A high-speed packaging wear-resistant anti-fog bopla heat-shrinkable film and a preparation method and application thereof

Abstract

The present application relates to a kind of high-speed packaging wear-resistant anti-fog BOPLA heat shrinkable film and its preparation method and application, the BOPLA heat shrinkable film includes the following components: high molecular weight polylactic acid resin, low molecular weight polylactic acid resin, layered double hydroxide microcapsule;According to mass ratio, high molecular weight polylactic acid resin: low molecular weight polylactic acid resin= (1-15) :1, the amount of layered double hydroxide microcapsule accounts for 1.5-5% of total polylactic acid resin amount.The preparation method of the BOPLA heat shrinkable film is that each component is mixed uniformly according to content, melt base, cast sheet, and the BOPLA heat shrinkable film is obtained by biaxial stretching method.The obtained BOPLA film has low friction coefficient, good heat sealing performance, high heat shrinkage rate, excellent mechanical properties, and can be used for high-speed packaging.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polylactic acid film, 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

[0002] With the increasing environmental and resource problems such as large-scale exploitation of oil and plastic waste disposal, and people's pursuit of life quality and health, the market's demand for safety and environmental protection of plastic is also increasing. Biobased and degradable materials have attracted the attention of researchers. As a semi-crystalline linear aliphatic polyester, polylactic acid (PLA) is an excellent synthetic polymer material with biocompatibility and biodegradability. It is considered to be the most promising green and pollution-free polymer material. Unlike traditional plastics derived from petroleum, PLA is derived from renewable plant resources such as corn, sugarcane and cassava, and has the basic properties of general-purpose polymers. PLA has good mechanical processing properties and can be processed by various methods such as extrusion, injection molding, blow molding, stretching, spinning and other forming processes. In particular, the BOPLA film prepared by using the biaxial stretching forming technology has excellent mechanical properties, optical transparency and water vapor barrier properties, and can be widely used in packaging, agriculture, engineering, textiles, automobiles, biomedical and tissue engineering fields, and has broad market prospects and significant economic benefits. In recent years, with the increasing application of biodegradable BOPLA film in various fields, the development and application research of its forming technology have attracted more and more attention from many teams at home and abroad.

[0003] At present, the PLA film forming technology mainly adopts the blow molding method, but there are problems such as uneven film thickness, low transparency and low tensile strength. Biaxial stretching is a kind of directional polymer film forming and processing technology. The change of microstructure makes the mechanical properties of polymer film change dramatically, and it has the characteristics of high gloss, high transparency and high barrier property. Due to its special forming and processing technology, PLA is stretched in the transverse direction (TD) and longitudinal direction (MD) during film forming. The biaxial stretching process parameters such as controllable stretching plastic, stretching ratio, temperature and stretching mode (synchronous or asynchronous) can make the PLA molecular chain (crystallize) orientation, so that the tensile strength, transparency, heat resistance and other properties of the film are greatly improved.

[0004] However, with the continuous progress 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, the following performance requirements need to be met: 1. Smooth running, i.e. low friction coefficient, and good wear resistance and scratch resistance; 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, the glass transition temperature of PLA is relatively high, the usability at room temperature is brittle, and the thermal stability is poor, which is difficult to meet the requirements of high-speed packaging film. SUMMARY

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

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

[0007] In some embodiments of the present application, the weight average molecular weight of the high molecular weight polylactic acid resin is 200-230 thousand, the molecular weight dispersity is 1-2, the density is 1.30-1.35 g / cc, and the peak melting temperature is 175-180℃.

[0008] In some embodiments of the present application, the weight average molecular weight of the low molecular weight polylactic acid resin is 10-30 thousand, the molecular weight dispersity is 2-3, the density is 1.30-1.35 g / cc, and the peak melting temperature is 165-170℃.

[0009] In some embodiments of the present application, the preparation method of the layered double hydroxide microcapsule comprises the following steps: dissolving fumaric acid and urea in deionized water to obtain solution A, and then adding at least two of iron nitrate nonahydrate, zinc nitrate hexahydrate and aluminum nitrate nonahydrate to solution A; stirring the obtained mixed solution at room temperature for 30-45 min, and then transferring it into a polytetrafluoroethylene reaction kettle, and reacting at 100-120℃ for 10-12 h; after the reaction is completed, cooling it to room temperature, and centrifuging at a rotation speed of 3000-4000 rpm to obtain a precipitate, and then washing and drying the precipitate to obtain the layered double hydroxide microcapsule.

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

[0011] Further, the total molar amount of the at least two of the nine-water ferric nitrate, six-water zinc nitrate and nine-water nitric acid is 3.25 mmol.

[0012] The preparation method of 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 contents, melt extruding, casting a sheet, and preparing by a two-way stretching method.

