Preparation method and use of polylactic acid for producing matte biaxially oriented film

Abstract

The present invention relates to a method for preparing polylactic acid for producing a matte biaxially stretched film in the field of polylactic acid materials. A matting agent is added before the ring-opening polymerization reaction of polylactic acid and its copolymer, and then polylactic acid and its copolymer are prepared by ring-opening polymerization of lactide and comonomer under polymerization conditions. The polylactic acid and copolyester resin materials obtained after the polymerization have good film-making stability and excellent matting performance. The raw material components and their weight parts are as follows: 100 parts of lactide and comonomer, 0.3-5 parts of matting agent, 0.01-0.4 parts of initiator, 0.5-2 parts of antioxidant, and 0.1-3 parts of catalyst. The present invention adopts a method of physically blending a matting agent with a monomer raw material, improves the dispersibility of the matting agent, and the matting degree is convenient to control. Polylactic acid and its copolymer can obtain a film material with high haze, low gloss and good matting effect after biaxial stretching.

Description

Technical Field

[0001] The invention relates to a matte polylactic acid material, in particular to a method for producing a matte biaxially stretched polylactic acid film. Background Art

[0002] At present, transparent and glossy stretch films are widely used as packaging materials. The films are mainly made of resin materials such as polyethylene terephthalate, polypropylene, polyethylene, and polyvinyl chloride. Patent CN105968272A discloses a method for preparing a matte polyvinyl chloride resin, which can effectively reduce the number of crystal points of the resin. The obtained matte polyvinyl chloride resin has regular particles, loose structure, few crystal points, and good matte effect. CN103160039A discloses a matte film or diaphragm, which is formed by a skeleton agent and a sensitizer, and the polyvinyl chloride cross-linked gel content in the matte film or diaphragm is controlled to be 15-85% by electron beam radiation. CN102152576A discloses a polypropylene matte film with good flexibility, puncture resistance, and tear resistance, which is prepared by casting three layers of raw materials A, B, and C. The A layer is the matte surface layer, the B layer is the core layer, and the C layer is the bottom layer. The weight ratio of the raw material components of each layer is: A layer: 100% all-polymer matte masterbatch; B layer: 97-98% polypropylene, 2.0-3.0% antistatic agent; C layer: 95-97% polypropylene, 3.0-5.0% anti-adhesive agent. However, there is still no effective recycling method for these traditional petroleum-based non-degradable material wastes, which has caused soil impoverishment, reduced crop yields, and aggravated environmental pollution and greenhouse effects.

[0003] Polylactic acid is biodegradable and can be hydrolyzed or degraded by microorganisms into CO in the natural environment. 2 and H 2 O, harmless and non-toxic to the human body. Patent CN105733000A discloses a method for preparing a polylactic acid film, which forms a high molecular weight polylactic acid by ring-opening polymerization of lactide. In the prior art, after the polylactic acid material is synthesized and prepared, a blending method is used to achieve the addition of a matting agent. According to patent CN105734701A, titanium dioxide dry powder and polylactic acid slices need to be heated to 200-300°C to make a polylactic acid melt. The blending temperature is high, the energy consumption is large, and it is easy to cause thermal degradation of the product, resulting in a decrease in molecular weight and a widening of the molecular weight distribution. The viscosity of the polylactic acid slices is relatively large, and the resulting matte polylactic acid titanium dioxide has poor dispersion uniformity. At present, there are few reports on biodegradable matte films or sheets formed by polylactic acid resins. Therefore, it is necessary to seek a method with low energy consumption, simple process, and a matting agent that can be evenly dispersed in the polylactic acid material. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and to provide a method for preparing polylactic acid for the production of matte biaxially stretched film. The matte biaxially stretched film further prepared has high haze, low gloss, excellent matte effect and comprehensive mechanical properties.

[0005] The technical scheme provided by the present invention is as follows: a method for preparing polylactic acid for producing matte biaxially stretched film, wherein a matting agent inert to the polymerization reaction is added before the ring-opening polymerization reaction of polylactic acid and its copolymer, and then lactide and comonomer are ring-opening polymerized under polymerization conditions to prepare polylactic acid and its copolymer, and the weight parts of the production raw materials are as follows: 100 parts of lactide and comonomer, 0.3-5 parts of matting agent, 0.01-0.4 parts of initiator, 0.5-2 parts of antioxidant, and 0.1-3 parts of catalyst; in the lactide and comonomer, the weight percentage of the comonomer is 5-12%.

