HK1164816B - Storage method - Google Patents

Description

Preservation method

Technical Field

The present invention relates to a method for preserving foods, beverages, medicines, electronic components, and the like.

Background

In order to protect contents from various treatments such as distribution, preservation such as refrigeration, and heat sterilization, a packaging material for packaging foods, beverages, and the like is required to have various functions such as excellent transparency and the like, which allows the contents to be confirmed from the outside, in addition to mechanical properties such as strength, hard cracking property, and heat resistance. Further, in recent years, in order to suppress oxidation of foods, it has been required to have an oxygen barrier property for preventing oxygen from entering from the outside, a carbon dioxide barrier property, and a barrier property against various aroma components and the like.

Sheets and films made of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate (PET), and aliphatic polyamides such as nylon 6 are widely used as packaging materials because they are not only transparent and excellent in mechanical properties but also easy to handle and process. However, since it has a poor barrier property against gaseous substances such as oxygen, it is likely to cause oxidative deterioration of the contents, or it is likely to permeate aroma components and carbon dioxide, thereby having a disadvantage that the shelf life of the contents is shortened.

Plastic containers (such as bottles) mainly composed of polyesters such as polyethylene terephthalate are widely used for tea, fruit juice beverages, carbonated beverages, and the like. In addition, among plastic containers, the proportion of small plastic bottles is increasing year by year. Since the ratio of the surface area per unit volume of the bottle increases as the bottle is miniaturized, the shelf life of the contents tends to be shortened when the bottle is miniaturized. In recent years, beer susceptible to oxygen and light is sold in plastic bottles, and tea in plastic bottles is sold hot, and the range of use of plastic containers is expanding, and further improvement in gas barrier property (gas barrier property) of plastic containers is required.

Films and the like comprising a combination of the thermoplastic resin and a gas barrier resin such as vinylidene chloride, an ethylene-vinyl alcohol copolymer, or polyvinyl alcohol are used for improving the barrier property against gaseous substances such as oxygen. However, although a film in which vinylidene chloride is laminated has excellent gas barrier properties regardless of storage conditions, it has a problem that dioxin is generated when it is burned, and the environment is polluted. Although the ethylene-vinyl alcohol copolymer and polyvinyl alcohol do not have the above-mentioned problem of environmental contamination, and a multilayer film having these as a barrier layer can exhibit excellent gas barrier properties in an environment with low humidity, if the water activity of the stored contents is high, or the contents are stored in an environment with high humidity, or further heat sterilization treatment is performed after the contents are filled, the gas barrier properties tend to be greatly reduced, and there is a problem in the storage properties of the contents in some cases.

On the other hand, xylylene-containing polyamide obtained by polycondensation of xylylenediamine and an aliphatic dicarboxylic acid, particularly polyamide MXD6 obtained from m-xylylenediamine and adipic acid, is a material exhibiting high barrier properties against gaseous substances such as oxygen and carbon dioxide. Although the gas barrier property under high humidity is superior to that of the ethylene-vinyl alcohol copolymer and polyvinyl alcohol, the ethylene-vinyl alcohol copolymer and polyvinyl alcohol have a disadvantage that the gas barrier property under low and medium humidity is slightly inferior to those of these materials.

Further, a resin having a function of trapping oxygen in the container while isolating oxygen from outside the container has been developed and applied to a multilayer bottle. As the oxygen gas-trapping bottle, there is a multilayer bottle using polyamide MXD6 mixed with a transition metal catalyst as a gas barrier layer in terms of oxygen absorption rate, transparency, strength, moldability, and the like. However, the addition of the transition metal accelerates the oxidative decomposition of the polyamide MXD6, which leads to a problem of a decrease in resin strength.

On the other hand, as an oxygen trapping technique without using a transition metal, an oxygen absorption method utilizing a case where a compound obtained by reducing a reduced organic compound is oxidized by oxygen is disclosed (see patent documents 1 and 2). According to this document, the oxygen barrier property can be surely improved under the conditions of room temperature and low humidity. However, this requires a step of reducing the organic compound to be reduced, and improvement is desired from the viewpoint of cost.

