A BOPP matte film and its preparation method

Abstract

The present invention relates to a kind of BOPP matt film and preparation method thereof, belong to matt film technical field.The BOPP matt film of the present invention, including matt layer, core layer and lower surface layer arranged in sequence; The matt layer includes copolymerized polypropylene, 46-51wt% high-density polyethylene and 2-4wt% hyperbranched polyethylene, and the branching degree of the hyperbranched polyethylene is 8-12%; The core layer includes homopolymerized polypropylene and 6-10wt% block copolymer of ethylene oxide and propylene oxide, and the total proportion of ethylene oxide segment in the block copolymer of ethylene oxide and propylene oxide is 60-70wt%, and the total proportion of propylene oxide segment is 30-40wt%.The present invention improves the film surface bright spot problem of BOPP matt film by adding a certain proportion of hyperbranched polyethylene in the matt layer and a certain proportion of block copolymer of ethylene oxide and propylene oxide in the core layer, and the two work together to ensure the matt effect.

Description

Technical Field

[0001] The present invention relates to the technical field of matt films, in particular to a BOPP matt film and a preparation method thereof. Background Art

[0002] BOPP matte film achieves its matte effect primarily by scattering light, significantly enhancing the texture and quality of printed packaging. This is why it is widely used in the paper-plastic composite and electronics packaging industries. The matte properties of BOPP film impart a soft, stylish, and elegant high-end visual appearance, while also effectively alleviating visual fatigue. Consequently, BOPP matte film is increasingly used in the packaging industry.

[0003] To achieve the ideal matte effect, the matte layer of BOPP matte film is primarily composed of high-density polyethylene (HDPE) and copolymerized polypropylene (PP). Utilizing the soft-to-hard principle, whereby the copolymerized polypropylene (soft phase) encapsulates the HDPE (hard phase), this structure creates a microscopic "island" structure during biaxial stretching, ultimately achieving the desired matte effect. However, during the processing of BOPP matte film, bright spots may appear on the film surface, resulting in cosmetic defects that seriously impact its application. The reasons for bright spots on the BOPP matte film surface are as follows:

[0004] (1) Mirror bright spots in the matt layer: Due to the high crystallinity of the high-density polyethylene in the matt layer, large-sized spherulites are easily formed, resulting in the presence of high-density polyethylene-rich areas in the matt layer, which will reduce the scattering efficiency or form a "scattering blind area", destroying the uniform scattering structure and forming local bright spot defects.

[0005] (2) Translucent bright spots: Since the main component of the core layer of BOPP matte film is homopolymer polypropylene, and the main components of the matte layer are high-density polyethylene and copolymer polypropylene, the interfacial tension between the core layer and the matte layer is large, and local stratification is prone to occur. Light in the stratified area directly passes through the core layer, forming translucent bright spots. Summary of the Invention

[0006] Based on this, the object of the present invention is to provide a BOPP matte film and a preparation method thereof, by adding a certain proportion of hyperbranched polyethylene in the matte layer and a certain proportion of block copolymer of ethylene oxide and propylene oxide in the core layer, the two work together to improve the bright spot problem on the film surface of the BOPP matte film while ensuring the matte effect.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The present invention provides a BOPP matte film, comprising a matte layer, a core layer and a lower surface layer which are arranged in sequence; the matte layer comprises copolymerized polypropylene, 46-51 wt% of high-density polyethylene and 2-4 wt% of hyperbranched polyethylene, wherein the degree of branching of the hyperbranched polyethylene is 8-12%; the core layer comprises homopolymerized polypropylene and 6-10 wt% of a block copolymer of ethylene oxide and propylene oxide, wherein the block copolymer of ethylene oxide and propylene oxide contains 60-70 wt% of ethylene oxide segments and 30-40 wt% of propylene oxide segments.

[0009] The BOPP matte film of the present invention suppresses the crystallization of high-density polyethylene in the matte layer by adding the hyperbranched polyethylene to the matte layer, thereby reducing the specular bright spot defects of the matte layer caused by local "scattering blind areas" caused by large-sized spherulites; and adds the block copolymer of ethylene oxide and propylene oxide to the core layer, thereby building a "molecular bridge" at the interface between the core layer and the matte layer, enhancing the interlayer adhesion, suppressing local delamination, and improving the light-transmitting bright spot defects of the core layer of the BOPP matte film. The two work together to improve the film surface bright spot problem of the BOPP matte film while ensuring the matte effect.

[0010] The hyperbranched polyethylene added to the matte layer has short branches generated by the polymerization of ethylene chains in its molecules and is randomly and densely distributed, forming a three-dimensional dendritic compact structure. The hyperbranched polyethylene inhibits the crystallization of the high-density polyethylene in the matte layer through two effects: first, van der Waals forces are formed between the short branches of the hyperbranched polyethylene and the high-density polyethylene molecular chains, so that the hyperbranched polyethylene is inserted between the linear molecular chains of the high-density polyethylene during melt blending, destroying the regular arrangement of the high-density polyethylene molecular chains and hindering the crystallization of the high-density polyethylene; second, the dense distribution of the short branches of the hyperbranched polyethylene produces a steric hindrance effect, which limits the freedom of movement of the high-density polyethylene molecular chains and the crystallization diffusion path, and promotes the high-density polyethylene to form small crystals of uniform size, thereby reducing the crystallinity of the high-density polyethylene and reducing the specular bright spot defects in the matte layer caused by local "scattering blind spots" caused by large-sized spherulites of the high-density polyethylene. The present invention limits the addition amount of the hyperbranched polyethylene in the matte layer to 2-4wt%. If the addition amount of the hyperbranched polyethylene is less than 2wt%, due to the insufficient number of short branches, they cannot be completely inserted into the high-density polyethylene molecular chains to form effective interference, resulting in the high-density polyethylene still being able to form large-sized spherulites through regular arrangement of molecular chains, ultimately leading to uneven light scattering and bright spot defects in the BOPP matte film; if the addition amount of the hyperbranched polyethylene in the matte layer is greater than 4wt%, the short branches of the excessive hyperbranched polyethylene tightly wrap the high-density polyethylene molecular chains due to their highly dense distribution, making it impossible for them to crystallize regularly, resulting in anisotropic scattering structure of the matte layer, poor matte effect, local uneven light scattering and bright spot defects, and affecting the processing stability of the matte film. The present invention limits the branching degree of the hyperbranched polyethylene to 8-12%. If the branching degree of the hyperbranched polyethylene is less than 8%, the hyperbranched polyethylene molecular chains with low branching degree are close to a linear structure, the steric hindrance is small, and the interference with the crystallization process of the high-density polyethylene is relatively weak, so that the high-density polyethylene is still easy to form large-sized spherulites with high crystallinity. Local areas form "scattering blind spots" due to the large-sized spherulites, which ultimately lead to mirror bright spot defects in the matte layer. If the branching degree of the hyperbranched polyethylene is greater than 12%, the hyperbranched polyethylene molecular chains are highly branched and the intermolecular entanglement is strong, resulting in significantly reduced melt fluidity of the matte layer, difficult film formation due to sticking to the roller during production, and affected matte effect.

