WO1991018048A1

WO1991018048A1 - Use of a nucleation agent in a process for the production of loose-fill packing material

Info

Publication number: WO1991018048A1
Application number: PCT/EP1990/002150
Authority: WO
Inventors: Hans Reichenecker
Original assignee: Storopack Hans Reichenecker Gmbh + Co.
Priority date: 1990-05-23
Filing date: 1990-12-11
Publication date: 1991-11-28
Also published as: DE9017904U1; BR9008025A; EP0530194A1; AU645285B2; AU7050691A; JPH05506675A; DE9017926U1; DE4016597A1; DE4016597C2

Abstract

The description relates to the use of a nucleation agent in a process for the production of loose-fill packing from starch. The nucleation agent is applied to the surface of starch granulates in finely divided form in quantities of 0.1 to 0.2 % of the weight of the granulates and in a grain size of about 50 ν. The granulates thus coated with nucleation agent are taken to an extruder (14) in which they are converted from their solid to a viscous fluid state so that a starch foam produced by the decomposition of the nucleation agent with the action of heat in the extruder (14) is extruded from the moulding aperture (15) of an extruder (14) and cut off directly at the moulding aperture (15) even before any substantial expansion has taken place. The starch particles (18) thus formed are taken into a storage container and, after intermediate storage, expanded to their final size in a post-expansion unit (23).

Description

Title: Use of a nucleating agent in a process for producing pourable packaging material bodies

description

The invention relates to the use of a nucleating agent in a method for producing pourable packaging material bodies.

Such packaging material bodies are known. These loose-fill, spherical segment-shaped packaging material bodies, which are referred to as "loose-fill", are widely used for packaging transport goods. The known packaging material bodies have the disadvantageous property that they are made of plastic material - such as polystyrene or other polymerization products of the benzene derivative styrene - which can only be disposed of with difficulty after use. This fact is perceived as an eminent disadvantage, especially from the point of view of the constantly increasing environmental and environmental protection awareness.

To avoid these disadvantages, the object of the invention is to provide a method which enables the efficient and economical production of biodegradable "loose-fill" packaging material bodies. The technologies that are suitable for plastic packaging material bodies should be applicable, which is not to be expected, particularly for reasons of simple production.

This object is achieved in that the nucleating agent is applied to the surface of granules of starch finely distributed in an amount of 0.1-0.2% based on the weight of the granules and in a grain size of approximately 50 u, that the such granules with nucleating agent are fed to an extruder in which they are converted from their solid to a viscous-liquid state, and that one by the decomposition of the nucleating agent under

Starch foam, which arises in the extruder, is extruded from the mold opening of an extruder and immediately at the mold opening, before significant expansion has taken place, is cut off, and that the starch particles formed in this way are taken up in a storage container "and after an intermediate storage in a post-expansion unit are expanded to their final dimensions.

The measures according to the invention allow, in a particularly advantageous manner, the production of a ^' biodegradable' loose-fill 'packaging material body which is distinguished by its high environmental compatibility. The starch used as the base material is a natural product and can be degraded by environmentally occurring microorganisms and / or by its natural aging process without environmentally harmful residues.

Advantageous developments of the invention emerge from the subclaims and relate in particular to shapes of the starch packaging material bodies which are particularly expedient for handling.

Further details of the invention are the

Examples can be found, which are described below with reference to the drawings. Show it:

Figure 1 is a schematic side view of a

Device for producing packaging material bodies, Figure 2 is a partial side view of the

Extrusion device with material feed zone,

Figure 3 is a broken partial plan view of the

Material feed zone,

Figure 4 is a partially enlarged portion of a

Extruder sleeve with grooves,

FIG. 5 shows a section along the line V-V in FIG. 4,

FIG. 6 shows the development of the screw helix of the grooves,

Figure 7 shows an embodiment of a

Starch packaging material body,

Figure 8 shows a second embodiment of a

Starch packaging material body, and

Figure 9 shows a third embodiment of a

Starch packaging material body.

