JP2007253349A - Biaxially oriented polypropylene film and packaging bag - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially oriented polypropylene film which stably develops excellent anticlouding properties and especially excellent fusion cutting seal strength under high speed. <P>SOLUTION: The biaxially oriented polypropylene film has a layer (A) containing a propylene homopolymer having an NMR pentad fraction of 93-98% and a layer (B) containing a propylene random copolymer and a polyethylene resin. The film can be processed into a bag with its excellent anticlouding properties and stable strong fusion cutting seal strength even under high speed kept and is effective as a packaging bag for foods such as vegetables. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a biaxially stretched polypropylene film excellent in antifogging properties as well as fusing sealability and a packaging bag obtained from the film.

Biaxially stretched polypropylene film is excellent in transparency, gloss and rigidity, and is widely used as a packaging material, and a packaging bag is produced using a sealing method such as fusing sealing.

A number of biaxially stretched polypropylene films having such fusing and sealing properties have been proposed. For example, a polypropylene film for packaging has been proposed that can be melt-sealed with high productivity and that satisfies both anti-fogging performance and fusing seal strength. (For example, refer patent document 1.) Moreover, the biaxially stretched polypropylene film for general packaging which is excellent in bag-breaking resistance is proposed when fusing and sealing without impairing the characteristics of excellent transparency, surface gloss and rigidity. Yes. (For example, refer to Patent Document 2.)

JP 2003-11297 A Japanese Patent Laid-Open No. 9-169050

In recent years, there has been a demand to increase the process speed of the fusing seal for the purpose of improving productivity. However, with conventional biaxially stretched polypropylene films, the fusing seal strength becomes unstable by increasing the process speed, and a value that falls below the standard is becoming a problem in products. .

An object of the present invention is to find a biaxially stretched polypropylene film having improved fusing seal stability under high speed and a packaging bag obtained from the film without impairing excellent transparency, rigidity and antifogging properties. is there.

The present invention relates to a biaxially stretched polypropylene having two layers of (A) layer containing a propylene homopolymer having an NMR pentad fraction of 93 to 98% and (B) layer containing a propylene random copolymer and a polyethylene resin. It is a system film.

Moreover, this invention is a biaxially stretched polypropylene film in which the (A) layer and the (B) layer are adjacent to each other.

The present invention also relates to a biaxially stretched polypropylene system in which a propylene random copolymer and a polyethylene resin are contained in a proportion of 80 to 99% by weight of a propylene random copolymer and 1 to 20% by weight of a polyethylene resin. It is a film.

The present invention is also characterized in that the polyethylene resin is a biaxially stretched polypropylene film in which the linear low density polyethylene is used.

The present invention also provides a biaxially oriented polypropylene system in which the propylene random copolymer is a propylene-ethylene random copolymer, a propylene-butene random copolymer, a propylene-ethylene-butene random copolymer, or a mixture thereof. It is a film.

Further, the present invention is characterized in that the (A) layer containing a propylene homopolymer having an NMR pentad fraction of 93 to 98% is a biaxially stretched polypropylene film containing an amorphous polyolefin and an antifogging agent. To do.

Moreover, the present invention is a packaging bag obtained by fusing and sealing the biaxially oriented polypropylene film.

The present invention, which is configured as described above, has the following effects.

A biaxially oriented polypropylene film having excellent antifogging properties and stable fusing and sealing properties can be obtained.

With this film, the sealing strength does not fall below the standard even in high-speed fusing sealing.

The propylene homopolymer of the present invention has an NMR pentad fraction of 93 to 98%, preferably 94 to 97%. If the NMR pentad fraction is less than 93%, the rigidity of the film is lowered, and a film with weak fusing seal strength is obtained. If the NMR pentad fraction exceeds 98%, molding becomes difficult.

The NMR pentad fraction referred to here means A. It is the fraction in which five propylene units quantified based on the peak assignment of the ¹³ C-nuclear magnetic resonance spectrum published in Macromolecules, ¹³ , 267 (1980) by Zambelli et al.

The density of the propylene homopolymer is preferably 0.89 to 0.92 g / cm ³ , and the MFR (temperature 230 ° C., load 21.2 N) is 1.0 to 5.0 g / 10 minutes, preferably 2 0.0 to 4.0 g / 10 min.

