A nylon film with high heat seal strength and low heat seal temperature containing a heteroepitaxial heat seal layer and a method of making the same

Abstract

The application discloses a nylon film with high heat-sealing strength and low heat-sealing temperature and containing a hetero-twin sealing layer and a preparation method thereof. The nylon film comprises a heat-sealing layer, a core layer and a surface layer arranged in sequence. The surface layer is made of 98-99.5 parts by weight of nylon 6 and 0.5-2 parts by weight of an anti-sticking agent, or made of 98-99.5 parts by weight of nylon 66 and 0.5-2 parts by weight of an anti-sticking agent. The core layer is made of nylon 6 or nylon 66. The heat-sealing layer is made of a random copolymer nylon capable of hetero-twinning, which is selected from any one of nylon 6 / 10 copolymer, nylon 6 / 12 copolymer, nylon 66 / 610 copolymer and nylon 66 / 612 copolymer. The random copolymer nylon capable of hetero-twinning is used as the heat-sealing layer, so that the heat-sealing temperature of the nylon film is significantly reduced, the heat-sealing strength is improved, and the interlayer bonding force of the nylon film is improved. The obtained nylon film has simple structure, high mechanical strength and good barrier property, and can be applied to the packaging field with high requirements on barrier property and mechanical property.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of heat-sealable film in packaging technology, in particular to a nylon film with high heat-seal strength and low heat-seal temperature containing a heteromorphic twin heat-seal layer and a preparation method thereof. BACKGROUND

[0002] Heat-sealable film is widely used in packaging field, involving food, medicine, logistics, household appliances and many other industries. Heat sealing is the main process of polymeric film bagging and packaging, and the heat sealing performance determines the specific application of the polymeric film. The most commonly used heat-sealable film in the prior art is a cast or biaxially oriented polypropylene or polyethylene film. In order to improve the mechanical properties and barrier properties of the heat-sealable film, a layer or more layers of nylon film are often compounded in the heat-sealable film due to the advantages of nylon film such as high temperature resistance, cold resistance, organic solvent resistance, puncture resistance, high barrier and the like. However, there is a problem of poor interfacial compatibility between polypropylene or polyethylene film and nylon film, and the adhesion strength between layers is low. In addition, compared with polyolefin film, the melting point of nylon film is high, for example, the melting point of nylon 6 is about 220℃, which leads to high heat-seal temperature, increases heat-seal energy consumption, limits the improvement of heat-seal speed, reduces the service life of heat-seal equipment, and the heat-seal performance is poor. Since the heat-sealing process is a process of polymer melting and recrystallization, the melting point can be reduced and the crystallinity can be improved by regulating the crystalline structure of nylon, so as to reduce the heat-seal temperature of nylon and improve the heat-seal strength at the same time.

[0003] Random copolymerization is an effective means to regulate the crystalline structure and heat-seal performance of nylon. For binary nylon random copolymer, the chemical structure of the copolymer unit is relatively similar, the component with high mass fraction as the main copolymer unit, and the component with low mass fraction as the secondary copolymer unit. The secondary copolymer unit can be arranged in the crystal lattice of the main copolymer unit and crystallized with the main unit, showing a heteromorphic twin crystallization behavior. In the random copolymer with heteromorphic twin behavior, the secondary copolymer unit can be regarded as a structural defect, resulting in changes in the thermodynamic properties of the copolymer, such as crystallization temperature, melting temperature, melting enthalpy and crystallization enthalpy. When the concentration of the two copolymer units is close, a pseudo-melting point appears, and the melting temperature and crystallization temperature of the copolymer at this component ratio are significantly lower than those of the corresponding homopolymer. For ordinary copolymers, although the melting point can be reduced by copolymerization, it is difficult to crystallize and recrystallize, and the crystallinity is low and the crystallization rate is slow, resulting in low heat-seal strength and heat-seal efficiency. SUMMARY

