JPH0139936B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an easy-to-open heat-sealed lid, and more particularly to an easy-to-open heat-sealed lid that has excellent tear-openability at the score portion and excellent corrosion resistance at the processed portion. Conventionally, it consists of a laminate of a metal foil base and a heat-sealable inner surface material, and the part of the laminate that should be opened inward from the periphery of the laminate to be heat-sealed is opened halfway in the thickness direction of the metal foil. The present inventors have already proposed a heat-seal lid that is divided by engraved scores and provided with an opening tab in the portion to be opened. It goes without saying that the inner surface material of this heat-seal lid must be able to form a highly reliable sealing structure with the container body by heat sealing, but at the same time, when the lid is opened by shearing the score, It must be sheared sharply along the line and at the same time as the score. In addition, in such a heat-sealing lid, a circumferential rim portion is formed between the heat-sealing peripheral portion and the center panel on which the score is engraved by drawing or extruding the laminate in the thickness direction. It is also common practice to form reinforcing ribs or recesses to facilitate gripping of the opening tab by stretch molding. During these forming processes, the inner material needs to plastically flow in response to the denaturation of the metal foil, but the heat-sealable resin, which has excellent tearability at the score position mentioned above, can be There is a tendency for fine cracks to occur in the molded part, and the metal foil corrodes through these cracks, which tends to cause problems such as a reduction in the gas barrier properties of the lid and the elution of metal into the contents. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an easy-to-open heat-sealed lid of the score-opening type, which eliminates the above-mentioned drawbacks. Another object of the present invention is to provide an easy-to-open heat-sealed lid of a laminated metal foil/heat-sealing material type that has excellent tear-openability at the score part and corrosion resistance at the drawing or stretch-forming part. There is something to do. Still another object of the present invention is to provide a scored heat-seal lid that includes a plurality of olefinic resin interior materials having a specific combination of tensile modulus. According to the present invention, there is provided an easily openable heat-sealable lid for sealing the container body by forming a heat-sealing portion with the container body, and the lid is made of a laminated layer of a metal foil base and a heat-sealable inner material. The laminate includes a score carved halfway in the thickness direction of the metal foil to define a peripheral part to be heat-sealed and a part to be opened inward from the peripheral part. , has a reinforcing structure formed by stretch molding or the like in the thickness direction of the laminate, and the inner material has an olefin resin layer with a relatively large tensile modulus on the innermost side and a reinforcing structure on the metal foil side. Provided is a heat-sealed lid that has an excellent combination of easy-openability and corrosion resistance, and is characterized by having a laminated structure with another olefin resin layer having a low tensile modulus. The present invention will be explained in detail below based on specific examples shown in the accompanying drawings. In Figures 1, 2, 3 and 4,
The heat-sealable lid 1 of the present invention comprises a peripheral portion 2 to be heat-sealed, a center panel portion 3, and an annular rim portion 4 formed between the two by drawing. This center panel portion 3 is provided with a score 6 that partitions the portion 5 to be opened, and a reinforcing structure (rib )7 is provided. An opening tab 8 is provided integrally with the portion 5 to be opened. This heat-sealable lid 1 includes a metal foil base 9 and heat-sealable inner materials 10 and 11, which will be described in detail later.
1 is attached to a metal foil base 9 via an adhesive layer 12, for example.
A protective coating layer 13 is provided on the outer surface of the metal foil base 9, if desired. Third
As clearly shown in Figs.
