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Desiccant powder, its use for the drying of solid substrates, in particular grains or seeds

Abstrict

The present invention relates to a novel desiccant powder and its use for the drying of solid substrates wetted by an aqueous or oily liquid such as, in particular, grains or seeds having undergone a coating or surface film-forming treatment. According to the invention, this desiccant powder contains at least 50% by weight of absorbents with respect to the toal weight of the said powder, being preferably available in the form of particles having a mean diameter less than about 100.mu., the said absorbents being constituted of at least one aluminosilicate, in particular mica, to at least 25% by weight with respect to the total weight of the said absorbents. This powder makes possible, in particular, the drying of colored grains or seeds.

Claims

We claim:

1. A process for drying a germinative substrate of grains or seeds which have been wetted in a coating or surface film-forming treatment, said process comprising dusting said substrate with a desiccant powder comprising absorbents in an amount of at least 50% by weight with respect to the total weight of the powder, said absorbents comprising at least one aluminosilicate in an amount of at least 25% by weight with respect to the total weight of the absorbents, said substrate being dusted with 0.5 to 50 g of dessicant powder per kilogram of substrate, said powder being substantially free of components which would interfere with germination of the substrate.

2. A process according to claim 1 wherein the dessicant powder further comprises a pigment, said pigment being present in said powder in an amount of up to 50% by weight.

3. A process according to claim 2 wherein said pigment is a micaceous pigment.

4. A process according to claim 2 wherein said pigment is present in the form of a pigmentary paste.

5. A process according to claim 2 wherein said powder further comprises a flow-promoting agent, said flow-promoting agent being present in said powder in an amount of up to 20% by weight.

6. A process according to claim 5 wherein the flow-promoting agent is powdered silicas.

7. A process according to claim 1 wherein said absorbents are in the form of particles having a mean diameter of less than 100 um.

8. A process according to claim 1 wherein said at least one aluminosilicate is selected from the group consisting of

mica, the illites, the micaceous clays, the micaceous pigments, kaolin, kaolinite, dickite, nacrite, the montmorillonites, the smectites, the glauconites, the attapulgites and the vermiculites.

9. A process according to claim 1 wherein said at least one aluminosilicate comprises mica.

10. A process according to claim 1 wherein said absorbents further comprise at least one substance selected from the group consisting of talc, cellulose and its derivatives, and silica.

11. A process according to claim 10 wherein said absorbents consist essentially of said at least one aluminosilicate and said at least one substance, said at least one substance being present in said absorbents in an amount of up to 75% by weight.

12. A process according to claim 10 wherein the powder consists essentially of said at least one aluminosilicate, said at least one substance, a pigment, and a flow-promoting agent.

13. A process according to claim 10 wherein the powder consists essentially of said at least one aluminosilicate, said at least one substance, a pigment, a film-forming agent and a flow-promoting agent.

14. A process according to claim 1 wherein the powder further comprises a pigment and a film-forming agent, and wherein the pigment and the film-forming agent are present in the powder in an amount of up to 50% by weight.

15. A process for coating a germinative substrate of grains or seeds with a dressing to protect or to accelerate the germination of said substrate, said process comprising

(a) forming a film or coating on the substrate by treating said substrate with a fluid composition comprising said dressing, a film-forming agent and water, said composition being sufficiently fluid to ensure uniform distribution of the dressing on the substrate; and

(b) removing at least some of said water from said substrate by dusting the substrate with a dessicant powder comprising absorbents in an amount of at least 50% by weight with respect to the total weight of the powder, said absorbents comprising at least one aluminosilicate in an amount of at least 25% by weight with respect to the total weight of the absorbents, said substrate being dusted with 0.5 to 50 g of dessicant powder per kilogram of substrate, said powder being substantially free of components which would interfere with germination of the substrate.

16. A process as claimed in claim 15 wherein the film-forming agent is glossy, and the substrate after it has been dusted with said powder has a glossy appearance.

17. A process as claimed in claim 15 wherein the fluid composition comprises about 50 grams/kilo of substrate treated.

Description

Substantially, the object of the present invention is a novel desiccant powder intended, in particular, for the drying of solid substrates wetted by an aqueous or oily liquid such as, in particular, grains or seeds having undergone a coating or surface film-forming treatment.

