JP2002020554A - Thin tube-like plastic film and method for forming the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a thin plastic film heavier than a conventional film. SOLUTION: Powdery barium sulfate in a high proportion is mixed with a raw material resin of a polyethylene, and the obtained mixture is fed to a multi-screw extruder to provide a pellet-shaped masterbatch. The proportion of the barium sulfate based on the whole weight of the masterbatch is 80%. The masterbatch in a proportion of 2-4 wt.% is added to the raw material pellet of the polyethylene resin, and mixed well. The mixed product is fed to an extruder as a raw material resin, and subjected to an inflation molding to provide a film having about 10 μm thickness and a tube shape. The tube- shaped film roll 9 formed thus is subjected to a bag-making machine to form the film into a plastic bag 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin tubular plastic film, a plastic bag made therefrom, and a method for molding the same.

[0002]

2. Description of the Related Art Recently, when shopping at a supermarket or a store, products are usually put in a plastic bag (shopping bag). This plastic bag is made from inexpensive polyethylene resin, and the method of making it is to first form a tubular film by the inflation method, put it on a bag making machine, cut it into a bag size with a heat knife, Further, the handle portion is cut by a cutting machine. Such a plastic bag is destined to be immediately disposed of as garbage, and there is a social demand that the plastic bag be made as thin as possible to reduce the amount of garbage.

The thickness of a conventional plastic bag is as thin as 20
Of the order of a micron, but thinner, for example 1
It is technically possible to mold 0 micron tube films. However, there is a problem with the bag making machine.

[0004] The bag making machine blows air from between the conveying rollers, and feeds the tip of the tubular film to a heat knife along with the flow. The cut bag is blown off with air and skewered by a downward pressing member downstream of the heat knife. In this way, since a number of bags are bundled, the bags are cut and formed into a handle at the top of the bags.

[0005] As described above, in the bag making machine, the bag cut by the heat knife is further conveyed to the next skewering step by the flow of air, and the thinner the bag, the lighter the weight. In addition, stable transport is not possible due to the wind in the factory. As a result, the bags are bundled in an irregular state, and there is a problem that the handle cannot be attached properly later.

[0006]

However, even if the plastic bag is thin, if the weight is heavy, no problem occurs in the air conveyance in such a bag making machine. Therefore, a thin plastic bag may be molded using a plastic molding material having a large specific gravity.

Heretofore, there has been known a method of adding lead powder or iron oxide to a plastic molding material in order to make the plastic heavy and to have characteristics such as sound insulation. However, since plastic bags are also used for packaging foods, these additives have safety problems for the human body. In addition, if the plastic bag contains lead powder and the like, extra costs are required for garbage disposal. In addition, there is an adverse effect on the strength and color of the bag.

An object of the present invention is to form a plastic film that is thin and heavier than usual.

[0009]

The inventor of the present invention has found barium sulfate as a result of extensively searching for an additive for increasing the specific gravity by mixing with a polyethylene resin raw material. Barium sulfate is not only high in specific gravity but also thermally stable, safe for the human body, and white in color, so that the product is not colored and is convenient. Since the specific gravity of barium sulfate is about 4.5 and the specific gravity of polyethylene resin is about 0.95, there is about a 5-fold difference between the two. Thus, for example, if 2% of barium sulfate is added to a polyethylene resin, the specific gravity of the mixture increases by about 10% to about 1.0. If the proportion of barium sulfate is increased, the specific gravity increases, but problems such as uneven thickness of the film become noticeable, so the upper limit is about 10%.
It is preferable to use it in a range not exceeding 5%.

In the present invention, a thin-film tubular plastic film is formed using a polyethylene resin material containing 0.1 to 10% by weight of barium sulfate (BaSO ₄ ) of the total forming material. As a molding method, general inflation molding is used. Plastic made in this way can produce a plastic film that is heavier than just molded with polyethylene resin. Therefore, even if the plastic film is extremely thin, such as a film thickness of 10μ,
When this is processed into a bag by a bag making machine, the transfer by the air flow is reliably performed without being affected by the wind in the factory, and there is an effect that a reduction in the yield of products can be prevented.

