JPS6213904B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a food packaging container. Specifically, the present invention relates to a method for producing food packaging containers that enable retort sterilization and significantly enrich the variety of filling materials. In recent years, containers for food packaging such as liquid beverages, whose main body is a cylindrical body made by laminating and bonding laminated sheets of synthetic resin, paper, and aluminum foil as appropriate, are rolled up, stacked, and welded at both ends. It is being used in large numbers because of its light weight, excellent display properties as a container, printability, and ease of incineration. However, such food packaging containers
Most containers use low-density polyethylene resin alone, which has good sealing properties, for both outer layers of the cylindrical body, which is the main body of the container, and the joints of the cylindrical bodies are simply overlapped and welded. No special efforts were made. On the other hand, retort sterilization is known as a relatively inexpensive device and severe sterilization conditions under high temperature and pressure. However, if retort sterilization is performed at a temperature of about 120°C with a conventional container configured as described above, the low-density polyethylene resin on the surface of the container will melt, and the outer surface of the container will melt. When sterilized by placing a large amount of them side by side, they fuse together, and when they are separated after sterilization, the film peels off. On the other hand, on the inner surface of the container, rough skin and pinholes occur, causing problems in terms of appearance and food hygiene. In addition, the strength of the joints between the container cylinder and the lid and container cylinder decreases dramatically due to the melting of the low-density polyethylene resin, and the slight pressure inside and outside the container during retort sterilization Fluctuations easily caused joints to shift and bags to break. Furthermore, the paper absorbs water from the joint end surface of the container cylinders that are simply overlapped and welded together.
The strength of the paper decreased, which caused the container itself to buckle and cause wrinkles and other deformations. Therefore, when conventional containers are used for distribution at room temperature, heat sterilization at about 90° C. is the limit, and the types of contents to be filled are extremely limited. Therefore, in order to increase the variety of filling materials, it is necessary to increase the heat sterilization conditions, and the general indicator for this is an F ₀ value of 4 or more. The F ₀ value represents the heating time required to kill a certain concentration of bacteria (spores) at a certain temperature, and is the killing time in minutes at 250°C (121°C). Other temperatures are also expressed in terms of 250〓. For example, Clostridium botulinum is said to die in 4 minutes in phosphate buffer, and F ₀ = 4
It is expressed as In order to overcome these drawbacks of conventional containers, the present inventors used thermoplastic resin, mainly high-density polyethylene resin, as the material for both outer layers of the container cylinder, and also devised improvements to the joints of the cylinder (waterproofing). I made a proposal for processing). However, it turned out that this proposal still had some shortcomings. In other words, no matter how carefully the materials of the outer layers of the container cylinder are selected and the joints of the cylinders are carefully selected, the paper in the laminated sheet made of synthetic resin, paper, and aluminum foil, with both outer layers made of synthetic resin, If the material contains more than a certain amount of moisture, when the lid material is heat-sealed, the water vapor evaporated from the paper corresponding to the sealing part will cause bubbles (usually called "blister") in the outermost resin layer of the laminated sheet. occurs. This phenomenon is most noticeable when the laminated sheet forming the container cylinder has a laminated structure of synthetic resin/paper/aluminum foil/synthetic resin from the outer surface. The container where this type of blistering has occurred must be heated to 90°C.
