JP7773031B2 - plastic containers - Google Patents

Description

The present invention relates to a plastic container.

Containers with an inner surface made of polyolefin resin are commonly used to store contents such as seasonings. Such containers require the contents to slide smoothly down the inner surface of the container so that they can be used up without loss. Patent Document 1 discloses a plastic container whose sliding properties are improved by adding an unsaturated aliphatic amide and a saturated aliphatic amide as a lubricant to the polyolefin resin that constitutes the innermost layer of the plastic container.

JP 2009-214914 A

Even if the container exhibits good sliding properties immediately after filling, this may deteriorate over the course of subsequent storage. Therefore, there is a demand for plastic containers that have long-lasting sliding properties and that do not deteriorate much even after long-term storage.

The present invention was made in light of these circumstances, and provides a plastic container for storing contents such as seasonings, which has excellent sliding properties and long-lasting sliding properties.

The present invention provides a plastic container for storing contents, comprising an innermost layer that comes into contact with the contents, the innermost layer being made of a resin composition in which a lubricating liquid is retained in a mixed resin of a polyolefin resin and an elastomer, and at least a portion of the surface of the innermost layer that comes into contact with the contents is covered with a liquid film formed by the lubricating liquid.

The innermost layer that comes into contact with the contents is made from a resin composition in which a lubricating liquid is held in a mixed resin of polyolefin resin and elastomer, and at least a portion of the surface of the innermost layer that comes into contact with the contents is coated with a liquid film formed by the lubricating liquid. This has resulted in the discovery that the container exhibits excellent sliding properties when the contents are placed inside, with little deterioration in sliding properties even after long-term storage of more than 20 days, leading to the completion of the present invention.

Various embodiments of the present invention will be described below as examples, and the embodiments shown below can be combined with each other.
Preferably, the lubricating liquid is liquid paraffin.
Preferably, the polyolefin resin is low-density polyethylene.
Preferably, the content of the elastomer in the mixed resin is 1 to 30% by mass.
Preferably, the amount of lubricating liquid retained in the innermost layer is 1 to 20 g/ ^m2 .
Preferably, the elastomer is an olefin-based elastomer.
Preferably, the protective film includes an intermediate layer and an outermost layer made of EVOH resin.

1 is a front view of a plastic container 1 according to an embodiment of the present invention. 1 is a diagram showing an example of a layer structure of a container body 2 of a plastic container 1. FIG.

Embodiments of the present invention will be described below with reference to the drawings. The features shown in the following embodiments can be combined with each other. Furthermore, each feature can be an independent invention.

1. Plastic Container Configuration FIG. 1 is a diagram showing an example of the configuration of a plastic container 1 according to an embodiment of the present invention. The contents accommodated in the plastic container 1 are not particularly limited, and various condiments can be accommodated. Examples of condiments include aqueous substances such as sauces and oily substances such as mayonnaise. The plastic container 1 of this embodiment is particularly suitable for accommodating aqueous contents. In this invention, aqueous contents refer to contents having a water content of 30% by mass or more and a lipid content of less than 20% by mass, such as Worcestershire sauce, medium-thick sauce, and thick sauce. The plastic container 1 exhibits particularly excellent sliding properties and long-lasting sliding properties for the above-mentioned aqueous contents, and particularly for relatively viscous contents having a water content of 50% by mass or more, a lipid content of less than 20% by mass, and a viscosity of 150 mPa·s or more, and long-lasting sliding properties.

A plastic container 1 according to an embodiment of the present invention comprises a container body 2 and a cap 3. The container body 2 comprises a storage section 21 for storing the contents, and a mouth section 22 having an opening for discharging the contents from the storage section 21.

The cap 3 comprises a cap body 32 and a cap cover 31. The cap body 32 and cap cover 31 are connected at a connecting portion 33, allowing the cap cover 31 to be opened and closed. The cap body 32 comprises an upper portion 32a, a discharge port 32b provided in the upper portion 32a, and a cylindrical portion 32c extending cylindrically from the outer periphery of the upper portion 32a.

