DE2159886A1 - Process for the production of cup-shaped bodies from polyolefin plastic films - Google Patents

Description

" Process for the production of cup-shaped bodies from polyolefin plastic films "

Polyolefins such as polypropylene, polyethylene, copolymers of such substances, and others, crystalline plastics have favorable properties, such as high tensile strength in the heat, high resistance to harmful environmental factors, a low odor and taste and a pleasant appearance and a pleasant Handle, which makes it suitable for packaging a large number of substances, especially foodstuffs containing oil, are well suited.

However, polyolefins have certain properties, such as a low melt viscosity, which make it very difficult to a melted film, e.g. by vacuum forming or pressing

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to shape, as the film flows too much (sheet sag). To have a favorable level of melt strength for this To achieve materials, it is necessary to use extremely high molecular substances. Such substances however, are difficult to manufacture in the form of a film with a good surface. Also perform the thermal Properties of polyolefins such as low thermal conductivity and high heat capacity at unusually long molding times compared to those for polystyrene and Acrylic-Butadisi] -Styrene-Gopcil3ra3ere, the standard substances for hot forming. Therefore, polyolefins have not been used very widely for hot molding.

When attempting to heat polyolefins and in the melt phase on conventional hot molding equipment To shape, the film sags unusually strong, even in relatively small areas and dirty the device and both during heating and molding, wrinkles are formed which are preserved in the article stay and therefore it is necessary to keep the shaped body in the shape for a long time in order to achieve that it retains its shape, which of course is extremely disadvantageous.

It is an object of the present invention to provide a method for the shaping of polyolefin plastic films, thin-walled cup-shaped bodies are to be created without the need for the conventional hot-molding processes occurring problems occur «

The invention therefore relates to a method for producing thin-walled, cup-shaped objects from polyolefin plastic films, that is characterized by the fact that one

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thin polyolefin plastic film in solid state a temperature below the melting point with a melt flow above 0.7 between a die insert (or punch) and a mold with an opening at the end, insert the die insert into the opening of the mold, leaving a bulged portion of the film penetrates into the mold and presses a medium into this bulged part of the film around the object to shape.

The plastic film is in the solid phase, i.e. at a temperature below the melting temperature and above the glass transition temperature. The film is first applied with the help of a die insert or a Doms bulged out and the final shape of the object is achieved by a pressure medium, that acts against an evacuated room or one that does not offer any significant resistance to the medium. Since the film material is in a solid state, the film may sag or run away much less than if the sheet material were in the molten state and thereby becomes a Wrinkles are avoided and objects are created with thinner and more even walls. The. at Processes in which the film is used in the molten phase, even at the openings of the mold through the The present method prevents wrinkles from sagging. The item can be made a film without being held in the vicinity of the opening of the mold or optionally from a film that is attached around the cavity of the mold.

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The process is particularly suitable for thin foils with a thickness of less than about 3) 2 mm, preferably 0.5 to 1.5mm easily made by extrusion and rolling can be produced. Here, a material that is suitable for injection molding, with a lower molecular weight and higher melt flow can be used. A high molecular weight is a over 600,000. The molding times are of the same order of magnitude as those for high-impact polystyrene and much shorter, almost half as long as when molding polypropylene in the melt phase.

The invention is explained by way of example with reference to the accompanying drawings.

Fig. 1 is a schematic vertical section of an apparatus for heating and shaping plastic films in individual stages into a group of cup-shaped Objects;

Fig. 2 is a plan view of a group of articles produced in one operation with the press have been;

Fig. 3 is an enlarged section showing the sheet between the punch and the mold;

Fig. 4 corresponds to Fig. 3 and shows the device, after the punch has fully entered the mold;

5 corresponds to FIGS. 3 and 4 and shows the state

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after the print medium has the body to its has formed its final shape and

Jig. Figure 6 is still further enlarged and shows a finished article partially in section.

The device shown comprises a heating unit 10 into which the sheet material V with Ms, for example a width of 56 cm is introduced by a coil 11 and a pressing device 12. The heating unit comprises heating devices for three levels 13, 14 and 15 with upper and lower Radiant heating elements 16, each having approximately the same length as that of the printing unit. Devices (not shown) are provided for the film in each case by one such piece through the various Heat levels and move the press forward as it corresponds to the length of the press. These devices have e.g. in the form of continuous, tipped chains on the sides which capture the indene of the film and they pass a certain length through the heating and pressing unit. The molded sections of the film can cut to the length of the press, as they are made in the press, and to a device in which the individual objects are separated or the press can be built that way be that the formed film is fed directly to a device that cuts out the individual objects. The scrap pieces of foil can be remelted and rolled out or discarded, as the case may be the economic expediency.

