JP4690678B2 - Oxygen-absorbing resin composition and multilayer structure - Google Patents

Description

  The present invention relates to an oxygen-absorbing resin composition having an oxygen-absorbing property and a sustained gas barrier property, and a multilayer structure such as a multilayer film and a multilayer container having a layer made of the resin composition as an oxygen-absorbing layer. .

  Since the development of ethylene-vinyl alcohol copolymer (EVOH), which has excellent gas (oxygen, carbon dioxide) barrier properties, EVOH has been replaced by glass, metal, or conventional plastic materials. In the field of industrial chemicals and the like, it is a resin that is widely used as a gas barrier material for packaging materials or containers for products that dislike oxygen. The EVOH has a hygroscopic property, and if it absorbs moisture, the gas barrier property is lowered. Therefore, is EVOH covered with a hydrophobic thermoplastic resin such as polyolefin resin or polyester resin? Or, it is usually used as a multilayer structure in which EVOH is an intermediate layer and thermoplastic resin is an inner layer and an outer layer.

  EVOH is widely used for packaging materials by utilizing its gas barrier property, but it does not completely block oxygen, but does not have the function of absorbing oxygen, so that a slight permeation of oxygen is avoided. Is inevitable. In addition to this permeated oxygen, the removal of oxygen that is already inside when sealed or, especially in food containers that are often used with the lid open and closed, is mainly in the food sector. As a result, active development of materials having gas barrier properties and oxygen-absorbing properties by blending an oxidizing resin or an oxidation catalyst with a gas barrier resin has been actively conducted.

Recently, with respect to polyolefin-based oxygen absorbers, reports have been made on the relationship between chemical structure (unit structure) and oxygen absorption capacity, additives, and the like. According to this, the reactivity differs depending on the bonding method of polyolefin, and tertiary hydrogen and allyl hydrogen react with oxygen in the air even at a low temperature in a refrigerated state to form hydroperoxide. It has been reported that the most worrisome is the malodor of low molecular weight volatile aldehydes, ketones and carboxylic acids generated by the reaction of the polymer with oxygen (see, for example, Non-Patent Document 1).
Specific resin compositions having oxygen-absorbing properties include styrene-isoprene-styrene triblock copolymer (a thermoplastic resin having a carbon-carbon double bond: referred to as an acidified polymer) and boronic acid 1, There has been proposed a resin composition in which a composition comprising a triblock copolymer (compatibility agent) having a 3-butanediol group and a transition metal is blended in EVOH (for example, see Patent Document 1). However, although this resin composition has an effect of improving oxygen absorption (oxygen scavenging function) due to the blending of the thermoplastic resin having a carbon-carbon double bond, There is a risk that a thermoplastic resin having a heavy bond is oxidatively decomposed to generate volatile substances that cause odors such as aldehydes, ketones, and carboxylic acids. Moreover, it is necessary to use an adhesive for lamination.

  Moreover, in order to suppress the permeation | transmission of the said odor substance, the multilayer container which provided the odor barrier layer between the oxygen absorptive barrier layer and the inner layer is proposed (for example, refer patent document 2). However, the material of the odor barrier layer is EVOH or a cyclic olefin resin used as a gas barrier layer, and no special odor barrier material is used. Therefore, the multilayer container of Patent Document 2 has the same problem as that of Patent Document 1, and since the odor barrier layer is added, the thickness of the container increases and the manufacturing cost increases.

  Further, as an oxygen absorber, a polyamide composition containing polyamide (PA) and a PA-reactive oxidizable polybutadiene or oxidizable polyether, and a polyamide composition containing an oxidation promoting metal salt catalyst in the polyamide composition, In addition, a multilayer product in which a thermoplastic resin layer is provided on one side or both sides of an oxygen-barrier polyamide layer made of this polyamide composition has been proposed (see, for example, Patent Document 3).

Global Packaging News No.7 May, (1999) JP 2002-146217 A JP2004-196337 Special table 2003-531929

  The object of the present invention is to develop an oxygen-absorbing resin composition that can improve the gas barrier properties and oxygen-absorbing properties, does not generate volatile substances that cause odors, and can be laminated without using an adhesive. It is also to develop a multilayer structure composed of an oxygen-absorbing layer made of the oxygen-absorbing resin composition, particularly a multilayer film and a multilayer container.