It is known that the germination capacities of grains or seeds can be improved by a coating or surface film operation designed to affix dressing agents for specific additives in predetermined amounts to these grains or seeds, preferably in a uniform manner.

More precisely, this operation consists of applying to the grains or seeds, for example, by spraying, blending, churning or any other known means, a "paste" of surface film or coating containing essentially plant protection, fungicidal or insecticidal dressings, additives designed to accelerate germination (micro-organisms, trace elements) in an aqueous solution of film-forming agents. In addition, this paste may contain various additional agents, such as binders, pigments or coloring materials, plasticizers and wetting agents.

The film-forming agents which may be used for the surface film formation are usually film-forming polymers soluble or dispersible in water, not exhibiting phytotoxicity and not causing delay or decline in germination. Such polymers are, for example, acrylic polymers, polyvinyl alcohols, polylactones and cellulose derivatives. The document EP-O 133 827 incorporated here for reference, describes various examples of film-forming compositions for the coating of solid substrates.

The operation of film formation or coating makes possible a more rational and more efficient use of the dressing agents and additives dosed with precision for each seed.

In addition, the application of a surface film to grains or seeds offers the following three advantages:

it gives to the grain or seed a smooth and attractive appearance, in particular when the film is colored;

it permits easy identification, for example, as a result of surface coloration;

finally, it provides better flow in the drills and other mechanical transfer devices in which the grains slip easily over each other.

Moreover, in order to ensure a good distribution of the dressing agents and additives on the grains and seeds, the paste from which the surface film is formed and in particular the film-forming solution must be sufficiently fluid. For this purpose, the dry material content rarely exceeds 15 to 20% by weight. Consequently, relatively large amounts of water (up to about 50 g per kilo of seeds treated) are to be removed by a drying operation.

This drying operation which, from an industrial point of view, must be rapid, efficient and inexpensive, usually proves to be difficult. In fact, some grains, as for example soja, rapidly absorb water when they are in contact with the surface film paste. The resulting excess internal humidity may lead to undesirable biochemical reactions, impair grain storage and modify its germination capacity. Furthermore, the absorption of water is usually accompanied by swelling of the grain, which only very slowly resumes its initial form. Now, the film surrounding the grain is not always sufficiently elastic to cope with these variations in volume and there is a risk of signs of disintegration and/or cracking appearing.

Moreover, the formation of agglomerates of film-coated grains is observed when drying is insufficient or too slow. Such agglomerates do not lead to uniform seeding and are thus to be avoided.

Finally, in the case of many types of seeds, particularly those of large-scale crops, the initial cost created by the operation of surface film formation, and in particular the drying operation, must be kept to a minimum. This constraint makes it practically impossible to use sophisticated and expensive machinery.

Among the known drying techniques, hot air blowing is one of the most commonly used.

In the case of grains with high added value representing small volumes (kitchen garden and flower seeds, some hybrid species), equipment of the fluidized air bed type is used. On the other hand, for less select seeds, simple tunnels or ventilated turbines, operating at high throughput, are used.

However, air blowing presents a certain number of disadvantages which limits its value.

In fact, the efficiency of this drying technique remains low on account of the low temperatures used in order not to damage the seeds.

In addition, this technique entails heavy expenditure owing to the depreciation costs of the equipment and the expensive energy consumption.

Finally, this technique causes certain pollution problems.

The problem of drying has been resolved by the use of desiccant powders. More precisely, powders are dusted onto the film-coated grains, by remaining fixed to the film former, by thus avoiding any correlative risk of dust formation during the subsequent handling of the grains or seeds.

The use of desiccant powders is a technique which does not require any expensive investment and which can be implemented easily on all existing types of film-forming or coating materials.

All of the desiccant powders used hitherto are based on magnesium silicate, in particular they are based on talc or serpentine.

However, the grains dried with talc possess a dull, lackluster, whitish appearance. This disadvantage is negligible when the grains are coated or covered with a surface film by means of a colorless film-forming agent, but becomes quite flagrant when the surface film is formed with colored or glossy film-forming agents, one of the objectives of which is to give to the grain or seed an attractive appearance.

