JP7790102B2 - double structure container - Google Patents

Description

The present invention relates to a double-structure container, and more specifically to a double-structure container consisting of an outer container and an inner bag container inserted and held within the outer container.

Conventionally, double-layered containers having a double layered structure consisting of an inner bag container and an outer container have been used in practical applications, such as airless bottles, for storing seasoning liquids such as soy sauce. Such airless bottles are used in combination with caps equipped with check valves and air valve mechanisms. By squeezing and depressing the body wall of the bottle, which is the outer container, from the outside, the contents filled in the inner bag container are dispensed through a dispensing passage formed in the cap. When the pressure on the body wall of the bottle is stopped to terminate the dispensing of the contents, the check valve in the cap spout prevents air from flowing back into the inner bag container from the spout, and instead, air is introduced into the space between the inner bag container and the outer container through a flow path (air valve) different from the dispensing passage in the cap.
As a result, each time the contents are dispensed, the inner bag container shrinks and reduces in volume by the amount of the contents dispensed, but the outer container is able to restore its original shape. Airless bottles that dispense the contents in this way have the advantage that the desired amount of contents can be dispensed in small amounts, and because air is effectively prevented from entering the inner bag container filled with the contents, oxidation deterioration of the contents can be effectively prevented and the contents can be kept fresh for a long period of time.

In the above-described double structure, when the squeeze (pressure) on the body of the bottle (outer container) is stopped and the body of the outer container returns to its original shape after the contents have been discharged from the inner bag container, the outer surface of the inner bag container must quickly peel off from the inner surface of the body of the outer container. If the outer surface of the inner bag container is in close contact with the inner surface of the body of the outer container, air cannot be introduced between the two, which can cause the outer container to not restore its original shape or air to be sucked into the inner bag from the spout (backflow), impairing its function as an airless bottle.
In particular, when the bottle is unused, the inner bag container is in close contact with the inside of the body of the outer container, making this problem of the inner bag peeling off quite likely, which is a major issue with airless bottles.
Furthermore, as the amount of liquid remaining in the bottle decreases over time, the inner bag becomes more likely to come off the bottom of the deflated outer container. If the bottom is not fixed, the inner bag will not shrink properly, and the next time the contents are drained, the body will have to be indented to accommodate the amount of liquid that has been drained, which is another factor that impairs the bottle's functionality.

As a double-structure container that solves the above-mentioned problems, Patent Document 1 proposes a double-structure container in which a heat-resistant silicone oil release layer is provided between the inner bag container and the outer container. Furthermore, Patent Document 2 proposes a double-structure container in which liquid paraffin is used as the release layer provided between the inner bag container and the outer container.

However, in these double-structure containers, the release layer is formed from a liquid, so it easily runs off, making it difficult to maintain a thin film layer thick enough to exhibit a release effect even during actual use (initial squeezing). Furthermore, there are problems such as the release layer forming even on the bottom, where it is not actually necessary, and there is still room for improvement.

Furthermore, Patent Documents 3 and 4 propose a double-structure container in which a layer of wax is provided between the inner bag container and the outer container.

However, Patent Document 3 does not aim to improve the peelability between the inner bag container and the outer container by using a wax layer, but rather to prevent noise (squeaks) when squeezing. For this reason, the wax layer is provided fairly thickly at or near the bottom, and is not intended to form a thin, uniform peelable layer that quickly peels the outer surface of the inner bag container from the inner surface of the outer container and creates an air layer between the two.

In addition, Patent Document 4 is a technology that forms an air layer between the inner bag container and the outer container from the early stage to ensure heat insulation. Therefore, as in Patent Document 3, the wax layer formed between the inner bag container and the outer container is quite thick, and also does not form a thin and uniform peel layer that quickly peels the outer surface of the inner bag container from the inner surface of the outer container and forms an air layer between them.
Furthermore, in order to achieve the objectives of both Patent Documents 3 and 4, it is necessary to provide a fairly thick wax layer, and improvement is also required from the viewpoint of the Food Sanitation Act.

JP 2010-082916 A JP 2017-186059 A Japanese Patent Application Laid-Open No. 2019-112088 Japanese Patent Application Laid-Open No. 2020-152409

The object of the present invention is therefore to provide a double-structure container and a method for manufacturing the same, which consists of an outer container and an inner bag container inserted and held within the outer container, and which, when the outer container is squeezed to discharge the contents, forms a thin, uniform peelable layer that allows the outer surface of the inner bag container to be quickly peeled from the inner surface of the outer container, forming an air layer between the two.

