JPS5923982B2 - Method for manufacturing thermoplastic resin bands - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a thermoplastic resin band.

Conventionally, thermoplastic resin bands for packaging, for example, have been manufactured by extruding thermoplastic resin into a band shape using an extruder and stretching the band-shaped extrudate in its length direction.

However, since such a band is only uniaxially stretched in its length direction, its strength in the width direction is substantially reduced;
There is a drawback that when a force such as twisting, bending, or deflection is applied to the band, vertical cracks occur along its length.

In addition, in order to prevent this vertical cracking, there is a method of manufacturing a band in which the surface of the above-mentioned band-shaped extrudate is embossed and the molecular orientation in the length direction is mechanically disturbed, but this method also has a cracking prevention effect. In addition, the embossment creates a serrated edge on the edge of the band, which poses the risk of cutting one's hand when packing. In view of these conventional drawbacks, the present invention has completed intensive research and has completed a method for manufacturing a thermoplastic resin band that eliminates the above-mentioned drawbacks.

An embodiment of the method of the present invention will be described below with reference to the drawings.

A rod-shaped extrudate 21 is produced by extruding a molten crystalline thermoplastic resin from a mold 11 attached to the tip of the extruder 1.

At that time, the mold 11 has a plurality of discharge ports 12, 12... opened in a row, and a plurality of rod-shaped extrudates 21, 21...
Push out... Next, the rod-shaped extrudates 21, 21, . As the cooling tank 3, a water tank is normally used. Further, the extrudates 21, 21... are taken out from the cooling tank 3 and preheated with a heating device 4 such as a hot roll, steam, or an infrared heater. This preheating temperature may be in a range of not less than the softening temperature and not more than the melting temperature of the thermoplastic resin.

In addition, if the extrudates 21, 21... contain water when being rolled and stretched, they will easily slip on the rolling rolls 5, making it impossible to roll and stretch smoothly, so they must be kept in an anhydrous state when passing through the heating device 4. It is made to become. Then extrudate 2
1, 21... are guided to the rolling roll 5 and rolled into a strip shape in the width direction, and the adjacent extrudates 21, 21 are crimped and integrated, and the peripheral speed of the rolling roll 5 is set such that the peripheral speed of the rolling roll 5 is lower than the rolling roll 51.
Since the rolls are made larger in the order of rolling rolls 52<rolling rolls 53<rolling rolls 54, they are gradually stretched in the length direction. Therefore, by stretching the extrudate 2 in its length and width directions, the molecules are oriented in biaxial directions. Note that the rolling roll 5 has not only the shape shown in FIG.
As shown in the figure, several pairs of roll rolls 5 may be used, with the peripheral speeds increasing in the order of roll 51, roll 52, roll 53, and roll 54. Also, the width of the extrudate 2 is determined by rolling. Before and after stretching, there are no particular limitations, but
rolling. After stretching, it may be made to have a width several times the predetermined width, and later cut vertically to divide it into a plurality of pieces.

Note that the extrudate 2 is usually rolled when passing through the rolling rolls 5. It is preferable that the rolling rolls 5 are heated so that the stretching can be carried out quickly. Next, the extrudate 2 is introduced into an annealing device, heated to a temperature above the softening temperature and below the melting temperature, and rolled. After removing internal strain caused by stretching and passing through a cooling bath 7 to cool and solidify below the softening temperature, a take-up roll 8,
It is taken up at 8 and wound up at winder 9. In addition, rolling. Fine irregularities may be made on the surface of the extrudate 2 using an embossing roll to such an extent that the edges do not become serrated after stretching. Next, one embodiment of the present invention will be described.

Example Polypropylene was used as the crystalline thermoplastic resin.

In addition, extruder 1 (screw diameter 507 m, rotation speed 85 r.
p. m. ) is fitted with a mold 11 having five circular (diameter 5Tm) discharge ports 12, 12, . . . opened in a line as shown in FIG. ℃
The above polypropylene was extruded into five rod shapes, and the extrudates 21, 21... were once rapidly cooled and solidified in a water bath (20°C), and then preheated to 110°C with an infrared heater. Then the fourth
The extrudates 21, 21, . . . are guided between rolling rolls 5 having two pairs of upper and lower rolls as shown in the figure, and rolled to 1.2 times the width in the width direction between the first rolling rolls 51, 52. Also, the adjacent extrudates 21, 21... are crimped and integrated, and at the same time, they are stretched 1.5 times in the length direction, and further stretched 5 times in the length direction with the next rolling rolls 53, 54, and then It was heated to 110° C. with an infrared heater and rapidly solidified in a water bath (20° C.) to obtain a polypropylene band with a thickness of 1 rfm and a width of 20 fins. At this time, the rolling rolls 51, 52, 53,
54 and the circumferential speeds of the take-up rolls 8, 8 were as shown in Table 1.

The polypropylene band thus obtained hardly suffered any vertical cracking even when twisted in the longitudinal direction, and was particularly suitable for packaging heavy items.

As detailed above, in the present invention, since the resin is divided into a plurality of extrudates and extruded, the cooling is more uniform and sufficient compared to the conventional single thick plate-shaped extrudate. Almost no internal distortion occurs.

Furthermore, since the extrudate is preheated and then passed through a plurality of opposing pairs of rolling rolls whose circumferential speeds are successively increased, the extrudate is rolled and stretched at the same time while being heated. It is possible to obtain a band whose density is increased and whose strength is improved by stretching in the width direction by rolling, and which is prevented from longitudinal cracking along its length. Furthermore, since multiple rod-shaped extrudates are rolled and crimped together, the moving layer of the resin becomes large, and the molecular orientation in the width direction is uniform, so that the strength in the length and width directions is biased to one side. It is well-balanced, and is less prone to uneven strength or thickness, making it particularly suitable for packaging heavy items.

Furthermore, there is no need for embossing to mechanically disturb the molecular orientation as in the past, and there is no need to cut one's hands at the edge of the band with a sawtooth shape caused by the embossing.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the manufacturing method of the present invention, and FIG.
The figure is a front view showing the shape of the mold used in the present invention, FIG. 3 is an explanatory view showing the state from preheating to rolling in the present invention, and FIG.
The figure is an explanatory diagram showing another embodiment of the rolling roll used in the present invention. 1... Extruder, 11... Mold, 12... Discharge port,
2, 21... Extrudate, 3... Cooling tank, 4... Heating device, 5, 51, 52, 53, 54... Rolling roll,
6... Annealing device, 7... Cooling tank, 8... Take-up roll, 9... Winder, 10... Guide roll.

Claims (1)

[Claims] 1 A mold having multiple discharge ports is attached to the tip of the extruder, and the molten crystalline thermoplastic resin is extruded into rod shapes from the discharge ports, and each of the rod-shaped extrudates is guided into a cooling tank. Once rapidly cooled and solidified, preheated with a heating device,
Next, the above extrudate is heated and passed between multiple pairs of rolling rolls facing each other whose circumferential speeds are gradually increased, and the adjacent extrudates are crimped and integrated by the pressing force of the rolling rolls. A method for producing a thermoplastic resin band, which comprises rolling and stretching in biaxial directions.