WO2016005033A1

WO2016005033A1 - Method for producing thin-walled containers by means of injection molding, and thin-walled containers produced in such a manner

Info

Publication number: WO2016005033A1
Application number: PCT/EP2015/001314
Authority: WO
Inventors: Maurizio CONTE
Original assignee: Weidenhammer Packaging Group Gmbh
Priority date: 2014-07-09
Filing date: 2015-06-30
Publication date: 2016-01-14
Also published as: DE102014010139A1

Abstract

The invention relates to a method for producing a thin-walled container, wherein a thermoplastic polymer is plasticized and the plasticized polymer is injected into the molding chamber (4) of a mold (1) with a wall/flow ratio of at least 250 via an injection channel (5). The polymer is then distributed along the base and wall of the molding chamber (4) in the molding chamber (4) so that the polymer completely fills the molding chamber. The polymer is then solidified, thereby forming the container, and removed from the mold (1). The aim of the invention is to allow the production of a thin-walled container which is mixed with solid filler or reinforcing materials by means of injection molding. This is achieved in that a powder or particulate filler is added to the polymer or a polymer which is mixed with such a filler is used, and a propellant is added to the polymer or a polymer which is mixed with a propellant is used, said propellant being expanded in the molding chamber (4) of the mold (1). The invention further relates to a thin-walled container which is produced in such a manner, in particular as a packing container.

Description

Process for producing thin-walled containers by means of injection molding and thus produced

thin-walled containers

The invention relates to a method for producing a thin-walled container by plasticizing at least one thermoplastic or thermoelastic polymer and the plasticized polymer is injected via at least one injection channel into the mold space of a mold with a wall / flow ratio of at least 250, after which it along the floor and the wall of the mold space is distributed in the mold space, so that it substantially completely fills it, after which the polymer solidifies to form the container and the mold cavity of the mold ^¬ tool is removed. The invention further relates to a thin-walled container made of at least one thermoplastic or thermoelastic polymer produced by injection molding by means of a molding tool with a wall / flow ratio of at least 250, in particular by means of a method of the aforementioned type.

Such produced by injection molding plastic molded parts in the form of thin-walled containers are used in particular as packaging containers for food and luxury products widespread use. Their preparation is usually done by using a thermoplastic or thermoelastic polymer by means of an injection unit, e.g. an extruder, under increased pressure and elevated

Temperature is plasticized, after which the plasticized polymer via one or possibly more

1

CONFIRMATION COPY Injection channels in the mold cavity of a mold

is injected. In the mold cavity, which has a complementary shape to the molded part in the form of thin-walled container, the plasticized polymer must then be distributed due to a corresponding injection pressure, so that it flows in the still molten state along the bottom and the walls until it Fills mold space completely. Then, the polymer can be solidified to form the thin-walled container, in particular due to cooling, after which the finished molded part is removed from the mold. As thermoplastic or thermoplastic polymer materials can practically any known representatives of such

Materials used, such as

Polyolefins, polystyrene, polyalkylene terephthalates and the like. If desired, one or more labels, such as bottom and / or banderole labels, can be introduced into the mold cavity of the mold, which are back-injected with the plasticized polymer material, the label or labels serving as a barrier layer to the mold

Increase the diffusion-tightness of the plastic container or can serve as a carrier for the packaged identifiable imprints. The latter approach is also referred to as "in-mold labeling" (IML).

In general, the efforts go in particular at receiving containers for packaging goods to form the container as thin as possible, although a certain (shape) stability must be maintained in order to prevent untimely damage and proper handling of the container, be it on the occasion the transport or, on the occasion of the removal of the packaged goods, sure. This on the one hand for reasons of economy, on the other hand for environmental reasons with regard to the conservation of the natural resources of fossil fuels, from which the polymers used are usually obtained, as well as with regard to a

the lowest possible carbon dioxide emissions in the thermal utilization of the container usually formed by disposable packaging. Although thermoplastic and thermoelastic polymers can be recycled relatively well compared with thermosetting polymers due to their property of being plasticized or melted several times, the large amount of waste arising from such packaging containers nevertheless poses a certain environmental risk.