[0013] Further, the melt extrusion temperature is 230-250 DEG C, the melt plasticizing temperature of the casting sheet is 210-220 DEG C, and the discharge end temperature is 210-220 DEG C.

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

[0015] The application of the high-speed packaging wear-resistant anti-fog BOPLA heat-shrinkable film in the high-speed packaging industry.

[0016] Beneficial effects: compared with the prior art, the low-molecular-weight polylactic acid and the high-molecular-weight polylactic acid are used together, and the layered double hydroxide microcapsules are added:

[0017] The low-molecular-weight polylactic acid requires lower energy for movement unit activation and smaller space for movement, the addition of the low-molecular-weight polylactic acid lowers the peeling temperature of the mixed resin, and the addition of the low-molecular-weight polylactic acid lowers the average molecular weight of the polylactic acid, widens the molecular weight distribution, reduces the force between the high-molecular-weight polylactic acid chains, lowers the crystallinity of the mixed resin, and finally improves the brittleness and increases the flexibility of the film;

[0018] A certain amount of layered double hydroxide microcapsules is mixed with the polylactic acid, which lowers the surface energy of the BOPLA heat-shrinkable film, increases the contact angle of the film surface, makes the water droplets slide off, achieves the anti-fog effect, also plays the role of anti-adhesion particles, lowers the friction coefficient, and fills the micro-cavities on the film surface caused by the difference in intermolecular force between the high-molecular-weight and low-molecular-weight polylactic acid resins, lowers the surface roughness of the film, and improves the surface properties of the film.

[0019] The BOPLA film prepared by the technical scheme of the application has low friction coefficient, good heat sealing performance and high heat shrinkage rate, and meets the requirements of the heat-shrinkable film for high-speed packaging. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0021] The preparation process of the layered double hydroxide microcapsule used in the embodiments is exemplarily described below.

[0022] Layered double hydroxide microcapsule-1:

[0023] 0.01 mol of fumaric acid and 0.08 mol of urea were dissolved in 200 ml of deionized water, denoted as A liquid, 2 mmol of iron nitrate nonahydrate and 1.25 mmol of zinc nitrate hexahydrate were sequentially added to the A liquid; the obtained mixed solution was stirred at room temperature for 30 min, and then transferred into a polytetrafluoroethylene reaction kettle, and reacted at 100 ℃ for 12 h; after the reaction was completed, it was cooled to room temperature, and the precipitate was obtained by centrifugal separation at a rotation speed of 3000 rpm, and then washed and dried, to obtain the layered double hydroxide microcapsule-1.

[0024] Layered double hydroxide microcapsule-2:

[0025] 0.012 mol of fumaric acid and 0.08 mol of urea were dissolved in 200 ml of deionized water, denoted as A liquid, 2 mmol of zinc nitrate hexahydrate and 1.25 mmol of aluminum nitrate nonahydrate were sequentially added to the A liquid; the obtained mixed solution was stirred at room temperature for 35 min, and then transferred into a polytetrafluoroethylene reaction kettle, and reacted at 110 ℃ for 11 h; after the reaction was completed, it was cooled to room temperature, and the precipitate was obtained by centrifugal separation at a rotation speed of 3500 rpm, and then washed and dried, to obtain the layered double hydroxide microcapsule-2.

[0026] Layered double hydroxide microcapsule-3:

[0027] 0.015 mol of fumaric acid and 0.08 mol of urea were dissolved in 200 ml of deionized water, denoted as A liquid, 1 mmol of iron nitrate nonahydrate and 2.25 mmol of aluminum nitrate nonahydrate were sequentially added to the A liquid; the obtained mixed solution was stirred at room temperature for 40 min, and then transferred into a polytetrafluoroethylene reaction kettle, and reacted at 120 ℃ for 10 h; after the reaction was completed, it was cooled to room temperature, and the precipitate was obtained by centrifugal separation at a rotation speed of 4000 rpm, and then washed and dried, to obtain the layered double hydroxide microcapsule-3.

[0028] Example 1

[0029] Preparation of materials: the ratio of high molecular weight polylactic acid resin to low molecular weight polylactic acid resin is 1:1 by mass ratio, and the layered double hydroxide microcapsule-1 is 1.5% of the total polylactic acid resin;

[0030] Pre-treatment of raw materials: the polylactic acid resin and the layered double hydroxide microcapsule-1 are stirred uniformly by a mixer, and then are extruded and granulated by a twin-screw extruder, wherein the temperature of the extruder is 230°C; the obtained mixture is dried to remove water in a vacuum drum drying system, the drying temperature is 120°C, and the drying time is 4h;

[0031] Cast sheet: the master batch obtained by pre-treatment is melt blended and extruded by a twin-screw extruder, and is tightly cooled and solidified while being conveyed by a cold roller with electrostatic charge applied to the surface at a temperature of 30-40°C, to obtain unstretched polylactic acid cast film sheet; wherein the feeding speed is 40r / min, the screw speed is 200r / min, the rotation speed of the metering pump is 38r / min, the melt plasticizing temperature is 210°C, and the die temperature is 210°C;

