JPH0335736Y2 - - Google Patents

Description

[Detailed explanation of the idea]

(Industrial Application Field) The present invention relates to a heat-sealed container formed by drawing, and more particularly to a heat-sealed container having a heat-sealed structure that is easy to open and can withstand retort sterilization. (Prior art and its problems) Conventionally, single-layer or multi-layer (laminated) plastic films or sheets have been processed by vacuum forming, pressure forming,
There are various types of containers that are drawn into a cup shape with a flange using methods such as plug assist molding, press molding, and stretch molding, and that have a heat-sealed seal between the flange of the container body and the lid. It has come to be widely used as a container for preserving foods, etc. Particularly in this type of heat-sealed container, in the case of a container whose contents have been sterilized by retort, the T-peel strength after sterilization is required to be in the range of 2.3 kg/1.5 cm width or more. However, in this type of heat-sealed container, particularly in a square container, the peel strength of the heat-sealed portions at flange portions that are adjacent to each other tends to differ in peel strength. In other words, parts with high peel strength and parts with low peel strength are formed. Therefore, the minimum peel strength of the heat-sealed part is
If the value is 2.3Kg/1.5cm width or more, a portion with extremely high peel strength will be formed. The presence of such a portion with high peel strength is undesirable from the standpoint of ease of opening at the heat-sealed interface. That is, the present invention provides a heat-sealed container by drawing that has peel strength within a certain range regardless of the position of the flange around the opening, can withstand retort sterilization, and is easy to open. The technical challenge is to form a heat-sealed part. (Structure of the invention) The heat-sealing container of the invention has the following features: (a) The flange of the container body is formed with a protruding sealing surface that is oriented upward when viewed in a vertical section; (b) A plastic film or is a flange in which a protrusion formed on a flange portion (hereinafter sometimes simply referred to as a parallel flange portion) extending in a direction substantially parallel to the extrusion direction of the sheet extends in a direction substantially perpendicular to the extrusion direction of the sheet. The structure is characterized by being taller than the protrusions formed on the orthogonal flange section (hereinafter sometimes simply referred to as the orthogonal flange section). (Function) In the present invention, providing a sealing surface of a protrusion oriented upward in a vertical section on the flange portion of the container body increases the minimum peel strength of the heat-sealed portion to 2.3 kg/1.5 cm width or more. This is important for determining the value of That is, by forming a sealing surface of such a protrusion, when heat sealing with a predetermined lid material,
A protruding part of the heat seal resin is formed at the heat seal interface, and even after retort sterilization, the
A peel strength of Kg/1.5cm width or more is maintained. In addition, as shown in (b) above in the present invention,
Differentiating the height of the protrusions depending on the position of the flange corrects the difference in peel strength of the heat seal between the flanges, and allows all the flanges to be within a certain range with virtually no difference. A heat-sealed portion having peel strength is formed. That is, in this type of heat seal container,
The container body is formed by drawing a plastic film or sheet, and during this drawing, as shown in FIG. and,
Chamfering is performed in such a positional relationship that substantially orthogonal sides 2, 2 exist. In such a case, the film or sheet that is the container material can be used most effectively and without waste. However, when containers are manufactured using this method,
2-A and 2-A showing the top and side surfaces of the container.
- In figure B, flange portions 5a, 5 corresponding to sides 1, 1 parallel to the extrusion direction of the film or sheet.
