High-heat-sealing-strength and low-heat-sealing-temperature nylon film containing heterogeneous homo-crystal heat sealing layer and preparation method of high-heat-sealing-strength and low-heat-sealing-temperature nylon film

Abstract

The invention discloses a nylon film with high heat-sealing strength and low heat-sealing temperature and containing a heterogeneous homo-crystal heat-sealing layer and a preparation method of the nylon film. The nylon film comprises the heat-sealing layer, a core layer and a surface layer which are arranged in sequence, the surface layer is prepared from 98 to 99.5 parts by weight of nylon 6 and 0.5 to 2 parts by weight of an anti-sticking agent, or is prepared from 98 to 99.5 parts by weight of nylon 66 and 0.5 to 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 heterogeneity homo-dicrystalline random copolymer nylon, and the heterogeneity homo-dicrystalline random copolymer nylon is selected from any one of a nylon 6 / 10 copolymer, a nylon 6 / 12 copolymer, a nylon 66 / 610 copolymer and a nylon 66 / 612 copolymer. According to the invention, the heterogeneity homodimorph random copolymer nylon is used as the heat-sealing layer, the heat-sealing strength is improved while the heat-sealing temperature of the nylon film is obviously reduced, the interlayer binding force of the nylon film is improved, and the obtained nylon film is simple in structure, high in mechanical strength and good in barrier property, and can be applied to the packaging field with high requirements on barrier property and mechanical property.

Description

Technical Field

[0001] The invention relates to the field of heat-sealing films in packaging technology, and in particular to a nylon film with high heat-sealing strength and low heat-sealing temperature containing a heterogeneous isomorphous heat-sealing layer and a preparation method thereof. Background Art

[0002] Heat-sealing films are widely used in the field of packaging, involving many industries such as food, medicine, logistics, and home appliances. Heat sealing is the main process for polymer film bag making and packaging, and the heat sealing performance determines the specific application of the polymer film. The most commonly used heat-sealing films in the prior art are cast or biaxially stretched polypropylene or polyethylene films. Since nylon film has the advantages of high temperature resistance, cold resistance, organic solvent resistance, puncture resistance, and high barrier, in order to improve the mechanical properties and barrier properties of the heat-sealing film, one or more layers of nylon film are often compounded in the heat-sealing film, but there is a problem of poor interface compatibility between polypropylene or polyethylene film and nylon film, and the bonding strength between layers is low. In addition, compared with polyolefin films, nylon films have a high melting point. Taking nylon 6 as an example, its melting point is about 220°C, which leads to high heat sealing temperature, increased heat sealing energy consumption, limited heat sealing speed, reduced heat sealing equipment service life, and poor heat sealing performance. Since the heat sealing process is a process of polymer melt recrystallization, the melting point can be reduced and the crystallinity can be increased by regulating the nylon crystal structure, thereby reducing the nylon heat sealing temperature and improving the heat sealing strength.

[0003] Random copolymerization is an effective means to regulate the crystal structure and heat sealing properties of nylon. For binary nylon random copolymers, the chemical structures of the copolymer units are relatively similar. The component with a high mass fraction is the main copolymer unit, and the component with a low mass fraction is the secondary copolymer unit. The secondary copolymer unit can be arranged in the crystal lattice of the main copolymer unit and co-crystallize with the main unit, showing a heterogeneous iso-dimorphic crystallization behavior. In random copolymers with heterogeneous iso-dimorphic behavior, the secondary copolymer units can be regarded as structural defects, resulting in changes in the thermodynamic properties of the copolymers, such as a decrease in crystallization temperature, melting temperature, melting enthalpy and crystallization enthalpy. When the concentrations of the two copolymer units are close, a pseudo-eutectic point appears. At this component ratio, the melting temperature and crystallization temperature of the copolymer are significantly lower than those of the corresponding single-component homopolymer. For ordinary copolymers, although the melting point can be lowered by copolymerization, it is difficult to crystallize and recrystallize, and the crystallinity is low and the crystallization rate is slow, resulting in low heat sealing strength and heat sealing efficiency. Summary of the invention

