Wear-resistant anti-fog BOPLA heat-shrinkable film for high-speed packaging as well as preparation method and application thereof

Abstract

The invention relates to a wear-resistant and anti-fog BOPLA heat-shrinkable film for high-speed packaging as well as a preparation method and application thereof. The BOPLA heat-shrinkable film comprises the following components: high-molecular-weight polylactic resin, low-molecular-weight polylactic resin and layered double hydroxide microcapsules, the mass ratio of the high-molecular-weight polylactic resin to the low-molecular-weight polylactic resin is (1-15): 1, and the dosage of the layered double hydroxide microcapsules accounts for 1.5-5% of the total dosage of the polylactic resin. The preparation method of the BOPLA heat-shrinkable film comprises the following steps: uniformly mixing the components according to the content, melting, casting, and preparing the BOPLA heat-shrinkable film by a two-way stretching method. The obtained BOPLA film is low in friction coefficient, good in heat sealability, high in heat shrinkage rate and excellent in mechanical property, and can be used for high-speed packaging.

Description

Technical Field

[0001] The invention relates to the technical field of polylactic acid films, and in particular to a wear-resistant and anti-fog BOPLA heat shrinkable film for high-speed packaging, and a preparation method and application thereof. Background Art

[0002] With the increasing prominence of environmental resource issues such as large-scale oil extraction and the inability to handle plastic waste, as well as people's pursuit of quality of life and health, the market's requirements for the safety and environmental protection of plastics are also increasing; bio-based and degradable materials have attracted the attention of researchers from all walks of life. Polylactic acid (PLA), as a semi-crystalline linear aliphatic polyester, is a synthetic polymer material with excellent biocompatibility and biodegradability. As the leader among many bio-based polymer materials, it is considered to be the most promising green and pollution-free polymer material. Unlike traditional plastics that come from petroleum, PLA comes from renewable plant resources such as corn, sugarcane and cassava, and has the basic characteristics of general polymer materials; PLA has good mechanical processing properties and can be processed in a variety of ways, such as extrusion, injection molding, blow molding, stretching, spinning and other molding processes. In particular, the BOPLA film prepared by biaxial stretching molding technology has excellent mechanical properties, optical transparency, water vapor barrier properties and other characteristics, which can be widely used in packaging, agriculture, engineering, textiles, automobiles, biomedicine and tissue engineering, and has broad market prospects and significant economic benefits. In recent years, with the increasingly wide application of biodegradable BOPLA film, the development and application research of its molding technology has attracted more and more attention from many teams at home and abroad.

[0003] At present, most PLA film forming technologies use blow molding, but there are problems such as uneven film thickness, low transparency and low tensile strength. Biaxial stretching is a directional polymer film forming and processing technology. The change in its microstructure causes a dramatic change in the mechanical properties of the polymer film, and gives it high gloss, high transparency, high barrier properties and other characteristics. Due to its special forming and processing technology, BOPLA stretches PLA in both the transverse (TD) and longitudinal (MD) directions during the film forming process. The controllable stretching plastic, stretch ratio, temperature and stretching mode (synchronous or asynchronous) and other biaxial stretching process parameters promote the (crystallization) orientation of the PLA molecular chain, which greatly improves the film's tensile strength, transparency, heat resistance and stability and other properties.

[0004] However, with the continuous advancement of science and technology, high efficiency and energy saving have become the focus of people's increasing attention. When PLA is used in the high-speed packaging industry, it must meet the following performance requirements: 1. Smooth running, that is, low friction coefficient, good wear resistance and anti-scratch performance; 2. High heat sealing strength, low sealing temperature or wide heat sealing temperature range; 3. Good heat shrinkage; 4. Good stiffness and excellent folding stability. However, PLA has a high glass transition temperature, is brittle at room temperature, and has poor thermal stability, which makes it difficult to meet the requirements of high-speed packaging films. Summary of the invention

[0005] Based on the above-mentioned problems existing in the prior art, the present invention provides a wear-resistant and anti-fog BOPLA heat-shrinkable film for high-speed packaging, and a preparation method and application thereof.

[0006] A technical solution adopted by the present invention to solve its technical problem is: a wear-resistant and anti-fog BOPLA heat-shrinkable film for high-speed packaging, comprising the following components: a high molecular weight polylactic acid resin, a low molecular weight polylactic acid resin, and layered double hydroxide microcapsules, wherein the mass ratio of the high molecular weight polylactic acid resin to the low molecular weight polylactic acid resin is (1-15): 1, and the amount of the layered double hydroxide microcapsules is 1.5-5% of the total amount of the polylactic acid resin.

