JP7562964B2 - Multi-layer container - Google Patents

Description

The present invention relates to a multi-container.

Multi-layer containers, also known as freshness-preserving containers, airless bottles, or peelable laminated containers, are known as containers that can hold contents such as liquid seasonings or liquid cosmetics and preserve their freshness (see, for example, Patent Document 1).

JP 2017-186059 A

Methods of filling contents into multi-layer containers include the room temperature filling method, in which the contents are filled at room temperature, and the high temperature filling method, in which hot contents heated to a specified temperature above room temperature are filled. In the room temperature filling method, the room temperature contents are filled, and then a cap is attached to finish the filling process. On the other hand, in the high temperature filling method, after the hot filling process in which hot contents are filled into the blow-molded container in the hot filling process, a cooling process is carried out in which cooling water is sprayed over the entire container with the cap attached and sealed to cool the contents to room temperature.

In general multi-layer containers, including the multi-layer container of Patent Document 1, the inner container thermally shrinks due to high-temperature filling, causing the gap (hereinafter simply referred to as the "gap") formed between the outer container and the inner container to be in a decompressed state. As a result, cooling water sprayed after high-temperature filling can be sucked through the gap between the cap and the mouth, and into the gap through the outside air inlet hole provided in the mouth. It is difficult to remove the cooling water that has entered the gap, and depending on the amount of water that has entered, it may be necessary to dispose of the product as a defective product.

The present invention was made in consideration of the above circumstances, and an example of the objective of the present invention is to solve the above problems. That is, an example of the objective of the present invention is to provide a multi-layer container that can prevent water from entering the gap between the inner container and the outer container that occurs after high-temperature filling.

The multi-layer container of the present invention is a multi-layer container including a container body in which an inner container for accommodating contents and an outer container which contains the inner container and has an outside air inlet hole for introducing outside air into a gap formed between the inner container and the outer container are peelably laminated, the outer container and the inner container are formed into a bottle shape by stretch blow molding using a polyester-based resin, an outside air inlet path is provided for guiding the outside air introduced from the outside air inlet hole to the gap, the difference between the shrinkage rate of the inner container due to thermal shrinkage after filling with the contents which are at a high temperature above room temperature and the shrinkage rate of the outer container is 2.5% or less, and in a cooling process which is a process after high-temperature filling of the contents and which cools the contents by spraying cooling water, when the gap becomes a negative pressure state due to the thermal shrinkage of the contents after high-temperature filling , the outside air is introduced into the gap through the outside air inlet path from the outside air inlet hole, while infiltration of the cooling water into the gap from the outside air inlet hole is prevented .

Preferably, in the multi-container, the intrinsic viscosity of the resin of the outer container is greater than the intrinsic viscosity of the resin of the inner container.

Preferably, in the multi-layer container, the intrinsic viscosity of the resin used to mold the outer container is 0.78 or more and 0.88 or less, and the intrinsic viscosity of the resin used to mold the inner container is 0.68 or more and 0.78 or less.

Preferably, in the multi-layer container, the resin of the molded outer container has an intrinsic viscosity of 0.75 or more and 0.85 or less, and the resin of the molded inner container has an intrinsic viscosity of 0.65 or more and 0.75 or less.

Preferably, in the multi-layer container, the outer container bends inward and deforms when pressed by a squeeze operation, and returns to its original shape before pressing when the pressure is released by stopping the squeeze operation, and the inner container shrinks as the contents decrease when the contents are poured out by squeezing the outer container.

Preferably, in the multi-layer container, the container body has heat resistance to the contents that are filled at temperatures above room temperature.

Preferably, in the multi-layer container, the outside air introduction hole is provided in the mouth of the container body, and the mouth of the container body is thermally crystallized.

The multi-layer container of the present invention can prevent water from penetrating into the gap between the inner container and the outer container that occurs after high-temperature filling.

