JP3136197B2 - Multi-layer biaxially stretched film for high temperature sterilization - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer biaxially stretched film suitable as a barrier substrate for packaging materials for high-temperature sterilization such as boil or retort.

[0002]

2. Description of the Related Art Saponified ethylene-vinyl acetate copolymer (hereinafter referred to as "EVOH") has excellent gas barrier properties, oil resistance, fragrance retention and the like, and is therefore frequently used as a packaging film for foods or pharmaceuticals. It is originally EV
OH is hardly used in a single film because of its hydrophilicity and poor hot water resistance, and is generally used in the form of a composite film with a polyamide resin, a polyolefin resin, a polyester resin, or the like.

[0003] Among these, a multilayer film in which a polyamide resin is laminated on both sides of an EVOH is excellent in combination with the gas barrier properties of the EVOH, the impact resistance of the polyamide resin, the pinhole resistance, the film formability, and the like. In addition to being expected to have a composite effect, it has the advantage that a multilayer structure can be easily formed by a coextrusion method or the like without using an adhesive resin. No. 6276, JP-A-52-1158
Numerous proposals have been made in JP-A-81-81, JP-A-1-154758 and the like.

However, since the multilayer film made of EVOH and polyamide resin is a hydrophilic resin, when it is subjected to a heat sterilization treatment at, for example, about 90 ° C., hot water or hot steam as its heat medium is used. Since water such as permeates through the polyamide resin of the inner and outer layers and reaches the EVOH layer, the moisture content of EVOH increases and the gas barrier property is inevitably reduced.In addition, when the processing temperature becomes 95 ° C. or more, In this case, it is known that delamination (hereinafter, simply referred to as delamination) occurs as well as a decrease in gas barrier properties, which leads to a fatal problem that the commercial value is completely lost.

Therefore, the polyamide resin / EVOH
In order to improve the problem of hot water resistance of a polyamide resin-based multilayer film, Japanese Patent Application Laid-Open No. 1-2242245 discloses that a main component is caproamide and that (CH ₂ / NHCO)
A multilayer structure in which a polyamide resin having a specific ratio in a specific range is laminated on both sides of EVOH is disclosed in JP-A-50-12134.
No. 7, Japanese Patent Publication No. 60-46138, etc., each proposes a method of blending a polyamide resin with the EVOH of the intermediate layer. However, each of these methods relatively does not cause delamination up to a temperature of about 95 ° C. Although excellent hot water resistance was obtained, when the treatment temperature was close to 100 ° C., delamination also occurred in some parts, and a sufficient improvement effect was not recognized, which was not a practically satisfactory method.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances.
An object of the present invention is to provide a multilayer biaxially stretched film having excellent hot water resistance, gas barrier properties, impact resistance, and the like without causing delamination even at a high temperature sterilization treatment of about 00 ° C.

[0007]

Means for Solving the Problems In order to achieve the above object, the present inventors have observed in detail the presence / absence of delamination by high-temperature sterilization treatment and the mechanism of generation thereof, and found that the polyamide resin / polyamide resin has various structures. The inventors have found that the delamination phenomenon of the EVOH / polyamide resin-based multilayer film is mainly caused by partial dissolution of EVOH constituting the intermediate layer due to moisture and heat entering from the outside during the high-temperature sterilization treatment. From this point of view, the delamination countermeasures were further examined, and after identifying the EVOH of the intermediate layer and the polyamide resin of the inner and outer layers, and further laminating both of them through a polyolefin-based adhesive resin, a delamination was considered. The present inventors have found that excellent hot water resistance can be obtained without performing the present invention, and have completed the present invention.

