JP5224108B2 - Packaging material - Google Patents

Description

 The present invention relates to a packaging material made of a polypropylene film. More specifically, the present invention relates to a packaging material made of a polypropylene film that has excellent packaging suitability for rice balls, sandwiches, etc., has excellent transparency and appearance, and generates very little odor from the film. In particular, the present invention relates to a packaging material having an excellent tearing property that a tearing direction in a resin extrusion direction (hereinafter referred to as a longitudinal direction) during film production has high linearity even in a heating environment and low tear strength. .

  Conventionally, various packaging materials using a film made of a thermoplastic resin have been proposed. These packaging materials are used for packaging food, clothing, industrial parts, etc., and are used in a wide range of packaging bags that are sealed by heat sealing to preserve the contents and protect them from dust, dust, etc. It has been.

  When using a packaged product, it is necessary to open the packaging bag before use. In this case, it is possible to tear without applying a large force. If the tearing direction is linear, the packaging bag can be torn without breaking the shape of the contents, and can be easily opened.

  In order to facilitate opening, it is common to provide a notch for opening. Furthermore, it is necessary for the film to be torn in the same direction as the cut end, and a film having a linear tearing direction and a low tearing strength is required.

  As a conventional olefin-based film having a tear directionality, a stretched film that has been stretched in the longitudinal direction and utilizes molecular orientation in the longitudinal direction has been proposed (see Patent Document 1).

  In addition, for the purpose of improving the tear direction by non-stretching or uniaxial stretching at a low magnification, it has been proposed to form a film comprising a composition comprising a polypropylene resin and a sorbitol derivative (see Patent Document 2). .

  Furthermore, an easily tearable heat-sealing film formed by molding a resin mixture of a propylene polymer and a styrene polymer (see Patent Document 3), an easy tear property obtained by blending a polypropylene resin, polyethylene, and polybutene-1. There is a cast film (see Patent Documents 4 and 5).

  However, in the above stretched film, a stretching device is required, and roll contamination is likely to occur because it is necessary to increase the roll temperature during stretching. When high-strength stretching is performed, there are problems that unevenness in film thickness and stretching are likely to occur during production, and transparency is lowered.

  In addition, when a composition comprising a polypropylene resin and a sorbitol derivative is formed into a film, the tear directionality is improved, but an odor is generated from the formed film, and its use is restricted for food applications. In addition, the sorbitol derivative bleeds to the film surface over time after film formation, lowers transparency, and causes roll contamination during secondary processing such as slitting and printing.

  Furthermore, in the case of a film formed by molding a resin mixture of a propylene polymer and a styrene polymer, the propylene polymer and the styrene polymer are incompatible with each other, and therefore are inferior in transparency. Further, since the styrene polymer is brittle, the impact resistance is not sufficient.

 In addition, in the case of an easily tearable cast film obtained by blending polypropylene resin, polyethylene, and polybutene-1, especially when a rice ball packaged in a convenience store or the like is heated in a microwave oven and eaten, Inferior.

There are problems as described above, so far, it has excellent tearing properties with good longitudinal directionality and low tear strength, excellent tearing direction even under heating environment, and has no odor and is transparent It was difficult to obtain a film having good properties and appearance.
Japanese Patent No. 3556460 Japanese Patent Laid-Open No. 1-299831 Japanese Unexamined Patent Publication No. 64-56740 JP 2006-117906 A Japanese Patent No. 3813263

  The present invention has been made to solve the above-mentioned problems, has excellent packaging suitability, particularly excellent tear characteristics even in a heating environment, has good transparency and good appearance, and generates odor. It aims at providing the packaging material which consists of few polypropylene films.

 As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention consisted of a base layer having a specific thickness containing a specific polypropylene resin and an organic nucleating agent, and a specific propylene-α-olefin copolymer. By laminating a surface layer having a specific thickness, the polypropylene film has excellent packaging suitability, particularly excellent tear characteristics even in a heating environment, transparency, good appearance, and very little odor generation. It has been found that a packaging material comprising the above can be obtained.

