DE4118624C1 - - Google Patents

Abstract

In order to produce, simply and inexpensively, extruded or coextruded sheet with a colour pattern, a blowing agent is added to at least one layer of the sheet before extrusion of the heterogenous mixture of coloured and transparent or differently coloured plastic material. The mixture is then heated to a temperature above the softening point of the plastic material, the blowing agent being at the same time at least partly activated. The mixture is subsequently extruded, retaining the heterogeneity in at least part of the extrusion. The addition of the blowing agent prevents the plastic materials, at least in part, from mixing together to form a homogeneous mixture. This leads to the formation in the extruded sheet of e.g. transparent areas (4) and distinct coloured areas (3) in the layer (12). The differently coloured layer (10) underneath is visible through the transparent areas (4). Any colour pattern required can thus be produced. Deep-drawing of the sheet to produce beakers or plates distorts these transparent areas (4) and coloured areas (3), leading to a change in the colour pattern.

Description

The invention relates to a method for manufacturing a plastic film in which at least one Layer is extruded, for at least one Layer a heterogeneous mixture before extrusion from at least two plastic materials will be produced. The invention also relates to Containers, especially plates or cups thermoformed plastic film that has at least one Layer.

Containers, especially cups made from deep-drawn Plastic film made up of several layers is known. To visually close the containers shape the outer layer by adding Colored master batches. Such manufactured containers are, however, of one color, so that for the optical design of the container after Thermoforming process still further work steps have to undergo.

These additional process steps exist in that the products are partly in the Offset process with the desired print motifs be printed. Other procedures provide that a printed film on the outside of the Applied container, in particular is glued. All measures to improve the optical Appearance of the deep-drawn objects make the product more expensive, so that especially with so-called Vending machine cups mainly only single-colored Cups are used.

The object of the present invention is a Provide procedures that are simple and an at least one layer in a cost-saving manner extruded plastic film with a color structure can be provided. It is also the job of Invention to create containers that a different colors and color structure have without the container printed or have to be laminated.

This task is accomplished with a method according to the Claim 1 solved. The invention Container is the subject of claim 9. Advantageous Refinements are the subject of the dependent claims.

The invention is based on known extrusion processes with which it is possible to on or to produce multilayer plastic films, wherein the layer or layers have been colored can. For example, it is possible to use known coextrusion process To produce two-layer film, the one Layer as a white layer and the second layer as Color layer is formed. From this in Cups produced by deep-drawing processes then have a white inner layer and a colored one Outer layer. However, that is the possibilities the color scheme is exhausted.

To a color structure in the layer or layers to train, according to the invention, before extrusion the heterogeneous mixture of the at least two A blowing agent is added to plastic materials. The the mixture forming plastic materials differ either in that the one Plastic material transparent and the other Plastic material is provided with color pigments  or in that the plastic materials are colored differently. Preferably be the plastic materials used as granules.

The heterogeneous mixture is then over the softening temperature of the plastic material warmed, while the blowing agent is at least partially activated.

Additives are known as blowing agents understood that usually for foaming Plastics such as B. polystyrene or polypropylene be used. These blowing agents form certain temperatures gases that are foaming of the plastic.

It has now surprisingly turned out that such propellants in conjunction with the colored plastic material the property develop a homogeneous mixture of transparent and colored Plastic material or different colored plastic materials at least to partially prevent. This means that the The heterogeneity of this mixture is largely preserved remains. To what extent the heterogeneity of this mixture when heating above the softening temperature of the Plastic material can be retained via the Amount of blowing agent and the selected temperature to be controlled.

After heating the heterogeneous mixture and the at least partial activation of the blowing agent while maintaining heterogeneity Extruded material.

With the method according to the invention, both  single-layer as well as by coextrusions multilayer films are produced, wherein preferably mixtures of colored and transparent material can be used because thereby the color design options especially in the case of multilayer films can.

The extruded or coextruded film is according to the color used Colored plastic material and also shows in this colored material that is called a color matrix can be designated, stored areas transparent or different colored material. It it has been found that these areas all the more are larger, the greater the proportion of blowing agent is chosen.