That is, the present invention provides an ethylene content of 20 to 50.
Mol.%, A saponified ethylene-vinyl acetate copolymer having a saponification degree of 95% or more, a composition comprising 60 to 93% by weight of a saponified polyamide resin and 5 to 38% by weight of a polyamide resin and 2 to 15% by weight of a polyolefin resin. On both sides of the intermediate layer
Melting point 17 via the modified polyolefin-based adhesive resin layer
The present invention relates to a multilayer biaxially stretched film for high-temperature sterilization, wherein a polyamide resin layer at 0 to 220 ° C. is laminated.

Hereinafter, the present invention will be described in detail.

In the present invention, EVOH is obtained by hydrolyzing a vinyl acetate unit in a copolymer of ethylene and vinyl acetate, and specifically has an ethylene content of 20 to 50 mol%, preferably 25 to 45 mol%. With a saponification degree of 95
%, Preferably 98% or more. here,
If the ethylene content is less than 20 mol%, the extrusion moldability is poor and the thermal stability is poor, which is not preferable. If the ethylene content exceeds 50 mol%, the gas barrier properties are lost. On the other hand, when the degree of saponification is less than 95%, the gas barrier property is significantly reduced and the thermal stability is also deteriorated.

The multilayer biaxially stretched film of the present invention has a EVOH content of 60 to 93% by weight, preferably 70 to 90% by weight.
The intermediate layer of the film is composed of a composition in which the polyolefin resin is blended in an amount of 2 to 15% by weight with respect to the polyamide resin in an amount of 5 to 38% by weight, preferably 10 to 30% by weight.

Here, the polyamide resin blended in the EVOH is polycaprolactam (nylon-
6), polyundecaneamide (nylon-11), polylaurolactam (nylon-12), polyhexamethylene adipamide (nylon-6,6), polyhexamethylene dodecamide (nylon-6,12), or poly (Caprolactam / laurolactam) copolymer (nylon-6 / 12), poly (caprolactam / aminoundecanoic acid) copolymer (nylon-6 / 11), poly (caprolactam / hexamethylene diammonium adipate) copolymer ( Nylon-6 / 6,6), poly (caprolactam / hexamethylenediammonium adipate /
Hexamethylene diammonium sebacate) copolymer (nylon-6 / 6, 6/6, 12) or the like. Among these, in the present invention, polycaprolactam or polycaprolactam block is
A poly (caprolactam / laurolactam) copolymer (nylon-6 / 12) containing 0 to 95% by weight of EVO
It is preferably used because it has excellent compatibility with H, has few problems of thermal stability, and can obtain an excellent effect of improving hot water resistance.

The polyolefin resin blended in the EVOH includes polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, ethylene-methacrylate copolymer, ionomer and the like. Among them, an ethylene-vinyl acetate copolymer having a vinyl acetate content of 20 to 40% by weight is preferable because it is excellent in compatibility with EVOH and an effect of improving hot water resistance.

In the present invention, the reason why the polyamide resin is blended with the EVOH constituting the intermediate layer of the multilayer film is mainly to improve the hot water resistance of the EVOH. If the amount of the polyamide resin is less than 5% by weight, the effect of improving hot water resistance is poor and the occurrence of delamination during high-temperature sterilization cannot be prevented, whereas the amount of the polyamide resin exceeds 38% by weight. In addition to the fact that the multilayer film aimed at by the present invention is not obtained due to reduced gas barrier properties, gels, lumps, etc., which are considered to be due to the deterioration of thermal stability during melt extrusion in the film forming process, are likely to occur frequently. A good quality film cannot be obtained. The EVOH of the present invention further contains 2 to 15% by weight of a polyolefin resin in addition to the polyamide resin. The polyolefin resin has the effect of further improving the hot water resistance of the composition comprising the EVOH and the polyamide resin, and is also effective in improving the thermal stability. However, if the amount is too large, the gas barrier property is not significantly reduced.