 That is, this invention which solves the said subject contains the following matter as a summary.

[1] A packaging material comprising a polypropylene film, which is an unstretched film including at least two layers of a base layer and a surface layer, and satisfies the following (1) to (3).

(1) The base layer contains 99 to 99.97% by mass of a propylene homopolymer having a melting point of 162 ° C. or higher and 0.03 to 1% by mass of a phosphoric acid ester metal salt as an organic crystal nucleating agent, and has a thickness of 10 μm or more. Have

(2) The surface layer is made of a propylene-α-olefin copolymer having a melting point of 155 ° C. or less and has a thickness of 1 μm or more.

(3) The thickness of the base layer is in the range of 50% to less than 98% with respect to the total thickness of the packaging material.

[2] The packaging material according to [1], wherein the organic crystal nucleating agent is a phosphate aluminum salt.

[3] 0.1 to 4 parts by mass of an antifogging agent is added to 100 parts by mass of the resin constituting the base layer and the surface layer, and the surface of at least one of the layers is subjected to corona discharge treatment. [1] Or the packaging material as described in [2].

  According to the present invention, it is possible to obtain a packaging material made of a polypropylene-based film having excellent packaging suitability, particularly excellent tear characteristics even in a heating environment, excellent transparency and appearance, and very little odor generation. .

  Furthermore, the packaging material which consists of a polypropylene film with improved anti-fogging property can be obtained by containing an anti-fogging agent.

  Hereinafter, the present invention will be described more specifically including the best mode.

  The packaging material of the present invention is a polypropylene film excellent in tearing property in the longitudinal direction, and includes a base layer mainly composed of a propylene homopolymer and a surface layer mainly composed of a propylene-α-olefin copolymer.

 The base layer contains 99 to 99.97% by mass of a propylene homopolymer having a melting point of 162 ° C. or higher and 0.03 to 1% by mass of an organic crystal nucleating agent, has a thickness of 10 μm or more, and the surface layer has a melting point of 155 ° C. It is very important to achieve the predetermined effect that the propylene-α-olefin copolymer is used and has a thickness of 1 μm or more.

 In the packaging material of the present invention, the propylene homopolymer used for the base layer has a melting point measured by a differential scanning calorimeter of 162 ° C. or higher, preferably 163 ° C. or higher, and particularly preferably in the range of 163 to 170 ° C. When the melting point of polypropylene used for the base layer is less than 162 ° C., the tear directionality in a heating environment is inferior, and the tear strength at that time increases.

 Further, the melt mass flow rate (MFR) at 230 ° C. of the propylene homopolymer is 2 to 50 g / 10 min, preferably 4 to 40 g / 10 min in consideration of film forming properties.

 An organic crystal nucleating agent is blended in the base layer constituting the packaging material of the present invention. Inorganic crystal nucleating agents do not improve tearability and are inferior in transparency.

 As the organic crystal nucleating agent, phosphate ester metal salts, particularly phosphate ester aluminum salts, are excellent in tearability and generate very little odor, and are therefore preferably used in the present invention.

 In contrast, sorbitol derivatives such as dibenzylidene sorbitol and dimethyl benzylidene sorbitol, rosin metal chlorides, benzoic acid metal salts and the like are generally known as organic crystal nucleating agents, but sorbitol derivatives are used in microwave ovens and the like. It is not preferable because odor is likely to occur during heating. Rosin metal chloride and benzoic acid metal salt are inferior in tearability.

