JPH03197566A - Resin composition and multilayered container prepared therefrom - Google Patents

Abstract

PURPOSE:To prepare a resin compsn. excellent in the oxygen barrier properties under the action of both moisture and heat as well as in the transparency by compounding a specific gas-barrier resin with a polyhydric phenol and an electron-donating substance. CONSTITUTION:A thermoplastic gas-barrier resin (e.g. an ethylene-vinyl alcohol copolymer) having an oxygen transmission constant at 20 deg.C and 0% relative humidity of 10<-12>cc.cm/cm<2>-sec.cmHg or lower and water adsorption at 20 deg.C and 100% relative humidity of 0.5% or higher is compounded with a polyhydric phenol (e.g. hydroquinone) and an electron-donating substance (e.g. an oxide or hydroxide of an alkali or alkaline earth metal) to give a resin compsn., which is excellent in the oxygen barrier properties under the action of both water and heat as well as in the transparency. The compsn. is used as the interlayer of a laminated sheet wherein both sides of the interlayer is bonded to moisture-resistant thermoplastic resin layers, and the laminated sheet is used to make a multilayered plastic container.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a resin composition that has excellent oxygen permeability and transparency under conditions where moisture and heat act, and a resin composition that uses the composition. Regarding multilayer plastic containers.

(Prior Art) Conventionally, metal cans, glass bottles, various plastic containers, etc. have been used as packaging containers, but plastic containers are being used for various purposes due to their light weight, impact resistance, and cost. There is.

However, in metal cans and glass bottles, oxygen permeation through the container wall is zero, whereas in the case of plastic containers, oxidation permeation through the container wall occurs on an order of magnitude that cannot be ignored, and the shelf life of the contents is affected. This is a problem.

In order to prevent this, plastic containers have a multi-layered container wall, and at least one layer of the container is made of a resin that is oxidation-resistant and permeable, such as ethylene-vinyl alcohol copolymer. .

In order to remove oxygen inside a container, oxygen scavengers have been used for a long time, and an example of applying this to the container wall is the invention in Japanese Patent Publication No. 1824/1983, which states that oxygen A multilayer structure for packaging is obtained by laminating a layer made of a permeable resin mixed with an oxygen scavenger whose main ingredient is a reducing substance and a layer having oxygen gas barrier properties.

(Problems to be Solved by the Invention) In the prior art described above, the oxygen scavenger present in the container wall absorbs oxygen within the container and maintains the interior of the container in a highly anoxic state. Packaging containers of this type generally still have the problem that under conditions of simultaneous moisture and heat, ie, heat sterilization conditions, oxygen within the container cannot be suppressed to low levels.

In general, oxygen barrier resins such as ethylene-vinyl alcohol copolymers have hygroscopic properties, and have the property that their oxygen permeability coefficient increases due to moisture absorption. For this reason, a multilayer structure is generally adopted in which an oxygen barrier resin is used as an intermediate layer, and inner and outer layers of moisture-resistant resin such as olefin resin are provided on both sides. Therefore, it is recognized that moisture permeation occurs through the olefin resin layer, and the amount of oxygen in the container increases due to an increase in oxygen gas permeability due to moisture absorption in the oxygen barrier resin layer and an increase in oxygen permeability due to a rise in temperature. It will be done.

Contrary to the teachings of the above-mentioned prior art, the present inventors have discovered that when a combination of a polyhydric phenol and an electron-donating substance among oxygen scavengers is added to an oxygen gas barrier resin, moisture and heat act simultaneously. We have discovered that oxygen permeation through a layer made of this resin is suppressed to a significantly low level even under conditions of Ta.

(Means for Solving the Problems) According to the present invention, the oxygen permeability coefficient at 20°C and 0% RH is 10-''cc-cm/cm2·sec-cmt.
Provided is a resin composition comprising a polyhydric phenol and an electron-donating substance blended with a gas barrier plastic resin having an amount of 1 g or less and a water adsorption amount of 0.5% or more at 20° C. and 100% RH. Ru.

According to the present invention, there is also provided a multilayer plastic container characterized by comprising a laminated structure in which the above resin composition is used as an intermediate layer and moisture-resistant thermoplastic resin layers are provided on both sides of the intermediate layer.