According to the present invention, there is provided a double-structure container comprising an outer container and an inner bag container inserted and held within the outer container, in which the contents contained in the inner bag container are discharged by squeezing the outer surface of the body of the outer container, and as the contents are discharged, the inner bag container contracts, forming a gap between the inner bag container and the outer container,
A double-structure container is provided, characterized in that, when the contents have not been discharged and the container is unused, a coating layer of low-melting-point wax having a melting point in the range of 40°C to 70°C is present between the inner bag container and the outer container in an amount of 50 mg/m2 ^to 150 mg/ ^m2 , excluding at least the portion facing the bottom of the outer container, the low-melting-point wax is a low-crystalline paraffin wax with an n-paraffin content of less than 50% by mass, and the low-melting-point wax coating layer is a solid layer and is in close contact with at least the inner surface of the body portion of the outer container that is squeezed.

According to the present invention, a first preform having a test tube shape for molding an outer container and a second preform having a test tube shape for molding an inner bag container are further prepared,
a wax layer is formed on the outer surface of the second preform by roll coating a low-melting-point wax having a melting point of 40°C to 70°C on the stretch-molded portion excluding the bottom portion of the curved shape;
With the low-melting-point wax coating layer formed, inserting the second preform into the first preform to form a stack preform;
blow molding by supplying a blowing fluid into a second preform in the stack preform;
The method for manufacturing the double-structured container is characterized by the following.

An important feature of the double-walled container of the present invention is the use of a low-melting wax that is solid at room temperature, with a melting point in the range of 40°C to 70°C, as the release agent for separating the outer surface of the inner bag container from the inner surface of the outer container. This low-melting wax is not only solid at the temperature (room temperature) at which the double-walled container is stored and used, but also rapidly melts and becomes fluid when heated to approximately 50°C to 60°C. Therefore, this low-melting wax can be applied by roll coating to the outer surface of the inner bag preform (second preform) used to form the inner bag container, selectively forming a coating layer on areas other than the bottom, for example. Furthermore, the amount of wax applied can be easily controlled by the contact time between the applicator roll holding the wax and the outer surface of the second preform. For example, roll coating is not suitable for liquid release agents, and when applying them using methods such as spraying or dipping, masking is required to accurately determine the area to be applied, and there is also a large amount of loss due to splashing during spraying or dipping, making the application process cumbersome and costly. However, all of these problems can be overcome by applying low-melting point wax using a roller.

In this way, in the present invention, by forming a thin and uniform low-melting point wax coating peel layer, the outer surface of the inner bag container can be quickly peeled off from the inner surface of the outer container when the outer container is squeezed to eject the contents.
Furthermore, in the present invention, by using a low-crystalline paraffin wax having an n-paraffin content of less than 50% by mass as the low-melting-point wax, white granulation upon solidification can be suppressed, making it easier to use, improving application properties, and preventing deterioration of appearance. In particular, the use of such a low-crystalline paraffin wax is most preferable in order to achieve the target amount of wax required by the Food Sanitation Act.

FIG. 2 is a longitudinal cross-sectional view showing a double-structure container according to the present invention. 2A and 2B are schematic cross-sectional side views showing a first preform (a preform for molding an outer container) and a second preform (a preform for molding an inner bag container) used in manufacturing the double-structure container of FIG. 1, where (a) shows the first preform and (b) shows the second preform. 1 is a schematic cross-sectional side view showing a stack preform in which a second preform is contained and held within a first preform; FIG.

Referring to Figure 1, which shows the double-structure container of the present invention (hereinafter sometimes simply referred to as an airless container), the airless container, generally designated 1, consists of a bottle-shaped outer container 3 and an inner bag container 5 in which contents such as soy sauce are stored.

The outer container 3 includes a nozzle portion 11, a shoulder portion 13 connected to the nozzle portion 11, and a body portion 15. The body portion 15 extends to a ground portion 16, and the area surrounded by the ground portion 16 is closed by a dome-shaped recessed bottom portion 17.

The inner bag container 5 consists of a cylindrical opening 21 and a thin-walled bag-like body 23 that is connected to the cylindrical opening 21. The cylindrical opening 21 is thick and has a fixed shape (i.e., this part is not stretched and has enough rigidity to not easily deform). The bag-like body 23 is filled with the contents and shrinks and deforms as the contents are discharged.

The nozzle portion 11 of the outer container 3 is a rigid portion (non-stretched portion) that is not stretched, while the shoulder portion 13, body portion 15, and bottom portion 17 that are connected to this nozzle portion 11 are stretched portions (stretched portions). The body portion 15 of this outer container 3 is elastically deformable, and when the outer container body portion 15 is pressed, the inner bag body portion 23 is depressed. When pressure is stopped, the depressed outer container body portion 15 returns to its original shape, but the inner bag body portion 23 does not return to its original shape. This prevents air, which can cause oxidative degradation, from entering the interior of the inner bag container 5, which is filled with the contents. To ensure smooth depression due to pressure and elastic recovery when pressure is stopped, the central portion of the outer container body portion 15 is generally a squeeze region. This squeeze region generally has a slightly depressed shape to facilitate recovery.