The multilayer biaxially stretched film for high-temperature sterilization according to the present invention has a melting point of 170 ° on both surfaces of an intermediate layer composed of the EVOH and a polyamide-based resin and a polyolefin-based resin via a modified polyolefin-based adhesive resin layer. Polyamide resin layers of up to 220 ° C are laminated. Only the combination of these intermediate layer, adhesive resin layer and polyamide resin layer gives excellent properties such as hot water resistance, gas barrier properties and impact resistance. It is done.

That is, the multilayer film of the present invention can provide a sufficient adhesive strength without the use of an adhesive resin.
It has a great feature in that a modified polyolefin-based adhesive resin layer is interposed between the VOH and the polyamide resin. In this case, the adhesive resin layer improves the adhesive strength between the EVOH-polyamide resin, Rather, the excellent water vapor barrier property inherent to the polyolefin resin suppresses the penetration of moisture during the heat sterilization treatment into the EVOH layer, which acts very effectively to prevent delamination.

In the present invention, the modified polyolefin-based adhesive resin is not particularly limited as long as it is basically a polyolefin-based resin having an adhesive property with EVOH or polyamide resin. A modified polyolefin resin obtained by graft polymerization of a saturated carboxylic acid or a derivative thereof is used.

The polyolefin resin used as the base of the modified polyolefin resin includes olefin homopolymers such as polyethylene, polypropylene and polybutene-1 and copolymers with α-olefins such as ethylene, propylene and butene-1. Α-olefins having 2 to 12 carbon atoms (eg, propylene, butene-1, pentene-1, hexene-1, etc.) or unsaturated esters (eg, vinyl acetate, methyl acrylate, propyl acrylate, methyl methacrylate, methacryl) And the like are exemplified.

On the other hand, unsaturated carboxylic acids used in producing these graft copolymers of polyolefin resins include acrylic acid, methacrylic acid, maleic acid, and the like.
In addition to fumaric acid, itaconic acid, crotonic acid and the like, acid anhydrides, esters, amides, imides, and metal salts as derivatives thereof, such as maleic anhydride, itaconic anhydride, methyl acrylate, ethyl acrylate, methyl methacrylate,
Acrylamide, maleimide, sodium acrylate and the like can be mentioned, and among them, acrylic acid, methacrylic acid, maleic acid and anhydride thereof are particularly preferable.

The content of the unsaturated carboxylic acid or its derivative in the modified polyolefin resin is EV
From the viewpoint of adhesion to OH and polyamide resin, usually 0.0
An appropriate amount is 1 to 10 parts by weight, preferably 0.05 to 5 parts by weight. If the amount is outside this range, the adhesive strength tends to decrease. Regarding the thickness of the adhesive resin layer, if it is too thin, the effect of improving hot water resistance is poor, and if it is too thick, it is economically inferior.
5 to 10 μm, especially about 1 to 5 μm, is preferable.

Next, as the polyamide resin constituting the inner and outer layers of the multilayer biaxially stretched film of the present invention, nylon-
6, nylon-11, nylon-12, nylon-6
12, or at least one of nylon-6 / 6,6 copolymer, nylon-6 / 12 copolymer, nylon-6 / 11 copolymer, and has a melting point of 170 to 220.
° C, preferably 180 to 210 ° C.

When the melting point of the polyamide resin is lower than 170 ° C., the resulting multilayer film has poor hot water resistance and easily causes delamination during high-temperature sterilization treatment. On the other hand, when the melting point of the polyamide resin is higher than 220 ° C. Since the melt extrusion temperature in the film forming process must be increased, the thermal stability of the EVOH used for the intermediate layer deteriorates, and frequent bumps, gels, and the like tend to occur.

The above-mentioned EVOH, adhesive resin, polyamide resin and the like used in the present invention are added with other thermoplastic resins such as polyester resin and polycarbonate resin as long as the properties are not largely changed. In addition to antioxidants, UV absorbers, plasticizers, antistatic agents, antiblocking agents, lubricants, coloring agents, fillers,
An antifogging agent or the like may be appropriately added as needed.