[0004] In view of the deficiencies of the prior art, the present invention proposes a nylon film with high heat-sealing strength and low heat-sealing temperature containing a heterogeneous isomorphic heat-sealing layer and a preparation method thereof. The heterogeneous isomorphic random copolymer nylon has the advantages of low and adjustable melting point, which can significantly reduce the sealing temperature of the nylon heat-sealing film. Due to its fast crystallization speed, easy melting and recrystallization, and high crystallinity, it can improve the heat-sealing strength and heat-sealing efficiency. By using the randomly blended nylon with heterogeneous isomorphic behavior as the heat-sealing layer, the prepared nylon heat-sealing film has low heat-sealing temperature, high heat-sealing strength and high heat-sealing efficiency compared to the heat-sealing film with nylon 6 or nylon 66 as the heat-sealing layer, and the compatibility between the layers is better than that of the heat-sealing film containing both the nylon layer and the polypropylene layer, the bonding strength is higher, and the mechanical properties and puncture resistance are better.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A nylon film with high heat-sealing strength and low heat-sealing temperature containing a heterogeneous isomorphous heat-sealing layer, comprising a heat-sealing layer, a core layer and a surface layer arranged in sequence;

[0007] 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 98-99.5 parts by weight of nylon 66 and 0.5-2 parts by weight of an anti-sticking agent;

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

[0009] The heat-sealing layer is made of a heterogeneous isomorphic random copolymer nylon, and the heterogeneous isomorphic random copolymer nylon 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 degree of the heterogeneous iso-dimorphic random copolymer nylon is between 0.91-1.12, and the intrinsic viscosity is between 1.8-2.5 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; 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 of silicon dioxide and oleic acid amide or a mixture of the two in any ratio.

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

[0015] S1: For nylon 6 / 10 copolymer and nylon 6 / 12 copolymer: ε-caprolactam, 10-aminodecanoic acid and a molecular weight regulator, or ε-caprolactam, 12-aminododecanoic acid and a molecular weight regulator, are heated at 190-210° C. for 1.5-2 h in a nitrogen atmosphere, then the temperature is raised to 235-245° C., vacuumed and polycondensed, granulated after water cooling, and dried to obtain a heat seal layer raw material;

[0016] For nylon 66 / 610 copolymer and nylon 66 / 612 copolymer: 1,6-hexanediamine and 1,6-hexanediamine, or 1,6-hexanediamine and 1,10-decanedioic acid, or 1,6-hexanediamine and 1,12-dodecanediamine are dissolved in ethanol, cooled and crystallized at room temperature, and centrifuged to obtain nylon 66 salt, nylon 610 salt, or nylon 612 salt; nylon 66 salt and nylon 610 salt or 612 salt are dried respectively, ethanol is removed, a molecular weight regulator is added, and the mixture is heated at 190-210° C. for 1.5-2 h in a nitrogen atmosphere, and then the temperature is raised to 270-280° C., vacuumized, and polycondensed, and granulated after water cooling, and dried to obtain a heat sealing layer raw material;

[0017] S2: mixing 98-99.5 parts by weight of nylon 6 and 0.5-2 parts by weight of an anti-sticking agent, or mixing 98-99.5 parts by weight of nylon 66 and 0.5-2 parts by weight of an anti-sticking agent, mixing them uniformly in a molten state, and extruding and granulating the blend 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, and are treated with a chilled roller and 50-60°C hot water, and the water is blown dry, and then synchronously stretched, annealed, fixed and rolled after stretching to obtain a nylon film with a low heat sealing temperature.

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

[0020] Furthermore, the molecular weight regulator used in step S1 is 1,6-adipic acid, which accounts for 1% of the total molar number of the reaction raw materials.

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

[0022] 1. The present invention uses a binary random copolymer nylon that can be heterogeneous and isomorphous as a heat-sealing layer, and can adjust the thermodynamic properties of nylon by changing the copolymer composition. 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 the sealing temperature of the nylon heat-sealing film can be significantly reduced.

[0023] 2. Compared with the disadvantages of common copolymers such as difficulty in crystallization and recrystallization, low crystallinity, and low heat-sealing strength, the heterogeneous iso-dimorphic random copolymer nylon used in the present invention has a fast crystallization speed, is easy to melt and recrystallize, and has a high degree of crystallinity. It can reduce the sealing temperature while improving the heat-sealing strength and heat-sealing efficiency.

[0024] 3. The surface layer, core layer and heat sealing layer of the heat sealing film of the present invention are all made of nylon material, which effectively avoids the problem of poor interface compatibility between nylon film and polyolefin film in traditional nylon-polyolefin composite heat sealing film, is beneficial to improve the interlayer bonding strength, and enhances the strength and puncture resistance of the heat sealing film. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of a nylon film with high heat-sealing strength and low heat-sealing temperature containing a heterogeneous isomorphous heat-sealing layer.

