DE102010038076B4 - Device for mono- or biaxial stretching of film sections (stretching frame) - Google Patents

Abstract

Device for the monoaxial or biaxial stretching of film sections (1), preferably by means of a stretching frame, for films (7) made of polymers, a square or rectangular section of such a film (7) being secured on four sides by at least two clips (2; 11, 13, 15), characterized in that both the lower fixed clip (13) and/or the upper movable clip (11, 15), preferably independently of the heating of the film (7), by at least one heating system, preferably each are heatable.

Description

The invention relates to a device for the monoaxial or biaxial stretching of film sections, which consist essentially of polymers, a square or rectangular section of such a film being gripped on four sides by at least two clips each, with a fixed lower clip part forming the support and an upper part of the clip that is brought down from above, perpendicular to the plane of the film, clamps the film at the peripheral edge.

Advantageously, the lowering of the upper clip part and the construction of the clamping force by z. B. pneumatic or hydraulic cylinders can be effected.

In a further advantageous manner could after heating the clamped film by such. B. hot air or IR rays, the four groups of clips move apart on all four sides to perform a stretching process.

The clips are each guided in guide rails which z. B. be moved by geared motors or hydraulic cylinders.

The movement of the clips is synchronized by a pantograph system (a system of crosswise arranged, parallel strips which are connected to one another in an articulated manner) in order to ensure an even stretching process on all sides (see sheet 1, 1 ).

Devices of this type are, inter alia, from JP S55 158 936 A famous.

Executed devices of this type use z. B. to clamp a square foil sample in sizes of 100 x 100 mm on each of the four sides five clips with a width of 10 to 12 mm (see 1 )

According to the prior art, the arrangement of the clamping cylinders is perpendicular from top to bottom for the movement of the upper clip in the direction of the lower, fixed flap.

A rather small width of the clips, but a larger number of clips, is required in order to guarantee a uniform stretching of the film.

The limited width of the clip also limits the size of the incorporated pneumatic or hydraulic cylinder to apply the clamping force. For high-temperature applications in particular, the use of air or N2 is required to actuate the cylinders, where the specific pressures are limited. The use of hydraulics is not recommended due to the risk of fire.

As a result, the clamping force applied by the pneumatic clamping cylinder is not sufficient for larger film thicknesses and the resulting higher stretching forces, and the films can slip out of the clip.

According to another patent application DE 10 2009 003 751 of the applicant, the content of which is hereby made part of the content of the present application, the upper clip part is articulated on an axis of rotation lying outside the film to be stretched in such a way that the lower, fixed clip part carries the joint, while the upper clip part can be pivoted upwards is carried out and that at least one cylinder for applying the clamping force is rotated by 90° on a vertical web of the lower, fixed clamp part, is arranged horizontally and fastened and thus applies the clamping force to the upper, pivotable clamp part.

Furthermore, several clamping cylinders arranged horizontally next to one another are arranged axially offset on the respective clip, as a result of which the clamping cylinders have a significantly larger diameter and significantly greater compressive forces can be built up (with the same maximum pneumatic pressure).

The devices according to the prior art also have the following disadvantages:

In order to bring the necessary stretching temperature into the film and also into the clips themselves, according to the prior art, the heating medium air or IR radiation is used both for heating the film and for heating the clips.

This is a method that works well for foils from approx. 0.1 mm to approx. 1.5 mm thickness.

For larger foils or plate thicknesses of e.g. B. 2 mm to 5 mm or even more, it becomes more and more difficult to heat the clips to the stretching temperature with the film/plate. However, if the clips are not heated sufficiently, the plastic areas between the upper and lower clips will not be heated or will be heated too slowly as a result. Likewise, the narrow surfaces of the foil are heated laterally between the individual pairs of clips only too slowly.

The consequence of this slow heating is a very much longer heating process until a uniform stretching temperature is reached in the free film surfaces and inside the clips. This long heating-up time makes the whole stretch run uneconomically and also leads to possible disadvantageous changes in the structure of the film/plate to be stretched.

It is known that before the film is clamped in the stretching frame, initially only the clips are heated with the heating medium hot air or IR radiation. Then the heating system is shut down or the stretching frame is moved out of the hot-air oven. The foils are inserted, the clips are closed, the heating system closes again, or the stretching frame is moved back into the hot-air oven and now heats both the foil and the clips. With this method, too, the temperature initially reached in the clips drops quickly and can no longer be reached even after prolonged post-heating together with the film.

This effect becomes more and more evident with increasing thickness of the film/plate and makes problem-free stretching with thicknesses over 2 mm and temperatures over approx. 150 (200)°C very difficult and very time-consuming.

Another disadvantage is the insufficient transmission of the stretching force acting at an angle of 90° to the clip surface to the surface of the compressed clips.

