JP2007021814A - Laminated polypropylene resin film for container lid material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated polypropylene resin film for a container lid material which has enough heat-seal strength and easy openability. <P>SOLUTION: The laminated polypropylene resin film for a container lid material is is a stretched polypropylene resin film comprising at least three layers of: a substrate layer of a crystalline polypropylene resin; an intermediate layer of a crystalline polypropylene resin and a propylene-α-olefin; and a heat-fusion layer with a melting point of 150°C or below. In the intermediate layer, at least 30 wt.% of the propylene-α-olefin copolymer is incorporated, and the thickness of the intermediate layer is at least 7 μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a laminated polypropylene-based resin film for a lid material of a container, and more specifically, it can be heat sealed to a polypropylene container and has sufficient heat seal strength and easy opening when used as a lid material. The present invention relates to a laminated polypropylene resin film for container lid materials.

  Conventionally, films made of various polyolefins have been proposed for packaging foods and the like. These polyolefin-based films are used to protect the contents from dust, dust and the like during distribution and display, and are usually used after heat sealing in fields requiring sealing properties. In this case, if the heat seal portion can be peeled without applying a large force, it is not necessary to use a knife or scissors, and even a weak child or an elderly person can easily open the seal. For this reason, the polyolefin film for packaging is required to have a heat seal strength that is easy to open, that is, has an easy peel property.

In response to these requirements, proposals have been made to use an ethylene-based polymer as an adhesive layer, an amorphous ethylene-α-olefin as an intermediate layer, and a propylene-based polymer as a surface layer as countermeasures against narrow objects during heat sealing. (For example, refer to Patent Document 1). As a measure for stringing from the adhesive surface at the time of peeling, a mixture of an ethylene polymer and an ethylene / 1-butene polymer is used for the base material layer, and an ethylene polymer and a 1-butene copolymer are used for the sealant layer. There has been a proposal to use a mixture (see, for example, Patent Document 2).
JP 2003-251766 A JP 2004-66603 A

  However, these are all cast films, and depending on the heat-sealing conditions, there is a problem that the film stretches during peeling and is difficult to open.

Furthermore, a lid material having heat sealability is disclosed (for example, see Patent Document 3).
JP 2000-309069 A

  However, when it exceeds a certain strength (for example, 20 N / 15 mm), there is a problem that breakage occurs at the time of peeling, and it cannot be opened cleanly.

  The present invention solves the problems of the above-mentioned conventional laminated polyolefin resin film for containers of containers, and provides a laminated polypropylene resin film for containers of containers having sufficient heat seal strength and easy opening properties. For the purpose.

  In order to achieve the above object, a laminated polypropylene resin film for a lid material of a container according to the present invention comprises a base layer composed of a crystalline polypropylene resin and an intermediate layer composed of a crystalline polypropylene resin and a propylene α-olefin copolymer. And a stretched polypropylene resin film comprising a laminate of three or more layers having a heat fusion layer having a melting point of 150 ° C. or lower, wherein a propylene α-olefin copolymer is blended in an intermediate layer by 30% by weight or more, The thickness of the layer is 7 μm or more.

  The laminated polypropylene resin film for a lid material of the container of the present invention having the above-described configuration can be suitably used for applications requiring sufficient heat seal strength and easy opening as a lid material.

  In this case, it is characterized by being biaxially stretched.

  Hereinafter, an embodiment of a laminated polypropylene resin film for a lid material of a container according to the present invention will be described.