In the present invention, the layer (A) comprises the above propylene homopolymer as a main component, but in order to further improve the transparency of the film, a propylene homopolymer having an NMR pentad fraction of 98.5 to 99.7% is molded. A small amount can be added as long as it does not affect the properties. The proportion of the addition is 100 to 90% by weight of propylene homopolymer having an NMR pentad fraction of 93 to 98%, and 0 to 10% by weight of propylene homopolymer having an NMR pentad fraction of 98.5 to 99.7%. Preferably there is. If the amount of the propylene homopolymer having an NMR pentad fraction of 98.5 to 99.7% exceeds 10% by weight, the moldability is affected, which is not preferable.

The density of the propylene homopolymer having an NMR pentad fraction of 98.5 to 99.7% is preferably 0.89 to 0.92 g / cm ³ , and the MFR (temperature 230 ° C., load 21.2 N) is 1.0. It is -5.0g / 10min, Preferably it is 2.0-4.0g / 10min.

In the present invention, the layer (A) preferably contains an amorphous polyolefin and an antifogging agent. Here, the antifogging agent has a function of imparting antifogging performance to the film, and the amorphous polyolefin is more likely to obtain an excellent antifogging effect when used in combination with the antifogging agent.

Here, the amorphous polyolefin specifically includes ethylene or propylene as a main component, and an α-olefin having 3 to 8 carbon atoms (4 to 8 carbon atoms when propylene is a main component) as a metallocene. An amorphous random or block copolymer obtained by polymerization under a catalyst. Among these combinations, an amorphous propylene-butene random copolymer obtained by copolymerizing butene-1 having 4 carbon atoms with propylene as a main component is preferable. In this case, the content of butene-1 is preferably 3 to 7% by weight. Specifically, Sumitomo Chemical Co., Ltd. Tough Selenium T3732 can be illustrated.

Moreover, generally known as an antifogging agent, for example, alkyldiethanolamine, alkyldiethanolamine fatty acid ester, or glycerin fatty acid ester can be mentioned.

The alkyl group in the first alkyldiethanolamine has 8 to 22 carbon atoms, preferably 12 to 18 carbon atoms. Specific examples include lauryl diethanolamine, myristyl diethanolamine, palmityl diethanolamine, stearyl diethanolamine, and oleyl diethanolamine.

The fatty acid ester group in the second alkyldiethanolamine fatty acid ester is a saturated or unsaturated fatty acid ester having 8 to 22 carbon atoms, preferably 12 to 22 carbon atoms, and preferably an unsaturated fatty acid ester. Specific examples include lauryl diethanolamine monostearate, myristyl diethanolamine monooleate, lauryl diethanolamine monostearate, palmityl diethanolamine monostearate, stearyl diethanolamine monostearate or oleyl diethanolamine monostearate.

The fatty acid ester group in the third glycerin fatty acid ester is the same as the above-mentioned fatty acid ester group, and one obtained by reacting one or two of the three hydroxyl groups in the glycerin molecule with the fatty acid ester is more preferred. It is the fatty acid ester monoglyceride which one reacted. Specific examples include lauryl monoglyceride, myristyl monoglyceride, palmityl monoglyceride, stearyl monoglyceride, and oleyl monoglyceride.

Such an antifogging agent is used in the form of the above-mentioned one kind or a mixture of two to three kinds, or in the form of a mixture of two or three kinds of different ones. It is preferable to use it in a mixture, that is, a mixture of three kinds of fatty acid ester monoglyceride, alkyldiethanolamine and alkyldiethanolamine fatty acid ester, and the alkyldiethanolamine fatty acid ester as a main component. The ratio of the three types of antifogging agents is fatty acid ester monoglyceride / alkyldiethanolamine / alkyldiethanolamine fatty acid ester = 5 to 15% by weight / 5 to 10% by weight / 75 to 90% by weight (the total of the three types is 100% by weight) Preferably there is.

