DE10235845A1 - To produce preforms, for molding into beverage bottles, compression molding is used with an inner and an outer mold to compress a pellet into a blank which is then shaped into the preform by compression and deep drawing - Google Patents

Abstract

To produce a preform, the pellet material (1) is initially compressed into a blank (6) in a mold with a relative axial movement between the outer mold section (2) and the inner mold section (5). This shapes the pellet into a blank with the mouth opening (8), the base (7), and the cylindrical section (10) between the mold walls. In a second stage, the inner mold exerts additional pressure on the blank, and the base (3) of the outer mold is lowered to extend the cylindrical section of the blank to shape the cylindrical part (12) and the beading (15) of the preform (11).

Description

State of the art

The invention is based on one Method and an apparatus for producing a preform the preamble of claim 1.

Such preforms are also called Called preforms. It is a tubular part with a thread in the mouth area. Preforms consist of a thermoplastic material. For manufacturing a container, for example a bottle, the preform is heated and blown into a given shape.

For the production of preforms known from the prior art injection molding process. Doing so the material warmed up so much that he's in fluid Form is present. For this purpose, temperatures are typically between 250 and 300 degrees Celsius necessary. The liquefied material is through a nozzle injected into a mold. Because the preforms and thus the injection molds especially for larger containers relatively the liquefied material must be long cover a relatively long way in the injection mold. This is only possible when the material heats up to the above high temperature and work with a high spray pressure. As a disadvantage It turns out in these known methods that a high energy must be applied.

In addition, the Using PET as a material at these high temperatures acetaldehyde. This substance is not harmful to health, but it can help Drinks, which are stored in containers made from preforms, one cause unpleasant taste. The amount of acetaldehyde in the preform hangs from the temperature at which the preform is manufactured. A Reducing the amount of acetaldehyde is therefore only possible through a lower temperature possible during production. With injection molding processes, the temperature cannot be reduced for the reasons given above become. The high spray pressure also creates shear forces, that to an additional warming of the material. About that In addition, it proves to be disadvantageous that the injection molding process the heated material must displace the air from the entire mold. The volume of this to be repressed Air is relatively large. Moreover is the shape of the preform at least in part by the injection molding process conditionally. For example, the bottom of the preform can only be curved otherwise it cannot be guaranteed that the material the entire mold during injection molding fills.

The invention and their advantages

In contrast, the method according to the invention and the inventive device for Manufacture of preforms according to claim 1 the advantage that Preform not by injection molding but by the action of pressure and the occurrence of a suction effect is produced. The pressure molding is called compression in the English language Molding called. This technical term has also changed in German Language area enforced. Compression molding involves the above Disadvantages of the injection molding process do not arise. The material is in the form of a round block in an outer molding brought in. In this form, the material is also called pellet. Exercises in a first stage an inner molded part by a driven relative axial movement of the two molded parts to each other on the pellet. The pellet is between the inner and outer molded part formed into a blank. In the first stage, the pellet goes into a blank. This blank already has the mouth area and the bottom the preform. A relatively short cylindrical one extends in between Section. Due to the inner and outer molded part, a larger diameter and a larger wall thickness as well a shorter length than the cylindrical section of the preform. In this first one Stage of manufacture is made up of the space between the inner and the outer molding all the air is displaced. There the volume of the gap in the first stage of manufacture is smaller than the volume of the preform, in the method according to the invention less air volume displaced than with the injection molding process.

In a second stage of manufacture the blank goes into the preform. Doing this the inner molding additional Pressure on the blank, leaving the bottom of the outer molding compared to the sidewalls lowers. It is long the cylindrical area of the blank. The short cylindrical one Section of the blank with large Wall thickness changes into one long cylindrical section of the preform with thin walls. Between the mouth area and a bead, the diameter of which remains in the cylindrical portion corresponds to the diameter of the cylindrical region of the blank. Regarding the mouth area and the blank match the blank and the preform. The mouth area and change the floor no longer in this second stage. The strength of the soil is already specified in the first of the manufacturing stage. If the desired strength in the The first stage is reached, the second stage begins and it moves the inner molding and the bottom of the outer molding at the same time downwards, so that the distance between the two molded parts is in the area of the soil no longer changed in the second stage.

Since all air was displaced from the space between the inner and outer molded part in the first stage of production, there is no resistance to overcome in the second stage due to the displacement of air. When the inner molded part is lowered at the same time as the bottom of the outer molded part, the deformation of the cylindrical region of the blank to the cylindrical region of the preform is not primarily due to the action of pressure, but rather by suction.