Since a smooth surface has too low a coefficient of friction, the surface of the clips must also be shaped in a suitable manner in order to be able to transfer the stretching force acting at an angle of 90° to the clip surface to the plastic film.

The slight corrugation of the clip surface used according to the state of the art in a parallel but also arrow-shaped form is suitable for thin foils to introduce a lower stretching force into the foil. With thicker foils, e.g. B. between 2 mm and 5 mm thickness, much higher stretching forces would have to be transferred to the film. As a rule, the foils slip out of the clips despite the fine corrugation.

The object of the present invention is to overcome the existing disadvantages.

The object is achieved according to the invention by the features of patent claim 1, further design features of the invention are the subject of subclaims 2 to 7. According to the invention, it is thus possible for each lower, fixed clip and each upper, movable clip to be completely independent of the heating of the Foil are heated individually, preferably by at least one heating system, which allows the setting and/or regulation of any temperatures or a common temperature control with preselectable ramps and changes over time for at least one, particularly preferably all, heated clips.

A specific embodiment provides that an electric heating element, preferably a resistance heating element, is installed in each individual clip, for example with at least one associated temperature sensor and/or a suitable flexible power supply and/or a separate temperature controller in each case, which is preferably installed in a separate control cabinet .

The problem of insufficient transmission of the stretching force over the surface of the compressed clips is solved according to the invention by the features of patent claim 2. Advantageously, the lower fixed clip and/or the upper movable clip are not each a part with a firmly incorporated gripping surface, but consist of each having a clip base body and clip caps attached thereto, which are preferably easily exchangeable, whereby these clip caps could be provided with transverse grooves, saw teeth or other form-fitting surfaces which can be adapted to the thickness of the films/sheets to be stretched as well as to the corresponding thermoplastic material and/or the after heating of tenter caps and film / plate under the pressure of z. B. pneumatic cylinder deep, for example in a range of tenths to half or more of the film / plate penetrate into the thermoplastic material, whereby the intimate interlocking of tenter cap and film is created and in this way particularly high stretching forces can be transmitted.

This version allows z. B. with very fine grooves (teeth) of only 0.1 mm depth, a film of z. B. 0.2 mm thick to about 1 mm thick to take but not cut off. With significantly deeper grooves (teeth) of approx. 0.5 mm deep, a 2 mm thick film/plate can be securely gripped and many larger stretching forces can be safely transmitted. With in turn deeper teeth of approx. 0.8 mm depth, even thicker plates of approx. 2.5 mm to 4 mm thickness can be gripped securely.

A further advantageous embodiment of the invention provides that the electric heating element and/or the temperature sensor are installed directly in the tenter cap. This allows the highest possible temperatures in the grip area of the butt plate to be achieved. This variant is advantageous when the highest temperatures have to be driven. The effort is somewhat higher, since the electrical connections also have to be disconnected when changing the caliper cap.

A further advantageous embodiment is the installation of the electrical resistance heater in the clip base body, preferably flush with the contact side of the clip cap. This guarantees good heat transfer from the heated clip body to the clip cap. This makes it easier to change the clip cap for use with thinner or thicker foils or plates without having to disconnect the heating elements and temperature sensors.

• Durch diese Anordnung wird erstmals erreicht, dass bis zu höchsten Recktemperaturen von ca. 450°C alle einzelnen Kluppen bzw. Kluppengrundkörper und Kluppenkappen eine absolut gleiche und reproduzierbare Temperatur aufweisen.

Such a device constructed according to the measures of the invention has the following advantages:

• With this arrangement it is achieved for the first time that up to the highest stretching temperatures of approx. 450° C. all individual clips or clip base bodies and clip caps have an absolutely identical and reproducible temperature.

The heating of the clips is independent of the heating system for heating the foil such. B. hot air or IR radiation.

The heating of the clamps is also guaranteed if the clamps are not arranged close together in the primary clamping state when clamping the still unstretched specimen, but also if the clamps have moved far apart after the stretching process and z. B. an annealing process is followed.

Another advantage is the enormous reduction in test time, since the clips are heated up separately and very quickly to the target temperature immediately after removal of the stretched sample, so that no temperature is lost even when the film is inserted when the stretching frame is open.

Another advantage is that parallel to the temperature program for heating the film, another, e.g. B. slightly higher or lower temperature profile for the edge can be controlled.

Thicker films or plates can thus be securely gripped in the inventive manner, with gripping edges adapted to the thickness of the film, in order to transfer the high stretching forces to the material to be stretched, and the Clip caps and thus all gripping surfaces between the clips are heated to the appropriate temperature of up to 450°C in order to allow the heated gripping surfaces to be immersed in the plastic and to also heat up the plastic in the space between the clips and on the sides of the clips sufficiently for the stretching process .