is provided so as to reach the middle of the metal foil base 9 in the thickness direction. The opening rib 8 has a ring-shaped grip portion 14 . In order to fix this tab 8 in the part 5 to be opened, in this embodiment an opening 16 of small cross-sectional area is provided in said part 5, close to the tear initiation part 15 (FIG. 4) of the score. It will be done. Opening tab 8
has a rivet portion 17 which is inserted into the opening 16 of the rivet portion 17 and whose tip 18
is expanded in the surface direction of the lid body and is heat-sealed to the inner surface material 11, thereby fixing the tab and sealing the tab attachment portion. In this embodiment, the rivet tip 18 of the opening tab is provided in substantially overlapping relationship with the tear initiation portion 15 of the score. In FIG. 2, which shows the easy-open lid 1 of the present invention attached to a container body, the container body is composed of a cylindrical body 19 that is open at both ends and a bottom 20 that is provided in a sealing relationship at one end of the cylindrical body 19. There is. This body part 19 is made of a flexible laminated material, and this laminated body is provided with a paper substrate 21, a metal foil 22, and a heat-sealable inner material 23, and the paper substrate 21 and the metal foil 22 are They are bonded together with a sealable resin 24, and a heat-sealable protective resin layer 25 is also provided on the outside of the paper substrate 21. Torso 19
There is a flange 26 at the open end of the lid, and the flange 26 and the lid peripheral portion 2 are sealed by heat sealing and seaming is performed. When opening the package, grasp the grip part 14 of the opening tab 8 with your fingers and lift it upward, and the rivet part 17 will serve as a fulcrum, and the crushed tip 18 of the rivet will also be lifted upward. Along with this, a cut is made in the tear starting part 15 of the score, and from then on, the score 6 is sheared as the tab 8 is pulled,
The container lid is opened. An important feature of the present invention is that the heat-sealable inner material of the lid is composed of an olefin resin layer 11 having a relatively high elastic modulus on the innermost surface side and an olefin resin layer 11 having a relatively low tensile modulus on the metal foil side. This is based on the fact that a laminated structure with the resin layer 10 provides a desirable combination of tear-openability in the score section 6 and corrosion resistance in the processed sections 4 and 7. As already mentioned, in this container lid, the score section 6
It is necessary for the laminate to be torn accurately and smoothly, but when most common heat sealants, such as low-density polyethylene, are used as the inner material, metal foils are torn at the score, whereas Therefore, the inner surface material is not torn, or even if it is torn, the tear occurs at a position different from the tearing position of the metal foil, and the opening operation is often difficult. This is because the elongation of the resin at break is too large in the low-density polyethylene mentioned above.
This seems to be because the tear position of this resin layer is not fixed to the shear position of the score. On the other hand, if a layer of crystalline polypropylene is used as the inner material, the tearing position of this resin layer is fixed at the shearing position of the score, and the tearing of the inner material layer is performed precisely and smoothly along the score. The present inventors have also already discovered that a laminate having an inner surface made of a resin with good tearability can be formed with unevenness in the thickness direction by drawing or stretch forming. When molded into a lid, the inner surface material was noticeably whitened in the areas deformed by these moldings, and many cracks were observed in the resin layer in the whitened areas. Since this crack naturally has the property of permeating liquid, the metal foil serving as the base is corroded by this crack, and the gas barrier properties of the metal foil are lost. In the present invention, by providing the olefin resin layer 10 with a small tensile elastic modulus on the metal foil side, the generation of cracks reaching the metal foil base is prevented even in the drawing part and the overhanging part, and the resin By providing the olefin resin layer 11 with a high tensile modulus on the layer 10, the tear position of the inner surface material can be adjusted to the shear position (score position) of the metal foil.
is fixed to provide excellent opening performance. Heat-sealable olefin resins include low-, medium-, or high-density polyethylene, acid-modified polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, and ionically crosslinked olefin copolymer (ionomer). A wide variety of olefin resins are known, such as polypropylene, random or block propylene-ethylene copolymers, acid-modified polypropylene, propylene-ethylene-butene-1 copolymers, or blends of two or more of these. There is. In the present invention, the resin composition and degree of crystallinity of the resin layers 10 and 11 are selected so as to satisfy the above-mentioned requirements. Generally, the ASTM D-
When the tensile elastic modulus (Kg/cm ² ) of 638 is E _L and the tensile elastic modulus of the high elastic modulus resin layer 11 is E _H , E _L = 0.4 to 10×10 ³ E _H = 3 to 20×10 ³ It is desirable to select and combine resins so that E _H −E _L =0.5 to 15×10 ³ . Table 1 below shows the tensile modulus of various olefin resins listed in "Plastics Reader" published by Plastics Age on May 10, 1978.

[Table] In the present invention, as shown in Table 1 above,
In addition to selecting the composition, crystallinity, etc. of the resin so that the tensile modulus value is the above value, reinforcing materials for the resin,
A desired combination of tensile modulus can be obtained by changing the presence or absence of fillers or the amount of fillers blended. That is, when a reinforcing material or a filler is added to a resin, the tensile modulus of the resin layer generally increases considerably. For example, if approximately 40% by weight of filler such as talc is added to HDPE, its tensile modulus will be 2.
