Lightweight anti-shrinkage BOPP (biaxially-oriented polypropylene) laser film and preparation method thereof

Abstract

The invention relates to the field of films, in particular to a light-weight anti-shrinkage BOPP (biaxially-oriented polypropylene) laser film and a preparation method thereof.The laser film comprises a mold pressing layer, an upper secondary surface layer, a core layer, a lower secondary surface layer and a light layer which are sequentially arranged, the total thickness is 13-15 microns, and the mold pressing layer comprises ethylene-propylene binary co-polypropylene; the weight-average molecular weight of first homo-polypropylene in the core layer is 250000-35000 g / mol, the number-average molecular weight of the first homo-polypropylene in the core layer is 90000-160000 g / mol, the molecular weight distribution index of the first homo-polypropylene in the core layer is 2-3, the upper secondary surface layer and the lower secondary surface layer are composed of modified polypropylene with the melting point of 170-180 DEG C and the melt index of 2-4 g / 10 min, the grafting rate of N-vinyl pyrrolidone is 2-5%, and the light layer comprises second homo-polypropylene. The modified polypropylene subjected to NVP grafting modification is adopted to form the upper secondary surface layer and the lower secondary surface layer, and the weight-average molecular weight, the number-average molecular weight and the molecular weight distribution index of the first homo-polypropylene are limited, so that the BOPP laser film is light in weight; the heat shrinkage rate of the laser film is reduced, the low haze of the laser film is ensured, and smooth production of the laser film is ensured.

Description

Technical Field

[0001] The invention relates to the field of films, and in particular to a lightweight, shrinkage-resistant BOPP laser film and a preparation method thereof. Background Art

[0002] BOPP laser film, namely biaxially oriented polypropylene laser film, is a BOPP film with unique charm and broad application prospects. It is usually made of a molded layer, a core layer and a light layer through co-extrusion and biaxial stretching. The molded layer of the biaxially oriented polypropylene laser film has been specially treated to reflect rainbow-like laser light, presenting a colorful visual effect. At different angles and light, the colors and patterns are unpredictable, which can give people a strong visual impact. BOPP laser film is widely used in the packaging of food, medicine, cosmetics, gifts and other products. It can not only improve the grade and added value of the products, but also play a role in anti-counterfeiting and promotion. At the same time, BOPP laser film is also widely used in decorative materials, labels and other fields, adding more color and creativity to people's lives.

[0003] At present, the thickness of BOPP laser film on the market is generally above 18μm. In order to reduce the consumption of raw materials and energy and achieve sustainable development, it is necessary to promote the lightweight of BOPP laser film and reduce the thickness of BOPP laser film.

[0004] The inventors discovered through extensive practice that after the laser film is thinned, its mechanical properties decrease. In the past, at the same molding temperature, the laser film has a large thermal shrinkage, resulting in product specifications that cannot meet the processing needs of downstream customers. If the molding temperature is lowered, the activity of the molecular chains of the molded layer will be weaker, the fluidity of the material will be poor, and patterns such as grating stripes cannot be effectively formed on the surface, resulting in poor laser effects. Summary of the invention

[0005] Based on this, the purpose of the present invention is to provide a lightweight, shrinkage-resistant BOPP laser film and a preparation method thereof. On the one hand, modified polypropylene grafted with N-vinyl pyrrolidone (NVP) is used to form the upper surface layer and the lower surface layer. On the other hand, the weight average molecular weight, number average molecular weight and molecular weight distribution index of the first homopolypropylene of the core layer are limited, so as to synergistically achieve the premise of making the BOPP laser film lightweight, effectively reduce the thermal shrinkage rate of the BOPP laser film, ensure the low haze of the BOPP laser film, and ensure the smooth production of the BOPP laser film.

[0006] The technical solution of the present invention is achieved by the following methods: A lightweight shrinkage-resistant BOPP laser film comprises a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer which are arranged in sequence, wherein the molded layer comprises ethylene-propylene binary copolymer polypropylene, the core layer comprises a first homopolypropylene, the weight average molecular weight of the first homopolypropylene is 250,000-350,000 g / mol, the number average molecular weight of the first homopolypropylene is 90,000-160,000 g / mol, the molecular weight distribution index of the first homopolypropylene is 2-3, the upper surface layer and the lower surface layer both comprise 100 wt% modified polypropylene, the grafting rate of N-vinyl pyrrolidone in the modified polypropylene is 2-5%, the light layer comprises a second homopolypropylene, and the total thickness of the BOPP laser film is 13-15 μm.

[0007] The lightweight, shrinkage-resistant BOPP laser film of the present invention, on the one hand, is a modified polypropylene obtained by grafting polypropylene with N-vinyl pyrrolidone, and the grafting rate of N-vinyl pyrrolidone is limited, and the upper surface layer and the lower surface layer are composed of the modified polypropylene, and on the other hand, the weight average molecular weight, number average molecular weight and molecular weight distribution index of the first homopolypropylene of the core layer are limited, which synergistically achieves the premise of thinning the BOPP laser film and making the BOPP laser film lightweight, effectively reducing the thermal shrinkage rate of the BOPP laser film, ensuring the low haze of the BOPP laser film, and ensuring the smooth production of the BOPP laser film.

[0008] NVP molecules contain pyrrolidone rings, which have a certain spatial volume. When NVP is grafted onto the polypropylene (PP) molecular chain to obtain modified polypropylene, the pyrrolidone ring produces a steric hindrance effect between the modified polypropylene molecular chains. This steric hindrance prevents the modified polypropylene molecular chains from arbitrarily entangled with each other and arranged chaotically; in addition, the nitrogen atoms and carbonyl groups on the pyrrolidone ring can interact with the groups on the adjacent molecular chains, such as hydrogen bonds or dipole-dipole interactions. These interactions guide the modified polypropylene molecular chains to arrange in a certain direction and manner, making the distance and relative position between the modified polypropylene molecular chains more regular. The improvement of the stacking order of the modified polypropylene molecular chains effectively reduces the gaps and refractive index differences inside the modified polypropylene; therefore, when light propagates through the upper and lower surface layers of the film, due to its regular overall structure, scattering is reduced, thereby ensuring low haze in the film.