[0006] Specifically, it includes the following steps:

[0007] (1) Lactide and comonomer, matting agent, initiator, catalyst and antioxidant are transported to the circulation reactor through a metering pump. After being fully mixed, a primary ring-opening polymerization reaction is carried out in the circulation reactor. The reaction temperature is 130-160°C, the flow rate is 10-30 mm / s, and the shear rate is 50-350s -1 Within the range, the reactants are circulated in the circulation reactor for 10-30 times, and reacted for 1-5 hours under a nitrogen atmosphere to obtain oligomers;

[0008] (2) The oligomer is further polymerized by increasing the temperature to 170-200° C. in a plug flow reactor, the reaction system flow rate is 2-15 mm / s, the shear rate reaches 10-100 s-1, and the reaction time is 3-10 h, to obtain a matte polylactic acid resin, the molecular weight of the matte polylactic acid resin is 50,000-1,000,000, preferably 60,000-300,000; and then extrusion molding is performed by a screw extruder to obtain a cast sheet to obtain the target product.

[0009] As a further improvement of the present invention, the lactide is selected from one or more of L-lactide, D-lactide and meso-lactide.

[0010] As a further improvement of the present invention, the comonomer is selected from one or more of ε-caprolactone, δ-valerolactone, β-methyl-δ-valerolactone and glycolide.

[0011] The matting agent is TiO 2 and BaSO 4 The matting agent has no effect on the molecular weight and distribution of the product of the ring-opening polymerization of lactide and comonomer. The amount of the matting agent is preferably 0.6-2 parts.

[0012] The antioxidant is one of Antioxidant 1010, Antioxidant 168, Antioxidant 626, Antioxidant 1098 and TPH-24.

[0013] The catalyst is one of stannous octoate, tin oxide, dibutyltin oxide, stannous chloride, tin lactate, stannous benzoate, dibutyltin dilaurate, zinc oxide, zinc lactate, and zinc acetate. Stannous octoate is the most preferred. The catalyst can promote the ring-opening polymerization of lactide and other cyclic monomers and has strong reactivity. The amount of the catalyst is preferably 0.1-0.5 parts.

[0014] The initiator is selected from one or more compounds containing hydroxyl groups, preferably one or more alcohol compounds. The alcohol compound described herein may be one or more of monohydric alcohol, dihydric alcohol and polyhydric alcohol; for example, benzyl alcohol, dodecanol (lauryl alcohol), 1,2-ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, trimethylolpropane, pentaerythritol, isomeric decanol.

[0015] Preferably, the molecular weight of the polylactic acid and its copolymer resin described in step (2) is preferably 50,000-1,000,000, and particularly preferably 60,000-300,000. If the molecular weight is less than 50,000, it is difficult to form a film and the mechanical properties are poor; if the molecular weight exceeds 1,000,000, the melt viscosity is high and it is difficult to obtain a film with stable physical properties during mechanical processing.

[0016] The polylactic acid for producing a matte biaxially stretched film obtained in the above steps can be used for the production of a matte biaxially stretched film, and the steps are: preheating the cast sheet longitudinally, stretching it longitudinally, and then entering the longitudinal stretching shaping zone for heat setting. At the same time, preheating it transversely, stretching it transversely, and then entering the transverse stretching shaping zone for heat setting. After corona treatment, winding, aging, and slitting, a biaxially stretched polylactic acid film with matte properties is obtained.

[0017] Compared with the prior art, the advantages of the present invention are: before the ring-opening polymerization reaction of polylactic acid and its copolymer, a matting agent inert to the polymerization reaction is added, and then the ring-opening polymerization of lactide and comonomer is carried out under polymerization conditions to prepare polylactic acid and its copolymer; the polylactic acid and copolyester resin materials obtained after the polymerization have good film-making stability and excellent matting performance; after biaxial stretching, the biodegradable matting polylactic acid film has high haze, low gloss, excellent matting effect and comprehensive mechanical properties.

