Biaxially oriented polypropylene aluminized label film and preparation method thereof

Abstract

The present invention relates to a biaxially oriented polypropylene aluminized label film and a preparation method thereof, and belongs to the technical field of aluminized label films. The biaxially oriented polypropylene aluminized label film comprises an aluminized layer, an intermediate layer and a lower surface layer arranged in sequence; the aluminized layer comprises copolymerized polypropylene and 5-10wt% nadic anhydride grafted polyolefin elastomer; the grafting rate of nadic anhydride in the nadic anhydride grafted polyolefin elastomer is 15-25%; the intermediate layer comprises homopolymerized polypropylene, 10-20wt% pearlescent masterbatch and 4-7wt% polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer. The biaxially oriented polypropylene aluminized label film of the present invention has a large surface tension of the aluminized layer and a long-lasting surface tension through the coordinated design of the aluminized layer and the intermediate layer, and the aluminum layer formed on the surface of the aluminized layer after the film is vacuum-deposited has strong adhesion.

Description

Technical Field

[0001] The invention relates to the technical field of aluminized label films, in particular to a biaxially oriented polypropylene aluminized label film and a preparation method thereof. Background Art

[0002] Biaxially oriented polypropylene (BOPP) aluminized label film is usually white opaque BOPP film. When used, the biaxially oriented polypropylene aluminized label film is first vacuum-deposited (aluminized) to form an aluminum layer on the surface of the aluminized layer of the biaxially oriented polypropylene aluminized label film, so that the film has a metallic luster. Then, it is made into a wraparound label or self-adhesive label through coating, printing and other processes. It is widely used in the labeling of polyester bottles and spray bottles, giving the products a decorative and anti-counterfeiting effect.

[0003] However, the surface tension of the aluminum layer of the traditional biaxially oriented polypropylene aluminized label film is insufficient. After vacuum evaporation, the aluminum layer on the surface of the aluminized layer is prone to poor adhesion and aluminum falling off. Furthermore, even after the aluminum layer is attached, corona attenuation of the aluminum layer will occur, affecting subsequent coating and printing work. Summary of the invention

[0004] Based on this, the object of the present invention is to provide a biaxially oriented polypropylene aluminized label film and a preparation method thereof, wherein the aluminized layer of the biaxially oriented polypropylene aluminized label film has a large surface tension and a long-lasting surface tension, and the aluminum layer formed on the surface of the aluminized layer after the film is vacuum evaporated (aluminized) has strong adhesion.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The invention provides a biaxially stretched polypropylene aluminized label film, comprising an aluminized layer, an intermediate layer and a lower surface layer which are arranged in sequence; the aluminized layer comprises copolymerized polypropylene and 5-10wt% of nadic anhydride grafted polyolefin elastomer; the grafting rate of nadic anhydride in the nadic anhydride grafted polyolefin elastomer is 15-25%; the intermediate layer comprises homopolymerized polypropylene, 10-20wt% of pearlescent masterbatch and 4-7wt% of polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer; the molecular chain of the polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer is formed by sequential block copolymerization of a polymethyl methacrylate segment, a polypropylene segment and a polymethyl methacrylate segment, wherein two polymethyl methacrylate segments are respectively connected by 3 or 4 methyl methacrylate copolymerization units, and the polypropylene segment is connected by 8 or 9 propylene copolymerization units.

[0007] The biaxially oriented polypropylene aluminized label film of the present invention adds the nadic anhydride grafted polyolefin elastomer to the aluminizable layer, which is beneficial to blocking the migration of small molecular substances in the middle layer to the surface of the aluminizable layer; adding the polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer to the middle layer is beneficial to reducing the migration of small molecular substances in the middle layer to the aluminizable layer; through the coordinated design of the aluminizable layer and the middle layer, the surface tension of the aluminizable layer of the biaxially oriented polypropylene aluminized label film is large and the surface tension is long-lasting; the aluminum layer formed on the surface of the aluminizable layer after the film is vacuum evaporated (aluminized) has strong adhesion and is not prone to aluminum shedding; the surface tension of the aluminum layer is large and the surface tension is long-lasting, which is beneficial to subsequent coating, printing and other work.