The method for producing the multilayer biaxially stretched film for high-temperature sterilization according to the present invention is as follows. First, a composition for an intermediate layer in which a polyamide resin or a polyolefin resin is blended with EVOH and a modified polyolefin adhesive The resin and the polyamide resin for the inner and outer layers are supplied to different extruders, and are combined and extruded in the same die to form a multilayer unstretched film by a so-called co-extrusion molding method. Above, preferably 0.3 to 3%
, While preheating at a temperature of 30 to 80 ° C., then biaxially stretching and, if necessary, heat setting. In this case, the extrusion temperature is preferably set to 170 to 250 ° C. in terms of the extrudability and the thermal stability of each resin to be used, and the extruded molten film is immediately cooled with water at a temperature of 40 ° C. or less and crystallized. It is preferable that the film formation be suppressed since the film can be stably stretched in the subsequent stretching step.

As the method of biaxial stretching, any method such as a sequential or simultaneous biaxial stretching method using a tenter and a tubular simultaneous biaxial stretching method may be used, but the crystallization rate is relatively high as in the present invention. In a multilayer film in which a polyamide resin is disposed in the inner and outer layers, the tubular stretching method, in which the stretching speed is high and the stretching is performed simultaneously in the longitudinal and transverse directions, suppresses the orientation crystallization in the stretching process and can be stretched uniformly and stably. preferable.

Here, specific examples of stretching conditions in the tubular simultaneous biaxial stretching method include a stretching zone designed so that the time from the start to the end of stretching is within 5 seconds. It is preferable to perform biaxial stretching so that the area magnification becomes 3 to 25 times at a temperature of 85 to 150 ° C. depending on the degree of conversion, and when the area magnification is less than 3 times, the thickness accuracy of the obtained film is poor. While a film having good gas barrier properties cannot be obtained, the area magnification is 2
When it is larger than 5 times, puncture of the bubble occurs frequently, so that stable stretching cannot be performed and impact resistance is further reduced.

The multilayer film of the present invention has good thermal dimensional stability by heat-setting the above biaxially stretched film in an atmosphere at a temperature of 150 to 220 ° C. under a tension or a relaxation rate of 30% or less. Generally, a film made of a transparent film is used.
It is performed at a low temperature of about 0 to 120 ° C., and even if it is used as a heat-shrinkable film for high-temperature sterilization treatment, there is no problem.

The thickness of the multilayer biaxially stretched film of the present invention is not particularly limited. However, when it is used as a barrier base material for packaging materials for high temperature sterilization treatment such as boiling or retort, strength, barrier properties, etc. Usually 5 to 50
μ, preferably about 10 to 30 μ, and particularly, the thickness of the intermediate layer is preferably 3 to 20 μ from the viewpoint of gas barrier properties, economy and the like.

Further, since the multilayer film of the present invention has poor heat sealability, it is usually a polyolefin-based sealant material such as polyolefin, polypropylene, ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, and ionomer. Is generally used in the form of being laminated by a method such as dry lamination or extrusion lamination. Further, by providing a resin layer such as polypropylene, polyester, or polycarbonate on the opposite surface of the sealant layer, strength, hot water resistance, etc. Can be further improved.