[0007] In some embodiments of the present invention, the high molecular weight polylactic acid resin has a weight average molecular weight of 200,000-230,000, a molecular weight dispersion of 1-2, a density of 1.30-1.35 g / cc, and a peak melting temperature of 175-180°C.

[0008] In some embodiments of the present invention, the low molecular weight polylactic acid resin has a weight average molecular weight of 10,000-30,000, a molecular weight dispersion of 2-3, a density of 1.30-1.35 g / cc, and a peak melting temperature of 165-170°C.

[0009] In some embodiments of the present invention, the preparation method of the layered double hydroxide microcapsules comprises the following steps: dissolving fumaric acid and urea in deionized water, denoted as liquid A, and sequentially adding at least two of ferric nitrate nonahydrate, zinc nitrate hexahydrate and aluminum nitrate nonahydrate to liquid A; stirring the obtained mixed solution at room temperature for 30-45 minutes, transferring it into a polytetrafluoroethylene reactor, and reacting it at 100-120°C for 10-12 hours; after the reaction is completed, cooling it to room temperature, centrifuging it at a speed of 3000-4000rpm to obtain a precipitate, washing and drying the obtained precipitate to obtain the layered double hydroxide microcapsules.

[0010] Furthermore, the mixing molar ratio of fumaric acid to urea is 1-1.5:8.

[0011] Furthermore, the total molar amount of at least two of the ferric nitrate nonahydrate, zinc nitrate hexahydrate and nitric acid nonahydrate is 3.25 mmol.

[0012] The method for preparing the BOPLA heat shrinkable film comprises the following steps: uniformly mixing high molecular weight polylactic acid resin, low molecular weight polylactic acid resin and layered double hydroxide microcapsules according to the above contents, melt extruding, casting and preparing the film by biaxial stretching.

[0013] Furthermore, the melt extrusion temperature is 230-250°C, the melt plasticization temperature of the cast sheet is 210-220°C, and the discharge end temperature is 210-220°C.

[0014] Furthermore, the biaxial stretching method adopts step-by-step stretching, first longitudinal stretching and then transverse stretching; the longitudinal stretching temperature is 50-70°C, and the stretching ratio is 2.2-3.5 times; the transverse stretching temperature is 80-100°C, and the stretching ratio is 3.5-4.5 times.

[0015] The above-mentioned wear-resistant and anti-fog BOPLA heat shrinkable film for high-speed packaging is used in the high-speed packaging industry.

[0016] Beneficial effects: Compared with the prior art, the present invention uses low molecular weight polylactic acid and high molecular weight polylactic acid in combination, and adds layered double hydroxide microcapsules: The low molecular weight polylactic acid motion unit requires lower energy for activation and smaller space for movement. Its addition reduces the peeling transition temperature of the mixed resin. The addition of low molecular weight polylactic acid reduces the average molecular weight of polylactic acid and broadens its molecular weight distribution, which reduces the interaction between high molecular weight polylactic acid chains and reduces the crystallinity of the mixed resin, which ultimately improves the brittleness of the film and improves its flexibility. A certain amount of layered double hydroxide microcapsules are mixed with polylactic acid to reduce the surface energy of the BOPLA heat shrinkable film, increase the contact angle of the film surface to the surface, and make water droplets slide off to achieve an anti-fog effect. It also plays an anti-adhesion particle role and reduces the friction coefficient. It also fills the tiny holes on the surface of the final film caused by the difference in the size of the intermolecular forces between high and low molecular weight polylactic acid resins, reduces the surface roughness of the film, and improves the surface properties of the film.

[0017] The BOPLA film prepared by adopting the technical solution of the present invention has a low friction coefficient, good heat sealing performance and high heat shrinkage rate, and meets the requirements of heat shrinkable films for high-speed packaging. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0019] The following is an exemplary description of the preparation process of the layered double hydroxide microcapsules used in the examples: Layered double hydroxide microcapsules-1: 0.01 mol of fumaric acid and 0.08 mol of urea were dissolved in 200 ml of deionized water, which was recorded as liquid A. 2 mmol of ferric nitrate nonahydrate and 1.25 mmol of zinc nitrate hexahydrate were added to liquid A in sequence. The obtained mixed solution was stirred at room temperature for 30 minutes, and then transferred into a polytetrafluoroethylene reactor to react at 100° C. for 12 hours. After the reaction was completed, it was cooled to room temperature, centrifuged at a speed of 3000 rpm to obtain a precipitate, and the obtained precipitate was washed and dried to obtain the layered double hydroxide microcapsule-1.