[0011] The ethylene oxide and propylene oxide block copolymer added to the core layer, comprising ethylene oxide segments and propylene oxide segments, can form a "molecular bridge" at the interface between the core layer and the matte layer. The propylene oxide segments in the ethylene oxide and propylene oxide block copolymer, due to their side chain methyl groups, are structurally similar to the homopolypropylene segments in the core layer, enabling them to anchor to the core layer interface through random segment entanglement and van der Waals forces. The ethylene oxide segments in the ethylene oxide and propylene oxide block copolymer, through their weakly polar ether bonds, can bridge the matte layer interface. The two (propylene oxide segments and ethylene oxide segments) are oriented at the interface, reducing the interfacial tension between the core layer and the matte layer, shifting the two layers from "high-tension repulsion" to "low-tension compatibility," enhancing interlayer adhesion, suppressing localized delamination, and improving the bright spots of light transmission in the core layer of the BOPP matte film. The present invention limits the amount of the block copolymer of ethylene oxide and propylene oxide added to the core layer to 6-10wt%. If the amount of the block copolymer of ethylene oxide and propylene oxide added to the core layer is less than 6wt%, a complete "molecular bridge" cannot be formed at the interface between the core layer and the matte layer, the interface anchor points are limited, the interfacial tension reduction and interlayer adhesion enhancement effects are weak, local delamination will still occur, and the improvement of the core layer's light-transmitting bright spots is not obvious; if the amount of the block copolymer of ethylene oxide and propylene oxide added to the core layer is greater than 10wt%, a new phase separation interface will be generated inside the core layer, the interlayer interfacial tension will rebound, the interlayer adhesion will decrease, and the bright spot problem will be aggravated. The present invention limits the total proportion of ethylene oxide segments in the block copolymer of ethylene oxide and propylene oxide to 60-70wt%, and the total proportion of propylene oxide segments to 30-40wt%; by limiting the total proportion of ethylene oxide segments and propylene oxide segments in the block copolymer of ethylene oxide and propylene oxide to be within the above range, it is beneficial to maintain processing stability. If the total proportion of ethylene oxide segments in the block copolymer of ethylene oxide and propylene oxide is less than 60wt%, and the total proportion of propylene oxide segments is greater than 40wt%, due to insufficient ethylene oxide segments, the matt layer anchor point of the "molecular bridge" is missing, resulting in limited reduction of the interfacial tension and adhesion between the core layer and the matt layer, and "bright spot" defects appear on the film surface; if the total proportion of ethylene oxide segments in the block copolymer of ethylene oxide and propylene oxide is greater than 70wt%, and the total proportion of propylene oxide segments is less than 30wt%, the core layer melt fluidity deteriorates, it is difficult to stretch and the film is easy to break, and the film processing stability deteriorates.

[0012] As a preferred embodiment of the present invention, the hyperbranched polyethylene in the matte layer has a melt index of 15-25 g / 10 min at 190°C and a load of 21.6 kg. Controlling the melt index of the hyperbranched polyethylene within the above range helps ensure the matte effect and processability of the matte layer. If the melt index of the hyperbranched polyethylene is too low, the melt flowability of the matte layer may deteriorate, making it difficult to stretch and prone to film breakage, affecting the processing stability of the matte film. If the melt index of the hyperbranched polyethylene is too high, the melt flowability of the matte layer may be good, affecting the matte effect of the matte film.

[0013] As a preferred embodiment of the present invention, in the matt layer, the preparation method of the hyperbranched polyethylene is a chain walking polymerization method. Chain walking polymerization method is a commonly used technical means in this field. Those skilled in the art can obtain the hyperbranched polyethylene of the present invention based on this method, which will not be described in detail here. The molecular structure of the hyperbranched polyethylene prepared by the chain walking polymerization method has the following exemplary structural formula:

[0014]

[0015] The short branches in the hyperbranched polyethylene molecules (such as branch 1, branch 2, ... branch n shown in the above formula) are randomly and densely distributed, forming a three-dimensional dendritic compact structure.

[0016] As a preferred solution of the present invention, in the matt layer, the copolymerized polypropylene is one or more of ethylene-propylene binary copolymerized polypropylene or ethylene-propylene-butylene terpolymer.

[0017] As a preferred embodiment of the present invention, in the matte layer, the copolymerized polypropylene has a melt index of 6-12 g / 10 min at 230°C and a load of 2.16 kg, and the high-density polyethylene has a melt index of 12-20 g / 10 min at 190°C and a load of 21.6 kg. Controlling the melt indexes of the copolymerized polypropylene and high-density polyethylene within the above ranges facilitates providing an excellent matte effect.

[0018] As a preferred solution of the present invention, in the core layer, the block copolymer of ethylene oxide and propylene oxide is at least one of an ethylene oxide-propylene oxide diblock copolymer and an ethylene oxide-propylene oxide-ethylene oxide triblock copolymer.

[0019] In the ethylene oxide-propylene oxide diblock copolymer, the ethylene oxide segment and the propylene oxide segment are respectively located at the "two ends" of the molecular structure; the propylene oxide segment at one end anchors the core layer interface through random segment entanglement and van der Waals force; the ethylene oxide segment at the other end connects to the matte layer interface through its weak polar ether bond; the two (propylene oxide segment at one end and ethylene oxide segment at the other end) are oriented at the interface, reducing the interfacial tension between the core layer and the matte layer, so that the two layers change from "high tension repulsion" to "low tension compatibility", enhancing the interlayer adhesion, inhibiting local delamination, and improving the bright spot defects in the core layer of the BOPP matte film.