[0009] After PP is grafted with NVP, the presence of pyrrolidone rings enhances the interaction between the modified polypropylene molecular chains. When heated during molding, this interaction can limit the movement of the modified polypropylene molecular chains, thereby reducing the thermal shrinkage rate. Moreover, during the biaxial stretching process, the NVP-grafted PP molecular chains can better maintain the stretching orientation because the pyrrolidone ring structure can provide a certain steric hindrance to prevent the modified polypropylene molecular chains from easily shrinking when heated.

[0010] The polypropylene (PP) molecular chain itself has a certain flexibility, and its glass transition temperature (Tg) mainly depends on factors such as the flexibility of the molecular chain and the interaction force between chains; while the pyrrolidone ring in the NVP molecular structure has a certain rigidity, but because NVP is grafted to the PP molecular chain through vinyl, the grafting process does not change the basic chemical structure of the PP molecular chain and the flexibility of the main chain. Therefore, the carbon-carbon main chain of the modified polypropylene molecular chain can still rotate freely, maintaining the flexibility of the molecular chain, which makes the Tg of the modified polypropylene not change significantly due to grafting. Therefore, after NVP is grafted to PP, it can effectively reduce the thermal shrinkage of the film and ensure low haze of the film, while not affecting the smoothness of production.

[0011] During the grafting process, since the NVP molecule contains vinyl, the vinyl at the other end of some grafted NVP molecules may react again with other polypropylene macromolecular free radicals or grafted NVP molecules to form a small number of crosslinking points and construct a micro-crosslinking structure. The present invention controls the grafting rate of NVP to 2-5%, which effectively restricts the NVP concentration and reaction activity, thereby making the crosslinking degree controllable and preventing the formation of a dense crosslinking network that is not conducive to subsequent processing.

[0012] If the grafting rate of NVP is higher than 5%, too many NVP units will be connected to the PP molecular chain. On the one hand, the pyrrolidone ring and vinyl structures in the NVP molecule increase the rigidity and reduce the flexibility of the modified polypropylene molecular chain; on the other hand, too much NVP grafting will also cause the interaction between the modified polypropylene molecular chains to be too complicated, forming too many cross-linking points or entanglement points, which will reduce the fluidity and processing performance of the material and affect the smoothness of production. If the grafting rate of NVP is lower than 2%, there are too few sites for the pyrrolidone ring to interact with the PP molecular chain, which cannot effectively guide the modified polypropylene molecular chain to arrange regularly and form a micro-cross-linking structure, resulting in a high thermal shrinkage rate of the film.

[0013] The present invention also appropriately defines the weight average molecular weight, number average molecular weight, and molecular weight distribution index of the first homopolypropylene in the core layer. Appropriate weight average molecular weight, number average molecular weight, and molecular weight distribution index mean that the molecular chain is longer, the molecular chain length is uniform and reasonably distributed, the intermolecular force is stronger, and the molecular structure is more regular, which makes the movement of the molecular chain of the film more restricted when heated. Wherein, molecular weight distribution index = weight average molecular weight ÷ number average molecular weight.

[0014] If the weight-average molecular weight of the first homopolypropylene is greater than 350,000 g / mol, the high molecular weight molecular chains are more tightly entangled with each other, making it difficult to stretch them during the production process. Long-chain molecules need to absorb more energy to melt, and the fluidity of the melt becomes poor, which will make production more difficult and affect the smoothness of production. If the weight-average molecular weight of the first homopolypropylene is less than 250,000 g / mol, it will lead to greater thermal shrinkage during subsequent processing, affecting customer use.

[0015] If the number average molecular weight of the first homopolypropylene is greater than 160000g / mol, the crystallinity of the material is too high, the molecular chain is long, the molecular movement is greatly hindered, and the long-chain molecules need longer time to adjust the conformation and form crystal nuclei during the crystallization process, so the crystallization speed slows down, the crystallinity is low, and the thickness is uneven and excessive deformation causes film breakage during the stretching process. If the number average molecular weight of the first homopolypropylene is less than 90000g / mol, the molecular chain is short and it is easier to form a regular arrangement. This allows the molecules to be more densely packed during the crystallization process, forming a higher degree of crystallinity, which will make the product haze larger, and excessive crystallinity may cause the film to break during the stretching process.

[0016] If the molecular weight distribution index of the first homopolypropylene is less than 2, the material melt viscosity is relatively high, the fluidity is poor, the melt film forming property is poor, and poor molding is likely to occur during the production process. If the molecular weight distribution index of the first homopolypropylene is greater than 3, the material has poor heat resistance, resulting in a large thermal shrinkage rate of the material, which is not conducive to reducing the thermal shrinkage rate of the film.

[0017] The technical solution of the present invention limits the weight average molecular weight, number average molecular weight and molecular weight distribution index of the core layer, limits the components of the upper surface layer and the lower surface layer and the grafting rate of NVP, and synergistically ensures the low haze, low heat shrinkage and smooth production of the BOPP laser film product.

[0018] Furthermore, the melting point of the modified polypropylene is 170-180°C, and the melt index of the modified polypropylene is 2-4 g / 10 min at 230°C and 2.16 kg. Limiting the modified polypropylene to the aforementioned melting point and melt index is beneficial to stretching during the production process, reducing problems such as film breakage and thickness difference.

[0019] Furthermore, the molded layer comprises 94-96 wt % of ethylene-propylene copolymerized polypropylene and 4-6 wt % of an anti-blocking agent masterbatch, and the particle size of the anti-blocking agent in the anti-blocking agent masterbatch is 4-5 μm.

[0020] Furthermore, the optical layer comprises 94-96 wt % of the second homopolypropylene and 4-6 wt % of an anti-blocking agent masterbatch, and the particle size of the anti-blocking agent in the anti-blocking agent masterbatch is 4-5 μm.

[0021] Furthermore, the initial heat sealing temperature of the ethylene-propylene binary copolymer polypropylene is 115-118°C, the melting point is 133-135°C, and the melt index of the ethylene-propylene binary copolymer polypropylene is measured to be 6-8g / 10min at 230°C and 2.16kg, which is conducive to ensuring the embossing laser effect.

