JPS5812139B2 - Method for manufacturing microwave oven containers made from metal-deposited resin sheets - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing containers for microwave ovens made of metallized resin sheets (including films and plates). The purpose is to mass-produce safe products that do not cause spark discharge (spark discharge) at low cost.

Metal-deposited resin sheet, i.e., base material resin sheet 1 (Fig. 1)
A metal vapor deposited layer 2, generally made of aluminum, is uniformly formed on one or both sides of the metal according to a conventional method (the thickness of the vapor deposited layer 2 is generally about 0.05 μm).

Alternatively, a resin 3 (top coat layer) is laminated on two sides of the metal vapor deposited layer (in this case, one or both of the layers 1 and 3 are transparent, colored transparent, or translucent), with metallic luster on one or both sides. It is widely used in decorative materials, packaging materials, building materials, and other applications due to its beautiful appearance.

For example, packaging containers for various foods such as fresh foods, cooked foods, and semi-cooked foods, disposable bento boxes for station lunches and catered meals,
Various types of disposable tableware used in simple cafeterias, food stalls, mock shops, etc. are made from the metal-deposited resin sheets mentioned above (usually by vacuum forming or pressure forming), and are made to look like heavy, ornate metalware. It is possible to obtain items with a sense of noble taste and cleanliness, to increase the commercial value and quality of the container itself or the food contained therein, and to obtain tableware that has a good appearance without any sense of strangeness or resistance. As a simple lightweight container made of resin for food, we use ordinary synthetic resin-filled sheets, foamed sheets,
In addition to those made from the same various laminate sheets, those made from the above-mentioned metal-deposited resin sheets have also been produced in large quantities and won awards.

By the way, microwave ovens for cooking have become extremely popular in recent years, and their popularity and usage in general households is also increasing, and various cooking methods that utilize microwave ovens have been developed.

Under these circumstances, the connection between packaged foods and microwave ovens is inevitable.For example, food manufacturers may be able to take cooked or semi-cooked packaged foods and then pack them at restaurant businesses or ordinary households. A rational system is established in which the food is cooked in the microwave and the package container is used as tableware to serve at the table.

In fact, for example, some retailers of packaged lunches offer a service where the packaged lunches are heated in a microwave oven and handed to customers, and simple restaurants also use disposable containers that serve as tableware. In some places, food is placed on a plate and the entire container is placed in the microwave to cook.

However, in such a case, a problem arises when the pack container or simple tableware is made of the metal vapor-deposited resin sheet as described above.

In other words, even if this type of container or tableware has a metal vapor deposited layer 2 covered with a resin top coat layer 3, if it is used in a microwave oven, electric discharge (sparks) may occur due to microwaves, and general metal Along with containers, woven wire mesh, molds with rings, and containers coated with gold or silver powder, these containers are considered unsuitable for microwave ovens and should be avoided. .

The present invention has been proposed in view of the above, and an object of the present invention is to provide a method for easily and inexpensively mass-producing simple, lightweight containers made of metal-deposited resin sheets that are safe and do not generate electric discharge even when used in a microwave oven. With the goal.

This will be explained in detail below.

(1) As mentioned above, when a conventional container obtained by vacuum or pressure forming a metal-deposited resin sheet as a material is used in a microwave oven, two sides of the metal-deposited layer are covered with the top coat layer 3. Even objects can cause discharge.

Even with the top coat layer 3, the container opening edge c (Fig. 2)
Since the end face of the metal vapor deposited layer 2 is exposed on the trimmed end face of the container, we thought that this might cause discharge, and we decided to use a container with the end face of the opening edge c of the container coated with resin c' as shown in Figure 3. I wrapped the whole thing in a resin bag and used it in a microwave oven, but discharge occurred regardless of the treatment.

(2) On the other hand, if the molded container has a relatively deep bottom, the discharge will occur at the opening edge c of the container, and no discharge will be seen on the bottom surface a and side walls of the container.

