JP4652803B2 - Polylactic acid biaxially stretched film with excellent antistatic properties - Google Patents

Description

  The present invention relates to a polylactic acid biaxially stretched film having excellent antistatic properties.

  Currently, polyethylene terephthalate stretched films, polypropylene stretched films and the like are known as materials having excellent mechanical strength, heat resistance, and dimensional stability, and are widely used in industry.

  However, when these plastic films are disposed in the natural environment, they are not decomposed due to their chemical stability, but are accumulated as garbage. In the future, it will become more difficult to secure garbage disposal sites and landfill sites, and there are concerns about problems such as adverse effects on the natural environment and wild animals. In place of these plastic films, there is a film made of polylactic acid that can be hydrolyzed in soil and then become a harmless degradation product by microbial degradation.

  An unstretched film or sheet of polylactic acid is a material having low strength and elongation and inferior impact resistance, and as it is, its practicality is insufficient. Therefore, in order to improve brittleness, a method of aligning by uniaxial or biaxial stretching is known. Polylactic acid biaxially stretched films have been developed in information recording materials (magnetic cards), industrial packages, food packaging, etc., and some have been put into practical use.

  However, in these polylactic acid stretched films, the polylactic acid resin itself has a high degree of electrical insulation, so it is very easy to be charged. Due to the generation and accumulation of static electricity, secondary processing such as printing and bag making, etc. , Causing various problems. Moreover, since dust and dust are easily adsorbed, there is a problem that the appearance is impaired.

  In general, as a method for imparting antistatic properties to plastic films and sheets, it is known to add an anionic alkyl sulfonate to polylactic acid. Patent Document 1 discloses that nonionic glycerin fatty acid esters are added to a polylactic acid polymer.

  However, these conventional methods are not only satisfactory in antistatic properties, but also have poor practicality due to deterioration of transparency and deterioration of mechanical properties caused by hydrolysis.

  Patent Document 2 discloses that a coating composition is applied to the surface of a polylactic acid resin film.

However, in the method of applying the coating composition to the film surface, the antistatic property of the non-coated surface is poor, and when it is applied to both surfaces, the equipment is complicated and cannot be easily implemented.
JP 2002-114900 A JP 2001-354789 A

  An object of the present invention is to solve such problems, and to provide a polylactic acid biaxially stretched film having transparency and excellent antistatic properties.

  The polylactic acid biaxially stretched film according to the present invention comprises (A) 90 to 10% by mass of a dialkylsulfosuccinate and (B) a reaction product of glyceryl stearate and boric acid in an amount of 10 to 90% by mass. Is contained in an amount of 0.1 to 10% by mass.

  According to the present invention, a polylactic acid biaxially stretched film having transparency and excellent antistatic properties can be provided.

  As a result of intensive studies to solve the above problems, the present inventors include (A) a dialkylsulfosuccinate and (B) a reaction product of glycerin stearate and boric acid in a polylactic acid resin. It has been found that the inclusion of the surfactant composition can impart excellent antistatic properties to the biaxially stretched film without significantly degrading the transparency, leading to the present invention.

  Hereinafter, various embodiments of the present invention will be described.

  In the present invention, the polylactic acid resin includes a homopolymer having L-lactic acid as a main structural unit and a copolymer having L-lactic acid and D-lactic acid as main structural units. In order to promote orientation crystallization by biaxial stretching and to develop practical strength, the polylactic acid resin should satisfy the composition ratio of L-lactic acid / D-lactic acid = 100/0 to 94/6 (molar ratio). Is preferred. When D-lactic acid exceeds 6 mol%, the melting point becomes extremely low and the crystallinity is poor, and the heat resistance and dimensional stability of the resulting film may be deteriorated. The composition ratio of L-lactic acid and D-lactic acid is more preferably L-lactic acid / D-lactic acid = 99/1 to 96/4 (molar ratio).