[0022] Furthermore, the melting point of the first homopolypropylene is 165-175° C., and the melt index of the first homopolypropylene measured at 230° C. and 2.16 kg is 1.5-2.5 g / 10 min.

[0023] Furthermore, the melting point of the second homopolypropylene is 160-170° C., and the melt index of the second homopolypropylene measured at 230° C. and 2.16 kg is 2-4 g / 10 min.

[0024] Furthermore, the thickness of the molded layer is 1.6-1.8 μm, the thickness of the optical layer is 1.2-1.5 μm, and the thickness of the upper surface layer and the lower surface layer are both 0.8-1 μm.

[0025] The present invention also provides a method for preparing any of the above-mentioned lightweight, shrink-resistant BOPP laser films, comprising the following steps: weighing and mixing the raw materials of each layer according to a ratio, and then conveying them to the extruders of each layer to form a homogenized melt, the melt passing through a filter and then being co-extruded through a die head in multiple layers, and according to a flat film method, the cast film is quenched into a thick sheet, and the thick sheet is subjected to a biaxial stretching method of first longitudinal stretching and then transverse stretching to form a biaxially stretched film, and after the biaxially stretched film is cooled, the corona treatment is performed, and then the mother roll is rolled up, and after the mother roll is subjected to aging treatment, it is slit into finished products.

[0026] Further, the melt extrusion temperature of the molded layer is 200℃~250℃, the melt extrusion temperature of the upper surface layer is 240℃~260℃; the melt extrusion temperature of the core layer is 240℃~270℃, the melt extrusion temperature of the lower surface layer is 240℃~260℃, and the melt extrusion temperature of the optical layer is 240℃~260℃; the temperature of the chilling water and the chilling roller during chilling is 15℃~50℃; the longitudinal stretching temperature of the molded layer is 110℃~125℃; the longitudinal stretching temperature of the optical layer is 135℃~155℃; the transverse stretching temperature is 140℃~180℃; the longitudinal stretching ratio is 4.5~5.0 times; the transverse stretching ratio is 6.0~8.0 times. Under the production conditions specified in this application, it is conducive to the rapid and stable production of the lightweight, low heat shrinkage, and low haze lightweight anti-shrinkage BOPP laser film of this scheme.

[0027] In order to better understand and implement the present invention, the present invention is described in detail below. DETAILED DESCRIPTION

[0028] It should be clear that the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the embodiments of the present application.

[0029] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the embodiments of the present application. The singular forms of "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0030] The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. On the contrary, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the attached claims. In the description of the present application, it should be understood that the terms "first", "second", "third", etc. are only used to distinguish similar objects, and do not have to be used to describe a specific order or sequence, nor can they be understood as indicating or implying relative importance. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0031] In addition, in the description of this application, unless otherwise specified, "plurality" means two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0032] It should be understood that the embodiments of the present application are not limited to the precise structure described above, and various modifications and changes can be made without departing from the scope thereof. The scope of the embodiments of the present application is limited only by the appended claims.

[0033] As an embodiment of the present invention, this embodiment provides a lightweight, shrinkage-resistant BOPP laser film, comprising a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, the molded layer comprises ethylene-propylene binary copolymer polypropylene, the core layer comprises a first homopolypropylene, the weight average molecular weight of the first homopolypropylene is 250,000~350,000 g / mol, the number average molecular weight of the first homopolypropylene is 90,000~160,000 g / mol, the molecular weight distribution index of the first homopolypropylene is 2~3, the upper surface layer and the lower surface layer both comprise 100wt% modified polypropylene, the grafting rate of N-vinyl pyrrolidone in the modified polypropylene is 2~5%, the light layer comprises a second homopolypropylene, and the total thickness of the BOPP laser film is 13~15μm.

[0034] Furthermore, the melting point of the modified polypropylene is 170-180° C., and the melt index of the modified polypropylene measured at 230° C. and 2.16 kg is 2-4 g / 10 min.

[0035] It should be noted that the preparation method of the modified polypropylene of the present invention comprises the following steps: Homopolymer polypropylene (melting point 165-175°C, melt index 3-6 g / 10 min at 230°C, 2.16 kg) was placed in a vacuum oven at 80°C and dried for 4 hours to avoid moisture interfering with the reaction; Weigh 91.3-96.65wt% homopolypropylene, 3-8wt% NVP, 0.2-0.5wt% DCP (diisopropylbenzene peroxide), 0.05-0.1wt% DVB (divinylbenzene), 0.1wt% BHT (antioxidant) and place in a mixer and stir for 5-10 minutes. Add the mixture to an internal mixer, set the temperature to 170-190℃, add nitrogen protection, and the reaction time is 5-10 minutes; The product was crushed, extracted with acetone for 24 hours to remove unreacted NVP, and then vacuum dried to constant weight to obtain modified polypropylene.

[0036] Furthermore, the molded layer comprises 94-96 wt % of ethylene-propylene copolymerized polypropylene and 4-6 wt % of an anti-blocking agent masterbatch, and the particle size of the anti-blocking agent in the anti-blocking agent masterbatch is 4-5 μm.

[0037] Furthermore, the optical layer comprises 94-96 wt % of the second homopolypropylene and 4-6 wt % of an anti-blocking agent masterbatch, and the particle size of the anti-blocking agent in the anti-blocking agent masterbatch is 4-5 μm.

[0038] Furthermore, the initial heat sealing temperature of the ethylene-propylene binary copolymer polypropylene is 115-118° C., the melting point is 133-135° C., and the melt index of the ethylene-propylene binary copolymer polypropylene is 6-8 g / 10 min when measured at 230° C. and 2.16 kg.

[0039] Furthermore, the melting point of the first homopolypropylene is 165-175° C., and the melt index of the first homopolypropylene measured at 230° C. and 2.16 kg is 1.5-2.5 g / 10 min.

[0040] Furthermore, the melting point of the second homopolypropylene is 160-170° C., and the melt index of the second homopolypropylene measured at 230° C. and 2.16 kg is 2-4 g / 10 min.