A phenomenon is observed in which the peel strength at the heat-sealed portion of a is considerably lower than that at the heat-sealed portions of the flange portions 5b, 5b corresponding to the orthogonal sides 2, 2. This is thought to be due to the fact that extrusion of the film or sheet causes flow orientation in the flow direction, which brings about a difference in peelability at the heat-sealed interface. Therefore, it is necessary to set heat-sealing conditions etc. so that the peel strength at the heat-sealed portion is 2.3 kg/1.5 cm width or more after retort sterilization. Therefore, if the minimum peel strength of the heat-sealed portions of the flange portions 5a, 5a is set to 2.3 kg/1.5 cm width or more, the peel strength of the heat-sealed portions of the flange portions 5b, 5b will exceed the desired value. It will be understood that this will show an extremely high value. That is, in such a case, even if the strength is satisfactory, the problem arises that it becomes difficult to open the lid. According to the present invention, by making the height of the protrusions formed on the parallel flanges larger than the height of the protrusions formed on the orthogonal flanges, the peel strength of the heat-sealed parts in these flanges can be improved. It becomes possible to perform heat sealing so that there is no substantial difference in value, and the above-mentioned problems are effectively solved. That is, as will be described in detail later, when heat sealing is performed with the height of the protrusions increased, the degree of protrusion of the heat seal resin provided on the inner surface of the lid material from the heat seal interface increases. Therefore, the peel strength increases. Therefore, increasing the height of the protrusions in the parallel flange portion increases the peel strength in that portion, thereby making the peel strength of the heat-sealed portion of the parallel flange portion and the orthogonal flange portion substantially the same. It has a range of effects. In addition, in the present invention, the height H of the protrusion on the parallel flange portion and the height h of the protrusion on the orthogonal flange portion
It is preferable that H/h=1.05 to 1.36, especially satisfying the relationship of 1.15 to 1.25. In other words, when H/h is smaller than the above range, the degree of protrusion of the heat seal resin that occurs during heat sealing in the parallel flange portion and the degree of protrusion of the heat seal resin in the orthogonal flange portion become to the same extent. , the purpose of the present invention, which is to correct the difference in releasability between these flange parts, cannot be achieved. Also, if H/h is larger than the above range,
Since the difference in height of the protrusions becomes too large, the flange portion may be distorted and the appearance and mechanical properties of the container may be impaired. (Effects) Thus, the heat-sealed container of the present invention has a well-balanced peel strength after retort sterilization of 2.3 kg/1.5 cm width or more, and maintains sufficient ease of opening. The heat-sealing container of the present invention is particularly useful as a container for storing foods, which is filled with foods, sealed, and then heated and sterilized. (Preferred embodiment of the invention) The present invention is based on the specific example shown in the attached drawings.
This will be explained in detail below. In FIGS. 3 and 4 showing the cup-shaped or tray-shaped container body of the present invention and FIG. 5 showing an enlarged flange portion, the container body 10 is formed as a seamless integral structure made of thermoplastic resin. It consists of a circumferential side wall portion 12, a bottom portion 13 continuous to the lower end of the circumferential side wall portion, and a heat sealing flange 14 continuous to the upper end of the side wall portion. The cup-shaped or tray-shaped container body 10 is formed by drawing a plastic film or sheet by means such as vacuum forming, pressure forming, press forming, plug assist forming, and stretch forming. Further, the flanges 14a, 14a have sides 1, 1 (first side) substantially parallel to the extrusion direction of the film or sheet.
(see figure), and is the part corresponding to the flange part 14
b, 14b are portions corresponding to orthogonal sides 2, 2. In this case, the thickness of the flange 14 and the thickness of the bottom part 13 and the side wall part 12 may be the same, or
Further, the circumferential side wall portion 12 may be stretched in the axial direction to be thinned. The container may be formed from a single layer of resin or a plurality of layers of resin, provided that at least the upper surface side of the flange 14 must be formed from a heat-sealable thermoplastic resin. Most preferably, the container body comprises a multi-layer structure including a heat-sealing resin and a gas barrier resin, and in this embodiment, the container wall comprises a sixth layer.
