JPH0517022B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a method for producing ultrathin films with improved tear strength in the direction perpendicular to the drawing direction (hereinafter referred to as the transverse direction or T direction) by melt extrusion using polyolefin resins at high speed. Prior Art When producing film using the inflation method, the overall cooling state can be achieved by finely adjusting cooling conditions such as the resin melting temperature, the air volume of the cooling air ring, and the shape and angle of the ring slit. In addition to being able to regulate the film properties, it is also possible to select the physical properties of the film depending on processing conditions such as expansion ratio and take-up speed. When manufacturing a film from a crystalline polyolefin resin by the inflation method, molecular orientation in the direction caused by the flow or deformation of the molten resin before it cools and solidifies.
On the one hand, physical properties can be improved, but due to the characteristics of the inflation method, the orientation in the take-up direction (hereinafter referred to as the longitudinal direction or M direction) is much greater than that in the horizontal direction.
Obtaining a good balance is an important issue. However, in the production of blown film, the distribution of molecules in the longitudinal direction is usually better than in the lateral direction of the tubular film, so by filling the extruded tubular film with pressurized gas and inflating it, By forming bubbles and stretching in the transverse direction, molecular orientation in the transverse direction is added to balance the molecular orientation in the longitudinal direction. That is, in order to obtain an extremely thin film with high strength in both the longitudinal and transverse directions with high productivity, it is necessary to take it off at high speed and to have a large expansion ratio. However, if a bubble with a large expansion ratio is drawn at high speed, the bubble may sway or the expansion start point or frost line may move up and down, and in severe cases, it may become impossible to form the bubble. Furthermore, if the bubble becomes unstable, uneven thickness, wrinkles, sagging, and fluctuations in fold diameter appear in the formed film. For this reason, especially in the inflation method using high-density polyethylene, a cylindrical shape having a diameter smaller than the diameter of the resin extrusion die slit 2 of the die is placed at the center of the surface of the die 1, as shown in Fig. 2 a, b, and c. The bubble stabilizer 3 is projected, the resin is extruded while blowing out air from the air ring 4, the constriction 5a of the bubble 5 is brought into contact with the stabilizer 3, and the resin is then expanded and crystallized at the frost line 5b. A method (Japanese Patent Publication No. Sho 55-2180) came to be used after the paper was collected and folded using a Nippro roll (not shown) and then rolled up. Problems with the prior art By the way, the above method stabilizes the bubbles and enables high-speed take-up, but if the expansion ratio is set high, the film becomes thinner, and the load during use after bag making becomes smaller. Depending on the situation, a phenomenon of horizontal tearing, so to speak, occurring. Normally, blown film is made into bags by heat-sealing it at right angles to the take-up direction, but the phenomenon of ring breakage occurs due to the load when objects are placed inside, so it is difficult to make bags. It becomes a fatal defect. Purpose of the Invention In view of the above circumstances, the present invention uses a polyolefin resin, preferably high-density polyethylene, to produce an ultra-thin film with high strength in both longitudinal and transverse directions at high speed by an inflation method. The purpose is to provide a method for molding. Composition of the Invention The present invention has been made to achieve the above object, and the gist thereof is that when manufacturing a film using a polyolefin resin by an inflation method, grooves are formed on the outer peripheral surface of the mandrel in the flow direction. Melt and extrude the resin from a die slit with
This is an inflation film forming method in which a bubble stabilizer is projected from the die surface, the narrow part of the bubble is brought into contact with the stabilizer, and then the bubble is taken off while being expanded. Figures 1a and 1b show an example of an apparatus for carrying out the blown film forming method according to the present invention, and the same parts as in Figures 2a, b, and c are given the same reference numerals and explanations will be given. Omitted. FIG. 1a is a partially enlarged plan view of the die 1, in which grooves 7 in the flow direction are provided at predetermined intervals on the outer peripheral surface of the mandrel 6 forming the die slit 2'. It has been found that a large number of longitudinal protrusions are formed on the inner surface of the polyolefin resin tubular body melted and extruded from the die slit 2', and that the ring breakage phenomenon does not occur even when the expansion ratio is increased.
Further, since a bubble stabilizer is protruded from the surface of the die 1, the constriction of the bubble 5 comes into close contact with the bubble stabilizer, thereby stabilizing the bubble 5 and flattening the surface of the film having an uneven surface to some extent. In this case, there is a possibility that traces of protrusions or draft patterns may remain on the film, but compared to films obtained by conventional molding methods, the film has improved tear resistance in the T direction and is free from cuts. You can get it with speed. That is, as shown in FIG. 1b, the tubular resin in the range 8, which is extruded from the die slit 2' and has a large number of protrusions formed on the inner surface by the grooves 7, is attached to the bubble stabilizer 3 at the constriction part 5a. The bubbles are brought into close contact, the bubbles are stabilized, and the ridges leave a history of vertical streaks, and although traces of the ridges and draft patterns may remain, they are flattened to some extent, and expanded at a predetermined ratio in range 9. From the frost line 5b onward, the film becomes a solidified film and is folded and wound up by Nitzprol. Note that by providing the grooves on the mandrel as described above, the appearance after film bag making is more convenient than when providing the grooves on the die. Further, it is preferable that the formed film has at least one trace or pattern of protrusions within 7 mm in the width direction. Examples, Comparative Examples Examples 1 to 4 High-density polyethylene with MI (melt index): 0.5 g/10 min, density: 0.958 g/cc, and a V with a depth of 0.5 mm and a width of 1.0 mm are placed on the outer peripheral surface of the mandrel. The mandrel has a die slit with an outer diameter of 59 mmφ (non-grooved part) and a die inner diameter of 60 mmφ, with 240 grooves in the flow direction in the shape of a cylindrical shape, and a cylindrical bubble stabilizer with an outer diameter of 55 mmφ and a height of 700 mm protrudes from the center of the surface. Expansion ratio (blow ratio): 3 and 4, withdrawal speed: 80 m/min using a 65 mmφ extruder equipped with a die.
Inflation films with a thickness of 12 μm were prepared at a speed of 100 m/min and used as samples, and the Elmendorf tear strength and impact strength of each sample were measured. Comparative Examples 1 to 4 Inflation films were prepared using the same equipment and conditions as in Examples, except that the die slit was a normal smooth annular die slit with no grooves on the outer surface of the mandrel, and the Elmendorf tear strength of each sample was determined. , the impact strength was measured. Table 1 shows the measurement results of Examples and Comparative Examples.