[0041] Furthermore, the thickness of the molded layer is 1.6-1.8 μm, the thickness of the optical layer is 1.2-1.5 μm, and the thickness of the upper surface layer and the lower surface layer are both 0.8-1 μm.

[0042] The present invention also provides a method for preparing any of the above-mentioned lightweight, shrink-resistant BOPP laser films, comprising the following steps: weighing and mixing the raw materials of each layer according to a ratio, and then conveying them to the extruders of each layer to form a homogenized melt, the melt passing through a filter and then being co-extruded through a die head in multiple layers, and according to a flat film method, the cast film is quenched into a thick sheet, and the thick sheet is subjected to a biaxial stretching method of first longitudinal stretching and then transverse stretching to form a biaxially stretched film, and after the biaxially stretched film is cooled, the corona treatment is performed, and then the mother roll is rolled up, and after the mother roll is subjected to aging treatment, it is slit into finished products.

[0043] Further, the melt extrusion temperature of the molded layer is 200℃~250℃, the melt extrusion temperature of the upper surface layer is 240℃~260℃; the melt extrusion temperature of the core layer is 240℃~270℃, the melt extrusion temperature of the lower surface layer is 240℃~260℃, and the melt extrusion temperature of the optical layer is 240℃~260℃; the temperature of the chilling water and the chilling roller during chilling is 15℃~50℃; the longitudinal stretching temperature of the molded layer is 110℃~125℃; the longitudinal stretching temperature of the optical layer is 135℃~155℃; the transverse stretching temperature is 140℃~180℃; the longitudinal stretching ratio is 4.5~5.0 times; the transverse stretching ratio is 6.0~8.0 times. Under the production conditions specified in this application, it is conducive to the rapid and stable production of the lightweight, low heat shrinkage, and low haze lightweight anti-shrinkage BOPP laser film of this scheme.

[0044] The physical properties and test methods of the embodiments or comparative examples of the present invention are as follows: The melt index (melt mass flow rate MFR) is based on GB / T3682-2018, and homopolymer polypropylene and copolymer polypropylene are measured at 2.16 kg and 230°C.

[0045] Glossiness is tested according to GB / T8807-88 at a 45° angle.

[0046] The haze is tested according to GB / T2410-2008.

[0047] The weight average molecular weight, number average molecular weight and molecular weight distribution index are tested using a gel permeation chromatograph. Grind PP into small particles, add 1,2,4-trichlorobenzene, heat and stir at 130-150°C to fully dissolve it. After dissolution, filter it with a disposable microporous filter membrane. After the instrument is stable, set the mobile phase speed to 1ml / min, and inject the polystyrene standard solution into the gel permeation chromatograph for analysis. Record the elution time and corresponding molecular weight of each standard. Inject 50-100μL of the treated PP sample solution into the gel permeation chromatograph. Avoid bubbles and leakage during injection. According to the established calibration curve, convert the elution time of the PP sample into molecular weight.

[0048] According to GB / T10003-2008, cut a 100mm*100mm square sample from the sample to be tested along the direction parallel to the longitudinal direction, mark the longitudinal and transverse directions, and place the sample on a stainless steel plate in a 120℃ constant temperature oven. The stainless steel plate is located in the middle of the oven. During the test, blow air for 120s, take out the sample and cool it to the test environment temperature. Measure the length of the longitudinal and transverse marked straight lines to an accuracy of 0.5mm, and convert the thermal shrinkage rate.

[0049] The heat sealing pressure is 270N, the time is 1 second, the temperature is set according to the test requirements, and the starting heat sealing temperature is tested (heat sealing strength ≥ 2.5N).

[0050] Determination of heat seal strength: Refer to QB / T 2358-1998 test, test the heat seal strength at 135℃ heat seal temperature. After heat sealing the sample, the width of the sample is (15±0.1)mm, the unfolded length is (100±1)mm, and the heat seal part is taken as the center, open 180°, clamp the two ends of the sample on the two fixtures of the testing machine, the axis of the sample should coincide with the center line of the upper and lower fixtures, and the tightness should be appropriate to prevent the sample from slipping or breaking in the fixture before the test. The distance between the fixtures is 50mm, the test speed is 300mm / min, and the maximum load when the sample breaks is read.

[0051] The melting point was tested by DSC instrument under the conditions of 10K / min heating and cooling speed and 50mL / min N2 filling rate. The temperature was raised from 20°C to 200°C, then kept at 200°C for 2 minutes, then cooled from 200°C to 20°C, then kept at 20°C for 2 minutes, and finally raised from 20°C to 200°C.

[0052] Example 1 This embodiment provides a lightweight anti-shrinkage BOPP laser film, including a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 116℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 3.5%); Core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000 g / mol, number average molecular weight 120000 g / mol, molecular weight distribution index 2.5, melting point 170°C, melt index 2g / 10min measured at 230°C and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 3.5%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the BOPP film of this embodiment comprises the following steps: weighing and mixing the raw materials of each layer according to the ratio, and then conveying them to the extruders of each layer to form a homogenized melt, passing the melt through a filter and then co-extruding it through a die head, casting a film according to the flat film method, and then chilling it into a thick film, and the thick film adopts a biaxial stretching method of first longitudinal stretching and then transverse stretching to form a biaxially stretched film, and after cooling, the biaxially stretched film is subjected to corona treatment, and then rolled into a mother roll, and after the mother roll is subjected to aging treatment, it is cut into finished products. The longitudinal stretching ratio is 4.8 times, and the transverse stretching ratio is 7 times.

[0053] The total thickness of the film is 14µm, of which the molded layer thickness is 1.7µm, the upper surface layer thickness is 0.9µm, the lower surface layer thickness is 0.9µm, and the smooth layer thickness is 1.3µm.

[0054] Example 2 This embodiment provides a lightweight anti-shrinkage BOPP laser film, including a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 116℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene is 3.5%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 350000g / mol, number average molecular weight 160000g / mol, molecular weight distribution index 2.2, melting point 171℃, melt index 1.9g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 3.5%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this embodiment is the same as that of Embodiment 1, so it is not described in detail.

[0055] The total thickness of the film is 14µm, of which the molded layer thickness is 1.7µm, the upper surface layer thickness is 0.9µm, the lower surface layer thickness is 0.9µm, and the smooth layer thickness is 1.3µm.