In addition, the wall thickness of containers produced by injection molding are limited not only because of their necessary (shape) stability downwards, but also in particular with regard to the injection molding process as such, in which it must be ensured that in the - very very " narrow "- molding space of the molding ^¬ zeugs injected plasticized molten polymer is substantially entirely distributed in the mold space by due to a high injection pressure from the

Injection channel along the bottom and walls of the

Formraumes flows along until it almost completely fills the mold cavity. It is known to heat the mold for this purpose in order to keep the polymer melt as liquid and slightly viscous, after which the mold must be cooled to remove the finished molding after solidification of the polymer. Depending on the ver ^¬ wendetem polymer, this results from a Wandungs- / flow ratio of about 250 or more problems on the one hand to the effect that the molten polymer not or only at immensely high injection pressures (and associated, correspondingly high closing forces of the mold) can be distributed entirely in the mold space, on the other hand to the effect that the wall thickness of the container produced is too small to the desired requirements to fulfill its stability. The latter also applies to a (too) small absolute wall thickness of plastic containers from a thickness of about 1.5 mm or smaller, although this value in turn of the respective

used polymer and also depends on the size and the capacity of the container. The wall / flow ratio (WFV) here is the ratio between the longest flow path (F) of the plasticized polymer in the mold cavity of the mold, i. the distance between the injection channel and the point furthest from the molding cavity of the mold, and the average wall thickness (b) of the finished molded part in the form of the thin-walled container, which corresponds to the average width of the mold cavity: WFV = F / b.

In the case of the production of conventional compact molded parts, it is known in the case of the use of thermoplastic plastics processing methods, the plasticized

Polymer fillers and / or fibers to add or already with fillers and / or fibers premixed polymer raw materials, the fillers / fibers on the one hand to increase the strength and rigidity of the finished polymer molding and on the other hand the

Reduce polymer consumption, which is desirable for the above reasons in terms of economy and environmental friendliness. Investigations, however, have shown that such an addition of solid, powdered or particulate fillers or reinforcing materials in the production of thin-walled container by injection molding is not or only in a very small amount of a few a few Mass .-% based on the polymer composition is possible. The reason for this is that even without the addition of such fillers or reinforcing agents a very high injection pressure and a very low viscosity of the plasticized polymer melt are required to ensure that the latter is distributed entirely in the very narrow, gap-shaped mold space. If the polymer melt contains powdery or particulate additives, these not only prevent the polymer melt from "flowing in" from the injection channel into the mold space, so that the latter can only be filled up to a certain extent, but also a segregation and the fillers accumulate in the mold Form space in the form of aggregations locally, so that they form a barrier to the inflowing polymer melt and thus further block of the injection channel remote areas of the mold space, so that the mold cavity of the mold often remains partially "empty" even in the case of very high injection pressures, which results in a substantial committee. Even if it is statistically possible in some cases to distribute the polymer melt mixed with the powdered or particulate fillers essentially completely in the mold space, the molded part produced in the form of the thin-walled container is useless, since it has deposited several particles , in the absence of a sufficient proportion of polymer matrix, is so brittle that it already breaks down into many fragments upon manual seizure. The invention is therefore based on the object

Injection molding process for producing a thin-walled container with a wall / flow ratio of

at least 250 of the type mentioned in a simple and cost-effective manner to the effect that an addition of relatively large amounts of fillers is possible without the material properties of the produce polymer molding in the form of thin-walled

Container in a significant way to affect. It is also based on a thin-walled container manufactured in particular by means of such a method

directed at the beginning.

In procedural terms, this object is achieved in a method of the type mentioned in that the polymer on the one hand at least added a powder or particulate filler or a filler added with such a filler polymer is used, and that the polymer on the other hand at least one blowing agent added or with a propellant added polymer is used, wherein the blowing agent is expanded in the mold cavity of the mold.