Patent document 1: japanese patent No. 2922306

Patent document 2: japanese Kokai publication Hei-2001-514131

Disclosure of Invention

The present invention has been made to solve the above problems, and an object of the present invention is to provide a storage method capable of improving the gas barrier property of a package by a simple method.

As a result of intensive studies, the present inventors have found that gas barrier properties are improved when a package containing a polyamide resin having a specific composition is irradiated with light, and have completed the present invention.

That is, the present invention relates to a storage method for storing a content in a package at least a part of which is formed of a polyamide (a) obtained by polycondensation of a diamine component containing 70 mol% or more of m-xylylenediamine and a dicarboxylic acid component containing 70 mol% or more of an α, ω -linear aliphatic dicarboxylic acid having 4 to 20 carbon atoms, and storing the content under irradiation with light.

According to the present invention, the gas barrier property of the package can be improved by a simple method, and the deterioration of the contents can be effectively controlled, and therefore, the present invention is industrially significant.

Drawings

Fig. 1 is a spectral distribution curve of a light source a used in the example.

Fig. 2 is a spectral distribution curve of the light source B used in the embodiment.

Fig. 3 is a spectral distribution curve of the light source C used in the example.

Fig. 4 is a spectral distribution curve of the light source D used in the embodiment.

Detailed Description

At least a part of the package used in the present invention is formed of a polyamide (a) obtained by polycondensation of a diamine component containing 70 mol% or more of m-xylylenediamine and a dicarboxylic acid component containing 70 mol% or more of a, ω -linear aliphatic dicarboxylic acid having 4 to 20 carbon atoms.

The polyamide (A) has high gas barrier properties and good heat resistance and moldability. The diamine component of the polyamide (a) contains 70 mol% or more, preferably 75 mol% or more, and more preferably 80 mol% or more of m-xylylenediamine (each content is 100%). The dicarboxylic acid component contains 70 mol% or more, preferably 75 mol% or more, more preferably 80 mol% or more, and still more preferably 90 mol% or more of an α, ω -linear aliphatic dicarboxylic acid having 4 to 20 carbon atoms (each content being 100%).

In the present invention, examples of the diamine other than m-xylylenediamine that can be used include aliphatic diamines such as tetramethylenediamine, pentamethylenediamine, 2-methylpentanediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, dodecamethylenediamine, 2, 4-trimethyl-hexamethylenediamine, and 2, 4, 4-trimethyl-hexamethylenediamine; alicyclic diamines such as 1, 3-bis (aminomethyl) cyclohexane, 1, 4-bis (aminomethyl) cyclohexane, 1, 3-diaminocyclohexane, 1, 4-diaminocyclohexane, bis (4-aminocyclohexyl) methane, 2-bis (4-aminocyclohexyl) propane, bis (aminomethyl) decalin, and bis (aminomethyl) tricyclodecane; diamines having an aromatic ring such as bis (4-aminophenyl) ether, p-phenylenediamine, p-xylylenediamine, and bis (aminomethyl) naphthalene.

Examples of the α, ω -linear aliphatic dicarboxylic acid having 4 to 20 carbon atoms include aliphatic dicarboxylic acids such as succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, adipic acid, sebacic acid, undecanedioic acid, and dodecanedioic acid, and among these, adipic acid and sebacic acid are preferable. In the present invention, examples of dicarboxylic acids other than the c 4 to c 20 α, ω -linear aliphatic dicarboxylic acid include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and 2, 6-naphthalenedicarboxylic acid. The dicarboxylic acid component may contain isophthalic acid in an amount of preferably 1 to 20 mol%, more preferably 3 to 10 mol%. When isophthalic acid is contained in the dicarboxylic acid component, whitening immediately after molding can be further suppressed.

