A lightweight shrink-resistant BOPP laser film and its preparation method

Abstract

The present invention relates to the field of thin films, and particularly to a lightweight shrink-resistant BOPP laser film and a preparation method thereof. The laser film comprises a hot stamping layer, an upper sub-surface layer, a core layer, a lower sub-surface layer and a light layer which are arranged in sequence, and has a total thickness of 13-15 μm. The hot stamping layer comprises ethylene-propylene copolymerized polypropylene. In the core layer, the weight-average molecular weight of the first homopolypropylene is 250,000-350,000 g / mol, the number-average molecular weight is 90,000-160,000 g / mol, and the molecular weight distribution index is 2-3. The upper sub-surface layer and the lower sub-surface layer are composed of modified polypropylene with a melting point of 170-180 °C and a melt index of 2-4 g / 10 min, wherein the grafting rate of N-vinylpyrrolidone is 2-5%. The light layer comprises a second homopolypropylene. By using modified polypropylene grafted with NVP to form the upper sub-surface layer and the lower sub-surface layer, and by defining the weight-average molecular weight, number-average molecular weight and molecular weight distribution index of the first homopolypropylene, the present invention synergistically realizes the reduction of the thermal shrinkage rate of the laser film, ensures the low haze of the laser film and ensures the smooth production of the laser film on the premise of lightweight of the BOPP laser film.

Description

Technical Field

[0001] The present invention relates to the field of thin films, and particularly to a lightweight shrink-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 prepared by co-extrusion and biaxial stretching of a mold pressing layer, a core layer and a light layer. The mold pressing layer of the biaxially oriented polypropylene laser film is specially treated to be able to reflect laser light like a rainbow, presenting a colorful visual effect. Moreover, at different angles and under different light conditions, the colors and patterns are unpredictable, which can give people a strong visual impact. BOPP laser film is widely used in the packaging of products such as food, medicine, cosmetics, gifts, etc. It can not only improve the grade and added value of products, but also play a role in anti-counterfeiting and promotion. At the same time, BOPP laser film also has extensive applications in the fields of decorative materials, labels, etc., adding more colors and creativity to people's lives.

[0003] Currently, the thickness of BOPP laser films on the market is generally above 18μm. In order to reduce raw material and energy consumption and achieve sustainable development, it is necessary to promote the lightweighting of BOPP laser films and reduce the thickness of BOPP laser films.

[0004] The inventor found through a large number of practices that after the laser film is thinned, its mechanical properties decrease. At the previous same mold pressing temperature, the thermal shrinkage of the laser film is relatively large, resulting in the product specifications not meeting the processing requirements of downstream customers. If the mold pressing temperature is reduced, the activity ability of the molecular chains of the mold pressing layer is weak, the fluidity of the material is poor, and patterns such as grating stripes cannot be effectively formed on the surface, resulting in poor laser effect. Summary of the Invention

[0005] Based on this, the purpose of the present invention is to provide a lightweight shrink-resistant BOPP laser film and a preparation method thereof. On the one hand, the modified polypropylene grafted with N-vinylpyrrolidone (NVP) is used to form the upper sub-surface layer and the lower sub-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. Cooperatively, on the premise of making the BOPP laser film lightweight, the thermal shrinkage rate of the BOPP laser film is effectively reduced, the low haze of the BOPP laser film is ensured, and at the same time, the smooth production of the BOPP laser film is ensured.

[0006] The technical solution of the present invention is realized in the following way:

[0007] A lightweight shrink-resistant BOPP laser film, comprising a molding layer, an upper surface layer, a core layer, a lower surface layer, and a light layer arranged in sequence. The molding layer comprises ethylene-propylene 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. Both the upper surface layer and the lower surface layer comprise 100 wt% modified polypropylene, and the grafting rate of N-vinylpyrrolidone in the modified polypropylene is 2 - 5%. The light layer comprises a second homopolypropylene. The total thickness of the BOPP laser film is 13 - 15 μm.

[0008] For the lightweight shrink-resistant BOPP laser film of the present invention, on the one hand, modified polypropylene obtained by graft-modifying polypropylene with N-vinylpyrrolidone is adopted, and the grafting rate of N-vinylpyrrolidone is limited. The upper surface layer and the lower surface layer are composed of the modified polypropylene. On the other hand, the weight-average molecular weight, number-average molecular weight, and molecular weight distribution index of the first homopolypropylene in the core layer are limited. Coordinately, on the premise of thinning the BOPP laser film and making the BOPP laser film lightweight, the thermal shrinkage rate of the BOPP laser film is effectively reduced, the low haze of the BOPP laser film is ensured, and the smooth production of the BOPP laser film is ensured at the same time.

[0009] The NVP molecule has a pyrrolidone ring, and the pyrrolidone ring has a certain spatial volume. When NVP is grafted onto the polypropylene (PP) molecular chain to obtain modified polypropylene, a steric hindrance effect is generated between the pyrrolidone rings in the modified polypropylene molecular chain. This steric hindrance makes the modified polypropylene molecular chains unable to randomly entangle and arrange disorderly. In addition, functional groups such as nitrogen atoms and carbonyl groups on the pyrrolidone ring can interact with groups on 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 voids and refractive index differences inside the modified polypropylene. Therefore, when light passes through the upper surface layer and the lower surface layer of the film and propagates inside, due to its overall regular structure, the scattering is reduced, thereby ensuring the low haze of the film.

[0010] After PP is grafted with NVP, the presence of the pyrrolidone ring enhances the intermolecular force between the modified polypropylene molecular chains. When heated under molding, this intermolecular force can restrict the movement of the modified polypropylene molecular chains, thereby reducing the thermal shrinkage rate. Moreover, during the biaxial stretching process, the PP molecular chains grafted with NVP can better maintain the tensile orientation because the pyrrolidone ring structure can provide a certain steric hindrance to prevent the modified polypropylene molecular chains from easily retracting when heated.

[0011] The polypropylene (PP) molecular chains themselves have a certain flexibility, and its glass transition temperature (Tg) mainly depends on factors such as the flexibility of the molecular chains and the intermolecular force; while the pyrrolidone ring in the NVP molecular structure has a certain rigidity, but since NVP is grafted to the PP molecular chains through vinyl groups, the grafting process does not change the basic chemical structure of the PP molecular chains and the flexibility of the main chain. Therefore, the carbon-carbon main chain of the modified polypropylene molecular chains can still rotate freely, maintaining the flexibility of the molecular chains, which makes the Tg of the modified polypropylene not change significantly due to grafting. Therefore, after NVP is grafted onto PP, it can effectively reduce the thermal shrinkage rate of the film, ensure low haze of the film, and at the same time does not affect the smoothness of production.

[0012] During the grafting process, since the NVP molecules contain vinyl groups, the vinyl groups at the other end of some grafted NVP molecules may react with other polypropylene macromolecular free radicals or the grafted NVP molecules again, forming a small number of cross-linking points and constructing a micro-crosslinked structure. In the present invention, the grafting rate of NVP is controlled to be 2 - 5%, which effectively restricts the concentration and reactivity of NVP, so that the degree of crosslinking is controllable and a dense crosslinked network will not be formed, which is not conducive to subsequent processing.

