JP3137320B2 - Multilayer sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer sheet for a container which is excellent in heat resistance, rigidity, impact resistance, moldability, easy opening property and sealing property, and which can withstand retort sterilization. More specifically, the present invention eliminates sealing failure due to variations in the thickness of the flange of the container, and has a sealing property to withstand the pressure applied during retort sterilization by only flat sealing the flange portion and the lid material, and heat, The present invention also relates to a multilayer sheet for containers which has an easy-opening property and is peeled off only at the seal portion, and has excellent peeling surfaces for both the container and the cover material.

[0002]

2. Description of the Related Art Easy-open plastic sealed containers whose lids can be easily opened are widely used as food packaging containers. The most common easy-open method conventionally performed is to appropriately control the sealing strength with a container by changing the composition of a resin constituting a sealing layer of a lid material (usually 500 to 1500 g / 15 m).
m), an interface peeling or cohesive peeling type in which the interface between the lid member and the container is peeled and opened.

[0003] However, the sealing strength of this type is easily affected by the conditions at the time of sealing, environmental temperature, adhesion of contents, and the like, and the strength often varies. If this variation is biased toward the weak side, there is a danger of leaking the seal,
Conversely, if it is biased toward the strong side, the peelability will be poor and it will be difficult to open. However, since seal leakage is a fatal defect, in order to avoid this phenomenon and ensure safety, it is necessary to increase the seal strength even at the expense of easy-opening. In order to improve such a problem, a method of opening the seal layer by delamination between the seal layer and the layer adjacent thereto has been attempted, but the seal layer does not break well with a normal seal, and it is difficult to take out the contents. There are difficulties.

Further, a structure in which a notch is formed in a flange portion to facilitate separation of a peeling layer from an adjacent layer has been proposed (Japanese Patent Application Laid-Open Nos. 62-251363 and 63-251).
No. 78, 63-25037). However, in the case of these structural containers, since the outside of the cut portion must be sealed at the manufacturing stage, there is a manufacturing problem that requires strict control of the position setting at the time of sealing. In addition, in the method of peeling the main body container sealing layer, in order to seal up to the peripheral edge of the flange portion,
The peeling has to be started from the peripheral edge, which has the disadvantage that the shape of the container is also restricted.

Further, as described in Japanese Patent Application Laid-Open No. 2-98560, by providing a weakening line for starting peeling outside the flange portion and a weakening line for stopping peeling inside the flange portion and a hole portion, the sealing plate can be formed. There has also been proposed a structure that eliminates the inconvenience in the manufacturing process that the position accuracy must be strictly set. However, in the case of this structural container, there is a drawback that a step of providing a weakening line on the outside and inside of the flange portion and further providing a hole portion is required, which increases costs.

As a measure for solving this drawback, Japanese Patent Laid-Open Publication No. Hei.
As described in Japanese Patent No. 148464, the innermost layer thickness of the seal portion of the flange portion with the lid material, the innermost layer thickness of the inflection point portion, and the breaking strength of the innermost layer material are limited, and the innermost layer material at the inflection point portion is limited. There has also been proposed a structure in which the inner layer has a breaking strength smaller than the peel strength of the innermost layer and the layer in contact with the innermost layer, and can be easily opened with a flat seal alone. However, in the case of this structural container, a special mold and clamp are required to form the inflection point, and after opening the lid material, the inflection point of the part from the inner edge of the innermost seal part to the inside of the flange or the flange paragraph There is a disadvantage that the innermost non-seal portion adheres to the lid material to impair the appearance.

[0007] Further, the thickness accuracy of the container flange portion is important in container forming by vacuum forming and pressure forming, and if the variation in the thickness becomes large, there is a possibility that the sealing performance may be impaired due to sealing leakage in the sealing step with the lid material. Normal,
Sealing is performed at a sealing surface pressure of about 15 kg / cm ² . In order to prevent the leakage of the seal due to the thickness variation of the flange portion, a method of increasing the pressure of the seal or performing the linear sealing has been performed. Further, in the molding of the container, the thickness of the flange portion is adjusted by the sheet heating temperature, the heating time, the timing of the assist plug, and the like, but the control is difficult.