  The number average molecular weight of the polylactic acid resin is preferably in the range of 50,000 to 300,000. When the number average molecular weight is less than 50,000, the resulting film has insufficient mechanical strength, and also frequently undergoes cutting during the stretching and winding processes, resulting in a decrease in operability. On the other hand, when the number average molecular weight exceeds 300,000, the fluidity at the time of heating and melting becomes poor, and the film forming property is lowered. A more preferable range of the number average molecular weight of the polylactic acid resin is 80,000 to 150,000.

  As a polymerization method for obtaining a polylactic acid-based resin, any of a condensation polymerization method and a ring-opening polymerization method can be adopted, and a small amount of chain extender such as a diisocyanate compound or diepoxy is used for the purpose of increasing the molecular weight. Compounds, acid anhydrides and the like may be used.

  In the present invention, the surfactant composition blended in the polylactic acid-based resin is a blend of (A) a dialkylsulfosuccinate and (B) a reaction product of glycerin stearate and boric acid.

In the present invention, as the (A) dialkylsulfosuccinate, an anionic surfactant represented by the following general formula (1) can be preferably used.

(However, R ₁ and R ₂ are alkyl groups, M is a counter ion)
Here, R ₁ and R ₂ in the general formula (1) are the same or different alkyl groups, and R ₁ and R ₂ preferably have 6 to 20 carbon atoms, and more preferably 8 to 16 carbon atoms. Specifically, dioctylsulfosuccinate (carbon number of R ₁ and R ₂ having 8 carbon atoms) can be suitably used as the dialkylsulfosuccinate. As the salt represented by —SO ₃ M, alkali metals such as sodium, potassium, calcium and magnesium, alkaline earth metals, or sulfonates such as diethanolamine and triethanolamine can be preferably used.

  In the present invention, dialkylsulfosuccinate can be obtained by a known method. Specifically, for example, 1 mol of maleic anhydride is reacted with, for example, 2 mol of octyl alcohol under basic conditions at 120 ° C., then sodium sulfite is added, and at 50 ° C. until a transparent liquid is obtained. Although the method of stirring and distilling a solvent off is mentioned, it is not limited to this.

  In the present invention, (B) a reaction product of glycerin stearate and boric acid is a surfactant obtained by reacting glycerin stearate with boric acid. The fatty acid in the glycerin stearic acid ester is desirably stearic acid, but can be suitably used even if a fatty acid having 12 to 20 carbon atoms is contained. Glycerin stearate can be obtained by esterification reaction of glycerin and stearic acid. From this esterification reaction, monoesters, diesters, and triesters are obtained depending on the reaction molar ratio of glycerin and stearic acid. Although it is desirable to increase the purity of the monoester by molecular distillation, the degree of esterification is not particularly limited. The reaction molar ratio of boric acid to glycerin stearate is preferably 0.1 to 1 mol, more preferably 0.2 to 0.5 mol, of boric acid with respect to 1 mol of glycerin stearate.

  In the present invention, a reaction product of glycerin stearic acid ester and boric acid can be obtained by a known method. Specifically, for example, 1 mol of stearic acid per 1 mol of glycerin is esterified at 230 ° C. under a basic catalyst to obtain a glycerin stearic acid ester, and then boric acid is added to 1 mol of the compound. The desired product can be obtained by reacting 5 mol at 230 ° C.

  In the present invention, the surfactant composition includes (A) 90 to 10% by mass of a dialkylsulfosuccinate and (B) 10 to 90% by mass of a reaction product of glycerin stearate and boric acid. When the (A) dialkylsulfosuccinate is less than 10% by mass, not only a sufficient antistatic effect cannot be obtained, but the compatibility with the polylactic acid resin is deteriorated, resulting in poor appearance such as whitening of the film. When (A) dialkyl sulfosuccinate exceeds 90% by mass, the compatibility with the polylactic acid resin is improved, but a sufficient antistatic effect cannot be obtained. The surfactant composition is more preferably composed of (A) 90 to 50% by mass of a dialkylsulfosuccinate and (B) 10 to 50% by mass of a reaction product of glycerin stearic acid ester and boric acid.