[0004] To address the shortcomings of existing technologies, this invention proposes a nylon film with high heat-sealing strength and low heat-sealing temperature containing a heterodimorphic heat-sealing layer, and its preparation method. The heterodimorphic random copolymer nylon has the advantages of a low and adjustable melting point, which can significantly reduce the initial sealing temperature of the nylon heat-sealing film. Due to its fast crystallization speed, easy melting and recrystallization, and high crystallinity, it can improve heat-sealing strength and efficiency. By using a random blend of nylon with heterodimorphic behavior as the heat-sealing layer, the prepared nylon heat-sealing film exhibits lower heat-sealing temperature, higher heat-sealing strength, and higher heat-sealing efficiency compared to heat-sealing films using nylon 6 or nylon 66 as the heat-sealing layer. Furthermore, compared to heat-sealing films containing both nylon and polypropylene layers, it shows better compatibility between layers, higher bonding strength, and superior mechanical properties and puncture resistance.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A nylon film with high heat-sealing strength and low heat-sealing temperature containing a heterogeneous dimorphic heat-sealing layer includes a heat-sealing layer, a core layer and a surface layer arranged sequentially.

[0007] The surface layer is made of 98-99.5 parts by weight of nylon 6 and 0.5-2 parts by weight of anti-adhesion agent, or of 98-99.5 parts by weight of nylon 66 and 0.5-2 parts by weight of anti-adhesion agent;

[0008] The core layer is made of nylon 6 or nylon 66;

[0009] The heat-sealing layer is made of heterogeneous dimorphic random copolymer nylon, which is selected from any one of nylon 6 / 10 copolymer, nylon 6 / 12 copolymer, nylon 66 / 610 copolymer, and nylon 66 / 612 copolymer.

[0010] Furthermore, the thickness of the heat-sealing layer is 2-5 μm, and the total thickness of the nylon film is 20-30 μm.

[0011] Furthermore, the random copolymer nylon that can be heterodimorphically dimorphic has a randomness degree between 0.91 and 1.12 and an intrinsic viscosity between 1.8 and 2.5 dL / g.

[0012] Furthermore, when the heat-sealing layer is made of nylon 6 / 10 copolymer, the heat-sealing temperature is 135-155°C; when the heat-sealing layer is made of nylon 6 / 12 copolymer, the heat-sealing temperature is 115-135°C; when the heat-sealing layer is made of nylon 66 / 610 copolymer, the heat-sealing temperature is 200-230°C; and when the heat-sealing layer is made of nylon 66 / 612 copolymer, the heat-sealing temperature is 190-220°C.

[0013] Furthermore, the anti-sticking agent is selected from any one or two of silica and oleamide in any ratio.

[0014] A method for preparing a nylon film with high heat sealing strength and low heat sealing temperature and a heteromorphic homodimer heat sealing layer, the method comprising the following steps:

[0015] S1: for nylon 6 / 10 copolymer, nylon 6 / 12 copolymer: ε-caprolactam, 10-amino n-decanoic acid and a molecular weight regulator, or, ε-caprolactam, 12-aminododecanoic acid and a molecular weight regulator, are heated at 190-210℃ for 1.5-2h in a nitrogen atmosphere, then heated to 235-245℃, vacuumized and subjected to polycondensation reaction, cooled by water, granulated, dried to obtain a heat sealing layer raw material;

[0016] for nylon 66 / 610 copolymer, nylon 66 / 612 copolymer: 1,6-hexanediamine and 1,6-hexanedioic acid, or 1,6-hexanediamine and 1,10-decanedioic acid, or 1,6-hexanediamine and 1,12-dodecanedioic acid are dissolved in ethanol, cooled and crystallized at room temperature, centrifuged to obtain nylon 66 salt or nylon 610 salt or nylon 612 salt; the nylon 66 salt is dried with the nylon 610 salt or 612 salt respectively, ethanol is removed, a molecular weight regulator is added, heated at 190-210℃ for 1.5-2h in a nitrogen atmosphere, then heated to 270-280℃, vacuumized and subjected to polycondensation reaction, cooled by water, granulated, dried to obtain a heat sealing layer raw material;