Although the blister remains unchanged after several degrees of hot filling and subsequent cooling process and is therefore not flooded, its appearance is impaired. Furthermore, when a similar container is retort sterilized as described above, the synthetic resin coating on the blister portion ruptures due to minute fluctuations in pressure, allowing hot water to penetrate into the paper. As a result, the strength of the container was extremely reduced, causing the container itself to buckle and wrinkles to form on its surface. Similarly, immersion in hot water caused the printing ink applied to the paper to smear, and the synthetic resin coating to peel off, resulting in a complete loss of marketability. In addition, in order to avoid such inconveniences, if the laminated structure of the laminated sheet is reversed from that described above, that is, the outer surface is stacked with synthetic resin/aluminum foil/
In the case of paper/synthetic resin, blisters are generated on the inner surface of the container and are torn during retort sterilization, resulting in the same disadvantages as described above, as well as the disadvantage of leakage of the contents. In this way, the present inventors have solved the drawbacks of the prior art, retaining the advantages of using a laminated sheet made of synthetic resin, paper, and aluminum foil as the main body of the container, and making retort sterilization possible. As a result of intensive studies, we have developed the above-mentioned method to provide a manufacturing method for food packaging containers that not only greatly increases the variety of filling materials, but also eliminates the inconvenience caused by blisters that occur in the synthetic resin coatings on both outer layers of the laminated sheet. We discovered that this objective could be achieved by selecting the materials for both outer layers of the container cylinder, devising the joining part of the cylinder, and using a laminated sheet with a specified moisture content in the paper when heat-sealing with the lid material. I came up with an invention. In other words, the gist of the present invention is to waterproof a laminated sheet made of synthetic resin, paper, and aluminum foil, with both outer layers made of thermoplastic resin mainly made of high-density polyethylene resin, overlapped, and then waterproofed on both sides and welded together. A cylindrical body is formed, and both the upper and lower openings of the obtained cylindrical body are heat-sealed with a lid material made of aluminum foil whose inner surface is coated with a synthetic resin of the same type as the synthetic resin in the laminated sheet to produce a container. The present invention provides a method for producing a food packaging container, characterized in that the paper constituting the laminated sheet has a moisture content of 6.5% by weight or less during heat sealing of the lid. The present invention will be explained in more detail below. The food packaging container obtained according to the present invention basically consists of a cylinder 1 and upper and lower lids 3, as shown in FIG. The cylindrical body 1 is formed by welding both ends of laminated sheets 2 made of synthetic resin, paper, and aluminum foil rolled up and stacked one on top of the other. Both outer layers of the laminated sheet 2 are made of a synthetic resin mainly composed of high-density polyethylene resin among thermoplastic resins. Here, high-density polyethylene resin refers to a resin with a density of 0.941 or higher, as usual. "Mainly composed of high-density polyethylene resin" includes high-density polyethylene resin alone or blended with other resins. However, if high-density polyethylene resin is used alone, there are some disadvantages in the extrusion laminate molding method that is often used for molding the laminated sheet 2 as described below, so blends with other resins are preferred. used. Therefore, the processability required for the extrusion lamination method is the ability to form thin objects (the ability to make the resin thinner, that is, the ability to form thinner films at higher speeds as the processing speed increases). Good quality and low net-in (a phenomenon in which the width of the extruded film is much smaller than the effective width of the die when forming a film using a T-die, and the thickness at both ends of the film becomes large) is required. be done. Although it was not possible to satisfy all of the above requirements using high-density polyethylene resin alone, it was found that this could be improved by blending low-density polyethylene resin with good fluidity. In the present invention, the blending amount of low density polyethylene resin is 10% by weight with respect to high density polyethylene resin.
~25% by weight, and is mainly composed of high-density polyethylene resin. If the blend amount is less than this, the effect of blending will not be produced, and if it is too large, the heat resistance will be extremely reduced. By the way, in retort sterilization under heat conditions of 120°C, the blended amount of low density polyethylene resin is limited to 25% by weight as mentioned above. Note that the low-density polyethylene resin here refers to one having a density of 0.925 or less, as usual. The laminated structure of the laminated sheet 2 is, for example, from the outer surface of the cylinder: thermoplastic resin mainly made of high-density polyethylene resin/paper/aluminum foil/thermoplastic resin mainly made of high-density polyethylene resin, but of course this However, the present invention is not limited to this, and may have a laminated structure with more layers, and may be changed as desired. Note that there is substantially an adhesive layer between each layer of the thermoplastic synthetic resin, which is mainly composed of high-density polyethylene resin, paper, and aluminum foil. This adhesive layer is interposed between the thermoplastic synthetic resin, which is mainly made of high-density polyethylene resin, and the aluminum foil, and between the aluminum foil and the paper to ensure good adhesion between each layer.
