Biaxially oriented 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 suitable for 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 are lower than those 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 used for packaging. In the bag-making process, to maintain the flatness and high melting strength of the bag, the speed at which biaxially oriented polypropylene film is used for packaging must not be too high. Specifically, the bag-making speed must not exceed 170 bags per minute.

[0004] Increasing the bag-making speed can result in incomplete heat sealing of the biaxially oriented polypropylene film during the heat-sealing process, resulting in insufficient hot melt strength. In addition, increasing the bag-making speed can result in insufficient rigidity of the biaxially oriented polypropylene film, making it prone to bending and wrinkling during the bag folding process.

[0005] Therefore, improving the speed of bag production, provided that the quality of the bags is not adversely affected by improving the materials, is an important issue for this project. Summary of the Invention [Problem to be solved by the invention]

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

[0007] To solve the above technical problems, one technical solution 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 to 99.5 parts by weight, the content of the petroleum resin is 1.5 to 10 parts by weight, and the content of the crystallization agent is 0.1 to 0.5 parts by weight. The first surface layer includes a second polypropylene having a second melting point 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 carboxylic acid metal compounds, aromatic carboxylic acid 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, where the total weight of the first surface layer is 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. [Effects 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 comprises 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 explanation of the drawings]

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

[0019] 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 following describes a "biaxially oriented polypropylene film" according to an embodiment of the present invention through certain specific embodiments, and those skilled in the art can understand the advantages and effects of the present invention based on the disclosure herein. The present invention can be implemented or applied in other different specific embodiments, and various modifications and changes can be made to the details herein based on different perspectives and applications without departing from the concept of the present invention. As previously explained, the accompanying drawings are for simple schematic illustrations and are not drawn to scale. The technical content of the present invention will be described in more detail based on the following embodiments, but the disclosed content does not limit the scope of protection of the present invention. Furthermore, the term "or" used in this specification may include any one or more combinations of the relevant listed items depending on the actual situation.

[0021] In order to overcome the problem of being unable to improve the production speed of biaxially oriented polypropylene film, the biaxially oriented polypropylene film of the present invention has a composite structure including multiple layers, each of which 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 Figure 1, the biaxially oriented polypropylene film 1 according to the present invention comprises 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 formed by a co-extrusion process, and the final biaxially oriented polypropylene film 1 can be manufactured by a further stretching process.

[0023] After producing the biaxially oriented polypropylene film 1, 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 1.5 centimeters from the edge. This forms a hot-press area 2 in the folded biaxially oriented polypropylene film 1, which then forms a storage space inside the packaging bag Z.

[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 this specification.

[0025] Regarding materials, the intermediate layer 11 and the first surface layer 12 are both primarily made of polypropylene, but the types of polypropylene are different. The intermediate layer is primarily made of a first polypropylene having a melting point greater than 135°C. The first surface layer 12 is primarily made of a second polypropylene having a melting point 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 example, 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 of 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 hot melt strength of the biaxially oriented polypropylene film 1 after heat sealing. Specifically, the melt index of the propylene homopolymer is 2 g / min to 4 g / min.

[0028] 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 improving the crystallinity of the propylene homopolymer not only improves the rigidity of the intermediate layer 11 but also improves the heat-melt strength of the biaxially oriented polypropylene film 1. However, if the biaxially oriented polypropylene film 1 has a relatively high heat-melt strength, the time required for heat-sealing also increases. If the bag-making speed is increased, the heat-sealing time is insufficient, and an ideal heat-sealing effect cannot be achieved. Therefore, if the crystallinity of the propylene homopolymer is too high, it may not be suitable for high-speed bag-making processes.

[0030] On the other hand, if 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 of the material itself, the hot melt strength of the biaxially oriented polypropylene film 1 after bag formation cannot be improved, and there is a possibility that the desired product cannot be manufactured. Furthermore, if the crystallinity of the propylene homopolymer is relatively low, the problem of insufficient rigidity of the intermediate layer 11 occurs. In a high-speed process, the property of insufficient rigidity adversely affects the flatness of the biaxially oriented polypropylene film 1 bag formed.

[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, these properties cannot be achieved simply by improving the crystallinity.

[0032] In the present invention, the addition of a petroleum resin and a crystallizing agent improves the crystallinity of the crystalline and amorphous phases in the propylene homopolymer, thereby improving the hot melt strength of the biaxially oriented polypropylene film 1 after bag formation. After improving the hot melt strength, the biaxially oriented polypropylene film 1 can achieve the desired heat sealing effect even when bags are formed at a relatively high speed. Therefore, the biaxially oriented polypropylene film 1 of the present invention can be applied to high-speed bag-forming processes.

[0033] Furthermore, experiments have shown that adding only petroleum resin without adding a crystallizing agent, or adding only a crystallizing agent without adding petroleum resin, does not provide good hot melt strength to the biaxially oriented polypropylene film 1. Specific experimental data will be described later. By simultaneously improving the crystallinity of the crystalline and amorphous phases in the propylene homopolymer, the present invention enables the biaxially oriented polypropylene film 1 to be used in high-speed bag-making processes.