[0018] (1) The present invention disperses the matting agent in the lactide and comonomer melt before the reaction, which is simple in process and convenient in operation. It is simpler and more efficient than the conventional matting film process using matting masterbatch mixed with other extrusion resins.

[0019] (2) The present invention can maintain the matting performance and the ring-opening polymerization reaction of lactide and comonomers. Compared with the matting agent and high molecular weight polylactic acid chip blending technology, the lactide and comonomer melts used in this technology have low melting points, which can reduce the blending temperature, effectively save energy, and significantly reduce energy consumption.

[0020] (3) Compared with the matting agent and high molecular weight polylactic acid chip blending technology, the melt viscosity of lactide and comonomer is low, and blending under liquid phase conditions can achieve a more uniform dispersion.

[0021] (4) The present invention can adjust the matting performance by adjusting the amount of matting agent added without affecting the polymerization reaction. The matting agent can be used alone or mixed with other materials.

[0022] (5) The main component of the matte polylactic acid of the present invention, polylactic acid, is biodegradable and more environmentally friendly than petroleum-based polyester materials. DETAILED DESCRIPTION

[0023] Hereinafter, preferred embodiments of the present invention will be described in detail in conjunction with the embodiments, but the present invention is not limited in any way.

[0024] Example 1

[0025] A method for producing a matte biaxially stretched film comprises first preparing polylactic acid for producing the matte biaxially stretched film, and then biaxially stretching the prepared polylactic acid to obtain the matte biaxially stretched film, wherein the steps are:

[0026] (1) In a production device, melted L-lactide / ε-caprolactone (88 / 12 parts by weight), TiO 2 (0.8 parts by weight), lauryl alcohol (0.23 parts by weight), stannous octoate (0.25 parts by weight) and antioxidant 1010 (1.5 parts by weight) were transported to the circulation reactor via a metering pump, and the fully mixed reaction system was subjected to primary ring-opening polymerization in the circulation reactor. The temperature of the reaction device was 145°C, the flow rate of the reaction system was controlled at 20 mm / s, and the shear rate was 200 s -1 The reaction system was cycled 25 times in the reaction device and reacted for 5 hours in a nitrogen atmosphere to obtain an oligomer.

[0027] (2) The obtained oligomer was further polymerized by raising the temperature to 185°C in a plug flow reactor. The reaction system flow rate was 10 mm / s and the shear rate reached 50 s -1 The reaction time is 5 hours to obtain a matte polylactic acid resin, the molecular weight of the polylactic acid and its copolymer resin is in the range of 50,000-1,000,000, preferably 60,000-300,000; and then extrusion molding is performed by a screw extruder to obtain a casting sheet; the monomer conversion rate reaches more than 95%.

[0028] (3) The cast sheet obtained in step (2) is longitudinally preheated, longitudinally stretched, and then heat-set in the longitudinal stretching shaping zone. At the same time, it is transversely preheated, transversely stretched, and then heat-set in the transverse stretching shaping zone. After corona treatment, winding, aging, and slitting, a biaxially oriented polylactic acid film is obtained.

[0029] Example 2

[0030] A method for producing a matte biaxially stretched film comprises first preparing polylactic acid for producing the matte biaxially stretched film, and then biaxially stretching the prepared polylactic acid to obtain the matte biaxially stretched film, the steps comprising:

[0031] (1) In a production device, melted L-lactide / δ-valerolactone (90 / 10 parts by weight), TiO 2 (1.0 parts by weight), 1,4-butanediol (0.09 parts by weight), stannous octoate (0.3 parts by weight) and antioxidant 1010 (1.3 parts by weight) were transported to the circulation reactor via a metering pump, and the fully mixed reaction system was subjected to primary ring-opening polymerization in the reaction device. The temperature of the reaction device was 150°C, the flow rate of the reaction system was controlled at 23 mm / s, and the shear rate was 190 s -1 The reaction system was cycled 18 times in the reaction apparatus and reacted for 3 h in a nitrogen atmosphere.