[0020] In the ethylene oxide-propylene oxide-ethylene oxide triblock copolymer, the propylene oxide segment is located in the "middle" of the molecular structure, and the two ethylene oxide segments are located at both ends of the molecular structure; the propylene oxide segment located in the middle is anchored to the core layer interface through random segment entanglement and van der Waals force; the ethylene oxide segments located at both ends are connected to the matte layer interface through their weak polar ether bonds. This invention takes into account the relatively weak effect of the "weakly polar ether bonds" of the ethylene oxide segments compared to the "random segment entanglement and van der Waals forces" of the propylene oxide segments. In addition to designing the overall ratio of ethylene oxide to propylene oxide segments, the present invention utilizes a triblock molecular structure of ethylene oxide segment-propylene oxide segment-ethylene oxide segment. The two segments (the propylene oxide segment in the middle and the ethylene oxide segments at the ends) are oriented at the interface. This not only reduces the interfacial tension between the core layer and the matte layer, but also makes the interfacial tension more uniform across the interface between the core layer and the matte layer. This shifts the interfacial tension from "high-tension repulsion" to a more uniform "low-tension compatibility," enhancing interlayer adhesion, further suppressing local delamination, and improving the bright spot defects in the core layer of the BOPP matte film. Therefore, as a more preferred embodiment, the block copolymer of ethylene oxide and propylene oxide in this invention is more preferably an ethylene oxide-propylene oxide-ethylene oxide triblock copolymer. Of course, ethylene oxide-propylene oxide diblock copolymer can also meet the needs of improving the bright spot defects in the core layer of BOPP matte film.

[0021] Furthermore, in the ethylene oxide-propylene oxide-ethylene oxide triblock copolymer, the two ethylene oxide segments account for 30-35 wt% respectively, and the total proportion of the two ethylene oxide segments is 60-70 wt%.

[0022] As a preferred embodiment of the present invention, the block copolymer of ethylene oxide and propylene oxide (the ethylene oxide-propylene oxide diblock copolymer or the ethylene oxide-propylene oxide-ethylene oxide triblock copolymer) in the core layer has a melt index of 1-3 g / 10 min at 230°C under a load of 2.16 kg. Controlling the melt index of the block copolymer of ethylene oxide and propylene oxide (the ethylene oxide-propylene oxide diblock copolymer or the ethylene oxide-propylene oxide-ethylene oxide triblock copolymer) within the above range ensures good melt flow compatibility with the homopolypropylene in the core layer, thereby reducing bright spots on the film surface and ensuring processing stability. If the melt index of the block copolymer of ethylene oxide and propylene oxide (the ethylene oxide-propylene oxide diblock copolymer or the ethylene oxide-propylene oxide-ethylene oxide triblock copolymer) is too low, the fluidity of the core layer melt deteriorates, which is not conducive to its dispersion in the core layer, and there may be an increase in translucent bright spots; if the melt index of the block copolymer of ethylene oxide and propylene oxide (the ethylene oxide-propylene oxide diblock copolymer or the ethylene oxide-propylene oxide-ethylene oxide triblock copolymer) is too high, it is not conducive to the stable co-extrusion of the core layer melt and affects the processing stability.

[0023] As a preferred embodiment of the present invention, in the core layer, the preparation method of the ethylene oxide-propylene oxide block copolymer (the ethylene oxide-propylene oxide diblock copolymer or the ethylene oxide-propylene oxide-ethylene oxide triblock copolymer) is an anionic ring-opening polymerization method, which uses a strong alkaline initiator (such as hydroxide, alkoxide) to initiate anionic ring-opening polymerization of ethylene oxide or propylene oxide, and realizes a block structure by step-by-step addition of monomers to prepare the ethylene oxide and propylene oxide block copolymer (the ethylene oxide-propylene oxide diblock copolymer or the ethylene oxide-propylene oxide-ethylene oxide triblock copolymer).

[0024] As a preferred solution of the present invention, the core layer further comprises 0.5-1.0 wt% of an antistatic agent masterbatch.

[0025] As a preferred solution of the present invention, the effective content of the antistatic agent in the antistatic agent masterbatch is 35-50wt%, and the carrier is homopolypropylene.

[0026] As a preferred solution of the present invention, the homopolypropylene in the core layer has a melt index of 2-5 g / 10 min at 230° C. and a load of 2.16 kg.

[0027] As a preferred solution of the lower surface layer, the lower surface layer is a smooth lower surface layer, comprising homopolypropylene and 0.5-1.0 wt % anti-blocking agent masterbatch.

[0028] As a preferred solution of the present invention, in the lower surface layer, the homopolypropylene has a melt index of 2-5 g / 10 min at 230° C. and a load of 2.16 kg.

[0029] As a preferred solution of the present invention, the effective content of the anti-blocking agent in the anti-blocking agent masterbatch is 5-6 wt %, the anti-blocking agent is preferably fumed silica with an average particle size (D50) of 4.0-5.0 μm, and the carrier is homopolypropylene.

[0030] As another preferred embodiment of the lower surface layer, the lower surface layer is a matte lower surface layer, comprising copolymerized polypropylene, 46-51 wt% high-density polyethylene and 2-4 wt% hyperbranched polyethylene, wherein the degree of branching of the hyperbranched polyethylene is 8-12%.

[0031] As a preferred embodiment of the present invention, the hyperbranched polyethylene in the lower surface layer has a melt index of 15-25 g / 10 min at 190° C. and a load of 21.6 kg. Controlling the melt index of the hyperbranched polyethylene within this range helps ensure the matte effect and processing performance of the lower surface layer.

[0032] As a preferred solution of the present invention, in the lower surface layer, the hyperbranched polyethylene is prepared by chain walking polymerization.

[0033] As a preferred solution of the present invention, in the lower surface layer, the copolymerized polypropylene is one or more of ethylene-propylene binary copolymerized polypropylene or ethylene-propylene-butylene terpolymer.

[0034] As a preferred embodiment of the present invention, the copolymerized polypropylene in the lower surface layer has a melt index of 6-12 g / 10 min at 230°C and a load of 2.16 kg, and the high-density polyethylene has a melt index of 12-20 g / 10 min at 190°C and a load of 21.6 kg. Controlling the melt indexes of the copolymerized polypropylene and high-density polyethylene within the aforementioned ranges facilitates providing an excellent matte effect.

[0035] As a preferred embodiment of the present invention, the thickness of the matte layer is 1.5-2.3 μm, the thickness of the lower surface layer is 0.7-0.9 μm or 1.5-2.3 μm (when the lower surface layer is a glossy lower surface layer, the thickness is 0.7-0.9 μm; when the lower surface layer is a matte lower surface layer, the thickness is 1.5-2.3 μm), and the total thickness of the BOPP matte film is 16-23 μm.

[0036] The present invention also provides a method for preparing any of the above-mentioned BOPP matte films, comprising the following steps: the raw materials of the matte layer, the core layer and the lower surface layer are weighed in a dry ratio and then added to each extruder; the raw materials of each layer are melted and plasticized in each extruder and then metered by a metering pump; then, according to different extruder flow channels, they are merged at a T-die to form a thick sheet; after the thick sheet is extruded, it is chilled and cast; after the cast sheet is shaped, it first enters a longitudinal stretching zone for longitudinal stretching and then enters a transverse stretching zone for transverse stretching; after the biaxial stretching of the film is completed, it is trimmed, corona treated, rolled up, and aged; finally, it is slit and packaged to obtain the BOPP matte film.

