AU645285B2

AU645285B2 - Use of a nucleation agent in a process for the production of loose-fill packing material

Info

Publication number: AU645285B2
Application number: AU70506/91A
Authority: AU
Inventors: Hans Reichenecker
Original assignee: Storopack Hans Reichenecker GmbH
Current assignee: Storopack Hans Reichenecker GmbH
Priority date: 1990-05-23
Filing date: 1990-12-11
Publication date: 1994-01-13
Anticipated expiration: 2010-12-11
Also published as: DE9017926U1; WO1991018048A1; AU7050691A; JPH05506675A; DE4016597C2; BR9008025A; DE9017904U1; DE4016597A1; EP0530194A1

Description

WO 91/18048 PCT/EP90/02150 Title: Use of a nucleation agent in a process for the production of loose-fill packing material Specification The invention relates tq the use of a nucleation agent in a process for the production of loose-fill packing material.

Packing materials of this kind are known. These pourable packing materials in the form of spherical segments, known as "loose-fill" materials, are widely used for the packing of material for transport.

The known packing materials have the inconvenient property of being made of plastic material polystyrene or other polymerization products of the benzene derivative styrene) which can be disposed of only with difficulty after use. This circumstance is found to be a pronounced disadvantage, especially from the viewpoint of the constantly increasing consciousness of the environment and environmental protection.

To avoid these d.isadvantages, the invention is posed the problem of providing a process which makes possible an efficient and economical production of biodegradable "loose-fill" packing materials. The technologies that are suitable for plastic packing materials should be able to be applied here, especially for reasons of simplicity of production, which is unexpected.

This problem is solved through the fact that the nucleation agent is applied, finely distributed, to the surface of starch granules, in a quantity of 0.1 0.2 relative to the weight of the granules and in a grain size of about 50 i; that the granules to which the nucleation agent is applied in this way are fed to an extruder, in which they are changed from their solid state into a viscous liquid state; and that PROCESS FOR THE PRODUCTION OF LOOSE-FILL PACKING MATERIALS The invention relates to a process for the production of loose-fill packing materials.

The known packing materials have the inconverient property of being made of plastic material polystyrene or other polymerization products of the benzene derivative styrene) which can be disposed of only with difficulty after use. This circumstance is found to be a pronounced disadvantage, especially from the viewpoint of the constantly increasing consciousness of the environment and environmental protection.

To avoid these disadvantages, the invention is posed the problem of providing a process which makes possible an efficient and economical production of biodegradable "loose-fill" packing materials. The technologies that are suitable for plastic materials should be able to be applied here, especially for reasons of simplicity of production, which is unexpected.

This problem is solved through the fact that a nucleation agent is used, said nucleation agent is applied finely distributed to the surface of i;il: granules essentially consisting of starch; that the granules coated in this way with nucleation agent are passed to an extruder, in which they are transformed from their solid state into a liquid state; and that a starch foam produced with the application of heat in *o o la the extruder is extruded from the orifice of an extruder (14) and expanded.

The measures according to the invention permit in a particularly convenient manner the production of a biologically degradable loose-fill packing material which is characterized by its high environmental compatibility. The starch used as the base material is a natural product and can be degraded without any environmentally harmful residues by micro-organisms which occur in nature and/or by its natural aging process.

Advantageous further developments of the invention can be seen from the subsidiary c' ms and relate in particular to the application of the nucleation agent and to forms of the starch packing materials especially convenient for handling.

a *i *4 U IU Further details of the invention can be seen from the embodiments, which are described below by means of the drawings.

Figure 1 shows a diagrammatic side view of a device for producing packing materials, Figure 2 is a partial side view of the extrusion device with the material feed zone, Figure 3 is a broken partial plan view of the material feed zone, Figure 4 is a partially enlarged section of an extruder lining with grooves, Figure 5 is a section along the line V V in Figure 4, Figure 6 is the development of the screw helix of the grooves, Figure 7 is one embodiment of a starch packing material, e

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55 S S S S S 55 eo 3 figure 8 a second embodiment of a starch packing material, and figure 9 a third embodiment of a starch packing material.