For this purpose, low density polyethylene resin can be used as the adhesive layer. In addition, paper is paperboard in the JIS terminology, and is a general term for thick paper made mainly of chemical pulp, ground wood pulp, straw pulp, waste paper, etc., and is made using a paperboard machine. This paper is hard and stiff, so it is often used as a packaging material, and there are cardboard base paper, yellow paperboard, and white paperboard, but white paperboard made by combining white paper stock is particularly preferred. used. Appropriate printing such as gravure printing is applied to the paper. The weight of paper is usually about 180 to 400 g/ ^m2 . In the present invention, such paper is basically used, and in particular, paper with a moisture content of 6.5% by weight or less is used for heat sealing the lid material as described below. Here, "at the time of heat sealing" means the time of actual heat sealing and immediately before that. If the water content of the paper is higher than 6.5% by weight, for example, if the laminated structure of the laminated sheet forming the container cylinder is synthetic resin/paper/aluminum foil/synthetic resin from the outer surface,
When heat-sealing the lid, water vapor evaporates from the paper and causes blisters on the synthetic resin on the outer surface. When a container with blisters is sterilized by retort, the synthetic resin coating on the blister part ruptures due to minute fluctuations in pressure, allowing hot water to seep into the paper. As a result, the strength of the container was extremely reduced, causing the container itself to buckle and wrinkles to form on its surface. Similarly, immersion in hot water causes the printing ink applied to the paper to smear, and the synthetic resin coating to bleed, completely losing its marketability as a food container. In addition, in order to avoid such inconveniences, if the laminated structure of the laminated sheet is changed to have synthetic resin/aluminum foil/paper/synthetic resin from the outer surface, blisters will occur on the inner surface of the container, which will tear during retort sterilization, resulting in In addition to the same inconvenience, the contents may leak. In order to adjust the moisture content of the paper to 6.5% by weight or less, the laminated sheet that makes up the cylinder is kept in an equilibrium state in a drying room that has been adjusted to a specified humidity until just before the lid material is heat-sealed, as described below. Alternatively, this can be done by adding a step of drying by blowing hot air into the entire container manufacturing process. Theoretically, even an extremely low moisture content of paper is included in the present invention as long as it is 6.5% by weight or less, but when considering actual moisture adjustment operations, the range of approximately 3% by weight to 6.5% by weight is considered to be acceptable. preferred. By adjusting the moisture content of paper within the above range, the occurrence of blisters can be suppressed or eliminated.
Further, as will be described later, a relatively high adhesive strength (90 degree peel strength) between the paper and the synthetic resin layer adjacent thereto tends to be synergistically preferable. That is, it goes without saying that the higher the adhesive strength (90 degree peel strength) between the paper and the synthetic resin in the laminated sheet 2, the better. but,
As described above, printing such as gravure printing is applied to the paper. When comparing the printed surface with such printing and the non-printed surface, the adhesive strength of the non-printed surface is approximately twice as high, although there is some variation due to the difference in pigment components. By the way, the adhesive strength on non-printed surfaces is usually
It is recognized that the amount is 100mg/15mm or more. Therefore, when heat sealing the lid material as described later, the portion of the laminated sheet 2 corresponding to the heat sealing (both the upper and lower openings of the cylinder formed by the laminated sheet 2)
The paper preferably has a non-printing surface. The explanation so far has been based on the difference in adhesive strength between paper and synthetic resin based on the difference between printed and non-printed surfaces, but even if it is the printed surface, other surface treatments etc. 100g/15mm by further applying
This does not apply if there is something that exceeds the general adhesive strength. Of course, the adhesive strength on the printed surface is 100g/
Even if the paper is less than 15 mm, the moisture content of the paper is 6% by weight.
Below, if the heat sealing temperature is less than 220°C, the occurrence of blisters can be sufficiently eliminated. On the other hand, aluminum foil is a common material often used as packaging material, and its thickness is 5μ to 150μ.
That's about it. In particular, the cylindrical main body of the container is 5μ to 20μ,
A lid with a diameter of about 100μ to 150μ is preferably used. The laminated sheet 2 made of such a material is molded by an appropriate molding method such as the extrusion lamination method as described above. To obtain the food packaging container of the present invention, first, the laminated sheets 2 are rolled up and overlapped, and both ends thereof are waterproofed and welded to form a cylinder. This "waterproofing treatment" refers to a treatment that prevents both ends of the rolled and stacked laminated sheet 2 from coming into direct contact with the contents or being exposed to the outside air.