[0017] S2: 98-99.5 parts by weight of nylon 6 and 0.5-2 parts by weight of an anti-sticking agent are mixed, or 98-99.5 parts by weight of nylon 66 and 0.5-2 parts by weight of an anti-sticking agent are mixed, uniformly mixed in a molten state, and the blend is extruded and granulated to obtain a surface layer raw material;

[0018] S3: the surface layer raw material, the core layer raw material and the heat sealing layer raw material are melt-extruded through a three-layer co-extrusion casting device, treated by a chilling roller and 50-60℃ hot water, and after the water is blown dry, subjected to synchronous stretching, annealing and shaping after stretching, and winding, to obtain a nylon film with low heat sealing temperature.

[0019] Further, in the co-extrusion casting process, when the surface layer and the core layer are both nylon 6, the extrusion temperature is 230℃; when the surface layer and the core layer are both nylon 66, the extrusion temperature is 270℃; and the extrusion temperatures of the heat sealing layer being nylon 6 / 10 copolymer, nylon 6 / 12 copolymer, nylon 66 / 610 copolymer, nylon 66 / 612 copolymer are 140℃, 120℃, 200℃ and 190℃ respectively.

[0020] Further, the molecular weight regulator used in step S1 is 1,6-hexanedioic acid, accounting for 1% of the total moles of the reaction raw materials.

[0021] The beneficial effects of the present application are as follows:

[0022] 1. The application uses a heteromorphic twin binary random copolymer nylon as a heat sealing layer, which can regulate the thermodynamic properties of the nylon by changing the copolymer composition, and the melting temperature and crystallization temperature of the copolymer near the pseudo-eutectic point are lower than those of the corresponding single-component homopolymer, so that the heat sealing temperature of the nylon heat sealing film can be significantly reduced.

[0023] 2. Compared with the common copolymer, the random copolymer nylon used in the application has the advantages of fast crystallization speed, easy melting and recrystallization, high crystallinity, and can reduce the heat sealing temperature while improving the heat sealing strength and heat sealing efficiency.

[0024] 3. In the application, the surface layer, core layer and heat sealing layer of the heat sealing film all use nylon materials, which effectively avoids the problem of poor interfacial compatibility between the nylon film and the polyolefin film in the traditional nylon-polyolefin composite heat sealing film, and is beneficial to improve the interlayer bonding strength and improve the strength and puncture resistance of the heat sealing film. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a schematic diagram of a high heat sealing strength and low heat sealing temperature nylon film with a heteromorphic twin heat sealing layer.

[0026] Figure 2 is the DSC curve of different component random copolymer nylon 66 / 610.

[0027] Figure 3 is the WAXS curve of different component random copolymer nylon 66 / 610. DETAILED DESCRIPTION

[0028] The application will become more apparent from the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings, and the purposes and effects of the application will become more apparent. It should be understood that the specific embodiments described herein are only used to explain the application and do not limit the application.

[0029] Example 1

[0030] Heat-seal layer raw material synthesis: 1,6-hexanediamine and 1,6-hexanedioic acid were dissolved in ethanol at 80°C, and the mixture was cooled to room temperature to crystallize. The nylon 66 salt was separated by centrifugation. 1,6-hexanediamine and 1,10-decanedioic acid were dissolved in ethanol at 80°C, and the mixture was cooled to room temperature to crystallize. The nylon 610 salt was separated by centrifugation. The nylon 66 salt and the nylon 610 salt were dried at 50°C for 48 h, and then added to a reaction kettle in a molar ratio of 3:7. 1% of 1,6-hexanedioic acid based on the total amount of raw materials was added. The mixture was heated at 190°C for 2 h under a nitrogen atmosphere, and then heated to 270°C. Vacuum was applied and the mixture was subjected to polycondensation for 2 h. The mixture was discharged from the bottom of the reaction kettle at a discharge pressure of 0.5 MPa. After cooling, the mixture was granulated. The granules were treated in hot water for 24 h, and then dried to obtain the heat-seal layer raw material. The intrinsic viscosity of the obtained raw material was 2.3 dL / g, and the degree of randomness was 0.91.