To achieve this object, the invention further provides for a thin-walled container made of thermoplastic or thermoelastic polymer materials of the type mentioned that the polymer material of the container on the one hand contains at least one powdered or particulate filler, and that the polymer material on the other

is foamed at least partially.

Surprisingly, it has been found that, as a result of a blowing agent added to the plasticized polymer, which is expanded during or immediately after the injection of the polymer melt into the narrow mold space of the mold, so that the polymer is foamed, is possible, the polymer considerable amounts of far more than 50 Mass .-% of powder or particulate filling or Reinforcing agents, wherein the strength, in particular the tensile strength, the toughness and also the dimensional stability of the produced, thin-walled polymer molding is not reduced due to the blowing agent, but is even increased due to the filler content. In this way, the amount of polymer required for the preparation of the container can be significantly reduced, as it is desirable for economic reasons and in particular also with regard to increased environmental friendliness. Furthermore, the wall thickness of the injection molded container can be further reduced, which is also associated with a corresponding polymer savings.

The propellant thereby evidently significantly improves the flowability of the molten polymer loaded with the fillers in the narrow cavity so that it can flow along the bottom and walls of the mold cavity from the injection channel and completely fill the latter. Demixing of the fillers or reinforcing materials from the polymer melt are reliably prevented, so that a homogeneous distribution of the fillers is achieved, which corresponds to the distribution of the fillers in the polymer melt, as for example by homogenizing the filler / polymer mixture in an injection unit, as an extruder has been obtained. In this case, of course, pre-filled with fillers polymers can be used, as they are commercially available, or the fillers are the injection unit together with the Polymer or placed at a separate point of application and mixed as homogeneously as possible in the plasticized polymer melt, as it by means of commercially available single or Mehrschneckendextrudern according to the prior art in a manner similar to the production of compact, with fillers or reinforcing added polymer moldings is possible. Of course, the method of the invention also allows, of course, the back injection of labein inserted into the mold cavity of the mold in the manner of so-called in-mold labeling, as in

generic thin-walled containers in the form of packaging containers is often desirable. A thin-walled container according to the invention consequently has a thermoplastic or thermoelastic polymer matrix which contains both powdered or particulate fillers and is also foamed at least in regions, in particular completely.

In addition, it has surprisingly been found that due to the addition of the blowing agent according to the invention also in the case of high levels of powder or

Particulate fillers of significantly greater than 50% by mass, both the injection time and the injection pressure and thus the required closing force of the mold can be significantly reduced compared to a corresponding injection molding of the pure polymer, so that on the one hand the cycle times, on the other hand, the investment cost for a corresponding injection molding machine including their molds can be reduced. The same applies to the energy expenditure, because the

Propellant of the polymer melt added with the fillers gives such a high flowability that it is the very narrow mold space of the mold even with a Wall / flow ratio of significantly greater than 250 can be completely filled without the mold necessarily has to be additionally heated, which also results in a further shortening of the cycle times. In this context, reference is also made to the exemplary embodiments reproduced below.

While basically any desired known powdered or particulate fillers or reinforcing materials, including short fibers, can be used according to the invention, it can be used, for hygienic reasons in particular, if the thin-walled container produced is e.g. as a packaging container for receiving sensitive filling material, in particular food, to serve, be useful if at least one mineral filler, in particular from the group of phyllosilicates, such as talc, added or a polymer added with such a filler is used.

The filler can be used, for example, with a particle size of about 0.1 pm to about 100 pm, in particular from about 0.1 pm to about 50 pm, for example from about 0.1 pm to about 40 pm, as is the case for On the other hand, it has proved to be advantageous in view of the high strength of the thin-walled container produced and, on the other hand, good flowability of the blowing agent-laden polymer melt in the narrow mold cavity of the molding tool. In a further advantageous embodiment, the filler can be used in platelet form, whereby the thin-walled container increased barrier properties or an improved diffusion density to gases, such as moisture or air (oxygen) can be imparted, for example, to keep sensitive against oxidative attack sensitive filling fresh. For this purpose, in particular platelet-shaped talc has proved to be favorable, which also in

Hygienic is harmless.

