JP2014094520A - Polylactic acid-based biaxially stretched film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide, at an unprecedentedly low stretching temperature, a polylactic acid-based biaxially stretched film excellent in terms not only of slipperiness and an anti-blocking property but also of transparency.SOLUTION: The provided polylactic acid-based biaxially stretched film is a polylactic acid-based biaxially stretched film including (A) polylactic acid and (B) inorganic particles whose surfaces are coated with a siloxane bond-containing compound wherein the average particle diameter of (B) is 0.5 to 5 μm and wherein the (A)/(B) mass ratio is 99.99/0.01 to 99.85/0.15.

Description

  The present invention relates to a polylactic acid biaxially stretched film.

  In recent years, attention has been focused on problems such as environmental pollution caused by plastic waste, and biodegradable polyester has attracted attention from the viewpoint of environmental conservation. Among them, polylactic acid, polyethylene succinate, polybutylene succinate, and the like are low in cost and highly useful because they can be mass-produced. In particular, polylactic acid has already been industrially produced from plants such as corn and sweet potato, and even if incinerated after use, considering the carbon dioxide absorbed during the growth of these plants, the carbon balance is neutral. Therefore, it is considered as a resin with a low impact on the global environment. Therefore, various developments using polylactic acid are thriving.

  However, although the polylactic acid film is excellent in rigidity, there is a problem that when the product itself is handled, the films are blocked with each other, and productivity is lowered due to poor slipperiness. For this reason, in polylactic acid films, inorganic particles such as silica, titanium dioxide, calcium carbonate, alumina, talc, and kaolinite are blended to give moderate irregularities on the film surface, improving anti-blocking and slipping properties. It is normal.

  For example, Patent Document 1 discloses a film obtained by blending silica with polylactic acid and biaxially stretching.

JP 2009-74097 A

  However, the biaxially stretched film of Patent Document 1 has a high transparency when stretched at a high temperature of 80 ° C. or higher, but seeks a more energy-efficient condition, for example, at a low temperature of 70 ° C. or lower. When stretched, there was a problem of whitening.

  An object of this invention is to provide the polylactic acid-type biaxially stretched film excellent in transparency in addition to slip property and anti-blocking property at lower stretch temperature.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by including polylactic acid with inorganic particles whose surfaces are coated with a compound having a siloxane bond. The present invention has been reached.

That is, the gist of the present invention is as follows.
(1) A polylactic acid biaxially stretched film comprising polylactic acid (A) and inorganic particles (B) whose surfaces are coated with a compound having a siloxane bond, wherein (A) / (B) A polylactic acid biaxially stretched film having a mass ratio of 99.99 / 0.01 to 99.85 / 0.15, a haze of 8% or less, and a dynamic friction coefficient of 0.7 or less.
(2) The polylactic acid biaxially stretched film according to (1), wherein the inorganic particles are silica.
(3) The polylactic acid biaxially stretched film according to (1) or (2), wherein the average particle diameter of the inorganic particles is 0.5 to 5 μm.
(4) The polylactic acid biaxially stretched film according to any one of (1) to (3), wherein the haze is 8% or less.
(5) The polylactic acid biaxially stretched film according to any one of (1) to (4), wherein the dynamic friction coefficient is 0.7 or less.
(6) Thickness is 10-50 micrometers, The polylactic acid-type biaxially stretched film in any one of (1)-(5) characterized by the above-mentioned.
(7) An unstretched film containing polylactic acid (A) and inorganic particles (B) whose surfaces are coated with a compound having a siloxane bond is biaxially stretched at 60 to 80 ° C. (1 )-(6) The manufacturing method of the polylactic acid-type biaxially stretched film of description.

  According to the present invention, it is possible to provide a polylactic acid biaxially stretched film that is excellent in transparency in addition to slipping and antiblocking properties. In addition, according to the production method of the present invention, an unstretched film is not whitened even if it is stretched at a low temperature of 60 to 80 ° C., and a biaxially stretched film can be produced under more advantageous conditions in terms of energy it can.

  The biaxially stretched film of this invention is comprised from the resin composition containing polylactic acid (A) and the inorganic particle (B) which coat | covered the surface with the compound which has a siloxane bond.

  The polylactic acid (A) used in the present invention is a polymer of D-lactic acid and / or L-lactic acid, and is usually polymerized using lactide which is a dimer of D-lactic acid or L-lactic acid as a raw material. Examples of the lactide include L-lactide, which is a cyclic dimer of L-lactic acid, D-lactide, which is a cyclic dimer of D-lactic acid, and meso-lactide in which D-lactic acid and L-lactic acid are cyclic dimerized. And DL-lactide, which is a mixture of D-lactide and L-lactide. These lactides may be used alone or in combination.

