5. A process as claimed in claim 1, in which the granules are of urea or a fertilizer containing urea and an alkylolurea is used in which the molar ratio of urea:aldehyde is from 1:1 to 1:4.5.

6. A process as claimed in any of claims 1 to 5 in which the solution or suspension containing the urea-formaldehyde condensation product or alkylolurea contains 0.5 to 4 per cent by weight of an ammonium salt.

7. A process as claimed in any of claims 1 to 6, in which the polyene is a homopolymer or copolymer of vinyl chloride, vinylidene chloride, vinyl acetate, vinyl propionate, acrylic acid, an acrylate ester, an acrylamide, butadiene or styrene.

8. A process as claimed in claim 7, in which the polyene is a copolymer of from 80 to 95 parts by weight of vinylidene chloride, from 20 to 5 parts by weight of acrylamide.

9. A process as claimed in claim 7, in which the polyene is a copolymer of from 40 to 60 parts by weight of n-butyl acrylate, from 60 to 40 parts by weight of vinyl acetate and/or vinyl propionate and up to 2 parts by weight of acrylic acid.

10. A process as claimed in claim 7, in which the polyene is a copolymer of from 30 to 70 parts by weight of styrene and from 65 to 25 parts by weight of butadiene, with or without up to 15 parts by weight of acrylic acid, acrylamide, methacrylamide or N-methylolacrylamide.

11. A process as claimed in any of claims 1 to 10, in which the urea-formaldehyde condensation product and/or alkylolurea constitutes from 30 to 90 per cent by weight of the total of this material and the polyene.

12. A process as claimed in any of claims 1 to 11, in which the components (a) and (b) are applied to the granules in a single step from a single aqueous medium.

13. A process as claimed in claim 12. in which the aqueous medium contains a total of from 30 to 65 per cent by weight of urea-aldehyde condensation product and/or alkylolurea plus polyene.

14. A process as claimed in any of claims 1 to 13, in which a non-ionic, cationic or anionic surfactant is added to the solution(s) or suspension(s) in an amount of up to 1 per cent by weight, based on the amount of solids.

15. A process as claimed in any of claims 1 to 14, wherein irregularly shaped granules are coated.

16. A process as claimed in any of claims 1 to 15, where-in granules of a fertilizer or a salt are coated.

17. A process for the manufacture of dust-free and non-caking granules as claimed in claim 1 and carried out substantially as described in any one of the foregoing specific examples.

18. Granules whenever obtained by a process as claimed in any preceding claim.