Incidentally, when a deep-bottomed container was used in a microwave oven after cutting off the edge "c" (Fig. 3) where the discharge occurs, no discharge was observed in the container.

On the other hand, for containers with a fairly shallow bottom, the bottom surface a and the side wall b of the container
・Discharge was observed everywhere around the opening edge c.

(3) Therefore, we tried to magnify and observe the state of the metal vapor deposited layer 2 in each part of the container using a microscope.
In the case of a container with a deep bottom, the metal vapor deposited layer 2 on the bottom surface a and the side walls has microscopic extremely fine network cracks 2 on the entire surface as shown in the fourth figure.
As a result, the vapor deposited layer 2 consists of numerous small-area layers 2' of fine irregular shapes that are discontinuous in the plane direction (for example, 20 to 3
However, the metal vapor deposited layer at the edge c of the opening of the container has almost no cracks, or there are vertical or horizontal striped cracks as shown in Figure 5, and the entire edge c is essentially broken. The continuous layer morphology was maintained.

On the other hand, in the case of a shallow container, there are no cracks in the metal vapor deposited layer on any part of the bottom surface (a), side wall (b), or opening edge (c), or there are only localized cracks, and the entire container is in the form of a substantially continuous layer. It was retained.

The fine splitting of the vapor deposited layer 2 on the side wall of the bottom surface a, which is observed in the case of the deep-drawn container mentioned above, is caused by the fact that the portion of the material sheet corresponding to the bottom surface a and the side wall of the deep-drawn container is formed by vacuum or pressure forming. Forming is achieved by stretching the sheet at a fairly high rate both vertically and horizontally, but the metal vapor deposited layer on the sheet (
The base material resin sheet 1 or the base material resin sheet 1 and top coat layer 3) cannot follow the above-mentioned high rate of vertical and horizontal elongation, and as a result, cracks occur all over the surface and fragmentation occurs as described above. .

On the other hand, since the material sheet portion corresponding to the container opening edge c does not elongate at such a high rate during molding, the metal vapor deposited layer 2 in that portion remains substantially in a continuous layer state.

In addition, in the case of a shallow container, there is no high rate of elongation in any of the material sheet parts corresponding to the bottom surface a, side wall b, and opening edge c of the special molded container, so that the metal vapor deposited layer 2 has continuity over the entire container. is substantially maintained.

(4) Also, a sheet in which a metal vapor-deposited continuous layer 2 is uniformly applied on one side of the base resin sheet 1 (no top coat layer 3)
A deep-bottomed container (with the vapor deposition surface as the inner surface) obtained by vacuum forming or pressure forming according to the conventional method using the material as a material, was tested with a tester on the vapor deposition surface of each part of the bottom surface a, side wall b, and opening edge c. When we checked for conductivity by applying a negative bipolar needle, we found that there was no conductivity on the vapor deposition surfaces of the bottom surface a and side walls even when the bipolar needles were brought as close as possible (distance/mm or less) to the vapor deposition surface. On the other hand, on the vapor deposition surface of the opening edge c, there was conduction regardless of the mutual spacing between the two electrode needles.

Based on the facts (1) to (4) above, the present inventor believes that when the metal vapor deposited resin sheet has a continuous layer type, discharge occurs, but when the metal vapor deposited layer 2 is of a continuous layer type, as shown in FIG. The reason for this is unclear, but it has the property of not causing discharge even when exposed to microwaves with the strength of at least the output of a general microwave oven (for example, high frequency output of 600 W, oscillation frequency of 2450 MHz, power consumption of 125 KW). I found that.

