DE102010038076A1 - Device for mono- or biaxial stretching of film sections (stretching frame) - Google Patents

Abstract

Device for mono- or biaxial stretching of film sections, preferably by means of a stretching frame, for films substantially of polymers, wherein a square or rectangular cutout of such a film is taken on four sides by at least two clips, is in view of an improved process, such designed and developed that both the lower fixed clip and / or the upper movable clip are preferably independent of the heating of the film, by at least one heating system, preferably in each case, are heated.

Description

The invention relates to a device for mono- or biaxial stretching of film sections, which consist essentially of polymers, wherein a square or rectangular section of such a film is taken on 4 sides by at least two clips, with a solid lower clip part forms the support and a from above, perpendicular to the film plane, lowered upper clasp part clamps the film at the peripheral edge.

Advantageously, the lowering of the upper clasp part and the structure of the clamping force by z. B. pneumatic or hydraulic cylinders are effected.

In a further advantageous manner, after heating the clamped film by, for. B. hot air or IR rays, the 4 groups of clips apart on all 4 sides apart 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 clips are synchronized in their movement by a pantograph system (a system of crosswise arranged parallel strips which are hinged together) to ensure a uniform stretching process on all sides (schematic diagram see page 1, 1 ).

Implemented devices of this type, use z. For example, for clamping a square film pattern in sizes of 100 × 100 mm on each of the 4 sides of each 5 clips with the widths of 10 to 12 mm (see 1 )

The arrangement of the clamping cylinder is according to the prior art vertically from top to bottom for movement of the upper clamp in the direction of the lower, fixed flap.

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

The limited width of the clip also limits the size of the incorporated pneumatic or hydraulic cylinder for applying the clamping force. For high temperature applications in particular, the use of air or N _{2 is} required for actuating the cylinders, whereby the specific pressures are limited. The use of hydraulics is not recommended due to the risk of fire.

This means that with larger film thicknesses and resulting higher stretching forces applied by the pneumatic clamping cylinder clamping force is insufficient and the slides can slip out of the clip.

According to another patent application DE 10 2009 003 751 the applicant, the content of which is hereby incorporated into the content of the present application, the upper clasp part is articulated to a lying outside the film to be stretched axis such that the lower, fixed clip part carries the joint, while the upper clip part pivoting upward is performed and that at least one cylinder for applying the clamping force to a vertical web of the lower, fixed clip portion rotated by 90 °, is arranged horizontally and fixed and so applies the clamping force on the upper, pivotable clip part.

Further, a plurality of horizontally juxtaposed clamping cylinder are arranged axially offset on the respective clip, whereby the clamping cylinder can be made substantially larger in diameter and much larger pressure forces can be constructed (at the same maximum pneumatic pressure).

The device according to the prior art still has the following disadvantages:
In order to introduce the necessary stretching temperature in the film as well as in the clips themselves, according to the prior art, the heating medium air or IR radiation is used both for heating the film as well as the clips.

This is a well-functioning method for films of about 0.1 mm to about 1.5 mm thickness.

For larger films or plate thicknesses of z. B. 2 mm to 5 mm or even stronger, it is increasingly difficult to heat with the film / plate and the clips on stretching temperature. However, if the clips are not heated enough, the plastic areas between the upper and lower clips will not or too slowly heat up. Likewise, the narrow surfaces of the film are heated only too slowly laterally between the individual pairs of clips.

The result of this slow heating is a very prolonged heating process until a uniform stretching temperature in the free film surfaces and within the clips is achieved. This long heating time makes the whole stretching process uneconomical and also leads to possible adverse changes in the structure of the stretched film / plate.

It is known that, before clamping the film into the stretching frame, at first only the clips are heated with the heating medium hot air or IR radiation. Thereafter, the heating system is driven off, or the stretching frame moved out of the hot air oven. The films are inserted, the clips closed, the heating system closes again, or the stretching frame is retracted again in the hot air oven and now heats both the film and the clips. Also in this method, the initially reached temperature drops rapidly in the clips and can not be achieved by prolonged reheating, together with the film.

This effect becomes more and more pronounced as the thickness of the film / plate increases and makes easy stretching at thicknesses above 2 mm and temperatures above approximately 150 (200) ° C very difficult and very time-consuming.

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

Since a smooth surface has too low coefficients 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 engaging the plastic film at an angle of 90 ° to the clamping surface.

The light corrugation of the clip surface in parallel but also arrow-shaped form used in the prior art is suitable for thin films to introduce a lower stretching force into the film. For thicker films, eg. B. between 2 mm and 5 mm thickness, much higher stretching forces would have to be transferred to the film. As a rule, the films slip out of the clips despite the fine ribbing.

Object of the above invention is to overcome the existing disadvantages.

The object is achieved by the features of claim 1. According to the invention, it is thus possible that each lower, fixed clip as well as each upper, movable clip are heated independently of the heating of the film individually, preferably by at least one heating system, which controls the setting and / or regulation of any temperature or a common temperature control with pre-selectable ramps and temporal changes allowed for at least one, most preferably all heated clips.