[0037] As a preferred embodiment of the present invention, the extrusion temperature of the matte layer is 230-255°C; the extruder temperature of the core layer and the lower surface layer is 230-260°C (when the lower surface layer is a glossy lower surface layer, the temperature is preferably 250-260°C; when the lower surface layer is a matte lower surface layer, the temperature is preferably 230-255°C); the temperature of the T-die is 230-245°C, the temperature of the chilled roller is 30-35°C, the temperature of the longitudinal stretching preheating roller is between 128-145°C, the temperature of the longitudinal stretching zone is 120-135°C, the longitudinal stretching ratio is 4-5 times, the transverse stretching preheating temperature is 160-175°C, the temperature of the transverse stretching zone is 155-165°C, and the transverse stretching ratio is 7-9 times. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic structural diagram of the BOPP matte film of the present invention. DETAILED DESCRIPTION

[0039] To facilitate understanding of the present invention, the present invention will be described in more detail below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0040] For the components and contents of each layer of the BOPP matte film in the following examples or comparative examples, please refer to Table 1 below:

[0041] Table 1 BOPP matte film formulations of Examples 1-5 and Comparative Examples 1-11

[0042]

[0043] In the following examples or comparative examples:

[0044] Homopolymer polypropylene in the core layer and the lower skin layer: melt index is 3 g / 10 min (230°C, 2.16 kg).

[0045] Copolymer polypropylene in the matt layer and the lower surface layer: ethylene-propylene binary copolymer polypropylene, with a melt index of 9 g / 10 min (230° C., 2.16 kg).

[0046] Antistatic agent masterbatch: The effective component is glycerol monostearate, the effective content is 42wt%, and the carrier is homopolymer polypropylene.

[0047] Anti-blocking agent masterbatch: The effective component is fumed silica, the effective content is 5.5wt%, the average particle size (D50) is 4.5μm, and the carrier is homopolymer polypropylene.

[0048] Hyperbranched polyethylene: The preparation method is chain walking polymerization.

[0049] Ethylene oxide-propylene oxide diblock copolymer: The preparation method is anionic ring-opening polymerization, which uses a strong alkaline initiator (such as hydroxide, alkoxide) to initiate the anionic ring-opening polymerization of ethylene oxide or propylene oxide. The block structure is achieved by step-by-step addition of monomers to prepare ethylene oxide-propylene oxide diblock copolymer. The ethylene oxide-propylene oxide diblock copolymer has a diblock molecular structure (ethylene oxide chain segment-propylene oxide chain segment).

[0050] Ethylene oxide-propylene oxide-ethylene oxide triblock copolymer: The preparation method is anionic ring-opening polymerization, using a strong alkaline initiator (such as hydroxide, alkoxide) to initiate the anionic ring-opening polymerization of ethylene oxide or propylene oxide, and the block structure is achieved by step-by-step addition of monomers to prepare ethylene oxide-propylene oxide-ethylene oxide triblock copolymer. The ethylene oxide-propylene oxide-ethylene oxide triblock copolymer has a triblock molecular structure (ethylene oxide segment-propylene oxide segment-ethylene oxide segment).

[0051] Example 1

[0052] This embodiment provides a BOPP matte film, please refer to Figure 1 , including a matt layer 1, a core layer 2 and a lower surface layer 3 arranged in sequence, wherein the components of each layer are shown in Table 1 and the following specific components:

[0053] Matt layer 1: 52 wt% copolymerized polypropylene (melt index of 9 g / 10 min), 46 wt% high-density polyethylene (melt index of 16 g / 10 min) and 2 wt% hyperbranched polyethylene (melt index of 15 g / 10 min, degree of branching of 8%).

[0054] Core layer 2: 89.5wt% homopolypropylene (melt index of 3g / 10min), 10wt% ethylene oxide-propylene oxide diblock copolymer (melt index of 3g / 10min, total ethylene oxide segment proportion of 60wt%, total propylene oxide segment proportion of 40wt%) and 0.5wt% antistatic agent masterbatch.

[0055] Lower surface layer 3: 99.5wt% homopolymer polypropylene (melt index of 3g / 10min) and 0.5wt% anti-blocking agent masterbatch.

[0056] The preparation method of the BOPP matte film of this embodiment comprises the following steps:

[0057] The raw materials of each layer are added to each extruder after being weighed in a dry ratio, wherein the temperature of the extruders of the core layer 2 and the lower surface layer 3 is 250°C, and the temperature of the extruder of the matt layer 1 is 240°C. The raw materials of each layer are melted and plasticized in each extruder and then metered by a metering pump. Then they enter different extruder flow channels, merge and extrude at the T-die, and are cast into thick sheets through chilled rollers. After the thick sheets are extruded, they are chilled and cast. After the cast sheets are shaped, they first enter the longitudinal stretching zone for longitudinal stretching preheating, and then longitudinal stretching is performed. The longitudinal stretching ratio is 5 times, and the longitudinal stretching temperature is 125°C. After the longitudinal stretching is shaped, they enter the transverse stretching zone for transverse stretching preheating, and then transverse stretching is performed. The transverse stretching ratio is 8 times, and the transverse stretching temperature is 160°C. After the biaxial stretching of the film is completed, the edges are trimmed and trimmed, followed by corona treatment, winding, and aging treatment, and finally slitting and packaging to obtain the finished product.

[0058] The total thickness of the BOPP matte film of this embodiment is 21 μm, the matte layer 1 has a thickness of 1.5 μm, the core layer 2 has a thickness of 18.7 μm, and the lower surface layer 3 has a thickness of 0.8 μm.

[0059] Example 2

[0060] This embodiment provides a BOPP matte film, please refer to Figure 1 , including a matt layer 1, a core layer 2 and a lower surface layer 3 arranged in sequence, wherein the components of each layer are shown in Table 1 and the following specific components:

[0061] Matt layer 1: 50 wt% copolymerized polypropylene (melt index of 9 g / 10 min), 46 wt% high-density polyethylene (melt index of 16 g / 10 min) and 4 wt% hyperbranched polyethylene (melt index of 20 g / 10 min, degree of branching of 10%).

[0062] Core layer 2: 93.5wt% homopolypropylene (melt index of 3g / 10min), 6wt% ethylene oxide-propylene oxide diblock copolymer (melt index of 1g / 10min, total ethylene oxide segment proportion of 65wt%, total propylene oxide segment proportion of 35wt%) and 0.5wt% antistatic agent masterbatch.

[0063] Lower surface layer 3: 99.5wt% homopolymer polypropylene (melt index of 3g / 10min) and 0.5wt% anti-blocking agent masterbatch.

