JPS6140551B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a laminated film of propylene homopolymer films and a food packaging bag made from the film. Biaxially stretched polypropylene film has excellent tensile strength and impact resistance, making it suitable for packaging bags for storing various contents, especially foods.
It has the disadvantage that a seal cannot be obtained. On the other hand, a polypropylene film produced by a conventional method and without stretching can be heat-sealed, but has the disadvantage that its tear strength is too high and it is difficult to open the film to remove the food contents. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a laminated film of polypropylene film that is easy to tear and has heat-sealable properties. Another object of the present invention is to provide a packaging bag made of a heat-sealable laminated polypropylene film that is easy to open. The object of the present invention is to have a film density of 0.904 or more, and each ^{orientation coefficient} cos ² and satisfies the relationships of 1.0≧ ^cos2X / ^cos2Y ≧0.35 and 1.0≧ ^cos2X / ^cos2Z ≧0.35, and is not stretched or stretched only in one axis direction This is achieved by the laminated film of the propylene homopolymer film of the present invention and the food packaging bag made from the film. ^The orientation ^coefficients cos ²
By measuring x, △y, and △z, the following formula = (n _x + n _y + n _z )/ ₃ ...(2) and [However, in the above formula, the average refractive index, the intrinsic birefringence (birefringence when fully axially oriented) n⊥-n〓, and the refractive index perpendicular to the axis when fully axially oriented n⊥
can be calculated from the following equations for homopolypropylene: =1.508, n⊥−n⊥=0.040, and n⊥=1.495 (Saburo Okajima, Kazuhiko Kurihara; Sengaku Shi 22 , 206 (1966)). The homopolypropylene film laminated film of the present invention satisfies the film density, orientation coefficient, and stretching conditions described above, and has good heat sealability, 1.8 to 5.0 kg/cm in length and 15.0 to 80.0 kg/cm in width.
cm; preferably length 1.8-4.0Kg/cm, width 15.0-65.0
It has a moderate tear strength (measured by JIS-Z1072 method) of Kg/cm, and when used to make sealed bags for food packaging, for example, it is easy to open.
It has sufficient strength and impact resistance, and can store and hold the food contents without leaking during transportation. Moreover, it can withstand heat sterilization treatment after the food contents are sealed. The orientation coefficients of the preferable homopolypropylene film used in the present invention are: 0.50 ^≧ cos ² X, cos ² Y, ^{cos 2} Z≧0.20 ^1.0 ≧cos ² Satisfies the relationship Y≧0.40. The propylene homopolymer used in the film used in the present invention has a polymer MI of 0.5 to 15, preferably 0.8 to 10.0, and an isotact coefficient (value expressed as a percentage of boiling n-heptane extraction residue).
is 80 to 99, preferably 90 to 98; the intrinsic viscosity of the film (expressed herein as [η]) measured at 135°C using decalin as a solvent is 1.3 to 3.5, preferably 1.5 to 3.0. It's good to have one. Common propylene homopolymers available on the market can be used, such as J-300 manufactured by Mitsui Petrochemical Co., Ltd., and the like. The homopolypropylene film used in the present invention is made of, for example, the above-mentioned homopolypropylene resin,
It is extruded through an annular die at a resin temperature of 200-250°C, preferably 200-240°C, expanded at a blow ratio of 1.0-1.5, and the cooling rate from the melting temperature of the resin to 120°C is 4-20°C per second, preferably 4-240°C. It can be obtained by controlling cooling to 15°C. In addition to the methods exemplified above, any film forming method that allows the density and orientation coefficient of an unstretched or uniaxially stretched film to satisfy the above conditions can be used. The above propylene homopolymer used for the inner layer of the package of the present invention has a density of 0.899 to 0.903 in pellet form as produced, but when it is formed into a film under normal film forming conditions. , the density of the obtained film decreased to 0.895-0.885, which does not satisfy the conditions of the present invention. When the film used in the present invention is used in a packaging bag for heat sterilization, the density of the film described above changes depending on the subsequent heat sterilization treatment, but
A film density of 0.904 or more is the density before heat sterilization. The density of the film changes only slightly due to the sterilization process, which usually increases to 1.0001 to 1.02 times the density of the film before the sterilization process. When a bag is made from the laminated film of the present invention, it can be easily heat-sealed by using a homopolypropylene film layer as the innermost layer. The food packaging bag of the present invention is suitable for use as a food packaging bag for heat sterilization. In the laminated film or laminated bag of the present invention, other layers to be laminated are not particularly limited, and can be used in conventional laminated films or laminated bags, particularly for food packaging, especially for heat-sterilized food packaging laminated bags. Any material can be used. When used in heat-sterilized food packaging bags, it is preferable to provide a layer of heat-resistant resin. For the heat-resistant resin layer in the above case, a thermoplastic resin or thermosetting resin having a melting temperature or decomposition temperature higher than the heat-sealing temperature of the homopolypropylene film of the present invention, which is the inner layer, is conveniently used. Examples of these resins are polyesters such as polyethylene terephthalate, polyethylene terephthalate-isophthalate, poly-1,4-cyclohexylene dimethylene terephthalate, polyethylene oxybenzoate, polycaprolactam, polylaurinlactam, polyhexamethylene adipamide. , polyamides such as polyhexamethylene sebamide, poly-1,4-cyclohexylene adipamide, poly-dioxydiphenyl methane carbonate, polydioxydiphenyl ethane carbonate, poly-dioxydiphenyl-2, 2-propane carbonate, poly-
These include polycarbonates such as P-xylene glycol biscarbonate, cellulose esters such as cellulose acetate, fluororesins such as polyvinyl fluoride, polytetrafluoroethylene, and tetrafluoroethylene-hexafluoropropylene copolymer. Biaxially oriented isotactic polypropylene films can also be used. Furthermore, various infusible resins, such as heat-resistant polymers containing heterocyclic rings such as imide ring, imidazopyrrolone ring, imidazole ring, oxazole ring, oxadiazole ring, and thiazole ring in the molecular chain, are used. can. Examples of these infusible resins include polyimide, polyamideimide, polyesterimide, polyamideimide ester, polyesteramideimide, polyimideimidazopyrrolone, polyimideimidazopyrroloneimide, polyesterimideimidazopyrrolone, polybenzoxazoleimide, polyimideoxadiazole, Polysulfone etherimide, polyimide benzoxazole imide, organopolysiloxane imide, polybenzimidazole imide, polyoxazinone imide, polybenz thiazole imide, polybenzimidazole imidazo pyrrolon imide, polybenzo oxazinone imidazo pyrrolon imide, polybenz thiazole imidazo pyrrolon imide , polybenzoxazole imidazopyrrolone imide, polyimide urea, polybenzoxazole, polybenzimidazole, polybenzthiazole and mixtures thereof. An aluminum foil layer, a shock-absorbing thermoplastic resin layer, or both may be provided between the inner layer and outer layer described above, or similar layers may be provided. Examples of thermoplastic resins suitable for forming the shock absorbing layer are polyamides such as polycaprolactam, polylaurinlactam, polyhexamethylene adipamide, polyhexamethylene sebacamide, poly-1,4-cyclohexylene adipamide. , copolyamides, polydioxydiphenylmethane carbonate, polydioxydiphenyl ethane polycarbonate, polydioxydiphenyl-2,2
- Polycarbonates such as propane carbonate, poly-p-xylene glycol biscarbonate, polyoxyethylene-ethylene terephthalate, poly-1,4-oxybutylene-1,4
-Butylene terephthalate, polyoxyethylene-ethylene terephthalate/isophthalate, poly-1,3-oxypropylene-1,4-butylene terephthalate, poly-1,2-oxypropylene-1,4-butylene terephthalate, poly1,4 -Polyester polyethers such as oxybutylene-oxyethylene-ethylene terephthalate, poly-ε-caprolactone polyethylene terephthalate, poly-ε-caprolactone-
Polyester polylactones such as polyethylene terephthalate/isophthalate. The polymer film exemplified above can be uniaxially or biaxially
It can be used after being stretched in the axial direction, or it can be used in an unstretched form. Also, some stretched polypropylene films can be used as shock absorbing layers. Each layer does not need to be of a particular thickness, but the inner layer is typically 30-100μ, preferably 40-80μ
range, the outer layer usually has a thickness of 1 to 30μ, preferably 5 to 20μ
The range of .mu. for the shock-absorbing thermoplastic resin layer is usually 5 to 40 .mu., preferably 10 to 30 .mu.. A laminated sheet consisting of the above-mentioned layers can be made by adhering the films or foils of these layers by any known means. For example, these layers can be bonded together using an adhesive. In this case, polyester-isocyanate adhesive, epoxy adhesive, polyester-isocyanate adhesive,
Any known adhesive can be used, such as an adhesive made of a thermosetting resin such as an isocyanate-epoxy adhesive, a synthetic rubber adhesive, and an adhesive made of a thermoplastic resin. However, the aforementioned polyester-isocyanate, epoxy and polyester-isocyanate-epoxy adhesives are preferred. When adhesives are used to bond each layer of film and foil, propylene homopolymer film and/or
Alternatively, the surface of the heat-resistant resin film to be bonded can be treated with ozone, corona discharge, flame and/or an oxidizing agent to improve its adhesion. When the heat-resistant resin layer is formed of an infusible resin, a solution of a precursor polymer of these resins can be applied to the surface of aluminum foil and baked to form a heat-resistant resin film layer. . When providing a shock absorbing layer as an intermediate layer, polyamides such as nylon 6, nylon 12, etc., which are particularly suitable for the shock absorbing layer, are excellent hot melt adhesives, so if they are used as the shock absorbing layer, this layer will adhere. It has the advantage that it acts as an adhesive layer and does not require the use of a separate adhesive. The homopolypropylene resin, heat-resistant resin, and shock-absorbing thermoplastic resin forming each layer of the homopolypropylene laminated film of the present invention or the laminated bag for food packaging made from the same are within the range that does not impede achievement of the objects of the present invention. To this, known additives such as other resins, natural or synthetic rubbers, plasticizers, lubricants, fillers, colorants, stabilizers, antistatic agents, etc. can be optionally added. From the laminated sheets explained above, any known method can be used, for example, by stacking a pair of laminated sheets so that the propylene homopolymer film layers face each other,
The laminated bag for food packaging of the present invention can be made by a method of heat sealing so as to form a desired peripheral edge of the bag. Methods for heat-sealing are known, such as heating the desired part from the outside of the laminated seal, such as with a heating bar, heating knife, heating wire or impulse seal, or using ultrasonic sealing or induction heating sealing. An internal heating method can be used. The bag obtained as described above is filled with the food contents, and if necessary, any known method such as vacuum degassing, hot filling degassing, steaming degassing, steam injection degassing, or pressurization is performed. The inside of the bag is evacuated by a method such as degassing, or the food contents are sterilized by heating, and then the food contents are sealed by heat-sealing the food filling opening. The package filled with the food contents is then subjected to heat sterilization treatment, if necessary. The heat sterilization treatment can be performed by either a batch method or a continuous method. The packaging bag of the present invention allows a very wide range of foods to be sealed and, if necessary, sterilized. Examples of foods particularly suitable for filling and sealing in the packaging bag of the present invention include cooked curry, cooked hash, various stews such as borscht and beef stew, various gravies such as meat sauce, sweet and sour pork, sukiyaki, Chinese bean paste, and Stewed, steamed and boiled products of various vegetables, seafood and/or livestock products such as boiled vegetables, boiled asparagus, simmered tuna cream, etc.: Various soups such as consommé and potage yu, miso soup,
Pork soup, kenchin soup, and other soups: Rice dishes such as rice, sekihan, kamameshi, fried rice, pilaf, and porridge; Various types of noodles such as spaghetti, soba, udon, ramen, and noodles: Attachments such as kamameshi base and Chinese soba base, etc. Favorite foods such as boiled azuki beans, red bean paste, and anmitsu: Meat balls, hamburgers, beef steaks, roast pork, sautéed pork, corned beef, ham, sausages, grilled fish, yakiniku, yakitori, roast chicken, pork chips, fish meat dumplings, Cooked or semi-cooked foods such as processed meat or fish products such as bacon and kamaboko. The present invention will be further explained below with reference to Examples and Comparative Examples. Tear strength and heat seal strength in Examples and Comparative Examples were determined according to the methods of JIS-Z1702 and Ministry of Health and Welfare Notification No. 17, respectively. Example 1 A homopolypropylene resin with an MI of 1.3 (grade J-300 manufactured by Mitsui Petrochemical Co., Ltd.) was heated at a resin temperature of 230°C.
The film was formed using the air-cooled extrusion inflation method at a cooling rate of 13°C/sec to 120°C and an expansion ratio of 1.2.
A film with a thickness of 50μ was obtained. The film density of this film is 0.905 g/cm ³ and the orientation coefficient cos ²
cos ² Y and cos ² Z were 0.25, 0.30, and 0.45, respectively, cos ² X/cos ² Y=0.83, and cos ² X/cos ² Z=0.56. The tear strength of this film was 2.42 kg/cm in the vertical direction and 17.6 kg/cm in the horizontal direction. A 12 μm thick polyethylene terephthalate film, 9 μm thick aluminum foil, and the above polypropylene film were laminated with a urethane adhesive, and a bag with a size of 100 mm x 130 mm was made by heat sealing with the above polypropylene film as the inner surface. The heat seal strength of this bag was 3.5 kg/15 mm width. This bag was filled with cheese and subjected to an opening test by a panel of 18 people. The results are shown in Table 1. Example 2 A three-layer laminate sheet of polyethylene terephthalate film/aluminum foil/polypropylene film, exactly the same as in Example 1, was used as a lid material for a blow-molded polypropylene multilayer bottle. In this case as well, it withstood retort sterilization at 120°C, and the lid material could be easily opened by tearing. Comparative Example 1 The same resin as in Example 1 was formed into a film by the T-die method under normal conditions to obtain a film with a thickness of 50 μm. The film density of this film is 0.891, and the orientation coefficients are cos ² X = 0.31, cos ² Y = 0.33, cos ² Z =
0.36, cos ² X/cos ² Y=0.94, cos ² X/cos ² Z=0.73
It was hot. The tear strength of this film was 8.75 kg/cm in the vertical direction and 25.8 kg/cm in the horizontal direction. Further, a three-layer laminated bag was made using this film in the same manner as in Example 1, and an opening test was conducted in the same manner as in Example 1. The results are shown in Table 1. Further, the heat sealing strength of this laminated bag was 3.2 kg/15 mm width.

[Table] Comparative Example 2 Commercially available biaxially oriented polypropylene film (25μ
The film density is 0.909 ^, and the orientation coefficients ^are cos ² X = 0.10, cos ² Y = 0.63, and cos ² Z = 0.27, ^respectively , and cos ² 0.37
It was hot. The tear strength of this film is 3.67
Kg/cm, width 2.4 Kg/cm, and tearability was good. However, using this film, a three-layer laminated film was made in the same manner as in Example 1, and an attempt was made to obtain a bag by heat-sealing this laminated film with the above-mentioned film as an inner layer, but the sealed portion contracted and the appearance In addition to being defective, the sealing performance of the seal portion could not be obtained.

Claims (1)

[Claims] 1. Having a film density of 0.904 or more, each orientation coefficient in the thickness direction, transverse direction, and machine direction of the film.
^{cos 2 _ _ _ _ _} A two- or more-layer laminated film comprising a propylene homopolymer film laminated with another film or sheet, characterized in that it is unstretched or uniaxially stretched. 2 Having a film density of 0.904 or more, each orientation coefficient in the film thickness direction, transverse direction, and machine direction
^{cos 2 _ _ _ _ _} A propylene homopolymer film that satisfies the above requirements and is characterized by being unstretched or uniaxially stretched, and consisting of two or more laminated films in which other films or sheets are laminated. A food packaging bag characterized in that the propylene homopolymer film is the innermost layer.