The tool for making the Preform essentially consists of an inner and an outer molded part. The inner molded part is designed as a cylindrical mandrel. The outer molding has a bottom and cylindrical side walls. The cylindrical side walls have two sections: a first section with a larger diameter and a second section with a smaller diameter. A drive ensures a relative axial movement of the two molded parts.

To the thermoplastic material Molding under pressure requires lower temperatures than injection molding, because the material does not have to be liquefied as much. temperatures between 100 and 200 degrees Celsius are usually sufficient. This temperature is about 100 degrees Celsius lower than the temperature in the injection molding process. This has the advantage of acetaldehyde in a much smaller amount that arises during manufacture less energy is necessary and that the temperature of about 60 up to 80 degrees Celsius, at which the finished preform from the Moldings can be removed, is achieved faster. Because the material while of the molding process does not cool down like injection molding, the molding process can be designed individually.

The shape of the floor is not through the manufacturing process and therefore can be almost arbitrary chosen become. In addition to a spherical As with the injection molding process, square shapes are also possible.

To remove the finished one Preform from the tool, the inner and outer molded part in opposite Directions moved. So that the preform is not damaged, they are cooled to a temperature of approx. 80 degrees Celsius.

According to an advantageous embodiment the device according to the invention are the inner and / or the outer molded part stored by springs. It can be mechanical springs, for example coil springs, or pneumatic or hydropneumatic booster act. Other feather-like Devices are also possible.

After another advantageous one Design of the device according to the invention rods are provided, which in a first stage, in the a blank is formed into the material present as a pellet, on the outer molding seated. This ensures that in the second stage Manufacturing the cylindrical side walls of the outer molding their position no longer change while the inner molding and the bottom of the outer molding at the same time Lower. On the outer molding can Recordings for the rods may be provided. Instead of rods and mounts other devices are possible which achieve the same effect.

Other advantages and beneficial Embodiments of the invention are the following description, the drawing and the claims removable.

drawing

In the drawing, an embodiment of the Invention shown and described in more detail below. Show it:

1 different stages of the method according to the invention,

2 different positions of the tool in accordance with 1 .

3 Arrangement of several tools in a circle.

description of the embodiment

In the 1 and 2 Different stages of the method and the device according to the invention are shown. The left part of 1 shows the insertion of a pellet 1 in the direction of the arrow in an outer molded part 2 , The outer molding 2 has a bottom 3 with spherical shape and cylindrical side walls 4 , The middle part of 1 shows the first stage of manufacture. In this stage is the inner molding 5 , which is designed as a cylindrical mandrel, has been moved in the direction of the arrow by a drive which cannot be seen in the drawing. Because the outer molding 2 the pellet experiences its position 1 a deformation by pressure and goes into a blank 6 about. The floor is already forming 7 and the mouth area 8th the preform. In order to provide the mouth area with a thread that cannot be seen in the drawing, for example, is on the inner molded part 5 a threaded molding 9 intended. Between the floor 7 and the mouth area 8th creates a cylindrical area 10 , The blank is in the first stage of manufacture 6 tight on all sides of the inner and outer molded part 2 and 5 enclosed. All the air is thus displaced from the space between the inner and the outer molded part.

In the second stage of manufacture, the inner molded part 5 moved further in the direction of the arrow. This is in the right part of 1 shown. At the same time, the floor sinks 3 of the outer molded part 2 from. The blank 6 deforms to the preform 11 , The cylindrical area 10 of the blank 6 lengthens. The amount of material in the cylindrical area 10 of the blank 6 must be such that it sufficient to cover the cylindrical area 12 the preform 11 to build. The cylindrical side walls 4 of the outer molded part have a first section 13 with a larger diameter and a second section 14 with a smaller diameter. At the transition between the mouth area 8th and the cylindrical area 12 there remains a bead 15 , This arises at the step-like transition 16 between the first and the second section 13 . 14 of the cylindrical side walls 4 , The molded thread presses from above 9 against the bead 15 ,

In 2 the various stages of manufacture are shown together with the device. 1 shows the tool before the pellet 1 is introduced. The pellet is located in II 1 already in the outer molding 2 , III corresponds to the first stage of manufacture, in which the pellet 1 already to a blank 6 was pre-compressed. IV shows the second stage of manufacture, in which the blank 6 to a preform 11 is reshaped. In V is the finished preform 11 removed from the tool. In this illustration, the coil spring 17 recognizable via which the inner molded part 5 is stored. Also shows 2 the poles 18 with which the inner molding 5 surrounding part of the tool on the outer molding 2 supported. For these rods there are receptacles on the outer molded part 19 intended. In contrast to the one in 1 The process shown in III does not move the inner molded part downwards but the outer molded part upwards. The effect is the same, however, because the relative movement of the two molded parts is important.