The device necessary for putting the process into effect is shown diagrammatically in fig. 1. Its main functional units comprise a drum Qnc an extrusion device 10, *4 storage container 22. a final expansion.

The drum 5 has openings 6 and 7, through which starch granules and a nucleation agent (bubble-forming agent) are introduced. The starch granules used here are composed of pure starch material. But it is also possible to conduct the process described with starch granules that contain admixtures which, however, do not disrupt the process described below. In the description that follows the term "starch granules" is used for both types.

The nucleation agent was ground extremely fine before introduction into the drum 5 and has a grain size of about 40 v. The nucleation agent, which is added in a quantity of about 0.1 0.2 by weight, isAtumbled on to the starch granules in the drum 5. The effect of this tumbling of the nucleation agent on to the starch granules is that they are coated with a layer of the nucleation agent distributed uniformly over the surface and firmly adhering due to adhesive forces.

The nucleation agent tumbled on to the starch granules serves as an initiator of a bubble nucleus formation in the subsequent extrusion process. This is due to the fact that the solid nucleation agent is decomposed in the extruder 14 with the generation of gas. The gas released forms in the viscously liquid starch material (see below) a large number of bubble nuclei which act as "nuclear cells" of the cellular structure of the expanded starch material and thus influence the fine proosity of the resultant starch packing material.

The quantity of nucleation agent introduced into the drum 5 is determined essentially by the decomposition behaviour of the nucleation agent under the action of heat ,which takes place in the following extrusion process. An important parameter of the nucleation agent and one that has a decisive influence on the quantity of additive is here represented by the "theoretical gas yield", i.e. the quantity of gas carbon dioxide) released per unit weight of the nucleation agent at a specific temperature. The specialist can clearly see from these remarks how the quantity of nucleation agent must be adjusted in order to achieve the required degree of fine porosity of the expanded starch material at a specific temperature in the extruder 14.

The nucleation agent may particularly advantageously Aconsist of a carbonate and an acid component. The acid component then also makes possible, for the decomposition of the carbonate component through the heat action of the extrusion process, a chemical reaction with the carbonate component which brings about an intensified generation of carbon dioxide. It is also possible to use the multi-component nucleation agent, which has become known under the registered trade mark "Hydrocerol".

The acid component of this consists either of anhydrocitric acid rendered water-repellent or of citric acid monohydrate. This component is treated in such a way as to be water-repellent, and thus miscible with the carbonate component sodium hydrogen carbonate) and storable for a prolonged period without absorbing moisture from its surroundings.

A further known nucleation agent suitable for the process described here is known by the designation CF 0556.

The starch granules treated in this way are introduced by kieans of a conveyor device 8 and a delivery line 9 into a feed hopper 17 connected with the extrusion unit 0. Pigments or other required additives may possibly also be added in the feed hopper 17.

The extrusion unit 10 comprises a drive motor 11, a set of gears 12, a material feed zone 13 and a cutting device 16 which is disposed before an orifice 15 of the extruder 14. The tumbled starch granules pass by way of the feed hopper 17 disposed at the end of the delivery line 9 to the material feed zone 13. The mixture, comprising the starch granules with the nucleation agent applied by tumbling and the add .ives possibly introduced, is fed into the material feed zone 13 of the t..ruder 14 by means of an extruder worm (not shown in fig. The starch granules with the nucleation agent applied by tumbling are taken by the feed flanks of :he extruder worm rotating at a suitably selected speed and in this way delivered in an axial direction from the material feed zone 13 of the extruder 14 to the orifice 15 located at the other end of the extruder 14. The core diameter of the extruder worm, which increases constantly in the direction of the extruder, causes the starch granules to be subjected to a constantly increasing pressure in the course of their forward movement through the extruder 14. At the same time, the mixture composed of the compacted starch granules and the nucleation agent applied to them by tumbling is heated to a higher temperature until it melts and passes into a viscous liquid state.

