Biaxially stretching polypropylene film

Abstract

To provide a biaxially stretching polypropylene film.SOLUTION: A biaxially stretching polypropylene film comprises an intermediate layer, and a first surface layer arranged on the intermediate layer. The intermediate layer comprises first polypropylene having a first melting point, a petroleum resin, and a crystallizing agent. The first melting point exceeds 135°C. The first polypropylene has a content of 88 to 99.5 pts.wt., the petroleum resin has a content of 1.5 to 10 pts.wt. and the crystallizing agent has a content of 0.1 to 0.5 pts.wt. with a total weight of the intermediate layer as 100 pts.wt. The first surface layer comprises second polypropylene having a second melting point of less than 135°C.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a biaxially oriented polypropylene film, and more particularly to a biaxially oriented polypropylene film applicable to high speed bag making. [Background technology]

[0002] Due to the difference in the nature of the materials, the heat resistance and rigidity of biaxially oriented polypropylene (BOPP) film is lower than that of biaxially oriented polyester film, so the application fields of biaxially oriented polypropylene film are more limited than those of biaxially oriented polyester film.

[0003] For example, biaxially oriented polypropylene film can be applied to packaging materials. In the process of making bags, in order to maintain the flatness and high melting strength after making bags, the speed of making packaging materials with biaxially oriented polypropylene film should not be too high. Specifically, the speed of making bags should not exceed 170 bags per minute.

[0004] When the bag making speed is increased, the heat sealing of the biaxially oriented polypropylene film becomes incomplete during the heat sealing process, and the heat melt strength may be insufficient. Also, when the bag making speed is increased, the rigidity of the biaxially oriented polypropylene film becomes insufficient, and the bag is easily bent or wrinkled during the folding process.

[0005] Therefore, an important issue for this project is how to increase the speed of bag production by improving materials, without adversely affecting the quality of the bags. Summary of the Invention [Problem to be solved by the invention]

[0006] The technical problem to be solved by the present invention is to provide a biaxially oriented polypropylene film in response to the shortcomings of the prior art. [Means for solving the problem]

[0007] In order to solve the above technical problems, one technical means adopted by the present invention provides a biaxially oriented polypropylene film. The biaxially oriented polypropylene film includes an intermediate layer and a first surface layer disposed on the intermediate layer. The intermediate layer includes a first polypropylene having a first melting point, a petroleum resin, and a crystallization agent. The first melting point is greater than 135°C. When the total weight of the intermediate layer is 100 parts by weight, the content of the first polypropylene is 88 parts by weight to 99.5 parts by weight, the content of the petroleum resin is 1.5 parts by weight to 10 parts by weight, and the content of the crystallization agent is 0.1 parts by weight to 0.5 parts by weight. The first surface layer includes a second polypropylene having a second melting point that is less than 135°C.

[0008] In one embodiment, the first melting point is at least 10° C. higher than the second melting point.

[0009] In one embodiment, the first polypropylene is a propylene homopolymer.

[0010] In one embodiment, the second polypropylene is a random propylene copolymer synthesized from ethylene and propylene monomers.

[0011] In one embodiment, the petroleum resin is an aromatic copolymer-based hydrogenated petroleum resin.

[0012] In one embodiment, the petroleum resin is a hydrogenated petroleum resin having 5 or 9 carbon atoms.

[0013] In one embodiment, the ratio of the petroleum resin to the crystallization agent (petroleum resin / crystallization agent) is 5-25.

[0014] In one embodiment, the crystallization agent is selected from the group consisting of aliphatic carboxylate metal compounds, aromatic carboxylate metal compounds, organic phosphates, benzylidene sorbitol derivatives, and lignic acid and its derivatives.

[0015] In one embodiment, the first surface layer contains 90 to 98 parts by weight of the propylene random copolymer and 2 to 10 parts by weight of the anti-blocking agent, with the total weight of the first surface layer being 100 parts by weight.

[0016] In one embodiment, the biaxially oriented polypropylene film further comprises a second surface layer disposed on the intermediate layer opposite the first surface layer, the second surface layer comprising a third polypropylene having a third melting point less than 135°C. Effect of the Invention

[0017] As an advantageous effect of the present invention, the biaxially oriented polypropylene film of the present invention improves the bag-making speed of the biaxially oriented polypropylene film due to the technical features that "the middle layer contains a first polypropylene, a petroleum resin, and a crystallization agent" and "the first melting point is greater than 135°C, and the second melting point is less than 135°C." [Brief description of the drawings]

[0018] [Figure 1] 1 is a schematic side view of a biaxially oriented polypropylene film according to the present invention. [Diagram 2] FIG. 1 is a schematic diagram of a packaging structure of a biaxially oriented polypropylene film according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] In order to better understand the features and technical contents of the present invention, please refer to the following detailed description of the present invention and the accompanying drawings, which are provided for reference and explanation only and are not intended to limit the scope of the present invention.