  The present inventors conducted extensive research to solve the above-mentioned problems, and found that a resin composition containing a reaction product of polyamide and oxidizable polydiene or oxidizable polyether in EVOH was oxygen-absorbing. By constituting as a gas barrier layer, it is possible to obtain a multilayer structure having a good gas barrier property and oxygen absorption property and having a required interlayer adhesive strength without providing a special odor barrier layer or an adhesive layer. I found it. The present invention has been made based on such findings.

That is. The present invention provides an oxygen-absorbing resin composition, a multilayer structure, a multilayer squeeze container and a multilayer film having the constitutions described in 1) to 7) below.
1) A) ethylene-vinyl alcohol copolymer 55 to 80% by weight, (B) 10 to 35 % by weight of reaction product and transition metal salt of polyamide and polyamide-reactive oxidizable polydiene or oxidizable polyether %, and (C) an oxygen-absorbing resin composition characterized by comprising an ethylene copolymer 10-30 wt% having a carboxyl group.
2) The group in which the polyamide-reactive oxidizable polydiene is a polymer containing polybutadiene, and the ethylene copolymer having a carboxyl group is composed of an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, or an ionomer. The oxygen-absorbing resin composition according to 1), which is at least one kind of thermoplastic resin selected from the above.

3) The oxygen-absorbing resin composition according to 1) or 2), wherein the polyamide is an amorphous polyamide or a mixture of a crystalline polyamide and an amorphous polyamide.
4) An oxygen-absorbing multilayer structure comprising a layer made of the oxygen-absorbing resin composition according to any one of 1 to 3 above.
5) The oxygen-absorbing multilayer structure according to 4), wherein the interlayer adhesive strength (JISZ0238) between the layer composed of the oxygen-absorbing resin composition of the multilayer structure and at least one adjacent layer is 10 g / 15 mm width or more. .

6) A base resin layer made of low-density polyethylene and an oxygen-absorbing layer made of the oxygen-absorbing resin composition according to any one of items 1) to 3), wherein the inner and outer layers are base resin layers. In addition, squeeze property comprising two types and three layers provided with an oxygen absorbing layer as an intermediate layer or two types and five layers provided with a sandwich structure in which a base resin layer is sandwiched between oxygen absorbing layers. Multi-layer container.

7) An outer layer having a sandwich structure in which a resin layer made of polymetaxylylene adipamide is sandwiched between resin layers made of polyamide 6, and an oxygen-absorbing resin composition according to any one of items 1) to 3) The oxygen-absorbing resin composition according to any one of claims 1 to 3 , and an inner / outer layer made of a laminate of an intermediate layer made of the above and an inner layer made of a polyolefin-based resin, or a linear low density polyethylene. A multilayer film comprising: an oxygen absorption layer comprising: an intermediate layer obtained by laminating an oxygen barrier layer comprising an ethylene-vinyl alcohol copolymer;

The oxygen-absorbing resin composition of the present invention comprises the above components (A) to (C), in particular, the reaction product of the polyamide (B) and the oxidizable polydiene + the transition metal salt and the component (A). By using in combination with EVOH, the following excellent characteristics can be obtained.
1) It has a good balance of characteristics such as oxygen permeability, oxygen absorption, and light transmission required for a multilayer structure, and a suitable oxygen absorption ability is exhibited.
2) Interlayer adhesive strength (10 g / 15 mm width or more) required for a squeeze container can be obtained without providing an adhesive layer. Therefore, the layer configuration is simplified.
3) Volatile substances that cause odors are not by-produced. Accordingly, the odor barrier layer is not required, and the layer structure is simplified as in the above 2).

Hereinafter, the present invention will be described in detail.
The ethylene-vinyl alcohol copolymer (EVOH) as the component (A) is not particularly limited, but is generally EVOH obtained by saponifying an ethylene-vinyl acetate copolymer having an ethylene content of 60 mol% or less to a saponification degree of 90% or more. Is used.

