JPH0210098Y2 - - Google Patents

Description

[Detailed description of the invention] Inflation films made of polyolefin resins such as polypropylene and polyethylene are inexpensive, have excellent transparency, have a good appearance and feel, have excellent mechanical properties, and have good moisture permeability. It has many advantages such as good protection of contents from moisture, and is widely used in various packaging applications.
Several attempts have been made to provide such useful polyolefin films with functionality not previously provided.

A method of forming a film with a unique vertical striped pattern using an inflation method or a T-die method is disclosed in, for example, Japanese Patent Application Laid-open Nos. 150515-1982 and 5852-1980. This method adds a striped pattern to the film and increases its commercial value in terms of design.

A method of blending an inorganic filler with a polyolefin film to enable writing with pencils, ballpoint pens, or similar writing instruments is known, for example, in Japanese Patent Publication No. 40794/1983. The purpose of this method, as stated in the specification, is to provide an opaque film that is a substitute for conventional paper and has improved printability and printability.

A laminated film of a polyolefin layer containing an inorganic filler and a polyolefin layer not containing an inorganic filler is known from Japanese Utility Model Application No. 48-48351, Japanese Patent Application Laid-open No. 74577-1980, and the like. Utility Model Application No. 48351 (1973) adds calcium carbonate to reduce the amount of heat generated during incineration, and forms a laminated film to maintain the heat-sealing properties of polyolefin.
The method of No. 74577 is aimed at producing opaque films.

The inventors of the present invention focused on the drawback that it is difficult to write on polyolefin film with a pencil, ballpoint pen, or similar writing instrument, without substantially impairing the inherent advantages of polyolefin film, such as transparency and heat sealability. As a result of intensive study to obtain a polyolefin film with excellent writing properties, we arrived at the present invention.

That is, the present invention is a polyolefin inflation film, in which a part of the cross section perpendicular to the flow of the resin is made up of two layers, and the two layers are an inner layer and an outer layer, and the outer layer is made of an inorganic material. An blown polyolefin resin containing a filler, wherein the amount of the inorganic filler is 5 to 40% by weight in the polyolefin resin containing the inorganic filler, and the inner layer is a polyolefin resin containing no inorganic filler. It is a film.

Suitable polyolefin resins used in the production of the polyolefin film of the present invention include polypropylene, medium-low density polyethylene, high-density polyethylene, and polyolefin resin compositions containing these as main ingredients, with polypropylene being particularly suitable. Further, as the inorganic filler to be used, calcium carbonate and tank are suitable for writing with a pencil or ballpoint pen, and more preferably calcium carbonate is most suitable. The amount added is in the range of 5 to 40% by weight, more preferably 15 to 30% by weight in the polyolefin resin containing the inorganic filler.
It is. Furthermore, if the inorganic filler-containing portion is colored with a trace amount of cadmium yellow, phthalocyanine blue, etc., it is effective to make characters written with a pencil or ballpoint pen more clearly visible.

In order to produce the polyolefin film of the present invention, the film may be formed by directly employing a commonly used film forming method using an inflation method. For example, using two extruders, one extruder extrudes the polypropylene resin that makes up the transparent layer, the other extruder extrudes the polypropylene resin containing the inorganic filler, and these are simultaneously fed into one die. A polyolefin in-film having a thickness of usually 20 to 80 η is produced by coextruding the two materials while fusing them in a die. In this case, the cross section of the film is always partially formed of polyolefin resin containing an inorganic filler, and this layer is present as an outer layer, and the cross section of the film is always partially formed of polyolefin resin containing no inorganic filler. Shape the film so that it is formed by.

In the polyolefine film of the present invention, the direction of resin flow is, for example, the direction of the arrow on the film shown in FIG. 1, and the direction perpendicular to the direction of resin flow is the cross section of the film.

In this invention, the cross section of the film is always partially formed of polyolefin resin containing an inorganic filler, and this layer is present as an outer layer, and the cross section of the packaging bag is always partially free of inorganic filler. It is necessary that it is made of polyolefin resin, and the reason is as follows.

That is, in order to improve the writability, a fairly large amount of inorganic filler, 5 to 40% by weight, must be added to the resin. However, because of this, the heat sealability of the film deteriorates, and it may not be possible to seal the bag by heat sealing, or even if it is possible, the sealing strength is low. Therefore, we decided to make the film partially double-layered so that a part of the cross section perpendicular to the resin flow is double-layered, and that part is on the outer layer of the film and contains an inorganic filler. .

As a result, the inner surface becomes a layer made only of polyolefin resin, resulting in good heat-sealability, and a portion of the outer surface becomes a layer of polyolefin resin containing an inorganic filler, so that writing can be performed on this portion.

The most typical application of the present invention is packaging bags. The packaging bag may be made by heat-sealing the bottom of the blown film obtained by the method of the present application.

This will be explained below with reference to the drawings.

FIG. 1 shows a packaging bag in which the bottom of a polypropylene blown film is heat-sealed, and 1 is made of a propylene homopolymer containing, for example, 20% by weight of calcium carbonate. On the other hand, 2 is made of, for example, a propylene-ethylene random copolymer (ethylene content: 2.5% by weight), and the contents can be seen through the highly transparent portion of 2, and writing can be written on the 1 portion.

The portion 1 may be provided at one location, or may be provided at two or more locations as shown in FIG. This can be appropriately selected depending on the purpose, such as the decorative effect and function of the product, when producing, for example, a packaging bag from the polyolefin film raw fabric of the present invention.

The polyolefin packaging bag using the film of the present invention is used, for example, for packaging stationery, drawings, films, etc. The contents can be seen through the transparent part 2, and the contents can be marked with a pencil, ballpoint pen, etc. on the part 1 of the packaging bag. This makes it a beautiful packaging bag, and at the same time it is useful for purposes such as storing and organizing documents.

[Brief explanation of drawings]

Figure 1 is a diagram showing an example of a packaging bag in which the bottom of polypropylene film is heat-sealed, and one part of the cross section perpendicular to the flow has two layers.
Figure 2 is an enlarged view of part A, Figure 3 is a diagram showing an example where two parts are partially formed into two layers, and Figure 4 is an enlarged view of part B. The arrows indicate the flow of resin. Represents direction. 1... A part formed of a polyolefin resin containing an inorganic filler, 2... A part formed of a polyolefin resin with good transparency,
3...Heat seal part, 4...Bag opening.

Claims (1)

[Claims for Utility Model Registration] (1) A polyolefin inflation film, in which a part of the cross section perpendicular to the resin flow has two layers, and the two layers are an inner layer and an outer layer. The outer layer contains an inorganic filler, and the amount of the inorganic filler is 5 to 40% by weight of the polyolefin resin containing the inorganic filler, and the inner layer is a polyolefin containing no inorganic filler. polyolefin film. (2) The packaging bag according to claim 1, wherein the inorganic filler is calcium carbonate.