An improvement of about 4 to 4 times is observed. Thus, in the present invention, the low elastic modulus resin layer 1
A desired combination of elastic moduli can be obtained by using an unblended olefin resin as the layer 0 and using an olefin resin containing a reinforcing material or a filler as the high elastic modulus resin layer 11. . In the present invention, it is particularly advantageous for the low elastic modulus resin layer 10 and the high elastic modulus resin layer 11 to have thermal adhesiveness to each other, but even when there is no thermal adhesiveness between them, Of course, it can be used if an adhesive layer is interposed therebetween. When the thickness of the low elastic modulus resin layer is t _L and the thickness of the high elastic modulus resin layer is t _H , from the standpoint of heat sealing performance, tearability at the score area, and corrosion resistance at the processed area, t _L It is particularly desirable that the relationship satisfies +t _H =20 to 200 microns and t _L /t _H =0.1 to 0.6. In the present invention, the olefin resin inner material of the two layers 10 and 11 can be conveniently formed by coextruding two types of resin through a multilayer die and forming a film by a T-die method, an inflation film forming method, etc. Of course, it is also possible to laminate two layers of film produced separately, or to use two layers of film.
The coextrusion melt of the layer may be applied by extrusion coating onto the metal foil. From the viewpoint of gas barrier properties, pressure resistance, drop impact resistance, etc., it is important that the score 6 is provided so as to reach the middle of the thickness direction of the metal foil 9; Depth 6 means that the thickness of the metal foil remaining on the score part is 20μ or more,
In particular, it must be such that the thickness is 30μ or more. In the present invention, light metal foil such as aluminum foil is preferably used as the metal foil, but it is of course also possible to use iron foil, steel foil, tin foil, etc. From the viewpoint of heat sterilization resistance, these metal foils are preferably subjected to pretreatment such as alumite treatment, boehmite treatment, chemical treatment with phosphoric acid and/or chromic acid, or chemical conversion treatment. The metal foil needs to have some rigidity so that it can be torn with a score, and from this point of view it is desirable to have a thickness of 50μ or more, particularly 80μ or more. The upper limit of the thickness of the metal foil is desirably 200 μm or less, particularly 150 μm or less, from the viewpoint of economy and prevention of damage to fingers etc. when opening the package. The depth of score 6 is preferably in the range of 3/10 to 7/10, particularly 2/5 to 3/5, of the thickness of the metal foil from the viewpoint of the above characteristics and ease of opening. As the adhesive layer 12, acid-modified ethylene-based or propylene-based resins are preferably used, but other known adhesives such as isocyanate-based adhesives can also be used. Note that if the low elastic modulus resin layer 10 has adhesiveness to metal foil, it is natural that there is no need to provide a special adhesive layer 12. Further, as the resin protective layer 13 in FIGS. 3 to 4, a high-strength plastic film such as a biaxially oriented polyester film, a biaxially oriented polypropylene film, a biaxially oriented nylon film, an epoxy-phenolic paint, an epoxy-urea based paint, etc. Paints, epoxy-melamine paints, vinyl paints,
A coating film such as an acrylic paint or an epoxy-acrylic paint is used. In the molding of the container lid of the present invention, drawing molding refers to molding that does not substantially cause a change in the thickness of the laminate that constitutes the lid, while stretch molding refers to a molding process that does not substantially cause a change in the thickness of the deformed portion. ) refers to molding that occurs. In the former, the periphery of the part to be changed is not fixed during molding, but in the latter, the periphery is fixed. The shape of the score may be a small circle or a raindrop in only a part of the center panel, or it may be circular, square, or shaped so as to open the entire center panel.