• 1 Eine Draufsicht auf einen an sich bekannt aufgebauten Reckrahmen zum mono- oder biaxialen Recken von Folienabschnitten.
• 2 Eine Schnittdarstellung durch die Reckgruppe nach 1.
• 3 Eine Schnittdarstellung durch eine Spannkluppe nach 2 mit 2 Varianten der vorstehenden Erfindung.
• 4 Eine Schnittdarstellung mit in die Kluppen eingebauten Heizkörpern.
• 5 Eine Schnittdarstellung mit auswechselbaren Kluppenkappen und Beheizung der Kluppengrundkörper.
• 6 Eine Schnittdarstellung mit direkt elektrisch beheizten auswechselbaren Kluppenkappen.

The advantages and features of the invention also result from the following description of an exemplary embodiment in conjunction with the drawings and the statements. Show it:

• 1 A plan view of a stretching frame of known construction for monoaxial or biaxial stretching of film sections.
• 2 A sectional view through the horizontal bar 1 .
• 3 A sectional view through a tension clip 2 with 2 variants of the above invention.
• 4 A sectional view with radiators built into the tents.
• 5 A sectional view with interchangeable clip caps and heating of the clip body.
• 6 A sectional view with directly electrically heated interchangeable caliper caps.

In 1 a top view of a stretching frame of known construction for monoaxial or biaxial stretching of film sections is shown. The section on the bottom left shows the initial situation in which an unstretched, square film section 1 is gripped by five clips on each side and clamped at the edges. The clips 2 are each guided in guide rails 3 and 4, respectively.

The pantograph system 6 synchronizes the movement of the individual clips to ensure an even stretching process on all four sides of the film.

The side on the right and above shows the stretching frame in the extended state after stretching with the stretched film 7. The drive for the stretching process is effected by one (or two separate, synchronously running) geared motors or hydraulic cylinders, which move the right guide rail 3 to the right . Likewise, the upper rail 4 is moved upwards. In a particularly advantageous manner, the cylinders for applying the clamping force could be rotated by 90° on a vertical web of the lower, preferably fixed, clip part, arranged horizontally and fastened and thus apply the clamping force to the upper, preferably pivotable clip part, as is shown in DE10 2009 003 751 is shown.

2 shows a sectional view through the stretching group 1 . The primary film 1 is through the vertically arranged clamps 2 are clamped with a fixed support at the bottom and clamping bolts 18 movable from above in the vertical direction and a clamping cylinder 19 built above them. The clips 2 are guided in the guide rail 3 and the movement of the individual clips is synchronized by the pantograph system 6.

The foil and the clips gripping the foil are heated together by hot air 17 from above and below or e.g. B. by IR radiation.

The installation situation shows that the uniform heating of the clamped foil is already difficult in the central free area, but very difficult in the area in the clips.

The film to be clamped is pushed into a slot in the clip holder at the bottom. This completely covers the edge area from above and below.

3 shows a sectional view of the horizontal bar group 2 with the innovations according to the invention.

The right side of the figure shows that the lower support side of the clip 2 is heated directly by an electrical resistance heater 21 . A temperature sensor can be integrated into the radiator or installed separately.

A flexible connection cable leads to the electrical control and regulation system. In the same way, the clamping bolt 20 moved from top to bottom by the clamping cylinder is heated with an electrical resistance heater 22 just below the clamping surface.

It is thus possible to heat each clip part independently of the heating system for the foil heating and to control the temperature of the foil section 1 clamped between the clip halves very precisely.

The gripping side of the clips is usually not smooth, but has a surface that increases the coefficient of friction, e.g. B. with milled grooves at 90° to the pulling direction. However, these grooves must be adapted to the thickness of the film to be stretched and to the polymer, so the clip can only be used for a narrower range of thicknesses.

The left side of the shows how this problem can be solved 3 . Here an easily exchangeable clip cap 23 is placed on the lower fixed side of the clip 2 and fastened by means of a screw 27 . A resistance heater 25 with an integrated temperature sensor heats the caliper cap directly. In the same way, the clamping bolt 18, which can be engaged from above, is provided with an easily exchangeable clamp cap 24; a resistance heater 26 with an integrated temperature sensor heats the upper tenter cap directly.

With this combination, it is now possible to cover a wide temperature range between 20°C and 450°C of the clip tempering, as well as a wide range of thicknesses, also over 1.5 mm, of the clamped foils by simply exchanging the clip caps, which have different depths Handle geometries are equipped.

4 shows a section through two tension clips, like these from the DE 10 2009 003 751 are known.