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

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

[0028] The present invention will be described in detail below based on the accompanying drawings and preferred embodiments, and the purpose and effects of the present invention will become more clear. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] Example 1

[0030] Synthesis of heat-sealing layer raw materials: 1,6-hexanediamine and 1,6-hexanediol were dissolved in ethanol at 80°C, cooled and crystallized at room temperature, and centrifuged to obtain nylon 66 salt; 1,6-hexanediamine and 1,10-decanedioic acid were dissolved in ethanol at 80°C, cooled and crystallized at room temperature, and centrifuged to obtain nylon 610 salt. Nylon 66 salt and nylon 610 salt were dried at 50°C for 48 hours and added to the reactor in a molar ratio of 3:7, and 1,6-hexanediol was added at a molar fraction of 1% of the total raw material. Heat at 190°C for 2 hours in a nitrogen atmosphere, then heat to 270°C, vacuum and perform polycondensation reaction for 2 hours, discharge from the bottom of the reactor, the discharge pressure is 0.5MPa, granulate after cooling, treat the granules in hot water for 24 hours, and dry to obtain the heat-sealing layer raw materials. The intrinsic viscosity of the obtained raw materials is 2.3dL / g, and the randomness is 0.91.

[0031] Preparation of heat-sealing film and heat-sealing performance: 99 parts of nylon 6, 0.5 parts of silica and 0.5 parts of oleic acid amide are added to an internal mixer at a temperature of 220°C, a rotation speed of 50 rpm, and a time of 5 minutes. The blend is extruded and granulated to obtain the surface layer raw material. The core layer raw material is nylon 6. 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, wherein the extrusion temperature of the surface layer and the core layer is 230°C, and the extrusion temperature of the heat-sealing layer is 200°C. After being treated with a 20°C chilled roller, 55°C hot water and dried with cold air, it is synchronously stretched in a stretching furnace, with the longitudinal and transverse stretching ratios being 3. After stretching, annealing, shaping and winding are performed to obtain a nylon film with a low heat-sealing temperature. The structure of the nylon film is as follows Figure 1 As shown. The heat sealing layer thickness of the heat sealing film is 3μm, and the total thickness is 25μm. The heat sealing temperature of the heat sealing film is 200℃, the heat sealing pressure is 0.20MPa, the heat sealing time is 1s, and the heat sealing strength is 7.9N / 15mm.

[0032] Example 2

[0033] Synthesis of heat-sealing layer raw materials: 1,6-hexanediamine and 1,6-hexanediol are dissolved in ethanol at 80°C, cooled and crystallized at room temperature, and centrifuged to obtain nylon 66 salt; 1,6-hexanediamine and 1,12-dodecanediol are dissolved in ethanol at 80°C, cooled and crystallized at room temperature, and centrifuged to obtain nylon 612 salt. Nylon 66 salt and nylon 612 salt are dried at 50°C for 48 hours and added to the reactor in a molar ratio of 5:5, and 1,6-hexanediol is added at a molar fraction of 1% of the total raw material. Heat at 210°C for 1.5 hours in a nitrogen atmosphere, then heat to 280°C, vacuum and perform polycondensation reaction for 2 hours, discharge from the bottom of the reactor, the discharge pressure is 0.5MPa, granulate after cooling, treat the granules in hot water for 24 hours, and obtain the heat-sealing layer raw materials after drying. The intrinsic viscosity of the obtained raw materials is 2.3dL / g, and the randomness is 1.04.

[0034] Preparation and heat sealing performance of heat-sealing film: 99 parts of nylon 66 and 1 part of silica were added to an internal mixer at a temperature of 220°C, a rotation speed of 50 rpm, and a time of 5 minutes. The blend was extruded and granulated to obtain the surface layer raw material. The core layer raw material is nylon 66. The surface layer raw material, the core layer raw material and the heat sealing layer raw 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 sealing layer was 190°C. After being treated with a 20°C chilled roller, 55°C hot water and dried with cold air, it was synchronously stretched in a stretching furnace, with both the longitudinal and transverse stretching ratios of 3. After stretching, annealing, shaping and winding were performed to obtain a nylon film with a low heat sealing temperature. The heat sealing layer thickness of the heat sealing film is 5μm, and the total thickness is 30μm. The sealing temperature of the heat-sealing film is 190°C, the heat-sealing pressure is 0.20MPa, the heat-sealing time is 1s, and the heat-sealing strength is 7.5N / 15mm.

