Ternary random copolymers and methods for their preparation, multilayer film structures

Abstract

The application provides a ternary random copolymer, a preparation method thereof and a multilayer film structure, and belongs to the technical field of heat-seal copolymer resins. The ternary random copolymer has the structure shown in the following formula (I), formula (I), wherein 0 < x < 1, 0 < y < 1, and 0 < x + y < 1; 150 < n < 2000. The ternary random copolymer has a rigid structural unit, so that the ternary random copolymer has good temperature resistance and a high melting temperature, and is beneficial to subsequent application as a heat-seal layer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat-seal copolymer resin, and particularly relates to a ternary random copolymer, a preparation method thereof and a multilayer film structure. BACKGROUND

[0002] Polyolefin polymers are formed from hydrocarbons (such as propylene and alpha-olefins) obtained from petrochemicals and are abundantly available, and the polyolefin polymers can be used in various applications and fields.

[0003] In one of the applications, the polyolefin polymers are configured and designed for producing heat-seal films and packaging. The heat-seal films for packaging usually comprise a plurality of polymer layers. Among them, at least one surface layer is called a heat-seal layer. The working principle of the heat-seal layer can be understood as follows: when heated, the material of the heat-seal layer melts and flows rapidly, bonding two or more different materials together; after cooling, the heat-seal layer solidifies rapidly, forming a tight and firm bond, which provides a strong guarantee for the sealing of the packaging.

[0004] One way in the related art provides a ternary random copolymer of propylene, ethylene and 1-butene, which can reduce the sealing initiation temperature of the polymer. Although the heat-sealable film has been produced in the related art, there is still room for further improvement. SUMMARY

[0005] Therefore, in order to at least partially solve the above-mentioned technical problems, the present application provides a ternary random copolymer, a preparation method thereof and a multilayer film structure.

[0006] According to an embodiment of one aspect of the present application, a ternary random copolymer is provided, having a structure as shown in the following formula (I),

[0007] Formula (I), 0 < x < 1, 0 < y < 1, and 0 < x + y < 1; 150 < n < 2000.

[0008] In some embodiments, in the ternary random copolymer, the mole content percentage of the structural unit from the 1-butene monomer is 2-30%, and the mole content percentage of the 1,3-cyclopentylidene is 0.1-20%.

[0009] In some embodiments, the weight average molecular weight of the ternary random copolymer is 6 x 10 4 ~6 x 10 5 g / mol; and the molecular weight distribution index is 1.8-3.2.

[0010] In some embodiments, the melting point of the terpolymer is 100-136℃, and the crystallization temperature is 50-105℃; the isotacticity of the structural units from propylene and the structural units from 1-butene in the terpolymer is 92-99%, respectively.

[0011] According to an embodiment of another aspect of the present application, there is provided a method for preparing the terpolymer as described above, comprising: under anhydrous and anaerobic conditions, copolymerizing propylene monomers, 1-butene monomers and 1,5-hexadiene monomers in an organic solvent in the presence of a hafnium pyridyl amine catalyst and a cocatalyst to obtain a terpolymer solution; and precipitating and drying the terpolymer solution to obtain the terpolymer; the cocatalyst is aluminoxane or methyl aluminoxane, or a combination of an organoaluminum compound and an organoboron compound.

[0012] In some embodiments, the hafnium pyridyl amine catalyst has a structure as shown in formula (II):

[0013] Formula (II).

[0014] In some embodiments, the organoaluminum compound comprises at least one of an alkyl aluminum and an alkyl aluminum halide; and the organoboron compound comprises at least one of triphenylcarbenium tetra(pentafluorophenyl)borate, N,N-dimethylanilinium tetra(pentafluorophenyl)borate, N,N-dimethylcyclohexylammonium tetra(pentafluorophenyl)borate or N,N-dimethylbenzylammonium tetra(pentafluorophenyl)borate.

[0015] In some embodiments, the copolymerization reaction is carried out at a temperature of 25-100℃ for 5-60 min; the drying treatment is carried out at a temperature of 70-100℃ for 4-12 h; and the organic solvent comprises at least one of benzene, toluene, xylene, pentane, hexane, heptane, octane and nonane.

[0016] According to an embodiment of still another aspect of the present application, there is provided a multilayer film structure comprising: a base layer comprising a thermoplastic polymer; and a heat-seal layer comprising the terpolymer as described above.

[0017] In some embodiments, the multilayer film structure is prepared by multilayer co-extrusion casting.

[0018] According to the embodiments of the present application, the present application introduces 1,3-cyclopentylidene with cyclic structure into the structure of the copolymer, the introduced cyclic structure can increase the rigidity and thermal stability of the terpolymer, and improve the mechanical properties of the terpolymer. When the terpolymer is used as a heat sealing layer, the introduction of the cyclic structure makes it have easy-to-control and wide temperature operating space between crystallization and melting. The terpolymer has more excellent mechanical strength and thermal properties due to the introduction of the cyclic structure, and has excellent transparency. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 FIG. 1 shows the temperature rising and falling curve of differential scanning calorimetry of the terpolymer 1 of the embodiment 1 of the present application;

[0020] Figure 2 FIG. 2 shows the nuclear magnetic resonance carbon spectrum of the terpolymer 2 of the embodiment 2 of the present application;

[0021] Figure 3 FIG. 3 shows the gel permeation chromatogram of the terpolymer prepared in the embodiment 2 and the embodiment 3 of the present application;

[0022] Figure 4 FIG. 4 shows the stress-strain curve of the terpolymer prepared in the embodiment 1 to the embodiment 3 of the present application;

[0023] Figure 5 FIG. 5 shows the temperature rising curve of differential scanning calorimetry of the terpolymer 3 of the embodiment 3 of the present application;

[0024] Figure 6 FIG. 6 shows the curve of the transmittance of the terpolymer prepared in the embodiment 2, the embodiment 4 and the embodiment 6 of the present application changing with wavelength;

[0025] Figure 7 FIG. 7 shows the temperature rising curve of differential scanning calorimetry of the terpolymer prepared in the embodiment 3 and the embodiment 8 of the present application. DETAILED DESCRIPTION

[0026] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings. It is to be understood, however, that these descriptions are merely exemplary and are intended to provide a thorough and complete disclosure of the embodiments of the present application as defined by the appended claims. Accordingly, various modifications and changes can be made in the embodiments without departing from the scope of the present application as set forth in the claims. In the following description, descriptions of well-known functions and constructions are omitted to provide a clear and concise description of embodiments of the present application.

[0027] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "includes" indicates the presence of what is recited but does not rule out the presence of additional integers.