[0056] Example 3 This embodiment provides a lightweight anti-shrinkage BOPP laser film, including a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 116℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene is 3.5%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 250000g / mol, number average molecular weight 90000g / mol, molecular weight distribution index 2.7, melting point 168℃, melt index 2.1g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 3.5%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this embodiment is the same as that of Embodiment 1, so it is not described in detail.

[0057] The total thickness of the film is 14µm, of which the molded layer thickness is 1.7µm, the upper surface layer thickness is 0.9µm, the lower surface layer thickness is 0.9µm, and the smooth layer thickness is 1.3µm.

[0058] Example 4 This embodiment provides a lightweight anti-shrinkage BOPP laser film, including a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 116℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene is 3.5%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000g / mol, number average molecular weight 100000g / mol, molecular weight distribution index 3, melting point 165℃, melt index 2.5g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 3.5%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this embodiment is the same as that of Embodiment 1, so it is not described in detail.

[0059] The total thickness of the film is 14µm, of which the molded layer thickness is 1.7µm, the upper surface layer thickness is 0.9µm, the lower surface layer thickness is 0.9µm, and the smooth layer thickness is 1.3µm.

[0060] Example 5 This embodiment provides a lightweight anti-shrinkage BOPP laser film, including a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 116℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene is 3.5%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000g / mol, number average molecular weight 150000g / mol, molecular weight distribution index 2, melting point 173℃, melt index 1.6g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 3.5%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this embodiment is the same as that of Embodiment 1, so it is not described in detail.

[0061] The total thickness of the film is 14µm, of which the molded layer thickness is 1.7µm, the upper surface layer thickness is 0.9µm, the lower surface layer thickness is 0.9µm, and the smooth layer thickness is 1.3µm.

[0062] Example 6 This embodiment provides a lightweight anti-shrinkage BOPP laser film, including a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 116℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 5%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000g / mol, number average molecular weight 120000g / mol, molecular weight distribution index 2.5, melting point 170℃, melt index 2g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 5%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this embodiment is the same as that of Embodiment 1, so it is not described in detail.

[0063] The total thickness of the film is 14µm, of which the molded layer thickness is 1.7µm, the upper surface layer thickness is 0.9µm, the lower surface layer thickness is 0.9µm, and the smooth layer thickness is 1.3µm.

[0064] Example 7 This embodiment provides a lightweight anti-shrinkage BOPP laser film, including a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 116℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 2%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000g / mol, number average molecular weight 120000g / mol, molecular weight distribution index 2.5, melting point 170℃, melt index 2g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 2%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this embodiment is the same as that of Embodiment 1, so it is not described in detail.

[0065] The total thickness of the film is 14µm, of which the molded layer thickness is 1.7µm, the upper surface layer thickness is 0.9µm, the lower surface layer thickness is 0.9µm, and the smooth layer thickness is 1.3µm.

[0066] Example 8 This embodiment provides a lightweight anti-shrinkage BOPP laser film, including a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 116℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene is 3.5%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000g / mol, number average molecular weight 120000g / mol, molecular weight distribution index 2.5, melting point 170℃, melt index 2g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 3.5%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this embodiment is the same as that of Embodiment 1, so it is not described in detail.

[0067] The total thickness of the film is 14µm, of which the molded layer thickness is 1.7µm, the upper surface layer thickness is 0.8µm, the lower surface layer thickness is 0.8µm, and the smooth layer thickness is 1.3µm.

[0068] Example 9 This embodiment provides a lightweight anti-shrinkage BOPP laser film, including a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 116℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene is 3.5%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000g / mol, number average molecular weight 120000g / mol, molecular weight distribution index 2.5, melting point 170℃, melt index 2g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 3.5%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this embodiment is the same as that of Embodiment 1, so it is not described in detail.

[0069] The total thickness of the film is 14µm, of which the molded layer thickness is 1.7µm, the upper surface layer thickness is 1μm, the lower surface layer thickness is 1μm, and the smooth layer thickness is 1.3µm.

[0070] Example 10 This embodiment provides a lightweight anti-shrinkage BOPP laser film, including a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 116℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene is 3.5%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000g / mol, number average molecular weight 120000g / mol, molecular weight distribution index 2.5, melting point 170℃, melt index 2g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 3.5%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this embodiment is the same as that of Embodiment 1, so it is not described in detail.

[0071] The total thickness of the film is 13µm, of which the molded layer thickness is 1.7µm, the upper surface layer thickness is 0.9µm, the lower surface layer thickness is 0.9µm, and the smooth layer thickness is 1.3µm.

[0072] Embodiment 11 This embodiment provides a lightweight anti-shrinkage BOPP laser film, including a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃ and 2.16kg, initial heat sealing temperature 115℃) and 5wt% anti-blocking agent masterbatch (the active ingredient is PMMA, the effective content is 5%, the carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene is 3.5%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000g / mol, number average molecular weight 120000g / mol, molecular weight distribution index 2.5, melting point 170℃, melt index 2g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 3.5%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this embodiment is the same as that of Embodiment 1, so it is not described in detail.

[0073] The total thickness of the film is 14µm, of which the molded layer thickness is 1.6µm, the upper surface layer thickness is 0.9µm, the lower surface layer thickness is 0.9µm, and the smooth layer thickness is 1.3µm.

[0074] Example 12 This embodiment provides a lightweight anti-shrinkage BOPP laser film, including a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 118℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene is 3.5%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000g / mol, number average molecular weight 120000g / mol, molecular weight distribution index 2.5, melting point 170℃, melt index 2g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 3.5%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this embodiment is the same as that of Embodiment 1, so it is not described in detail.

[0075] The total thickness of the film is 14µm, of which the molded layer thickness is 1.8µm, the upper surface layer thickness is 0.9µm, the lower surface layer thickness is 0.9µm, and the smooth layer thickness is 1.3µm.