In addition, we conducted a separate tensile test on the material sheet (metal vapor-deposited resin sheet) to investigate the elongation rate of the material sheet and the state of subdivision of the metal vapor-deposited layer 2. As a result, we found that the material sheet (metal vapor-deposited resin sheet) has a general metal vapor deposition that is conventionally used for manufacturing metalware-like containers. For sheets, in most cases, if the material sheet is stretched by more than 5% vertically and horizontally, the elongation of the metal vapor deposited layer 2 will exceed the breaking limit, and the vapor deposited layer 2 will become extremely microscopically fine as shown in the example in Figure 4. Network-like cracks 2'' are generated, and as a result, the vapor deposited layer 2 is made up of a large number of irregularly shaped small-area layers 2' that are discontinuous in the plane direction (for example, 2' in the vertical and horizontal directions).
It was found that the microorganisms split into 0 to 30μ range).

In this case, the vertical and horizontal stretching ratio is set to a small value of 5% or less.

Or, when stretched in one direction, no cracks occur in the deposited layer 2, or only cracks are observed locally, or
As shown in the figure, cracks are formed in vertical and horizontal or horizontal stripes, and in both cases, the form of a substantially continuous layer is maintained as a whole in which discharge is caused by microwaves.

In addition, as the amount of stretching in the vertical and horizontal directions increases, the width of the network crack lines 2'' also increases, resulting in a decrease in reflectance and gloss when looking at the metal vapor deposited layer 2 as a whole. It turns out.

Therefore, it is better to avoid increasing the amount of stretching to an extremely large extent, and in order to maintain a good reversal rate and gloss as a metal vapor deposited sheet, it is generally about 5 to 100%, especially 10 to 5.
It is possible to set the amount of vertical and horizontal stretching to about 0%.

The present invention is based on the above-mentioned facts and knowledge, and when manufacturing containers by vacuum or pressure forming metallized resin sheets, it is possible to manufacture containers by forming metal-deposited resin sheets in vacuum or under pressure. The upper part of the opening edge c of the special molded container is actively stretched to create a finely divided state in which no discharge occurs in the metal vapor deposited layer on the opening edge c, as well as on the bottom surface a and side walls of the container. As a result, it is possible to obtain a container that does not cause electrical discharge throughout the container.

As a means for actively stretching the sheet portion of the opening edge c of the container, as shown in FIGS. An annular groove 13 is formed surrounding the groove 12.

The illustrated mold 10 is a so-called multi-cavity vacuum molding mold in which a plurality of container molding recesses 11 are formed on the mold surface.

/1 indicates a vacuum hole opened in each container molding recess 11.

Then, the material sheet A is heated and softened in accordance with a conventional method and placed over the mold 10 to vacuum form the intended container (solid line), and at the same time, the portion of the material sheet corresponding to the annular groove 13 is drawn into the groove 13. Or rush in.

In the illustrated example, a vacuum hole 131 is opened in the groove 13 and the sheet portion is drawn into the groove 13 by vacuum suction. A pusher 14 may be provided to push the sheet portion into the groove 13.

In this way, the sheet surface of the mold part 12 that forms the opening edge c of the container based on the drawing or thrusting of the sheet into the annular recessed groove 13 has a forming tool that acts in the width direction based on the container forming. A tensile force F1 in the direction of the concave portion 11 and a tensile force F2 in the opposite direction to the concave groove 13 act, and a tensile force F3 based on sheet retraction or thrust in the concave groove 13 at both ends in each length direction. - F3 (FIG. 7) acts, as a result of which the sheet portion undergoes active stretching in the width and length directions (i.e. length and width directions).

If the depth d of the groove 13 is increased to increase the degree of sheet retraction or entry into the groove 13, the sheet tensile forces F2, F3, and F3 will become stronger.

Therefore, the present invention uses tensile forces F2, F3, and F3 that act on the sheet surface at the container opening edge c when the sheet is pulled into or thrust into the annular groove 13 to exceed the elongation limit of the metal vapor deposited layer in the vertical and horizontal directions, respectively. The depth d of the annular groove 13 is set so as to cause positive elongation, that is, elongation of about 5% or more.

Specifically, the design depth d varies depending on various conditions such as the tensile strength of the entire material sheet A when it is heated and softened, the overall thickness, the overall shape of the container to be molded, and the width and length dimensions of the container opening edge.
may vary, and the appropriate depth d is determined on a case-by-case basis.