It is important for the extrusion process that the nucleation agent should be uniforly and finely distributed in the viscous liquid nixture of starch and nucleation agent. This is necessary in order to obtain a regular and fine cell structure in the expanded stach material. The application of the iucleation agent to the starch granules by tumbling causes only an extremely slight abrasion of the nucleation agent to occur when individual granuls rub against each other due to the translational or rotary motion of the extruder worm. Through this, the nucleation agent is prevented from accumulating in the interstices between the individual starch granules during the passage of the starch granules through the material feed zone 13, in which there is as yet no phase transformation.

The squeezing and shearing of the starch granules also improves the mixing of the starch and nucleatio. agent, without the "close arrangement" in the microscopic range of the mixture of starch and nucleation agent, brought about by the application of the nucleation agent by tumbling, being destroyed. This ensures in an advantageous manner that a very fine and very regular spatial distribution of the solid nucleation agent is obtained, even after the passage of the starch granules from their solid phase to their viscous liquid phase. This means, however, that very many finely distributed nucleation agent particles, which act as centres for the formation of bubble nuclei, are present in a volumetric element.

The finely distributed nucleation agent is decomposed by the action of heat with the generation of gas. The t:eat yield brought about by the I 6 temperature of about 110" 1300C prevailing in the extruder, combined with the frictional heat generated by the friction of the starch granules, results in a thermal splitting of the carbonate component of the nucleation agent, whereby gaseous carbon dioxide is released. This release of gas from the nucleation agent leads to the aforementioned formation of bubble nuclei in the viscous liquid starch material. Because of the fine and approximately homogeneous distribution of the nucleation agent, a uniform distribution of bubbles viewed over the entire volume is obtained. This substantial homogeneity in the spatial distribution of the bubble nuclei produced by the decomposing nucleation agent represents an important basis for the fine porosity of the packing material to be produced which is to be obtained.

A so-called "direct gas treatment" with an appropriately selected propellant gas is carried out in the extruder 14 during the heating of the starch mixture. This causes the propellant to pass into the viscous liquid starch mass and to be dissolved in it. Because of the pressure and temperature conditions prevailing in the extruder 14, the mixture of starch and nucleation agent is supersaturated with propellant gas, ie. more propellant gas is dissolved than under standard conditions.

Alternatively, it is possible to use starch granules in which the propellant gas is contained from the outset.

The dissolved propellant gas now diffuses into the bubble nuclei produced by the decomposition of the nucleation agent and causes the expansion of them. The growth of the bubbles is here determined essentially by the rate of diffusion and the supersaturation of the dissolved propellant in the mixture composed of viscous liquid starch and nucleation agent, and by the difference between the pressure prevailing i the extruder and the partial pressure of the propellant dissolved in the mixture of viscous liquid starch and nucleation agent.

The mixture of starch and nucleation agent emerges from the orifice of the extruder 14 in the form of a mass of melted starch foam.

The starch "'billet" emerging from the orifice 15 is cut off m ta after its emergence by the cutting device 16.

The pressure difference between the excess pressure prevailing in the interior of the extruder and the (lower) pressure of the surrounding room atmosphere causes the propellant gas bound in the starch material to expand.

The starch particles cut off then expand in free fall into a expanded state, in which they assume their shape. This expansion is accompanied by a simultaneous cooling, so that the bodies solidify shortly after the orifice 15 or the cutting device 16 and before they have reached the collection container 19.

The cooled and solidified expanded starch particles 18, are caught in the collection container 19 and delivered by a blower 20, through a collection line 21, to the storage container 22.

The starch particles 18 prepared in this way can be ",sed for various purposes as packing material, for example.

An alternative solution of the problem on which the invention is based is described below by means of a second embodiment. This process is conducted with equipment which essentially resembles the equipment shown in Fig. 1 and described in detail above.

In relation to the process described above, an important difference 4* S 4* N 45 *545 4 ii0o S 9* 0 r 8 between the two processes and thus between the equipment used to apply the process lies in the fact that the starch granules are passed to a specially designed material feed zone 13 of the ext.-uder 14. This "grooved feed zone", which is shown in detail in fig. 2 6, makes it possible for the material throughput to be approximately do'lbled at the same rotational speed of the extruder screw. This increased throughput of starch material brings about very advantageously an increased process production rate.

