SE444660B - PROCEDURE AND DEVICE FOR TREATMENT OF PACKAGING MOVIES - Google Patents

Description

. â som f ai »i 5191- .r (ß, 20 30 35 40 rsfnsss-o _ 2 åarean. The force required for this cold stretching of the stretch film to a permanent elongation is initially proportional to the yield strength of the stretch film material and then increases gradually according to the degree of strain.

If most of the force used in the pre-stretching moment is retained during the winding of such a pre-stretched stretch film, a force is obtained per the new cross-sectional area which holds the goods units with considerably higher film tension than if the stretch film had not been pre-stretched. This has been used for several years in stretch film packaging technology either to reduce material consumption or to improve. Consolidation of freight units without increased material consumption.

The method and apparatus described above for stretching stretch film with controlled width reduction is based on the thermoplastic stretch film being forced to stretch in the cold state between the very short distance from the last tangent point of the film on a roll to the first tangent point on adjacent roll driven with a significant greater peripheral speed than the former. Because the film is partly self-adhesive or has high friction due to high gloss and encloses said rollers with usually more than half its circumference, the acceleration and pre-tension are concentrated to the part of the film which spans freely between the tangent points.

Pre-stretching according to this generally known technique; however, bone is an enormous strain on the stretch films and far from all materials can withstand this jerky load without coming off. The slightest breakage in the form of edge damage or any undigested particle in the stretch film knocks out even the most advanced materials, which have been specially developed to be able to be stretched. The pre-stretching units available on the market so far have therefore not been able to be used with respect to a maximum pre-stretching capacity of around 300%, but rather around 150% in practical use.

RECOVERY OF THE INVENTION The method is based on the prior art which appears from the preamble of the appended claim 1 and is thereby characterized in that the stretch film is brought to width-controlled pre-stretching in a separate pre-stretching assembly in a first step moderately pre-stretching with oo and con. 00 OGI 00 I c O 0 c 0 c 0 0 8501555-0 consideration of the cold stretching moment, and immediately, after an extremely short resting moment, is then intensively pre-stretched in a second step by utilizing the heat generated from the first step in the film.

The force conversion to heat takes place momentarily during the stretching moment, but only after so much force has been applied that the film material yield strength has been exceeded and the molecules flow cold through the elongation process to permanent deformation. The extremely fast first tensile moment in the cold state therefore constitutes the greatest threat to the film, but can by the method according to this invention be kept at a moderate level before the subsequent in the tensile tensile moment in step two, which on the contrary can be allowed to give the stretch film by the wax production. a final degree of pre-stretch far above all previously known theoretical and practical levels. Due to elevated temperature in the film, immediately before the intense pre-stretching step in step two, the film gains both greater elasticity and significantly reduced yield strength, making the film smoother and more insensitive to the sudden and much more intense elongation at the second time.

Another significant factor which further characterizes the method according to this invention is to divide the pre-stretching moment into two separate steps, whereby the time required for the total degree of pre-stretching and the required free span between the tangent points is more than doubled without increasing the width reduction. The acceleration moments in the two individual pre-stretching steps can thereby be kept significantly lower, and not even added up achieve the acceleration that can be calculated at conventional pre-stretching in one step.

The device according to the invention is based on a device of the type which appears from the preamble of the appended device requirement, and is characterized mainly in that the rolling system for the two pre-tensioning elements consists of non-driven rollers, of which always one of the two outer rollers, with selectable mechanical gear ratio, transmits a specific constant rotational movement to the second outer roller, and that between and next to these two outer rollers a completely free-rolling third roller is placed so that the stretch film has the greatest possible envelopment And contact with all three rollers in the system, while the distances between the adjacent the tangent points of the roller / film are so short that the largest possible width reduction control can v! QIO QIO I !! 000 IQ al! Il I 0 I 0 I 0 l I n n n. _ 10 15 20 30 35 10 achieved.

A further characteristic of the device according to this invention is that the two outer rollers always rotate in the same direction through the mechanical rotation transmission, and that the driving force of the stretch film web shoes from separate motor driven roller immediately after the rolling system moves the two load stackers, so arranged with web tension regulating spring roller control steplessly selectable speed on the drive roller, that during winding on load, the pre-stretched film is discharged from the pre-stretching device evenly and continuously while maintaining the selected film tension against the load during the entire winding operation. The pre-tensioning rollers included in the roller system which rotate in the same direction, by the mechanical motion transmission, can advantageously be given different diameters, so that a larger number of alternative gear ratios with respect to the mutual peripheral speed of the rollers can be obtained with a few gears and a common toothed belt. but does not constitute a precondition for carrying out the method or the design of the device according to this invention.