The nozzle portion 11 of the outer container 3 has a cylindrical shape with an open top, to which a cap (not shown in FIG. 1) with a check valve function (described later) is attached by stoppering. The upper end of this nozzle portion 11 is formed with an enlarged head portion 11a, which stably holds the stoppered container lid with a check valve (hereinafter simply referred to as the cap). In addition, a support ring 11b is formed below the nozzle portion 11, which makes it easy to transport the airless container 1 (or preform) using a jig.
The cap can also be attached by providing a screw on the outer surface of the nozzle portion 11 and screwing it in place, rather than by tapping.

The nozzle portion 11 described above is a non-stretched portion that has not been stretched, and its lower portion is a stretched portion that has been stretched by blow molding. A shoulder portion 13 with an enlarged diameter is formed connected to the lower end of the nozzle portion 11, and a body portion 15 is connected to this shoulder portion 13, and the body portion 15 is closed by a bottom portion 17.
The bottom 17 of the outer container and the inner bag container 5 are fixed together by crimping during blow molding, preventing the inner bag container 5 from hanging in the air while the container is in use. The dome-shaped bottom 17 also contributes to improving the bottle's sitting position.

As can be seen from Figure 1, the inner bag container 5 is housed within the outer container 3, and its cylindrical mouth 21 (i.e., non-extended portion) extends within the nozzle portion 11 of the outer container 3 so as to form a gap between it and the inner surface of the nozzle portion 11. A fixing ring 25 is formed on the outer surface of this cylindrical mouth 21, and the outer peripheral surface of this fixing ring 25 is in close contact with the inner surface of the nozzle portion 11 of the outer container 3. As a result, the inner bag container 5 housed within the outer container 3 is held stably within the outer container 3 without rattling.

As shown in Figure 1, the fixing ring 25 has a notch 25a formed in a portion thereof to form a flow path for air to pass through. This notch 25a creates an air passage X that runs through in the axial direction, and this air passage X is connected to the outside of the airless container 1 via the air valve in the cap. This air passage X allows air to be supplied to the space Z between the bag-shaped body 23 of the inner bag container 5 and the body 15 of the outer container 3.

A container lid with a check valve (not shown in Figure 1) is attached to the airless container 1 having the above-described structure, allowing the contents contained in the bag-shaped body 23 to be discharged repeatedly and smoothly.

For example, immediately after molding, the bag-shaped body 23 of the inner bag container 5 is held in tight contact with the inner surface of the shoulder 13, body 15, and bottom 17 of the outer container 3. In this state, the contents are filled into the bag-shaped body 23 of the inner bag container 5, and a container lid with a check valve (not shown) is attached and sold. With the airless container 1 filled with contents in this way, the top lid of the container lid is opened to allow the contents to be discharged, and the body 15 (squeeze area) of the outer container 3 is pressed to discharge and remove the contents.

That is, when the body 15 (squeeze area) of the outer container 3 is pressed and depressed, the bag-shaped body 23 of the inner bag container 5, which is in close contact with the inside surface of the body 15, also depressions and enters a reduced volume state (the shape shown by the chain line in Figure 1). This causes the contents contained within the bag-shaped body 23 to be expelled. When pressure on the body 15 is stopped, the body 15 returns to its original shape due to its elasticity, and the depression disappears. Meanwhile, the bag-shaped body 23 remains in its contracted state due to volume reduction, and air, which can cause oxidative deterioration, does not enter the interior of the inner bag container 5. Therefore, a negative pressure is created in the space Z between the bag-shaped body 23 and the body 15 of the outer container 3, corresponding to the reduced volume of the contents.

In this way, space Z becomes negative pressure, but as mentioned above, because air path X leading to the outside is formed, air flows into this space Z, forming an air layer between bag-shaped body portion 23 and body portion 15 of outer container 3. Therefore, when body portion 15 is next pressed and depressed, bag-shaped body portion 23 will be pressed through this air layer.

A container lid (not shown) equipped with an air valve is placed over the air passage X, allowing air to flow in from the outside through the air passage X but preventing air from escaping to the outside. That is, when the body 15 of the outer container 3 is pressed and depressed, thereby reducing the volume of the bag-shaped body 23, an air layer is always present between the two. Therefore, even if the contents are discharged and the bag-shaped body 23 shrinks significantly as a result of the discharge, pressing the body 15 of the outer container 3 to the same extent as when the contents are full can contract the bag-shaped body 23 and allow the contents to be discharged quickly. For example, if air is discharged from space Z when the body 15 of the outer container 3 is pressed and depressed, a greater deformation of the body 15 is required to contract the bag-shaped body 23, increasing the pressure required for squeezing. Therefore, the greater the volume reduction due to the discharge of the contents, the more difficult it becomes to discharge the contents. This problem is effectively avoided by the present invention.