The left half of the figure shows that the upper clip part 11 is articulated on an axis of rotation 12 outside the film to be stretched but approximately in the plane of the film, with the lower fixed clip part 13 carrying the joint. The cylinder for applying the clamping force 14 is attached to a vertical web of the lower fixed clip part, rotated through 90 degrees, arranged horizontally and thus applies the clamping force to the upper pivoting clip part.

It is easy to see that the clip parts and the clamped raw film with z. B. 110 mm width are better exposed to warm air or IR radiation to allow optimal heating.

However, when the film thicknesses to be stretched are greater than 1.5 mm and at high temperatures, the joint heating of film and clips by hot air or IR radiation is not sufficient to heat the clips sufficiently and sufficiently uniformly.

According to the invention, the lower, stationary clip half 13 is heated directly by an electrical resistance heating element 28 with an integrated temperature sensor that is installed just below the gripping surface. A flexible connection cable leads to the electrical control and regulation system.

Likewise, the upper pivotable clip part 11 is heated directly by an electrical resistance heater 28 .

The right side of the drawing shows a division of the pivoting upper clip portion 11 such that the front clip portion 15 is separate and height adjustable on the base lever 11 is attached in order to be able to optimally adapt the clip surface to different film thicknesses.

In this variant, too, both the lower, fixed clamp half 13 and the upper, pivotable and height-adjustable clamp part 15 are heated separately by electrical resistance heaters 28 installed just below the handle surface.

5 shows a section through two tension clips, like these from the bottom of the DE 10 2009 003 751 are known. In contrast to the installation of resistance heaters directly in the clips described in Figure 4, clip caps 29 that can be easily removed and replaced are also used here. These clip caps 29 are each placed on the lower fixed clip 13 or the upper pivotable clip part 11 and fastened by means of screws 30 .

Electrical resistance heaters 31 are built into the fixed lower clamp parts 13 or the movable upper clamp parts 11 and 15 in such a way that they lie flush on the screwed-on clamp caps 29 and thus ensure good heat transfer.

Quick couplings 32 also allow a resistance heater 31 to be removed easily in the event of a defect.

Cover plates 33 and 34 protect the cables from mechanical damage and overheating from the hot air or IR radiation.

6 shows a section through two tensioning clips like these from the bottom up DE 10 2009 003 751 are known. In this variant, tenter caps 35 are used, in which heating elements 36 with integrated temperature sensors are inserted directly. The clip caps 35 are screwed to the base bodies of the clips 13 or 11 or 15 with the screws 37 . This variant is used for the highest temperatures, since heat transfer into the film to be stretched is best and heat dissipation via the clip base can be reduced.

Claims (7)

Device for the monoaxial or biaxial stretching of film sections (1), preferably by means of a stretching frame, for films (7) made of polymers, a square or rectangular section of such a film (7) being secured on four sides by at least two clips (2; 11, 13, 15), characterized by: that both the lower fixed clip (13) and/or the upper movable clip (11, 15) can be heated, preferably independently of the heating of the film (7), by at least one heating system, preferably each. device after claim 1 , characterized in that the heating system permits the setting and/or regulation of any temperature, preferably in the range from 20 to 450°C and/or that the heating system uses a suitable control system to maintain a common temperature and/or a common temperature sensor with preselectable ramps and changes over time for the heated clips (2; 11, 13, 15). device after claim 1 or 2 , characterized in that both the lower fixed (13) and/or the upper movable clip (11, 15) each consist of a clip base body and clip caps (23, 24, 29) placed on it which are preferably easily exchangeable. device after claim 3 , characterized in that the clip caps (23, 24, 29) are provided with transverse grooves, saw teeth and/or other form-fitting surfaces which can be adapted to the thickness of the films (7)/plates to be stretched and to the corresponding thermoplastic material and / or after heating the tenter caps (23, 24, 29) and / or foil (7) / plate under the pressure of z. B. pneumatic cylinders (19) penetrate into the thermoplastic material, whereby high stretching forces can be transmitted by such a resulting interlocking of tenter cap (23, 24, 29) and film (7). Device according to one of Claims 1 until 4 , characterized in that an electrical heating element (21, 22, 25, 26, 28, 31, 36), which is preferably designed as a resistance heating element, is installed in each individual clip, with an associated temperature sensor and/or a suitable flexible current supply and / or a separate temperature controller, which is preferably installed in a separate control cabinet. device after claim 5 , characterized in that the electric heating element and/or the temperature sensor are installed directly in the tenter cap, so that the highest possible temperatures can be achieved in the grip area of the tenter cap. device after claim 5 , characterized in that the electrical heating element (31) and/or the temperature sensor is/are integrated into the clip base body (11, 13, 15), preferably installed flush with the support side of the tenter cap (29).

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