[Table] As is clear from the table, the blown film produced by the method of the present invention has a higher tear strength in the T direction than the blown film produced by the conventional method. Extremely high impact strength. Effects of the Invention As described above, in the method for forming a blown film according to the present invention, the constriction of a bubble in which a large number of protrusions are formed is brought into close contact with the bubble stabilizer, and the protrusions are smoothed out. Since the bubbles remain and are stabilized, it is a method that enables high-speed molding of an inflation film with high tear strength in the T direction and high impact strength.

[Brief explanation of the drawing]

Figures 1a and 1b are schematic explanatory views of the inflation film forming method according to the present invention; Figure 1a is a partially enlarged plan view of the die (corresponding to Figure 2b);
Figure b is a side view showing the state in which a blown film is made using the die of Figure 1 a, and Figures 2 a, b, and c are schematic illustrations of the conventional method;
Figure 2a is a side view, Figure 2b is a partially sectional plan view taken along the - line in Figure 2a, and Figure 2c is a -'-- in Figure 2a.
FIG. 1...Dice, 2'...Dice slit, 3...
Bubble stabilizer (stable body), 5...Bubble, 5a...
...Neck part, 5b...Frost line, 6...
Mandrel, 7...concave groove.

Claims (1)

[Claims] 1. When manufacturing a film using a polyolefin resin by the inflation method, the resin is melted and extruded through a die slit having grooves in the flow direction on the outer circumferential surface of the mandrel, a bubble stabilizer is protruded from the die surface, and the stabilizer is An inflation film forming method characterized by bringing the constrictions of bubbles into contact and then taking them off while expanding.