[0008] The present invention adds 4-7wt% of polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer to the intermediate layer, which can effectively improve the situation that the surface tension of the conventional biaxially oriented polypropylene aluminized label film on the aluminizable layer is significantly attenuated (i.e., the surface tension of the aluminizable layer is not persistent), and the surface tension of the aluminum layer formed after the aluminizing on the surface of the aluminizable layer is significantly attenuated (i.e., the surface tension of the aluminum layer is not persistent). At present, the effective components of pearlescent masterbatch are mainly small molecular substances such as small molecular fatty acids and small molecular esters that coat the surface of calcium carbonate, but these small molecular substances only exist on the surface of calcium carbonate particles through physical action, and are unstable in combination with the surface of calcium carbonate. Moreover, these small molecular substances will migrate to the surface of the aluminizable layer over time, further embedding the polar groups on the surface of the aluminizable layer. Moreover, the biaxially oriented polypropylene aluminized label film is usually subjected to corona treatment before aluminizing, which will further aggravate the migration of small molecular substances, cover the polar groups generated by the corona treatment, and cause the surface of the aluminizable layer to have extremely low surface tension after being stored for a period of time, affecting the subsequent processing of aluminizing. The present invention adds 4-7wt% of polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer into the middle layer, wherein the molecular chain of the polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer comprises polymethyl methacrylate segments, polypropylene segments and polymethyl methacrylate segments which are connected in sequence; wherein the ester groups on the two polymethyl methacrylate segments interact with small molecular substances on the surface of calcium carbonate or polar groups of calcium carbonate itself, and such interaction is conducive to enhancing the compatibility and binding force between the polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer and the pearlescent masterbatch; meanwhile, the polypropylene segments can be compatible with the homopolymerized polypropylene in the middle layer and be combined and anchored in the homopolymerized polypropylene matrix in the middle layer, and finally the small molecular substances are anchored on the homopolymerized polypropylene matrix, thereby reducing the small molecular substances in the pearlescent masterbatch from migrating to the aluminum-platable layer and covering the polar groups generated by corona treatment on the surface of the film, and is conducive to improving the situation that the surface of the aluminum-platable layer has low surface tension after being stored for a period of time, which affects subsequent processing. The content of the polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer in the intermediate layer is 4-7wt%. If the content of the polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer in the intermediate layer is lower than 4wt%, it will not reduce the migration of small molecules, and will easily lead to a small surface tension and non-persistent surface tension of the aluminum-platable layer itself or the aluminum layer formed after aluminum plating on the surface of the aluminum-platable layer. If the content of the polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer in the intermediate layer is higher than 7wt%, the molecular chains of the substances in the intermediate layer will be entangled to a certain extent, causing the shear viscosity of the melt to increase, affecting the smoothness of production.

[0009] The molecular chain of the polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer is formed by sequential block copolymerization of polymethyl methacrylate segments, polypropylene segments and polymethyl methacrylate segments, wherein two polymethyl methacrylate segments are connected by 3 or 4 methyl methacrylate copolymerization units, and the polypropylene segment is connected by 8 or 9 propylene copolymerization units. If the amount of methyl methacrylate as a copolymerization unit in the polymethyl methacrylate segment is too low, the effect of maintaining the high surface tension of the aluminum layer after the film is aluminized cannot be achieved; if the amount of methyl methacrylate as a copolymerization unit in the polymethyl methacrylate segment is too high, due to the high rigidity of the polymethyl methacrylate segment, stress concentration may occur in the film when it is subjected to force, thereby increasing the risk of smooth production. If the amount of propylene as a copolymer unit in the polypropylene segment is too low, it is easy to cause the compatibility and bonding strength of the polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer with the homopolypropylene in the intermediate layer to be too low, which is not conducive to anchoring small molecules on the homopolypropylene matrix, resulting in the possibility that small molecules may migrate to the aluminum-plated layer and cover the polar groups on the surface of the aluminum-plated layer, resulting in a decrease in the surface tension of the aluminum-plated layer after being stored for a period of time; if the amount of propylene as a copolymer unit in the polypropylene segment is too high, it is easy to cause the compatibility and bonding strength of the polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer with the homopolypropylene in the intermediate layer to be too high, increasing the possibility of entanglement between molecular chains, resulting in an increase in the shear viscosity of the melt, and affecting the smoothness of production.

[0010] The biaxially oriented polypropylene aluminized label film described in the present invention also designs an aluminized layer, which includes copolymerized polypropylene and 5-10wt% nadic anhydride grafted polyolefin elastomer. The aluminized layer can block the migration of small molecular substances in the middle layer, which is beneficial to slowing down the attenuation rate of the surface tension of the aluminized layer, ensuring that the aluminum layer formed after aluminizing and the coating formed by subsequent processing have strong adhesion.

[0011] The present invention can play a role in blocking the migration of small molecular substances in the middle layer by adding nadic anhydride grafted polyolefin elastomer to the aluminum-platable layer, while ensuring the surface tension of the aluminum-platable layer. The nadic anhydride grafted polyolefin elastomer added to the aluminum-platable layer contains a cyclic norbornene structure, has large steric hindrance, belongs to a non-crystalline unit, can be filled into the amorphous region of the copolymerized polypropylene with high crystallinity, and through the joint action of the crystalline region and the non-crystalline region, the interaction force in the process of blending the nadic anhydride grafted polyolefin elastomer and the copolymerized polypropylene is improved, which is conducive to reducing the gap between the molecular chain of the nadic anhydride grafted polyolefin elastomer and the molecular chain of the copolymerized polypropylene, and finally plays a certain role in blocking the migration of small molecular substances in the middle layer, so that the polar groups generated by the aluminum-platable layer are not easily covered. At the same time, the acyloxy group in the nadic anhydride grafted polyolefin elastomer can chemically bond with the aluminum layer to form a strong binding force. In addition, there is a physical adsorption effect such as van der Waals force, which can improve the wettability and adhesion of the surface of the aluminum-platable layer, making it easier to accept the attachment of the aluminum layer, and can improve the film adhesion ability and the surface wettability of the aluminum-platable layer. The content of the nadic anhydride grafted polyolefin elastomer in the aluminum-platable layer is 5-10wt%. If the content of the nadic anhydride grafted polyolefin elastomer in the aluminum-platable layer is lower than 5wt%, it will not play a role in improving the adhesion of the aluminum layer on the surface of the aluminum-platable layer, which is not conducive to the durability of the surface tension of the aluminum-platable layer; if the content of the nadic anhydride grafted polyolefin elastomer in the aluminum-platable layer is higher than 10wt%, the introduction of too many ring structures will increase the steric hindrance effect of the copolymerized polypropylene molecular chain, so that the movement of the molecular chain is restricted, resulting in a decrease in the mechanical properties of the film.