[0013] If the grafting rate of NVP is higher than 5%, too many NVP units will be grafted onto the PP molecular chains. On the one hand, the structures such as the pyrrolidone ring and vinyl groups in the NVP molecules increase the rigidity and reduce the flexibility of the modified polypropylene molecular chains; on the other hand, too much NVP grafting will also lead to overly complex intermolecular interactions of the modified polypropylene molecular chains, forming too many cross-linking points or entanglement points, resulting in a decrease in the fluidity and processing performance of the material and affecting the smoothness of production. If the grafting rate of NVP is lower than 2%, there are too few interaction sites between the pyrrolidone ring and the PP molecular chains, and it is impossible to effectively guide the regular arrangement of the modified polypropylene molecular chains and form a micro-crosslinked structure, resulting in a relatively high thermal shrinkage rate of the film.

[0014] The present invention also appropriately limits 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 chains are longer, the molecular chain lengths are uniform and reasonably distributed, the intermolecular forces are stronger, and the molecular structure is more regular. This makes the movement of molecular chains more restricted when the film is heated. Among them, the molecular weight distribution index = weight-average molecular weight ÷ number-average molecular weight.

[0015] If the weight-average molecular weight of the first homopolypropylene is greater than 350,000 g / mol, the entanglement between high-molecular-weight molecular chains is closer, it is difficult to stretch during the production process, long-chain molecules need to absorb more energy to melt, the fluidity of the melt becomes poor, which will make the 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 cause a large increase in thermal shrinkage during subsequent processing, affecting the use by customers.

[0016] If the number-average molecular weight of the first homopolypropylene is greater than 160,000 g / mol, the crystallinity of the material is too high, the molecular chains are longer, and the hindrance to molecular movement is greater. Long-chain molecules need more time to adjust their conformations and form crystal nuclei during the crystallization process, so the crystallization speed is slow, the crystallinity is low, and during the stretching process, it is easy to cause uneven thickness and excessive deformation resulting in film breakage. If the number-average molecular weight of the first homopolypropylene is less than 90,000 g / mol, the molecular chains are shorter and it is easier to form a regular arrangement. This enables the molecules to pack more closely during the crystallization process, forming a higher crystallinity, which will make the haze of the product relatively large, and too high crystallinity may cause the phenomenon of film breakage during the stretching process.

[0017] If the molecular weight distribution index of the first homopolypropylene is less than 2, the melt viscosity of the material is relatively high, the fluidity is poor, and the melt film-forming property is poor, and it is easy to have the phenomenon of poor molding during the production process. If the molecular weight distribution index of the first homopolypropylene is greater than 3, the heat resistance of the material is poor, resulting in a large thermal shrinkage rate of the material, which is not conducive to reducing the thermal shrinkage rate of the film.

[0018] The technical solution of the present invention, by limiting the weight-average molecular weight, number-average molecular weight, and molecular weight distribution index in the core layer, and limiting the components of the upper sub-surface layer and the lower sub-surface layer and the grafting rate of NVP, synergistically ensures the low haze, low thermal shrinkage rate, and smooth production of the BOPP laser film product.

[0019] Furthermore, the melting point of the modified polypropylene is 170~180 °C, and the melt index of the modified polypropylene is measured to be 2~4 g / 10 min under the conditions of 230 °C and 2.16 kg. Limiting the modified polypropylene within the foregoing melting point and melt index is beneficial to stretching during the production process, reducing problems such as film breakage and thickness difference.

[0020] Further, the compression molding layer comprises 94 - 96 wt% of ethylene - propylene random copolymer polypropylene and 4 - 6 wt% of anti - blocking masterbatch, and the particle size of the anti - blocking agent in the anti - blocking masterbatch is 4 - 5 μm.

[0021] Further, the optical layer comprises 94 - 96 wt% of second homopolypropylene and 4 - 6 wt% of anti - blocking masterbatch, and the particle size of the anti - blocking agent in the anti - blocking masterbatch is 4 - 5 μm.

[0022] Further, the starting heat - sealing temperature of the ethylene - propylene random copolymer polypropylene is 115 - 118 °C, the melting point is 133 - 135 °C, and the melt index of the ethylene - propylene random copolymer polypropylene measured under the conditions of 230 °C and 2.16 kg is 6 - 8 g / 10 min, which is beneficial to ensuring the compression molding laser effect.

[0023] Further, the melting point of the first homopolypropylene is 165 - 175 °C, and the melt index of the first homopolypropylene measured under the conditions of 230 °C and 2.16 kg is 1.5 - 2.5 g / 10 min.

[0024] Further, the melting point of the second homopolypropylene is 160 - 170 °C, and the melt index of the second homopolypropylene measured under the conditions of 230 °C and 2.16 kg is 2 - 4 g / 10 min.

[0025] Further, the thickness of the compression molding layer is 1.6 - 1.8 μm, the thickness of the optical layer is 1.2 - 1.5 μm, and the thicknesses of the upper surface layer and the lower surface layer are both 0.8 - 1 μm.

[0026] The present invention also provides a preparation method of the lightweight anti - shrinkage BOPP laser film as described in any one of the above, comprising the following steps: weighing and mixing each layer of raw materials according to the ratio, respectively conveying them to each layer of extruder to make a homogenized melt, passing the melt through a filter and then co - extruding multiple layers through a die, casting a film by the flat - film method, casting a thick sheet after chill - rolling, and making a biaxially stretched film by the biaxial stretching method of first longitudinally stretching and then transversely stretching. After the biaxially stretched film is cooled, corona treatment is carried out, and then it is wound into a master roll. After the master roll is subjected to aging treatment, it is slit into finished products.

[0027] Furthermore, the melt extrusion temperature of the compression molding layer is 200°C to 250°C, the melt extrusion temperature of the upper surface layer is 240°C to 260°C; the melt extrusion temperature of the core layer is 240°C to 270°C, the melt extrusion temperature of the lower surface layer is 240°C to 260°C, and the melt extrusion temperature of the optical layer is 240°C to 260°C; when quenching, the temperature of the quenching water and the quenching roll is 15°C to 50°C; the longitudinal stretching temperature of the compression molding layer is 110°C to 125°C; the longitudinal stretching temperature of the optical layer is 135°C to 155°C; the transverse stretching temperature is 140°C to 180°C; the longitudinal stretching ratio is 4.5 to 5.0 times; the transverse stretching ratio is 6.0 to 8.0 times. Under the production conditions defined in this application, it is beneficial to realize the rapid and stable production of the lightweight anti-shrinkage BOPP laser film with lightweight, low thermal shrinkage rate, and low haze.

[0028] For better understanding and implementation, the present invention will be described in detail below. Detailed implementation manners

[0029] It should be clear that the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope protected by the embodiments of this application.

[0030] The terms used in the embodiments of this application are only for the purpose of describing specific embodiments, and are not intended to limit the embodiments of this application. The singular forms of "a", "the" and "said" used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the term "and / or" as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0031] The implementation manners described in the following exemplary embodiments do not represent all the implementation manners consistent with this application. On the contrary, they are only examples of devices and methods consistent with some aspects of this application as detailed in the appended claims. In the description of this 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 this application can be understood according to specific circumstances.

[0032] In addition, in the description of this application, unless otherwise specified, "a plurality" means two or more. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0033] It should be understood that the embodiments of this application are not limited to the precise structures described above, and various modifications and changes can be made without departing from its scope. The scope of the embodiments of this application is only limited by the appended claims.

[0034] As an implementation manner of the present invention, this embodiment provides a lightweight shrink-resistant BOPP laser film, which includes a molding layer, an upper surface layer, a core layer, a lower surface layer, and a light layer arranged in sequence. The molding layer includes ethylene-propylene copolymer polypropylene, the core layer includes 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, both the upper surface layer and the lower surface layer include 100 wt% modified polypropylene, the grafting rate of N-vinylpyrrolidone in the modified polypropylene is 2 - 5%, the light layer includes a second homopolypropylene, and the total thickness of the BOPP laser film is 13 - 15 μm.

