JPH0476301B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a multilayer film for food packaging.
More specifically, it has polyether ester amide resin as a surface layer, which has excellent gloss, transparency, and gas barrier properties, as well as flexibility and heat resistance, as well as pinhole resistance, skin formation, and deep drawability at low temperatures. The present invention relates to a film that is excellent for use as a lid material for air-containing packaging. Conventional technology Conventionally, films for food packaging, especially for packaging processed meat products, have been made using nylon Ny/polyethylene PE, Ny/ethylene vinyl acetate saponified copolymer EVOH/PE, and vinyl chloride resin PVC/vinylidene chloride. Multilayer films such as resin PVDC/ethylene vinyl acetate copolymer EVA are used. Most of these have a layer structure of surface layer/intermediate layer/seal layer, and the required role of each layer is as follows. In other words, the surface layer plays the role of surface gloss, transparency, heat resistance during molding, anti-blocking properties with the sealing layer, and cold resistance.
As an intermediate layer, it plays a role of excellent gas barrier properties and transparency. The role of the sealing layer is not only heat sealability but also heat resistance and oil resistance. The heat resistance required for these multilayer films usually means that they can withstand molding temperatures of 130°C or higher, and the cold resistance that they require means that they can withstand distribution at temperatures near 0°C. Generally, the melting point of resins used as sealing layers, such as PE and EVA, is 90.
Since the temperature is between 110°C and 110°C, the molding temperature for sealing is usually 120 to 135°C, and it is preferable to seal at 130°C or higher to obtain stable sealing properties. Therefore, the temperature of the multilayer film is 130℃.
It is necessary to withstand the above molding temperature. On the other hand, film-packaged products are generally kept at a storage temperature of 5°C to 15°C during the distribution process, such as in retail store cases, but depending on the season and location, the storage temperature may be 0°C.
Or even less, and the biggest problem is distribution during the depths of winter. It is required to maintain flexibility even in such a low-temperature environment, withstand transportation and handling, and not cause bag breakage or pinholes. In this way, the multilayer film
It is required to satisfy both properties of heat resistance during molding and cold resistance during distribution. Incidentally, as a recent trend, packaging materials with flexibility are required, but the biggest problem in imparting flexibility to packaging materials made of multilayer films is what kind of resin to select as the material for the surface layer. That is to say. An example is a combination of soft PVC/PVDC with plasticized PVC as the surface layer, but softening of the surface layer resin by adding a plasticizer can reduce the surface gloss due to plasticizer bleed-out or change the layer from soft PVC to PVDC. There are many drawbacks such as a decrease in gas barrier properties due to the migration of a large amount of plasticizer to the resin. On the other hand, non-plasticized resins with excellent gloss include polystyrene, polycarbonate,
There are amorphous polymers such as polyethylene terephthalate and PVC, but these polymers generally all have a high glass transition temperature Tg of 70 to 150°C and therefore lack flexibility and cold resistance. vice versa
Polymers with low Tg are prone to blocking,
It also has poor heat resistance. In the case of crystalline polymers, if the melting point of the crystals is higher than the molding temperature, a film with good heat resistance can be obtained, but the presence of crystals reduces gloss and transparency. This tendency is unavoidable, especially for crystalline polymers with low Tg. For example, nylon has a high melting point Tm of 200 to 250°C, and has excellent heat resistance, as well as excellent transparency and gloss.