FIG. 2 is a schematic diagram showing a vertical cross section of the multi-layer container according to the present embodiment. 1 is a table showing various characteristics of the outer container and inner container of the multi-layer container according to the present embodiment and various characteristics of the outer container and inner container of a conventional multi-layer container. 1 is a table showing various characteristics and evaluation results of examples and comparative examples.

The following describes an embodiment of the present invention with reference to the drawings.

In this embodiment, the direction along the central axis Z of the bottle-shaped multi-container 1 is also referred to as the "axial direction", the direction rotating around the central axis Z of the multi-container 1 as the axis of rotation is also referred to as the "circumferential direction", and the direction perpendicular to the central axis Z of the multi-container 1 is also referred to as the "radial direction". In this embodiment, the axial direction from the mouth 3 to the bottom 6 of the multi-container 1 is also referred to as the "downward direction", and the axial direction from the bottom 6 to the mouth 3 of the multi-container 1 is also referred to as the "upward direction". In this embodiment, the cross section of the multi-container 1 cut along a plane along the central axis Z of the multi-container 1 is also referred to as the "longitudinal cross section", and the cross section of the multi-container 1 cut along a plane perpendicular to the central axis Z of the multi-container 1 is also referred to as the "transverse cross section".

Figure 1 is a schematic diagram showing a vertical cross section of a multi-layer container 1 according to this embodiment. Note that the multi-layer container 1 shown in Figure 1 shows a state after the inner surface of the outer container 10 and the outer surface of the inner container 20 have been peeled off, as in the state after the contents have been filled.

The multi-layer container 1 is a container having a bottle shape. As shown in FIG. 1, the multi-layer container 1 has a mouth portion 3 which is one end of the container body 2 and has a pouring outlet 21 for the contents, a bottom portion 6 which is the other end of the container body 2 and has a grounding surface, a shoulder portion 4 which extends downward while spreading outward in the radial direction from the mouth portion 3, and a body portion 5 which extends downward from the shoulder portion 4 and is connected to the bottom portion 6.

The multi-layer container 1 comprises a bottle-shaped outer container 10 that constitutes the outer shell of the multi-layer container 1 and encloses an inner container 20, and an inner container 20 that contains the contents and has a shape that conforms to the inner surface of the outer container 10. The multi-layer container 1 is a freshness-preserving container (also called an airless bottle) in which the inner surface of the outer container 10 and the outer surface of the inner container 20 are layered in a peelable manner.

The multi-container 1 has an outside air introduction hole 11 that can introduce outside air between the outer container 10 and the inner container 20. Specifically, the outside air introduction hole 11 is provided in the mouth 3 of the outer container 10 as shown in FIG. 1, and is connected to the gap A. Alternatively, the outside air introduction hole 11 can be provided as a slit in the part where the mouth 3 of the outer container 10 and the mouth 3 of the inner container 20 are fixed. In addition, the multi-container 1 has an outside air introduction path A1 between the mouth 3 of the outer container 10 and the mouth 3 of the inner container 20, which guides the outside air introduced from the outside air introduction hole 11 to the gap A. When the gap A becomes negative pressure, the outside air is introduced from the outside air introduction hole 11 and introduced into the gap A via the outside air introduction path A1.

The outer container 10 and the inner container 20 are containers made of thermoplastic resin and are manufactured by blow molding. Preferably, the outer container 10 and the inner container 20 are manufactured by biaxial stretch blow molding using a tubular preform such as a test tube shape. Specifically, the outer container 10 and the inner container 20 are manufactured by simultaneously stretch blow molding the preform of the outer container 10 and the preform of the inner container 20 in a state where the preform of the inner container 20 is inserted into the preform of the outer container 10 and stacked. Alternatively, the outer container 10 and the inner container 20 may be manufactured by stretch blow molding the preform of the outer container 10 and then stretch blow molding the preform of the inner container 20 inside the outer container 10. In blow molding, the mouth portion 3 of the outer container 10 and the inner container 20 become the non-stretched portion, and the shoulder portion 4, the body portion 5, and the bottom portion 6 become the stretched portion.