[0032] (2) The obtained oligomer was further polymerized by raising the temperature to 175°C in a plug flow reactor. The reaction system flow rate was 15 mm / s and the shear rate reached 60 s -1 The reaction time is 6 hours, and the matte polylactic acid resin is obtained. The molecular weight of polylactic acid and its copolymer resin is in the range of 60,000 to 300,000; a casting sheet is obtained by extrusion molding through a screw extruder.

[0033] (3) The cast sheet of step (2) is longitudinally preheated and then longitudinally stretched, then enters the longitudinal stretching shaping zone for heat setting and transverse preheating, then transversely stretched, then enters the transverse stretching shaping zone for heat setting, and then corona treated, rolled, aged, and slit to obtain a biaxially stretched polylactic acid film.

[0034] Example 3

[0035] A method for producing a matte biaxially stretched film comprises first preparing polylactic acid for producing the matte biaxially stretched film, and then biaxially stretching the prepared polylactic acid to obtain the matte biaxially stretched film, wherein the steps are:

[0036] (1) In a production device, melted D-lactide / glycolide (92 / 8 parts by weight), BaSO 4(0.8 parts by weight), trimethylolpropane (0.09 parts by weight), stannous chloride (0.3 parts by weight) and antioxidant 1010 (1.2 parts by weight) were transported to the circulation reactor via a metering pump, and the fully mixed reaction system was subjected to primary ring-opening polymerization in the reaction device. The temperature of the reaction device was 155°C, the flow rate of the reaction system was controlled at 20 mm / s, and the shear rate was 200 s -1 The reaction system was cycled 20 times in the reaction apparatus and reacted for 3 h in a nitrogen atmosphere.

[0037] (2) The obtained oligomer was further polymerized by raising the temperature to 180°C in a plug flow reactor. The reaction system flow rate was 10 mm / s and the shear rate reached 50 s -1 The reaction time is 6 hours, and the matte polylactic acid resin is obtained. The molecular weight of polylactic acid and its copolymer resin is in the range of 60,000 to 300,000; a casting sheet is obtained by extrusion molding through a screw extruder.

[0038] (3) The cast sheet of step (2) is longitudinally preheated and then longitudinally stretched, and then enters the longitudinal stretching shaping zone for shaping and transverse preheating, and then transversely stretched, and then enters the transverse stretching shaping zone for heat setting, and then corona treatment, winding, aging, and slitting to obtain a biaxially stretched polylactic acid film.

[0039] Example 4

[0040] A method for producing a matte biaxially stretched film comprises first preparing polylactic acid for producing the matte biaxially stretched film, and then biaxially stretching the prepared polylactic acid to obtain the matte biaxially stretched film, wherein the steps are:

[0041] (1) In a production device, melted meso-lactide / β-methyl-δ-valerolactone (95 / 5 parts by weight), TiO 2 / BaSO 4 (0.5 / 0.5 parts by weight), pentaerythritol (0.07 parts by weight), stannous octoate (0.3 parts by weight) and antioxidant 1010 (0.9 parts by weight) were transported to the circulation reactor via a metering pump, and the fully mixed reaction system was subjected to primary ring-opening polymerization in the reaction device. The temperature of the reaction device was 153°C, the flow rate of the reaction system was controlled at 20 mm / s, and the shear rate was 195 s -1 The reaction system was cycled 30 times in the reaction apparatus and reacted for 4 h in a nitrogen atmosphere.

[0042] (2) The obtained oligomer was further polymerized by raising the temperature to 182°C in a plug flow reactor. The reaction system flow rate was 8 mm / s and the shear rate reached 60 s -1The reaction time is 7 hours, and the matte polylactic acid resin is obtained. The molecular weight of polylactic acid and its copolymer resin is in the range of 60,000 to 300,000; a casting sheet is obtained by extrusion molding through a screw extruder.

[0043] (3) The cast sheet described in (2) is longitudinally preheated and then longitudinally stretched, and then enters the longitudinal stretching shaping zone for shaping and transverse preheating, and then transversely stretched, and then enters the transverse stretching shaping zone for heat setting, and then corona treatment, winding, aging, and slitting to obtain a biaxially stretched polylactic acid film.