An engaging portion (not shown) that can be threaded onto the outer surface of the mouth portion 22 is formed on the inner surface of the cylindrical portion 32c. By threading the cap 3 onto the mouth portion 22 from above, the engaging portion engages with the outer surface of the mouth portion 22, and the cap 3 is attached to the container body 2. Note that the method of attaching the cap 3 to the container body 2 is not limited to the screw method described above, and a stopper method may also be used.

2 is a diagram showing an example of the layer structure of the container body 2. The container body 2 has a multilayer structure including, from the inside out, an innermost layer 4, an adhesive resin layer 5, an intermediate layer 6, an adhesive resin layer 7, and an outermost layer 8. The thickness ratios of the layers are, for example, as follows:
Innermost layer 4: 10-40%
Adhesive resin layer 5: 1-15%
Middle layer 6: 5-10%
Adhesive resin layer 7: 1-15%
Outermost layer 8: 20-60%
Each layer will be described below.

(Innermost layer 4)
The innermost layer 4 is the layer that comes into contact with the contents and is composed of a resin composition in which a lubricating liquid is retained in a mixed resin of a polyolefin resin and an elastomer. Examples of polyolefin resins include polyethylenes such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE), as well as polypropylene (PP), poly-1-butene, and poly-4-methyl-1-pentene. The polyolefin resin may also be a random or block copolymer of α-olefins such as ethylene, propylene, 1-butene, or 4-methyl-1-pentene, or may further be a so-called cyclic olefin resin (cycloolefin polymer (COP)) or a so-called cyclic olefin copolymer (cycloolefin copolymer (COC)), which is a copolymer of a cyclic olefin and an α-olefin (a chain olefin), etc. These polyolefin resins may be used alone or in combination of two or more.

Among the polyolefin resins exemplified above, polyethylene is preferably used, and it is preferable for polyethylene to be the main component of the mixed resin, i.e., to account for 50% by mass or more of the entire mixed resin. Furthermore, from the standpoint of moldability, it is preferable to use low-density polyethylene as the polyethylene.

The elastomer in the mixed resin serves to absorb and retain the lubricating liquid. Examples of elastomers that can be used include thermoplastic elastomers such as olefin-based elastomers, styrene-based elastomers, ester-based elastomers, and urethane-based elastomers, and thermosetting elastomers such as silicone rubber. Furthermore, one type of elastomer may be used alone, or two or more types may be used in combination.

Among the elastomers listed as examples, thermoplastic elastomers are preferred. Thermoplastic elastomers are composed of soft segments that exhibit elasticity and hard segments that act as crosslinking points. Olefin-based elastomers have hard segments made of polyolefin and soft segments made of rubber components such as ethylene-propylene rubber. Examples include ethylene-based elastomers such as ethylene-α-olefin copolymers and propylene-based elastomers such as propylene-α-olefin copolymers. Styrene-based elastomers have hard segments made of polystyrene and soft segments made of block copolymers of olefins, dienes, etc., and examples of styrene-butadiene block copolymers (SBS), styrene-isoprene block copolymers (SIS), styrene-ethylene-butylene-styrene block copolymers (SEBS), and styrene-ethylene-propylene-styrene block copolymers (SEPS), which have different soft segments.

Of the thermoplastic elastomers exemplified above, it is more preferable to use an olefin-based elastomer. When an olefin-based elastomer is used, it has high dispersibility in the mixed resin with the polyolefin-based resin, resulting in a resin composition with high transparency and good surface properties. Olefin-based elastomers include ethylene-based elastomers such as ethylene-α-olefin copolymers, and propylene-based elastomers such as propylene-α-olefin copolymers. When polyethylene is used as the polyolefin-based resin, it is preferable to use an ethylene-based elastomer as the olefin-based elastomer.

The elastomer content in the mixed resin is preferably 1 to 30% by mass, more preferably 5 to 25% by mass, and specifically, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30% by mass, and may be within a range between any two of the values exemplified here. If the elastomer content is within the above range, a sufficient amount of lubricating liquid can be retained. On the other hand, if the elastomer content is greater than the above range, moldability decreases, making it difficult to form a uniform innermost layer 4 when manufacturing a multilayer container by extrusion molding or blow molding.