The device required to carry out the method is shown schematically in FIG. 1. Its essential functional complexes consist of a drum 5, an extrusion device 10, a storage container 22, a post-expansion unit 23 and a further storage container The drum 5 has openings 6 and 7 through which starch granules and a nucleating agent (bubble form) are added. The starch granules used here consist of pure starch material. However, it is also possible to use the starch method described Granules which contain admixtures but which do not interfere with the process described below. In the following description the term "starch granules" is used for both types.

The nucleating agent was ground extremely finely before being introduced into the drum 5 and has a grain size of approximately 40 μ. The nucleating agent added in an amount of approximately 0.1-0.2 percent by weight is drummed onto the starch granules in the drum 5. This drumming of the nucleating agent onto the starch granules has the effect that they are coated with a layer of the nucleating agent which is firmly adhered by adhesive forces and is uniformly distributed over the surface.

The nucleating agent tumbled onto the starch granules serves as an initiator of bubble nucleation in the subsequent extrusion process: this is done by the solid nucleating agent in the extruder 14 decomposing with gas formation. The released gas forms in the viscous-liquid starch mass (see below) a large number of vesicles, which act as "germ cells" of the expanded cell structure Starch material function and thus influence the fine porosity of the resulting starch packaging material body.

The amount of nucleating agent introduced into the drum 5 is essentially determined by the decomposition behavior of the nucleating agent under the action of heat taking place in the subsequent extrusion process. An important parameter of the nucleating agent, which has a decisive influence on the amount added, is the "theoretical gas yield", i.e. the amount of gas released (e.g. carbon dioxide) per unit weight of nucleating agent at a certain temperature. From these considerations, the person skilled in the art can clearly see how he has to measure the addition amount of nucleating agent in order to achieve the desired degree of fine porosity of the expanded starch material at a certain temperature in the extruder 14.

The nucleating agent can particularly advantageously consist of a carbonate and an acid component. The acid component then enables, in addition to the decomposition of the carbonate component due to the heat of the extrusion process, a chemical reaction with the carbonate component, which reinforces it

Carbon dioxide development. It is also possible to use the multicomponent nucleating agent known under the protected brand name "Hydrocerol": Its acid component consists either of hydrophobicized anhydrocitric acid or of citric acid monohydrate. This component is treated in such a way that it is water-repellent and therefore miscible with the carbonate component - for example sodium hydrogen carbonate - and can be stored in the long term without attracting moisture from the environment. Another nucleating agent known and suitable for the described method is known under the designation CF 0556.

The starch granules treated in this way are fed into a filling funnel 17 connected to the extrusion device 10 by means of a conveying device 8 and a conveying line 9. Color pigments or other desired additives may also be added in the filling funnel 17.

The extrusion device 10 consists of a drive motor 11, a gear 12, a material feed zone 13 and an extruder 14 and a cutting device 16 which is arranged in front of a mold opening 15 of the extruder 14. The tumbled starch granules reach the material inlet zone 13 via the filling funnel 17 arranged at the end of the conveying line 9. The mixture consisting of the starch granules with the tumbled nucleating agent and any additives added is fed by an extruder screw (not shown in FIG. 1) drawn into the material feed zone 13 of the extruder 14. The starch granules with the Tumbled nucleating agents are carried along by the driving flanks of the extruder screw rotating at a suitably selected speed and are thereby conveyed in the axial direction from the material feed zone 13 of the extruder 14 to the mold opening 15 arranged at the other end of the extruder 14. The continuously increasing core diameter of the extruder screw in the extruder direction causes the starch granules to be subjected to a constantly increasing pressure as they move forward through the extruder 14. At the same time, the mixture formed from the compacted starch granules and the nucleating agent tumbled thereon is heated to a higher temperature until it melts and thereby changes into a viscous-liquid state.