It was also found that the higher the temperature in the extruder is chosen, the more more pronounced the training of demarcated, is preferably transparent areas. This means that the boundary between the color matrix and the transparent area, for example increasing temperature in the extruder becomes sharper. This is due to the fact that with increasing Temperature in the extruder also more blowing agent is activated so that a mixing of the colored plastic material with the transparent material is largely prevented. The lower the temperature chosen in the extruder becomes, the less the influence of the Blowing agents and the limits between the transparent areas and the colored areas are increasingly blurring. The effects described are additionally by the dwell time of the plastic material in the extruder  influenced. To the size and sharpness of the Controlling transparent areas is preferred a temperature in the extruder chosen between 70 ° to 150 ° above the softening temperature of the each plastic material used.

The training of transparent areas in the Color matrix, which is essentially a closed one have a circular shape and are characterized by the extend the entire layer thickness offers the advantage that in these areas the underlying layer the coextrusion film can be seen. If both Layers are colored differently one has a two-tone structure. So it's up easy way to get a color structure achieve without the need for printing.

This color structure becomes apparent when thermoforming the film to form a container such. B. one Mug or a plate more or less strong changed. Those transparent areas that are in Foil sections are very strong when Thermoforming process accordingly, far apart. Depending on Size and sharpness of the after extrusion present transparent or different colored Areas you get in the sections that are very be stretched a lot or more during deep drawing less rough structure that has some similarity with a wood grain. Areas at Thermoforming process are only slightly stretched, keep their initial structure largely. Depending on The shape of the deep-drawn object is obtained thus a color structure that in the highly stretched Sections an essentially line or has a linear shape and less highly stretched sections rather closed shows circular design.  

Known blowing agents are known as blowing agents added, preferably endothermic Use blowing agents. As a blowing agent can for example acid-carbonate systems be used.

The proportion of blowing agent in the layer constituting material is 1 to 20 wt .-%. The respective amount of blowing agent depends on what temperature is selected in the extruder and whether large or small transparent or different colors Areas with sharp or less sharp Limitation may be desired.

As a plastic material for the production of such extruded film is suitable for polystyrene or Polypropylene. The proportion of the transparent Plastic material is preferably 65-98 % By weight also based on the total amount of Layer.

Table 1 shows the mean diameters of the transparent areas in the extruded and not yet deep-drawn film evaluated. As Plastic granules became polystyrene with a share of 71 wt .-% used. The colored one Has plastic material (colored polystyrene) a proportion of 20 wt .-%. The share of Blowing agent is 9% by weight. As from the table 1 can be seen, the average diameter of the transparent areas with increasing Extruder temperature from approx. 1 to approx. 3 mm.  

Table 1

Table 2 was for a given one Extruder temperature the proportion of the blowing agent varies. Here too it is evident that with increasing Blowing agent proportion of the diameter of the transparent Areas increases. At about a doubling of the The amount of blowing agent is approximately one Doubling the average diameter of the transparent areas.

Table 2

Extruder temperature: 220 ° C

To the color structure of the deep-drawn containers, such as Make cups or plates even more diverse, carries the through the transparent areas structured layer at least one more structured layer, the transparent Areas of the structured layers at least partially overlap. For example, if a Container made from a four-layer film which is a white inner layer as well differently colored structured layers (e.g. red, green, blue) can be obtained by the overlap of the transparent areas Color pattern consisting of red, green and blue Stains or lines.

About what arises in the manufacturing process Recycle waste material from Advantage if this material in another Layer is introduced between the Inner layer and the first outer textured Layer is arranged. If the inner layer is colored, this is the backing layer only about the transparent areas of the structured layer visible.

Preferably is structured on the outer Layer another transparent antistatic layer upset. There is also the option of outer structured layer already with a antistatic material.

Preferred thicknesses of the structured layers are 50-120 µm. The backing layer has preferably a thickness of 400 to 950 microns and the Inner layer between 50 and 250 µm.  

In Table 3 the composition is one four layers of co-extruded film compiled.

Table 3

The use of blowing agents offers the others Advantage that in addition to the extensive Maintaining the heterogeneity of the mixture also a certain foaming of the Plastic material takes place. Since the coextruded film with its structured layer on the deep-drawing tool, the surface is the  structured layer almost completely smooth. Any thickening of the film due to the The foaming effect of the blowing agent can only to a certain roughness on the inner layer to lead. Due to this roughness of the inner layer the inner surface enlarges, which is particularly the case with is beneficial for yogurt cups, because it fixes the filled in Material is achieved.