[0028] In the event of using expressions such as "at least one of A, B, and C, etc.", it should be generally interpreted that the meaning is the same as "at least one of the group consisting of A, B, and C" (for example, "a system having at least one of A, B, and C" should include a system having A alone, a system having B alone, a system having C alone, a system having A and B together, a system having A and C together, a system having B and C together, and / or a system having A, B, and C together, etc.). In the event of using expressions such as "at least one of A, B, or C, etc.", it should be generally interpreted that the meaning is the same as "at least one of the group consisting of A, B, and C" (for example, "a system having at least one of A, B, or C" should include a system having A alone, a system having B alone, a system having C alone, a system having A and B together, a system having A and C together, a system having B and C together, and / or a system having A, B, and C together, etc.).

[0029] In food packaging, the presence of a heat-seal layer effectively blocks the invasion of oxygen, moisture and microorganisms, effectively prolonging the shelf life of the food. The material of the heat-seal layer is usually a multi-copolymer (such as a copolymer of propylene and 1-butene), which has excellent adhesion to various material surfaces after heating, for example, the multi-polymer can be tightly combined with plastic film, paper, metal foil, etc., so that the multi-polymer is widely used in composite packaging materials. Through its adhesive effect, the layered structure of different materials can be firmly combined together, greatly improving the overall performance of the packaging material. For example, when making a composite packaging bag, the multi-polymer can tightly bond multiple layers of materials such as polyester film, aluminum foil and polyethylene film, so that the packaging bag has good barrier properties, certain strength and flexibility.

[0030] The related art provides a 1-butene / propylene / ethylene ternary random copolymer, which helps to reduce the seal initiation temperature (SIT) of the polymer and can be used as an important component, but the ternary random copolymer is prepared by using a relatively expensive metallocene-based catalyst. The related art also provides a propylene-based random block copolymer or a resin composition containing the same, which aims to provide a sealing packaging material suitable for packaging food and the like, but its thermal stability is poor and may be decomposed at high temperatures, reducing the sealing effect.

[0031] In the process of implementing the concept of the present application, it is found that by introducing 1,3-cyclopentylidene into the ternary random copolymer, the rigidity of the ternary random copolymer is improved, and thus the thermal stability and mechanical properties thereof are improved.

[0032] Specifically, according to an embodiment of one aspect of the present application, a terpolymer is provided, the terpolymer has a structure as shown in the following formula (I),

[0033] Formula (I), wherein 0 < x < 1, 0 < y < 1, and 0 < x + y < 1; 150 < n < 2000.

[0034] According to an embodiment of the present application, by introducing 1,3-cyclopentyl in the main chain of the terpolymer, the cyclic structure helps to improve the rigidity of the terpolymer, limit the movement of the chain segment, and help to improve the glass transition temperature of the terpolymer, and thus improve its thermal stability. At the same time, the introduction of the cyclic structure helps to provide a certain steric hindrance, improve the chemical corrosion resistance of the terpolymer, reduce the possibility of oxidative degradation, and thus improve the service life of the terpolymer as a heat-sealing layer. In addition, the introduction of propylene can bring higher crystallinity; the addition of 1-butene can appropriately improve the flexibility and appropriately reduce the crystallinity, and based on the synergy of propylene, 1-butene and 1,3-cyclopentyl, the terpolymer can have good processability while improving the thermal stability.

[0035] It should be noted that the presence of the cyclic structure can hinder the regular arrangement of the molecular chain segments of the terpolymer, and can form semi-crystalline or amorphous regions, thereby improving the transparency of the terpolymer, and having good mechanical properties, thermal properties and excellent transparency when used as a heat-sealing layer. In addition, the structural units from propylene monomers, the structural units from 1-butene monomers, and 1,3-cyclopentyl in the terpolymer are not limited to the arrangement shown in formula (I), and the three structural units can be irregularly distributed.

[0036] For example, 0 < x < 1, x can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9; 0 < y < 1, y can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9; and at the same time, 0 < x + y < 1. In this way, by adjusting the amount of the three monomers, the mechanical properties and thermal properties of the terpolymer can be adjusted based on different application requirements, and by adjusting the structure of the terpolymer, the starting temperature (SIT) of the heat-sealing film can be obtained for different requirements when used as a heat-sealing layer.

[0037] It can be understood that the heat-seal film starting temperature can be defined as the sealing temperature at which the heat-seal strength of the heat-seal film starts to increase from zero heat-seal strength, and the heat-seal film starting temperature marks the critical point at which the heat-seal film starts to transform from a glassy or crystalline state to a viscous flow state. The heat-seal film starting temperature is determined as the sealing temperature at which a sealing strength of 1.0 N / 15 mm is achieved.

[0038] Exemplarily, 150 < n < 2000, and n can be, for example, 155, 300, 500, 700, 900, 1100, 1300, 1500, 1700, 1900, 1950, etc. In this way, the ternary random copolymer has a relatively high molecular weight, and the molecular chains are more closely entangled, which helps to improve the tensile strength, Young's modulus, impact resistance and other mechanical properties of the ternary random copolymer. In addition, the relatively high molecular weight can ensure that the ternary random copolymer has better heat resistance. If n ≤ 150, the melting temperature is relatively low, and the heat resistance is poor. If n ≥ 2000, the viscosity after melting is too large, the flowability is poor, and it is relatively difficult to apply in the heat-seal layer.

[0039] In some embodiments, the ternary random copolymer has a mole content percentage of structural units from the 1-butene monomer of 2-30%, for example, 2%, 5%, 10%, 15%, 20%, 25% or 30%, etc. In this way, by introducing a suitable content of 1-butene, the flexibility of the ternary random copolymer can be improved, and the transparency of the ternary random copolymer can be optimized. The mole content percentage of 1,3-cyclopentylidene is 0.1-20%, for example, 0.1%, 2%, 5%, 10%, 15% or 20%, etc. In this way, the thermal stability of the ternary random copolymer can be improved while widening the heat-seal temperature window when subsequently applied to the heat-seal layer.

[0040] In some embodiments, the weight average molecular weight of the ternary random copolymer is 6 x 10 4 g / mol, for example, 6 x 10 5 g / mol, 1 x 10 4 g / mol, 1.5 x 10 5 g / mol, 2 x 10 5 g / mol, 3 x 10 5 g / mol, 4 x 10 5 g / mol, 5 x 10 5 g / mol, 6 x 10 5 g / mol, 6 x 10 5g / mol, etc. In this way, the terpolymer has good mechanical properties; the molecular weight distribution index is 1.8-3.2, for example, it can be 1.8, 2, 2.5, 3, or 3.2, etc. In this way, by balancing the low molecular weight part, the viscosity of the terpolymer after melting is reduced, and the processing fluidity is improved; the high molecular weight part helps to maintain the elasticity of the molten part, reducing the rupture of the terpolymer during extrusion, and further improving the stability of the terpolymer. When the molecular weight distribution is adjusted to the above width, the low molecular weight component melts at low temperature, and the high molecular weight component maintains strength at high temperature, which helps to widen the processing window of the terpolymer, and has more flexible processing temperature control space.