 In the present invention, the addition amount of the organic crystal nucleating agent is 0.03 to 1% by mass relative to 99 to 99.97% by mass of the propylene homopolymer, and preferably 99.5 to 99.9% of the propylene homopolymer. The organic crystal nucleating agent is preferably 0.1 to 0.5% by mass with respect to% by mass, and further the organic crystal nucleating agent is 0.12 to 0.4% by mass with respect to 99.6 to 99.88% by mass of the propylene homopolymer. % Range is particularly preferred. When the addition amount of the organic crystal nucleating agent is less than 0.03% by mass, the tearability and transparency are inferior. On the other hand, when the amount of the organic crystal nucleating agent exceeds 1% by mass, the effect of improving the tearing property reaches its peak, which is economically disadvantageous. For the surface layer, the presence or absence of the addition of the organic crystal nucleating agent is not particularly limited.

 In the present invention, the addition of the nucleating agent also exhibits the effect of increasing the tensile modulus of the film, in addition to the effect of improving the tearability of the packaging material made of a polypropylene film. That is, by adding the organic crystal nucleating agent, the tensile elastic modulus in the extrusion direction (longitudinal direction) during the production of the film exhibits a value exceeding 1000 MPa. Thereby, in this invention, when forming a printing layer in the packaging material which consists of a polypropylene-type film, it is excellent in pitch stability.

 The thickness of the base layer mainly composed of the propylene homopolymer as described above is 10 μm or more, preferably 12 μm or more, and particularly preferably in the range of 12 to 80 μm. When the thickness of the base layer is less than 10 μm, the tear directionality in a heating environment is inferior, and the tear strength at that time increases.

 The propylene-α olefin copolymer used for the surface layer is a copolymer of propylene and α-olefin (including ethylene). As the α-olefin, ethylene and an α-olefin having 4 to 10 carbon atoms are preferable, and specifically, ethylene, butene, pentene-1, hexene-1, octene-1, and the like are preferably used. The content rate of the propylene unit in a propylene-alpha olefin copolymer is 99.7-85 mass%, Preferably it is 99-90 mass%. The copolymer composition of the propylene-α olefin copolymer can be measured using a nuclear magnetic resonance apparatus described later.

 Among these, the propylene-α olefin copolymer is preferably a propylene-ethylene copolymer or a propylene-ethylene-butene copolymer, and more preferably a propylene-α olefin copolymer having a narrow composition distribution. As a particularly preferred propylene-α olefin copolymer, the ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) measured by gel permeation chromatography produced by a metallocene catalyst is used. A propylene-α olefin copolymer of 4.5 or less can be exemplified. These propylene-α olefin copolymers may be used alone or in combination of two or more.

 For the propylene-α-olefin copolymer, the melting point measured by a differential scanning calorimeter is preferably 155 ° C. or less, more preferably 150 ° C. or less. When the melting point exceeds 155 ° C., the heat sealability at the time of packaging is inferior, and when it is less than 100 ° C., the tearability after heating with a microwave oven or the like is inferior. Therefore, the melting point of the propylene-α olefin copolymer is preferably in the range of 100 to 150 ° C, more preferably in the range of 130 to 150 ° C. The melting point of the propylene-α-olefin copolymer can be adjusted by a known method of appropriately selecting the type and proportion of the monomer to be copolymerized in the production process.

 The MFR at 230 ° C. of the propylene-α-olefin copolymer is 2 to 50 g / 10 minutes, preferably 4 to 20 g / 10 minutes considering the film forming property. More preferably, the range of 6 to 15 g / 10 min is preferable in order to stabilize the thickness during film formation.

 The thickness of the surface layer composed mainly of the propylene-α-olefin copolymer as described above is 1 μm or more, particularly preferably in the range of 2 μm or more and 2 to 10 μm. When the thickness of the surface layer is less than 1 μm, the heat sealability is inferior. Moreover, when it exceeds 10 micrometers, it is inferior to tearability.

 The surface layer may be laminated directly or via an adhesive layer on at least one surface of the base layer, and other resin layers are interposed between the base layer and the surface layer as long as they do not greatly affect tearability. Also good.