[0035] Example 3

[0036] Synthesis of heat-sealing layer raw materials: ε-caprolactam, 10-aminodecanoic acid and 1,6-hexanodioic acid (1% by mole fraction) were heated at 200°C for 2h in a nitrogen atmosphere, then heated to 235°C, vacuumed and subjected to polycondensation reaction for 2h, and discharged from the bottom of the reactor at a discharge pressure of 0.4MPa. After cooling, the pellets were granulated, and the pellets were treated in hot water for 24h and dried to obtain the heat-sealing layer raw materials. The molar ratio of ε-caprolactam to 10-aminodecanoic acid was 5:5, and the intrinsic viscosity of the obtained raw material was 2.0dL / g, and the randomness was 0.99.

[0037] Preparation and heat sealing performance of heat-sealing film: 98 parts of nylon 6 and 2 parts of silica were added to an internal mixer at a temperature of 220°C, a rotation speed of 50 rpm, and a time of 5 minutes. The blend was extruded and granulated to obtain the surface layer raw material. The core layer raw material is nylon 6. The surface layer raw material, the core layer raw material and the heat sealing layer raw 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 sealing layer was 140°C. After being treated with a 20°C chilled roller, 50°C hot water and cold air drying, it was synchronously stretched in a stretching furnace, and the longitudinal and transverse stretching ratios were both 3. After stretching, annealing, shaping and winding were performed to obtain a nylon film with a low heat sealing temperature. The heat sealing layer thickness of the heat sealing film is 3μm, and the total thickness is 25μm. The sealing temperature of the heat-sealing film is 135°C, the heat-sealing pressure is 0.20MPa, the heat-sealing time is 0.8s, and the heat-sealing strength is 6.8N / 15mm.

[0038] Example 4

[0039] Synthesis of heat-sealing layer raw materials: ε-caprolactam, 12-aminododecanoic acid and 1,6-hexanediol acid (1% by mole fraction) were heated at 200°C for 2h in a nitrogen atmosphere, then heated to 245°C, vacuumed and subjected to polycondensation reaction for 2h, discharged from the bottom of the reactor, with a discharge pressure of 0.4MPa, granulated after cooling, treated in hot water for 24h, and dried to obtain heat-sealing layer raw materials. The molar ratio of ε-caprolactam to 12-aminododecanoic acid was 4:6, and the intrinsic viscosity of the obtained raw material was 1.8dL / g, and the randomness was 1.03.

[0040] Preparation and heat sealing performance of heat-sealing film: 99.5 parts of nylon 6 and 0.5 parts of oleic acid amide were added to an internal mixer at a temperature of 220°C, a rotation speed of 50 rpm, and a time of 5 minutes. The blend was extruded and granulated to obtain the surface layer raw material. The core layer raw material is nylon 6. The surface layer raw material, the core layer raw material and the heat sealing layer raw 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 sealing layer was 120°C. After being treated with a 20°C chilled roller, 60°C hot water and dried with cold air, it was synchronously stretched in a stretching furnace, and the longitudinal and transverse stretching ratios were both 3. After stretching, annealing, shaping and winding were performed to obtain a nylon film with a low heat sealing temperature. The heat sealing layer thickness of the heat sealing film is 2μm, and the total thickness is 20μm. The sealing temperature of the heat-sealing film is 115°C, the heat-sealing pressure is 0.20MPa, the heat-sealing time is 0.8s, and the heat-sealing strength is 5.8N / 15mm.

[0041] Example 5

[0042] Synthesis of heat seal layer raw material: The process is the same as in Example 1, and the molar ratio of nylon 66 salt to nylon 610 salt is 4:6. The intrinsic viscosity of the obtained raw material is 2.5 dL / g, and the randomness is 1.12.

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

[0044] Example 6

[0045] Synthesis of heat seal layer raw material: The process is the same as in Example 1, and the molar ratio of nylon 66 salt to nylon 610 salt is 5:5. The intrinsic viscosity of the obtained raw material is 2.2 dL / g, and the randomness is 1.01.