Although various aspects are conceivable, preferred aspects will be described below. That is, a tape-shaped aluminum foil 4 coated on both sides with the same type of synthetic resin as the synthetic resin in the laminated sheet 2 is used. Here, the synthetic resin of the same type as the synthetic resin in the laminated sheet 2 basically means "mainly high-density polyethylene resin" as described above, and includes differences in density within the specified range. It is something that Thus, the aluminum foil 4 wraps each of both side ends of the laminated sheet 2 in its width direction, and at least one end of the tape-shaped aluminum foil 4 is placed inwardly within one side of the laminated sheet 2. Fold and pinch. In the embodiment shown in FIG.
An example of this is shown below. As shown in FIG. 2, the sides on which the tape-shaped aluminum foils 4 on both side ends of the laminated sheet 2 are bent as described above are within the same plane on one side of the laminated sheet 2. If the sides on which both tape-shaped aluminum foils 4 are bent are not on the same side of one side of the laminated sheet 2, that is, when the upper or lower surfaces of the laminated sheet 2 are bent on opposite sides, the laminated sheet When forming a cylindrical body by welding the ends of both rolled and stacked aluminum foils 2 and 2, the end of the tape-shaped aluminum foil 4 on the unbent side comes into contact with the filling material, resulting in food hygiene issues. Not good. The form of use of the tape-shaped aluminum foil 4 is not limited to the form shown in FIG.
The present invention also includes one in which the tip of at least one end of the tape-shaped aluminum foil 4 provided on both side ends of the laminated sheet 2 is bent inward within one side surface of the laminated sheet 2. The laminated sheet 2 with the tape-shaped aluminum foil 4 provided on both side ends is rolled up in the direction of the arrow shown in FIG. This corresponds to rolling one side of the tape-shaped aluminum foil 4, which has been bent, so that it becomes the inner surface of the container. The laminated sheet 2 rolled up in this manner is formed into a cylinder by welding the stacked ends on both sides. During this welding, one end of the tape-shaped aluminum foil 4 at both ends of the laminated sheet 2 is bent.
When the tape-shaped aluminum foil 4 is applied only to one side, the ends of the tape-shaped aluminum foils 4 adjacent to each other are sandwiched and welded together as shown in FIG. If the tape-shaped aluminum foils 4 are applied to both tape-shaped aluminum foils 4, as shown in FIG. 2, the tape-shaped aluminum foils 4 are simply made adjacent to each other and welded without overlapping each other. When one end of the tape-shaped aluminum foil 4 is bent, as shown in FIG. In this case, the welded portion becomes thick, which is not practical. In addition, when welding, a method is adopted in which the outer synthetic resin layer of the welded portion is locally heated and compressed in order to prevent the formation of blisters due to vaporization of water in the paper. In any case, the end of the laminated sheet 2 located inside the overlapping part of the cylinder obtained in this way is completely softened, and the inconvenience caused by water absorption inside the cylinder (from the water content of the filling) is eliminated. be done. Furthermore, since the ends of the tape-shaped aluminum foil 4 do not come into contact with the filling material, there is no problem in terms of food hygiene. Both the upper and lower openings of the cylindrical body are heat-sealed with a lid member 3 made of aluminum foil whose inside is coated with a synthetic resin of the same type as the synthetic resin in the laminated sheet 2. Immediately before heat sealing, the laminated sheet that makes up the cylinder is kept in an equilibrium state in a drying room that has been adjusted to a predetermined humidity, or it is dried by blowing hot air during the entire process of container manufacturing. Adjust the moisture content to 6.5% by weight or less. Heat sealing with the lid material is performed by sealing the cylindrical body 1 and the lid material 3 as shown in FIG.
are pressed together using a heated hot stamp 5 and a jaw 6. The heating temperature of the hot stamp 5 and the jaw 6 is preferably 190 to 230°C. If the heating temperature is lower than this, poor adhesion between the cylindrical body 1 and the lid member 3 will occur, and if it is higher, on the other hand, overmelted resin will flow out and the adhesive force will become weak. The food packaging container of the present invention has such a structure, and is applied to normal retort sterilization after being filled with food, such as a liquid beverage. As detailed above, the food packaging container of the present invention retains the advantages of using a laminated sheet mainly made of synthetic resin, paper, and aluminum foil, and can be sterilized by retort.