[0031] Heat-seal film preparation and heat-seal performance: 99 parts of nylon 6, 0.5 parts of silicon dioxide, and 0.5 parts of oleic acid amide were added to a banbury mixer, and the temperature was set to 220°C. The rotation speed was set to 50 rpm, and the mixing time was set to 5 min. The mixture was extruded and granulated to obtain the surface layer raw material. The core layer raw material was nylon 6. The surface layer raw material, the core layer raw material, and the heat-seal layer raw material were melt-extruded through a three-layer co-extrusion casting device. The extrusion temperature of the surface layer and the core layer was 230°C, and the extrusion temperature of the heat-seal layer was 200°C. After passing through a 20°C chill roll, a 55°C hot water treatment, and cold air drying, the mixture was subjected to synchronous stretching in a stretching oven. The longitudinal and transverse stretching ratios were both 3. After stretching, the mixture was annealed, shaped, and wound to obtain a low-heat-seal-temperature nylon film. The structure of the nylon film is shown in FIG. 1. The thickness of the heat-seal layer of the heat-seal film was 3 µm, and the total thickness was 25 µm. The heat-seal film had a heat-seal initiation temperature of 200°C, a heat-seal pressure of 0.20 MPa, a heat-seal time of 1 s, and a heat-seal strength of 7.9 N / 15 mm. Figure 1

[0032] Example 2

[0033] Heat-seal layer raw material synthesis: 1,6-hexanediamine and 1,6-hexanedioic acid were dissolved in ethanol at 80°C, and the mixture was cooled to room temperature to crystallize. The nylon 66 salt was separated by centrifugation. 1,6-hexanediamine and 1,12-dodecanedioic acid were dissolved in ethanol at 80°C, and the mixture was cooled to room temperature to crystallize. The nylon 612 salt was separated by centrifugation. The nylon 66 salt and the nylon 612 salt were dried at 50°C for 48 h, and then added to a reaction kettle in a molar ratio of 5:5. 1% of 1,6-hexanedioic acid based on the total amount of raw materials was added. The mixture was heated at 210°C for 1.5 h under a nitrogen atmosphere, and then heated to 280°C. Vacuum was applied and the mixture was subjected to polycondensation for 2 h. The mixture was discharged from the bottom of the reaction kettle at a discharge pressure of 0.5 MPa. After cooling, the mixture was granulated. The granules were treated in hot water for 24 h, and then dried to obtain the heat-seal layer raw material. The intrinsic viscosity of the obtained raw material was 2.3 dL / g, and the degree of randomness was 1.04.

[0034] ​Preparation of heat-sealable film and heat-sealability: 99 parts of nylon 66 and 1 part of silica were added into an internal mixer, the temperature was 220°C, the rotating speed was 50 rpm, and the time was 5 min. The blend was extruded and pelletized to obtain the surface layer material. The core layer material was nylon 66. The surface layer material, the core layer material and the heat-sealable layer material were melt-extruded through a three-layer co-extrusion casting device, wherein the extrusion temperature of the surface layer and the core layer was 270°C, and the extrusion temperature of the heat-sealable layer was 190°C. After being treated by a 20°C chill roller, 55°C hot water and cold air blowing, the simultaneous stretching was carried out in a stretching oven, the longitudinal and transverse stretching ratios were both 3. After stretching, annealing, setting and winding were carried out to obtain the nylon film with low heat-sealable temperature. The thickness of the heat-sealable layer of the heat-sealable film was 5 μm, and the total thickness was 30 μm. The heat-sealable film had a seal initiation temperature of 190°C, a heat-seal pressure of 0.20 MPa, a heat-seal time of 1 s, and a heat-seal strength of 7.5 N / 15 mm.