It is essential for the extrusion process that the nucleating agent is evenly and finely distributed in the viscous-liquid starch-nucleating agent mixture. This is necessary in order to obtain a regular and fine cell structure of the expanded starch material after extrusion. The drumming of the nucleating agent onto the starch granules has the effect that when the individual granules are rubbed against one another, there is only extremely little abrasion of the nucleating agent due to the pushing or rotating movement of the extruder screw. This prevents the nucleating agent from passing through the starch granules Material feed zone 13, in which no phase transition takes place yet, accumulates in the spaces between the individual granules. The squeezing and shearing of the starch granules caused by the rotary movement of the extruder screw also improves the mixing of starch and nucleating agent without the "short-range order" caused by the tumbling of the nucleating agent being destroyed in the microscopic range of the starch-nucleating agent mixture. This has the advantage that even after the starch granules have passed from their solid phase to their viscous-liquid phase, there is still a very fine and very regular spatial distribution of the solid nucleating agent. However, this means that a volume element contains a large number of finely divided nucleating agent granules which act as bubble nucleating agents.

The finely divided nucleating agent decomposes due to the heat with the formation of gas. The heat input caused by the temperature prevailing in the extruder of approx. 110 ° -130 ^β C results, in conjunction with the frictional heat generated by the friction of the starch granules, in a thermal splitting of the carbonate component of the nucleating agent, as a result of which carbon dioxide gas is released. This gas release of the nucleating agent leads to the above-mentioned formation of bubble nuclei in the viscous liquid starch material. Because of the fine and almost homogeneous Distribution of the nucleating agent is achieved - seen over the entire volume - even distribution of bubble germs. This extensive homogeneity in the spatial distribution of the bubble nuclei caused by the decomposing nucleating agent represents an essential basis for the fine porosity of the packaging material bodies to be produced.

In the extruder 14, a so-called direct gassing with a suitably selected blowing agent gas is carried out while the starch mixture is being heated. This causes the blowing agent to get into the viscous liquid starch mass and to be dissolved therein. This is due to the pressure and temperature conditions prevailing in the extruder 14

Starch-nucleating agent mixture supersaturated with propellant gas, i.e. more propellant gas dissolves than under normal conditions. Alternatively, it is possible to use starch granules in which the propellant gas is contained right from the start.

The dissolved propellant gas now diffuses into the bubble nuclei caused by the decomposition of the nucleating agent and causes them to expand. The growth of the bubbles is essentially dependent on the

Diffusion rate and the supersaturation of the dissolved blowing agent in the viscous liquid

Starch-nucleating agent mixture and the pressure difference between the pressure prevailing in the extruder and the Partial pressure of the blowing agent dissolved in the viscous-liquid starch-nucleating agent mixture is determined. The starch-nucleation mixture emerges from the mold opening 15 of the extruder 14 in the form of a mass of melted starch foam.

The starch strand emerging from the mold opening 15 is cut off by the cutting device 16 immediately after it emerges.

The pressure difference between the excess pressure prevailing inside the extruder and the - lower - pressure of the surrounding room atmosphere causes the propellant gas bound in the starch material to expand. The cut-off starch particles then expand in free fall into a first expanded state, where they already assume their shape. This expansion is accompanied by simultaneous cooling, so that the bodies solidify shortly behind the mold opening 15 or the cutting device 16 - and before they have reached the collecting container 19. The cooled and solidified starch particles 18, which are in their first expanded state, are collected in the collecting container 19 and conveyed by a blower 20 through a collecting line 21 to the storage container 22.

The starch particles 18 produced in this way can be used for various purposes - such as Packing material.

After a certain storage time, the starch particles 18 can be conveyed out of the storage container 23 into a post-expansion unit 23. In this, the starch particles 18 expand again after exposure to heat, so that "loose-fill" packaging material bodies of lower mass density are formed, which advantageously have a substantially lower bulk density. It is essential in this post-expansion step that the heat required for renewed expansion is introduced "dry". It is therefore not allowed to use hot steam to introduce heat. A "wet" treatment would lead to the destruction of the starch packaging material bodies.

After leaving the post-expansion unit 23, the re-expanded starch particles 18 are fed to a further storage container 24. This preferably consists of screen fabric or another open-mesh material, so that free air circulation and thus easy drying of the re-expanded starch particles 18 is made possible.

An alternative solution to the object on which the invention is based is described below with reference to a second exemplary embodiment. This method is carried out with a device which is essentially that shown in FIG. 1 and described in detail above Device reached.