[0046] Preparation of heat-sealing film and heat-sealing performance: The process is the same as that of Example 1, and the extrusion temperature of the heat-sealing layer is 200°C. The heat-sealing layer thickness of the heat-sealing film is 3 μm, and the total thickness is 25 μm. The sealing temperature of the heat-sealing film is 210°C, the heat-sealing pressure is 0.20 MPa, the heat-sealing time is 1 s, and the heat-sealing strength is 8.1 N / 15 mm.

[0047] Comparative Example 1

[0048] Preparation of heat-sealing film and heat-sealing performance: The process is the same as that of Example 1, the raw material of the heat-sealing layer is nylon 6, and the extrusion temperature of the heat-sealing layer is 225°C. The heat-sealing layer thickness of the heat-sealing film is 3 μm, and the total thickness is 25 μm. The sealing temperature of the heat-sealing film is 225°C, the heat-sealing pressure is 0.20 MPa, the heat-sealing time is 1.5 s, and the heat-sealing strength is 7.7 N / 15 mm.

[0049] Comparative Example 2

[0050] Preparation of heat-sealing film and heat-sealing performance: The process is the same as that of Example 1, the raw material of the heat-sealing layer is nylon 6, and the extrusion temperature of the heat-sealing layer is 225°C. The heat-sealing layer thickness of the heat-sealing film is 3 μm, and the total thickness is 25 μm. The sealing temperature of the heat-sealing film is 260°C, the heat-sealing pressure is 0.20 MPa, the heat-sealing time is 1.5 s, and the heat-sealing strength is 7.8 N / 15 mm.

[0051] Table 1 Monomers, component ratios and intrinsic viscosities of heat seal layer materials

[0052]

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

[0054] Serial number Heat seal material Melting point Crystallization temperature Example 1 PA66 / 610-0.3 195.8 163.4 Example 5 PA66 / 610-0.4 196.8 159.0 Example 6 PA66 / 610-0.5 208.3 174.1

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

[0056]

[0057]

[0058] Compared with the nylon 6 and nylon 66 homopolymer heat-sealing layers in the comparative examples, the heat-sealing layers in the embodiments of the present invention use binary random copolymer nylons that can be heterogeneous and isomorphous. Taking nylon 6 / 10 and nylon 6 / 12 copolymers as examples, the sealing temperatures are 135°C and 115°C, respectively, which are much lower than 225°C of nylon 6 and 260°C of nylon 66. The heat-sealing efficiency is significantly improved, and the heat-sealing energy consumption is greatly reduced, so they can be used in the field of fast low-temperature heat-sealing packaging. Taking nylon 66 / 610 and nylon 66 / 612 copolymers as examples, the sealing temperature is around 200°C, which is lower than the sealing temperature of 225°C of nylon 6 and much lower than the sealing temperature of 260°C of nylon 66. The heat-sealing time is reduced, and the heat-sealing strength is basically the same as that of nylon 6 and nylon 66, that is, the heat-sealing energy consumption is reduced and the heat-sealing efficiency is improved without affecting the heat-sealing strength. Specifically for nylon 66 / 610 random copolymers, from Figure 2 From the differential scanning calorimetry (DSC) curve, it can be seen that the melting point of random copolymer nylon can be adjusted by changing the proportion of copolymer components, and the melting point is significantly lower than that of single-component nylon. Therefore, the preparation of heterogeneous isomeric nylon by random copolymerization and its application in the heat sealing layer can significantly reduce the heat sealing temperature. When the 66 unit ratio is 0.5, compared with the nylon 6 and nylon 66 heat sealing layers, the sealing temperature is lowered, the heat sealing time is shortened, and the heat sealing strength is increased, that is, all three aspects of performance are improved. Figure 3 It can be seen from the wide-angle X-ray scattering (WAXS) spectrum that both single-component nylon and heterogeneous iso-dimorphic random copolymer nylon have sharp scattering peaks of the α crystal form, indicating that they have high crystallinity and can therefore achieve high heat sealing strength after heat sealing.