[0020] The "biaxially oriented polypropylene film" according to the embodiment of the present invention will be described below by way of certain specific embodiments, and those skilled in the art will be able to understand the advantages and effects of the present invention based on the contents disclosed herein. The present invention can be implemented or applied by other different specific embodiments, and various modifications and changes can be made to each detail in the present specification based on different perspectives and applications, without departing from the concept of the present invention. In addition, as described in advance, the accompanying drawings of the present invention are simple schematic illustrations and are not drawn to actual size. The technical contents of the present invention will be described in more detail based on the following embodiments, but the disclosure does not limit the scope of protection of the present invention. In addition, the term "or" used in the present specification may include any one or more combinations of the relevant items listed according to the actual situation.

[0021] In order to overcome the problem of being unable to improve the production speed of the biaxially oriented polypropylene film, the biaxially oriented polypropylene film of the present invention has a composite structure including multiple layers, and each layer is mainly composed of polypropylene. In the present invention, by further adjusting the components of each layer, the biaxially oriented polypropylene film can achieve both high hot melt strength and high rigidity.

[0022] As shown in Fig. 1, the biaxially oriented polypropylene film 1 according to the present invention includes at least an intermediate layer 11 and a first surface layer 12 disposed on the intermediate layer 11. The intermediate layer 11 and the first surface layer 12 are integrally molded by a co-extrusion process, and the final biaxially oriented polypropylene film 1 can be manufactured by a further stretching process.

[0023] After the biaxially oriented polypropylene film 1 is produced, a packaging bag Z can be produced using a bag making machine as shown in Figure 2. The biaxially oriented polypropylene film is folded in half and then heat sealed at a position 1.5 cm from the edge. Thus, a hot press area 2 is formed in the biaxially oriented polypropylene film 1 folded in half, and a storage space is formed inside the packaging bag Z by the hot press area 2.

[0024] 1, the main components of both the intermediate layer 11 and the first surface layer 12 are polypropylene. After coextrusion, no clear boundaries are observed in the cross-sectional structure of the biaxially oriented polypropylene film 1, but for convenience of explanation, they are described as independent layers in the specification.

[0025] Regarding the material, the main component of both the intermediate layer 11 and the first surface layer 12 is polypropylene, but the types of polypropylene are different. The main component of the intermediate layer is a first polypropylene having a melting point of more than 135°C. The main component of the first surface layer 12 is a second polypropylene having a melting point of less than 135°C. That is, the melting point of the first polypropylene is higher than the melting point of the second polypropylene. In one embodiment, the melting point of the first polypropylene is at least 10°C higher than the melting point of the second polypropylene.

[0026] In one exemplary embodiment, the melting point of the first polypropylene is 150° C. to 175° C., and the melting point of the second polypropylene is 115° C. to 135° C. Preferably, the melting point of the first polypropylene is 160° C. to 166° C., and the melting point of the second polypropylene is 125° C. to 135° C.

[0027] The main component in the intermediate layer 11 is a propylene homopolymer (first polypropylene). The propylene homopolymer has favorable crystallinity so as to improve the rigidity of the intermediate layer 11. The high crystallinity also improves the thermal melt strength of the biaxially oriented polypropylene film 1 after heat sealing. More specifically, the melt index of the propylene homopolymer is 2 g / min to 4 g / min.

[0028] In order to further improve the crystallinity of the propylene homopolymer, the intermediate layer 11 further contains a petroleum resin and a crystallizing agent. The petroleum resin can improve the crystallinity of the amorphous phase in the propylene homopolymer, and the crystallizing agent can improve the crystallinity of the crystalline phase in the propylene homopolymer.

[0029] It is worth noting that by improving the crystallinity of the propylene homopolymer, not only the rigidity of the intermediate layer 11 is improved, but also the heat melt strength of the biaxially oriented polypropylene film 1 is improved. However, if the biaxially oriented polypropylene film 1 has a relatively high heat melt strength, the time required for heat sealing is also long. If the bag making speed is increased, the heat sealing time is insufficient and the ideal heat sealing effect cannot be achieved. Therefore, if the crystallinity of the propylene homopolymer is high to a certain extent, it may not be suitable for a high-speed bag making process.