[0032] Stretching into film: the unstretched polylactic acid cast film sheet is biaxially stretched, and the stretching method adopts the sequential biaxial stretching method of longitudinal stretching in the present length direction and then transverse stretching in the width direction, specifically as follows: a, longitudinal stretching: the cast film sheet is sent into a longitudinal stretching roller to stretch in the longitudinal direction of the film, the stretching ratio is 2.2 times, the stretching temperature is 50°C, and then the film is cooled by a cooling roller group at 25°C; b, transverse stretching: the thick sheet after longitudinal stretching is sent into a transverse stretching machine to stretch in the transverse direction, 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 while being heat set, the heat setting temperature is 170°C, the time is 15s, the relaxation rate is 5%, and finally the film is cooled to room temperature, to obtain a BOPLA heat-shrinkable film for high-speed packaging.

[0033] Example 2

[0034] Preparation of materials: the ratio of high molecular weight polylactic acid resin to low molecular weight polylactic acid resin is 8:1 by mass ratio, and the layered double hydroxide microcapsule-2 is 3% of the total polylactic acid resin;

[0035] Pre-treatment of raw materials: the polylactic acid resin and the layered double hydroxide microcapsule-2 are stirred uniformly by a mixer, and then are extruded and granulated by a twin-screw extruder, wherein the temperature of the extruder is 240°C; the obtained mixture is dried to remove water in a vacuum drum drying system, the drying temperature is 120°C, and the drying time is 4h;

[0036] The obtained mother material is melt-blended and extruded through a double screw extruder, and is simultaneously fed to a cold roller with surface temperature of 30-40°C for close cooling and solidification, to obtain unstretched polylactic acid casting film; wherein the feeding speed is 40 r / min, the screw speed is 200 r / min, the metering pump speed is 38 r / min, the melt plasticizing temperature is 215°C, and the die temperature is 215°C;

[0037] Stretching into film: the unstretched polylactic acid casting film is biaxially stretched by using the sequential biaxial stretching method of longitudinal stretching in the present length direction and then transverse stretching in the width direction, specifically as follows: a, longitudinal stretching: the casting film is fed into a longitudinal stretching roller for stretching in the longitudinal direction of the film, the stretching ratio is 3.0 times, the stretching temperature is 60°C, and then the film is cooled by a cooling roller group with temperature of 30°C; b, transverse stretching: the thick film after longitudinal stretching is fed into a transverse stretching machine for transverse stretching, the preheating temperature is 72°C, the preheating time is 15 s, 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 simultaneously heat set, the heat setting temperature is 160°C, the time is 10 s, the relaxation ratio is 4%, and finally the film is cooled to room temperature, to obtain the BOPLA heat-shrinkable film for high-speed packaging.

[0038] Example 3

[0039] Preparation of material: the ratio of high molecular weight polylactic acid resin to low molecular weight polylactic acid resin is 15:1 by mass ratio, and the layered double hydroxide microcapsule-3 accounts for 5% of the total polylactic acid resin;

[0040] Pre-treatment of raw material: the polylactic acid resin and the layered double hydroxide microcapsule-3 are uniformly stirred by a mixer, and then are extruded and granulated by a double screw extruder, wherein the extruder temperature is 250°C; the obtained mixture is dried in a vacuum drum drying system, the drying temperature is 120°C, and the drying time is 4 h;

[0041] Casting: the obtained mother material is melt-blended and extruded through a double screw extruder, and is simultaneously fed to a cold roller with surface temperature of 30-40°C for close cooling and solidification, to obtain unstretched polylactic acid casting film; wherein the feeding speed is 40 r / min, the screw speed is 200 r / min, the metering pump speed is 38 r / min, the melt plasticizing temperature is 220°C, and the die temperature is 220°C;

[0042] Stretching film forming: the unstretched polylactic acid cast film was biaxially stretched, the stretching method was sequential biaxial stretching method of longitudinal stretching in the present length direction, and then transverse stretching in the width direction, specifically as follows: a, longitudinal stretching: the cast film was sent into the longitudinal stretching roller to stretch in the longitudinal direction of the film, the stretching ratio was 3.5 times, the stretching temperature was 70℃, and then the film was cooled by a cooling roller group of 30℃; b, transverse stretching: the thick piece after longitudinal stretching was sent into the transverse stretching machine to stretch in the transverse direction, the preheating temperature was 77℃, the preheating time was 15s; the stretching temperature was 100℃, the stretching ratio was 4.5 times; then the stretched film was relaxed in the width direction while being heat set, the heat setting temperature was 160℃, the time was 10s, the relaxation rate was 4%, and finally the film was cooled to room temperature, thereby a BOPLA heat-shrinkable film for high-speed packaging was obtained.

