WO1996014927A1

WO1996014927A1 - Method and apparatus for coating particles

Info

Publication number: WO1996014927A1
Application number: PCT/IT1995/000176
Authority: WO
Inventors: Lorenzo Rodriguez; Maurizio Cini
Original assignee: G.S. S.R.L. Coating System
Priority date: 1994-11-09
Filing date: 1995-11-06
Publication date: 1996-05-23
Also published as: ITBO940492A1; IT1274102B; ITBO940492A0

Abstract

A method for coating particles (2) includes transporting them, suspended in a fluid carrier formed by an air flow along with a coating forming solution. An apparatus that carries out this method includes a pan (1) aimed at receiving a mass of particles (2) to be coated. A recirculation conduit (5) extends axially from the pan (1) and leads to the opposite side thereof. A pipe (6), aimed at introducing an air flow forming the fluid carrier for conveying the particles (2) along the conduit (5), is situated inside the pan (1), in coaxial relation therewith, and opens in a narrowed part (4) thereof. A tube (7), delivering the coating forming solution, is situated inside the said pipe (6), in coaxial relation therewith.

Description

METHOD AND APPARATUS FOR COATING PARTICLES

TECHNICAL FIELD

The present invention relates to coating various articles.

BACKGROUND ART

At present, there are known machines that coat various articles, as tablets, pills and the like, with e.g. a film obtained from a suitable solution or suspension.

According to a known solution, these machines include a rotating pan, inside which particles to be coated are introduced.

The coating forming solution is sprayed on these particles, while a hot air flow circulates inside the pan in order to dry the solution and form the said coating.

Some apparatuses introduce and aspirate the air freely on the surface of the particles mass, made to move by rotation of the pan.

However, this method needs very long working time and causes production of powder whose quantity increases continuously during the process.

In another solution, the air is introduced and aspirated through suitably shaped hollow bodies that penetrate the mass of moving particles.

The disadvantage of this method results in a big consumption of energy necessary for ventilation.

Another drawback of this method is the size limit of the particles to be coated, because coating of very small particles is difficult . An improved coating machine is disclosed in the EP-A-0 131 152 of the same Applicant. In this case, the air is introduced freely inside the rota¬ ting pan, and it is aspirated by one or more hollow perforated bodies, immersed in the mass of moving particles. Inside the pan, there are plates aimed at facilitating the particles mixing.

Further known method uses blowers, situated vertically inside a suitable container, aimed at producing a jet of vaporisation air directed up¬ wards,- this jet of air creates a fluid bed that, in coating stage, keeps the mass of particles raised.

The drawback of this solution consists in a considerable delivery of air necessary to create the said fluid bed, that leads to high production cost.

In fact, in order to supply air, a turbine is usually used and, moreover, suitable filters for pulling down the powder are required.

Another reported disadvantage of this inven- tion lies in fact that it does not allow small particles to be coated.

DISCLOSURE OF THE INVENTION

The object of the present invention is to propose a method that permits to coat, in an innova¬ tive way, various, even very small articles, in a rapid working cycle, without producing powder. Another object of the present invention is to propose a simple and versatile apparatus, carrying out the above mentioned method, requiring a limited air supply.

The above mentioned objects are obtained by means of a method for coating particles that in¬ cludes a recirculation of particles to be coated, - 3

conveyed suspended in a fluid carrier formed by an air flow with the coating substance.

The apparatus for carrying out the method includes a pan, designed to receive the mass of particles to be coated, a recirculation conduit, extending axially from the pan and leading to the opposite side thereof, a pipe, aimed at introducing an air flow forming the fluid carrier for conveying the particles along the conduit, and situated inside the pan, in coaxial relation therewith, and opening in a narrow part thereof, and a tube 7, delivering the coating forming solution, situated inside the said pipe, coaxially therewith.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristic features of the present invention are pointed out in the following descrip- tion with reference to the enclosed drawings, in which:

- figure 1 shows a schematic longitudinal section view of the apparatus for coating particles,-

- figure 2 shows a correspondent partial plan view of this apparatus;

- figure 3 shows a schematic longitudinal section view of another embodiment of the subject apparatus.