[0030] On the other hand, when the crystallinity of the propylene homopolymer is relatively low, the biaxially oriented polypropylene film 1 can be heat-sealed in a relatively short time, but due to limitations in the material itself, the heat melt strength of the biaxially oriented polypropylene film 1 after bag making cannot be improved, and there is a possibility that the desired product cannot be manufactured. In addition, when the crystallinity of the propylene homopolymer is relatively low, a problem occurs in which the rigidity of the intermediate layer 11 is insufficient. In a high-speed process, the property of insufficient rigidity adversely affects the flatness of the biaxially oriented polypropylene film 1 bag making.

[0031] Therefore, while the bag making speed can be improved by adjusting the crystallinity of the propylene homopolymer, the rigidity of the biaxially oriented polypropylene film 1, the hot melt strength after bag making, and the flatness during the bag making process must also be taken into consideration; furthermore, the above characteristics cannot be achieved simply by improving the crystallinity.

[0032] In the present invention, the crystallinity of the crystalline phase and the amorphous phase in the propylene homopolymer is improved by adding a petroleum resin and a crystallizing agent, and thus the hot melt strength of the biaxially oriented polypropylene film 1 after the film is made into a bag is improved. After the hot melt strength is improved, the biaxially oriented polypropylene film 1 can achieve the desired heat sealing effect even when the film is made into a bag at a relatively high speed. Therefore, the biaxially oriented polypropylene film 1 according to the present invention can be applied to a high-speed bag making process.

[0033] Moreover, according to experiments, when only petroleum resin is added without adding a crystallizing agent, or when only a crystallizing agent is added without adding a petroleum resin, it is not possible to impart good hot melt strength to the biaxially oriented polypropylene film 1. Specific experimental data will be described later. The present invention improves the crystallinity of the crystalline phase and the amorphous phase in the propylene homopolymer at the same time, so that the biaxially oriented polypropylene film 1 can be applied to a high-speed bag making process.

[0034] In order to adjust the crystallinity of the crystalline phase and the amorphous phase in the propylene homopolymer, the weight ratio of the petroleum resin to the crystallizing agent is 5 to 25. This makes it possible to achieve a balance between the rigidity of the biaxially oriented polypropylene film 1, the hot melt strength after bag making, and the flatness during the bag making process.

[0035] Specifically, assuming that the total weight of the intermediate layer 11 is 100 parts by weight, the intermediate layer 11 contains 88 to 99.5 parts by weight of a propylene homopolymer, 1.5 to 10 parts by weight of a petroleum resin, and 0.1 to 0.5 parts by weight of a crystallization agent.

[0036] Preferably, the intermediate layer 11 contains 90 to 98 parts by weight of a propylene homopolymer, 1.8 to 6 parts by weight of a petroleum resin, and 0.15 to 0.45 parts by weight of a crystallization agent, where the total weight of the intermediate layer 11 is 100 parts by weight. More preferably, the intermediate layer 11 contains 91 to 96 parts by weight of a propylene homopolymer, 2 to 5 parts by weight of a petroleum resin, and 0.2 to 0.4 parts by weight of a crystallization agent.

[0037] The petroleum resin is a hydrogenated petroleum resin for imparting suitable crystallinity to the propylene homopolymer. For example, the petroleum resin may be a hydrogenated petroleum resin having 5 or 9 carbon atoms, for example, the petroleum resin may be a piperylene hydrogenated resin or a dicyclopentadiene (DCPD) hydrogenated resin. The petroleum resin may also be an aromatic copolymer-based hydrogenated petroleum resin.

[0038] The crystallizing agent is an organic crystallizing agent, for example, the crystallizing agent may be, for example, an aliphatic carboxylate metal compound, an aromatic carboxylate metal compound, an organic phosphate, a benzylidene sorbitol derivative, or lignic acid and its derivatives. In one exemplary embodiment, the aromatic carboxylate metal compound is sodium benzoate and aluminum carboxyl-di(p-tert-butylbenzoate).

[0039] In one embodiment, an antifogging agent may be further included as a material of the intermediate layer 11. The amount of the antifogging agent added is 1 part by weight to 5 parts by weight, with the total weight of the intermediate layer 11 being 100 parts by weight.