The laminated polypropylene-based resin film for the lid material of the container of the present invention is a base layer, a heat-sealing layer, and a film of three or more layers in which an intermediate layer is provided between the base material layer and the heat-sealing layer. It is preferable.
The base material layer is preferably made of a crystalline polypropylene resin. The crystalline polypropylene resin used for the base layer of the laminated film of the present invention contains 70% by weight or more of an n-heptane-insoluble isotactic propylene homopolymer or propylene used in ordinary extrusion molding or the like. Any copolymer of polypropylene and another α-olefin may be used.
The insolubility of n-heptane indicates the crystallinity of polypropylene and indicates safety when used for food packaging. In the present invention, n-heptane insolubility according to Notification No. 20 of the Ministry of Health and Welfare in February 1982 is used. It is a preferred embodiment to use a material that conforms to (the elution amount when extracted at 25 ° C. for 60 minutes is 150 pPm or less [the usage temperature exceeds 100 ° C. is 30 pPm or less]).

As an α-olefin copolymer component of a copolymer of propylene and another α-olefin, an α-olefin having 2 to 8 carbon atoms, for example, ethylene, butene-1, pentene-1, hexene-1, 4 -Methyl-1-pentene is preferred. Here, the copolymer is preferably a random or block copolymer obtained by polymerizing one or more α-olefins exemplified above with propylene.
Moreover, a melt flow rate (MFR) is 0.1-100 g / 10min, Preferably it is 0.5-20 g / 10min, More preferably, the thing of the range of 1.0-10 g / 10min can be illustrated.

  The resin used for the heat-sealing layer of the laminated polypropylene resin film for the lid material of the container of the present invention is a thermoplastic resin having a melting point of 150 ° C. or less, and is ethylene, propylene, butene, pentene, hexene, octene, decene. Random copolymers or block copolymers obtained by polymerizing two or more selected from α-olefin monomers having 2 to 10 carbon atoms such as these are preferable, and these copolymers are used alone or in combination. Can be used.

  Here, the resin constituting the particularly preferable heat-sealing layer preferably contains a propylene-butene copolymer having a high butene content, and the butene content in the propylene-butene copolymer is 20% by mass or more. Preferably there is. The upper limit of the butene content is not particularly limited, but if the butene content is too much, the film surface may become sticky, and slipperiness and blocking resistance may be reduced. Good. Examples of the propylene-butene copolymer having a high butene content include “SPX78J1” manufactured by Sumitomo Chemical Co., Ltd. and “XR110H” manufactured by Mitsui Chemicals, Inc.

  The propylene-butene copolymer is preferably blended in an amount of 65% by mass or more in the resin component constituting the heat-sealing layer. More preferably, it is 70% by mass or more, preferably 99% by mass or less, and more preferably 95% by mass or less. When the blending amount of the propylene-butene copolymer is too small, the sealing force at the time of sealing may be low, and it may be difficult to obtain a sufficient sealing strength with the container. The interlaminar strength may decrease.

Furthermore, the melting point of the thermoplastic resin forming the heat-sealing layer is desirably 150 ° C. or less, preferably 60 to 150 ° C. By doing in this way, sufficient heat seal intensity | strength can be given to the laminated polypropylene resin film for lid | cover materials of a container. When the melting point of the thermoplastic resin forming the heat-sealing layer is less than 60 ° C., the heat resistance of the heat seal portion is poor, and when it exceeds 150 ° C., improvement in heat seal strength cannot be expected.
Moreover, MFR is 0.1-100 g / 10min, Preferably it is 0.5-20 g / 10min, More preferably, the thing of the range of 1.0-10 g / 10min can be illustrated.

  In addition, the laminated polypropylene resin film for the lid material of the container of the present invention has an intermediate layer containing 30% by weight or more of a propylene-α-olefin copolymer between the base material layer and the heat fusion layer. Preferably, it is desirable to blend the propylene-α-olefin copolymer in the range of 35 wt% to 60 wt%. Here, when the blending amount of the propylene-α-olefin copolymer is less than 35% by weight, the heat seal strength with the container is insufficient, which is not preferable. On the other hand, if it exceeds 60% by weight, it is not preferable because the film may become dull and difficult to handle, or the adhesive strength with the container may become too strong to be opened cleanly.