[0012] The present invention limits the grafting rate of nadic anhydride in the nadic anhydride grafted polyolefin elastomer to 15-25%, so that the surface tension of the aluminum layer after aluminum plating of the aluminum-platable layer can be best maintained. If the grafting rate of nadic anhydride in the nadic anhydride grafted polyolefin elastomer is lower than 15%, it cannot achieve the effect of maintaining the surface tension of the aluminum plating layer itself or the aluminum layer after aluminum plating on the surface of the aluminum-platable layer to be large and the surface tension to be long-lasting; if the grafting rate of nadic anhydride in the nadic anhydride grafted polyolefin elastomer is higher than 25%, due to the rigid structure of nadic anhydride, excessive nadic anhydride will make the film brittle, resulting in a decrease in the mechanical properties of the film.

[0013] Furthermore, in the aluminum-platable layer, the melt index of the nadic anhydride grafted polyolefin elastomer is 8-12g / 10min (measurement conditions: 230°C, 2.16kg). If the melt index of the nadic anhydride grafted polyolefin elastomer is lower than 8g / 10min, the nadic anhydride grafted polyolefin elastomer has poor fluidity during the mixing process with copolymerized polypropylene, resulting in uneven mechanical properties and affecting production smoothness; if the melt index of the nadic anhydride grafted polyolefin elastomer is higher than 12g / 10min, the structure of the aluminum-platable layer may become loose, thereby reducing the barrier performance to small molecules in the middle layer.

[0014] Furthermore, the preparation method of the nadic anhydride grafted polyolefin elastomer is: grafting nadic anhydride monomer onto polyolefin elastomer by melt grafting method.

[0015] Furthermore, the polyolefin elastomer is an ethylene-butene copolymer elastomer, and nadic anhydride is grafted onto the secondary carbon of butene in the ethylene-butene copolymer elastomer.

[0016] Furthermore, in the aluminum-platable layer, the melt index of the copolymerized polypropylene is 6-10 g / 10 min (measurement conditions: 230° C., 2.16 kg), and the copolymerized polypropylene is a random ethylene-propylene copolymer.

[0017] Furthermore, in the intermediate layer, the pearlescent masterbatch is a mixture of 15-25wt% copolymerized polypropylene and 75-85wt% inorganic filler; the inorganic filler is obtained by treating 3-5wt% of at least one of small molecule fatty acids (such as stearic acid) and small molecule esters (such as phthalate, aluminate) as a surface treatment agent and 95-97wt% of calcium carbonate as a filler in a high-speed mixer.

[0018] Furthermore, the particle size of the calcium carbonate is 0.5-1.5 μm; in order to balance the foaming effect and cost considerations, it is preferably 0.8-1.3 μm.

[0019] Furthermore, the lower surface layer includes homopolymer polypropylene and 1-5wt% anti-adhesion masterbatch. Adding an appropriate amount of anti-adhesion masterbatch to the lower surface layer is beneficial to increasing the smoothness of winding and unwinding the biaxially oriented polypropylene aluminized label film. If the content of the anti-adhesion masterbatch in the lower surface layer is lower than 1wt%, it will not have an effective anti-adhesion effect; if the content of the anti-adhesion masterbatch in the lower surface layer is higher than 5wt%, the anti-adhesion agent is likely to fall off during the production process, resulting in contamination of the guide roller and affecting the appearance of the product.

[0020] Furthermore, the effective component of the anti-adhesion masterbatch is at least one of silicon dioxide, talc and calcium carbonate, and the particle size of the effective component of the anti-adhesion masterbatch is 3-6 μm, preferably 4-5 μm in order to take into account the thickness of the lower surface layer and the problem of shedding.

[0021] Furthermore, the homopolypropylene in the middle layer, the homopolypropylene in the pearlescent masterbatch, and the homopolypropylene in the lower surface layer have a melt index of 3-8 g / 10 min (measurement conditions: 230° C., 2.16 kg).

[0022] The present invention also provides a method for preparing a biaxially oriented polypropylene aluminized label film, comprising the following steps:

[0023] Step 1: Batching and plasticization: The proportion of each layer of raw materials is set in the control system of the biaxial stretch film production line, and then the batching system will automatically transport the dried raw materials of each layer to each layer extruder according to the input ratio. After melting and plasticizing in each layer extruder, the melt enters the die head through the runner and distributor;

[0024] Step 2: Slice casting: After being extruded through the die, the melt immediately contacts the cooling roller to form a thick sheet;

[0025] Step 3: Longitudinal stretching: The thick sheet is heated to the set temperature by multiple sets of preheating rollers, and then longitudinal stretching is started, and then shaping is performed;

[0026] Step 4: Horizontal stretching: After preheating the thick sheet after longitudinal stretching to the set temperature, start horizontal stretching, and then perform shaping and cooling treatment after horizontal stretching;

[0027] Step 5: Traction and rewinding: The multi-layer film from the horizontal pulling unit enters the traction unit, and after thickness measurement and corona treatment, enters the rewinding unit to obtain a parent roll;

[0028] Step 6: Slitting: Slitting the aged mother roll to obtain film rolls of specified width and length.