[0059] In summary, since the melting temperature and crystallization temperature of the copolymer are lower than the corresponding single-component homopolymer near the pseudo-eutectic point, and as the component ratio of the random copolymer nylon changes, its crystallization temperature and melting point both change, the present invention achieves the regulation of thermodynamic properties such as the melting point and crystallization temperature of the random copolymer nylon by changing the component ratio of the random copolymer nylon that can be heterogeneous iso-dimorphic, and then regulates its heat sealing performance when used as a heat sealing layer. Since the melting point of the binary random copolymer nylon that can be heterogeneous iso-dimorphic is lower than that of the corresponding single-component homopolymer, it is possible to reduce the sealing temperature and reduce the heat sealing energy consumption. Due to the lower melting point and fast crystallization rate, the heat sealing time is shortened and the heat sealing efficiency is improved. Since the random copolymer nylon that can be heterogeneous iso-dimorphic is easy to melt and recrystallize and has a high degree of crystallinity, the heat sealing strength is high. Therefore, the nylon film containing a heterogeneous iso-dimorphic heat sealing layer proposed in the present invention has high heat sealing strength, low heat sealing temperature and high heat sealing efficiency.

[0060] Those skilled in the art can understand that the above are only preferred examples of the invention and are not intended to limit the invention. Although the invention is described in detail with reference to the above examples, those skilled in the art can still modify the technical solutions recorded in the above examples or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, etc. made within the spirit and principle of the invention shall be included in the protection scope of the invention.

Claims

1. A nylon film with high heat-sealing strength and low heat-sealing temperature containing a heterogeneous isomorphous heat-sealing layer, characterized in that: It includes 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 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 heterogeneous isomorphic random copolymer nylon, and the heterogeneous isomorphic random copolymer nylon is selected from any one of nylon 6 / 10 copolymer, nylon 6 / 12 copolymer, nylon 66 / 610 copolymer, and nylon 66 / 612 copolymer.

2. The nylon film with high heat-sealing strength and low heat-sealing temperature containing a heterogeneous isomorphous 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 isomorphous heat-sealing layer according to claim 1, characterized in that: The random degree of the heterogeneous iso-dimorphic random copolymer nylon is between 0.91 and 1.12, and the intrinsic viscosity is between 1.8 and 2.5 dL / g.

4. The nylon film with high heat-sealing strength and low heat-sealing temperature containing a heterogeneous isomorphous heat-sealing layer according to claim 1, characterized in that: 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; when the heat-sealing layer is made of nylon 66 / 612 copolymer, the heat-sealing temperature is 190-220°C.

5. The nylon film with high heat-sealing strength and low heat-sealing temperature containing a heterogeneous isomorphous heat-sealing layer according to claim 1, characterized in that: The anti-sticking agent is selected from any one of silicon dioxide and oleic acid amide or a mixture of the two in any ratio.

6. A method for preparing a nylon film with high heat-sealing strength and low heat-sealing temperature containing a heterogeneous isomorphous heat-sealing layer, characterized in that: The method comprises the following steps: S1: For nylon 6 / 10 copolymer and nylon 6 / 12 copolymer: ε-caprolactam, 10-aminodecanoic acid and a molecular weight regulator, or ε-caprolactam, 12-aminododecanoic acid and a molecular weight regulator, are heated at 190-210° C. for 1.5-2 h in a nitrogen atmosphere, then the temperature is raised to 235-245° C., vacuumed and polycondensed, granulated after water cooling, and dried to obtain a heat seal layer raw material; For nylon 66 / 610 copolymer and nylon 66 / 612 copolymer: 1,6-hexanediamine and 1,6-hexanediamine, or 1,6-hexanediamine and 1,10-decanedioic acid, or 1,6-hexanediamine and 1,12-dodecanediamine are dissolved in ethanol, cooled and crystallized at room temperature, and centrifuged to obtain nylon 66 salt, nylon 610 salt, or nylon 612 salt; nylon 66 salt and nylon 610 salt or 612 salt are dried respectively, ethanol is removed, a molecular weight regulator is added, and the mixture is heated at 190-210° C. for 1.5-2 h in a nitrogen atmosphere, and then the temperature is raised to 270-280° C., vacuumized, and polycondensed, and granulated after water cooling, and dried to obtain a heat sealing layer raw material; S2: mixing 98-99.5 parts by weight of nylon 6 and 0.5-2 parts by weight of an anti-sticking agent, or mixing 98-99.5 parts by weight of nylon 66 and 0.5-2 parts by weight of an anti-sticking agent, mixing them uniformly in a molten state, and extruding and granulating the blend to obtain a surface layer raw material; 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, and are treated with a chilled roller and 50-60°C hot water, and the water is blown dry, and then synchronously stretched, annealed, fixed and rolled after stretching to obtain a nylon film with a low heat sealing temperature.

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

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

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