US 3366570 A
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United States Patent 3,366,570 PROCESS OF PREPARING DETERGENT TABLETS Arie Willem Slob, Schiedam, Netherlands, assignor to Lever Brothers Company, New York, N.Y., a corporation of Maine No Drawing. Filed May 14, 1962, Ser. No. 194,658 Claims priority, application Great Britain, May 15, 1961, 17,536/ 6 1 12 Claims. (Cl. 252-99) This invention relates to detergent tablets and, in particular, to a method of preparing detergent tablets from detergent powders.
It is an object of the invention to provide a detergent tablet which is sufficiently hard for handling, packing and storing but which easily dissolves when added to water.
The invention provides a process for preparing a detergent tablet in which a detergent tablet containing a liquefiable substance and other ingredients, said liquefiable substance being capable of being liquefied by heating without affecting said other ingredients, is agglomerated into the form of a tablet; the agglomerated detergent powder is heated at a temperature and for a time sufii cient to convert at least part of said liquefiable substance into liquid but insufiicient to affect said other ingredients; and the agglomerated detergent powder is cooled to convert said liquid into solid material, whereby said solid material binds the agglomerated detergent powder into a tablet.
The liquefiable substance referred to must be compatible with the other ingredients of the detergent powder and its liquefaction temperature must not be too high. Suitable substances include salts containing water of crystallization such as sodium sulphate -hydrate, sodium carbonate l-hydrate, sodium perborate 4-hydrate, aluminum sulphate IS-hydrate, sodium borate IO-hydrate and alum 24-hydrates, especially potassium aluminum sulphate 24-hydrate. The same salts with a lower hydrate content may also be used. Salts such as anhydrous sodium carbonate and sodium hexametaphosphate which, it is believed, become at least partially hydrated when incorporated in a detergent powder by absorption of water from the other ingredients of the powder and from the atmosphere may be suitable under certain conditions. Other substances which may be used are sugar and gelatin.
Heating may be carried out in such a way that the agglomerated detergent powder is uniformly heated or that only the surface of the agglomerated powder is heated. In the first case heating may be conveniently carried out in microwave furnaces or by means of capacitive heating apparatus; in the second case heating may be carried out by contact heating, that is, the surface of the agglomerated detergent powder may be heated by contact for a short time with hot plates or hot air. Contact heating gives particularly good results when hydrated sodium perborate is used as the liquefiable substance. Contact heating may be carried out so that the tablet formed has a hard smooth crust, and a core of powder. The crust sufiiciently protects the powder contained in the interior of the tablet while the tablet is being handled. When such a tablet is put into water it generally dissolves very quickly. The water penetrates into the small pores on the hardened surface layer, rapidly disintegrating this layer and freeing the powder contained in the interior of the tablet. Alternatively, the process may be carried out in such a way that the whole tablet is hard. Itis necessary that the liquefiable substance be distributed homogeneously throughout the detergent powder.
3,366,570 Patented Jan. 30, 1968 The heating process of the invention may be compared to a sintering process, for the heating process must be such that the detergent powder is not completely melted.
The temperature to be used during the process of the invention depends on the liquefiable substance which is used, the composition of the detergent powder and the desired qualities of the product. If hydrated sodium perborate, which is the preferred material, is used the temperature used is preferably between 60 and C. if all the agglomerated powder is heated, in order to restrict the decomposition of the perborate, but if only the surface of the agglomerated powder is heated, much higher temperatures may be used. When heat is applied only to the surface of the agglomerated powder, the heat conductivity of the material is of importance. If the heat penetrates only slowly into the powder it is in general possible to use temperatures of up to 300 C. In other modifications of the invention temperatures as low as 40 C. may be used depending on the type of composition.
The amount of the liquefiable substance to be used also depends on the properties of the substance itself and the detergent powder. The minimum amount of the liquefiable substance must be such that a satisfactory sintering action is obtained. The minimum amount of liquefiable substance is about 2% by weight of the powder; the upper limit is determined by the properties of the product which are desired. Percentages as high as 40% of liquefiable substance by weight of detergent powder may be used.
After the agglomerated detergent powder has been heated, the agglomerate must be left for a certain time to cool before a satisfactory tablet results. This resting time may be very much shortened by irradiating the product or placing it in a stream of air or under vacuum. In the last case, resting times of a few minutes are sufficient to obtain a very good hard product.
The tablet may be further improved by a coating with a suitable substance. As g; sulastgpc gjhere maybe used, for example, xinyljfilfgl f iggl ng; water glass. A
Further improvements may be obtained by treating the tablet for a short time with steam. In that way surface irregularities are removed and the surface made smooth. The same effect may be obtained by sprinkling the surface with water.
Very slight pressure is needed to bring the detergent powder into the enecessary agglomerated form for heat treatment; if it is desired to make a very compact tablet, the pressure employed in this operation may be slightly increased but it is a feature of the invention that tablets may be obtained without the use of high pressure compacting.