  The component (B) is composed of a reaction product of polyamide and polyamide-reactive oxidizable polydiene or oxidizable polyether and a transition metal salt. The oxidizable polydiene or polyether is reacted with a polyamide, and the polydiene or polyether is preferably acid-modified, contains an epoxy group or an anhydrous functional group, and includes a carboxyl group or amino end group of the polyamide, and further It reacts with the amide group in the polyamide skeleton.

The polyamide may be a polymer having an amide bond, and includes a polymer having an amide bond obtained by a reaction between a carboxylic acid and an isocyanate, in addition to a polymer obtained by a dehydration condensation reaction between a carboxylic acid and an amine.
Specifically, polycaproamide (nylon-6), polyundecanamide (nylon-11), polylaurolactam (nylon-12), polyhexamethylene adipamide (nylon-6,6), polyhexamethylene Aliphatic polyamide homopolymers such as bacamide (nylon-6,10); caprolactam / laurolactam copolymer (nylon-6 / 12), caprolactam / aminoundecanoic acid copolymer (nylon-6 / 11), caprolactam / Ω-aminononanoic acid copolymer (nylon-6 / 9), caprolactam / hexamethylene adipamide copolymer (nylon-6 / 6,6), caprolactam / hexamethylene adipamide / hexamethylene sebacamide Aliphatic polyamide copolymers such as polymers (nylon-6 / 6,6 / 6,10); Xylylene adipamide (MX- nylon) can be used hexamethylene terephthalamide / hexamethylene isophthalamide copolymer (Nylon-6T / 6I) aromatic polyamide or a mixture of these, and the like.

In particular, amorphous polyamide or a blend of crystalline polyamide and amorphous polyamide is suitable. Here, the amorphous polyamide is one having a calorie of crystal fusion measured by a differential scanning calorimeter (DSC) of 1 cal / g or less, so that the polymer is hardly crystallized or has a very high crystallization rate. A small group of polyamide resins.
Examples of the oxidizable polydiene include epoxy-functionalized polybutadiene, epoxy-functionalized polyisoprene, maleic anhydride graft or copolymerized polybutadiene, maleic anhydride graft or copolymerized polyisoprene.

Examples of the oxidizable polyether include amine, epoxy or anhydrous functional polypropylene oxide, polybutylene oxide, and polystyrene oxide.
Furthermore, a transition metal salt is added to the component (B) as an oxidation catalyst in a range of 5000 ppm or less in terms of metal atomic weight. Transition metal salts are inorganic salts, organic salts, or complex salts of transition metals such as cobalt, iron, nickel, and copper, titanium, chromium, manganese, ruthenium, and especially organic acid salts such as carboxylates and sulfonates. Specific examples thereof include acetate, stearate, propionate, hexanoate, octanoate, neodecanoate, stearate and the like.

Component (C) is an ethylene copolymer containing a carboxyl group, an ethylene copolymer having an ethylene content of 65 to 98 mol%, an ethylene content of 70 to 98 mol%, and a saponification rate of 20% or more. An ethylene-vinyl acetate copolymer saponified product or a mixture of 40% by weight or more and 60% by weight or less of the saponified product. Specific examples of the polymer include an ethylene-acrylic acid copolymer (EAA) and an ethylene-methacrylic acid copolymer obtained by copolymerization of a monomer having a carboxyl group or a carboxylic anhydride group using an α-olefin. (EMA), various ionomers, and copolymers of these metal salts and the like are suitable.
This (C) component, especially EAA, is blended with EVOH of the (A) component, so that the oxygen absorption amount per unit weight can be improved compared with the case where the oxygen absorbing layer is composed of the (B) component alone, and the cost can be reduced. An oxygen-absorbing multilayer structure can be obtained.

The blend ratio of the component (A), the component (B), and the component (C) is 30 to 80% by weight: 10 to 70% by weight: 10 to 30% by weight, and preferably 50 to 80% by weight: 15 -40 wt%: 10-20 wt%. Moreover, the usage-amount of the transition metal salt in (B) component is 1-5000 ppm in conversion of a metal atom.
The resin composition of the present invention has various known additives, colorants, heat and weathering agents, antistatic agents, and carbon-carbon double bonds as oxidizable organic components, as long as the properties are not impaired. A thermoplastic resin or polymetaxylylene adipamide (MX-nylon) may be added as necessary.