[0041] Preferably, the weight average molecular weight of the terpolymer is 6 x 10 4 ~3 x 10 5 g / mol; the molecular weight distribution index is 1.8-3.0. In this way, the mechanical properties and thermal stability of the terpolymer are further improved, and the processing window is more suitable.

[0042] In some embodiments, the melting point of the terpolymer is 100-136°C, for example, it can be 100°C, 110°C, 120°C, 130°C, or 136°C, etc. Since the terpolymer has a large melting point range, the melting point near 100°C is suitable for low-temperature processing of the heat-sealable film, reducing thermal degradation; and the melting point near 136°C helps to promote high-temperature forming. In this way, the terpolymer has good thermal stability and high transparency, which helps to widen the application range of the terpolymer. The crystallization temperature is 50-105°C, for example, it can be 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, or 105°C, etc. In this way, the crystallinity of the terpolymer can be adjusted by adjusting the cooling conditions, and the transparency of the terpolymer is optimized. The isotacticity of the structural units from propylene and 1-butene in the terpolymer is 92-99%, for example, it can be 92%, 94%, 96%, 98%, or 99%. The isotacticity can be understood as the terpolymer having a stereoscopic configuration, which has good selectivity. In the repeating unit, the side chains of the structural units from propylene and 1-butene point to the same side of the main chain plane, forming a highly ordered structure, providing good rigidity and support. Based on the high isotacticity of the terpolymer, the structure is more ordered, and the processing performance is good during subsequent processing and molding, which helps to prepare a more transparent heat-sealable layer.

[0043] In some embodiments, the crystallinity of the terpolymer is 25-35%, such as 25%, 28%, 30%, 33%, or 35%, and the like. Such a crystallinity is configured to provide the terpolymer with a better ordered structure, which is helpful to prepare a more transparent heat-seal layer.

[0044] It should be noted that the melting point or melting temperature and the crystallization temperature are measured by differential scanning calorimetry (DSC). The melting point is the temperature at which the material changes from a solid to a liquid, i.e., the critical temperature at which the molecular chain segments begin to move freely and the material loses its rigidity. The endothermic peak formed by DSC during the heating process is usually the second peak formed (the first is to eliminate the thermal history). The crystallinity is the proportion (percentage) of the crystalline region in the whole. The molecular chains in the crystalline region are arranged in an orderly and regular manner, and the amorphous region is disordered and entangled. The higher the crystallinity of the polymer material, the greater the rigidity, hardness, melting point and chemical resistance of the material, but the lower the toughness and transparency. If the crystallinity is low, the material is soft, tough and has high transparency.

[0045] One method for determining the crystallinity of the terpolymer is by differential scanning calorimetry (DSC). The terpolymer sample is sealed in a DSC pan and placed in a DSC cell with a nitrogen purge rate of 25 cm / min, cooled to about -80°C, and a standard thermal history of the terpolymer sample is established by heating to 225°C at 10°C / min. Then it is cooled to 10°C / min and re-heated to 225°C, and the observed enthalpy of fusion is recorded. Then the observed enthalpy of fusion is divided by the enthalpy of fusion of isotactic polypropylene (164.92 J / g) and multiplied by 100, and the crystallinity of the terpolymer is obtained.

[0046] According to another aspect of the embodiments of the present application, a method for preparing the terpolymer as described above is provided, which comprises the following operation S1 to operation S2.

[0047] In operation S1, under anhydrous and anaerobic conditions, the propylene monomer, 1-butene monomer and 1,5-hexadiene monomer are subjected to a copolymerization reaction in an organic solvent in the presence of a hafnium amide pyridine catalyst and a cocatalyst to obtain a terpolymer solution.

[0048] In the present embodiment, the pyridylamine hafnium catalyst is used as the main catalyst, in which the hafnium metal center is combined with monomer molecules (propylene monomer, 1-butene monomer, 1,5-hexadiene) to form active centers through coordination, and the pyridylamine ligand regulates the catalytic activity and selectivity through electronic effect and steric hindrance. The addition of the cocatalyst helps to generate cationic active centers by activating the hafnium metal center. The copolymerization reaction proceeds through the insertion of the three monomers into the metal-carbon bond, and the chain growth reaction is carried out to obtain a terpolymer solution. Among them, 1,5-hexadiene is cyclized under the catalysis of the pyridylamine hafnium catalyst, which helps to improve the rigidity of the terpolymer and further improve its thermal stability.

[0049] In operation S2, the terpolymer solution is precipitated and dried to obtain a terpolymer.

[0050] In the present embodiment, the precipitation can be carried out by adding a poor solvent to reduce the solubility of the terpolymer and then precipitating it, for example, using a non-solvent method. The drying can be carried out by vacuum drying or heating drying, preferably heating and vacuum drying, to remove the residual solvent and unreacted comonomer in the terpolymer, so as to reduce the generation of bubbles or degradation in the subsequent processing process.

[0051] According to the embodiment of the present application, the cocatalyst is aluminoxane or methylaluminoxane, or a combination of an organic aluminum compound and an organic boron compound. The addition of aluminoxane or methylaluminoxane helps to activate the hafnium metal active center. The steric hindrance effect constructed by the pyridylamine hafnium makes the double bond of 1,5-hexadiene inserted into the hafnium metal active center, and the coordination promotes the cyclization of 1,5-hexadiene. The addition of the above-mentioned cocatalyst helps to promote the molecular chain growth of the terpolymer. The combination of the organic aluminum compound and the organic boron compound can form a complex effect, which helps to activate the hafnium metal active center, and cooperates with the steric hindrance effect constructed by the pyridylamine hafnium to promote the cyclization of 1,5-hexadiene. Similarly, the combination of the two also helps to promote the molecular chain growth of the terpolymer.

[0052] The preparation method of the present application is simple, and the raw materials are easy to obtain. The terpolymer with adjustable physical properties can be prepared by using known materials.

[0053] It can be understood that the organic solvent can be selected from C5~C 20 hydrocarbon compounds, preferably C5~C 12 hydrocarbon compounds. The hydrocarbon compounds specifically include at least one of monocyclic or polycyclic aromatic hydrocarbons, straight-chain, branched, or cyclic aliphatic hydrocarbons, or mixtures thereof.

[0054] In some embodiments, after the copolymerization reaction is completed, the copolymerization reaction is preferably terminated by using a poor solvent, thereby obtaining a ternary random copolymer solution. Subsequently, the ternary random copolymer solution is slowly added into a polymer poor solvent for precipitation treatment, and the obtained precipitate is vacuum dried to obtain the ternary random copolymer.

[0055] The present application does not make special restrictions on the type and source of the poor solvent, and the main component thereof may, for example, be at least one of anhydrous ethanol, methanol, n-hexane, petroleum ether, etc. Preferably, the poor solvent used in the present application is a mixed solution of 98% ethanol by volume and 2% hydrochloric acid by volume.

