JPH0543502B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a method for producing a paper-like film particularly suitable for producing square bottom bags by an inflation method. Prior Art Square bottom bags are generally made from paper and are widely used in various fields, but recently, as inflation film is inexpensive and can be mass-produced, attempts have been made to manufacture square bottom bags using synthetic resin film. It is being There are various methods for producing film by inflation, but as shown in Fig. 2 a, b, and c, there is a method in which the die 1 has a diameter smaller than the diameter of the resin extrusion die slit 2 in the center of the surface of the die. A cylindrical valve stabilizer 3 is protruded, and 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 then expanded and crystallized at the frost line 5b.
A method was developed (Japanese Patent Publication No. 1983-2180) that took it up, folded it, and then rolled it up using a Nitsub roll (not shown), making it possible to produce films with good productivity and a well-balanced stretching ratio in the longitudinal and transverse directions. Summer. Problems with the conventional technology However, films made from polyolefin resins, which are generally used in the inflation method, have less stiffness than paper, so they are difficult to hold onto gripping tools during the bag-making process. It lacks folding suitability, returns to its original shape even after folding, and has high elongation and tear strength, making it difficult to cut.
Furthermore, it was slippery and unsuitable for use in the production of square-bottomed bags instead of paper. Purpose of the Invention In view of the above circumstances, an object of the present invention is to provide a method for manufacturing a paper-like film suitable for manufacturing square bottom bags. Structure of the Invention The present invention has been made to achieve the above object, and the gist thereof is as follows: High density polyethylene: 40~
90% by weight, isotactic polypropylene: 5
~40% by weight, talc: 5~40% by weight to produce a film by the inflation method, by melt extruding the resin through a die slit having grooves in the flow direction on the outer circumferential surface of the mandrel; The method of producing a paper-like film includes protruding a bubble stabilizer from the die surface, bringing the narrow part of the bubble into contact with the stabilizer, and then taking it off while expanding it. The resin used in the method for producing the paper-like film according to the present invention is a composition consisting of high-density polyethylene, isotactic polypropylene, and talc. %, preferably 50-70% by weight, isotactic polyprene 5-40% by weight, preferably 10-25% by weight, talc 5-40% by weight,
Preferably, it is blended at a ratio of 10 to 20% by weight. If the density of high-density polyethylene is less than 0.940g/cc, the stiffness of the film will be insufficient, and the amount will be less than 40g/cc.
If it is less than 90% by weight, the molding stability will be poor, and if it exceeds 90% by weight, the elongation will be large and the folding properties will be poor.
In addition, the melt index is 0.01~3g/10min
is preferable, and if it is less than 0.01 g/10 min, molding becomes difficult. If it exceeds 3g/10min, the film strength will deteriorate. Isotactic polypropylene increases the stiffness of the film through a synergistic effect with high-density polyethylene, but if the amount is less than 5% by weight, the stiffness of the film will be insufficient, and if it exceeds 40% by weight, the stiffness of the film will be insufficient. Film strength becomes weaker. The melt flow rate is preferably 3 to 15 g/10 min, and 3 g/10 min.
If it is less than 10 minutes, your back will become stiff. If it exceeds 15g/10min, the film strength will deteriorate. Furthermore, talc roughens the surface of the film to give it a paper-like texture and increases its stiffness, but if it is less than 5% by weight, the film will lack the stiffness and paper-like texture;
If it exceeds this value, the tear strength decreases and it becomes unusable. An example of an apparatus for making a blown film using the above composition is shown in Fig. 1 a, b, and the same parts as in Fig. 2 a, b, c are given the same reference numerals and their explanations are omitted. . FIG. 1a is a partially enlarged plan view of the die 1, and the outer circumferential surface of the mandrel 6 forming the die slit 2' includes:
Concave grooves 7 in the flow direction are provided at predetermined intervals. Therefore, a large number of longitudinal protrusions are formed on the inner surface of the resin composition tubular body melt-extruded from the die slit 2'. If a film is formed by expanding with these protrusions still in place, the concave portions between the protrusions will be mainly stretched, reducing the longitudinal strength of the film as a whole. Since the bubble 5 protrudes, the constricted portion 5a of the bubble 5 comes into close contact with the bubble 5, thereby stabilizing the bubble 5 and flattening the uneven surface of the film to a certain extent so that the film is expanded almost uniformly. Although traces of the ridges and striped patterns may remain, the vertical streaks of the history of the ridges remain, resulting in a strong film with improved vertical independence. 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 with each other, the bubbles are stabilized, and the protrusions become flat to some extent leaving a history of vertical streaks, and are expanded at a predetermined ratio in range 9, and from frost line 5b onwards range 1
It solidifies at 0 and forms a paper-like film.
Note that by providing the grooves on the mandrel as described above, the appearance of the film after bag making is more convenient than when providing the grooves on the die. This film is suitable for making square bottom bags due to the physical properties of the composition and the effect of the history of the ridges. Examples and Comparative Examples Examples 1 to 5 A composition prepared by blending high-density polyethylene with a density of 0.945, isotactic polypropylene with a melt flow rate of 7.5 g/10 min, and talc in a predetermined ratio range was applied to the outer circumferential surface of the mandrel. V-shaped streamwise groove with depth: 0.5mm, width 1.0mm
Mandrel outer diameter (non-groove part) with 240 pieces 59
mmφ, a die slit with a die inner diameter of 60mmφ, and a die with a cylindrical bubble stabilizer with an outer diameter of 55mmφ and a height of 700mm protruding from the center of the surface is attached.65
Using a mmφ extruder, an inflation film with a thickness of 70 μm was created at a blow ratio of 3 and a take-up speed of 80 m/min, and a manufacturing test of a square bottom bag with a height of 350 mm, a length of 200 mm, and a width of 150 mm was carried out. I did this. Comparative Examples 1 to 3 Films were prepared and tested under the same operating 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. Comparative Examples 4 to 9 Films were prepared and tested under exactly the same operating conditions as in Examples, except that the density of high-density polyethylene, the blending ratio, the isotactic polypropylene, and the blending ratio of talc were partially outside the predetermined ranges. provided. Table 1 shows the test results of Examples and Comparative Examples.