[0030]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

The methods for measuring and evaluating the physical properties performed in the present invention are as follows. (1) Film Appearance A composition in which a polyamide resin is blended with EVOH tends to react and gel during melt extrusion, and generally has poor thermal stability. Therefore, as a method for evaluating the appearance of the film, the occurrence of gels, tubs and the like during continuous operation for 30 hours was checked in consideration of practicality, and the quality was judged. The sample having no problem was evaluated as (○), and the sample having many lumps or gels and poor film quality was evaluated as (x). (2) Oxygen permeability (unit: cc / m ² · day · at)
m) According to ASTM-D3985, the oxygen permeability of the multilayer biaxially stretched film was measured at 23 ° C. and 0% RH.
The measurement was performed using OX manufactured by Modern Control.
-TRAN 10/50 was used. (3) Hot water resistance A multilayer biaxially stretched film and a 70 μm thick CPP film (sealant material) were dry-laminated using a urethane-based two-component adhesive. This dry laminated film was formed into a bag having a size of 10 × 15 cm by a bag making machine, 200 cc of water was put in the bag, the bag was sealed, and then immersed in boiling water at 100 ° C. for 30 minutes to perform a boil test. This boil test is performed 10 times for each type of film.
Pass / fail was determined based on the number of delaminations out of ten (delamination number / 10). (4) Comprehensive evaluation Comprehensively evaluated the suitability of packaging materials for high-temperature sterilization as a barrier substrate based on the measurement results of film appearance, oxygen permeability, hot water resistance, etc. (◎), suitable ones (○), inappropriate ones (×)
And

Example 1 EVOH having an ethylene content of 32 mol% and a saponification degree of 99% or more (melting point: 193 ° C.) using a three-layer, five-layer multi-layer extruder.
To 72% by weight, 20% by weight of a nylon-6 / 12 copolymer (melting point: 209 ° C.) having a copolymerization ratio of nylon-6 and nylon-12 of 90:10 by weight and a vinyl acetate content of 28% by weight. % Of ethylene-vinyl acetate copolymer in a weight of 8% by weight, the resin for the intermediate layer (A) is fed to the first extruder, and maleic anhydride is added to linear low-density polyethylene in the presence of an organic peroxide. The modified polyolefin-based adhesive resin (B) obtained by the graft polymerization is supplied to the second extruder, and the copolymerization ratio of nylon-6 and nylon-6,6 is 8 by weight.
5:15 nylon-6 / 6,6 copolymer (melting point; 19
6 ° C.) for the inner and outer layers are supplied to the third extruder, respectively, are joined in an annular die set at 230 ° C., are co-extruded, and immediately cooled with water at a temperature of 20 ° C. As a result, a tubular multilayer unstretched film having a layer configuration of C / B / A / B / C, a folded diameter of 300 mm, and a thickness of 140 μ was obtained. This unstretched film is heated at 40 to 60 ° C.
2. While being preheated at a temperature of, the liquid is guided to a pair of upper and lower nip rolls having different peripheral speeds, and pressurized air is fed at a stretching temperature of 90 to 130 ° C., and the stretching ratio is 2.5 times in the longitudinal direction and 3 times in the transverse direction.
Tubular simultaneous biaxial stretching was performed so as to be 0 times (area magnification 7.5 times). Subsequently, the tube was heat-set at 185 ° C. for 5 seconds while giving a relaxation of about 5% while maintaining the tube shape, whereby a folding diameter of about 860 mm and a thickness of 20 μm [thickness of each layer; C (5.6 μm) / B (1.4 μ) / A (6.0)
μ) / B (1.4 μ) / C (5.6 μ)]. Table 1 shows the results of performance evaluation of the multilayer film thus obtained.

Comparative Example 1 As a resin (A) for an intermediate layer, EVOH having an ethylene content of 32 mol% and a saponification degree of 99% or more (melting point: 193 ° C.)
The above-mentioned resin was used except that a resin obtained by blending 20% by weight of a nylon-6 / 12 copolymer (melting point: 209 ° C.) having a copolymerization ratio of nylon-6 and nylon-12 of 90:10 by weight to 80% by weight was used. In the same manner as in Example 1, a multilayer biaxially stretched film having a folded diameter of about 860 mm and a thickness of 20 μm was produced. Table 1 shows the results of performance evaluation of the multilayer film thus obtained.

COMPARATIVE EXAMPLE 2 Resin for intermediate layer (A) using a two-layer three-layer multilayer extruder
In the same manner as in Example 1 except that the resin (C) for the inner and outer layers was co-extruded, a folded diameter of about 860 mm and a thickness of 18 μm were used.
[Thickness of each layer; C (6μ) / A (6μ) / C (6μ)]
Was produced. Table 1 shows the performance of the obtained multilayer film.