[0044] Example 5

[0045] A method for producing a matte biaxially stretched film comprises first preparing polylactic acid for producing the matte biaxially stretched film, and then biaxially stretching the prepared polylactic acid to obtain the matte biaxially stretched film, wherein the steps are:

[0046] (1) In a production device, melted D-lactide / ε-caprolactone / δ-valerolactone (90 / 5 / 5 parts by weight), BaSO 4 (0.3 parts by weight), 1,2-ethylene glycol (0.01 parts by weight), stannous octoate (0.01 parts by weight) and antioxidant 1010 (1.3 parts by weight) were transported to the circulation reactor via a metering pump, and the fully mixed reaction system was subjected to primary ring-opening polymerization in the reaction device. The temperature of the reaction device was 148°C, the flow rate of the reaction system was controlled at 25 mm / s, and the shear rate was 195 s -1 Within the range, the reaction system was cycled 10 times in the reaction device and reacted for 5 h in a nitrogen atmosphere;

[0047] (2) The obtained oligomer was further polymerized by raising the temperature to 178°C in a plug flow reactor. The reaction system flow rate was 2 mm / s and the shear rate reached 65 s -1 The reaction time is 4 hours, and the matte polylactic acid resin is obtained. The molecular weight of polylactic acid and its copolymer resin is in the range of 60,000 to 300,000; a casting sheet is obtained by extrusion molding through a screw extruder.

[0048] (3) The cast sheet in step (2) is longitudinally preheated and then longitudinally stretched, then enters the longitudinal stretching shaping zone for heat setting and transverse preheating, then transversely stretched, then enters the transverse stretching shaping zone for heat setting, and then corona treated, rolled, aged, and slit to obtain a biaxially stretched polylactic acid film.

[0049] Example 6

[0050] A method for producing a matte biaxially stretched film comprises first preparing polylactic acid for producing the matte biaxially stretched film, and then biaxially stretching the prepared polylactic acid to obtain the matte biaxially stretched film, wherein the steps are:

[0051] (1) L-lactide / D-lactide / meso-lactide / ε-caprolactone / δ-valerolactone / β-methyl-δ-valerolactone / glycolide (40 / 30 / 20 / 3 / 3 / 2 / 2 parts by weight), matting agent BaSO 4 (0.3 parts by weight), initiator benzyl alcohol / isomeric decanol (0.2 / 0.2 parts by weight), catalyst tin oxide / dibutyltin oxide / tin lactate (0.1 / 0.2 / 0.2 parts by weight), antioxidant antioxidant 168 / antioxidant 626 (0.3 / 0.2 parts by weight) are transported to the circulation reactor through a metering pump, and after being fully mixed, a primary ring-opening polymerization reaction is carried out in the circulation reactor. The reaction temperature is 130°C, the flow rate is 30 mm / s, and the shear rate is 50s -1 The reactants were circulated in the circulation reactor for 10 times and reacted for 1 h under a nitrogen atmosphere to obtain oligomers;

[0052] (2) The oligomer was further polymerized by raising the temperature to 200 °C in a plug flow reactor. The reaction system flow rate was 15 mm / s and the shear rate was 100 s -1 The reaction time is 3 hours, and a matte polylactic acid resin is obtained, and the molecular weight of the matte polylactic acid resin is 60,000-300,000; and then a casting sheet is obtained by extrusion molding through a screw extruder;

[0053] (3) The cast sheet obtained in step (2) is subjected to biaxial stretching to obtain a biaxially stretched matte film.

[0054] Example 7

[0055] A method for producing a matte biaxially stretched film comprises first preparing polylactic acid for producing the matte biaxially stretched film, and then biaxially stretching the prepared polylactic acid to obtain the matte biaxially stretched film, wherein the steps are:

[0056] (1) L-lactide / D-lactide / ε-caprolactone / δ-valerolactone (45 / 45 / 5 / 5) and matting agent BaSO 4 (5 parts by weight), initiator 1,5-pentanediol / 1,6-hexanediol / trimethylolpropane / pentaerythritol (0.05 / 0.05 / 0.05 / 0.05 parts by weight), catalyst zinc oxide / zinc lactate / zinc acetate (1 / 1 / 1 parts by weight), antioxidant antioxidant 168 / antioxidant 626 / antioxidant 1098 / TPH-24 (0.5 / 0.5 / 0.5 / 0.5 parts by weight) are transported to the circulation reactor via a metering pump, and after being fully mixed, a primary ring-opening polymerization reaction is carried out in the circulation reactor, the reaction temperature is 160°C, the flow rate is 10 mm / s, and the shear rate is 350 s -1 Within the range, the reactants were circulated in the circulation reactor for 30 times and reacted for 1.5 h under a nitrogen atmosphere to obtain oligomers;