The outer container 10 and the inner container 20 are molded using a polyester-based resin. Examples of polyester-based resins include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and copolymer polyesters thereof. Preferably, the outer container 10 and the inner container 20 are molded using a polyethylene terephthalate resin.

As an example of a method for peeling the inner container 20 from the outer container 10, the peeling is promoted by thermally shrinking the inner container 20 through a high-temperature filling process. In addition, since the high-temperature content liquid is filled in the high-temperature filling process, the mouth portion 3 may be heat-treated at the preform stage to thermally crystallize and suppress deformation of the mouth portion 3. The contents of the multi-layer container 1 may be, for example, a beverage heated to a high temperature (either hot or cold), or a liquid seasoning heated to a high temperature. Here, "high temperature" refers to a temperature at which the contents are heated to a temperature higher than room temperature, and refers to, for example, about 65°C to 85°C.

In the blow molding process for the multi-layer container 1, blow air is blown into the preform inside the heated blow mold, and the stretch rod is stretched and pressed against the blow mold, and then cooled air is blown in to mold the outer container 10 and inner container 20 in a shape that matches the blow mold.

During this process, distortion occurs in both the outer container 10 and the inner container 20 due to stretching and the like. This distortion is alleviated by heat setting the blow mold, but is not completely removed and remains in the outer container 10 and the inner container 20 after molding. For this reason, when the multi-layer container 1 is heated after molding, the residual distortion present in the outer container 10 and the inner container 20 is alleviated and thermal shrinkage occurs. In particular, in the filling process of the contents that is carried out after molding, the container is heat sterilized and the contents are filled at a high temperature, so that the multi-layer container 1 is heated after molding and thermal shrinkage occurs.

FIG. 2 is a table showing various characteristics of the outer container 10 and the inner container 20 of the multi-layer container 1 according to this embodiment and various characteristics of the outer container and the inner container of a conventional multi-layer container.
As shown in FIG. 2, in the conventional multi-layer container, the resins used are the same from the viewpoint of recyclability and production efficiency, and the resins are manufactured using resins with a relatively low intrinsic viscosity (IV) so as to be able to withstand high-temperature filling. Therefore, the amount of thermal shrinkage occurring after molding of the conventional multi-layer container is likely to be greater in the inner container than in the outer container. This is because the inner container may have a larger residual strain than the outer container. One factor that causes the residual strain of the inner container to be greater than that of the outer container is that the inner container has a geometrically higher stretch ratio than the outer container. Another factor that causes this is that when the residual strain is relieved by heat setting, the outer container is in contact with the blow mold while the inner container is not in contact with the blow mold, so the effect of relieving the residual strain by heat setting is smaller than that of the outer container. Another factor that causes this is that the thermal crystallization of the inner container is more difficult to promote than that of the outer container during heat setting, so the inner container has a lower degree of crystallization and lower heat resistance.

As described above, in conventional multi-layer containers, the amount of thermal shrinkage of the inner container is relatively greater than that of the outer container, so the outer surface of the inner container that was in close contact with the inner surface of the outer container may peel off from the inner surface of the outer container, forming a gap between the outer container and the inner container. In other words, the gap is a space formed between the outer container and the inner container as a result of the outer container and the inner container peeling off. Generally, the mouth of a multi-layer container is a non-stretched portion that is not stretched, and the bottom can be configured not to peel off, so the gap is at least a space formed by the body of the inner container and the body of the outer container peeling off due to thermal shrinkage after molding.

However, conventional multi-layer containers are manufactured using resins with a relatively low intrinsic viscosity, which means that large voids tend to form due to the difference in the amount of thermal shrinkage between the inner container and the outer container. This causes the gap to reduce pressure and become negative when the inner container thermally shrinks, resulting in the problem that the cooling water sprayed during the cooling process is sucked in through the outside air inlet and seeps into the voids.