[0076] Comparative Example 1 This comparative example provides a lightweight anti-shrinkage BOPP laser film, comprising a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 116℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000 g / mol, number average molecular weight 120000 g / mol, molecular weight distribution index 2.5, melting point 170°C, melt index 2g / 10min measured at 230°C and 2.16kg); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000 g / mol, number average molecular weight 120000 g / mol, molecular weight distribution index 2.5, melting point 170°C, melt index 2g / 10min measured at 230°C and 2.16kg); Next surface layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000 g / mol, number average molecular weight 120000 g / mol, molecular weight distribution index 2.5, melting point 170°C, melt index 2g / 10min measured at 230°C and 2.16kg); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this comparative example is the same as that of Example 1, so it is not repeated here.

[0077] The total thickness of the film is 14µm, of which the molded layer thickness is 1.7µm, the upper surface layer thickness is 0.9µm, the lower surface layer thickness is 0.9µm, and the smooth layer thickness is 1.3µm.

[0078] The lightweight, shrink-resistant BOPP laser film in this comparative example has a normal rainbow effect after embossing, but its heat shrinkage after embossing is too large and cannot meet the processing needs of downstream customers.

[0079] Comparative Example 2 This comparative example provides a lightweight anti-shrinkage BOPP laser film, comprising a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 116℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene is 3.5%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 240000g / mol, number average molecular weight 60000g / mol, molecular weight distribution index 4, melting point 163℃, melt index 3.6g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 3.5%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this comparative example is the same as that of Example 1, so it is not repeated here.

[0080] The total thickness of the film is 14µm, of which the molded layer thickness is 1.7µm, the upper surface layer thickness is 0.9µm, the lower surface layer thickness is 0.9µm, and the smooth layer thickness is 1.3µm.

[0081] The lightweight anti-shrinkage BOPP laser film in this comparative example has a large haze after molding, which affects the rainbow effect, and the heat shrinkage after molding is large, which cannot meet the processing needs of downstream customers.

[0082] Comparative Example 3 This comparative example provides a lightweight anti-shrinkage BOPP laser film, comprising a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 116℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene is 3.5%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 360000g / mol, number average molecular weight 200000g / mol, molecular weight distribution index 1.8, melting point 176℃, melt index 1.3g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 3.5%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this comparative example is the same as that of Example 1, so it is not repeated here.

[0083] The total thickness of the film is 14µm, of which the molded layer thickness is 1.7µm, the upper surface layer thickness is 0.9µm, the lower surface layer thickness is 0.9µm, and the smooth layer thickness is 1.3µm.

[0084] Comparative Example 4 This comparative example provides a lightweight anti-shrinkage BOPP laser film, comprising a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 116℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 6%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000g / mol, number average molecular weight 120000g / mol, molecular weight distribution index 2.5, melting point 170℃, melt index 2g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 6%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this comparative example is the same as that of Example 1, so it is not repeated here.

[0085] The total thickness of the film is 14µm, of which the molded layer thickness is 1.7µm, the upper surface layer thickness is 0.9µm, the lower surface layer thickness is 0.9µm, and the smooth layer thickness is 1.3µm.

[0086] Comparative Example 5 This comparative example provides a lightweight anti-shrinkage BOPP laser film, comprising a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 116℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 1%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000g / mol, number average molecular weight 120000g / mol, molecular weight distribution index 2.5, melting point 170℃, melt index 2g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 1%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this comparative example is the same as that of Example 1, so it is not repeated here.

[0087] The total thickness of the film is 14µm, of which the molded layer thickness is 1.7µm, the upper surface layer thickness is 0.9µm, the lower surface layer thickness is 0.9µm, and the smooth layer thickness is 1.3µm.

[0088] The lightweight, shrink-resistant BOPP laser film in this comparative example has a normal rainbow effect after embossing, but its heat shrinkage after embossing is too large and cannot meet the processing needs of downstream customers.

[0089] Comparative Example 6 This comparative example provides a lightweight anti-shrinkage BOPP laser film, comprising a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 116℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene is 3.5%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000g / mol, number average molecular weight 120000g / mol, molecular weight distribution index 2.5, melting point 170℃, melt index 2g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 3.5%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this comparative example is the same as that of Example 1, so it is not repeated here.

[0090] The total thickness of the film is 14µm, of which the molded layer thickness is 1.7µm, the upper surface layer thickness is 1.2µm, the lower surface layer thickness is 1.2µm, and the smooth layer thickness is 1.3µm.

[0091] Comparative Example 7 This comparative example provides a lightweight anti-shrinkage BOPP laser film, comprising a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 116℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene is 3.5%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000g / mol, number average molecular weight 120000g / mol, molecular weight distribution index 2.5, melting point 170℃, melt index 2g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 3.5%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this comparative example is the same as that of Example 1, so it is not repeated here.

[0092] The total thickness of the film is 14µm, of which the molded layer thickness is 1.7µm, the upper surface layer thickness is 0.6µm, the lower surface layer thickness is 0.6µm, and the smooth layer thickness is 1.3µm.

[0093] The lightweight, shrink-resistant BOPP laser film in this comparative example has a normal rainbow effect after embossing, but its heat shrinkage after embossing is too large and cannot meet the processing needs of downstream customers.

[0094] Comparative Example 8 This comparative example provides a lightweight anti-shrinkage BOPP laser film, comprising a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 116℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene is 3.5%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000g / mol, number average molecular weight 120000g / mol, molecular weight distribution index 2.5, melting point 170℃, melt index 2g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 3.5%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this comparative example is the same as that of Example 1, so it is not repeated here.

[0095] The total thickness of the film is 14µm, of which the molded layer thickness is 1.0µm, the upper surface layer thickness is 0.9µm, the lower surface layer thickness is 0.9µm, and the smooth layer thickness is 1.3µm.

[0096] When the lightweight anti-shrinkage BOPP laser film of this comparative example is actually used, the suitable molding temperature is too high, and the heat shrinkage rate is large at the suitable molding temperature, which affects the use of downstream customers.

[0097] Comparative Example 9 This comparative example provides a lightweight anti-shrinkage BOPP laser film, comprising a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 116℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene is 3.5%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000g / mol, number average molecular weight 120000g / mol, molecular weight distribution index 2.5, melting point 170℃, melt index 2g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 3.5%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this comparative example is the same as that of Example 1, so it is not repeated here.