  The content of the surfactant composition contained in the polylactic acid biaxially stretched film of the present invention is in the range of 0.1 to 10% by mass. When the content of the surfactant composition is less than 0.1% by mass, a sufficient antistatic effect cannot be obtained. On the other hand, when the content of the surfactant composition exceeds 10% by mass, the antistatic effect reaches saturation, so that not only is the content excessive with respect to the antistatic performance, but also the transparency deteriorates, the high temperature increases. It causes various problems such as blocking phenomenon between films under humidity and poor extrusion during film formation. A preferable range of the content of the surfactant composition is 0.5 to 2% by mass. When it is within this range, particularly excellent antistatic properties can be provided.

  In the present invention, the film raw material containing the polylactic acid resin and the surfactant composition can be obtained by heating and kneading the polylactic acid resin and the surfactant composition in an extruder. The reaction product of (A) dialkylsulfosuccinate and (B) glycerin stearic acid ester and boric acid may be added separately to the polylactic acid resin, or mixed in advance and then added to the polylactic acid resin. May be. When the amount of the surfactant composition to be added is small relative to the amount of the polylactic acid-based resin, it becomes difficult to uniformly disperse them in the resin. For this reason, a master batch containing a reaction product of (A) dialkylsulfosuccinate and / or (B) glyceryl stearate and boric acid in a high concentration was prepared in advance, and this was used as a polylactic acid containing no surfactant composition. It is preferable to employ a master batch method in which a predetermined content is obtained by kneading with a resin.

  Examples of the method for producing the polylactic acid-based biaxially stretched film of the present invention include a T-die method, an inflation method, a calendar method, and the like. Among these, a T-die method in which a T-die is melt-kneaded and extruded is preferable. As an example of the production method of the T-die method, the film raw material and, if necessary, a polylactic acid resin composition containing an appropriate amount of a plasticizer and a lubricant are supplied to an extruder hopper, and the extruder has a cylinder temperature of 180 to 240, for example. C., T-die temperature 200-230.degree. C., melt kneaded and extruded, cooled with a cooling roll controlled at 20-40.degree. C. to obtain an unstretched sheet having a thickness of 100-500 .mu.m.

  As a biaxial stretching method of the unstretched sheet, any of a simultaneous biaxial stretching method using a tenter method and a sequential biaxial stretching method using a roll and a tenter may be used. As a typical example of simultaneous biaxial stretching, an unstretched sheet obtained as described above is stretched to a surface magnification of 9 to 16 times with a tenter having a preheating / stretching temperature of 70 to 90 ° C. and a heat setting temperature of 100 to 150 ° C. Get. As a representative example of sequential biaxial stretching, an unstretched sheet is stretched in the longitudinal direction at a roll surface temperature of 50 to 80 ° C. and a stretch ratio of 1.5 to 5 times according to the rotational speed ratio of the drive roll, and continuously. A film is obtained by stretching in the transverse direction under conditions of a stretching temperature of 50 to 90 ° C., a stretching ratio of 1.5 to 8 times, and a heat setting temperature of 100 to 150 ° C.

  The thickness of the polylactic acid biaxially stretched film according to the present invention is not particularly limited, and may be set as appropriate depending on the application, required performance, price, and the like. Generally, a thickness of about 10 to 100 μm can be exemplified. Furthermore, surface treatment may be performed for the purpose of improving the printability, laminating property, coating suitability, etc. of the film. Examples of the surface treatment method include corona discharge treatment, plasma treatment, and acid treatment, and any method can be used. Among these, the corona discharge treatment can be exemplified as the most preferable from the viewpoint of simplicity.

  In the polylactic acid-based biaxially stretched film of the present invention, a known anionic surfactant other than the above-described surfactant of the present invention, a cationic surfactant, and a nonionic surfactant, as long as the object of the present invention is not impaired. Agents and amphoteric surfactants may be used alone or in combination of two or more.