A significant difference between the two processes and the devices used to carry out the process, as compared to the process described above, is that the starch granules are fed to a specially designed material feed zone 13 of the extruder 14. This "slot entry zone" shown in detail in FIGS. 2-6 has the effect that the material throughput can be approximately doubled with the same speed of rotation of the extruder screw. This increased throughput of starch material brings about an increased production rate of the process in a particularly advantageous manner.

2 shows, on an enlarged scale, the material feed zone 13 with the filling funnel 17 attached. The material feed zone 13 is connected on the right-hand side to a reduction gear 25 which is driven by a motor 11.

In the direction of conveyance of the extruder screw, the melting zone 26 adjoins the material feed zone 13, in which the starch material changes from its solid to the viscous-liquid state. It is essential here that the melting zone 26 and the material feed zone 13 are thermally insulated along their connection 27. The extruder screw extends through the material feed zone 13 and the melting zone 26 and is driven by the motor 11 via the reduction gear 25. The extruder screw is guided in the material feed zone 13 in a bushing 28 which is held by a carrier 29. The bushing 28 is provided with an opening 30 through which the starch material is drawn from the hopper 17 into the extruder 14. The underside 31 of the filling funnel 17 is connected to a flange 32 of the carrier 29. The area of the bushing delimited by the opening 30 forms the groove entry zone 33. The area of the bushing 28 adjoining this groove entry zone 33 in the conveying direction of the extruder screw comprises a transition zone 34. As can best be seen from FIG. 3, there are several in the bushing 28 longitudinal grooves 35 cut. In the area of the groove entrance zone 33, the grooves 35 have a constant incision depth 36. In the transition zone 34 adjoining the groove entrance zone 33 in the conveying direction, the incision depth 36 decreases to zero in the conveying direction.

The main effect of these grooves 35 in the sleeve 28 so that these grooves form a kind of a certain number of starch granules above a certain cross-sectional slice through the extruder in ^'the material input zone 13 "escape niche". This prevents in a particularly advantageous manner that the material transport of the starch granules in the axial direction by on the sales flanks spiral-shaped extruder screw adhering starch granules cannot be hindered. In addition, this ensures a continuity of the material drawn by the extruder screw, thereby ensuring a constant quality of the starch foam emerging from the mold opening 15 of the extruder 14.

In the construction of the components just described, it is provided that the opening 30 in the socket 28 has a length of approximately 80 mm and a width of 50 mm. The transition zone 34 has a length of approximately 185 mm. The socket 28 has a wall thickness 37 of approximately 13 mm.

4 shows an enlarged section of a bushing 28 in the area of the groove entry zone 33 with grooves 35 which have a constant depth of cut 36.

The grooves 35 have a cross-sectionally U-shaped profile 38, the two legs 39 of which are inclined outward by an angle Ct. The angle of inclination 0 is 15 ° in the present exemplary embodiment. The depth of cut 36 of the grooves 35 is approximately 1.5 mm. The width 40 of the grooves 35 is approximately 10 mm. The grooves in the exemplary embodiment described here have a constant distance 41 from one another which is approximately 15.5 mm.

The distance between the grooves is determined by the diameter of the bushing 28 and the number of incised grooves 35 and their width is determined.

FIG. 5 shows a section along the line V-V in FIG. 4, which runs through a groove 35. The grooves 35, viewed in the direction of transport of the extruder screw, have an initial region 42 at the start of the bush 28, after which they reach their maximum incision depth 36, which is then constant in the groove input zone 33.

FIG. 6 shows the development of the groove helix in the material feed zone 13. The bushing 28 is cut open in the longitudinal direction and has a rectangular contour in the rolled-out state. Eight grooves 35 are cut at regular intervals around a circumference 43 of the socket 28. The helix helix has made a full 360 "turn in the transport direction after a section 44. In the present exemplary embodiment, the section 44 is approximately 203 mm.

The process of making

"Loose-fill" packaging material body using the device just described is carried out as follows: The starch material is drawn through the opening 30 into the socket 28. The extruder screw pulls the starch granules into the space between the extruder screw and the groove entry zone 33, which is provided with grooves 35 with a constant depth of cut 36. The starch granules, which have an average core diameter of 0.5 mm, for example, can escape into the grooves 35 in the groove entrance zone 33. As a result of this mobility and the possibility of evasion, fewer starch granules simultaneously rotate in a circle with the extruder screw, so that more starch material can be brought into the transition zone 34 through the extruder screw in the direction of transport.