[0020] Layered Double Hydroxide Microcapsules-2: 0.012 mol of fumaric acid and 0.08 mol of urea were dissolved in 200 ml of deionized water, which was recorded as liquid A. 2 mmol of zinc nitrate hexahydrate and 1.25 mmol of aluminum nitrate nonahydrate were added to liquid A in sequence. The obtained mixed solution was stirred at room temperature for 35 minutes, and then transferred into a polytetrafluoroethylene reactor to react at 110° C. for 11 hours. After the reaction was completed, it was cooled to room temperature, centrifuged at a speed of 3500 rpm to obtain a precipitate, and the obtained precipitate was washed and dried to obtain the layered double hydroxide microcapsule-2.

[0021] Layered Double Hydroxide Microcapsules-3: 0.015 mol of fumaric acid and 0.08 mol of urea were dissolved in 200 ml of deionized water, which was recorded as liquid A. 1 mmol of ferric nitrate nonahydrate and 2.25 mmol of aluminum nitrate nonahydrate were added to liquid A in sequence. The obtained mixed solution was stirred at room temperature for 40 minutes, and then transferred into a polytetrafluoroethylene reactor to react at 120° C. for 10 hours. After the reaction was completed, it was cooled to room temperature, centrifuged at a speed of 4000 rpm to obtain a precipitate, and the obtained precipitate was washed and dried to obtain the layered double hydroxide microcapsule-3.

[0022] Example 1 Prepare materials: by mass ratio, the ratio of high molecular weight polylactic acid resin to low molecular weight polylactic acid resin is 1:1, and the layered double hydroxide microcapsule-1 is 1.5% of the total amount of polylactic acid resin; Raw material pretreatment: polylactic acid resin and layered double hydroxide microcapsule-1 are uniformly stirred in a mixer, and then extruded into granules in a twin-screw extruder, wherein the extruder temperature is 230°C; the obtained mixture is placed in a vacuum drum drying system for drying and dehydration, the drying temperature is 120°C, and the drying time is 4h; Cast film: The masterbatch obtained by pretreatment is melt-blended and extruded through a twin-screw extruder, and is conveyed to a cold roller with an electrostatic charge at a surface temperature of 30-40°C for close cooling and solidification to obtain an unstretched polylactic acid cast film; wherein the feeding speed is 40r / min, the screw speed is 200r / min, the metering pump speed is 38r / min, the melt plasticization temperature is 210°C, and the die head temperature is 210°C; Stretching film: The unstretched polylactic acid cast film is biaxially stretched, and the stretching method adopts the biaxial stretching method of longitudinal stretching in the length direction and then transverse stretching in the width direction, which is as follows: a. Longitudinal stretching: The cast film is fed into the longitudinal stretching roller and stretched in the longitudinal direction of the film, the stretching ratio is 2.2 times, the stretching temperature is 50°C, and then cooled with a cooling roller group at 25°C; b. Transverse stretching: The thick film that has been longitudinally stretched is fed into a transverse stretching machine for transverse stretching, the preheating temperature is 75°C, the preheating time is 15s; the stretching temperature is 80°C, and the stretching ratio is 3.5 times; then the stretched film is relaxed in the width direction and heat-set at the same time, the heat-setting temperature is 170°C, the time is 15s, the relaxation rate is 5%, and finally cooled to room temperature to obtain the BOPLA heat-shrinkable film for high-speed packaging.

[0023] Example 2 Prepare materials: by mass ratio, the ratio of high molecular weight polylactic acid resin to low molecular weight polylactic acid resin is 8:1, and layered double hydroxide microcapsule-2 is 3% of the total amount of polylactic acid resin; Raw material pretreatment: polylactic acid resin and layered double hydroxide microcapsule-2 are mixed evenly in a mixer, and then extruded into granules by a twin-screw extruder, wherein the extruder temperature is 240°C; the obtained mixture is placed in a vacuum drum drying system for drying and dehydration, the drying temperature is 120°C, and the drying time is 4h; Cast film: The masterbatch obtained by pretreatment is melt-blended and extruded through a twin-screw extruder, and is conveyed to a cold roller with an electrostatic charge at a surface temperature of 30-40°C for close cooling and solidification to obtain an unstretched polylactic acid cast film; wherein the feeding speed is 40r / min, the screw speed is 200r / min, the metering pump speed is 38r / min, the melt plasticization temperature is 215°C, and the die head temperature is 215°C; Stretching film: The unstretched polylactic acid cast film is biaxially stretched, and the stretching method adopts a biaxial stretching method of longitudinal stretching in the length direction and then transverse stretching in the width direction, which is specifically as follows: a. Longitudinal stretching: The cast film is fed into a longitudinal stretching roller and stretched in the longitudinal direction of the film, with a stretching ratio of 3.0 times and a stretching temperature of 60°C, and then cooled with a cooling roller group at 30°C; b. Transverse stretching: The thick film that has been longitudinally stretched is fed into a transverse stretching machine for transverse stretching, with a preheating temperature of 72°C and a preheating time of 15s; the stretching temperature is 90°C and the stretching ratio is 4.0 times; then the stretched film is relaxed in the width direction and heat-set at the same time, with a heat-setting temperature of 160°C, a time of 10s, and a relaxation rate of 4%, and finally cooled to room temperature to obtain a BOPLA heat-shrinkable film for high-speed packaging.