 Moreover, you may provide an adhesive layer in the base layer surface opposite to a surface layer in the packaging material of this invention for the purpose of improving a heat seal property further. The adhesive layer can be formed, for example, by laminating 1 μm or more of a propylene-α-olefin copolymer having a melting point of 100 ° C. or higher, preferably 130 ° C. or higher. When the adhesive layer is provided, the thickness is 1 μm or more, and the range of 1 to 10 μm is particularly preferable. If the thickness of the adhesive layer is less than 1 μm, a sufficient effect of improving adhesiveness may not be obtained, and if it exceeds 10 μm, the tearability is inferior. Although it does not restrict | limit in particular about the propylene-alpha olefin copolymer which comprises an contact bonding layer, The propylene-alpha olefin copolymer used for the said surface layer can use it conveniently.

 The total thickness of the packaging material of the present invention including these base layer, surface layer and, if necessary, the adhesive layer is not particularly limited as long as the total thickness can ensure the thickness of the base layer and the surface layer. The thickness is 100 μm, preferably 18 to 60 μm. Further, it is essential that the thickness of the base layer is 50% or more and less than 98% of the total thickness of the packaging material. When the thickness of the base layer is less than 50% of the total thickness, the tearability is inferior, and particularly the tearability after heating is lowered. On the other hand, when the thickness of the base layer exceeds 98% of the total thickness, the heat sealability is inferior.

 Moreover, in the packaging material of this invention, an antifogging agent can be added to a base layer and / or a surface layer as needed. As the antifogging agent, generally known antifogging agents, antistatic agents and surfactants are used. For example, polyhydric alcohols such as glycerin, polyethylene glycol, pentaerythritol, sorbitol, polypropylene glycol and lauric acid, Typical examples include esters with higher fatty acids such as stearic acid and oleic acid, ethylene oxide adducts of higher aliphatic amines, higher aliphatic alkanolamides, higher alcohol phosphate esters, and mixtures thereof. The addition amount of the antifogging agent is 0.1 to 4 parts by weight with respect to 100 parts by weight of the propylene-based polymer (propylene homopolymer in the base layer and propylene-α-olefin copolymer in the surface layer), Preferably, it is 0.2 to 2 parts by weight. When the amount of the antifogging agent is less than 0.1 parts by weight, the effect of developing the antifogging property is small. On the other hand, when it exceeds 4 parts by weight, the antifogging agent may bleed on the surface and the film may be blocked. , Transparency tends to decrease.

 The method for blending the antifogging agent is not particularly limited and may be a conventionally known method. For example, when the propylene polymer is produced, a method of blending the antifogging agent at the same time, Examples include a method of preparing a master batch and blending a necessary amount at the time of film formation.

 Moreover, you may mix | blend well-known additives, such as an antiblocking agent, antioxidant, a light stabilizer, a lubricant, a coloring agent, an antibacterial agent, with the raw material resin of the packaging material of this invention as needed.

 The packaging material of the present invention can be used by laminating other films such as polypropylene, polyethylene, polystyrene, polyamide, and polyethylene terephthalate by a known method such as dry lamination or extrusion laminating as necessary. In this case, the surface to be laminated is preferably subjected to corona discharge treatment in advance.

 The packaging material of the present invention is formed by a non-stretching method. Examples of typical methods include an extrusion molding method using a T die and an inflation molding method using an annular die. In the molding method, for example, a co-extrusion method using a T-die by a feed block method or a multi-manifold method is preferably used.

  About the extrusion method using the above-mentioned T dice, specifically, the temperature can be adjusted by extruding the melt by the T dice method in each extruder of the resin composition constituting the packaging material made of polypropylene film. Examples thereof include a method of cooling and winding with a roll or a temperature-adjustable water tank, or a method of cooling and winding the melt by an air cooling method or a water cooling method.

  The resulting packaging material is a low-stretched or substantially unstretched film that is slightly stretched by the tension during winding.

 The packaging material of the present invention can be surface-treated according to the application and printed. The surface treatment method is not particularly limited, but generally, a corona discharge treatment, a flame treatment, or the like may be performed for the purpose of improving the adhesion with the printing ink. Further, the surface to be surface-treated is not particularly limited, and may be either one side or both sides.