[0056] In some embodiments, the hafnium pyridyl amine catalyst has a structure as shown in formula (II):

[0057] Formula (II). As shown in formula (II), by constructing the asymmetric structure of the hafnium pyridyl amine catalyst, the steric hindrance effect thereof is constructed, which can confine the 1,5-hexadiene monomer to a small spatial range for coordination, thereby promoting the cyclization of the 1,3-cyclopentyl group, thereby improving the rigidity of the ternary random copolymer prepared and improving the thermal stability thereof. The hafnium pyridyl amine catalyst shown in formula (II) has the characteristics of high activity, good polymerization tolerance, and high selectivity, which can promote the copolymerization reaction and the cyclization reaction to proceed.

[0058] It can be understood that the hafnium pyridyl amine catalyst can be prepared by the method in the literature (the name of the literature referred to is: Nonconventional catalysts for isotactic propene polymerization in solution developed by using high-throughput-screening technologies. The name and volume of the journal are Angewandte Chemie International Edition, 2006, 45(20): 3278-3283.). All operations sensitive to water and oxygen are carried out in a glove box filled with high-purity nitrogen, and all containers are baked to dryness. The preparation process is shown in formula (III) as follows:

[0059] Formula (III).

[0060] It should be noted that the hafnium pyridyl amine catalyst belongs to a non-metallocene catalyst, and the cost thereof is lower than that of a metallocene catalyst, which helps to reduce the production cost of the ternary random copolymer.

[0061] From the perspective of promoting the activation of hafnium metal active centers, the organic aluminum compound includes at least one of an alkyl aluminum and an alkyl aluminum halide, preferably the organic aluminum compound is a trialkyl aluminum, further preferably the organic aluminum compound is selected from at least one of trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, and more preferably the organic aluminum compound is triisobutyl aluminum. The organic boron compound includes at least one of a triphenyl carbenium tetra(pentafluorophenyl)borate, an N,N-dimethyl anilinium tetra(pentafluorophenyl)borate, an N,N-dimethyl cyclohexylammonium tetra(pentafluorophenyl)borate, or an N,N-dimethyl benzylammonium tetra(pentafluorophenyl)borate.

[0062] In some embodiments, when the co-catalyst is triphenyl carbenium tetra(pentafluorophenyl)borate and triisobutyl aluminum, and the main catalyst is a pyridine amine hafnium catalyst represented by formula (II), the molar ratio of the three catalysts (triisobutyl aluminum: triphenyl carbenium tetra(pentafluorophenyl)borate: pyridine amine hafnium catalyst represented by formula (II)) is (50-500):(1-10):1, and more preferably (100-300):(2-5):1.

[0063] From the perspective of improving the solubility of several reaction raw materials, the organic solvent includes at least one of benzene, toluene, xylene, pentane, hexane, heptane, octane, and nonane, and further preferably the organic solvent is hexane or xylene, and more preferably the organic solvent is xylene. The amount of the solvent used in the present application is not particularly limited, and the amount of the solvent used in the polymerization reaction known to those skilled in the art can be used.

[0064] In some embodiments, the temperature of the copolymerization reaction is 25-100°C, for example, it can be 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C, and the like, and preferably 40-80°C; the reaction time is 5-60 min, for example, it can be 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, or 60 min, and the like, and preferably 15-30 min; the temperature of the drying treatment is 70-100°C, for example, it can be 70°C, 80°C, 90°C, or 100°C, and the like, and preferably 80°C; and the drying time is 4-12 h, for example, it can be 4 h, 6 h, 8 h, 10 h, or 12 h, and the like, and preferably 8 h.

[0065] In a specific embodiment, the preparation method of the terpolymer can be as follows:

[0066] Preparation of the reaction raw materials and temperature setting: Before the polymerization reaction, check the performance of the full-mixing stirred tank reactor to ensure that the performance indicators are normal, and set the reaction temperature to be between 40-80°C, and then start the heating unit.

[0067] The addition of the organic solvent and the three monomers: when the temperature in the reactor reaches the set value accurately and is stable, the prepared organic solvent is added to the full-mixing stirred tank reactor (total polymerization volume is 200 mL), and the addition speed and flow are controlled to prevent large fluctuations in pressure and temperature. After the organic solvent is added and uniformly distributed, the three monomers of propylene, butene, and 1,5-hexadiene are added in proportion and order, and the stirring device is turned on at an appropriate speed to fully mix the organic solvent and the three monomers.

[0068] The addition of the polymerization promoter and the catalyst: before the polymerization reaction starts, the polymerization promoter (2-1000 μmol) and the hafnium catalyst (5 μmol, 3.6 mg) are added to the reactor, and the two are uniformly mixed in the reaction system.

[0069] Termination of the polymerization reaction: after the polymerization reaction reaches the predetermined time or degree, a mixed solution of 98% ethanol and 2% hydrochloric acid (1 mL) is added to the reactor, which can quickly react with the catalyst to deactivate it. After the addition is complete, continue to stir to allow the quenching reaction to proceed fully, ensuring that the reaction stops completely, and then further process and separate the product, and dry the ternary random copolymer under vacuum conditions at 80°C for 8 h.

[0070] According to an embodiment of the application, a multilayer film structure is provided, the multilayer film structure comprising: a base layer comprising a thermoplastic polymer; and a heat seal layer comprising a ternary random copolymer as described above.

[0071] It should be understood that the base layer can be a single layer film, or can be made of multiple layers of different thermoplastic polymers, and the thermoplastic polymers used to produce one or more base layers include polyolefins, such as polypropylene, polyethylene, polybutylene, polystyrene, polyvinyl chloride, ethylene-containing copolymers, propylene-containing copolymers, and blends thereof. The heat seal layer is formed on the outer surface of the base layer, and the thickness of the heat seal layer is relatively thin, for example, the thickness of the heat seal layer can be less than 20 μm, preferably less than 5 μm, further less than 3 μm, and greater than 0.1 μm, for example, it can be 0.2 μm, 0.5 μm, 1 μm, 1.5 μm, or 2 μm, etc. The thickness of the base layer can be greater than 10 μm and less than 50 μm, for example, it can be 15 μm, 20 μm, 30 μm, 40 μm, or 45 μm, etc.

[0072] Based on the use of the multilayer film structure combined by the base layer and the heat seal layer, the heat seal initiation temperature of the multilayer film structure is reduced to a certain extent compared to the base layer, thereby reducing the sealing time, reducing the cycle time, and improving the production rate.

[0073] The heat seal initiation temperature (SIT) can be understood as the sealing temperature at which the heat seal strength first starts to trend upwards from zero heat seal strength on a heat seal curve using a sealing film. The heat seal initiation temperature (SIT) is determined as the sealing temperature at which a seal strength of 1.0 N / 15 mm is achieved.