[0024] Example 3 Prepare materials: by mass ratio, the ratio of high molecular weight polylactic acid resin to low molecular weight polylactic acid resin is 15:1, and layered double hydroxide microcapsule-3 is 5% of the total amount of polylactic acid resin; Raw material pretreatment: polylactic acid resin and layered double hydroxide microcapsule-3 are mixed evenly in a mixer, and then extruded into granules by a twin-screw extruder, wherein the extruder temperature is 250°C; the obtained mixture is placed in a vacuum drum drying system for drying and dehydration, the drying temperature is 120°C, and the drying time is 4h; Cast film: The masterbatch obtained by pretreatment is melt-blended and extruded through a twin-screw extruder, and is conveyed to a cold roller with an electrostatic charge at a surface temperature of 30-40°C for close cooling and solidification to obtain an unstretched polylactic acid cast film; wherein the feeding speed is 40r / min, the screw speed is 200r / min, the metering pump speed is 38r / min, the melt plasticization temperature is 220°C, and the die head temperature is 220°C; Stretching film: The unstretched polylactic acid cast film is biaxially stretched, and the stretching method adopts the biaxial stretching method of longitudinal stretching in the length direction and then transverse stretching in the width direction, which is as follows: a. Longitudinal stretching: The cast film is fed into a longitudinal stretching roller and stretched in the longitudinal direction of the film, with a stretching ratio of 3.5 times and a stretching temperature of 70°C, and then cooled with a cooling roller group at 30°C; b. Transverse stretching: The thick film that has been longitudinally stretched is fed into a transverse stretching machine for transverse stretching, with a preheating temperature of 77°C and a preheating time of 15s; the stretching temperature is 100°C and the stretching ratio is 4.5 times; then the stretched film is relaxed in the width direction and heat-set at the same time, with a heat-setting temperature of 160°C, a time of 10s, and a relaxation rate of 4%, and finally cooled to room temperature to obtain a BOPLA heat-shrinkable film for high-speed packaging.

[0025] Comparative Example 1 The process is the same as in Example 3, except that the layered double hydroxide microcapsule-3 is not added.

[0026] Comparative Example 2 The process is the same as in Example 3, except that no low molecular weight polylactic acid resin is added.

[0027] Performance Test: Haze: in accordance with GB / T 2410; Heat seal strength: Cut 5 samples with a width of (15±0.1) mm and a length of 150 mm evenly in the width direction of the film roll, align the two ends of the samples and heat seal them on the heat machine. The heat sealing conditions are: temperature (130±1)℃, time 1s, pressure 1.8×10Pa. With the heat seal part as the center line, clamp the two ends of the sample on the two fixtures of the testing machine respectively. The longitudinal axis of the sample should coincide with the center line of the upper and lower fixtures, and the tightness should be appropriate to prevent the sample from slipping and breaking in the fixture. The distance between the fixtures is 100mm, and the test speed of the tensile machine is (100±10) mm / min. Read the maximum load when the sample breaks at the heat seal. Take the arithmetic mean of the 5 samples and express it in N / 15mm; Thermal shrinkage rate: Cut a 100mm×100mm film sample, mark the longitudinal and transverse directions, accurately measure the longitudinal and transverse lengths as L0, place it at 120℃ without load for 30 minutes, measure the longitudinal and transverse lengths again as L1, and calculate the thermal shrinkage rate according to the formula; Thermal shrinkage rate T = (L0-L1) / L0×100%; Friction coefficient: in accordance with GB / T 10006.