In the present invention, the outer container 3 and the inner bag container 5 are formed from a blow-moldable thermoplastic resin, and examples of such thermoplastic resins include the following.
Olefin resins, for example, low-density polyethylene, high-density polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, or random or block copolymers of α-olefins such as ethylene, propylene, 1-butene, and 4-methyl-1-pentene, and cyclic olefin copolymers;
Ethylene-vinyl copolymers, for example, ethylene-vinyl acetate copolymers, ethylene-vinyl alcohol copolymers, ethylene-vinyl chloride copolymers, etc.;
Styrene-based resins, such as polystyrene, acrylonitrile-styrene copolymers, ABS, and α-methylstyrene-styrene copolymers;
Vinyl resins, such as polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinylidene chloride copolymers, polymethyl acrylate, polymethyl methacrylate, etc.;
Polyamide resins, for example, nylon 6, nylon 6-6, nylon 6-10, nylon 11, nylon 12, etc.;
Polyester resins, for example, polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, and copolymer polyesters thereof;
Polycarbonate resin;
Polyphenylene oxide resin;
Biodegradable resins, such as polylactic acid;
Of course, blends of these thermoplastic resins can also be used as long as moldability is not impaired.

Furthermore, since they can be blow molded under the same molding conditions, it is preferable that the outer container 3 and the inner bag container 5 are made of the same type of resin. For example, from the standpoint of transparency, it is optimal for both the outer container 3 and the inner bag container 5 to be made of a polyester resin such as PET. Furthermore, polyester resin, particularly PET, is the most suitable resin, as it ensures the strength to quickly return to its original shape when the concave portion of the body of the outer container 3 is squeezed to further concave it.

To ensure the airless container's aforementioned properties, the outer surface of the bag-shaped body 23 of the inner bag container 5 must quickly peel away from the inner surface of the body 15 of the outer container 3 when the body 15 of the outer container 3 is depressed by squeezing and then the squeezing is stopped and the body 15 returns to its original shape. In other words, immediately after molding, and while the contents have been filled into the inner bag container 5 (bag-shaped body 23) but not yet been discharged, the outer surface of the bag-shaped body 23 of the inner bag container 5 remains in close contact with the inner surface of the body 15 of the outer container 3. Therefore, when the squeezing is stopped and the body 15 returns to its original shape, the two must quickly peel away, forming a gap between them. If no gap is formed, air will not flow between the outer surface of the bag-shaped body portion 23 and the inner surface of the body portion 15 of the outer container 3, and as mentioned above, space Z will not be formed. As the contents are discharged, the body portion 15 will have to be significantly deformed. Therefore, the more the contents are discharged and the greater the volume reduction, the more difficult it becomes to discharge the contents.

In the present invention, to ensure peelability between the outer surface of the bag-shaped body portion 23 and the inner surface of the body portion 15 of the outer container 3, a wax coating layer 40 is provided on the outer surface of the bag-shaped body portion 23 of the inner bag container 5. As can be seen from Figure 1, this wax coating layer 40 is not formed on the portion facing the bottom portion 17 of the outer container 3 (the region between the ground portions 16).
That is, the portion facing the bottom 17 does not require peelability, and it is preferable that the bottom 17 of the outer container 3 and the bottom of the inner bag container 5 are fixed together, so providing the wax layer 40 in such a portion not only increases the amount of wax used, but also leads to poor discharge of the content liquid, an increase in the amount of residual liquid, and an increase in squeeze pressure. It is also undesirable from the viewpoint of the Food Sanitation Act.

Furthermore, in the present invention, the wax coating layer 40 is not provided on the portion facing the bottom 17, so that releasability can be ensured with as small an amount as possible. For example, the application amount can be set so that, calculated from the surface area, it is 150 mg/ ^m² or less, preferably 125 mg/ ^m² or less, and more preferably 100 mg/ ^m² or less per unit. To ensure a certain level of releasability, an amount of 50 mg/ ^m² or more is sufficient. Furthermore, since the wax coating layer 40 is provided by roll coating, as described below, it is not provided above the fixing ring 25 for molding purposes. Furthermore, in terms of its function, it does not need to be provided on the outer surface of the tubular mouth 21 (the portion that does not expand or contract), but only on the bag-shaped body 23 (the portion that expands and contracts), excluding the portion facing the bottom 17.

The double-structure container (airless container) of Patent Document 3 also has a wax layer, but this wax layer is provided to suppress noise (ringing) that occurs when the body 15 of the outer container 3 is squeezed, and therefore the wax layer needs to be thicker than in the present invention. In other words, in the present invention, the wax coating layer 40 is thin, so there is almost no noise suppression effect. For example, in Patent Document 3, noise is suppressed to 60 dB or less, but with the thin wax layer 40 of the present invention, although sufficient peelability is exhibited during initial squeezing, it has been experimentally confirmed that the noise generated at this time is at most about 70 dB. This shows that the wax coating layer 40 provided in the present invention is thinner than that of Patent Document 3.

The airless container of Patent Document 4 also has a wax layer, but this wax layer is even thicker than that of Patent Document 3. In other words, Patent Document 4 creates a space between the outer surface of the bag-shaped body 23 of the inner bag container 5 and the inner surface of the body 15 of the outer container 3 when the contents are filled, and this space functions as an insulating layer, effectively suppressing temperature changes in the contents and preserving their freshness.