[0074] In some embodiments, the multilayer film structure is prepared by multilayer co-extrusion casting.

[0075] Further, when the base layer is a high isotacticity (isotacticity index of 97) polypropylene film and the ternary random copolymer of the present application is used as the heat seal layer for co-extrusion casting, the heat seal initiation temperature of the multilayer film structure is at least 10°C lower than that of the single-layer base layer, preferably at least 20°C lower.

[0076] The present application further adjusts the proportions of the three monomers (propylene monomer, 1-butene monomer, 1,5-hexadiene monomer) to adjust the structure of the ternary polymer, thereby obtaining a heat seal layer copolypropylene resin for cast polypropylene film (CPP) with adjustable mechanical properties from strong and hard to soft and tough, wherein the yield strength of the ternary polymer is controlled at 3 MPa to 30 MPa, and the elongation at break is 50% to 1200%.

[0077] Using the ternary random copolymer of the present application as the heat seal layer has the advantages of low melting point, good hot melt property, wide heat seal temperature, easy sealing, etc., which is conducive to subsequent use as packaging, such as use in food packaging, medicine packaging, commodity packaging, etc., and helps to provide better health and safety protection, bringing more development to the packaging industry and widening the application field. By combining the heat seal layer with the polypropylene film to form a multilayer film structure, the application range of polypropylene materials is further widened. And by introducing cyclic structure units to generate ternary polymers with crystallization ability, the proportion of soluble structure units from propylene and 1-butene is reduced, thereby helping to be applied in the field of food packaging.

[0078] The present application is further illustrated by the following examples, figures, and related test experiments and their results. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present application. It will be apparent, however, that one or more embodiments can be practiced without these specific details. In other instances, well-known methods have not been described in detail in order to not unnecessarily obscure the embodiments presented herein.

[0079] It should be noted that the following specific examples are only illustrative, and the protection scope of the present application is not limited thereto. The chemicals and raw materials used in the following examples are commercially available or self-prepared by recognized processing methods. It should be noted that the pyridine amine hafnium catalyst represented by formula (II) can be prepared by the preparation method of the known literature described above.

[0080] When performing nuclear magnetic resonance detection, the embodiment of the present application uses a high-precision and stable Varian Unity-400 nuclear magnetic resonance spectrometer to measure at a constant temperature of 100 DEG C, which can reduce the interference of molecular movement and chemical bond vibration on the results, and ensure accuracy and repeatability. Tetramethylsilane (TMS) is used as an internal standard, which has a unique chemical structure and stable properties, and can provide accurate chemical shift reference; deuterated tetrachloroethane is selected as a solvent, which does not interfere with the sample signal, thereby ensuring that the detection results are accurate and reliable.

[0081] The number average molecular weight M n , weight average molecular weight M w , and Z average molecular weight M Z of the random terpolymer containing 1,3-cyclopentylidene structural units w , and polydispersity (M n / M n ) are determined using the standard determination method of ASTM D6474, and the molecular weight distribution of the random terpolymer is illustrated by high-temperature gel permeation chromatography (GPC). The present application selects a PL-GPC-220 high-temperature gel permeation chromatograph (GPC), which is equipped with a differential (RI), viscosity, light scattering detector and three PL-Mix-B chromatographic columns. The combination of the three chromatographic columns can separate and detect polymers of different molecular weights. This method uses commercially available polystyrene standards to calibrate the GPC.

[0082] The present application uses a differential scanning calorimeter (TA Instruments, Q2000) and a Shimadzu UV-3600 ultraviolet-visible light-near infrared spectrophotometer to analyze the thermal properties and transparency of the random terpolymer containing 1,3-cyclopentylidene structural units.

[0083] The thermal property analysis aims to determine the melting temperature (T m ) and the crystallization temperature (T c ) of the random terpolymer. During testing, 5-10 mg of the random terpolymer is placed in a sample cell and heated to 200 DEG C at a rate of 10 DEG C / min, and kept for 10 min to eliminate the influence of thermal history. Then, the temperature is lowered at a rate of 10 DEG C / min, and the crystallization behavior is observed to determine T c . The second time, the temperature is raised at the same rate, and the temperature range is 25-200 DEG C, covering the main physical state change of the material. By analyzing the heat flow curve and combining the theory of thermal analysis, the temperature parameters are determined.

[0084] Example 1:

[0085] The copolymerization of propylene, 1-butene and 1,5-hexadiene was carried out in anhydrous and anaerobic environment, with xylene as the solvent, and the total volume of the reaction system in the polymerization kettle was 200 mL. The specific operation was as follows: first, xylene, triisobutylaluminum (1 mL, 1.0 mol / L) and 1,5-hexadiene (1.5 mL) were added to the polymerization kettle, then propylene and 1-butene mixed gas (1-butene volume fraction accounted for 15%) were added, and then a catalyst system composed of pyridylamine hafnium catalyst (5 μmol, 3.6 mg) represented by formula (II) and triphenylphosphonium tetrakis(pentafluorophenyl)borate (10 μmol) were added in sequence. The molar ratio of the three elements in the pyridylamine hafnium catalyst represented by formula (II), triisobutylaluminum and triphenylphosphonium tetrakis(pentafluorophenyl)borate was [Hf]:[Al]:[B]=1:200:2. The polymerization temperature was set to 60℃, the polymerization pressure was maintained at 0.6 MPa, and the copolymerization reaction lasted for 15 min. Finally, a terpolymer solution containing 1,3-cyclopentylidene structural units was obtained.

[0086] The obtained terpolymer solution was poured into an ethanol solution containing 2% (by volume) hydrochloric acid, and the terpolymer was precipitated and separated out by suction filtration to obtain a filter cake. Then, it was placed in a vacuum oven at 80℃ and dried for 8 hours to obtain a terpolymer 1 containing 1,3-cyclopentylidene structural units, with a mass of 26.8 g.

[0087] Figure 1 The differential scanning calorimetry temperature rising and falling curve of the terpolymer 1 of Example 1 of the present application is shown in the figure. Figure 1 As shown in the figure, the melting point of the terpolymer 1 was 124.2℃, and the crystallization temperature was 81.5℃, which had a relatively wide operating temperature space.

[0088] Example 2:

[0089] The propylene, 1-butene and 1,5-hexadiene are subjected to copolymerization reaction in anhydrous and anaerobic environment, with xylene as a solvent, and the total volume of the reaction system in the polymerization kettle is 200 mL. The specific operation is as follows: first, the toluene, triisobutylaluminum (1 mL, 1.0 mol / L) and 1,5-hexadiene (1 mL) are added into the polymerization kettle, then the propylene and 1-butene mixed gas (the volume fraction of 1-butene is 15%) is added, and then the catalyst system composed of the pyridylamine hafnium catalyst (5 μmol, 3.6 mg) shown in formula (II) and the N,N-dimethyl anilinium tetrakis(pentafluorophenyl)borate (10 μmol) is added in sequence, and the molar ratio of the three elements in the pyridylamine hafnium catalyst, triisobutylaluminum and N,N-dimethyl anilinium tetrakis(pentafluorophenyl)borate is [Hf]:[Al]:[B]=1:200:2. The polymerization temperature is set to 45°C, the polymerization pressure is maintained at 0.6 MPa, and the copolymerization reaction lasts for 15 min, and finally the terpolymer solution containing 1,3-cyclopentylidene structural units is obtained.