[0028] The test results are detailed in Table 1: Table 1 Performance test results of polylactic acid films prepared in Examples 1-3 and Comparative Example 1 It can be seen from the data in the above table that, compared with Comparative Example 1, the heat sealing strength of the BOPLA heat shrinkable film for high-speed packaging obtained by the technical solution of the embodiment is improved, and the friction coefficient is reduced. Among them, the comprehensive performance of Example 3 is the best. The addition of low molecular weight polylactic acid resin has a greater influence on the heat sealing strength and haze of the film, and the friction coefficient, haze and thermal shrinkage rate of the layered double hydroxide microcapsules are greatly affected. The processing technology of the BOPLA heat shrinkable film prepared according to the technical solution provided by the present invention is also simple and easy, which is conducive to promoting the application of polylactic acid in films, saving energy and protecting the environment.

Claims

1. A wear-resistant and anti-fog BOPLA heat shrinkable film for high-speed packaging, characterized in that: The invention comprises the following components: high molecular weight polylactic acid resin, low molecular weight polylactic acid resin and layered double hydroxide microcapsules. The mass ratio of high molecular weight polylactic acid resin to low molecular weight polylactic acid resin is (1-15):

1. The amount of layered double hydroxide microcapsules is 1.5-5% of the total amount of polylactic acid resin.

2. The wear-resistant and anti-fog BOPLA heat shrinkable film for high-speed packaging according to claim 1, characterized in that: The high molecular weight polylactic acid resin has a weight average molecular weight of 200,000-230,000, a molecular weight dispersion of 1-2, a density of 1.30-1.35 g / cc, and a peak melting temperature of 175-180°C.

3. The wear-resistant and anti-fog BOPLA heat shrinkable film for high-speed packaging according to claim 1, characterized in that: The low molecular weight polylactic acid resin has a weight average molecular weight of 10,000-30,000, a molecular weight dispersion of 2-3, a density of 1.30-1.35 g / cc, and a peak melting temperature of 165-170°C.

4. The wear-resistant and anti-fog BOPLA heat shrinkable film for high-speed packaging according to claim 1, characterized in that: The preparation method of the layered double hydroxide microcapsules comprises the following steps: dissolving fumaric acid and urea in deionized water, which is referred to as liquid A, and sequentially adding at least two of ferric nitrate nonahydrate, zinc nitrate hexahydrate and aluminum nitrate nonahydrate into the liquid A; stirring the obtained mixed solution at room temperature for 30-45 minutes, transferring the mixed solution into a polytetrafluoroethylene reactor, and reacting at 100-120° C. for 10-12 hours; after the reaction is completed, cooling the mixed solution to room temperature, centrifuging at a rotation speed of 3000-4000 rpm to obtain a precipitate, washing and drying the obtained precipitate to obtain the layered double hydroxide microcapsules.

5. The wear-resistant and anti-fog BOPLA heat shrinkable film for high-speed packaging according to claim 4, characterized in that: The mixing molar ratio of the fumaric acid to the urea is 1-1.5:

8.

6. The wear-resistant and anti-fog BOPLA heat shrinkable film for high-speed packaging according to claim 4, characterized in that: The total molar amount of at least two of the ferric nitrate nonahydrate, zinc nitrate hexahydrate and aluminum nitrate nonahydrate is 3.25 mmol.

7. The method for preparing the wear-resistant and anti-fog BOPLA heat shrinkable film for high-speed packaging according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: uniformly mixing high molecular weight polylactic acid resin, low molecular weight polylactic acid resin and layered double hydroxide microcapsules according to the content, melting and extruding, casting and sheeting, and adopting a biaxial stretching method to prepare the microcapsules.

8. The method for preparing the wear-resistant and anti-fog BOPLA heat shrinkable film for high-speed packaging according to claim 7, characterized in that: The melt extrusion temperature is 230-250°C, the melt plasticization temperature of the cast sheet is 210-220°C, and the discharge end temperature is 210-220°C.

9. The method for preparing the wear-resistant and anti-fog BOPLA heat shrinkable film for high-speed packaging according to claim 7, characterized in that: The biaxial stretching method adopts step-by-step stretching, first longitudinal stretching and then transverse stretching; the longitudinal stretching temperature is 50-70°C, and the stretching ratio is 2.2-3.5 times; the transverse stretching temperature is 80-100°C, and the stretching ratio is 3.5-4.5 times.

10. Use of the wear-resistant and anti-fog BOPLA heat-shrinkable film for high-speed packaging according to any one of claims 1 to 6 in the high-speed packaging industry.

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