[0029] As a preferred scheme, in the above process, the melt extrusion temperature of the aluminum-plated layer is: 200-260℃; the melt extrusion temperature of the middle layer and the lower surface layer is: 230-260℃; in the process of the melt contacting the cooling roller, the temperature of the chilling water and the chilling roller is: 15-50℃; the temperature of the longitudinal stretching zone is: 90-130℃; the temperature of the transverse stretching zone is: 155-165℃; the longitudinal stretching ratio is 4.5-5.5 times; the transverse stretching ratio is: 8-10 times; the corona power factor of the aluminum-plated layer is: 20-25W·min / m. DETAILED DESCRIPTION

[0030] The present invention will be described in more detail below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. The experimental methods in the following examples or comparative examples without specifying specific conditions are generally carried out according to conventional conditions in the art or according to conditions recommended by the manufacturer; the raw materials, reagents, etc. used, unless otherwise specified, are all raw materials and reagents that can be obtained from commercial channels such as conventional markets.

[0031] In the following examples or comparative examples:

[0032] The melt index (melt mass flow rate MFR) is determined according to GB / T3682-2018.

[0033] The melt index of the copolymerized polypropylene is 8 g / 10 min (measurement conditions: 230° C., 2.16 kg), and the copolymerized polypropylene is a random ethylene-propylene copolymer.

[0034] The melt index of homopolymer polypropylene is 3.0 g / 10min (measurement conditions: 230 °C, 2.16 kg), and the density is 0.905 g / cm 3 , the isotacticity is 96%.

[0035] The preparation method of the nadic anhydride grafted polyolefin elastomer is as follows: by melt grafting, nadic anhydride monomer is grafted onto a polyolefin elastomer to obtain the elastomer; wherein the polyolefin elastomer is an ethylene-butene copolymer elastomer, and the nadic anhydride monomer is grafted onto the secondary carbon of the butene of the ethylene-butene copolymer elastomer.

[0036] The pearlescent masterbatch is mixed with 20wt% homopolypropylene and 80wt% inorganic filler; the preparation method of the inorganic filler is: 4wt% stearic acid is used as a filler surface treatment agent and 96wt% calcium carbonate is used as a filler in a high-speed mixer to obtain the pearlescent masterbatch.

[0037] The effective component of the anti-blocking masterbatch is silicon dioxide, and the particle size of silicon dioxide is 4.5 μm.

[0038] Example 1

[0039] This embodiment provides a biaxially oriented polypropylene aluminized label film, comprising an aluminized layer, an intermediate layer and a lower surface layer which are arranged in sequence.

[0040] Among them, the formula of each layer is as follows:

[0041] Aluminum-platable layer: 95wt% copolymerized polypropylene and 5wt% nadic anhydride grafted polyolefin elastomer (melt index is 10g / 10min, measurement conditions: 230℃, 2.16kg, nadic anhydride grafting rate is 15%);

[0042] Middle layer: 83wt% homopolypropylene, 10wt% pearlescent masterbatch and 7wt% polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer (two polymethyl methacrylate segments are connected by 4 methyl methacrylate copolymer units, and the polypropylene segment is connected by 9 propylene copolymer units);

[0043] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0044] The total thickness of the biaxially oriented polypropylene aluminized label film of this embodiment is 30 μm, the thickness of the aluminized layer is 1.8 μm, and the thickness of the lower surface layer is 1.0 μm.

[0045] This embodiment also provides a method for preparing a biaxially oriented polypropylene aluminized label film, comprising the following steps:

[0046] Step 1: Batching and plasticization: The proportion of each layer of raw materials is set in the control system of the biaxial stretch film production line, and then the batching system will automatically transport the dried raw materials of each layer to each layer extruder according to the input ratio. After melting and plasticizing in each layer extruder, the melt enters the die head through the runner and distributor;

[0047] Step 2: Slice casting: After being extruded through the die, the melt immediately contacts the cooling roller to form a thick sheet;

[0048] Step 3: Longitudinal stretching: The thick sheet is heated to the set temperature by multiple sets of preheating rollers, and then longitudinal stretching is started, and then shaping is performed;

[0049] Step 4: Horizontal stretching: After preheating the thick sheet after longitudinal stretching to the set temperature, start horizontal stretching, and then perform shaping and cooling treatment after horizontal stretching;

[0050] Step 5: Traction and rewinding: The multi-layer film from the horizontal pulling unit enters the traction unit, and after thickness measurement and corona treatment, enters the rewinding unit to obtain a parent roll;

[0051] Step 6: Slitting: Slitting the aged mother roll to obtain film rolls of specified width and length.

[0052] In the above process, the melt extrusion temperature of the aluminum-plated layer is 235°C; the melt extrusion temperature of the middle layer and the lower surface layer is 250°C; in the process of the melt contacting the cooling roller, the temperature of the chilling water and the chilling roller is 40°C; the temperature of the longitudinal stretching zone is 125°C; the temperature of the transverse stretching zone is 160°C; the longitudinal stretching ratio is 5.3 times; the transverse stretching ratio is 8.5 times; the corona power factor of the aluminum-plated layer is 23.5W·min / m.

[0053] Example 2

[0054] This embodiment provides a biaxially oriented polypropylene aluminized label film, comprising an aluminized layer, an intermediate layer and a lower surface layer which are arranged in sequence.

[0055] Among them, the formula of each layer is as follows:

[0056] Aluminum-platable layer: 92wt% copolymerized polypropylene and 8wt% nadic anhydride grafted polyolefin elastomer (melt index is 10g / 10min, measurement conditions: 230℃, 2.16kg, nadic anhydride grafting rate is 20%);

[0057] Middle layer: 80wt% homopolypropylene, 15wt% pearlescent masterbatch and 5wt% polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer (two polymethyl methacrylate segments are connected by 4 methyl methacrylate copolymer units, and the polypropylene segment is connected by 8 propylene copolymer units);

[0058] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0059] The total thickness and thickness of each layer of the biaxially oriented polypropylene aluminized label film of this embodiment are the same as those of Embodiment 1.