If between the inner layer and the first structured layer a backing layer is provided, then comes the roughness of the Inner layer essentially due to the rest Proportions of the propellant that occur at the first Passage of the material not yet or not yet have been fully activated.

Exemplary embodiments are as follows explained in more detail with reference to the drawings. It shows

Fig. 1 is a thermoformed cup in a perspective view;

Fig. 2 marked in Fig. 1 field X in an enlarged scale;

Fig. 3 is a sectional view of the illustrated in Fig. 2 wall section along the line III-III,

Fig. 4a, 4b a plan view of an extruded and then thermoformed film according to one embodiment,

FIGS. 5a, 5b are plan views of an extruded and thermoformed film according to another embodiment,

Fig. 6 is a section through a four-layer film,

Fig. 7 shows the section through a six-layer film and

Fig. 8 is a plan view of a section shown in Fig. 7 Six-layer film.

In FIG. 1, a deep-drawn cup 1 is shown in perspective. This cup 1 consists of two layers, the structure of which can be seen from FIG. 3. The inside 7 of the cup wall 5 has isolated elevations 2 , which are due to the effect of the blowing agent as a foaming agent. The outside 6 of the cup wall 5 shows a kind of wood grain, which is achieved in that the transparent areas 4 and the areas made of colored plastic material (color matrix 3 ) have been pulled apart by the great expansion of the container wall 5 during the deep-drawing process.

The area X of the container wall 5 shown in FIG. 1 is shown enlarged in FIG. 2. The transparent areas 4 and the color matrix 3 can be seen, which have sharp boundaries in the illustration shown here. Such sharp limits are reached if on the one hand a high proportion of blowing agent and / or on the other hand a high temperature is selected in the extruder.

In Fig. 3 a section through such a container wall portion. It is a co-extruded film that consists of two layers. A structured layer 12 is applied to the inner layer 10 and has the color matrix 3 and embedded transparent regions 4 . Since the transparent regions 4 extend through the total thickness of the structured layer 12 , the inner layer 10 underneath can be seen in the viewing direction A. If the layer 12 has a different color than the inner layer 10 , a color structure is obtained, viewed in the direction of arrow A, which is essentially determined by the size of the transparent regions.

In FIG. 4a is a top view is shown on an extruded sheet 8, which also consists of two layers. The extruded film 8 shows small, circular, sharply delimited transparent areas 4 which are embedded in the color matrix 3 . The subsequent deep-drawing of an extruded film structured in this way then leads to an appearance as can be seen in FIG. 4b. This extruded film shows a line pattern which is characterized by the line-shaped transparent regions 4 .

In Fig. 5a the subsequent view is shown on an extruded sheet 8, in which a greater proportion of blowing agent has been added as in the embodiment shown in Fig. 4a film. Accordingly, the transparent areas are also larger, with some transparent areas 4 merging into one another. The subsequent deep-drawing of the extruded film 8 leads to the deep-drawn film 9 , which is shown in FIG. 5b. In contrast to FIG. 4b, a much coarser line structure is obtained. By choosing the proportion of blowing agent and / or the extruder temperature, it is thus possible to control the fineness of the color structure.

In FIG. 6 the cut is represented by a 4-layer film. A backing material layer 11 is provided on the inner layer 10 and is formed from the production waste. This backing layer 11 carries two structured layers 12 and 13 , which are colored differently. Transparent areas 4 a and 4 b are embedded in the structured layers 12 and 13 in the form of continuous islands. The transparent areas 4 a and 4 b are of different sizes and at least partially overlap. When viewed in the direction of arrow B, the colored area 3 a of the structured layer 12 below can be seen through the transparent area 4 b.

Seen in the direction of arrow A, one looks through the transparent regions 4 a and 4 b of the layers 13 and 12 onto the backing material layer 11 . Since the color matrix 3 b is not transparent (see arrow direction B), a color pattern is obtained which is composed of three different colors.

In Fig. 7 is a multilayer film in section according to another embodiment is illustrated. A backing material layer 11 , which carries three structured layers 12, 13 and 14 , is again provided on an inner layer 10 . The transparent areas 4 a, 4 b, 4 c of the structured layers 12, 13 and 14 are of different sizes and at least partially overlap. A transparent, antistatic layer 15 is additionally applied to the outer structured layer 14 .