As shown in the cross-sectional view of the figure, thermoplastic resins that have heat-sealability and moisture resistance, such as polyolefins such as polyethylene, polypropylene, and ethylene-propylene copolymers, and thermoplastics such as polyethylene terephthalate and polybutylene terephthalate. An inner surface layer 15 and an outer surface layer 16 made of polyester, a gas barrier thermoplastic resin,
For example, it has an intermediate layer 17 made of ethylene vinyl alcohol copolymer, vinylidene chloride resin, high nitrile resin, or nylon resin, and these inner and outer surface layers and the intermediate layer are made of a resin that exhibits thermal adhesive properties to both. For example, they may be bonded via adhesive layers 18 and 19 made of acid-modified olefin resin, copolyester adhesive resin, epoxy-modified thermoplastic adhesive resin, or the like. The container of the present invention is shown in the enlarged cross-sectional view in Fig. 5 and in Fig. 3.
As best shown in the parallel view of the figure, the flange portion 14 is provided with an upwardly convex protrusion 20, and the upper surface of this protrusion 20 forms an upwardly convex curved sealing surface 21 when viewed in a vertical section. To explain further, the protrusion 20
are provided over the entire circumference of the flange portion 14, thus forming an upwardly convex curved sealing surface 21 over the entire circumference of the flange portion 14 to be heat-sealed. The protrusion dimension of the protrusion 20 from the flat surface of the flange portion 14 can be arbitrarily changed depending on the container dimensions, etc., but generally speaking, the height may be in the range of 0.3 to 5 mm, particularly 0.5 to 3 mm. desirable. If this height is smaller than the above range, it will be difficult to clearly form the protruding part, which will be described in detail later.On the other hand, if it is larger than the above range, the strength of the container will be reduced.
This is disadvantageous in terms of both appearance and economy. In addition, the width of the protrusion 20 in the plane direction also varies depending on the size and purpose of the container, but generally speaking, it is 0.2
It is preferably in the range of 5 mm to 5 mm, particularly 0.5 to 3 mm. That is, when this width is narrower than the above range, it tends to be difficult to guarantee sufficient heat-sealing strength and heat-sealing reliability. On the other hand, when the width is wider than the above range, the heat-sealed width tends to become wider and it becomes difficult to open the seal by hand. Further, the curved surface 21 of the protrusion 20 may also have an arbitrary shape, for example, an arbitrary curve such as a semicircle, a semiellipse, a parabola, or a hyperbola. The lid material used in the present invention is formed from a flexible laminated material 22, as shown in FIG. 14 almost completely. In FIG. 7 showing the cross-sectional structure of the lid 22, the lid 22 includes a metal foil substrate 23 for providing gas barrier properties, and an adhesive layer 24 provided on the outside surface of the substrate. It consists of an outer surface protective resin coating layer 25, and a heat-sealing inner material layer 27 provided on the inner surface of the metal foil substrate with an adhesive layer 26 interposed therebetween. As the metal foil substrate 23, aluminum foil, copper foil, iron foil, tin foil, etc. are used.
A surface treatment known per se such as plating, chemical conversion treatment, chemical treatment, etc. may be performed. As the heat-sealing inner material 27, the same resin as that described for the container body is used, and the adhesive layers 24, 2
As 6, a urethane adhesive, an epoxy adhesive, an acid-modified olefin resin adhesive, a copolyester adhesive, etc. are used. Outer protective resin layer 2
As the material 5, a resin film known per se with excellent mechanical properties and heat resistance is used, such as a biaxially oriented polyester film (for example, polyethylene terephthalate) film, a biaxially oriented nylon film, or a biaxially oriented polypropylene film. In the case of a heat-seal structure in which the heat-sealing resin of the lid material and the heat-sealing surface of the container body are both made of polypropylene, the peel strength of the heat-sealing surface is increased to the cohesive failure strength of polypropylene. It is generally difficult to peel the interface by hand, and if peeling is forced, the container body and lid material will be destroyed. From this point of view, it is necessary to form an interfacial peeling type heat seal structure between the inner surface layer 15 serving as the heat seal surface of the container body 10 and the inner surface material layer 27 of the lid member 22. Materials for forming such an interfacial peeling type heat seal structure are already known to those skilled in the art, and for example, for heat sealing olefin resin, for example, ethylene-propylene rubber (EPM), ethylene-propylene - Non-conjugated diene rubber (EPDM), polyisobutylene, butyl rubber, polybutadiene rubber, polyisoprene rubber,
The above object can be achieved by blending a synthetic rubber such as styrene-butadiene rubber or nitrile-butadiene rubber, or an olefin resin different from the olefin resin. These synthetic rubbers or foreign olefin resins are preferably blended in an amount of 3 to 30 parts by weight, particularly 5 to 20 parts by weight, per 100 parts by weight of the base olefin resin. The heat sealing material that can withstand heat sterilization and has easy peelability is a resin composition containing 5 to 20 parts by weight of polyethylene per 100 parts by weight of polypropylene. Nos. 8-A and 8-B showing enlarged views of the main parts of the heat-sealed container of the present invention before and after heat-sealing.