[0035] Furthermore, the melting point of the modified polypropylene is 170 - 180 °C, and the melt index of the modified polypropylene measured under the conditions of 230 °C and 2.16 kg is 2 - 4 g / 10 min.

[0036] It should be noted that the preparation method of the modified polypropylene of the present invention includes the following steps:

[0037] Place the homopolypropylene (with a melting point of 165 - 175 °C and a melt index of 3 - 6 g / 10 min measured under the conditions of 230 °C and 2.16 kg) in a vacuum oven at 80 °C and dry it for 4 hours to avoid moisture interfering with the reaction;

[0038] Weigh 91.3 - 96.65 wt% of homopolypropylene, 3 - 8 wt% of NVP, 0.2 - 0.5 wt% of DCP (dicumyl peroxide), 0.05 - 0.1 wt% of DVB (divinylbenzene), and 0.1 wt% of BHT (antioxidant) and place them in a blender and stir for 5 - 10 min. Add the mixture to a kneader, set the temperature to 170 - 190 °C, add nitrogen protection, and the reaction time is 5 - 10 min;

[0039] After the product is pulverized, it is extracted with acetone in a Soxhlet extractor for 24 hours to remove unreacted NVP, and then dried in vacuum to constant weight to obtain modified polypropylene.

[0040] Further, the molding layer comprises 94-96 wt% of ethylene-propylene random copolymer polypropylene and 4-6 wt% of an anti-blocking masterbatch, and the particle size of the anti-blocking agent in the anti-blocking masterbatch is 4-5 μm.

[0041] Further, the optical layer comprises 94-96 wt% of a second homopolypropylene and 4-6 wt% of an anti-blocking masterbatch, and the particle size of the anti-blocking agent in the anti-blocking masterbatch is 4-5 μm.

[0042] Further, the starting heat-sealing temperature of the ethylene-propylene random copolymer polypropylene is 115-118 °C, the melting point is 133-135 °C, and the melt index of the ethylene-propylene random copolymer polypropylene is measured to be 6-8 g / 10 min under the conditions of 230 °C and 2.16 kg.

[0043] Further, the melting point of the first homopolypropylene is 165-175 °C, and the melt index of the first homopolypropylene is measured to be 1.5-2.5 g / 10 min under the conditions of 230 °C and 2.16 kg.

[0044] Further, the melting point of the second homopolypropylene is 160-170 °C, and the melt index of the second homopolypropylene is measured to be 2-4 g / 10 min under the conditions of 230 °C and 2.16 kg.

[0045] Further, the thickness of the molding layer is 1.6-1.8 μm, the thickness of the optical layer is 1.2-1.5 μm, and the thicknesses of the upper surface layer and the lower surface layer are both 0.8-1 μm.

[0046] The present invention also provides a method for preparing the lightweight anti-shrinkage BOPP laser film as described in any one of the above, comprising the following steps: weighing and mixing the raw materials of each layer according to the ratio, and respectively feeding them into the extruders of each layer to make a homogenized melt. The melt passes through a filter and is co-extruded through a die in multiple layers. According to the flat film method, after casting and quenching into a thick sheet, the thick sheet is subjected to a biaxial stretching method of first longitudinal stretching and then transverse stretching to make a biaxially stretched film. After the biaxially stretched film is cooled, corona treatment is carried out, and then it is wound into a master roll. After the master roll is subjected to aging treatment, it is slit into finished products.

[0047] Furthermore, the melting and extrusion temperature of the compression molding layer is 200°C to 250°C, the melting and extrusion temperature of the upper surface layer is 240°C to 260°C; the melting and extrusion temperature of the core layer is 240°C to 270°C, the melting and extrusion temperature of the lower surface layer is 240°C to 260°C, and the melting and extrusion temperature of the optical layer is 240°C to 260°C; when quenching, the temperature of the quenching water and the quenching roller is 15°C to 50°C; the longitudinal stretching temperature of the compression molding layer is 110°C to 125°C; the longitudinal stretching temperature of the optical layer is 135°C to 155°C; the transverse stretching temperature is 140°C to 180°C; the longitudinal stretching ratio is 4.5 to 5.0 times; the transverse stretching ratio is 6.0 to 8.0 times. Under the production conditions defined in this application, it is beneficial to achieve the rapid and stable production of the lightweight shrinkage-resistant BOPP laser film with lightweight, low thermal shrinkage rate, and low haze.

[0048] The physical property indexes and their testing methods of the embodiments or comparative examples of the present invention are specifically as follows:

[0049] The melt index (melt mass flow rate MFR) is measured according to GB / T3682-2018 for homopolypropylene and copolymer polypropylene at 2.16 kg and 230°C.

[0050] The glossiness is tested at a 45° angle according to GB / T8807-88.

[0051] The haze is tested according to GB / T2410-2008.

[0052] The weight-average molecular weight, number-average molecular weight, and molecular weight distribution index are tested using a gel permeation chromatograph. Grind the 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 velocity to 1 ml / min, and inject the polystyrene standard sample solution into the gel permeation chromatograph for analysis in turn. Record the elution time and corresponding molecular weight of each standard sample. Inject 50 - 100 μL of the processed PP sample solution into the gel permeation chromatograph. Avoid generating air bubbles and leakage during injection. According to the established calibration curve, convert the elution time of the PP sample into the molecular weight.

[0053] The thermal shrinkage rate is measured according to GB / T10003-2008. On the test sample, cut a 100 mm * 100 mm square specimen along the direction parallel to the longitudinal direction, mark the longitudinal and transverse directions, place the sample on a stainless steel plate in a constant temperature oven at 120°C. The stainless steel plate is located in the middle of the oven. During the test, blow air, and the heating time is 120 s. Take out the specimen and cool it to the test environment temperature. Measure the lengths of the longitudinal and transverse marked straight lines, accurate to 0.5 mm, and convert the thermal shrinkage rate.

[0054] The heat-sealing pressure is 270 N, the time is 1 second, and the temperature is set according to the test requirements. The initial heat-sealing temperature is detected (heat-sealing strength ≥ 2.5 N).

[0055] Determination of heat-sealing strength: Refer to QB / T 2358-1998 for testing, and test the heat-sealing strength at a heat-sealing temperature of 135 °C. After heat-sealing the sample, the width of the specimen is (15 ± 0.1) mm, and the unfolded length is (100 ± 1) mm. With the heat-sealed part as the center, open it to 180 °, clamp the two ends of the specimen on the two clamps of the testing machine. The axis of the specimen should coincide with the center line of the upper and lower clamps, and it is required to be properly tightened to prevent the specimen from slipping off or breaking in the clamp before the test. The distance between the clamps is 50 mm, the test speed is 300 mm / min, and read the maximum load when the specimen breaks.

[0056] The melting point is tested by a DSC instrument. The melting point test conditions are a heating and cooling rate of 10 K / min and an N2 inflation rate of 50 mL / min. Heat from 20 °C to 200 °C, then hold at 200 °C for 2 min, then cool from 200 °C to 20 °C, then hold at 20 °C for 2 min, and finally heat from 20 °C to 200 °C again.