  The D-form content of the polylactic acid (A) used in the present invention is not particularly limited, but is preferably 1.0 mol% or less or preferably 99.0 mol% or more from the viewpoint of heat resistance. . The D-form content is preferably 0.6 mol% or less, or more preferably 99.4 mol% or more. The D-form content of polylactic acid is the ratio (mol%) occupied by D lactic acid units in the total lactic acid units.

  The weight average molecular weight of the polylactic acid (A) used in the present invention is preferably 70 to 500,000, and more preferably 100 to 300,000. When the weight average molecular weight is in the above range, a film excellent in mechanical strength and toughness can be obtained while having excellent melt moldability.

  The polylactic acid (A) used in the present invention may be any of crystalline polylactic acid, amorphous polylactic acid, or a combination thereof. From the viewpoint of film formation stability and heat resistance, crystalline polylactic acid is preferable. Crystalline polylactic acid here refers to polylactic acid having a melting point in the range of 140 to 175 ° C., and amorphous polylactic acid refers to polylactic acid that does not substantially have a melting point. When crystalline polylactic acid and amorphous polylactic acid are used in combination, the blending ratio of crystalline polylactic acid and amorphous polylactic acid is (crystalline polylactic acid) / (amorphous polylactic acid) = 80 / 20- The range is preferably 100/0 (mass ratio), more preferably 90/10 to 100/0 (mass ratio). By making the blending ratio of the crystalline polylactic acid 80% by mass or more, the film forming stability is improved.

  The amount of lactide contained in the polylactic acid (A) used in the present invention is preferably 0.5% by mass or less, and more preferably 0.1 to 0.4% by mass. By setting the amount of lactide to 0.5% by mass or less, it is possible to efficiently suppress smoke generation during film formation and contamination of devices in the vicinity of the die. If the device near the die is heavily contaminated, it may be transferred to the film surface via a cast roll and the operability may deteriorate.

  As a method of reducing the amount of lactide of polylactic acid (A), for example, a method of reducing by reducing the pressure at a temperature equal to or higher than the melting point during polymerization, a method of gasifying and removing pellet-shaped polylactic acid under high temperature reduced pressure, or A method of extracting and removing pellet-shaped polylactic acid by immersing it in warm water can be mentioned.

  In the polylactic acid (A) used in the present invention, a crosslinking agent such as an organic peroxide and a crosslinking aid may be used in combination for the purpose of suppressing a decrease in melt tension during film formation.

  Although it does not specifically limit as an inorganic particle used for the inorganic particle (B) which coat | covered the surface with the compound which has a siloxane bond, For example, a silica, a zeolite, a talc, or an alumina is mentioned, Among these, a silica is preferable. Examples of the compound having a siloxane bond include a silane coupling agent, silicone oil, and modified silicone oil.

  Examples of the silane coupling agent include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, vinyltriacetoxysilane, methyltrimethoxysilane, methyltriethoxysilane, isobutyltrimethoxysilane, decyltri Examples include methoxysilane, dimethyldimethoxysilane, and dimethyldiethoxysilane.

  Examples of the silicone oil include dimethylpolysiloxane, methylphenylpolysiloxane, methylhydropolysiloxane, and fluoropolysiloxane. Among them, dimethylpolysiloxane is preferable.

  Examples of the modified silicone oil include carbinol-modified polysiloxane, polyether-modified polysiloxane, amino-modified polysiloxane, epoxy-modified polysiloxane, carboxyl-modified polysiloxane, methacryl-modified polysiloxane, mercapto-modified polysiloxane, phenol-modified polysiloxane, Examples include alkyl group-modified polysiloxane, methylstyryl group-modified polysiloxane, and fluorine-modified polysiloxane. Among them, carbinol-modified polysiloxane, amino-modified polysiloxane, epoxy-modified polysiloxane, carboxyl-modified polysiloxane, methacryl-modified polysiloxane, or mercapto Modified polysiloxane is preferred. The modified silicone oil may have an organic functional group only in the side chain, may have an organic functional group only in the terminal, or has an organic functional group in both the side chain and the terminal. May be.

  As a method for coating the surface of the inorganic particles with a compound having a siloxane bond, various known methods can be used. For example, a dilute solution of a silane coupling agent (a solution diluted with water or an organic solvent) or a dilute solution of silicone oil (a solution diluted with toluene, xylene, petroleum ether, isopropyl alcohol, volatile silicone oil, etc.) After impregnating the diluted particles with the inorganic particles while stirring, a method of removing the solvent by filtration, pressing, centrifuging, etc. and drying, or spraying the diluted solution while stirring the inorganic particles using a mixer or blender And then a drying process or a heat baking process.

