JP4817858B2 - Lid material - Google Patents

Description

  The present invention relates to a lid used for packaging containers for foods, pharmaceuticals, chemicals and the like that require gas barrier properties.

As one form of food packaging, a container body formed from a polypropylene resin sheet or the like is filled with food contents, and then a lid material is hermetically sealed on the upper portion of the container body. In particular, when the food is jelly, pudding, teacup, etc., the contents are filled and hermetically sealed, and then boiled or retorted for sterilization of the contents. The laminated film, which is a material, is thermally shrunk, and there is a package with a beautiful pack appearance without tension and wrinkles and sagging on the lid.
In general, it is effective to use a film that is easily heat-shrinkable to a certain extent in order to prevent wrinkles and sagging of the lid material. In this case, the lid provided as an opening knob on the lid material due to the thermal shrinkage of the laminated film The problem of curling in the material knob is likely to occur. This is because a non-stretchable film made of polyolefin resin is generally used for the sealant film of the lid material from the viewpoint of sealing properties, and in order to impart shrinkage, it is stretched further with hot water shrinkage. It is necessary to use a film, and as a result, when the lid member is thermally contracted, a property that the film easily curls to the outer layer side occurs. When such curling is remarkable, there is a problem that the lid material is peeled off in a process other than the time of opening, or that the lid material knob portion is difficult to grasp with a finger at the time of opening.

In order to prevent the occurrence of curling as described above, it has been proposed to use a PET film having a low thermal shrinkage rate, but in this case, the lid material was insufficiently stretched. In addition, a biaxially stretched polyamide resin film (ONy) having a low shrinkage rate is used for the outermost layer of the lid material, and an ONy film having a high shrinkage rate by lowering the heat setting temperature after the biaxial stretching process during film production is used for the intermediate layer. However, when the heat setting temperature is lowered, the plane orientation of the resulting film becomes stronger, so the adhesive strength between the layers is not sufficient, and the interlayer between the adjacent sealant layers when opening the lid There was a problem that peeling (delamination) occurred.
Ideally, the lid material knob portion should not curl at all, but even if it is slightly curled, it is more desirable to curl downward than to curl upward on the lid material from the viewpoint of appearance or sealing. It is said that. As a method for improving the curling of such a lid material, for example, Patent Document 1 discloses a base film and an intermediate layer film having a hot water shrinkage ratio of 1.5 to 3.0% in the vertical direction and the horizontal direction. A method of laminating a sealant film on a laminated film obtained by laminating and further laminating a sealant film on the laminated film is set to 0.5 to 1.0 times the tension of the laminated film. ing. However, the laminated film obtained by such a method also has a problem in appearance due to insufficient improvement of the curl on the upper side and insufficient tension of the lid.

Japanese Patent Laid-Open No. 11-156983

  It is an object of the present invention to provide a container lid material that has excellent appearance with a small amount of curling when the container lid material is opened and boiled and curled during retort sterilization. To do.

  The present inventors have an outer layer made of a biaxially stretched polyamide film, an intermediate layer made of a coextruded biaxially stretched polyamide film of aliphatic polyamide / ethylene-vinyl alcohol copolymer / aliphatic polyamide, and a sealant in this order. It has a laminated film, and the hot water shrinkage rate when held at 95 ° C. for 5 minutes is 0.5 to 3% in both the longitudinal direction and the transverse direction for the biaxially stretched polyamide film of the outer layer. It has been found that a cover material of 0.5 to 3% in the longitudinal direction and 3.5 to 6% in the transverse direction of the axially stretched polyamide film can solve the above-described problems of the present invention.

  According to the present invention, it is possible to provide a container lid having an excellent appearance with little boil on the opening knob portion of the container lid, generation of curling during retort sterilization, especially curl to the upper side of the lid. it can.

The present invention is described in detail below.
The lid material of the present invention comprises an outer layer composed of a biaxially stretched polyamide film, an intermediate layer composed of an aliphatic polyamide / ethylene-vinyl alcohol copolymer / aliphatic polyamide coextruded biaxially stretched polyamide film, and a sealant. It has a laminated film in order.
The biaxially stretched polyamide film constituting the outer layer is made of aliphatic polyamide, aromatic polyamide or the like. Aliphatic polyamides include ring-opening polymers of cyclic lactams such as homopolymers of ε-caprolactam (nylon-6), polycondensates of aminocarboxylic acids, and dicarboxylic acids such as polyhexamethylene adipamide (nylon-66). Examples thereof include polycondensates of acids and diamines.
Among these aliphatic polyamides, ε-caprolactam homopolymer (nylon-6) and polyhexamethylene adipamide (nylon-66) are available at a low cost and can be smoothly stretched. ) Is preferred, and a homopolymer of ε-caprolactam (nylon-6) is more preferred.