Since the temperature is as high as 40℃, cold resistance generally does not develop unless the Tg drops to near 0℃ by absorbing moisture and softening. High density polyethylene has a Tg of -120
℃, Tm is 135°C, and polypropylene has a Tg of -18°C and a Tm of 176°C, but in both cases, gloss cannot be obtained unless quenched or stretched. Polyisobutylene, polybutadiene, etc. have a Tg of -
The temperature is as low as 70 to -90°C, so although it is flexible, it lacks heat resistance and is prone to blocking. Therefore, it has conventionally been difficult to obtain packaging materials that are flexible and also have excellent gloss, transparency, heat resistance, cold resistance, gas barrier properties, and the like. Problems to be Solved by the Invention As a result of intensive research aimed at solving the above problems, the present inventors found that the invention consists of at least three layers: a surface layer, an intermediate layer with gas barrier properties, and a sealing layer with heat sealability. Discovered that by using polyether ester amide resin as the surface layer of a multilayer film, a multilayer film with excellent gloss, transparency, heat resistance, gas barrier properties, etc., as well as flexibility and cold resistance, could be obtained. Based on this, the present invention was completed. Means for Solving the Problems That is, the gist of the present invention is that the present invention consists of at least three layers: a surface layer made of a polyether ester amide resin, an intermediate layer made of a gas barrier resin, and a sealing layer made of a resin having heat sealability. A multilayer film characterized by: In the present invention, in particular, a polyether ester amide resin with a high crystal melting point and low Tg is used as the surface layer, and by combining this with a gas barrier resin intermediate layer and a heat sealable resin layer, heat-resistant sealing is achieved. It is possible to obtain a multilayer film that not only has excellent properties but also cold resistance during distribution and has good physical properties such as gloss and transparency. Hereinafter, the constituent elements of the present invention will be explained in detail. (Polyetheresteramide resin) The polyetheresteramide resin used in the present invention is a block copolymer in which a polyamide-forming component and polyalkylene ether glycol are bonded in a block manner through ester bonds. As the polyether ester amide resin used in the present invention, aminocarboxylic acid or lactam or nylon salt a having 6 or more carbon atoms, poly(alkylene oxide) having a number average molecular weight of 300 to 6000
It is composed of glycol b and dicarboxylic acid c having 4 to 20 carbon atoms, and the proportion of component b in the total copolymer is 5 to 85% by weight, and the crystal melting point is
A temperature of 110 to 230°C, preferably 130 to 220°C can be used. In addition, the glass transition temperature Tg of these polyether ester amide resins is usually
The temperature is about -60°C, and some polyether components show -70°C depending on the type of polyether component, but in the present invention, any temperature below -50°C can be preferably used. The crystal melting point and glass transition temperature of the polyether ester amide were measured using a differential scanning calorimeter (hereinafter referred to as "DSC"). Measurement by DSC is performed using Mettler's TA3000 system.
Using a DSC30 model, the sample weight was 15 mg, the temperature scan gradient was 10°C/min, liquid nitrogen was used for cooling, and the temperature was raised from -100°C. The crystal melting point Tm was defined as the peak value on the endothermic side, and the glass transition temperature Tg was defined as the inflection point in the shift to the endothermic side. Examples of polyamide-forming components include ω-aminocarboxylic acids or lactams such as caprolactam and laurolactam, and NH ₂ (CH ₂ ) _n NH ₂ (m is 6 to
12) and HOOC(CH ₂ ) _o COOH (n is 6 to 12). Polyalkylene ether glycol components include polyethylene glycol, poly(1,2-propylene oxide) glycol, poly(1,3-
(propylene oxide) glycol, poly(tetramethylene oxide) glycol, poly(hexamethylene oxide) glycol, block copolymer or random copolymer of ethylene oxide and propylene oxide glycol, block copolymer or random copolymer of ethylene oxide and tetrahydrofuran Glycol etc. are used. As the dicarboxylic acid used to form the ester bond, dicarboxylic acids such as terephthalic acid, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, sebacic acid, and dodecanedioic acid are used. Gas Barrier Resin Gas barrier resins used in the intermediate layer in the present invention include saponified ethylene vinyl acetate copolymers, vinylidene chloride copolymers, acrylonitrile resins, and especially ethylene vinyl acetate copolymers. Saponified products and vinylidene chloride copolymers are preferred. Further, blends of various polymers such as polyester elastomer and nylon with these resins within a range that does not impair the gas barrier properties can also be used as the gas barrier resin of the present invention. The saponified ethylene-vinyl acetate copolymer used in the present invention is a copolymer of 20 to 50 mol% ethylene and 80 to 50 mol% vinyl acetate that has been saponified to 90% or more. This saponified copolymer can be obtained by a known method. A vinylidene chloride-based copolymer is a copolymer consisting of vinylidene chloride and a monomer copolymerizable with vinylidene chloride. Examples of copolymerizable monomers include:
Vinyl chloride, acrylonitrile, acrylic acid, methacrylic acid, acrylic acid alkyl esters in which the alkyl group has 1 to 18 carbon atoms, methacrylic acid alkyl esters in which the alkyl group has 1 to 18 carbon atoms, maleic anhydride, maleic acid, maleic acid alkyl esters, Examples include itaconic acid, itaconic acid alkyl ester, vinyl acetate, ethylene, propylene, isobutylene, and butadiene. Usually vinylidene chloride 60
A copolymer obtained by copolymerizing ~95% by weight with 5~40% by weight of one or more of these comonomer polymers,
Alternatively, these copolymers can be added with a common non-toxic plasticizer.