However, since the bag-shaped body portion 23 expands when the contents are filled, in order to form the above-described space, the outer surface of the bag-shaped body portion 23 of the inner bag container 5 and the inner surface of the body portion 15 of the outer container 3 must be separated immediately after molding, when the bag-shaped body portion 23 is pressed against the inner surface of the body portion 15 of the outer container 3. If the two are in contact, it is unlikely that a space will be formed between them once the contents are filled. In Patent Document 4, the space is formed by utilizing thermal contraction caused by heating during blow molding, but this is presumed to require the presence of a large amount of wax between the outer surface of the bag-shaped body portion 23 and the inner surface of the body portion 15 of the outer container 3. That is, it is believed that a large amount of wax exists between the two, and that this large amount of wax is heated to the blow molding temperature (above the glass transition temperature of the resin) and in a fluid state, resulting in the wax flowing down in a hollowed-out state, forming a space between the two. In fact, in Figure 1 of Patent Document 4, a space is formed between the outer surface of the bag-shaped body and the inner surface of the body of the outer container, but a wax layer is shown as a peelable portion 30 on both the outer surface of the bag-shaped body and the inner surface of the body of the outer container.
Thus, the layer of wax provided in US Pat. No. 5,649,999 is significantly thicker than that of the present invention.

Furthermore, in the present invention, it is important to use a low-melting-point wax having a melting point in the range of 40°C to 70°C as the wax used to form the wax coating layer 40. This low-melting-point wax exists in a solid state not only when the container is stored in a refrigerator, but also when it is sold, when the contents are discharged, and even during transportation. Furthermore, when moderately heated, it easily melts and becomes fluid. A low-melting-point wax exhibiting these characteristics is highly suitable for roll coating, allowing it to be applied so that the wax is present only in the desired locations on the bag-shaped body 23. A coating layer can be easily formed on the roll surface when heated and molten, and can be maintained on the roll surface by cooling and solidifying after application. Furthermore, because the wax coating layer 40 present in the predetermined location between the body 23 of the inner bag container 5 and the body 15 of the outer container 3 is solid, it is effectively prevented from running off during molding, ensuring a consistent coating amount. With ordinary liquid lubricants (such as liquid paraffin), gravity causes the lubricant to flow downward when the container is upright, making it difficult to maintain a consistent amount of lubricant applied to achieve release properties during actual use (initial squeezing).Furthermore, the low-melting waxes mentioned above have the advantage of producing almost no odor when melted.
Furthermore, the wax must be non-aqueous, and emulsion wax, for example, cannot be used in the present invention, because the water content is likely to change depending on the environment, causing changes in the components and making the amount applied unstable.

Examples of the low-melting point waxes mentioned above include rice wax, carnauba wax, paraffin wax, microcrystalline wax, polyethylene wax, candelilla wax, rice wax, Japan wax, and beeswax. Mixed waxes of these can also be used as long as the melting point is within the aforementioned range.

In the present invention, of the low-melting-point waxes mentioned above, low-crystalline paraffin wax is most preferably used. Unlike crystalline paraffins, which are primarily n-paraffins, low-crystalline paraffin waxes are primarily isoparaffins or cycloparaffins, and have a low n-paraffin content of, for example, less than 50% by mass.

Low-crystalline paraffin waxes such as those described above do not easily turn into white powder (granules) upon solidification, making them easy to handle and roll-coat, and are also advantageous for forming a coating layer of uniform thickness. In particular, since the present invention sets the thickness of the wax coating layer 40 to be extremely thin, such low-crystalline paraffin wax is ideal. For example, crystalline paraffin waxes primarily composed of n-paraffin tend to turn into white powder (granules) upon solidification, making them less applicable by roll than low-crystalline paraffin wax and also resulting in uneven coating layer thickness. Furthermore, when the outer container 3 and inner bag container 5 are made of transparent PET, crystalline paraffin wax significantly impairs visibility of the interior due to whitening, whereas low-crystalline paraffin wax has the advantage of minimizing the reduction in visibility.

Manufacture of double-structured container 1;
The double-structure container 1 of the present invention, which is provided with the above-mentioned wax coating layer 40, is manufactured by a method (stack method) in which a first preform (preform for molding the outer container) obtained by injection molding using a resin for the outer container and a second preform (preform for molding the inner bag container) obtained by injection molding using a resin for the inner bag container are inserted into the first preform to form a stack preform with a multi-layer structure, and this stack preform is then subjected to biaxial stretch blow molding.
That is, according to this method, the layer of the low melting point wax can be uniformly formed on a predetermined portion of the second preform by roll coating.