The aromatic polyamide is not particularly limited, and examples thereof include resins containing 70 mol% or more of polyamide constituent units composed of xylylenediamine and an α, ω aliphatic dicarboxylic acid having 6 to 12 carbon atoms in the molecular chain. Preferably mentioned.
Specifically, homopolymers such as polymetaxylylene adipamide, polymetaxylylene pimeramide, polymetaxylylene azelamide, polyparaxylylene azelamide, polyparaxylylene decanamide, metaxylylene / paraxylylene azamide Examples of the copolymer include a amide copolymer, a metaxylylene / paraxylylene pimeramide copolymer, a metaxylylene / paraxylylene azeramide copolymer, and a metaxylylene / paraxylylene sepacamide copolymer.

In the present invention, as an outer layer made of a biaxially stretched polyamide film, a polyamide film coated with polyvinylidene chloride (PVDC), EVOH, polyvinyl alcohol (PVA), or the like, or these polyamide films with silicon oxide, aluminum oxide The film etc. which vapor-deposited etc. can also be used.
In the present invention, it is preferable to use an ε-caprolactam homopolymer (nylon-6) as the biaxially stretched polyamide film from the viewpoint of strength, printability, and cost.
The thickness of the outer layer is preferably 10 to 50 μm and more preferably 12 to 30 μm from the viewpoints of printability, strength, and cost.

  The aliphatic polyamide / ethylene-vinyl alcohol copolymer / aliphatic polyamide co-extruded biaxially stretched polyamide film constituting the intermediate layer is used as the above-described biaxially stretched polyamide film of the outer layer. In the present invention, it is preferable to use a homopolymer of ε-caprolactam (nylon-6) from the viewpoint of strength, interlayer adhesion strength with an ethylene-vinyl alcohol copolymer, and cost. .

The ethylene-vinyl alcohol copolymer (hereinafter referred to as EVOH) is not particularly limited in its kind, and any conventionally known one can be used, but in the present invention, the ethylene content is 25 to 38 mol%. In the range of 29 to 35 mol%, and the saponification degree is preferably 95 mol% or more, more preferably 98 mol% or more. When the ethylene content is in the range of 25 to 38 mol%, the melt extrudability at the time of melt extrusion becomes good, and the oxygen gas barrier property is good. Moreover, when the saponification degree of EVOH is 95 mol% or more, oxygen gas barrier properties and moisture resistance are good.
In addition to the saponified product of ethylene and vinyl acetate binary copolymer, the EVOH includes a small amount of an α-olefin such as propylene, isobutene, α-octene, α-dodecene and α-octadecene as a copolymer component; Saturated carboxylic acids, or salts thereof, partial alkyl esters, fully alkyl esters, nitriles, amides, anhydrides; unsaturated sulfonic acids, salts thereof, and the like may be included. A mixture of thermoplastic resins such as polyolefin, polyester and polyamide may be used.

As the thickness of each layer of aliphatic polyamide / EVOH / aliphatic polyamide, each of the aliphatic polyamide layers is preferably 96 to 50% of the total layer, more preferably 94 to 95%, from the viewpoint of strength, oxygen barrier property, and aroma retention. The 70% EVOH layer is preferably 4 to 50% of the total layer, more preferably 6 to 30%. The thickness of the entire intermediate layer is preferably 10 to 50 μm, more preferably 12 to 30 μm from the viewpoint of strength and cost.
Note that various additives such as a lubricant, an antistatic agent, an antioxidant, an antiblocking agent, a stabilizer, a dye, a pigment, and inorganic fine particles can be added to each of the outer layer and the intermediate layer.

  In the present invention, a sealant is applied to an outer layer composed of a biaxially stretched polyamide film and a laminated film composed of an intermediate layer composed of an aliphatic polyamide / ethylene-vinyl alcohol copolymer / aliphatic polyamide coextruded biaxially stretched polyamide film. Laminate.

The sealant is a film having heat sealability made of polyethylene, polypropylene, or the like. In the present invention, it is preferable to use an easy peel film excellent in unsealing properties.
The thickness of the sealant film is preferably 20 to 60 μm, and more preferably 25 to 50 μm.
As a method for laminating the film such as the outer layer, the intermediate layer, and the sealant, in the present invention, any of a dry laminating method and a polysand laminating method may be used. Processing is preferred.