  The amount of the compound having a siloxane bond with respect to the inorganic particles cannot be unconditionally determined because of the degree of surface treatment and the specific surface area of the inorganic particles, but usually about 0.5 to 20 parts by mass with respect to 100 parts by mass of the inorganic particles. Perform surface treatment with.

  When dimethyl silicone oil is used as the compound having a siloxane bond, the heat baking treatment is preferably performed at 200 to 350 ° C. for about 5 to 30 minutes, and when methyl hydrogen silicone oil is used, 1 to 2 at 120 to 150 ° C. It is preferable to carry out for about an hour.

  The average particle diameter of the inorganic particles (B) whose surface is coated with a compound having a siloxane bond is required to be 0.5 to 5.0 μm, and preferably 1.0 to 3.0 μm. When the average particle diameter is smaller than 0.5 μm, (B) is not preferable because particle aggregation and poor dispersion occur. In addition, the blocking property is high, the running property and abrasion resistance of the film are insufficient, haismism is generated, and the quality is lowered. On the other hand, when the average particle diameter exceeds 5 μm, the surface roughness of the film increases, transparency is lowered, and the appearance of the film is lowered due to the generation of fish eyes. In addition, the shape of (B) is not specifically limited.

  The method for producing a biaxially stretched film of the present invention includes, for example, a method of mixing polylactic acid (A) and inorganic particles (B) whose surfaces are coated with a compound having a siloxane bond, forming a film, and biaxially stretching. It is done. The mixing method of (A) and (B) is not particularly limited. For example, (A) and (B) are previously mixed with a blender and compounded with an extruder to prepare a master batch, The method of adding (B) at the time of superposition | polymerization of (A) is mentioned.

  The inorganic particles (B) whose surfaces are coated with the polylactic acid (A) and the compound having a siloxane bond in the polylactic acid-based biaxially stretched film are (A) / (B) = 99.99 / 0.01 to 99. 0.85 / 0.15 (mass ratio) is required, and 99.98 / 0.02 to 99.90 / 0.10 (mass ratio) is preferable. When the content of (B) is less than 0.01% by mass with respect to the total of (A) and (B), sufficient adhesion of the molten film to the processing roll and blocking between the films is sufficient. Since it cannot suppress, it is not preferable. On the other hand, when the content of (B) exceeds 0.15% by mass, it is not preferable because the transparency is lowered or the moldability is lowered.

  The film forming method is not particularly limited, and can be manufactured by a known film forming method, and examples thereof include a T-die method, an inflation method, and a calendar method. Of these, the T-die method is preferable. In the T-die method, polylactic acid (A) and a master batch, or polylactic acid (A) and inorganic particles (B) whose surfaces are coated with a compound having a siloxane bond are melt-kneaded, extruded, and cooled with a cast roll. Thus, an unstretched sheet is obtained. At this time, the cylinder temperature is preferably 160 to 250 ° C, the T-die temperature is preferably 200 to 250 ° C, and the cast roll temperature is preferably 30 to 60 ° C. By setting the cast roll temperature within the above range, it is possible to suppress the adhesion of the monomer of polylactic acid (A) to the cast roll, so that the unstretched film is hardly soiled and can be sufficiently cooled. Therefore, it is easy to produce an unstretched film stably. The thickness of the unstretched film is preferably 100 to 600 μm.

  The unstretched film may be coated with an antistatic or easy adhesion coating agent as necessary. The coating method is not particularly limited, and examples thereof include gravure roll coating, reverse roll coating, wire bar coating, lip coating, air knife coating, curtain flow coating, spray coating, and dip coating.

  The unstretched film can be stretched by a known stretching method. Known stretching methods include a roll method and a tenter method, and in either method, either a sequential biaxial stretching method or a simultaneous biaxial stretching method may be employed. The surface magnification during stretching is preferably 6 to 16 times. By setting the surface magnification within the above range, the mechanical properties of the film, particularly the tensile strength, can be improved without breaking during stretching.

  The stretching temperature is preferably 60 to 100 ° C., and the uniformity of the film is further increased, and the film can be made suitable for secondary processing such as printing and laminating. More preferred. If the stretching temperature is less than 60 ° C., the film may break at the initial stage of stretching due to insufficient heat for stretching. On the other hand, when the stretching temperature exceeds 80 ° C., heat is excessively applied to the film, and draw stretching is performed, so that there is a high tendency for stretch spots to occur and uneven thickness. In addition, you may preheat before extending | stretching, and it is preferable to set it as 60-100 degreeC as preheating temperature.