Therefore, not only can the types of filling materials be greatly increased, but also the synthetic resin films of both outer layers of the laminated sheet will not form blisters, making it extremely useful as a food container. The present invention will be further described below based on Examples, but the present invention is not limited to the following Examples unless the gist of the invention is exceeded. Examples 1 and 2 and Comparative Examples 1 and 2 A laminated sheet for forming a cylinder, a tape-shaped aluminum foil for covering the joint of the laminated sheet, and a lid material were manufactured into the following configuration by extrusion lamination method. did. Laminated sheet for cylinder formation (width 240mm): outer layer side,
Polyethylene resin ⁽¹⁾ (45μ)/Paperboard (270g/
m ² ) / LDPE ⁽²⁾ (20μ) / Aluminum foil ⁽³⁾ (12
μ)/LDPE ⁽²⁾ (20μ)/Polyethylene resin
⁽¹⁾ (65μ), inner layer tape-shaped aluminum foil (width 20
mm): Polyethylene resin ⁽¹⁾ (50μ) / Aluminum foil ⁽³⁾ (25μ) / Polyethylene resin ⁽¹⁾ (50μ) Lid material: Inner layer side, polyethylene resin ⁽¹⁾ (50μ) /
LDPE ⁽²⁾ (30μ) / Aluminum foil ⁽³⁾ ′ (130μ) (1) High-density polyethylene resin (Novatec
JV040, MI=5.0, ρ=0.968, Novatek is a registered trademark of Mitsubishi Chemical Industries, Ltd.) 80% by weight and low density polyethylene resin (Novatek-L L-300,
MI = 3.5, ρ = 0.922) 20% by weight blend. (2) Low-density polyethylene resin (Novatec-L
L-300, MI=3.5, ρ=0.922, Novatec-
(L is a registered trademark of Mitsubishi Chemical Industries, Ltd.) (3) Both sides are treated with a regular urethane anchor coating agent. (3)' Only one side in contact with LDPE is treated with a regular urethane anchor coating agent. Among these parts, there are those in which the paperboard in both the upper and lower openings (corresponding to the heat sealing part of the lid material) is printed in the same way as the other parts, and those in which the paperboard is not printed, that is, the non-printed surface (plain white). A desired number of two types of cylindrical bodies were manufactured. (Made by F, L, Hetsselmaschinenfabrik AG, HYPA system equipment.) The joints of the obtained cylinders were made as shown in Figure 3. Note that the tape-shaped aluminum foil 4 at the joint portion
(Width: 20 mm) The width at the unbent end side was approximately 8 mm. Place the obtained cylindrical body in a desiccator and JIS
According to Z8806 (humidity control method using salt saturated solution),
Water - relative humidity (RH) 100%, KCl - relative humidity (RH) 86
%, CaCl ₂ 6H ₂ O−same (RH) 33% and NaOH
- The humidity was adjusted by placing it in four types of 20°C air with the same (RH) 6% until equilibrium was reached. The moisture content of the paper in the cylindrical body whose humidity was adjusted in this way was measured according to JIS P8127, and the humidity (RH) was 22.9% by weight, 10.7% by weight, 6.2% by weight, and 6.2% by weight, respectively.
It was 3.5% by weight. Immediately after adjusting the water content of the paperboard in this way, one opening of the cylinder was heat-sealed with a lid material. For this heat sealing, the difference between the printed side and the non-printed side of the paper at both the upper and lower openings of the cylinder (corresponding to the heat sealing part of the lid material), and the difference in heat sealing temperature (190℃, 210℃) ℃ and 230℃), the number of blisters generated around the lid was counted. Table 1 shows the results.
Shown below.