  The thickness of the lid material of the present invention is preferably 50 to 110 μm. When the thickness of the film is within this range, a film sufficient for packaging use can be obtained from the viewpoint of balance between oxygen gas barrier property and bending pinhole resistance, wear resistance, and suitable for soft packaging use. . The thickness of the entire film is more preferably 60 to 100 μm, still more preferably 70 to 90 μm.

  Each of the outer layer and the intermediate layer constituting the lid member of the present invention can be manufactured by various methods. For example, it is preferable to manufacture by the following method. That is, a film which is substantially amorphous and not oriented (hereinafter referred to as “unstretched film”) is usually produced by a coextrusion method using aliphatic polyamide, EVOH or the like as a raw material. The unstretched film is produced, for example, by melting the above raw material with 1 to 5 extruders, extruding from a flat die or an annular die, and then rapidly cooling to obtain a flat or annular unstretched film. A coextrusion method can be employed.

Next, the above-mentioned unstretched film is usually 2.5 to at least in one direction from the viewpoint of stretching effect, film strength, etc. in the film flow direction (longitudinal direction) and in a direction perpendicular to the film direction (transverse direction). The film is stretched 5 times, preferably 2.6 to 4.0 times in the longitudinal and lateral biaxial directions.
As the biaxial stretching method, any conventionally known stretching method such as tenter-type sequential biaxial stretching, tenter-type simultaneous biaxial stretching, tubular simultaneous biaxial stretching, and the like can be adopted. For example, in the case of the tenter type sequential biaxial stretching method, the unstretched film is heated to a temperature range of 50 to 110 ° C., and stretched 2.6 to 3.5 times in the longitudinal direction by a roll type longitudinal stretching machine, Then, it can manufacture by extending | stretching 2.6 to 4.0 time in a horizontal direction within the temperature range of 60-140 degreeC with a tenter type horizontal extending | stretching machine. Moreover, in the case of the tenter type simultaneous biaxial stretching and the tubular type simultaneous biaxial stretching method, for example, in the temperature range of 60 to 130 ° C., it is manufactured by stretching 2.5 to 5 times in each axial direction simultaneously in the longitudinal and lateral directions. can do.

  It is preferable that the stretched film stretched by the above method is subsequently heat-set. Dimensional stability at room temperature can be imparted by heat setting. In this case, the treatment temperature is preferably in the range of 210 to 225 ° C, more preferably 210 to 220 ° C. If the heat setting temperature is within the above range, heat setting is sufficiently performed, stress during stretching is relaxed, and sufficient laminate strength is maintained. Moreover, sufficient mechanical strength, impact resistance and pinhole resistance of the film can be obtained, and an excellent film free from troubles such as breakage and whitening of the film surface can be obtained.

  It is preferable to perform relaxation within the range of 0 to 15% and further 3 to 10% in the lateral direction during the heat setting. By relaxing, the stress of crystallization shrinkage due to heat fixation can be relaxed. If the relaxation rate is within the above range, the film is sufficiently relaxed and uniformly relaxed in the lateral direction of the film, so that the lateral shrinkage rate becomes uniform and a film having excellent room temperature dimensional stability can be obtained. Further, since relaxation is performed following the shrinkage of the film, there is no fluttering in the film, no fluttering in the tenter, and no breakage of the film.

After the relaxation, it is cooled to a temperature of 120 to 200 ° C., preferably 150 to 200 ° C., and at that temperature, it is in the range of 0.5 to 10%, preferably 2 to 9%, more preferably 3 to 7%. Re-lateral stretching is performed.
If the re-lateral stretching temperature is within the above range, an appropriate stress at the time of stretching can be obtained and uniform stretching can be performed, so that the shrinkage rate in the lateral direction becomes uniform. In addition, heat setting is not applied after stretching, and the transverse shrinkage tends to be developed. Further, if the re-lateral stretching ratio is within the above range, a sufficient transverse shrinkage rate to follow the solidification shrinkage of the sealant is obtained, the heat seal part has a good appearance, and an appropriate shrinkage rate is obtained. Thus, troubles such as wrinkles and pattern displacement can be prevented in the printing and laminating processes.