(Function) The composition of the present invention is characterized in that a combination of a polyhydric phenol and an electron-donating substance is selected from among oxygen scavengers, and this is blended into a specific gas barrier passion plastic polymer. be.

Polyhydric phenol scavenges oxygen by reacting with oxygen as shown in the following formula, and this oxidation reaction is promoted in the presence of an electron donating substance.

Further, the presence of moisture is essential for this oxidation reaction, that is, the capture of oxygen. In the present invention, the fact that oxygen barrier resins are generally highly hygroscopic is skillfully utilized, and the moisture trapped by the oxygen barrier resins is
It is effectively used to promote the oxidation of polyhydric phenols.

In addition, the polyhydric phenol and electron-donating substance used in the present invention are often colorless, and the polyhydric phenol is compatible with the gas barrier resin, and the electron-donating substance is also dispersed in the resin. This gives transparency to the blended resin composition. Thus, a multilayer container having the resin composition of the present invention as an intermediate layer has the advantage that the container wall is transparent and the contents can be seen through.

In a container using the resin composition of the present invention, especially a multilayer container, under normal conditions, it is the gas barrier oil layer as an intermediate layer that is useful for preventing oxygen permeation, that is, blocking oxygen, but heat sterilization Under such conditions where moisture and heat act simultaneously, the polyhydric phenol-based oxygen scavenger present in the gas barrier fat layer effectively blocks oxygen, and the division of functions is effective depending on the condition in which the container is placed. This is done in a specific manner. That is, as already pointed out, under conditions where moisture and heat act simultaneously, moisture permeation occurs significantly through the moisture-resistant resin layer, and the gas barrier resin loses its original oxygen content due to moisture absorption and also due to an increase in temperature. Although this will reduce the barrier performance, the absorbed moisture activates the polyhydric phenol-based oxygen scavenger, and the polyhydric phenol-based oxygen scavenger effectively captures oxygen, and as a result,
Oxygen permeation during heat sterilization is also suppressed.

Considering its original purpose, the gas barrier resin used in the present invention has an oxygen permeability coefficient of 1 at 20°C and 0% RH.
0-”cc-cm/cm2・sec/cmHg or less,
Especially 5 x 10-13cc-cm/cm2・sec
/cmHg or less. This gas barrier resin is 0.5% or more at 20°C and 100%RH, especially 10%
% or more. If the amount of water adsorption is smaller than the above range, the oxygen scavenging ability of the polyhydric phenol-based oxygen scavenger tends to decrease.

In the layer of the gas barrier resin composition containing the polyhydric phenol-based oxygen scavenger used in the present invention, when the water content or temperature in the layer is high, the oxygen blocking by the polyhydric phenol-based oxygen scavenger does not work effectively. When the moisture content and temperature are low, the gas barrier resin acts as an oxygen barrier.

(Preferred Embodiment) As the gas barrier resin, a thermoplastic resin which has the above-mentioned oxygen permeability coefficient and hygroscopicity and is thermoformable is used. The most suitable example of the gas barrier resin is ethylene-vinyl alcohol copolymer,
For example, if the ethylene content is 20 to 60 mol%, especially 2
A saponified copolymer obtained by saponifying an ethylene-vinyl acetate copolymer having a content of 5 to 50 mol % to a degree of saponification of 96 mol % or more, particularly 99 mol % or more is used. This saponified ethylene vinyl alcohol copolymer should have a molecular weight sufficient to form a film, and generally has a weight ratio of phenol and water of 85:15.
0.0161/g or more when measured at 30°C in a mixed solvent of
In particular, it is desirable to have a viscosity of 0.05617 g or more.

Further, other examples of gas barrier resins having the above-mentioned properties include amide groups having a number of 5 to 5 amide groups per 100 carbon atoms.
Polyamides containing 0, especially in the range from 6 to 20, such as nylon 6, nylon 6.6, nylon 6/6,6
Copolymer, metaxylylene adipamide, nylon 6.1
0, nylon 11, nylon 12, nylon 13, etc. are used. These polyamides also have a molecular weight sufficient to form a film, and in concentrated sulfuric acid 1.0 g/
Relative viscosity [η
rel] is desirably 11.1 or more, particularly 1.5 or more.

As the polyhydric phenol, a polyhydric phenol represented by the following formula is used, in which R represents a hydrogen atom, a hydroxyl group, an alkyl group, an amino group, or a halogen atom. The above formula (
In 2), it is desirable that the two phenolic hydroxyl groups be in the para position.