2 and 3, which are used to explain the stack method, the stack preform for molding the double-structured container of FIG. 1 is generally designated by 70 in FIG. 3, and is formed from a first preform 50 (see FIG. 2(a)) and a second preform 60 (see FIG. 2(b)), both of which have a test tube shape as shown in FIG. 2.
That is, the first preform 50 is a preform for molding the outer container, and the second preform 60 is a preform for molding the inner bag container, and by inserting the second preform 60 into the first preform 50 and holding them in place, a stack preform 70 is assembled to be used in the blow-stretching process.

As can be seen from Fig. 2, both the first preform 50 and the second preform 60 have portions (non-stretch molded portions) that correspond to the nozzle portion 11 of the outer container 3 and the cylindrical mouth portion 21 of the inner bag container 5. In other words, these portions are not stretch molded (see Fig. 3), and the nozzle portion 11 of the first preform 50 is provided with a support ring 11b.
When air is introduced through the wall of the nozzle portion 11, an air inlet, a screw, or the like is provided in the nozzle portion 11.

The portion below the nozzle portion 11 of the first preform 50 is the portion to be stretch-molded (see FIG. 3), and this portion includes a body portion 53, the lower end of which forms a curved bottom portion 55. That is, this stretch-molded portion (see FIG. 3) is blow-stretched to be shaped into the shoulder portion 13, body portion 15, ground portion 16, and bottom portion 17 of the outer container 3.
In the first preform 50, the body portion 53 has a straight body shape, but its upper end has a shape that expands in diameter outward, making it easy to insert the second preform 60 inside.

The upper end of the second preform 60 is a cylindrical mouth 21, which is a non-stretched molding portion, and this cylindrical mouth 21 is provided with a fixing ring 25. The stretched molding portion connected to this cylindrical mouth 21 is composed of a body 63 and a bottom 65 consisting of a curved surface that closes the lower end of the body 63. Furthermore, to make it easier to insert the second preform 60 into the first preform 50, the body 63 is composed of a straight body 63a and an enlarged tapered portion 63b connected to the upper end of the straight body 63a.

A coating layer 80 of the aforementioned low-melting-point wax is applied to the stretch-molded portion of the second preform 60 in the above-described configuration. This wax coating layer 80 is applied to the body portion 63, but not to the curved bottom portion 65. In this case, the coating layer 80 is typically applied selectively to the straight body portion 63a. However, by also forming the coating layer 80 on the portion that faces the inner surface of the shoulder portion 13 of the outer container 3 when molded into the double-walled container 1, the peelability of the bag-shaped body portion 23 can be improved and air can be quickly introduced into the space Z through the air path X. Therefore, the coating layer 80 may extend from the straight body portion 63a to the tapered portion 63b. Furthermore, the coating layer 80 may extend to the non-stretch-molded portion, directly below the cylindrical mouth portion 21.

In the present invention, the coating layer 80 is formed by roll coating. Roll coating is typically performed on flat objects such as films, and it can be said that rolls are rarely used to coat three-dimensional objects. In fact, Patent Documents 3 and 4 make no mention of roll coating, and instead use spray atomization or other methods to coat.

However, in the present invention, by utilizing the properties of the low-melting-point wax and the shape of the stretched portion of the second preform 60 and using a roll, it is possible to selectively form a coating layer 80 of low-melting-point wax in the desired location (body portion 63), and it is also possible to make this coating layer 80 thin and uniform in thickness.

Specifically, a roll coated with a molten low-melting-point wax heated to a temperature 0 to 20°C, preferably 0 to 15°C, and most preferably 0 to 10°C higher than the melting point of the wax is used, and while rotating the roll, the roll surface is brought into contact with the surface of the barrel portion 63 of the second preform 60, which is also rotating, and the wax is transferred to coat the surface of the barrel portion 63 with the molten low-melting-point wax. The coated second preform 60 is then separated from the roll surface, whereby the coated wax quickly solidifies, forming a coating layer 80 of a consistent thickness without flowing off the surface of the barrel portion 63. The thickness (amount of coating) of the coating layer 80 can be adjusted by adjusting the contact pressure and contact time (number of rotations) of the second preform 60 (barrel portion 63) with the roll surface, and the amount of wax coating layer 40 applied when molded into a double-walled container can be set within the aforementioned range (150 mg/ ^m2 or less).

Note that there is no problem if the above coating layer 80 is formed only on the straight body portion 63a, but if the coating layer 80 is also formed on the tapered portion 63b, a roll with a gradually smaller diameter can be used to match the tapered portion 63b.

For example, if a coating is applied by spraying molten low-melting-point wax without using a roll, uneven thickness will naturally occur, and the coating layer will be quite thick and difficult to adjust. Furthermore, masking or other measures will be required to prevent the coating from reaching the bottom 65, making the coating process quite tedious.

