DE69309421T2 - Composite plastic film with a line for bending - Google Patents

Description

The present invention relates to a composite plastic sheet having a preformed line for bending. More particularly, the present invention relates to the construction of a preformed line for bending a composite plastic sheet to be assembled into a box-like body as a packaging material for various kinds of articles.

GB-A-1 362 242 discloses a plastic hinge consisting of a simple plastic film.

Composite plastic films have been widely used as materials for various types of containers. The composite plastic film was formed by laminating a thinner transparent plastic film which was printed and a thicker plastic film to form a single film, and lines for bending were formed in the film material to thereby impart good bending properties.

In order to provide good bending properties in the composite plastic film, various types of formed lines for bending have been proposed. For example, Japanese Patent Application Laid-Open No. 37092/1986 proposes that a line consisting of cut notches, grooves and non-notched portions be formed in a composite plastic film. Further, Japanese Patent Application Laid-Open No. 128023/1989 proposes a method for forming holding lines in a laminated film, in which a film material having a high melting point and another film material having a low melting point which is 20°C lower than that of the film having the high melting point are laminated and lines are formed by pressing a heated linear metal die from the side of the film material having the high melting point.

The line formed by cut notches and unnotched portions formed by the former method has a disadvantage in bending properties at the unnotched portions, and it has been impossible to feed composite plastic films having such lines formed into an automatic folding machine for making boxes. When a vinyl chloride film is used, the unnotched portions are bleached when a tension is applied thereto, causing the appearance to become poor.

In the latter method, since a plastic sheet is pressed with a heated metallic tool, resin beads are generated on both sides of the formed line, causing a disadvantage that it is impossible to bend the composite sheet along a formed line by 180º to the side where the line is located (therefore, a box-like container made of the composite sheet cannot be made completely flat for convenient transportation). Further, it is difficult to insert the metallic tool into a case where a plastic film having a large surface area is treated, whereby the depth of the line formed changes, with the result that uniform treatment cannot be obtained. Since the metallic tool cannot be pressed rapidly until heat flow is caused in the film (ie, the film is softened by heat), it is difficult to obtain high-speed treatment.

Furthermore, in the conventional processes, it is necessary to change the thickness of the plastic films if the bending properties of the film materials are to be changed. Accordingly, the total thickness of the plastic films must be changed in each operation so that it corresponds to the size of the containers to be formed.

It is an object of the present invention to provide a composite plastic film with a pre-formed line for bending, which provides good bending properties, sufficient strength and enables easy formation of the line.

According to the present invention, there is provided a composite plastic sheet with a formed line for bending, comprising a plurality of laminated plastic films in which a line is formed, the depth of the formed line being larger than the thickness of a plastic film disposed on the side from which a line-forming knife is pressed at the time of forming the line, and the formed line having at least two depths in the longitudinal direction in the line, the depth of the deep portions of the formed line being in a range of 60% to 100% with respect to the total thickness of the laminated plastic films, and the depth of the flat portions being in a range of 20% to 95%.

The depth of a formed line of 100% with respect to the total thickness of the laminated plastic films means that the formed line completely penetrates the film material in the direction of thickness.

In the drawing show:

Figure 1 is a perspective, partially omitted view of a first embodiment of the composite film according to the invention;

Figure 2 is a cross-sectional view of the composite film shown in Figure 1;

Figure 3 is a cross-sectional view taken along the line II-II in Figure 2;

Figure 4 is a cross-sectional view showing a second embodiment of the present invention;

Figure 5 is a cross-sectional view taken along a line V-V in Figure 4;

Figure 6 is a cross-sectional view showing another embodiment of the composite plastic film according to the present invention;

Figure 7 is a front view, partially omitted, of a line forming knife used for forming a line in the composite plastic film of the present invention;

Figure 8 is a diagram showing a state of forming a line and

Figure 9 is a diagram showing a state of bending the composite plastic sheet of the present invention.

Preferred embodiments of the composite plastic film of the invention will be described with reference to the drawings, in which like reference numerals designate like or corresponding parts.

In Figures 1 to 3, a composite plastic sheet 1 comprises a thinner plastic film 2 and a thicker plastic film 3 which are laminated. The thinner plastic film 2 is arranged on the side from which a line-forming knife is pressed.