[0057] (2) The oligomer is further polymerized by raising the temperature to 170-200°C in a plug flow reactor. The reaction system flow rate is 2 mm / s and the shear rate is 10 s -1 The reaction time is 10 hours, and a matte polylactic acid resin is obtained, and the molecular weight of the matte polylactic acid resin is 60,000-300,000; and then a casting sheet is obtained by extrusion molding through a screw extruder;

[0058] (3) The cast sheet in step (2) is subjected to biaxial stretching to obtain a biaxially stretched matte film.

[0059] Comparative Example 1

[0060] A method for producing a biaxially stretched film, comprising the steps of:

[0061] (1) In the production device, molten L-lactide / ε-caprolactone (80 / 20 parts by weight), lauryl alcohol (0.19 parts by weight), stannous octoate (0.3 parts by weight) and antioxidant 1010 (1.2 parts by weight) are transported to the circulation reactor via a metering pump, and the fully mixed reaction system is subjected to primary ring-opening polymerization in the reaction device. The temperature of the reaction device is 150°C, the flow rate of the reaction system is controlled at 20 mm / s, and the shear rate is 200 s -1 The reaction system was cycled 20 times in the reaction apparatus and reacted for 3 h in a nitrogen atmosphere.

[0062] (2) The obtained oligomer was further polymerized by raising the temperature to 180°C in a plug flow reactor. The reaction system flow rate was 10 mm / s and the shear rate reached 50 s -1 After the reaction time was 6 hours, polylactic acid resin was obtained, and 1.0 weight part of TiO 2 , control flow rate to 30 mm / s, shear rate to 350 s -1 After being fully mixed, the mixture is extruded through a screw extruder to obtain a casting sheet.

[0063] (3) The cast sheet described in (2) is longitudinally preheated and then longitudinally stretched, then enters the longitudinal stretching shaping zone and is transversely preheated, then transversely stretched, then enters the transverse stretching shaping zone for heat setting, and then undergoes corona treatment, winding, aging, and slitting to obtain a biaxially stretched polylactic acid film.

[0064] Comparative Example 2

[0065] (1) In the production device, molten D-lactide (100 parts by weight), lauryl alcohol (0.19 parts by weight), stannous octoate (0.25 parts by weight) and antioxidant 1010 (1.2 parts by weight) are transported to the circulation reactor via a metering pump, and the fully mixed reaction system is subjected to primary ring-opening polymerization in the reaction device. The temperature of the reaction device is 150°C, the flow rate of the reaction system is controlled at 20 mm / s, and the shear rate is 200 s -1 The reaction system was cycled 20 times in the reaction apparatus and reacted for 3 h in a nitrogen atmosphere.

[0066] (2) The obtained oligomer was further polymerized by raising the temperature to 180°C in a plug flow reactor. The reaction system flow rate was 10 mm / s and the shear rate reached 50 s -1 After the reaction time was 6 hours, polylactic acid resin was obtained, and 0.8 parts by weight of TiO 2 , control flow rate to 30 mm / s, shear rate to 350 s -1 After being fully mixed, the mixture is extruded through a screw extruder to obtain a cast sheet.

[0067] (3) The cast sheet described in (2) is longitudinally preheated and then longitudinally stretched, then enters the longitudinal stretching shaping zone and is transversely preheated, then transversely stretched, then enters the transverse stretching shaping zone for heat setting, and then undergoes corona treatment, winding, aging, and slitting to obtain a biaxially stretched polylactic acid film.