The second preform 60, on which the wax coating layer 80 has been formed in the predetermined portion as described above, is inserted into the first preform 50 as shown in FIG. 3, thereby assembling the stack preform 70.
Such a stack preform 70 is placed in a blow mold, the nozzle portion 11 is fixed with a predetermined jig, and the stack preform 70 is heated by external heating or the like to a temperature at which it can be stretched (above the glass transition temperature and below the melting point of the resins forming the preforms 50 and 60). A stretch rod is inserted into the stack preform 70 (second preform 60) to stretch it uniaxially, and the bottoms of the first and second preforms are fixed together. Further, a blowing fluid such as air is supplied to expand the second preform 60 in the circumferential direction, thereby spreading and expanding the first preform 50 and forcing it against a predetermined cooling mold, thereby obtaining the double-structure container 1 having the configuration shown in FIG. 1 . That is, in FIG. 3 , the stretch-molded portion of the stack preform 70 is blown and stretched, resulting in the configuration shown in FIG. 1 . At this time, support blow molding may be performed between the first preform 50 and the second preform 60. When support blowing is performed, the support blow pressure is greater than the blow pressure when the shaping of the shoulder is completed, so the support blow air remains in the middle of the inner bag and the outer container, forming an indeterminate area from the shoulder of the inner bag to the bottom of the mouth. As a result, before the inner bag is tightly attached to the outer container, the support blow air forms a wall, and there is a region that does not come into contact with the inner surface of the outer container. In other words, shaping begins from the bottom to the mouth, and eventually the entire shaping is completed.

Therefore, in the double-walled container 1 formed in this manner, the outer surface of the bag-shaped body 23 of the inner bag container 5 is in close contact with the inner surface of the body 15 of the outer container 3. When contents are filled into the bag-shaped body 23 of the bag-shaped container 5 in this state, the outer surface of the bag-shaped body 23 is pressed even more firmly against the inner surface of the body 15 of the outer container 3. However, in the present invention, because the layer 40 of solidified low-melting-point wax exists between the bag-shaped body 23 and the body 15 of the outer container, even when pressed firmly by filling with contents, the bag-shaped body 23 has enhanced releasability to the inner surface of the body 15. Therefore, when the body 15 is squeezed to make it concave and then returns to its original shape upon completion of squeezing, the bag-shaped body 23 does not follow the body 15 in returning to its original shape but easily peels away from the body 15, forming a space Z between them.

When the low-melting-point wax mentioned above is heated to the blowing temperature during blow molding, it enters a molten state. At this time, the blow presses it firmly against the inner surface of the body 53 of the first preform, minimizing its flow and falling. Furthermore, the bottom 17 of the outer container 3, which is formed during molding, has a dome-shaped recess. Therefore, even if this wax coating layer 40 melts and falls, it will not flow around to the part facing the dome-shaped bottom 17 (it will be blocked by the ground contact portion 16), and the wax coating layer 40 will remain only in the area facing the body 15.

The double-structure container 1 of the present invention manufactured as described above is used by placing the contents (e.g., a seasoning liquid such as soy sauce) in the bag-shaped body portion 23 of the inner bag container 5, and then attaching a known check valve cap to the nozzle portion 11 of the outer container 3.

The present invention is illustrated by the following experimental examples.

Wax was applied to the body (stretched portion excluding the bottom portion) of a second preform molded by injection molding of polyethylene terephthalate (PET). The following waxes were prepared for coating.
Plant-derived emulsion wax;
Melting point: 85°C
Petroleum-derived emulsion wax (high melting point type);
Melting point: 110°C
Petroleum-derived emulsion wax (low melting point type);
Melting point: No data available Liquid paraffin;
Melting point: No data available Low-crystallinity paraffin wax (low-melting wax A);
n-Paraffin content: less than 50% by mass Melting point: 50°C
High melting point wax (High melting point wax B);
Melting point: 80°C

<Experimental Example 1>
A plant-derived emulsion wax was roll-coated onto the outer surface of the body of the second preform, but the solvent components contained in the wax volatilized, causing the component balance to change in a very short time, making it impossible to maintain a stable coating amount and resulting in a lack of applicability.In addition, the wax itself had a distinctive odor (an unpleasant smell), so it was determined to be unsuitable for use as a food container.

<Experimental Example 2>
Petroleum-derived emulsion-type high-melting-point wax and low-melting-point wax were roll-coated onto the outer surface of the body of the second preform, but both had unstable properties due to the evaporation of the solvent components, poor wettability, and the coated surface was repelled and uneven, resulting in poor applicability. Furthermore, the high-melting-point wax, like the plant-derived wax in Experimental Example 1, had a strong, peculiar odor (a foul odor) and was therefore deemed unsuitable for food containers. Furthermore, the low-melting-point wax had an unpleasant odor, although not as strong as the high-melting-point wax.

<Experimental Example 3>
The outer surface of the body of the second preform was roll-coated with liquid paraffin, and the second preform was stacked inside the first preform. The body was then heated and blow-molded to produce a double-walled container.
It was easy to apply and had no problems with functionality, but when held upright, the liquid paraffin dripped downwards, causing the oily components to spread to undesired areas, preventing the formation of a uniform coating layer and making it difficult to apply.