[0035]

[Table 1]

From the results shown in Table 1, the multilayer biaxially stretched film of the present invention provided with the modified polyolefin adhesive resin layer showed almost no occurrence of delamination in a 100 ° C. boil test, and was excellent in hot water resistance. .

Examples 2-4, Comparative Examples 3-6 EVOH and nylon-6 / 12 of resin (A) for the intermediate layer
A multilayer biaxially stretched film was produced in the same manner as in Example 1 except that the mixing ratio of the copolymer and the ethylene-vinyl acetate copolymer was variously changed at the ratios shown in Table 2. Table 2 shows the performance of the obtained multilayer biaxially stretched film.

[0038]

[Table 2] The composition of the intermediate layer in the table is EVOH and nylon-6 /
The mixing ratio (EVOH / NY / EVA) of the 12 copolymer and the ethylene-vinyl acetate copolymer was indicated by weight%. The unit of the melting point of the inner and outer layers NY is ° C.

Examples 5-7, Comparative Examples 7-8 As the resin (C) for the inner and outer layers, polyamide resins having various melting points shown in Table 3 were used, and the temperatures of the third extruder and the annular die were adjusted for each polyamide resin. Coextrusion molding at a temperature higher by 10 to 30 ° C. than the melting point, and a multi-layer biaxially stretched film by the same method as in Example 1 except that the heat setting temperature is respectively 10 to 30 ° C. lower than the melting point of each polyamide resin. Was prepared. Table 3 shows the performance of the multilayer film thus obtained.

[0040]

[Table 3] The meanings of the words in the table are the same as in Table 2 above.

From the results shown in Tables 2 and 3, the mixing ratio of the EVOH of the resin (A) for the intermediate layer to the polyamide resin, the polyolefin resin and the like, and the melting point of the polyamide resin for the inner and outer layers are within the ranges of the present invention. Is good in film quality without gels and bumps even after continuous operation for a long time,
In addition, the gas barrier properties and the hot water resistance were also excellent.

[0042]

The multilayer biaxially stretched film of the present invention has excellent gas barrier properties, impact resistance,
In the field of packaging materials that require high-temperature sterilization such as boil or retort, it has been considered difficult to use EVOH-based films due to the problem of delamination because of the pinhole resistance. Can be used particularly preferably as

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Claims (4)

(57) [Claims] 1. A saponified ethylene-vinyl acetate copolymer having an ethylene content of 20 to 50 mol% and a saponification degree of 95% or more, 60 to 93 wt%, a polyamide resin of 5 to 38 wt%, and a polyolefin resin of 2 to 50 wt%. On both sides of an intermediate layer made of a composition blended with a melting point of from 170 to 220 % by weight through a modified polyolefin-based adhesive resin layer.
A multilayer biaxially stretched film for high-temperature sterilization treatment, wherein a polyamide resin layer at a temperature of ° C is laminated. 2. A polyamide resin blended in a saponified ethylene-vinyl acetate copolymer, comprising polycaprolactam or polycaprolactam block in an amount of 60 to 95% by weight.
The multilayer biaxially stretched film for high-temperature sterilization according to claim 1, which is a poly (caprolactam / laurolactam) copolymer contained therein. 3. The high-temperature sterilization treatment according to claim 1, wherein the polyolefin resin blended in the saponified ethylene-vinyl acetate copolymer is an ethylene-vinyl acetate copolymer having a vinyl acetate content of 20 to 40% by weight. Multi-layer biaxially stretched film. 4. The multilayer biaxially stretched film for high-temperature sterilization according to claim 1, wherein the adhesive resin is a modified polyolefin resin obtained by graft-polymerizing an unsaturated carboxylic acid or a derivative thereof.