[0090] The terpolymer 2 containing 1,3-cyclopentylidene structural units is prepared by using the same precipitation and drying method as in Example 1, and the mass of the terpolymer 2 is 30.1 g.

[0091] Figure 2 The nuclear magnetic resonance carbon spectrum of the terpolymer 2 prepared in Example 2 of the present application is shown. As shown in the figure, Figure 2 it is proved that the terpolymer 2 prepared has a cyclic structural unit.

[0092] Example 3:

[0093] The process for preparing the terpolymer 3 containing 1,3-cyclopentylidene structural units in this example 3 is basically the same as that in Example 1, except that the polymerization temperature is adjusted to 50°C, and the mass of the terpolymer 3 is 27.8 g.

[0094] The terpolymers prepared in Example 2 and Example 3 are tested. Figure 3 The gel permeation chromatograms of the terpolymers prepared in Example 2 and Example 3 of the present application are shown. As shown in the figure, Figure 3 the ordinate is used to represent the weight fraction of the polymer in the unit logarithmic molecular weight interval (ΔlogM), and the abscissa represents the logarithm of the weight average molecular weight. It can be seen that the molecular weight of Example 2 is 33.4×10 4 g / mol, and the molecular weight of Example 3 is 29.4×10 4 g / mol. Figure 4 The stress-strain curve diagrams of the terpolymers prepared in Example 1~Example 3 of the present application are shown. As shown in the figure, Figure 4The specific stress-strain values are shown in Table 3 below, and it should be noted that the stress-strain test was performed at a tensile rate of 10 mm / min. It can be seen that Examples 1-3 have good tensile strength.

[0095] Figure 5 The differential scanning calorimetry heating and cooling curves of the terpolymer 3 of Example 3 are shown. As shown in Table 3 below, the melting point of the terpolymer 3 is 123.2℃, and the crystallization temperature is 83.9℃, which has a wide operating temperature space. Figure 5

[0096] Example 4:

[0097] Propylene, 1-butene and 1,5-hexadiene were copolymerized in anhydrous and anaerobic environment, with xylene as the solvent, and the total volume of the reaction system in the polymerization kettle was 200 mL. The specific operation was as follows: first, xylene, methylaluminoxane (5 mL, 10 wt%) and 1,5-hexadiene (8 mL) were added to the polymerization kettle, then propylene and 1-butene mixed gas (1-butene volume fraction accounted for 10%) was added, and then formula (II) pyridylamine hafnium catalyst (5 μmol) was added, and the molar ratio of formula (II) pyridylamine hafnium catalyst to methylaluminoxane of the two elements was [Hf]:[Al]=1:100. The polymerization temperature was set to 60℃, the polymerization pressure was maintained at 0.4 MPa, and the copolymerization reaction lasted for 20 min. Finally, a terpolymer solution containing 1,3-cyclopentylidene structural units was obtained.

[0098] Using the same precipitation and drying method as in Example 1, a terpolymer 4 containing 1,3-cyclopentylidene structural units was prepared, and the mass was 23.2 g.

[0099] Example 5:

[0100] ​The propylene, 1-butene and 1,5-hexadiene are subjected to copolymerization reaction in anhydrous and anaerobic environment, with xylene as solvent, and the total volume of the reaction system in the polymerization kettle is 200 mL. The specific operation is as follows: first, xylene, triisobutylaluminum (2 mL, 1.0 mol / L) and 1,5-hexadiene (2 mL) are added to the polymerization kettle, then propylene and 1-butene mixed gas (1-butene accounts for 20% by volume) are added, and then a catalyst system composed of the pyridylamine hafnium catalyst (5 μmol) shown in formula (II) and tetra(pentafluorophenyl)boron N,N-dimethylbenzyl ammonium (10 μmol) is added in sequence. The molar ratio of the three elements in the pyridylamine hafnium catalyst shown in formula (II), triisobutylaluminum and tetra(pentafluorophenyl)boron N,N-dimethylbenzyl ammonium is [Hf]:[Al]:[B]=1:400:2. The polymerization temperature is set to 70°C, the polymerization pressure is maintained at 0.6 MPa, and the copolymerization reaction lasts for 10 min, and finally a terpolymer solution containing 1,3-cyclopentylidene structural units is obtained.

[0101] The terpolymer 5 containing 1,3-cyclopentylidene structural units is prepared by using the same precipitation and drying method as in Example 1, and the mass of the terpolymer is 23.2 g.

[0102] Example 6:

[0103] The propylene, 1-butene and 1,5-hexadiene are subjected to copolymerization reaction in anhydrous and anaerobic environment, with xylene as solvent, and the total volume of the reaction system in the polymerization kettle is 200 mL. The specific operation is as follows: first, xylene, triisobutylaluminum (2 mL, 1.0 mol / L) and 1,5-hexadiene (2 mL) are added to the polymerization kettle, then propylene and 1-butene mixed gas (1-butene accounts for 20% by volume) are added, and then a catalyst system composed of the pyridylamine hafnium catalyst (5 μmol) shown in formula (II) and tetra(pentafluorophenyl)boron N,N-dimethylbenzyl ammonium (10 μmol) is added in sequence. The molar ratio of the three elements in the pyridylamine hafnium catalyst shown in formula (II), triisobutylaluminum and tetra(pentafluorophenyl)boron N,N-dimethylbenzyl ammonium is [Hf]:[Al]:[B]=1:400:2. The polymerization temperature is set to 70°C, the polymerization pressure is maintained at 0.6 MPa, and the copolymerization reaction lasts for 10 min, and finally a terpolymer solution containing 1,3-cyclopentylidene structural units is obtained.

[0104] The terpolymer 6 containing 1,3-cyclopentylidene structural units is prepared by using the same precipitation and drying method as in Example 1, and the mass of the terpolymer is 25.2 g.

[0105] Figure 6 The transmittance of the terpolymer prepared in Example 2, Example 4 and Example 6 is shown in the curve graph of transmittance changing with wavelength. Figure 6As shown, it can be seen that the transmittance of Example 2, Example 4 and Example 6 is higher, especially the visible light transmittance of Example 4 and Example 6 is higher, which indicates that the transparency of the prepared terpolymer random copolymer is better.