The aim of the present invention is to resolve the technical problem consisting in the provision of a novel desiccant powder possessing the same advantages as the magnesium silicate-based desiccant powders without having their disadvantages previously mentioned.

It has been discovered, and that constitutes the basis of the present invention, that the use of aluminosilicate-based, and in particular mica-based, desiccant powders enables the appearance of the grains thus dried to be considerably improved. In fact such grains possess a vivid appearance and their coloration is unaltered.

In addition, it has been quite unexpectedly discovered that the amounts of such novel desiccant powders required for use are much lower than the amounts of known desiccant powders based on talc in order to obtain the same degree of drying.

Thus, according to a first feature, the present invention relates to a desiccant powder intended in particular for the drying of solid substrates wetted by an aqueous or oily liquid such as, in particular, grains or seeds having undergone a coating or surface film-forming treatment, characterized in that it contains at least 50% by weight, with respect to the total weight of the said powder, of absorbents preferably available in the form of particles having a mean diameter of less than about 100.mu., the said absorbents being constituted of at least one aluminosilicate to at least 25% by weight with respect to the total weight of the said absorbents.

According to a particular characteristic of the invention, this aluminosilicate is selected from the group constituted by mica, the illites or micaceous clays, the micaceous pigments, kaolin and its modifications, such as kaolinite, dickite, nacrite, the montmorillonites or smectites, the glauconites, the attapulgites, the vermiculites.

According to a preferred embodiment, the aforementioned aluminosilicate is mica.

The absorbents contained in a desiccant powder conforming to the invention may be constituted exclusively of one or several aluminosilicates, but may also be constituted of one or several aluminosilicates in a mixture with one or several traditional absorbents such as talc, cellulose, silica. The person skilled in the art will easily be able to define compositions of absorbents according to the intensity of the glossy effect which it is desired to give to the substrates.

According to another particular characteristic of the invention, this desiccant powder contains, in addition, up to 50% by weight, with respect to the total weight of the said powder, of a pigment, a micaceous pigment, a coloring matter or a pigmentary paste.

According to another particular characteristic, a desiccant powder conforming to the invention contains, in addition, up to 50% by weight, with respect to the total weight of the powder of at least one film-forming agent. The presence of such a film-forming agent within the powder confers on this latter an improved adherence to the solid substrate to be dried. It is possible to use any known type of film-forming agent, and in the particular case of seeds or grains, film-forming agents of the same type as those used for the coating operation.

According to another particular characteristic, a desiccant powder conforming to the invention contains, in addition, up to 20% by weight, with respect to the total weight of the powder, of at least one flow-promoting agent such as, in particular, powdered silicas. The addition of one or several flow-promoting agents to the desiccant powder improves the uniformity of the dusting of the substrate. It is possible to use as flow-promoting agent all of those commonly used in the food or pharmaceutical industries and, in particular, powdered silicas, in particular Aerosil.RTM. (registered trademark) or Sipernat.RTM. (registered trademark).

The novel desiccant powders conforming to the present invention possess the following general characteristics:

they are not toxic towards the substrates; in the case in which the substrate is a grain, no modification of germination is observed;

they are compatible with plant protection products and do not bring about any impairment of their activity;

they exhibit a high absorbent capacity (large specific surface), and stable physical structures.

According to a second feature, the present invention relates to the use of a desiccant powder such as previously defined for the drying of solid substrates wetted by an aqueous or oily liquid such as, for example, grains or seeds having undergone a coating or surface film-forming treatment.

Finally, according to a last feature, the present invention aims to cover a process for the drying of solid substrates wetted by an aqueous or oily liquid such as, in particular, grains or seeds having undergone a coating or surface film-forming treatment, characterized in that it comprises the dusting of a desiccant powder such as previously defined in an amount of 0.5 to 50 g per kilogram of solid substrates.

The following non-limiting examples illustrate the novel desiccant powders conforming to the invention and their utilization.

In these examples, the aluminosilicate is usually mica, which has proved to be particularly useful for the manufacture of these novel desiccant powders.


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