A concrete embodiment provides that in each individual clip an electric heater, preferably a resistance heater is installed, for example with at least one associated temperature sensor and / or a suitable flexible power and / or a separate temperature controller, which is preferably installed in a separate cabinet ,

The problem of insufficient transfer of the stretching force over the surface of the compressed clips is inventively achieved by the features of claim 2. Advantageously, the lower fixed and / or the upper movable clip are not each a part with a firmly machined grip surface, but consist of in each case a staple body and preferably easily replaceable, attached Kluppenkappen, said clap caps could be provided with transverse grooves, saw teeth or other positive surfaces that can be adapted to the thickness of the stretched films / plates as well as the corresponding thermoplastic material and / or after heating of Klappenkappen and foil / plate under the pressure of z. B. pneumatic cylinder deep, penetrate, for example, in a range of tenths to half or more of the film / plate in the thermoplastic material, whereby the intimate toothing of clip cap and film is created and can transmit particularly high stretching forces in this way.

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

A further advantageous embodiment of the invention provides that the electric heater and / or the temperature sensor are installed directly in the clip cap. This can be the highest possible temperatures in the grip area of the clip cap can be achieved. This variant is advantageous when the highest temperatures have to be driven. The effort is slightly higher because when changing the dome cap and the electrical connections must be disconnected.

A further advantageous embodiment is the installation of the electrical resistance heating in the Kluppengrundkörper, preferably flush with the support side of the clip cap. This guarantees good heat transfer from the heated one Kluppengrundkörper on the Kluppenkappe. This makes it easier to replace the clip cap for use with thinner or thicker films or plates, without the radiator and temperature sensor must be disconnected.

Such a device constructed according to the measures of the invention has the following advantages:
By this arrangement is achieved for the first time that up to the highest stretching temperatures of about 450 ° C all individual clips or Kluppengrundkörper and Klappenkappen have an absolutely same and reproducible temperature.

The heating of the clips is, regardless of the heating system for heating the film such. As hot air or IR radiation.

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

Another advantage is the enormous shortening of the trial period, since the clips are heated again immediately after removal of the stretched pattern separately and very quickly to the target temperature, so that even when inserting the film in the open state of the stretching frame no temperature is lost.

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

It can be safely gripped in accordance with the invention thus thicker sheets or plates, with adapted to the thickness of the film handle cutting to transfer the high stretching forces on the material to be stretched, and it can in a much shorter time and with much higher security and uniformity the Klappenkappen and thus all gripping surfaces between the clips are heated to the appropriate temperature of up to 450 ° C to allow immersion of the heated gripping surfaces in the plastic and the plastic in the space between the clips and the side of the clips also warm enough for the stretching process ,

The advantages and features of the invention will become apparent from the following description of an embodiment in conjunction with the drawings and the statements. Show it:

1 A plan view of a known per se stretching frame for mono- or biaxial stretching of film sections.

2 A sectional view through the stretching group after 1

3 A sectional view through a clamp after 2 with 2 variants of the above invention.

4 A sectional view with incorporated in the clips radiators.

5 A sectional view with interchangeable Kluppenkappen and heating the Kluppengrundkörper.

6 A sectional view with directly electrically heated exchangeable clip caps.

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

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

The side right and above shows the stretch frame in apart condition after stretching with the stretched film 7 , The drive for the stretching operation is effected by one (or two separate, synchronously running) geared motors or hydraulic cylinders, which the right guide rail 3 move to the right. Likewise, the upper rail 4 move upwards. In a particularly advantageous manner, the cylinders for applying the clamping force on a vertical web of the lower, preferably fixed clip part could be rotated by 90 °, arranged horizontally and fastened and so apply the clamping force on the upper, preferably pivotable clip part, as shown in the DE 10 2009 003 751 is shown.

2 shows a sectional view through the stretching group after 1 , The primary foil 1 is through the vertically arranged clips 2 with bottom fixed support and from above in the vertical direction movable clamping bolt 18 and above it built-up clamping cylinder 19 clamped. The clips 2 be in the guide rail 3 guided and the movement of the individual clips through the pantograph system 6 synchronized.

The heating of the film and the film engaging clips together by hot air 17 from above and below or z. B. by IR radiation.

The installation situation shows that uniform heating of the clamped film is difficult even in the mid-free area, but very difficult in the area in the clips.

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

3 shows a sectional view of the stretching group after 2 with the innovations of the invention.

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

A flexible connecting cable leads to the electrical control and regulation system. In the same way the moving through the clamping cylinder from top to bottom clamping bolt 20 with an electrical resistance heater 22 heated close to the clamping surface.

This makes it possible independently of the heating system for heating the film each clip part to heat and the clamped between the clip halves film section 1 to temper very precisely.

The handle side of the clips is usually not smooth, but provided with a friction-increasing surface, for. B. with grooves milled in 90 ° to the pulling direction. However, these grooves must be adapted to the thickness of the stretched film, as well as to the polymer, so the clip can only be used for a narrower thickness range.