[0057] Example 1

[0058] This example provides a lightweight shrink-resistant BOPP laser film, which includes a die-pressed layer, an upper sub-surface layer, a core layer lower sub-surface layer, and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0059] Die-pressed layer: 95 wt% ethylene-propylene copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg, initial heat-sealing temperature 116 °C) and 5 wt% 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 4.5 μm);

[0060] Upper sub-surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, and the grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%);

[0061] Core layer: 100 wt% 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 2 g / 10 min measured under the conditions of 230 °C and 2.16 kg);

[0062] Next surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%);

[0063] Light layer: 95 wt% second homopolypropylene (melting point 165 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene PP, and the particle size of the anti-blocking agent is 4.5 μm);

[0064] The preparation method of the BOPP film in this example includes the following steps: Weigh and mix the raw materials of each layer according to the ratio, and then transport them to the extruders of each layer respectively to make a homogenized melt. After passing through the filter, the melt is co-extruded through the die head in multiple layers. According to the flat film method, after casting the film, it is rapidly cooled into a thick sheet. The thick sheet is subjected to a biaxial stretching method of first longitudinal stretching and then transverse stretching to make a biaxially stretched film. After the biaxially stretched film is cooled, corona treatment is carried out, and then it is wound into a master roll. After the master roll is subjected to aging treatment, it is slit into finished products. The longitudinal stretching ratio is 4.8 times, and the transverse stretching ratio is 7 times.

[0065] The total thickness of the film is 14 µm, among which the thickness of the embossing layer is 1.7 µm, the thickness of the previous surface layer is 0.9 µm, the thickness of the next surface layer is 0.9 µm, and the thickness of the light layer is 1.3 µm.

[0066] Example 2

[0067] This example provides a lightweight shrink-resistant BOPP laser film, which includes an embossing layer, a previous surface layer, a core layer, a next surface layer, and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0068] Embossing layer: 95 wt% ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured under conditions of 230 °C and 2.16 kg, initial heat-sealing temperature 116 °C) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene PP, and the particle size of the anti-blocking agent is 4.5 μm);

[0069] Previous surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%); Core layer: 100 wt% first homopolypropylene (weight average molecular weight 350000 g / mol, number average molecular weight 160000 g / mol, molecular weight distribution index 2.2, melting point 171 °C, melt index 1.9 g / 10 min measured under conditions of 230 °C and 2.16 kg);

[0070] Next surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%);

[0071] Light layer: 95 wt% second homopolypropylene (melting point 165 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene PP, and the particle size of the anti-blocking agent is 4.5 μm);

[0072] The preparation method of the lightweight shrink-resistant BOPP laser film in this example is the same as that in Example 1, so it will not be elaborated here.

[0073] The total thickness of the film is 14 μm, among which the thickness of the embossing layer is 1.7 μm, the thickness of the previous surface layer is 0.9 μm, the thickness of the next surface layer is 0.9 μm, and the thickness of the light layer is 1.3 μm.

[0074] Example 3

[0075] This example provides a lightweight shrink-resistant BOPP laser film, which includes an embossing layer, a previous surface layer, a core layer, a next surface layer and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0076] Embossing layer: 95 wt% ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg, initial heat-sealing temperature 116 °C) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene PP, and the particle size of the anti-blocking agent is 4.5 μm);

[0077] Previous surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%); Core layer: 100 wt% first homopolypropylene (weight-average molecular weight 250000 g / mol, number-average molecular weight 90000 g / mol, molecular weight distribution index 2.7, melting point 168 °C, melt index 2.1 g / 10 min measured under the conditions of 230 °C and 2.16 kg);

[0078] Next surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%);

[0079] Optical layer: 95 wt% of second homopolypropylene (melting point 165 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 5 wt% of anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene, and the particle size of the anti-blocking agent is 4.5 μm);

[0080] The preparation method of the lightweight anti-shrinkage BOPP laser film in this example is the same as that in Example 1, so it will not be elaborated here.

[0081] The total thickness of the film is 14 µm, among which the thickness of the embossing layer is 1.7 µm, the thickness of the upper surface layer is 0.9 µm, the thickness of the lower surface layer is 0.9 µm, and the thickness of the optical layer is 1.3 µm.

[0082] Example 4

[0083] This example provides a lightweight anti-shrinkage BOPP laser film, which includes an embossing layer, an upper surface layer, a core layer, a lower surface layer, and an optical layer arranged in sequence. The components and contents of each layer are as follows:

[0084] Embossing layer: 95 wt% of ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg, initial heat-sealing temperature 116 °C) and 5 wt% of anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene, and the particle size of the anti-blocking agent is 4.5 µm);

[0085] Upper surface layer: 100 wt% of modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%); Core layer: 100 wt% of first homopolypropylene (weight-average molecular weight 300000 g / mol, number-average molecular weight 100000 g / mol, molecular weight distribution index 3, melting point 165 °C, melt index 2.5 g / 10 min measured under the conditions of 230 °C and 2.16 kg);

[0086] Lower surface layer: 100 wt% of modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%);

[0087] Optical layer: 95 wt% of second homopolypropylene (melting point 165 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 5 wt% of anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene, and the particle size of the anti-blocking agent is 4.5 µm);

[0088] The preparation method of the lightweight shrink-resistant BOPP laser film in this example is the same as that in Example 1, so it will not be elaborated here.

[0089] The total thickness of the film is 14 µm, among which the thickness of the embossing layer is 1.7 µm, the thickness of the upper surface layer is 0.9 µm, the thickness of the lower surface layer is 0.9 µm, and the thickness of the optical layer is 1.3 µm.

[0090] Example 5

[0091] This example provides a lightweight shrink-resistant BOPP laser film, which includes an embossing layer, an upper surface layer, a core layer, a lower surface layer, and an optical layer arranged in sequence. The components and contents of each layer are as follows:

[0092] Embossing layer: 95 wt% ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg, initial heat-sealing temperature 116 °C) and 5 wt% anti-blocking 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 4.5 µm);

[0093] Upper surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, and the grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%); Core layer: 100 wt% first homopolymer polypropylene (weight average molecular weight 300000 g / mol, number average molecular weight 150000 g / mol, molecular weight distribution index 2, melting point 173 °C, melt index 1.6 g / 10 min measured under the conditions of 230 °C and 2.16 kg);

[0094] Lower surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, and the grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%);

[0095] Optical layer: 95 wt% second homopolymer polypropylene (melting point 165 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 5 wt% anti-blocking 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 4.5 µm);

[0096] The preparation method of the lightweight shrink-resistant BOPP laser film in this example is the same as that in Example 1, so it will not be elaborated here.

[0097] The total thickness of the film is 14 µm, among which the thickness of the embossing layer is 1.7 µm, the thickness of the upper surface layer is 0.9 µm, the thickness of the lower surface layer is 0.9 µm, and the thickness of the optical layer is 1.3 µm.

[0098] Example 6

[0099] This example provides a lightweight shrink-resistant BOPP laser film, which includes a die-pressing layer, an upper sub-surface layer, a core layer, a lower sub-surface layer, and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0100] Die-pressing layer: 95 wt% ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg, initial heat-sealing temperature 116 °C) and 5 wt% anti-blocking 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 4.5 μm);

[0101] Upper sub-surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, the grafting rate of N-vinylpyrrolidone in the modified polypropylene is 5%); Core layer: 100 wt% 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 2 g / 10 min measured under the conditions of 230 °C and 2.16 kg);

[0102] Lower sub-surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, the grafting rate of N-vinylpyrrolidone in the modified polypropylene is 5%);

[0103] Light layer: 95 wt% second homopolymer polypropylene (melting point 165 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 5 wt% anti-blocking 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 4.5 μm);

[0104] The preparation method of the lightweight shrink-resistant BOPP laser film in this example is the same as that in Example 1, so it will not be elaborated here.