Since barium sulfate does not mix well if it is directly mixed with polyethylene resin, a masterbatch in which barium sulfate is mixed with polyethylene resin at a high concentration is prepared, mixed with polyethylene resin pellets, and supplied to a molding machine. It is better to do it. In this case, the barium sulfate and the polyethylene resin are uniformly mixed, and the workability is good.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Powdered barium sulfate (specific gravity: 4.
5) is mixed in a high ratio into polyethylene raw resin, heated and melted in a cylinder barrel of an extruder, extruded with a screw, given a shape with a die at the tip, cooled, and pelletized masterbatch. Get. The proportion of barium sulfate in the total weight of the masterbatch was 80%.

The masterbatch is added at a ratio of about 2 to 4% by weight based on the polyethylene resin raw material pellets,
A well-mixed product is supplied to an extruder as a raw material resin.
FIG. 1 shows a process for producing a tubular film by an inflation molding method. The extruder A includes a cylinder barrel 2 having a heater 1, a screw shaft 3 rotating in the cylinder barrel 2, a motor 4 for driving the screw shaft, and the like. The raw resin supplied from the hopper 2a is melted in the cylinder barrel 2 and is pushed out of the barrel by the screw shaft 3. A ring die 5 is provided at the end of the barrel, from which a molten tube is extruded, air is blown into the tube to expand it to a predetermined size, and is continuously wound around a winding machine 8 through a guide plate 6 and a nip roll 7. take. Adjust the lip clearance and air pressure of the ring die 5, and adjust the film thickness to about 10μ.
Was obtained.

The tubular film roll 9 thus produced is set on a bag making machine. In FIG. 2, reference numeral 10 denotes a pair of upper and lower feed rollers, which are continuously rotated and pulled out from the roll so as to sandwich the tubular film 9. The feed roller 10 is provided with a number of grooves 11 in the circumferential direction, and compressed air is blown in the film feed direction from a nozzle 12 incorporated in the grooves. The leading end of the film 9 is fed horizontally further beyond the feed roller 10 by riding this air flow. Thus, when the leading end of the film reaches an appropriate position, the heat knife 13 descends, and the film is cut into an appropriate length, and at the same time, the cut portion is heat-sealed.

The bag 14 thus cut is further transported downstream so as to be blown off by the air ejected from the nozzle 12, and soon the holding member 15 comes down from above and is transferred to the skewer 16 waiting below. It is pierced. The skewered and neatly stacked bags 14 are collectively passed through a cutting machine to form a handle 17 by cutting off the upper portion 18 (FIG. 3). This completes the plastic bag.

If the film is thin and therefore light, the bag after being cut by the heat cutter is susceptible to the wind in the factory and flies in an unstable manner. In the present invention, barium sulfate having a large specific gravity is added, so that the weight is large in spite of its small thickness, so that it is hardly affected by wind and is pneumatically conveyed in a stable state. It does not hinder the cutting of this.

Table 1 shows the physical properties of a plastic bag prepared by adding barium sulfate and a material not containing barium sulfate. In the case of barium sulfate, the strength is slightly reduced, but there is no practical problem.

[Table 1]

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of inflation molding.

FIG. 2 is an explanatory view showing the operation of the bag making machine, wherein the upper part shows a plane and the lower part shows a longitudinal section.

FIG. 3 is an explanatory view of a plastic bag.

[Description of Signs] A Extruder 5 Die 9 Tubular film 13 Heat knife 14 Plastic bag 17 Handle

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Claims (3)

[Claims] 1. A thin-film tubular plastic film formed from a polyethylene resin material containing 0.1 to 10% by weight of barium sulfate based on the whole molding material. 2. A plastic bag made from the plastic film of claim 1. 3. The method for forming a plastic film according to claim 1, wherein a masterbatch in which barium sulfate is mixed at a high concentration in a polyethylene resin is prepared, mixed with a polyethylene resin pellet, and supplied to a molding machine.