[0064] The preparation method of the BOPP matte film of this embodiment is the same as that of Example 1.

[0065] The total thickness and thickness of each layer of the BOPP matte film of this embodiment are the same as those of Example 1.

[0066] Example 3

[0067] This embodiment provides a BOPP matte film, please refer to Figure 1 , including a matt layer 1, a core layer 2 and a lower surface layer 3 arranged in sequence, wherein the components of each layer are shown in Table 1 and the following specific components:

[0068] Matt layer 1: 51wt% copolymerized polypropylene (melt index of 9g / 10min), 46wt% high-density polyethylene (melt index of 16g / 10min) and 3wt% hyperbranched polyethylene (melt index of 25g / 10min, degree of branching of 12%).

[0069] Core layer 2: 91.5wt% homopolypropylene (melt index of 3g / 10min), 8wt% ethylene oxide-propylene oxide diblock copolymer (melt index of 2g / 10min, total ethylene oxide segment proportion of 70wt%, total propylene oxide segment proportion of 30wt%) and 0.5wt% antistatic agent masterbatch.

[0070] Lower surface layer 3: 99.5wt% homopolymer polypropylene (melt index of 3g / 10min) and 0.5wt% anti-blocking agent masterbatch.

[0071] The preparation method of the BOPP matte film of this embodiment is the same as that of Example 1.

[0072] The total thickness and thickness of each layer of the BOPP matte film of this embodiment are the same as those of Example 1.

[0073] Example 4

[0074] This embodiment provides a BOPP matte film, please refer to Figure 1 , including a matt layer 1, a core layer 2 and a lower surface layer 3 arranged in sequence, wherein the components of each layer are shown in Table 1 and the following specific components:

[0075] Matt layer 1: 51wt% copolymerized polypropylene (melt index of 9g / 10min), 46wt% high-density polyethylene (melt index of 16g / 10min) and 3wt% hyperbranched polyethylene (melt index of 20g / 10min, branching degree of 10%).

[0076] Core layer 2: 91.5wt% homopolypropylene (melt index 3g / 10min), 8wt% ethylene oxide-propylene oxide diblock copolymer (melt index 2g / 10min, total ethylene oxide segment proportion of 65wt%, total propylene oxide segment proportion of 35wt%) and 0.5wt% antistatic agent masterbatch.

[0077] Lower surface layer 3: 48 wt% copolymerized polypropylene (melt index 9 g / 10 min), 49 wt% high-density polyethylene (melt index 16 g / 10 min) and 3 wt% hyperbranched polyethylene (melt index 20 g / 10 min, branching degree 10%).

[0078] The preparation method of the BOPP matte film of this embodiment is basically the same as that of Example 1, except that the temperature of the extruder of the lower surface layer 3 is 240°C.

[0079] The total thickness of the BOPP matte film of this embodiment is 21.7 μm, the matte layer 1 has a thickness of 1.5 μm, the core layer 2 has a thickness of 18.7 μm, and the lower surface layer 3 has a thickness of 1.5 μm.

[0080] Example 5

[0081] This embodiment provides a BOPP matte film, please refer to Figure 1 , including a matt layer 1, a core layer 2 and a lower surface layer 3 arranged in sequence, wherein the components of each layer are shown in Table 1 and the following specific components:

[0082] Matt layer 1: 51wt% copolymerized polypropylene (melt index of 9g / 10min), 46wt% high-density polyethylene (melt index of 16g / 10min) and 3wt% hyperbranched polyethylene (melt index of 25g / 10min, degree of branching of 12%).

[0083] Core layer 2: 91.5wt% homopolypropylene (melt index is 3g / 10min), 8wt% ethylene oxide-propylene oxide-ethylene oxide triblock copolymer (melt index is 2g / 10min, the total proportion of ethylene oxide segments is 70wt%, of which the two ethylene oxide segments at both ends account for 35wt% respectively, and the total proportion of propylene oxide segments is 30wt%) and 0.5wt% antistatic agent masterbatch.

[0084] Lower surface layer 3: 99.5wt% homopolymer polypropylene (melt index of 3g / 10min) and 0.5wt% anti-blocking agent masterbatch.

[0085] The preparation method of the BOPP matte film of this embodiment is the same as that of Example 1.

[0086] The total thickness and thickness of each layer of the BOPP matte film of this embodiment are the same as those of Example 1.

[0087] Comparative Example 1

[0088] This comparative example provides a BOPP matte film, please refer to Figure 1 , including a matt layer 1, a core layer 2 and a lower surface layer 3 arranged in sequence, wherein the components of each layer are shown in Table 1 and the following specific components:

[0089] Matt layer 1: 53 wt% copolymerized polypropylene (melt index 9 g / 10 min) and 47 wt% high-density polyethylene (melt index 16 g / 10 min).

[0090] Core layer 2: 99.5wt% homopolypropylene (melt index 3g / 10min) and 0.5wt% antistatic agent masterbatch.

[0091] Lower surface layer 3: 99.5wt% homopolymer polypropylene (melt index of 3g / 10min) and 0.5wt% anti-blocking agent masterbatch.

[0092] The preparation method of the BOPP matte film of this comparative example is the same as that of Example 1.

[0093] The total thickness and thickness of each layer of the BOPP matte film in this comparative example are the same as those in Example 1.

[0094] Comparative Example 2

[0095] This comparative example provides a BOPP matte film, please refer to Figure 1 , including a matt layer 1, a core layer 2 and a lower surface layer 3 arranged in sequence, wherein the components of each layer are shown in Table 1 and the following specific components:

[0096] Matt layer 1: 48 wt% copolymerized polypropylene (melt index of 9 g / 10 min), 49 wt% high-density polyethylene (melt index of 16 g / 10 min) and 3 wt% hyperbranched polyethylene (melt index of 20 g / 10 min, branching degree of 10%).

[0097] Core layer 2: 99.5wt% homopolypropylene (melt index 3g / 10min) and 0.5wt% antistatic agent masterbatch.

[0098] Lower surface layer 3: 99.5wt% homopolymer polypropylene (melt index of 3g / 10min) and 0.5wt% anti-blocking agent masterbatch.

[0099] The preparation method of the BOPP matte film of this comparative example is the same as that of Example 1.

[0100] The total thickness and thickness of each layer of the BOPP matte film in this comparative example are the same as those in Example 1.

[0101] Comparative Example 3

[0102] This comparative example provides a BOPP matte film, please refer to Figure 1 , including a matt layer 1, a core layer 2 and a lower surface layer 3 arranged in sequence, wherein the components of each layer are shown in Table 1 and the following specific components:

[0103] Matt layer 1: 50 wt% copolymerized polypropylene (melt index 9 g / 10 min) and 50 wt% high-density polyethylene (melt index 16 g / 10 min).