In the present invention, the shrinkage rate when the outer layer made of the biaxially stretched polyamide film is hydrothermally treated at 95 ° C. for 5 minutes is 0.5 to 3% in both the machine direction (MD) and the transverse direction (TD), preferably 1.0 to 2.5%. If the shrinkage rate is within the above range, the lid material performs appropriate thermal shrinkage during boil and retort sterilization, so that the tension of the lid material is good and the upper curl can be further suppressed.
Further, the MD shrinkage ratio when an intermediate layer film composed of a coextruded biaxially stretched polyamide film of aliphatic polyamide / ethylene-vinyl alcohol copolymer / aliphatic polyamide was hydrothermally treated at 95 ° C. for 5 minutes was 0.5. It is -3%, Preferably it is 1.0-2.5%, It is 3.5-6% in TD, Preferably it is 4-5.5%. If the shrinkage rate is within the above range, the lid material sufficiently heat shrinks during boil and retort sterilization, and thus the tension of the lid material is good, and further the upper side curl of the knob portion can be suppressed.

In the present invention, the combination of the outer layer with the hot water area shrinkage rate that is equal to or smaller than the intermediate layer with the hot water area shrinkage rate is preferable because the curl of the obtained lid member can be reduced. Here, the area shrinkage rate is calculated by calculating the hot water shrinkage rate per unit area of each layer film from the hot water shrinkage in the vertical direction and the hot water shrinkage in the horizontal direction. After cutting and shrinking, when the length and width become 98 mm (2% shrinkage), [(100 × 100) − (98 × 98)] / 100 ² = 0.0396, that is, 3.96% is the area shrinkage rate. Become.

The lid material obtained by the method of the present invention is hermetically sealed in close contact with the opening edge of the container body filled with the contents. As a result, even by heat sterilization treatment such as boiling and retort treatment, the occurrence of curling, particularly curling on the upper side of the lid material is small, and an excellent appearance is obtained. Moreover, the lid | cover material of this invention can be used suitably for the container provided with the process of sterilizing for 5 to 120 minutes with the hot water of 70 to 100 degreeC after sealing from the point of gas-barrier property and intensity | strength. it can. Furthermore, it is possible to prevent the cover material from shrinking and shrinkage after heat sterilization and drying, and curling, especially curling on the upper side of the cover material is small, and the seal layer side curl tendency It becomes.
Moreover, as a container using the lid material of the present invention, a coextruded sheet made of polypropylene / modified polypropylene / ethylene-vinyl alcohol copolymer / modified polypropylene / polypropylene is formed from the viewpoint of gas barrier properties, waist, and transparency. A container is preferably used.

  An example of a sealed container using the lid of the present invention is shown in FIG. 1, and an example of the lid of the present invention is shown in FIG. In FIG. 1, the sealed container includes a container body 1 and a lid member 2. In FIG. 2, the lid member 2 has a lid member knob portion 21. The container body 1 is filled with an article 3 to be packaged and has an opening edge 11. The lid 2 is made of the above-described laminated film for lid.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these examples. In the following examples, the obtained film was evaluated by the following method. In addition, Table 1 and Table 2 show the film production conditions and evaluation results in each Example and the like, respectively.

(1) Hot water shrinkage The stretched polyamide film test piece is cut into a width of 120 mm and a length of 120 mm, and a line of about 100 mm is drawn on the sample in the longitudinal (MD) direction and the transverse (TD) direction. This sample is allowed to stand for 24 hours in an atmosphere of 23 ° C. and 50% RH, and the reference line is measured. The measured length is defined as a length F before the heat treatment. This sample is immersed in hot water heated to 95 ° C. for 5 minutes and further left in an atmosphere of 23 ° C. and 50% RH for 30 minutes, and then the reference line is measured to obtain a length G after heat treatment.
The heat shrinkage rate is calculated by [(F−G) / F] × 100 (%).
With the above method, each shrinkage rate in the MD direction and TD direction was measured at n = 5, and the average value was defined as the heat shrinkage rate.

(2) Fracture At the tenter exit, whether or not stable film formation for 1 hour or more is possible was visually evaluated according to the following criteria.
○: Stable film formation △: 1 or 2 breaks occurred ×: 3 or more breaks occurred (3) Curling tendency of the knob part The container was filled with water, hermetically sealed, and then heated to 85 ° C It was immersed in hot water for 30 minutes, and the degree of curling of the lid knob part after the treatment was evaluated as follows.
○: It does not curl and is flat. Or weak downward curling tendency Δ: Slightly curled but upward curled.
X: The curl is tight and the appearance is bad.