[0060] The preparation method of the biaxially oriented polypropylene aluminized label film of this embodiment is the same as that of embodiment 1.

[0061] Example 3

[0062] This embodiment provides a biaxially oriented polypropylene aluminized label film, comprising an aluminized layer, an intermediate layer and a lower surface layer which are arranged in sequence.

[0063] Among them, the formula of each layer is as follows:

[0064] Aluminum-platable layer: 90wt% copolymerized polypropylene and 10wt% nadic anhydride grafted polyolefin elastomer (melt index is 10g / 10min, measurement conditions: 230℃, 2.16kg, nadic anhydride grafting rate is 25%);

[0065] Middle layer: 76wt% homopolypropylene, 20wt% pearlescent masterbatch and 4wt% polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer (two polymethyl methacrylate segments are connected by 3 methyl methacrylate copolymer units, and the polypropylene segment is connected by 8 propylene copolymer units);

[0066] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0067] The total thickness and thickness of each layer of the biaxially oriented polypropylene aluminized label film of this embodiment are the same as those of Embodiment 1.

[0068] The preparation method of the biaxially oriented polypropylene aluminized label film of this embodiment is the same as that of embodiment 1.

[0069] Comparative Example 1

[0070] The comparative example provides a biaxially oriented polypropylene aluminized label film, comprising an aluminized layer, an intermediate layer and a lower surface layer which are arranged in sequence.

[0071] Among them, the formula of each layer is as follows:

[0072] Aluminum-plated layer: 100wt% copolymerized polypropylene;

[0073] Middle layer: 80wt% homopolypropylene, 15wt% pearlescent masterbatch and 5wt% polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer (two polymethyl methacrylate segments are connected by 4 methyl methacrylate copolymer units, and the polypropylene segment is connected by 8 propylene copolymer units);

[0074] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0075] The total thickness and thickness of each layer of the biaxially oriented polypropylene aluminized label film of this comparative example are the same as those of Example 1.

[0076] The preparation method of the biaxially oriented polypropylene aluminized label film of this comparative example is the same as that of Example 1.

[0077] Comparative Example 2

[0078] The comparative example provides a biaxially oriented polypropylene aluminized label film, comprising an aluminized layer, an intermediate layer and a lower surface layer which are arranged in sequence.

[0079] Among them, the formula of each layer is as follows:

[0080] Aluminum-platable layer: 98wt% copolymerized polypropylene and 2wt% nadic anhydride grafted polyolefin elastomer (melt index is 10g / 10min, measurement conditions: 230℃, 2.16kg, nadic anhydride grafting rate is 20%);

[0081] Middle layer: 80wt% homopolypropylene, 15wt% pearlescent masterbatch and 5wt% polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer (two polymethyl methacrylate segments are connected by 4 methyl methacrylate copolymer units, and the polypropylene segment is connected by 8 propylene copolymer units);

[0082] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0083] The total thickness and thickness of each layer of the biaxially oriented polypropylene aluminized label film of this comparative example are the same as those of Example 1.

[0084] The preparation method of the biaxially oriented polypropylene aluminized label film of this comparative example is the same as that of Example 1.

[0085] Comparative Example 3

[0086] The comparative example provides a biaxially oriented polypropylene aluminized label film, comprising an aluminized layer, an intermediate layer and a lower surface layer which are arranged in sequence.

[0087] Among them, the formula of each layer is as follows:

[0088] Aluminum-platable layer: 85wt% copolymerized polypropylene and 15wt% nadic anhydride grafted polyolefin elastomer (melt index is 10g / 10min, measurement conditions: 230℃, 2.16kg, nadic anhydride grafting rate is 20%);

[0089] Middle layer: 80wt% homopolypropylene, 15wt% pearlescent masterbatch and 5wt% polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer (two polymethyl methacrylate segments are connected by 4 methyl methacrylate copolymer units, and the polypropylene segment is connected by 8 propylene copolymer units);

[0090] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0091] The total thickness and thickness of each layer of the biaxially oriented polypropylene aluminized label film of this comparative example are the same as those of Example 1.

[0092] The preparation method of the biaxially oriented polypropylene aluminized label film of this comparative example is the same as that of Example 1.

[0093] Comparative Example 4

[0094] The comparative example provides a biaxially oriented polypropylene aluminized label film, comprising an aluminized layer, an intermediate layer and a lower surface layer which are arranged in sequence.

[0095] Among them, the formula of each layer is as follows:

[0096] Aluminum-platable layer: 92wt% copolymerized polypropylene and 8wt% nadic anhydride grafted polyolefin elastomer (melt index is 10g / 10min, measurement conditions: 230℃, 2.16kg, nadic anhydride grafting rate is 10%);

[0097] Middle layer: 80wt% homopolypropylene, 15wt% pearlescent masterbatch and 5wt% polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer (two polymethyl methacrylate segments are connected by 4 methyl methacrylate copolymer units, and the polypropylene segment is connected by 9 propylene copolymer units);

[0098] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0099] The total thickness and thickness of each layer of the biaxially oriented polypropylene aluminized label film of this comparative example are the same as those of Example 1.

[0100] The preparation method of the biaxially oriented polypropylene aluminized label film of this comparative example is the same as that of Example 1.

[0101] Comparative Example 5

[0102] The comparative example provides a biaxially oriented polypropylene aluminized label film, comprising an aluminized layer, an intermediate layer and a lower surface layer which are arranged in sequence.