  The polylactic acid-based biaxially stretched film of the present invention can contain a pigment, an antioxidant, a plasticizer, an ultraviolet absorber, a lubricant, a crystal nucleating agent, and the like as required. If further antistatic performance is required, an antistatic agent can be further applied to the film surface. In addition, in order to make secondary processing etc. easy, it is also possible to apply | coat coating liquids, such as an easily bonding coating agent, to a film surface as needed.

The surface resistivity (Ω / □) of the polylactic acid-based biaxially stretched film of the present invention is preferably low, but it is an electric shock in the film winding and slitting process, and in the secondary processing such as printing and bag making, to the roll. As long as it does not cause production problems such as wrinkling or wrinkling due to meandering. As a guide, the surface resistivity is preferably 10 ¹⁵ Ω / □ or less, more preferably 10 ¹⁴ Ω / □ or less.

  The polylactic acid-based biaxially stretched film of the present invention is suitable as a packaging film for calendars, stationery, clothing, foods, etc., but others are overlap shrink films such as OA media products, envelope window pasting films, Examples include wrapping of electronic parts and the like, print lamination, and the like, which can be used without any particular limitation.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

[Example]
EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not restrict | limited by the following Example.

Example 1
Polylactic acid containing L-lactic acid and D-lactic acid in L-form / D-form = 99/1 (molar ratio), having a number average molecular weight of 95,000 and MFR of 5.0 g / 10 min (210 ° C.) Resin (manufactured by Cargill Dow, Nature Works) was prepared. Further, ((A) -1) sodium dioctylsulfosuccinate 80% by mass and ((B) -1) a reaction product of glycerol monostearate and boric acid (reaction molar ratio (glycerol monostearate: boric acid) 1: 0 .5) A surfactant composition containing 20% by mass was obtained.

  The number average molecular weight of the polylactic acid resin was measured as described below.

  That is, the number average molecular weight was determined by gel permeation chromatography (GPC) using LC10AD manufactured by Shimadzu Corporation. At this time, measurement was performed with a column temperature of 40 ° C. and a chloroform solvent, and calculation was performed by a polystyrene conversion method.

  10.0% by mass of the surfactant composition obtained with respect to 90.0% by mass of the polylactic acid resin described above was added, melt-kneaded using a twin screw extruder, and the resulting strand was cut. Pelletized to prepare master batch a.

  Add 10% by mass of masterbatch a to 90% by mass of the polylactic acid resin described above, and use a 50 mmφ extruder equipped with a coat hanger type T die, and melt extrude at a T die temperature of 230 ° C. for 5 minutes. The cast roll was temperature-controlled at 25 ° C., and was closely adhered and cooled to obtain an unstretched sheet having a thickness of 150 μm. The obtained unstretched sheet was stretched in the longitudinal direction 3.0 times at a preheating roll 60 ° C. and a stretching roll 70 ° C. Next, in the tenter, the film was stretched 3.5 times in the transverse direction at a stretching temperature of 80 ° C., and then subjected to heat treatment at 150 ° C. with a transverse relaxation rate of 5% to obtain a sequentially biaxially stretched film having a thickness of 15 μm. .

(Examples 2 to 8)
Example 1 except that the type of masterbatch (types of surfactants (A) and (B), blending ratio) and the amount added (surfactant composition content) were changed as shown in Table 1. In the same manner, a biaxially stretched film was obtained sequentially.

Example 9
10% by mass of masterbatch a was added to 90% by mass of the polylactic acid resin similar to Example 1, and a residence time of 5 minutes and a T-die temperature of 230 ° C. using a 50 mmφ extruder equipped with a coat hanger type T-die. The resulting mixture was melt-extruded and cooled tightly on a cast roll whose temperature was controlled at 25 ° C. to obtain an unstretched sheet having a thickness of 150 μm. Subsequently, an unstretched sheet was introduced into a tenter having a preheating of 80 ° C. and a stretching of 78 ° C., and after stretching at a surface magnification of 10 times, heat treatment was performed at a relaxation rate of 4% and a heat setting temperature of 150 ° C. An axially stretched film was obtained.