Therefore, in the multi-layer container 1 of this embodiment, in order to reduce the difference in the amount of thermal shrinkage between the outer container 10 and the inner container 20, the intrinsic viscosities of the outer container 10 and the inner container 20 are configured as shown in Figure 2.

As shown in FIG. 2, the multi-layer container 1 of this embodiment is configured so that the intrinsic viscosity of the resin of the outer container 10 is greater than the intrinsic viscosity of the resin of the inner container 20. The intrinsic viscosity of a resin is correlated with the molecular weight of the resin, and resins with small intrinsic viscosity are often low molecular weight resins, while resins with large intrinsic viscosity are often high molecular weight resins.

The outer container 10, which is molded from a resin with a relatively high intrinsic viscosity, has relatively long molecular chains that tend to tangle when stretched during blow molding, and many of the molecular chains are difficult to move and solidify while remaining tangled, which tends to result in large residual distortion. The residual distortion of the outer container 10 is easily alleviated during heat setting, but because a resin with a relatively high intrinsic viscosity is used, thermal crystallization due to heat setting is less likely to occur than in the outer container of a conventional multi-layer container, and distortion is also less likely to be alleviated, resulting in large residual distortion. For this reason, when the outer container 10 is heated after molding, the amount of thermal shrinkage is greater than that of the outer container of a conventional multi-layer container.

On the other hand, the inner container 20, which is molded from a resin with a relatively low intrinsic viscosity, has relatively short molecular chains, similar to the inner containers of conventional multi-layer containers, and the molecular chains are less likely to become entangled when stretched in blow molding, resulting in relatively small residual distortion. The inner container 20 uses a resin with a relatively low intrinsic viscosity, so the residual distortion is relatively small, but like conventional inner containers, the residual distortion is difficult to alleviate during heat setting.

In this way, in the multi-container 1 of this embodiment, the resins of each container are set so that the intrinsic viscosity of the resin used when molding the outer container 10 is relatively higher than the intrinsic viscosity of the resin used when molding the inner container 20. As a result, the amount of thermal shrinkage of the outer container 10 approaches the amount of thermal shrinkage of the inner container 20, and the difference between the amount of thermal shrinkage of the outer container 10 and the amount of thermal shrinkage of the inner container 20 due to thermal shrinkage after molding is approximately equal or the amount of thermal shrinkage of the inner container 20 is slightly smaller, so that the amount of void A formed is reduced to the extent that the outer container 10 and the inner container 20 are peeled off. Therefore, even if the pressure of void A is reduced due to thermal shrinkage after the high-temperature filling process, cooling water will not enter void A through the outside air introduction hole 11.

In particular, in the multi-layer container 1, the resin (pellets) used to mold the outer container 10 has an intrinsic viscosity of 0.78 to 0.88, and the resin (pellets) used to mold the inner container 20 has an intrinsic viscosity of 0.68 to 0.78, so that the molded outer container 10 has an intrinsic viscosity of 0.75 to 0.85, and the molded inner container 20 has an intrinsic viscosity of 0.65 to 0.75. The intrinsic viscosity of the resin (pellets) used to mold the outer container 10 and inner container 20 is slightly higher than the intrinsic viscosity of the molded outer container 10 and inner container 20, because it is considered that when the outer container 10 and inner container 20 are molded using polyester-based resin, the intrinsic viscosity value becomes smaller due to injection molding caused by the hydrolysis reaction of the polyester-based resin.

Here, the resin used to mold the inner container 20 can be polyethylene terephthalate resin used to mold so-called heat-resistant PET bottles. Furthermore, the resin used to mold the outer container 10 can be polyethylene terephthalate resin used to mold general non-heat-resistant PET bottles. In the multi-layer container 1, the difference between the amount of thermal shrinkage of the outer container 10 and the amount of thermal shrinkage of the inner container 20 due to thermal shrinkage after molding can be reduced to be equal or slightly smaller for the inner container 20, thereby making it possible to reduce the amount of gap A to a level where the outer container 10 and the inner container 20 can be peeled off.