BEST MODES OF CARRYING OUT THE INVENTION

With reference to the above described fig¬ ures, the particles 2 to be coated are introduced into the pan 1 of the coating apparatus . in its lower part, the pan 1 features a narrow portion 3 , suitably connected with the wider central band of the pan. The narrow portion 3 of the pan is connected, by a conical section 4, with a recirculation conduit 5; this recirculation conduit 5 is linked with the pan 1 at its other end. More precisely, a section 5a of the recircu¬ lation conduit 5, tangential with respect to the pan 1, enters the upper part of the central band of the same pan. The conduit 5 extends according to an axis inclined in a suitable way so as to lift gradually the particles.

A pipe 6, aimed at introducing an air flow, is inserted inside the pan 1, in coaxial relation therewith, and opens in the narrow portion of the conical section 4 of the same pan 1. At its free end, the pipe 6 features a ta¬ pered segment 6a.

The tapering angle of the segment 6a is smaller than the tapering angle of the conical section 4 of the pan, so that the free section between the two of them decreases in direction of the above mentioned narrow portion.

The air flow is aimed at creating a kind of fluid bed conveying the particles 2 along the recir¬ culation conduit 5. A tube 7, delivering the solution for coating the particles 2, is situated inside the said pipe 6 for introducing air, coaxially therewith.

The coating forming solution is suitably pumped through the tube 7 by dosing means, not shown. In its upper part, the pan 1 features also a plurality of outlets 8, through which the recircula¬ tion air goes out.

Therefore, the particles 2, introduced into the pan 1, are exposed to the action of the air flow introduced through the pipe 6. The air flow that enters the recirculation conduit 5 sucks the particles 2, due to the Venturi effect produced at the outlet of the pipe 6, by the narrowing of the conical part 4 of the pan.

Likewise, the solution fed by the tube 7 is sucked, due to the Venturi effect produced by the tapering of the pipe 6 in the tapered segment 6a.

In this way, along the recirculation conduit 5, a fluid carrier is formed by the air flow along with the coating forming solution; particles 2 are conveyed suspended in this carrier to be coated by the above mentioned solution, while simultaneously, the air flow dries them.

As a consequence, the fluid carrier pushes the particles 2, that in this way can be brought to the processing zone. The fluid carrier returns to the pan 1, where the air goes out through the upper outlets 8, while the particles 2 fall down in the lower part of the pan 1, so as to continue the processing cycle. Consequently, the coating of the particles 2 is increased with each passage through the recircu¬ lation conduit 5.

The number of passages can be reckoned on a statistical basis, and, in a sufficiently long period of time, all the particles 2 are supposed to have performed the same number of coating cycles .

Obviously, the processing time depends on the characteristics of the products to be obtained, i.e. in particular on the type of processed particles. it is to be noted that the air flow, flowing in the recirculation conduit 5, is reintroduced to the pan 1 according to a tangential direction: as a consequence, the particles 2, dragged by the said flow, during their downward movement, are set in vortical movement, like a whirlwind, while the bigger part of the air reintroduced to the pan, goes out through the outlets 8.

This allows to better mix the particles 2, thus optimising the downward movement and separation of discharge air, and consequently, obtaining a final product of better quality.

In order to improve the mixing efficiency, it is possible to create a relative movement of the pan 1 with respect to the pipe 6, be e.g. making the pan 1 rotate axially. Obviously, this operation would need suitable connections of the mutually rotating parts.

It is also possible to pre-heat the air introduced in the pan 1, so as to improve drying efficiency. It is also possible to suck the air inside the pan, instead of delivering it under pressure.