[0035] Example 3

[0036] Synthesis of heat-sealable layer material: ε-caprolactam, 10-amino-n-decanoic acid and 1,6-hexanedioic acid with a molar fraction of 1% of the total amount of the material were heated at 200°C for 2 h under nitrogen atmosphere, then the temperature was increased to 235°C, vacuum was applied and the polycondensation reaction was carried out for 2 h. The material was discharged from the bottom end of the reaction kettle, the discharge pressure was 0.4 MPa, and after cooling, the pellets were treated in hot water for 24 h, and then dried to obtain the heat-sealable layer material. The molar ratio of ε-caprolactam and 10-amino-n-decanoic acid was 5:5, and the inherent viscosity of the obtained material was 2.0 dL / g, and the randomness was 0.99.

[0037] Preparation of heat-sealable film and heat-sealability: 98 parts of nylon 6 and 2 parts of silica were added into an internal mixer, the temperature was 220°C, the rotating speed was 50 rpm, and the time was 5 min. The blend was extruded and pelletized to obtain the surface layer material. The core layer material was nylon 6. The surface layer material, the core layer material and the heat-sealable layer material were melt-extruded through a three-layer co-extrusion casting device, wherein the extrusion temperature of the surface layer and the core layer was 230°C, and the extrusion temperature of the heat-sealable layer was 140°C. After being treated by a 20°C chill roller, 50°C hot water and cold air blowing, the simultaneous stretching was carried out in a stretching oven, the longitudinal and transverse stretching ratios were both 3. After stretching, annealing, setting and winding were carried out to obtain the nylon film with low heat-sealable temperature. The thickness of the heat-sealable layer of the heat-sealable film was 3 μm, and the total thickness was 25 μm. The heat-sealable film had a seal initiation temperature of 135°C, a heat-seal pressure of 0.20 MPa, a heat-seal time of 0.8 s, and a heat-seal strength of 6.8 N / 15 mm.

[0038] Example 4

[0039] Heat-seal layer raw material synthesis: ε-caprolactam, 12-aminododecanoic acid and 1,6-hexanedioic acid with a mole fraction of 1% of the total raw material were heated at 200°C for 2h under nitrogen atmosphere, then the temperature was raised to 245°C, vacuum was applied and the polycondensation reaction was carried out for 2h, the discharge was taken from the bottom of the reactor, the discharge pressure was 0.4 MPa, and after cooling, the granules were treated in hot water for 24h, dried and obtained the heat-seal layer raw material. The mole ratio of ε-caprolactam and 12-aminododecanoic acid was 4:6, and the inherent viscosity of the obtained raw material was 1.8 dL / g, and the degree of randomness was 1.03.

[0040] Heat-seal film preparation and heat-seal performance: 99.5 parts of nylon 6 and 0.5 parts of oleic acid amide were added to the internal mixer, the temperature was 220°C, the rotation speed was 50 rpm, and the time was 5 min, the blend was extruded and granulated to obtain the surface layer raw material. The core layer raw material was nylon 6. The surface layer raw material, the core layer raw material and the heat-seal layer raw material were melt extruded through a three-layer co-extrusion casting device, the extrusion temperature of the surface layer and the core layer was 230°C, and the extrusion temperature of the heat-seal layer was 120°C. After passing through a 20°C chill roller, 60°C hot water treatment and cold air drying, synchronous stretching was carried out in a stretching oven, the longitudinal and transverse stretching ratios were both 3, and after stretching, annealing, setting and winding were carried out to obtain a low heat-seal temperature nylon film. The heat-seal layer thickness of the heat-seal film was 2μm, and the total thickness was 20μm. The heat-seal film had a heat-seal initiation temperature of 115°C, a heat-seal pressure of 0.20 MPa, a heat-seal time of 0.8s, and a heat-seal strength of 5.8N / 15mm.