The proportion of the amorphous polyolefin and the anti-fogging agent is as follows: propylene homopolymer (NMR pentad fraction 93-98% propylene homopolymer simple substance or NMR pentad fraction 93-98% propylene homopolymer simple substance and NMR (Mixture with propylene homopolymer having a pentad fraction of 98.5 to 99.7%) to 100 parts by weight of amorphous polyolefin, 0.5 to 15 parts by weight, preferably 1 to 5 parts by weight. It is 0.2-2 weight part of clouding agents, Preferably it is 0.5-1.5 weight part. (An antifogging agent in this case is a mixture of fatty acid ester monoglyceride, alkyldiethanolamine and alkyldiethanolamine fatty acid ester in the above proportions.)

If the proportion of the amorphous polyolefin is less than 0.5 parts by weight, sufficient antifogging effect cannot be obtained, and if it exceeds 5 parts by weight, the bleedout to the surface of the antifogging agent is too early and more than necessary. Bleed out easily occurs, which is not preferable. Further, if the ratio of the antifogging agent is less than 0.2 parts by weight, a sufficient antifogging effect cannot be obtained, and if it exceeds 2 parts by weight, bleeding to the surface more than necessary occurs, leading to deterioration of transparency. Absent.

In the present invention, the layer (B) can contain a propylene-based random copolymer as a main component and a polyethylene-based resin. The mixing ratio of the propylene random copolymer and the polyethylene resin is preferably 80 to 99% by weight of the propylene random copolymer and 1 to 20% by weight of the polyethylene resin. If the polyethylene resin is less than 1% by weight, a stable fusing seal strength cannot be obtained, and if it exceeds 20% by weight, the transparency is undesirably lowered.

The polyethylene resin used in the (B) layer of the present invention is preferably a linear low density polyethylene. The linear low-density polyethylene is a copolymer of ethylene and an α-olefin having 4 to 8 carbon atoms, and a copolymer of ethylene and octene-1 having 8 carbon atoms is preferable. The density is preferably 0.87 to 0.91 g / cm ³ and the MFR (temperature 190 ° C., load 21.2 N) is 2.0 to 5.0 g / 10 minutes, preferably 2.5 to 3.5 g / 10 minutes.

The propylene random copolymer used in the layer (B) of the present invention is a propylene-ethylene random copolymer, a propylene-butene random copolymer, a propylene-ethylene-butene random copolymer, or these A mixture is preferred.

Here, the propylene-ethylene random copolymer preferably has an ethylene content of 1 to 6% by weight and a density of 0.89 to 0.92 g / cm ³ . The MFR (temperature 230 ° C., load 21.2 N) is 6.0 to 8.0 g / 10 minutes, preferably 6.5 to 7.5 g / 10 minutes, and the melting point is 130 to 150 ° C., preferably 135. It should be ~ 145 ° C. When the ethylene content is less than 1% by weight, the fusing and sealing properties tend to deteriorate, and when it exceeds 6% by weight, the transparency is deteriorated. Also, the density, MFR and melting point are in a range suitable for forming a stable film with excellent appearance by mixing with the linear low density polyethylene of the present invention, and in order to obtain a stable fusing seal strength Is also a preferred range.

The propylene-butene random copolymer preferably has a butene content of 4 to 8% by weight and a density of 0.89 to 0.92 g / cm ³ . The MFR (temperature 230 ° C., load 21.2 N) is 1.0 to 10.0 g / 10 minutes, preferably 3.0 to 6.0 g / 10 minutes, and the melting point is 120 to 150 ° C., preferably 130. It should be ~ 140 ° C. When the butene content is less than 4% by weight, the fusing and sealing properties tend to be poor, and when it exceeds 8% by weight, the transparency is deteriorated. Also, the density, MFR and melting point are in a range suitable for forming a stable film with excellent appearance by mixing with the linear low density polyethylene of the present invention, and in order to obtain a stable fusing seal strength Is also a preferred range.

The propylene-ethylene-butene random copolymer has an ethylene content of 2 to 5% by weight and a butene content of 4 to 8% by weight (the total content of propylene, ethylene and butene is 100% by weight), and the density is The thing of 0.89-0.92g / cm < ³ > is preferable. The MFR (temperature 230 ° C., load 21.2 N) is 4.0 to 8.0 g / 10 minutes, preferably 5.0 to 7.0 g / 10 minutes, and the melting point is 120 to 140 ° C., preferably It is good that it is 125-135 degreeC. If the ethylene content is less than 2% by weight, the fusing sealability tends to deteriorate, and if it exceeds 5% by weight, molding becomes difficult. Further, if the butene content is less than 4% by weight, the fusing sealability becomes unstable, and if it exceeds 8% by weight, molding becomes difficult, which is not preferable. Also, the density, MFR and melting point are in a range suitable for forming a stable film with excellent appearance by mixing with the linear low density polyethylene of the present invention, and in order to obtain a stable fusing seal strength Is also a preferred range.