[0008]

SUMMARY OF THE INVENTION In the prior art, the sealing performance and the easy-opening property due to delamination, which are contradictory performances in the prior art, are inconvenient in the manufacturing process. Accordingly, it is an object of the present invention to provide a sheet for an easily-openable sealed container which can achieve both compatibility and eliminate sealing failure due to variation in thickness of a flange portion.

[0009]

According to the present invention, a polyethylene resin is used for a sealing layer, and a buffer layer made of a resin such as a polypropylene resin and an ethylene-methacrylic acid copolymer is provided adjacent to the sealing layer. Thus, even when the various conditions at the time of sealing slightly fluctuate, the sealing property and the delamination property of the sealing portion in the multilayer container are compatible. That is, the seal layer having a peeling function is made of a polyethylene resin, and the buffer layer adjacent to the seal layer is made of a polypropylene resin and an ethylene-methacrylic acid copolymer, a polypropylene resin and an ethylene-methyl methacrylate copolymer or a mixture thereof. Wherein the thickness of the sealing layer is 1 to 30 μm, the thickness of the buffer layer is 10 μm or more, and the proportion of the polypropylene resin in the copolymer resin of the buffer layer is 10 to 10 μm. It is a multilayer sheet that is 90% by weight.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION As the polyethylene resin used for the seal layer of the present invention, linear low-density polyethylene resin (hereinafter referred to as LLDPE) alone, high-density polyethylene resin (hereinafter referred to as HDPE) alone, or LLDPE and HDPE are used. Are preferred. LLDPE and HDPE
Can be arbitrarily selected, and when the cutability and heat resistance are taken into consideration, the higher the proportion of HDPE, the better, and when the lower temperature sealability is taken into account, the better the proportion of LLDPE, the better the product. The thickness of the seal layer is 1 to 30μ
m is preferred, and more preferably 3 to 20 μm. 1
If it is less than μm, insufficient sealing, resistance to shock and vibration may be caused, and if it exceeds 30 μm, cutting properties may be deteriorated, opening feeling may be impaired, and appearance may be impaired due to fluffing or stringing. Considering the delicate sealing strength and heat resistance of the sealing layer, low-density polyethylene, ethylene-α-olefin copolymer, propylene-α-olefin copolymer, ethylene-vinyl acetate copolymer, polybutene, unsaturated carboxylic acid-modified polyolefin, It is also possible to blend at least one of polypropylene, polymethylpentene and the like in an amount of 3 to 30% by weight.

The buffer layer is composed of 10 to 90% by weight of a polypropylene resin and an ethylene-methacrylic acid copolymer (hereinafter referred to as EM).
AA), 10 to 90% by weight of a polypropylene resin and an ethylene-methyl methacrylate copolymer (hereinafter referred to as E).
MMA). When the proportion of the polypropylene-based resin is less than 10% by weight, the peeling strength with the seal layer is increased and the effect of easy opening is reduced. When the proportion is more than 90% by weight, the effect as the buffer layer cannot be obtained. The thickness of the buffer layer is 10 μm
If the thickness is less than 10 μm, the effect of the buffer layer cannot be obtained.

As the polypropylene resin used for the buffer layer, there are propylene homopolymer, random copolymer with ethylene, block copolymer and the like, and any of them can be used arbitrarily. Further, an arbitrary resin can be laminated outside the buffer layer. Examples of the resin to be laminated include polyethylene terephthalate (hereinafter referred to as PET), polycarbonate, polybutylene terephthalate, polypropylene (hereinafter referred to as PP), polyamide (hereinafter referred to as Ny), vinylidene chloride resin, ethylene vinyl alcohol copolymer (hereinafter referred to as EVOH), and the like. is there. The resin to be laminated is not limited to a single layer, and may be arbitrarily selected, such as a multilayer resin. In this case, the adhesive layer (hereinafter referred to as AD) is preferably an unsaturated carboxylic acid-modified polyolefin. Examples of the multilayer body to be laminated in consideration of the oxygen gas barrier and the moldability include, for example, AD / EVOH / PP, AD
/ EVOH / PET or the like can be arbitrarily selected. The multilayer sheet for containers of the present invention can be produced by a coextrusion method, a dry lamination method, or an extrusion lamination method.