[0105] The total thickness of the film is 14 µm, among which the thickness of the die-pressing layer is 1.7 µm, the thickness of the upper sub-surface layer is 0.9 µm, the thickness of the lower sub-surface layer is 0.9 µm, and the thickness of the light layer is 1.3 µm.

[0106] Example 7

[0107] This example provides a lightweight shrink-resistant BOPP laser film, which includes a die-pressing layer, an upper sub-surface layer, a core layer, a lower sub-surface layer, and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0108] Molding layer: 95 wt% ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured at 230 °C and 2.16 kg, initial heat-sealing temperature 116 °C) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5 μm);

[0109] Upper surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured at 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 2%); Core layer: 100 wt% 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 2 g / 10 min measured at 230 °C and 2.16 kg);

[0110] Lower surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured at 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 2%);

[0111] Light layer: 95 wt% second homopolymer polypropylene (melting point 165 °C, melt index 3 g / 10 min measured at 230 °C and 2.16 kg) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5 μm);

[0112] The preparation method of the lightweight anti-shrinkage BOPP laser film in this example is the same as that in Example 1, so it will not be elaborated here.

[0113] The total thickness of the film is 14 µm, among which the thickness of the molding layer is 1.7 µm, the thickness of the upper surface layer is 0.9 µm, the thickness of the lower surface layer is 0.9 µm, and the thickness of the light layer is 1.3 µm.

[0114] Example 8

[0115] This example provides a lightweight anti-shrinkage BOPP laser film, which includes a molding layer, an upper surface layer, a core layer, a lower surface layer and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0116] Molding layer: 95 wt% ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured at 230 °C and 2.16 kg, initial heat-sealing temperature 116 °C) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolymer PP, and the particle size of the anti-blocking agent is 4.5 μm);

[0117] Previous surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%); Core layer: 100 wt% first homopolypropylene (weight average molecular weight 300,000 g / mol, number average molecular weight 120,000 g / mol, molecular weight distribution index 2.5, melting point 170 °C, melt index 2 g / 10 min measured under the conditions of 230 °C and 2.16 kg);

[0118] Next surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%);

[0119] Light layer: 95 wt% second homopolypropylene (melting point 165 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene, and the particle size of the anti-blocking agent is 4.5 μm);

[0120] The preparation method of the lightweight shrink-resistant BOPP laser film in this example is the same as that in Example 1, so it will not be elaborated here.

[0121] The total thickness of the film is 14 µm, among which the thickness of the embossing layer is 1.7 µm, the thickness of the previous surface layer is 0.8 µm, the thickness of the next surface layer is 0.8 µm, and the thickness of the light layer is 1.3 µm.

[0122] Example 9

[0123] This example provides a lightweight shrink-resistant BOPP laser film, which includes an embossing layer, a previous surface layer, a core layer, a next surface layer and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0124] Embossing layer: 95 wt% ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg, initial heat-sealing temperature 116 °C) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene, and the particle size of the anti-blocking agent is 4.5 μm);

[0125] Previous surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%); Core layer: 100 wt% first homopolypropylene (weight average molecular weight 300,000 g / mol, number average molecular weight 120,000 g / mol, molecular weight distribution index 2.5, melting point 170 °C, melt index 2 g / 10 min measured under conditions of 230 °C and 2.16 kg);

[0126] Next surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%);

[0127] Light layer: 95 wt% second homopolypropylene (melting point 165 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene, and the particle size of the anti-blocking agent is 4.5 μm);

[0128] The preparation method of the lightweight anti-shrink BOPP laser film in this example is the same as that in Example 1, so it will not be elaborated here.

[0129] The total thickness of the film is 14 µm, among which the thickness of the embossing layer is 1.7 µm, the thickness of the previous surface layer is 1 µm, the thickness of the next surface layer is 1 µm, and the thickness of the light layer is 1.3 µm.

[0130] Example 10

[0131] This example provides a lightweight anti-shrink BOPP laser film, including an embossing layer, a previous surface layer, a core layer, a next surface layer, and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0132] Embossing layer: 95 wt% ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured under conditions of 230 °C and 2.16 kg, initial heat-sealing temperature 116 °C) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene, and the particle size of the anti-blocking agent is 4.5 μm);

[0133] Previous surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%); Core layer: 100 wt% first homopolypropylene (weight average molecular weight 300,000 g / mol, number average molecular weight 120,000 g / mol, molecular weight distribution index 2.5, melting point 170 °C, melt index 2 g / 10 min measured under the conditions of 230 °C and 2.16 kg);

[0134] Next surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%);

[0135] Light layer: 95 wt% second homopolypropylene (melting point 165 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene PP, and the particle size of the anti-blocking agent is 4.5 μm);

[0136] The preparation method of the lightweight anti-shrink BOPP laser film in this example is the same as that in Example 1, so it will not be elaborated here.

[0137] The total thickness of the film is 13 μm, among which the thickness of the embossing layer is 1.7 μm, the thickness of the previous surface layer is 0.9 μm, the thickness of the next surface layer is 0.9 μm, and the thickness of the light layer is 1.3 μm.

[0138] Example 11

[0139] This example provides a lightweight anti-shrink BOPP laser film, including an embossing layer, a previous surface layer, a core layer, a next surface layer and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0140] Embossing layer: 95 wt% ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg, initial heat-sealing temperature 115 °C) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene PP, and the particle size of the anti-blocking agent is 4.5 μm);

[0141] Previous surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%); Core layer: 100 wt% first homopolypropylene (weight-average molecular weight 300,000 g / mol, number-average molecular weight 120,000 g / mol, molecular weight distribution index 2.5, melting point 170 °C, melt index 2 g / 10 min measured under the conditions of 230 °C and 2.16 kg);

[0142] Next surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%);

[0143] Light layer: 95 wt% second homopolypropylene (melting point 165 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene, and the particle size of the anti-blocking agent is 4.5 μm);

[0144] The preparation method of the lightweight anti-shrink BOPP laser film in this example is the same as that in Example 1, so it will not be elaborated here.

[0145] The total thickness of the film is 14 µm, among which the thickness of the embossing layer is 1.6 µm, the thickness of the previous surface layer is 0.9 µm, the thickness of the next surface layer is 0.9 µm, and the thickness of the light layer is 1.3 µm.

[0146] Example 12

[0147] This example provides a lightweight anti-shrink BOPP laser film, which includes an embossing layer, a previous surface layer, a core layer, a next surface layer and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0148] Embossing layer: 95 wt% ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg, initial heat-sealing temperature 118 °C) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene, and the particle size of the anti-blocking agent is 4.5 μm);

[0149] Previous surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%); Core layer: 100 wt% first homopolypropylene (weight average molecular weight 300,000 g / mol, number average molecular weight 120,000 g / mol, molecular weight distribution index 2.5, melting point 170 °C, melt index 2 g / 10 min measured under the conditions of 230 °C and 2.16 kg);

[0150] Next surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%);

[0151] Light layer: 95 wt% second homopolypropylene (melting point 165 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene, and the particle size of the anti-blocking agent is 4.5 μm);

[0152] The preparation method of the lightweight shrinkage-resistant BOPP laser film in this example is the same as that in Example 1, so it will not be elaborated here.

[0153] The total thickness of the film is 14 µm, among which the thickness of the embossing layer is 1.8 µm, the thickness of the previous surface layer is 0.9 µm, the thickness of the next surface layer is 0.9 µm, and the thickness of the light layer is 1.3 µm.