Suitable examples of the phenols represented by formula (2) above include hydroquinone, catechol, methylhydroquinone, pyrogallol, and the like, with hydroquinone and methylhydroquinone being particularly preferred.

Further, from the viewpoint of hygiene, a larger molecular weight is preferable, and polyhydric phenols such as novolacs and resols can be prepared and used by addition condensation of the above-mentioned polyhydric phenols and formalin.

As already pointed out, the oxygen absorption reaction of polyhydric phenol is
Since the reaction tends to be significantly accelerated in the presence of an electron-donating substance (generally on the alkaline side), an electron-donating substance is also used.

Examples of electron-donating substances include inorganic electron-donating substances such as alkali metal or alkaline earth metal or zinc oxides, hydroxides, carbonates, and silicates, anion exchange resins, melamine resins, and urea resins. and organic electron-donating substances such as ammonia aresol resin. Among these substances, water-insoluble solid substances are recommended from the viewpoint of flavor retention and hygienic properties of the contents. These electron-donating substances may be used singly or in combination of two or more, and may also be used with various fillers such as amorphous silica clay, carbonaceous, zeolite, etc., so that they can be easily dispersed in the resin. It can also be used by being supported on the surface of. From the transparency of the final resin composition, the refractive index of the gas barrier resin used is n. , when the refractive index of the electron donating substance is 01, nl
/n. The ratio of 0.80 to 1.2, especially 0.90 to 1
．． It is desirable that it be in the range of 1.

In the composition of the present invention, per 100 parts by weight of gas barrier resin, polyhydric phenol is contained in 1 to 30 parts by weight, particularly 5 to 20 parts by weight, and electron donating substance is contained in 0.1 to 30 parts by weight, in particular 1 to 30 parts by weight. Preferably, it is used in an amount of 15 parts by weight. If the amount of the added component is less than the above range, the oxygen absorption effect tends to be insufficient, and if it is more than the above range, the oxygen barrier properties of the composition tend to decrease.

The resin composition of the present invention is used as a material for containers by dry blending the above-mentioned ingredients or further kneading and pelletizing the composition, if necessary, and then supplying the resin composition to an extruder, injection machine, etc. This composition is preferably used as an oxygen barrier absorbent layer of a multilayer container by coextrusion or co-injection.

In FIG. 1 showing an example of the multilayer structure of the container of the present invention,
This container wall 1 consists of an intermediate layer 2 of polyhydric phenol-based deoxidizing compounded gas barrier resin, and a moisture-resistant resin layer provided on both sides of the intermediate layer 2 with adhesive layers 3a and 3b as required. It consists of an inner layer 4 and an outer layer 5.

The polyhydric phenol-based deoxidizing compound gas barrier resin layer varies depending on the amount of oxygen allowed in the container.
It is generally desirable to have a thickness of 5 to 200 μm, particularly 10 to 120 μm.

In the present invention, the moisture-resistant resin (low water absorption resin) provided on both sides of these intermediate layers is a thermoplastic resin with a water absorption rate of 0.5% or less, particularly 0.1% or less, as measured by H8STM D570. Typical examples include low-1 medium- or high-density polyethylene, tactical polypropylene, ethylene-120 pyrene copolymer, polybutene-1, ethylene-butene-1 copolymer, propylene-butene-1 Examples include olefin resins such as copolymers, ethylene-vinyl acetate copolymers, ionically crosslinked olefin copolymers (ionomers), and blends thereof, as well as polystyrene, styrene-butadiene copolymers, and styrene-isoprene. Copolymers, styrene resins such as ABS resins, thermoplastic polyesters such as polyethylene phthalate, polytetramethylene terephthalate, and polycarbonates can also be used.

As in the case of ethylene-vinyl alcohol copolymer,
In some cases, sufficient adhesiveness cannot be obtained between the gas barrier resin and the moisture-resistant thermoplastic resin used during lamination, but in this case, an adhesive resin layer is interposed between the two.