It can be provided in any shape such as a rectangle. 5 and 6 show other examples of the container lid of the present invention, in which the score 6 is provided in a circular shape so that the entire center panel portion 3 can be opened. The opening tab 8 has a tearing tip 27, and so that the tip 27 matches the score 6,
It is bonded to the center panel 3 at a fulcrum 28. This center panel 3 is provided with a recess 30 through the overhang molded part 29, and this recess 30
The gripping ring 14 of the opening tab 8 can be easily gripped at this position. This easy-open container lid 1 can also be used for heat-sealing a cup-shaped container 34 having a tapered side wall portion 31, a bottom portion 32 continuous to the tapered side wall portion 31, and a flange portion 33 provided at the upper end of the side wall portion. In the present invention, the container body may be a plastic cup container, particularly a plastic cup formed by vacuum forming, a uniaxially or biaxially stretched plastic cup formed by plug assist forming, pressure forming, etc., a metal foil container, a metal foil/plastic composite container, a metal foil/plastic cup, etc. Examples include paper/plastic composite containers. The heat-sealing conditions are a temperature higher than the melting point of the heat-sealable inner material, and a pressure of generally 1 to 10
Perform under pressure of Kg/cm ² gauge. This heat sealing operation can be easily performed using a heat sealing means known per se, such as a heat seal bar or high frequency induction heating. The heat-sealed portion of the container of the present invention can withstand sterilization operations such as hot filling, boiling water sterilization, and retort sterilization, and has a high degree of sealing reliability. It has the advantage that it can be stored stably over time and can be opened easily and reliably. The excellent effects of the present invention will be explained with the following examples. Examples 1 to 3 Using the materials shown in Table 2, a laminated sheet having the following composition: outer layer/aluminum foil/adhesive layer/low tensile modulus resin inner layer/high tensile modulus resin inner material was prepared in Example 1. is powder coat lamination method,
Example 2 was laminated by an extrusion coat lamination method, and Example 3 was laminated by a dry lamination method. Circular blanks were punched out from these laminated sheets, and a panel was formed into a drop-lid shape by drawing as shown in FIG. 1, and then a bead was formed at the center of the panel by stretch molding. Next, a liquid hole type score was applied to the panel part, and a small hole with a diameter of 3.5 mmφ was punched in the center. Separately, an opening tab in which an opening ring and a rivet were integrated as shown in FIG. 1 was manufactured by injection molding using the materials shown in Table 2. The rivet part of this opening tab is inserted into the small hole in the center of the lid intermediate body, and the head of the rivet is shaped as shown in FIG. 4 by ultrasonic riveting method.
It was welded to the inner resin layer by high frequency heating. The three types of molded score lids thus obtained were loaded into an enamelator, and the inner surface was coated with 1 part sodium chloride.
% and a surfactant in an aqueous solution of 0.02% to serve as a cathode, the aluminum foil side from which the outer paint has been partially peeled serves as an anode, and a metal foil is placed between the electrolyte and the metal foil.
When a voltage of 15V was applied for 5 minutes, the enamelator value was 0.00mA in each case. Therefore, the aluminum foil surface was not exposed due to cracks occurring in the inner surface material due to panel molding and bead processing. Next, Examples 1 and 3 are made of polypropylene/paper/polypropylene/aluminum foil/polypropylene, and Example 2 is made of a polyethylene/paper/polyethylene/aluminum foil/polyethylene laminate material with a diameter of 55 mmφ, a height of 132 mm, and both ends. The bottom lid, which has the same material composition as the score lid but is not scored or tabbed, is first heated with high frequency on the curled opening of the convolute type can body shown in Figure 2. It was sealed with a sealer. This container body is filled with orange juice containing 50% fruit juice heated to 80℃,
Each liquid pouch type score lid obtained in the previous step was sealed to the can body opening curl portion using a high frequency sealer. When each container filled with the contents was opened from the ring tab at the opening of the lid, the opening could be carried out smoothly along a predetermined score line. In addition, the condition of the opening after opening is delamination,
It was in good condition with no defects such as feathering. Separately, when the condition of the molded part on the inner surface of the lid was observed for each container filled with the contents after being left at room temperature for 6 months, no corrosion of the aluminum foil was observed. In addition, when tests were conducted to see if aluminum was leached into the youth contents, no aluminum was detected in any of the products. Furthermore, when each container was opened after being aged for 6 months at room temperature, the opening was performed smoothly along the score line, and no delamination or feathering occurred. Comparative Example 1 In Example 1, the inner material had a high tensile modulus of 16000 Kg/ ^cm2 , a melting point of 165°C, and an MI of 9 g/cm2.