The method for producing the polyamide (a) is not particularly limited, and the polyamide (a) can be produced by a conventionally known method and polymerization conditions. In the polycondensation of polyamide, a small amount of monoamine or monocarboxylic acid may be added as a molecular weight modifier. For example, the polyamide (A) can be prepared by the following method: a nylon salt comprising m-xylylenediamine and adipic acid is heated under pressure in the presence of water, and the added water and water of condensation are removed and polymerized in a molten state. Alternatively, the m-xylylenediamine can be produced by a method in which m-xylylenediamine is directly added to adipic acid in a molten state and polycondensation is carried out under normal pressure. In this case, m-xylylenediamine is continuously added to adipic acid in order to keep the reaction system in a uniform liquid state, and during this time, the reaction system is heated to a temperature not lower than the melting points of the oligoamide and the polyamide to be formed, while the polycondensation is being performed.

Further, after the polyamide (a) is produced by the melt polymerization method, solid-phase polymerization may be performed. The solid-phase polymerization method of the polyamide (a) is not particularly limited, and can be carried out by a conventionally known method and polymerization conditions.

The number average molecular weight of the polyamide (A) is preferably 18000 to 43500, more preferably 20000 to 30000. When the amount is within this range, the heat resistance and moldability are good.

The relative viscosity of the polyamide (A) is preferably 1.8 to 3.9, more preferably 2.4 to 3.7, and still more preferably 2.5 to 3.7. When the relative viscosity is 1.8 to 3.9, the inward bending (edge) during extrusion molding is small, and therefore, it is easy to widen the width of the obtained film or sheet or adjust the width dimension.

The relative viscosity referred to herein is a falling time (t) measured at 25 ℃ with a Cannon-Fenske viscometer (Cannon-Fenske typeviscometer) in which 1g of the polyamide (A) is dissolved in 100cc (1dl) of 96% sulfuric acid, and a falling time (t) of 96% sulfuric acid measured in the same manner₀) The ratio of (A) to (B) is represented by the following formula.

Relative viscosity ═ t)/(t₀)

The polyamide (a) may contain additives such as impact resistance modifiers such as various elastomers, crystal nucleating agents, lubricants such as fatty amide-based, fatty acid metal salt-based and fatty acid amide-based compounds, antioxidants such as copper compounds, organic or inorganic halogen-based compounds, hindered phenol-based, hindered amine-based, hydrazine-based and sulfur-based compounds, phosphorus-based compounds such as sodium hypophosphite, potassium hypophosphite, calcium hypophosphite and magnesium hypophosphite, heat stabilizers, coloring inhibitors, ultraviolet absorbers such as benzotriazole-based, release agents, plasticizers, colorants, flame retardants, and alkali compounds for preventing gelation of polyamide resins.

In the present invention, the oxygen barrier property of the package can be improved by irradiating the package at least partially formed of the polyamide (a) with light. That is, if the content is stored in the package and irradiated with light, the oxygen barrier property of the package can be improved and the oxidative degradation of the content can be suppressed. The wavelength of light used in the present invention is preferably 10 to 1000nm, more preferably 200 to 800nm, and further preferably 400 to 750 nm. In addition, the spectral distribution curve preferably has a peak at 600nm or less, and peaks at 405nm, 436nm, 546nm, 578nm, 589nm, 450nm, 538nm, 583nm, and the like can be illustrated.

In the present invention, the illuminance of the light to be irradiated is preferably 100 to 10000lux, more preferably 1000 to 10000lux, and still more preferably 3000 to 10000lux on the surface of the package.

The temperature in the light irradiation process is preferably 0 to 60 ℃, more preferably 5 to 50 ℃, and further preferably 10 to 40 ℃. Within this range, the oxygen permeability of the container is favorably reduced at the time of light irradiation, that is, the oxygen barrier property is favorably improved. The light irradiation time may be determined according to the period of time during which the contents are stored by a known method.

The degree of improvement of the oxygen barrier property varies depending on the content of the polyamide (a) in the package, the illuminance of light, and the like, and the content of the polyamide (a) is preferably 0.1 to 100% by weight, more preferably 1 to 100% by weight, from the viewpoint of improving the oxygen barrier property. When the polyamide (a) is blended with another resin, the content is preferably 1 to 50% by weight, more preferably 2 to 10% by weight. The average thickness of the package is preferably 10 to 3000 μm, and the average thickness of the polyamide (A) -containing layer is preferably 1 to 400 μm, and more preferably 5 to 400 μm. When the packages are irradiated with light having a wavelength of 10 to 1000nm at an illuminance of 100 to 10000lux, the oxygen permeability after 24 hours of irradiation is preferably reduced to 1 to 75% before the irradiation, more preferably 1 to 70% before the irradiation.