As already mentioned, it makes the invention Ver ^¬ ride possible, the fillers or reinforcing material the

Add polymer in relatively high proportions, wherein the filler in a proportion of at least about 1 mass .-%, in particular at least about 5 mass .-%, preferably at least about 10 mass .-%, based on the mass of the polymer used can be. In view of a high saving of polymer while ensuring proper stability of the thin-walled container produced, it may be particularly advantageous if the filler with a proportion of at least about

20% by mass, in particular of at least about 30% by mass, preferably of at least about 40% by mass or more preferably of at least about 50% by mass, based on the mass of the polymer, and higher Filler levels of at least about 60 mass% or even at least about 70 mass% are conceivable. An inventive thin-walled container contains

Consequently, preferably at least one powder or

particulate filler or reinforcing material from the

Group of sheet silicates, such as talc, which expediently has a particle size in the aforementioned ranges and in particular may have a platelet-shaped configuration. In terms of the

Proportion of filler or reinforcing material is on the

referenced above. In an advantageous embodiment of the invention

Method may be provided that at least one physical blowing agent is added to the plasticized polymer, which is in particular at least partially dissolved in the plasticized polymer, wherein the blowing agent is degassed in the mold cavity of the mold. The loading of the molten polymer with the

physical blowing agent can be done, for example, by the blowing agent of an injection unit, such as an extruder, under pressure on a

Gassing point is added downstream of the feed point for the polymer to which the polymer is already in a plasticized, molten state, so that the blowing agent can be dispersed in the polymer melt and in particular at least partially dissolved therein. When injected into the mold cavity of the mold, the physical blowing agent is then expanded, in particular due to pressure relief, so that it forms gas bubbles, which the (still) plasticized, molten polymer with the Füllbzw therein. Foam reinforcing materials. Such

For example, physical blowing agent may be selected from the group of inert gases, e.g. Nitrogen, carbon dioxide, argon or the like.

However, it is of course also conceivable that instead of a physical blowing agent, a chemical blowing agent is added, which is still in the injection unit, in particular immediately upstream of the injection nozzle (s), or in the mold, eg thermally activated, so that here formed gaseous decomposition products also foam the molten polymer. To the function of the propellant according to the invention

in terms of ensuring a flawless

Flowability of the mixed with the powdered or particulate fillers polymer melt through the narrow

Shaping space of the molding tool Suffice to do, relatively small amounts of blowing agents are sufficient, and in particular in the case of the use of physical blowing agents proportions between about 0.01 mass .-% and about 5 mass .-%, in particular between about 0.05 mass. % and 3 mass%, such as between about 0.1 mass% and about 2 mass%, have been shown to be effective.

Consequently, a thin-walled container according to the invention preferably has inclusions of at least one physical one

Propellant of the abovementioned type with proportions mentioned in the preceding paragraph.

As already mentioned, the method according to the invention makes it possible to further increase the wall thickness of thin-walled, injection-molded containers compared to conventional thin-walled containers without fillers and without blowing agent, due to the addition of both powdery or particulate fillers or reinforcing agents and propellants so that even very high wall / flow ratios can be set, such as those of at least about 260, in particular of at least 270, preferably of at least 280 or more preferably of at least about 290. In addition, even higher wall / Flow ratios of at least about 300 or at least about 350 possible. Consequently, the absolute width of the mold cavity of the mold, in which the plasticized polymer injected into it is distributed, can be further reduced compared with the prior art, for example to at most approximately 1.5 mm, in particular to at most approximately

1.4 mm, preferably at most 1.3 mm, most preferably at most about 1.2 mm. In addition, in particular molds can be used, the width of the mold space is at most about 1.1 mm or more preferably at most about 1 mm or less.

A thin-walled container according to the invention can consequently be produced by injection molding by means of a molding tool with a wall / flow ratio of the above-mentioned measure, its wall thickness preferably having the dimensions mentioned in the preceding paragraph.