A resin to which 10% by weight or less of auxiliary agents such as stabilizers and colorants are added is used. Among them, vinylidene chloride
Vinyl chloride copolymers are preferred. (Resin having heat-sealing properties) As the resin having heat-sealing properties used in the present invention, polyolefin resins can be preferably used. For example, homopolymers of α-olefins such as ethylene and propylene; copolymers of α-olefins with vinyl acetate, acrylic esters, or methacrylic esters; copolymers of ethylene and propylene; ethylene and methacrylic Na ion, Zn ion, Mg in copolymer with acid, acrylic acid or itaconic acid, etc.
Examples include ionomer resins treated with ions and the like; or blends of two or more of these. Among these polyolefin resins, polyethylene, ethylene-vinyl acetate copolymer, and ionomer resin are particularly preferred. (Thickness of film layer) The surface polyether ester amide resin layer in the present invention has cold resistance, flexibility,
It imparts heat resistance and has a thickness of 10 to 100 μm, preferably 10 to 40 μm. If the surface layer is thinner than 10μm, sufficient effects such as cold resistance cannot be obtained;
If it is thicker, the formability of the film will deteriorate. The gas barrier resin layer of the intermediate layer imparts gas barrier properties to the multilayer film, and has a layer of 5 to 5.
It has a thickness of 50 μm, preferably 5 to 30 μm. If the intermediate layer is thinner than 5 μm, the effect of imparting gas barrier properties to the multilayer film will be small, and if it is thicker than 50 μm, the multilayer film will become stiff, leading to deterioration in film formability. The resin layer with heat sealing properties of the sealing layer is
It imparts sealing properties and good moldability to the multilayer film, and also has the effect of protecting the gas barrier resin layer, particularly the saponified ethylene-vinyl acetate copolymer, from moisture. The seal layer preferably has a thickness of at least 20 μm or more in order to fulfill this role. The total thickness of the multilayer film is 40 to 200 μm, and this range is suitable for food packaging. (Layer composition) The multilayer film of the present invention is composed of at least three layers: a polyether ester amide resin layer A, a gas barrier resin layer B, and a heat-sealable resin layer C, with layer A being a surface layer and layer B being an intermediate layer. Layer C is a heat-sealable resin layer. Therefore, the basic layer structure of the multilayer film in the present invention is A/
It is B/C. Between the surface layer of the multilayer film and the gas barrier layer or between the gas barrier layer and the sealing layer,
An adhesive resin layer may be interposed to improve the adhesion between the two. As the adhesive resin, for example, maleic anhydride-modified polyolefin is used between the polyether ester amide layer and the EVOH layer and between the EVOH layer and the sealing layer. The polyether ester amide layer and the PVDC layer exhibit good adhesion without using an adhesive resin, but maleic anhydride-modified EVA may be used as the adhesive resin between them.
Furthermore, EVA, ethylene-acrylic acid ester copolymer, or the like is used as an adhesive resin between the PVDC layer and the sealing layer made of polyolefin. Adhesive resins are usually used in layers with a thickness of 1 to 20 μm. (Molding of multilayer film) The multilayer film of the present invention can be molded by a conventional molding method such as T-die molding or inflation molding. EXAMPLES The present invention will be explained in more detail below using Examples and Comparative Examples, but the present invention is not limited to these Examples. Example 1 Vinylidene chloride-vinyl chloride copolymer 100 with a polyether ester amide resin (product name PEBAX manufactured by ATOCHEM) having a crystal melting point of 168°C and a glass transition temperature of -60°C as a surface layer and a vinylidene chloride content of 80% by weight. 2 parts by weight of epoxidized soybean oil
The resin composition added and mixed in parts by weight was used as an intermediate layer, and the ethylene-vinyl acetate copolymer with a vinyl acetate content of 10% by weight was used as a sealing layer, and these resins were extruded into three circular dies using three extruders. They were made to meet from two channels. Next, air is blown into the molten cylindrical three-layer parison directly under the die, using so-called inflation molding to reduce the thickness of each layer to 30 μm for the surface layer and 30 μm for the middle layer.