Examples of the package include a storage container used heretofore, such as a multilayer film bag, a multilayer sheet bag, a multilayer bottle, a multilayer blown bottle (multilayer bottle), a single-layer film bag, and a single-layer bottle. For example, various packaging materials such as a bag-shaped container such as a four-side sealed bag, various pillow bags, and a standing pouch, and a lid material for a container can be obtained by a known production method and production conditions using a substantially unstretched polyamide (a) single-layer film or a substantially unstretched multilayer film having at least one polyamide (a) layer.

Further, a stretched film obtained by uniaxially or biaxially stretching a roll multilayer film having at least one polyamide (a) layer may be used for producing the container. Alternatively, the multilayer unstretched film may be thermoformed to form a cup-shaped container. Further, the polyamide (a) film may be laminated with paper to form a multilayer container. These containers can also be manufactured by known manufacturing methods and manufacturing conditions.

Examples of the resin forming the layer other than the polyamide (a) layer of the multilayer container include polyesters such as low-density polyethylene, high-density polyethylene, linear low-density polyethylene, polypropylene, ethylene-vinyl acetate copolymer, polystyrene, polyethylene terephthalate, modified polyolefins, polyamides other than the polyamide (a), and the like, and these may be used alone or in combination of two or more.

The package can contain and store various articles. For example, various articles such as liquid beverages, liquids, powdery or pasty seasonings, pasty foods, liquid foods, raw noodles, boiled noodles, grains, processed products of grains, dairy products, solid or solution-like chemicals, liquid or pasty pharmaceuticals, cosmetics, electronic parts, and the like can be stored.

In particular, when storing articles having high moisture activity, when exposed to high humidity during storage, and when heat sterilization treatment such as boiling or boiling is performed, it is preferable to use a multilayer container.

Examples

The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples. The oxygen permeability of the package (bottle, film) was measured by the following method.

(1) Oxygen permeability of film

The oxygen permeability (cc/m) of the film before and after light irradiation was measured according to ASTM D3985 under an atmosphere of 60% RH (relative humidity)²Day atm). OX-TRAN 2/21, manufactured by Modern Controls Inc., was used for the measurement. A lower value indicates better gas barrier properties. In addition, in the case of light irradiation, measurement was performed under the temperature conditions described in examples 24 hours after the start of light irradiation. Measurement in the light-shielded state was performed under the condition of 23 ℃.

(2) Oxygen permeability of bottle

The oxygen permeability (cc/bottle · day · 0.21atm) of the bottle before and after the light irradiation was measured according to astm d3985 under an atmosphere of 100% RH inside the bottle and 50% RH outside the bottle. OX-TRAN 2/61, manufactured by Modern Controls Inc., was used for the measurement. A lower value indicates better oxygen barrier properties. In addition, in the case of light irradiation, measurement was performed under the temperature conditions described in examples 24 hours after the start of light irradiation. Measurement in the light-shielded state was performed under the condition of 23 ℃.

The light source used in the examples is as follows.

A light source A: straight tube fluorescent lamp manufactured by Panasonic Corporation (model FL 40S. WW)

The spectral distribution curve is shown in fig. 1.

A light source A: high color rendering fluorescent lamp manufactured by Panasonic Corporation (model FL 40S. L-EDL)

The spectral distribution curve is shown in fig. 2.

A light source C: polyhalogen lamps (model MF 100. L/BU) made by Panasonic Corporation

The spectral distribution curve is shown in fig. 3.

A light source D: long-life quartz bulb manufactured by Panasonic Corporation (model LW 100V54WL)

The spectral distribution curve is shown in fig. 4.

Each spectral distribution curve is provided by Panasonic Corporation.