Further features and advantages of the invention will become apparent from the following description of exemplary

Embodiments of embodiments of the injection molding process according to the invention for the production of thin-walled containers, such. in the form of packaging containers, with reference to the drawing. The only one shows

FIG. 1 shows a schematic partial cross section of a molding tool for producing a thin-walled container.

In the drawing, a schematic partial cross-section of a mold 1 is shown, as has been used in the following embodiments, it being understood that the drawing

Illustrative reasons not true to scale. The Forming tool 1 comprises, for example, a lower tool 2 and an upper tool 3 in the manner of a mold core, which in the closed state when the upper tool 3 in its inserted into the lower tool 2 position

is, between them define a narrow, gap-shaped cavity 4, the width b in the present case is about 0.8 mm. The upper tool 3 has an injection channel 5, which, for example, in the central

Bottom area of the mold cavity 4 opens and to the injection unit, such as an extruder, an injection molding machine

(not shown) is connected and via which the plasticized plastic material in the mold space. 4

can be injected. The flow paths of injected into the mold cavity 4 polymer melt are indicated by the arrows F, wherein the distance between the junction of the injection channel 5 in the mold space 4 and the farthest from the point of the mold space (cut in the drawing, upper end of the lateral Walls) here is about 24 cm, so that a

Wall / flow ratio of about 300 results.

From examples:

With the schematically reproduced in the drawing

Forming tool various embodiments of the injection molding and comparative examples were performed, and for comparison reasons always the same

thermoplastic polymer (polypropylene (PP) of the type

"Metocene HMM 648T" from Basell Orlen Polyolefins Sp. Z o.o., Poland) was used, which in a

Commercially available twin-screw extruder plasticized and on the one hand with 0.8 Mass .-% (based on the

Polymer composition) of a physical blowing agent in the form of technical nitrogen (N ₂ ) (Embodiments 4, 6 and 8 and Comparative Example 2), on the other hand, for comparison, was not added with a blowing agent (Comparative Examples 1, 3, 5 and 7). The filler used was in each case fine particulate talc having an average particle size of about 30 μm in various proportions between 0 (comparative examples 1, 3, 5 and 7) and 50% by mass.

(Embodiments 4 and 8 and Comparative Examples 3 and 7) and 60 Mass .-% (Embodiment 6 and

Comparative Example 5), each in turn based on the polymer composition used.

In the table below are the essential

Process parameters and results summarized:

Note: By means of Comparative Examples 1, 2 and the

Exemplary embodiments 4, 6 and 8 were able to produce durable containers. Comparative Examples 3, 5 and 7 resulted in non-demouldable moldings which were still broken in the mold, becoming practically dusty disintegrated. Moreover, in Comparative Example 7, the mold cavity of the mold could be filled with the plasticized polymer only to a little less than half.

From the examples, it is first clear that by means of the mold used with a wall / flow ratio of about 300 no thin-walled containers treated with talc can be sprayed, because the

Molding either decomposes (Comparative Examples 3, 5 and 7) or the polymer melt is not completely in the

Forming cavity of the mold is able to flow in (Comparative Example 7), whereas with otherwise corresponding formulations, stable thin-walled containers with degrees of filling of 50% by mass (Example 4) or 60% by mass

(Embodiment 6) can be easily obtained on talc, when the polymer melt 0.8 wt .-% nitrogen are added as a blowing agent. Furthermore, it can be seen that the injection time can be reduced by about half even at a filling level of 60% by weight (exemplary embodiment 6) compared with the conventional spraying of a thin-walled container made of pure polypropylene (comparative example 1), whereby a 60% by mass % of talc does not adversely affect. The injection time corresponds in this respect to about one with a corresponding proportion of propellant added polypropylene without talc (Comparative Example 2). In addition, the closing force of the mold can be about 40% (at a 50 wt .-% content of talc according to the embodiment 4) or about 35% (at a 60 wt .-% content of talc according to the embodiment - Example 6) compared to the conventional spraying of a thin-walled container made of pure polypropylene (Comparative Example 1), wherein even in comparison with the only with the blowing agent, but not with talc

offset polypropylene according to Comparative Example 2 only moderately higher closing pressures are required.