[0041] Example 5

[0042] Heat-seal layer raw material synthesis: The process was the same as that of Example 1, and the mole ratio of nylon 66 salt and nylon 610 salt was 4:6. The inherent viscosity of the obtained raw material was 2.5 dL / g, and the degree of randomness was 1.12.

[0043] Heat-seal film preparation and heat-seal performance: The process was the same as that of Example 1, and the extrusion temperature of the heat-seal layer was 200°C. The heat-seal layer thickness of the heat-seal film was 3μm, and the total thickness was 25μm. The heat-seal film had a heat-seal initiation temperature of 200°C, a heat-seal pressure of 0.20 MPa, a heat-seal time of 1s, and a heat-seal strength of 7.6N / 15mm.

[0044] Example 6

[0045] Heat-seal layer raw material synthesis: The process was the same as that of Example 1, and the mole ratio of nylon 66 salt and nylon 610 salt was 5:5. The inherent viscosity of the obtained raw material was 2.2 dL / g, and the degree of randomness was 1.01.

[0046] Heat-seal film preparation and heat-seal performance: the process was the same as Example 1, and the extrusion temperature of the heat-seal layer was 200°C. The heat-seal layer thickness of the heat-seal film was 3 μm, and the total thickness was 25 μm. The heat-seal film had a seal initiation temperature of 210°C, a heat-seal pressure of 0.20 MPa, a heat-seal time of 1 s, and a heat-seal strength of 8.1 N / 15 mm.

[0047] Comparative Example 1

[0048] Heat-seal film preparation and heat-seal performance: the process was the same as Example 1, and the extrusion temperature of the heat-seal layer was 225°C. The heat-seal layer thickness of the heat-seal film was 3 μm, and the total thickness was 25 μm. The heat-seal film had a seal initiation temperature of 225°C, a heat-seal pressure of 0.20 MPa, a heat-seal time of 1.5 s, and a heat-seal strength of 7.7 N / 15 mm.

[0049] Comparative Example 2

[0050] Heat-seal film preparation and heat-seal performance: the process was the same as Example 1, and the extrusion temperature of the heat-seal layer was 225°C. The heat-seal layer thickness of the heat-seal film was 3 μm, and the total thickness was 25 μm. The heat-seal film had a seal initiation temperature of 260°C, a heat-seal pressure of 0.20 MPa, a heat-seal time of 1.5 s, and a heat-seal strength of 7.8 N / 15 mm.

[0051] Table 1 Monomer, component ratio, and intrinsic viscosity of heat-seal layer materials

[0052]

[0053] Table 2 Melting point and crystallization temperature of different component ratios of nylon 66 / 610

[0054] Serial number Heat-seal layer material Melting point Crystallization temperature Example 1 PA 66 / 610-0.3 195.8 163.4 Example 5 PA 66 / 610-0.4 196.8 159.0 Example 6 PA 66 / 610-0.5 208.3 174.1

[0055] Table 3 Heat-seal process and performance of different heat-seal layer materials

[0056]

[0057]