<Experimental Example 4>
A double-walled container was produced by blow molding in the same manner as in Experimental Example 3, except that the low-crystalline paraffin wax A was heated to 60° C. and roll-coated onto the outer surface of the body of the second preform. The rotation speed of the application roller and the amount of application during roll coating are shown in Table 1.
The wax-specific smell was suppressed and it was possible to apply it evenly to the desired areas, but the amount applied was too large, resulting in a thick layer.

<Experimental Example 5>
A double-layered container was prepared in the same manner as in Experimental Example 4, except that the low-crystalline paraffin wax A was heated to 50° C. during roll coating. The rotation speed of the application roller and the amount of application during roll coating are shown in Table 1.
In this case too, the wax-specific odor was suppressed, it could be applied evenly to the desired area, and the amount applied could be kept to a small amount.
Considering this together with the results of Experimental Example 4, it can be seen that by using roll coating as the application method rather than spraying or dipping, and by appropriately adjusting the melting temperature, roll rotation number and speed, it is possible to adjust the application amount to the minimum necessary and reduce the amount of wax used.

<Experimental Example 6>
A double-layered container was produced in the same manner as in Experimental Example 4, except that high-melting-point wax B was heated to 80°C and roll-coated onto the outer surface of the body of the second preform. The rotation speed of the application roller and the amount of application during roll coating are shown in Table 1.
These high-melting waxes B were easy to handle because they solidified immediately after application, but they tended to be applied in excess, resulting in a thick coating. Furthermore, after application, the wax would easily break apart between the inner and outer layers when squeezed, and its performance could not be maintained until the contents were used up. Furthermore, the powdered wax appeared as dust or foreign matter adhering to the container.

The results of the sensory evaluations of the property stability, wettability, odor, applicability, application amount, and container appearance in Experimental Examples 1 to 6 are summarized in Table 2 below. The evaluation criteria are as follows:
Property stability;
◯: The coating was stably held on the roll with consistent properties, and consistently showed consistent coating properties.
×: The solvent component volatilizes, resulting in unstable properties and variations in coating properties.
Wettability;
◯: When applied with a roller, the material quickly spreads onto the preform surface.
×: When applied with a roller, it was difficult to wet and spread on the preform surface.
Smell;
◯: No strange odor △: Not as bad as a bad odor, but has a strange odor specific to wax.
×: There is a bad smell and it is not suitable for sale.
Spreadability;
◯: Visually observed to be uniformly coated.
△: Dripping occurs or the product quickly turns into powder due to crystallization, making it difficult to handle.
x: Coating unevenness is clearly observed even with the naked eye.
Application amount:
Good: 150 mg/ ^m2 or less.
△: More than 150 mg/ ^m2 .
Container appearance:
○: No foreign matter was found by visual inspection.
x: Foreign matter is clearly visible.

In addition, in Experimental Examples 4 to 6, coating was performed with the application roller rotating once and twice, but the sensory evaluation results were the same, so the evaluation results are shown together and not by rotation speed.

1: Double-structure container 3: Outer container 5: Inner bag container 11: Nozzle portion of outer container 13: Shoulder portion of outer container 15: Body portion of outer container 16: Ground portion 17: Bottom portion 21: Cylindrical opening portion 23: Bag-shaped body portion 25: Fixing ring 40: Coating layer of low-melting-point wax 50: First preform 60: Second preform 70: Stack preform 80: Coating layer of low-melting-point wax

Claims (2)

A double-structure container comprising an outer container and an inner bag container inserted and held in the outer container, in which the contents contained in the inner bag container are discharged by squeezing the outer surface of the body of the outer container, and the inner bag container contracts as the contents are discharged, forming a gap between the inner bag container and the outer container,
Between the inner bag container and the outer container, in an unused state in which the contents have not been discharged, except for at least a portion facing the bottom of the outer container, there is present a coating layer of low-melting-point wax having a melting point in the range of 40°C to 70°C in an amount of 50 mg/m2 ^or more and 150 mg/ ^m2 or less;
The low-melting point wax is a low-crystalline paraffin wax having an n-paraffin content of less than 50% by mass, and the coating layer of the low-melting point wax is a solid layer that is in close contact with at least the inner surface of the body portion of the outer container that is to be squeezed. A first preform having a test tube shape for molding an outer container and a second preform having a test tube shape for molding an inner bag container are prepared;
A wax layer is formed on the outer surface of the second preform, on the stretch-molded portion excluding the bottom of the curved shape, by heating and melting a low-melting wax having a melting point of 40°C to 70°C at a temperature equal to or higher than the melting point and roll-coating the wax;
With the low-melting-point wax coating layer formed, inserting the second preform into the first preform to form a stack preform;
blow molding by supplying a blowing fluid into a second preform in the stack preform;
2. The method for manufacturing a double-walled container according to claim 1,