Example 1

A3-layer preform (26g) composed of a polyester layer/a polyamide layer/a polyester layer was produced by injection molding using as the polyamide (A) poly (m-xylylene adipamide) (MXD6, MXNylon S6007 manufactured by Mitsubishi gas chemical Co., Ltd.). After the preform is cooled, it is heated to be biaxially stretched and blow molded to obtain a multilayer bottle. As a resin constituting the polyester layer, polyethylene terephthalate (1101 made by Invista) having an intrinsic viscosity (measured at 30 ℃ using a mixed solvent of phenol/tetrachloroethane (6/4 (weight ratio)) of 0.80 was used. Wherein the polyamide (A) content in the multilayer bottle is 6% by weight. The average thickness of the multilayer bottle body part was 150 μm/30 μm/150 μm, polyester layer/polyamide layer/polyester layer.

The obtained multilayer bottle was kept in a light-shielded state, and the oxygen permeability was measured. The oxygen permeability was 0.012 cc/bottle-day-0.21 atm.

The oxygen permeability was measured while irradiating the resulting multilayer bottle with 200lux (light source A). The oxygen gas permeability was reduced to 0.008 cc/bottle.day.0.21 atm, and good gas barrier properties were exhibited. The test temperature was set at 23 ℃. The results are shown in Table 1 (the same applies hereinafter).

Example 2

The oxygen gas permeability was measured in the same manner as in example 1, except that the multilayer bottle obtained in the same manner as in example 1 was irradiated with light of 3000lux (light source a). The oxygen gas permeability was reduced to 0.005 cc/bottle.day.0.21 atm, and good gas barrier properties were exhibited. The test temperature was set at 23 ℃. Further, the polyamide (A) content in the multilayer bottle was 6% by weight.

Example 3

Oxygen permeability was measured in the same manner as in example 1, except that the multilayer bottle obtained in the same manner as in example 1 was irradiated with light of 5000lux (light source B). The oxygen gas permeability was reduced to 0.004 cc/bottle-day-0.21 atm, and good gas barrier properties were exhibited. The test temperature was set at 23 ℃. Further, the polyamide (A) content in the multilayer bottle was 6% by weight.

Example 4

Oxygen gas permeability was measured in the same manner as in example 1, except that 8000lux (light source C) of light was irradiated to the multilayer bottle obtained in the same manner as in example 1. The oxygen gas permeability was reduced to 0.003 cc/bottle-day-0.21 atm, and good gas barrier properties were exhibited. The test temperature was set at 23 ℃. Further, the polyamide (a) content in the multilayer bottle was 8% by weight.

Example 5

5% by weight of poly (m-xylylene adipamide) (MX Nylon S6007 manufactured by Mitsubishi gas chemical Co., Ltd.) as the polyamide (A) and 95% by weight of polyethylene terephthalate (1101 manufactured by Invista) were dry-blended. A single-layer preform (26g) was produced by injection molding using the dry-blended resin. After the preform is cooled, it is heated to be biaxially stretched and blow molded to obtain a single-layer bottle. The average thickness of the bottle body was 300. mu.m.

The obtained monolayer bottle was kept in a light-shielded state, and the oxygen permeability was measured. The oxygen permeability is 0.035 cc/bottle-day-0.21 atm.

The obtained bottle was irradiated with 2000lux (light source B) of light, and the oxygen permeability was measured. The oxygen gas permeability was reduced to 0.005 cc/bottle.day.0.21 atm, and good gas barrier properties were exhibited. The test temperature was set at 35 ℃.

Example 6

A bottle was produced in the same manner as in example 5, except that 2% by weight of the polyamide (a) and 98% by weight of the polyethylene terephthalate were dry blended. The oxygen permeability of the obtained bottle in a light-shielded state was 0.039 cc/bottle-day-0.21 atm. The oxygen permeability was measured in the same manner as in example 5 except that the obtained bottle was irradiated with 5000lux of light (light source B) and the test temperature was set to 10 ℃. The oxygen gas permeability was reduced to 0.015 cc/bottle · day · 0.21atm, and good gas barrier properties were exhibited.