[0154] Comparative Example 1

[0155] This comparative example provides a lightweight shrinkage-resistant BOPP laser film, which includes an embossing layer, a previous surface layer, a core layer, a next surface layer and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0156] Embossing layer: 95 wt% ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg, initial heat-sealing temperature 116 °C) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene, and the particle size of the anti-blocking agent is 4.5 µm);

[0157] Previous surface layer: 100 wt% of the first homopolypropylene (weight average molecular weight 300,000 g / mol, number average molecular weight 120,000 g / mol, molecular weight distribution index 2.5, melting point 170 °C, melt index 2 g / 10 min measured under the conditions of 230 °C and 2.16 kg); Core layer: 100 wt% of the first homopolypropylene (weight average molecular weight 300,000 g / mol, number average molecular weight 120,000 g / mol, molecular weight distribution index 2.5, melting point 170 °C, melt index 2 g / 10 min measured under the conditions of 230 °C and 2.16 kg);

[0158] Next surface layer: 100 wt% of the first homopolypropylene (weight average molecular weight 300,000 g / mol, number average molecular weight 120,000 g / mol, molecular weight distribution index 2.5, melting point 170 °C, melt index 2 g / 10 min measured under the conditions of 230 °C and 2.16 kg);

[0159] Light layer: 95 wt% of the second homopolypropylene (melting point 165 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 5 wt% of an anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene PP, and the particle size of the anti-blocking agent is 4.5 μm);

[0160] 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 will not be elaborated here.

[0161] The total thickness of the film is 14 µm, among which the thickness of the embossing layer is 1.7 µm, the thickness of the previous surface layer is 0.9 µm, the thickness of the next surface layer is 0.9 µm, and the thickness of the light layer is 1.3 µm.

[0162] The rainbow effect of the lightweight anti-shrinkage BOPP laser film of this comparative example is normal after embossing, but the thermal shrinkage after embossing is too large and cannot meet the processing requirements of downstream customers.

[0163] Comparative Example 2

[0164] This comparative example provides a lightweight anti-shrinkage BOPP laser film, which includes an embossing layer, a previous surface layer, a core layer, a next surface layer and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0165] Embossing layer: 95 wt% of ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg, initial heat-sealing temperature 116 °C) and 5 wt% of an anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene PP, and the particle size of the anti-blocking agent is 4.5 µm);

[0166] Previous surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%); Core layer: 100 wt% first homopolypropylene (weight average molecular weight 240,000 g / mol, number average molecular weight 60,000 g / mol, molecular weight distribution index 4, melting point 163 °C, melt index 3.6 g / 10 min measured under conditions of 230 °C and 2.16 kg);

[0167] Next surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%);

[0168] Light layer: 95 wt% second homopolypropylene (melting point 165 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene PP, and the particle size of the anti-blocking agent is 4.5 μm);

[0169] The preparation method of the lightweight shrink-resistant BOPP laser film of this comparative example is the same as that of Example 1, so it will not be elaborated.

[0170] The total thickness of the film is 14 µm, among which the thickness of the embossing layer is 1.7 µm, the thickness of the previous surface layer is 0.9 µm, the thickness of the next surface layer is 0.9 µm, and the thickness of the light layer is 1.3 µm.

[0171] The embossed haze of the lightweight shrink-resistant BOPP laser film of this comparative example is too large, affecting the rainbow effect, and the thermal shrinkage after embossing is too large, which cannot meet the processing requirements of downstream customers.

[0172] Comparative Example 3

[0173] This comparative example provides a lightweight shrink-resistant BOPP laser film, including an embossing layer, a previous surface layer, a core layer, a next surface layer, and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0174] Embossing layer: 95 wt% ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured under conditions of 230 °C and 2.16 kg, initial heat-sealing temperature 116 °C) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene PP, and the particle size of the anti-blocking agent is 4.5 μm);

[0175] Previous surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%); Core layer: 100 wt% first homopolypropylene (weight average molecular weight 360,000 g / mol, number average molecular weight 200,000 g / mol, molecular weight distribution index 1.8, melting point 176 °C, melt index 1.3 g / 10 min measured under conditions of 230 °C and 2.16 kg);

[0176] Next surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%);

[0177] Light layer: 95 wt% second homopolypropylene (melting point 165 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene PP, and the particle size of the anti-blocking agent is 4.5 μm);

[0178] The preparation method of the lightweight anti-shrink BOPP laser film in this comparative example is the same as that in Example 1, so it will not be elaborated here.

[0179] The total thickness of the film is 14 µm, among which the thickness of the embossing layer is 1.7 µm, the thickness of the previous surface layer is 0.9 µm, the thickness of the next surface layer is 0.9 µm, and the thickness of the light layer is 1.3 µm.

[0180] Comparative Example 4

[0181] This comparative example provides a lightweight anti-shrink BOPP laser film, including an embossing layer, a previous surface layer, a core layer, a next surface layer and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0182] Embossing layer: 95 wt% ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured under conditions of 230 °C and 2.16 kg, initial heat-sealing temperature 116 °C) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene PP, and the particle size of the anti-blocking agent is 4.5 µm);

[0183] Previous surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 6%); Core layer: 100 wt% first homopolypropylene (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 2 g / 10 min measured under the conditions of 230 °C and 2.16 kg);

[0184] Next surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 6%);

[0185] Light layer: 95 wt% second homopolypropylene (melting point 165 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene, and the particle size of the anti-blocking agent is 4.5 μm);

[0186] The preparation method of the lightweight anti-shrinkage BOPP laser film in this comparative example is the same as that in Example 1, so it will not be elaborated here.

[0187] The total thickness of the film is 14 µm, among which the thickness of the embossing layer is 1.7 µm, the thickness of the previous surface layer is 0.9 µm, the thickness of the next surface layer is 0.9 µm, and the thickness of the light layer is 1.3 µm.

[0188] Comparative Example 5

[0189] This comparative example provides a lightweight anti-shrinkage BOPP laser film, which includes an embossing layer, a previous surface layer, a core layer, a next surface layer, and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0190] Embossing layer: 95 wt% ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg, initial heat-sealing temperature 116 °C) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene, and the particle size of the anti-blocking agent is 4.5 µm);

[0191] Previous surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 1%); Core layer: 100 wt% first homopolypropylene (weight average molecular weight 300,000 g / mol, number average molecular weight 120,000 g / mol, molecular weight distribution index 2.5, melting point 170 °C, melt index 2 g / 10 min measured under conditions of 230 °C and 2.16 kg);

[0192] Next surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 1%);

[0193] Light layer: 95 wt% second homopolypropylene (melting point 165 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene PP, and the particle size of the anti-blocking agent is 4.5 μm);

[0194] 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 will not be elaborated.

[0195] The total thickness of the film is 14 µm, among which the thickness of the embossing layer is 1.7 µm, the thickness of the previous surface layer is 0.9 µm, the thickness of the next surface layer is 0.9 µm, and the thickness of the light layer is 1.3 µm.

[0196] The embossed rainbow effect of the lightweight anti-shrinkage BOPP laser film of this comparative example is normal after embossing, but the thermal shrinkage after embossing is too large to meet the processing requirements of downstream customers.