Moreover, as these mixtures, propylene-ethylene random copolymer and propylene-butene random copolymer, propylene-ethylene random copolymer, propylene-ethylene-butene random copolymer, propylene-butene random copolymer, Examples thereof include a propylene-ethylene-butene random copolymer, or a combination of a propylene-ethylene random copolymer, a propylene-butene random copolymer, and a propylene-ethylene-butene random copolymer. The mixing ratio here may be appropriately set in consideration of the transparency, rigidity or fusing seal strength of the film, and is not particularly limited.

In the present invention, the (A) layer and the (B) layer are preferably adjacent to each other, but are not necessarily limited to two layers. For example, (B) layer / (A) layer / (B) layer (B ′) layer / (A) layer / (B ) Layer, or a (C) layer / (A) layer / (B) layer including a (C) layer having a different resin structure.

Here, the (C) layer having a different resin structure is preferably composed of a propylene random copolymer, and the propylene random copolymer includes a propylene-ethylene random copolymer, a propylene-butene random copolymer, A propylene-ethylene-butene random copolymer or a mixture thereof is preferable.

Here, the propylene-ethylene random copolymer preferably has an ethylene content of 1 to 6% by weight and a density of 0.89 to 0.92 g / cm ³ . The MFR (temperature 230 ° C., load 21.2 N) is 6.0 to 8.0 g / 10 minutes, preferably 6.5 to 7.5 g / 10 minutes, and the melting point is 130 to 150 ° C., preferably 135. It should be ~ 145 ° C. When the ethylene content is less than 1% by weight, proper bleed-out of the antifogging agent does not occur and the antifogging property tends to deteriorate, and when it exceeds 6% by weight, the transparency deteriorates, which is not preferable. Further, the density, MFR, and melting point are in a range suitable for forming a film having a three-layer structure of the (A) layer and the (B) layer of the present invention.

The propylene-butene random copolymer preferably has a butene content of 4 to 8% by weight and a density of 0.89 to 0.92 g / cm ³ . The MFR (temperature 230 ° C., load 21.2 N) is 1.0 to 10.0 g / 10 minutes, preferably 3.0 to 6.0 g / 10 minutes, and the melting point is 120 to 150 ° C., preferably 130. It should be ~ 140 ° C. If the butene content is less than 4% by weight, suitable bleed-out of the antifogging agent does not occur and the antifogging property tends to deteriorate, and if it exceeds 8% by weight, the transparency deteriorates, which is not preferable. Further, the density, MFR, and melting point are in a range suitable for forming a film having a three-layer structure of the (A) layer and the (B) layer of the present invention.

The propylene-ethylene-butene random copolymer has an ethylene content of 2 to 5% by weight and a butene content of 4 to 8% by weight (the total content of propylene, ethylene and butene is 100% by weight), and the density is The thing of 0.89-0.92g / cm < ³ > is preferable. The MFR (temperature 230 ° C., load 21.2 N) is 4.0 to 8.0 g / 10 minutes, preferably 5.0 to 7.0 g / 10 minutes, and the melting point is 120 to 140 ° C., preferably It is good that it is 125-135 degreeC. When the ethylene content is less than 2% by weight, proper bleed-out of the antifogging agent does not occur, and the antifogging property tends to deteriorate, and when it exceeds 5% by weight, molding becomes difficult. Further, if the butene content is less than 4% by weight, an appropriate bleed-out of the antifogging agent does not occur and the antifogging property tends to deteriorate, and if it exceeds 8% by weight, molding becomes difficult, which is not preferable. Further, the density, MFR, and melting point are in a range suitable for forming a film having a three-layer structure of the (A) layer and the (B) layer of the present invention.