The invention is defined in the appended claims.

The invention will be described in the following in connection with non-limiting examples of a method in the pre-stretching device, in connection with the accompanying drawing.

DRAWING Figure 1 schematically shows a vertical view of a pre-stretching device according to the invention, including the required supply roll with stretch film and turntable with load for winding. Figure 2A / B shows in a diagram the speed increase of the stretch film measured over time, and compares the method and the device according to this invention (A), with conventional pre-stretching (B) to the same final degree of pre-stretching. Figure 3A / B shows the actual change in length of the stretch film as a result of the stepwise increase in the peripheral speed across the rollers. A and B in Figure 3 refer to the same comparison as in Figure 2 and both figures are further described in connection with the following exemplary embodiments.

ICQ Û. Ü Ü I I ooo on 'Ü Û Û Il Ile: It 100 III OI 0 Û' Û n vara c o o o own to: Ino '... f _'. 9 0 O once 0: 0: 0000 nous '4' pre-stretching rollers 1 and 2 freely tension the film for a very short EXTENSION EXAMPLE ..

Figure 1 shows a rolling system through which a stretch film web runs from the supply roll 0, to the load 4 arranged on the turntable.

The roller system consists of the pre-stretching rollers 1 and 3, as well as the intermediate free-rolling roller Z1. For proper abutment around roller 1, the film web of roller 9 is forced to increased envelope. The rollers 1 and 3 always roll in the same direction by means of the gear 5 and the toothed belt 6. The film web is driven by roller 7 and receives a starting impulse from a spring-loaded web tension roller 8.

The track is pre-stretched in several steps starting immediately after unrolling 10 from the supply roll, which is frictionally braked 14. Between distances 11, and also between pre-stretching rollers 2 and 3 in the distance 12 between the tangent points of the film. In the considerably longer distance 13 from the device up to the load, the pre-stretch É is determined by the speed at which the load rotates on the turntable 15. The method according to the invention is shown in the exemplary embodiment in Figures M 2A and 3A, and can be compared with the conventional method according to Figures 2B and 3B.

Figure 2A diagrammatically describes the acceleration of the stretch film (change of speed / unit of time) at continuous pre-stretching to a total of 300%. The% spool is mechanically braked to a peripheral speed of V0 (in the example 20 m / min) while the turntable with the load gives a winding speed of V4 (80 m / min). In the rolling system of the device according to this invention, the speed of the drive roller is set according to the desired winding force, whereupon the speed V3 becomes constant.

The large resilience property of the stretch film means that the winding force g usually becomes too large if the speed V4 is equal to or greater than V3. The most common is because V4 is slightly lower than V3 (in this example 7% lower at V3 = 86 m / min).

Through gear gears and toothed belts, the two pre-tensioning rollers are in a fixed selected speed ratio to each other, which together with the respective diameters gives a constant peripheral speed co nu: nu: Ica 0 n 0 n 0 nu 0 lin II: 000 ... v 5. - 3 4. » . * wav 10 15 20 v »- w .gšfrflglv 25 30 35 40 8501555-0 V1 on the first pre-stretching roller (in the example selected to approx. 28 m / min).

The velocity V2 over the free-rolling roller in the roller system arises from the enclosing of the stretch film and is dependent on the elongation which takes place in the film between V3 and V2. The free-rolling roller means that the elongation force for the acceleration of the film between V1 and V2 is equal to that between V2 and V3, which together with the residence time of the film over this roller without acceleration and the heat released from the first elongation step to the film, is crucial for the process. according to this invention.

The speed V2 of the free-rolling roller is therefore difficult to predict as it depends primarily on the speed range chosen for V3 and V1 by setting the speed of the drive roller, and secondly depending on the stretching characteristics of the particular roller. Under constant test conditions, the velocity V2 can therefore also be a measure of the tensile property of the stretch film.

In this exemplary embodiment, the speed V2 = 49 m / min has been selected, which constitutes a 75% speed increase from -V1 = 28 and at the same time requires a further 75% speed increase to reach V3 = 86 m / min. ~ These two percentage equal strain steps are found in practical applications of certain stretch film materials and is therefore fully relevant in this embodiment. # 31 Figure 2A thus outlines the curve of the process of this invention, where the stretch film accelerates slowly between the supply roll and the rolling system but then accelerates very rapidly in the first step, to then flatten out at a constant speed of 49 m / min for a short time. then the film runs over the free-rolling roller, and then while the film is still hot from the first step again accelerates very quickly in a second elongation moment before it is wound on the load with slight deceleration. The various moments along the time axis in the diagram approximately correspond to the advance of the stretch film through the rolling systems drawn immediately below the diagram.