[0197] Comparative Example 6

[0198] This comparative example provides a lightweight anti-shrinkage BOPP laser film, including an embossing layer, a previous surface layer, a core layer, a next surface layer, and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0199] Embossing layer: 95 wt% ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured under conditions of 230 °C and 2.16 kg, initial heat-sealing temperature 116 °C) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene PP, and the particle size of the anti-blocking agent is 4.5 μm);

[0200] Previous surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%); Core layer: 100 wt% first homopolypropylene (weight average molecular weight 300,000 g / mol, number average molecular weight 120,000 g / mol, molecular weight distribution index 2.5, melting point 170 °C, melt index 2 g / 10 min measured under the conditions of 230 °C and 2.16 kg);

[0201] Next surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%);

[0202] Light layer: 95 wt% second homopolypropylene (melting point 165 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene PP, and the particle size of the anti-blocking agent is 4.5 μm);

[0203] The preparation method of the lightweight anti-shrinkage BOPP laser film in this comparative example is the same as that in Example 1, so it will not be elaborated here.

[0204] The total thickness of the film is 14 µm, among which the thickness of the embossing layer is 1.7 µm, the thickness of the previous surface layer is 1.2 µm, the thickness of the next surface layer is 1.2 µm, and the thickness of the light layer is 1.3 µm.

[0205] Comparative Example 7

[0206] This comparative example provides a lightweight anti-shrinkage BOPP laser film, which includes an embossing layer, a previous surface layer, a core layer, a next surface layer, and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0207] Embossing layer: 95 wt% ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg, initial heat-sealing temperature 116 °C) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene PP, and the particle size of the anti-blocking agent is 4.5 μm);

[0208] Previous surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%); Core layer: 100 wt% first homopolypropylene (weight average molecular weight 300,000 g / mol, number average molecular weight 120,000 g / mol, molecular weight distribution index 2.5, melting point 170 °C, melt index 2 g / 10 min measured under conditions of 230 °C and 2.16 kg);

[0209] Next surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%);

[0210] Light layer: 95 wt% second homopolypropylene (melting point 165 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg) and 5 wt% anti-blocking masterbatch (active ingredient is PMMA, active content is 5%, carrier is homopolypropylene, and the particle size of the anti-blocking agent is 4.5 μm);

[0211] 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 will not be elaborated here.

[0212] The total thickness of the film is 14 µm, among which the thickness of the embossing layer is 1.7 µm, the thickness of the previous surface layer is 0.6 µm, the thickness of the next surface layer is 0.6 µm, and the thickness of the light layer is 1.3 µm.

[0213] The rainbow effect of the lightweight anti-shrinkage BOPP laser film of this comparative example is normal after embossing, but the thermal shrinkage after embossing is too large to meet the processing requirements of downstream customers.

[0214] Comparative Example 8

[0215] This comparative example provides a lightweight anti-shrinkage BOPP laser film, which includes an embossing layer, a previous surface layer, a core layer, a next surface layer and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0216] Embossing layer: 95 wt% ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured under conditions of 230 °C and 2.16 kg, initial heat-sealing temperature 116 °C) and 5 wt% anti-blocking masterbatch (active ingredient is PMMA, active content is 5%, carrier is homopolypropylene, and the particle size of the anti-blocking agent is 4.5 μm);

[0217] Previous surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%); Core layer: 100 wt% first homopolypropylene (weight average molecular weight 300,000 g / mol, number average molecular weight 120,000 g / mol, molecular weight distribution index 2.5, melting point 170 °C, melt index 2 g / 10 min measured under conditions of 230 °C and 2.16 kg);

[0218] Next surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%);

[0219] Light layer: 95 wt% second homopolypropylene (melting point 165 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene, and the particle size of the anti-blocking agent is 4.5 μm);

[0220] The preparation method of the lightweight shrink-resistant BOPP laser film of this comparative example is the same as that of Example 1, so it will not be elaborated here.

[0221] The total thickness of the film is 14 µm, among which the thickness of the embossing layer is 1.0 µm, the thickness of the previous surface layer is 0.9 µm, the thickness of the next surface layer is 0.9 µm, and the thickness of the light layer is 1.3 µm.

[0222] When the lightweight shrink-resistant BOPP laser film of this comparative example is actually used, the appropriate embossing temperature is too high, and the thermal shrinkage rate is relatively large at the appropriate embossing temperature, which affects the use of downstream customers.

[0223] Comparative Example 9

[0224] This comparative example provides a lightweight shrink-resistant BOPP laser film, including an embossing layer, a previous surface layer, a core layer, a next surface layer, and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0225] Embossing layer: 95 wt% ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 7 g / 10 min measured under conditions of 230 °C and 2.16 kg, initial heat-sealing temperature 116 °C) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene, and the particle size of the anti-blocking agent is 4.5 μm);

[0226] Previous surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%); Core layer: 100 wt% first homopolypropylene (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 2 g / 10 min measured under conditions of 230 °C and 2.16 kg);

[0227] Next surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%);

[0228] Light layer: 95 wt% second homopolypropylene (melting point 165 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene, particle size of the anti-blocking agent is 4.5 μm);

[0229] The preparation method of the lightweight shrink-resistant BOPP laser film in this comparative example is the same as that in Example 1, so it will not be elaborated here.

[0230] The total thickness of the film is 14 µm, among which the thickness of the embossing layer is 2.0 µm, the thickness of the previous surface layer is 0.9 µm, the thickness of the next surface layer is 0.9 µm, and the thickness of the light layer is 1.3 µm.

[0231] The lightweight shrink-resistant BOPP laser film in this comparative example can only be used at a die-cutting temperature of 130 - 135 °C. When used at 134 - 135 °C, the phenomenon of too large heat shrinkage rate is likely to occur, and the product quality is unstable, affecting the use. If the customer strengthens the rainbow effect and raises the die-cutting temperature to 140 - 150 °C, the heat shrinkage will reach 8 - 12 mm, and the quality is unstable, affecting the use.

[0232] Comparative Example 10

[0233] This comparative example provides a lightweight shrink-resistant BOPP laser film, including an embossing layer, a previous surface layer, a core layer, a next surface layer, and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0234] Embossing layer: 95 wt% ethylene-propylene random copolymer polypropylene (melting point 135 °C, melt index 7 g / 10 min measured under conditions of 230 °C and 2.16 kg, initial heat-sealing temperature 125 °C) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene, particle size of the anti-blocking agent is 4.5 μm);

[0235] Previous surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%); Core layer: 100 wt% first homopolypropylene (weight average molecular weight 300,000 g / mol, number average molecular weight 120,000 g / mol, molecular weight distribution index 2.5, melting point 170 °C, melt index 2 g / 10 min measured under conditions of 230 °C and 2.16 kg);

[0236] Next surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%);

[0237] Light layer: 95 wt% second homopolypropylene (melting point 165 °C, melt index 3 g / 10 min measured under conditions of 230 °C and 2.16 kg) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene, and the particle size of the anti-blocking agent is 4.5 μm);

[0238] The preparation method of the lightweight anti-shrink BOPP laser film in this comparative example is the same as that in Example 1, so it will not be elaborated here.

[0239] The total thickness of the film is 14 µm, among which the thickness of the embossing layer is 1.7 µm, the thickness of the previous surface layer is 0.9 µm, the thickness of the next surface layer is 0.9 µm, and the thickness of the light layer is 1.3 µm.

[0240] When the lightweight anti-shrink BOPP laser film in this comparative example is actually used, the appropriate embossing temperature is too high, and the thermal shrinkage rate is relatively large at the appropriate embossing temperature, which affects the use by downstream customers.