[0040] The main component of the first surface layer 12 is a propylene random copolymer (second polypropylene). The propylene random copolymer can rapidly melt and heat seal the first surface layer 12. In this way, the biaxially oriented polypropylene film 1 can be applied to a high-speed bag making process. More specifically, the melt index of the propylene homopolymer is 6 g / 10 min to 7 g / 10 min.

[0041] In one embodiment, the propylene random copolymer is synthesized by ethylene monomer and propylene monomer. Since the polymerization arrangement of the monomers is not fixed, the propylene random copolymer has low crystallinity and low melting point. Therefore, during the bag making process, the first surface layer 12 can be bonded quickly to improve the heat sealing effect of the biaxially oriented polypropylene film 1.

[0042] Specifically, the first surface layer 12 contains 90 to 98 parts by weight of the propylene random copolymer and 2 to 10 parts by weight of the anti-tack agent, with the total weight of the first surface layer 12 being 100 parts by weight. Preferably, the first surface layer 12 contains 93 to 97 parts by weight of the propylene random copolymer and 3 to 7 parts by weight of the anti-tack agent, with the total weight of the first surface layer 12 being 100 parts by weight.

[0043] The addition of an anti-adhesive agent can improve the ease of opening a packaging bag. Specifically, the anti-adhesive agent contains silicon dioxide. The anti-adhesive agent contains silicon dioxide having a particle diameter of 2 μm to 15 μm. In one example, anti-adhesive agents having two different particle diameters can be used together. For example, an anti-adhesive agent having a particle diameter of 1 μm to 3 μm and an anti-adhesive agent having a particle diameter of 3.1 μm to 5 μm are used together.

[0044] For application in a relatively high-temperature bag-making process, the thickness of the intermediate layer 11 may be 10 μm to 30 μm, the thickness of the first surface layer 12 may be 0.2 μm to 2 μm, and the total thickness of the biaxially oriented polypropylene film 1 is 10.2 μm to 34 μm. Preferably, the thickness of the intermediate layer 11 may be 18 μm to 19 μm, the thickness of the first surface layer 12 may be 0.5 μm to 1 μm, and the total thickness of the biaxially oriented polypropylene film 1 is 18.5 μm to 21 μm.

[0045] If the thickness of the intermediate layer 11 is too thin, the rigidity is insufficient, which may adversely affect the flatness of the biaxially oriented polypropylene film 1 after bag making. If the thickness of the intermediate layer 11 is too thick, the time required for heat sealing increases, which is disadvantageous for accelerating the bag making process. If the thickness of the first surface layer 12 is too thin, the biaxially oriented polypropylene film 1 cannot be bonded quickly in the bag making process. If the thickness of the first surface layer 12 is too thick, the hot melt strength decreases.

[0046] 1, the biaxially oriented polypropylene film 1 may further include a second surface layer 13. The second surface layer 13 is disposed on the intermediate layer 11 and is opposite to the first surface layer 12. Due to the design of the composite structure, the biaxially oriented polypropylene film 1 can be applied to a high-speed bag making process.

[0047] The main component of the second surface layer 13 is a propylene random copolymer (third polypropylene). The propylene random copolymer rapidly melts and heat seals the second surface layer 13. In this way, the biaxially oriented polypropylene film 1 can be applied to a relatively expensive bag making process.

[0048] In one exemplary embodiment, the propylene random copolymer is synthesized by polymerization of ethylene monomer and propylene monomer. The melting point of the third polypropylene is less than 135°C. That is, the melting point of the first polypropylene is higher than the melting point of the third polypropylene. In one embodiment, the melting point of the first polypropylene is at least 10°C higher than the melting point of the third polypropylene. Specifically, the melting point of the third polypropylene is 115°C to 135°C. Preferably, the melting point of the third polypropylene is 125°C to 135°C.

[0049] The second surface layer 13 contains 90 to 98 parts by weight of the propylene random copolymer and 2 to 10 parts by weight of the anti-tack agent, where the total weight of the second surface layer 13 is 100 parts by weight. Preferably, the second surface layer 13 contains 93 to 97 parts by weight of the propylene random copolymer and 3 to 7 parts by weight of the anti-tack agent, where the total weight of the second surface layer 13 is 100 parts by weight.

[0050] For application in a relatively high speed bag making process, the thickness of the second surface layer 13 may be from 0.2 μm to 2 μm, and preferably, the thickness of the second surface layer 13 may be from 0.5 μm to 1 μm.

[0051] [Experimental data] In order to prove that the biaxially oriented polypropylene film 1 of the present invention can be applied to a relatively high-speed bag-making process, materials for the intermediate layer 11, the first surface layer 12, and the second surface layer 13 were prepared and the biaxially oriented polypropylene films 1 of Examples 1 to 3 and Comparative Examples 1 to 3 were produced by coextrusion.