Figure ÉB describes the corresponding process for a stretch film in a conventional process where the critical acceleration moment is performed in a single large step, from cold film under an extreme II Ino III Ota II; O! 000 II u n n 0 o I I I 0 0 I I I: III I o I 0 o I 0 I un. ... ... _ - - - O O C 1O pip '15 20 30 35 40 _the film is forced on in the hot state.

I 'of a single large elongation of stress in cold film over a very short distance 8501555-0 short moments without any rest phase in the meantime.

In Figure 3A, the percentage length increase has been marked step by step with diagonally dashed and dotted fields. From V1 to V2, in this exemplary embodiment, a percentage length increase of 75% takes place and an additional 75% is added in step V2 to V3; However, the relative increase in length of the film is clearly much larger in the later step marked here, as it also constitutes the length change that Att heat really develops and the film benefits from the greater elongation moment in the second step is proved by the speed of V2 'average of V1 and V3. In addition, there is the rest moment ¿where the elongation force achieved from the first cold step has time to relax to a slightly lower force before the next moment. Because it quickly adjusts to a level clearly lower than the mathematical; the free-rolling roller distributes the elongation forces equally in the two acceleration ranges immediately after the starting moment, the film has time to stretch considerably more in step two than in step one, before the elongation force is up to the same level again as it reached in the first step, thereby explaining the different relative length increases that occur automatically.

Figure 3B shows that with conventional pre-stretching technology it is possible to reach the same high degree of pre-stretching (300%), but this at the expense and for a very short period of time. This limits the practical applicability of the method and excludes many types of stretch film and prevents the possibility of achieving the optimum packaging economy. With the method according to this invention, new possibilities are achieved with the majority of on. g market types of stretch film further increase the degree of pre-stretching and reduce the material consumption without sacrificing the cohesive force. cs oc: non Ola non al oc. Ia - 0 0 I o i | 0 0 0 0 I _ I I IIIOI _ I I I I I n n n l

Claims (2)

1. ... v 10 'Év /: ff 15 20 30 35 8501555-0 PATENTA CLAIMS k 1) Procedure for continuous pre-stretching of packaging film, so-called stretch film (10), which is unrolled from braked supply roll, and after width-controlled pre-stretching between closely spaced fi stretches. rollers are wound with a certain force around a load (4) set up on a turntable (15) for complete cohesion of the load with the greatest possible force to the lowest possible stretch film consumption, characterized in that the main stretch of the stretch film, by acceleration in mechanical rolling system, is carried out in two rapidly successive but clearly defined elongation steps (11, 12) within which elongation ranges the stretch film is subjected to the same elongation force in the first step (11) as in the second step (12) and that the elongation force between them is momentarily lowered so much that the elongation in the film is briefly interrupted, but not for longer periods of time than that, by force conversion from the first stage, it generates the heat in the film, facilitates the elongation in the second step (12) and always allows an actual increase in length in the film substantially in excess of the length increase achieved in the first elongation step (11) by the corresponding elongation force. 2.) Device for continuous stretching of packaging film, so-called stretch film (10), which is unrolled from a braked supply roll, and after width-controlled pre-stretching between tightly placed pre-stretching rollers is wound with a certain force around a load (4) arranged on a turntable (15) ) of goods units for total cohesion of the load ', with the greatest possible force to the lowest possible stretch film consumption, felt c'k nadav ¿a rolling system consisting of two gear gears (5) fitted with gears (5) and 1 belt (6) connected. , 3) for uniform rotational movement and selectable gear ratio between the rollers | speed, and an undrived and free-rolling É¿ roller (2) placed between these rollers, which, by enclosing the stretch film during passage through; the rolling system rotates in the opposite direction to the pre-stretching rollers, and completely self-leveling, with respect to the elongation force in the pre-stretching areas before (11) and after (12) the roll, assumes a peripheral velocity which is always lower than the mathematical mean peripheral velocities of the two the pre-stretching rollers (1, 3), the length increase of the film in step two (12) always being greater than the length increase in step one (11). 3501555-0 3) Device according to claim 2, characterized in that the drive roller (7) lies outside and after the roller system (1, 2, 3), for feeding the film. 4) Device according to claim 2, characterized in that either of the two pre-tensioning rollers connected to gear (5) and gear belt (6) is motor-driven for the propulsion of the film through the rolling system. 5) Device according to claim 2, characterized in that both the pre-stretching rollers (1, 3) included in the rolling system and the free-rolling roll (2) can have generally equal or different diameters, however, the free-rolling roll (2) can advantageously have a relative large diameter for increased film enclosure and thereby longer residence time and rest phase between the two elongation stages (11, 12). J! bl! : OI bl! OQO nl Ilo IQ _? .f