[0106] Example 7:

[0107] Propylene, 1-butene and 1,5-hexadiene were copolymerized in anhydrous and anaerobic environment, with xylene as the solvent, and the total volume of the reaction system in the polymerization kettle was 200 mL. The specific operation was as follows: xylene, triisobutylaluminum (1 mL, 1.0 mol / L) and 1,5-hexadiene (15 mL) were first added to the polymerization kettle, then propylene and 1-butene mixed gas (1-butene volume fraction accounted for 5%) was added, and then the catalyst system composed of pyridylamine hafnium catalyst (5 μmol) represented by formula (II) and triphenylcarbenium tetrakis(pentafluorophenyl)borate was added in sequence, and the ratio of the main catalyst to the cocatalyst was strictly controlled to be [Hf]:[Al]:[B]=1:200:2. The polymerization temperature was set to 60°C, the polymerization pressure was maintained at 0.5 MPa, and the copolymerization reaction lasted for 20 min, finally a terpolymer random copolymer containing 1,3-cyclopentylidene structural unit was obtained.

[0108] The terpolymer random copolymer 7 containing 1,3-cyclopentylidene structural unit was prepared by using the same precipitation and drying method as in Example 1, and the mass was 14.2 g.

[0109] Example 8:

[0110] Propylene, 1-butene and 1,5-hexadiene were copolymerized in anhydrous and anaerobic environment, with xylene as the solvent, and the total volume of the reaction system in the polymerization kettle was 200 mL. The specific operation was as follows: xylene, triisobutylaluminum (1 mL, 1.0 mol / L) and 1,5-hexadiene (15 mL) were first added to the polymerization kettle, then propylene and 1-butene mixed gas (1-butene volume fraction accounted for 5%) was added, and then the catalyst system composed of pyridylamine hafnium catalyst (5 μmol) represented by formula (II) and triphenylcarbenium tetrakis(pentafluorophenyl)borate was added in sequence, and the ratio of the main catalyst to the cocatalyst was strictly controlled to be [Hf]:[Al]:[B]=1:200:2. The polymerization temperature was set to 60°C, the polymerization pressure was maintained at 0.5 MPa, and the copolymerization reaction lasted for 20 min, finally a terpolymer random copolymer containing 1,3-cyclopentylidene structural unit was obtained.

[0111] The terpolymer random copolymer 8 containing 1,3-cyclopentylidene structural unit was prepared by using the same precipitation and drying method as in Example 1, and the mass was 26.2 g.

[0112] Figure 7The differential scanning calorimetry temperature rising curves of the terpolymer random copolymers prepared in Embodiment 3 and Embodiment 8 are shown. Figure 7 As shown in the figure, it can be seen that the melting point of the terpolymer random copolymer 3 prepared in Embodiment 3 is 123.2℃, and the melting point of the terpolymer random copolymer 8 prepared in Embodiment 8 is 103.3℃.

[0113] The terpolymer random copolymers containing 1,3-cyclopentylidene structural units in Embodiments 1-8 are subjected to performance tests. Embodiments 1-8 can successfully prepare the terpolymer random copolymers with cyclic structures under the adjusted reaction conditions, and the arrangement of the three structural units of the terpolymer random copolymers is random. The molecular structure and performance of the terpolymer random copolymers are different from the polypropylene copolymers in the related art, and the terpolymer random copolymers of the present application can be widely applied in the heat sealing field as the heat sealing layer of the cast polypropylene film (CPP),

[0114] The physical and chemical performance indexes of the terpolymer random copolymers in Embodiments 1-8 are specifically shown in Table 1.

[0115] Table 1: Related performance indexes of each embodiment

[0116]

[0117] wherein, ΔH m represents the heat enthalpy, and the crystallinity of the terpolymer random copolymer can be determined by ΔH m Based on the data in Table 1, it can be seen that the introduced 1,3-cyclopentylidene with cyclic structure can improve the thermal stability of the terpolymer random copolymer, and make the temperature operation space from crystallization to melting easy to control and wide. In Embodiments 4 and 7, the high content of 1,3-cyclopentylidene and butene units significantly reduces the melting point of the polymer; wherein, the crystallization ability of the polymer in Embodiment 7 is completely inhibited, and the melting point and crystallization temperature are not detected.

[0118] In order to comprehensively evaluate the performance of the terpolymer random copolymers containing 1,3-cyclopentylidene structural units, especially the mechanical properties, the present application strictly tests the mechanical properties by using a mechanical property testing instrument (model: INSTRON 5969). The instrument has high loading and displacement control accuracy, and can simulate the actual mechanical load. The test is performed according to the GB / T1040-1992 standard to ensure that the results are normative and comparable. The tensile sample is dumbbell-shaped, and the effective size is 10×5×1mm 3The stress is concentrated on the effective part, and the accurate size is beneficial to the accuracy of the results. The test rate is 20 mm / min (wherein the stress-strain test is tested at a stretching rate of 10 mm / min), and the material is allowed to fully exhibit the mechanical response. Each sample is tested at least 5 times to reduce the influence of material unevenness and experimental error. Statistical analysis of the data is shown in Table 2 below to obtain representative and reliable results, which provide data support for the performance evaluation and application development of the copolymer.

[0119] Table 2 Mechanical data of ternary random copolymer

[0120]

[0121] As shown in Table 2, the ternary random copolymers of Examples 1-8 have good mechanical properties, indicating that the introduction of 1,3-cyclopentylidene with a cyclic structure has a great improvement and promotion effect on the performance of the ternary polymer, which helps to further expand the application space of polypropylene as a heat-sealing layer.

[0122] Application Examples 1-5:

[0123] A single screw extruder (length / diameter ratio of screw 25) was used to extrude the ternary random copolymers prepared in Examples 1, 2, 4, 6, and 8, respectively, using 5 g at a melt temperature of 210-250°C, at a film stretching speed of 7 m / min, to obtain copolymer films with a thickness of 50 μm. An isotacticity index of 97, a melt flow rate of 2 g / 10 min, and a propylene homopolymer film with a thickness of 1000 μm were obtained. Each of the above prepared copolymer films was stacked on the propylene homopolymer film. Then, the stacked film was placed in a press (Carver Company) under the conditions of 200°C and 9000 kg load for 5 minutes, so that each layer of the film formed a laminated body bonded to each other.

[0124] Each of the obtained laminated bodies was stretched longitudinally and transversely (i.e., biaxially) at 150°C using a film stretcher, and the stretching ratio was 6 times, to finally obtain a multilayer film structure with a thickness of 20 μm (containing a propylene homopolymer film with a thickness of 18 μm and a copolymer film of the example with a thickness of 2 μm). A sample with a size of 2 cm x 5 cm was cut from the above prepared multilayer film structure. The ternary random copolymers of Examples 1, 2, 4, 6, and 8 correspond to Application Examples 1-5, respectively.

[0125] The multilayer film structure of Application Examples 1-5 was tested for heat-sealing initiation temperature. The test procedure is as follows: in each test, two above prepared multilayer film structures were placed in alignment, and it was ensured that the adjacent layers were the specific copolymer films of the example.