The propylene-α-olefin copolymer used here is not particularly limited, but is preferably a propylene-α-olefin copolymer having a cold xylene soluble content (CXS) of 3% by weight or less. . When a propylene-α-olefin copolymer having a cold xylene soluble content (CXS) exceeding 3% by weight is used, it is not preferable because it tends to lose elasticity.
The α-olefin copolymer is excellent in mechanical strength such as impact strength and tearing properties, low temperature properties, weather resistance, etc., and by blending such components, it is excellent in laminated polypropylene resin films for lid materials. Properties can be imparted. However, since the α-olefin copolymer has a structure in which a different α-olefin is randomly introduced as the second component or the third component in the α-olefin molecular chain as the main component, it is crystallized. Is suppressed, and the crystallinity is low as compared with a homopolymer of α-olefin such as homopolypropylene, and the blending of the α-olefin copolymer results in lowering the feeling of the film.

The above-mentioned “cold xylene-soluble matter” indicates the amount of amorphous part contained in the α-olefin copolymer, and it is said that “cold xylene-soluble matter is 3% by mass or less” It means an α-olefin copolymer having few crystal parts and high crystallinity.
Here, the cold xylene-soluble component means that 1 g of a sample is completely dissolved in 100 ml of boiling xylene, then cooled to 20 ° C., left for 4 hours, and then separated into a precipitate and a solution. The weight is determined by measuring the weight when the liquid is dried and dried at 70 ° C. under reduced pressure.

Examples of the α-olefin having a cold xylene soluble content of 3% by mass or less include JP-A-2003-277.
Examples of the polymer synthesized by the continuous gas phase polymerization method described in No. 412 include, for example, “FS
X66E8 "(manufactured by Sumitomo Chemical Co., Ltd.) can be used.

The thickness of the intermediate layer of the laminated polypropylene resin film for the lid material of the container of the present invention needs to be 7 μm or more. A preferable thickness is 8 μm or more and 50 μm or less. If the thickness is less than 7 μm, the interlayer adhesion strength between the base material layer and the heat-sealing layer is insufficient, and peeling between the layers occurs at the time of opening, and the lid cannot be removed cleanly. This is not preferable because it is not preferable in handling.
The thicknesses of the base material layer and the heat fusion layer are not particularly limited. For example, the base material layer is in the range of 15 to 90% of the total thickness, and the heat fusion layer is in the range of 0.85 to 15%. It is preferable to set by. As a more preferable range, the base material layer is 20 to 85% of the total thickness, and the heat fusion layer is 1.5 to 10%. Here, when the layer thickness of the base layer is less than 15% and the heat-sealing layer exceeds 15%, the sensation of the waist tends to be lost, which is not preferable in handling the product. Further, the thickness of the base layer exceeds 90%, the heat-sealing layer is less than 0.85%, and the desired seal strength may not be obtained, which is not preferable.

  In the present invention, the resin forming each layer includes various additives and fillers, for example, a heat stabilizer, an antioxidant, a light stabilizer, an antistatic agent, as long as the properties of each layer are not impaired as necessary. Lubricant, nucleating agent, flame retardant, pigment, dye, calcium carbonate, barium sulfate, magnesium hydroxide, mica, talc, clay, zinc oxide, magnesium oxide, aluminum oxide, antibacterial agent, antifogging agent, natural degradability Additives and the like can be added. Furthermore, other thermoplastic resins, thermoplastic elastomers, rubbers, hydrocarbon resins, petroleum resins, and the like may be blended within a range that does not impair the characteristics of the film of the present invention.