Such adhesive resins include carbonyl (-C-) groups based on carboxylic acids, carboxylic acid anhydrides, carboxylic acid salts, carboxylic acid amides, carboxylic acid esters, etc. in the main chain or side chain, with a length of 1 to 700 mi. ■Requivalent (meq) 7100 g resin, especially 10 to 50. Examples include thermoplastic resins containing at a concentration of Omeq/100g resin. Suitable examples of adhesive resins include ethylene-acrylic acid copolymers, ionically crosslinked olefin copolymers, maleic anhydride grafted polyethylene, maleic anhydride grafted polypropylene, acrylic acid grafted polyolefins, ethylene-vinyl acetate copolymers,
One or two of copolymerized polyester, copolymerized polyamide, etc.
It is a combination of more than just species. These resins are useful for lamination, such as by coextrusion or sandwich lamination. In addition, thermosetting adhesive resin such as isocyanate or epoxy adhesive resin is also used for adhesive lamination between the gas barrier resin film and the moisture-resistant resin film that have been formed in advance.

In the multilayer structure of the present invention, the moisture-resistant resin layer generally has a thickness of 20 to 3000 μm, especially 100 to 1500 μm, and 4 to 600 times the thickness of the intermediate layer, especially 10 to 15
Is it possible to have 0 times the thickness?

Further, the inner layer and the inner layer may have the same thickness, or may have a structure in which either the inner layer or the outer layer is thicker than the other layer.

The container of the present invention can be manufactured by a method known per se, except that it has the layered structure described above.

In multilayer simultaneous extrusion, each resin layer is melt-kneaded using an extruder corresponding to the resin layer, and then extruded into a predetermined shape through a multilayer die such as a T-die or a circular die. Further, after melting and kneading each resin layer with an injection machine corresponding to the resin layer, the resin is co-injected or sequentially injected into an injection mold to produce a multilayer container or a preform for a container. Furthermore, lamination methods such as tri-lamination, sandwich lamination, and extrusion coating may also be employed. The molded article can take the form of a film, a sheet, a parison or vibrator for forming bottles or tubes, a preform for forming bottles or tubes, and the like. Formation of bottles from parisons, vibes, or preforms is facilitated by binging off the extrudate through a pair of split molds and blowing fluid into the interior. Further, after cooling the vibrator or preform, it is heated to a stretching temperature, stretched in the axial direction, and blow-stretched in the circumferential direction using fluid pressure, thereby obtaining a stretched blow bottle or the like. In addition, by subjecting the film or sheet to vacuum forming, pressure forming, stretch forming, plug assist forming, etc., cup-shaped,
A packaging container such as a tray shape is obtained.

Furthermore, in the case of a multilayer film, it is also possible to form a bag-like container by stacking or folding the films and heat-sealing the periphery.

(Effects of the Invention) According to the present invention, by blending a polyhydric phenol and an electron-donating substance in a gas barrier resin, the resin composition under normal conditions is Even under conditions such as heat sterilization, where moisture and heat act simultaneously and the original oxygen barrier properties of the oxygen barrier resin are significantly reduced,
The polyhydric phenol oxygen scavenger activated by moisture absorption and heat effectively captures oxygen that attempts to permeate through the container wall, prevents its permeation, and significantly reduces the oxygen concentration inside the container. In addition, this resin composition has the advantage of being extremely transparent as a container constituent material.

Example 1 Oxygen permeability coefficient at 20°C and 0% RH is 4 x 10-
"cc-cm/cm-8ec-cmHg and 20℃
and an ethylene-vinyl alcohol copolymer with a water adsorption amount of 4.8% at 100% RH and an ethylene content of 32
mol %, degree of saponification 996 mol %) pellets and hydroquinone were mixed using a Hutch type high-speed stirring blade type mixing material (Henschel mixer) so that the hydroquinone content was 15% by weight. Next, this mixture was pelletized using a pelletizer consisting of an extrusion material/strand die/blower/cooling tank/cutter equipped with a 50 mm diameter screw. The above pelletized ethylene vinyl alcohol copolymer and hydroquinone mixture (EH) is used as an intermediate layer, and polypropylene (pp) having a melt index of 0.5 g 710 m1n (230°C) is used as an inner and outer layer.
0g710 min maleic anhydride modified PP (AD)
Blow-molded three-dimensional container with symmetrical three types and five layers with adhesive layer (
Surface area/inner volume AFL, 7, body thickness 04 mm, composition ratio P P/A D/E H/A D/P P = 8/
1/2/1/8) 65mm diameter inner and outer layer extrusion material/32mm
It was molded using a blow container molding device consisting of a diameter adhesive extruder/40 mm span layer extruded material/feed block/blow mold. The internal volume of this container was 75 cm' and the surface area was 125 cm2. This container was filled with 2 ml of distilled water in an N2τ atmosphere, and heat-sealed with a sealing material made of aluminum foil/PP. This container was heated to 120℃ for 30 minutes.
Heat sterilization was performed for minutes. After sterilization, it was stored at 20° C. and 60% RH, and the oxygen concentration in the container was measured at regular intervals using a gas chromatography device (GC). Further, as a control product, the same test was conducted on a container of the same name using an ethylene-vinyl alcohol copolymer containing no hydroquinone in the intermediate layer. The results are shown in Table 1.