In addition, in order to reduce the amount of void A, it is preferable to set the difference in shrinkage rate between the outer container 10 and the inner container 20 before and after high-temperature filling to 2.5% or less. This difference in shrinkage rate is the difference in the rate at which the volumes of the outer container 10 and the inner container 20 change due to thermal shrinkage before and after high-temperature filling (shrinkage rate). By making the intrinsic viscosity of the outer container 10 relatively higher than the intrinsic viscosity of the inner container 20, the difference between the amount of thermal shrinkage of the outer container 10 and the amount of thermal shrinkage of the inner container 20 can be reduced.

In a conventional multi-layer container, as shown in FIG. 2, the difference in the amount of thermal shrinkage between the outer container and the inner container is relatively large, so the amount of void (porosity) of gap A is naturally large. In contrast, in the multi-layer container 1 of this embodiment, the amount of thermal shrinkage of the outer container 10 is larger than in a conventional multi-layer container, so the difference with the amount of thermal shrinkage of the inner container 20 is reduced, and the amount of void A formed after thermal shrinkage can be reduced.

[Action and Effect]
As described above, in the multi-layer container 1 according to the present embodiment, the outer container 10 and the inner container 20 are molded using the same type of resin and are configured to have the characteristics shown in FIG. 2. As a result, in the multi-layer container 1 according to the present embodiment, the difference between the thermal shrinkage amount of the outer container 10 and the thermal shrinkage amount of the inner container 20 can be reduced so that they are substantially equal or the inner container 20 is slightly smaller. Therefore, in the multi-layer container 1 according to the present embodiment, the difference in the thermal shrinkage amount between the outer container 10 and the inner container 20 is reduced, so that the amount of void A formed by thermal shrinkage after high-temperature filling is reduced. This means that when the void A is in a negative pressure state, the amount of outside air introduced can be controlled to a small amount. Therefore, the multi-layer container 1 according to the present embodiment 1 can prevent the cooling water sprayed in the cooling process after the high-temperature filling process from being sucked into the void A, and can suppress the occurrence of defective products in which water has entered the void A.

[others]
In the above-described embodiment, the multi-layer container 1 is a container in which the outer container 10 forms the outer shell of the multi-layer container 1 and the inner container 20 contains the contents. However, the multi-layer container 1 is not limited to a container in which the outer container 10 forms the outer shell of the multi-layer container 1 and the inner container 20 contains the contents. In other words, the multi-layer container 1 may have a container that forms the outer shell of the multi-layer container 1 provided further outside the outer container 10, or a container that contains the contents provided further inside the inner container 20. In this way, the multi-layer container 1 only needs to function as a laminate in which the outer container 10 and the inner container 20 are peelably stacked adjacent to each other and form a gap A between them, and may naturally be a container having a triple or more multi-layer structure capable of forming a plurality of gaps A.

In the above embodiment, the multi-layer container 1 corresponds to an example of a "multi-layer container" as described in the claims. The container body 2 corresponds to an example of a "container body" as described in the claims. The mouth portion 3 corresponds to an example of a "mouth portion" as described in the claims. The outer container 10 corresponds to an example of an "outer container" as described in the claims. The inner container 20 corresponds to an example of an "inner container" as described in the claims. The outside air introduction hole 11 corresponds to an example of an "outside air introduction hole" as described in the claims. The gap A corresponds to an example of a "gap" as described in the claims. The outside air introduction path A1 corresponds to an example of an "outside air introduction path" as described in the claims.

The terms used in the above embodiments and claims should be interpreted as open-ended terms. For example, the term "including" should be interpreted as "not limited to what is described as including." The term "comprises" should be interpreted as "not limited to what is described as comprising." The term "has" should be interpreted as "not limited to what is described as having."

The present invention will be described in more detail below using examples, but the present invention is not limited to these.