  The laminated polypropylene resin film for the lid material of the container of the present invention can be arbitrarily produced by a method known per se, and is not particularly limited. For example, after melt lamination by T-die method or inflation method using an extruder suitable for the number of layers, it is cooled by a cooling roll method, water cooling method or air cooling method to form a laminated film, sequentially biaxial stretching method, simultaneous biaxial Examples of the stretching method include a stretching method and a tube stretching method. Here, if the conditions at the time of manufacturing by a sequential biaxial stretching method are illustrated, the resin melt-extruded from the T-shaped die is cooled and solidified by a casting machine to produce a raw sheet. At this time, the roll temperature for melt casting is preferably set between 15 ° C. and 40 ° C. for the purpose of suppressing crystallization of the resin and improving transparency. Next, after heating the raw sheet to a temperature suitable for stretching, the sheet is stretched in the flow direction of the sheet using the difference in speed between the stretching rolls. Considering this, it is preferable to set between 3 and 6 times. Next, both ears of the longitudinally stretched sheet are gripped by a tenter clip, and stretched while being sequentially expanded in a direction perpendicular to the flow of the sheet while being heated to a temperature suitable for stretching with hot air. In this case, the transverse draw ratio is preferably set between 7 times and 10 times in consideration of thickness variation and productivity.

  The laminated polypropylene resin film for the lid material of the container of the present invention has the same kind of polypropylene resin layer and other resin layers on the surface of the base material layer, for example, a gas barrier such as saponified ethylene-vinyl acetate copolymer, polyvinyl alcohol, etc. Further, the conductive resin layer may be further laminated, and the lamination in the same manner between the base material layer and the intermediate layer and between the intermediate layer and the heat-sealing layer is not particularly limited as long as the characteristics are not impaired.

  The laminated polypropylene resin film for the lid material of the container of the present invention can be subjected to a surface treatment as long as it does not impair the characteristics of the present invention. Examples of the surface treatment method include corona discharge treatment, plasma treatment, flame treatment, and acid treatment, and are not particularly limited. It is preferable to perform corona discharge treatment, plasma treatment, and flame treatment that can be carried out continuously and can be easily carried out before the winding process of the film production process. Is particularly preferably a corona discharge treatment. In addition, special processing such as punching can be performed on the film as long as the characteristics of the present invention are not impaired depending on the application. It can be used for freshness-maintaining packaging of fruits and vegetables by punching 1 to 5000 μm.

  Hereinafter, specific examples of the present invention will be further described with reference to examples. However, the present invention is not limited to the following examples without departing from the gist thereof. In addition, the characteristic in this specification evaluated by the following method.

(Particle size)
Using a FRA particle size distribution analyzer (Microtrac FRA manufactured by Reeds & Northtrop & SA-CP3 manufactured by Shimadzu Corporation), a sample in which particles used in Examples and Comparative Examples were dispersed with ultrasonic waves for 30 seconds was measured.

(Heat seal strength)
A laminated polypropylene resin film for a lid material and a pudding cup (Product No. 71-11064, manufactured by Shinni Co., Ltd.) of a container obtained in the following experiment is an autocup sealer (Type NC-24 MFG. 1.2 Kw), heat sealing was performed under conditions of a sealing temperature of 180 ° C., an actual pressure of 696 kPa (7.1 kg / cm ² ), a cylinder pressure of 196 kPa (2 kg / cm ² ), and a heat sealing time of 1 second. FIG. 1 and FIG. 2 are schematic views of the shape of the pudding cup and a heat seal mold.
The obtained sample was cut into a shape as shown in FIG. 3 and used as a test piece. The test piece was left in an atmosphere at a temperature of 20 ° C. and a humidity of 65% RH for 24 hours, and then “Tensilon” manufactured by Toyo Seiki Co., Ltd. (UTM-IIIL), grip the lid and the container with the chuck so that the adhesion point of the container and the lid material is at the center between the chucks at a distance of 20 mm between the chucks, and a speed of 200 mm / min. The strength at the time of peeling at a chart speed of 200 mm / min was measured to obtain heat seal strength [N].

(Peelability)
The method of peeling when measuring the peel strength of the test piece was evaluated.
○: The lid film can be peeled off without tearing or breaking. △: The lid film can be peeled off slightly, but the lid film can be peeled off immediately and removed to the end. I can't.
X: The film for the lid material cannot be cut off at the adhesion point between the container and the film for the lid material.