  In addition, the conventional unstretched film using silica that does not cover the surface required a temperature of 80 ° C. or higher to avoid whitening and obtain transparency, but in the present invention, the unstretched film As a matter of course, at a temperature exceeding 80 ° C., even if the film is stretched at 60 to 80 ° C., whitening does not occur, and a biaxially stretched film can be produced under more advantageous conditions in terms of energy.

  The stretched film preferably has a thickness of 10 to 50 μm. By setting the thickness within the above range, a packaging bag having sufficient stiffness can be produced.

  The stretched film may be subjected to a thermal relaxation treatment after stretching for the purpose of imparting dimensional stability. Examples of the method of thermal relaxation treatment include a method of blowing hot air, a method of irradiating infrared rays, a method of irradiating microwaves, and a method of contacting on a heat roll. Among them, from the viewpoint of heating uniformly and accurately, A method of blowing hot air is preferred. The conditions for the thermal relaxation treatment are preferably 1 second or longer at 80 to 160 ° C. under the condition of a relaxation rate of 2 to 8%.

  Further, the biaxially stretched film of the present invention may be added with a heat stabilizer, an antioxidant, a plasticizer, a lubricant, a flame retardant, a release agent, an impact resistance, a terminal blocker, etc. Good.

  Examples of the heat stabilizer and the antioxidant include hindered phenols, hindered amines, sulfur compounds, copper compounds, and alkali metal halides.

  Examples of the plasticizer include one or more plasticizers selected from aliphatic ester derivatives or aliphatic polyether derivatives. Specific examples of the compound include glycerol diacetomonocaprate and glycerol diacetomonolaurate.

  Examples of the lubricant include carboxylic acid compounds and fatty acid amides. Among these, fatty acid metal salts are preferable, and magnesium stearate and calcium stearate are more preferable.

  Examples of the flame retardant include bromine-based flame retardants, phosphorus-based flame retardants, intomesent flame retardants, nitrogen-based flame retardants, silicone-based flame retardants, and inorganic flame retardants.

  Examples of the release agent include carboxylic acid compounds.

  Examples of the impact resistance agent include (meth) acrylic acid ester impact resistance agents having a core-shell type structure. Examples of commercially available products include “Metablene” series manufactured by Mitsubishi Rayon Co., Ltd.

  Examples of the terminal blocking agent include carbodiimide, epoxy, isocyanate, and oxazoline.

  The biaxially stretched film of the present invention preferably has a haze of 8.0% or less, more preferably 6.0% or less, and even more preferably 4.0% or less. If the haze exceeds 8%, it is not preferable because the appearance is low in transparency and the commercial value is lowered in applications such as packaging materials.

  The biaxially stretched film of the present invention preferably has a dynamic friction coefficient of 0.7 or less, more preferably 0.6% or less, and even more preferably 0.5% or less. If the dynamic friction coefficient exceeds 0.7, the slip property is poor, and the appearance quality such as the occurrence of scratches due to friction with the roll is lowered, which is not preferable.

  The biaxially stretched film of the present invention can provide a good package even with a single layer, but other resins may be laminated in accordance with the contents, storage method, and bag making method. Examples of the lamination method include coating, dry lamination, and extrusion lamination, and can be appropriately selected according to required performance.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

1. Raw material (1) Polylactic acid · 4032D: manufactured by Nature Works, D-form content 1.2 mol%, residual lactide amount 0.22 mass%, weight average molecular weight 180,000 (2) inorganic particles · SAZ-20B: Tosoh Silica, average particle size 0.3, 1.3, 2.1, 2.6 μm, surface silicone oil treated product, AZ-200: manufactured by Tosoh Silica, average particle size 2.4 μm
AZ-204: manufactured by Tosoh Silica Co., Ltd., average particle size 1.7 μm

2. Measurement Method (1) Thickness Measured using a thickness meter (“MT12B” manufactured by HEIDENHAIN).
(2) Haze (transparency)
According to JIS-K7105, it measured using Nippon Denshoku Industries Co., Ltd. haze meter NDH2000.
The haze indicates that the smaller the numerical value, the better the transparency.
(3) Coefficient of dynamic friction Measured according to JIS-K7125 using a friction measuring device TR-2 manufactured by Toyo Seiki Seisakusho.
The smaller the numerical value of the dynamic friction coefficient, the better the slip property.
(4) Anti-blocking property The film was cut into 60 mm × 60 mm, and two of these films were superposed and left in an atmosphere of 40 ° C. and 70% humidity for 24 hours with a load of 2 kg on top. Thereafter, the two films were pinched with fingers, and the sensory evaluation was performed on the blocking state when the two films were peeled off with the force of the fingertips.
○: No blocking ×: With blocking