For the plastic film 2, any film having good printing properties and good destaticization may be used, e.g., polyvinyl chloride, polypropylene, polyester, polystyrene and the like are used alone or as a composite film. For the plastic film 3, the material has sufficient elongation without breakage even when stretched at the time of line formation, which material is such as A-PET film (i.e., a transparent film made of polyethylene terephthalate having a degree of crystallization of 5% or less), polypropylene, polyethylene, polyvinyl chloride or the like. The films 2 and 3 are bonded together by suitable bonding agents such as dry lamination to form the composite plastic film 1.

The thickness of the films 2 and 3 is not particularly limited. However, if the thickness of the film 2 on which a line-forming knife is pressed exceeds 50% of the total thickness of the laminated films, there is a possibility that a bonding layer with poor elongation remains at the part immediately below the formed line, thereby reducing the strength and also deteriorating the bending properties. A preferable range of the thickness of the plastic film 2 is from 0.005 mm to 0.1 mm and from 0.1 mm to 2.0 mm for the plastic film 3.

Generally, printing is performed on the bonding surface of the plastic film 2. Therefore, when the feasibility of printing is considered, it is preferable to use a thin film for the plastic film 2.

As shown in Figures 1 to 3, a line for bending is formed in the composite plastic film 1 by pressing a knife to form a line from the side of the plastic film 2. The depth of the formed line 10 is greater than the thickness of the plastic film 2. Further, deep notch portions 11 and shallow notch portions 12 are formed alternately at appropriate intervals in the longitudinal direction of the formed line.

The depth of the deep notch portions 11 and the shallow notch portions 12 of the formed line 10 can be appropriately determined depending on the structure, bending angle, required bonding properties and strength of the plastic film 1 used. However, if the depth of the formed line 10 is less than the thickness of the plastic film 2 from which the line forming knife is pressed, then the bending ability of the sheet material is reduced because the bonding layer with a small elongation remains in the remaining portions. If the depth of the deep notch portions 11 is less than 60% of the total thickness of the sheet material 1 or the depth of the shallow notch portions 12 is less than 20% of the total thickness of the sheet material 1, then the bending properties are poor. On the other hand, if the depth of the shallow notch portions 12 exceeds 95% of the total thickness of the sheet material 1, then the strength is reduced. It is accordingly, it is preferred that the thickness of the deep notch portions 11 is in the range of 60% to 100% with respect to the total thickness of the sheet material 1, and the depth of the shallow notch portions 12 is in the range of 20% to 95%.

Figures 4 and 5 show a formed line 20 in which the depth of the deep notch portions 21 is 100% with respect to the total thickness of the sheet material 1, i.e., the deep notch portions 21 completely penetrate the sheet material 1. Accordingly, openings 23 are formed between the shallow notch portions 22 in the formed line 20.

The lengths or intervals of the deep notch portions 11 (21) and the shallow notch portions 12 (22) in the formed line 10 (20) are determined depending on the required bending properties and strength. For example, the strength of the plastic sheet material can be increased by keeping the deep notch portions 11 as they are and making the shallow notch portions 12 flat. However, if the wall thickness of the remaining portions is increased, the beige properties of the plastic sheet are impaired. Further, bleaching may be generated in the sheet material. Therefore, in order to increase the strength of the portion of the formed line, it is preferable to increase the proportion of the shallow notch portions 12 having a greater depth rather than increasing the remaining portions. In order to improve the bending properties, it is preferable that the depth of the deep notch portions 11 is large, particularly that the depth is 100%. It is possible that the deep notch portions 11 and the shallow notch portions 12 are connected by a step, an inclined surface or a curved surface.

As shown in Figure 6, there may be a case where, depending on the shape of the edge of the line forming knife and the material of the plastic film 1, the plastic film 2 is not cut away at the formed line but is made thin by stretching, whereby the portions of remaining thickness are arranged at the central part in the direction of the thickness of the plastic film 1 due to the restoring force of the film 2. In this case, it is possible to bend the film to the side of the plastic film 2 in contrast to the normal bending direction. If the area of the formed line is printed, the printed area is not broken, thereby improving the appearance.