[0103] Among them, the formula of each layer is as follows:

[0104] Aluminum-platable layer: 92wt% copolymerized polypropylene and 8wt% nadic anhydride grafted polyolefin elastomer (melt index is 10g / 10min, measurement conditions: 230℃, 2.16kg, nadic anhydride grafting rate is 30%);

[0105] Middle layer: 80wt% homopolypropylene, 15wt% pearlescent masterbatch and 5wt% polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer (two polymethyl methacrylate segments are connected by 4 methyl methacrylate copolymer units, and the polypropylene segment is connected by 8 propylene copolymer units);

[0106] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0107] The total thickness and thickness of each layer of the biaxially oriented polypropylene aluminized label film of this comparative example are the same as those of Example 1.

[0108] The preparation method of the biaxially oriented polypropylene aluminized label film of this comparative example is the same as that of Example 1.

[0109] Comparative Example 6

[0110] The comparative example provides a biaxially oriented polypropylene aluminized label film, comprising an aluminized layer, an intermediate layer and a lower surface layer which are arranged in sequence.

[0111] Among them, the formula of each layer is as follows:

[0112] Aluminum-platable layer: 92wt% copolymerized polypropylene and 8wt% nadic anhydride grafted polyolefin elastomer (melt index is 10g / 10min, measurement conditions: 230℃, 2.16kg, nadic anhydride grafting rate is 20%);

[0113] Middle layer: 85wt% homopolymer polypropylene and 15wt% pearlescent masterbatch;

[0114] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0115] The total thickness and thickness of each layer of the biaxially oriented polypropylene aluminized label film of this comparative example are the same as those of Example 1.

[0116] The preparation method of the biaxially oriented polypropylene aluminized label film of this comparative example is the same as that of Example 1.

[0117] Comparative Example 7

[0118] The comparative example provides a biaxially oriented polypropylene aluminized label film, comprising an aluminized layer, an intermediate layer and a lower surface layer which are arranged in sequence.

[0119] Among them, the formula of each layer is as follows:

[0120] Aluminum-platable layer: 92wt% copolymerized polypropylene and 8wt% nadic anhydride grafted polyolefin elastomer (melt index is 10g / 10min, measurement conditions: 230℃, 2.16kg, nadic anhydride grafting rate is 20%);

[0121] Middle layer: 83wt% homopolypropylene, 15wt% pearlescent masterbatch and 2wt% polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer (two polymethyl methacrylate segments are connected by 4 methyl methacrylate copolymer units, and the polypropylene segment is connected by 9 propylene copolymer units);

[0122] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0123] The total thickness and thickness of each layer of the biaxially oriented polypropylene aluminized label film of this comparative example are the same as those of Example 1.

[0124] The preparation method of the biaxially oriented polypropylene aluminized label film of this comparative example is the same as that of Example 1.

[0125] Comparative Example 8

[0126] The comparative example provides a biaxially oriented polypropylene aluminized label film, comprising an aluminized layer, an intermediate layer and a lower surface layer which are arranged in sequence.

[0127] Among them, the formula of each layer is as follows:

[0128] Aluminum-platable layer: 92wt% copolymerized polypropylene and 8wt% nadic anhydride grafted polyolefin elastomer (melt index is 10g / 10min, measurement conditions: 230℃, 2.16kg, nadic anhydride grafting rate is 20%);

[0129] Middle layer: 75wt% homopolypropylene, 15wt% pearlescent masterbatch and 10wt% polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer (two polymethyl methacrylate segments are connected by 4 methyl methacrylate copolymer units, and the polypropylene segment is connected by 9 propylene copolymer units);

[0130] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0131] The total thickness and thickness of each layer of the biaxially oriented polypropylene aluminized label film of this comparative example are the same as those of Example 1.

[0132] The preparation method of the biaxially oriented polypropylene aluminized label film of this comparative example is the same as that of Example 1.

[0133] Comparative Example 9

[0134] The comparative example provides a biaxially oriented polypropylene aluminized label film, comprising an aluminized layer, an intermediate layer and a lower surface layer which are arranged in sequence.

[0135] Among them, the formula of each layer is as follows:

[0136] Aluminum-platable layer: 92wt% copolymerized polypropylene and 8wt% nadic anhydride grafted polyolefin elastomer (melt index is 10g / 10min, measurement conditions: 230℃, 2.16kg, nadic anhydride grafting rate is 20%);

[0137] Middle layer: 80wt% homopolypropylene, 15wt% pearlescent masterbatch and 5wt% polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer (two polymethyl methacrylate segments are connected by two methyl methacrylate copolymer units, and the polypropylene segment is connected by five propylene copolymer units);

[0138] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0139] The total thickness and thickness of each layer of the biaxially oriented polypropylene aluminized label film of this comparative example are the same as those of Example 1.

[0140] The preparation method of the biaxially oriented polypropylene aluminized label film of this comparative example is the same as that of Example 1.

[0141] Comparative Example 10

[0142] The comparative example provides a biaxially oriented polypropylene aluminized label film, comprising an aluminized layer, an intermediate layer and a lower surface layer which are arranged in sequence.

[0143] Among them, the formula of each layer is as follows:

[0144] Aluminum-platable layer: 92wt% copolymerized polypropylene and 8wt% nadic anhydride grafted polyolefin elastomer (melt index is 10g / 10min, measurement conditions: 230℃, 2.16kg, nadic anhydride grafting rate is 20%);

[0145] Middle layer: 80wt% homopolypropylene, 15wt% pearlescent masterbatch and 5wt% polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer (two polymethyl methacrylate segments are connected by 6 methyl methacrylate copolymer units, and the polypropylene segment is connected by 15 propylene copolymer units);

[0146] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0147] The total thickness and thickness of each layer of the biaxially oriented polypropylene aluminized label film of this comparative example are the same as those of Example 1.