[0104] Core layer 2: 91.5wt% homopolypropylene (melt index 3g / 10min), 8wt% ethylene oxide-propylene oxide diblock copolymer (melt index 2g / 10min, total ethylene oxide segment proportion of 65wt%, total propylene oxide segment proportion of 35wt%) and 0.5wt% antistatic agent masterbatch.

[0105] Lower surface layer 3: 99.5wt% homopolymer polypropylene (melt index of 3g / 10min) and 0.5wt% anti-blocking agent masterbatch.

[0106] The preparation method of the BOPP matte film of this comparative example is the same as that of Example 1.

[0107] The total thickness and thickness of each layer of the BOPP matte film in this comparative example are the same as those in Example 1.

[0108] Comparative Example 4

[0109] This comparative example provides a BOPP matte film, please refer to Figure 1 , including a matt layer 1, a core layer 2 and a lower surface layer 3 arranged in sequence, wherein the components of each layer are shown in Table 1 and the following specific components:

[0110] Matt layer 1: 51wt% copolymerized polypropylene (melt index of 9g / 10min), 46wt% high-density polyethylene (melt index of 16g / 10min) and 3wt% hyperbranched polyethylene (melt index of 20g / 10min, branching degree of 10%).

[0111] Core layer 2: 84.5wt% homopolypropylene (melt index of 3g / 10min), 15wt% ethylene oxide-propylene oxide diblock copolymer (melt index of 2g / 10min, total ethylene oxide segment proportion of 65wt%, total propylene oxide segment proportion of 35wt%) and 0.5wt% antistatic agent masterbatch.

[0112] Lower surface layer 3: 99.5wt% homopolymer polypropylene (melt index of 3g / 10min) and 0.5wt% anti-blocking agent masterbatch.

[0113] The preparation method of the BOPP matte film of this comparative example is the same as that of Example 1.

[0114] The total thickness and thickness of each layer of the BOPP matte film in this comparative example are the same as those in Example 1.

[0115] Comparative Example 5

[0116] This comparative example provides a BOPP matte film, please refer to Figure 1 , including a matt layer 1, a core layer 2 and a lower surface layer 3 arranged in sequence, wherein the components of each layer are shown in Table 1 and the following specific components:

[0117] Matt layer 1: 51wt% copolymerized polypropylene (melt index of 9g / 10min), 46wt% high-density polyethylene (melt index of 16g / 10min) and 3wt% hyperbranched polyethylene (melt index of 20g / 10min, branching degree of 10%).

[0118] Core layer 2: 96.5wt% homopolypropylene (melt index of 3g / 10min), 3wt% ethylene oxide-propylene oxide diblock copolymer (melt index of 2g / 10min, total ethylene oxide segment proportion of 65wt%, total propylene oxide segment proportion of 35wt%) and 0.5wt% antistatic agent masterbatch.

[0119] Lower surface layer 3: 99.5wt% homopolymer polypropylene (melt index of 3g / 10min) and 0.5wt% anti-blocking agent masterbatch.

[0120] The preparation method of the BOPP matte film of this comparative example is the same as that of Example 1.

[0121] The total thickness and thickness of each layer of the BOPP matte film in this comparative example are the same as those in Example 1.

[0122] Comparative Example 6

[0123] This comparative example provides a BOPP matte film, please refer to Figure 1 , including a matt layer 1, a core layer 2 and a lower surface layer 3 arranged in sequence, wherein the components of each layer are shown in Table 1 and the following specific components:

[0124] Matt layer 1: 44 wt% copolymerized polypropylene (melt index of 9 g / 10 min), 46 wt% high-density polyethylene (melt index of 16 g / 10 min) and 10 wt% hyperbranched polyethylene (melt index of 20 g / 10 min, branching degree of 10%).

[0125] Core layer 2: 91.5wt% homopolypropylene (melt index 3g / 10min), 8wt% ethylene oxide-propylene oxide diblock copolymer (melt index 2g / 10min, total ethylene oxide segment proportion of 65wt%, total propylene oxide segment proportion of 35wt%) and 0.5wt% antistatic agent masterbatch.

[0126] Lower surface layer 3: 99.5wt% homopolymer polypropylene (melt index of 3g / 10min) and 0.5wt% anti-blocking agent masterbatch.

[0127] The preparation method of the BOPP matte film of this comparative example is the same as that of Example 1.

[0128] The total thickness and thickness of each layer of the BOPP matte film in this comparative example are the same as those in Example 1.

[0129] Comparative Example 7

[0130] This comparative example provides a BOPP matte film, please refer to Figure 1 , including a matt layer 1, a core layer 2 and a lower surface layer 3 arranged in sequence, wherein the components of each layer are shown in Table 1 and the following specific components:

[0131] Matt layer 1: 53.5wt% copolymerized polypropylene (melt index of 9g / 10min), 46wt% high-density polyethylene (melt index of 16g / 10min) and 0.5wt% hyperbranched polyethylene (melt index of 20g / 10min, branching degree of 10%).

[0132] Core layer 2: 91.5wt% homopolypropylene (melt index 3g / 10min), 8wt% ethylene oxide-propylene oxide diblock copolymer (melt index 2g / 10min, total ethylene oxide segment proportion of 65wt%, total propylene oxide segment proportion of 35wt%) and 0.5wt% antistatic agent masterbatch.

[0133] Lower surface layer 3: 99.5wt% homopolymer polypropylene (melt index of 3g / 10min) and 0.5wt% anti-blocking agent masterbatch.

[0134] The preparation method of the BOPP matte film of this comparative example is the same as that of Example 1.

[0135] The total thickness and thickness of each layer of the BOPP matte film in this comparative example are the same as those in Example 1.

[0136] Comparative Example 8

[0137] This comparative example provides a BOPP matte film, please refer to Figure 1 , including a matt layer 1, a core layer 2 and a lower surface layer 3 arranged in sequence, wherein the components of each layer are shown in Table 1 and the following specific components:

[0138] Matt layer 1: 51wt% copolymerized polypropylene (melt index of 9g / 10min), 46wt% high-density polyethylene (melt index of 16g / 10min) and 3wt% hyperbranched polyethylene (melt index of 7g / 10min, branching degree of 4%).

[0139] Core layer 2: 91.5wt% homopolypropylene (melt index 3g / 10min), 8wt% ethylene oxide-propylene oxide diblock copolymer (melt index 2g / 10min, total ethylene oxide segment proportion of 65wt%, total propylene oxide segment proportion of 35wt%) and 0.5wt% antistatic agent masterbatch.

[0140] Lower surface layer 3: 99.5wt% homopolymer polypropylene (melt index of 3g / 10min) and 0.5wt% anti-blocking agent masterbatch.