Moreover, as these mixtures, propylene-ethylene random copolymer and propylene-butene random copolymer, propylene-ethylene random copolymer, propylene-ethylene-butene random copolymer, propylene-butene random copolymer, Examples thereof include a propylene-ethylene-butene random copolymer, or a combination of a propylene-ethylene random copolymer, a propylene-butene random copolymer, and a propylene-ethylene-butene random copolymer. The mixing ratio here may be set as appropriate in consideration of the transparency or rigidity of the film, and is not particularly limited.

As the propylene random copolymer constituting the (C) layer, a propylene-ethylene random copolymer is preferable because transparency is improved.

In this invention, you may add an antiblocking agent to the layer used as the outer surface of a biaxially-stretched polypropylene film in the range which does not impair transparency. Examples of the anti-blocking agent include generally used inorganic silica and kaolin, and organic crosslinked acrylic beads. Moreover, it is preferable that it is 0.05-1.0 weight part with respect to 100 weight part of resin which comprises a layer as addition amount of an antiblocking agent.

The thickness of each layer of the biaxially stretched polypropylene film in the present invention is as follows.
When the total thickness of the film is 14 to 66 μm, preferably 19 to 55 μm, in the case of a two-layer configuration of (A) layer / (B) layer, the (A) layer is 13 to 58 μm, preferably 17 to The layer (B) has a thickness of 1 to 5 μm, preferably 1.5 to 4.0 μm. In the case of a three-layer configuration such as (B ′) layer / (A) layer / (B) layer or (C) layer / (A) layer / (B) layer, the (A) layer is 13 to 58 μm, preferably 17-50 μm, (B) layer is 1-5 μm, preferably 1.5-4.0 μm, (B ′) layer or (C) layer is 1-5 μm, preferably 1. 5 to 4.0 μm. When the thickness of the layer (A) is within this range, the film is preferable because the film has appropriate rigidity, antifogging properties and fusing seal strength. Moreover, when the thickness of the layer (B) is within this range, the fusing seal strength of the film is preferably an appropriate value.

The production method of the biaxially stretched polypropylene film in the present invention is not particularly limited, and a known method can be used. However, in consideration of productivity, physical properties of the completed film, etc., a flat shape having a two-layer or three-layer structure. It is preferable to form a sheet by extrusion molding, and then sequentially biaxially stretch it into a film.

Here, a three-layer structure will be described as an example. The resin constituting the (A) layer, the resin constituting the (B) layer, and the resin constituting the (C) layer are respectively charged into three extruders set at appropriate temperatures, and the resin is placed in the extruder. After melting and kneading, it is extruded into a sheet form from a T die of 210 to 250 ° C. In this case, a feed block system or a multi-manifold system may be used to form a three-layer structure. The extruded sheet is cooled and solidified by a cooling roll at 25 ° C. and sent to the longitudinal stretching step. The longitudinal stretching is constituted by a heated roll set at 130 to 140 ° C., and is stretched in the longitudinal direction (hereinafter referred to as MD direction) due to a speed difference between the rolls. There are no particular restrictions on the number of heating rolls, but at least two heating rolls on the low speed side and the high speed side are necessary. The draw ratio of longitudinal stretching is 4 to 6 times, preferably 4.5 to 5.5 times. Next, it is sent to a transverse stretching step by a tenter and stretched in the transverse direction (hereinafter referred to as TD direction). The tenter is divided into preheating, stretching, and annealing zones. The preheating zone is set to 165 to 170 ° C, the stretching zone is set to 165 to 170 ° C, and the annealing zone is set to 165 to 170 ° C. The stretching ratio in the stretching zone is preferably about 6 to 10 times. After being stretched, it is cooled and fixed in an annealing zone, and then wound up by a winder to form a film roll.

In the present invention, it is preferable to perform corona discharge treatment after leaving the annealing zone of the tenter and before winding with a winder. In the corona discharge treatment, both the front surface and the back surface may be processed, or either the front surface or the back surface may be processed. The strength of the corona discharge treatment is preferably in the range of 1.8 × 10 ^{2 to} 9.0 × 10 ² J / m ^2. May be.