[0148] The preparation method of the biaxially oriented polypropylene aluminized label film of this comparative example is the same as that of Example 1.

[0149] Performance Evaluation

[0150] The following performance evaluations were performed on the biaxially oriented polypropylene aluminized label films of Examples 1-3 and Comparative Examples 1-10, respectively. The performance evaluation results are shown in Table 1:

[0151] Tensile strength: tested according to GB / T1040.3;

[0152] Production smoothness (qualitative): membrane rupture;

[0153] Surface tension and durability of the aluminum-platable layer: The films prepared in Examples 1-3 and Comparative Examples 1-10 were subjected to aging treatment for 0 days, 30 days, 60 days and 90 days, and the surface tension of the aluminum-platable layer of the films was tested. The surface tension was tested according to GB / T2913.

[0154] Surface tension and durability of the aluminum layer: The films prepared in Examples 1-3 and Comparative Examples 1-10 were aluminum-plated (vacuum evaporation) to form an aluminum layer on the surface of the aluminum-platable layer. After aging treatment for 0 days, 30 days, 60 days and 90 days, the surface tension of the aluminum layer was tested. The surface tension was tested according to GB / T2913.

[0155] Table 1 Film performance evaluation results

[0156]

[0157] Table 2 Performance evaluation results of thin film after aluminum plating

[0158]

[0159] Please refer to Table 1 and Table 2. The biaxially oriented polypropylene aluminized label films of Examples 1-3 of the present invention have a durable surface tension of the aluminized layer, and the aluminum layer formed after aluminum plating on the surface of the aluminized layer has strong adhesion, and there is no problem of loose adhesion and aluminum falling off of the aluminum layer. Furthermore, after the aluminum layer is firmly adhered, the aluminum layer does not undergo corona attenuation, and will not affect subsequent coating, printing and other processes.

[0160] The biaxially oriented polypropylene aluminized label film of comparative example 1 contains only copolymerized polypropylene in the aluminized layer, and no nadic anhydride-grafted polyolefin elastomer is added to the aluminized layer, which cannot effectively block the migration of small molecular substances in the middle layer, resulting in a significant decrease in the surface tension of the aluminized layer of the film and the aluminum layer formed after aluminizing the surface of the aluminized layer after being stored for a period of time.

[0161] In the biaxially oriented polypropylene aluminized label film of Comparative Example 2, the content of the nadic anhydride grafted polyolefin elastomer added in the aluminized layer is too low, the aluminized layer of the film does not play a significant role in blocking the migration of small molecules in the middle layer, the surface tension and durability of the aluminized layer of the film cannot be significantly improved, and the surface tension of the aluminum layer formed after aluminizing the surface of the aluminized layer of the film is not durable.

[0162] In the biaxially oriented polypropylene aluminized label film of Comparative Example 3, the content of the nadic anhydride grafted polyolefin elastomer added to the aluminized layer is too high. The excessive introduction of the ring structure will increase the steric hindrance effect of the copolymerized polypropylene molecular chain, restricting the movement of the molecular chain and causing a decrease in the mechanical properties of the film.

[0163] In the biaxially oriented polypropylene aluminized label film of Comparative Example 4, the grafting rate of nadic anhydride in the polyolefin elastomer grafted with nadic anhydride added to the aluminized layer is too low, and it cannot effectively block the migration of small molecular substances in the middle layer. The surface tension and durability of the aluminized layer of the film cannot be significantly improved, and the surface tension of the aluminum layer formed after aluminizing the surface of the aluminized layer of the film is not durable.

[0164] In the biaxially oriented polypropylene aluminized label film of comparative example 5, the grafting rate of nadic anhydride in the polyolefin elastomer grafted with nadic anhydride added to the aluminized layer is too high. Due to the rigid structure of nadic anhydride, too much nadic anhydride will make the film brittle, resulting in a decrease in the mechanical properties of the film.

[0165] The biaxially oriented polypropylene aluminized label film of Comparative Example 6 contains only homopolypropylene and pearlescent masterbatch in the middle layer, and no polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer is added to the middle layer, which cannot effectively reduce the migration of small molecular substances in the middle layer, resulting in a significant decrease in the surface tension of the aluminizable layer of the film and the aluminum layer formed after aluminizing the surface of the aluminizable layer after being stored for a period of time.

[0166] In the biaxially oriented polypropylene aluminized label film of comparative example 7, the content of the polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer added in the middle layer is too low, and the effect of reducing the migration of small molecular substances in the middle layer is not obvious. The surface tension of the aluminizable layer of the film and the aluminum layer formed after aluminizing the surface of the aluminizable layer is significantly reduced after being stored for a period of time.

[0167] In the biaxially oriented polypropylene aluminized label film of Comparative Example 8, the content of polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer added in the middle layer is too high, and the molecular chains of the substances in the middle layer will be entangled to a certain extent, causing the shear viscosity of the melt to increase, affecting the smoothness of production.