[0098] The total thickness of the film is 14µm, of which the molded layer thickness is 2.0µm, the upper surface layer thickness is 0.9µm, the lower surface layer thickness is 0.9µm, and the smooth layer thickness is 1.3µm.

[0099] The lightweight anti-shrinkage BOPP laser film in this comparative example can only be used at a molding temperature of 130~135℃. When used at 134~135℃, it is easy to have a large heat shrinkage rate, and the product quality is unstable, affecting the use. If the customer enhances the rainbow effect and raises the molding temperature to 140~150℃, the heat shrinkage will reach 8-12mm, and the quality is unstable, affecting the use.

[0100] Comparative Example 10 This comparative example provides a lightweight anti-shrinkage BOPP laser film, comprising a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 135℃, melt index 7g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 125℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene is 3.5%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000g / mol, number average molecular weight 120000g / mol, molecular weight distribution index 2.5, melting point 170℃, melt index 2g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 3.5%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this comparative example is the same as that of Example 1, so it is not repeated here.

[0101] The total thickness of the film is 14µm, of which the molded layer thickness is 1.7µm, the upper surface layer thickness is 0.9µm, the lower surface layer thickness is 0.9µm, and the smooth layer thickness is 1.3µm.

[0102] When the lightweight anti-shrinkage BOPP laser film of this comparative example is actually used, the suitable molding temperature is too high, and the heat shrinkage rate is large at the suitable molding temperature, which affects the use of downstream customers.

[0103] Comparative Example 11 This comparative example provides a lightweight anti-shrinkage BOPP laser film, comprising a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence, and the components and contents of each layer are as follows: Molding layer: 95wt% ethylene-propylene copolymer polypropylene (melting point 134℃, melt index 8g / 10min measured at 230℃, 2.16kg, initial heat sealing temperature 110℃) and 5wt% anti-blocking agent masterbatch (active ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5μm); Upper surface layer: 100wt% modified polypropylene (melting point 175℃, melt index 3g / 10min measured at 230℃ and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene is 3.5%); core layer: 100wt% first homopolymer polypropylene (weight average molecular weight 300000g / mol, number average molecular weight 120000g / mol, molecular weight distribution index 2.5, melting point 170℃, melt index 2g / 10min measured at 230℃ and 2.16kg); Next surface layer: 100wt% modified polypropylene (melting point 175°C, melt index 3g / 10min measured at 230°C and 2.16kg, grafting rate of N-vinyl pyrrolidone in modified polypropylene 3.5%); Light layer: 95wt% second homopolymer polypropylene (melting point 165°C, melt index 3g / 10min measured at 230°C, 2.16kg) and 5wt% anti-blocking agent masterbatch (active ingredient PMMA, effective content 5%, carrier homopolymer PP, anti-blocking agent particle size 4.5μm); The preparation method of the lightweight anti-shrinkage BOPP laser film of this comparative example is the same as that of Example 1, so it is not repeated here.

[0104] The total thickness of the film is 14µm, of which the molded layer thickness is 1.7µm, the upper surface layer thickness is 0.9µm, the lower surface layer thickness is 0.9µm, and the smooth layer thickness is 1.3µm.

[0105] The molding parameters of the lightweight anti-shrinkage BOPP laser film in this comparative example are difficult to control, and roller sticking may occur, affecting the film surface quality and molding effect, and corona blackening may occur when the customer increases the corona power.

[0106] The performance test results of the lightweight anti-shrinkage BOPP laser films of Examples 1 to 12 are shown in Table 1 below, and the performance test results of the lightweight anti-shrinkage BOPP laser films of Comparative Examples 1 to 11 are shown in Table 2 below.

[0107] Table 1

[0108] Table 2

[0109] Combined with the above performance test data, it can be seen that the lightweight anti-shrinkage BOPP laser film of Examples 1-12 of the present invention can effectively reduce the thermal shrinkage rate of the BOPP laser film, ensure the low haze of the BOPP laser film, and ensure the smooth production of the BOPP laser film while making the BOPP laser film lightweight.

[0110] The upper and lower surface layers of the BOPP laser film in Comparative Example 1 do not use modified polypropylene. Although the BOPP laser film can obtain a normal molded rainbow effect after molding at the molding temperature commonly used by customers, the heat shrinkage rate after molding is relatively large and cannot meet the processing needs of downstream customers.

[0111] The weight-average molecular weight and number-average molecular weight of the first homopolypropylene in the core layer of the BOPP laser film of Comparative Example 2 are both relatively small, and the molecular weight distribution index is relatively large. The haze of the prepared BOPP laser film is relatively large, resulting in a poor rainbow effect after molding, and there is a problem that the heat shrinkage rate after molding is relatively large and cannot meet the processing needs of downstream customers.

[0112] The weight average molecular weight and number average molecular weight of the first homopolypropylene in the core layer of the BOPP laser film of Comparative Example 3 are both too large, and the molecular weight distribution index is too small. The problem of continuous film breakage is prone to occur during the preparation of the BOPP laser film, and the production is not smooth.

[0113] The NVP grafting rate in the modified polypropylene of the BOPP laser film of Comparative Example 4 is too large, and the problem of continuous film breakage is prone to occur during the preparation of the BOPP laser film, resulting in unsmooth production.

[0114] The NVP grafting rate in the modified polypropylene of the BOPP laser film of Comparative Example 5 is too small. Although the BOPP laser film can obtain a normal molded rainbow effect after molding at the molding temperature commonly used by customers, the heat shrinkage rate after molding is too large and cannot meet the processing needs of downstream customers.

[0115] The thickness of the upper surface layer and the thickness of the lower surface layer of the BOPP laser film in Comparative Example 6 are both too large, and the problem of continuous film breakage is prone to occur during the preparation of the BOPP laser film, resulting in unsmooth production.

[0116] The thickness of the upper surface layer and the thickness of the lower surface layer of the BOPP laser film in Comparative Example 7 are both too small. Although the BOPP laser film can obtain a normal molded rainbow effect after molding at the molding temperature commonly used by customers, the heat shrinkage rate after molding is too large and cannot meet the processing needs of downstream customers.