The wetting tension of the surface of the biaxially stretched polypropylene film thus obtained is preferably 38 to 44 mN / m. When the wetting tension is less than 38 mN / m, the antifogging property is not sufficiently exhibited, and in the case of printing, the adhesiveness of the printing ink is inferior. If the wetting tension exceeds 44 mN / m, the anti-fogging agent bleeds out to the surface, causing whitening and blocking, and also causing a decrease in the fusing seal strength.

The obtained biaxially stretched polypropylene film is sealed with a fusing sealing machine to form a packaging bag. In the present invention, a stable seal strength can be obtained even when fusing and sealing at high speed, but the fusing seal at high speed is as follows.
First, in the process of fusing sealing, the biaxially stretched polypropylene film unwound from the roll is half-folded (folded in half) along the flow direction with a triangular plate, and then cut with a heated fusing blade. While welding, it is a bag. In this case, it is preferable that the layer (B) is half-folded with the inside.
Conventionally, the film was cut and welded with this cutting blade at 160 shots / minute (the film feed speed was about 32 m / minute). Recently, this has been 180 shots / minute (about 36 m / minute as the film feed speed), preferably 200 shots / minute (about 40 m / minute as the film feed speed), and more than 180 shots / minute. This is a fusing seal under high speed.

In the present invention, the fusing seal strength of the packaging bag obtained by fusing sealing at such a high speed is 20 N / 15 mm or more. When the fusing seal strength is less than 20 N / 15 mm, troubles such as breaking the bag when filling contents such as food as a packaging bag or breaking the bag during transportation are not preferable. The upper limit of the seal strength is a case where no breakage occurs at the seal portion until the film breaks, and a film having a total thickness of 25 μm can be exemplified as 40 N / 15 mm.

In the case of a fusing seal, the sealing strength becomes unstable as the sealing speed increases. As a general phenomenon, a product having a very weak seal strength comes out, for example, products that are less than the standard are frequently used. The process in which the fusing seal is stable is a process in which a product exceeding the standard is always obtained.

Hereinafter, specific examples of the present invention and comparative examples for confirming the effects thereof will be described. Moreover, each physical property in an Example and a comparative example is measured as follows.

● Anti-fogging property 150 ml of water at 30 ° C. was placed in a 200 ml wide-mouth container, and the mouth was sealed with the obtained biaxially oriented polypropylene film. (The film may be a single sheet, and the surface on the side of the wide-mouthed container may be either the front surface or the back surface.) After storing for 1 hour at an ambient temperature of 5 ° C., the state of water droplets adhering to the film surface was visually confirmed. As a result, it is transparent without fogging (transparently wet with a thin water film on the whole), transparent on the whole, but with water droplets with relatively large diameters scattered, o cloudy (small on the whole) Water droplets adhered and were opaque).

● Fusing seal (bag making)
Using a bag making machine (H-65V type bag making machine manufactured by Totani Giken Kogyo Co., Ltd.), bags were made at a cutting edge of 420 ° C., at a cutting interval of 200 mm, and 180 shots / minute. The size of the obtained bag was 400 mm × 200 mm, and 500 sheets were produced per film.

● Seal strength (seal stability)
From the obtained 500 bags, 100 were randomly extracted and the following measurements were performed.
A measurement sample was cut into a size of 100 mm in length and 15 mm in width so that the seal portion was in the center with the direction perpendicular to the seal direction of the obtained bag as the vertical direction. In one bag, the measurement material was cut out by the above method from a total of 6 locations, 3 locations at the seal portion on one side and 3 locations at the seal portion on the other side. The cut out measurement sample was set in a tensile tester (Strograph manufactured by Toyo Seiki Co., Ltd.), pulled at a pulling speed of 200 mm / min, and the strength when the seal broke was defined as the seal strength. The same measurement was performed 6 times in total. Among these six measurements, when a value of less than 20 N / 15 mm was obtained even once, a seal failure was indicated as x.
The same measurement was further performed on 99 bags, and it was confirmed how many bags had become “x” as a sealing failure.
Of the 100 sheets, one that was not defective was stable, and when even one sheet was defective, it was unstable.