[0052] The weights of the materials added to each layer in the biaxially oriented polypropylene film 1 are shown in Table 1. The thicknesses of the intermediate layer 11, the first surface layer 12, and the second surface layer 13 were 18 μm, 1 μm, and 1 μm, respectively, and therefore the total thickness of the biaxially oriented polypropylene film 1 was 20 μm.

[0053] The biaxially oriented polypropylene films 1 according to Examples 1 to 3 and Comparative Examples 1 to 3 were fed to a bag making machine to produce packaging bags at a speed of 200 bags / min. The set temperature of the fusion knife in the bag making machine was 400° C. After the bag making was completed, the thermal melt strength, anti-fogging and ease of opening were measured, and the results are shown in Table 2.

[0054] In the thermal melt strength measurement test, the packaging bag was cut at the melted portion to obtain a sample with a length of 15 mm. The sample was clamped to a tensile tester and a strength test was performed at an angle of 180° and a tensile speed of 300 mm / min. Five samples were taken from the biaxially oriented polypropylene film 1, and the average value of the five measurement results is shown in Table 1. In Table 1, if the thermal melt strength was more than 18 N / 15 mm, it was indicated with "○". If the thermal melt strength was 16 N / 15 mm to 17.9 N / 15 mm, it was indicated with "△". If the thermal melt strength was less than 15.9 N / 15 mm, it was indicated with "X".

[0055] In the anti-fogging test, 100ml of water was measured into a 250ml beaker. The packaging bag was placed over the beaker and placed in a 4℃ refrigerator for 10 minutes, and the adhesion of water droplets to the surface of the packaging bag was observed. In Table 1, if the moisture formed a water film on the surface of the packaging bag and no fogging occurred, it was indicated with "○". If the moisture formed droplets on the surface of the packaging bag and could not be seen through, it was indicated with "×".

[0056] In the ease of opening test, the opening of the packaging bag was rubbed with the thumb and index finger to check whether it was easy to open. In Table 1, if the opening of the bag could be easily opened after rubbing with the fingers, it was indicated with "O". If the opening of the bag was sticky and difficult to open after rubbing with the fingers, it was indicated with "X".

[0057] In Table 1, the propylene random copolymer used in the first and second surface layers was Formosa Plastics' product number 5050 propylene random copolymer (melt index 6.5 g / min, melting point 133°C). The antiblocking agents used in the first and second surface layers included silicon dioxide PSE-55 (antiblocking agent A, particle size 2 μm) from Kemfar and silicon dioxide CONSTAB® AB 06019 PP (antiblocking agent B, particle size 4 μm) from Constance Engineering. The propylene homopolymer used in the middle layer was propylene homopolymer PPR-FT03-S (melt index 3.1 g / 10 min, melting point 165°C) from Sinopec Maoming Petrochemical Company (also known as Sinopec Maoming Petrochemical Company). The anti-fog agent used in the middle layer was anti-fog agent pellets, PAT-381, manufactured by Japan Riken Vitamin Co., Ltd. The petroleum resin added to the middle layer was an aromatic copolymer-based hydrogenated petroleum resin, P125, manufactured by Idemitsu Kosan Co., Ltd. The crystallization agent added to the middle layer was a sorbitol-based crystallization agent.

[0058] [Table 1]

[0059] [Table 2]

[0060] According to the contents of Tables 1 and 2, the biaxially oriented polypropylene film of the present invention can be applied to a high-speed (200 bags / min) bag-making process and has good hot melt strength (more than 18N / 15mm). By adding a petroleum resin and a crystallizing agent to the middle layer, the crystallinity of the crystalline phase and the amorphous phase in the propylene homopolymer can be improved, and the rigidity and hot melt strength can be improved. Even if the bag-making speed is increased, the packaging bag still has good hot melt strength, and the hot melt strength does not decrease due to the increase in the bag-making speed.

[0061] According to the results of Examples 1 to 3, when the weight ratio of the petroleum resin to the crystallizing agent is 5 to 25, the biaxially oriented polypropylene film can be applied to a high-speed bag-making process. To be more specific, the addition of the crystallizing agent improves the crystallinity of the crystalline phase in the propylene homopolymer, and the addition of the petroleum resin improves the crystallinity of the amorphous phase in the propylene homopolymer, changing the texture of the amorphous phase from soft to hard. Therefore, when the amount of the crystallizing agent is increased, the amount of the petroleum resin can be reduced. However, when the amount of the crystallizing agent is excessive, the biaxially oriented polypropylene film becomes hard and brittle, and the film breaks during the film-making process, which is disadvantageous to production.