And in the multilayer structure which has a layer which consists of an oxygen absorptive resin composition in this invention, the following layer structures are especially suitable.
1) Squeeze multilayer container formed by blow molding a) Two types and three layers: From the inner layer side, it is a low density polyethylene layer / oxygen-absorbing resin composition layer / low density polyethylene layer, and the thickness of each layer is 240: 40: 120 (μm).
B) 2 types and 5 layers: from the inner layer side, low density polyethylene layer / oxygen absorbing resin composition layer / low density polyethylene layer / oxygen absorbing resin composition layer / low density polyethylene layer, each layer having a thickness of 200 : 16: 40: 24: 120 (μm).
2) Multi-layer container made from a film formed by dry lamination a) From the outer layer, nylon 6 layer / MX nylon layer / nylon 6 / oxygen-absorbing resin composition layer / polypropylene layer.
3) A multilayer container made from a film formed by inflation molding a) From the outer layer, linear low density polyethylene layer / oxygen-absorbing resin composition layer / EVOH layer / adhesive layer / linear low density polyethylene layer To do.
In each of the multilayer structures, a repro layer made of a recycled resin or a gas barrier layer can be separately provided as necessary. In a multilayer container made of blow molding, burrs generated during molding can be crushed and reused as recycled resin.
Next, the present invention will be described in more detail by way of examples.

Two types of oxygen absorbing resin compositions described in each example and comparative example as an oxygen absorbing layer, a sandwich structure in which a low density polyethylene layer is sandwiched between the oxygen absorbing layers, and an inner and outer layer as a low density polyethylene A multilayer container composed of five layers was formed, and the physical properties of the multilayer container and the oxygen absorbing layer were evaluated by the following measurement methods and standards.
1) Oxygen permeability (barrier property)
After forming the multi-layer container, let it pass for 3 days at room temperature, and set the temperature and humidity to 30 ° C outside the container.
Under an environment of 60% RH and 30 ° C x 100% RH inside the container, the oxygen permeability per container was measured with an oxygen permeation measuring device (Ox-Tran 10/50, manufactured by MOCON). Evaluation was made according to the following criteria.
A: Less than 0.05, O: 0.05 to less than 0.1, Δ: Less than 0.01 to 0.3,
×: 0.3 or more (Unit: cc / bottle, day, air)

2) By-product permeation amount In the same environment as 1), aldehyde compounds generated in the multi-layer container after 365 days were measured by gas chromatography. Evaluation was based on the following criteria.
◎: Less than 1, ○: Less than 1-5, △: Less than 5-10, X: 10 or more (unit: ppm)

3) Adhesive strength The body wall of the multilayer container was cut at a width of 15 mm, the oxygen absorbing layer and the adjacent layer were peeled off, and the strength at that time was measured. Evaluation was based on the following criteria.
A: 20 or more, O: less than 20 to 10, Δ: less than 10 to 5, x: less than 5 (unit: g)

4) Oxygen absorption amount Immediately after forming a multilayer container, only the oxygen absorption layer was peeled off, placed in a glass bottle together with moisture, and left in a constant temperature bath at 55 ° C. For each elapsed time, the ratio of oxygen and nitrogen in the glass bottle was measured by gas chromatography, the rate of decrease in oxygen concentration was calculated, and the amount of oxygen absorbed by the oxygen absorbing layer was converted from the volume in the glass bottle per gram. The evaluation was based on the following criteria.
A: 5 or more, O: less than 5 to 1, Δ: less than 0.1 to 0.1, x: less than 0.1 (unit: cc
/ G)

5) Compatibilization Extruded as a multilayer parison having an oxygen absorbing layer, the number of fish eyes having a diameter of 0.1 mm or more was measured. Evaluation was based on the following criteria.
A: 0 to 5, O: 6 to 10, Δ: 11 to 20, x: 21 or more (unit: m ² )