 Since the packaging material of the present invention surface-treated in this way is excellent in printing pitch stability, a highly accurate printing film can be obtained. The surface on which the printing layer is formed is not particularly limited, and may be the base layer side or the surface layer side.

Hereinafter, the present invention will be described with reference to examples and comparative examples, but the present invention is not limited to these examples. The raw material resins for the packaging materials used in the following examples and comparative examples are shown in Table 1, and the crystal nucleating agents used are shown in Table 2.

 Measurements of resin and film properties in Examples and Comparative Examples were performed by the following methods.

(1) Copolymerization composition It measured on the following conditions using the nuclear magnetic resonance spectrometer (JNM-GSX-270 ( ^13C- nuclear resonance frequency 67.8MHz) by JEOL Co., Ltd.).

Measurement mode: ¹ H-complete decoupling Pulse width: 90 degree pulse Pulse repetition time: 3 seconds Integration number: 10000 times Solvent: Mixed solvent of orthodichlorobenzene / heavy benzene (76/24 vol%)
Sample concentration: 120 mg / 2.5 ml solvent Measurement temperature: 120 ° C.
The quantification of the copolymer composition is described in M.C. Kakugo, Y, Naito, K .; Mizunuma, T .; According to Miyatake, [Macromolecules, 15, 1150 (1982)].

(2) Melt mass flow rate (MFR)
MFR at 230 ° C. was measured according to JIS K7210.

(3) Tear directionality (Tear straightness)
A test piece having a length of 300 mm and a width of 210 mm is cut from the film. Two cuts having a length of 15 mm are placed in the center of the short piece (lateral direction) of the test piece so that the interval is 10 mm. Holding the center (between the cuts) by hand, the film is pulled in the longitudinal direction of the film at a speed of about 150 mm / sec. The width of the torn strip at a point 150 mm from the cutting position was measured and evaluated as follows. When the width is 10 mm, the tear straightness is the best. The measurement temperature was set at 23 ° C. and 120 ° C. for 10 minutes and then at room temperature for 2 minutes.
○: When the width of the torn strip is 10 to 15 mm Δ: When the width of the torn strip is more than 15 mm and less than 20 mm ×: When the width of the torn strip is less than 10 mm or exceeds 20 mm

(4) Tear strength (trouser tear method)
It measured at the temperature of 23 degreeC and 70 degreeC according to JISK7121-1.

(5) Transparency (haze)
It measured according to JISK7105.

(6) Melting point and crystallization temperature measured by differential scanning calorimeter Approximately 5 to 6 mg of sample was weighed and sealed in an aluminum pan, and 20 ml / ml was measured with a differential scanning calorimeter (DSC6200R manufactured by Seiko Denshi Kogyo Co., Ltd.). The temperature is raised to 230 ° C. in a nitrogen stream supplied in minutes, maintained at this temperature for 10 minutes, and then cooled to 20 ° C. at a temperature lowering rate of 10 ° C./min. Next, the peak temperature showing the maximum endotherm in the endothermic curve obtained when the temperature was raised to 230 ° C. at a rate of temperature rise of 10 ° C./min was taken as the melting point. The crystallization temperature was measured by melting the resin once according to JIS K7121 and then cooling to start crystallization.

(7) Tensile modulus A sample with a width of 10 mm and a length of 100 mm is cut from the film in the film flow direction during film formation, and both ends of the sample are chucks of a tensile tester (Autograph: manufactured by Shimadzu Corporation) Fixed with. In this case, the chuck gap in the length direction of the sample was adjusted to 20 mm. A tensile test was performed at a tensile speed of 20 mm / min to prepare a tensile stress-strain curve.
The tensile elastic modulus was calculated by the following formula using the first linear portion of the tensile stress-strain curve.
Em = Δδ / Δε
Em: Tensile modulus
Δδ: Stress difference between two points on the straight line due to the original average cross-sectional area of the sample
Δε: Difference in strain between the same two points

(8) Dimensional change rate A sample having a width of 100 mm and a length of 100 mm was cut out from the film in the direction of film flow during film formation, and a 10N weight was attached and placed in an oven heated to an atmosphere of 100 ° C. for 10 minutes. The dimensional change rate after being allowed to stand in an atmosphere at 2 ° C. for 2 minutes was measured.