A three-layer film with a thickness of 15 μm and a seal layer of 40 μm was prepared. This film was used to fill sausages with a height of 4 cm and a diameter of 9 cm using a deep drawing method, and the same film was used as a lid material to vacuum seal packaging.
Next, a cold resistance test was conducted using 10 of these vacuum packaged products. As a method of cold resistance test, one side is
Place it in a hexagonal rotating box with a width of 20 cm and a width of 30 cm.
Rotate under the conditions of ℃ and 30 RPM, after 2 minutes, after 5 minutes,
The incidence of vacuum-returned products was measured by the number of broken bags due to rotational impact after 10 minutes. The results are shown in Table 1. Example 2 A polyether ester amide resin (trade name: PEBAX manufactured by ATOCHEM) with a crystal melting point of 190°C and a glass transition temperature of -60°C was used as the surface layer, and an ethylene content of 30°C was used.
A saponified ethylene-vinyl acetate copolymer with a mole% saponification degree of 98% is used as the intermediate layer, and low-density polyethylene is used as the sealing layer, and they are assembled through three channels in a circular die using three extruders. Ta. Next, air is blown into the molten cylindrical three-layer parison directly under the die, using the so-called inflation molding method, to reduce the thickness of each layer to 25 μm for the surface layer and 25 μm for the middle layer.
A three-layer film with a thickness of 20 μm and a seal layer of 50 μm was prepared. Using this film, deep drawing was performed in the same manner as in Example 1, and a cold resistance test was conducted in the same manner. The results are shown in Table 1. Comparative Example 1 A multilayer film was prepared in the same manner as in Example 1 except that 12-nylon was used as the surface layer instead of the polyetheresteramide resin in Example 1. The thickness of each layer is the same as in Example 1, 30 μm for the surface layer,
The intermediate layer was 15 μm thick, and the seal layer was 40 μm thick. This multilayer film was also subjected to the same cold resistance test as in Example 1. The results are shown in Table 1. Control example 2 In place of the polyether ester amide resin in Example 1, a polyester plasticizer was used as a plasticizer.
A multilayer film was prepared in the same manner as in Example 1 except that a plasticized vinyl chloride resin containing % by weight was used as the surface layer. The thickness of each layer is 40 μm for the surface layer,
The intermediate layer was 15 μm thick, and the seal layer was 35 μm thick. This multilayer film was also subjected to the same cold resistance test as in Example 1. The results are shown in Table 1.

Table 2 also shows the physical property values of the films obtained in Examples 1 and 2 and Control Examples 1 and 2.

【table】

[Table] Effects of the Invention The present invention uses a polyether ester amide resin as the surface layer of a multilayer film, and combines this with a gas barrier resin layer and a heat-sealing resin layer to form a multilayer film. It was possible to obtain a film that has excellent transparency and gas barrier properties, as well as flexibility and heat resistance, as well as excellent pinhole resistance at low temperatures, skin formation properties, and deep drawability. In particular, in the present invention, the crystal melting point is as high as 110 to 230°C,
Moreover, by using polyether ester amide resin with a low glass transition temperature of -50°C or less as the surface layer of the multilayer film, it has the remarkable effect of not only excellent heat-resistant sealing properties but also excellent cold resistance during the distribution process. I was able to play it. Furthermore, since there is no need to use a plasticizer in the surface layer resin, problems such as contamination due to bleed-out of the plasticizer and changes in the material of each film do not occur. The multilayer film of the present invention can be used in a wide range of applications such as vacuum packaging and air-containing packaging as a packaging film for various foods.

Claims (1)

[Scope of Claims] 1. A multilayer film comprising at least three layers: a surface layer made of a polyether ester amide resin, an intermediate layer made of a gas barrier resin, and a sealing layer made of a resin having heat-sealing properties. 2. The multilayer film according to claim 1, wherein the gas barrier resin is a saponified ethylene vinyl acetate copolymer or a vinylidene chloride copolymer. 3. The polyether ester amide resin has a crystal melting point of 110 to 230°C, preferably 130 to 220°C,
The multilayer film according to claim 1, which is a resin having a glass transition temperature of -50°C or lower. 4. The total thickness of the multilayer film is 40 to 200 μm, and the surface layer is 10 to 100 μm, preferably 10 to 40 μm,
A multilayer film according to claim 1, wherein the intermediate layer has a respective thickness of 5 to 50 .mu.m, preferably 5 to 30 .mu.m, and the sealing layer has a respective thickness of at least 20 .mu.m.