JPS61108530A - Film for bag - Google Patents

Abstract

PURPOSE:To obtain extremely thin film excellent for bag with both high longitudinal and lateral strengths by a structure wherein a plurality of convex beads extending in the extrusion direction are provided in blown film consisting of polyethylene resin with specified density, melt index and blow-up ratio. CONSTITUTION:A film for bag, which has a plurality of convex beads extending in the extrusion direction, is made of blown film, the blow-up ratio of which is 3 or more, and which consists of polyester resin with density of 0.940g/cm<2> or more and melt index of 1g/10mm or less. A tubular resin, which lies within the range 7 and on the inner surface of which a large number of convex beads are formed with concave grooves 4... by being extruded through a die slit 2, closely contacts with a bubble stabilizer 5 at the shoulder part 6a so as to flatten the convex beads to some degree. Further, the resin is expanded at he predetermined ratio by means of the air passing through the stabilizer 5 within the range 8. Finally, the resin solidifies itself and turns into thin film 13 with longitudinal flat parts 11 and convex beads 12 within the range 9, which lies after the frost line 6b of the resin. The film 13 has stronger lateral tear strength due to the convex beads 12, resulting in preventing ring-breaking phenomenon from occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a thin blown film made of polyethylene resin, which is suitable for use in bags and has strong strength in both the longitudinal and transverse directions.

Conventional technology Generally speaking, to manufacture film by the inflation method,
The tubular film is taken out at a high speed relative to the extrusion speed of the resin, and gas is enclosed in the extruded tubular film to cause it to expand. In this case, if the expansion ratio is small, the pulling direction (vertical direction or M
direction)) increases, and the tear strength in the longitudinal direction is extremely reduced. For this reason, the expansion ratio is usually increased to add molecular orientation in the direction perpendicular to the drawing direction (lateral direction or #'iT direction) to balance the molecular orientation in the longitudinal direction. In addition, when the expansion ratio is increased, the bubbles formed become unstable, and when these bubbles are taken off at high speed, uneven thickness, wrinkles, and sag occur in the film that can be formed. Protruding the stabilizer K
This problem was solved (Special Publication No. 55-2180).

Problems with the conventional technology However, if the expansion ratio is increased and the film thickness is reduced, the bag may tear in the lateral direction depending on the load during use after making the bag.
A phenomenon of cut-offs occurs. Normally, to make bags from blown film, the bags are made by sealing them at right angles to the take-up direction, but the phenomenon of ring tearing occurs due to the load when an object is placed inside, and is a major defect in bags. .

Purpose of the Invention The present invention uses a polyethylene resin, particularly a high-density polyethylene resin, to produce a film that is particularly excellent for use in thin bags and has high strength in both the longitudinal and lateral directions by an inflation method. The purpose is to provide.

Structure of the Invention The present invention has been made to achieve the above objects.
The gist is a blown film with an expansion ratio of 3 or more, made of a polyethylene resin with a density of αq40fl/c or more and a melt index of IJil/10m1 or less, and has a plurality of protrusions extending in the extrusion direction. It is in the bag film.

The polyethylene resin used in the present invention is a polyethylene homopolymer, a copolymer of polyethylene and a foreign olefin such as an α-olefin such as propylene, 1-butene, hexene, or a blend mainly composed of these. The density of α940 p /Cd or more,
The mel index is IN/10m or less. To this, stabilizers, ultraviolet absorbers, lubricants, colorants, anti-blocking agents, etc. may be added as necessary.

If the density of the polymer is less than a, tpaa9/c+d,
The strength of the formed film is insufficient and the stiffness becomes weak.
Moreover, when the melt index exceeds 1y/1oiox, the strength of the film becomes weak.

Step K for producing the bag film of the present invention is carried out as follows.

Figures 1 and 2 show an example of the device.
The figure is a partial plan view of the die, and FIG. 2 is a side view of the apparatus for manufacturing blown film. Concave grooves 4 in the flow direction are provided at predetermined intervals on the outer peripheral surface of the mandrel 3 forming the die slit 2, and a bubble stabilizer 5 is protruded from the surface of the die 1.