Example 1
NMR pentad fraction 95%, density 0.91 g / cm ³ , MFR 3.3 g / 10 min, melting point 163 ° C. with 100 parts by weight of propylene homopolymer, polymerized with metallocene catalyst, butene content 5 wt. % Amorphous propylene-butene copolymer 2.4 parts by weight, antifogging agent 1.6 parts by weight (stearyl monoglyceride 0.25 parts by weight, stearyl diethanolamine monostearate 1.23 parts by weight, stearyl diethanolamine 0.12 parts (Part by weight, 1.6 parts by weight in total) and 0.1 part by weight of PMMA fine particles having an average particle diameter of 2.5 μm are mixed as the resin constituting the layer (A), containing 3% by weight of ethylene and containing butene Propylene-ethylene-butene random copolymer of 6% by weight, density 0.91 g / cm ³ , MFR 5.5 g / 10 min, melting point 140 ° C. 90% by weight of a body, a density of 0.88 g / cm ³ , an MFR of 3.0 g / 10 min, a melting point of 75 ° C., and a linear low density polyethylene having a melting point of 75 ° C. A mixed resin in which 0.4 parts by weight of PMMA fine particles having an average particle diameter of 2.5 μm was mixed with 100 parts by weight of the mixed mixture was used as a resin constituting the layer (B).

The resin constituting each layer is put into two extruders, and is laminated in the order of (A) / (B), and is co-extruded from a three-layer T die having a temperature of 230 ° C., and a cooling roll at 25 ° C. And cooled and solidified to obtain an original fabric sheet. Next, the sheet was heated to 130 ° C. and roll-stretched 4.6 times in the MD direction, preheated at a set temperature of 165 ° C. with a tenter, stretched 10 times in the TD direction at a set temperature of 165 ° C., and then set temperature 165 After annealing at ℃ and exiting the tenter, corona discharge with 6.6 × 10 ² J / m ² on the surface layer (A) side and 4.8 × 10 ² J / m ² on the back layer (C) side After the treatment, it was wound up with a winder to obtain a biaxially stretched polypropylene film. The total thickness of the obtained biaxially stretched polypropylene film was 25 μm, and the thickness of each layer was (A) layer / (B) layer = 23 μm / 2 μm.

Using the obtained biaxially stretched polypropylene film, the antifogging property, the seal strength and the seal stability were evaluated. The results are shown in Table 1.

(Example 2)
NMR pentad fraction 95%, density 0.91 g / cm ³ , MFR 3.3 g / 10 min, melting point 163 ° C. with 100 parts by weight of propylene homopolymer, polymerized with metallocene catalyst, butene content 5 wt. % Amorphous propylene-butene copolymer 2.4 parts by weight and antifogging agent 1.6 parts by weight (stearyl monoglyceride 0.25 parts by weight, stearyl diethanolamine monostearate 1.23 parts by weight, stearyl diethanolamine 0.12 parts by weight (Part by weight, 1.6 parts by weight in total) The mixed resin is used as the resin constituting the layer (A), the ethylene content is 4% by weight, the density is 0.91 g / cm ³ , the MFR is 7.0 g / 10 minutes, and the melting point is 140 ° C. 0.1 parts by weight of PMMA fine particles having an average particle diameter of 2.5 μm were mixed with 100 parts by weight of the propylene-ethylene random copolymer. A biaxially stretched polypropylene film is obtained in the same manner as in Example 1 except that the mixed resin is a resin constituting the (C) layer and has a three-layer constitution of (C) layer / (A) layer / (B) layer. It was. The total thickness of the obtained biaxially oriented polypropylene film was 25 μm, and the thickness of each layer was (C) layer / (A) layer / (B) layer = 2 μm / 21 μm / 2 μm.
Using the obtained biaxially stretched polypropylene film, the antifogging property, the seal strength and the seal stability were evaluated. The results are shown in Table 1.

(Example 3)
NMR pentad fraction 95%, density 0.91 g / cm ³ , MFR 3.3 g / 10 min, melting point 163 ° C. propylene homopolymer 93% by weight, NMR pentad fraction 99%, density 0.91 g / cm ³ , An amorphous propylene-butene copolymer having a butene content of 5% by weight was polymerized using a metallocene catalyst with 100 parts by weight of a mixed resin obtained by mixing 7% by weight of a propylene homopolymer having an MFR of 2.1 g / 10 minutes and a melting point of 165 ° C. 2.4 parts by weight of polymer and 1.6 parts by weight of antifogging agent (0.25 parts by weight of stearyl monoglyceride, 1.23 parts by weight of stearyl diethanolamine monostearate, 0.12 parts by weight of stearyl diethanolamine, 1.6 parts by weight in total Biaxially stretched polypropylene in the same manner as in Example 2 except that the mixed resin obtained by mixing ()) is the resin constituting the layer (A). To obtain a film.
Using the obtained biaxially stretched polypropylene film, the antifogging property, the seal strength and the seal stability were evaluated. The results are shown in Table 1.