[Table] As is clear from the table, the paper-like film produced by the method according to the present invention is extremely excellent for producing square bottom bags. Effects of the Invention As described above, the method according to the present invention can produce a film that has properties similar to paper, such as a somewhat rough surface, improved vertical independence, and strong stiffness. It has become possible to replace products with synthetic resin films, and the field of application is extremely wide.

[Brief explanation of the drawing]

1a and 1b are schematic explanatory diagrams of the paper-like film manufacturing method according to the present invention. FIG. 1a is a partially enlarged plan view of the die (corresponding to FIG. 2b), and FIG. Figure 1a is a side view showing how a paper-like film is made using the die; Figures 2a, b, and c are schematic explanatory diagrams of a conventional method for manufacturing an inflation film; FIG. 2b is a partial sectional view taken along the line -- in FIG. 2a, and FIG. 2c is a sectional view taken along the line '--' in FIG. 2a. 1...Dice, 2'...Dice slit, 3...
Valve stabilizer (stabilizer), 5...Valve, 5a...
...Neck part, 5b...Frost line, 6...
Mandrel, 7...concave groove.

Claims (1)

[Claims] 1. When producing a film by the inflation method using a composition consisting of high-density polyethylene: 40 to 90% by weight, isotactic polypropylene: 5 to 40% by weight, and talc: 5 to 40% by weight, the outer periphery of the mandrel is A paper-like paper product characterized by melting and extruding a resin through a die slit having grooves in the flow direction on its surface, protruding a valve stabilizer from the die surface, bringing the constriction of a bubble into contact with the stabilizer, and then taking it off while expanding. Film manufacturing method.