Example 2 A mixture of hydroquinone and alkali-coated white carbon (
A mixture ratio of 97:3) was blended with the resin according to the method of Example 1 to form a blow-molded container. The container was similarly filled, sealed, and heat sterilized, and after a certain period of time, the oxygen concentration in the container was measured by GC. The results are shown in Table 1.

Example 3 Methylhydroquinone was mixed with the ethylene-vinyl alcohol copolymer of Example 1 according to the method of Example 1, a blow-molded container was prepared in the same manner, and the oxygen permeability was measured. The results are shown in Table 1.

Example 4 Oxygen permeability coefficient at 20°C and O%RH is 5×10-”c
c-crn/ctn2・se, c-cmHg and 20
Moisture adsorption amount at ℃ and 100% RH is 0.5% or less,
Melt index is 0.5g/10m1n (230
Methylhydroquinone (
MHA) was mixed at 15% by weight using a batch type high speed stirring vane type mixer. A symmetrical two-type three-layer blow-molded container with the pelletized MHA-blended pp (ppo) as the middle layer and unblended pp as the inner and outer layers (total thickness 0.4 mm, composition ratio PP/PPO/PP=5:5) 65III11
Molding was performed using a blow container molding device consisting of an extruder for inner and outer diameter layers, an extruder for interlayers with a 40 mm span, a feed block, and a blow mold. Container surface area 125cm2. Internal volume 75
cm'. As in Example 1, the container was filled and sealed in a nitrogen atmosphere, and the change in the concentration of 02 in the container was measured after heat sterilization (120° C. for 30 minutes). The results are shown in Table 1.

Example 5 Oxygen permeability coefficient at 20°C and O%RH is to-13cc
-cm/cm''-set-cmHg and a mixture of hydroquinone and alkali-coated white carbon in polymethaxylylene adipamide (Mitsubishi Gas Chemical Industries, MXD6) with a water adsorption amount of 3.1 at 20 ° C. and 100% R11. (97:3) was made into pellet 90 using the method of Example 1, and a symmetrical three-type, five-layer blow-molded container was made using the pellet.Similarly, after filling and sealing, heat sterilization was performed, and after a certain period of time, the container was The oxygen concentration in the sample was measured using a gas chromatograph.The results are shown in Table 1.

Example 6 An addition condensed methylhydroquinone-formalin polymer (molecular weight range 150 to 350) prepared from methylhydroquinone and formalin was blended into a resin in the same manner as in Example 1,
A blow molded container was created. The oxygen concentration inside the container was measured in the same manner. The results are shown in Table 1.

[Brief explanation of drawings]

In FIG. 1, each number represents the following. 1... Film wall 2...Oxygen absorber compounded intermediate layer 3a, b...adhesive layer 4...Moisture-resistant resin inner layer 5...Moisture-resistant resin outer layer hand Continued Supplementary Positive 1■ (method) %formula% 1.Display of the incident 1999 Patent Application No. 334948 name of invention Resin composition and multilayer container using the same 3. Person who makes corrections Relationship with the incident

Claims (2)

[Claims] (1) Oxygen permeability coefficient at 20℃ and 0%RH is 10
^-^1^2cc・cm/cm^2・sec・cmHg
A resin composition comprising a polyhydric phenol and an electron-donating substance blended with a gas barrier thermoplastic resin having a water adsorption amount of 0.5% or more at 20° C. and 100% RH. (2) A multilayer plastic container comprising a laminated structure comprising the resin composition according to claim 1 as an intermediate layer and moisture-resistant thermoplastic resin layers on both sides of the intermediate layer.