6) Transparency After forming a multilayer container in which the thickness of the oxygen absorption layer was adjusted to 0.4 mm, only the oxygen absorption layer was immediately peeled off, and the light transmittance at a wavelength of 450 nm was measured in air.
Evaluation was based on the following criteria.
A: 50 or more, O: less than 50 to 40, Δ: less than 40 to 30, x: less than 30 (unit:
%)

[Example 1]
A resin composition having a blend ratio (A) :( B) :( C) = 55: 30: 15 (wt%) composed of the following components (A) to (C) was prepared.
Component (A): an ethylene-vinyl alcohol copolymer having an ethylene content of 29 mol% and a saponification degree of 99%. (Product name: Soarnol D2908, manufactured by Nippon Synthetic Chemical Co., Ltd.)
Component (B): reaction product of polyamide (including amorphous polyamide) and maleic anhydride-modified polybutadiene. (Product name: Aegis, manufactured by Honeywell) In addition, an organic acid salt of cobalt is added to the reaction product as a transition metal catalyst.
Component (C): An ethylene-acrylic acid copolymer was used. (Product name: Novatec A210M, manufactured by Nippon Polyethylene Corporation)
An intermediate layer having a sandwich structure in which the resin composition is an oxygen-absorbing layer and a low-density polyethylene layer is sandwiched between the oxygen-absorbing layers by blow molding, and two types and five layers in which the inner and outer layers are low-density polyethylene A multilayer squeeze container composed of polyethylene layer / oxygen absorbing layer / low density polyethylene layer / oxygen absorbing layer / low density polyethylene layer) was prepared. The thickness of each layer was 200: 16: 40: 24: 120 (μm) from the inner layer. The interlayer adhesive strength was 50 (g / 15 mm width).

[Example 2 to Example 6], [Comparative Example 1 to Comparative Example 6]
In accordance with the method described in Example 1, a resin composition used for an oxygen absorption layer having a composition ratio of the components (A) to (C) shown in Table 1 below was prepared. Here, in Example 3, the component (C) is an ethylene-methacrylic acid copolymer (trade name: Lexpearl RB3240, manufactured by Nippon Polyethylene Co., Ltd.), and in Example 4, the component (C) is an ionomer (trade name: High Milan). 1652, Mitsui DuPont Polychemical Co., Ltd.) was used.
Further, in Example 5, a multilayer film of nylon 6 layer / MX nylon layer / nylon 6 layer, a film made of the oxygen-absorbing resin composition of Example 1 and a film made of polypropylene were laminated by dry lamination to absorb oxygen. A multilayer multilayer film was formed, and a multilayer container was bag-made and evaluated so that the layer made of polypropylene became the inner sealant layer. Example 6 uses the oxygen-absorbing resin composition of Example 1 to form a film consisting of a linear low density polyethylene layer / oxygen absorbing layer / EVOH layer / adhesive layer / linear low density polyethylene layer by inflation molding. Then, the multilayer container was made into a bag and evaluated.

[Test Example 1]
A multi-layer container made of two types, five layers, or the above-mentioned film having each resin composition described in Examples 1 to 6 and Comparative Examples 1 to 6 as an oxygen absorbing layer is prepared, and each physical property is measured by the above measurement method. It was measured. The results are summarized in Table 1.

In addition, the symbol in Table 1 represents the following compound.
EVOH: ethylene-vinyl alcohol copolymer PA-Pb: reaction product of polyamide and maleic anhydride modified polybutadiene SIS: styrene-isoprene-styrene triblock copolymer MAnPb: maleic anhydride modified polybutadiene EAA: ethylene-acrylic acid Copolymer EMA: Ethylene-methacrylic acid copolymer