Resins constituting each layer used in the following production examples are as follows.
Propylene homopolymer-1: “FS2011DG3” manufactured by Sumitomo Chemical Co., Ltd., MFR: 2.5 g / 10 min, melting point: 158 ° C., cold xylene solubles (CXS): 3.3% by mass
Propylene / Ethylene / Butene Random Copolymer 1: “FSX6” manufactured by Sumitomo Chemical Co., Ltd.
6E8 ", ethylene content: 2.5 mol%, butene content: 7 mol%, MFR: 3.1 g
/ 10 minutes, melting point: 133 ° C., cold xylene solubles (CXS): 1.6% by mass
Propylene / butene copolymer-1: manufactured by Sumitomo Chemical Co., Ltd .: SPX78J1 ", butene content: 25 mol%, MFR: 8.5 g / 10 min, melting point: 128 ° C., cold xylene solubles (C
XS): 14. O mass%
Propylene / Butene Copolymer-2: “XR110H” manufactured by Mitsui Chemicals, MFR: 6.0 g / 10 min, melting point: 110 ° C.

Example 1
(Method for producing heat-sealable laminated polypropylene resin film)
Using three melt extruders, propylene homopolymer-1 (density 0.90 g / cm ³ , MFR 2.5 g / 10 min, melting point 158 ° C., cold xylene soluble content 3.3 in the first extruder. Organic polymer fine particles (CS11: manufactured by Sumitomo Chemical Co., Ltd., particle diameter 1.1 μm and CS18: manufactured by Sumitomo Chemical Co., Ltd., 5: 1) Is added as a base material layer A with a second extruder, propylene / butene random copolymer-1 (density 0.89 g / cm ³ , MFR 8.5 g / 10 min, melting point 128 ° C., cold xylene possible) 90 wt%, propylene / ethylene / butene random copolymer-1 (density 0.89 g / cm ³ , MFR 3.1 g / 10 min, melting point 133 ° C., cold xylene soluble content 1. 6 wt%) to 10 wt% Inactive fine particles (Silicia 350: manufactured by Fuji Silysia Chemical Co., Ltd., particle size 1.8 μm, CUBE50KAS: manufactured by Maruo Calcium Co., Ltd., particle size 5.5 μm, CUBE80KAS: manufactured by Maruo Calcium Co., Ltd., particles 1800 ppm of 8.5 μm diameter blended 15 to 3 to 2) was added to form a heat-sealing layer C. In a third extruder, propylene / ethylene / butene random copolymer-1 (density 0.89 g / cm ³ , MFR 3.1 g / 10 min, melting point 133 ° C., cold xylene soluble content 1.6 wt%) 45 wt%, propylene homopolymer-1 (density 0.90 g / cm ³ , MFR 2.5 g / 10) A mixed resin having a melting point of 158 ° C. and a cold xylene soluble content of 3.3% by weight) of 55% by weight as a layer B positioned between the base material layer and the heat-sealing layer. Like / C After melt coextrusion by T-die method, it is cooled and solidified with a chill roll at 20 ° C., stretched 4.5 times in the vertical direction and 8 times in the horizontal direction, and the thickness of the A / B / C structure is 11 μm and 28 μm, respectively. A laminated film having a thickness of 2 μm was obtained. The surface of the base layer A of the obtained heat-sealable film is subjected to corona discharge treatment, and the wetting tension of the surface of the base layer A after the corona discharge treatment is 39 mN / m. A polypropylene resin film was obtained. Table 1 shows the evaluation results. The obtained laminated polypropylene resin film for a lid material of a container had sufficient heat seal strength and peelability, and was excellent as a lid material for a container.