The lubricating liquid forms a liquid film 9 on the surface (inner surface) 4a of the innermost layer 4 that comes into contact with the contents. By covering at least a portion of the inner surface 4a of the innermost layer 4 with the liquid film 9, the contents are less likely to adhere to the inner surface 4a, providing excellent sliding properties. In addition, some of the lubricating liquid is absorbed by the elastomer and retained in the mixed resin. As the amount of lubricating liquid present as the liquid film 9 on the inner surface 4a of the innermost layer 4 decreases, the lubricating liquid absorbed by the elastomer seeps out of the resin composition onto the inner surface 4a, maintaining the liquid film 9, thereby enabling the sliding properties to be maintained over a long period of time.

The lubricating liquid is selected from substances that are liquid at room temperature and can be absorbed by elastomers. For example, hydrophobic lubricating liquids such as hydrocarbon compounds and silicone oils can be used. One type of lubricating liquid may be used alone, or two or more types may be used in combination. Of the lubricating liquids listed above, hydrocarbon compounds are preferred, and liquid paraffin is even more preferred. Liquid paraffin is a hydrocarbon oil obtained by removing impurities from petroleum lubricating oil fractions and refining the oil to a high degree. Liquid paraffin is easily absorbed by elastomers, and because it is tasteless, odorless, colorless, and transparent, it has little effect on the contents.

The liquid film 9 formed by the lubricating liquid preferably covers at least 60% of the inner surface 4a of the innermost layer 4, and more preferably at least 80%. If the coverage of the inner surface 4a of the innermost layer 4 by the liquid film 9 is within the above-mentioned range, sufficient sliding properties can be achieved.

The viscosity of the lubricating liquid is preferably 70 mPa·s or higher, and more preferably 150 to 300 mPa·s. If the viscosity of the lubricating liquid is within the above range, a liquid film 9 is easily formed on the inner surface 4a of the innermost layer 4, and the formed liquid film 9 is maintained for a relatively long period of time. Viscosity is measured at 25°C in accordance with JIS Z8803.

The amount of lubricating liquid retained in the innermost layer 4 is preferably 1 to 25 g/ ^m2 per unit area of the inner surface 4a, more preferably 5 to 20 g/ ^m2 , and specifically, for example, 1, 2, 3, ⁴ , 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25 g/m2, and may be within a range between any two of the values exemplified here. If the amount of lubricating liquid retained is within the above range, good sliding properties can be exhibited while the impact on the contents is sufficiently small.

The thickness of the innermost layer 4 is, for example, 50 to 70 μm. The thickness of the liquid film 9 formed by the lubricating liquid on the inner surface 4a of the innermost layer 4 is preferably 0.5 to 2.5 μm, more preferably 1.1 to 2.5 μm, and specifically, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, or 2.5 μm, or may be within a range between any two of the values exemplified here. A liquid film 9 thickness within the above range can exhibit good sliding properties.

The lubricating liquid can be retained in the mixed resin by, for example, manufacturing a plastic container 1 having an innermost layer 4 composed of a mixed resin of polyolefin resin and elastomer, and then applying the lubricating liquid to the inner surface 4a of the innermost layer 4 using a spray gun or the like. Alternatively, the resin composition of the innermost layer 4 can be prepared using a masterbatch in which the lubricating liquid is mixed with the polyolefin resin or elastomer.

(Outermost layer 8)
The outermost layer 8 is the layer disposed on the outermost side of the container body 2, and is composed of a resin composition containing a polyolefin-based resin. The preferred polyolefin-based resin is the same as that of the innermost layer 4, and it is more preferred that the polyolefin-based resins constituting the innermost layer 4 and the outermost layer 8 are the same.

It is preferable to add a fatty acid amide as a lubricant to the polyolefin resin. The addition of a fatty acid amide enables the plastic container 1 to exhibit slip properties that are suited to various environmental temperatures in each process, from molding the plastic container 1 to filling, transferring, and packaging the contents, eliminating problems such as poor slipperiness on the surface of the plastic container 1 in each process. For the outermost layer 8, it is preferable to use a resin composition in which a lubricant (particularly a fatty acid amide-based lubricant, described below) is added to, mixed with, and kneaded into the polyolefin resin to impart slipperiness, for example, in food filling lines and the like that are primarily made of metal materials such as stainless steel.