[0168] In the biaxially oriented polypropylene aluminized label film of Comparative Example 9, in the polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer added in the middle layer, the amount of methyl methacrylate as a copolymer unit in the polymethyl methacrylate segment is relatively low, which is not conducive to maintaining the surface tension of the aluminizable layer itself and the aluminum layer after aluminizing the surface of the aluminizable layer; and the amount of propylene as a copolymer unit in the polypropylene segment is relatively low, which easily leads to low compatibility and bonding strength between the polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer and the homopolypropylene in the middle layer, which is not conducive to anchoring small molecules to the homopolypropylene matrix, resulting in the failure to maintain the surface tension of the aluminizable layer itself and the aluminum layer after aluminizing the surface of the aluminizable layer.

[0169] In the biaxially oriented polypropylene aluminized label film of Comparative Example 10, in the polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer added in the middle layer, the amount of methyl methacrylate as a copolymer unit in the polymethyl methacrylate segment is relatively high. Due to the high rigidity of the polymethyl methacrylate segment, stress concentration may occur in the film when subjected to force, thereby increasing the risk of smooth production; and the amount of propylene as a copolymer unit in the polypropylene segment is relatively high, which increases the possibility of entanglement between molecular chains, resulting in an increase in the shear viscosity of the melt, resulting in high compatibility and bonding strength between the polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer and the homopolypropylene in the middle layer, increasing the possibility of entanglement between molecular chains, resulting in an increase in the shear viscosity of the melt, affecting the smoothness of production.

[0170] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and the present invention is also intended to include these modifications and modifications.

Claims

1. A biaxially oriented polypropylene aluminized label film, characterized in that: It includes an aluminum-platable layer, an intermediate layer and a lower surface layer arranged in sequence; The aluminum-platable layer comprises copolymerized polypropylene and 5-10wt% nadic anhydride grafted polyolefin elastomer; the grafting rate of nadic anhydride in the nadic anhydride grafted polyolefin elastomer is 15-25%; The intermediate layer comprises homopolymerized polypropylene, 10-20wt% pearlescent masterbatch and 4-7wt% polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer; the molecular chain of the polymethyl methacrylate-polypropylene-polymethyl methacrylate block copolymer is formed by sequential block copolymerization of polymethyl methacrylate segments, polypropylene segments and polymethyl methacrylate segments, wherein two polymethyl methacrylate segments are respectively connected by 3 or 4 methyl methacrylate copolymerization units, and the polypropylene segment is connected by 8 or 9 propylene copolymerization units.

2. The biaxially oriented aluminized polypropylene label film according to claim 1, characterized in that: In the aluminum-platable layer, the nadic anhydride grafted polyolefin elastomer has a melt index of 8-12 g / 10 min at 230° C. and a load of 2.16 kg.

3. The biaxially oriented aluminized polypropylene label film according to claim 1, characterized in that: In the aluminum-platable layer, the preparation method of the nadic anhydride-grafted polyolefin elastomer is: grafting nadic anhydride onto the polyolefin elastomer through a melt grafting method to obtain the elastomer.

4. The biaxially oriented aluminized polypropylene label film according to claim 3, characterized in that: The polyolefin elastomer is an ethylene-butene copolymer elastomer; in the preparation method of the nadic anhydride grafted polyolefin elastomer, nadic anhydride is grafted onto the secondary carbon of butene in the ethylene-butene copolymer elastomer.

5. The biaxially oriented aluminized polypropylene label film according to claim 1, characterized in that: In the aluminum-platable layer, the copolymerized polypropylene has a melt index of 6-10 g / 10 min at 230° C. and a load of 2.16 kg.

6. The biaxially oriented aluminized polypropylene label film according to claim 1, characterized in that: In the intermediate layer, the pearlescent masterbatch is mixed with 15-25wt% homopolypropylene and 75-85wt% inorganic filler; the inorganic filler is prepared by treating 3-5wt% of at least one of small molecule fatty acid and small molecule ester as a surface treatment agent and 95-97wt% of calcium carbonate as a filler in a high-speed mixer.

7. The biaxially oriented aluminized polypropylene label film according to claim 6, characterized in that: The particle size of the calcium carbonate is 0.5-1.5 μm.

8. The biaxially oriented aluminized polypropylene label film according to claim 1, characterized in that: In the middle layer, the homopolypropylene has a melt index of 3-8 g / 10 min at 230° C. and a load of 2.16 kg.

9. The biaxially oriented polypropylene aluminized label film according to claim 1, characterized in that: The lower surface layer includes homopolymer polypropylene and 1-5wt% anti-blocking masterbatch.

10. A method for preparing a biaxially oriented polypropylene aluminized label film according to any one of claims 1 to 9, characterized in that: The following steps are involved: Step 1: Batching and plasticization: The proportion of each layer of raw materials is set in the control system of the biaxial stretch film production line, and then the batching system will automatically transport the dried raw materials of each layer to each layer extruder according to the input ratio. After melting and plasticizing in each layer extruder, the melt enters the die head through the runner and distributor; Step 2: Slice casting: After being extruded through the die, the melt immediately contacts the cooling roller to form a thick sheet; Step 3: Longitudinal stretching: The thick sheet is heated to the set temperature by multiple sets of preheating rollers, and then longitudinal stretching is started, and then shaping is performed; Step 4: Horizontal stretching: After preheating the thick sheet after longitudinal stretching to the set temperature, start horizontal stretching, and then perform shaping and cooling treatment after horizontal stretching; Step 5: Traction and rewinding: The multi-layer film from the horizontal pulling unit enters the traction unit, and after thickness measurement and corona treatment, enters the rewinding unit to obtain a parent roll; Step 6: Slitting: Slitting the aged mother roll to obtain film rolls of specified width and length.

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