Example 1
After dry blending 95 parts by mass of 4032D as polylactic acid and 5 parts by mass of SAZ-20B as inorganic particles, a PCM-30 type twin screw extruder (screw diameter 30 mmφ, average groove depth 2.5 mm) manufactured by Ikegai Co., Ltd. The resin composition was obtained by melt kneading under the conditions of 190 ° C., screw rotation speed of 200 rpm, residence time of 1.6 minutes, and discharge of 250 g / min.
The obtained resin composition was mixed with 4032D so that the content of inorganic particles was as shown in Table 1, and supplied to a single screw extruder of 25 mmΦ, and melt extruded at a T die temperature of 230 ° C. The film was tightly cooled on a cast roll whose temperature was controlled at 35 ° C. to obtain an unstretched sheet having a thickness of 250 μm.
Next, the end of the unstretched film is held by a clip of a simultaneous biaxial stretching machine, preheated at 60 ° C., and then simultaneously at a temperature of 60 ° C. in the vertical direction by 3.0 times and in the horizontal direction by 3.3 times. Biaxially stretched. Thereafter, the film was subjected to a heat treatment for 4 seconds at a temperature of 140 ° C. with a transverse relaxation rate of 5%, and then cooled to room temperature to obtain a biaxially stretched film having a thickness of 25 μm.

Examples 2-11, Comparative Examples 1-7
Except for changing the kind of inorganic particles used, the amount added, and the production conditions as shown in Table 1, melt-kneading was performed in the same manner as in Example 1 to prepare an unstretched film, and the biaxially stretched film was stretched. Obtained. The preheating temperature was the same as the stretching temperature.

Example 12
Except for setting the stretching temperature and preheating temperature to 80 ° C. and the thickness of the biaxially stretched film to 50 μm, it was melt-kneaded in the same manner as in Example 11 to prepare an unstretched film and stretched to obtain a biaxially stretched film. .

  Table 1 shows the characteristic values of the obtained film.

Since the biaxially stretched film of Examples 1-12 used what contained the inorganic particle which coat | covered the surface with the compound which has a siloxane bond in polylactic acid, haze is low, a dynamic friction coefficient is small, and blocking of films is blocking. It was suppressed.
Further, when Examples 1 to 12 and Comparative Examples 1 and 2 are compared, both of Examples 1 to 12 using inorganic particles that are not coated with silicone oil despite being stretched at 60 to 80 ° C. It can be seen that the axially stretched film has an extremely low haze as compared with the biaxially stretched films of Comparative Examples 1 and 2 using inorganic particles not coated with silicone oil.

The biaxially stretched films of Comparative Examples 1 and 2 are films corresponding to conventional products. Since the inorganic particles whose surface was not treated were used, the haze was high.
Since the biaxially stretched films of Comparative Examples 3 and 4 had a small content of inorganic particles covering the surface, the antiblock property was inferior and the dynamic friction coefficient was high.
The biaxially stretched films of Comparative Examples 5 and 6 had high haze because the content of inorganic particles covering the surface was large.
In Comparative Example 7, since the average particle diameter of the inorganic particles covering the surface was small, particle agglomeration and poor dispersion occurred and haismura occurred. Therefore, the quality was clearly inferior.

Claims (7)

  A polylactic acid-based biaxially stretched film containing polylactic acid (A) and inorganic particles (B) whose surfaces are coated with a compound having a siloxane bond, wherein the average particle size of (B) is 0.5 A polylactic acid-based biaxially stretched film having a mass ratio of ˜5 μm and (A) / (B) of 99.99 / 0.01 to 99.85 / 0.15.   The polylactic acid biaxially stretched film according to claim 1, wherein the inorganic particles are silica.   The polylactic acid biaxially stretched film according to claim 1 or 2, wherein the compound having a siloxane bond is silicone oil.   The polylactic acid biaxially stretched film according to any one of claims 1 to 3, wherein the haze is 8% or less.   5. A polylactic acid biaxially stretched film according to any one of claims 1 to 4, wherein the dynamic friction coefficient is 0.7 or less.   The polylactic acid biaxially stretched film according to any one of claims 1 to 5, wherein the thickness is 10 to 50 µm.   An unstretched film containing polylactic acid (A) and inorganic particles (B) whose surfaces are coated with a compound having a siloxane bond is biaxially stretched at 60 to 80 ° C. The manufacturing method of the polylactic acid-type biaxially stretched film of description.