Saturated fatty acid amides and unsaturated fatty acid amides can be used as the fatty acid amide. Examples of saturated fatty acid amides include butylamide, hexylamide, decylamide, lauric acid amide, myristic acid amide, palmitic acid amide, and stearic acid amide. Of these saturated fatty acid amides, stearic acid amide is preferred. These saturated fatty acid amides may be used alone or in combination of two or more.

Examples of unsaturated fatty acid amides include acrylamide, methacrylamide, crotonamide, isocrotonamide, undecylenic acid amide, cetoleic acid amide, oleic acid amide, erucic acid amide, ethylene bisoleic acid amide, oleyl palmitamide, stearyl erucamide, linoleic acid amide, linolenic acid amide, and arachidonic acid amide. Among these, those having 14 to 24 carbon atoms, such as cetoleic acid amide, oleic acid amide, erucic acid amide, linoleic acid amide, linolenic acid amide, and arachidonic acid amide, are preferred, with oleic acid amide being particularly preferred. These unsaturated fatty acid amides may be used alone or in combination of two or more.

The content of fatty acid amide in the outermost layer 8 is preferably 0.01 to 10% by mass of the entire resin composition constituting the outermost layer 8. By adding fatty acid amide in the amount within the above range, good slip properties can be achieved. It is particularly preferable that the content of fatty acid amide be 0.1 to 5% by mass of the entire resin composition constituting the outermost layer 8.

(Intermediate layer 6)
The intermediate layer 6 is a layer disposed between the innermost layer 4 and the outermost layer 8, and is made of a relatively high-density resin. Examples of such resins include ethylene vinyl alcohol copolymer (EVOH: saponified ethylene vinyl acetate copolymer, etc.) and a resin composition in which a filler is added to a polyolefin resin. The provision of the intermediate layer 6 can prevent the lubricating liquid held in the innermost layer 4 from penetrating into the outer layers.

Of the resins listed as examples, it is preferable to use EVOH resin. EVOH resin is highly effective in preventing the penetration of lubricating liquid, and because it also has high gas barrier properties, it can effectively prevent the contents from oxidizing and deteriorating due to oxygen permeation.

(Adhesive resin layers 5, 7)
The adhesive resin layers 5, 7 are composed of an adhesive resin. Examples of adhesive resins include acid-modified polyolefin resins (e.g., maleic anhydride-modified polyethylene and maleic anhydride-modified polypropylene). The adhesive resin layers 5, 7 improve the adhesion between the intermediate layer 6 and the innermost layer 4 or the outermost layer 8. Instead of providing the adhesive resin layers 5, 7, an adhesive resin may be blended into the intermediate layer 6.

The layer structure of the plastic container 1 is not limited to the above example. For example, a layer composed of a resin composition containing a thermoplastic resin may be further provided between the intermediate layer 6 and the outermost layer 8, or between the innermost layer 4 and the intermediate layer 6. This layer may be composed of a resin composition containing a recycled material obtained by recycling scrap generated during the molding of the plastic container 1. Since the scrap contains all layers of the plastic container 1, the recycled material will be a mixture of the resin compositions that make up each layer. Alternatively, it may be composed of a mixture of the recycled material and a new thermoplastic resin.

In addition, various additives commonly used in the field of resin materials, such as plasticizers, antistatic agents, antioxidants, antifogging agents, UV absorbers, heat stabilizers, nucleating agents, release agents, colorants, and neutralizing agents, may be added to each of the above-mentioned layers, provided they do not impair the objectives and effects of the present invention.

2. Manufacturing Method of Plastic Container 1 The plastic container 1 can be formed by blow molding of a parison. Blow molding may be direct blow molding or injection blow molding. In direct blow molding, a molten cylindrical parison extruded from an extruder is sandwiched between a pair of split molds and air is blown into the interior of the parison to manufacture the plastic container 1. In injection blow molding, a test-tube-shaped parison with a bottom, called a preform, is formed by injection molding, and blow molding is performed using this parison.