Fig. 6 shows a cup-shaped object 20 with the

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Side wall 21, the bottom 22 and the edge 23.

The elements of the press unit 12 are in their effect shown in Figs. 3, 4 and 5. The press unit includes a mold 25 with a line 26 for vacuum or / pressure medium a male mold or a stamp 27 and a liquid line 28 for the pressure medium, which the Object gives its final shape.

3 shows the film W in its original position between the shaping elements. The shape can be up to the height of the film is lowered and the film is pressed against it. The stamp then becomes that shown in Figure 4- Position pushed up while the air is removed from the mold through line 26.

Sealing rings 29 around the space for each individual item, or a sealing ring 30 around the entire group of items, or both with air ducts 28 within the enclosed space, are provided to allow the druoknaeuium to shape the item. The sealing locations are indicated in broken lines in Fig. 2 to show their location on the formed sheet.

Then, as shown in Fig. 5, the print medium, e.g. compressed air, with 5> 5 atm or above lines 28 are introduced around each punch to compress the film into the mold.

of the body After a dwell time to solidify the shape / become the stamp and the mold are separated. In this case, the film can with the help of a pressure introduced through the lines 26

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media or other devices for ejecting the film ₍ as far as necessary, can be ejected and the formed film is removed from the press after its removal from the press parts.

The shaped piece of film can be cut off the length of the press and removed by hand or in any other suitable manner. Later the individual will be cup-shaped Separated objects from the film in any suitable manner.

The film entering the press is heated to a temperature which is sufficiently far below the melting point that the film holds together and sagging or sticking is avoided when it is moved between the supporting side chains gripping the film. As will be explained later, it is sometimes beneficial to mold at lower temperatures when sufficient pressure can be applied. In the case of polypropylene with a melting point of approximately 168 ^° C., the film is introduced into the press at a temperature of approximately 160 to 166 ^{° C.} In the conventional hot-forming of the same material, it is heated to about 177 ⁰ C.

The post-molding residence time necessary for the film to retain its shape is largely determined by the use of solid polypropylene compared to molding in the melt the same material. For example, the dwell time in the melt during shaping can be / 6 s, while at the molding of the solid material according to the invention, the residence time is reduced by half. The same cons

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ORIGINAL INSPECTED

ratio occurs "with other film thicknesses as well.

During the usual hot molding of polypropylene, you can only the products with a low melt flow, such as 0.5 or 0.6, are used. Substances with a higher Melt flow have a lower melt viscosity and therefore have a very strong tendency to sag or tear, even if the area above the mold opening, is small and thus lead to difficult processing problems. They are therefore generally used for common Hot molding process not considered suitable. The method according to the invention, in which molding takes place in the solid phase, can easily produce polymers with a higher melt flow, such as 5> 0 can be used, without sagging.

The stamp is in the solid phase when shaping at the end a little more rounded and a little shorter than the stamps used for shaping in the melting phase be used. The forming punches in melt forming are quite flat at the end to allow for a larger amount of material to take with you who.after the movement of the stamp came to a standstill, blown away or pressed away will.

The higher the blowing or molding pressure that is applied, the sharper the corners and shapes of the object will be and the higher the temperature, the better the formation of the shape.

This auxiliary stamp remains on a proportionate when working high temperature, e.g. 138 ° C or above, and thus does not cool the film excessively. Proportional

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less than in the melting phase, where the temperature of the film is much higher. The! Form works at a much lower temperature. In order to achieve the shortest possible molding times, the mold can be cooled by circulating cooling water, which has a temperature of 10 ^° C., for example. The colder and thicker the film and the greater the applied stamp pressure, the more rounded and tapered the end of the stamp is in order to achieve the best possible drainage of the material. Compared to this, the punch for shaping in the melting phase is almost flat and has only slightly rounded corners.

The film material is preferably polypropylene or polyethylene or a copolymer of these substances. Preferably the melt flow is between 4.5 and 5 »2, usually around 5> 0. The ones in the description and the Melt flow values given in the claims relate to the ASTM values.