(Example 2)
In Example 1, 0.64% by weight of polyoxyethylene (2) stearylamine monostearate, 0.16% by weight of N, N bis (2hydroxyethyl) stearylamine, and stearic acid mono 0.15% by weight of glycerin ester was added, and 0.32% by weight of polyoxyethylene (2) stearylamine monostearate ester and 0.08% by weight of N, Nbis (2hydroxyethyl) stearylamine were added to the intermediate layer B. Then, 0.02% by weight of stearic acid monoglycerin ester is added, and the surface of the heat-sealing layer C is subjected to a corona discharge treatment so that the wetting tension of the surface of the heat-sealing C after the corona discharge treatment is 39 mN / m. A laminated polypropylene resin film for a container lid material was obtained in the same manner as in Example 1 except that. The obtained laminated polypropylene resin film for a lid material of a container had sufficient heat seal strength and peelability as in Example 1, and was excellent as a lid material for a container.

(Example 3)
The resin of the intermediate layer B in Example 2 was the same as Example 2 except that 40% by weight of propylene / ethylene / butene random copolymer-1 and 60% by weight of propylene homopolymer-1 were used. Thus, a laminated polypropylene resin film for the lid material of the container was obtained. The obtained laminated polypropylene resin film for a lid material of a container had sufficient heat seal strength and peelability, and was excellent as a lid material for a container.

(Comparative Example 1)
In Example 1, the thickness of the base layer A is 33 μm, the thickness of the intermediate layer B is 4 μm, and the resin of the intermediate layer B is 100% by weight of propylene / ethylene / butene random copolymer-1 and heat-sealed. As the resin of the layer, propylene / butene random copolymer-1 50% by weight, propylene / butene random copolymer-2 (density 0.89 g / cm ³ , MFR 6.0 g / 10 minutes, melting point 110 ° C.) 50% by weight A laminated polypropylene resin film for a lid material of a container was obtained in the same manner as in Example 1 except that the mixed resin was used. The obtained laminated polypropylene resin film for the lid material of the container could not be peeled cleanly and was insufficient as a lid material for the container.

(Comparative Example 2)
A laminated polypropylene system for a lid material of a container in the same manner as in Example 2 except that the intermediate layer B is eliminated, the thickness of the base material layer A is 37 μm, and the thickness of the heat sealing layer C is 3 μm. A resin film was obtained. The obtained laminated polypropylene resin film for the lid material of the container could not be peeled cleanly and was insufficient as a lid material for the container.

(Comparative Example 3)
A biaxially stretched polypropylene film (trade name Pyrene P2161 (manufactured by Toyobo Co., Ltd.)) having a thickness of 20 μm was prepared as a base film, and an unstretched polypropylene film (trade name Pyrene P1128 20 μm (Toyobo Co., Ltd.) was used as a heat sealable film. ))) And prepared by a dry lamination method through a polyester adhesive (trade name TM590 / CAT56 (manufactured by Toyo Morton Co., Ltd., coating amount: 3.0 g (dry) / m ² )). Thereafter, an aging treatment was performed at 40 ° C. for 72 hours to obtain a laminated polypropylene resin film for the lid material of the container.The laminated polypropylene resin film for the lid material of the obtained container had an adhesive point with the container at the time of opening. It was cut and could not be opened, and was insufficient as a container lid.

  The laminated polypropylene resin film for a lid material of a container according to the present invention has a sufficient heat seal strength as a lid material for a container and is excellent in unsealing property and can be suitably used as a lid material for a container.

It is a schematic diagram of a polypropylene container. It is a schematic diagram of a cup seal seal mold. It is a schematic diagram of the state of a cup seal and a tensile test piece.

Claims (2)

  Stretching comprising a base material layer composed of a crystalline polypropylene resin, an intermediate layer composed of a crystalline polypropylene resin and a propylene α-olefin copolymer, and a laminate of three or more layers having a heat fusion layer having a melting point of 150 ° C. or lower. A laminated polypropylene resin for a lid material of a container, which is a polypropylene resin film, wherein a propylene α-olefin copolymer is blended in an intermediate layer by 30% by weight or more, and the thickness of the intermediate layer is 7 μm or more. Film.   2. The laminated polypropylene resin film for a lid material according to claim 1, wherein the film is biaxially stretched.

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