[0034] In order to adjust the crystallinity of the crystalline phase and amorphous phase in the propylene homopolymer, the weight ratio of the petroleum resin to the crystallizing agent is 5 to 25. This allows a balance to be achieved between the rigidity of the biaxially oriented polypropylene film 1, the hot melt strength after bag making, and 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 propylene homopolymer, 1.5 to 10 parts by weight of 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 that imparts suitable crystallinity to a propylene homopolymer. For example, the petroleum resin may be a hydrogenated petroleum resin having 5 or 9 carbon atoms, such as a hydrogenated piperylene resin or a hydrogenated dicyclopentadiene (DCPD) resin. The petroleum resin may also be an aromatic copolymer-based hydrogenated petroleum resin.

[0038] The crystallization agent is an organic crystallization agent, for example, an aliphatic carboxylic acid metal compound, an aromatic carboxylic acid metal compound, an organic phosphate, a benzylidene sorbitol derivative, or lignic acid and its derivatives. In one exemplary embodiment, the aromatic carboxylic acid 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, where the total weight of the intermediate layer 11 is 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 allows the first surface layer 12 to be rapidly melted and heat-sealed. In this way, the biaxially oriented polypropylene film 1 can be applied to high-speed bag-making processes. Specifically, the melt index of the propylene homopolymer is 6 g / 10 min to 7 g / 10 min.

[0041] In one example, a propylene random copolymer is synthesized from ethylene monomer and propylene monomer. Because the monomer configuration is not fixed, the propylene random copolymer has low crystallinity and a low melting point. Therefore, during the bag-making process, the first surface layer 12 can be quickly bonded, improving 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-blocking agent, where the total weight of the first surface layer 12 is 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-blocking agent, where the total weight of the first surface layer 12 is 100 parts by weight.

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

[0044] For application in a relatively high-speed 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 will be insufficient, which may adversely affect the flatness of the biaxially oriented polypropylene film 1 after bag formation. If the thickness of the intermediate layer 11 is too thick, the time required for heat sealing will increase, which will be 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 during the bag-making process. If the thickness of the first surface layer 12 is too thick, the hot melt strength will be reduced.

[0046] As shown in Figure 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 on the opposite side of the first surface layer 12. Due to the composite structure design, the biaxially oriented polypropylene film 1 can be applied to high-speed bag-making processes.

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

[0048] In one exemplary embodiment, the propylene random copolymer is synthesized by polymerizing 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-blocking 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-blocking 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 second surface layer 13 may be 0.2 μm to 2 μm, and preferably, the thickness of second surface layer 13 may be 0.5 μm to 1 μm.

[0051] [Experimental data] In order to prove that the biaxially oriented polypropylene film 1 of the present invention is applicable 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 co-extrusion.

[0052] The weight of the material added for each layer in the biaxially oriented polypropylene film 1 is shown in Table 1. The thicknesses of the intermediate layer 11, first surface layer 12, and 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, where packaging bags were produced 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, measurements of hot melt strength, anti-fogging properties, and ease of opening were carried out, and the results are shown in Table 2.

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

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

[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 by "○". If the bag was sticky and difficult to open after rubbing with the fingers, it was indicated by "×".

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

[0058] [Table 1]

[0059] [Table 2]

[0060] According to 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 (greater than 18 N / 15 mm). The addition of a petroleum resin and a crystallizing agent to the middle layer improves the crystallinity of the crystalline and amorphous phases in the propylene homopolymer, thereby improving rigidity and hot melt strength. Even when the bag-making speed is increased, the packaging bag still has good hot melt strength, and the hot melt strength does not decrease as the bag-making speed is increased.

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

[0062] According to the results of Example 1, when the weight ratio of petroleum resin to crystallization agent is 12 to 16.9, the petroleum resin and the crystallization agent complement each other, improving both the crystallinity of the crystalline phase and the hardness of the amorphous phase in the propylene homopolymer. According to the results of Example 2, when the weight ratio of petroleum resin to crystallization agent is 17 to 25, the petroleum resin is the main cause of improving the crystallinity of the propylene homopolymer, and in this case, 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 petroleum resin to crystallization agent is 5 to 11.9, the crystallization agent is the main cause of improving the crystallinity of the propylene homopolymer, so a relatively small amount of petroleum resin can be added. In this case, the crystallinity of the crystalline 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 comprises 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 using 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...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 that is a propylene homopolymer 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 91.5 parts by weight to 99.5 parts by weight, the content of the petroleum resin is 1.5 parts by weight to 5 parts by weight, the content of the crystallization agent is 0.1 parts by weight to 0.5 parts by weight, the ratio of the petroleum resin to the crystallization agent (petroleum resin / crystallization agent) is 5 to 25, and the thickness of the intermediate layer is 10 μm to 30 μm. a first surface layer comprising a second polypropylene having a second melting point less than 135°C, and a thickness of the first surface layer ranging from 0.2 μm to 2 μm;

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. The biaxially oriented polypropylene film according to claim 1, wherein the melt index of the second polypropylene is 6 g / 10 min to 7 g / 10 min.

4. 2. 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 intermediate layer further contains an anti-fogging agent, and the amount of the anti-fogging agent added is 1 part by weight to 5 parts by weight, where the total weight of the intermediate layer is 100 parts by weight.

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, where the total weight of the first surface layer is 100 parts by weight.

10. a second surface layer disposed on the intermediate layer opposite 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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