When a single-layer polypropylene film with a density of 0.90 g/cc was used, the panel molding area and bead processing area turned white, and when the aluminum exposure was inspected using an enamellator under the same conditions as in Example 1, the enamellator The value showed 2.10mA. Further, when an aging test was conducted at room temperature for 6 months in the same manner as in Example 1 using orange juice containing 50% fruit juice as the content, corrosion of the aluminum foil was observed in the panel molding area and the bead processing area. Furthermore, when the amount of aluminum eluted was measured, it was detected to be 5.2 ppm. Comparative Example 2 In Example 1, the inner material had a low tensile modulus of 4500Kg/ ^cm2 , an MI of 7g/10min, and a density of
When a single layer polypropylene film of 0.90 g/cc was used, no whitening occurred during panel molding and bead processing, and the enamellator value was 0.00 mA under the same conditions as in Example 1, with no exposed aluminum. However, when the container was opened from the ring tab of the lid of the container filled with the contents, feather ringing occurred and it was difficult to open the container smoothly along the score. Example 4 A polymer with a carboxyl group concentration of 200 meq/100 g, a melting point of 162°C, and a maleic anhydride grafted onto the uncoated surface of a 100μ thick soft aluminum foil whose outer surface was coated with an epoxyphenol paint was used. but
20g/10min modified polypropylene 40% by weight, ethylene content 6mol%, melting point 147℃, MI 18
g/10min ethylene-propylene random copolymer 53% by weight, melting point 109℃, density 0.919
g/cc, MI of 12.0 g/10 min, a blend of 7 wt.
g/cc, melting point of 162°C, MI of 9.0 g/10 min, isotactic polypropylene was heated using a second extruder with a screw having a diameter of 90 mmφ.
Co-pressing is performed from a T-shaped two-layer die kept at 250℃,
A temporary laminate was obtained by pressure bonding with a cooling roll and a nip roll. This temporary laminate is heat-treated in an oven maintained at 220°C and then cooled to room temperature with a cooling roll, resulting in a structure of outer layer/100μm aluminum foil/25μm modified polypropylene blend layer/
A laminated sheet with a 35 μm polypropylene layer was obtained. Separately, a modified polypropylene blend and an isotactic polypropylene film are prepared,
When the tensile modulus was measured, each was 6700Kg/
^cm2 and 16500Kg/ ^cm2 . A circular blank is punched out from this laminated sheet,
As shown in FIGS. 5 and 6, panel molding was performed by the stretch molding method, and full-open scoring processing was performed. Next, an aluminum opening tab was bonded to nylon using an adhesive at the position shown in FIG. 5 on the panel portion by high-frequency induction heating. When the enamel value of the thus obtained molded score lid was measured under the same conditions as in Example 1, it was found that
0.00 mA, and no aluminum exposure due to panel molding was observed. Next, a cup as shown in FIG. 6, which was molded from a laminated sheet of epoxy phenol paint/120 μm aluminum foil/70 μm polypropylene, was filled with orange jelly, and the molded score lid was sealed using a high-frequency sealer. When the sealed container filled with the contents was heated and sterilized at 110°C for 30 minutes and then opened from the tab, it was opened smoothly along the predetermined score line. The condition of the opening after opening was good, with no defects such as delamination or feathering. Separately, when we observed the condition of the molded part on the inner surface of the lid of a container filled with the contents and heat sterilized after being left at room temperature for 6 months, no corrosion of the aluminum foil was observed. Furthermore, when the amount of aluminum eluted into the contents was measured, no amount was detected. Furthermore, when the aged sample was opened from the tab, there were no defects such as delamination or feathering, and the opening could be carried out smoothly according to the score. Example 5 Between the uncoated side of a 100μ thick soft aluminum foil whose outer surface was coated with epoxyphenol paint and the ethylene-propylene random copolymer side of the polypropylene two-layer coextruded film used in Example 1. , the maleic anhydride-modified polypropylene blend for extrusion used in Example 4 was
Using an extruder with a screw of 90 mmφ, melt extrusion was performed through a T-die at a resin temperature of 260° C. at the die portion, and temporary bonding was performed by pressing with a cooling roll and a nip roll. Next, this temporary bonded body was passed through an oven maintained at a temperature of 220°C, and rapidly cooled under pressure using a cooling roll and a nip roll, and the composition was formed by coating the outer surface/100μm aluminum foil/10μm maleic anhydride-modified polypropylene blend layer/20μm ethylene. - A laminate sheet of propylene random copolymer layer/30 μm polypropylene layer was obtained. A molded score lid similar to that in Example 4 was prepared from the obtained laminated sheet, and the same tests as in Example 4 were conducted, and no problems occurred. Example 6 In Example 2, the two-layer coextruded film of low density polyethylene and high density polyethylene was replaced with a tensile modulus of 1200 Kg/cm ² , MI of 1.2 g/10 min, and density of 0.920.