One of the main advantages of the method according to the invention is that it is possible to produce clear making transparent objects such as containers from polypropylene. A factor in making clear walls it is that they have a high surface gloss on both sides of the film. The one with a 45 ° Gardner gloss meter measured gloss should preferably be about 50 or more. To get a high gloss on the surface To achieve the film, the forming rollers must be highly polished and the roller temperature in a tight Regulated area.

For films with a high melt flow, such as 5 »0,

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the top and middle roll of a device with three rolls for making the film at one temperature of about 27 ° C and the bottom roller at about 66 ° C. Some moderately clear articles were hit with a Film produced with a melt flow of about 0.7, but the transparency becomes higher as the melt flow increases better. The clarity also improves with lower temperatures in film production. A higher one Mold pressure allows the molding of objects at lower temperatures and this allows the others Requirements for producing a good surface gloss for the production of clear, transparent objects be reduced. Applicable prints depend on the devices available and the number of Items to be crafted in a cycle. With some devices, the cup formation necessary pressure to be limited to 5 »5 atm, if a Number of large cup-shaped objects to be produced in one operation. By changing the However, this limitation can be overcome by designing the device.

Clarity increases as the stretch of an area increases. In order to achieve a clear object, the Aspect ratio should be at least 3: 1 and 6 or 8: 1 for good clarity.

A polypropylene that has a good balance between the processability in extrusion and the clarity at all thicknesses is a nucleated Homopolymer with a melt flow rate of 5 · Ein ke.rn— condensed polymer also allows higher extruder output provided that the necessary capacity of the extrusion device for

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Addition is included, as materials condensed on the cores solidify at higher temperatures,

Another factor for high clarity in molded parts is the presence of a sheet made from a melt from an extruder of a high melting point material that is essentially devoid of crystalline structure invisible remaining crystallinity in the melt forms crystallization nuclei which lead to coarse crystallization. In order to avoid residual crystallinity in the melt, which is formed by the extrusion device and the rolls, the following temperatures have proven to be suitable for the extrusion device: in the feeding zone 177 ° C, in the compression zone 232 ° C, in the measuring zone 204- ° G, and in which in the region of the die 204- ⁰ C. A higher temperature in the pressure zone, resulting in the melting of the polymer is terminated earlier and thereby ensures the formation of a homogeneous melt which is essentially free of crystalline polymer r.

Clearer objects are formed when the melt flow factor of the polymer increases. Above 5 »0 is the Clarity excellent. Below the objects become increasingly transparent.

Clarity also gets better at lower mold temperatures for all materials, but the lower limit for applicable mold temperatures depends on the available mold pressure and the sharpness of the shape that is desired or required.

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The method according to the invention thus represents a simple and convenient method of production clearer transparent articles made of polypropylene are made by shaping the film in the solid phase on certain Way from certain foil material.

PATENT CLAIMS:

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Claims (9)

PATEHTA Ή PROVERBS 1.] Process for the production of thin-walled cup-shaped Body made of polyolefin plastic films, characterized in that a thin "film made of a polyolefin plastic material in the solid state "at a temperature below the melting point with a melt flow above 0.7 between inserts a forming punch and a mold with an open end, moving the punch into the opening of the mold and into the resulting one Bulge of the film presses a print medium » 2. The method according to claim 1, characterized in that that the film in the vicinity of the opening of the mold is free to move during the movement of the punch and around the Opening above the foil prior to the introduction of the print medium into the bulged part of the foil a liquid seal is located. 3. The method according to claim 2, characterized in that that one produces a plurality of cup-shaped bodies from the width of the film, the film only on the sides is being held. 4. The method according to claim 1 to 3, characterized in that one ^{uses a polypropylene film with a melting point of 167-169 0} C and molded at a temperature of 160-166 C under a pressure of 5.5 atmospheres. 5. The method according to claim 1, characterized in that that a film material with a melt flow rate of 4.5-5> 2 is used. -14- 209825/0784 -H- 6. The method according to claim 1, characterized in that that you have a polypropylene film with a melt flow of more than 1, o used which has been rolled out of an essentially crystal-free melt and one Has a surface gloss of more than 45, 7. The method according to claim 6, characterized in that that one molds at a temperature which is below the melting point. 8. The method according to claim 6, characterized in that that a sheet material with a melt flow rate of at least 5, ο and a surface gloss of at least 5o used. 9. The method according to claim 6, characterized in that that the EoIi e in a ratio of at least 3: 1 stretches. 209825/0784