By doing the above, the metal vapor deposited layer 2 on the opening edge c of the container is also fragmented in the same way as on the bottom surface a and the side wall of the container. Containers made of metal vapor-deposited resin sheets that do not cause oxidation are molded.

After the molding, each molded product that has been molded in series is punched out into a number of individual pieces using a trimming press blade (not shown), for example, at position e1, e2, or e3 in Fig. 6. Separate it and make it into a product.

In the case of the compressed air molding method, an annular groove 13 of an appropriate depth is formed on the outside of the mold part 12 for molding the container opening edge c of the mold, surrounding the mold part, in the same manner as described above. A material sheet is applied to the mold to form the container using air pressure, and the sheet portion that corresponds to the annular groove is pushed in using air pressure or the pusher member 14, thereby micro-forming the entire container using the same principle as above. It is possible to mold and manufacture a container that does not cause electrical discharge due to waves.

Embodiment In the vacuum forming mold 10 shown in FIGS. 6 and 7, the individual container forming recesses 11 have bottom dimensions of about 155 mm in length and about 101 mm in width.
The opening dimensions were designed to be approximately 168 mm in length, approximately 116 mm in width, and approximately 33 mm in depth, and the width dimension of the mold portion 12 for molding the edge of the container opening connected to the opening was approximately 4 mm.

Further, regarding the above-mentioned example container molding recess 11, a depth of 10 mm is provided on the outside of the container opening edge molding mold portion 12 to surround it.
, an annular groove 13 having a width of 10 mm was formed.

A vacuum hole 131 was opened at the bottom of the annular groove 13.

As material sheet A, one side of a hard biimpact styrene resin sheet with a thickness of about 0.3 mm was coated with a purity of 99.
The material used was one in which 98% aluminum was uniformly vapor-deposited to a thickness of about 0.04 μm.

Then, the material sheet A is heated and softened at about 140° C. and applied to the vacuum forming mold 10 to perform vacuum forming of the container, and the sheet portions corresponding to the respective annular grooves 13 are also formed into the vacuum holes 13. was sufficiently drawn into the groove 13 by the suction force of .

The individual molded containers were then punched out and separated using a trimming press blade at the e1 position to obtain single containers.

Into the containers obtained above, (1) 8 minutes of cold rice, (2) 3 large pieces of raw fish, and (3) 6 pieces of halved potatoes were placed. ) was heated for 3 minutes, (2) for 6 minutes, and (3) for 10 minutes in a general household microwave oven (2450 MHz).

No abnormalities such as sparking or deformation of the container were observed at all during the set period of time, and the contents of (1) to (3) were all successfully heat-treated.

Comparative Example In the example, the vacuum hole 13 of each annular groove 13 was closed and the container was vacuum-formed without retracting the sheet portion corresponding to the groove 13, and the container was punched out at the e1 position. When the container was used in a microwave oven in the same manner as in the example, discharge was observed at the opening edge c of the container.

Note that this kind of container is preferably made of a relatively heat-resistant resin that does not easily deform when the contents are heated in a microwave oven. Polypropylene, polyester, polycarbonate, etc. are effective, and as the top coat resin, polypropylene, polyethylene, etc. are effective.

The polystyrene sheet that has conventionally been generally used as the base material sheet 1 is inferior to the above-mentioned example in terms of heat resistance.

However, there is no problem if it is used while heating within its heat resistance limit.

For reference, the following experiment was conducted in order to determine the upper limit of the size of each splitting layer 2' of the metal vapor deposited layer 2 at which no discharge occurs.

In other words, a continuous layer of metal such as aluminum (approximately 0.05 μm in thickness) is uniformly formed on one side of a base resin sheet using a conventional method as a source material, and the metal-deposited side of the material is scribed with a fine tip. Using a needle, mark a grid pattern as shown in Figures 8 and 9, and in this case, completely scrape off the evaporated metal on the 2'' part of the line. Layer 2' form.