(9) Odor Ten test pieces (300 mm × 210 mm) of the formed film were sealed in a glass bottle with a capacity of 300 ml and left in a constant temperature bath at 120 ° C. for 1 hour, then left at room temperature for 30 minutes, A sensory test was conducted with 10 persons on the odor to determine the presence or absence of the odor.
○: When all 10 people judge that there is no odor △: When 1 to 4 people judge that there is odor ×: When 5-10 people judge that there is odor

(10) Evaluation of anti-fogging property A film is cut out to 100 mm × 100 mm, 50 ml of tap water is put into a 100 ml beaker, covered with a beaker so that the anti-fogging surface becomes the inner surface, and left in a refrigerator at 5 ° C., and after 30 minutes. The state of adhesion of water droplets on the inner surface of the film after 24 hours was visually observed and evaluated as follows.
○: No cloudiness △: Slightly cloudy ×: Cloudy (the contents cannot be seen)

(11) Heat seal property The corona-treated surface of the film and the non-corona-treated surface are overlapped, and the maximum strength when heat-sealed under the following conditions is 15 mm in width with a tensile tester (Autograph: manufactured by Shimadzu Corporation), A 180 ° peel tensile test was conducted at a tensile speed of 300 mm / min, and the following two stages were evaluated.

Heat seal conditions: Upper seal: temperature 160 ° C. (lower seal temperature: room temperature), pressure 0.1 MPa, time 1 second ○: Adhesive strength 3.0 N / 15 mm or more ×: Adhesive strength 3.0 N / 15 mm or less

Example 1
As a raw material resin for film, 99.8% by mass of resin A (propylene homopolymer having a melting point of 165 ° C. (FLX80G7 manufactured by Sumitomo Chemical Co., Ltd.)) shown in Table 1 was blended with 0.2% by mass of nucleating agent I shown in Table 2 to obtain 65 mmφ. Extrusion pelletization was performed at 250 ° C. with an extruder, and the obtained resin was used for a base layer. Resin E shown in Table 1 (propylene-ethylene random copolymer having an ethylene content of 3.4% by mass and a melting point of 146 ° C. (FW3GT manufactured by Nippon Polypro)) was used as the first surface layer resin. Next, the resin for the first surface layer is supplied to the extruder A (50 mmφ extruder), the resin for the base layer is supplied to the extruder B (75 mmφ extruder), heated and melted at 250 ° C., and the die lip 1 by the coextrusion method using the feed block method. Extruded from a 2 mm T-die and cooled and solidified on a 40 ° C. cooling roll, adjusted so that the first surface layer is 5 μm and the base layer is 20 μm, and a total 25 μm film is formed. The surface tension on the base layer side surface is 40 mN / m After being subjected to corona discharge treatment, the film was wound with a winder to obtain an unstretched film. The obtained film was excellent in tear directionality, low tear strength, and good heat sealability.

Examples 2-3
Adjust the first surface layer to 2 μm and the base layer to 23 μm and adjust the total to 25 μm (Example 2), adjust the first surface layer to 10 μm and the base layer to 15 μm, and change to a total of 25 μm (Example 3). Except for the above, a film was produced in the same manner as in Example 1 to obtain an unstretched film. The obtained film was excellent in tear directionality, low tear strength, and good heat sealability.