[0013]

EXAMPLES The present invention will be described below by way of examples, which are merely examples, and the present invention is not limited to these examples. (Examples 1 to 10 and Comparative Examples 1 to 5) The seal layers and the buffer layers of the examples and the comparative examples were made of the resins and layer thicknesses shown in Tables 1 and 2. AD (50
μm) / EVOH (50 μm) / AD (50 μm) / P
P (500 μm), and a multilayer sheet was formed by a co-extrusion method.

The resins used in Tables 1 and 2 are as follows.・ LLDPE: Linear low-density polyethylene MI = 2 Mitsui Petrochemical
Ultrasex 2022L manufactured by Co., Ltd. ・ HDPE: High-density polyethylene MI = 8 Shellex A6080A manufactured by Nippon Polyolefin Co., Ltd. ・ PP: Polypropylene MI = 5 Polymer MI = 3 Nucrel N0903HC manufactured by Mitsui Tufone Chemical Chemicals EMMA: Ethylene-methacrylate copolymer MI = 2
Acriflift WD201 manufactured by Sumitomo Chemical Co., Ltd.

The lid is made of PET (15 μm) / Ny (15 μm).
m) / LLDPE (60 μm) film was used. The container is 65 mmφ, 70 mm by vacuum forming this multilayer sheet.
A round-shaped container with a cc flange (flange width: 5 mm) was molded into a large number of 42 pieces / 1 shot (7 rows × 6 pieces), and the temperature was set to 1 using a hollow ring-shaped seal plate.
The lid was sealed twice on the LLDPE side of the lid under the conditions of 80 ° C., a surface pressure of 8 kg / cm ² , and a sealing time of 1.5 seconds.

The following evaluation methods were used, and the evaluation results are shown in Tables 1 and 2. -The puncture pressure was measured as an internal pressure resistance test method by injecting air little by little through a hollow needle into a container in which a lid material was sealed, and measuring the internal pressure of the container when it burst. The peel feeling was evaluated as "O" when the lid material was peeled by hand and easily peelable, and "X" when the lid material was not easily peelable. After the appearance was evaluated for peeling, the appearance was evaluated as ○ when there was no stringing, fluff, or whisker near the seal portion of the container or lid, and x when there was a noticeable occurrence.・ The sealability is as follows. Five molded products at both ends in the sheet flow direction where the thickness variation of the flange part is likely to occur are randomly sampled, and the seal leakage of the flange part is visually observed. But it was x. -The overall evaluation was "good" when the peel feeling, appearance, and sealability were good and the puncture pressure was 0.5 kg / cm ² or more, and "good" was given for the others.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

The container formed by using the multi-layer sheet of the present invention has the disadvantages of the prior art in that the sealing performance with the lid material and the easy-open property due to delamination are inconvenient in the manufacturing process, and there is no restriction on the shape of the container. In addition, it is possible to achieve both by providing only a flat seal on the container flange portion, and it is suitable as a container multilayer sheet that eliminates poor sealing due to variations in container flange thickness.

Claims (4)

(57) [Claims] 1. A sealing layer having a peeling function is made of a polyethylene resin, and a polypropylene resin and an ethylene-methacrylic acid copolymer, a polypropylene resin and an ethylene-methyl methacrylate copolymer or a mixture thereof is provided adjacent to the sealing layer. A multilayer sheet comprising a buffer layer comprising a mixture. 2. The multilayer sheet according to claim 1, wherein said seal layer has a thickness of 1 to 30 μm. 3. The multilayer sheet according to claim 1, wherein the thickness of the buffer layer is 10 μm or more. 4. The multilayer sheet according to claim 1, wherein the proportion of the polypropylene resin in the copolymer resin of the buffer layer is 10 to 90% by weight.