[Table] As is clear from Table 1, the number of blisters that occur around the lid increases as the moisture content of the paperboard increases and as the heat sealing temperature increases. The lower the adhesive strength between resin and paperboard, the more likely it is to occur. By suppressing the water content of the paperboard to 6.5% by weight or less, the number of blisters is extremely reduced at each heat sealing temperature, and the adhesive strength between the synthetic resin and paper in the heat sealing area of the lid material is high. More favorable results have been obtained. In addition, it is clear that when the water content of paper is reduced to around 3% by weight, the occurrence of blisters is completely eliminated without being particularly affected by the adhesive strength between similar synthetic resins and paper. Example 3 In exactly the same manner as in Example 1, the moisture content of the paperboard was adjusted,
Furthermore, using a heat-sealable paperboard without printing, it was filled with 700ml of Cotia coffee (trade name, manufactured by Zenkoku Nokyo Direct Sales Co., Ltd.) at a heat-sealing temperature of 210°C, as shown in Figure 1. A container with a lid on the top and bottom was manufactured. (F, El, Hethselmashii)
Manufactured by Nenfa Brig AG, by HYPA system equipment. ) The joints of the cylindrical bodies of the resulting containers were made as shown in Figure 4. Note that the tape-shaped aluminum foil 4 at the joint portion
(Width: 20 mm) The width at the unbent end side was approximately 8 mm. This container was retort sterilized under the following conditions. The sterilizer used was ROTORZWERG・
It is a hot water rotary retort (manufactured by Stock, West Germany). Retort sterilization conditions: From the initial product temperature of 15°C, raise the temperature to 120°C in 2 minutes and hold at 120°C for 20 minutes. Set pressure 2Kg/cm ² (gauge pressure), cooling 12 minutes (under the same set pressure), rotation speed of container holding cage in retort pot 8rpm After retort sterilization, containers should not be damaged or deformed. There was no shape abnormality, and there was no water intrusion from the end face of the joint of the cylinder or water intrusion due to the occurrence of pinholes. The weight increase after sterilization was 0.3 g (most likely due to moisture absorption by the outer layer resin). The F ₀ value during the main sterilization was 6.3. Comparative Example 3 Cotia was prepared in the same manner as in Example 3, except that the tape-shaped aluminum foil was not applied to the joints of the cylinders of the container.
A container filled with coffee was obtained and further sterilized in the same manner. The container after sterilization was not broken, but the strength of the paper was extremely reduced due to the paper absorbing water from the end surface of the joint of the cylindrical body, resulting in buckling of the container and deformation such as wrinkles. Can be seen. Additionally, the weight of the container increased by 13.7g. Example 4 A container filled with Cochia coffee was obtained and then sterilized in the same manner as in Example 3, except that the sterilization conditions were changed as follows. Retort sterilization conditions: Temperature rise time 2 from initial product temperature 18℃
Achieve the temperature of 125℃ in minutes and hold at 125℃ for 20 minutes. Set pressure: 2.5 Kg/cm ² (gauge pressure), cooling for 14 minutes (under the same set pressure), rotation speed of the container holding gauge in the retort pot: 8 r.pm There was no change in the container. The weight increase of the container after retort sterilization was 0.4 g. The F ₀ value during the main sterilization was 20.6. Comparative Example 4 Cotia was prepared in the same manner as in Example 4, except that the tape-shaped aluminum foil was not applied to the joints of the cylinders of the container.
A container filled with coffee was obtained and further sterilized in the same manner. After sterilization, the container was not broken, but the strength of the paper was extremely reduced due to water absorption from the end surface of the joint of the cylindrical body, causing the container to buckle and show deformation such as wrinkles. It was done. The weight increase after sterilization was 14.1g.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view of the container of the present invention, FIG. 2 is a sectional view showing a laminated sheet coated with tape-shaped aluminum foil, FIG. FIG. 4 is an enlarged partial cross-sectional view of the joint of another example of the container cylindrical body, and FIG. 5 is a schematic cross-sectional view showing the state of heat sealing with the lid material. 1: Cylindrical body, 2: Laminated sheet constituting the cylinder body, 2
a: thermoplastic resin mainly consisting of high-density polyethylene resin, 2b: paper, 2c: aluminum foil, 3: lid material,
4: Tape-shaped aluminum foil, 5: Hot stamp,
6: Jiyo.

Claims (1)

[Claims] 1 Laminated sheets made of synthetic resin, paper, and aluminum foil with both outer layers made of thermoplastic resin, mainly high-density polyethylene resin, are rolled up and stacked on top of each other, and both ends are waterproofed and welded to form a cylinder. and a method for producing a container by heat sealing both the upper and lower openings of the obtained cylinder with a lid made of aluminum foil whose inner surface is coated with a synthetic resin of the same type as the synthetic resin in the laminated sheet, the method comprising: A method for producing a food packaging container, characterized in that when heat sealing the lid material, the paper constituting the laminated sheet has a water content of 6.5% by weight or less.