(4) Tension of lid material It was immersed in hot water heated to 85 ° C. for 30 minutes, and the appearance of the lid material after treatment was evaluated as follows.
○: No wrinkles or tarmi Δ: Some wrinkles or tarmi
X: There is no tension and there are tight wrinkles and tarmi.
(5) Delami pack at the time of opening The product was opened with an easy peel, and it was confirmed whether delamination occurred between the interlayer of the intermediate layer coextruded nylon film and the easy peel sealant film.
○: No delamination occurs ×: Delamination occurs

Example 1
Each of the following films was dry laminated, and a laminated film having a structure of ONy 15 μm / (6 Ny (6 μm) / EVOH (3 μm) / 6 Ny (6 μm)) 15 μm / easy peel 50 μm was produced under the conditions shown in Table 1. Performance evaluation was performed. The evaluation results are shown in Table 2.
Outer layer: 6Ny (Novamid 1022C6 (Mitsubishi Engineering Plastics Co., Ltd.)) was extruded with a T-die, stretched 3.0 times in the MD direction with a roll, and then stretched 3.4 times in the TD direction with a tenter. Thereafter, the film was obtained by heat-fixing at 215 ° C. and performing relaxation in the width direction of 7%.
Intermediate layer: 6Ny (Novamid 1022C6 (manufactured by Mitsubishi Engineering Plastics Co., Ltd.)) and EVOH (Soarnol DC3203FB) were coextruded with a T die in a 6Ny / EVOH / 6Ny configuration, and 3.0 in the MD direction by a roll. Double stretched, stretched 3.4 times in the TD direction with a tenter, heat-set at 215 ° C, relaxed in the width direction by 7%, and then re-stretched 5% in the 180 ° C temperature zone Obtained film.
Seal layer: Easy peel (CMPS017C (manufactured by Tosero Co., Ltd.))

Using the above-mentioned lid material, using a sheet molded article having a PP / EVOH / PP configuration of 800 μm for the cup and filling with water, the cup sealer (MFT-500 manufactured by Minamoto Co., Ltd.) is used for sealing for 2 seconds at a sealing temperature of 180. A packed product was produced. The packaged product was boiled with hot water at 85 ° C. for 20 minutes, cooled with water, allowed to stand in an atmosphere of 23 ° C. × 50% RH for 24 hours, and then evaluated.

Examples 2-6 and Comparative Examples 1-8
In Example 1, Examples 2 to 6 and Comparative Examples 1 to 8 were performed in the same manner except that the manufacturing conditions of the outer layer and the intermediate layer were as shown in Table 1. The results are shown in Table 2.

  The lid material of the present invention is suitably used for packaging containers for foods, pharmaceuticals, chemicals and the like that require gas barrier properties.

It is a fragmentary sectional view which shows the cross section of an example of the container using the lid | cover material of this invention. It is a perspective view which shows an example of the cover material of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Container body 2 Cover material 3 Packaged object 11 Opening edge 21 Cover material knob part

Claims (5)

Outer layer made of biaxially stretched polyamide film, biaxially stretched, heat-set, and then stretched again in the transverse direction by 0.5-10%, aliphatic polyamide / ethylene-vinyl alcohol copolymer / It has an intermediate layer composed of a coextruded biaxially stretched polyamide film of an aliphatic polyamide, and a laminated film having a sealant in this order, and the hot water shrinkage when held at 95 ° C. for 5 minutes is biaxially stretched in the outer layer. The polyamide film is 0.5 to 3% in both the longitudinal direction and the transverse direction, and the biaxially stretched polyamide film of the intermediate layer is 0.5 to 3% in the longitudinal direction and 3.5 to 6% in the transverse direction. Lid material. The lid according to claim 1 , wherein the biaxially stretched polyamide film of the intermediate layer is produced by stretching in the lateral direction after heat setting in an atmosphere of 120 to 200 ° C. 3. The lid | cover material of Claim 1 or 2 used for the container with which it uses for the process of sterilizing for 5 to 120 minutes with a hot water of 70 to 100 degreeC after sealing. The lid according to any one of claims 1 to 3 , wherein the curl of the lid knob portion after sterilization, cooling, and drying by boil or retort tends to cause a seal layer side curl. The lid according to any one of claims 1 to 4 , which is used for a container formed by molding a coextruded sheet made of polypropylene / modified polypropylene / ethylene-vinyl alcohol copolymer / modified polypropylene / polypropylene.

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