The following examples illustrate the invention:
Example 1 A high sudsing heavy duty detergent powder base of the following composition was made:
Fluorescent brightening agent, perfume and preservative Water 10 11 parts by weight of sodium perborate tetrahydrate were homogeneously mixed with this detergent powder base. The resulting detergent powder was placed in a per- The tablets obtained had very good properties, were re- I sistant to handling and were radially soluble in water.
The metal container may also be heated by means of high-frequency inductive heating (eddy-currents and/or hysteresis losses).
If no perborate was added to the detergent no satisfactory tablet was obtained.
Example 2 A controlled sudsing heavy duty detergent powder base of the following composition was made:
12 parts by weight of sodium perborate tetrahydrate were homogeneously mixed with this detergent powder base. An amount of the resulting detergent powder suflieient to produce a tablet of dimensions of 69 x 57 x 25 mm. was heated in a microwave oven with microwaves of 2450 me. The heating by this method was homogeneous, that is to say, the energy absorption of each part of the tablet was the same. The temperature of the powder rose above 120 C. within a few minutes. The perborate decomposition, which is dependent on the amount of energy supplied, was estimated at 10-15%. The tablets produced were very strong and could be dropped several times without breaking. They were readily soluble in water.
Tablets were also produced by homogeneously sintering the powder together by means of capacitive heating. The agglomerated detergent powder was brought between two condenser plates, to which an alternating voltage of 30 me. was applied. The tablets obtained were readily soluble, but somewhat brittle.
Tablets were made of similar detergent powders in which the sodium perborate was replaced by an equal amount of powdered sugar, sodium carbonate 10-hydrate, potassium aluminum sulphate 24-hydrate and aluminum sulphate 18-hydrate. Tablets with the same good properties were obtained.
Tablets prepared without the addition of the above-mentioned components were very soft and rapidly fell to pieces.
Example 3 To each of a number of the units of agglomerated detergent powder described in Example 2, 1.2 kcal. heat was transferred in 90 seconds by means of inhomogeneous heating. Subsequently the disintegration time under practical conditions of the tablets obtained was measured. This was done by moving the tablets constantly up and down in a basket in a certain amount of water at a constant temperature. The disintegration time of tablets obtained by using inhomogeneous heating methods with a heat transfer of 1.2 kcal. per 90 seconds, varied between 30 and 15 seconds. The disintegration time of tablets obtained by using more heat, namely, 3.5 kcal. in 8.5 min., on average was 45 seconds.
4 Example 4 A controlled sudsing heavy duty detergent powder base of the following composition was made:
Parts by weight Sodium alkylbenzene sulphonate 6 1 Soap 4 Sodium silicate 8 Sodium sulphate 15 t Nonionic 5 10 Sodium tripolyphosphate 42 l Sodium carboxymethylcellulose 0.5 Fluorescent brightening agent, perfume and preservai tive 0.5 Water 9 In preparing the detergent composition the first four ingredients were spray-dried and mixed with the other ingredients.
10 parts by weight of sodium perborate tetrahydrate were thoroughly mixed with this detergent powder base. An amount of the resulting detergent powder was just sufiiciently pressed to obtain an agglomerate suitable for the sintering operation. Such an agglomerate has no impact resistance. The tablet was brought into an electrically heated oven and heated for about 2 to 3 minutes with hot air, the temperature in the oven ranging from 240 to 275 C. In view of the low heat-conductivity of the powder the heating is inhomogeneous. The temperature inside the tablet reached values up to 65 C.
After cooling a tablet was obtained which could be dropped more than ten times before breaking and which dissolved in water in about 75 seconds. The tablet was totally hardened.
Example 5 A controlled sudsing heavy duty detergent powder base of the following composition was made:
Parts by weight i Sodium alkylbenzene sulphonate 4 1 Soap 6 49 Sodium silicate 8 Sodium sulphate l4 Nonionic 3 Sodium tripolyphosphate 27 Sodium pyrophosphate 18 Sodium carboxymethylcellulose 1 Fluorescent brightening agent, perfume and preservative 0.5 Water 10 The first four ingredients were spray-dried and mixed 50 with the other ingredients.
8.5 parts by weight of sodium perborate tetrahydrate were thoroughly mixed with the detergent powder base. An amount of the resulting detergent powder was brought into tablet form by means of weak pressure. The agglo crate thus obtained had no impact resistance.
. The agglomerate was heated in an oven by means of circulating hot air to a temperature of about 190 C. for 6 minutes. The temperature in the centre of the tablet was about 65 C. After cooling the tablet thus obtained could be dropped more than twenty times before breaking. It dissolved in water in less than seconds. The tablet was totally hardened.