[0058] Compared with the nylon 6 and nylon 66 homopolymer heat-seal layers in the comparative examples, the heat-seal layer in the embodiment of the present application uses a binary random copolymer nylon that can be heteromorphic homodimer. Taking nylon 6 / 10 and nylon 6 / 12 copolymers as examples, the seal initiation temperature is 135°C and 115°C, respectively, which is much lower than 225°C of nylon 6 and 260°C of nylon 66, the heat-seal efficiency is significantly improved, and the heat-seal energy consumption is greatly reduced, which can be used in the field of rapid low-temperature heat-seal packaging. Taking nylon 66 / 610 and nylon 66 / 612 copolymers as examples, the seal initiation temperature is near 200°C, which is lower than the seal initiation temperature 225°C of nylon 6 and much lower than the seal initiation temperature 260°C of nylon 66, the heat-seal time is reduced, and the heat-seal strength is basically the same as that of nylon 6 and nylon 66, that is, the heat-seal energy consumption is reduced and the heat-seal efficiency is improved without affecting the heat-seal strength. Specifically to the nylon 66 / 610 random copolymer, from Figure 2 It can be seen from the differential scanning calorimetry (DSC) curves that by changing the copolymer component ratio, the melting point of the random copolymer nylon can be adjusted, and the melting point is obviously lower than that of a single component nylon. Therefore, by preparing a nylon containing heteromorphic homodimer through random copolymerization and applying it to the heat-seal layer, the heat-seal temperature can be significantly reduced. When the 66 unit ratio is 0.5, compared with the nylon 6 and nylon 66 heat-seal layer, the seal initiation temperature is reduced, the heat-seal time is shortened, and the heat-seal strength is improved, that is, all three performances are improved. From Figure 3 It can be seen from the wide-angle X-ray scattering (WAXS) spectrum that both the single component nylon and the heteromorphic homodimer random copolymer nylon have sharp scattering peaks of α crystal type, indicating that the crystallinity is high, so that high heat-seal strength can be achieved after heat-sealing.

[0059] In summary, since near the pseudo-eutectic point, the melting temperature and crystallization temperature of the copolymer are lower than those of the corresponding single component homopolymer, and as the component ratio of the random copolymer nylon changes, the crystallization temperature and melting point change, therefore, by changing the component ratio of the random copolymer nylon that can be heteromorphic homodimer, the present application realizes the regulation of the thermodynamic properties such as the melting point and crystallization temperature of the random copolymer nylon, and further regulates the heat-seal performance when it is used as a heat-seal layer. Since the melting point of the random copolymer nylon that can be heteromorphic homodimer is lower than that of the corresponding single component homopolymer, the seal initiation temperature can be reduced, and the heat-seal energy consumption can be reduced. Due to the low melting point and fast crystallization rate, the heat-seal time is shortened, and the heat-seal efficiency is improved. Since the random copolymer nylon that can be heteromorphic homodimer is easy to melt and recrystallize and has high crystallinity, the heat-seal strength is high. Therefore, the nylon film with a heteromorphic homodimer heat-seal layer proposed in the present application has high heat-seal strength, low heat-seal temperature, and high heat-seal efficiency.

[0060] Those skilled in the art can understand that the above description is only the preferred examples of the present application and is not used to limit the present application, and although the present application is described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacements for part of the technical features. Any modification, equivalent replacement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A nylon film with high heat-sealing strength and low heat-sealing temperature containing a heterogeneous dicrystalline heat-sealing layer, characterized in that, It includes a heat-sealing layer, a core layer, and a surface layer arranged sequentially; The surface layer is made of 98-99.5 parts by weight of nylon 6 and 0.5-2 parts by weight of anti-adhesion agent, or of 98-99.5 parts by weight of nylon 66 and 0.5-2 parts by weight of anti-adhesion agent; The core layer is made of nylon 6 or nylon 66; The heat-sealing layer is made of heterogeneous dimorphic random copolymer nylon, which is selected from any one of nylon 6 / 10 copolymer, nylon 6 / 12 copolymer, nylon 66 / 610 copolymer, and nylon 66 / 612 copolymer. The random copolymer nylon that can be heterodimorphically dimorphic has a randomness degree between 0.91 and 1.12 and an intrinsic viscosity between 1.8 and 2.5 dL / g. When the heat-sealing layer is made of nylon 6 / 10 copolymer, the heat-sealing temperature is 135-155 ℃; when the heat-sealing layer is made of nylon 6 / 12 copolymer, the heat-sealing temperature is 115-135 ℃; when the heat-sealing layer is made of nylon 66 / 610 copolymer, the heat-sealing temperature is 200-230 ℃; and when the heat-sealing layer is made of nylon 66 / 612 copolymer, the heat-sealing temperature is 190-220 ℃.