In either blow molding method, the layer structure of the parison is the same as the layer structure of the plastic container 1. Multi-layer parisons can be formed by co-extrusion molding, multi-layer injection molding, etc.

1. Production of Sample A plastic container 1 (capacity: 500 ml) was produced having the shape shown in Fig. 1 and a layer structure including, from the inside out, an innermost layer 4, an adhesive resin layer 5, an intermediate layer 6, an adhesive resin layer 7, and an outermost layer 8 as shown in Fig. 2. The plastic container 1 was produced by forming the container body 2 by blow molding and the cap 3 by injection molding.

In all examples and comparative examples, low-density polyethylene (Suntec® M2206, manufactured by Asahi Kasei Corporation) was used as the polyolefin resin constituting the innermost layer 4. In examples 1 to 6, an olefin-based elastomer (Tafmer® DF605, manufactured by Mitsui Chemicals, Inc.) was used as the elastomer, and the innermost layer 4 was constructed using a mixed resin of low-density polyethylene and olefin-based elastomer, with the elastomer content adjusted to the value shown in Table 1. In example 7, an olefin-based elastomer (Tafmer® DF605, manufactured by Mitsui Chemicals, Inc.) was used as the elastomer, and the innermost layer 4 was constructed using a mixed resin of low-density polyethylene and olefin-based elastomer, with the elastomer content adjusted to 40% by mass. In comparative examples 1 to 3, the innermost layer 4 was constructed using a resin consisting solely of low-density polyethylene, without any elastomer mixed in.

In all examples and comparative examples, liquid paraffin (liquid paraffin (food additive) manufactured by Kosakai Pharmaceutical Co., Ltd.) was used as the lubricating liquid. The viscosity of the liquid paraffin was 194 mPa·s (25°C). The liquid paraffin was sprayed onto the entire inner surface 4a of the innermost layer 4 using a spray gun so that the amount of liquid paraffin applied per unit area on the inner surface 4a of the innermost layer 4 was the value shown in Table 1, and the liquid paraffin was retained in the mixed resin, forming a liquid film 9.

In all examples and comparative examples, low-density polyethylene (Suntec (registered trademark) M2206, manufactured by Asahi Kasei Corporation) was used as the resin constituting the outermost layer 8.

In all examples and comparative examples, ethylene-vinyl alcohol copolymer (SF7503B, manufactured by Mitsubishi Chemical Corporation) was used as the resin constituting the intermediate layer 6.

In all examples and comparative examples, the adhesive resin layer 5 was formed using an adhesive resin (MODIC (registered trademark) L522, manufactured by Mitsubishi Chemical Corporation). Furthermore, in all examples and comparative examples, the adhesive resin layer 7 was formed using an adhesive resin (MODIC (registered trademark) L522, manufactured by Mitsubishi Chemical Corporation).

2. Evaluation 2.1. Sliding Speed Evaluation A test to evaluate sliding speed was conducted on the plastic containers 1 of Examples 1 to 6 and Comparative Examples 1 to 3. A rectangular test piece (7 cm long, 1 cm wide) was cut from the storage section 21 of the container body 2, and 1 ml of seasoning was dropped onto the inner surface 4a of the innermost layer 4 near one longitudinal end of the test piece. Okonomiyaki sauce (manufactured by Otafuku Sauce Co., Ltd., water content: approximately 60%, viscosity: 840 mPa·s (23°C), ingredients: vegetables, fruits, spices, etc.), which is classified as a Worcestershire sauce, was used as the seasoning. The test piece was left standing upright in the vertical direction with the end where the seasoning was dropped facing up, and the seasoning droplets were observed sliding down the inner surface 4a. The sliding distance per unit time in the vertical direction was measured, and the sliding speed [mm/min] was calculated.

The day the initial test was conducted was designated Day 1. The plastic container 1 used on Day 1 was stored, and the test specimens were cut from the storage section 21, the seasoning was dripped, and observations of sliding were made on Days 3, 7, 14, and 21. The evaluation results of the sliding speed obtained in this manner are shown in Table 1.