Several devices for producing a preform can either be linear in a row as in 2 or in a circle like in 3 be arranged. This means that several preforms can be produced at the same time.

All Features of the invention can be both individually as well as in any combination with one another essential to the invention his.

Claims (11)

A process for producing a preform from thermoplastic material for producing a container, for example by blow molding, the preform consisting of a cylindrical part with a bottom on the underside, an upwardly open mouth area on the top and a bead between the cylindrical part and the mouth area following process steps that the material in the form of a pellet ( 1 ) in an outer molded part ( 2 ) is introduced, the outer molded part ( 2 ) a floor ( 3 ) and cylindrical side walls ( 4 ), the diameter of which is at least partially larger than the diameter of the base ( 3 ) that in an initial stage an inner molded part ( 5 ) by a driven relative axial movement of the two molded parts ( 2 . 5 ) to each other on the pellet ( 1 ) exerts pressure and thereby the area of the mouth ( 8th ), the ground ( 7 ) and in between a cylindrical section ( 10 ) of a blank ( 6 ) forms, the cylindrical portion ( 10 ) of the blank ( 6 ) is shorter than the cylindrical section ( 12 ) the preform ( 11 ) and has a greater wall thickness than this, and that in a second stage the inner molded part ( 5 ) additional pressure on the blank ( 6 ) exercises the ground ( 3 ) of the outer molded part ( 2 ) opposite the side walls ( 4 ) of the outer molded part ( 2 ) is lowered, the cylindrical region of the blank ( 6 ) and the cylindrical area ( 12 ) and the bead ( 15 ) the preform ( 11 ) are shaped. A method according to claim 1, characterized in that in the first stage the pellet ( 11 ) of the inner and outer molded part ( 2 . 5 ) tightly enclosed in the shape from the mouth area ( 8th ), Ground ( 7 ) and cylindrical section ( 10 ) is pressed, and that thereby the in the space between the inner and the outer molded part ( 2 . 5 ) existing air or other gases are displaced. Method according to claim 1 or 2, characterized in that in the second stage the blank ( 6 ) tightly enclosed between the first and second molded part ( 2 . 5 ) to the preform ( 11 ) is deformed. Method according to one of the preceding claims, characterized in that in the second stage the floor ( 3 ) of the outer molded part ( 2 ) is lowered against a spring force, and that the inner molded part ( 5 ) is lowered against a spring force by a drive, the inner molded part ( 5 ) assigned spring force is greater than that of the floor ( 3 ) of the outer molded part ( 2 ) assigned spring force. Method according to one of the preceding claims, characterized in that the preform ( 11 ) by a relative axial movement of the two molded parts ( 2 . 5 ) is stripped in opposite directions. Device for producing a preform made of thermoplastic material, which is used to manufacture a container, for example by blow molding, the preform consisting of a cylindrical part with a bottom on the underside, an upwardly open mouth area on the top and a bead between the cylindrical part and the mouth area , in particular for carrying out the method according to one of the preceding claims, characterized in that that a molding tool with an inner molding ( 5 ) and an outer molded part ( 2 ) it is provided that the inner molded part ( 5 ) is designed as a cylindrical mandrel that the outer molded part ( 2 ) a floor ( 3 ) and cylindrical side walls ( 4 ), the cylindrical side walls in a first section ( 13 ) have a larger diameter than in a second section ( 14 ) that a drive for a relative axial movement of the two molded parts ( 2 . 5 ) is provided to each other. Apparatus according to claim 6, characterized in that the bottom ( 3 ) of the outer molded part ( 2 ) opposite the cylindrical side walls ( 4 ) is slidably mounted. Apparatus according to claim 6 or 7, characterized in that the inner and / or the outer molded part ( 2 . 5 ) by springs ( 17 ) are mounted, which experience a deflection during the relative axial movement of the two molded parts. Device according to one of claims 6 to 8, characterized in that on the inner molded part ( 5 ) Rods ( 18 ) are provided, which in a first stage, in which the pellet ( 1 ) present material a blank ( 6 ) with a mouth area ( 8th ), a floor ( 7 ) and a cylindrical area ( 10 ) is molded on the outer molded part ( 2 ) sit on. Device according to one of claims 6 to 9, characterized in that that several molding tools are arranged in parallel in a circle are. Device according to one of claims 6 to 9, characterized in that that several forming tools are arranged linearly parallel to each other are.