[0062] According to the results of Example 1, when the weight ratio of the petroleum resin to the crystallizing agent is 12 to 16.9, the petroleum resin and the crystallizing agent complement each other, improving both the crystallinity of the crystal phase and the hardness of the amorphous phase in the propylene homopolymer. According to the results of Example 2, when the weight ratio of the petroleum resin to the crystallizing agent is 17 to 25, the petroleum resin is the main cause of improving the crystallinity of the propylene homopolymer, and at this time, the hardness of the amorphous phase in the propylene homopolymer is relatively high. According to the results of Example 3, when the weight ratio of the petroleum resin to the crystallizing agent is 5 to 11.9, the crystallizing agent is the main cause of improving the crystallinity of the propylene homopolymer, so a relatively small amount of petroleum resin can be added. At this time, the crystallinity of the crystal phase in the propylene homopolymer is relatively high.

[0063] According to the results of Comparative Examples 2 and 3, when only petroleum resin or crystallizing agent is added, the hot melt strength of the biaxially oriented polypropylene film cannot exceed 18N / 15mm.

[0064] [Advantageous Effects of the Embodiments] As an advantageous effect of the present invention, the biaxially oriented polypropylene film of the present invention improves the bag-making speed of the biaxially oriented polypropylene film due to the technical features that "the middle layer contains a first polypropylene, a petroleum resin, and a crystallization agent" and "the first melting point is greater than 135°C, and the second melting point is less than 135°C."

[0065] The above disclosure is merely a preferred embodiment of the present invention, and the scope of the claims of the present invention is not limited thereto. Therefore, all equivalent technical modifications made by utilizing the specification and drawings of the present invention are included in the scope of the claims of the present invention. [Explanation of symbols]

[0066] 1. Biaxially oriented polypropylene film 11...Middle class 12...First Surface 13...The second surface 2. Hot press area Z...Packaging bag

Claims

1. A biaxially oriented polypropylene film comprising an intermediate layer and a first surface layer disposed on the intermediate layer, The intermediate layer comprises a first polypropylene having a first melting point greater than 135° C., a petroleum resin, and a crystallization agent; When the total weight of the intermediate layer is 100 parts by weight, the content of the first polypropylene is 88 parts by weight to 99.5 parts by weight, the content of the petroleum resin is 1.5 parts by weight to 10 parts by weight, and the content of the crystallization agent is 0.1 parts by weight to 0.5 parts by weight, The biaxially oriented polypropylene film, wherein the first surface layer comprises a second polypropylene having a second melting point less than 135°C.

2. 2. The biaxially oriented polypropylene film of claim 1, wherein the first melting point is at least 10° C. higher than the second melting point.

3. 2. The biaxially oriented polypropylene film of claim 1, wherein the first polypropylene is a propylene homopolymer.

4. The biaxially oriented polypropylene film according to claim 1 , wherein the second polypropylene is a propylene random copolymer synthesized from ethylene monomers and propylene monomers.

5. The biaxially oriented polypropylene film according to claim 1 , wherein the petroleum resin is an aromatic copolymer-based hydrogenated petroleum resin.

6. The biaxially oriented polypropylene film according to claim 1 , wherein the petroleum resin is a hydrogenated petroleum resin having 5 or 9 carbon atoms.

7. The biaxially oriented polypropylene film according to claim 1, wherein the ratio of the petroleum resin to the crystallization agent (petroleum resin / crystallization agent) is 5 to 25.

8. 2. The biaxially oriented polypropylene film according to claim 1, wherein the crystallization agent is selected from the group consisting of an aliphatic carboxylic acid metal compound, an aromatic carboxylic acid metal compound, an organic phosphate, a benzylidene sorbitol derivative, and lignic acid and its derivatives.

9. 2. The biaxially oriented polypropylene film according to claim 1, wherein the first surface layer comprises 90 to 98 parts by weight of a propylene random copolymer and 2 to 10 parts by weight of an anti-blocking agent, with the total weight of the first surface layer being 100 parts by weight.

10. Further comprising a second surface layer disposed on the intermediate layer so as to be opposite to the first surface layer; 10. The biaxially oriented polypropylene film of claim 1, wherein the second surface layer comprises a third polypropylene having a third melting point less than 135°C.

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