[0043] Comparative Example 1

[0044] The process was the same as that in Example 3, except that no layered double hydroxide microcapsule-3 was added.

[0045] Comparative Example 2

[0046] The process was the same as that in Example 3, except that no low molecular weight polylactic acid resin was added.

[0047] Performance test:

[0048] Haze: according to GB / T 2410;

[0049] Heat sealing strength: five samples of (15±0.1) mm in width and 150 mm in length were uniformly cut from the film roll in the width direction, and the two ends of the samples were aligned on a heat sealing machine for heat sealing. The heat sealing conditions were: temperature (130±1)℃, time 1s, and pressure 1.8×10Pa. With the heat sealing part as the center line, the two ends of the sample were clamped in the two clamps of the testing machine, the longitudinal axis of the sample should coincide with the center line of the upper and lower clamps, and the tension should be appropriate to prevent the sample from slipping and breaking in the clamp. The distance between the clamps was 100 mm, and the testing speed of the tensile testing machine was (100±10) mm / min. The maximum load at the breaking point of the sample was read. The arithmetic mean value of the five samples was taken as the heat sealing strength, which was expressed in N / 15mm;

[0050] Heat shrinkage rate: a film sample of 100mm×100mm was cut, the longitudinal and transverse directions were marked, and the longitudinal and transverse lengths were accurately measured as L0. The sample was placed at 120℃ without load for 30min, and then the longitudinal and transverse lengths were measured again as L1. The heat shrinkage rate was calculated according to the formula: heat shrinkage rate T=(L0-L1) / L0×100%;

[0051] Friction coefficient: according to GB / T 10006.

[0052] The test results are shown in Table 1:

[0053] Table 1. Performance test results of the polylactic acid film prepared in Examples 1-3 and Comparative Example 1

[0054]

[0055] As can be seen from the data in the above table, compared with Comparative Example 1, the heat sealing strength of the BOPLA heat-shrinkable film prepared by using the technical solutions of the examples is improved, and the friction coefficient is decreased. 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 layered double hydroxide microcapsule has a greater influence on the friction coefficient, haze and heat shrinkage rate. The processing technology of the BOPLA heat-shrinkable film prepared according to the technical solutions provided in the application is also simple and easy to operate, 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-fogging BOPLA heat-shrinkable film for high-speed packaging, characterized in that, It contains the following components: high molecular weight polylactic acid resin, low molecular weight polylactic acid resin, and layered double hydroxide microcapsules. By mass ratio, the 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 polylactic acid resin. 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℃. 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℃. The preparation method of the layered double hydroxide microcapsules includes the following steps: dissolving fumaric acid and urea in deionized water, denoted as solution A, and sequentially adding at least two of ferric nitrate nonahydrate, zinc nitrate hexahydrate, and aluminum nitrate nonahydrate to solution A; stirring the resulting mixed solution at room temperature for 30-45 min, then transferring it to a polytetrafluoroethylene reactor and reacting at 100-120℃ for 10-12 h; after the reaction is completed, cooling it to room temperature, centrifuging at 3000-4000 rpm to obtain a precipitate, washing and drying the precipitate to obtain the layered double hydroxide microcapsules; The molar ratio of fumaric acid to urea is 1-1.5:8; The total molar amount of at least two of the following: ferric nitrate nonahydrate, zinc nitrate hexahydrate, and aluminum nitrate nonahydrate is 3.25 mmol.

2. The method for preparing the wear-resistant and anti-fogging BOPLA heat-shrinkable film for high-speed packaging as described in claim 1, characterized in that, The process includes the following steps: mixing high molecular weight polylactic acid resin, low molecular weight polylactic acid resin, and layered double hydroxide microcapsules in the stated amounts, melting and extruding, casting, and preparing by biaxial stretching.

3. The method for preparing the wear-resistant and anti-fogging BOPLA heat-shrinkable film for high-speed packaging according to claim 2, characterized in that, The melt extrusion temperature is 230-250℃, the melt plasticizing temperature of the cast sheet is 210-220℃, and the discharge end temperature is 210-220℃.

4. The method for preparing the wear-resistant and anti-fogging BOPLA heat-shrinkable film for high-speed packaging according to claim 2, characterized in that, The biaxial stretching method employs step-by-step stretching, first longitudinal stretching and then transverse stretching; the longitudinal stretching temperature is 50-70℃, and the stretching ratio is 2.2-3.5 times; the transverse stretching temperature is 80-100℃, and the stretching ratio is 3.5-4.5 times.

5. The application of the wear-resistant and anti-fog BOPLA heat-shrinkable film for high-speed packaging as described in claim 1 in the high-speed packaging industry.

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