In the figure, the curved sealing surface 21 of the flange portion 14
An interfacial peeling type heat-sealing surface 28 is formed between the inner surface material layer 27 of the lid material 22, and at least one of the inner and outer peripheral portions of this heat-sealing surface 28, preferably both. One of the remarkable features of the present invention is that the protruding parts 29a and 29b are formed integrally with the lid body 22 and the flange part 14. That is, in this specific example, the protruding portion 2
9a and 29b have the shape of a droplet or an ear when viewed in vertical section, and have a shape in which the thickness gradually decreases toward the center of the sealing surface. In fact, it can be seen that a groove 30 is formed between the protruding portions 29a, 29b and the flange curved surface 21, the distance of which decreases toward the center of the sealing surface 28. In addition, the protruding portion 29a,
It will also be understood that the thickness of 29b is the smallest at the base 31. Functions and Effects of Container When peeling the lid 22 from the container body 10 by grasping one end of the lid 22 in this heat-sealed container, the protruding portions 29a, 29b and the lid 22 are integrated. Because of this, no peeling occurs between the protruding parts 29a, 29b and the lid material 22, and after the bases 31 of the protruding parts 29a, 29b are broken, interfacial peeling, etc. at the sealing surface 28 progresses. . Therefore, in the container of the present invention, the initial opening force is
The breaking strength has been increased to b, and it is possible to increase the T-peel strength after sterilization (Fig. 9) to 2.3 kg/1.5 cm width or more. This is because when a heat-sealed container filled with contents is subjected to retort sterilization or when it is cooled, a pressure difference is generated inside and outside the container, and this pressure difference creates a peeling force on the inner circumference of the heat-sealed part. The same is true when the heat-sealed portion is applied, and exhibits the effect of significantly improving the initial breaking force based on the pressure difference at the heat-sealed portion. In the present invention, it is important that the protruding parts 29a, 29b have the shape shown above, that is, a droplet shape, and when the protruding parts 29a, 29b are integrated with the sealing flange 14 of the container body 10, It was found that the initial opening force after sterilization was actually lower than when a droplet-shaped protruding part was formed, and the T-
It is extremely difficult to obtain peel strength. If the heat-sealing surface of the container body is completely flat, it is difficult to form a droplet-shaped protruding part. Therefore, in the present invention, an upwardly directed protrusion 20 is formed on the heat-sealing part. , the importance of forming a curved sealing surface 21 will be appreciated. In addition, in the present invention, the above-mentioned protrusion 20 is
Height H at parallel flange portions 14a, 14a
and the height h at the orthogonal flange portions 14b, 14b is 0.3 to 5 mm, particularly 0.5 to 3 mm.