[0117] The thickness of the BOPP laser film molding layer of Example 8 is too small, and the BOPP laser film needs to be molded at an increased molding temperature to obtain a normal molded rainbow effect. However, after the molding temperature is increased, the thermal shrinkage rate of the BOPP laser film is relatively large and cannot meet the processing needs of downstream customers.

[0118] The thickness of the BOPP laser film molding layer of Example 9 is too large, and the adjustable range of the BOPP laser film molding temperature becomes smaller, which is not convenient for customers to make flexible adjustments. For example, when customers need to enhance the rainbow effect, increasing the molding temperature will cause excessive heat shrinkage, which cannot meet the processing needs of downstream customers. For example, when the temperature control effect of the customer's equipment is relatively inaccurate, it is more likely to cause problems such as excessive shrinkage and unstable product quality.

[0119] The initial heat sealing temperature of the ethylene-propylene binary copolymer polypropylene in the molding layer of the BOPP laser film of Comparative Example 10 is too high, and the molding temperature needs to be increased before molding to obtain a normal molded rainbow effect. However, after the molding temperature is increased, the thermal shrinkage rate of the BOPP laser film is too large and cannot meet the processing needs of downstream customers.

[0120] The initial heat sealing temperature of the ethylene-propylene binary copolymer polypropylene in the molding layer of the BOPP laser film of Comparative Example 11 is too low. The BOPP laser film needs to lower the molding temperature before molding to obtain a normal molded rainbow effect and ensure a suitable shrinkage rate. However, the molding parameters are difficult to control, and roller sticking will occur, affecting the film surface quality and the molding effect. It is not suitable for production scenarios that use high corona power for processing. Increasing the corona power makes corona blackening more likely to occur.

[0121] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and the present invention is also intended to include these modifications and modifications.

Claims

1. A lightweight, shrink-resistant BOPP laser film, characterized in that: The invention comprises a molded layer, an upper surface layer, a core layer, a lower surface layer and a light layer which are arranged in sequence, wherein the molded layer comprises ethylene-propylene binary copolymer polypropylene, the core layer comprises a first homopolypropylene, the weight average molecular weight of the first homopolypropylene is 250000-350000 g / mol, the number average molecular weight of the first homopolypropylene is 90000-160000 g / mol, the molecular weight distribution index of the first homopolypropylene is 2-3, the upper surface layer and the lower surface layer both comprise 100wt% modified polypropylene, the grafting rate of N-vinyl pyrrolidone in the modified polypropylene is 2-5%, the light layer comprises a second homopolypropylene, and the total thickness of the BOPP laser film is 13-15 μm.

2. The lightweight anti-shrinkage BOPP laser film according to claim 1, characterized in that: The melting point of the modified polypropylene is 170-180° C., and the melt index of the modified polypropylene is 2-4 g / 10 min when measured at 230° C. and 2.16 kg.

3. The lightweight anti-shrinkage BOPP laser film according to claim 1, characterized in that: The molded layer comprises 94-96 wt % of ethylene-propylene binary copolymerized polypropylene and 4-6 wt % of anti-blocking agent masterbatch, wherein the particle size of the anti-blocking agent in the anti-blocking agent masterbatch is 4-5 μm.

4. The lightweight anti-shrinkage BOPP laser film according to claim 1, characterized in that: The optical layer includes 94-96 wt % of the second homopolypropylene and 4-6 wt % of an anti-blocking agent masterbatch, wherein the particle size of the anti-blocking agent in the anti-blocking agent masterbatch is 4-5 μm.

5. The lightweight anti-shrinkage BOPP laser film according to claim 1, characterized in that: The initial heat sealing temperature of the ethylene-propylene binary copolymer polypropylene is 115-118° C., the melting point is 133-135° C., and the melt index of the ethylene-propylene binary copolymer polypropylene is 6-8 g / 10 min when measured at 230° C. and 2.16 kg.

6. The lightweight anti-shrinkage BOPP laser film according to claim 1, characterized in that: The melting point of the first homopolypropylene is 165-175° C., and the melt index of the first homopolypropylene measured at 230° C. and 2.16 kg is 1.5-2.5 g / 10 min.

7. The lightweight anti-shrinkage BOPP laser film according to claim 1, characterized in that: The melting point of the second homopolypropylene is 160-170° C., and the melt index of the second homopolypropylene measured at 230° C. and 2.16 kg is 2-4 g / 10 min.

8. The lightweight anti-shrinkage BOPP laser film according to claim 1, characterized in that: The thickness of the molded layer is 1.6-1.8 μm, the thickness of the optical layer is 1.2-1.5 μm, and the thickness of the upper surface layer and the lower surface layer are both 0.8-1 μm.

9. A method for preparing a lightweight anti-shrinkage BOPP laser film according to any one of claims 1 to 8, characterized in that: The following steps are involved: The raw materials of each layer are weighed and mixed according to the ratio, and then conveyed to each layer extruder respectively to make a homogenized melt. The melt passes through the filter and then is co-extruded through the die head. According to the flat film method, the cast sheet is quenched into a thick sheet. The thick sheet is made into a biaxially stretched film by a biaxially stretched method of first longitudinally stretching and then transversely stretching. After cooling, the biaxially stretched film is subjected to corona treatment and then rolled into a mother roll. After the mother roll is subjected to aging treatment, it is slit into finished products.

10. The method for preparing a lightweight, shrink-resistant BOPP laser film according to claim 9, characterized in that: The melt extrusion temperature of the molded layer is 200℃~250℃, the melt extrusion temperature of the upper surface layer is 240℃~260℃; the melt extrusion temperature of the core layer is 240℃~270℃, the melt extrusion temperature of the lower surface layer is 240℃~260℃, and the melt extrusion temperature of the light layer is 240℃~260℃; the temperature of the chilling water and the chilling roller during chilling is 15℃~50℃; the longitudinal stretching temperature of the molded layer is 110℃~125℃; the longitudinal stretching temperature of the light layer is 135℃~155℃; the transverse stretching temperature is 140℃~180℃; the longitudinal stretching ratio is 4.5~5.0 times; the transverse stretching ratio is 6.0~8.0 times.

Images