[0141] The preparation method of the BOPP matte film of this comparative example is the same as that of Example 1.

[0142] The total thickness and thickness of each layer of the BOPP matte film in this comparative example are the same as those in Example 1.

[0143] Comparative Example 9

[0144] This comparative example provides a BOPP matte film, please refer to Figure 1 , including a matt layer 1, a core layer 2 and a lower surface layer 3 arranged in sequence, wherein the components of each layer are shown in Table 1 and the following specific components:

[0145] Matt layer 1: 51wt% copolymerized polypropylene (melt index of 9g / 10min), 46wt% high-density polyethylene (melt index of 16g / 10min) and 3wt% hyperbranched polyethylene (melt index of 35g / 10min, degree of branching of 18%).

[0146] Core layer 2: 91.5wt% homopolypropylene (melt index 3g / 10min), 8wt% ethylene oxide-propylene oxide diblock copolymer (melt index 2g / 10min, total ethylene oxide segment proportion of 65wt%, total propylene oxide segment proportion of 35wt%) and 0.5wt% antistatic agent masterbatch.

[0147] Lower surface layer 3: 99.5wt% homopolymer polypropylene (melt index of 3g / 10min) and 0.5wt% anti-blocking agent masterbatch.

[0148] The preparation method of the BOPP matte film of this comparative example is the same as that of Example 1.

[0149] The total thickness and thickness of each layer of the BOPP matte film in this comparative example are the same as those in Example 1.

[0150] Comparative Example 10

[0151] This comparative example provides a BOPP matte film, please refer to Figure 1, including a matt layer 1, a core layer 2 and a lower surface layer 3 arranged in sequence, wherein the components of each layer are shown in Table 1 and the following specific components:

[0152] Matt layer 1: 51 wt% copolymerized polypropylene (melt index of 9 g / 10 min), 46 wt% high-density polyethylene (melt index of 16 g / 10 min) and 3 wt% hyperbranched polyethylene (melt index of 20 g / 10 min, branching degree of 10%).

[0153] Core layer 2: 91.5wt% homopolypropylene (melt index of 3g / 10min), 8wt% ethylene oxide-propylene oxide diblock copolymer (melt index of 4g / 10min, total ethylene oxide segment proportion of 40wt%, total propylene oxide segment proportion of 60wt%) and 0.5wt% antistatic agent masterbatch.

[0154] Lower surface layer 3: 99.5wt% homopolymer polypropylene (melt index of 3g / 10min) and 0.5wt% anti-blocking agent masterbatch.

[0155] The preparation method of the BOPP matte film of this comparative example is the same as that of Example 1.

[0156] The total thickness and thickness of each layer of the BOPP matte film in this comparative example are the same as those in Example 1.

[0157] Comparative Example 11

[0158] This comparative example provides a BOPP matte film, please refer to Figure 1 , including a matt layer 1, a core layer 2 and a lower surface layer 3 arranged in sequence, wherein the components of each layer are shown in Table 1 and the following specific components:

[0159] Matt layer 1: 51 wt% copolymerized polypropylene (melt index of 9 g / 10 min), 46 wt% high-density polyethylene (melt index of 16 g / 10 min) and 3 wt% hyperbranched polyethylene (melt index of 20 g / 10 min, branching degree of 10%).

[0160] Core layer 2: 91.5wt% homopolypropylene (melt index 3g / 10min), 8wt% ethylene oxide-propylene oxide diblock copolymer (melt index 0.8g / 10min, total ethylene oxide segment proportion of 90wt%, total propylene oxide segment proportion of 10wt%) and 0.5wt% antistatic agent masterbatch.

[0161] Lower surface layer 3: 99.5wt% homopolymer polypropylene (melt index of 3g / 10min) and 0.5wt% anti-blocking agent masterbatch.

[0162] The preparation method of the BOPP matte film of this comparative example is the same as that of Example 1.

[0163] The total thickness and thickness of each layer of the BOPP matte film in this comparative example are the same as those in Example 1.

[0164] Performance testing

[0165] The BOPP matte films of Examples 1-5 and Comparative Examples 1-11 were subjected to the following performance tests:

[0166] Gloss: According to GB / T 10003-2008 standard, measured using the 45° angle method;

[0167] Haze: measured according to GB / T 10003-2008 standard;

[0168] Bright spot density: The test method uses a high-speed line array camera to detect the number of visible bright spots per unit area, with the unit being / m².

[0169] The results are shown in Table 2:

[0170] Table 2 Performance test results of BOPP matte films of Examples 1-5 and Comparative Examples 1-11

[0171]

[0172] From the above performance test data, we can see that:

[0173] The BOPP matte films of Examples 1-5 of the present invention incorporate 2-4 wt% of hyperbranched polyethylene (with a degree of branching of 8-12%) into the matte layer and 6-10 wt% of a block copolymer of ethylene oxide and propylene oxide (e.g., an ethylene oxide-propylene oxide diblock copolymer or an ethylene oxide-propylene oxide-ethylene oxide triblock copolymer, wherein the ethylene oxide segments comprise 60-70 wt% and the propylene oxide segments comprise 30-40 wt%) into the core layer. These two components synergistically improve the bright spot problem of the BOPP matte film while maintaining a matte effect and facilitating a smooth production process. The BOPP matte film of Example 5, in which the ethylene oxide-propylene oxide-ethylene oxide triblock copolymer is incorporated into the core layer, achieves the best effect in improving the bright spot problem.

[0174] In the BOPP matte film of Comparative Example 1, no hyperbranched polyethylene is added to the matte layer, and no block copolymer of ethylene oxide and propylene oxide (such as ethylene oxide-propylene oxide diblock copolymer, ethylene oxide-propylene oxide-ethylene oxide triblock copolymer) is added to the core layer. The BOPP matte film of Comparative Example 1 has many bright spots.

[0175] In the BOPP matte film of Comparative Example 2, the core layer does not contain block copolymers of ethylene oxide and propylene oxide (such as ethylene oxide-propylene oxide diblock copolymer and ethylene oxide-propylene oxide-ethylene oxide triblock copolymer). The interfacial tension between the core layer and the matte layer is high, the interlayer adhesion is weak, and the improvement of the bright spots of the matte film is not obvious.

[0176] In the BOPP matte film of Comparative Example 3, no hyperbranched polyethylene is added to the matte layer. The high-density polyethylene has high crystallinity and is prone to forming large-sized spherulites. The local "scattering blind area" caused by the large-sized spherulites of high-density polyethylene leads to bright spot defects in the matte film, and the improvement of the bright spots of the matte film is not obvious.