[0126] The multi-layer film structures of application examples 1-5 were tested, and the relevant performance parameters are shown in Table 3. Among them, the transparency test uses a high-precision, wide-wavelength-range spectrophotometer. The prepared sample is placed in the sample cell, and the test wavelength range is set to 250-400 nm (near ultraviolet light region) and 400-800 nm (visible light region). The near ultraviolet light region transmittance reflects the material's ability to block ultraviolet light, and the visible light region transmittance relates to the actual transparency effect. By measuring the transmittance in the two wavelength ranges, the material's transparency and transmittance characteristics for different wavelengths of light can be comprehensively evaluated.

[0127] A sealing machine (model HSG-ETK 745) was used to seal along one of the 2 cm sides of the sample. The sealing pressure was set to 0.1 N / mm², and the sealing time was 0.5 seconds. Starting from about 10°C below the melting temperature of the ternary random copolymer, the sealing temperature was increased by 4°C each time the sample was sealed.

[0128] After sealing was complete, the sample was cooled. After cooling, the unsealed end of the sample was connected to a mechanical testing machine (manufacturer Instron), and the sample was tested at a pulling speed of 50 mm / min. Table 3 below shows the results of the relevant performance tests of the multi-layer film structures of the application examples.

[0129] Table 3 Performance of multi-layer film structures of application examples

[0130]

[0131] Note: The transmittance (%) data in Table 3 corresponds to the examples, not the application examples. For example, application example 3 corresponds to example 4, which has a transmittance of 90%. Temperature range test method: A heat sealing tester (such as a heat sealer) is used to accurately control temperature, pressure, and heat sealing time. The equipment must meet relevant standards (such as ASTM F2029, ISO 18738). The test steps are as follows: (1) Take a 10 cm x 10 cm film sample, ensuring that the surface is clean and free of impurities. (2) Fix the pressure (usually 0.1-0.3 MPa) and time (1-3 seconds), and gradually adjust the temperature (recommended from low to high, with an increase of 5-10°C each time). (3) Seal the film at different temperatures, and each test requires at least 3 parallel samples.

[0132] Temperature range determination method: Observe whether the seal is smooth, bubble-free, crack-free, or excessively melted. Peel strength test: Use a tensile testing machine to measure the peel strength of the seal (unit: N / 15 mm), and record the temperature range corresponding to the maximum peel strength. Determine the temperature range: The temperature range in which the peel strength reaches more than 80% of the material's nominal value is considered the effective temperature range.

[0133] As shown in Table 3, experiments using the ternary random copolymers of several examples as copolymerized polypropylene revealed that the incorporation of 1,3-cyclopentylene units and butene units resulted in lower heat-sealing temperatures and a wider temperature range, with the heat-sealing initiation temperature remaining generally between 30°C and 85°C, and the temperature range spanning approximately 40°C to 60°C. The heat-sealing initiation temperature (SIT) of the multilayer film structure was at least 10°C lower than that of a single-layer cast polypropylene (CPP) film. Furthermore, the SIT of the multilayer film structure was at least 20°C lower than that of a single-layer CPP film. Hot tack strength remained generally between 6 and 18 N / 15 mm, and transmittance remained between 68 and 92%, demonstrating excellent performance. The multilayer film structure of Example 2, due to its superior molecular regularity, readily formed thick lamellar structures, resulting in a slightly higher heat-sealing temperature. The corresponding example 5 is now explained: the heat seal layer is a ternary random copolymer containing 1,3-cyclopentylene structural units prepared in Example 8, and its melting point T m The temperature range of the heat-sealing film is 103.3°C, and it is used as the heat-sealing layer. The initial heat-sealing temperature is 58.6°C, the temperature range is 67.3-114.5°C, the hot tack strength is 12N / 15mm, and the light transmittance of the ternary random copolymer is 84%. For other application examples, please refer to Application Example 5. The temperature range of the heat-sealing film refers to the temperature range in which it can be effectively heat-sealed, that is, within this temperature range, the film material can be reliably bonded after heating while maintaining the sealing strength and appearance quality. The width of the temperature range directly affects the stability and applicability of the heat-sealing process.

[0134] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A ternary random copolymer, characterized in that: The ternary random copolymer has a structure as shown in the following formula (I): Formula (I), wherein 0<x<1, 0<y<1, and 0<x+y<1; 150<n<2000; In the ternary random copolymer, the molar content percentage of the structural unit derived from the 1-butene monomer is 2-30%, and the molar content percentage of the 1,3-cyclopentylene monomer is 0.1-20%; The melting point of the ternary random copolymer is 100-136°C and the crystallization temperature is 50-105°C; The isotacticity of the structural units derived from propylene and the structural units derived from 1-butene in the terpolymer is 92-99%, respectively.

2. The ternary random copolymer according to claim 1, characterized in that The weight average molecular weight of the ternary random copolymer is 6×10 4 ~6×10 5 g / mol; molecular weight distribution index is 1.8~3.

2.

3. A method for preparing a ternary random copolymer as claimed in claim 1 or 2, characterized in that: The preparation method comprises: Under anhydrous and oxygen-free conditions, propylene monomer, 1-butene monomer and 1,5-hexadiene monomer are copolymerized in an organic solvent in the presence of a hafnium pyridylamine catalyst and a co-catalyst to obtain a ternary random copolymer solution. precipitating and drying the ternary random copolymer solution to obtain the ternary random copolymer; The co-catalyst is aluminoxane or methylaluminoxane, or a combination of an organic aluminum compound and an organic boron compound.

4. The preparation method according to claim 3, characterized in that The hafnium pyridinamine catalyst has a structure as shown in formula (II): Formula (II).

5. The preparation method according to claim 3, characterized in that The organoaluminum compound comprises at least one of an alkyl aluminum and an alkyl aluminum halide; The organic boron compound includes at least one of triphenylcarbonium tetrakis(pentafluorophenyl)borate, N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, N,N-dimethylcyclohexylammonium tetrakis(pentafluorophenyl)borate, or N,N-dimethylbenzylammonium tetrakis(pentafluorophenyl)borate.

6. The preparation method according to claim 4, characterized in that The copolymerization reaction temperature is 25-100°C, and the reaction time is 5-60 minutes; The drying temperature is 70-100°C and the drying time is 4-12 hours; The organic solvent includes at least one of benzene, toluene, xylene, pentane, hexane, heptane, octane, and nonane.

7. A multilayer film structure, characterized in that The multilayer film structure comprises: a substrate layer comprising a thermoplastic polymer; and A heat-sealing layer comprising the ternary random copolymer as claimed in claim 1 or 2.

8. The multilayer film structure according to claim 7, characterized in that The multi-layer film structure is prepared by multi-layer co-extrusion casting.

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