[0241] Comparative Example 11

[0242] This comparative example provides a lightweight anti-shrink BOPP laser film, including an embossing layer, a previous surface layer, a core layer, a next surface layer, and a light layer arranged in sequence. The components and contents of each layer are as follows:

[0243] Embossing layer: 95 wt% ethylene-propylene random copolymer polypropylene (melting point 134 °C, melt index 8 g / 10 min measured under conditions of 230 °C and 2.16 kg, initial heat sealing temperature 110 °C) and 5 wt% anti-blocking masterbatch (effective ingredient is PMMA, effective content is 5%, carrier is homopolypropylene, and the particle size of the anti-blocking agent is 4.5 µm);

[0244] Previous surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%); Core layer: 100 wt% first homopolypropylene (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 2 g / 10 min measured under the conditions of 230 °C and 2.16 kg);

[0245] Next surface layer: 100 wt% modified polypropylene (melting point 175 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg, grafting rate of N-vinylpyrrolidone in the modified polypropylene is 3.5%);

[0246] Optical layer: 95 wt% second homopolypropylene (melting point 165 °C, melt index 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 5 wt% anti-blocking masterbatch (active ingredient is PMMA, active content is 5%, carrier is homopolypropylene, and the particle size of the anti-blocking agent is 4.5 μm);

[0247] The preparation method of the lightweight anti-shrinkage BOPP laser film in this comparative example is the same as that in Example 1, so it will not be elaborated.

[0248] The total thickness of the film is 14 µm, among which the thickness of the embossing layer is 1.7 µm, the thickness of the previous surface layer is 0.9 µm, the thickness of the next surface layer is 0.9 µm, and the thickness of the optical layer is 1.3 µm.

[0249] The embossing parameters of the lightweight anti-shrinkage BOPP laser film in this comparative example are difficult to control, and the phenomenon of sticking to the roller will occur, which will affect the film surface quality and embossing effect, and the problem of corona blackening may occur when the customer increases the corona power.

[0250] The performance test results of the lightweight anti-shrinkage BOPP laser films in Examples 1 to 12 are shown in Table 1 below, and the performance test results of the lightweight anti-shrinkage BOPP laser films in Comparative Examples 1 to 11 are shown in Table 2 below.

[0251] Table 1

[0252]

[0253] Table 2

[0254]

[0255] Combined with the above performance test data, it can be seen that the lightweight shrinkage-resistant BOPP laser films of Examples 1-12 of the present invention can all achieve the following effects: on the premise of 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 at the same time ensuring smooth production of the BOPP laser film.

[0256] For the BOPP laser film of Comparative Example 1, neither the upper surface layer nor the lower surface layer adopted modified polypropylene. Although a normal embossed rainbow effect can be obtained after embossing the BOPP laser film at the embossing temperature commonly used by customers, the thermal shrinkage rate after embossing is too large to meet the processing requirements of downstream customers.

[0257] For the BOPP laser film of Comparative Example 2, both the weight-average molecular weight and the number-average molecular weight of the first homopolypropylene in the core layer are too small, and the molecular weight distribution index is too large. The prepared BOPP laser film has a large haze, resulting in a poor embossed rainbow effect, and there is also a problem that the thermal shrinkage rate after embossing is too large to meet the processing requirements of downstream customers.

[0258] For the BOPP laser film of Comparative Example 3, both the weight-average molecular weight and the number-average molecular weight of the first homopolypropylene in the core layer are too large, and the molecular weight distribution index is too small. When preparing the BOPP laser film, continuous film breakage is likely to occur, and the production is not smooth.

[0259] For the BOPP laser film of Comparative Example 4, the NVP grafting rate in the modified polypropylene is too large. When preparing the BOPP laser film, continuous film breakage is likely to occur, and the production is not smooth.

[0260] For the BOPP laser film of Comparative Example 5, the NVP grafting rate in the modified polypropylene is too small. Although a normal embossed rainbow effect can be obtained after embossing the BOPP laser film at the embossing temperature commonly used by customers, the thermal shrinkage rate after embossing is too large to meet the processing requirements of downstream customers.

[0261] For the BOPP laser film of Comparative Example 6, both the thickness of the upper surface layer and the thickness of the lower surface layer are too large. When preparing the BOPP laser film, continuous film breakage is likely to occur, and the production is not smooth.

[0262] For the BOPP laser film of Comparative Example 7, both the thickness of the upper surface layer and the thickness of the lower surface layer are too small. Although a normal embossed rainbow effect can be obtained after embossing the BOPP laser film at the embossing temperature commonly used by customers, the thermal shrinkage rate after embossing is too large to meet the processing requirements of downstream customers.

[0263] For the BOPP laser film of Comparative Example 8, the thickness of the embossed layer is too small. The BOPP laser film needs to be embossed at an increased embossing temperature to obtain a normal embossed rainbow effect, but after increasing the embossing temperature, the thermal shrinkage rate of the BOPP laser film is too large to meet the processing requirements of downstream customers.

[0264] The thickness of the embossing layer of the BOPP laser film in Comparative Example 9 is too large, and the adjustable range of the embossing temperature of the BOPP laser film becomes smaller, which is not convenient for flexible adjustment by customers. For example, when customers need to enhance the rainbow effect, increasing the embossing temperature will result in too large a heat shrinkage rate, unable to meet the processing requirements of downstream customers; another example is that when the temperature control effect of the customer's equipment is relatively inaccurate, problems such as too large a shrinkage rate and unstable product quality are more likely to occur.

[0265] The starting heat-sealing temperature of the ethylene-propylene random copolymer polypropylene in the embossing layer of the BOPP laser film in Comparative Example 10 is too high. It is necessary to increase the embossing temperature to obtain a normal embossed rainbow effect during embossing, but after increasing the embossing temperature, the heat shrinkage rate of the BOPP laser film is too large, unable to meet the processing requirements of downstream customers.

[0266] The starting heat-sealing temperature of the ethylene-propylene random copolymer polypropylene in the embossing layer of the BOPP laser film in Comparative Example 11 is too low. The BOPP laser film needs to reduce the embossing temperature to obtain a normal embossed rainbow effect and ensure an appropriate shrinkage rate during embossing, but the embossing parameters are difficult to control, and the phenomenon of sticking to the roller will occur, affecting the film surface quality and embossing effect, and it is not suitable for the production scenario of processing with a large corona power. Increasing the corona power is more likely to cause the problem of corona blackening.

[0267] The above-described embodiments only represent several implementation manners of the present invention, and the description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and the present invention also intends to include these modifications and deformations.

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, N-vinyl pyrrolidone in the modified polypropylene is ethylene-propylene copolymerized ... 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 olefin group is grafted with the polypropylene, the grafting rate of N-vinyl pyrrolidone in the modified polypropylene is 2-5%, the raw material for preparing the modified polypropylene also includes 0.05-0.1wt% of divinylbenzene, the melting point of the modified polypropylene is 170-180°C, and the melt index of the modified polypropylene measured at 230°C and 2.16kg is 2-4g / 10min, the optical layer includes a second homopolymer polypropylene, the total thickness of the BOPP laser film is 13-14μm, and the thickness of the upper surface layer and the lower surface layer are both 0.8-1μm.

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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, and the thickness of the optical layer is 1.2-1.5 μm.

8. A method for preparing a lightweight anti-shrinkage BOPP laser film according to any one of claims 1 to 7, characterized in that: The method comprises 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 respectively to form a homogenized melt; the melt is filtered and then co-extruded through a die head in multiple layers; according to a flat film method, a film is cast and then quenched into a thick film; the thick film is subjected to a biaxial stretching method of first longitudinal stretching and then transverse stretching to form a biaxially stretched film; after cooling, the biaxially stretched film is subjected to a corona treatment, and then rolled into a mother roll; after an aging treatment, the mother roll is slit into a finished product.

9. The method for preparing a lightweight anti-shrinkage BOPP laser film according to claim 8, 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