Fig. 2 shows on a larger scale the material feed zone 13 with the feed hopper 17 in place. Thematerial feed zo.ne 13 is connected on the right-hand side with a reduction gear ,system 25 which is driven by a motor 11.

The melting zone 26, in which the starch material passes from the solid state into the viscous liquid state, adjoj s the material feed zone 13 in the direction of delivery of the extruder worm. It is important here that the melting zone 26 and the material feed zone 13 should be thermally insulated along their connexion 27.

The extruder worm extends through the material feed zone 13 and the melting zone 26 and is driven by the motor 11 through the reduction gear system 25. The extruder worm is guided in the material feed zone 13 in a sleeve 28 which is held by a bearer 29. The sleeve 28 is provided with an opening 30 through which the starch material is fed from the feed hopper 17 into the extruder 14. The lower side 31 of the feed hopper 17 is connected with a flange 32 of the bearer 29. The region of the sleeve bounded by the opening 30 forms the grooved feed zone 33. The region of the sleeve 28 adjoining this grooved feed zone 33 in the direction of delivery of the extruder worm covers an extruder zone. As can be seen best from fig. 3, a plurality of longitudinal groove, is cut into the sleeve 28. The grooves 35 have a constant cut depth 36 in the region of the grooved feed zone 33. In the transitional zone 34 adjoining the grooved feed zone 33 in the direction of delivery, the cut depth 36 decreases to zero in the direction of delivery.

The main effect of these grooves 35 in the sleeve 28 is that these t 9 grooves form a kind of "passing niche" for a certain number of starch granules over a specific cross-section through the extruder in the material feed zone 13. This prevents in a particularly advantageous manner the possibility of any impeding of material transport of the starch granules in an axial direction through starch grains adhering to the distributing flanks of the spiral extruder worm. In addition, a constancy of the material drawn along by :he extruder worm is thus ensured, whereby a uniform quality of the starch foam emerging from the orifice 15 of the extruder 14 is guaranteed.

Provision is made in the design of the components just described for the opening 30 in the sleeve 28 to have a length of about 80 mm and a width of 50 mm. The transitional zone 34 has a length of about 185 mm. The sleeve 28 has a wall thickness 37 of about 13 mm.

Fig. 4 shows an enlarged section of a sleeve 28 in the region of the grooved feed zone 33 with grooves 35 that have a constant cut depth 36.

The grooves 35 have a profile 38 which is U-shaped in cross-section and both arms 39 of which are inclined outwards at an angle a. The angle of inclination a is 15° in this embodiment. The cut depth 36 of the grooves 35 is about 1.5 mm. The width 40 of the g ooves 35 is about mm. The grooves in the embodiment described here are at a constant distance 41 from each other which is about 15.5 mm.

The distance between the grooves is determined by the diameter of the sleeve 28 and the number of grooves 35 cut and by the width of them.

Fig. 5 shows a section along the line V V in fig. 4, which runs through a groove. The grooves 35 have, viewed in the direction of transport of the extruder worm, an initial region 42 at the start of the sleeve 28, after which they reach their maximum cut depth 36, which is then constant in the grooved feed zone 33.

Fig. 6 shows the development of the groove spiral in the material feed zone 13. The sleeve 28 is cut in the longitudinal direction and ,V has a rectangular outline in the unrolled state. Eight grooves 35 are cut at regular intervals about a periphery 43 of the sleeve 28. The helix has completed a full 3600 rotation after a distance 44 in the direction of transport. The distance 44 in this embodiment is about 203 mm.

The procedure for preparing loose-fill packing material by means of the equipment just described is as follows. The starch material is fed through the opening 30 into the sleeve 28. The extruder worm draws the starch granules into the space between the extruder worm and the grooved feed zone 33 which is pfovided with grooves 35 of constant cut depth 36. The starch granules, which have, for example, a mean core diameter of 0.5 mm, may deviate into the grooves 35 in the grooved feed zone 33. Through this mobility and the possibility of deviation, fewer starch granules rotate simultaneously in a circule with the extruder worm, so that more starch material can be brought by the extruder worm into the transitional zone 34 in the direction of transport.