Due to the intrinsic pressure of the starch material and the mobility in the groove input zone 33, more material can be transported from the extruder screw in the axial direction of the extruder 14. Due to the faster removal and the greater mobility, fewer starch particles "block" the space for the starch granules pushing out of the hopper 17.

In the transition zone 34, the depth of cut 36 of the grooves decreases to zero in the T ₌ sport direction. The starch granules are packed and consolidated more tightly.

The resulting frictional heat must not be sufficient to convert the starch granules into their viscous, liquid state. Therefore, cooling fins 45 (see FIG. 2) are arranged around the bushing 28 in the transition zone 34 in order to allow heat to be dissipated.

To achieve that the starch granules only in the Melting zone 26 are converted into their viscous-liquid state, the transition zone 34 is thermally insulated from the melting zone 26.

The core size of the starch granules to be processed can be varied within a certain range without significantly reducing the advantageous effect of the method and the device described.

Depending on the feed speed, the bushing 28 in the groove input zone 33 can also be provided with cooling fins, so that it is always ensured that the starch material does not change into the viscous-liquid state in the entire material feed zone 13. Such a phase transition of the solid starch granules would "smear" the grooves 35 and would not allow their advantageous effect to come into play.

Figure 7 shows a preferred form of a

Starch packing material body 50. It has the shape of a 25-28 mm long block or rod with the cross-section of two hollow tubes 51, 52 connected via a short web 53. The shape arises with a corresponding design of the mold opening 15. As indicated, the The surface of the starch packaging material body 50 still exhibits a certain irregularity due to the homogenization of the starch extrusion process by using the nucleating agent, but this leads to an increased friction of such Packing material body leads to each other and can therefore be quite advantageous.

Alternative forms are quite conceivable, e.g. about rods with the cross-section of a four-leaf clover - cf. Figure 8 - or a thinner spirally wound stick - cf. Figure 9 -, as by appropriate design of the. Mold openings can be obtained.

Claims

1. Use of a nucleating agent in a process for the production of pourable packing material bodies made of starch, characterized in that the nucleating agent is finely distributed on the surface of granules of starch in an amount of 0.1-0.2% based on the weight of the granules and in a grain size of about 50 microns is applied that the granules so contaminated with nucleating agent are fed to an extruder (14) in which they are converted from their solid to a viscous-liquid state, and that by the decomposition of the nucleating agent with heat input Starch foam produced in the extruder (14) is extruded from the mold opening (15) of an extruder (14) and cut off directly at the mold opening (15), even before considerable expansion has taken place, and that the starch particles formed in this way ( 18) in a storage container (22) and after an intermediate storage in a post-expansion unit (23) to their final dimensions can be expanded.

2. Use of a nucleating agent according to claim 1, characterized in that the coating of the starch granules with the nucleating agent takes place in a drum.

3. Use of a nucleating agent according to claim 1 or 2, characterized in that the processing temperature in the extruder is approximately 110 ° C-130 ° C.

4. Use of a nucleating agent according to claims 1-3, characterized in that the nucleating agent consists of a carbonate and an acid component without adhesion.

5. Pourable starch packaging material body, produced according to claim 1 or one of the following using a nucleating agent, characterized in that the starch foam strand emerging from the mold opening (15) of the extruder is cut to a length which after expansion a length of

15-30 mm and the shaped opening (15) is shaped such that the starch packing material body (50) has the shape of two parallel hollow tubes (51, 52) connected to one another by a narrow web (53). Has.

6. pourable starch packaging material body produced according to claim 1 or one of the following using a nucleating agent, characterized in that the starch packaging material body (60) has the cross section of about a four-pointed star or a four-bladed Clover leaf.

7. pourable starch packing material body produced according to claim 1 or one of the following using a nucleating agent, characterized in that the starch packing material body (70) has the shape of a spiral.