1. Preparation of multiple containers
- Preform molding -
The preforms for the outer container and the inner container were produced by injection molding using an existing injection molding machine using the PET resin used in Example 1. Similarly, the preforms for the outer container and the inner container were each produced by injection molding using the PET resin used in Comparative Examples 1 to 3.
- Molding of multi-layer containers -
The preform to become the inner container was inserted into the preform to become the outer container of Example 1, and heated to 100 to 110°C in this stacked state, after which the preform to become the outer container and the preform to become the inner container were simultaneously stretch-blow molded to obtain a multi-layer container 1. Similarly, the preform to become the outer container and the preform to become the inner container were simultaneously stretch-blow molded to obtain a multi-layer container for Comparative Examples 1 to 3. The multi-layer containers produced in Example 1 and Comparative Examples 1 to 3 each had a full capacity (maximum amount of liquid that can be accommodated in the container) of about 460 ml.

2. Heat shrink method for multi-layer containers
The prepared multi-layer container was filled with 400 g of hot water heated to 75°C as the content, and after sealing the opening with a cap, it was kept in an upright position for 5 minutes. The cap used was a cap equipped with an outside air inlet that can introduce outside air into the outside air inlet hole, and a check valve that opens the outside air inlet when introducing outside air and closes the outside air inlet after introducing outside air.
Next, the multi-layer container filled with hot water was cooled for 3 minutes by spraying 20° C. cooling water from a shower onto the top of the container. The amount of cooling water sprayed from the shower was set so that the temperature of the contents (water) after cooling would be 50° C. After this point, no thermal shrinkage of the multi-layer container was observed even when the temperature of the contents dropped.

3. Measurement of multi-container characteristics
3 is a table showing the various properties, measurement results, and evaluation results of the multi-layer containers of Example 1 and Comparative Examples 1 to 3. The properties (intrinsic viscosity, shrinkage rate, shrinkage amount, porosity, and void volume) of Example 1 and Comparative Examples 1 to 3 were measured and calculated by the following methods.

--Intrinsic Viscosity--
Of the multi-layer containers after blow molding, a portion near the mouth, which was a non-stretched portion that had not been thermally crystallized, was cut out, dried at 150°C for 4 hours, and then weighed out at 0.3 g. A mixed solvent of 1,1,2,2-tetrachloroethane and phenol in a weight ratio of 50:50 was added to this to adjust the concentration to 1.00 g/dl, and the mixture was stirred at 120°C for 20 minutes to completely dissolve. After cooling the dissolved solution to room temperature, the relative viscosity was measured using a relative viscometer (Y501, manufactured by Viscotek) adjusted to a temperature of 30°C, and the intrinsic viscosity was calculated.

As shown in FIG. 3, the intrinsic viscosity of the polyester resin pellets (PET resin) of the outer container and the intrinsic viscosity of the polyester resin pellets (PET resin) of the inner container used in the multi-layer container according to this embodiment (Example 1) were as follows:
Intrinsic viscosity of PET resin pellets of outer container: 0.85
Intrinsic viscosity of PET resin pellets in the inner container: 0.74
As shown in FIG. 3, the intrinsic viscosities of the polyester resin pellets (PET resin) of the outer container and the polyester resin pellets (PET resin) of the inner container used in Comparative Examples 1 to 3 were as follows.
(Comparative Example 1)
Intrinsic viscosity of PET resin pellets of outer container: 0.85
Intrinsic viscosity of PET resin pellets in the inner container: 0.85
(Comparative Example 2)
Intrinsic viscosity of PET resin pellets of outer container: 0.74
Intrinsic viscosity of PET resin pellets in the inner container: 0.74
(Comparative Example 3)
Intrinsic viscosity of PET resin pellets of outer container: 0.74
Intrinsic viscosity of PET resin pellets in the inner container: 0.85