Through the inherent pressure of the search material and the mobility in the grooved feed zone 33, altogether more material can be delivered by the extiuder worm in the axial direction of the extruder 14. Because of the more rapid removal and the greater mobility, fewer starch particles "shut off" the space for the starch granules following from the feed hopper 17.

The cut depth 36 of the grooves decreases to zero in the direction of transport in the transitional zone 34. Through this the starch granules are more densely packed and stabilized.

The frictional heat generated at this time must not be sufficient to transform the starch granules into the viscous liquid state. Cooling ribs 45 (see fig. 2) are therefore disposed about the sleeve 28 in the transitional zone 34 in order to permit the removal of heat.

In order to ensure that the starch granules are not brought into their viscous liquid state until they enter the melting zone 26, the transitional zone 34 is thermally insulated from the melting zone 26.

11 The core size of the starch granules to be processed can be varied within certain limits without the advantageous effect of the process described and the equipment discussed being greatly restricted.

Depending on the feed rate, the sleeve 28 may also be provided with cooling ribs in the grooved feed zone 33, so that it is always ensured that the starch material does not pass into the viscous liquid state in the entire material feed zone 13. Such a phase transition of the solid starch granules would "fill in" the grooves 35 and not allow their advantageous effect to be felt.

Fig. 7 shows a preferred form of a starch packing material 50. It has the shape of a block or bar 25 28 mm long with a cross-section of two hollow tubes 51, 52 joined by a short cross-piece 53. The shape is produced with an appropriate design of the orifice 15. As indicated, the surface of the starch packing material 50, despite the smoothing ation of the starch extrusion process through the use of the nucleation agent, still has a certain irregularity, which, however, leads to an increased friction of such packing material bodies against each other and thus may certainly be of advantage.

Alternative forms of starch packing material are certainly feasible, such as, for example, rods with a crozs-section shape of a four-pointed star or four-leaved clover (cf. fig. 8) or of a thinner spiral rod (cf. fig. such as can be obtained by appropriate design of the orifices.

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Claims

1. Process for the production of loose-fill packing materials, characterized in that a nucleation agent is used, said nucleation agent is applied finely distributed to the surface of granules essentially consisting of starch; that the granules coated in this way with nucleation agent are passed to an extruder, in which they are transformed from their solid state into a liquid state; and that a starch foam produced with the application of heat in the extruder is extruded from the orifice of an extruder and expanded.

2. Process for the production of loose-fill packing materials according to claim 1, characterized in that the nucleation agent is applied in a quantity of 0,1-0,2% by weight of the starch granules.

3. Process for the production of loose-fill packing materials according to claim 1 or 2, characterized in that the grain size of the nucleation agent is about

4. Process for the production of loose-fill packing materials according to any one of claims 1 to 3, characterized in that the nucleation agent consists of a carbonate and an acid component without adhesive additives. Process for the production of loose-fill packiig materials according to any one of claims 1 to 4, characterized in that the coating of the starch granules with the nucleation agent takes place in a drum. a a Process for the production of loose-fill packing materials according to any one of claims 1 to 5, characterized in that the processing temperature in the extruder is 1100C 1300C. 13

7. Process for the production of loose-fill packing materials according to any one of claims 1 to 6, characterized in that a direct gas treatment is carried out in the extruder during the heating.

8. Loose-fill packing prepared according to any one of claims 1 to 7 using a nucleation agent, characterized in that the starch foam strand emerging from the orifice of the extruder is cut off in a length which, after expansion, gives a length of the starch packing material of 15 30 mm and the orifice is designed so that the starch packing material has the shape of two parallel hollow tubes joined by a narrow cross-piece.

9. Loose-fill starch packing material prepared according to any one of claims 1 to 7 using a nucleation agent, characterized in that the starch packing material has a cross-section shaped like a four-pointed star or a four-leafed clover. Loose-fill starch packing material prepared according to any one of claims 1 to 7 using a nucleation agent, characterized in that the starch packing material has the shape of a spiral. *4 4 DATED this 6th day of September, 1993 STOROPACK HANS REICHENECKER GMBH CO WATERMARK PATENT TRADEMARK ATTORNEYS THE ATRIUM 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA 4 4. t 4 4 0 4 04