[0068] Comparative Example 3

[0069] (1) In the production device, molten L-lactide / ε-caprolactone (97 / 3 parts by weight), lauryl alcohol (0.19 parts by weight), XG-1 matting agent (0.8 parts by weight), stannous octoate (0.3 parts by weight) and antioxidant 1010 (1.5 parts by weight) are transported to the circulation reactor via a metering pump, and the fully mixed reaction system is subjected to primary ring-opening polymerization in the reaction device. The temperature of the reaction device is 150°C, the flow rate of the reaction system is controlled at 20 mm / s, and the shear rate is 200 s -1 The reaction system was cycled 20 times in the reaction apparatus and reacted for 3 h in a nitrogen atmosphere.

[0070] (2) The obtained oligomer was further polymerized by raising the temperature to 180°C in a plug flow reactor. The reaction system flow rate was 10 mm / s and the shear rate reached 50 s -1 After a reaction time of 6 hours, polylactic acid resin was obtained, and a casting sheet was obtained by extrusion molding through a screw extruder.

[0071] (3) The cast sheet described in (2) is longitudinally preheated and then longitudinally stretched, then enters the longitudinal stretching shaping zone and is transversely preheated, then transversely stretched, then enters the transverse stretching shaping zone for heat setting, and then undergoes corona treatment, winding, aging, and slitting to obtain a biaxially stretched polylactic acid film.

[0072] The polylactic acid films prepared in Example 1 and Comparative Examples 1-2 were subjected to various performance tests, and the test standards were as follows:

[0073] Average thickness: Tested in accordance with GB / T20220-2006 "Test Standards for Average Thickness of Plastic Film and Sheet Samples, Average Thickness of Rolls and Unit Mass Area";

[0074] Friction coefficient: Tested in accordance with GB / T10006-1988 "Determination of friction coefficient of plastic films and sheets";

[0075] Haze: Tested in accordance with GB / T2410-2008 "Standard for Determination of Light Transmittance and Haze of Transparent Plastics";

[0076] Gloss: Tested in accordance with GB / T8807-1988 "Plastic Mirror Gloss Test Method";

[0077] The performance of the polylactic acid films obtained in Examples 1-7 and Comparative Examples 1-3 was tested, and the test results are shown in Table 1 below:

[0078]

[0079] The present invention makes the obtained biaxially stretched polylactic acid matte film have high haze, low gloss and excellent matte effect by selecting the matte agent. In contrast, the use of matte agent XG-1 has a negative impact on the lactide ring-opening polymerization process, and the designed molecular weight is greatly different from the actual molecular weight, making it difficult to prepare polylactic acid and its copolymer resin with excellent performance, and unable to form a biaxially stretched polylactic acid film.

[0080] In the present invention, the lactide can be selected from one or more of L-lactide, D-lactide and meso-lactide. The comonomer is selected from one or more of ε-caprolactone, δ-valerolactone, β-methyl-δ-valerolactone and glycolide.

[0081] The matting agent is one of TiO2 and BaSO4, and the matting agent does not affect the molecular weight and distribution of the lactide and the comonomer ring-opening polymerization reaction product. The amount of the matting agent is preferably 0.6-2 parts by weight.

[0082] The antioxidant is one of Antioxidant 1010, Antioxidant 168, Antioxidant 626, Antioxidant 1098 and TPH-24.

[0083] The catalyst is one of stannous octoate, tin oxide, dibutyltin oxide, stannous chloride, tin lactate, stannous benzoate, dibutyltin dilaurate, zinc oxide, zinc lactate, and zinc acetate. Stannous octoate is the most preferred. The catalyst can promote the ring-opening polymerization of lactide and other cyclic monomers and has strong reactivity. The amount of the catalyst is preferably 0.1-0.5 parts by weight.

[0084] The initiator is selected from one or more hydroxyl-containing compounds, preferably one or more alcohol compounds. The alcohol compound described herein can be one or more of monohydric alcohol, dihydric alcohol and polyhydric alcohol; for example, benzyl alcohol, dodecanol (lauryl alcohol), 1,2-ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, trimethylolpropane, pentaerythritol, isomeric decanol.