2.2. Moldability Evaluation As a moldability evaluation, the state of formation of the innermost layer 4 was observed for the plastic containers 1 of Examples 1 to 7 and Comparative Examples 1 to 3. Specifically, the presence or absence of tears in the innermost layer 4 was observed, and it was evaluated whether the innermost layer 4 was formed uniformly.

2.3. Results On the first day of the slide-down speed evaluation test, all of Examples 1 to 6 and Comparative Examples 1 to 3 had slide-down speeds greater than 40 mm/min, demonstrating good slide-down performance. When Examples 1 and 2 and Comparative Example 1 were compared with Examples 3 and 4 and Comparative Example 2, and Examples 5 and 6 and Comparative Example 3, which had the same amount of lubricating fluid applied, Comparative Examples 1, 2, and 3 showed the highest slide-down speeds, respectively. In Examples 1 to 6, a portion of the applied lubricating fluid was absorbed by the elastomer. On the other hand, the innermost layers 4 of Comparative Examples 1, 2, and 3 did not contain elastomer, and the applied lubricating fluid was not absorbed, with almost the entire amount remaining as a liquid film 9 on the inner surface 4a, which is thought to be why they exhibited better slide-down performance.

In Comparative Examples 1, 2, and 3, the sliding speed rapidly decreased over the storage period. In Comparative Example 1, the sliding speed became less than 40 mm/min after the 7th day of testing, and in Comparative Examples 2 and 3, the sliding speed became less than 40 mm/min after the 14th day of testing. This is thought to be due to a decrease in the liquid film 9 covering the inner surface 4a of the innermost layer 4.

On the other hand, in Examples 1 to 5, in which the innermost layer 4 contained an elastomer, the decrease in sliding speed over the storage period was smaller, and even on the 21st day of the test, the sliding speed was still greater than 40 mm/min, demonstrating good sliding properties. It is believed that the lubricating liquid absorbed by the elastomer gradually seeped out onto the inner surface 4a of the innermost layer 4, maintaining the liquid film 9 on the inner surface 4a. Thus, in Examples 1 to 5, improved durability of sliding properties was observed compared to Comparative Examples 1 to 3.

In the moldability evaluation, the innermost layer 4 of the plastic containers 1 of Examples 1 to 6 and Comparative Examples 1 to 3 was uniformly formed with no observed tears or other defects. In Example 7, which had an elastomer content of 40% by mass, tears occurred in some areas of the innermost layer 4, resulting in slightly lower uniformity compared to Examples 1 to 6.

1: Plastic container, 2: Container body, 3: Cap, 4: Innermost layer, 4a: Inner surface, 5: Adhesive resin layer, 6: Intermediate layer, 7: Adhesive resin layer, 8: Outermost layer, 9: Liquid film, 21: Storage section, 22: Mouth section, 31: Cap cover, 32: Cap body, 32a: Upper section, 32b: Discharge port, 32c: Cylindrical section, 33: Connecting section

Claims (5)

A plastic container for containing contents,
An innermost layer that contacts the contents,
the innermost layer is made of a resin composition in which a lubricating liquid is retained in a mixed resin of a polyolefin resin and an elastomer,
At least a part of the surface of the innermost layer that comes into contact with the contents is covered with a liquid film formed by the lubricating liquid,
the lubricating liquid is liquid paraffin,
The content of the elastomer in the mixed resin is 10 to 20 % by mass,
A plastic container, wherein the elastomer is an olefin-based elastomer. 10. The plastic container of claim 1,
A plastic container, wherein the polyolefin resin is low-density polyethylene. The plastic container according to claim 1 or claim 2,
A plastic container, wherein the amount of lubricating liquid held in the innermost layer is 1 to 20 g/ ^m2 . The plastic container according to any one of claims 1 to 3,
A plastic container comprising an intermediate layer and an outermost layer made of EVOH resin. The plastic container according to any one of claims 1 to 4,
A plastic container configured such that the elastomer absorbs and retains a portion of the lubricating liquid, and when the amount of lubricating liquid in the liquid film formed on the surface of the innermost layer that comes into contact with the contents decreases, the lubricating liquid retained in the elastomer seeps out from within the resin composition onto the surface, thereby maintaining the liquid film.