2. The nylon film with high heat-sealing strength and low heat-sealing temperature containing a heterogeneous dichroic heat-sealing layer according to claim 1, characterized in that, The thickness of the heat-sealing layer is 2-5 μm, and the total thickness of the nylon film is 20-30 μm.

3. The nylon film with high heat-sealing strength and low heat-sealing temperature containing a heterogeneous dicrystalline heat-sealing layer according to claim 1, characterized in that, The anti-sticking agent is selected from any one or two of silica and oleamide, mixed in any ratio.

4. A method for preparing a nylon film with high heat-sealing strength and low heat-sealing temperature containing a heterogeneous dicrystalline heat-sealing layer as described in claim 1, characterized in that, The method includes the following steps: S1: For nylon 6 / 10 copolymer and nylon 6 / 12 copolymer: ε-caprolactam, 10-aminodecanoic acid and molecular weight regulator, or ε-caprolactam, 12-aminododecanoic acid and molecular weight regulator, are heated at 190-210 ℃ for 1.5-2 h in a nitrogen atmosphere, then heated to 235-245 ℃, vacuumed and subjected to polycondensation reaction, granulated after water cooling, and dried to obtain heat-sealing layer raw material; For nylon 66 / 610 copolymer and nylon 66 / 612 copolymer: 1,6-hexanediamine and 1,6-adipic acid, or 1,6-hexanediamine and 1,10-decanoic acid, or 1,6-hexanediamine and 1,12-dodecanoic acid are dissolved in ethanol, cooled and crystallized at room temperature, and centrifuged to obtain nylon 66 salt, nylon 610 salt, or nylon 612 salt; the nylon 66 salt and nylon 610 salt or 612 salt are dried respectively, the ethanol is removed, a molecular weight regulator is added, and the mixture is heated at 190-210 ℃ for 1.5-2 h in a nitrogen atmosphere, then heated to 270-280 ℃, vacuumed and subjected to polycondensation reaction, cooled with water, granulated, and dried to obtain heat-sealing layer raw material; S2: Mix 98-99.5 parts by weight of nylon 6 and 0.5-2 parts by weight of anti-sticking agent, or mix 98-99.5 parts by weight of nylon 66 and 0.5-2 parts by weight of anti-sticking agent, mix evenly in the molten state, and extrude the blend to granulate to obtain the surface raw material; S3: The surface layer material, core layer material and heat-sealing layer material are melt-extruded through a three-layer co-extrusion casting device, treated with a chilling roller and 50-60 ℃ hot water, and after the water is dried, they are simultaneously stretched, annealed and shaped and then wound up to obtain a nylon film with a low heat-sealing temperature.

5. The method for preparing a nylon film with high heat-sealing strength and low heat-sealing temperature containing a heterogeneous dicrystalline heat-sealing layer according to claim 4, characterized in that, During the co-extrusion casting process, when both the surface layer and the core layer are nylon 6, the extrusion temperature is 230 ℃; when both the surface layer and the core layer are nylon 66, the extrusion temperature is 270 ℃; and when the heat-sealing layer is a nylon 6 / 10 copolymer, a nylon 6 / 12 copolymer, a nylon 66 / 610 copolymer, or a nylon 66 / 612 copolymer, the extrusion temperatures are 140 ℃, 120 ℃, 200 ℃, and 190 ℃, respectively.

6. The method for preparing a nylon film with high heat-sealing strength and low heat-sealing temperature containing a heterogeneous dicrystalline heat-sealing layer according to claim 4, characterized in that, The molecular weight regulator used in step S1 is 1,6-adipic acid, which accounts for 1% of the total molar amount of the reaction raw materials.

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