[0177] In the BOPP matte film of Comparative Example 4, the addition amount of ethylene oxide-propylene oxide diblock copolymer in the core layer is greater than 10 wt %, a new phase separation interface is generated inside the core layer, the interlayer interfacial tension increases, and the interlayer adhesion decreases, exacerbating the bright spot problem defect.

[0178] In the BOPP matte film of Comparative Example 5, the amount of ethylene oxide-propylene oxide diblock copolymer added to the core layer is less than 6 wt %, and a complete "molecular bridge" cannot be formed at the interface between the core layer and the matte layer. The interface anchor points are limited, the interfacial tension reduction and interlayer adhesion enhancement effects are weak, local delamination still occurs, and the improvement of the light-transmitting bright spots is not obvious.

[0179] In the BOPP matte film of Comparative Example 6, the amount of hyperbranched polyethylene added to the matte layer is greater than 4 wt %. The excessive hyperbranched polyethylene causes the scattering structure of the matte layer to be anisotropic, the matte effect to deteriorate, and local light scattering to be uneven and produce bright spot defects, while affecting the processing stability of the matte film.

[0180] In the BOPP matte film of Comparative Example 7, the amount of hyperbranched polyethylene added to the matte layer is less than 2 wt %. Due to the insufficient number of short chain branches, they cannot be completely inserted into the high-density polyethylene molecular chains to form effective interference, which ultimately leads to uneven light scattering of the BOPP matte film and the inability to effectively reduce the bright spots of the matte film.

[0181] In the BOPP matte film of Comparative Example 8, the branching degree of the hyperbranched polyethylene in the matte layer is less than 8%. Due to the low branching degree, the hyperbranched polyethylene molecular chain is close to a linear structure, the steric hindrance is small, and the interference with the crystallization process of high-density polyethylene is weak. Large-sized spherulites in local areas form a "scattering blind area". The matte film still has many bright spots, and the film is often broken and difficult to form.

[0182] In the BOPP matte film of Comparative Example 9, the degree of branching of the hyperbranched polyethylene in the matte layer is greater than 12%. Since the hyperbranched polyethylene molecular chain is highly branched, the melt index is too high, and the intermolecular entanglement is strong, the fluidity of the matte layer is significantly reduced, and it is difficult to form a film on the sticky roller, which affects the matte effect.

[0183] In the BOPP matte film of Comparative Example 10, the proportion of ethylene oxide segments in the ethylene oxide-propylene oxide diblock copolymer in the core layer is less than 60wt%, and the proportion of propylene oxide segments is greater than 40wt%. The melt index is too high, and due to insufficient ethylene oxide segments, the anchor point of the matte layer of the "molecular bridge" is missing, resulting in limited improvement in the interfacial tension and adhesion between the core layer and the matte layer, and "bright spot" defects appear on the film surface.

[0184] In the BOPP matte film of Comparative Example 11, the ethylene oxide segment in the core layer of the ethylene oxide-propylene oxide diblock copolymer accounts for more than 70wt%, and the propylene oxide segment accounts for less than 30wt%. The melt index is too low, the fluidity of the core layer components deteriorates, the film is difficult to stretch and easily broken, and the film processing stability deteriorates.

[0185] The above-described embodiments merely represent several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous modifications and improvements without departing from the spirit of the present invention, and the present invention is intended to encompass such modifications and variations.

Claims

1. A BOPP matte film, characterized by: The invention comprises a matte layer, a core layer and a lower surface layer which are arranged in sequence; the matte layer comprises copolymerized polypropylene, 46-51 wt% high-density polyethylene and 2-4 wt% hyperbranched polyethylene, the branching degree of the hyperbranched polyethylene is 8-12%, and the hyperbranched polyethylene in the matte layer has a melt index of 15-25 g / 10 min at 190° C. and a load of 21.6 kg; the core layer comprises homopolymerized polypropylene and 6-10 wt% of a block copolymer of ethylene oxide and propylene oxide, the total proportion of ethylene oxide segments in the block copolymer of ethylene oxide and propylene oxide is 60-70 wt%, and the total proportion of propylene oxide segments is 30-40 wt%, and the melt index of the block copolymer of ethylene oxide and propylene oxide is 1-3 g / 10 min at 230° C. and a load of 2.16 kg.

2. The BOPP matte film according to claim 1, characterized in that: In the matt layer, the copolymerized polypropylene has a melt index of 6-12 g / 10 min at 230° C. and a load of 2.16 kg, and the high-density polyethylene has a melt index of 12-20 g / 10 min at 190° C. and a load of 21.6 kg.

3. The BOPP matte film according to claim 1, characterized in that: The block copolymer of ethylene oxide and propylene oxide is at least one of an ethylene oxide-propylene oxide diblock copolymer and an ethylene oxide-propylene oxide-ethylene oxide triblock copolymer.

4. The BOPP matte film according to claim 3, characterized in that: The ethylene oxide-propylene oxide diblock copolymer and / or the ethylene oxide-propylene oxide-ethylene oxide triblock copolymer has a melt index of 1-3 g / 10 min at 230° C. and a load of 2.16 kg.

5. The BOPP matte film according to claim 1, characterized in that: The core layer further comprises 0.5-1.0 wt% of an antistatic agent masterbatch; the effective content of the antistatic agent in the antistatic agent masterbatch is 35-50 wt%, and the carrier is homopolypropylene.

6. The BOPP matte film according to claim 1, characterized in that: The lower surface layer comprises homopolymer polypropylene and 0.5-1.0 wt % of anti-blocking agent masterbatch.

7. The BOPP matte film according to claim 1, characterized in that: The lower surface layer comprises copolymerized polypropylene, 46-51 wt% high-density polyethylene and 2-4 wt% hyperbranched polyethylene, and the branching degree of the hyperbranched polyethylene is 8-12%.

8. The BOPP matte film according to claim 1, characterized in that: The matt layer has a thickness of 1.5-2.3 μm, the lower surface layer has a thickness of 0.7-0.9 μm or 1.5-2.3 μm, and the total thickness of the BOPP matt film is 16-23 μm.

9. A method for preparing the BOPP matte film according to any one of claims 1 to 8, characterized in that: The following steps are involved: The raw materials of the matt layer, the core layer and the lower surface layer are weighed in a dry ratio and then added to each extruder. The raw materials of each layer are melted and plasticized in each extruder and then metered by a metering pump. Then, according to different extruder flow channels, they are merged at a T-die to form a thick sheet. After the thick sheet is extruded, it is chilled and cast. After the cast sheet is shaped, it first enters a longitudinal stretching zone for longitudinal stretching and then enters a transverse stretching zone for transverse stretching. After the biaxial stretching of the film is completed, it is trimmed, corona treated, rolled, and aged, and finally slit and packaged to obtain the BOPP matt film.

Images