From the results of Test Example 1 (Table 1), the following was clarified.
1) The resin composition of the present invention has a good balance of oxygen permeability, by-product permeability, adhesive strength, oxygen absorption, compatibilized state, and light transmittance (Examples 1 to 6).
2) As for (A) component and (B) component, correlation is recognized between each characteristic and usage-amount (Comparative Examples 1-3), On the other hand, when (A) component decreases, oxygen absorption amount is large. When the oxygen permeability increases (Comparative Example 1) and the component (B) decreases, the oxygen absorption amount decreases (Comparative Example 2).
3) In the resin composition in which the component (B) is replaced with a styrene-isoprene-styrene triblock copolymer, the amount of by-product permeation increases remarkably (Comparative Example 4).
4) The resin composition consisting of the components (A) and (B) (Comparative Example 5) and the resin composition containing only the component (B) (Comparative Example 6) have the present invention in terms of oxygen permeability and oxygen absorption. Although the same result as that of the resin composition is obtained, other characteristics are remarkably inferior.

[Test Example 2]
The resin composition of Example 1 was used as an oxygen absorption layer (intermediate layer) with various film thicknesses. The average thickness of the inner and outer layers made of low-density polyethylene was 400 μm, and the total film thickness ratio of the oxygen absorption layer was 4 %, 7%, 10%, and 15% of multi-layer squeeze containers were prepared, and the change in oxygen permeation amount (barrier property) in each multi-layer container was measured in an environment of 30 ° C.-60% RH. . The results are shown in Table 2.
As is clear from Table 2, it was found that the oxygen permeation was substantially suppressed for 325 days or more when the film thickness ratio of the oxygen absorbing layer made of the resin composition of the present invention was 10%.

As described above, according to the oxygen-absorbing and gas-barrier resin composition of the present invention, the resin composition is an intermediate layer, and the inner layer and the outer layer are formed of a hydrophobic thermoplastic resin, for example, an olefin resin. The structure can provide a multilayer film or a multilayer container that is excellent in oxygen absorption, gas barrier properties, and light transmittance and does not generate odor components. Therefore, the resin composition of the present invention is extremely useful as a packaging material for products that are particularly sensitive to oxygen in a wide range of fields such as foods, pharmaceuticals, and cosmetics.

Claims (7)

(A) an ethylene - vinyl alcohol copolymer 55 to 80 wt%, (B) polyamide and a reaction product of a polyamide reactive oxidizable polydiene or oxidizable polyether, and a transition metal salt 10-35 wt% And (C) an oxygen-absorbing resin composition comprising 10 to 30% by weight of an ethylene copolymer having a carboxyl group.   The polyamide-reactive oxidizable polydiene is a polymer containing polybutadiene, and the ethylene copolymer having a carboxyl group is selected from the group consisting of an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, or an ionomer. The oxygen-absorbing resin composition according to claim 1, which is at least one kind of thermoplastic resin.   The oxygen-absorbing resin composition according to claim 1 or 2, wherein the polyamide is an amorphous polyamide or a mixture of a crystalline polyamide and an amorphous polyamide. An oxygen-absorbing multilayer structure comprising a layer made of the oxygen-absorbing resin composition according to any one of claims 1 to 3 .   The oxygen-absorbing multilayer structure according to claim 4, wherein an interlayer adhesive strength (JISZ0238) between the layer composed of the oxygen-absorbing resin composition of the multilayer structure and at least one adjacent layer is 10 g / 15 mm width or more. It is comprised by the base material resin layer which consists of low density polyethylene, and the oxygen absorption layer which consists of the oxygen absorptive resin composition of any one of Claim 1 to 3, and uses an inner and outer layer as a base resin layer, A squeeze multi-layer container comprising two types and three layers provided with an oxygen absorbing layer as a layer or two types and five layers provided with a sandwich structure in which a base resin layer is sandwiched between oxygen absorbing layers. An outer layer having a sandwich structure in which a resin layer made of polymetaxylylene adipamide is sandwiched between resin layers made of polyamide 6, and an intermediate layer made of an oxygen-absorbing resin composition according to any one of claims 1 to 3. And an oxygen-absorbing resin composition according to any one of claims 1 to 3, and an oxygen-absorbing resin composition according to any one of claims 1 to 3 , and an inner and outer layer made of linear low-density polyethylene. A multi-layer film comprising a multi-layer coextrusion layer laminated with an intermediate layer on which an oxygen barrier layer made of an ethylene-vinyl alcohol copolymer is laminated.