Example 4
The resin for the first surface layer of Example 1 is resin F shown in Table 1 (propylene-ethylene-butene copolymer having an ethylene content of 3.2% by mass, a butene content of 1.5% by mass, and a melting point of 137 ° C.) Except that it was (Nippon Polypro Co., Ltd. FW4BT)), an unstretched film was obtained in the same manner as in Example 1. The obtained film was excellent in tear directionality, low tear strength, and good heat sealability.

Example 5
The resin for the first surface layer of Example 1 is the resin G shown in Table 1 (propylene-ethylene random copolymer having an ethylene content of 4.2 mass% and a melting point of 135 ° C. (WFW4 metallocene catalyst system manufactured by Nippon Polypro)). Except that, an unstretched film was obtained in the same manner as in Example 1. The obtained film was excellent in tear directionality, low tear strength, and good heat sealability.

Example 6
The base layer resin of Example 1 was added to 99.8% by mass of resin B (propylene homopolymer having a melting point of 164 ° C. (PC600A manufactured by Sun Allomer Co., Ltd.)) shown in Table 1, and 0.2% by mass of nucleating agent I shown in Table 2. % Unblended film was obtained in exactly the same manner as in Example 1 except that it was made into a pellet by extrusion at 250 ° C. using a 65 mmφ extruder. The obtained film was excellent in tear directionality, low tear strength, and good heat sealability.

Example 7
A non-stretched film was obtained in the same manner as in Example 1 except that the thickness of the base layer of Example 1 was 30 μm, the first surface layer thickness was 10 μm, and the total thickness was 40 μm. The obtained film was excellent in tear directionality, low tear strength, and good heat sealability.

Example 8
The resin A 99.8% by mass shown in Table 1 was blended with 0.2% by mass of the nucleating agent I shown in Table 2 and extruded into pellets at 250 ° C. with a 65 mmφ extruder, and the resulting resin was used for the base layer. Resin E shown in Table 1 was used as the resin for the first surface layer and the second surface layer. The first surface layer resin is supplied to Extruder A (50 mmφ extruder), the base layer resin is supplied to Extruder B (75 mmφ extruder), and the surface layer 2 resin is supplied to Extruder C (50 mmφ extruder) and heated at 250 ° C. It is melted and extruded from a T die with a die lip of 1.2 mm by a coextrusion method using a feed block method. The film was adjusted to a total film thickness of 25 μm, and the second surface layer side surface was subjected to corona discharge treatment so that the surface tension was 42 mN / m, and then wound up with a winder to obtain an unstretched film. The obtained film had a structure in which the first surface layer / base layer / second surface layer were laminated in this order, had excellent tear directionality, low tear strength, and good heat sealability.

Example 9
A non-stretched film was obtained in the same manner as in Example 8 except that the resin G shown in Table 1 was used as the resin for the first surface layer and the second surface layer of Example 8. The obtained film was excellent in tear directionality, low tear strength, and good heat sealability.

Example 10
As a resin for the first surface layer of Example 1, 0.2% by mass of the nucleating agent I shown in Table 2 was blended with 99.8% by mass of the resin E shown in Table 1, and the pellet was extruded at 250 ° C. with a 65 mmφ extruder. A non-stretched film was obtained in the same manner as in Example 1 except that it was used. The obtained film was excellent in tear directionality, low tear strength, and good heat sealability.

Example 11
97% by mass of resin A shown in Table 1 and 3% by mass of resin H (antifogging agent master batch based on a propylene homopolymer as a base resin (Elest Master 320 manufactured by Kao Corporation)) were blended. 0.2% by mass of the nucleating agent I shown in Table 2 was blended with 99.8% by mass of the blended product, and the mixture was extruded and pelletized at 250 ° C. with a 65 mmφ extruder, and the obtained resin was used for the base layer. First surface layer obtained by blending 95% by mass of resin E shown in Table 1 and 5% by mass of resin I (antifogging agent masterbatch based on propylene-ethylene random copolymer (Riken Vitamin PAR-380 manufactured by Riken Vitamin Co., Ltd.)) Except for the above, an unstretched film was obtained in the same manner as in Example 1. The obtained film was excellent in tear directionality, low tear strength, good heat sealability, and good antifogging properties.