Then, each rice is made using a grid pattern with different cutter dimensions in mm units, and each material is heated in a general microwave oven (for example, high frequency output 600 W, oscillation frequency 2450 MHz).

The presence or absence of discharge was observed by applying microwaves to the battery (power consumption 1.25KW), and the results showed that grids with a grid size of approximately 5 mm and larger caused discharge, but those with a grid size smaller than that It was discovered that none of them caused discharge.

In this case, similar discharge observations were also conducted for various types of layers in which layer 2 was divided into rectangular grid patterns in which one of the vertical and horizontal grid dimensions was 5 mm or less and the other was 5 mm or more, but in this case, discharge was observed. .

From this, the presence or absence of microwave discharge in each divided layer 2 is not only related to the size of its area, but also to its length, and in the end, the size of each divided layer 2' is approximately 5 mm in the vertical and horizontal directions.
If it is below this range, it is considered that the metal vapor-deposited sheet will not generate electric discharge due to microwaves as a whole.

Further, the shape of the dividing layer 2' is arbitrary as long as it is within the area range and is irrelevant to the discharge.

Further, the deposition thickness of each divided layer 2' is also unrelated to discharge, at least within the range of deposition thickness usually used to obtain a beautiful metallic luster.

[Brief explanation of the drawing]

Fig. 1 is a layer configuration diagram of an example of a metallized resin sheet, Fig. 2 is a perspective view of an example of a molded container, Fig. 3 is an enlarged sectional view of an example in which the trimmed end surface of the opening edge is treated with insulation coating, and Fig. Figure 4 is an enlarged plan view of the fine network crack pattern that occurs on the surface of the vapor deposited layer when the metal vapor-deposited sheet is stretched by 5% or more in the vertical and horizontal directions. An enlarged plan view of a horizontally striped crack pattern, FIG. 6 is a cross-sectional view of a part of a multi-cavity mold in which a material sheet is vacuum-formed by the method of the present invention, and FIG. 7 is a plan view of a part of the mold. , FIG. 8 is a plan view of a sheet in which the metal-deposited surface is divided into grid patterns, and FIG. 9 is a cross-sectional view thereof. 1 is a base material resin sheet, 2 is a metal vapor deposition layer, 3 is a top coat layer, 2' is a splitting layer or a dividing layer of the vapor deposited layer, 2'' is a splitting crack or a dividing line thereof, 10 is a vacuum forming mold, 11 is a 12 is an edge forming part; 13 is an annular groove provided surrounding the edge forming part; 11 and 131 are vacuum holes.

Claims (1)

[Claims] 1. When manufacturing containers for microwave ovens by vacuum or pressure forming metallized resin sheet A as a material, the molded container is relatively deep drawn and the material sheet portion corresponding to the bottom surface a and side wall of the container is Metal vapor deposition layer 2 is created vertically and horizontally using deep drawing force.
When the metal vapor deposited layer 2 is stretched at a high rate exceeding the elongation limit of In the case where the material sheet portion corresponding to the edge c has a small or substantially no stretching rate due to molding and substantially no small-area stratification occurs in the metal vapor deposited layer 2 of the material sheet portion, A groove 13 is formed in an annular shape on the outside of the mold part 12 for molding the opening edge c of the container, surrounding the mold part 12;
At the same time as the container is vacuum- or pressure-formed, the material sheet portion corresponding to the annular groove 13 is drawn into or thrust into the groove 13, and in this case, the sheet is pulled in or thrust into the groove, thereby forming the container opening edge c. The annular groove 13 is formed so that the material sheet portion is subjected to an active stretching force in the vertical and horizontal directions exceeding the elongation limit of the metal vapor deposited layer 2, thereby causing small-area split layering of the metal vapor deposited layer 2 in the material sheet portion. A method for manufacturing microwave oven containers made of a metal vapor-deposited resin sheet, characterized by setting a depth d of .