Within the range of H/h=1.05 to 1.36, in particular, it is set so as to satisfy the relationship of 1.15 to 1.25. As a result, the peel strength of the parallel flange parts 14a, 14a is increased to the same level as the peel strength of the orthogonal flange parts 14b, 14b, as is clear from the examples described later, and within a certain range with no difference between the respective flange parts. A heat-sealed portion is formed having a peel strength of . That is, since the height H of the protrusion 20 provided on the parallel flange portions 14a, 14a is higher than that of the orthogonal flange portions 14b, 14b, sufficient pressure is applied to the portion during heat sealing, and the protruding portion is This is because the effect of improving peel strength is greater than that of the orthogonal flange portions 14b, 14b. As explained above, according to the present invention, the initial opening force is regulated by forming an interfacial peeling type heat seal structure in the opening part and a protruding part (droplet) breakage type opening initiation structure in front and behind it. 2.3Kg/cm
While maintaining the above values, it is possible to create an easy-to-open structure that allows the lid to be opened by hand, and the package can be subjected to retort sterilization after filling and sealing the contents. This advantage is also achieved. Manufacture of Heat-Seal Container In manufacturing the heat-seal container of the present invention, a film or sheet obtained by extrusion molding of the resin constituting the container body described above is heated to a temperature at which it can be thermoformed. In this state, it is drawn into a substantially rectangular shape, for example, a cup shape, with flanges having a predetermined height relationship, using means such as vacuum forming, pressure forming, plug assist forming, press forming, and stretch forming. molded. After filling this rectangular container body with the contents, a lid member whose inner surface is made of heat-sealable resin is heat-sealed at the flange portion of the container body. Heat sealing conditions such as temperature, time, pressure, etc.
Although it varies significantly depending on the type and physical properties of the heat-sealing resin used, as mentioned above, within the range where the resin protrudes into the specified shape from the heat-sealed part and easy opening is maintained, it is 2.3 kg / 1.5 cm width or less. T of
- It may be set to have peel strength. The present invention described above is particularly effective for square containers, but is of course also applicable to containers having an opening shape such as circular or elliptical. In this case, the relationship between the parallel flange portion, the orthogonal flange portion, and the extrusion direction is as shown in FIG. (Example) The present invention will be explained with the following example. Example 1 A low-density polyethylene-polypropylene mixture (melt index: 0.6 g/10 min) containing 13% by weight of low-density polyethylene was heated to a diameter of 65 mm.
A sheet with a thickness of 0.6 mm was formed using a sheet forming apparatus consisting of an extruder equipped with a full-flight screw with an effective length of 1430 mm, a T-die, and three vertical cooling rolls. This sheet was heated to 190°C and formed by plug-assisted vacuum-pressure forming to the outer diameter (maximum distance between opposite sides of the square container) shown in the plan view in Figure 3 and the longitudinal cross-sectional view in Figure 4.
A container measuring 107mm and 17mm in height was molded. In addition, the width (W) of the convex seal part is 1.5 mm,
The height H of the convex seal part of the parallel flange part is 0.83
mm, the height h of the convex seal part of the orthogonal flange part is
It was set to 0.7mm. (H/h=1.18) As a sealing lid, dry lamination and extrusion of a laminate film consisting of 12 micron biaxially oriented polyethylene terephthalate/15 micron biaxially oriented nylon 6/20 micron aluminum foil/40 micron polypropylene/polyethylene blend composition Molded using coating method. Fill the container almost completely with water, attach the lid so that the polypropylene/polyethylene blend layer of the lid material serves as the sealing surface, and use a hot disc sealer set at 220°C to give 3 kg/cm ²
(Compressed air pressure of an air cylinder having a cylinder diameter of 80 mmφ) Hot plate heat sealing was performed for 1.8 seconds. Fifty containers filled with water and heat-sealed with lids were subjected to constant differential pressure retort sterilization at 120°C for 30 minutes. All 50 containers sterilized by retort showed no peeling of the seal portion during retorting, and the sealing properties were not lost by retorting. Furthermore, when we randomly selected 10 containers from these 50 retort containers and attempted to peel off the entire lid using a Karasulo (reference number 32 in Figure 3), all of them were easily peelable. When three of these retort-sterilized containers were randomly sampled and the cross-section of the sealed portion was observed using a stereomicroscope, the cross-sectional shape was as shown in Figure 8-B. The sealed width was approximately 1 mm on average, and the length of the protruding portion was 98 microns on average. Next, randomly select 10 containers from the retort sterilized containers, cut 15 mm wide pieces perpendicular to the four sides of the container,
The 90 degree peeling shown in FIG. 9 was carried out at a peeling speed of 300 mm/min. One sample was taken from each side of one container, and the peel strength was measured. The results are shown in Table 1.