From the embodiment 8 is also clear that also the injection and thus the melting temperature of the polypropylene can be reduced by 50 ° C from 230 ° C to 180 ° C, which is due to the 0.8 Mass .-% by weight of nitrogen Even with a proportion of 50 wt .-% talc give about the same injection times and closing forces of the mold, as is the case with conventional injection molding of pure polypropylene (Comparative Example 1). In this way, sensitive polymers in particular can be protected against thermal damage.

Claims

claims

A method for producing a thin-walled container by plasticizing at least one thermoplastic or thermoelastic polymer and the plasticized polymer via at least one injection channel (5) in the mold space (4) of a mold (1) with a

Wall / flow ratio of at least 250 is injected, after which it along the floor and the

Wall of the mold space (4) in the mold space (4) is distributed so that it substantially completely fills it, after which the polymer solidifies to form the container and the mold space (4) of the mold (1) is removed, characterized in that the polymer on the one hand at least one powder or

added particulate filler or a polymer added with such a filler is used, and that the polymer on the other hand added at least one blowing agent or a propellant-added polymer is used, wherein the blowing agent in the mold space (4) of the mold (1) is expanded.

A method according to claim 1, characterized in that the polymer is added to at least one mineral filler, in particular from the group of phyllosilicates, or a polymer added with such a filler is used. A method according to claim 1 or 2, characterized in that the filler having a particle size of 0.1 μπι to 100 μπι, in particular from 0.1 μιη to 50 pm, is used.

Method according to one of claims 1 to 3, characterized in that the filler is used in platelet form.

Method according to one of claims 1 to 4, characterized in that the filler in a proportion of at least 1 Mass .-.%, In particular of at least 5 Mass .-%, preferably of at least 10 Mass. -%, Based on the mass of the polymer is used.

Method according to one of claims 1 to 5, characterized in that the plasticized polymer at least one physical blowing agent is added, which is in particular at least partially dissolved in the plasticized polymer, wherein the blowing agent in the mold space (4) of the mold (1) is degassed ,

Method according to one of claims 1 to 6, characterized in that the blowing agent from the group of inert gases, such as nitrogen, carbon dioxide, argon or the like is selected.

Method according to one of claims 1 to 7, characterized in that the blowing agent in a proportion between 0.01 wt .-% and 5 wt .-%, in particular with a proportion between 0.05 Mass .-% and 3 Mass. -% is used based on the mass of the polymer.

Method according to one of claims 1 to 8, characterized in that the wall / flow ratio of at least 260, in particular at least 270, preferably at least 280, is.

Method according to one of claims 1 to 9, characterized in that the width (b) of the mold space (4) of the molding tool (1), in which the injected into this plasticized polymer is distributed, at most 1.5 mm, in particular at most 1 , 4 mm, preferably at most 1.3 mm.

Thin-walled container of at least one thermoplastic or thermoelastic polymer, which is produced by injection molding by means of a molding tool (1) with a wall / flow ratio of at least 250, in particular according to a method according to one of claims 1 to 10, characterized in that the polymer material the container on the one hand at least one powdered or particulate filler contains, and that the polymer material on the other hand is at least partially foamed.

A thin-walled container according to claim 11, characterized in that the polymer material of the container contains at least one filler according to one of claims 2 to 4 and / or with a proportion according to claim 5.

A thin-walled container according to claim 11 or 12, characterized in that the foamed polymer material Inclusions of at least one propellant according to claim 7 and / or having a proportion according to claim 8.

14. Thin-walled container according to one of claims 11 to

13, characterized in that it is produced by injection molding by means of a molding tool (1) with a flow / flow ratio of at least 260, in particular of at least 270, preferably of at least 280.

15. Thin-walled container according to one of claims 11 to

14, characterized in that its wall thickness is at most 1.5 mm, in particular at most 1.4 mm, preferably at most 1.3 mm.