In FIG. 8, the top view of such a six-layer film is shown. The areas visible in the direction of the arrows A, B, C and D (see in FIG. 7) are shown in FIG. 8 by different hatching. Because different layers are visible through the overlapping transparent areas, a color pattern is obtained which is characterized by a total of four colors.

Reference symbol list

1 cup, container
2 increases
3 color matrix, colored plastic
4, 4 a, b, c transparent areas
5 cup wall
6 outside
7 inside
8 extruded film
9 thermoformed film
10 inner layer
11 backing layer
12 structured layer
13 structured layer
14 structured layer
15 structured layer

X area
A, B, C, D arrow directions

Claims (21)

1. A method for producing a plastic film, in which at least one layer is extruded, a heterogeneous mixture of at least two plastic materials being produced for this layer before the extrusion, at least one of which consists of colored plastic material, characterized in that
that a blowing agent is added before the heterogeneous mixture is extruded,
that the heterogeneous mixture is then heated to above the softening temperature of the plastic materials, the blowing agent being at least partially activated at the same time and
that the mixture is then extruded while at least partially maintaining the heterogeneity of the mixture. 2. The method according to claim 1, characterized characterized that at least two layers be coextruded, the heterogeneous Mix for at least one layer colored plastic granulate and transparent plastic granulate becomes.   3. The method according to claim 1 or 2, characterized characterized in that the mixture of Plastic material and blowing agent in the extruder is heated to a temperature which is 70 ° C to 150 ° C above the softening temperature of the Plastic material lies. 4. The method according to any one of claims 1 to 3, characterized in that as a blowing agent endothermic blowing agent is added. 5. The method according to any one of claims 1 to 4, characterized in that as a blowing agent Acid-carbonate mixture is added. 6. The method according to any one of claims 1 to 5, characterized in that the endothermic Blowing agent in a proportion of 1 to 20% by weight based on the total weight of a shift is added. 7. The method according to any one of claims 1 to 6, characterized in that the transparent Plastic material with a share of 65 to 98 wt .-% based on the total weight of one Layer is added. 8. The method according to any one of claims 1 to 7, characterized in that as Plastic material polystyrene or polypropylene is used. 9. Container, in particular mug or plate, made of deep-drawn plastic film having at least one layer, characterized in that the layer is a structured layer ( 12, 13, 14 ) made of colored plastic ( 3 ) with embedded areas ( 4 a, b, c ) is made of a different colored or transparent plastic material. 10. A container according to claim 9, characterized in that the predominant portion of the transparent or differently colored areas ( 4 a, b, c) extends through the entire layer thickness of the structured layer ( 12, 13, 14 ). 11. A container according to claim 9 or 10, characterized in that the transparent or differently colored areas ( 4 a, b, c) have a substantially closed circular shape. 12. Container according to one of claims 9 or 10, characterized in that the transparent or differently colored areas ( 4 a, b, c) have a substantially linear or linear shape. 13. Container according to one of claims 9 to 12, characterized in that the structured layer ( 12 ) carries at least one further structured layer ( 13, 14 ), the transparent regions ( 4 a, b, c) of the structured layers ( 12 , 13, 14 ) overlap at least partially. 14. Container according to one of claims 9 to 13, characterized in that a layer consisting of monochrome or transparent plastic material, the inner layer ( 10 ) of the container ( 1 ) and the structured layer ( 12, 13, 14 ) forms the outer layer. 15. A container according to claim 14, characterized in that a backing material layer ( 11 ) is provided between the inner layer ( 10 ) and the structured layer ( 12 ). 16. Container according to one of claims 14 or 15, characterized in that the outer structured layer ( 14 ) carries a transparent antistatic layer ( 15 ). 17. Container according to one of claims 14 or 16, characterized in that the outer structured layer ( 14 ) additionally contains antistatic material. 18. Container according to one of claims 9 to 17, characterized in that the structured layers ( 12, 13, 14 ) have a thickness of 50 to 120 microns. 19. Container according to one of claims 15 to 18, characterized in that the backing layer ( 11 ) has a thickness between 400 and 950 microns. 20. Container according to one of claims 14 to 19, characterized in that the inner layer ( 10 ) has a thickness between 50 and 250 microns. 21. Container according to one of claims 14 to 20, characterized in that the inner layer ( 10 ) has a rough surface.