Comparative Example 1
Except that the nucleating agent was not added to the base layer of Example 1, a film was formed in the same manner as in Example 1 to obtain an unstretched film. The obtained film was inferior in tear directionality and high in tear strength.

Comparative Example 2
An unstretched film was obtained in the same manner as in Example 1 except that the amount of the nucleating agent I added to the base layer of Example 1 was 0.025% by mass. The obtained film was inferior in tear directionality and high in tear strength.

Comparative Example 3
An unstretched film was obtained in the same manner as in Example 1 except that the first surface layer was adjusted to 20 μm and the base layer was adjusted to 5 μm, and the total was changed to 25 μm. The obtained film was inferior in tear directionality and high in tear strength.

Comparative Example 4
An unstretched film was obtained in the same manner as in Example 1 except that the first surface layer was adjusted to 0.5 μm and the base layer was adjusted to 24.5 μm, and the total was changed to 25 μm. The obtained film had excellent tear directionality and low tear strength, but was inferior in heat sealability.

Comparative Example 5
Resin C shown in Table 1 (propylene homopolymer having a melting point of 161 ° C. (FLX80G1 manufactured by Sumitomo Chemical Co., Ltd.)) 99.8% by mass was blended with 0.2% by mass of the nucleating agent I shown in Table 2 and 250 times in a 65 mmφ extruder. Extruded and pelletized at 0 ° C., and a non-stretched film was obtained in the same manner as in Example 1 except that the obtained resin was used for the base layer. The obtained film was inferior in tear directionality.

Comparative Example 6
Resin D (propylene homopolymer having a melting point of 157 ° C. (FB3EBT manufactured by Nippon Polypro Co., Ltd.)) shown in Table 1 was blended with 99.8% by mass of 0.2% by mass of the nucleating agent I shown in Table 2, and 250 times in a 65 mmφ extruder. Extruded and pelletized at 0 ° C., and a non-stretched film was obtained in the same manner as in Example 1 except that the obtained resin was used for the base layer. The obtained film was inferior in tear directionality.

Comparative Example 7
A non-stretched film was obtained in the same manner as in Example 1 except that the nucleating agent added to the base layer of Example 1 was changed to nucleating agent II (sorbitol derivative) shown in Table 2. The resulting film had an odor. Also, the tear directionality was slightly inferior.

Comparative Example 8
A non-stretched film was obtained in the same manner as in Example 1 except that 95% by mass of the resin A shown in Table 1 and 5% by mass of the nucleating agent III shown in Table 2 were blended as the base layer resin. The obtained film was inferior in tear directionality and high in tear strength.

Table 3 summarizes the layer structure of the packaging materials obtained in the above Examples and Comparative Examples. The results of these examples and comparative examples are summarized in Table 4.

Claims (3)

A packaging material comprising a polypropylene film, which is an unstretched film including at least two layers of a base layer and a surface layer, and satisfies the following (1) to (3).
(1) The base layer contains 99 to 99.97% by mass of a propylene homopolymer having a melting point of 162 ° C. or higher and 0.03 to 1% by mass of a phosphoric acid ester metal salt as an organic crystal nucleating agent, and has a thickness of 10 μm or more. Have
(2) The surface layer is made of a propylene-α-olefin copolymer having a melting point of 155 ° C. or less and has a thickness of 1 μm or more.
(3) The thickness of the base layer is in the range of 50% to less than 98% with respect to the total thickness of the packaging material.  The packaging material according to claim 1, wherein the organic crystal nucleating agent is a phosphate aluminum salt.  The antifogging agent is added in an amount of 0.1 to 4 parts by mass with respect to 100 parts by mass of the resin constituting the base layer and the surface layer, and corona discharge treatment is performed on the surface of at least one of the layers. The packaging material described.