Patent GB-977507-A (GB)
IPC: B29C55/14
Abstract: 977,507. Film stretching machines. LINDAUER DORNIER G.m.b.H. March 11, 1963 [March 17, 1962; May 25, 1962], No. 9496/63. Heading B5B. In a machine for stretching webs of films consisting of synthetic organic thermoplastic material in a continuous manner, stretching in the longitudinal and in the transverse directions taking place in successive working steps, the stretching operation for each of the two directions is subdivided into at least two lesser stretching stages and the stretching stages for one direction and stretching stages for the other direction alternate. In the embodiment of the invention shown in Figs.1 and 2, a web of unstretched film F is supplied from a feed roll E to a longitudinal stretching zone L1 which is followed successively by a first transverse stretching zone Q1, a second longitudinal stretching zone L2 and a second transverse stretching stage Q2. The longitudinal stretching zones are of known construction and each comprise two groups of parallel rollers W1, W1<SP>1</SP> and W2, W2<SP>1</SP> respectively over and in contact with which the film is caused to travel in a sinuous path. The upper groups of rollers can be raised out of their operative positions to facilitate the introduction of the film into the machine before the commencement of the stretching operation. The peripheral speeds of the rollers increase progressively from roller to roller in both stretching zones in the usual manner. The first and second transverse stretching zones Q1 and Q2 are provided with pairs of driven endless chains K1 and K2 which diverge in the direction of travel of the belt and which are provided in the usual manner with clamps or other devices for gripping the edges of the web of film during its travel between each pair of chains. The second transverse stretching zone Q2 is followed by a heat setting zone Th in which the pair of chains K2 are parallel to one another. The heat setting zone may be followed by a cooling zone. The stretched film is collected on the wind-up roll A. As shown in Fig. 2, the film is heated during its passage through the stretching zones by directing streams of hot air on to its lower and upper surfaces from the nozzles of the pair of blow boxes H1 and H1<SP>1</SP>. During its passage through the heat setting zone Th, the film is heated by means of the separate pair of blow boxes H2 and H2<SP>1</SP>, since the temperature at which the film is heat set differs from that at which it is stretched. The whole of the machine is enclosed in a thermally insulated casing (shown by dot-dash lines) to minimize heat losses. In the second embodiment of the invention shown in Fig. 3, a web of film to be stretched F is supplied from a feed roll E to a vertical longitudinal stretching zone L1 comprising two roller groups W1 and W1<SP>1</SP> over the rollers of which the film travels in a sinuous path in a generally downward direction. The zone L1 is followed successively, as in the previous embodiment, by a first transverse stretching zone Q1, a second longitudinal stretching zone L2, a second transverse stretching zone Q2, a heat setting zone Th and a wind-up roll A. The general construction of these zones is substantially the same as those of the previous embodiment, except that the longitudinal stretching zones are both vertical, the film being drawn downwards through these zones and then first horizontally and then vertically upwards over guide rollers to the horizontal transverse stretching zones. Furthermore, endless conveyer belts T1 and T2 are provided between the longitudinal and transverse stretching zones to convey the film from the longitudinal to the transverse stretching zones when the film is first fed through the machine prior to the stretching operation. As shown in Fig. 4, which is an enlarged side elevation of the first longitudinal stretching zone and conveyer belt zone of the embodiment shown in Fig. 3, the roller group W1<SP>1</SP> and the nip rollers W3 and W3<SP>1</SP> are displaceable from the operative position to the positions shown by dotted lines in order to enable the film F to fall freely between the roller groups W1 and W1<SP>1</SP> through the longitudinal stretching zone on to the upper run of the conveyer belt T1 during the initial introduction of the film into and through the machine prior to the stretching operation. The film is conveyed by the belt T1 first horizontally and then almost vertically to the transverse stretching zone. The path of the film during this threading up stage is indicated by a dash-dot line. Adhesion of the film to the conveyer belt is assisted by directing streams of heated air on to the film from the blow boxes S1 and S2. The film is caused to travel from the conveyer belt T1 to the pair of gripper equipped chains K1 in the stretching zone Q1 between the guides R1 and R2 and over the guide roller U and the rollers W3 and W3<SP>1</SP> and the roller group W1<SP>1</SP> are then moved into their operative positions. The film now travels from the pair of nip rollers W3<SP>1</SP> over guide rollers V and U to the zone Q1 along the path indicated by the full line above the upper run of the conveyer belt T1. Operating platforms B1 and B2 are provided above the horizontal portions of the housings of the conveyer belts and control apparatus for the longitudinal and transverse stretching zones may be mounted on opposite sides of the platforms, e.g. at B11  and B12. The machine is enclosed in a thermally insulated housing and access to the machine is given by means of hoods such as is shown at P in Fig. 4 and in dotted lines in Fig. 3. The micro-structure or orientation of films stretched in machines according to the invention is identical with that of films which have been stretched in both directions simultaneously and superior to that of films which have been stretched first longitudinally and then transversely in each case in only one stage.