This modification would require a suitable depression inside the pan 1, improving the drying of the coating. Figure 3 presents a different embodiment of the apparatus, in which a reservoir 9, with conical bottom, aimed at increasing the equipment capacity, is provided along the recirculation conduit 5, upstream of the tangential section 5a connecting the recirculation conduit 5 to the pan 1.

A channel 10, designed to allow the air flow to flow freely, is situated inside the reservoir 9.

The channel 10, suitably tapered, extends from the top of the reservoir 9, where the recircu- lation conduit 5 opens, to the outlet of the same reservoir.

The particles 2 are blown from the conduit 5 inside the reservoir 9 and fall on the bottom of the latter, where the dragging force of the air flow passing through the low resistance way formed by the channel 10, acts. The disclosed method and apparatus allow to coat various articles in an innovative way. In particular, it is possible to process all kinds of articles, in particle size, even very small. Obviously, the above mentioned coating can be also include an active element, not only protection of the particles like tablets and the like.

For instance, the subject method permits to combine active principles, like those used in home- opathy, with suitable carrier, as saccharose gra¬ nules and the like.

The active principles can be diluted in water nebulized inside the apparatus and absorbed by the above mentioned granules. It is possible to use the method also in zootechnics, for incorporating suitable substances in conventionally used articles.

It is to be pointed out that in traditional solutions a fluid bed maintained the mass of parti- cles lifted, whereas the present invention provides a fluid conveyor that allows to move the particles to the desired zone with a very reduced delivery of air and limited power.

The above mentioned fluid bed requires con- duits of reduced diameter and consumes less air.

Moreover, it is to be pointed out that the quantity of powders and the like is drastically reduced during the coating procedure,- in addition, the powders formed during the coating stages, set down on the particles, since they belong to the same category of components contained in the solution fed by the tube 7 ; in other words, the powders become an integral part of the particles coating.

It is understood that what above has been described as a mere, not limitative example, there¬ fore all possible constructive variants are protec- ted by the present technical solution, as described above and claimed in the following.

Claims

1. Method for coating particles, characterised in that including recirculating the particles to be coated, conveyed suspended in a fluid carrier formed by an air flow with the coating substance.

2. Apparatus for coating particles, characterised in that it includes: a pan (1) designed to receive the mass of particles (2) to be coated; a recirculation conduit (5) extending axially from the pan (1) and leading to the opposite side there¬ of; a pipe (6) , aimed at introducing an air flow forming the fluid carrier for conveying the particles (2) along the conduit (5) , and situated inside the pan (1) , in coaxial relation therewith, and opening in a narrow part (3) thereof; a tube (7) , delivering the coating forming solution, situated inside the said pipe (6) , coaxially there^¬ with.

3. Apparatus, according to claim 2, characterised in that a section (5a) of the recirculation conduit

(5) , tangential with respect to the pan (1) , enters the upper part of the central band of the same pan, so as to set the particles, dragged by the said air flow at the outlet of the recirculation conduit (5) , in vortical movement.

4. Apparatus, according to claim 2, characterised in that a conical section (4) , linking the said pan (1) with the said recirculation conduit (5) , includes a narrow segment that produces a Venturi effect, due to which the air flow that enters the recirculation conduit (5) sucks the particles (2) .

5. Apparatus, according to claim 2, characterised in that at its free end, the said pipe (6) features a tapered segment (6a) producing said Venturi effect, due to which the solution fed by the tube (7) is sucked.

6. Apparatus, according to claim 2, characterised in that in its upper part, the pan (1) has a plurality of outlets (8) , for allowing discharge of the air getting out from the recirculation conduit (5) .

7. Apparatus, according to claim 2, characterised in that a reservoir (9) , aimed at receiving the parti¬ cles (2) blown by the recirculation conduit (5) , is provided on the recirculation conduit (5) , with a channel (10) situated inside the reservoir (9) and designed to allow the air flow to flow freely.

8. Apparatus, according to claim 2, characterised in that the said pan (1) is rotated with respect to the said pipe (6) introducing air.