Example 6 To a controlled sudsing heavy duty detergent powder base of the composition given in Example 2, 10% by weight of sodium perborate tetrahydrate was added. After thorough mixing a quantity of the detergent powder was heated in a perforated metal box having dimensions of 10 x 22 x 27 mm. by flame. A strong tablet was obtained, which readily disintegrated in water. The decomposition of perborate, however, was relatively high and more than 20% of the perborate originally present in the superficial layer was decomposed. A quantity of the same detergent powder W45 heated in a metal mould of dimensions 50 x 50 x 30 mm., placed in a transformer coil, as described in Example 1. In this way the heating conditions could be better controlled, which resulted in a reduced decomposition of the perborate. With a heat transfer of 1.2 kcal. in 90 seconds to the powder mixture, only about 15% of the perborate originally present in the superficial layer of about 1.5 mm. was decomposed. The mean perborate content was reduced from 10.2 to 9.1%. The temperature reached at the centre of the tablet was about 50 C. The same type of inhomogeneous heating may be effected by heating the mould in an oven or by means of induction coils. The same results could be obtained without the use of moulds, by means of slightly prepressing the powder into the form of a tablet and then applying the heating method described above. Two kinds of tablets were produced, the one being hard on the outside and brittle inside and the other having a very hard surface under which there was a somewhat brittle layer, the remainder consisting of loose powder. Both tablets had very good properties, being resistant to handling and readily soluble in water.
The resting time of the tablets made according to the foregoing examples can be reduced to a few minutes by cooling the tablets after the heating step under vacuum. The surface of the tablets can be made smooth by additional surface treatments, e.g. by treating the surface with steam, or hot water. The appearance of the tablets can be further improved by coating the surface with polyvinyl alcohol, paraffin wax or water glass. A surface treatment with steam or hot water did not increase the disintegration time of the tablets. Coating the tablets with water glass, however, resulted in a slight increase of the disintegration time. Tablets with a disintegration time of 15-30 seconds had, after coating with water glass, a disintegration time of about 50 seconds.
What is claimed is:
1. A process for the preparation of a strong, hard surface, rapidly disintegrating and dissolving detergent tablet which comprises thoroughly mixing together a powdered detergent composition and from about 2% to about 40% by weight of the powdered detergent composition of a liquefiable substance selected from the group consisting of hydrated sodium sulfate, hydrated sodium carbonate, hydrated sodium perborate, hydrated aluminum sulfate, hydrated sodium borate, hydrated potassium aluminum sulfate, anhydrous sodium carbonate, anhydrous sodium hexametaphosphate, sugar and gelatin having a liquefication temperature from about 40 C. to about 300 C. and being compatible with the ingredients in the powdered detergent composition, forming the resulting mixture having the compatible liquefiable substance uniformly distributed therethrough into the shape of a tablet, heating the tablet-shaped mixture at a temperature from about 40 C. to about 300 C. for from about 90 seconds to about 6 minutes to liquefy thereby at least the portion of the liquefiable substance at the surface of the tablet-shaped mixture without completely melting the powdered detergent composition, and cooling the tablet-shaped mixture to convert the liquefied liquefiable substance to solid state and thereby bind together at least the portion of the powdered detergent composition at the surface of the tablet-shaped mixture, whereby there is formed a strong detergent tablet which disintegrates and dissolves in water in about 15 to 75 seconds and which has a hard agglomerated surface portion and a center portion having a consistency in the range from hard agglomerates to loose powder.
2. The process as set forth in claim 1 wherein the forming of said mixture into the shape of a tablet is performed by placing the mixture into a tablet-shaped mold.
3. The proces as set forth in claim 1 wherein the forming of said mixture into the shape of a tablet is performed by lightly compressing the mixture to tablet shape.
4. The process as set forth in claim 1 wherein the tablet-shaped mixture is uniformly heated therethrough during the heating step.
5. A detergent tablet prepared by the process of claim 4 which comprises hard agglomerates throughout.
6. The process as set forth in claim 1 wherein only the surface portion of the tablet-shaped mixture is heated during the heating step.
7. A detergent tablet prepared by the process of claim 6 which comprises a hard agglomerated surface portion and a center portion of loose powder.
8. The process as set forth in claim 1 wherein the cooling of the tablet-shaped mixture is performed by placing it in a stream of air.
9. The process as set forth in claim 1 wherein the cooling of the tablet-shaped mixture is performed by placing it under vaccuum.
10. The process as set forth in claim 1 which comprises the further step of coating the cooled detergent tablet with a material selected from the group consisting of polyvinyl alcohol, paraffin wax and water glass.
11. The process as set forth in claim 1 which comprises the further step of treating the surface of the cooled detergent tablet with moisture to smoothen the surface of the tablet.
12. The process as set forth in claim 1 wherein the liquefiable substance is a hydrated sodium perborate.
References Cited UNITED STATES PATENTS 1,457,217 5/1923 Dostal 252-92 2,444,837 7/1948 MacMahon 252-l35 2,807,559 9/1957 Steiner 16782.7 2,875,155 2/1959 Miles 252-138 2,876,200 3/1959 Strain et a1. 252-99 3,120,378 2/1964 Lee et a1 25299 X FOREIGN PATENTS 510,555 3/1955 Canada.
OTHER REFERENCES Merrill, Industrial Applications of the Sodium Silicates February 1949, Industrial and Engineering Chemistry, p. 341.
LEON D. ROSDOL, Primary Examiner.
JULIUS GREENWALD, ALBERT T. MEYERS,