The polyethylene resin tubular body melted and extruded from the die slit 2 has protrusions formed on the inner surface, and the stable body 51C
(The fin portions 6a are brought into close contact, the bubble 6 is stabilized, and the protruding stripes remain although they are to some extent distorted, resulting in tear resistance in the T direction with no ring breakage compared to films obtained by conventional molding methods. In other words, the tubular resin in the region 7 extruded from the die slit 2 and having a large number of protrusions formed on the inner surface by the concavities #4 is formed in the bubble stabilizer 5 at the constriction part 61. The protrusions are leveled in close contact with the stabilizer 5, expanded at a predetermined ratio in the range 8 by air passing through the stabilizer 5 (not shown), and solidified in the range 9 after the frost line 6b, as shown in FIG. As shown, a thin film 13 consisting of a longitudinal flat portion 11 and a convex strip 12 is formed and wound around a nip 9. Note that the reference numeral 14 in the figure
is an air ring that blows out air.

Since the film 13 has the ridges 12, it has high tear strength in the transverse direction, and the occurrence of ring breakage is prevented. Convex strip 1
The density of 2 varies depending on the thickness of the flat part 11, but it is particularly preferably used when the thickness of the flat part is 15 μm or less, and the density is 77 mm or more per piece in the width direction, preferably 1 piece/1.
If it is 5gg or more and less than 77mm per piece, the flat part 11 will be easily torn. Furthermore, the bag film of the present invention is a blown film, and as mentioned above, the ridges are provided on the inside of the blown film so that the ridges come into contact with the stabilizer and are relatively flattened after bag making. preferred in terms of appearance.

Examples, comparative examples Next, the present invention will be explained by showing examples and comparative examples.

[Example 1] Density (JIS [6740); α9589 /c+a
.

Melt index (JI8 11760); α5J'
/1om ethylene homopolymer was melted at 200°C,
Apply this to the outer circumferential surface of the mandrel to a depth of I15 mm and a width of 15 mm.
l 5 mwr (1) V-shaped f) at L direction groove 240 kerbed mandrel outer diameter (non-groove part); 59
uIJil, 65II with a die having a die slit with a die inner diameter of 60Bp and a cylindrical stabilizer with an outer diameter of 55mm and a height of 700B protruding from the center of the surface.
Using a mg extruder, expansion ratio: 4, withdrawal speed: 8
A blown film was prepared with Q m / 11111 g, and this was used as a sample to measure impact strength, Elmendorf tear strength, and high speed impact strength.

[Example 2] Example except that the expansion ratio was set to 3 and the extrusion amount was changed! A film was made using the same K as above and its physical properties were measured.

[Comparative Example 1] Example 1 except that a die with a die slit without unevenness was used.
The physical properties of four filters were measured in the same manner as above.

[Comparative Example 2] Same as Example 2 except that a die with a die slit without unevenness was used.
A film was made in the same manner as above, and its physical properties were measured.

[Comparative Example 3] A film was prepared in the same manner as in Example 1, except that the raw material citrus was changed, the film was melted at 190"C, and the expansion ratio was set to 2, and each physical property was measured.

[Comparative Example 4] A film was made using the same K as in Example 1 except that it was melted at 19 (1° C.) with a different raw material resin, and each physical property was measured.

The results of Examples 1 and 2 and Comparative Examples 1 to 4 are shown in Table 1.

In addition, the impact strength ζ is ASTM D781, Elmendol 7
Tear strength [t! According to JIS z1702, K. In addition, high-speed impact strength was determined by punching out a sample film into a dumbbell shape, making the thinnest part 518W x 12μm thick, and pulling it at a speed of 529rH/MJI. It was calculated by dividing.

Effects of the Invention As mentioned above, since the film for bags according to the present invention is provided with a large number of protrusions, it has high cutting strength in both the vertical and horizontal directions, and does not cause ring breakage due to load, and is particularly It is extremely excellent as a film for thin bags.

[Brief explanation of drawings]

FIGS. 1 and 2 show an example of an apparatus for manufacturing a film for bags according to the present invention. FIG. 1 is a partially enlarged plan view of a die, and FIG. FIG. 3 is a cross-sectional view of the film shown in FIG. 2 taken along the line N-1. 11... Flat part, 12 Convex part, 13...
film. Figure 1

Claims (1)

[Claims] A blown film made of a polyethylene resin with a density of 0.940 g/cm^3 or more, a melt index of 1 g/10 mm or less, and an expansion ratio of 3 or more, having a plurality of protrusions extending in the extrusion direction. A film for bags that is characterized by: