JP2012045884A - Coextruded multilayer film, and lid material using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coextruded multilayer film with no other base material laminated thereto, which can be singularly used without degradation in the easy-to-open property conventionally required for lid materials, that is to say, can be prevented from fusing to a hot plate upon heat sealing and from generating an elongation of the film upon opening by having a high rigidity.SOLUTION: The coextruded multilayer film includes: an outermost layer (A) containing 80 mass% or more of a propylene homopolymer (a1) having a melting temperature of 160°C or higher as a resin component; a central layer (B) containing 60 mass% or more of a propylene-based polymer (b1) having a melting temperature of 120°C or higher as a resin component; and an easy-to-peel layer (C). The layers (A), (B) and (C) are laminated in the coextruded multilayer film whose overall thickness is in a range of 30 to 150 μm, and a sum total of thicknesses of the outermost layer (A) and the central layer (B) is in a range of 70% to 95% of the overall thickness.

Description

  TECHNICAL FIELD The present invention relates to a coextruded multilayer film that can be suitably used as an easy-open packaging material for foods and medical devices, and a lid material using the coextruded multilayer film alone.

  In the field of packaging films such as food packaging and medical device packaging, there is an increasing demand for easily-openable films that can be opened more easily. In particular, there is a strong demand for an easy peel film that can be easily peeled off and used for a container lid or the like.

  Generally, a lid member using an easy peel film is used by laminating and bonding an easy peel film and a base film through an adhesive or the like. This is used for the purpose of preventing adhesion to a hot plate during heat sealing, improving mechanical strength, and adding functions such as barrier properties (see, for example, Patent Document 1).

  Also in Patent Document 1, a lid material is formed by laminating a 50 μm unstretched polypropylene film and a 60 μm unstretched nylon film as a reinforcing material. In order to bond such a base film, an adhesive lamination method by a dry lamination method is generally used. However, the organic solvent contained in the adhesive is discharged, the process is complicated, and the content due to the residual solvent is reduced. There are problems such as odor migration, and further improvement methods are required.

JP 2010-5935 A

  An object of the present invention has been made in view of the above problems, and without damaging the easy-open performance required for conventional lid materials, and without performing lamination or the like of other base materials. It is intended to provide a coextruded laminated film having a high rigidity that can be used in a case where it can be used, that is, can be prevented from being fused to a hot plate with a heat seal, and the film does not stretch when opened.

  As a result of diligent research to solve the above-mentioned problems, the present inventors made propylene-based resin layers having specific performances as an outermost layer and a central layer, and these layers have a thickness of a certain level or more, so that the conventional lid The present invention was completed by finding that it can be used alone without impairing the easy-openability required for the material.

  That is, the present invention comprises an outermost layer (A) containing 80% by mass or more of a propylene homopolymer (a1) having a melting point of 160 ° C. or higher as a resin component, and a propylene polymer (b1) having a melting point of 120 ° C. or higher. It is a coextruded multilayer film having a total thickness of 30 to 150 μm formed by laminating a central layer (B) containing 60% by mass or more as a resin component and an easy peel layer (C), and the outermost layer (A) and the central layer ( The present invention provides a coextruded multilayer film characterized in that the total thickness with B) is 70 to 95% of the total thickness, and a lid made of the film.

  The laminated film of the present invention has high rigidity and mechanical strength, can be used alone, and exhibits the same easy-opening property as conventional ones. Also, there is no contamination of the seal bar during heat sealing. Therefore, it can be suitably used as a lid material for containers such as food and medical devices.

  The outermost layer (A) in the laminated film of the present invention must contain 80% by mass or more of the propylene homopolymer (a1) having a melting point of 160 ° C. or more as a resin component. The melting point as used in the present application refers to the peak top value when measured with a differential scanning calorimeter (DSC).

  Generally, a heat sealing method is performed by allowing a seal bar heated from the upper part of the film to adhere to a portion to be sealed and left for several seconds. That is, since the outermost layer of the film is in contact with the heated seal bar, if the outermost layer is melted at that temperature, the seal bar is contaminated, which may disturb the manufacturing cycle, or the appearance after sealing. May be damaged. Therefore, in order to use the easy peel film alone, it is necessary to increase the heat resistance of the outermost layer.

  In the present invention, the resin used for the outermost layer (A) for this purpose is the specific propylene homopolymer (a1). More preferable from the above viewpoint and the stability of the film formation by the coextrusion method is a polymerized using a multi-site catalyst (Ziegler-Natta catalyst). Furthermore, it is preferable to contain 90% by mass or more of the propylene homopolymer (a1) as the resin used for the outermost layer (A). Furthermore, it is preferable that MFR (230 degreeC) is 0.5-30.0 g / 10min, More preferably, MFR (230 degreeC) is 2.0-15.0 g / 10min. When the MFR is within this range, the film shrinks at the time of sealing, and the film formability is further improved.

  In addition, as other resin which can be used for outermost layer (A), what is necessary is just a thing compatible with the said propylene homopolymer (a1) in the range which does not impair the characteristic of this invention, for example, propylene- Mention may be made of copolymers of propylene and other olefins, such as ethylene copolymers.

  When using in applications where the heat resistance of the outermost layer (A) needs to be increased, such as when sealing at a higher temperature to increase the sealing strength, the outermost layer (A) should further contain a nucleating agent (a2). Is preferred.

  Examples of the nucleating agent (a2) include sodium benzoate, aromatic carboxylic acids such as p-tert-butylbenzoic acid and aluminum benzoate and derivatives thereof, sodium di (4-t-butylphenyl) phosphate, and the like. Organophosphate metal salts, benzylidene sorbitol derivatives, polyvinylcycloalkanes such as talc and polyvinylcyclohexane, and certain organic dicarboxylic acid derivatives such as sebacic acid Rosin alkali metal salts, alkaline earth metal salts, lithium salts Compounds such as sodium salt, potassium salt, calcium salt, magnesium salt, aluminum salt, and those provided as nucleating agents for polypropylene resins in JP 2010-53248 A, JP 2010-150500 A, etc. Any of them can be used alone or in combination.

  Among these, from the viewpoint of improving heat resistance, it is preferable to use 3-methylbutene-1 and vinylcycloalkane, which are polymer nucleating agents.

  The use ratio of the nucleating agent (a2) is not particularly limited, and can be appropriately selected according to the intended use site (seal temperature, seal strength, etc.), but too much. If the propylene homopolymer (a1) melted during co-extrusion causes precipitation, it may affect the homogeneity of the film obtained in terms of heat resistance and transparency, and if it is too little Since the effect for improving heat resistance may not be sufficient, it is preferably used in the range of 100 to 800 ppm with respect to the mass of the resin used for the outermost layer (A).

  The resin used for the center layer (B) of the present invention must contain 60% by mass or more of the propylene polymer (b1) having a melting point of 120 ° C. or more as a resin component. At this time, the propylene polymer (b1) may be the same as the propylene homopolymer (a1) used in the outermost layer (A). More preferably, it is a propylene-based polymer having a melting point of 140 ° C. or higher, and is preferably polymerized using a multi-site catalyst. Examples of the propylene polymer (b1) include a propylene homopolymer, a propylene-ethylene random copolymer, and the like. Furthermore, it is preferable to contain 80% by mass or more of the propylene polymer (b1) as a resin used for the center layer (B). Furthermore, it is preferable that MFR (230 degreeC) is 0.5-30.0 g / 10min, More preferably, MFR (230 degreeC) is 2.0-15.0 g / 10min. When the MFR is within this range, the film shrinks at the time of sealing, and the film formability is further improved.

  In the center layer (B), other resins compatible with the propylene polymer (b1), other olefin resins, and the like may be mixed as long as the effects of the present invention are not impaired. Further, recycled products of propylene resin may be mixed and used.

  In the present invention, it is essential that the total thickness of the outermost layer (A) and the center layer (B) is 70 to 95% of the total film thickness. By making it in this range, it becomes easy to maintain the rigidity of the resulting coextruded laminated film, and the elongation of the film when peeled off can be suppressed, and the strength as a lid can be maintained. More preferably, the thickness is adjusted to 80 to 90% with respect to the total thickness of the coextruded laminated film.

  In the present invention, in addition to the outermost layer (A) and the center layer (B), it is essential to stack an easy peel layer (C) for imparting easy opening.

  The easy peel layer (C) is intended to be adhered to the outermost layer of a container by applying a temperature to a desired part when a film is used as a lid material, and further peeled off. It is necessary to easily cause cohesive failure or interfacial peeling. In the present invention, since the film is produced by the coextrusion method, it is essential that the resin layer is coextrudable with the outermost layer (A) and the center layer (B).

  From these viewpoints, the resin type that can be used for the easy peel layer (C) is preferably a mixed resin of a propylene resin (c1) and an ethylene resin (c2).

  Examples of the propylene resin (c1) include propylene homopolymers, propylene-α-olefin copolymers such as propylene-ethylene copolymers, propylene-butene-1 copolymers, and propylene-ethylene-butene-1. A copolymer, a metallocene catalyst type | system | group polypropylene, etc. are mentioned. These may be used alone or in combination. From the viewpoints of easy opening in the obtained laminated film and easy adjustment of the sealing strength, ethylene-propylene random copolymer, ethylene-propylene-butene-1 terpolymer or single It is preferable to use an ethylene-propylene copolymer polymerized using a site catalyst.

  These propylene resins (c1) preferably have an MFR (230 ° C.) of 0.5 to 30.0 g / 10 min and a melting point of 120 to 165 ° C., more preferably MFR (230 ° C.). ) Is 2.0 to 15.0 g / 10 min and the melting point is 125 to 162 ° C. If MFR and melting | fusing point are this range, there will be little shrinkage | contraction of the film at the time of sealing, and also the film-forming property of a film will improve.

Examples of the ethylene resin (c2) include polyethylene resins such as very low density polyethylene (VLDPE), linear low density polyethylene (LLDPE), and low density polyethylene (LDPE), and ethylene-vinyl acetate copolymer. (EVA), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl acrylate (EMA) copolymer, ethylene-ethyl acrylate-maleic anhydride copolymer ( E-EA-MAH), ethylene copolymers such as ethylene-acrylic acid copolymer (EAA), ethylene-methacrylic acid copolymer (EMAA); and ethylene-acrylic acid copolymer ionomers, ethylene- Examples thereof include ionomers of methacrylic acid copolymers. Among these, from the viewpoint of compatibility when used in combination with the above-described propylene-based resin (c1), it is possible to easily perform cohesive failure or interfacial peeling, and from the viewpoint of surface appearance after peeling, density, etc. There low density polyethylene and / or density of 0.91~0.93g / cm ³ it is preferred to use high density polyethylene 0.94~0.96g / cm ^3. Furthermore, the melt flow rate (190 ° C., 21.18 N) is preferably 1 g / 10 min or more from the viewpoint of film formability.

  Furthermore, as a use ratio of the propylene resin (c1) and the ethylene resin (c2), the mass ratio represented by (c1) / (c2) is in the range of 60 to 90 / 40-10. However, it is preferable from the point which can express easily openability, and it is especially preferable that it is the range of 70-85 / 15-30.

  The easy peel layer (C) of the present invention may be used in combination with other olefin resins such as polybutene resins from the viewpoint of further facilitating easy opening and adjusting the sealing strength.

  As described above, the thickness of the easy peel layer (C) in the laminated film of the present invention must be in the range of 5 to 30% of the total thickness from the viewpoint of the rigidity and strength of the film, and is 10 to 20%. A range is preferable.

  In addition, the total thickness of the coextruded laminated film of the present invention must be in the range of 30 to 150 μm, and is preferably 40 μm or more, particularly from the viewpoint of strength when used alone.

  The coextruded laminated film of the present invention is not limited in any way except that it is formed by laminating the specific outermost layer (A), the central layer (B), and the easy peel layer (C). In each layer, components such as an antifogging agent, an antistatic agent, a heat stabilizer, an antioxidant, a lubricant, an antiblocking agent, a release agent, an ultraviolet absorber, and a colorant can be added.

  The production method of the laminated film of the present invention is not particularly limited as long as it is a coextrusion method. For example, each resin used for the outermost layer (A), the center layer (B), and the easy peel layer (C) or The resin mixture is heated and melted with separate extruders, and laminated in the order of (A) / (B) / (C) in a molten state by a method such as a coextrusion multi-layer die method or a feed block method. Examples thereof include a method of forming into a film by a T-die / chill roll method or the like. In this coextrusion method, the ratio of the thickness of each layer can be adjusted relatively freely, and a multilayer film having excellent hygiene and cost performance can be obtained. Furthermore, since the difference in melting point between the propylene resin (c1) and the ethylene resin (c2) used in the easy peel layer (C) of the present invention is large, the film appearance deteriorates during coextrusion processing. There is. In order to suppress such deterioration, a T-die / chill roll method that can perform melt extrusion at a relatively high temperature is preferable.

  Since the coextruded laminated film of the present invention is obtained as a substantially unstretched multilayer film by the above production method, secondary molding such as deep drawing by vacuum molding is also possible.

  Further, when printing or the like is performed on the outermost layer (A), it is preferable to perform a surface treatment on the outermost layer (A) in order to improve adhesion with printing ink. Examples of such surface treatment include corona treatment, plasma treatment, chromic acid treatment, flame treatment, hot air treatment, surface oxidation treatment such as ozone / ultraviolet treatment, and surface unevenness treatment such as sandblasting. Corona treatment is preferable.

  Although it does not specifically limit as a use of the coextruded laminated film of this invention, It can be used suitably for the lid | cover material etc. of a packaging container used for uses, such as a foodstuff, a chemical | drug | medicine, an industrial part, miscellaneous goods, and a magazine. In particular, the outermost layer of the packaging container (the part that adheres to the easy peel layer of the coextruded laminated film of the present invention) contains various propylene-based resins, from the viewpoint of the balance between easy-openability and seal strength. preferable.

  Next, the present invention will be described in more detail with reference to examples and comparative examples. Hereinafter, unless otherwise specified, “part” is based on mass.

Example 1
Propylene-ethylene random copolymer (hereinafter referred to as COPP) synthesized using a multi-site catalyst as a resin for the easy peel layer (C) [melt flow rate (hereinafter referred to as MFR) (230 ° C.) 8 g / 10 min] 80 Part and 20 parts of low density polyethylene (hereinafter referred to as LDPE) [density 0.92 g / cm ³ , MFR (190 ° C.) 7 g / 10 min], and synthesized using a multisite catalyst as the central layer (B). Using a propylene homopolymer (hereinafter referred to as HOPP) having an MFR (230 ° C.) of 9 g / 10 min and a melting point of 164 ° C., using HOPP as the resin for the outermost layer (A), an easy peel layer extruder (caliber 30 mm) ), A central layer extruder (40 mm diameter) and an outermost layer extruder (30 mm diameter), respectively, Extrusion was performed at an extrusion temperature of 230 ° C. by an extrusion method so that the thickness of each layer of (A) / (B) / (C) was 25 μm / 70 μm / 25 μm, and cooled by a 30 ° C. water-cooled metal cooling roll, The film was wound on a roll and aged in a aging room at 35 ° C. for 48 hours to obtain a laminated film of the present invention having a total thickness of 120 μm.

Example 2
Example (A) / (B) / (C) was carried out in the same manner as in Example 1 except that the thickness of each layer was 10 μm / 45 μm / 15 μm and the total thickness was 70 μm. 2 laminated films were obtained.

Example 3
Example (A) / (B) / (C) was carried out in the same manner as in Example 1 except that the thickness of each layer was 8 μm / 32 μm / 10 μm and the total thickness was 50 μm. 3 laminated films were obtained.

Example 4
Example (A) / (B) / (C) was carried out in the same manner as in Example 1 except that the thickness of each layer was 5 μm / 19 μm / 6 μm and the total thickness was 30 μm. 4 laminated films were obtained.

Example 5
A laminated film of Example 5 was obtained in the same manner as in Example 2 except that a mixture of 90 parts of COPP and 10 parts of LDPE was used as the resin for the easy peel layer (C).

Example 6
As the resin for the easy peel layer (C), a mixture of 60 parts of propylene-ethylene-butene-1 terpolymer (hereinafter referred to as EPB) [MFR (230 ° C.) 7 g / 10 min] and 40 parts of LDPE was used. A laminated film of Example 6 was obtained in the same manner as Example 2 except for the above.

Example 7
A laminated film of Example 7 was obtained in the same manner as in Example 2 except that a mixture of 70 parts of EPB and 30 parts of LDPE was used as the resin for the easy peel layer (C).

Example 8
As a resin for the easy peel layer (C), a mixture of 60 parts of COPP (hereinafter referred to as metallocene COPP) [MFR (230 ° C.) 7 g / 10 min, melting point 125 ° C.] synthesized using a metallocene catalyst and 40 parts of LDPE A laminated film of Example 8 was obtained in the same manner as Example 2 except that it was used.

Example 9
A laminated film of Example 9 was obtained in the same manner as in Example 2 except that a mixture of 70 parts of metallocene COPP and 30 parts of LDPE was used as the resin for the easy peel layer (C).

Example 10
Example except that 70 parts of COPP and 30 parts of high density polyethylene (hereinafter referred to as HDPE) [density 0.96 g / cm ³ , MFR 15 g / 10 min] were used as the resin for the easy peel layer (C). In the same manner as in Example 2, a laminated film of Example 10 was obtained.

Example 11
A laminated film of Example 11 was obtained in the same manner as in Example 2 except that 70 parts of COPP, 15 parts of HDPE and 15 parts of LDPE were used as the resin for the easy peel layer (C).

Example 12
The laminated film of Example 12 was the same as Example 2 except that a mixture of 99.95 parts of HOPP and 0.05 part of nucleating agent [3-methylbutene-1] was used as the resin for the outermost layer (A). Got.

Example 13
A laminated film of Example 13 was obtained in the same manner as Example 2 except that a mixture of 90 parts of HOPP and 10 parts of COPP was used as the resin for the outermost layer (A).

Example 14
A laminated film of Example 14 was obtained in the same manner as Example 2 except that a mixture of 90 parts of HOPP and 10 parts of LDPE was used as the resin for the outermost layer (A).

Example 15
Example (A) / (B) / (C) is the same as Example 11 except that the thickness of each layer is 19 μm / 45 μm / 6 μm and the total thickness is 70 μm. 15 laminated films were obtained.

Example 16
A laminated film of Example 16 was obtained in the same manner as in Example 2 except that metallocene COPP was used as the resin for the center layer (B).

Comparative Example 1
A laminated film of Comparative Example 1 was obtained in the same manner as in Example 2 except that COPP was used as the center layer (B) and COPP was also used as the resin for the outermost layer (A).

Comparative Example 2
As in Example 2, except that a propylene homopolymer [melting point: 155 ° C., MFR (230 ° C.): 8 g / 10 min, (hereinafter referred to as HOPP (2))] was used as the resin for the outermost layer (A). A laminated film of Comparative Example 2 was obtained.

Comparative Example 3
Comparative example as in Example 1 except that the thickness of each layer of (A) / (B) / (C) was 3 μm / 13 μm / 4 μm and the total thickness was 20 μm. 3 laminated films were obtained.

  The obtained film was evaluated by the following method. The results are summarized in Tables 1 to 4.

Heat seal test:
The obtained coextruded multilayer film was cut out to 10 cm × 10 cm, and was laminated with a polypropylene sheet having a thickness of 0.3 mm so that the heat seal surface was on the polypropylene sheet side. The upper heat seal bar adjusted to a predetermined temperature was set to be on the outermost layer side of the coextruded laminated film using a sealer, and heat sealed under conditions of 0.2 MPa and 1 second.

Evaluation of stickiness to heat seal bar:
The behavior of the heat seal test was evaluated according to the following criteria.
○: The sticker bar was not sticky.
Δ: The outermost layer was slightly sticky on the seal bar.
X: The outermost layer was sticky to the seal bar and welded to the seal bar. Or the whole film was melted.

Evaluation of peel strength:
A strip-shaped sample having a width of 15 mm was cut out in a direction perpendicular to the heat-sealed portion, and the maximum strength when peeled at a speed of 300 mm / min was determined as the peel strength using a tensile tester.

Evaluation of peelability:
The behavior when the heat-sealed sample was peeled was evaluated according to the following criteria.
○: The film was not stretched and could be peeled off smoothly.
Δ: Although the film was slightly stretched, it could be peeled relatively easily.
X: The film was stretched and could not be easily peeled off.

rigidity:
In accordance with ASTM D882, 1% Secant Modulus was measured in an atmosphere of 23 ° C. and 50% relative humidity.

Claims (10)

An outermost layer (A) containing 80% by mass or more of a propylene homopolymer (a1) having a melting point of 160 ° C. or more as a resin component;
A center layer (B) containing 60% by mass or more of a propylene polymer (b1) having a melting point of 120 ° C. or more as a resin component;
It is a coextruded multilayer film having a total thickness of 30 to 150 μm formed by laminating an easy peel layer (C),
A coextruded multilayer film characterized in that the total thickness of the outermost layer (A) and the central layer (B) is 70 to 95% of the total thickness. The coextruded multilayer film according to claim 1, further comprising a nucleating agent (a2) in the outermost layer (A). The coextruded multilayer film according to claim 1 or 2, wherein the propylene homopolymer (a1) is polymerized using a multisite catalyst. The coextruded multilayer film according to any one of claims 1 to 3, wherein the propylene polymer (b1) is a propylene homopolymer or an ethylene-propylene random copolymer. The coextruded multilayer film according to any one of claims 1 to 4, wherein the easy peel layer (C) is a mixed resin layer of a propylene resin (c1) and an ethylene resin (c2). 6. The propylene-based resin (c1) is an ethylene-propylene random copolymer, an ethylene-propylene-butene-1 terpolymer, or an ethylene-propylene copolymer polymerized using a single site catalyst. Coextruded multilayer film. The coextruded multilayer film according to claim 5 or 6, wherein the ethylene-based resin (c2) is high-density polyethylene and / or low-density polyethylene. The use ratio of the propylene-based resin (c1) and the ethylene-based resin (c2) is in a range of 60 to 90/40 to 10 as a mass ratio represented by (c1) / (c2). 8. The coextruded multilayer film according to any one of 7 above. A lid material comprising the coextruded multilayer film according to any one of claims 1 to 8. The lid material according to claim 9, which is for a container having a propylene-based resin layer as an outermost layer.