Example 4
Average with respect to 100 parts by weight of a propylene-ethylene-butene random copolymer having an ethylene content of 3% by weight, a butene content of 6% by weight, a density of 0.91 g / cm ³ , an MFR of 5.5 g / 10 minutes, and a melting point of 140 ° C. A mixed resin in which 0.4 parts by weight of PMMA fine particles having a particle diameter of 2.5 μm are mixed is used as a resin constituting the (C) layer, except for a three-layer configuration of (C) layer / (A) layer / (B) layer. Obtained a biaxially oriented polypropylene film in the same manner as in Example 2. The total thickness of the obtained biaxially oriented polypropylene film was 25 μm, and the thickness of each layer was (C) layer / (A) layer / (B) layer = 2 μm / 21 μm / 2 μm.
Using the obtained biaxially stretched polypropylene film, the antifogging property, the seal strength and the seal stability were evaluated. The results are shown in Table 1.

(Comparative Example 1)
PMMA fine particles having an average particle diameter of 2.5 μm were added to 100 parts by weight of a propylene-ethylene random copolymer having an ethylene content of 4% by weight, a density of 0.91 g / cm ³ , an MFR of 7.0 g / 10 minutes, and a melting point of 140 ° C. A biaxially stretched polypropylene film was obtained in the same manner as in Example 2 except that 0.1 parts by weight of the mixed resin was used as the resin constituting the layer (B).
Using the obtained biaxially stretched polypropylene film, the antifogging property, the seal strength and the seal stability were evaluated. The results are shown in Table 1.

(Comparative Example 2)
Butene-containing polymerized using metallocene catalyst for 100 parts by weight of propylene-ethylene random copolymer having an ethylene content of 4% by weight, a density of 0.91 g / cm ³ , an MFR of 7.0 g / 10 min, and a melting point of 140 ° C. 2.4 parts by weight of an amorphous propylene-butene copolymer in an amount of 5% by weight, and 1.6 parts by weight of an antifogging agent (0.25 parts by weight of stearyl monoglyceride, 1.23 parts by weight of stearyl diethanolamine monostearate, stearyl A biaxially stretched polypropylene film was obtained in the same manner as in Example 2 except that the mixed resin mixed with 0.12 parts by weight of diethanolamine (1.6 parts by weight in total) was used as the resin constituting the layer (A).
Using the obtained biaxially stretched polypropylene film, the antifogging property, the seal strength and the seal stability were evaluated. The results are shown in Table 1.

Claims (7)

Biaxial stretching characterized by having two layers: (A) layer containing propylene homopolymer with NMR pentad fraction of 93-98% and (B) layer containing propylene random copolymer and polyethylene resin Polypropylene film. The biaxially oriented polypropylene film according to claim 1, wherein the (A) layer and the (B) layer are adjacent to each other. The propylene random copolymer and the polyethylene resin are contained in a proportion of 80 to 99% by weight of the propylene random copolymer and 1 to 20% by weight of the polyethylene resin. The biaxially stretched polypropylene film described. The biaxially stretched polypropylene film according to any one of claims 1 to 3, wherein the polyethylene resin is a linear low density polyethylene. The propylene random copolymer is a propylene-ethylene random copolymer, a propylene-butene random copolymer, a propylene-ethylene-butene random copolymer, or a mixture thereof. The biaxially stretched polypropylene film according to any one of the above. 6. The layer (A) containing a propylene homopolymer having an NMR pentad fraction of 93 to 98% contains an amorphous polyolefin and an antifogging agent. Axial oriented polypropylene film. A packaging bag obtained by fusing and sealing the biaxially stretched polypropylene film according to any one of claims 1 to 6.