How to fix this problem is shown on the left side of the page 3 , Here's on the lower solid side of the tackle 2 an easily replaceable dome cap 23 put on and by means of a screw 27 attached. A resistance radiator 25 with integrated temperature sensor heats the clip cap directly. In the same way is the adjustable from above clamping bolt 18 with an easily replaceable clip cap 24 Mistake; a resistance heater 26 with integrated temperature sensor heats the upper clip cap directly.

With this combination, it is now possible to cover a wide temperature range between 20 ° C and 450 ° C Kluppentemperierung, as well as a wide thickness range, even over 1.5 mm, cover the clamped films by simply replacing the Klappenkappen, which with different depths Gripping geometries are equipped.

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

The left half of the picture shows that the upper clasp part 11 in this case on a lying outside of the stretched film but approximately in the plane of the film axis of rotation 12 articulated, the lower fixed clip part 13 the joint carries. The cylinder for applying the clamping force 14 is attached to a vertical web of the lower fixed clip part, rotated by 90 degrees, arranged horizontally and thus brings the clamping force on the upper pivotable clip part.

It is easy to see that the clip parts and the clamped raw foil with z. B. 110 mm width of the hot air or the IR radiation are exposed to allow optimum heating.

For larger film thicknesses to be stretched above 1.5 mm and at high temperatures, however, the joint heating of film and clips by hot air or IR radiation is insufficient to heat the clips sufficiently high and sufficiently uniformly.

According to the invention, the lower, stationary clip half 13 with a built-in electric under the grip surface electric resistance heater 28 directly heated with integrated temperature sensor. A flexible connection cable leads to the electrical control and regulation system.

Likewise, the upper pivoting clip part becomes 11 through an electrical resistance heater 28 heated directly.

The right side of the drawing shows a division of the pivoting upper clasp part 11 , such that the front clip part 15 separated and height adjustable on the base lever 11 is attached to the pad surface optimally adapted to different film thicknesses.

Also in this variant, both the lower solid half-shell 13 as well as the upper swiveling and height-adjustable clip part 15 by built under the handle surface electrical resistance heater 28 heated separately.

5 shows a section through two clamping clips, as this basically from the DE 10 2009 003 751 are known. In contrast to the installation of resistance heaters directly into the clips as described in Figure 4, here also removable and replaceable clip caps are easily removable 29 used. These club caps 29 are each on the lower fixed clip 13 or the upper pivotable clip part 11 put on and by means of screws 30 attached.

In the fixed lower parts of the tether 13 or the movable upper clip parts 11 respectively. 15 are each electrical Widerstandsheizköper 31 Installed so that the flush on the screwed Klappenkappen 29 rest and thus a good heat transfer is ensured.

Quick couplings 32 also allow easy removal of a resistance heater 31 in case of a defect.

flashings 33 respectively. 34 protect the cables from mechanical damage and overheating due to hot air or IR radiation.

6 shows a section through two clamps like this basically from the DE 10 2009 003 751 are known. In this variant, Klappenkappen 35 used in which radiator 36 with integrated temperature sensor are used directly. The Klappenkappen 35 be with the screws 37 to the main body of the clips 13 respectively. 11 respectively. 15 screwed. This variant is used for highest temperatures, as the heat transfer in the stretched films is best and heat dissipation can be reduced via the Kluppengrundkörper.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102009003751 [0011, 0044, 0056, 0064, 0068]

Claims (7)

Apparatus for mono- or biaxial stretching of film sections, preferably by means of a stretching frame, for films substantially of polymers, wherein a square or rectangular cutout of such a film is taken on four sides by at least two clips, characterized in that: that both the lower fixed clip and / or the upper movable clip can preferably be heated independently of the heating of the film by at least one heating system, preferably in each case. Apparatus according to claim 1, characterized in that the heating system, the adjustment and / or regulation of any temperatures preferably in the range of 20 to 450 ° C allowed and / or that the heating system via a suitable control system compliance with a common temperature and / or a common Temperature sensing with pre-selectable ramps and temporal changes allowed for the heated clips. Device according to claim 1 or 2, characterized in that: that both the lower fixed and / or the upper movable clip each consist of a staple body and thereon preferably easily interchangeable, patch Klappenkappen. Device according to claim 3, characterized in that: in that the clip caps are provided with transverse grooves, saw teeth and / or other form-fitting surfaces which are adaptable to the thickness of the films / plates to be stretched as well as to the corresponding thermoplastic material and / or after the heating of the clip caps and / or foil / plate under the pressure of z. B. pneumatic cylinder penetrate into the thermoplastic material, whereby such a toothing of clip cap and foil high stretching forces are transferable. Device according to one of claims 1 to 4, characterized that in each individual screw an electric heater, which is preferably designed resistance heater is installed with associated temperature sensor, and / or a suitable flexible power supply and / or in each case a separate temperature controller is provided, which is preferably installed in a separate cabinet. Device according to claim 5, characterized in that: that the electric heater and / or the temperature sensor are installed directly in the clip cap, so that the highest possible temperatures can be achieved in the grip area of the clip cap. Device according to claim 5, characterized in that: that the electrical heating element and / or the temperature sensor in the clip base body, preferably flush with the bearing side of the clip cap is installed.

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