The above-mentioned formed line 10 (20) can be easily produced by using a line forming knife 33 having convex portions 31 for forming the deep notch portions 11 and concave portions 32 for forming the shallow notch portions 12, as shown in Figure 7. In the line forming knife 33, the length A of the convex portions 31, the length B of the concave portions 32 and the height difference C between the concave and convex portions are determined depending on the shape of the line to be formed. By adjusting the pitch of pressing the line forming knife 33, the line 10 shown in Figures 1 to 3 can be formed. By pressing the line forming knife 33 until the edge of the convex portions 31 comes into contact with a lower plate 34, the line 20 as shown in Figures 4 and 5 can be produced.

An example of producing the composite plastic sheet having a formed line for bending according to the present invention will be described below. However, the present invention is not limited to the specific example.

As a material for the composite plastic film 1, a stretched polyester film having a thickness of 20 µm and an A-PET film having a thickness of 0.25 mm were used as the plastic film 2 and the plastic film 3, respectively. Printing was performed on the bonding surface of the plastic film 2. The plastic film 2 and the plastic film 3 were dry laminated to obtain a film material whose total thickness was 0.27 mm and whose bonding layer thickness was 5 µm. A knife 33 was used for forming the line with an angle of the knife edge of 45º, a length A of the convex portions 31 of 0.6 mm, a length B of the concave portions 32 of 0.4 mm, and a height difference C of the convex and concave portions of 0.15 mm. The line forming knife 33 was pressed into the material of the plastic sheet 1 from the side of the stretched polyester film until the convex portions 31 of the knife 33 came into contact with a lower plate 34 as shown in Fig. 8. In this way, the line 20 as shown in Figs. 4 and 5 was formed. As a result, the deep notch portions 21 of the formed line 20 became a fully open state, and the wall thickness of the portion immediately below the shallow notch portions 22 was 0.15 mm. The above-mentioned operations were carried out in a cold state. However, it is possible to carry out the above-mentioned operations with a heated line forming knife 33 and/or the heated lower plate 34.

The plastic film 1 thus obtained was bent along the formed line 20 so that the cut portion opened as shown in Figure 9. As a result, excellent bending properties could be obtained.

Lines 20 were formed at predetermined portions in sheets 1 to form transparent cases of 90 x 30 x 65 mm in size. The sheets 1 were set in a machine for automatically making boxes (an upright cartoning machine, model CMV-B, manufactured by Osaka Jidoki Kabushiki Kaisha) to investigate the ease of forming boxes. As a result, boxes could be efficiently manufactured at a rate of 70/min.

Further, solid soap bars were placed in the prepared containers and a comparison was made to examine the strength of the containers with boxes having the same dimensions but made of a different film material. As a result, it was found that in practical use, breakage did not occur at the portions with the line formed. Further, the line portions were repeatedly bent 180º thirty times. As a result, there was no breakage at the line portions formed.

As described above, in the composite plastic sheet having a formed line for bending according to the present invention, excellent bending properties can be obtained at the formed line while having sufficient strength. Furthermore, it is easy to line, and it can be formed at a high speed. The line forming and bending can be carried out continuously at a high speed in an automatic container making machine, whereby containers can be efficiently manufactured from the composite plastic film.

By adjusting the wall thickness at the shallow notch portions, bleaching can be prevented, and the appearance of the line-formed portions is excellent. In addition, regardless of the design of the plastic film, by changing the knife for forming the line, a change in the strength at the line-formed portions and the bending properties can be achieved.

Claims (3)

1. A composite plastic sheet (1) with a formed line (10,20) for bending, consisting of a thinner plastic film (2) and a thicker plastic film (3) which are laminated, and in which the line is formed from the side of the thinner plastic film, and the depth of the formed line is greater than the thickness of the thinner plastic film (2) which is arranged on the side from which a knife (3) for forming the line is pressed at the time of forming the line (10,20), and the formed line has at least two depths in the longitudinal direction of the line (10,20), and the depth of the deep portions (11,21) of the formed line is in a range of 60% to 100% with respect to the total thickness of the laminated plastic films, and the depth of the flat portions (12,22) is in a range of 20% to 95% . 2. Composite plastic film (1) according to claim 1, wherein the deep portions (11) and the flat portions (12) are formed alternately in the line (10, 20). 3. Composite plastic film (1) according to claim 1, wherein openings (23) are formed at the bottom of the deep portions (21).