(Comparative Examples 1-3)
Example 1 except that the type of masterbatch (types of surfactants (A) and (B), blending ratio) and the amount added (surfactant composition content) were changed as shown in Table 1. In the same manner, a biaxially stretched film was obtained sequentially.

  The types (A) -1, (A) -2, (B) -1, and (B) -2 of the surfactants shown in Table 1 are as follows.

(A) -1: sodium dioctyl sulfosuccinate (A) -2: sodium dilauryl sulfosuccinate (B) -1: reaction product of glycerin monostearate and boric acid (reaction molar ratio (glycerin monostearate: boric acid) 1 : 0.5)
(B) -2: Reaction product of glycerol monostearate and boric acid (reaction molar ratio (glycerol monostearate: boric acid) 1: 1.0)

  About the obtained biaxially stretched film of Examples 1-9 and Comparative Examples 1-3, evaluation demonstrated below was performed. Each evaluation method is as follows. These results are shown in Table 2.

(1) Surface resistivity value The surface resistivity value was allowed to stand for 1 day under the conditions of a temperature of 23 ° C. and a relative humidity of 50%, and then measured according to JIS-K6911 under the same conditions (manufacturer: Kawaguchi Electric Works, Device name: Measured using a super insulation meter (model P-616). In the present invention, a product that did not hinder production (film production) was determined to be acceptable (excellent in antistatic performance).

(2) Friction Withstand Voltage After standing for 1 day under the conditions of a temperature of 23 ° C. and a relative humidity of 50%, cotton / polyester was measured with a friction withstand voltage measuring instrument (model: EC-3N) manufactured by Intex under the same conditions. A 60/40 white cloth was brought into contact with the corona-treated surface of the film, and the maximum withstand voltage for 60 seconds was evaluated. In the present invention, 3 kv or less was accepted.

(3) Tensile strength and elongation It measured with the sample of length 10cm and width 10mm according to the measuring method of JIS-K7127.

(4) Haze It measured according to JIS-K7105.

  As shown in Table 1, the biaxially stretched films of Examples 1 to 9 according to the present invention have low surface resistivity and friction withstand voltage, and are not only excellent in antistatic performance, but at the same time mechanical strength (tensile It was also excellent in strength and tensile elongation. In addition, Examples 1 to 3 and 6 to 9 in which the content of the surfactant composition is in a preferable range of 0.5 to 2% by mass have lower haze than Examples 4 and 5, and are transparent. Was particularly good.

  On the other hand, the film of the comparative example 1 using the surfactant composition which does not contain a dialkyl sulfosuccinate, the comparative example 2 which used the surfactant composition which does not contain the reaction material of glycerol stearic acid ester and boric acid And the film of Comparative Example 3 that does not contain a surfactant composition (a reaction product of dialkylsulfosuccinate and glycerin stearic acid ester and boric acid) have a friction withstand voltage as compared with Examples 1-9. High and antistatic performance was poor. In particular, the film of Comparative Example 3 was not only very high in friction withstand voltage, but also high in surface resistivity, and was static.

  Since the polylactic acid biaxially stretched film of the present invention has transparency and excellent mechanical strength, particularly antistatic properties, it is highly useful as a packaging material for clothing, stationery, food, pharmaceuticals and the like. Moreover, when discarded as garbage, it is decomposed by microorganisms in the soil, and the environmental load on the natural environment and wild animals can be reduced.

Claims (1)

  A surfactant composition containing (A) 90 to 10% by mass of a dialkylsulfosuccinate and (B) 10 to 90% by mass of a reaction product of glycerin stearic acid ester and boric acid is added to a polylactic acid resin in an amount of 0.1 to 0.1%. A polylactic acid-based biaxially stretched film excellent in antistatic properties, characterized by containing 10% by mass.