The intrinsic viscosities of the outer container 10 and the inner container 20 of the multi-layer container 1 molded from the PET resin pellets were as follows.
Example 1
Intrinsic viscosity of outer container: 0.75
Intrinsic viscosity of inner container: 0.65
(Comparative Example 1)
Intrinsic viscosity of outer container: 0.75
Intrinsic viscosity of inner container: 0.75
(Comparative Example 2)
Intrinsic viscosity of outer container: 0.65
Intrinsic viscosity of inner container: 0.65
(Comparative Example 3)
Intrinsic viscosity of outer container: 0.65
Intrinsic viscosity of inner container: 0.75

- Shrinkage rate -
(Shrinkage rate of inner container)
A full volume (g) of water at 20°C was poured into the inner container of the multi-layer container after blow molding (hereinafter referred to as the "container before shrinkage") and the multi-layer container after heat shrinkage by the heat shrinking method (hereinafter referred to as the "container after shrinkage"), and the volumes before and after heat shrinkage were measured. The measured content volume (g) was converted to volume (cc), and the shrinkage rate (%) of the inner container was calculated from the change in volume before and after heat shrinkage. For the container after shrinkage, the cap used during filling was removed before measuring the full volume (g).
Example 1
Container shrinkage rate: 5%
(Comparative Example 1)
Inner container shrinkage rate 10%
(Comparative Example 2)
Inner container shrinkage rate: 4%
(Comparative Example 3)
Inner container shrinkage rate: 9%
(Shrinkage rate of outer container)
For the container before shrinkage, 400 g of water at 20°C was poured in as the content, and the container was capped, and in this state, the container was immersed in a container containing a predetermined amount of water as the immersion liquid, and the volume (cc) was measured by Archimedes' method. During the measurement, water was poured into the container, and the outer container had a predetermined thickness, so it was assumed that shrinkage due to water pressure could be ignored. In addition, since the container thickness was about 300 μm, which was thin enough to be negligible, the volume including the container thickness was substituted for the content (g) of the outer container.
For the shrunken container, the container filled with warm water by the above-mentioned heat shrinkage method was cooled to room temperature, and in the same manner as for the unshrunken container, it was immersed in a container with a capped state into which a predetermined amount of water was placed as an immersion liquid, and the volume (cc) was measured by the Archimedes method.
The shrinkage rate (%) of the outer container was calculated from the volume change of the outer container before and after the shrinkage.
Example 1
Outer container shrinkage rate: 3%
(Comparative Example 1)
Outer container shrinkage rate: 4%
(Comparative Example 2)
Outer container shrinkage rate 0%
(Comparative Example 3)
Outer container shrinkage rate 0%

-Difference in shrinkage rate-
The difference in shrinkage rate between the outer container and the inner container was calculated from the shrinkage rate of the inner container and the shrinkage rate of the outer container using the following formula 1.
Formula 1: "Difference in shrinkage rate (%)" = "Shrinkage rate of inner container (%)" - "Shrinkage rate of outer container (%)"
Example 1
Shrinkage rate difference: 2%
(Comparative Example 1)
Shrinkage difference: 6%
(Comparative Example 2)
Shrinkage difference: 4%
(Comparative Example 3)
Shrinkage rate difference: 9%

-Void volume and porosity-
The void volume (cc) was calculated from the following formula 2.
Formula 2: "Void volume (cc)" = "Shrinkage volume of inner container (cc)" - "Shrinkage volume of outer container (cc)"
The porosity (%) of the multi-layer container was calculated from the following formula 3.
Formula 3: "Void ratio (%)" = "Void volume (cc)" / "Full capacity of inner container before shrinkage (cc)" x 100
Example 1
Void amount: 9cc, porosity: 1.95%
(Comparative Example 1)
Void amount: 26cc, porosity: 5.65%
(Comparative Example 2)
Void amount: 18cc, porosity: 3.91%
(Comparative Example 3)
Void amount: 40cc, porosity: 8.96%

5. Evaluation Results
The presence or absence of water infiltration into the gaps of the multi-layer container of Example 1 and the multi-layer containers of Comparative Examples 1 to 3 was evaluated. The evaluation method was a visual sensory evaluation of the multi-layer containers that had been subjected to the high-temperature filling process and the cooling process by the above-mentioned heat shrinkage method. The evaluation results are shown in FIG.
--Criteria--
○: No cooling water infiltration was confirmed in the gap (good enough to be offered as a product)
×: Cooling water was found to have entered the gap (defective product that cannot be used as a product)