[0085] Selection of dosage ratio of lactide and comonomer:

[0086] On the basis of Example 1, only the usage ratio of L-lactide to ε-caprolactone was changed, and the data listed in Table 2 below were obtained:

[0087]

[0088] It can be seen from Table 2 that in lactide and comonomers, when the weight percentage of comonomers is 5-12%, the product has high haze, low gloss and good extinction effect. When the weight percentage of comonomers is below 5%, the product haze decreases, the gloss increases, and the extinction effect becomes significantly worse; when the weight percentage of comonomers is above 12%, the product haze decreases, the gloss increases, and the extinction effect becomes significantly worse; when the weight percentage of comonomers is above 20%, the product haze and gloss remain basically unchanged.

[0089] Changing the type of lactide and comonomer shows the same trend as in the above table. When the weight percentage of the comonomer is 5-12%, the product has high haze, low gloss and good matting effect.

[0090] The present invention is not limited to the above-mentioned embodiments. On the basis of the technical solution disclosed in the present invention, technicians in this field can make some substitutions and deformations to some technical features therein according to the disclosed technical content without creative labor, and these substitutions and deformations are all within the protection scope of the present invention.

Claims

1. A method for preparing a matte biaxially oriented polylactic acid film, characterized in that: Before the ring-opening polymerization of polylactic acid and its copolymer, a matting agent inert to the polymerization reaction is added, and then the lactide and the comonomer are ring-opened polymerized under polymerization conditions to prepare polylactic acid and its copolymer. The weight parts of the raw materials are as follows: 100 parts of lactide and the comonomer, 0.3-5 parts of the matting agent, 0.01-0.4 parts of the initiator, 0.5-2 parts of the antioxidant, and 0.1-3 parts of the catalyst; in the lactide and the comonomer, the weight percentage of the comonomer is 5-12%; the comonomer is one or more of ε-caprolactone, δ-valerolactone, β-methyl-δ-valerolactone, and glycolide; The preparation method comprises the following steps: (1) Lactide and comonomer, matting agent, initiator, catalyst and antioxidant are transported to the circulation reactor through a metering pump. After being fully mixed, a primary ring-opening polymerization reaction is carried out in the circulation reactor. The reaction temperature is 130-160°C, the flow rate is 10-30 mm / s, and the shear rate is 50-350s -1 Within the range, the reactants are circulated in the circulation reactor for 10-30 times, and reacted for 1-5 hours under a nitrogen atmosphere to obtain oligomers; (2) Raise the temperature of the oligomer to 170-200°C in a plug flow reactor for further polymerization. The reaction system flow rate is 2-15 mm / s and the shear rate is 10-100 s -1 The reaction time is 3-10 hours to obtain a matte polylactic acid resin; and then a casting sheet is obtained by extrusion molding through a screw extruder; (3) After longitudinal preheating, the cast sheet is longitudinally stretched and then enters the longitudinal stretching shaping zone for heat setting. At the same time, after transverse preheating, it is transversely stretched and then enters the transverse stretching shaping zone for heat setting. After corona treatment, winding, aging and slitting, a biaxially stretched polylactic acid film with matte properties is obtained.

2. The method for preparing a matte biaxially oriented polylactic acid film according to claim 1, characterized in that The lactide is one or more of L-lactide, D-lactide and meso-lactide.

3. The method for preparing a matt biaxially oriented polylactic acid film according to claim 1 or 2, characterized in that: The matting agent is TiO2 or BaSO4.

4. The method for preparing a matte biaxially oriented polylactic acid film according to claim 1 or 2, characterized in that The antioxidant is one or more of antioxidant 1010, antioxidant 168, antioxidant 626, antioxidant 1098 and TPH-24.

5. The method for preparing a matte biaxially oriented polylactic acid film according to claim 1 or 2, characterized in that The catalyst is one of stannous octoate, tin oxide, dibutyltin oxide, stannous chloride, tin lactate, stannous benzoate, dibutyltin dilaurate, zinc oxide, zinc lactate and zinc acetate.

6. The method for preparing a matte biaxially oriented polylactic acid film according to claim 1 or 2, characterized in that The initiator is at least one of a monohydric alcohol, a dihydric alcohol or a polyhydric alcohol.

7. The method for preparing a matt biaxially oriented polylactic acid film according to claim 1 or 2, characterized in that: In step (2), the molecular weight of the matte polylactic acid resin is 60,000 to 300,000.

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