g/cc, 15μm thick low density polyethylene layer, tensile modulus 14000Kg/cm ² , melting point 132℃, density 0.955
g/cc, MI0.5g/10min high density polyethylene
When a two-layer coextruded film with a 35 μm thick resin blend layer containing 60% by weight and 40% by weight of talc was used, the conditions were the same as in Example 1, although the talc blend layer slightly whitened during molding. The enamelator value was 0.00 mA, and no aluminum exposure was observed. In addition, the test results for openability and content resistance similar to those in Example 2 were also good, with no problems at all. Comparative Example 3 In Example 3, instead of the two-layer coextruded film of ethylene-propylene random copolymer/polypropylene, a film with a melting point of 132°C and a density of 0.955 g/
cm ³ , high density polyethylene 60 with MI 0.5g/10min
When a 50 μm thick film made of a resin blend of 40% by weight and 40% by weight of talc was used, the panel molding area and bead processing area became white, and the enamel rate value was measured under the same conditions as in Example 1.
It was 1.80mA. Further, when an aging test was conducted at room temperature for 6 months in the same manner as in Example 1 using orange juice containing 50% fruit juice as the content, corrosion of the aluminum foil was observed in the panel forming part and the heat processing part. Furthermore, when the amount of aluminum eluted was measured, it was detected to be 4.9 ppm.

[Table] *Note: Remaining thickness of aluminum foil

[Brief explanation of drawings]

FIG. 1 is a plan view of a lid that is a specific example of the present invention, FIG. 2 is a sectional view showing the structure of a container in which the lid of FIG. 1 is heat-sealed, and FIG. , FIG. 4 is an enlarged sectional view of the annular rim molded part A of the lid shown in FIG. 2, FIG. 4 is an enlarged sectional view of the tab attachment part B of the lid shown in FIG. 2, and FIG. FIG. 6 is a sectional view showing the structure of a container obtained by heat-sealing the lid of FIG. Peripheral area to be heat sealed, 3 is center panel part, 4 is annular rim part, 6 is score, 7 is rib, 8 is opening tab, 9
1 is a metal foil substrate, 10 and 11 are heat-sealable inner materials, 12 is an adhesive layer, 13 is a protective coating layer, 14
15 is the ring-shaped gripping part, 15 is the tearing start part of the score,
16 is a small hole, 17 is a rivet, 18 is a tip protruding from the inner surface of the rivet, 19 is a cylindrical body of the container body, 20 is a bottom, 21 is a paper substrate, 22 is a metal foil, and 23 is a heat sealing property. Inner surface material, 24 is a heat-sealable resin layer, 25 is a heat-sealable protective resin layer, 26 is a flange portion, 27 is a tip for tearing, 28
is a fulcrum, 29 is a stretch molded part, 30 is a recessed part, 31
32 represents a tapered side wall portion, 32 represents a bottom portion, and 33 represents a flange portion.

Claims (1)

[Scope of Claims] 1. An easily openable heat-sealable lid for sealing the container body by forming a heat-sealing portion with the container body, the lid comprising a metal foil base and a heat-sealable inner surface material. Consisting of a laminate, the laminate has a score carved halfway in the thickness direction of the metal foil to demarcate a peripheral part to be heat-sealed and a part to be opened inward from the peripheral part. and a reinforcing structure formed by stretch molding or the like in the thickness direction of the laminate, and the inner material has an olefin resin layer with a relatively large tensile modulus on the innermost side and an olefin resin layer on the entire metal foil side. A heat-sealed lid that has a laminated structure with another olefin resin layer having a relatively low tensile modulus and has an excellent combination of easy opening and corrosion resistance.