As shown in Figure 3, in Example 1, no water was found to have infiltrated into the gaps, and good results were obtained. As shown in Figure 3, in Example 1, by selecting a resin such that the intrinsic viscosity of the outer container was higher than that of the inner container, the amount of thermal shrinkage of the outer container approached that of the inner container, and the difference in the shrinkage rates of the outer container and the inner container was reduced, and as a result, the gaps formed after thermal shrinkage were confirmed to be smaller. Therefore, the multi-layer container of Example 1 was proven to be useful as a container for products that store high-temperature contents through a high-temperature filling process, as it prevents water sprayed during the cooling process after high-temperature filling from infiltrating into the gaps.

On the other hand, in Comparative Examples 1 to 3, as shown in Figure 3, water infiltration into the gap was confirmed. It is presumed that the reason water infiltrated into the gap was that the difference between the amount of thermal shrinkage of the outer container and the amount of thermal shrinkage of the inner container was relatively large compared to Example 1 due to the use of containers in which the intrinsic viscosity of the outer container and the inner container were equal (Comparative Example 1 and Comparative Example 2) or a container in which the intrinsic viscosity of the outer container was lower than that of the inner container (Comparative Example 3), resulting in a larger void volume in the gap that was formed as a result.

REFERENCE SIGNS LIST 1 Multi-layer container 2 Container body 3 Mouth 4 Shoulder 5 Body 6 Bottom 10 Outer container 11 Outside air introduction hole 20 Inner container 21 Spout A Space A1 Outside air introduction path S Storage space Z Central axis

Claims (7)

A multi-layer container including an inner container for accommodating a content, and an outer container for containing the inner container and having an outside air introduction hole for introducing outside air into a gap formed between the inner container and the outer container, the multi-layer container including a container body that is peelably stacked,
The outer container and the inner container are formed into a bottle shape by stretch blow molding using a polyester resin,
an outside air introduction path is provided to introduce the outside air introduced through the outside air introduction hole into the gap;
The difference between the shrinkage rate of the inner container and the shrinkage rate of the outer container due to thermal shrinkage after filling the contents at a temperature equal to or higher than room temperature is 2.5% or less;
In a cooling step after the hot filling of the contents, the contents are cooled by spraying cooling water,
When the gap is put into a negative pressure state due to the thermal contraction of the contents after the high-temperature filling , the outside air is introduced into the gap from the outside air introduction hole through the outside air introduction path.
preventing the cooling water from entering the gap through the outside air introduction hole;
Multiple containers. The intrinsic viscosity of the resin of the outer container is greater than the intrinsic viscosity of the resin of the inner container.
The multi-container of claim 1. The intrinsic viscosity of the resin used for molding the outer container is 0.78 or more and 0.88 or less,
The intrinsic viscosity of the resin used to mold the inner container is 0.68 or more and 0.78 or less.
The multi-container of claim 2. The intrinsic viscosity of the resin of the molded outer container is 0.75 or more and 0.85 or less,
The intrinsic viscosity of the resin of the molded inner container is 0.65 or more and 0.75 or less.
The multi-container according to claim 2 or 3. When the outer container is pressed by a squeezing operation, it bends inward and deforms, and when the pressure is released by stopping the squeezing operation, it returns to its original shape before the pressure was applied.
When the contents are poured out by squeezing the outer container, the inner container shrinks as the contents decrease.
The multi-layer container according to any one of claims 1 to 4. The container body has heat resistance against the contents to be filled at a temperature equal to or higher than room temperature.
The multi-layer container according to any one of claims 1 to 5. The outside air introduction hole is provided at the mouth of the container body,
The mouth of the container body is thermally crystallized.
The multi-layer container according to any one of claims 1 to 6.