Example 7

A 3-layer stretched film composed of a Nylon 6 layer/a polyamide (a) layer/a Nylon 6 layer was produced using poly (m-xylylene adipamide) (mxnylon S6007, manufactured by mitsubishi gas chemical corporation) as the polyamide (a). The resin constituting the nylon 6 layer was UBE nylon 1022B manufactured by yuken corporation. Further, the thickness of the nylon 6 layer/polyamide layer/nylon 6 layer was 5 μm/5 μm/5 μm. The polyamide (a) content in the multilayer film was 35% by weight.

The obtained multilayer film was measured for oxygen permeability while being kept in a light-shielding state. Oxygen permeability of 8cc/m²Day atm.

The obtained film was mounted on a jig capable of measuring the oxygen permeability while irradiating 5000lux (light source C) of light with one surface thereof exposed to the atmosphere and the other surface thereof maintained in a nitrogen gas flow. Oxygen permeability is reduced to 5cc/m²Day atm, showing good gas barrier properties. The test temperature was set to 40 ℃.

Example 8

The oxygen gas permeability was measured in the same manner as in example 6 except that the film obtained in example 7 was irradiated with 7000lux (light source a) of light and the test temperature was set to 5 ℃. Oxygen permeability is reduced to 1cc/m²Day atm, showing good gas barrier properties.

Example 9

The oxygen gas permeability was measured in the same manner as in example 6 except that the film obtained in example 7 was irradiated with 1000lux (light source B) of light and the test temperature was set to 50 ℃. Oxygen permeability is reduced to 6cc/m²Day atm, showing good gas barrier properties.

Example 10

A monolayer bottle (27g) was prepared in the same manner as in example 5 except that 100 parts by weight of a polyamide composed of m-xylylenediamine and sebacic acid was used as the polyamide (A), and the average thickness of the bottle body was 330. mu.m. The obtained multilayer bottle was kept in a light-shielded state, and the oxygen permeability was measured. The oxygen permeability is 0.011 cc/bottle-day-0.21 atm.

The obtained bottle was irradiated with 4000lux of light (light source A) and the oxygen permeability was measured. The oxygen gas permeability was reduced to 0.0003 cc/bottle · day · 0.21atm, and a good gas barrier property was exhibited. The test temperature was set at 23 ℃.

Example 11

The oxygen gas permeability was measured in the same manner as in example 10, except that the bottle obtained in example 10 was irradiated with light of 4000lux (light source D). The oxygen gas permeability was reduced to 0.008 cc/bottle.day.0.21 atm, and good gas barrier properties were exhibited. The test temperature was set at 23 ℃.

[ Table 1]

TABLE 1

[ Table 2]

TABLE 1 (continuation)

Oxygen transmission rate: cc/bottle/day 0.21atm in the case of bottle, and cc/m in the case of film²Day atm.

Improvement rate: (oxygen transmission after 24 hours of irradiation/oxygen transmission in light-shielded state). times.100

As shown in the above examples, it is understood that when a package containing a polyamide (a) having a specific composition is irradiated with light, the oxygen permeability is reduced and the storage stability of the contents is improved as compared with the case where irradiation is not performed.

Claims (5)

1. A storage method characterized by containing a content in a package at least a part of which is formed of a polyamide (A) obtained by polycondensation of a diamine component containing 70 mol% or more of m-xylylenediamine and a dicarboxylic acid component containing 70 mol% or more of an alpha, omega-linear aliphatic dicarboxylic acid having 4 to 20 carbon atoms, and storing the obtained package containing the content under irradiation with light having a wavelength of 400 to 750nm to reduce the oxygen permeability of the package.

2. The storage method according to claim 1, wherein the package contains 0.1 to 100% by weight of the polyamide (A), has an average thickness of 10 to 3000 μm, and has an oxygen transmission rate of 1 to 75% before irradiation after irradiation with light having a wavelength of 400 to 750nm for 24 hours at an illuminance of 100 to 10000 lux.

3. The preservation method according to claim 1, wherein the illuminance of the light is 3000 to 10000 lux.

4. The preservation method according to claim 1, wherein the light is light having a peak at 600nm or less in a spectral distribution curve.

5. The preservation method according to claim 1, wherein the light has a peak at any one or more of 405nm, 436nm, 546nm, 578nm, 589nm, 450nm, 538nm, and 583nm in a spectral distribution curve.