[Table] From the above results, the heat seal container of the present invention has
It is understood that the peel strength is adjusted within a certain range in a well-balanced manner for each side. Comparative Example 1 A heat-sealed container was manufactured in the same manner as in Example 1, except that the height of the convex seal portion was uniformly set to 0.65 mm. After retort sterilization of this heat-sealed container, the peel strength was measured on each side in the same manner as in Example 1. The results were as shown in Table-2.

[Table] From the above results, a considerable difference is recognized between the peel strength of the parallel flange portion and the peel strength of the orthogonal flange portion. Example 2 In the same manner as in Example 1, low-density polyethylene containing 13% by weight of low-density polyethylene in the inner and outer layers was prepared.
Polypropylene mixture (melt index:
0.6g/10min), a multilayer sheet (thickness
1.0mm), and the height H (mm) of the convex seal part of the parallel flange part and the height h (mm) of the convex seal part of the orthogonal flange part are cut by vacuum-pressure forming method. A rectangular container was molded. These containers were heat-sealed with sealing lids under the same conditions as in Example 1, and sterilized by retort. Randomly select 10 containers from the retort sterilized containers, cut 1.5 cm wide pieces perpendicular to the four sides of the container,
90 degree peeling was performed at a peeling speed of 300 mm/min. One sample was taken from each side of one container, and the peel strength was measured. The results are shown in Table 3.

【table】 [Brief explanation of drawings]

Fig. 1 is a diagram showing the positional relationship of chamfering from a film or sheet when manufacturing a heat-sealing container, and Figs. 2-A and 2-B are a top view and a side cross-section of a conventional heat-sealing container. Figure 3 is a top view of the container body used in the present invention, Figure 4 is a cross-sectional view of the container body shown in Figure 3, and Figure 5 shows the main parts of the container body shown in Figure 3 together with the lid. Enlarged sectional view, No. 6
The figure is an enlarged sectional view showing an example of the layer structure of the container body, FIG. 7 is an enlarged sectional view showing an example of the layer structure of the lid material, and FIGS. 8-A and 8-B are the containers before and after heat sealing. FIG. 9 is an explanatory diagram of the peel test method in the example, and FIG. 10 is a diagram showing the relationship between the flange part and the extrusion direction in a circular container. Reference number 10 is the container body, 14 is the flange part,
15 and 27 are heat-sealable resins, 20 is a protrusion,
21 is a curved heat sealing surface, 22 is a lid material, 29
29a and 29b are protruding parts, 30 is a groove, and 31 is the base thereof.

Claims (1)

[Claims for Utility Model Registration] (1) A container body having a flange around the opening and at least the surface of the flange made of heat-sealable resin, and at least the inner surface made of heat-sealable resin. The container body is formed by drawing a plastic film or sheet, and the flange part has an upper part in a vertical section. A heat-sealed surface of a protrusion oriented toward the direction of A heat seal container characterized in that the protrusion is taller than the protrusion formed on the flange portion (orthogonal flange portion) extending substantially at right angles. (2) When the height of the protrusion on the parallel flange part is H, and the height of the protrusion on the orthogonal flange part is h, the protrusion is formed so as to satisfy H/h = 1.05 to 1.36. A heat seal container according to claim 1 of the utility model registration claim.